Patent Publication Number: US-6341772-B1

Title: In line rotatable stapling device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a sheet fastening apparatus and, more particularly, to a sheet fastening apparatus for fastening sheet bundles within an image forming apparatus such as a photocopier or within a sheet processor connected to the image forming apparatus. 
     2. Description of Related Art 
     Some sheet fastening apparatus for fastening partly a sheet bundle made of multiple sheets has been used in connecting to, e.g., an apparatus body of an image forming apparatus such as a photocopier. In such an image forming apparatus body, a sheet on which an image is recorded is conveyed from a prescribed outlet of the apparatus body at a prescribed time into a sheet fastening apparatus through an inlet of the fastening apparatus. The sheet is nipped by a pair of conveyance rollers in the sheet fastening apparatus and conveyed to a stock section at which sheets are temporarily stocked to pile sheets orderly until a prescribed number of sheets are stored. When a prescribed number of sheets are piled at the stock section, the image forming apparatus temporarily stops conveyance of sheets, and during this temporary stop the sheet fastening apparatus fastens sheets by staples or other means at designated positions on the sheet bundle made of multiple sheets. 
     Various sheet sizes and conveyance directions are used in image forming apparatuses these days, and number and positions of stapling may vary depending on users. To comply with those variations, a sheet fastening apparatus has been proposed capable of traveling a stapling mechanism or unit in a width direction perpendicular to the sheet conveyance direction and fastening sheets at multiple positions on a rear side in the sheet conveyance direction of the sheet bundles, which has been piled in the manner described above at the stock section. In this fastening apparatus, the sheet bundle fastened partially is nipped by a delivery roller disposed in the apparatus but having stayed away from the sheet bundle and another delivery roller opposed to the delivery roller and delivered onto a stock tray formed at a side of the apparatus. By repeating this operation, the fastening apparatus can pile sheet bundles each including a prescribed number of sheets on the stock tray, sequentially. The stock tray can move up and down in a direction that the sheets are piled up and travels downward in the piling direction corresponding to the thickness of the piled sheet bundles. 
     With such a conventional apparatus, however, the stapling unit has to move in the width direction perpendicular to the sheet conveyance direction to fasten one or more positions on the sheet bundle, so that such stapling operation takes much time and prevents the fastening apparatus from processing quickly. The stapling unit has to travel by about a sheet width, so that the stapling unit raises problems that the unit comes to have a complicated structure, consumes much electrical power for traveling, and becomes expensive. 
     With a conventional apparatus having a movable stapling unit, when fastening is performed in an oblique way to the sheet conveyance direction, the stapling unit is required to move further outward in addition to the normal traveling amount. However, it is difficult to place a number of guide rails to rotate the stapling unit obliquely corresponding to respective sizes of sheets, so that the fastening apparatus unit fastenes the sheets of only specific sizes. 
     Moreover, in the conventional apparatus which stacks sheets in a face down manner, the staples for fastening sheets are hit from a top face to a bottom face of the sheets, namely front side of the first page, and therefore, bent portions of a staple are projected from the bottom of the sheets. Furthermore, the sheet bundle is fastened by staples in a direction perpendicular to the sheet conveyance direction, so that the staples serve as conveyance resistance when the sheet bundles are conveyed bundle by bundle. It is difficult for such a conventional apparatus to convey the sheet bundles stably, and the apparatus cannot orderly pile up the sheet bundles. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a sheet fastening apparatus capable of rendering a structure of the fastening apparatus simple, improving processing speed including stapling operation, and rendering conveyance of sheet bundles stable. 
     In one form of the invention to accomplish the foregoing objects, a sheet fastening apparatus includes sheet bundle conveying means for conveying sheet bundles, and sheet bundle fastening means for fastening sheet bundles, wherein the sheet bundle fastening means is disposed on either side, of the sheet bundles, extending substantially parallel with a sheet conveyance direction and fastens the sheet bundle at least at a position upon stop of conveyance of the sheet bundle by the sheet bundle conveying means. 
     According to the structure above, the sheet bundle fastening means is disposed on either side, of sheet bundles, extending substantially parallel in a sheet conveyance direction. For example, when the sheet bundle is fastened at two positions, a first stapling operation is done after the sheet bundle is conveyed to a prescribed position and stopped at the position, and then, a second stapling operation is done after the sheet bundle is conveyed to another position and stopped at the position. The sheet fastening apparatus can fasten the sheet bundles without traveling of the sheet bundle fastening means, thereby rendering the fastening apparatus structurally simple. The sheet fastening apparatus can shorten the time necessary for fastening sheet bundles, thereby greatly improving throughput of the fastening operation. 
     According to preferred embodiments, by disposing the sheet bundle fastening means so that fastenings extend parallel with the sheet conveyance direction on the sheet bundle, the conveyance resistance of the sheet bundle due to the fastenings is reduced to the minimum value. The sheet bundle fastening means may move pivotally as to direct the sheet bundle fastening means at any angle. This pivotable movement allows the sheet bundle fastening means to fasten any number of fastening means at any position and at any angle on either edge extending parallel to the sheet conveyance direction. 
     The sheet bundle conveying means can be placed on the same side as the sheet bundle fastening means to reduce positional shifts of the sheet bundles during conveyance of the sheet bundles. The sheet bundle conveying means may include a first sheet bundle conveying means and a second sheet bundle conveying means disposed on a downstream side of the first sheet bundle conveying means. In this embodiment, a conveyance speed V 1  of the first sheet bundle conveying means is set equal to or less than a conveyance speed V 2  of the second sheet bundle conveying means to convey the sheet bundles so that a tension is exerted to the sheet bundles, thereby conveying the sheet bundles having trued edges without disorder of the sheets. 
     In preferred embodiments, the sheet fastening apparatus has a third sheet conveying means placed on a downstream side in the sheet conveyance direction of the sheet bundle fastening means. After the sheet bundle arrives at the third sheet conveying means, the third sheet conveying means conveys the sheet bundle by nipping the sheet bundle, thereby reducing positional shifts of the sheet bundle during conveyance of the sheet bundles. 
     The sheet bundle fastening means may hit staples from a bottom face to a top face of the sheet bundles. By this structure, projections of bent staples come on the top face of the sheet bundles, thereby reducing conveyance resistance of the sheet bundles, rendering conveyance of the sheet bundles stable, and improving the piling property of the sheet bundles. 
     In one form of the sheet fastening apparatus, an arranging means for orderly arranging the edges of sheets in a width direction perpendicular to the sheet conveyance direction is provided traveling in the sheet conveyance direction in synchronism with the conveying operation of the sheet bundle conveying means during conveyance of the sheet bundles after arranging operation of the arranging means. The arranging means suppresses disorders of the sheet edges and brings stable conveyance of the sheet bundles. A roller pair may be disposed on a downstream side of the sheet bundle fastening means to make projections of staples flat, thereby making conveyance of the sheet bundles smooth. The roller pair may serve as a sensor for the staples. 
     In another aspect of the invention, a sheet bundle fastening means is provided on either side, left side or right side, of the sheet bundle, extending parallel with the sheet conveyance direction. When the sheet bundle is fastened at a single position in an oblique way, the sheet bundle fastening means having a home position at a position oblique with respect to the sheet conveyance direction fastens the sheet bundles at the oblique position after the sheet bundle&#39;s edges are trued up. When the sheet bundle is fastened at two positions, the sheet bundle is moved to a prescribed position after the sheets are piled and sheets&#39; edges are trued up, and the sheet bundle fastening means moves pivotally in association with the sheet bundle&#39;s movement. When the sheet bundle reaches the prescribed position, the sheet bundle fastening means already moves pivotally to a parallel fastening position and fastens the sheet bundle at two positions on the sheet bundle. Since this fastening apparatus can reduce time for stapling operation for the sheet bundles, the fastening apparatus can improve the throughput of the stapling operation. 
     To eliminate positional shifts of the orderly arranged edges of sheets when the sheet bundle is stapled at plural positions, the sheet fastening apparatus may perform orderly arranging operation of sheet edges at least one time in a direction crossing the sheet conveyance direction before respective fastening operations of the sheet fastening apparatus. This orderly arranging operation allows correcting the edges of sheet bundle even if shifted during conveyance of the sheet bundle, before respective fastening operations. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic cross section showing a structural outline of a sheet stapler according to the invention; 
     FIG. 2 is a top view showing the sheet stapler according to the invention; 
     FIGS.  3 ( a ) to  3 ( c ) are top views showing a stapler unit with its structure and operating positions, respectively; 
     FIG. 4 is a block diagram showing a controlling system of the sheet stapler according to the invention; 
     FIG. 5 is a plan view showing partially an input portion for stapling mode on a control panel of the sheet stapler according to the invention; 
     FIG. 6 is an enlarged view showing a sheet bundle fastening section of the sheet stapler according to the invention; 
     FIGS.  7 ( a ),  7 ( b ) are illustrations showing two-position stapling done by the sheet stapler according to the invention; 
     FIGS.  8 ( a ), ( b ) are illustrations showing oblique stapling done by the sheet stapler according to the invention; 
     FIG. 9 is a flowchart showing an operation of the double position stapling done by the sheet stapler according to the invention; 
     FIG. 10 is a flowchart showing an operation of front end oblique stapling done by the sheet stapler according to the invention; 
     FIG. 11 is a flowchart showing an operation of rear end oblique stapling done by the sheet stapler according to the invention; 
     FIG. 12 is a top view showing the sheet stapler according to the invention; 
     FIGS.  13 ( a ),  13 ( b ) are enlarged views showing a sheet bundle fastening section of the sheet stapler according to the invention; 
     FIG. 14 is a schematic cross section showing a printer having a sheet stapler according according to the invention; 
     FIG. 15 is a top view showing the sheet stapler according to the invention; 
     FIGS.  16 ( a ),  16 ( b ) are top views illustrating operation of a stapler unit of the sheet stapler according to the invention; 
     FIG. 17 is an enlarged view showing a sheet bundle fastening section of the sheet stapler according to the invention; 
     FIGS.  18 ( a ),  18 ( b ) are schematic side views showing the stapler unit of the sheet stapler according to the invention; 
     FIGS.  19 ( a ) to  19 ( c ) are illustrations showing operation of a sheet arranging tray according to the invention; 
     FIG. 20 is a block diagram showing a controlling system for the sheet stapler according to the invention; 
     FIGS.  21 ( a ),  21 ( b ) are illustrations showing staple pressing operation of the sheet stapler according to the invention; 
     FIG. 22 is an illustration showing error detecting operation of the sheet stapler according to the invention; and 
     FIG. 23 is a flowchart showing stapling operation of the sheet stapler according to the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to the drawings, sheet fastening apparatus as embodiments according to the invention will be described in details. In those embodiment, sheet fastening apparatuses are explained as using sheet staplers for fastening means. This invention is effective even for an apparatus for fastening the sheet bundle with items other than staples, e.g., an apparatus fastening the sheet bundles by pressing the sheet bundles without using staples. 
     First Embodiment 
     Referring to the drawings, a sheet stapler as a first embodiment of the invention is described. In the subsequent description, a sheet stapler used in connecting to an image forming apparatus is exemplified. FIG. 1 is a schematic cross section showing a structure of the sheet stapler; FIG. 2 is a top view showing the sheet stapler. 
     In FIGS. 1,  2 , numeral  1  represents an image forming apparatus indicated by a two-dot chain line as a virtual line. A sheet P, on which the image forming apparatus  1  records images, is conveyed to a sheet stapler A connected below the image forming apparatus  1 . The image forming apparatus  1  has the same structure shown as a fourth embodiment, which is described in detail below. 
     Numeral A indicates the sheet stapler, which is connected at a prescribed position below the image forming apparatus  1 . Numeral  2  is a loading roller pair for conveying a sheet fed from the image forming apparatus  1  by nipping the sheet and is disposed to the sheet inlet. Numeral  3  indicates a loading sensor for detecting the sheet P proceeding in the sheet stapler A. 
     Numeral  4  indicates a guide plate for guiding the sheet P; numeral  5  indicates a conveying roller pair for conveying the sheet P to a sheet piling section B; numeral  6  indicates an upper guide plate, which guides a front end of the sheet P conveyed by the conveying roller pair  5  and introduces the sheet P to the sheet piling section B. 
     Numeral  7  indicates a first rocker guide, which prevents disorders of the piled sheets P and stably guides the front end of the sheet P to the roller pair of the subsequent process. Numeral  8  indicates a first rocker roller in which plural rollers are arranged coaxially (width direction perpendicular to a sheet conveyance direction), rotatively driven by a driver M 8 , and moved up and down at a prescribed timing by a clutch C 8 . Numeral  9  indicates a first conveying roller, which is disposed in opposition to the first rocker roller  8  and rotatively driven by a driver M 9  at a prescribed timing. A first conveying roller pair serving as a first sheet bundle conveying means is constituted of the first rocker roller  8  and the first conveying roller  9 . 
     Numeral  10  indicates a second rocker guide, which has the same function as the first rocker guide  7 . Numeral  11  indicates a second rocker roller, which has the same function as the first rocker roller  8 . Numeral  12  indicates a second conveying roller, which has the same function as the first conveying roller  9 . Similarly, in FIG. 2, numerals M 11 , M 12  indicates drivers, and numeral C 11  indicates a clutch. A second conveying roller pair serving as a second sheet bundle conveying means is constituted of the second rocker roller  11  and the second conveying roller 12 . Numeral  13  indicates a sheet detection sensor for detecting whether the sheet P exists in the sheet piling section B. 
     Numeral  14  indicates an arranging means for orderly arranging the edges of sheets P in a width direction perpendicular to the sheet conveyance direction. The arranging means  14  has a drive motor and pushes the sheet edges in the width direction of the sheets toward a center of the sheets with a prescribed pushing force at multiple times at each piling of the sheet P, thereby truing up the edges of the sheets P (sheet bundle). 
     Numeral  15  indicates a reference face to be pushed, which is formed at a position opposing to the arranging means  14 . The sheets&#39; edges in opposition to edges pushed by the arranging means  14  are pushed onto the reference face  15 , thereby orderly arranging the edges in the width direction of the sheets P. 
     Numeral  16  indicates a stopper gate for stopping the front end of the sheets P to set the sheets orderly in the sheet conveyance direction, extending in the width direction perpendicular to the sheet conveyance direction. The stopper gate  16  is driven to rotate by a clutch  17  and can travel selectively between a stopper position and an escaped position. 
     Numeral  18  indicates a stapler unit as a sheet bundle fastening means, which fastens the properly arranged sheet bundles with staples at a prescribed position or positions with a prescribed angle and has a structure as shown in FIG.  3 . The structure of the stapler unit  18  is described in detail below. 
     Numeral  19  indicates a sheet bundle tray for piling stapled sheet bundles. Numeral  20  indicates a delivery roller pair serving as a third sheet conveying means for delivering the sheet bundles onto the sheet bundle tray  19 . Numeral  21  indicates a sheet bundle front stopper for briefly arranging the front of sheet bundles delivered onto the sheet bundle tray  19 . 
     Referring to FIG. 3, the structure of the stapler unit  18  is described. FIG. 3 is a top view showing the structure and operation of the stapler unit. 
     In FIG. 3, numeral  31  indicates a stapler head for stapling sheet bundles with staples and is constituted of a known structure. Numeral  32  is a support, which supports the stapler head  31 . Numeral  33  indicates a rotary base disposed below the support  32  and rotates the stapler head  31  at any angle by rotating the support  32 . 
     The stapler head  31  is formed with a reference face to be pushed at the same position as the reference face  15  and positions the sheet bundles together with the reference face  15  by pushing force of the arranging means  14 . 
     FIG.  3 ( a ) is a view showing a home position of the stapler head  18 . The stapler unit  18  is set at a front end oblique stapling position with a prescribed angle (about 30 degrees in thin embodiment). FIG.  3 ( b ) is a view showing a state that the stapler head  31  is rotated to a parallel stapling position by the rotary base  33  in association with conveyance of the sheet bundles. FIG.  3 ( c ) is a view showing a state that the stapler head  31  is rotated to a rear end oblique stapling position by rotation of the rotary base  33 . 
     Next, referring to FIG. 4, a controlling system for the sheet stapler thus described is described. In FIG. 4, numeral  61  indicates a controller controlling respective drives of the stapler unit  18 , the respective rollers  8 ,  9 ,  11 ,  12 , the arranging means  14 , the stopper gate  16 , etc. according to various information signals such as sheet size information, mode information, and signals from the respective sensors  3 ,  13 . 
     The sheet size information may be detected automatically from a sheet size detection sensor  62  or can be inputted from a sheet size input panel  63  on the control panel. 
     The staple mode information is inputted from a staple mode input panel  70  (in this embodiment, respective mode keys  71 ,  72 ,  73  on the control panel shown in FIG.  5 ). The respective modes (double position stapling, front end single position stapling, rear end single position stapling) shown in FIG. 5 are described below. 
     The sheet stapler thus constructed operates as follows: 
     First, a sheet P on which an image is recorded by the image forming apparatus  1  is conveyed out by a delivery roller pair, not shown, incorporated in the image forming apparatus  1  and is conveyed into the sheet stapler A through a sheet inlet. The front end of the sheet P is taken by the loading roller  2  and conveyed into the sheet stapler A. 
     The conveyed sheet P informs the sheet stapler A of a correct position of the sheet P when the front end of the sheet P passes by the loading sensor  3 . Although the sheet P is conveyed to the sheet piling section B by the conveying roller  5 , the first rocker roller  8  waits at a upper position separated from the first conveying roller  9 . At that time, the first rocker roller  8  and the first conveying roller  9  are not rotating. When the sheet P proceeds in a nip portion between the first rocker roller  8  and the first conveying roller  9 , where they are separated from each other, and when the sheet is further conveyed for a while after the loading sensor  3  detects the sheet P, the first rocker roller  8  moves down by operation of the clutch C 8 , thereby nipping the sheet P proceeded in the nip portion together with the first conveying roller  9 . 
     If the sheet detection sensor  13  detects that no sheet is piled on the sheet piling section B, the sheet P is conveyed by rotary drive force given from the first rocker roller  8  and the first conveying roller  9  in a downstream direction of the sheet conveyance direction. If the sheet detection sensor  13  detects that some sheet or sheets P are plied on the sheet piling section B, the first conveying roller  9  remains stop without having rotary drive force, and the sheet P is conveyed by rotary drive force given from the first rocker roller  8  in a downstream direction of the sheet conveyance direction. That is, the sheet P is conveyed in slipping over the sheets already piled on the sheet piling section B. 
     As shown in FIG. 6, the sheet P conveyed onto the sheet piling section B stops upon striking the stopper gate  16  by the front end of the sheet P. At that time, the first rocker roller  8  slips on the sheet P. The sheet P is therefore piled on the sheet piling section B in a manner that the front end of the sheet is orderly arranged. Then, the first rocker roller  8  moves up again by the clutch C 8  and enters in a waiting mode. 
     Subsequently, the arranging means  14  trues up the edges of the sheets, as side adjustment, in the width direction perpendicular to the sheet conveyance direction. This operation is implemented every sheet&#39;s piling on the sheet piling section B, and the sheets P are pushed against the reference face  15  located in opposition to the arranging means  14  and the reference face of the stapler unit  18  to true up the edges of the sheets P. 
     The operation regarding a single sheet P thus described is repeated until the sheet piling section B stores sheets P of a target number as designated. A sheet bundle formed by using the entire processes goes to the next stapling process. 
     Referring to FIGS. 7,  8 ,  9  to  11 , the stapling process is described. FIGS.  7 ( a ),  7 ( b ) are illustrations for double position stapling; FIGS.  8 ( a ),  8 ( b ) are illustrations for oblique stapling (front end stapling and rear end stapling); FIGS. 9 to  11  are flowcharts for stapling operation of the sheet stapler. It is to be noted that the respective stapling modes, namely, edge double position stapling mode, front end single stapling mode, and rear end single stapling mode are described in this order. 
     First, referring to FIG. 9, double position stapling performed at the edge of the sheet bundle is described. When the sheet bundle is arranged orderly by truing up the sheets P as described above (step  11 ), the first rocker roller  8  and the second rocker roller  11  move down by the clutches C 8 , C 11  (step  12 ). The sheet bundle is therefore nipped by the first conveying roller pair  8 ,  9  and the second conveying roller pair  10 ,  11 . Because a relation between a nip portion conveyance speed V 1  of the first rocker roller  8  and a nip portion conveyance speed V 2  of the second rocker roller  11  is set as V 1 ≦V 2 , when the sheet bundle is fed by the two roller pairs, the sheet bundle is conveyed in a state that the sheet bundle always receives a tension (a tightly tensioned state: step  13 ) since the conveyance speed on the downstream side in the sheet conveyance direction is faster than the conveyance speed on the upstream side in sheet conveyance direction. By this conveyance, the properly arranged sheet bundle is conveyed in maintaining the properly arranged state to the prescribed position without experiencing any disorder. 
     Because the arranging means  14  travels toward the downstream side in the sheet conveyance direction in synchrony with conveyance by the two roller pairs during conveyance of the sheet bundle after orderly arranging operation thus described (step  14 ), the sheet bundle is restricted at opposite ends in the width direction, thereby suppressing disorder of the trued sheet bundle, and rendering the conveyance of the sheet bundle stable. 
     In synchronism with the conveyance of the sheet bundle, the stapler unit  18  pivotally moves from the front end oblique stapling position as the home position as shown in FIG.  3 ( a ) to the parallel stapling position as shown in FIG.  3 ( b ) (steps  15 ,  16 ). The stapler unit  18  executes first parallel stapling operation (see, FIG.  7 ( a ): step  17 ) on the sheet bundle fed to the prescribed position by the two roller pairs (and the arranging means  14 ). During this operation, a staple fastens the sheet bundle at a single position. The first rocker roller  8  and the second rocker roller  11  hold the sheet bundle firmly during this stapling operation, so that the sheet bundle would not be shifted due to stapling operation executed by the stapler unit  18 . 
     The first conveying roller  9 , the second conveying roller  12 , and the delivery roller pair  20  then begin to rotate again at the same timing (step  18 ), thereby conveying the sheet bundle to the subsequent prescribed position. A relation between a nip portion conveyance speed V 3  of the delivery roller pair  20  and a nip portion conveyance speed V 2  of the second rocker roller  11  is set as V 2 ≦V 3 . That is, this relation is the same as the relation between the conveyance speed of the first rocker roller  8  and the conveyance speed of the second rocker roller  11 . This structure allows the sheet bundle to be orderly conveyed. 
     It is to be noted that the prescribed positions (the first stapling position and the second stapling position), or namely the respective stapling positions are determined with respect to a center of the sheets in the sheet conveyance direction as to be located equally away from the center. 
     The sheet bundle conveyed in a prescribed amount by the conveying roller group, stops at a prescribed position upon rotation stop of the conveying roller group (step  19 ), and then, the stapler unit  18  implements the second parallel stapling operation (see, FIG.  7 ( b ): step  20 ). Thus, the sheet bundle stapled at double positions is conveyed according to rerotation of the conveying roller group (step  21 ) and delivered onto the sheet bundle tray  19  and then piled one by one. At the same time, the stapler unit  18  returns to the home position shown in FIG.  3 ( a ) (in this embodiment, the front end oblique position: step  22 ). The sheet bundle delivered on the sheet bundle tray  19  is orderly arranged briefly by the sheet bundle front end stopper  21  at the front end of the sheet bundle. 
     Referring to FIG. 10, a single position oblique stapling operation executed at the front end of the sheet bundle is described. In the case of the front end oblique stapling, the same processes are used until the sheets are trued up (step  31 ). Then, as shown in FIG.  8 ( a ), because the stapler unit  18  is located at the front end oblique stapling position as the home position oblique with respect to the sheet conveyance direction toward the upstream side at a prescribed angle (in this embodiment, about 30 to 45 degrees), the unit  18  staples the sheet bundle at the position right after the sheets are orderly arranged (step  32 ). At the same time, the stopper gate  16  is released by the clutch  17  (broken line in FIG.  6 : step  33 ). Then, the sheet bundle is conveyed by the first roller pair  8 ,  9  and the second roller pair  11 ,  12  on the downstream side in the sheet conveyance direction (step  34 ) down to the delivery roller  20 . The sheet bundle is subsequently delivered onto the sheet bundle tray  19  by the conveying roller group (step  35 ) and piled up on the tray. The sheet bundle delivered on the sheet bundle tray  19  is, similarly, orderly arranged briefly by the sheet bundle front end stopper  21  at the front end of the sheet bundle. 
     Finally, referring to FIG. 11, a single position oblique stapling operation executed at the rear end of the sheet bundle is described. In the case of the rear end oblique stapling, the same processes are used until the sheets are trued up (step  41 ). After the stopper gate  16  is released by the clutch  17  (broken line in FIG.  6 : step  42 ), the sheet bundle is conveyed by the first roller pair  8 ,  9  and the second roller pair  11 ,  12  on the downstream side in the sheet conveyance direction (step  43 ) down to the delivery roller  20  and further down to the prescribed position by the conveying roller group (step  44 ). Then, as shown in FIG.  8 ( b ), the stapler unit  18  pivotally moves to the rear end oblique stapling position oblique with respect to the sheet conveyance direction toward the downstream side at a prescribed angle (in this embodiment, about 30 degrees: steps  45 ,  46 ). That is, the rotary base  33  formed in the stapler unit  18  rotates the stapler head  31  to the position as shown in FIG.  3 ( c ). The staple unit  18  staples the sheet bundle at the same time when this rotation stops (step  47 ). When this stapling operation ends, the rotary base  33  formed in the stapler unit  18  rotates the stapler head  31  to the home position (see, FIG.  3 ( a ): step  48 ). At the same time, the sheet bundle is delivered onto the sheet bundle tray  19  by the conveying roller group (step  49 ) and piled on the tray. The sheet bundle delivered on the sheet bundle tray  19  is, similarly, orderly arranged briefly by the sheet bundle front end stopper  21  at the front end of the sheet bundle. 
     It is to be noted that, in addition to the relation between the rocker rollers and the conveying rollers, after the sheet bundle reaches the delivery roller pair  20 , the sheet bundle can be conveyed solely by the delivery roller pair  20  where the rocker rollers  8 ,  11  are separated from the conveying rollers  9 ,  12  by clutches (not shown), thereby solving problems such as influences of conveyance speed shifts between roller pairs, tilting of rollers themselves, and thereby further reducing positional shifts of the sheet bundle during conveyance of the sheet bundles. 
     Second Embodiment 
     Referring to the drawings, a sheet stapler according to a second embodiment is described. FIG. 12 is a top view showing the sheet stapler. Among numerals set forth in FIG. 12, any element having the same numeral as of the first embodiment is the same as the element shown in the first embodiment. 
     In FIG. 12, numeral  41  indicates a first rocker roller, and similarly to the first rocker roller  8  in the First Embodiment, a single roller is arranged coaxially (a width direction perpendicular to the sheet conveyance direction), rotatively driven by a driver M 41 , and moved up and down by the clutch C 41  at a prescribed timing. Numeral  42  indicates a first conveying roller and disposed in opposition to the first rocker roller  41 , similarly to the first conveying roller  9  in the First Embodiment. The first conveying roller  42  is formed at the bottom face of the sheet piling section B on which sheets P are piled one by one and rotatively driven by a driver M 42  at a prescribed timing. The first conveying roller pair as the first sheet bundle conveying means is constituted of the first rocker roller  41  and the first conveying roller  42 . 
     Numeral  43  indicates a second rocker roller, which has the same function as the first rocker roller  41 . Numeral  44  indicates a second conveying roller, which has the same function as the first conveying roller  42 . A second conveying roller pair serving as a second sheet bundle conveying means is constituted of the second rocker roller  43  and the second conveying roller  44 . Similarly, in FIG. 2, numerals M 43 , M 44  indicates drivers, and numeral C 43  indicates a clutch. 
     Numeral  45  indicates a delivery roller pair as a third sheet bundle conveying means for delivering the sheet bundles onto the sheet bundle tray  19 . 
     The first conveying roller pair  41 ,  42 , the second conveying roller pair  43 ,  44 , and the delivery roller pair  45  are disposed only on a side on which the stapler unit  18  is disposed as a sheet bundle&#39;s stapling side, and thereby nip only edges on the side of the sheet bundle on which the unit  18  is disposed. 
     According to the structure above, similarly to the embodiment above, the sheets P conveyed from the image forming apparatus  1  are piled up on the sheet piling section B one by one and can be subject selectively to the double position stapling, the front end oblique stapling,, and the rear end oblique stapling, in the same manner as in the First Embodiment. With this embodiment, when the stapled sheet bundle is conveyed, only the stapled edge side (vicinities of stapled portions) is held and conveyed without holding the entire portion in the width direction of the sheet bundle, thereby capable of conveying the sheet bundle without positional shifts of the sheet bundle. Because the roller for conveyance itself is short in the width direction of the sheets, influences of oblique conveyance due to differences of conveyance speed in the width direction of the sheet would be avoided. This structure is effective for conveying the sheet bundles by conveying roller pairs made of two pairs or more. 
     Third Embodiment 
     Referring to the drawings, a sheet stapler according to the third embodiment is described. FIG. 13 is an enlarged cross section of stapler for sheet bundles. 
     FIG.  13 ( a ) is an enlarged cross section showing a situation that the stapler unit  18  hit a staple  51  (strike from top) from a top side to a bottom side (guide face  52 ) of the sheet bundle, and bent portions  51   a  of the staple  51  are projected on the guide face  52  side of the sheet bundle P. In this embodiment, as opposed to the above hitting direction, as shown in FIG.  13 ( b ), the staple  51  is hit from the bottom face (the guide face  52 ) of the sheet bundle P to the top face (strike from bottom). More specifically, for example, a sheet staple having a stapler unit hitting staples  51  from the guide face  52 , a sheet stapler interchangeably having stapler units for strikes from top and bottom, etc. are used. The structure of such a sheet stapler can operate in the same manner as in the embodiments described above, and therefore, a detailed description is omitted. 
     Since the bent portions  51   a  of the staple  51  shown in FIG.  13 ( a ) is located on a side of the guide face  52 , the bent portions  51   a  of the staple  51  may be caught by the guide face  52  while the sheet bundle P is conveyed. The bent portions  51   a  of the staple  51  directly receives the weight of the sheet bundle. The bent portions  51   a  of the staple  51  therefore becomes conveyance resistance, thereby rendering the conveyance of the sheet bundle possibly unstable. To solve this problem, this embodiment has a structure for striking from the bottom in which the bent portions  51   a  of the staple  51  are on a top face of the sheet bundle P. Since the flat portion  51   b  of the staple  51  is located on the side of the guide face  52  of the conveyance guide, and since the staple  51  is hardly projected from the sheet bundle P toward the guide face  52 , the sheet bundle P can be conveyed smoothly. This structure allows the sheet bundle to be conveyed stably and smoothly, thereby improving the piling capability of the sheet bundles P. In particular, this structure is very effective for an apparatus for stapling sheet bundles at least a position with staples  51  extending substantially parallel to the sheet conveyance direction. 
     Although in the embodiments above, a double position stapling is exemplified as stapling operation to staple sheet bundle parallel to the sheet conveyance direction as shown in FIG. 7, such stapling is not limited to the above operation, and stapling number and stapling positions may be set according to necessity (such as sheet size or the like). Although the angle for oblique stapling operation (front end oblique stapling and rear end oblique stapling) is exemplified as about 30 to 45 degrees, the angle is not limited to the above angle range. 
     Although in the embodiments above, the sheet stapler according to the invention is connected to the image forming apparatus, the sheet stapler is not limited to such a structure and the same effects are obtainable where the sheet stapler according to the invention is incorporated in or apply to sheet processing apparatuses such as sorters or finishers connected to image forming apparatuses such as, e.g., facsimile machines, photocopiers, etc. 
     Although in the embodiments above the sheet stapler staples the sheet bundles with staples, the sheet stapler according to the invention is not limited to this structure, and this invention is effective even for an apparatus for fastening the sheet bundle with items other than staples, e.g., an apparatus fastening the sheet bundles by pressing the sheet bundles without using staples. 
     Fourth Embodiment 
     FIGS. 14,  15  are the best illustrative drawings for the invented structure. The structure shown in FIGS. 14,  15  is described as follows. Numeral  101  indicates an image forming apparatus, which transfers an image onto a sheet (paper or transfer medium) P, and the sheet P is conveyed to a sheet stapler A connected below the image forming apparatus A. In FIG. 14, numeral  101   a  indicates a sheet cassette; numeral  101   b  indicates a pickup roller; numeral  101   c  indicates a register roller; numeral  101   d  indicates a photosensitive drum; numeral  101   e  indicates a fixing roller; numeral  101   f  indicates a flapper; numeral  101   g  indicates a delivery roller; numeral  101   j  indicates a delivery tray; and numeral  101   k  indicates a conveying roller. 
     Reference character A indicates a sheet connected at a prescribed position below the image forming apparatus  101 . Numeral  102  is a loading roller disposed to the sheet inlet; numeral  103  indicates a loading sensor for detecting the sheet P proceeding in the sheet stapler A; numeral  104  indicates a guide plate for guiding the sheet P to the next process; numeral  105  indicates a conveying roller pair for conveying the sheet P to a sheet stapling section as a subsequent process to pile the sheet P at the section; numeral  106  indicates an upper guide plate for conveying the sheet by the conveying roller pair  5  and guides a front end of the sheet P to the sheet piling section  160  (FIG.  17 ). Numeral  107  indicates a first rocker guide, which prevents disorders of the piled sheets P and stably guides the front end of the sheet P to the roller pair of the subsequent process. Numeral  108  indicates a first rocker arm in which plural first conveying rollers  108   a  are arranged coaxially on a front end shaft (width direction perpendicular to a sheet conveyance direction) and can be moved up and down repetitively at a prescribed timing by a driver M 1  through a clutch not shown. The conveying rollers  108   a , notedly, are rotatively driven by a motor M 3  and a belt  108   b . Numeral  109  indicates a first opposing roller, which is disposed in opposition to the first rocker rollers  108   a  and disposed below the sheet piling section  160  on which sheets are piled sheet by sheet and has a structure rotatively driven by a driver M 5  at a prescribed timing. A belt  108   b  is suspended between a rocker shaft  108   c  of the arm  108  and rollers  108   a . Numeral  110  indicates a second rocker guide, which has the same function as the first rocker guide  1017 . Numeral  111  indicates a sheet detection sensor for detecting whether the sheet P exists in the sheet piling section. Numeral  112  indicates a second rocker arm having the same function as the first rocker arm  108  and rocking by means of a motor M 2 , on which plural second conveying rollers  112   a  are arranged coaxially. Numeral  113  indicates a second opposing roller having the same function as the first opposing roller  109 . The conveying rollers  112   a  are rotated by a motor M 4  and a belt  112   b . Numeral  14  indicates a sheet arranging unit for orderly arranging the edges of sheets P in a direction perpendicular to the sheet conveyance direction. The sheet arranging unit  14  has a drive motor M 6  in the unit and pushes the sheet edges in the width direction of the sheets toward a center of the sheets with a prescribed pushing force at multiple times at each piling of the sheet P, thereby truing up the edges of the sheet bundles P. A belt  112   b  is suspended between a rocker shaft  112   c  of the arm  112  and rollers  112   a . Numeral  115  indicates a reference face to be pushed, which is formed at a position opposing to the sheet arranging unit  114  with respect to the sheet bundles. The sheets&#39; edges in opposition to edges pushed by the sheet arranging unit  14  are pushed onto the reference face  115 , thereby truing up the edges of the sheets P (FIG.  15 ). Numeral  116  indicates a sheet front end stopper gate for stopping the front end of the sheets P to set the sheets orderly in the sheet conveyance direction, extending in a direction perpendicular to the sheet conveyance direction (FIGS. 15,  17 ). The stopper gate  116  is driven to rotate by a motor M 7  through a clutch  117  and can travel selectively between a stopper position and an escaped position. 
     Numeral  118  indicates a stapler unit which fastens the properly arranged sheet bundles with staples at a prescribed position or positions with a prescribed angle and has a structure as shown in FIG.  16 . FIG.  16 ( a ) shows a home position of the stapler unit  118 ; the home position is set at an oblique position for stapling the sheet bundle with staples for oblique stapling operation at an angle of about 30 degrees. Numeral  132  indicates a stapler head; numeral  133  indicates a stapler head support for supporting the stapler head  132 ; numeral  134  indicates a rotary base disposed below the support  133  and made rotatable at any angle. FIG.  16 ( b ) shows a situation that the rotary base  134  is rotated to the parallel stapling position in association with the conveyance of the sheet bundles. The parallel position herein means, more or less, to extend along the edge of the sheets. Numeral  119  indicates a sheet bundle tray for piling the stapled sheet bundles; numeral  120  indicates piled sheet bundles; numeral  121  indicates a delivery roller pair for delivering sheets on the tray  119 ; and numeral  122  indicates a sheet bundle front end stopper for briefly, properly arranging the front end of the sheet bundles  120 . The stopper  122  is disposed on a front side of the image forming apparatus. 
     FIG. 18 shows a drive unit for stapler unit for changing the stapling angle and position of the stapler unit. In FIG. 18, numeral  151  indicates a groove formed on the rotary base  134 , with which a worm gear  152   a  provided coaxially to a partially toothless gear  152 . Accordingly, the stapler unit  118  on the rotary base  134  rotates at a prescribed angle by rotation of the partially toothless gear  152 . Numeral  153  indicates a gear formed on a shaft of the second rocker arm  112  movable up and down and engages alternatively with gears  156 ,  154  according to the up and down movement of the gear  153 . The gear  154  is formed on a shaft of the second opposing roller  113 . A gear  155  is an idler A drive force of a motor M 4  is transmitted to the gear  153  by a belt. 
     With this structure, hereinafter, operation of the sheet stapler according to the invention is described. A sheet P on which an image is recorded by the image forming apparatus  1  is conveyed and guided by a delivery roller pair, not shown, in the image forming apparatus  101  to the inlet of the sheet stapler A through a sheet inlet. The front end of the sheet P is taken by the loading roller  102  and conveyed into the sheet stapler A. The conveyed sheet P informs the sheet stapler A of a correct position of the sheet P when the front end of the sheet P passes by the loading sensor  103  (or, the sensor can detect the correct position). Although the sheet P is conveyed to the sheet piling section B by the conveying roller  105 , the first rocker arm  108  waits at a upper position. At that time, the first conveying roller  109  is not rotating. When the sheet P proceeds in a nip portion opened between the first rocker rollers  108   a  and the first opposing roller  109  (at that time, the nip portion is in a separated state), and when the sheet is further conveyed for a while after the loading sensor  103  detects the sheet P, the first rocker arm  108  moves down by operation of the clutch not shown thereby nipping the sheet P by the first conveying rollers  108   a  and the first opposing roller  109 . When no sheet is piled on the sheet piling section B at a time of delivery of the first sheet (as detected by a sheet existence detection sensor  111 ), the sheet is conveyed by rotary drive force given from the first opposing roller  109  together with the first conveying rollers  108   a  in a downstream direction of the sheet conveyance direction. When a sheet or sheets P are already plied on the sheet piling section B at a time of delivery of a subsequent sheet, the first opposing roller  109  remains stop without having rotary drive force, and the sheet P is conveyed solely by rotary drive force given from the first conveying rollers  108   a  in a downstream direction of the sheet conveyance direction. That is, the sheet P is conveyed in slipping over the sheets already piled on the sheet piling section B. 
     As shown in FIG. 17, the sheet P conveyed onto the sheet piling section B stops upon striking the stopper gate  116  by the front end of the sheet P. At that time, the first rocker roller  8  and the sheet slip with each other. The sheet P is therefore piled on the sheet piling section B in a manner that the front end of the sheet is arranged orderly. Then, the first rocker arm  108  moves up again by the clutch not shown according to a reverse rotation of the motor M 1  and enters in a waiting mode. 
     Subsequently, the sheet arranging unit  114  trues up the side edges of the sheets. This operation is implemented every sheet&#39;s piling on the sheet piling section B, and the sheets P are pushed against the reference face  115  located in opposition to the sheet arranging unit  114  and the reference face of the stapler unit  118  to true up the side edges of the sheets P. 
     The operation regarding a single sheet P thus described is repeated until the sheet piling section B stores sheets P of a target number as designated. A sheet bundle formed by using the entire processes goes to the next stapling process. In use of FIGS. 16 to  18 , a stapling process, first, of double position stapling and movement of the sheets is described. 
     When the sheet bundle is arranged orderly as the front end of sheets is pushed against the stopper gate  16 , the first rocker arm  108  and the second rocker arm  112  move down by the clutches. The sheet bundle is therefore nipped by the conveying rollers  108   a ,  112   a  and the opposing rollers  109 ,  113 . Because a relation between a nip portion conveyance speed V 1  of the first conveying rollers  108   a  and a nip portion conveyance speed V 2  of the second conveying rollers  112   a  is set as: 
     Speed of the first conveying rollers V 1 ≦Speed of the second conveying rollers V 2 , 
     when the sheet bundle is fed by the two roller pairs, the sheet bundle is conveyed in a state that the sheet bundle always receives a tension since the conveyance speed on the downstream side in the sheet conveyance direction (conveyance speed of the second conveying roller  112   a  and the second conveying roller  113 ) is faster than the conveyance speed on the upstream side in sheet conveyance direction. By this conveyance, the properly arranged sheet bundle is conveyed in maintaining the properly arranged state to the prescribed position. This conveyance mechanism for sheet bundles thus constructed allows the sheet bundles keep the properly arranged state without experiencing any disorder. Where the sheet arranging unit  114  is so constituted as to travel on the downstream side in the sheet conveyance direction in association with the conveyance of the sheet bundles, the sheet bundle is held at opposing edges of the sheet bundle, so that disorder of sheet bundle&#39;s arrangement can be made further smaller. 
     In synchronism with the conveyance of the sheet bundle, the stapler unit  118  pivotally moves from the front end oblique stapling position as the home position as shown in FIG.  16 ( a ) to the parallel stapling position as shown in FIG.  16 ( b ). This movement is illustrated in referring to FIG.  18 . When the second rocker arm  112  moves down as described above to convey the sheet bundle, the gear  153  on the shaft of the rocker arm  112  engages with the gear  154  on the second opposing roller  113 . The gear  152  therefore rotates in the arrow P direction until reaching the toothless portion (FIG.  18 ( a )). According to this rotation, the stapler unit  18  rotates to be positioned parallel to the sheet conveyance direction. Then, the gear  155  rotates idly. 
     The sheet bundle conveyed to the prescribed position is stopped at the position (by stop of rotation of rollers  108   a ,  112   a ,  109 ,  113 ), and upon rotation of the motor M 8 , the stapler unit  118  executes the first stapling operation (parallel stapling). The sheet bundle is fastened at a single position by a staple. The staple will not cause positional shifts of the sheet bundle because the first conveying rollers  108   a  and the second conveying rollers  112   a  firmly nips the sheet bundle at that time. The first opposing roller  109 , the second opposing roller  113 , and the delivery roller pair  121  begin rotating again at the same timing and convey the sheet bundle to the next prescribed position. The delivery roller pair  121  has, with the nip conveyance speed of the second conveying roller, the following relation as: 
     Speed of the first conveying rollers V 2 ≦Speed of the delivery roller V 3 . 
     This relation is the same as the relation between the speed of the first conveying roller and the speed of the second conveying rollers, and the stapler can convey the sheet bundle without disorder. 
     The sheet bundle conveyed in a prescribed amount by the conveying roller group, stops at a prescribed position upon rotation stop of the conveying roller group, and then, the stapler unit  118  implements the second parallel stapling operation. Thus, the sheet bundle stapled at double positions is conveyed according to rerotation of the conveying roller group and delivered onto the sheet bundle tray  119  and then piled one by one. When the sheet stapler finishes the delivery of the sheet bundle, the first and second rocker arms  108 ,  112  move up. In the stapler unit  118  at the same time, the gear  153  comes in mesh with the gear  156  upon moving up of the second rocker arm  112 . The gear  152  continues to rotate in the arrow U-direction by this engagement until reaching the toothless portion (FIG.  18 ( b )). The rotary base  143  of the stapler  118  rotates according to rotation of the gear  152 , and thereby the stapler unit  118  returns to the home position (FIG.  18 ( a )). The sheet bundle delivered on the sheet bundle tray  119  is orderly arranged briefly by the sheet bundle front end stopper  121  at the front end of the sheet bundle. 
     Next, a single position oblique stapling operation executed at the front end of the sheet bundle is described. In the case of the front end oblique stapling, the same processes are used until the sheets are trued up. Because the second rocker arm  112  remains as moved up, and because the stapler unit  118  is as shown in FIG.  18 ( a ) located as the home position on the upstream side in the sheet conveyance direction At an angle of about 30 to 45 degrees, the stapler unit  118  staples the sheet bundle at the position right after the sheets are orderly arranged. At the same time, the stopper gate  116  is released by the clutch  117 . Then, the sheet bundle is conveyed by the first conveying roller pair  108   a ,  109  and the second conveying roller pair  112   a ,  113  on the downstream side in the sheet conveyance direction, and after conveyed down to the delivery roller pair  121 , the sheet bundle is delivered onto the sheet bundle tray  119  by the conveying roller group and piled up on the tray. After delivery of the sheet bundle, the staple unit  118  enters in a situation shown in FIG.  18 ( b ) because the first and second rocker arms  108 ,  112  move up. 
     A sheet arranging tray during a stapling operation after the sheet bundle is trued up, is described as follows. FIG.  19 ( a ) is an illustration for describing problems occurring in a conventional tray. Numeral  161  indicates a sheet bundle; numeral  162  indicates an anvil of the stapler unit  118 ; numeral  163  indicates a cam rotating by a gear in the stapler unit. Numeral  164  indicates a head in which staples are pushed out by a built-in hammer. In FIG.  19 ( a ), since the sheet bundle is piled on an immobilized arranging tray  160 , the anvil  162  of the stapler unit  118  pushes up only the end of the sheet bundle. The sheet bundle, because a narrow portion of the sheet bundle is pushed up, frequently suffers from disorders of the trued edges of the sheets and from bad arrangements of the edges. 
     With the sheet arranging tray in the sheet stapler according to the invention, as shown in FIG.  19 ( b ), the arranging tray  260  has a rotation center  166 , and a pivotable end member  260   a  is pivotably connected to a lower anvil of the stapler unit with a pin  165   a  at one end  165  of the end member  260   a . According to this structure, when the sheet bundle is stapled, the arranging tray  119  pivotally moves around the rotation center  166  and renders the sheet bundle upward (FIG.  19 ( c )), thereby preventing the edges of the sheet bundle from disorderly arranged as shown in FIG.  19 ( a ). The staple is as shown in FIG.  19 ( c ) pushed out by the hammer in the head  64  while the anvil  162  is pushed up, and the anvil bends the tip of the staple to fasten the sheet bundle. 
     It is to be noted that reference character  163   a  is a cam link rotatively supported to a shaft  163   c ; a cam follower  163   b  is supported at one end of the cam link  163   a ; and an anvil  162  is supported at another end of the cam link  163   a . The cam  163  is rotated by a motor M 8 , and a cam portion  163   d  pushes the cam link  163  to rock the cam link  163 . When the cam portion  163   d  passes, the cam link  163   a  returns to a situation shown in FIG.  19 ( b ) by turning clockwise by self-weight of the end member  260   a  of the arranging tray  260 . 
     FIG. 21 is the best illustrative drawing of the structure of a roller according to the invention. Hereinafter, the structure in FIG. 21 is described. Numeral  161  indicates a sheet bundle stapled by the stapler; numeral  172  indicates a staple fastening the sheet bundle, in which the bent portions are not adequately bent after stapling. Such forms of the staples occur when the paper has a thick thickness or when the stapler unit&#39;s durability is impaired. Numeral  121  indicates a part of a delivery roller pair formed on the downstream side in the sheet conveyance direction and nips the sheet bundle with adequate pressure of the upper and lower rollers. The delivery roller  121  has a nip portion having a pressuring structure thus described only at a portion where the staples pass in the longitudinal direction (has a spring only where the staples pass). 
     With this structure, a sheet bundle  161  whose staple  172  is not adequately bent passes by the roller pair  173 . The staple  172  is nipped between the roller pair  172  while conveyed, so that the inadequately bent portions are made to closely contact the sheet by pressure. This pressure makes the staple closely contact parallel with the sheet without space. 
     The staple contacts with the sheet adequately by the operation above, so that the sheet bundle when delivered would not be caught by other sheet bundles to be delivered. Even if the staples are loosely bent, the roller thus structured contacts with the staples, thereby giving an adequate margin to durability of the stapler unit. Moreover, the thickness of the staple portion may be reduced, thereby increasing a piling amount of the sheet bundles, and improving piling and arranging performance of the sheet stapler. 
     It is to be noted that application of the pressure roller is not limited to the delivery roller pair, and a special roller can be provided between the delivery roller and the second conveying roller. In the case of the special exclusive roller, the roller may be formed only at a portion where staples pass. 
     Fifth Embodiment 
     FIG. 22 shows a fifth embodiment according to the invention. In FIG. 22, numerals  181 ,  182  indicate rollers having electrical conductivity, and in this embodiment, made of SUS metal rollers. Numerals  183 ,  184  indicate pressurizing springs for pressing the SUS rollers  181 ,  182  with a prescribed pressure; numeral  185  indicates a metal staple having electrical conductivity. Reference character P indicates a sheet bundle; numeral  186  indicates a detector connected to the metal rollers  181 ,  182  for detecting that the sheet bundle is fastened by staples by flowing a current of a very small amount between the metal rollers. With this structure, when the sheet bundle fastened with a staple or staples passes by the nip portion of the metal roller  181 ,  182 , the detector  186  can detect that the a prescribed number of staples surely fastened the sheet bundle. By matching timings between the conveyance of the sheet bundle and the detection (or counting time from start of the conveyance to the detection of staples), the stapler can detect as to whether the staple is fastened at the prescribed position or positions. This is a very beneficial structure to detect stapling errors possibly occurring due to disordered sheet bundles or the like. When an error occurs, the stapler may warn by a beeper and stops its operation. 
     It is to be noted that the sheet arranging tray&#39;s structure shown in FIG. 19 is, as a matter of course, applicable to the respective sheet staplers in First to Third Embodiment. Similarly, the roller structure shown in FIGS. 21,  22  is also applicable to the sheet staplers in the first to third embodiments. 
     Referring to FIG. 23, a flow of conveyance of a sheet P from the image forming apparatus  1  to the sheet stapler A is described. The sheet stapler is powered on, and conditions are initialized (step  101 ). A paper discarding job is started (step  102 ). Then, the conveying roller  1   e  is driven (step  103 ), and a flapper is switched as to direct the sheet stapler A (step  104 ). The controller judges as to whether a stapling operation is requested (step  105 ), and if not, the execution jumps to step  121  described below, and the sheet if any is delivered to a tray to finish the job. If the stapling operation is requested, a gate to the sheet stapler A is opened (step  106 ); the sheet P is introduced into the sheet stapler A using the conveying roller  2  (step  107 ); and the arranging means  14  arranges the edges of the sheet orderly and the trued sheets are piled on the sheet piling section B (step  108 ). Whether the piled number of sheets reaches the target number is judged (step  109 ), and upon completion of piling operation, the flapper  1   f  is switched (step  110 ). Then, the execution moves to stapling operation. In the stapling operation, the stapler judges as to whether position(s) to be fastened is double (parallel stapling) or single (front end oblique stapling) (step  111 ). If “yes”, the side register plate holds itself at the width of the sheets (step  118 ), and the sheet bundle is stapled (step  119 ). In this situation, the side register plate is then released (step  120 ), and the conveying roller is moved down (step  121 ). After the gate is released (step  122 ), the sheet bundle is delivered to the tray by driving the conveying rollers (step  123 ) upon moving down the delivery roller (step  124 ). If “No” at step  111 , the side register plate maintains the sheet width (step  112 ), and the gate is released (step  114 ) upon moving down the conveying rollers (step  113 ). Where the conveying rollers are driven (step  115 ), the sheet bundle is stapled at a prescribed position (step  116 ). To staple at plural positions for parallel stapling operation, the execution goes back to steps  115  from step  117  and repeats this. That is, the sheet bundle is moved by a prescribed distance, the sheet bundle is stapled again (step  116 ). At step  117 , the stapling operation of the prescribed number is confirmed, and then, the execution goes to step  123 , thereby finally delivering the sheet bundle onto the tray.