Patent Publication Number: US-7914216-B2

Title: Printer and method of interrupting printing operation in continuous transport process

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a printer and a method of interrupting a printing operation in a continuous transport process. 
     2. Related Art 
     Printers having an LD (Load) roller for supplying a printing medium into the printers and a PF (Paper Feed) roller for transporting the printing medium supplied into the printers are known as ink jet printers for performing a printing operation on a printing medium such as a sheet of regular paper (for example, see JP-A-2002-284373 and JP-A-2002-284374). 
     Specifically, in the printer described in JP-A-2002-284373 or JP-A-2002-284374, it is possible to continuously feed plural printing sheets by the use of the LD roller with a hopper kept in a raised state. When the plural printing sheets are continuously fed, a feed gap of the printing mediums is shortened, thereby enhancing the number of printing sheets which can be subjected to the printing operation per unit time. 
     In the printer described in JP-A-2002-284373 or JP-A-2002-284374, the hopper is kept in the raised state. In this state, by continuously feeding the plural printing mediums on the feed tray to the printing area, it is possible to enhance the number of printing mediums that can be fed per unit time, in comparison with the case where the plural printing mediums on the feed tray are individually transported. 
     However, when the operation of continuously feeding the plural printing mediums is carried out, the printer cannot interrupt the printing operation in the way. In the related printer for individually transporting the printing mediums for print, the sheet under print is discharged at the time of interrupting the printing operation. Such a print interrupting process of the related printer cannot be applied to printers for continuously feeding plural printing mediums without any change. After the printing operation is interrupted, the hopper is maintained in the raised state. Accordingly, the printer cannot start a next printing operation. As a result, in the printer for continuously feeding the plural printing mediums, all the printing mediums corresponding to the expected number of sheets are discharged without stopping the printing operation and then it is necessary to wait until the LD follower roller is separated from the LD roller. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide a printer which can continuously transport printing mediums by maintaining a state where an upstream follower roller comes in contact with an upstream driving roller and can interrupt a printing operation in the continuous transport process and a method of interrupting a printing operation in a continuous transport process. 
     According to an aspect of the invention, there is provided a method of interrupting a printing operation in a continuous transport process in which a first roller and a second roller transports plural printing mediums including a first medium on a tray in a transport direction to a printing area at which the printing operation is performed to each printing medium, the second roller is arranged at a downstream side of the first roller in the transport direction, and a third roller comes in contact with the first roller at a contact point to transport the printing mediums together with the first roller and is separated from the first roller not to transport the printing mediums, the method comprising: 
     separating the third roller from the first roller, when a trailing end edge of the first medium at least a part of which is disposed in the printing area is located at an upstream side of a predetermined point in the transport direction, wherein the predetermined point is arranged at a downstream side of the contact point in the transport direction, and 
     driving the second roller to transport the first medium after the third roller is separated from the first roller. 
     The present disclosure relates to the subject matter contained in Japanese patent application No. 2006-267606 filed on Sep. 29, 2006, which is expressly incorporated herein by reference in its entirety. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a side view of an ink jet printer according to an embodiment of the invention. 
         FIG. 2  is a block diagram illustrating a control system of the ink jet printer shown in  FIG. 1 . 
         FIG. 3  is a diagram illustrating a data structure of continuous-printing print data in the embodiment. 
         FIG. 4  is a flowchart illustrating a flow of processes that are performed by a feed process instructing section shown in  FIG. 2  in a continuous print mode. 
         FIG. 5  is a flowchart illustrating a flow of processes that are performed by a paper feeding process instructing section shown in  FIG. 2  in the continuous print mode. 
         FIG. 6  is a flowchart illustrating a flow of processes that are performed by a discharge process instructing section shown in  FIG. 2  in the continuous print mode. 
         FIG. 7  is a flowchart illustrating a flow of processes that are performed by a process judgment section shown in  FIG. 2  in the continuous print mode. 
         FIG. 8  is a diagram illustrating a feature comparison table of a synchronization (tracing) control and a simultaneous drive control. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, a printer and a method of interrupting a printing operation in a continuous transport mode according to exemplary embodiments of the invention will be described with reference to the accompanying drawings. An ink jet printer is described as an example of the printer. The method of interrupting a printing operation in a continuous transport mode is described as a part of an operation of the ink jet printer. 
       FIG. 1  is a side view illustrating a part of a mechanism structure of an ink jet printer according to an embodiment of the invention. 
     An ink jet printer  1  has a rear feed tray  2  and a front feed tray  3  as a feed tray. The rear feed tray  2  is disposed to protrude upward from a back portion of the ink jet printer  1 . The front feed tray  3  is disposed to be substantially parallel to a bottom portion of the ink jet printer  1 . The rear feed tray  2  and the front feed tray  3  can receive a variety of printing mediums such as sheets of regular paper, glossy paper, photo paper, postcard paper, and L-size photo paper. 
     The printing mediums P placed on the rear feed tray  2  and the front feed tray  3  are transported along a predetermined printing-medium transport path and are discharged to a discharge tray (not shown) disposed on the front side of the ink jet printer  1 . In  FIG. 1 , a rear printing-medium transport path  4  as the printing-medium transport path is indicated by a dot-dashed line. A guide member  5  regulating the transport direction of the printing mediums P or a platen  6  is disposed along the rear printing-medium transport path  4 . 
     The ink jet printer  1  includes mechanism members for transporting the printing mediums P placed on the rear feed tray  2 , such as a load (LD) roller  11 , an LD follower roller  12 , a hopper  13 , a paper feed (PF) roller  14 , a PF follower roller  15 , a discharge roller  16 , and a discharge follower roller  17 . The ink jet printer  1  further includes a mechanism member for transporting the printing mediums P placed on the front feed tray  3 , such as a second LD roller  18 . 
     The LD roller  11  is disposed to be rotatable adjacent to the lower edge of the rear feed tray  2 . The LD roller  11  includes a roller shaft  11   a  having an axis perpendicular to the paper plane of  FIG. 1  and a rubber member  11   b  provided around the roller shaft. The LD roller  11  is formed in a substantially cylindrical shape. The LD roller  11  rotates with the actuation of an auto sheet feeder (ASF) motor  32  to be described later. 
     The LD follower roller  12  has a cylindrical shape having a width substantially equal to that of the LD roller  11  and is rotatably disposed below the LD roller  11 . The LD follower roller  12  moves to be contacted with and separated from the LD roller  11  with the actuation of an ASF sub motor  33  to be described later. The LD roller  11  and the LD follower roller  12  come in contact with each other in the vicinity of the lower edge of the rear feed tray  2 . The LD roller  11  and the LD follower roller  12  come in pressing contact with each other with a predetermined pressing force. 
     The hopper  13  is disposed so that the lower portion of the rear feed tray  2  is pivotable. The hopper  13  changes its posture to come close to the LD roller  11  when the LD follower roller  12  comes in pressing contact with the LD roller  11 , and changes its posture to be separated from the LD roller  11  when the LD follower roller  12  is separated from the LD roller  11 . When printing mediums P are placed on the rear feed tray  2 , the lower end of the uppermost printing medium P comes in contact with the LD roller  11  by allowing the hopper  13  to come close to the LD roller  11 . The uppermost printing medium P on the rear feed tray  2  is nipped between the hopper  13  and the LD roller  11 . 
     The PF roller  14  is disposed below the rear printing-medium transport path  4  between the guide member  5  and the platen  6 . The PF roller  14  is formed in a cylinder shape out of a metal material and is disposed to be rotatable in a state where the axis direction of the cylinder is substantially perpendicular to the paper plane of  FIG. 1 . Slide-preventing ceramic particles are fixed to the outer peripheral surface of the metal rod so as to form micro unevenness on the outer peripheral surface. The PF roller  14  rotates with the actuation of the PF motor  31  to be described later. 
     The PF follower roller  15  has a cylinder shape having a width substantially equal to that of the PF roller  14  and is rotatably disposed above the PF roller  14 . The PF follower roller  15  is held by a PF-follower-roller arm  19 . An urging force which is downward in  FIG. 1  acts on the PF-follower-roller arm  19  by a spring not shown. Accordingly, the PF follower roller  15  comes in pressing contact with the PF roller  14  with a large pressing force. 
     Accordingly, the transport capability (the total transport capability including a holding force) of the printing medium P by the PF roller  14  and the PF follower roller  15  which are in contact with each other is higher than the transport capability of the printing medium P by the LD roller  11  and the LD follower roller  12  which are in contact with each other. Accordingly, when a sheet of printing medium P is nipped between the PF roller  14  and the PF follower roller  15  and is also nipped between the LD roller  11  and the LD follower roller  12 , the transport distance of the printing medium P is under a transport control using the PF roller  14  and the PF follower roller  15 . 
     The discharge roller  16  is rotatably disposed below the rear printing-medium transport path  4  between the platen  6  and a discharge tray not shown. The discharge roller  16  rotates with the actuation of the PF motor  31  to be described later. 
     The discharge follower roller  17  is rotatably disposed above the discharge roller  16 . The discharge follower roller  17  comes in pressing contact with the discharge roller  16  with a small pressing force. 
     The ink jet printer  1  has a printing mechanism for ejecting ink to the printing medium P to perform a printing operation, such as a carriage  21 , in addition to the above-mentioned transport mechanism of the printing mediums P. 
     The carriage  21  is disposed above the platen  6  so as to be movable in a direction perpendicular to the paper plane of  FIG. 1 . For example, an ink tank not shown and the like are disposed inside the carriage  21 . The carriage  21  moves in the direction perpendicular to the paper plane of  FIG. 1  with the actuation of a carriage (CR) motor not shown. 
     A print head  22  is disposed on the bottom of the carriage  21  so as to be opposed to the platen  6 . The print head  22  has plural ink ejection nozzles  23 . The plural ink ejection nozzles  23  are supplied with the ink from the ink tank. The plural ink ejection nozzles  23  are arranged, for example, in the transport direction of the printing medium P. A piezoelectric element not shown is disposed in each ink ejection nozzle  23 . The piezoelectric element is deformed with the applied voltage. When each piezoelectric element is deformed, the amount of ink corresponding to the deformation is extruded from the corresponding ink ejection nozzle  23  and is ejected from the corresponding ink ejection nozzle  23 . The ink ejected from the plural ink ejection nozzles  23  is adhered to a portion of the printing medium P between the platen  6  and the print head  22 . 
     By applying voltages of waveforms corresponding to print data to the plural piezoelectric elements while moving the carriage  21  in the direction perpendicular to the paper plane of  FIG. 1 , it is possible to adhere the ink to the portion of the printing medium P between the platen  6  and the print head  22  on the basis of the print data. By repeatedly performing the printing process and the paper feeding process of feeding the printing medium P by a predetermined distance, the ink jet printer  1  can print an image based on the print data on the printing medium P. 
       FIG. 2  is a block diagram illustrating a partial configuration of a control system of the ink jet printer  1  shown in  FIG. 1 . The rear printing-medium transport path  4  and various mechanism members disposed along the path are schematically illustrated in the upper portion of  FIG. 2 . As a control reference position, an inter-page control start position, a feed standby position, and a print start position are set in the rear printing-medium transport path  4 . 
     The ink jet printer  1  has a restoring arm  20  as an arm member. The restoring arm  20  is disposed coaxially with the LD follower roller  12  so as to be rotatable. As generally shown in  FIGS. 1 and 2 , the restoring arm  20  is positioned at a position retreating from the transport path of the printing mediums P. During a control operation that the LD follower roller  12  separated from the LD roller  11  moves to a predetermined retreating position, the restoring arm  20  moves to a restoration position in a direction opposite to the transport direction of the printing mediums P around the LD follower roller  12  and then goes back to the original retreating position. As can seen from  FIGS. 1 and 2 , the restoring arm  20  moves to the vicinity of the rear feed tray  2  (or hopper  13 ) to right from the shown retreating position and then returns to the shown retreating position. When the restoring arm  20  reciprocates once, the printing medium P of which the leading end edge is nipped between the LD roller  11  and the LD follower roller  12  is hooked by the reciprocating restoring arm  20  and is pushed back to the rear feed tray  2 . 
     The inter-page control start position is set in the transport path of the printing mediums P between the LD roller  11  and the PF roller  14 . The inter-page control start position is set within the range in which the printing medium P can be restored to the rear feed tray  2  by the restoring arm  20 . The inter-page control start position is a reference position for executing a control for setting a predetermined inter-page gap length (predetermined inter-sheet distance) between two printing mediums P continuously transported when the plural printing mediums P placed on the rear feed tray  2  are continuously transported. The printing medium P subsequently transported is stopped when its leading end edge reaches the inter-page control start position. When the trailing end edge of the printing medium P previously transported is spaced apart by a predetermined inter-page gap length from the inter-page control start position, the transport of the printing medium P subsequently transported is resumed. By executing such an inter-page control, it is possible to set the inter-page gap length between the plural printing mediums P continuously transported. 
     The feed standby position is a target stop position of the leading end edge of the printing medium P in a usual feed process. The feed standby position is set to a position separated downstream by a predetermined distance (for example, 3 to 5 mm) from the most upstream nozzle (close to the rear feed tray  2 ) in the transport direction of the printing mediums P among the plural ink ejection nozzles  23  formed in the print head  22 . 
     The print start position is a target stop position of the leading end edge of the printing medium P at the time of starting a printing operation on the printing medium P. The print start position is set to a position separated upstream by a predetermined distance (for example, 3 to 5 mm) from the most downstream nozzle (close to the discharge tray) in the transport direction of the printing mediums P among the plural ink ejection nozzles  23  formed in the print head  22 . 
     In this way, by providing the feed standby position more upstream in the transport direction of the printing mediums P than the print start position, the printing medium P is temporarily stopped at the feed standby position and then is fed to the print start position in the usual feed process. Accordingly, compared with the case where the printing medium P is transported at a time from the rear feed tray  2  to the print start position by means of one time of control, it is possible to enhance the precision of the stop position of the printing medium P relative to the print start position. 
     In the following description, it is assumed that a range from the rear feed tray  2  to the inter-page control start position is referred to as area A, a range from the inter-page control start position to a position separated downstream by the inter-page gap length therefrom is referred to as area B, and a range from the position separated by the inter-page gap length to the discharge tray is referred to as area C. 
     The ink jet printer  1  includes a PF motor  31  for driving the PF roller  14  and the discharge roller  16  to rotate, an ASF motor  32  for driving the LD roller  11  to rotate, an ASF sub motor  33  contacting and separating the LD follower roller  12  with and from the LD roller  11 , a CR, motor not shown, a PF rotary encoder  34 , an ASF rotary encoder  35 , a page edge (PE) sensor  36  as a sensor, an ASIC (Application Specification Integrated Circuit)  37 , and a micro computer  38 . 
     A pulse motor such as a DC (direct current) motor and a stepping motor can be used for the PF motor  31 , the ASF motor  32 , the ASF sub motor  33 , and the CR motor. The DC motor rotates at a rated speed when a predetermined DC voltage is applied thereto. When the applied voltage is controlled in a PWM (Pulse Width Modulation) manner, the DC motor rotates at a speed corresponding to a duty ratio lower than the rated speed. The DC motor rotates inversely when the polarity of the DC voltage is inverted. 
     The PF rotary encoder  34  has a PF scale plate  34   a  rotating along with the PF roller  14  and a PF photo interrupter  34   b  for detecting plural slits formed along the outer periphery of the PF scale plate  34   a . When the PF scale plate  34   a  rotates together with the PB roller  14 , the PF photo interrupter  34   b  of the PF rotary encoder  34  generates a detection signal of which the level varies with the detection of the slits. The detection signal has a pulse waveform. The pulse period of the detection signal varies with the rotation speed of the PF scale plate  34   a . For example, when the rotation speed of the PF scale plate  34   a  is enhanced, the pulse period of the detection signal is shortened. 
     The ASF rotary encoder  35  includes an ASF scale plate  35   a  rotating along with a rotor of the ASF motor  32  and an ASF photo interrupter  35   b  for detecting plural slits formed along the outer periphery of the ASF scale plate  35   a . The rotation amount of the rotor of the ASF motor  32  has a predetermined relation with the rotation amount of the LD roller  11 . The rotation amount of the ASF scale plate  35   a  can correspond to the rotation amount of the LD roller  11 . When the ASF scale plate  35   a  rotates together with the ASF motor  32  and the LD roller  11 , the ASF photo interrupter  35   b  of the ASF rotary encoder  35  generates a detection signal which has a pulse waveform and of which the level varies with the detection of the slits. 
     In the PE sensor  36 , a light-emitting element and a light-receiving element not shown are opposed to each other with a predetermined gap therebetween. The PE sensor  36  is disposed so that the rear printing-medium transport path  4  is located between the light-emitting element and the light-receiving element. The PE sensor  36  is disposed at a position separated downstream by at least the inter-page gap length from the inter-page control start position and between the LD roller  11  and the PF roller  14 . The light-receiving element of the PE sensor  36  outputs a detection signal which varies depending on the light-receiving state of the light emitted from the light-emitting element. The PE sensor  36  outputs a detection signal which varies depending on the existence or absence of the printing medium P between the light-emitting element and the light-receiving element. 
     The ASIC  37  is a kind of a micro computer and includes a memory  39 , a CPU (Central Processing Unit) not shown, a timer, and an input/output port. The detection signal of the PF rotary encoder  34 , the detection signal of the ASF rotary encoder  35 , and the detection signal of the PE sensor  36  are input to the input/output port. By allowing the CPU not shown to execute a predetermined program, the ASIC  37  embodies a PF control executing section  41 , an ASF control executing section  42 , and a detection value calculator  43 . 
     The micro computer  38  includes a memory  70 , a CPU not shown, a timer, and an input/output port. The memory  70  of the micro computer  38  stores distance data  71  as data on the inter-page control start position (predetermined control start position) and the inter-page gap length data  72 . The distance data  71  is data on the distance, which is indicated by distance D in  FIG. 2 , from the inter-page control start position to the detection position of the PE sensor  36 . Distance D is greater than the inter-page gap length. The input/output port of the micro computer  38  is connected to the input/output port of the ASIC  37 . By allowing the CPU not shown to execute a predetermined program, the micro computer  38  embodies a process judgment section  51 , a feed process instructing section  52 , a paper feeding process instructing section  53 , a discharge process instructing section  54 , and a print process instructing section  55 . 
     The program executed by the CPU of the ASIC  37  may be stored, for example, in the memory  39  or the like of the ASIC  37 . The program executed by the CPU of the micro computer  38  may be stored, for example, in the memory  70  or the like of the micro computer  38 . The programs or parts thereof may be stored in the memories  39  and  70  before shipping the ink jet printer  1  or may be stored in the memories  39  and  70  after shipping the ink jet printer  1 . The programs or parts thereof stored in the memories  39  and  70  after shipping the ink jet printer  1  may be those which have been recorded in a computer-readable recording medium such as a CD-ROM and have been read and stored in the memories  39  and  70  by the use of a personal computer connected to the ink jet printer  1 , or may be those which have stored in a server unit and have been downloaded through a transmission medium such as Internet and stored in the memories  39  and  70  by the use of the personal computer connected to the ink jet printer  1 . 
     The detection value calculator  43  embodied by the ASIC  37  generates various detection values on the basis of the detection signal of the PF rotary encoder  34 , the detection signal of the ASF rotary encoder  35 , and the detection signal of the PE sensor  36  which are input to the ASIC  37  and updates the data stored in the memory  39 . The detection value calculator  43  periodically generates various detection values, for example, with a PID control period and updates the memory  39 . 
     Specifically, the detection value calculator  43  measures the number of pulses per unit time in the detection signal of the PF rotary encoder  34  as a PF interval pulse number. The detection value calculator  43  stores the PF interval pulse number in the memory  39  as a PF detection speed  61  representing a transport speed by the PF roller  14 . 
     The detection value calculator  43  measures a cumulative number of pulses in the detection signal of the PF rotary encoder  34  as a PF cumulative pulse number. The detection value calculator  43  stores the PF cumulative pulse number in the memory  39  as an absolute PF transport distance  62  representing a cumulative transport distance by the PF roller  14 . 
     The detection value calculator  43  measures the number of pulses per unit time in the detection signal of the ASF rotary encoder  35  as an ASF interval pulse number. The detection value calculator  43  stores the ASF interval pulse number in the memory  39  as an ASF detection speed  63  representing a transport speed by the LD roller  11   
     The detection value calculator  43  measures a cumulative number of pulses in the detection signal of the ASF rotary encoder  35  as an ASF cumulative pulse number. The detection value calculator  43  stores the ASF cumulative pulse number in the memory  39  as an Absolute ASF transport distance  64  representing a cumulative transport distance by the LD roller  11 . 
     The detection value calculator  43  judges whether the printing medium P is detected by the PE sensor  36 , on the basis of the level of the detection signal of the PE sensor  36 . When the printing medium P is detected, the detection value calculator  43  counts the number of pulses in the detection signal of the PF rotary encoder  34  after the detection. The detection value calculator  43  stores the counted number of pulses in the memory  39  as an after-PE-detection PF transport distance  65 . When the printing medium P is detected, the detection value calculator  43  counts the number of pulses in the detection signal of the ASF rotary encoder  35  after the detection. The detection value calculator  43  stores the counted number of pulses in the memory  39  as an after-PE-detection ASF transport distance  66 . 
     The PF control executing section  41  controls the actuation of the PF motor  31 . The PF control executing section  41  generates an instantaneous current value for controlling the driving speed or the rotation direction of the PF motor  31  so that the PF detection speed  61  stored in the memory  39  complies with a predetermined speed profile. The PF control executing section  41  generates an instantaneous current value so as to stop with a transport distance based on an instruction or the like. 
     The ASF control executing section  42  controls the actuation of the ASF motor  32 . The ASF control executing section  42  generates an instantaneous current value for controlling the driving speed or the rotation direction of the ASF motor  32  so that the ASF detection speed  63  stored in the memory  39  complies with a predetermined speed profile. The ASH control executing section  42  generates an instantaneous current value so as to stop with a transport distance based on an instruction or the like. 
     The feed process instructing section  52  embodied by the micro computer  38  generates an instruction for performing a feed process of transporting a non-printed printing medium P, for example, from the rear feed tray  2  to a print start position. Specifically, the feed process instructing section  52  instructs the PF control executing section  41  to perform a feed control and instructs the ASF control executing section  42  to perform a feed control. The feed process instructing section  52  gives an instruction for actuating the ASF sub motor  33  to the ASIC  37 . 
     The paper feeding process instructing section  53  generates an instruction for performing a paper feeding process of transporting a printing medium P, which is being fed in a printing area between the print head  22  and the platen  6 , by a predetermined distance. Specifically, the paper feeding process instructing section  53  instructs a target PF transport distance to the PF control executing section  41 . In a continuous print mode in which plural printing mediums P are continuously transported for print, the paper feeding process instructing section  53  a target ASF transport distance to the ASF control executing section  42 . 
     The discharge process instructing section  54  generates an instruction for performing a discharge process of transporting a printing medium P, which has been fed to the printing area, for example, from the printing area to the discharge tray. Specifically, the paper feeding process instructing section  53  instructs the target PF transport distance to the PF control executing section  41 . In the continuous print mode, the discharge process instructing section  54  instructs the target ASF transport distance to the ASF control executing section  42 . 
     The print process instructing section  55  generates an instruction for once scanning a printing medium P having been fed to the printing area. Specifically, the print process instructing section  55  instructs the ASIC  37  to actuate the CR motor not shown and instructs to apply voltages of waveforms corresponding to the print data to the plural piezoelectric elements in a state where the print head  22  is opposed to the printing medium P. 
     The process judgment section  51  judges the state when the ink jet printer  1  is stopped. Then, the process judgment section  51  selects one out of the plural process instructing sections of the feed process instructing section  52 , the paper feeding process instructing section  53 , the discharge process instructing section  54 , and the print process instructing section  55  as the judgment result and instructs the selected process instructing section to perform its process. 
     For example, when print data are supplied to the ink jet printer from a personal computer not shown and the ink jet printer is in a printable state, the process judgment section  51  sequentially selects one of the feed process instructing section  52 , the paper feeding process instructing section  53 , the discharge process instructing section  54 , and the print process instructing section  55  and instructs the selected process instructing section to perform its process every selection, so as to perform a printing operation based on the print data. When the printing operation is performed normally, the process judgment section  51  first selects the feed process instructing section  52 , alternately selects the print process instructing section  55  and the paper feeding process instructing section  53  until the non-printed print data do not remain, and selects the discharge process instructing section  54  when the non-printed print data do not remain. Accordingly, the printing medium P is fed to the printing area opposed to the print head  22 , is subjected to the printing operation based on the print data by repeating the printing scan and the paper feeding by a predetermined distance, and then is discharged to the discharge tray. 
     Next, operations of the ink jet printer  1  according to the embodiment having the above-mentioned configuration will be described. Here, the operation in the continuous print mode will be specifically described. 
       FIG. 3  is a diagram illustrating a data structure of continuous-printing print data supplied to the ink jet printer  1  shown in  FIG. 1 . 
     The continuous-printing print data supplied to the ink jet printer  1  includes print data by printing medium which is used to control the printing operation on the corresponding printing medium P. The print data by printing medium includes print setting data for specifying a size of a sheet to be subjected to the printing operation, plural ink ejection pattern data in which an image to be printed on the printing medium P is divided, for example, by a print width, plural paper feeding distance data interposed between two continuous ink ejection pattern data, and page identifying data. The plural ink ejection pattern data and the plural paper feeding distance data are alternately arranged in the print data by printing medium. 
     The print setting data includes sheet size data for specifying a size of a sheet to be subjected to the printing operation. In a continuous printing operation, the sheet size data included in the print data by printing medium are constant basically. The print setting data in the continuous printing operation additionally include next page existence data or next page non-existence data. When it is assumed that the number of pages is n (where n is an integer equal to or greater than 2), the next page existence data is included in the print data by printing medium of the first to (n−1)-th page and represents that a next printing page exists. The next page non-existence data is included in the print data by printing medium of the n-th page and represents that a next printing page does not exist. The print setting data is asked to the print data by a printer driver not shown and installed in a personal computer communicating with the ink jet printer  1  at the time of generating the print data. In controlling the continuous printing operation to be described later, the control can be performed even when the next page non-existence data is not included. 
     The continuous-printing print data are generated when a high-speed printing operation on plural sheets of regular paper in which the rear feed tray  2  of the ink jet printer  1  is designated is specified in the personal computer. In the other printing operation, for example, when the printing operation is performed on a sheet of exclusive-use paper, the personal computer generates the usual print data. The usual print data has a data structure which is obtained by removing the next page existence data or the next page non-existence data from the print data by printing medium shown in  FIG. 3 . 
     When the continuous-printing print data having the above-mentioned data structure are supplied, the ink jet printer  1  performs a printing operation in the continuous print mode. The ink jet printer  1  performs the printing operation while continuously transporting plural printing mediums P placed on the rear feed tray. Similarly to the usual print mode, the process judgment section  51  of the ink jet printer  1  first selects the feed process instructing section  52 , alternately selects the print process instructing section  55  and the paper feeding process instructing section  53  until the non-printed print data does not remain, and then selects the discharge process instructing section  54  when the non-printed print data does not remain, every printing medium P. The process judgment section  51  transports the printing mediums P of the number of sheets designated by the continuous-printing print data and performs the printing operation on the printing mediums. 
     Now, detailed printing operations of the ink jet printer  1  in the continuous print mode will be described. 
       FIG. 4  is a flowchart illustrating a flow of processes that are performed by the feed process instructing section  52  shown in  FIG. 2  in a continuous print mode.  FIG. 5  is a flowchart illustrating a flow of processes that are performed by the paper feeding process instructing section  53  shown in  FIG. 2  in the continuous print mode.  FIG. 6  is a flowchart illustrating a flow of processes that are performed by the discharge process instructing section  54  shown in  FIG. 2  in the continuous print mode.  FIG. 7  is a flowchart illustrating a flow of processes that are performed by the process judgment section  51  shown in  FIG. 2  in the continuous print mode. 
     When the continuous-printing print data shown in  FIG. 3  is supplied to the ink jet printer  1 , the process judgment section  51  judges that non-printed data remains and starts a data process, as shown in  FIG. 7 . The process judgment section  51  checks that the ink jet printer  1  is in a printable state. The process judgment section  51  checks that there is no job cancel instruction from a user (No in step ST 52 ). Thereafter, the process judgment section  51  reads data from the head of the continuous-printing print data. The process judgment section  51  reads print setting data of the print data of the first printing medium and instructs the feed process instructing section  52  to perform its process (step ST 4 ). 
     A reception buffer for print data (not shown) of the ink jet printer  1  is limited in physical capacity. Accordingly, the continuous-printing print data are divided into plural pieces depending on the empty state of the reception buffer and are supplied to the ink jet printer  1 . In this situation, the process judgment section  51  can read data from the head of the continuous-printing print data. The tracing in physical capacity of the reception buffer does not cause any problem in control. 
     The feed process instructing section  52  instructed to perform its process performs the flowchart of the feed process shown in  FIG. 4 . The feed process instructing section  52  first resets the absolute PF transport distance  62  and the absolute ASF transport distance  64  stored in the memory  39  of the ASIC  37  to “0” (step ST 1 ). Accordingly, the absolute PF transport distance  62  and the absolute ASF transport distance  64  represent a transport distance from the feed tray for each printing medium P. 
     After resetting the absolute position, the feed process instructing section  52  judges whether this feed process is performed on the second or subsequent printing medium in the continuous printing operation (step ST 2 ). The feed process instructing section  52  judges that this feed process is for the continuous printing operation, for example, when the print data by printing medium includes the next page existence data and judges that it is the second or subsequent printing medium when the printing operation is being performed. This feed process is for a first printing medium in the continuous printing operation. Accordingly, the feed process instructing section  52  judges No in step ST 2 . 
     When judging that it is not the second or subsequent printing medium in the continuous printing operation, the feed process instructing section  52  instructs the ASIC  37  to actuate the ASF sub motor  33  (step ST 3 ). The ASIC  37  actuates the ASF sub motor  33 . Accordingly, the LD follower roller  12  comes in pressing contact with the LD roller  11 . The hopper  13  nips the plural printing mediums P on the rear feed tray  2  with the LD roller  11 . 
     After actuating the ASF sub motor  33  to bring the LD follower roller  12  into pressing contact with the LD roller  11 , the feed process instructing section  52  instructs the ASF control executing section  42  to start the feed process (step ST 4 ). Specifically, the feed process instructing section  52  instructs the ASF control executing section  42  to perform the feed control. The ASF control executing section  42  starts the actuation of the ASF motor  32 . The LD roller  11  starts its rotation with the actuation of the ASF motor  32 . The uppermost printing medium P coming in contact with the LD roller  11  starts its transport with the rotation of the LD roller  11 . 
     The LD follower roller  12  is in pressing contact with the LD roller  11 . Accordingly, even when a printing medium P other than the uppermost printing medium P, for example, the second upper printing medium P, starts its transport along with the uppermost printing medium P with the rotation of the LD roller  11 , the printing medium P other than the uppermost printing medium P can hardly pass through the nip position between the LD roller  11  and the LD follower roller. The LD follower roller  12  serves as a load for hindering the second printing medium P from being transported. 
     When the ASF motor  32  is actuated, the ASF rotary encoder  35  starts outputting the detection signal having a pulse waveform. The detection value calculator  43  updates the ASF detection speed  63  and the absolute ASF transport distance  64  in the memory  39  on the basis of the detection signal. 
     The ASF control executing section  42  having started the actuation of the ASF motor  32  reads the AS detection speed  63  stored in the memory  39  with a predetermined period such as a PID control period. The ASF control executing section  42  generates an instantaneous current value having a PID control value corresponding to a deviation of the ASF detection speed  63  from the target ASF speed. The rotation speed of the ASF motor  32  varies depending on the instantaneous current value. The ASF control executing section  42  performs the PID control so that the ASF detection speed  63  complies with a predetermined speed profile. The printing medium is transported at a predetermined speed. 
     The printing medium P having started its transport with the rotation of the LD roller  11  moves toward the discharge tray along the rear printing-medium transport path  4 . The printing medium P passes the PE sensor  36  and then collides with the PF roller  14  and the PF follower roller  15 . 
     When the leading end edge of the printing medium P goes between the light-emitting element and the light-receiving element of the PE sensor  36 , the detection signal of the PE sensor  36  is changed from sheet existence to sheet non-existence. When the sheet of printing medium is detected by the PE sensor  36 , the detection value calculator  43  starts updating the After-PE-detection PF transport distance  65  and the After-PE-detection ASF transport distance  66  stored in the memory  39 . At this time, the actuation of the PF motor  31  is not started. The detection value calculator  43  repeatedly updates the After-PE-detection PF transport distance  65  to “0”. 
     The detection value calculator  43  updates the After-PE-detection PF transport distance  65  on the basis of the transport distance of the LD roller  11  calculated based on the detection signal of the PF rotary encoder  34  after the printing medium P is detected by the PE sensor  36 . The detection value calculator  43  updates the After-PE-detection ASF transport distance  66  on the basis of the transport distance of the LD roller  11  calculated based on the detection signal of the ASF rotary encoder  35  after the printing medium P is detected by the PE sensor  36 . 
     The detection value calculator  43  may always update the After-PE-detection PF transport distance  65  or the After-PE-detection ASF transport distance  66  on the basis of the detection signal of the ASF rotary encoder  35  or the PF rotary encoder  34 . 
     The feed process instructing section  52  recognizes that the PE sensor  36  detects the printing medium P, for example, on the basis of the After-PE-detection PF transport distance  65  or the After-PE-detection ASF transport distance  66 , after starting driving the LD roller  11  in step ST 4  (step ST 5 ). The feed process instructing section  52  judges whether this feed process is for a continuous printing operation (step ST 6 ). When this feed process is for the continuous printing operation, the feed process instructing section  52  judges whether a next page remains to be printed (step ST  7 ). The feed process instructing section  52  judges that this feed process is for the continuous printing operation and a next page remains to be printed, for example, when the next page existence data is included in the print data by printing medium. It is assumed that this feed process is for the first printing medium in the continuous printing operation and a next page remains to be printed. The feed process instructing section  52  judges Yes in step ST 7  and starts a simultaneous driving control to the feed standby position to be described later (step ST 9 ). The LD follower roller  12  is kept pressed on the LD roller  11 . 
     When this feed process is not for the continuous printing operation (No in step ST 6 ) or when a next page does not remain (No in step ST 7 ), the feed process instructing section  52  instructs a nip release to the ASIC  37  (step ST 8 ). The ASIC  37  actuates the ASF sub motor  33  to separate the LD follower roller  12  from the LD roller  11 . 
     Next, the feed process instructing section  52  executes the simultaneous driving control to the feed standby position (step ST 9 ). The feed process instructing section  52  instructs the PF control executing section  41  to actuate the PF motor  31  and instructs the ASF control executing section  42  to actuate the ASF motor  32 . The PF control executing section  41  starts actuating the PF motor  31 . The ASF control executing section  42  starts actuating the ASF motor  32 . The PF roller  14  and the PF follower roller  15  start their rotations along with the LD roller  11  and the LD follower roller  12 . The printing medium P in contact with the PF roller  14  and the PF follower roller  15  is nipped between the PF roller  14  and the PF follower roller  15 , and then is fed to the printing area with the rotations of the LD roller  11 , the LD follower roller  12 , the PF roller  14  and the PF follower roller  15 . 
     When the PF motor  31  is actuated, the PF rotary encoder  34  starts outputting the detection signal of a pulse waveform with the rotation of the PF roller  14 . The detection value calculator  43  updates the PF detection speed  61 , the absolute PF transport distance  62 , and the After-PE-detection PF transport distance  65  in the memory  39 . The After-PE-detection PF transport distance  65  is updated to a value other than “0”. The PF control executing section  41  actuating the PF motor  31  reads the PF detection speed  61  stored in the memory  39  with a predetermined period such as a PID control period. The PF control executing section  41  generates an instantaneous current value having a PID control value corresponding to the deviation of the PF detection speed  61  from the target PF speed. The rotation speed of the PF motor  31  varies depending on the instantaneous current value. The PF control executing section  41  performs a PID control so that the PF detection speed  61  complies with a predetermined speed profile. The printing medium P is transported a predetermined speed. 
     The PF control executing section  41  instructed to perform the feed control periodically reads the After-PE-detection PF transport distance  65  stored in the memory  39  of the ASIC  37 . When the read after-PE-detection PF transport distance  65  reaches a predetermined transport distance, the PF control executing section  41  starts a deceleration control with a predetermined number of pulses so as to stop the PF motor  31 . The PF control executing section  41  reduces a current instruction value to the PF motor  31  and stops. 
     Similarly, the ASF control executing section  42  periodically reads the absolute ASF transport distance  64  stored in the memory  39  of the ASIC  37 . When the read after-PE-detection ASF transport distance  66  reaches a predetermined transport distance, the ASF control executing section  42  starts a deceleration control with a predetermined number of pulses so as to stop the PF motor  31 . The ASF control executing section  42  reduces a current instruction value to the ASF motor  32  and stops. 
     In this way, the uppermost printing medium P placed on the rear feed tray  2  is fed so that the leading end edge thereof is stopped at the feed standby positions. The first printing medium P is fed to the feed standby position by the simultaneous driving control of the PF motor  31  and the ASF motor  32 . 
     When feeding the first printing medium P to the feed standby position, the feed process instructing section  52  instructs the PF control executing section  41  and the ASF control executing section  42  to perform the feed control to the print start position. The PF control executing section  41  and the ASF control executing section  42  further transport the printing medium P to the print start position by the simultaneous driving control of the PF motor  31  and the ASF motor  32  (step ST 10 ). 
     When the feed process under the simultaneous driving control is ended, the feed process instructing section  52  ends the feed process of the first printing mediums. The PF roller  14  and the LD roller  11  are stopped. The PF detection speed  61  or the ASF detection speed  63  stored in the memory  39  of the ASIC  37  is updated to “0”. The process judgment section  51  judges that non-printed data remains (Yes in step ST 51 ) and checks that there is no jop cancel instruction from the user (N 0  in step ST 52 ). Thereafter, the process judgment section  51  reads the print data of the first printing medium in the continuous-printing print data. The process judgment section  51  reads the first ink ejection pattern data in the print data of the first printing medium and instructs the print process instructing section  55  (step ST 54 ). 
     The print process instructing section  55  instructed to perform its process performs the print process. The print process instructing section  55  supplies the ink ejection pattern data to the ASIC  37  and instructs the ASIC to actuate the CR motor not shown. The carriage  21  moves with the actuation of the CR motor by the ASIC  37 . With the plural ink ejection nozzles  23  of the print head  22  opposed to the fed printing medium P, the ASIC  37  applies voltages of waveforms based on the ink ejection pattern data to the plural piezoelectric elements. Ink is ejected from the plural ink ejection nozzles  23  and is adhered to the printing medium P. 
     When the first print control process is ended, the print process instructing section  55  ends the first print scanning operation. The process judgment section  51  judges that non-printed data remains (Yes in step ST 51 ) and checks that there is no job cancel instruction from the user (No step ST 52 ). Thereafter, the process judgment section  51  reads the print data of the first printing medium in the continuous-printing print data. The process judgment section  51  reads the first paper feeding distance data in the print data of the first printing medium and instructs the paper feeding process instructing section  53  to perform its process (step ST 54 ). 
     The paper feeding process instructing section  53  instructed to perform its process executes the flow of the paper feeding process shown in  FIG. 5 . The paper feeding process instructing section  53  first judges whether this paper feeding process is for the continuous printing operation and a next page remains on the basis of the continuous-printing print data (step ST 21 ). For example, when the next page existence data is included in the print data by printing medium, the paper feeding process instructing section  53  judges that this paper feeding process is for the continuous printing operation and a next page remains. It is assumed that this paper feeding process is for the first printing medium P in the continuous printing operation. Accordingly, the paper feeding process instructing section  53  judges Yes in step ST 21 . 
     The paper feeding process instructing section  53  then judges whether the current position of the trailing end edge of the printing medium P under print passes the inter-page control start position (step ST 22 ). The paper feeding process instructing section  53  specifies the length in the transport direction of the printing medium P by the use of the sheet size data included in the print data by printing medium, and compares the specified length with the distance (hereinafter, referred to as a feed ending distance) from the inter-page control start position to the leading end edge of the printing medium P under print. For example, when the feed ending distance is great, the paper feeding process instructing section  53  judges that the current position of the trailing end edge of the printing medium P under print passes the inter-page control start position. This paper feeding process is the first paper feeding process of the printing medium P and the printing medium P under print exists at the inter-page control start position. Accordingly, the paper feeding process instructing section  53  judges No (not pass) in step ST 22 . 
     In feeding the first printing medium, the after-PE-detection PF transport distance  65  is repeatedly updated to “0” until the leading end edge of the printing medium P moves to the PF roller  14  from the detection position of the PE sensor  36 . Accordingly, when the after-PE-detection PF transport distance  65  is used to calculate the feed ending distance, the known distance (for example, the measured distance or the designed distance) from the detection position of the PF sensor  36  to the PF roller  14  is added to the after-PE-detection PF transport distance  65 . Accordingly, it is possible to obtain the feed ending distance from the inter-page control start position to the leading end edge of the printing medium P under print. 
     The paper feeding process instructing section  53  judges whether the trailing end edge of the printing medium P under print passes the inter-page control start position as a result of this paper feeding process (step ST 23 ). The paper feeding process instructing section  53  specifies the length in the transport direction of the printing medium P on the basis of the sheet size data included in the print data by printing medium and compares the specified length with the value obtained by adding this instructed paper feeding distance to the calculated feed ending distance. For example, when the value obtained by adding this instructed paper feeding distance to the feed ending distance is great, the paper feeding process instructing section  53  judges that the position of the trailing end edge of the printing medium P under print passes the inter-page control start position. This paper feeding process is the first paper feeding process of the printing mediums P. Accordingly, the paper feeding process instructing section  53  usually judges No in step ST 23 . 
     When judging No in step ST 23 , the paper feeding process instructing section  53  sets as a new target PF transport distance (number of pulses) a difference between a value, which is obtained by adding the newly instructed paper feeding distance to the cumulative value of the target PF transport distance instructed to the PF control executing section  41  after the feed process is ended, and the absolute PF transport distance  62  (actual transport distance based on the previous instruction) after the feed process is ended and calculates a new target ASF transport distance (number of pulses) additionally including a correction distance (step ST 24 ). Specifically, the paper feeding process instructing section  53  calculates the new target ASF transport distance including the correction distance by the use of Expression 1. The new target ASF transport distance including the correction distance is slightly larger than the new target PF transport distance. 
     In Expression 1, “1.05” is a target transport distance correction ratio coefficient representing an extra transport by 5%. The target transport distance correction ratio coefficient may be larger than 1 and equal to or smaller than, for example, 1.05. When the coefficient is 1 or less, the effect of correction is not sufficient and when the coefficient is larger than 1.05, the warp of the printing medium P going into the PD roller  11  increases and the transport distance of the printing medium P does not suitably follow the transport distance of the PF roller  14 .
 
Target ASF transport distance(number of pulses) =target PF transport distance(number of pulses) 1.05  Expression 1
 
     When the resolution of the transport distance of the PF rotary encoder  34  is different from the resolution of the transport distance of the ASF rotary encoder  35 , a correction coefficient of the resolution based on the ratio of the number of detection pulses of the PF rotary encoder  34  and the number of detection pulses of the ASF rotary encoder  35  in a predetermined transport distance is multiplied by the target ASF transport distance calculated from Expression 1 and the calculation result is set as the new target ASF transport distance (number of pulses) instructed to the ASF control executing section  42 . 
     After calculating the target PF transport distance (number of pulses) and the target ASF transport distance (number of pulses), the paper feeding process instructing section  53  executes a synchronization (tracing) control based on the instructed feeding distance (that is, the target PF transport distance and the target ASF transport distance) (step ST 25 ). 
       FIG. 8  is a diagram illustrating a comparison table of features of the synchronization (tracing) control and features of the simultaneous driving control in the ink jet printer  1  shown in  FIG. 1 . The left side of  FIG. 8  shows a list of features of the synchronization (tracing) control and the right side of  FIG. 8  shows a list of features of the simultaneous driving control. The features are described below. 
     First, in the synchronization (tracing) control, the PF motor  31  and the ASF motor  32  are simultaneously driven, similarly to the simultaneous driving control as shown in Column A of  FIG. 8 . Specifically, in the synchronization (tracing) control, the actuation of the ASF motor  32  is started earlier than the actuation of the PF motor  31 . In the simultaneous driving control, the actuations of the motors are not limited and both motors are simultaneously actuated. 
     Second, as shown in Column B of  FIG. 8 , in the synchronization (tracing) control, the target ASF transport distance (number of pulses) is set slightly larger than the target PF transport distance (number of pulses) by the use of the calculation of Expression 1. In the simultaneous driving control, such a correction of transport distance is not performed. The target PF transport distance (number of pulses) and the target ASF transport distance (number of pulses) are independently calculated. 
     Third, as shown in Column C of  FIG. 8 , in the synchronization (tracing) control, the target ASF transport distance instructed to the ASF control executing section  42  is based on the target PF transport distance instructed to the PF control executing section  41  as can be seen from Expression 1. On the contrary, in the simultaneous driving control, the target ASF transport distance instructed to the ASF control executing section  42  is a difference between a value, which is obtained by adding this newly instructed paper feeding distance to the cumulative value of the target ASF transport distance instructed to the ASF control executing section  42  after the feed process is ended, and the absolute ASF transport distance  64  after the feed process is ended (actual transport distance based on the previous instruction). That is, the absolute ASF transport distance  64  serves as a reference. The target PF transport distance instructed to the PF control executing section  41  is a difference between a value, which is obtained by adding this newly instructed paper feeding distance to the cumulative value of the target PF transport distance instructed to the PF control executing section  41  after the feed process is ended, and the absolute PF transport distance after the feed process is ended (actual transport distance based on the previous instruction). 
     Fourth, in the synchronization (tracing) control, as shown in column D of  FIG. 8 , the feed position of the second or subsequent printing mediums under continuous print is determined so that the after-PE-detection ASF transport distance  66  after the PE sensor  36  detects the printing medium is equal to the transport distance corresponding to the distance from the PE sensor  36  to the print start position. In the simultaneous driving control, the feed position is determined so that the after-PE-detection PF transport distance  65  after the PE sensor  36  detects the printing medium is equal to the transport distance corresponding to the distance from the PE sensor  36  to the print start position. 
     The synchronization (tracing) control has the above-mentioned features in comparison with the simultaneous driving control. 
     The paper feeding process instructing section  53  instructs the target PF transport distance to the PF control executing section  41  and instructs the target ASF transport distance to the ASF control executing section  42  in the synchronization (tracing) control (step ST 25 ) based on an instructed feeding distance. 
     In the synchronization (tracing) control, first, the ASF control executing section  42  starts actuating the ASF motor  32 . Accordingly, the printing medium P nipped between the LD roller  11  and the LD follower roller  12  is transported. At this time, the printing medium P is loosened between the LD roller  11  and the PF roller  14 . 
     When the value of the absolute ASF transport distance  64  varies by a predetermined amount, the PF control executing section  41  starts actuating the PF motor  31 . Accordingly, the printing medium P nipped between the PF roller  14  and the PF follower roller  15  starts its transport. The printing medium P is transported in a state where the printing medium is loosened between the LD roller  11  and the PF roller  14 . 
     The ASF control executing section  42  stops the ASF motor  32  so that the variation of the absolute ASF transport distance  64  after starting the paper feeding process is equal to the target ASF transport distance. The PF control executing section  41  starting its drive later stops the PF motor  31  so that the variation of the absolute PF transport distance  62  after starting the paper feeding process is equal to the target PF transport distance. The transport distance of the printing medium P transported downstream in the transport direction of the printing medium P from the PF roller  14  is the transport distance (number of pulses) of the PF roller  14  and is the instructed target PF transport distance. 
     The ASF motor  32  starts its actuation earlier than the PF motor  31 . However, the target ASF transport distance of the LD roller  11  is substantially equal to the target PF transport distance of the PF roller  14 . Accordingly, in the state where the ASF motor  32  and the PF motor  31  are stopped, the looseness between the LD roller  11  and the PF roller  14  is substantially removed. 
     The target ASF transport distance of the LD roller  11  is slightly greater than the target PF transport distance of the PF roller  14 . Accordingly, the stopped LD roller  11  does not hinder the PF motor  31  transporting the printing medium P. The printing medium P does not expanded and drawn between the LD roller  11  and the PF roller  14  by means of the rotation of the PF roller  14  after the ASF motor  32  is stopped. As a result, the actual transport distance of the printing medium P on the downstream side from the PF roller  14  suitably follows the target PF transport distance of the PF roller  14  and is equal to the instructed paper feeding distance with high precision. 
     In this way, the first paper feeding process of the paper feeding process instructing section  53  is ended. 
     In the print data by printing medium, the ink ejection pattern data and the paper feeding distance data are alternately arranged as shown in  FIG. 3 . The print process instructing section  55  and the paper feeding process instructing section  53  are alternately selected in accordance with the arrangement order of the ink ejection pattern data and the paper feeding distance data. Accordingly, the printing operation based on the print data is performed on the printing medium P, for example, every scanning width. 
     As described above, when the printing operation on the first printing medium P is performed and the trailing end edge of the first printing medium P goes out of between the LD roller  11  and the LD follower roller  12 , the second printing medium P which is the uppermost printing medium on the rear feed tray  2  pushed up by the hopper  13  is fed with the rotation of the LD roller  11  and is nipped between the LD roller  11  and the LD follower roller  12 . In the paper feeding control, the second printing medium P starts its transport with the rotations of the PF motor  31  and the LD roller  11  controlled in the synchronization (tracing) control manner, subsequently to the first printing medium P. The second printing medium P usually starts its transport without any gap from the first printing medium P. 
     In the paper feeding process for the first printing medium, the paper feeding process instructing section  53  switches the instructions of the paper feeding process depending on the position of the trailing end edge of the first printing medium P under print. Specifically, the paper feeding process instructing section  53  switches the instructions of the paper feeding process depending on the following patterns. The paper feeding process in the patterns will be described with reference to  FIGS. 2 and 5 . 
     First, right after the first printing medium P starts its transport, the paper feeding process instructing section  53  judges No in step ST 23  when the trailing end edge of the printing medium P under print does not pass the inter-page control start position (when it is in area A of  FIG. 2 ) and is expected not to pass the inter-page control start position at the time of ending this paper feeding process (when it is in area A of  FIG. 2 ). The paper feeding process instructing section  53  sets as a new target PF transport distance (number of pulses) a difference between a value, which is obtained by adding this newly instructed paper feeding distance to the cumulative value of the target PF transport distance instructed to the PF control executing section  41  after the feed process is ended, and the absolute PF transport distance  62  after the feed process is ended (actual transport distance based on the previous instruction), calculates the target ASF transport distance of the LD roller  11  slightly larger than the new target PF transport distance by the use of Expression 1 (step ST 24 ), and performs the synchronization (tracing) control (step ST 25 ). 
     Second, at the time of ending this paper feeding process, the paper feeding process instructing section  53  judges Yes in step ST 23  when the trailing end edge of the printing medium P under print is expected to pass the inter-page control start position (when it moves from area A to area B in  FIG. 2 ). The paper feeding process instructing section  53  sets as a new target PF transport distance (number of pulses) a difference between a value, which is obtained by adding the transport distance to the inter-page control start position to the cumulative value of the target PF transport distance instructed to the PF control executing section  41  after the feed process is ended, and the absolute PF transport distance  62  after the feed process is ended (actual transport distance based on the previous instruction), calculates the target ASF transport distance of the LD roller  11  slightly larger than the new target PF transport distance by the use of Expression 1 (step ST 26 ), and performs the synchronization (tracing) control (step ST 27 ). The subsequent printing medium P starting its transport without any gap from the printing medium under print is transported to the inter-page control start position. 
     Thereafter, the paper feeding process instructing section  53  sets a new target PF transport distance (number of pulses) of the PF roller  14  a difference between a value, which is obtained by adding the remaining portion of the newly instructed paper feeding distance to the cumulative value of the target PF transport distance (which includes the previous transport distance to the inter-page control start position) instructed to the PF control executing section  41  after the feed process is ended, and the absolute PF transport distance after the feed process is ended (the variation based on the previous control to the inter-page control start position) and thus supplies the new target PF transport distance to the PF control executing section  41  (step ST 28 ). Accordingly, the printing medium P is transported by only the PF roller  14 . The printing medium under print is transported by this newly instructed paper feeding distance. 
     Third, when the current position of the trailing end edge of the printing medium P under print passes the inter-page control start position, the paper feeding process instructing section  53  judges Yes in step ST 22 . Then, the paper feeding process instructing section  53  sets as a new target PF transport distance (number of pulses) a difference between a value, which is obtained by adding this newly instructed paper feeding distance to the cumulative value of the target PF transport distance instructed to the PF control executing section  41  after the feed process is ended, and the absolute PF transport distance after the feed process is ended (actual transport distance based on the previous instructions) and supplies the new target PF transport distance to the PF control executing section  41  (step ST 29 ). Accordingly, the printing medium P is transported by only the PF roller  14 . The printing medium under print is transported by the newly instructed paper feeding distance. 
     The paper feeding process instructing section  53  has a fourth pattern. The fourth pattern is selected, for example, in the paper feeding process of the final printing medium P in the continuous printing operation. In the fourth pattern, the paper feeding process instructing section  53  sets as a new target PF transport distance (number of pulses) a difference between a value, which is obtained by adding this newly instructed paper feeding distance to the cumulative value of the target PF transport distance instructed to the PF control executing section  41  after the feed process is ended, and the absolute PF transport distance after the feed process is ended (actual transport distance based on the previous instructions) and supplies the new target PF transport distance to the PF control executing section  41  (step ST 37 ). Accordingly, the printing medium P is transported by only the PF roller  14 . The printing medium under print is transported by the newly instructed paper feeding distance. In the fourth pattern, the hopper  13  goes down from the feed position to a retreat position and the LD follower roller  12  is in a retreat state where it is separated from the LD roller  11 . 
     When the leading end edge of the next printing medium P passes the PE sensor  36  by means of the paper feeding controls, the detection value calculator  43  updates the after-PE-detection PF transport distance  65  and the after PE-detection ASF transport distance  66  stored in the memory  39  to the transport distance after a new sheet is detected by the PE sensor  36 . 
     As described above, the paper feeding process and the print process on the first printing medium P are repeated while the instruction pattern in the paper feeding process of the paper feeding process instructing section  53  is switched. Thereafter, the process judgment section  51  reads the first page identification data for identifying the first and second pages in step ST 51  of  FIG. 7 . The process judgment section  51  instructs the discharge process instructing section  54  to perform its process. 
     The discharge process instructing section  54  instructed to perform its process performs the flowchart of discharge process shown in  FIG. 6 . The discharge process instructing section  54  judges whether this discharge process is in the continuous print mode and whether a next page exists (step ST 41 ). The discharge process instructing section  54  can judge that it is in the continuous print mode and a next page exists, for example, when the next page existence data is included in the print data by printing medium. The discharge process instructing section  54  may perform the judgment with reference to a re-writable flag on the basis of the next page existence data or the next page non-existence data read from the print data by the process judgment section  51 . It is assumed that this discharge process is on the first printing medium P in the continuous print mode. Accordingly, the discharge process instructing section  54  judges Yes in step ST 41 . 
     The discharge process instructing section  54  judges whether the current position of the trailing end edge of the printing medium P under print passes the inter-page control start position (step ST 42 ). The discharge process instruction section  54  specifies the length in the transport direction of the printing medium P on the basis of the sheet size data included in the print data by printing medium and compares the specified length with the feed ending distance. The discharge process instructing section  54  judges that the current position of the trailing end edge of the printing medium P under print passes the inter-page control start position, for example, when the feed ending distance is greater. 
     For example, when the printing operation on the first printing medium P is ended in the halfway of the printing medium, the current position of the trailing end edge of the printing medium P under print does not pass the inter-page control start position. In this case, the discharge process instructing section  54  judges No in step ST 42 . 
     When judging that the current position of the trailing end edge of the printing medium P under print does not pass the inter-page control start position, the discharge process instructing section  54  sets the remaining distance to the inter-page control start position as the target PF transport distance (number of pulses) of PF roller  14  so that the position of the trailing end edge of the printing medium P under print is the inter-page control start position, calculates the target ASF transport distance (number of pulses) of the LD roller  11  slightly greater than the target PF transport distance, and executes the synchronization (tracing) control (step ST 43 ). Accordingly, the position of the trailing end edge of the printing medium P under print reaches the inter-page control start position. The leading end edge of the next printing medium P starting its transport subsequently to the printing medium P under print is located at the inter-page control start position. 
     For example, when the printing operation on the first printing medium P is performed up to the trailing end edge of the printing medium P, the position of the trailing end edge of the printing medium P under print already passes the inter-page control start position. In this case, the discharge process instructing section  54  judges Yes in step ST 42 . The discharge process instructing section  54  ends the discharge process without executing a specific transport control. 
     As described above, when the discharge process on the first printing medium P is ended by the discharge process instructing section  54 , the process on the print data of the first printing medium is ended. At the time of ending the discharge control on the first printing medium P, the leading end edge of the second printing medium P is located at the inter-page control start position. The process judgment section  51  reads the print data of the second printing medium in step ST 54  of  FIG. 7  and instructs the feed process instructing section  52  to perform the feed process on the second printing medium P. 
     The feed process instructing section  52  starts the feed process on the second printing medium in accordance with the flowchart shown in  FIG. 4 . The feed process instructing section  52  resets the absolute PF transport distance  62  and the absolute ASF transport distance  64  stored in the memory  39  of the ASIC  37  to “0” (step ST 1 ) and then judges that this feed process is a print printing operation on the second or subsequent printing medium in the continuous print (Yes in step ST 2 ). 
     When judging that this feed process is the printing operation on the second or subsequent printing medium in the continuous print, the feed process instructing section  52  judges whether the inter-page control of setting a gap between plural printing mediums P which are continuously fed has been ended (step ST 11 ). The feed process instructing section  52  specifies the length in the transport direction of the printing medium P on the basis of the sheet size data included in the print data by printing mediums and compares the feed ending distance calculated from the absolute PF transport distance  62  or the absolute ASF transport distance before the reset with a value which is obtained by adding distance D indicated by the distance data  71  to the specified length. The feed process instructing section  52  judges that the inter-page control is ended, for example, when the feed ending distance before the reset is greater. 
     Referring to a flag which goes upright when the paper feeding process instructing section  53  executes the PF control of step ST 28  or ST 29  or when the paper feeding process instructing section  53  generates a gap greater than the inter-page gap length between the previous printing medium P and the current printing medium P, the feed process instructing section  52  may judge that the inter-page control is ended when the flag is upright. 
     Similarly to the case where the discharge control is executed so that the trailing end edge of the first printing medium P is located at the inter-page control start position, for example, when the inter-page control is not ended, the feed process instructing section  52  executes the inter-page control (step ST 12 ). Specifically, the feed process instructing section  52  sets the remaining distance of the inter-page gap length as the target PF transport distance of the PF roller  14  and instructs the target PF speed to only the PF control executing section  41 . Accordingly, the printing medium P is transported by only the PF roller  14 . A predetermined gap length is secured between the trailing end edge of the first printing medium P and the leading end edge of the second printing medium P by means of the inter-page control. The gap between the trailing end edge of the first printing medium P and the leading end edge of the second printing medium P is equal to or greater than the predetermined inter-page gap length. The feed process instructing section  52  may set the inter-page gap length as the target PF transport distance of the PF roller  14  and may instruct the target PF speed to only the PF control executing section  41 . 
     In this way, after the inter-page control is executed in step ST 12  or when the inter-page control is already ended, the feed process instructing section  52  instructs the feed control including the synchronization (tracing) control up to the print start position to the PF control executing section  41  and the ASF control executing section  42  (step ST 13 ). 
     In the synchronization (tracing) control on the second or subsequent printing mediums under the continuous print up to the print start position, the ASF control executing section  42  stops the actuation of the ASF motor  32  so that the after-PE-detection ASF transport distance  66  corresponds to the distance from the PE sensor  36  to the print start position. As described as the fourth feature in  FIG. 8 , the PF control executing section  41  stops the actuation of the PF motor  31  so as to stop when the after-PE-detection ASF transport distance  66  corresponds to the distance from the PE sensor  36  to the print start position. 
     The PF roller  14  starts its actuation later than the LD roller  11 . In step ST 13 , the transport distances of the absolute ASF transport distance  63  and the after-PE-detection PF transport distance  65  are smaller than those of the absolute ASF transport distance  63  and the after-PE-detection ASF transport distance  66  by the delay timer that is, by the hatched portion in Column A of  FIG. 8 . As a result, by allowing the PF control executing section  41  to control the PF motor  11  so as to stop when the after-PE-detection PF transport distance  65  corresponds to the distance from the PE sensor  36  to the print start position, the precision in feed position of the second or subsequent printing mediums is deteriorated when the plural printing mediums P are continuously fed. Specifically, the feed position of the second or subsequent printing mediums tends to depart upstream in the transport direction  4  of the printing medium P from the feed position of the first printing medium. That is, the second or subsequent printing mediums P under the continuous print tend to depart upstream in the transport direction  4  from the accurate feed position of the first printing medium. As a result, the leading end edge of the printing medium P is fed only to the front of the print start position. 
     On the contrary, when the PF control executing section  41  controls the PF motor  31  to stop when the after-PE-detection ASF transport distance  66  corresponds to the distance from the PE sensor  36  to the print start position, the leading end edge of the printing medium P is fed to the print start position with high precision. The feed position of the second or subsequent printing medium P is substantially matched with the feed position of the first printing medium P. 
     Actually, the PF control executing section  41  starts at the same time as the ASF control executing section  42  starts the deceleration and stop control. Right before starting the deceleration and stop control, the ASF detection speed  63  by the LD roller  11  and the PF detection speed  61  by the PF roller  14  are set to a substantially constant speed. Accordingly, by matching the start timing of the deceleration and stop controls with each other, the PF control executing section  41  can stop the PF roller  14  when the ASF control executing section  42  stops the LD roller  11 . The PF control executing section  41  can control the PF roller  14  to stop when the transport distance of the LD roller  11  after the PE sensor  36  detects a new printing medium P subsequently fed is a predetermined transport distance. 
     After feeding the second printing medium P to the print start position, the feed process instructing section  52  judges whether a next page to be printed exists on the basis of the continuous-printing print data or the like (step ST 14 ). For example, when the third or subsequent page does not exist, the feed process instructing section  52  supplies the ASIC  37  with an instruction for actuating the ASF sub motor  33  (step ST 15 ). The ASIC  37  actuates the ASF sub motor  33  and the LD follower roller  12  is separated from the LD roller  11 . On the contrary, when the third or subsequent page to be printed exists, the feed process instructing section  52  ends the feed process without separating the LD follower roller  12  from the LD roller  11 . 
     When the second printing medium P starts its transport by the paper feeding process on the first printing medium P or when the second printing medium P starts its transport by the feed process on the second printing medium, the second printing medium P is fed to the print start position by the above-mentioned feed process on the second printing medium P. 
     Thereafter, in the ink jet printer  1 , the print control of the print process instructing section  55  and the paper feeding control of the paper feeding process instructing section  53  are repeated on the basis of the print data of the second printing medium. When the process judgment section  51  reads the final page identification data of the print data of the second printing medium in step ST 54  of  FIG. 7 , the discharge process of the discharge process instructing section  54  is started. 
     The ink jet printer  1  reads the print data by printing medium included in the continuous-printing print data and executes on the third or subsequent printing medium the same control as the second printing medium. When the process judgment section  51  under the continuous print mode reads the print data of the final printing medium in step ST 54  of  FIG. 7 , a control different from the previous controls is executed. 
     Specifically, since a next page to be printed does not exist in the paper feeding process on the final printing medium P, the feed process instructing section  52  judges No (final page) in step ST 14  of  FIG. 4 . The feed process instructing section  52  judges No (final page), for example, on the basis of the next page non-existence data in the print setting data. The paper feeding process instructing section  53  gives to the ASIC  37  an instruction for actuating the ASF sub motor  33  (step ST 15 ). The ASIC  37  actuates the ASF sub motor  33  and the LD follower roller  12  is separated from the LD roller  11 . 
     The paper feeding process instructing section  53  judges No in step ST 21  of  FIG. 5 , because a next page to be printed does not exist. The paper feeding process instructing section  53  controls the paper feeding in accordance with the fourth pattern of the paper feeding control. That is, the paper feeding process instructing section  53  sets as a new PF target transport distance (number of pulses) a difference between a value, which is obtained by adding this newly instructed paper feeding distance to the cumulative value of the target PF transport distance instructed to the PF control executing section  41  after the feed process is ended, and the absolute PF transport distance  62  after the feed process is ended (actual transport distance based on the previous instruction) and instructs the target PF speed to only the PF control executing section  41  (step ST 30 ). Accordingly, the printing medium P is transported by only the PF roller  14 . The pressing contact state of the LD follower roller  12  with the LD roller  11  is released and the printing medium P is transported with the rotation of the PF roller  14 . 
     Since no next page to be printed remains, the discharge process instructing section  54  judges No (final page) in step ST 41  of  FIG. 6  with reference to the above-mentioned flag. The paper feeding process instructing section  53  further checks that the LD follower roller  12  is in the nip state where it is in contact with the LD roller (step ST 44 ), sets a predetermined transport distance, by which the printing medium P under transport can be transported to the discharge tray, as the target PF transport distance (number of pulses) of the PF roller  14 , and instructs the target P speed to only the P control executing section  41  (step ST 45 ). The nip state between the LD follower roller  12  and the LD roller  11  is released and the printing medium P having been subjected to the printing operation is transported by only the PF roller  14  and then is discharged to the discharge tray. 
     In this way, when the print data of the final page among the continuous-printing print data is supplied to the ink jet printer  1 , a control different from the control on the printing mediums P under the continuous print is executed. That is, the ink jet printer  1  executes substantially the same control as the paper feeding control in a usual print mode based on the usual print data. 
     The ink jet printer  1  can perform a printing operation on various printing mediums P such as sheets of regular paper and sheets of photo paper. The ink jet printer  1  can perform a printing operation on the printing medium P with different resolutions. The ink jet printer  1  has plural print modes depending on the types of the printing mediums P or the print quality. The print modes include a mode for performing a printing operation on a sheet of regular paper and a mode for performing a printing operation on a sheet of photo paper with high quality. 
     In a mode for performing a printing operation on the sheet of regular paper at a high speed among the plural print modes, the ink jet printer  1  performs the printing operation using the above-mentioned continuous print mode. That is, the ink jet printer  1  actuates both the ASF motor  32  and the PF motor  31  to continuously feed the plural printing mediums P on the rear feed tray  2 , with the LD follower roller  12  in contact with the LD roller  11 . 
     In the other print modes, the ink jet printer  1  feeds the printing mediums P sheet by sheet similarly to known ink jet printers, discharges the printing mediums when the printing operation on the printing mediums P is ended, and feeds the next printing medium P on the rear feed tray  2  to the printing area. 
     Next, an operation will be described when a user gives an interrupt (job cancel) instruction in the course of performing a continuous print mode for continuously transporting the plural printing mediums P and performing a printing operation thereon. Non-printed data remains in the course of performing the continuous print mode. Accordingly, the process judgment section  51  judges non-printed data remains that in step ST 51  of  FIG. 7  and then judges in step ST 52  that a job cancel instruction is given. The process judgment section  51  sets no next page in the ink jet printer  1 . The process judgment section  51  can re-write a flag (not shown) changed by the value of “next page existence” or “next page non-existence” finally read from the print data and referred to, under print, by the discharge process instructing section  54 , and the like to the value of “next page non-existence”, or can re-write all the values of “next page existence” to the value of “next page non-existence” in the continuous-printing print data of  FIG. 3 . 
     Thereafter, the process judgment section  51  processes the non-printed data. The process judgment section  51  instructs the discharge process instructing section  54  to perform the discharge process, when the end of the print data of the printing medium, which is printed at a time when the job cancel instruction is given, is reached (when the page identification data is read). 
     The discharge process instructing section  54  judges No (final page) in step ST 41  of  FIG. 6  with reference to the above-mentioned flag and judges whether the LD follower roller  12  is in the nip state where it is in contact with the LD roller (step ST 44 ). When the printing process is interrupted by the job cancel instruction, the feed process instructing section  52  judges in step ST 14  of  FIG. 4  that a next page exists. Accordingly, the LD follower roller  12  is in the nip state where it is in contact with the LD roller. Accordingly, the discharge process instructing section  54  judges Yes in step ST 44  of  FIG. 6 . 
     When judging Yes in step ST 44  of  FIG. 6 , the discharge process instructing section  54  judges whether the trailing end edge of the printing medium P under print passes the inter-page control start position (step ST 46 ). When the trailing end edge of the printing medium P under print does not pass the inter-page control start position, the discharge process instructing section  54  actuates the ASF submotor  33  and separates the LD follower roller  12  from the LD roller  11  (step ST 48 ). 
     In the control of moving the LD follower roller separated from the LD roller  11  to a predetermined retreating position, the restoring arm  20  moves to a restoring position from the retreating position and then returns to the retreating position. Accordingly, for example, the printing medium P of which the leading end edge is nipped between the LD roller  11  and the LD follower roller  12  is hooked by the rotating restoring arm  20  and is pushed back to the rear feed tray  2 . 
     When the LD follower roller  12  is separated from the LD roller, the discharge process instructing section  54  sets a predetermined transport distance, by which the printed print medium P can be transported to the discharge tray, as the target PF transport distance (number of pulses) of the PF roller  14  and instructs the target PF speed to only the PF control executing section  41  (step ST 45 ). The nip state between the LD follower roller  12  and the LD roller  11  is released and the printed printing medium P is transported and discharged to the discharge tray by only the PF roller  14 . The printed printing medium P is discharged to the discharge tray. 
     When the trailing end edge of the printing medium P under print has been already passed the inter-page control start position (Yes in step ST 46 ), the discharge process instructing section  54  instructs a synchronization (tracing) control by a predetermined transport distance (step ST 47 ). The PF motor  31  drives the PF roller  14  and the ASF motor  32  drives the LD roller  11 . The PF motor  31  and the ASF motor  32  control the driving by the synchronization (tracing) control until the leading end edge of the printing medium P subsequent to the printing medium P under print is nipped between the PF roller  14  and the PF follower roller  15 . 
     After nipping the leading end edge of the subsequent printing medium P between the PF roller  14  and the PF follower roller  15  by the synchronization (tracing) control, the discharge process instructing section  54  actuates the ASF sub motor  33  and separates the LD follower roller  12  from the LD roller (step ST 48 ). 
     Thereafter, the discharge process instructing section  54  sets a predetermined transport distance, by which the printed printing medium P can be transported to the discharge tray, as the target PF transport distance (number of pulses) of the PF roller  14  and instructs the target PF speed to only the PF control executing section  41  (step ST 45 ). The nip state of the LD follower roller  12  with the LD roller  11  is released and the subsequent printing medium P is then transported and discharged to the discharge tray by only the PF roller  14 . The printed printing medium P is discharged to the discharge tray prior to the subsequent printing medium P. The printed printing medium P and the subsequent blank printing medium P are discharged to the discharge tray. 
     In this embodiment, with the LD follower roller  12  in contact with the LD roller  11 , it is possible to continuously transport the plural printing mediums P on the rear feed tray  2  by driving together the LD roller  11  and the PF roller  14 . Compared with the case where the plural printing mediums P on the rear feed tray  2  are individually transported, it is possible to enhance the number of printing mediums which can be subjected to a printing operation per unit time. 
     In this embodiment, during the process of continuously transporting the plural printing mediums P and performing a printing operation thereon, it is possible to interrupt the printing operation. When the trailing end edge of the printing medium P under print is more located upstream in the transport direction than the inter-page control start position, the process judgment section  51  and the discharge process instructing section  54  first discharge the printing medium P under print, then stop the printing operation, and are restored to a printable state. The ink jet printer  1  can early stop the printing process without discharging all the expected number of printing mediums P and waiting until the LD follower roller  12  is separated from the LD roller  11   
     In this embodiment, in the control of separating the LD follower roller  12  from the LD roller  11 , the restoring arm  20  for hooking the printing medium P interposed therebetween and restoring it to the rear feed tray  2  is provided. The inter-page control start position is set within the range in which the printing medium can be restored by the restoring arm  20 . Accordingly, when the printing medium P subsequent to the printing medium P under print is transported more upstream in the transport direction of the printing mediums P than the inter-page control start position at the time of interrupting the printing operation in the course of continuously transporting the printing mediums P, it is possible to restore the subsequent printing medium P to the rear feed tray  2 . When the printing medium P subsequent to the printing medium P under print starts its transport from the rear feed tray  2  but the position of the printing medium P at the time of interrupt is more upstream in the transport direction of the printing medium P than the inter-page control start position, it is possible to restore the subsequent printing medium to the rear feed tray  2 . A user need not perform an operation of restoring the subsequent printing medium P to the rear feed tray  2  after the interrupt. 
     In this embodiment, at the time of interrupting the printing operation in the course of continuously transporting the printing mediums P, the subsequent printing medium P which is being transported from the inter-page control start position to the downstream side in the transport direction of the printing mediums P is discharged to the discharge tray in the discharge control of the discharge process instructing section  54 . The ink jet printer  1  discharges the printing medium P under print and the subsequent blank printing medium P and stops the printing operation. 
     Accordingly, the ink jet printer  1  can interrupt the print process of continuously transporting the printing mediums P and performing the printing operation thereon and can be early restored to a printable state, regardless of the positions of the printing medium P under print and the subsequent blank printing medium P at the time of interrupt. It can be early restored to the state where no printing medium P remains in the transport path of the printing mediums P. The user need not perform an operation of pulling the subsequent printing medium P out of the transport path after the interrupt. 
     In this embodiment, when the user gives a job cancel instruction, the print process is interrupted in the course of performing the process of continuously transporting the plural printing mediums P and performing a printing operation thereon. At this time the process judgment section  51  sets the next page non-existence and then instructs the discharge process instructing section  54  to perform the discharge process, even when the non-printed print data of the printing medium remains. The discharge process instructing section  54  first judges whether the LD follower roller  12  is in contact with the LD roller  11 . When judging that the LD follower roller  12  is in contact with the LD roller  11 , the discharge process instructing section drives the LD roller  11  and the PF roller  14  together (until the printing medium is supplied to the PF roller  14 ) with the LD follower roller  12  in contact with the LD roller  11 , then separates the LD follower roller  12  from the LD roller  11  similarly to the case where the LD follower roller  12  is not in contact with the LD roller  11 , and then drives the PF roller  14  to discharge the printed printing medium P and the subsequent blank printing medium P. 
     Accordingly, the process judgment section  51  and the discharge process instructing section  54  can be used in common to continuously transport plural printing mediums P and to individually transport the printing mediums P. The process judgment section  51  and the discharge process instructing section  54  can be used to individually transport the printing mediums P along with the feed process instructing section  52  or the paper feeding process instructing section  53  which cooperate with each other for print. 
     That is, the process judgment section  51  and the discharge process instructing section  54  can be used in both operation modes of a print mode for continuously transporting plural printing mediums P and a print mode for individually transporting the printing mediums P. The flow and structure of a basic control for print in the ink jet printer  1  can be used in common to the print mode for individually transporting the printing mediums P. For example, the error process and the like can be used in common to the print mode for individually transporting the printing mediums P. 
     As a result, the ink jet printer  1  can pursue an enhancement in printing speed by the use of the print mode for continuously transporting the plural printing mediums P while pursuing an improvement in quality by the use of the print mode for individually transporting the printing mediums P. The balance between the print quality and the printing speed of the ink jet printer  1  becomes a level higher than that of the ink jet printer  1  for individually alone transporting the printing mediums P. 
     The above-mentioned embodiment is an exemplary embodiment of the invention, but the invention is not limited to the embodiment. The invention can be modified or changed in various forms without departing from the gist of the invention. 
     In the above-mentioned embodiment, the inter-page control start position can be set within the restorable range of the restoring arm  20 . The inter-page control start position may be set between the restorable range of the restoring arm  20  and the PF roller  14 . In this modified example, when the printing medium P subsequent to the printing medium P under print is not being transported by the PF roller  14 , the printing operation can be interrupted. Since the LD follower roller  12  is separated from the LD roller  11  by the interrupting process, the user can pull out the subsequent printing medium P from the transport path without any damage and place the pulled-out printing medium on the rear feed tray  2  after the interrupt. 
     In the above-mentioned embodiment, the discharge process instructing section  54  executes the synchronization (tracing) control until the trailing end edge of the printing medium P under print reaches the inter-page controls start position, and the feed process instructing section  52  executes the inter-page control. In addition, the discharge process instructing section  54  may execute the synchronization (tracing) control and the inter-page control until the trailing end edge of the printing medium P under print reaches the inter-page control start position. 
     In the above-mentioned embodiment, the PE sensor  36  serving to detect the printing medium P between the LD roller  11  and the PF roller  14  is an optical sensor that optically detects the printing medium P. In addition, a sensor serving to detect the printing medium P between the LD roller  11  and the PF roller  14  may include a lever lifted and revolved by the printing medium P transported in the rear printing-medium transport path  4  and an optical sensor that optically detects the position of the lever. 
     In the above-mentioned embodiment, the detection value calculator  43  stores the transport distance after the detection of the PE sensor  36  in the memory  39  as the after-PE-detection PF transport distance  65  and the after-PE-detection ASF transport distance  66 . In addition, for example, the detection value calculator  43  may store in the memory  39  the value of the absolute PF transport distance  62  or the absolute ASF transport distance  64  when the PE sensor  36  detects the printing medium P. 
     In this modified example, the PB control executing section  41  or the ASF control executing section  42  subtracts the value of the measured absolute PF transport distance stored in the memory  39  from the absolute PF transport distance  62  stored in the memory  39  and can use the subtraction result as the after-PE-detection PF transport distance  65 . The PF control executing section  41  or the ASF control executing section  42  subtracts the value of the detected absolute ASF transport distance stored in the memory  39  from the absolute ASF transport distance  64  stored in the memory  39  and can use the subtraction result as the after-PE-detection ASF transport distance  66 . 
     In the above-mentioned embodiments for example, when feeding plural printing mediums P on the rear feed tray  2 , the ink jet printer  1  continuously feeds the plural printing mediums P. In addition, for example, when feeding plural printing mediums on the front feed tray  3 , the ink jet printer  1  may continuously feed the plural printing mediums P. 
     In the above-mentioned embodiment, the print data supplied to the ink jet printer  1  is exemplified as being generated from the personal computer which can communicate with the ink jet printer  1 . In addition, for example, a digital still camera (DSC) or the like may supply the print data by communicating with the ink jet printer  1 . In a so-called multifunction device equipped with the ink jet printer  1 , a scanner unit or an IC card reader disposed therein can supply the print data by communicating with the ink jet printer  1 . 
     The invention can be suitably applied to an ink jet printer and the like.