Patent Publication Number: US-6341843-B1

Title: Ink jet printer having an ink cleaning mechanism

Description:
This application is a division of application Ser. No. 08/972,138, filed Nov. 17, 1997 now U.S. Pat. No. 6,206,506. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to a cartridge receptacle for an ink jet printer, which holds a cartridge having a print head and at least one removable ink reservoir. The receptacle includes a lever that covers at least a portion of the ink reservoir such that the ink reservoir cannot be changed without lifting the lever. Upon lifting and closing of the lever, a signal is output which prompts cleaning of the print head. 
     2. Description of the Related Art 
     As is generally known, color ink jet printers print images by superimposing dots having different colors. These dots are typically formed by ejecting different colored inks from a print head. The inks are typically stored in ink reservoirs, and are ejected from holes or nozzles on the print head. As might be expected, these holes or nozzles can clog from time to time, making it difficult to eject ink therefrom. In such cases, it is necessary to clean ink from the head before additional printing can take place. Such cleaning is often required when ink reservoirs are changed. 
     Conventional ink jet printers ensure that head cleaning takes place each time an ink reservoir is changed by cleaning their print heads in response to opening and closing of an access door on the exterior of the printer. However, this can result in unnecessary print head cleaning, particularly in cases where the access door is being opened for reasons unrelated to the print heads. As a result of such unnecessary cleanings, the amount of ink in the ink reservoirs is unnecessarily depleted. 
     To address this problem, printer hardware designers conceived of other methods for initiating cleaning of print heads. However, these methods met with limited success, since it was always possible to change an ink reservoir on a cartridge without initiating print head cleaning. Consequently, these other methods proved unsatisfactory. 
     Thus, there exists a need for a way to prevent changing of an ink reservoir in an ink jet printer without initiating cleaning of a corresponding print head. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the foregoing needs by providing a cartridge receptacle which receives a cartridge having a print head and at least one removable ink reservoir, and a lever which extends over at least part of the ink reservoir so as to prevent access to the ink reservoir. The lever can pivot away from the ink reservoir so as to provide access thereto. Print head cleaning is prompted in response to the lever pivoting away from the ink reservoir and then back over the ink reservoir. 
     By virtue of the foregoing configuration, it is not possible to change an ink reservoir without pivoting the lever. As a result, each time an ink reservoir is changed, and the lever is subsequently pivoted away from and back over the ink reservoir, print head cleaning is initiated. Thus, in the present invention, unlike in its conventional counterparts, it is not possible to change an ink reservoir without initiating print head cleaning. 
     Thus, according to one aspect, the present invention is a cartridge receptacle which is mounted on a carriage for releasably receiving a cartridge having a print head and at least one removable ink reservoir. The receptacle includes a pivoting lever which permits removal of the at least one ink reservoir. The lever extends over at least a portion of the at least one ink reservoir so as to prevent access to the at least one ink reservoir until such time as the lever is pivoted away from the at least one ink reservoir. When the lever is pivoted away from the at least one ink reservoir, and then the lever is pivoted over the at least a portion of the at least one ink reservoir, a signal is output which prompts cleaning of the print head. 
     In preferred embodiments of the invention the cartridge has a circuit contact, and the cartridge receptacle includes a circuit contact which is contactable with the circuit contact mounted on the cartridge. When the lever is pivoted over the at least a portion of the at least one ink reservoir, the circuit contact on the cartridge receptacle contacts the circuit contact on the cartridge. On the other hand, when the lever is pivoted away from the at least one ink reservoir, the circuit contact on the cartridge receptacle breaks contacts with the circuit contact on the cartridge. 
     In particularly preferred embodiments, a break in contact between the circuit contact on the cartridge receptacle and the circuit contact on the cartridge, and subsequent contact between the circuit contact on the cartridge receptacle and the circuit contact on the cartridge causes output of the signal which prompts cleaning of the print head. By virtue of these features, the invention provides a simple manual construction which can issue the signal to prompt print head cleaning. 
     According to another aspect, the present invention is an ink jet printer which includes a first cartridge receptacle mounted on a carriage for releasably receiving a first cartridge having a first print head and at least one removable first ink reservoir, the first receptacle including a first pivoting lever which permits removal of the at least one first ink reservoir. The first lever extends over at least a portion of the at least one first ink reservoir so as to prevent access to the at least one first ink reservoir until such time as the first lever is pivoted away from the at least one first ink reservoir. When the first lever is pivoted away from the at least one first ink reservoir, and then the first lever is pivoted over the at least a portion of the at least one first ink reservoir, a signal is output which prompts cleaning of the first print head. Also included in the printer is a second cartridge receptacle mounted on the carriage for releasably receiving a second cartridge having a second print head and at least one removable second ink reservoir, the second receptacle including a second pivoting lever which permits removal of the at least one second ink reservoir. The second lever extends over at least a portion of the at least one second ink reservoir so as to prevent access to the at least one second ink reservoir until such time as the second lever is pivoted away from the at least one second ink reservoir. When the second lever is pivoted away from the at least one second ink reservoir, and then the second lever is pivoted over the at least a portion of the at least one second ink reservoir, a signal is output which prompts cleaning of the second print head. 
     By virtue of the foregoing configuration, it is possible to ensure that cleaning of a print head will be initiated upon changing of an ink reservoir. Moreover, because a signal is output to prompt ink cleaning of a particular print head when a lever is pivoted away and towards an ink reservoir, the invention makes it possible to designate only one or both print heads in the printer for cleaning. 
     This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiment thereof in connection with the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a perspective view of computing equipment used in connection with the printer of the present invention. 
     FIG. 2 is a front perspective view of the printer shown in FIG.  1 . 
     FIG. 3 is a back perspective view of the printer shown in FIG.  1 . 
     FIG. 4 is a front, cut-away perspective view of the printer shown in FIG.  1 . 
     FIG. 5 is a back, cut-away perspective view of the printer shown in FIG.  1 . 
     FIGS. 6A and 6B show front and back views, respectively, of a cartridge receptacle used in connection with the present invention. 
     FIG. 7 shows an example of a disposable ink cartridge used with the present invention. 
     FIGS. 7A and 7B shows views of an example of a second type of ink cartridge that is used with the present invention. 
     FIG. 8 shows a face-on view of head configurations for print heads used with the present invention. 
     FIG. 9 shows dot configurations which are printed by the printer of the present invention. 
     FIG. 10 is a block diagram showing the hardware configuration of a host processor interfaced to the printer of the present invention. 
     FIG. 11 shows a functional block diagram of the host processor and printer shown in FIG.  10 . 
     FIG. 12 is a block diagram showing the internal configuration of the gate array shown in FIG.  10 . 
     FIG. 13 shows the memory architecture of the printer of the present invention. 
     FIG. 14 shows an overall system flowchart detailing the operation of the printer of the present invention. 
     FIG. 15 is a flowchart showing printer response to user operation of the printer of the present invention. 
     FIG. 16 is a flowchart showing print control flow in accordance with the present invention. 
     FIG. 17 is a flowchart showing setting of scan parameters in the present invention. 
     FIG. 18 depicts a table showing command flow during a printing sequence. 
     FIG. 19 is a flow diagram which depicts a hard power-on sequence for the printer of the present invention. 
     FIG. 20 is a flow diagram which depicts a soft power-on sequence for the printer of the present invention. 
     FIG. 21 is a flow diagram which depicts a soft power-off sequence for the printer of the present invention. 
     FIG. 22 shows cyclic handlers for various tasks including a Centronics interface task. 
     FIG. 23 is a flow diagram illustrating controller timer control according to a cyclic handler for controlling timer operations. 
     FIG. 24 shows a detailed perspective view of the printer shown in FIG. 1, in which the printer has its ejection tray set up for operation. 
     FIG. 25 shows a detailed perspective view of the ejection tray of FIG.  24 . 
     FIG. 25A is a close-up perspective view of an example of a beveled edge which is included on flaps used in the ejection tray of FIG.  25 . 
     FIGS. 25B and 25C are views of the flap shown in FIG. 25A used to explain the beveled edge. 
     FIG. 26 shows a detailed perspective view of connections of a flap on the ejection tray of FIG.  24 . 
     FIG. 27 shows an alternate detailed perspective view of the ejection tray of FIG.  24 . 
     FIG. 28 shows a bottom view of the printer of FIG.  1 . 
     FIGS. 29A to  29 D show the operation of the ejection tray of FIG.  24 . 
     FIG. 29E is a perspective view of a second embodiment of the paper ejection tray of the present invention. 
     FIGS. 30A and 30B show the operation of a cartridge receptacle in the printer of the present invention. 
     FIGS. 31A and 31B show an ink cartridge installed in the cartridge receptacle of FIGS. 30A and 30B. 
     FIG. 32 shows the configuration of an ink cleaning mechanism used on the printer of FIG.  1 . 
     FIGS. 33A and 33B show ink cleaning of each print head installed in the printer of FIG.  1 . 
     FIG. 34 is a flowchart showing compensation of print head command data in a host processor. 
     FIG. 35 is a flowchart showing time based cleaning performed in accordance with the present invention. 
     FIG. 36 is a flowchart showing the steps by which the printer of the present invention maintains an elapsed time schedule. 
     FIGS. 37,  38 ,  39  and  40  are flowcharts showing the automatic cleaning sequence performed by the printer of the present invention. 
     FIG. 41 is a flowchart showing ink cartridge head replacement in accordance with the present invention. 
     FIG. 42 shows steps which are performed when paper is loaded in the printer of the present invention and an automatic cleaning sequence is initiated. 
     FIG. 43 is a timing diagram showing a cleaning schedule in accordance with the present invention. 
     FIG. 43A is a flowchart for describing control of printer nozzle driving times. 
     FIG. 43B is a diagram showing exploded views of tables for heat-up coefficients and tables for driving times stored in a printer. 
     FIG. 43C is a flowchart for describing control of nozzle firing sequence and droplet size. 
     FIGS. 43D to  43 F illustrate correlations between head usage and print buffer usage for various printing conditions. 
     FIG. 43G illustrates nozzle heating sequences for various print conditions. 
     FIGS. 43-1A to  43 - 1 E show transfer of data from a host processor to a print buffer in a printer. 
     FIGS. 43-2A to  43 - 2 E show print data transfer in drawing a backward scan following a forward scan. 
     FIGS. 43-3A to  43 - 3 F show transfer of print data during forward scan of a single print head across a print medium. 
     FIGS. 43-4A to  43 - 4 F show print data transfer during a forward scan in an alternative embodiment of the invention. 
     FIGS. 43-5A to  43 - 5 F show print data transfer during a backward scan after a forward scan has been performed. 
     FIGS. 43-6A to  43 - 6 F show print data transfer during a forward scan of a single print head. 
     FIGS. 43-7A to  43 - 7 L show print data transfer in a forward direction for a pair of print heads. 
     FIG. 44A shows print data transfer in a forward direction for a pair of print heads. 
     FIG. 44B shows print data transfer in a backward direction for a pair of print heads. 
     FIGS. 44C to  44 M are flowcharts illustrating transfer of print data from a print data store in a host processor to a print buffer in a printer. 
     FIG. 44N shows two block diagrams illustrating possible applications of a shift buffer technology within a printing system. 
     FIG. 45 is a representational view for explaining the benefits of printout with different resolutions for each of different heads. 
     FIG. 45A is a flow diagram showing process steps executed by a print driver in the host processor so as to control print resolution for each print head independently, and to command printout to be effectuated thereby. 
     FIG. 46 shows a user interface associated with the printer of the present invention. 
     FIG. 46A is a representational view for explaining the benefits of printing with different resolutions for a print head. 
     FIG. 46B is a flow diagram showing process steps executed by a print driver in the host processor so as to control print resolution for a print head, and to command printout to be effectuated thereby. 
     FIG. 47 is a flow diagram illustrating process steps performed by a printer for independent print resolution setting. 
     FIG. 48 is a flow diagram for describing a method of ink selection. 
     FIG. 49 illustrates a region used for determining whether a black target pixel lies within a differently-colored region. 
     FIG. 49A is a flow diagram describing selection of CMYK black ink or pigment-based black ink. 
     FIGS. 50A,  50 B and  50 C illustrate printing a region adjacent to a boundary between a black region and a differently-colored region. 
     FIG. 51 is a flow diagram for describing a method for printing a region adjacent to a boundary between a black region and a differently-colored region. 
     FIG. 52 is a flow diagram for describing a method for printing a region adjacent to a boundary between a black region and a differently-colored region. 
     FIGS. 53A,  53 B and  53 C illustrate a method for printing data based on print data of a region adjacent to a boundary between a black region and a differently-colored region. 
     FIG. 54 shows color processing according to one embodiment of the invention. 
     FIGS. 54A and 54B show binarization of pixels in accordance with one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     This detailed description of the preferred embodiment is organized into sections, as follows: 
     1.0 Mechanical 
     1.1 Structure 
     1.2 Functions 
     1.2.1 Manual Cleaning 
     1.2.2 Cartridge Replacement 
     1.3 Ink Cartridge 
     1.4 Print Head Structure 
     1.5 Print Modes 
     2.0 Electrical 
     2.1 System Architecture 
     2.2 System Function 
     2.3 Control Logic 
     2.4 General Operation 
     3.0 Architecture of Printer Software 
     3.1 Operating System 
     3.2 Initialization 
     3.3 Tasks 
     3.4 Interrupt Handlers 
     3.5 Cyclic Handlers 
     3.6 Commands To And From The Host Processor 
     3.6.1 Control Commands 
     3.6.2 Setting Commands 
     3.6.3 Maintenance Commands 
     3.7 Commands To And From The Printer Engine 
     4.0 Paper Ejection Tray 
     4.1 First Embodiment 
     4.2 Second Embodiment 
     5.0 Ink Cleaning Mechanism 
     6.0 Storing Printer Profile Parameters 
     7.0 Scheduling Cleaning Of Print Heads 
     7.1 Cleaning Schedule Process 
     7.2 Automatic Cleaning Process 
     7.3 Cleaning Of A Print Head 
     8.0 Setting And Modifying Print Head Driving Parameters 
     9.0 Print Buffer Operation 
     9.1 Single Print Buffer 
     9.2 General Description Of Buffer Control 
     10.0 Multi-Head Printing With Differing Resolutions 
     11.0 Selection of Alternative Inks 
     11.1 Selection of CMYK Black or Pigment Black 
     11.2 Boundary Region Printing 
     11.3 Printing With Different Inks at Different Resolutions 
     1.0 Mechanical 
     This section describes the mechanical layout and functionality of a printer which includes the inventions described herein. 
     1.1 Structure 
     FIG. 1 is a view showing the outward appearance of computing equipment used in connection with the inventions described herein. Computing equipment  20  includes host processor  23 . Host processor  23  comprises a personal computer (hereinafter “PC”), preferably an IBM PC-compatible computer having a windowing environment, such as Microsoft® Windows95. Provided with computing equipment  20  are display screen  22  comprising a color monitor or the like, keyboard  26  for entering text data and user commands, and pointing device  27 . Pointing device  27  preferably comprises a mouse for pointing and for manipulating objects displayed on display screen  22 . 
     Computing equipment  20  includes a computer-readable memory medium, such as fixed computer disk  25 , and floppy disk interface  24 . Floppy disk interface  24  provides a means whereby computing equipment  20  can access information, such as data, application programs, etc., stored on floppy disks. A similar CD-ROM interface (not shown) may be provided with computing equipment  20 , through which computing equipment  20  can access information stored on CD-ROMs. 
     Disk  25  stores, among other things, application programs by which host processor  23  generates files, manipulates and stores those files on disk  25 , presents data in those files to an operator via display screen  22 , and prints data in those files via printer  30 . Disk  25  also stores an operating system which, as noted above, is preferably a windowing operating system such as Windows95. Device drivers are also stored in disk  25 . At least one of the device drivers comprises a printer driver which provides a software interface to firmware in printer  30 . Data exchange between host processor  23  and printer  30  is described in more detail below. 
     In preferred embodiments of the invention, printer  30  is a multi-head serial printer. Accordingly, although the inventions described herein are not limited to use with such a printer, the inventions will be described in the context of a such a printer. 
     In this regard, FIGS. 2 and 3 show close-up perspective front and back views, respectively, of printer  30 . As shown in these figures, printer  30  includes housing  31 , access door  32 , automatic feeder  34 , automatic feed adjuster  36 , manual feeder  37 , manual feed adjuster  39 , media eject port  40 , ejection tray  41 , tray receptacle  42 , indicator light  43 , power button  44 , resume button  46 , power supply  47 , power cord  49 , and parallel port connector  50 . 
     Housing  31  is approximately 498 mm in width by 271 mm in depth by 219 mm in height, and houses the internal workings of printer  30 , including the print engine described below which prints images onto recording media. Included on housing  31  is access door  32 . Access door  32  is manually openable and closeable so as to permit a user to access the internal workings of printer  30  and, in particular, to access print cartridges installed in printer  30 . To this end, printer  30  also includes a sensor (not shown) which senses when access door  32  has been opened and closed. Once it is sensed that access door  32  has been opened, cartridge receptacles which releasably hold the cartridges within printer  30  are moved to a position which corresponds to open access door  32 . Details of this feature are provided below. 
     Disposed on the top of access door  32  is a front panel comprising indicator light  43 , power button  44 , and resume button  46 . Power button  44  is a control by which a user can turn printer  30  on and off. Additional functions, however, are also available through power button  44 . For example, a test print function can be selected by holding down power button  44  until a speaker (not shown) in printer  30  emits a sound, such as one beep. In response to this test print function, printer  30  prints a test pattern. 
     Resume button  46  provides control by which an operator can resume printing after an error condition has occurred. In addition, resume button  46  can be used to activate other functions. For example, a print head cleaning function can be activated by holding down resume button  46  until the speaker in printer  30  produces a beep. 
     In this regard, printer  30  is able to provide a variety of consecutive beeping sounds. Each of these sounds indicates a different type of error, such as paper empty, paper jam, etc. 
     Indicator light  43  is comprised of a single light pipe, a green light emitting diode (hereinafter “LED”), and an orange LED. Indicator light  43  provides a user with an indication of the operational state of printer  30 . Specifically, when indicator light  43  is off, this indicates that printer  30  is powered off. When indicator light  43  is illuminated green (i.e., the green LED is activated), this indicates that printer  30  is powered on and is ready for printing. When indicator light  43  is green and blinking, this indicates an operational state of the printer, such as that the printer is currently powering on. 
     Indicator light  43  can also be illuminated orange by the orange LED. When indicator light  43  is illuminated orange, this indicates that a recoverable error, i.e., an operator call error, has occurred in printer  30 . Recoverable errors comprise paper empty, paper jam, defective cartridge installed in printer  30 , cartridge replacement in process, etc. It is possible to distinguish the type of recoverable error based on a number of beeps from printer  30 &#39;s speaker. By counting these beeps when indicator LED is continuously orange, a user can determine which error has occurred and act accordingly. 
     When indicator light  43  is orange and blinking, this indicates that a fatal error, i.e., a service call error, has occurred in printer  30 . It is possible to distinguish the type of fatal error that has occurred merely by counting how many times the orange light has blinked. 
     As shown in FIGS. 2 and 3, automatic feeder  34  is also included on housing  31  of printer  30 . Automatic feeder  34  defines a media feed portion of printer  30 . That is, automatic feeder  34  stores recording media onto which printer  30  prints images. In this regard, printer  30  is able to print images on a variety of types of recording media. These types include, but are not limited to, plain paper, high resolution paper, transparencies, glossy paper, glossy film, back print film, fabric sheets, T-shirt transfers, bubble jet paper, greeting cards, brochure paper, banner paper, thick paper, etc. 
     Automatic feeder  34  is able to accommodate a recording media stack which is approximately 13 mm thick. This means that automatic feeder  34  can hold, e.g., approximately 130 sheets of paper having a density of 64 g/m 2  or approximately 15 envelopes. During printing, individual sheets which are stacked within automatic feeder  34  are fed from automatic feeder  34  through printer  30 . Specifically, rollers (described below) in printer  30  draw individual media from automatic feeder  34  into printer  30 . These individual media are then fed in a “J” type path through the rollers to eject port  40  shown in FIG.  2 . 
     Automatic feeder  34  includes automatic feed adjuster  36 . Automatic feed adjuster  36  is laterally movable to accommodate different media sizes within automatic feeder  34 . Automatic feeder  34  also includes backing  55 , which is extendible to support recording media held in automatic feeder  34 . When not in use, backing  55  is stored within a slot in automatic feeder  34 , as shown in FIG.  2 . An example of backing  55  extended is shown in FIG. 24 below. 
     Individual sheets also can be fed through printer  30  via manual feeder  37  shown in FIG. 3, which also defines a media feed portion of printer  30 . In preferred embodiments, manual feeder  37  can accommodate media having a density of at least between 64 g/m 2  and 550 g/m 2 , and having a thickness of 0.8 mm. Sheets fed through manual feeder  37  are fed straight through the rollers in printer  30  to eject port  40 . As was the case with automatic feeder  34 , manual feeder  37  includes manual feed adjuster  39 . By sliding manual feed adjuster  39  laterally, a user can vary the media which manual feeder  37  can accommodate. 
     Using manual feeder  37  and automatic feeder  34 , printer  30  can print images on media having a variety of different sizes. These sizes include, but are not limited to, letter, legal, A 4 , A 3 , A 5 , B 4 , B 5 , tabloid, #10 envelope, DL envelope, banner, wide banner, and LTR full bleed. Custom-sized recording media can also be used with printer  30 . 
     As noted above, media are fed through printer  30  and ejected from eject port  40  into ejection tray  41 . As described in greater detail below in section 4.0, ejection tray  41  includes spring-biased flaps which support media ejected from printer  30 , and which move downwardly as more media are piled thereon. When not in use, ejection tray  41  is stored within tray receptacle  42  of printer  30 , as shown in FIG.  2 . 
     Power cord  49  connects printer  30  to an external AC power source. Power supply  47  is used to convert AC power from the external power source, and to supply the converted power to printer  30 . Parallel port  50  connects printer  30  to host processor  23 . Parallel port  50  preferably comprises an IEEE-1284 bi-directional port, over which data and commands, such as those described below in section 3.0, are transmitted between printer  30  and host processor  23 . 
     FIGS. 4 and 5 show back and front cut-away perspective views, respectively, of printer  30 . As shown in FIG. 5, printer  30  includes rollers  60 , noted above, for transporting media from either automatic feeder  34  or manual feeder  37  through printer  30  to media eject port  40 . Rollers  60  rotate in a counterclockwise direction during media transport, as indicated by arrow  60   a  shown in FIG.  5 . 
     Line feed motor  61  controls the rotation of rollers  60 . Line feed motor  61  comprises a 96-step, 2-2 phase pulse motor and is controlled in response to commands received from circuit board  62 . Line feed motor  61  is driven by a motor driver having four level current control. 
     In preferred embodiments, line feed motor  61  is able to cause rollers  60  to rotate so that a recording medium is fed through printer  30  at 120 mm/sec. In a primary mode of operation for printer  30 , line feed resolution is (1/720) inches/pulse (2-2 phase), and in a 1440 dpi mode, line resolution is (1/1440) inches/pulse (1-2 phase). Print modes are described in more detail below. 
     As shown in FIG. 4, printer  30  is a dual-cartridge printer which prints images using two print heads (i.e., one head per cartridge). Specifically, these cartridges are held side-by-side by cartridge receptacles  64   a  and  64   b  such that respective print heads on the cartridges are offset horizontally from each other. Carriage motor  66 , shown in FIG. 5, controls the motion of cartridge receptacles  64   a  and  64   b  in response to commands received from circuit board  62 . Specifically, carriage motor  66  controls the motion of belt  67 , which in turn controls the movement of cartridge receptacles  64   a  and  64   b  along carriage  69 . In this regard, carriage motor  66  provides for bi-directional motion of belt  67 , and thus of cartridge receptacles  64   a  and  64   b . By virtue of this feature, printer  30  is able to print images from both left to right and right to left. 
     Carriage motor  66  comprises a 96-step, 2-2 phase pulse motor having a carriage resolution of (9/360) inches/pulse. Carriage motor  66  is driven by a motor driver having four level current control. When printer  30  is printing in a 360 dpi mode, carriage motor  66  is driven to cause cartridge receptacles  64   a  and  64   b  to move along carriage  69  at a default speed of 459.32 mm/sec (10 Khz). In contrast, when printer  30  is printing in a 720 dpi mode, carriage motor  66  is driven to cause cartridge receptacles  64   a  and  64   b  to move along carriage  69  at a default speed of 229.66 mm/sec (5.0 Khz). Printing speed can also be decreased to 3.26 Khz, as described below in section 3.6.2. 
     FIG. 6A is a detailed perspective view of cartridge receptacle  64   b  from FIG.  4 . Both of cartridge receptacles  64   a  and  64   b  are identical in structure, except for the presence of an auto-alignment (“AA”) sensor, which is only included on cartridge receptacle  64   b . Accordingly, for the sake of brevity, only cartridge receptacle  64   b  is described in detail herein. 
     Cartridge receptacle  64   b  is used to hold an ink cartridge (which includes a print head and can include one or more removable ink reservoirs for storing ink) in printer  30 . In this regard, FIGS. 7A and 7B show the configuration of ink cartridge  300   b  which may be installed within cartridge receptacle  64   b  (see FIG.  4 ). As shown in FIGS. 7A and 7B, ink cartridge  300   b  comprises print head  80 , ink reservoirs  83 , cartridge circuit contact  81 , and hole  90 . At this point, it is noted that the present invention can also be used with ink cartridges that do not contain removable ink reservoirs, but instead store all ink internally. 
     Ink reservoirs  83  are removable from ink cartridge  300   b  and store ink used by printer  30  to print images. Specifically, ink reservoirs  83  are inserted within cartridge  300   b  and can be removed by pulling along the direction of arrow  85 , as shown in FIG.  7 B. Reservoirs  83  can store color (e.g., cyan, magenta and yellow) ink and/or black ink, as described in more detail below. Print head  80  includes a plurality of nozzles (not shown) which eject ink from ink reservoirs  83  during printing. Cartridge circuit contact  81  is used by printer  30  to trigger ink cartridge cleaning, as described below. Cartridge hole  90  mates to pin  93  on cartridge receptacle  64   b  so as to hold ink cartridge  300   b  in place. 
     Returning to FIG. 6A, cartridge receptacle  64   b  includes opening  79  at a bottom thereof. A print head, such as print head  80 , of an installed cartridge protrudes through opening  79 . By virtue of this configuration, the cartridge&#39;s print head is able to contact a recording medium in printer  30 . Cartridge receptacle  64   b  also includes lever  72  and capsule  73 . As described in more detail in section 5.0 below, lever  72  pivots relative to ink reservoirs of an ink cartridge stored in cartridge receptacle  64   b  such that lever  72  extends over at least a portion of the ink reservoirs, and pivots away from the ink reservoirs so as to permit user access to the ink reservoirs. 
     Capsule  73  holds the ink cartridge (including the print head and ink reservoirs) within cartridge receptacle  64   b  and is laterally movable within cartridge receptacle  64   b  in response to pivoting of lever  72 . During this lateral motion, finger  282  on capsule  73  slidably engages sleeve  284  on stationary section  502 . By virtue of this lateral motion, a cartridge circuit contact, such as cartridge circuit contact  81  on ink cartridge  300   b , engages and disengages a circuit contact on cartridge receptacle  64   b , namely device circuit contact  71 . This process is used to output a signal which prompts cleaning of a print head, and is described in more detail below. 
     FIG. 6B shows a back view of the construction of cartridge receptacle  64   b . Specifically, FIG. 6B shows the interconnection of capsule  73 , lever  72 , back piece  501 , and stationary section  502  (shown in two dotted/dashed lines). In this regard, lever  72  includes fingers  507  which connect to corresponding holes  504  in back piece  501 . By virtue of this arrangement, when lever  72  is pivoted downward in the direction of arrow Al shown in FIG. 6B, back piece  501  moves upward in the direction of arrow A 2  also shown in FIG.  6 B. Conversely, when lever  72  is pivoted upward in the direction of arrow B 1 , back piece  501  moves downward in the direction of arrow B 2 . This upward and downward movement of back piece  501  controls the lateral movement of capsule  73  described above. 
     To this end, back piece  501  includes cam surface  509  which interacts with spring-loaded push rod  510  when the lever/back piece assembly is installed in stationary section  502 . Specifically, the lever/back piece assembly is connected to stationary section  502  via fingers  508  and corresponding holes  506 . When connected in this manner, cam surface  509  of back piece  501  contacts spring-loaded push rod  510  on the back of capsule  73 . This connection causes capsule  73  to move laterally when lever  72  is pivoted. 
     More specifically, because cam surface  509  includes angled side  511  and straight side  512 , when cam surface  509  moves upwards (i.e., when lever  72  is pivoted toward capsule  73  in the direction of arrow A 1 , causing back piece  501  and thus cam surface  509  to move upward in the direction of arrow A 2 ), push rod  510  is pushed in the direction of arrow A 4  by angled side  511  of cam surface  509 . This motion causes capsule  73  to move in the direction of arrow A 3  shown in FIG.  6 B. 
     Conversely, when cam surface moves downward (i.e., when lever  72  is pivoted away from capsule  73  in the direction of arrow B 1 , causing back piece  501  and thus cam surface  509  to move downward in the direction of arrow B 2 ), push rod  510  no longer contacts angled side  511 . Instead, cam surface  509  moves such that push rod  510  corresponds to straight side  512 . In this position, spring  513 , which is disposed underneath capsule  73  and which biases capsule  73  relative to stationary section  502 , moves capsule  73  in the direction of arrow B 3  shown in FIG.  6 B. 
     As shown in FIG. 6B, lever  72  also includes flanges  287  which contact shoulders  286  on the capsule/stationary section assembly. As described in more detail below, this contact reduces the chances that lever  72  will engage a cartridge and/or ink reservoir in cartridge receptacle  64   b.    
     As shown in FIG. 6A, cartridge receptacle  64   b  includes automatic alignment sensor  82 . Automatic alignment sensor  82  senses a position of a dot pattern formed by printer  30 . This information is used to align all print heads in printer  30 . Also included in connection with cartridge receptacles  64   a  and  64   b  is a home location sensor (not shown), which is used to detect when cartridge receptacles  64   a  and  64   b  are at a home location relative to carriage  69 . The position and significance of the home location are described in detail below. 
     Returning to FIG. 4, printer  30  includes wipers  84   a  and  84   b  and ink cleaning mechanism  86 . Ink cleaning mechanism  86  is disposed at home location  87  and comprises a rotary pump (not shown) and print head connection caps  88   a  and  88   b . Print head connection caps connect to print heads of cartridges installed in cartridge receptacles  64   a  and  64   b , respectively, during print head cleaning and at other times, such as when printer  30  is powered off, so as to protect the print heads. 
     Line feed motor  61  drives the rotary pump of ink cleaning mechanism  86  so as to suction excess ink from a print head connected to print head connection cap  88   a . As described in more detail in section 5.0 below, ink is suctioned only from a user-designated one or ones of the cartridges. User designation is described below. 
     Wipers  84   a  and  84   b  can comprise blades or the like which are driven by carriage motor  66  to wipe excess ink from cartridge print heads. Specifically, wipers  84   a  and  84   b  are lifted to contact a print head after a predetermined condition has occurred. For example, wipers  84   a  and  84   b  can be lifted after a predetermined number of dots have been printed by a print head. 
     1.2 Functions 
     Printer  30  includes a variety of functions and features which are available via access door  32  and printer  30 &#39;s front panel. A description of these functions follows. 
     1.2.1 Manual Cleaning 
     Printer  30  includes a manual cleaning function which can be activated via its front panel. Specifically, manual cleaning is activated by pressing resume button  46  until printer  30  emits a beep which is two seconds long. To indicate that manual cleaning has been activated, indicator light  43  blinks. Any medium in the process of printing is then ejected from eject port  40 . Ink cleaning mechanism  86  then cleans, e.g., suction ink from and wipes ink off of, the print heads of ink cartridges stored in cartridge receptacles  64   a  and  64   b , and the suctioned and wiped ink is stored in a waste ink storage area. Thereafter, indicator light  43  stops blinking and is turned on if no errors have occurred. In the event that a waste ink error has occurred, e.g., the waste ink storage area is near capacity, the orange LED will illuminate indicator light  43  and printer  30  will emit six beeping sounds. 
     1.2.2 Cartridge Replacement 
     Printer  30  enters a cartridge replacement mode once access door  32  is opened unless any of the following conditions is present: printer  30  is powered off, a recording medium has been fed from a sheet feeder, printer  30  is printing or has received data from host processor  23 , a paper empty error or a paper jam has occurred, the temperature of a print head in printer  30  is too high, or a fatal error has occurred. 
     In this regard, the cartridge replacement mode is generally entered either at printer setup to install either entire ink cartridges or ink reservoirs, or during the printer&#39;s lifetime to replace used or defective cartridges or reservoirs. At initial printer setup, there is no ink cartridge or reservoir in one of cartridge receptacles  64   a  or  64   b . To make this known, indicator light  43  blinks. To install a cartridge or reservoir, a user opens access door  32 , which, as described below, causes cartridge receptacles  64   a  and  64   b  to move to a center position along carriage  69 . At this position, a user can install an ink cartridge simply by lifting levers  72  of cartridge receptacles  64   a  and  64   b , dropping the cartridges, print head first, into cartridge receptacles  64   a  and  64   b , and closing levers  72 . The process of replacing an empty or defective ink cartridge is identical to that described here. To replace an ink reservoir, the user can pull the defective or empty ink reservoir off of the cartridge, and insert a new ink reservoir in its place. 
     To terminate the cartridge replacement mode, a user need simply close access door  32 . Once the replacement mode has been terminated, printer  30  checks the newly-installed cartridge to determine if it has been installed correctly. If the cartridge or reservoir is correctly installed, printer  30  causes cartridge receptacles  64   a  and  64   b  to move to home location  87 . On the other hand, if the cartridge or reservoir is installed incorrectly, or cannot be used for some reason (e.g., it is defective), then indicator light  43  illuminates orange. In addition, printer  30  emits three beeps to indicate that there is a problem with an ink cartridge in cartridge receptacle  64   b , and emits four beeps to indicate that there is a problem with an ink cartridge in cartridge receptacle  64   a.    
     1.3 Ink Cartridge 
     The printer described herein can use ink cartridges which include removable ink reservoirs for storing different types of ink. An example of such a cartridge is shown in FIGS. 7A and 7B. As noted above, however, the present invention can also be used with disposable ink cartridges that do not contain removable ink reservoirs, but instead store all ink internally. An example of such a cartridge is shown in FIG.  7 . 
     In general, printer  30  can operate with a variety of different cartridge types. For example, printer  30  can use a cartridge which stores dye-based black ink and which has a print head with 128 nozzles extending in the vertical direction. An example of such a cartridge is a Canon BC-20 cartridge. A similar type cartridge may also be used which stores pigment black ink. In this regard, generally speaking, dye-based black ink has high penetration characteristics relative to a recording medium. On the other hand, pigment-based black ink generally has low penetration characteristics (and in some cases no penetration) relative to a recording medium. 
     Printer  30  can also operate with color ink cartridges. For example, printer  30  can operate with an ink cartridge which stores cyan, magenta, yellow and black inks, and which includes 136 nozzles extending in the vertical direction. In such a cartridge, 24 nozzles print with cyan ink, 24 nozzles print with magenta ink, 24 nozzles print with yellow ink, and 64 nozzles print with black ink. An example of such a cartridge is a Canon BC-21(e) cartridge. 
     Still another example of an ink cartridge that may be used with printer  30  stores reduced optical density (e.g., “photo”) ink, and includes 136 nozzles arranged in the vertical direction. Such a cartridge also has the same nozzle configuration as the color cartridge described above. 
     1.4 Print Head Structure 
     With regard to the physical construction of the print heads of cartridges that may be used with the present invention, FIG. 8 shows a close-up, face-on view of nozzle configurations for a case in which printer  30  includes print head  98  having 128 nozzles and arranged near-vertical, with each nozzle closely spaced to adjacent nozzles. Such an arrangement is preferred for single color (such as black) printing. The nozzles are preferably arranged at a slight oblique slant so that as the print head is moved across the recording medium, it is possible to fire the nozzles in rapid succession, rather than all at once, so as to print a vertical line. The power and control requirements for firing nozzles in rapid succession are significantly reduced relative to those for firing all at once. One preferable arrangement of slant angle would correspond to a one pixel horizontal change for every 16 vertical nozzles, at 360 dpi resolution. 
     Print head  99  has 136 nozzles, with 24 nozzles preferably for yellow ink, 24 nozzles preferably for magenta ink, 24 nozzles preferably for cyan ink, and 64 nozzles preferably for black ink, arranged at a slight slant angle to vertical, one on top of another. Each color group of nozzles is separated from an adjacent group by a vertical gap corresponding to 8 nozzles. The slight slant angle is, again, arranged to provide one pixel of horizontal change for every 16 vertical nozzles, at 360 dpi. 
     1.5 Print Modes 
     During its operation, printer  30  includes different modes which may be set via commands issued to printer  30  by host processor  23  (see FIG.  1 ). In these modes, cartridges installed in printer  30  may eject different-sized ink droplets to form images having different resolutions. Whether certain modes of printer  30  are available depends, in part, on the type of cartridge installed in printer  30 . That is, print heads on some types of cartridges are capable of ejecting different-sized droplets, e.g., large or small ink droplets, whereas print heads on other types of cartridges are capable of ejecting droplets having a single size. 
     As noted above, different ink droplet sizes are used during different printer operational modes to form images having different resolutions. More specifically, ink jet printers create images by forming dots on a page. The resolution of a formed image corresponds in part to the number of dots formed and in part to the arrangement in which those dots are formed. In the printer of the present invention, images can be formed at a variety of different resolutions using either the large or small ink droplets described above. 
     At this point, it is noted that dot allocation and arrangement during printing is limited, in part, based upon the type of paper used during printing. Specifically, plain paper can absorb approximately a maximum of four small droplets in a 360 dpi pixel, whereas high resolution (hereinafter “HR-101”) paper can absorb a maximum of 6 small droplets in a 360 dpi pixel. 
     With the foregoing in mind, FIG. 9 shows droplet arrangements for each pixel in a 180 horizontal (H) by 180 vertical (V) rasterization using regular (i.e., non-photo) ink and any type of paper. As shown in FIG. 9, this arrangement provides for three levels, and can attain a 360(H) by 360(V) dpi printout using large droplets. 
     2.0 Electrical 
     As described in section 1.0 above, printer  30  may use multiple print heads in different combinations, such as black-black, black-color, color-color, or color-photo, so that several print modes may be executed at different resolutions (e.g., 180 dpi, 360 dpi, 720 dpi). Further, print head combinations may be changed for different print modes, such as text, text and color, color and high quality color. As a result, printing tasks for the different modes require complex operations that vary based on the print head combination, recording media and print quality. In the information processing system of FIG. 1, printer parameters relating to print head configuration, print head alignment, etc. are stored in printer  30  and sent to host processor  23  based on data obtained by printer  30 . Accordingly, a printer driver in host processor  23  performs the complex processing of print data and printer set up for the various print modes and sends dictated command sequences to the printer that simplify printing execution. Advantageously, the architecture of the printer is simplified while the demands of the print processing on host processor  23  have little or no effect on the operation of host processor  23 . 
     2.1 System Architecture 
     FIG. 10 is a block diagram showing the internal structures of host processor  23  and printer  30 . In FIG. 10, host processor  23  includes a central processing unit  100  such as a programmable microprocessor interfaced to computer bus  101 . Also coupled to computer bus  101  are display interface  102  for interfacing to display  22 , printer interface  104  for interfacing to printer  30  through bi-directional communication line  106 , floppy disk interface  24  for interfacing to floppy disk  107 , keyboard interface  109  for interfacing to keyboard  26 , and pointing device interface  110  for interfacing to pointing device  27 . Disk  25  includes an operating system section for storing operating system  111 , an applications section for storing applications  112 , and a printer driver section for storing printer driver  114 . 
     A random access main memory (hereinafter “RAM”)  116  interfaces to computer bus  101  to provide CPU  100  with access to memory storage. In particular, when executing stored application program instruction sequences such as those associated with application programs stored in applications section  112  of disk  25 , CPU  100  loads those application instruction sequences from disk  25  (or other storage media such as media accessed via a network or floppy disk drive  24 ) into random access memory (hereinafter “RAM”)  116  and executes those stored program instruction sequences out of RAM  116 . RAM  116  provides for a print data buffer used by printer driver  114  according to the invention, as described more fully hereinbelow. It should also be recognized that standard disk-swapping techniques available under the windowing operating system allow segments of memory, including the aforementioned print data buffer, to be swapped on and off of disk  25 . Read only memory (hereinafter “ROM”)  43  in host processor  23  stores invariant instruction sequences, such as start-up instruction sequences or basic input/output operating system (BIOS) sequences for operation of keyboard  26 . 
     As shown in FIG. 10, and as previously mentioned, disk  25  stores program instruction sequences for a windowing operating system and for various application programs such as graphics application programs, drawing application programs, desktop publishing application programs, and the like. In addition, disk  25  also stores color image files such as might be displayed by display  22  or printed by printer  30  under control of a designated application program. Disk  25  also stores a color monitor driver in other drivers section  119  which controls how multi-level RGB color primary values are provided to display interface  102 . Printer driver  114  controls printer  30  for both black and color printing and supplies print data for print out according to the configuration of printer  30 . Print data is transferred to printer  30 , and control signals are exchanged between host processor  23  and printer  30 , through printer interface  104  connected to line  106  under control of printer driver  114 . Other device drivers are also stored on disk  25 , for providing appropriate signals to various devices, such as network devices, facsimile devices, and the like, connected to host processor  23 . 
     Ordinarily, application programs and drivers stored on disk  25  need first to be installed by the user onto disk  25  from other computer-readable media on which those programs and drivers are initially stored. For example, it is customary for a user to purchase a floppy disk, or other computer-readable media such as CD-ROM, on which a copy of a printer driver is stored. The user would then install the printer driver onto disk  25  through well-known techniques by which the printer driver is copied onto disk  25 . At the same time, it is also possible for the user, via a modem interface (not shown) or via a network (not shown), to download a printer driver, such as by downloading from a file server or from a computerized bulletin board. 
     Referring again to FIG. 10, printer  30  includes CPU  121  such as an 8-bit or a 16-bit microprocessor including programmable timer and interrupt controller, ROM  122 , control logic  124 , and I/O ports unit  127  connected to bus  126 . Also connected to control logic  124  is RAM  129 . Control logic  124  includes controllers for line feed motor  61 , for print image buffer storage in RAM  129 , for heat pulse generation, and for head data. Control logic  124  also provides control signals for nozzles in print heads  130   a  and  130   b  of print engine  131 , carriage motor  66 , line feed motor  61 , and print data for print heads  130   a  and  130   b , and receives information from print engine  131  for alignment of print heads  130   a  and  130   b  through I/O ports unit  127 . EEPROM  132  is connected to I/O ports unit  127  to provide non-volatile memory for printer information such as print head configuration and print head alignment parameters. EEPROM  132  also stores parameters that identify the printer, the driver, the print heads, alignment of the print heads, the status of ink in the cartridges, etc., which are sent to printer driver  114  of host processor  23  to inform host processor  23  of the operational parameters of printer  30 . 
     I/O ports unit  127  is coupled to print engine  131  in which a pair of print heads  130   a  and  130   b  (which would be stored in cartridge receptacles  64   a  and  64   b , respectively) perform recording on a recording medium by scanning across the recording medium while printing using print data from a print buffer in RAM  129 . Control logic  124  is also coupled to printer interface  104  of host processor  23  via communication line  106  for exchange of control signals and to receive print data and print data addresses. ROM  122  stores font data, program instruction sequences used to control printer  30 , and other invariant data for printer operation. RAM  129  stores print data in a print buffer defined by printer driver  114  for print heads  130   a  and  130   b  and other information for printer operation. 
     Print heads  130   a  and  130   b  of print engine  131  correspond to ink cartridges that are stored in cartridge receptacles  64   a  and  64   b , respectively. Sensors generally indicated as  134  are arranged in print engine  131  to detect printer status and to measure temperature and other quantities that affect printing. A photo sensor (e.g., automatic alignment sensor  82  shown in FIG. 6A) in cartridge receptacles  64  measures print density and dot locations for automatic alignment. Sensors  134  are also arranged in print engine  131  to detect other conditions such as the open or closed status of access cover  32 , presence of recording media, etc. In addition, diode sensors, including a thermistor, are located in print heads  130   a  and  130   b  to measure print head temperature, which is transmitted to I/O ports unit  127 . 
     I/O ports unit  127  also receives input from switches  133  such as power button  44  and resume button  46  and delivers control signals to LEDs  135  to light indicator light  43 , to buzzer  128 , and to line feed motor  61  and carriage motor  66  through line feed motor driver  61   a  and carriage motor driver  66   a , respectively. As described above, buzzer  128  may comprise a speaker. 
     Although FIG. 10 shows individual components of printer  30  as separate and distinct from one another, it is preferable that some of the components be combined. For example, control logic  124  may be combined with I/O ports  127  in an ASIC to simplify interconnections for the functions of printer  30 . 
     2.2 System Function 
     FIG. 11 shows a high-level functional block diagram that illustrates the interaction between host processor  23  and printer  30 . As illustrated in FIG. 11, when a print instruction is issued from image processing application program  112   a  stored in application section  112  of disk  25 , operating system  111  issues graphics device interface calls to printer driver  114 . Printer driver  114  responds by generating print data corresponding to the print instruction and stores the print data in print data store  136 . Print data store  136  may reside in RAM  116  or in disk  25 , or through disk swapping operations of operating system  111  may initially be stored in RAM  116  and swapped in and out of disk  25 . Thereafter, printer driver  114  obtains print data from print data store  136  and transmits the print data through printer interface  104 , to bi-directional communication line  106 , and to print buffer  139  through printer control  140 . Print buffer  139  resides in RAM  129  and printer control  140  resides in control logic  124  and CPU  121  of FIG.  10 . Printer control  140  processes the print data in print buffer  139  responsive to commands received from host processor  23  and performs printing tasks under control of instructions stored in ROM  122  (see FIG. 10) to provide appropriate print head and other control signals to print engine  131  for recording images onto recording media. 
     Print buffer  139  has a first section for storing print data to be printed by one of print heads  130   a  and  130   b , and a second section for storing print data to be printed by the other one of print heads  130   a  and  130   b.  Each print buffer section has storage locations corresponding to the number of print positions of the associated print head. These storage locations are defined by printer driver  114  according to a resolution selected for printing. Each print buffer section also includes additional storage locations for transfer of print data during ramp-up of print heads  130   a  and  130   b  to printing speed. Print data is transferred from print data store  136  in host processor  23  to storage locations of print buffer  139  that are addressed by printer driver  114 . As a result, print data for a next scan may be inserted into vacant storage locations in print buffer  139  both during ramp up and during printing of a current scan. 
     2.3 Control Logic 
     FIG. 12 depicts a block diagram of control logic  124  and I/O ports unit  127  from FIG.  10 . As mentioned above, I/O ports unit may be, alternatively, included within control logic  124 . In FIG. 10, user logic bus  146  is connected to printer bus  126  for communication with printer CPU  121 . Bus  146  is coupled to host computer interface  141  which is connected to bi-directional line  106  for carrying out bi-directional such as IEEE-1284 protocol communication. Accordingly, bi-directional communication line  106  is also coupled to printer interface  104  of host processor  23 . Host computer interface  141  is connected to bus  146  and to DRAM bus arbiter/controller  144  for controlling RAM  129  which includes print buffer  139  (see FIGS.  10  and  11 ). Data decompressor  148  is connected between bus  146  and DRAM bus arbiter/controller  144  to decompress print data when processing. Also coupled to bus  146  are line feed motor controller  147  that is connected to line feed motor driver  61   a  of FIG. 10, image buffer controller  152  which provides serial control signals and head data signals for each of print heads  130   a  and  130   b , and heat pulse generator  154  which provides block control signals and analog heat pulses for each of print heads  130   a  and  130   b.  Carriage motor control is performed by CPU  121  through I/O ports unit  127  and carriage motor driver  66   a  since line feed motor  61  and carriage motor  66  may operate concurrently. 
     Control logic  124  operates to receive commands from host processor  23  for use in CPU  121 , and to send printer status and other response signals to host processor  23  through host computer interface  141  and bi-directional communication line  106 . Print data and print buffer memory addresses for print data received from host processor  23  are sent to print buffer  139  in RAM  129  via DRAM bus arbiter/controller  144 , and the addressed print data from print buffer  139  is transferred through controller  144  to print engine  131  for printing by print heads  130   a  and  130   b . In this regard, heat pulse generator  154  generates analog heat pulses required for printing the print data. 
     FIG. 13 shows the memory architecture for printer  30 . As shown in FIG. 13, EEPROM  132 , RAM  129 , ROM  122  and temporary storage  161  for control logic  124  form a memory structure with a single addressing arrangement. Referring to FIG. 13, EEPROM  132 , shown as non-volatile memory section  159 , stores a set of parameters that are used by host processor  23  and that identify printer and print heads, print head status, print head alignment, and other print head characteristics. EEPROM  132  also stores another set of parameters, such as clean time, auto-alignment sensor data, etc., which are used by printer  30 . ROM  122 , shown as memory section  160 , stores information for printer operation that is invariant, such as program sequences for printer tasks and print head operation temperature tables that are used to control the generation of nozzle heat pulses, etc. A random access memory section  161  stores temporary operational information for control logic  124 , and memory section  162  corresponding to RAM  129  includes storage for variable operational data for printer tasks and print buffer  139 . 
     2.4 General Operation 
     FIG. 14 is a flowchart illustrating the general operation of the information processing system shown in the block diagram of FIG.  10 . After power is turned on in printer  30  in step S 1401  of FIG. 14, printer  70  is initialized in step S 1402 . In the initialization, as discussed in greater detail in section 3.2 below and shown in FIGS. 19 and 20, CPU  121 , control logic  124  and a system timer are set to an initial state. In addition, ROM  121 , RAM  129  and EEPROM  132  of printer  30  are checked and interrupt request levels in CPU  121  are assigned on application of power to printer  30 . When printer  30  is set to its on state, EEPROM  132  is read by printer driver  114 , controller tasks are started by printer CPU  121  such as resetting the printer, determining if print head cleaning should be performed based on the system timer, etc. Also in the initialization process of step S 1402 , a data compression mode is selected, heat pulses for print heads  130   a  and  130   b  are defined, buffer control is defined, print buffer  139  is cleared, and messages are displayed indicating the status of printer  30 . 
     Next, step S 1403  is performed. In step S 1403 , printer driver  114  calculates printer parameters from data obtained by printer CPU  121  based on printer measurements related to head configuration and alignment if it is determined that the print head configuration has changed. The alignment system is described more fully in U.S. patent application Ser. No. 08/901,560, entitled “Auto-Alignment System For A Printing Device”, filed on Jul. 28, 1997, which is incorporated herein by reference. 
     Following step S 1403 , processing proceeds to step S 1404 , in which it is determined if printer  30  is on-line. Once it is determined that printer  30  is on-line, processing proceeds to step S 1405 , in which the calculated printer parameters are registered in printer EEPROM  132 . 
     Specifically, when printer  30  is determined to be on-line, the printer parameters stored in the EEPROM  132  are registered by printer driver  114  in step S 1405 . The parameters are then sent, in step S 1405 , by CPU  121  for storage in host processor  23  so that printer driver  114  can generate appropriate commands for printer operation. Such commands are indicated in the steps of the dashed box of FIG.  14  and take into account the current identification of printer  30 , the print head configuration, print head alignment and cartridge ink status. 
     A method in accordance with step S 1405  for sending the parameters comprises sending data representative of the printer parameters for the current head configuration to the host processor. A printer driver in the host processor generates commands for controlling printer function according to the characteristics of the attached print devices and sends the generated commands to the printer controller. The commands include parameters corresponding to the characteristics of the attached print devices to allow control of printer operations for a variety of multiple print device configurations. The sending of printer parameter data to the printer driver in the host processor and the generation and sending of commands are described in greater detail in section 6.0. 
     With regard to print head cleaning, cleaning can be scheduled at various times during operation of the printer, such as in step S 1405 A. The method for scheduling cleaning a print head in accordance with step S 1405 A includes receiving real time/date (time and/or date) information from an external source, storing the real time/date information in a volatile memory, storing, in a non-volatile RAM, a last cleaning time for at least one print head in the ink jet printer, and calculating an elapsed time by subtracting the stored real time/date information and the stored last cleaning time. The method further includes comparing the calculated elapsed time to a predetermined elapsed time, controlling the at least one print head to perform a cleaning process when the calculated elapsed time is greater than or equal to the predetermined elapsed time, and storing, in the non-volatile memory, the latest last time for cleaning the at least one print head. When the calculated elapsed time is less than the predetermined elapsed time, the method waits to perform a cleaning based on either an elapsed internal time, a comparison of the next downloaded time, or an occurrence of a cleaning event such as replacing a print head. The scheduling of print head cleaning is described in greater detail in section 7.0 below. 
     The parameters registered in step S 1405  are used to control print head operation. A method in accordance with step S 1405  for controlling a print head of an image printing device having at least one print head includes obtaining profile information of the at least one print head comprising the parameters registered in step S 1405 . The method includes storing the profile parameters in a non-volatile RAM and outputting, upon request, the profile information to a host processor connected to the image printing device. The host processor utilizes the print head profile information to produce compensation parameters which compensate print information to be sent from the host processor to the print head for printing. This method is described in greater detail in section 8.0. 
     After registration of the printer parameter information in step S 1405 , and cleaning scheduling in step S 1405 A, the status of each of print head cartridges  300   a  and  300   b  (see FIG. 4) is checked in step S 1406 . This is done by ascertaining whether access door  32  has been opened and closed and detecting whether one or more of the ink cartridges or ink reservoirs has been changed. If a cartridge or reservoir has been changed, a cleaning operation is performed on the corresponding print head, in which the nozzles of the print head are cleaned. 
     A device used in step S 1406  for cleaning a print head during ink reservoir/cartridge change comprises a cartridge receptacle which is mounted on a carriage for releasably receiving a cartridge having a print head and at least one removable ink reservoir. The receptacle includes a pivoting lever which permits removal of the at least one ink reservoir. The lever extends over at least a portion of the at least one ink reservoir so as to prevent access to the at least one ink reservoir until such time as the lever is pivoted away from the at least one ink reservoir. When the lever is pivoted away from the at least one ink reservoir and then is pivoted over the at least a portion of the at least one ink reservoir, a signal is output which prompts cleaning of the print head. Print head cleaning arrangements are described in greater detail in section 5.0. 
     Following the cartridge change processing performed in step S 1406 , processing proceeds to step S 1407 . In step S 1407 , it is determined whether an interrupt has been requested by printer  30  for operations such as print head heater control. In response to such an interrupt request, the requested printer operation is performed in step S 1408 . Thereafter, processing returns to step S 1406 . 
     If an interrupt has not been requested by the printer in step S 1407 , processing proceeds to step S 1409 . In step S 1409 , it is determined if printer driver  114  has requested a command sequence. In the system of FIG. 10, tasks of printer  30  are controlled by commands from printer driver  114  which have been generated in accordance with parameter and status information received from printer  30 . When a user interface sequence is selected, step S 1414  is entered and the processing shown in FIG. 15 is executed. 
     Upon selection of the user interface, in step S 1501 , the current status of printer  30  is requested and received from printer  30  over bi-directional communication line  106 . Then, in step S 1502 , it is determined if printer  30  has a new print head. When a new print head is detected, an automatic alignment is performed in step S 1503 , and in step S 1504  the status information of printer  30  is stored in printer driver  114 . Otherwise, the latest printer driver information is obtained for the user in step S 1505 . In either event, it is then determined in step S 1506  if the page to be printed is a utility page for head exchange and/or alignment or the top page of a document. When a utility page is selected, the current head configuration is displayed in step S 1507  and the user selects whether to enable or disable printer  30  in step S 1508 . Selection step S 1509  is then entered and the user may select alignment by step S 1510 , head exchange and alignment by steps S 1510  and S 1511  followed by storing of printer status information in step S 1512 , a recovery operation to clean print heads  130   a  and  130   b  by step S 1513 , or cancellation of the user interface in step  1514 . Once the tasks selected in step S 1509  are performed, control is returned to step S 1409  of FIG.  14 . 
     When the print mode is selected in step S 1506  of FIG. 15, the current head configuration is displayed to the user (step S 1515 ). After operation of an enable-disable button in step S 1516 , the user may select, in step S 1517 , print, media type, media size, target image, custom page setting, utility or cancel operations. The selection of media type (step S 1518 ), media size (step S 1519 ), target image (step S 1520 ) (i.e., text and color or photo-color), custom paper size (step S 1521 ), and custom setting page (step S 1522 ) causes information to be stored in printer driver  114  which controls the print parameters and print data for the print sequence to be performed. Upon completion of the user selections by means of keyboard and pointer entry on the user interface display, control is returned to step S 1409  and is directed to use print command sequence step S 1410 . 
     If a print sequence is selected in step S 1409 , processing proceeds to step S 1410 . In step S 1410 , printer driver  114  generates a sequence of commands based on print head configuration, print head alignment, media type and size and target image information stored therein. These commands are sent to printer control  140  (see FIG. 11) in printer  30 . In the printer, printer control  140  receives the commands and the firmware from printer ROM  122  and causes execution of command tasks in print engine  131 . 
     The print command sequence includes transferring print data from print driver  114  to print buffer  139  which is defined for each print job. The print data transfer is performed without a receiving buffer in printer  30 . Print data for a next scan is sent to empty storage locations of the current scan in print buffer  139  during ramp-up of the print heads in the current scan. 
     In brief, the print buffer to which commands are transferred in step S 1410  includes a set of storage locations corresponding to the print positions of the current scan for each print head. The printer driver identifies empty storage locations of the current scan in the print buffer and sends print data for the next scan of the print head to the identified empty storage locations during the ramp-up period of the current scan of the print head. The print data transfer in the print command sequence according to the invention is described more fully below in section 9.0. 
     The command sequence of step S 1410  includes commands to set print resolution of print heads  130   a  and  130   b . These commands are set by controlling the size of ink droplets based on digital data stored in a print buffer for a print head and the order in which the print data is read out of the print buffer for the print head. Specifically, a method for controlling print resolution in a printer having first and second print heads includes controlling resolution of the first and second heads independently of each other. For ink jet type print heads which eject ink droplets based on digital data stored in a print buffer, resolution is controlled by controlling ink droplet size and by controlling readout order from the print buffer, with droplet size and readout order being controlled independently for each print head. Print resolution control is described in greater detail in section 10.0. 
     Further in the print command sequence of step S 1410 , printer driver  114  selects the type of ink that is to be used in printing a target pixel based on an analysis multi-level image data of adjacent pixels. As an example, a dye-based ink may be selected for a black target pixel surrounded by color pixels in an image while a pigment-based ink may be selected for a black target pixel surrounded by black pixels. 
     In summary, a method, in accordance with the present invention, of controlling printing of pixels corresponding to a multi-level image includes determining, based on multi-level image data for a target pixel and multi-level image data for pixels adjacent to the target pixel, whether the target pixel should be printed using a dye-based ink or whether the target pixel should be printed using a pigment-based ink, instructing a printer to print the target pixel using the dye-based ink in a case that it is determined that the target pixel should be printed using the dye-based ink, and instructing the printer to print the target pixel using the pigment-based ink in a case that it is determined that the target pixel should be printed using the pigment-based ink. The control of pixel printing is described in greater detail in section 11.0. 
     Upon completion of printing one page, flow proceeds to step S 1411  of FIG. 14, wherein the page is output from printer  30  responsive to a paper eject command. Printer  30  then ejects the page to a pair of angled retractable flaps adjustably positioned by springs on a tray as described in section 4.0. While moving onto the tray during printing, the level at which a page slides onto previously-ejected pages is maintained by downward movement the flaps so that the page does not bend in the print head area. Such bending may cause distortion of an image being printed. Moreover, the paper ejection tray has a structure which facilitates storage and setup. 
     To this end, this aspect of the invention is an ejection tray for a printer having a housing defining a media feed portion and a media eject port, where the housing is adapted to house a print engine for printing onto recording media. The ejection tray includes a base slidably receivable in the printer&#39;s housing at a position laterally distanced from the media eject port. The base includes at least a pair of recesses extending in a sliding direction of the base. A pair of flaps are also included in the ejection tray. The pair of flaps each have at least one width portion corresponding to the lateral distance between the base and the eject port. Each flap is hinged into a corresponding recess of the base and is biased in an upward direction via a spring which provides for angular motion of the flap relative to the base. Upon sliding action of the base out of the housing, the flaps are biased upward out of the recesses to a height corresponding to the position of the media eject port. 
     FIG. 16 is a flowchart that illustrates in greater detail a command sequence generated by printer driver  114  for printing and operating printer  30 . In FIG. 16, the print command sequence is started by a printer initialization command in step S 1601 , which is sent to printer control  140  to reset printer operation. A paper load command (step S 1602 ) is then provided to printer control  140 , which selects a load paper operation in selection step S 1603  and executes a start paper load (step S 1604 ). When a paper load end is detected in printer control  140  in step S 1605 , a signal indicating end paper load is sent to printer driver  114 , and the print data is prepared for a first scan of print heads  130   a  and  130   b  in step S 1606 . Printer control  140  is notified of this scan preparation. The preparation of print data in printer driver  114  is described more fully in U.S. patent application Ser. No. 08/901,719, entitled “Print Driver For A Color Printer”, filed Jul. 28, 1997. If no print data for the scan is determined in decision step S 1607 , a virtual skip is performed in printer driver  114  in step S 1608 . Control is returned to step S 1607  when a page finish is not detected in step S 1609 . Until the page finish is detected, steps S 1610  through S 1614  and S 1608  are performed. 
     In step S 1610 , an actual skip command is provided by printer driver  114  to printer control  140  for printing correct print data. Printer control  140  selects the actual skip operation (step S 1603 ) and executes the actual skip (step S 1615 ). Scan setting is then performed (step S 1611 ) in printer driver  114 , and printer control  140  is notified. Next, print data generated in printer driver  114  and print buffer addresses for the print data are transferred to printer control  140  which stores this information in print buffer  139  (step S 1612 ). The next scan is then prepared in printer driver  114 , and printer control  140  is notified (step S 1613 ). Then, a print command generated in printer driver  114  is sent to printer control  140 . In response, printer control  140  selects a print operation in step S 1619  and executes the print task in step S 1614 . A virtual skip is then performed by printer driver  114  in step S 1608  to keep track of the lines of the page being printed. When a page finish is determined in decision step S 1609 , a page eject command is sent by printer driver  114  to printer control.  140 , which selects a page eject operation (step S 1616 ) and starts page eject (step S 1617 ). Upon completion of the page eject (step S 1618 ), printer driver  114  is notified of the completion of the page eject and control is passed to step S 1409  of FIG.  14 . 
     FIG. 17 is a flowchart illustrating the set of commands used in scan setting step S 1611  for the current scan of FIG.  16 . Referring to FIG. 17, a [SPEED] command is issued in step S 1701  to set the scan speed, a [DROP] command is issued (step S 1702 ) to set the droplet size for one print head (A) and another [DROP] command is issued (step S 1703 ) to set the droplet size for the other print head (B). In steps S 1704  and S 1705 , a [SELECT_PULSE] command is issued to set a heat pulse for printing and a [PCR] command is issued to set a pulse control ratio for temperature table adjustment. [SELECT_CONTROL] commands are issued in steps S 1706  and S 1707  to select the buffer control for each print head to determine a firing time of print head nozzles. [DEFINE_BUF] commands are issued in steps S 1708  and S 1709  to define the print buffer for each of print heads  130   a  and  130   b . Accordingly, each aspect of a printer operation such as scan setting is controlled by host processor printer driver  114  taking into account the print head configuration and the print mode. The tasks performed by printer  30  are thereby defined in detail by printer driver  114  so that the printer architecture is substantially simplified and less costly. 
     An example of the command sequence from the host processor  23  to printer  30  to print a page in color mode with two color print heads is set forth in Table A shown in FIG.  18 . Initially as indicated in Table A, the current time is set by a [UCT] command and printer  30  is reset by a [RESET] command. Data compression is selected to pack the print data by a [COMPRESS] command. Print buffers for print heads  130   a  and  130   b  are defined by [DEFINE_BUF] commands. The heat pulse and buffer control tables are defined for the color mode of the print head configuration by [DEFINE_PULSE] and [DEFINE_CONTROL] commands. 
     After the printer tasks are executed for the foregoing initializing commands, a paper load command [LOAD] to load a page or other print medium and a raster skip command [SKIP] to skip to the print position of the first print head scan are sent to printer  30 , and the print direction and edges for printing of print heads  130   a  and  130   b  are set for the first scan. A loop of commands is then sent to control printer tasks for printing the lines of the page. In the first portion of the loop for each line, the scanning parameters for the line are set as described with respect to FIG.  17 . Following completion of the printer tasks for the select buffer control table commands [SELECT_CONTROL], the print data blocks are selected by the [BLOCK] command, and the print colors are selected and transmitted by repeated select color [COLOR] and data transmission [DATA] commands according to the determined print areas for print heads  130   a  and  130   b.    
     The direction of the second scan and the left and right edges of the print areas for the second scan are then set by the [DIRECTION] and [EDGE] commands. At this time, a [PRINT] command is transferred from host processor  23  to printer  30  to execute printing for the first scan, and a [SKIP] command is sent to skip to the print position of the second scan. When the last line has been printed, a paper eject command is given to printer  30  to execute paper ejection. 
     As can be seen from the command sequences for set scan operations and the example of the printing operations according to the invention, each aspect of printer operation, such as scan setting or printing, is controlled by printer driver  114  taking into account print head configuration and the print mode. The tasks to be performed by printer  30  are thereby defined in detail by printer driver  114  so that the printer architecture is substantially simplified to be less costly. 
     Returning to FIG. 14, when a printer status request is determined in step S 1409 , flow proceeds to step S 1412 . In step S 1412 , a printer status command sequence is performed. The status commands that provide requests for printer status information are described in detail in section 3.6. In general, each of the status commands is sent from host processor  23  to printer  30  to request the information on printer operation or information stored in printer  30 . For example, a base status command [BASE-STATUS] requests the current status of the printer. In response, printer  30  returns one data byte indicating one of the following: printing status, whether print buffer  139  can or cannot receive data, whether printer  30  is busy performing start-up, cartridge replacement, print head cleaning, test printing, etc., and whether an error or alarm has been detected. A [HEAD] command requests return of print head configuration, and a [DATA_SEND] command requests return of EEPROM data to host processor  23 . After return of the requested data in step S 1412 , control is returned to step S 1406 . 
     3.0 Architecture of Printer Software 
     Control over functionality of printer  30  is effected by individual programs executing on CPU  121 . The individual programs include initialization routines such as routines executed on power-on, tasks to interpret commands received from host processor  23 , interrupt handlers such as handlers to process real time hardware interrupts, and cyclic handlers that handle cyclic processes such as handlers for control over bi-directional communications with host processor  23 . 
     Printer CPU  121  further executes an operating system so as to coordinate execution of each of the individual programs (i.e., the initialization routines, the tasks, the interrupt handlers, and the cyclic handlers). The operating system is responsible for inter-program communication through messaging and the like, and inter-program switching so as to switch execution from one program to another when appropriate. Details of the operating system follow. 
     3.1 Operating System 
     The operating system is a real-time operating system (or “kernel” or “monitor”) created to modularize printer control programs and to facilitate maintenance, inheritance, and expansion. The real-time operating system is system software that provides for a preemptive multi-task software environment, in which a currently executing program can be suspended in favor of a switch to another program with a higher priority. 
     The operating system allows for four different types of programs, each of which is executed by the operating system in accordance with its specific type. The types are initialization routines, tasks, interrupt handlers, and cyclic handlers. Initialization routines are routines scheduled by the operating system immediately after printer  30  is reset but after the operating system initializes itself. Tasks are ordinary programs (sometimes called “execution units”) of continuous processing that are executed sequentially. Thus, tasks are one or more sequences of instructions handled by the operating system as units of work executed by CPU  121  in a multiple-programming or multiple-processing environment. An illusion of concurrent processing is created by the operating system by scheduling processing in individual task units. 
     An interrupt handler is a (usually short) program unit that is activated by the operating system immediately upon receipt of a hardware interrupt. Cyclic handlers are similar to interrupt handlers, but rather than being activated by a hardware interrupt, cyclic handlers are activated by a timer interrupt of the operating system. 
     When printer  30  is reset, execution of the operating system is the first software executed by CPU  121 . CPU registers are set according to predefined requirements, and then user-defined initialization routines are executed if any exist. Thereafter, control reverts to the operating system, which activates each of the tasks in the system. One such task is a start task. After the start task begins, the operating system is activated each time a system call is issued or an interrupt occurs. After executing the system call, or handling the interrupt, execution reverts back to the operating system, which schedules tasks so as to execute the executable task with the highest priority. 
     Scheduling of tasks involves a determination of which task is executed if there are several tasks currently eligible for execution. Tasks are scheduled according to an assigned priority in which a higher priority task is executed before all other lower priority tasks. Tasks eligible for execution but not currently being executed because of their lower priority level are placed in a ready queue based on their priorities. 
     As each task becomes newly eligible for execution, it is placed at the end of the ready queue. Scheduling is then performed when returning from a system call issued by a task or when returning from interrupt processing to a task, both of which can cause new tasks to be entered into a queue or can cause a change in priority of tasks already existing in the queue. Scheduling orders the tasks in the task queue based on each task&#39;s priority and makes the task with the highest priority the currently executable run task. If there are two or more tasks in the ready queue of the same priority, the decision as to which task should be selected is made based on which task first entered into the queue. 
     The operating system uses semaphores as one basic means of communication between tasks and for control or synchronization between tasks. Tasks can also communicate and transfer data therebetween using messages. Messages are sent to mailboxes by one task, and a task that needs to receive the message issues a receive request to the mailbox so as to obtain the message. 
     The operating system further uses event flags to synchronize tasks. Any task desiring to be released from a wait state based on a certain event can register an event flag pattern, upon the occurrence of which the operating system will release the task from the wait state. 
     Interrupt management by the operating system is provided by an interrupt handler and by interrupt permission level settings. Time management is provided by the operating system&#39;s actuation of an interrupt handler based on the system timer. 
     Cyclic handlers carry out processing at each of specified time intervals, based on cyclic handlers registered with the operating system. Typically, a cyclic handler is a short program that specifies a task that is performed at each of specified time intervals. 
     Initialization routines, tasks, interrupt handlers, and cyclic handlers that are preferred for printer  30  are described in the following sections. 
     3.2 Initialization 
     During power-up, initialization functions are performed to initialize printer  30 , such as initializing control logic  124 , checking ROM  122 , checking RAM  129 , and checking EEPROM  132 . 
     FIGS. 19 and 20 illustrate a hard power-on sequence and a soft power-on sequence, respectively. In this regard, it is noted that so long as power is supplied to printer  30 , CPU  121  is executing software regardless of the status of power button  44 . Thus, a “hard power-on” refers to initial application of power to printer  30 . Thereafter, user activation of power button  44  simply causes a soft power-on or soft power-off. This arrangement is preferred, since it allows printer  30  to monitor ongoing events (such as elapsed time) even when printer  30  is “off”. 
     Referring to FIG. 19, which shows a hard power-on sequence, upon initial application of power, step S 1901  performs memory checks such as a ROM check, a RAM check, and an EEPROM check. Step S 1902  initializes software tasks, and in step S 1903 , CPU  121  enters an idle loop, awaiting a soft power on. 
     FIG. 20 indicates the soft power-on sequence. Step S 2001  performs mechanical initialization of printer engine  131 , such as a reset to the home position, step S 2002  starts the software control tasks including Centronics communication tasks, and step S 2003  enters the main processing mode. 
     FIG. 21 details a soft power-off sequence. Step S 2101  terminates all software tasks, and step S 2102  enters an idle loop during which, in step S 2103 , printer  30  awaits the next soft power-on sequence. 
     3.3 Tasks 
     In the preferred embodiment of the invention, printer tasks are designed to isolate functionality so that each task is responsible for a single cohesive aspect of printer control. Generally speaking, the tasks can be divided into three conceptual groups, namely engine tasks, controller tasks, and miscellaneous tasks. 
     With respect to the engine-related tasks, tasks are provided to control carriage motor  66  for carriage movement, to control line feed motor  61  for paper advance, and to control both paper feeding and cleaning operations for print heads  130   a  and  130   b , such as ink suction, purging, and the like. Other tasks transmit messages from print engine  131  to other tasks, and control printer engine  131  based on a message from another task. 
     With respect to the control tasks, tasks are provided to interpret commands received from host processor  23 ; these commands are described in detail below in section 3.6. Test-related tasks may be provided if desired. 
     With respect to the miscellaneous tasks, an initializer task, which was discussed above in section 3.2, initializes printer  30 . Other tasks are provided to control displays on printer  30 , to scan key switches corresponding to buttons on the printer  30 &#39;s front panel and detect their status, to initialize hardware related to host computer interface  141  and I/O ports unit  127 , to control Centronics output signals, and to interpret and transmit those signals to other tasks. A task is provided to control the engine control task and the communications tasks. In addition, this task initiates, suspends and resumes other tasks. An idle task basically does nothing and is provided for use by the operating system when no other tasks are queued in a wait state. 
     Interface and other communications between tasks are accomplished through use of mailboxes into which messages are placed and semaphores to coordinate message communication. This arrangement is illustrated in FIG.  22 . Shown in FIG. 22 are controller tasks  201 , user interface tasks  202 , bi-directional communications tasks  204 , miscellaneous tasks  205 , and engine tasks  206 . Each task in the task group has an associated mailbox, which are illustrated diagrammatically in FIG. 22, with  210  indicating mailboxes for each task in the controller tasks  201 ,  213  indicating mailboxes for each task in user interface tasks  202 ,  215  indicating mailboxes for each task in communications task  204 ,  217  indicating mailboxes for each task in miscellaneous tasks  205 , and  219  indicating mailboxes for each task in engine tasks  206 . With the exception of engine tasks  206 , coordination of messages sent to, and retrieved from, the mailboxes are controlled by semaphores. For the engine tasks  206 , no semaphores are used since a detection of memory usage is sufficient. 
     Each mailbox is adapted to receive messages from each of the other tasks and is further adapted to deliver messages to its associated task. Thus, mailbox  210  can receive messages from any of user interface tasks  202 , communications tasks  204 , miscellaneous tasks  205 , and engine tasks  206 ; and can deliver those messages to its associated task in task group  201 . Likewise, mailbox  213  is adapted to receive messages from any of controller tasks  201 , communications tasks  204 , miscellaneous tasks  205 , and engine tasks  206 ; and to deliver those messages to the associated tasks in user interface task  202 . Likewise, mailbox  215  is adapted to receive messages from any of controller tasks  201 , user interface tasks  202 , miscellaneous tasks  205 , and engine tasks  206 ; and to deliver those messages to the communications task  204 . Likewise, mailbox  217  is adapted to receive messages from any of controller tasks  201 , user interface tasks, communications tasks  204 , and engine tasks  206 ; and to deliver those messages to the associated tasks in miscellaneous task group  205 . Finally, mailbox  219  is adapted to receive messages from any of controller tasks  201 , user interface tasks  202 , communications tasks  204 , and miscellaneous tasks  205 ; and to deliver those messages to the associated tasks in engine tasks  206 . 
     3.4 Interrupt Handlers 
     Although the operating system can accommodate interrupt handlers such as handlers for periodic clock interrupts, such cyclic events can also be handled with cyclic handlers. 
     3.5 Cyclic Handlers 
     Cyclic handlers are provided for communications task  204  and for user interface tasks  202 , as shown and described above in connection with FIG.  22 . 
     In addition, a cyclic handler is provided for controller timer operations. FIG. 23 is a flow diagram illustrating controller timer control according to this cyclic handler. As shown in FIG. 23, upon receipt of a 10 ms interrupt, sub heater control is effected. The purpose of sub heater control is to drive the temperature of each print head in printer  30  (namely, print heads  130   a  and  130   b ) toward a target temperature. This is done by setting a sub heater driving time based on a difference between a calculated head temperature and a target head temperature. 
     The 50 ms interrupt as shown in FIG. 23 calculates head temperature for each head based on the amount of head driving pulses applied at each head. Calculations are based on pre-stored tables in ROM  122  which provide constants for use in calculating temperature increase as well as temperature decrease based on head firings. 
     The 50 ms interrupt further controls pulse width modulation control in accordance with prestored tables in ROM  122  so as to set the pre-heat pulse for each print nozzle as well the actual main pulse width for each nozzle. The pulse parameters are then sent to control logic  124 . 
     The 50 ms interrupt further effects head protect control so as to ensure that the width of the pre-heat pulse and the width of the main pulse are not in excess of limits that might damage the print head. 
     As shown in FIG. 23, the 500 ms interrupt effects main heating control. As also shown in FIG. 23, the 1 sec. interrupt calculates environmental temperature, and then proceeds to update target temperatures based on the calculated environmental temperature. 
     It should be noted that each of the 10 ms, 50 ms, 500 ms, and 1 sec. durations are merely illustrative and may be altered. 
     3.6 Commands To And From The Host Processor 
     The following summarizes the commands sent to and from host processor  23  over bi-directional printer interface  104 . Generally speaking, each command will include one or more parameters, with some commands (such as the [DATA] image data transmission command) also including data. 
     The status request command [STATUS] is a generalized command that elicits a response over bi-directional interface  104  from printer  30 . Through use of the status request command, host processor  23  can obtain detailed information concerning printer  30 , such as the contents of EEPROM  132 , alignment and density sensor results, and the like. The status request command is therefore discussed in considerable detail below. 
     In the sections below, a mnemonic for each command is shown enclosed by square brackets (“[ ]”). The mnemonics shown below are simply examples. The actual sequence and combinations of letters used to form the command mnemonics is immaterial, so long as usage is consistent in the printer side and the host processor side such that commands sent by one are understandable to the other. 
     3.6.1 Control Commands 
     Control commands serve to control print operations of printer  30 . The following is a description of the various control commands. 
     [LOAD]—Paper Load 
     The load command causes paper loading, but does not eject the recording medium currently loaded. This command must be sent to printer  30  even when a medium is already loaded manually. 
     [EJECT]—Paper Eject 
     This command prints all data remaining in the print buffer, then ejects the medium currently loaded. 
     [PRINT]—Print Execution 
     The Print Execution command causes the data in the print buffer to be printed on a currently-loaded recording medium. The printing area extends from the left edge to the right edge of each print buffer specified by the Left and Right parameters of the [EDGE] command described below. 
     [CARRIAGE]—Carriage Movement 
     The Carriage Movement command includes a Position parameter which specifies carriage position in units of column position. This command is used for forward and reverse seeking. 
     [SKIP]—Raster Skip 
     The Raster Skip command is used to advance the vertical print position by the number of raster lines specified by a Skip parameter. 
     [DATA]—Image Data Transmission 
     This command is used to transmit bit image data of yellow (Y), magenta (M), cyan (C) or black (Bk or K) to printer  30  individually in column image format. Multiple sequences of this command may be issued to make a single scan line. Bit image data is stored into the area specified by the block [BLOCK] and color [COLOR] commands described below. Printer  30  will actually start printing when the [PRINT] command is received. 
     3.6.2 Setting Commands 
     Setting commands specify settings for print operations performed by printer  30 . Once these commands are set, they are valid until the settings are changed by another command. If no settings are provided for a page, the settings will be reset to default settings. Setting commands are described in more detail below: 
     [RESET]—Printer Reset 
     The Mode parameter defines the Printer Reset command and specifies the reset mode. Default settings are included for data compression flag, buffer size, droplet size, print speed, pulse control tables, buffer control tables, and the like. 
     [COMPRESS]—Select Data Compression 
     The Mode parameter of the Select Data Compression command specifies whether the image data is compressed or un-compressed, with un-compressed being the default setting. 
     [DEFINE_BUF]—Define Print Buffer 
     The Define Print Buffer command is used to define the memory size and configuration of print buffer  139 , for each of heads A and B in common. 
     [DROP]—Select Droplet Size 
     This command is used to specify the ink droplet size (large or small) for each print head. 
     [SPEED]—Select Print Speed 
     This command is used to specify the printing speed. 
     [DIRECTION]—Set Print Direction 
     The Direction parameter of this command specifies whether printing will be in the forward direction (left to right) or the backward direction (right to left). 
     [EDGE]—Set Print Edge 
     The Set Print Edge command specifies the left edge and the right edge of print position in units of column position; the left edge must be smaller than the right edge. 
     [BLOCK]—Select Print Block 
     This command is used to specify the left edge and the right edge of a data block in units of column position from the top of each print buffer. The [BLOCK] command also specifies where bit images following a [DATA] command (described above) are stored. 
     [COLOR]—Select Print Color 
     This command is used to specify the location, corresponding to color, in print buffer  139  where bit images data following a [DATA] command (described above) are stored. 
     [DEFINE_PULSE]—Define Heat Pulse Table 
     The [DEFINE_PULSE] command is used to define up to plural different heat pulse block tables. The pulse block table must be defined before printer  30  receives the [SELECT_PULSE] command which will be defined below. 
     [SELECT_PULSE]—Select Heat Pulse Table 
     The Select Heat Pulse Table command is used to select one heat pulse block table, from among plural tables defined by the [DEFINE_PULSE] command above, that is in common with all heads. 
     [DEFINE_CONTROL]—Define Buffer Control Table 
     This command is used to define up to plural different print buffer control tables. The print buffer control table must be defined before the printer receives [SELECT_CONTROL] command (described below). 
     [SELECT_CONTROL] Select Buffer Control Table 
     This command is used to select a print buffer control table for each print head  130   a  and  130   b , from among the plural tables defined in the [DEFINE_CONTROL] command. 
     3.6.3 Maintenance Commands 
     Maintenance commands serve to maintain print operations of printer  30  and are described in more detail below. 
     [RECOVER]—Head Recover 
     Receiving this command causes printer  30  to go into head recovery mode, such as cleaning and ink suction operations. 
     [PCR]—Change Pulse Control Ratio 
     This command is used to change a ratio of the Pulse Control Table. Each ratio can be set from 1 through 200, which means 1% through 200%. Default setting is 100 which means 100%. 
     [UCT]—Universal Coordinated Time 
     This command is used to set the current time in printer  30 , and must be sent to printer  30  at the onset of a print job start. Printer  30  uses the time to determine whether or not printer  30  should recover the print head. The time value is expressed as the number of seconds elapsed since midnight (00:00:00), Jan. 1, 1970, Universal Coordinated Time (UCT), according to the system clock of host processor  23 . 
     [SCAN]—Scan Sensor 
     This command is used to read an auto-alignment sensor value and to send the result back to host processor  23 . Scanning speed, direction, resolution and area are defined by the [SPEED], [DIRECTION], [DEFINE_BUF] and [EDGE] commands, respectively, as described above. 
     [NVRAM]—NV-RAM Control 
     This command is used to read data from EEPROM  132  and send the read data back to host processor  23 . 
     [STATUS]—Status Request 
     This command is used as a prefix command to send status requests to printer  30 . Requests can be made for basic settings, main status, and detailed status. 
     Basic Setting Commands are commands used by host processor  23  to set printer  30  and do not necessarily require a response from printer  30 . 
     Main Status Request/Response commands are commands which are used to obtain status information in regular mode and include Base Status [BASE_STATUS], Echo Command [ECHO], print head configuration [HEAD], Alignment Sensor Results [SENSOR_RESULTS], EEPROM data sending to host [DATA_SEND], and Shift Buffer Size sending to host [BUFFER_SIZE]. For each Main Status Request/Response command issued, a response is automatically returned to host processor  23 . 
     Detailed Status Request/Response commands are used to obtain detailed status information. These commands include Detailed Job Status [JOB_STATUS], Detailed Busy Status [BUSY_STATUS], Detailed Warning Status [WARNING_STATUS], Detailed Operator Call Status [OPERATOR_CALL], and Detailed Service Call Status [SERVICE_CALL]. Like Main Status Request/Response commands, for each Detailed Status Request/Response command issued, a response is automatically returned to host processor  23 . 
     3.7 Commands To And From The Printer Engine 
     Host processor  23  and printer  30  send commands to printer engine  131  through insertion of messages into mailbox  219  (see FIG.  22 ). The messages are processed by engine tasks  206 . 
     4.0 Paper Ejection Tray 
     In brief, this aspect of the present invention is an ejection tray for use with the printer described herein. Structurally, the printer includes a housing defining a media feed portion and a media eject port, where the housing is adapted to house a print engine for printing onto recording media. The ejection tray includes a base slidably receivable in the printer&#39;s housing at a position laterally distanced from the media eject port. The base includes at least a pair of recesses extending in a sliding direction of the base. A pair of flaps are also included in the ejection tray. The pair of flaps each have at least one width portion corresponding to the lateral distance between the base and the eject port. Each flap is hinged into a corresponding recess of the base, and is biased in an upward direction via a spring which provides for angular motion of the flap relative to the base. Upon sliding action of the base out of the housing, the flaps are biased upward out of the recesses to a height corresponding to the position of the media eject port. 
     As described in more detail below, the foregoing configuration provides for easy set-up and storage of the paper ejection tray. In addition, the foregoing configuration reduces the chances that paper ejected from the printer will block the printer&#39;s ejection area. 
     4.1 First Embodiment 
     FIG. 24 shows a perspective view of printer  30  with paper ejection tray  41  set up for use. At this point it should be noted that although the paper ejection tray of the present invention will be described with respect to printer  30  shown in FIGS. 1 and 24, the paper ejection tray of the present invention can be used to receive paper or other types of recording media ejected from any type of apparatus (e.g,. a facsimile machine, etc.). In this regard, for ease of description the invention will be described with respect to paper, as opposed to other types of recording media. 
     FIG. 25 shows a detailed perspective view of paper ejection tray  41 . As shown in the figures, paper ejection tray  41  includes base  240 , two flaps  241   a  and  241   b , springs  242   a  and  242   b , and tray extension  244 . Each of flaps  241   a  and  241   b  is hinged at one edge to one of recesses  264   a  and  264   b  of base  240 , as described in more detail below. Additionally, each of flaps  241   a  and  241   b  is biased is an upward direction relative to base  240  via springs  242   a  and  242   b , respectively. Additionally, springs  242   a  and  242   b  provide for controlled upward and downward angular motion of flaps  241   a  and  241   b  relative to base  240 . 
     FIG. 26 shows a closeup side view of the connection of flap  241   b  to base  240 . In this regard, both of flaps  241   a  and  241   b  are hinged to base  240  in the same manner. Accordingly, only the connection of flap  241   b  is described here. Specifically, flap  241   b  is hinged via dowels  246  and  247  which are disposed at each end thereof, and which fit into corresponding receiving holes (not shown) in recess  264   b  of base  240 . These dowels form an axis about which flap  241   b  rotates angularly relative to base  240 . 
     Also included on flap  241   b  is center rod  248 , shown in FIG.  26 . spring  242   b  is wound around center rod  248  and connected to both flap  241   b  and base  240 . Inherent tension in spring  242   b  biases flap  241   b  in an upward direction out of recess  264   b  when paper ejection tray  41  is outside of housing  31 . Thus, flap  241   b  is at an initial angle relative to base  240  when no downward force is applied to flap  241   b . Examples of this initial angle, labelled  249   a  and  249   b , are shown in FIG.  24 . In preferred embodiments of the invention, the initial angle is less than 90°. 
     When downward pressure is applied to flaps  241   a  and  241   b , springs  242   a  and  242   b  are compressed. However, springs  242   a  and  242   b  prevent flaps  241   a  and  241   b  from contacting base  240  at least until a predetermined amount of pressure is applied to flaps  241   a  and  241   b . Thus, when pressure is applied to flaps  241   a  and  241   b , flaps  241   a  and  241   b  move angularly downward towards base  240 , but do so in a controlled manner. During this motion, the angle between each of flaps  241   a  and  241   b  and base  240  decreases from the initial angle, eventually down to 0° if the pressure is sufficiently great. In this regard, the amount of pressure required to move each of flaps  241   a  and  241   b  down to 0° is based on the tension of a corresponding one of springs  242   a  and  242   b.    
     Preferably, each of flaps  241   a  and  241   b  has a width portion which roughly corresponds to a lateral distance between base  240  and media eject port  40 . To illustrate this, FIG. 27 shows flaps  241   a  and  241   b  flat against base  240 . Specifically, as shown in FIG. 27, flap  241   a  includes four edges, namely top edge  250  which supports paper ejected from printer  30 , bottom edge  251  which connects to base  240 , and side edges  254  and  252  (i.e., the width portion noted above), respectively. 
     Preferably, the edge of each flap which faces printer  30 , i.e., side edge  252  for flap  241   a  and side edge  252   b  for flap  241   b , is beveled (e.g., tapered) and is angled away from printer  30  as shown in FIG.  25 . More specifically, because edges  252  and  252   b  are beveled, when these edges contact housing  31  of printer  30 , the edges slide relative to housing  31  causing flaps  241   a  and  241   b  to fold. Eventually, flaps  241   a  and  241   b  fold enough so that the lateral pushing forces printer  30  and into tray receptacle  42 . This feature is described in more detail below. 
     FIG. 25A shows a close-up view of edge  252   b  of flap  241   b . As noted above, and as shown in FIG. 25A, edge  252   b  is beveled, meaning that it is angled relative to top edge  250   b  and to base  240 . FIGS. 25B and 25C illustrate this feature even further. In this regard, FIG. 25B shows a close-up side view of flap  241   b . FIG. 25C shows a view, taken from position A—A, of a cross section of flap  241   b  taken along dashed line  63 . Thus, as depicted in FIG. 25C, beveled edge  252   b  is angled relative to top edge  250   b  and base  240 . This angle is labelled  255  in FIG. 25C and, in preferred embodiments of the invention, is roughly 45°. 
     Thus, when ejection tray  41  is pushed towards printer  30 , as is the case during storage of tray  41 , the beveled edges of flaps  141   a  and  141   b  contact housing  31  of printer  30 , in particular exterior edge  272 . In response to this contact, and as additional lateral pushing force is applied, contact between exterior edge  272  and the beveled edges force flaps  241   a  and  241   b  downwards toward the recesses in base  240 . If enough force is applied, flaps  241   a  and  241   b  are forced sufficiently downward to slide underneath exterior edge  272  and into tray receptacle  42 . This feature of the invention is described in greater detail below. 
     Side edge  252  also includes portion  253  (corresponding side edge  252   b  includes similar portion  253   b ), which is preferably not beveled or angled. Such an arrangement provides a flat surface for engaging each of flaps  241   a  and  241   b  to base  240  via dowel  246 , thereby increasing structural strength at the engagement. Side edges  253  and  253   b  fit underneath exterior edge  272  and thus do not adversely affect storage of ejection tray  41  into receptacle  42 . 
     With regard to side edge  254 , that edge is neither angled nor beveled in the example shown. However, side edge  254  may be angled and beveled if desired so as to facilitate pulling of paper ejection tray  41  from printer  30 . 
     With regard to top edge  250  and bottom edge  251 , these edges preferably are not parallel to each other so as to reduce the chances that ejected paper will bend. That is, in preferred embodiments of the invention, top edge  250  is angled slightly upwards relative to bottom edge  251  and base  240  so as to facilitate downward movement of ejected paper. Thus, a distance between top edge  250  and bottom edge  251  is at a minimum at intersection point  260  between side edge  252  (the beveled edge) and top edge  250 . This distance increases farther away from intersection point  260  such that the distance is at a maximum at intersection point  261 , i.e., the point where side edge  254  intersects top edge  250 . This angled construction of top edge  250  relative to bottom edge  251  reduces the chances that paper will fall off of flaps  241   a  and  241   b  during ejection. 
     As noted above, base  240  also includes recesses  264   a  and  264   b  (see FIGS.  24  and  25 ), which correspond to respective ones of flaps  241   a  and  241   b  and which extend in a sliding direction of base  240 . In preferred embodiments, each of recesses  264   a  and  264   b  has a shape which corresponds to a shape of a respective one of flaps  241   a  and  241   b . By virtue of this configuration, when the angle between a flap, such as flap  241   a , and base  240  is roughly 0°, the flap can fit almost entirely within its corresponding recess. When both flaps are fitted thusly, top surface  266  of base  240 , including flaps  241   a  and  241   b , is substantially planar, as shown in FIG.  27 . This facilitates sliding of paper ejection tray  41  into receptacle  42 , a described below. 
     More specifically, as noted above, printer  30  includes tray receptacle  42  (see FIG. 24) which stores paper ejection tray  41  when printer  30  is not in use. FIG. 28 is an underside view of printer  30 , which shows tray receptacle  42 . As shown, tray receptacle  42  preferably comprises a slot or the like on the underside of printer  30 , into which paper ejection tray  41  (including tray extension  244 ) fits. When flaps  241   a  and  241   b  are at 0°, or substantially close to 0°, relative to base  240 , paper ejection tray  41  can slide within tray receptacle  42 . In this regard, FIG. 1 shows a front view of paper ejection tray  41  stored within printer  30 . 
     Paper ejection tray  41  also may include tray extension  244  noted above. As shown in FIG. 24, tray extension  244  preferably slides into and out of a slot within base  240 . This facilitates storage of paper ejection tray  41  within printer  30 . Additionally, tray extension  244  includes manual stop  269 . Manual stop  269  is used to slide tray extension  244  into or out of the slot in ejection tray  41  and to keep ejected sheets of paper from falling off of paper ejection tray  41 . 
     In addition, manual stop  269  can be helpful in setting up and storing paper ejection tray  41 . That is, as shown in FIG. 1, when paper ejection tray  41  is stored within tray receptacle  42 , manual stop  269  does not fit entirely within tray receptacle  42  and therefore remains accessible to a user. By grasping manual stop  269  and pulling manual stop  269  away from printer  30 , the user is able to set paper ejection tray  41  up for operation. Conversely, by pushing on manual stop  269  towards printer  30 , the user can store paper ejection tray  41  within printer  30 . These operations are described in greater detail below. 
     In this regard, FIGS. 29A to  29 D show the operation of paper ejection tray  41  during use. Reference is also made to FIGS. 2 and 24 to describe setup and storage of paper ejection tray  41 . To begin, FIG. 1 shows printer  30  when not in use. In this configuration, paper ejection tray  41  is stored within receptacle  42 . It is preferable to store paper ejection tray  41  when printer  30  is not in use, since storage reduces the chances that paper ejection tray  41  will be inadvertently damaged. 
     To set up paper ejection tray  41 , a user simply pulls paper ejection tray  41  out of printer  30 , thereby causing paper ejection tray  41  to slide out of receptacle  42  in housing  31 . This is typically done by pulling on manual stop  269 ; although pulling on other portions of paper ejection tray  41  will accomplish the same result. During this pulling action, flaps  241   a  and  241   b  remain relatively flat against base  240  until flaps  241   a  and  241   b  are freed from tray receptacle  42 . 
     Once flaps  241   a  and  241   b  are freed from tray receptacle  42 , flaps  241   a  and  241   b  are biased upward out of recesses  264   a  and  264   b , respectively, to a height corresponding to the position of media eject port  40 . That is, when flaps  241   a  and  241   b  are freed from tray receptacle  42 , there is no longer anything to hold flaps  241   a  and  242   b  against base  240 . Consequently, springs  242   a  and  242   b  cause flaps  241   a  and  241   b  to bias upwards so that the flaps assume a rough “V” shape when viewed head-on. As noted above, at this point, each of flaps  241   a  and  241   b  is at an angle relative to base  240  which is preferably less than 90°. Once flaps  241   a  and  241   b  are in this position, printer  30  may begin ejecting paper onto paper ejection tray  41 . 
     FIGS. 29A to  29 D show front views of paper ejection tray  41  set up to receive paper ejected from printer  30 . As shown in FIG. 29A, angles  249   a  and  249   b , referred to above as the initial angles, are less than 90° relative to base  240 . Because angles  249   a  and  249   b  are less than 90°, the weight of paper ejected onto flaps  241   a  and  241   b  will cause the flaps to move downward, thereby decreasing angles  249   a  and  249   b , respectively. This is shown in FIG.  29 B. 
     More specifically, FIG. 29B shows a case in which paper ejection tray  41  has received several sheets of paper  270  which have been ejected from printer  30 . As shown, weight from paper  270  causes flaps  241   a  and  241   b  to move downward, toward base  240 . As a consequence, angles  249   a  and  249   b  between the flaps and the base decrease from the initial angle. FIG. 29C shows a case in which even more sheets have been added to paper ejection tray  41 , thus forcing flaps  241   a  and  241   b  still further downward, and thus decreasing angles  249   a  and  249   b  still further. This action reduces the chances that sheets of paper ejected from media eject port  40  will block media eject port  40  during operation of printer  30 . 
     FIG. 29D shows a case in which still more sheets of paper have been received by flaps  241   a  and  241   b . In this case, the weight of paper  270  on flaps  241   a  and  241   b  is sufficient to force flaps  241   a  and  241   b  to roughly a 0° angle relative to base  240 . As a result, each of flaps  241   a  and  241   b  will be forced into a corresponding one of recesses  264   a  and  264   b . Thus, as compared with its conventional counterparts, printer  30  is able to print more paper without substantially blocking media eject port  40 . 
     As described above, the degree to which flaps  241   a  and  241   b  move downward in response to an applied force depends on the tension of springs  242   a  and  242   b  biasing flaps  241   a  and  241   b  relative to base  240 . As noted above, in preferred embodiments of the invention, springs  242   a  and  242   b  have a tension such that flaps  241   a  and  241   b  are biased to a height of media eject port  40  when no paper is ejected thereon. In particularly preferred embodiments of the invention, the position to which paper is ejected remains relatively the same for all sheets of paper. 
     Moreover, in preferred embodiments of the invention, both of flaps  241   a  and  241   b  have substantially the same shape and, as noted above, the same connections to base  240 . Springs  242   a  and  242   b  in connection with both of flaps  241   a  and  241   b  also preferably have roughly the same tension. By virtue of this symmetry, the present invention is able to hold more paper with fewer mechanical malfunctions. In this regard, it should also be noted that paper ejection tray  41  also operates in cases where flaps  241   a  and  241   b  have different shapes, and springs  242   a  and  242   b  produce different biases. 
     Next, storage of paper ejection tray  41  within printer  30  will be described with reference to FIGS. 2 and 24. In this regard, as shown in FIG. 24, receptacle  42  on printer  30  includes exterior edge  272 . Additionally, each of flaps  241   a  and  241   b  includes a side edge (i.e., side edges  252  and  252   b  shown in FIGS. 25 and 27) which faces printer  30 , which is angled away from printer  30 , and which is beveled, as described above with respect to FIGS. 25A,  25 B and  25 C, such that the side edge is substantially flat and angled relative to the top edge and base. As described below, these side edges, namely side edges  252  and  252   b , are constructed in this manner so as to facilitate storage of paper ejection tray  41  within tray receptacle  42 . 
     More specifically, to store paper ejection tray  41  within tray receptacle  42 , a user need only push laterally on base  240  (or tray extension  269 ). This lateral pushing forces the flaps to co-act with housing  31  so as to fold the flaps back into the recesses upon sliding action back into housing  31 . Specifically, the lateral pushing action forces portion  253  underneath tray receptacle  42  and forces side edges  252  and  252   b  against exterior edge  272  of tray receptacle  42 . Exterior edge  272  “responds” with an equal, but opposite, force against the side edges. Because side edges  252  and  252   b  are beveled and angled (see, e.g., FIG.  25 A), this equal but opposite force includes a downward component which forces flaps  241   a  and  241   b  to move downward towards base  240 . As additional lateral pushing force is applied to ejection tray  41 , side edges  252  and  252   b  slide against exterior edge  272 , forcing flaps even further downward. 
     As was the case above, as flaps  241   a  and  241   b  move downward, the angles between flaps  241   a  and  241   b  and base  240  decrease. Due to the angle of the side edge, as additional force is applied to the side edges, flaps  241   a  and  241   b  continue to slide along exterior edge  272 , thus forcing flaps  241   a  and  241   b  still further downwards. Eventually, if enough lateral pushing force is applied, flaps  241   a  and  241   b  are forced downward such that they fold within recesses  249   a  and  249   b . Thus, paper ejection tray  41  slides easily into tray receptacle  42 . FIG. 1 shows paper ejection tray  41  stored within tray receptacle  42  of printer  30 . 
     Accordingly, unlike its conventional counterparts, the present invention provides a means for storing paper ejection tray  41  which does not require significant physical manipulations by the user. Moreover, because the shape of flaps  241   a  and  241   b  and housing  31  is primarily responsible for the ease with which paper ejection tray  41  can be stored, the number of additional mechanical components on paper ejection tray  41  is reduced. 
     At this point, it is noted that the shape of the holding members (e.g., the flaps) used to hold the recording material may also vary. In this regard, the present invention also can be implemented using a single holding member of more than two holding members. For example, the invention can be implemented using a single “V”-shaped holding member in which one or more biasing springs are positioned between opposing arms of the holding member. An example of a second embodiment of the paper ejection tray of the present invention that may be used with printer  2460  is shown in FIG.  29 E. 
     4.2 Second Embodiment 
     As shown in FIG. 29E, paper ejection tray  2400  includes a single flap, namely flap  2410 . Flap  2410  is hinged inside single recess  2440  and biased by a spring (not shown) relative to recess  2440 . Flap  2410  operates in a similar manner to the flaps described in the first embodiment above. Accordingly, a detailed description will be omitted here for the sake of brevity. Suffice it to say that top surface  2450  of flap  2410  co-acts with printer  2460  when tray  2400  is pushed towards printer  2460  so that flap  2410  folds within recess  2440 . This permits flap  2410  to be stored within printer  2460 . Likewise, when tray  2400  is withdrawn from printer  2460 , a spring (not shown) underneath flap  2410  biases flap  2410  to a height roughly equal to that of media eject port  2465  of printer  2460 . 
     During printing, flap  2410  operates in a manner similar to the flaps described above in the first embodiment. Specifically, as paper is ejected onto flap  2410 , flap  2410  moves downwardly toward recess  2440  and eventually, when enough paper has been ejected, into recess  2440 . As was the case above, downward motion of flap  2410  is controlled via a spring (not shown) which biases flap  2410  relative to recess  2440 . 
     Finally, it is noted that although the paper ejection tray of the present invention has been described with respect to a single flap and a pair of flaps, the invention can be used with multiple flaps as well. 
     5.0 Ink Cleaning Mechanism 
     In brief, this aspect of the present invention is a cartridge receptacle which is mounted on a carriage for releasably receiving a cartridge having a print head and at least one removable ink reservoir. The receptacle includes a pivoting lever which permits removal of the at least one ink reservoir. The lever extends over at least a portion of the at least one ink reservoir so as to prevent access to the at least one ink reservoir until such time as the lever is pivoted away from the at least one ink reservoir. When the lever is pivoted away from the at least one ink reservoir, and then the lever is pivoted over the at least a portion of the at least one ink reservoir, a signal is output which prompts cleaning of the print head. 
     As described above with respect to FIG. 4, printer  30  includes cartridge receptacles  64   a  and  64   b . Access to ink cartridges (and thus to ink reservoirs in those cartridges) in cartridge receptacles  64   a  and  64   b  is provided automatically via access door  32  shown in FIG.  2 . More specifically, as noted above, printer  30  includes a sensor which senses when access door  32  has been opened or closed. In response to this sensor sensing that access door  32  has opened, carriage motor  66  is driven so that cartridge receptacles  64   a  and  64   b  move roughly to the center of carriage  69 , i.e., to roughly the location shown in FIG.  4 . This area of printer  30  corresponds to the internal portion of printer  30  which is accessible when access door  32  is open. Thus, it is possible to access cartridge receptacles  64  merely by opening access door  32 . The significance of this will become apparent below. 
     FIGS. 6A and 6B, described above, show the physical construction of cartridge receptacle  64   b . FIGS. 7A and 7B, described above, show the physical construction of ink cartridge  300   b , which can be installed in cartridge receptacle  64   b . As noted above, circuit contacts for the cartridge receptacle shown in FIGS. 6A and 6B and the ink cartridge shown in FIGS. 7A and 7B are used in connection with ink cartridge cleaning. More specifically, according to the present invention, a circuit contact on a cartridge receptacle engages and disengages a circuit contact on an ink cartridge in response to opening and closing a lever of the cartridge receptacle. 
     Front views of the cartridge receptacle shown in FIGS. 6A and 6B during operation are shown in FIGS. 30A and 30B. As shown in FIGS. 30A and 30B, cartridge receptacle  64   b  includes capsule  73  and lever  72 , among other things. Lever  72  is hinged so that it pivots relative to capsule  73 . This pivoting action permits a user to access and to remove either an entire ink cartridge in cartridge receptacle  64   b  or just an ink reservoir from the cartridge. 
     Lever  72  is also connected to capsule  73  so that when lever  72  is pivoted, e.g., opened or closed, capsule  73  moves laterally, as described in detail above with respect to FIG.  6 B. More specifically, when lever  72  is pivoted from the open position shown in FIG. 30B to the closed position as shown in FIG. 30A, capsule  73  moves laterally within cartridge receptacle  64   b  in the direction of arrow  280  (see FIG.  30 A). This movement causes side wall  75  of capsule  73  to come into contact with side wall  78  of cartridge receptacle  64   b . On the other hand, when lever  72  is moved from the closed position shown in FIG. 30A to the open position shown in FIG. 30B, capsule  73  moves laterally within cartridge receptacle  64   b  in the direction of arrow  281  (see FIG.  30 B). This movement causes side wall  75  of capsule  73  to move away from side wall  78  of cartridge receptacle  64   b.    
     During the motion described above, namely the movement of capsule  73  between the position shown in FIG.  30 A and the position shown in FIG. 30B, finger  282  on capsule  73  slidably engages sleeve  284 . As also shown in FIGS. 30A and 30B, capsule  73  includes shoulders  286 , and lever  72  includes flanges  287 . Thus, when lever  72  is closed, as shown in FIG. 30A, flanges  287  contact shoulders  286 , and not an installed ink cartridge or ink reservoir. By virtue of these features, cartridge movement caused by inadvertent contact with lever  72  can be reduced. 
     FIGS. 31A and 31B show views of cartridge receptacle  64   b  with ink cartridge  300   b  installed therein. As shown in FIG. 31A, when lever  72  is pivoted over a portion of ink reservoirs  83 , i.e., lever  72  is in the closed position, an operator is prevented from accessing ink reservoirs  83 . That is, in this position, the tops of ink reservoirs  83  are covered, at least in part, by lever  72 , thereby restricting access thereto. In addition, in this position, cartridge circuit contact  81  on ink cartridge  300   b  engages device circuit contact  71  on cartridge receptacle  64   b . In contrast, when lever  72  is pivoted away from ink reservoirs  83 , i.e., lever  72  is in the open position, an operator can access ink reservoirs  83 . In this position, cartridge circuit contact  81  on ink cartridge  300   b  is disengaged from device circuit contact  71  on cartridge receptacle  64   b.    
     Thus, during the lateral motion of capsule  64   b  described above with respect to FIGS. 30A and 30B, circuit contacts  71  and  81  engage and disengage. Specifically, circuit contacts  71  and  81  disengage when lever  72  is opened, and engage when lever  72  is closed. This engaging and disengaging of circuit contacts is the means by which a user designates print head  300   b  for cleaning, and causes a signal to be output which prompts cleaning of print head  300   b . A controller (such as CPU  121  described above) in printer  30  receives this signal and initiates the cleaning process described below. 
     In this regard, it is noted that either one of both of the ink cartridges in printer  30  can be designated for cleaning in the foregoing manner. It is further noted that ink cleaning is performed only for the cartridge or cartridges that have been designated in this manner. 
     Once an ink cartridge has been designated, ink cleaning does not actually take place until access door  32  is closed. That is, during ink cartridge designation, access door  32  must be open. Ink cleaning will not take place until the access door sensor noted above senses that access door  32  is closed. In this regard, once it is sensed that access door  32  is closed, cartridge receptacles  64   a  and  64   b  move automatically to home location  87 , i.e., the position corresponding to ink cleaning mechanism  86 . Ink cleaning mechanism  86  is then used to clean (i.e., suction) ink from the print head of a designated cartridge. 
     To this end, ink cleaning mechanism  86  includes two print head connection caps  88   a  and  88   b  (see FIG.  4 ). Each of these print head connection caps corresponds to a print head of an ink cartridge in one of cartridge receptacles  64   a  and  64   b , respectively. However, only one of print head connection caps, namely cap  88   a , is connected to a rotary pump which cleans (i.e., suction) ink from print heads. An example of this configuration is shown in FIG. 32, in which print head connection cap  88   a  is connected to pump  294 . 
     Thus, when access door  32  is closed, the print head of the ink cartridge which has been designated for cleaning connects with print head connection cap  88   a . For example, as shown in the block diagram of FIG. 33A, if ink cartridge  300   b  has been designated for cleaning, ink cartridge  300   b  is moved into contact with cap  88   a . On the other hand, if ink cartridge  300   a  has been designated for cleaning, ink cartridge  300   a  is moved into contact with cap  88   a  when access door  32  is closed, as shown in the block diagram depicted in FIG.  33 B. In the case that both ink cartridges have been designated for cleaning in the manner set forth above, the ink cartridges connect with cap  88   a  in sequence. 
     Once connection is sensed via the home location sensor noted above, ink is extracted (i.e., suctioned) by pump  294  from nozzles or holes in the print head of the cartridge. Following this cleaning operation, the cartridge may then be used for printing. 
     6.0 Storing Printer Profile Parameters 
     In brief, this aspect of the invention is a method for controlling a print head of an image printing device having at least one print head. The method includes the steps of obtaining profile information of the at least one print head, storing the profile parameters in a non-volatile RAM, outputting, upon request, the profile information to a host processor connected to the image printing device, wherein the host processor utilizes the print head profile information to produce compensation parameters which compensate print information to be sent from the host processor to the print head for printing. 
     In detail, when applying power and performing a hard power-on, printer  30  enters an offline mode. In this mode, CPU  121  in printer  30  retrieves from ROM  122  initialization software and executes a power-on self-test program (POST). Among many of the self-tests and status-checking programs that it performs, CPU  121  checks the status of print head  130   a  and print head  130   b  to determine whether either or both print heads have been installed in printer  30 . One way in which CPU  121  checks this status is by determining whether access door  32  has been opened and, if so, comparing print head identification (ID) information stored in EEPROM  132  with a current print head&#39;s ID. If a new print head has been installed, this change will be noted in EEPROM  132  with other stored printer profile parameters, as discussed below. 
     However, at an initial installation and power-on, CPU  121  gathers various profile parameters regarding printer  30  as part of its installation programming. For example, CPU  121  will obtain the printer ID, print head ID information (or, if more than one print head is installed, then printer IDs for all print heads), as well as the current status of printer  30  and print head  130   a  and  130   b  (this feature is also performed after any subsequent power-on as well as at specific predetermined times and events, which will be discussed in greater detail below). 
     Once POST processing has been performed, printer  30  enters an online mode and awaits commands from host processor  23 . As shown in FIG. 10, host processor  23  sends commands through printer interface  104  directly to control logic  124  of printer  30 . Commands from host processor  23  to read/write to EEPROM  132  of printer  30  are also directed through printer interface  104  and control logic  124 . 
     Typically, after going online, host processor  23  will send a status request command [STATUS] to printer  30  via control logic  124 . Upon receiving such a status request command, CPU  121  of printer  30  will send stored printer profile parameters from EEPROM  132 , I/O ports unit  127 , and control logic  124  to host processor  23 . An example of printer profile parameters which are stored in a specific area in EEPROM  132  and registered with host processor  23  are shown below in Table 1. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 CONTENTS OF EEPROM 
               
               
                   
                   
               
             
            
               
                   
                 Waste Ink Amount 
               
               
                   
                 Print Head Change Count 
               
               
                   
                 Driver&#39;s Information 
               
               
                   
                 Print Head Clean Time 
               
               
                   
                 Print Head Changed 
               
               
                   
                   
               
            
           
         
       
     
     These foregoing printer profile parameters are used by host processor  23  to compensate print head command data during a print operation. 
     Thus, with reference to the flow diagram shown in FIG. 34, in step S 3401 , upon performing a hard power-on, printer  30  enters an offline mode. During this offline mode, in step S 3402  printer  30  performs a POST operation so as to gather status and functional data, and to check for any hardware or software faults. After initialization, in step S 3403 , CPU  121  of printer  30  determines if a new print head has been installed. In the case that step S 3403  is encountered during the initial power-on after installing printer  30  and one or more ink cartridges having one or more print heads, respectively, have been installed, CPU  121  obtains information from the newly-inserted print heads and stores that information in EEPROM  132  and commands a cleaning process at a next soft power-on. However, if printer  30  is only offline because a user has opened access door  32  and has installed a new print head, in step S 3404  CPU  121  will gather the print head ID and set a flag in EEPROM  132 , which indicates that the print head has been changed. This flag instructs host processor  23  that an ink cartridge has been changed. This process will be performed when a print head has been installed for the very first time as well as when a print head has been subsequently changed. 
     In this regard, EEPROM  132  stores a plurality of printer profile parameters which are registered with host processor  23  for various purposes, such as for providing compensation parameters to host processor  23  which are in turn used to compensate for physical characteristics of both a print head and ink within a print head cartridge. For example, as shown in Table 2 below, EEPROM  132  stores, in addition to print head alignment and optical density information, information and parameters relating to a waste ink amount, print head change count, print head cleaning times, print head ID, print head type, etc. 
     
       
         
           
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Contents 
                 Note 
               
               
                   
               
             
            
               
                 Driver&#39;s Information 
                 The Printer Driver reads/writes 
               
               
                   
                 alignment data, etc. 
               
               
                 Check Sum 
                 The check sum of this data block 
               
               
                 Cleaned Time for RIGHT Head 
                 The last cleaned time for the 
               
               
                 (A_Head) 
                 RIGHT head (A_Head) 
               
               
                 Cleaned Time for LEFT Head 
                 The last cleaned time for the 
               
               
                 (B_Head) 
                 LEFT head (B_Head) 
               
               
                 Check Sum 
                 The check sum of this data block 
               
               
                 Print head changed 
                 The status whether print head 
               
               
                   
                 changed or not 
               
               
                 Cleaned Time for RIGHT Head 
                 Backup for recovering in System 
               
               
                 (A_Head) 
                 Master 
               
               
                 [Mirror] 
                   
               
               
                 Cleaned Time for LEFT Head 
                 Backup for recovering in System 
               
               
                 (B_Head) 
                 Master 
               
               
                 [Mirror] 
                   
               
               
                 Check Sum 
                 The check sum of this data block 
               
               
                   
               
            
           
         
       
     
     Returning to FIG. 34, if a new ink cartridge has not been installed, in step S 3405  printer  30  enters an online mode in which printer  30  is capable of communicating with host processor  23 , or if networked, with a host server. Once online, printer  30  waits to receive commands from host processor  23 . These commands, some of which have been listed previously, are typical of the commands which can be sent to printer  30  once printer  30  is online. In this regard, normally, after going online, host processor  23  will output a status request [STATUS] command to printer  30  in order to obtain any new information or parameters which may have changed while the printer was offline. In response, in step S 3406  printer  30  will transmit printer profile parameters stored in EEPROM  132  to host processor  23 . Upon receiving the parameters, host processor  23  will review the parameters, in particular, the parameters dealing with the print heads, to determine if a print head has been changed. If it is determined that a print head has been changed, in step S 3407  host processor  23  will determine if a test pattern should be requested. Normally, a test pattern will be printed so that print head alignment and optical density of the printed image can be measured. If a print head has been changed and a test pattern is required, in step S 3408  host processor  23  transmits one or more commands through printer interface  104  and control logic  124  to print engine  131 . For example, host processor  23  can transmit a series of commands, as shown in Table 3 below. These commands can be transmitted together with print data to print engine  131  so as to print a test pattern to be scanned. 
     
       
         
           
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 EXAMPLE OF TEST PATTERN AND SCAN COMMAND FLOW 
               
               
                 The sample command flow in case of BC-21 × 2, 
               
               
                 Color Mode, 360 dpi and 8.5″ of print buffer 139 is 
               
               
                 described below: 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 [UCT] 
                 Universal Coordinated Time (Set 
               
               
                   
                 Current Time) 
               
               
                 [RESET] 
                 Printer Reset (Software Reset) 
               
               
                 [COMPRESS] 
                 Select Data Compression (Byte 
               
               
                   
                 Packing Mode) 
               
               
                 [DEFINE_BUF] 
                 Define Print Buffer A (360 dpi, 
               
               
                   
                 12 bytes × 3,060 columns, . . . ) 
               
               
                 [DEFINE_BUF] 
                 Define Print Buffer B (360 dpi, 
               
               
                   
                 12 bytes × 3,060 columns, . . . ) 
               
               
                 [DEFINE_PULSE] 
                 Define Heat Pulse Table (16 
               
               
                   
                 partition) 
               
               
                 [DEFINE_CONTROL] 
                 Define Buffer Control Table (BC-21 
               
               
                   
                 Color Mode) 
               
               
                 [LOAD] 
                 Paper Load (Letter size of Plain 
               
               
                   
                 Paper, 8.5 inch × 11 inch) 
               
               
                 [SKIP] 
                 Raster Skip to the print position 
               
               
                   
                 for the 1st scan 
               
               
                 [DIRECTION] 
                 Set Print Direction for the 1st scan 
               
               
                 [EDGE] 
                 Set Left and Right Edge of Head A 
               
               
                   
                 for the 1st scan 
               
               
                 [EDGE] 
                 Set Left and Right Edge of Head B 
               
               
                   
                 for the 1st scan 
               
               
                 Loop 1: Begin 
                 Repeat until [EJECT] command 
               
               
                 [SPEED] 
                 Select Print Speed for the 1st scan 
               
               
                   
                 (6.51 Khz) 
               
               
                 [DROP] 
                 Select Droplet Size of Head A for 
               
               
                   
                 the 1st scan 
               
               
                 [DROP] 
                 Select Droplet Size of Head B for 
               
               
                   
                 the 1st scan 
               
               
                 [SELECT_PULSE] 
                 Select Heat Pulse Table to next scan 
               
               
                 [SELECT_CONTROL] 
                 Select Buffer Control Table of Head 
               
               
                   
                 A for the 1st scan 
               
               
                 [SELECT_CONTROL] 
                 Select Buffer Control Table of Head 
               
               
                   
                 B for the 1st scan 
               
               
                 Loop 2: Begin 
                 Repeat 18 times for 9 Block 
               
               
                   
                 (4.5 inch/0.5 inch) × 2 Head (Head A 
               
               
                   
                 and Head B) 
               
               
                 [BLOCK] 
                 Select Print Block 
               
               
                 Loop 3: Begin 
                 Repeat 4 times for 4 Color (Yellow, 
               
               
                   
                 Magenta, Cyan, Black) 
               
               
                 [COLOR] 
                 Select Print Color 
               
               
                 [DATA] 
                 Image Data Transmission 
               
               
                   
                 (540 byte/block) 
               
               
                 Loop 3: End 
               
               
                 Loop 2: End 
               
               
                 [DIRECTION] 
                 Set Print Direction for the 2nd scan 
               
               
                 [EDGE] 
                 Set Left and Right Edge of Head A 
               
               
                   
                 for the 2nd scan 
               
               
                 [EDGE] 
                 Set Left and Right Edge of Head B 
               
               
                   
                 for the 2nd scan 
               
               
                 [PRINT] 
                 Print Execution for the 1st scan 
               
               
                 [SKIP] 
                 Raster Skip to the print position 
               
               
                   
                 for the 2nd scan (24 raster) 
               
               
                 [SCAN] 
                 Scan Test Pattern and Store Data in RAM 
               
               
                 [SENSOR_RESULTS] 
                 Transmit Scanning Results 
               
               
                 [NVRAM] 
                 Write compensation parameters into 
               
               
                   
                 EEPROM 
               
               
                 [EJECT] 
                 Paper Eject (Eject Only) 
               
               
                   
               
            
           
         
       
     
     Once the test pattern has been printed, in step S 3409  host processor  23  outputs a scan [SCAN] command to printer  30  which initiates a scan of the printed test pattern by sensors  82  on print heads  130   a  and  130   b . Specifically, upon receiving the [SCAN] command, each print head  130   a  and  130   b  will return to home location  87  at which time covers of each sensor  82  are uncapped and a sheet of paper on which a test pattern is printed is advanced so as to align the printed test pattern with sensors  82 . 
     Each sensor  82  scans a portion of the printed test pattern which has been printed by its corresponding print head, and stores the resulting test pattern data (e.g., alignment measurements) in RAM  129 . This test pattern data is 8-bit digitized data obtained from analog-to-digital conversion of the output voltage level of sensor  82 . 
     The test pattern data stored in RAM  129  remains there until host processor  23  sends a status request [SENSOR_RESULTS] command to printer  30 . Upon receiving the [SENSOR_RESULTS] command, in step S 3410  printer  30  transmits the test pattern data stored in RAM  129  to host processor  23 . When the data is received, host processor  23  retrieves compensation equations from disk  25  and uses the equations with the received data in order to derive compensation parameters. Once the compensation parameters are computed, host processor  23  sends a [NVRAM] control command to printer  30  which causes printer  30  to write the compensation parameters into EEPROM  132  in step S 3411 . 
     As stated previously, EEPROM  132  stores separate parameters and measurements for each print head  130   a  and  130   b  and compensation parameters are separately computed and downloaded based on each print heads&#39; alignment and optical density. An example of the type of compensation parameters downloaded by host processor  23  is shown in Table 4 below. 
     
       
         
           
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Contents 
               
               
                   
                   
               
             
            
               
                   
                 Printer Id 
               
               
                   
                 Head Id (Head A) 
               
               
                   
                 Status (Head A) 
               
               
                   
                 X-Align (Head A) 
               
               
                   
                 Y-Align (Head A) 
               
               
                   
                 Frd-Align (Head A) 
               
               
                   
                 Rev-Align (Head A) 
               
               
                   
                 Fwd_Optical Density (Head A) 
               
               
                   
                 Bwd_Optical Density (Head A) 
               
               
                   
                 Head Id (Head B) 
               
               
                   
                 Status (Head B) 
               
               
                   
                 X-Align (Head B) 
               
               
                   
                 Y-Align (Head B) 
               
               
                   
                 Frd-Align (Head B) 
               
               
                   
                 Rev-Align (Head B) 
               
               
                   
                 Fwd_Optical Density (Head B) 
               
               
                   
                 Bwd_Optical Density (Head B) 
               
               
                   
                 Reserved 
               
               
                   
                   
               
            
           
         
       
     
     The information and parameters shown above relate to alignment of print heads  130   a  and  130   b  as well as the optical density of an image printed by each print head  130   a  and  130   b . This information is utilized by host processor  23  when sending print head command signals to print heads  130   a  and  130   b  during a print operation. 
     Returning to the flow diagram in FIG. 34, in step S 3411 , printer  30  awaits further commands from host processor  23 . 
     In step S 3413 , host processor  23  s ends a status request [DATA_SEND] command t o printer  30  and printer profile parameters are again registered with host processor  23 . The [STATUS] commands may be sent to printer  30  at specific time intervals or after a specific printer event such as replacing a print head. Next, in step S 3414  host processor  23  utilizes the printer profile parameters in order to compensate for physical characteristics and variations in each of print heads  130   a  and  130   b  as well as the inks in ink cartridges attached to each print head  130   a  and  130   b  when sending print information to each of print heads  130   a  and  130   b.    
     Therefore, printer  30  memorizes a profile individually or separately from host processor  23 . That makes it possible for another host processor to read the registered profile from printer  30  in order to compensate for physical characteristics related to printer  30 . 
     7.0 Scheduling Cleaning Of Print Heads 
     In brief, one aspect of the invention disclosed in this embodiment is an ink jet printer which includes an interface for interfacing with a host processor and for receiving print data, print commands, and real time/date information from the host processor, a memory for storing the print data, print commands and real time/date information, a print engine for printing an image in accordance with the print data and print commands, the print engine controlling at least one print head to print the image, and a processor for controlling processing events of the print engine based on the real time/date information received via the interface from the host processor and based on printer-related events. 
     More specifically, since print head nozzles clog due to bubbles or dry ink being trapped therein, print heads  130   a  and  130   b  of printer  30  must be cleaned. The cleaning process consists of moving a print head to its home location where rotary pump  294  suction ink from the print head. Resulting waste ink is deposited into a waste storage area, such as a waste well, where the waste ink eventually evaporates over time. It is important to clean print heads  130   a  and  130   b  after a predetermined time, which in the present invention has been determined to be an elapse of seventy-three ( 73 ) hours since a last cleaning. If this is not done, print head nozzles may clog, thereby adversely affecting print quality. In addition, in order to ensure proper operation of ink jet printer  30 , each print head  130   a  and  130   b  is cleaned at ink cartridge installation and each time an ink cartridge is replaced. 
     As discussed previously, with the exception of event-scheduled cleaning, printer  30  performs a print head cleaning based on an elapsed time. The elapsed time is calculated by determining how much time has elapsed since a last cleaning. An example of manual initiation of a cleaning operation is described above in section 5.0. The determination of elapsed time is based on a real-time/date stamp which is downloaded from host processor  23  at the beginning of every print job. In this manner, printer  30  will be able to keep track of how much time has elapsed since the last cleaning process. 
     The foregoing process will now be discussed in greater detail with respect to the flow diagram in FIG.  35 . Upon installation and applying power to printer  30  for the first time, in step S 3501 , a hard power-on begins a cleaning schedule process for printer  30 . In steps S 3502  and S 3503 , CPU  121  of printer  30  performs its power-on self-test initialization programs by executing process steps stored in ROM  122 . CPU  121  uses these programs to check on and define various hardware parameters. In step S 3504 , CPU  121  reads the various parameters stored in EEPROM  132 . These parameters have been discussed above in section 6.0. For the purpose of this aspect of the invention, CPU  121  is interested in a last cleaning time listed for each print head  130   a  and  130   b . It is this information which is required for scheduling a next cleaning time. However, if EEPROM  132  has not been initialized yet, the last cleaning times will be set to zero. 
     As explained above, EEPROM  132  maintains profile information on all print heads used in printer  30 . Therefore, in the presently-disclosed embodiment, EEPROM  132  maintains last cleaning times for print heads  130   a  and  130   b  in separate memory locations. Each cleaning time also is stored with a check sum value. That is, the cleaning times are secured with data error correction by check-sum processing or CRC check processing. Both the cleaning times and check-sums are mirrored in separate locations or EEPROM  132  in order to prevent loss of the cleaning times which may occur at an accidental power-down, or if a hard-on reset occurs during the middle of a writing operation to EEPROM  132 . As a result, at least one set of cleaning times is quarantined even if an accident occurs. 
     In step S 3505 , CPU  121  resets variables Delta T_A, which represents an elapsed time since print head A (e.g., print head  130   a  from FIG. 10) was last cleaned. This variable, when enabled, is incremented in one second intervals and is cleared after every hard power-off. Similarly, CPU  121  also resets Delta T_B for a print head B (e.g., print head  130   b  from FIG.  10 ). CPU  121  resets other indicator flags at this time, such as FlagRealTimeActive which indicates whether a real-time has been set or not, FlagRealTimeReset which indicates whether the real-time has been reset or not, FlagRecordYet_A which indicates that Delta T_A value indicates the time of the last cleaning of print head A only when the real-time is not yet set, and FlagRecordYet_B which indicates similar information from print head B. Each of the variables and flags which are set and reset during the cleaning scheduling process of the present invention are listed below in Table 5. 
     
       
         
           
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                 Variable/Flag 
                 Definition 
               
               
                   
               
             
            
               
                 RealTime 
                 This indicates that the current time and its 
               
               
                   
                 values are valid only when FlagRealTimeActive is 
               
               
                   
                 set. Also, this will be incremented at every one 
               
               
                   
                 second if the value is valid. 
               
               
                 Delta T_A 
                 This indicates the passed time of A-head from the 
               
               
                   
                 last cleaning and its value is valid only when 
               
               
                   
                 FlagRealTimeActive is reset. Also, this will be 
               
               
                   
                 incremented at every one second if it is valid. 
               
               
                 Delta T_B 
                 This indicates the passed time of B-head from the 
               
               
                   
                 last cleaning and its value is valid only when 
               
               
                   
                 FlagRealTimeActive is reset. Also, this will be 
               
               
                   
                 incremented at every one second if it is valid. 
               
               
                 FlagRealTimeActive 
                 This indicates whether or not the RealTime flag 
               
               
                   
                 has been set. 
               
               
                 FlagRealTimeReset 
                 This indicates whether or not the RealTime flag 
               
               
                   
                 has been reset. 
               
               
                 FlagRecordYet_A 
                 This indicates whether the Delta_A value is 
               
               
                   
                 indicating a passed time from the last cleaning of 
               
               
                   
                 A-head only when RealTime flag is not yet set. 
               
               
                 FlagRecordYet_B 
                 This indicates whether the Delta_B value is 
               
               
                   
                 indicating a passed time from the last cleaning of 
               
               
                   
                 B-head only when RealTime flag is not yet set. 
               
               
                   
               
            
           
         
       
     
     In step S 3506 , CPU  121  determines if the last cleaning time for each of the print heads equals zero. In this regard, in a case that the printer is newly installed, these variables will read zero. Therefore, in step S 3507 , the elapsed time since cleaning print head A will be set to a predetermined time, which, as noted above, is 73 hours. As a result, upon performing a soft power-on, printer  30  will perform a cleaning operation on print head A. Steps S 3508  and S 3509  perform similar processing for print head B. 
     In step S 3510 , CPU  121  enables the cleaning schedule process. In step S 3511 , CPU  121  awaits a soft power-on and commands from host processor  23 . In the case of an initial installation, a cleaning process will be performed on each print head at this step. 
     7.1 Cleaning Schedule Process 
     As discussed above, after initialization, CPU  121  enables a cleaning schedule in step S 3510  of FIG.  35 . The manner by which an elapsed time schedule is maintained will now be discussed in greater detail with respect to the flow diagram shown in FIG.  36 . The shown process is performed at every one second in the case the cleaning process has been enabled as an interrupt process. 
     Specifically, in step S 3601 , the cleaning schedule process is enabled and the elapsed time is incremented every second for both print heads A and B. In step S 3602 , it is determined if the FlagRealTimeActive has been set. This flag will indicate that a real-time has been downloaded from host processor  23 . In the case this flag has not been set, flow proceeds to step S 3603 , in which it is determined if the elapsed time since the last cleaning of print head A has reached the predetermined maximum time of 73 hours or the maximum value of its variable range. If it has, then flow proceeds to the automatic cleaning process, discussed below. Alternatively, if the value of DeltaT_A reaches maximum value, it can be ignored and reset. This will prevent the value from overflowing in memory. 
     If the time since last cleaning has not reached the maximum time, then in step S 3604  Delta T_A is incremented by one second. This process is performed because printer  30  may sit idle for more than 73 hours before receiving a real-time. If this is the case, cleaning will be performed based on an elapsed time from the printer  30 &#39;s internal clock, later on at soft power-on, or at the automatic cleaning procedure. A similar process is performed for print head B in steps S 3605  and S 3606 . 
     In the case that the FlagRealTimeActive has been set, which means that host processor  23  has downloaded a time/date stamp, in step S 3607 , it is determined if the RealTime reaches the maximum value of 73 hours or at the maximum value of its variable range. If it has, then flow proceeds to the automatic cleaning sequence, discussed below. Alternatively, if the value of RealTime reaches the maximum value, it may be ignored and reset. This prevents the value from overflowing in memory. On the other hand, if the real-time has not reached the maximum value, then the real-time is incremented by one second in step S 3608 . 
     Returning to step S 3511  of FIG. 35, upon soft power-on, flow proceeds to step S 3701  in FIG. 37, which waits for a soft power-on. Next, in step S 3702 , CPU  121  determines if the user has requested a soft power-on. If the answer is yes, then in steps S 3703  and S 3704  CPU  121  performs initialization of software programs and printer unit mechanics. Upon completing initialization, CPU  121  directs, in step S 3705 , each print head to perform an automatic cleaning operation if needed (the automatic cleaning operation will be discussed in greater detail below). 
     After performing the automatic cleaning operation, printer  30  goes online in step S 3706  and awaits either print commands from host processor  23  or a soft power off entered by the user in step S 3707 . If neither of these events occurs, printer  30  remains in a wait state for commands from host processor  23 . On the other hand, if a soft power-off request has been received, printer  30 , in step S 3708  performs its soft power-off process by performing a status check and updating parameters in EEPROM  132  based on the current status of printer  30 . 
     In the present invention, printer  30  awaits commands from host processor  23 , such as a command to print a test pattern, scan the test pattern and so on. One command which printer  30  looks for is the universal coordinated time (UCT) which provides a time/date stamp to printer  30 . The UCT command is used to set the current time in printer  30 , and must be sent to printer  30  at the onset of a print job start. Printer  30  uses the time to determine whether or not printer  30  should recover print head. The time value is expressed as the number of seconds elapsed since midnight (00:00:00), Jan. 1, 1970, Universal Coordinated Time (UCT) according to the system clock of host processor  23 . In this regard, the UCT command is downloaded at the beginning of a print command such that each print command is preceded by the. UCT command. However, it is to be noted that only after a hard power-off is there a need to store the downloaded time/date stamp since the time which is incremented by printer  30 &#39;s own internal clock is cleared from memory at hard power-off. 
     Thus, with reference to the flow diagram of FIG. 38, in step S 3801 , host processor  23  sends a UCT command. In step S 3802 , it is determined if the time and date are valid. In this regard, it is possible that a downloaded time/date stamp is invalid, e.g., if printer  30  has been connected to a host processor which has an internal clock that is ahead of the real-time clock of host processor  23 . In some instances, a time and date could be later than the actual last time and date stored in printer  30 . If the time/date is not valid due to data formatting error or value out of range, etc., then the flow will proceed to the automatic cleaning process described in detail below. Alternatively, if the time is invalid, an error processing program may be executed, or the invalid time may be ignored. 
     If, in step S 3802 , it is determined that the current time and date are valid, flow proceeds to step S 3803 . In step S 3803 , it is determined if the real-time has actually been stored in printer  30 . For example, FlagRealTimeActive may not be set. This will be the case when no real-time has yet been set in printer  30 , as would normally occur when printer  30  is being used for the first time and no print jobs have been printed. If FlagRealTimeActive has not been set, then in step S 3804  the current time and date provided at the beginning of the print job is set as the real-time. 
     Flow then proceeds to step S 3805 . In step S 3805 , CPU  121  determines, in the case the real-time has not been set, whether the elapsed time for a print head A, such as print head  130   a  from FIG. 10, corresponds to a time of the last cleaning of print head A. If it is determined that the elapsed time has been recorded, then in step S 3806 , printer  30  determines the last cleaning time by subtracting the real-time from the stored elapsed time. In step S 3807 , the last cleaning time is written to EEPROM  132  and, in step S 3808 , FlagRecordYet_A is reset for print head A. Similar processing is performed for a print head B, such as print head  130   b  from FIG. 10, in steps S 3809  to S 3812 . In this manner, the last cleaning time and check-sum are updated and are written to EEPROM  132  in separate respective memory locations for each print head A and B. 
     Returning to step S 3805 , if FlagRecordYet_A and FlagRecordYet_B have not been set, flow proceeds to step S 3813  where FlagRealTimeActive is set in order to indicate that the real-time has been set. 
     Returning to step S 3803 , if the real-time has been stored from a previous printing operation and it is determined to be a valid time, flow proceeds to step S 3814  in which previously-downloaded new time data is compared to the real-time data. If the differences between the new time data and the real-time data are acceptable in step S 3815 , then the difference is ignored in step S 3818  and flow proceeds. 
     On the other hand, if step S 3815  determines that the differences are not acceptable due to a change in the host&#39;s real-time clock or an error in the printer&#39;s internal clock, in step S 3816 , the real-time is reset with the new time data. In step S 3817 , FlagRealTimeReset is set so as to indicate that the real-time has been reset. As a result, the new time data will be used to calculate when the automatic cleaning should be scheduled for print heads A and B. This prevents a cleaning process from occurring even if a user accidently resets the host computer&#39;s real-time clock to some distant time in the future followed by a print job and [UCT] command and then reset back to actual current time. 
     7.2 Automatic Cleaning Process 
     FIG. 39 describes the automatic cleaning process. If cleaning is the result of an initial use of printer  30  or is a result of a time scheduled cleaning, in step S 3901 , it is determined if print head A exists in the printer. If print head A does exist in step S 3901 , CPU  121  checks to see if FlagRealTimeActive has been set. If yes, flow proceeds to step S 3902  to check to see if FlagRealTimeReset has been set. If no, then CPU  121  calculates the Cleaning Time by subtracting the last cleaning time for print head A stored in EEPROM  132  from the real-time. If the difference is greater than the preset cleaning time of 73 hours, then in step S 3905 , print head A is cleaned. However, if the difference is less than the preset cleaning time, then flow proceeds to step S 3903  and FlagRealTimeReset is set so that the new time data is reset as the real-time. In this case, print head A is forcibly cleaned, because real-time has been reset in step S 3817 . 
     Reverting to step S 3902 , if FlagRealTimeActive is not set flow proceeds to Step S 3906 . In step S 3906 , the elapsed time for print head A is compared to the Cleaning Time. If greater than or equal to 73 hours has elapsed since print head A was cleaned, and print head B is not installed, flow proceeds to step S 3913  at which time FlagRealTimeReset is reset. Step S 3913  will normally be executed when printer  30  has not been used since a hard power-on. 
     In the case that print head B is installed, similar processing is performed for print head B in steps S 3907  to steps S 3912 . 
     7.3 Cleaning Of A Print Head 
     FIG. 40 is a more detailed description of the operations performed in steps S 3905  and S 3911  of FIG.  39 . In step S 4001 , it is determined if a print head is installed. If it is determined that a print head is installed in step S 4001 , a cleaning operation is performed in step S 4002 . The cleaning operation consists of moving the print head to its home location, aligning nozzles on the print head to be cleaned with print head connection cap  88   a  (see FIG.  4 ), suctioning ink from the nozzles, and depositing waste ink in a waste well. The number of droplets sucked from the print head is counted and this information is updated in EEPROM  132  in the same manner as discussed above with respect to updating last cleaning times. 
     In step S 4003 , it is determined if FlagRealTimeActive is set. In the case that the flag is set, the last cleaning time of the cleaned print head is set as the real-time in step S 4004 . In step S 4005 , the real-time, which is the last cleaning time of the print head, is written to EEPROM  132 . 
     Returning to step S 4003 , if FlagRealTimeActive is not set, since a UCT command has not been downloaded to the printer in the last  73  hours, in step S 4006  the elapsed time is set to zero and FlagRecordYet for the particular print head is set in step S 4007 . This will indicate that the real time has not been set in step S 4007  and the elapsed time counter restarts. 
     As mentioned previously, cleaning of a print head will be performed in the case that the print head or the ink cartridge has been replaced. FIG. 41 is a detailed flow diagram regarding the cleaning of a print head following such an event. 
     In step S 4101 , print head replacement processing begins. In step S 4102 , CPU  121  awaits the termination of a head replacement mode by the user. In step S 4103 , the replacement process is terminated. Therefore, in step S 4104 , CPU  121  checks to see which head has been removed; i.e., which print head has engaged and disengaged a circuit contact on its corresponding cartridge receptacle. If print head A has been removed, then in step S 4105  print head A is cleaned. The cleaning is performed in the same fashion as described with respect to the flow in FIG.  40 . Similar processing is performed for print head B in steps S 4106  and S 4107 . 
     The flow diagram in FIG. 42 describes what occurs when an automatic cleaning process is scheduled and paper has been loaded into a printing position in printer  30 . In the case that paper has been loaded into the printing position and an automatic cleaning has been scheduled, the paper is ejected by a command in order to complete the printing in step S 4201 . Once the paper has been ejected, automatic cleaning of one or more print heads is performed in step S 4202 . Following the automatic cleaning process, a new paper is loaded into the printing position in step S 4203 . In this regard, steps S 4201  and S 4202  will be executed following every automatic cleaning regardless of whether a paper was previously loaded. 
     FIG. 43 is an example of a typical cleaning schedule for a print head, which is performed in accordance with the present invention as described above with respect to FIGS. 35 to  42 . Before describing the typical cleaning schedule, it should be understood that printer  30  maintains separate cleaning times and cleaning schedules for each of print heads  130   a  and  130   b . The reason for this is that one print head may be replaced before the other or one may not be used in a 73 hour period. For example, when printing only text documents, the black print head will be used more than the colored print head. Therefore, the black print head may need to be cleaned more frequently than the color print head. That is, it may not be necessary to clean the color print head until immediately before a printing even if it has been more than 73 hours from last cleaning and soft power-on has occurred. In this manner, ink may be saved. 
     FIG. 43 is a time table which shows five separate time periods (T 1 -T 5 ) being downloaded to printer  30 . The time periods shown in FIG. 43 begin at a time period of when the printer is first installed. 
     At initial hard power-on, printer  30  performs its initialization process and the last cleaning times are read from EEPROM  132 . Because it is the first power-on, all flags and variables are reset. As discussed above, this reset will initiate a cleaning process upon the soft power-on. In the example shown in FIG. 43, because a soft power-on is performed prior to installing a head into the printer, a cleaning will not be performed until the head is installed. Once the head is installed, an automatic cleaning is performed for each of print heads  130   a  and  130   b . The Delta_T variable is set to  0  for all print heads and FlagRecordYet is set as discussed above in steps S 4006  and S 4007 . 
     Once the print heads are cleaned and software has been initialized, printer  30  goes online. Recognizing that printer  30  is online, host processor  23  sends the first print job and a universal coordinated time (UCT) command, which provides the current date and time stamp. When the UCT command is received for the first time, FlagRealTimeActive is set and the new time is set as the real-time. In the present example, because the last cleaning was less than 73 hours since the print head was installed, an automatic cleaning process is not performed at T 1 . 
     In the time chart example shown in FIG. 43, the next time at which a cleaning time is set is when the head is replaced at T 2  and it is at this time that cleaning will take place regardless of elapsed time. 
     As mentioned previously, the UCT command prefaces every print command. Therefore, according to this sample time chart shown in FIG. 43, a print command provides the next new time data at T 3 . Assuming that it is a valid time and FlagRealTimeActive has been set, the difference between the new time data and the real-time data is calculated. In the case shown in FIG. 43, the difference between time T 3  and time T 2  is greater than 73 hours, and a cleaning is performed. Since the internal clock of printer  30  has been active since the previous date stamp, the elapsed real-time should be the same as the new real-time downloaded at the beginning of the print job. As a result, there is no need to store the newly downloaded time. 
     Following printing of the print job, printer  30  performs a hard power-off which clears all stored times. A hard power-on follows and resets all flags and variables. The hard power-on is followed by a soft power-on which places printer  30  online. Once online, the host processor sends a print job which is prefaced with a UCT command which provides the current time and date at T 4 . As discussed with respect to FIG. 38, since FlagRealTimeActive has not been set, the real-time that is download is stored as the new time and FlagRealTimeActive is set. 
     At this time, CPU  121  determines if print heads  130   a  and  130   b  are installed, if FlagRealTimeActive is set and whether FlagRealTimeReset is set. Because a new time has been provided by host processor  23 , the difference between the real-time and the last cleaning time of a print head is calculated. As shown in FIG. 43, the difference between time T 4  and time T 3  is greater than 73 hours. As a result, a cleaning is preformed at T 4 . 
     Following the last print job, a hard power-off occurs which clears the stored times. The next hard power-on resets all variables and flags. As previously discussed, after a hard power-on, elapsed time variables are incremented in intervals of one second. As shown in the example in FIG. 43, a period of 73 hours elapses before the next soft power-on. As a result, a cleaning is performed. This cleaning is performed based on printer  30 &#39;s own internal elapsed clock and not a real-time download because printer  30  has been idle for more than 73 hours without receiving a print job. Alternatively, cleaning of the print head, after 73 hours has elapsed on the internal clock, may not be required and may be rescheduled for immediately before a printing operation. By postponing cleaning until immediately before printing in this manner, ink can be conserved. 
     As mentioned above, EEPROM  132  can be replaced with any kind of non-volatile memory such as a static-ram with battery backup, or flash memory, etc. In this case information, including the last cleaning time discussed above, can be stored in similar types of non-volatile memory devices. 
     Furthermore, ROM  122  can be replaced with any kind of rewritable memory device, such as a flash memory, etc. In this case, such memory devices can receive program code downloaded to printer  30  via interface  104  of host processor  23  and host computer interface  141  of printer  30 . It is also possible to utilize a memory device to memorize all information in a specific area of the memory device instead of EEPROM  132 . 
     In addition, although communication line  106  was described as bi-directional, even a unidirectional interface can be used with this invention. More specifically, while the IEEE-1284 interface was implemented in the above description, any kind of interface like SCSI, USB (Universal Serial Bus), and IEEE-1394 (high speed serial bus interface), etc. may be used in its place. 
     Finally, the present invention was described using two print heads. However, it should be understood that this number could be increased or decreased. Likewise, the number of memory locations in EEPROM  132  and RAM  129  can be either increased or decreased based on the number of print heads used in printer  30 . 
     8.0 Setting And Modifying Print Head Driving Parameters 
     Because print heads  130   a  and  130   b  are designed to be removable and replaceable into printer  30 , and because different kinds of cartridges (such as cartridges having different nozzle configurations and different ink characteristics) can be loaded into print head receptacles  64   a  and  64   b , printer  30  is pre-loaded with print head driving parameters for many different types of print heads. For example, the pulse width sequence for driving each individual nozzle so as to eject an ink droplet is heavily dependent on temperature of the print head, ink characteristics (for example, whether color or black and whether dye or pigment), temperature of the surrounding environment, ink droplet size, and the like. As a consequence, ROM  122  includes pre-stored tables defining driving pulse sequences for various head/ink/resolution combinations. The pre-stored tables in ROM  122  cover various known combinations of head/ink/resolutions, as well as anticipated combinations of head/ink/resolutions. 
     Likewise, parameters used to make internal calculations such as calculations of print head temperature are also dependent on each particular combination of printer head and nozzle configurations, ink type, and resolution. For the same reason, therefore, printer  30  includes within ROM  122  various tables of heat-up coefficients for known combinations of head/ink/resolution, as well as anticipated combinations of head/ink/resolution. 
     The inventors herein have recognized that it is not possible to anticipate all possible combinations of head, ink and resolution, and to pre-store suitable tables for all such combinations. The reason for this is simple: It is not known what new developments in printer heads and inks might occur in the future. At the same time, there is a desire to utilize printer  30  with any combination of head and ink and resolution that might occur in the future, without requiring a new set of tables in ROM  122 . Particularly, new tables would require remanufacture of printers, and an upgrade program to distribute new ROM&#39;s to existing customers. 
     The present invention addresses this desire by providing for modification of the values in pre-stored tables via commands from host processor  23 , and by permitting real-time definition of print head control parameters from host processor  23 . By virtue of these features, it is possible through the use of commands from host processor  23  to define print head driving parameters which are suitable for controlling the functionality of newly-developed cartridges, or other cartridges for which pre-stored tables in ROM  122  are not available, ordinarily without changing ROM tables or other printer hardware. 
     Briefly, according to this aspect of the invention, a printer controller that receives commands from an external processor controls a process function of a printer having a detachable cartridge based on the commands. The commands are capable of defining new cartridge driving parameters which are tailored to control functionality of new cartridges for which pre-stored driving parameters are not already available in the printer. Such parameters include, for example, timing for heat pulse sequences so as to eject ink droplets, heat-up coefficients for calculating print head temperatures needed for such heat pulse sequences, print speed, droplet size, buffer readout control, nozzle firing sequence, and the like. 
     FIG. 43A is a flow diagram illustrating a first embodiment of the invention, in which a command that defines driving control parameters for a print head is comprised by a command to modify values in pre-stored tables of print head driving conditions. Briefly, according to FIG. 43A, to control print head driving conditions in a printer having a pre-stored look-up table defining pre-stored print head driving conditions for at least one of plural detachable print heads, an external host processor sends a command to modify the pre-stored look-up table such as by modification through multiplication by a control ratio. A print controller obtains print head driving conditions form the pre-stored look-up table and modifies the print head driving conditions so as to obtain modified print head driving parameters. The modified print head driving parameters are then subsequently used for print operations. 
     In more detail, in step S 43101 , printer  30  receives a command to set a control ratio for driving a print head pulse width sequence. The command is sent by host processor  23  (step S 43102 ), and in the absence of receiving any such command, printer  30  maintains a default value of 100%. The control ratio for driving that is received in step S 43101  is a factor applied to look-up values from a pre-stored table in ROM  122 , as described more fully below in step S 43112 . 
     In step S 43103 , printer  30  receives a command for a control ratio for head temperature calculations. The command is received from host processor  23  (step S 43104 ), and in the absence of receipt of such a command, printer  30  maintains a default value of 100%. The control ratio for head temperature calculations is applied as a multiplication factor against pre-stored values of heat-up coefficients used for calculating head temperature, as described more fully below in connection with step S 43115 . 
     Preferably, steps S 43101  through S 43104  are effected through use of the change pulse ratio command ([PCR]) defined above in Section 3.6. As described above, the [PCR] command is used to change a ratio of pulse control tables such as a ratio of heat-up coefficients used for calculating head temperature, and such as changing a ratio of pulse widths for a pulse width driving sequence for each individual nozzle of print heads  130   a  and  130   b  when ejecting an ink droplet from the nozzle. 
     Flow continues in printer  30  with steps S 43106  through S 43115  which are executed repeatedly at cyclic intervals of, for example, 50 ms so as to maintain in real time the most current values for print head driving parameters. More specifically, as described above in connection with FIG. 23, steps S 43106  through S 43115  are executed at 50 ms cyclic intervals, for example, so as to calculate head temperature and to derive pulse width timings for a pulse width sequence applied to eject an ink droplet from a nozzle, together with other tasks also executed at 50 ms intervals. 
     Referring again to FIG. 43A, step S 43106  reads current environmental temperature (T env ) from an unshown thermistor in printer  30 . The current environmental temperature may be the most current value read from the thermistor, or more preferably the actual value read from the thermistor is subjected to low pass filtering so as to smooth any irregularities, discount bad readings of the thermistor, remove noise such as analog-to-digital sampling noise, and the like. 
     Based on the environmental temperature T env  read in step S 43106 , a target temperature (T tgt ) is calculated in step S 43107 . The target temperature is the preferred operational temperature for printer  30  based on the current environmental temperature. Generally speaking, printer  30  is controlled through unshown heaters in print heads  130   a  and  130   b  so as to reach the target temperature, as explained above in connection with FIG. 23 at the 500 ms interrupt level. The target temperature is the most preferred temperature for print head operation based on the current environmental temperature. The relationship between target temperature and environmental temperature is inverse, meaning that low environmental temperatures result in relatively higher target temperatures, whereas high environmental temperatures result in relatively lower target temperatures. For example, at extremely low environmental temperatures such as T env =5° C., a preferred target temperature might be T tgt =35° C., whereas at extremely high environmental temperatures such as T env =35° C., a preferred target temperature might be T tgt =15° C. 
     Step S 43109  calculates the effect on print head temperature caused by actual ink droplet ejection from print heads  130   a  and  130   b . More particularly, the environmental temperature read in step S 43106  is based on an environmental temperature read by a thermistor mounted exteriorly of print heads  130   a  and  130   b . Proper control over print head driving parameters, on the other hand, is more directly affected by the internal temperature of ink adjacent the print head nozzles. It is not generally considered practicable to mount a thermistor within such a small area. At the same time, it is known that active ink droplet ejection will cause a rise in ink temperature and that in the absence of any ink ejection, ink temperature will generally fall. It is the purpose of step S 43109  to calculate the effect of print head temperature caused by ink droplet ejection to make this calculation. 
     The calculation of print head temperature in step S 43109  is made based in part on the number of ink droplets actually ejected over a previous time interval such as 50 ms. Each ejection of an ink droplet within the predetermined time interval is assigned a heat coefficient weight. Based on the number of ink droplet ejections within the predetermined time period, it is possible to calculate the effect of ink droplet ejection on print head temperature. 
     At the same time, it is known that such heat-up coefficients vary in dependence on the particular type of print head used, the ink characteristics used in the read, the resolution of printout by the head, and the like. Each different combination of head/ink/resolution changes heat-up coefficient values corresponding to the number of dots printed. Accordingly, ROM  122  is pre-stored with tables for heat-up coefficients. This situation is illustrated in FIG.  43 B. 
     As shown in FIG. 43B, one portion of ROM  122  includes pre-stored tables  701  for heat-up coefficients. The tables include plural tables  702   a ,  702   b , etc., one table for each different combination of printer head, ink characteristics, and resolution. Each of the plural tables includes tabularly accessed coefficients such as the coefficients labelled  1 ,  2  and  3  (reference numerals  703 ,  704  and  705 ), which are accessed through look-up operation based on the number of ink drops ejected in any one particular interval, for example, 50 ms (as indicated at reference numeral  706 ). Printer  30  selects one heat-up table from the tables stored at  701 , based on a default selection or based on a commanded selection (as described below in connection with FIG.  43 C), and then selects heat-up coefficients from the selected table based on the number of droplets ejected in a 50 ms period. 
     The coefficients obtained through look-up operation in tables  701  are used to calculate the effect on print head temperature by ink droplet ejection. One suitable calculation is as follows: 
     
       
           ΔT   main =(coeff 1 *(#black droplets ejected))+(coeff 2 *(#color droplets ejected))+(coeff 3 *(heater duty cycle))−coeff 4   
       
     
     where coeff 1   1  is a heat-up coefficient based on the number of black ink droplets ejected, coeff 2  is a heat-up coefficient based on the number of color droplets ejected, coeff 3  is a heat-up coefficient based on the current duty cycle of the heater, and coeff 4  is a heat-up coefficient which actually shows cool down of the print head based on inactivity. Of course, the actual coefficients and calculations used depend on the head/ink/resolution combination. For example, the calculation given above is suitable for a four-color print head whereas an all-black print head would use a different calculation that excludes, for example, dependence on the number of color droplets ejected. 
     Armed with the environmental temperature T env , the target temperature T tgt  and the print head temperature effect ΔT main , step S 43110  calculates the difference ΔT diff , as follows: 
     
       
         T diff =T tgt −T env −ΔT main   
       
     
     Step S 43111  accesses a look-up table in ROM  122  that stores pulse width times for a pulse width driving sequence, based on the temperature difference T diff . Suitable tables are illustrated diagrammatically in FIG. 43B as described below. 
     Specifically, as shown in FIG. 43B, ROM  122  includes look-up table  710  for storing driving times. The driving times are pulse widths for a pulse sequence used to drive nozzle heaters to eject an ink droplet. A typical pulse sequence is shown at  43311  in FIG. 43A, and includes a pre-heat pulse of width T pre , a quiescent period of width T int , and a main heating pulse of width T main . Such a pulse sequence is applied to nozzle heaters in each nozzle of print heads  130   a  and  130   b  so as to eject a droplet of ink for printing. It is the purpose of table  710  to calculate each of T rep , T int  and T main  based in part on the temperature difference calculated in step S 43110 . 
     At the same time, it is recognized that the pulse widths of the pulse driving sequence differ based on particular combinations of print head, ink characteristics, resolution, and the like. Accordingly, as shown in FIG. 43B, tables  710  include individual tables such as  712   a ,  712   b , etc. Each table  712   a ,  712   b , etc. is tailored for a particular combination of print head, ink type and resolution. As shown at  710 , each table includes entries  714  for the width of the pre-heat pulse T pre , entries  715  for the width of the quiescent interval T int , and entries  716  for the width of the main heating pulse T main . Any one particular entry is accessed through look-up operation based on the temperature difference T diff  calculated at step S 43110 . 
     Printer  30  selects one table of driving time from the tables stored at  710 , based on a default selection or based on a commanded selection (as described more fully below in connection with FIG.  43 C). Printer  30  thereafter accesses the entries in the selected table, and looks up appropriate times for the pre-heat pulse, the quiescent interval, and the main heat pulse, all based on the temperature difference calculated in step S 43110 , and in a particular combination of print head/ink/resolution. 
     Reverting to FIG. 43A, step S 43112  modifies the driving times obtained by look-up operation from table  710 , based on the control ratio for driving that was received in step S 43101 . The purpose of this step is to allow for modification of pre-stored values from look-up tables  710 , taking into consideration any difference between an actual print head mounted in printer  30 , and the print head combination stored in table  710 . In more detail, and as explained previously, although ROM  122  of printer  30  is pre-stored with plural tables for driving times, with each table tailored to a particular combination of print head/ink and resolution, it is not possible to anticipate each and every combination of print head/ink and resolution. Modification in step S 43112 , therefore, allows for use of previously unknown, or otherwise unstored, combinations of print head/ink and resolution. 
     Modification in step S 43112  is preferably through multiplication of the driving times obtained through look-up operation in step S 43111  by the control ratio received in step S 43101 . For this reason, the default control ratio is 100%. The control ratio that is commandable through the change pulse control ratio command [PCR] is constrained to lie between 1% to 200%, thereby allowing modification of pulse times from effectively negligible pulse times up to twice the values stored in tables  710 . 
     Flow then advances to step S 43114 , in which printer  30  looks up heat-up coefficients for head temperature calculations. As described previously in connection with tables  701  of FIG. 43B, heat-up coefficients are obtained based on a particular combination of print head, ink and resolution, and are looked up from one of tables  702   a , etc. based on the number of dots printed per cycle, each having a duration of approximately 50 ms. 
     Step S 43115  modifies the heat-up coefficients based on the control ratio received in step S 43103 . Again, the purpose of such modification is to permit usage of a particular combination of print head, ink and resolution not already stored in one of tables  701 . 
     Preferably, modification of the heat-up coefficients in step S 43115  is through multiplication of the coefficients obtained through look-up operation in step S 43114  by the control ratio received in step S 43103 . For this reason, the default control ratio is 100%. The control ratio that is commandable through the change pulse control ratio command [PCR] is constrained to lie between 1% to 200%, thereby allowing modification of heat-up coefficient from effectively negligible values up to twice the values stored in tables  701 . 
     In step S 43116 , printer  30  controls nozzle driving based on the modified driving times obtained in step S 43112 , all in response to a command from host processor  23  that sends print data to printer  30 , and a command for printer  30  to print such data (step S 43117 ). Flow repeats as before, with steps S 43106  through S 43115  being executed at 50 ms cyclic intervals, for example, and with control over nozzle driving based on modified driving times, as set out in step S 43116 , being executed as commanded by host processor  23 . In addition, it should be recognized that control ratios for driving, as well as control ratios for head temperature calculations, may be sent from host processor  23  at any time, and are responded to by printer  30  as set out in steps S 43101  and S 43103  described above. 
     FIG. 43C shows another embodiment of the present invention by which commands capable of defining print head driving parameters for a printer having a detachable print head are sent from an external device such as host processor  23  to a print controller. One difference in the embodiment shown in FIG. 43C from that shown in FIG. 43A, is that rather than responding to a parameter that modifies pre-stored print head driving parameters, the embodiment of FIG. 43C responds to actual print head driving parameters. Generally speaking, parameters received in FIG. 43C control readout order for data in print buffer  139 , control the nozzle firing sequence for individual nozzles in a print head, control droplet size for droplets ejected from the nozzles, and control other print head driving parameters. Preferably, commands from host processor  23  define plural sets of each of buffer controls and nozzle firing sequences. These buffer controls and nozzle firing sequences are registered in RAM  129  of printer  30 . By subsequent commands from host processor  23 , any of the registered sets of buffer controls or nozzle firing sequences may be selected for use in a particular scan, or plural scans, of a print head across the printing medium. 
     In more detail, in step S 43351 , host processor  23  sends a buffer control command to printer  30 , and in step S 43352  printer  30  receives the buffer control command and responds appropriately as described below. The buffer control commands sent in step S 43351  may be of two types: a first type that defines a buffer control sequence, and a second type that selects one of plural buffer control sequences already defined in printer  30 . With respect to the first type, which defines buffer control sequences, host computer  23  defines buffer control sequences by which data is read out from print buffer  139  during print operation by printer  30 . In response to such a command, the buffer control readout order is stored in RAM  129  by printer  30  for later selection. Preferably, to define a buffer control readout order, the define buffer control table command ([DEFINE_CONTROL]), described above in Section 3.6, is used. 
     Once plural buffer control readout orders are registered in RAM  129 , the second type of buffer control command allows host processor  23  to select any one of them for use in subsequent printout operations. Preferably, the select buffer control table ([SELECT_CONTROL]) command defined above in Section 3.6 is used in this operation. 
     FIG. 43D illustrates two different buffer control readout orders, as examples of the buffer control tables that may be registered in RAM  129  based on the [DEFINE_CONTROL] command. The reason that such buffer control readout orders are needed is to accommodate at least three different factors that affect how data must be read from print buffer  139  during a print operation. The first such factor is the a slant adjust of print nozzles as they are arranged on the print head. This factor has been described above in connection with FIG. 8, which illustrates that nozzles are preferably in a slightly slanted (oblique) direction such that for every 16 nozzles there is a lateral displacement of one pixel/360 dpi, two pixels/720 dpi, and four pixels/1440 dpi. 
     The second factor among those affecting buffer readout order is the print head configuration, and the nozzles actually used during a printing operation. This factor is explained in connection with FIGS. 43D,  43 E and  43 F, which show examples of buffer readout order for a variety of print head configurations and nozzles, as well as resolution. 
     FIG. 43D shows one possible print head configuration, in which a print head consists of 24 nozzles for each of yellow, magenta and cyan inks, arranged slantingly vertically on top of 64 nozzles for black in. For four-color printing, usually only 24 black nozzles out of the total of 64 such black nozzles are used, in correspondence to the 24 nozzles for the three other colorants. Physically, however, there is a considerable offset between the 24 black nozzles used for printing, and the closest adjacent nozzle of cyan. In addition, the cause of the nozzle offset length, explained above in connection with FIG. 8, buffer readout order must compensate for the nozzle offsets in the horizontal direction. 
     Buffer readout order compensates for these effects as follows. First, the actual nozzle arrangement  740  is defined with respect to a fictitious standard: a print head having 256 nozzles. Since the print head of FIG. 43D actually has the 24-24-24-64 nozzle arrangement described above for the yellow, magenta, cyan and black inks, the start position for nozzles actually commences at a location 15 bytes lower in a print buffer than would begin with a 256 nozzle head. Thus, a nozzle start position  741  is defined as 15 bytes. Thereafter, byte locations for nozzle offsets are defined for each successive group of nozzles. As shown in  742 , nozzle offsets correspond to one byte for each of the yellow, magenta and cyan inks. Because the gap between the last adjacent cyan nozzle and the first black nozzle actually used for printing corresponds to six bytes against the standard 256 nozzle head, a nozzle offset of six is defined for the first black nozzle actually used in printing. 
     A buffer readout control further defines the buffer data height  743  in bytes (in this example, buffer data height is 12 bytes) and print buffer height  744  (in this example, print buffer height is 12 bytes). 
     To control buffer readout order in compensation for nozzle slant, a start position  745  is defined for locations in the print buffer, a portion of which is designated at  746 . Each subsequent offset for eight nozzles, which correspond to a single eight bit byte in the print buffer, is specified as shown at  747 . In the example of FIG. 43D, buffer readout order is being specified for 360 dpi printing. At this resolution, the nozzle slant corresponds to one printed pixel horizontally for 16 vertical nozzles. Accordingly, the first two bytes in the print buffer (corresponding to 16 bits, one for each of the first 16 nozzles in yellow ink), are read out sequentially. However, at 360 dpi resolution, the next nozzle for yellow ink will actually be printed one pixel horizontally away from the previous 16 nozzles. To compensate for this horizontal offset, a buffer offset of 13 bytes is provided, so as to permit printing of the final eight nozzles of yellow ink in proper vertical relationship to the previous 16 nozzles. Since there is a physical gap corresponding to eight nozzles between yellow and cyan inks, as shown in FIG. 8, there is no need to provide readout data for the non-existent nozzles in the gap. 
     Since the first nozzle for magenta printing is located a physical distance of 16 nozzles away from the beginning of the last print buffer readout for yellow nozzles, an additional 13 bytes offset must be provided between printing for the last set of yellow nozzles and the first set of magenta nozzles. Similarly, offsets of plus one byte, plus 13 bytes, plus 13 bytes, plus 1 byte and plus 13 bytes are provided, in sequence, for the remainder of magenta printing, and for the cyan printing. 
     With respect to black ink printing, because the location of the 24 black nozzles actually used for printing corresponds to a horizontal shift of three pixels due to the slant angle shown in FIG. 8, and because of the eight nozzle between cyan and black nozzles, an offset of 37 bytes is needed for buffer readout order. This also is depicted at  747 . 
     Thus, in summary, buffer readout order is affected by physical arrangement of nozzles on the print head, including gaps and slant angles, actual nozzles used for printing, print resolution and the like. One way to specify buffer readout order therefore involves a specification of the nozzle start position, nozzle offsets, print buffer data height, print buffer height, and byte offsets for bytes in the print buffer that correspond to nozzles used in printing. 
     This arrangement is shown again in connection with FIG. 43D which shows printing at 720 dpi. Since print head configuration has not changed, nozzle offsets and the like are not necessarily different. However, since at 720 dpi the slant angle of FIG. 8 corresponds to a two pixel horizontal offset for every 16 vertical nozzles, buffer offsets must be changed as shown at  749 . 
     Additional examples of how to specify buffer readout order for different combinations of print head configuration (including physical arrangement of nozzles on the print head and slant angle of the nozzles), actual nozzles used during printing, and print resolution, are given in FIGS. 43E and 43F. FIG. 43E, for example, shows printout using the same print head shown in FIG. 43D, but using only all 64 black nozzles and without using any color nozzles. Thus, as shown at  750 , with respect to a fictitious standard of a 256 nozzle head, the first nozzle involved in printing is located 24 bytes lower. Accordingly, the nozzle start position  751  is altered appropriately, as are the nozzle offsets  752  which include eight successive eight bit bytes. Print buffer data height changes as shown at  754  to eight bytes, although print buffer height  755  remains at 12 bytes. Buffer offsets  756 , overlayed onto a portion  746  of the physical print buffer, indicate offsets for proper readout order of each byte from the print buffer. 
     Buffer offsets for printing at 720 dpi resolution are shown at  757 . 
     FIG. 43F shows examples of buffer readout order when using a print head comprised of 128 nozzles of black ink arranged sequentially on a print head with a slant angle, as shown at  98  in FIG.  8 . Such a nozzle arrangement  759  differs from the fictitious standard of a 256 nozzle head by beginning at a nozzle start position  760  of 16 bytes lower. Nozzle offset  761  indicate 16 sequential eight bit groups of nozzles. Print buffer data height  762  is set at 16 bytes, as is print buffer height  764 . Buffer offset  765  shows how the buffer readout order is affected by the slant of the print heads, as overlayed onto a portion  746  of the print buffer. 
     For printing at 720 dpi resolution, buffer offsets are as indicated at  766 . 
     The third factor among other factors affecting readout order is print resolution. In particular, when printing at a high resolution, a slower carriage speed is used than when printing at a low resolution. Because of the difference in carriage speed, and how the difference calculates into the effect of the non-oblique arrangement of the print nozzles, it is necessary to modify buffer readout order based on print resolution. 
     Thus, in summary, step S 43351  sends plural buffer control tables to printer  30 , where they are registered in step S 43352 . One such table is selected for use during actual printing operations. 
     In step S 43354 , host processor  23  sends nozzle firing sequence commands to printer  30 . Nozzle firing sequence commands sent from host processor  23  are received by printer  30  in step S 43355  and processed appropriately as described below. Generally speaking, step S 43354  sends one of two types of nozzle firing sequence commands: a first type which defines plural different nozzle firing sequences, and a second type in which one of the previously-defined nozzle firing sequences is selected for use during a subsequent printing operation. For the first type of nozzle firing sequence command, in which nozzle firing sequences are defined, host processor  23  preferably sends the define heat pulse table command ([DEFINE_PULSE]), described above in Section 3.6. For each such nozzle firing sequence defined by host processor  23 , printer  30  responds by registering the nozzle firing sequence in RAM  129 . 
     For the second type of nozzle firing sequence command, host processor  23  selects one of the plural previously registered nozzle firing sequences for use in subsequent printing operations. Preferably, host processor  23  utilizes the select heat pulse table command ([SELECT_PULSE]) described above in Section 3.6. Upon receipt of the select heat pulse table command, printer  30  retrieves the designated one of the previously registered heat pulse tables from RAM  129 , and utilizes it for subsequent printing operations such as the next scan or plural scans of print heads  130   a  and  130   b  across the print medium. 
     Examples of different nozzle heating sequences are illustrated in FIG.  43 G. The reason that different nozzle firing sequences are needed is because the actual nozzle firing sequence is dependent on many factors including resolution, direction of scan (i.e., forward or backward), and slant angle of the nozzles. Other factors also affect nozzle firing sequence. Resolution, for example, affects nozzle firing sequence since for a low resolution printout, a print head is moved across a carriage at a high speed. This speed is calculated so that as 16 nozzles are fired, the carriage advances by exactly one pixel/360 dpi, two pixels/720 dpi, or four pixels/1440 dpi, in correspondence to the slant angle of the nozzles. This results in a situation where a vertical line will be printed if the nozzles are fired sequentially, from top to bottom. On the other hand, at a low resolution, the carriage speed is slowed. Accordingly, so as to result in a vertical line, it is necessary to fire every other nozzle in sequence. Thus, resolution is one factor that affects the nozzle firing sequence. 
     Print direction is another factor among others that affect nozzle firing sequence, as can be readily understood. Specifically, because of the slant angle, the nozzle firing sequence must be reversed between forward and backward printing. 
     FIG. 43G illustrates some examples of nozzle firing sequences that can be defined by host processor  23  and registered in printer RAM  129 , for subsequent selection of one sequence. As shown in FIG. 43E, nozzle firing sequences for nozzle numbers  1  through  16  are defined for each of four different printing conditions: 360 dpi printing in a forward direction, 360 printing in a reverse direction, 720 dpi printing in a forward direction, and 720 printing in a reverse direction. Each of the four nozzle firing sequences is defined by host processor  23 , and transmitted to printer  30  whereupon printer  30  registers the nozzle firing sequence in RAM  129 . Thereafter, host processor  23  selects one of the nozzle firing sequences, as appropriate to the currently desired printing condition, and transmits a suitable select command to printer  30 . Printer  30  responds to the command by selecting the designated nozzle firing sequence, and using it for subsequent printing operations. 
     Thus, in summary, step S 43354  allows host processor  23  to define plural different nozzle driving sequences, one of which is designated for use in a subsequent printing operation. In step S 43355 , printer  30  responds to commands from host processor  23  by registering each of plural nozzle firing sequences in RAM  129 , and selecting a designated one of the registered nozzle firing sequences for use in subsequent printing operations. 
     In step S 43356 , host processor  23  sends a droplet size command such as the [DROP] command described above in Section 3.6, and in step S 43357 , printer  30  responds to the droplet size command by selecting the droplet size commanded thereby. Printing is thereafter effected in the droplet size. 
     In step S 43359 , host processor  23  sends print data (preferably with the [DATA] command), and thereafter commands printer  30  to effect printing of the data (with the [PRINT] command). Printer  30  responds in step S 43360  through S 43362 , by controlling readout order from printer buffer  139  based on the buffer control command selected in step S 43352 , by controlling nozzle firing sequence based on the nozzle firing sequence command received in step S 43355 , and by controlling droplet size based on the droplet size command received in step S 43357 . 
     Thus, by virtue of the foregoing processing, a printer can be controlled to utilize print heads having configurations not envisioned at the time of design, by use of commands from an external host processor that set parameters for driving the print heads. As a consequence, the flexibility of printer  30  to accept new print heads as they are developed with different head configurations and other characteristics is greatly increased. 
     9.0. Print Buffer Operation 
     FIGS. 43-1A through  43 - 1 E illustrate the transfer of print data from print data store  136  in host processor  23  to print buffer  139  (depicted in FIGS.  10  and  11 ), for printing in a forward direction. The print transfer in FIGS. 43-1A through  43 - 1 E is controlled by stored program codes in print driver  114  and by stored program codes in printer  30 . In FIGS. 43-1A through  43 - 1 E, a single print head  4330  performs scanning across a recording medium by ramping up from a stationary position to a uniform scanning speed in a forward direction, by scanning across the recording medium, and by ramping down from the uniform scanning speed to the stationary position. The ramp-up position is indicated by reference  4335 , the scan area is indicated by reference  4338 , and the ramp-down is indicated at  4339 . Reference numeral  4320  represents an area in print buffer  139  in which is stored print data for the current scan. Areas  4321  are extra areas of the print buffer reserved for storage of print data corresponding to the slant angle of the print head. (The need for extra storage in print buffer  139 , so as to store data corresponding to the slant angles of the print nozzles, was described above in connection with FIGS. 43D to  43 F, with respect to the description in the preceding section concerning buffer readout order.) Reference numeral  4325  represents print data derived by printer driver  114  and stored in print data store  136  in host processor  23 . The print data is for a next scan. Reference numeral  4315  represents a printed image on the recording medium, the printed image being stored in accordance with current scan data in print buffer  4320 . 
     As shown in FIG. 43-1A, there is print data for the current scan in all print positions of the print buffer, and there is print data for the next scan in all print positions of print data store  136 . During the ramp-up period  4335 , print head  4330  moves in the forward direction without any printing until it reaches a uniform scanning speed. Since there is no printing, there is no emptying of any print data in print buffer  4320  and there is consequently no room in print buffer  4320  so as to transfer print data for a next scan from print data store  136 . 
     FIG. 43-1B illustrates a situation in which print head  4330  has reached a scanning speed and has begun printout as illustrated at  4315 . Since print data for the current scan has been emptied (or, more precisely, is no longer needed since it has already been printed) from print buffer  4320 , a first block of print data for a next scan can be transmitted from printer driver  114  from print data store  4325  to print buffer  4320 . No further room is yet available in print buffer  4320  for additional data from print data store  4325 ; accordingly, no further data is transmitted. 
     One mechanism by which printer driver  114  determines that there is a vacant or empty area in printer buffer  4320  is through use of a signal from printer  30  that indicates that data transfer to printer  30  can not currently be accepted. Examples of such a signal include a “busy” signal or a “not-ready” signal or the like, and will hereinafter be referred to as a “busy signal”. The busy signal is generated by printer  30  and transmitted over host computer interface  141  to host processor  23 . specifically, since printer  30  utilizes a stepper motor for stepping its carriage across the recording medium, printer  30  at all times knows the print position of its print head  4330 . Printer  30  further knows the left and right edges of the currently unprinted areas in printer buffer  4320 . By comparison between the position of print head  4330  and the left and right edges of print buffer  4320 , printer  30  can determine whether there is an empty area in the print buffer into which to store data received from print driver  114 . If there is no empty area in the print buffer, then printer  30  generates a busy signal to host processor  23 . On the other hand, if there is an empty area in the printer buffer  4320 , then printer  30  clears the busy signal, indicating that it is ready to accept print data. 
     In FIGS. 43-1C through  43 - 1 E, more and more print data from the current scan is printed from print buffer  4320  onto the recording medium, as signified at  4315 . As each successive block of print data is emptied from buffer  4320 , print driver  114  transmits successive blocks of print data for a next scan from area  4325  of print data store  136  to print buffer  4320 . Thus, as shown in FIG. 43-1C, a second block of print data is transmitted from  4325  to  4320 , in FIG. 43-1D, successive blocks  3  through  8  are transmitted from print data store  4325  to print buffer  4320 , and in FIG. 43-1E, a sixteenth block of print data for a next scan is transmitted from print data store  4325  to print buffer  4320 . In FIG. 43-1E, the entirety of a current scan has been printed, as signified at  4315 , and print head  4330  begins its ramp-down operation. As will be appreciated, it is now possible for print head  4330  to begin printing in a reverse direction, utilizing the print data for the next scan that has now been stored in print buffer  4320 , during which print data for a further successive scan will be transmitted by printer driver  114  from print data store  136  to print buffer  139 . 
     Reverse printing is described as follows, in connection with FIGS. 43-2A through  43 - 2 E. 
     Specifically, FIG. 43-2A illustrates a situation like that in FIG. 43-1A, in which the size of the print data for a current scan (stored in print buffer  4320 ) is the same as or larger than the size of the print data for a subsequent scan (stored in print data store  4325 ). Reference numeral  4321  refers to extra storage of print buffer  4320  so as to accommodate the buffer readout order that compensates for slant angle of nozzles on print head  4330 . Hereinafter, such an area will be referred to as the “nozzle offset length”. Numeral  4315  refers to printed data already on the recording medium from a forward scan. During a ramp-up period as signified at  4339 , print head  4330  ramps-up from a stationary position to a uniform scanning speed; no data is printed and none is emptied from print buffer  4320 . In FIG. 43-2B, print head  4330  is moving at a uniform speed in a reverse direction and has begun to print data corresponding to print data for a current scan in print buffer  4320 . The printed data on the recording medium is signified at  4316 . Because a sufficiently large area of print buffer  4320  has been emptied by printout on the recording medium, a first block of data from print data store  4325  is transferred by printer driver  114  to print buffer  4320 . 
     With continued printing in the reverse direction, subsequent blocks of data are printed on the recording medium, thereby emptying print data from print buffer  4320 . This situation is illustrated in FIGS. 43-2C and  43 - 2 D, in which a second and subsequent blocks  3  through  8  are transferred by printer driver  114  from print data store  4325  into emptied areas of buffer  4320 . As in the situation of FIG. 43-1, printer driver  114  transmits data to printer  30  so long as a busy signal is not received from printer  30 . In FIG. 43-2E, a final block of print data has been printed from print buffer  4320  onto recording medium at  4316 , thereby permitting transfer of the final block of print data for the next scan from print data store  4325  to print buffer  4320 . The print head  4330  subsequently ramps-down from the uniform scanning speed to a stationary position, as indicated at  4335 . 
     FIGS. 43-3A through  43 - 3 F illustrate transfer of print data from print data store  136  in host processor  23  to print buffer  139  of printer  30 , during a forward scan of a single print head  4330  across a recording medium, in a situation in which current print data stored in print buffer  4320  is smaller than the print data for a next scan as stored in print data store  4325  in host processor  23 . Because the amount of current print data is smaller than the next print data, there are empty areas in print buffer  4320  even before printing has begun. It is therefore possible to take advantage of this situation, by transferring print data for a next scan into the already-empty areas of print buffer  4320 . Such processing is explained below, in connection with FIGS. 43-3A through  43 - 3 F. 
     In this situation, print driver  114  does not need to rely exclusively on busy/ready signal generation from printer  30 , in order to determine whether there are empty spaces in the print buffer into which to store print data for a next scan. specifically, because it was the print driver that previously transmitted data for the current scan for storage into particular print buffer locations, the print driver can determine without any feedback from the printer exactly which locations in the print buffer should be empty and ready to receive print data for a next scan. Printer  30  might generate a busy signal during print driver transmission of print data, but the busy signal would ordinarily be generated for reasons unrelated to the empty/full status of print buffer locations (e.g., the printer might not be ready to receive new data because it is occupied with other tasks such as head cleaning). 
     In FIG. 43-3A, a single print head  4330  prints across a recording medium by ramping up from a stationary position to a uniform scanning speed in area  4335 , printing (or seeking in a forward direction to a next print area) in a uniform speed across area  4338 , and then ramping down from a uniform scanning speed to a stationary position at area  4339 .  4320  refers to a print buffer which includes areas  4320 - 1 ,  4320 - 2 , and  4320 - 3 , of which only the latter area contains print data for a current scan. The remaining areas are empty, indicating that no data is to be printed at the corresponding locations on the recording medium.  4321  refers to the nozzle offset areas of print buffer  4320 .  4325  refers to data for a next scan in print data store  136 , as yet to be transmitted from host processor  23  to printer  30 . 
     In FIG. 43-3B, during a ramp-up period of print head  4330 , since there are empty locations in print buffer  4320 , a first block of information is transferred by printer driver  114  from print data store  4325  to print buffer  4320 . Likewise, in FIG. 43-3C, since print buffer  4320 - 2  is empty, a second block of print data is transmitted from print data store  4325  to print buffer  4320 . At this point, print head  4330  has reached its uniform scanning speed, and commences forward seeking to its first printing area corresponding to current print data in print buffer  4320 . This situation is depicted at FIG. 43-3D, in which printed data  4315  is printed by print head  4330  on the recording medium. Moreover, since printing of print data  4315  empties the area in print buffer  4320 , a subsequent block of print data is transferred by printer driver  114  from print data store  4325  to print buffer  4320 . As print head  4330  continues to move in the forward direction, FIG. 43-3E depicts the situation in which additional printed data is printed at  4315 , and subsequent blocks of print data are transferred by printer driver  114  from print data store  4325  to print buffer  4320 . In FIG. 43-3F, print head  4330  has completed printing of all current print data in print buffer  4320 , as depicted at  4315 , and is commencing forward seeking toward the end of the next print data which at this point has all been transferred from print data store  4325  into print buffer  4320 . When forward seeking is completed, print head  4330  ramps down in area  4339  from its uniform scanning speed to a stationary position, and commences ramp-up in a reverse direction to a uniform scanning speed for printing of print data now all stored in print buffer  4320 . 
     Reverse printing proceeds generally along the lines shown in FIG. 43-2, and involves transfer of next scan data into empty locations of print buffer  4320  during ramp-up, and sequential transfer of blocks of print data to the print buffer as print buffer locations are emptied during printout. 
     9.1 Single Print Buffer 
     In the forward printing operation of FIG. 43-1, and the reverse printing operation of FIG. 43-2, since the amount of print data for a current scan is the same or larger than the amount of print data for a subsequent scan, it is not possible to transfer print data in advance from printer store  4325  to print buffer  4320 . As a consequence, performance suffers since it is necessary to wait for the print head  4330  to empty data in the print buffer  4320  by printing before new data can be transmitted from printer driver  114  to printer  30 . 
     In contrast, in the situation of FIG. 43-3, since the amount of print data for a current scan is smaller than the amount of print data for a subsequent scan, it is possible for printer driver  114  to transfer data for a subsequent scan to empty areas of print buffer  4320 , even before print head  4330  begins printing. This arrangement provides advantageous processing speeds. At the same time, the situation where a current scan is smaller than a next scan occurs relatively infrequently, since it is much more ordinary for print data for each successive scan to be the same as, or approximately the same as, print data for a previous scan. 
     To improve performance of print data transfer for all scans, the inventors herein have considered to provide an additional area in print buffer  4320  corresponding to the ramp-up period of print head  4330 . The additional area will hereinafter be referred to as the “shift area”. Provision of an additional shift area for print buffer  4320  means that, for all times, even when print head  4330  is not printing, there will be empty areas in print buffer  4320  into which printer driver  114  can deposit print data for a next scan. Particularly, printer driver  114  can transfer print data into the shift area during or in advance of completion of ramp-up of print head  4330 . Moreover, the print driver need not rely exclusively on the printer&#39;s generation of a busy/read signal to determine whether the printer is ready to accept print data to this shift area; because it is the print driver itself that designates where print data for a current scan and a next scan are stored in the print buffer, the print driver can determine whether the shift area is ready to receive print data, ordinarily without feedback from the printer. 
     FIGS. 43-4A through  43 - 4 F illustrate use of a shift area to improve efficiency of data transfer, during a forward printing in a situation analogous to that illustrated in FIG. 43-1, that is, where print data for a current scan is approximately the same size as that for a next scan. In FIG. 43-4A, print buffer  4320  includes a shift area  4320 - 1  which is appended at the forward most edge of area  4320 - 2 .  4321  refers to areas in the print buffer that compensate for nozzle offset length. Region  4320 - 2  stores print data for a current scan, shift area  4320 - 1  is empty, and print data store  4325  stores print data for a next scan that is awaiting transmission from printer driver  114 . Unlike the illustration in FIG. 43-1, print data for a next scan is illustrated in a shifted position from its actual print position, with the shift from its actual print position being indicated by dotted lines. The purpose for this shift is only for illustrative purposes so as to simplify illustration of transfer of data into the shift area  4320 - 1  and area  4320 - 2  of print buffer  4320 . 
     In the absence of a busy signal from printer  30 , printer driver  114  determines that it is permissible to transmit print data from print data store  4325  to print buffer  4320 . Thus, as illustrated in FIG. 43-4B, during ramp-up period  4335  of print head  4330 , printer driver  114  transmits a first block of print information for a next scan from print data store  4325  to the shift area  4320 - 1  of print buffer  4320 . After the shift area has been filled, printer  30  generates a busy signal which stops further transmission of data. In FIG. 43-4C, print head  4320  has reached a uniform scanning speed and commences printout of print data for a current scan by printing out data in area  4320 - 2  of print buffer  4320 . Printing is illustrated at  4315 . After an area of print buffer  4320 - 2  has been emptied, printer  30  releases the busy signal indicating to printer driver  114  that it is ready to receive additional data. As a consequence, printer driver  114  commences transmission of a second block of print data for a next scan from print data store  4325  to print buffer  4320 . 
     As print head  4330  continues printing in a forward direction, successive areas of print buffer  4320  are emptied of print data, thereby freeing those locations in print buffer  4320  for receiving print data for a next scan from print data store  4325 . This situation is illustrated in FIGS. 43-4D and  43 - 4 E in which successive areas of print buffer  4320  are emptied of print data by printout at  4315 , and successive blocks of print data are transmitted by printer driver  114  from print data store  4325  into print buffer  4320 . 
     In FIG. 43-4E, a last block of print data for a next scan has been transmitted from print data store  4325  to print buffer  4320 . However, printing for a current scan has not yet been completed, since print data for the current scan remains unprinted in print buffer  4320 . Thus, as shown in FIG. 43-4F, print head  4330  continues to print, freeing additional area of print buffer  4320 . The additionally freed area of print buffer  4320  is not needed for print data for a next scan, since all print data has already been transmitted as shown at FIG. 43-4E. As a consequence, the newly-freed areas of print buffer  4320  are re-allocated into a shift area during reverse printing, which is shown in FIGS. 43-5A through  43 - 5 F. In any event, at the conclusion of printing in the forward direction, print head  4330  ramps down from a uniform scanning speed to a stationary position, at  4339 . 
     FIGS. 43-5A through  43 - 5 F illustrate transfer of print data from print data store  4325  for a next scan into print buffer  4320 , which contains print data for a current scan in area  4320 - 2  as well as an empty shift area  4320 - 1 . Thus, printing illustrated in FIG. 43-5 is similar to that illustrated in FIG. 43-2, that is, printing in a reverse direction. However, data transfer of FIG. 43-5 is different from data transfer illustrated in FIG. 43-2, primarily because of the use of shift area at  4320 - 1  which provides for more efficient data transfer. 
     Before conclusion of ramp-up period of print head  4330  from a stationary position to a uniform scanning speed at ramp-up area  4335 , since printer  30  has an empty area in its print buffer  4320 , it indicates a ready signal to host computer  23 . As a consequence, printer driver  114  transmits print data for a first block of a next scan from print data store  4325  to shift area  4320 - 1 . This is illustrated in FIG. 43-5B, in which print head  4330  is commencing its ramp-up to a uniform scanning speed. After print data for block  1  has been transmitted from print data store  4325  to shift area  4320 - 1 , printer  30  generates a busy signal indicating to printer driver  114  that no further print data is to be transmitted. 
     In FIG. 43-5C, print head  4330  has reached uniform scanning speed and has commenced printing in the reverse direction. Printout at  4316  in the reverse direction has emptied an area in print buffer  4320 . As a consequence, printer  30  generates a ready signal signifying to printer driver  114  that printer  30  can accept print data. Printer driver  114  consequently transmits block  2  of print data for a next scan from print data store  4325  to print buffer  4320 . 
     FIGS. 43-5D and  43 - 5 E illustrate continued printing in the reverse direction. Thus, in FIG. 43-5D, print head  4330  continues printing in a reverse direction, thereby emptying print locations in print buffer  4320 . In response to emptied print locations, printer driver  114  transmits print data for successive blocks of a next scan into successively emptied locations of print buffer  4320 . In FIG. 43-5E, a last block of print data for a next scan is being transmitted from print data store  4325  to print buffer  4320 . However, printing in the reverse direction has not yet completed, since there are remaining unprinted data in print buffer  4320 . Therefore, as illustrated in FIG. 43-5F, printing continues in the reverse direction, emptying successive locations of print buffer  4320 . The emptied locations are not needed for any print data for a next scan, since all such data was transmitted in FIG. 43-5E. The emptied locations of print buffer  4320  therefore become a shift area for a succeeding printing in the forward direction. 
     By virtue of the processing shown in FIGS. 43-4 and  43 - 5 , transfer of print data is made more efficient by the use of a shift area in which the shift area is prefixed at a forward end of print buffer  4320  during a forward print, and is created at the tail end of print buffer  4320  as a current line of print data is finished printing. The shift buffer created at the tail end of print buffer  4320  is used in a succeeding scan in a reverse print direction. As a consequence, since printer driver  114  has empty locations of print buffer  4320  in which to transmit data during ramp-up of the print data, efficiency of print data transfer is increased. 
     FIG. 43-6 illustrates transfer of data in a situation similar to that of FIG. 43-3 in the sense that the size of print data for a current scan is smaller than the size of print data for a next scan. However, in the data transfer illustrated in FIG. 43-6, a shift area  4320 - 5  is provided corresponding to a ramp-up period of print head  4330 , so as to increase efficiency of data transfer. 
     In FIG. 43-6, print buffer  4320  includes area  4320 - 1  which contains print data for a current scan. Areas  4320 - 2 ,  4320 - 3  and  4320 - 4  are empty areas that do not contain print data. Areas  4321  are areas of print buffer  4320  provided for nozzle offset length. Area  4320 - 5  is a shift area corresponding to the ramp-up period of print head  4330 . 
     As shown in FIG. 43-6A, print data for a next scan, which is currently stored in print data store  4325  in host processor  23 , is larger than print data for a current scan. Accordingly, there are areas of print buffer  4320  that are empty and can accept data even though print head  4330  has not yet commenced printing. This situation is illustrated in FIG. 43-6B, which before completion of a ramp-up of print head  4330  from a stationary position to a uniform scanning speed, a first block of print data for a next scan is transmitted by printer driver  114  from print data store  4325  to print buffer  4320 . The print data is stored into shift area  4320 - 5  and empty area  4320 - 4 . Thereafter, as shown in FIG. 43-6C, print head  4330  has reached a uniform scanning speed and commences forward seeking to the first printing position corresponding to print data in area  4320 - 1  of print buffer  4320 . During this period, since there still remain empty areas in print buffer  4320 , printer driver  114  transmits a second block of print data for a next scan from print data store  4325  into empty area  4320 - 2  of print buffer  4320 . 
     In FIG. 43-6D, print head  4330  has reached the first print position and commences printout as shown at  4315 . As print head  4330  continues to print, it empties print data from print buffer  4320 , thereby freeing those areas of print buffer  4320  to receive print data for a next scan. Thus, printer driver  114  transmits a third block of print data for a next scan from print data store  4325  to print buffer  4320 . 
     As print head  4330  continues to print in the forward direction, it continues to empty storage locations in print buffer  4320 . This situation is illustrated in FIG. 43-6E in which print head  4320  has completed printing of all print information in a current scan at  4315 . Printer driver  114  continues to transfer subsequent blocks of print data for a next scan into the emptied locations of print buffer  4320 . At the same time, print head  4320  commences forward seeking to the first print position of the print data for the next scan. In FIG. 43-6F, print head  4330  reaches that position and begins ramp-down from a uniform scanning speed to a stationary speed so as to reverse scanning direction for reverse direction printing. 
     During ramp-down and prior to ramp-up for reverse printing, area  4320 - 3  is now available as an empty location for a shift area for reverse printing. As a consequence, even if print data for a next sequential scan is the same size or larger than the print data stored in print buffer  4320 , there is still empty locations in print buffer  4320  at area  4320 - 3  to accept print data for the next sequential scan. As a consequence, transmission of print data from printer driver  114  to print buffer  4320  is increased. 
     Reverse printing proceeds generally along the lines shown in FIG. 43-2, and involves transfer of next scan data into empty locations of print buffer  4320  during ramp-up, and sequential transfer of blocks of print data to the print buffer as print buffer locations are emptied during printout. 
     In summary, use of a shift area so as to increase efficiency of transmitting print data involves cooperation between control on the printer driver and control on the printer side. On the printer driver side, the printer driver monitors the left and right edges for the current scan (which has previously been transmitted) and a next scan (which has yet to be transmitted). If the next scan&#39;s left edge is smaller than the current scan&#39;s left edge, then the printer driver sends a data block until the current scan&#39;s left edge has been reached. Likewise, if the next scan&#39;s right edge is larger than the current scan&#39;s right edge, then the printer driver sends a data block for the right side of the next scan until the current scan&#39;s right edge has been reached. This processing ensures that, in a situation where a next scan is larger than a current scan, data is transmitted as efficiently as possible. 
     In addition, for overlapping areas where a next scan&#39;s print area overlaps onto a current scan&#39;s print area, the printer driver divides the overlapping area into small blocks. In dependence on receipt of busy or ready signals from the printer, the printer driver transmits the overlapping areas in units of the small blocks. If the current scan is in a forward direction, then the printer driver transmits the next scan&#39;s overlap data in small blocks from left to right; whereas if the current scan is in a reverse direction, the printer driver sends the overlapping area of the next scan in small blocks from right to left. 
     On the printer side, when printing starts for a current scan, the printer maintains a monitor on the location of the print head. If the right edge of a received block of printer data is smaller than the current scan&#39;s left edge (as updated by the printer&#39;s monitor of carriage movement), then the printer puts the received data block into the print buffer immediately. Likewise, if the left edge of a received block of print data for a next scan is larger than the right edge of a current scan (as updated by the printer&#39;s monitor of carriage movement), then the printer puts the received data block into the print buffer immediately. For overlapped areas, that is, where a received block overlaps onto a current scan&#39;s print area, the printer issues a busy signal so as to stop transmission of any additional print data from the printer driver. When the block specified by the printer driver becomes vacant entirely, as updated by the printer&#39;s monitor of carriage movement, then the printer puts the received data block into the print buffer, and releases the busy signal so as to signify to the printer driver that the printer is ready to receive additional information. 
     In any event, if a current scan is in the forward direction, then the printer prints commencing from the end of the shift area (as measured in the forward direction) of the print buffer, whereas, if the current scan is in the backward direction, then the printer prints commencing from the end of the shift area (as measured in the backward direction). 
     These generalized procedures are illustrated in FIG. 43-7, which illustrates printing by two print heads using two print buffers, each with a shift area, in a situation where current print data is smaller than print data for a next scan. Printing illustrated in FIG. 43-7 is for a forward direction, but as will be appreciated from the general guidelines outlined above, printing and data transfer in a reverse direction proceeds complementarily. 
     In FIG. 43-7A, dual print heads  4330 A and  4330 B are displaced with a lateral distance  4340  therebetween, and are arranged to print in a uniform scanning speed from a stationary position, through a ramp-up period at  4335  to a uniform scanning speed, through a print area  4338  at a uniform scanning speed, and through a ramp-down period at  4339  from the uniform scanning speed to the stationary position. One print buffer is provided for each print head, with print buffer  4320 A being provided for print head  4330 A, and with print buffer  4320 B being provided for print head  4330 B. Each print buffer includes print data for a current scan, with the size of print data for a next scan being larger than the size of print data for the current scan. Thus, for print buffer  4320 A, print data for a current scan is stored in area  4320 A- 4 , with empty areas  4320 A- 1 ,  4320 A- 2  and  4320 A- 3  being empty. A shift area  4320 A- 5  prefixes print buffer  4320 A so as to increase efficiency of data transfer.  4321  denotes storage locations for the nozzle offset length. 
     Likewise, for print buffer  4320 B, area  4320 B- 4  contains print data for a current scan. Areas  4320 B- 1 ,  4320 B- 2  and  4320 B- 3  are empty. A shift area  4320 B- 5  precedes print buffer  4320 B so as to increase the efficiency of data transmission to print buffer  4320 B, and  4321  indicates storage locations for the nozzle offset. 
     At the host processor side, one print data store is provided for each print head. Thus, data store  4325 A is provided for print head  4330 A and stores print data for a next scan; and print data store  4325 B is provided for print head  4330 B and contains print data for a next scan for print head  4330 B. 
     In FIG. 43-7B, print heads  4330 A and  4330 B begin to ramp-up from a stationary position to a uniform scanning rate across a recording medium. Printer driver  114 , in the absence of a busy signal from printer  30 , determines based on previously transmitted print data that the left edge of next scan data for print head  4330 A is smaller than the left edge for current print data, and consequently sends a first block of print data from print data store  4325 A to print buffer  4320 A, which is stored in shift area  4320 A- 5  and area  4320 A- 1 . Likewise printer driver  114  determines that the left edge of next scan data for print head  4330 B is smaller than the left edge of the current scan data for print head B. As a consequence, printer driver  114  transmits one block of print data for print head  4330 B from print data store  4325 B to print buffer  4320 B. The block of print data for the next scan is stored in shift area  4320 B- 5  and in area  4320 B- 1 . 
     In FIG. 43-7C print heads  4330 A and  4330 B have reached their uniform scanning speed and commence forward seeking to the first print position for either of print head  4330 A and  4330 B. Printer  30  still has not sent a busy signal since empty areas remain in print buffers  4320 A and  4320 B and printer driver  114  has not sent data that overlaps onto existing print data for a current scan. Since printer driver  114  therefore concludes that printer  30  is ready to accept additional print data, it transmits print data appropriately. In this case, since the right edge of next scan data for print head  4330 A is larger than the right edge of print data for a current scan, printer driver  114  transmits a block of print data from print data store  4325 A to print buffer  4320 A. In this case, the transmitted data is stored in area  4320 A- 2 . Printer driver  114  may attempt to send new print data for print head  4330 A, but since the transmitted data would overlap onto non-empty locations in the print buffer, any such transmission would cause the printer to generate the busy signal. At this point printer driver  114  determines that, for print head  4330 A, the left edge for next scan is not smaller than the left edge for the current scan, and that the right edge for the next scan is not larger than the right edge for the current scan. Consequently, no print data for head  4330 A is transmitted by the printer driver until the busy signal clears. 
     On the other hand, printer driver  114  determines that the right edge of next scan data for print head  4330 B is larger than the right edge for print data for the current scan. Accordingly, a block of print data is transmitted from print data store  4325 B to print buffer  4320 B. In this case, the block of transmitted data is stored in area  4320 B- 2 . Printer driver  114  may attempt to transmit additional print data for head  4330 B, but since the transmitted data would overlap onto non-empty locations in the print buffer, any such transmissions would cause the printer to generate the busy signal. At this point printer driver  114  determines that, for print head  4330 B, the left edge of the next scan print data is not smaller than the left edge of the current scan print data, and that the right edge of the next scan print data is not larger than the right edge of the current scan print data. Consequently, no print data for head  4330 B is transmitted to the print driver until the busy signal clears. 
     At this point, no further data is transmitted from printer driver  114  to printer  30 . If printer driver  114  were to transmit print data for either of print heads  4330 A or  4330 B, the printer driver would precede the data with an [EDGE] command which specifies to the printer the locations in the print buffer to which the succeeding block of print data should be stored. Based on the locations specified in the [EDGE] command, the printer would realize that any succeeding blocks of print data from driver  114  would overlap onto non-empty locations in the print buffer. The printer thereupon issues the busy signal since any transmitted print data would—unprinted print data, and printer  30  would is therefore not ready to receive additional print data. 
     At FIG. 43-7D, through continued forward seeking of print heads  4330 A and  4330 B, print head  4330 B has reached its first print position. Accordingly, printout commences as indicated at  4315 B, thereby emptying locations in print buffer  4320 B. Printer driver  114 , which has divided the next scan&#39;s print area into small blocks, transmits a first one of the small blocks from print data store  4325 B into print buffer  4320 B. Printer  30 , sensing that the buffer locations in  4320 B are empty based on the current location of print head  4330 B, permits immediate storage of the transmitted block. 
     In FIG. 43-7E, upon continued forward printing of print head  4330 B, additional locations in print buffer  4320 B are emptied, thereby permitting transfer of data by printer driver  114  from print data store  4325 B into print buffer  4320 B. At the same time, print head  4330 A has reached its first print position (more accurately, print head  4330 A has reached the first print position in the nozzle offset area  4321 A). Printing therefore commences by print head  4330 A, and continues for print head  4330 B. 
     In FIG. 43-7F, with continued printing by print head  4330 B at  4315 B, additional locations in print buffer  4320 B are emptied. Printer driver  114  transmits additional blocks of print data for a next scan from print data store  4325 B to print buffer  4320 B. Since these locations are empty, printer  30  permits immediate storage of the transmitted blocks. 
     In the meantime, print head  4330 A has commenced printing as indicated at  4315 A, thereby emptying locations in print buffer  4320 A. As a consequence, printer driver  114  transmits a block of print data for a next scan from print data store  4325 A to print buffer  4320 A. Since the locations in print buffer  4320 A are empty and do not contain overlapped data (as-yet-unprinted data for a current scan), printer  30  allows the transmitted data to be stored immediately into print buffer  4320 A. 
     At FIGS. 43-7G and  43 - 7 H, print heads  4330 A and  4330 B continue printing, as indicated respectively at  4315 A and  4315 B. With continued printing, additional locations in print buffers  4320 A and  4320 B are emptied. As a consequence, printer driver  114  transmits additional print data for a next scan from print data stores  4325 A and  4325 B, block-by-block, into empty locations of print buffers  4320 A and  4320 B, respectively. During this processing, and all processing in which print data for a next scan is available for transmission from driver  114  to both heads, driver  114  determines which head will have data transmitted first (i.e., A before B or B before A). the driver makes this determination based on which head is more likely to empty a block first, based on the relative positions of the overlapped areas. This processing is described below in FIGS. 44C to  44 J, which explains the procedure by which the driver decides whether to send blocks of print data for head A before B, or head B before A. 
     In FIG. 43-7I, printing has concluded for print head  4330 B, thereby emptying the last location for print buffer  4320 B. Accordingly, printer driver  114  transmits the last remaining block of print data for a next scan from print data store  4325 B to print buffer  4320 B. At the same time, printout for print head  4330 A continues as indicated at  4315 A, emptying additional locations in print buffer  4320 A. As those locations are emptied, printer driver  114  transmits blocks of print data for a next scan from print data store  4325 A to print buffer  4320 A. 
     In FIGS. 43-7J and  43 - 7 K, printing continues for print head  4330 A, emptying additional locations in print buffer  4320 A. As those locations are emptied, they are filled by print data for a next scan transmitted by driver  114  from print data store  4325 A, block-by-block, to print buffer  4320 A. In FIG. 43-7K, printout of current print data for print head  4330 A is completed, resulting in a last block being transmitted from print data store  4325 A to print buffer  4320 A. Heads  4330 A and  4330 B then commence forward seeking so as to reach the first print position for print data in the next scan. 
     In FIG. 43-7L, after print heads  4330 A and  4330 B have reached the first print position for reverse printing of the next scan line, the print heads ramp-down from the uniform scanning speed to a stationary position. At that time, areas  4320 A- 3  and  4320 B- 3  are empty locations in buffers  4320 A and  4320 B, respectively. These empty areas therefore become shift areas that receive print data for a next subsequent scan during a ramp-up period for reverse printing of the now-current scan print data currently stored in print buffers  4320 A and  4320 B. 
     9.2 General Description of Buffer Control 
     The flowcharts of FIGS. 44C through 44J illustrate the process steps performed by CPU  100  of host processor  23  as part of execution of printer driver  114 , so as to effect data transmission of print data for a next scan line from print data store  136  to print buffer  139 , in accordance with the shift buffer control according to the invention. The process steps illustrated in these flowcharts are stored as computer executable process steps on a computer-readable medium such as disk  25  or in RAM  116 , and executed by CPU  100  so as to effect shift buffer control according to the invention. 
     Likewise, the flowcharts of FIGS. 44K through 44M illustrate process steps performed by CPU  121  of printer  30 , so as to effect print buffer control according to the invention. The process steps shown in these flowcharts are stored as computer executable process steps on a computer-readable medium such as ROM  122  or in RAM  129 , for execution by CPU  121  so as to effect print control according to the invention. 
     In accordance with the process steps illustrated in these flow diagrams, print buffer control according to the invention defines a print buffer with a shift area prefixed to the print buffer, with the shift area corresponding to a ramp-up period in a forward direction of a print head. For reverse printing, the print buffer includes a shift area appended at the end thereof, with the shift buffer corresponding to the ramp-up period of the print head during reverse printing. The shift buffer for forward printing is part of the print buffer for reverse printing, and the shift buffer for reverse printing is part of the print buffer for forward printing. 
     By virtue of this arrangement, in which a shift buffer is appended or prefixed to a print buffer, a printer driver always has locations to transmit print data for a next scan line during a ramp-up period of the print head. Thus, efficiency of transmitting print data for a next scan line from a printer driver to a printer is increased. 
     Moreover, because the shift area corresponds to the ramp-up period, and because the shift buffer in the forward direction is part of the print buffer for printing in the reverse direction, and vice-versa, the increase in efficiency in print data transmission is obtained without the need to provide large amounts of additional print buffer locations, such as conventional double buffering arrangements. 
     Before explaining the flow diagrams of FIGS. 44C through 44J, and the flow diagrams of FIGS. 44K through 44M, FIGS. 44A and 44B will be used to give an explanation of certain variables used in those flow diagrams. These variables correspond to physical distances on printer  30 , to storage locations within print buffers, and to the correspondence of storage locations within print buffers and their printout position on a recording medium. 
     FIG. 44A provides variable identifications for printing in the forward direction. Thus, for forward printing with print heads  4330 A and  4330 B using current print data in print buffers  4320 A and  4320 B, and with transmission of next scan print data from print data stores  4325 A and  4325 B, the following variables are defined: head gap  4340  defines the distance between heads  4330 A and  4330 B, head position A and head position B define the current carriage positions of heads A and B, respectively, BuffTop_F and BuffEnd_F define the top and the end of print buffers  4320 A and  4320 B for forward direction printing, EdgeL_Ac and EdgeR_Ac define the left and right edges of the current scan data for head  4330 A, EdgeL_Bc and EdgeR_Bc define the left and right edges of the current print data for print head  4330 B, ShiftLen defines the length of the shift area, reference numeral  1203  defines the nozzle offset length so as to compensate for the slant angle of the nozzles in the print heads, EdgeL_An and EdgeR_An refer to the left and right edges of next scan data for print head  4330 A, EdgeL_Bn and EdgeR_Bn define the left and right edges of next print data for head  4330 B, BlockLen defines the width of blocks into which printer driver  114  divides next scan print data for transmission block-by-block to print buffers  4320 A and  4320 B, and BlockLeft and BlockRight indicate the left and right addresses of an individual block currently being considered for transmission. 
     FIG. 44B identifies variables for printing by print heads  4330 A and  4330 B in a reverse (or “backward”) direction. Thus, for backward printing with print heads  4330 A and  4330 B using current print data in print buffers  4320 A and  4320 B, and with transmission of next scan print data from print data stores  4325 A and  4325 B, the following variables are defined: head gap  4340  defines the distance between heads  4330 A and  4330 B, head position A and head position B define the current carriage positions of heads A and B, respectively, BuffTop_B and BuffEnd_B define the top and the end of print buffers  4320 A and  4320 B for backward direction printing, EdgeL_Ac and EdgeR_Ac define the left and right edges of the current scan data for head  4330 A, EdgeL_Bc and EdgeR_Bc define the left and right edges of the current print data for print head  4330 B, ShiftLen defines the length of the shift area, reference numeral  1203  defines the nozzle offset length so as to compensate for the slant angle of the nozzles in the print heads, EdgeL_An and EdgeR_An refer to the left and right edges of next scan data for print head  4330 A, EdgeL_Bn and EdgeR_Bn define the left and right edges of next print data for head  4330 B, BlockLen defines the width of blocks into which printer driver  114  divides next scan print data for transmission block-by-block to print buffers  4320 A and  4320 B, and BlockLeft and BlockRight indicate the left and right addresses of an individual block currently being considered for transmission. 
     Representative examples of suitable values of the above-noted variables are as follows: 8 inches as the length for print buffers A and B, ½ inch as the length as a small data block, 2½ inches as the gap between head A and head B, 752 columns as the shift buffer area, and 32 columns for the nozzle offset length. The length of the current scan area and the next scan area depend upon the actual data being printed. For example, in connection with the example given at FIG. 43-7, the length of current scan print data is approximately 3 inches, whereas the length of next scan print area is 8 inches. 
     Referring now to the flowchart of FIGS. 44C through 44J, a detailed description will now be given of processing undertaken by printer driver  114  in accordance with stored program instructions sequences executed by CPU  100  in host processor  23 . 
     Initially in step S 4401 , a command from host processor  23  to printer  30  sets the next scan direction (forward or backward) and the edges of print data of the current scan are defined in step S 4402 . The left edge of the print data in print buffer A, EdgeL_A, is set to set to EdgeL_Ac (left edge of current scan print data)−nozzle-offset-length. The right edge of the print data in print buffer A, EdgeR_A, is set to EdgeR_Ac (right edge of print data in the current scan)+nozzle-offset-length. The left edge of the print data in print buffer B, EdgeL_B, is set to set to EdgeL_Bc (left edge of print data for the current scan)−nozzle-offset-length. The right edge of the print data in print buffer B, EdgeR_B, is set to EdgeR_Bc (right edge of current scan print data)+nozzle-offset-length. As aforementioned, the nozzle-offset-length corresponds to storage locations in a print buffer for an area corresponding to the slant of the nozzles on a print head. 
     In step S 4404 , printer driver  114  decides whether the current scan is forward or backward. For forward printing, flows advances to step S 4405  which determines the printing direction of the next scan. If step S 4405  determines that the print direction of the next scan is backwards, the edges EdgeL_A, EdgeL_B, EdgeR_A and EdgeR_B are adjusted in step S 4406  by adding the length of the shift area corresponding to the storage locations of each print buffer to be filled during the ramp-up period. 
     Steps S 4407  through S 4416  determine, for each of heads  4330 A and  4330 B, whether the next scan&#39;s left edge is less than the current scan&#39;s left edge (meaning that empty areas exist in the left edge of the print buffer), and if so, transmit print data for the next scan from print data stores  4335 A and/or  4335 B to print buffers  4320 A and/or  4320 B, so as to fill up the left side of the buffer including the shift area when current printing is in a forward direction. Print buffer  4320 A is processed for left edge data transfer in steps S 4407  through S 4411 . When it is determined that the left edge of print data for the next scan, EdgeL_An, is less than EdgeL_A corresponding to the current scan, a block select command [BLOCK] and a data command [DATA] are sent to printer  30 . The block select command is sent with a block left edge address of EdgeL_An (i.e., next scan left edge) and a block right edge address of EdgeL_A−1 (i.e., current scan left edge−1). The left edge of the next scan EdgeL_An is thereafter reset to Edge_A (S 4411 ). Flow then advances to process buffer  4320 B for left edge data transmit availability. 
     It should be pointed out that the processing of all the steps in FIGS. 44C and 44D are designed so that printer driver  114  can determine which locations in printer  30 &#39;s print buffer are empty, and transmit data to those empty locations. It is therefore unlikely that printer  30  will issue a busy signal, which would signify that printer  30  is not prepared to accept data. However, if printer  30  does issue a busy signal (it may, for example, be involved in non-printing operations such as head cleaning or the like), then printer driver  114  stops transmitting data until the busy signal clears and printer  30  is again ready to accept data. 
     Print buffer  4320 B is then processed for left edge data transfer in steps S 4412  through S 4416 . When it is determined that the left edge of print data for the next scan, EdgeL_Bn, is less than EdgeL_B set for the current scan, a block select command [BLOCK] and a data command [DATA] are sent to printer  30 . The block select command is sent with a block left edge address of EdgeL_Bn (i.e., next scan left edge) and a block right edge address of EdgeL_B−1 (i.e., current scan left edge−1). The left edge of the next scan EdgeL_Bn is thereafter reset to EdgeL_B (S 4416 ). 
     Steps S 4417  through S 4426  determine, for each of print heads  4330 A and  4330 B, whether the next scan&#39;s right edge is greater than the current scan&#39;s right edge (meaning that empty areas exist in the right edge of the print buffer), and if so, transmit print data for the next scan from print data stores  4325 A and/or  4325 B to print buffers  4320 A and/or  4320 B, so as to fill up the right side of the buffer when current printing is in a forward direction. Print buffer  4320 A is processed for right edge data transfer in steps S 4417  through S 4421 . When it is determined that the right edge of print data for the next scan, EdgeR_An, is greater than EdgeR_A, a block select command [BLOCK] and a data command [DATA] are sent to printer  30 . The block select command is sent with a block left edge address of EdgeR_A+1 (i.e., current scan right edge+1) and a block right edge address of EdgeR_An (i.e., next scan right edge). The block right edge of the next scan EdgeR_An is thereafter reset to EdgeR_A (S 4421 ). Flow then advances to process buffer  4320 B for right edge data transmit availability. 
     Print buffer  4320 B is then processed for right edge data transfer in steps S 4425  through S 4426 . When it is determined that the right edge of print data for the next scan, EdgeR_Bn, is greater than EdgeR_B set for the current scan, a block select command [BLOCK] and a data command [DATA] are sent to printer  30 . The block select command is sent with a block left edge address of EdgeR_B+1 (i.e., current scan right edge) and a block right edge address of EdgeR_Bn (i.e., next scan right edge). The right edge of the next scan EdgeR_Bn is thereafter reset to EdgeR_B (S 4426 ). 
     The foregoing operations of steps S 4405  through S 4426  are performed during and before the ramp-up period of the print heads  4330 A and  4330 B. In accordance with the invention, it is determined where there are vacant storage locations in the print buffers  4320 A and  4320 B and print data is sent from print data store  136  of host processor  23  to the respective print buffers prior to the current scan of print positions of the buffers. 
     Steps S 4427  through S 4435  illustrate print data transfer during the current scan after transfer of data according to steps S 4405  to S 4426 . Depending on speed of print data transfer, portions of these steps might actually be performed during the ramp-up period, if data transfer in steps S 4405  to S 4426  is completed before the end of the ramp-up period. These steps determine whether there is overlapped data only in buffer  4320 A, only in buffer  4320 B, or in both buffers  4320 A and  4320 B. In a case where there is overlap in both of buffers  4320 A and  4320 B, these steps further determine whether data for buffer  4320 A should precede that for buffer  4320 B, or vice-versa. 
     The steps illustrated at FIGS. 44E and 44F are executed at a time when it is likely that there will be an overlap between data transmitted by the printer driver  114  and as-yet-unprinted data in printer buffer  139 . Accordingly, transmission of data by printer driver  114  is conditional on the busy signal from printer  30 . If there is a busy signal then printer driver  114  stops transmission of data until the busy signal clears and printer  30  is again ready to accept new print data. 
     Thus, in steps S 4427  and S 4429 , printer driver  114  tests whether EdgeL_An for the next scan is less than EdgeR_An for the next scan but EdgeL_Bn for the next scan is not less than EdgeR_Bn for the next scan. If these conditions are met, there is overlapped data only in buffer  4320 A. Consequently, one predetermined small block of print data for print buffer  4320 A is sent from the left block to the right block addresses of the block to print buffer  4320 A (step S 4431 ; see FIG.  44 G). Step S 4427  is then reentered for transfer of the print data of the next small block transfer. 
     In steps S 4427  and S 4432 , printer driver  114  tests whether EdgeL_An for the next scan is not less than EdgeR_An for the next scan but that EdgeL_Bn for the next scan is less than EdgeR_Bn for the next scan. If these conditions are met, there is overlapped data only in buffer  4320 B. Consequently, one predetermined small block of print data for print buffer  4230 B is sent from the left to the right addresses of the block to print buffer  4320 B (step S 4434 ; see FIG.  44 H). Step S 4427  is then reentered for transfer of the print data of the next small block transfer. 
     In steps S 4427  and S 4429 , printer driver  114  also determines whether EdgeL_An for the next scan is less than EdgeR_An for the next scan and that EdgeL_Bn for the next scan is less than EdgeR_Bn for the next scan. If these conditions are met, there is overlapped data in both buffers  4320 A and  4320 B. Step S 4430  then determines whether data for buffer  4320 A precedes that for buffer  4320 B or vice-versa. 
     Specifically, step S 4430  decides whether EdgeL_Bn is greater than or equal to EdgeL_An+ the gap between print heads  4330 A and  4330 B. If so, data for buffer  4320 A precedes that for buffer  4320 B. Consequently, a small predetermined print data block for print buffer  4320 A is sent to print buffer  4320 A from print data store  136  of host processor  23  (step S 4431 ). On the other hand, a “NO” decision in step S 4430  indicates that data for buffer  4320 B precedes that for buffer  4320 A. Consequently, a small predetermined print data block for print buffer  4320 B is sent to print buffer  4320 B from print data store  136  of host processor  23  (step S 4434 ) and control is returned to step S 4427 . 
     When it is decided in steps S 4427  and S 4432  that EdgeL_An is not less than EdgeR_An and that EdgeL_Bn is not less than EdgeR_Bn, the data transfer is complete and a print command [PRINT] for the next scan line is sent to printer  30  in step S 4435 . 
     Referring again to FIG. 44C, when step S 4404  decides that the current scan is backward, step S 4445  determines the printing direction of the next scan. If step S 4445  determines that the nest scan is forward, the edges EdgeL_A, EdgeL_B, EdgeR_A and EdgeR_B are adjusted in step S 4446  by subtracting the length of the shift area for storage locations of each print buffer to be filled during the ramp-up period. 
     Steps S 4447  through S 4466  determine, for each print heads  4330 A and  4330 B, whether the next scan&#39;s right edge is greater than the current scan&#39;s right edge (meaning that empty areas exist in the right edge of the print buffer), and if so, transmit print data for the next scan from print data store  4325 A and/or  4325 B to print buffers  4320 A and/or  4320 B, so as to fill up the right side of buffers  4320 A and/or  4320 B including the shift area when the current printing is in a reverse direction. Print buffer  4320 A is processed for right edge data transfer in steps S 4447  through S 4451 . When it is determined that the right edge of print data for the next scan, EdgeR_An, is greater than EdgeR A corresponding to the current scan (step S 4447 ), a block select command [BLOCK] and a data command [DATA] are sent to printer  30 . The block select command is sent with a block left edge address of EdgeR_A+1 (i.e., current scan right edge+1) and a block right edge address of EdgeR_An (i.e., next scan right edge). The right edge of the next scan EdgeR_An is then reset to EdgeR_A (step S 4451 ). 
     Print buffer  4320 B is then processed for right edge print data transfer in steps S 4452  through S 4456 . When it is determined that the right edge of print data for the next scan, EdgeR_Bn, is greater than EdgeR_B corresponding to the current scan, a block select command [BLOCK] and a data command [DATA] are sent to printer  30 . The block select command is sent with a block left edge address of EdgeR_B+1 (i.e., current scan right edge+1) and a block right edge address of EdgeR_Bn (i.e., next scan right edge). The right edge of the next scan, EdgeR_Bn, is then reset to EdgeR_B (step S 4456 ). 
     Steps S 4459  through S 4456  determine, for each of heads  4330 A and  4330 B, whether the next scan&#39;s left edge is less than the current scan&#39;s left edge (meaning that empty areas exist in the left edge of print data stores  4325 A and/or  4325 B to print buffers  4320 A and/or  4320 B), so as to fill up the left side of buffers  4320 A and/or  4320 B when current printing is in a reverse direction. Print buffer A is processed for left edge print data transfer in steps S 4457  through S 4461 . When it is determined that the left edge of print data for the next scan, EdgeL_An, is less than EdgeL_A corresponding to the current scan (step S 4457 ), a block select command [BLOCK] and a data command [DATA] are sent to printer  30 . The block select command is sent with a block left edge address of EdgeL_An (i.e., next scan left edge) and a block right edge address of EdgeL_A−1 (i.e., current scan left edge1). The left edge of the next scan, EdgeL_An, is then reset to EdgeL_A (step S 4461 ). 
     Print buffer  4320 B is then processed for left edge print data transfer in steps S 4462  through S 4466 . When it is determined that the left edge of print data for the next scan, EdgeL_Bn, is less than EdgeL_B corresponding to the current scan, a block select command [BLOCK] and a data command [DATA] are sent to printer  30 . The block select command is sent with a block left edge address of EdgeL_Bn (i.e., next scan left edge) and a block right edge address of EdgeL_B−1 (i.e., current scan left edge−1). The left edge of the next scan, EdgeL_Bn, is then reset to EdgeL_B (step S 4466 ). 
     The foregoing steps are executed during and before ramp-up of heads  4330 A and  4330 B. Steps S 4467  through S 4475  illustrate data processing during the current scan after transfer of data according to steps S 4445  to S 4466 . Depending on the speed of print data transfer, portions of these steps might actually be performed during the ramp-up period, if data transfer in steps S 4445  to S 4466  is completed before the end of the ramp-up period. These steps determine whether there is overlapped data only in buffer  4320 A, only in buffer  4320 B, or in both buffers  4320 A and  4320 B. In a case there is overlap in both of buffers  4320 A and  4320 B, these steps further determine whether data for buffer  4320 A should precede that for buffer  4320 B, or vice-versa. 
     Thus, in steps S 4467  and S 4469 , printer driver  114  tests whether EdgeL_An for the next scan is less than EdgeR_An for the next scan but EdgeL_Bn for the next scan is not less than EdgeR_Bn for the next scan. If these conditions are met, there is overlapped data in buffer  4320 A only. Consequently, one predetermined small block of print data for print buffer  4320 A is sent from the left block to the right block addresses of the block to print buffer  4320 A (step S 4471 , see FIG.  44 I). Step S 4467  is then reentered for transfer of the print data of the next small block transfer. 
     In steps S 4467  and S 4472 , printer driver  114  tests whether EdgeL_An for the next scan is not less than EdgeR_An for the next scan but that EdgeL_Bn for the next scan is less than EdgeR_Bn for the next scan. If these conditions are met, there is overlapped data in buffer  4320 B only. Consequently, one predetermined small block of print data for print buffer  4320 B is sent from the left to the right addresses of the block to print buffer  4320 B (step S 4474 ; see FIG.  44 J). S 4467  is then reentered for transfer of the print data of the next small block transfer. 
     In steps S 4467  and S 4469 , printer driver  114  also determines whether EdgeL_An for the next scan is less than EdgeR_An for the next scan and that EdgeL_Bn for the next scan is less than EdgeR_Bn for the next scan. If these conditions are met, there is overlapped data in both buffer  4320 A and  4320 B. Step S 4470  then determines whether data for buffer  4320 A precedes that for buffer  4320 B, or vice-versa. 
     Specifically, step S 4470  decides whether EdgeR_Bn minus the gap between print heads  4330 A and  4330 B is less than or equal to EdgeR_An. If so, data for buffer  4320 A precedes that for buffer  4320 B. Consequently, a small predetermined print data block for print buffer  4320 A is sent to print buffer  4320 A from print data store  136  of host processor  23 (step S 4471 ). If a “NO” decision is reached in step S 4470 , data for buffer  4320 B precedes that for buffer  4320 A. Consequently, a small predetermined print data block for print buffer  4320 B is sent to print buffer  4320 B from print data store  136  of host processor  23  (step S 4474 ) and control is returned to step S 4467 . 
     When it is decided in steps S 4467  and S 4472  that EdgeL_An is not less than EdgeR_An and that EdgeL_Bn is not less than EdgeR_Bn, the data transfer is complete and a print command [PRINT] for the next scan line is sent to printer  30  in step S 4475 . 
     FIGS. 44G and 44H show detailed flowcharts of the steps S 4431  and S 4434  of FIG. 44E for a left block to right block addressed print data transfer for print buffers  4320 A and  4320 B. Referring to FIG. 44G with respect to print buffer  4320 A, EdgeL_A is set to EdgeL_An for the next scan plus the predetermined small block length in step S 4476 . Step S 4477  is then entered wherein it is decided whether EdgeR_An for the next scan is less than EdgeL_A. If “YES”, a block command is sent to print buffer  4320 A with a left block address of EdgeL_An and a right block address of EdgeR_An (step S 4478 ), print data so addressed is sent to print buffer  4320 A (S 4479 ) and the left edge of the next scan print data, EdgeL_An, is set to EdgeR_An (S 4480 ). If “NO” in step S 4477 , a block command is sent to print buffer  4320 A with a left block address of EdgeL_An and a right block address of EdgeR_A−1 (step S 4481 ), print data so addressed is sent to print buffer  4320 A (S 4482 ) and the left edge, EdgeL_An, of the next scan print data is set to EdgeL_A (step S 4483 ). 
     FIG. 44H shows a detailed flowchart of step S 4434  of FIG. 44E for a left block to right block addressed print data transfer for print buffer  4320 B. Referring to FIG. 44H, EdgeL_B is set to EdgeL_Bn for the next scan plus the predetermined small block length in step S 4486 . Step S 4487  is then entered wherein it is decided whether EdgeR_Bn for the next scan is less than EdgeL_B. If “YES”, a block command is sent to print buffer  4320 B with a left block address of EdgeL_Bn and a right block address of EdgeR Bn (step S 4488 ), print data so addressed is sent to print buffer  4320 B (S 4489 ) and the left edge of the next scan print data, EdgeL_Bn, is set to EdgeR_Bn (S 4490 ). If “NO” in step S 4487 , a block command is sent to print buffer  4320 B with a left block address of EdgeL_Bn and a right block address of EdgeL_B−1 (step S 4491 ), print data so addressed is sent to print buffer  4320 B (S 4492 ) and the left edge, EdgeL_Bn, of the next scan print data is set to EdgeL_B (step S 4493 ). 
     FIGS. 44I and 44J show detailed flowcharts of the steps S 4471  and S 4474  of FIG. 44F for a right block to left block addressed print data transfer for print buffer  4320 A. Referring to FIG. 44I with respect to print buffer  4320 A, EdgeR_A is set to EdgeR_An for the next scan minus the predetermined small block length in step S 4506 . Step S 4507  is then entered wherein it is decided whether EdgeL_An for the next scan is less than EdgeR_A. If “YES”, a block command is sent to print buffer  4320 A with a left block address of EdgeL_An and a right block address of EdgeR_An (step S 4508 ), print data so addressed is sent to print buffer  4320 A (S 4509 ) and the right edge of the next scan print data, EdgeR_An, is set to EdgeL_An (S 4510 ). If “NO” in step S 4507 , a block command is sent to print buffer  4320 A with a left block address of EdgeR_A+1 and a right block address of EdgeR_An (step S 4511 ), print data so addressed is sent to print buffer  4320 A (S 4512 ) and the right edge of the next scan print data, EdgeR_An is set to EdgeR_A (step S 4513 ). 
     FIG. 44J shows a detailed flowchart of step S 4474  of FIG. 44F for a right block to left block addressed print data transfer for print buffer  4320 B. Referring to FIG. 44J, EdgeR_B is set to EdgeR_Bn for the next scan minus the predetermined small block length in step S 4516 . Step S 4517  is then entered wherein it is decided whether EdgeL_Bn for the next scan is less than EdgeR_B. If “YES”, a block command is sent to print buffer  4320 B with a left block address of EdgeL_Bn and a right block address of EdgeR_Bn (step S 4518 ), print data so addressed is sent to print buffer  4320 B (S 4519 ) and the left edge of the next scan print data, EdgeR_Bn, is set to EdgeL_Bn (S 4520 ). If “NO” in step S 4517 , a block command is sent to print buffer  4320 B with a left block address of EdgeR_B+l and a right block address of EdgeR_Bn (step S 4521 ), print data so addressed is sent to print buffer  4320 B (S 4522 ) and the right edge of the next scan print data, EdgeR_Bn, is set to EdgeR_B (step S 4523 ). 
     FIGS. 44K through 44M are flowcharts showing the processing in printer  30  for print data transfer which correspond to stored computer executable program codes residing in ROM  122  of printer  30 . In general, these steps provide for printer operation as follows: (1) When the current scan&#39;s printing starts, the printer monitors the position of the carriage and of carriage movement; (2) If the right edge of a received block is smaller than the current scan&#39;s left edge, then put the data block into the printer buffer immediately. If the left edge of a received block is larger than the current scan&#39;s right edge, then put the data block into the printer buffer immediately; (3) If the block which is specified by the printer driver is overlapping on current scan&#39;s printer area, then issue a busy signal so as to cause the printer driver to wait until the specified block become vacant entirely. If the block which is specified by the printer driver becomes vacant entirely, then put the data block into the printer buffer and release any busy signal so as to signify to the printer driver that the printer is ready to accept data; and (4) If the current scan is forward direction, then the printer prints shifted buffer. If the current scan is backward direction, then printer prints the non-shifted buffer. Referring to FIG. 44K, decision steps S 4545 , S 4548 , S 4550 , S 4553  and others, indicated by a dashed line, are sequentially performed when a command from printer driver  114  is received in step S 4544 . If the received command is determined to be a direction command in step S 4545 , the next scan direction (i.e., forward or backward) is received (step S 4546 ), the current scan and next scan directions are set (step S 4547 ) and control is passed to step S 4548 . When the command received in step S 4544  is detected as a block command in step S 4548 , the block address processing of step S 4549  is performed. The block address processing will be described in greater detail with respect to FIGS. 44L and 44M. 
     When the received command in step S 4544  is decided to be a data command in step S 4550 , print data received in step S 4551  is put into the designated print buffer (step S 4552 ) and control is passed to step S 4553  wherein whether the received command in step S 4554  is a print command is determined. If “YES” in step S 4553 , it is then determined in step S 4554  whether the current scan has been set to the forward direction. When the set current scan direction is the forward direction, printing is executed from the top of the designated print buffer which corresponds to the first print position of a print head after the shift area to the opposite end of the designated print buffer (step S 4555 ). For a backward direction scan, printing is executed from the other end of the print buffer which corresponds to the last print position of the print head to the top of the designated buffer. Control is then returned to step S 4544  to await another command from printer driver  114 . 
     FIGS. 44L and 44M show the block address processing of step S 4549  of FIG. 44K is greater detail. Referring to FIG. 44L, the block left and block right addresses in the block command are received in step S 4534  and it is decided in step S 4535  whether print data of the current scan remains in the designated print buffer. If the print buffer does not have remaining current scan print data in step S 4535 , control is passed to step S 4550  in FIG. 44K to determine if a data command has been received. Otherwise, it is determined in step S 4536  whether the designated print buffer is print buffer A or print buffer B, a variable X is appropriately set to A or B in one of steps S 4537  and S 4538 , and control is passed to step S 4539 . In step S 4539 , the left edge of the designated print buffer X, Edge_X, is set to the EdgeL_Xc (i.e., the left edge of print data for the current scan in the designated buffer) minus the nozzle offset length, where no printing can occur. The right edge of the designated buffer, EdgeR_X is set to EdgeR_Xc (i.e., right edge of print data for the current scan in the designated buffer) plus the nozzle offset length, where no printing can occur. Control is then passed to step S 4540  in which the current scan direction is checked. 
     When the current scan direction in step S 4540  is the forward direction, the left and right edges of the designated print buffer are set to provide shifting of the print data of the next scan. Accordingly, in step S 4541  the left edge EdgeL_X is set to EdgeL_X plus the shift area length and the right edge EdgeR_X is set to EdgeR_X plus the shift area length. When the current scan direction is the backward direction, no adjustment is needed since there are no predefined shift areas at the bottom ends of the print buffers. The next scan direction is checked in step S 4542 . If the scan direction is the forward direction in Step S 4542 , step S 4543  is executed wherein the block left and block right addresses, BlockLeft and BlockRight, are set to BlockLeft plus the shift area length and BlockRight plus the shift area length, respectively, to account for shifting of the next scan print data when inserted into the designated print buffer X. 
     Step S 4525  of FIG. 44M is then entered from step S 4543  through connection 10-11. In decision steps S 4525  and S 4526 , it is determined if the BlockRight address is less than EdgeL_X (i.e., the left edge of print data in the print buffer X) or if the BlockLeft address is greater than EdgeR_X (i.e., the right edge of print data in the print buffer X). If either of these conditions is true, the block of print data of the next scan to be transferred to the print buffer is outside the area of the print buffer X containing print data so that an immediate transfer can be performed and control is returned to step S 4550  of FIG. 44K for data command processing. 
     When there are “No” decisions in both steps S 4525  and S 4526 , there is overlap of next scan print data and the current scan print data in the print buffer X and step S 4527  is entered wherein it is determined if the current scan direction is the forward direction. If there is a “YES” decision in step S 4527 , it is determined whether the BlockRight address is less than or equal to EdgeR_X (S 4528 ). Responsive to a “YES” decision in step S 4528 , the return to step S 4550  of FIG. 44K for data command is delayed until the BlockRight address is less than HeadPos_X (step S 4529 ) which is the position of the print head associated with print buffer X, so as to assure inserting the block print data into a vacated area of the print buffer X. Responsive to a “NO” decision in step S 4528 , return to step S 4550  of FIG. 44K is delayed until the print head for the print buffer X is finished printing the current print position (step S 4530 ). 
     Responsive to a backward direction current scan in step S 4527 , step S 4531  is entered in which it is determined whether the BlockLeft address is greater than or equal to EdgeL_X (S 4531 ). Responsive to a “YES” decision in step S 4531 , the return to step S 4550  of FIG. 44K for data command is delayed until the BlockLeft address is greater than HeadPos_X (step S 4532 ) so as to assure inserting the block print data into a vacated area of the print buffer X. Responsive to a “NO” decision in step S 4531 , return to step S 4550  of FIG. 44K is delayed until the print head for the print buffer X is finished printing the current print position (step S 4533 ). 
     In accordance with the invention, the transfer of print data for a next scan from host processor  23  to print buffer  139  during the current scan obviates the need for a separate receiving buffer of the same size as print buffer  139  and increases the efficiency of print data transfer. Further, the size of the shift area is not fixed but is set by the [DEFINE_BUF] command for each printing task so that the shift area size may be selected according to the storage capacity of printer  30 . 
     Moreover, printer buffer shift area technology can be applied in the transfer of any data between any top processors. FIG. 44N illustrates at  850  the embodiment described here in which shift buffer technology is applied to transfer print data between a printer driver and a printer controller.  860  illustrates that shift buffer technology can also be applied to transfer print data between a print controller and a print engine. 
     10.0 Multi-Head Printing With Differing Resolutions 
     Because printer  30  has multiple print heads, and because of software architecture in which commands affecting resolution are sent to each print head independently, printer  30  can print and can be controlled to print with differing resolutions for each print head so as to increase overall print efficiency in situations where print data for one page includes print information for which a higher resolution is desired mixed with print data for which a lower resolution is adequate. 
     Generally speaking, this section describes control over a printer having at least first and second print heads such that the resolution of the first and second print heads is controlled independently of each other. As described above in section 1.0, printer  30  includes two ink jet print heads A and B, designated  130   a  and  130   b , respectively; and as described in section 3.0, the software architecture includes commands sent from host processor  23  that affects print resolution. Printing is effected by transmission of image data from host processor  23  to print buffer  139  in printer  30  (using the [DATA] command), and subsequent transmission of the [PRINT] print execution command. Control over print resolution is effected by transmission of commands which change ink droplet size (the [DROP] command), commands which select print speed (the [SPEED] command), commands which select nozzle firing order (the [SELECT_PULSE] command), and commands that select the readout order for reading out image data from printer buffer  139  (the [SELECT_CONTROL]command). 
     The resolution with which each print head prints may be determined manually by user input, or automatically based, for example, on relative head configuration for print heads  130   a  and  130   b , content of print data, and type of recording (or print) media. A user interface in printer driver  114  is provided for this purpose. 
     From the perspective of the printer, printer  30  receives commands to set resolution for each of print heads  130   a  and  130   b  independently, and effects printout at the selected resolution. 
     FIG. 45 is a representational view for explaining the benefits of printout with different resolutions for each of different heads. In FIG. 45,  400  depicts a printed sheet on recording media  401  which contains mixed print information of different types. Areas  402   a ,  402   b ,  402   c  and  402   d  are text areas consisting of primarily black-and white areas, for which a low resolution is adequate. Area  404 , on the other hand, represents a non-text area, such as a color image or graphic or line drawing, for which a high resolution is desired. Thus, as can be seen in FIG. 45, printout  400  consists of mixed print information, some of which is desired to be printed at high resolution, whereas others of which low resolution is adequate. The print information is mixed on a single recording medium  401 , and in some cases, such as area  404  and  402   b , is mixed across a horizontal print band in the scan direction of printer  30 . 
       405  is an enlarged view of a portion of area  402   a . Enlarged view  405  depicts print heads  130   a  and  130   b  which differ in configuration. Specifically, print head  130   a  includes yellow, magenta, cyan and black print nozzles arranged vertically with 24 nozzles for yellow, 24 nozzles for magenta, 24 nozzles for cyan and 64 nozzles for black. Print head  130   b  includes  128  print nozzles for black ink only. Thus, print heads  130   a  and  130   b  differ in configuration, with print head  130   a  being adapted to print high resolution color images, whereas print head  130   b  is adapted to print black and white images only. Of course, other configurations for heads  130   a  and  130   b  are possible so as to result in a situation in which one print head is adapted to print high resolution images whereas the other is adapted to print lower resolution images. 
     Because area  402   a  is a text area for which low resolution is adequate, printing of area  402  is effected by print head  130   b . This arrangement is shown at  405  in which one band  406  from print head  130   b  is depicted in cross-hatched emphasis. To print at this resolution, printer  30  is commanded to put print head  130   b  into a large droplet ejection mode, and print data readout order from print buffer  139  is selected in accordance with the head configuration of print head  130   b  and in accordance with the selected resolution. These steps are described more fully below in connection with the flowchart of FIG.  45 A. 
     In contrast to area  402   a , area  404  is an area for which high-resolution printout is desired. This situation is depicted in the enlarged area at  407  which shows printout by print head  130   a  only at band  409 . As described more fully below in connection with the flowchart of FIG. 45A, to effect printout in the band shown at  409 , print head  130   a  is commanded to eject ink in small droplets, and the data readout order from print buffer  139  is selected-in accordance with the head configuration of print head  130   a  and the selected resolution. 
     To print areas like  402   b , which are mixed laterally in the direction of a scan of print heads  130   a  and  130   b  across recording media  401 , a two-step procedure is employed. In one step, sequential bands like  409  are printed by print head  130   a.  The number of sequential bands printed corresponds to the ratio between the number of print nozzles in a band for print head  130   a  and the number of nozzles in a band for print head  130   b . In the other step, a single pass from print head  130   b  is effected in area  402   b . By virtue of this two-step process, recording media  401  can be advanced in a single direction continuously, without requiring reverse feed, so as to effect printout of area  402   b.    
     FIG. 45A is a flow diagram showing process steps executed by printer driver  114  in host processor  23  so as to control print resolution for each print head independently, and to command printout to be effectuated thereby. Generally speaking, the process steps shown in FIG. 45A are stored program instruction sequences that set print resolution by controlling ink droplet size for each head independently, and by controlling readout order from print buffer  139  for each print head independently. 
     More specifically, in step S 4501 , a user of host processor  23  issues a command from an application to print print data, thereby actuating printer driver  114 . Printer driver  114  actually performs many more functions than indicated in the remainder of FIG. 45, but only those functions having some bearing on setting of print resolution independently are described. Thus, in step S 4502 , printer driver  114  determines whether print resolution should be designated automatically by printer driver  114 , or whether the print resolution should be designated manually by the user. In step S 4502 , a user interface is displayed to the user, such as the representative user interface shown in FIG.  46 . As seen there, section  410 , when selected by the user, provides for automatic designation of print resolution. On the other hand, when  411  is selected, the user manually designates print resolution. Separate resolutions may be specified for non-text graphics as well as for text, with the user being able to designate manually either high speed (i.e., low resolution) or high quality (i.e., high resolution) for each of text and non-text regions. 
     Reverting to FIG. 45, if automatic designation has been selected, then flow branches to step S 4504  in which printer driver  114  automatically selects resolution for graphics, and then to step S 4505  in which printer driver  114  automatically selects resolution for text. Selection of resolution for graphics and for text is based on continuous-tone print data, and is made in accordance with the presence of graphics and other non-text information, the presence of text information, the type of recording media selected for printout, and the relative print head configurations of print head  130   a  and print head  130   b.    
     Flow next advances to step S 4506  in which the printer driver determines whether dual resolutions have been specified, either manually or automatically. If no dual resolutions have been specified, then flow branches to step S 4507  to proceed with printing in a uniform resolution for both heads. On the other hand, if dual resolutions have been specified, then flow advances to step S 4509  so as to control print resolution of each print head independently and to effect printout thereby. 
     Thus, step S 4509  defines buffer control tables, one of which is selectable for each head and by which each print head can determine readout order for readout of print data from its respective print buffer. Actual selection of which buffer control table to use is not effectuated until later in the procedure, but step S 4509  merely defines suitable buffer control tables for each resolution and for each direction of printout. Preferably, the define buffer control table command [DEFINE_CONTROL] described above in section 3.6 is used. 
     Likewise, step S 4510  defines suitable heat pulse tables by which the firing sequence for each nozzle in print heads  130   a  and  130   b  is controlled. The actual heat pulse tables used by print heads  130   a  and  130   b  are not selected at this point, but rather suitable tables are defined for later selection. Preferably, the define heat pulse table command [DEFINE_PULSE] described above in section 3.6 is used. 
     Flow then proceeds to steps S 4511  through S 4530  which (with the exception of steps S 4520  and S 4521 ) determine the resolution of a current print band, set print control conditions such as ink ejection drop size and buffer readout order, send print data, and command printout of the transmitted print data. 
     In more detail, step S 4511  determines whether printout for a particular band or a portion of a band is a high resolution printout or a low resolution printout. If the band or portion of the band is a low resolution printout, flow advances to step S 4512  which sets appropriate ink ejection droplet sizes for each of heads  130   a  and  130   b . Using the example from FIG. 45, the droplet size for head  130   b  is set to large and the droplet size for head  130   a  is set to small. Preferably, the droplet size command [DROP] defined above in section 3.6 is used. 
     In Step S 4514 , printer driver  114  selects high print speed, corresponding to low resolution printout. Preferably, the select speed command [SPEED] defined above in section 3.6 is used. 
     Step S 4516  selects offsets for readout order of print buffer  139  in accordance with the selected low resolution. Specifically, step S 4516  selects one of the buffer control tables set above in step S 4509 . Preferably, the select buffer control table command [SELECT_CONTROL] defined above in section 3.6 is used. 
     Step S 4517  transmits image data, block-by-block as discussed in section 3.6 from printer driver  114  to printer  30  over a bi-directional interface. Once an entire band of print data has been transmitted to printer  30 , printer driver  114  initiates printout of the band in step S 4519  by transmission of the print execution command [PRINT]. Step S 4520  then determines whether further bands need to be printed in accordance with which flow either returns to step S 4511  or flow terminates at step S 4521 . 
     Reverting to step S 4511 , if a high resolution band of print information is to be transmitted and printed, then steps S 4522  through S 4530  execute in the printer driver  114  so as to perform complementary steps to the low resolution steps of S 4512  through S 4519 . Thus, step S 4522  sets small drop sizes, step S 4525  sets a low print speed corresponding to high resolution, step S 4526  selects a high resolution nozzle firing sequence, step S 4527  selects readout order from print buffer  139  by selecting one of the pre-defined buffer control offset tables, step S 4529  transmits high resolution image data band by band to printer  30 , and step S 4530  initiates printout of a fully-transmitted band. 
     According to a second embodiment, a print head prints pixels of a horizontal print band in the scan direction of printer  30  in differing resolutions without requiring reverse sheet feed, thereby increasing overall printing efficiency. 
     Although this embodiment is described below with reference to a printer having multiple print heads, it will be noted that the below-described embodiment also provides significant benefits when used in conjunction with single print head printing. 
     As described above, the resolution with which a print head prints may be determined manually by user input, or automatically based, for example, on content of print data, type of recording medium, or, in the case of a multiple print head system, a relative head configuration of print heads  130   a  and  130   b.    
     Advantageously, printer  30  therefore receives commands to set resolution for each of print heads  130   a  and  130   b  independently, and effects printout at the set resolutions. 
     FIG. 46A is a representational view for explaining the benefits of controlling a print head to print out at multiple resolutions. In FIG. 46A,  420  indicates a printed sheet on recording medium  421  having various types of print information. Area  420   a ,  420   b  ,  420   c , and  420   d  are text areas consisting primarily of black and white areas. Accordingly, information contained in these text areas is satisfactorily printed in a low resolution. In contrast, area  424  is a non-text area, such as a color image or graphic or line drawing, for which a high resolution is preferred. It should be noted that areas  420   b  and  424  are located on a common horizontal print band in the scan direction of printer  30 . 
       425  is an enlarged view of a portion of area  420   b . Enlarged view  425  depicts print heads  130   a  and  130   b . Each of print heads  130   a  and  130   b  include yellow, magenta, cyan and black print nozzles arranged vertically, with 24 nozzles for yellow, 24 nozzles for magenta, 24 nozzles for cyan and 64 nozzles for black. of course, other configurations for heads  130   a  and  130   b  are possible. 
     Because area  420   b  is a text area for which low resolution is adequate, printing of area  420   b  is performed in a low resolution/high speed mode, as shown at  425 . In area  425 , one low resolution band  426  is printed by print heads  130   a  and  130   b  and depicted in cross-hatched emphasis. To print at this resolution, printer  30  is commanded to put print heads  130   a  and  130   b  into a large droplet ejection mode, and print data read out from print buffer  139  is selected in accordance with the selected resolution. These steps are described more fully below in connection with the flowchart of FIG.  46 B. 
     In contrast to area  420   b , area  424  is an area for which high resolution print out is desired. This situation is depicted in the enlarged area at  427  which shows printout by print heads  130   a  and  130   b  only at band  429 . As described more fully below in connection with the flow chart of FIG. 46B, to effect printout in the band shown at  429 , print heads  130   a  and  130   b  are commanded to eject ink in small droplets, and the data read out from print buffer  139  is selected in accordance with the selected resolution. 
     To print areas such as  420   b  and  424  which are mixed in a lateral direction in the direction of a scan of print heads  130   a  and  130   b  across recording medium  421 , a two-step procedure is employed. In one step, sequential bands such as band  429  are printed by print heads  130   a  and  130   b . The number of sequential bands such as  429  which are printed corresponds to the ratio between the number of print nozzles for each of cyan, magenta and yellow inks, in this case 24, and the number of nozzles used for black color, in this case 64. In the second step, a single pass from print heads  130   a  and  130   b  is effected, thereby printing a band of area  420   b . During the second pass, ink is ejected in a low resolution from the black nozzles of print heads  130   a  and  130   b . By virtue of this two step process, recording medium  420  can be advanced in a single direction, without requiring reverse feed, so as to effect a varied-resolution printout of area  402   b  and  424 . 
     FIG. 46B is a flow diagram showing process steps executed by printer driver  114  in host processor  23  so as to control print resolution for each print head, and to command printout to be effectuated thereby. Generally speaking, the process steps shown in FIG. 46B are stored program instruction sequences that set print resolution by controlling ink droplet size for each head, and by controlling readout order from print buffer  139  for each print head. 
     More specifically, in step S 4601 , a user of host processor  23  issues a command from an application to print print data, thereby actuating printer driver  114 . Printer driver  114  actually performs many more functions than indicated in the remainder of FIG. 46, but only those functions having some bearing on setting of print resolution are described. Thus, in step S 4602 , printer driver  114  determines whether print resolution should be designated automatically by printer driver  114 , or whether the print resolution should be designated manually by the user. In step S 4602 , a user interface is displayed to the user, such as the representative user interface shown in FIG.  46 . As seen there, section  410 , when selected by the user, provides for automatic designation of print resolution. On the other hand, when  411  is selected, the user manually designates print resolution. Separate resolutions may be specified for non-text graphics as well as for text, with the user being able to designate manually either high speed (i.e., low resolution) or high quality (i.e., high resolution) for each of text and non-text regions. 
     Reverting to FIG. 46B, if automatic designation has been selected, then flow branches to step S 4604  in which printer driver  114  automatically selects resolution for graphics, and then to step S 4605  in which printer driver  114  automatically selects resolution for text. Selection of resolution for graphics and for text is based on continuous-tone print data, and is made in accordance with the presence of graphics and other non-text information, the presence of text information, the type of recording media selected for printout, and, in the case of a multiple printed system such as that described herein, the relative print head configurations of print head  130   a  and print head  130   b.    
     Flow next advances to step S 4606  in which printer driver  114  determines whether dual resolutions have been specified, either manually or automatically. If no dual resolutions have been specified, then flow branches to step S 4607  to proceed with printing in a uniform resolution for both heads. On the other hand, if dual resolutions have been specified, then flow advances to step S 4609  so as to control print resolution of each print head and to effect printout thereby. 
     Thus, step S 4609  defines buffer control tables, one of which is selectable for each head and by which each print head can determine readout order for readout of print data from its respective print buffer. Actual selection of which buffer control table to use is not effectuated until later in the procedure, but step S 4609  merely defines suitable buffer control tables for each resolution and for each direction of printout. Preferably, the define buffer control table command [DEFINE_CONTROL] described above in section 3.6 is used. 
     Likewise, step S 4610  defines suitable heat pulse tables by which the firing sequence for each nozzle in print heads  130   a  and  130   b  is controlled. The actual heat pulse tables used by print heads  130   a  and  130   b  are not selected at this point, but rather suitable tables are defined for later selection. Preferably, the define heat pulse table command [DEFINE_PULSE] described above in section 3.6 is used. 
     Flow then proceeds to steps S 4611  through S 4630  which (with the exception of steps S 4620  and S 4621 ) the resolution of a current print band is determined, print control conditions such as ink ejection drop size and buffer readout order are set, print data is sent, and printout of the transmitted print data is commanded. 
     In more detail, step S 4611  determines whether printout for a particular band or a portion of a band is a high resolution printout or a low resolution printout. If the band or portion of the band is a low resolution printout, flow advances to step S 4612  which sets appropriate ink ejection droplet sizes for each of heads  130   a  and  130   b . Using the example from FIG. 44, the droplet size for heads  130   a  and  130   b  is set to large. Preferably, the droplet size command [DROP] defined above in section 3.6 is used. 
     In Step S 4614 , printer driver  114  selects the high print speed, corresponding to low resolution printout. Preferably, the select speed command [SPEED] defined above in section 3.6 is used. 
     Step S 4616  selects offsets for readout order of print buffer  139  in accordance with the selected low resolution. Specifically, step S 4616  selects one of the buffer control tables set above in step S 4609 . Preferably, the select buffer control table command [SELECT_CONTROL] defined above in section 3.6 is used. 
     Step S 4617  transmits image data, block-by-block as discussed in section 3.6, from printer driver  114  to printer  30  over a bi-directional interface. Once an entire band of print data has been transmitted to printer  30 , printer driver  114  initiates printout of the band in step S 4619  by transmission of the print execution command [PRINT]. Step S 4620  then determines whether further bands need to be printed in accordance with which flow either returns to step S 4611  or flow terminates at step S 4621 . 
     Reverting to step S 4611 , if a high resolution band of print information is to be transmitted and printed, then steps S 4622  through S 4630  execute in the printer driver  114  so as to perform complementary steps to the low resolution steps of S 4612  through S 4619 . Thus, step S 4622  sets small drop sizes, step S 4624  sets appropriately large buffer sizes, step S 4625  sets a low print speed corresponding to high resolution, step S 4626  selects a high resolution nozzle firing sequence, step S 4627  selects readout order from print buffer  139  by selecting one of the pre-defined buffer control offset tables, step S 4629  transmits high resolution image data band by band to printer  30 , and step S 4630  initiates printout of a fully-transmitted band. 
     From the perspective of printer  30 , FIG. 47 is a flow diagram illustrating the process steps performed by printer  30  for independent print resolution setting. Thus, in step S 4701 , printer  30  receives control commands so as to prepare printer  30  for high or low print resolution for each print head. As discussed above, these control commands include commands to set the speed of printing, the size of the ejected nozzle, the nozzle firing sequence, and the print buffer readout order. 
     In step S 4702 , print data is received from printer driver  114 , followed in step S 4703  by a print command. Thereafter, in step S 4704 , depending on whether a high or a low print resolution has been commanded, the print data received in step S 4702  is printed as commanded in step S 4701 . Thus, as shown in step S 4705 , for a high print resolution, print data is printed at a low speed, with small droplet size, with a high resolution nozzle pulse sequence table, and with a high resolution buffer control readout order. Likewise, at step S 4706 , for a low resolution printout, printout is effected at a high speed, with a large droplet size, with a low resolution nozzle pulse sequence table, and with a low resolution buffer offset readout sequence. In either event, flow proceeds to step S 4707  to await the next print command sequence. 
     As described with respect to FIGS. 46A and 46B, a single print head may be controlled to print print data on a single print band in a scanning direction,using both sets of printing characteristics set forth in step S 4705  and step S 4706 . 
     11.0 Selection of Alternative Inks 
     As described above, printer  30  can be configured to output several types of ink onto a single recording media. Advantageously, this feature allows printer  30  to print an image using both dye-based black ink and pigment-based black ink. 
     In a preferred embodiment, dye-based black ink is used in conjunction with differently-colored inks to facilitate color printing. As a result, when used to print black pixels within a color image, dye-based black ink allows the color image to maintain a substantially uniform optical density. 
     In contrast, pigment-based black ink, when used to print black pixels within a color image, contrasts sharply with other regions of the color image, thereby disturbing uniformity of the color image. However, many cases exist in which it is desirable to maintain significant contrast between a black printed region and a differently-colored region. Most notable among these cases is the printing of black text upon a white recording medium. Therefore, pigment-based black ink is preferably used to print text data. 
     Therefore, in the above-described embodiment, selection of dye-based black ink or pigment-based black ink to print a black target pixel is based upon content of image data surrounding the black target pixel. More specifically, in a case that a black target pixel is judged to correspond to a differently-colored region of image data, the target pixel is printed using a dye-based black ink. If not, the target pixel is printed using a pigment-based black ink. One method of judging whether a black pixel corresponds to a differently-colored region of image data is described below with respect to FIG.  49 . Preferably, such judging is performed based on multi-level image data so that accurate characterization of image content can be achieved. 
     Since the above-described visual properties of various inks depend upon degrees of ink penetration into a recording medium, recording media type plays a significant role in determining whether dye-based, or other high-penetration black inks, or low-penetration black inks such as pigment-based inks are more appropriate for a particular print job. 
     Plain paper, for example, has been shown to exhibit poor ink absorption qualities and therefore is not desirable for use with high-penetration black inks because the inks do not effectively combine within the recording media so as to produce consistently-reproducible colors. On the other hand, specially-coated paper is available which provides for a more uniform combination of variously-colored high-penetration inks deposited thereon. Unfortunately, such specially-coated paper is unsuitable for use with low-penetration inks. 
     In view of the foregoing, a type of ink used to print pixels on a recording medium preferably depends on both the type of image containing the pixel data and the recording medium upon which the ink is to be placed. 
     FIG. 48 is a flow diagram for describing a method of ink selection based on recording medium type and image content. Generally, in order to control an ink jet printer to print pixels corresponding to multi-level image data upon a recording medium using either a first ink or a second ink, it is determined whether the recording medium is plain paper or specially-coated paper, and, in a case that the recording media is determine to be specially-coated paper, the printer is commanded to print a target pixel using the first ink. On the other hand, in a case that the recording media is determined to be plain paper, it is determined whether or not the target pixel corresponds to a differently-colored region. In a case that the target pixel corresponds to a differently-colored region, the printer is instructed to print the target pixel using the first ink. Conversely, in a case that the target pixel does not correspond to a differently-colored region, the printer is instructed to print the target pixel using the second ink. 
     In more detail, flow begins at step S 4801 , wherein a paper type is determined. As shown in the Figure, the preferred embodiment contemplates the use of either plain paper or specially-coated paper. Preferably, the specially-coated paper is “high resolution” paper HR- 101 , as described in section 1.0. 
     In a case that the paper type is determined to be specially-coated paper, flow proceeds to step S 4802 , wherein it is determined that a high-penetration ink should be used for printing black pixel data. This determination is based on an assumption that high-penetration black ink is always more suitable for printing black pixel data upon a specially-coated recording medium, regardless of image type. 
     If, in step S 4801 , the paper type is determined to be plain, flow proceeds to step S 4803 , in which it is determined whether a black target pixel exists within a color region of the image to be printed. If so, flow proceeds to step S 4802 , as described above. If not, flow proceeds to step S 4804 , wherein it is determined to print the target pixel using low-penetration black ink. 
     According to a preferred embodiment, the determination of step S 4803  is made by examining image pixels surrounding the target pixel. FIG. 49 is a diagram for describing this particular embodiment. 
     FIG. 49 shows black target pixel  415  within 5×5 grid of image data  416 . Each subdivision of grid  416  represents a single image pixel. Preferably, each image pixel is represented by three 8-bit values, each 8-bit value representing red, green, and blue components of the image pixel. In order to determine whether black target pixel  415  is located within a differently-colored region, the red, green, and blue components of each pixel in grid  416  are compared using the following equations: 
     
       
         
           |R−B|&lt;α; |B−G|&lt;β; 
         
       
     
     and 
     
       
         
           |G−R|&lt;γ, 
         
       
     
     wherein α, β, and γ are relatively small values. 
     If each equation is satisfied for each pixel within grid  416 , black target pixel  415  is determined not to exist within a differently-colored region. Alternatively, step S 4803  may require that the red, green, and blue components of each pixel in grid  416  satisfy the equation R=G=B in order to determine that the target pixel does not exist within a differently-colored region. However, this alternative method is susceptible to errors in image data caused by noise, poor scanning, or the like. Accordingly, α, β, and γ are used as shown above to provide a small tolerance for data errors. Of course, other methods may be used in step S 4803  for determining whether black target pixel  415  is within a differently-colored region. 
     Advantageously, multi-level data is used to determine differently-colored regions in the above-described embodiment. In contrast, a system utilizing binarized data to determine differently-colored regions may mistakenly interpret a 50% gray region of original image data to consist of alternate regions of black and white pixels. As a result, inappropriate inks might be used to print the “black” regions. 
     It should be understood that, although the above description of selection of alternative inks specifically focuses on high-penetration black ink and low-penetration black ink, it is contemplated to utilize the foregoing in conjunction with any first ink and second ink differing from one another in color, penetration characteristic, or other characteristic, such as viscosity or density. 
     Furthermore, although plain and specially-coated high-resolution papers are discussed above, a determination of appropriate ink may be based upon any media type. Additional contemplated media include transparencies, glossy paper, glossy film, back print film, fabric sheets, T-shirt transfers, Bubble Jet paper, greeting card stock, and brochure paper, among others. In this regard, paper type can be detected by a paper sensor located within printer  30 , or input through a user interface displayed on display screen  22 , or input via a button located on printer  30 . 
     It should also be noted that, in the preferred embodiment, printer driver  114  contains computer-executable steps to execute the flow of FIG.  48 . of course, these steps could be wholly contained within ROM  122  of printer  30  or could be stored jointly within computer-readable memories of host computer  23  and printer  30 . 
     11.1 Selection of CMYK Black or Pigment Black 
     It has been noted that PCBk may be utilized to print black pixels upon a recording medium. Alternatively, pigment-based black inks and dye-based black inks have also been used to print such pixels. Printer  30  provides additional functionality by providing selectable printing of black pixels using either pigment-based black ink or a combination of cyan, magenta, yellow, and black dye-based inks. 
     In order to do so, it is initially determined whether a black target pixel corresponds to a differently-colored region. In a case that it is determined that the black target pixel does not correspond to a differently-colored region, a printer is instructed to print the black target pixel using a pigment-based black ink. Otherwise, the printer is instructed to print the black target pixel using a dye-based black ink and dye-based ink of each of subtractive primary colors. 
     FIG. 49A is a flow diagram for specifically describing the foregoing features. In step S 4901 , it is determined whether a black target pixel corresponds to a color region. Preferably, this determination is based upon multi-level data representing a region adjacent to the black target pixel. Such a method is described in detail above with respect to FIG. 49, and is therefore omitted at this point. 
     In a case that the target pixel is determined to exist within a color region, flow proceeds to step S 4902 , in which the target pixel is printed using a combination of dye-based black ink and dye-based cyan, magenta, and yellow inks. Upon reaching step S 4904 , the target pixel has been determined not to exist within a color region. As a result, the target pixel is printed using a pigment-based black ink. 
     Notably, the foregoing features allow black pixels within color areas of an image to exhibit a truer black color than that achieved using PCBk, while utilizing blending of various dye-based inks in order to maintain a relatively uniform output density within the color area. In addition, the foregoing selectability allows isolated black pixels to be printed using pigment-based black ink, thereby allowing more accurate reproduction of such black image data. 
     As stated with respect to previous embodiments, printer driver  114  contains computer-executable steps to execute the flow of FIG.  49 A. Of course, these steps could be wholly contained within ROM  122  of printer  30  or could be stored jointly within computer-readable memories of host computer  23  and printer  30 . 
     11.2 Boundary Region Printing 
     As mentioned above, conventionally-printed black/color boundary regions suffer from several deficiencies. First, such regions are often identified based on binarized data of an original multi-level image. However, binarized image data often does not accurately approximate actual multi-level image data. As a result, a boundary region may be “identified” at a position where no such region exists within the original image. 
     Second, low-penetration black inks used to print a black region tend to bleed into adjacent color regions printed using high-penetration ink. PCBk has been proposed as a buffer between such a color region and a region of low-penetration black ink. However, as shown in FIG. 50A, such a buffer is unsatisfactory because the different optical densities of PCBk region  422  and low-penetration black ink region  424  cause an abrupt visual discontinuity. 
     It has also been proposed to print black/color boundary regions using high-penetration black ink and a PCBk “buffer”. As shown in FIG. 50B, although optical densities of PCBk region  426  and high-penetration black ink region  427  are more similar than shown in FIG. 50A, the black color produced by high-penetration black ink is unsuitable for producing high-quality solid black regions. 
     FIG. 51 is a flow diagram describing a method for printing a boundary region. Generally, the method includes detecting a boundary between a black region of an image and a differently-colored region of the image, instructing a printer to print a first region of black pixels within the black region and adjacent to the boundary using process black, instructing the printer to print a second region of black pixels within the black region and adjacent to the first region using high-penetration black ink, and instructing the printer to print a third region of black pixels within the black region and adjacent to the second region using low-penetration black ink. 
     In particular, flow begins at step S 5101 , in which a boundary between a black region of an image and a differently-colored region of the image is detected. With reference to FIG. 50C, step S 5101  results in detection of boundary  429  between differently-colored region  430  and black region  432 . As described above, boundary detection is preferably based on multi-level image data so as to detect black/differently-colored boundaries more accurately than systems which perform boundary detection using binarized image data. 
     Flow proceeds to step S 5102 , in which a printer is instructed to print a first region of black pixels using PCBk. As shown in FIG. 50C, first region  431  is within black region  432  and adjacent to boundary  429 . 
     Next, in step S 5103 , the printer is instructed to print a second region of black pixels using a high-penetration black ink. The second region is depicted in FIG. 50C as region  434 . Advantageously, second region  434  is adjacent to first region  431  and within black region  432 . 
     Lastly, the printer is instructed, in step S 5104 , to print a third region of black pixels using a low-penetration black ink. As shown in FIG. 50C, third region . 436  is adjacent to second region  434  and within black region  432 . 
     It should be understood that sizes of the first, second, and third regions may be adjusted based on a number of PCBk pixels desired and on a number of high-penetration black ink pixels desired in a boundary region between a black region and a differently-colored region. 
     As a result of the FIG. 51 flow, optical density changes gradually across a boundary between a black region and a differently-colored region, bleeding between the black region and the color region is reduced, and a high-quality black region is obtained. 
     Printer driver  114  may contain computer-executable steps to execute the flow of FIG.  51 . These steps may also be contained within ROM  122  of printer  30  or may be stored jointly within computer-readable memories of host processor  23  and printer  30 . 
     FIG. 52 illustrates a more detailed method for printing a boundary region between a black region and a differently-colored region. 
     In general, FIG. 52 describes a system to control printing of pixels corresponding to image data using an ink jet printer which includes a reservoir of a high-penetration black ink, a reservoir of ink of a low-penetration black ink, and a reservoir of ink to create process black. According to the system, it is determined, based on the image data, whether or not a first region of a first predetermined size adjacent to a black target pixel includes a differently-colored region. In a case that it is determined that the first region includes a differently-colored region, the printer is instructed to print the target pixel using process black. In a case that it is determined that the first region does not include a differently-colored region, it is determined, based on the image data, whether or not a second region of a second predetermined size adjacent to the target pixel includes a differently-colored region, the second region being larger than the first region. Finally, in a case that it is determined that the second region includes a differently-colored region the printer is instructed to print the target pixel using the high-penetration black ink, otherwise the printer is instructed to print the target pixel using the low-penetration black ink. 
     More specifically, flow begins at step S 5201 , in which a black target pixel is identified within original image data. Flow proceeds to step S 5202 , in which it is determined whether a first region adjacent to the target pixel includes a differently-colored region. If so, flow proceeds to step S 5204 , wherein printer  30  is instructed to print the target pixel using PCBk. If not, flow proceeds to step S 5205 . 
     It is determined, in step S 5205 , whether a second region adjacent to the target pixel identified in step S 5201  includes a differently-colored region. Notably, the second region is larger than the first region analyzed in step S 5202 . Accordingly, step S 5205  confirms whether the target pixel is located near to a differently-colored region. If so, flow proceeds to step S 5206 , in which printer  30  is instructed to print the target pixel using high-penetration black ink. If not, flow continues to step S 5208 , at which printer  30  is instructed to print the target pixel using low-penetration black ink. 
     FIG. 53A illustrates detection of a first differently-colored region according to a preferred embodiment of step S 5202 . FIG. 53A shows a region of differently-colored multi-level image data  450  and a region of black multi-level image data  451 . For the foregoing explanation, the target pixel identified in step S 5201  is represented by pixel data location  452 . In addition, 5×5 region  454  is the first region analyzed in step S 5202 . 
     In order to determine whether region  454  includes a differently-colored region, the algorithm described above with respect to FIG. 49 is applied to the pixel values within region  454 . Preferably, multi-level pixel values are used in order to accurately detect black pixels and differently-colored pixels within region  454 . Since region  454  contains color values from region  450 , printer  30  is instructed, in step S 5204 , to print target pixel  4524  using PCBk. 
     This instruction is reflected in FIG. 53C, which is a representation of printed pixels corresponding to the image data of FIG.  53 A. As shown in FIG. 53C, printed pixel  456 , representing pixel location  452 , is printed using PCBk. In this regard, it should be understood that printed pixel  457 , representing pixel location  459 , is also printed using PCBk. 
     Steps S 5205  to S 5208  are described in more detail below with respect to FIGS. 53B and 53C. In particular, second region  460 , adjacent to pixel data location  461  and larger than first region  454 , is analyzed to determine whether it includes a differently-colored region. Accordingly, printer  30  is instructed to print pixel  462 , which corresponds to pixel data location  461 , using high-penetration black ink. 
     As can be seen from FIG. 53B, second region  464  adjacent to pixel data location  466  does not contain a differently-colored region. Therefore, in accordance with step S 5208 , printer  30  is instructed to print pixel  467 , which corresponds to pixel data location  466 , using low-penetration black ink. 
     As a result of the FIG. 52 flow, a boundary region such as that shown in FIG. 50C is obtained. specifically, optical density changes gradually across the boundary region, bleeding between the black region and the differently-colored region is reduced, and the black region is printed using low-penetration black ink. 
     Of course, sizes of the first region and of the second region may be adjusted based on a number of PCBk pixels desired and on a number of high-penetration black ink pixels desired in a boundary region between a black region and a differently-colored region. 
     As discussed with respect to the previous embodiments, printer driver  114  may contain computer-executable steps to execute the flow of FIG.  52 . These steps may also be contained within ROM  122  of printer  30  or may be stored jointly within computer-readable memories of host processor  23  and printer  30 . 
     11.3 Printing With Different Inks at Different Resolutions 
     FIG. 54 is a flow diagram which depicts processing according to another embodiment. As shown in FIG. 54, upon input of pixel data such as 5×5 pixel region  416 , it is determined, in steps S 5402  to S 5407 , whether a target pixel in the input pixel data is within a color region. This process is the same as that described above with respect to FIG.  49 . Accordingly, a detailed description thereof is omitted here for the sake of brevity. 
     Steps S 5409  to S 5412  set forth color correction, i.e., black correction, which is performed in accordance with the present invention. Specifically, in step S 5409 , color correction is performed on the target pixel so as to change the pixel from RGB data into CMYK data. Next, step S 5410  determines if the target pixel is within a color region. If the pixel is not within a color region, processing proceeds to step S 5411 . In a case that the target pixel is not within a color region, pigment ink (i.e., K1 ink) is set to form the pixel. In contrast, in a case that step S 5410  determines that the pixel is in a color region, black is formed from process black, i.e., cyan, magenta, and yellow ink and dye-based (i.e., K2) black ink. 
     Next, step S 5413  performs output color correction on the pixel data. For example, gamma correction or the like can be performed in this step. Thereafter, processing proceeds to steps S 5414  to S 5419 . These steps set forth binarization in accordance with the present invention. 
     More specifically, step S 5414  determines whether the target pixel is within a color region. In a case that the target pixel is within a color region, processing proceeds to step S 5418 , in which the target pixel is binarized with a 2×2 index, and to step S 5419  in which the pixel is printed in 720×720 resolution with dye-based black pigment ink (see FIG.  54 A). On the other hand, in a case that step S 5414  determines that the target pixel is not within a color region, processing proceeds to step S 5415 , in which the pixel is binarized with a 1×1 index, and to steps S 5417  in which the pixel is printed in 360×360 dpi with pigment-based black ink (see FIG.  54 B). Thereafter, processing ends. 
     The invention has been described with respect to particular illustrative embodiments. It is to be understood that the invention is not limited to the above-described embodiments and that various changes and modifications may be made by those of ordinary skill in the art without departing from the spirit and scope of the invention.