Patent Publication Number: US-8109497-B2

Title: Sheet post-processing apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a sheet post-processing apparatus for sequentially receiving sheets successively fed from an image formation apparatus of, for example, a copier, printer or the like to process in a bunch form, and performing post-processing such as end binding processing, punching processing, saddle-stitching center-folding processing and the like on the bunch of sheets. 
     2. Description of the Related Art 
     Conventionally, sheet post-processing apparatuses have been known which gather sheets discharged from an image formation apparatus such as a copier or the like, and perform end binding processing, saddle-stitching center-folding processing to make a booklet, and further, bookbinding processing by applying an adhesive to the spine of a bunch of sheets to attach a front cover. In recent sheet post-processing apparatuses, with improvements in performance of a stapler for performing binding processing, for example, such post-processing has been made possible that a bunch of several tens of sheets are bound in book form. With increases in the number of sheets to form a single bunch of sheets, when a bunch of sheets subjected to saddle-stitching processing undergo center-folding processing to be in book form, in the so-called fore-edge portion (fore-edge end) that is an open side of the bunch of sheets, center-folded inner sheet edges jut more outwardly than outer sheet edges, and the problem arises that the appearance of the booklet is not good. To solve such a problem, sheet post-processing apparatuses have been developed which have trimming means for trimming the fore-edge portion of a bunch of sheets subjected to center-folding processing. 
     As a first conventional example of such a sheet post-processing apparatus provided with the trimming means, Patent Document 1 discloses a paper processing apparatus having a configuration where a stapling processing section for processing sequentially fed sheets in a bunch form to bind a bunch of sheet is disposed in the center portion of the apparatus, and under the stapling processing section are disposed a saddle-stitching unit for binding the center portion of the paper bunch, and a center-folding unit  50  for folding the paper bunch along the bound portion. Herein, it is configured that a cutter unit  60  for cutting an edge portion of the bound paper bunch is provided in the downstream stage of the center-folding unit  50 , and that a press lever  65  included in the cutter unit  60  holds the paper bunch when the paper is cut. 
     Further, as a second conventional example of the sheet post-processing apparatus provided with the trimming means, Patent Document 2 discloses a paper processing apparatus in which disposed are a paper carry-in entrance  55  situated in one side face, a saddle-stitching paper discharge outlet  56  disposed in the other side face that is the side opposite to the paper carry-in entrance  55 , a saddle-stitching compile tray  21  extending from above the one side face side to below the other side face side, while aligning and holding a plurality of sheets fed from the paper carry-in entrance  55 , and a saddle-stitching stapler  24  for binding a predetermined portion of the paper bunch held and aligned, and provided further are a folding knife  25  for folding the bound paper bunch, a rotary cutter unit  30  provided above the saddle-stitching compile tray  21  in the vertical direction to cut the folded paper using a blade traveling in the horizontal direction, and a booklet tray  51  to load the paper which is cut by the rotary cutter unit  30  and discharged from the saddle-stitching paper discharge outlet  56 . 
     Furthermore, as a third conventional example of the sheet post-processing apparatus provided with the trimming means, Patent Document 3 discloses a post-processing apparatus which has a feeder for feeding a cover sheet, a carrying path for carrying the cover sheet and paper, center-folding means for making a fold in the direction perpendicular to the carrying direction of the cover sheet and paper on the path, carrying means for carrying the cover sheet and paper each with the fold made and opened on a sheet basis, loading means for loading the cover sheet and paper, saddle-stitching means having staple putting means and staple receiving means for performing saddle-stitching processing on a paper bunch formed of the cover sheet and paper on the loading means, and trimming means for trimming a fore edge of the paper bunch subjected to the saddle-stitching processing to be a book, and which has the feature that the feeder, trimming means and the saddle-stitching means are arranged in the vertical direction.
     [Patent Document 1] Japanese Laid-Open Patent Publication No. 2003-261260   [Patent Document 2] Japanese Laid-Open Patent Publication No. 2004-195569   [Patent Document 3] Japanese Laid-Open Patent Publication No. 2004-115237   

     However, in the sheet post-processing apparatus thus provided with the trimming means, since it is necessary to arrange the end binding processing means, saddle-stitching processing means, center-folding means and also the trimming means in the limited space within the apparatus frame, as in the above-mentioned first and third conventional examples, the trimming means for finally trimming a fore-edge portion of a bunch of sheets subjected to the center-folding processing is situated in the lower portion of the apparatus frame or near the sheet discharge outlet for discharging the bunch of sheets subjected to the post-processing. Further, a sheet branch portion for turning a sheet fed from the carry-in entrance to the center-folding means is disposed in the carrying path between the punch means and the end binding means. Therefore, the space becomes small which is under the end binding means and surrounded by the center-folding means and the discharge outlet. 
     Therefore, in such a conventional sheet post-processing apparatus, it is not possible to reserve a sufficient spade to drop trimming debris occurring in the trimming processing to store, a debris storage box is filled fully with the trimming debris, and the need arises to halt the apparatus frequently. Further, a discharge outlet for discharging a trimming-processed bunch of sheets should also be disposed in the lower portion of the apparatus, the discharge tray is filled fully with bunches of sheets in a short time, and it is necessary to halt the apparatus frequently as in removing the trimming debris. 
     Further, in the second conventional example as described above, such a configuration is adopted that in the apparatus frame  10  are provided, from the top, a carrying path for passing a sheet with an image formed without processing and sequentially discharging onto a first discharge tray  52 , an end binding processing path for forming a bunch of sheets to perform end binding processing and collecting bunches of sheets on a second discharge tray  54 , and a saddle-stitching center-folding processing path for performing saddle-stitching center-folding processing on a bunch of sheets and trimming a fore edge of the bunch of sheets which are arranged in the vertical direction. Therefore, as well as the problem that the apparatus size increases, since the trimming means for performing dangerous processing of trimming a fore edge of a bunch of sheets is disposed near the sheet discharge outlet of the apparatus frame, the risk is high for causing an accident of inflicting a wound on the finger and/or hand of an operator when the operator handles a jam and the like. 
     The present invention was made to solve various problems in the conventional sheet post-processing apparatus as described above, and it is an object of the invention to secure a space for sufficiently storing trimming debris, while enabling the high number of trimmed bunches of sheets to be stored as much as possible within the limited space inside the sheet post-processing apparatus, thereby reduce the frequency of halting the sheet post-processing apparatus and dramatically improve efficiency of the sheet post-processing. 
     BRIEF SUMMARY OF THE INVENTION 
     Therefore, the present invention provides a sheet post-processing apparatus having a carry-in entrance ( 23   a ) disposed in one side face of an apparatus frame to receive a sheet fed from an image formation apparatus, end binding means ( 31 ) for gathering sheets received from the carry-in entrance in a bunch form and performing binding processing in the end portion of a bunch of sheets, saddle-stitching means ( 40 ) for gathering sheets received from the carry-in entrance in a bunch form and performing binding processing in the center portion of a bunch of sheets, center-folding means (folding processing mechanism  44  described later) for performing center-folding processing on the bunch of sheets subjected to the saddle-stitching processing, cutting means (trimmer unit  90  described later) for cutting a fore edge of the bunch of sheets subjected to the center-folding processing, a first discharge outlet ( 29   x ) disposed in the other side face of the apparatus frame to discharge the bunch of sheets subjected to the end binding processing, and a second discharge outlet ( 22   x ) disposed below the first discharge outlet to discharge the bunch of sheets subjected to the center-folding processing in the center-folding means, characterized in that the saddle-stitching means and the center-folding means are disposed below the carry-in entrance on the side of the one side face of the apparatus frame, the end binding means is disposed, above the saddle-stitching means and the center-folding means, between the carry-in entrance and the first discharge outlet, and that the cutting means is disposed within a space, below the end binding means, surrounded by the saddle-stitching means, the center-folding means and the second discharge outlet. 
     By this means, the sheet post-processing apparatus has a rational arrangement of means (units) for performing various kinds of post-processing, and thereby enables the apparatus size to be drastically reduced as compared with the conventional apparatus. Further, since the first discharge outlet can be situated in a relatively high position, it is possible to use the lower area outside the first discharge outlet as a space for a discharge tray, and to enhance the discharge capacity. Furthermore, since the lower space inside the apparatus frame can be used as a storage space for cutting debris, the storage amount of debris is also increased, and it is possible to reduce the frequency of halting the apparatus and improve the processing efficiency of the entire apparatus. 
     Moreover, the branch portion is disposed on the upstream side of the punch means in the carrying direction, in other words, the punch means is disposed in the carrying path between the sheet branch portion, which turns a sheet fed from the carry-in entrance to the center-folding means, and the end binding means, and therefore, the center-folding means can be shifted to the lower side from the lower center in the apparatus. It is thereby possible to effectively use the lower space inside the apparatus frame, and the lower space can be used as a storage section for center-folded sheets. 
     Then, since the punch means is disposed on the downstream side of the carrying path, it is possible to install the saddle-stitching center-folding processing means sufficiently close to the sheet carry-in entrance side, such a configuration also enables the cutting means to be situated on the inner side than the second discharge outlet, and the risk is eliminated that an operator receives a wound in the finger and/or hand by the cutting apparatus. Further, it is made possible to maximize the storage capacity of bunches of sheets in a stack tray, and by sharing a plurality of trays as the stack tray and a booklet tray, the effect is produced of dramatically improving the entire storage capacity of bunches of sheets subjected to various kinds of post-processing in the sheet post-processing apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an entire configuration view of an image formation system according to the invention; 
         FIG. 2  is an entire configuration view of a post-processing apparatus (sheet handling apparatus) in the system of  FIG. 1 ; 
         FIG. 3  is an explanatory view of main parts of the post-processing apparatus of  FIG. 2 ; 
         FIG. 4  is a configuration explanatory view of a rear end regulating means and aligning means of a processing tray; 
         FIG. 5  contains explanatory views of a sheet discharge mechanism of the processing tray, where  FIG. 5(   a ) is an explanatory view showing a configuration of a switch back roller,  FIG. 5(   b ) is an explanatory view showing a standby state of the switch back roller, and  FIG. 5(   c ) is an explanatory view showing a sheet engagement state of the switch back roller; 
         FIG. 6  contains explanatory views of a sheet aligning mechanism of the processing tray, where  FIG. 6(   a ) is an explanatory view showing the entire structure,  FIG. 6(   b ) is an explanatory view showing a state with a small sheet load amount,  FIG. 6(   c ) is an explanatory view showing a state with a large sheet load amount,  FIG. 6(   d ) is an explanatory view showing a positional relationship between a carry-in guide and carrying-out guide,  FIG. 6(   e ) is an explanatory view showing a structure of a kick means, and  FIG. 6(   f ) is an explanatory view showing its driving mechanism; 
         FIG. 7  shows a position moving mechanism of the rear end regulating means in the processing tray, where  FIG. 7(   a ) is an explanatory view showing a regulation state of a large-size sheet, and  FIG. 7(   b ) is an explanatory view showing a regulation state of a middle-size sheet; 
         FIG. 8  shows the position moving mechanism of the rear end regulating means in the processing tray, where  FIG. 8(   c ) is an explanatory view showing a regulation state of a small-size sheet, and  FIG. 8(   d ) is an explanatory view showing an offset state of large-size sheets; 
         FIG. 9  is a perspective view showing an entire configuration of a sheet-bunch carrying-out means; 
         FIG. 10  is an explanatory view showing a planar structure of the sheet-bunch carrying-out means; 
         FIG. 11  is an explanatory view of a guide mechanism of the sheet-bunch carrying-out means; 
         FIG. 12  is an explanatory view of a driving mechanism of the sheet-bunch carrying-out means; 
         FIG. 13  contains explanatory views of a grip mechanism of the sheet-bunch carrying-out mechanism, where  FIG. 13(   a ) is an explanatory view of a state where a bunch of sheets are nipped, and  FIG. 13(   b ) is an explanatory view of a state where the bunch of sheets are released from the nip; 
         FIG. 14  is an explanatory view of the grip mechanism of the sheet-bunch carrying-out mechanism, where  FIG. 14(   c ) is an explanatory view of a state where the bunch of sheets are carried out to a stack tray; 
         FIG. 15  contains operating state explanatory views of the sheet-bunch carrying-out means, where  FIG. 15(   a ) shows a first standby position state, and  FIG. 15(   c ) shows an initial state to back to a second standby position; 
         FIG. 16  contains operating state explanatory views of the sheet-bunch carrying-out means, where  FIG. 16(   e ) shows a second standby position state,  FIG. 16(   f ) shows a state where the bunch of sheets are nipped, and  FIG. 16(   g ) shows a state where the bunch of sheets are carried out; 
         FIG. 17  contains operating state explanatory views of the sheet-bunch carrying-out means, where  FIG. 17(   h ) shows a state where a bunch of sheets are moved to above the stack tray,  FIG. 17(   i ) shows a state where the bunch of sheets are carried out onto the stack tray,  FIG. 17(   j ) shows a state immediately after the bunch of sheets are stacked on the stack tray, and  FIG. 17(   k ) is a state where the means returns to the first standby position; 
         FIG. 18(   a ) is an explanatory view showing a safety mechanism of a bunch means carrying-out outlet in the processing tray,  FIG. 18(   b ) shows a cross-sectional view taken along line A-A; 
         FIG. 19  is an explanatory view showing another safety mechanism of a bunch means carrying-out outlet in the processing tray different from the form in  FIG. 18 ; 
         FIG. 20  is an explanatory view of a positioning mechanism of a punch unit in the apparatus of  FIG. 3 ; 
         FIG. 21  is an explanatory view of a positioning sate in the positioning mechanism of the punch unit of  FIG. 20 ; 
         FIG. 22(   a ) is an explanatory view of an entire configuration of a trimmer unit in the apparatus of  FIG. 3 ,  FIG. 22(   b ) is an explanatory view of a driving system; 
         FIG. 23  contains explanatory views of the positioning state in the trimmer unit of  FIG. 22 , where  FIG. 23(   a ) shows a state where a bunch of sheets are carried, and  FIG. 23(   b ) shows a state where a pressurizing roller of the bunch of sheets is released; 
         FIG. 24  contains explanatory views of the positioning state in the trimmer unit of  FIG. 22 , where  FIG. 24(   c ) shows a register modification state for positioning a bunch of sheets, and  FIG. 24(   d ) shows a state for trimming the bunch of sheets; 
         FIG. 25  is an explanatory view of a lifting/lowering mechanism of the stack tray in the apparatus of  FIG. 3 ; 
         FIGS. 26  contains explanatory views of rising and lowering states of the stack tray in the apparatus of  FIG. 3 , where  FIG. 26(   a ) shows a state where a sheet is stored in the stack tray from a sheet discharge path,  FIG. 26(   b ) shows a state where sheets are collected as a set on the processing tray from the sheet discharge path, and  FIG. 26(   c ) shows a state where a bunch of sheets are carried out onto the stack tray from the processing tray; 
         FIG. 27  contains explanatory views of a fold roll mechanism in the apparatus of  FIG. 2 , where  FIG. 27(   a ) shows a state where a bunch of sheets are gathered,  FIG. 27(   b ) shows a state where the bunch of sheets are inserted between fold rolls with a fold blade,  FIG. 27(   c ) shows an initial state for folding with the fold rolls, and  FIG. 27(   d ) shows a state where the bunch of sheets are folded with the fold rolls, 
         FIGS. 28  contains explanatory views of an end binding stapling means in the apparatus of  FIG. 2 , where  FIG. 28(   a ) shows the entire configuration, and  FIG. 28(   b ) shows a traveling mechanism in the sheet width direction; 
         FIG. 29  contains explanatory views of a saddle-stitching stapling means in the apparatus of  FIG. 2 , where  FIG. 29(   a ) is an explanatory view of the entire configuration, and  FIG. 29(   b ) is an explanatory view of an anvil portion; and 
         FIG. 30  is a block diagram of a control configuration in the image formation system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will specifically be described below based on preferred embodiments of the invention as shown in accompanying drawings.  FIG. 1  is an entire configuration view showing an image formation system provided with an image formation apparatus A and a post-processing apparatus B according to the invention,  FIG. 2  is an explanatory view of a detailed configuration of the post-processing apparatus B, and  FIG. 3  is an explanatory view of main parts of the apparatus B. 
     [Configuration of the Image Formation System] 
     The image formation system as shown in  FIG. 1  is formed of the image formation apparatus A and the post-processing apparatus (sheet processing apparatus; which is the same in the following description) B. Then, a carry-in entrance  23   a  of the post-processing apparatus B is coupled to a sheet discharge outlet  3  of the image formation apparatus A, and it is configured that sheets with images formed thereon in the image formation apparatus A are stapled in the post-processing apparatus B and stored in a stack tray  21  and saddle tray (booklet tray)  22 . 
     [Configuration of the Image Formation Apparatus] 
     The image formation apparatus A will be described according to  FIG. 1 . The image formation apparatus A is configured so that a sheet is fed to an image formation section  2  from a paper feeding section  1 , printed in the image formation section  2 , and discharged from the sheet discharge outlet  3 . In the paper feeding section  1 , sheets with different sizes are stored in paper cassettes  1   a  and  1   b , and designated sheets are separated on a sheet basis and fed to the image formation section  2 . In the image formation section  2  are arranged, for example, an electrostatic drum  4 , and a print head (laser emitter)  5 , developer  6 , transfer charger  7  and fuser  8  disposed around the drum, an electrostatic latent image is formed on the electrostatic drum  4  with the laser emitter  5 , the developer  6  adds toner to the image, and the image is transferred onto the sheet with the transfer charger  7 , and heated and fused with the fuser  8 . The sheet with the image thus formed is sequentially carried out from the sheet discharge outlet  3 . “ 9 ” shown in the figure denotes a circulating path, and is a path for two-side printing for revising the side of the sheet with printing on its front side from the fuser  8  via a switch-back path  10 , and feeding the sheet again to the image formation section  2  so as to print on the back side of the sheet. The side of the two-side printed sheet is reversed in the switch-back path  10 , and the sheet is carried out from the sheet discharge outlet  3 . 
     “ 11 ” shown in the figure denotes an image scanning apparatus, where an original sheet set on a platen  12  is scanned with a scan unit  13 , and electrically read with a photoelectric conversion element not shown. The image data is subjected to, for example, digital processing in an image processing section, and then transferred to a data storing section  14 , and an image signal is sent to the laser emitter  5 . Further, “ 15 ” shown in the figure is an original feeding apparatus, and is a feeder apparatus for feeding an original sheet stored in a stack tray  16  to the platen  12 . 
     The image formation apparatus A with the above-mentioned configuration is provided with a control section (controller)  150  as shown in  FIG. 30 , and from a control panel  18  are set image printing conditions such as, for example, sheet size designation, color/monochrome printing designation, number-of-printed sheet designation, one-side/two-side printing designation, scaling printing designation and the like. Meanwhile, it is configured in the image formation apparatus A that image data read by the scan unit  13  or image data transferred from an external network is stored in a data storing section  17 , the image data is transferred to a buffer memory  19  from the data storing section  17 , and that a data signal is sequentially output to the laser emitter  5  from the buffer memory  17 . 
     A post-processing condition is also input and designated from the control panel  18 , concurrently with the image formation conditions such as one-side/two-side printing, scaling printing, monochrome/color printing and the like. Selected as the post-processing condition is, for example, a “print-out mode”, “binding finish mode”, “brochure finish mode” or the like. 
     [Configuration of the Post-processing Apparatus] 
     The post-processing apparatus B according to the invention has a punch means (punch unit described later)  60  for performing punching processing on a sheet received from the carry-in entrance  23   a , and the punch means  60  is disposed in a carrying path between a sheet branch portion, which turns a sheet fed from the carry-in entrance  23   a  to a saddle-stitching means and center-folding means, and an end binding means. Then, the apparatus B has a stack tray  21  disposed on the side face side of the apparatus frame, and the stack tray  21  is configured to move up and down to receive a bunch of sheets subjected to end binding processing discharged from a first discharge outlet  29   x , and a bunch of sheets subjected to center-folding processing discharged from a second discharge outlet  22   x  described later. Herein, the stack tray  21  has a plurality of sheet discharge trays capable of moving up and down, and when a volume of bunches of sheets discharged onto the uppermost sheet discharge tray reaches a predetermined amount, a sheet discharge tray located under the uppermost sheet discharge tray receives bunches of sheets that are sequentially discharged. 
     The post-processing apparatus B further has a booklet stacker  22  disposed below the stack tray  21 , and the booklet stacker  22  receives a bunch of sheets discharged from the second discharge outlet  22   x , and when bunches of sheets stacked on the stack tray reach a predetermined amount, sequentially receives bunches of sheets subsequently discharged from the second discharge outlet  22   x.    
     The post-processing apparatus B is configured as described below to receive a sheet with the image formed thereon from the sheet discharge outlet  3  of the image formation apparatus A, and to (i) store the sheet in the stack tray  21  (“print-out mode” as described above), (ii) collate sheets from the sheet discharge outlet  3  in a bunch form to staple, and store in the stack tray (first stack tray)  21  (“binding finish mode” as described above), or (iii) collate sheets from the sheet discharge outlet  3  in a bunch form, staple its center, fold in book form and store in the saddle tray (second stack tray)  22  (“brochure finish mode” as described above). 
     A casing (exterior cover)  20  of the post-processing apparatus B is provided with the carry-in entrance  23   a , and the carry-in entrance  23   a  is coupled to the sheet discharge outlet  3  of the image formation apparatus A. In the casing  20  are provided a first processing section BX 1  that collects sheets from the carry-in entrance  23   a  for each set to perform a binding finish, and a second processing section BX 2  that collects sheets from the carry-in entrance  23   a  for each set to perform a brochure finish. A first carry-in path P 1  is provided between the first processing section BX 1  and the carry-in entrance  23   a , and a second carry-in path P 2  is provided between the second processing section BX 2  and the carry-in entrance  23   a , so that the sheet from the carry-in entrance  23   a  is distributed and guided to the first processing section BX 1  or the second processing section BX 2  (sheet branch portion). The carry-in entrance  23   a  is provided with carry-in rollers  25 , sheet sensor S 1 , and a path switching means (flapper member)  24  that distributes the sheet to the first or second carry-in path P 1  or P 2 . 
     The first carry-in path P 1  is provided with a buffer path P 3  between a punch unit  60  and a processing tray  29 . The buffer path  3  is a path for piling the predetermined number of sheets received from the carry-in entrance  23   a , thereby delaying the sheets by a predetermined time, and then carrying the sheets to the end binding means side. Therefore, as shown in  FIG. 2 , the buffer path  3  is disposed to branch off from the first carrying-path P 1  in the vertical direction of the casing  20  on the upstream side in the path reaching the processing tray  29 . Then, the sheet from the first carry-in path P 1  is switched back and stays in this path. Accordingly, when the post-processing (end binding processing described later) is performed on a bunch of sheets collected for each set on the processing tray  29 , it is made possible that a subsequent sheet sent to the carry-in entrance  23   a  temporary stays, and that the subsequent sheet in this path is moved to the processing tray  29  after a predetermined time has elapsed and the processed sheets on the processing tray  29  are carried out. 
     The first carry-in path P 1  is disposed substantially in the horizontal direction in the upper portion of the apparatus housing formed of the casing  20 , the first processing section BX  1  is disposed on the downstream side of the first carry-in path P 1 , and the stack tray  21  is disposed on the downstream side of BX 1 . The second carry-in path P 2  is disposed substantially in the vertical direction in the lower portion of the casing  20 , the second processing section BX 2  is disposed on the downstream side of the second carry-in path P 2 , and the saddle tray (booklet stacker)  22  is disposed on the downstream side of BX 2 . In addition, in the first carry-in path P 1 , the punch unit  60  described later is disposed between the carry-in entrance  23   a  and the first processing section BX 1 . In the second carry-in path P 2 , a trimmer unit  90  described later is disposed between the second processing section BX 2  and the saddle tray  22 . 
     The first carry-in path P 1  is provided at its path outlet end with sheet discharge rollers  25  and a sheet discharge outlet  25   x . A sheet discharge sensor S 2  is disposed in the sheet discharge outlet  25   x , and is configured to detect a sheet passed through the first carry-in path P 1  to detect a jam and count the number of passed sheets. Then, a level difference is formed on the downstream side of the sheet discharge outlet  25   x , and the processing tray  29  described below is disposed. Further, the second carry-in path P 2  is provided with feeding rollers  27 , a level difference is formed on the downstream side of the rollers  27 , and a collection guide  45  described later is disposed. 
     [Configuration of the First Processing Section] 
     The first processing section BX 1  is formed of the processing tray  29  disposed in the first carry-in path P 1 , an end binding stapling unit  31  disposed in the processing tray  29 , and an aligning means  51 . 
     [Configuration of the Processing Tray] 
     The processing tray  29  is formed of a synthetic resin plate or the like, and is provided with a sheet support surface  29   a  to support sheets loaded therewith. The sheet support surface  29   a  is disposed to form a level difference on the downstream side of the sheet discharge outlet  25   x , and stores sheets from the sheet discharge outlet  25   x . The sheet support surface  29   a  as shown in the figure is formed in dimension with a length shorter than the length of the sheet in the discharge direction, and supports the rear end portion of the sheet from the sheet discharge outlet  25   x , while the sheet front end portion is supported (bridge-supported) on the uppermost sheet on the stack tray  21 . 
     The processing tray  29  is provided with a sheet end regulating means  32 , against which the rear end (or front end) of the sheet from the sheet discharge outlet  25   x  is pushed to be aligned. Then, above the processing tray  29  are disposed switch back rollers  26  (movable roller  26   a , fixed roller  26   b ) for feeding a sheet carried onto the tray to the sheet end regulating means  32 , aligning means  51 , and side aligning means  34 . Each structure will be described below. 
     [Configuration of the Sheet End Regulating Means] 
     In the processing tray  29  is disposed a sheet end regulating means  32  for positioning one end edge of the front end and rear end of the fed sheet. The sheet end regulating means  32  as shown in  FIG. 4  is formed of a sheet end face regulating surface  32   a  with which the rear end edge of a sheet is pushed against to be regulated, and a stopper member having a sheet upper face regulating surface  32   b  for positioning the top surface of the uppermost sheet to regulate. The sheet end regulating means  32  is disposed in the rear end edge of the processing tray  29 , pushes the rear end edge of a sheet fed by the switch back roller  26  and aligning means  51  described later to regulate, and positions the sheet in a predetermined post-processing position (binding position, which is the same in the following). At this point, the sheet upper face regulating surface  32   b  regulates a curled surface of the sheet of which the front end curls, while the sheet end face regulating surface  32   a  positions and regulates the sheet end edge. 
     The sheet end face regulating surface  32   a  and sheet upper face regulating surface  32   b  shown in the figure are integrally formed as the stopper member made of resin, metal plate or the like, and can be formed of separate members. In the sheet end regulating means  32  shown in the figure, the fixed stopper member  32 A is situated in the center in the sheet width direction, first and second movable stopper members  32 B and  32 C are situated in the sheet right and left end portions, members  32 A,  32 B and  32 C are arranged at predetermined intervals, and the means  32  is comprised of such a plurality of stopper members and others. In addition, “ 32   s ” shown in the figure denotes a plate spring attached to each stopper member to correct curl at the front end of the sheet. 
     Thus, the first and second movable stopper members  32 B and  32 C positioned in the sheet right and left portions thus move to positions corresponding to the sheet size. Therefore, with the bottom wall of the processing tray  29  are fitted and supported a right slide member  38   a  and left slide member  38   b  to be movable in the sheet width direction. Then, the first movable stopper member  32 B and second movable stopper member  32 C are fixed to the right and left slide members  38   a  and  38   b . The right and left slide members  38   a  and  38   b  are coupled to alignment plates  34 R and  34 L for aligning the sheet side to move in synchronization therewith as described later. 
     In the sheet end regulating means  32  configured as described above, at least the sheet upper face regulating surface  32   b  is configured to be able to move up and down in the sheet load direction. This is because a sheet-bunch carrying-out means  100  as described later sometimes lifts a bunch of sheets on the processing tray upward in carrying out the bunch of sheets on the tray, and the sheet upper face regulating means  32   b  should be moved up and down according to up-and-down movements of the bunch of sheets. 
     Therefore, as shown in  FIG. 4 , the fixed stopper member  32 A is pivotally supported by the bottom wall of the processing tray  29 , biased and supported downward as viewed in the figure by a biasing spring  33 . Further, the first and second movable stopper members  32 B and  32 C are respectively attached to the right and left slide members  38   a  and  38   b  to be elastically deformable ( 32   a  portion in the figure). 
     [Configuration of the Sheet Carrying Means] 
     In the processing tray  29  is disposed the sheet carrying means (switch back roller)  26  for guiding a sheet fed from the sheet discharge outlet  25   x  to the sheet end regulating means  32 . The sheet carrying means  26  is made of a friction rotating body such as a roller, belt or the like for carrying a sheet fed to the processing tray  29  from the sheet discharge outlet  25   x  to the sheet end regulating means  32 . The following description is given according to the switch back roller mechanism as shown in the figure. 
     As shown in  FIG. 5 , the switch back roller  26  is disposed above the processing tray  29 , and is configured to carry the uppermost sheet on the processing tray in the forward and backward directions. Then, the switch back roller  26  is axially supported by a lifting/lowering support arm  28  to move up and down between an operation position (state of  FIG. 5(   c )) coming into contact with the sheet on the processing tray  29  and a standby position (state of  FIG. 5(   b )) separate upward from the sheet. In other words, the lifting/lowering support arm  28  is pivotably supported by the apparatus frame (not shown) by a pivot rotary shaft  28   a , and the pivot rotary shaft  28   a  is coupled to a lifting/lowering motor (arm driving means, which is the same in the following) MY via a pinion  28   p . In addition, a position sensor not shown is disposed in the lifting/lowering support arm  28 , and detects a position of the lifting/lowering support arm  28  so as to control lifting and lowering between the standby position and the operation position. 
     The movable-side switch back roller  26   a  axially supported by the lifting/lowering arm  28  is coupled to a forward/backward motor not shown via a transmission means, and rotates forward and backward in the discharge direction of the sheet carried onto the processing tray  29  and the opposite direction. Therefore, the roller rotary shaft  26   z  of the switch back roller  26   a  is axially supported by a long groove  28   u  formed in the lifting/lowering support arm  28  as shown in  FIG. 5(   a ), and thus supported to be able to move up and down in the sheet load direction (vertical direction as viewed in the  FIG. 5(   a )). Then, a paper surface contact sensor Ss is provided in the movable-side switch back roller  26   a.  In addition, “ 28   z ” in the figure denotes a plate spring biasing the roller rotary shaft  26   z  always downward, and is to prevent a malfunction of the paper surface detection sensor Ss caused by the shaft floating upward when the switch back roller  26   a  moves downward. 
     [Paper Surface Contact Sensor] 
     The switch back roller  26   a  is provided with the paper surface contact sensor Ss for detecting a position of the roller rotary shaft  26   z  moving up and down along the long groove  28   u . The paper surface contact sensor Ss is secured to the lifting/lowering support arm  28 , and is configured to detect a position of the roller rotary shaft  26   z  traveling (moving upward) in the long groove  28   u  by the contact pressure that the switch back roller  26   a  comes into contact with the uppermost sheet on the processing tray. Therefore, the lifting/lowering arm  28  is provided with a sensor lever  30  having a rotation center o 1  in a position different from the pivot rotary shaft  28   a , and the roller rotary shaft  26   z  is axially coupled to the front end portion of the sensor lever  30 . Then, the paper surface contact sensor Ss is formed of a photosensor for detecting a sensor flag  30   f  formed in the rear end portion of the sensor lever  30 . 
     Thus configured switch back roller  26   a  moves up and down between the standby position ( FIG. 5(   b )) above the processing tray and the operation position ( FIG. 5(   c )) coming into contact with the sheet carried onto the processing tray by causing the lifting/lowering support arm  28  to pivot up and down by the lifting/lowering motor MY. Then, the paper surface contact sensor Ss disposed in the lifting/lowering support arm  28  detects that the switch back roller  26   a  comes into contact with the sheet carried onto the processing tray  29 . 
     [Configuration of the Control Means] 
     A control means  165  for controlling the lifting/lowering motor MY is configured as described below. The control means  165  is formed of a control CPU  161  as described later, and controls the lifting/lowering support arm  28  to move up and down between the standby position and the operation position. First, the control means  165  controls the lifting/lowering support arm  28  to rest in the standby position using a position sensor (not shown) disposed in the arm  28 . Then, when the sheet sensor S 2  detects the front end of a sheet carried out from the sheet discharge outlet  25   x , after a lapse of predicted time that the sheet front end is passed through immediately below, the control means  165  rotates the lifting/lowering motor MY counterclockwise as viewed in  FIG. 5(   a ). Upon the rotation, the lifting/lowering support arm  28  rotates around the pivot rotary shaft  28   a  counterclockwise in  FIG. 5(   a ). By this means, since the roller rotary shaft  26   z  of the switch back roller  26   a  is supported by the long groove  28   u , the roller  26  moves downward from the standby position ( FIG. 5(   b )) to the operation position ( FIG. 5(   c )) at the substantially same velocity as that of the lifting/lowering support arm  28 . At this point, the sensor lever  30  coupled to the switch back roller  26   a  moves (falls) in the same direction at the same velocity as those of the lifting/lowering support arm  28 . 
     At this point, the control means  165  sets that the downward velocity (rotation speed of the lifting/lowering motor MY) Va of the lifting/lowering support arm  28  is equal to or slower than the velocity (free fall velocity) Vr that the movable-side switch back roller  26   a  falls inside the long groove  28   u  under the roller&#39;s own weight (Va≦Vr). This is because when the falling velocity Va of the lifting/lowering support arm  28  is faster than the velocity of the switch back roller  26   a  freely falling inside the long groove  28   u , the roller becomes unstable. The paper surface contact sensor Ss is thus prevented from malfunctioning due to a rebound or the like. In other words, by limiting the velocity Vr that the switch back roller  26   a  falls using the velocity of the lifting/lowering support arm  28 , and thereby causing the roller  26   a  to fall gently, the paper surface contact sensor Ss is prevented from malfunctioning such as chattering and the like. 
     Next, when the periphery of the switch back roller  26   a  comes into contact with the top of the uppermost sheet on the processing tray  29 , the switch back roller  26   a  is rested on the uppermost sheet, and the lifting/lowering support arm  28  pivots and falls in the same direction. At this point, with respect to the paper surface contact sensor Ss, the sensor lever  30  pivots around the rotation center o 1  in its center clockwise (in the direction shown by the arrow in  FIG. 5(   c )). Then, the paper surface contact sensor Ss detects the sensor lever  30  and is “ON”. The detection signal of the paper surface contact sensor Ss causes the lifting/lowering motor MY to halt. By thus controlling, the switch back roller  26   a  comes into contact with the uppermost sheet always with a constant pressure-contact force (for example, self weight) irrespective of whether the load amount of sheets stacked on the processing tray  29  is large or small (see  FIG. 5(   c )). 
     In tandem with falling of the switch back roller  26   a  to the operation position, the control means  165  drives the forward/backward rotation motor (not shown) to rotate the switch back roller  26   a  forward and backward. Then, the sheet carried onto the uppermost sheet on the processing tray  29  from the sheet discharge outlet  25   x  receives a constant transport force, and is moved in the sheet discharge direction and the direction opposite to the sheet discharge direction. In addition, in the apparatus as shown in the figure, when a sheet from the sheet discharge outlet  25   x  is carried from the sheet discharge outlet in the sheet discharge direction, the switch back roller  26   a  rotates clockwise as viewed in the figure, and draws the sheet front end into the processing tray  29 . Then, when the sheet rear end is passed through the sheet discharge outlet  25   x , the switch back roller  26   a  is rotated backward, and carries the sheet by switch back to the sheet end regulating means  32  side. In the process of sheet transport, the sheet and the switch back roller  26   a  are engaged with each other with a constant pressing force irrespective of the load amount of sheets on the processing tray, and a beforehand set given transport force is applied to the sheet. 
     On the processing tray  29  is provided the aligning mechanism (aligning means)  51  for carrying a sheet to the sheet end regulating means  32  together with the switch back roller  26   a . As shown in  FIG. 6(   a ), the aligning means  51  is formed of a friction rotating body  52  which is disposed immediately below the sheet discharge outlet  25   x  and draws the rear end of the sheet fed to the processing tray  29  to move toward the sheet end regulating means  32 . 
     The friction rotating body  52  is formed of a rotating body such as a roller, belt or the like made of a rubber material, sponge (porous foam), etc., and engages with the uppermost sheet on the tray to carry in the predetermined direction by its friction force. The friction rotating body  52  as shown in the figure is configured to move up and down corresponding to the load amount of sheets collected on the processing tray  29 . Therefore, the friction rotating body (roller)  52  is axially supported by a lifting/lowering support arm  54  pivotally supported by the apparatus frame (not shown in the figure) on a pivot rotary shaft  53 . A driving pinion  53   p  is attached to the pivot rotary shaft  53 , and the driving pinion  53   p  is coupled to a stepping motor MC. Then, a torque limiter (not shown in the figure) is incorporated into between the driving pinion  53   p  and pivot rotary shaft  53 . Accordingly, in the lifting/lowering support arm  54 , when the friction rotating body  52  attached to the arm  54  comes into contact with the uppermost sheet on the processing tray  29 , the torque limiter idles by the reaction force, and the body  52  engages with the uppermost sheet always by a constant pressure. 
     Therefore, the friction rotating body  52  engages with the uppermost sheet irrespective of whether the load amount of sheets collected on the processing tray  29  is large or small, and the lifting/lowering support arm  54  halts in this position. Then, after the lifting/lowering support arm  54  halts on the uppermost sheet, the torque limiter not shown idles and applies a predetermined pressing force to the friction rotating body  52 . In addition, a floating pulley is axially supported by the pivot rotary shaft  53 , and a driving motor not shown is coupled to the pulley. Then, the rotation force of the driving motor is conveyed to the friction rotating body  52  from the pulley by a belt or the like. Thus configured friction rotating body  52  rotates counterclockwise as viewed in  FIG. 6  in the operation position shown in  FIGS. 6(   b ) and  6 ( c ), and transfers the sheet carried onto the processing tray toward the sheet end regulating means  32 . 
     To the lifting/lowering support arm  54  are attached a carry-in guide  54   a  on the upstream side of the friction rotating body  52  and a carrying-out guide  54   b  on the downstream side. Then, the carry-in guide  54   a  is formed in the shape of a guide for guiding the sheet front end to the friction rotating body  52 , while the carrying-out guide  54   b  is situated between the friction rotating body  52  and the sheet end regulating means  32 , and formed in the shape of a guide for guiding the sheet front end to the sheet end regulating means  32 . 
     [Carry-in Guide] 
     As shown in  FIG. 6(   a ), the carry-in guide  54   a  is integrally formed with the lifting/lowering support arm  54 , and provided with a tapered plane  54   a   1  tilting so that the sheet carry-in side is high while the friction rotating body side is low so as to guide the sheet front end to the periphery direction of the friction rotating body  52 . Accordingly, even when the rear end of the sheet fed toward the sheet end regulating means  32  by the switch back roller  26   a  is curled and warped up, the sheet is guided to the friction rotating body  52  along the tapered plane  54   a   1 . The carry-in guide  54   a  is integrally formed with the lifting/lowering support arm  54 , and therefore, is lifted according to the load amount of sheets on the processing tray. The reason why the carry-in guide  54  is thus integrally formed with the friction rotating body  52  is as described below. When the roller diameter of the rotating body is formed to be small (for downsizing), a sheet with the rear end curled is entangled with the roller and jams. Then, when the sheet is guided by the carry-in guide, the relationship of angle between the guide plane (tapered plane as described above) and the roller periphery varies and causes a jam corresponding to the load amount of sheets. To solve such a problem, the friction rotating body  52  and carry-in guide  54   a  are integrally formed and configured to move up and down corresponding to the load amount of sheets. 
     [Carrying-out Guide] 
     The carrying-out guide  54   b  is provided with a guide plane  54   b   1  for guiding the rear end side of the sheet fed by the friction rotating body  52  to the sheet end regulating means  32  from above the sheet. The carrying-out guide  54   b  is also integrally formed with the lifting/lowering support arm  54  as in the carry-in guide  54   a , and integrally configured with the friction rotating body  52 . Accordingly, the guide  54   b  is raised upward corresponding to the load amount of sheets on the processing tray. 
     Therefore, as shown in  FIG. 6(   d ), with respect to the uppermost sheet on the processing tray  29 , the carry-in guide  54   a  and carrying-out guide  54   b  are set so that a distance (L 1 ) between the carry-in guide  54   a  and the uppermost sheet is larger than another distance (L 2 ) between the carrying-out guide  54   b  and the uppermost sheet (L 1 &gt;L 2 ). 
     [Configuration of Kicker Means] 
     The carry-in guide  54   a  works together with a kicker means  55  situated on its upstream side to guide the sheet from the sheet discharge outlet  25   x  to the friction rotating body  52 . The kicker means  55  will be described. As mentioned previously, a level difference is formed between the sheet discharge outlet  25   x  and the processing tray  29 , and the rear end of the sheet fed from the sheet discharge outlet  25   x  by the switch back roller  26   a  falls onto the processing tray  29 . Therefore, the sheet discharge outlet  25   x  is provided with the kicker means  55 . 
     As shown in  FIG. 6(   a ), the kicker means  55  is formed of a base end pivot lever  55   a  attached to the apparatus frame by a rotary shaft  56  and a front end kick lever  55   b . The rotary shaft  56  of the base end pivot lever  55   a  is coupled to a driving motor MK with a gear. Further, the front end kick lever  55   b  is rotatably coupled to the front end. Then, as shown in  FIGS. 6(   e ) and  6 ( f ), the rotary shaft  56  pivots by a predetermined rotation angle by the driving motor MK, and a shaft  55   b   1  of the front end kick lever  55   b  is coupled to the rotary shaft  56  via a gear and belt. Then, the kicker means  55  in the chain-line position (standby position) in  FIG. 6(   e ) pivots in the direction shown by the arrow a in  FIG. 6(   e ) (counterclockwise rotation) when the driving motor  57  is rotated in the clockwise direction in the figure. At this point, the front end kick lever  55   b  is coupled to the rotary shaft  56  via the gear and belt, and therefore, rotates in the direction shown by the arrow b in  FIG. 6(   e ) (clockwise direction). Accordingly, by rotating the driving motor  57  forward (clockwise direction shown in  FIG. 6(   e )), the kicker means  55  shifts from the chain-line state to the solid-line state in  FIG. 6(   e ), and at this point, hits the rear end of the sheet from the sheet discharge outlet  25   x  onto the processing tray  29  in the lower portion. 
     Then, the control CPU  161  described later applies power to the driving motor  57  at timing at which the sheet rear end is passed through the sheet discharge roller  25  with a detection signal that the sheet rear end is passed through the sheet discharge sensor S 2  of the sheet discharge outlet  25   x , and causes the kicker means  55  to kick and drop the sheet rear end onto the tray. The arrangement is made so that the sheet rear end dropped by the kicker means  55  is guided to the friction rotating body  52  by the carry-in guide  54   a.    
     [Configuration of the Side Aligning Means] 
     In the processing tray  29  is disposed the side aligning means  34  for pushing and aligning the width of a sheet. The side aligning means  34  adopts a center reference for positioning a sheet carried into the processing tray  29  from the sheet discharge outlet  25   x  with reference to the center of the sheet, or a side reference for positioning the sheet with reference to a left or right side edge of the sheet. Descriptions are given according to the perspective view shown in  FIG. 4  and operating state views shown in  FIGS. 7 and 8 . 
     As shown in  FIG. 4 , the side aligning means  34  is formed of a left aligning plate  34 L for engaging with the left-side edge of a sheet on the processing tray  29 , and a right aligning plate  34 R for engaging with the right-side edge of the sheet. Each of the left and right aligning plates  34 L,  34 R is fitted and supported with a guide groove (see  FIG. 4 ) formed in the sheet support surface  29   a  of the processing tray, and is able to travel to positions in the sheet width direction. Then, a pair of pulleys  35  are disposed along each guide groove as shown in  FIG. 7  in the bottom of the processing tray  29 . A belt  36  is laid between the pulleys  35 . Each of the left and right aligning plates  34 L,  34 R is fixed to the belt  36 . Further, one of the pulleys  35  is coupled to a shift motor MZ 1  or MZ 2 . 
     The left aligning plate  34 L and right aligning plate  34 R integrally formed as a pair at the left and right with such a configuration travel to positions leftward and rightward in the sheet width direction by driving respective shift motors MZ 1 , MZ 2 . Therefore, by driving and rotating the left and right shift motors MZ 1 , MZ 2  by the same amount in the opposite directions in synchronization with each other, it is possible to align the sheet carried onto the processing tray in the center reference.  FIG. 7(   a ) shows a state for aligning a large-size sheet, and  FIG. 7(   b ) shows a state for aligning a middle-size sheet. Further,  FIG. 8(   c ) shows a state for aligning a small-size sheet. Meanwhile, a bunch of sheets aligned in the center reference on the processing tray are allowed to be offset by driving and rotating the left and right shift motors MZ 1 , MZ 2  by the same amount in the same direction.  FIG. 8(   d ) shows the case of shifting large-size sheets to offset. When the post-processing position is displaced to a corner of the sheets (corner stapling as described later), the need arises to move the post-processing means  31  to the apparatus side, and results in an increase in apparatus size. Therefore, the large-size sheets are thus offset by a predetermined amount. By offsetting a bunch of sheets stacked on the processing tray  29  by a predetermined amount, the post-processing is made possible such as corner biding and the like. It is thereby achieved to obtain a small compact apparatus. 
     [Cooperative Mechanism of the Aligning Plates and Movable Stopper] 
     A pair of aligning plates  34 L,  34 R at the left and right configured as described above coordinate with the sheet end regulating means  32  mentioned previously as described below. Further, the sheet end regulating means  32  is provided with the left movable stopper (second movable stopper member)  32 C and the right movable stopper (first movable stopper member)  32 B. The right and left movable stoppers  32 B,  32 C are coupled to the right and left slide members  38   a  and  38   b  fitted and supported with the processing tray  29  to be movable in the sheet width direction. 
     Therefore, the left and right movable stoppers  32 C,  32 B are coupled to the left and right aligning plates  34 L,  34 R by coupling springs  37  as shown in  FIG. 7(   a ). In other words, the right slide member  38   a  provided with the right movable stopper  32 B is coupled by a coupling spring  37   a , and the left slide member  38   b  provided with the left movable stopper  32 C is coupled by a coupling spring  37   b . Then, the left and right aligning plates  34 L,  34 R reciprocate between a stoke LS 1  in the sheet width direction. In contrast thereto, the right and left movable stoppers  32 B,  32 C reciprocate between a stoke LS 2 . Therefore, the right and left movable stoppers  32 B,  32 C are provided with stopper members not shown on the processing tray  29  side. 
     Then, the strokes LS 1 , LS 2  are set at LS 1 &gt;LS 2 , and the right and left movable stoppers  32 B,  32 C travel by the same amount in conjunction with movements of the left and right aligning plates  34 L,  34 R until hitting the stopper members. After hitting the stopper members, the right and left movable stoppers  32 B,  32 C stop in these positions, and the aligning plates  34 L,  34 R further travel At this point, the coupling springs  37   a ,  37   b  for coupling the plate and stopper elongate (extend). Accordingly, the left and right aligning plates  34 L,  34 R move to positions between the stroke LS 1  corresponding to the sheet size, while the movable stoppers  32 B,  32 C move between the stroke LS 2 . The reason why the stroke of the right and left movable stoppers  32 B,  32 C is set shorter is that the sheet-bunch carrying-out means  100  described later is situated in the sheet center. 
     As described above, in the case where the right and left movable stoppers  32 B,  32 C constituting the sheet end regulating means  32  work in conjunction with the side aligning means  34  and travel strokes are different between the stopper and means  34 , the form of using the coupling spring  37  is described in the embodiment as shown in the figure, but the left and right aligning plates  34 L,  34 R and the right and left movable stoppers  32 B,  32 C may be provided with a “slide transmission mechanism” or “deceleration transmission mechanism”. 
     In the case of the “slide transmission mechanism”, it is configured that the left and right aligning plates  34 L,  34 R and the right and left movable stoppers  32 B,  32 C are coupled by slide friction clutches, and that after the right and left movable stoppers  32 B,  32 C hit the stopper members, the clutch plates perform sliding movement. Meanwhile, in the “deceleration transmission mechanism”, the left and right aligning plates  34 L,  34 R and the right and left movable stoppers  32 B,  32 C are coupled by gear transmission mechanisms, and the gear ratio is set so that the left and right aligning plates  34 L,  34 R travel in the stroke LS 1 , while the right and left movable stoppers  32 B,  32 C travel in the stroke LS 2 . 
     Control of the side aligning means  34  will be described. The left and right aligning plates  34 L,  34 R are provided with position sensors in beforehand set home positions, and positioned in the home position in starting the apparatus. Then, the control CPU  161  described later receives size information of a sheet undergoing image formation from the image formation apparatus A, and based on the information, the control means  166  places the left and right aligning plates  34 L,  34 R in predetermined standby positions. The standby positions are set at positions (positions to form a travel width enabling alignment) spaced a predetermined distance away from the width size of a sheet fed to the processing tray  29 . Then, after a lapse of predicted time the rear end of the sheet carried out from the sheet discharge outlet  25   x  is carried onto the processing tray (after a lapse of timer time from the sheet discharge sensor S 2 ), the control CPU  161  rotates the left and right shift motors MZ 1 , MZ 2  in the opposite directions by a predetermined amount in synchronization with each other. Upon the rotation, the sheet carried onto the processing tray is pushed in the width and aligned. 
     [Corner Stapling Mode] 
     Further, the control CPU  161  is configured to offset sheets by shifting the left and right aligning plates  34 L,  34 R by a predetermined amount in the sheet width direction, in binding a bunch of sheets collected for each set on the processing tray by the stapling means (end binding stapling unit)  31  described later. In the case of an apparatus configuration for shifting the stapling means  31  to this position in binding a sheet corner, the apparatus is increased in size in the sheet width direction. Therefore, the apparatus shown in the figure offsets a bunch of sheets on the processing tray by driving shift motors MZ 1 , MZ 2  of the left and right aligning plates  34 L,  34 R in the same direction by the same amount in the corner stapling mode. 
     [Configuration of the Sheet-bunch Carrying-out Means] 
     In the processing tray  29  is disposed the sheet-bunch carrying-out means  100  for carrying out a bunch of processed sheets to the stack tray  21  on the downstream side. The sheet-bunch carrying-out means  100  is disposed in the bottom of the processing tray  29 , and is formed of a sheet engagement member  105  which protrudes above the sheet support surface  29   a  and engages with a bunch of sheets, and a carrier member  110  that supports the sheet engagement member  105  mounted thereon.  FIG. 9  is an explanatory view showing a perspective structure of the sheet-bunch carrying-out means  100 ,  FIG. 10  is an explanatory view showing the planar structure, and  FIG. 12  is an explanatory view of a driving mechanism. 
     As shown in  FIG. 9 , the sheet-bunch carrying-out means  100  is formed of the sheet engagement member  105 , carrier member  110 , engagement member driving means  127 , and carrier-member driving means  114 . The sheet engagement member  105  is formed of a movable gripper  105   a  and fixed gripper  105   b . Further, the carrier member  110  is mounted with the sheet engagement member  105 , and is configured to reciprocate between a base end portion (post-processing position) and a front end portion (bunch carrying-out position) of the processing tray  29 . Each structure will be described below. 
     [Sheet Engagement Member] 
     The sheet engagement member  105  is formed of an engagement member such as a protruding piece, gripper or the like for engaging with a rear end edge of a bunch of sheets collected on the processing tray, and is disposed inside a guide groove  29 G formed on the sheet support surface  29   a  of the processing tray  29 . As shown in  FIG. 10 , in the processing tray  29 , the guide groove  29 G is formed in the sheet-bunch carrying-out direction (hereinafter, simply referred to as a “bunch carrying-out direction”) between the processing position and the stack tray  21  disposed on the downstream side of the processing tray  29 . In the apparatus as shown in the figure, two guide grooves  29 G 1 ,  29 G 2  are formed spaced apart from each other in the sheet width direction, and the sheet engagement member  105  is disposed in each of the left and right guide grooves  29 G 1 ,  29 G 2  as described below. 
     The sheet engagement member  105  as shown in the figure is formed of a gripper mechanism for gripping the rear end edge of a bunch of sheets on the processing tray  29  to carry out. As shown in  FIGS. 9 and 13 , the movable gripper  105   a  and fixed gripper  105   b  are coupled by a pivot pin (coupling pin)  106  to mutually pivot. Then, a biasing spring  107  is provided between the movable and fixed grippers, and a front-end nip portion  105   ax  of the movable gripper  105   a  and a front-end nip portion  105   bx  of the fixed gripper  105   b  are always brought into contact with each other by pressuring (see  FIG. 13(   a )). 
     Then, the fixed gripper  105   b  is fitted and supported in the guide groove  115  formed in the carrier member  110  to be able to move to positions in the carrying-out direction. Further, the rear end portion of the movable gripper  105   a  is coupled to a traveling belt  116  incorporated into the carrier member  110  by a coupling spring  117 . Accordingly, when the traveling belt  116  of the carrier member  110  described later travels leftward as viewed in  FIG. 13 , the fixed gripper  105   b  and movable gripper  105   a  shift in the sheet-bunch carrying-out direction with the front-end nip portions  105   ax  and  105   bx  pressed and brought into contact with each other (state of  FIG. 13(   a )). When the traveling belt  116  inversely travels rightward as viewed in  FIG. 13 , the movable gripper  105   a  pivots clockwise about the pivot pin  106  as the center, and the front-end nip portion  105   ax  separates from the front-end nip portion  105   bx  of the fixed gripper  105   b  to release the nip (state of  FIG. 13(   b )). 
     [Carrier Member] 
     Described next is the carrier member  110  mounted with the above-mentioned sheet engagement member (hereinafter, a “gripper member (means)”)  105  to support. As shown in  FIGS. 9 and 13 , the carrier member  110  is formed of a frame member with an appropriate shape for supporting the gripper member (means)  105 , and is supported movable in the sheet-bunch carrying-out direction along the guide groove  29 G formed in the processing tray  29 . 
     The support structure will be described. A rear end portion  110   b  of the carrier member  110  is supported to reciprocate linearly along a slide member  119  as shown in  FIG. 10 . Meanwhile, a front end portion  110   a  of the carrier member  110  reciprocates while drawing a loop along loop guide grooves  29 Ga described below. By this means, the gripper member (means)  105  mounted on the carrier member  110  shifts from a standby position to a carrying-out position by an upper path protruding above the processing tray, and returns to the standby position by a lower path sinking in the processing tray after carrying out a bunch of sheets to the stack tray  21 . “ 111 ” shown in the figure denotes a guide pin provided at the front end portion of the carrier member  110 , and is fitted with the loop guide groove  29 Ga. 
     [Slide Member] 
     As shown in  FIG. 10 , the slide member  119  is fitted and supported with guide rails  121  disposed in the bottom of the processing tray  29 , and supported to be able to reciprocate by a predetermined stroke in the same direction (vertical direction in  FIG. 10 ) as that of the guide groove  29 G. A driving rotary shaft  125  is laid over the slide member  119 , and the rear end portion  110   b  of the carrier member  110  is axially coupled to the driving rotary shaft  125 .  FIG. 13  shows a state of this axially coupling, where the carrier member  110  is coupled to reciprocate in a predetermined stroke in the sheet-bunch carrying-out direction by the driving rotary shaft  125  in the rear end portion  110   b , while the front end portion  110   a  is pivotable about the driving rotary shaft  125 . In addition, the slide member  119  is coupled to a driving arm (crank member)  126  described later, and reciprocates between a predetermined stroke by the driving arm (crank member)  126 . Further, the driving rotary shaft  125  is coupled to a driving pulley of the traveling belt  116  described later, and further, coupled to the engagement member driving means  127 . 
     [Loop Guide Groove] 
     The mutually opposite loop guide grooves  29 Ga are formed on left and right side walls of the guide groove  29 G (see  FIG. 10 ). The guide pin  111  formed in the front end portion  110   a  of the carrier member  110  is fitted and supported with the loop guide grooves  29 Ga. As shown in  FIG. 11 , each loop guide groove  29 Ga is formed in the shape of a loop having an upper traveling path  113   a  and lower traveling path  113   b  along the sheet support surface  29   a  of the processing tray. Then, the guide pin  111  travels (outward) from the standby position to the carrying-out position along the upper traveling path  113   a , and travels (homeward) from the carrying-out position to the standby position along the lower traveling path  113   b.    
     As described above, when the carrier member  110  supported by the slide member  119  and loop guide grooves  29 Ga travels from the standby position to the stack tray  21  side as shown in  FIG. 11 , the guide pins  111  track the upper traveling path  113   a , and the carrier member  110  thereby travels in the substantially horizontal attitude. Meanwhile, when the carrier member  111  returns to the standby position from the stack tray  21 , the guide pins  111  track the lower traveling path  113   a , and the carrier member  110  thereby travels while tilting. 
     Further, as shown in  FIG. 11 , in the guide groove  29 G is provided a loop groove  112  for guiding a guide pin  108  provided in the sheet engagement member (movable gripper member)  105   a . The movable gripper  105   a  and fixed gripper  105   b  travel along the loop groove  112 . 
     Then, as described later, the sheet engagement member (gripper member)  105  mounted on the carrier member  110  is in an operation attitude protruding above the processing tray  29  when the guide pins  111  of the carrier member  110  are guided by the upper traveling path  113   a  and travel in the sheet-bunch carrying-out direction, while being in a standby attitude sinking in the guide groove when the guide pints  111  are guided by the lower traveling path  113   b  and travel to the standby position. These states will be described later according to  FIGS. 15 to 17 . 
     Thus configured carrier member  110  is provided with a pair of pulleys,  130   a ,  130   b , at the front and back in the sheet-bunch carrying-out direction as shown in  FIG. 13 , and the traveling belt  116  is looped between the pulleys. Then, one driving pulley  130   b  is axially supported on the driving rotary shaft  125  described previously. Accordingly, by rotation of the driving rotary shaft  125 , the sheet engagement member (gripper member)  105  is configured to be movable between a base-end storing position (state of  FIG. 15(   a ) described later) overlapping with the carrier member  110  and a front-end carrying-out position (state of  FIG. 17(   h ) described later) protruding from the carrier member  110  in the sheet-bunch carrying-out direction. 
     [Installation Structure of the Sheet Engagement Member] 
     The carrier member  110  is disposed in the bottom of the processing tray  29 , and the sheet engagement member (gripper member)  105  is mounted on the top of the carrier member  110 . In the sheet engagement member (gripper member)  105 , as described previously, the movable gripper  105   a  is coupled to the upper portion of the fixed gripper  105   b  with the pivot pin  106 . Then, the fixed gripper  105   b  is supported by the carrier member  110  to be able to move to positions in the sheet-bunch carrying-out direction. “ 115 ” shown in the figure denotes the slide guide groove formed in the carrier member  110 , and the fixed gripper  105   b  is fitted and supported with the guide groove  115 . Further, the movable gripper  105   a  is supported by the fixed gripper  105   b  to be pivotable by the pivot pin  106 , and the rear end portion is coupled to the traveling belt  116  incorporated into the carrier member  110  by the coupling sprint  117 . The carrier member  110  and sheet engagement member (gripper member)  105  are respectively provided with the carrier driving means  114  and engagement member driving means  127  as shown in  FIGS. 12 and 13 . 
     [Carrier Driving Means] 
     As shown in  FIG. 10 , the carrier member  110  is coupled (connected) to the slide member  119  with the driving rotary shaft  125 . Then, as conceptually shown in  FIG. 13 , the slide member  119  is integrally formed with a shaft pin  122 , and the driving arm  126  is fitted with the shaft pin  122 . The driving arm  126  is coupled to a driving motor MH to pivot about a pivot shaft  131  axially supported on the apparatus frame by the crank member. Then, the driving arm  126  and shaft pin  122  are coupled in a slit (long-hole) manner. Accordingly, when the driving arm  126  is moved back and forth by a predetermined angle by the driving motor MH, the slide member  119  reciprocates back and forth in a predetermined stroke. By back-and-forth motion of the driving arm  126 , the rear end portion  110   b  of the carrier member  110  moves back and forth with a linear locus, while the front end portion  110   a  moves back and forth with a loop locus along the loop guide groove  29 Ga. Thus, the carrier member  110  is provided with the carrier driving means  114  that moves the carrier member  110  to positions in the sheet-bunch carrying-out direction along the processing tray  29 . 
     [Engagement Member Driving Means] 
     The fixed gripper  105   b  and movable gripper  105   a  forming the sheet engagement member (gripper member)  105  are mutually coupled with the pivot pin  106 . Then, the fixed gripper  105   b  is supported by the carrier member  110  to be able to move back and forth in the sheet-bunch carrying-out direction along the slide guide groove  115 . Further, the rear end portion of the movable gripper  105   a  is coupled to the traveling belt  116  of the carrier member  110  by the coupling sprint  117  (see  FIG. 13  for the aforementioned description). Then, as conceptually shown in  FIG. 13 , in the traveling belt  116  provided in the carrier member  110 , the driving pulley  130   b  thereof is coupled to a driving motor ME. The driving motor ME is formed of a motor capable of rotating forward and backward, and the traveling belt  116  moves leftward as viewed in  FIG. 13  when the motor ME is rotated forward. According to moving of the traveling belt  116 , the movable and fixed grippers  105   a ,  105   b  move (bunch carrying-out direction) from the standby position to the carrying-out position along the slide guide groove  115 . 
     Further, when the driving motor ME is rotated backward, as shown in  FIG. 13(   b ), the movable and fixed grippers  105   a ,  105   b  move from the carrying-out position to the standby position (in the return direction). Concurrently with the movement, when the traveling belt  116  further travels from the standby position to the back side, the coupling spring  117  moves clockwise according to the driving pulley  130   b . By the backward operation of the driving pulley  130   b , the coupling spring  117  pulls the rear end portion of the movable gripper  105   a  downward. At this point, the movable gripper  105   ax  rotates clockwise about the pivot pin  106 , and the nip portion  105   ax  at the front end is extended upward to open (see  FIG. 13(   b )). Thus, the sheet engagement member (gripper member)  105  is provided with the engagement member driving means  127  for moving the sheet engagement member (gripper member)  105  to positions in the sheet-bunch carrying-out direction along the carrier member  110 . 
     [Operation of the Sheet Engagement Member] 
     The operation of the sheet engagement member (gripper member)  105  configured as described above will be described below. Although a configuration of its control means will be described later, the gripper means (gripper member)  105  is controlled to move to “first standby position Gp 1 ”, “second standby position Gp 2 ”, “nip position Gp 3 ”, “bunch carrying-out position Gp 4 ”, “nip releasing position Gp 5 ”, and “first standby position Gp 1 ” in this order. 
     [First Standby State] 
     The control means  167  described later moves the gripper means (gripper member, which is the same in the following)  105  to the first standby position Gp 1  as shown in  FIG. 15(   a ) by the “initial operation” (describe later) in starting the apparatus. In this first standby position Gp 1 , the gripper means  105  is in a standby attitude sinking in the guide groove  29 G of the processing tray  29 . In this attitude, sheets carried onto the processing tray  29  are pushed against the sheet end regulating means  32  and aligned as shown in  FIG. 15(   b ). Accordingly, in this attitude, sheets from the sheet discharge outlet  25   x  are collected for each set on the processing tray  29 , and undergo post-processing in a beforehand set processing position of a bunch of sheets. 
     [Backward Operation of the Gripper Means] 
     Upon receiving a job finish signal from the image formation apparatus A, the control means  167  backs the gripper means  105  toward the second standby position Gp 2  on the rear side. Therefore, the control means  167  rotates the driving motor MH of the driving arm  126  backward by a predetermined amount. In the process of backing toward the second standby position Gp 2 , in the gripper means  105 , the guide pins  111  of the carrier member  110  shift to the upper traveling path  131   a  from the lower traveling path  131   b  of the loop guide groove  29 Ga. Then, the movable gripper  105   a  protrudes above the sheet support surface  29   a  (see  FIG. 15(   c )). At this point, sheet front ends are pushed upward by the movable gripper  105   a , and the sheet end regulating means  32  elastically deforms, follows the sheet front ends, and bends to deform upward as shown in  FIG. 15(   d ). By this means, smooth movement of the gripper means  105  is ensured. 
     [Second Standby Position State] 
     Next, the control means  167  rotates the driving motor MH of the driving arm  126  backward by a predetermined amount, and halts the motor. Then, the control means  167  rotates the driving motor ME of the driving pulley  130   b  provided in the carrier member  110  clockwise (see  FIGS. 13(   a ) and  13 ( b )). Upon the rotation, the movable gripper  105   a  shifts from a nip attitude of  FIG. 15(   c ) to a nip releasing attitude of  FIG. 16(   e ). In this state, the gripper means  105  is positioned in the second standby position Gp 2 . 
     [Nip Operation] 
     Then, the control means  167  rotates the driving motor MH of the driving arm  126  forward, and moves the carrier member  110  in the bunch carrying-out direction. Concurrently with this driving control, the control means  167  rotates the driving pulley  130   b  of the carrier member  110  clockwise (see  FIGS. 13(   a ) and  13 ( b )). At this point, by adjusting the moving velocity Vb of the traveling belt  116  with respect to the moving velocity Vc of the carrier member  110 , it is possible to rest the gripper member  105 . In other words, by moving the gripper member  105  in the direction opposite to the moving direction of the carrier member  110  with respect to the sheets on the processing tray, the gripper means  105  is at rest with respect to the sheets. For example, when the velocities Vc and Vb are the same velocity, the equation of Vc=−Vc holds, and the gripper means  105  remains at rest. By this means, the gripper means  105  performs the grip operation with reliability. 
     Next, the control means  167  continues the forward rotation of the driving motor MH of the driving arm  126 , and concurrently therewith, rotates the driving pulley  130   b  of the carrier member  110  counterclockwise (see  FIGS. 13(   a ) and  13 ( b )). Upon the rotation, as described in  FIGS. 13(   a ) and  13 ( b ), movement of the traveling belt  116  loosens the coupling spring  117 , and the movable gripper  105   a  is pressed and brought into contact with the fixed gripper  105   b , and at this point, nips the rear end portion of a bunch of sheets on the processing tray. This state is shown in  FIG. 16(   f ). 
     [Bunch Carrying-out Position Movement] 
     The control means  167  halts the driving pulley  130   b  of the carrier member  110 , and continues the forward rotation of the driving motor MH of the driving arm  126 . Upon the rotation, the bunch of sheets nipped by the gripper means  105  are moved from the state of  FIG. 16(   f ) to a state of  FIG. 16(   g ) along the processing tray  29 . In a state where the bunch of sheets are moved to the carrying-out position in the state of  FIG. 16(   g ), the control means  167  rotates the driving pulley  130   b  of the carrier member  110  counterclockwise. Upon the rotation, the fixed and movable grippers  105   a ,  105   b  coupled to the traveling belt  116  protrude to above the processing tray from the carrier member  110  in a state of  FIG. 17(   h ). By this means, the rear end of the bunch of sheets is carried out above the stack tray  21 , and the front end thereof is stored on the uppermost sheet on the tray. 
     [Nip Release State] 
     Next, the control means  167  temporarily halts the driving motor MH of the driving arm  126 . Upon the halt, the carrier member  110  falls in the loop guide groove  29 Ga. The gripper means  105  thereby falls onto the uppermost sheet on the tray in a state of  FIG. 17(   i ). Then, the control means  167  rotates the driving motor MH of the driving arm  126  backward. Upon the rotation, the carrier member  110  returns to the first standby position side along the lower traveling path  113   b  of the loop guide groove  29 Ga. At this point, the bunch of sheets nipped by the gripper means  105  are stopped by the tray sidewall, and released from the nip (state of  FIG. 17(   j )). 
     [Return State] 
     Further, the control means  167  continues the rotation of the driving motor MH of the driving arm  126  to return the carrier member  110  to the first standby position Gp 1  from the bunch carrying-out position Gp 4 . Then, the gripper member  105   a  returns to the state of sinking in the guide groove  29 G of the processing tray  29  in a state of  FIG. 17(   k ). 
     [Safety Mechanism of the Tray Sheet Discharge Outlet] 
     In the processing tray  29 , a safety mechanism  135  as described below is disposed at an exit end (hereinafter, referred to as a “tray sheet discharge outlet”)  29   x  for carrying out a bunch of sheets to the stack tray  21 . The safety mechanism  135  is formed of a “foreign body detecting means  137 ” disposed in the tray sheet discharge outlet  29   x  and “control means” for prohibiting the operation of the post-processing means (stapling means)  31  based on the detection information from the foreign body detecting means  137 . 
     The foreign body detecting means  137  is formed of a shield member  133  for opening and closing the tray sheet discharge outlet  29   x , and a position detection sensor St for detecting a position of the shield member  133 . The shield member  133  is disposed at the exit end (tray sheet discharge outlet)  29   x  to open and close a sheet discharge opening formed above the sheet support surface  29   a . The shield member  133  shown in the figure is formed of a shutter plate coming into contact with the uppermost sheet on the tray support surface, and always comes into contact with the upper surface of the uppermost sheet under its own weight to shield the opening. The reason why the shield member  133  is provided at the exist end (tray sheet discharge outlet)  29   x  is to prevent a foreign body such as, for example, an office article from entering the post-processing section and prevent an operator from putting the finger accidentally. 
     The shield member  133  is attached to the apparatus frame (exterior casing  20  in the apparatus shown in the figure) to be able to move up and down not to prevent a sheet from being loaded on the processing tray  29 , or prevent a bunch of sheets, which are subjected to post-processing and to be carried out to the stack tray  21 , from being carried out. Then, when a paper jam occurs in the sheet to be gathered on the processing tray  29 , or an operation fault such as clogging of staples or the like occurs in the post-processing means (stapling means)  31 , the shield member  133  is opened upward to handle the jam. 
     The shield member  133  configured to move up and down to open and close the sheet discharge opening of the exterior casing  20  as described above is provided with a position sensor St for detecting an open/close state. Therefore, the shield member  133  is provided with a detected section (sensor flag)  134 , and a sensor means  138  (micro-switch in the member as shown in the figure) provided with a sensor actuator Se for detecting the detected section  134  is disposed on the apparatus frame side. A detection signal of the sensor means  138  is transferred to a control means  168  described later to prohibit the operation of the post-processing means (stapling means)  31 . 
     Therefore, the height position of the shield member  133  varies corresponding to the sheet load amount on the processing tray  29 , and is a low position when the sheet load amount is small, while being a high position when the load amount is large. At this point, when it is configured that the sensor means  138  detects a constant height position of the shield member  133  to permit or prohibit the operation of the post-processing means  31 , the following problem occurs. When the maximum permissible thickness loaded on the processing tray is set at a large value, with the value set, it is necessary to set a high position also on the height position of the shield member  133  for the sensor means  138  to detect (when a low position is set, the operation of the post-processing means is prohibited in the normal operation.) Therefore, when an abnormal operation is performed that the shield member  133  is lifted upward in a state where about several sheets are loaded on the processing tray, such a problem occurs that the post-processing means  31  operates without the sensor means  138  detecting the shield member  133 . 
     To solve the aforementioned problem, the apparatus shown in the figure adopts the method of (i) adjusting the height of a detection position of the sensor means  138  corresponding to a thickness of a bunch of sheets to load, or (ii) detecting a plurality of height positions by the sensor means  138 , and determining whether or not to prohibit the post-processing operation corresponding to a thickness of a bunch of sheets to load. Each configuration will be described below. 
     (i) An embodiment of adjusting the height of a detection position of the sensor means  138  corresponding to a thickness of a bunch of sheets. As shown in  FIG. 18 , the micro-switch forming the sensor means  138  is supported by a guide rail (not shown) and the like to be able to move up and down along the sheet load direction in the apparatus frame  20 . Then, a sensor bracket  140  installed with the micro-switch is provided with a rack gear  141 , and the rack gear  141  is meshed with a pinion  142  coupled to a stepping motor MT. Accordingly, by rotating the stepping motor MT, the sensor means  138  is able to move up and down in the sheet load direction, and the actuator Se of the sensor means  138  varies the height portion for detecting the detected section  134  disposed in the shield member  133 . 
     (ii) An embodiment of detecting a plurality of height positions by the sensor means  138 . As shown in  FIG. 19 , in the shield member  133  configured to be able to move up and down in the sheet load direction as described previously, as a plurality of detected sections  134  with different height positions, a first flag  134   a , second flag  134   b  and third flag  134   c  are arranged in this order. Then, the control means  168  described later determines whether or not to prohibit the post-processing operation based on a signal from the sensor means  138  for detecting the plurality of detected sections,  134   a  to  134   c.    
     [Control Means] 
     The control means  168  is formed of the control CPU  161  described later. In above-mentioned embodiment (i) the control means  168  acquires the number of sheets gathered on the processing tray  29  from the image formation apparatus A, for example, using the image data. Then, the means  168  calculates a thickness of a bunch of sheets to be gathered on the processing tray  29  from a beforehand set standard paper thickness, and corresponding to the thickness of a bunch of sheets, sets a height position of the sensor means (micro-switch)  138 . For the height position of the micro-switch, a power supply pulse is supplied to the stepping motor MT corresponding to the set height position. Then, the actuator Se of the sensor means  138  detects the detected section (flag)  134  of the shield member  133  in the height position corresponding to the thickness of a bunch of sheets collected for each set on the processing tray  29 . 
     By thus configuring, when the shield member  133  is lifted to a position higher than the thickness of a bunch of sheets collected on the processing tray  29 , the sensor means  138  detects the detected section  134 . In addition, in this case, the height position of the sensor means  138  is set at a position slightly higher than the thickness of a bunch of sheets collected for each set. Then, the control means  168  is configured to prohibit the processing operation of the post-processing means  31  when the sensor means  138  detects the detected section  134  of the shield member  133 . 
     In above-mentioned embodiment (ii), the control means  168  compares the bunch thickness of a bunch of sheets loaded on the processing tray with beforehand set height positions of flags  134   a  to  134   c  when the sensor means  138  detects the first flag  134   a . Then, the means  168  is configured to determine “abnormal” when the height position of the flag is high and prohibit the processing operation of the post-processing means  31 . Therefore, the control means  168  is provided with a number-of-sheet counter for detecting the number of sheets carried out to the processing tray  29 , and calculating means (not shown) for calculating the thickness of a bunch of sheets from the count number. Then, when the sensor means  138  detects the first flag  134   a , the control means  168  compares the beforehand set height position of the first flag with the bunch thickness of a bunch of sheets loaded on the processing tray to make a determination. Next, when the sensor means  138  detects the second flag  134   b , the control means  168  compares the beforehand set height position of the second flag with the bunch thickness of a bunch of sheets loaded on the processing tray to determine “whether or not the height is abnormal”. Similarly, for the third flag  134   c , the control means  168  determines “whether or not the height is abnormal”. 
     In addition, the “abnormal determination” in this case is configured that the thickness of a bunch of sheets loaded on the processing tray is compared with a beforehand set detection position (height position) of the flag, and that a state where the shied member  133  is lifted above the uppermost sheet of the processing tray  29  is determined to be “abnormal”. The detection results of the first, second and third flags  134   a ,  134   b ,  134   c  are stored in a storage means, and it is identified that a signal from the sensor means  138  is a signal of the first flag, a signal of the second flag, or a signal of the third flag. 
     By thus configuring, when the sensor means  138  issues a first detection signal from the initial state, the means  168  compares the bunch thickness of a bunch of sheets loaded on the processing tray with the height position of the first flag  134   a . Sequentially, in the second diction signal, the bunch thickness of a bunch of sheets is compared with the height position of the second flag  134   b  to make a determination. By this means, it is possible to detect an open/close state of the shield member  133  in stages to determine “abnormal” corresponding to the thickness of a bunch of sheets collected on the processing tray  29 . 
     [Configuration of the End Binding Stapling Unit] 
     The post-processing means (stapling means)  31  is formed of a driver  70  and clincher  75  as shown in  FIG. 28(   a ). The driver  70  is formed of a head member  70   a  that inserts a staple needle into a bunch of sheets set in the binding position, cartridge  71  for storing staple needles, drive cam  77 , and staple motor MD for driving the drive cam  77 . The clincher  75  is formed of a bending groove  75   a  to bend front ends of the staple needle inserted into a bunch of sheets. Then, in the end binding stapling unit (post-processing means)  31 , the driver  70  and clincher  75  are integrally attached to a unit frame. The head member  70   a  of the driver  70  reciprocates vertically as viewed in  FIG. 28(   a ) by the drive cam  77 , and incorporates a former  73  and bending block  74  thereinto. In addition, configurations of the former  73  and bending block  74  are the same as those in the saddle-stitching stapling unit  40  described later, and will be described later according to  FIG. 29 . 
     [Configuration of the Punch Unit] 
     In the first carry-in path P 1 , the punch unit  60  is situated between the carry-in roller  23  and sheet discharge roller  25 , and punches a file hole in a sheet passed through the first carry-in path P 1 . A configuration of the punch unit  60  is described according to  FIG. 20 . The punch unit  60  is formed of punch members  62 , blade receiving member (die)  63 , driving cams  64  and driving motor MX. A plurality of the punch members  62  is arranged a distance apart from one another in the sheet width direction in a unit frame  61 , and axially supported to be able to move up and down in the punching direction. Then, each of the punch members  62  is meshed with the driving cam  64  (slide groove cam, eccentric cam or the like), moved up and down by the driving cam  64  coupled to the driving motor MX, and thereby punches a file hole. Further, the blade receiving member  63  is disposed opposite to the punch members  62  with a sheet passed through the first carry-in path P 1  therebetween. 
     The unit frame  61  is supported by the apparatus frame (not shown) to be able to move to positions in the sheet width direction. This is because the side end edge of a sheet fed to the first carry-in path P 1  is aligned with respect to the punch positions. In other words, a sheet sent to the first carry-in path P 1  is fed with a dimension error of the sheet, displacement (to the right or left) in the width direction or being skewed to the right or left (right skew or left skew). At this point, when punch holes are formed irrespective of the side end edge position of the sheet, the sheet end edges are not aligned when the sheets are filed. Therefore, a positioning mechanism as described below is required. 
     [Positioning Mechanism] 
     The positioning mechanism for aligning relative positions of the punch unit (post-processing means)  60  and the sheet end edge is formed of a sheet end detecting means  67  and positioning means  68 . The sheet end detecting means  67  is formed of a sensor means  66  for detecting a side edge of a sheet sent to the processing position, and the positioning means  68  is configured to travel to positions in the relative position between the sheet and post-processing means  60  based on the detection information. 
     [Sheet End Detecting Means] 
     As shown in  FIG. 20 , the sheet end detecting means  67  is formed of the sensor means  66  for detecting one of the left or right side end edge of the sheet sent to the processing position, and a shift means  69  for shifting the sensor means  66  to positions in the sheet width direction from a beforehand set initial position. The sensor means  66  is formed of a pair of a light-emitting element  66   a  and light-receiving element  66   b  arranged opposite to each other, and disposed in a position for detecting the side edge corresponding to the sheet size. In the apparatus as shown in the figure, from the relation that the sheet sizes are JIS A4-size and JIS B5-size, an A4 detection sensor S 4   a  and B5 detection sensor S 5   b  are disposed in positions for detecting respective sheet side edges. Then, the sensor means  66  is situated in the unit frame  61  for supporting the punch member  62 . 
     [Positioning Means] 
     The unit frame  61  installed with the punch member  62  and sensor means  66  as described above is supported by a guide rail (not shown) to be able to travel to positions in the sheet width direction. Then, the unit frame  61  is provided with a rack gear  61 R, and the driving motor MX is coupled to a pinion  61 P meshed with the rack gear  61 R. By this means, the unit frame  61  is able to travel to positions leftward and rightward in the sheet width direction according to forward and backward rotation of the stepping motor (driving motor) MX. 
     [Sensor Position Control Means] 
     A sensor position control means  169  is formed of the control CPU  161  as described later. The sensor position control means  169  is electrically connected to a driving circuit of the stepping motor MX to move the unit frame  61  to positions leftward and rightward in the sheet width direction from a beforehand set home position. Therefore, for a sheet carried to the processing position, when the sensor means  66  is in the initial position (home position), the sensor position control means  169  is configured to (i) move the sensor means  66  to outward positions (left and right directions in  FIG. 21(   c )) in the sheet width direction to detect the sheet end edge when the sheet is detected, or (ii) move the sensor means  66  to inward positions (left and right directions in  FIG. 21(   b )) to detect the sheet end edge when the sheet is not detected. 
     For this position detection of the sheet end edge, when the sensor means  66  changes “from OFF to ON” or “from ON to OFF”, the position is determined to be the sheet end edge, and the unit frame  61  is halted. Then, the positional relationship between the sensor means  66  and punch member  62  is set so that the post-processing means (punch member)  62  installed in the unit frame  61  punches punch holes in the set positions spaced from the end edge of the sheet. 
     [Configuration of the Second Processing Section] 
     As described previously, the second processing section BS 2  is formed of the collection guide  45  disposed in the second carry-in path P 2 , and a saddle-stitching stapling unit  40  and folding processing mechanism  44  disposed in the collection guide  45 . In the following, the collection guide  45 , saddle-stitching stapling unit  40  and folding processing mechanism  44  will be described in this order. 
     [Collection Guide] 
     The collection guide  45  is situated on the downstream side of the second carry-in path P 2  continuously, and is configured to sequentially load and store in the upright position sheets from the carry-in entrance  23   a  upwardly. Particularly, the collection guide  45  shown in the figure is disposed in the substantially vertical direction to traverse the casing  20  longitudinally, and configured to collect sheets in the upright position, and the apparatus is thereby configured to be small and compact. Further, the collection guide  45  shown in the figure is formed of a guide plate curved in the center, and is formed in the shape with the length for accommodating the maximum-size sheet therein. The collection guide  45  is configured in the shape curved or bent to protrude to the side in which are arranged the saddle-stitching stapling unit  40  and folding processing mechanism  44  described later. Then, the collection guide  45  is provided with a front end stopper  43  for regulating the sheet front end, and the front end stopper  43  travels to positions corresponding to the sheet size (length in the sheet discharge direction). 
     [Saddle-stitching Stapling Unit] 
     In the collection guide  45  is disposed the saddle-stitching stapling unit (hereinafter referred to as a “saddle-stitching unit”)  40  to staple-binding the center portion of a bunch of sheets collected for each set in the collection guide  45 . The configuration will be described based on  FIGS. 29(   a ) and  29 ( b ). The saddle-stitching stapling unit  40  is formed of a driver  70  and clincher  75 . The driver  70  is formed of a head member  70   a  that inserts a staple needle into a bunch of sheets set in the binding position, cartridge  71  for storing staple needles, drive cam  77 , and staple motor MD for driving the drive cam  77 . As shown in  FIG. 29(   b ), in the driver  70 , into the head member  70   a  of the frame are incorporated a driver member  72 , former  73  and bending block  74  in this order in the vertical direction. Then, the driver member  72  and former  73  are supported by the head member  70   a  to be slidable upward and downward so as to reciprocate vertically between the top dead center and the bottom dead center, and the bending block  74  is fixed to the head member  70   a  as a forming mold to bend a linear staple needle in the shape of a U. 
     Further, the frame is installed therein with the cartridge  71  having staple needles therein to sequentially supply a staple needle to the bending block  74 . The driver member  72  and former  73  are coupled to a drive lever  76  pivotably attached to the frame, and are driven vertically between the top dead center and the bottom dead center. The frame is provided with a force-storing spring (not shown) for driving the drive lever  76  up and down, and the force-storing spring is provided with the drive cam  77  for storing force in the force-storing spring and staple motor MD for driving the drive cam  77 . 
     The clincher  75  is situated in a position opposite to the driver  70  with a bunch of sheets therebetween. The clincher  75  as shown in the figure is formed of a structure separated from the driver  70 , and bends needle tips of the staple needle inserted into a bunch of sheets by the driver  70 . Therefore, the clincher  75  is provided with a folding groove (anvil)  75   a  for bending the front ends of the staple needle. Particularly, the clincher  75  shown in the figure is provided with a plurality of bending grooves  75   a   1 ,  75   a   2  in two or more portions in the width direction of a bunch of sheets collected in the collection guide  45 , and it is a feature that the driver  70  traveling to these positions staple-binds a plurality of positions in the sheet width direction. By thus configuring, it is possible to staple-bind a bunch of sheets supported on the collection guide  45  in two portions at the left and right with the clincher  75  fixed without moving the clincher  75 . 
     Alternately, it is possible to adopt a configuration that a wing member (not shown) for bending needle tips of the staple needle is provided as the clincher  75 , and is pivotably rotated in conjunction (synchronization) with needle tips inserted into a bunch of sheets by the driver  70 . In this case, a pair of bending wings are pivotally supported by the frame of the clincher  75  in positions opposite to opposite ends of the needle in the shape of a U. Then, a pair of bending wings are made pivot in conjunction with the operation that the driver  70  inserts a staple needle into a bunch of sheets. By the pivot movement of the pair of wings, the front ends of the staple needle are bent while being flat along the backside of the bunch of sheets. In other words, when the staple is bent by the bending groove, the front ends of the needle are in the state bent in the shape of a U (glasses clinch), while being in the state linearly bent (flat clinch) when the staple is bent by the wing member. The invention is capable of adopting both of the configurations. 
     By such a configuration, for the driver member  72  and former  73  incorporated into the head member  70   a , the drive cam  77  presses the drive lever  76  from the top dead center located upward to the bottom dead center located downward via the force-storing spring by rotation of the staple motor MD. By the downward operation of the drive lever  76 , the driver member  72  and former  73  coupled to the drive lever  76  travel from the top dead center to the bottom dead center. The driver member  72  is formed of a plate-shaped member to press the rear portion of the staple needle bent in the shape of a U, and the former  73  is formed of a member in the shape of a U as shown in  FIG. 29(   b ) and bends the staple needle in the shape of a U together with the bending block  74 . That is, the cartridge  71  supplies a staple needle to the bending block  74 . The linear staple needle is pressed and formed in the shape of a U between the former  73  and the bending block  74 . Then, the staple needle bent in the shape of a U is inserted into a bunch of sheets by the driver member  72  being pressed down vigorously toward a bunch of sheets. 
     [Folding Processing Mechanism] 
     In a folding position situated on the downstream side of the saddle-stitching stapling unit  40  are provided a fold roll means  46  for folding a bunch of sheets, and a fold blade  47  for inserting the bunch of sheets into a nip position of the fold roll means  46 . As shown in  FIG. 27 , the fold roll means  46  is comprised of rolls  46   a ,  46   b  coming into pressure-contact with each other, and each of the rolls is formed substantially in the length of the width of the maximum sheet. 
     The pair of fold rolls  46   a ,  46   b  are formed of material with a relatively high coefficient of friction such as a rubber roller and the like. This is because of transferring sheets in the rotation direction while folding the sheets by a soft material such as rubber and the like, and the rolls may be formed by performing lining processing on a rubber material. In the fold rolls  46   a ,  46   b  are formed gaps in the sheet-value width direction that are formed in the shape of asperities. These gaps are arranged to accord with asperities of the fold blade  47  described later, and it is considered that the front end of the fold blade is easy to enter the nip between the rolls. In other words, the pair of fold rolls  46   a,    46   b  coming into pressure-contact with each other are provided with the shape of asperities having gaps in the sheet width direction, and the staple-binding portions of the sheet and a blade edge of the fold blade  47  also formed to have the shape of asperities enter the gaps. 
     The operation for folding the sheets in the fold roll means  46  will be described below according to  FIGS. 27(   a ) to  27 ( d ). This pair of fold rolls  46   a ,  46   b  are positioned on the protrusion side where the collection guide  45  is curved or bent, and the fold blade  47  having a knife edge is provided in the position opposite to the means  46  with a bunch of sheets supported by the collection guide  45  located therebetween. The fold blade  47  is supported by the apparatus frame to be able to reciprocate between a standby position of  FIG. 27(   a ) and a nip position of  FIG. 27(   c ). 
     Then, a bunch of sheets supported in a bunch form by the collection guide  45  are seized by a front end stopper  43  in a state shown in  FIG. 27(   a ), and positioned in a folding position with the fold position staple-bound. After obtaining a set finish signal of the bunch of sheets, a driving control means (sheet-bunch folding operation control section  164   d , which is the same in the following) makes the clutch means OFF. 
     Next, the driving control means  164   d  moves the fold blade  47  toward the nip position from the standby position at a predetermined velocity. Then, as in the state shown in  FIG. 27(   b ), the bunch of sheets are bent by the fold blade  47  in the fold position and inserted into between the rolls. At this point, the fold rolls  46   a ,  46   b  are rotated according the sheets moving by the fold blade  47 . Then, after a lapse of predicted time a bunch of sheets reaches a predetermined nip position, the driving control means  164   d  halts a blade driving motor (not shown), and rests the fold blade  47  in the position shown in  FIG. 27(   c ). Almost in tandem therewith, the driving control means  164   d  switches the clutch means to ON, and drives the fold rolls  46   a ,  46   b  to rotate. Upon the rotation, the bunch of sheets are sent in the drawing direction (leftward in  FIG. 27(   c )). Then, the driving control means  164   d  moves the fold blade  47  situated in the nip position to return to the standby position as in the state shown in  FIG. 27(   d ), concurrently with drawing of the bunch of sheets by the fold rolls  46   a ,  46   b.    
     When thus folded bunch of sheets are first drawn into between a pair of fold rolls  46   a ,  46   b , a sheet coming into contact with the roll surface is not pulled in between the rolls by the rotating rolls. In other words, since the fold rolls  46   a ,  46   b  are rotated by following (being driven by) inserted (pushed) sheets, it does no happen that only a sheet coming into contact with the roll is first entangled. Further, since the rolls are driven and rotated by following the inserted sheets, the roll surface and sheet contacting the roll do not rub against each other, and image fading does not occur. 
     [Trimmer Unit] 
     On the downstream side of the folding processing mechanism  44  is provided a sheet transport path (hereinafter referred to as a “sheet discharge path”)  85  for guiding the folded sheets to the saddle tray (second stack tray, which is the same in the following)  22 , and the bunch of sheets folded in book form in the folding processing mechanism  44  are carried out to the saddle tray  22 . Then, the trimmer unit  90  is disposed in the sheet discharge path  85 . This trimmer unit  90  cuts a fore-edge portion of the folded sheets folded in the folding processing mechanism  44  by a predetermined amount to trim. In other words, when a bunch of a plurality of sheets are folded in the center in book form (magazine fold) in the folding processing mechanism  44 , folded front edge portions (fore-edge portion) are not aligned, and by cutting the fore-edge portion by a predetermine amount, the sheet end edge is finished neatly. 
     As a configuration of the trimmer unit  90 , various configurations are known, and therefore, not described specifically, but for example, the trimmer unit  90  is formed of a cutting blade (plate-shaped cutting blade or disk-shaped rotating cutting blade) for cutting the end edge of a bunch of sheets, a cutter motor for driving the cutting blade, and trimming edge pressing means for pressing the trimming edge of the bunch of sheets to hold. In the unit as shown in the figure, a unit frame  91  is provided in the sheet discharge path  85 , and a cutting blade  92  and pressing member (not shown) are disposed in the unit frame  91  to move up and down. Then, the cutting blade  92  and pressing member are positioned in the sheet width direction, and configured so that the pressing member presses and holds a bunch of sheets when falling from an upper standby position to a lower cutting position, and that the cutting blade  92  cuts the sheets. 
     Therefore, in the sheet discharge path (sheet transport path)  85  are disposed a “carrying mechanism” for carrying a folded bunch of sheets to a cutting position of the trimmer unit  99  from the folding processing mechanism  44 , and a “positioning mechanism” for position the folded sheets in the cutting position. 
     [Carrying Mechanism] 
     The carrying mechanism is formed of a carrying roller pair  93  for nipping the folded bunch of sheets to carry. The carrying roller pair  93  is formed of a pair of rollers coming into pressure-contact with each other with the sheet discharge path  85  located therebetween. One of the rollers is a fixed roller, the other roller is a movable roller, and the rollers are able to come into pressure-contact with and separate from each other. In the carrying roller pair  93  shown in the figure, provided are a front carrying roller pair  93   a  and rear carrying roller pair  93   b . The distance between the front and rear carrying roller pairs  93   a ,  93   b  is set shorter than the length in the carrying direction of the folded bunch of sheets. Then, movable rollers  93   a   1 ,  93   b   1  of both carrying roller pairs are installed in a same support frame  95 , and as shown in  FIG. 22(   a ), the support frame  95  is supported by a guide rail to move up and down with respect to the apparatus frame (not shown). Accordingly, the carrying roller pairs  93   a ,  93   b  disposed at the front and back along the sheet discharge path  85  are arranged so that the movable rollers  93   a   1 ,  93   b   1  come into pressure-contact with and separate from the fixed rollers  93   a   2 ,  93   b   2 , respectively. “MF” shown in the figure denotes a shift motor for moving the support frame  95  up and down. In addition, the movable rollers  93   a   1 ,  93   b   1  are provided with pressuring springs, and come into pressure-contact with the respective fixed rollers by predetermined pressure. 
     [Driving Mechanism] 
     Further, the front carrying roller pair  93   a  and rear carrying roller pair  93   b  rotate at the same peripheral velocity by a driving mechanism shown in  FIG. 22(   b ). Transmission belts are used to couple so that the rotation of fold rollers  46   a ,  46   b  forming the fold roll means  46  acts on the rear carrying roller pair  93   b  and front carrying roller pair  93   a . “MG” shown in the figure denotes its driving motor. 
     [Positioning Mechanism] 
     The positioning mechanism is formed of a register means  96  for positioning the folded bunch of sheets carried by the carrying roller pair  93  in a predetermined cutting position to set. The register means  96  is configured as described below to position the folded bunch of sheets, while correcting its attitude. The register means  96  is formed of a regulating stopper for striking and regulating a front end edge of the folded bunch of sheets and backing in the carrying direction and opposite direction by a predetermined amount. The regulating stopper shown in the figure is formed of a pivot arm member  97  for pivoting forward and backward in the sheet carrying direction. The pivot arm member  97  is axially supported to pivot between a solid attitude (standby position) withdrawing from the sheet discharge path  85  and a chain-line attitude (operation position) where the folded bunch of sheets are backed along the sheet discharge path  85  as shown in  FIG. 22(   a ), and at the base end portion is provided an operation solenoid SL 1 . 
     A frame  97 U (referred to as a stopper frame)  97 U installed with the pivot arm member  97  and operation solenoid SL 1  is attached to the apparatus frame to be able to move to positions forward and backward in the carrying direction, and is provided with a stopper shift motor MJ for shifting the stopper frame  97 U to positions. Accordingly, the pivot arm member  97  is moved to positions forward and backward in the carrying direction by controlling rotation of the stopper shift motor MJ corresponding to the length size of the folded bunch of sheets. 
     [Biasing Guide Member] 
     When the folded bunch of sheets are backed by the pivot arm member  97 , the carrying roller pair  93  releases the nip of the folded bunch of sheets, and the movable rollers  93   a   1 ,  93   b   1  are controlled to separate from the folded bunch of sheets (see “Stopper position control means” as described later). At this point, the folded bunch of sheets in the sheet discharge path are in a free state, and may be displaced by impact of the pivot arm member  97 . Therefore, in the sheet discharge path  85  is disposed a biasing guide member  98  for adding a displacement force in the forward direction to the sheets when the sheets are backed by a predetermined amount by the pivot arm member (regulating stopper)  97 . The biasing guide member  98  is formed of a plate member, shoe member or the like coming into contact with the folded bunch of sheets, and exerts brake action on the folded bunch of sheets backing. The biasing guide member  98  as shown in the figure is formed of a guide piece pivotably supported by the support frame  95  to press the top sheet of the folded bunch of sheets under its own weight. 
     [Front End Detection Sensor] 
     In the sheet discharge path  85  is disposed a front end detection sensor Sh for detecting that the folded bunch of sheets arrive at the predetermined cutting position. The front end detection sensor Sh is formed of a sensor flag  86  for engaging with the sheet front end moving in the carrying direction in the sheet discharge path  85 , and a sensor element  87  for detecting a position of the sensor flag  86 . 
     [Stopper Position Control Means] 
     A control means  170  formed of the control CPU  161  as described later moves the pivot arm member  97  to positions corresponding to the length size information (for example, information transferred from the image formation means) of the folded bunch of sheets sent from the folding processing mechanism  44 . In other words, for example, the means  170  moves the member  97  to an “A4 position” shown in the figure when the folded bunch of sheets are of JIS A4-size, while moving the member  97  to a “B4 position” shown in the figure when the sheets are of JIS B5-size with the stopper shift motor. At this point, the pivot arm member  97  is held at the standby attitude, and at the same time, the carrying roller pair  93  is held at a pressure-contact state (home position) 
     Then, the control means  170  detects that the folded bunch of sheets arrive at the cutting position by the front end detection sensor Sh, halts rotation of the carrying roller pair  93  with the detection signal, and concurrently, starts the shift motor MF to release the nip of the folded bunch of sheets. At this point, the biasing guide member  98  maintains the state for pressing the folded bunch of sheets under its own weight. 
     Next, the control means  170  starts the operation solenoid SL 1  after a lapse of predetermined time since the front end detection signal of the front end detection sensor Sh. By this means, the pivot arm member  97  rotates clockwise from the standby position shown by the solid line in  FIG. 22(   a ) and shifts to the operation position in the chain-line state. With the pivot arm member  97  shifted, the folded bunch of sheets are backed. At this point, the folded bunch of sheets undergo the brake action of the biasing guide member  98 , and the front end edge undergoes skew correction following the pivot arm member  97 . In other words, even when the folded bunch of sheets are sent to the cutting position while tilting, the attitude is corrected in positioning in the cutting position. 
     Further, in the apparatus as shown in the figure, the carrying roller pair  93  and biasing guide member  98  are arranged in the positional relationship as described below. The folding processing mechanism  44  for folding a plurality of sheets is disposed on the upstream side of the register means in the sheet discharge path  85 . Then, the folding processing mechanism  44  is formed to transfer the folded end forward in the carrying direction. Further, in the sheet discharge path  85  is disposed the cutting means (cutting blade)  92  for trimming the rear end edge of the folded bunch of sheets. Then, on the downstream side of the cutting means  92  are disposed the biasing guide member  98 , carrying roller pair  93  and regulating stopper  97  in this order. Then, the carrying roller pair  93  is situated in the position for pressing the folded front end portion of folded sheets, and the biasing guide member  98  is situated in the position for pressing the center portion of the folded sheets. This is because of pressing the rear folded portion by the roller pair in trimming the folded bunch of sheets, and concurrently, preventing the sheet center portion from rising by the pressuring guide (the biasing guide member  98 ). 
     The carrying roller pair  93  is configured to be able reciprocate between the nip releasing position separate from the sheets and the nip position for nipping the sheets. The control means (1) moves the carrying roller pair to the nip releasing position, then (2) backs the stopper member to back the sheets by a predetermined amount, and at this point, (3) pushes the sheets in the forward direction by the biasing guide to bias the sheet front end toward the stopper member. 
     [Storage Section] 
     On the side wall of the casing  20  are disposed the stack tray  21  and saddle tray  22  in the vertical direction as shown in  FIG. 2 , and the stack tray  21  is situated on the downstream side of the processing tray  29  to store a bunch of sheets undergoing binding processing from the first processing section BX 1 . The saddle tray  22  is provided with the sheet discharge outlet  22   x , and situated on the downstream side of the collection guide  45  to store a bunch of sheets processed in book form from the second processing section BX 2 . Then, the stack tray  21  is adjacent to the exit end (tray sheet discharge outlet)  29   x  of the processing tray  19  to be coupled, and the saddle tray  22  is disposed on the downstream side of the collection guide  45  via the folding processing mechanism  44  and trimmer unit  90 . 
     [Lifting/Lowering Mechanism of the Stack Tray] 
     A configuration of the stack tray  21  will be described below according to  FIG. 25 . The stack tray (hereinafter, referred to as an “up-and-down tray”)  21  is configured to move up and down corresponding to a load amount of sheets. The up-and-down tray  21  is formed in the shape of a tray for holding sheets, and configured to protrude outside the apparatus from the side wall of the casing  20 . Therefore, as shown in  FIG. 25 , a tray base end portion  21   a  is provided at its lower and upper portions with two guide rollers  20   r , and the guide rollers  20   r  are fitted and supported with an up-and-down guide  20   u  provided in the apparatus frame (not shown). 
     Then, the up-and-down tray  21  is installed in its bottom with a lifting/lowering motor MS, and a driving pinion  21   p  is coupled to the lifting/lowering motor MS via a reduction mechanism. Meanwhile, in the apparatus frame provided with the up-and-down guide  20   u  is disposed a rack gear  20   h  in the sheet load direction (vertical direction as viewed in  FIG. 25 ), and the driving pinion  21   p  meshes with the rack gear  20   h . Meanwhile, the lifting/lowering motor MS is formed of a motor capable rotating forward and backward, and its driving shaft is provided with an encoder (not shown) for detecting the amount of rotation. Further, the up-and-down tray  21  is provided with a level sensor Sr for detecting a height position of the uppermost sheet loaded on the up-and-down tray  21 . Accordingly, the up-and-down tray  21  moves to positions in the sheet load direction (vertical direction as viewed in  FIG. 25 ) by rotating the lifting/lowering motor MS forward and backward by a predetermined amount. Then, the level sensor Sr detects a height position of the up-and-down tray  21 , and based on the detection result, the lifting/lowering motor MS is driven and rotated forward or backward. The amount of rotation of the lifting/lowering motor MS is detected by the encoder. 
     [Configuration of the Level Sensor] 
     As shown in  FIG. 25 , the level sensor Sr is formed of an arm lever  58 , and a sensor for detecting a position of the arm lever  58 , and the arm lever  58  is coupled to an operation solenoid SL 2 . Then, a lifting/lowering means  164  moves the arm lever  58  up and down with a sheet discharge instruction signal. The sheet discharge instruction signal is notified at timing after a lapse of predicted time that a sheet reaches the stack tray  21 , for example, after a rear end pass signal of the sheet from the sheet discharge sensor S 2 . Meanwhile, the stack tray  21  is moved up and down with a timing signal after a lapse of predicted time that a rear end of a bunch of sheets reaches the stack tray  21  after an operation signal of the bunch carrying means described previously. 
     [Lifting/Lowering Control Means] 
     The lifting/lowering control means (control CPU  161  as described later)  164  for controlling the lifting/lowering motor (shift means) MS is configured in the following way. Described first are control modes for carrying a sheet from the sheet discharge outlet  25   x  onto the stack tray. A sheet is carried out from the sheet discharge outlet  25   x  in a “straight sheet discharge mode”, “bridge carrying-out mode”, or “processed bunch carrying-out mode”. The carrying-out mode is selected, for example, in setting the post-processing mode of the image formation apparatus A. 
     Then, the “straight sheet discharge mode” is to directly carry out a sheet with an image formed thereon from the sheet discharge outlet  25   x  without performing post-processing. In this mode, the sheet sent to the carry-in entrance  23   a  is sent to the first carry-in path P 1 , and carried out onto the processing tray  29  via the sheet discharge rollers  25  and sheet discharge sensor S 2 . On the processing tray  29 , the switch back roller  26   a  rotates in the sheet discharge direction (clockwise as viewed in  FIG. 26(   a )) while being in pressure-contact with the following roller  26   b  disposed on the sheet support surface  29   a . Accordingly, the sheet from the sheet discharge outlet  25   x  is carried out onto the processing tray  29 , sent onto the up-and-down tray  21  by the switch back rollers  26   a ,  26   b  prepared on the tray, and loaded on the upper most sheet. 
     The “bridge carrying-out mode” is to collect sheets with images formed thereon from the sheet discharge outlet  25   x  on the processing tray  29  for each set to perform post-processing. In this mode, a sheet sent to the carry-in entrance  23   a  is sent to the first carry-in path PI, and carried out to the processing tray  29  via the sheet discharge rollers  25  and sheet discharge sensor S 2 . In the processing tray  29  are prepared the sheet end regulating means  32 , switch back roller  26   a , aligning means  51 , and side aligning means  34 . Then, the sheet from the sheet discharge outlet  25   x  is collected in a bunch form on the uppermost sheet on the processing tray  29 . The “processed bunch carrying-out mode” is to carry out a bunch of sheets which are collected for each set on the processing tray and undergo biding processing by the end binding stapling means  31  from the processing tray  29  to the up-and-down tray  21 . Therefore, the processing tray  29  is provided with the sheet-bunch carrying-out means  100  as described previously. 
     Then, the lifting/lowering control means  164  sets a height different H between the uppermost sheet stored in the up-and-down tray  21  and the sheet support surface  29   a  of the processing tray  29  at a first height position H 1  in the “straight sheet discharge mode”, at a second height position H 2  in the “bridge carrying-out mode”, and at a third height position H 3  in the “processed bunch carrying-out mode”. The height differences H are set to increase in the order of the first, second and third height positions (H 1 &lt;H 2 &lt;H 3 ). The control of the height position is performed, as described previously, by detecting a position of the uppermost sheet on the tray by the level sensor Sr, and rotating the lifting/lowering motor MS by a predetermined amount with respect to the detection signal to set the height difference H. 
     The first height position H 1  is set to make a height difference between the uppermost sheet and the sheet support surface  29   b  substantially zero. In other words, it is set to smoothly carry a discharged sheet sent to the sheet support surface  29   a  onto the uppermost sheet. At this point, considering that the rear end of the uppermost sheet curls and rises, and that the uppermost sheet is positioned upward by control error, the setting is made so that the uppermost sheet is slightly lower than the sheet support surface  20   a.    
     Concurrently with such considerations, it is difficult to control the processing tray  29  to lower corresponding to a thickness of a single sheet whenever the sheet is carried in. Therefore, usually, the processing tray  29  is configured to lower after the level sensor Sr detects that the sheet is carried out from the sheet discharge outlet  25   x  repeatedly several times. Therefore, the first height position H 1  is set at, for example, 5 mm to 10 mm. 
     The second height position H 2  is set so that the height difference between the uppermost sheet and the sheet support surface  29   a  is at least equal to or slightly greater than a bunch thickness of a bunch of sheets to load, in collecting sheets on the processing tray  29  for each set. This is because when the height difference therebetween is set at substantially zero, sheets carried out from the sheet discharge outlet  25   x  are gradually piled thereon, and a problem arises that the sheet collected on the top should be displaced while feeding out the uppermost sheet whenever carrying in. Concurrently with the displacement problem, when the up-and-down tray  21  is arranged to tilt so that the forward portion in the sheet discharge direction is higher (see  FIG. 26(   b )), a bunch of sheets collected on the processing tray  29  curve so that the front end side in the sheet discharge direction rises upward. The curving causes rear end edges (binding processing end) of sheets collected in a bunch form for each set to become ragged, and when the sheets undergo binding processing in this state, the sheet end edges are displaced to the front and back and become ragged. 
     Therefore, the second height position H 2  is formed to be a height difference greater than the first height position H 1 , and the height difference is experimentally determined from a position displacement amount of the processing end edge due to curving when a bunch of sheets with the maximum acceptable amount are loaded on the sheet support surface  29   a  of the processing tray. The second height position H 2  shown in the figure is set at about 10 mm to 30 mm. 
     In the third height position H 3 , the height difference between the uppermost sheet and the sheet support surface  29   a  is set at a value sufficiently larger than a thickness of a bunch of sheets with the beforehand set maximum acceptable amount. In other words, when a bunch of sheets which are collected for each set on the processing tray  29  and undergo the binding processing are carried onto the up-and-down tray  21 , the height difference H 3  between the uppermost sheet and the sheet support surface  29   a  is set at a value sufficiently larger than at least a thickness of a bunch of sheets with the maximum acceptable amount. In this case, the apparatus as shown in the figure adopts the configuration that a bunch of sheets are gripped by the gripper member (means)  105  and carried out from the processing tray  29 . This is because when a bunch of sheets are dropped from the sheet support surface  29   a  of the processing tray  29  and stored, the alignment state deteriorates. Therefore, the rear end portion of a bunch of sheets is gripped by the gripper member (means)  105  and released from the grip immediately before the sheet rear end lands on the uppermost sheet on the up-and-down tray  21 , and the alignment state is thereby maintained. In the apparatus as shown in the figure, the third height position H 3  is set at 30 mm to 50 mm. 
     In moving the up-and-down tray  21  from the second height position to the third height position in the “processed bunch carrying-out mode”, the lifting/lowering control means  164  controls the tray  21  to move from the second height position to the third height position by (i) starting the lifting/lowering motor MS using an operation completion signal of the stapling means  31  or a timing signal for starting the carrier member  110  to move in the sheet carrying-out direction by the operation completion signal, or controls the tray  21  to move from the second height position to the third height position by (ii) starting the lifting/lowering motor MS immediately before a binding-processed bunch of sheets reach the up-and-down tray  21  subsequently to an operation completion signal of the stapling means  31  and the sheet rear end falls onto the uppermost sheet. 
     Further, the lifting/lowering control means  164  controls the grip releasing means so that the grip of the gripper member (means)  105  is released in the process during which the rear end of the bunch of sheets falls in the height difference (the third height position H 3 ) between the sheet support surface  29   a  of the processing tray  29  and the up-and-down tray  21 . Accordingly, the bunch of sheets gently fall onto the uppermost sheet by a small drop and are collected. It is thereby possible to maintain alignment of sheets collected on the up-and-down tray  21 . 
     [Explanation of the Control Configuration] 
     A control configuration of the image formation system as described above will be described below according to a block diagram of  FIG. 30 . The image formation system as shown in  FIG. 1  is provided with a control section (hereinafter referred to as a “main body control section”)  150  of the image formation apparatus A and a control section (hereafter referred to as a “post-processing control section”)  160  of the post-processing apparatus B. The main body control section  150  is provided with an image formation control section  151 , feeding control section  152  and input section  153 . Then, the settings of “image formation mode” and “post-processing mode” are made from a control panel  18  provided in the input section  153 . As described previously, the image formation mode is to set image formation conditions such as the number of print out sets, sheet size, color/monochrome printing, scaling printing, one-side/two-side printing and others. Then, the main body control section  150  controls the image formation control section  151  and feeding control section  152  corresponding to the set image formation conditions, forms an image on a predetermined sheet, and then, sequentially carries out the sheet from the main-body sheet discharge outlet  3 . 
     Concurrently therewith, the post-processing mode is set by input from the control panel  18 . For example, the “print-out mode”, “end binding finish mode”, “sheet-bunch folding finish mode” or the like is set. Then, the main body control section  150  transfers the finish mode of post-processing, the number of sheets, information of the number of sets, and binding mode (one-portion binding, two-portion binding, or multiple-portion binding) information to the post-processing control section  160 . Concurrently therewith, the main body control section  150  transfers a job finish signal to the post-processing control section  160  whenever image formation is completed. 
     The post-processing control section  160  is provided with the control CPU  161  for operating the post-processing apparatus B corresponding to the designated finish mode, ROM  162  for storing an operation program, and RAM  163  for storing control data. Then, the control CPU  161  is comprised of a sheet feeding control section  164   a  for executing feeding of a sheet sent to the carry-in entrance  23   a , sheet collection operation control section  164   b  for executing the operation of collecting sheets, end binding operation control section  164   c  for executing sheet binding processing, and sheet-bunch folding operation control section  164   d  for executing the operation of folding a bunch of sheets. 
     The sheet feeding control section  164   a  is coupled to a control circuit of driving motors (not shown) of the carry-in roller  23  and sheet discharge roller  25  of the first carry-in path P 1 , and is configured to receive a detection signal from the sheet sensor S 1  disposed in this carry-in path. Further, the sheet feeding control section  164   a  is connected to the forward/backward rotation motor MY of the switch back roller  26   a  to gather a sheet on the processing tray  29 . The sheet collection operation control section  164   b  is connected to the shift motors MZ 1  and MZ 2  of the left and right aligning plates  34 L,  34 R for aligning the sheet on the processing tray, and further, the end binding operation control section  164   c  is connected to a driving circuit of driving motors MD incorporated into the end binding stapling unit  31  of the processing tray  29  and into the saddle-stitching stapling unit  40  of the collection guide  45 . 
     The sheet-bunch folding operation control section  164   d  is connected to a driving circuit of a driving motor for driving and rotating the fold rolls  46   a ,  46   b , and a driving circuit of the clutch means. Further, the sheet-bunch folding operation control section  164   d  is connected to a control circuit of the shift means for controlling the feeding rollers  27  of the second carry-in path P 2  and the front end stopper  43  of the collection guide  45  to shift to predetermined positions. Furthermore, the section  164   d  is connected to receive detection signals from sheet sensors disposed in these paths. 
     The control section configured as described above causes the post-processing apparatus B to execute the following processing operation. 
     [Print-out Mode] 
     In this mode, the image formation apparatus A forms images as a series of documents, for example, starting with the first pate, and carries out the sheet face down sequentially from the main-body sheet discharge outlet  3 , and the sheet sent to the first carry-in path P 1  is guided to the sheet discharge rollers  25 . Then, using a signal for detecting the sheet front end in the sheet discharge outlet  25   x , after a lapse of predicted time the sheet front end reaches the switch back roller  26   a  of the processing tray  29 , the sheet feeding control section  164   a  lowers the switch back roller  26   a  from the upper standby position onto the tray, and rotates the roller  26  clockwise as viewed in  FIG. 2 . Upon the rotation, the sheet entering onto the processing tray  29  is carried out toward the stack tray  21  by the switch back roller  26   a , and stored on the tray  21 . Thus, subsequent sheets are sequentially carried out to the stack tray  21 , and stacked and stored on the tray. 
     Accordingly, in this print-out mode, sheets with images formed thereon in the image formation apparatus A are held on the stack tray  21  via the first carry-in path P 1  of the post-processing apparatus B, and for example, loaded and stored in the order of from the first page to nth page upward in the attitude of face-down. 
     [Staple Binding Finish Mode] 
     In this mode, as in the aforementioned mode, the image formation apparatus A forms images as a series of documents in the order of from the first page to nth page, and carries out the sheet from the main-body sheet discharge outlet  3  face down, and the sheet sent to the first carry-in path P 1  is guided to the sheet discharge rollers  25 . Then, using a signal for detecting the sheet front end in the sheet discharge outlet  25   x , after a lapse of predicted time the sheet front end reaches the switch back roller  26   a  of the processing tray  29 , the sheet feeding control section  164   a  lowers the switch back roller  26   a  from the upper standby position onto the tray, and rotates the switch back roller  26   a  clockwise as viewed in  FIG. 2 . Next, after a lapse of predicted time the sheet rear end is carried onto the processing tray  29 , the sheet feeding control section  164   a  rotates and drives the switch back roller  26   a  counterclockwise as viewed in  FIG. 2 . Upon the rotation, the sheet entering from the sheet discharge outlet  25   x  is switch-backed and fed onto the processing tray  29 . By repeating this sheet feeding, a series of sheets is collected on the processing tray  29  face down in a bunch form. 
     In addition, whenever the sheet is collected on the processing tray  29 , the control CPU  161  operates the side aligning means  34 , and aligns the position in the width direction of the sheet to collect. Next, the control CPU  161  operates the end edge binding stapling unit  31  by a job finish signal from the image formation apparatus A to bind the rear end edge of a bunch of sheets collected on the processing tray. After this stapling operation, the control CPU  161  moves the sheet-bunch carrying-out means  100 . Upon the moving, the bunch of sheets bound by stapling are carried out and stored on the stack tray  21 . By this means, a series of sheets with images formed in the image formation apparatus A is bound by stapling and stored on the stack tray  21 . 
     In addition, this application claims priority from Japanese Patent Application No. 2008-111415 incorporated herein by reference.