Abstract:
A sheet cutting device includes: an interposing section that interposes a sheet bundle in which a plurality of sheets are bundled; a cutting blade section having a cutting blade that cuts a sheet bundle interposed by the interposing section; a blade receiving member that receives a cutting edge of the cutting blade in the case of cutting; and a controller that controls a stop position of the cutting blade in the case of cutting. The controller controls the cutting blade section so that an amount of movement from a standby position of the cutting blade to the stop position becomes great when the number of times of cutting operations is increased.

Description:
[0001]    This application is based on Japanese Patent Application No. 2008-305749 filed on Nov. 29, 2008, which is incorporated hereinto by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a sheet cutting device that cuts a sheet bundle and relates to an image forming system equipped with the sheet cutting device. 
         [0003]    Up to now, there has been put to practical use a sheet finisher equipped with a sheet cutting device that aligns an edge of a sheet bundle by cutting an edge portion of the sheet bundle, for sheet bundles processed in terms of center stapling or of center folding, in the business world of printing. 
         [0004]    Further, in recent years, there has been made an for a sheet finisher equipped with a sheet cutting device that conducts center stapling processing or center folding processing after receiving a sheet on which an image has been formed by a main body of an image forming apparatus such as a copying machine or a printer, and aligns an edge portion by cutting the edge portion of a sheet bundle with the sheet cutting device, after bookbinding, as in the case of the weekly magazines. 
         [0005]    Many of the sheet cutting devices of this kind are those wherein a sheet bundle is fixed on a placing stand, and a cutting blade is moved for cutting operations. In this case, a position for the cutting blade to be stopped is established to be a position where a cutting edge of the cutting blade intrudes slightly into a blade receiving section that is provided on the side of the placing stand. 
         [0006]    A stop position of the cutting edge is sometimes varied by influences of operation errors and manufacturing errors, and in this case, there are caused problems such as unfinished cutting and excessive intrusion of a cutting edge of the cutting blade into the blade receiving section. 
         [0007]    In Unexamined. Japanese Patent Application Publication No. 2006-297535, there is disclosed a sheet cutting device wherein an electric current value of a motor that increases gradually with an increase of loads caused by striking of a blade holder against a stopper in the ca cutting sheets, detected to control the stop position for a blade. Owing to the aforesaid device, excessive force is not applied on a cutting edge, resulting in promotion of a long life. 
         [0008]    A surface of the blade receiving section is damaged little by little, each time a bundle of sheets is cut by a cutting blade. When damage on a surface of the blade receiving section grows to be too large, cutting ability is lowered. In the sheet cutting device disclosed in Unexamined Japanese Patent Application Publication No. 006-51592, when the number of times of cutting reaches a prescribed number, the blade receiving section is shifted in the direction perpendicular to the cutting edge to renew a surface to be used of the blade receiving section, so that defective cutting that is caused by deterioration of a surface of the blade receiving section may not occur. Then, when the surface to be used of the blade receiving section becomes impossible to be renewed after being used up, the blade receiving section is replaced with a new one. 
         [0009]    A blade and a blade receiving section of the sheet cutting device are deteriorated when cutting operations are repeated, and the blade and the blade receiving section need to be replaced for the prescribed number of cutting operations. For extending a replacement cycle of a blade by decreasing damages of the blade, it is better for the blade receiving section to be made of a softer material. However, in that case, the blade receiving section tends to be damaged easily, resulting in a short cycle of replacement of the blade receiving section. It is also possible to make a size of the blade receiving section to be large for the purpose of extending a replacement cycle for the blade receiving section. In that case, however, there is caused a problem that the device grows to be gigantic. 
         [0010]    In the sheet cutting device described in Unexamined Japanese Patent Application Publication No. 2006-297535, there is employed construction to detect an elastic current value of a motor and thereby to stop the blade by load fluctuations in the case of striking of a holder against a stopper. However, there is no consideration about an influence on the blade receiving section, and it is feared that accurate cutting of a sheet bundle is disturbed by deterioration of the blade receiving section. 
         [0011]    In the sheet cutting device described in Unexamined Japanese Patent Application Publication No. 2006-51592, a replacement cycle is extended by renewing a surface used of the blade receiving section. However, an object of this construction IC not using the blade receiving section effectively, and when the blade receiving section is deteriorated so early by fluctuations of a biting amount of blade receiving section of the blade, it is feared that defective cutting may be caused. 
       SUMMARY OF THE INVENTION 
       [0012]    An embodiment of the present invention is as follows. 
         [0013]    A sheet cutting device composed of interposing section that interposes a sheet bundle in which a plurality of sheets are bundled, a cutting blade section equipped with a cutting blade that cuts a sheet bundle interposed by the aforesaid interposing section, a blade receiving member that receives a cutting edge the aforesaid blade in the case of cutting and a controller that controls a stop position of the aforesaid blade in the case of cutting, wherein the aforesaid controller controls the aforesaid cutting blade section so that an amount of movement from a standby position of the blade to the stop position may become great when the number of times of cutting operations is increased. 
         [0014]    An image forming system characterized, to have an image forming apparatus that forms an image on a sheet, and a sheet finisher that is equipped with the aforesaid sheet cutting device, and forms a sheet bundle by bundling sheets on which images have been formed by the aforesaid image forming apparatus, and conducts cutting of the sheet bundle with the aforesaid sheet cutting device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a sectional view of an image forming system wherein sheet finisher B that conducts center stapling processing and cutting processing is connected to the sheet ejection side of image forming apparatus A. 
           [0016]      FIG. 2  is a schematic diagram showing sheet conveyance for center folding and center stapling which are carried out by sheet finisher B. 
           [0017]      FIG. 3  is a side view on the left side for sheet finisher B. 
           [0018]      FIG. 4A  is a front view of main parts showing the state of standing by for sheet cutting device  100 , and  FIG. 4B  is its side view of main parts. 
           [0019]      FIG. 5  is a sectional view of sheet cutting device  100 . 
           [0020]      FIG. 6A  is a front view of the circumference of position detection section  140  showing the state of standing by of sheet cutting device  100 , and  FIG. 6E  is its side view. 
           [0021]      FIG. 7A  is a front view of the circumference of position detection section  140  showing the state of sheet cutting for sheet cutting device  100 , and  FIG. 7B  is its side view. 
           [0022]      FIG. 8  is a plan view of shifting section  160  and the circumstances of blade receiving member  116 . 
           [0023]      FIG. 9  is a sectional view of shifting section  160  and the circumstances of blade receiving member  116 . 
           [0024]      FIG. 10A  is an  10 A- 10 A sectional view showing the state wherein blade receiving member  116  is pressure-connected to edge pressure member  115 .  FIG. 10B  is an  10 A- 10 A sectional view showing the state wherein blade receiving member  116  is away from edge pressure member  115 . 
           [0025]      FIG. 11  shows contents of a control flow which are carried out by sheet finishing control device  10 E of sheet finisher B. 
           [0026]      FIG. 12  is a timing chart showing timing of position detection sensor PS 2  and timing of drive motor M 2  that moves cutting blade  121 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0027]    The invention will be explained as follows based on an embodiment to which, however, the invention is not limited. 
         [0028]      FIG. 1  is a sectional view of an image forming system wherein sheet finisher B that conducts center stapling processing and cutting processing is connected to the sheet ejection section side of image forming apparatus A. The cutting processing is conducted in sheet cutting device  100 . Meanwhile, the sheet finisher having therein the built-in sheet cutting device relating to the invention can also be of the construction that can be used independently. Incidentally, the image forming system equipped with the sheet finisher of the invention and with a sheet finisher is not limited to the following embodiment. 
       [Image Forming Apparatus A] 
       [0029]    Image forming apparatus A shown in  FIG. 1  is equipped with image reading section  1 , image processing section  2 , image writing section  3 , image forming section  4 , sheet cassette  5 , first sheet feeding section  6 A, second sheet feeding section  6 B, fixing device  7 , sheet ejection section  8  and with automatic two-sided copy feeding unit (ADU)  8 A. 
         [0030]    Sheet finisher B having sheet cutting device  100  is connected to the sheet ejection section  8  side on the illustrated left side surface of the image forming apparatus A. 
         [0031]    Operation section  9  selects and sets processing functions of an image forming system composed of image forming apparatus A and sheet finisher B. 
         [0032]    Main control section  10 A of the image forming apparatus A is connected to sheet finisher control section  10 B of sheet finisher B, through communication sections  10 C,  10 D and communication line  10 E. 
       [Sheet Finisher B] 
       [0033]      FIG. 2  is a schematic diagram showing sheet conveyance for center folding and center stapling of sheet finisher B.  FIG. 3  is a left side view of sheet finisher B. 
         [0034]    As shown in the aforesaid drawings, after the bookbinding operations such as center folding and center stapling are established in operation section  9 , sheet S ejected from the image forming apparatus A is guided into entrance section  11  of sheet finisher B, and is interposed by entrance rollers  12  to be conveyed to sheet conveyance path r 1  that is below conveyance path switching section Z. 
         [0035]    The sheet S conveyed to the sheet conveyance path r 1  that is below the conveyance path switching section Z descends almost vertically, and it stops temporarily at a prescribed position to be stored. In this first stop position Q 1 , succeeding plural sheets S are superposed on aforesaid sheet S to be housed. 
         [0036]    Sheet S thus housed is moved in the rectangular direction by conveyance pairs rollers  18 A and  18 B, first conveyance pairs of rollers  18 C and  18 D and by an unillustrated guide plate in the rectangular direction, then, it passes through sheet conveyance path r 2  that turns round to front surface side Bf in sheet finisher B under the condition that a sheet surface is standing vertically, and it stops temporarily in second stop position Q 2 . 
         [0037]    Next, the sheet S is conveyed upward vertically by second conveyance pair of rollers  18 E, then, is deflected in the horizontal direction, and is moved along sheet conveyance path r 3 . 
         [0038]    An unillustrated aligning section is arranged at the downstream side of sheet conveyance path r 3  in the sheet conveyance direction, and sheet lining up is conducted by causing a leading edge of a sheet to hit the aligning section for positioning, and the sheet stops temporarily at third stop position Q 3 . 
         [0039]    On the downstream side of the aligning section in the sheet conveyance direction, there is arranged center folding section  30 . The center folding section  30  is composed of folding rollers and a folding plate, and it causes folding rollers to pass through the center of the sheet while pressing the nearly center of the sheet down, and causes folding rollers to turn round to conduct center folding. 
         [0040]    Folded sheet SA on which folding processing is conducted by center folding device  30  and a fold portion “b” is formed is returned to its original horizontal conveyance path. The folded sheet SA continues to be conveyed to sheet conveyance path r 4  in the direction of an extended line of the fold portion “b” by conveying belt  41  of conveying section  40 , conveying claw  42  and by introduction guide member  51  of folded sheet guide section  50 , and is sent into center stapling section  60 . 
         [0041]    As stated above, the center folding section  30  conducts center folding processing for a few sheets such as one sheet through three sheets to form fold portions “b” surely, and then, it sends them into center stapling section  60  one after another. Thereby, it is possible to prepare sheet bundles SS each having a little swelling of fold portion “b”. 
         [0042]    The folded sheet SA center folded in the center folding section  30  is moved toward sheet conveyance path r 4  by conveying section  40 , and is placed on saddle-shaped stacking section  61  of the center stapling section  60  (see  FIG. 3 ). Succeeding center-folded sheet SA having been processed in term center folding also passes continuously through sheet conveyance path r 4 , to be stacked on the saddle-chap stacking section  61 . 
         [0043]    The saddle-shaped stacking section  61  is composed of two guide plates which cross almost at right angles each other, to be fixed on a main body of sheet finisher B. In the vicinity of a top portion of the saddle-shaped stacking section  61 , there is arranged pressure member  61 A that is spring-urged and is capable of going up and down under the condition to be supported by staple-receiving mechanism  64 . 
         [0044]    A top portion of the pressure member  61 A is in a convex form that is almost rectangular upward, and fold portion “b” of center-folded sheet SA is placed on the ridge on its top portion. 
         [0045]    A plurality of center-folded sheets SA placed on the saddle-shaped stacking section  61  and on pressure member  61 A are aligned in terms of a position by width aligning device  62 . 
         [0046]    Stapling mechanism  63  is arranged to be fixed, above the pressure member  61 A. Inside the saddle-shaped stacking section  61 , pressure member  61 A and staple-receiving mechanism  64  are supported to be movable upward and downward. Two sets of stapling devices of two-division construction composed of stapling mechanism  63  and staple-receiving mechanism  64  are arranged in the direction of fold portion “b” of sheet S. In operation section  9 , after the center stapling processing is set, staple-receiving mechanism  64  ascends to conduct center stapling processing. In operation section  9 , when center stapling is set, the staple-receiving mechanism  64  ascends to conduct center stapling processing. Namely, two sets of stapling devices drive staples SP at two locations which are symmetrical about the center, along fold portion “b” or folded sheet SA on pressure member  61 A. 
         [0047]    Sheet bundle SS that has been subjected to center stapling processing in center stapling section  60  is held by supporting member  72  fixed on a tip portion of arm member  71  of booklet taking out device  70 , then, is swung by the arm member  71  in the direction of an arrow shown with a one-dot chain line, and is conveyed to bundle conveyance section  80 . 
         [0048]    The sheet bundle SS conveyed to the bundle conveyance section  80  is placed on conveyance belt  82 . Owing to a rotation of the conveyance belt  82 , the sheet bundle SS is conveyed downward obliquely, and it is further held aslant, and is moved by rotating conveyance belt  83  to be stopped at a prescribed position. After that, the conveyance belt  83  is swung to be supported horizontally. 
         [0049]    Since edge a representing a free end portion on the opposite side of the fold portion “b” of the sheet bundle placed on the conveyance belt  83  that has become to be in the horizontal state is not aligned in terms of the number of sheets of the sheet bundle SS, edge portion “a” is cut to be aligned by cutting blade  121  of sheet cutting device  100  and by blade receiving member  116 . Details of the sheet cutting device  100  will be described later. 
         [0050]    Booklet SSS prepared through cutting processing is placed on the conveyance belt  83  that rotates inversely, to be conveyed under the condition where a rear end portion the booklet SSS is pressed by movable aligning member  84  that is fixed on the conveyance belt  83 , and the booklet SSS falls in the direction of an arrow from a tip portion of the conveyance belt  83 . The booklet SSS that has fallen is ejected in sheet ejection tray  86  arranged to be outside of front surface side Bf of sheet finisher B by ejection belt  85  that rotates. 
         [0051]    Below booklet conveyance section  80  and sheet cutting device  100 , there is arranged chip processing device  190 . Chips SB resulted from cutting of edge portion “a” by cutting blade  121  of sheet cutting device  100  and by blade receiving member  116  fall on rotating chip conveyance belt  191 , to be moved and stored in chip container  192 . 
         [0052]    Though an explanation has been given for sheet cutting device  100  of sheet finisher B having functions for center folding and center stapling in the present embodiment, it is also possible to apply to a sheet cutting device of a sheet finisher that conducts center folding processing after conducting preceding processing for center stapling. Or, sheet finisher B may also be a sheet bundle making apparatus such as a starching book-binding apparatus. 
         [0053]    It is also possible to conduct processing from first to last for multipurpose and multifunctional sheet finishing, by connecting selectively sheet finisher B equipped with sheet cutting device  100  of the invention with a bookbinding machine connected to a shortrun printing machine. It is further possible to obtain same effects by applying also on a sheet finisher to be used after connection to image forming apparatus A such as a shortrun printing machine, a printer, facsimile machine and a multifunction peripheral. 
       [Sheet Cutting Device  100 ] 
       [0054]      FIG. 4A  is a front view of primary parts showing the state of standing by of sheet cutting device  100 , and  FIG. 4B  is a side view of primary parts thereof. 
         [0055]    On the upper part of a main body of sheet cutting device  100 , there is arranged pressure member  110 , and on the lower part of the main body, there is arranged cutting section  120 . 
         [0056]    In  FIG. 4B , the numeral  127  represents a placing stand of a fixed type on which sheet bundle SS conveyed in sheet cutting device  100  is placed. The sheet placed on placing stand  127  is pressed by falling pressure section  110 . The aforesaid pressure section  110  and placing stand  127  function as “an interposing section”. Edge “a” of the sheet bundle SS interposed by the interposing section is cut by cutting blade  121  that is moved upward obliquely by cutting section  120 . 
         [0057]    On the bottom surface of edge pressure member  115  of pressure section  110 , there is fixed “blade receiving member” that is composed of blade receiving member  116  and reinforcing sheet  117 , and it conducts parallel displacement in the vertical direction together with the edge pressure member  115 . The blade receiving member  116  is made of resin material. As shown in  FIG. 4E , the blade receiving member is provided on the pressure section  110  side. 
       [Pressure Section  110 ] 
       [0058]    Above the pressure section  110 , there is constructed rotating shaft  111  whose both ends are supported. The rotating shaft  111  is rotated by drive motor M 1 . The rotating shaft  111  has thereon screw section  111 A and screw section  111 B whose helix angles are opposite each other, and the screw section  111 A engages with screw  112 A and the screw section  111 B engages with screw  112 B. When the rotating shaft  111  rotates, movable holder  113 A that holds the screw  112 A and movable holder  113 B that holds the screw  112 B move linearly in the opposite directions each other. 
         [0059]    A lower end of interconnecting rod  114 A that is supported on a part of the movable holder  113 A to be capable of oscillating is engaged with an illustrated upper portion on the left side of the edge pressure member  115 , to support it to be capable of going up and down. In the same way, a lower end of interconnecting rod  114 B that is supported on a part of the movable holder  113 B to be capable of oscillating is engaged with an illustrated upper portion on the right side of the edge pressure member  115 , to support it to be capable of going up and down. 
         [0060]    Therefore, the rotating shaft  111  is rotated by driving rotation of the drive motor M 1 , thereby, the movable holder  113 A and the movable holder  113 B move from side to side, and inclination angles of the interconnecting rods  114 A and  114 B are changed to cause the edge pressure member  115  to conduct parallel displacement in the vertical direction. 
       [Cutting Section  120 ] 
       [0061]    Cutting section  120  is composed of a fixing device including cutting blade  121 , cutting blade holder  122 , supporting plates  123 A and  123 B, space holding member  124  and connection member  125  and of placing stand  127 . 
         [0062]    The cutting blade  121  having its cutting edge that is formed on an upper edge is fixed, and held on the cutting blade holder  122  by means of screw member  121 A. The cutting blade holder  122  is supported movably between surfaces facing each other of the paired supporting plates  123 A and  123 B which are arranged to be in parallel. Between the surfaces facing each other of the paired supporting plates  123 A and  123 B, there is interposed space holding member  124 , and a space between the paired supporting plates  123 A and  123 B is maintained so that the cutting blade holder  122  may be moved in the space. 
         [0063]    Connecting member  125  passes through the supporting plates  123 A and  123 B and the space holding member  124  in a shape of hollow cylinder, to fix the supporting plates  123 A and  123 B by maintaining them to be in a prescribed distance. 
         [0064]    A distance between sliding surfaces facing respectively the supporting plates  123 A and  123 B regulated by the space holding member  124  is set to be within a range of 0.1 to 0.5 mm for a thickness of the cutting blade holder  122 , to create a gap through which the cutting blade holder  122  can go up and down smoothly. 
         [0065]    A connecting device composed of the connecting member  125  and the space holding member  124  is arranged at each of plural positions for the supporting plates  123 A and  123 B, to maintain the prescribed distance firmly. 
         [0066]    On the cutting blade holder  122 , there are fixed rollers  128 A and  128 B, and these rollers  128 A and  128 B are guided respectively by guide members  129 A and  129 B which are arranged to be inclined downward to the right side. 
         [0067]    Drive motor M 2  representing the driving source is a drive motor that moves cutting section  120  including cutting blade  121 . The drive motor M 2  moves pin  122 A fixed on the cutting blade holder  122  linearly from side to side as illustrated, and when the cutting blade holder  122  moves linearly from side to side through pin  122 A, rollers  128 A and  128 B fixed on the cutting blade holder  122  move upward and downward obliquely as shown in the direction of arrow J, along guide members  129 A and  129 B. 
         [0068]    Next, operations of sheet cutting device  100  will explained as follows. 
         [0069]    In the state of standing by, movable holder  113 A is positioned at a left end and movable holder  113 B is positioned at a right end, while, blade receiving member  116  is located at the uppermost position, and cutting blade  121  is standing by at the lowermost position. 
         [0070]    When sheet bundle SS is introduced into the oh cutting device  100 , drive motor M 1  is started to drive movable holders  113 A and  113 B, and edge pressure member  115  goes down through interconnecting rods  114 A and  114 B. At the position where the edge pressure member  115  is detected by detection sensor PS, drive motor M 1  is stopped and the edge pressure member  115  is stopped. A stop position for the edge pressure member  115  is determined by position setting conducted by the detection sensor PS, and a position of the detection sensor PS is determined by the number (thickness) of sheets forming the sheet bundle SS. Therefore, a position of descending for the edge pressure member  115  is established by the number (thickness) of sheets forming the established sheet bundle SS, in an operation section of an image forming system. 
         [0071]    In the course of sheet cutting which will be explained later, the edge pressure member  115  interposes sheet bundle SS under the high pressure so that any slippage may not occur even when force in the horizontal direction is applied on many stacked sheets by cutting blade  121 . 
         [0072]    When interposing operations for sheet bundle are completed, drive motor M 2  is started to move the cutting blade  121  upward in the direction of arrow J on the left. Owing to this movement of the cutting blade  121 , the sheet bundle SS is cut. Since the cutting operations by the cutting blade  121  is cutting performed by sliding of a blade, it is possible to cut with relatively small drive force, and even when the number of sheets to be cut is increased, the drive force remains unchanged, with only a change in a movement stroke of the cutting blade  121 . 
         [0073]    When edge cutting processing is completed, drive motor M 2  rotates inversely, and the cutting blade  121  descends to the prescribed position that is in a lower part obliquely on the right side in  FIG. 1 . 
         [0074]    When the descent of the cutting blade  121  is completed, the edge pressure member  115  ascends to the initial position. 
         [0075]    When an unillustrated fold holding member and a receiving plate which have been interposing the vicinity of fold portion “b” of sheet bundle SF return to their initial positions after the completion of the ascendance of the edge pressure member  115 , the edge pressure member  115  and the blade receiving member  116  ascend, and interposing for sheet bundle SS is released. With a series of operations described above, edge cutting processing for the sheet bundle SS is completed. 
         [0076]      FIG. 5  is a sectional view of sheet cutting device  100 . 
         [0077]    The sheet cutting device  100  cuts edge portion a of sheet bundle SS with cutting blade  121  that is arranged below the conveyance path for sheet bundle SS and with blade receiving member  116  arranged above the conveyance path. The cutting blade  121  is fixed on movable cutting blade holder  122 . The cutting blade holder  122  is held by supporting plates  123 A and  123 B on a slidable basis, and, it can be moved upward obliquely by drive motor M 2  in  FIG. 4A . 
         [0078]    When the cutting blade holder  122  is moved upward obliquely, the cutting blade  121  is placed on the upper surface of placing stand  127 , to cut edge portion “a” of the sheet bundle SF that is pressed by the blade receiving member  116 . 
         [0079]    The blade receiving member  116  interconnects with interconnecting rods  114 A and  114 B which are swung by drive motor M 1  serving as a driving source in  FIG. 4A  to go up and down, and it presses sheet bundle SS placed on the upper surface of the placing stand  127 , and touches a cutting edge when the sheet bundle SS is cut. A biting amount of the cutting blade  121  into the blade receiving member  116  is made to be changeable within a range from 0.4 mm to 0.7 mm, through regulation. Details for this will be described later. 
       [Position Detection Section  140 ] 
       [0080]    The position detection section  140  will be explained as follows, based on  FIGS. 6A and 6B  and on  FIGS. 7A and 7B . Each of  FIGS. 6A and 6B  is a diagram of the state of standing by, and each of  FIGS. 7A and 7B  is a diagram of the state of sheet cutting.  FIG. 6A  is a front view of the surroundings of the position detection section  140  showing the state of standing by of the sheet cutting device  100 , and  FIG. 6B  is side view.  FIG. 7A  is a front view of the surroundings of the position detection section  140  showing the state of cutting by the sheet cutting device  100 , and  FIG. 7B  is its side view. In the state of standing by, cutting blade  121  of cutting section  120  is at “a position of standing by”. 
         [0081]    The position detection section  140  is composed of position detection sensor PS 2 , guide place  141  that adjusts a position of the position detection sensor PS 2  and of actuator  142 . 
         [0082]    The actuator  142  is equipped with arm  142   a  and arm  142   b , and it rotates around a center represented by fulcrum A. During a period of standing by shown in  FIGS. 6A and 6B , the actuator  142  is located at its initial position under the empty weight thereof. During a period of cutting operations shown in  FIGS. 7A and 7B , a movement of the cutting blade  121  upward obliquely causes upper surface edge portion “e” the moved cutting blade holder  122  to touch contact shaft provided on arm  142   b , and the actuator  142  rotates clockwise on the center represented by the fulcrum A as illustrated in  FIG. 7A . With the aforesaid rotation of the actuator  142 , a tip of the other arm  142   a  moves to a detection position of position detection sensor PS 2 . 
         [0083]    The actuator  142  and the position detection sensor PS 2  are fixed on the same panel  145 . Further, the panel  145  is fixed to edge pressure member  115  and to blade receiving member  116 . Owing to the aforesaid construction, the blade receiving member  116 , the actuator  142  and the position detection sensor PS 2  move up and down integrally. 
         [0084]    A position of arrangement for the position detection sensor PS 2  is adjusted by corresponding to the position of arm  142   a  under the condition that a distance between blade receiving member  116  and a cutting edge of the cutting blade  121  is a prescribed value, for example, a value of 0.0 mm to −0.4 mm (a symbol minus represents the direction of biting). Adjustment of a position of arrangement for the position detection sensor PS 2  can be carried out by sliding guide plate  141  along pins C and C, and guide plate  141  is fixed on panel  145  by screw member  141 A. 
         [0085]    Since detection signals of the position detection sensor PS 2  can detect that the cutting blade  121  has arrived at a prescribed position, signals for stopping are sent to drive motor M 2  based on detection signals, to stop the cutting blade  121 . 
         [0086]    Though the cutting blade  121  is stopped based on detection signals of the position detection sensor PS 2 , in the present embodiment, it is also possible to provide a mechanical stopper that touches the cutting blade holder  122  at a prescribed position, and thereby to stop the cutting blade  121  at a prescribed position with the mechanical stopper. It is further possible to create a construction wherein the stop position can be varied by changing a position for the mechanical stopper. 
       [Shifting Section  160 ] 
       [0087]      FIG. 8  is a plan view of shifting section  160  and of the circumstances of blade receiving member  116 , and  FIG. 9  is a sectional view of the same. In the shifting section  160 , a blade receiving member that is composed of blade receiving member  116  and reinforcing sheet  117  is shifted in the direction intersecting a cutting surface (direction of cutting edge) of the cutting blade  121  at right angles. 
         [0088]    Pinion gear G 2  that engages with rack gear G 1  of blade receiving member  116  is engaging with drive gear G 3  constantly. The pinion gear G 2  is engaging with the rack gear G 1  constantly, when feeding the blade receiving member  116  on an incremental basis. Further, the pinion gear G 2  engages with the rack gear G 1  as occasion demands when mounting and dismounting the blade receiving member  116 . 
         [0089]    On shaft  163  that is supporting the drive gear G 3 , there are arranged torque limiter  161  and one-way clutch  162 . On the side surface of edge pressure member  115 , there arranged solenoid  165  that is fixed on supporting plate  165 . Lever  168  connected with plunger  167  of the solenoid  165  is connected to drive gear G 3 , and each time the plunger  167  drives for suction, the lever  168  is vibrated to advance the drive gear G 3  counterclockwise in the illustration on an incremental basis for one tooth of the gear. The pinion gear G 2  engaging with the drive gear G 3  rotates clockwise in the illustration, to advance (shift) the blade receiving member  116  having rack gear G 1  toward the left side in the illustration on an incremental basis. The numeral  169  represents a spring that generates idling torque of the torque limiter. An amount of a single advancement for the blade receiving plate is established, for example, to be about 1.0 mm. 
         [0090]    The one-way clutch  162  prevents an inverse rotation of drive gear G 3  when the plunger  167  of the solenoid  165  operates returning operations. Further, when returning operations of the lever  168  are completed, an end portion of the lever  168  touches an inner wall of the edge pressure member  115  to stop oscillation of the lever  168 . Incidentally, the direction for shifting a blade receiving member does not always need to be the direction to intersect the cutting edge of cutting blade  121  at right angles, and direction to intersect simply is accepted. 
       [Mounting Blade Receiving Member] 
       [0091]      FIG. 10A  is a sectional view taken on line  10 A- 10 A (see showing the state wherein blade receiving member  116  is pressure-connected to edge pressure member  115 . The blade receiving member  116  that is pressure-connected to edge pressure member  115  of pressure member  110  stops while keeping a prescribed distance from cutting blade  121  of lower cutting section  120 . In this stop position, sheet bundle SS is introduced. 
         [0092]    Stop member  154  fixed on a main body of the apparatus is arranged above the edge pressure member  115 . Stop surface  155  on the bottom portion of the stop member  154  and a top surface of pressure bar  152  are kept to be in the state where both of them are away from each other. 
         [0093]      FIG. 10B  is a sectional view taken on line  10 A- 10 A (see  FIG. 8 ) showing the state wherein the blade receiving member  116  is away from edge pressure member  115 . Drive motor M 1  shown in  FIGS. 4A-4B  drives edge pressure member  115  of pressure member  110  to ascend and drives a top surface of pressure bar  152  to touch the stop surface  155  on the bottom portion of the stop member  154 . Then, when the edge pressure member  115  ascends, pressure bar  152  is pressed down by the stop member  154 , and pressure-connection plate  151  that is united with the pressure bar  152  is also pressed down, thus, a bottom surface of the edge pressure member  115  and a top surface of reinforcing sheet  117  are separated from each other, and clearance section g is formed. 
         [0094]    When the blade receiving member  116  is gripped to be fed out in the direction of an outlined arrow in the illustration, to be pushed in the clearance section “g” formed between the edge pressure member  115  and the pressure-connection plate  151  shown in  FIG. 9 , rack gear G 1  of the blade receiving member  116  rotates pinion gear G 2 , and rotates drive gear G 3  against torque pressure of torque limiter  161 , to stop the blade receiving member  116  at a prescribed position. 
         [0095]    When the blade receiving member  116  is taken out of the clearance section “g” formed between the edge pressure member  115  and the pressure-connection plate  151 , pinion gear G 2  is rotated regularly by rack gear G 1  of the blade receiving member  116 , and drive gear G 3  and one-way clutch  162  are yen to rotate. 
       [Control Flow] 
       [0096]    Next, a control flow will be explained.  FIG. 11  shows contents of a control flow which are carried out by sheet finisher control section  10 B of sheet finisher B. 
         [0097]    In step S 11 , information of cumulative number of cutting operations “n” up the present time is acquired. 
         [0098]    In step S 12 , biting amount “y” for a cutting edge corresponding to cumulative number of cutting operations “n” acquired in step S 11  is determined based on a correspondence table shown in Table 1. 
         [0000]    
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Cumulative number 
                 Biting amount y 
               
               
                 of cutting operations n 
                 (Amount of movement x) 
               
               
                   
               
             
             
               
                  1-250 
                 0.4 mm(tss + 5.4 mm) 
               
               
                 251-500 
                 0.5 mm(tss + 5.5 mm) 
               
               
                 501-750 
                 0.6 mm(tss + 5.6 mm) 
               
               
                 751-000 
                 0.7 mm(tss + 5.7 mm) 
               
               
                   
               
             
          
         
       
     
         [0099]    Table 1 is a correspondence table showing relationship between cumulative number of cutting operations “n” and biting amount “y” for a cutting edge of cutting blade  121 . Contents of this correspondence table are stored in a memory section of sheet finisher control device  10 B. 
         [0100]    The parenthesized numerical values in Table 1 are those showing amount of movement “x” of a cutting edge of cutting blade  121  to the blade receiving member  116 . The symbol tss represents a thickness of sheet bundle SS, and thickness tss may be calculated either by measuring a distance from edge pressure member  115  to placing stand  127  in the case of interposing sheet bundle SS, or by converting based on the number of sheets of sheet bundle SS. As shown in Table 1, the amount of movement “x” from the position of standing by the stop position for cutting blade  121  of cutting section  120  (or biting amount “y”) is made to be large with an increase of the number of times for cutting in the present embodiment. Incidentally, the amount of movement “x” mentioned here means an amount of movement in the direction perpendicular to a surface of sheet bundle SS among movement amounts of cutting blade  121 . 
         [0101]    Now, how change the biting amount y will be explained.  FIG. 12  is a timing chart showing timing for position detection sensor PS 2  and for drive motor M 2  that moves cutting blade  121 . In the present embodiment, when prescribed delay time t 1  (a period of time up to outputting stop signals) has passed from the moment of detection signals by the position detection sensor PS 2 , stop signals are outputted to drive motor M 2 , and cutting blade  121  is stopped. As explained in the aforesaid  FIGS. 6A and 6B  and  FIGS. 7A and 7B , the position detection sensor PS 2  is established so that it can detect when a distance between cutting blade  121  and blade receiving member  116  satisfies prescribed relationship. For example, under the condition that a distance between a cutting edge of cutting blade  121  and blade receiving member  116  is set to be −0.4 mm (biting amount 0.4 mm), if delay time t 1  is made to be zero, a biting amount of the cutting edge into the blade receiving member  116  is 0.4 mm. The biting amount “y” can be increased by prolonging the delay time t 1 . 
         [0102]    In returning to the explanation of the control flow in  FIG. 11 , the cutting blade  121  is moved upward by cutting section  120 , in step S 13 , based on biting amount “y” cutting edge acquired in step S 12 . 
         [0103]    In step S 14 , cumulative number of cutting operations “n” is incremented. Then, in step S 15 , the cumulative number of cutting operations “n” thus incremented is judged whether it exceeds prescribed number “m” or not. The prescribed number “m” in this case means the maximum number of times for a blade receiving plate to be used at one position, and prescribed number of times “m” in the present embodiment is set to 1000 times. Meanwhile, in the present embodiment, biting amount “y” up to a stop position (amount of movement “x”) is judged whether it exceeds a prescribed upper limit value or not, by judging the prescribed number of whether it is exceeded or not, in the present embodiment. 
         [0104]    When the prescribed number of times “m” is judged to exceeded (Yes in step S 15 ), the blade receiving member is shifted by shifting section  160  to be in the direction perpendicular to a cutting surface. 
         [0105]    Owing to this shifting, a surface of contact between blade receiving member  116  and cutting blade  112  is updated, thereby, the cumulative number of cutting operations “n” is reset (being set to zero) for a termination. Incidentally, resetting of the cumulative number of cutting operations “n” causes the biting amount “y” (amount of movement “x”) to set again to the initial value. 
         [0106]    In the present embodiment, control is taken to make a biting amount of a blade of cutting section up to the stop position (an amount of movement) to be large, with an increase of the number of times for cutting (cumulative number of cutting operations). By doing this, it is possible to prevent occurrence of defective cutting in advance even when blade receiving member  116  is deteriorated unexpectedly, because an amount of biting into the blade receiving member  116  grows greater gradually. 
         [0107]    Further, by controlling so that a biting amount grows greater gradually with an increase of the cumulative number of cutting operations as stated above, it is possible to increase the number of times for the blade receiving member  116  to be used for one surface (prescribed number of times “m”). Though the aforesaid prescribed number of times “m” was 700 in the case of using under the fixed condition of biting amount of 0.5 mm, in Comparative Example, the prescribed number of times “m” was 1000 as stated above in the present example, resulting in an increase of the number of times to be used, in a comparison with the Comparative Example, which has become possible to prolong the life of a blade receiving section. 
         [0108]    In the present embodiment, it is possible to increase a biting amount of a cutting edge into a blade receiving member gradually, by controlling so that an amount of movement of a blade of the aforesaid cutting section from a position of standing by to the aforesaid stop position may grow greater with an increase of the number of times for cutting, thus, it is possible to utilize a blade receiving section effectively. Therefore, it is possible to provide a sheet cutting device wherein occurrence of defective cutting can be lowered and a life of the blade receiving section can be prolonged.