Patent Publication Number: US-7708482-B2

Title: Method for controlling the operation of a printer connected to an automatic sheet feeder or roll paper holder

Description:
The present invention is a divisional application of Ser. No. 11/254,178, filed on Oct. 18, 2005 now abandoned and relates to a control method for operating a printer. 
    
    
     BACKGROUND ART 
     An inkjet printer discharges ink drops on paper using, for example, piezoelectric elements, thermal elements, or electrostatic actuators so that the discharged ink forms images on the paper. A continuous paper holder or automatic sheet feeder (ASF) is also typically attached to the inkjet printer, and the printer conveys roll paper supplied from the continuous paper holder or feeds individual sheets of paper supplied from an automatic sheet feeder in a specific direction to record images on the supplied paper while controlling the transportation of the paper and the discharge of the ink drops on the paper. 
     An inkjet printer of this general type supplies paper from a paper supply opening rendered at the back of the printer case (housing) to a paper transportation path and, at the same time, discharges ink drops on the paper from an ink head disposed to a carriage at a specific position on the paper. The paper is discharged from a paper exit rendered at the front of the housing. 
     The roll paper holder or ASF (automatic sheet feeder) can be freely installed to and removed from some inkjet printers built so that the roll paper holder or ASF (automatic sheet feeder) can be installed appropriately to the printer for carrying out a desired printing application. An inkjet printer of this type is taught and described in Japanese Unexamined Patent Appl. Pub. H 11-348364 (FIG. 1). This inkjet printer requires the user to recognize whether the roll paper holder or the ASF is installed to the printer for the printer to operate properly. To do so requires changing the setup which increases the burden on the user and is bothersome. In addition, the user must also load the appropriate paper into the paper transportation path according to whether the roll paper holder is installed, the ASF is installed, or if neither is installed. If the paper is mistakenly loaded problems can occur as different types of paper may collide inside the paper transportation path. 
     DISCLOSURE OF INVENTION 
     In view of the foregoing problem, an object of the present invention is to provide a control method for operating a printer that will electronically recognize whether the roll paper holder is installed, the ASF is installed, or if neither is installed and will control the operation of the printer based upon such recognition to reduce the burden on the user. 
     (1) A control method for operating a printer ( 1 ) comprising the steps of: detecting if the roll paper holder is installed to the printer when power to the printer is turned on, and if so: detecting when a paper transportation path in the printer is in a closed position; detecting a leading end and a trailing end of paper in the paper transportation path; and discharging the paper from the paper transportation path when only the leading end of the paper is detected. 
     (2) A control method for operating the printer ( 1 ) comprising the steps of: detecting if the roll paper holder is installed to the printer when power to the printer is turned on, and if so: detecting when the paper transportation path is in a closed position; detecting a leading end and a trailing end of paper in the paper transportation path; and indexing the paper in the paper transportation path when only the trailing end of the paper is detected. 
     (3) A control method for operating the printer ( 1 ) comprising the steps of: detecting if the ASF is installed to the printer when power to the printer is turned on, and if so: detecting when the paper transportation path is in a closed position; detecting a leading end and a trailing end of paper in the paper transportation path; and discharging the paper from the paper transportation path when either the leading end or the trailing end of the paper is detected. 
     (4) A control method for operating the printer ( 1 ) comprising the steps of: detecting if the paper transportation path is in a closed position during manual printer operation, and if so: detecting a leading end and a trailing end of paper in the paper transportation path; and indexing the paper in the paper transportation path when both the leading end and the trailing end of the paper are detected. 
     (5) A control method for operating the printer ( 1 ) comprising the steps of: detecting if the paper transportation path is in a closed position when paper is supplied from the ASF, and if so: detecting a leading end and a trailing end of paper in the paper transportation path before paper is supplied from the ASF; and discharging the paper from the paper transportation path when either the leading end or the trailing end of the paper is detected. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an oblique view from the front of the main printer unit of an inkjet printer according to a preferred embodiment of the invention. 
         FIG. 2  is an oblique view from the back of the main printer unit. 
         FIG. 3  is a section view through line III-III in  FIG. 2 . 
         FIG. 4  is an oblique view showing the arrangement in the proximity of the paper transportation path. 
         FIG. 5  is a section view showing the paper transportation path when the parts constituting the bottom surface of the paper transportation path are lowered. 
         FIG. 6  is an oblique view from the front showing how the roll paper holder is attached to the main printer unit. 
         FIG. 7  is an oblique view from the back showing how the roll paper holder is attached to the main printer unit. 
         FIG. 8  is a section view showing the roll paper holder attached to the main printer unit. 
         FIG. 9  is an oblique view showing an ASF which can be attached to the main printer unit. 
         FIG. 10  shows the ASF attached to the main printer unit. 
         FIG. 11  is a block diagram showing the structure of the control circuit board and other parts controlling the main printer unit. 
         FIG. 12  is a flow chart describing the startup operation of the main printer unit. 
         FIG. 13  is a flow chart of paper detection process A shown in  FIG. 12 . 
         FIG. 14  is a flow chart of paper detection process B shown in  FIG. 12 . 
         FIG. 15  is a state diagram showing the internal status and state changes in the main printer unit when the roll paper holder is installed. 
         FIG. 16  is a state diagram showing the internal status and state changes in the main printer unit when the ASF is installed. 
         FIG. 17  is a state diagram showing the internal status and state changes in the main printer unit when printing with manual paper insertion. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     A preferred embodiment of an inkjet printer according to the present invention is hereafter described with reference to the accompanying figures. 
     The inkjet printer according to this embodiment of the invention has a main printer unit  1  (shown in  FIG. 1  to  FIG. 5 ) to which a continuous paper holder (referred to hereafter as a “roll paper holder”)  40  as is shown in  FIG. 6  to  FIG. 8  and a slip supply apparatus (referred to hereafter as a “ASF”)  60  as shown in see  FIG. 9  and  FIG. 10  may individually but not in combination be removably attached to the main printer unit  1 . 
     The general external arrangement of the main printer unit  1  in this embodiment of the invention includes an image recording unit  3  supported in a cantilevered manner at one end of a base unit  2  by way of an intervening cantilever unit  4 . A paper transportation path  5  for conveying paper from the back side to the front side is rendered between the base unit  2  and image recording unit  3 . 
     The paper transportation path  5  has a front opening  5   a , a back opening  5   b , and a contiguous side opening  5   c . Paper inserted to the paper transportation path  5  is conveyed in the direction from the back opening  5   b  side to the front opening  5   a  side (referred to below as the “paper transportation direction”). In a main printer unit  1  according to this embodiment of the invention paper can be inserted to the paper transportation path  5  from any one of these openings, that is, the front opening  5   a , back opening  5   b , or side opening  5   c.    
     More specifically, paper can be inserted to the paper transportation path in the main printer unit  1  of the present embodiment not only from the back but also from the front and side. More particularly, paper can be manually inserted to the paper transportation path  5  of the main printer unit  1  for printing from a direction substantially perpendicular to the paper transportation direction through the side opening  5   c . In other words, the main printer unit  1  is arranged so that paper can be inserted through the side opening  5   c  to the paper transportation path  5  from a direction parallel to the paper transportation surface that functions as the paper transportation path  5  between the base unit  2  and image recording unit  3 . 
     The outside walls of the base unit  2 , image recording unit  3 , and cantilever unit  4  are formed by fitting a front case  11  and a back case  12  together with the front case  11  composed of a base unit front case  2   a , cantilever unit front case  4   a , and image recording unit front case  3   a  integrally formed in a roughly U-shaped arrangement, and the back case  12  composed of a base unit back case  2   b , cantilever unit back case  4   b , and image recording unit back case  3   b  integrally formed in a roughly U-shaped arrangement. As shown in  FIG. 1 , an opening  13  composed of opposing U-shaped cut-outs  11   a  and  12   a  is formed in the top of image recording unit front case  3   a  and image recording unit back case  3   b.    
     A cover  14  is openably and closably attached via a hinge  14   a  to the edge portion of cut-out  12   a  in the image recording unit back case  3   b . This cover  14  is attached so that it covers the opening  13  when closed as shown in  FIG. 2 . By thus covering the opening  13 , cover  14  protects the internal components (not shown in  FIG. 1 ) of the image recording unit  3  from the outside of the main printer unit  1 . A protruding tab  14   b  for opening and closing the cover is disposed to the cover  14  on the edge on the opposite side as the side on which the hinge  14   a  is formed. This protruding tab  14   b  is formed so that the user can easily catch the tab  14   b  with a finger to open the cover  14 . The user can access the internal components of the image recording unit  3  for maintenance when the cover  14  is open as shown in  FIG. 1  so that, for example, an ink cartridge removably installed to the carriage  25  described below can be replaced. 
     A release lever  15  is further disposed to the cantilever unit back case  4   b . This release lever  15  is rendered so that the release lever  15  can be pushed down and the platen  21  (see  FIG. 3 ) forming part of the paper transportation path  5  as described below moves up and down in conjunction with other parts attached to the platen  21  when the release lever  15  is operated so that paper can be inserted to the paper transportation path  5 . Operation of the release lever  15  is described in further detail below. 
     A power cable connector  16  to which a cable connected to an external power source is connected to supply power for driving the printer, a data communication terminal  17  to which is connected a USB cable, for example, for data communication between the printer and a personal computer or other host computer, and an ASF drive cable connector  18  to which is connected a power cable for supplying power to the ASF (automatic sheet feeder)  60  described below, are disposed to a portion of the base unit back case  2   b  below the cantilever unit  4 . 
     A cable connection confirmation pin (not shown in the figure) for confirming whether a cable for supplying power to the ASF  60  is connected is also disposed to the ASF drive cable connector  18 . The main printer unit  1  determines whether the ASF  60  described below is connected from the cable connection confirmation pin, which is shorted when a cable is connected to the ASF drive cable connector  18 . The cable connection confirmation pin of the ASF drive cable connector  18  thus also functions as an ASF connection/disconnection sensor  18   a  for determining whether the ASF  60  is installed (see  FIG. 11 ). 
     As also shown in  FIG. 2 , slots  19   a  for attaching the ASF  60  are formed on the back of the image recording unit back case  3   b . In addition, slots  19   b  for attaching the roll paper holder  40  described below are formed in the back of the base unit back case  2   b . Attaching the roll paper holder  40  and ASF  60  is described further below. 
     A power switch  7 , cleaning button  8 , and paper feed button  9  are rendered on the front of the cantilever unit front case  4   a  as shown in  FIG. 1 . 
     The power switch  7  turns the power to the main printer unit  1  on and off. Pressing the power switch  7  when the power cable connected to an external power source is inserted to the power cable connector  16  causes the main printer unit  1  to start and begin the initialization process. Pressing the power switch  7  again when the power is on interrupts the power supply to the main printer unit  1  and turns the power off. 
     An LED or other lamp (not shown in the figure) is disposed behind the power switch  7 . The power switch  7  is made from an optically transparent plastic material so that this lamp can be seen through the power switch  7  when the lamp is on. This lamp turns on when the power switch  7  is on in this embodiment of the invention, thus enabling the user to visually confirm that the main printer unit  1  power is on. 
     The cleaning button  8  is used for cleaning the head of the main printer unit  1 . Pressing the cleaning button  8  causes a cleaning means not shown to clean the head of the main printer unit  1  as described further below. The cleaning system could also be arranged so that pressing the cleaning button  8  when the ASF  60  is installed also causes the supply roller  78  of the ASF  60  to be cleaned at the same time. 
     As with the power switch  7 , an LED or other lamp (not shown in the figure) is disposed behind the cleaning button  8 . The cleaning button  8  is made from an optically transparent plastic material so that the lamp can be seen through the cleaning button  8  when the lamp is on. This lamp can be designed to start flashing after a specified period of time has passed so that, for example, the user can know from the flashing lamp that cleaning is needed and the flashing indicator causes the user to press the cleaning button  8 . 
     The paper feed button  9  is used to feed paper from the ASF  60  described below into the paper transportation path  5  of the main printer unit  1 . Paper is normally fed automatically when a page break command is received to start printing, but the paper may not be fed for various reasons. In such circumstances the user can press the paper feed button  9  to feed paper into the paper transportation path  5  of the main printer unit  1 . 
     As with the power switch  7 , an LED or other lamp (not shown in the figure) is disposed behind the paper feed button  9 . The paper feed button  9  is made from an optically transparent plastic material so that the lamp can be seen through the paper feed button  9  when the lamp is on. This lamp can be designed to start flashing when the ASF  60  fails to automatically feed paper, for example. The user can thus know from seeing the flashing indicator that the ASF  60  failed to automatically feed paper into the paper transportation path  5 , press the paper feed button  9  after confirming why the paper failed to feed, and thus cause the ASF  60  to attempt supplying paper again. 
     (Internal Structure of the Main Printer Unit) 
       FIG. 3  is a section view through line III-III and line IIIa-IIIa in  FIG. 2  showing the major components of the internal structure of the main printer unit  1 .  FIG. 4  is an oblique view showing the arrangement around the paper transportation path, and  FIG. 5  is a section view showing the parts constituting the bottom surface of the paper transportation path in the lowered position. 
     A platen  21  constitutes the major part of the bottom surface of the paper transportation path  5  from the back opening  5   b  to the front opening  5   a . The platen  21  is a plate-like member forming the top surface of the base unit  2 , and the top surface  21   a  thereof is substantially flat as shown in  FIG. 4 . Disposed to the top of the paper transportation path  5  opposite the platen  21  in order from the upstream side are a paper guide  22 , main paper transportation roller  23 , carriage  25 , automatic paper cutter  29 , and TOF lever  33 . A control circuit board  35  is located below the platen  21 . These components are further described below as they relate to the platen  21 . 
     The paper guide  22  is disposed opposite the platen  21  on the upstream side of the paper transportation path  5 . The paper guide  22  forms a convexly curving surface on the side facing the paper transportation path  5  so that paper supplied from the back opening  5   b  is inserted smoothly to the paper transportation path  5 . Paper inserted from the back opening  5   b  is conveyed between the platen  21  and paper guide  22  to the main paper transportation roller  23 . 
     Multiple recessed portions  21   b  are formed at approximately the middle of the platen  21  in the paper transportation direction. A paper feed roller  24  is rotatably disposed in each of these recessed portions  21   b . The paper feed rollers  24  are located opposite the main paper transportation roller  23  located thereabove, and thus follow rotation of the main paper transportation roller  23 , which is driven by a motor not shown. The paper is nipped between the main paper transportation roller  23  and paper feed rollers  24 , and can thus be conveyed in the paper transportation direction or the opposite direction. 
     A BOF lever  27  is disposed to the platen  21  near the main paper transportation roller  23 . This BOF lever  27  is a part of the paper trailing-end detector, and is arranged so that conveying paper over the platen pushes the BOF lever  27  down. This depression of the BOF lever  27  is sensed by a BOF sensor  27   a  (see  FIG. 11 ) which is composed of an optical sensor and linkage mechanism formed integrally to the BOF lever  27 , for example. This BOF sensor  27   a  detects a state change in the BOF lever  27  and outputs a signal to the control circuit board  35 . As a result, the paper is known to be above the BOF lever  27 . This BOF sensor  27   a  also senses the timing at which the BOF lever  27  returns to the previous state, and outputs a signal to the control circuit board  35 . That the paper is not above the BOF lever  27  can thus be determined. 
     The carriage  25  is disposed opposite the platen  21  on the downstream side of the main paper transportation roller  23 . The carriage  25  is supported by a guide plate  28  and guide shaft  26  extending lengthwise along the direction (perpendicular to the paper transportation path  5 , that is, widthwise to the paper) joining the paper transportation path  5  side  4   c  of the cantilever unit  4  and the side opening  5   c . The carriage  25  can thus slide freely along the guide shaft  26  and guide plate  28  perpendicularly to the paper transportation path  5 . 
     The carriage  25  carries an inkjet head (not shown in the figure) having a plurality of nozzles for discharging ink to the paper disposed facing the platen  21 . Images are recorded on paper positioned on the platen  21  by discharging ink from plural nozzles of the ink head while the carriage  25  travels along the guide shaft  26 . An ink cartridge (not shown in the figure) for supplying ink to the ink head is also removably installed to the carriage  25 . 
     An automatic paper cutter  29  is disposed on the downstream side of the carriage  25 . The automatic paper cutter  29  is composed of a cutter guide  29   a  which is slidably fixed on the image recording unit  3  side, and a disk-shaped rotating cutter blade  31  rotatably axially supported by a rotating shaft  30  on the cutter guide  29   a  between the cutter guide  29   a  and guide plate  28 . The rotating cutter blade  31  is located opposite a stationary cutter blade  32  disposed to the platen  21 . The automatic paper cutter  29  cuts roll paper positioned over the stationary cutter blade  32  by moving widthwise to the paper in conjunction with the cutter guide  29   a  while pressing the rotating cutter blade  31  against the stationary cutter blade  32 . 
     Paper transportation subrollers  34  are located near the front opening  5   a  on the downstream side of the automatic paper cutter  29 . The paper transportation subrollers  34  are rotatably axially supported on the platen  21  by means of rotary shaft  34   a . The paper transportation subrollers  34  are opposite a paper transportation subroller guide not shown, and thus convey paper in the paper transportation direction or the opposite direction with the paper nipped between the paper transportation subrollers  34  and this paper transportation subroller guide. The paper conveyed in the paper transportation direction by the paper transportation subrollers  34  is discharged from the front opening  5   a.    
     The TOF lever  33  is disposed to the paper transportation subroller guide not shown. This TOF lever  33  is a part of a paper leading-edge detector, and is disposed so that paper passing below the TOF lever  33  pushes the TOF lever  33  up. This raising of the TOF lever  33  is sensed by a TOF sensor  33   a  (see  FIG. 11 ) which is composed of an optical sensor and linkage mechanism formed integrally to the TOF lever  33 , for example. This TOF sensor  33   a  detects a state change in the TOF lever  33  and outputs a signal to the control circuit board  35 . As a result, the paper is known to be below the TOF lever  33 . This TOF sensor  33   a  also senses the timing at which the TOF lever  33  returns to the previous state, and outputs a signal to the control circuit board  35 . That the paper is not below the TOF lever  33  can thus be determined. 
     The control circuit board  35  disposed below the platen  21  is populated with a control chip for centrally controlling the operation of other parts of the main printer unit  1 , and memory chips for temporarily storing print commands and print data received through the command data communication terminal  17  from an external source. Detection signals from the TOF sensor, BOF sensor, ASF connection sensor, and a roll paper holder connection sensor  38  described below are sent to the control circuit board  35  for determining the position of the paper and whether the ASF  60  and roll paper holder  40  are installed. The specific arrangement of the control circuit board  35  is further described below. 
     When the release lever  15  is pushed down to the open position, the platen  21  and the parts attached to the platen  21  are also displaced downward as shown in  FIG. 5 . Displacing the platen  21  downward vertically opens the paper transportation path  5  so that slips can be manually inserted or roll paper can be loaded. The platen  21  returns to the position shown in  FIG. 3  when the release lever  15  is returned to the original closed position, thus preventing manual insertion of slips and inserting roll paper. 
     As shown in  FIG. 3  and  FIG. 5 , the release lever  15  is disposed so that the distal end of the operating portion  15   a  housed inside the back case  12  can contact release lever sensor  36 . This release lever sensor  36  is composed of, for example, a sensor unit  36   a  and a detection lever  36   b  that is installed pivoting on the sensor unit  36   a . When the release lever  15  is pushed down, the operating portion  15   a  of the release lever  15  pushes down against the detection lever  36   b , thus causing the detection lever  36   b  to swing. The sensor unit  36   a  detects this pivoting motion of the detection lever  36   b  and outputs to the control circuit board  35 . The control unit of the control circuit board  35  thus knows that the release lever  15  was pushed down, that is, that the paper transportation path  5  was opened. In this state the release lever  15  is said herein to be in the open position. 
     When the release lever  15  is then returned from this depressed position to the original position, the detection lever  36   b  also swings back to its original position in conjunction with the movement of the operating portion  15   a  of the release lever  15 . The sensor unit  36   a  detects this circular movement of the detection lever  36   b  and outputs to the control circuit board  35 . The control unit of the control circuit board  35  thus knows that the release lever  15  returned to the original position, that is, that the paper transportation path  5  closed. In this state the release lever  15  is said herein to be in the closed position. 
     As described above, printing to manually inserted paper is possible using only the main printer unit  1 . When printing to manually inserted forms, the user can insert paper to the paper transportation path  5  inside the main printer unit  1  from any of the front opening  5   a , back opening  5   b , and side opening  5   c  to print images without worrying about the paper size. 
     More particularly, when using the main printer unit  1  alone, images can be printed with no concern for the shape of the part of the paper that is not inserted into the paper transportation path  5 . This enables inserting only one of multiple pages bound at one edge, such as in a book or notebook, to the paper transportation path  5  so that an image can be printed to just that one page. Specialized printing applications, such as printing an image on only one page or each page in a bound notebook, can thus be easily accommodated. 
     (Roll Paper Holder) 
       FIG. 6  is an oblique view showing installing a roll paper holder  40  to the main printer unit  1  as seen from the front,  FIG. 7  is an oblique view showing installing a roll paper holder  40  to the main printer unit  1  as seen from the back, and  FIG. 8  is a section view showing the roll paper holder  40  installed to the main printer unit  1 . 
     The roll paper holder  40  is configured for installation as a first attachment to the main printer unit  1  in this embodiment of the invention. The roll paper holder  40  and installation thereof are described next below. 
     The roll paper holder  40  is a part for supplying roll paper CS to the main printer unit  1  as continuous paper. The roll paper holder  40  is composed of main printer unit base  41  and a roll paper holding unit  45  attached in unison with the main printer unit base  41 . 
     The main printer unit base  41  is a base in which the base unit  2  of the main printer unit  1  fits, and is composed of a platform  41   a  which conforms to the shape of the bottom of the main printer unit  1  and is substantially rectangular when seen in plan view, four leg portions  42  formed in unison with the four corners of the platform  41   a , and side guide walls  41   b ,  41   c  rising vertically from the widthwise end portions of the platform  41   a . A portion of guide wall  41   b  curves from the widthwise end portion of the platform  41   a , and another portion of the guide wall  41   b  extends between the front edge and the back edge of the platform  41   a . The base unit  2  of the main printer unit  1  fits inside these guide walls  41   b ,  41   c  and is thus stationed on the platform  41   a . The bottom of the main printer unit  1  is thus raised by the main printer unit base  41  and the height of the paper transportation path  5  (the height from the installation surface) is thus higher than when the roll paper holder  40  is not installed. 
     Notch  41   d  is also formed in a portion of the guide wall  41   b  extending to the back-side edge of the platform  41   a  as shown in  FIG. 7  so that the power cable connector  16  and data communication terminal  17  disposed to the main printer unit  1  are not covered by the guide wall  41   b . A power supply cable and USB cable can thus be connected through this notch  41   d  to the power cable connector  16  and data communication terminal  17  while the main printer unit  1  is stationed on the main printer unit base  41 . Because the ASF  60  described below cannot be installed when the roll paper holder  40  is installed, the ASF drive cable connector  18  is covered by the guide wall  41   b  in this embodiment. 
     Back guide wall  43  rises from the platform  41   a  at the back edge of the platform  41   a . Positioning ribs  44  corresponding to the slots  19   b  formed in the main printer unit  1  are disposed to the front of this back guide wall  43  as shown in  FIG. 6  and  FIG. 7 . These positioning ribs  44  fit into the slots  19   b  in the main printer unit  1  and thus position the main printer unit  1  on the platform  41   a . Note that  FIG. 7  is drawn to emphasize the installation parts for the roll paper holder  40 , and the roll paper holding unit  45  of the roll paper holder  40  is thus omitted from the figure. 
     A tab  44   a  is disposed to the vertical top end of one of the positioning ribs  44  (the left positioning rib  44  as seen in  FIG. 7 ). As shown in  FIG. 7  and  FIG. 8 , this tab  44   a  is inserted to the base unit back case  2   b  through an opening  19   c  formed at one lengthwise end of slot  19   b . A roll paper holder connection sensor  38  is installed at a position corresponding to this opening  19   c  inside the base unit back case  2   b.    
     This roll paper holder connection sensor  38  is composed of, for example, a sensor base  38   a  and a detection trigger  38   b  which is attached in order to move circularly to the sensor base  38   a . When the tab  44   a  of the positioning rib  44  is inserted to opening  19   c , the tab  44   a  contacts the detection trigger  38   b  and causes the detection trigger  38   b  to swing. The sensor base  38   a  detects this operation of the detection trigger  38   b  and outputs to the control circuit board  35 . The controller on the control circuit board  35  thus knows that the roll paper holder  40  was installed. 
     The roll paper holding unit  45  is attached to the back of the back guide wall  43 . The roll paper holding unit  45  is composed of guide members  46  and  47  which guide the widthwise sides of the roll paper CS, and a stationary spindle  49  which is fixed to the guide members  46  and  47  and allows the roll paper CS to turn. As shown in  FIG. 8  the stationary spindle  49  supports the roll paper CS by passing through a through-hole formed in the center of the take-up spool, and allows the roll paper to roll around the stationary spindle  49  as the leading end of the roll paper is pulled out. 
     As also shown in  FIG. 8  the roll paper holding unit  45  holds the roll paper CS so that when the roll paper is wound around the stationary spindle  49 , the maximum height H of the roll paper CS is substantially equal to or slightly below the height of the paper transportation path. More specifically, when an unused roll of roll paper CS is loaded, the roll paper holding unit  45  holds the roll paper CS so that the maximum height H of the roll paper CS is substantially equal to or slightly below the height of the paper transportation path. 
     By thus holding the roll paper CS so that the maximum height H of the roll paper CS is substantially equal to or slightly below the height of the paper transportation path, the roll paper CS pulled out and conveyed through the paper transportation path  5  is not curled in the opposite direction as the curl of the wound roll when the paper enters the paper transportation path  5 . It is thus more difficult for problems such as the leading edge of the roll paper CS snagging or jamming inside the paper transportation path  5  inside the main printer unit  1  to occur when the roll paper is inserted, and the roll paper CS can be conveyed smoothly through the paper transportation path  5  when the paper is transported. 
     This is achieved by means of this arrangement whereby the main printer unit base  41  raises the bottom of the main printer unit  1  and positions the paper transportation path  5  at a greater height from the desk surface so that the stationary spindle  49  can be positioned at a low position even when the diameter of the roll paper CS is large. Conversely, because the height of the stationary spindle  49  can be set low, the maximum height H of the roll paper CS can be held at substantially the same height or slightly lower than the height of the paper transportation path even when the diameter of the roll paper CS is large. 
     Note that the roll paper CS is loaded in the main printer unit  1  by depressing the release lever  15  so that the paper transportation path  5  is open and then inserting the paper to the paper transportation path  5  from the back opening  5   b.    
     Manual insertion prevention tabs  50  and  51  are also formed as part of the guide members  46  and  47 . As shown in  FIG. 8 , these manual insertion prevention tabs  50  and  51  are rendered so that when the main printer unit  1  is stationed in the main printer unit base  41  of the roll paper holder  40  the manual insertion prevention tabs  50  and  51  intersect the plane extending the paper transportation path  5  of the main printer unit  1  in the paper transportation direction. When the roll paper holder  40  is installed to the main printer unit  1 , it is generally assumed that roll paper CS will be used for printing. Because roll paper CS will thus be loaded into the paper transportation path  5 , manually inserting paper from the side opening  5   c  is undesirable because a paper jam or other problem will result (of course, this is undesirable even if roll paper CS is not located in the paper transportation path  5 ). These manual insertion prevention tabs  50  and  51  are therefore disposed to the roll paper holder  40  in the present embodiment so that these manual insertion prevention tabs  50  and  51  interfere with inserting paper from the side opening  5   c  and thus prevent improper manual paper insertion by the operator. 
     As described above, using roll paper holder  40  enables the main printer unit  1  to print images to roll paper CS. More specifically, printing on roll paper CS is enabled by simply attaching the roll paper holder  40  to the main printer unit  1  and loading roll paper CS in the paper transportation path  5 . 
     Furthermore, when the roll paper holder  40  is installed, supplying paper by manual insertion is structurally prohibited as described above. 
     (ASF (Automatic Sheet Feeder)) 
       FIG. 9  is an oblique view showing an ASF  60  installed to the main printer unit  1 , and  FIG. 10  is a section view showing the ASF  60  installed to the main printer unit  1 . 
     A main printer unit  1  according to this embodiment of the invention is constructed so that an ASF  60  can be removably attached as a second attachment. The ASF  60  and installation thereof are described below. 
     The ASF  60  is a sheet feeding device that holds a plurality of slips of a specific size and supplies the slips one sheet at a time into the main printer unit  1 . The ASF  60  is primarily composed of a bottom case  61  and a top cover  70 . These parts are further described below. 
     The bottom case  61  is an integrally molded plastic box-like member having a front cover  62  and mutually opposing back cover  65  formed in unison with intervening side covers  63 ,  64 , and a bottom cover  66  rendered on the bottom formed in unison with the side covers  63 ,  64  and back cover  65 . An opening  60   a  is rendered at the top of the bottom case  61  between the front cover  62 , side covers  63 ,  64 , and back cover  65 . The top cover  70  is inserted from the opening  60   a  and fit to the bottom case  61  such that a portion of the opening  60   a  is covered. The uncovered portion of the opening  60   a  is the paper insertion opening from which a plurality of slips S are inserted at an angle. 
     A flat paper guide  68  which supports the part of the slips S located above the back cover  65  is attached to the top end of the back cover  65 . A paper size limiter  69  which limits the maximum size of slip paper that can be inserted from the opening  60   a  is also disposed at the top end of the back cover  65 . This paper size limiter  69  can slide along the top end of the back cover  65  and the position of the paper size limiter  69  can thus be appropriately adjusted to limit the paper size. By setting the width between the paper size limiter  69  and the side cover  61  to substantially the same as the width of the paper that is to be inserted, the paper can be guided by the side cover  61  and paper size limiter  69  and inserted without tipping sideways. 
     A slope  66   a  is disposed on top of the bottom cover  66  of the bottom case  61  so that the surface of the slope  66   a  is inclined towards the bottom cover  66  as shown in  FIG. 10 . Inserted slips are thus held by the back cover  65  and the flat paper guide  68  in a stack in contact with the slope  66   a  or bottom cover  66 . 
     Another opening  60   b  is rendered at the bottom of the bottom case  61  between the front cover  62 , side covers  63 ,  64 , and bottom cover  66 . This opening  60   b  forms a slip discharge opening from which slips inserted from opening  60   a , which is the slip insertion opening, exit. 
     As shown in  FIG. 9 , L-shaped hooks  67  are disposed on the front edges of the side covers  63 ,  64 . These hooks  67  are rendered to match the slots  19   b  provided in the image recording unit back case  3   b  as shown in  FIG. 2 , and the ASF  60  is attached to the main printer unit  1  by engaging these hooks  67  in the slots  19   b .  FIG. 10  shows the ASF  60  installed to the main printer unit  1 . 
     A mounting rib  71  is formed in unison with the top cover  70  on the inside of the top cover  70  (the side facing the back cover back cover  65 ), and paper feed roller unit  72  is attached to this mounting rib  71 . This paper feed roller unit  72  has a gear  73  connected to a drive shaft  73   a  which is driven by a motor and cable not shown connected to the ASF drive cable connector  18 , gear  74  meshing with gear  73 , gear  75  meshing with gear  74 , gear  76  meshing with gear  75 , gear  77  meshing with gear  76 , and a supply roller  78  with a gear  78   a  meshing with gear  77 . 
     When the drive shaft  73   a  of gear  73  is driven forward or in reverse, the paper feed roller unit  72  moves circularly closer to the slips or away from the slips, and is held either in a position with the supply roller  78  in contact with the paper or in a position with the supply roller  78  separated from the paper. When the drive shaft  73   a  rotates with the supply roller  78  touching the paper, gear  73  turns, the torque of gear  73  is transferred through gears  74 ,  75 ,  76 ,  77  to gear  78   a , and the supply roller  78  disposed coaxially to gear  78   a  turns. 
     Rotationally driving the drive shaft  73   a  of paper feed roller unit  72  to supply a slip to the main printer unit  1  causes paper feed roller unit  72  to move circularly to the slips S and causes the supply roller  78  to contact the surface of the slips S. Further rotationally driving the drive shaft  73   a  causes the supply roller  78  to rotate in the forward paper transportation direction (clockwise as seen in  FIG. 10 ), feeds the topmost slip S on the stack of plural slips S at a constant speed from the opening  60   b , and thus supplies the slip through the back opening  5   b  of the main printer unit  1  into the paper transportation path  5 . The main printer unit  1  then records an image on the supplied paper and discharges the paper from the front opening  5   a . If a next page is to be printed, paper is again fed from the ASF  60  into the paper transportation path  5  and an image is printed. 
     As shown in  FIG. 10 , when the ASF  60  is installed to the main printer unit  1 , the bottom cover  66  is positioned near an extension of the paper transportation path  5 . Because the back opening  5   b  is not closed by the ASF  60  when thus installed, paper can be manually supplied from the side opening  5   c  to the paper transportation path when the ASF  60  is installed. 
     As will be easily understood by comparison with  FIG. 8 , if the user attempts to install the ASF  60  to the main printer unit  1  while the roll paper holder  40  is installed to the main printer unit  1 , the manual insertion prevention tabs  50  and  51  of the roll paper holder  40  will contact the bottom cover  66  of the ASF  60  and thus obstruct installing the  60 . As a result, the ASF  60  cannot be installed to the main printer unit  1  if the roll paper holder  40  is also installed. 
     Likewise, if the user attempts to install the roll paper holder  40  to the main printer unit  1  while the ASF  60  is installed, the manual insertion prevention tabs  50  and  51  of the roll paper holder  40  will contact the bottom cover  66  of the ASF  60  and thus obstruct installing the roll paper holder  40 . The roll paper holder  40  thus cannot be installed to the main printer unit  1  if the ASF  60  is installed. The arrangement of an inkjet printer according to this embodiment of the invention thus prohibits installing both the ASF  60  and roll paper holder  40  to the main printer unit  1  at the same time. 
     Installing the ASF  60  to the main printer unit  1  enables continuously supplying slips into the paper transportation path and enables printing images on the conveyed slips. Manual paper supply is also possible when the ASF  60  is installed. 
     (Inkjet Printer Control Circuit) 
       FIG. 11  is a block diagram showing the control circuit board  35  and other parts of the control mechanism for controlling the main printer unit  1 . 
     In addition to control circuit board  35 , the main printer unit  1  also has an ASF connection/disconnection sensor  18   a , roll paper holder connection sensor  38 , release lever sensor  36 , TOF sensor  33   a , BOF sensor  27   a , ASF drive cable connector  18 , data communication terminal  17 , operating unit  110 , and display unit  120 . 
     The control circuit board  35  is the central control unit or control means which oversees the various control components of the main printer unit  1 . More particularly, the control circuit board  35  has a paper transportation controller  101 , printing controller  102 , ASF controller  103 , command interpreter  104 , main control unit  105 , memory  106 , communication controller  107 , and status transmission unit  108  connected to communicate with each other over a bus  100 . 
     The paper transportation controller  101  is a control unit which generates control signals for driving the main paper transportation roller  23  and paper transportation subrollers  34  according to a paper feed command, and thus controls the main paper transportation roller  23  and paper transportation subrollers  34 . The main paper transportation roller  23  and paper transportation subrollers  34  convey paper located inside the paper transportation path  5  in the paper transportation direction based on drive signals sent from the paper transportation controller  101 . The main paper transportation roller  23  and paper transportation subrollers  34  thus index the paper in the paper transportation path  5 , advance the paper one line at a time, and discharge the paper based on drive signals from the paper transportation controller  101 . 
     The printing controller  102  controls driving the carriage  25 , and based on print commands and image data received from an external source controls movement of the carriage  25  and discharging ink from the ink head (not shown in the figure) disposed to the carriage  25 . 
     The ASF controller  103  is the control unit that controls the paper feed operation of the ASF  60  installed to the main printer unit  1 . More specifically, the ASF controller  103  rotationally drives the supply roller  78  of the ASF  60  to feed slips S into the paper transportation path  5  according to received page break commands sent from an external host computer  150 , operation of release lever  15 , or operation of the paper feed button  9 . 
     The command interpreter  104  is an interpreter for interpreting the content of control commands sent from an external host computer  150 . The command interpreter  104  then sends the interpreted results to the controllers, including the paper transportation controller  101 , printing controller  102 , and ASF controller  103 , according to the interpreted results. The controllers thus apply control according to the received control commands. 
     The main control unit  105  is a CPU, for example, which centrally controls communication between and operation of the paper transportation controller  101 , printing controller  102 , ASF controller  103 , command interpreter  104 , memory  106 , communication controller  107 , and status transmission unit  108  populating the control circuit board  35 . 
     Memory  106  is a data storage area for temporarily storing commands and print data sent from the host computer  150 . 
     The communication controller  107  is a control unit for controlling communication with the host computer  150  through the data communication terminal  17 . The communication controller  107  temporarily stores commands and data sent from the host computer  150  to memory  106  for use by the other controllers and command interpreter. 
     The status transmission unit  108  generates status signals denoting the status of the main printer unit  1 , and outputs the status signals to the host computer  150  through communication controller  107  and data communication terminal  17 . The host computer  150  can thus determine the current status of the main printer unit  1  from the received status signals. Based on the status signals generated by the status transmission unit  108 , status information could also be displayed on display unit  120  or printed out on paper. 
     The TOF sensor  33   a , BOF sensor  27   a , release lever sensor  36 , ASF connection/disconnection sensor  18   a , and roll paper holder connection sensor  38  respectively detect the presence of paper, whether the paper transportation path  5  is open or closed, and whether the ASF  60  and roll paper holder  40  are installed or not, and output corresponding detection signals to the control circuit board  35 . In this embodiment of the invention the TOF sensor  33   a  and BOF sensor  27   a  constitute a paper detection means, and ASF connection/disconnection sensor  18   a  and roll paper holder connection sensor  38  constitute an installation detection means. The detection signals output by the TOF sensor  33   a , BOF sensor  27   a , release lever sensor  36 , ASF connection/disconnection sensor  18   a , and roll paper holder connection sensor  38  are sent over bus  100  to the main control unit  105 . Based on these detection signals, the main control unit  105  controls the paper transportation controller  101 , printing controller  102 , and ASF controller  103 , for example. 
     The operating unit  110  of the main printer unit  1  is composed of the power switch  7 , cleaning button  8 , and paper feed button  9  disposed on cantilever unit front case  4   a . The display unit  120  of the main printer unit  1  consists of the power switch  7 , cleaning button  8 , and paper feed button  9  lighting steady or flashing as a result of the lamp member disposed behind the power switch  7 , cleaning button  8 , and paper feed button  9  lighting steady or flashing. The components of the operating unit  110  and display unit  120  are connected to the bus  100  of control circuit board  35 , thus enabling communication with the control circuit board  35 . 
     (Operational Control of the Inkjet Printer) 
     Controlling the operation of an inkjet printer according to this embodiment of the invention is described next with reference to  FIG. 12  to  FIG. 17 .  FIG. 12  is a flow chart describing the startup operation of the main printer unit  1 ,  FIG. 13  is a flow chart of the paper detection process A shown in  FIG. 12 ,  FIG. 14  is a flow chart of paper detection process B shown in  FIG. 12 , and  FIG. 15  to  FIG. 17  are state transition diagrams showing the internal status and state transitions of the main printer unit  1  when the roll paper holder  40  is installed, when the ASF  60  is installed, and when printing with manual paper insertion, respectively. 
     As shown in  FIG. 12 , when the power switch  7  of the main printer unit  1  turns on, the main printer unit  1  runs a specific startup process and gets ready for printing (step S 101 ). When the specific startup process ends, the main control unit  105  determines if the roll paper holder connection sensor  38  is on (step S 102 ). 
     If the roll paper holder connection sensor  38  is on, that is, if the roll paper holder  40  is installed to the main printer unit  1 , the main control unit  105  determines that roll paper will be used for printing and thus runs paper detection process A in step S 103 . However, if the roll paper holder connection sensor  38  is off, that is, the roll paper holder  40  is not installed to the main printer unit  1 , control goes to step S 104 . 
     In the paper detection process A run in step S 103 , the main control unit  105  first determines if BOF sensor  27   a  is on or off (step S 201 ) as shown in the flow chart in  FIG. 13 . If the BOF sensor  27   a  is on, that is, if paper is present at the position detected by the BOF lever  27  inside the paper transportation path  5 , the main paper transportation roller  23  is driven to index the paper in step S 202 , and paper detection process A ends. 
     The paper is indexed for printing by advancing the paper until the paper is detected by the TOF sensor  33   a , then conveying the paper a specified distance in the reverse direction so that the leading edge of the paper is located at a specified position. Note this procedure is always used when the paper is indexed in this embodiment of the invention. 
     If the BOF sensor  27   a  is off, that is, if paper is not present at the position detected by the BOF lever  27  in the paper transportation path  5 , control goes to step S 203  and the on/off state of the TOF sensor  33   a  is detected. 
     Furthermore, if the release lever sensor  36  detects that the paper transportation path  5  is open before paper detection process A is executed, the user could be prompted to close the paper transportation path  5  by, for example, causing the lamp members disposed behind the power switch  7 , cleaning button  8 , and paper feed button  9  and constituting the display unit  120  to flash. 
     Instead of causing these lamp members to flash, the status transmission unit  108  could alternatively generate a status signal indicating that the release lever is in the open position and send this status signal to the host computer  150  so that the host computer  150  displays a message such as “The release lever is open” on a display. 
     The main control unit  105  determines if the TOF sensor  33   a  is on or off in step S 203 . If the TOF sensor  33   a  is on, that is, if paper is present at the position detected by the TOF lever  33 , the paper inside the paper transportation path  5  is discharged from the front opening  5   a  in step S 204 , and the paper detection process ends. On the other hand, if TOF sensor  33   a  is off, that is paper is not located in the paper transportation path  5  at the position detected by the TOF lever  33 , the paper detection process A ends immediately. 
     As a result of executing this paper detection process A, paper is discharged if paper is present only at the position in the paper transportation path  5  detected by the TOF lever  33 , and the paper is indexed if the paper is only present at the position in the paper transportation path  5  detected by the BOF lever  27 . More specifically, if paper is located in the paper transportation path  5  at a position that is not useful for roll paper printing (specifically at a position detected only by the TOF sensor  33   a ), the paper will be discharged as a result of executing this paper detection process A. After paper detection process A ends, one of the states shown in the state transition diagram shown in  FIG. 15  is assumed.  FIG. 15  is described in further detail below. 
     Returning first to  FIG. 12 , the main control unit  105  determines if the ASF connection/disconnection sensor  18   a  is on in step S 104 . 
     If the ASF connection/disconnection sensor  18   a  is on, that is, if the ASF  60  is installed to the main printer unit  1 , paper detection process B is executed in step S 105 . If the ASF connection/disconnection sensor is off, that is, the ASF  60  is not installed to the main printer unit  1 , manual paper insertion will be used for printing and paper detection process B is executed in step S 106 . 
     In the paper detection process B executed in step S 1105 , the main control unit  105  first determines if the BOF sensor  27   a  is on or off (step S 301 ) as shown in the flow chart in  FIG. 14 . If the BOF sensor  27   a  is on, that is, paper is present at the position detected by the BOF lever  27 , the main paper transportation roller  23  is driven and the paper in the paper transportation path  5  is discharged from the front opening  5   a  in step S 303 . 
     If the BOF sensor  27   a  is off, that is, paper is not present at the position detected by the BOF lever  27 , whether the TOF sensor  33   a  is on or off is detected in step S 302 . 
     Furthermore, if the release lever sensor  36  detects that the paper transportation path  5  is open before paper detection process B is executed, the user could be prompted to close the paper transportation path  5  by, for example, causing the lamp members disposed behind the power switch  7 , cleaning button  8 , and paper feed button  9  and constituting the display unit  120  to flash. 
     Instead of causing these lamp members to flash, the status transmission unit  108  could alternatively generate a status signal indicating that the release lever is in the open position and send this status signal to the host computer  150  so that the host computer  150  displays a message such as “The release lever is open” on a display. 
     The main control unit  105  detects if the TOF sensor  33   a  is on or off in step S 302 . If the TOF sensor  33   a  is on, that is, if paper is present at the position detected by the TOF lever  33 , the paper inside the paper transportation path  5  is discharged from the front opening  5   a  in step S 303 , and the paper detection process B ends. On the other hand, if TOF sensor  33   a  is off, that is paper is not located in the paper transportation path  5  at the position detected by the TOF lever  33 , the paper detection process B ends immediately. 
     Paper present in the paper transportation path  5  at the position detected by the TOF lever  33  or BOF lever  27  is thus discharged as a result of executing this paper detection process B. More specifically, if paper is present in the paper transportation path  5  (and is positioned where the paper is detected by at least one of the TOF sensor  33   a  and BOF sensor  27   a ) before slip printing starts, the paper is discharged as a result of executing paper detection process B. After paper detection process B ends, one of the states shown in the state transition diagram shown in  FIG. 15  is assumed.  FIG. 15  is described in further detail below. 
     Returning again to the flow chart in  FIG. 12 , whether a manual paper insertion command was asserted by the user is detected in step S 107  after the paper detection process is completed in step S 105 . This manual insertion command can be asserted by operating the operating unit  110  or by a print command from the host computer  150 . If the operating unit  110  is used to control printing with manual paper insertion, a manual printing command could be asserted by, for example, holding the paper feed button depressed for an extended time. 
     Alternatively, a DIP switch or memory switch could be provided in the main printer unit  1  and said switch could be operated to control manual insertion printing. 
     If a manual insertion command is detected, printing is to proceed with manually inserted paper even though the ASF  60  is installed, and one of the states shown in the state transition diagram in  FIG. 17  is assumed. If a manual insertion command is not detected, printing is to proceed using the ASF  60 , and one of the states shown in the state transition diagram in  FIG. 16  is assumed.  FIG. 16  and  FIG. 17  are further described below. 
     Paper detection process B is executed in step S 106  in  FIG. 12  in the same way as in step S 105  according to the flow chart shown in  FIG. 14 . After paper detection process B ends, one of the states shown in the state transition diagram shown in  FIG. 17  is assumed. 
     As described above, an inkjet printer according to this embodiment of the invention changes the paper detection process and prepares for printing to paper according to whether a roll paper holder is installed, an ASF is installed, or neither is installed. 
     (State Transitions During Roll Paper Printing) 
     State transitions during roll paper printing are described below with reference to the state transition diagram shown in  FIG. 15 . The states of the main printer unit  1  during roll paper printing include a “release-lever-closed, no-paper state”  210 , a “release-lever-closed, paper-waiting state”  220 , a “release-lever-open state”  230 , a “page_break command wait state”  240 , a “release-lever-open, paper-waiting state”  250 , and a “printing enabled state”  260 . These states are grouped according to the state of the release lever, the presence of roll paper in the paper transportation path, and the presence of a page break command. The states shown in the state transition diagram in  FIG. 15 , the state transition conditions, and the destination state are described first below. 
     The release-lever-closed, no-paper state  210  is the state in which the release lever  15  is closed, roll paper. CS is not present in the paper transportation path  5 , and a page break command, which is a print command, has not been received from the host computer  150 . If when in this release-lever-closed, no-paper state  210  the release lever  15  is operated so that the release lever  15  changes to the open position, there is a transition to the release-lever-open state  230 . However, if a page break command is received from the host computer  150  while in the release-lever-closed, no-paper state  210 , there is a transition to the release-lever-closed, paper-waiting state  220 . 
     The release-lever-closed, paper-waiting state  220  is the state in which the release lever  15  is closed, roll paper CS is not present in the paper transportation path  5 , and a page break command has been received from the host computer  150 . Roll paper CS must be inserted for printing when in this release-lever-closed, paper-waiting state  220 . When the release lever  15  is opened to insert the roll paper CS, there is a transition to the release-lever-open, paper-waiting state  250 . 
     In the release-lever-open state  230  the release lever  15  is open, roll paper CS is not present in the paper transportation path  5 , and a page break command has not been received from the host computer  150 . That is, because the release lever  15  is open in this release-lever-open state  230 , the roll paper CS is not located in the paper transportation path  5 , and the page break command that is the print command has not been received. 
     If roll paper CS is inserted to the paper transportation path  5 , the release lever sensor  36  confirms that the release lever  15  is in the closed state because the release lever  15  was closed, and TOF sensor  33   a  and BOF sensor  27   a  turn on and thus detect the roll paper CS when in the release-lever-open state  230 , there is a transition to the page_break command wait state  240 . If a page break command is received in the release-lever-open state  230 , there is a transition to the release-lever-open, paper-waiting state  250 . 
     If the release lever  15  is closed without roll paper CS being inserted when in the release-lever-open state  230 , the release lever sensor  36  confirms that the release lever  15  is closed, both TOF sensor  33   a  and BOF sensor  27   a  turn off, and there is a transition to the release-lever-closed, no-paper state  210 . 
     In the page_break command wait state  240  the release lever  15  is closed, roll paper CS is present in the paper transportation path  5 , and a page break command has not been received from the host computer  150 . The page break command asserted as a print command has thus not been received but the roll paper CS has been indexed for printing in the paper transportation path  5  when in the page_break command wait state  240 . If a page break command is then received from the host computer  150  when in this page_break command wait state  240 , there is a transition to the printing enabled state  260 . If the release lever  15  is operated so that the release lever  15  is opened when in the page_break command wait state  240 , there is a transition to the release-lever-open state  230 . 
     In the release-lever-open, paper-waiting state  250  the release lever  15  is open, roll paper CS is not present in the paper transportation path  5 , and the page break command has been received from the host computer  150 . Because the page break command is received when in the release-lever-open, paper-waiting state  250 , printing is enabled once the roll paper CS is inserted to the paper transportation path  5 . 
     If roll paper CS is loaded into the paper transportation path  5 , the release lever  15  is closed and the release lever sensor  36  thus recognizes that the release lever  15  is closed, and the TOF sensor  33   a  and BOF sensor  27   a  detect the roll paper CS and thus turn on when in the release-lever-open, paper-waiting state  250 , the roll paper CS is indexed and there is a transition to the printing enabled state  260 . 
     If the release lever  15  is closed without roll paper CS being inserted when in the release-lever-open, paper-waiting state  250 , the release lever sensor  36  confirms that the release lever  15  is closed, TOF sensor  33   a  and BOF sensor  27   a  both turn off, and there is a transition to the release-lever-closed, paper-waiting state  220 . 
     In the printing enabled state  260  the release lever  15  is closed, roll paper CS is indexed for printing in the paper transportation path  5 , and a page break command has been received from the host computer  150 . When the image data to be printed according to the page break command is received from the host computer  150  in this printing enabled state  260 , printing commences immediately. 
     If the roll paper holder  40  is installed to the main printer unit  1  the printable area after a page break command is received when in the printing enabled state  260  is the entire length of the paper roll. As a result, there is no state change, or more specifically there is a recursive transition returning to the printing enabled state  260 , when the image data for one print command is printed and a printing termination command or page break command is received. 
     Furthermore, if the release lever  15  is operated in the printing enabled state  260  so that the release lever  15  opens, printing is interrupted while printing is in progress, and there is a transition to the release-lever-open state  230 . Image data relating to the page break command processed before the release lever  15  opened is destroyed in this state transition. More specifically, the image data being printed is immediately killed without being printed as soon as the release lever  15  is opened. However, page break commands that have been received but not processed at that time and related image data are stored to memory  106  and thus not lost, and there is a transition from the release-lever-open state  230  to the release-lever-open, paper-waiting state  250 . 
     If the roll paper CS is printed to the end of the roll and the roll paper is completely discharged, BOF sensor  27   a  turns off and the release-lever-closed, no-paper state  210  is entered. If there is any image data relating to page break commands processed before the BOF sensor  27   a  turned off, that image data is lost during this state transition. In other words, any image data that was in the process of being printed when the BOF sensor  27   a  turns off is deleted without being printed. However, any page break commands that have been received but not yet processed when the BOF sensor  27   a  turns off and the related image data are written to memory  106 , and there is a state transition from the release-lever-closed, no-paper state  210  to the release-lever-closed, paper-waiting state  220 . 
     In the process continuing from the flow shown in the flow chart in  FIG. 12 , operation starts from the page_break command wait state  240  if the roll paper CS is indexed inside the paper transportation path  5 . If the roll paper CS has not been indexed in the paper transportation path  5  after completing the process shown in  FIG. 12 , operation starts from the release-lever-closed, no-paper state  210 . A transition from these states to the printing enabled state  260  is then triggered by appropriately loading roll paper and sending a page break command to the main printer unit  1 , and image data received in the printing enabled state  260  is then printed. 
     The roll paper CS is described above as being indexed when both the TOF sensor  33   a  and BOF sensor  27   a  turn on while the release lever  15  is closed. The invention shall not be so limited, however. For example, the BOF sensor  27   a  turning on could cause the paper to be advanced in the paper transportation direction until the paper is sensed by the TOF sensor  33   a , and the paper could then be indexed. 
     (State Transitions During Slip Printing Using the ASF  60 ) 
     State transitions during slip printing using the ASF  60  are described next with reference to the state transition diagram shown in  FIG. 16 . 
     The states of the main printer unit  1  during slip printing using the ASF  60  include a “release-lever-open state I”  310 , a “release-lever-closed state II”  320 , “paper-wait state”  330 , “page-break-command wait state”  340 , and “printing enabled state”  350 . These states are grouped according to the state of the release lever and the presence of a page break command. During slip printing using the ASF  60  paper is only supplied after a page break command is received and the printing enabled state  350  is entered. The states of the main printer unit  1  and the state transition conditions are thus slightly different from when roll paper is used for printing. 
     In release-lever-open state I  310  the release lever  15  is open and a page break command has not been received. If the release lever  15  is operated in this state so that the release lever  15  closes, paper detection process B shown in  FIG. 14  is executed to discharge the unneeded paper from the paper transportation path  5 , and there is a transition to the page —break-command wait state  340 . If a page break command is received from the host computer  150  while in release-lever-open state I  310 , there is a transition to the release-lever-closed state II  320 . 
     In release-lever-closed state II  320  the release lever  15  is open and the page break command was received. If the release lever  15  is operated so that the release lever  15  is closed in this state, paper detection process B shown in  FIG. 14  is executed to discharged unnecessary paper from the paper transportation path  5 , and a slip S is then supplied from the ASF  60  to the paper transportation path  5 . 
     If the BOF sensor  27   a  turns on within a specified time after paper feeding starts, that is, if the BOF sensor  27   a  confirms that a slip S was fed into the paper transportation path  5 , the slip S is indexed and the printing enabled state  350  is entered. 
     If the BOF sensor  27   a  remains off after a specified time after paper feeding starts, supplying a slip S into the paper transportation path  5  is determined to have failed and there is a transition to the paper-wait state  330 . 
     In the paper-wait state  330  the release lever  15  is closed, a page break command was received, but supplying a slip S failed. Supplying a slip S again is not automatically attempted in the paper-wait state  330 . Instead, paper feeding is tried again when the paper feed button  9  turns on as a result of the user pressing the paper feed button  9  on the operating unit  110 . 
     If the BOF sensor  27   a  turns on within a specified time after the paper feeding operation resumes, that is, if it is confirmed that a slip S was supplied into the paper transportation path  5 , the slip S is indexed and there is a transition to the printing enabled state  350 . 
     However, if the BOF sensor  27   a  remains off after a specified time after paper feeding starts, supplying a slip S into the paper transportation path  5  is determined to have failed again and there is a recursive transition to the paper-wait state  330 . 
     In the page-break-command wait state  340  the release lever  15  is closed and the page break command has not been received. Supplying a slip S from the ASF  60  starts when a page break command is received in this state. 
     If the BOF sensor  27   a  turns on within a specified time after the paper feeding operation resumes, that is, if it is confirmed that a slip S was supplied into the paper transportation path  5 , the slip S is indexed and there is a transition to the printing enabled state  350 . 
     If the BOF sensor  27   a  remains off after a specified time after paper feeding starts, supplying a slip S into the paper transportation path  5  is determined to have failed and there is a transition to the paper-wait state  330 . 
     In the printing enabled state  350  the release lever  15  is closed, a slip S has been indexed in the paper transportation path  5 , and a page break command has been received from the host computer  150 . When the image data to be printed for the received page break command is then received from the host computer  150  in this state, printing commences immediately. 
     If a printing termination command is received from the host computer  150  in this printing enabled state  350 , or if the BOF sensor  27   a  turns off because printing one page ends and the slip S is discharged, there is a transition to the page-break-command wait state  340 . 
     However, if the release lever  15  is operated in the printing enabled state  350  so that the release lever  15  opens, printing is interrupted even in the middle of the printing process, and there is a transition to release-lever-open state I  310 . Image data relating to page break commands processed before the release lever  15  was opened is destroyed by this state transition. That is, image data being printed when the release lever  15  is opened is deleted without being printed. However, any page break commands and corresponding image data that has already been received but not yet processed is saved to memory  106  instead of being deleted, and there is a transition from release-lever-open state I  310  to release-lever-closed state II  320 . 
     The process following the flow shown by the flow chart in  FIG. 12  starts from the page-break-command wait state  340 . When a page break command is received in the page-break-command wait state  340 , there is a transition to the printing enabled state  350 . When image data is then received in the printing enabled state  350 , printing commences immediately. 
     (State Transitions During Manual Printing) 
     The state transitions during printing with manual paper insertion are described next with reference to the state transition diagram in  FIG. 17 . 
     The states of the main printer unit  1  during manual printing include a release-lever-closed, no-paper state  210 , release-lever-closed, paper-waiting state  220 , release-lever-open state  230 , page_break command wait state  240 , release-lever-open, paper-waiting state  250 , and printing enabled state  260 . 
     These states are grouped according to the state of the release lever, the presence of roll paper in the paper transportation path, and the presence of a page break command. The release-lever-closed, no-paper state  210 , release-lever-closed, paper-waiting state  220 , release-lever-open state  230 , page_break command wait state  240 , and release-lever-open, paper-waiting state  250  and the related state transition conditions differ only according to whether the paper inserted to the paper transportation path  5  is roll paper or manually inserted paper, and these states are identical to the roll paper printing states shown in  FIG. 15  and identified by the same reference numerals. 
     The only differences between manual printing and roll paper printing are the state transition conditions from the printing enabled state  260 . 
     In the printing enabled state  260  the release lever  15  is closed, manually inserted paper is indexed to the desired position in the paper transportation path  5 , and a page break command has been received from the host computer  150 . Printing commences immediately in this state when image data to be printed for the page break command is received from the host computer  150 . 
     Unlike during roll paper printing, in the printing enabled state  260  during manual printing the printable area corresponding to the page break command is limited to the manually inserted slip. As a result, there is a transition to the page_break command wait state  240  when the BOF sensor  27   a  turns off because printing some image data ends and a print termination command is received from the host computer  150 , or printing one page ends and the manually inserted page is discharged. 
     If the release lever  15  is operated in this printing enabled state  260  so that the release lever  15  is opened, printing in any printing process in progress is interrupted and there is a transition to the release-lever-open state  230 . Image data relating to page break commands processed before the release lever  15  was opened is destroyed by this state transition. That is, image data being printed when the release lever  15  is opened is deleted without being printed. However, any page break commands and corresponding image data that has already been received but not yet processed is saved to memory  106  instead of being deleted, and there is a transition from release-lever-open state  230  to release-lever-open, paper-waiting state  250 . 
     If the manually inserted paper is printed to the end of the slip and the manually inserted paper is completely discharged in the printing enabled state  260 , BOF sensor  27   a  turns off and the release-lever-closed, no-paper state  210  is entered. If there is any image data relating to page break commands processed before the BOF sensor  27   a  turned off, that image data is lost during this state transition. That is, if the end of the page is reached before printing ends, the unprinted image data left in that printing process is deleted without being printed. However, any page break commands that have been received but not yet processed when the BOF sensor  27   a  turns off and the related image data are written to memory  106 , and there is a state transition from the release-lever-closed, no-paper state  210  to the release-lever-closed, paper-waiting state  220 . 
     In the process continuing from the flow shown in the flow chart in  FIG. 12 , operation starts from the release-lever-closed, no-paper state  210 . A transition from this state to the printing enabled state  260  is then triggered by manually inserting paper and sending a page break command to the main printer unit  1 , and image data received in the printing enabled state  260  is then printed. 
     In summary, an inkjet printer according to this embodiment of the invention as described above has a main printer unit  1  which has a image recording unit  3 , which has a carriage  25  on which an ink head for discharging ink to paper and a guide shaft  26  for slidably guiding the carriage  25 , and a base unit  2 , which is disposed opposite the image recording unit  3  and supports the image recording unit  3 . A paper transportation path  5  is rendered between the image recording unit  3  and base unit  2 . A roll paper holder  40  for supplying roll paper CS as the print medium to the paper transportation path  5  can be removably installed to the main printer unit  1 , and an ASF  60  for continuously supplying a plurality of single sheets as the recording medium to the paper transportation path  5  can be removably installed to the main printer unit  1 . 
     Because the roll paper holder  40  and ASF  60  can thus be installed to and removed from the main printer unit  1 , the arrangement of the inkjet printer can be changed according to the printing application to enable printing to manually fed paper, slip printing, and roll paper printing. 
     This main printer unit  1  also has an ASF connection/disconnection sensor  18   a  as a sheet feeding device detector for determining if the ASF  60  is installed to the main printer unit  1 ; a roll paper holder connection sensor  38  as a roll paper holder detector for determining if the roll paper holder  40  is installed to the main printer unit  1 ; and a control circuit board  35  for controlling operation of the main printer unit  1  according to the detection status of the ASF connection/disconnection sensor  18   a  and roll paper holder connection sensor  38 . 
     In an inkjet printer according to this embodiment of the invention the control circuit board  35  controls operation of the main printer unit  1  according to the detection status of the ASF connection/disconnection sensor  18   a  and roll paper holder connection sensor  38 . More specifically, operation of the main printer unit  1  is controlled according to the printing pattern, which varies according to whether the roll paper holder  40  is installed to the main printer unit  1 , the ASF  60  is installed to the main printer unit  1 , or paper is manually inserted for printing. 
     An inkjet printer according to this embodiment of the invention thus easily enables various printing operations with minimal user intervention required. Without being greatly aware of the differences in roll paper printing, slip printing, and manual printing, the user can thus load the desired paper and send print commands from the host computer  150  to easily accomplish the desired printing task. 
     The main printer unit  1  in this embodiment of the invention yet further preferably also has a TOF sensor  33   a  as a top of form detector for detecting the leading end of the paper in the paper transportation path  5 , a BOF sensor  27   a  as a bottom of form detector for detecting the trailing end of the paper in the paper transportation path  5 , and a release lever sensor  36  as a paper detector for detecting whether the paper transportation path  5  is open or closed. The inkjet printer according to this embodiment of the invention controls operation of the main printer unit  1  according to the detection status of the TOF sensor  33   a , BOF sensor  27   a , and release lever sensor  36 . 
     More specifically, an inkjet printer according to this embodiment of the invention prints only when the TOF sensor  33   a , BOF sensor  27   a , and release lever sensor  36  are on and a page break command has been supplied. Meaningless printing operations are thus not executed when printing is not possible, and an inkjet printer that is easy to use can be provided. 
     Furthermore, if the release lever sensor  36  determines that the paper transportation path  5  is closed and the TOF sensor  33   a  and BOF sensor  27   a  each detect paper when the roll paper holder  40  is installed, the control circuit board  35  determines that printing to paper is possible and thus prints the received image data. Meaningless printing operations are thus not executed when printing is not possible, and an inkjet printer that is easy to use can be provided. 
     Furthermore, if the release lever sensor  36  determines that the paper transportation path  5  is closed when the ASF  60  is installed to the main printer unit  1  and either the TOF sensor  33   a  or BOF sensor  27   a  detects paper, the detected paper is discharged. Because paper in the paper transportation path  5  is automatically discharged if paper is already in the paper transportation path  5  before the ASF  60  supplies a slip S, the inkjet printer can prevent problems such as incomplete printing on the paper without the user needing to bother with removing the paper. 
     Furthermore, if the release lever sensor  36  determines that the paper transportation path  5  is closed and the TOF sensor  33   a  and BOF sensor  27   a  both detect paper during manual printing when neither the roll paper holder  40  or the ASF  60  is installed to the main printer unit  1 , image recording on the paper is determined possible, and printing proceeds according to the received image data. Meaningless printing operations are thus not executed when printing is not possible, and an inkjet printer that is easy to use can be provided. 
     An inkjet printer according to this embodiment of the invention also has a side opening  5   c  enabling inserting paper to the paper transportation path  5  from a direction substantially perpendicular to the paper transportation direction rendered between the image recording unit  3  and base unit  2 . More specifically, the side opening  5   c  is provided by securing the image recording unit  3  cantilevered from one end of the base unit  2  on an intervening cantilever unit  4 . 
     An inkjet printer according to this embodiment of the invention thus easily enables manually supplying paper through the side opening  5   c  into the paper transportation path  5 . Furthermore, because paper can be supplied from the side (a direction substantially perpendicular to the paper transportation path), there is no limit to the size of paper and paper can be manually supplied to the paper transportation path  5  regardless of the shape of the paper. It is therefore possible to supply only one page of an already bound volume such as a book or notebook into the paper transportation path  5 , and special printing applications such as printing images on individual pages of a bound volume are possible. 
     The roll paper holder  40  is attached to the base unit  2  of the main printer unit  1  and the ASF  60  is attached to the image recording unit of the main printer unit  1  in an inkjet printer according to this embodiment of the invention, but the invention shall not be so limited and could be arranged so that the roll paper holder  40  is attached to the image recording unit  3  using slots  19   a , for example. 
     Furthermore, the manual insertion prevention tab  50  could be disposed projecting in front of the side opening  5   c  in order to obtrude the side opening  5   c . The guide wall  41   b  could also be shaped so that it extends and obtrudes the side opening  5   c . Manually supplying paper can be structurally prohibited by means of these variations. 
     The present invention has been described using an inkjet printer by way of example above, but a printer according to the present invention shall not be limited to an inkjet printer and the present invention can be applied to other types of printers, including thermal and dot impact printers. 
     INDUSTRIAL APPLICABILITY 
     The control unit of a printer according to the present invention controls the main printer unit according to the detection status of a sheet feeding device detector and a roll paper supply device detector. More specifically, operation of the main printer unit is controlled according to a printing pattern which varies according to whether a roll paper holder is installed to the main printer unit, a sheet feeding device is installed to the main printer unit, or manual feed printing is selected. 
     Therefore, a printer according to the present invention easily enables various printing operations with minimal user intervention. Without being greatly aware of the differences in roll paper printing, slip printing, and manual printing, the user can thus load the desired paper and send print commands from an external host to easily accomplish the desired printing task.