Abstract:
A sheet processing apparatus including a stacking tray that stacks sheets, a conveying member that conveys a sheet to the stacking tray and discharges the sheet bundle from the stacking tray, wherein the conveying member includes a conveying roller and a conveying belt stretched by a plurality of stretch rollers, and a sheet processor that performs predetermined processing to the sheet bundle. When the conveying member conveys the sheet to the stacking tray, a part of the conveying belt that is not wound on the stretch roller contacts the conveying roller by moving the conveying belt as such a nip for conveying the sheet is formed. When the conveying member discharges the sheet bundle from the stacking tray, a part of the conveying belt that is wound on the stretch roller contacts the conveying roller by moving the conveying belt so that a nip for conveying the sheet is formed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to Japanese Application No. 2013-154477, filed Jul. 25, 2013, and Japanese Application No. 2014-006541, filed Jan. 17, 2014. The contents of the above-identified applications are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present inventions relate to a sheet processing apparatus and an image forming system. In particular, the present inventions relate to a sheet processing apparatus and an image forming system including the sheet processing apparatus and an image forming apparatus, such as a copier, a printer, a facsimile machine, or a digital multifunction peripheral, and a sheet folding method performed by the sheet processing apparatus. 
       BACKGROUND ART 
       [0003]    Conventionally, an image forming system includes an image forming apparatus that forms an image on a sheet, and a sheet processing apparatus that temporarily stacks the image formed sheets on a processing tray and processes the sheet bundle, such as by stapling. 
         [0004]    JP2004-262656 discloses that a size of a processing tray in a sheet-conveying direction is half the size of the sheet.  FIGS. 22A-22C , reproduced from JP2004-262656, show a diagram in which a first sheet S is conveyed on a processing tray  540 . 
         [0005]    In  FIG. 22A , a swing roller  550  is located at a position apart from a driven roller  571  on standby. The sheet discharged from an image forming apparatus is conveyed to a stacking tray  504  by a discharging roller pair  508   a  and  508   b.    
         [0006]    In  FIG. 22B , when the trailing end of the sheet S passes through the discharging roller pair  508   a  and  508   b,  the sheet S is held by the swing roller  550  and the driven roller  571 . 
         [0007]    In  FIG. 22C , the sheet S is conveyed to a sheet trailing end stopper  562  by rotating the swing roller  550  and the driven roller  571  in a reverse direction to the sheet conveying direction. Next, the swing roller  550  moves upward to the standby position shown in  FIG. 22A  and the swing roller  550  prepares for a next sheet S to be discharged. 
         [0008]      FIG. 23A  shows a diagram that an after-next sheet S is conveyed on a processing tray  540 . 
         [0009]    However, in  FIG. 23B , a following sheet S 1  is conveyed to the sheet trailing end stopper  562  by rotating the swing roller  550  and the driven roller  571  while the following sheet S 1  is rubbed on the previous sheet S. As such, the rear side of the following sheet S 1  may be dirty with the image of the previous sheet S, and the image of the previous sheet S may deteriorate. This is because the following sheet S 1  and the previous sheet S contact each other with a high surface pressure from the swing roller  550  and the driven roller  571 . 
       SUMMARY 
       [0010]    In light of the problems and circumstances described above, an object of the present application is to provide a sheet processing apparatus and an image forming system that prevent the rear side of the following sheet from being dirty, and prevent the image of the previous sheet from being deteriorated. 
         [0011]    According to an embodiment of the present application, a sheet processing apparatus includes: a stacking tray that stacks sheets, a conveying member that conveys a sheet to the stacking tray and discharges the sheet bundle from the stacking tray, wherein the conveying member includes a conveying roller and a conveying belt stretched by a plurality of stretch rollers, and a sheet processing unit that performs predetermined processing to the sheet bundle. When the conveying member conveys the sheet to the stacking tray, a part of the conveying belt that is not wound on the stretch roller contacts the conveying roller by moving the conveying belt or the conveying roller so that a nip for conveying the sheet is formed. When the conveying member discharges the sheet bundle from the stacking tray, a part of the conveying belt that is wound on the stretch roller contacts the conveying roller by moving the conveying belt or the conveying roller so that a nip for conveying the sheet is formed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIGS. 1A and 1B  are diagram showing an overall configuration of an image forming system according to an embodiment of the present application; 
           [0013]      FIG. 2  is a diagram showing an overall configuration of an image forming apparatus according to an embodiment of the present application; 
           [0014]      FIG. 3  is a diagram showing an overall configuration of a sheet processing apparatus according to an embodiment of the present application; 
           [0015]      FIG. 4  is a front view of the sheet processing apparatus according to an embodiment of the present application; 
           [0016]      FIG. 5  is a diagram showing a home position of a branching claw for guiding a sheet that the sheet processing apparatus receives; 
           [0017]      FIG. 6  is a diagram showing a position of the branching claw for guiding a sheet to a branching pass; 
           [0018]      FIG. 7  is a diagram showing a binding unit in a state in which the teeth of the binding unit is opened; 
           [0019]      FIG. 8  is a diagram showing a binding unit in a state in which the teeth of the binding unit are closed; 
           [0020]      FIGS. 9A and 9B  are diagrams showing a configuration of the sheet processing apparatus when an initialization is completed; 
           [0021]      FIGS. 10A and 10B  are diagrams showing a configuration of the sheet processing apparatus for receiving a sheet; 
           [0022]      FIGS. 11A and 11B  are diagrams showing a configuration of the sheet processing apparatus when a sheet is positioned in a direction orthogonal to a conveying direction; 
           [0023]      FIGS. 12A and 12B  are diagrams showing a configuration of the sheet processing apparatus when a sheet is positioned in a conveying direction; 
           [0024]      FIGS. 13A and 13B  are diagrams showing a configuration of the sheet processing apparatus for receiving a following sheet; 
           [0025]      FIGS. 14A and 14B  are diagrams showing a configuration of the sheet processing apparatus for further receiving a following sheet; 
           [0026]      FIGS. 15A and 15B  are diagrams showing a configuration of the sheet processing apparatus when a process for aligning a sheet bundle is completed; 
           [0027]      FIGS. 16A and 16B  are diagrams showing a configuration of the sheet processing apparatus when a process for binding the sheet bundle is completed; 
           [0028]      FIGS. 17A and 17B  are diagrams showing a configuration of the sheet processing apparatus when a bound sheet bundle is discharged; 
           [0029]      FIGS. 18A and 18B  are diagrams showing a configuration of a nip formed and a non-nip formed by a discharging roller pair; 
           [0030]      FIG. 19  is a diagram showing an overall configuration of a discharging part according to an embodiment of the present application; 
           [0031]      FIGS. 20A-C  are diagrams showing a configuration of a nip formed and a non-nip formed by a discharging roller and a discharging belt; 
           [0032]      FIGS. 21A-C  are diagrams illustrating a operation for changing three positions shown in  FIGS. 20A-C ; 
           [0033]      FIGS. 22A-C  are diagrams illustrating a configuration of a conventional sheet processing apparatus that conveys a first sheet to a processing tray; and 
           [0034]      FIGS. 23A and 23B  are diagrams illustrating a configuration of a conventional sheet processing apparatus that conveys an after-next sheet to a processing tray. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    Embodiments of the present application are described in detail with reference to the drawings. 
         [0036]    In  FIG. 1A , an image forming system  100  includes an image forming apparatus  101  that forms an image on a sheet, and a sheet processing apparatus  201  that processes the image formed sheet and is arranged inside the image forming apparatus  101 . On the other hand, in  FIG. 1B , the image forming system  100  includes the image forming apparatus  101  and the sheet processing apparatus  201  that is arranged outside the image forming apparatus  101 . 
         [0037]    In  FIG. 2 , an imaging unit  110  is arranged in the image forming apparatus  101  and includes 4 color imaging stations  111 Y,  111 M,  111 C, and  111 K. 
         [0038]    The image forming apparatus  101  further includes a sheet feeding tray  120 , a conveying pass  130  that conveys the sheet from the sheet feeding tray  120  to a secondary transfer part  140  and a fixing part  150 , a scanner  180  that scans an image of a document, and an automatic document feeder  185  (ADF) that feeds the document to the scanner  180 . 
         [0039]    The imaging unit  110  forms an image on a sheet, and the fixing part  150  fixes the image on the sheet. Next, the fixed sheet is conveyed to the sheet processing apparatus  201 . 
         [0040]    In  FIG. 3  and  FIG. 4 , the sheet processing apparatus  201  includes a inlet sensor  202 , a inlet roller pair  203 , a branching claw  204 , a driving discharge roller  205   a,  a driven discharge roller  205   b,  a shift link  206 , a shift cam  207 , a shift cam stud  208 , a shift home position sensor  209 , a binding unit  210 , and a returning roller  211 . 
         [0041]    The inlet sensor  202  detects a leading end and a trailing end of a sheet conveyed by a discharging roller pair  102  in the image forming apparatus  101 . 
         [0042]    The driving discharge roller  205   a  conveys a sheet and shifts a sheet conveying direction. The driven discharge roller  205   b  contacts the driving discharge roller  205   a  and is driven by the driving discharge roller  205   a.    
         [0043]    The shift link  206  is arranged at a shaft end of the driving discharge roller  205   a.  The shift cam  207  includes the shift cam stud  208 , which is linked to the shift link  206 . The driving discharge roller  205   a  is moved along an axis by rotating the shift cam  207 . 
         [0044]    The binding unit  210  binds a sheet bundle. In  FIG. 7  and  FIG. 8 , the mechanism of the binding unit  210  is that the sheet bundle is held by a pair of teeth  210  with convex and concave shapes so that the fibers of the sheets are tangled with each other. In one embodiment, the binding unit  210  may be a stapler. 
         [0045]    The returning roller  211  conveys a sheet to an abutting surface  242 . A sheet edge sensor  220  detects a side edge of a sheet. A conveying pass  240  guides a sheet to a discharging direction. A branch pass  241  guides a sheet to a processing tray  243 . The abutting surface  242  aligns a trailing end of a sheet on the processing tray  243 . 
         [0046]    In  FIG. 5 , the branching claw  204  is rotatable to change the conveying pass  240  and the branch pass  241 . As shown in  FIG. 5 , the branching claw  204  is pressed by a spring  251 . 
         [0047]    In  FIG. 6 , when a solenoid  250  is turned ON, the branching claw  204  rotates in an A1 arrow direction shown in  FIG. 6  so that the sheet is guided to the branch pass  241 . 
         [0048]    Next, in  FIG. 9  to  FIG. 17 , a binding mechanism of the sheet processing apparatus  201  is illustrated. The sheet processing apparatus  201  includes a straight mode, a shifting mode, and a binding mode. 
         [0049]    In the straight mode, as shown in  FIGS. 10A and 10B , a sheet P from the image forming apparatus  101  is conveyed by the inlet roller pair  203 , and is discharged by the driving discharge roller  205   a  and the driven discharge roller  205   b.    
         [0050]    In the shifting mode, as shown in  FIGS. 11A and 11B , a sheet P from the image forming apparatus  101  is conveyed by the inlet roller pair  203 . When the sheet P passes through the inlet roller pair  203 , the driving discharge roller  205   a  moves with the sheet P in an axis direction by rotating the shift cam  207 . The shift cam  207  returns to a home position for a next sheet when the sheet P is discharged by the driving discharge roller  205   a  and the driven discharge roller  205   b.    
         [0051]    In the binding mode, a sheet P from the image forming apparatus  101  is conveyed by the inlet roller pair  203 . When the sheet P passes through the inlet roller pair  203 , the driving discharge roller  205   a  moves with the sheet P in an axis direction by rotating the shift cam  207 , as shown in  FIG. 11A . The sheet P is further conveyed in an A8 arrow direction by rotating the driving discharge roller  205   a  in an A9 arrow direction, as shown in  FIG. 11B . 
         [0052]    Next, as shown in  FIG. 12B , when the trailing end of the sheet P passes through the tip of the branching claw  204 , the branching claw  204  rotates in an A10 arrow direction. The sheet P is conveyed to the returning roller  211  in the branch pass  241  by rotating the driving discharge roller  205   a  in an All arrow direction. When the returning roller  211  receives the sheet P, the driven discharge roller  205   b  moves in the A14 arrow direction shown in  FIG. 12B , and is apart from the driving discharge roller  205   a.  The sheet P is further conveyed to the abutting surface  242  by rotating the returning roller  211  in an A13 arrow direction. The returning roller  211  stops rotating when the trailing end of the sheet P contacts the abutting surface  242 . 
         [0053]    Next, in  FIG. 13B , the branching claw  204  rotates in an A15 arrow direction and presses the sheet P strongly. A following sheet P′ is conveyed to the driving discharge roller  205   a  by the inlet roller pair  203 . When the tip of the following sheet P′ passes through the driving discharge roller  205   a,  the driven discharge roller  205   b  moves in an A18 arrow direction shown in  FIG. 14B  and the following sheet P′ is held by the driving discharge roller  205   a  and the driven discharge roller  205   b.  The sheet P on the processing tray  243  is too strongly pressed by the branching claw  204  to be conveyed by the driving discharge roller  205   a  and the driven discharge roller  205   b.    
         [0054]    Next an operation that is the same as the operation illustrated in  FIG. 11  to  FIG. 13  is conducted, and the sheets P′ are stacked on the processing tray  243 . Thus, following sheets are conducted repeatedly with the same operation illustrated in  FIG. 11  to  FIG. 14 , and the sheet bundle is stacked on the processing tray  243 . 
         [0055]    Next, in  FIGS. 15A  and B, the driven discharge roller  205   b  moves in an A19 arrow direction and the sheet bundle Ps is held by the driving discharge roller  205   a  and the driven discharge roller  205   b.  The branching claw  204  rotates in an A21 arrow direction and is apart from sheet bundle Ps. In  FIG. 16A , the binding unit  210  moves to a binding position of the sheet bundle Ps in an A22 arrow direction. As illustrated in  FIG. 7  and  FIG. 8 , the sheet bundle Ps is bound by the binding unit  210 . Finally, the sheet bundle Ps is discharged by rotating the driving discharge roller  205   a  in an A25 arrow direction in  FIG. 17A . 
         [0056]      FIG. 18A  is a diagram showing a configuration of a nip formed by the driving discharge roller  205   a  and the driven discharge roller  205   b.    FIG. 18B  is a diagram showing a configuration of a non-nip formed by the driving discharge roller  205   a  and the driven discharge roller  205   b.    
         [0057]      FIG. 19  is a diagram showing an overall configuration of a discharging part that discharges a sheet bundle Ps on the processing tray  243 . The discharging part includes the driving discharge roller  205   a,  a discharging belt  301  stretched by downstream stretch rollers  302  and upstream stretch rollers  303 . The downstream stretch rollers  302  and the upstream stretch rollers  303  are attached rotatably to an end part of a holder  311 . A hole part  311   a  is formed at another end part of the holder  311  and into which a projection  312   a  arranged at a cam  312  is inserted. On the other hand, a long hole  311   b  is formed around a center part of the holder  311  and is engaged with a fixed axis  313 . 
         [0058]    In  FIGS. 20A-20C , the discharging belt  301  is moved to three positions by rotating the cam  312 . A first position shown in  FIG. 20A  is the non-nip position at which the discharging belt  301  is apart from the driving discharge roller  205   a.  A second position shown in  FIG. 20B  is the roller nip position at which the part of the discharging belt  301  that is wound on the downstream stretch roller  302  contacts the driving discharge roller  205   a.  A third position shown in  FIG. 20C  is the belt nip position at which the part of the discharging belt  301  that is not wound on the downstream stretch roller  302  contacts the driving discharge roller  205   a.    
         [0059]    When the returning roller  211  receives the sheet, as shown in  FIG. 12B , the discharging belt  301  moves to the non-nip position that is apart from the driving discharge roller  205   a  in  FIG. 20A . 
         [0060]    When the sheet bundle is discharged from the processing tray  243 , as shown in  FIG. 16  and  FIG. 17 , the discharging belt  301  moves to the roller nip position at which the part of the discharging belt  301  that is wound on the downstream stretch roller  302  contacts the driving discharge roller  205   a  in  FIG. 20B . Thus, this structure can prevent the sheet bundle from binding too much along the driving discharge roller  205   a,  and the structure can prevent the binding part of the sheet bundle from being broken. 
         [0061]    When the sheet after the second sheet is conveyed to the processing tray  243 , as shown in  FIG. 14  and  FIG. 15 , the discharging belt  301  moves to the belt nip position at which the part of the discharging belt  301  that is not wound on the downstream stretch roller  302  contacts the driving discharge roller  205   a  in  FIG. 20C . As such, the nip face pressure (a pressure/a nip area) is less than that in a nip of a roller pair without reducing a pressure. Therefore, this structure can prevent the stacked sheet on the processing tray  243  and the conveying sheet from strongly rubbing each other, and the structure can prevent the image of the stacked sheet from transferring to the rear side of the conveying sheet. 
         [0062]      FIGS. 21A-21C  are diagrams illustrating an operation for changing three positions shown in  FIGS. 20A-20C . 
         [0063]    In the non-nip position shown in  FIG. 21A , the projection  312   a  arranged at the cam  312  is located above a cam axis  312   b.    
         [0064]    The roller nip position shown in  FIG. 21B  is replaced from the non-nip position by rotating the cam  312  clockwise in that figure. Thus, in  FIG. 21B , the holder  311  moves in an upstream direction to a sheet conveying direction and turns around the fixed axis as a fulcrum. Therefore, the part of the discharging belt  301  that is wound on the downstream stretch roller  302  contacts the driving discharge roller  205   a.    
         [0065]    In one embodiment, the belt nip position shown in  FIG. 21C  is replaced from the non-nip position by rotating the cam  312  counterclockwise in that figure. Thus, in  FIG. 21C , the holder  311  moves in a downstream direction to a sheet conveying direction and turns around the fixed axis as a fulcrum. Therefore, the part of the discharging belt  301  that is not wound on the downstream stretch roller  302  contacts the driving discharge roller  205   a.    
         [0066]    A pressure of the discharging belt  301  in the belt nip position may be less than a pressure of the discharging belt  301  in the roller nip position by changing a rotary angle of the cam  312  or the structure of the holder  311 . 
         [0067]    The driving discharge roller  205   a  may be replaced with a conveying belt stretched by a plurality of stretch rollers. 
         [0068]    The above three positions, i.e., the non-nip position, the belt nip position, and the roller nip position may be changed by moving the driving discharge roller  205   a.