Patent Publication Number: US-7708265-B2

Title: Sheet Feeder

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of Japanese Patent Application No. 2006-228623 filed on Aug. 25, 2006, which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a sheet feeder. 
   Conventional sheet feeders are disclosed in JP-A-2005-292236 and JP-A-2006-176321. The sheet feeder has a housing, a sheet feed cassette, a pressure plate, and a pressure mechanism. 
   The housing has a cassette housing part. The cassette housing part is recessed horizontally from the front surface toward the depth direction. Further, a pick-up roller that is driven rotationally about a horizontal axis perpendicular to the depth direction is provided in the upper part at the front surface side within an opening of the cassette housing part. 
   The sheet feed cassette has a holding chamber having an open top for storing stacked sheets of paper, and can be housed within the cassette housing part and drawn from the cassette housing part. 
   The pressure plate is provided pivotably about a pivot in parallel with the horizontal axis so as to be inclined downwardly toward the depth direction of the sheet feed cassette. 
   The pressure mechanism presses sheets of paper against the pick-up roller by increasing the angle of inclination of the pressure plate when the sheet feed cassette is pushed into the cassette housing part. 
   The conventional sheet feeder having such a configuration is applied to an image forming apparatus such as an electrophotographic printer. As described below, the sheets of paper are loaded in the sheet feed cassette and the sheets of paper are fed to the image forming apparatus. 
   First, a user draws the sheet feed cassette from the cassette housing part of the housing to draw the sheet feed cassette by the length more than the length of sheets in the depth direction. Concurrently, the pressure plate is horizontal at the reduced angle of inclination. 
   Next, the user stacks sheets of paper from above the holding chamber of the sheet feed cassette, and then, inserts the sheet feed cassette from the front of the housing to the depth direction to make the sheet feed cassette housed in the cassette housing part. 
   In this manner, when the sheet feed cassette is pushed into the cassette housing part, the pressure mechanism increases the angle of inclination of the pressure plate and presses the sheets of paper against the pick-up roller. Thereby, the loading of sheets of paper in the sheet feeder is completed. Further, in the sheet feeder, when the sheets of paper are fed to the image forming apparatus, the pick-up roller rotates and associated components such as rollers and guides provided around work in conjunction with the pick-up roller. Thus, the sheets of paper can be fed one by one to the image forming apparatus from the upper part of the front surface side within the opening. 
   By the way, image forming apparatuses such as printers have been recently downsized and often placed near the work areas on the desks or the like. Accordingly, it is desired for the image forming apparatus to occupy the smaller space so as not to reduce the work area. On this account, it is also desired for the above described conventional sheet feeder to occupy the smaller space. 
   However, in the above described conventional sheet feeder, it has been difficult to make the occupied space smaller at the front surface side of the sheet feeder because the sheet feed cassette must be drawn by the length more than the length of sheets in the depth direction when the sheets of paper are loaded in the sheet feed cassette. 
   BRIEF SUMMARY OF THE INVENTION 
   The invention has been achieved in view of the above described conventional circumstances, and a purpose of the invention is to provide a sheet feeder that can occupy the smaller space. 
   The sheet feeder of the invention includes a housing, a sheet feed cassette, a pressure plate, a pressure mechanism, and a pressure plate regulation mechanism. The housing has a cassette housing part. The cassette housing part is recessed horizontally from the front surface toward the depth direction, and provided with a pick-up roller that is driven rotationally about a horizontal axis perpendicular to the depth direction in the upper part at the front surface side within an opening thereof. The sheet feed cassette has a holding chamber having an open top for storing stacked sheets. The sheet feed cassette is can be housed within the cassette housing part and drawn from the cassette housing part. The pressure plate is provided pivotably about a pivot in parallel with the horizontal axis so as to be inclined downwardly toward the depth direction of the sheet feed cassette. The pressure mechanism presses sheets against the pick-up roller by increasing the angle of inclination of the pressure plate when the sheet feed cassette is pushed into the cassette housing part. The pressure plate regulation mechanism inclines the pressure plate downwardly toward the depth direction while separating the sheets on the pressure plate or the pressure plate from the pick-up roller when the sheet feed cassette is drawn from the cassette housing part by a length less than a length of sheets in the depth direction. 
   In the sheet feeder of the invention, when a user tries to load sheets in the holding chamber of the sheet feed cassette, the user draws the sheet feed cassette from the cassette housing part of the housing by the length less than the length of the sheets of paper in the depth direction (in the “half-open” state in which the depth side of the holding chamber is located within the cassette housing part and the front side of the holding chamber is located outside of the cassette housing part). Then, the pressure plate regulation mechanism separates the sheets on the pressure plate or the pressure plate from the pick-up roller. Accordingly, no sheet remains between the upper most sheet remaining in the holding chamber of the sheet feed cassette and the pick-up roller or in the holding chamber, and a clearance is produced between the pressure plate and the pick-up roller. Further, the pressure plate regulation mechanism inclines the pressure plate downwardly toward the depth direction so that the sheets to be loaded can be guided by the remaining uppermost sheet or the pressure plate. 
   On this account, the user inserts the sheets from above the front side of the holding chamber toward the depth direction into the sheet feed cassette in this condition, the sheets are guided by the remaining uppermost sheet or the pressure plate and easily stacked in the holding chamber without rubbing against the pick-up roller. Thus, in the sheet feeder, if the sheet feed cassette is not completely drawn from the cassette housing part of the housing, the sheets can be loaded along the pressure plate downwardly inclined toward the depth direction in the holding chamber of the sheet feed cassette. 
   Therefore, the sheet feeder of the invention can occupy the smaller space so as not to reduce the work area on the desk or the like. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     Hereinafter, embodiments 1 to 3 that embody the invention will be described with reference to the drawings. In  FIGS. 1 ,  2 ,  4  to  17 , the right side is the front side and the left side is the depth side. 
       FIG. 1  is a sectional view of a sheet feeder of embodiment 1 (in the condition in which the sheet feed cassette is housed in the cassette housing part). 
       FIG. 2  is a sectional view of the sheet feeder of embodiment 1 (in the condition in which the sheet feed cassette is detached from the cassette housing part). 
       FIG. 3  is an elevational view along an arrow A in  FIG. 2  according to the sheet feeder of embodiment 1. 
       FIG. 4  is a sectional view of the sheet feed cassette (in the condition in which the pressure plate is horizontal) according to the sheet feeder of embodiment 1. 
       FIG. 5  is a top view of the sheet feed cassette (in the condition in which the pressure plate is horizontal) according to the sheet feeder of embodiment 1. 
       FIG. 6  is a sectional view of the sheet feed cassette (in the condition in which the pressure plate is inclined) according to the sheet feeder of embodiment 1. 
       FIG. 7  is a sectional view of the sheet feeder of embodiment 1 (in the condition in which sheets of paper within the holding chamber can be fed to the image forming unit). 
       FIG. 8  is a sectional view of the sheet feeder of embodiment 1 (in the condition in which there is no sheets of paper within the holding chamber). 
       FIG. 9  is a sectional view of the sheet feeder of embodiment 1 (in the condition in which the sheet feed cassette is slightly drawn from the cassette housing part). 
       FIG. 10  is a schematic diagram showing the positional relationship between guide rails and guide rollers according to the sheet feeder of embodiment 1. 
       FIG. 11  is a sectional view of the sheet feeder of embodiment 1 (in the condition in which the sheet feed cassette is nearly halfway drawn from the cassette housing part). 
       FIG. 12  is a sectional view of the sheet feed cassette (in the condition in which the pressure plate is horizontal) according to a sheet feeder of embodiment 2. 
       FIG. 13  is a top view of the sheet feed cassette (in the condition in which the pressure plate is horizontal) according to the sheet feeder of embodiment 2. 
       FIG. 14  is a sectional view of the sheet feeder of embodiment 2 (in the condition in which the sheet feed cassette is nearly halfway drawn from the cassette housing part). 
       FIG. 15  is a sectional view of the sheet feed cassette (in the condition in which the pressure plate is horizontal) according to a sheet feeder of embodiment 3. 
       FIG. 16  is a top view of the sheet feed cassette (in the condition in which the pressure plate is horizontal) according to the sheet feeder of embodiment 3. 
       FIG. 17  is a sectional view of the sheet feeder of embodiment 3 (in the condition in which the sheet feed cassette is nearly halfway drawn from the cassette housing part). 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiment 1 
   As shown in  FIGS. 1 to 3 , a sheet feeder  1  of embodiment 1 configures a printer  9  as an image forming apparatus together with a printer main body  8 . 
   The printer main body  8  includes a housing  90  having a substantially rectangular parallelepiped shape, and an image forming unit  7  provided in the upper part within the housing  90 . The image forming unit  7 , though details of which are not shown, adopts a general image forming system including electrophotographic, thermal, inkjet, or other systems. 
   The sheet feeder  1  includes the housing  90  in common use with the printer main body  8 , a sheet feed cassette  10 , a pressure plate  20 , a pressure mechanism  30 , and a pressure plate regulation mechanism  40 . 
   The housing  90  has a cassette housing part  91 . The cassette housing part  91  is located below the image forming unit  7  and recessed horizontally from the front surface  90   a  of the housing  90  toward the depth direction. Further, a pick-up roller  6  that is driven rotationally about a horizontal axis perpendicular to the depth direction is provided in the upper part at the front surface  90   a  side within an opening  91   a  of the cassette housing part  91 . Furthermore, a sheet feed assistance part  5  is provided in front of the pick-up roller  6 , though the details are not shown. The sheet feed assistance part  5  has a separation roller mechanism that separates sheets of paper  99  one by one, a paper dust collection roller mechanism, a turning mechanism that turns the sheet of paper  99  along the pick-up roller  6  and guides it in the depth direction, etc. 
   As shown in  FIGS. 3 and 5 , guide rails  92   c ,  92   d , the details of which will be described later, are formed in the inner walls  91   c ,  91   d  in the width direction of the cassette housing part  91 . The depth parts of the guide rails  92   c ,  92   d  are downward horizontal surfaces, and the front parts are downwardly inclined surfaces that continue with the horizontal surfaces and rise frontward. Further, a drive gear  34 , the details of which will be described later, is provided in one inner wall  91   c  in the width direction of the cassette housing part  91 . 
   As shown in  FIGS. 4 and 5 , the sheet feed cassette  10  has a box shape with an open top and a front wall part  10   a , a depth wall part  10   b , side wall parts  10   c ,  10   d , a front bottom part  10   e , and a depth bottom part  10   f . The front bottom part  10   e  is recessed deeper than the depth bottom part  10   f . At the front surface side of the front wall part  10   a , a handle  19   a  that can catch fingers when the sheet feed cassette  10  is drawn is formed. Further, the sheet feed cassette  10  can be inserted from the opening  91   a  of the cassette housing part  91  in the depth direction and housed within the cassette housing part  91  as shown in  FIG. 1 , drawn from the cassette housing part  91  as shown in  FIG. 11 , and further, detached from the cassette housing part  91  as shown in  FIGS. 2 to 4 . 
   The pressure plate  20  formed of a substantially rectangular metal thin plate is provided in the sheet feed cassette  10 . The front edge of the pressure plate  20  is located near the inner surface of the front wall part  10   a . On the other hand, the depth edge of the pressure plate  20  is journaled by a first pivot  21  in parallel with the horizontal axis provided near the front edge of the depth bottom part  10   f . Accordingly, the pressure plate  20  is pivotable about the first pivot  21  from the horizontal state in which the plate forms substantially the same plane with the depth bottom part  10   f  as shown in  FIG. 4  to the downwardly inclined state in which the plate descends toward the depth direction as shown in  FIG. 6 . The pressure plate  20  pivots according to the pressure mechanism  30  or the pressure plate regulation mechanism  40 , which will be described later. 
   The space defined by the front wall part  10   a , the depth wall part  10   b , the side wall parts  10   c ,  10   d , and the depth bottom part  10   f  of the sheet feed cassette  10  as well as the upper surface of the pressure plate  20  is a holding chamber  11  that can store stacked sheets of paper  99 . 
   To the part between the upper surface at the first pivot  21  side in the pressure plate  20  (that is, the depth edge of the pressure plate  20 ) and the depth bottom part  10   f  that forms part of the bottom surface of the holding chamber  11 , a sheet member  29  that covers a gap  10   g  produced between them is attached. The sheet member  29  is an elastically deformable thin resin sheet in a belt shape. The front edge of the sheet member  29  is fixed so as not to produce irregularities on the upper surface at the first pivot  21  side in the pressure plate  20 , and the depth edge of the sheet member  29  is in contact with the upper surface of the depth bottom part  10   f . Accordingly, as shown in  FIG. 6 , even when the pressure plate  20  pivots from the horizontal state to the downwardly inclined state toward the depth direction, the sheet member  29  can elastically deform to cover the gap  10   g  between the pressure plate  20  and the depth bottom part  10   f  with a smooth curved surface. 
   As shown in  FIGS. 4 and 5 , in the space defined by the lower surface of the pressure plate  20  and the front bottom part  10   e , the pressure mechanism  30  (except the drive gear  34  described as below), the pressure plate regulation mechanism  40 , and a pressure plate positioning mechanism  80  are provided. 
   The pressure mechanism  30  has a lever  31 , a rotating shaft  32 , and a driven gear  33  provided at the sheet feed cassette  10  side, and the drive gear  34  provided at the housing  90  side. 
   More specifically, the rotating shaft  32  is buried rotatably about the horizontal axis perpendicular to the depth direction within the front wall part  10   a  of the sheet feed cassette  10 . Further, one end of the rotating shaft  32  projects out of the sheet feed cassette  10  and the driven gear  33  is fixed thereto. On the other hand, the other end of the rotating shaft  32  projects into a recessed portion for lever  19   b  formed at the inner center of the front wall part  10   a , and the lever  31  is fixed thereto. The lever  31  extends from the other end of the rotating shaft  32  in the depth direction to position the depth edge of the lever  31  below the front side of the pressure plate  20 . 
   As shown in  FIGS. 3 and 5 , the drive gear  34  is provided to project from the inner wall  91   c  within the cassette housing part  91 . When the sheet feed cassette  10  is housed in the cassette housing part  91 , the drive gear  34  meshes with the driven gear  33  as shown in  FIGS. 1 and 5 . Further, the drive gear  34  is controlled by a pressure mechanism control unit  34   a  including a sensor that senses that the sheet feed cassette  10  is pushed into the cassette housing part  91 , a sensor for remaining amount of paper, an electric motor, etc. Accordingly, when the drive gear  34  rotates in the condition in which the sheet feed cassette  10  is housed in the cassette housing part  91 , the driven gear  33  and the rotating shaft  32  also rotate to pivot the lever  31 . Further, when the lever  31  pivots, the depth edge of the lever  31  pushes up the front side of the pressure plate  20  from below, and thereby, the pressure plate  20  can be downwardly inclined toward the depth direction as shown in  FIGS. 7 and 8 . 
   The pressure plate regulation mechanism  40  includes a first link  60 , a supporting member  50 , and a second link  70 . 
   The first link  60  commonly uses component members with the pressure mechanism  30  and includes the lever  31 , the rotating shaft  32 , the driven gear  33 , and the drive gear  34 . Further, in the condition in which the pressure plate  20  is inclined as shown in  FIGS. 7 and 8 , when the sheet feed cassette  10  is drawn from the cassette housing part  91  slightly by the length L 1  (L 1 =about 1 mm to several millimeters), the driven gear  33  and the drive gear  34  are separated and no longer meshed. Further, the driven gear  33  that has been restrained in rotation by the drive gear  34  becomes free to rotate. Accordingly, the force of the lever  31  to push up the pressure plate  20  no longer acts and the pressure plate  20  and the lever  31  return from the inclined state to the horizontal state due to the weight of the pressure plate  20  itself and the weight of the sheets of paper  99 . Thus, the first link  60  can reduce the angle of inclination of the pressure plate  20  so that the sheets of paper  99  on the pressure plate  20  or the pressure plate  20  and the pick-up roller  6  may be separated when the sheet feed cassette  10  is drawn from the cassette housing part  91 . 
   As shown in  FIGS. 4 and 5 , the supporting member  50  is formed of a metal thin plate having a substantially rectangular shape smaller than that of the pressure plate  20 , and provided underneath the pressure plate  20  to overlap with each other. The depth edge of the supporting member  50  is journaled by a second pivot  51  provided near the first pivot  21  in parallel with the first pivot  21  and pivotable about the second pivot  51 . On the other hand, two coil springs  52   a ,  52   b  are provided between the front lower surface of the supporting member  50  and the front bottom part  10   e , and energize the front side of the supporting member  50  to push it upwardly. A pair of guide roller shafts  53   a ,  53   b  is provided at edges of the supporting member  50  in the width direction. The guide roller shafts  53   a ,  53   b  project through slots  59   a ,  59   b  formed in the side wall parts  10   c ,  10   d  of the sheet feed cassette  10  to the outside, and guide rollers  54   a ,  54   b  are rotatably supported on the respective ends thereof. 
   The second link  70  includes the guide roller shafts  53   a ,  53   b , the guide rollers  54   a ,  54   b , the two coil springs  52   a ,  52   b , and the above described guide rails  92   c ,  92   d . Further, when the sheet feed cassette  10  is drawn from the cassette housing part  91 , the angle of inclination of the supporting member  50  and the pressure plate  20 , which has been reduced to the horizontal state by the first link  60 , can be increased by the second link  70  again in the following manner. 
   First, when the sheet feed cassette  10  is housed in the cassette housing part  91  as shown in  FIG. 1 , the guide rollers  54   a ,  54   b  energized upwardly by the coil springs  52   a ,  52   b  are in contact with the horizontal surface at the depth side of the guide rails  92   c ,  92   d  from below as shown by (a) in  FIG. 10 . Concurrently, the supporting member  50  is in the horizontal state as shown in  FIG. 1 . 
   Then, as the sheet feed cassette  10  is being drawn from the cassette housing part  91 , the guide rollers  54   a ,  54   b  are being brought into contact with the inclined surface at the front side from the horizontal surface at the depth side of the guide rails  92   c ,  92   d  and gradually rise as shown by (b) and (c) in  FIG. 10 . With the rise, the angle of inclination of the supporting member  50  increases. 
   Then, as shown in  FIG. 11 , when the sheet feed cassette  10  is drawn from the cassette housing part  91  by the length L 2  (L 2  is about one-half of the length of sheets of paper  99  in the depth direction) less than the length of sheets of paper  99  in the depth direction (brought into a half-open state) as shown in  FIG. 11 , the guide rollers  54   a ,  54   b  separate from the inclined surface at the front side of the guide rails  92   c ,  92   d  as shown by (d) in  FIG. 10 , and the supporting member  50  is held at the maximum angle of inclination. 
   Thus, when the sheet feed cassette  10  is drawn from the cassette housing part  91  by the length L 2  less than the length of sheets of paper  99  in the depth direction, the second link  70  can increase the angle of inclination of the supporting member  50  and push up the pressure plate  20  from below by the front edge of the supporting member  50  to downwardly incline the pressure plate  20  toward the depth direction. Concurrently, a clearance having a height that may prevent interference of the sheets of paper  99  being loaded is secured between the inclined pressure plate  20 , and the pick-up roller  6  and the cassette housing part  91  as shown in  FIG. 11 . When the sheet feed cassette  10  is pushed into the cassette housing part  91 , the second link  70  performs the reverse operation to the above described operation. 
   As shown in  FIGS. 4 and 5 , the pressure plate positioning mechanism  80  has a latch member  81  provided to project downwardly from the center of the front edge of the supporting member  50 , and a locking member  82  that extends from a recessed portion for locking member  91   c  formed in the lower part of the front surface of the front wall part  10   a  in the depth direction in a rod shape slidable in the depth direction. A locking lug  82   a  is formed on the depth end of the locking member  82 . Further, as shown in  FIG. 4 , when the supporting member  50  is horizontal, the locking member  82  is slid in the depth direction, so that the locking lug  82   a  may lock the latch member  81 . Accordingly, as shown in  FIGS. 6 and 11 , when the locking member  82  is drawn to the front side (not slid in the depth direction) and the guide rollers  54   a ,  54   b  are not in contact with the guide rails  92   c ,  92   d , the locking lug  82   a  separates from the latch member  81 , the supporting member  50  is energized by the coil springs  52   a ,  52   b  and downwardly inclined in the depth direction, and the pressure plate  20  is pushed up by the supporting member  50  and downwardly inclined in the depth direction. From the state, the user pushes down the pressure plate  20  to the horizontal state, and then, the supporting member  50  is also pushed down and the latch member  81  descends. Further, the user slides the locking member  82  in the depth direction, and then, the locking lug  82   a  locks the latch member  81  to position the supporting member  50  in the horizontal state as shown in  FIG. 4 . That is, the pressure plate positioning mechanism  80  can indirectly position the pressure plate  20  in the horizontal state (i.e., the state along the bottom surface of the holding chamber  11 ). As a modified example of the embodiment, an elastic member that energizes the locking member  82  in the direction to slide the locking member  82  in the depth direction may be provided. By the configuration, the locking member  82  can be slid in the depth direction by the elastic force of the elastic member to lock the latch member  81  with the locking lug  82   a  instead of the user sliding the locking member  82  in the depth direction. Accordingly, the user can position the supporting member  50  in the horizontal state only by pushing down the pressure plate  20  without operating the locking member  82 . Therefore, the operation is performed more easily and the usability is improved. The elastic member may be a metal spring or resin spring. 
   Furthermore, as shown in  FIG. 1 , when the sheet feed cassette  10  is housed in the cassette housing part  91 , if the locking member  82  is slid in the depth direction and the supporting member  50  is positioned in the horizontal state, the pressure plate positioning mechanism  80  does not prevent the inclination of the pressure plate  20  by the operation of the pressure mechanism  30  because it only indirectly positions the pressure plate  20 . 
   In the sheet feeder  1  of embodiment 1 having the above described configuration, sheets of paper  99  are fed to the printer  9  and sheets of paper  99  are loaded in the sheet feed cassette  10  as below. 
   First, as shown in  FIG. 1 , when many sheets of paper  99  are held in the holding chamber  11  of the sheet feed cassette  10 , the printer  9  is activated and a command is issued from a control unit (not shown), then, the drive gear  34  is rotated by the pressure mechanism control unit  34   a , and accordingly, the lever  31  pivots to push up the pressure plate  20  from below. Thus, the pressure mechanism  30  increases the angle of inclination of the pressure plate  20  and presses the sheets of paper  99  against the pick-up roller  6 . When the pick-up roller  6  rotates according to the command from the control unit, the uppermost sheet of paper  99  is fed one by one to the image forming unit  7  through the sheet feed assistance part  5  as shown by a sheet feed path  5   a , and images are formed thereon and the sheets of paper  99  are ejected to the outside. Concurrently, the pressure mechanism  30  increases the angle of inclination of the pressure plate  20  and presses the sheets of paper  99  against the pick-up roller  6  constantly with an optimum pressing force as the sheets of paper  99  within the holding chamber  11  are reduced. 
   When the sheets of paper  99  within the holding chamber  11  are reduced as shown in  FIG. 7  or there is no sheet of paper as shown in  FIG. 8  after the sheets of paper  99  are fed from the sheet feeder  1 , the user loads the sheets of paper  99  in the sheet feeder  1 . 
   In this regard, when the user draws the sheet feed cassette  10  from the cassette housing part  91  slightly by the length L 1 , the driven gear  32  and the drive gear  34  of the first link  60  are separated and the driven gear  32  becomes freely rotatable, and then, the pressure plate  20  and the lever  31  moves downwardly due to the weight of the pressure plate  20  itself. In this manner, the first link  60  reduces the angle of inclination of the pressure plate  20  to turn the pressure plate  20  into the horizontal state and separates the sheets of paper  99  on the pressure plate  20  or the pressure plate  20  from the pick-up roller  6 . Accordingly, no sheet of paper  99  remains between the upper most sheet of paper  99  remaining in the holding chamber  11  of the sheet feed cassette  10  and the pick-up roller  6  or in the holding chamber  11 , and a clearance is produced between the pressure plate  20  and the pick-up roller  6 . Consequently, even when the user draws the sheet feed cassette  10  further, the sheets of paper  99  remaining on the pressure plate  20  or the pressure plate  20  may not rub against the pick-up roller  6 . 
   Then, as the user draws the sheet feed cassette  10  further from the cassette housing part  91 , the positional relationships between the guide rails  92   c ,  92   d  and the guide rollers  54   a ,  54   b  of the second link  70  change to increase the angle of inclination of the supporting member  50  as shown in  FIG. 10 , and accordingly, the angle of inclination of the pressure plate  20  is increased again. In this manner, when the sheet feed cassette  10  is drawn from the cassette housing part  91  by the length L 2  less than the length of sheets of paper  99  in the depth direction, the second link  70  may downwardly incline the pressure plate  20  toward the depth direction again as shown in  FIG. 11 . 
   Next, the user inserts the sheets of paper  99  to be loaded into the sheet feed cassette  10  from above the front side of the holding chamber  11  toward the depth direction. In this regard, the sheets of paper  99  are guided by the remaining uppermost sheet of paper  99  or the pressure plate  20  and easily stacked in the holding chamber  11  without rubbing against the pick-up roller  6 . Further, when the sheets of paper  99  are loaded along the inclined pressure plate  20 , the sheets of paper  99  are not caught by the gap  10   g  because the sheets of paper  99  are inserted slidingly on the upper surface of the sheet member  29 . Thus, in the sheet feeder  1 , even if the sheet feed cassette  10  is not completely drawn from the cassette housing part  91  of the housing  90 , the sheets of paper  99  can be easily and reliably loaded along the pressure plate  20  downwardly inclined toward the depth direction in the holding chamber  11  of the sheet feed cassette  10 . 
   Further, in the condition of  FIG. 11 , if the user pushes down the pressure plate  20  to the horizontal state and further slides the locking member  82  in the depth direction, the locking lug  82   a  of the locking member  82  engages with the latch member  81  of the supporting member  50  and the supporting member  50  is positioned in the horizontal state. Consequently, also the pressure plate  20  is indirectly positioned in the horizontal state. Through the pressure plate positioning mechanism  80 , the sheet feeder  1  can hold back the sheets of paper  99  rising upwardly by the inclined pressure plate  20  after the sheets of paper  99  are loaded in the sheet feed cassette  10  in the half-open state. Further, when the sheet feed cassette  10  is detached from the sheet feeder  1 , the sheets of paper  99  are hard to come out of the holding chamber  11 . To unlock the positioning of the pressure plate  20 , the locking member  82  may be slid forward to separate the locking lug  82   a  and the latch member  81 . 
   From the condition shown in  FIG. 11 , the user pushes the sheet feed cassette  10  into the cassette housing part  91 , and then, the positional relationships between the guide rails  92   c ,  92   d  and the guide rollers  54   a ,  54   b  of the second link  70  change oppositely to those in the case of drawing the cassette to reduce the angles of inclination of the supporting member  50  and the pressure plate  20 . Then, when the sheet feed cassette  10  is completely housed in the cassette housing part  91  as shown in  FIG. 1 , the driven gear  33  and the drive gear  34  of the pressure mechanism  30  mesh with each other. In this manner, the load of the sheets of paper  99  in the printer  9  is completed and the sheet feeder  1  becomes ready to feed the sheets of paper  99  again. 
   Here, the sheet feeder  1  of embodiment 1 includes the pressure plate regulation mechanism  40  that separates the sheets of paper  99  on the pressure plate  20  or the pressure plate  20  and the pick-up roller  6  while downwardly inclining the pressure plate  20  toward the depth direction when the sheet feed cassette  10  is drawn from the cassette housing part  91  by the length less than the length of the sheets of paper  99  in the depth direction. Accordingly, in the sheet feeder  1 , the sheets of paper  99  can be loaded in the holding chamber  11  of the sheet feed cassette  10  along the pressure plate  20  downwardly inclined toward the depth direction even when the sheet feed cassette  10  is not completely drawn from the cassette housing part  91  as described above. 
   Therefore, the sheet feeder  1  of embodiment 1 can occupy the smaller space so as not to reduce the work area on the desk or the like. 
   Further, in the sheet feeder  1 , the pressure plate regulation mechanism  40  includes the supporting member  50  that can support the pressure plate  20  from below, and the first link  60  and the second link  70  provided between the housing  90  and the sheet feed cassette  10  for guiding the supporting member  50  while the sheet feed cassette  10  is drawn from the cassette housing part  91  by the length less than the length of the sheets of paper  99  in the depth direction. According to the sheet feeder  1 , the conventional sheet feeder can be easily improved to exert effects of the invention only by making small modifications to the pressure plate, the pressure mechanism, etc. thereof, and the rise in manufacturing cost can be suppressed. 
   Furthermore, in the sheet feeder  1 , the first link  60  reduces the angle of inclination of the pressure plate  20  to separate the sheets of paper  99  on the pressure plate  20  or the pressure plate  20  from the pick-up roller  6  when the sheet feed cassette  10  is drawn from the cassette housing part  91 , and the second link  70  downwardly inclines the pressure plate  20  toward the depth direction again when the sheet feed cassette  10  is drawn from the cassette housing part  91  by the length less than the length of sheets of paper  99  in the depth direction. Accordingly, in the sheet feeder  1 , the effects of the invention can be realized more reliably by switching from the pressure mechanism  30  to the first link  60 , and then, switching from the first link  60  to the second link  70 , and the conventional sheet feeder can be improved more easily. 
   Moreover, in the sheet feeder  1 , since the supporting member  50  is the plate-like member provided between the pressure plate  20  and the front bottom part  10   e  as part of the bottom surface of the holding chamber  11 , the thickness of the pressure plate  20  and the supporting member  50  can be made thinner and the reduce in size of the holding chamber  11  of the sheet feed cassette  10  can be suppressed. Thereby, a large number of sheets of paper  99  can be held within the sheet feed cassette  10 . 
   In addition, the printer  9  as the image forming apparatus including the sheet feeder  1  can occupy the smaller space so as not to reduce the work area on the desk or the like. 
   Embodiment 2 
   As shown in  FIGS. 12 to 14 , a sheet feeder  2  of embodiment 2 includes a sheet width regulation mechanism  100  provided on the bottom surface of the holding chamber  11  (on the upper surface of the front bottom part  10   e ) of the sheet feeder  1  of embodiment 1, a depth direction regulating plate  102  provided on the upper surface of the depth bottom part  10   f , a pressure plate  20   a  having a T-shape, and a supporting member  50   a  having a “rectangular frame” shape. The other configuration is the same as that of the sheet feeder  1  of embodiment 1, and the description thereof will omitted. 
   The sheet width regulation mechanism  100  has a pair of width direction regulating plates  101   a ,  101   b . The width direction regulating plates  101   a ,  101   b  are disposed to face each other at both sides on the upper surface of the front bottom part  10   e  in the width direction, and slidable in the width direction by a general sliding mechanism or the like (not shown). 
   The pressure plate  20   a  has a front side corresponding to an upper lateral part of the T-shape and a depth side corresponding to a lower longitudinal part of the T-shape, and the depth side of itself is narrower than the sliding range of the width direction regulating plates  101   a ,  101   b  of the sheet width regulation mechanism  100 . Accordingly, the pressure plate  20   a  has the shape that does not interfere with the width direction regulating plates  101   a ,  101   b  when the width direction regulating plates  101   a ,  101   b  slide to accommodate sheets of paper of different sizes. In addition to the shorter width of the depth side of the pressure plate  20   a , the widths of a first pivot  21   a  and a sheet member  29   a  are also made shorter. Further, extending surfaces  10   h ,  10   i  located at both ends of the depth edge of the pressure plate  20   a  and extending forward are formed from the front end of the depth bottom part  10   f . The extending surfaces  10   h ,  10   i  are guides that, when a wider sheet of paper is inserted along the inclined pressure plate  20   a , if the both depth ends are not supported by the depth side of the pressure plate  20   a  but downwardly suspended, guides the ends so that they may not caught by the front edge of the front bottom part  10   e.    
   The supporting member  50   a  has a substantially “rectangular frame” shape in which a large opening surrounding the sliding range of the width direction regulating plates  101   a ,  101   b  of the sheet width regulation mechanism  100  is formed. Accordingly, the supporting member  50   a  has the shape that does not interfere with the width direction regulating plates  101   a ,  101   b  when the plates slide to accommodate sheets of paper of different sizes. 
   As shown in  FIG. 12 , when the pressure plate  20   a  and the supporting member  50   a  are horizontal, the width direction regulating plates  101   a ,  101   b  nearly entirely protrude into the holding chamber  11 . As shown in  FIG. 14 , when the pressure plate  20   a  and the supporting member  50   a  are inclined, the width direction regulating  101   a ,  101   b  plates partly protrude into the holding chamber  11 . 
   The depth direction regulating plate  102  is slidable along a rail  103  in the depth direction, and the position of the depth direction regulating plate  102  can be adjusted to conform sheets of paper in different sizes. 
   The sheet feeder  2  of embodiment 2 having such a configuration can also exert the same effects as those of the sheet feeder  1  of embodiment 1. Further, the sheet feeder  2  can accommodate plural sheet sizes by the sheet width regulation mechanism  100  and the depth direction regulating plate  102 . 
   Furthermore, in the sheet feeder  2 , the pressure plate  20   a  has the T-shape, not the substantially “H”-shape that is common in a conventional sheet feeder provided with a sheet width regulation mechanism. Accordingly, the problem that, when sheets of paper are inserted along an inclined pressure plate having a substantially “H”-shape, both ends at the depth side are apt to be caught by the lower lateral part of the substantially “H”-shape can be solved. 
   Moreover, in the sheet feeder  2 , after sheets of paper are loaded in the sheet feed cassette  10  in the half-open state as shown in  FIG. 14 , the width adjustment with the sheet width regulation mechanism  100  can be performed by pushing down the pressure plate  20   a  and positioning the pressure plate  20   a  with the pressure plate positioning mechanism  80  in the horizontal state. 
   Embodiment 3 
   As shown in  FIGS. 15 to 17 , a sheet feeder  3  of embodiment 3 includes a sheet width regulation mechanism  110  provided on the upper surface of a pressure plate  20   b  having substantially the same shape as that of the pressure plate  20  of the sheet feeder  1  of embodiment 1, and a depth direction regulating plate  102  provided on the upper surface of the depth bottom part  10   f . The other configuration is the same as that of the sheet feeder  1  of embodiment 1, and the description thereof will omitted. 
   The sheet width regulation mechanism  110  has a pair of width direction regulating plates  111   a ,  111   b . The width direction regulating plates  111   a ,  111   b  are disposed to face each other at both sides on the upper surface of the pressure plate  20   b  in the width direction, and slidable in the width direction by a general sliding mechanism or the like (not shown) provided at the lower surface side of the pressure plate  20   b.    
   The configuration of the depth direction regulating plate  102  is the same as that of the sheet feeder  2  of embodiment 2. 
   The sheet feeder  3  of embodiment 3 having such a configuration can also exert the same effects as those of the sheet feeders  1 ,  2  of embodiments 1, 2. Further, the sheet feeder  3  can accommodate plural sheet sizes by the sheet width regulation mechanism  110  and the depth direction regulating plate  102  as is the case of the sheet feeder  2  of embodiment 2. 
   Furthermore, the sheet feeder  3  is different from the sheet feeder  2  of embodiment 2 in that the sheet width regulation mechanism  110  is provided not on the bottom surface of the holding chamber  11 , but on the upper surface of the pressure plate  20   b . Accordingly, in the sheet feeder  3 , as shown in  FIG. 17 , sheets of paper in different sizes can be loaded while the pressure plate  20   b  remains inclined by adjusting the sheet width regulation mechanism  110 . In addition, in the sheet feeder  3 , it is no longer necessary for the pressure plate  20   b  to have a shape that does not interfere with the sheet width regulation mechanism  110 , and the pressure plate  20   b  may have a simple rectangular shape. Accordingly, the pressure plate  20   b  of the sheet feeder  3  can more reliably support from smaller sheets of paper to larger sheets of paper even in the inclined state compared to the pressure plate  20   a  having the T-shape in the sheet feeder  2  of embodiment 2. 
   By the way, in a sheet feeder disclosed in FIGS. 12 and 13 of JP-A-2003-212363, a sheet feed cassette having a box shape itself is drawn by the length less than the length of sheets of paper in the depth direction and inclined, the front wall of the sheet feed cassette is downwardly pivoted, and sheets of paper are loaded from the front surface side of the sheet feed cassette. The sheet feeder has a different configuration from the configuration of the sheet feeder of the invention in which not the sheet feed cassette itself but the pressure plate is inclined. Further, the sheet feeder is more complex in configuration and more difficult in downsizing and reduction of manufacturing cost compared to the sheet feeder of the invention. 
   The invention has been described according to embodiments 1 to 3 as above, however, as will be understood, the invention is not limited to the embodiments 1 to 3 and appropriate changes may be made without departing from the scope of the invention. 
   For example, as the links, general combinations of gears, levers, cams, guide rails, and other mechanical elements can be employed. Further, the links may be integrally formed or separately formed. 
   As the pressure plate positioning mechanism, for example, a mechanism having a movable locking member that directly locks the pressure plate along the bottom surface of the holding chamber may be employed. Further, as the pressure plate positioning mechanism, a mechanism having a movable locking member that locks the supporting member along the bottom surface of the holding chamber for indirectly positioning the pressure plate may be employed. In the case where the pressure plate positioning mechanism directly locks the pressure plate for positioning, it is preferable that the pressure plate positioning mechanism has a function of automatically unlocking the positioning of the pressure plate so as not to hinder the operation of the pressure mechanism when the sheet feed cassette is pushed into the cassette housing part. In this regard, in the case where the pressure plate positioning mechanism locks the supporting member to indirectly position the pressure plate, such a function is not required because the operation of the pressure mechanism is not hindered. 
   As the sheet member, a resin film or sheet, an elastically deformable metal thin plate, or other general members may be employed. 
   The invention is applicable to an electrophotographic printer or the like.