Abstract:
A sheet processing apparatus which perform a process to sheets comprising a stacking tray on which stacks the sheets to be performed a process; a discharge roller pair; a first path in which conveys a sheet to the discharge roller pair, shorter than the length of the minimum sheet size being conveyed in the sheet conveying direction; a second path branched from the first path and meeting with the first path at the upstream side in the sheet conveying direction of the discharge roller pair; and a path switching member, wherein a first sheet conveyed while processing the sheets on the stacking tray is guided into the first path by the path switching member, and when the front end of the first sheet projects from the discharge roller pair, the discharge roller pair is apart from each other and the first sheet is held in the first path, and the path switching member is changed over, and a second conveyed sheet is guided into the second path, when the front end of the second sheet projects from the discharge roller pair by a prescribed length, the discharge roller pair is closed to each other, and the first and second sheets are discharged onto the stacking tray in superimposed state by the discharge roller pair.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a sheet processing apparatus connected to an image forming apparatus for collecting, aligning and post-processing the sheets discharged from the image forming apparatus, and more particularly to an apparatus having a stacking tray for stacking and aligning a plurality of sheets temporarily. 
   2. Description of the Related Art 
   Hitherto, the sheet processing apparatus is connected to an image forming apparatus, for conveying the sheets discharged from the image forming apparatus, aligning and sewing, and moving the sewn sheet bundle to a stacking tray. At this time, while processing the sheet bundle, next sheet bundle cannot be sent into the stacking tray, and the throughput is lowered. To solve the problem of throughput decline, it has been attempted to produce a post-processing time by temporarily superimposing and stacking two sheets before the nip section of the roller for discharging the sheets to the sheet stacking tray, before discharging sheets to the sheet stacking tray, and discharging two sheets in superimposed state onto the stacking tray, thereby preventing decline of throughput. 
   However, as shown in Japanese Patent Application Laid-Open (JP-A) No. 9-235069, in the configuration designed to discharge sheets to a stacking tray, after superimposing while aligning the ends of two sheets by hitting the sheets conveyed from above to below against the roller for discharging sheets to the stacking tray, since the end of sheet abuts against the discharge roller as sheet end stopper by the own weight, a wide space is needed for temporarily stacking the sheet in the conveyance path up to the discharge roller (a longer conveyance path than the maximum sheet size for post-processing is needed), and the apparatus is larger in size, and is higher in cost. 
   Or as disclosed in JP-A No. 1-127556, by stopping a first sheet conveyance roller, a first sheet is stopped before stacking tray discharge roller, and when the end of second sheet reaches before discharge roller pair by second sheet conveyance roller, by driving the first sheet conveyance roller, two sheets are conveyed simultaneously, and two sheets in superimposed state are discharged onto stacking tray, and even in such configuration, enough space for completely holding the first sheet within the conveyance path is required, and the apparatus is larger in size and higher in cost. 
   In the configurations disclosed in JP-A No. 9-235069 and in JP-A No. 1-127556, by stopping second sheet once when superimposing two sheets, the paper space to third sheet (the time until third sheet is stacked on stacking tray) is shortened, and enough aligning process time may not be produced. 
   SUMMARY OF THE INVENTION 
   It is hence an object of the invention to provide an inexpensive sheet processing apparatus of small size, not lowered in throughput of the connected image processing apparatus. 
   To solve the problems, a representative configuration of sheet processing apparatus of the invention is a sheet processing apparatus for processing sheets including a stacking tray for stacking sheets for post-processing, a discharge roller pair aparting from each other for discharging sheets on the stacking tray, a first path for conveying sheets to the discharge roller pair, shorter than the length of the minimum sheet size being conveyed in the sheet conveying direction, a second path branched from the first path and meeting with the first path at the upstream side of the discharge roller pair in the sheet conveying direction, a path switching member disposed at the branching point for guiding the sheets selectively to the first path or second path, a first conveyance roller disposed at the upstream side in the sheet conveying direction from the branching point, and a controlling device for controlling sheet conveyance, in which the controlling device controls to change over the path switching member, guide the conveyed first sheet into the first path, apart the discharge roller pair from each other after the front end of the first sheet has passed the discharge roller pair, change over the path switching member after the rear end of the first sheet has passed the discharge roller pair, guide the conveyed second sheet into the second path, hold the first sheet in the first path, convey the second sheet by a specified extent and then hit against the discharge roller pair, and discharge the first sheet and second sheet in superimposed state on the stacking tray by the discharge roller pair. 
   According to the invention, by aparting the discharge roller pair from each other, the sheet can be stacked in a state of sheet front end projecting from the discharge roller pair, and therefore not only the space for temporarily placing the sheet can be used as the conveyance path before discharge roller pair, but also the space above the stacking tray can be used as temporary stacking space. As a result, unlike the prior art, it is not required to have a wide space for placing the sheets temporarily in the conveyance path before the discharge roller pair, and therefore decline of throughput can be prevented without increasing the size of the apparatus. Besides, abutting of front end is not required at the time of temporary placing, sheet damage by abutting of front end can be prevented. Besides, jamming by sheet buckling due to abutting of front end is avoided, and a product of high reliability can be provided. When superimposing the second sheet, the second sheet is not stopped temporarily, and jamming of paper space between the second sheet and a third sheet is avoided, so that a sufficient aligning process time can be reserved. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic sectional view of image processing apparatus having a sheet processing apparatus according to a first embodiment. 
       FIG. 2(   a ) is a diagram explaining the operation of sheet processing apparatus. 
       FIG. 2(   b ) is a diagram explaining the operation of sheet processing apparatus. 
       FIG. 2(   c ) is a diagram explaining the operation of sheet processing apparatus. 
       FIG. 2(   d ) is a diagram explaining the operation of sheet processing apparatus. 
       FIG. 2(   e ) is a diagram explaining the operation of sheet processing apparatus. 
       FIG. 2(   f ) is a diagram explaining the operation of sheet processing apparatus. 
       FIG. 2(   g ) is a diagram explaining the operation of sheet processing apparatus. 
       FIG. 2(   h ) is a diagram explaining the operation of sheet processing apparatus. 
       FIG. 2(   i ) is a diagram explaining the operation of sheet processing apparatus. 
       FIG. 3(   a ) is a top view of sheet processing apparatus. 
       FIG. 3(   b ) is a top view of sheet processing apparatus. 
       FIG. 4  is a diagram explaining the configuration of sheet processing apparatus according to a second embodiment. 
       FIG. 5(   a ) is a diagram explaining the operation of sheet processing apparatus. 
       FIG. 5(   b ) is a diagram explaining the operation of sheet processing apparatus. 
       FIG. 6  is a diagram explaining the configuration of sheet processing apparatus according to a third embodiment. 
       FIG. 7(   a ) is a diagram explaining the operation of sheet processing apparatus. 
       FIG. 7(   b ) is a diagram explaining the operation of sheet processing apparatus. 
       FIG. 7(   c ) is a diagram explaining the operation of sheet processing apparatus. 
       FIG. 7(   d ) is a diagram explaining the operation of sheet processing apparatus. 
       FIG. 7(   e ) is a diagram explaining the operation of sheet processing apparatus. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   First Embodiment 
     FIG. 1  is a schematic sectional view of image processing apparatus having a sheet processing apparatus according to a first embodiment. The image processing apparatus on the whole shown in the drawing is an internal discharge type configuration in which an image reading apparatus  300  is disposed above an image forming apparatus  100 , and sheets on which images are formed are discharged into a space formed between the image forming apparatus  100  and image reading apparatus  300 , and a sheet processing apparatus  200  can be installed in this space. The image forming apparatus  100  receives image information or print signal and the like sent directly from a computer connected thereto or via network of LAN or facsimile, or image information read by the image reading apparatus  300 , and forms images on sheets by specified image process based on such information, and discharges sheets. 
   First, referring to  FIG. 1 , the configuration of the image forming apparatus  100  is explained along the route of conveyed sheet S. In the image forming apparatus  100 , a plurality of sheets S are stacked in an upper feed cassette  101  and a lower feed cassette  102 , and the top sheet is separated and supplied each from either cassette by various rollers. By a specified print signal supplied from the computer, network or image reading apparatus  300 , the sheet S supplied from the upper feed cassette  101  or lower feed cassette  102  is processed in the image forming apparatus  100 , and a toner image is transferred on the top of the sheet S in the image forming unit  103  for forming a toner image by image forming process of laser beam system. In succession, in the sheet S, heat and pressure are applied from a fixing device  104  at downstream side, and the toner image is permanently fixed. 
   The image forming apparatus  100  includes a controlling device  110  for controlling various operations, and the operation of sheet processing apparatus  200  described below is also controlled by the controlling device  110 . A control unit may be provided at the sheet processing apparatus  200  side, and the operation of the sheet processing apparatus  200  may be controlled through this control unit. 
   The sheet S of which image side is fixed in the upper side state is conveyed in a U-shaped sheet conveyance route up to discharge roller  105  as shown in  FIG. 1 , and the image side is inverted, and with the image side at the lower side, it is discharged face-down to outside from the image forming apparatus  100  by the discharge roller  105 . Based on control signal from the controlling device  110 , the position of discharge port switching flapper  106  is changed over, and it is selected whether the sheet S is discharged directly into a face-down discharge unit  107  provided in the upper part of the image forming apparatus  100 , or discharged by way of the sheet processing apparatus  200 . 
   Referring to  FIG. 1 , the configuration of the sheet processing apparatus  200  is explained together with conveying operation of sheet S by switching of the conveyance route by the discharge port switching flapper  106 . The sheet S is conveyed by a transfer roller  108 , and conveyed into the sheet processing apparatus  200 . 
   As shown in  FIG. 1 , the sheet processing apparatus  200  includes a stacking tray  203  for stacking sheets for post-processing, a discharge roller pair  202  for discharging sheets onto the stacking tray and contacting with or aparting from a nip, a first path  209  shorter than minimum sheet size for post-processing for conveying sheets onto the stacking tray  203 , and a second path  210  branched from the first path  209  and meeting with the first path  209  at the upstream side of the discharge roller pair  202 . The sheet processing apparatus  200  further comprises a switching flapper  212  as an example of path switching member for selectively guiding the sheet into the first path  209  or second path  210 , a first path roller  201  as an example of first conveyance roller disposed at the upstream side from the branching point, and a second path roller  211  as an example of second conveyance roller disposed in the second path  210  working with the first path roller  201 . The second path  210  is the outer side of the first path  209 , that is, the conveying side of the first path  209 , and is disposed at the opposite side of the mounting side to the stacked tray  203 . 
   The stacking tray  203  includes a return roller  204  for aligning the stacked sheets in the sheet conveying direction, a reference wall  205  against which rear ends of sheets returned by the return roller  204  abut, a lateral aligning plate  206  for aligning the sheets in a direction orthogonal to the sheet conveying direction, a stapler H for sewing the matched sheet bundle, and a discharge roller  207  for discharging the post-processed sheet bundle to the discharge tray  208  outside of the machine. 
   In this constitution, the conveyance route is changed over to the sheet processing apparatus  200  side by the discharge port switching flapper  106 , and the sheet S is introduced into the sheet processing apparatus  200  by the transfer roller  108 . The sheet S is discharged onto the stacking tray  203  by the discharge roller pair  202 , and matched and processed by the return roller  204  and lateral aligning plate  206 , and sewn and processed by the stapler H, and discharged outside of the machine as sheet bundle by the discharge roller  207 . 
   Referring now to  FIGS. 2(   a ) to  2 ( i ) and  FIGS. 3(   a ) and  3 ( b ), the next explanation is about stapling process conducted consecutively for executing plural jobs sent from the computer or the like through the network. That is, from placing of final sheet of preceding job on the stacking tray  203  in operation of sheet processing apparatus  200  until stapling and discharge of next job, the operation is specifically described below.  FIGS. 2(   a ) to  2 ( i ) explains the operation of sheet processing apparatus, and  FIGS. 3(   a ) and  3 ( b ) is a top view of sheet processing apparatus. 
     FIG. 2(   a ) shows a mode of placing of final sheet S 1 L of preceding job on the stacking tray. At this time, first sheet S 21  of next job is conveyed into the sheet processing apparatus  200  at ordinary sheet interval to final sheet S 1 L of preceding job. When final sheet S 1 L is discharged onto the stacking tray  203 , the set-away return roller  204  approaches and compresses final sheet S 1 L, and conveys final sheet S 1  in the direction of reference wall  205 , and thereby matches in the sheet conveying direction ( FIG. 2(   b )), and is aparted again after aligning ( FIG. 2(   c )). 
   In this period, the sheet S 21  is conveyed through the first path  209  without stop, and the sheet front end passes over the discharge roller pair  202  ( FIG. 2(   d )). Herein, the lateral aligning plate  206  begins to match in orthogonal direction to sheet conveying direction of final sheet S 1 L before the front end of sheet S 21  reaches the discharge roller pair  202  ( FIG. 3(   a )), and until the front end of sheet S 21  passes over the discharge roller pair  202 , the move in orthogonal direction to sheet conveying direction to stapler H side is terminated ( FIG. 3(   b )). At this time, sheet S 21  is conveyed while contacting with the upper end side of the lateral aligning plate  206 . 
   Next, when the front end of sheet S 21  has passed over the discharge roller pair  202 , the discharge roller pair  202  is aparted. Further, when the sheet rear end of sheet S 21  has passed over the first path roller  201 , the switching flapper  212  is changed over, and the front end of sheet S 21  projects into the upper space of the stacking tray  203 , and the sheet rear end is held by the switching flapper  212  in the first path  209 . At the same time, sheet S 22  of second job can be introduced into the second path  210  ( FIG. 2(   d )). Before the rear end of sheet S 21  passes over the first path  201 , aligning of sheet bundle S 1  of preceding job in direction orthogonal to sheet conveying direction, and sewing process by stapler H have been terminated. In this embodiment, the sheet rear end of sheet S 21  is held by the switching flapper  212 , but alternatively a sheet rear end stopper for holding sheet rear end of sheet S 21  after passing over the first path roller  201  may be provided at the downstream side of the first path roller  201 . By such structure of holding the sheet rear end, the sheet front end side can be held in a state projecting from the first path  209  while the discharge roller pair  202  of processing tray is aparted, and the first path  209  can be set shorter than the sheet length, so that the apparatus can be smaller in size. 
   In succession, while the first sheet S 21  is being held by the switching flapper  212 , a second sheet S 22  is conveyed into the second path  210 . At this time, the discharge roller  207  nips and conveys the sheet bundle S 1  of preceding job, and the sheet bundle S 1  is discharged ( FIG. 2(   e )), and when discharge of sheet bundle S 1  is complete, the discharge roller  207  is aparted again ( FIG. 2(   f )). Since the first path  209  and second path  210  are disposed as independent paths as being partitioned by guide plate, and second sheet S 22  does not contact directly to push out first sheet S 21  held in the first path  209 . However, since the first path  209  and second path  210  meet together before the discharge roller pair  202 , the front end of sheet S 21  may contact with sheet S 21  to push out, but in this embodiment, the first path  209  is curved widely to provide sheet S 21  with tenacity, and frictional resistance in the first path  209  is increased to preventing from pushing out. Holding of sheet S 21  in first path  209  may be realized only by curved structure of first path  209 , but it is preferred to combine with sheet holding by switching flapper  212 . More secure holding is possible by adhering a frictional member to the contact portion of switching flapper  212  and sheet, or forming a frictional member such as undulated surface. The switching flapper  212  may be formed of an elastic material, and the rear end of sheet S 21  may be pressed down. 
   The sheet S 22  continues to be conveyed by a specified distance by the second path roller  211 , after the sheet rear end has passed over the first path roller  201 , until it is aligned with the front end of sheet S 21  or the front end of sheet S 22  moves ahead of the front end of sheet S 21 . At the timing of the front end of sheet S 22  aligning with the front end of sheet S 21 , or the front end of sheet S 22  moving ahead of the front end of sheet S 21 , the discharge roller pair  202  is compressed ( FIG. 2(   g )), and two sheets S 21 , S 22  are superimposed in the aligned state of front ends of S 21  and S 22 , or in the state front end of S 22  ahead of front end of S 21 , and discharged onto the stacking tray  203  ( FIG. 2(   h )). 
   The sheet S 22  is superimposed on the sheet S 21  and discharged onto the stacking tray  203 , and the return roller  204  pushes the sheet rear end against the reference wall  205  and matches in the sheet conveying direction, and at this time, the return roller  204  acts only on the top of the sheet S 22 . The return roller  204  continues the returning action until the rear end of the upper sheet S 22  abuts against the reference wall  205 , but by the frictional action between sheet S 22  and sheet S 21 , sheet S 22  and sheet S 21  are pushed back together. At this time, if the sheets are stacked with the front end of sheet S 22  with projecting, first, the rear end of sheet S 21  hits against the reference wall  205 , and then the rear end of sheet S 22  hits against the reference wall  205 , and aligning is complete, but on the contrary if the sheets are stacked with the front end of the first sheet S 21  with projecting, aligning is complete when the front end of sheet S 22  hits against the reference wall  205 . This is the reason why the front end of the second sheet S 22  is moved ahead of the front end of the first sheet S 21 . 
   Incidentally, the second path  210  is disposed outside of the first path  209 , that is, at the opposite side of stacking side on stacking tray  203  with respect to the conveying side of the first path  209 , and hence the sheet S 21  is located at the stacking tray  203  side from the sheet S 22 . Since the sheets are discharged face-down, with the image surface at the stacking tray  203  side, with sheet S 22  superimposed on sheet S 21 , the sheets are stacked in the page sequence. Herein, the sheet S 22  does not stop until discharged onto the stacking tray  203 . The lateral aligning plate  206  completely moved away to the sheet receiving position (outside of sheet passing range) before sheets S 21 , S 22  are discharged onto the stacking tray  203 . 
   Afterwards, until a third sheet S 23  is fed in, the return roller  204  matches in the sheet conveying direction, and the lateral aligning plate  206  matches in the orthogonal direction to sheet conveying direction ( FIG. 2(   i )). After third sheet S 23 , without stopping in the first path  209 , the sheets directly pass over the first path  209  and are consecutively discharged and matched on the stacking tray  203 , and are finally stapled and discharged. The sheet S 23  and the following sheets are discharged face-down on the top of the stacked sheets with the image surface at the stacking tray  203  side, so that the page sequence will not be disturbed. 
   Second Embodiment 
   A second embodiment of sheet processing apparatus of the invention is described.  FIG. 4  is a diagram explaining the configuration of sheet processing apparatus of the second embodiment, and  FIGS. 5(   a ) and  5 ( b ) is a diagram explaining the operation of sheet processing apparatus, and same parts as in the first embodiment are identified with same reference numerals, their explanation is not described. 
   This embodiment is different from the first embodiment in the shape of the conveyance path from first path roller  201  to discharge roller pair  202 . 
   As shown in  FIG. 4 , a sheet processing apparatus  400  of the embodiment is disposed in an upper and side portion of image forming apparatus  100 , and is designed to discharge the sheet bundle after post-processing to outside of the machine. A first path  401  is nearly straight, and a second path  402  is curved and disposed closely to the first path  401 . In this embodiment, after images are formed in the image forming apparatus  100 , sheets are conveyed in face-up state, and to discharge the sheets in page sequence, by the control of image formation, images may be formed in reverse order from final page to first page, or by switching back by using the face-down discharge unit on the image forming apparatus  100 , the sheets may be conveyed in face-down state in the first path  401  and second path  402  by an inverting path (not shown). Besides, a friction member  404  is provided at the position of the first path  401  opposite to the switching flapper  403  for changing over the first path  401  and second path  402 . 
   Referring to  FIGS. 5(   a ) and  5 ( b ), stapling operation of consecutive jobs in the sheet processing apparatus  400  of the preferred embodiment is explained. 
   In this embodiment, same as in the first embodiment, after the final sheet S 1 L of preceding job is discharged, it is matched and sewn, and in this process, a first sheet S 21  of next job is conveyed ( FIG. 5(   a )), and then a second sheet S 22  is conveyed. At this time, by the switching flapper  403  and friction member  404 , the rear end of first sheet S 21  is gripped and held ( FIG. 5(   b )). In this embodiment, the friction member  404  is provided at the first path  401  side, but the friction member  404  may be provided at least at one side of the first path  401  and switching flapper  403 . A greater effect will be obtained by forming the switching flapper  403  by an elastic member. 
   In this configuration, if the sheet processing apparatus does not have a widely curved path as in the first embodiment, at least the front end of second sheet S 22  does not push out the first sheet S 21  by friction. Therefore, in addition to the same effects as in the first embodiment, since curve path is not particularly required, the apparatus can be composed by using paths of free shape, and the apparatus may be further reduced in size, and it is possible to connect to various image forming apparatuses, and the applicability of the apparatus can be extended. 
   Third Embodiment 
   A third embodiment of sheet processing apparatus of the invention is described.  FIG. 6  is a diagram explaining the configuration of sheet processing apparatus of the third embodiment, and  FIG. 7(   a ) to  7 ( e ) is a diagram explaining the operation of sheet processing apparatus, and same parts as in the first embodiment are identified with same reference numerals, their explanation is not described. 
   This preferred embodiment is different from the first embodiment in the aligning means in a direction orthogonal to sheet conveying direction. 
   In a sheet processing apparatus  500  shown in  FIG. 6 , a lateral aligning roller  501  for aligning sheets in a direction orthogonal to sheet conveying direction is provided beneath discharge roller pair  202  and at the upstream side in sheet conveying direction. In this embodiment, the lateral aligning roller  501  moves the sheet in a direction orthogonal to sheet conveying direction, but the lateral aligning roller  501  may have an angle against reference wall  205  so as to move the sheet while pushing against the reference wall  205  and match also in sheet conveying direction. 
   Referring to  FIG. 7(   a ) to  7 ( e ), stapling operation of consecutive jobs in the sheet processing apparatus  500  of the preferred embodiment is explained. 
     FIG. 7A  shows a mode of final sheet S 1 L of preceding job stacked on the stacking tray. At this time, first sheet S 21  of next job is conveyed into the sheet processing apparatus  500  at an ordinary sheet interval with respect to final sheet S 1 L of preceding job. When final sheet S 1 L is discharged onto the stacking tray  203 , the set-away return roller  204  approaches and compresses final sheet S 1 L, and conveys the sheet in the direction of reference wall  205 , and thereby matches in the sheet conveying direction ( FIG. 7(   b )), and is aparted again after aligning ( FIG. 7(   c )). During this operation, the lateral aligning roller  501  is set away from the top of the sheet bundle. 
   In this period, the sheet S 21  is conveyed through the first path  209  without stop, and the sheet front end passes over the discharge roller pair  202 . At this time, the lateral aligning roller  501  compresses the final sheet S 1 L, and matches the sheet in a direction orthogonal to sheet conveying direction ( FIG. 7(   d )). 
   When the front end of sheet S 21  passes over the discharge roller pair  202 , the discharge roller pair  202  is aparted. Further, when the sheet rear end of sheet S 21  passes over the first path roller  201 , the sheet S 21  is held by the first path  209 , with its front end projecting into the upper space of the stacking tray  203 . At this time, the switching flapper  212  is changed over, and second sheet S 22  of next job can be introduced into the second path  210  ( FIG. 7(   e )). Herein, before the rear end of first sheet S 21  passes over the first path roller  201 , aligning of sheet bundle S 1  of preceding job in a direction orthogonal to sheet conveying direction, and sewing process by the stapler H have been terminated, and the lateral aligning roller  501  is aparted from the top of the sheet bundle. 
   The subsequent operation of stapling mode is same as in the first embodiment, and explanation is not described. 
   In this configuration, aligning in direction orthogonal to sheet conveying direction is realized by using a lateral aligning roller provided at the upstream side from the discharge roller pair  202 , and the stacking tray  203  can be reduced in size, and the apparatus can be further reduced in size. 
   The invention is applied in a sheet processing apparatus for collecting, aligning and post-processing the sheets discharged from an image forming apparatus. 
   This application claims priority from Japanese Patent Application No. 2004-249952 filed Aug. 30, 2004, which is hereby incorporated by reference herein.