Patent Publication Number: US-2023137030-A1

Title: Punching blade, punching unit, image forming apparatus, and finishing device

Description:
TECHNICAL FIELD 
     The present invention relates to a punching blade for punching holes in sheets, a punching unit provided with the punching blade, an image forming apparatus, and a finishing device. 
     BACKGROUND ART 
     A punching unit is known to perform a punching process of punching holes in sheets before the sheets are discharged to a sheet discharge tray after image formation. Such a punching unit is provided with punching blades extending along punching axes and moving mechanisms that reciprocate the punching blades along the punching axes, and reciprocates the punching blades to punch holes in sheets. 
     PTLs 1 and 2 disclose techniques for reducing loads generated when the punching unit punches holes in sheets. In the techniques, a blade edge portion of each punching blade includes alternately formed edge peaks and edge valleys, and the blade edge line of the blade edge portion has a shape capable of reducing loads generated when the edge peaks penetrate a sheet and reducing loads generated when the edge valleys cut through the sheet. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] Japanese Patent Application Publication No. 2011-148040 
     [PTL 2] Japanese Patent Application Publication No. 2012-56040 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in the known techniques, no consideration for the shape of the blade edge line of the blade edge portion in the punching blade is given to the length between the edge peaks and the edge valleys along the punching axis. The length between the edge peaks and the edge valleys along the punching axis correlates with punching time required by the punching blade to punch a hole in a sheet. 
     An object of the present invention is to provide a punching blade, a punching unit, an image forming apparatus, and a finishing device capable of reducing loads in a punching process of punching holes in sheets and, furthermore, capable of reducing punching time. 
     Solution to the Problems 
     A punching blade according to an aspect of the present invention is included in a punching unit. The punching blade is configured to be inserted into a die hole in a die member along a punching axis and punch a binding hole in a sheet together with a hole edge of the die hole. The punching blade is provided with a body portion and a blade edge portion. The body portion has a cylindrical shape extending along the punching axis. The blade edge portion is formed at one end of the body portion and has a waveform including a plurality of peaks and a plurality of valleys formed alternately in a circumferential direction. A blade edge line that forms an edge end of the blade edge portion has first areas corresponding to the valleys, second areas corresponding to the peaks, and third areas connecting the first areas and the second areas. In a case where highest points of the peaks that face each other are located at both ends in a side view of the blade edge portion, lowest points of the valleys are located in a middle, the first areas form curved lines along first arcs having a center point on the punching axis and passing through the lowest points of the valleys, the second areas form curved lines along second arcs having center points located in areas between the punching axis and the highest points of the peaks, and the third areas form straight lines along common tangents to the first arcs and the second arcs. 
     In addition, an image forming apparatus according to another aspect of the present invention is provided with an image forming portion configured to perform an image formation process of forming an image on a sheet and the punching unit configured to punch a hole in a sheet that has undergone the image formation process. 
     In addition, a finishing device according to another aspect of the present invention is disposed adjacent to an image forming apparatus configured to form an image on a sheet. The finishing device is provided with a carry-in port configured to receive a sheet discharged from the image forming apparatus, the punching unit configured to punch a hole in the sheet, a carry-out port configured to discharge the sheet, and a discharge tray on which the sheet discharged from the carry-out port can be stacked. 
     Advantageous Effects of the Invention 
     The present invention can provide the punching blade, the punching unit, and the image forming apparatus capable of reducing loads in the punching process of punching holes in sheets and, furthermore, capable of reducing punching time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a cross-sectional view schematically showing an internal configuration of an image forming apparatus provided with a main image forming portion and a finishing device including a punching unit equipped with punching blades according to an embodiment of the present invention. 
         FIG.  2    is a perspective view of the punching unit. 
         FIG.  3    is a front view of a punching portion of the punching unit and shows a punching blade in a raised state. 
         FIG.  4    is a front view of the punching portion of the punching unit and shows the punching blade in a lowered state. 
         FIG.  5    is a perspective view of the punching blade. 
         FIG.  6    is a diagram showing the shape of a blade edge portion of the punching blade, in which  FIG.  6 A  is a plan view of the blade edge portion viewed from below and  FIG.  6 B  is a net showing the shape of the edge end of the blade edge portion. 
         FIG.  7    is an enlarged view of the blade edge portion of the punching blade. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following describes a punching blade according to an embodiment of the present invention, a punching unit provided with the punching blade, and an image forming apparatus with reference to the drawings. 
       FIG.  1    is a cross-sectional view schematically showing an internal configuration of an image forming apparatus  1 . The image forming apparatus  1  is provided with a main image forming portion  1   a  and a finishing device  5  including a punching unit  51  equipped with punching blades according to an embodiment of the present invention. The main image forming portion  1   a  shown in  FIG.  1    is a monochrome copier of a so-called “in-body discharge type”. However, the main image forming portion  1   a  may be a color copier, printer, a facsimile apparatus, or a multifunction peripheral equipped with those functions. 
     The image forming apparatus  1  includes the main image forming portion  1   a  and the finishing device  5 . The main image forming portion  1   a  performs an image formation process on sheets. The finishing device  5  is provided with a finishing portion that performs predetermined finishing processes on sheets or sheet stacks each including multiple sheets that have undergone the image formation process, and is disposed adjacent to the main image forming portion  1   a.  The finishing processes include a punching process of punching binding holes in sheets, a stapling process of inserting staples into sheet stacks, a folding process of folding sheets, and an alignment process of shifting sheets, aligning the widthwise edges of sheets, and the like. 
     The main image forming portion  1   a  is provided with a main portion housing  100 , an image reading portion  2   a  disposed in an upper part of the main portion housing  100 , and an automatic document feeder (ADF)  2   b  disposed on the upper surface of the image reading portion  2   a.  The main portion housing  100  houses a sheet feed portion  3   a,  a conveyance path  3   b,  an image forming portion  4   a,  a fixing portion  4   b,  and a sheet discharge portion  3   c . 
     The automatic document feeder  2   b  automatically feeds document sheets to be duplicated to a predetermined first document sheet reading position. The first document sheet reading position corresponds to a position at which a first contact glass  24  is assembled in the image reading portion  2   a.  In a case where document sheets are placed on a predetermined second document sheet reading position, the automatic document feeder  2   b  is lifted up from the upper surface of the image reading portion  2   a.  The second document sheet reading position corresponds to a position at which the second contact glass  25  is disposed in the image reading portion  2   a.  The automatic document feeder  2   b  includes a document sheet tray  21  on which document sheets are placed, a document sheet conveying portion  22  that conveys the document sheets through the first document sheet reading position, and a document sheet discharge tray  23  to which the read document sheets are discharged. 
     The image reading portion  2   a  includes a box-shaped housing, and the first contact glass  24  and the second contact glass  25  are fitted in the upper surface of the image reading portion  2   a.  The first contact glass  24  is used to read images on the document sheets automatically fed from the automatic document feeder  2   b.  The second contact glass  25  is used to read images on the manually placed document sheets. The image reading portion  2   a  optically reads the images on the document sheets. 
     The sheet feed portion  3   a  inside the main portion housing  100  includes multiple cassettes  31  ( 31 A,  31 B,  31 C, and  31 D). The cassettes  31  are respectively provided with sheet feed rollers  32  ( 32 A,  32 B,  32 C, and  32 D) that are rotationally driven. The sheet feed rollers  32  feed sheets to the conveyance path  3   b  one by one during the image formation process. 
     The conveyance path  3   b  is disposed inside the main portion housing  100 . The sheets are conveyed from the sheet feed portion  3   a  to an in-body discharge tray  33  or to the finishing device  5  along the conveyance path  3   b.  The conveyance path  3   b  is provided with guide plates for guiding the sheets, pairs of conveying rollers  34  ( 34 A,  34 B, and  34 C), and a pair of registration rollers  35 . The pairs of conveying rollers  34  are rotationally driven while the sheets are being conveyed. The pair of registration rollers  35  keeps the sheets that are being conveyed at a position before the image forming portion  4   a  and feeds the sheets in synchronization with transfer of formed toner images. 
     The image forming portion  4   a  creates toner images and transfers the toner images onto the sheets. That is, the image forming portion  4   a  forms images on the sheets. The image forming portion  4   a  includes a photoconductor drum  41  and other components including a charging unit  42 , an exposure unit  43 , a developing device  44 , a transfer roller  45 , and a cleaning device  46  disposed around the photoconductor drum  41 . 
     The photoconductor drum  41  includes a peripheral surface on which electrostatic latent images and toner images are formed as the photoconductor drum  41  rotates around its axis. The charging unit  42  uniformly charges the surface of the photoconductor drum  41 . 
     The exposure unit  43  includes a laser source and optical instruments such as mirrors and lenses. The exposure unit  43  emits a laser beam L based on image data about the images on the document sheets onto the peripheral surface of the photoconductor drum  41  to form the electrostatic latent images. The developing device  44  supplies toner to the peripheral surface of the photoconductor drum  41  to develop the electrostatic latent images formed on the photoconductor drum  41 . The transfer roller  45  forms a transfer nip portion between itself and the photoconductor drum  41  and receives a transfer bias. The toner images on the photoconductor drum  41  are transferred to the sheets passing through the transfer nip portion. The cleaning device  46  includes a cleaning roller and the like to clean the peripheral surface of the photoconductor drum  41  after the toner images are transferred. 
     The fixing portion  4   b  fixes the toner images transferred to the sheets. The fixing portion  4   b  includes a heating roller  47  with a built-in heating element and a pressure roller  48  in pressure contact with the heating roller  47 . The sheets with the toner images transferred thereto pass through a fixing nip formed by the heating roller  47  and the pressure roller  48 . This heats and fuses the toner to fix the toner images to the sheets. The sheets after the fixing process are sent to the sheet discharge portion  3   c.    
     The sheet discharge portion  3   c  includes a pair of outward discharge rollers  36 A and a pair of inward discharge rollers  36 B. The pair of outward discharge rollers  36 A feeds the sheets after the image formation to the finishing device  5 . The pair of inward discharge rollers  36 B feeds the sheets after the image formation to the in-body discharge tray  33 . The pairs of discharge rollers  36 A and  36 B are rotationally driven during a discharge operation to discharge the sheets to the exterior of the apparatus. In addition, the sheet discharge portion  3   c  includes a switch lever  37  that switches the conveying direction of the sheets. 
     The finishing device  5  includes a finishing device housing  500  disposed adjacent to the main portion housing  100  and the finishing portion disposed inside the finishing device housing  500 . In the present embodiment, the finishing portion is provided with the punching unit  51 , a stapling unit  52 , a folding unit  53 , and an alignment portion  57 . The punching unit  51 , the stapling unit  52 , and the alignment portion  57  are housed in an upper part of the finishing device housing  500 . The folding unit  53  is housed in a lower part of the finishing device housing  500 . 
     The finishing device housing  500  has a carry-in port  60  in a side face facing the main portion housing  100 . The sheets after the image formation process are taken into the finishing device housing  500  through the carry-in port  60 . The finishing device housing  500  has a main carry-out port  61  and a sub carry-out port  62  in a side face remote from the main portion housing  100 . The sheets are discharged from the finishing device housing  500  through these carry-out ports. A main discharge tray  54  corresponding to the main carry-out port  61  and a sub discharge tray  55  corresponding to the sub carry-out port  62  are attached to the finishing device housing  500 . In addition, the finishing device housing  500  is provided therein with a first conveyance route L 1 , a second conveyance route L 2 , a third conveyance route L 3 , a fourth conveyance route L 4 , a first merge point Q 1 , a first branch point B 1 , a second branch point B 2 , a third branch point B 3 , and a turnout drum  63 . 
     The first conveyance route L 1  is used to convey the sheets delivered through the carry-in port  60  to the main carry-out port  61 . The sheets discharged from the main carry-out port  61  is discharged to the main discharge tray  54 . 
     The third conveyance route L 3  branches off from the first conveyance route L 1  at the first branch point B 1 . The third conveyance route L 3  extends from the first branch point B 1  to the sub carry-out port  62 . The sheets discharged from the sub carry-out port  62  is discharged to the sub discharge tray  55 . 
     The second conveyance route L 2  branches off from the first conveyance route L 1  at the second branch point B 2 . The second conveyance route L 2  extends from the second branch point B 2  to the folding unit  53 . The fourth conveyance route L 4  branches off from the second conveyance route L 2  at the third branch point B 3 , curves along the perimeter of the turnout drum  63 , and merges with the first conveyance route L 1  at the first merge point Q 1 . 
     A first switch blade  64  is disposed at the first branch point B 1 . The first switch blade  64  keeps the sheets conveyed on the first conveyance route L 1  on the same first conveyance route L 1  or switches the destination of the sheets to the third conveyance route L 3 . A second switch blade  65  is disposed at the second branch point B 2 . The second switch blade  65  switches the destination of the sheets between the first conveyance route L 1  and the second conveyance route L 2 . 
     A pair of first conveying rollers  66  is disposed upstream of the first branch point B 1 . In addition, a pair of fourth conveying rollers  68  is disposed at the downstream end of the first conveyance route L 1  and adjacent to the main carry-out port  61 . Furthermore, a pair of second conveying rollers  69  is disposed on the first conveyance route L 1  upstream of the pair of fourth conveying rollers  68 . The sheets passing through the first conveyance route L 1  are conveyed from the carry-in port  60  to the main discharge tray  54  through the main carry-out port  61  by the pair of first conveying rollers  66 , the pair of second conveying rollers  69 , and the pair of fourth conveying rollers  68 . 
     A pair of third conveying rollers  67  is disposed at the downstream end of the third conveyance route L 3  and adjacent to the sub carry-out port  62 . The sheets conveyed on the third conveyance route L 3  are discharged to the sub discharge tray  55  by the pair of third conveying rollers  67 . 
     The punching unit  51  is disposed adjacent to the entrance of the first conveyance route L 1 . The punching unit  51  performs the punching process of punching binding holes on sheets at predetermined timings. The punching unit  51  punches the holes in the sheets at positions adjacent to the trailing edges in the conveying direction of the sheets. During the punching process, the sheets are temporarily stopped. The details of the punching unit  51  will be described later. 
     The stapling unit  52  performs the stapling process of inserting staples into sheet stacks each including multiple sheets. The stapling process here is a process for so-called edge binding in which the staples are inserted into the corners or edges of the sheet stacks. In a case where the stapling process is performed, the sheets are conveyed to a position adjacent to the main carry-out port  61  along the first conveyance route L 1  and then delivered onto a staple tray  521  while a conveyance nip portion of the pair of fourth conveying rollers  68  is released. Thus, the sheets are stacked on the staple tray  521 . The sheet stacks that have undergone the stapling process are taken out from the staple tray  521  to the main discharge tray  54  by the pair of fourth conveying rollers  68  of which the conveyance nip portion is recovered. 
     The folding unit  53  performs the folding process of folding the sheet stacks into two in the midsection in addition to middle binding of inserting staples into the midsection of the sheet stacks. The sheets that undergo the folding process are guided from the first conveyance route L 1  to the second conveyance route L 2  via the second branch point B 2  and delivered to the folding unit  53 . The sheet stacks that have undergone the folding process are discharged to a folded sheet discharge tray  56  disposed in the lower part of the finishing device housing  500 . It is noted that the folding unit  53  may perform only the folding process. 
     The alignment portion  57  performs the shifting operation or the alignment process. The shifting operation is an operation to shift sheets or sheet stacks in a sheet width direction orthogonal to the conveying direction of the sheets. The alignment process includes the edge alignment operation to align the widthwise edges of the sheet stacks. When the stapling unit  52  performs the stapling process, the alignment portion  57  performs the shifting operation or the edge alignment operation on the sheet stacks to set stapling positions. In addition, the alignment portion  57  may also operate without the stapling process. For example, the alignment portion  57  also operates in a case where the sheets are stacked on the main discharge tray  54  while undergoing offset discharge. The offset discharge is an operation to stack, for example, multiple sets of copies created from one group of multiple document sheets on the main discharge tray  54  while shifting the sets of the copies from one another in the sheet width direction. 
     The sheets or sheet stacks that have undergone the stapling process, the shifting operation, or the edge alignment operation are discharged from the main carry-out port  61  by the pair of fourth conveying rollers  68  and stacked on the main discharge tray  54 . The main discharge tray  54  gradually moves downward from the uppermost position as the discharged sheet stacks increase. Subsequently, after the sheet stacks are removed from the main discharge tray  54 , the main discharge tray  54  moves upward to return to the standard position. The sub discharge tray  55  receives the sheets discharged from the sub carry-out port  62  by the pair of third conveying rollers  67 . The sheets discharged without any specific finishing process by the finishing device  5  or the sheets that have undergone only the punching process are mainly stacked on the sub discharge tray  55 . 
     The turnout drum  63  has a peripheral surface and is rotationally driven in a predetermined rotation direction. In a case where multiple sheet stacks are successively stapled, the turnout drum  63  allows the first page of a sheet stack to be wrapped around the surface of the turnout drum  63  to wait for the stapling unit  52  to staple the previous sheet stack. The function of the turnout drum  63  eliminates the need for temporary halt of the delivery of the sheets from the main image forming portion  1   a  during the stapling process, thereby increasing the productivity. 
     Next, the punching unit  51  according to the present embodiment will be described in detail with reference to  FIGS.  2  to  4    in addition to  FIG.  1   .  FIG.  2    is a perspective view of the punching unit  51 . In addition,  FIGS.  3  and  4    are front views of a punching portion  51 A of the punching unit  51 .  FIG.  3    shows a punching blade  7  in a raised state, and  FIG.  4    shows the punching blade  7  in a lowered state. 
     A sheet S delivered to the finishing device  5  through the carry-in port  60  is conveyed on the first conveyance route L 1  to reach the punching unit  51 . The punching unit  51  includes the punching portion  51 A, detection portions  51 B, and a shifter  51 C. The punching portion  51 A performs the punching process of punching binding holes in the sheet S conveyed on the first conveyance route L 1 . The detection portions  51  B detect the positions of both side edges of the sheet S in a sheet width direction D 2  orthogonal to a conveying direction D 1  of the sheet S. The shifter  51 C shifts the punching portion  51 A and the detection portions  51 B in the sheet width direction D 2 . The punching portion  51 A and the detection portions  51 B are shiftable in the sheet width direction D 2  on a rail portion (not shown) provided for the finishing device housing  500 . 
     The punching portion  51 A is provided with the four punching blades  7 , raising and lowering mechanisms  7 M (moving mechanisms), guide members  8 , and a die member  9 . The four punching blades  7  are disposed at predetermined intervals in the sheet width direction D 2 . The raising and lowering mechanisms  7 M reciprocate (raise and lower) the respective punching blades  7  along punching axes  7 A. The guide members  8  guide the ascending and descending of the respective punching blades  7 . The punching blades  7 , the raising and lowering mechanisms  7 M, and the guide members  8  are supported by an upper guide frame  51 D. The die member  9  is supported by a lower guide frame  51 E to face the guide members  8  with the first conveyance route L 1  in between. 
     The upper guide frame  51 D is a frame member having a substantially U-shaped cross-section with an open top and extending in the sheet width direction D 2 . The lower guide frame  51 E is a frame member extending in the sheet width direction D 2 . The lower guide frame  51 E has a substantially U-shaped cross-section with an open bottom. The lower guide frame  51 E is provided with rollers  51 E 1  in a lower end part near either end in the sheet width direction D 2 . The rollers  51 E 1  can travel on the rail portion of the finishing device housing  500  in the sheet width direction D 2 . 
     The punching blades  7  include a punching blade  7   a  disposed on one side in the sheet width direction D 2 , a punching blade  7   b  on another side in the sheet width direction D 2 , and two punching blades  7   c  disposed between the punching blade  7   a  and the punching blade  7   c.  The punching blades  7  have a cylindrical shape extending in the respective punching axes  7 A. The distance between the punching axis  7 A of the punching blade  7   a  and the punching axis  7 A of the punching blade  7   b  is equal to the width of the sheet S. The details of the punching blades  7  will be described later. 
     Each of the guide members  8  has a cylindrical shape with a circular guide hole  81  through which the corresponding punching blade  7  can be placed. The guide member  8  guides the ascending and descending of the punching blade  7  placed through the guide hole  81 . The punching blade  7  is driven to ascend and descend along the punching axis  7 A by the corresponding raising and lowering mechanism  7 M (described later). The guide members  8  are provided for the respective punching blades  7 . Each of the guide members  8  is positioned on the upper guide frame  51 D such that the center of the guide hole  81  is located on the corresponding punching axis  7 A. 
     The die member  9  is a rectangular tube member extending in the sheet width direction D 2 . The die member  9  faces the guide members  8  with the first conveyance route L 1  in between. The die member  9  is shared among all the punching blades  7 . In the upper surface of the die member  9 , circular die holes  91  that allow the blade edge portions of the punching blades  7  to be fitted therein are formed to correspond to the respective punching blades  7 . The die member  9  is secured to the lower guide frame  51 E such that the center of each die hole  91  is located on the punching axis  7 A of the corresponding punching blade  7 . 
     The blade edge portions of the punching blades  7  descending as being guided to the guide holes  81  of the guide members  8  are inserted into the die holes  91  of the die member  9 . At this moment, the punching blades  7  and the hole edges of the die holes  91  punch binding holes in the sheet S conveyed on the first conveyance route L 1 . 
     The raising and lowering mechanisms  7 M are mechanisms that raise and lower the respective punching blades  7  along the punching axes  7 A. The raising and lowering mechanisms  7 M are provided for the respective punching blades  7 . Each of the raising and lowering mechanisms  7 M includes a support member  7 M 1  that supports the corresponding punching blade  7  and a cam  7 M 2  that engages with the support member  7 M 1 . The support member  7 M 1  is composed of a flat portion  7 M 1   a  extending in the sheet conveying direction D 1  and a curved portion  7 M 1   b  formed by bending a thin, flat piece into a substantially semicircular shape. The punching blade  7  is secured to the lower surface of the flat portion  7 M 1   a  in the vicinity of the middle in the sheet conveying direction D 1  to be substantially vertical. Both ends of the curved portion  7 M 1   b  are supported on the upper surface of the flat portion  7 M 1   a  at both ends in the sheet conveying direction D 1 . A hollow portion  7 M 1   c  having a substantially semicircular shape when viewed from front is formed between the flat portion  7 M 1   a  and the curved portion  7 M 1   b  of the support member  7 M 1 . 
     A coil spring  7 M 3  is placed between the support member  7 M 1  and the upper guide frame  51 D around the outer perimeter of the guide member  8 . The coil spring  7 M 3  biases the support member  7 M 1  upward. 
     The cam  7 M 2  of each raising and lowering mechanism  7 M has a flattened cylindrical shape and is supported by a rotation shaft  7 M 21  at a position eccentric to the axis center. The rotation shaft  7 M 21  passes through the hollow portions  7 M 1   c  of the support members  7 M 1 . The ends of the rotation shaft  7 M 21  in the sheet width direction D 2  are rotatably supported by a first side plate portion  51 D 1  and a second side plate portion  51 D 2 . The first side plate portion  51 D 1  and the second side plate portion  51 D 2  extend upward from the upper surface of the upper guide frame  51 D at the respective ends in the sheet width direction D 2 . 
     In addition, a coil spring  7 M 4  is placed between the first side plate portion  51 D 1  and one end of the rotation shaft  7 M 21  in the sheet width direction D 2 . The coil spring  7 M 4  biases the rotation shaft  7 M 21  to the one side in the sheet width direction D 2 . The rotation shaft  7 M 21  is movable in the axial direction by a solenoid (not shown). The rotation shaft  7 M 21  selectively engages the cams  7 M 2  with the support members  7 M 1  in the two raising and lowering mechanisms  7 M in the middle and in the two raising and lowering mechanisms  7 M at both ends in the sheet width direction D 2 . That is, when the cams  7 M 2  engage with the support members  7 M 1  in the two raising and lowering mechanisms  7 M at both ends, the cams  7 M 2  disengage from the support members  7 M 1  in the two raising and lowering mechanisms  7 M in the middle. This allows the two punching blades  7   a  and  7   b  at both ends in the sheet width direction D 2  to ascend and descend. On the other hand, when the cams  7 M 2  engage with the support members  7 M 1  in the two raising and lowering mechanisms  7 M in the middle, the cams  7 M 2  disengage from the support members  7 M 1  in the two raising and lowering mechanisms  7 M at both ends. This allows the two punching blades  7   c  in the middle in the sheet width direction D 2  to ascend and descend. As described above, in a normal condition, the rotation shaft  7 M 21  is biased by the coil spring  7 M 4  to the one side in the sheet width direction D 2 . This causes the cams  7 M 2  to engage with the support members  7 M 1  in the two raising and lowering mechanisms  7 M at both ends, allowing the two punching blades  7   a  and  7   b  at both ends in the sheet width direction D 2  to ascend and descend. When the solenoid is switched, the rotation shaft  7 M 21  moves to the other side in the sheet width direction D 2  against the biasing force of the coil spring  7 M 4 , and the cams  7 M 2  engage with the support members  7 M 1  in the two raising and lowering mechanisms  7 M in the middle. This allows the two punching blades  7   c  in the middle to ascend and descend. 
     Another end of the rotation shaft  7 M 4  in the sheet width direction is connected to the rotation shaft of a motor  7 M 5  with a gear train in between. When the motor  7 M 5  drives the rotation shaft  7 M 4 , the cams  7 M 2  rotate inside the hollow portions  7 M 1   c  of the support members  7 M 1 . At this moment, when cam surfaces  7 M 2 S of the cams  7 M 2  engage with the inner surfaces of the curved portions  7 M 1   b  of the support members  7 M 1 , the punching blades  7  are kept in the raised state (see  FIG.  3   ). In addition, when the cam surfaces  7 M 2 S of the cams  7 M 2  engage with the upper surfaces of the flat portions  7 M 1   a  of the support members  7 M 1 , the support members  7 M 1  are pushed downward against the biasing force of the coil springs  7 M 3  (see  FIG.  4   ). Thus, the punching blades  7  vertically descend as being guided by the guide holes  81  of the guide members  8 , and the blade edge portions of the punching blades  7  protruding toward the first conveyance route L 1  punch binding holes in the sheet S between the die holes  91  of the die member  9  and themselves. 
     In addition, a sensor  7 M 22  for detecting the home position, a rotary encoder  7 M 23  for controlling the rotational speed of the rotation shaft  7 M 21 , and the like are disposed at the other end of the rotation shaft  7 M 21  in the sheet width direction D 2 . 
     As shown in  FIG.  2   , the detection portions  51 B include a first detection portion  51 B 1  and a second detection portion  51 B 2 . The first detection portion  51 B 1  is disposed on the one side in the sheet width direction D 2  and upstream in the sheet conveying direction D 1  relative to the punching blade  7   a.  The second detection portion  51 B 2  is disposed on the other side in the sheet width direction D 2  and upstream in the sheet conveying direction D 1  relative to the punching blade  7   b.    
     For example, optical sensors may be adopted as the detection portions  51 B. Each of the optical sensors includes a light emitting portion and a light receiving portion facing each other. Either the light emitting portions or the light receiving portions are secured to the upper guide frame  51 D, and the others are secured to the lower guide frame  51 E. That is, the detection portions  51 B are integral to the punching portion  51 A. When the sheet S lies between the light emitting portions and the corresponding light receiving portions, the optical paths of light emitted from the light emitting portions are blocked, and the amounts of light received by the light receiving portions change. The detection portions  51 B detect the side edges of the sheet S in the sheet width direction D 2  based on the change in the amounts of light. 
     The shifter  51 C is disposed on the other side in the sheet width direction D 2  relative to the punching portion  51 A. The shifter  51 C includes a drive mechanism  51 C 1  composed of a rack and pinion gear and a motor  51 C 2  that rotates the pinion gear. The rack is disposed on the lower surface of the lower guide frame  51 E to extend in the sheet width direction D 2 . The pinion gear is connected to the rotation shaft of the motor  51 C 2 , and the motor  51 C 2  is attached to a support plate  51 E 2 . When the pinion gear is rotated by the motor  51 C 2 , the punching portion  51 A and the detection portions  51 B reciprocate with the rack meshing with the pinion gear. At this moment, the punching portion  51 A and the detection portions  51 B reciprocate in the sheet width direction D 2  between a first punching position and a second punching position with the standard position in the middle. 
     Next, the punching blades  7  will be described in detail with reference to  FIGS.  5  to  7    in addition to  FIGS.  3  and  4   .  FIG.  5    is a perspective view of one of the punching blades  7 .  FIG.  6    is a diagram showing the shape of a blade edge portion  72  of the punching blade  7 .  FIG.  7    is an enlarged view of the blade edge portion  72  of the punching blade  7 . It is noted that  FIG.  6 A  is a plan view of the blade edge portion  72  viewed from below and that  FIG.  6 B  is a net showing the shape of the edge end of the blade edge portion  72 . 
     The punching blade  7  is provided with a body portion  71  and the blade edge portion  72  formed at one end of the body portion  71 . The body portion  71  has a cylindrical shape extending along the punching axis  7 A. The blade edge portion  72  includes multiple peaks  721  and multiple valleys  722  formed alternately in the circumferential direction. The body portion  71  and the blade edge portion  72  are integral to each other, and the punching blade  7  as a whole has a cylindrical shape extending along the punching axis  7 A serving as the central axis passing through the center of the punching blade  7 . In the present embodiment, as shown in  FIGS.  5  and  6 A , the blade edge portion  72  includes two peaks  721  facing each other and two valleys  722  facing each other. In the blade edge portion  72  having the above-described configuration, the peaks  721  and the valleys  722  are alternately arranged every 90 degrees in the circumferential direction. That is, as the net in  FIG.  6 B  shows, the edge end of the blade edge portion  72  has a waveform having, in a case where the lowest point  7221  of one of the valleys  722  is located at 0 degrees in the circumferential direction, the highest point  7211  of one of the peaks  721  located at 90 degrees, the lowest point  7221  of the other valley  722  located at 180 degrees, and the highest point  7211  of the other peak  721  located at 270 degrees. 
     In the blade edge portion  72 , the peaks  721  protrude the most to one side (downward) in the axial direction of the punching axis  7 A. The peaks  721  serve as the starting point of the punching process in which the punching blade  7  punches a binding hole in the sheet S. The peaks  721  penetrate the sheet S during the punching process by the punching blade  7 . In the blade edge portion  72 , the valleys  722  are recessed the most to another side (upward) in the axial direction of the punching axis  7 A. The valleys  722  serve as the ending point of the punching process by the punching blade  7 . The valleys  722  cut through the sheet S during the punching process by the punching blade  7 . 
     The edge end of the blade edge portion  72  forms a blade edge line  73  having first areas  731 , second areas  732 , and third areas  733 . The first areas  731  are areas corresponding to the valleys  722 . The second areas  732  extend from the peaks  721  to the valleys  722 . The second areas  732  are areas corresponding to the peaks  721 . The third areas  733  connect the first areas  731  and the second areas  732 . As shown in  FIG.  7    in which the blade edge portion  72  is viewed from the side, in a case where the highest points  7211  of the two peaks  721  facing each other are located at both ends, the lowest points  7221  of the two valleys  722  are located in the middle. The first areas  731  form curved lines along first arcs  741  having a center point  7411  on the punching axis  7 A and passing through the lowest points  7221  of the valleys  722 . The second areas  732  form curved lines along second arcs  742  having center points  7421  located in areas between the punching axis  7 A and the highest points  7211  of the peaks  721  in the second areas  732 . The third areas  733  form straight lines along common tangents to the first arcs  741  and the second arcs  742 . 
     When the punching blade  7  provided with the blade edge portion  72  having the above-described configuration punches a binding hole in the sheet S, the peaks  721  penetrate the sheet S first, the curved parts in the second areas  732  and the straight parts in the third areas  733  in the blade edge line  73  of the blade edge portion  72  tear the sheet S, and then the entire faces of the valleys  722  including the curved parts in the first areas  731  cut through the sheet S. Here, the punching blade  7  provided with the blade edge portion  72  having the above-described configuration is compared with an inverted V-shaped blade. The inverted V-shaped blade is a punching blade having an inverted V-shaped blade edge line when viewed from the side. It is noted that the length of sections between the peaks  721  and the valleys  722  in the blade edge portion  72  having the above-described configuration in a direction along the punching axis  7 A is assumed to be equal to the length of sections between the peaks and the valleys in the inverted V-shaped blade in the direction along the punching axis  7 A. In this case, the peaks  721  of the blade edge portion  72  having the above-described configuration are sharper than the peaks in the inverted V-shaped blade and have higher penetrability into the sheet S. In addition, the valleys  722  of the blade edge portion  72  are gently curved compared with the valleys in the inverted V-shaped blade, and thereby the entire faces of the valleys  722  demonstrate higher performance in cutting through the sheet S. Accordingly, in the punching blade  7  provided with the blade edge portion  72  having the above-described configuration, the blade edge portion  72  can punch a binding hole in the sheet S smoothly along the blade edge line  73  between when the peaks  721  penetrate the sheet S and when the valleys  722  cut through the sheet S. As a result, loads in the punching process by the punching blade  7  can be reduced. Furthermore, loads on the motor  7 M 5  in the raising and lowering mechanisms  7 M that reciprocate the punching blades  7  can be reduced. Accordingly, noise such as operating noise and vibrating noise generated as the motor  7 M 5  is driven can be eliminated or minimized. In addition, small motors can be adopted as the motor  7 M 5 , leading to a reduction in the size of the punching unit  51 . 
     In addition, the center points  7421  of the second arcs  742  formed by the second areas  732  extending from the peaks  721  to the valleys  722  in the blade edge line  73  of the blade edge portion  72  are not on the punching axis  7 A, that is, off the punching axis  7 A. On the other hand, in a known technique, the centers of arcs corresponding to the peaks  721  are on the punching axis  7 A. In a case where the punching blade  7  is adopted, the length of the sections between the peaks  721  and the valleys  722  in the direction along the punching axis  7 A can be reduced compared with a case where the known technique is adopted. As a result, time for the punching process by the punching blade  7  can be reduced. 
     Furthermore, in the side view of the blade edge portion  72  in the punching blade  7  of the present embodiment, in the case where the highest points  7211  of the two peaks  721  facing each other are located at both ends, the lowest points  7221  of the two valleys  722  are located in the middle, and the blade edge line  73  is symmetric about the punching axis  7 A. In this case, when the punching blade  7  punches a binding hole in the sheet S, regions on the blade edge line  73  brought into contact with the sheet S are symmetric about the punching axis  7 A in the side view of the blade edge portion  72 . Thus, the blade edge portion  72  can cut through the sheet S along the blade edge line  73  evenly in directions orthogonal to the punching axis  7 A. As a result, a binding hole can be smoothly punched in the sheet S. 
     Furthermore, in the punching blade  7  of the present embodiment, the center point  7411  of the first arcs  741  is closer to the lowest points  7221  of the valleys  722  than the center points  7421  of the second arcs  742  in the direction along the punching axis  7 A, and the radius  7412  of the first arcs  741  is smaller than the radius  7422  of the second arcs  742 . This improves the performance of the valleys  722  in cutting through the sheet S.