Abstract:
A sheet cutting apparatus includes: a cutting blade for cutting an edge of a sheet bundle conveyed to a cutting position of the sheet bundle; a cutting blade moving section for moving obliquely the cutting blade with respect to a sheet surface of the sheet bundle; a fixed supporting table for supporting the sheet bundle in a vicinity of the cutting position; a blade receiving member for pressing the sheet bundle and receiving the cutting blade in the vicinity of the cutting position; and a blade receiving member moving section for ascending or descending the blade receiving member. A center position of a load application action of the blade receiving member by the blade receiving member moving section, is set to a position upstream of the sheet cutting position in a conveying direction of the sheet bundle, and in the vicinity of the sheet cutting position.

Description:
This application claims priority from Japanese Patent Application No. 2004-299765 filed on Oct. 14, 2004, which is incorporated hereinto by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a sheet cutting device that cut several sheets of paper, to a sheet finishing apparatus equipped with the sheet cutting device, and to an image forming systems provided with the sheet finishing apparatus. 
     A Sheet finisher carrying out various types of finishing is connected to a high speed image forming apparatus such as an image forming apparatus employing the electro-photography method, and multiple-functional image forming systems have come into wide use that make it possible to carry out within a single apparatus various types of finishing operations such as stapling and folding of paper sheets on which images have been formed. 
     Among the different types of finishers there is the sheet cutting apparatus that aligns the edges of a bundle of a plurality of sheets, and an image forming system having a sheet cutting apparatus that cuts the edges of sheets that have been subjected to center-folding and center-stapling has been disclosed, for example, in Japanese Unexamined Patent Application Laid-Open No. 2003-228205. The sheet cutting apparatus disclosed in the Japanese Unexamined Patent Application Laid-Open No. 2003-228205 is of the type commonly referred to as the guillotine type and is one in which the cutting done by pressing the cutting blade from a direction perpendicular to the sheet surface. 
     In the sheet cutting apparatus disclosed in Japanese Unexamined Patent Application Laid-Open No. 2003-136471, there is a sheet pressing member that presses the bundle of sheets including a plurality of sheets placed one upon the other so that the position of the bundle of sheets does not get shifted, the cutting blade (cutter) is placed below the sheet pressing member and can move in a diagonally upward direction. A link is attached to the sheet pressing member so that it can be raised or lowered using a drive section. In this sheet cutting apparatus, the positioning of parts is made so that the central position of the load application action of the sheet pressing member capable of being raised and lowered is almost directly above the cutting edge of the cutter. 
     Since the guillotine type of sheet cutting apparatus described in the Japanese Unexamined Patent Application Laid-Open No. 2003-228205 cuts the bundle of sheets by moving the cutting blade in a direction perpendicular to the sheet surface, a large force is required for driving it. And also, since it is necessary to set the power of the driving section at the maximum value in the usable range, there is the requirement for a large power and large sized motor and a power supply with a large power capacity resulting in the problems that not only the apparatus becomes large but also the power consumption becomes large. In particular, it becomes difficult to incorporate a sheet cutting apparatus in a sheet finishing apparatus that is a part constituting an image forming system. 
     In the sheet cutting apparatus disclosed in the Japanese Unexamined Patent Application Laid-Open No. 2003-136471, since the central point of the lower surface of the sheet pressing member is in a state in which it has projected beyond the edge surface of the table supporting the bundle of sheets, at the time of cutting the edge of the bundle of sheets by raising the cutting blade in a diagonally upward direction while pressing the sheets placed on the table using a sheet pressing member, it is likely that the sheet pressing member becomes inclined thereby applying a load on the cutter. In particular, at the time of cutting a number of sheets of paper such as when cutting 50 to 100 sheets, an abnormally high load may be applied on the cutting blade. Because of this, the driving load of the cutting blade moving section becomes large. In addition, the cut edge surface of the bundle of sheets does not become perpendicular to the sheet surface and the sheets do not become aligned, thereby lowering the quality of the finished booklets. 
     SUMMARY 
     The present invention was made with an object of solving the problems of conventional sheet cutting apparatuses such as the apparatus becoming too large or the quality of the cut edge surface becoming deteriorated, and in particular, an object of the present invention is to provide a sheet cutting apparatus that is ideally suited for use as a part of an image forming system, a sheeting finishing apparatus provided therewith and an image forming system equipped therewith. 
     The above objects can be achieved by having the following configuration. 
     A sheet cutting apparatus including the following: a cutting blade that cuts the bundle of sheets transported to the cutting position; a cutting blade moving section that moves the cutting blade in a diagonal direction with respect to the sheet surface of the bundle of sheets; a fixed supporting table that supports the bundle of sheets in the neighborhood of the cutting position; a cutting blade receiving member that not only presses the bundle of sheets in the neighborhood of the cutting position but also receives the cutting blade; and a cutting blade receiving member moving section that raises and lowers the cutting blade receiving member, wherein the central position of the load application action of the cutting blade receiving member by the cutting blade receiving member moving section is set on the upstream side of the sheet bundle transporting direction relative to the cutting position and in the neighborhood of the cutting position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1(   a ) and  1 ( b ) are respectively the front view and the side view of the important parts of the sheet cutting apparatus according to the present invention. 
         FIGS. 2(   a ) and  2 ( b ) are respectively the front view of the important parts and the side view of the important parts showing the standby state of the sheet cutting apparatus. 
         FIGS. 3(   a ) and  3 ( b ) are respectively the front view of the important parts and the side view of the important parts showing the sheet cutting starting state of the sheet cutting apparatus. 
         FIGS. 4(   a ) and  4 ( b ) are respectively the perspective view of the important parts and the cross-sectional view of the important parts of the cutting blade moving section. 
         FIG. 5  is the enlarged cross-sectional view showing the sheet bundle pressing state due to the cutting blade receiving member moving section and the cutting blade moving section. 
         FIG. 6  is the enlarged cross-sectional view showing the sheet bundle cutting state due to the cutting blade receiving member moving section and the cutting blade moving section. 
         FIGS. 7(   a ) and  7 ( b ) are the partial cross-sectional views of the cutting blade receiving member moving section and the cutting blade moving section showing an example in which the central position of the load application action of the cutting blade receiving member due to the cutting blade receiving member moving section is set outside a specific distance range. 
         FIGS. 8(   a ),  8 ( b ),  8 ( c ), and  8 ( d ) are the perspective views and the cross-sectional views of different types of sheet bundles that are cut. 
         FIG. 9  is an overall configuration diagram of a sheet finishing apparatus employing a sheet cutting apparatus according to the present invention and of a corresponding image forming system. 
         FIG. 10  is a schematic diagram showing the sheet transport during the center-folding and center-stapling processes of the sheet finishing apparatus. 
         FIG. 11  is a right side view of the sheet finishing apparatus. 
         FIG. 12  is a left side view of the sheet finishing apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention will be described while referring to the drawings, as follows. 
       FIG. 1(   a ) is the front view of the sheet cutting apparatus according to the embodiment and  FIG. 1(   b ) is the side view of its important parts.  FIG. 2(   a ) is the front view of the important parts showing the standby state of the sheet cutting apparatus and  FIG. 2(   b ) is the side view of its important parts.  FIG. 3(   a ) is the front view of the important parts showing the sheet cutting starting state of the sheet cutting apparatus and  FIG. 3(   b ) is the side view of its important parts.  FIG. 4(   a ) is the perspective view of the important parts of the cutting blade moving section  120  and  FIG. 4(   b ) is the cross-sectional view of the important parts of the cutting blade moving section  120 . 
     In  FIGS. 1(   a ) and  1 ( b ), the cutting blade receiving member moving section  110  is placed on top of the body  101  of the sheet cutting apparatus  100 , the cutting blade moving section  120  is placed under the body  101 , and the cutting blade moving section  130  is placed on the left side surface of the body  101  as shown in the figure. 
     The edge of the bundle of the sheets SS transported into the sheet cutting apparatus  100  is cut due to the vertically downward movement of the cutting blade receiving member  116  of the cutting blade receiving member moving section  110  and the diagonally upward movement of the cutting blade  121  of the cutting blade moving section  120 . The details of the cutting blade receiving member moving section  110 , the cutting blade moving section  120 , and the cutting blade moving section  130  are described below. 
     (Cutting Blade Receiving Member Moving Section) 
     A rotating shaft  111  supported at both ends is provided on top of the cutting blade receiving member moving section  110 . The rotating shaft  111  is rotated by the first driving section having the drive transmission section Z 1  constituted by a motor M 1 , a belt, and gear wheels. 
     The rotating shaft  111  is provided with the screw sections  111 A and  111 B having the same pitch but having helix angles in mutually opposite directions, and the nut  112 A mates with the screw section  111 A while the nut  112 B mates with the screw section  111 B. Due to the rotation of the rotating shaft  111 , the moving body  113 A carrying the nut  112 A and the moving body  113 B carrying the nut  112 B carry out linear movement in mutually opposite directions. 
     The bottom end of the coupling link  114 A supported rotatably at a part of the moving body  113 A mates with the left top part in the figure of the edge pressing member  115  and supports it so that it can be raised or lowered. In a similar manner, the bottom end of the coupling link  114 B supported rotatably at a part of the moving body  113 B mates with the right top part in the figure of the edge pressing member  115  and supports it so that it can be raised or lowered. 
     Therefore, the rotating shaft  111  is rotated by the rotation of the motor M 1 , the moving bodies  113 A and  113 B move in the left to right direction, thereby changing the inclinations of the coupling links  114 A and  114 B as a result of which the edge pressing member  115  moves up and down in a parallel state. 
     The cutting blade receiving member  116  is fixed to the lower surface of the edge pressing member  115 , and moves in the up and down direction while being parallel to the cutting edge of the cutting blade  121  along with the edge pressing member  115 . The cutting blade receiving member  116  is made of a synthetic resin. 
     In this manner, the first drive section constituted by the motor M 1  and the drive transmission section, the rotating shaft  111 , the moving bodies  113 A and  113 B, the coupling links  114 A and  114 B, the edge pressing member  115 , and the cutting blade receiving member  116  constitute the cutting blade receiving member moving section  110 . 
     Since the edge pressing member  115  supporting the cutting blade receiving member  116  is driven by a drive mechanism with a large reduction ratio and including the screw sections  111 A and  111 B, it presses and holds the bundle of sheets SS gripped between the cutting blade receiving member  116  and the fixed supporting table  127  with a strong force. 
     The edge pressing member  115  carrying the cutting blade receiving member  116  is made to slide by a solenoid S L after a predetermined number of cutting operations by a driving section not shown in the figure in the direction of the arrow K, that is, in a direction at right angles to the longitudinal direction of the cutting blade  121 . 
     (Cutting Blade Moving Section) 
     In  FIGS. 2(   a ) and  2 ( b ), the cutting blade moving section  120  is constituted by the cutting blade  121 , the cutting blade holder  122 , the supporting plates  123 A and  123 B that support the cutting blade holder  122  in a movable manner, the spacing retention member  124  that sets the spacing between the surfaces of the supporting plates  123 A and  123 B, the fixing section comprising the coupling member  125  that links the supporting plates  123 A and  123 B via the spacing retention member  124  and the tightening member  126 , and the fixed supporting table  127  placed in the neighborhood of the edge part of the bundle of sheets SS. 
     The cutting blade  121  having the cutting edge formed on its top edge is fixed to the cutting blade holder  122  by the male screw member  121 A. The cutting blade holder  122  is supported so that it can move between the opposing surfaces of the pair of supporting plates  123 A and  123 B arranged in parallel. The spacing retention member  124  is gripped between the opposing surfaces of the supporting plates  123 A and  123 B and the spacing is maintained so that the cutting blade holder  122  can move in that space. 
     The coupling member  125  provided with a male screw passes through the supporting plates  123 A and  123 B and the spacing retention member  124  having a hollow cylindrical shape, mates with the tightening member  126  having a spring washer and a hexagonal nut, and holds and tightens the supporting plates  123 A and  123 B with a specific spacing between them. 
     The spacing between the opposing surfaces of the supporting plates  123 A and  123 B provided due to the spacing retention member  124  is set to be in a range of dimensions to have a gap of about 0.1 mm to 0.5 mm relative to the thickness of the cutting blade holder  122  and the spacing is such that the cutting blade holder  122  can move up and down without any hindrance. 
     A plurality of coupling section composed of the coupling member  125  and the tightening member  126  are provided at various locations of the supporting plates  123 A and  123 B (for example, at the seven locations shown in  FIGS. 2(   a ) and  2 ( b )) and maintain the specific spacing firmly. 
     The rollers  128 A and  128 B are fixed to the cutting blade holder  122 , and the rollers  128 A and  128 B are guided in the direction of the arrow J by the guide members  129 A and  129 B fixed to the body  101  in a state in which they are inclined downward toward the right. 
     (Cutting Blade Driving Section) 
     In  FIGS. 1(   a ) and  1 ( b ), the cutting blade driving section  130  is constituted by the motor M 2 , the drive transmission section Z 2 , and the moving body  133 , etc. 
     The rotating shafts  131 A and  131 B supported at both ends are mounted in parallel on the body  101 . The rotating shafts  131 A and  131 B with screws threaded on them rotate in the same direction being driven by the second driving section that has the motor M 2  and the drive transmission section Z 2  comprising a belt and gear wheels. 
     The screws threaded on the rotating shafts  131 A and  131 B are respectively provided with the nuts  132 A and  132 B. The moving body  133  carrying the nuts  132 A and  132 B carries out linear movement due to the rotation of the rotating shafts  131 A and  131 B. 
     The pin  134  fixed to the cutting blade holder  122  engages in a movable manner with the long hole section  133 A provided in the moving body  133 . Because the moving body  133  carries out left-right linear motion as shown in the figure and the cutting blade holder  122  carries out left-right linear motion via the pin  134 , the rollers  128 A and  128 B fixed to the cutting blade holder  122  move in a diagonally upward direction indicated by the arrow J along the guide members  129 A and  129 B. 
     The bundle of sheets SS introduced into the sheet cutting apparatus  100  is transported by a transport section not shown in the figure on to the fixed supporting table  127  of the cutting blade moving section  120  with its edge ‘a’ at the front and comes to a stop at a specific position, the bundle of sheets SS is clamped between the fixed supporting table  127  and the blade receiving member  116  that moves down, and the edge ‘a’ is cut by the raising cutting blade  121 . 
     (Operation of the Sheet Cutting Apparatus) 
     Next, the operation of the sheet cutting apparatus  100  is described below. 
     In  FIGS. 1(   a ),  1 ( b ),  2 ( a ), and  2 ( b ), in the standby state, the moving body  113 A is positioned at the left end and the moving body  113 B is positioned at the right end, the blade receiving member  116  is at the upper limit position, and the cutting blade  121  waits at the lower limit position. 
     When the bundle of sheets SS is introduced into the sheet cutting apparatus  100 , the motor M 1  starts rotating and drives the moving bodies  113 A and  113 B and the edge pressing member  115  is lowered via the coupling links  114 A and  114 B. The motor M 1  stops when the edge pressing member  115  is at a position where it is detected by the detection section PS and the edge pressing member  115  stops. 
     As described later, the edge pressing member  115  can press the bundle of sheets SS with a sufficiently large force so that there is no shifting of the bundle of sheets comprising a plural number of sheet one upon the other when they are subjected to a force in the horizontal direction due to the cutting blade  121  because of the above configuration. 
     When the pressing of the bundle of sheets SS is completed, the motor M 1  starts rotating, and the cutting blade  121  starts moving upward towards the left in the direction of the arrow J. The bundle of sheets SS is cut due to this movement of the cutting blade  121 . Since the cutting effect of the cutting blade  121  is the cutting due to the sliding of the cutting blade  121  in a diagonally upward direction, the cutting can be made with a comparatively small driving force, and also, even when the number of sheets to be cut is large only the movement stroke of the cutting blade  121  changes but the driving force does not change. 
     As is shown in  FIGS. 3(   a ) and  3 ( b ), when all the sheets in the bundle of sheets are cut the cutting edge of the cutting blade  121  comes into contact with the cutting blade receiving member  116  and the driving force of the cutting blade  121  increases. The increase in the motor drive current due to the increase in the load of motor M 1  caused by this increase of the driving force is detected by the control section which then stops the drive of the motor M 1 . In this manner, all the sheets in the bundle of sheets SS are cut. 
     When the edge cutting process is completed, the motor M 2  rotates in the reverse direction thereby lowering the cutting blade  121  in the downward right direction of the arrow J in  FIGS. 1(   a ) and  1 ( b ). When the lowering of the cutting blade  121  is completed, the edge pressing member  115  is raised to the initial position due to the reverse rotation of the motor M 1 . 
     After the raising of the edge pressing member  115  is completed, and when the folding line pressing member and the receiving plate, not shown in the figure, that had been pinching the bundle of sheets SS at the folding line section ‘b’ return to their initial positions, the edge pressing member  115  and the cutting blade receiving member  116  raise up thereby releasing the clamping of the bundle of sheets SS. 
     The edge cutting process of the bundle of sheets SS is completed at the end of the above sequence of operations. 
     Due to repeated cutting operations, the cutting blade receiving member  116  gets cut by the cutting blade  121 , although to a very small extent, and as a result, a cut groove T is formed in the cutting blade receiving member  116 . When the depth of this cut groove T becomes large, cutting defects may occur, such as uncut portions remaining in the bundle of sheets or the end surface of the cut edge ‘a’ not being flat. 
     In order to prevent this, a setting is made so that the cutting blade receiving member  116  is displaced at the right angles to the longitudinal direction of the cutting blade  121  in the direction of arrow K, so that an unused part of the cutting blade receiving member  116  starts receiving the cutting edge of the cutting blade  121 . In other words, by operating the solenoid SL shown in  FIGS. 1(   a ) and  1 ( b ) the cutting blade receiving member moving section  110  is operated thereby moving slightly the cutting blade receiving member  116  in the direction of the arrow K. 
     Because of this, although a plural number of cut grooves T are formed, it is possible to limit their depths to within a permissible range and hence there is no occurrence of cutting defects due to deep cut grooves. 
     (Central Position of Load Application Action of Cutting Blade Receiving Member Moving Section and Cutting Blade Moving Section) 
       FIG. 5  is the enlarged cross-sectional view showing the sheet bundle pressing state due to the cutting blade receiving member moving section  110  and the cutting blade moving section  120 .  FIG. 6  is the enlarged cross-sectional view showing the sheet bundle cutting state due to the cutting blade receiving member moving section  110  and the cutting blade moving section  120 . 
     The central position P of load application action of the cutting blade receiving member  116  due to the cutting blade receiving member moving section  110  was set to be in the neighborhood of the upstream side in the sheet transport direction beyond the sheet cutting position of the cutting edge of the cutting blade  121 . The central position P of load application action is the point of action of the cutting edge receiving member  116  pressing on the bundle of sheets SS via the coupling links  114 A and  114 B and the edge pressing member  115  and is vertically below the rotating shaft  111  shown in  FIG. 5 . 
     The central position of load application action refers to the center point of the part of the receiving member  115  where it receives the load. When there are a number of areas in which the cutting blade receiving member  116  receives the load, The central position is a central position of the areas. 
     Explaining this using  FIG. 5  for the present preferred embodiment, the central position of load application action will be the central position of the two points in the cutting blade receiving member  116  receiving the load via the coupling link  114 A, that is, the position at the lower part of the point P in the figure. 
     The distance L from the position of the cutting edge of the cutting blade  121  to the central position P of load application action is set to within about 0.5 to 5 mm on the upstream side looking towards the sheet bundle transport direction. 
       FIGS. 7(   a ) and  7 ( b ) are the partial cross-sectional views of the cutting blade receiving member moving section  110  and the cutting blade moving section  120  showing an example in which the central position of the load application action of the cutting blade receiving member  116  is set outside a specific distance range. 
       FIG. 7(   a ) shows the example when the central position P of load application action is set to a distance L 1  on the outside of the cutting blade  121 . When this distance L 1  is set to less than 0.5 mm, that is, when the central point P of load application action is either directly above the cutting edge of the cutting blade  121  or is towards the downstream side (towards the left in the figure) in the sheet transport direction in the neighborhood of the cutting edge of the cutting blade  121 , the side of the cutting blade receiving member  116  that is not in pressure contact with the sheet bundle SS goes down thereby pressing the sheet bundle in an inclined state (the state of right part going down in the figure). If the cutting operation is made in this state, an abnormal load is applied on the cutting blade  121  that rises while sliding on the inner surfaces of the supporting plates  123 A and  123 B, thereby increasing the driving load of the cutting blade moving section  120 . In addition, an abnormal force acts on the pointed cutting edge of the cutting blade  121  thereby causing the problems of damage to the cutting edge or reduction in its life, etc. 
       FIG. 7(   b ) shows the example when the central position P of load application action is set to a distance L 2  that is at a distant position of 5 mm or more upstream side of the sheet transport direction of the cutting edge of the cutting blade  121 . This distance L 2  is set to more than or equal to 5 mm, that is, the central point P of load application action is set to a distance of L 2 , specifically, on the outside of the sheet supporting surface of the fixed supporting table  127  towards the upstream side in the sheet transport direction. In this case, due to the rising of the cutting edge of the cutting blade  121  a rotating moment acts in the neighborhood of one end of the cutting blade receiving member  116  and gets pushed up centering on the point X where the load is acting, thereby going into the inclined state (the state of right part going down in the figure). Because of this, the cutting blade receiving member  116  does not press fully in the neighborhood of the cutting position of the bundle of sheets SS, and hence it is likely that cutting defects are generated. In addition, an abnormal force acts on the pointed cutting edge of the cutting blade  121  coming into contact with the inclined cutting blade receiving member  116  thereby causing the problems of damage to the cutting edge or reduction in its life, etc. 
     It is possible to determine the pressing force of the cutting blade  121  depending on the specifications of the sheet bundle to be cut (type and thickness of sheets, etc.). Further, in order to cut while keeping the sheet bundle fixed, it is necessary that if the pressing force of the cutting blade receiving member  116  is at least larger than the pressing force of the cutting blade. While stability can be obtained by making large the pressing force of the cutting blade receiving member  116 , it is inefficient in terms of equipment design and cost to make it too large. Therefore, it is desirable that the two pressing forces are almost equal and that their difference is not too large. In view of this, it is desirable to set the ratio (pressing force of the cutting blade receiving member  116 )/(pressing force of the cutting blade  121 ) in the range of 1 to 1.3. At this time, by making the central position of load application action in the neighborhood along the sheet transport direction, it is possible to carry out good and accurate cutting without the cutting blade receiving member  116  from becoming inclined during cutting. 
     As a concrete example, when cutting sheet bundle of about 10 mm thickness, it is possible to carry out satisfactory cutting without the cutting blade receiving member from becoming inclined during cutting by setting the total pressing force of the cutting blade to 600 kg, the total pressing force of the blade receiving member to 800 kg, and the central position of load application action to 3 mm on the upstream side. 
     In the sheet cutting apparatus  100  according to the present invention, by setting the central position P of load application action of the cutting blade receiving member  116  due to the cutting blade receiving member moving section  110  to a point in the neighborhood on the upstream side along the sheet bundle transport direction relative to the cutting position, it is possible to carry out normal cutting of the edge ‘a’ of the sheet bundle SS without having an abnormal load acting on the cutting blade  121  and also while making smooth the drive of the cutting blade moving section  210 . In addition, since there is no abnormal force acting on the pointed cutting edge of the cutting blade  121 , the problems of damage to the cutting edge or reduction in its life, etc. will be solved. 
       FIGS. 8(   a ),  8 ( b ),  8 ( c ), and  8 ( d ) are the perspective views and the cross-sectional views of different types of sheet bundles that are cut. 
       FIG. 8(   a ) is a perspective view of a center-folded and center-stapled bundle of sheets SS,  FIG. 8(   b ) is a cross-sectional diagram of the bundle of sheets SS, where ‘a’ indicates the edge, ‘b’ the folding line section, ‘c’ the cutting line, and SP indicates the staple. 
       FIG. 8(   c ) is a perspective view of a side-stapled bundle of sheets SS, where ‘a’ indicates the edge, ‘c’ the cutting line, and SP indicates the staple. 
       FIG. 8(   d ) is a perspective view of a bundle of sheets SS after adhesive coating, where ‘a’ indicates the edge, ‘c’ the cutting line, and ‘d’ is the adhesive tape. 
     (Sheet Finishing Apparatus and Image Forming System Provided with a Sheet Cutting Apparatus) 
     Here, a sheet finishing apparatus and an image forming system provided with a sheet cutting apparatus refers to an a sheet finishing apparatus with a built-in sheet cutting apparatus, or an image forming system configured by connecting externally a sheet finishing apparatus with a built-in sheet cutting apparatus as shown in the figure. Further, it is possible to have a configuration in which the sheet finishing apparatus with a built-in sheet cutting apparatus according to the present invention can be used independently. Also, the sheet finishing apparatus and image forming systems having a sheet finishing apparatus according to the present invention need not be limited to the following preferred embodiments. 
     (Image Forming Apparatus) 
       FIG. 9  is an overall configuration diagram of a sheet finishing apparatus employing a sheet cutting apparatus according to the present invention and of a corresponding image forming system. 
     The image forming system is constituted by an image forming apparatus A, an automatic document feeding apparatus DF, a sheet finishing apparatus B, and a large capacity sheet feeding apparatus LT. 
     The image forming apparatus A shown in the figure is provided with the image reading section  1 , the image processing section  2 , the image writing section  3 , the image forming section  4 , the sheet loading cassettes  5 A,  5 B,  5 C, and the manual sheet loading tray  5 D, the first sheet loading sections  6 A,  6 B,  6 C, and  6 D, the second sheet loading section  6 F, the fixing apparatus  7 , the sheet discharging section  8 , and an automatic double-side copy sheet feeding section (ADU)  8 B. 
     The sheet finishing apparatus B having the sheet cutting apparatus  100  described above is coupled on the side of the sheet discharge section  8  on the left side face shown in the figure of the image forming apparatus A. 
     The image on one side or on both sides of the original document placed on the document table of the automatic document feeding apparatus DF is read by the optical system of the image reading section  1 , read in as electrical data by the CCD image sensor  1 A, and the analog signal obtained by photoelectric conversion is subjected in the image processing section  2  to various processing such as analog signal processing A/D conversion, shading correction, image compression, etc., and sent to the image writing section  3 . 
     In the image writing section  3 , the output light from a semiconductor laser is irradiated on the photosensitive drum  4 A of the image forming section  4 , thereby forming the latent image. The different processes of electrostatic charging, exposure, development, transfer, separation, cleaning, etc., are carried out in the image forming section  4 . The sheet S fed and transported from each of the first sheet feeding sections  6 A to  6 C of the sheet feeding cassettes  5 A to  5 C, the first sheet feeding section  6 D of the manual sheet feeding tray  5 D, and the first sheet feeding section  6 E of the large capacity sheet feeding apparatus LT is passed through the second sheet feeding section  6 F and the image is transferred on to it by the transfer section  4 B. The sheet carrying the image is fixed by the fixing apparatus  7 , and is sent to the sheet finishing apparatus B from the sheet discharging section  8 . On the other hand, a sheet S with image forming completed on one of its sides and sent by the transport path selection plate  8 A to the automatic double-side copy sheet feeding section  8 B is again subjected to the processing in the image forming section  4 , and is discharged from the sheet discharging section  8  after images are formed on both sides of the sheet. 
     The operation section  9  is used for selecting and setting the processing functions of the image forming system constituted by the image forming apparatus A and the sheet finishing apparatus B, etc. 
     The main control section  10  of the image forming apparatus A is connected to the sheet finisher control section  10 C of the sheet finishing apparatus B via the communication section  10 A and the communication lines  10 B. 
     (Sheet Finishing Apparatus) 
       FIG. 10  is a schematic diagram showing the sheet transport during the center-folding and center-stapling processes of the sheet finishing apparatus B.  FIG. 11  is a right side view of the sheet finishing apparatus B and  FIG. 12  is a left side view of the sheet finishing apparatus B. 
     To start with, the sheet transport process from introduction to just before folding is described here. 
     As is shown in  FIGS. 9 and 10 , when the sheet S discharged from the image forming apparatus A is introduced into the inlet section  11  of the sheet finishing apparatus B, it is pinched by the inlet roller  12 , and is transported to the upper sheet transportation path r 1  or the lower sheet transportation path r 2  of the sheet transportation path selection section G 1 . 
     &lt;Straight Discharge&gt; 
     The sheet S branched to the sheet transportation path r 1  is gripped and transported by the transport rollers  13 A to  13 E, and is transported to either the upper sheet transportation path r 3  or the lower sheet transportation path r 4  of the sheet transportation path selection section G 2 . 
     The sheet S that has proceeded to the upper sheet transportation path r 3  is discharged by the discharge roller  14 , and is stacked on the auxiliary sheet discharge tray  15  provided in the top part of the sheet finishing apparatus B. 
     The sheet S that has proceeded to the lower sheet transportation path r 4  is gripped and transported by the transport rollers  16 A to  16 D, and is discharged by the discharge roller  17 . 
     &lt;First Right Angle Direction Change Transport&gt; 
     The sheet S that has proceeded to the lower sheet transportation path r 2  of the transportation path selection section G 1  is lowered almost vertically and is stored after making a temporary stop at a specific position. At this first stopping position Q 1  several succeeding sheets of paper S are stacked one upon the other and stored. 
     &lt;Second Right Angle Direction Change Transport&gt; 
     The stored sheet S is moved after changing the orientation to a direction at right angles to the sheet surface towards the front as shown in  FIG. 11  by the transport roller pairs  18 A and  18 B, the first transport roller pairs  18 C and  18 D, and a guide plate not shown in the figure, and passes through the sheet transport path r 5  that goes around the inner front side Bf of the sheet finishing apparatus B in a state in which the sheet surface is vertical, and makes a temporary stop at the second stopping position Q 2 . 
     &lt;Third Right Angle Direction Change Transport&gt; 
     Next, after the sheet S is transported vertically by the second transport roller pair  18 E, its direction is changed to the horizontal direction, and is transported by the transport roller pair  19  and the transportation aligning belt  20  (refer to sheet transportation path r 6  in  FIG. 10 ). 
     &lt;Alignment Before Folding Operation&gt; 
     As is shown in  FIG. 11 , the alignment section is placed on the downstream side in the sheet transportation direction with respect to the sheet transportation path r 6 , and has an aligning member  21  that is used for positioning by pushing the leading edge part of the sheets against it, and the movable aligning member  20 A that moves the sheet S by pushing against its trailing edge part. The aligning member  20 A pushes the trailing edge part of the sheet S transported by the transport roller pair  19  placed on the upstream side in the sheet transport direction with respect to the sheet transportation path r 6  and moves the sheet up to the aligning member  21 , carries out aligning of the sheets by making the leading edge part of the sheets to come into contact with the aligning member  21 , and finally comes to a temporary stop at the third stopping position Q 3 . 
     Next, the processes of center-folding, center-stapling, and booklet edge cutting of the sheet S in the sheet finishing apparatus B are described here concretely. 
     The folding section  30  is provided on the downstream side of the transportation aligning belt  20  along the sheet transportation direction. The folding section  30  is constituted by the folding rollers  31 ,  32 , and  33 , the first folding plate  34 , and the second folding plate  35 , etc. When carrying out the operation of folding into three, in the folding section  30 , the first folding line part is formed in the sheet S by the folding rollers  31  and  32  and the first folding plate  34 , the second folding line part is formed in the sheet S by the folding rollers  32  and  33  and the second folding plate  35 , and the folded sheet SA folded into three passes through a sheet transportation path r 8  comprising a plurality of transport rollers  36  and guide plates, and is discharged to the sheet discharge tray  38  by the sheet discharge roller  37  (see  FIG. 11 ). 
     &lt;Center-Folding Process&gt; 
     The one or several sheets of paper S arriving at the folding section  30  are gripped by the rollers  31  and  32  that rotate in mutually opposite direction and by the first folding plate  34  that moves forward thereby carrying out the center-folding operation of the sheet S, and the folded sheet SA is formed in which has been formed the folding line part ‘b’ along the breadth direction of the sheet at the center of the sheet transportation direction. 
     The folded sheet SA which has been folded into two and the folding line part ‘b’ formed in it by the folding rollers  31  and  32 , and the first folding plate  34  is separated from the nipping position of the folding rollers  31  and  32  and returned to the original horizontal transportation path due to the reverse rotations of the folding rollers  31  and  32 . In  FIG. 10 , the folded sheet SA is transported further to the sheet transportation path r 7  in the direction of an extension line of the folding line part ‘b’ by the transport belt  41  of the transportation section  40  to be described later, the transportation tab  42 , and the introduction guiding member  51  of the folding sheet guiding section  50 , and is then transported to the center-folding section  60  (see  FIG. 10 ). 
     In this manner, because the folding section  30  carries out center-folding of a small number of sheets such as 1 to 3 sheets, firmly forms the folding line part ‘b’ and successively sends them to the folding section  60 , it is possible to produce a high quality bundle of sheets SS with very small bulging of the folding line part ‘b’. 
     &lt;Center-Folding Process&gt; 
     The folded sheet SA center-folded in the folding section  30  is transported in the direction of the sheet transportation path r 7  by the transportation section  40  to be described later, and is placed on top of the saddle-shaped stacking section  61  of the center-folding section  60 . The succeeding center-folded sheets SA also pass through the sheet transportation path r 7  and are stacked on top of the saddle-shaped stacking section  61 . 
     In  FIG. 12 , the saddle-shaped stacking section  61  is formed from two guide plates that are almost at right angles to each other, and is fixed to the body of the sheet finishing apparatus B. Near the apex part of the saddle-shaped stacking section  61  is placed a pressing member  61 A that can move up or down due to the action of a spring and in the state in which it is supported by the staple receiving mechanism  64 . 
     The apex part of the pressing member  61 A has a projection shape at the top that is almost right angle, and the folding line part ‘b’ (see  FIG. 12 ) of the center-folded sheet SA is placed on the ridge line of the apex part. 
     The plurality of folded sheets SA placed on top of the saddle-shaped stacking section  61  and the pressing member  61 A are adjusted for position by the width aligning section  62 . 
     The stapling mechanism  63  is placed in a fixed position above the pressing member  61 A. Inside the saddle-shaped stacking section  61 , the pressing member  61 A and the staple receiving mechanism  64  are supported in a movable manner along the up-down direction. 
     Two sets of the stapling section having a divided structure and comprising the stapling mechanism  63  and the staple receiving mechanism  64  are provided along the sheet folding line direction. If the center-folding process has been set in the operating section, the staple receiving mechanism  64  rises thereby carrying out the center-folding operation. In other words, the two sets of stapling section staple the staple pins SP at two locations equidistant from the center along the folding line part ‘b’ of the folded sheet SA above the pressing member  61 A. The center-folded and center-stapled bundle of sheets SS is shown by the schematic diagrams in  FIGS. 8(   a ) and  8 ( b ). 
     &lt;Taking Out Booklets&gt; 
     The bundle of sheets SS center-stapled in the center-stapling section  60  is supported by the supporting member  72  fixed to the tip part of the arm member  71  of the booklet take-out section  70 , and is transported to the booklet transporting section  80  after being swung in the direction of the dot and dash arrow by the arm member  71 . 
     &lt;Booklet Transportation&gt; 
     The bundle of sheets SS transported to the booklet transporting section  80  is placed above the transportation belt  82 . The bundle of sheets SS is transported in the diagonally downward direction due to the rotation of the transportation belt  82  is subsequently retained in the inclined state, transported by the rotating transportation belt  83 , and stops at a specific position. Thereafter, the transportation belt  83  swings and is supported in the horizontal state. 
     &lt;Booklet Cutting Operation&gt; 
     Since the edge ‘a’ of the bundle of sheets SS (the free end part on the side opposite to the folding line part) placed above the transportation belt  83  after it has gone into the horizontal state would not be aligned depending on the number of sheets in the bundle of sheets SS, the edge ‘a’ is cut and aligned by cutting using the sheet cutting apparatus  100  according to the present invention. 
     The booklet SSS prepared by cutting the edge is placed above the transportation belt  83  that is rotating in the reverse direction, and is transported in the state in which the rear end part of the booklet SSS is pushed by the movable aligning member  84  fixed to the transportation belt  83 , and the booklet falls from the front end part of the transportation belt  83  in the direction of the arrow. The booklet SSS that has fallen is discharged by the rotating discharge belt  85  to the sheet discharge tray  86  placed outside the front panel side Bf of the sheet finishing apparatus B. 
     Further, the sheet cutting apparatus  100  according to the present invention need not be limited to the processing of edge cutting of the bundles of sheets SS that has been center-folded and center-stapled by the sheet finishing apparatus B, and can also be applied to the edge cutting operation of side-stapled bundles of sheets SS shown in  FIG. 8(   c ), or the edge cutting operation of bundles of sheets SS after adhesive application as shown in  FIG. 8(   d ). 
     According to the present preferred embodiment, a sheet cutting apparatus is realized that is small in size, can offer good finish of the booklets irrespective of whether the number of sheets is large or small, and also has reduced cutting blade driving load making it possible to drive using a small power. 
     According to the present preferred embodiment, a sheet cutting apparatus is realized that produces booklets by cutting the edges of sheets of bundle that have been subjected to the finishing operation of center-folding and center-stapling. 
     According to the present preferred embodiment, an image forming system is realized that provides in an on-demand manner booklets that are prepared by subjecting to finishing operations of the sheets on which images have been formed.