Patent Publication Number: US-8976213-B2

Title: Image forming apparatus and control method thereof

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus which performs an image forming operation on continuous printing sheet wound in a roll shape, and a control method thereof. 
     2. Description of the Related Art 
     Currently, a roll paper printer which performs an image forming operation on continuous printing paper wound in a roll shape (roll paper) has merits of high degrees of freedom in an output size (image forming length), low cost of roll paper, and the like. On the other hand, in the roll paper printer, since a curl unique to the roll paper is required to be removed, a printer engine includes a curl correction unit. In the roll paper printer, since the curl correction unit forms a curl in an opposing direction during the image forming operation, the curl unique to the roll paper is removed. The image-forming processed printing paper, the curl of which has been removed by the curl correction unit, is cut by a cutter and is discharged outside the printer, while the remaining paper is rolled up and stored in a cartridge. 
     When an electric power failure, forced termination, battery dead state, or the like has occurred during the image forming operation of the roll paper printer, and a power supply is stopped, paper in the middle of the image forming operation may remain in the printer engine. When a power supply is turned on again from this state, an image forming operation may be unwantedly restarted from a position on the paper in the middle of the image forming operation. When the image forming operation is restarted from the position on the paper in the middle of the image forming operation, not only image forming quality impairs, but also a peeling error of an ink sheet occurs in case of a thermal transfer printer, thereby causing jamming of the paper and ink sheet. 
     In order to prevent such problems, when the paper remains in the printer engine upon power-ON, processing for discharging the remaining paper is executed. 
     For example, Japanese Patent Laid-Open No. 2008-137226 describes that a roll paper printer includes a storage unit which stores an image forming status, a previous image forming status is referred to from image forming statuses stored in the storage unit upon power-ON, and when the previous image forming status indicates that the previous image forming operation was incomplete, printing paper is cut by a maximum image forming length based on the length of an ink sheet and is discharged. 
     The roll paper printer normally includes the curl correction unit used to correct a roll-shaped curl. When the curl correction unit holds paper for a predetermined time period or longer, a curl in the opposing direction is locally formed on the paper. When an image forming operation is performed using the paper with such curl, not only the local curl remains on the paper, but also image forming quality on a curl region lowers. 
     Since Japanese Patent Laid-Open No. 2008-137226 adopts the method of clipping printing paper by the maximum image forming length based on the length of the ink sheet, the paper may be clipped before the curl region. 
     By contrast, when paper is cut by adding a length from an image forming unit such as a thermal head to the curl correction unit to the maximum image forming length, a portion formed with the curl can be removed, thereby solving the above problem. 
     However, when the paper is cut by adding the length from the image forming unit to the curl correction unit to the maximum image forming length, the paper clipping amount increases, thereby decreasing the number of sheets that can undergo image forming operations. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of the aforementioned problems, and realizes an image forming apparatus which can suppress wasteful use of sheet and deterioration of image forming quality in remaining sheet processing at an activation timing, and a control method thereof. 
     In order to solve the aforementioned problems, the present invention provides an image forming apparatus comprising: an accommodation unit configured to accommodate a continuous printing sheet wound in a roll shape; a conveyance unit configured to pull out and convey the printing sheet from the accommodation unit; a printing unit configured to perform image forming processing on the printing sheet which is conveyed by the conveyance unit to an image forming start position; a cutting unit configured to cut the printing sheet after completion of the image forming processing at a predetermined cutting position; and a processing unit configured to execute, when a printing sheet remaining on a conveyance path is detected at an activation timing, processing for removing the remaining printing sheet, wherein the processing unit controls the conveyance unit to convey the printing sheet at the activation timing to detect a leading end, compares a first distance from the leading end to a portion which was located at a curl correction unit before the activation with a second distance from the leading end, which distance is required for image forming processing set before the activation, and sets a larger distance as a cutting position of the remaining printing sheet. 
     In order to solve the aforementioned problems, the present invention provides a control method of an image forming apparatus having: an accommodation unit configured to accommodate a continuous printing sheet wound in a roll shape; a conveyance unit configured to pull out and convey the printing sheet from the accommodation unit; a printing unit configured to perform image forming processing on the printing sheet which is conveyed by the conveyance unit to an image forming start position; and a cutting unit configured to cut the printing sheet after completion of the image forming processing at a predetermined cutting position, the method comprising: a remaining sheet processing step of executing, when a printing sheet remaining on a conveyance path is detected at an activation timing, processing for removing the remaining printing sheet, wherein in the remaining sheet processing step, the conveyance unit is controlled to convey the printing sheet at the activation timing to detect a leading end, a first distance from the leading end to a portion which was located at a curl correction unit before the activation is compared with a second distance from the leading end, which distance is required for image forming processing set before the activation, and a larger distance is set as a cutting position of the remaining printing sheet. 
     According to the present invention, wasteful use of sheet and deterioration of image forming quality can be suppressed in remaining sheet processing at an activation timing. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view showing the arrangement of a printer engine of a thermal printer according to an embodiment; 
         FIG. 2  is a block diagram showing the arrangement of the thermal printer according to the embodiment; 
         FIG. 3  is a flowchart showing processing from an activation timing until an image forming start timing of the thermal printer according to the embodiment; 
         FIG. 4  is a view showing the outer appearance of an operation unit of the thermal printer according to the embodiment; 
         FIG. 5  is a flowchart showing image forming processing by the thermal printer according to the embodiment; 
         FIG. 6  is a view showing an ink sheet for the thermal printer; 
         FIGS. 7A and 7B  are views showing examples of to-be-detected portions of a terminal end of printing paper for the thermal printer; 
         FIG. 8  is a flowchart showing a first example of remaining paper processing according to the embodiment; 
         FIGS. 9A and 9B  are views for explaining the remaining paper processing shown in  FIG. 8 ; 
         FIG. 10  is a flowchart showing a second example of remaining paper processing according to the embodiment; 
         FIGS. 11A and 11B  are views for explaining the remaining paper processing shown in  FIG. 10 ; and 
         FIGS. 12A and 12B  are views for explaining the remaining paper processing shown in  FIG. 10 . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     A mode for carrying out the present invention will be described in detail hereinafter. Note that an embodiment to be described hereinafter is an example required to implement the present invention and should be modified or changed as needed depending on configurations of apparatus and various conditions to which the present invention is applied, and the present invention is not limited to the following embodiment. Some of embodiments to be described later may be combined as needed. 
     Note that in the following description, “printing” indicates a series of overall operations from an image forming operation based on a printing instruction from the user until a paper discharge operation. Also, “image forming” indicates an operation for recording an image on a printing medium such as printing paper by thermally transferring an ink applied on an ink sheet to the printing paper of the print operations. Also, continuous printing paper wound in a roll shape will be referred to as roll paper hereinafter. 
     An image forming apparatus and method using a thermal transfer or dye sublimation thermal printer will be described hereinafter. However, the present invention is not limited to a printer alone, but is applicable to, for example, a copying machine, facsimile apparatus, computer system, and the like as long as they include apparatuses having an image forming function of this embodiment. Also, the printing paper of the present invention includes not only that of a paper material, but also sheet members such as plastic films made up of other materials. 
     &lt;Apparatus Configuration&gt; 
     A principal configuration of a thermal printer of this embodiment will be described below with reference to  FIG. 1 . 
     Referring to  FIG. 1 , roll paper  101  is accommodated in a printer main body to be rotatable via a roll paper shaft  102 . Printing paper  112  pulled out from the roll paper  101  is pinched between a grip roller  103  and a pinch roller  104 , which is disposed at its opposite position, is fed onto a conveyance path, and is reciprocally conveyed in directions of arrows A and B during an image forming operation. A plurality of projections are formed on the surface of the grip rollers  103  at predetermined intervals in circumferential and axial directions. 
     A curl correction unit  105  is arranged on the downstream side of the grip roller  103 . The curl correction unit  105  curls the printing paper  112  in a direction opposite to a winding direction of the roll paper  101 , thereby correcting a curl of the roll paper. On the downstream side of the curl correction unit  105 , a platen roller  106  is arranged. At a position opposite to the platen roller  106 , a thermal head  109  is disposed, and an ink sheet  113  passes through a gap between the thermal head  109  and printing paper  112 . 
     The curl correction unit  105  includes a paper detection sensor  114  which detects the leading end of the printing paper  112  conveyed by the grip roller  103 . As the paper detection sensor  114 , a photoreflector or the like is used. 
     The ink sheet  113  is fed from a roll bobbin  110  on the ink sheet supply side, and is taken up by an ink-sheet take-up bobbin  108  via a gap between the thermal head  109  and printing paper  112 . 
     A marker detection sensor  115  detects markers applied to leading end portions of respective colors of the ink sheet  113 , as will be described later. As the marker detection sensor  115 , a photoreflector or the like is used. 
     A cutter  111  cuts image-forming processed printing paper  112  or printing paper  112  in remaining paper processing (to be described later). 
     A pair of discharge rollers  107  pinch the leading end of the printing paper  112  to convey the printing paper  112  to an image forming start position, and discharge the printing paper  112  cut by the cutter  111  to the outside of the printer. 
     &lt;Block Arrangement&gt; 
     The block arrangement of the thermal printer of this embodiment will be described below with reference to  FIG. 2 . 
     Referring to  FIG. 2 , a main controller  201  controls the overall thermal printer. The main controller  201  controls the printer according to control programs stored in a ROM  210  and executes calculation processing according to various programs. The main controller  201  also executes, for example, processing for giving modification processing to image data to generate image data required for an image forming operation, and storing the generated image data in a RAM  211 . The RAM  211  is also used as a temporary storing area of image data, and work areas of various control programs such as a resize processing program of an image. The ROM  210  stores system control programs and various parameters such as adjustment values. 
     A paper conveyance motor driver  202  is required to drive a paper conveyance motor  203 . The paper conveyance motor  203  is coupled to the roll paper shaft  102 , grip roller  103 , discharge rollers  107 , and the like via a rotation mechanism, and drives these rollers, thereby conveying the printing paper. 
     An ink sheet conveyance motor driver  204  is required to drive an ink sheet conveyance motor  205 . The ink sheet conveyance motor  205  drives the ink-sheet take-up bobbin  108  via a rotation mechanism to take up the used ink sheet  113 . 
     A thermal head lifting motor driver  206  controls rotation of a thermal head lifting motor  207  required to move the thermal head  109  (to be described later) up and down, thereby operating the thermal head  109  between an image forming position and retracted position. 
     A cutter motor driver  208  controls a cutter motor  209  required to drive the cutter  111 , thereby cutting the printing paper. 
     A cartridge detection sensor  212  determines an attached state of a cartridge used to accommodate roll paper, and types of a plurality of available cartridges. Based on this determination result, image forming processing according to the cartridge is executed according to control programs stored in the ROM  210 . 
     A paper detection sensor  213  is arranged between the grip roller  103  and curl correction unit  105 , and detects if the leading end portion of the printing paper  112 , which is pulled out from the cartridge at an image forming start timing, has passed through a position behind the grip roller  103 . Also, the paper detection sensor  213  detects a to-be-detected portion such as a terminal end hole  701  or terminal end marker  702  of roll paper, as will be described later. 
     An ink sheet mark detection sensor  214  of the ink sheet, which detects a marker applied to a leading end portion for each color of the ink sheet  113 . 
     A memory I/F  216  is used to write and read out data in and from a memory card or the like, which is attached to the printer. 
     A display controller  217  controls to display a menu required to input image data to be printed and setting data required for printing on a display unit  218 . 
     An image data input unit  219  fetches image data from an external apparatus such as a PC (Personal Computer), digital camera, or digital television connected to the printer. 
     Image buffer memories  220 Y,  220 M, and  220 C are used to store image data acquired via the memory I/F  216  or image data input unit  219 . A yellow image buffer memory  220 Y is used to temporarily store yellow (Y) image data; and  220 M and  220 C, image buffer memories used to temporarily store magenta (M) and cyan (C) image data, respectively. 
     A thermal head deriving circuit  222  drives heat generating members incorporated in the thermal head  109 . A driver controller  221  connected to the main controller  201  controls the thermal head driving circuit  222  using image data recorded in a bitmap format in the image buffer memories  220 Y,  220 M, and  220 C, thereby attaining an image forming operation. 
     The main controller  201  converts image data in the image buffer memories  220 Y,  220 M, and  220 C into thermal head driving data, and the driver controller  221  controls the thermal head driving circuit  222  according to the thermal head driving data, thereby attaining an image forming operation. 
     &lt;Operation Until Image Forming Start Timing&gt; 
     Operations from an activation (power-ON) timing until an image forming start timing of the thermal printer according to this embodiment will be described below with reference to  FIGS. 3 and 4 . Note that  FIG. 3  is a flowchart showing operations until the image forming start timing of the thermal printer according to this embodiment. Processing of this flowchart is implemented when the main controller  201  loads a control program stored in the ROM  210  onto a work area of the RAM  211 , and executes the developed program.  FIG. 4  shows the outer appearance of an operation unit  215  of the thermal printer according to this embodiment. On the operation unit  215 , a power button  401  used to turn on/off the power supply of the printer, a print/stop button  406  used to issue image forming execution/stop instruction, and a liquid crystal screen  404  used to display a GUI screen are arranged. 
     Referring to  FIG. 3 , when the user turns on the power supply by pressing the power button  401  in step S 301 , the process advances to step S 302 , and the main controller  201  controls the cartridge detection sensor  212  to determine whether or not a cartridge is detected. If no cartridge is detected, the process advances to step S 303 , and the main controller  201  displays a message which prompts the user to attach a cartridge on the liquid crystal screen  404 . 
     If a cartridge is detected in step S 302 , the process advances to step S 304 , and the main controller  201  controls the paper detection sensor  213  to determine whether or not printing paper remains in the printer engine. If remaining paper is detected, the main controller  201  executes remaining paper processing in step S 305 , as will be described in detail later. 
     On the other hand, if no remaining paper is detected in step S 304  or if the remaining paper processing in step S 305  is properly complete, the process advances to step S 306 . 
     In step S 306 , the main controller  201  reads out image data via the memory I/F  216  or image data input unit  219 , and displays the readout image data on the liquid crystal screen  404 . In this image display state, the user selects an image to be formed and makes image forming settings by operating a four-way selector/SET button  405 . The user can switch the current screen to a trimming/editing screen of image data by pressing an edit button  410 , and can determine a trimming size of an image by pressing a zoom button  408  or pan button  407 . Also, the user can display information such as a file name and size of designated image data by pressing a display button  409 . The user can switch the current screen to a selection screen of edit functions such as creation of a calendar, that of a multi-layout (to lay out a plurality of image data in a given pattern), that of a multi-aspect image (for example, an image having an aspect ratio of 1:1, 4:3, 3:2, 16:9, or the like), and so forth by pressing a fun button  402 . 
     In this way, after the user selects an image to be formed and completes various image forming settings in a print image selection operation in step S 306 , when he or she presses the print/stop button  406  in step S 307 , the main controller  201  starts image forming processing. 
     &lt;Image Forming Operation&gt; 
     An image forming operation (printing control processing) by the thermal printer according to this embodiment will be described below with reference to  FIGS. 1 and 5 . Note that processing shown in  FIG. 5  is implemented when the main controller  201  develops a control program stored in the ROM  210  onto a work area of the RAM  211 , and executes the developed program. 
     Referring to  FIG. 5 , in step S 508 , the main controller  201  pulls out the printing paper  112  from the roll paper  101  by rotating the roll paper shaft  102 , and conveys the leading end of the printing paper  112  to the grip roller  103 . In step S 509  and subsequent steps, the printing paper  112  is conveyed by rotation of the grip roller  103  which is driven and controlled by the paper conveyance motor  203 . 
     In step S 509 , the main controller  201  detects the leading end of the printing paper  112  conveyed upon rotation of the grip roller  103  using the paper detection sensor  114 . After the paper detection sensor  114  detects the leading end of the printing paper  112 , a conveyance position of the printing paper  112  is controlled in an open loop. 
     In step S 510 , the main controller  201  further rotates the grip roller  103 , so that the printing paper  112  reaches the curl correction unit  105 . The printing paper  112  whose curl is corrected by the curl correction unit  105  is conveyed to the thermal head  109  and platen roller  106 , and the ink sheet  113  passes through a gap between the thermal head  109  and printing paper  112 . As shown in  FIG. 6 , the ink sheet  113  includes yellow (Y), magenta (M), and cyan (C) sublimation dye ink portions  601  to  603  and a hot-melt ink OP layer  604 . Then, sets each including the sublimation ink portions and hot-melt ink portion, which are arrayed frame-sequentially, are periodically arranged. Also, sheet top position detecting markers  605 Y,  605 M,  605 C, and  6050 P of the ink sheet  113  are arranged between the neighboring sublimation ink portions and between the sublimation ink portion and hot-melt ink portion. The printing paper  112  which has passed through the platen roller  106  reaches the discharge rollers  107 , and is conveyed to an image forming start position by the thermal head  109 . 
     In step S 511 , the main controller  201  detects the terminal end of the roll paper  101 . As the terminal end of the roll paper  101 , a terminal end hole  701  shown in  FIG. 7A  or a dedicated terminal end marker  702  shown in  FIG. 7B  is detected by a dedicated sensor or the sensor used to detect the leading end of the printing paper. This embodiment will explain a case in which the terminal end position of the roll paper  101  is determined by detecting the terminal end hole  701  shown in  FIG. 7A  by the paper detection sensor  114 . That is, when the detection result of the paper detection sensor  114  changes from a “paper detected” state to a “no paper detected” state during the pulling-out operation of the printing paper  112 , it is determined that the terminal end of the printing paper is detected. When the terminal end of the roll paper  101  is detected by the paper detection sensor  114  while the printing paper is fed out to the image forming start position, the printing paper  112  is accommodated, and a message which prompts the user to exchange paper is displayed on the liquid crystal screen  404 . 
     If no terminal end of the printing paper is detected in step S 511 , the process advances to step S 512 , and the main controller  201  conveys the printing paper  112  to the image forming start position. 
     In step S 513 , the main controller  201  sets sheet top position of the Y ink sheet. In this case, the ink sheet  113  is taken up until the marker  605 Y (only the Y marker is identifiable as a double line) of the Y sheet portion is detected by the marker detection sensor  115 . Upon completion of the sheet top position setting of the Y ink sheet, the thermal head  109 , which stands by during conveyance of the printing paper and sheet top position setting of the ink sheet, is brought into pressure contact with the platen roller  106  while clamping the printing paper  112  and ink sheet  113 . 
     In step S 514 , the main controller  201  reads out image data via the memory I/F  216  or image data input unit  219 , and converts the image data in the image buffer memories  220 Y,  220 M, and  220 C into thermal head driving data (image forming data). Then, the driver controller  221  controls the thermal head driving circuit  222  according to the thermal head driving data, thereby performing image forming. Thus, the ink sheet  113  of each color is heated according to the image forming data, and a dye is sublimated and fixed onto the printing paper  112 , thereby forming (transferring) an image for one line. Since an image forming operation for the predetermined number of lines is performed while conveying the printing paper  112  upon rotation of the grip roller  103 , a Y image is formed. Note that, in step S 514 , the printing paper  112  is conveyed in the direction of the arrow A in  FIG. 1  by rotating the grip roller  103  by the number of steps corresponding to an image size. At this time, the printing paper  112  is in pressure contact with the curl correction unit  105  and is handled while being clamped between the thermal head  109  and platen roller  106 , thereby correcting a curl of the printing paper  112 . 
     Upon completion of image forming of the Y image, the process advances to step S 515 , and the main controller  201  moves the thermal head  109  to the retracted position, and sets the printing paper  112  and ink sheet  113  to be freely movable. Then, the main controller  201  rotates the grip roller  103  in a direction opposite to that of an image forming operation, and conveys the printing paper  112  in the direction of the arrow B until the transfer start position of the first image on the printing paper  112  matches positions of the heat generating members of the thermal head  109 . 
     In step S 516 , the main controller  201  sets sheet top position of the M ink sheet by detecting the marker  605 M of the M ink sheet portion by the marker detection sensor  115  while taking up the ink-sheet take-up bobbin  108 . 
     In step S 517 , the main controller  201  executes an image forming operation of an M image using the M ink sheet portion as in step S 514  so as to overlap the image portion formed using the Y ink sheet portion. Likewise, in steps S 518  to S 523 , image forming operations of a C image and OP layer are performed so as to overlap the image portion formed using the Y ink sheet portion. Note that the OP layer assumes a role of formation of a protection layer which coats the surface of the color image on the printing paper on which the Y, M, and C images have been transferred. 
     Upon completion of the image forming operation of the OP layer in step S 523 , the process advances to step S 524 , and the main controller  201  moves the thermal head  109  to the retracted position and rotates the grip roller  103  in a direction opposite to that in the image forming operation. The main controller  201  conveys the printing paper  112  in the direction of the arrow B until a cutting position of the printing paper  112  reaches a position of the cutter  111 . In step S 525 , the main controller  201  executes cutting processing of the printing paper  112  by the cutter  111 . 
     In step S 526 , the main controller  201  clamps the printing paper  112  cut in step S 525  by the discharge roller pair  107 , and conveys the printing paper  112  in the direction of the arrow B by rotating the paper conveyance motor  203 , thereby discharging the image-forming processed printing paper  112  outside the printer. 
     Finally, in step S 527 , the main controller  201  winds up the remaining printing paper  112  by rotating the grip roller  103  and roll paper shaft  102 . 
     With the aforementioned processing, the image forming operations are complete. 
     &lt;Remaining Paper Processing 1&gt; 
     The first example of the remaining paper processing in step S 305  in  FIG. 3  will be described below with reference to  FIG. 8  and  FIGS. 9A and 9B .  FIGS. 9A and 9B  show positions of the remaining paper at the activation timing of the thermal printer of this embodiment. 
     Referring to  FIG. 8 , in step S 801 , the main controller  201  conveys the printing paper  112  in the printer engine to the position of the paper detection sensor  114  in the direction of the arrow A by rotating the grip roller  103 . At this time, a driving step count of the paper conveyance motor  203  from the beginning to the end of driving is counted by the main controller  201 . Let Xc [steps] be the driving step count. The count value is temporarily stored in the RAM  211 . 
     In step S 802 , the main controller  201  adds a step count m [steps] stored in the ROM  210  and required to convey the printing paper from the curl correction unit  105  to the paper detection sensor  114  to the Xc [steps]. Thus, a step count Xc′ [steps] required to convey the printing paper leading end position at the activation timing to the curl correction unit  105  is calculated. 
     Note that when the curl correction unit  105  includes the paper detection sensor  114 , Xc′ equals Xc, and the process of step S 802  can be omitted. 
     In step S 803 , the main controller  201  compares a first distance Xc′ [steps] with a second distance Xp [steps] stored in the ROM  210 . Note that Xp [steps] corresponds to a driving step count of the motor  203  required to convey the printing paper by an image-forming processed object length in the previous image forming operation. 
     As a method for calculation of the image-forming processed object length in the previous image forming operation, a method of storing information of the image-forming processed object length in the RAM  211  or the like, and reading out that information before step S 803  is available. On the other hand, when such storage cannot be made or when it has failed, a maximum image forming length stored in the ROM  210  is read out as the image-forming processed object length in the previous image forming operation based on the detection result of the cartridge type at the activation timing before step S 803 . Alternatively, in case of a printer which creates an image-forming processed object having a margin portion at a leading end portion of printing paper, Xp [steps] has to be set to include the length of the margin portion in addition to the aforementioned image forming length. 
     If the main controller  201  determines in step S 803  that Xp [steps]≧Xc′ [steps], the process advances to step S 804 . When Xp [steps]≧Xc′[steps], since an image-forming processed region includes a portion formed with a curl, as shown in  FIG. 9A , the image-forming processed region is clipped to also clip the curl portion. 
     Hence, in step S 804 , the main controller  201  conveys the printing paper  112  until the image forming trailing end position overlaps the cutter position, so as to clip the image-forming processed region. Let I [steps] be a driving step count of the paper conveyance motor  203  required to convey the printing paper by a spacing between the paper detection sensor  114  and cutter  111 , the paper conveyance motor  203  is driven by (Xp+I) [steps] in step S 804 . At this time, the printing paper may be conveyed more by a slight step count α [steps] under the assumption of a feed precision error by the paper conveyance motor  203 , a detection position error of the paper detection sensor  114 , an attachment error, and the like. After completion of paper conveyance in step S 804 , the process advances to step S 808 . 
     On the other hand, if the main controller  201  determines in step S 803  that Xp [steps]&lt;Xc′ [steps], the process advances to step S 805 . When Xp [steps]&lt;Xc′ [steps], since the curl portion includes an image-forming processed region, the image-forming processed region can be clipped by clipping the curl portion, as shown in  FIG. 9B . Since a portion between the trailing end of the image-forming processed region and the curl portion has not undergone any image forming operation, if a portion from the leading end of the printing paper until the curl portion is clipped, a long image-forming processed object having a margin on its trailing end portion is discharged. In order to remove an unnecessary margin portion, it is desirable to separately discharge a portion from the leading end of the printing paper to the trailing end of the image-forming processed region and that from the trailing end of the image-forming processed region to the curl portion. 
     Hence, in step S 805 , the main controller  201  conveys the printing paper  112  in the direction of the arrow B until the trailing end of the image-forming processed region overlaps the position of the cutter  111 , so as to clip the image-forming processed region. That is, in step S 805 , the paper conveyance motor  203  is driven by (Xp+I) [steps] as in step S 804 . After completion of paper conveyance in step S 805 , the process advances to step S 806 . 
     In step S 806 , the main controller  201  cuts the printing paper  112  using the cutter  111 , and discharges the image-forming processed printing paper  112  outside the printer by rotating the discharge rollers  107 . After completion of step S 806 , the process advances to step S 807 . 
     In step S 807 , the main controller  201  conveys the printing paper  112  in the direction of the arrow B until the curl portion overlaps the position of the cutter  111 , so as to clip the curl portion. Since the printing paper  112  is already conveyed in the direction of the arrow B until the trailing end position of the image-forming processed region overlaps the position of the cutter  111  in step S 805 , the printing paper  112  is conveyed in the direction of the arrow B by a length from the trailing end position of the image-forming processed region to the curl portion in step S 807 . That is, the paper conveyance motor  203  is driven by (Xc′−Xp) [steps] in step S 807 . In this step, likewise, the printing paper may also be conveyed more by the slight step count α [steps]. On the other hand, when the single paper conveyance motor  203  simultaneously rotates the grip roller  103  and discharge rollers  107 , it has to be driven in step S 807  by subtracting a driven amount required to discharge the printing paper  112  in step S 806 . After completion of step S 807 , the process advances to step S 808 . 
     In step S 808 , the main controller  201  cuts the printing paper  112  using the cutter  111 , and discharges the image-forming processed printing paper  112  outside the printer by rotating the discharge rollers  107 . 
     Finally, in step S 809 , the main controller  201  winds up the remaining printing paper  112  by rotating the grip roller  103  and roll paper shaft  102 . With the aforementioned processing, the remaining paper processing ends. 
     The remaining paper processing can prevent a re-image forming operation from a position on the image-forming processed printing paper in a next image forming operation while suppressing wasteful use of the printing paper, and can also suppress deterioration of image forming quality caused by a curl portion in the next image forming operation by a minimum printing paper clipping amount. 
     In this embodiment, when the curl portion includes the image-forming processed region, the printing paper is cut twice, that is, by a portion from the leading end of the printing paper to the trailing end of the image-forming processed region and that from the trailing end of the image-forming processed region to the curl portion. However, in consideration of shortening of a processing time and the like, a portion from the leading end of the printing paper to the curl region may be cut once. In this case, the driving amount of the paper conveyance motor  203  in step S 805  is (Xc′+I) [steps], and the need for the processes of steps S 806  and S 807  can be obviated. 
     In this embodiment, the local curl portion in the opposing direction by the curl correction unit  105  is removed. Also, a region formed with projection marks by the grip roller may be removed. In this case, the aforementioned processing can be executed intact by replacing the curl correction unit  105  of this embodiment by the grip roller  103 . That is, the driving step count m [steps] of the paper conveyance motor  203  used in step S 802  can be replaced by a driving step count n [steps] of the paper conveyance motor  203  required to convey the printing paper from the grip roller  103  to the paper detection sensor  114 . 
     &lt;Remaining Paper Processing 2&gt; 
     The second example of the remaining paper processing in step S 305  in  FIG. 3  will be described below with reference to  FIGS. 10 to 12B .  FIGS. 11A and 11B  and  FIGS. 12A and 12B  show positions of the remaining paper at the activation timing of the thermal printer of this embodiment. 
     Referring to  FIG. 10 , in step S 1001 , the main controller  201  conveys the printing paper  112  in the printer engine in the direction of the arrow A by rotating the grip roller  103 . At this time, the paper detection sensor  114  monitors whether or not the printing paper is detected, and if the “paper detected” state is switched to the “no paper detected” state, the process advances to step S 1002 . 
     In step S 1002 , the main controller  201  further conveys the printing paper in the direction of the arrow A by I [steps]. Note that I [steps] is the driving step count of the paper conveyance motor  203  required to convey the printing paper by a length slightly larger than the width of the terminal end hole  701  in the paper conveyance direction, as shown in  FIGS. 7A and 7B . In step S 1002 , the main controller  201  checks the output of the paper detection sensor  114  again after conveyance by l [steps]. 
     If the output of the paper detection sensor  114  returns to “paper detected” in step S 1002 , the process advances to step S 1003 . In this case, since the terminal end hole  701  is located between the printing paper leading end position at the activation timing and the paper detection sensor  114 , the main controller  201  executes the same operation as in step S 1001  in step S 1003 . That is, in step S 1003 , the paper detection sensor  114  monitors whether or not the printing paper is detected while conveying the printing paper  112  in the engine in the direction of the arrow A, and conveyance is continued until a timing at which the “paper detected” state is switched to the “no paper detected” state. Since the second detection of the “no paper detected” state means that the leading end of the printing paper has passed by the paper detection sensor  114 , the process advances to step S 1004 . 
     On the other hand, if the detection result “no paper detected” of the paper detection sensor  114  is still obtained after conveyance by I [steps] in step S 1002 , the leading end of the printing paper has passed by the paper detection sensor  114  in place of detection of the terminal end hole  701  at the “no paper detected” detection timing. In this case as well, the process advances to step S 1004 . 
     In step S 1004 , the main controller  201  conveys the printing paper in the direction of the arrow B until a position separated by Yp from the leading end of the printing paper overlaps the position of the cutter  111 . Note that Yp is the image-forming processed object length in the previous image forming operation. As a method for calculation of the image-forming processed object length in the previous image forming operation, a method of storing information of the image-forming processed object length in the RAM  211  or the like, and reading out that information before step S 1004  is available. On the other hand, when such storage in the RAM  211  cannot be made or when it has failed, a maximum image forming length stored in the ROM  210  is read out as the image-forming processed object length in the previous image forming operation based on the detection result of the cartridge type at the activation timing before step S 1004 . Alternatively, in case of a printer which creates an image-forming processed object having a margin portion at a leading end portion of printing paper, Xp [steps] has to be set to include the length of the margin portion in addition to the aforementioned image forming length. 
     The main controller  201  determines in step S 1005  whether or not the detection state of the printing paper by the paper detection sensor  114  is temporarily switched from the “no paper detected” state to the “paper detected” state, and is then switched from the “paper detected” state to the “no paper detected” state again in the middle of step S 1004 . Note that the reason why the “no paper detected” state is temporarily switched to the “paper detected” state is that the leading end of the printing paper is conveyed to a point on the upstream of the paper detection sensor  114  (on the side of the direction of the arrow A) in step S 1001  or S 1003 . That is, this “paper detected” state is equivalent to detection of the leading end of the printing paper. In step S 1005 , the main controller  201  counts driving steps t [steps] of the paper conveyance motor  203  from detection of the leading end of the paper until the terminal end hole  701  is detected. 
     If the conveyance is complete without being switched from the “paper detected” state in step S 1005 , since no terminal end of the printing paper is detected, the process advances to step S 1009 .  FIG. 11A  shows the position of the remaining paper at the activation timing in this case. 
     On the other hand, if the “no paper detected” state is detected in step S 1005 , the process advances to step S 1006 . In step S 1006 , the main controller  201  compares a conveyance amount Ye calculated from the driving steps t [steps] of the paper conveyance motor  203  from the leading end of the printing paper to the terminal end hole  701  (to be referred to as a “remaining amount Ye of printing paper” hereinafter) with Ym. Note that Ym indicates a shortest image-forming processed object length which can be printed by the printer. In order to calculate the shortest image-forming processed object length, a shortest image forming length stored in the ROM  210  need only be read out before step S 1006  based on the detection result of the cartridge type at the activation timing. Alternatively, in case of a printer which creates an image-forming processed object having a margin portion at a leading end portion of printing paper, Ym has to be set to include the length of the margin portion in addition to the aforementioned image forming length. On the other hand, in a printer which cannot perform image forming operations of image-forming processed objects of a plurality of image forming lengths, Yp equals Ym. 
     If the remaining amount Ye of the printing paper &lt;the shortest image-forming processed object length Ym in step S 1006 , the process jumps to step S 1010 .  FIG. 11B  shows the position of the remaining paper at the activation timing in this case. In this case, since the remaining amount of the printing paper is small, the printing paper may not be pulled out by Yp. Also, since the remaining amount Ye of the printing paper &lt;the shortest image-forming processed object length Ym, an image is unlikely to be formed on the remaining paper. For this reason, the remaining paper is not cut, and the printing paper  112  is accommodated in the cartridge in step S 1010 . After the printing paper  112  is accommodated in the cartridge, a message which prompts the user to exchange printing paper may be displayed on the liquid crystal screen  404 , or the processing may end without prompting the user to exchange printing paper, so as to commonize processing with other cases to be described later. Even in this case, at the paper feed timing (step S 511  in  FIG. 5 ) before the next image forming operation, since the terminal end of the printing paper is detected, a problem of a detection failure of the terminal end of the printing paper never occurs. 
     On the other hand, if the remaining amount Ye of the printing paper ≧the shortest image-forming processed object length Ym in step S 1006 , the process advances to step S 1007 . In step S 1007 , the main controller  201  compares the remaining amount Ye of the printing paper with the previous image-forming processed object length Yp. 
     If the remaining amount Ye of the printing paper≦the the previous image-forming processed object length Yp in step S 1007 , the process advances to step S 1008 .  FIG. 12A  shows the position of the remaining paper at the activation timing in this case. 
     In step S 1008 , the main controller  201  cuts the printing paper  112  using the cutter  111  at a position at which a cutting amount is less than Ye and is larger than (Ye−Ym), so as not to cut the terminal end hole  701  by mistake. The reason why the printing paper is cut at the position at which the cutting amount is larger than (Ye−Ym) is that it is not guaranteed that the clipped remaining printing paper does not undergo any image forming operation. When the printing paper is cut at this position, since the remaining amount Ye of the printing paper is less than the shortest image-forming processed object length Ym, even when an image forming operation of the shortest image-forming processed object length Ym is attempted at the next image forming timing, the terminal end of the printing paper can be detected at the paper feed timing before the image forming operation (step S 511  in  FIG. 5 ). After completion of the discharge operation of the printing paper  112 , the process advances to step S 1010 , and the remaining printing paper is accommodated in the cartridge. After the printing paper  112  is accommodated in the cartridge, a message which prompts the user to exchange printing paper may be displayed on the liquid crystal screen  404 , or the processing may end without prompting the user to exchange printing paper, so as to commonize processing with other cases to be described later. 
     On the other hand, if the remaining amount Ye of the printing paper is larger than the previous image-forming processed object length Yp in step S 1007 , the process advances to step S 1009 .  FIG. 12B  shows the position of the remaining paper at the activation timing in this case. Step S 1009  is executed after step S 1005  or S 1007 . In either case, the printing paper  112  is cut using the cutter  111  at a position corresponding to a cutting amount=Yp so as to prevent the terminal end hole  701  from being cut by the cutter  111  by mistake. Note that the printing paper may be cut by a length slightly larger than Yp under the assumption of a feed precision error by the paper conveyance motor  203 , a detection position error of the paper detection sensor  114 , an attachment error, and the like. However, the terminal end hole  701  does not have to be cut by slightly increasing the cutting amount, as a matter of course. After the printing paper  112  is cut, the cut printing paper  112  is discharged, and the process advances to step S 1010 . 
     In step S 1010 , the main controller  201  accommodates the remaining printing paper in the cartridge. After the printing paper  112  is accommodated in the cartridge, since an image forming operation is likely to be executed depending on an image forming length even via step S 1007 , it is desirable to end processing without prompting the user to exchange printing paper. 
     With the aforementioned processing, the remaining paper processing ends. 
     The remaining paper processing can prevent a re-image forming operation from a position on image-forming processed printing paper in the next image forming timing, and can also prevent a terminal end detection portion of the roll paper from being clipped by mistake. Furthermore, the roll paper having the small remaining amount can be prevented from being pulled out forcedly. 
     In this embodiment, a portion from the leading end of the printing paper to the trailing end of the image-forming processed region or to a position before the terminal end hole is cut by a single cutting operation. However, the portion of the printing paper need not always be cut by the single cutting operation. For example, in a printer in which a margin portion is set at the leading end of the printing paper, and is discarded as waste in a normal image forming operation, the printing paper may be cut by a single cutting operation at the margin portion at the leading end of the printing paper by the remaining paper processing of this embodiment. 
     Note that the printing paper of this embodiment is not limited to paper, but the present invention is applicable to print sheets such as plastic films which are made up of other materials. 
     This embodiment has exemplified the case in which the image forming apparatus of the present invention is applied to a thermal transfer or sublimation type thermal printer. However, the present invention is not limited to the thermal printer. For example, in an inkjet printer, adhesion is never caused by a re-image forming operation on image-forming processed printing paper, but deterioration of image forming quality due to the re-image forming operation on the image-forming processed printing paper cannot be avoided. Hence, by practicing the remaining paper processing of the present invention, deterioration of image forming quality can be avoided. In this manner, the present invention is applicable to various types of image forming apparatuses using roll paper. 
     This embodiment has explained the case in which the sensor required to set the sheet top position of the printing paper is common to that required to detect the terminal end of the printing paper. However, the common sensor need not always be used. 
     Other Embodiments 
     Aspects of the present invention can also be realized by a computer of a system or apparatus (or devices such as a CPU or MPU) that reads out and executes a program recorded on a memory device to perform the functions of the above-described embodiment(s), and by a method, the steps of which are performed by a computer of a system or apparatus by, for example, reading out and executing a program recorded on a memory device to perform the functions of the above-described embodiment(s). For this purpose, the program is provided to the computer for example via a network or from a recording medium of various types serving as the memory device (for example, computer-readable medium). In such a case, the system or apparatus, and the recording medium where the program is stored, are included as being within the scope of the present invention. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2012-109927, filed May 11, 2012, which is hereby incorporated by reference herein in its entirety.