Patent Publication Number: US-6698745-B2

Title: Sheet post-processing apparatus and image forming apparatus equipped with the same

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a sheet post-processing apparatus for selectively applying a process such as aligning or binding to sheets sent from an image forming apparatus such as a laser printer or copier, and also relates to an image forming apparatus equipped with this sheet post-processing apparatus. 
     Conventionally, as shown in FIG.  34  and FIG. 35, it is known that there is a sheet post-processing apparatus  201  mounted to an image forming apparatus such as a laser printer or a copier. The sheet post-processing apparatus is equipped with an intermediate tray  222  to support an upstream side of a sheet fed from an image forming apparatus  200  and discharged by tray discharge rollers  214  and  215 , and a stack tray  225  established at downstream of the intermediate tray  222  and below with the level  221  (FIG.  36 ( b )) being vertically moveable in the Z direction. The Sheet once discharged in a state of straddling both trays as shown in FIG.  36 ( a ) is aligned by forcibly transporting to an alignment reference using an abutting plate  217  and a position plate  223  by a discharge alignment belt  216  and a second alignment belt  302 . While maintaining the sheet straddling both trays, a sheet bundle is formed by sequentially discharging the sheet as shown in FIG.  36 ( b ). Then, after a post-processing of the sheet bundle such as stapling with the stapler  224 , the sheet bundle is pressed by discharge means composed of the abutting plate  217  as shown in FIG.  36 ( c ), and the apparatus discharges the sheet sequentially to the stacking tray  225  (Japanese Patent No. 08-9451). Note that a trailing edge of the sheet on the stack tray  225  is regulated by the level  221  relative to the intermediate tray  222  (a regulating plate  226 ). 
     However, the conventional sheet post-processing apparatus described above has the intermediate tray  222  first, then the stack tray  225  in the sheet transport direction, and is configured to perform the alignment and the stapling on the intermediate tray  222 . Subsequently, the sheet bundle is removed and stacked downstream in the transport direction. Thus, since the intermediate tray  222  and the stack tray  225  are aligned sequentially in a plane, the dimensions of the apparatus becomes larger by a size of the intermediate tray  222  in addition to a length of the stack tray  225 . 
     Also, even if the length of the intermediate tray  222  is shortened as much as possible in the transport direction, as a sheet for the next one cycle is received after post-processing for one cycle of the sheet to be stapled, it is necessary to have a space on the intermediate tray  222 . Thus, the finished sheet bundle needs to be pushed downstream in the sheet transport direction. In other words, it is required to have a distance for offsetting the sheet bundle in the transport direction between an aligning position (an abutting plate  217 ) for stapling the sheet bundle and a position for regulating the trailing edge of the sheet (a level  221 ). Because a length equivalent to the distance is established as a length in the transport direction, a dimension of the sheet post-processing apparatus in the transport direction becomes longer. Also, it is necessary to transport the sheet bundle that is finished such as by stapling to a position on the stack tray  225  where the trailing edge of the sheet is regulated by the level  221 , thereby causing a wasted time corresponding to an amount of time for the transport. 
     On the other hand, because the sheet tends to move to the stacking tray  225  due to the level  221  between the aforementioned intermediate tray  222  and the stacking tray  225  when stapling the sheet bundle, it is necessary to halt the movement of the sheet bundle and stabilize it to execute the stapling. 
     In the aforementioned conventional apparatus, it is tried to stop the sheet bundle on the stacking tray  225  through an engagement between a sheet surface including two downstream corners and a stacking surface of the stacking tray. However, in an actual case, the engagement of the sheet surface including the two downstream corners is not enough to fully prevent the sheet from moving, resulting in a problem that the sheet bundle is stapled while each sheet in the sheet bundle is shifted. 
     To handle this problem, a method is known in which the stacking tray  225  is elevated to eliminate the level  221  between the intermediate tray  222  and the stacking tray  225 . However, in that case, it is necessary to add a mechanism for elevating and lowering the stacking tray  225 . For that reason, the apparatus becomes larger and the cost increases. Further, because the stacking tray needs to be elevated and lowered in an appropriate range, a control becomes more complex, thereby causing a new problem. 
     Furthermore, this approach can not be applied to a compact apparatus with a fixed stacking tray, thus can not obtain a perfect solution for the problem. 
     An object of the present invention is to resolve the issues in the conventional technology, and to provide a compact sheet post-processing apparatus with a small size in the sheet transport direction and an image forming apparatus equipped with the aforementioned sheet post-processing apparatus. Further, an object is to provide a sheet post-processing apparatus and an image forming apparatus equipped with the sheet post-processing apparatus that can stabilize the sheet bundle to accurately execute the post-processing on the sheet bundle stacked straddling an intermediate tray and a stacking tray. 
     SUMMARY OF THE INVENTION 
     To attain the aforementioned objectives, the sheet post-processing (finishing) apparatus according to the present invention is provided with discharge means for discharging a sheet; sheet single corner portion support means for supporting one corner of the sheet discharged by the aforementioned discharge means; sheet storage means established under the aforementioned sheet single corner portion support means; and post-processing means for post-processing the sheet straddling the aforementioned sheet single corner portion support means and the aforementioned sheet storage means. 
     The sheet post-processing apparatus according to the present invention may be further provided with sheet moving means for moving the sheet finished by the aforementioned post-processing means and for discharging the sheet to the aforementioned storage means. 
     In the sheet post-processing apparatus according to the present invention, the aforementioned sheet storage means supports three corners of the sheet, excluding a corner portion of the sheet supported by the aforementioned sheet single corner portion support means, when the aforementioned post-processing means applies the post-processing. 
     The sheet post-processing apparatus according to the present invention may be further provided with drive means for driving the aforementioned sheet moving means between the aforementioned support means and the aforementioned storage means. 
     In the sheet post-processing apparatus according to the present invention, the aforementioned sheet single corner portion support means is formed so that an edge of an upper surface of the aforementioned sheet single corner portion support means supporting the sheet is completely positioned closer to a side of a single corner of the aforementioned sheet than a line drawn between two neighboring corners relative to the one corner of the aforementioned sheet when the aforementioned discharge means discharges the smallest size of the sheet to be handled. 
     The image forming apparatus according to the present invention is equipped with the aforementioned sheet post-processing apparatus. 
     As described above, the sheet post-processing apparatus or the image forming apparatus according to the present invention is provided with the discharge means for discharging the sheet; the sheet single corner portion support means for supporting one corner of the sheet discharged by the aforementioned discharge means; the sheet storage means established under the aforementioned sheet single corner portion support means; and the post-processing means for post-processing the sheet straddling the aforementioned sheet single corner portion support means and the aforementioned sheet storage means. More specifically, an intermediate tray, where the sheet is to be finished, needs to support just one corner of the sheet, as opposed to the conventional apparatus that supports two corners of the sheet. Therefore, the intermediate tray itself can be made compact, and the whole sheet post-processing apparatus can be made compact. 
     Also, the sheet storage means is established under the sheet single corner portion support means to support three corners of the sheet, thus the sheet is securely supported by the sheet storage means. Since the sheet is stable even in the state of straddling the sheet single corner portion support means and the sheet storage means, the post-processing means can apply the post-processing in a stable manner. Therefore, no shifting of the sheet will occur when the sheet bundle is stapled. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an external view showing a sheet finishing apparatus according to the present invention; 
     FIG. 2 is a sectional view showing the sheet finishing apparatus divided vertically at a paper path portion according to the present invention; 
     FIG. 3 is a perspective view showing the sheet finishing apparatus with a cover and a storage tray removed according to the present invention; 
     FIG. 4 is a perspective view seen from above showing the sheet finishing apparatus shown in FIG. 3 with a base frame removed; 
     FIG. 5 is an expanded view showing a stand frame for supporting a right edge of a supporting shaft of the sheet finishing apparatus shown in FIG. 4; 
     FIG. 6 is an enlarged view showing a part of FIG. 5; 
     FIG. 7 is a perspective view seen from the inside of the apparatus showing sheet shift means (also used as pre-alignment moving means and sorting means) disposed in the stand frame shown in FIG. 5; 
     FIG. 8 is a view showing a position of a HP detection sensor to be established in the stand frame on the sheet finishing apparatus; 
     FIG. 9 is a perspective view showing a structure of the HP detection sensor; 
     FIG. 10 is an enlarged view showing a structure supporting a left edge of the supporting shaft of the sheet finishing apparatus shown in FIG. 4; 
     FIG. 11 is an enlarged view showing a left edge side of the supporting shaft of the sheet finishing apparatus shown in FIG. 4; 
     FIG. 12 is a perspective view showing a drive mechanism of the supporting shaft of the sheet finishing apparatus shown in FIG. 4; 
     FIG. 13 is a drawing showing a relationship between a position of the sheet discharged from the sheet finishing apparatus according to the present invention with a center as a reference and a pre-alignment position as well as an alignment position; 
     FIG. 14 is a drawing showing a relationship between a position of the sheet discharged from the sheet finishing apparatus according to the present invention with a side edge as a reference and the pre-alignment position as well as the alignment position; 
     FIG. 15 is a drawing showing a sheet discharge position when the sheet finishing apparatus according to the present invention operates in a jog mode; 
     FIG. 16 is a plan view showing a power transmission system for rotating a belt unit support shaft added to the sheet finishing apparatus according to the present invention as alignment means; 
     FIG. 17 is a perspective view showing a belt unit portion added to the sheet finishing apparatus according to the present invention as the alignment means; 
     FIG. 18 is a perspective view showing the belt unit in FIG. 17 having only a drive pulley with a follower support pulley and an alignment belt removed; 
     FIG. 19 is a perspective view showing one of a pair of the belt units in FIG. 17 having only the drive pulley; 
     FIG. 20 is a drawing showing a configuration of a control apparatus on the sheet finishing apparatus according to the present invention; 
     FIG. 21 is a chart showing a part of a control flow for performing the pre-alignment, the alignment and the sheet finishing process in the sheet finishing apparatus according to the present invention; 
     FIG. 22 is a chart showing a part of the control flow continued from FIG. 21 for performing the pre-alignment, the alignment and the sheet finishing process according to the present invention; 
     FIG. 23 is a chart showing a part of the control flow continued from FIG. 22 for performing the pre-alignment, the alignment and the sheet finishing process according to the present invention; 
     FIG. 24 is a chart showing a portion of another control flow for performing the alignment and the sheet finishing process (without the pre-alignment) corresponding to FIG. 22 in the sheet finishing apparatus according to the present invention; 
     FIG. 25 is a chart showing a portion of another control flow continued from FIG. 24 for performing the alignment and the sheet finishing process (without the pre-alignment) in the sheet finishing apparatus according to the present invention; 
     FIG. 26 is a drawing showing a relationship of sizes and shapes between a fixed stacking portion (the first tray), a storage tray (the second tray) and a sheet in the sheet finishing apparatus according to the present invention; 
     FIG. 27 is a drawing showing an example of the fixed stacking portion (the first tray) in FIG. 26 modified by having a rectangular shape in the sheet finishing apparatus according to the present invention; 
     FIG. 28 is a partial sectional view showing a positional relationship in a vertical direction between the fixed stacking portion (the first tray), the storage tray (the second tray), and a sheet bundle in the sheet finishing apparatus according to the present invention; 
     FIG. 29 is a partial sectional side view showing sheet bundle discharge means (sheet moving means) in the sheet finishing apparatus according to the present invention; 
     FIG. 30 is a perspective view seen from below showing a structure of the sheet bundle discharge means (the sheet moving means) in the sheet finishing apparatus according to the present invention; 
     FIG. 31 is a rear view seen from below showing the structure of the sheet bundle discharge means (the sheet moving means) in the sheet finishing apparatus according to the present invention; 
     FIGS.  32 ( a ) and  32 ( b ) are views showing an operation of the sheet bundle discharge means (the sheet moving means) in the sheet finishing apparatus according to the present invention, wherein FIG.  32 ( a ) is a rear view showing a state during discharge and FIG.  32 ( b ) is a rear view showing a state immediately after the discharge is completed; 
     FIGS.  33 ( a ) to  33 ( c ) are views showing the operation of the sheet bundle discharge means (the sheet moving means) in the sheet finishing apparatus according to the present invention, wherein FIG.  33 ( a ) is a partial plan view showing a state before the discharge, FIG.  33 ( b ) is a partial plan view showing a state during the discharge, and FIG.  33 ( c ) is a partial plan view showing a state immediately after the discharge is completed; 
     FIG. 34 is a side view showing a configuration of a conventional sheet finishing apparatus; 
     FIG. 35 is a view seen from above showing the configuration of the conventional finishing apparatus; 
     FIGS.  36 ( a ) to  36 ( c ) are views explaining an operation of the conventional finishing apparatus; and 
     FIG. 37 is a drawing showing a relationship between a position of the sheet discharged from the sheet finishing apparatus according to the present invention with a side edge as a reference and the pre-alignment position as well as the alignment position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereunder, preferred embodiments according to the present invention will be described in detail with reference to the accompanied drawings. 
     A. Mounting Structure and Transport System (FIG. 1) 
     FIG. 1 is a view showing an embodiment of an image forming apparatus provided with a sheet finishing apparatus employing a sheet discharge apparatus according to the present invention. In this embodiment, it is structured that a sheet finishing apparatus  1  according to the present invention is detachably assembled to a top of an image forming apparatus  100  composed of a page printer. More specifically, to connect the sheet finishing apparatus  1  and the image forming apparatus  100 , a lock arm  1   a  (FIG. 2) is established and protruding on a lower side of the sheet finishing apparatus  1 . The lock arm engages a holding portion (not shown in the drawings) inside of the image forming apparatus  100  to thereby mount the sheet finishing apparatus  1  on the top of the image forming apparatus  100 . 
     Note that in this embodiment the image forming apparatus  100  is composed of a page printer. However, it is also possible to apply the sheet finishing apparatus according to the present invention to a copier as well. 
     FIG. 2 shows a configuration of a transport system for receiving and discharging a printed or copied sheet from the image forming apparatus  100 . 
     After the sheet is discharged upward of a discharge portion, not shown in the drawings, on the image forming apparatus  100 , the sheet is sent to a paper path  2  (a sheet transport path) formed of an upper guide  2   a  and a lower guide  2   b  inside the sheet finishing apparatus  1 . The paper path  2  extends substantially vertically at a back of the sheet finishing apparatus  1 , then bends toward front. A pair of transport rollers  3  is disposed at a lower inlet of the paper path. In other words, the aforementioned copied sheet is fed into the paper path  2  by the pair of the transport rollers  3  disposed at the lower inlet of the paper path  2 , and is fed further downstream into the sheet finishing apparatus to be discharged from a discharge outlet  7 . 
     B. Sheet Discharge Means  6   
     In FIG. 1, a pair of tray discharge rollers  4  and  5  composed of a discharge roller  4  that is a follower roller and a tray discharge roller  5  that is a drive roller as a sheet discharge means  6  is arranged at the discharge outlet  7  of the sheet finishing apparatus  1 . 
     Also, at downstream of the pair of the tray discharge rollers  4  and  5  in a sheet transport direction is disposed a fixed stacking portion  8  (the first tray) as a constituent of support means  10  (sheet single corner portion support means) that supports one corner of the sheet at an upstream side in a discharge direction discharged by the aforementioned discharge means  6 . In this embodiment, it is configured that the fixed stacking portion  8  supports one corner at a trailing edge side of the sheet. Furthermore, a storage tray  9  (the second tray) having a size large enough to receive the maximum sized sheet discharged as sheet storage means is disposed below the fixed stacking portion  8 . Then, it is configured that the sheet is discharged from the discharge outlet  7  to the fixed stacking portion  8  and a top of a stacking surface of the storage tray  9  by the pair of the tray discharge rollers  4  and  5 , and is stacked as shown in FIG.  28  and FIG.  29 . 
     To configure the pair of the tray discharge rollers  4  and  5  on the sheet discharge means  6  to freely rotate, as shown in FIG.  3  and FIG. 4, two supporting shafts  11  and  12  that extend in parallel vertically are rotatably arranged near the discharge outlet  7  inside of the sheet finishing apparatus  1 . The aforementioned pair of the tray discharge rollers  4  and  5  is in an appropriate plurality (in this case, two pairs) mounted at a middle portion of each of the supporting shaft  11  and the supporting shaft  12 . 
     As shown in FIG.  5  and FIG. 6, leading ends (on the right side in the FIG. 3) of the two supporting shafts  11  and  12  are inserted into an ear portion  41   a  established and protruding at an outer edge of an upper surface of a sliding joint plate  41 , which is a constituent of sheet pre-alignment moving means  40  (side alignment means) used also as sheet shift means of sorting means (jog means), thereby being supported to rotate freely and integrated to move along with the sliding joint plate  41 . 
     That is, an E ring  13  is disposed at a leading edge of each of the supporting shafts of  11  and  12  after passing through the ear portion  41   a  of the sliding joint plate  41 . A moving removal preventing member  14  for commonly both supporting shafts  11  and  12  is disposed at an outer end in the shaft direction of each of the supporting shafts  11  and  12 . The supporting shafts are integrated not to come out in the shaft direction through actions of the E ring  13  and the moving removal preventing member  14  disposed on an outer side thereof. 
     Also, among the two supporting shafts  11  and  12  unitized as described above, a leading end of the lower supporting shaft  11  is rotatably and movably supported in the shaft direction at an upper portion of a U-shaped stand frame  15  established on one side in the sheet width direction of the base frame  1   c  (FIG. 7) in the sheet finishing apparatus  1  by a U-shaped first bearing member  17  that is elastically movable in a vertical direction. 
     On the other hand, with regard to the base side (the left side in FIG. 3) of the aforementioned two supporting shafts  11  and  12 , the shafts are rotatably and slidably supported in the shaft direction. That is, in FIG.  10  and FIG. 11, the base side of the supporting shaft  11  among the two support shafts  11  and  12  is rotatably and movably supported in the shaft direction relative to the first support member  16  mounted to the side frame  1   b  of the sheet finishing apparatus  1  by a U-shaped second bearing member  18  that is elastically movable in a vertical direction. In this embodiment, as shown in FIG.  10  and FIG. 11, the base side of the shaft  11  is formed in an angled shape portion  11   a  having a D shape section. The angled shape  11   a  is rotatably and movably supported in the shaft direction by the U-shaped second bearing member  18  that is elastically movable in a vertical direction relative to the first support member  16 . 
     Also, a discharge paddle  20  made of an elastic material (in this case, a rubber) comprising a plurality of teeth in a circumference direction is fitted to the squared shape  11   a  of the supporting shaft  11 , thereby allowing the squared shape  11   a  to slide freely in the shaft direction. To fix an absolute position of the discharge paddle  20  in the shaft direction, the first slide regulating member  19  is mounted on the supporting shaft  11  at a position slightly away from the aforementioned second bearing member  18 . The discharge paddle  20  is disposed between the aforementioned second bearing member  18  and the first slide regulating member  19 , so that the supporting shaft  11  moves freely relative to the discharge paddle  20 , and the discharge paddle  20  position does not change. Also, the supporting shaft  11  is configured to advance and retract freely in the shaft direction with penetrating a shaft hole of the first slide regulating member  19  and the notched opening portion  38  established in the side frame  1   b , while leaving the discharge paddle  20 , whose movement in the shaft direction is regulated by the first slide regulating member  19 , between the first slide regulating member  19  and the second bearing member  18 . Note that the aforementioned squared shape  11   a  with the D shaped section formed on the base side of the supporting shaft  11  slidably penetrates not only the discharge paddle  20  but also the first slide regulating member  19  in the shaft direction. 
     In other words, the supporting shaft  11  is formed in a D shape at least by a distance for the support shaft to advance and retract from both sides of the discharge paddle  20 , and the shaft hole in the discharge paddle  20  also is formed in a D shape. By configuring the advancing and retracting portion passing through the shaft hole of the discharge paddle  20  of the supporting shaft  11  to be formed in a non-circular shape including an oval, a rotation of the supporting shaft  11  can be transmitted to the discharge paddle  20  positioned between the second bearing member  18  and the first slide regulating member  19  even when the supporting shaft  12  and the supporting shaft  11  are advanced or retracted (sliding in the shaft direction). Therefore, while the pair of the tray discharge rollers  4  and  5  is advancing and retracting in the shaft direction along with the supporting shafts  11  and  12  to discharge the sheet, the discharge paddle  20  stays at a predetermined position between the first slide regulating member  19 , in other words, rotating without moving in the shaft direction, for the discharge paddle  20  to apply a discharge action to the sheet. 
     Furthermore, the base side of the upper supporting shaft  12  also is supported to be able to move in the shaft direction relative to the second supporting member  31  mounted on the side frame  1   b . In other words, as shown in FIG. 10, an upper surface wall  31   a  that extends slightly inside from the side frame  1   b  and the second supporting member  31  having a vertical downward bent wall  31   b  that continues downward from the upper surface wall are disposed on an inner wall of the side frame  1   b . Further, the second slide regulating member  32  having a reversed U-shaped that comprises the leg portion  32   a  and the leg portion  32   b  is disposed with the leg portion  32   a  penetrating vertically downward the upper surface wall  31   a  of the aforementioned second supporting member  31 . Also, between the leg portion  32   a  of the second slide regulating member  32  and the vertical downward wall  31   b  of the second supporting member  31 , the interlock gear  33  is disposed on the supporting shaft  12 . The aforementioned interlock gear  33  allows a relative sliding in the shaft direction with regard to the supporting shaft  12  penetrating therethrough, but does not allow a relative rotation. 
     In the case of this embodiment, as shown in FIG.  10  and FIG. 11, the base side of the supporting shaft  12  is formed as a squared shape  12   a  having a D shape section. A cooperative action of the squared shape  12   a  and a bearing portion of the second supporting member  31  allows the base side of the supporting shaft  12  to rotate via the interlock gear  33  and move in the shaft direction. 
     Through the slide support structure described above, the supporting shafts  11  and  12  can rotate freely and move together with a movement of the slide joint plate  41  in the shaft direction with the leading ends thereof joined together by the slide joint plate  41 . 
     As shown in FIG. 12, a transport motor  34  for driving the aforementioned supporting shaft  12  to rotate to apply a transport force to the sheet and a force transmission mechanism are disposed on the side frame  1   b . That is, the force transmission mechanism is configured so that an output of the transport motor  34  is transmitted from a motor pulley  35   a  mounted on a output shaft to an intermediate pulley  35   b , a transport roller pulley  35   c  and a follower pulley  35   d  via a timing belt  36 , and further to the interlock pulley  37  disposed on the same shaft as that of the follower pulley  35   d . An interlock gear  33  disposed on the aforementioned supporting shaft  12  engages the interlock gear  37  that is an output side of the force transmission mechanism. Thus, a drive from the transport motor  34  is received at the interlock gear  33  and rotates the supporting shaft  12 , accompanying that a supporting shaft  11  at a follower side also rotates. 
     That is, the tray discharge roller  5  is a drive roller rotated by the transport motor  34  via the aforementioned force transmission mechanism. On the other hand, the tray discharge roller  4  is a follower roller in contact with the tray discharge roller  5  and rotates by the rotation of the tray discharge roller  5 . 
     C. Alignment Reference Position and Finishing Means (FIG. 13, FIG. 14) 
     In the sheet discharge means  6  of the aforementioned configuration, the sheet is nipped and applied with a transport force by the pair of the rotating tray discharge rollers  4  and  5 , and discharged from the discharge outlet  7  to the fixed stacking portion  8  (the first tray) and the storage tray  9  (the second tray). FIG. 13 is a view showing a state that the sheet is discharged with a center as a reference, and FIG. 14 is a view showing a state that the sheet is discharged with a rear side as a reference. FIG. 37 is a view showing a state that the sheet is discharged with a one front side as a reference. 
     Also, FIG. 15 is a view showing a state that the sheet is discharged in a jog mode, which is described below. In the jog mode, while shifting each of the sheet bundles alternately by a distance D 5 , which is an offset amount, the sheet bundles are sequentially discharged and stacked, thereby obtaining the vertical offsetting (offset) between the stacked sheet bundles. 
     The storage tray  9  (the second tray) as the sheet storage means is established to support three corners, excluding a sheet corner portion supported by sheet single corner portion support means, when the stapler (finishing means)  23  applies a finishing process to the sheets, which is described later. However, it is also possible to be an embodiment having a size to support one of the upstream corners of the three corners and a part of the backside of the sheets. In this example, the storage tray  9  (the second tray) has a rectangular shape, whose size has a dimension capable of storing a vertically long size of full sized sheets such as A3 or B4 (in this case, a length of A3 size). 
     On the other hand, the fixed stacking portion  8  (the first tray) as the aforementioned sheet single corner portion support means is formed so that an edge of the upper surface that supports the sheet on the fixed stacking portion  8  (the first tray) is positioned closer to a side of a single corner of the sheet than a diagonal line drawn between two neighboring corners and a single corner of the sheet when discharging the smallest size of the sheet to be handled using the sheet discharge means  6 . Here, the fixed stacking portion  8  (the first tray) as the aforementioned sheet single corner portion support means is arranged above a single corner portion (the upper left corner in FIG. 13) at upstream of the storage tray  9  in the sheet discharge direction to compensate a part of a sheet storage surface of the storage tray  9  seen from above. 
     In this embodiment, a shape of the fixed stacking portion  8  (the first tray) is substantially triangle seen from above inclined at the single corner portion upstream of the storage tray  9  in the sheet discharge direction. However, a rectangular shape as shown in FIG. 27, or any polygonal shape or a circular shape is possible. 
     As shown in FIG.  3  and FIG. 4, an abutting plate  21  as one of the positioning reference means (an alignment reference member) is arranged at upstream of the fixed stacking portion  8  to align at least one side of the sheet discharged by the discharge means  6 , thereby configuring a discharge direction reference surface for providing a discharge direction alignment reference position when aligning the sheets. 
     On one side of the fixed stacking portion  8  is arranged a positioning plate  22  composed of an abutting reference (a width direction alignment reference position) in the traverse direction to the sheet discharge direction (hereinafter referred to as the width direction) as one of the position alignment reference means (an alignment reference member) to align at least one side of the sheet discharged by the discharge means  6 . 
     The abutting plate  21  (the discharge direction alignment reference position) and the positioning plate  22  (the width direction alignment reference position) regulate the finishing position. 
     A stapler  23  that pierces staples into to bind the sheet bundles aligned by being pushed against the finishing position is disposed on the aforementioned fixed stacking portion  8  (the first tray) as the finishing means. 
     D. Pre-Alignment Movement Means (Sheet Shift Means)  40   
     Upon discharging the sheet with aside and a center as a reference, the sheet is horizontally moved to a side of the width direction alignment reference position by a distance of D 1  to D 4  in FIG.  13  and FIG. 14 by the sheet shift means of the jog means described below along with the pre-alignment movement means (the side alignment means)  40 , and is bound by the aforementioned stapler  23 . Also, in the jog mode, the sheet is horizontally fed (a traverse movement) by an amount of D in FIG. 15 for sorting. 
     For that purpose, the pre-alignment movement means  40  is configured to include the sliding joint plate  41  and its sliding drive portion  45  to move the supporting shafts  11  and  12  together in the shaft direction with a presumption of the aforementioned sliding structure wherein the supporting shafts  11  and  12  on the pair of the tray discharge rollers  4  and  5  can freely advance and retract in the shaft direction. 
     As already described, as shown in FIG. 7, the sliding joint plate  41  as a constituent of the pre-alignment movement means  40  is equipped with the head portion  41   b  forming a guide surface for the sheet; the ear portion  41   a  established and protruding on the upper surface of the head portion; the neck portion  41   c  vertically downward in the lower surface of the head portion  41   b ; the rectangular torso portion  41   d  extending from the neck portion; and one leg portion  41   e  formed to have approximately the same thickness as the neck portion. Also, the neck portion  41   d  and the leg portion  41   e  are supported movably in the shaft direction by the two upper and lower guide rods  43  and  44  suspended in the horizontal direction between the side walls  15   a  and  15   c  of the U-shaped stand frame  15 . 
     It is configured that the supporting shafts  11  and  12  are rotatably supported with the leading ends thereof inserted into the ear portion  41   a  of the sliding joint plate  41 , and are integrated with the sliding joint plate  41  to slide together in the shaft direction. 
     Next, a configuration of the sliding drive portion  45  will be explained. 
     To configure the sliding drive portion  45 , the rack  42  is established to the torso portion  41   d  of the aforementioned sliding joint plate  41  along the supporting shaft  11  direction. Also, a slide motor  47  is established to an inner wall of the stand frame  15  as a slide support frame via the mounting plate  46 , and the pinion gear  48  mounted on the output shaft of the slide motor  47  engages the aforementioned rack  42 . 
     In the sliding drive portion  45  of the aforementioned configuration, the pinion gear  48  rotates while engaging the rack  42  of the sliding joint plate  41  according to forward and reverse drive of the slide motor  47  controlled by control means described below, and transmits a drive to the sliding joint plate  41  along the guide rods  43  and  44 . Finally, the supporting shafts  11  and  12  linked to the sliding joint plate  41  and the pair of the tray discharge rollers  4  and  5  mounted on each of the supporting shafts advance and retract. 
     In a different view, the sliding drive portion  45  is composed of the sliding joint plate  41  for rotatably linking the supporting shafts  11  and  12 ; the guide rods  43  and  44  for retractably supporting the sliding joint plate  41  in the shaft direction; the stand frame  15  mounted to the base frame  1   c  for supporting and fixing the guide rods  43  and  44 ; and the slide motor  47  equipped with the pinion gear  48  on the shaft. Furthermore, the sliding joint plate  41  is configured to include a linking portion (the ear portion  41   a ) for rotatably linking the supporting shafts  11  and  12 , supporting portions (neck portion  41   c  and leg portion  41   e ) having shaft holes for inserting the guide rods  43  and  44 , and the rack  42  for engaging the pinion gear  48  mounted on the rotating shaft of the slide motor  47 . 
     Incidentally, a slide opening portion  49  is formed on the side walls  15   a  and  15   c  on the stand frame  15  that is a slide supporting frame, so that the rack  42  escapes toward outside of the side walls  15   a  and  15   c  on the stand frame  15  when the pinion gear  48  advances and retracts the sliding joint plate  41 . 
     Further, as shown in FIG. 9, a position detection protrusion  51  extending in a plate shape in the horizontal direction is established on a backside of the torso portion  41   d  on the sliding joint plate  41 . The position detection protrusion  51  also functions to prevent warping of the sliding joint plate  41  due to bending. Also, as shown in FIG.  8  and FIG. 9, to the front wall  15   b  on the stand frame  15 , an interrupter  52  (a pair of optical elements for emitting and receiving light) composing a transmission type optical sensor along with the position detection protrusion  51  is mounted via an auxiliary plate  53 . Also, the transmission type optical sensor comprised of the position detection protrusion  51  and the interrupter  52  (a pair of optical elements for emitting and receiving light) functions as a HP detection sensor  50  for detecting a home position (HP) of the sliding joint plate  41 , namely the supporting shafts  11  and  12 , and for turning on when the position detection protrusion  51  interrupts the light of the interrupter  52  (a pair of optical elements for emitting and receiving light). 
     In a conventional apparatus, a sheet starts to be discharged after sliding the discharge rollers in a state that the transport of the sheet is stopped after the pair of the discharge rollers nip the sheet. On the other hand, in the sheet finishing apparatus  1 , it is possible to transmit the drive from the transport motor  34  via the linking gear  33  to the supporting shaft  12  even while the supporting shafts  11  and  12  are advancing or retracting in the shaft direction according to the aforementioned configuration. That is, the tray discharge roller  5  mounted on the supporting shaft  12  and the tray discharge roller  4  mounted on the supporting shaft  11  can advance and retract in the shaft direction at the same time the sheet is transported by the pair of the tray discharge rollers  4  and  5 . 
     Through this configuration, it becomes possible to shorten a process time for the alignment and the sorting. 
     It is configured that the supporting shaft  11  linked to the supporting shaft  12  by the sliding joint plate  41  advances and retracts in the shaft direction by a sliding drive portion  45  (FIG.  9 ), described later, with penetrating a shaft hole of the discharge paddle  20 , a shaft hole of the first slide regulating member  19  and the notched opening portion  38  established in the side frame  1   b  along with the supporting shaft  12 , while leaving the discharge paddle  20 , whose movement in the shaft direction is regulated by the first slide regulating member  19 , between the first slide regulating member  19  and the second bearing member  18 . 
     Through this structure, the tray discharge roller  4  mounted on the supporting shaft  11  advances and retracts in the shaft direction along with the tray discharge roller  5  that is the drive roller mounted to the supporting shaft  12 . Also, it is configured that the tray discharge roller  4  nips and transports the sheet along with the tray discharge roller  5  upon advancing and retracting. 
     Furthermore, the supporting shaft  11  is formed in a D shape for at least a distance that the support shaft advances and retracts from both sides of the discharge paddle  20 , and the shaft hole in the discharge paddle  20  also formed in a D shape. Through this structure, it is possible to transmit the rotation of the supporting shaft  11  to the discharge paddle  20  positioned between the first slide regulating member  19  by the sliding drive portion  45  even when the supporting shaft  11  is advancing and retracting along with the supporting shaft  12 . As opposed to that the sheet is discharged while the pair of the tray discharge rollers  4  and  5  advances and retracts in the shaft direction along with the supporting shafts  11  and  12 , the discharge paddle  20  is arranged to apply the discharge action to the sheet at a predetermined position between the first slide regulating member  19 . 
     E. Alignment Means (Pulling Means)  60   
     The sheet finishing apparatus  1  comprises the alignment means  60  for securely pulling the sheet to a finishing position on the fixed stacking portion  8  and aligning the same. The configuration of the alignment means  60  will be described with reference to FIG. 16 to FIG.  19 . 
     As shown in FIG.  16  and FIG. 17, the alignment means  60  is composed of a belt unit  61  for sweeping the sheet to pull the same to the finishing position. According to this embodiment, two units are mounted in serial to the supporting shaft  62 , to which the rotational drive force is applied from the aforementioned supporting shaft  12  at the upper side. These two belt units  61  and  61  are operated together by the forward rotation of the common supporting shaft  62 . It is configured that the belt units urge and align the sheet, which is discharged while aligning at one side toward the pre-alignment position (a nipping position) or the width direction alignment reference position (the positioning plate  22 ) by the pair of the tray discharge rollers  4  and  5 , to further move to a finishing position for accurate alignment determined by both the abutting plate  21  (the discharge direction alignment reference position) and the positioning plate  22  (the width direction alignment reference position). 
     Here, in this specification, the “pre-alignment position” is referred to a nipping position of the belt unit  61 , and more accurately, the furthermost inner position of the nipping position where the belt unit  61  can nip the sheet. 
     As already described in FIG. 12, the upper supporting shaft  12  is a drive shaft rotated by the transport motor  34  via the linking gear  33  engaging the shaft and the force transmission mechanism ( 35   a  to  35   d  and  37 ). Furthermore, the linking gear  33  engaging the supporting shaft  12  is regulated in its movement in the shaft direction of the supporting shaft  12  by the leg portion  32   a  of the second slide regulating member  32  and the downward wall  31   b  of the second supporting member  31  (see FIG.  10 ). 
     To attain the drive force for the belt units  61  from the supporting shaft  12 , in other words, to transmit the rotational drive force from the supporting shaft  12  to the supporting shaft  62 , as shown in FIG.  16  and in FIG. 17, the first beveled gear  63  is disposed at inside from the linking gear  33  of the supporting shaft  12  in the shaft direction. As shown in FIG.  18  and in FIG. 19, the first beveled gear  63  is positioned between the downward wall  31   b  of the second supporting member  31  and the leg portion  32   b  of the second slide regulating member  32 , thereby regulating its movement in the shaft direction of the supporting shaft  12  by the downward wall  31   b  of the second supporting member  31  and the leg portion  32   b  of the second slide regulating member  32 . 
     On the other hand, the supporting shaft  12  penetrates a plurality of members and is retractably mounted in the shaft direction. That is, the supporting shaft  12  is arranged to freely advance and retract in the shaft direction, while penetrating a shaft hole of the linking gear  33 , shaft holes of the leg portions  32   a  and  32   b  of the second slide regulating member  32 , a shaft hole of the vertical downward wall  31   b  of the second supporting member  31 , and the opening portion  39  established in the side frame  1   b . Also, the supporting shaft  12  can slide in the shaft direction by the slide drive portion  45 , while leaving the linking gear  33 , whose movement in the shaft direction is regulated by the leg portion  32   a  of the second slide regulating member  32  and the vertical downward wall  31   b  of the second supporting member  31 , between the regulating space. Further, the supporting shaft  12  can slide in the shaft direction, while leaving the first beveled gear  63 , whose movement in the shaft direction is regulated by the vertical downward wall  31   b  of the second supporting member  31  and the leg portion  32   b  of the second slide regulating member  32 , between the regulating space. 
     Note that the supporting shaft  12  is formed in a D shape for at least a distance that the support shaft advances and retracts from both sides of the linking gear  33  and the first beveled gear  63 . Also, shaft holes of the linking gear  33 , the discharge paddle  20  and the first beveled gear  63  are formed in a D shape. 
     On the other hand, to rotatably support one end of the supporting shaft  62  of the belt units  61 , as shown in FIG. 12, an L shaped mounting plate  65  is mounted to the side frame  1   b . One end of the supporting shaft  62  is rotatably supported to the mounting plate, while the other end of the supporting shaft  62  is rotatably supported to a support arm portion  31   c  established and extending from the vertical downward wall  31   b  of the second supporting member  31  to above the fixed stacking portion  8  (the first tray). 
     The second beveled gear  64  is mounted to an end of the supporting shaft  62  at a side of the support arm portion  31   c . The second beveled gear  64  engages the first beveled gear  63 , which is established and regulated in its movement in the shaft direction at a predetermined position in the shaft direction of the supporting shaft  12 . Through this structure, the supporting shaft  62  receives the drive from the transport motor  34  to rotate. 
     One of the two belt units  61  and  61  constituting the alignment means  60  is disposed at a position near the discharge outlet of the supporting shaft  62 , and the other is disposed at the supporting shaft  62 , far away from the discharge outlet  7 . Since both of the belt units  61  and  61  have the same configuration, just one unit will be explained. 
     The belt unit  61  is composed of a drive pulley  66  (FIG. 18) mounted to the supporting shaft  62  and rotating along with the supporting shaft  62 ; support plates  67  (FIG. 17) disposed on both sides of the drive pulley with its back edge attached to the supporting shaft  62 ; a follower supporting pulley  68  (FIG. 19) rotatably supported on a front edge of the support plate  67  and positioned at a side of the fixed stacking portion  8  with a predetermined gap from the drive pulley  66 ; and an alignment belt  69  (FIG. 19) trained between the drive pulley  66  and the follower support pulley  68 . 
     The support plate  67 , as shown in FIG. 19, comprises a notch  67   a  for engaging a trailing end thereof with the supporting shaft  62 , and a back portion of the notch portion  67   a  detachably is mounted to the supporting shaft  62  with a constant gripping force. Therefore, the support plate  67  revolves as a unit with the supporting shaft  62  with a constant frictional force, and, is also configured to slide and rotate around the supporting shaft  62  when an external force enough to overcome the constant frictional force is applied. 
     When the supporting shaft  12  receives the drive of the transport motor  34  (FIG. 12) and the tray discharge roller  5  rotates in a direction to discharge the sheet S, the supporting shaft  62  is rotatably driven from the supporting shaft  12  and the alignment belt  69  of the belt units  61  rotates to sweep and pull the sheet. A direction of the rotation is toward where the alignment belt  69  intersects the positioning plate  22  and the abutting plate  21 , in other words, the rotation in a direction to transport the sheet toward the stapler  23  as a finishing position. In other words, the belt unit  61  is arranged in a direction to be able to transport the sheet S toward the stapler  23  as the finishing position. The support arm portion  31   c  and the support plate  67  position the supporting shaft  62  so that the belt units  61 ,  61  urge and align the sheet discharged by the pair of the tray discharge rollers  4  and  5  toward the abutting plate  21  and the positioning plate  22  on the fixed stacking portion  8 . 
     A length of the belt unit  61  from the supporting shaft  62  is determined to be longer than a distance from the supporting shaft  62  to a top surface of the fixed stacking portion  8  (the first tray). Therefore, when the belt unit  61  revolves along with the supporting shaft  62  by the frictional force, a leading end of the belt unit  61  touches the upper surface of the fixed stacking portion  8  (the first tray) from above with an angle (see FIG.  19 ). The belt unit  61  is unable to revolve further, and an idling position shown in FIG. 19 is maintained as the support plate  67  of the belt unit  61  overcomes the frictional force and slips with regard to the supporting shaft  62 . 
     In the belt unit  61  at the idling position, a position where the alignment belt  69  touches the sheet is the pre-alignment position (the nipping position), described above. As described in FIG.  13  and FIG. 14, in an operating mode with the pre-alignment, the sheet is pre-aligned to the pre-alignment position by the distance of D 1  or d 1  (the distance of D 4  or d 4 ), and moved to the finishing position by the distance of D 2  or d 2  (D 5  or d 5 ) by the belt units  61 , thereby touching the abutting plate  21  and the position plate  22  to be aligned. Alternatively, the sheet is moved directly to the finishing position by the distance of D 3  or d 3  (D 6  or d 6 ) after passing through the pre-alignment position, thereby touching the abutting plate  21  and the position plate  22  to be aligned. 
     However, as long as the supporting shaft  12  is rotating forward, the alignment means (the pulling means)  60  operates constantly hanging downward at an angle toward the sheet from the supporting shaft  62 , thus it acts as a load that applies a resistance force to the discharging sheet. For that reason, the sheet might be pushed back by a reverse transportation effect (pulling in) of the alignment belts  69 , resulting in that an edge of the sheet toward the fixed stacking portion  8  is not completely discharged, or is arranged obliquely. To eliminate this problem, the discharge paddle  20  is established to the supporting shaft  11 . That is, the discharge paddle  20  is disposed at a position corresponding to the fixed stacking portion  8  above the supporting shaft  11  and between the first slide regulating member  19  mounted to the support member  16 . The discharge paddle  20  touches the sheet portion corresponding to the fixed stacking portion  8  while rotating, thereby applying an additional discharging force to the aforementioned sheet portion (to forcibly push it out). 
     F. Control Means 
     The control means will be described next. 
     (a) Control Apparatus (FIG. 20) 
     FIG. 20 is a block diagram showing a circuit configuration of the sheet finishing apparatus according to this embodiment.  111  is a micro-computer CPU (a central processing unit) constituting a main body of the control unit;  112  is a ROM (a read only memory) storing program data that the CPU  111  uses to control each part;  113  is a RAM (a random access memory) provided with a memory for the CPU  111  to use for processing data;  114  is an I/O port; and  115  is an interface (I/F) for connecting externally a host computer  116  of the image forming apparatus main unit  100  using a communications line. 
     The aforementioned CPU  111 , ROM  112 , RAM  113 , I/O port  114  and interface  115  are electrically connected via a bus line  117 . 
     To the aforementioned I/O port  114  are connected the HP detection sensor  50  for detecting the home position of the supporting shafts  11  and  12  on the pair of the tray discharge rollers  4  and  5 , an inlet sensor  131  (FIG. 2) established at an inlet of the paper path  2  that is a transport path, and a discharge sensor  134  established near the discharge outlet  7  of the paper path  2 . The discharge sensor  134  is a sensor supplementary disposed and can be omitted. 
     The inlet sensor  131  and the discharge sensor  134  are composed of a transmission type light sensor including a light source and a light receptor element arranged to sandwich the sheet transport path, and turn on when the sheet passes therethrough and interrupts the light. That is, when the sheet S passing through the paper path  2  between the upper guide  2   a  and the lower guide  2   b  in the processing apparatus  1  is discharged, the detection sensors composed of the light source and the light receptor element arranged to sandwich the paper path  2  determine whether the each single sheet S passes through, thereby performing detection of a passing sheet and detection of a stalled sheet. Also, the detection sensor composed of the light source and the light receptor element arranged to sandwich the sheet discharge outlet  7  at downstream of the pair of the tray discharge rollers  4  and  5  detects whether the sheet S is discharged. 
     Further, the I/O port  114  is connected to a motor driver  118  of the transport motor  34 , which drives the supporting shafts  11  and  12  of the pair of the tray discharge rollers  4  and  5  to rotate according to the data from the host computer  116 , and a motor driver  119  of the slide motor  47 , which moves the supporting shafts  11  and  12  of the pair of the tray discharge rollers  4  and  5  in the shaft direction according to the data from the host computer  116 . 
     The aforementioned transport motor  34  and slide motor  47  are comprised of, for example, stepping motors. The CPU  111  controls the drive by sending a motor control signal with a predetermined number of pulses to the motors  34  and  47 . 
     An output from each of the inlet sensor  131 , the discharge sensor  134  and the HP detection sensor  50  is supplied to the CPU  111  of the micro-computer in the discharge apparatus. Also, information from operating means composed of a start key, a sorting sheet count setting key, a total recording count setting key and ten keys (not shown) in the image forming apparatus main unit  100  is input to the CPU  111  of the micro-computer in the discharge apparatus. 
     (b) Control (FIG. 21 to FIG. 23) 
     The aforementioned CPU  111  is configured to control the pre-alignment and the sheet finishing process shown in FIG. 21 to FIG. 23 based on a program. 
     That is, at step ST 1  in FIG. 21, a status of the transport motor  34  is checked, and starts the transport motor  34  to rotate in a forward direction if the motor is in idle (step ST 2  and ST 3 ). It waits until the sheet arrives at the inlet sensor  131  (step ST 4 ). 
     Next, because a precedent sheet (a previous sheet) may exist in the paper path  2 , it determines the presence of the sheet (if the previous sheet is being processed) (step ST 5 ). It is possible to determine by monitoring the output of the aforementioned discharge sensor  134 , however, a configuration employed here measures the transport time of the sheet or the number of pulses of the sheet after passing the inlet sensor  131 . 
     Next, it waits until the trailing edge of the sheet passes the inlet sensor  131  (step ST 6 ). This is to prevent an accident that the supporting shaft  11  and the supporting shaft  12  move in the shaft direction to slide the sheet despite the trailing edge of the sheet is still nipped by the pair of the transport rollers  3 . 
     Once the trailing edge of the sheet passes the inlet sensor  131 , it sets “an alignment roller retracting pulse”, which is the number of pulses adjusted for the sheet to exit the pair of the tray discharge rollers  4  and  5  (step ST 7 ). It waits until the sheet is transported by 15 mm after passing through the inlet sensor  131  (step ST 8 ). This absorbs a chattering action caused by bounding of the sheet. 
     Next, in FIG. 22, based on the data and the instruction supplied from the image forming apparatus main unit  100 , it checks a discharge destination to determine a reference of the discharge destination from a “straight position”, an “offset position (a jog position)” or a “staple position.” 
     In the case that the discharge destination is the “straight position”, nothing happens to pass through the flow shown in FIG. 22 (step ST 10 ). 
     In the case that the discharge destination is the “offset position (the jog position)”, to ensure a predetermined offset movement amount and a jog movement amount, it is determined that an adjusted alignment speed is 150 mm/s and an adjusted alignment position is a position 20 mm offset to the right (−20 mm) from the HP (step ST 11 ), and the alignment process is started to move to the position (step ST 12 ). 
     In the case that the discharge destination is the “staple position”, it checks whether the sheet is discharged from the image forming apparatus main unit  100  with either of the “center reference”, the “front reference (one side edge reference discharge)” or the “rear reference (one side edge reference discharge)” based on the data and instructions received from the image forming apparatus main unit  100  (step ST 13 ). Then, a distance of movement from each discharge reference to the pre-alignment position (the adjusted alignment position) is calculated, and the distance and the adjusted alignment speed (step ST 14  to ST 20 ) are determined. Then, the alignment process is started to move to the position (step ST 12 ). 
     That is, in the case of the “center reference”, the distance of movement to the pre-alignment position is calculated according to the width of the sheet (for example, D 1  and D 4  shown in FIG.  13 ). The result is set as the adjusted alignment position, and the adjusted alignment speed is set to be 150 mm/s (step ST 15 ). Then, the alignment process is started to move to the position (step ST 12 ). 
     Also, in the case of the “front reference (on side edge reference discharge)”, that is, when discharging with the right edge of the tray as the reference shown in FIG. 37, the distance of movement to the pre-alignment position according to the width of the sheet is calculated (step S 16 ) (for example, d 7  and d 9  shown in FIG.  37 ). The result is set as the adjusted alignment position, and the adjusted alignment speed is set at 150 mm/s (step STl 7 ) Then, the alignment process is started to move to the position (step STl 2 ). 
     Next, in the case of the “rear reference (one side edge reference discharge)” (step ST 18 ), that is, when discharging with the right edge of the tray as the reference shown in FIG. 37, the distance of movement (a distance a) of the supporting shafts  11  and  12  in this discharge apparatus relative to the sheet is already known. Thus, the constant distance of movement α mm from the discharge reference (for example, d 1  and d 4  shown in FIG. 14) is set as the adjusted alignment position (step ST 19 ), and the adjusted alignment position is set and the adjusted alignment speed is set at 150 mm/s (step ST 20 ). Then, the alignment process is started to move to the position (step ST 12 ). 
     However, when the discharge position itself matches to the pre-alignment position, the pre-alignment is not necessary, thus it skips to the alignment process as it is (step ST 12 ). 
     In the alignment process, the sheet is actually moved only by the aforementioned calculated distance, and the alignment process is started to send the sheet to the preparatory (pre-) processing position (step ST 12 ). Through this process, while the sheet is transported and discharged by the rotation of the pair of the tray discharge rollers  4  and  5 , the pair of the tray discharge rollers  4  and  5  move in the shaft direction executed by the aforementioned alignment process, thereby pushing the sheet to the nipping position of the belt units  61  that is the pre-alignment position. 
     Then, in FIG. 23, when the “alignment roller retracting pulse” set at the aforementioned step ST 11  is counted up, and it is verified that the sheet passes the pair of the tray discharge rollers  4  and  5  (step ST 21 ), it checks if there is a request for discharging the next sheet, that is, if there is the sheet to be discharged (step ST 22 ). In the case that there is the request for discharging the next sheet, it returns to step ST 1 , and the sheet to be discharged next is stacked and aligned. 
     After a predetermined number of the sheets are stacked, and it is determined that there is no request for discharging the next sheet at step ST 22 , it verifies if there is a staple instruction (step ST 23 ). If there is no staple instruction, the process is completed (step ST 23 ). 
     In the case that there is the staple instruction in determining at step ST 23 , it sets the pulling pulse count, in other words, the necessary pulse count to pull the sheet from the pre-alignment position (the nipping position) to the finishing position to perform the alignment (pulling to the finishing position) using the caterpillar (the belt units  61  and  61 ) as the alignment means (the pulling means)  60  (step ST 24 ). 
     Then, it waits for the transport motor  34  and the slide motor  47  to stop (step ST 25 ), and the staple motor (not shown in the drawings) is rotated forward to execute the finishing process (step ST 26 ). In the finishing process, the stapler  23  as the finishing means operates to staple the sheet bundle. Then, the staple operation is completed (step ST 27 ). 
     When the stapling operation is completed, a series of the operations from the discharging to the pre-alignment, to the alignment and finishing (the stapling) is completed. (c) Modified Example of Control (FIG. 24 to FIG. 25) 
     In FIG. 24 to FIG. 25, an example of control without the alignment means  60  (the pulling means) is shown. That is, the sheet is moved to the finishing means all at once without (pre-) aligning preparatorily to the pre-alignment position, more accurately, the sheet is moved to the width direction alignment reference position (the positioning plate  22 ). 
     The following points in FIG. 24 differ from those in the aforementioned FIG.  22 . That is, in the aforementioned FIG. 22, the distance of movement (D 1  and D 4  in FIG. 13, and d 1  and d 4  in FIG. 14) to the pre-alignment position is calculated, and the adjusted alignment position is set according to the calculated result at step ST 14  and step ST 16 . However, at step ST 14   a  and step ST 16   a  in FIG. 24, the distance of movement (D 6  in FIG.  13  and d 6  in FIG. 14) to the width direction alignment reference position (the positioning plate  22 ) is calculated, and the calculated result is set as the adjusted alignment position according. 
     Further, the following points in FIG. 25 differ from those in the aforementioned FIG.  23 . That is, in the aforementioned FIG. 23, it sets the caterpillar pulling pulse at step ST 24  and step ST 25 , and waits for the transport motor to stop. However, at step ST 25   a  in FIG. 25, because the alignment means (the pulling means)  60  does not exist, just the transport motor is stopped. 
     G. Sheet Bundle Discharge Means  70  (FIG. 29 to FIG. 31) 
     As described above, the sheet passes through the pre-alignment (the pre-alignment movement means  40 ) and the alignment (the belt units  61 ), and is aligned sequentially at the finishing position and stacked. When the stacked sheets become a sheet bundle having a determined number of the sheets, the stapling operation as the finishing means is performed on a single corner by the stapler  23 . The sheet bundle  90 , as shown in FIG. 28, is stacked from the fixed stacking portion  8  (the first tray) to the storage tray  9  (the second tray) below. At this time, because there is a space, or a step, for stacking and storing the sheets between the fixed stacking portion  8  (the first tray) and the storage tray  9  (the second tray) below, the sheet bundle  90  has a bending portion  90   a  composed of a bent level along the level. 
     The sheet bundle discharge means  70  shown in FIG. 29 to FIG. 31 is means to push the sheet bundle  90  in this state in the direction traversing the sheet transport direction from a side for discharging the bundle to a region outside of the fixed stacking portion  8  (the first tray). The sheet bundle discharge means  70 , in this embodiment, is composed of a pushing member  71  engaging the curved portion  90   a  of the sheet bundle  90  for pushing the sheet bundle in a direction traversing the transport direction to move the bundle from the fixed stacking portion  8  (the first tray) to the storage tray  9  (the second tray) below, and a revolution drive mechanism  72  (drive means) for revolving the member. 
     To constitute the revolution drive mechanism  72 , the rotating lever  74  that rotates around the rotating center  73  is disposed in a gap between the fixed stacking portion  8  (the first tray) and the storage tray  9  (the second tray) below, as shown in FIG.  29 . The aforementioned pushing member  71  extending vertically in a form of a pushing bar is disposed at the leading edge of the rotating lever  74 . The rotating lever  74  is equipped with a contact arm  75  formed of a contact portion  75   a  on the leading end thereof (FIG. 31) and extending obliquely downward at a side opposite to the rotating center shaft  73 . 
     Further, to rotatably drive the aforementioned rotating lever  74 , a worm-wheel  76  with a cam having a cam  77  that acts on the contact portion  75   a  is rotatably mounted on a circumference of the shaft  78  near the contact portion  75   a . When the worm-wheel  76  with the cam reciprocally rotates around the shaft  78  as described below, it is configured that the cam  77  touches the aforementioned contact portion  75   a  to revolve in a predetermined fashion. Also, a worm gear  79  engaging the worm wheel  76  with the cam is established on a side opposite to a side where the aforementioned rotating lever  76  exists. The worm gear  79  is established on a shaft  81  having a pulley with a single direction clutch  80 , and the pulley with the single direction clutch  80  is arranged as one of a gear chain composing the rotating drive mechanism of the aforementioned supporting shafts  11  and  12 . 
     That is, as shown in FIG. 30, a shaft  81  of the pulley with the single direction clutch  80  is rotatably mounted to the side frame  1   b  and the support plate  82 , and the intermediate pulley  35   e  is rotatably mounted to the side frame  1   b . Then, a force transmission mechanism is configured such that the output from the transport motor  34  is transmitted from the motor pulley  35   a  mounted on the output shaft to the intermediate pulley  35   b , the transport roller pulley  35   c  and the follower pulley  35   d  via the timing belt  36 , and further to the pulley with the single direction clutch  80  via the intermediate pulley  35   e . The aforementioned worm gear  79  engages the shaft  81  that is the output side of the pulley with the single direction clutch  80 . Through the action of the single direction clutch, when the transport motor  34  is rotated forward, the single direction clutch turns off, causing the pulley with the single direction clutch  80  to rotate free. On the other hand, when the transport motor  34  is rotated in reverse, the single direction clutch turns on, thereby transmitting the rotational drive force to the shaft  81  to rotate the worm gear  79 . 
     When the worm gear  79  rotates, the worm wheel with the cam  76  engaging the worm gear rotates. The cam  77  integrated with the worm wheel in the state shown in FIG. 31 touches and presses the contact portion  75   a  of the contact arm  75  to rotate the rotating lever  74  around the rotating center shaft  73  as depicted in FIGS.  32 ( a ) and  32 ( b ). Through this, the pushing member  71  revolves around the rotating center shaft  73  as depicted in FIGS.  32 ( a ) and  32 ( b ) to push the sheet bundle  90  to outside of the region of the fixed stacking portion  8  (the first tray). 
     As a result, the sheet bundle  90 , as shown in FIG.  33 ( a ) to FIG.  33 ( c ), is discharged from the fixed stacking portion  8  (the first tray) to the storage tray  9  (the second tray). 
     When the sheet bundle  90  reaches the position shown in FIG.  32 ( b ) pushed out of the region of the fixed stacking portion  8  (the first tray), the rotational direction of the transport motor  34  switches from reverse to forward. The shaft  81  becomes free, and the recovery spring  83  mounted to the shaft  81  returns the worm wheel with the cam  76  to the state in FIG.  31 . The rotating lever  74  also returns to the state in FIG. 31 by the action of the recovery spring  84 . 
     The aforementioned elements  74  to  84  constitute the mechanism (revolving drive mechanism  72 ) for driving and revolving the pushing bar  72 . 
     In the conventional apparatus, after the sheet is completely discharged to the tray, either the alignment plate or the alignment bar pushes the sheet to move to the alignment reference member to be aligned. On the other hand, in the sheet finishing apparatus  1  of this embodiment, the sorting means disposed further upstream in the sheet transport direction than the belt units  61  and  61  that are the alignment means can perform the pre-alignment for the sheet SS, thereby improving the precision and efficiency of the alignment without having to add a dedicated alignment device. 
     Further, because the slide joint plate  41  as the sorting means, the supporting shafts  11  and  12  and the pair of the tray discharge rollers  4  and  5  mounted on each supporting shaft, can advance and retract at the same time the pair of the tray discharge rollers  4  and  5  transports the sheet, the alignment operation to the pre-alignment position can be started while the sheet SS is being discharged by the pair of the tray discharge rollers  4  and  5 , thereby further increasing the alignment efficiency. 
     Note that according to the present embodiment, in the case that the pre-alignment finally is performed, it is necessary to perform the main alignment in which the sheets move to the positioning plate  22  (the alignment reference position) by the belt units  61  and  61  after that. However, before the main alignment by the belt units  61  and  61 , the sheet shift means of the sorting means (the pre-alignment movement means)  40  moves the sheets SS to the position near the alignment position regulated by the positioning plate  22 . Thus, it is possible to align the sheets more efficiently in a shorter period of time than the conventional apparatus, in which the sheets move from the discharge position separated far from the alignment reference to the side alignment reference member. 
     Furthermore, in the configuration according to this embodiment, it is configured that the sheets SS are pre-aligned in advance by the sorting means. However, it is possible to provide a discharge apparatus that is even more compact by setting the slide movement distance of the slide joint plate  41  and the supporting shaft  11  and the supporting shaft  12  so that the sorting means directly aligns the sheets SS at the alignment reference position defined by the positioning plate  22 . 
     The belt units  61  and  61  rotate to drive the sheets to the positioning plate  22 , which is the finishing position, and the abutting plate  21 , while the sheets are being discharged by the pair of the tray discharge rollers  4  and  5  and are being aligned. Therefore, the alignment action (the pre-alignment) is applied to the sheets by the sorting means in addition to the alignment action applied by the belt units  61  and  61 , thereby enabling the more reliable alignment to the finishing position. 
     Note that this invention can be configured as the sheet finishing apparatus, as well as it can also be configured as an image forming apparatus equipped with the sheet finishing apparatus. 
     As described above, according to the present invention, the sheet finishing (post-processing) apparatus or the image forming apparatus is equipped with the discharge means for discharging the sheet; the sheet single corner portion support means for supporting one corner of the sheet discharged by the aforementioned discharge means; the sheet storage means with an area larger than that of the sheet single corner portion support means established below the same; and the post-processing means for post-processing the sheet straddling the aforementioned sheet single corner portion support means and the aforementioned sheet storage means. That is, because the sheet single corner portion support means and the sheet storage means are arranged overlapping with a gap therebetween in the vertical direction, compared to the apparatus in which the sheet single corner portion support means and the sheet storage means front are arranged back and forth in the sheet transport direction, the dimension of the sheet post-processing apparatus in the transport direction becomes smaller by at least the amount corresponding to the overlap. 
     Also, since the sheet storage means with an area larger than that of the sheet single corner portion support means is established below the same, a majority part of the area of the sheet is supported by the sheet storage means. Therefore, the sheet is stable straddling the sheet single corner portion support means and the sheet storage means, and the post-processing of the sheet can be completed in a stable manner by the post-processing means. Therefore, no shifting of the sheet will occur when the sheet bundle is stapled.