Abstract:
A sheet post-processing device comprises: a processing tray; a discharge tray; and a discharge rollers pair. The discharge rollers pair is constituted by a discharge roller which contacts the uppermost surface of sheets stacked in the processing tray and a discharge roller which contacts the lowermost surface of the sheets stacked in the processing tray). The sheet post-processing device discharges a sheet from the processing tray to the discharge tray by rotating the discharge rollers pair in the forward direction, and causes the sheet to be drawn into the processing tray by rotating the discharge roller in the reverse direction in a state in which the rotation of the discharge roller is stopped.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a sheet post-processing device that performs post-processing such as a punch hole forming process and a binding process with respect to a sheet such as a paper sheet on which an image has been formed by an image forming apparatus such as a copy machine, a facsimile, or a printer, and an image forming system provided with the same. 
       BACKGROUND ART 
       [0002]    Conventionally, there is used a paper sheet post-processing device that is capable of executing a binding process of loading a plurality of paper sheets on each of which an image has been formed by an image forming apparatus such as a copy machine or a printer and binding together a bundle of the thus loaded paper sheets with a staple(s), a punch hole forming process of forming punch holes (perforations) therethrough by using a punch hole forming device, and so on. 
         [0003]    In the paper sheet post-processing device described above, in performing a binding process, it is necessary that a paper sheet bundle be loaded in an aligned manner. For example, Patent Documents 1 and 2 disclose a paper sheet post-processing device provided with a carry-in roller pair that carries in a paper sheet on a processing tray and a discharge roller pair that discharges a paper sheet from the processing tray onto a discharge tray. 
         [0004]    The discharge roller pair is composed of a discharge roll and a discharge roller that comes in pressure contact with or is separated from the discharge roll, and in a state where the discharge roller and the discharge roll are separated from each other, a paper sheet is carried in on the processing tray by the carry-in roller pair. Then, after a rear end of the paper sheet has passed through the carry-in roller pair, the discharge roller and the discharge roll are brought in pressure contact with each other and made to rotate reversely. Thus, the paper sheet is drawn in to an upstream side in a conveyance direction and comes in contact with a rear end restriction surface of the processing tray. In this manner, a paper sheet bundle on the processing tray is aligned. 
       LIST OF CITATIONS 
     Patent Literature 
       [0005]    Patent Document 1: JP-A-H09-156820 
         [0006]    Patent Document 2: JP-A-2013-224221 
       SUMMARY OF THE INVENTION 
     Technical Problem 
       [0007]    In the method described in Patent Documents 1 and 2, however, when, in a state where paper sheets are already loaded on the processing tray, a succeeding paper sheet is drawn in, the loaded paper sheets are also drawn in together with the succeeding paper sheet, which has led to a problem that an alignment property of a paper sheet bundle is decreased. 
         [0008]    Specifically, as shown in  FIG. 5 , in a case where a discharge roller pair  29  is made to rotate reversely to draw in a paper sheet P 2  on a processing tray  30 , when both of a discharge roller  29   a  and a discharge roll  29   b  that constitute the discharge roller pair  29  are made to rotate reversely, a paper sheet bundle P 1  that has been butted against a butting portion  30   a  of the processing tray  30  and thus is already aligned might also be drawn in at the same time as the paper sheet P 2 . As a result, as shown by a broken line in  FIG. 5 , the paper sheet bundle P 1  is bent, which has led to a fear that an alignment property of a paper sheet bundle is decreased. 
         [0009]    In view of the above-described problem, it is an object of the present invention to provide a sheet post-processing device that, when drawing in a sheet on a processing tray by using a discharge roller pair and aligning a sheet bundle, can prevent an alignment failure of the sheet bundle, and an image forming system provided with the same. 
       Solution to the Problem 
       [0010]    In order to achieve the above-described object, the present invention provides a sheet post-processing device that is provided with a processing tray, a discharge tray, and a discharge roller pair. The processing tray accepts and loads thereon a prescribed number of sheets. The discharge tray is disposed on a downstream side of the processing tray in a sheet conveyance direction, and onto which sheets loaded on the processing tray are discharged. The discharge roller pair is composed of a discharge roller that comes in contact with an uppermost surface of sheets loaded on the processing tray and a discharge roll that comes in contact with a lowermost surface of the sheets loaded on the processing tray. The sheet post-processing device discharges a sheet from the processing tray onto the discharge tray by forwardly rotating the discharge roller pair, and draws in a sheet on the processing tray by reversely rotating the discharge roller in a state where the discharge roll is stopped from rotating. 
       Advantageous Effects of the Invention 
       [0011]    According to a first configuration of the present invention, a sheet is drawn in on the processing tray by reversely rotating only the discharge roller in a state where the discharge roll is stopped from rotating, and thus a drawing-in force is exerted only on a sheet being newly carried in and not on a sheet bundle that has already been aligned on the processing tray. Accordingly, there is no fear that a sheet bundle that has already been aligned is drawn in together with a sheet being newly carried in and thus is bent, so that an alignment property of a sheet bundle on the processing tray can be effectively prevented from being decreased. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]    [ FIG. 1 ] is a schematic view showing an internal configuration of an image forming apparatus  100  and a paper sheet post-processing device  20  of the present invention. 
           [0013]    [ FIG. 2 ] is a partially enlarged view of a periphery of a processing tray  30  in the paper sheet post-processing device  20  shown in  FIG. 1 , which shows a state where a discharge roller  29   a  is disposed at a separated position. 
           [0014]    [ FIG. 3 ] is a partially enlarged view of the periphery of the processing tray  30  in the paper sheet post-processing device  20  shown in  FIG. 1 , which shows a state where the discharge roller  29   a  is disposed at a contact position. 
           [0015]    [ FIG. 4 ] is a side sectional view showing, in a paper sheet post-processing device of the present invention, how a succeeding paper sheet P 2  is drawn in a state where a paper sheet bundle P 1  is loaded on a processing tray  30 . 
           [0016]    [ FIG. 5 ] is a side sectional view showing, in a conventional paper sheet post-processing device, how a succeeding paper sheet P 2  is drawn in a state where a paper sheet bundle P 1  is loaded on a processing tray  30 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0017]    With reference to the appended drawings, the following describes an embodiment of the present invention. First, with reference to  FIG. 1 , a description is given of an image forming system composed of an image forming apparatus  100  and a paper sheet post-processing device  20  of the present invention.  FIG. 1  is a schematic view showing an internal configuration of the image forming apparatus  100  and the paper sheet post-processing device  20  according to the present invention. While this embodiment illustratively describes a multi-functional peripheral as one example of the image forming apparatus  100 , the paper sheet post-processing device  20  of the present invention can be joined similarly also to other types of apparatuses than a digital multi-functional peripheral, such as, for example, a laser printer, an ink-jet printer, and a facsimile apparatus. 
         [0018]    As shown in  FIG. 1 , the image forming apparatus  100  is a digital multi-functional peripheral of a so-called intra-body paper discharge type and is composed roughly of a main body housing  2   a  and an upper housing  2   b  arranged above the main body housing  2   a.  In the upper housing  2   b,  there are provided after-mentioned various types of mechanisms for reading an image of an original document as an electric signal, and an auto document feeder  3  is additionally provided above the upper housing  2   b.  On the other hand, in the main body housing  2   a,  there are provided after-mentioned various types of mechanisms for, based on the electric signal of the original document image thus read, transferring an image on a paper sheet, and the paper sheet post-processing device  20  is additionally provided in a left side portion of the main body housing  2   a.    
         [0019]    In this embodiment, the main body housing  2   a  is composed of a lower housing  2   aa  and a joint housing  2   ab  that is positioned above the lower housing  2   aa  along a right side portion and joined to the upper housing  2   b.  In the lower housing  2   aa , there are provided a paper feed portion  4  that feeds a paper sheet P, an image forming portion  6  that forms a toner image on the paper sheet P, a fixing device  7  for fixing the toner image on the paper sheet, and so on. In the joint housing  2   ab , there is provided a paper sheet discharge portion (discharge portion)  18  for conveying the paper sheet P after being subjected to fixing and discharging it from the main body housing  2   a.    
         [0020]    Furthermore, on a left side of the joint housing  2   ab  immediately below the upper housing  2   b,  an intra-body paper discharge space  16  is formed that is widely open toward a left side surface and a front. In the intra-body paper discharge space  16 , there is provided a relay unit  19  that accepts and loads thereon the paper sheet P discharged from a left side surface of the joint housing  2   ab  and, in a case of subjecting the paper sheet P to a prescribed type of post-processing, enables conveyance of the paper sheet P to the paper sheet post-processing device  20 . 
         [0021]    In the main body housing  2   a,  there are provided the paper feed portion  4  that is arranged in a lower portion, a paper sheet conveyance path  5  that is arranged laterally to and above the paper feed portion  4 , the image forming portion  6  that is arranged above the paper feed portion  4 , and a fixing portion  7  that is arranged on a downstream side of the image forming portion  6  in a paper sheet conveyance direction (a right side in  FIG. 1 ). 
         [0022]    In the paper feed portion  4 , there are provided a plurality of paper feed cassettes  4   a  that each have a separate-feed unit such as a paper feed roller provided on a downstream side in the paper sheet conveyance direction. By a rotation operation of the paper feed roller, a bundle of the paper sheets P placed in any one of the paper feed cassettes  4   a  are fed one by one from an uppermost one of the paper sheets P to the paper sheet conveyance path  5 . By using conveyance roller pairs  5   a,  the paper sheet conveyance path  5  conveys the paper sheet P fed from the paper feed portion  4  to the image forming portion  6 . 
         [0023]    Inside an apparatus main body  100 , the image forming portion  6  and the fixing portion  7  are arranged so as to be elongated in a width direction (a front-back direction, a direction orthogonal to a paper plane of  FIG. 1 ) orthogonal to the paper sheet conveyance direction. In an upper portion in the lower housing  2   aa , from a left side in  FIG. 1 , the image forming portion  6  and the fixing portion  7  are provided in this order side by side along the conveyance direction of the paper sheet P (a left-to-right direction). 
         [0024]    The image forming portion  6  forms a prescribed toner image on the paper sheet P by the electrophotographic process. The image forming portion  6  is provided with a photosensitive drum  9  that is an image carrier supported rotatably about an axis, and around the photosensitive drum  9 , there are arranged along a rotation direction thereof, a charging device  11 , an exposure device  12 , a developing device  13 , a transfer device  14 , a cleaning device  15 , and an unshown static elimination device. In the fixing portion  7 , the paper sheet P on which a toner image has been transferred at the image forming portion  6  is sandwiched between a fixing roller pair  7   a  that is composed of a heating roller and a pressing roller and thus is heated and pressed so that the unfixed toner image is fixed on the paper sheet P. 
         [0025]    In the upper housing  2   b,  an image reading portion  8  is provided. The image reading portion  8  reads image information of an original document. In a case where an original document is manually placed one by one so as to be read by the image reading portion  8 , an auto document feeder  3  is opened, and an original document is placed on a contact glass  8   a  that is provided on an upper surface of the upper housing  2   b.  In a case where an original document is automatically supplied one by one from an original document bundle so as to be read by the image reading portion  8 , the original document bundle is placed on a paper feed tray  3   a  of the auto document feeder  3  in a closed state. In this configuration, when an original document bundle is placed on the paper feed tray  3   a,  an original document is automatically and sequentially fed one by one from said original document bundle onto the contact glass  8   a.  In either case, an original document positioned on the contact glass  8   a  is irradiated with light from an unshown exposure lamp, and light reflected therefrom is guided as image light to a photoelectric conversion portion (a CCD) via an optical system such as a reflection mirror and an imaging lens (none of them is shown). 
         [0026]    The following describes a basic operation of the image forming apparatus  100  configured as above. First, a surface of the photosensitive drum  9  that rotates counterclockwise in  FIG. 1  is uniformly charged by the charging device  11 . Subsequently, based on image information read at the image reading portion  8 , a circumferential surface of the photosensitive drum  9  is irradiated with a laser beam from the exposure device  12  (a laser device or the like), so that an electrostatic latent image is formed on the surface of the photosensitive drum  9 . The electrostatic latent image is supplied with toner as a developer from the developing device  13 , and thus a toner image is formed. 
         [0027]    Next, the paper sheet P from the paper feed portion  4  passes through the paper sheet conveyance path  5  and is conveyed at prescribed timing toward the photosensitive drum  9  on which the toner image has been formed. Further, by the transfer device  14  formed of a transfer roller or the like, the toner image on the surface of the photosensitive drum  9  is transferred on the paper sheet P. Then, the paper sheet P on which the toner image has been transferred is separated from the photosensitive drum  9  and conveyed toward the fixing portion  7 . The paper sheet P is heated and pressed while passing through the fixing roller pair  7   a,  and thus the toner image is fixed. 
         [0028]    After completion of a transfer process of transferring the toner image on the paper sheet P, the photosensitive drum  9  is subjected to removal of residual toner remaining on an outer circumferential surface thereof by the cleaning device  15  and then to a static elimination process of eliminating residual charge by the static elimination device (not shown). After that, the outer circumferential surface of the photosensitive drum  9  is subjected again to a charging process by the charging device  11 , and thereafter, subsequent image formation is performed in a similar manner. 
         [0029]    The paper sheet P that has passed through the fixing device  7  is conveyed, as it is, perpendicularly upward along the paper sheet conveyance path  5  into the joint housing  2   ab . Inside the joint housing  2   ab , an upper portion of the paper sheet conveyance path  5  is branched leftward into two upper and lower conveyance paths, and the conveyance direction of the paper sheet P is switched by a switch claw  17  that is disposed at a branching portion. 
         [0030]    Inside the joint housing  2   ab , the paper sheet discharge portion  18  is provided. 
         [0031]    The paper sheet discharge portion  18  has an upper discharge roller pair  18   a  and a lower discharge roller pair  18   b  that is disposed immediately below the upper discharge roller pair  18   a,  and the paper sheet P conveyed along the paper sheet conveyance path  5  is guided to the upper conveyance path or the lower conveyance path by the switch claw  17 . 
         [0032]    When guided to the upper conveyance path by the switch claw  17 , the paper sheet P is discharged leftward from the upper discharge roller pair  18   a.  When guided to the lower conveyance path by the switch claw  17 , the paper sheet P is discharged leftward by the lower discharge roller pair  18   b.  A guiding direction of the switch claw  17  is switched by an unshown control portion. 
         [0033]    The relay unit  19  is demountably mounted to a bottom surface  16   a  of the intra-body paper discharge space  16 . In the intra-body paper discharge space  16 , a detection sensor (not shown) that detects mounting of the relay unit  19  is provided. The detection sensor is formed of a PI sensor or the like and transmits a detection result to the control portion. 
         [0034]    Furthermore, the bottom surface  16   a  has an inclined surface formed thereon, which is inclined upward toward a downstream side in a paper sheet discharge direction (a left side in  FIG. 1 ). When the relay unit  19  has been demounted from the intra-body paper discharge space  16 , the bottom surface  16   a  is used as a paper sheet discharge tray. In this case, the detection sensor detects that the relay unit  19  has not been mounted, and upon this detection result being transmitted to the control portion, the switch claw  17  guides the paper sheet P to the upper discharge roller pair  18   a.  Then, the paper sheet P, after being discharged from the upper discharge roller pair  18   a,  is discharged on the bottom surface  16   a.    
         [0035]    On the other hand, in a case where the detection sensor detects that the relay unit  19  has been mounted in the intra-body paper discharge space  16 , and this detection result is transmitted to the control portion, the switch claw  17  guides the paper sheet P to the lower discharge roller pair  18   b.  Then, after being discharged from the lower discharge roller pair  18   b,  the paper sheet P is carried into the relay unit  19 . The paper sheet P that has been carried into the relay unit  19  passes through the relay unit  19  and is carried into the paper sheet post-processing device  20 . 
         [0036]    It is also possible to display a detection result on an operation portion (not shown) so as to allow a user to switch, on an operation panel, the guiding direction in which the paper sheet P is guided. Furthermore, an upper surface portion of the relay unit  19  also has a function as a paper sheet discharge tray on which the paper sheet P discharged from the upper discharge roller pair  18   a  is placed. 
         [0037]    Inside the paper sheet post-processing device  20 , there are provided a punch hole forming device  21  that performs punch hole formation with respect to the paper sheet P that has been carried in, a processing tray  30  that loads (stacks) thereon a plurality of the paper sheets P that have been carried in, and a stapler  40  that binds a paper sheet bundle loaded on the processing tray  30  with a staple(s). On a side surface of the paper sheet post-processing device  20 , a discharge tray  50  is provided that is vertically movable to a position appropriate for discharging the paper sheet P. 
         [0038]    The punch hole forming device  21  is disposed at an upper portion in the paper sheet post-processing device  20  and forms a plurality of punch holes through the paper sheet P along either of its side end edges (a front side or a rear side of the apparatus) parallel to the conveyance direction of the paper sheet P. On an upstream side of the punch hole forming device  21  and at a substantially middle portion in a direction orthogonal to the paper sheet conveyance direction (a direction perpendicular to the paper plane of  FIG. 1 ), a carry-in detection sensor (not shown) is disposed that detects a tip end of the paper sheet P carried into the paper sheet post-processing device  20  by a paper sheet carry-in roller pair provided in the relay unit  19 . 
         [0039]    Based on detection timing at which the tip end of the paper sheet P is detected by the carry-in detection sensor, the control portion (not shown) controls driving of the paper sheet carry-in roller pair in the relay unit  19  and thereby adjusts punch hole forming positions on the paper sheet P in the conveyance direction thereof, which is conveyed to the punch hole forming device  21 . Specifically, a conveyance direction pulse adjustment value is set that is used to perform addition/subtraction to/from a reference conveyance pulse value for a period from a time when the tip end or a rear end of the paper sheet P is detected by the carry-in detection sensor to a time when the paper sheet carry-in roller pair is stopped. 
         [0040]      FIG. 2  and  FIG. 3  are each a partial sectional view of a periphery of the processing tray  30  in the paper sheet post-processing device  20 . With respect to the paper sheet conveyance direction, on a downstream side of the punch hole forming device  21  (see  FIG. 1 ), a first discharge roller pair  27  is arranged. On an upstream side of the first discharge roller pair  27 , an actuator-type paper sheet detection sensor  28  that detects passing of the paper sheet P is disposed. 
         [0041]    Moreover, below the first discharge roller pair  27 , there are provided the processing tray  30  that loads thereon, in an aligned manner, a prescribed number of the paper sheets P conveyed by the first discharge roller pair  27  and the stapler  40  (see  FIG. 1 ) that performs a binding process with respect to a bundle of the paper sheets P (paper sheet bundle) loaded on the processing tray  30 . 
         [0042]    With respect to the paper sheet conveyance direction, on a downstream side of the processing tray  30 , a second discharge roller pair  29  is arranged that discharges a paper sheet bundle from the processing tray  30  onto the discharge tray  50 . The second discharge roller pair  29  is composed of a discharge roller  29   a  that is made of rubber and is rotatable forwardly and reversely by a drive motor (not shown) and a discharge roll  29   b  that is made of resin and rotates following rotation of the discharge roller  29   a.  The discharge roller  29   a  is supported by a roller holder  31  that is swingable up and down about a pivot shaft  31   a  as a fulcrum. 
         [0043]    Above the processing tray  30  and on a downstream side of the first discharge roller pair  27  (a left side in  FIG. 2 ), there is arranged a tapping member  33  for tapping, in a processing tray  30  direction, the paper sheet P carried in by the first discharge roller pair  27  so that the paper sheet P is aligned in line with a tray surface. The processing tray  30  is provided so as to be inclined downward toward a rear end side of the paper sheet P loaded thereon (a downstream side with respect to a direction in which the paper sheet is drawn in on the processing tray  30 , namely, the right side in  FIG. 2 ). The second discharge roller pair  29  rotates reversely, and thus the paper sheet P is drawn in from the rear end side on the processing tray  30 , and the rear end of the paper sheet P comes in contact with the butting portion  30   a.  Thus, on the processing tray  30 , a bundle of paper sheets is loaded in a state where rear ends of the paper sheets are aligned. Furthermore, on the processing tray  30 , there is provided a pair of side end alignment cursors  60  that aligns a paper sheet bundle loaded on the processing tray  30  in a width direction (a direction perpendicular to a paper plane of  FIG. 2 ). 
         [0044]    The stapler  40  is movable in the paper sheet width direction orthogonal to the conveyance direction by a movement mechanism (not shown) and, depending on how a binding process is to be performed, moves to a prescribed position along a lower end portion of the processing tray  30 . 
         [0045]    Next, a description is given of an operation of the paper sheet post-processing device  20 . When the paper sheet P (shown by a broken line in  FIG. 2  and  FIG. 3 ) that has been subjected to an image forming process at the image forming apparatus  100  is carried in, in a case where an instruction has been given to perform punch hole formation, by the punch hole forming device  21 , punch holes are formed at prescribed positions on the paper sheet P conveyed (for example, two positions along its side end edge on the front side of the apparatus). In a case where no instruction has been given to perform punch hole formation, the paper sheet P passes, as it is, through the punch hole forming device  21 . 
         [0046]    Then, the paper sheet P is conveyed further to a downstream side by the first discharge roller pair  27 . At this time, as shown in  FIG. 2 , the roller holder  31  has swung upward, so that the discharge roller  29   a  is disposed at a position (retracted position) away from the discharge roll  29   b.  Thus, the paper sheet P conveyed by the first discharge roller pair  27  passes through a gap between the discharge roller  29   a  and the discharge roll  29   b  to protrude to the discharge tray  50 . 
         [0047]    At timing at which the rear end of the paper sheet P has passed through the first discharge roller pair  27 , the roller holder  31  is made to swing downward so that the discharge roller  29   a  is disposed at a position (contact position) where the discharge roller  29   a  comes in contact with the discharge roll  29   b.  After that, the tapping member  33  is driven to align the paper sheet P in line with the processing tray  30 . In this state, the discharge roller  29   a  is made to rotate reversely (a counterclockwise direction in  FIG. 3 ), and thus the paper sheet P is drawn in along the processing tray  30 , and the rear ends of the paper sheets P thus drawn in are aligned by the butting portion  30   a.  The butting portion  30   a  is not formed continuously over an entire region in the paper sheet width direction but formed to be partially cut out. At this time, an upper portion of the paper sheet P is in a state of being nipped by the second discharge roller pair  29 , with a tip end thereof protruding from the second discharge roller pair  29  to above the discharge tray  50 . In drawing in the paper sheet P along the processing tray  30 , in order to prevent the paper sheet P from being drawn in to an extent more than necessary, the paper sheet P is nipped in a state where the discharge roller  29   a  is brought to pressure contact with the discharge roll  29   b  by using only a self-weight of the roller holder  31 . 
         [0048]    Then, when acceptance of a bundle of the paper sheets P is completed, the stapler  40  is made to move to cut-out positions of the butting portion  30   a,  and rear ends of the paper sheet bundle are inserted into a staple portion  40   a  where a binding process with respect to the paper sheet bundle is performed. After the binding process with respect to the paper sheet bundle has been performed at the staple portion  40   a,  the second discharge roller pair  29  is made to rotate forwardly (an arrow direction in  FIG. 3 ), and thus the paper sheet bundle is conveyed upward along the processing tray  30  to be discharged onto the discharge tray  50 . In discharging a paper sheet bundle onto the discharge tray  50 , the discharge roller  29   a  is brought to pressure contact with the discharge roll  29   b  by, besides using the self-weight of the roller holder  31 , biasing the roller holder  31  downward using a biasing member such as a spring. Thus, a paper sheet bundle is nipped by a force greater than that in a case of drawing in the paper sheet P, so that the paper sheet bundle can be reliably discharged onto the discharge tray  50 . 
         [0049]    Furthermore, in a case where an instruction has been given to perform shift-discharge, in discharging a paper sheet bundle onto the discharge tray  50  by driving the second discharge roller pair  29 , first, the roller holder  31  is made to move to the retracted position. After that, the side end alignment cursors  60  are disposed at a position (reference position) at which the paper sheet P has been accepted or a position (shifted position) that is shifted from the reference position by a prescribed amount in a direction (paper sheet width direction) orthogonal to the discharge direction. Then, the roller holder  31  is made to move to the contact position so that the paper sheet is discharged. Thus, a paper sheet bundle is discharged alternately to a reference discharge position on the discharge tray  50  and to a shifted discharge position that is shifted from the reference discharge position by a prescribed amount in the direction (paper sheet width direction) orthogonal to the discharge direction, so that when discharged onto the discharge tray  50  (see  FIG. 2 ), paper sheet bundles are sorted by being loaded so as to be staggered in the paper sheet width direction. 
         [0050]    In the paper sheet post-processing device  20  of this embodiment, the discharge roll  29   b  that is a component of the second discharge roller pair  29  is configured to be rotatable only in a forward direction (the counterclockwise direction in  FIG. 2  and  FIG. 3 ) in which the paper sheet P is discharged onto the discharge tray  50 . 
         [0051]    By this configuration, as shown in  FIG. 4 , in drawing in a paper sheet P 2  on the processing tray  30  by using the second discharge roller pair  29 , in a state where the discharge roll  29   b  is stopped from rotating, only the discharge roller  29   a  is made to rotate reversely. As a result, a drawing-in force is exerted only on the paper sheet P 2  being newly carried in and not on a paper sheet bundle P 1  that has been butted against the butting portion  30   a  of the processing tray  30  and thus is already aligned. Accordingly, there is no fear that the paper sheet bundle P 1  is drawn in together with the paper sheet P 2  and thus is bent, so that an alignment property of a paper sheet bundle on the processing tray  30  can be effectively prevented from being decreased. 
         [0052]    As a method for configuring the discharge roll  29   b  to be rotatable only in a forward direction, for example, a one-way mechanism that is rotatable only in one direction, such as a one-way gear or a one-way clutch, is built into a rotary shaft of the discharge roll  29   b.    
         [0053]    Furthermore, the roller holder  31  supporting the discharge roller  29   a  is configured to be swingable, and thus the discharge roller  29   a  can be easily switched in its position between the position (retracted position) away from the discharge roll  29   b  and the position (contact position) where the discharge roller  29   a  comes in contact with the discharge roll  29   b.    
         [0054]    Other than the above, the present invention is not limited to the above-described embodiment, and various modifications thereto are possible without departing from the spirit of the present invention. For example, while the above-described embodiment has been described by using, as an example, a configuration in which the image forming apparatus  100  and the paper sheet post-processing device  20  are directly connected to each other, the present invention is applicable also to a configuration in which an insertion device that inserts interleaving paper is installed between the image forming apparatus  100  and the paper sheet post-processing device  20 . 
         [0055]    The present invention is usable in a sheet post-processing device that loads sheets in an aligned manner on a processing tray by using a discharge roller pair. The use of the present invention can provide a sheet post-processing device that, in drawing in a sheet on a processing tray by using a discharge roller pair and aligning a sheet bundle, can prevent an alignment failure of the sheet bundle, and an image forming system provided with the same.