Abstract:
A recording medium supply apparatus includes: a conveyance member that conveys a recording medium; a retard member, in contact with the conveyance member, that forms a contact portion between the conveyance member and the retard member and retards the recording medium by holding the recording medium in the contact portion; and a buckling prevention unit, configured to contact with the recording medium on the upstream side of the contact portion between the conveyance member and the retard member in a conveyance direction of the recording medium, that prevents buckling of the recording medium in the conveyance direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2007-034448 filed Feb. 15, 2007. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a recording medium supply apparatus and an image forming apparatus having the recording medium supply apparatus. 
         [0004]    2. Related Art 
       SUMMARY 
       [0005]    According to an aspect of the invention, there is provided a recording medium supply apparatus including: a conveyance member that conveys a recording medium; a retard member, in contact with the conveyance member, that forms a contact portion between the conveyance member and the retard member and retards the recording medium by holding the recording medium in the contact portion; and a buckling prevention unit, configured to contact with the recording medium on the upstream side of the contact portion between the conveyance member and the retard member in a conveyance direction of the recording medium, that prevents buckling of the recording medium in the conveyance direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
           [0007]      FIG. 1  is a cross-sectional view showing an image forming apparatus according to a first exemplary embodiment of the present invention; 
           [0008]      FIG. 2A  is a front view showing a sheet feeding device according to the first exemplary embodiment of the present invention; 
           [0009]      FIG. 2B  is a cross-sectional view of the sheet feeding device according to the first exemplary embodiment of the present invention cut along a line A-A in  FIG. 2A ; 
           [0010]      FIG. 3A  is a front view showing the sheet feeding device according to a second exemplary embodiment of the present invention; 
           [0011]      FIG. 3B  is a cross-sectional view of the sheet feeding device according to the second exemplary embodiment of the present invention cut along a line B-B in  FIG. 3A ; 
           [0012]      FIG. 4A  is a front view showing the sheet feeding device according to a third exemplary embodiment of the present invention; 
           [0013]      FIG. 4B  is a cross-sectional view of the sheet feeding device according to the third exemplary embodiment of the present invention cut along a line C-C in  FIG. 4A ; 
           [0014]      FIG. 5A  is a front view showing the sheet feeding device according to a fourth exemplary embodiment of the present invention; 
           [0015]      FIG. 5B  is a cross-sectional view of the sheet feeding device according to the fourth exemplary embodiment of the present invention cut along a line D-D in  FIG. 5A ; 
           [0016]      FIG. 6  is a cross-sectional view showing the sheet feeding device according to the fourth exemplary embodiment of the present invention; 
           [0017]      FIG. 7A  is a cross-sectional view showing an operation of the sheet feeding device according to the fourth exemplary embodiment of the present invention in a state where a deforming member has been moved to a position away from a sheet; 
           [0018]      FIG. 7B  is a cross-sectional view showing the operation of the sheet feeding device according to the fourth exemplary embodiment of the present invention in a state where the deforming member has been moved to a position to contact the sheet; 
           [0019]      FIG. 8  is a flowchart showing an example of an operation (S 10 ) of the sheet feeding device according to the fourth exemplary embodiment of the present invention; 
           [0020]      FIG. 9  is a flowchart showing another example of the operation (S 20 ) of the sheet feeding device according to the fourth exemplary embodiment of the present invention; 
           [0021]      FIG. 10  is a flowchart showing another example of the operation (S 30 ) of the sheet feeding device according to the fourth exemplary embodiment of the present invention; and 
           [0022]      FIG. 11  is a cross-sectional view explaining buckling of a sheet. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Next, exemplary embodiments of the present invention will be described based on the drawings. 
         [0024]      FIG. 1  schematically shows the structure of an image forming apparatus  10  according to the exemplary embodiments of the present invention. The image forming apparatus  10  has an image forming apparatus main body  12 . An image forming unit  14  is provided in the image forming apparatus main body  12 . A discharge part  16  to be described later is provided in an upper part of the image forming apparatus main body  12 , and sheet feeding devices  18 , as an example of two-stage recording medium supply apparatus, are provided in a lower part of the image forming apparatus main body  12 . 
         [0025]    The sheet feeding devices  18  respectively have a sheet feeding cassette  22  in which sheets  20 , as an example of recording media, are stacked. A pickup roller  24  is provided in an upper position around a rear end of the sheet feeding cassette  22 , and a retard roller  26  as an example of a retard member and a feed roller  28  as an example of a conveyance member are provided on the upstream side of the pickup roller  24  in a sheet conveyance direction. The pickup roller  24 , the retard roller  26  and the feed roller  28  may be provided in the image forming apparatus main body  12  or may be provided in the sheet feeding cassette  22 . 
         [0026]    A main conveyance path  32  is a sheet passage from the feed roller  28  to a discharge port  34 . The main conveyance path  32  has a portion placed around a rear side (right side of  FIG. 1 ) of the image forming apparatus main body  12  and approximately vertically formed from the sheet feeding device  18  on the bottom end to a fixing device  36  to be described later. A transfer device  42  and an image holder  44  to be described later are provided on the upstream side of the fixing device  36  on the main conveyance path  32  in the sheet conveyance direction, and further, a registration roller  38  is provided on the upstream side of the transfer device  42  and the image holder  44  in the sheet conveyance direction. Further, a discharge roller  40  is provided around the discharge port  34  of the main conveyance path  32 . 
         [0027]    Accordingly, the sheets  20  fed with the pickup roller  24  from the sheet feeding cassette  22  of the sheet feeding device  18  are retarded with the retard roller  26  and the feed roller  28  in cooperation with each other, and only the top sheet is guided to the main conveyance path  32 . The sheet is temporarily stopped with the registration roller  38 , then passed between the transfer device  42  and the image holder  44  to be described later at predetermined timing, while a developing material image is transferred to the sheet. Then the transferred developing material image is fixed to the sheet with the fixing device  36 , and the sheet is discharged with the discharge roller  40  from the discharge port  34  to the discharge part  16 . 
         [0028]    Note that in the case of double sided printing, the sheet is returned to a reverse path. That is, in the main conveyance path  32 , a portion in front of the discharge roller  40  is branched into two parts. A switching device  46  is provided on the branch portion, and a reverse path  48  which returns from the branched part to the registration roller  38  is formed. The reverse path  48  is provided with conveyance rollers  50   a  to  50   c . In the case of double sided printing, the switching device  46  is switched to a side to open the reverse path  48 . When a part of the sheet around its rear end arrives at the discharge roller  40 , the discharge roller  40  is reversed, then the sheet is guided to the reverse path  48 , then passed through the registration roller  38 , the transfer device  42 , the image holder  44  and the fixing device  36 , and discharged from the discharge port  34  to the discharge part  16 . 
         [0029]    The discharge part  16  has a slope member  52  rotatable with respect to the image forming apparatus main body  12 . In the slope member  52 , a part at the discharge port is low, then the slope gradually becomes steep toward a frontforward direction (leftward direction in  FIG. 1 ). The part at the discharge port is a lower end and the high end is an upper end of the slope member  52 . The slope member  52  is supported with the image forming apparatus main body  12  such that the slope member  52  is rotatable about the lower end. As indicated with an alternate long and two dash line in  FIG. 1 , when the slope member  52  is rotated upward thereby is opened, an open portion  54  is formed. A process cartridge  64  to be described later can be attached/removed via the open portion  54 . 
         [0030]    The image forming unit  14 , which is e.g. an electrophotographic unit, has the image holder  44  having a photoreceptor, a charging device  56  having e.g. a charging roller to charge the image holder  44 , an optical writing device  58  to optically write a latent image on the image holder  44  charged with the charging deice  56 , a developing device  60  to visualize the latent image on the image holder  44 , formed with the optical writing device  58 , with developing material, the transfer device  42  having e.g. a transfer roller to transfer the developing material image developed with the developing device  60  to the sheet  20 , a cleaning device  62  having e.g. a blade to remove developing material remaining on the image holder  44 , and the fixing device  36  to fix the developing material image on the sheet  20 , transferred with the transfer device  42 , to the sheet  20 . 
         [0031]    The image holder  44 , the charging device  56 , the developing device  60  and the cleaning device  62  are integrated as the process cartridge  64 . The process cartridge  64  is provided below and immediately near the slope member  52  of the discharge part  16 . As described above, the process cartridge  64  is attached/removed via the open portion  54  formed by opening the slope member  52 . 
         [0032]    A controller  30  is provided in the image forming apparatus main body  12 . The controller  30  is electrically connected to respective constituent elements such as the sheet feeding device  18 , a motor  96  and a displacement sensor  98  to be described later, and controls operations of these respective constituent elements. 
         [0033]    A user interface device  31  as an example of an input unit is provided integrally with the image forming apparatus main body  12  or via a network, and is electrically connected to the controller  30 . The user interface device  31  is provided with a display panel  31   a , input buttons  31   b  and the like, to select processing contents in the image forming apparatus  10  and display the selected contents. 
         [0034]    Next, the details of the sheet feeding device  18  will be described based on  FIGS. 2A and 2B . 
         [0035]    As shown in  FIG. 2A and 2B , the sheet feeding device  18  has the feed roller  28 , the retard roller  26  and a deforming member  66  as an example of a buckling preventing unit. 
         [0036]    The feed roller  28  has a first support shaft  68  rotatably supported with the image forming apparatus main body  12  and two first main bodies  70  supported with the first support shaft  68 . The two first main bodies  70 , having circumferential surfaces  70   a  with the center of the first support shaft  68  as their center, are provided away from each other by a predetermined interval. A gear  72  is provided on one end of the first support shaft  68 , and the gear  72  is connected to a driving source (not shown). 
         [0037]    The deforming member  66  is configured to contact with the recording medium on the upstream side of a contact portion  80  between the feed roller  28  and the retard roller  26  in a sheet conveyance direction. More particularly, the deforming member  66  is provided between the two first main bodies  70 , and is rotatably provided on the first support shaft  68 . The deforming member  66 , formed in a cylindrical shape, has a circumferential surface  66   a  larger than the first main bodies  70 . A boss  66   b  is provided at a rotational center of the deforming member  66 . The boss  66   b  is formed in a cylindrical shape projected from both end surfaces of the deforming member  66 . The boss  66   b , having a predetermined length, regulates movement of the deforming member  66  in its axial direction. 
         [0038]    The retard roller  26  has a second support shaft  74  rotatably supported with the image forming apparatus main body  12  and two second main bodies  76  supported with the second support shaft  74 . The second main bodies  76  have circumferential surfaces  76   a  with the center of the second support shaft  74  as their center. The second main bodies  76  are provided in positions opposite to the first main bodies  70  of the feed roller  28 . The contact portion  80  is formed between the first main bodies  70  of the feed roller  28  and the second main bodies  76  of the retard roller  26 . The retard roller  26  is rotated with a rotational force from the feed roller  28 . 
         [0039]    A gear  78  is provided on one end of the second support shaft  74 , and is connected to a torque limiter (not shown). Accordingly, when two or more sheets  20  are guided to the contact portion  80  between the first main bodies  70  of the feed roller  28  and the second main bodies  76  of the retard roller  26 , since a friction force between the sheets is smaller in comparison with a torque set at the torque limiter, the second main bodies  76  of the retard roller  26  reverse-rotate, then the sheet(s) other than the sheet in contact with the first main bodies  70  of the feed roller  26  are returned to the opposite side to the sheet conveyance direction. In this manner, the retard roller  26 , in contact with the feed roller  28 , and forming the contact portion  80  between the feed roller  28  and the retard roller  26 , retards the sheet  20  by holding the sheet  20  in this contact portion  80 . 
         [0040]    Note that it may be arranged such that when two or more sheets  20  are guided to the contact portion  80  between the first main bodies  70  of the feed roller  28  and the second main bodies  76  of the retard roller  26 , rotation of the second main bodies  76  of the retard roller  26  is stopped. 
         [0041]    The deforming member  66  comes into contact with the sheet  20  fed with the pickup roller  24  from the sheet feeding cassette  22 , and rotates along with the conveyance of the sheet  20 . By this arrangement, the deforming member  66  deforms the sheet  20  in a C-shape viewed from a direction other than a direction orthogonal to the sheet conveyance direction, e.g., the sheet conveyance direction, on the upstream side of the contact portion  80  between the feed roller  28  and the retard roller  26  in the sheet conveyance direction. 
         [0042]    Note that the deforming member  66  may be provided on the second support shaft  74 . Further, the retard roller  26  may be replaced with a non-rotating friction member or the like. 
         [0043]    Next, a second exemplary embodiment of the present invention will be described based on  FIGS. 3A and 3B . 
         [0044]    The feed roller  28  according to the present exemplary embodiment has the first support shaft  68  rotatably supported with the image forming apparatus main body  12  and the first main body  70  supported with the first support shaft  68 . Two deforming members  66  are provided between both ends of the first main body  70  and the image forming apparatus main body  12 , and rotatably supported with the first support shaft  68 . Further, the deforming members  66  formed in a cylindrical shape have circumferential surfaces  66   a  larger than the first main body  70 . 
         [0045]    The retard roller  26  has the second support shaft  74  rotatably supported with the image forming apparatus main body  12  and the second main body  76  supported with the second support shaft  74 . The second main body  76  is provided in a position opposite to the first main body  70  of the feed roller  28 . The contact portion  80  is formed between the first main body  70  of the feed roller  28  and the second main body  76  of the retard roller  26 . The retard roller  26  is rotated with a rotational force from the feed roller  28 . 
         [0046]    The deforming members  66  come into contact with the sheet  20  fed with the pickup roller  24  from the sheet feeding cassette  22 , and rotate along with the conveyance of the sheet  20 . By this arrangement, the deforming members  66  deform the sheet  20  in a C-shape viewed from a direction other than a direction orthogonal to the sheet conveyance direction, e.g., the sheet conveyance direction, on the upstream side of the contact portion  80  between the feed roller  28  and the retard roller  26  in the sheet conveyance direction. 
         [0047]    Note that the deforming members  66  may be provided on the second support shaft  74 . 
         [0048]    Note that in the second exemplary embodiment of the present invention, the elements corresponding to those of the first exemplary embodiment of the present invention have the same reference numerals and the explanations of the elements are omitted. 
         [0049]    Next, a third exemplary embodiment of the present invention will be described based on  FIGS. 4A and 4B . 
         [0050]    The feed roller  28  in the present exemplary embodiment has the first support shaft  68  and two first main bodies  70  supported with the first support shaft  68 . The interval between the two first main bodies  70  is longer than that between the two first main bodies  70  of the first exemplary embodiment. Two deforming members  66  are rotatably supported with the first support shaft  68 , and respectively provided in positions near the first main bodies  70  from the center of the first support shaft  68 . A spacer  82  formed in a cylindrical shape is provided between the two deforming members  66 , thereby regulates movement of the two deforming members  66  in the axial direction. 
         [0051]    The deforming members  66  come into contact with the sheet  20  fed with the pickup roller  24  from the sheet feeding cassette  22 , and rotate along with the conveyance of the sheet  20 . By this arrangement, the deforming members  66  deform the sheet  20  in a C-shape viewed from a direction other than a direction orthogonal to the sheet conveyance direction, e.g., the sheet conveyance direction, on the upstream side of the contact portion  80  between the feed roller  28  and the retard roller  26  in the sheet conveyance direction. 
         [0052]    Note that the deforming members  66  and the spacer  82  may be provided on the second support shaft  74 . 
         [0053]    Note that in the third exemplary embodiment of the present invention, the elements corresponding to those of the first exemplary embodiment of the present invention have the same reference numerals and the explanations of the elements are omitted. 
         [0054]    Next, a fourth exemplary embodiment of the present invention will be described based on  FIGS. 5A to 11 . 
         [0055]    The retard roller  26  in the present exemplary embodiment has two second main bodies  76  and two second support shafts  74 . The two support shafts  74  are respectively rotatably supported with two main body frames  84  having an approximately U-shaped cross-section. The two second main bodies  76  are respectively supported with the two second support shafts  74 . 
         [0056]    As shown in  FIG. 6 , a deforming member moving device  86  has the deforming member  66 , a lever  88 , a first gear  90 , a support shaft  92 , a second gear  94  and a motor  96 . The deforming member  66  is rotatably provided on one end of the lever  88 , and the first gear  90  is fixed to the other end of the lever  88 . The first gear  90  is rotatably provided on the support shaft  92  provided in the image forming apparatus main body  12 . The motor  96  is forward/reverse rotatable, and the second gear  94  is fixed to an output shaft of the motor  96 . The second gear  94  is provided in a position to be engaged with the first gear  90 . 
         [0057]    As shown in  FIG. 7A , when the second gear  94  of the motor  96  forward-rotates (rotates in an arrow A direction in  FIG. 7A ), the lever  88  rotates in an arrow B direction in  FIG. 7A  about the support shaft  92  along with the second gear  92 . By this rotation, the deforming member  66  moves to a position away from the sheet  20 . Further, as shown in  FIG. 7B , when the second gear  94  of the motor  96  reverse-rotates (rotates in an arrow C direction in  FIG. 7B ), the lever  88  rotates in an arrow D direction about the support shaft  92  along with the second gear  94 . By this rotation, the deforming member  66  moves to a position to contact the sheet  20 . 
         [0058]    A displacement sensor  98  as an example of a detection unit having a light emitting device and a photoreception device is provided on the upstream side of the sheet conveyance direction from the contact portion  80  between the feed roller  28  and the retard roller  26 . The displacement sensor  98  emits light from the light emitting device to the sheet  20 , and receives reflected light with the photoreception device, thereby detects buckling of the sheet  20  as shown in  FIG. 11 . The displacement sensor  98  is electrically connected to the controller  30 , and outputs buckling of the sheet  20 , i.e., a displacement amount (e.g., “L” in  FIG. 11 ) of the sheet  20  to the controller  30 . Note that it is known that as shown in  FIG. 11 , the buckling of the sheet  20  easily occurs when contact between sheets is high and the basic weight of the sheet is light. 
         [0059]    As described later, the controller  30  performs control to move the deforming member  66  to the position to contact the sheet  20  and to the position away from the sheet  20  in correspondence with the result of detection by the displacement sensor  98 . 
         [0060]    Next, an example of the operation of the sheet feeding device  18  will be described based on  FIG. 8 . 
         [0061]      FIG. 8  shows an example of the operation (S 10 ) of the sheet feeding device  18 . 
         [0062]    As shown in  FIG. 8 , at step S 100 , the controller  30  actuates the sheet feeding device  18 , the image forming unit  14  and the like, thereby starts printing. 
         [0063]    At step S 102 , the displacement sensor  98  detects buckling of the sheet  20 , and outputs the result of detection to the controller  30 . 
         [0064]    At step S 104 , the controller  30  determines based on the result of detection by the displacement sensor  98  whether or not the buckling of the sheet  20  is within a predetermined range. When it is determined that the buckling of the sheet  20  is within the predetermined range, the controller  30  continues sheet supply in the sheet feeding device  18 , while when it is determined that the buckling of the sheet  20  is beyond the predetermined range, the process proceeds to processing at step S 106 . 
         [0065]    At step S 106 , the controller  30  stops supply of the sheet  20  in the sheet feeding device  18 , i.e., stops the operations of the pickup roller  24  and the feed roller  28 . 
         [0066]    At step S 108 , after the stoppage of the supply of the sheet  20 , the controller  30  drives the motor  96  to move the deforming member  66  to the position to contact the sheet  20 . 
         [0067]    At step S 110 , the controller  30  starts supply of the sheet  20  by the sheet feeding device  18 , i.e., restarts the operations of the pickup roller  24  and the feed roller  28 . At this time, the deforming member  66  comes into contact with the sheet  20 , and deforms the sheet  20  in a C-shape viewed from a direction other than a direction orthogonal to the sheet conveyance direction, e.g., the sheet conveyance direction. 
         [0068]    Next, another example of the operation (S 20 ) of the sheet feeding device  18  will be described based on  FIG. 9 . 
         [0069]    As shown in  FIG. 9 , at step S 200 , the controller  30  actuates the sheet feeding device  18 , the image forming unit  14  and the like, thereby starts printing. 
         [0070]    At step S 202 , the displacement sensor  98  detects buckling of the sheet  20 , and outputs the result of detection to the controller  30 . 
         [0071]    At step S 204 , the controller  30  determines based on the result of detection by the displacement sensor  98  whether or not the buckling of the sheet  20  is within a predetermined range. When it is determined that the buckling of the sheet  20  is within the predetermined range, the controller  30  continues the supply of the sheet  20  in the sheet feeding device  18 , while when it is determined that the buckling of the sheet  20  is beyond the predetermined range, the process proceeds to step S 206 . 
         [0072]    At step S 206 , after the completion of the current printing, the controller  30  drives the motor  96 , to move the deforming member  66  to the position to contact the sheet  20 . In this manner, the controller  30  previously moves the deforming member  66  to the position to contact the sheet  20  before the next printing. 
         [0073]    At step S 208 , the controller  30  starts the supply of the sheet  20  by the sheet feeding device  18  for the next printing, i.e., starts the operations of the pickup roller  24  and the feed roller  28 . At this time, the deforming member  66  comes into contact with the sheet  20 , and deforms the sheet  20  in a C-shape viewed from a direction other than a direction orthogonal to the sheet conveyance direction, e.g., the sheet conveyance direction. 
         [0074]    Next, another example of the operation (S 30 ) of the sheet feeding device  18  will be described based on  FIG. 10 . 
         [0075]    As shown in  FIG. 10 , at step S 300 , a user inputs information on the sheet  20  to be used in printing via the user interface device  31 . For example, the user inputs information on the sheet  20  (e.g., sheet type (coated sheet, normal sheet or the like), basic weight, thickness and the like). 
         [0076]    At step S 302 , the controller  30  determines based on the information on the sheet  20  inputted via the user interface device  31  whether or not the occurrence of buckling is anticipated regarding the sheet  20 . When it is determined that the occurrence of buckling is not anticipated, the process proceeds to processing at step S 306 , while when it is determined that the occurrence of buckling is anticipated, the process proceeds to processing at step S 304 . For example, when the basic weight of the sheet is light and the contact between the sheet is high (e.g., thin coated sheet), the controller  30  determines that the occurrence of buckling is anticipated. 
         [0077]    At step S 304 , the controller  30  drives the motor  96  to move the deforming member  66  to the position to contact the sheet  20 . 
         [0078]    At step S 306 , the controller  30  starts the supply of the sheet  20  by the sheet feeding device  18 , i.e., starts the operations of the pickup roller  24  and the feed roller  28 . At this time, the deforming member  66  comes into contact with the sheet  20 , and deforms the sheet  20  in a C-shape viewed from a direction other than a direction orthogonal to the sheet conveyance direction, e.g., the sheet conveyance direction. 
         [0079]    Note that in the fourth exemplary embodiment of the present invention, the elements corresponding to those of the first exemplary embodiment of the present invention have the same reference numerals and the explanations of the elements are omitted. 
         [0080]    The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.