Abstract:
A post-processing apparatus capable of carrying out a plurality of post-processing operations, wherein for carrying out a post-processing operation, a tray for some other post-processing operations can also be utilized, without a special-purpose buffer tray being provided for each of the post-processing operations.

Description:
[0001]     This application is based on Japanese Patent Application No. 2005-232901 filed on Aug. 11, 2005 and No. 2006-123183 filed on Apr. 27, 2006 in Japanese Patent Office, the entire content of which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a post-processing apparatus for post-processing the sheets ejected from an image forming apparatus, particularly to a post-processing apparatus provided with a plurality of post-processing devices.  
         [0003]     In recent years, a post-processing apparatus equipped with a plurality of post-processing devices has been introduced in the market. Such a post-processing apparatus applies a plurality of processing steps to a sheet with an image recorded thereon by an image forming apparatus such as a copying machine, printer and a multifunction apparatus containing the functions of these apparatuses. For example, such processing includes a step of binding by a stapling device, and a step of wrapping-binding wherein an adhesive is applied on one end face of the bundle of sheets, and a cover sheet is bonded onto the end face, and then a bundle of sheets is wrapped with the cover sheet.  
         [0004]     Such a post-processing apparatus requires time to perform processing. When a plurality of copy files are to be made, the post-processing apparatus is provided with a buffer tray for temporary loading of the succeeding sheets continuously ejected from the image forming apparatus, before the processing for the next file starts. Thus, the sheets for processing for the next file can be loaded continuously into the buffer tray even when the preceding processing is being executed. This arrangement ensures high speed processing.  
         [0005]     If a post-processing apparatus containing a plurality of such post-processing devices is provided with a stack tray and a buffer tray for each of the post-processing devices, the size of the apparatus must be increased and such a problem has been left unsolved.  
         [0006]     To solve this problem, Patent Document 1 proposes a method wherein a buffer tray is arranged between the image forming apparatus and a post-processing apparatus, so that the apparatus need not wait for the succeeding step of image formation, and the processing capability of the image forming apparatus is not sacrificed.  
         [0007]     The method of placing a buffer tray in-between as described in the Patent Document 1, however, is inevitably accompanied by the problems of increased apparatus size and higher costs.  
         [0008]     [Patent Document 1] Unexamined Japanese Patent Application Publication No. 2003-89473  
       SUMMARY  
       [0009]     The present invention is the following Structures:  
         [0010]     (1) A post-processing apparatus for post-processing a sheet ejected from an image forming apparatus used for image formation, the aforementioned post-processing apparatus including:  
         [0011]     a plurality of post-processing devices of different types; and  
         [0012]     a stack tray for post-processing devices to stack the sheets ejected from the aforementioned image forming apparatus, the aforementioned sheets being to be processed by any one of the post-processing devices;  
         [0013]     wherein this stack tray for post-processing devices also serves as a buffer tray for any one of other post-processing devices. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1 . is a front view of a bookbinding apparatus as an embodiment of the present invention.  
         [0015]      FIG. 2  is a diagram representing how the sheets S 1  held in a vertical position by a collecting section  50  are pasted;  
         [0016]      FIG. 3  is a diagram representing the process of coating an adhesive.  
         [0017]      FIG. 4  is a diagram representing the traveling of a coating head.  
         [0018]      FIG. 5  is an outline cross-sectional view diagram related to the cover sheet storing section storing the cover sheets and the cover sheet supporting section that supports the cover sheet.  
         [0019]      FIG. 6  is a schematic perspective view of a cover sheet support section viewed in the direction A of  FIG. 5 .  
         [0020]      FIG. 7  is a top view of a cover sheet support device.  
         [0021]      FIG. 8  is a diagram representing the process of bonding a cover sheet to book structural sheets.  
         [0022]      FIG. 9  is a diagram illustrating the processing of the cover sheet subsequent to bonding.  
         [0023]      FIG. 10  is a partial-diagram representing a stapling device having been installed.  
         [0024]      FIG. 11  is a diagram representing the installed position of the stapling device as viewed in the direction of arrow M. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]     The following describes embodiments in the present invention. The following assertive description in the embodiments of the present invention refers to the best mode, without the terminology or technical scope being restricted thereto.  
         [0026]      FIG. 1  is an schematic cross sectional view representing the front of a post-processing apparatus equipped with a pasting and binding device as a wrapping-binding device of the present invention and a stapling device as a stitching device.  
         [0027]     The post-processing apparatus B includes a conveyance section  10  for conveying the sheets S 1  ejected from an image forming apparatus based on electrophotographic technology, terminal line printer for computer, printing machine and others (not illustrated; hereinafter collectively referred to as “image forming apparatus”), to the sheet ejection tray  20  or sheet stacking section  40  for post-processing step, a stapling device  110  for stitching the ends of sheets, a collecting section  50  for stacking the sheets S 1  fed from a sheet stacking section  40  for post-processing step one sheet at a time or a predetermined number of sheets at a time, a coating device  60 , a cover sheet storage section  80  for storing the cover sheet S 2 , a cover sheet support section  90  for supporting the cover sheet, and an end-bound booklet storage section  120  for stacking the end-bound booklets (hereinafter referred to as “elevator tray”).  
         [0028]     The sheets S 1  ejected from the image forming apparatus is discharged to the sheet ejection tray  20  through the ejection path  12  from the switching gate  11  on the conveyance section  10 , or is fed to the sheet stacking section  40  for post-processing step. The sheets S 1  are ejected to the sheet ejection tray  20  when not in the bookbinding mode.  
         [0029]     The bookbinding mode provides a function of selecting any one of a plurality of post-processing devices of the post-processing apparatus B, and can be designated from a post-processing apparatus operation system (not illustrated).  
         [0030]     When stapling process is selected in the bookbinding mode, the sheets S 1  are fed to the sheet stacking section  40  for post-processing step through a conveyance path  13 . When the preset number of sheets S 1  have been stacked, the sheets are stitched by the stapling device  110 , and are ejected to the elevator tray  120 . When the preceding bundle of sheets S 1  bound together by stitching is ejected from the sheet stacking section  40  for post-processing step, the succeeding sheets S 1  are sequentially fed into the sheet stacking section  40  for post-processing step.  
         [0031]     When the pasting-binding designation has been made in the bookbinding mode, the sheet S 1  is conveyed to the collecting section  50  after it is switched back in the sheet stacking section  40 . In the collecting section  50 , the sheets S 1  are accumulated, and once the set number of sheets have been accumulated in the collecting section  50 , they are gripped and rotated, and the resultant bundle of sheets made of sheets S 1  is held in the approximately vertical state.  
         [0032]     A coating device  60  applies adhesive onto the spine surface as one end face of the bundle of sheets S 1  held in the vertical direction.  
         [0033]     The bundle of sheets S 1  having been book-bound by being coated with adhesive is ejected to the bound booklet storage section  100 . While adhesive is applied to the preceding bundle of sheets S 1  and sheets S 1  are bound in the form of a book, the succeeding sheets S 1  are sequentially fed to the sheet stacking section  40  for post-processing step. In this case, the succeeding sheets S 1  are made to wait on the sheet stacking section  40  for post-processing step, and are accumulated on the sheet stacking section  40  for post-processing step. After that, the preceding bundle of sheets S 1  having been bound is discharged from the collecting section  50 . After the collecting section  50  has been arranged in a tilted position, the bundle of sheets S 1  having been kept waiting temporarily is fed to the collecting section  50 . After that, until the preset number has been reached, sheets S 1  are immediately switched backed on the sheet stacking section  40  for post-processing step and are conveyed to the collecting section  50 , without being kept to wait temporarily on the sheet stacking section  40  for post-processing step. When a preset number of sheets S 1  have been stacked on the collecting section  50 , the collecting section  50  is turned and the bundle of sheets S 1  are kept almost in the vertical direction, similarly to the case of the preceding bookbinding step. Then one end face of a bundle of sheets is coated with adhesive by the coating device  60 .  
         [0034]     Further, when the mode is switched to the wrapping-binding process mode wherein one cover sheet is used as a front cover sheet, spine cover sheet and back cover sheet, the cover sheet S 2  conveyed from the cover sheet storage section  80  is cut to a predetermined length by a cutting device  81  according to the size of the sheets S 1 , thickness of the bundle of sheets and the size of the cover sheet S 2 . After that, it is fed to the cover sheet support section  90 , and is bonded to the spine surface of the bundle of sheets Si coated with adhesive. Then square spine formation processing is carried out. In the wrapping-binding mode, similarly to the case of pasting-binding mode, the succeeding sheets S 1  are temporarily kept waiting on sheet stacking section  40  for the post-processing step, while pasting and binding process is applied to the preceding bundle of sheets on the collecting section  50 .  
         [0035]     The sheet stacking section  40  for post-processing step of the post-processing apparatus B having a plurality of post-processing devices performs a stack tray function for temporarily stacking the sheets S 1  having been ejected from the image forming apparatus, in the sheet stacking section  40  for post-processing step, and stapling them. The sheet stacking section  40  also has a buffer tray function of temporarily stacking the succeeding sheets S 1  continuously ejected during the pasting and binding operation of the preceding bundle of sheets.  
         [0036]     The following describes the details of each component of the bookbinding apparatus:  
         [0037]     &lt;Pasting and Binding Device&gt; 
         [0038]      FIG. 2  is a drawing representing how the sheets S 1  held in a vertical position by a collecting section  50  is pasted.  
         [0039]     When the first booklet is bound, the sheets S 1  conveyed along the conveyance path  13  is ejected by the sheet ejection roller  14 , and is conveyed by the conveyance roller  401 . After the sheets S 1  have been raised along the tilted stacking tray  402 , the conveyance roller  401  is reversed so that the sheets S 1  are sequentially conveyed downward. The conveyance roller  401  can be swung around a fulcrum J 1 . Despite increase or decrease in the number of the stacked sheets, the conveyance roller  401  can be brought in contact with the topmost surface of the sheet to conform thereto (arrow Y 1 ). The sheets S 1  having been conveyed downward are stacked onto the collecting section  50 .  
         [0040]     A leading edge receiving plate  404  is provided to stack the sheets S 1  temporarily in the sheet stacking section  40  for post-processing step in this case. When the first booklet is made, it swings around the fulcrum J 2  in the direction marked by an arrow Y 2  to convey the sheets S 1  one by one to the collecting section  50 .  
         [0041]     As soon as the set number of sheets S 1  are collected in the collecting section  50 , a holding plate  503  is actuated thereby gripping and holding the bundle of sheets S 1 .  
         [0042]     The part designated by the number  504  is a member for suppressing the rising-up of the accumulated sheet S 1 , and gets separated and again comes into contact every time a sheet S 1  is fed to the collecting section  50  thereby pressing the sheet S 1 . The part designated by the number  505  is an alignment plate that aligns the side edges of the sheets.  
         [0043]     With the bundle of sheet S 1  in the gripped and held state, the collecting section  50  swings with the shaft  501  as the axis, and the bundle of sheet S 1  is changed from the inclined state to the vertical state as shown by two-dot chain line in  FIG. 2 .  
         [0044]     The following describes the sheet stacking operation for making preparation for the second booklet binding work, during the step of binding the first booklet:  
         [0045]     To ensure that the sheets S 1  for the second booklet is not fed to the collecting section  50  during the step of binding the first booklet, the leading edge receiving plate  404  swings around the fulcrum J 2  in the direction opposite to the arrow Y 2 , and stops at a predetermined position. When a predetermined number of sheets S 1  have been stacked in the stacking tray  402  and the collecting section  50  has come to the home position in an inclined form shown by the bold line in the figure, namely, when the succeeding sheet has become ready to be received after the bundle of sheets for the first booklet has been conveyed out of the collecting section  50 , the leading edge receiving plate  404  swings in the direction marked by an arrow Y 2 . A predetermined number of sheets S 1  having been stacked so far are collectively fed to the collecting section  50  by the nipping roller  410  and nipping conveyance roller  411 . The rest of the sheets S 1  of the bundle of sheets for the second booklets are fed one by one to the collecting section  50 , without being stacked on the stacking tray  402 .  
         [0046]     &lt;Adhesive Coating Process&gt; 
         [0047]      FIG. 3  shows the process of coating an adhesive to the bundle of sheets S 1 .  
         [0048]     Before describing the coating process, the supporting of the sheets by the holding plate  503  in  FIG. 3 ( a ) is described below.  
         [0049]     Before rotating the collecting section  50  to the vertical state, the holding plate  503  moves due to the drive of the motor M 4 , and presses the bundle of sheets S 1 . By stopping after detecting that the driving torque for pressing has reached a prescribed value, the bundle of sheets S 1  is retained strongly by the supporting plate  502  and the holding plate  503 . The stopping position of the holding plate  503  is detected by the encoder  509  and the sensor  510 , and is stored in the storage device of the position detection device  511 .  
         [0050]     With the sheet bundle Sa in the retained state, the receiving plate  506  is rotated by 90 degrees thereby making it recede as shown in  FIG. 3 ( b ) while the collecting section  50  is being rotated from the inclined state to the vertical state.  
         [0051]     In the state of  FIG. 3 ( c ), the bottom surface SA of the bundle of sheets S 1  is separated from the coating roller  63 .  
         [0052]     As is shown in  FIG. 3 ( d ), the coating device  60  in which a hot melt adhesive material  653  is stored rises up, and the coating roller  63  touches the bottom surface SA of the bundle of sheets S 1  in the figure. The coating roller  63  moves in a direction at right angles to the surface of the paper sheet on which  FIG. 3  is illustrated, thereby coating the bottom surface of the bundle of sheets S 1  with the adhesive material  653 .  
         [0053]     The coating process is described next referring to  FIG. 4 .  
         [0054]     At the stage of starting the bookbinding in  FIG. 4 ( a ), the coating device  60  is at the right end position (the first position) which is its home position. In this home position, blocks of solid adhesive material are replenished to the coating device  60  via the replenishment path  66  and are heated to melt. At the beginning of the bookbinding process, the coating device  60  moves from the home position towards the left, and the movement from this home position to the left end position (the second position) is carried out by the drive of a belt  67  (the second moving device) which is driven by a motor M 3 . The movement is conducted based on the signal of the detection of the passing of the leading edge of the last of the sheets S 1  constituting the bundle of sheets S 1  collected in the collecting section  50 , transmitted from the sheet sensor SE which is provided immediately below on the downstream side of the stacking tray  402  (see  FIG. 1 ). While the coating device  60  is moving to the left end position, the coating roller  63  is separated from the bottom surface SA of the bundle of sheet S 1 .  
         [0055]     Further in the stage of  FIG. 4 ( b ) in which the coating device  60  moves from the left end position towards the right end position, the coating roller  63  rises due to the drive of the motor M 2  and comes into contact with the bottom surface SA of the bundle of sheets S 1  thereby applying the adhesive material.  653 . The timing of starting the coating process of  FIG. 4 ( b ) is controlled so that, when the bundle of sheet S 1  has been put in the vertical state in which it can be coated, the coating is started after waiting for the transportation of the cover sheet to stop after trimming by the cutter  81 . The right end position of the coating device  60  in  FIG. 4  is located at the deep end when viewed from the front of the post-processing apparatus like in  FIG. 1 , and the left end position in  FIG. 4  is the near side when viewed from the front of the apparatus.  
         [0056]     Because of such timing control, the operations of respective parts are performed continuously and the bookbinding operation is conducted with a high efficiency. When the wrapping-binding process mode is designated, after the coating device  60  moves to the home position, the cover sheet S 2  is joined to the bottom surface SA of the bundle of sheets S 1 .  
         [0057]     &lt;Joining Process&gt; 
         [0058]     Next, the process of joining the bundle of sheets S 1  and the cover sheet S 2  in the wrapping-binding process mode is explained below referring to  FIGS. 5-9 .  
         [0059]      FIG. 5  is an outline cross-sectional view diagram related to a cover sheet storing section  80  storing the cover sheets S 2  and the cover sheet support section  90  that supports the cover sheet.  FIG. 6  is a schematic perspective view of the cover sheet support section  90  viewed in the direction A of  FIG. 5 .  
         [0060]     The cover sheet S 2  is stored in a sheet supply tray  801  of a cover sheet storing section  80  provided in a lower portion of the bookbinding apparatus as shown in  FIG. 5 . The cover sheet is fed by sheet supply conveyance rollers  82  and after being aligned and switched back in the cover sheet support section  90 , is cut to a length corresponding to the bundle of sheets S 1  by the cutting device  81  as a trimming device, and conveyed by the transporting rollers  84  again, and then is placed in the horizontal condition on the cover sheet support unit  901  indicated by a single-dot and dash line. The cover sheet support unit  901  is constituted using a plurality of members such as the pressing members  91  and  92 , the cams  93  and  94  that drive the pressing members  91  and  92 .  
         [0061]     Further, the cutting device  81  cuts the cover sheet S 2  to a length based on the information of the size of the cover sheet S 2 , the information of the size of sheets S 1 , and the information of the thickness of the bundle of sheets S 1  that is stored in the position detection device  511 . The cutting shreds of the cover sheet S 2  after trimming are stored in the storage box  83 .  
         [0062]     The cover sheet S 2  cut to a prescribed length is conveyed by transporting rollers  84  and is inserted between a top guide plate  95 - 5  and a bottom guide plate  956  provided with a spacing of about 5 mm. The cover sheet S 2  is transported by the cover sheet transporting rollers  951  and the follower rollers  952  provided at the tips of the cover sheet pressing members  95  and  96 . The cover sheet S 2  is controlled so that it stops when it arrives at a prescribed position based on the size information of the cover sheet S 2 , and the information of the thickness of the bundle of sheets S 1 . A cover sheet pressing member  97  enters below the cover sheet and lifts it.  
         [0063]      FIG. 7  is the top view diagram of the cover sheet support unit  901 .  
         [0064]     The belts  98 A and  98 B carry out a function of alignment operation of correcting the inclination of the cover sheet S 2  that has been conveyed, and an operation of conveying the book S 3  that has been bound, to the book discharging section  100 .  
         [0065]     In order to set the cover sheet S 2  at a predetermined position, the aligning members.  981 A and  981 B are provided, that carry out alignment of both end surfaces of the cover sheet S 2  in directions parallel to the direction of transportation, and belts  98 A and  98 B and drum-shaped rollers to extend the belts  98 A and  98 B are provided on the aligning members  981 A and  981 B and the belts  98 A and  98 B are movable along the both end surfaces of the cover sheet. The aligning members  981 A and  981 B carry out the aligning operation every time a cover sheet S 2  is supplied. When the alignment operation is conducted, both sides of the cover sheet S 2  enter clearances below the belts  98 A and  98 B and the cover sheet S 2  is aligned by the aligning members  981 A and  981 B. In addition, when the cover sheet support unit  901  to be described later rises, the aligning members  981 A and  981 B and the belts  98 A and  98 B recede to the position shown by two-dots and one dash line in  FIG. 6 ( a ) and belts  98 A and  98 B are receded from above the cover sheet S 2 .  
         [0066]      FIG. 8  is a diagram showing the cover sheet S 2  pressed by pressing members  95  and  96 , and being raised in that state along with the cover sheet support unit  901  due to the motor M 1  that drives the belts  99 A and  99 B (the first moving device).  
         [0067]      FIG. 8 ( a ) shows that the adhesive  653  has been coated. In  FIG. 8 ( a ), the cover sheet support unit  901  supports the cover sheet S 2  at a lower position away from the bottom surface of the bundle of sheets S 1 , as shown in  FIG. 5 .  
         [0068]     When the cover sheet support unit  901  has started to rise, the cover sheet pressing members  95  and  96  holds the cover sheet S 2  from above so that the cover sheet S 2  is held in a plane state. Before the cover sheet S 2  has risen to contact the surface SA of the bundle of sheets S 1 , engagement with the cover sheet pressing members  95 ,  96  and  97  is released by a motor M 9  ( FIG. 6 ). The resulting state is as shown in  FIG. 8 ( b ). In this case, the cover sheet S 2  is raised by the cover sheet pressing member  97  placed under the cover sheet S 2 .  
         [0069]     The cover sheet support unit  901  rises further by a few millimeters from the position shown in  FIG. 8 ( b ). This position after rising by a few millimeters is the position shown in  FIG. 8 ( c ). After rising, the pressing members  91  and  92  press the cover sheet S 2  from left and right, make corners at the boundary between the front cover sheet and the spine cover of the book, and at the boundary between the spine cover and the back cover sheet, and the book S 3  is formed by closely contacting the cover sheet S 2  with the bundle of sheets S 1 . The duration for which the pressing members  91  and  92  are pressing is about 5 seconds, and the pressing force is about 200 Nf.  
         [0070]     Further, the movement in the lateral direction of the pressing members  91  and  92  is obtained from the cams  93  and  94  (see  FIG. 7 ) that are driven by motors (not shown in the figure). In addition, the device for the movement of the pressing members  91  and  92  can also have a configuration in which a rack is provided for each member, so that the member can be moved by the rotation of a pinion that engages with the rack.  
         [0071]     The processing of the cover sheet S 2  after it has been joined is explained below using  FIG. 9 .  
         [0072]     When the joining of the cover sheet S 2  has been completed, the cover sheet support unit  901  that released the pressing members  91  and  92 , lowers by about 100 mm due to the drive of the belts  99 A and  99 B and returns to the home position.  
         [0073]     At this time, in order to lift up the left and right sides of cover sheet S 2  by about 50 mm, the cover sheet pressing members  95 ,  96 , and  97  once go to the horizontal state from the vertical state, and again swing in the opposite direction and then a cover sheet lifting member  971  is raised as shown in  FIG. 9 ( b ).  
         [0074]     Next, the belts  98 A and  98 B are moved so as to return to the positions being narrower than the width of the cover sheet S 2 , and the cover sheet support unit  901  is raised by about 70 mm.  
         [0075]     The holding plate  503  moves to the retracted position, so that the holding pressure is released. Because of this, the book S 3  made up of the bundle of sheets S 1  and the cover sheet S 2  falls on the belts  98 A and  98 B. While the cover sheet support unit  901  is being lowered again, the belts  98 A and  98 B are rotated by the drive of motor M 8  (see  FIG. 6 ) and the book S 3  is conveyed toward the book discharging section  100  while being tumbled. At this time, the cover sheet pressing members  96  and  97  are swung toward the upward direction, and the left side cover sheet is lifted up as is shown in  FIG. 9 ( c ). The book S 3  is conveyed up to the left end by the belts  98 A and  98 B and is discharged, as it is, to the book discharging section  100  when the cover sheet support unit  901  arrives at its home position ( FIG. 9 ( d )).  
         [0076]     To ensure that the position of the ejection port  105  and the top position of the booklets stacked in the bound booklet storage section  100  is located approximately at the same level independently of the number of the booklets, the bound booklet storage section  100  is provided with a position sensor  106  and a motor M 21  for causing vertical movement of the sheet ejection stand  101  on which the sheets S 3  are placed, wherein the position sensor  106  is located below the ejection port  105 . The height is adjusted by the drive belt  103  synchronized with the motor M 21  in response to the signal from the position sensor  106 .  
         [0077]     The position sensor  106  is an optical position sensor made of a light emitting device and light receiving device. If the light path is interrupted, the position sensor  106  issues an ON signal or OFF signal, thereby performing sensing operation. The light emitting device and light receiving device are provided separately.  
         [0078]     In the case of pasting-binding operation without bonding the cover sheet, the coating device  60  retracts to the home position on the right end shown in  FIG. 4 , upon completion of the process shown in  FIG. 3 . Then the booklet S 4  drops onto the belts  98 A and  98 B.  
         [0079]     The booklet S 4  having dropped is conveyed by the belts  98 A and  98 B, and is ejected into the bound booklet storage section  100  shown in  FIG. 1 .  
         [0080]     &lt;Stapling Device&gt; 
         [0081]     The following describes the stapling device:  
         [0082]      FIG. 10  is a cross sectional view showing that the sheets S 1  are stacked on the sheet stacking section  40  for post-processing step by the leading edge receiving plate  404 .  FIG. 11 ( a ) shows a view from the direction M in  FIG. 10  and  FIG. 11 ( b ) shows the side view. The stapling device  110  is located where the staple SP is stapled at one position close to the corner of the sheets S 1 .  
         [0083]     The reference numeral  111  denotes a pair of widthwise alignment members arranged movably on each side of the stacking tray  402 . The alignment members  111  can be moved in the direction orthogonal to the direction of sheet conveyance. When the sheets S 1  are conveyed to the stacking tray  402  and are received, the alignment members are opened wider than the sheets. When the sheets are conveyed on the stacking tray  402  and are stopped by coming into contact with the leading edge receiving plate  404 , the side edges of the sheets S 1  across the width are tapped, whereby a bundle of sheets are subjected to widthwise alignment (arrow Y 3 ). At this stop position, a predetermined number of sheets S 1  are stacked on the stacking tray  402  and are aligned. Then binding operation is performed by the stapling device  110  whereby the bundle of sheets S 1  is bound together.  
         [0084]     The bundle of sheets having been stapled (referred to as “booklet SB”) are driven by the conveyance section  112  located on the lower surface of the stacking tray  402 , and are fed to the elevator tray  120 . As shown in  FIG. 11 ( a ), the conveyance section  112  has an opening formed on part of the sheet stacking surface of the stacking tray  402  in such a way that a plurality of ejection belt  113  wound around the driving pulleys  112 A and driven pulleys  112 B are fitted to the opening. Further, an ejection claw  114  is integrally formed on part of the ejection belt  113 , and the tip thereof forms an oblong locus, as shown by the one-dot chain line. The conveyance section  112  receives a signal from the control device, notifying termination of binding operation. After that, the driving shaft equipped with a driving pulley  112 A starts rotation, and the ejection claw  114  formed integrally with the ejection belt  113  pushes out the trailing edge of the booklet SB, whereby the booklet SB is ejected to the elevator tray  120 .  
         [0085]     The reference numeral  115  is a stacked booklet height adjustment device that keeps the distance between the top face of the stacked booklets SB and ejection port  114  approximately constant in order to ensure that the booklet SB ejected to the elevator tray  120  can be stacked in an aligned form.  
         [0086]     As shown in  FIG. 10 , the stacked booklet height adjustment device  115  is provided with a position sensor  116  arranged outside the ejection port  114 , and a height adjustment control device (not illustrated) capable of adjusting the height position of the elevator tray  120  in response to the signal of the position sensor  116 .  
         [0087]     The position sensor  116  is an optical position sensor made up of a light emitting device and a light receiving device. It is a sensing device emitting an ON signal or OFF signal when the optical path has been cut off.  
         [0088]     The height adjustment control device provides control so that when the booklet SB has been ejected to a position higher than the position sensor (so as to cut off the light path), the sensor signal is turned off, and the elevator tray  120  start to be lowered. When the light path has been turned on, the elevator tray  120  is stopped.  
         [0089]     The position sensor  116  can be any of the following devices such as a separation type optical switch wherein the light emitting device is separated from the light receiving device; a reflection type switch wherein the light emitting device is located on the same plane as the light receiving device; and a mechanical switch wherein the switching operation is performed by the actuator coming into contact with the booklet SB.  
         [0090]     The stacked booklet height adjustment device  115  includes the frame F 1 , a driving shaft driven by the motor M  20 , a driven shaft, and a belt or a drive wire wound around a driving pulley connected to the driving shaft and a driven pulley connected to the driven shaft. The height is adjusted by rotating the motor M 20  or stopping the rotation based on the instruction of the control device (not illustrated) in response to signals issued from the position sensor  116 .  
         [0091]     The present invention provides a post-processing apparatus equipped with a plurality of post-processing devices, wherein a stack tray for a post-processing apparatus to stack the sheets ejected from an image forming apparatus also serves as a buffer tray for other post-processing devices, thereby ensuring apparatus downsizing and cost reduction.