Patent Publication Number: US-2012027428-A1

Title: Sheet finisher, image forming apparatus and sheet finishing method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from: U.S. provisional application 61/368,591 filed on Jul. 28, 2010, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     The invention relates to a sheet finisher, an image forming apparatus, and a sheet finishing method. 
     BACKGROUND 
     Conventionally, a sheet finisher is known which is disposed on the downstream side of an image forming apparatus such as a copier, a printer, or a multi-functional peripheral (MFP) device and which performs finishing such as hole punching or binding with regard to a sheet which has been printed on. 
     Recently, the functions of the sheet finisher have become varied and a sheet finisher has been proposed which has a saddle-stitching function with which a sheet is folded in the center portion of the sheet after the center portion has been stapled, in addition to the functions of hole opening or binding. 
     In the sheet finisher which has the saddle-stitching function, it is possible to form a booklet (manufacture a book) from a plurality of printed sheets. 
     In the saddle-stitching process in the past, after binding by stapling or the like in the center portion of the sheet, a fold line is formed in a binding portion by a pair of rollers called fold rollers. A fold line is formed in a sheet bundle by a member with a plate shape which is called a fold blade being brought into contact with the binding portion of the sheet bundle and pressed into a nip portion of the pair of fold rollers. 
     However, since there is only a short time for pressing the fold portion of the sheet bundle using the nip portion of the fold rollers and the entire fold portion is simultaneously pressed by the fold rollers, pressure is dispersed on the entire fold. As a result, sufficient pressure is not necessarily applied to the fold line. In particular, the fold line is often incomplete when the number of sheets is large or when a thick sheet is included in the sheet bundle. 
     In order to solve the problem, a fold reinforcing device is known which reinforces the fold line by nipping the fold line pushed out from the fold rollers in a nip portion of a pair of fold reinforcing rollers and moving the pair of reinforcing rollers along the folding line while pressing the fold line. 
     When there is a paper jam during movement of the reinforcing rollers due to any cause, the reinforcing rollers stop in a state where pressure is applied to the fold line. The sheet bundle which has caused the paper jam stays in a position which is not normally visually identifiable from the outside. In addition, since a high pressure by the reinforcing rollers is applied to the sheet bundle, it is not easy to remove the jammed sheet bundle. 
     Thus, a sheet finisher, an image forming apparatus, and a sheet finishing method are desired which make it possible to easily remove the sheet bundle from inside the sheet finisher even when such paper jam occurs. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective diagram illustrating an example of an outer appearance of an image forming apparatus according to an embodiment of the invention. 
         FIG. 2  is a cross-sectional diagram illustrating a configuration example of an image forming apparatus according to an embodiment of the invention. 
         FIG. 3  is a cross-sectional diagram illustrating a configuration example of a saddle stitching unit. 
         FIG. 4  is a perspective diagram illustrating an outer appearance of an entire configuration of a fold reinforcing unit. 
         FIGS. 5A and 5B  are schematic cross-sectional diagrams mainly describing a configuration of a support unit. 
         FIG. 6  is a perspective diagram illustrating an outer appearance of a configuration example of a roller unit. 
         FIG. 7  is a diagram of the fold reinforcing unit viewed from where a sheet bundle has been sent. 
         FIG. 8  is a first diagram describing up-and-down driving mechanism of an upper roller. 
         FIG. 9  is a second diagram describing the up-and-down driving mechanism of the upper roller. 
         FIG. 10  is a first diagram describing a first jam release mechanism. 
         FIGS. 11A and 11B  are second diagrams describing the first jam release mechanism. 
         FIGS. 12A and 12B  are third diagrams describing the first jam release mechanism. 
         FIGS. 13A and 13B  are first diagrams describing a second jam release mechanism. 
         FIG. 14  is a second diagram describing the second jam release mechanism. 
         FIGS. 15A and 15B  are third diagrams describing the second jam release mechanism. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of a sheet finisher, an image forming apparatus, and a sheet finishing method will be described with reference to the attached diagrams. 
     The sheet finisher according to the embodiment is provided with a fold roller which folds the center of a sheet bundle and forms a fold line in the sheet bundle; a roller unit which is provided with an upper roller and a lower roller and which moves the upper roller and the lower roller along a fold line direction, while nipping and pressing the fold line by the upper roller and the lower roller to reinforce the fold line; and a jam release handle which separates the upper roller and the lower roller in a thickness direction of the sheet bundle and weakens or removes pressure between the upper roller and the lower roller when the upper roller and the lower roller stops in a state of pressing the fold line. 
     (1) Configuration 
       FIG. 1  is a perspective diagram illustrating an outer appearance of a basic configuration of an image forming apparatus  10  according to an embodiment. The image forming apparatus  10  is configured by being provided with a read-out unit  11  which reads out an original document, an image forming unit  12  which prints out image data of the read-out original document onto a sheet using an electrophotographic method, a sheet finisher  20  which performs finishing such as sorting, hole opening, folding, and saddle stitching in regard to a sheet which has been printed. In addition, the image forming unit  12  is provided with an operation unit  9  for a user to perform various operations. 
       FIG. 2  is a cross-sectional diagram illustrating a detailed configuration example of the image forming apparatus  10 . 
     The image forming unit  12  of the image forming apparatus  10  has a photoconductor drum  1  in the vicinity of a center portion, and a charging unit  2 , an exposure unit  3 , a development unit  4 , a transfer unit  5 A, a charge removing unit  5 B, a separating claw  5 C, and a cleaning unit  6  are each provided in the vicinity of the photoconductor drum  1 . In addition, a transfer unit  8  is provided on the downstream side of the charge removing unit  5 B. Image forming is performed as in the sequence outlined next using each of these units. 
     First, uniform charging is performed on the surface of the photoconductor drum  1  using the charging unit  2 . On the other hand, the original document which is readout at the read-out unit  11  is converted to image data and the image data is input into the exposure unit  3 . In the exposure unit  3 , a laser beam is radiated onto the photoconductor drum  1  according to the level of the image data and an electrostatic latent image is formed on the photoconductor drum  1 . The electrostatic latent image is developed using toner supplied from the development unit  4  and a toner image is formed on the photoconductor drum  1 . 
     On the other hand, a sheet accommodated in a sheet accommodation unit  7  is transported to a transfer position (gap between the photoconductor drum  1  and the transfer unit  5 A) by several transport rollers. At the transfer position, the toner image is transferred from the photoconductor drum  1  to the sheet by the transfer unit  5 A. The electric charge on the surface is erased by the charge removing unit  5 B, and the sheet on which the toner image has been transferred is separated from the photoconductor drum  1  by the separating claw  5 C. After that, the sheet is transported by an intermediate transport unit  7 B and is heated and pressed by a fixing unit  8 , so that the toner image is fixed to the sheet. The sheet which has been subjected to the fixing is discharged from a discharge unit  7 C and is outputted to the sheet finisher  20 . 
     Developing agent which remains on the surface of the photoconductor drum  1  is removed by the cleaning unit  6  at the downstream side of the separating claw  5 C, and preparation is performed for next image formation. 
     Here, when double-sided printing is performed, the sheet which has had the toner image fixed to its surface is branched off from the normal discharge path by a transport path switching plate  7 D, is switched back at a reverse transport unit  7 E, and is turned inside-out. Printing in the same manner as the single sided printing is performed on the back surface of the reversed sheet, and the sheet is output from the discharge unit  7 C to the sheet finisher  20 . 
     The sheet finisher  20  has a saddle stitching unit  30  and a sheet bundle placement unit  40  in addition to a sorter unit (not shown) which performs sorting of the sheets. 
     The saddle stitching unit  30  performs a process (binding) in which a center portion of a plurality of sheets which has been printed upon and discharged from the image forming unit  12  is bound with staples, and then, folding is performed to form a booklet. 
     The booklet which is subject to binding by the saddle stitching unit  30  is output to the sheet bundle placement unit  40 , and the made booklet is finally arranged. 
       FIG. 3  is a cross-sectional diagram illustrating a detailed configuration example of the saddle stitching unit  30 . 
     In the saddle stitching unit  30 , the sheet discharged from the discharge unit  7 C of the image forming unit  12  is received by a pair of input rollers  31  and is delivered to a pair of intermediate rollers  32 . The pair of intermediate rollers  32  further delivers the sheet to a pair of output rollers  33 . The pair of output rollers  33  sends the sheet to a standing tray  34  with an inclined placement surface. The leading edge of the sheet is directed to the upper portion of the inclination of the standing tray  34 . 
     A stacker  35  waits below the standing tray  34 , and receives the lower edge of the sheet which has been switched back and has fallen from the upper part of the inclination of the standing tray  34 . 
     A stapler  36  is provided at substantially the middle of the standing tray  34 . When binding (stapling) is performed on the sheet bundle, the position of the stacker  35  is adjusted so that the position of the sheet bundle which is to be stapled (the center of the sheet bundle in the up-and-down direction) faces the stapler  36 . 
     When the sheet bundle is bound by the stapler  34 , next, the stacker  35  is lowered until the position of the sheet bundle, where a fold line is to be formed (the center of the sheet bundle in the up-and-down direction and the position where the staples have been inserted), is in front of a fold blade  37 . 
     When the position where the fold line is to be formed is in front of the fold blade  37 , a leading edge  37 a of the fold blade  37  pushes a surface which becomes an inner surface after the sheet bundle is folded. 
     A pair of fold rollers  38  is provided ahead of the movement direction of the fold blade  37 . The sheet bundle pushed by the fold blade  37  is rolled into a nip portion of the pair of fold rollers  38 , and the fold line is formed at the center portion of the sheet bundle. 
     The sheet bundle where the fold line has been formed by the pair of fold rollers  38  is transported to a fold reinforcing unit  50  provided at the downstream side thereof. The transportation of the sheet bundle transported to the fold reinforcing unit  50  is temporarily stopped there. 
     The fold reinforcing unit  50  is provided with reinforcing rollers  51  formed from a pair of rollers of an upper roller  51   a  and a lower roller  51   b . The reinforcing rollers  51  move in the direction which is perpendicular to the transport direction of the sheet bundle (direction along the line of the fold line) while pressing the fold line and reinforce the fold line. 
     The sheet bundle, whose fold line has been reinforced by the reinforcing rollers  51  starts to be transported again, is pulled by a pair of discharge rollers  39 , and is output to the sheet bundle placement unit  40 . The sheet bundle (booklet) subjected to binding is placed on the sheet bundle placement unit  40 . 
     (2) Configuration and Operation of Fold Reinforcing Unit 
       FIG. 4  is a perspective diagram illustrating an outer appearance of an entire configuration of the fold reinforcing unit (excluding the pair of discharge rollers  39 ). The fold reinforcing unit  50  includes a fold reinforcing roller unit  60  (simply referred to below as a roller unit  60 ), a support unit  70  and a drive unit  80 . 
     The roller unit  60  has the reinforcing rollers  51 , and the reinforcing rollers  51  nip and press the fold line of the sheet bundle pushed out from the pair of fold rollers  38  which are upstream and reinforce the fold line by moving along the fold line. 
     The support unit  70  supports the roller unit  60  so that the roller unit  60  is able to slide in the fold line direction and is configured from a member which nips the sheet bundle, a structural member of the entire fold reinforcing unit  50 , and the like. 
     The drive unit  80  has a drive motor  81  and drives the roller unit  60  along the fold line using the drive motor  81 . 
     Out of the roller unit  60 , the support unit  70  and the drive unit  80 , the structure of the support unit  70  will be described first using  FIGS. 4 ,  5 A, and  5 B.  FIGS. 5A and 5B  are schematic cross-sectional diagrams mainly describing a configuration of the support unit  70 .  FIG. 5A  is a cross-sectional diagram when the roller unit  60  is at a home position (standby position: position at the left end of  FIG. 4 ), and  FIG. 5B  is a cross-sectional diagram when the roller unit  60  is moving (reinforcing the fold line). 
     The support unit  70  includes a frame  71  (inner housing and fixing frame), and the frame  71  is configured by a top plate  711 , right and left side plates  712   a  and  712   b , a bottom plate  713 , a back plate  714 , a sheet bundle placement table  715  (see  FIGS. 5A ,  5 B, and the like), and the like. 
     The top plate  711  is provided with a support hole  711   a  which extends in the longitudinal direction thereof. 
     In addition, a support shaft  75  which supports the roller unit  60 , a transport guide  72  with an cross-section surface with an L shape, a drive shaft  76  (see  FIGS. 5A ,  5 B, and the like) for driving the transport guide  72  in the up-and-down direction and the like are provided between the both side plates  712   a  and  712   b.    
     A flexible member  73  with a strip shape, which is formed by a resin member such as polyethylene terephthalate (PET) in a film form, extends from a bottom plate  72   a  of the transport guide  72 . A similar flexible member  74  also extends from the sheet placement table  715 . 
     As shown in  FIGS. 5A and 5B , a fold line  100   a  of a sheet bundle  100  is nipped between the flexible members  73  and  74  and is pressed by the pair of reinforcing rollers  51  (the upper roller  51   a  and the lower roller  51   b ) through the flexible members  73  and  74 , and the fold line is reinforced. Damage or wrinkles in the fold line and in the vicinity thereof is prevented by using the flexible members  73  and  74 . 
     Here, incisions  73   a  and  74   b  are provided at the leading ends of the flexible members  73  and  74 . The incisions  73   a  and  74   b  are provided at positions corresponding to positions of staples on the fold line and prevent the flexible members  73  and  74  from being damaged by the staples. 
     A through hole  61  through which the support shaft  75  passes is provided in the lower portion of the roller unit  60 . In addition, a support roller  62  for maintaining positioning is provided in the upper portion of the roller unit  60  and the support roller  62  moves along the support hole  711   a  provided in the top plate  711 . 
     The position (excluding changing positions in the movement direction) and the positioning in the three axial directions of the roller unit  60  are regulated by the support shaft  75  and the through hole  61  described above, and the support hole  711   a  and the support roller  62 , and the movement of the roller unit  60  is also kept constant. 
     Next, the configuration of the roller unit  60  will be described. 
       FIG. 6  is a perspective diagram illustrating an outer appearance of a configuration example of the roller unit  60  and is a diagram viewed in the direction the sheet bundle has been sent (opposite direction to  FIG. 4 ). 
     The roller unit  60  is a unit with the pair of reinforcing rollers  51 , and has a unit support section  63  provided with the through hole  61  and positioned at a lower part thereof and a unit frame  67  fixed to the upper part of the unit support section  63 . 
     In the unit frame  67 , an upper frame  67   a  which has a hollow section and a lower frame  67   b  which similarly has a hollow section are fixed and coupled by a frame plate  67   c.    
     In addition, the roller unit  60  has an upper link member  65  and a lower link member  66 , which are both spring coupled by a spring  68 . One end of the spring  68  is engaged with a hook hole  65   b  of the upper link member  65  and the other end of the spring  68  is engaged with an incision  66   b  in the lower link member  66 . The spring  68  is shown in  FIG. 6  in a free state where the other end of the spring  68  is released from the incision  66   b , but in a state where the other end of the spring  68  is actually engaged with the incision  66   b , the pulling force of the spring  68  is applied between the upper link member  65  and the lower link member  66 . 
     The lower roller  51   b  which is one of the pair of reinforcing rollers  51  is accommodated in the hollow section of the lower frame  67   b . The lower roller  51   b  is pivotally-supported so as to be able to freely rotate around a lower roller shaft (not shown) fixed to the lower frame  67   b.    
     On the side of the lower frame  67   b , the lower link member  66  is coupled so as to be rotatable via a lower link shaft  66   a  (see  FIG. 4 ) fixed to the lower frame  67   b.    
     The upper roller  51   a  which is one of the pair of reinforcing rollers  51  is accommodated in the hollow section of the upper frame  67   a . The upper roller  51   a  is pivotally supported so as to be able to freely rotate around an upper roller shaft (not shown) fixed to the upper link member  65  (and not the upper frame  67   a ). 
     The rotation shaft (lower roller shaft) of the lower roller  51   b  is fixed to the lower frame  67   b  (that is, fixed to the unit frame  67 ), and even if the roller unit  60  moves, the position of the lower roller  51   b  does not change in the up-and-down direction. The position of the upper end of the lower roller  51   b  is adjusted to be the same as the position of the flexible member  74 , and when the roller unit  60  moves, the lower roller  51   b  rotates while coming in contact with the lower surface of the flexible member  74 . 
     On the other hand, the upper roller shaft of the roller  51   a  is fixed to the upper link member  65 . When the roller unit  60  separates from the home position and starts to move, the upper link member  65  is pulled by the spring  68  and starts to rotate downward around the upper link shaft  65   a . Due to this rotation, the upper roller  51   a , which is attached to the upper link member  65  so as to be rotatable, starts to be lowered and moves to a position where the upper roller  51   a  comes in contact with the lower roller  51   b . A pressing force caused by the pulling force of the spring  68  mutually operates between the upper roller  51   a  and the lower roller  51   b . In practice, since the sheet bundle is nipped between the upper roller  51   a  and the lower roller  51   b  through the flexible members  73  and  74 , the fold line of the sheet bundle is reinforced by the pressing force between the upper roller  51   a  and the lower roller  51   b.    
       FIG. 7  is a diagram illustrating the positional relationship of the drive unit  80 .  FIG. 7  is a diagram viewing in the direction where the sheet bundle has been sent from the sheet bundle is to be sent, and also shows the roller unit  60  at the home position, the pair of fold rollers  38  and the drive mechanism of the pair of fold rollers  38 . In addition, illustration of the structural members of the support unit  70  is partially omitted for convenience of description. 
     The drive unit  80  has the drive motor  81  and a row of gears in a portion encompassed by the dashed line in  FIG. 7 . The drive motor  81  is a DC motor, and it is possible for the rotation direction and rotation speed to be controlled from the outside. 
     The drive force due to the drive motor  81  is transmitted to a drive side gear pulley  86   a  via the row of gears. On the other hand, a unit drive belt  87  is stretched between the drive side gear pulley  86   a  and a driven side pulley  86   b . The unit drive belt  87  moves between the drive side pulley  86   a  and the driven side pulley  86   b  using the drive force due to the drive motor  81 . 
     A rack is formed on the surface of the unit drive belt  87 , and due to the engagement of the rack and teeth of a fastening unit  63   a  (refer to  FIG. 6 ) provided at the lower part of the roller unit  60 , it is possible for the roller unit  60  to be reliably moved without sliding in the fold line direction. The movement direction of the unit drive belt  87  is able to be changed by reversing the rotation direction of the drive motor  81  and it is possible to move the roller unit  60  back and forward. 
     In the fold reinforcing unit  50 , other than movement in the fold line direction of the roller unit  60 , up-and-down driving of the upper roller  51   a  at an inner portion of the roller unit  60  and up-and-down driving of the transport guide  72  are performed and the drive source for both of the up-and-down driving is the driving motor  81 . That is, the drive operation in the fold reinforcing unit  50  is all performed in total by the single drive motor  81 . 
     A home position sensor  89 , which detects the separation of the roller unit  60  from the home position and the return of the roller unit  60  to the home position is also shown in  FIG. 7 . 
       FIGS. 8 and 9  are diagrams describing up-and-down driving mechanism of the upper roller  51   a . As described above, the upper link member  65  and the lower link member  66  of the roller unit  60  is spring coupled by the spring  68  in a position farthest from each of the rotation shafts ( 65   a  and  66   a ). In addition, a guide roller  66   c  (refer to  FIG. 4 ) is provided so as to be able to freely rotate in the lower link member  66 . That is, the lower link member  66  supports the guide roller  66   c  so as to be able to rotate between the rotation shaft  66   a  at one end thereof and the incision  66   b  at another end thereof (where the lower end of the spring  68  is engaged). 
     On the other hand, the support unit  70  has a guide rail  77  as shown in  FIGS. 8 and 9 . The guide rail  77  has a slope portion  77   a  which is inclined in the vicinity of the home position, and except for the slope portion  77   a , the guide rail  77  is parallel to the fold line direction of the sheet bundle, i.e., horizontal. 
     When the roller unit  60  is driven by the drive belt  87  and is separated from the home position, and in time, the guide roller  66   c  comes into contact with the bottom surface of the slope portion  77   a  of the guide rail  77 . After that, as shown in the second diagram from the left of  FIG. 9 , the guide roller  66   c  is lowered along the bottom surface of the slope portion  77   a . As the guide roller  66   c  is lowered, the lower link member  66  rotates centered around the lower link shaft  66   a  in the counterclockwise direction of  FIG. 9 . In addition, the upper link member  65  is also pulled by the spring  68  and rotates centered around the upper link shaft  65   b  in the counterclockwise direction. As a result, the upper roller  51   a  between the upper link shaft  65   a  and the hook hole  65   b  of the spring  68  is gradually lowered while the roller unit  60  moves the slope portion  77   a , and the gap between the upper roller  51   a  and the lower roller  51   b  is gradually narrowed. Then, the upper roller  51   a  and the lower roller  51   b  come in contact with each other in the vicinity of an area where the slope portion  77   a  ends. At this time, pressure (pushing force) acts between the upper roller  51   a  and the lower roller  51   b  which push against each other. The pushing force is based on the pulling force of the spring  68 . 
     In a horizontal area (that is, the effective drive area) of the guide rail  77 , the upper roller  51   a  and the lower roller  51   b  apply pressure to the fold line of the sheet bundle and reinforce the fold line while keeping the pushing force. 
     (3) Paper Jam Release Mechanism 
     If a paper jam occurs during fold reinforcing due to any cause, the fold reinforcing rollers  51  stop in a state where the fold line of the sheet bundle is being nipped. In this situation, it is necessary to remove the sheet bundle, that is, perform a paper jam release. 
     The sheet finisher  20  according to the embodiment has two paper jam release mechanisms described below, and it is possible to easily remove the sheet bundle which has caused the paper jam using the following two paper jam release mechanisms. 
     The first paper jam release mechanism makes access of a user easy with regard to the sheet bundle which has caused the paper jam. The second paper jam release mechanism is a mechanism which makes the removal of the sheet bundle easy by weakening or removing the pressure of the fold reinforcing rollers which are nipping the sheet bundle. 
     (4) First Paper Jam Release Mechanism 
     First, the first paper jam release mechanism will be described using  FIGS. 10 ,  11 A,  11 B,  12 A and  12 B. 
     As shown in  FIG. 10 , the saddle stitching unit  30  of the sheet finisher  20  has an external housing  300  and an internal housing  500 . The external housing  300  mainly accommodates the unit which performs the center folding such as the standing tray  34 , the stapler  36 , and the pair of fold rollers  38 . 
     On the other hand, the internal housing  500  accommodates the unit of the roller unit  60  and the like which is mainly related to fold reinforcing. 
     The internal housing  500  has support shafts  302   a  and  302   b  in a lower portion thereof on a front side and rear side, respectively. The internal housing  500  is pivotally supported so as to be able to rotate freely with the external housing  300  due to the support shafts  302   a  and  302   b . In  FIG. 10 , only a support shaft  302   a  on the front side can be seen. 
     In addition, the internal housing  500  has engaging rods  501   a  and  501   b , jam release handles  502   a  and  502   b , and fixed handles  503   a  and  503   b  in an upper portion of both sides. During normal driving, the engaging rods  501   a  and  501   b  are inserted in elongated holes  301   a  and  301   b  which are formed on both sides of the external housing  300 , that is, during normal driving, the internal housing  500  engages with the external housing  300  using the engaging rods  501   a  and  501   b  and the elongated holes  301   a  and  301   b.    
     On the other hand, when a paper jam occurs, the engagement of the external housing  300  and the internal housing  500  is manually released and it is possible to open the internal housing  500  around the support shafts  302   a  and  302   b  in a discharging direction of the sheet bundle. 
       FIG. 11A  is a diagram illustrating the configuration of the engaging rod  501   b  on the rear side and the vicinity thereof.  FIG. 11A  shows a state (during normal driving) when the internal housing  500  (that is, the fold reinforcing unit  50 ) is accommodated in the external housing  300 . As shown in  FIG. 11A  (also refer to  FIG. 10 ), one end of the engaging rod  501   b  is connected and fixed to the jam release handle  502   b  while the other end of the engaging rod  501   b  is inserted in the elongated hole  301   b  of the external housing  300 . In addition, the fixed handle  503   b  is provided adjacent to the jam release handle  502   b . The jam release handle  502   b  is configured to be able to move in a rear-and-front direction (that is, the fold line direction of the sheet bundle) along with the engaging rod  501   b . That is, the jam release handle  502   b  and the engaging rod  501   b  are able to slide in the rear-and-front direction with regard to the internal housing  500 . On the other hand, the fixed handle  503   b  is fixed with regard to the internal housing  500 . The rod  501   a , the jam release handle  502   a , and the fixed handle  503   a  on the front side have the same configuration. 
     Releasing a paper jam, as shown in  FIG. 11B , for example, the jam release handle  502   b  and the fixed handle  503   b  on the rear side are pinched by a thumb and an index finger of a left hand, and the jam release handle  502   a  and the fixed handle  503   a  on the front side are pinched by a thumb and an index finger of a right hand. Then, by the jam release handles  502   a  and  502   b  being each moved to the inner side and the engaging rods  501   a  and  501   b  being extracted from the elongated holes  301   a  and  301   b  of the external housing  300 , the engagement of the internal housing  500  and the external housing  300  is released. After that, by the jam release handles  502   a  and  502   b  and the fixed handles  503   a  and  503   b  being pinched with both hands while being pulled downwards toward the front, it is possible to open down the internal housing  500  (that is, the fold reinforcing unit  50 ) toward the outside. 
       FIGS. 12A and 12B  are schematic cross-sectional diagrams viewed from the rear side which are for more clearly describing the movement of the fold reinforcing unit  50  described above. 
       FIG. 12A  shows a state where the fold reinforcing unit  50  is accommodated. It is assumed that a paper jam has occurred in this state and the roller unit  60  stops in a state where the sheet bundle is nipped. For this case, a user manually moves the jam release handles  502   a  and  502   b , as described above, to extract the engaging rods  501   a  and  501   b  from the elongated holes  301   a  and  301   b of the external housing  300 , resulting that the fold reinforcing unit  50  is pulled downwards toward the outside. In this manner, the fold reinforcing unit  50  rotates around the support shafts  302   a  and  302   b  in the lower portion thereof and the fold reinforcing unit  50  is opened down as shown in  FIG. 12B . When the fold reinforcing unit  50  is opened down, a sheet bundle  100  is exposed in a state of being nipped by the pair of fold rollers  38  and a space between the fold reinforcing unit  50  and the pair of fold rollers  38  is widely formed. Accordingly, it is possible for the user to easily visually recognize the sheet bundle  100  which has caused the paper jam and it is also possible to easily remove the sheet bundle  100 . 
     (5) Second Paper Jam Release Mechanism 
     As mentioned above, if a paper jam occurs during fold reinforcing, the roller unit  60  is stopped in a state where the upper roller  51   a  and the lower roller  51   b  apply pressure to the fold line of the sheet bundle. Therefore, when a user opens the fold reinforcing unit  50  using the first paper jam release mechanism described above, the user needs to pull the fold reinforcing unit  50  downwards against the pressure of the upper roller  51   a  and the lower roller  51   b  which are nipping the fold line, and the user needs to pull it down while applying a certain degree of strong force. In addition, since the rotation direction of the upper roller  51   a  and the lower roller  51   b  and the downward pulling direction of the fold reinforcing unit  50  are orthogonal, there is a possibility of damaging the roller unit  60 . 
     In view of this problem, the second paper jam release mechanism is provided with a unit for weakening or removing the pressure between the upper roller  51   a  and the lower roller  51   b  in releasing a paper jam. 
       FIGS. 13A and 13B  are diagrams illustrating the operating concept of the second paper jam release mechanism.  FIG. 13A  shows a state in which a paper jam has occurred due to any cause during reinforcing of the fold line of the sheet bundle  100  using the upper roller  51   a  and the lower roller  51   b , and the movement of the upper roller  51   a  and the lower roller  51   b  (movement along the fold line) has stopped. 
     As described above, during fold reinforcing, the upper surface of the guide roller  66   c  of the roller unit  60  is in contact with the lower surface of the guide rail  77 . The contact position is lower than the supporting point of the lower link member  66  (lower link shaft  66   a ). Also, the incision  66   b  which is at the leading end of the lower link member  66  is further lower than the contact position of the guide roller  66   c . As a result, one end of the spring  68  which is engaged with the incision  66   b  is pulled downward and a pushing force is generated based on the pulling force of the spring  68  between the upper roller  51   a  and the lower roller  51   b.    
     Therefore, in order for the pushing force between the upper roller  51   a  and the lower roller  51   b  to be weakened or removed, it is sufficient to move the incision  66   b , which is engaged with the spring  68 , upward (in the thickness direction of the sheet bundle) and to weaken the pulling force of the spring  68 . Further, in order to move the incision  66   b  upward, it is sufficient to move the guide roller  66   c  upward, and for this, it is sufficient to move the guide rail  77 , which is in contact with the upper surface of the guide roller  66   c , upward. That is, as shown in  FIG. 13B , it is possible to weaken or remove the pushing force between the upper roller  51   a  and the lower roller  51   b  by moving the guide rail  77  upward in the thickness direction of the sheet bundle. 
       FIGS. 14 ,  15 A, and  15 B are diagrams describing the second jam release mechanism, more specifically, a mechanism which raises the guide rail  77 . 
     As shown in  FIG. 14 , the second jam release mechanism operates in conjunction with the first jam release mechanism. That is, even in the second jam release mechanism, the jam release handles  502   a  and  502   b  are also manually moved to the inner side for raising the guide rail  77 . 
       FIGS. 15A and 15B  are diagrams describing the second jam release mechanism in more detail. The front side and rear side have basically the same configuration and only the front side of the second jam release mechanism is shown in  FIGS. 15A and 15B . 
     The second jam release mechanism is provided with a connection member  504   a  which connects the jam release handle  502   a  and the guide rail  77 . The connection member  504   a  has a slide rod  505   a  which is fixed and connected to the jam release handle  502   a  and a connection plate  506   a  which is fixed and connected to the guide rail  77 . A elongated hole  507   a  with a level difference is formed in the connection plate  506   a . The slide rod  505   a  is able to slide up or down the level difference in a longitudinal direction of the elongated hole  507   a  in a state of being inserted in the elongated hole  507   a.    
     Here, a connection member  504   b  (slide rod  505   b , connection plate  506   b ) and elongated hole  507   b  are provided in the same manner also on the rear side. 
     Due to a manual operation, movement of the jam release handle  502   a  along an inner side and an outer side direction with respect to the internal housing  500  is allowed. By contrast, movement of the jam release handle  502   a  along the up-and-down direction (in the thickness direction of the sheet bundle) with respect to the internal housing  500  is restricted. That is, a vertical position of the jam release handle  502   a  with respect to the internal housing  500  is not changed even if the jam release handle  502   a  is manually moved in a horizontal (an inner side and an outer side) direction. 
       FIG. 15A  is a diagram illustrating a state before jam release, and at this time, the slide rod  505   a  is in a high position on the level difference of the elongated hole  507   a . When the user pinches and moves the jam release handle  502   b  to the inner side, the slide rod  505   a  also moves to the inner side. Then, as shown in FIG.  15 B, the slide rod  505   a  moves to a low position on the level difference of the elongated hole  507   a . As described above, the position in the up-and-down direction of the jam release handle  502   b  (and the slide rod  505   a  which is connected and fixed to the jam release handle  502   b ) does not change with regard to the internal housing  500  (fixed frame). As a result, when the slide rod  505   a  moves to the low position of the level difference of the elongated hole  507   a , the connection plate  506   a  and the guide rail  77  which is connected and fixed to the connection plate  506   a  are raised with regard to the internal housing  500 . 
     When the guide rail  77  is raised with regard to the internal housing  500 , as shown in  FIG. 13B , the pulling force of the spring  68  is weakened and the pushing force between the upper roller  51   a  and the lower roller  51   b  is weakened or removed. 
     At this time, in conjunction with the manual operation of the jam release handles  502   a  and  502   b , the engaging rods  501   a  and  501   b  are extracted from the elongated holes  301   a  and  301   b  of the internal housing  500 . That is, due to the operation where the jam release handles  502   a  and  502   b  are moved to the inner side, it is possible to weaken or remove the pushing force between the upper roller  51   a  and the lower roller  51   b , and at the same time, release the engagement of the internal housing  500  of the fold reinforcing unit  50  and the external housing  300  of the saddle stitching unit  30 . 
     As a result, excess force from a user is not necessary, there is no concern of damage to the upper roller  51   a  and the lower roller  51   b , and it is possible to open up the fold reinforcing unit  50  to the outer side. 
     After that, it is possible for the user to easily remove the sheet bundle as shown in  FIG. 12B . 
     As described above, according to the sheet finisher, the image forming apparatus, and the sheet finishing method of the embodiment, it is possible to easily remove the sheet bundle which caused a paper jam by an extremely simple operation even in a case where fold reinforcing is stopped by the paper jam. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. Indeed, the novel apparatuses and units described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the apparatuses and units described herein may be made without departing from the spirit of the invention. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.