Abstract:
A sheet holding apparatus having: first and second folding rollers; and first and second pressurizing rollers, wherein the apparatus introduces a sheet of paper by rotating at least the first folding roller to pass the sheet of paper between the first folding roller and the first pressurizing roller, while the two folding rollers are separated when the first pressurizing roller pressurizes the first folding roller; and folds the paper by creasing between the two folding rollers by rotating the two folding rollers in opposite directions when the pressurizing rollers respectively pressurize the two folding rollers, and by conveying the sheets of paper while holding them by the two folding rollers, wherein when folding, the two folding rollers are pressurized to each other, and a driving force is transferred from the first to the second folding roller, and the two folding rollers are rotated in the opposite directions.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is based on Japanese Patent Application No. 2006-143698 filed with Japan Patent Office on May 24, 2006, the entire content of which is hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a sheet folding device suitable for using as an auxiliary device of an image forming apparatus and a sheet post-processing apparatus. 
         [0004]    2. Description of the Related Art 
         [0005]    As a sheet folding device used as an auxiliary device of an image forming apparatus, for example, as described in Unexamined Japanese Utility Model Application Publication No. 62-96067(Hereinafter we refer to Patent Document 1), there is a folding device for using a pair of folding rollers, driving the folding rollers to rotate in the opposite directions, conveying a sheet of paper by one and the other of the folding rollers, folding the sheet of paper between both folding rollers, passing it through a nip between both folding rollers, thereby conveying it with creating a holding line. 
         [0006]    In an apparatus described in Patent Document 1, folding motors as a driving source are connected respectively to a first folding roller and a second folding roller and by driving by the folding motors, the folding rollers are driven to rotate in the opposite directions. 
         [0007]    In Unexamined Japanese Patent Application Publication 2005-96990(Hereinafter we refer to Patent Document 2), disclosed is a sheet folding device for driving the first and second folding rollers to rotate in the opposite directions by a power transfer mechanism having a switching mechanism for transferring or canceling the transfer from one driving source, thereby folding a sheet of paper. 
         [0008]    In an apparatus described in Patent Documents 1, the first folding roller and the second folding roller are respectively driven by the driving sources, thereby are rotated in the opposite directions thus sheets of paper are folded. In such a folding device, caused by a time lag between start timings of driving motors the start timing of the first folding roller may be varied from the start timing of the second folding roller. 
         [0009]    Further, in an apparatus described in Patent Document 2, although one driving source is used, when switching the first folding roller and second folding roller from the separation state to the pressurized state, in cases where the gear meshing condition of the driving system of each roller is bad, and when the mutual crests collide with each other, one of the gear rotates slightly, thus an appropriate meshing condition is obtained. Due to the slight rotation, a time lag between the start timings of the two folding rollers may be caused. 
         [0010]    When the first and second folding rollers are varied in the start timing, a side of the sheet in contact with the roller at early start timing is sent into the nip portion between the rollers earlier than the side in contact with the roller at later start timing. Therefore, the fold line is shifted for example from the predetermined position T 1  to T 2  as shown in  FIG. 1 . 
         [0011]    The shift of the folding position as shown in  FIG. 1  reaches about 1 mm and when folded sheets of paper are bundled, the spine of the paper bundle becomes uneven, thus the quality of the processed article is deteriorated. 
       SUMMARY OF THE INVENTION 
       [0012]    A sheet holding apparatus reflecting one aspect of the present invention has a first folding roller, a second folding roller, and a first pressurizing roller; and a second pressurizing roller. The sheet folding apparatus executes an introducing step to introduce a sheet of paper by driving to rotate at least the first folding roller to pass the sheet of paper between the first folding roller and the first pressurizing roller, while the first folding roller and second folding roller are separated in a state where at least the first pressurizing roller pressurizes the first folding roller; and executes a folding step for folding the sheet of paper by creasing the sheets of paper between the first and second folding rollers by rotating the first folding roller and the second folding roller in opposite directions in a state where the first and second pressurizing rollers respectively pressurize the first and second folding rollers, and by conveying the sheets of paper while holding them by the first folding roller and second folding roller. In the folding step, the first folding roller and second folding roller are pressurized to each other, and by pressurizing of the first and second folding rollers a driving force is transferred from the first folding roller to the second folding roller, and the first and second folding rollers are rotated mutually in the opposite directions. 
     
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0013]    These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings in which: 
           [0014]      FIG. 1  is a drawing for explaining a shift of the folding position; 
           [0015]      FIGS. 2(   a ) and ( b ) are drawings showing the sheet folding device relating to the embodiment of the present invention; 
           [0016]      FIG. 3  is a drawing showing the drive mechanism at the step of conveying a sheet of paper S; 
           [0017]      FIG. 4  is a drawing showing the drive mechanism at the step of folding the sheet of paper S; 
           [0018]      FIG. 5  is a drawing showing the mechanism for moving the second folding roller; 
           [0019]      FIG. 6  is a drawing showing the power transfer mechanism between the gears; and 
           [0020]      FIG. 7  is a schematic view of the image forming apparatus having the sheet post-processing apparatus relating to the embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    Hereinafter, the present invention will be explained by referring to the embodiment, though the present invention is not limited to the embodiment. 
         [0022]      FIGS. 2(   a ) and  2 ( b ) are drawings to explain a folding operation of the sheet folding device relating to the embodiment of the present invention. 
         [0023]      FIG. 2(   a ) shows the step for introducing the sheet of paper S to the sheet folding device and  FIG. 2(   b ) shows the folding step of the sheet of paper S. 
         [0024]    Opposite to a folding roller  301  as a first folding roller, a folding roller  302  as a second folding roller is arranged, and a pressurizing roller  303  is pressurized to the folding roller  301 , and a pressurizing roller  304  is pressurized to the folding roller  302 . The pressurizing forces of the pressurizing rollers  303  and  304  are respectively given by a spring  370  via rollers  305  and  306 . The spring  307  is fit to a fixed pin  308  at its center and compresses the shafts of the rollers  305  and  306 , thus the pressurizing rollers  303  and  304  are respectively pressurized to the folding rollers  301  and  302 . 
         [0025]    As explained later, at the introduction step shown in  FIG. 2(   a ), the folding roller  302  is away from the folding roller  301  and is driven to rotate in the same direction as the folding roller  301  as shown by the arrow. 
         [0026]    Therefore, in the step of  FIG. 2(   a ), the sheet of paper S introduced from underneath is conveyed upward by being held between the folding roller  301  and the pressurizing roller  303  and being held between the folding roller  302  and the pressurizing roller  304 . 
         [0027]    At the stage of conveying of the sheet of paper S with a predetermined length (for example, ½ or ⅓ of the length of the sheet of paper), the introducing step of the sheet of paper S is finished. 
         [0028]    Next, the process goes to the folding step and as shown in  FIG. 2(   b ), the folding roller  302  is pressurized to the folding roller  301 . Further, at the folding step, the pressurizing rollers  303  and  304  are respectively kept in the pressurized state with the folding rollers  301  and  302 . 
         [0029]    At the folding step, the folding roller  302  is pressurized to the folding roller  301  and the driving of the folding roller  302  is shut off. Therefore, to the folding roller  302 , the rotation driving force is transferred by contact with the folding roller  301  and the folding roller  302  is rotated. 
         [0030]    In this way, the folding roller  301  and folding roller  302  are rotated mutually in the opposite directions, and midway between the folding roller  301  and the folding roller  302 , the sheet of paper S is bent and enters the nip portion formed by the folding roller  301  and folding roller  302  with the fold line SA at the head. 
         [0031]    The folding rollers  301  and  302  are rotated further, thus as shown in  FIG. 2(   b ), the sheet of paper S is conveyed with the fold line SA at the head and folded. 
         [0032]      FIGS. 3 and 4  show the driving mechanism including the power transfer system of the sheet folding device shown in  FIGS. 2(   a )and  2 ( b ), and  FIG. 3  shows the driving mechanism at the step of conveying the sheet of paper S, and  FIG. 4  shows the driving mechanism at the step of folding the sheet of paper S. 
         [0033]    The rotations of the folding rollers  301  and  302  shown in  FIGS. 2(   a ) and  2 ( b ) by the arrow are driven by a motor Ml. 
         [0034]    To a shaft AX 1 , the folding roller  301  and a gear  323  are fixed, and to a shaft AX 2 , the folding roller  302  and a gear  324  are fixed, and to a shaft AX 3 , the pressurizing roller  303  and a gear  326  are fixed, and to a shaft AX 4 , the pressurizing roller  304  and a gear  327  are fixed. 
         [0035]    Driving to move the folding roller  302  from the position shown in  FIG. 2(   a ) to the position shown in  FIG. 2(   b ) and switching of the rotation driving of the folding roller  302  are executed by a motor M 2 . 
         [0036]    A cam  330  is rotated by the motor M 2 , and a cam follower  332  is moved by the rotation of the cam  330 , and a lever  331  is rotated around the shaft AX 1 . 
         [0037]    By the rotation of the lever  331 , a gear  325  born by the lever  331  is moved and meshed with the gear  324 . 
         [0038]    Further, by the rotation of the motor M 2 , the folding roller  302  is separated from the folding roller  301 . The mechanism for moving the folding roller  302  like this is shown in  FIG. 5 . To the shaft to which the cam  330  is fixed, a gear  321 A is fixed and a gear  323 A rotatably born by the shaft AX 1  is meshed with the gear  321 A. A cam  323 B rotating integrally with the gear  323 A born by the shaft AX 1  makes contact with a circular cam follower  324 A born by the shaft AX 2  by which the folding roller  302  is born, and the contact is ensured surely by the weight of a lever  335  born by a shaft AX 5 , the folding roller  302 , and gears  324  and  324 A. 
         [0039]    On the lever  335 , the folding roller  302  is born by the shaft AX 2  and the pressurizing roller  327  is born by the shaft AX 4 . Further, the shaft AX 4  is supported by an oblong hole  335 A formed in the lever  335  and can be moved and as explained above, the pressurizing roller  304  is pressurized to the folding roller  302  by the spring  307 . 
         [0040]    The pressurizing roller  303  and shaft AX 3  of the gear  326  are guided by an oblong hole  336 A formed in a fixing support plate  336  and can be moved and by the spring  307 , the pressurizing roller  303  is pressurized to the folding roller  301 . 
         [0041]    A spring  334  presses the lever  331  so as to rotate counterclockwise as shown in  FIGS. 3 and 4  and makes the cam follower  332  touch with the cam  330 . 
         [0042]    The outside diameter of the gear  323  and the outside diameter of the folding roller  301  are almost the same and the outside diameter of the gear  324  and the outside diameter of the folding roller  302  are almost the same. Therefore, at the sheet folding step, when the folding roller  302  is pressurized to the folding roller  301 , as shown in  FIG. 4 , the teeth of the gear  323  and the teeth of the gear  324  are overlaid on each other viewed in the shaft direction. 
         [0043]    Even if the teeth of the gear  323  and the teeth of the gear  324  are overlaid on each other, the power is not transferred from the gear  323  to the gear  324 . 
         [0044]    Such a power transfer mechanism to the gear  323  and gear  324  will be explained by referring to  FIG. 6 . 
         [0045]    In  FIG. 6 , teeth  323 A of the gear  323  and teeth  324 A of the gear  324  are installed at shifted positions in the directions of the shafts AX 1  and AX 2 . Therefore, even if the gear  323  and gear  324  are installed so that the teeth  323 A and  324 A are overlaid on each other viewed in the directions of the shafts AX 1  and AX 2 , the power of the gear  323  is not transferred to the gear  324 . On the other hand, teeth  325 A of the gear  325  are formed in a length of meshing with the teeth  323 A and  324 A, so that when the gear  325  approaches the gears  323  and  324 , the power of the gear  323  is transferred to the gear  324  via the gear  325 . 
         [0046]    At the step of introducing sheets of paper into the folding device, as shown in  FIG. 3 , the small diameter portion of the cam  330  is opposite to the cam follower  332 . As a result, the lever  331  is at the position rotated counterclockwise by the spring  334  and the power of the gear  323  is transferred to the gear  324  via the gear  325 . Further, the folding roller  302  is pushed up by the cam  323 B and is separated from the folding roller  301 . 
         [0047]    By doing this, the folding roller  301  and folding roller  302 , as shown in  FIG. 2(   a ), are rotated in the same direction, thereby convey the sheet of paper S, and introduce it into the folding device. 
         [0048]    At the folding step of the sheets of paper S, the cam  330  rotates and the large diameter portion presses the cam follower  332 . By doing this, the lever  331  rotates clockwise and separates the gear  325  from the gear  324 , and the cam  323 B rotates to the phase position where the folding roller  302  is moved down, thus the folding roller  302  makes contact with the folding roller  301 . And, the folding roller  302 , by the contact with the folding roller  301 , rotates by following the folding roller  301 . 
         [0049]    As explained above, the folding roller  302 , at the step of introducing the sheets of paper S into the folding device, is separated from the folding roller  301 , is driven by the motor M 1 , and rotates in the same direction as that of the folding roller  301 , and at the step of folding the sheets of paper S, the folding roller  302  makes contact with the folding roller  301 , is separated from the power transfer system, so that rotates by following the folding roller  301 . 
         [0050]    Therefore, the start timing of the folding step, that is, the reverse start timing in the rotational direction of the folding roller  302  is set precisely and the fold line of each sheet of paper is formed at the precise position. 
         [0051]      FIG. 7  is a schematic view of the image forming apparatus having the sheet post-processing apparatus relating to the embodiment of the present invention. 
         [0052]    In  FIG. 7 , numeral  10  indicates an image forming unit for forming an image on a sheet of paper by the electrophotographic method, numeral  20  indicates an image reading unit for reading an image of a document and outputting image data, numeral  30  indicates a sheet post-processing apparatus having a perforating device  31  and a sheet folding device  32 , and numeral  40  indicates a sheet post-processing apparatus having a binding device  44 . 
         [0053]    The image forming unit  10  includes a photoreceptor  11 , an image forming unit  12  for charging, exposing the photoreceptor  11 , and developing to form a toner image, and transferring the toner image formed on the photoreceptor  11  onto a sheet of paper, storage units  13   a ,  13   b ,  13   c , and  13   d  for distinguishing and storing sheets of paper of various sizes for each size, paper feed units  18   a ,  18   b ,  18   c , and  18   d  having rollers for taking out sheets of paper one by one from the storage units  13   a ,  13   b ,  13   c , and  13   d  and conveying them to the image forming unit  12 , a reverse paper feed unit  14 , when forming an image on both sides of each sheet of paper, for inverting the sheet of paper and conveying the sheet of paper with one side recorded to the image forming unit  12 , and a fixing device  15  for fixing the toner image transferred onto the sheet of paper. 
         [0054]    The image reading unit  20  includes a document feed table  21  on which documents are loaded, a platen roller  22  for conveying documents and forming a reading position, a document ejection table  23  on which a read document is loaded, and an image sensor  24  for receiving image light reflected from a document and generating a reading signal. 
         [0055]    The sheet post-processing apparatus  30  includes the perforating device  31  for making a hole for a file and the sheet folding device  32  explained previously. 
         [0056]    A sheet post-processing apparatus  40  connected to the sheet post-processing apparatus  30  includes a fixed paper receiving tray  41  for receiving sheets of paper when forming few images, an elevating paper receiving tray  42  for receiving sheets of paper when forming a large amount of images and in the binding mode, an intermediate stacker  43  for stacking sheets of paper, and a stapler  44  for binding a corner or one side of a sheet of paper. 
         [0057]    According to the present invention, at the step of folding sheets of paper, the second folding roller is pressured to the first folding roller, and the driving force is transferred by pressurizing from the first folding roller to the second folding roller, thus both folding rollers are rotated mutually in the opposite directions, so that the timing of sending sheets of paper to the nip portion between both folding rollers is not varied, and shifts of the folding position due to the time lag can be eliminated.