Abstract:
The present invention relates to a sheet operative member contacting a sheet and conveying with frictional force the sheet or separating the sheet, the sheet operative member comprising a plurality of protrusions on an operative surface with the sheet. Each of the protrusions includes a standing portion standing up from the operative surface and a spherical portion disposed at a distal end of the standing portion.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a sheet operative member such as a conveyance roller for contacting and conveying sheets by frictional force thereof, and a separation pad for separating sheets, to a sheet conveying apparatus using this member, and to an image processing apparatus such as an electrophotographic photocopier, a printer, a word processor, and a facsimile machine.  
           [0003]    2. Description of Related Art  
           [0004]    Image forming apparatuses such as printers and photocopiers using one of electrophotographic methods or other recording methods are widely available these days. In accordance with tendency of higher performance and longer duration of the apparatuses, improvements in feeding accuracy and durability in conveyance rollers used in the image forming apparatus are required. Separation pads used for the image forming apparatuses also require in the same manner improvements in separation accuracy and durability.  
           [0005]    A conventional conveyance roller  100  is formed, as shown in FIG. 8, of a core metal  101  made of a metal or molded material and a cylindrical rubber portion  102  made of a rubber material such as EPDM (ethylene propylene rubber), CR rubber (chloroprene rubber), silicone rubber, or urethane rubber for contacting a recording sheet and conveying the recording sheet by frictional force. Polishing is made in arrow C or D direction shown in FIG. 8 on a cylindrical surface  102   a  of the cylindrical rubber portion  102 .  
           [0006]    A separation pad  103  shown in FIG. 9 is formed of a rubber material such as EPDM, CR rubber, silicone rubber, or urethane rubber in substantially the same manner as the conveyance roller  100  described above and is constituted of a rubber portion  104  in contact with the conveyance roller, and a holder  105  holding the rubber portion  104 . Polishing is made in arrow E or F direction shown in FIG. 9 on a rubber surface  104   a  of the rubber portion  104 .  
           [0007]    The conventional conveyance roller and the conventional separation pad, however, raised the following problems.  
           [0008]    Where the conventional conveyance roller conveys a recording sheet, paper powder generated from surfaces of the recording sheets may attach to the cylindrical surface of the conveyance roller according to an increased conveyance sheet number of the recording sheets, thereby slipping in recording sheet conveyance with lowered frictional force of the conveyance roller, and thereby raising a problem of impaired images and jamming occurrences. To extend the product duration of the apparatus body, users were required to make cleaning, or the apparatuses had a structure that the users can replace the conveyance rollers. As a result, this invited lowered usability and increased costs from additional parts in a structure that the conveyance roller is replaceable.  
           [0009]    Where the conventional separation pad separates and conveys the recording sheets, paper powder generated from surfaces of the recording sheets may attach to the surface of the separation pad according to an increased conveyance sheet number of the recording sheets, thereby raising a problem of doubly feeding of the recording sheets due to lowered frictional force of the separation pad. Therefore, substantially the same problem is raised as in the case of the conveyance roller.  
         SUMMARY OF THE INVENTION  
         [0010]    This invention is to solve the above problems. It is an object of the invention to provide a sheet operative member such as a conveyance roller or the like avoiding lowered frictional force due to paper powder attachments, realizing highly durable roller members or the like, and having an inexpensive structure of a longer duration with maintenance free and to provide a sheet conveying apparatus and an image processing apparatus using the member.  
           [0011]    A preventative structure according to the invention to accomplish the above object is a sheet operative member contacting a sheet and conveying with frictional force the sheet or separating, including a plurality of protrusions on an operative surface with the sheet; and each of the protrusions including: a standing portion standing up from the operative surface; and a spherical portion disposed at a distal end of the standing portion.  
           [0012]    Where a conveyance roller is structure of the sheet operative member thus structured, the sheet is conveyed with frictional force from contact with the spherical portions of the protrusions of the conveyance roller. Because the contact between the conveyance roller and the sheet is at the spherical portion at the distal end of the protrusion, paper powder or the like generated from the sheet surfaces is not attached to the spherical portions of the protrusions but deposited in an attaching manner on a circumferential surface of the conveyance roller. This realizes a conveyance roller having property of stable conveyance and high durability. The same advantages can be provided in a case where the sheet operative member is used as a separation pad.  
           [0013]    According to the invention, where fine protrusions described above are formed to the sheet operative member, a sheet apparatus is hardly affected from paper powder or the like generated from the sheet surfaces and can enjoy a stable sheet processing performance. Therefore, where structured in use of the sheet operative member described above, the sheet apparatus such as a sheet conveying apparatus can be provided with maintenance free and inexpensive costs. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a schematic perspective view showing the whole conveyance roller;  
         [0015]    [0015]FIG. 2 is an enlarged perspective view showing a portion where fine protrusions formed on the conveyance exist;  
         [0016]    [0016]FIG. 3 is a side view showing the fine protrusions formed on the conveyance roller;  
         [0017]    [0017]FIG. 4 is an illustration showing a contact state between the fine protrusions and the recording sheet while the conveyance roller is conveying the sheet;  
         [0018]    [0018]FIG. 5 is a whole schematic view showing an image processing apparatus using a sheet operative member according to the invention;  
         [0019]    [0019]FIG. 6 is a schematic perspective view showing the entire structure of a separation pad;  
         [0020]    [0020]FIG. 7 is an illustration showing a contact state between the fine protrusions and the recording sheet while the separation pad is in a sheet separation state;  
         [0021]    [0021]FIG. 8 is a schematic perspective view showing a conventional conveyance roller;  
         [0022]    [0022]FIG. 9 is a schematic perspective view showing a conventional separation pad; and  
         [0023]    [0023]FIG. 10 is an illustration showing an image reading apparatus using a sheet operative member according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    An image forming apparatus for forming images on a sheet is exemplified as an image processing apparatus using a sheet operative member according an embodiment of the invention.  
         [0025]    [First Embodiment] 
         [0026]    The first embodiment is an example in which the sheet operative member is used as a conveyance roller, and is described in reference to FIG. 1 to FIG. 5. It is to be noted that: FIG. 1 is a schematic perspective view showing the whole conveyance roller; FIG. 2 is an enlarged perspective view showing a portion where fine protrusions formed on the conveyance exist; FIG. 3 is a side view showing the fine protrusions formed on the conveyance roller; FIG. 4 is an illustration showing a contact state between the fine protrusions and the recording sheet while the conveyance roller is conveying the sheet; FIG. 5 is a whole schematic view showing an image processing apparatus using a sheet operative member according to the invention.  
         [0027]    [Image Processing Apparatus] 
         [0028]    First, the whole structure of the image forming apparatus is described in reference to FIG. 5. In FIG. 5, the image forming apparatus A is for conveying separately one by one the sheets P stacked by a sheet conveying apparatus B, and for conveying the recording sheet P to an image forming portion by a conveyance roller pair  1  made of a conveyance roller  1   a  and a conveyance roller  1   b  to recording images in an electrophotographic method. That is, a photosensitive drum  3  contained in a process cartridge  2  is rotated in synchrony with the conveyance of the recording sheet; a electrostatic latent image is formed by selective photo-radiation out of a laser scanning optical system  5  after a primary charger  4  charges the surface of the photosensitive drum  3 ; the latent image is developed with toner at the developing unit  6 . The toner image is transferred to the recording sheet P by application of a transfer bias to a transfer roller  7  with respect to the recording sheet thus conveyed.  
         [0029]    With the structure, the recording sheet P transferred with the toner image is heated and pressed by a fixing unit  8  to fix the toner image on the recording sheet P, and the recording sheet P thus fixed is delivered to a delivery tray  10  by a delivery roller pair  9  made of a delivery roller  9   a  and a delivery roller  9   b.    
         [0030]    [Sheet Conveying Apparatus] 
         [0031]    The sheet conveying apparatus B is a feeding tray  11  for supporting the recording sheet P, a pressing plate  13  serving as a pushing means for pushing a front end portion of the recording sheet P supported by the feeding tray  11  to a conveyance roller  12 , a pressing spring  14  for urging the pressing plate  13 , a separation pad  15  serving as a separating means for separating one by one the recording sheets fed out by the conveyance roller  12 , and a separation spring  16  for urging the separation pad  15  to the conveyance roller  12 .  
         [0032]    A cam  17  is secured to a shaft  18  of the conveyance roller  12  and urges the pressing plate  13  in opposing to the pressing spring  14  so that the recording material P does not contact with the conveyance roller  12  in an apparatus waiting state as contacting to a cam portion  13   a  of the pressing plate  13 .  
         [0033]    The conveyance roller  12  is for feeding the recording sheet P separated into one sheet by the separation pad  15  to a conveyance route  19  as being in contact with the topmost sheet surface of the plural recording sheets P supported to the feeding tray  11  as stacked.  
         [0034]    [Sheet Operative Member] 
         [0035]    Next, a structure of the conveyance roller  12  used in the sheet conveying apparatus B is described in reference to FIG. 1 to FIG. 4.  
         [0036]    The conveyance roller  12  is a sheet operative member applying conveyance force to a sheet by frictional force and as shown in FIG. 1, is structured of a core portion  20  whose material is a metal or molded one, and a cylindrical rubber portion  21  formed of a rubber material whose material is made of EPDM, CR rubber, silicone rubber, urethane rubber, or the like, contacting the recording sheet P and conveying the recording sheet P by the frictional force. Fine protrusions  22  shown in FIG. 2 and FIG. 3 are formed on a cylindrical surface  21   a  (operative surface to the sheet) of the cylindrical rubber portion  21  of the conveyance roller  12 .  
         [0037]    Each of the fine protrusions  22  is formed, as shown in FIG. 2 and FIG. 3, of a standing portion  22   a  standing from the cylindrical surface  21   a  of the cylindrical rubber portion  21 , and a spherical portion  22   b  in a spherical shape formed at a distal end of the standing portion  22   a . The fine protrusions are arranged to have substantially equal interval L with the adjacent fine protrusions  22 . The height of the fine protrusion  22  is formed in a range of 1 to 500 μm in consideration of the size and thickness of the recording sheet to be conveyed.  
         [0038]    This is because, if the height is lower than 1 μm, the preventive effect of the paper powder attachments to the conveyance roller  12  and the improvement in durability is rarely obtained, and if the height is higher than 500 μm, elastic force from elastic transformation of the fine protrusions affects much more the conveyance force during the conveyance of the recording sheet P, thereby rendering difficult to maintain stable conveyance force. Therefore it is desired to set the height of the fine protrusions  22  in the above range.  
         [0039]    It is to be noted that in this embodiment the standing portion  22   a  of the fine protrusions is in a cylindrical shape. The diameter R of the spherical portion  22   b  is structured larger than the cylindrical diameter r of the standing portion  22   a  but smaller than the length h of the standing portion  22   a.    
         [0040]    When the recording sheet P is conveyed with the conveyance roller  12  formed with the fine protrusions  22  with the above structure, the conveyance roller  12  rotates in arrow A direction as shown in FIG. 4( a ), and the recording sheet P is conveyed in arrow A direction. The recording sheet P is at that time conveyed from the frictional force generated in contact with the spherical portion  22   b  of the conveyance roller  12 . The fine protrusions  22  conveying the recording sheet P as in contact with the recording sheet P are in a falling down state as elastically transformed in a direction opposing to the conveyance direction (arrow A direction) of the recording sheet P as shown in FIG. 4( a ). The recording sheet P is conveyed under this situation, but during conveyance of the recording sheet P fine dropped objects (hereinafter simply referred to as “paper powder S”) such as paper powder from the surface of the recording sheet P are generated at the contact portion between the recording sheet P and the spherical portion  22   b  and are increased around the contact portion.  
         [0041]    When the conveyance of the recording sheet P is finished, the fine protrusions  22  return to a molded state as released from the elastically transformed state as shown in FIG. 4( b ). At that time, the paper powder S generated at the contact portion between the spherical portion  22   b  and the recording sheet P may be deposited in an attaching manner on the cylindrical surface  21   a  without attaching the spherical portion  22   b  because the spherical portion  22   b  is very small.  
         [0042]    Since the diameter of the standing portion  22   a  is smaller than the diameter of the spherical portion  22   b , the dropped paper powder is likely deposited at the proximal end of the standing portion  22   a  and hardly attached to the spherical portion  22   b.    
         [0043]    Thus, the paper powder S is not attached and deposited to the spherical portion  22   b  conveying the recording sheet P upon contacting to the recording sheet P, so that frictional force is not reduced due to paper powder attachments, and so that the conveyance roller&#39;s durability is advantageously improved.  
         [0044]    Because the contact portion to the recording sheet P is in a spherical shape, the contact area to the recording sheet is constant, and the stable conveyance property can be maintained.  
         [0045]    Furthermore, because the fine protrusions  22  are made of the cylindrical standing portion  22   a  and the spherical portion  22   b  in a spherical shape, no fabrication is required in consideration of the directionality with respect to the recording sheet P, and it is excellent in fine fabrication of the surface of the conveyance roller.  
         [0046]    Since the plural fine protrusions  22  are arranged with substantially the same intervals, a uniform sheet conveyance force is provided over the entire roller surface.  
         [0047]    It is to be noted that in this embodiment the sheet operative member is described as a conveyance roller  12 , but this conveyance roller  12  can obtain substantially the same advantages where structured in the same way for others such as the conveyance roller  1   a , the transfer roller  7 , and the delivery roller  9   a . Substantially the same advantages can be obtained where structured in the same way as that in this embodiment for the roller for feeding sheets to the image forming section even where the cross sectional shape is in a letter D shape.  
         [0048]    [Second Embodiment] 
         [0049]    In the above first embodiment, exemplified is the fine protrusions  22  formed on the conveyance roller  12 . Now, as a second embodiment, referring to FIG. 6 and FIG. 7, an example in which fine protrusions  22  are formed at a separation pad  15  as a sheet operative member is described. It is to be noted that: FIG. 6 is a schematic perspective view showing the entire structure of a separation pad; FIG. 7 is an illustration showing a contact state between the fine protrusions and the recording sheet while the separation pad is in a sheet separation state.  
         [0050]    The separation pad  15  is, as shown in FIG. 6, constituted of a holder portion  23  whose material is metal or molded one, and a rubber material  24   b  whose material is a rubber material such as EPDM, silicone rubber, and urethane rubber for contacting with the recording sheet P and separating the recording sheet P by frictional force. Fine protrusions  22  substantially the same as the fine protrusions  22  formed on the conveyance roller  12  of the first embodiment are formed on a surface  24   a  of the rubber portion  24  of the separation pad  15 . The shape of the fine protrusion  22  is substantially the same as that in the first embodiment shown in FIG. 2, FIG. 3.  
         [0051]    Where the recording sheet P is separated with the above separation pad, as shown in FIG. 7( a ), the recording sheets P are separated to one sheet by frictional force generated upon contact to the spherical portion  22   b  of the separation pad  15  as conveyed by the conveyance roller  12 . The fine protrusions  22  contacting to the recording sheet P are, as shown in FIG. 7( a ), in a falling down state in which the standing portions  22   a  are elastically transformed in a conveyance direction (arrow B direction) of the recording sheet P. Under this state, the recording sheet P is separated and conveyed, but during conveyance of the recording sheet P paper powder from the surface of the recording sheet P are generated at the contact portion between the recording sheet P and the spherical portion  22   b  and are increased around the contact portion.  
         [0052]    When the separation conveyance of the recording sheet P is finished, the fine protrusions  22  return to a molded state as released from the elastically transformed state as shown in FIG. 7( b ). At that time, the paper powder S generated at the contact portion between the spherical portion  22   b  and the recording sheet P may be deposited in an attaching manner on the cylindrical surface  21   a  without attaching the spherical portion  22   b  because the spherical portion  22   b  is very small.  
         [0053]    Thus, where the separation pad is formed with fine protrusions  22 , the apparatus is hardly affected from the paper powder in substantially the same way as in the first embodiment, and the separation ability can be maintained for a long time.  
         [0054]    [Other Embodiments] 
         [0055]    Although in the above embodiments exemplified is the standing portion  22   a  of the fine protrusion  22  in a cylindrical shape, the shape of the standing portion  22   a  is not limited to the cylindrical shape but can be in a cone shape, polygonal pyramid shape, or polygonal rectangular pillar shape.  
         [0056]    Although in the above embodiments exemplified is an image forming apparatus in which a sheet is conveyed and images are recorded on the sheet as an image processing apparatus, the invention can be used suitably to an image reading apparatus in which a sheet conveying apparatus B separately conveys the plural original document sheets one by one and in which the images on the original document are read by an image reading means RA, as shown in FIG. 10.