Abstract:
A paper feeder includes a sheet container including a platen member on which sheet-like recording media is placed, the platen member having one end portion on an upstream side of a paper feed direction rotatably supported to a spindle, such that the other end portion on a downstream side of the paper feed direction is lifted, and a paper feed member which draws and feeds the sheet-like recording media, and the sheet container includes a stepped portion which presses down the downstream side of the paper feed direction of the platen member when inserting the sheet container in the direction opposite to the paper feed direction, and a sliding portion which maintains the pressing down.

Description:
PRIORITY CLAIM 
       [0001]    The present application is based on and claims priority from Japanese Patent Application No. 2008-229894, filed on Sep. 8, 2008, the disclosure of which is hereby incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a paper feeder which draws a sheet-like recording medium such as paper from a paper feed tray, and feeds the sheet-like recording medium, and to an image forming device such as a copier, a printer, a facsimile each having the paper feeder, or a device having two of these functions. 
         [0004]    2. Description of the Related Art 
         [0005]    A conventional paper feeder including a unit which contains a stack of sheet-like recording media such as paper (hereinafter, recording paper) has a rotatable platen which biases the recording paper stack by means of a pressing unit such as a spring such that the top sheet of the recording paper stack has contact with a paper feed roller. In such a paper feeder, the top sheet of recording paper stack is fed by the paper feed roller, and the recording paper stack is separated sheet by sheet by a separator such as a friction pad. 
         [0006]      FIG. 3  is a structural view of a conventional paper feeder, which illustrates a relationship between a feed part of recording paper P and a separator. Referring to  FIG. 3 , a paper feed roller  48  is disposed in the paper feeder on the downstream side of the paper feed direction of a paper feed tray, and a friction pad  49  which separates the recording paper P is disposed in the paper feed tray on the downstream side of the paper feed direction. The friction pad  49  is made of a material which generates dynamic friction resistance larger than that between recording paper, and generates predefined dynamic friction resistance by predetermined pressure applied from a spring  52  via a retaining member  51 . When two sheets of the recording paper P are fed on top of one another, the sheet which has contact with the paper feed roller  48  is separated from the sheet which has contact with the friction pad  49  because the dynamic friction between the recording paper is smaller than the dynamic friction between the recording paper P and the friction pad  49 . 
         [0007]    The paper feed tray provided with the friction pad  49 , the retaining member  51  and the spring  52  includes a platen  53  having a top face to which the recording paper P is placed. The end portion of the platen  53  on the paper feed roller  48  side is elastically biased upward by the spring  52 , and is always biased in the direction of the paper feed roller  48  regardless of the carrying capacity of the recording paper. 
         [0008]    If a paper feed operation is performed without placing the recording paper stack in an appropriate position, i.e., a large number of sheets exceed the friction pad  49  by inertia force or the like in the operation of the paper feed tray, the sheets are not separated. For this reason, the sheets are fed on top of one another. If the paper feed operation is performed without placing the recording paper stack in an appropriate position, i.e., more than the expected amount of recording sheets are disposed between the paper feed face and the paper feed roller, the paper feed roller becomes overloaded, resulting in the inability to rotate, which stops the feeding. Moreover, due to such an overload, the recording paper becomes damaged, and the paper feeder becomes overloaded, thereby causing problems relating to paper insertion and drawing operations of the paper feed tray. 
         [0009]    In order to place the recording paper stack in an appropriate position, a paper feeder including mechanism capable of locking a platen in a lower position and releasing the lock when the paper feed tray is housed in the paper feeder is provided. When a user places the recording paper, the user locks the platen in this paper feeder. 
         [0010]      FIG. 4  is a view illustrating the end portion of the platen on the paper feed roller side when the platen is locked in a lower position. In addition, reference number  41  denotes a paper feed tray. In this case, a user pushes down the platen  53  when placing the recording paper P, so as to lock the platen  53  in a defined position. Then, the user houses the paper feed tray  41  in the paper feeder, so that the paper feed operation is started while maintaining the recording paper in an appropriate position. 
         [0011]    However, the paper feed tray may be inserted in the paper feeder without locking the platen  53  by an operation error of a user.  FIG. 5  is a view illustrating a condition in which the platen is not locked in a lower position. Since a member which controls the recording paper P is not provided in the platen  53  on the downstream side of the paper feed direction, the recording paper P is placed in an inappropriate position by inserting and drawing the paper feed tray  41 . 
         [0012]    If the paper feed tray is housed in the paper feeder in this condition, the recording paper P is placed as illustrated in  FIG. 6 .  FIG. 6  is a view illustrating the platen set in the paper feeder without being locked in a lower position. As illustrated in  FIG. 6 , a large number of sheets enter into a position exceeding the end portion of the friction pad  49  on the upstream side of the paper feed direction, so that the sheets are fed on top of one another upon the start of the paper feed operation. The paper feed roller  48  is thereby overloaded according to the amount of recording paper P that enters that position, resulting in the inability of the paper feed operation and damage to the recording paper. If the paper feed tray is overloaded, the inserting and drawing operation of the tray may not be able to be performed. Accordingly, the above problems depend on a user&#39;s operation as to whether performing the locking operation of the platen or not. A method of placing recording paper stack in an appropriate position by lowering a platen in response to the housing operation of a paper feed tray in the paper feeder is proposed. With this method, however, depending on the housing operation of the paper feed tray, inertia force relative to the recording paper is generated, so that the recording paper stack may not be placed in an appropriate position. 
         [0013]    JP H05-97255A describes that a position of an end face is changed according to a position of recording paper when the recording paper is placed in an inappropriate position in a paper feed cassette, so as to prevent the recording paper from being damaged when the recording paper is placed in an inappropriate position. Moreover, JP2003-246480A describes that a control member which projects downwardly is provided in a part of an image forming device, so as to prevent a feeding error of a sheet by the running of the leading end of the sheet over a separation inclination face, which shifts the sheet in an inappropriate position. 
         [0014]    The techniques described above are aimed to prevent sheets from being fed on top of one another. Such feeding, however, can not be completely prevented by the above techniques. 
       SUMMARY OF THE INVENTION 
       [0015]    It is, therefore, an object of the present invention to provide a paper feeder which prevents a paper feeding error and an operation error by guiding recording paper to an appropriate position. 
         [0016]    A first aspect of the present invention relates to a paper feeder, comprising: a sheet container including a platen member on which sheet-like recording media is placed, the platen member having one end portion on an upstream side of a paper feed direction rotatably supported by a spindle, such that the other end portion on a downstream side of the paper feed direction is lifted; and a paper feed member which draws and feeds the sheet-like recording media, the sheet container including a stepped portion which presses down the downstream side of the paper feed direction of the platen member when inserting the sheet container in the direction opposite to the paper feed direction, and a sliding portion which maintains the pressing down. 
         [0017]    Preferably, the stepped portion and the sliding portion are pressed to a locking member by a biasing member which elastically supports the platen member. 
         [0018]    Preferably, the stepped portion and the sliding portion are integrally provided in the platen member. 
         [0019]    Preferably, the stepped portion is provided above a straight line connecting the spindle of the platen member and a leading end of the platen member. 
         [0020]    Preferably, a relationship of Ls/L&gt;f/F is satisfied where a biasing force of the platen member to the paper feed member is F, a sliding load in the platen member and the sliding portion is f, a distance from the spindle of the platen member to a biasing position is Ls, and a distance from the spindle to the stepped portion is L. 
         [0021]    Preferably, the sheet container includes a control member which controls a top sheet of the sheet-like recording media, and a relationship of Lt/L&gt;Y/y is satisfied where a height from a surface from which the sheet-like recording media is fed in the platen member to the control member is Y, a height of the stepped portion y, a distance from the spindle of the platen member to a leading end position of the platen member is Lt, and a distance from the spindle to the stepped portion is L. 
         [0022]    Preferably, the stepped portion is formed in a circular shape and the circular stepped portion is concentric with the spindle of the platen member. 
         [0023]    A second aspect of the present invention relates to an image forming device including the above paper feeder. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The accompanying drawings are included to provide further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate an embodiment of the invention and, together with the specification, serve to explain the principle of the invention. 
           [0025]      FIG. 1  is a view illustrating a schematic structure of an image forming device according to one embodiment of the present invention. 
           [0026]      FIG. 2  is a view illustrating a structure of a paper feed tray in a paper feeder and a part of the image forming device near the paper feed tray. 
           [0027]      FIG. 3  is a view illustrating a structure of a conventional paper feeder. 
           [0028]      FIG. 4  is a view illustrating an end portion of a conventional platen on a paper feed roller side when the platen is locked in a lower position. 
           [0029]      FIG. 5  is a view illustrating a conventional platen when the platen is not locked. 
           [0030]      FIG. 6  is a view when the conventional platen is set in a main body of an image forming device without being locked in a lower position. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0031]    Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. 
         [0032]    Referring to  FIG. 1  illustrating a schematic structure of an image forming device according to one embodiment of the present invention, the image forming device is a tandem color image forming device of an indirect transfer system as a printer in which four color image forming units, cyan (C), magenta (M), yellow (Y) and black (K), each having one development station on an outer circumferential surface of an image carrier are arranged. In  FIG. 1 , the development station and the image carrier unit are mounted on the main body of the image forming device. 
         [0033]    In  FIG. 1 , the color image forming device includes an optical writing station  2 , an image forming station  3 , a paper feed station  4 , a fusing station  5 , a paper discharging station  6 , and a transport station  7 . 
         [0034]    The details of the optical writing station  2  are not illustrated in the figure. In the optical writing station  2 , an LD unit as a light source emits laser light of respective colors, the respective emitted laser light is irradiated on photoreceptor drums  31 C,  31 M,  31 Y,  31 K, which are image carriers of the image forming units  30 C,  30 M,  30 Y,  30 K of the image forming station  3 , via a polygon mirror and a plurality of reflection mirrors, so as to perform laser writing. The laser writing is conducted by irradiating laser light modulated by modulation signals obtained according to writing data, so that latent images are formed on the surfaces of the photoreceptor drums  31 C,  31 M,  31 Y,  31 K, respectively. 
         [0035]    The image forming station  3  is disposed in the central portion of the main body of the image forming device  1 , and includes the image forming units of respective colors  30 C,  30 M,  30 Y,  30 K, an intermediate transfer belt  38  as an image carrier, and a secondary transfer roller  39 . The image forming units  30 C,  30 M,  30 Y,  30 K include the photoreceptor drums  31 C,  31 M,  31 Y,  31 K, respectively. Electrophotography forming elements are disposed along the outer circumference of each photoreceptor drum  31 C,  31 M,  31 Y,  31 K. In this embodiment, since the same structure is applied for each color, a reference sign for black (K) is only applied, and reference signs for other colors (C, M, Y) will be omitted. The image forming units each having the same structure are arranged in series along the moving direction of the intermediate transfer belt  38 . Moreover, when generally describing each element, the reference signs indicating colors C, M, Y, K will be omitted. 
         [0036]    The photoreceptor drum  31 K includes, as the image formation elements, in the outer circumference thereof in the clockwise direction a charging roller  32 K which charges the surface of the photoreceptor drum  31 K, a development units  33 K which houses developer including toner and develops a latent image on the photoreceptor drum  31 K as a toner image, a primary transfer roller  34 K which transfers the toner image on the photoreceptor drum  31 K onto the intermediate transfer belt  38 , a cleaning unit  35 K having a cleaning blade which scrapes residual toner after the primary transfer, and an electricity removal unit (not shown) which removes electric charge remaining on the photoreceptor drum  31 K after the primary transfer. The laser light  21 K performs optical writing from an exposure unit  36 K placed between the charging roller  32 K and the development unit  33 K. The image forming units  30 C,  30 M,  30 Y,  30 K are arranged in order along the movement direction (arrow A direction) of the intermediate transfer belt  38 . The primary transfer roller  34 K is disposed in a position which faces the photoreceptor drum  31 K while sandwiching the intermediate transfer belt  38  therebetween. Reference number  37  is a collection unit which collects waste toner. 
         [0037]    The secondary transfer roller  39  is provided on the upstream side of the paper feed direction of the intermediate transfer belt  38  of the image forming unit  30 C while sandwiching a recording paper transport path  42  from the paper feed station  4  therebetween. The secondary transfer roller  39  transfers the toner image on the intermediate transfer belt  38  onto recording paper P (sheet-like recording media). In addition, the residual toner after the transfer of the secondary transfer roller  39  is cleaned by an intermediate transfer belt cleaning unit  38   a  provided on the upstream side of the image forming unit  30 C which is the downstream side of the paper feed direction of the intermediate transfer belt  38  of the secondary transfer roller  39 , and is sent to the image forming unit on the downstream side. 
         [0038]    Negative bias voltage in which alternate current and direct current from a not shown bias power source are superimposed is applied to a core of the development roller  33   a  ( 33   a K in  FIG. 1 ) of each development unit  33 . Direct negative voltage is applied to each charging roller  32  from another bias power source. 
         [0039]    The cleaning blade of the cleaning unit  35  cleans toner remaining on the outer circumferential surface of the photoreceptor drum  31 . The charging roller  32  uniformly charges the outer circumferential surface of the cleaned photoreceptor drum  31  to a high potential, so that the charged charging roller  32  is initialized. Then, the laser beam  21  is irradiated on the photoreceptor drum  31  of the image forming unit  30  of each color, and the outer circumferential surface of the photoreceptor drum  31  of each color, which is uniformly charged to high potential is selectively exposed by laser light modulated according to the image data. By this exposure, an electrostatic latent image having a low potential part in which the electric potential is attenuated by the exposure and a high potential part by the initialization is formed. The development unit  33  transfers the toner to the low potential part (or high potential part) of the electrostatic latent image so as to form (develop) the toner image. The photoreceptor drum  31  transfers the toner image to the intermediate transfer belt  38  while rotating and carrying the toner image. 
         [0040]    The operation of image forming units  30 K,  30 Y,  30 M,  30 C is timely performed such that the four-color (CMYK) toner images formed on the outer circumferential surfaces of the photoreceptor drums  31 K,  31 Y,  31 M,  31 C, respectively, are timely transferred onto the same position of the intermediate transfer belt  38  to be overlapped, and a full color toner image is thereby formed. 
         [0041]    The full color toner image on the intermediate transfer belt  38  is transferred onto the recording paper P transported along the transport path  42  from the paper feed station  4  by the secondary transfer roller  39 , is fused by heat and pressure in the fusing station  5 , and then is discharged onto the discharging tray  6   b  by the discharging roller  6   a  of the paper discharging station  6 . Here, in a paper feed tray  41  (sheet container) of the paper feed station  4 , which houses a recording paper stack, the recording paper P is separated sheet by sheet by a paper feed roller  48  (paper feed member) and a friction pad  49 , the separated sheet is transported to the resist roller  46 , and the leading end of the separated sheet of the recording paper P has contact with a nip of the resist roller  46  such that the leading end is aligned. The resist roller  46  temporarily stops the transport of the recoding paper P, and timely starts rotating such that the toner image of the intermediate transfer belt  38  and the leading end of the recording paper P are located in a predetermined position. 
         [0042]    When forming an image on both faces of the recording paper P, an image is transferred onto the first face of the recording paper P by the secondary transfer roller  39 . Then, the rotation direction of the paper discharging roller  6   a  is reversed when the back end of the recording paper P fused by the fusing station  5  is passed a switching point  71 , and the leading end and the back end of the recording paper P are switched, and then the recording paper is transported to the transport path  72 . The recording paper P is again transported to the resist roller  46  via a re-feeding path  74 , and is sent to the secondary transfer roller  39  side by the resist roller  46  at the toner image&#39;s timing, which is formed on the intermediate transfer belt  38 . Then, the toner image is transferred onto the second face of the recording paper P. The recording paper P having an image on the second face is fused by the fusing station  5 , and discharged onto the discharging tray  6   b  from the paper discharging roller  6   a . In addition, a filler  73  which detects paper is provided near the upstream side of the paper feed direction of the switching point  71 . In addition, reference number  44  is a filler which detects the passage of the paper supplied from the paper feed tray  41  or the paper fed via the re-feeding path  74 . 
         [0043]    The paper feed station  4  includes the paper feed tray  41  which houses unused recording paper P. This paper feed tray  41  is disposed to be drawable in the right direction in  FIG. 1  together with the friction pad  49  and the installation position of the re-feeding path  74  while leaving the paper feed roller  48 , a sensor  45  which detects recording paper, and the like in the main body of the image forming device. 
         [0044]      FIG. 2  is a view illustrating the structure of the paper feed tray in the paper feeder and the structure of a part of the image forming device near the paper feed tray. The paper feed tray  41  includes inside thereof a platen  53  (platen member). The platen  53  includes on both side portions thereof side walls  61  which extend in the paper feed direction. Since a spindle  62  (rotation axis) having both ends attached to the main body of the paper feeder penetrates the end portions of the side walls  61  on the upstream side of the paper feed direction, the platen  53  is rotatable about the spindle  62 . A spring (biasing member)  54  is disposed in the back face of the platen  53  on the downstream side of the paper feed direction. The platen  53  is elastically biased upward by the spring  54 , and is supported such that the end portion has elastic contact with the paper feed roller  48 . 
         [0045]    The side wall  61  of the platen  53  extends near the end portion of the platen  53  on the downstream side of the paper feed direction. The upper end portion of the side wall  61  includes a sliding face (sliding portion)  63  which substantially extends in the horizontal direction and has contact with a lower face of a rib (locking member)  64  provided in the main body of the image forming device. Since the sliding face  63  is formed in the upper end portion of the side wall  61 , the sliding face  63  and the platen  53  move together. The height of the sliding face  63  is set such that the sliding face does not have contact with the rib  64  when the platen  53  is locked in a lower position as illustrated in  FIG. 4 . The sliding face  63  includes a circular stepped portion  63   a  which has contact with the rib  64  provided in the main body of the image forming device when the platen  53  is inserted into the main body of the image forming device without being locked in a lower position. The height of the sliding face  63  is also set such that the platen  53  is pushed down to the locking position by the rib  64  after passing through the stepped portion  63   a  when the platen  53  is set in the main body of the image forming device without being locked. In addition, reference number  65  is a control member which controls the top of the recording paper P stack, and is provided in the side wall of the paper feed tray  41 . 
         [0046]    The stepped portion  63   a  is provided above the straight line connecting the spindle  62  and the leading end of the platen  53 . Accordingly, inertia force is applied to the recording paper P and sliding load of the recording paper P and the control member  65  is reduced by performing an operation lowering the platen  53 ; thus, the moving amount of the recording paper P by the inertial force can be improved. More particularly, if the paper feed tray  41  is inserted into the main body of the image forming device without locking the platen  53 , the stepped portion  63   a  hits the rib  64 , and then if the paper feed tray  41  is further pushed to the main body of the image forming device, the stepped portion  63   a  is guided by the rib  64 , and the platen  53  is lowered. Therefore, the recording paper P can be placed in an appropriate position by the inertial force of the recording paper P in the inserting direction of the paper feed tray  41  when the stepped portion  63   a  hits the rib  64 , and the upward inertial force of the recording paper P when the platen  53  is lowered. In addition, even if the paper feed tray  41  is inserted into the main body of the image forming device without locking the platen  53 , the load by the contact and sliding between the recording paper P and the control member  65  can be reduced because the platen  53  is lowered. Since the stepped portion  63   a  has a circular form and is concentric with the spindle  62  which is the rotation axis of the platen  53 , the reaction force in the stepped portion  63   a  can be constantly maintained regardless of an angle of the platen  53 . 
         [0047]    If a relationship of Ls/L&gt;f/F is satisfied where biasing force of the platen  53  to the paper feed roller  48  is F, sliding load in the paper feed tray  41  and a sliding portion of the main body of the device is f, a distance from the spindle  62  of the platen  53  to a biased position is Ls, and a distance from the spindle  62  to the stepped portion  63   a  is L, the reaction force in the stepped portion which is necessary for moving the recording paper P to a regular position can be obtained while using the biasing force of the platen  53 . 
         [0048]    Since the paper feed tray  41  includes the control member  65  which controls the top of the recording paper P stack, if a relationship of Lt/L&gt;Y/y is satisfied where a height from a surface from which the recording paper in the paper feed tray  41  is fed to the control member  65  is Y, a height of the stepped portion  63   a  is y, a distance from the spindle  62  to the position of the leading end of the platen  53  is Lt, and a distance from the spindle  62  to the stepped portion  63   a  is L, the recording paper P can be positioned in a regular position by lowering the top face of the recording paper P stack when inserting the paper feed tray  41  into the main body of the image forming device than the paper feed face. 
         [0049]    As described above, when inserting the paper feed tray into the main body of the image forming device, the platen  53  slides with the rib  64  provided in the main body of the image forming device. The stepped portion  63   a  is provided on the sliding face  63  of the platen  53 . When inserting the paper feed tray  41  into the main body of the image forming device with the platen  53  being locked in a lower position, the sliding portion  63  and the stepped portion  63   a  do not have contact with the rib  64 ; however, the stepped portion  63   a  has contact with the rib  64  when inserting the paper feed tray  41  into the main body of the image forming device without locking the platen  53  in a lower position, so that reaction force is generated in the platen  53 . By this reaction force, inertial force is applied to the recording paper P, so that the recording paper P moves in the inserting direction of the paper feed tray  41  (position which controls the back end of the recording paper P. For this reason, the recording paper P can be moved to an appropriate position even when inserting the paper feed tray  41  without locking the platen  53 ; thus, the problems can be prevented. If the stepped portion  63   a  has contact with the rib  64 , the platen  53  rotates in the direction lowering the platen  53 , so that the sliding load of the control member  65  on the upper end of a sheet and the recording paper is reduced, and loss to the inertial force can be controlled. Therefore, the moving amount of the recording paper can be sufficiently ensured. 
         [0050]    According to the embodiment of the present invention, when inserting the paper feed tray (sheet container) into the main body of the image forming device, the operational ability when inserting is increased, so that the inertial force is generated in the sheet-like recording paper which is not placed in an appropriate position. Therefore, the recording paper can be guided to an appropriate position, and the feeding error and operation error can be thereby prevented. 
         [0051]    Although the embodiments of the present invention have been described above, the present invention is not limited thereto. It should be appreciated that variations may be made in the embodiments described by persons skilled in the art without departing from the scope of the present invention.