Patent Publication Number: US-7594645-B2

Title: Sheet processing device and image formation apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is related to U.S. Patent Application, entitled “Folded Back Portion Flattening Device, Sheet Processor, And Image Forming Apparatus”, filed concurrently herewith, and is incorporated in its entirety by reference herein. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a sheet processing device which flattens down a folded back portion of a folded and curved sheet bundle, and an image formation apparatus incorporating this device. In particular, the present invention relates to a sheet processing device which flattens down the folded back portion of the sheet bundle, the sheet processing device including a function for sending the sheet bundle through a gripping roller pair and a function for gripping the sheet bundle when flattening down the folded back portion of the sheet bundle with a pressing unit, and to an image formation apparatus. 
   2. Description of the Related Art 
   Conventionally, sheets of a predetermined number (e.g., around twenty) are stacked and folded into booklet-like form with stitching/folding equipment. The sheet bundles that are folded down with such stitching/folding equipment include sheet bundles that are simply folded, sheet bundles that are saddle-stitched and folded, sheet bundles that are not bound with string or staples but are glued (perfect binding) and folded, and so forth. 
   However, all types of sheet bundles possess some degree of resilience, and accordingly, following folding, the area of the curved folded back portion (folded tip portion, back cover) bulges and bends and forms a U-shape, and tends to form a small opening on the open side of the folded sheet bundle. Such sheet bundles become unstable when bundled and collapse easily, and storage and conveying of such sheet bundles have been troublesome. 
   To solve this problem so that the folded sheet bundles can be placed flat, a folded back flattening processing device that flattens down the folded back portion of the folded sheet bundles is known (see U.S. Pat. No. 6,692,208). 
   As illustrated as an example in  FIG. 17 , a conventional folded back flattening processing device  901  is integrated into a sheet processing device  920 . Further, the sheet processing device  920  is connected to a main device unit  922  of a photocopier  921  (image formation apparatus). The photocopier  921  forms images on the sheets. This conventional sheet processing device  920  forms booklet-like sheet bundles as illustrated in  FIGS. 17 and 20 . 
   The sheet processing device  920  receives and makes bundles S with a saddle tray  960  from sheets that are sent in order and having an image formed by the main device unit  922 . The center of the sheet bundle is bound with a stapler  962 . Then, the sheet bundle is conveyed in the lower direction, and is received and stopped by a stopper  963 . After this, an abutting plate  961  abuts the bound portion of the sheet bundle, and presses the sheet bundle into a nip portion of a folding roller pair  907 . The folding roller pair  907  folds the sheet bundle with the nip portion while discharging the sheet bundle to a discharge belt pair  906 . The folded sheet bundle S is conveyed in the direction of arrow B with the folded back portion Sb at the leading edge, by the discharge belt pair  906 , and is sent through one pair of separated gripping members  902  and  903  ( FIG. 19A ). Then the folded back portion Sb of the sheet bundle S is received by a stopping plate  905  and stops. The discharge belt pair  906  then stops conveying the sheet bundle, and the pair of gripping members  902  and  903  grip the sheet bundle. At this time, the folded back portion Sb protrudes from the gripping members  902  and  903 . 
   After this, the stopping plate  905  rises and separates from the folded back portion Sb ( FIG. 19B ). Then, a pressing roller  904  runs along the folded back portion Sb in the direction of the arrow A while pressing the folded back portion Sb, and flattens down the curved folded back portion Sb ( FIGS. 18 ,  19 B, and  20 ). Finally, the discharge belt pair  906  discharges the processed sheet bundle S onto a discharge sheet tray  908  ( FIG. 19C ). 
   As described above, the gripping members  902  and  903  of the conventional sheet processing device  920  only functions to grip the sheet bundle S. 
   Thus, the conventional sheet processing device  920  have the gripping members  902  and  903  which only function to grip the sheet bundle S, therefore necessitating the discharge belt pair  906  as a sheet conveying device for discharging the sheet bundle from the gripping members  902  and  903 , increasing the size and complexity of the configuration of the device. This further has led to increased overall size of the image formation apparatus having such a sheet conveying device. 
   SUMMARY OF THE INVENTION 
   The present invention provides a sheet processing device, wherein the configuration of the device is simple and compact, having a function for conveying a sheet bundle to a conveying rotary member pair, and a function for gripping the sheet bundle while the folded back portion of the sheet bundle is being flattened down with a pressing unit. 
   The present invention also provides for a compact image formation apparatus incorporating a sheet processing device having a simple and compact configuration. 
   In one aspect of the present invention, a sheet processing device is operable to process a sheet bundle in a booklet-like form and having a folded back portion. The sheet processing device includes a conveying rotary member configured to grip and convey the sheet bundle, a pressing unit configured to press and flatten the folded back portion of the sheet bundle gripped by the conveying rotary member, and a control unit controlling the conveying rotary member. The control unit controls the conveying rotary member to stop conveying the sheet bundle when the folded back portion of the sheet bundle protrudes from the conveying rotary member by a predetermined amount. The pressing unit flattens down the protruding aforementioned folded back portion while the conveying rotary member pair is stopped by the control unit and is gripping the sheet bundle. 
   In another aspect of the present invention, an image formation apparatus includes an image forming unit configured to form images on a sheet, and the sheet processing device described above which flattens down the folded back portion of a sheet bundle in the booklet-like form and having images formed thereon by the image forming unit. 
   The sheet processing device according to the present invention has a function wherein the conveying rotary member grips and rotationally conveys the sheet bundle in booklet-like form, and a function wherein the conveying of the sheet bundle is temporarily stopped and the sheet bundle is gripped while the pressing unit is pressing the folded back portion of the sheet bundle, and therefore the configuration can be simplified, use of space is more efficient, and the device can be made more compact. 
   The image formation apparatus according to the present invention includes a sheet processing device wherein the configuration is simplified and compact, and therefore the device can be more compact and space-efficient. 
   Further features and advantages 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 schematic cross-sectional front view of a photocopier incorporating a sheet processing device according to a first embodiment of the present invention. 
       FIGS. 2A through 2F  are front schematic views and action description diagrams of the folded back portion flattening processing device illustrated in  FIG. 1 . 
       FIGS. 3A through 3D  are plan views and action description diagrams of the folded back portion flattening processing device illustrated in  FIG. 1 . 
       FIG. 4  is a flowchart for describing the action of the folded back portion flattening processing device illustrated in  FIG. 1 . 
       FIGS. 5A through 5C  are front views of another example of the pressing roller in the folded back portion flattening processing device illustrated in  FIG. 1 . 
       FIG. 6  is a schematic cross-sectional front view of a photocopier incorporating a sheet processing device according to a second embodiment, having the folded back face processing device according to the first embodiment relating of the present invention. 
       FIGS. 7A through 7F  are front views and action description diagrams of the folded back face processing device according to the first embodiment illustrated in FIG.  6 . 
       FIGS. 8A through 8D  are plan view schematic diagrams and action description diagrams of the folded back face processing device illustrated in  FIG. 6 . 
       FIG. 9  is a flowchart for describing the action of the folded back face processing device illustrated in  FIG. 6 . 
       FIG. 10  is a front view schematic diagram of a photocopier in a case wherein the sheet processing device according to the first embodiment illustrated in  FIG. 6  externally discharges the sheet bundle. 
       FIGS. 11A through 11F  are front view schematic diagrams and action description diagrams of the folded back face processing device according to the second embodiment. 
       FIGS. 12A through 12D  are plan view schematic diagrams and action description diagrams of the folded back face processing device according to the second embodiment as illustrated in  FIGS. 11A through 11F . 
       FIG. 13  is a flowchart for describing the action of the folded back face processing device according to the second embodiment as illustrated in  FIGS. 11A through 11F . 
       FIGS. 14A through 14F  are front view schematic diagrams and action description diagrams of the folded back face processing device according to a third embodiment. 
       FIGS. 15A through 15F  are front view schematic diagrams and action description diagrams of the folded back face processing device according to a fourth embodiment. 
       FIGS. 16A through 16F  are front view schematic diagrams and action description diagrams of the folded back face processing device according to a fifth embodiment. 
       FIG. 17  is a front view cross-sectional schematic diagram of a photocopier that is one example of a conventional image formation apparatus. 
       FIG. 18  is a plan view of a folded back portion flattening processing device included in a sheet processing device of a conventional photocopier. 
       FIGS. 19A through 19C  are front views of the folded back portion flattening processing device illustrated in  FIG. 18 . 
       FIG. 20  is an enlarged schematic view of the folded back portion in  FIG. 19 . 
   

   DESCRIPTION OF THE EMBODIMENTS 
   The sheet processing device according to the first embodiment of the present invention, and a photocopier incorporating the sheet processing device, will be described below while referencing the diagrams. 
   Photocopier 
   (Configuration of Photocopier) 
   A photocopier, which is one example of an image formation apparatus, incorporating a sheet processing device according to a first embodiment of the present invention will be described based on  FIG. 1 . A photocopier  1 , such as a full color photocopier, includes platen glass  71  serving as an original document table, a light source and lens system  72 , a sheet supply unit  64 , a resist roller pair  76 , an image forming unit  65 , an automatic document feeding device (ADF)  73  that automatically feeds documents to the platen glass  71 , a sheet processing device  2  that processes the sheets whereupon an image has been formed and discharged from a main device unit  3  of the photocopier  1 , a photocopier control unit  81  that controls the entire photocopier  1 , and the like. 
   The sheet supply unit  64  has multiple cassettes  68  that store sheets for recording, and that are detachable from the main device unit  3 . The image forming unit  65  includes cylindrical photosensitive drums  74 , and developing units  75  supporting various colors of yellow, magenta, cyan, and black positioned surrounding the photosensitive drums  74 . On the downstream side of the image forming unit  65 , a fixing device  66  that fixes onto the sheet a color toner image transferred from the photosensitive drums  74 , a discharge roller pair  63  that discharges the sheet, and the like, are positioned. 
   (Operations of Photocopier) 
   Upon a sheet supply signal being output from the main device unit  3  of the photocopier  1 , a sheet is supplied from the cassette  68  to the resist roller pair  76 . Meanwhile, light, illuminated from the light source and lens system  72  onto the document placed on the original document table  71  and is reflected therefrom, passes through the light source and lens system  72 , is subjected to signal processing, and is irradiated onto the photosensitive drum  74  from a write optical system (not shown). The photosensitive drum  74  is charged beforehand by a primary charger (not shown), and a electrostatic latent image is formed on the photosensitive drum by irradiation of light. The electrostatic latent image on the photosensitive drum  74  is developed by the developing unit  75  and becomes a toner image. 
   After the sheet that is supplied from the sheet supply unit  64  has its angle corrected by the resist roller pair  76 , the sheet is sent to the image forming unit  65  while matching the timing to the position of the toner image of the photosensitive drum  74 , and the color toner image of the photosensitive drum  74  is transferred thereupon. Then the color toner image is permanently fixed onto the sheet by the fixing device  66 . The sheet whereupon the color toner image is fixed is discharged from the main device unit  3  by the discharge roller pair  63 . Thus, the sheet supplied from the sheet supply unit  64  receives a color toner image formed thereupon, and is sent from the main device unit  3  to the sheet processing device  2 . 
   Now, the sheet processing device denoted by the reference numeral  2  is a sheet processing device of the first embodiment. Alternatively, a sheet processing device  102  (see  FIG. 6 ) of a second embodiment may also be connected to the main device unit  3 . 
   Sheet Processing Device of the First Embodiment 
   (Configuration of Sheet Processing Device of First Embodiment) 
   As illustrated in  FIG. 1 , the sheet processing device  2  includes a fixed tray  69  to which a sheet upon which an image has been formed is discharged and stacked, having been discharged from the discharge roller pair  63  of the main device unit  3  by passing through the sheet processing device  2 , a stapler  70  that binds the sheets formed into a bundle after being discharged from the main device unit  3 , a stacking tray  78  capable of being raised or lowered and supporting the sheet bundles bound by the stapler  70 , a binding device  79  that binds the sheets that are discharged from the main device unit  3  in bundle form, a folding device  58  that folds the bound sheet bundle in half, a folded back flattening processing device  21  of the present embodiment, a processing device control unit  20  that controls the entire sheet processing device  2 , and so forth. 
   Now, the processing device control unit  20  can be built into the photocopier control unit  81  and provided in either the main device unit  3  or the sheet processing device  2  of the photocopier  1 . Further, bundled sheets may be discharged and stacked on the stacking tray  78  without being bound by the stapler  70 . 
   The binding device  79  includes a saddle tray  60  and a stapler  62 . The binding device  79  bundles the multiple sheets discharged from the discharge roller pair  63  into a bundle, and then binds the bundle in the middle. While two positions are bound in the present embodiment, the present invention is by no means restricted to this. The member denoted by ST in  FIGS. 3A and 3C  is a binding staple. 
   The folding device  58  serving as a folding unit includes an abutting plate  61  and a folding roller pair  59 , and is configured so that the bound portion of the sheet bundle that is sent from the binding device  79  is thrust by the abutting plate  61 , thereby folding the sheet bundle in half with the folding roller pair  59 , so as to be in the form of a folded booklet. 
   (Operations of Sheet Processing Device of First Embodiment) 
   The binding device  79  receives and arranges the sheets into a bundle at the saddle tray  60  in the order sent from the discharge roller pair  63 . The arranged sheet bundle is bound in the middle by the stapler  62 . After this, the abutting plate  61  that is an abutting member is moved by an abutting plate motor (not shown) and abuts the bound portion of the sheet bundle in the direction of the thickness of the sheet bundle, and presses the sheet bundle into the nip portion of the folding roller pair  59 . The abutting plate  61  retreats after pushing the sheet bundle between the folding roller pair  59 . The folding roller pair  59  is rotated by a motor (not shown), and while gripping and conveying the sheet bundle, folds it in half, and sends it through to the folded back portion flattening processing device  21 . Lastly, the folded back portion flattening processing device  21  flattens down the folded back portion of the sheet bundle, and discharges the sheet bundle onto a discharge tray  16 . 
   As described above, the sheet processing device  2  takes the sheets upon which an image is formed within the main device unit  3 , forms a bundle thereof at the saddle tray  60 , binds the bundle with the stapler  62 , then folds this bundle in half into a booklet-like form with the folding device  58 , and flattens down the folded back portion of the sheet bundle S into a booklet-like form by the folded back portion flattening processing device  21 . 
   Folded Back Portion Flattening Processing Device 
   (Configuration of Folded Back Portion Flattening Processing Device) 
   As illustrated in  FIGS. 1 through 4 , the folded back portion flattening processing device  21  presses and flattens the folded back portion (back cover) Sb, that is curved into a U-shape of the sheet bundle in a booklet-like form and sent from the folding device  58 , with a pressing roller  7 , so that the cross-sectional form of the folded back portion area is a somewhat square shape with essentially no bulging. 
   The folded back portion flattening processing device  21  includes a gripping device  14  (gripping unit) that has a gripping roller pair  4  and  5  as a conveying rotary member pair that grip the folded sheet bundle S, a pressing device  15  (pressing unit) having a pressing roller  7  that presses the folded back portion Sb of the sheet bundle S gripped by the gripping device  14 . 
   The lower gripping roller  5  is a roller on the drive side, and is rotated by a rotational force of a roller drive motor  8  via a gear train  6  and a rotating shaft  9 . The upper gripping roller  4  has a rotating shaft  12 , and rotates with the lower gripping roller  5 . The gripping roller pair  4  and  5  has a length longer than the width of the sheet bundle. The gripping device  14  includes the gripping roller pair  4  and  5  and the roller drive motor  8 . On the downstream side of a nip portion N of the gripping roller pair  4  and  5 , a back folded portion detecting sensor  10  is provided as a detecting unit for detecting the folded back portion Sb of the sheet bundle that protrudes from the nip portion N. 
   Alternative to the folded back portion detecting sensor  10 , an arrangement may be made wherein the rotational force of the roller drive motor  8  is detected and the amount of protrusion of the folded back portion from the nip portion N of the gripping rollers  4  and  5  is detected. The roller drive motor  8  and the folded back portion detecting sensor  10  are connected to the processing device control unit  20 . 
   (Operations of Folded Back Portion Flattening Processing Device) 
   The conveying belt pair  13  conveys the sheet bundle in the direction of the arrow B, with the folded back portion Sb of the sheet bundle S in front. The processing device control unit  20  starts the roller drive motor  8  ( FIG. 4  (S 1 )). The gripping roller pair  4  and  5  starts rotating ( FIGS. 2A and 3A , (S 2 )). The gripping roller pair  4  and  5  grips and conveys the sheet bundle S when the folded back portion Sb of the sheet bundle arrives and enters the nip portion N ( FIGS. 2B and 3B ). When the folded back portion Sb protrudes from the nip portion N and is detected by the folded back portion detecting sensor  10  ( FIGS. 2C and 3C  (S 3 )), the processing device control unit  20  stops the roller drive motor  8  (S 4 ). 
   The gripping roller pair  4  and  5  stops rotating while still gripping the sheet bundle (S 5 ). At this time, the folded back portion Sb is protruding only by the predetermined length (L 4 ) from the nip portion N of the gripping roller pair  4  and  5  in the position in which the portion Sb is being pressed by the pressing roller  7 . On the downstream side of the nip portion N, a stopper can be provided that includes an abutting face in the direction perpendicular to the conveying direction of the sheet bundle wherein the folded back portion Sb is abutted in a predetermined position, and the angle of the conveying direction of the sheet bundle can be corrected. In the instance of abutting to a stopper, the gripping pressure of the gripping roller pair  4  and  5  needs to be reduced or eliminated so that correcting the position of the sheet bundle is facilitated. 
   After this, the pressing roller  7  moves while rotating in the direction of arrow A (in the direction along the folded back portion Sb) while pressing the folded back portion Sb ( FIGS. 2D and 3D  (S 6 )). The folded back portion Sb of the sheet bundle is pressed by the pressing roller  7  while in the state of being gripped by the gripping roller pair  4  and  5 . The cross-sectional form of the folded back portion area becomes a somewhat squared shape with essentially no bulging. The distance between the pressing face of the pressing roller  7  and the nip portion N of the gripping roller pair  4  and  5  at this time is set to be shorter than the protruding length (L 4 ) of the folded back portion Sb, and is sufficient for flattening down the folded back portion Sb, and the appropriate pressure is placed so as not to cause damage to the folded back portion Sb. 
   When the flattening processing of the folded back portion Sb is completed by the pressing roller  7  (S 7 ), the processing device control unit  20  restarts the roller drive motor  8  (S 8 ). The gripping roller pair  4  and  5  rotates and conveys the sheet bundle S ( FIG. 2E  (S 9 )). The sheet bundle S is discharged onto the discharge tray  16  ( FIG. 2F ). When the sheet bundle is sent out from the gripping roller pair  4  and  5 , and the folded back portion Sb is no longer detected by the folded back detecting sensor  10  (S 10 ), the processing device control unit  20  determines that the sheet bundle S has been discharged onto the discharge tray  16 , and stops the roller drive motor  8  (S 11 ). Thus, the gripping roller pair  4  and  5  also stops (S 12 ). 
   After this, in the case that a subsequent sheet bundle exists (S 13 ), the folded back portion flattening processing device  21  returns to S 1 , and flattens down the folded back portion of the subsequent sheet bundle. In the case of no subsequent sheet bundle, the folded back portion flattening processing device  21 , the sheet processing device  2 , and the photocopier  1  end their actions. 
   Now, the pressing roller  7  stops in the position illustrated by the dotted line in  FIG. 3D  after flattening down the folded back portion Sb of the sheet bundle S, but can flatten down the folded back portion Sb of the next sheet bundle while returning to the position illustrated by a solid line in  FIG. 3A  from the dotted line position. Alternatively, upon returning to the position illustrated with the solid line of  FIG. 3A , the back folded portion Sb of the subsequent sheet bundle can be flattened down while moving again to the position illustrated by the dotted line in  FIG. 3D . 
   With the above configuration, a conveying belt  13  is not necessarily required. A directional plate that supports the sheet bundle may be provided. In this case, the sheet bundle is directly handed from the folding roller pair  59  to the gripping roller pair  4  and  5 . 
   Now,  FIGS. 5A through 5C  illustrate a pressing roller  18  serving as a pressing unit that has a different configuration from the pressing roller  7  illustrated in  FIGS. 2A through 2F . As illustrated in  FIG. 5B , with the pressing roller  18 , the length of a rotating face  18   a  (L 1 ) of the pressing roller  18  that presses on the folded back portion Sb is of a length that can enter a region SP formed by the common tangent lines of the gripping roller pair  4  and  5  and the periphery faces  4   a  and  5   a . In other words, the axial direction length of the pressing face of the pressing roller  18  that presses the folded back portion Sb is set to be shorter than the distance between the center of the gripping roller pair  4  and  5 , and thus can enter in the region that is formed by the common tangent lines of the gripping roller pair  4  and  5  and the periphery faces  4   a  and  5   a . On the other hand, the length L 2  of a rotating face  7   a  of the pressing roller  7  (see  FIGS. 2A through 2F ) is set to a length that cannot enter the region that is formed by the common tangent lines of the gripping roller pair  4  and  5  and the periphery faces  4   a  and  5   a . Therefore, the pressing roller  18  can approach the nip portion N of the gripping rollers  4  and  5  closer than the pressing roller  7 , and the protruding length L 3  of the sheet bundle of the pressing roller  18  can be made shorter than the protruding length L 4  (see  FIGS. 2A through 2F ) of the sheet bundle of the pressing roller  7  (L 3 &lt;L 4 ). As a result, the pressing roller  18  of  FIG. 5B  allows for a shorter protruding length of the sheet bundle than the pressing roller  7  of  FIG. 2C , and pressing the folded back portion results in less deformation such as the folded back portion escaping, and the folded back portion can be more easily flattened down. 
   The gripping roller pair  4  and  5  is formed with a circular cross-section. Alternatively, the gripping roller pairs  204  and  205 ,  304  and  305 ,  404  and  405 , and  504  and  505  as illustrated in  FIGS. 11A through 11F  and  FIGS. 14A through 16F  to be described below can be formed as relief flat faces  204   b  and  205   b , relief notches  304   c  and  305   c , relief faces  404   d  and  405   d , relief flat faces  504   b  and  505   b , and relief faces  504   d  and  505   d . Further, a conveying belt pair (rotary member pair) can be used in place of the gripping roller pair  4  and  5 . 
   The pressing roller  7  or  18  that moves in the sheet width direction is used as a pressing unit to flatten down the folded back portion of the sheet bundle, but a circulating belt can be used that has a straight line portion greater than the sheet width wherein the folded back portion is pressed. In the case of using belts, in order to correspond to the pressing roller  18 , the belt width should be made to the width that can enter the external periphery on the inner side of the common tangent lines of the gripper roller pair. 
   The folded back portion flattening processing device  21  of the above embodiment is configured to flatten down the folded back portion of the sheet bundle that is bound with the stapler  62 . Alternatively, flattening down the folded back portion of sheet bundles that are not bound, or sheet bundles that are bound using perfect binding can be performed. 
   As described above, the gripping roller pair  4  and  5  in the sheet processing device  2  of the present embodiment performs conveying of the sheet bundle, gripping of the sheet bundle when the pressing roller  7  is flattening down the folded back portion, and conveying of the sheet bundle after the folded back flattening process. Therefore, the sheet processing device  2  of the present embodiment can use the gripping roller pair  4  and  5  for the function of gripping the sheet bundle and the function for conveying the sheet bundle. As such, the configuration can be made simpler, and the device can be made more compact so as to take up less space. 
   Further, the sheet processing device  2  of the present embodiment folds and conveys the sheet bundle with the folding roller pair  59 , and then grips and conveys with the gripping roller pair  4  and  5 , resulting in the folding action of the sheet bundle being performed twice. Therefore, the sheet processing device  2  of the present embodiment can improve the folding quality of the sheet bundle. 
   Further, with the sheet processing device  2  of the present embodiment, at the point in which the gripping roller pair  4  and  5  is gripping the sheet bundle, the back edge of that sheet bundle is extended from the folding roller pair  59 , the subsequent sheet bundle can be folded with the folding device  28  during the folded back flattening processing, and productivity can be improved. That is to say, the photocopier  1  of the present invention has a sheet processing device  2  wherein the configuration is simple and compact, and therefore the device can be made more compact and take up less space. 
   Sheet Processing Device of Second Embodiment 
   (Configuration of Sheet Processing Device of Second Embodiment) 
   As illustrated in  FIGS. 6 through 9 , the sheet processing device  102  of the second embodiment has a folded back face processing device  130  wherein the folding device  58  of the sheet processing device  2  of the first embodiment and the folded back portion flattening processing device  21  are integrated. 
   Now, with the sheet processing device  102  illustrated in  FIG. 6 , and the photocopier  101  including this sheet processing device  102  in the main device unit  3 , components which are the same as those of the sheet processing device  2  of the first embodiment and the photocopier  1  having this sheet processing device  2  will be denoted by the same reference numerals and description thereof will be omitted. Further, the sheet processing device  102  of the second embodiment can have folded back face processing devices  230 ,  330 ,  430 , or  530  of the second through fifth embodiments, in place of the folded back face processing device  130  of the first embodiment. 
   Folded Back Face Processing Device of First Embodiment 
   (Configuration of Folded Back Face Processing Device of First Embodiment) 
   As illustrated in  FIG. 7A  through  FIG. 8D , the folded back face processing device  130  of the present embodiment includes an abutting plate  161  that is an abutting member for abutting the bound portion of the sheet bundle that has been bound with the binding device  79 , a gripping device  114  serving as a sheet gripping unit having a gripping roller pair  104  and  105  serving as a conveying rotary unit which receives the sheet bundles abutted by the abutting plate  161  in the nip portion N, a pressing device  115  serving as a pressing unit having a pressing roller  107  serving as a pressing unit that presses the folded back portion Sb of the sheet bundle S gripped by this gripping device  114 , an abutting plate detecting sensor  111  that detects the tip of the abutting plate  161 , and a folded back portion detecting sensor  10  serving as a detecting unit that detects the folded back portion Sb of the sheet bundle protruding from the nip portion N. The abutting plate detecting sensor  111  and the folded back portion detecting sensor  10  are connected to the processing device control unit  120 . 
   Now, the abutting plate  161  is moved by the abutting plate motor (not shown), and the position can be detected based on the rotations of the abutting plate motor. In this case, the abutting plate detecting sensor  111  does not need to be provided. 
   The lower gripping roller  105  is a roller on the drive side, and is rotated by the gear train  6  and the rotating shaft  109  from the rotational force of the roller drive motor  8 . The upper gripping roller  104  has a rotating shaft  112 , and rotates in accordance with the rotations of the lower gripping roller  105 . The gripping device  114  includes the gripping roller pair  104  and  105  and the roller drive motor  8 . 
   (Operations of Sheet Processing Device of Second Embodiment and Folded Back Face Processing Device of First Embodiment) 
   The binding device  79  receives and arranges the sheets into a bundle in the saddle tray  60  in the order that they are sent from the discharge roller pair  63 . The arranged sheet bundle is bound in the middle by the stapler  62 . 
   After this, the abutting plate  161  is moved by the abutting plate motor (not shown), and moves closer to the bound portion of the sheet bundle ( FIGS. 7A and 8A ). Upon the abutting plate detecting sensor  111  detecting the tip  161   a  of the abutting plate  161 , the processing device control unit  120  starts the roller drive motor  8  ( FIG. 9  (S 101 ) (S 102 )). The gripping roller pair  104  and  105  starts to rotate ( FIGS. 7A and 8A  (S 103 )). 
   Now, in a case wherein the abutting plate detecting sensor  111  is not provided, and the position of the abutting plate  161  is detected by the rotations of the abutting motor (not shown) which moves the abutting plate  161 , the roller drive motor  8  can be started with the ON signal of this abutting plate motor as a trigger. 
   The abutting plate  161  presses the sheet bundle into the nip portion N of the gripping roller pair  104  and  105 . The gripping roller pair  104  and  105  receives the sheet bundle pushed in with the nip portion N, and grips and conveys the sheet bundle S ( FIGS. 7B and 8B ). The abutting plate  161  that has pushed the sheet bundle into the nip portion N retreats in the direction of the arrow C ( FIG. 8B ). The gripping roller pair  104  and  105  conveys the sheet bundle while folding, so that the sheet bundle assumes a booklet-like form. When the folded back portion Sb protrudes from the nip portion N and is detected by the folded back portion detecting sensor  10  ( FIGS. 7C and 8C  (S 104 )), the processing device control unit  120  stops the roller drive motor  8  (S 105 ). 
   The gripping roller pair  104  and  105  stops rotating while still gripping the sheet bundle (S 106 ). At this time, the folded back portion Sb protrudes only by a predetermined length (0.7 mm to 1.5 mm for example; however, the present embodiment is not restricted to this range, and the range may vary according to the material and/or the thickness of the sheet) from the nip portion N of the gripping roller pair  104  and  105  in the position wherein it is pressed by the pressing roller  107 . 
   After this, the pressing roller  107  moves while rotating in the direction of arrow A (in the direction along the folded back portion Sb) while pressing the folded back portion Sb ( FIGS. 7D and 8D  (S 107 )). The folded back portion Sb of the sheet bundle is pressed by the pressing roller  107  while in the state of being gripped by the gripping roller pair  104  and  105 . The cross-sectional form of the folded back portion area becomes a somewhat squared shape with essentially no bulging. 
   When the flattening processing of the folded back portion Sb is completed by the pressing roller  107  (S 108 ), the processing device control unit  120  restarts the roller drive motor  8  (S 109 ). The gripping roller pair  104  and  105  rotates and conveys the sheet bundle S ( FIG. 7E  (S 110 )). The sheet bundle S is discharged onto the discharge tray  16  ( FIG. 7F ). When the sheet bundle is sent out from the gripping roller pair  104  and  105 , and the folded back portion Sb is no longer detected by the folded back detecting sensor  10  (S 111 ), the processing device control unit  120  determines that the sheet bundle S has been discharged onto the discharge tray  16 , and stops the roller drive motor  8  (S 112 ). Thus, the gripping roller pair  104  and  105  also stops (S 113 ). 
   After this, in the case that a subsequent sheet bundle exists (S 114 ), the folded back face processing device  130  returns to S 101 , and flattens down the folded back portion of the subsequent sheet bundle. In the case of no subsequent sheet bundle, the folded back face processing device  130 , the sheet processing device  102 , and the photocopier  101  end their actions. 
   Now, if the length of the rotating face  107   a  of the pressing roller  107  that presses the folded back portion Sb is set to a length that can enter between the periphery faces  104   a  and  105   a  of the gripping roller pair  104  and  105 , similar to the pressing roller  18  illustrated in  FIGS. 5A through 5C , a similar result as that of the pressing roller  18  can be obtained. 
   As described above, the gripping roller pair  104  and  105  in the folded back face processing device  130  of the present embodiment performs the conveying of the sheet bundle, the folding action of the sheet bundle while conveying the sheet bundle, the gripping of the sheet bundle when the pressing roller  107  is flattening down the folded back portion, and the conveying of the sheet bundle after the folded back flattening process. Therefore, the sheet processing device  102  of the present embodiment that has the folded back face processing device  130  of the present embodiment can use the gripping roller pair  104  and  105  for the function of folding the sheet bundle and forming it into a booklet-like form, and the function of gripping the sheet bundle and the function for conveying the sheet bundle, and the configuration can be made simpler, the device can be more compact, and can take up less space. Thus, the photocopier  101  of the present invention has the sheet processing device  102  wherein the configuration is simple and is compact, therefore the device can be more compact, and can take up less space. 
   Now, as illustrated in  FIG. 10 , the sheet bundle that is folded and the back face processed by the sheet folded back face processing device  130  of the present embodiment can be discharged by the conveying belt pair  24  onto the discharge tray  16  that is provided externally. Further, in place of the discharge tray  16 , a sheet cutter connected online to the main unit of the sheet processing device  102  can be provided. In this case, the sheet bundle can be taken out more easily. 
   Folded Back Face Processing Device of Second Embodiment 
   (Configuration of Folded Back Face Processing Device of Second Embodiment) 
   As illustrated in  FIG. 11A  through  FIG. 13 , the folded back face processing device  230  of the present embodiment differs from the folded back face processing device  130  of the first embodiment in that the gripping rollers  204  and  205  a D-shape cross-section, and in that a sensor flag  221  (the shaded area of the diagram) that detects the rotation position of this gripping roller pair  204  and  205  and a rotating position sensor  222  that detects the rotation position of the sensor flag  221  are provided. 
   Now, the portions of the folded back face processing device  230  according to the present embodiment that differ from the folded back face processing device  130  of the first embodiment will be described, and portions which are the same will be denoted with the same reference numerals and description thereof will be omitted. 
   As illustrated in  FIG. 11C , flat faces  204   b  and  205   b  of the gripping roller pair  204  and  205  that serve as a conveying rotary member pair making up the gripping device  214  which is a gripping unit are flat faces that are formed along the thrust direction of the gripping roller pair  204  and  205 , and upon the gripping roller pair  204  and  205  projecting the folded back portion Sb from the nip portion N in the downstream side in the direction that the sheet bundle is conveyed and the sheet bundle conveying is temporarily stopped, the flat faces are formed at a position facing the pressing roller  107 . The gripping roller pair  204  and  205  synchronically rotates, and as illustrated in  FIG. 11D , the flat faces  204   b  and  205   b  face the pressing roller  107 . Therefore, the rotating shafts  212  and  209  of the gripping roller pair  204  and  205  are provided with mutually meshing gears (not shown). 
   The sensor flag  221  is provided integrally on the rotating shaft  209  of the lower gripping roller  205 , and is formed in a fan shape. The rotating position sensor  222  is fixed in a position that can detect the rotating sensor flag  221 . The sensor flag  221  and the rotating position sensor  222  make up a detecting device  223  serving as a detecting unit for detecting whether the folded back portion Sb is protruding from the nip portion N in the position that is pressed by the pressing roller  107 . The abutting plate detecting sensor  111  and the rotating position sensor  222  are connected to the processing device control unit  120 . 
   (Operations of Folded Back Face Processing Device of Second Embodiment) 
   The processing device control unit  120  starts the roller drive motor  8 , and rotates the gripping roller pair  204  and  205  ( FIG. 13  (S 201 )). The sensor flag  221  that is integral with the shaft  209  of the gripping roller  205  also rotates (S 202 ). When the rotation position sensor  222  detects the sensor flag  221  (S 203 ), the processing device control unit  120  stops the roller drive motor  8 , and stops the gripping roller pair  204  and  205  (S 204 ). As illustrated in  FIG. 12A  and  FIG. 11A , the gripping roller pair  204  and  205  is in a standby state wherein the flat faces  204   b  and  205   b  are parallel to one another, and waits for the sheet bundle to be sent through. This position is the home position of the gripping roller pair  204  and  205 . 
   The bound sheet bundle S is sent through from the upstream direction, and the portion bound with a stapler faces the tip of the abutting plate  161 . The abutting plate  161  nears the gripping roller pair  204  and  205 . When the abutting plate detecting sensor  111  detects the tip  161   a  of the abutting plate  161  (S 205 ), the processing device control unit  120  starts the roller drive motor  8  (S 206 ). The gripping roller pair  204  and  205  starts to rotate (S 206 ). 
   Alternatively, the position of the abutting plate  161  can be detected by the rotations of the abutting motor (not shown) which moves the abutting plate  161 , without the abutting plate detecting sensor  111  being provided. In this case, the roller drive motor  8  can be started with the ON signal of this abutting plate motor as a trigger. 
   At approximately the same time that the gripping roller pair  204  and  205  rotates and the nip portion N is formed, the abutting plate  161  presses the sheet bundle into this nip portion N ( FIGS. 12B and 13B  (S 207 )). The gripping roller pair  204  and  205  receives the sheet bundle pushed in with the nip portion N, and grips and conveys the sheet bundle S ( FIGS. 11B and 12B ). The abutting plate  161  that has pushed the sheet bundle into the nip portion N retreats in the direction of the arrow C ( FIGS. 11B and 12B ). The gripping roller pair  204  and  205  conveys while folding the sheet bundle, and accordingly, the sheet bundle assumes a booklet-like form. 
   Upon the rotating position sensor  222  detecting the sensor flag  221  (S 208 ), the processing device control unit  120  stops the roller drive motor  8 , and stops the gripping roller pair  204  and  205  (S 209 ). The gripping roller pair  104  and  105  stops rotating while still gripping the sheet bundle. At this time, the folded back portion Sb protrudes only by a predetermined length from the nip portion N of the gripping roller pair  204  and  205  at the position of being pressed by the pressing roller  107  ( FIGS. 11C and 12C ). Further, the flat faces  204   b  and  205   b  are in the position that allows the pressing roller  107  to pass. 
   After this, the pressing roller  107  moves while rotating in the direction of arrow A (in the direction along the folded back portion Sb) while pressing the folded back portion Sb ( FIGS. 11D and 12D  (S 210 )). The folded back portion Sb of the sheet bundle is pressed by the pressing roller  107  while in the state of being gripped by the gripping roller pair  204  and  205 . The cross-sectional form of the folded back portion area becomes a somewhat squared shape with essentially no bulging. 
   When the flattening processing of the folded back portion Sb is completed by the pressing roller  107  (S 211 ), the processing device control unit  120  restarts the roller drive motor  8  (S 212 ). The gripping roller pair  204  and  205  rotates and conveys the sheet bundle S ( FIG. 11E  (S 212 )). The sheet bundle S is discharged onto the discharge tray  16  ( FIG. 11F  (S 213 )). 
   After this, in the case that a subsequent sheet bundle exists (S 214 ), the folded back face processing device  230  returns to S 203 , and flattens down the folded back portion of the subsequent sheet bundle. In the case of no subsequent sheet bundle, the folded back face processing device  230 , the sheet processing device  102 , and the photocopier  101  end their actions. The roller driving motor and the gripping roller pair  204  and  205  are stopped (S 215 ). 
   The above described folded back face processing device  230  of the present embodiment has the flat faces  204   a  and  205   a  of the gripping roller pair  204  and  205  in the position that corresponds to the pressing roller  107 , and since the pressing roller  107  is placed near the nip portion N, the protruding length of the sheet bundle from the nip portion N can be reduced. Therefore, the sheet processing device that has the folded back face processing device  230  of the present embodiment can have similar results as the folded back face processing device  130  of the first embodiment. Additionally, even when the pressing roller  107  flattens down the folded back portion, deformation such as the folded back portion escaping occurs less, the folded back portion can be more easily flattened down, and the quality of the folded back portion can be improved. 
   Folded Back Face Processing Device of Third Embodiment 
   (Configuration of Folded Back Face Processing Device of Third Embodiment) 
   As illustrated in  FIGS. 14A through 14F , the folded back face processing device  330  of the present embodiment differs from the configuration of the folded back face processing device  130  and  230  of the first and second embodiments in that notches  304   c  and  305   c  are formed so that the gripping roller pair  304  and  305  is capable of receiving the pressing roller  107 . The notches  304   c  and  305   c  are formed with a cross-sectional recess form along the direction of thrust of the gripping roller pair  304  and  305 . 
   Now, with the folded back face processing device  330  of the present embodiment as well, the sensor flag that determines the relative position of the notches  304   c  and  305   c  and the folded back portion Sb of the sheet bundle S, and the rotating position sensor by which the rotating position of this sensor flag is detected, are not illustrated in the diagram, but are similar to that of the folded back face processing device  230  of the second embodiment. 
   Further, the portions of the folded back face processing device  330  of the present embodiment that differ from the folded back face processing device  130  of the first embodiment will be described, and portions which are the same will be denoted with the same reference numerals and description thereof will be omitted. 
   (Operations of Folded Back Face Processing Device of Third Embodiment) 
   The gripping roller pair  304  and  305 , serving as a conveying rotary pair making up the gripping device  314  serving as a gripping unit, is rotated by the roller drive motor, to a standby state wherein the notches  304   c  and  305   c  are parallel to one another, and waits for the sheet bundle to be sent through ( FIG. 14A ). This position is the home position of the gripping roller pair  304  and  305 . 
   The bound sheet bundle S is sent through from the upstream direction, and the portion bound with a stapler faces the tip of the abutting plate  161 . The gripping roller pair  304  and  305  begins rotating. At approximately the same time that the gripping roller pair  304  and  305  rotates and the nip portion N is formed, the abutting plate  161  pushes the sheet bundle into this nip portion N ( FIG. 14B ). The gripping roller pair  304  and  305  receives the sheet bundle pushed in at the nip portion N, and grips and conveys the sheet bundle S. The abutting plate  161  that has pushed the sheet bundle into the nip portion N retreats in the direction of the arrow C. The gripping roller pair  304  and  305  conveys while folding the sheet bundle, such that the sheet bundle assumes a booklet-like form. 
   When the folded back portion Sb protrudes only by a predetermined length from the nip portion N of the gripping roller pair  304  and  305  to the position to be pressed by the pressing roller  107 , the gripping roller pair  304  and  305  stops rotating ( FIG. 14C ). At this time, the notches  304   c  and  305   c  are in a position capable of receiving the pressing roller  107 . 
   After this, the pressing roller  107  rotates and moves along the folded back portion Sb, and while pressing the folded back portion Sb within the notches  304   c  and  305   c  ( FIG. 14D ). The folded back portion Sb of the sheet bundle is pressed by the pressing roller  107  while in the state of being gripped by the gripping roller pair  304  and  305 . The cross-sectional form of the folded back portion area is a somewhat squared shape with essentially no bulging. 
   When the flattening processing of the folded back portion Sb by the pressing roller  107  ends, the gripping roller pair  304  and  305  rotates and conveys the sheet bundle S ( FIGS. 14E and 14F ). The sheet bundle S is discharged to the discharge tray  16 . 
   After this, in the case that a subsequent sheet bundle exists, the gripping roller pair  304  and  305  returns to the state of  FIG. 14A . In the case of no subsequent sheet bundle, the folded back face processing device  330 , the sheet processing device  102 , and the photocopier  101  end their actions. 
   As illustrated in  FIGS. 14A through 14F , the above described folded back face processing device  330  of the present embodiment forms the notches  304   c  and  305   c  of the gripping roller pair  304  and  305  in the position that is capable of receiving the pressing roller  107 , and because the pressing roller is placed near the nip portion N, the protruding length of the sheet bundle from the nip portion N can be made short. Therefore, the sheet processing device that has the folded back face processing device  330  of the present embodiment can have similar results as the folded back face processing device  130  of the first embodiment, and additionally even when the pressing roller  107  flattens down the folded back portion, deformation such as the folded back portion escaping occurs less, the folded back portion can be more easily flattened down, and the quality of the folded back portion can be improved. 
   Further, the notches  304   c  and  305   c  are sizes such that the pressing roller  107  can be received, and therefore the gripping roller pair  304  and  305  can increase the amount of sheet bundle conveying when discharging the sheet bundles to the discharge tray  16 , after the folded back portion Sb flattening is processed. 
   Thus, the sheet processing device that has the folded back face processing device  330  of the present embodiment does not enlarge the diameter of the gripping roller pair  304  and  305 , and can accurately discharge even a large size sheet bundle onto the discharge tray  16 . 
   Now, a flat face to be described below can be formed onto the gripping roller pair  504  and  505  of the folded back face processing device  330  of the present embodiment. In this case, the protruding length of the folded back portion is shortened and the sheet is gripped by the flat faces. Therefore, even when the folded back portion is pressed with the pressing roller  107 , deformation such as the folded back portion escaping occurs far less, the folded back portion can be more easily flattened down, and the quality of the folded back portion can be improved. 
   Folded Back Face Processing Device of Fourth Embodiment 
   (Configuration of Folded Back Face Processing Device of Fourth Embodiment) 
   As illustrated in  FIGS. 15A through 15F , the folded back face processing device  430  of the present embodiment differs from the configuration of the folded back face processing devices  130 ,  230 , and  330  of the first, second, and third embodiments in that the gripping roller pair  404  and  405  is formed with a cross-sectional D-shape and the sheet bundle is gripped with the flat faces  404   d  and  405   d.    
   Now, the portions of the folded back face processing device  430  of the present embodiment that differ from the folded back face processing device  130  of the first embodiment will be described, and the similar portions will use the same reference numerals, and the description thereof will be abbreviated. 
   The flat faces  404   d  and  405   d  are formed along the direction of thrust of the gripping roller pair  404  and  405 , and are formed in the position to grip the sheet bundle when the gripping roller pair  404  and  405  protrudes the folded back portion to the downstream side and temporarily stops the conveying of the sheet bundle. 
   Further, with the folded back face processing device  430  of the present embodiment also, the sensor flag that determines the relative position of the flat faces  404   d  and  405   d  and the folded back portion Sb of the sheet bundle S, and the rotating position sensor by which the rotating position of this sensor flag is detected are not illustrated in the diagram, but are similar to that of the folded back face processing device  230  of the second embodiment. However, the relative position relationship between the flat face  405   b  and the sensor flag differs from the relative position relationship between the flat face  205   d  according to the second embodiment and the sensor flag thereof. 
   Further, the pressing roller  418  serving as a pressing unit of the pressing device  415  which is a pressing unit has the length (L 1 ) of the rotating face  418   a  that presses the folded back portion Sb set to a length to allow entering the periphery faces  404   a  and  405   a  of the gripping roller pair  404  and  405 , as with the pressing roller  18  illustrated in  FIGS. 5A through 5C . Now, the pressing roller  418  does not necessarily need to be of a length enabling entering between the periphery  404   a  and  405   a  of the gripping roller pair  404  and  405  as with the pressing roller  7  illustrated in  FIG. 2C . 
   (Operations of Folded Back Face Processing Device of Fourth Embodiment) 
   The gripping roller pair  404  and  405 , serving as a conveying rotary pair making up the gripping device  414  which is a gripping unit, is rotated by the roller drive motor to position the flat faces  404   d  and  405   d  perpendicular to the abutting plate  161 , and waits for the sheet bundle to be sent through ( FIG. 15A ). This position is the home position of the gripping roller pair  404  and  405 . 
   The bound sheet bundle S is sent through from the upstream direction, and the portion bound with a stapler faces the tip of the abutting plate  161 . The gripping roller pair  404  and  405  begins rotating. At approximately the same time that the gripping roller pair  404  and  405  rotates and the nip portion N is formed, the abutting plate  161  pushes the sheet bundle into this nip portion N ( FIG. 15B ). The abutting plate  161  that has pushed the sheet bundle into the nip portion N retreats in the direction of the arrow C. The gripping roller pair  404  and  405  rotates and receives the sheet bundle pushed in at the nip portion N, and grips and conveys the sheet bundle S. 
   At the point when the flat faces  404   d  and  405   d  are facing one another and have become parallel, the gripping roller pair  404  and  405  stops rotating while still gripping the sheet bundle with the flat faces  404   d  and  405   d  ( FIG. 15C ). At this time, the sheet bundle is in the state of being gripped by the flat faces  404   d  and  405   d  and folded. Further, the folded back portion Sb protrudes from the gripping roller pair  404  and  405  and in the position to be pressed by the pressing roller  418 . 
   After this, the pressing roller  418  rotates and moves along the folded back portion Sb, while pressing the folded back portion Sb ( FIG. 15D ). The folded back portion Sb of the sheet bundle is pressed by the pressing roller  418  while in the state of being gripped by the gripping roller pair  404  and  405 . The cross-sectional form of the folded back portion area is a somewhat squared shape with essentially no bulging. 
   When the flattening processing of the folded back portion Sb by the pressing roller  418  ends, the gripping roller pair  404  and  405  rotates and conveys the sheet bundle S ( FIGS. 15E and 15F ). The sheet bundle S is discharged to the discharge tray  16 . 
   After this, in the case that a subsequent sheet bundle exists, the pressing roller pair  404  and  405  returns to the state of  FIG. 14A . In the case of no subsequent sheet bundle, the folded back face processing device  430 , the sheet processing device  102 , and the photocopier  101  end their actions. 
   As illustrated in  FIG. 15C , the above described folded back face processing device  430  of the present embodiment is such that the sheet bundle is gripped by the flat faces  404   d  and  405   d  of the gripping roller pair  404  and  405 . Therefore, the sheet processing device that has the folded back face processing device  430  of the present embodiment achieves the same advantages as those of the folded back face processing device  130  of the first embodiment. Conventionally, a greater gripping force has been necessary when gripping a sheet bundle with a large number of sheets. However, the gripping force can be lessened and the equipment can be made more compact with the present embodiment. Further, the folded back portion can be gripped closer, and a folded back portion with a flat form of high quality can be made easily. 
   Additionally, the risk of the sheet bundle being pressed by the pressing roller  418  and pushed into the gripping roller pair  404  and  405  is reduced, and therefore, a folded back portion with a flat form of even higher quality can be made more easily. 
   Further, as with the pressing roller  18  illustrated in  FIGS. 5A through 5C , the pressing roller  418  is set to a length that can enter between the periphery faces  404   a  and  405   a  of the gripping roller pair  404  and  405 , and therefore, the pressing roller  418  can be brought that much closer to the nip portion, and the protruding length of the sheet bundle can be shortened. As a result, the sheet processing device that has the folded back face processing device  430  has less deformation such as the folded back portion escaping even when pressing the folded back portion with the pressing roller, and the folded back portion can be more easily flattened down. 
   Folded Back Face Processing Device of Fifth Embodiment 
   (Configuration of Folded Back Face Processing Device of Fifth Embodiment) 
   As illustrated in  FIGS. 16A through 16F , the folded back face processing device  530  of the present embodiment differs from the configuration of the folded back face processing devices  130 ,  230 ,  330 , and  430  of the first through the fourth embodiments in that the gripping roller pair  504  and  505  is formed with flat faces  504   b  and  505   b , and flat faces  504   d  and  505   d.    
   The flat faces  504   b  and  505   b  are formed along the direction of thrust of the gripping roller pair  504  and  505 , as illustrated in  FIGS. 16C and 16D , and are formed in the position to face the pressing roller  107  when the gripping roller pair  504  and  505  protrudes the folded back portion Sb from the nip portion N and temporarily stops the conveying of the sheet bundle. Further, these fulfill similar functions to those of the flat faces  204   b  and  205   b  of the gripping roller pair  204  and  205  illustrated in  FIGS. 11C and 11D . 
   The flat faces  504   d  and  505   d  are formed along the direction of thrust of the gripping roller pair  504  and  505 , as illustrated in  FIGS. 16C and 16D , and are the portions that grip the sheet bundle. Further, these fulfill similar functions to those of the flat faces  404   d  and  405   d  of the gripping roller pair  404  and  405  illustrated in  FIGS. 15C  and  15 D. 
   Now, with the folded back face processing device  530  of the present embodiment, the sensor flag that determines the relative position of the flat faces  504   d  and  505   d  and the folded back portion Sb of the sheet bundle S, and the rotating position sensor by which the rotating position of this sensor flag is detected are not illustrated in the diagram, but are similar to that of the folded back face processing device  230  of the second embodiment. However, the relative position relationship between the flat face  505   d  and the sensor flag differs from the relative position relationship between the flat face  205   b  according to the second embodiment and the sensor flag thereof. 
   Further, in order to lengthen the periphery faces  504   a  and  505   a , the flat faces  504   d  and  505   d  are bent rather than being in a straight line, in the state of gripping the sheet bundle with the flat faces  504   d  and  505   d . Therefore, the pressing roller  518  of the pressing device  415  that is a pressing unit sets the length (L 1 ) of the rotating face  518   a  that flattens down the folded back portion Sb as the length that can enter between the flat faces  504   d  and  505   d . Now, the pressing roller  518  does not necessarily need to be at the length that can enter between the periphery faces  504   a  and  505   a  of the gripping roller pair  504  and  505  as does the pressing roller  7  illustrated in  FIG. 2C . 
   (Operations of Folded Back Face Processing Device of Fifth Embodiment) 
   The gripping roller pair  504  and  505 , serving as a conveying rotary member pair making up the gripping device  514  which is a gripping unit, is rotated by the roller drive motor to position the flat faces  504   d  and  505   d  perpendicular to the abutting plate  161 , and waits for the sheet bundle to be sent through ( FIG. 16A ). This position is the home position of the gripping roller pair  504  and  505 . 
   The bound sheet bundle S is sent through from the upstream direction, and the portion bound with a stapler faces the tip of the abutting plate  161 . The gripping roller pair  504  and  505  begins rotating. The abutting plate  161  that has pushed the sheet bundle between the rotating gripping roller pair  504  and  505  retreats in the direction of the arrow C ( FIG. 16B ). The gripping roller pair  504  and  505  rotates, grips, and conveys the sheet bundle with the nip portion N. 
   At the point when the flat faces  504   d  and  505   d  are facing one another and have become parallel, the gripping roller pair  504  and  505  stops rotating while still gripping the sheet bundle with the flat faces  504   d  and  505   d  ( FIG. 16C ). At this time, the sheet bundle is gripped by the flat faces  504   d  and  505   d , and folded to have a booklet-like form. Further, the folded back portion Sb protrudes from the gripping roller pair  504  and  505  to the position to be pressed by the pressing roller  518 . Further, the flat faces  504   b  and  505   b  are in the position capable of receiving the pressing roller  518 . 
   After this, the pressing roller  518  rotates and moves along the folded back portion Sb, while pressing the folded back portion Sb ( FIG. 16D ). The folded back portion Sb of the sheet bundle is pressed by the pressing roller  518  while in the state of being gripped by the gripping roller pair  504  and  505 . The cross-sectional form of the folded back portion area is a somewhat square shape with essentially no bulging. 
   When the flattening processing of the folded back portion Sb by the pressing roller  518  ends, the gripping roller pair  504  and  505  rotates and conveys the sheet bundle S ( FIGS. 16E and 16F ). The sheet bundle S is discharged to the discharge tray  16 . 
   After this, in the case that a subsequent sheet bundle exists, the gripping roller pair  504  and  505  returns to the state of  FIG. 14A . In the case of no subsequent sheet bundle, the folded back face processing device  530 , the sheet processing device  102 , and the photocopier  101  end their actions. 
   As illustrated in  FIG. 16C , the above-described folded back face processing device  530  of the present embodiment is such that the sheet bundle is gripped by the flat faces  504   d  and  505   d  of the gripping roller pair  504  and  505 . Therefore, with the sheet processing device that has the folded back face processing device  530  of the present embodiment, the risk of the sheet bundle being pressed by the pressing roller  518  and pushed into the gripping roller pair  504  and  505  is reduced, and therefore a folded back portion Sb with a flat form can be made more easily. 
   Additionally, as illustrated in  FIGS. 16A through 16F , with the above described folded back face processing device  530  of the present embodiment, the pressing roller  518  faces the flat faces  504   a  and  505   a  of the gripping roller pair  504  and  505 , and is placed near the gripping roller pair  504  and  505 , and therefore the length that the sheet bundle protrudes from the gripping roller pair  504  and  505  can be shortened. Therefore, with the sheet processing device that has the folded back face processing device  530  of the present embodiment, even when the pressing roller  518  flattens down the folded back portion, deformation such as the folded back portion escaping occurs less, the folded back portion can be more easily flattened down, and the quality of the folded back portion can be improved. 
   Further, the pressing roller  518  is set to a length that can enter between the flat faces  504   b  and  505   b , and therefore, the pressing roller  518  can be brought that much closer to the gripping roller pair  504  and  505 , and the protruding length of the sheet bundle can be shortened. As a result, the sheet processing device that has the folded back face processing device  530  has less deformation such as the folded back portion escaping, even when the folded back portion is flattened down with the pressing roller, and the folded back portion can be more easily flattened down. 
   Now, the folded back face processing devices  130 ,  230 ,  330 ,  430 , and  530  according to the various embodiments above use a pressing roller  107 ,  418 , or  518  as a pressing unit to flatten down the folded back portion of the sheet bundle, but a belt that circulates while moving, having a linear portion greater than the width of the sheets of which the folded back portion is to be pressed down, may be used. In the case of using a belt, the width of the belt should be a width that can enter between the periphery of the gripping roller pair, in order to correspond to the gripping rollers  418  and  518 . Alternatively, the pressing unit may be a member in a spatula form or a member in a cylindrical form. 
   Further, the gripping roller pair should have at least one roller that is resilient or that can move away, in order to facilitate receiving the sheet bundle. In this case the roller pair needs to have only sufficient gripping force so that the position of the sheet stack does not shift even when the gripped sheet bundle is pressed by the pressing roller. 
   Further, the folded back face processing devices  130 ,  230 ,  330 ,  430 , and  530  according to the various embodiments above are such that the folded back portion of the sheet bundle that has been bound with the stapler  62  is flattened down. However, sheet bundles that are not bound in the middle and perfect-binding sheet bundles can also have the folded back portion flattened down. 
   Note that the shape of a roller is expressed as “having a notch wherein the cross-section has a notched periphery”, this means that the roller is of a shape with a notched form, and does not necessarily mean that a roller was actually cut to form it. The roller may also include shapes that appear notched, by drawing or molding formation techniques. 
   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 embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 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 priority from Japanese Patent Application No. 2004-055559 filed Feb. 27, 2004, which is hereby incorporated by reference herein.