Abstract:
A sheet processing device in the form of an offset stacker, a sheet fence ( 103, 104 ) is provided on a side of sheets (S) to be processed stacked on a stack tray ( 3 ) opposite from a jogger ( 101, 102 ) so that the sheet fence accurately defines a final offset position of the sheets. When a transient offset position at which the sheets are stacked on the stack tray varies from one sheet to another, the side edges of sheets selected for offset stacking can be lined up without fail owing to the jogging action of the jogger and the supporting action of the sheet fence. A pair of joggers may be arranged on either side of the sheets, along with a pair of corresponding sheets fences on the opposing sides. The jogger and sheet fence on a same side may be supported by a common moveable frame ( 107, 108 ).

Description:
[0001]    This is a continuation of prior U.S. application Ser. No. 12/478,803, filed Jun. 5, 2009. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a sheet processing device for transporting a plurality of sheets and stacking them on a sheet table such as a stack tray selectively at transversely offset positions with respect to a sheet transporting direction. 
       BACKGROUND OF THE INVENTION 
       [0003]    To facilitate the handling of sheets such as paper sheets which are ejected from an imaging device such as photocopiers and printers, it is desirable to use an offset stacker that stacks the sheets on a stack table as individual sets that are transversely offset from one set to another. Japanese patent laid open publications JP2003-312931A (patent document 1) and JP2003-341908A (patent document 2) disclose such offset stackers. 
         [0004]    In such an offset stacker, typically, a transversely moveable jogger is used for jogging of pushing each sheet to a transversely offset position with respect to the transport direction of the sheet. See patent document 1, for instance. 
         [0005]    However, according the prior art, as the jogger pushes each sheet transversely, the offset distance could vary from one sheet to another owing to the unevenness in the frictional property between the sheets. Therefore, the side edges of the sheets in each set may not be lined up evenly, and this may cause some inconvenience in the subsequent handling of each set of sheets. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    In view of such problems of the prior art, a primary object of the present invention is to provide a sheet processing device such as an offset stacker that can transport a plurality of sheets and stack the sheets on a stack table as individual sets that are transversely offset from one set to another and contain sheets with highly neatly lined up side edges. 
         [0007]    According to the present invention, such an object can be accomplished by providing a sheet processing device for transporting sheets having first side edges and second side edge in a sheet transporting direction and stacking the sheets on a stack tray selectively at a regular position and at least one transversely offset position, comprising: an offset transport unit configured to eject sheets onto the stack tray selectively at the regular position and a first transitional offset position which is more transversely offset than a first final offset position; a first jogger provided on a first side of the stack tray to jog the first side edges of first selected sheets; and a first sheet fence provided on a second side of the stack tray to support the second side edges of the first selected sheets; wherein the first sheet fence is positioned to support the first selected sheets at the first final offset position when the first side edges are jogged by the first jogger. 
         [0008]    Because the first final offset position is defined by the first sheet fence, even when the transient offset position at which the sheets are stacked on the stack tray varies from one sheet to another and/or the jogging action produces uneven results, the side edges of the first selected sheets can be lined up by the jogging action of the first joggers without fail. 
         [0009]    According to a preferred embodiment of the present invention, the sheet processing device further comprises a second jogger provided on the second side of the stack tray to jog the second side edges of second selected sheets; and a second sheet fence provided on the first side of the stack tray to support the first side edges of the second selected sheets; wherein the offset transport unit is additionally configured to eject sheets to a second transitional offset position which is more transversely offset than a second first final offset position, the second final offset position being offset from the regular position opposite to the first final offset position; and the second sheet fence is positioned to support the second selected sheets at the second final offset position when the second side edges are jogged by the second jogger. 
         [0010]    Thereby, the side edges of the sheets can be neatly lined up at two different offset positions, and this enhances the convenience of the present invention. According to a certain embodiment of the present invention, the first jogger and first sheet fence are used for a simple stack mode in which the sheets are always stacked at a regular position, and the second jogger and second sheet are selectively used for an offset stack mode which is transversely offset from the regular position. It is also possible not to use the joggers and sheet fences in a simple stack mode by stacking the sheets directly at a regular position. The first jogger and first sheet fence are used for a first offset stack mode in which the sheet stack is offset in a first transverse direction, and the second jogger and second sheet fence are used for a second offset stack mode in which the sheet stack is offset in a second transverse direction which is opposite to the first transverse direction. 
         [0011]    According to a certain aspect of the present invention, the second jogger is located transversely further away from the sheets than the first sheet fence, and the first jogger is located transversely further away from the sheets than the second sheet fence, the first and second sheet fences being configured to be raised selectively so as not to interfere with transportation of sheets to the stack tray. Thereby, space requirements are minimized. In this case, it is preferable if the first and second sheet fences comprise fence members each provided with an upper end pivotally supported by a moveable frame and a free end that can be placed on a sheet stack of the stack tray, each fence member extending obliquely downward in a downstream direction, so that the sheet fences may be pushed out of the way by the incoming sheets without requiring any complex powered arrangement. 
         [0012]    According to a particularly preferred embodiment of the present invention, the first jogger and second sheet fence are both attached to a first moveable frame configured to be moved transversely with respect to the sheet transporting direction to effect a jogging movement of the first jogger and to adjustably define the second final offset position; and the second jogger and first sheet fence are both attached to a second moveable frame configured to be moved transversely with respect to the sheet transporting direction to effect a jogging movement of the second jogger and to adjustably define the first final offset position. 
         [0013]    Thereby, the jogging action and sheet fence adjustment can be achieved by a common structure and a common drive unit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Now the present invention is described in the following with reference to the appended drawings, in which: 
           [0015]      FIG. 1  is a simplified front view of a sheet processing device embodying the present invention; 
           [0016]      FIG. 2  is a fragmentary front view of the sheet processing device shown in  FIG. 1 ; 
           [0017]      FIG. 3  is a side view of the offset transport unit shown in  FIG. 2 ; 
           [0018]      FIG. 4  is a plan view showing the first sheet lineup unit shown in  FIG. 2 ; 
           [0019]      FIG. 5  is a plan view showing the second sheet lineup unit shown in  FIG. 2 ; 
           [0020]      FIGS. 6A to 6C  are fragmentary side views showing the sequential steps of stacking sheets on the stack tray at a position offset toward the front; and 
           [0021]      FIGS. 7A to 7C  are fragmentary side views showing the sequential steps of stacking sheets on the stack tray at a position offset toward the rear. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]      FIG. 1  illustrates an offset stacker embodying the present invention. This stacker  1  may be used, for instance, in a printing system for on-demand printing, and comprises a stack tray (sheet table)  3  which supports a stack of paper sheets S ejected from an imaging device  2  such as a photocopier, printer or the like located on the left hand side of  FIG. 1  and a dolly  4  which is configured to carry the stack tray  3  supporting the paper stack and carrying it out of the stacker  1 . In the following description, the side of the system facing the user is referred to as a front side ( FIG. 1 ), and the side of the system facing away from the user is referred to as a rear side. The sheets are transported from left to right or in a sheet transporting direction as seen from the user. 
         [0023]    The stacker  1  further comprises a sheet processing unit  5  for placing the paper sheets S on the stack tray  3  with their edges in a properly lined-up condition as will be described hereinafter. The paper sheets S ejected from the imaging device  2  are transported to the sheet processing unit  5  via a sheet transport passage L 1  fitted with rollers or other means for transporting paper sheets. 
         [0024]    The stacker  1  is configured to stack paper sheets S either in a simple stack mode or an offset stack mode as desired. In the simple stack mode, the paper sheets S are stacked strictly on a standard position of the stack tray  3 . In the offset stack mode, the paper sheets S may be stacked in a position slightly offset from the standard position in a direction (transverse direction) perpendicular to the direction of transporting the paper sheets S as required. 
         [0025]    This stacker  1  is additionally configured to operate in a top-pass ejection mode and a bypass mode. In the top-pass ejection mode, each sheet S is ejected onto an upper tray  6  located at an uppermost part of the stacker via a corresponding sheet transport passage L 2 . In the bypass mode, each sheet S is ejected out of the stacker  1  via a corresponding sheet transport passage L 3 , and is passed on to another device such as a second stacker that may be connected to a downstream end of the stacker  1 . 
         [0026]    In the illustrated embodiment, the stacker  1  includes a tray lift mechanism  11  that can raise and lower a tray lift table  12  supporting the stack tray  3  to a height corresponding to the number of paper sheets S stacked on the stack tray  3 . The height of the tray lift table  12  may be determined by counting the number of paper sheets S stacked on the stack tray  3 , and lowering the tray lift table  12  by a corresponding distance. Thereby, the stack tray  3  can be maintained at a height that is suitable for receiving the sheets S transported through the sheet transport passage L 1 . 
         [0027]      FIG. 2  is a front view of the sheet processing unit  5  shown in  FIG. 1 . The sheet processing unit  5  comprises an offset transport unit  21  for transporting or ejecting paper sheets S onto the stack tray  3  in a transversely offset relationship as required, a first sheet lineup unit  22  for lining up the paper sheets S in the sheet transporting direction and a second sheet lineup unit  23  for lining up the paper sheets S in the transverse direction or in the direction perpendicular to the sheet transporting direction. 
         [0028]    The offset transport unit  21  comprises outlet rollers  31 , pinch rollers  32  nipping the paper sheets S in cooperation with the corresponding outlet rollers  31  and a moveable frame  33  supporting the outlet rollers  31  and pinch rollers  32 . The moveable frame  33  is in turn supported by a fixed frame (not shown in the drawing) so as to be moveable in the transverse direction (perpendicular to the paper plane of  FIG. 2 ). Adjacent to the moveable frame  33  is provided a detector  34  for detecting the axial position of the outlet rollers  31  and pinch rollers  32 , and the detected signal is used for the purpose of controlling the positions of these rollers. 
         [0029]    The outlet rollers  31   a  are integrally and commonly supported by a shaft  65  ( FIG. 3 ) which is in turn rotatably supported by the moveable frame  33 . Each pinch roller  32  is resiliently and individually supported by the moveable frame  33  via a sheet spring  35 , and is urged thereby against the corresponding outlet roller  31 . A paddle wheel  36  provided under each outlet roller  31  turns in synchronism with the outlet roller  31 . Each paddle wheel  36  strikes the rear edge of each paper sheet S ejected onto the stack tray  3 , and forces it downward. A detector  37  for detecting the passage of each sheet S transported along the sheet transport passage L 1  is provided at an upstream end of the outlet rollers  31 . 
         [0030]    Above the stack tray  3  is provided a first sensor bar  41  having a base end pivotally supported by a fixed frame, and extending obliquely downwardly and toward the downstream direction. The free end of the first sensor bar  41  rests upon the paper sheet stack S on the stack tray under the gravitational force, and a first detector  42  for detecting the movement of the first sensor bar  41  is provided on the fixed frame adjacent to the sensor bar  41 . Below the outlet rollers  31  is provided a second sensor bar  43  having a lower end pivotally supported by the fixed frame and extending substantially upright so as to be engaged by the trailing edge of the paper sheets on the stack tray  3 . Adjacent to the second sensor bar  43  is provided a second detector  44  for detecting the movement of the second sensor bar  43 . The presence of paper sheets S on the stack tray  3  and the height thereof can be determined from the detection signals of the detectors  42  and  44  and the vertical position of the stack tray  3 . 
         [0031]      FIG. 3  is a side view of the offset transport unit  21  shown in  FIG. 2 . The offset transport unit  21  comprises a drive unit  51  for transversely moving the moveable frame  33 , along with the outlet rollers  31  and pinch rollers  32 , so that the outlet rollers  31  and pinch rollers  32 , with a paper sheet nipped between them, can be moved by a small distance in the axial (transverse) direction, and the paper sheets S can be ejected onto the stack tray  3  in a transversely offset relationship. 
         [0032]    The drive unit  51  incorporates a rack and pinion mechanism for producing a linear movement, and causes the axial movement of the outlet rollers  31  and pinch rollers  32 . The drive unit  51  includes an electric motor  52 , a rack member  53  having a rack formed along the lower edge thereof and extending in parallel with the shaft  65  integrally supporting the outlet rollers  31 , a pinion  54  meshing with the rack of the rack member  53 , and reduction gears  55  and  56  interposed between the output shaft of the electric motor  52  and pinion  54 . 
         [0033]    The rack member  53  is connected to the moveable frame  33 , and is integrally provided with a pair of sliders  59  sliding along a guide slot  58  formed in the fixed frame  57  in parallel with the shaft  65  so that the rack member  53  moves along the guide slot  58  as the motor  52  is actuated in either direction. Thereby, the outlet rollers  31  and pinch rollers  32  are enabled to move in either axial direction. 
         [0034]    The outlet rollers  31  are actuated by an electric motor  61 . The actuating force of the electric motor  61  is transmitted from a pulley  62  on the output shaft of the motor  61  to a pulley  63  connected to a drive gear  67  via an endless belt  64 . The drive gear  67  meshes with a driven gear  66  coaxially attached to an end of the shaft  65  integrally supporting the outlet rollers  31  so that the outlet rollers  31  are turned as the electric motor  61  is actuated. The drive gear  67  is elongated in the axial direction so that the meshing between the drive gear  67  and driven gear  66  is maintained even when the driven gear  66  along with the shaft  65  is actuated over the entire stroke thereof by the drive unit  51 . 
         [0035]      FIG. 4  is a plan view of the first sheet lineup unit  22  shown in  FIG. 2  which lines up or makes even the leading edges of the paper sheets S in the sheet transporting direction. The first sheet lineup unit  22  comprises a pair of stoppers  71  that engage the leading edges of the paper sheets S ejected from the offset transport unit  21  to the stack tray  3  and a drive unit  72  for adjusting the position of the stoppers  71 . 
         [0036]    The drive unit  72  is configured to move the support member  73  for the stoppers  71  to adjust the position of the stoppers  71  in the sheet transporting direction, and comprises an electric motor  81 , pulleys  82  to  84  pivotally supported by a fixed frame  80  in a triangular arrangement, an endless belt  85  passed around these pulleys and attached to the support member  73  at a point of a section thereof extending in the sheet transporting direction, and reduction gears  86  to  88  interposed between the output shaft of the electric motor  81  and one of the pulleys  82 . 
         [0037]    The support member  73  for the stoppers  71  is provided with sliders  90  slidably guided by a pair of parallel guide slots  89  formed in the fixed frame  80  and elongated along the direction of ejecting the paper sheets S (sheet transporting direction). Thereby, as the electric motor  81  turns in either direction, the support member  73  is actuated along the guide slots  89 , and this in turn causes the stoppers  71  to move in the sheet transporting direction for the adjustment of the position of the stoppers  71 . 
         [0038]    Referring to  FIG. 2 , each stopper  71  comprises a stem portion  76  which is received in a guide portion  75  of a base member  74  connected to the support member  73  so that the stopper  71  is moveable vertically between a lowermost position and an uppermost position over a prescribed stroke. Thus, the stoppers  71  are supported by the base member  74  in such a manner that the stoppers  71  rest upon the stack tray  3  or upon the stack of paper sheets S on the stack tray  3  under its own weight. When there is no paper sheet stack or stack tray to limit the downward movement of the stoppers  71 , the guide portions  75  retain the stoppers  71  at the lowermost position thereof. 
         [0039]    Supposed that a relatively small sheet S is stacked upon a relatively large sheet S. The stoppers  71  have been previously at the position corresponding to the leading edge of the larger sheet S. When the smaller sheet S is about to be stacked on the stack tray  3 , the tray lift mechanism  11  (see  FIG. 1 ) lowers the lift table  12  until the stoppers  71  drop to the lowermost position and are cleared from the upper surface of the paper stack, and are then moved horizontally to a position corresponding to the leading edge of the smaller sheet S. Thereafter, the lift table  12  is raised until the stoppers  71  come into engagement with the uppermost sheet on the stack tray  3 , and are pushed slightly upward thereby. As a result, the leading edges of the smaller sheets that will follow the larger sheets can be lined up by the stoppers  71 . 
         [0040]      FIG. 5  is a plan view of the second sheet lineup unit  23  illustrated in  FIG. 2 . The second sheet lineup unit  23  lines up the position of the sheets S in the transverse direction which is perpendicular to the sheet transporting direction, and comprises a front jogger  101  and rear jogger  102  for jogging each sheet to a prescribed offset position, a front sheet fence  103  and rear sheet fence  104  that engage the front and rear side edges of the paper sheet, respectively, to support the paper sheets against the jogging action performed by the corresponding joggers  101  and  102  and drive units  105  and  106  for actuating the corresponding joggers  101  and  102 . 
         [0041]    The front jogger  101  is supported by a front support member  107 , and the rear jogger  102  is supported by a rear support member  108 . The front sheet fence  103  is mounted on a part of the front support member  107  more inwardly or closer to the paper stack S than the front jogger  101 , and the rear sheet fence  104  is mounted on apart of the rear support member  108  more inwardly or closer to the paper stack S than the rear jogger  102 . Thus, the front and rear sheet fences  103  and  104  are actuated integrally with the front and rear joggers  101  and  102 , respectively. 
         [0042]    As shown in  FIG. 2 , each sheet fence  103 ,  104  comprises a rod member having a base end  111  pivotally supported by the corresponding support member  107 ,  108  via a pivot shaft  112  and a middle part  114  extending obliquely downward in a downstream direction and a free end  113  having a convex or otherwise smoothly curved surface facing downward. Therefore, even when each sheet fence  103 ,  104  is located in a position that could interfere with the sheets S ejected from the offset transport unit  21  onto the stack tray  3 , the sheet fence is swung upward by the incoming sheets S, and does not prevent the sheets S to be properly stacked upon the stack tray  3 . 
         [0043]    Referring to  FIG. 5 , the drive unit  105  is provided for actuating the front jogger  101  transversely or in the direction perpendicular to the sheet transporting direction. The drive unit  105  comprises an electric motor  121  attached to a fixed frame  120 , a rack member  122  attached to the front support member  107  and provided with a rack extending in the transverse direction, a pinion  123  meshing with the rack and a plurality of reduction gears  124  to  127  interposed between the output shaft of the electric motor  121  and the pinion  123 . The rack member  122  is provided with a pair of sliders  129  guided by a transversely extending guide slot  128  formed in the fixed frame  120 . Thus, the rack member  122  and front support member  107  are actuated in either transverse direction while the sliders  129  are guided by the guide slot  128  as the electric motor  131  is actuated in a corresponding direction, and this causes the front jogger  101  to perform the prescribed jogging movement in the transverse direction. 
         [0044]    Similarly, the drive unit  106  is provided for actuating the rear jogger  102  transversely or in the direction perpendicular to the sheet transporting direction. The drive unit  106  comprises an electric motor  131  attached to the fixed frame  120 , a rack member  132  attached to the rear support member  108  and provided with a rack extending in the transverse direction, a pinion  133  meshing with the rack and a plurality of reduction gears  134  to  137  interposed between the output shaft of the electric motor  131  and the pinion  133 . The rack member  132  is provided with a pair of sliders  139  guided by a transversely extending guide slot  138  formed in the fixed frame  120 . Thus, the rack member  132  and front support member  108  are actuated in either transverse direction while the sliders  139  are guided by the guide slot  138  as the electric motor  131  is actuated in a corresponding direction, and this causes the rear jogger  102  to perform the prescribed jogging movement in the transverse direction. 
         [0045]    Adjacent to the front rack member  122  is provided a position detector  141  for detecting the current position of the rack member  122 . The position of the front jogger  101  can be adjusted according to the output signal of the position detector  141  and a control signal from the electric motor  121 . Similarly, adjacent to the rear rack member  132  is provided a position detector  142  for detecting the current position of the rack member  132 . The position of the rear jogger  102  can be adjusted according to the output signal of the position detector  142  and a control signal from the electric motor  131 . As can be appreciated from the foregoing and following description, at each given moment while the offset stacking mode is in progress, only one of the joggers  101  and  102  is actuated by the corresponding drive unit. The other drive unit can be conveniently used for positioning the sheet fence for the particular offset stack mode. 
         [0046]      FIGS. 6 and 7  are side views (as seen from the downstream end of the sheet transporting direction) showing the sequential states of the sheet processing unit  5  shown in  FIG. 2 .  FIG. 6  illustrates the case where the sheets S are offset toward the front side, while  FIG. 7  illustrates the case where the sheets S are offset toward the rear side. 
         [0047]    Referring to  FIG. 6A , when the sheets S are desired to be offset toward the front side, the sheets S ejected from the imaging device are forwarded to the outlet rollers  31  and pinch rollers  32  which are at their neutral positions. At this time, the front support member  107  supporting the front jogger  101  and front sheet fence  103  is at an outermost (frontmost) position thereof. The rear support member  108  supporting the rear jogger  102  and rear sheet fence  104  is at a prescribed offset position which is slightly more inwardly located than an outermost (rearmost) position thereof. When the trailing edge of an incoming sheet S is detected by the detector  37  (see  FIG. 2 ) located at the inlet end of the outlet rollers  31  or the sheet S is fully pulled into the sheet processing unit  5 , following a prescribed short waiting time period, the outlet rollers  31  and pinch rollers  32  are shifted transversely toward the front by a prescribed distance (15 mm, for instance) while the incoming sheet S is being nipped by the rollers  31  and  32 , and this causes the incoming sheet S to be stacked upon the stack tray  3  at a correspondingly transversely offset position on the stack tray  3  which is more offset than a final offset position as shown in  FIG. 6B . At this time, the incoming sheet S pushes up the front sheet fence  103  to move it out of the way of the incoming sheet to be stacked upon the stack tray  3 , and the free end of the sheet fence  103  rests upon the sheet S once the sheet S has been stacked upon the stack tray  3 . 
         [0048]    Thereafter, the front jogger  101  is actuated toward the opposing side edge of the sheet S by a prescribed distance (10 mm, for instance). This causes the sheet S to be pushed into engagement with the rear sheet fence  104 , and reach the final offset position toward the front as shown in  FIG. 6C . The final offset position is offset by 5 mm (=15 mm−10 mm) from the regular position at which the paper sheet S would have been stacked if the outlet rollers  31  and pinch rollers  32  were at their neutral position. Therefore, even when there are some variations in the positions of the sheets stacked upon the stack tray  3  in the offset stack mode, the front jogger  101  jogs or pushes them toward the final offset position in cooperation with the rear fence  104 . 
         [0049]    When the sheets S are desired to be stacked upon the stack tray  3  at a position offset toward the rear, it can be accomplished in a similar fashion with appropriate modifications. When the incoming sheet S is about to be stacked upon the stack tray  3  but is still nipped between the outlet rollers  31  and pinch rollers  32 , the outlet rollers  31  and pinch rollers  32  are shifted toward the rear by a prescribed distance (15 mm, for instance) as shown in  FIG. 7A . Once the incoming sheet S is stacked upon the stack tray  3 , the rear jogger  102  is moved inwardly by a prescribed distance (10 mm, for instance) as illustrated in  FIG. 7B . This causes the incoming sheet S to be pushed against the front sheet fence  103  and to reach the prescribed final offset position as illustrated in  FIG. 7C . 
         [0050]    When all the sheets are desired to be stacked at a same position, it is possible to position the outlet rollers  31  and pinch rollers  32  at the neutral position, and eject the sheets S onto the stack tray  3  without using the joggers, or to offset all the sheets to the front or rear final offset position by using the corresponding jogger. 
         [0051]    Although the present invention has been described in terms of a preferred embodiment thereof, it is obvious to a person skilled in the art that various alterations and modifications are possible without departing from the scope of the present invention which is set forth in the appended claims. 
         [0052]    The contents of the original Japanese patent application which is published as Japanese patent laid open publication No. 2008-308243 as well as those of the prior art mentioned in the disclosure are incorporated in this application by reference.