Abstract:
A sheet folding apparatus for folding a set of sheets into two at a center thereof, includes: a sheet number recognition section that recognizes the number of sheets in the set; a pair of rotating rollers pressed against each other to form a nip portion; a blade member retractably moves with respect to the nip portion; and a blade member control section that controls the blade member to move toward the nip portion to push the set of sheets in the nip portion at a depth corresponding to the number of sheets recognized by the sheet number recognition unit.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a sheet folding apparatus for folding a set of sheets into two at the center.  
         [0003]     2. Description of the Related Art  
         [0004]     Conventionally, some of image forming apparatuses such as a copying machine or printer have a function called a booklet process. In the booklet process, the center of the sheets in which the image is formed is stapled and the set of sheets is folded into two at the center.  
         [0005]     In the image forming apparatus having this kind of function, while the set of sheets stapled at the center is delivered to the nip portion where the pair of rotating rollers is pressed against each other, the set of sheets is folded into two at the center by passing the set of sheets through the nip portion (for example, see Japanese Patent Laid-Open Publication No. 11-332734).  
         [0006]     However, in the image forming apparatus proposed by the above reference, forming an image on the sheet sometimes decreases frictional force between a sheet in direct contact with the rotating roller and a sheet beneath the sheet in direct contact with the rotating roller. In this case, it is reported that only the sheet in direct contact with the rotating roller is stripped from the set of sheets and thereby taken into the nip portion ahead of other sheets.  
         [0007]     As a countermeasure, it is proposed to use a blade member to deliver the set of sheets to the nip portion by pushing them in. In this proposal, a sheet in direct contact with the rotating roller and a sheet beneath the sheet in direct contact with the rotating roller are caused to come into contact with each other by pressure of the blade member, which prevents the sheet in direct contact with the rotating roller from being stripped from the set of sheets and taken into the nip portion ahead of other sheets.  
         [0008]     However, only by pushing the set of sheets in with the blade member, a trace of the blade member may remain on the sheet depending on the number of sheets included in the set of sheets.  
         [0009]     The above problem is generated not only in the case where the blade is pressed against paper, but also in the case where the blade is pressed against sheet-like medium other than paper. Further, the problem is also generated in the set of sheets which is not stapled.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention has been made in view of the above circumstances and provides a sheet folding apparatus which passes the set of sheets through the nip portion without stripping off, and reduces a load on the set of sheets, which is caused by the push-in of the set of sheets with the blade member.  
         [0011]     According to an aspect of the present invention, a sheet folding apparatus for folding a set of sheets into two at a center thereof, includes: a sheet number recognition section that recognizes the number of sheets in the set; a pair of rotating rollers pressed against each other to form a nip portion; a blade member retractably moves with respect to the nip portion; and a blade member control section that controls the blade member to move toward the nip portion to push the set of sheets in the nip portion at a depth corresponding to the number of sheets recognized by the sheet number recognition unit. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     An embodiment of the present invention will be described in detail based on the following figures, wherein:  
         [0013]      FIG. 1  schematically shows part of a copying machine provided with a sheet folding apparatus according to an embodiment of the invention;  
         [0014]      FIG. 2  is a schematic view showing a sequence of actions of a booklet processing portion shown in  FIG. 1 ;  
         [0015]      FIG. 3  shows a blade member and a pair of rotating rollers when viewed from a top surface side;  
         [0016]      FIG. 4  shows an inside of a drive unit which retractably moves the blade member with respect to a nip portion of the rotating rollers;  
         [0017]      FIG. 5  shows a state in which the blade member pushes a set of sheets in the nip portion; and  
         [0018]      FIG. 6  is a flowchart of a routine which determines a distance a according to the number of sheets included in the set of sheets. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     Referring now to the accompanying drawings, an embodiment of the invention will be described in detail.  
         [0020]      FIG. 1  schematically shows part of a copying machine provided with a sheet folding apparatus according to the embodiment of the invention.  
         [0021]     A copying machine  1  has an image forming apparatus  10  and a post-processing apparatus  11 . A recording sheet in which the image is already formed is conveyed from the image forming apparatus  10  to the post-processing apparatus  11 , and the post-processing apparatus  11  performs a stapling process and a folding process to the recording sheet.  
         [0022]     The post-processing apparatus  11  has a stapling-processing unit  12  and a booklet processing unit  13 . The stapling-processing unit  12  staples end portions of the stacked plural sheets. The booklet processing unit  13  performs the stapling process of stapling central portions of the stacked plural sheets, and also performs the folding process of folding the set of sheets whose central portions are folded into two at the central portions of the sheets. The sheet folding apparatus according to the embodiment of the invention is installed in the booklet processing unit  13 .  
         [0023]     The post-processing apparatus  11  has a first sheet conveying path A, a second sheet conveying path B, and a third sheet conveying path C. The first sheet conveying path A directly discharges the recording sheet conveyed from the image forming apparatus to a top surface of the post-processing apparatus  11 , the second sheet conveying path B conveys the recording sheet to the stapling-processing unit  12 , and the third sheet conveying path C conveys the recording sheet to the booklet processing portion  13 . Conveying rollers  15  are provided in each sheet conveying path. The recording sheet conveyed by the first sheet conveying path A is discharged toward a first sheet-discharge tray  14  provided on the top surface of a frame  11   a  of the post-processing apparatus  11 . Because the stapling-processing unit  12  has no relation to the invention, the description of the stapling-processing unit  12  is omitted, and only the booklet processing portion  13  will be described below.  
         [0024]     The booklet processing portion  13  has a compiler tray  131 , a stapler  132 , a sheet folding device  133 , control unit  134 , a second paper-discharge tray  135 , a photosensor  136 , and a fourth sheet conveying path D. The recording sheets are temporarily stored in the compiler tray  131  to arrange the sheets to be conveyed through the third sheet conveying path C. The stapler  132  staples the central portions of the sheets which are arranged and stacked on one another in the compiler tray  131 . The sheet folding device  133  folds the set of sheets stapled by the stapler  132  into two at the central portions of the sheets. The control unit  134  controls the whole booklet processing portion  13 . The set of sheets to which the booklet processing has been performed is discharged to the second paper-discharge tray  135 . The photosensor  136  is used in order to count the number of sheets included in the set of sheets. The fourth sheet conveying path D conveys the set of sheets folded into two to the second paper-discharge tray  135 . The sheet folding apparatus according to the embodiment of the invention has the sheet folding device  133 , the control unit  134 , and the photosensor  136 .  
         [0025]     The sheet folding device  133  shown in  FIG. 1  has a drive unit  1331 , a blade member  1332 , and a pair of rotating rollers  1333  which is pressed against each other. The blade member  1332  pushes the set of sheets in a nip portion formed between the pair of rotating rollers  1333 . The drive unit  1331  is retractable with respect to the nip portion and pushes the set of sheets in the nip portion to a predetermined depth by protruding the blade member  1332  according to an instruction from the control unit  134 .  
         [0026]     The compiler tray  131  has a positioning member  1311  and a stepping motor  1312 . The positioning member  1311  is attached to a rack (not shown) which engages a pinion gear  1312   a , and the pinion gear  1312   a  is attached to a rotating axis of the stepping motor  1312 . When the stepping motor  1312  receives the instruction from the control unit  134 , the stepping motor  1312  moves the positioning member  1311  attached to the rack. The positioning member  1311  is moved in an approximately vertical direction to change a position of the sheet while supporting a bottom portion of the sheet stored in the compiler tray.  
         [0027]     A flow of the process in the booklet processing portion  13  will be described.  
         [0028]      FIG. 2  is a schematic view showing a sequence of actions of the booklet processing portion shown in  FIG. 1 .  
         [0029]     Part (a) of  FIG. 2  shows the state in which the plural sheets sequentially conveyed to the compiler tray  131  are supported and arranged by the positioning member  1311 . In part (a) of  FIG. 2 , the positioning member  1311  is moved upward from a home position shown by a dotted line.  
         [0030]     Part (b) of  FIG. 2  shows the state in which, when all the sheets are stored in the compiler tray  131 , the positioning member  1311  is moved downward from the position shown in part (a) of  FIG. 2  so that a center P of the sheets corresponds to a stapling position of the stapler  132 . Then, the stapler  132  staples the center P of the sheets to form the set of the sheets.  
         [0031]     In part (c) of  FIG. 2 , the positioning member  1311  supporting the set of sheets is moved upward from the position shown in part (b) of  FIG. 2  so that the center P of the set of sheets is arranged in front of the blade member  1332  of the sheet folding device  133 .  
         [0032]     In part (d) of  FIG. 2 , when the blade member  1332  proceeds to the nip portion of the pair of rotating rollers  1333 , the center P of the set of sheets is pushed in the nip portion of the pair of rotating rollers  1333 , thereby being folded into two.  
         [0033]     In part (e) of  FIG. 2 , the blade member  1332  is extracted from the nip portion of the pair of rotating rollers  1333 , and the set of sheets folded into two is being discharged to the second paper-discharge tray  135  by the conveying rollers  15 .  
         [0034]      FIG. 3  shows the blade member and the pair of rotating rollers when viewed from a top surface side.  
         [0035]     Grooves  1333   b  are intermittently provided in the pair of rotating rollers  1333  shown in  FIG. 3 . The grooves  1333   b  are formed in a circumference of the roller  1333 . In the blade member  1332  shown in  FIG. 3 , leading edges  1332   a  are intermittently formed corresponding to the grooves  1333   b  provided in the pair of rotating rollers  1333 . Because of the shape of the blade member  1332  described above, the leading edges  1332   a  of the blade member  1332  enter the grooves  1333   b  of the pair of rotating rollers  1333  through the set of sheets when the blade member  1332  proceeds toward the pair of rotating rollers  1333 . The detail of the shape of the blade member  1332  and the rotating roller  1333  will be described later. A central shaft  1333   a  of the rotating roller  1333  is also shown in  FIG. 3 .  
         [0036]      FIG. 4  shows the inside of the drive unit which retractably moves the blade member with respect to the nip portion of the rotating rollers.  
         [0037]     The drive unit  1331  shown in  FIG. 4  has a wheel  1331   b , an arm  1331   d , and a guide frame  1331   f . The wheel  1331   b  is fixed to the rotating shaft  1331   a  of the stepping motor. One end portion of the arm  1331   d  is attached to the wheel  1331   b  by a first shaft  1331   c . The guide frame  1331   f  has a long hole into which a second shaft  1331   e  is fitted, and the second shaft  1331   e  is fixed to the other end portion of the arm  1331   d . The blade member  1332  is attached to the end portion of the arm  1331   d  on the side where the second shaft  1331   e  is fixed. Further, the stepping motor and the guide frame  1331   f  are fixed to predetermined positions in the apparatus respectively. Therefore, in the drive unit  1331 , rotational motion of the stepping motor is converted into linear motion of the blade member  1332 .  
         [0038]     Part (a) of  FIG. 4  shows the state in which the blade member  1332  is retracted to the most backward position. In the sheet folding device  133 , the position shown in part (a) of  FIG. 4  is the home position of the blade member  1332 .  
         [0039]     Part (b) of  FIG. 4  shows the state in which the wheel  1331   b  is rotated by 90° in an arrow A direction from the position shown in part (a) of  FIG. 4 . Part (c) of  FIG. 4  shows the state in which the wheel  1331   b  is further rotated by 90° in the arrow A direction from the position shown in part (b) of  FIG. 4 . Part (c) of  FIG. 4  shows the state in which the blade member  1332  is protruded to the most forward position.  
         [0040]     In the sheet folding device  133 , a push-in depth is changed according to the number of sheets included in the set of sheets. The push-in depth is the depth to which the set of sheets is pushed in the nip portion of the pair of rotating rollers. The push-in depth is changed by controlling the rotation angle of the stepping motor of the drive unit  1331 .  
         [0041]     Therefore, in the sheet folding device  133 , when the control unit  134  provides the instruction that the stepping motor is rotated to the predetermined rotation angle so that the set of sheets is pushed in the nip portion to the push-in depth according to the number of sheets included in the set of sheets. After the stepping motor is rotated to the predetermined rotation angle, the stepping motor is rotated in the opposite direction to the arrow A to return the blade member  1332  to the home position shown in part (a) of  FIG. 4 . Alternatively, the blade member  1332  may be returned to the home position by rotating the stepping motor further in the arrow A direction, after the set of sheets is pushed in the nip portion to the push-in depth according to the number of sheets included in the set of sheets and the set of sheets is drawn in the nip portion.  
         [0042]      FIG. 5  shows the state in which the blade member pushes the set of sheets in the nip portion.  
         [0043]      FIG. 5  shows the state in which the leading edge  1332   a  of the blade member  1332  pushes the set of sheets in the nip portion. In the sheet folding device  133 , the number of sheets included in the set of sheets is recognized by the control unit  134  which receives a signal from the photosensor  136 , and the control unit  134  controls a distance α between a chain double-dashed line L which links centers of the rotating rollers  1333  and a folded position Q of the set of sheets according to the number of sheets recognized by the control unit  134 . The distance α is a push-in amount of the set of sheets by the blade member  1332 . Further, in the sheet folding device  133 , the rotation angle of the stepping motor is determined according to a combination of the number of sheets included in the set of sheets and the distance α. As shown in  FIG. 3 , the leading edge  1332   a  of the blade member  1332  is configured so as to enter the groove  1333   b  of the pair of rotating rollers  1333  through the set of sheets. This aims to prevent pullback of the set of sheets by causing the leading edge  1332   a  of the blade member  1332  to intrude in a non-nip portion (where a pair of rotating rollers are not in contact with each other,  1333   b ) to push the set of sheets in while reducing the frictional force between the blade member and the set of sheets when the blade member  1332  is extracted from the nip portion while the set of sheets is nipped. Therefore, the set of sheets can be pushed in without applying excessive force which causes wrinkle to the set of sheets.  
         [0044]      FIG. 6  is a flowchart of a routine which determines the distance α according to the number of sheets included in the set of sheets.  
         [0045]      FIG. 6  shows the routine to be started up when the sheets, of which the number of sheets is previously specified, are stored in the compiler tray  133 . In Step S 1 , it is decided whether the number of the sheets is less than six or not. When the number of the sheets is not less than six, the routine proceeds to Step S 2 . In Step S 2 , it is decided whether the number of the sheets is less than eleven or not. When the number of the sheets is not less than eleven, the routine proceeds to Step S 3 , and the control unit  134  provides the instruction of the push-in amount, i.e. the distance a of 2 mm to the drive unit  1331 . Then, the routine is ended. Therefore, the folded position Q of the set of sheets pushed in with the blade member  1332  is further pushed in the position 2 mm deeper than the chain double-dashed line L, which links the centers of the rotating rollers  1333 .  
         [0046]     On the other hand, in Step S 1 , when the number of the sheets is less than six, the routine proceeds to Step S 4 , and the control unit  134  provides the instruction of the distance α of 0 mm to the drive unit  1331 . Then, the routine is ended. Therefore, the folded position Q of the set of sheets pushed in with the blade member  1332  is further pushed in to reach the chain double-dashed line L which links the centers of the rotating rollers  1333 . In Step S 2 , when the number of the sheets is less than eleven, the routine proceeds to Step S 5 , and the control unit  134  provides the instruction of the distance α of 1 mm to the drive unit  1331 . Then, the routine is ended.  
         [0047]     As described above, when the number of sheets included in the set of sheets is small, the set of sheets can pass completely through the nip portion, even if the push-in amount of the set of sheets in the nip portion by the blade member is decreased when compared with the case in which the number of sheets included in the set of sheets is large. Therefore, in the sheet folding device  13 , since the set of sheets is pushed in the nip portion with the push-in amount (distance α) into the nip portion according to the number of sheets included in the set of sheets, the load on the set of sheets including the small number of sheets can be reduced. This is not the case in which the set of sheets is pushed in the nip portion uniformly regardless of the number of sheets included in the set of sheets. As a result, according to the invention, no trace remains in the sheet, which makes the set of sheets look better.  
         [0048]     In the embodiment, the grooves  1333   b  formed in the circumference of the roller  1333  are intermittently provided in the pair of rotating rollers  1333 , and the leading edges  1332   a  are intermittently formed in the blade member  1332  corresponding to the grooves  1333   b  provided in the pair of rotating rollers  1333 . However, in the invention, the rotating roller may be formed in a common cylindrical shape and the blade member may be formed in the blade shape in which the leading edges  1332   a  shown in  FIG. 3  are omitted. In the embodiment, the set of sheets in which the stapling process is performed to the center is described by way of example. However, it is also possible to process the set of sheets to which the stapling process is not performed.  
         [0049]     The entire disclosure of Japanese Patent Laid-Open Publication No. 2004-257162 filed on Sep. 3, 2004, including specification, claims, drawings and abstract is incorporated herein by reference in its entirety.