Patent Publication Number: US-9403655-B2

Title: Post-processing device having shifted sheets

Description:
INCORPORATION BY REFERENCE 
     The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2014-136730, filed Jul. 2, 2014. The contents of this application are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The present disclosure relates to sheet post-processing devices and image forming apparatuses. 
     More and more recent image forming apparatuses such as copiers and multifunction peripherals are equipped with a sheet post-processing device, such as a finisher, for performing post-processing of sheets, such as stapling of sheets. A sheet post-processing device sequentially receives sheets having been printed by the main body of an image forming apparatus. To staple printed sheets, a conveyance section of the sheet post-processing device conveys the printed sheets to a processing tray provided within the sheet post-processing device. After conveying the sheets to the processing tray, the sheet post-processing device moves the sheets using a paddle along the processing tray toward a regulating member that is mounted on one end of the processing tray. In the manner described above, the sheets stacked on the processing tray are aligned at the edges thereof. The sheet post-processing device then staples the thus aligned sheets. 
     Until the sheets on the processing tray are stapled and conveyed to the exit port, subsequent sheets to be stapled cannot be conveyed to the processing tray. The sheet post-processing device is therefore provided with an evacuating member. During the time until the stapled sheets are conveyed from the processing tray to the exit port, the evacuating member evacuates, from the conveyance section, sheets sequentially fed from the image forming apparatus. The sheets evacuated by the evacuating member are stacked into a pile and held in standby. The pile of evacuated sheets is conveyed through the conveyance section onto the processing tray after the stapled sheets are conveyed from the processing tray to the exit port. 
     However, when three sheets are stacked into a pile, moving the pile toward the regulating member using a paddle may fail to ensure that the edges of the uppermost, lowermost, and intermediate sheets reach the regulating member. Thus, the edges of the three sheets may remain unaligned. One solution disclosed to address the problem noted above involves stacking three sheets into a pile such that, in a state where the pile is conveyed onto the processing tray and not yet moved toward the regulating member, the edge of each sheet protrudes toward the regulating member beyond the edge of an immediately lower sheet. 
     SUMMARY 
     A sheet post-processing device according to the present disclosure includes a tray, an evacuating member, a regulating member, and a feed mechanism. The tray can receive sheets thereon. The evacuating member temporarily evacuates, from a conveyance path, sheets being conveyed, stacks the evacuated sheets into a pile, and conveys the pile of sheets onto the tray through the conveyance path. The regulating member is mounted on the tray. The feed mechanism includes a spongy elastic member. The feed mechanism moves the pile of sheets along the tray toward the regulating member. When stacking three or more sheets into a pile, the evacuating member performs the stacking such that, in the pile conveyed to the tray, an edge of each intermediate sheet protrudes toward the regulating member beyond an edge of an uppermost sheet and an edge of a lowermost sheet. 
     An image forming apparatus according to the present disclosure includes a main body for printing an image on one or more sheets, and the sheet post-processing device described above. The main body feeds sheets requested to be fed to the sheet post-processing device from among the one or more printed sheets. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an image forming apparatus according to embodiments of the present disclosure. 
         FIG. 2  is a schematic diagram of a main body of the image forming apparatus according to the embodiments of the present disclosure. 
         FIG. 3  is a schematic diagram of major parts of the sheet post-processing device according to the embodiments of the present disclosure. 
         FIG. 4  is a schematic diagram of feed rollers and ejection rollers according to the embodiments of the present disclosure. 
         FIG. 5A  is a schematic diagram of a pile of sheets according to Embodiment 1 of the present disclosure. 
         FIG. 5B  is another schematic diagram of a pile of sheets according to Embodiment 1 of the present disclosure. 
         FIG. 6  is a schematic diagram of a pile of sheets according Embodiment 2 of the present disclosure. 
         FIG. 7  illustrates the forces acting on a pile of sheets according to Embodiment 2. 
         FIG. 8A  is a schematic diagram of feed rollers and ejection rollers according to a variation of the present disclosure. 
         FIG. 8B  is a schematic diagram of a different state of the feed rollers and the ejection rollers according to the variation of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to the accompanying drawings, the following describes an embodiment of a sheet post-processing device and an image forming apparatus according to the present disclosure. Throughout the drawings, the same or corresponding parts are denoted by the same reference signs, and no overlapping description is given. 
     Embodiment 1 
       FIG. 1  is a schematic diagram of an image forming apparatus according to Embodiment 1 of the present disclosure. The image forming apparatus  1  according to the present embodiment is a copier. 
     As shown in  FIG. 1 , the image forming apparatus  1  includes a sheet post-processing device  100  and a main body  200  that is for printing an image on a sheet S. The sheet post-processing device  100  performs post-processing, such as stapling, of sheets S fed from the main body  200  after printing on the sheets S. The sheet post-processing device  100  includes a conveyance section  120 , an evacuating member  141 , a processing tray  142 , a regulating member  143 , and at least one feed roller pair  144 . In the present embodiment, a sheet S is a sheet of paper. 
     The conveyance section  120  sequentially conveys printed sheets S fed from the main body  200 . 
     The processing tray  142  can receive a plurality of sheets S thereon. The regulating member  143  is mounted on one end of the processing tray  142 . The processing tray  142  is inclined such that sheets S conveyed on the processing tray  142  slide toward the regulating member  143  under their own weight. 
     The evacuating member  141  is a cylindrical rotary body that is driven to rotate by a driving mechanism such as a motor. The evacuating member  141  temporarily evacuates sheets S one by one from the conveyance section  120  as the sheets S are conveyed by the conveyance section  120  toward the processing tray  142 . The evacuating member  141  can stack sheets S evacuated from the conveyance section  120  into a pile. The conveyance section  120  conveys the sheets S stacked into a pile by the evacuating member  141  onto the processing tray  142 . The feed roller pair  144  serving as a feed mechanism can move the pile of sheets along the processing tray  142  toward the regulating member  143 . Each roller in the feed roller pair  144  is a spongy elastic member. 
     When stacking three or more sheets S into a pile, the evacuating member  141  performs the stacking such that, once the pile is moved to the processing tray  142 , an edge of each intermediate sheet S protrudes toward the regulating member  143  beyond the edges of the uppermost and lowermost sheets S. The uppermost sheet S refers to a sheet S at the top of the pile on the processing tray  142 . The lowermost sheet S refers to a sheet S at the bottom of the pile on the processing tray  142 . An intermediate sheet S refers to a sheet S located between the uppermost sheet S and the lowermost sheet S among the three or more sheets in the pile. 
     Since a pile of sheets S stacked in the manner described above is conveyed to the processing tray  142 , the feed roller pair  144  can move the pile so as to ensure that an edge of each sheet S reaches the regulating member  143  even if the pile includes three or more sheets S. Consequently, the edges of the respective sheets S in the pile are aligned as detailed below. 
     The uppermost and lowermost sheets S in a pile receive force directly from the feed roller pair  144 . Therefore, the uppermost and lowermost sheets S are moved until their edges reach the regulating member  143 . On the other hand, intermediate sheets S do not receive force directly from the feed roller pair  144 . However, in the pile of sheets S on the processing tray  142 , the edge of each intermediate sheet S protrudes toward the regulating member  143  beyond the edges of the uppermost and lowermost sheets S. This ensures that each intermediate sheet S is moved until its edge reaches the regulating member  143 , despite the force applied by the feed roller pair  144  acting less on the intermediate sheets S than on the uppermost and lowermost sheets S. In addition, each roller in the feed roller pair  144  is a spongy elastic member. This effectively prevents the edge of an intermediate sheet S from being creased, even if the feed roller pair  144  continues to move the uppermost and lowermost sheets S after the edge of the intermediate sheet S abuts against the regulating member  143 . 
     The following now describes the image forming apparatus  1  according to Embodiment 1 of the present disclosure. First, the main body  200  of the image forming apparatus  1  is described with reference to  FIG. 2 .  FIG. 2  is a schematic diagram of the main body  200  of the image forming apparatus  1 . 
     The main body  200  includes a document reading section  210 , a paper feed section  220 , a conveyance section  230 , an imaging section  240 , a transfer section  250 , a fixing section  260 , an ejection section  270 , and a control section  280 . 
     The document reading section  210  reads an image of a document placed on a document table  211  to generate image data. 
     The paper feed section  220  is located at the bottom of the main body  200 . The paper feed section  220  can store a plurality of sheets S and feeds sheets S one by one to the conveyance section  230 . 
     The conveyance section  230  conveys a sheet S fed by the paper feed section  220  sequentially to the transfer section  250 , the fixing section  260 , and the ejection section  270 . 
     The imaging section  240  forms a toner image based on image data generated by the document reading section  210 . The imaging section  240  includes an exposure device  241 , a plurality of photosensitive drums  242 , and a plurality of development rollers  243 . 
     The exposure device  241  scans each photosensitive drum  242  with a laser beam based on the image data. Through the laser beam scanning, an electrostatic latent image is formed on the photosensitive drum  242 . Each development roller  243  supplies toner to a corresponding photosensitive drum  242  so as to develop the electrostatic latent image. As a result of the development, a toner image is formed on each photosensitive drum  242 . 
     The transfer section  250  includes a plurality of primary transfer rollers  251 , a secondary transfer roller  252 , a driven roller  253 , and an intermediate transfer belt  254 . The transfer section  250  transfers the toner images formed on the respective photosensitive drums  242  to the intermediate transfer belt  254  so as to overlay the toner images. The overlaid toner images are transferred from the intermediate transfer belt  254  to a sheet S. 
     Each primary transfer roller  251  is located opposite to a corresponding photosensitive drum  242  with the intermediate transfer belt  254  therebetween. The primary transfer rollers  251  press the intermediate transfer belt  254  against the respective photosensitive drums  242 . With this configuration, the toner images formed on the photosensitive drums  242  are transferred to be overlaid on the intermediate transfer belt  254 . 
     The secondary transfer roller  252  is pressed against the driven roller  253 . Consequently, a nip is formed between the secondary transfer roller  252  and the driven roller  253 . When a sheet S passes through the nip, the secondary transfer roller  252  and the driven roller  253  cause the toner image to be transferred from the intermediate transfer belt  254  to the sheet S. 
     The fixing section  260  includes a fixing member  261  and a pressure member  262 . The fixing section  260  applies heat and pressure to a sheet S to fix an unfixed toner image which has been transferred to the sheet S by the transfer section  250 . 
     The ejection section  270  ejects a sheet S having a fixed toner image to outside of the main body  200 . 
     The control section  280  has a storage area for storing data such as programs and setting information. The storage area is implemented by random access memory (RAM) and read only memory (ROM). The control section  280  controls the overall operation of the image forming apparatus  1  by executing different control programs stored in advance in the storage area. 
     With reference to  FIGS. 3, 4, 5A, and 5B , the following now describes the sheet post-processing device  100  in detail.  FIG. 3  is a schematic diagram of major parts of the sheet post-processing device  100 .  FIG. 4  is a schematic diagram of two feed roller pairs  144  and two ejection roller pairs  132 . Sheets S ejected from the main body  200  through the ejection section  270  are sequentially fed into a housing  101  of the sheet post-processing device  100 . The sheet post-processing device  100  performs post-processing of sheets, such as stapling, offsetting, and hole punching, on the sheets S. 
     As shown in  FIG. 3 , the sheet post-processing device  100  includes the housing  101  roughly having a box shape, an entrance section  111 , a first ejection section  131 , a first ejection tray  134 , a second ejection section  135 , and a second ejection tray  136 . The sheet post-processing device  100  additionally includes a puncher  151 , a stapler  152 , and a controller  181 . 
     The entrance section  111  receives a sheet S having an image printed by the main body  200  of the image forming apparatus  1 . 
     The conveyance section  120  includes a first conveyance section  121 , a second conveyance section  122 , and a third conveyance section  123 . 
     The first conveyance section  121  extends from the entrance section  111  to a first branching member  121   a . The first branching member  121   a  is rotatably supported. A sheet S conveyed by the first conveyance section  121  is selectively fed into the second conveyance section  122  or the third conveyance section  123  by the first branching member  121   a.    
     The second conveyance section  122  extending from the first branching member  121   a  to the second ejection section  135  conveys a sheet S to the second ejection section  135 . The second ejection tray  136  receives sheets S ejected through the second ejection section  135 . 
     The third conveyance section  123  extends from the first branching member  121   a  to the processing tray  142 . The third conveyance section  123  includes a second branching member  123   a  and an intermediate roller pair  123   b . A sheet S conveyed to the third conveyance section  123  is moved by the intermediate roller pair  123   b  onto the processing tray  142 . The stapler  152  performs stapling (one example of post-processing) of a plurality of sheets S on the processing tray  142 . The plurality of sheets S stapled together are ejected by the first ejection section  131  onto the first ejection tray  134 . 
     The evacuating member  141  rotates in a rotation direction R 1  shown in  FIG. 3  in accordance with the direction of conveyance by the third conveyance section  123 . An evacuation path  141   a  is formed between the circumferential surface of the evacuating member  141  and a guide member located opposite to the circumferential surface. As the evacuating member  141  rotates in the rotation direction R 1 , the sheet S conveyed to the third conveyance section  123  wraps around the circumferential surface of the evacuating member  141 . 
     More specifically, to evacuate a sheet S from the third conveyance section  123 , the second branching member  123   a  is rotated to a position for forwarding sheets S into the evacuation path  141   a  as the sheet S is conveyed thereto in the third conveyance section  123 . As a result, the sheet S conveyed to the third conveyance section  123  is evacuated into the evacuation path  141   a . The evacuation path  141   a  is provided with conveyance rollers. Each conveyance roller is located opposite to the circumferential surface of the evacuating member  141 . The sheet S fed into the evacuation path  141   a  is nipped between the evacuating member  141  and each of the conveyance rollers to be moved in the rotation direction R 1  of the evacuating member  141 . As a result, the sheet S wraps around the circumferential surface of the evacuating member  141 . 
     The second branching member  123   a  is rotated back to the initial position after the first ejection section  131  conveys a preceding sheet S having been subjected to post-processing from the processing tray  142  to the first ejection tray  134 . Consequently, a subsequent sheet S having been held in standby in the evacuation path  141   a  is conveyed through the third conveyance section  123  onto the processing tray  142 . 
     When evacuating a plurality of sheets S and holding them in standby, the evacuating member  141  stacks the plurality of sheets S into a pile. In other words, the sheets S wrap around the circumferential surface of the evacuating member  141  in layers. The pile of evacuated sheets S is conveyed to the processing tray  142  after preceding sheets S on the processing tray  142  are subjected to post-processing and moved to the first ejection tray  134 . 
     More specifically, during the time a plurality of sheets S on the processing tray  142  are aligned, stapled, and ejected onto the first ejection tray  134 , subsequent sheets S fed into the third conveyance section  123  are sequentially evacuated by the evacuating member  141  and stacked into a pile in the evacuation path  141   a.    
     The puncher  151  is located upstream from the first branching member  121   a  in the conveyance path of sheets S. The puncher  151  performs hole punching with predetermined timing on sheets S conveyed by the first conveyance section  121 . The second conveyance section  122  is for conveying sheets S that are not to be subjected to post-processing or are only to be subjected to hole punching. 
     The stapler  152  staples sheets S having aligned edges with a staple. After the stapler  152  staples the sheets S, the first ejection section  131  ejects the stapled sheets S onto the first ejection tray  134 . 
     The controller  181  controls operation of each part of the sheet post-processing device  100  according to a request from the control section  280  of the main body  200  (see  FIG. 2 ). 
     Reference is now made to  FIG. 4  to describe the feed roller pairs  144  and the ejection roller pairs  132 . The ejection roller pairs  132  are included in the first ejection section  131 .  FIG. 4  is a schematic diagram of the feed roller pairs  144  and the ejection roller pairs  132  according to Embodiment 1 of the present disclosure. Note that  FIG. 4  shows the processing tray  142  seen from the side of the first ejection tray  134 . 
     As shown in  FIG. 4 , each feed roller pair  144  includes a first feed roller  144   a  and a second feed roller  144   b . In the present embodiment, each of the rollers  144   a  and  144   b  in the respective feed roller pairs  144  is a spongy roller having a layer of elastomeric foam (an example of a spongy elastomeric member). The sheet post-processing device  100  also includes a first support shaft  161   a  and a second support shaft  161   b . The first feed rollers  144   a  are attached to the first support shaft  161   a  and rotate in accordance with the rotation of the first support shaft  161   a . The second feed rollers  144   b  are attached to the second support shaft  161   b , which is embedded in the processing tray  142 , and rotate in accordance with the rotation of the second support shaft  161   b . Each second feed roller  144   b  has a circumferential surface partially exposed above a sheet placement surface  142   a  of the processing tray  142 . Therefore, each second feed roller  144   b  abuts against a corresponding one of the first feed rollers  144   a  with a conveyed sheet S sandwiched therebetween. 
     Each ejection roller pair  132  includes a first ejection roller  132   a  and a second ejection roller  132   b . In the present embodiment, each of the rollers  132   a  and  132   b  in the ejection roller pairs  132  are made of rubber and are smaller in diameter than the rollers  144   a  and  144   b  in the feed roller pairs  144 . The first ejection rollers  132   a  are attached to the first support shaft  161   a  at positions axially inward from the first feed rollers  144   a . The first ejection rollers  132   a  rotate in accordance with the rotation of the first support shaft  161   a . The second ejection rollers  132   b  are attached to the second support shaft  161   b  at positions axially inward from the second feed rollers  144   b . The second ejection rollers  132   b  rotate in accordance with the rotation of the second support shaft  161   b . Each second ejection roller  132   b  has a circumferential surface partially exposed to protrude beyond the sheet placement surface  142   a  of the processing tray  142 . Therefore, each second ejection roller  132   b  abuts against a corresponding one of the first ejection rollers  132   a  with a conveyed sheet S sandwiched therebetween. 
     The first support shaft  161   a  is movable toward and away from the second support shaft  161   b . When a pile of sheets S is conveyed from the third conveyance section  123  onto the processing tray  142 , the first support shaft  161   a  is moved to a position closer to the second support shaft  161   b . More specifically, the first support shaft  161   a  is moved toward the second support shaft  161   b  such that the sheet pile is nipped between the first ejection roller  132   a  and the second ejection roller  132   b . Since the first support shaft  161   a  and the second support shaft  161   b  are being rotated, the leading edge of the sheet pile is nipped by the ejection roller pairs  132  and conveyed toward the first ejection tray  134 . The rollers  144   a  and  144   b  in the feed roller pairs  144  at this time are partially compressed. 
     As the leading edge of the sheet pile is conveyed toward the first ejection tray  134 , the trailing edge of the sheet pile eventually drops onto the processing tray  142  from the third conveyance section  123 . When the trailing edge of the sheet pile being conveyed reaches such a position, each ejection roller pair  132  stops rotating. In one example, the third conveyance section  123  may be provided with a detection sensor in order to stop the rotation of the ejection roller pairs  132  with appropriate timing. That is, output of the detection sensor may be used to detect that the trailing edge of the sheet pile has reached a position to be dropped from the third conveyance section  123  onto the processing tray  142 . Alternatively, the controller  181  may be provided with a function of measuring a time period starting when the second branching member  123   a  is rotated back to the initial position. That is, the measured time period may be used to detect that the trailing edge of the sheet pile has reached the position to be dropped from the third conveyance section  123  onto the processing tray  142 . 
     Subsequently, the first support shaft  161   a  moves away from the second support shaft  161   b . More specifically, the first support shaft  161   a  moves away from the second support shaft  161   b  to a position where the nip formed by the respective ejection roller pairs  132  is released while the feed roller pairs  144  still nip the sheet pile. 
     According to the present embodiment, each of the rollers  144   a  and the  144   b  in the feed roller pairs  144  is larger in diameter than each of the rollers  132   a  and  132   b  in the ejection roller pairs  132 . Therefore, as the first support shaft  161   a  moves away from the second support shaft  161   b , the nip formed by the respective ejection roller pairs  132  is released before the nip formed by the respective feed roller pairs  144  is released. When the first support shaft  161   a  is moved away from the second support shaft  161   b  to a position where only the nip formed by the ejection roller pairs  132  is released, the first and second support shafts  161   a  and  161   b  start to rotate in reverse to the rotation direction that is for conveying a sheet pile to the first ejection tray  134 . 
     As a result, the sheet pile is moved toward the regulating member  143  only by the feed roller pairs  144 . For conveying sheets S from the processing tray  142  to the first ejection tray  134  after post-processing, the first support shaft  161   a  moves toward the second support shaft  161   b . More specifically, the first support shaft  161   a  moves toward the second support shaft  161   b  to a position where the respective ejection roller pairs  132  can nip the sheets S on the processing tray  142 . Then, the first and second support shafts  161   a  and  161   b  rotate in reverse to the rotation direction for moving a sheet pile toward the regulating member  143 . As a result, the sheets S after post-processing are nipped by the respective feed roller pairs  144  as well as the ejection roller pairs  132  and conveyed to the first ejection tray  134 . 
     With reference to  FIGS. 3, 5A, and 5B , the following now describes an example in which the evacuating member  141  evacuates three sheets S.  FIG. 5A  shows the state where a pile St of sheets S on the processing tray  142  is moved by the feed roller pairs  144  toward the regulating member  143 .  FIG. 5B  shows the state where a plurality of (three or more) sheets S in the sheet pile St abut against the regulating member  143 . 
     As shown in  FIGS. 3, 5A, and 5B , when evacuating three sheets S, the evacuating member  141  sequentially stacks the sheets S into a sheet pile St in order of entry into the evacuation path  141   a . Thus, the first one of the sheets S fed into the evacuation path  141   a  will be the lowermost sheet S 1 , which is located lowest in the sheet pile St on the processing tray  142 . The second one of the sheets S fed into the evacuation path  141   a  will be the intermediate sheet S, which is located between the top and the bottom in the sheet pile St on the processing tray  142 . The third one of the sheets S fed into the evacuation path  141   a  will be the uppermost sheet S 3 , which is located highest in the sheet pile St on the processing tray  142 . The evacuating member  141  stacks the sheets S into the sheet pile St such that an edge of the intermediate sheet S 2  protrudes beyond edges of the uppermost and lowermost sheets S 3  and S 1  toward the regulating member  143  in a state where the sheet pile St is on the processing tray  142 . 
     For example, when a sheet S, which will be the lowermost sheet S 1 , is fed into the evacuation path  141   a , the evacuating member  141  conveys the lowermost sheet S 1  along the evacuation path  141   a . When the leading edge (the edge at the front of the sheet S in the conveyance direction) reaches a stop position P, the evacuating member  141  stops rotating. The evacuating member  141  resumes the conveyance of the lowermost sheet S 1  a predetermined time period after a sheet-passage sensor  111   a  disposed in the entrance section  111  detects passage of a subsequent sheet S, which will be the intermediate sheet S 2 . Through the above operation, the intermediate sheet S 2  is stacked on the lowermost sheet S 1  such that one edge (the trailing edge) of the intermediate sheet S 2  protrudes beyond one edge (the trailing edge) of the lowermost sheet S 1 . A subsequent sheet S, which will be the uppermost sheet S 3 , is stacked on the intermediate sheet S 2  such that one edge (the trailing edge) of the intermediate sheet S 2  protrudes beyond the one edge (the trailing edge) of the uppermost sheet S 3 . Consequently, the three sheets S are stacked into the sheet pile St in a manner that the aforementioned one edge of the intermediate sheet S 2  protrudes toward the regulating member  143  beyond the respective edges of the uppermost sheet S 3  and the lowermost sheet S 1 . 
     The sheet pile St produced by the evacuating member  141  is conveyed onto the processing tray  142  through the third conveyance section  123 . Then, the sheet pile St is moved toward the regulating member  143  by the feed rollers  144   a  and  144   b  each rotating in the direction of an arrow shown in  FIGS. 5A and 5B . As the sheet pile St is moved, the intermediate sheet S 2  abuts against the regulating member  143  first and then the lowermost and uppermost sheets S 1  and S 3  abut against the regulating member  143 . Consequently, the edges of sheets S in the sheet pile St are aligned. 
     When a subsequent sheet S is to be stacked on the sheet pile St that is on the processing tray  142 , the first support shaft  161   a  moves (ascends) to move the first feed rollers  144   a  away from the second feed rollers  144   b . The subsequent sheet S then drops onto the processing tray  142  to be stacked on the sheet pile St. Then, the first support shaft  161   a  moves (descends) toward the second support shaft  161   b  to cause each feed roller pair  144  to form a nip. Then, the first and second support shafts  161   a  and  161   b  rotate and thus the feed roller pairs  144  move the subsequent sheet S toward the regulating member  143 . Consequently, the edges of all the sheets S in the sheet pile St, including the subsequent sheet S, are aligned as shown in  FIG. 5B . The aligned sheets S are stapled, for example, and then ejected to the ejection tray  134  by the ejection roller pairs  132 . 
     As has been described with reference to  FIGS. 1 to 5A and 5B , when evacuating three sheets S, the evacuating member  141  stacks the three sheets S into a sheet pile St such that an edge of the intermediate sheet S 2  protrudes toward the regulating member  143  in a state where the sheet pile St is on the processing tray  142 . Such stacking ensures that when the sheet pile St is moved toward the regulating member  143 , the intermediate sheet S 2  abuts against the regulating member  143  first and then the lowermost and uppermost sheets S 1  and S 2  abut against the regulating member  143 . Consequently, the edges of all the sheets S in the sheet pile St are aligned. 
     The rollers  144   a  and  144   b  in the feed roller pairs  144  are spongy rollers each having a layer of elastic foam. Thus, Expression 1 is satisfied when the feed roller pairs  144  move the sheet pile St toward the regulating member  143 .
 
Friction Force  Fa &gt;Sheet Creasing Force&gt;Friction Force  Fb   Expression 1
 
     In Expression 1, Fa denotes a friction force applied to a sheet S by each of the rollers  144   a  and  144   b  in the feed roller pairs  144 , Sheet Creasing Force denotes a force causing creasing of a sheet S, and Fb denotes a friction force arising between adjacent sheets S by the nip produced by each feed roller pair  144 . 
     As long as Expression 1 is satisfied, each intermediate sheet S is less likely to be creased when the uppermost and lowermost sheets S are continued to be moved toward the regulating member  143  after the edge of an intermediate sheet S abuts against the regulating member  143 . This is because the use of spongy feed rollers  144   a  and  144   b  ensures that the force applied to the intermediate sheet S 2  by each of the rollers  144   a  and  144   b  once the intermediate sheet S 2  abuts against the regulating member  143  at an edge does not exceed the stiffness of the intermediate sheet S 2  (the force required to cause creasing of the intermediate sheet S 2 ). Consequently, occurrence of creasing of the intermediate sheet S 2  is reduced. 
     Embodiment 2 
     The following describes the sheet post-processing device  100  according to Embodiment 2 of the present disclosure with reference to  FIGS. 3, 6, and 7 . In Embodiment 2, the evacuating member  141  evacuates four sheets S. The following description focuses on differences with Embodiment 1 and no overlapping description is given.  FIG. 6  shows a state where a pile of four sheets S is on the processing tray  142 .  FIG. 7  illustrates the forces acting on the four sheets S on the processing tray  142 . 
     The evacuating member  141  shown in  FIG. 3  can stack four sheets S into a sheet pile St. As shown in  FIG. 6 , the first one of the four sheets S fed into the evacuation path  141   a  will be a lowermost sheet S 1 , which is at the bottom of the sheet pile St on the processing tray  142 . The last one of the four sheets S fed into the evacuation path  141   a  will be an uppermost sheet S 3 , which is at the top of the sheet pile St on the processing tray  142 . The second one of the four sheets S fed into the evacuation path  141   a  will be a first intermediate sheet S 2   a , which is on the lowermost sheet S 1 , and the third one will be a second intermediate sheet S 2   b , which is on the first intermediate sheet S 2   a  and immediately below the uppermost sheet S 3 . The first and second intermediate sheets S 2   a  and S 2   b  are stacked such that the edge of each intermediate sheet increasingly protrudes toward the regulating member  143  in order of an increasing distance from the processing tray  142 . 
     Similarly to the example of stacking three sheets, when a sheet S, which will be the lowermost sheet S 1 , is fed into the evacuation path  141   a , the evacuating member  141  conveys the lowermost sheet S 1  along the evacuation path  141   a . When the leading edge of the lowermost sheet S 1  (the edge at the front of the sheet S in the conveyance direction) reaches the stop position P, the evacuating member  141  stops rotating. The evacuating member  141  resumes the conveyance of the lowermost sheet S 1  a predetermined time period after the sheet-passage sensor  111   a  detects passage of a subsequent sheet S, which will be the first intermediate sheet S 2   a . Through the above operation, the first intermediate sheet S 2   a  is stacked on the lowermost sheet S 1  such that one edge (the trailing edge) of the first intermediate sheet S 2   a  protrudes beyond one edge (the trailing edge) of the lowermost sheet S 1 . A subsequent sheet S, which will be the second intermediate sheet S 2   b , is stacked on the first intermediate sheet S 2   a  in a similar manner that one edge (the trailing edge) of the second intermediate sheet S 2   b  protrudes beyond one edge (the trailing edge) of the first intermediate sheet S 2   a . A subsequent sheet S, which will be the uppermost sheet S 3 , is stacked on the second intermediate sheet S 2   b  such that one edge (the trailing edge) of the second intermediate sheet S 2   b  protrudes beyond one edge (the trailing edge) of the uppermost sheet S 3 . Consequently, the first and second intermediate sheets S 2   a  and S 2   b  are stacked such that the edges of the intermediate sheets protrude toward the regulating member  143  more and more in order of an increasing distance from the processing tray  142 . 
     According to the present embodiment, the nip pressure Np of each feed roller pair  144 , the friction coefficient μS between a sheet S and each of the feed rollers  144   a  and  144   b  in the feed roller pair  144 , the friction coefficient μP between adjacent sheets S, and the weight g of a sheet S need to satisfy Expression 2 below.
 
μ S ×Np&gt;μ P ×(Np+ g )  Expression 2
 
     Therefore, the nip pressure Np of each feed roller pair  144  as well as the material of each of the feed rollers  144   a  and  144   b  is selected so as to satisfy Expression 2. 
     Once the respective feed roller pairs  144  starts rotating with the sheet pile St sandwiched therebetween, the forces F 4  to F 1  respectively given by Expressions 3 to 6 act on the respective sheets S in the sheet pile St as shown in  FIG. 7 . More specifically, the force F 4  acts on the sheet S 3 , the force F 3  acts on the sheet S 2   b , the force F 2  acts on the sheet S 2   a , and the force F 1  acts on the sheet S 1 .
 
 F 4=μ S ×Np+μ P ×(Np+ g )  Expression 3
 
 F 3=μ P ×(Np+ g )+μ P ×(Np+2 g )  Expression 4
 
 F 2=μ P ×(Np+2 g )+μ P ×(Np+3 g )  Expression 5
 
 F 1=μ P ×(Np+3 g )+μ S ×(Np+4 g )  Expression 6
 
     In Expressions 3 to 5 above, F 1  denotes the force applied to the lowermost sheet S 1 , F 2  to the first intermediate sheet S 2   a , F 3  to the second intermediate sheet S 2   b , and F 4  to the uppermost sheet S 3 . 
     As described above, the second intermediate sheet S 2   b  protrudes toward the regulating member  143  most among all of the sheets S in the sheet pile St. Thus, the second intermediate sheet S 2   b  reaches the regulating member  143  first among the sheets S in the sheet pile St. Once the second intermediate sheet S 2   b  reaches the regulating member  143 , the forces F 4 , F 2 , and F 1  respectively given by Expressions 7 to 9 are applied to the other sheets S in the sheet pile St. More specifically, the force F 4  is applied to the sheet S 3 , the force F 2  to the sheet S 2   a , and the force F 1  to sheet S 1 .
 
 F 4=μ S ×Np−μ P ×(Np+ g )  Expression 7
 
 F 2=μ P ×(Np+3 g )−μ P ×(Np+2 g )=μ P×g   Expression 8
 
 F 1=μ S ×(Np+4 g )−μ P ×(Np+3 g )  Expression 9
 
     Based on Expression 2 above, F 4 &gt;0 is satisfied in Expression 7, and F 1 &gt;0 is satisfied in Expression 9. In addition, F 2 &gt;0 is satisfied in Expression 8. Since force F continues to act on the sheets S 3 , S 2   a , and S 1  in the sheet pile St in a direction toward the regulating member  143 , the sheets S 3 , S 2   a , and S 1  continue to move toward the regulating member  143 . 
     Once the first intermediate sheet S 2   a  has reached the regulating member  143 , the forces F 4  and F 1 , which are respectively equal to the forces F 4  and F 1  given by Expressions 7 and 9 above, are applied to the other sheets S 3  and S 1 . Since the force F continues to act on the sheets S 3  and S 1  in a direction toward the regulating member  143 , the sheets S 3  and S 1  continue to move toward the regulating member  143 . 
     As a result, the edges of the four sheets S (S 1 , S 2   a , S 2   b , and S 3 ) included in the sheet pile St all abut against the regulating member  143  and thus align. 
     The present embodiment is described through an example in which four sheets S are evacuated. However, the number of sheets to be evacuated is not limited to four and may be five or more. 
     The above has described the embodiments of the present disclosure with reference to the accompanying drawings ( FIGS. 1 to 7 ). However, the present disclosure is not limited to the embodiments described above and may be practiced through different variations without departing from the essence of the present disclosure. 
     For example, according to the embodiments described above, the first feed rollers  144   a  are coaxial with the first ejection rollers  132   a , whereas the second feed rollers  144   b  are coaxial with the second ejection rollers  132   b . However, the present disclosure is not limited to this configuration. For example, as shown in  FIGS. 8A and 8B , the first feed rollers  144   a  and the first ejection rollers  132   a  may have mutually different axes, and the second feed rollers  144   b  and the second ejection rollers  132   b  may have mutually different axes. More specifically, the first feed rollers  144   a  are attached to a third support shaft  162   a , and the second feed rollers  144   b  are attached to a fourth support shaft  162   b . The first ejection rollers  132   a  are attached to a fifth support shaft  163   a , and the second ejection rollers  132   b  are attached to a sixth support shaft  163   b . The third support shaft  162   a  is movable toward and away from the fourth support shaft  162   b . Similarly, the fifth support shaft  163   a  is movable toward and away from the sixth support shaft  163   b . The third and fourth support shafts  162   a  and  162   b  are located toward the regulating member  143  relative to the fifth and sixth support shafts  163   a  and  163   b . That is, the feed roller pairs  144  are located closer to the regulating member  143  than the ejection roller pairs  132  are to the regulating member  143 . The feed first rollers  144   a  may be attached at positions axially inward or outward from the first ejection rollers  132   a , whereas the second feed rollers  144   b  may be attached at positions axially inward or outward from the second ejection rollers  132   b.    
     The feed roller pairs  144  and the ejection roller pairs  132  operate in the same manner as in Embodiment 1. In short, as shown in  FIG. 8A , to forward a sheet pile St to the regulating member  143 , the fifth support shaft  163   a  moves away from the sixth support shaft  163   b  and the third support shaft  162   a  moves toward the fourth support shaft  162   b . More specifically, the third to sixth support shafts  162   a ,  162   b ,  163   a , and  163   b  are moved to positions such that the sheet pile St is nipped only between each first feed roller  144   a  and the corresponding second feed roller  144   b . Then, through rotation of the feed roller pairs  144 , the sheet pile St is moved toward the regulating member  143 . In short, the sheet pile St is moved only by the feed roller pairs  144  in the direction toward the regulating member  143 . As has been described above, each of the feed rollers  144   a  and  144   b  has a layer of elastomeric foam. This reduces occurrence of creasing of the sheets S. 
     When the sheet pile St is conveyed toward the first ejection tray  134 , the third support shaft  162   a  moves away from the fourth support shaft  162   b  and the fifth support shaft  163   a  moves toward the support shaft  163   b , as shown in  FIG. 8B . More specifically, the third to sixth support shafts  162   a ,  162   b ,  163   a , and  163   b  are moved to the positions such that the sheet pile St is nipped only between each first ejection roller  132   a  and the corresponding second ejection rollers  132   b . Through the rotation of the ejection roller pairs  132 , the sheet pile St is conveyed toward the first ejection tray  134 . 
     According to the embodiments described above, each of the feed rollers  144   a  and  144   b  has a layer of elastomeric foam. However, this is only an example and the feed rollers  144   a  and  144   b  are not limited to such a configuration. For example, the feed rollers  144   a  and  144   b  may be any rollers that are more pliable than the ejection rollers  132   a  and  132   b  made of rubber, and that have a lower friction coefficient with a sheet S than that of the rubber-made ejection rollers  132   a  and  133   b  with a sheet S. 
     According to the embodiments described above, the sheet post-processing device includes two feed roller pairs  144 . However, the present disclosure is not limited to such a configuration. For example, the sheet post-processing device may include one feed roller pair  144  or three or more feed roller pairs  144 . 
     Additionally, according to the embodiments described above, the sheet post-processing device includes the two feed roller pairs  144 . However, the present disclosure is not limited to such a configuration. For example, a single roller may be used as the feed mechanism. 
     Additionally, according to the embodiments described above, the sheet post-processing device includes two ejection roller pairs  132 . However, the present disclosure is not limited to such a configuration. For example, the sheet post-processing device may include one ejection roller pair  132  or three or more ejection roller pairs  132 . 
     Additionally, according to the embodiments described above, the sheet post-processing device includes two ejection roller pairs  132  for ejection of sheet S onto the first ejection tray  134 . However, the present disclosure is not limited to such a configuration. For example, the sheet post-processing device may include a single roller for ejection of sheet S onto the first ejection tray  134 . 
     In the embodiments, the feed roller pairs  144  are described as an example of the feed mechanism. However, the present disclosure is not limited such. For example, the feed mechanism may be a caterpillar mechanism having a spongy elastic member. 
     According to the embodiments described above, the feed roller pairs  144  are used alone to move a sheet pile St or a sheet S toward the regulating member  143 . However, the present disclosure is not limited to such. For example, a paddle may be used in addition to the feed roller pairs  144 . In this variation, the sheet pile St is preferably stacked such that an edge of the lowermost sheet S 1  protrudes toward the regulating member  143  beyond the edge of the uppermost sheet S 3  (see  FIG. 5 ). Stacking sheets S into a sheet pile St in this manner ensures that the lowermost sheet S 1  reaches the regulating member  143  before the uppermost sheet S 3 . After the lowermost sheet S 1  reaches the regulating member  143 , the paddle is used to move the uppermost sheet S 3  toward the regulating member  143 . Through the above operation, the edges of all of sheets S in the sheet pile St can reach the regulating member  143  and the edges of the sheets S in the sheet pile St are aligned. When a subsequently fed sheet S is further stacked on the sheet pile St, the paddle may be used to move the subsequent sheet S toward the regulating member  143  after the uppermost sheet S 3  reaches the regulating member  143 . This ensures that that the edge of the subsequent sheet S reaches the regulating member  143  and the edge of the subsequent sheet S is aligned with the edge of the sheet pile St. 
     In the embodiments described above, all sheets S printed by and ejected out of an image forming apparatus are fed to the sheet post-processing device  100 . However, the present disclosure may be used with an image forming apparatus that selectively feeds sheets S on which post-processing is requested to be performed. In this case, the main body of the image forming apparatus selectively feeds requested sheets S to the sheet post-processing device  100  out of sheets S having been printed. 
     In the embodiments described above, sheets of paper are used as sheets S. However, other types of sheets S such as resin sheets may be used as sheets S. 
     Note that the accompanying drawings schematically show the components described above. Thus, the dimensions such as thicknesses and lengths may differ from actual ones for the convenience of preparing the drawings.