Patent Publication Number: US-6666443-B2

Title: Sheet finisher having stapler and image forming apparatus for use therewith

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a sheet finisher having a stapler to conduct a staple processing on sheets after the image formation, and an image forming apparatus having the sheet finisher. 
     The finisher in which, after the image formation is conducted on the sheet, a bundle of a plurality of sheets is stapled, is fitted to the image forming apparatus as a standard function of the high speed image forming apparatus by which an image is formed by the electro-photographic method. 
     A stapler generally composed of a stacking means for stacking the sheets conveyed in the finisher one by one sheet after the image formation, by the preset number of sheets, and a stapling means for stapling the stacked sheets by staples. In the continuous image forming process, the image formed sheet conveyed-in from the image forming apparatus main body is conveyed in the sheet finisher at a predetermined sheet interval. In the stapler, however, it is necessary that a comparatively long sheet interval is taken between the bundles of the sheets to be stapled, and because the sheet interval between the sheet bundles is longer than the sheet interval between the sheets to be conveyed in, it is necessary to have an adjustment between the conveying control of the sheet in the image forming apparatus main body and the conveying control in the sheet finisher. 
     As the image formation speed is increased, the mismatching as described above between the sheet interval of the sheet to be conveyed-in from the image forming apparatus main body and the sheet interval of the sheet which can be received by the stapler becomes a problem, thereby a case in which the high speed performance of the image forming apparatus main body is sacrificed to some extent and the productivity of the image formation is necessarily lowered, is generated. 
     As a countermeasure for such a problem, in Japanese Tokkaihei No. 1-127556, a sheet finisher in which conveying paths of two long and short system are provided upstream the stacking means and the top sheet after the second bundle of the sheet bundles to be stapled, is conveyed in the stacking means through the long conveying path, and the other sheets are conveyed in the stacking means through the short conveying path, is proposed. 
     Further, in Japanese Tokkaihei No. 9-235069, a sheet finisher in which a sheet stand-by section for making standby two sheets is provided, is proposed. 
     In the sheet finisher in Japanese Tokkaihei No. 1-127556, because the exclusive use long conveying path for delaying the conveying timing to the stacking means is provided, there is a problem that the image forming speed is high speed, and as the difference between the conveying-in speed of the sheet from the image forming apparatus and the processing speed of the stapler is increased, the length of the conveying path is increased, and the apparatus size is increased. Further, when the long conveying path is arranged in a small sized finisher, the shape of the conveying path becomes complex, and it is difficult that the stable conveying property is secured. As described above, although the sheet finisher in Japanese Tokkaihei No. 1-127556 aims the high speed image formation, the problem becomes conspicuous in the high speed area. 
     In the sheet finisher in the Japanese Tokkaihei No. 9-235069, because the stand by section for the sheet is provided in the conveying path by which the sheet is conveyed in the stacking means, it is required that the conveying path has both conveying function and accommodation function together, and there is a problem that, for the sheets ranging from the large size to the small size, it is difficult that these requirements are satisfied. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to solve the above described problem relating to the mismatching between the image forming speed of the image forming apparatus main body and the processing speed of the stapler. 
     The object of the present invention is attained by any one of Structures (1)-(8). 
     (1) A sheet finisher which has a stacking means for stacking a sheet conveyed-in from an image forming apparatus and a stapling means for stapling the stacked sheets, the sheet finisher is characterized in that: it has a conveying timing adjustment section arranged upstream of the stacking means, and the conveying timing adjustment section has; a conveying-in section; a conveying-out section separately provided from the conveying-in section; a reversal conveying section to reverse the conveying direction of the sheet conveyed from the conveying-in section in one direction and to convey-out it from the conveying-out section; and a control means for conducting the control of the reversal conveying section, wherein the control means controls the reversal conveying section such that at least a second bundle or a bundle after the second bundle of the sheet bundles to be stapled by the stapler, in which a plurality f sheets having at least a top sheet and a succeeding sheet to the top sheet are overlapped each other, is conveyed-out from the reversal conveying section. 
     (2) A sheet finisher according to the Structure (1), wherein the reversal conveying section has a sheet accommodation section vertically arranged for accommodating the sheet conveyed-in and a stopping member for stopping the sheet conveyed-in, wherein the control means controls the stopping member to send out the sheet to the conveying-out section after stopping the sheet conveyed-in the sheet accommodation section. 
     (3) A sheet finisher according to either one of the Structure (1) or the Structure (2), wherein the control means controls the reversal conveying section such that the bundle having at least the top sheet and a sheet succeeding to the top sheet which are overlapped each other in the reversal conveying section, and remaining sheets other than the top and the succeeding sheets of said second bundle and sheets of a preceding first bundle is conveyed-out one by one from the reversal conveying section. 
     (4) A sheet finisher according to any one of the Structures (1)-(3), wherein the reversal conveying section is arranged in the vicinity of the sheet conveying-in inlet of the sheet finisher. 
     (5) A sheet finisher according to any one of the Structures (1)-(4), wherein the stapling means staples at edge or center position of the sheets. 
     (6) A sheet finisher according to any one of the Structures (1)-(5), wherein it has an alignment means. 
     (7) A sheet finisher according to any one of the Structures (1)-(6), wherein it has a folding section. 
     (8) An image forming apparatus characterized in that: it has the sheet finisher described in any one of Structures (1)-(7), and an image forming apparatus main body by which an image is formed on the sheet and the sheet is conveyed into the sheet finisher. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view showing an outline structure of an image forming apparatus according to an embodiment of the present invention. 
     FIG. 2 is a view showing a conveying timing adjustment section in a sheet finisher according to the embodiment of the present invention. 
     FIG. 3 is a side view of a reversal conveying section. 
     FIGS.  4 ( a )- 4 ( d ) are views showing the conveying timing of a sheet. 
     FIG. 5 is a typical view of a conveying timing adjustment section. 
     FIG. 6 is a view showing a conveying process forming a short sheet interval. 
     FIG. 7 is a view showing a conveying process forming a short sheet interval. 
     FIG. 8 is a view showing a conveying process forming a short sheet interval. 
     FIG. 9 is a view showing a conveying process forming a long sheet interval. 
     FIG. 10 is a view showing a conveying process forming a long sheet interval. 
     FIGS.  11 ( a ) and  11 ( b ) are views showing the structure of a folding section. 
     FIGS.  12 ( a )- 12 ( f ) are views showing a folding process. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     (Image Forming Apparatus) 
     FIG. 1 is an overall structural view of an image forming apparatus composed of an image forming apparatus main body A, automatic document feeder ADF and sheet finisher B. 
     The image forming apparatus main body A is provided with an image reading means  1 , image processing means  2 , image writing means  3 , image forming means  4 , sheet feeding means S, conveying means  6 , fixing means  7 , re-conveying means (automatic duplex unit ADU)  8 , and control means  9 . 
     The sheet feeding means  5  is composed of a cassette sheet feeding section  5 A and large capacity sheet feeding tray (LCT)  5 B, manual sheet feeding section  5 C, intermediate sheet feeding roller  5 D, and register roller  5 E. 
     The conveying means  6  has a conveying belt  6 A, conveying path switching plate  6 B, and sheet delivery roller  6 C. 
     On the upper portion of the image forming apparatus A, the automatic document feeder ADF is mounted. The sheet finisher B is connected to the sheet delivery roller  6 C side on the left side surface shown in the drawing of the image forming apparatus min body A. 
     The document “d” placed on the document table of the automatic document feeder ADF is conveyed in the arrowed direction, and an image of a single side or double sides of the document is read by an optical system of the image reading means  1 , and read in a CCD image sensor  1 A. 
     An analog signal which is photo-electrically converted by the CCD image sensor  1 A is sent to the image writing means  3 , after analog processed, A/D converted, shading corrected, and image compression processed in the image processing means  2 . 
     In the image writing means  3 , output light from a semiconductor laser is radiated onto a photoreceptor drum of the image forming mean  4  and a latent image is formed. In the image forming means  4 , processing such as charging, exposing, developing, transferring, separation, and cleaning, is conducted. Onto the sheet S sent from the sheet feeding means  5 , an image is transferred in a transfer section. 
     The sheet S on which the image is carried, is conveyed by a conveying belt  6 A, fixed by a fixing means  7 , and sent from a sheet delivery roller  6 C into a sheet introduction section  10 A of the sheet finisher B. Or by the conveying path switching plate  6 B, the sheet S whose one side is image processed, which is sent into a re-conveying means  8 , is, in the image forming means  4  again, after the double-side image processing, delivered from the sheet delivery roller  6 C. The sheet S delivered from the sheet delivery roller  6 C, is sent into the sheet finisher B. 
     The sheet finisher B has: the sheet introduction section  10 A by which the sheet P on which the image is formed is received; sheet feed apparatus  11  to feed an additional sheet F; branching section  12 ; reversal conveying section  13 , folding sections  14 ,  15 ; intermediate tray  16 ; stapling section  17 ; fixed sheet delivery tray  18 ; elevation sheet delivery tray  19  which can move upward and downward; center folding section  25 ; and fixed sheet delivery section  27 , and those are connected by the conveying paths  10 ,  20 ,  21 ,  22 , and  23 . 
     The sheet finisher B conducts finishing in the following process modes. 
     (1). Simple Sheet Delivery Mode 
     The sheet P introduced from the sheet introduction section  10 A is simple-delivered in the order of introduction. In this mode, the sheet P is delivered onto the fixed sheet delivery tray  18  through the conveying path  10 , reversal conveying path  13  and conveying path  20 . 
     (2). Folding Mode 
     The sheet P is two-folding processed or three-folding processed (for example, Z-folding processed) by which the sheet P is folded at one portion or two-portions, and delivered. 
     The sheet P introduced from the sheet introduction section  10 A is conveyed to the folding sections  14 ,  15 , and after it is folding processed by the folding sections  14  and  15 , it is delivered onto the elevation sheet delivery tray  19  through the conveying path  10 , and the conveying path  22 . There is a case where tree-folding processing is conducted by the folding sections  14  and  15  and a case where two-folding processing is conducted by using only the folding section  14 . 
     (3). Stapling Mode 
     Stapling processing is conducted for each sheet bundle of a plurality of sheets, and the stapled sheet bundle is delivered. 
     After the sheet P conveyed from the conveying path  10  to the conveying path  23  is stacked on the intermediate tray  16  as a stacking means by set number of sheets, the sheets are staple processed by the stapling section  17  as a staple processing means, and after staple processing, the sheets are delivered onto the elevation sheet delivery tray  19 . In the stapling mode, there is an end stapling mode by which a corner portion of the sheet is stapled or an edge portion is stapled, and a center stapling mode by which the central portion of the sheets is stapled. 
     (4). A Mode in Which (2) Folding Mode and (3) Stapling Mode are Combined and Processed 
     By conducting the center stapling and center folding, a booklet is made. In the center stapling and center folding modes, after the sheets are staple processed by the stapling section  17 , the sheets are center folding processed by the center folding section  25  and the bundle of sheets is delivered on the fixed sheet delivery section  27 . 
     In the above each mode, when an additional sheet F is fed from the sheet feed tray  11 , and added to the sheet P which is supplied from the image forming apparatus main body A, the cover, back cover and partition can be added for each bundle of the sheets P. 
     (Sheet Stapling Process) 
     After the preset number of sheets P are stacked on the intermediate tray  16  as the stacking means, the alignment in the width direction is conducted by the well known method, and next, the stapling process is conducted by the stapling section  17  as the staple processing means. 
     There are an edge stapling mode to staple the peripheral portion of the sheets and a center stapling mode which is conducted together with the center folding process. In the case of the edge stapling mode, the sheet P is stopped by the stopping member  16 A and adjusted in the conveying direction, and after it is further aligned in the sheet width direction by the alignment means (not shown), it is stapled by the stapling section  17  and a bundle of the stapled sheets is elevated by a sheet push-up member (not shown) and delivered onto an elevation sheet delivery tray  19 . In the case of the center stapling, the sheet P is stopped by the stopping member  16 B and aligned in the conveying direction, and after it is further aligned in the sheet width direction, it is center-stapled by the stapling section  17  and the center folding processing is conducted on the bundle of the stapled sheets by the center folding section  25 , and it is delivered onto the fixed sheet delivery section  27  through the delivery roller  26 . 
     The stapler and the center folding section  25  are known, and they can be conducted by the known arbitrary methods. 
     (Conveying Timing Adjustment Section) 
     The conveying timing adjustment section is composed of a branching section  12  and a reversal conveying section  13 . 
     The conveying timing adjustment section will be described by FIG. 2 which is a sectional view of the conveying timing adjustment section. 
     The branching section  12  conveys the sheet P from the conveying path  10  as the main conveying path into the reversal conveying section  13  and conveys it from the reversal conveying section  13  to the conveying path  10 . The branching section  12  is composed of: an upper side guiding member  124 ; lower side guiding members  125 B and  126 B; drive roller  122  driven by a stepping motor M 1  and follower rollers  121  and  123 , and the branching section  12  has a conveying-in path  127  formed of the upper side guiding member  124  and lower side guiding member  125 B, and a conveying-out path  128  formed of the upper side guiding member  124  and lower side guiding member  126 B. 
     The conveying-in section is structured by the drive roller  122  as the first drive roller, the follower roller  121  as the first follower roller, and conveying-in path  127 , and the conveying-out section is structured by the drive roller  122  as the second drive roller, follower roller  123  as the second drive roller and a conveying-out path  128 . A protrusion  124 A (also referred to as a branching guide) of the upper side guiding member  124  separates the conveying-in path  127  from the conveying-out path  128 . 
     Vertical portions parallely opposed to each other of guiding plates  125  and  126 , structure a sheet accommodation portion having a passage  129 , further, an upwardly opened upper portion of the guiding plates  125  and  126  structures the lower side guiding members  125 B and  126 B, and as described above, forms the conveying-in path  127  and the conveying-out path  128  of the sheet P. 
     The upper side guiding member  124  has a protrusion  124 A as the guiding member on its lower end. The leading edge Q of the protrusion  124 A is, as shown by the vertical line L drawn at the leading edge Q, set such that it is positioned on more conveying-in path  127  side than a vertical parallel portion (sheet accommodation section) of the guiding plate  125 . By such the shape of the protrusion  124 A, the sheet P conveyed-in from the conveying-in path  127  is surely moved from the conveying-in path and guided to the conveying-out path  128 , when its upper end portion is separated from the nip between the drive roller  122  and follower roller  121  and drops, and supported by the stopping member  131 . 
     In the guiding plates  125  and  126 , as shown in FIG. 3, cutout portions  125 A and  126 A are formed at a central portion of the conveying path width direction. As shown in FIG. 3, in a portion of the cutout portions  125 A and  126 A, as shown in FIG. 2, the stopping member  131  having the upwardly opened introduction portion is provided. The stopping member  131  is connected to a toothed belt  135  by a connection member  130 , and moves upward and downward, by being driven by a stepping motor M 2 . The stopping member  131 , as will be described later, positions the first-third positions V 1 -V 3 , and the first-third positions V 1 -V 3  are changed corresponding to the sheet size. 
     (Conveying Control in the Sheet Stapling Process) 
     FIGS.  4 ( a )- 4 ( d ) show the conveying timing of the sheet, and an example in which 5 sheets form one bundle and the stapling processing is conducted on it, is shown. An arrow T in FIGS.  4 ( a )- 4 ( d ) shows the time. 
     FIG.  4 ( a ) shows the conveying timing of the sheet conveyed-in from the image forming apparatus main body A. From the image forming apparatus main body A, as shown in FIG.  4 ( a ), the sheets are continuously delivered at a predetermined short sheet interval D 1 , and conveyed in the sheet finisher B. 
     FIG.  4 ( b ) is an example in which a bundle is formed of the leading sheet P 6  of the bundle of the sheets subsequent to the second bundle and the second sheet P 7  succeeding to the leading sheet P 6 , and by conveying these sheets simultaneously, the sheet interval between bundles of sheets is enlarged as shown by D 2 . 
     The sheets P 1 -P 5  forming the first one bundle are conveyed at an equal sheet interval D 1  and stacked onto the intermediate tray  16 . On the intermediate tray  16 , for the time period to conduct the alignment in the sheet width direction and stapling processing, in the conveying into the intermediate tray  16  of the leading sheet P 6 , it is necessary that the sheet interval to the last sheet P 5  of the first sheet bundle is enlarged. In the present embodiment, the wide sheet interval D 2  is secured by overlapping the leading sheet P 6  of the second sheet bundle with the succeeding second sheet P 7 . In the same manner, by overlapping the leading sheet P 11  of the third sheet bundle with the second sheet P 12 , the wide sheet interval D 2  is secured. 
     FIG.  4 ( c ) is an example in which, by basically simultaneously conveying two sheets as one bundle, the sheet interval is enlarged to the long interval D 2 , and when the number of sheets of the bundle of the sheets to be stapling processed can be divided by the number of sheets of the bundle of sheets which are overlapping conveyed in the conveying timing adjustment section, the conveying mode in which the all sheets are bundled in the conveying timing adjustment section, can be applied. 
     FIG.  4 ( d ) is an example in which, by simultaneously conveying three sheets as one bundle, the sheet interval is enlarged to further long interval D 3 . 
     Next, referring to FIG. 5 which is a typical view of the timing adjustment section and FIGS. 6-8 which are views showing the conveying process, a normal conveying control to convey the sheets with the short sheet interval D 1  will be described. 
     The conveying timing adjustment section of the sheet finisher according to the present embodiment is provided with the drive roller  122 , follower rollers  121  and  123 , two parallel guiding plates  125  and  126 , protrusion  124 A and stopping member  131 , as already described above. 
     The drive roller  122  is rotated clockwise as shown by an arrow, and conveys the sheet into the reversal conveying section, and conveys the sheet from the reversal conveying section. 
     The guiding plates  125  and  126  accommodate the conveyed-in sheet, and the protrusion  124 A guides the sheet at the time of its conveying-in and conveying-out, and the protrusion  124 A separates the conveying-in path  127  from the conveying-out path  128 , and guides the sheets so that the preceding sheet and the succeeding sheet do not collide with each other. 
     In the present embodiment, after the sheet is conveyed between the guide plates  125  and  126 , the sheet is switched back and conveyed. 
     S 1 A-S 7 A in FIGS. 6-8 show the process in which a plurality of sheets are conveyed at a short sheet interval D 1 . 
     In the conveying-in stage of the first sheet P 1 , the sheet P 1  is conveyed-in by the drive roller  122  and the follower roller  121 , and the sheet P 1  is dropped to the stopping member  131 . The stopping member  131  is set at the first position V 1  at which the upper end (trailing edge in the conveying direction) P 1 U of the sheet P 1  is lower than the lower end (guiding end) of the protrusion  124 A. The S 1 A in FIG. 6 shows the condition that the conveying-in stage is completed and the sheet P 1  is supported by the stopping member  131 . 
     In the stage S 2 A, the stopping member  131  is set at the second position V 2  at which the upper end P 1 U of the sheet P 1  is elevated to the upper portion than the lower end (guiding end) of the protrusion  124 A. By the elevation to the second position V 2  of the stopping member  131  in the stage S 2 A, the upper end P 1 U of the sheet P 1  is moved from the conveying-in path  127  to the conveying-out path  128 . 
     Such the introduction to the conveying-out path  128  of the upper end P 1 U of the sheet P 1 , as described above, is realized by the shape of the conveying-in path  127 , protrusion  124 A and the conveying-out path  128 . Further, by the movement of the protrusion  124 A, the upper end P 1 U can also be introduced to the conveying-out path  128 . 
     The stage S 34  is a stage in which the upper end P 1 U is introduced into the conveying-out path  128 , and in this stage, the second sheet P 2  is conveyed in by the drive roller  122  and follower roller  121 . 
     In the next stage S 4 A, the stopping member  131  is elevated, and the upper end P 1 U (leading edge in the conveying direction) of the preceding first sheet P 1  is nipped between the drive roller  122  and the follower roller  123 . While the sequence transfers from the stage S 3 A to stage S 4 A, the succeeding sheet P 2  is conveyed and runs downward between guiding plates  125  and  126  as shown in the drawing. 
     In the next stage S 5 A, the stopping member  131  is lowered to the first position V 1 . During this, the sheet P 1  is continuously conveyed, and as shown in the drawing, runs upward, and the sheet P 2  runs downward. 
     The stage S 6 A is a stage in which the upper end (trailing edge in the conveying direction) of the sheet P 2  is separated from the drive roller  122  and the follower roller  121  and drops, and it is supported by the stopping member  131 , and the stage is equal to the stage S 1 A. 
     Next, the third sheet P 3  is conveyed in. In the stage S 7 A in which the conveying-in of the sheet P 3  is started, 3 sheets P 1 , P 2  and P 3  simultaneously run in the reversal conveying section, that is, on a passage between the guiding plates  125  and  126 , as shown in the drawing. 
     Next, the conveying control to form the long sheet interval D 2  will be described by FIGS. 9 and 10 showing the conveying process. 
     In the conveying-in stage S 1 B of the first sheet P 1 , the sheet P 1  is conveyed in by the drive roller  122  and the follower roller  121 , and the sheet P 1  is dropped to the stopping member  131 . The stopping member  131  is set at the first position V 1  at which the upper end (trailing edge in the conveying-in direction) P 1 U of the sheet P 1  is lower than the lower end (guiding end) of the protrusion  124 A. 
     In the stage S 2 B, the stopping member  131  is set at the second position V 2  at which the upper end P 1 U of the sheet P 1  is elevated to the upper portion than the lower end (guiding end) of the protrusion  124 A. By the elevation to the second position V 2  of the stopping member  131  in the stage S 2 B, the upper end P 1 U of the sheet P 1  is withdrawn from the conveying-in path  127  to the conveying-out path  128 . 
     The stage S 3 B is a stage in which the second sheet P 2  is conveyed in. The conveying-in of the second sheet P 2  is conducted under the condition that the upper end (trailing edge in the conveying-in direction) P 1 U of the first sheet P 1  is moved from the conveying-in path  127  to the conveying-out path  128 . 
     The stopping member  131  is lowered to the first position V 1  from the stage of S 3 B, and transfers to the next stage S 4 B. In the stage S 4 B, the second sheet P 2  is separated from the nip between the drive roller  122  and the follower roller  121 , and it drops and stops on the stopping member  131 . 
     In the next stage S 5 B, the stopping member  131  is elevated to the third position V 3 , and the upper end (leading edge in the conveying-out direction) P 1 U of the first sheet P 1  and the upper end (leading edge in the conveying-out direction) P 2 U are made to reach the nip between the drive roller  122  and the follower roller  123 . Then, by the rotation of the drive roller  122 , two sheets P 1  and P 2  are simultaneously conveyed and conveyed-out to the conveying path  10 . 
     By repeating the stages S 1 B-S 5 B, because the conveying timing of the first sheet P 1  is delayed by one sheet, and the bundle of two sheets P 1  and P 2  is simultaneously conveyed-out on the conveying path  10 , the sheet interval D 2  is secured. 
     By combining the conveying control shown in FIGS. 6-8, and the conveying control shown in FIGS. 9 and 10, the conveying in which the sheet intervals D 1  and D 2  shown in FIGS.  4 ( b ) and  4 ( c ) mixedly exist can be conducted. Further, by repeating the conveying process composed of the stage S 2 B and S 3 B after the stage S 4 B, the number of sheets of the bundle of the sheets conveyed-out from the reversal conveying section  13  can be made larger than 3, and the sheet interval D 3  shown in FIG.  4 ( d ) can be secured. 
     In the conveying control described by FIGS. 6-10, the drive roller  122  driven by the stepping motor M 1  is continuously rotated in one direction and the conveying-in to the reversal conveying section  13  and conveying-out from the reversal conveying section  13  of the sheet are conducted. The stepping motor M 2  to control the position of the stopping member  131  conducts the displacement control of the stopping member  131  between the first-the third position during a predetermined time period set from of the output of the sheet leading edge detection signal, according to the sheet leading edge detection signal of the sensor SS 1  provided just upstream the conveying section, and these controls are conducted by the control means CR. 
     (Folding Process) 
     FIGS.  11 ( a ),  11 ( b ) show the structure of the folding sections  14  and  15 , and FIGS.  12 ( a )- 12 ( f ) show the three-folding process (Z-folding process) in which the sheet P is folded at 2 portions. 
     The folding section  14  shown in FIG.  11 ( a ) is structured by folding rollers  141 ,  142  as the drive roller, follower rollers  143 ,  144  which are driven respectively in contact with these folding rollers, and guiding member  145 . The folding roller  141  can be displaced as will be described later. 
     The folding section  15  shown in FIG.  11 ( b ) is structured by folding rollers  151 ,  152  as the drive roller, follower rollers  153  and  154  which are driven respectively in contact with these folding rollers, and guiding member  155 . The folding roller  151  can be displaced as will be described later. 
     In the folding mode, for example, the first folding processing is conducted on the sheet P at ¼ position from the leading edge by the folding section  14 , and further, the folding processing is conducted at ¼ position (¼ sheet entire length) from the leading edge of the folded sheet P by the folding section  15 , and the sheet P is, for example, Z-folding processed. 
     In FIG.  12 ( a ), under the condition that the folding roller  141  and the folding roller  142  are separated from each other, and follower rollers  143  and  144  are respectively in pressure-contact with the folding rollers  141  and  142 , the sheet P is conveyed and introduced into the folding section  14 . In the stage in which the sheet P is conveyed from the reference position R by a predetermined distance D, by the sheet leading edge detection signal of the sensor SS 2 , the drive of the folding rollers  141  and  142  is stopped, and the sequence transfers to the folding process in FIG.  12 ( b ). 
     In FIG.  12 ( b ), the folding roller  141  and the follower roller  143  are displaced, and after the folding roller  141  and the folding roller  142  are come into pressure-contact with each other, the folding roller  141  is rotated in the same direction as that at the time of the introduction, and the folding roller  142  is rotated in the opposite direction to that at the time of the introduction and the folding processing is started. By the conveying operation of the folding rollers  141  and  142  in the opposite direction onto the sheet P, the sheet P is bent and the fold of the sheet P enters between the folding roller  141  and the folding roller  142 . In this connection, a guiding member  145  having the protrusion  145 A by which the bent of the sheet P to the folding rollers  141  and  142  side is surely conducted, is provided. Further, as shown in FIG.  12 ( c ), the folding is conducted by continuously rotating the folding rollers  141  and  142 , and the folded sheet P is conveyed by the conveying roller  210 , and introduced into the folding section  15 . 
     As shown in FIG.  12 ( d ), the folding rollers  151  and  152  of the folding section  15  are separated, and under the condition that the follower roller  153  and the follower roller  154  are respectively in pressure-contact with the folding rollers  151  and  152 , the sheet P is introduced, and in the stage in which the leading edge of the folded sheet is conveyed from the reference position R by a predetermined distance D, according to the sheet leading edge detection signal of the sensor SS 3 , the folding roller  151  is displaced, and is made in pressure-contact with the folding roller  152 . After the pressure-contact, the folding roller  151  is rotated in the same direction as that at the time of the introduction and the folding roller  152  is rotated in the opposite direction to that at the time of the introduction. By the conveying operation of the folding roller  151  and  152  in the opposite direction onto the sheet P, the sheet P is bent and the fold of the sheet P enters between the folding roller  151  and the folding roller  152 . In this connection, a guiding member  155  having the protrusion  155 A by which the bending of the sheet P to the folding rollers  151  and  152  side is surely conducted, is provided. As shown in FIG.  12 ( e ), after the pressure-contact, the rotation direction of the folding roller  152  is reversed, and the sheet P is folded. As shown in FIG.  12 ( f ), the rotation of the folding rollers  151  and  152  are continued, and while the sheet P is folded, the sheet P is delivered from the folding section  15  and conveyed to the conveying path  10 . 
     In the example of FIGS.  12 ( a )- 12 ( f ), the folding is conducted at the position of ¼ from the leading edge of the sheet P. The sensor SS 2  and SS 3  respectively detect the leading edge of the sheet P at the reference position, that is, at D=¼×LT (LT is the length in the conveying direction of the sheet P) from the position shown by the tangential line of the outer periphery of folding rollers  141  and  142  and the position shown by the tangential line of the outer periphery of folding rollers  151  and  152 . Actually, the delay of the reversing time of the folding rollers  141 ,  142 ,  151 , and  152  is considered, and the position is set to a little shorter distance than ¼×LT. 
     The sensors SS 2  and SS 3  are set at various positions depending on the folding mode in the sheet P or sheet size. 
     As shown in the drawing, in the process in which the folding processing is conducted at two portions in the sheet P, the sheet P is introduced into the folding section  14  from the direction Z 1 , and conveyed and sent in the direction Z 2  almost perpendicular to the direction Z 1  from the folding section  14  into the folding section  15 . The sheet P folding processed in the folding section is conveyed in the direction Z 3  almost perpendicular to the direction Z 2 , that is, in the almost same direction Z 3  as the direction Z 1 . 
     According to the Structure (1), (3), (5), or (6), because, in the reversal conveying section, a plurality of sheets are overlapped and a bundle of the sheets is formed and conveyed, thereby the sheet interval is enlarged, the sheet interval necessary for the staple processing can be obtained enough, and can cope with the high speed image formation in the image forming apparatus main body, and the stable conveying can be conducted corresponding to the sheet size of the wide range from the small size to the large size. As the result, the high speed processing can be conducted. Further, because the high speed processing is possible, the conveying line speed is lowered and the processing can be conducted, and the high stable and reliable sheet finisher is realized. 
     According to the Structure (2), a sheet bend in the conveying direction is effectively corrected, and the size reduction is possible, and the sheet finisher having the high speed and high stability is realized. 
     According to the Structure (4), (5) or (7), because the sheet is conveyed to the finish processing section by which each kind of finish processing is conducted on the sheet interval adjusted sheet, each kind of finish processing can be stably conducted. 
     According to the Structure (8), the image forming apparatus by which the finish processing can be stably conducted even when the image forming apparatus main body is made high speed, is realized.