Abstract:
A sheet post-processing apparatus includes a sheet stacking unit, an aligning unit, a moving member, a discharging member, and a discharging motor. The discharging motor drives the discharging member for discharging a pile of sheets in an operation pattern that is selected, depending on a predetermined condition, from among a plurality of operation patterns.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to and incorporates by reference the entire contents of Japanese priority documents 2007-181368 filed in Japan on Jul. 10, 2007 and 2008-057041 filed in Japan on Mar. 6, 2008. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sheet post-processing apparatus, an image forming apparatus, and an image forming system including the sheet post-processing apparatus and the image forming apparatus. 
     2. Description of the Related Art 
     A sheet post-processing apparatus is widely used for performing post-processing, such as sorting, stapling, or stacking of sheets (printing sheets) received from an image forming apparatus, such as a copy machine or a printer. The sheet post-processing apparatus is, for example, a sorter or a finisher. The sheet post-processing apparatus is arranged downstream of the image forming apparatus. 
     For example, in Japanese Patent Application Laid-open No. H11-139673, a technology of such a sheet post-processing apparatus are disclosed in which a plurality of sheets conveyed to a staple tray in the sheet post-processing apparatus is aligned in a conveying direction by putting an edge of each of the sheets in contact with a rear-end fence arranged on a lower portion of the staple tray, and a discharging claw then directly scoops up the pile by supporting an edge of a pile of the sheets, thereby discharging the pile out of the staple tray. 
     In the conventional technology disclosed in Japanese Patent Application Laid-open No. H11-139673, a linear speed of the discharging claw when the discharging claw is moved into contact with the rear edge of the pile of the sheets is made different from a linear speed of the discharging claw when the rear edge of the pile is moved apart from the discharging claw, thereby preventing the sheets from being damaged by the discharging claw when the pile is discharged. 
     In the conventional technology, every time when the pile of the sheets is discharged from the staple tray, the discharging operation is controlled in the same control pattern. However, a load applied to the discharging claw during operation of discharging the pile depends on various conditions, such as a size and a type of the sheet, and the number of stapled sheets in the pile. 
     Therefore, if the discharging operation is always controlled in the same control pattern, it is difficult to improve a productivity of a high-speed machine in which a high accuracy and a high productivity are required. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to at least partially solve the problems in the conventional technology. 
     According to an aspect of the present invention, there is provided a sheet post-processing apparatus that includes a sheet stacking unit that receives a plurality of sheets from an upstream apparatus and stacks the sheets in a pile thereon; an aligning unit that aligns the sheets stacked on the sheet stacking unit in a direction orthogonal to a conveying direction of the sheets; a moving member that moves up the pile of the sheets aligned by the aligning unit; a discharging member that receives the pile from the moving member and scoops up the pile by supporting a bottom edge of the pile for discharging the pile out of the sheet stacking unit; and a discharging motor that drives the discharging member in an operation pattern that is selected, depending on a predetermined condition, from among a plurality of operation patterns in which the discharging motor can drive. 
     According to another aspect of the present invention, there is provided an image forming apparatus that transfers an image onto a recording medium and discharges the recording medium after fixing the image thereon to a sheet post-processing apparatus, wherein the above sheet post-processing apparatus is attached to the image forming apparatus. 
     According to still another aspect of the present invention, there is provided an image forming system that includes the above sheet post-processing apparatus; and the above image forming apparatus. 
     The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a sheet post-processing apparatus according to an embodiment of the present invention; 
         FIG. 2  is a schematic diagram of a staple tray of the sheet post-processing apparatus seen in a direction perpendicular to a surface of the staple tray on which a sheet is conveyed; 
         FIG. 3  is a schematic diagram for explaining a positional relation between an end stopper unit, a discharging claw, a rear-end fence unit, and a movable fence unit of the sheet post-processing apparatus; 
         FIG. 4  is a block diagram of a control circuit of the sheet post-processing apparatus; 
         FIG. 5  is a timing chart for explaining a first pattern for discharging a pile of sheets; 
         FIG. 6  is a timing chart for explaining a second pattern for discharging a pile of sheets; and 
         FIG. 7  is a flowchart of an operation performed by an image forming system for discharging the pile of the sheets according to the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments of the present invention are explained in detail below with reference to the accompanying drawings. 
       FIG. 1  is a schematic diagram of a sheet post-processing apparatus A according to an embodiment of the present invention. The sheet post-processing apparatus A is attached to an image forming apparatus B. The image forming apparatus B transfers a formed image onto a received sheet P (recording medium) and discharges the sheet P to a downstream apparatus after the image is fixed on the sheet P. 
     The sheet processing device A includes a guide path  1 , an upper conveying path  2 , and a lower conveying path  3 . The guide path  1  receives a sheet P that is discharged out of an image forming apparatus B. The upper conveying path  2  and the lower conveying path  3  are branched from the guide path  1 . The upper conveying path  2  extends toward a catch tray  4 . The lower conveying path  3  is arranged for a stapling process. 
     The sheet post-processing apparatus A is arranged downstream of the image forming apparatus B that is an upstream apparatus that discharges a processed sheet P to the sheet post-processing apparatus A. The sheet post-processing apparatus A and the image forming apparatus B configure an image forming (processing) system. When the image forming apparatus B starts performing an image forming operation, the catch tray  4  is moved to a predetermined level. When it is determined that the catch tray  4  is positioned at the level such that the catch tray  4  is full of the stacked sheets P, a control unit (not shown) stops the image forming system from performing the image forming operation. 
     A guide roller  10  and an entrance sensor  11  are arranged on the guide path  1 . A separation claw  20  is arranged at an end of the guide path  1 , i.e., arranged at a point where the upper conveying path  2  and the lower conveying path  3  are branched from the guide path  1 . The separation claw  20  rotates to switch a conveying direction of the sheet P between the upper conveying path  2  and the lower conveying path  3 . 
     A conveying roller  21 , a discharge sensor  22 , a discharging roller  23 , and a shifting roller  24  are arranged on the upper conveying path  2 . The sheet P that is not conveyed to the lower conveying path  3  is delivered along the upper conveying path  2 , and discharged to the catch tray  4 . The discharged sheet P is sequentially stacked on the catch tray  4 . 
     A rotatable filler  51  is arranged above a discharge opening of the sheet post-processing apparatus A. An end of the filler  51  is located at and in contact with a point near the center of the uppermost sheet P stacked on the catch tray  4 . 
     A first upper-surface detecting sensor  52  and a second upper-surface detecting sensor  53  are arranged near a base portion of the filler  51 . The first upper-surface detecting sensor  52  and the second upper-surface detecting sensor  53  detect a level of the end of the filler  51 , thereby detecting a level of the upper surface of the uppermost sheet P stacked on the catch tray  4 . 
     The first upper-surface detecting sensor  52  and the second upper-surface detecting sensor  53  are arranged in such a manner that the base portion of the filler  51  is vertically sandwiched therebetween. The base portion of the filler  51  is positioned in the middle between the first upper-surface detecting sensor  52  and the second upper-surface detecting sensor  53 , i.e., both the first upper-surface detecting sensor  52  and the second upper-surface detecting sensor  53  are OFF. A position near the second upper-surface detecting sensor  53 , i.e., a position at which the second upper-surface detecting sensor  53  is switched from ON to OFF is set to a home position of the base portion of the filler  51 . 
     When the number of the sheets P stacked on the catch tray  4  increases, i.e., the level of the upper surface of the uppermost sheet P becomes higher, the second upper-surface detecting sensor  53  is turned ON. The control unit then controls a driving unit (not shown) to move down the catch tray  4 . The driving unit is configured to move the catch tray  4  up and down. 
     When the catch tray  4  moves down, and the second upper-surface detecting sensor  53  is turned OFF, the control unit stops the catch tray  4  from moving down. This operation is repeatedly performed. When the catch tray  4  reaches a predetermined level at which the catch tray  4  is full of the stacked sheets P, the sheet post-processing apparatus A feeds a stop signal to the image forming apparatus B, thereby stopping the image forming system from performing the image forming operation. 
     Lower conveying rollers  30 , an ejection sensor  31 , and an ejecting roller  32  are arranged on the lower conveying path  3 . A stapling unit  5  is arranged at the end of the lower conveying path  3 , and includes a stapler S 1  and a staple tray  34 . The stapler S 1  for stapling an end portion of a pile of the sheets P moves forward and backward in a direction orthogonal to the surface of the sheet P. The staple tray  34  stacks thereon the sheets P to be discharged. 
     The stapling unit  5  further includes a jogger fence unit  36  including jogger fences  36   a  and  36   b  (see,  FIG. 2 ), a tapping roller  37 , a discharging belt  38 , a discharging claw  38   a , a rear-end fence unit  39  including rear-end fences  39   a  and  39   b  (see,  FIG. 2 ), and a rear-end presser  40 . The jogger fence unit  36  moves forward and backward in a direction orthogonal to the surface of the sheet P to align the sheets P stacked on the staple tray  34 . The rear-end presser  40  moves forward and backward in the thickness direction of the sheet P. 
     As described above, the stapling unit  5  includes the staple tray  34 , the discharging belt  38 , the discharging claw  38   a , and a discharging motor  35 . The discharging motor  35  drives the discharging belt  38  and the discharging claw  38   a . Thus, the stapling unit  5  functions also as a discharging unit. A movable fence unit  42  shown in  FIG. 1  includes movable fences  42   a  and  42   b  (see,  FIG. 2 ). 
     When the sheet post-processing apparatus A receives a staple mode signal for stapling an end portion of the pile from the image forming apparatus B, the stapler S 1  moves in the direction orthogonal to the surface of the sheet P to an appropriate position of the lower portion of the pile and then stands by at that position. When the sheet P is conveyed along the lower conveying path  3 , the sheet P is ejected to the staple tray  34  by the ejecting roller  32 , and is tapped at the upper surface thereof by the tapping roller  37 , so that the sheets P are aligned in the longitudinal direction. 
     The sheets P are aligned in the width direction by the jogger fence unit  36 . When the sheet P is put into the rear-end fence unit  39 , the rear-end presser  40  presses the rear end of the sheet P against the staple tray  34 , so that a subsequent sheet can be easily put into the rear-end fence unit  39 . 
     After the predetermined number of sheets P is stacked and aligned on the staple tray  34 , the stapler S 1  moves from the standby position to a stapling position, and staples the sheets P at the stapling position. The pile of the stapled sheets P is delivered along the discharging belt  38  in a counterclockwise direction while the lower edge of the pile is supported by the discharging claw  38   a . In this manner, the pile is moved upward, and then discharged to the catch tray  4 . 
     In a stapling mode, the home position of the discharging claw  38   a  is defined such that the base portion of the filler  51  is located near the first upper-surface detecting sensor  52 , i.e., the first upper-surface detecting sensor  52  is switched from OFF to ON. Thus, the first upper-surface detecting sensor  52  functions as a discharging-claw home sensor that detects the home position of the discharging claw  38   a.    
     As described above, when the number of the sheets P stacked on the catch tray  4  increases, i.e., the level of the upper surface of the uppermost sheet P becomes higher, the first upper-surface detecting sensor  52  as a discharging-claw home sensor is turned OFF. The control unit then controls the driving unit to move down the catch tray  4 . 
     When the catch tray  4  moves down, and the first upper-surface detecting sensor  52  is turned ON, the control unit stops the catch tray  4  from moving down. This operation is repeatedly performed. When the catch tray  4  reaches a predetermined level at which the catch tray  4  is full of the stacked sheets P, the sheet post-processing apparatus A feeds a stop signal to the image forming apparatus B, thereby stopping the image forming system from performing the image forming operation. 
       FIG. 2  is a schematic diagram of the staple tray  34  seen in the direction perpendicular to the surface of the staple tray  34  on which the sheet P is conveyed. 
     When the sheet post-processing apparatus A receives the sheets P from the image forming apparatus B that is an upstream apparatus, the sheets P are aligned in the width direction by the jogger fences  36   a  and  36   b  and in the longitudinal direction by an end stopper unit  41  that includes end stoppers  41   a  and  41   b  putting the sheets P in contact with the rear-end fences  39   a  and  39   b.    
     After the alignment of the sheets P is completed, the stapler S 1  staples the sheets P. The pile of the stapled sheets S 1  is moved up by the movable fences  42   a  and  42   b . Each of the movable fences  42   a  and  42   b  and the rear-end fences  39   a  and  39   b  includes a receiving member (not shown) that receives the sheet P. The receiving members of the movable fences  42   a  and  42   b  are located in a slightly lower position than the receiving members of the rear-end fences  39   a  and  39   b . With this configuration, the receiving members of the movable fences  42   a  and  42   b  do not interfere with the sheets P when the end stoppers  41   a  and  41   b  align the sheets P in the longitudinal direction by putting the sheets P in contact with the rear-end fences  39   a  and  39   b.    
     As described above, because the rear-end fences  39   a  and  39   b  are arranged in a position lower than the lower portion of the staple tray  34 , it is possible to prevent misalignment of the sheets P. The movable fences  42   a  and  42   b  are arranged as a mechanism of moving up the pile of the sheets P to an operating range of the discharging claw  38   a  in which the discharging claw  38   a  can receive the sheets P from the movable fence unit  42  and scoop up the received sheets P. 
     After the pile of the sheets P is moved up by the movable fences  42   a  and  42   b , the discharging belt  38  rotates in the counterclockwise direction in  FIG. 1 , and the discharging claw  38   a  attached to the discharging belt  38  receives the pile of sheets P from the movable fences  42   a  and  42   b . The discharging claw  38   a  then discharges the pile out of the staple tray  34 . 
     It should be noted that the above-described operation can be performed on unstapled sheets on which the stapling process is not performed after the alignment process is finished. As shown in  FIG. 2 , the staple tray  34  further includes a pulley  38   c  that rotates the discharging belt  38 , a front side plate  43   a , a back side plate  43   b , a movable guide  44 , a pile-separation drive motor  45 , a discharging roller  46 , conveying belts  47   a  and  47   b , and a sheet presence sensor  48 . 
       FIG. 3  is a schematic diagrams for explaining a positional relation between the end stopper unit  41 , the discharging claw  38   a  attached to the discharging belt  38 , the rear-end fence unit  39 , and the movable fence unit  42 . 
     The number of the sheets P that have been conveyed to and aligned on the staple tray  34  is counted by the CPU  71  of the sheet post-processing apparatus A, or is obtained based on data received from the image forming apparatus B. 
       FIG. 4  is a block diagram of a control circuit  70  of the sheet post-processing apparatus A according to the embodiment. 
     The control circuit  70  is also a control circuit of the image forming apparatus B, and includes a microcomputer having a central processing unit (CPU)  71 , an input/output (I/O) interface  72 , or the like. A detailed description on the control of respective members of the image forming apparatus B is omitted. 
     A signal is fed from a punch unit  73 , a switch of a control panel (not shown) included in a main body of the image forming apparatus B, and a sensor such as a sheet-surface detecting sensor, to the CPU  71  via the I/O interface  72 . 
     The CPU  71  controls based on an input signal a motor (not shown) for shifting a shift tray (not shown), a motor (not shown) for opening and closing a discharge guide plate (not shown), a motor for moving the shift tray, a motor (not shown) for driving the tapping roller  37  ( FIG. 1 ), a solenoid (SOL) such as a tapping SOL (not shown), a motor (not shown) for driving the conveying roller, and a motor (not shown) for driving the discharging roller. 
     The CPU  71  also controls motors, such as a motor (not shown) for driving the discharging belt  38  and the discharging claw  38   a  ( FIG. 1 ), a motor (not shown) for moving the stapler S 1  ( FIG. 2 ), a motor (not shown) for rotating the stapler S 1  in an oblique direction, a motor (not shown) for moving the jogger fences  36   a  and  36   b  ( FIG. 2 ), the pile-separation drive motor  45  ( FIG. 2 ) for rotating the movable guide  44 , and a motor (not shown) for driving the conveying roller that conveys the pile. 
     Furthermore, the CPU  71  controls a motor (not shown) for moving the movable fences  42   a  and  42   b  ( FIG. 2 ), a motor (not shown) for moving a folding plate (not shown), a motor (not shown) for driving a folding roller (not shown), and the like. 
     A pulse signal for driving a stapled-sheet conveying motor (not shown) that drives a stapled-sheet discharging roller (not shown) is input to the CPU  71 , and the input pulse signal is counted by the CPU  71 . The tapping SOL and the motor for moving the jogger fences  36   a  and  36   b  are controlled based on the counted pulse signal. 
       FIG. 5  is a timing chart for explaining a first pattern for discharging the pile of the sheets P.  FIG. 6  is a timing chart for explaining a second pattern for discharging the pile of the sheets P. 
     In the first pattern, after a driving linear speed of the discharging motor  35  is increased to a predetermined level for discharging the pile, the discharging claw  38   a  receives the pile from the movable fence unit  42 , and then discharges the received pile. 
     The discharging claw  38   a  discharges the pile in the first pattern when the number of the sheets P contained in the pile is small, i.e., a low load can be applied to the discharging claw  38   a  when the discharging claw  38   a  scoops up the pile. In this manner, a time required for discharging the sheets P can be shortened, and the productivity can be improved. 
     In the second pattern, when the discharging claw  38   a  receives the pile from the movable fence unit  42 , the discharging motor  35  operates at a low speed. After the discharging claw  38   a  receives the pile from the movable fence  42 , a driving linear speed of the discharging motor  35  is increased to a predetermined driving linear speed for discharging the pile. The discharging claw  38   a  then discharges the pile. 
     The number of the sheets P that have been conveyed to and aligned on the staple tray  34  ( FIG. 2 ) is counted by the CPU ( FIG. 4 ), or is obtained based on data received from the image forming apparatus B. 
     When it is determined that the number of the sheets P is equal to or more than the predetermined number, i.e., the high load can be applied to the discharging claw  38   a , the linear speed of the motor decreases to a low level to obtain a higher torque. The discharging claw  38   a  receives the pile from the movable fence unit  42  with the motor at the low linear-speed level. After that, the linear speed of the motor increases to a level for discharging the pile. 
     When it is determined that the number of the sheets P is less than the predetermined number, the discharging claw  38   a  receives the pile from the movable fence unit  42  at the linear speed that is the same as that for discharging the pile, and discharges the received pile, in the same manner as described in the first patter. 
     The driving linear speed of the motor for discharging the pile is determined and changed depending on the size of the sheet P and the number of the stapled sheets P. Specifically, it is determined whether the sheet P is small-sized or large-sized. Then, a linear speed v 1  for discharging the small-sized sheet P and a linear speed v 2  for discharging the large-sized sheet P are determined in such a manner that the relation v 1 &gt;v 2  is satisfied. 
     If the sheet P is large-sized, it is determined whether the number of the large-sized sheets P is equal to or more than the predetermined number, or less than the predetermined number. Then, a linear speed v 2  for discharging the sheets P larger than the predetermined number and a linear speed v 3  for discharging the sheets P smaller than the predetermined number are determined in such a manner that the relation v 2 &lt;v 3  is satisfied. 
     As described above, when the number of sheets P is large, i.e., the high load can be applied to the discharging claw  38   a , a torque of the discharging motor is increased when the discharging claw  38   a  receives the pile from the movable fence unit  42 . Therefore, it is possible to prevent step-out of the discharging motor. Thus, the reliability can be improved. 
       FIG. 7  is a flowchart of an operation performed by the image forming system for discharging the pile of the sheets P. 
     The sheet post-processing apparatus A receives the sheets P having images formed thereon from the image forming apparatus B (Step S 1 ). Then, the received sheets P are aligned in the width direction and the longitudinal direction by the jogger fence unit  36 , the end stoppers  41   a ,  41   b , and the rear-end fence unit  39  (Step S 2 ). 
     Subsequently, it is determined whether all the sheets P to be stapled have been received (Step S 3 ). If all the sheets P to be stapled have been received (Yes at Step S 3 ), the sheets P are stapled by the stapler S 1  (Step S 4 ). Then, it is determined whether the sheets P are large-sized (Step S 5 ). 
     If the sheets P are large-sized (Yes at Step S 5 ), it is determined whether the number of the stapled sheets P is equal to or more than N (Step S 6 ). If the number of the stapled sheets P is equal to or more than N (Yes at Step S 6 ), a linear speed of the discharging motor  35  for discharging the pile is set to a linear speed v 2  (Step S 7 ). Then, it is determined whether the number of the stapled sheets P is equal to or more than N (Step S 8 ). 
     If the number of the stapled sheets P is equal to or more than N (Yes at Step S 8 ), the discharging motor  35  operates at a linear speed for receiving the pile (at a low speed) (Step S 9 ). Then, it is determined whether the discharging claw  38   a  has received the pile from the movable fence unit  42  (Step S 10 ). If the discharging claw  38   a  has received the pile from the movable fence unit  42  (Yes at Step S 10 ), a linear speed of the discharging motor  35  is increased to a linear speed for discharging the pile (Step S 11 ). The discharging claw  38   a  then discharges the pile (Step S 12 ). 
     If the sheets P are not large-sized (No at Step S 5 ), a linear speed of the discharging motor  35  for discharging the pile is set to a linear speed v 1  (Step S 13 ), and the process control proceeds to Step S 8 . If the number of the stapled sheets P is less than N (No at Step S 6 ), a linear speed of the discharging motor  35  for discharging the pile is set to a linear speed v 3  (Step S 14 ), and the process control proceeds to Step S 8 . 
     If the number of the stapled sheets P is less than N (No at Step S 8 ), the discharging motor  35  operates at the linear speed for discharging the pile (Step S 15 ). The discharging claw  38   a  then receives the pile from the movable fence unit  42  that is moving (Step S 16 ). The discharging claw  38   a  then discharges the pile (Step S 12 ). 
     Therefore, in the embodiment, an operation mode of discharging the pile is switched based on a condition of the sheets P to be discharged, so that both the reliability and the productivity can be improved. 
     The load applied to the discharging claw  38   a  during the operation of discharging the sheets P depends on the number of sheets P, and the size and the thickness of the sheet P. Therefore, preferably, every time the sheet post-processing apparatus A receives the sheets P from the image forming apparatus B, the sheet post-processing apparatus A detects or receives information on the sheet P from the image forming apparatus B. In this manner, the discharge of the sheets P is controlled as appropriate. 
     In the embodiment, as described above, the operation of discharging the pile is variably controlled depending on conditions of the sheets P. Thus, it is possible to improve the reliability and the productivity of the sheet post-processing. Furthermore, the linear speed of the discharging motor  35  for discharging the pile is variable depending on conditions of the sheets P. Thus, it is possible to further improve the reliability and the productivity of the sheet post-processing. 
     Moreover, an image forming (processing) apparatus and an image forming (processing) system to which the sheet post-processing apparatus A is applied can provide improved reliability and the productivity of the sheet post-processing. 
     According to an aspect of the present invention, it is possible to shorten a time required for discharging the pile of the sheets, and to improve the productivity and the reliability. 
     Furthermore, it is possible to prevent step-out of the discharging motor. Thus, the reliability can be improved. 
     Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.