Abstract:
Feeding a plurality of successive sheets of a recording medium by calculating an expected time for a page end detection of a current sheet, and feeding a next sheet of the successive sheets in accordance with the calculated time, but prior to detection of the page end of the current sheet. Calculating the expected time may be detecting the page end for the current sheet, and mathematically filtering the page end detection of the current sheet with a current estimate of expected time for page end detection of the next sheet. The current estimate may be initialized after a first sheet of the successive sheets with a page end detection of the first sheet. The feeding of the next sheet may be controlled by controlling a time between the current sheet and the next sheet based on a time between the page end detection of the current sheet and a detection of the next sheet so as to obtain and maintain the time within a target range. Whether the page end detection of the current sheet is detected within a threshold amount of time after feeding of the next sheet has commenced may be determined, and where the page end of the current sheet is not detected within the threshold, the feeding of the next sheet is interrupted and a recovery process is engaged. The recovery process may be waiting for a page end detection of the current sheet and re-initiating feeding of the next sheet.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to feeding of a recording medium in printers. More specifically, the present invention relates to controlling the timing for feeding a next sheet of a recording medium based on a calculation of an expected detection of an end of a current sheet so that feeding of the next sheet is initiated prior to detection of the end of the current sheet. 
     2. Description of the Related Art 
     Printers print images onto a sheet of paper that is fed through the printer by a series of rollers that are actuated by one or more motors. Generally, paper feeding is performed by the following components: a paper tray, an automatic sheet feed (ASF) roller, a line feed (LF) roller, an ASF motor for actuating the ASF roller, a LF motor for actuating the LF roller, a page edge (PE) sensor, and a controller. Each of these components operate in conjunction with one another to feed a sheet of paper from the paper tray through the printer. 
     Generally, when printing is to commence, the controller sends a signal to the ASF motor to actuate and to begin turning the ASF roller. The ASF roller rotates to pick up a sheet of paper from the paper tray and feeds it into the printer so that a leading edge of the paper engages a registration position. The registration position provides for a known starting point for paper feeding during printing and is located in a proximity to the LF roller. As the paper is fed into the printer by the ASF roller, the PE sensor senses when the leading edge of the paper has been encountered and sends a signal to the controller, thereby confirming that the paper has been fed into the printer. 
     After the paper has been fed into the printer to the registration position, the controller stops the ASF motor and sends a signal to the LF motor to start turning. The LF motor engages the LF roller which rotates to pick up the leading edge of the paper and to feed it through the printer while a recording head prints an image onto the paper. When the image has been printed, the controller signals the LF motor to rotate to eject the paper from the printer. As the paper is being ejected from the printer, the PE sensor senses the trailing edge of the paper and sends a signal to the controller. When the controller receives the signal from the PE sensor indicating that the end of the sheet has been detected, the controller starts the process over for the next sheet. 
     Thus, when printing multi-page print jobs, conventional printers do not begin feeding the next sheet until the end of the current sheet has been detected. Waiting to detect the end of the current sheet before starting to feed the next sheet means that more time is required for processing the print job. For instance, if it takes one second from the time the end of the current sheet is detected until the next sheet begins to be fed, then the total processing time for a 60 page print job would be increased by one minute due to the page feeding operations. Therefore, one way to reduce the processing time for printing multi-page print jobs would be to reduce the time for loading a next sheet during printing. 
     One way to address the foregoing could be to locate the mechanical components closer to each other so that the paper does not have to travel as far during the feeding operation. However, this solution would not be practical for existing printers since it would require costly structural and mechanical changes. Moreover, physical constraints may limit the proximity that the components can be located relative to each other. 
     Another way to address the foregoing may be to provide a faster ASF motor. However, such a motor may be more costly than existing motors and may also require complex and costly hardware changes to existing printers. 
     Therefore, what is needed is a way to reduce printing time by reducing the time required for feeding successive sheets of paper without requiring costly hardware changes. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the foregoing by initiating feeding of a next sheet prior to detection of the end of a current sheet. Initiating feeding of a next sheet without waiting for the end of the current sheet to be detected reduces the time required for printing multi-page print jobs since the time required for feeding is reduced. 
     According to one aspect, the invention may be feeding a plurality of successive sheets of a recording medium into a printer by calculating an expected time when a page end detection of a current sheet of the successive sheets is expected, and feeding a next sheet of the successive sheets in accordance with the calculated time, but prior to detection of the page end of the current sheet. 
     As a result of the foregoing, successive sheets are fed into the printer faster than conventional printers since the next sheet begins being fed into the printer without waiting for the end of the current sheet to be detected. Therefore, the time required for printing multi-page print jobs is reduced since the time required for feeding the paper is reduced. Additionally, the invention can be implemented in existing printers as software or firmware without the need for costly and possibly impracticable hardware changes. 
     In calculating the expected time, the invention may provide for detecting the page end for the current sheet, and mathematically filtering the page end detection of the current sheet with a current estimate of expected time for page end detection of the next sheet so as to update the estimate throughout processing of the successive sheets. The current estimate may be initialized after a first sheet of the successive sheets with a page end detection of the first sheet. 
     Additionally, the feeding of the next sheet may be controlled by controlling a time between the current sheet and the next sheet based on a time between the page end detection of the current sheet and a detection of the next sheet. The time between the current sheet and the next sheet may be controlled to obtain and maintain the time within a target range. 
     Controlling the time for feeding the sheets based on the time between the page end detection of the current sheet and detection of the next sheet provides for a reduction in the distance between each successive sheet until a target distance is obtained. As a result, a more optimum spacing can be achieved, thereby reducing the processing time even more. 
     In related aspects, the invention may provide for determining whether the end of the current sheet is detected within a threshold amount of time after feeding of the next sheet has commenced, and, in a case where it is determined that the end of the current sheet is not detected within the threshold, feeding of the next sheet is interrupted and a recovery process is engaged. The recovery process may be waiting to detect the end of the current sheet and re-initiating feeding of the next sheet. 
     These further aspects provide additional ways for the printer to optimize the spacing between sheets being fed into the printer. This is accomplished by detecting whether the end of the current sheet has cleared the edge detector prior to the next sheet&#39;s leading edge approaching the detector. This helps to optimize the distance between sheets and reduces the possibility of a paper jam. 
     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 back, cut-away perspective view of the printer shown in FIG.  1 . 
     FIG. 5 is a front, cut-away perspective view of the printer shown in FIG.  1 . 
     FIGS. 6A and 6B show a geartrain configuration for an automatic sheet feeder of the printer shown in FIG.  1 . 
     FIG. 7 is a cross-section view through a print cartridge and ink tank of the printer of FIG.  1 . 
     FIG. 8 is a plan view of a print head and nozzle configuration of the print cartridge of FIG.  7 . 
     FIG. 9 is a block diagram showing the hardware configuration of a host processor interfaced to the printer of the present invention. 
     FIG. 10 shows a functional block diagram of the host processor and printer shown in FIG.  8 . 
     FIG. 11 is a block diagram showing the internal configuration of the gate array shown in FIG.  9 . 
     FIG. 12 shows the memory architecture of the printer of the present invention. 
     FIGS. 13A,  13 B and  13 C are flowcharts depicting process steps for performing an automatic sheet feeding operation according to the invention. 
     FIGS. 14A,  14 B and  14 C are flowcharts depicting process steps of a line feed motor interrupt process according to the invention. 
     FIG. 15 is a flowchart depicting process steps for performing a logical end of page detection process according to the invention. 
     FIG. 16A depicts a relationship between ASF motor pulses and an ASF roller feed amount. 
     FIG. 16B depicts a relationship between ASF motor pulses and an ASF roller feed amount, as well as line feed motor pulses and a line feed amount. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a view showing the outward appearance of computing equipment used in connection with the invention described herein. Computing equipment  1  includes host processor  2 . Host processor  2  comprises a personal computer (hereinafter “PC”), preferably an IBM PC-compatible computer having a windowing environment, such as Microsoft® Windows95. Provided with computing equipment  1  are display  4  comprising a color monitor or the like, keyboard  5  for entering text data and user commands, and pointing device  6 . Pointing device  6  preferably comprises a mouse for pointing and for manipulating objects displayed on display  4 . 
     Computing equipment  1  includes a computer-readable memory medium, such as fixed computer disk  8 , and floppy disk interface  9 . Floppy disk interface  9  provides a means whereby computing equipment  1  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  1 , through which computing equipment  1  can access information stored on CD-ROMs. 
     Disk  8  stores, among other things, application programs by which host processor  2  generates files, manipulates and stores those files on disk  8 , presents data in those files to an operator via display  4 , and prints data in those files via printer  10 . Disk  8  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  8 . At least one of the device drivers comprises a printer driver which provides a software interface to firmware in printer  10 . Data exchange between host processor  2  and printer  10  is described in more detail below. 
     FIGS. 2 and 3 show perspective front and back views, respectively, of printer  10 . As shown in FIGS. 2 and 3, printer  10  includes housing  11 , access door  12 , automatic feeder  14 , automatic feed adjuster  16 , media eject port  20 , ejection tray  21 , power source  27 , power cord connector  29 , parallel port connector  30  and universal serial bus (USB) connector  33 . 
     Housing  11  houses the internal workings of printer  10 , including a print engine which controls the printing operations to print images onto recording media. Included on housing  11  is access door  12 . Access door  12  is manually openable and closeable so as to permit a user to access the internal workings of printer  10  and, in particular, to access ink tanks installed in printer  10  so as to allow the user to change or replace the ink tanks as needed. Access door  12  also includes indicator light  23 , power on/off button  26  and resume button  24 . Indicator light  23  may be an LED that lights up to provide an indication of the status of the printer, i.e. powered on, a print operation in process (blinking), or a failure indication. Power on/off button  26  may be utilized to turn the printer on and off and resume button  24  may be utilized to reset an operation of the printer. 
     As shown in FIGS. 2 and 3, automatic feeder  14  is also included on housing  11  of printer  10 . Automatic feeder  14  defines a media feed portion of printer  10 . That is, automatic feeder  14  stores recording media onto which printer  10  prints images. In this regard, printer  10  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. 
     During printing, individual sheets which are stacked within automatic feeder  14  are fed from automatic feeder  14  through printer  10 . Automatic feeder  14  includes automatic feed adjuster  16 . Automatic feed adjuster  16  is laterally movable to accommodate different media sizes within automatic feeder  14 . These sizes include, but are not limited to, letter, legal, A4, B5 and envelope. Custom-sized recording media can also be used with printer  10 . Automatic feeder  14  also includes backing  31 , which is extendible to support recording media held in automatic feeder  14 . When not in use, backing  31  is stored within a slot in automatic feeder  14 , as shown in FIG.  2 . 
     As noted above, media are fed through printer  10  and ejected from eject port  20  into ejection tray  21 . Ejection tray  21  extends outwardly from housing  11  as shown in FIG.  2  and provides a receptacle for the recording media upon ejection for printer  10 . When not in use, ejection tray  21  may be stored within printer  10 . 
     Power cord connector  29  is utilized to connect printer  10  to an external AC power source. Power supply  27  is used to convert AC power from the external power source, and to supply the converted power to printer  10 . Parallel port  30  connects printer  10  to host processor  2 . Parallel port  30  preferably comprises an IEEE-1284 bi-directional port, over which data and commands are transmitted between printer  10  and host processor  2 . Alternatively, data and commands can be transmitted to printer  10  through USB port  33 . 
     FIGS. 4 and 5 show back and front cut-away perspective views, respectively, of printer  10 . As shown in FIG. 4, printer  10  includes an automatic sheet feed assembly (ASF) that comprises automatic sheet feeder  14 , ASF rollers  32   a,    32   b  and  32   c  attached to ASF shaft  38  for feeding media from automatic feeder  14 . ASF shaft  38  is driven by drive train assembly  42 . Drive train assembly  42  is made up of a series of gears that are connected to and driven by ASF motor  41 . Drive train assembly  42  is described in more detail below with reference to FIGS. 6A and 6B. ASF motor  41  is preferably a stepper motor that rotates in stepped increments (pulses). Utilization of a stepper motor provides the ability for a controller incorporated in circuit board  35  to count the number of steps the motor rotates each time the ASF is actuated. As such, the position of the ASF rollers at any instant can be determined by the controller. ASF shaft  38  also includes an ASF initialization sensor tab  37   a.  When the ASF shaft is positioned at a home position (initialization position), tab  37   a  is positioned between ASF initialization sensors  37   b.  Sensors  37   b  are light beam sensors, where one is a transmitter and the other a receiver such that when tab  37   a  is positioned between sensors  37   b,  tab  37   a  breaks continuity of the light beam, thereby indicating that the ASF is at the home position. 
     Also shown in FIG. 4 is a page edge (PE) detector lever  58   a  and PE sensors  58   b.  PE sensors  58   b  are similar to ASF initialization sensors  37   b.  That is, they are light beam sensors. PE lever  58   a  is pivotally mounted and is actuated by a sheet of the recording medium being fed through the printer  10 . When no recording medium is being fed through printer  10 , lever  58   a  is at a home position and breaks continuity of the light beam between sensors  58   b.  As a sheet of the recording medium begins to be fed through the printer by the ASF rollers, the leading edge of the recording medium engages PE lever  58   a  pivotally moving the lever to allow continuity of the light beam to be established between sensors  58   b.  Lever  58   a  remains in this position while the recording medium is being fed through printer  10  until the trailing edge of the recording medium reaches PE lever  58   a,  thereby disengaging lever  58   a  from the recording medium and allowing lever  58   a  to return to its home position to break the light beam. The PE sensor is utilized in this manner to sense when a page of the recording medium is being fed through the printer and the sensors provide feedback of such to a controller on circuit board  35 . 
     ASF gear train assembly  42  may appear as shown in FIGS. 6A and 6B. As shown in FIG. 6A, gear train assembly  42  comprises gears  42   a,    42   b  and  42   c.  Gear  42   b  is attached to the end of ASF shaft  38  and turns the shaft when ASF motor  41  is engaged. Gear  42   a  engages gear  42   b  and includes a cam  42   d  that engages an ASF tray detent arm  42   e  of automatic feeder  14 . As shown in FIG. 6A, when ASF shaft  38  is positioned at the home position, cam  42   d  presses against detent arm  42   e.  Automatic feeder  14  includes a pivotally mounted plate  50  that is biased by spring  48  so that when cam  42   d  engages detent arm  42   e,  automatic feeder  14  is depressed and when cam  42   d  disengages detent arm  42   e  (such as that shown in FIG.  6 B), plate  50  is released. Depressing detent arm  42   e  causes the recording media stacked in automatic feeder  14  to move away from ASF rollers  32   a,    32   b  and  32   c  and releasing detent arm  42   e  allows the recording to move close to the rollers so that the rollers can engage the recording medium when the ASF motor is engaged. 
     Returning to FIG. 4, printer  10  includes line feed motor  34  that is utilized for feeding the recording medium through printer  10  during printing operations. Line feed motor  34  drives line feed shaft  36 , which includes line feed pinch rollers  36   a,  via line feed geartrain  40 . The geartrain ratio for line feed geartrain  40  is set to advance the recording medium a set amount for each pulse of line feed motor  34 . The ratio may be set so that one pulse of line feed motor  34  results in a line feed amount of the recording medium equal to a one pixel resolution advancement of the recording medium. That is, if one pixel resolution of the printout of printer  10  is 600 dpi (dots per inch), the geartrain ratio may be set so that one pulse of line feed motor  34  results in a 600 dpi advancement of the recording medium. Alternatively, the ratio may be set so that each pulse of the motor results in a line feed amount that is equal to a fractional portion of one pixel resolution rather than being a one-to-one ratio. Line feed motor  34  preferably comprises a 200-step, 2 phase pulse motor and is controlled in response to signal commands received from circuit board  35  of course, line feed motor  34  is not limited to a 200-step 2 phase pulse motor and any other type of line feed motor could be employed, including a DC motor with an encoder. 
     As shown in FIG. 5, printer  10  is a single cartridge printer which prints images using dual print heads, one having nozzles for printing black ink and the other having nozzles for printing cyan, magenta and yellow inks. Specifically, carriage  45  holds cartridge  28  that preferably accommodates ink tanks  43   a,    43   b,    43   c  and  43   d,  each containing a different colored ink. A more detailed description of cartridge  28  and ink tanks  43   a  to  43   d  is provided below with regard to FIG.  7 . Carriage  45  is driven by carriage motor  39  in response to signal commands received from circuit board  35 . Specifically, carriage motor  39  controls the motion of belt  25 , which in turn provides for horizontal translation of carriage  45  along carriage guide shaft  51 . In this regard, carriage motor  39  provides for bi-directional motion of belt  25 , and thus of carriage  45 . By virtue of this feature, printer  10  is able to perform bi-directional printing, i.e. print images from both left to right and right to left. 
     Printer  10  preferably includes recording medium cockling ribs  59 . Ribs  59  induce a desired cockling pattern into the recording medium which the printer can compensate for by adjusting the firing frequency of the print head nozzles. Ribs  59  are spaced a set distance apart, depending upon the desired cockling shape. The distance between ribs  59  may be based on motor pulses of carriage motor  39 . That is, ribs  59  may be positioned according to how many motor pulses of carriage motor  39  it takes for the print head to reach the location. For example, ribs  59  may be spaced in 132 pulse increments. 
     Printer  10  also preferably includes pre-fire receptacle areas  44   a,    44   b  and  44   c,  wiper blade  46 , and print head caps  47   a  and  47   b.  Receptacles  44   a  and  44   b  are located at a home position of carriage  45  and receptacle  44   c  is located outside of a printable area and opposite the home position. At desired times during printing operations, a print head pre-fire operation may be performed to eject a small amount of ink from the print heads into receptacles  44   a,    44   b  and  44   c.  Wiper blade  46  is actuated to move with a forward and backward motion relative to the printer. When carriage  45  is moved to its home position, wiper blade  46  is actuated to move forward and aft so as to traverse across each of the print heads of cartridge  28 , thereby wiping excess ink from the print heads. Print head caps  47   a  and  47   b  are actuated in a relative up and down motion to engage and disengage the print heads when carriage  45  is at its home position. Caps  47   a  and  47   b  are actuated by ASF motor  41  via a geartrain (not shown). Caps  47   a  and  47   b  are connected to a rotary pump  52  via tubes (not shown). Pump  52  is connected to line feed shaft  36  via a geartrain (not shown) and is actuated by running line feed motor  34  in a reverse direction. When caps  47   a  and  47   b  are actuated to engage the print heads, they form an airtight seal such that suction applied by pump  52  through the tubes and caps  47   a  and  47   b  sucks ink from the print head nozzles through the tubes and into a waste ink container (not shown). Caps  47   a  and  47   b  also protect the nozzles of the print heads from dust, dirt and debris. 
     FIG. 7 is a cross section view through one of the ink tanks installed in cartridge  28 . Ink cartridge  28  includes cartridge housing  55 , print heads  56   a  and  56   b,  and ink tanks  43   a,    43   b,    43   c  and  43   d.  Cartridge body  28  accommodates ink tanks  43   a  to  43   d  and includes ink flow paths for feeding ink from each of the ink tanks to either of print heads  56   a  or  56   b.  Ink tanks  43   a  to  43   d  are removable from cartridge  28  and store ink used by printer  10  to print images specifically, ink tanks  43   a  to  43   d  are inserted within cartridge  28  and can be removed by actuating retention tabs  53   a  to  53   d,  respectively. Ink tanks  43   a  to  43   d  can store color (e.g., cyan, magenta and yellow) ink and/or black ink. The structure of ink tanks  43   a  to  43   b  may be similar to that described in U.S. Pat. No. 5,509,140, or may be any other type of ink tank that can be installed in cartridge  28  to supply ink to print heads  56   a  and  56   b.    
     FIG. 8 depicts a nozzle configuration for each of print heads  56   a  and  56   b.  In FIG. 8, print head  56   a  is for printing black ink and print head  56   b  is for printing color ink. Print head  56   a  preferably includes 304 nozzles at a 600 dpi pitch spacing. Print head  56   b  preferably includes 80 nozzles at a 600 dpi pitch for printing cyan ink, 80 nozzles at a 600 dpi pitch for printing magenta ink, and 80 nozzles at a 600 dpi pitch for printing yellow ink. An empty space is provided between each set of nozzles in print head  56   b  corresponding to 16 nozzles spaced at a 600 dpi pitch. Each of print heads  56   a  and  56   b  eject ink based on commands received from a controller on circuit board  35 . 
     FIG. 9 is a block diagram showing the internal structures of host processor  2  and printer  10 . In FIG. 9, host processor  2  includes a central processing unit  70  such as a programmable microprocessor interfaced to computer bus  71 . Also coupled to computer bus  71  are display interface  72  for interfacing to display  4 , printer interface  74  for interfacing to printer  10  through bi-directional communication line  76 , floppy disk interface  9  for interfacing to floppy disk  77 , keyboard interface  79  for interfacing to keyboard  5 , and pointing device interface  80  for interfacing to pointing device  6 . Disk  8  includes an operating system section for storing operating system  81 , an applications section for storing applications  82 , and a printer driver section for storing printer driver  84 . 
     A random access main memory (hereinafter “RAM”)  86  interfaces to computer bus  71  to provide CPU  70  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  82  of disk  8 , CPU  70  loads those application instruction sequences from disk  8  (or other storage media such as media accessed via a network or floppy disk interface  9 ) into random access memory (hereinafter “RAM”)  86  and executes those stored program instruction sequences out of RAM  86 . RAM  86  provides for a print data buffer used by printer driver  84 . 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  8 . Read only memory (hereinafter “ROM”)  87  in host processor  2  stores invariant instruction sequences, such as start-up instruction sequences or basic input/output operating system (BIOS) sequences for operation of keyboard  5 . 
     As shown in FIG. 9, and as previously mentioned, disk  8  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  8  also stores color image files such as might be displayed by display  4  or printed by printer  10  under control of a designated application program. Disk  8  also stores a color monitor driver in other drivers section  89  which controls how multi-level RGB color primary values are provided to display interface  72 . Printer driver  84  controls printer  10  for both black and color printing and supplies print data for print out according to the configuration of printer  10 . Print data is transferred to printer  10 , and control signals are exchanged between host processor  2  and printer  10 , through printer interface  74  connected to line  76  under control of printer driver  84 . Printer interface  74  and line  76  may be, for example an IEEE 1284 parallel port and cable or a universal serial bus port and cable. Other device drivers are also stored on disk  8 , for providing appropriate signals to various devices, such as network devices, facsimile devices, and the like, connected to host processor  2 . 
     Ordinarily, application programs and drivers stored on disk  8  first need to be installed by the user onto disk  8  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  8  through well-known techniques by which the printer driver is copied onto disk  8 . 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. 9, printer  10  includes a circuit board  35  which essentially contain two sections, controller  100  and print engine  101 . Controller  100  includes CPU  91  such as an 8-bit or a 16-bit microprocessor including programmable timer and interrupt controller, ROM  92 , control logic  94 , and I/O ports unit  96  connected to bus  97 . Also connected to control logic  94  is RAM  99 . Control logic  94  includes controllers for line feed motor  34 , for print image buffer storage in RAM  99 , for heat pulse generation, and for head data. Control logic  94  also provides control signals for nozzles in print heads  56   a  and  56   b  of print engine  101 , carriage motor  39 , ASF motor  41 , line feed motor  34 , and print data for print heads  56   a  and  56   b.  EEPROM  102  is connected to I/O ports unit  96  to provide non-volatile memory for printer information and also stores parameters that identify the printer, the driver, the print heads, the status of ink in the cartridges, etc., which are sent to printer driver  84  of host processor  2  to inform host processor  2  of the operational parameters of printer  10 . 
     I/O ports unit  96  is coupled to print engine  101  in which a pair of print heads  56   a  and  56   b  perform recording on a recording medium by scanning across the recording medium while printing using print data from a print buffer in RAM  99 . Control logic  94  is also coupled to printer interface  74  of host processor  2  via communication line  76  for exchange of control signals and to receive print data and print data addresses. ROM  92  stores font data, program instruction sequences used to control printer  10 , and other invariant data for printer operation. RAM  99  stores print data in a print buffer defined by printer driver  84  for print heads  56   a  and  56   b  and other information for printer operation. 
     Sensors, generally indicated as  103 , are arranged in print engine  101  to detect printer status and to measure temperature and other quantities that affect printing. A photo sensor (e.g., an automatic alignment sensor) measures print density and dot locations for automatic alignment. Sensors  103  are also arranged in print engine  101  to detect other conditions such as the open or closed status of access door  12 , presence of recording media, etc. In addition, diode sensors, including a thermistor, are located in print heads  56   a  and  56   b  to measure print head temperature, which is transmitted to I/O ports unit  96 . 
     I/O ports unit  96  also receives input from switches  104  such as power button  26  and resume button  24  and delivers control signals to LEDs  105  to light indicator light  23 , to line feed motor  34  ASF motor  41  and carriage motor  39  through line feed motor driver  34   a,  ASF motor driver  41   a  and carriage motor driver  39   a,  respectively. 
     Although FIG. 9 shows individual components of printer  10  as separate and distinct from one another, it is preferable that some of the components be combined. For example, control logic  94  may be combined with I/O ports  96  in an ASIC to simplify interconnections for the functions of printer  10 . 
     FIG. 10 shows a high-level functional block diagram that illustrates the interaction between host processor  2  and printer  10 . As illustrated in FIG. 10, when a print instruction is issued from image processing application program  82   a  stored in application section  82  of disk  8 , operating system  81  issues graphics device interface calls to printer driver  84 . Printer driver  84  responds by generating print data corresponding to the print instruction and stores the print data in print data store  107 . Print data store  107  may reside in RAM  86  or in disk  8 , or through disk swapping operations of operating system  81  may initially be stored in RAM  86  and swapped in and out of disk  8 . Thereafter, printer driver  84  obtains print data from print data store  107  and transmits the print data through printer interface  74 , to bi-directional communication line  76 , and to print buffer  109  through printer control  110 . Print buffer  109  resides in RAM  99 , and printer control  110  resides in firmware implemented through control logic  94  and CPU  91  of FIG.  9 . Printer control  110  processes the print data in print buffer  109  responsive to commands received from host processor  2  and performs printing tasks under control of instructions stored in ROM  92  (see FIG. 9) to provide appropriate print head and other control signals to print engine  101  for recording images onto recording media. 
     Print buffer  109  has a first section for storing print data to be printed by one of print heads  56   a  and  56   b,  and a second section for storing print data to be printed by the other one of print heads  56   a  and  56   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  84  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  56   a  and  56   b  to printing speed. Print data is transferred from print data store  107  in host processor  2  to storage locations of print buffer  109  that are addressed by printer driver  84 . As a result, print data for a next scan may be inserted into vacant storage locations in print buffer  109  both during ramp up and during printing of a current scan. 
     FIG. 11 depicts a block diagram of a combined configuration for control logic  94  and I/O ports unit  96 , which as mentioned above, I/O ports unit  96  may be included within control logic  94 . In FIG. 11, internal bus  112  is connected to printer bus  97  for communication with printer CPU  91 . Bus  112  is coupled to host computer interface  113  (shown in dashed lines) which is connected to bi-directional line  76  for carrying out bi-directional communication. As shown in FIG. 11, bi-directional line  76  may be either an IEEE-1284 line or a USB line. Bi-directional communication line  76  is also coupled to printer interface  74  of host processor  2 . Host computer interface  113  includes both IEEE-1284 and USB interfaces, both of which are connected to bus  112  and to DRAM bus arbiter/controller  115  for controlling RAM  99  which includes print buffer  109  (see FIGS.  9  and  10 ). Data decompressor  116  is connected to bus  112 , DRAM bus arbiter/controller  115  and each of the IEEE-1284 and USB interfaces of host computer interface  113  to decompress print data when processing. Also coupled to bus  112  are line feed motor controller  117  that is connected to line feed motor driver  34   a  of FIG. 9, image buffer controller  118  which provides serial control signals and head data signals for each of print heads  56   a  and  56   b,  heat timing generator  119  which provides block control signals and analog heat pulses for each of print heads  56   a  and  56   b,  carriage motor controller  120  that is connected to carriage motor driver  39   a  of FIG. 9, and ASF motor controller  125  that is connected to ASF motor driver  41   a  of FIG.  9 . Additionally, EEPROM controller  121   a,  automatic alignment sensor controller  121   b  and buzzer controller  121  are connected to bus  112  for controlling EEPROM  102 , an automatic alignment sensor (generally represented within sensors  103  of FIG.  9 ), and buzzer  106 . Further, auto trigger controller  122  is connected to bus  112  and provides signals to image buffer controller  118  and heat timing generator  119 , for controlling the firing of the nozzles of print heads  56   a  and  56   b.    
     Control logic  94  operates to receive commands from host processor  2  for use in CPU  91 , and to send printer status and other response signals to host processor  2  through host computer interface  113  and bi-directional communication line  76 . Print data and print buffer memory addresses for print data received from host processor  2  are sent to print buffer  109  in RAM  99  via DRAM bus arbiter/controller  115 , and the addressed print data from print buffer  109  is transferred through controller  115  to print engine  101  for printing by print heads  56   a  and  56   b.  In this regard, heat timing generator  119  generates analog heat pulses required for printing the print data. 
     FIG. 12 shows the memory architecture for printer  10 . As shown in FIG. 11, EEPROM  102 , RAM  99 , ROM  92  and temporary storage  121  for control logic  94  form a memory structure with a single addressing arrangement. Referring to FIG. 11, EEPROM  102 , shown as non-volatile memory section  123 , stores a set of parameters that are used by host processor  2  and that identify printer and print heads, print head status, print head alignment, and other print head characteristics. EEPROM  102  also stores another set of parameters, such as clean time, auto-alignment sensor data, etc., which are used by printer  10 . ROM  92 , shown as memory section  124 , 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  121  stores temporary operational information for control logic  94 , and memory section  126  corresponding to RAM  99  includes storage for variable operational data for printer tasks and print buffer  109 . 
     A more detailed description of an automatic sheet feeding process according to the invention will now be made with reference to FIGS. 13A to  16 B. 
     FIGS. 13A to  13 C are flowcharts of an automatic sheet feeding operation according to the invention. It should be noted that the process steps, which start with step  1301  in FIG. 13A, could begin either with the feeding of a first sheet during printing, or during the feeding of any successive sheet during printing of a multi-page print job. 
     In step S 1302 , a determination is made whether the load type is flying or if the previous sheet has not been completely ejected. Flying load means a non-registered load with page end detection and refers to the loading type of the invention. This is in contrast to a regular non-registered load which means a non-registered load without page end detection. If the load type is flying, or if the previous sheet needs to be completely ejected, then in step S 1303  a flag for the parameter NeedToEject is set to TRUE. If the load type is not flying and if the previous sheet has been completely ejected, then the flag NeedToEject is set to FALSE in step S 1304 . This flag is used in later processing as will be described below. 
     In step S 1305 , the number of steps (motor pulses) of the line feed motor to achieve the top of the printing margin are calculated. This step refers to printing without registration. Registration means the prior art process of registering the sheet against the line feed rollers to somewhat wrinkle the sheet and then the line feed motor being engaged to pick up the sheet and feed it through the printer. In this prior art process, the leading edge of the paper is “registered” against the line feed rollers before the line feed motor is engaged. In the present invention, however, there is no registration for flying load. That is, the paper is fed to the line feed rollers while the line feed rollers are already in motion. Therefore, step S 1305  calculates the number of line feed motor steps for the sheet to achieve the top of the printing margin. 
     Step S 1306  determines whether the load type is flying and if a simultaneous ejection is required. If not, then in step S 1307  a loading prefire is enabled and the carriage is moved to the prefire position. The loading prefire is a print head conditioning operation. If the load type is flying, and if a simultaneous eject is required, then flow proceeds to step S 1308 . It should be noted that if the process steps are being applied to a first sheet being fed into the printer, then step S 1306  has no meaning since there can be no simultaneous ejection of a previous sheet because there is no previous sheet to eject. Therefore, flow would automatically go to step S 1307  for a first sheet. 
     In step S 1308 , a determination is made whether the ASF unit is initialized. Initialized means being at the home position. As stated above, the ASF unit is at the home position when the ASF initialization sensors  37   b  detect that ASF initialization sensor tab  37   a  is at the home position (i.e. breaking the light beam between the sensors). If the ASF unit is not initialized, which is not the nominal case, then flow proceeds to step S 1309 . In step S 1309 , the previous sheet (if one is present) is ejected and in step S 1310 , the learned flying load parameters are reset. Flying load parameters refer to parameters calculated and determined throughout the process steps. For instance, the process performs operations to actually detect the end of page of a current sheet and to calculate an expected end of page for the next sheet. These are just some of the learned parameters and in step S 1310 , these and other parameters that have been learned by previous passes through the processing steps are reset. 
     After the learned parameters are reset, the ASF unit is initialized, i.e. moved to the home position, in step S 1311  and a determination is made in step S 1312  whether the ASF unit is initialized. If the ASF unit is still not initialized, then a Load Status flag is set to FAILED in step S 1313 . If the ASF unit has been initialized, then flow proceeds to step S 1314  where a determination is made whether the sheet has been detected by the PE sensor. Detecting the sheet by the PE sensor provides an indication of whether the paper has been partially fed by the ASF rollers during the re-initialization process of step S 1311 . If the sheet has been detected, then a recovery sequence is entered into in step S 1315  and the Load Status flag is set to SUCCEEDED in step S 1316 . If the PE sensor has not detected the sheet in step S 1314 , or if the ASF unit was initialized in step S 1308 , then flow proceeds to step S 1317 . It should be noted that the nominal case is that the ASF unit would be initialized in step S 1308  and flow would proceed directly to step S 1317 . 
     In step S 1317 , a determination is made whether the load type is non-registered. A non-registered load type may occur in one of two ways, flying load or a regular non-registered loading. As stated above, flying load is a non-registered load with page end detection, whereas, a regular non-registered load is a non-registered load without page end detection. If the load type is neither of the two types of non-registered load, i.e. it is a registered load, then flow proceeds to step S 1318 . In step S 1318 , the process waits for the previous sheet (if present) to eject and then a determination is made whether a paper jam occurred (step S 1319 ). If a paper jam did not occur, then flow proceeds to step S 1328  in FIG.  13 B. However, if a paper jam did occur, then flow proceeds to steps S 1320  and S 1313  where the learned flying load parameters are reset and the Load Status is set to FAILED. Nominally, for the flying load case, the load type in step S 1317  would be non-registered (flying) and flow would proceed to step S 1321 . 
     In step S 1321 , a determination is made whether the line feed motor is running, i.e. whether the line feed pinch rollers are up to speed. If the line feed motor is not running, then it is started in step S 1322 . Determining whether the line feed motor is running prevents the ASF motor from feeding paper into the line feed rollers when they are not running, which would cause a paper jam in a flying load case. Nominally, the line feed motor would be running and flow would proceed to step S 1323  where a determination is made whether the end of the ejected page has been detected. The determination in step S 1323  is a logical determination if the load type is flying and a physical determination if the load type is not flying but is a non-registered load. The process of a logical end of page detection is discussed in more detail with regard to FIG.  15 . If the end of the ejected page has not been detected (either logically or physically), the process remains in a loop to wait for the end of the ejected page to be detected, and once the end has been detected, flow proceeds to step S 1324 . 
     In step S 1324 , a determination is made whether the line feed motor is ramping up and if so, the process remains in a loop until the line feed motor has been ramped up to speed. The determination in step S 1324  is to determine whether the line feed motor rollers are running at the same speed as the ASF rollers so that the paper can be fed without causing a paper jam. Once the line feed motor has ramped up to speed, a determination is made in step S 1325  whether the line feed motor has reached a constant speed. If not, then flow proceeds to step S 1326  where the process waits for the line feed motor to stop (the process assumes that the line feed motor is ramping down) and then determines whether a paper jam occurred (step S 1319 ). If a paper jam has not occurred, then flow proceeds to step S 1328  of FIG.  13 B. If a paper jam has occurred, then flow proceeds to steps S 1320  and S 1313  where the learned flying load parameters are reset and the Load Status flag is set to FAILED. Nominally, however, the line feed motor will be at a constant speed in step S 1325  and flow would proceed to step S 1327 . 
     In step S 1327 , a determination is made whether there is sufficient motion remaining for line feed motor to feed the paper. That is, it is determined whether the line feed motor has enough motor steps remaining to feed the paper to the top margin. If not, then flow proceeds to step S 1326  where the process waits for the line feed motor to stop. If there is sufficient motion to feed the paper, then flow proceeds to step S 1328  of FIG.  13 B. 
     In step S 1328 , a RetriedLoad flag is set to FALSE. This flag is utilized later in the process when a second attempt to retry the paper loading is made. Next, in step S 1329  a determination is made whether the PE sensor has detected the sheet. This is a physical detection and not a logical detection. If the sheet has not been detected, then a SheetDetected flag is set to FALSE in step S 1330 , and if the sheet has been detected in step S 1329 , then the SheetDetected flag is set to TRUE in step S 1331 . 
     In step S 1332 , a determination is made whether the SheetDetected flag has been set to TRUE and if the load type is registered. If both are true (i.e. the load type is registered and the sheet detected flag is TRUE), then flow proceeds to step S 1333 . In step S 1333 , a determination is made whether the line feed motor is running, and if so, it is stopped in step S 1334 . If it is determined in step S 1333  that the line feed motor is not running, or after it has been stopped in step S 1334 , flow proceeds to steps S 1335  and S 1336  to perform a recovery process and to set the Load Status flag to Succeeded. 
     For flying load, the determination in step S 1332  would be that the load type is non-registered (i.e. flying) and therefore flow would proceed to step S 1337 . In steps S 1337  to S 1341 , a determination is made whether the load speed is low or medium, and if it is either, the ASF is started in the determined speed (i.e. either low speed or medium speed), and if the load speed is neither low nor medium, then the ASF is started in high speed. In steps S 1337  to S 1341 , the ASF motion is started to begin feeding the next sheet. 
     Next, in step S 1342 , a determination is made whether the SheetDetected flag is TRUE. This step looks at the PE state prior to starting the ASF motion. If the SheetDetected flag is not TRUE, then flow proceeds to step S 1354  of FIG.  13 C. If the SheetDetected flag is TRUE, then flow proceeds to step S 1343  to determine whether the line feed motor is still running. This determination determines whether the line feed motor is still running or if it has run out of a finite number of steps for feeding the next sheet. Nominally, for flying load the line feed motor will still be running and flow proceeds to step S 1344 . If the line feed motor is not running in step S 1343 , then flow proceeds to step S 1345 . In step S 1345 , a determination is made whether the end of the current page has been detected or if the end of the prediction window (time when the end of page detection has been predicted to occur, plus some tolerance) has been exceeded. If both of these have not occurred, then flow proceeds to steps S 1351  and S 1352  where the flying load learned parameters are reset and the Load Status is set to FAILED. If either the end of page has been detected or the end of the prediction window has been exceeded, then flow proceeds to step S 1346 . 
     Returning to step S 1343 , if it was determined that the line feed motor was still running, flow proceeds to step S 1344 , where, like step S 1345 , a determination is made whether the end of the current page has been detected or whether the end of the prediction window has been exceeded. If neither has occurred, then flow returns to step S 1343  to determine whether the line feed motor is still running. If either has occurred, then, like step S 1345 , flow proceeds to step S 1346 . 
     In step S 1346 , a determination is made whether the end of page detection occurred later than expected. Nominally, for flying load the determination is no and flow proceeds to step S 1347  to determine whether the ASF motor has been cut-off. If the ASF motor has not been cut-off, which is the nominal case for flying load, the flow proceeds to step S 1354  of FIG.  13 C. If either the end of page detection did occur later than expected in step S 1346 , or if the ASF motor has been cut-off in step S 1347 , then flow proceeds to step S 1348  where the current sheet is completely ejected. 
     Following step S 1348 , the ASF unit is initialized (moved to the home position) in step S 1349  and a determination is made in step S 1350  whether a paper jam has occurred on ejection of the current sheet. If a paper jam has occurred, then the flying load learned parameters are reset and the Load Status is set to FAILED in steps S 1351  and S 1352 . If a paper jam did not occur on eject, then a determination is made whether the ASF unit has been initialized (i.e. whether the ASF unit is at the home position) in step S 1353 . If the ASF has not been initialized, then flow proceeds to steps S 1351  and S 1352  to reset the learned flying load parameters and to set the Load Status to FAILED. If the ASF unit has been initialized, then flow proceeds to steps S 1335  and S 1336  to perform a recovery sequence and to set the Load Status to SUCCEEDED. 
     Turning to FIG. 13C, in step S 1354  a determination is made whether the ASF unit has rotated past the home position, i.e. if the ASF unit has rotated to start feeding the next sheet. If not, a loop is entered into to continue the inquiry until the ASF unit has rotated past the home position. Once the ASF unit has rotated past the home position, a determination is made whether the ASF unit is in motion in step S 1355 . If the ASF unit is not in motion, then flow proceeds to step S 1364 , which will be described below. Nominally, the ASF would be in motion and flow would proceed to step S 1356  where a determination is made whether the PE sensor has detected the sheet. Nominally, for flying load the sheet would be detected by the PE sensor and flow would proceed to step S 1359 . However, if the PE sensor has not detected the sheet in step S 1356 , then a determination is made whether the sheet slipped too much on the ASF roller (step S 1357 ). This determination is made by detecting whether a predetermined number of ASF motor steps have been exceeded for the PE sensor to detect the sheet. If not, then flow returns to step S 1355 . If the paper has slipped too much, then flow proceeds to step S 1358  where the line feed motor is stopped, and then on to step S 1364 . 
     As stated above, nominally the sheet would be detected by the PE sensor in step S 1356  and flow would proceed to step S 1359  where a determination is made whether the sheet has slipped too much on the ASF roller. Again, this determination is made as to whether a predetermined number of ASF motor steps have been exceeded to feed the paper to the PE sensor. If the sheet has slipped too much, then flow proceeds to step S 1364 . Nominally, the sheet would not have slipped too much and flow would proceed to step S 1360  where a determination is made whether the load type is registered. If the load type is not registered (which is the nominal case for flying load), then flow proceeds to step S 1363  where an EarlyLoadSuccess flag is set to TRUE and the loading task is suspended for 10 msec. If the load type is registered in step S 1360 , then the process waits for the top edge of the sheet to curl behind the line feed pinch rollers (step S 1361 ) and then the line feed motor is started (step S 1362 ) and the sheet is fed to the top margin. After step S 1362 , the EarlyLoadSuccess flag is set to TRUE and the loading task is suspended for 10 msec in step S 1363 . 
     Flow proceeds to step S 1364  if either the ASF unit was not in motion in step S 1355 , the line feed motor was stopped in step S 1358 , the sheet slipped too much in step S 1359 , or after the EarlyLoadSuccess flag has been set in step S 1363 . In step S 1364 , a determination is made whether the loading prefire condition for the print heads was previously enabled. Recall that the loading prefire may have previously been enabled in step S 1307 . If the loading prefire was previously enabled in step S 1307 , then the process waits for the carriage to reach the prefire position (step S 1365 ), performs the loading prefire operation (step S 1366 ), and proceeds to step S 1367 . If the loading prefire was not previously enabled, then flow proceeds directly to step S 1367 . 
     In step S 1367 , a determination is made whether the ASF unit is in motion. If the ASF unit is in motion, then a loop is entered into until the ASF unit is no longer in motion, whereby flow proceeds to step S 1368  to determine if the ASF unit is initialized (at the home position). If the ASF unit is not initialized, then the learned flying load parameters are reset and the Load Status is set to FAILED in steps S 1369  and S 1370 . If the ASF unit is initialized, which is the nominal case, then a determination is made whether the sheet is detected by the PE sensor (step S 1371 ). Nominally, the sheet would be detected and flow would proceed to step S 1372  where a determination is made whether the sheet has slipped too much on the ASF roller. Nominally, it would not have slipped too much and the Load Status would be set to SUCCEEDED in step S 1373 . However, if the sheet did slip too much, then a determination is made whether the media type is envelope or Hagaki in step S 1374 . If the media type is either of these, then the Load Status is set to FAILED (step S 1376 ). If the media type is neither of these, then a recovery sequence is entered into (step S 1375 ) and the Load Status is set to SUCCEEDED (step S 1373 ). 
     Returning to step S 1371 , if a determination is made that the sheet was not detected by the sensor, then the line feed motor is stopped in step S 1377 . Then, in step S 1378  a determination is made whether the RetriedLoad flag has been set to TRUE. That is, if the load has previously failed, a first attempt to retry the load will occur which changes the RetriedLoad flag that was set to FALSE in step S 1328  to TRUE. If a determination is made in step S 1378  that the RetriedLoad flag is TRUE, then the present attempt to try to load the paper is a second retry. The process provides for two attempts to retry to load the paper. If the RetriedLoad flag is TRUE, then flow proceeds to step S 1379  where a determination is made whether the NeedToEjectPreviousSheet flag is set to TRUE. If the RetriedLoad flag is not TRUE, then flow proceeds to step S 1382  where a determination is made whether the media type is envelope. If the media type is not envelope, then the Load Type is set to Low Speed, Registered (step S 1383 ) to override the registered mode and flow returns to step S 1329  of FIG.  13 B. If the media type is envelope, then a determination is made in step S 1384  whether the load type is non-registered. If the load type is not non-registered, then flow proceeds to step S 1329  of FIG.  13 B. If the load type is non-registered, then the line feed motor is started in step S 1385  and flow proceeds to step S 1329  of FIG.  13 B. 
     Returning to step S 1379 , if the NeedToEjectPreviousSheet flag is not TRUE, then the Load Status is set to FAILED in step S 1376 . If however, the NeedToEjectPreviousSheet is TRUE, then the previous sheet is ejected, the learned flying load parameters are reset and the Load Status is set to FAILED in steps S 1380 , S 1381  and S 1376 , respectively. 
     Thus, FIGS. 13A,  13 B and  13 C depict foreground process steps for performing a paper loading operation in printer  10  according to the invention. Part of the foreground process steps depicted in FIGS. 13A to  13 C include background processes that are not depicted in these figures. One background process is a line feed motor interrupt process which is depicted in FIGS. 14A,  14 B and  14 C. This process translates line feed motor steps into paper length and calculates PE sensor off time between sheets. In the present invention, the background process is performed every four pulses of the line feed motor. 
     In FIG. 14A, the line feed motor interrupt process is begun in step S 1401 . In step S 1402 , a determination is made whether the current sheet is detected by the sensor. If the current sheet is not detected by the sensor, then a determination is made whether the sheet was previously detected by the sensor (step S 1403 ). If the sheet was not previously detected by the sensor, then the interrupt process returns (step S 1404 ). If the sheet was previously detected by the sensor, then flow proceeds to step S 1445  in FIG.  14 C. The flowchart of FIG. 14C represents a paper eject case, i.e. a case where the interrupt process is being performed when the current sheet is being ejected. 
     Returning to step S 1402 , if the current sheet is detected by the sensor, then a determination is made whether the sheet was previously detected by the sensor (step S 1405 ). If the sheet was previously detected by the sensor, then this represents a case where the interrupt process is being performed in the middle of printing of the current sheet and flow proceeds to step S 1430  of FIG.  14 B. If the sheet was detected by the sensor in step S 1402  but was not previously detected by the sensor in step S 1405 , then this represents a case where the interrupt process is being performed during loading of a next sheet and flow proceeds to step S 1406 . 
     In step S 1406 , the FlyingLoad flag is set to FALSE and in step S 1407  a determination is made whether the ASF unit is in motion. If the ASF unit is in motion, then a PageBreakDetected flag is set to TRUE in step S 1408  and flow proceeds to step S 1409 . If the ASF unit is not in motion, flow proceeds directly to step S 1409 . 
     In step S 1409 , the time that the PE sensor is off between sheets (PE_OFF) is calculated as the distance between the end to the ejected sheet and the newly-loaded sheet. Then, in step S 1410  a determination is made whether the UPDATE_OFF_DISTANCE has been enabled. UPDATE_OFF_DISTANCE provides the ability to update the PE_OFF time so that the feeding distance between sheets can be reduced and updated during the flying load process. If the UPDATE_OFF_DISTANCE has not been enabled, then it is enabled in step S 1411  and flow proceeds to steps S 1423 , S 1424  and S 1425  where the upper limit of the target PE off time (MAX_PE_OFF) is set to the maximum of either the PE_OFF or the MAX_PE_OFF, the lower limit of the target PE off time (MIN_PE_OFF) is set to the minimum of the PE_OFF or the MIN_PE_OFF, and then the interrupt process returns (step S 1425 ). Once the interrupt process returns, a new process is performed after four pulses of the line feed motor. 
     Returning to step S 1410 , if the UPDATE_OFF_DISTANCE has been enabled, then a determination is made whether the FILTERED_PE_OFF is greater than or equal to the TARGET_PE_OFF (step S 1412 ). This step determines whether the current filtered PE off time is above or below the target PE off time. If the FILTERED_PE_OFF is not above the target, then this represents a case where the filtered PE off time is below the target and flow proceeds to step S 1426 . In step S 1426 , a SWITCH_POINT_MODIFIER (SPM) is calculated utilizing a switch point modifier algorithm. Then, in step S 1427  the LAST_SWITCH_POINT_MODIFIER (LSPM) is saved as the switch point modifier calculated in step S 1426 . Next, the switch point (SP) is updated by subtracting the SPM calculated in step S 1426  from the last SP (step S 1428 ), and a lag filter is applied to the FILTERED_PE_OFF time in step S 1422 . Flow then proceeds to steps S 1423 , S 1424  and S 1425  to set the MAX_PE_OFF and MIN_PE_OFF values and to return from the interrupt process. 
     Returning to step S 1412 , if a determination is made that the FILTERED_PE_OFF is greater than or equal to the TARGET_PE_OFF, then this represents an above target case and flow proceeds to step S 1413 . In step S 1413 , a SWITCH_POINT_FILTER_CONSTANT (SPFC) is calculated utilizing a switch point filter constant algorithm. Then, similar to steps S 1426  and S 1427 , the switch point modifier (SPM) is calculated and the last switch point (LSP) is set equal to the switch point (SP) (steps S 1414  and S 1415 ). Then, in step S 1416 , the switch point (SP) is updated by adding the last switch point (SP) with the switch point modifier (SPM) calculated in step S 1414 . 
     Flow then proceeds to step S 1417  where a determination is made whether the switch point (SP) is limited. If the switch point (SP) is not limited, then in step S 1429  the switch point (SP) is set to the minimum of the current switch point (SP) or the MAX_PE_OFF time. If however, the switch point is limited in step S 1417 , then in step S 1418  the switch point (SP) is set to the minimum of the current switch point (SP) or the LIMIT_SP. 
     Flow then proceeds from either steps S 1418  or S 1429  to steps S 1419  and S 1420  where an ASF_SWITCH_POINT_MODIFIER (ASPM) is calculated utilizing an ASF switch point modifier algorithm (step S 1419 ) and a determination is made whether the switch point (SP) is greater than the ASF switch point modifier (ASPM) (step S 1420 ). IF the SP is greater than the ASF switch point modifier (ASPM), then the switch point (SP) is set to the current SP minus the value of the ASPM (step S 1421 ) and flow proceeds to steps S 1422 , S 1423 , S 1424  and S 1425 , which were discussed above. If the SP is not greater than the ASPM, then flow proceeds directly to steps S 1422 , S 1423 , S 1424  and S 1425 . 
     Turning to FIG. 14B, a discussion will now be made of a case where the interrupt process is performed in the middle of the page case where flow proceeds from step S 1405  of FIG. 14A to step S 1430  of FIG.  14 B. In FIG. 14B, after the determination has been made in step S 1405  of FIG.  14 A that the sheet was previously detected by the sensor, a determination is made whether the FlyingLoad has been set to TRUE (step S 1430 ). If not, flow proceeds directly to step S 1439  where the value MEASURED_PAPER_LENGTH is updated and then the interrupt process returns at step S 1440 . If FlyingLoad is TRUE, then a determination is made in step S 1431  whether the FILTERED_PAPER_LENGTH is greater than zero. If the FILTERED_PAPER_LENGTH is not greater than zero, then the WaitForEndOfPage is set to TRUE (step S 1441 ) and flow proceeds to steps S 1439  and S 1440  to update the MEASURED_PAPER_LENGTH and return from the interrupt process. If the FILTERED_PAPER_LENGTH is greater than zero, then flow proceeds to step S 1432 . 
     In step S 1432 , the PAPER_LENGTH_LIMIT is calculated to be the FILTERED_PAPER_LENGTH plus a constant. Then, in step S 1433  a determination is made whether the MEASURED_PAPER_LENGTH is less than the PAPER_LENGTH_LIMIT. If it is not, then WaitForEndOfPage is set to FALSE (step S 1442 ), EndOfPageLaterThanExpected is set to TRUE (step S 1443 ) and the ASF motor is stopped (step S 1444 ). Then, flow proceeds to steps S 1439  and S 1440  to update the MEASURED_PAPER_LENGTH and to return from the interrupt process. 
     If the MEASURED_PAPER_LENGTH is less than the PAPER_LENGTH_LIMIT in step S 1433 , then WaitForEndOfPage is set to TRUE in step S 1434 . Then, in step S 1435 , a determination is made whether the ASF unit is in motion, and if so, a determination is made whether the ASF motion has fed the current sheet up to the PE sensor (step S 1436 ). If the ASF unit is not in motion in step S 1435 , or if the ASF unit has not fed the current sheet up to the PE sensor in step S 1436 , then flow proceeds directly to steps S 1439  and S 1440  to update the MEASURED_PAPER_LENGTH and return from the interrupt process. If however, the ASF motion has fed the current sheet up to the PE sensor, then WaitForEndOfPage is set to FALSE (step S 1437 ) and the ASF motor is stopped (step S 1438 ), with flow then proceeding to steps S 1439  and S 1440 . 
     Next a discussion will be made of the eject case where flow proceeds from step S 1403  of FIG. 14A to step S 1445  of FIG.  14 C. 
     In step S 1445 , a determination is made whether the ASF unit is in motion. If so, then PageBreakDetected is set to TRUE in step S 1446 , and if not, then flow proceeds to step S 1449  (described below). After the PageBreakDetected is set to TRUE in step S 1446 , a determination is made whether FlyingLoad is TRUE (step S 1447 ). If FlyingLoad is TRUE, then flow proceeds to steps S 1448 , S 1449 , S 1450  and S 1451  where the number of ASF motion steps taken are saved for the ASPM (see FIG.  14 A), WaitForEndOfPage is set to FALSE, EndOfPageLaterThanExpected is set to FALSE, and the paper length is stored. Flow then proceeds to step S 1452 . If FlyingLoad is not TRUE in step S 1447 , then flow bypasses step S 1448  and proceeds directly to step S 1449 . 
     In step S 1452 , a determination is made whether the PAPER_LENGTH is greater than or equal to the FILTERED_PAPER_LENGTH. If so, then another determination is made in step S 1453  whether the PAPER_LENGTH is much greater than the FILTERED_PAPER_LENGTH. If the PAPER_LENGTH is much greater than the FILTERED_PAPER_LENGTH, then a determination is made in step S 1454  whether the FILTERED_PAPER_LENGTH is greater than zero. If the PAPER_LENGTH is not much greater than the FILTERED_PAPER_LENGTH in step S 1453 , flow advances to step S 1456  which will be described below. Returning to step S 1454 , if the FILTERED_PAPER_LENGTH is not greater than zero, flow advances to step S 1456 . However, if the FILTERED_PAPER_LENGTH is greater than zero, then the UPDATE_OFF_DISTANCE is disabled in step S 1455  and then flow proceeds to step S 1456 . 
     If the result of step S 1453  is no, the result of step S 1454  is no, or if the result of step S 1454  is yes and the UPDATE_OFF_DISTANCE has been disabled in step S 1455 , then the FILTERED_PAPER_LENGTH is calculated in step S 1456 . After step S 1456 , the MAX_PAPER_LENGTH is set to the maximum of the PAPER_LENGTH or the MAX_PAPER_LENGTH (step S 1457 ) and the MIN_PAPER_LENGTH is set to the minimum of the PAPER_LENGTH or the MIN_PAPER_LENGTH (step S 1458 ), and the interrupt process returns (step S 1459 ). 
     Returning to step S 1452 , if the PAPER_LENGTH is not greater than or equal to the FILTERED_PAPER_LENGTH, flow proceeds to step S 1460  where a determination is made whether the PAPER_LENGTH is much less than the FILTERED_PAPER LENGTH. If the PAPER_LENGTH is not much less than the FILTERED_PAPER_LENGTH, then the FILTERED_PAPER_LENGTH is calculated in step S 1464  and flow proceeds to steps S 1457 , S 1458  and S 1459  to set the MAX_PAPER_LENGTH and the MIN_PAPER_LENGTH, and then to return from the interrupt process. If however, the PAPER_LENGTH is much less than the FILTERED_PAPER_LENGTH, then the UPDATE_OFF_DISTANCE is disabled in step S 1461  and flow proceeds to step S 1462 . 
     At step S 1462 , a determination is made whether the PAPER_LENGTH is greater than zero. If it is not, then flow proceeds directly to steps S 1457 , S 1458  and S 1459 . If the PAPER_LENGTH is greater than zero, then the FILTERED_PAPER_LENGTH is set to be equal to the PAPER_LENGTH in step S 1463 , with flow then proceeding to steps S 1457 , S 1458  and S 1459 . 
     Next, a discussion will be made of a logical end of page detection routine for performing a logical end of page detection such as that briefly described above with regard to step S 1323  of FIG.  13 A. 
     In FIG. 15, the logical end of page detection routine is started in step S 1500  and in step S 1501  a determination is made whether FlyingLoad is TRUE. If FlyingLoad is not TRUE, then flow proceeds to step S 1509  which will be discussed below. If FlyingLoad is TRUE, then flow proceeds to step S 1502  where a determination is made whether PageBreakDetected is TRUE. If it is TRUE, then flow proceeds to step S 1509 . If it is not TRUE, then flow proceeds to step S 1503  where a determination is made whether the FILTERED_PE_OFF is equal to zero. If the FILTERED_PE_OFF is zero, then flow proceeds to steps S 1509 . If the FILTERED_PE_OFF is not zero, then flow proceeds to step S 1504  where a determination is made whether the FILTERED_PAPER_LENGTH is equal to zero. If the FILTERED_PAPER_LENGTH is equal to zero, then flow proceeds to step S 1509 . If the FILTERED_PAPER_LENGTH is not equal to zero flow proceeds to step S 1505 . 
     As stated above, in each of steps S 1501 , S 1502 , S 1503  and S 1504 , flow could proceed to step S 1509 . In step S 1509 , a determination is made whether the sheet has been detected by the sensor. If it has, then EndOfPageDetected is set to FALSE (step S 1510 ), and if it has not been detected, then EndOfPageDetected is set to TRUE (step S 1511 ). The logical end of page detection process then returns after either of steps S 1510  or S 1511 . 
     Returning to step S 1505 , a determination is made whether the sheet has been detected by the sensor. If it has not been detected, then EndOfPageDetected is set to TRUE (step S 1512 ) and the process returns (step S 1508 ). If the sheet has been detected by the sensor, then a determination is made whether the MEASURED_PAPER_LENGTH plus the SWITCH_POINT is greater than the FILTERED_PAPER_LENGTH plus the TARGET_PE_OFF (step S 1506 ). If the the MEASURED_PAPER_LENGTH plus the SWITCH_POINT is greater than the FILTERED_PAPER_LENGTH plus the TARGET_PE_OFF, then EndOfPageDetected is set to TRUE (step S 1507 ) and the process returns (step S 1508 ). If the the MEASURED_PAPER_LENGTH plus the SWITCH_POINT is not greater than the FILTERED_PAPER_LENGTH plus the TARGET_PE_OFF, then EndOfPageDetected is set to FALSE (step S 1513 ) and the process returns (step S 1508 ). 
     The foregoing process steps provide for a sheet feeding operation which performs flying load. The flying load operation begins feeding a next sheet prior to detection of the end of the current sheet, thereby reducing the distance between the sheets being fed into the printer. The process calculates the time when the end of the current sheet will be detected and updates variables to begin feeding the next sheet within a target feed time. That is, the process includes a target minimum distance between the end of the current sheet and the beginning of the next sheet in order to provide for a more optimum feeding operation. The process steps track the distance between the sheets during the feeding operation and adjusts the timing for feeding the next sheet so as to maintain the distance within a target range. Next, a discussion will be made regarding a relationship between ASF motor pulses and a sheet feed amount by the ASF, and a relationship between line feed motor pulses and a line feed sheet amount. 
     FIG. 16A depicts a relationship between ASF motor pulses and a corresponding sheet feed amount (in millimeters) by ASF roller  32   a.  In FIG. 16A, the ASF motor  41  is assumed to be a 2-2 phase motor, the ASF drivetrain is assumed to have a gear ratio of 1:13.4375, and the ASF roller  32   a  has a diameter of 31.6 mm. As such, one complete (360°) rotation of ASF roller  32   a  is assumed to take 645 motor pulses of the ASF motor and that one motor pulse corresponds to a 0.1539 mm feed amount of the ASF roller. 
     In FIG. 16A, ASF roller  32   a  is depicted at its home position (i.e. initialization position) and rotates in a clockwise direction as shown by arrow A. Reference number  210  represents one sheet of a recording medium that is to be picked up and fed by ASF roller  32   a.  Reference number  200  represents a point of contact between ASF roller  32   a  and recording medium  210 . 
     As seen in FIG. 16A, ASF roller  32   a  includes a flat portion  211 . When ASF roller  32   a  is positioned at the home position, flat portion  211  provides for disengagement of ASF roller  32   a  from recording medium  210 . When the ASF motor is started, ASF roller  32   a  rotates clockwise from the home position. When ASF roller  32   a  has rotated so that point  201  along the circumference of ASF roller  32   a  rotates to point  200 , ASF roller  32   a  engages recording medium  210 . As seen in FIG. 16A, 68 pulses of the ASF motor are needed to rotate the ASF roller from point  201  to point  200 . When the ASF roller has rotated to point  201 , it begins feeding recording medium  210  into printer  10 . 
     As the ASF motor continues to turn, ASF roller  32   a  also continues to rotate until point  202  rotates to point  200 . When ASF roller  32   a  has rotated from point  202  to point  200 , recording medium  210  engages the PE sensor and the PE sensor is turned on. As seen in FIG. 16A, 190 pulses of the ASF motor are needed to rotate ASF roller  32   a  from point  201  to point  202 . Accordingly, 258 pulses (68 plus 190) are needed to rotate ASF roller  32   a  from the home position until the recording medium engages and turns on the PE sensor. 
     The ASF motor continues to turn and ASF roller  32   a  continues to feed recording medium  210  into printer  10  until recording medium  210  reaches line feed pinch rollers  36   a.  When recording medium  210  reaches line feed pinch rollers  36   a,  for flying load pinch rollers  36   a  are turning and they engage recording medium  210  to begin feeding it through printer  10 . At this point, in a flying load case, both ASF roller  32   a  and line feed pinch rollers  36   a  are engaged with recording medium  210 . Therefore, both ASF roller  32   a  and line feed pinch rollers  36   a  should be turning at the same rate. This was described above with reference to FIGS. 13A to  13 C. As seen in FIG. 16A, 157 ASF motor pulses are needed to feed recording medium  210  from the time it turns on the PE sensor until it reaches line feed pinch rollers  36   a.  Accordingly, the total ASF motor pulses for ASF roller  32   a  to rotate from its home position and to feed recording medium  210  to line feed pinch rollers  36   a  is 415 (68+190+157). 
     If the load type is not a flying load, but is a registered load, then line feed pinch rollers  36   a  will not be turning when recording medium  210  reaches them. That is, the line feed motor is not engaged to turn line feed rollers  36   a  until after recording medium  210  has been registered. As seen in FIG. 16A, the ASF motor continues to turn to register recording medium  210  against line feed pinch rollers  36   a.  The registration amount is 3 mm as shown in FIG. 16A, and a 3 mm registration amount corresponds to 19 pulses of the ASF motor. Therefore, once recording medium  210  reaches line feed pinch rollers  36   a,  the ASF motor performs 19 pulses to achieve registration. Accordingly, the total number of ASF motor pulses for ASF roller  32   a  to rotate from the home position to achieve registration of recording medium  210  is 434 (68+190+157+19). Once the ASF motor has performed 434 pulses, the line feed motor is engaged and line feed pinch rollers  36   a  pick up recording medium  210  and begin feeding it through printer  10 . At this point, like the flying load case, both ASF roller  32   a  and line feed pinch rollers  36   a  are feeding recording medium  210  simultaneously and therefore, should be running at the same rate. 
     Whether the load type is flying or registered, ASF roller  32   a  continues to feed recording medium  210  until a total of 577 ASF motor pulses have been achieved. Once the ASF motor has performed 577 pulses, point  205  on the circumference of ASF roller  32   a  has rotated to point  200  and flat portion  211  of ASF roller  32   a  disengages recording medium  210 . At this point, recording medium  210  is fed through printer  10  by line feed pinch rollers  36   a.  The ASF motor continues to turn however until 645 motor pulses have been performed. Recall that 645 motor pulses corresponds to one full rotation of ASF roller  32   a.  Therefore, after 645 motor pulses, ASF roller  32   a  returns to its home position and waits to begin feeding the next sheet. 
     FIG. 16B depicts a relationship between the ASF motor pulses and a corresponding ASF roller feed amount, as well as a relationship between line feed motor pulses and a corresponding line feed amount. As seen in FIG. 16B, the 190 motor pulses of the ASF motor described above for feeding the recording medium to turn on the PE sensor correspond to a 30.040 mm feed amount by the ASF roller. 
     Also depicted in FIG. 16B are a relationship between line feed motor pulses and a corresponding line feed amount. It is assumed that the line feed motor is a 2-2 phase motor, that the line feed drivetrain has a gear ratio of 1:8.333, and that the line feed roller has a diameter of 16.17 mm. As such, one rotation of the line feed roller is assumed to take 800 pulses of the line feed motor and that one pulse corresponds to a {fraction (1/400)} inch (0.0635 mm) line feed amount. The remaining motor pulses and feed amounts depicted in FIG. 16B depict a relationship between line feed motor pulses and line feed amounts, where the line feed amount correspond to distances for feeding the recording medium between various components of printer  10 . 
     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.