Abstract:
A sheet processing apparatus has a function of stapling sheets together, wherein the sheets are fed from an image forming apparatus one by one after images are formed on the sheets. The sheet processing apparatus includes a stapler to staple the sheets together, a sheet guide which guides the sheets along a sheet transporting path from the image forming apparatus to a position at which the sheets are stapled by the stapler, and a reference surface against which edges of the sheets are butted to stop movement of the sheets. The sheets are guided along the sheet transporting path by the sheet guide and the edges of the sheets are butted against the reference surface at a same position relative to a sheet conveying direction, irrespective of whether the sheet processing apparatus is in a stapling mode in which the stapler staples the sheets or a non-stapling mode in which the stapler does not staple the sheets, and irrespective of sizes of the sheets.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a sheet processing apparatus which receives sheets whereon an image is formed by an image forming apparatus such as an electrophotographic copying machine, a printer, or a printing machine and discharges them onto a receiving tray by a discharging means after finishing processes such as inverting upside down, stacking, and binding together. 
     For an apparatus which collates a plurality of sheets with an image formed by an image forming apparatus ejected from the apparatus for each set of copies and binds them with a stapler, a sheet processing apparatus, called as a finisher, is used. 
     This finisher is functionally connected to an image forming apparatus such as a copying machine, or a printer, and is designed to be driven corresponding to the sequential operation of the copying or printing process. 
     Accordingly, for an image forming apparatus capable of forming images at a high speed and for a high volume, it is required that the finisher be capable of high-speed and high-volume processing which can fulfill the function in accordance with the processing speed. 
     Concerning such kind of a finisher capable of high-speed processing, several proposals have already been disclosed in the Japanese laid open patents S60-142359, S60-158463, S62-239169, S62-288002, S63-267667, and H2-276691, and Japanese publicized patent H5-41991. 
     The sheets with an image formed on them, conveyed out of the image forming apparatus mainframe, are successively stacked in an intermediate stacking plate in the collated order, and are subjected to sheet processings such as stapling, etc., after a set of copy sheets are stacked. The bound set of copy sheets are carried on the discharging belt provided at the bottom of said intermediate stacking plate, transported, held between a pair of upper-and-lower ejecting rollers, and are discharged onto the receiving tray. 
     The sheet processing apparatus described in the Japanese laid open patent H8-42728 is provided with a stapler and a receiving tray corresponding to it. Further, the sheet processing apparatus described in the Japanese laid open patent H7-76190 is provided with two staplers and two receiving trays corresponding to them. 
     The sheet inverting system described in the Japanese laid open patent H8-85663 has two different positions for positioning the leading edge of sheets, a first one at which stapling is carried out, and at a second one at which stapling is not carried out; these two different positions are determined by a movable finger for position adjusting. 
     The tray apparatus described in the Japanese laid open patent H1-181672 is provided with a stopping portion made up of a soft member for stopping the trailing edge of the paper sheets stacked on the receiving tray and an urging member for urging one end portion of said soft member upward. 
     In the conventional sheet processing apparatus, the sheets with an image formed on them, conveyed out of the image forming apparatus, are subjected or not subjected to the processings by the sheet processing means (including stapler, shifting means, bookbinding means, punching means, etc.), transported, and ejected onto the receiving tray by the discharging means, where they are sliding down along the tilted surface of the tray until their trailing edges collide with the stopper to be stopped there. On the other hand, the sheets which are not to be subjected such processings are directly ejected onto the fixedly attached tray where they are sliding down the tilted surface of the tray until their trailing edges collide with the stopper to be stopped there. 
     In regard to the conventional sheet processing apparatus and the conventional sheet discharging apparatus, the problems to be solved will be described in the following. 
     (1) The sheets with an image formed on them are transported by the sheet processing apparatus; however, the sheet transport path in the stapling process mode having the intermediate stacking plate is different from the sheet transport path in the non-stapling process mode; hence, the sheet transport path is long and large and has a complex structure, which results in poor sheet transport. Further, because a bifurcating means for switching the path, a number of transport rollers, driving means for these, control means, and so forth are required, there are problems in that the apparatus is made complex and large-sized, and that the manufacturing cost is increased. 
     (2) In the sheet inverting system described in the Japanese laid open patent H8-85663, there are provided two different positions for positioning the leading edge of sheets, a first one at which stapling process is carried out, and a second one at which stapling process is not carried out; these two different positions are determined by a movable finger for position adjusting. Because this sheet inverting system uses the movable finger for positioning oscillation, there is a problem that it requires a driving source and a driving means, which makes its structure complex and increases the risk of malfunction. Further, because the movable finger oscillates at a fixed position, it is difficult to carry out the positioning of the leading edge of the sheet precisely for all sizes of the sheets from the minimum size (A 6 R size for example) to the maximum size (A3 size for example). 
     SUMMARY OF THE INVENTION 
     It is an objective of this invention to provide a sheet processing apparatus which achieves (1) accurate positioning regarding the leading edge of the sheets with an image formed on them to stop the sheets both in the stapling process mode and in the non-stapling process mode, and (2) accurate and stable sheet stopping with the member having a basic surface for sheet stopping made to have a simple structure. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     Other objectives and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the drawings in which: 
     FIG. 1 is a cross-sectional view showing the structure of a sheet processing apparatus of this invention; 
     FIG. 2 is a perspective view of the sheet inverting-transporting portion and the discharging portion of the sheet processing apparatus; 
     FIGS.  3 ( a ) and  3 ( b ) are partial cross-sectional views showing the sheet transporting process of the sheet processing apparatus; 
     FIGS.  4 ( a ) through  4 ( c ) are partial cross-sectional views showing the sheet transporting process of the sheet processing apparatus; 
     FIGS.  5 ( a ) and  5 ( b ) are partial cross-sectional views showing the sheet transporting process of the sheet processing apparatus; 
     FIG. 6 is the front view of the shift truing-up means; 
     FIGS.  7 ( a ) through  7 ( c ) are schematic plans showing the operation of truing-up plates at the time of stapling process; 
     FIGS.  8 ( a ) and  8 ( b ) are schematic drawings showing the operation of the truing-up plates at the time of shifting process; 
     FIG. 9 is a plan showing the process of moving of the stapler stapling sheets of various sizes being in contact with the stopper; 
     FIGS.  10 ( a ) and  10 ( b ) are a plan showing how the stapling is done at tow points of the sheets of various sizes and a plan showing the disposition of the stapler; 
     FIGS.  11 ( a ) and  11 ( b ) are the plan and the front view of the receiving tray means; 
     FIG. 12 is a perspective view of the receiving tray; and 
     FIGS.  13 ( a ) and  13 ( b ) are cross-sectional views showing the initial state of going up when sheets start to be stacked on the movable receiving tray, and the state of going down when the maximum number of sheets are stacked. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following, a sheet processing apparatus embodied in the present invention will be described in detail, referring the attached drawings. 
     FIG. 1 is a cross-sectional view showing the structure of the above-mentioned sheet processing apparatus (finisher). FIG. 2 is a perspective view of the sheet inverting-transporting portion and the paper ejecting portion of said sheet processing apparatus. 
     The aforesaid sheet processing apparatus is installed with its position and level adjusted in a manner such that the receiving portion for the sheet P coincides with the paper ejecting exit of the image forming apparatus (such as a copying machine or a printer) mainframe, and is connected to the control system so as to be driven corresponding to the operation of the image forming apparatus mainframe. 
     Regarding sheet P that is introduced into the aforesaid receiving portion, its transport path can be switched to upper transport path “a” and lower transport path “b” by the oscillating switch of switching gate  1  (diverging plate). 
     Sheet P ejected by the pair of ejecting rollers R 101  of image forming apparatus mainframe  100  passes the upper transport path by the switching of switching gate  1  of the aforesaid receiving portion, and is ejected to receiving tray  10  fixedly arranged at the uppermost stage of the sheet processing apparatus, held between the pair of ejecting rollers  2 . 
     On the other hand, sheet P, which has passed lower transport path “b” by the switching of switching gate  1  of the aforesaid receiving portion, is transported by the pair of intermediate transport rollers  3  composed of a driving roller and a pinch roller, passing transport path “c” made up of a fixed guiding plate, and is further transported onto the circumferential surface of sheet transporting drum  4  held between the pair of transporting rollers  5  located above drum  4 . Sheet transporting drum  4  is driven to rotate in the direction of the arrow by a driving source (not shown). Near the circumferential surface of sheet transporting drum  4 , sheet holding member  6  (hereinafter referred to as gripper  6 ) is supported to be able to oscillate. Gripper  6  is urged by a spring and is made to oscillate by a cam mechanism (not shown). 
     The leading edge of sheet P, which is conveyed out from the nip position of transporting roller pair  5  onto the circumferential surface of sheet transporting drum  4 , enters into the V-shaped clearance portion between the front end portion of gripper  6  which is made to be in the open state by the aforesaid cam mechanism and the circumferential surface of sheet transporting drum  4 , and is further transported with sheet transporting drum  4 , pressed and held between the front end portion of the spring-urged gripper  6  and the circumferential surface of the rotating sheet transporting drum  4 . In addition, at the time of this sheet transport, the circumferential speeds of transporting roller pair  5  and sheet transporting drum  4  are equal. 
     FIG.  3  through FIG. 5 are partial cross-sectional views showing the process of sheet transport in the sheet processing apparatus. 
     In FIG.  3 ( a ), in the process of transport of the leading edge of sheet P, which is pressed and held by the front end portion of aforesaid spring-urged gripper  6  on the circumferential surface of sheet transporting drum  4 , when the speed of transport roller pair  5  is increased, the portion near the trailing edge of sheet P has its speed increased by transport roller pair  5  to be fed excessively, resulting in the intermediate portion of sheet P to be of the shape swelling outward apart from the circumferential surface of sheet transporting drum  4 . 
     In FIG.  3 ( b ), while sheet transporting drum  4  further continues to rotate, at the moment when the trailing edge portion of sheet P is released out of the nip position of transporting roller pair  5 , sheet P is inverted by the transporting force of transporting roller pair  5  and the stiffness of sheet P, and is detached from the circumferential surface of sheet transporting drum  4 . When the leading edge portion of sheet P is butted at reference surface  7 S of reference surface member  7  (hereinafter referred to as stopper  7 ) to stop the movement of sheet P, gripper  6  releases sheet P. 
     As shown in FIG.  4 ( a ), in the process of continuing the rotation of sheet transporting drum  4 , two sheet truing-up members  8 A and  8 B supported to be able to rotate at the two positions in sheet transporting drum  4  rub the portions near the leading edge of sheet P successively one after another to make the leading edge of sheet P contact with reference surfaces  7 S of stopper  7 ; thus sheets P are trued up in the direction of transport. The leading edge portion of the trued up sheets P is placed on intermediate receiving tray  92 , and the trailing edge portion is placed on sheet stacking plate  21  of upper sheet receiving tray  20 . 
     As described above, the sheet transport path for the sheet with an image formed on it is the same in both the stapling process mode and non-stapling process mode. Further, the reference surfaces for butting the leading edge of the sheet are set at the same positions in both the stapling process mode and non-stapling process mode. 
     Further, reference surfaces  7 S are positioned inside the both side edges for all the sheet sizes discharged from image forming apparatus mainframe  100 , even when sheet P is shifted to the direction perpendicular to the sheet transport direction. 
     FIG.  4 ( b ) is a drawing showing the positional relationship between reference surfaces  7 S of stopper  7  and sheet transporting drum  4 . 
     Reference surfaces  7 S are positioned at the downstream side in the sheet transport direction from the position just under the rotational axis of sheet transporting drum  4  for holding the leading edge portion of the sheet to invert it. That is, distance L between the plumb line shown by the broken line just under the rotational axis of sheet transporting drum  4  and reference surfaces  7 S is set at a predetermined distance, for example, approximately 10 mm downstream the sheet transport direction. Owing to this, the leading edge portion of sheet P held between spring-urged gripper  6  and sheet transporting drum  4  is reliably butted at the reference surfaces  7 S to stop, and the gripper  6 , which has released the sheet P, rotates together with sheet transporting drum  4  to be ready to the successive sheet holding. 
     At least two reference surfaces  7 S are arranged in the sheet width direction perpendicular to the sheet transport direction and are movable in the sheet width direction corresponding to the movement of staplers  50  under stapling process. 
     Further, the upper portion of reference surface  7 S is formed to be a curved surface  7 R bending to the sheet side. This curved surface  7 R is formed to be a curved surface having a radius of curvature approximately 30 mm. Even if a number of transported sheets P, the leading edges of which are curved upward, are stacked, the leading edges of sheets P never rides over reference surfaces  7 S, because the leading edge portion proceeding to stopper  7  is hindered by this curved surface  7 R to be pressed downward. 
     Next, in the process shown in FIG.  4 ( c ) where the leading edge of sheet P is butted at reference surfaces  7 S of stopper  7 , truing-up members  91  trues up sheets P in the width direction (direction perpendicular to the sheet transport direction) (width truing-up). In another case where the shift mode is set, truing-up members  91  are alternately shifted to the predetermined plural positions to make said width truing-up. After completion of the positioning of first sheet P by one rotation of sheet transporting drum  4 , second sheet P is fed into sheet transporting drum  4 , further transported as mentioned above, with its position regulated, and then stopped. In this way, when the number of sheets P, which have been batted at the reference surface  7 S of the stopper  7  to be properly positioned, reaches the predetermined number, they are stapled at their specified positions and bound together by staplers  50 . Further, in the case where the shift mode is set, after the shifting operation by truing-up members  91 , sheet truing-up (width truing-up) is carried out and the sheet is made to collide with stopper  7 . When simple paper ejecting is done in the non-stapling process mode, the paper sheets are trued up and made to collide with stopper  7 . 
     Stopper  7  is fixed on the moving carriage of staplers  50 , and is movable together with the staplers as a united member. 
     FIG.  1  and FIG.  5 ( a ) are drawings showing how sheet P, for which a stapling-process or non-stapling process (shifting process, simple ejecting) is completed, is ejected onto sheet stacking plate  21  or onto fixed plate member  22 . FIG.  11 ( a ) is the plan of the upper sheet receiving tray  20 , FIG.  11 ( b ) is the front view of upper sheet receiving tray  20 , and FIG. 12 is a perspective view of upper sheet receiving tray  20 . 
     In FIG. 1, driving motor M 5  of ejecting unit  11  drives to rotate disk  12  through the drive transmitting system composed of timing belt TE 1 , gear G 25 , and gear G 26 . The other end of crank  13  with its one end supported at an eccentric position of disk  12 , is supported by a shaft to be able to rotate freely at a part of ejecting arm  14  which is capable of oscillating around supporting shaft  15 . Disk  12  driven to rotate by motor M 5  makes crank  13  to move eccentrically and further makes ejecting arm  14  oscillate. By this oscillating motion of ejecting arm  14 , front end portion  14 A of ejecting arm  14  presses the leading edge portion of sheet P, for which the sheet processing is completed, to push it out from the position in contact with stopper  7  toward sheet receiving plate  21  and fixed plate member  22  of upper sheet receiving tray  20 . Sheet P that has been pushed out by ejecting arm  14 , after sliding on the upper surfaces of sheet stacking plate  21  and fixed plate member  22 , goes down by their own weight until the leading edge portion collides with sheet stopping surface  21 B and stop. Front end portion  14 A of ejecting arm  14  comes forward to near the position just over sheet stopping surface  21 B of sheet stacking plate  21 ; hence, the bundle of the sheets is reliably moved onto sheet stacking surface  21 A of upper receiving tray  20 . 
     Now, because upper sheet receiving tray  20  and lower sheet receiving tray  30  have the same shape, upper sheet receiving tray  20  will be explained as the representative in the following. 
     Upper sheet receiving tray  20  comprises of fixed plate member  22 , sheet stacking plate  21 , supporting shaft  23  attached to the fixed receiving plate for supporting one end of sheet stacking plate  21  to be able to oscillate around it, and spring  24  for urging upward the other end of sheet stacking plate  21 . 
     Sheet stacking surface  22 A of fixed plate member  22  is formed to make an inclined surface in such a manner as to make the leading edge portion of the stacked sheets high and the trailing edge portion low. At the lower side of this inclined surface, curved stopping surface portion  22 B is formed integrally. 
     Fixed plate member  22  is engaged with and fixed to the going-up-and-down means of the sheet processing apparatus mainframe and is driven to go up and down. 
     Sheet stacking surface  21 A of sheet stacking plate  21  is disposed between side walls  22 A of the fixed plate member  22  positioned to the both sides of sheet stacking surface  21 A, is engaged with the fixed plate by supporting shaft  23  to be able to oscillate, and is urged upward by spring member  24 , with its engaging surface made to be in contact with the stopper (not shown), to be stopped at the upper limit position. The upper end of spring member  24  is positioned at the bottom of sheet stacking plate  21 , and fixed by an engaging member. The lower end of spring member  24  is loosely fitted in the concave portion provided at the bottom of fixed plate member  22  for positioning. 
     The sheets ejected out of the machine by ejecting unit  11 , after being discharged on sheet stacking surface  21 A, slide down along sheet stacking surface  21 A due to their own weight, and their trailing edges come down toward sheet stopping surface  21 B, until they collide with sheet stopping surface  21 B to be stopped, pushed by rotating roller  27  for truing up the edges. 
     In addition, upper surface  14 B of ejecting arm  14  is made to form a circular arc to extend to the rear direction. When the ejecting arm oscillates to the left to go forward as shown in the drawing, because above-mentioned upper surface  14 B extends backward to make no clearance between sheet transporting drum  4  and ejecting arm  14 , there is no risk for the operator to insert his fingers inadvertently to be gripped in between. 
     FIG.  5 ( b ) is a drawing showing how a number of sheets P are ejected and stacked on sheet stacking plate  21  and fixed plate member  22 , after being subjected to stapling process or non-stapling process. 
     When a lot of sheets P are stacked on sheet receiving tray  20  to exceed the specified weight, sheet stacking plate  21  oscillates around shaft  23  to go down against the urging force of spring member  24  due to the own weight of sheets P. In this case too, the leading edge portion of sheets P collides with sheet stopping surface  21 B to be stopped and is trued up. In the process of the above-mentioned sheet stacking, no frictional resistance is given to the leading edge portion of sheets P to let sheet stacking plate  21  go down smoothly, because the leading edge portion of sheets P contacts with sheet stopping surface  21 B of sheet stacking plate  21  capable of going up and down for truing up. 
     When the top of further stacked sheets P exceeds the top of sheet stopping surface  21 B, the leading edge portion of sheets P collides with stopping surface portion  22 B of fixed plate member  22  to be stopped. 
     In FIG.  11  and FIG. 12, ejecting rollers  27  are provided to be able to rotate for driving over sheet stopping surface  21 B of sheet stacking plate  21  and over fixed plate member  22 . Ejecting rollers  27  (elastic rollers) are formed of soft rollers having elasticity (sponge rollers) made up of a foamed resin or the like, and fixed on rotating shaft  28  through holding member  27 A. These plural ejecting rollers  27  are disposed on rotating shaft  28 . This rotating shaft  28  is supported to be able to rotate on the both side walls of fixed plate member  22  in the direction perpendicular to the sheet transport. 
     Rotating shaft  28  rotates in the counter-clockwise direction shown in FIG.  11 ( b ), with the driving force transmitted through the transmission system composed of gears G 21 , G 22 , G 23 , and G 24  from driving motor M 9  as a driving source. 
     Upper sheet receiving tray  20  according to this invention, comprises of driving motor M 9 , drive-transmitting members G 21  through G 24 , sheet stacking plate  21 , fixed plate member  22 , ejecting rollers  27 , and so forth, these members forming a paper discharging unit integrally assembled together. Accordingly, this unit as a whole can be separately assembled, adjusted, and exchanged with the other unit apart from the sheet processing apparatus mainframe. Lower receiving tray means  30  is also made up as a unit in the same manner. 
     In FIG.  5 ( a ), when sheet P is ejected onto upper sheet receiving tray  20  with the actuation of ejecting arm  14 , ejecting rollers  27  start to be driven to rotate in the counter-clockwise direction by the actuation of driving motor M 9 . By the start of oscillation of ejecting arm  14 , front end portion  14 A presses the leading edge portion of sheet P to eject sheet P onto upper sheet receiving tray  20 . At this time, the upper side surfaces of the rotating ejecting rollers contact with the lower side of sheet P to assist the transport of the leading edge portion of sheet P, making sheet P surely pass over sheet stopping surface  21 B of upper sheet receiving tray  20 . 
     When sheet P is conveyed to the stacking surfaces of sheet stacking plate  21  by ejecting arm  14  and ejecting rollers  27 , sheet P glides down along sheet stacking surface  21 A arranged with inclination or along the surface of the preceding stacked sheets with its leading edge downward; further, the leading edge portion of the sheet is pressed and held between the lower side surfaces of the rotating ejecting rollers and the inclined surface, until it is forced to collide with stopping surface portion  21 B of sheet stacking plate  21  and stopping surface portion  22 B of fixed plate member  22  to be stopped, with the leading edge trued up. 
     In FIG. 1, when the sensor detects that stacked sheets P are full (the upper limit of the stacking) of sheet receiving tray  20  and generates a signal, the control section (not shown) drives driving motor M 6  for making the trays going up and down in driving means  40  for making the trays going up and down to make upper sheet receiving tray  20  go up. That is, a series of gears, composed of gears G 5 , G 6 , G 7 , G 8 , G 9 , and G 10 , drive to rotate driving pulley  41 , driven by driving motor M 6 . Around said driving pulley  41  and upper driven pulley  42 , driving wire  43  is entrained. Driving wire  43  moves up and down in a vertical direction by means of driving pulley  41 . 
     At a certain point of driving wire  43 , the base portion of the framework of aforesaid upper sheet receiving tray  20  is fixed by a suspending metal fitting. Framework  26  of upper sheet receiving tray  20  and framework  36  of lower receiving tray  30  are coupled by coupling rod  45 . That is, long slot portion  451  is bored in coupling rod  45 , and pin  46  fixedly attached to framework  26  of upper sheet receiving tray  20  is inserted to slide in said slot. Further, the portion near the lower end of coupling rod  45  is fixed to framework  36  of lower sheet receiving tray  30 . 
     When upper sheet receiving tray  20  is removed upward by driving wire  43 , pin  46 , which is fixedly attached to framework  36  of upper sheet receiving tray  20  (refer to FIG.  1 ), slides in long slot portion  451  of coupling rod  45 , and only upper sheet receiving tray  20  is removed upward. When pin  46  collides with the topmost end of long slot portion  451  of coupling rod  45 , removed upper sheet receiving tray  20  is separated from still-standing lower sheet receiving tray  30  with the largest spacing distance. 
     When upper sheet receiving tray  20  is further removed upward by driving wire  43 , pin  46  of upper sheet receiving tray  20  makes coupling rod  45  move upward by pushing up the topmost end of long slot portion  451 , to raise lower receiving tray  30 , which is fixed to the lower end portion of coupling rod  45 , to move upward. Accordingly, upper sheet receiving tray  20  and lower sheet receiving tray  30  move upward as a united unit, keeping said largest spacing distance. 
     FIG. 6 is the front view of the shift truing-up means  9 . 
     Shift truing-up means  9  comprises of first unit  90 A shown in the left side in the drawing, which moves one truing-up member  91 A (hereinafter referred to as truing-up plate  91 A), and second unit  90 B shown in the right side in the drawing, which moves the other truing-up member  91 B (hereinafter referred to as truing-up plate  91 B). Because these two units  90 A and  90 B have substantially the same structure, in the following, first unit  90 A will be explained as the representative. 
     Truing-up plate  91 A is fixed to carriage  94 A, which is capable of straightly moving forward and backward sliding on guiding bar  93 A supported fixedly in the unit encasing member serving also as intermediate receiving plate  92 A. Said carriage  94 A is fixed to a predetermined point of timing belt  97 A, which is entrained around driving pulley  95 A and driven pulley  96 A, with fixing member  98 A. Driving pulley  95 A is driven to rotate by driving motor M 7  of the driving source through gears G 11  and G 12 . PS 1 A is the home position sensor. In the same way, second unit  90  B is driven to move forward and backward by driving motor M 8  of the other driving source through the aforesaid gears and timing belt  97 B. In this manner, truing-up plates  91 A and  91 B have their own driving motors respectively to be able to move independently. 
     The intermediate plates are separately and fixedly provided as central intermediate plate  92  and intermediate plates  92 A and  92 B disposed at both sides of said central intermediate plate  92 , and each upper surface of these intermediate plates  92 ,  92 A, and  92 B is flush with each other, forming the sheet stacking surface for sheets P. Ejecting arm  14  is provided to be capable of oscillating at the center of the paper width direction, which is perpendicular to the sheet transport direction, and end portion  14 A of its upper portion is inserted into the clearance portions formed between central intermediate receiving plate  92  and intermediate plates  92 A and  92 B disposed at the left and right of central plate  92 , with the upper portion of upper end portion  14 A protruded out of the sheet stacking surface of intermediate plates  92 A and  92 B to a height higher than the topmost sheet at the largest limit of the stacked sheets specified. 
     The end portions of stoppers  7 A and  7 B, engaging with the leading edge portion of sheet P for positioning, are provided at the outer sides of end portion  14 A of ejecting arm  14  respectively one at the left and the other at the right, and are movable. The upper end of the end portion of stoppers  7 A and  7 B is specified to have approximately the same height as end portion  14 A of ejecting arm  14 . 
     The base portion of stopper  7 A is fixed to moving stage  51 A which holds stapler  50 A (stapling unit) and is movable. The base portion of stopper  7 B is fixed to moving stage  51 B which holds stapler  50 B (stapling unit) and is movable. Accordingly, stoppers  7 A and  7 B move in the direction of the paper width with the straight movement of staplers  50 A and  50 B. 
     In addition, stoppers  7 A and  7 B is provided at the inner sides of staplers  50 A and  50 B respectively, however, it may be appropriate to make positioning reliable by providing auxiliary stoppers at the outer sides of staplers  50 A and  50 B to engage with the both sides of large-sized sheets. 
     FIG. 7 is a schematic plan showing the operation of truing-up plates  91 A and  91 B in stapling process. 
     FIG.  7 ( a ) shows how usual-sized sheet P 1  is trued up for the width and staple-processed. As shown in FIG. 6, truing-up plates  91 A and  91 B are removed from the initial positions where home position sensors PS 1 A and PS 1 B are disposed to the positions a little more distant than the paper width of sheet P 1 , where they wait for the sheets, by driving motors M 7  and M 8  which are used only for the plates respectively. Every time when sheet P 1  is fed in the vicinity of staplers  50 , they are removed to positions a little narrower than the paper width to strike the side edges of sheet P 1  for width truing-up. At the time of this width truing-up, the leading edge portion of sheet P 1  is already trued up by being butted at reference surfaces  7 S of stoppers  7 A and  7 B. 
     After the predetermined number of sheets P 1  have come to end portion  14 A of ejecting arm  14 , any one or both of staples SP A  and SP B  is processed (stapling process) by any one or both of staplers  50 A and  50 B. The trailing edge portion of stapled sheets P 1  is ejected onto sheet receiving tray  20  (or  30 ) by end portion  14 A of oscillating ejecting arm  14 . 
     FIG.  7 ( b ) shows how small-sized sheet P 2  (B6 size, A6 size, etc., for example) is trued up for the width and staple-processed. 
     When the stapling process is executed for small-sized sheets P 2 , every time when a sheet is fed from sheet transporting drum  4  into staplers  50 A and  50 B and collides with stoppers  7 , one of truing-up plates  91 B moves from the initial position and presses the side edge of sheets P 2  to shift sheets P 2  to one side, while the other of truing-up plates  91 A moves from the initial position and strikes the side edge of sheets P 2  to true them up for the width. At the time of this width truing-up, the leading edge portion of sheet P 2  is already trued up by being butted at reference surfaces  7 S of stoppers  7 A and  7 B. 
     Reference surfaces  7 S of stoppers  7 A and  7 B are specified to be positioned at the inner sides of the both side edges of smallest-sized sheet P in the width direction. 
     FIG.  7 ( c ) is a plan showing the sheets of various sizes and the positions of stapling. Staplers  50 A and  50 B are removed by a driving source (not shown) and stop at the predetermined different positions respectively for each sheet size to process staples SP A  and SP B . When small-sized sheet P is stapled, the stapling process is done after one of truing-up plates  91 B is shifted to move sheet P 2  to the other of truing-up plates  91 A, because staplers  50 A and  50 B can not approach the specified stapling positions due to ejecting arm  14  and so forth disposed in the vicinity of the center. 
     FIGS.  8 ( a ) and  8 ( b ) are schematic drawings showing the operation of truing-up plates  91 A and  91 B in shift processing. 
     FIG.  8 ( a ) shows how the bundle of the sheets of the odd-numbered order is processed. When the shift mode (off-set mode) is set, corresponding to the sheet size, truing-up plates  91 A and  91 B, each of which is located at the initial position with an equal distance apart from central line R, move to the positions where are a little wider than the sheet width, maintaining the equal distance from central line R. Then, the bundle of the sheets is received, and ejected after processing. 
     FIG.  8 ( b ) shows how the bundle of the sheets of the even-numbered order is processed. After the bundle is received at the same position as the bundle of the odd-numbered order, truing-up plates  91 A and  91 B move until they stop at the positions which are at the distance unequal for each against central line R in the direction of the sheet transport, and ejected after processing. In addition, in this shift mode, it may be appropriate to make the aforesaid width truing-up. 
     FIG. 9 is a plan showing the process of moving of staplers  50 A and  50 B which force staple SP A  or SP B  into one end of leading edge portion Pa of sheets P of various sizes being in contact with stoppers  7 A and  7 B. Stapler  50 A or  50 B moves straight in the direction parallel to the leading edge of sheet Pa, keeping the positions disposed at 45° inclination, and forces staple SP A  or SP B  at the stapling positions of specified distances A 2  and A 3 . 
     FIG.  10 ( a ) is a plan showing how staples SP A  and SP B  are forced into the two points each positioned with an equal distance from central line R of sheets P of various sizes. FIG.  10 ( b ) is a plan showing the arrangement of staplers  50 A and  50 B, which staple at the above-mentioned two points. Staplers  50 A and  50 B are disposed obliquely at the aforesaid home positions each being equally A 0  distant from central line R of sheet P (the positions shown by the broken lines in the drawing), however, when the two point stapling is instructed, they are rotated by the driving means, which will be described later, to be arranged in the positions parallel to central line R of sheet P, being in contact with stoppers  7 A and  7 B. By these parallel-arranged staplers  50 A and  50 B, staples SP A  and SP B  are forced parallel into the two points of sheet P. 
     The sheet processing apparatus of this invention has a compact structure and its mechanism relating to the basis for sheet stopping is simplified, by making the sheet transport path and the reference surface for butting the leading edge of the sheet the same for both the stapling process mode and non-stapling process mode. Further, the position of sheet stopping is made accurate and stabilized for the smallest size through the largest size. Moreover, because the leading edge of the sheet always contacts with the reference surface for butting the leading edge of the sheet, even in case of shift truing-up, sheet truing-up is accurately carried out. 
     FIG.  13 ( a ) is a cross-sectional view showing the initial uprising state of the sheet stacking plate  21  on which sheets P are being stacked. 
     The sheet stacking surface of sheet stacking plate  21  is made to be an inclined plane in a manner such that the downstream side in ejecting sheet P out of the outer peripheral surface of sheet transporting drum  4  is higher than the upstream side. In the initial going-up state of sheet stacking plate  21 , the angle of inclination of the sheet receiving plate against horizontal plane θ 3  is set to be not larger than 20°. If the angle of inclination of sheet stacking plate  21  is larger than 20°, for example, if sheet stacking plate  21  is inclined plane  21 ′ that is larger than inclination angle 20° shown by the single dot and dash line in the drawing, the trailing edge of sheet P of large size (for example, A3 size, 11 — 17 inch size, etc.) discharged from the nip position of transporting roller pair  5 , after contacting with inclined plane  21 ′, bends downward along inclined plane  21 ′, to make a curl-shape as shown by the single dot and dash line P′ in the drawing; further, the trailing edge of sheet P is made to have a shape as folded downward. If successive sheet P is fed onto inclined plane  21 ′ in such a state of sheet with its trailing edge deformed, poor paper ejecting occurs. 
     In addition, in the case where the receiving tray is of a type such that sheet P ejected onto sheet stacking plate  21  that is arranged inclined is made go down by its own weight in the direction reverse to the sheet transport to collide with sheet stopping surface  21 B, inclination angle θ 3  of sheet stacking plate  21  is set to be not larger than 20° and not smaller than 10°. 
     FIG.  13 ( b ) is a cross-sectional view showing the going-down state of sheet stacking plate  21  on which the maximum number of sheets P are stacked. 
     In the state where the maximum number (for example, about 500 sheets) of sheets P are stacked and sheet stacking plate  21  oscillates around supporting shaft  23  of fixed plate member  22  to the lowermost position, inclination angle θ 4  of the sheet stacking plane of sheet stacking plate  21  against the horizontal plane is set to be not larger than 35°. If the angle of inclination θ 4  of sheet stacking plate  21  is larger than 35°, as in the case of FIG.  13 ( a ), the trailing edge of large-sized sheet P discharged from the nip position of transporting roller pair  5 , after contacting with the topmost plane of the bundle of the sheets stacked on the steep inclined plane larger than 35°, bends downward to have a curled shape along the sheet surface on this steep inclined plane; further, the trailing edge of sheet P is made to have a shape as folded downward. If successive sheet P is fed onto inclined plane  21 ′ in such a state of sheet with its trailing edge deformed, poor paper ejecting occurs. 
     Further, inclination angle θ 4  of sheet stacking plate  21  should be most favorably not larger than 20°, but if it is not larger than 35°, when above-mentioned large-sized sheet P is stacked on sheet stacking plate  21 , no problem will occur. In the case of the oscillating type sheet stacking plate  21 , it is desirable that inclination angle θ 3  in the initial state is set to be not larger than 20°, and inclination angle θ 4  in the last state to be not larger than 35°. 
     In addition, in the embodiment of this invention, the sheet processing apparatus connected to a copying machine is shown, however, the invention can be employed in the after-record processing apparatus that is used connected with an image forming apparatus such as a printer and a facsimile, a low-volume printer, or the like. 
     As has been described in the foregoing, because the inclination angle of the sheet receiving plate is set to be not larger than 20° in the initial going-up state, and to be not larger than 35° in the going-down state where the maximum number of sheets are stacked, even when the large sized sheets are inverted and stacked, the poor paper ejecting such as folding, scattering, and jamming of the sheets is prevented. 
     Further, because an elastic roller rotating for driving is provided over the sheet stopping surface which is provided at the upstream side in the direction of sheet ejection, and by the driving-rotation of this elastic roller, the sheet on the stacking surface of the sheet receiving plate is pressed and transported so as to make the leading edge of the sheet collide with the sheet stopping surface, the topmost sheet ejected onto the sheet receiving plate is reliably made to collide with the sheet stopping surface and trued up.