Patent Publication Number: US-8967610-B2

Title: Sheet processing device and image forming system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2012-055961 filed in Japan on Mar. 13, 2012. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a sheet processing device and an image forming system that includes the sheet processing device and an image forming apparatus. 
     2. Description of the Related Art 
     Devices, which are called as sheet processing devices, that automatically perform sheet processing such as alignment, stapling, and/or punching on sheets on which images are formed have been widely known. Image forming systems that include an image forming apparatus and this type of sheet processing device connected to the downstream of the image forming apparatus are widely used in recent years. Such a sheet processing device performs sheet finishing, e.g., stacking and stapling. Stacking is a process of stacking sheets on an eject tray while sorting the sheets into sets of sheets. Stapling is a process of stapling each sheet bundle made up of a predetermined number of sheets and stacking the sheet bundles on a stack tray. 
     Known examples of this type of technique are disclosed in Japanese Patent Application Laid-open No. 9-175724 and Japanese Patent Application Laid-open No. 2007-31095. Specifically, Japanese Patent Application Laid-open No. 9-175724 discloses a sheet finisher that receives printed sheets ejected from an image forming apparatus and distributes the sheets onto a plurality of bins and staples each sheet bundle on the bins. The sheet finisher includes a chuck device that advances toward a trailing-edge center portion of the sheet bundle distributed on one of the bins, chucks the trailing-edge center portion, and conveys the sheet bundle to a stapler located to the rear of the bin. The chuck device performs this operation for each of the bins. The chuck device includes a chucker that clamps the trailing-edge center portion of the sheet bundle loaded on the inclined bin and a moving unit that moves the sheet bundle clamped by the chucker to the stapler disposed on a downstream extension of the sheet bundle. 
     Japanese Patent Application Laid-open No. 2007-31095 discloses a sheet finisher that performs postprocessing on sheets. The sheet finisher includes a hole puncher (lateral-hole punching unit) that punches holes for use in sheet binding (hereinafter, “binding holes”) in predetermined positions of sheets. The hole puncher, which is movable, moves to binding-hole positions and punches the binding holes. According to this technique, a line connecting the binding holes punched by the lateral-hole punching unit is parallel to a sheet conveying direction. The lateral-hole punch, which is movable, moves to the binding-hole positions and punches the binding holes. 
     However, the technique disclosed in Japanese Patent Application Laid-open No. 9-175724 is disadvantageous in that the sheet bundle is not moved up and down. This is because although the sheet bundle clamped by the chucker is movable in a conveying direction, the sheet bundle is unmovable in the vertical direction. The sheet finisher disclosed in Japanese Patent Application Laid-open No. 2007-31095 has disadvantageously complicated structure to allow the punching unit to move when punching the binding holes. In addition, a large driving source is necessary to move the punching unit. 
     Therefore, there is a need to provide a sheet processing device capable of moving sheets with a simple structure without using a large driving source, thereby achieving miniaturization. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to at least partially solve the problems in the conventional technology. 
     According to an embodiment, there is provided a sheet processing device that includes a clamp configured to clamp an edge portion of a sheet, the edge portion being on a side of an edge parallel to a direction in which the sheet has been conveyed; a first processing unit configured to perform a first process on the sheet at the side of the edge, the first processing unit being disposed at a first position; a second processing unit configured to perform a second process on the sheet at the side of the edge, the second processing unit being disposed at a second position that is different from the first position in a vertical direction; and a moving unit configured to move the clamp from the first position to the second position or vice versa so that the clamp moves on a loop passing through the first position and the second position. 
     According to another embodiment, there is provided an image forming apparatus that includes the sheet processing device according to the above embodiment. 
     The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a system configuration diagram schematically illustrating an inner structure of an image forming system according to an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view taken along the line E-E of  FIG. 1  to illustrate a schematic configuration of a sheet finisher; 
         FIG. 3  is a cross-sectional view taken along the line A-A of  FIG. 1  to illustrate the schematic configuration of the sheet finisher; 
         FIG. 4  is plan view of the sheet finisher illustrated in  FIG. 3 ; 
         FIG. 5  illustrates operations of a clamp unit; 
         FIG. 6  is a front view illustrating a configuration of the clamp unit and a moving mechanism for the clamp unit; and 
         FIG. 7  illustrates a configuration of a clamp. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments of the present invention are described below with reference to the accompanying drawings. According to an embodiment of the present invention, a plurality of processing units are set at vertically different positions. A clamp that clamps a portion of a sheet-like recording medium (hereinafter, simply referred to as “sheet”), such as paper, recording paper, transfer paper, or a transparency, is moved by a moving unit in a loop through the positions of the processing units by a simple mechanism, and predetermined processing is performed at the processing positions. 
     Overall Configuration 
       FIG. 1  is a system configuration diagram schematically illustrating an inner structure of an image forming system according to an embodiment of the present invention. The image forming system is, for example, a copier machine, a printer machine, a facsimile machine, or a multifunction peripheral (MFP) having at least two functions of these machines.  FIG. 2  is a cross-sectional view taken along the line E-E of  FIG. 1  to illustrate a schematic configuration of a sheet finisher, indicating relationship between arrangement of units and sheets. Referring to  FIGS. 1 and 2 , the image forming system according to the embodiment includes an image forming apparatus  100 , a sheet processing device  200 , and an image scanning apparatus  300 . The sheet processing device  200  is a sheet finisher that performs postprocessing on sheets ejected from the image forming apparatus  100 . Accordingly, the sheet processing device  200  is hereinafter referred to as the sheet finisher  200 . 
     The image forming apparatus  100  is a tandem color image forming apparatus using an indirect transfer method. The image forming apparatus  100  includes, at or near its center (see  FIG. 1 ), an image forming unit  110  having image forming stations for four colors, an optical writing unit (not shown) disposed below and adjacent to the image forming unit  110 , a sheet feeding unit  120  disposed below the image forming unit  110 , a sheet-feed conveying path (vertical conveying path)  130  for conveying a sheet picked up from the sheet feeding unit  120  to a secondary transfer unit  140  and a fixing unit  150 , an eject path  160  for conveying a sheet, onto which an image is fixed, to the sheet finisher  200 , and a duplex-printing conveying path  170  for turning a sheet, on one side of which an image is formed, upside down so that an image is formed on the other side. 
     The image forming unit  110  includes photosensitive drums for the colors, or Y, M, C and K, in the respective image forming stations  111 . There are provided an electrostatic charging unit, a developing unit, a primary transfer unit, a cleaning unit, and a neutralizing unit around each of the photosensitive drums. The image forming unit  110  also includes an intermediate transfer belt  112 , onto which images formed on the photosensitive drums are to be intermediately transferred by the primary transfer unit, and the optical writing unit that writes each color image on the surface of each drum. The optical writing unit is disposed below the image forming stations  111 . The intermediate transfer belt  112  is disposed above the image forming stations  111 . 
     The intermediate transfer belt  112  is rotatably supported by a plurality of support rollers. A support roller  114 , which is one of the support rollers, faces a secondary transfer roller  115  via the intermediate transfer belt  112  in the secondary transfer unit  140  so that secondary transfer of an image from the intermediate transfer belt  112  onto a sheet can be performed. Meanwhile, an image forming process performed by a tandem color image forming apparatus using an indirect transfer method is known and does not have direct relation with the scope of the present invention; accordingly, detailed description is omitted. 
     The sheet feeding unit  120  includes a sheet feed tray  121 , a pickup roller  122 , and sheet-feed conveying rollers  123 . The sheet feeding unit  120  picks up a sheet from the sheet feed tray  121  and delivers the sheet upward along the vertical conveying path  130 . The delivered sheet, onto which an image is transferred in the secondary transfer unit  140 , is delivered to the fixing unit  150 . 
     The fixing unit  150  includes a fixing roller and a pressing roller. During a course where the sheet passes through a nip between the fixing roller and the pressing roller, heat and pressure are applied to the sheet, causing toner to be fixed onto the sheet. The eject conveying path  160  and the duplex-printing conveying path  170 , into which bifurcation is made at a bifurcating claw  161 , are disposed downstream of the fixing unit  150 . One of the conveying paths is selected depending on whether a sheet is to be conveyed to the sheet finisher  200  or to the duplex-printing conveying path  170 . Meanwhile, bifurcation conveying rollers  162  are disposed immediately upstream of the bifurcating claw  161  with respect to a sheet conveying direction to apply a conveying force to the sheet. 
     The sheet finisher  200  arranged inside the image forming apparatus  100  performs predetermined processing on an image-formed sheet conveyed from the image forming apparatus  100 , and places the sheet on an eject tray  210  arranged most downstream. The sheet finisher  200  will be described in detail later. 
     The image scanning apparatus  300  is of a known type that scans a document placed on an exposure glass with light to read an image on a document surface. The configuration and function of the image scanning apparatus  300  are known and do not have direct relation with the scope of the present invention; accordingly, detailed description is omitted. 
     The image forming apparatus  100  configured as roughly described above generates image data for use in writing from document data obtained by the image scanning apparatus  300  by scanning or from print data transferred from an external PC or the like. The optical writing unit performs optical writing on the photosensitive drums based on the image data. Images formed by the image forming stations on a per-color basis are sequentially transferred onto the intermediate transfer belt  112 . A color image is formed on the intermediate transfer belt  112  by superimposing the four color images thereon. 
     Meanwhile, a sheet is fed from the sheet feed tray  121  according to the image forming operation. The sheet is temporarily stopped at a position of registration rollers (not shown) immediately upstream of the intermediate transfer unit  140  and, at timing synchronized to a leading end of the image on the intermediate transfer belt  112 , delivered to the intermediate transfer unit  140  where secondary transfer of the image onto the sheet is performed. The sheet is then delivered into the fixing unit  150 . 
     After the image is fixed in the fixing unit  150 , when the image is formed for one-side printing or as a second-side image of duplex printing, the bifurcating claw  161  is operated for path switching so that the sheet is conveyed to the eject path  160 . On the other hand, the sheet is conveyed to the duplex-printing conveying path  170  when the image is formed as a first-side image of duplex printing. The sheet conveyed to the duplex-printing conveying path  170  is turned upside down, and thereafter eventually delivered into the intermediate transfer unit  140  where an image is formed on a second side of the sheet. Thereafter, the sheet is conveyed to the eject path  160 . The sheet delivered to the eject path  160  is conveyed to the sheet finisher  200 . The sheet having undergone predetermined sheet processing or no processing in the sheet finisher  200  is ejected onto the eject tray  210 . 
     Sheet Processing Device 
       FIG. 3  is a cross-sectional view taken along the line A-A of  FIG. 1  to illustrate a schematic configuration of the sheet finisher  200 .  FIG. 4  is plan view of the sheet finisher  200  illustrated in  FIG. 3 . 
     Referring to  FIGS. 1 to 4 , the sheet finisher  200  includes a pair of inlet rollers  201 , an eject conveying path  202 , conveying rollers  203 , punching jogger fences (aligning plates)  211 , a clamp unit  400 , a staple tray  206 , trailing-end reference fences  207 , stapling jogger fences (aligning plates)  208 , eject rollers  209 , and the eject tray  210  that are arranged approximately in this order from upstream to downstream in the sheet conveying direction. 
     Specifically, at a sheet receiving section of the sheet finisher  200 , there are provided the pair of inlet rollers  201  that receives a sheet P from the eject path  160  of the image forming apparatus  100 , the eject conveying path  202  along which the received sheet P is conveyed to the punching unit, and the pair of conveying rollers  203 . An inlet motor rotates the pair of inlet rollers  201  and the pair of conveying rollers  203 , thereby conveying the sheet P along the eject conveying path  202  (in a direction indicated by arrow B 1 ). 
     An inlet sensor (not shown) that detects a leading end and a trailing end of the sheet P is disposed on the eject conveying path  202 . Based on (i) time when the inlet sensor detects the leading end and the trailing end, and (ii) numbers of steps taken by the inlet motor which is a stepping motor, timing for performing various sheet processing is determined. The inlet sensor is disposed near the inlet rollers  201  on the upstream side or the downstream side, for example. 
     In the image forming apparatus  100  according to the present embodiment, the sheet finisher  200  is arranged as illustrated in  FIG. 2  to configure the apparatus compact. Specifically, sheet processing is performed as follows. The sheet P is conveyed by short edge feed (SEF) in the conveying direction indicated by arrow B 1  in  FIG. 2 . When the sheet P has passed through the pair of conveying rollers  203 , the conveying direction of the sheet P is changed to a direction (indicated by arrow B 2  in  FIG. 2 ) perpendicular to the conveying direction (indicated by arrow B 1 ) along which the sheet P is conveyed from the image forming apparatus  100 . To enable such conveyance and sheet processing described above, hole punching positions C and stapling positions D are arranged in the sheet finisher  200  an illustrated in  FIG. 2 . Specifically, as illustrated in  FIG. 2 , it is necessary to perform hole punching and stapling on an edge face portion, which is parallel to the sheet conveying (sheet ejecting) direction (indicated by arrow B 1 ), of the sheets P. 
       FIG. 5  illustrates operations of the clamp unit. The sheet P ejected from the pair of conveying rollers  203  advances onto a punch stage  270 S as illustrated in (a) of  FIG. 5  in a state where the sheet P is supported at a portion of a far-side edge Pb by a punching unit  270  and supported at a portion of a near-side edge Pf by the staple tray  206 . The punching jogger fences  211  align a sheet leading end P 1  and a sheet trailing end P 2 . The clamp unit  400  is moved to bring the far-side edge Pb into contact with an abutting member  502  provided in the clamp unit  400  to position the sheet P. Subsequently, a first clamp  401   a  clamps the sheet P. Then, as illustrated in (b) of  FIG. 5 , the punching unit  270  punches a hole through the sheet P at a punching position. 
     After the punching unit  270  has punched the hole, the first clamp  401   a  moves along a guide  402  as illustrated in (c) of  FIG. 5 . As a result, the sheet P is pushed out of the punching unit  270  by the first clamp  401   a . Concurrently therewith, a second clamp  401   b  moves along the guide  402  to the punch stage  270 S, while the first clamp  401   a  moves down to a staple stage  250 S. When the far-side edge Pb reaches a position where the far-side edge Pb abuts on the trailing-end reference fences  207 , the sheet P is released from clamping by the first clamp  401   a , and falls (is placed) onto the staple stage  250 S. At this time, the second clamp  401   b  has been moved to a sheet receiving position for the punch stage  270 S. 
     In a mode that does not include hole punching, the punching operation to be performed by the punching unit  270  illustrated in (b) of  FIG. 5  is not performed, but the operations illustrated in (a) to (d) of  FIG. 5  are performed to cause the sheet P abutted against the trailing-end reference fences  207  of the staple stage  250 S to fall in a manner similar to that described above. After the sheet P has fallen from the punch stage  270 S to the staple stage  250 S, processing performed on the sheet P differs between the shift mode for shifting and ejecting the sheet P and a staple mode for forming a sheet bundle PBL by stacking a plurality of the sheets P, stapling the sheet bundle PBL, and ejecting the stapled sheet bundle PBL. Accordingly, the shift mode and the staple mode are individually described below together with description about configurations of relevant units. 
     Shift Mode 
     In the shift mode, the sheets P are not stapled but sorted into sets, each made up of predetermined number of sheets, that are alternately ejected on the eject tray  210  in a laterally staggered arrangement in the front view of the image forming apparatus ( FIG. 1 ). The stapling jogger fences  208  are disposed on the staple tray  206 . Guide shafts (not shown) fixed onto the staple tray  206  are inserted through the stapling jogger fences  208 . Each of the stapling jogger fences  208  is coupled to a stepping motor via a timing belt (not shown) to linearly reciprocate as the stepping motor rotates forward and backward. The stapling jogger fences  208  are configured to be movable independently from each other. 
     After the sheet P has fallen onto the staple stage  250 S, the clamp  401  brings the far-side edge Pb into contact with the trailing-end reference fences  207 , thereby aligning the sheet P in the sheet conveying direction. The stapling jogger fences  208  align the sheet P in the direction perpendicular to the conveying direction. 
     An eject guide plate  212  and the eject rollers  209  are disposed most downstream of the staple tray  206 . The sheet P conveyed in the direction indicated by arrow B 1  to a far-side position in  FIG. 2  is then conveyed in the direction indicated by arrow B 2  (to the near side) by a releasing claw (not shown). The sheet P is further conveyed in the same direction by the eject rollers  209  to be ejected onto the eject tray  210 . The eject rollers  209  perform sheet conveyance in cooperation with a driven roller  213 . The driven roller  213  is disposed at a movable end of the eject guide plate  212  and moved up and down by a stepping motor (not shown). The eject rollers  209  and the driven roller  213  convey the sheet P by pinching the sheet P therebetween. 
     When the sheets P are to be sorted into sets each made up of predetermined number of sheets, an aligning position (the position of the stapling jogger fences  208 ) for alignment in the direction perpendicular to the sheet conveying direction is shifted a preset distance. The sheet P is ejected from this position onto the eject tray  210 . When sheets are loaded onto the eject tray  210  in this manner, positions where the sheets are ejected on the eject tray  210  are alternately shifted every predetermined number of sheets. Sheet sorting is thus achieved. 
     A sheet hold-down member  220  for holding down the sheets P loaded on the eject tray  210  is disposed at a portion where the eject tray  210  is mounted on a body of the sheet processing device  200 . The sheet hold-down member  220  performs sheet hold-down releasing and sheet hold-down retention when a solenoid  221  is switched on and off. Specifically, in synchronization with conveyance of the sheet P, the solenoid  221  is switched on to cause the sheet hold-down member  220  to release hold-down retention; when the sheet P is conveyed past the eject rollers  209 , the solenoid  221  is switched off to hold down the sheet P. Even when the solenoid  221  is switched off just when the sheet P is conveyed past the eject rollers  209 , the solenoid  221  and the sheet hold-down member  220  are actuated after a certain time lag. This time lag allows the sheet P to be conveyed past the eject rollers  209  and fall onto the eject tray  210 , and thereafter be slipped down by the pull of gravity in a direction opposite to the conveying direction. After abutting on an end fence  225 , the sheet P is held down by the sheet hold-down member  220  on a movable tray member  222   b . Alternatively, a configuration in which a delay time is set in advance, and when triggered by passage of the sheet P over the eject rollers  209 , the sheet hold-down member  220  holds down the sheet P after the delay time can be employed. 
     The eject tray  210  includes a fixed tray member  222   a  on a downstream side with respect to the conveying direction and the movable tray member  222   b  on an upstream side. A tray DC motor  223   a  and a cam-link mechanism  223   b  move the movable tray member  222   b  up and down. The movable tray member  222   b  is pivotably supported at its pivot end, or an upstream end portion of the movable tray member  222   b , by the fixed tray member  222   a  via a support shaft  223   c . A moving end of the cam-link mechanism  221   b  is coupled to this movable tray  208   b . With this configuration, when the tray DC motor  223   a  runs, the movable tray member  222   b  pivots about the support shaft  223   c  according to rotation of the tray DC motor  223   a.    
     When the number of sheets ejected onto the movable tray member  222   b  reaches a certain value, the tray DC motor  223   a  rotates according to a command fed from a controller, which will be described later, thereby lowering a free end of the movable tray member  222   b . A tray-sheet-level sensor (not shown) is disposed on the sheet hold-down member  220 . The eject tray  210  loaded with the sheets P is maintained at a constant level as follows. When, in a state where the sheets P are held down by the sheet hold-down member  220 , the tray-sheet-level sensor outputs a signal indicating OFF, the eject tray  210  is elevated until the sheet-level sensor outputs a signal indicating ON. When the sheet-level sensor outputs a signal indicating ON, the eject tray  210  is lowered until the sheet-level sensor outputs a signal indicating OFF and then elevated until a signal indicating ON is output. 
     The distance between a nip between the eject rollers  209  and a sheet loading portion of the movable tray member  222   b  is maintained at a constant distance as described above by moving up and down the free end of the movable tray member  222   b  according to a sheet loading state of the eject tray  210  so that a constant contact angle is kept between a sheet ejected by the eject rollers  209  and the movable tray member  222   b . This allows maintaining consistent alignment quality of sheets loaded on the eject tray  210  and also loading a large number of sheets on the eject tray  210 . 
     By repeating the operations described above, the sheets P are loaded on the eject tray  210  as being sorted. 
     Staple Mode 
     In the staple mode, the sheets P are ejected as stapled sheet bundles each of which is made up of predetermined number of sheets and stapled by a stapler. 
     In the staple mode, the clamp  401  pushes the far-side edge Pb out of the punching unit  270 . As the clamp unit  400  vertically moves, the clamp  401  moves until the sheet trailing ends P 2  abut on the trailing-end reference fences  207 . Sheet alignment in the sheet conveying direction is thus performed. This sheet alignment is performed with reference to the trailing-end reference fences  207  by bringing the sheets P into contact with the trailing-end reference fences  207 . When the trailing ends of the sheets P have abutted on the trailing-end reference fences  207 , the stapling jogger fences  208  arranged on the staple tray  206  align the sheets P in the direction perpendicular to the sheet conveying direction in a manner similar to that in the shift mode described above. 
     The stapling jogger fences  208  are disposed on the staple tray  206  as illustrated in  FIG. 4 . The guide shafts (not shown) fixed onto the staple tray  206  are inserted through the stapling jogger fences  208 . Each of the stapling jogger fences  208  is coupled to the stepping motor via the timing belt (not shown) to linearly reciprocate as the stepping motor rotates forward and backward. The stapling jogger fences  208  are configured to be independently movable from each other. The staple tray  206  includes home-position sensors that detect the stapling jogger fences  208  at their standby positions. 
     The staple tray  206  includes the trailing-end reference fences  207  mounted on a guide shaft (not shown) via a slider. The trailing-end reference fences  207  are configured to be movable in the same direction as the stapling jogger fences  208 . A rack held by the slider is meshed with a gear disposed at approximately center of the staple tray  206 . The trailing-end reference fences  207  move symmetrically with respect to the gear. The trailing-end reference fences  207  include guide portions at their ends. When a stapler unit  250  is moved, a base (not shown) of the stapler unit  250  contacts an inner side of the guide portion and pushes the guide portion. Accordingly, when the stapler unit  250  is moved, the trailing-end reference fences  207  are moved to follow the stapler unit  250 . 
     Specifically, when the stapler unit  250  is moved toward an end of the staple tray  206 , the trailing-end reference fences  207  move away from each other. When the stapler unit  250  is moved toward the center of the staple tray  206 , the trailing-end reference fences  207  that are paired with each other approach to each other. This is because an elastic force is exerted to the trailing-end reference fences  207  by a spring (not shown) in a direction toward the center of the staple tray  206 . 
     After the stapling, the eject guide plate  212  is lowered. The sheet bundle PBL is pinched and held between the eject rollers  209  and the driven roller  213  mounted on the eject guide plate  212 , and ejected onto the eject tray  210 . While the sheet bundle PBL is being ejected, the solenoid  221  is switched on to cause the sheet hold-down member  220  to release hold-down retention, and the eject tray  210  is lowered a predetermined amount. Subsequently, at a time when the trailing end of the sheet bundle PBL passes by a bundle eject sensor  224 , the eject guide plate  212  is elevated to prepare for receiving a next sheet. At the same time, the solenoid  221  is switched off to perform sheet hold-down retention. At this time, the solenoid  221  and the sheet hold-down member  220  are actuated after a predetermined time lag. This time lag lets the sheet bundle PBL fall on the movable tray member  222   b , the trailing end of the sheet bundle PBL abut on the end fence  225 , and thereafter the sheet bundle PBL be held down by the sheet hold-down member  220  on the movable tray member  222   b.    
       FIG. 6  is a front view illustrating a configuration of the clamp unit and a moving mechanism for the clamp unit. The clamp unit  400  includes the first clamp  401   a , the second clamp  401   b , the guide  402  that is elliptical when viewed from the front, and a link  405 . A pivot point (rotation center)  404  of the link  405  is at center of the guide  402 . The first clamp  401   a  and the second clamp  401   b  include a first guide member  403   a  and a second guide member  403   b , respectively, on a base  501  which will be described later. The link  405  has first and second grooves  405   a  and  405   b . The guide  402  also has a guide groove  402   a.    
     The guide  402  is fixed to a casing of the sheet finisher  400 . The link  405  is mounted to be rotatable relative to the pivot point  404 . As illustrated in  FIG. 6 , the first and second grooves  405   a  and  405   b  are arranged so as to overlap the guide groove  402   a . The first and second guide members  403   a  and  403   b  are movably attached to the link  405  and to the guide  402  in such a manner that the first guide member  403   a  and the second guide member  403   b  extend through the first groove  405   a  and the second groove  405   b , respectively. With this configuration, when the link  405  is rotated about the pivot point  404  by a driving motor (not shown), the first and second guide members  403   a  and  403   b  move along the guide groove  402   a  while reciprocating inside the first and second grooves  405   a  and  405   b , respectively. As a result, the clamps  401  circle around in a loop through the position indicated by solid lines and the position indicated by dashed lines in  FIG. 6 . At this time, the first and second clamps  401   a  and  401   b  that stay horizontal move up and down and to the left and to the right along the guide  402 . Moving motions of the clamp unit  400  as a whole and operation timing for clamping and releasing clamping the sheet bundle PBL have already been described above with reference to  FIG. 5 . 
       FIG. 7  illustrates a configuration of the clamp  401 . The first and second clamps  401   a  and  401   b  are identical in configuration, and collectively referred to as the clamps  401  with reference symbols a and b omitted. The clamp  401  includes the base  501 , the abutting member  502 , an open/close member  503 , a torsion spring  504 , and a solenoid  505 . The open/close member  503  is rotatably supported by a pivot point  506  at a distal end of the abutting member  502 . The solenoid  505  is arranged on a side of a first end of the open/close member  503 . The torsion spring  504  constantly exerts an elastic force to the open/close member  503  in a direction that opens the first end. Illustrated in (a) of  FIG. 7  is a state where the open/close member  503  is closed. In this state, the sheet P is clamped. In this state, the torsion spring  504  exerts a pressure that allows clamping the sheet P between the open/close member  503  and the base  501 . In this state, the solenoid  505  is off. Accordingly, an actuator  505   a  of the solenoid  505  contacts the first end of the open/close member  503  and is pushed by the first end, thereby being placed in a most withdrawn state. 
     Illustrated in (b) of  FIG. 7  is the clamp  401  in an open state. When the solenoid  505  of the clamp  401  in the state illustrated in (a) of  FIG. 7  is switched on, the actuator  505  protrudes to push the first end of the open/close member  503 , thereby rotating the open/close member  503  clockwise in (a) of  FIG. 7  against the elastic force exerted by the torsion spring  504 . Consequently, a second end of the open/close member  503  moves away from the base  501  and separates therefrom to release the sheet P from the clamped state. 
     When associated with  FIG. 5  and  FIG. 6 , this open/close operations (clamping operation and clamp-releasing operation) illustrated in  FIG. 7  can be described as follows. In (a) of  FIG. 5 , the first clamp  401   a  is open (clamp-released state), and the second clamp  401   b  is closed (clamping state); the first clamp  401   a  is closed, and the second clamp  401   b  is open in (b) of  FIG. 5 ; the first clamp  401   a  is open, and the second clamp  401   b  is open in (c) of  FIG. 5 ; both the first clamp  401   a  and the second clamp  401   b  are open in (d) of  FIG. 5 . The clamping operation and the clamp-releasing operation are performed by the solenoid  505  as described above. These operations are executed by a central processing unit (CPU) of a control circuit (not shown) as in the case of the rotation of the link  405 . 
     As described above, according to the present embodiment, the following effects are obtained. 
     1) it is possible to position the sheets P on a desired one of the punch stage  270 S and the staple stage  250 S by simply moving the link  405  in a loop so as to move the clamps  401  along the guide  402 . Accordingly, because the sheet processing device can have a simple structure and does not require a large driving source to move the sheets P, device miniaturization can be achieved.
 
2) The sheet finisher  200  includes the punching unit  270  that punches holes at punching positions parallel to the sheet conveying direction B 1  in which the sheets P are received from the image forming apparatus  100 , and the stapler unit  250  that staples the sheets P at stapling positions parallel to the sheet conveying direction B 1 . The unit  270  and the unit  250  are arranged above and below with respect to each other. Delivery of the sheets P to the punch stage  270 S and to the staple stage  250 S is performed by clamping a portion of the sheets P with the first clamp  401   a  or the second clamp  401   b  and moving the sheets P along the guide  402 . Accordingly, an increase of the sheet finisher  200  in size is prevented.
 
3) When the punching unit  270  punches holes, an edge face of the sheets P on a side where the holes are to be punched is brought into contact with the abutting member  502  of the clamp  401  to perform positioning. Accordingly, hole punching through the sheets P can be performed accurately.
 
4) When the punching unit  270  punches holes, the edge face of the sheets P on the side where the holes are to be punched is brought into contact with the abutting member  502  of the clamp  401  to perform positioning. Thereafter, the sheets P are clamped by the clamping member and then punched. Accordingly, the holes can be punched accurately because the sheets P do not go out of order during punching.
 
5) After the holes are punched by the punching unit  270 , the sheets P are moved from the punch stage  270 S to the staple stage  250 S while being kept to be clamped by the clamp  401 . Accordingly, even when the sheets P are moved up and down, the sheets P are moved onto the staple tray  206  orderly without going out of order.
 
6) The clamp  401  provides double functions, which are a sheet-edge-face aligning function for the punching unit  270  and a sheet-edge-face aligning function for the stapler unit  250 . Accordingly, it is possible to perform punching and stapling on the sheets P accurately with an inexpensive structure.
 
7) The clamp unit  400  includes the first and second clamps  401   a  and  401   b  that are supported by the link  405 . Accordingly, it is possible to perform punching and stapling while maintaining high productivity.
 
8) A moving path of the clamps  401  are looped along the guide  402 . Accordingly, it is possible to perform punching and stapling while maintaining high productivity.
 
     According to the embodiments, a sheet processing device is capable of moving sheets with a simple structure without using a large driving source. Accordingly, device miniaturization can be achieved. 
     Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.