Patent Publication Number: US-8113513-B2

Title: Sheet processing apparatus with cross-directionally moving device

Description:
This is a divisional of U.S. patent application Ser. No. 11/237,776, filed Sep. 29, 2005, and allowed Sep. 21, 2009. 
    
    
     This application claims the priority benefits of Japanese Patent Applications Nos. 2004-290811 and 2004-290812 filed Oct. 1, 2004, the entire disclosure of which is hereby incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a sheet processing apparatus which moves sheets successively stacked on a tray in a direction crossing a sheet discharging direction to thereby align the side edges of the sheets, and an image forming apparatus provided with the same. 
     2. Description of the Related Art 
     There has heretofore been a sheet processing apparatus which moves sheets one by one on a tray in a direction crossing a sheet discharging direction by a cross-directionally moving member to thereby abut one side edge of the sheet against a cross-side restricting member and align the side edge (side edge alignment) (Japanese Patent Application Laid-open No. H8-67400). The side edge refers to that edge of the sheet which is along the sheet discharging direction. 
     The standby position of the cross-directionally moving member is coincident with the center of the sheet discharged to the tray in the width direction thereof. Therefore, the cross-directionally moving member is adapted to contact with the central portion of the sheet in the width direction thereof to thereby move the sheet in the width direction thereof and abut it against the cross-side restricting member. 
     Also, the sheet processing apparatus is adapted to be provided, for example, in the apparatus main body of an image forming apparatus for forming an image on a sheet, and effect the side edge alignment of the sheet on which an image has been formed and which has been discharged from the apparatus main body. 
     Further, the sheet processing apparatus is adapted to abut a sheet against the cross-side restricting member at a substantially constant speed to thereby effect side edge alignment. 
     However, the cross-directionally moving member of the conventional sheet processing apparatus, when it moves a succeeding sheet on a preceding sheet to thereby abut one side edge of the succeeding sheet against the cross-side restricting member, has sometimes slidden relative to the succeeding sheet because the cross-directionally moving member sides onto the other side edge of the preceding sheet through the succeeding sheet. Particularly, when the side edge portion of the preceding sheet is upwardly curled, the cross-directionally moving member has sometimes slidden on the succeeding sheet. 
     Therefore, the sheet processing apparatus has sometimes been incapable of reliably align the side edge of the succeeding sheet. Also, when the cross-directionally moving member rides onto the other side edge of the preceding sheet through the succeeding sheet, it has sometimes disturbed the alignment of the preceding sheet. 
     Further, there has been the problem that a sheet bundle thus subjected to a disturbed side edge aligning process, when subjected to post-processing such as stapling, becomes a poor-looking sheet bundle. 
     Also, the conventional sheet processing apparatus is adapted to abut a sheet against the cross-side restricting member at a substantially constant movement speed to thereby effect side edge alignment and therefore, the cross-directionally moving member has sometimes wrinkled the side edge portion of the sheet, and the sheet has sometimes been rebounded by the reaction resulting from the abutting. For this reason, in the conventional sheet processing apparatus, it has been difficult for the sheet to be reliably abutted against the cross-side restricting member without the side edge portion thereof being wrinkled and without being rebounded. Particularly, when the side edge of the sheet remains incapable of being aligned and thereafter, post-processing such as binding a sheet bundle is performed, there has arisen the problem that the sheet bundle becomes a poor-looking sheet bundle of which the side edges are not uniform. 
     Also, an image forming apparatus provided with a sheet processing apparatus poor in its side edge aligning performance cannot smoothly feed sheets into the sheet processing apparatus and therefore, has been incapable of enhancing its image forming efficiency. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a sheet processing apparatus which can reliably align the side edges of sheets. 
     It is also an object of the present invention to provide an image forming apparatus provided with a sheet processing apparatus which can reliably align the side edges of sheets in an apparatus main body. 
     In order to achieve the above object, a sheet processing apparatus according to an embodiment of the present invention is provided with a cross-directionally moving device for moving a sheet in a direction crossing a sheet discharging direction, and a cross-side restricting member for receiving one side edge of the sheet moved in the direction crossing the sheet discharging direction by the cross-directionally moving device, and restricting the movement of the sheet, and the cross-directionally moving device moves the next sheet from a position between the other side edge of the sheet received by the cross-side restricting member and the cross-side restricting member to the cross-side restricting member. 
     The sheet processing apparatus may be further provided with a sheet stacking portion on which sheets are stacked, and a sheet discharging member for discharging the sheets to the sheet stacking portion, and the sheet discharging member may preferably be capable of discharging the next sheet to a position overlapping the other side edge of the sheet received by the cross-side restricting member. 
     The aforedescribed position between the other side edge of the sheet and the cross-side restricting member may preferably be variable in accordance with the size of the sheet. 
     The sheet processing apparatus may be further provided with a curl detector for detecting the curl of the sheet, and may be designed such that when the curl detector detects that the sheet is curled, the cross-directionally moving device starts the movement of the sheet from a position nearer to the cross-side restricting member than the aforementioned position when the sheet is not curled. 
     In order to achieve the above object, an image forming apparatus according to an embodiment of the present invention is provided with an image forming portion for forming an image on a sheet, and any one of the aforedescribed sheet processing apparatuses, and the sheet processing apparatus aligns one side edge of the sheet on which the image has been formed by the image forming portion. 
     In order to achieve the above object, an image forming apparatus according to an embodiment of the present invention is provided with an image forming portion for forming an image on a sheet, a sheet stacking portion on which sheets are stacked, a cross-directionally moving device for moving the sheet in a direction crossing a sheet discharging direction, and a cross-side restricting member for receiving one side edge of the sheet moved in the crossing direction by the cross-directionally moving device, and restricting the movement of the sheet, and the cross-directionally moving device moves the sheet from a position between the other side edge of the sheet received by the cross-side restricting member and the cross-side restricting member to the cross-side restricting member. 
     It is also an object of the present invention to provide a sheet processing apparatus which causes little misalignment during the alignment of the side edge of a sheet. 
     It is also an object of the present invention to provide an image forming apparatus provided with a sheet processing apparatus excellent in the aligning property of the side edge of a sheet, and enhanced in image forming efficiency. 
     It is also an object of the present invention to provide a sheet processing apparatus which can decelerate the movement speed of a sheet and align the sheet when it moves the sheet on a tray in a direction crossing a sheet discharging direction to thereby align the side edge of the sheet, and an image forming apparatus provided with the same. 
     In order to achieve the above object, a sheet processing apparatus according to an embodiment of the present invention is provided with a cross-directionally moving device for moving a sheet in a direction crossing a sheet discharging direction, and a cross-side restricting member for receiving one side edge of the sheet moved in the crossing direction by the cross-directionally moving device, and restricting the movement of the sheet, and the cross-directionally moving device decelerates the movement speed of the sheet and causes the sheet to abut against the cross-side restricting member. 
     The movement distance of the sheet at a speed before decelerated may preferably be greater than the movement distance of the sheet at the decelerated speed. 
     The cross-directionally moving device may preferably further move the sheet by a predetermined amount still after it has caused the sheet to abut against the cross-side restricting member. 
     The cross-directionally moving device may preferably be separable from the sheet after it has caused the sheet to abut against the cross-side restricting member. 
     In order to achieve the above object, an image forming apparatus according to an embodiment of the present invention is provided with an image forming portion for forming an image on a sheet, and any one of the aforedescribed sheet processing apparatuses, and the sheet processing apparatus aligns that side edge of the sheet which is along a sheet discharging direction. 
     In order to achieve the above object, an image forming apparatus according to an embodiment of the present invention is provided with an image forming portion for forming an image on a sheet, a cross-directionally moving device for moving the sheet in a direction crossing a sheet discharging direction, and a cross-side restricting member for receiving one side edge of the sheet moved in the crossing direction by the cross-directionally moving device, and restricting the movement of the sheet, and the cross-directionally moving device decelerates the movement speed of the sheet and causes the sheet to abut against the cross-side restricting member. 
     These and other objects, features and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic front cross-sectional view of a copying machine which is an example of an image forming apparatus provided with a sheet processing apparatus according to an embodiment of the present invention in an apparatus main body. 
         FIG. 2  is a schematic front cross-sectional view of the sheet processing apparatus according to the embodiment of the present invention. 
         FIG. 3A  is a block diagram showing the connected relationships among the controlling portion of the sheet processing apparatus according to the embodiment of the present invention, sensors, motors, etc. 
         FIG. 3B  shows the contents of operating data stored in the RAM  120  of  FIG. 3A . 
         FIG. 4  is a schematic front view of the driving mechanism of the offset roller and conveying roller of the sheet processing and the driving mechanism of the clamp mechanism of the sheet processing apparatus according to the embodiment of the present invention. 
         FIG. 5  is a schematic plan view of the driving mechanism of the offset rollers and conveying rollers of the sheet processing apparatus according to the embodiment of the present invention. 
         FIG. 6  is a schematic front view showing the arrangement relationships among the offset rollers, the clamp mechanism and the post-processing tray of the sheet processing apparatus according to the embodiment of the present invention. 
         FIG. 7  is an illustration of the moving operation of the clamp mechanism of the sheet processing apparatus according to the embodiment of the present invention. 
         FIG. 8  which is composed of  FIGS. 8A ,  8 B and  8 C are flow charts for illustrating the operation of the sheet processing apparatus according to the embodiment of the present invention. 
         FIG. 9  is a perspective view of the offset roller, etc. when, in the sheet processing apparatus according to the embodiment of the present invention, a sheet has been discharged onto a post-processing tray. 
         FIG. 10  is a perspective view of the offset rollers, etc. when, in subsequence to  FIG. 9 , the offset rollers have moved the sheet to a trailing edge stopper. 
         FIG. 11  is a perspective view of the offset rollers, etc. when the offset rollers have caused the sheet to abut against a side edge alignment reference plate. 
         FIG. 12  shows a state in which in subsequence to  FIG. 11 , the offset rollers have been returned to their home position. 
         FIGS. 13A ,  13 B,  13 C and  13 D are illustrations of the sheet side edge aligning operation of the offset rollers.  FIG. 13A  shows a state in which the first sheet has been discharged.  FIG. 13B  shows a state in which the side edge alignment of the first sheet has been effected.  FIG. 13C  shows a state in which a succeeding sheet has been discharged.  FIG. 13D  shows the standby position of the offset rollers when L 3 ≧W. 
         FIGS. 14A ,  14 B and  14 C are illustrations of the side edge aligning operation of a curled sheet by the offset rollers.  FIG. 14A  shows a state in which the first sheet has been discharged.  FIG. 14B  shows a state in which the side edge alignment of the first sheet has been effected.  FIG. 14C  shows a state in which a succeeding sheet has been discharged. 
         FIG. 15  is a flow chart schematically showing the control of the offset rollers by a CPU. 
         FIG. 16  shows the operation during the movement of offset rollers according to another embodiment of the present invention in the width direction of the sheet. 
         FIG. 17  which is composed of  FIGS. 17A ,  17 B and  17 C are flow charts showing the operation of a sheet processing apparatus according to the embodiment shown in  FIG. 16 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A sheet processing apparatus according to an embodiment of the present invention will hereinafter be described with reference to the drawings. 
       FIG. 1  is a schematic front cross-sectional view of a copying machine which is an example of an image forming apparatus provided with the sheet processing apparatus of the present invention in an apparatus main body. Image forming apparatuses include a copying machine, a facsimile apparatus, a printer and a compound machine of these. Accordingly, the sheet processing apparatus of the present invention is not connected to only the apparatus main body of a copying machine. Also, the sheet processing apparatus may be incorporated in the apparatus main body of an image forming apparatus. 
     The sheet processing apparatus according to the present embodiment is provided with a stapler for binding a sheet bundle, but may be provided with a punching device for punching a sheet, instead of the stapler. 
     (Copying Machine) 
     The copying machine  500  is comprised of a reader portion  100 , a printer portion  200 , a sheet processing apparatus  400 , etc. In the upper portion of the copying machine  500 , there is provided an automatic document feeder  300  (hereinafter referred to as the “ADF”) for supplying documents one by one onto platen glass  102 . The sheet processing apparatus  400  for effecting post-processing on a sheet discharged from the apparatus main body  500 A of the copying machine  500  is connected to a side of the apparatus main body  500 A of the copying machine  500 . 
     In  FIG. 1 , the reader portion  100  is adapted to convert a document into image data. The printer portion  200  has plural types of sheet cassettes  204  and  205  stacking a plurality of sheets thereon, and is adapted to form image data as a visible image on the sheet by a print command. 
     The reader portion  100  conveys a document to a predetermined position on the platen glass  102  and passes the document through that position by the ADF  300  and at the same time, applies the light of the lamp  103  of a scanner unit  104  stopped at the predetermined position, or applies the light of the lamp  103  of the horizontally moved scanner unit  104  to the document placed on the platen glass  102  with the ADF  300  opened by a user. 
     Reflected light from the document is inputted to a CCD image sensor portion  109  via mirrors  105 ,  106 ,  107  and a lens  108 . The reflected light from the document applied to the CCD image sensor portion  109  is subjected to electrical processing such as photoelectric conversion by the CCD image sensor portion  109 , and is subjected to ordinary digital processing. Thereafter, the image signal is inputted to the printer portion  200 . 
     The image signal inputted to the printer portion  200  is modulated and converted into an optical signal by an exposure controlling portion  201 , and irradiates a photosensitive member  202  (constituting an image forming portion). A latent image formed on the photosensitive member  202  by this irradiating light is toner-developed into a toner image by a developing device  203 . In timed relationship with the leading edge of the toner image, a sheet is conveyed from one of sheet cassettes  204  and  205 , and the toner image is transferred to the sheet by a transferring portion  206 . This transferred toner image is fixed on the sheet by a fixing portion  207 . The sheet on which the toner image has been fixed is discharged from a sheet discharging portion  208  to the outside of the apparatus main body  500 A of the copying machine  500  via a path  214 . Thereafter, the sheet is subjected to sorting, binding, etc. in accordance with an operation mode designated in advance by the sheet processing apparatus  400 . 
     Description will now be made of the sequence in which images successively read in are formed on the two sides of a sheet. 
     A sheet having a toner image fixed on one side thereof by the fixing portion  207  is guided to paths  215  and  218  by direction changeover members  209  and  217  held at solid-line positions, and is guided to a reversing path  212  by a direction changeover member  213  held at a broken-line position. After the trailing edge of the sheet has passed the direction changeover member  213 , the direction changeover member  213  is changed over to a solid-line position to thereby reverse the rotation direction of a roller  211 , whereupon the sheet has its conveying direction reversed and is reversed, and then is conveyed to an image-transferred sheet stacking portion  210 . Then, the sheet is conveyed to the photosensitive member  202 . When the next document is prepared on the platen glass  102 , the image of the document is read in the same manner as the above-described process, but the sheet is supplied from the image-transferred sheet stacking portion  210  and therefore, after all, the images of two documents can be formed on the front side and back side of one and the same sheet. 
     (Sheet Processing Apparatus) 
       FIG. 2  is a schematic front cross-sectional view of the sheet processing apparatus  400 .  FIG. 3A  is a block diagram showing the connected relationships among the controlling portion of the sheet processing apparatus, sensors, motors, etc. 
     The sheet processing apparatus  400  is provided with a sheet receiving portion  401  for receiving the sheet discharged from the apparatus main body  500 A of the copying machine  500 , conveying rollers  405  (sheet discharging members) for conveying the sheet, a post-processing tray  410  (sheet stacking portion) for containing therein the sheets successively discharged by the conveying rollers  405 , offset rollers  407  for conveying the sheets on the post-processing tray  410 , a stacking tray  421  for finally stacking thereon a sheet bundle formed on the post-processing tray  410 , a CPU (controlling portion)  111  for controlling the sheet processing apparatus  400  on the basis of a control signal from a controlling portion  501  (see  FIG. 1 ) in the apparatus main body  500 A, sensors  403 ,  150 ,  160 - 1 ,  160 - 2 ,  230 - 1 ,  230 - 2 ,  415  and  440 , motors  431 ,  432 ,  430 - 1 ,  430 - 2  and  135 , solenoids  433 ,  434 - 1  and  434 - 2 , and a stapler unit  420  for binding the sheet bundle, and the sheet processing apparatus  400  is designed to form a bundle of a number of sheets corresponding to the number of documents on the post-processing tray  410 , and discharge each sheet bundle onto the stacking tray  421 . 
     The stapler unit  420  need not always be provided. 
     While in the present embodiment, the controlling portion  501  of the apparatus main body is provided in the apparatus main body  500 A, and the CPU  111  is provided in the sheet processing apparatus  400 , the controlling portion  501  and the CPU  111  may be made integral with each other, and be provided in one of the apparatus main body  500 A and the sheet processing apparatus  400 . 
     While in the present embodiment, the sheet processing apparatus  400  is connected to the apparatus main body  500 A of the copying machine  500 , the sheet processing apparatus according to the present invention may be incorporated in the interior of the apparatus main body  500 A of the copying machine  500 . In that case, the sheet discharged from the sheet discharging portion  208  may be directly received by the offset rollers  407 . 
       FIG. 5  is a schematic plan view of the driving mechanism of the offset rollers and conveying rollers of the sheet processing apparatus according to the embodiment of the present invention. In  FIG. 5 , an offset motor  432 , a pinion  439 , a rack  441 , a rack supporting member  444 , a square shaft  418 , offset roller arms  406  and the offset rollers  407  together constitute a cross-directionally moving device  445 . 
     The cross-directionally moving device  445  is adapted to move the offset roller arms  406  to an offset home position  416   d  (see  FIG. 9 ) and a position for moving the sheet to a side edge aligning position which will be described later in a direction crossing a sheet discharging direction. 
     The position in which the offset rollers  407  start movement is not always the offset home position  416   d . That is, as will be described later, it sometimes differs from the offset home position depending on the sheet size. Also, it sometimes differs from the offset home position when the sheet is curled. 
     Also, the conveying motor  431 , a belt  435 , the square shaft  418 , pulleys  442 ,  443 , a belt  437 , the offset roller arms  406  and the offset rollers  407  together constitute a conveying direction moving apparatus (conveying direction moving means)  446  for selectively moving the sheet to a downstream side and an upstream side in the sheet discharging direction. 
     In  FIG. 3A , the CPU  111  has a ROM  110 . The ROM  110  stores therein a program corresponding to a control procedure described in a flow chart shown in  FIGS. 8A ,  8 B and  8 C. The CPU  111  is adapted to read out and execute the program stored in the ROM  110 , and effect the control of each portion. Also, the CPU  111  has a RAM  120 . The RAM  120  stores therein operating data  121  shown in  FIG. 3B . The CPU  111  is adapted to control each portion on the basis of the operating data  121 . 
     The input port of the CPU  111  has connected thereto such sensors as an entrance sensor  403  for detecting the sheet conveyed from the apparatus main body  500 A of the copying machine  500  to a sheet receiving portion  401  shown in  FIG. 2 , an offset home position sensor  150  for detecting whether the offset rollers  407  shown in  FIG. 5  are in the offset home position  416   d , bundle discharge home position sensors  160 - 1  and  160 - 2  for detecting whether clamp mechanisms  413 - 1  and  413 - 2  shown in  FIG. 7  are in home positions  413   a - 1  and  413   a - 2 , respectively, sheet bundle discharge sensors  230 - 1  and  230 - 2  for detecting whether a sheet bundle has been discharged to the stacking tray  421  shown in  FIG. 2 , a sheet discharge sensor  415  for detecting whether the sheets have been discharged to and stacked on the post-processing tray  410  shown in  FIG. 6 , and a curl detecting sensor  440  shown in  FIG. 2  for detecting the curl of the sheet. 
     The sheet processing apparatus  400  need not always be provided with the curl detecting sensor  440 . 
     The CPU  111  is adapted to execute the program stored in the ROM  110 , on the basis of the detection signals of these sensors, and control motors, solenoids and the stapler unit  420  connected to an output port. The motors include a conveying motor  431  for rotating the offset rollers  407  shown in  FIG. 5  in a direction to convey the sheet to the downstream side and a direction to convey the sheet to the upstream side, an offset motor  432  for moving the offset rollers  407  shown in  FIG. 5  in the direction crossing the sheet discharging direction, sheet bundle discharging motors  430 - 1  and  430 - 2  for moving the clamp mechanisms  413 - 1  and  413 - 2  shown in  FIG. 4  to a bundle discharging home position and a sheet bundle discharging position, respectively, and a stacking tray lifting and lowering motor  135  for lifting and lowering the stacking tray  421  shown in  FIG. 2 . The solenoids include a pickup solenoid  433  for lifting and lowering the offset rollers  407  shown in  FIG. 5 , and clamp solenoids  434 - 1  and  434 - 2  for opening and closing clamp claws  412 - 1  and  412 - 2 , respectively, shown in  FIG. 4 . The offset home position  416   d  shown in  FIG. 9  is also a sheet discharging position which will be described later. 
     The CPU  111  is provided with a serial interface portion  130 . The CPU  111  is adapted to give and receive control data and a control signal to and from the controlling portion  501  of the apparatus main body  500 A by this serial interface portion  130 , and effect the control of each portion. 
       FIGS. 4 to 6  show the driving mechanism of the offset rollers  407 . The offset rollers  407  are supported by the offset roller arms  406  movable up and down and rotatable in the directions indicated by the arrows U and D so as to be capable of receiving the sheet on the post-processing tray  410 . The offset roller arms  406  are rotatably supported on the square shaft  418  having a square cross-sectional shape by a round hole  406   a . The offset roller arms  406 , in order to make their construction readily understood, is shown as being disposed outside the pair of offset rollers  407  in  FIG. 6  and  FIGS. 9 ,  10 ,  11  and  12  which will be described later, but actually is disposed between the pair of offset rollers  407 , as shown in  FIG. 5 . 
     The offset roller arms  406  are adapted to be lifted and lowered by the pickup solenoid  433  through a down lever. The offset rollers  407  are adapted to be rotated by the conveying motor  431  through the belt  435 , the square shaft  418 , the pulley  442 , the belt  437  and the pulley  443 . The conveying motor  431  is adapted to rotate the conveying roller  405  and the offset rollers  407  by an amount according to the amount of rotation in the sheet discharging direction or a direction opposite to the sheet discharging direction. The pulley  442  is provided on the square shaft  418  by a square hole (not shown), and is adapted to be rotated integrally with the square shaft  418  by the engagement between the square hole and the square shaft  418  and be movable on the square shaft  418  in a thrust direction. 
     Between the pair of offset roller arms  406 , the rack supporting member  444  of a U-shape as viewed in plan view having the rack  441  is supported by and disposed on the square shaft  418 . The rack supporting member  444  is rotatably provided on the square shaft  418  by a round hole (not shown). Therefore, the rack supporting member  444  is adapted to be not driven to rotate by the square shaft  418  even if the square shaft  418  is rotated, and be movable on the square shaft  418  in the thrust direction. The pinion  439  provided on the fixed offset motor  432  is in meshing engagement with the rack  441 . The pickup solenoid  433  is movable along the square shaft  418 . 
     Accordingly, the belt  437 , the pulley  443 , the offset roller arms  406  and the offset rollers  407  are adapted to be capable of being lifted and lowered and rotated in the directions indicated by the arrows U and D in  FIG. 4  about the square shaft  418 , and also be guided by the square shaft  418  and be movable toward and away from the stapler unit  420  with the movement of the rack supporting member  444 . 
     The offset rollers  407  (see  FIGS. 2 and 6 ) are adapted to be lowered from gravity by the pickup solenoid  433  shown in  FIG. 5  becoming OFF when the leading edge of the sheet is conveyed to the post-processing tray  410  and the trailing edge of the sheet is detected by the entrance sensor  403 , and urge the upper side of the sheet and convey the sheet to the downstream side so that the entire sheet may be stacked on the post-processing tray  410 . Also, the offset rollers  407  are adapted to convey the sheet to the post-processing tray  410 , and thereafter be stopped and rotated in the opposite direction to thereby abut the upstream edge of the sheet against a trailing edge stopper (upstream edge aligning means)  411 , and effect the alignment of the upstream edge. Further, the offset rollers  407 , when in  FIG. 5 , the offset motor  432  is rotated, is adapted to be movable toward a side edge aligning position which will be described later by the pinion  439  and the rack  441 . The reason why the offset rollers  407  are moved toward the side edge aligning position is for causing the sheet to be driven to move by the offset rollers  407  by the utilization of the frictional contact of the offset rollers  407  with the sheet to thereby move the sheet to the side edge aligning position. 
       FIGS. 4 ,  6  and  7  are views for illustrating the construction of the clamp mechanisms  413 - 1  and  413 - 2 . The clamp mechanisms  413 - 1  and  413 - 2  installed near the trailing edge stopper  411  are adapted to be movable toward and away from the stacking tray  421  by the pinions  451 - 1 ,  451 - 2  and the racks  452 - 1 ,  452 - 2  when the sheet bundle discharging motors  430 - 1  and  430 - 2  are rotated. That is, the clamp claws  412 - 1 ,  412 - 2  and the clamp solenoids  434 - 1 ,  434 - 2  are adapted to be moved. The clamp claws  412 - 1  and  412 - 2  of the clamp mechanisms  413 - 1  and  413 - 2 , respectively, are adapted to be opened and closed in the directions indicated by the arrows indicated in  FIG. 4  by the actuation of the clamp solenoids  434 - 1  and  434 - 2 . 
     In the above-described construction, the controlling portion  501  of the apparatus main body  500 A of the copying machine  500  to which the sheet processing apparatus  400  shown in  FIG. 1  is attached grasps the size of the sheet discharged from the sheet discharging portion  208 . 
     Therefore, the CPU  111  of the sheet processing apparatus  400  which comprises a microcomputer system effects serial communication with the controlling portion  501  of the apparatus main body  500 A. 
     The sheet side edge aligning operation will now be described with reference to  FIGS. 9 to 11 ,  13 A to  13 D,  14 A to  14 C and  15 . 
     The CPU  111  is adapted to control the offset motor  432 , and move the offset rollers  407  to the standby position when they receive the sheet, in accordance with the width size of the sheets stacked on the post-processing tray  410 . The width size of the sheets is sent from the controlling portion  501  of the apparatus main body  500 A of the copying machine  500 , or from a sensor (not shown) provided in the course until the sheet is discharged to the post-processing tray  410  ( FIG. 5 ).  FIG. 15  is a flow chart schematically showing the control of the offset rollers  407  by the CPU  111 . The CPU  111  obtains the data of the sheet width W from the controlling portion  501  or the sensor (not shown) (S 500 ). 
     The sheet is discharged onto the post-processing tray  410  by the conveying rollers  405  ( FIG. 5 ) so that the center of the sheet width W may substantially align with the center (the position indicated by the reference character  416   d  in  FIG. 10 ) of the post-processing tray  410 . The sheet width W refers to the length of the sheet along the direction crossing the sheet discharging direction. The standby position of the offset rollers  407  is usually substantially the center of the post-processing tray  410 , as shown in  FIGS. 10 and 13A , and is adapted to receive the inserted sheet at the center. That is, as shown in  FIG. 13A , usually the width center CL 1  of the sheet conveyed out by the conveying rollers  405 , the width center CL 2  of the offset rollers  407  and a position indicated by the offset home position  416   d  ( FIG. 9 ) align with one another. 
     The CPU  111  judges on the basis of sheet size information whether L 3 &lt;W (S 510 ). In  FIGS. 13A to 13D , L 1  is the width dimension of the post-processing tray  410 . L 2  is the width dimension of the offset rollers  407 . L 3  and L 5  are the distances between a side edge aligning reference plate (cross-side restricting member)  416  and the offset rollers  407 . W is the sheet width. 
     The CPU  111 , when it judges that L 3 &lt;W, does not change the position of the offset rollers  407 . The offset rollers  407  stand by at the offset home position  416   d  (S 520 ). In this case, the offset rollers  407 , as shown in  FIG. 13A , once move the sheet P 1  discharged onto the post-processing tray  410  in the downstream direction, and thereafter are reversely rotated and convey the sheet P 1  to the upstream side, and abut the trailing edge (the upstream side edge portion) of the sheet against the trailing edge stopper  411  to thereby align the trailing edge (S 530 ). Then, the offset rollers  407 , as shown in  FIG. 13B , move the sheet P 1  toward the side edge aligning reference plate  416  and abut one side edge P 1   a  of the sheet P 1  against the side edge aligning reference plate  416  to thereby align the side edge P 1   a  (S 540 ). Thereafter, the offset rollers  407  are returned to their original position (S 550 ). 
     Subsequently, as shown in  FIG. 13C , a succeeding (second) sheet P 2  is discharged onto the post-processing tray  410  by the conveying rollers  405  ( FIG. 5 ). At this time, the side edge portion of the succeeding sheet P 2  discharged by the conveying rollers  405  and the side edge portion of the preceding sheet P 1  are adapted to overlap each other. Since L 3 &lt;W, the offset rollers  407  urges the other side edge P 1   b  of the preceding sheet P 1  against the post-processing tray  410  through the succeeding sheet P 2  (S 560 ). Therefore, the offset rollers  407  need not ride onto the other side edge P 1   b  of the preceding sheet P 1  when they move the succeeding sheet to the side edge aligning reference plate  416  side. Consequently, the offset rollers  407  do not disturb the alignment of the side edge of the preceding sheet P 1 . Nor they slide on the succeeding sheet P 2 . Consequently, the offset rollers  407  can cause the succeeding sheet P 2  to accurately abut against the side edge aligning reference plate  416  to thereby align the side edge P 2   a  (S 570 ). 
     The CPU  111  judges whether there is a succeeding sheet (S 580 ), and if there is a succeeding sheet, shift is made to a step S 550 , where the steps S 550  to S 580  are repeated. If at the step S 580 , it is judged that there is no succeeding sheet, the processing is terminated. 
     As described above, when L 3 &lt;W, the offset rollers  407  can align the sheet with the side edge aligning reference plate  416  from a position in which the width center CL 2  of the offset rollers  407  and the width center CL 1  of the discharged sheet align with each other. 
     Now, when L 3 ≧W as shown in  FIG. 13D , the offset rollers  407  cannot urge the other side edge P 1   b  of the preceding sheet P 1  against the post-processing tray  410  through the succeeding sheet P 2 . In this case, the offset rollers  407  ride onto the other side edge P 1   b  of the preceding sheet P 1  through the succeeding sheet P 2  and therefore, in some cases, there is the undesirable possibility that the offset rollers slide on the succeeding sheet P 2  and cannot reliably align the side edge of the succeeding sheet P 2 . Therefore, the CPU  111  moves the offset rollers  407  by a distance L 4  on the other side edge P 1   b  of the preceding sheet P 1 , and sets the standby position of the offset rollers  407  to L 5 &lt;W (S 650 ). That is, the CPU  111  abuts one side edge P 1   a  of the preceding sheet P 1  against the side edge aligning reference plate  416  at steps S 620 , S 630  and S 640  in the same manner as at the aforedescribed steps S 520 , S 530  and S 540  to thereby align the side edge P 1   a , and thereafter changes the standby position of the offset rollers  407  from a solid-line position indicated in  FIG. 13D  to a broken-line position, and causes the offset rollers  407  to stand by above the other side edge P 1   b  of the preceding sheet P 1 . 
     Subsequently, as shown in  FIG. 13D , the succeeding (second) sheet P 2  is discharged onto the post-processing tray  410  by the conveying rollers  405  ( FIG. 5 ). At this time, the side edge portion of the succeeding sheet P 2  discharged by the conveying rollers  405  and the side edge portion of the preceding sheet P 1  are adapted to overlap each other. Since L 5 &lt;W, the offset rollers  407  urge the other side edge P 1   b  of the preceding sheet P 1  against the post-processing tray  410  through the succeeding sheet P 2  (S 660 ). 
     The offset rollers  407  from a new standby position need not ride onto the other side edge P 1   b  of the preceding sheet P 1  to side-edge-align the succeeding sheet P 2  with the side edge aligning reference plate  416 , and can cause the succeeding sheet P 2  to accurately abut against the side edge aligning reference plate  416  to thereby align the side edge P 2   a  without disturbing the alignment of the side edge of the preceding sheet P 1 , and without sliding on the succeeding sheet P 2  (S 670 ). 
     The CPU  111  judges whether there is a succeeding sheet (S 680 ), and if there is a succeeding sheet, shift is made to a step S 650 , where the steps S 650  to S 680  are repeated. If at the step S 680 , it is judged that there is no succeeding sheet, the processing is terminated. 
       FIGS. 14A to 14C  illustrate another embodiment in which the standby position is set on the basis of the amount of curl of the sheet. 
     If as shown in  FIGS. 14A to 14C , the preceding sheet P 1  is curled, the overhead width (the sheet width as it is seen from right above the sheet) becomes narrower by the amount of curl. Correspondingly, the standby position of the offset rollers  407  can be shifted to the side edge aligning reference plate  416  side. Depending on the amount of curl, the standby position need not be changed. 
     The preceding sheet P 1  has its curl detected by the curl detecting sensor (curl detector)  440  provided between the sheet receiving portion  401  (FIG.  2 ) and the conveying rollers  405 , during the time until it is discharged onto the post-processing tray  410 . Even if as shown in  FIG. 14A , the sheet is curled, in the case of the first sheet P 1 , the offset rollers  407  effect the side edge alignment of the sheet from a standby position in which the width center CL 2  and the width center CL 1  of the preceding sheet P 1  align with each other. When the succeeding sheet P 2  is then discharged, the CPU  111  shifts the standby position of the offset rollers  407  as shown in  FIG. 14C  in accordance with the amount of curl of the preceding sheet P 1 . Thereby, the offset rollers  407  can hold down the other side edge P 1   b  of the preceding sheet P 1 , and need not ride onto the other side edge P 1   b  of the preceding sheet P 1 , and can cause the succeeding sheet P 2  to accurately abut against the side edge aligning reference plate  416  to thereby align the side edge P 2   a  without disturbing the alignment of the preceding sheet P 1 , and without sliding on the succeeding sheet P 2 . The standby position of the offset rollers  407  may be changed with the sheet regarded as being curled. In this case, the curl detecting sensor  440  is not required. 
     As described above, the CPU  111  of the sheet processing apparatus  400  is adapted to grasp the sheet size of the sheet conveyed from the apparatus main body  500 A of the copying machine  500 , and control the offset motor  432  for moving the offset rollers  407  in the width direction, by an amount of movement according to the sheet size. That is, the CPU  111  is adapted to move the offset rollers  407  to a standby position adjusted to the sheet size and the state of the sheet. 
     Consequently, the sheet processing apparatus  400  according to the present embodiment is adapted to move the offset rollers  407  so as to move the next sheet P 2  from the position between the other side edge P 1   b  of the preceding sheet P 1  received, for example, by the side edge aligning reference plate  416  which is the cross-side restricting member and the side edge aligning reference plate  416  to the side edge aligning reference plate  416 . Therefore, the offset rollers  407  can hold down the other side edge P 1   b  of the preceding sheet P 1 , and need not ride onto the other side edge P 1   b  of the preceding sheet P 1 , and can cause the succeeding sheet P 2  to accurately abut against the side edge aligning reference plate  416  to thereby align the side edge P 2   a  without disturbing the alignment of the side edge of the preceding sheet P 1 , and without sliding on the succeeding sheet P 2 . 
       FIGS. 4 and 7  schematically show the construction of a sheet bundle discharging mechanism. 
     As shown in  FIG. 9 , a plurality of clamp mechanisms (holding means)  413 - 1  and  413 - 2  are provided in the sheet bundle discharging mechanism. The clamp mechanisms  413 - 1  and  413 - 2  are adapted to hold a sheet bundle PB aligned on the post-processing tray  410  (see  FIGS. 5 and 7 ) by the aligning operation of the offset rollers  407  which will be described later and at the same time, intactly move the sheet bundle PB to bundle discharging positions  413   b - 1  and  413   b - 2  from home positions  413   a - 1  and  413   a - 2  toward the stacking tray  421  as shown in  FIG. 7 , to thereby discharge the sheet bundle from the post-processing tray  410  to the stacking tray  421 . As shown in  FIG. 4 , the movement of the clamp mechanisms  413 - 1  and  413 - 2  is effected by sheet bundle discharging motors  430 - 1  and  430 - 2  rotating pinions  451 - 1  and  451 - 2  to thereby move racks  452 - 1  and  452 - 2 . The home positions  413   a - 1  and  413   a - 2  of the clamp mechanisms  413 - 1  and  413 - 2 , respectively, are adapted to be detected by bundle discharging home position sensors  160 - 1  and  160 - 2 . Also, whether the sheet bundle has been discharged onto the stacking tray  421  is adapted to be detected by sheet bundle discharge sensors  230 - 1  and  230 - 2  provided on the stacking tray  421 . 
     The sheet processing apparatus  400  (see  FIG. 2 ) according to the present embodiment is adapted to lower the stacking tray  421  to a position in which the uppermost surface of the sheet bundle PB stacked on the stacking tray  421  substantially aligns with the post-processing tray  410  by a stacking tray lifting and lowering motor  135  when the sheet bundle PB is discharged from the post-processing tray  410  because the sheet bundle PB stacked on the stacking tray  421  constitutes a portion of the post-processing tray  410 . 
     The operation of the sheet processing apparatus  400  according to the present embodiment will now be described with reference to the block diagram of  FIG. 3 , the flow chart shown in  FIGS. 8A ,  8 B and  8 C,  FIGS. 1 ,  2 ,  4  to  7 , and  FIGS. 9 to 15 . It is to be understood that this flow chart is a flow chart when as shown in  FIG. 12 , the sheets are stacked on one side of the post-processing tray  410 . Also, the side edge aligning operation described with reference to  FIGS. 13A to 13D  and  FIGS. 14A to 14C  is performed at the same time, and the description thereof is as described with reference to  FIG. 15 . 
     When a copying operation is started in the apparatus main body  500 A of the copying machine  500 , the CPU  111  waits for a sheet discharging signal to be sent from the controlling portion  501  of the copying machine  500  (S 100 ). The CPU  111 , when it receives a sheet discharging signal from the controlling portion  501  through the serial interface portion  130 , drives the pickup solenoid  433  shown in  FIG. 5  to thereby rotate the offset roller arms  406  in the direction indicated by the arrow U indicated in  FIGS. 4 and 6 , and lift the offset rollers  407  (S 110 ). The position to which the offset rollers  407  have been lifted is a position indicated by broken line in  FIG. 9 . The standby position of the offset rollers  407  is adjusted on the basis of the size information or the like of the sheet sent to the post-processing tray  410  (S 115 ). As described with reference to  FIG. 15 , in the case of the first sheet, the CPU  111  causes the offset rollers  407  to stand by at the offset home position  416   d  (S 520 ; S 620 ). Also, in the case of the second and subsequent sheets, the CPU  111  basically causes the offset rollers  407  to stand by at a standby position set at a step S 270  which will be described later. 
     Then, the CPU  111  rotates the conveying motor  431  to thereby rotate the conveying rollers  405  and the offset rollers  407  being rotated in the conveying direction in synchronism with the conveying rollers  405  in the direction indicated by the arrow E indicated in  FIG. 9  so as to be capable of conveying the sheet in the same direction as the sheet discharging direction of the copying machine (S 120 ). Thereby, the offset rollers  407  are lifted and rotated, and assumes a state in which it waits for the sheet to be conveyed thereto. 
     The CPU  111 , when it receives a sheet entry detection signal having detected the trailing edge of the first sheet from the entrance sensor  403  (S 130 ), releases the driving of the pickup solenoid  433 , and lowers the offset rollers  407  in the direction indicated by the arrow D from gravity as indicated by solid line in  FIG. 9 , to thereby bring the offset rollers into pressure contact with the surface of the sheet (S 140 ). When the sheet is the second or subsequent succeeding sheet P 2 , the CPU  111 , as described with reference to  FIG. 15 , urges the other side edge P 1   b  of the preceding sheet P 1  against the post-processing tray  410  by the offset rollers  407  through the succeeding sheet P 2  (S 560 ; S 660 ). The offset rollers  407  are already rotated in the direction indicated by the arrow E, and continues to be rotated by the conveying motor  431  to thereby convey the sheet in the direction indicated by the arrow F which is a downstream direction. The CPU  111 , when the sheet is conveyed to a predetermined position beyond the clamp claw  412 - 1  shown in  FIG. 6  (S 150 ), stops the conveying motor  431  to thereby once stop the rotation of the offset rollers  407 , and stop the conveyance of the sheet in the direction indicated by the arrow F (S 160 ). 
     The sheet is the first sheet and therefore, the CPU  111  actuates the clamp solenoid  434 - 1  shown in  FIG. 4  to thereby open the clamp claw  412 - 1  of the clamp mechanism  413 - 1  disposed at the sheet discharging position  416   d  (see  FIG. 9 ) as shown in  FIGS. 4 ,  6  and  7  and standing by at the home position  413   a - 1 , as shown in  FIG. 10  (S 170 ). Then, the CPU  111  reverses the rotation of the conveying motor  431  to thereby rotate the offset rollers  407  in the direction indicated by the arrow G opposite to the sheet discharging direction, as shown in  FIG. 10  (S 180 ), and reversely conveys the sheet in the direction indicated by the arrow K which is the upstream side, and abuts the upstream edge (trailing edge) of the sheet against the trailing edge stopper  411  to thereby effect the alignment of the trailing edge (upstream edge) of the sheet (S 190 ), and stops the rotation of the offset rollers  407  (S 200 ). 
     The CPU  111  judges by the information of the sheet discharged from the copying machine whether the sheet is a sheet on which a binding process is to be executed (S 210 ), and if the sheet is a sheet on which the binding process is to be executed, the CPU  111  opens the gripper claw  412 - 2  of another clamp mechanism  413 - 2 . Depending on the size of the sheet, the gripper claw  412 - 2  may be opened together with a gripper claw  412 - 1  when the latter is opened. Then, the CPU  111  moves the offset rollers  407  by the offset motor  432  to thereby move the sheet toward the side edge aligning reference plate  416 . As shown in  FIG. 11 , the sheet being in contact with the offset rollers  407  is also moved toward the side edge aligning reference plate  416  by the frictional force of the offset rollers  407  (S 220 ). Also, when the sheet is the second or subsequent sheet P 2 , as described with reference to  FIG. 15 , the CPU  111  moves the offset rollers  407  in the direction crossing the sheet discharging direction to thereby abut the succeeding sheet P 2  against the side edge aligning reference plate  416  and align the side edge P 2   a  thereof (S 570 ; S 670 ). 
     Thereafter, in order to correct the shift of the alignment in the sheet discharging direction effected at S 180 , by offset movement, as shown in  FIG. 11 , the offset rollers  407  are rotated in a direction opposite to the sheet discharging direction to thereby perform the operation of aligning the upstream edge (trailing edge) of the sheet (S 240 ). At this time, the sheet is abutted against the trailing edge stopper  411  so that some flexure may occur to the sheet, thereby enhancing the aligning property of the sheet. Thereafter, this flexure is eliminated by the elasticity of the sheet itself when the offset rollers  407  are lifted and separated from the sheet, and the sheet becomes flat. 
     Thereafter, as shown in  FIG. 12 , the offset rollers  407  are lifted by the driving of the pickup solenoid  433  (S 250 ), whereafter the driving of the clamp solenoids  434 - 1  and  434 - 2  is released and the clamp claws  412 - 1  and  412 - 2  are closed to thereby hold down the aligned sheet (S 260 ). Thus, it never happens that the sheet now discharged is carried away in the sheet conveying direction by a sheet discharged next. The offset rollers  407  in their lifted state are moved to a predetermined standby position by the offset motor  432  through the rack  441  and the pinion  439  (S 270 ). This standby position is the standby position described with reference to  FIGS. 13A to 13D  and  14 A to  14 C. That is, as described with reference to  FIG. 15 , the CPU  111  sets the standby position of the offset rollers  407  to the home position  416   d  (S 550 ) or L 5  (S 650 ), depending on whether the sheet width W is greater or smaller than the distance L 3  between the offset rollers  407  and the side edge aligning reference plate  416 . 
     Thereafter, the CPU  111  checks up whether the sheet stacked on the post-processing tray  410  is a sheet corresponding to the last page of the document to be copied (S 280 ), and when it judges on the basis of information sent from the copying machine that it is not the sheet corresponding to the last page, return is made to S 100 , where the CPU receives a sheet discharging signal sent next from the copying machine, and repeats the aforedescribed flow until a sheet corresponding to the last page is stacked on the post-processing tray  410 . Thereby, the CPU  111  of the sheet processing apparatus  400  grasps the size of a sheet and aligns the sheet with an offset position suited for the binding process of the sheet each time a sheet is discharged from the copying machine  500 . 
     On the other hand, if at S 280 , it is judged that the sheet is a sheet corresponding to the last page, it means that a sheet bundle corresponding to the document to be copied is formed on the post-processing tray  410  and therefore, whether a stapling process is selected is checked up (S 300 ), and if it is selected, the staple unit  420  is driven to thereby execute the stapling process (S 310 ). After the stapling process has been completed, or even when the stapling process is not selected, the clamp claws  412 - 1  and  412 - 2  of the clamp mechanisms  413 - 1  and  413 - 2 , respectively, are moved forward from the home position  413   a - 1  and  413   a - 2  of the clamp mechanisms  413 - 1  and  413 - 2  toward the stacking tray  421  by the sheet bundle discharging motors  430 - 1  and  430 - 2  through the racks  452 - 1 ,  452 - 2  and the pinions  451 - 1 ,  451 - 2  while gripping the sheet bundle, and are moved to the bundle discharging positions  413   b - 1  and  413   b - 2  of the clamp mechanisms  413 - 1  and  413 - 2 , respectively (S 320 ). Thereafter, the clamp solenoids  434 - 1  and  434 - 2  are driven, whereby the clamp claws  412 - 1  and  412 - 2  are opened, and the stacking tray  421  is lowered as will be described later (S 330 ). The clamp mechanisms  413 - 1  and  413 - 2  are returned to the home positions  413   a - 1  and  413   a - 2 , respectively (S 340 ). The conveying motor  431  is stopped to thereby stop the rotation of the conveying rollers  405  and the offset rollers  407  (S 350 ). Lastly, the offset rollers  407  are lowered (S 360 ), thus terminating a series of processes. 
     Thus, the sheet processing apparatus  400  has bound a sheet bundle formed by the trailing edges (upstream edges) of the sheets being aligned by the trailing edge stopper  411 , and the side edges of the sheets being aligned by the side edge aligning reference plate  416 , by the stapler unit  420 , and has discharged it onto the stacking tray  421 . 
     In the above-described operation, the sheet bundle formed by the trailing edges and side edges of the sheets being aligned may be discharged without being subjected to the binding process. 
     Also, the number of the clamp mechanisms may be one. In this case, it is necessary to provide the clamp mechanism at a position whereat it can hold down the sheet irrespective of the size thereof. 
     In the sheet processing apparatus  400  according to the present embodiment, in the moving process of the stacking tray at the step S 330 , the sheet bundle stacked on the stacking tray  421  constitutes a portion of the post-processing tray  410  and therefore, when the sheet bundle is discharged from the post-processing tray  410 , the stacking tray  421  is adapted to be lowered to a position in which the uppermost surface of the sheet bundle stacked on the stacking tray  421  is substantially flush with the post-processing tray  410 , by the stacking tray lifting and lowering motor  135 . 
     If at the step S 210 , the sheet binding process is not executed, the CPU  111  drives the pickup solenoid  433  to thereby lift the offset rollers  407  and separate it from the sheet (S 290 ). Then, the CPU  111  releases the driving of the clamp solenoids  434 - 1  and  434 - 2 , whereby the clamp claws  412 - 1  and  412 - 2  are closed to thereby hold down the aligned sheet (S 292 ). Thus, it never happens that the sheet now discharged is carried away in the sheet conveying direction by a sheet discharged next. 
     Thereafter, the CPU  111  checks up whether the sheet stacked on the post-processing tray  410  is a sheet corresponding to the last page of the document to be copied (S 280 ), and if it judges on the basis of information sent from the copying machine that the sheet is not a sheet corresponding to the last page, return is made to S 100 , where the CPU  111  receives a sheet discharging signal sent next from the copying machine, and repeats the aforedescribed flow until the sheet corresponding to the last page is stacked on the post-processing tray  410 . 
     On the other hand, if at S 280 , it is judged that the sheet is the sheet corresponding to the last page, a sheet bundle corresponding to the document to be copied is formed on the post-processing tray  410 . The CPU  111 , if it judges at a step S 300  that the stapling process is not executed, advances to a step S 320 , where it executes the processes of S 320  to S 360 , thus terminating the sheet processing. Thus, the sheet bundle not subjected to the binding process has its trailing edge (upstream edge) aligned, and is discharged onto the stacking tray  421 . 
     The sheet or the sheet bundle need not always be discharged onto the stacking tray  421 . 
     While in the sheet processing apparatus  400  according to the present embodiment, a program corresponding to the control procedure described in the flow chart shown in  FIGS. 8A ,  8 B and  8 C are stored in the ROM  110  shown in  FIGS. 3A and 3B , and the CPU  111  effects the control of each portion while reading out the program, processing on the control program may be designed to be effected by hardware to thereby obtain a similar effect. 
     In the sheet processing apparatus according to the present embodiment, the cross-directionally moving device is adapted to move the next sheet from a position between the other side edge of a sheet received by the cross-side restricting member and the cross-side restricting member to the cross-side restricting member and therefore, it never happens that the sheet rides onto the other side edge of the preceding sheet through a succeeding sheet. Therefore, the sheet processing apparatus can reliably abut one side edge of the succeeding sheet against the cross-side restricting member almost without sliding relative to the succeeding sheet, and can enhance the aligning property of the side edge of the sheet. 
     Further, it never happens that the cross-directionally moving member rides onto the other side edge of the preceding sheet through the succeeding sheet and therefore, the alignment of the preceding sheet is neither disturbed, and the aligning property of the side edge of the sheet can be enhanced. 
     Another embodiment of the present invention will now be described with reference to  FIG. 16 . 
     The CPU  111  in this embodiment judges the width size of sheets stacked on the post-processing tray  410 , and calculates the amount of movement to e.g. the side edge aligning reference plate  416  (see  FIG. 9 ) which is the cross-side restricting member. The offset rollers  407  are brought into contact with the sheet, whereafter the offset rollers  407  abut the sheet against the side edge aligning reference plate  416  by the utilization of the frictional force thereof with the sheet and executes a side edge aligning process. At that time, as shown in  FIG. 16 , before the sheet abuts against the side edge aligning reference plate  416 , the offset rollers are changed over to a speed different from the speed during the movement thereof (deceleration in  FIG. 16 ). After the speed of the offset rollers  407  has been changed over, the sheet is abutted against the side edge aligning reference plate  416 , and the offset rollers,  407  slide on the sheet, thus terminating the side edge aligning process. The offset rollers  407  are decelerated from a certain position and effects the abutting and alignment and therefore, in addition to sufficiently securing productivity, they make the mitigation of damage to the sheet after the aligning process possible. The speed and the movement distance are controlled by the CPU  111 . 
     The side edge aligning reference plate  416  is provided along and in parallelism to the sheet discharging direction. The side edges of the sheet are edges along the sheet discharging direction. 
       FIG. 16  shows the relation between the movement speed of the offset rollers  407  and time. In  FIG. 16 , the offset motor  432  is started and the offset rollers  407  start their movement, and at a point of time (time T 1 ) whereat the offset home position sensor  150  has become OFF, the offset rollers  407  are moved toward the side edge aligning reference plate  416  at a movement speed V 1  to thereby move the sheet. Then, the offset rollers  407  are decelerated from the movement speed V 1  to a movement speed V 2  (&lt;V 1 ) by the offset motor  432  between a time T 2  when it has come close to the side edge aligning reference plate  416  and a time T 3 , and cause the side edge PS of the sheet P to abut against the side edge aligning reference plate  416  between the time T 3  and a time T 4  (see  FIG. 11 ), thus effecting side edge alignment. Thereafter, the offset rollers  407  slide on the sheet received by the side edge aligning reference plate  416  at the speed V 2  till a time T 5 , and are stopped. The offset rollers  407  form flexure in the sheet while sliding on the sheet. Therefore, the sheet has its side edge reliably urged against the side edge aligning reference plate  416 , and is enhanced in side edge alignment accuracy. 
     Lastly, the offset rollers  407  are returned to and stopped at an offset home position whereat the offset home position sensor  150  becomes ON, by the reverse rotation of the offset motor  432 . The offset rollers  407 , when returned to the offset home position, are separated from the sheet and returned and therefore, do not disturb the side edge alignment of the sheet. 
     As described above, the sheet processing apparatus  400  is designed such that the offset rollers  407  move the sheet at a decelerated speed to thereby cause the sheet to abut against the side edge aligning reference plate  416  and therefore, can mitigate the disturbance of alignment due to the rebound or the like of the sheet by the reaction after the sheet has been abutted against the side edge aligning reference plate  416  to thereby execute a highly accurate side edge aligning process, and can decrease the misalignment of the sheet during the side edge alignment. 
     In the movement of the offset rollers  407 , the movement distance corresponding to the time between the time T 1  before the deceleration and the time T 2  is set longer than the decelerated movement distance corresponding to the time between the time T 2  and the time T 3 . Therefore, the sheet processing apparatus  400  can effect side edge alignment almost without lengthening the side edge aligning process time even if the sheet is decelerated and is abutted against the cross-side restricting plate  416 , and can enhance the accuracy of sheet side edge alignment almost without reducing the sheet processing efficiency. 
     As described above, the CPU  111  of the sheet processing apparatus  400  is adapted to grasp the sheet size of the sheet conveyed from the apparatus main body  500 A of the copying machine  500 , and control the offset motor  432  for moving the offset rollers  407  in the width direction by an amount of movement according to the sheet size. 
       FIGS. 17A ,  17 B and  17 C are flow charts showing the operation of the sheet processing apparatus according to the embodiment shown in  FIG. 16 . The differences of the flow chart shown in  FIGS. 17A ,  17 B and  17 C from the flow chart shown in  FIGS. 8A ,  8 B and  8 C reside in steps S 115 , S 220 , S 270 , S 1220  and S 1270 . The other steps in  FIGS. 17A ,  17 B and  17 C are similar to the steps in  FIGS. 8A ,  8 B and  8 C, and are given similar reference characters and need not be described. 
     In  FIGS. 17A ,  17 B and  17 C, there is not shown the adjustment (S 115 ) of the standby position of the offset rollers  407  after the CPU  111  has received a sheet discharging signal (S 100 ) and has lifted the offset rollers  407  (S 110 ). However, again in the embodiment shown in  FIG. 16 , the adjustment (S 115 ) of the standby position of the offset rollers  407  may be effected. 
     At the step S 1220  in  FIGS. 17A ,  17 B and  17 C, the CPU  111  moves the offset rollers  407  by the offset motor  432  to thereby move the sheet toward the side edge aligning reference plate  416 . The sheet being in contact with the offset rollers  407  is also moved toward the side edge aligning reference plate  416  by the frictional force of the offset rollers  407 . At this time, as shown in  FIG. 16 , the CPU  111  causes the sheet decelerated in the course of movement of the offset rollers  407 , and having completed the deceleration on this side of the side edge aligning reference plate  416  to be abutted against the side edge aligning reference plate  416  at a low speed. The sheet is received by the side edge aligning reference plate  416 . Thereafter, the offset rollers  407  slide on the sheet, thus completing the side edge aligning process. 
     At the step S 1270  in  FIGS. 17A ,  17 B and  17 C, the offset rollers  407  in their lifted state are moved to the standby position by the offset motor  432  through the rack  441  and the pinion  439 . In the present embodiment, the standby position is the offset home position  416   d . However, again in the present embodiment, as in the aforedescribed embodiment, the standby position may be changed in accordance with the sheet width. 
     In the sheet processing apparatus according to the present embodiment, the cross-directionally moving device is adapted to decelerate and move the sheet to thereby cause the sheet to abut against the cross-side restricting member and therefore, the disturbance of alignment due to the rebound or the like of the sheet by the reaction after the sheet has been abutted against the cross-side restricting member can be mitigated and a highly accurate side edge aligning process can be executed, and the misalignment of the sheet during the side edge alignment can be reduced. 
     In the sheet processing apparatus according to the present embodiment, the movement distance before deceleration is set longer than the decelerated movement distance and therefore, even if the sheet is decelerated and is abutted against the cross-side restricting member, side edge alignment can be done almost without the side edge aligning process time being lengthened, and the accuracy of the sheet side edge alignment can be enhanced almost without the sheet processing efficiency being reduced. 
     In the sheet processing apparatus according to the present embodiment, the cross-directionally moving device is adapted to move the sheet by a predetermined amount still after the sheet has been caused to abut against the cross-side restricting member and therefore, flexure occurs to the side edge portion of the sheet and the alignment accuracy of the side edge of the sheet can be enhanced. 
     An image forming apparatus according to the present embodiment is provided with the above-described sheet processing apparatus which can align the side edge of the sheet easily and with good accuracy and therefore, can enhance image forming efficiency. 
     While the invention has been described with reference to the structure disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purpose of the improvements or the scope of the following claims.