Patent Publication Number: US-11649131-B2

Title: Post-processing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2021-023642 filed Feb. 17, 2021. 
     BACKGROUND 
     (i) Technical Field 
     The present invention relates to a post-processing apparatus. 
     (ii) Related Art 
     JP2015-78031A discloses a sheet processing apparatus that performs processing of folding a sheet into a Z shape, the sheet being received from an image forming apparatus such as a copier or a printer, once pulls the folded sheet into a compile tray from a transport path to perform staple processing, and then discharges the stapled sheet to a stacker tray. 
     SUMMARY 
     Aspects of non-limiting embodiments of the present disclosure relate to a post-processing apparatus in which a rear end in a transport direction of a folded recording medium to be loaded on a processing unit is sent to a processing position of the processing unit. 
     Aspects of certain non-limiting embodiments of the present disclosure address the above advantages and/or other advantages not described above. However, aspects of the non-limiting embodiments are not required to address the advantages described above, and aspects of the non-limiting embodiments of the present disclosure may not address advantages described above. 
     According to an aspect of the present disclosure, there is provided a post-processing apparatus that includes: a processing unit configured to pull in a recording medium transported from an upstream apparatus and perform processing on the recording medium; a discharge unit to which the recording medium processed by the processing unit is discharged; and a lifting drive device configured to, in a case where a folded recording medium is pulled into the processing unit, move the discharge unit downward such that a height of the discharge unit is lower than a height of the discharge unit in a case where an unfolded recording medium is pulled into the processing unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiment(s) of the present invention will be described in detail based on the following figures, wherein: 
         FIG.  1    shows an overall configuration of an image forming system including a post-processing apparatus according to an exemplary embodiment of the present invention; 
         FIG.  2    shows a configuration of a staple function unit and a sheet loading function unit of the exemplary embodiment; 
         FIG.  3 A  shows a state in which a sheet having a short feed length is placed on a compile tray,  FIG.  3 B  shows a state in which a sheet which has a long feed length and is Z-folded is placed on the compile tray and a stacker tray is not moved downward, and  FIG.  3 C  shows a state in which a sheet which has a long feed length and is Z-folded is placed on the compile tray and the stacker tray is moved downward; 
         FIG.  4    is a flowchart showing a flow of processing of determining for which sheet downward movement processing of the stacker tray is to be performed; and 
         FIG.  5    is a flowchart showing a flow of the downward movement processing of the stacker tray according to the exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    shows an overall configuration of an image forming system  100  including a post-processing apparatus according to an exemplary embodiment of the present invention. The image forming system  100  includes an image forming apparatus  1  that forms a color image on a sheet as a recording medium by, for example, an electrophotographic method. Further, the image forming system  100  includes a sheet processing apparatus  2  that performs various kinds of predetermined processing on the sheet sent from the image forming apparatus  1 . 
     Here, the image forming apparatus  1  includes a photoreceptor drum configured to hold an electrostatic latent image, a charged body configured to charge the photoreceptor drum, a laser exposure device configured to form an electrostatic latent image by irradiating the photoreceptor drum with laser light, a developing device configured to develop the electrostatic latent image formed on the photoreceptor drum using toner, and a transfer device that transfers a toner image formed on the photoreceptor drum onto a sheet. The image forming apparatus  1  may be an image forming apparatus configured to form an image on a sheet by, for example, an inkjet method, in addition to an image forming apparatus configured to form an image on a sheet by an electrophotographic method. 
     The sheet processing apparatus  2  includes a transport unit  3  connected to the image forming apparatus  1 , a folding unit  4 , a finisher  5  configured to perform predetermined post-processing on the sheet that has passed through the folding unit  4 , an interposer  6  configured to supply laminated paper such as the cover of a booklet, and a controller  7  configured to control each function of the sheet processing apparatus  2 . Although the controller  7  is arranged in a housing of the finisher  5  in  FIG.  1   , the controller  7  may be arranged in a housing of another unit such as the transport unit  3  or the folding unit  4 . The image forming apparatus  1  may be configured to integrate all the control functions. 
     The sheet processing apparatus  2  will be described separately from the viewpoint of function. The sheet processing apparatus  2  includes a staple function unit  10  which is provided in the finisher  5  and is configured to generate a sheet bundle and execute staple binding, a laminated paper function unit  20  which is configured to include the interposer  6  or the like and is configured to supply laminated paper such as thick paper or open window paper used for the cover of the sheet bundle, a saddle stitch binding function unit  30  which is provided in the finisher  5  and is configured to bind the sheet bundle by performing saddle stitching, a punch function unit  40  which is provided in the finisher  5  and is configured to punch two holes or four holes in the sheet, and a folding function unit  50  which is provided in the folding unit  4  and is configured to perform Z-folding and C-folding on the sheet. Further, a sheet loading function unit  70  in which the sheet is finally discharged and loaded is provided in the sheet processing apparatus  2 . The post-processing apparatus of the invention includes the configuration of the staple function unit  10  and the configuration of the sheet loading function unit  70 , but only a part of each configuration may be included in the post-processing apparatus, or all the configurations may be included in the post-processing apparatus. 
     The folding function unit  50  of the folding unit  4  performs Z-folding or C-folding on the sheet transported from the transport unit  3  on the upstream side, and transports the sheet to the finisher  5  arranged on the downstream side. Since the exemplary embodiment relates to the processing for the Z-folded sheet, the Z-folded sheet will be mainly described in the following description. Here, the Z-folding is processing in which a valley fold is made at the ¼ position from the front end of the sheet in the transport direction, a mountain fold is made at the ½ position from the front end of the sheet in the transport direction so that the sheet is bent twice such that the sheet has a Z shape in a case where the sheet is viewed from a direction orthogonal to the transport direction. The Z-folding is not limited to the processing in which the folds are formed at the ¼ position and the ½ position from the front end of the sheet in the transport direction. The Z-folding includes all the folds as long as the folds on the front end side of the sheet in the transport direction are not aligned with the rear end of the sheet, are on the front end side in the transport direction from the rear end of the sheet, and the folds on the front end side of the sheet in the transport direction are below the entire sheet. 
     In the exemplary embodiment, the transport direction of the sheet refers to the transport direction of the sheet in a case where the staple function unit  10  or the finisher  5  is viewed as a whole, the front end side in the transport direction refers to the right side of the paper surface of  FIG.  1   , and the rear side in the transport direction refers to the left side of the paper surface of  FIG.  1   . As the recording medium, a sheet made of paper having predetermined shape and dimensions will be described as an example. Examples of the sheet include, for example, A4 sheets, B4 sheets, A5 sheets and the like. The recording medium may not be the sheet made of paper, and may be a sheet-shaped recording medium made of cloth or plastic. 
     The sheet that has been Z-folded by the folding function unit  50  of the folding unit  4  is selectively punched with two holes or four holes in the punch function unit  40  of the finisher  5 , and is transported to the staple function unit  10  and the sheet loading function unit  70  which constitute the post-processing apparatus on the downstream side. In a case where punching is not required, the sheet simply passes through the punch function unit  40  without being punched, and is transported to the staple function unit  10  on the downstream side. 
     The staple function unit  10  and the sheet loading function unit  70  of the exemplary embodiment will be described with reference to  FIG.  2   . The staple function unit  10  is configured to pull in the recording medium, that is, a sheet S, which has been transported from the upstream apparatus such as the folding function unit  50  and the punch function unit  40 , and performs the staple processing. The staple function unit  10  includes a receiving roll  11  which is a pair of rollers for receiving the sheet S from the upstream apparatus. The staple function unit  10  includes a sensor  12  which is provided on the downstream side of the receiving roll  11  and detects the sheet S. Further, the staple function unit  10  includes a compile tray  13  configured to collect and accommodate a plurality of sheets S, and an exit roll  14  which is provided on the downstream side of a detection portion of the sheet S by the sensor  12  and is a pair of rollers for discharging the sheet S toward the compile tray  13 . 
     Further, the staple function unit  10  includes a paddle  15  that is rotated to push the sheet S toward an end guide  13   b , which will be described later, of the compile tray  13 , and a tamper  16  that pushes the sheet S toward a side guide  13   c , which will be described later, of the compile tray  13 . The staple function unit  10  is an example of binding means, and includes a stapler  17  that binds the end portion of the bundle of sheets S accumulated on the compile tray  13  by using a staple needle. The staple function unit  10  includes a discharge roll  18  that pushes down the sheet S accumulated on the compile tray  13  and discharges the bundle of the stapled sheets S to a stacker tray  72  of the sheet loading function unit  70 . 
     The sheet loading function unit  70  includes an opening  71  that allows the bundle of the sheet S to pass through and to be discharged, the stacker tray  72  that stacks the processed sheet bundle such that the user easily picks up the sheet bundle, and a lifting drive device  73  that moves the stacker tray  72  up and down in an up-down direction. The stacker tray  72  constitutes a discharge unit to which the sheet S stapled by the staple function unit  10  is discharged. As will be described later, in a case where the Z-folded sheet S is pulled in the compile tray  13  of the staple function unit  10 , the lifting drive device  73  is configured to move the stacker tray  72  downward so that the height of the stacker tray  72  as the discharge unit is lower than the height of the stacker tray  72  in a case where the sheet S that has not been Z-folded is pulled in the compile tray  13 . 
     The compile tray  13  includes a loading platform  13   a  that receives and loads the sheet from the exit roll  14 , the end guide  13   b  that is formed on the surface of the loading platform  13   a  along a direction perpendicular to the transport direction of the sheet, and the side guide  13   c  that is formed on the surface of the loading platform  13   a  in a direction parallel to the transport direction of the sheet. The end guide  13   b  is a reference surface as a reference for aligning the end faces of the sheets on the rear end side in the transport direction in a case where the sheets discharged from the exit roll  14  are aligned, and the rear end faces of a plurality of sheets are abutted against the end guide  13   b  so that the positions of the sheets in the transport direction are aligned. 
     As will be described later, the sheet S is supplied toward the upper surface of the loading platform  13   a  of the compile tray  13  by being sent in a first traveling direction S 1  of  FIG.  2    after passing through the exit roll  14 . Then, in a state where a part of the sheet S on the front end side in the transport direction passes through the opening  71  from above a drive-side discharge roll  18   a , which will be described later, of the discharge roll  18  and is exposed to the outside, the traveling direction is reversed, and the sheet S falls along the upper surface of the loading platform  13   a  of the compile tray  13  in a second traveling direction S 2  of  FIG.  2   , and the rear end of the sheet S in the transport direction reaches the end guide  13   b.    
     That is, the end guide  13   b  has a surface substantially orthogonal to the loading platform  13   a  on the rear end side of the sheet S that falls along the upper surface of the loading platform  13   a , that is, on the left side of  FIG.  2   . That is, the end guide  13   b  is configured to align the rear end of the sheet S that falls along the loading platform  13   a . On the other hand, the side guide  13   c  has a surface that extends in a direction substantially parallel to the falling second traveling direction S 2  direction of the sheets S that falls along the loading platform  13   a , and that is substantially orthogonal to the loading platform  13   a . That is, the side guide  13   c  is configured to align one end portion of the sheet S, which is substantially parallel to the falling direction of the sheet S that falls along the loading platform  13   a.    
     The paddle  15  has, for example, three flexible sheet contact portions  15   a , and contacts the upper surface of the sheet S on the loading platform  13   a  or the uppermost surface of the bundle of sheets S to transport, that is, pull in the sheet toward the end guide  13   b . The paddle  15  is rotated in an R direction of  FIG.  2    to push the sheet S in the second traveling direction S 2  on the loading platform  13   a.    
     The tamper  16  is provided on a side surface that is one of the two side surfaces of the compile tray  13  and is opposite to the side surface on which the side guide  13   c  is provided, the two side surfaces being parallel to the transport direction of the sheet, and the tamper  16  is arranged such that the distance from the side guide  13   c  of the compile tray  13  is changed in response to the drive of a motor or the like. In the exemplary embodiment, the tamper  16  is provided on the back side of the paper surface of  FIG.  2    with respect to the compile tray  13 . The tamper  16  is moved in a direction orthogonal to the transport direction of the sheet so as to push the sheet S loaded on the compile tray  13  in a direction orthogonal to the transport direction of the sheet, to abut the side end of the sheet S against the side guide  13   c , and to align the sheet S. 
     The stapler  17  performs binding processing, that is, staple processing by pushing the staple needles one by one into the bundle of sheets S accommodated on the compile tray  13 . The stapler  17  is provided to be movable around the compile tray  13 . Specifically, the stapler  17  includes a staple head  17   a  that actually performs the staple processing using the staple needle, a base  17   b  that supports the staple head  17   a , and a rail  17   c  that is formed on the base  17   b  and forms a path where the staple head  17   a  is moved. The rail  17   c  is formed along the periphery of the compile tray  13 . The base  17   b  and the staple head  17   a  are moved on the rail  17   c  using a stapler motor (not shown) as a drive source, and performs staple processing on the sheet at a user&#39;s desired position. 
     The stapler  17  that performs the staple processing on the sheet has been described as an example of the processing unit, but a binding processing apparatus that performs binding processing on the sheet without using the staple needle, or a processing apparatus that performs compiling processing of aligning the positions of the sheets without performing the binding processing may be used as a mechanism of the processing unit that performs processing on the sheet. 
     Next, the discharge roll  18  will be described. As shown in  FIG.  2   , the discharge roll  18  has the drive-side discharge roll  18   a  and a driven-side discharge roll  18   b . The drive-side discharge roll  18   a  and the driven-side discharge roll  18   b  are arranged so as to be separated from each other. 
     The drive-side discharge roll  18   a  is rotatably supported by the housing of the finisher  5 , and is fixedly supported by a rotary shaft that is rotationally driven by an eject motor (not shown). 
     The driven-side discharge roll  18   b  is supported by a swingable support member (not shown). As the support member swings, the driven-side discharge roll  18   b  swings between a contact position where the driven-side discharge roll  18   b  contacts the upper surface of the sheet S loaded on the loading platform  13   a  of the compile tray  13  and a retreat position, that is, a non-contact position where the driven-side discharge roll  18   b  retreats from the upper surface of the sheet S loaded on the loading platform  13   a  of the compile tray  13 . 
     The driven-side discharge roll  18   b  is at the retreat position in a case where the sheet S is discharged from the exit roll  14  to the compile tray  13  and the rear end of the sheet S is aligned with the end guide  13   b . In a case where the sheet S is discharged from the compile tray  13  to the stacker tray  72 , the driven-side discharge roll  18   b  swings up to the contact position where the driven-side discharge roll  18   b  contacts the upper surface of the sheet S loaded on the loading platform  13   a  of the compile tray  13 , and then, as the eject motor is rotated, the drive-side discharge roll  18   a  is rotated, and the driven-side discharge roll  18   b  is driven to be rotated. As a result, the sheet loaded on the compile tray  13  is moved in a direction S 3  and is ejected onto the stacker tray  72 . The discharge roll  18  is arranged on the rear side in the transport direction with respect to the front end of the sheet with a relatively short feed length from the end guide  13   b  of the loading platform  13   a , for example, the A5LEF sheet, in the transport direction. That is, the distance from the end guide  13   b  to the discharge roll  18  is set to be shorter than the length of the short side of the A5 sheet. 
     Next, the opening  71  will be described. The opening  71  is an opening formed in the housing of the finisher  5 , and is a region through which the bundle of sheets S discharged toward the stacker tray  72  by the discharge roll  18  passes. 
     Next, the lifting drive device  73  will be described. The stacker tray  72  is moved downward and upward by the lifting drive device  73 . The downward movement and the upward movement by the lifting drive device  73  are controlled by the controller  7  shown in  FIG.  1   . 
     The lifting drive device  73  includes a guide  74  formed from the upper direction to the lower direction of the finisher  5 , and a slide member  75  that slides downward or upward while being guided by the guide  74 . The stacker tray  72  is fastened to the slide member  75  by fastening portions  76  provided at a plurality of places, for example, three places, and is moved downward or upward by the downward movement and the upward movement of the slide member  75 . 
     The lifting drive device  73  includes a belt member  77  formed in an endless shape, and a first pulley  78   a  and a second pulley  78   b  which are arranged with a gap in the up-down direction, support the belt member  77  from the inside, and apply tension to the belt member  77 . The lifting drive device  73  includes a motor  79  that drives the belt member  77  via the first pulley  78   a . The slide member  75  is fixed to the belt member  77 , and is moved in the up-down direction in conjunction with the movement of the belt member  77 . 
     In a case where the controller  7  rotationally drives the motor  79  in the forward direction, the slide member  75  is moved downward in accordance with the movement of the belt member  77 . As a result, the stacker tray  72  is moved downward. On the contrary, in a case where the controller  7  rotationally drives the motor  79  in the opposite direction, the slide member  75  is moved upward in accordance with the movement of the belt member  77 . As a result, the stacker tray  72  is moved upward. These movements are controlled by the stepping operation of the motor  79 . 
     Next, the operations of the staple function unit  10  and the sheet loading function unit  70  included in the post-processing apparatus of the exemplary embodiment will be described with reference to  FIGS.  3 A to  5   . First, for comparison, a state in which a sheet having a relatively short feed length is placed on the compile tray  13  will be described with reference to  FIG.  3 A . In  FIG.  3 A , the A5LEF sheet, that is, the long side of the A5 sheet is placed on the loading platform  13   a  of the compile tray  13  in a direction orthogonal to the transport direction. In this case, the rear end of the A5 sheet in the transport direction reaches the end guide  13   b  of the compile tray  13  due to the sheet&#39;s own weight and the rotation of the paddle  15  in the R direction. Further, in this case, the front end of the A5 sheet in the transport direction is located closer to the front end side in the transport direction than the drive-side discharge roll  18   a  of the discharge roll  18 . In this manner, after the A5LEF sheet is stapled by the stapler  17 , the A5LEF sheet having a short feed length is discharged to the stacker tray  72  by the rotation of the discharge roll  18 . 
       FIG.  3 B  illustrates a state in which a sheet having a relatively long feed length, for example, B4SEF, A3SEF, or LedgerSEF, that is, the short side of any sheet of the B4, A3, and Ledger sheet is transported in a direction orthogonal to the transport direction, is Z-folded, and is loaded on the loading platform  13   a  of the compile tray  13 . In this case, since the feed length of the Z-folded sheet is long, the folds of the sheet S are located outside the discharge roll  18  and the opening  71 . 
     That is, the sheet S is supplied toward the upper surface of the loading platform  13   a  of the compile tray  13  while passing through the exit roll  14 , but in this case, folds SA and SB of the sheet S both reach the outside of the discharge roll  18  and the opening  71  at the time when the rear end of the sheet S in the transport direction has passed through the exit roll  14 . 
     In this case, the paddle  15  is rotated and pulls the sheet S in the second traveling direction S 2 , that is, toward the end guide  13   b  of the compile tray  13 . In this case, since the fold SA on the front end side of the sheet S in the transport direction is outside the opening  71 , the fold SA is moved downward to the top of the stacker tray  72  due to the sheet&#39;s own weight. Then, the fold SA on the front end side in the transport direction is in a state of being caught in contact with the housing on the lower side of the opening  71 , on the stacker tray  72 . Therefore, in a case where the sheet S is pulled toward the end guide  13   b , the fold SA pulls the sheet S toward the stacker tray  72 , which prevents the rear end of the sheet S in the transport direction from reaching the end guide  13   b  of the compile tray  13 . 
     Therefore, in the exemplary embodiment, in a case where the sheet which has a relatively long feed length and is Z-folded is pulled into the compile tray  13 , the stacker tray  72  is moved downward by the lifting drive device  73 . The state in which the stacker tray  72  is moved downward will be described with reference to  FIG.  3 C . 
     In a case where the stacker tray  72  is moved downward, the fold SA on the front end side of the Z-folded sheet S in the transport direction is moved downward together with the stacker tray  72 . Then, the second fold SB from the front end side in the transport direction is opened. That is, the angle of the fold SB is increased. As a result, the force with which the first fold SA from the front end side in the transport direction pulls the sheet S toward the stacker tray  72  becomes small, and the second fold SB from the front end side of the sheet S in the transport direction is easily moved toward the end guide  13   b  of the compile tray  13 . 
     In a case where the paddle  15  is rotated in this state, the rear end of the sheet S in the transport direction can be pulled up to the end guide  13   b  of the compile tray  13  in the second traveling direction S 2 , and the rear ends of the sheets S in the transport direction are aligned. 
     With reference to  FIG.  4   , a method of determining for which sheet the downward movement processing of the stacker tray  72  described above is to be performed will be described. In Step S 401  of  FIG.  4   , the controller  7  determines whether the first sheet of a print job, that is, one image forming processing unit is a target sheet for the Z-folding processing, for the sheet S supplied to the compile tray  13 . Specifically, it is determined whether the sheet is a sheet having a feed length greater than a predetermined length, such as B4SEF, A3SEF, or LedgerSEF, and in a case where the sheet is the target sheet, the processing proceeds to Step S 402 . In a case where the sheet is Z-folded and the sheet has a length such that the first fold SA on the front end side in the transport direction is not placed on the loading platform  13   a  of the compile tray  13 , the sheet may be regarded as the target sheet. In a case where the sheet is not the target sheet, the processing proceeds to Step S 406  so that the sheet is excluded from the target for the downward movement processing of the stacker tray  72 . 
     In Step S 402 , in a case where a plurality of sheets are included in the processing unit as the post-processing target, and the sheets are pulled into the compile tray  13 , the controller  7  determines whether the first sheet is designated for the Z-folding processing, or whether the first sheet is Z-folded. In a case where the first sheet is designated for the Z-folding processing or is Z-folded, the processing proceeds to Step S 403 . Ina case where the sheet is not Z-folded, the processing proceeds to Step S 406  so that the sheet is excluded from the target for the downward movement processing of the stacker tray  72 . 
     In Step S 403 , the controller  7  determines whether the discharge destination of the sheet is the stacker tray  72 . In a case where the discharge destination is the stacker tray  72 , the processing proceeds to Step S 404 . In a case where the discharge destination is not the stacker tray  72 , the processing proceeds to Step S 406  so that the sheet is excluded from the target for the downward movement processing of the stacker tray  72 . 
     In Step S 404 , it is determined whether the sheet is set to be subjected to the staple processing. In a case where the sheet is set to be subjected to the staple processing, the downward movement processing of the stacker tray  72  shown in  FIG.  5    is executed. In a case where the sheet is not set to be subjected to the staple processing, the processing proceeds to Step S 406  so that the sheet is excluded from the target for the downward movement processing of the stacker tray  72 . 
     Next, with reference to  FIG.  5   , the flow of the downward movement processing of the stacker tray  72  and the staple processing in the exemplary embodiment will be described. In Step S 501  of  FIG.  5   , the controller  7  rotationally drives the motor  79  in the forward direction to move the stacker tray  72  downward by a predetermined distance. The amount of downward movement may be changed according to the size, material, and thickness of the sheet S. For example, the thinner the thickness of the sheet S, the easier it is for the angle of the second fold SB from the front end in the transport direction to be increased, and the easier it is for the sheet to be caught by the housing of the finisher  5 , so that the amount of the downward movement is increased as compared with the thick sheet S. These downward movement amounts may be the amounts directly designated by the operator. 
     As shown in  FIG.  3 B , the rear end of the sheet S in the transport direction is raised from the upper surface of the loading platform  13   a  of the compile tray  13  and does not reach the end guide  13   b . In this case, the downward movement processing is performed so that the stacker tray  72  is moved downward to a position where a portion from the rear end of the sheet S in the transport direction to the fold SB on the rear end side in the transport direction, that is, the second fold SB from the front end side in the transport direction is parallel to the upper surface of the loading platform  13   a.    
     In the exemplary embodiment, the downward movement processing of the stacker tray  72  is performed in the case of the sheet having a predetermined size and the predetermined setting, but the downward movement processing of the stacker tray  72  may be performed in a case where the rear end of the sheet S in the transport direction has not reached the end guide  13   b  or has not reached the staple processing by detecting whether the rear end of the Z-folded sheet S in the transport direction has reached the end guide  13   b  of the compile tray  13  using the sensor. 
     As described above, in a case where the sheet S having a relatively long feed length is Z-folded, the fold SA on the front end side of the sheet S in the transport direction is not on the loading platform of the compile tray  13 , but protrudes on the stacker tray  72 . This state may be detected by a sensor (not shown) or detected by the calculation based on the length along the transport direction of the sheet, and the downward movement processing of the stacker tray  72  may be performed in such a case. 
     In Step S 502 , the controller  7  rotates the paddle  15  to pull the sheet S in the second traveling direction S 2  such that the rear end of the sheet S in the transport direction reaches the end guide  13   b  of the compile tray  13 . As described above, since the first fold SA on the front end side of the sheet S in the transport direction is moved downward together with the stacker tray  72 , the force with which the first fold SA pulls the sheet S toward the stacker tray  72  becomes small. Therefore, the rear end of the sheet S in the transport direction is moved so as to reach the end guide  13   b  of the compile tray  13 . Further, the end face of the sheet S, which is parallel to the transport direction is aligned by the tamper  16 . That is, the end face of the sheet S, which is parallel to the transport direction is pushed to the side guide  13   c  of the compile tray  13  by the tamper  16 . As a result, the rear ends in the transport direction and the side ends of the sheets S placed on the loading platform  13   a  of the compile tray  13  are aligned. 
     In Step S 503 , the controller  7  moves the base  17   b  and the staple head  17   a  of the stapler  17  to a desired position around the compile tray  13  along the rail  17   c , and controls the staple head  17   a  to execute the staple processing on the sheet S. 
     In Step S 504 , the controller  7  rotationally drives the motor  79  in a direction opposite to the direction in Step S 501  to move the stacker tray  72  upward by a predetermined distance by the lifting drive device  73 . In this case, the distance of the upward movement of the stacker tray  72  is shorter than the distance of the downward movement in the case of moving the stacker tray  72  downward in Step S 501 . That is, the height in the case of raising the stacker tray  72  again is set to be lower than a normal position before the stacker tray  72  is moved downward, by a preset amount. As a result, the interference of the upper surface of the sheet bundle with a fixed tray located above the stacker tray  72  is avoided in a case where the sheet bundle is discharged to the stacker tray  72 . 
     In Step S 505 , the controller  7  swings the driven-side discharge roll  18   b  of the discharge roll  18  to the contact position where the driven-side discharge roll  18   b  contacts the upper surface of the sheet, and then drives the drive-side discharge roll  18   a . As a result, the stapled sheet bundle loaded on the loading platform  13   a  of the compile tray  13  is moved in the direction S 3  of  FIG.  2    in accordance with the rotation of the discharge roll  18 , passes through the opening  71 , and is discharged onto the stacker tray  72 . 
     In Step S 506 , the controller  7  determines whether the sheet bundle discharged in Step S 505  is the last sheet bundle, and in a case where the sheet bundle is the last sheet bundle, the processing is ended. In a case where the sheet bundle is not the last sheet bundle, that is, in a case where there is a sheet to be processed following the discharged sheet bundle, the processing proceeds to Step S 507 . 
     In Step S 507 , the controller  7  calculates the amount of the downward movement of the stacker tray  72  according to the number of Z-folds of the discharged sheet bundle, the processing returns to Step S 501 , the controller  7  moves the stacker tray  72  downward by the calculated amount of downward movement, and Steps S 501  to S 506  described above are repeatedly performed until all the processed bundles are discharged. 
     The controller  7  includes a CPU, a memory, a storage device, and a communication interface (which are not shown). The CPU is a control microprocessor, and controls the operations of the staple function unit  10 , the sheet loading function unit  70 , and each of other units based on a control program stored in the storage device. 
     In the embodiments above, the term “processor” refers to hardware in a broad sense. Examples of the processor include general processors (e.g., CPU: Central Processing Unit) and dedicated processors (e.g., GPU: Graphics Processing Unit, ASIC: Application Specific Integrated Circuit, FPGA: Field Programmable Gate Array, and programmable logic device). 
     In the embodiments above, the term “processor” is broad enough to encompass one processor or plural processors in collaboration which are located physically apart from each other but may work cooperatively. The order of operations of the processor is not limited to one described in the embodiments above, and may be changed. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.