Patent Publication Number: US-8109495-B2

Title: Spine formation device, post-processing apparatus, and bookbinding system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent specification is based on and claims priority from Japanese Patent Application No. 2009-212375, filed on Sep. 14, 2009 in the Japan Patent Office, the contents of which are hereby incorporated by reference herein in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a spine formation device to form a spine of a bundle of folded sheets, a post-processing apparatus including the spine formation device, and a bookbinding system including the spine formation device and an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction machine capable of at least two of these functions. 
     2. Discussion of the Background Art 
     Post-processing apparatuses to perform post processing of recording media, such as aligning, sorting, stapling, punching, and folding of sheets, are widely used and are often disposed downstream from an image forming apparatus to perform post-processing of the sheets output from the image forming apparatus. At present, post-processing apparatuses generally perform saddle-stitching along a centerline of sheets in addition to conventional edge-stitching along an edge portion of sheets. 
     However, when a bundle of sheets (hereinafter “booklet”) is saddle-stitched or saddle-stapled and then folded in two, its folded portion, that is, a portion around its spine, tends to bulge, degrading the overall appearance of the booklet. In addition, the bulging spine makes the booklet thicker on the spine side and thinner on the opposite side, making it difficult to stack, store, or transport them. Flattening the spines of the booklets improves their appearance and allows a relatively large number of booklets to be piled together with ease. 
     It is to be noted that the term “spine” used herein means not only the stitched side of the booklet but also portions of the front cover and the back cover continuous with the spine. 
     To improve the quality of the finished product, several approaches, described below, for shaping the folded portion of a bundle of saddle-stitched sheets have been proposed. 
     For example, in JP-2001-260564-A, the spine of the booklet is flattened using a pressing member configured to sandwich an end portion of the booklet adjacent to the spine and a spine-forming roller serving as a spine pressing member configured to roll in a longitudinal direction of the spine while contacting the spine of the booklet. The spine-forming roller moves at least once over the entire length of the spine of the booklet being fixed by the pressing member while applying to the spine a pressure sufficient to flatten the spine. 
     Although this approach can flatten the spine of the booklet to a certain extent, it is possible that the sheets might wrinkle and be torn around the spine or folded portion because the pressure roller applies localized pressure to the spine continuously. Further, it takes longer to flatten the spine because the pressure roller must move over the entire length of the spine of the booklet. 
     Moreover, this approach does not consider stapled booklets. More specifically, when staples project from the surface of the spine of the booklet, the spine pressing member simply presses the staples upstream in the direction in which the booklet is transported, thus making the surface of the spine uneven and degrading the appearance of the booklet. 
     To address the above-described problem, for example, JP-2007-237562-A proposes a spine formation device that includes a sandwiching member that sandwiches the booklet from the front side and the back side of the booklet, a pressure member disposed downstream from the sandwiching member in a direction in which the bundle of folded sheets is transported, and a spine pressing member (i.e., a spine pressing plate) that is pressed against the spine of the booklet. After the spine pressing plate is pressed against the spine of the booklet, the pressure member squeezes the spine from the side, that is, in the direction of the thickness of the booklet to reduce bulging of the spine. 
     This configuration can reduce the pressure exerted on the spine and accordingly reduce damage to the spine compared with the first method described above, in which the spine formation member applies relatively high pressure to the spine while moving along the spine. 
     Additionally, in the second method, recessed portions are formed in the surface of the spine pressing plate pressing against the spine to accommodate objects such as loop stitches projecting from the spine of the booklet. 
     However, although aiming at eliminating adverse effects caused by the objects projecting from the spine in spine formation, the second method is not very flexible in application. For example, this configuration cannot accommodate changes in the size of interval between staples or changes in the number of staples used in the booklet. 
     In view of the foregoing, the inventors of the present invention recognize that there is a need for an apparatus capable of flattening the spine of the booklet regardless of the position or the number of staples in used in the booklet. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, an object of the present specification is to improve flatness of the spine of the booklet regardless of the position or the number of staples used in the booklet. 
     In one illustrative embodiment of the present invention, a spine formation device includes a sheet conveyer that conveys a bundle of folded sheets in a sheet conveyance direction with a folded portion of the bundle of folded sheets forming a front end portion of the bundle of folded sheets, a contact member disposed downstream from the sheet conveyer in the sheet conveyance direction, a driving unit to move the contact member relative to the folded portion of the bundle of folded sheets, in a first direction perpendicular to the sheet conveyance direction, first and second sandwiching units disposed downstream from the sheet conveyer in the sheet conveyance direction, a discharge unit to discharge the bundle of folded sheets to a discharge tray, and a controller operatively connected to the sheet conveyer, to the first and second sandwiching units, and to the driving unit. The contact member includes a contact surface extending in the first direction, against which the folded portion of the bundle of folded sheets is pressed, and a first row of grooves is provided in the contact surface to house a projection projecting from the folded portion of the bundle of folded sheets. The first row of grooves extends in a second direction parallel to the folded portion of the bundle of folded sheets and includes at least a first pair of grooves inclined in different directions with an interval therebetween varying in size with location of the grooves in the first direction. The controller causes the driving unit to move the contact member to change the size of interval between the first pair of grooves at a position in the first direction, aligned with the projection projecting from the folded portion of the bundle of folded sheets. With the folded portion pressed against the contact member, the first sandwiching unit squeezes the bundle of folded sheets in a direction of thickness of the bundle of folded sheets. Then, the second sandwiching unit disposed downstream from the first sandwiching unit in the sheet conveyance direction forms a spine of the bundle of folded sheets by squeezing a bulging of the bundle of folded sheets created between the first sandwiching unit and the contact member. 
     Another illustrative embodiment of the present invention provides a post-processing apparatus to perform post processing of sheets transported from an image forming apparatus. The post-processing apparatus includes a saddle-stapler to staple a bundle of sheets together along a centerline of the bundle, a folding unit to fold the bundle of sheets along the centerline of the bundle, and the spine formation device described above. 
     Yet in another illustrative embodiment of the present embodiment, a bookbinding system includes an image forming apparatus and the post-processing apparatus described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  illustrates a bookbinding system including an image forming apparatus, a post-processing apparatus and a spine formation device according to an illustrative embodiment of the present invention; 
         FIG. 2  is a front view illustrating a configuration of the post-processing apparatus shown in  FIG. 1 ; 
         FIG. 3  illustrates the post-processing apparatus in which a bundle of sheets is transported; 
         FIG. 4  illustrates the post-processing apparatus in which the bundle of sheets is stapled along the centerline; 
         FIG. 5  illustrates the post-processing apparatus in which the bundle of sheets is set at a center-folding position; 
         FIG. 6  illustrates the post-processing apparatus in which the bundle of sheets is being folded in two; 
         FIG. 7  illustrates the post-processing apparatus from which the bundle of folded sheets is discharged; 
         FIG. 8  is a front view illustrating a configuration of the spine formation devices shown in  FIG. 1 ; 
         FIG. 9A  illustrates an initial state of a transport unit of the spine formation device shown in  FIG. 8  to transport a bundle of folded sheets; 
         FIG. 9B  illustrates a state of the transport unit shown in  FIG. 9A  in which the bundle of folded sheets is transported; 
         FIGS. 10A and 10B  are diagrams of another configuration of the transport unit illustrating an initial state and a state in which the bundle of folded sheets is transported, respectively; 
         FIG. 11  illustrates a state of the spine formation device in which the bundle of folded sheets is transported therein; 
         FIG. 12  illustrates a process of spine formation performed by the spine formation device in which the leading edge of the bundle of folded sheets is in contact with a contact plate; 
         FIG. 13  illustrates a process of spine formation performed by the spine formation device in which a pair of auxiliary sandwiching plates approaches the bundle of folded sheets to sandwich it therein; 
         FIG. 14  illustrates a process of spine formation performed by the spine formation device in which the pair of auxiliary sandwiching plates squeezes the bundle of folded sheets; 
         FIG. 15  illustrates a process of spine formation performed by the spine formation device in which a pair of sandwiching plates squeezes the bundle of folded sheets; 
         FIG. 16  illustrates completion of spine formation performed by the spine formation device in which the pair of auxiliary sandwiching plates and the pair of sandwiching plates are disengaged from the bundle of folded sheets; 
         FIG. 17  illustrates a state in which the bundle of folded sheets is discharged from the spine formation device after spine formation; 
         FIG. 18  is a block diagram illustrating a configuration of online control of the bookbinding system; 
         FIG. 19  is a cross-sectional diagram illustrating a state in which the folded leading-edge portion of the booklet is pressed against the contact plate; 
         FIG. 20  illustrates grooves formed in the contact surface of the contact plate for two-position stapling; 
         FIG. 21  illustrates the relation between the grooves shown in  FIG. 20  and the staples; 
         FIG. 22  illustrates the ratio between a horizontal length and a vertical length of the grooves shown in  FIG. 21 ; 
         FIG. 23  illustrates a contact plate having a contact surface in which grooves for two-position stapling as well as those for four-position stapling are formed; 
         FIG. 24  illustrates another contact plate having a contact surface in which grooves for two-position stapling as well as those for four-position stapling are formed; 
         FIG. 25  is a front view illustrating a configuration of a spine formation device including the contact plate shown in  FIG. 24 ; 
         FIG. 26  illustrates relations among the positions of the grooves, the intervals between the grooves, and the vertical position of the contact plate shown in  FIG. 24 ; 
         FIG. 27  illustrates positional adjustment of the contact plate for two-position stapling in which the contact plate is moved up; 
         FIG. 28  illustrates positional adjustment of the contact plate for two-position stapling in which the contact plate is moved down; and 
         FIG. 29  illustrates positional adjustment of the contact plate for four-position stapling. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve a similar result. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views thereof, and particularly to  FIG. 1 , a bookbinding system according to an illustrative embodiment of the present invention is described. 
     It is to be noted that, in the description below, a pair of transport belts  311  and  312  of a transport unit  31  serves as a sheet conveyer, a contact plate  330  serves as a contact member, a pair of auxiliary sandwiching plates  320  and  321  serves as a first sandwiching unit, a pair of sandwiching plates  325  and  326  serves as a second sandwiching unit, and a central processing unit (CPU)  3 - 1  serves as a controller. Further, a discharge guide plate  335  and a pair of discharge rollers  340  and  341  together form a discharge unit. 
       FIG. 1  illustrates a bookbinding system including an image forming apparatus  100  (shown in  FIG. 18 ), a post-processing apparatus  1 , a bookbinding device  2 , and a spine formation device  3  according to an illustrative embodiment of the present invention. 
     In  FIG. 1 , the post-processing apparatus  1  is connected to a downstream side of the image forming apparatus  100 , and the bookbinding device  2  is connected to a downstream side of the post-processing apparatus  1  in a direction in which a bundle of sheets is transported (hereinafter “sheet conveyance direction”). Further, the spine formation device  3  is connected to a downstream side of the bookbinding device  2  in the sheet conveyance direction. In this system, the bookbinding device  2  performs saddle-stitching or saddle-stapling, that is, stitches or staples, along its centerline, a bundle of sheets discharged thereto by a pair of discharge rollers  10  from the post-processing apparatus  1  and then folds the bundle of sheets along the centerline, after which a pair of discharge rollers  231  transports the bundle of folded sheets (hereinafter also “booklet”) to the spine formation device  3 . Then, the spine formation device  3  flattens the folded portion of the booklet and discharges it outside the spine formation device  3 . The image forming apparatus  100  may be a copier, a printer, a facsimile machine, or a multifunction peripheral (MFP) including at least two of those functions that forms images on sheets of recording media based on image data input by users or read by an image reading unit. The image forming apparatus  100  is hereinafter also referred to as the MFP  100 . 
     The spine formation device  3  includes transport belts  311  and  312 , auxiliary sandwiching plates  320  and  321 , sandwiching plates  325  and  326 , a contact plate  330 , and a pair of discharge rollers  340  and  341  disposed in that order in the sheet conveyance direction. 
     Referring to  FIGS. 1 and 2 , a configuration of the bookbinding device  2  is described below. 
       FIG. 2  illustrates a configuration of the bookbinding device  2 . 
     Referring to  FIG. 2 , an entrance path  241 , a sheet path  242 , and a center-folding path  243  are formed in the bookbinding device  2 . A pair of entrance rollers  201  provided extreme upstream in the entrance path  241  in the sheet conveyance direction receives a bundle of aligned sheets transported by the discharge rollers  10  of the post-processing apparatus  1 . It is to be noted that hereinafter “upstream” and “downstream” refer to those in the sheet conveyance direction unless otherwise specified. 
     A separation pawl  202  is provided downstream from the entrance rollers  201  in the entrance path  241 . The separation pawl  202  extends horizontally in  FIG. 2  and switches the sheet conveyance direction between a direction toward the sheet path  242  and that toward the center-folding path  243 . The sheet path  242  extends horizontally from the entrance path  241  and guides the bundle of sheets to a downstream device or a discharge tray, not shown, and a pair of upper discharge rollers  203  discharges the bundle of sheets from the sheet path  242 . The center-folding path  243  extends vertically in  FIGS. 1 and 2  from the separation pawl  202 , and the bundle of sheets is transported along the center-folding path  243  when at least one of stapling and folding is performed. 
     Along the center-folding path  243 , an upper sheet guide  207  and a lower sheet guide  208  to guide the bundle of sheets are provided above and beneath a folding plate  215 , respectively, and the folding plate  215  is used to fold the bundle of sheets along its centerline. A pair of upper transport rollers  205 , a trailing-edge alignment pawl  221 , and a pair of lower transport rollers  206  are provided along the upper sheet guide  207  in that order from the top in  FIG. 2 . The trailing-edge alignment pawl  221  is attached to a pawl driving belt  222  driven by a driving motor, not shown, and extends perpendicularly to a surface of the driving belt  222 . As the pawl driving belt  222  rotates opposite directions alternately, the trailing-edge alignment pawl  221  pushes a trailing-edge of the bundle of sheets toward a movable fence  210  disposed in a lower portion in  FIG. 2 , thus aligning the bundle of sheets. Additionally, the trailing-edge alignment pawl  221  moves away from the upper sheet guide  207  to a position indicated by broken lines shown in  FIG. 2  when the bundle of sheets enters the center-folding path  243  and ascends to a folding position from the alignment position. In  FIG. 2 , reference numeral  294  represents a pawl home position (HP) detector that detects the trailing-edge alignment pawl  221  at a home position indicated by the broken lines shown in  FIG. 2 . The trailing-edge alignment pawl  221  is controlled with reference to the home position. 
     A saddle stapler S 1 , a pair of jogger fences  225 , and the movable fence  210  are provided along the lower sheet guide  208  in that order from the top in  FIG. 2 . The lower sheet guide  208  receives the bundle of sheets guided by the upper sheet guide  207 , and the pair of jogger fences  225  extends in a sheet width direction perpendicular to the sheet conveyance direction. The movable fence  210  positioned beneath the lower sheet guide  208  moves vertically, and a leading edge of the bundle of sheets contacts the movable fence  210 . 
     The saddle stapler S 1  staples the bundle of sheets along its centerline. While supporting the leading edge of the bundle of sheets, the movable fence  210  moves vertically, thus positioning a center portion of the bundle of sheets at a position facing the saddle stapler S 1 , where saddle stapling is performed. The movable fence  210  is supported by a fence driving mechanism  210   a  and can move from the position of a fence HP detector  292  disposed above the stapler S 1  to a bottom position in the bookbinding device  2  in  FIG. 2 . A movable range of the movable fence  210  that contacts the leading edge of the bundle of sheets is set so that strokes of the movable fence  210  can align sheets of any size processed by the bookbinding device  2 . It is to be noted that, for example, a rack-and-pinion may be used as the fence driving mechanism  210   a.    
     The folding plate  215 , a pair of folding rollers  230 , and a discharge path  244 , and the pair of lower discharge rollers  231  are provided horizontally between the upper sheet guide  207  and the lower sheet guide  208 , that is, in a center portion of the center-folding path  243  in  FIG. 2 . The folding plate  215  can move reciprocally back and forth horizontally in  FIG. 2  in the folding operation, and the folding plate  215  is aligned with a position where the folding rollers  230  press against each other (hereinafter “nip”) in that direction. The discharge path  244  is positioned also on an extension line from the line connecting them. The lower discharge rollers  231  are disposed extreme downstream in the discharge path  244  and discharge the bundle of folded sheets to a subsequent stage. 
     Additionally, a sheet detector  291  provided on a lower side of the upper sheet guide  207  in  FIG. 2  detects the leading edge of the bundle of sheets that passes a position facing the folding plate  215   a  (hereinafter “folding position”) in the center-folding path  243 . Further, a folded portion detector  293  provided along the discharge path  224  detects the folded leading-edge portion (hereinafter simply “folded portion”) of the bundle of folded sheets, thereby recognizing the passage of the bundle of folded sheets. 
     Saddle-stapling and center-holding performed by the bookbinding device  2  shown in  FIG. 2  are described briefly below with reference to  FIGS. 3 through 7 . 
     When a user selects saddle-stapling and center-folding via an operation panel  105  (shown in  FIG. 18 ) of the image forming apparatus  100 , the separation pawl  202  pivots counterclockwise in  FIG. 2 , thereby guiding the bundle of sheets to be stapled and folded to the center-folding path  243 . The separation pawl  201  is driven by a solenoid, not shown. Alternatively, the separation pawl  201  may be driven by a motor. 
     A bundle of sheets SB transported to the center-folding path  243  is transported by the upper transport rollers  205  downward in the center-folding path  243  in  FIG. 3 . After the sheet detector  291  detects the passage of the bundle of sheet SB, the lower transport rollers  206  transport the bundle of sheets SB until the leading edge of the bundle of sheets SB contacts the movable fence  210  as shown in  FIG. 3 . At that time, the movable fence  210  is at a standby position that is varied in the vertical direction shown in  FIG. 3  according to sheet size data, that is, sheet size data in the sheet conveyance direction, transmitted from the image forming apparatus  100  shown in  FIG. 18 . Simultaneously, the lower transport rollers  206  sandwich the bundle of sheets SB therebetween, and the trailing-edge alignment pawl  221  is at the home position. 
     When the pair of lower transport rollers  206  is moved away from each other as indicated by arrow a shown in  FIG. 4 , releasing the trailing edge of the bundle of sheets SB whose leading edge is in contact with the movable fence  210 , the trailing-edge alignment pawl  221  is driven to push the trailing edge of the bundle of sheets SB, thus aligning the bundle of sheets SB in the sheet conveyance direction as indicated by arrow c shown in  FIG. 4 . 
     Subsequently, the bundle of sheets SB is aligned in the sheet width direction perpendicular to the sheet conveyance direction by the pair of jogger fences  225 , and thus alignment of the bundle of sheets SB in both the sheet width direction and the sheet conveyance direction is completed. At that time, the amounts by which the trailing-edge alignment pawl  221  and the pair of jogger fences  225  push the bundle of sheets SB to align it are set to optimum values according to the sheet size, the number of sheets, and the thickness of the bundle. 
     It is to be noted that, when the bundle of sheets SB is relatively thick, the bundle of sheets SB occupies a larger area in the center-folding path  243  with the remaining space therein reduced, and accordingly a single alignment operation is often insufficient to align it. Therefore, the number of alignment operations is increased in that case. Thus, the bundle of sheets SB can be aligned fully. Additionally, as the number of sheets increases, it takes longer to stack multiple sheets one on another upstream from the bookbinding device  2 , and accordingly it takes longer before the bookbinding device  2  receives a subsequent bundle of sheets. Consequently, the increase in the number of alignment operations does not cause a loss time in the sheet processing system, and thus efficient and reliable alignment can be attained. Therefore, the number of alignment operations may be adjusted according to the time required for the upstream processing. 
     It is to be noted that the standby position of the movable fence  210  is typically positioned facing the saddle-stapling position of the bundle of sheets SB or the stapling position of the saddle stapler S 1 . When aligned at that position, the bundle of sheets SB can be stapled at that position without moving the movable fence  210  to the saddle-stapling position of bundle of sheets SB. Therefore, at that standby position, a stitcher, not shown, of the saddle stapler S 1  is driven in a direction indicated by arrow b shown in  FIG. 4 , and thus the bundle of sheets SB is stapled between the stitcher and a clincher, not shown, of the saddle stapler S 1 . 
     It is to be noted that the positions of the movable fence  210  and the trailing-edge alignment pawl  221  are controlled with pulses of the fence HP detector  292  and the pawl HP detector  294 , respectively. Positioning of the movable fence  210  and the trailing-edge alignment pawl  221  is performed by a central processing unit (CPU)  2 - 1  of a control circuit, shown in  FIG. 18 , of the bookbinding device  2 . 
     After stapled along the centerline in the state shown in  FIG. 4 , the bundle of sheets SB is lifted to a position where the saddle-stapling position thereof faces the folding plate  215  as the movable fence  210  moves upward as shown in  FIG. 5  while the pair of lower transport rollers  206  does not press against the bundle of sheets SB. This position is adjusted with reference to the position detected by the fence HP detector  292 . 
       FIG. 6  illustrates a state in which a folded leading edge of the booklet SB is squeezed in the nip between the folding rollers  230 . 
     After the bundle of sheets SB is set at the position shown in  FIG. 5 , the folding plate  215  approaches the nip between the pair of folding rollers  230  as shown in  FIG. 6  and pushes toward the nip the bundle of sheets SB in a portion around the staples binding the bundle in a direction perpendicular or substantially perpendicular to a surface of the bundle of sheets SB. Thus, the bundle of sheets SB pushed by the folding plate  215  is folded in two and sandwiched between the pair of folding roller  230  being rotating. While squeezing the bundle of sheets SB caught in the nip, the pair of folding roller  230  transports the bundle of sheets SB. Thus, while squeezed and transported by the folding rollers  230 , the bundle of sheets SB is center-folded as a booklet SB. 
     After folded in two as shown in  FIG. 6 , the booklet SB is transported by the folding rollers  230  downstream and then discharged by the discharged rollers  231  to a subsequent stage. When the folded portion detector  293  detects a trailing edge portion of the booklet SB, both the folding plate  215  and the movable fence  210  return to the respective home positions. Then, the lower transport rollers  206  move to press against each other as a preparation for receiving a subsequent bundle of sheets. Further, if the number and the size of sheets forming the subsequent bundle are similar to those of the previous bundle of sheets, the movable fence  210  can wait again at the position shown in  FIG. 3 . The above-described control is performed also by the CPU  2 - 1  of the bookbinding device  2 . 
       FIG. 8  is a front view illustrating a configuration of the spine formation device  3  shown in  FIG. 1 . 
     Referring to  FIG. 8 , the spine formation device  3  includes the conveyance unit  31  serving as the sheet conveyer, an auxiliary sandwiching unit  32  serving as the first sandwiching unit, the vertically-arranged sandwiching plates  325  and  326  serving as the second sandwiching unit, the contact plate  330  serving as the contact member, and a discharge unit. 
     The conveyance unit  31  includes the vertically-arranged transport belts  311  and  312 , the auxiliary sandwiching unit  32  includes the vertically-arranged guide plates  315  and  316  and the vertically-arranged auxiliary sandwiching plates  320  and  321 , and the discharge unit includes the discharge guide plate  335  and the pair of discharge rollers  340  and  341  in  FIG. 8 . It is to be note that the lengths of the respective components are greater than the width of the bundle of sheets SB in a direction perpendicular to the surface of paper on which  FIG. 8  is drawn. 
     The upper transport belt  311  and the lower transport belt  312  are respectively stretched around driving pulleys  311   b  and  312   b  supported by swing shafts  311   a  and  312   a  and driven pulleys  311   c  and  312   c  disposed downstream from the driving pulleys  311   b  and  312   b . A driving motor, not shown, drives the transport belts  311  and  312 . The transport belts  311  and  312  are disposed on both sides of (in  FIG. 8 , above and beneath) a transport centerline  301  of a transport path  302 , aligned the line extended from the line connecting the folding plate  215 , the nip between the folding rollers  230 , and the nip between the discharge rollers  231 . The swing shafts  311   a  and  312   a  respectively support the transport belts  311  and  312  swingably so that the gap between the driven pulleys  311   c  and  312   c  is adjusted corresponding to the thickness of the bundle of sheets. The upper guide plate  315  and the lower guide plate  316  are respectively attached to the upper auxiliary sandwiching plate  320  and the lower auxiliary sandwiching plate  321  with pressure springs  317 . 
     It is to be noted that, in  FIG. 8 , reference characters SN 1  through SN 5  respectively represent a sheet detector, a discharge detector, an auxiliary sandwiching plate HP detector, a sandwiching plate HP detector, and a contact plate HP detector. Further, in the configuration shown in  FIG. 8 , the transport centerline  301  means a center of the transport path  302  in the vertical direction. 
     The conveyance unit  31  to transport the bundle of sheets SB using the vertically-arranged transport belts  311  and  312  is described in further detail below with reference to  FIGS. 9A and 9B .  FIGS. 9A and 9B  illustrate an initial state of the spine formation device  3  and a state in which the bundle of sheets SB is transported therein, respectively. 
     As shown in  FIGS. 9A and 9B , the driving pulleys  311   b  and  312   b  are connected to the driven pulleys  311   c  and  312   c  with support plates  311   d  and  312   d , respectively, and the transport belts  311  and  312  are respectively stretched around the driving pulleys  311   b  and  312   b  and the driven pulleys  311   c  and  312   c . With this configuration, the transport belts  311  and  312  are driven by the driving pulleys  311   b  and  312   b , respectively. 
     By contrast, rotary shafts of the driven pulleys  311   c  and  312   c  are connected by a link  313  formed with two members connected movably with a connection shaft  313   a , and a pressure spring  314  biases the driven pulleys  311   c  and  312   c  to approach each other. The connection shaft  313   a  engages a slot  313   b  extending in the sheet conveyance direction, formed in a housing of the spine formation device  3  and can move along the slot  313   b . With this configuration, as the two members forming the link  313  attached to the driven pulleys  311   c  and  312   c  move, the connection shaft  313   a  moves along the slot  313   b , thus changing the distance between the driven pulleys  311   c  and  312   c  corresponding to the thickness of the booklet SB while maintaining a predetermined or given pressure in a nip where the transport belts  311  and  312  press against each other. 
     Additionally, a rack-and-pinion mechanism can be used to move the connection shaft  313   a  along the slot  313   b , and the position of the connection shaft  313   a  can be set by controlling a motor driving the pinion. With this configuration, when the booklet SB is relatively thick, the distance between the driven pulleys  311   c  and  312   c  (hereinafter “transport gap”) can be increased to receive the booklet SB, thus reducing the pressure applied to the folded portion (folded leading-edge portion) of the booklet SB by the transport belts  311  and  312  on the side of the driven pulleys  311   c  and  312   c . It is to be noted that, when power supply to the driving motor is stopped after the folded portion of the booklet SB is sandwiched between the transport belts  311  and  312 , the driven pulleys  311   c  and  312   c  can transport the booklet SB sandwiched therebetween with only the elastic bias force of the pressure spring  314 . 
     A conveyance unit  31 A as another configuration of the conveyance unit is described below with reference to  FIGS. 10A and 10B .  FIGS. 10A and 10B  illustrate an initial state of the conveyance unit  31 A and a state in which the bundle of sheets SB is transported therein, respectively. 
     In the conveyance unit  31 A, the swing shafts  311   a  and  312   a  engage sector gears  311   e  and  312   e  instead of using the link  313 , respectively, and the sector gears  311   e  and  312   e  engaging each other cause the driven pulleys  311   c  and  312   c  to move vertically away from the transport centerline  301  symmetrically. Also in this configuration, the size of the transport gap to receive the booklet SB can be adjusted by driving one of the sector gears  311   e  and  312   e  with a driving motor including a decelerator similarly to the configuration shown in  FIGS. 9A and 9B . 
     As shown in  FIG. 8 , the guide plates  315  and  316  are disposed adjacent to the driven pulleys  311   c  and  312   c , respectively, and arranged symmetrically on both sides of the transport centerline  301 , that is, above and beneath the transport centerline  301  in  FIG. 8 . The guide plates  315  and  316  respectively include flat surfaces in parallel to the transport path  302 , extending from the transport nip to a position adjacent to the auxiliary sandwiching plates  320  and  321 , and the flat surfaces serve as transport surfaces. The upper guide plate  315  and the lower guide plate  316  are attached to the upper auxiliary sandwiching plate  320  and the lower auxiliary sandwiching plate  321  with pressure springs  317 , respectively. The upper guide plate  315  and the lower guide plate  316  are biased to the transport centerline  301  elastically by the respective pressure springs  317  and can move vertically. Further, the auxiliary sandwiching plates  320  and  321  are held by a housing of the spine formation device  3  movably in the vertical direction in  FIG. 8 . It is to be noted that, alternatively, the guide plates  315  and  316  may be omitted, and the booklet SB may be guided by only surfaces of the auxiliary sandwiching plates  320  and  321  facing the booklet SB, parallel to the transport path  302 . 
     The vertically-arranged auxiliary sandwiching plates  320  and  321  of the auxiliary sandwiching unit  32  approach and move away from each other symmetrically relative to the transport centerline  301  similarly to the transport belts  311  and  312 . A driving mechanism, not shown, provided in the auxiliary sandwiching unit  32  to cause this movement can use the link mechanism used in the conveyance unit  31  or the connection mechanism using the rack and the sector gear shown  FIGS. 10A and 10B . A reference position used in detecting a displacement of the auxiliary sandwiching plates  320  and  321  can be set with the output from the auxiliary sandwiching plate HP detector SN 3 . Because the vertically-arranged auxiliary sandwiching plates  320  and  321  and the driving unit, not shown, are connected with a spring similar to the pressure spring  314  in the transport unit  31 , or the like, when the booklet SB is sandwiched by the auxiliary sandwiching plates  320  and  321 , damage to the driving mechanism caused by overload can be prevented. The surfaces of the auxiliary sandwiching plates  320  and  321  (e.g., pressure sandwiching surfaces) that sandwich the booklet SB are flat surfaces in parallel to the transport centerline  301 . 
     The vertically-arranged sandwiching plates  325  and  326 , serving as the sandwiching unit, approach and move away from each other symmetrically relative to the transport centerline  301  similarly to the transport belts  311  and  312 . A driving mechanism to cause the sandwiching plates  325  and  326  this movement can use the link mechanism used in the transport unit  31  or the connection mechanism using the rack and the sector gear shown  FIGS. 10A and 10B . A reference position used in detecting a displacement of the sandwiching plates  325  and  326  can be set with the output from the sandwiching plate HP detector SN 4 . Other than the description above, the sandwiching plates  325  and  326  have configurations similar the auxiliary sandwiching plates  320  and  321  and operate similarly thereto, and thus descriptions thereof are omitted. It is to be noted that a driving source such as a driving motor is requisite in the auxiliary sandwiching unit  32  and the sandwiching unit although it is not requisite in the transport unit  31 , and the driving source enables the movement between a position to sandwich the booklet and a standby position away form the booklet. The surfaces of the auxiliary sandwiching plates  325  and  326  (e.g., pressure sandwiching surfaces) that sandwich the booklet are flat surfaces in parallel to the transport centerline  301  similarly to the auxiliary sandwiching plates  320  and  321 . 
     The contact plate  330  is disposed downstream from the sandwiching plates  325  and  326 . The contact plate  330  and a contact plate driving unit  331  (shown in  FIG. 18 ) to move the contact plate  330  vertically in  FIG. 8  together form a contact unit. The contact plate  330  moves vertically in  FIG. 8  to obstruct the transport path  302  and away from the transport path  302 , and a reference position used in detecting a displacement of the contact plate  330  can be set with the output from the contact plate HP detector SN 5 . When the contact plate  330  is away from the transport path  302 , a top surface of the contact plate  330  guides the booklet SB. Therefore, the top surface of the contact plate  330  is flat, in parallel to the sheet conveyance direction, that is, the transport centerline  301 . For example, the contact plate driving unit  331  can include rack-and-pinions provided on both sides of the contact plate  330 , that is, a front side and a back side of the spine formation device  3 , and a driving motor to drive the pinions. With this configuration, the contact plate  330  can be moved vertically and set at a predetermined position by driving the driving motor. 
     Next, operations performed by the spine formation device  3  to flatten the folded portion, that is, the spine, of the booklet SB are described in further detail below referring to  FIGS. 11 through 17 . It is to be noted that reference character SB 1  represents the folded portion (folded leading-edge portion) of the booklet SB. 
     In the spine formation according to the present embodiment, the spine of the booklet SB as well as the front cover side and the bock cover side thereof are flattened. 
       FIG. 11  illustrates a state before the booklet SB enters the spine formation device  3 . 
     Referring to  FIG. 11 , according to a detection signal of the booklet SB generated by an entrance sensor, not shown, of the spine formation device  3  or the folded portion detector  293  (shown in  FIG. 7 ) of the bookbinding device  2 , the respective portions of the spine formation device  3  perform preparatory operations to receive the booklet SB. In the preparatory operations, the pair of transport belts  311  and  312  starts rotating. Additionally, the upper auxiliary sandwiching plate  320  and the lower auxiliary sandwiching plate  321  move to the respective home positions detected by the auxiliary sandwiching plate HP detector SN 3 , move toward the transport centerline  301  until the distance (hereinafter “transport gap”) therebetween becomes a predetermined distance, and then stop at those positions. Similarly, the upper sandwiching plate  325  and the lower sandwiching plate  326  move to the respective home positions detected by the sandwiching plate HP detector SN 4 , move toward the transport centerline  301  until the distance (transport gap) therebetween becomes a predetermined distance, and then stop at those positions. 
     It is to be noted that, because the pair of auxiliary sandwiching plates  320  and  321  as well as the pair of sandwiching plates  325  and  326  are disposed and move symmetrically relative to the transport centerline  301 , when only one of the counterparts in the pair is detected at the home position, it is known that the other is at the home position as well. Therefore, the auxiliary sandwiching plate HP detector SN 3  and the sandwiching plate HP detector SN 4  are disposed on only one side of the transport centerline  301 . 
     The contact plate  330  moves to the home position detected by the contact plate HP detector SN 5 , moves toward the transport centerline  301  a predetermined distance, and then stops at a position obstructing the transport path  302 . 
     In this state, when the booklet SB is forwarded by the discharge rollers  231  of the bookbinding device  2  to the spine formation device  3 , the rotating transport belts  311  and  312  transport the booklet SB inside the device as shown in  FIG. 11 . The sheet detector SN 1  detects the folded portion SB 1  of the booklet SB, and then the booklet SB is transported the predetermined transport distance that is the sum of the first distance until the folded portion SB 1  contacts the contact plate  330  and the predetermined distance from the contact position, necessary to form the spine by expanding the folded portion SB 1  in the thickness direction, after which the booklet SB is kept at that position as shown in  FIG. 12 . The predetermined distance from the contact position can be determined according to the data relating to the booklet SB such as the thickness, the sheet size, the number of sheets, and the sheet type of the booklet SB. 
     When the booklet SB is stopped in the state shown in  FIG. 12 , referring to  FIG. 13 , the auxiliary sandwiching plates  320  and  321  start approaching the transport centerline  301 , and the pair of guide plates  315  and  316  presses against the booklet SB sandwiched therein with the elastic force of the pressure springs  317  initially. In this state, a bulging portion SB 2  is present upstream from the folded leading-edge portion SB 1 . After the pair of guide plates  315  and  316  applies a predetermined pressure to the booklet SB, the auxiliary sandwiching plates  320  and  321  further approach the transport centerline  301  to squeeze the booklet SB in the portion downstream form the portion sandwiched by the guide plates  315  and  316  and then stop moving when the pressure to the booklet SB reaches a predetermine or given pressure. Thus, the booklet SB is held with the predetermined pressure as shown in  FIG. 14 . With the folded leading-edge portion SB 1  of the booklet SB pressed against the contact plate  330 , the bulging portion SB 2  upstream from the folded leading-edge portion SB 1  is larger than that shown in  FIG. 13 . 
     After the auxiliary sandwiching plates  320  and  321  squeeze the booklet SB as shown in  FIG. 14 , the sandwiching plates  325  and  326  start approaching the transport centerline  301  as shown in  FIG. 15 . With this movement, the bulging portion SB 2  is localized to the side of the folded leading-edge portion SB 1 , pressed gradually, and then deforms following the shape of the space defined by the pair of sandwiching plates  325  and  326  and the contact plate  330 . After this compressing operation is completed, the folded portion SB 1  of the booklet SB is flat following the surface of the contact plate  330 , and thus the flat spine is formed on the booklet SB. In addition, referring to  FIG. 17 , leading end portions SB 3  and SB 4  on the front side (front cover) and the back side (back cover) are flattened as well. Thus, booklets having square spines can be produced. 
     Subsequently, as shown in  FIG. 16 , the auxiliary sandwiching plates  320  and  321  and the sandwiching plates  325  and  326  move away from the booklet SB to predetermined or given positions (standby positions), respectively. The contact plate  330  moves toward the home position and stops at a position where the top surface thereof guides the booklet SB. 
     After the auxiliary sandwiching plates  320  and  321 , the sandwiching plates  325  and  326 , and the contact plate  330  reach the respective standby positions, as shown in  FIG. 17 , the transport belts  311  and  312  and the pair of discharge rollers  340  and  341  start rotating, thereby discharging the booklet SB outside the spine formation device  3 . Thus, a sequence of spine formation operations is completed. The transport belts  311  and  312  and the pair of discharge rollers  340  and  341  stop rotating after a predetermined time period has elapsed from the detection of the booklet SB by the discharge detector N 2 . Simultaneously, the respective movable portions return to their home positions. When subsequent booklets SB are sequentially sent form the bookbinding device  2 , the time point at which the rotation of the transport belts  311  and  312  and the discharge rollers  340  and  341  is stopped is varied according to the transport state of the subsequent booklet SB. Additionally, it may be unnecessary to return the respective movable portions to their home positions each time, and the position to receive the booklet SB may be varied according to the transport state of and the data relating to the subsequent booklet SB. It is to be noted that the above-described CPU 2 - 1  of the bookbinding device  2  performs these adjustments. 
     A control block of the bookbinding system is described below with reference to  FIG. 18 . 
       FIG. 18  is a block diagram illustrating a configuration of online control of the bookbinding system. 
     The post-processing apparatus  1  is connected to the image forming apparatus (MFP)  100 , and the bookbinding device  2  is connected to the post-processing apparatus  2 . Further, the spine formation device  3  is connected to the bookbinding device  2 . The MFP  100 , the post-processing apparatus  1 , the bookbinding device  2 , and the spine formation device  3  respectively include the CPUs  100 - 1 ,  1 - 1 ,  2 - 1 , and  3 - 1 . The MFP  100  further includes an engine  110  and a communication port  100 - 2 . The post-processing apparatus  1  further includes communication ports  1 - 2  and  1 - 3 , the binding device  2  further includes communication ports  2 - 2  and  2 - 3 , and the spine formation device  3  further includes a communication port  3 - 2 . The MFP  1  and the post-processing apparatus  1  can communicate with each other using the communication ports  100 - 2  and  1 - 2 , and post-processing apparatus  1  and the bookbinding device  2  can communicate with each other using the communication ports  1 - 3  and  2 - 2 . Similarly, the bookbinding device  2  and the spine formation device  3  can communicate with each other using the communication ports  2 - 3  and  3 - 2 . Additionally, the CPU  100 - 1  of the MFP  100  controls indications on the operation panel  105  and inputs from users to the operation panel  105 , and thus the operation panel  105  serves as a user interface. 
     Each of the MFP  100 , the post-processing apparatus  1 , the bookbinding device  2 , and the spine formation device  3  further includes a read-only memory (ROM) and a random-access memory (RAM). Each of the CPUs  100 - 1 ,  1 - 1 ,  2 - 1 , and  3 - 1  thereof reads out program codes from the ROM, runs the program codes in the RAM, and then performs operations defined by the program codes using the RAM as a work area and a data buffer. With this configuration, various control and operations described above or below are performed. The MFP  100 , the post-processing apparatus  1 , the bookbinding device  2 , and the spine formation device  3  are connected in line via the communication ports  100 - 2 ,  1 - 2 ,  1 - 3 ,  2 - 2 ,  2 - 3 , and  3 - 2 . When post-processing of sheets is performed online, the post-processing apparatus  1 , the bookbinding device  2 , and the spine formation device  3  communicate with the CPU  100 - 1  of the MFP  100 , and thus the post-processing of sheets is controlled by the CPU  100 - 1  of the MFP  100 . 
     It is to be noted that, in this specification, “inline processing” means that at least two of image formation, processing of sheets, stapling of a bundle of sheets, and spine formation of the booklet are performed sequentially while the sheets are transported through the bookbinding system. 
     Referring to  FIGS. 19 through 24 , a shape of the contact surface of the contact plate  330  is described below. 
       FIG. 19  is a cross-sectional diagram illustrating a state in which the folded leading-edge portion SB 1  of the booklet SB is pressed against the contact plate  330 . 
     As shown in  FIG. 19 , in a portion where a staple H binds the booklet SB, the staple H projects from the spine of the booklet SB. The amount by which the staple H projects from the spine of the booklet SB equals to the thickness of the staple H at the least. 
     In other words, when the booklet SB is folded, a portion Ha of the staple H projects from the spine of the booklet SB (hereinafter “projecting portion Ha”). Therefore, in the present embodiment, grooves m are provided in the contact surface  330   a  of the contact plate  330  so that the projecting portion Ha of the staple H can enter the groove m, thus enabling the spine of the booklet SB to press against the contact surface  300   a  of the contact plate  330 . With this configuration, even when the projecting portion Ha of the staple H projects from the spine of the booklet SB, no steps are created by the projecting portion Ha when the spine of the booklet SB is pressed against the contact plate  330 . Therefore, it is preferable that the groove m have a depth equal to the thickness of the staple H at the least, for example. 
     Additionally, as shown in  FIG. 20 , the grooves m (m 1  and m 2 ) provided in the contact surface  330   a  of the contact plate  330  are oblique to a direction parallel to the folded front edge of the booklet SB, that is, the longitudinal direction of the staple H, and the contact plate  330  is movable vertically as described above with reference to  FIG. 11  or  17 . With this configuration, by forming the two oblique grooves m 1  and m 2  that are symmetrical relative to a centerline C of the contact plate  330  in the horizontal direction (main scanning direction) in  FIG. 20 , the distance between the grooves m 1  and m 2  can be changed with the vertical position of the contact plate  330 . In other words, when the booklet SB is bound with two staples, the positions of the grooves m 1  and m 2  can be changed according to the size of interval between the two staples in the main scanning direction. In  FIG. 20 , the higher the contact plate  330  is positioned, the narrower the interval between the two grooves m 1  and m 2 . 
       FIG. 21  illustrates the relation between the grooves m and the staples H in further detail. 
     As shown in  FIG. 21 , the grooves m (m 1  and m 2 ) have a width a greater than a width b of the staples H (a&gt;b). This relation can eliminate interference between the staples H and the grooves m. 
     Additionally, referring to  FIG. 22 , with the ratio of a horizontal length c and a vertical length d of the grooves m, the rate of changes in the distance X 1  between the grooves m according to the distance by which the contact plate  330  moves vertically (hereinafter “vertical travel distance”) can be adjusted. For example, in the configuration shown in  FIG. 22 , the horizontal length c and the vertical length d of the grooves m satisfies c:d=1:2. By using the vertical travel distance of the contact plate  330  as a variable, the distance X 1  can be calculated. 
       FIG. 23  illustrates a configuration of a contact plate  330 - 1  including grooves to accommodate both two-position stapling and four-position stapling meaning stapling a bundle of sheets at two positions and at four positions, respectively. 
     Referring to  FIG. 23 , a contact surface  330   a - 1  of the contact plate  330 - 1  includes a groove line (first row of grooves) mA consisting of the grooves m 1  and m 2  shown in  FIG. 22  to correspond to two-position stapling and a groove line (second row of grooves) mB corresponding to four-position stapling, positioned beneath the groove line mA. The groove line mB includes a grooves m 3 , m 1 ′, m 2 ′, and m 4  in that order from the left in  FIG. 23 , and the grooves m 1 ′ and m 2 ′ are identical or similar to grooves m 1  and m 2  in the groove line mA for two-position stapling. Also in the groove line mB, two grooves m 3  and m 1 ′ and the other two grooves m 2 ′ and m 4  are symmetrical relative to the centerline C of the contact plate  330 - 1  in the horizontal direction. Additionally, in the groove line mB, the relation between the width a of the grooves m and the width b of the staples H is similar to that shown in  FIG. 21  (a&gt;b) and the relation between the horizontal length c and the vertical length d of the grooves m is similar to that shown in  FIG. 22  (c:d=1:2). 
     This configuration enables, according to the vertical position of the contact plate  330 - 1 , adjustment of the number of the grooves m (in  FIG. 23 , two or four) formed in a portion facing the folded leading edge (spine) of the booklet SB as well as the size of interval between the grooves m corresponding to the interval between the staples H. 
     It is to be noted that, in the configuration shown in  FIG. 23 , although the interval between the grooves m 1 ′ and m 2 ′ and that between the grooves m 3  and m 4  are adjustable, the interval between the grooves m 1 ′ and m 3  and that between the m 2 ′ and m 4  are constant. By contrast,  FIG. 24  illustrates a configuration of a contact plate  330 - 2  including a groove line mC (third row of grooves) in addition to the groove lines mA and mB so that the size of interval between the grooves are more adjustable. 
     More specifically, in  FIG. 24 , the groove line mC includes grooves m 3 ′ and m 4 ′ that are inverted by 180 degrees from the grooves m 3  and m 4  in the groove line mB for four-position stapling and is positioned above the groove line mA for two-position stapling. The groove line mC includes grooves m 1 ′ and m 2 ′ identical or similar to the grooves m 1  and m 2  in addition to the grooves m 3 ′ and m 4 ′. With this configuration, each of two cases in which the interval between the grooves m 1 ′ and m 2 ′ is longer and shorter can have two patterns in which the interval between the grooves m 1 ′ and m 3  and that between the grooves  2 ′ and m 4  are longer and shorter, respectively. Additionally, when a width e, that is, the horizontal length in  FIG. 24 , of the grooves m 3  (m 3 ′) and m 4  (m 4 ′) is designed longer by about 2 mm than the width a of the grooves m 1 ′ and m 2 ′ (e&gt;a), the interval between the grooves m 1 ′ and m 3  and that between the grooves  2 ′ and m 4  are finely adjustable. It is to be noted that, although the groove m 1 ′ parallels the groove m 3  and the groove m 2 ′ parallels the groove m 4  in  FIGS. 23 and 24 , alternatively, inclination of them may be different. 
       FIG. 25  is a front view illustrating a configuration of a spine formation device  3 A including the contact plate  330 - 2  shown in  FIG. 24 . The spine formation device  3 A shown in  FIG. 25  has a configuration similar to that shown in  FIG. 12  except that position detectors SN 6  through SN 8  are added, and thus the descriptions of the similar portions are omitted. 
     In the spine formation device  3 A shown in  FIG. 25 , according to detection by the position detectors SN 5  through SN 8 , the vertical position (height) of the contact plate  330 - 2  against which the spine of the booklet SB is pressed is recognized. 
       FIG. 26  illustrates relations among the positions of the grooves, the size of interval between the grooves, and the vertical position of the contact surface  330   a - 2  of the contact plate  330 - 2 . In  FIG. 26 , reference characters g, h, and i respectively represent intervals between centers in the main scanning direction (horizontal direction) of the grooves m 3  and m 1 ′, that between the grooves m 1  and m 2  (m 1 ′ and m 2 ′), and that between the grooves m 2 ′ and m 4 . 
     In  FIG. 26 , the intervals h, g, and i between the grooves m 3  and m 1 ′, the grooves m 1  and m 2 , and the grooves m 2 ′ and m 4  in the main scanning direction are respectively identical at positions P 1 , P 2 , and P 3 , and these positions are used as reference positions (center values) of the staples H. The position P 1  is set based on detection by the position detector SN 7 , the position P 2  is set based on detection by the position detector SN 8 , and the position P 3  is set based on detection by the position detector SN 6 . 
     Based on the above-described configuration, positional adjustment of the contact plate  330 - 2  is described below. 
     1) Adjustment for Two-Position Stapling 
     When stapling the booklet SB with two staples H is selected, the standby position of the contact plate  330 - 2  is the position P 1 , and the contact plate  330 - 2  is moved up as shown in  FIG. 27  when the interval between the two staples H is longer and is moved down as shown in  FIG. 28  when the interval is shorter. The distance by which the contact plate  330 - 2  is moved vertically from the position P 1  depends on the inclination of the grooves. For example, when the ratios of the horizontal length and the vertical length of the grooves are 1:2 as described above and the interval between the staples H is longer by 1 mm than the reference value, the contact plate  330 - 2  is moved down 2 mm from the position P 1 . It is to be noted that the CPU  3 - 1  of the above-described control circuit performs these adjustments. 
     Similarly, when the size of interval between the staples H differs depending on staple size, the distance between the grooves is set by moving the contact plate  330 - 2  up or down from the position P 1  based on the interval between the staples H at the position P 1 . 
     2) Adjustment for Four-Position Stapling 
     As shown in  FIG. 29 , in adjustment for four-position stapling, the inner interval g between the grooves m 1 ′ and m 2 ′ is adjustable between a distance g and a distance g′, and, for the inner interval g, the outer intervals h is adjustable between a distance h′ and a distance h″ and the other outer interval i is adjustable between a distance i′ and a distance i″. In this configuration, the interval between the outer groove and the inner groove is identical or similar on both sides. That is, the distance h equals the distance i. More specifically, the user sets the inner interval g based on the distance between the inner staples H and then decides the outer intervals h and i settable at that time. Thus, the vertical position of the contact plate  330 - 2  is set. Since the width e of the outer groove m 3  or m 3 ′ is greater than the width a of the inner groove m 1 ′ (e&gt;a), the distances h and i can be adjusted finely. More specifically, the adjustment amount of the outer intervals h and i when the inner interval is determined according to the inner staples H is greater than the adjustment amount of the inner interval g. Therefore, the shorter distance h′ or i′ and the longer distance h″ or i″ are determined to enable this adjustment amount. That is, the maximum adjustment amount of the outer interval h is h″−h′. Then, the contact plate  330 - 2  is moved up or down from the position P 2  or P 3  and thus is set to the vertical position determined based on the intervals among the staples H similarly to the above-described adjustment for two-position stapling. 
     As described above, multiple grooves are formed in the contact surface  330 - a  of the contact plate  330  to house the projecting staples H, thereby eliminating steps formed by the staples H on the spine of the booklet. Therefore, steps between the spine of the booklet SB and the contact surface  330   a  of the contact plate  330  can be reduced or eliminated, thus improving the appearance of the spine of the booklet. 
     It is to be noted that, although grooves are used to reduce the steps between the spine of the booklet and the contact plate in the above-described embodiment, alternatively, elastic materials such as rubber or sponge may be provided on the contact surface of the contact plate in portions pressed against staples to prevent the staples from being buried in the spine of the booklet. In this case, effects similar to those in the configuration using grooves can be attained. 
     It is to be noted that, in the above-described two types of adjustment of the vertical position of the contact plate, the CPU  3 - 1  of the staples spine formation device  3  selects the grooves according to positional data of the staples transmitted from the CPU  2 - 1  of the bookbinding device  2 . Similarly, the CPU  3 - 1  of the staples spine formation device  3  adjusts the intervals between the grooves according to sheet size data of the booklet SB and changes the number of the grooves according to the number of the staples or the number of binding position, which is two or four in the above-described embodiment, transmitted from the CPU  2 - 1  of the bookbinding device  2 . 
     Additionally, the contact plate driving unit  331  (shown in  FIG. 18 ) may be configured to move the contact plate  330  in the direction in which the spine of the booklet extends in addition to the vertical direction in figures to correspond to changes in the position of the stapes binding the booklet in addition to the size of interval therebetween. 
     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.