Patent Publication Number: US-9409735-B2

Title: Sheet processing apparatus and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This disclosure relates to a sheet processing apparatus and an image forming apparatus. 
     2. Description of the Related Art 
     In the related art, an image forming apparatus such as a copier, a printer, a facsimile, and a multi-function printer includes a type provided with a sheet processing apparatus in a main body of the image forming apparatus and configured to perform processing such as binding or the like on sheets discharged from the main body of the image forming apparatus. Example of the sheet processing apparatus as described above includes a type configured to discharge a sheet discharged from the main body of the image forming apparatus once into a process tray, align the sheet with a sheet already stacked on the process tray, bind the sheets if needed in the process tray, and then discharge the processed sheets on a stacking tray as described in Japanese Patent Laid-Open No. 2003-128315. 
       FIGS. 13A and 13B  are drawings illustrating a configuration of the sheet processing apparatus of the related art as described above. As illustrated in  FIGS. 13A and 13B , a trailing end stopper  108  configured to stop and position the sheet(s) P is provided at an end of an intermediate processing tray  107 . The sheet P discharged onto the intermediate processing tray  107  by a sheet discharge roller  103  is conveyed by an endless knurled belt  1161  configured to be rotated by the sheet discharge roller  103 , and aligned at trailing ends thereof by abutting against the trailing end stopper  108 . 
     The shape of the knurled belt  1161  is changed by an moving roller X. 
     That is, as illustrated in  FIG. 13A , if there is no sheet bundle on the intermediate processing tray  107 , the moving roller X does not move. In this case, the knurled belt  1161  is not deformed and rotates in a state of being in contact with the intermediate processing tray  107 . In contrast, when a plurality of sheets P are stacked on the intermediate processing tray, the moving roller X moves to deform the shape of the knurled belt  1161  as illustrated in  FIG. 13B , so that a pressure as constant as possible is applied from the knurled belt  1161  to a sheet bundle PA. 
     In the sheet processing apparatus of the related art as described above, when the knurled belt  1161  is deformed, the distance between the sheet discharge roller  103  and the moving roller X changes. Therefore, tensile force of the knurled belt  1161  is increased in comparison with the case where the number of stacked sheets is small. 
     When the tensile force is increased, a conveying force of the knurled belt  1161  increases correspondingly. When the conveying force is increased, the sheet P in abutment with the trailing end stopper  108  may be bent between the knurled belt  1161  and the trailing end stopper  108  and, consequently, alignment of the sheet may be impaired. 
     As a countermeasure, a method of controlling the amount of movement of the moving roller X by considering a change in tensile force of the knurled belt  1161  is conceivable. However, if the hardness of the knurled belt  1161  is changed by a change in atmospheric temperature or time degradation, a deviation occurs between the amount of movement of the moving roller X and the conveying force. This deviation is increased with increase in amount of movement. Accordingly, when an actual conveying force is smaller than a desired conveying force, the sheet P does not reach the trailing end stopper  108 . In contrast, when the actual conveying force is larger than the desired conveying force, the sheet P is bent between the knurled belt  1161  and the trailing end stopper  108  and, consequently, alignment is impaired. 
     SUMMARY OF THE INVENTION 
     According an aspect of the present invention, a sheet processing apparatus including a sheet stacking portion on which a sheet is stacked, an endless belt configured to convey the sheet by coming in contact with an upper surface of the sheet stacked on the sheet stacking portion, an aligning portion against which the sheet conveyed by the endless belt is abutted and aligning a position in a sheet conveying direction of the sheet, a drive rotating member configured to contact with an inner peripheral surface of the endless belt, a shaft extending in a direction orthogonal to the sheet conveying direction, a supporting portion configured to be swingable about the shaft, rotatably supporting the drive rotating member, and supporting the endless belt through the drive rotating member, and a lifting portion configured to raise and lower the endless belt by swinging the supporting portion. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing illustrating a configuration of an image forming apparatus provided with a sheet processing apparatus of a first embodiment. 
         FIG. 2A  is a schematic drawing illustrating a state of a finisher with a sheet conveyed by a sheet discharge roller. 
         FIG. 2B  is a schematic drawing illustrating a state of the finisher with a sheet discharged into an intermediate processing tray. 
         FIG. 3  is a control block diagram of the image forming apparatus. 
         FIG. 4  is a control block diagram of the finisher. 
         FIG. 5A  is an explanatory drawing illustrating a sheet binding operation of the finisher. 
         FIG. 5B  is a schematic drawing illustrating a state of the finisher with a bound sheet bundle being discharged to a stacking tray. 
         FIG. 5C  is a schematic drawing illustrating a state of the finisher with the sheet bundle discharged to the stacking tray. 
         FIG. 6A  is a perspective view illustrating a configuration of a knurled belt portion provided on the finisher. 
         FIG. 6B  is an enlarged view of the knurled belt portion illustrated in  FIG. 6A . 
         FIG. 7A  is a side view illustrating a configuration of the knurled belt portion. 
         FIG. 7B  is a side view illustrating a gear mechanism of the knurled belt portion illustrated in  FIG. 7A . 
         FIG. 8A  is a schematic view illustrating a state of the knurled belt portion with a knurled belt moved downward to a large extent. 
         FIG. 8B  is a schematic drawing illustrating the state of the knurled belt portion with the knurled belt lowered to a medium extent. 
         FIG. 8C  is a schematic drawing illustrating the state of the knurled belt portion with the knurled belt lowered to a small extent. 
         FIG. 9  is a flowchart for explaining a sheet processing operation of the finisher; 
         FIG. 10  is a schematic drawing illustrating a configuration of the knurled belt portion provided in a sheet processing apparatus of a second embodiment. 
         FIG. 11A  is a drawing illustrating a configuration of the knurled belt portion of the second embodiment. 
         FIG. 11B  is a side view illustrating a gear mechanism of the knurled belt portion illustrated in  FIG. 11A . 
         FIG. 12A  is a schematic view illustrating a state of the knurled belt portion of the second embodiment with a knurled belt lowered to a large extent. 
         FIG. 12B  is a schematic drawing illustrating the state of the knurled belt portion of the second embodiment with the knurled belt lowered to a medium extent. 
         FIG. 12C  is a schematic drawing illustrating the state of the knurled belt portion of the second embodiment with the knurled belt lowered to a small extent. 
         FIG. 13A  is a schematic drawing illustrating a knurled belt of a sheet processing apparatus of the related art. 
         FIG. 13B  is a schematic drawing illustrating a state in which the knurled belt illustrated in  FIG. 13A  is deformed. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.  FIG. 1  is a drawing illustrating a configuration of an image forming apparatus provided with a sheet processing apparatus of a first embodiment. In  FIG. 1 , reference numeral  900  denotes an image forming apparatus, reference numeral  900 A denotes a main body of the image forming apparatus (hereinafter referred to as apparatus main body), and reference numeral  900 B denotes an image forming portion configured to form image on a sheet. Reference numeral  950  denotes an image reading apparatus provided on the top of the apparatus main body  900 A and provided with a document feeder  950 A, and reference numeral  100  denotes a finisher, i.e., a sheet processing apparatus, arranged between the upper surface of the apparatus main body  900 A and an image reading apparatus  950 . 
     Here, the image forming portion  900 B includes photoconductive drums (a) through (d) configured to form toner images in four colors, namely, yellow, magenta, cyan, and black, and an exposing unit  906  configured to radiate a laser beam on the basis of image information and form electrostatic latent images on the photoconductive drums. The photoconductive drums (a) through (d) are driven by a motor, not illustrated. Each photoconductive drum is provided with a primary charger, a developing unit and a transfer charger arranged in the periphery thereof and is unitized with them as process cartridges  901   a  through  901   d.    
     The image forming portion  900 B includes an intermediate transfer belt  902  driven and rotated in a direction indicated by an arrow, and a secondary transfer portion  903  configured to transfer a full-color image formed on the intermediate transfer belt  902  in sequence to a sheet P. By applying a transfer bias to the intermediate transfer belt  902  by transfer chargers  902   a  through  902   d , the respective color toner images on the photoconductive drums are sequentially transferred to the intermediate transfer belt  902  in a superimposed manner. Accordingly, a full-color image is formed on the intermediate transfer belt. 
     The secondary transfer portion  903  includes a secondary transfer counter roller  903   b  configured to support the intermediate transfer belt  902  and a secondary transfer roller  903   a  configured to abut against the secondary transfer counter roller  903   b  through the intermediate transfer belt  902 . In  FIG. 1 , reference numeral  909  denotes a registration roller, reference numeral  904  denotes a sheet feed cassette, reference numeral  908  denotes a pickup roller configured to feed the sheet P stored in the sheet feed cassette  904 . 
     Next, an image forming operation of the image forming apparatus  900  having the above-described configuration will be described. When the image forming operation is started, first of all, the exposing unit  906  radiates a laser beam on the basis of image information from a personal computer or the like, not illustrated, and exposes surfaces of the photoconductive drums (a) through (d), the photoconductive drums (a) through (d) being uniformly charged to predetermined polarity and potential in sequence, and forms electrostatic latent images on the photoconductive drums (a) through (d) respectively. Subsequently, the electrostatic latent images are developed and visualized by toner. 
     For example, the photoconductive drum (a) is irradiated with a laser beam on the basis of an image signal having a yellow color component of an document via a polygon mirror or the like of the exposing unit  906  to form an electrostatic latent image of yellow on the photoconductive drum (a). The electrostatic latent image of yellow is developed by yellow toner from a developing unit and hence is visualized as a yellow toner image. Subsequently, the toner image arrives at a primary transfer portion where the photoconductive drum (a) and the intermediate transfer belt  902  come into contact with each other in association with the rotation of the photoconductive drum (a). When the toner image arrives at the first transfer portion, the yellow toner image on the photoconductive drum (a) is transferred to the intermediate transfer belt  902  by a primary transfer bias applied to the transfer charger  902   a  (primary transfer). 
     Subsequently, when the portion of the intermediate transfer belt  902  carrying the yellow toner image moves, a magenta toner image formed on the photoconductive drum (b) in the same manner as describe above by this time is transferred to the intermediate transfer belt  902  over the yellow toner image. In the same manner, as the intermediate transfer belt  902  moves, a cyan toner image and a black toner image are transferred over the yellow toner image and the magenta toner image in a superimposed manner at respective primary transfer portions. Accordingly, a full-color toner image is formed on the intermediate transfer belt  902 . 
     In parallel to the toner image forming operation, the sheets P stored in the sheet feed cassette  904  are fed by the pickup roller  908  one by one. Next, the sheet P arrives at a registration roller  909  and is conveyed to the secondary transfer portion  903  at timing adjusted by registration roller  909  with the toner image. Subsequently, the toner image of four colors on the intermediate transfer belt  902  is transferred at once to the sheet P by the secondary transfer bias applied to the secondary transfer roller  903   a , i.e., the transfer portion, in the secondary transfer portion  903  (secondary transfer). 
     Subsequently, the sheet P having the toner image transferred thereto is conveyed from the secondary transfer portion  903  to a fixing portion  905  while being guided by a conveyance guide  920  and receives heat and pressure so that the image is fixed when the sheet p passes through the fixing portion  905 . Subsequently, the sheet P having the image fixed thereto passes through a discharge passage  921  provided on the downstream of the fixing portion  905 , and then is discharged by a discharge roller pair  918 , and is conveyed to the finisher  100 . 
     The finisher  100  receives the sheet P discharged from the apparatus main body  900 A in sequence as illustrated in  FIGS. 2A and 2B , and performs a process of aligning and bundling a plurality of received sheets into one bundle and a process of binding the bundled sheet bundle at upstream end in a sheet discharge direction (hereinafter, referred to as “trailing end”). As illustrated in  FIGS. 5A through 5C , the finisher  100  is provided with a processing portion  139  configured to perform binding as needed and discharge and stack the sheet bundle on a stacking tray  114 . The processing portion  139  includes an intermediate processing tray  107  as a sheet stacking portion configured to stack the sheet to be bound and a binding portion  100 A provided with a stapler  110  configured to bind (staple) the sheets stacked on the intermediate processing tray  107  and a staple-less binding portion, not illustrated. 
     The intermediate processing tray  107  is provided with front and back aligning plates  109   a  and  109   b  that regulate (align) both side end positions in the width direction (the depth direction) of the sheet conveyed into the intermediate processing tray  107  from a direction orthogonal to the depth direction of the apparatus main body  900 A. 
     The front and back aligning plates  109   a  and  109   b  as the side end aligning portion configured to align the side end positions in the width direction of the sheet stacked in the intermediate processing tray  107  are driven by an alignment motor M 253  illustrated in  FIG. 4  described later, and move in the width direction. 
     The front and back aligning plates  109   a  and  109   b  are normally moved to a receiving position where the sheet is received by the alignment motor M 253  driven on the basis of a detection signal detected by an alignment HP sensor, not illustrated. When regulating the both side end positions of the sheet stacked on the intermediate processing tray  107 , the alignment motor M 253  is driven to move the front and back aligning plates  109   a  and  109   b  along the width direction into abutment with the both side ends of the sheets stacked on the intermediate processing tray  107 . 
     A take-in paddle  106  and a knurled belt portion  116  are arranged above the intermediate processing tray  107 . The take-in paddle  106  is configured to be moved downward by driving of the puddle lifting motor M 252  illustrated in  FIG. 4  descried later when the sheet is discharged to the intermediate processing tray  107 , and rotates counterclockwise at the right timing by a paddle motor, not illustrated. Accordingly, the sheet P is conveyed toward the knurled belt portion  116 . The take-in paddle  106  is configured to be moved upward to a HP (home position) not disturbing the discharged sheet by reverse driving of the puddle lifting motor M 252  on the basis of the detection information detected by the puddle HP sensor S 243  before the sheet is conveyed to the processing portion  139 . 
     The knurled belt portion  116  includes a knurled belt  1161 , i.e., an endless sheet conveyance portion (endless belt), rotated by a conveyance motor M 250  illustrated in  FIG. 4  and described later, and configured to convey the sheet stacked in the intermediate processing tray  107  in contact with the upper surface thereof. When the sheet P is conveyed by the take-in paddle  106 , the sheet P is drawn by the knurled belt  1161 , is conveyed toward the trailing end stopper  108  as an aligning portion configured to align the position of the sheet P in the sheet conveying direction, and is aligned with the sheets already stacked on the intermediate processing tray  107  by being abutted against the trailing end stopper  108 . In the present embodiment, the take-in paddle  106 , the knurled belt portion  116 , the trailing end stopper  108 , and the front and back aligning plates  109   a  and  109   b  constitute an aligning portion  130  configured to align the sheet stacked on the intermediate processing tray  107 . 
     In  FIGS. 2A and 2B , reference numeral  112  denotes a trailing end assist. 
     The trailing end assist  112  is moved from a position not interfering with the movement of the stapler  110  to a receiving position where the sheet is received by an assist motor M 254  driven on the basis of a detection signal from an assist HP sensor S 244  described later and illustrated in  FIG. 4 . The trailing end assist  112  discharges the sheet bundle into the stacking tray  114  after the sheet bundle has been bound as described later. 
     The finisher  100  is provided with an inlet roller  101  and a sheet discharge roller  103  configured to take the sheet into the apparatus, and the sheet P discharged from the apparatus main body  900 A is delivered to the inlet roller  101 . 
     At this time, the sheet delivering timing is detected by an inlet port sensor S 240  simultaneously. The sheet P delivered to the inlet roller  101  is discharged to the intermediate processing tray  107  in sequence by the sheet discharge roller  103 , i.e., a sheet discharge portion, and subsequently, is brought into abutment with the trailing end stopper  108  by returning portion such as the take-in paddle  106  or the knurled belt  1161 . Accordingly, alignment of the sheet P in the sheet conveying direction is performed and an aligned sheet bundle is formed. 
     In  FIGS. 2A and 2B , reference numeral  105  denotes a trailing end dropper, and the trailing end dropper  105  is pushed upward by the sheet P passing through the sheet discharge roller  103  as illustrated in  FIG. 2A . When the sheet P passes through the sheet discharge roller  103 , the trailing end dropper  105  drops with its own weight as illustrated in  FIG. 2B , and pushes the trailing end of the sheet P downward from above. 
     Reference numeral  104  denotes a destaticizing needle, and reference numeral  115  denotes a bundle holder. The bundle holder  115  presses the sheet bundle stacked on the stacking tray  114  by being rotated by a bundle holding motor M 255  described later and illustrated in  FIG. 4 . Reference sign S 242  denotes a tray lower limit sensor, and reference sign S 245  denotes a bundle holder HP sensor. Reference sign S 241  is a tray HP sensor, and when the sheet bundle blocks light to the tray HP sensor S 241 , the tray lifting motor M 251  illustrated in  FIG. 4  moves the stacking tray  114  downward until the tray HP sensor S 241  is brought into a light-transmitting state, whereby the position of the sheet plane is fixed. 
       FIG. 3  is a control block diagram of the image forming apparatus  900 . In  FIG. 3 , reference numeral  200  denotes a CPU circuit portion, i.e., a control portion, arranged at a predetermined position in the apparatus main body  900 A as illustrated in  FIG. 1 , and configured to control the apparatus main body  900 A and the finisher  100 . The CPU circuit portion  200  includes a CPU  201 , a ROM  202  having a control program or the like stored therein, and a RAM  203  known as an area for temporarily holding control data, and a work area for computation in associated with the control. 
     In  FIG. 3 , reference numeral  209  denotes an external interface between the image forming apparatus  900  and an external PC (computer)  208 . Upon reception of print data from the external PC  208 , the external interface  209  expands the data into a bitmap image and outputs the bitmap image to in an image signal control portion  206  as image data. 
     The image signal control portion  206  outputs the data to a printer control portion  207 , and the printer control portion  207  outputs the data from the image signal control portion  206  to an exposure control portion, not illustrated. It is noted that an image of the document read by an image sensor, not illustrated, provided in the image reading apparatus  950  is output from an image reader control portion  205  to the image signal control portion  206 , and the image signal control portion  206  outputs the image output to the printer control portion  207 . 
     An operating portion  210  includes a plurality of keys used for setting respective functions relating to image formation, a display portion configured to display a set state, and the like. Key signals corresponding to an operation of respective keys by a user are output to the CPU circuit portion  200 , and on the basis of the signal from the CPU circuit portion  200 , corresponding information is displayed on the display portion. 
     The CPU circuit portion  200  is configured to control the image signal control portion  206  according to the control program stored in the ROM  202  and the setting of the operating portion  210 , and controls the document feeder  950 A (see  FIG. 1 ) through a DF (document feeder) control portion  204 . The CPU circuit portion  200  also controls the image reading apparatus  950  (see  FIG. 1 ) through the image reader control portion  205 , the image forming portion  900 B (see  FIG. 1 ) through the printer control portion  207 , and the finisher  100  through a finisher control portion  220 , respectively. 
     In the present embodiment, the finisher control portion  220  as a control portion is mounted on the finisher  100 , and performs drive control of the finisher  100  by sending and receiving information with the CPU circuit portion  200 . It is also possible to dispose the finisher control portion  220  on the apparatus main body side integrally with the CPU circuit portion  200 , and control the finisher  100  directly from the apparatus main body side. 
       FIG. 4  is a control block diagram of the finisher  100  of the present embodiment. 
     The finisher control portion  220  includes a CPU (microcomputer)  221 , a ROM  222 , and a RAM  223 . The finisher control portion  220  exchanges data by communicating with the CPU circuit portion  200  through a communication IC  224 , executes respective programs stored in the ROM  222  on the basis of an instruction from the CPU circuit portion  200 , and controls driving of the finisher  100 . 
     The finisher control portion  220  drives the conveyance motor M 250 , the tray lifting motor M 251 , the puddle lifting motor M 252 , the alignment motor M 253 , the assist motor M 254 , the bundle holding motor M 255 , and a STP motor M 256  through a driver  225 . The finisher control portion  220  drives a staple-less binding motor M  257  and a knurled motor M 258  through the driver  225 . 
     The inlet port sensor S 240 , a sheet discharge sensor S 246 , the tray HP sensor S 241 , the tray lower limit sensor S 242 , the puddle HP sensor S 243 , the assist HP sensor S 244 , and the bundle holder HP sensor S 245  are connected to the finisher control portion  220 . The sheet discharge sensor S 246 , a knurled belt HP sensor S 247 , and a counter CT configured to count the number of sheets stacked on the intermediate processing tray  107  are connected to the finisher control portion  220 . The finisher control portion  220  drives the alignment motor M 253 , the knurled motor M 258 , and the like on the basis of detection signals from the respective sensors described above. 
     Subsequently, the sheet binding operation of the finisher  100  according to the present embodiment will be described. The sheet P discharged from the image forming apparatus  900  is delivered to the inlet roller  101  driven by the conveyance motor M 250  as illustrated in  FIG. 2A  described above. At this time, the sheet delivering timing is detected from the leading end of the sheet P by the inlet port sensor S 240  simultaneously. 
     Subsequently, the sheet P delivered to the inlet roller  101  is delivered in turn from the inlet roller  101  to the sheet discharge roller  103 , and is conveyed while the leading end portion lifts the trailing end dropper  105 . Simultaneously, the sheet P is discharged into the intermediate processing tray  107  while being destaticized by the destaticizing needle  104 . The sheet P discharged into the intermediate processing tray  107  by the sheet discharge roller  103  is held by the weight of the trailing end dropper  105  from above, so that the time required for the trailing end of the sheet P to drop onto the intermediate processing tray  107  is reduced. 
     Subsequently, the finisher control portion  220  performs control relating to the sheet discharged to the intermediate processing tray  107  on the basis of a detection signal of the trailing end of the sheet P detected by the sheet discharge sensor S 246 . 
     That is, as illustrated in  FIG. 2B  described above, the puddle lifting motor M 252  is driven to lower the take-in paddle  106  toward the intermediate processing tray  107  and bring the paddle  106  into contact with the sheet P. At this time, the take-in paddle  106  is rotated counterclockwise by the conveyance motor M 250 . Therefore, the sheet P is conveyed rightward in the drawing toward the trailing end stopper  108  by the take-in paddle  106  and then the trailing end of the sheet P is delivered to the knurled belt  1161 . 
     When the trailing end of the sheet P is delivered to the knurled belt  1161 , the puddle lifting motor M 252  is driven in the reverse direction to cause the take-in paddle  106  to move upward. When the puddle HP sensor S 243  detects that the take-in paddle  106  arrives at the HP, the finisher control portion  220  stops driving of the puddle lifting motor M 252 . 
     Subsequently, the sheet P delivered to the knurled belt  1161  is drawn by the knurled belt  1161 , and the trailing end abuts against the trailing end stopper  108 . 
     After the trailing end of the sheet P has brought into abutment with the trailing end stopper  108 , the knurled belt  1161  rotates while slipping with respect to the sheet P, so that the sheet P is constantly biased toward the trailing end stopper  108 . With this slipping conveyance, skewing of the sheet P abutting against the trailing end stopper  108  may be corrected. 
     Subsequently, after the sheet P has brought into abutment with the trailing end stopper  108  in this manner, the finisher control portion  220  drives the alignment motor M 253  to move the aligning plate  109  in the width direction of the sheet P, and align the position in the width direction of the sheet P. By performing a series of operations described above for a predetermined number of sheets to be bound repeatedly, the sheet bundle PA aligned on the intermediate processing tray  107  as illustrated in  FIG. 5A  is formed. 
     Subsequently, after the aligning operation has been performed, if the binding mode is selected, binding is performed by the binding portion. That is, in the case where binding is performed on the sheet bundle with a staple, the sheet bundle is bound by driving the STP motor M 256  that drives the stapler  110 . In the case where the staple-less binding is performed on the sheet bundle, the sheet bundle is bound by driving the staple-less binding motor M  257  configured to drive the staple-less binding portion, not illustrated. 
     Subsequently, as illustrated in  FIG. 5B , the trailing end of the sheet bundle PA is pushed by the trailing end assist  112  and a discharge claw  113  which are the sheet discharge portion and driven synchronously by the assist motor M 254 , and the sheet bundle PA on the intermediate processing tray  107  is discharged onto the stacking tray  114  in the form of a bundle. 
     Subsequently, as illustrated in  FIG. 5C , in order to prevent the sheet bundle PA stacked on the stacking tray  114  from being pushed out in the direction of conveyance by a sheet bundle discharged subsequently, the bundle holder  115  rotates counterclockwise to hold the trailing end portion of the sheet bundle PA. If the sheet bundle PA blocks light to the tray HP sensor S 241  after the bundle holding operation by the bundle holder  115  has completed, the tray lifting motor M 251  moves the stacking tray  114  downward until the tray HP sensor S 241  is brought into a light-transmitting state, whereby the position of the sheet plane is determined. By performing a series of operations described above repeatedly, the required number of the sheet bundles PA may be discharged onto the stacking tray  114 . 
     It is noted that if the stacking tray  114  is moved downward and blocks light toward the tray lower limit sensor S 242  during the operations, the full of the stacking tray  114  is detected and the finisher control portion  220  notifies the full of the stacking tray  114  to the CPU circuit portion  200  of the image forming apparatus  900 . The CPU circuit portion  200  stops formation of the image when the full of the stacking tray  114  is notified. Subsequently, when the sheet bundle on the stacking tray  114  are removed, the stacking tray  114  moves upward until blocking light to the tray HP sensor S 241  and then moves downward to bring the tray HP sensor S 241  into a light-transmitting state, whereby the sheet plane of the stacking tray  114  is determined again. Accordingly, image formation of the image forming apparatus  900  is restarted. 
       FIGS. 6A and 6B  and  FIGS. 7A and 7B  are drawings illustrating a configuration of the knurled belt portion  116  of the present embodiment. As illustrated in  FIGS. 6A and 6B , the knurled belt portion  116  includes the knurled belts  1161  and holders  11612  configured to hold the knurled belts  1161 . Although there are two sets of the knurled belts and members, e.g., the holder  11612 , a frame  11610 , first through third gears  1162  through  1164 , associated with the knurled belt, the following description will be given for one set of those two sets for the sake of simplicity of the description, hereinafter. The knurled belt portion  116  also includes first through third gears  1162  through  1164  arranged inside the knurled belt  1161  and a driven roller  1165  opposing the first gear  1162  and configured to nip the knurled belt  1161  with the first gear  1162  as illustrated in  FIG. 7B . 
     The knurled belt portion  116  further includes a frame  11610  illustrated in  FIG. 7A  configured to hold rotation shafts  1166 ,  1167 , and  1169  of the first and second gears  1162  and  1163  and the driven roller  1165 . A rotation shaft  1168  of the third gear (first drive force transmitting rotating member)  1164  is provided inside the knurled belt  1161  and arranged in a direction orthogonal to the sheet conveying direction of the knurled belt  1161  in parallel to the intermediate processing tray  107 . The rotation shaft  1168  is rotatably supported by the frame  11610 . 
     As described later, when the knurled belt  1161  is raised, the frame  11610 , i.e. a supporting portion, configured to rotatably support the second gear (second drive force transmitting rotating member)  1163  and the driven roller  1165  swings about the rotation shaft  1168  of the third gear  1164  as a supporting point. That is, the rotation shaft  1168  of the third gear  1164  serves as a swinging shaft (lifting shaft) of the frame  11610  provided above the intermediate processing tray  107  so as to be rotatable (so as to be raised and lowered), and the third gear  1164  is provided on the swinging shaft of the frame  11610 . 
     The rotation shaft  1168  of the third gear  1164  is rotated upon reception of a drive force from the conveyance motor M 250  illustrated in  FIG. 4  described above. This rotation is transmitted to the first gears  1162  configured to nip the knurled belt  1161  with the driven roller  1165  through the third and second gears  1164  and  1163  as a drive transmission portion. The first gear  1162  as a drive rotating member and the third gear  1164  as an auxiliary rotating member are in contact with an inner peripheral surface of the knurled belt  1161  and rotatably support the knurled belt  1161 . Accordingly, when the conveyance motor M 250 , i.e., a shaft drive portion, is driven and the first gear  1162  and the third gear  1164  are rotated, the knurled belt  1161  rotates correspondingly. 
     In the embodiment, the first gear  1162  and the driven roller  1165  as a driven rotating member configured to nip the knurled belt  1161  with the first gear  1162  constitute a rotating portion  116 A configured to rotate the knurled belt  1161 . The first, second and third gears  1162 ,  1163  and  1164  are configured to rotate at the same velocity. Accordingly, the knurled belt  1161  moves between the first gear  1162  and the third gear  1164  while maintaining a constant tensile force without being tensed nor sagged. 
     In the embodiment, the knurled belt portion  116  includes two sets of the first through third gears  1162  through  1164  corresponding to two knurled belts  1161  as describe above and each set of gears is provided at predetermined interval on the rotation shafts  1166 ,  1167 , and  1168 . A retainer  1161   a  is provided at a widthwise center between the sets of gears in the width direction orthogonal to the direction of rotation of the knurled belt  1161 . Retention of the knurled belt  1161  is achieved by positioning the retainer  1161   a  between the two sets of the first through third gears  1162  to  1164 . 
     The holder  11612  is fixed to a holder shaft  11613  configured to driven by the knurled motor M 258  capable of rotating in normal and reverse directions illustrated in  FIG. 4  described above. Accordingly, when the holder shaft  11613  is rotated, the holder  11612  turns upward and downward. A flag  11613   a  is provided at one end of the holder shaft  11613 , and the finisher control portion  220  detects that the knurled belts  1161  are at a home position by the detection of the flag  11613   a  by the knurled belt HP sensor S 247 . 
     The holder  11612  includes a supporting shaft  11611  fixed at one end thereof to the frame  11610  so as to be locked thereto. Accordingly, when the holder  11612  is turned upward and downward, the frame  11610  swings about the rotation shaft  1168  of the third gear  1164  through the supporting shaft  11611 , whereby the knurled belt  1161  is raised and lowered. That is, when the knurled motor M 258  rotates, the holders  11612  are turned upward and downward, and the knurled belts  1161  move to abutment positions where the knurled belts  1161  come into contact with the sheet on the intermediate processing tray  107  and to the home position as a separate position where the knurled belts  1161  separates from the sheet on the intermediate processing tray  107 . 
     The abutment position of the knurled belt  1161  needs to be shifted upward in association with an increase in the number of stacked sheets so as to avoid conveying forces of the knurled belts  1161  in conveying the sheet from becoming excessive. 
     Therefore, in the present embodiment, the finisher control portion  220  changes the position of the knurled belts  1161  according to the number of stacked sheets of the sheet bundle on the processing tray (on the sheet stacking portion) to make the sheet conveying forces of the knurled belts  1161  fall within a predetermined range. In other words, the finisher control portion  220  controls the knurled motor M 258  such that the endless belt is positioned at a position corresponding to a number of sheets stacked on the sheet stacking portion. 
       FIGS. 8A to 8C  are drawings illustrating the state of the knurled belt portion  116  when conveying the sheet P on the intermediate processing tray  107 .  FIG. 8A  illustrates a state of conveying a topmost sheet P 1 .  FIG. 8B  illustrates a state of conveying a 21 st  sheet P 21  in a state in which 20 sheets of 64 g/m 2  are stacked on the intermediate processing tray.  FIG. 8C  illustrates a state of conveying a 41 st  sheet P 41  in a state in which 40 sheets of 64 g/m 2  are stacked on the intermediate processing tray. 
     Here, in this embodiment, a pulse motor is used as the knurled motor M 258  as a drive portion configured to drive the holders  11612  as lifting portion configured to raise and lower the frames  11610 . The raising and lowering amount (swinging amount) of the knurled belt  1161  that moves upward and downward integrally with the frame  11610  is controlled by driving the knurled motor M 258  at the number of pulses according to the number of stacked sheets. 
     Subsequently, a sheet processing operation of the finisher  100  according to the present embodiment will be described with reference to a flowchart illustrated in  FIG. 9 . When the sheet processing operation (job) is started, the finisher control portion  220  drives the knurled motor M 258 . When the knurled belt HP sensor S 247  detects the flag  11613   a  on the holder shaft  11613 , the knurled motor M 258  is stopped. Accordingly, the knurled belts  1161  are caused to wait at the home position (ST 1 ). 
     Subsequently, the sheet P is discharged into the intermediate processing tray  107  by the sheet discharge roller  103  (ST 2 ), and the sheet P is conveyed to the knurled belt portion  116  by the take-in paddle  106  (ST 3 ). 
     Subsequently, the finisher control portion  220  drives the knurled motor M 258 , and lowers knurled belt  1161 . At this time, the finisher control portion  220  determines whether the number of sheets stacked on the intermediate processing tray  107  falls within a range from 0 to 20 from information from the counter CT (ST 4 ). When the number of stacked sheets falls within the range from 0 to 20 (Y in ST 4 ), the finisher control portion  220  increases the lowering amount of the knurled belt  1161  as illustrated in  FIG. 8A  (ST 5 ). When the number of stacked sheets does not fall within the range from 0 to 20 (N in ST 4 ), whether the number of stacked sheets falls within a range from 20 to 40 is determined (ST 6 ). If the number of stacked sheets falls within the range from 20 to 40 (Y in ST 6 ), the lowering amount is reduced as illustrated in  FIG. 8B , and the lowering amount is set to medium (ST 7 ). 
     If the number of stacked sheets does not fall within the range from 20 to 40 (N in ST 6 ), the number of stacked sheets is determined to fall within a range from 40 to 50. Therefore, the lowering amount is further reduced as illustrated in  FIG. 8C , and the lowering amount is set to small (ST 8 ). Before lowering the knurled belts  1161  by an amount corresponding to the number of stacked sheets, driving of the conveyance motor M 250  is started and the knurled belts  1161  are rotated. Accordingly, when the knurled belt  1161  lowers by the amount corresponding to the number of stacked sheets subsequently, the knurled belts  1161  come into contact with the sheet stacked in the intermediate processing tray  107  while rotating, convey the sheet toward the trailing end stopper  108  (ST 9 ), and aligns the sheet. 
     When the alignment of the sheet P with sheet already stacked on the intermediate processing tray  107  in the sheet conveying direction by the trailing end stopper  108  is terminated, the finisher control portion  220  drives the knurled motor M 258  to rotate in the reverse direction, and raises the knurled belts  1161 . When the knurled belt HP sensor S 247  detects the flag  11613   a  of the holder shaft  11613 , the knurled motor M 258  is stopped and makes the knurled belts  1161  wait at the home position (ST 10 ). Subsequently, the alignment motor M 253  illustrated in  FIG. 4  described above is driven, and alignment of the sheet P in the width direction is performed by using the aligning plate  109  (ST 11 ). 
     After a series of aligning operations are terminated, the finisher control portion  220  determines whether the sheet P is the last sheet (ST 12 ). When it is not the last sheet (N in ST 12 ), the number of sheets to be counted by the counter CT is incremented by one (ST 13 ). When it is the last sheet (Y in ST 12 ), the presence or absence of the following binding job is determined (ST 14 ). 
     When a binding job is selected (Y in ST 14 ), the STP motor M 256  or the staple-less binding motor M  257  is driven, and binding is executed by the stapler  110  or the staple-less binding portion (ST 15 ). Subsequently, the assist motor M 254  is driven and the sheet bundle is discharged to the stacking tray  114  by the trailing end assist  112  (ST 16 ). If the binding job is not selected (N in ST 14 ), the sheet bundle is discharged by the trailing end assist  112  to the stacking tray  114  (ST 16 ). 
     In the present embodiment, as described above, the lowering amount of the knurled belts  1161  is controlled by driving the knurled motor M 258  at the number of pulses corresponding to the number of stacked sheets. Also, the frame  11610  that hold the rotation shafts  1166  and  1167  of the first and second gears and the rotation shaft  1169  of the driven roller  1165  is supported so as to be swingable about the rotation shaft  1168  of the third gear  1164  in the present embodiment. 
     Accordingly, when lowering the knurled belt  1161  corresponding to the number of stacked sheets, the knurled belts  1161  can be lowered while maintaining the positional relationship at least between the first gear  1162  and the third gear  1164  constant by lowering the frames  11610 . Consequently, the tensile force between the first gear  1162  and the third gear  1164  of each knurled belt  1161  can be maintained constant. 
     In other words, even though the positions of the knurled belts  1161  are changed according to the number of stacked sheets, the tensile force of the knurled belts  1161  may be maintained constant. 
     As described thus far, in the present embodiment, the rotation shaft  1168  of the third gear  1164  as the lifting shaft of frame  11610  is provided inside the knurled belt  1161 . When lowering the knurled belts  1161  according to the number of stacked sheets, the frame  11610  is swung about the rotation shaft  1168  of the third gear  1164 , so that the knurled belt  1161  is lowered integrally with the frame  11610 . In this manner, since the knurled belt  1161  is raised and lowered according to the number of stacked sheets and is rotated at a predetermined rotation speed, the circular shape can be maintained without deforming the knurled belt  1161  by a centrifugal force. Therefore, the tensile force may be maintained constant. 
     Accordingly, even when lowering the knurled belts  1161  according to the number of stacked sheets, the positional relationship (distance) between the first gear  1162  and the third gear  1164  can be maintained constant so that the tensile forces of the knurled belts  1161  are maintained constant. Consequently, increase in conveying force can be prevented, so that the position of the sheet in the sheet conveying direction may be aligned by the knurled belt  1161  without impairing alignment of the sheet. Even when the hardness of the knurled belts  1161  is changed due to a change in atmospheric temperature or time degradation, the tensile force of the belt is not changed due to the movement of the knurled belt  1161 , so that deviation in conveying force may be restrained. 
     Next, a second embodiment of the invention will be described.  FIG. 10  and  FIGS. 11A and 11B  are drawings for explaining a configuration of the knurled belt portion provided in a sheet processing apparatus according to the second embodiment. In  FIG. 10  and  FIGS. 11A and 11B , the same reference numerals as those in  FIGS. 6A and 6B  described above, and  FIGS. 7A and 7B  indicate the same or the corresponding portions. 
     As illustrated in  FIG. 10  and  FIGS. 11A and 11B , the knurled belt portion  116  is provided with auxiliary gears  11614  and  11615  as auxiliary rotating members configured to restrict the deformation of the knurled belt  1161  in cooperation with the third gear  1164  inside the knurled belt  1161 . Rotating axes  11616  and  11617  of the auxiliary gears  11614  and  11615  illustrated in  FIG. 11B  are rotatably supported by the frame  11610  as illustrated in  FIG. 11A . 
       FIGS. 12A to 12C  are drawings illustrating the state of the knurled belt portion  116  when conveying the sheet P on the intermediate processing tray  107 .  FIG. 12A  illustrates a state of conveying a first sheet P 1 .  FIG. 12B  illustrates a state of conveying a 21 st  sheet P 21  in a state in which 20 sheets of 64 g/m 2  are stacked on the intermediate processing tray.  FIG. 12C  illustrates a state of conveying a 41 st  sheet P 41  in a state in which 40 sheets of 64 g/m 2  are stacked on the intermediate processing tray. 
     In this embodiment as well, in the same manner as the first embodiment described above, the lowering amount of the knurled belts  1161  is controlled by driving the knurled motor M 258  at the number of pulses according to the number of stacked sheets. Accordingly, as illustrated in  FIG. 12A to 12C , when lowering the knurled belt  1161  according to the number of stacked sheets, the knurled belt  1161  can be lowered while maintaining the positional relationship at least between the first gear  1162  and the third gear  1164  constant. Consequently, even though the position of the knurled belt  1161  is changed according to the number of stacked sheets, the tensile force of the knurled belt  1161  may be maintained constant. 
     In the second embodiment, with the provision of a plurality of auxiliary gears  11614  and  11615 , a circular shape of the knurled belt  1161  is prevented from being deformed or sagging significantly downward by distortion or the like at the time of rotating. Accordingly, the surface area that the knurled belts  1161  come into contact with the upper surface of the sheet is increased, so that the alignment of the sheet is prevented from being impaired by the load of the knurled belts  1161  at the time of alignment with the aligning plate  109 . 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2013-162893, filed Aug. 6, 2013, which is hereby incorporated by reference herein in its entirety.