Abstract:
A sheet supplying device has: a base; a tray; a feed roller provided rotatably at the base and positioned above the tray. When the feed roller rotates while frictionally engaging with a topmost sheet of the stack of sheets, the feed roller can convey the sheet. The sheet supplying device further includes a driving mechanism able to drive the feed roller to rotate; an urging member urging the tray toward the feed roller; a first eccentric cam rotatably provided at the base, and including a large-radius outer peripheral portion and a small-radius outer peripheral portion, the first eccentric cam rotating interlockingly with rotation of the feed roller; and a second eccentric cam rotatably provided at the tray, and including a large-radius outer peripheral portion and a small-radius outer peripheral portion, the second eccentric cam being able to engage with the first eccentric cam.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority under 35 USC 119 from Japanese Patent Application No. 2003-432569, the disclosure of which is incorporated by reference herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an image forming device which records images on sheets of recording media (papers or the like of predetermined sizes), and to a sheet supplying device which conveys sheets one-by-one from a stack of sheets.  
         [0004]     2. Description of the Related Art  
         [0005]     Generally, in an image forming device such as a copier or a printer or the like, images are formed on recording media sheets in an image forming section. These sheets are stacked in a sheet supplying device which is provided within the image forming device, and are successively supplied from the sheet supplying device to the image forming section.  
         [0006]     As shown in  FIG. 16 , a sheet supplying device  100  has a presser plate  102  on which sheets (recording media) are placed. The presser plate  102  is urged upward by a coil spring  104 . Above the presser plate  102 , a supporting shaft  106  is supported so as to rotate freely with respect to a main body frame  130  (not all of the main body frame  130  is illustrated). A feed roller  108 , which is half-moon-shaped and conveys the sheets, is fixed to the supporting shaft  106 . Core rollers  110  are attached to the both sides of the feed roller  108 . The core rollers  110  rotate in a state of contacting a separating pad  112  provided at the main body frame  130 .  
         [0007]     Cams  114  are fixed to the both end portions of the supporting shaft  106 . The cams  114  abut rollers  124  provided at flanges  122  which project from the both side portions of the presser plate  102 .  
         [0008]     A driven gear  116  is attached to one end portion of the supporting shaft  106 . A portion of the peripheral surface of the driven gear  116  is cut out. A driving gear  118 , which is driven to rotate by a motor (not illustrated), is meshably disposed at the lower side of the driven gear  116 . The driving gear  118  meshes with the driven gear  116  at a predetermined timing so as to transmit the driving force of the driving gear  118  to the driven gear  116 , such that the supporting shaft  106  can rotate one time.  
         [0009]     As shown in  FIG. 17A , at times other than when sheets are being fed, the portions of the cams  114  where the eccentric radii are large abut the rollers  124  of the presser plate  102 , and press the presser plate  102  downward in a direction resisting the urging force of the coil spring  104 . At this time, the sheets stacked on the presser plate  102  are set apart from the feed roller  108 .  
         [0010]     As shown in  FIG. 17B , when the cams  114  rotate in the direction of the arrow due to the rotation of the supporting shaft  106 , the rollers  124  rotate while abutting the cams  114 , and the presser plate  102  is pushed upward by the urging force of the coil spring  104 . The feed roller  108  and the core rollers  110  also rotate together with the rotation of the supporting shaft  106 .  
         [0011]     As shown in  FIG. 17C , when the cams  114  rotate further in the direction of the arrow, the rollers  124  move along the cams  114 , and the presser plate  102  is gradually pushed upward. As shown in  FIG. 17D , the presser plate  102  rises to the position at which the rollers  124  abut bearing portions  114   a  of the cams  114 . At this time, the topmost portion of the stack of sheets stacked on the presser plate  102  contacts the feed roller  108 , and the sheets are fed out as the feed roller  108  rotates. Conveying, in an overlapping manner, of the sheets which are fed out is prevented by the friction with the separating pad  112 .  
         [0012]     When the cams  114  rotate further, the presser plate  102  is pushed downward in the direction of resisting the urging force of the coil spring  104 , and the cams  114  rotate one time. In this way, the presser plate  102  is lowered to the position shown in  FIG. 17A . (See, for example, Japanese Patent No. 2619959.)  
         [0013]     In the sheet supplying device  100  shown in  FIG. 16 , the presser plate  102  is moved upward and downward by the rotation of the cams  114  provided at the supporting shaft  106  of the feed roller  108 , and feeding of the topmost sheet of the stack of sheets is carried out. However, when an attempt is made to increase the accommodating capacity (the feeding capacity) of the sheets stacked on the presser plate  102 , a problem arises in that the cams  114  inevitably become large.  
         [0014]     Namely, in the feeding operations shown in  FIGS. 17A through 17D , when the presser plate  102  is raised, the topmost portion of the stack of sheets is pressed by the feed roller  108  and feeding is carried out. When the presser plate  102  is lowered, the topmost portion of the stack of sheets is moved away to a position at which it does not contact the feed roller  108 . Accordingly, when an attempt is made to increase the sheet accommodating capacity, the stroke of the presser plate  102  must be made to be large, and the cams  114  become large. Namely, there is the relation that the size of the cams  114  which move the presser plate  102  upward and downward determine the sheet accommodating capacity. Accordingly, a way to satisfy the antithetical needs for an increase in the sheet accommodating capacity and a decrease in the overall size of the device is desired.  
       SUMMARY OF THE INVENTION  
       [0015]     The present invention has been made in view of the above circumstances and provides a sheet supplying device and an image forming device which enable the device to be made compact overall and which enable an increase in the accommodating capacity of sheets (e.g., recording media).  
         [0016]     In accordance with one aspect of the present invention, there is provided a sheet supplying device comprising: a base; a tray on which a stack of sheets can be placed, the tray being able to be raised and lowered with respect to the base; a feed roller provided rotatably at the base and positioned above the tray, and when the feed roller rotates while frictionally engaging with a topmost sheet of the stack of sheets, the feed roller can convey the sheet; a driving mechanism able to drive the feed roller to rotate; an urging member urging the tray toward the feed roller; a first eccentric cam rotatably provided at the base, and including a large-radius outer peripheral portion whose radius is large and a small-radius outer peripheral portion whose radius is small, the first eccentric cam rotating interlockingly with rotation of the feed roller; and a second eccentric cam rotatably provided at the tray, and including a large-radius outer peripheral portion whose radius is large and a small-radius outer peripheral portion whose radius is small, the second eccentric cam being able to engage with the first eccentric cam, wherein, when the respective small-radius outer peripheral portions of the first eccentric cam and the second eccentric cam substantially contact one another, the tray approaches the feed roller so as to be able to convey the sheet, and when the respective large-radius outer peripheral portions of the first eccentric cam and the second eccentric cam substantially contact one another, the tray moves away from the feed roller so as to be unable to convey the sheet.  
         [0017]     In accordance with another aspect of the present invention, there is provided a sheet supplying device comprising: a base; a tray on which a stack of sheets can be placed, the tray being able to be raised and lowered with respect to the base; a feed roller provided rotatably at the base and positioned above the tray, and when the feed roller rotates while frictionally engaging with a topmost sheet of the stack of sheets, the feed roller can convey the sheet; a driving mechanism able to drive the feed roller to rotate; an urging member urging the tray toward the feed roller; a first eccentric cam provided rotatably at the base, and having a first rotating supporting shaft, and including a large-radius outer peripheral portion, whose radius is large, and a small-radius outer peripheral portion, whose radius is small, such that the first rotating supporting shaft is disposed between the large-radius outer peripheral portion and the small-radius outer peripheral portion, the first eccentric cam rotating interlockingly with rotation of the feed roller; a second eccentric cam provided rotatably at the tray, and having a second rotating supporting shaft, and including a large-radius outer peripheral portion, whose radius is large, and a small-radius outer peripheral portion, whose radius is small, such that the second rotating supporting shaft is disposed between the large-radius outer peripheral portion and the small-radius outer peripheral portion; and a third eccentric cam having a third rotating supporting shaft, and including a large-radius outer peripheral portion, whose radius is large, and a small-radius outer peripheral portion, whose radius is small, such that the third rotating supporting shaft is disposed between the large-radius outer peripheral portion and the small-radius outer peripheral portion, wherein the first rotating supporting shaft, the third rotating supporting shaft, and the second rotating supporting shaft are lined up in that order in a vertical direction and are separated from one another and parallel to one another, the third rotating supporting shaft can move translationally in the vertical direction, and in a first case in which the large-radius outer peripheral portion of the first eccentric cam substantially contacts one of the large-radius outer peripheral portion and the small-radius outer peripheral portion of the third eccentric cam, and the large-radius outer peripheral portion of the second eccentric cam substantially contacts another of the large-radius outer peripheral portion and the small-radius outer peripheral portion of the third eccentric cam, the tray moves away from the feed roller so as to be unable to convey the sheet, and in a second case in which the small-radius outer peripheral portion of the first eccentric cam substantially contacts the small-radius outer peripheral portion of the third eccentric cam, and the small-radius outer peripheral portion of the third eccentric cam substantially contacts the small-radius outer peripheral portion of the second eccentric cam, the tray approaches the feed roller so as to be able to convey the sheet.  
         [0018]     In accordance with yet another aspect of the present invention, there is provided a sheet supplying device comprising: a base; a tray on which a stack of sheets can be placed, the tray being able to be raised and lowered with respect to the base; a feed roller provided rotatably at the base and positioned above the tray, and when the feed roller rotates while frictionally engaging with a topmost sheet of the stack of sheets, the feed roller can convey the sheet; a driving mechanism able to drive the feed roller to rotate; an urging member urging the tray toward the feed roller; a first eccentric cam provided rotatably at the base, and having a first rotating supporting shaft, and including a large-radius outer peripheral portion, whose radius is large, and a small-radius outer peripheral portion, whose radius is small, such that the first rotating supporting shaft is disposed between the large-radius outer peripheral portion and the small-radius outer peripheral portion, the first eccentric cam being able to rotate independently of rotation of the feed roller; a second eccentric cam provided rotatably at the tray, and having a second rotating supporting shaft, and including a large-radius outer peripheral portion, whose radius is large, and a small-radius outer peripheral portion, whose radius is small, such that the second rotating supporting shaft is disposed between the large-radius outer peripheral portion and the small-radius outer peripheral portion; and a third eccentric cam having a third rotating supporting shaft, and including a large-radius outer peripheral portion, whose radius is large, and a small-radius outer peripheral portion, whose radius is small, such that the third rotating supporting shaft is disposed between the large-radius outer peripheral portion and the small-radius outer peripheral portion, wherein the first rotating supporting shaft, the third rotating supporting shaft, and the second rotating supporting shaft are lined up in that order in a vertical direction and are separated from one another and parallel to one another, the third rotating supporting shaft can move translationally in the vertical direction, and in a first case in which the large-radius outer peripheral portion of the first eccentric cam substantially contacts one of the large-radius outer peripheral portion and the small-radius outer peripheral portion of the third eccentric cam, and the large-radius outer peripheral portion of the second eccentric cam substantially contacts another of the large-radius outer peripheral portion and the small-radius outer peripheral portion of the third eccentric cam, the tray moves away from the feed roller so as to be unable to convey the sheet, and in a second case in which the small-radius outer peripheral portion of the first eccentric cam substantially contacts the small-radius outer peripheral portion of the third eccentric cam, and the small-radius outer peripheral portion of the third eccentric cam substantially contacts the small-radius outer peripheral portion of the second eccentric cam, the tray approaches the feed roller so as to be able to convey the sheet.  
         [0019]     In accordance with still yet another aspect of the present invention, there is provided an image forming device having a sheet supplying device, the sheet supplying device comprising: a base; a tray on which a stack of sheet-shaped recording media can be placed, the tray being able to be raised and lowered with respect to the base; a feed roller provided rotatably at the base and positioned above the tray, and when the feed roller rotates while frictionally engaging with a topmost recording medium of the stack of recording media, the feed roller can convey the recording medium; a driving mechanism able to drive the feed roller to rotate; an urging member urging the tray toward the feed roller; a first eccentric cam provided rotatably at the base, and including a large-radius outer peripheral portion whose radius is large and a small-radius outer peripheral portion whose radius is small, the first eccentric cam rotating interlockingly with rotation of the feed roller; and a second eccentric cam provided rotatably at the tray, and including a large-radius outer peripheral portion whose radius is large and a small-radius outer peripheral portion whose radius is small, the second eccentric cam able to engage with the first eccentric cam, wherein, when the respective small-radius outer peripheral portions of the first eccentric cam and the second eccentric cam substantially contact one another, the tray approaches the feed roller so as to be able to convey the recording medium, and when the respective large-radius outer peripheral portions of the first eccentric cam and the second eccentric cam substantially contact one another, the tray moves away from the feed roller so as to be unable to convey the recording medium.  
         [0020]     Other objects, features and advantages of the present invention will be apparent to those skilled in the art from the explanation of the preferred embodiments of the present invention illustrated in the appended drawings, and from the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     Preferred embodiments of the present invention will be described in detail based on the following figures, wherein:  
         [0022]      FIG. 1  is a perspective view showing a sheet supplying device relating to a first embodiment of the present invention;  
         [0023]      FIG. 2  is a perspective view showing a receiving portion and a pin which restrict rotation of a second cam of the sheet supplying device of the first embodiment;  
         [0024]      FIGS. 3A through 3D  are side views showing workings of the sheet supplying device of the first embodiment;  
         [0025]      FIGS. 4A through 4D  are side views showing other workings of the sheet supplying device of the first embodiment;  
         [0026]      FIGS. 5A through 5D  are side views showing yet other workings of the sheet supplying device of the first embodiment;  
         [0027]      FIGS. 6A through 6C  are side views showing still yet other workings of the sheet supplying device of the first embodiment;  
         [0028]      FIG. 7  is a schematic structural diagram showing an example of an image forming device into which the sheet supplying device of the first embodiment is incorporated;  
         [0029]      FIGS. 8A and 8B  are respectively a side view and a perspective view of a sheet supplying device relating to a second embodiment of the present invention;  
         [0030]      FIGS. 9A and 9B  are side views showing workings of a sheet supplying device relating to a third embodiment of the present invention;  
         [0031]      FIGS. 10A and 10B  are side views showing workings of the sheet supplying device of the third embodiment;  
         [0032]      FIG. 11  is a plan view showing a sheet supplying device relating to a fourth embodiment of the present invention;  
         [0033]      FIGS. 12A through 12C  are side views showing workings of the sheet supplying device of the fourth embodiment;  
         [0034]      FIGS. 13A through 13C  are side views showing other workings of the sheet supplying device of the fourth embodiment;  
         [0035]      FIGS. 14A and 14B  are side views showing workings of a sheet supplying device relating to a fifth embodiment of the present invention;  
         [0036]      FIGS. 15A and 15B  are side views showing other workings of the sheet supplying device of the fifth embodiment;  
         [0037]      FIG. 16  is a perspective view showing a conventional sheet supplying device; and  
         [0038]      FIGS. 17A through 17D  are side views showing workings of the conventional sheet supplying device. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
     FIRST EMBODIMENT  
       [0039]     Hereinafter, a sheet supplying device of a first embodiment of the present invention will be described in detail with reference to  FIGS. 1 through 7 .  
         [0040]     As shown in  FIG. 7 , a sheet supplying device  10  is provided at the lower portion of an image forming device  200 , and successively feeds, one-by-one, recording media (sheets) P to a process cartridge  204  structuring an image forming section.  
         [0041]     As shown in  FIGS. 1 and 7 , presser plates  14 , on which the sheets P are stacked, are provided in the sheet supplying device  10 . Insertion holes  58 , through which pass poles  56  which stand upright at a base  18 , are formed at both end portions of the presser plate  14  in a direction orthogonal to the sheet feeding direction. The presser plate  14  can move upward and downward while being guided by the poles  56 . The presser plate  14  is urged upward by coil springs  20  provided at the base  18 .  
         [0042]     A supporting shaft  22  is disposed above the presser plate  14 . The supporting shaft  22  is supported so as to be freely rotatable with respect to a main body frame of the image forming device  200 . A half-moon-shaped feed roller  24 , which feeds the sheets P (not shown in  FIG. 1 ) which are stacked on the presser plate  14 , is fixed to the supporting shaft  22 . Core rollers  26 , whose radii are somewhat smaller than the radius of the half-moon-shaped feed roller  24 , are fixed to the both sides of the feed roller  24 .  
         [0043]     As shown in  FIG. 1 , a separating roller  28  is rotatably supported at the portion of a main body frame  300  opposing the feed roller  24  and the core rollers  26 . The separating roller  28  is formed as a member whose surface has great frictional force. Due to the rotation of the supporting shaft  22 , the core rollers  26  rotate in a state of abutting the separating roller  28 . Further, the peripheral surface of the feed roller  24  can feed the topmost sheet P out by rotating while abutting the stack of sheets P stacked on the presser plate  14 .  
         [0044]     First cams  30  are fixed to both end portions of the supporting shaft  22 . The first cams  30  have arc-shaped portions  30 a which are fan-shaped and whose eccentric radii are larger than the radius of the feed roller  24 .  
         [0045]     A driven gear  32  is mounted to one end portion of the supporting shaft  22 . A portion of the outer periphery of the driven gear  32  is toothless. A driving gear  34 , which is driven to rotate by an unillustrated motor, can mesh with the driven gear  32 . When the sheets P are to be fed, the driving force of the driving gear  34  is transmitted to the driven gear  32  at a predetermined timing by an unillustrated control device, such that the supporting shaft  22 , the feed roller  24 , the core rollers  26  and the first cams  30  rotate one time in the direction of arrow A (see  FIGS. 3A through 3D ).  
         [0046]     As shown in  FIG. 1 , flanges  36  which project upward are formed at positions of the both sides of the presser plate  14  which positions oppose the first cams  30 . Second cams  38  are rotatably supported by rotating shafts  39  at the flanges  36 . First cam followers  40 , which can abut the first cams  30 , are provided so as to project out at end sides of the flanges  36 , at the sides of the second cams  38  which sides are opposite the sides in the feeding direction. Concave portions  42  are formed beneath the first cam followers  40 . The second cams  38  can enter into the concave portions  42  when the second cams  38  are rotating.  
         [0047]     Second cam followers  44  are mounted to the base  18  beneath the concave portions  42  of the first cam followers  40 . As shown in  FIG. 3A , due to the second cams  38  abutting the second cam followers  44 , the second cams  38  are held in a state (posture) in the direction of abutting the first cams  30 . Rollers  46  are provided at the regions of the second cams  38  which regions abut the first cams  30 . Convex and concave portions may be formed in the peripheral surfaces of the rollers  46  in order to prevent slippage between the rollers  46  and the first cams  30 . As shown in  FIG. 3A , when the arc-shaped portions  30   a  of the first cams  30 , whose eccentric radii are large, abut the portions of the second cams  38  where the eccentric radii are large, the presser plate  14  is pushed downward to its lowermost position.  
         [0048]     Because the coil springs  20  push the presser plate  14  upward, the second cams  38  abut the second cam followers  44  in addition to abutting the first cams  30 .  
         [0049]     When the first cams  30  rotate in the direction of arrow A, components of force which rotate the second cams  38  in the opposite direction so as to counteract this, are applied to the second cams  38  so that the second cams  38  rotate in the direction of arrow B (see  FIG. 3C ).  
         [0050]     As shown in  FIG. 2 , pins  48  project at the inner sides (the feed roller  24  sides) of the second cams  38 . L-shaped receiving portions  50 , which are structured by the flanges  36  and the first cam followers  40 , are provided at the presser plate  14 . When the second cams  38  rotate in the direction of arrow B, the pins  48  are received in the receiving portions  50 , and rotation of the second cams  38  is restricted due to the self-weights thereof.  
         [0051]     In this sheet supplying device  10 , the number of sheets P which can be stacked on the presser plate  14  (the number of sheets which can be accommodated) is about 250 sheets for regular paper, and about 200 sheets for thick paper.  
         [0052]     Hereinafter, operation of the sheet supplying device  10  will be described with reference to  FIGS. 3A through 6C .  
         [0053]     As shown in  FIG. 3A , when the sheets P are not being fed, the arc-shaped portions  30   a  of the first cams  30  abut the portions of the second cams  38  where the eccentric radii are large, so as to push the presser plate  14  downward in the direction of resisting the urging forces of the coil springs  20 . Pressing forces F in the direction of the arrow and due to the urging forces of the coil springs  20  are applied to the first cams  30 . At this time, the presser plate  14  is positioned at its lowermost position, and the sheets P (not illustrated) stacked on the presser plate  14  are set apart from the feed roller  24 .  
         [0054]     As shown in  FIG. 3B , when the first cams  30  rotate in the direction of arrow A due to the rotation of the supporting shaft  22 , components of force in the direction opposite the rotating direction are applied to the second cams  38  which are abutting the first cams  30 , and the second cams  38  rotate in the direction of arrow B while abutting the second cam followers  44 . The rollers  46  of the second cams  38  are abutting the first cams  30 , and the first cams  30  rotate smoothly due to the rollers  46 .  
         [0055]     As the second cams  38  rotate, the eccentric radii of the abutting regions thereof become shorter, and the presser plate  14  is pushed upward by the urging forces of the coil springs  20 . Due to the rotation of the supporting shaft  22 , the feed roller  24  and the core rollers  26  as well rotate in the direction of arrow A.  
         [0056]     As shown in  FIG. 3C , when the first cams  30  rotate 40° in the direction of arrow A, the second cams  38  rotate in the direction of arrow B while abutting the second cam followers  44 , and the presser plate  14  rises up smoothly. At this time, the second cams  38  enter into the concave portions  42  of the first cam followers  40  while rotating.  
         [0057]     As shown in  FIG. 3D , when the first cams  30  rotate 42.5° in the direction of arrow A, the second cams  38  rotate further in the direction of arrow B while abutting the top portions of the second cam followers  44 , and the presser plate  14  is raised upward by the urging forces of the coil springs  20 . When the second cams  38  rotate further in the direction of arrow B and the pins  48  of the second cams  38  engage with the receiving portions  50 , further rotation of the second cams  38  is impeded.  
         [0058]     As shown in  FIG. 4A , when the first cams  30  rotate 50° in the direction of arrow A, the angular positions of the second cams  38  do not change because the pins  48  are engaged with the receiving portions  50 . Accordingly, the second cams  38  come away from the second cam followers  44 . The presser plate  14  rises further due to the abutment of the first cams  30  and the second cams  38 . Then, due to the rotation of the supporting shaft  22 , the feed roller  24  and the core rollers  26  also rotate further in the direction of arrow A.  
         [0059]     The presser plate  14  rises until the topmost portion of the stack of sheets P stacked on the presser plate  14  abuts the feed roller  24 . Then, the stack of sheets P abuts/engages with the feed roller  24 , and due to the feed roller  24  rotating while abutting the topmost sheet P, the sheet P is fed out. At the conveying direction downstream side of the sheet P, the reverse surface side of the sheet P contacts the separating roller  28  at a predetermined pressure. Due to the friction between the sheet P and the separating roller  28 , feeding of the sheets P in an overlapping manner is prevented, and a single sheet P is conveyed.  
         [0060]     When a small number of the stacked sheets is conveyed, as shown in  FIG. 4B , when the first cams  30  rotate in the direction of arrow A by 64.43°, the second cams  38  abut bearing portions  30   b  of the first cams  30 , and the presser plate  14  reaches it uppermost position.  
         [0061]     When the presser plate  14  is at its uppermost position, the first cam followers  40  provided at the presser plate  14  are positioned rearward of the supporting shaft  22  (i.e., at the side opposite the feeding direction side of the supporting shaft  22 ), such that the first cam followers  40  are prevented from interfering with the supporting shaft  22 . Thereafter, as shown in  FIGS. 4C and 4D , when the first cams  30  rotate in the direction of arrow A, the second cams  38  slidingly contact the bearing portions  30   b  of the first cams  30 , and the presser plate  14  is held at its uppermost position.  
         [0062]     As shown in  FIG. 5A , when the first cams  30  rotate 250.79° in the direction of arrow A, due to the distal ends of the arc-shaped portions  30   a  abutting and pressing the first cam followers  40 , the presser plate  14  is pushed in the direction against the urging forces of the coil springs  20  (i.e., is pushed downward).  
         [0063]     As shown in  FIG. 5B , when the first cams  30  rotate 270° in the direction of arrow A, the second cams  38  abut the second cam followers  44  due to the lowering of the presser plate  14 . Then, the pins  48  of the second cams  38  separate from the receiving portions  50 , and the second cams  38  rotate in the direction of arrow C while abutting the second cam followers  44 .  
         [0064]     As shown in  FIG. 5C , when the first cams  30  rotate 290° in the direction of arrow A, due to the arc-shaped portions  30   a  pushing the first cam followers  40 , the presser plate  14  is lowered, and the second cams  38  rotate in the direction of arrow C by abutting the second cam followers  44 .  
         [0065]     As shown in  FIGS. 5D and 6A , when the first cams  30  rotate further, the arc-shaped portions  30   a  press the presser plate  14  downward while the arc-shaped portions  30   a  slide along the first cam followers  40 , and the second cams  38  rotate further in the direction of arrow C by abutting the second cam followers  44 .  
         [0066]     As shown in  FIG. 6B , when the first cams  30  rotate 340° in the direction of arrow A, the arc-shaped portions  30   a  move away from the first cam followers  40  and abut the second cams  38 .  
         [0067]     As shown in  FIG. 6C , due to the first cams  30  rotating 360° in the direction of arrow A (i.e., due to the first cams  30  rotating one time), while the first cams  30  and the rollers  46  abut one another, the second cams  38  are rotated to their initial positions, and the presser plate  14  is pushed downward to its lowermost position.  
         [0068]     In the present sheet supplying device  10 , by rotating the first cams  30  and the second cams  38  respectively, the presser plate  14  is raised and lowered. Therefore, the stroke of the presser plate  14  can be made to be large, and the first cam followers  40  and the supporting shaft  22  do not interfere with one another when the presser plate  14  is at its uppermost position. Therefore, even if the first cams  30  are made to be small, the sheet P accommodating capacity can be increased, and the sheet supplying device  10  can be made to be compact.  
       SECOND EMBODIMENT  
       [0069]     Hereinafter, a second embodiment of a sheet supplying device relating to the present invention will be briefly described with reference to  FIGS. 8A and 8B .  
         [0070]     Note that the same reference numerals are applied to members and portions which were described in the first embodiment, and repeat description will be appropriately omitted.  
         [0071]     In a sheet supplying device  70  shown in  FIGS. 8A and 8B , springs  74 , which urge the second cams  38  in the direction of arrow B, are wound around rotating shafts  72  of the second cams  38 . Ones of ends of the springs  74  are attached to the second cams  38 , whereas the other ends are attached to the flanges  36 .  
         [0072]     In this way, as the presser plate  14  rises, the second cams  38  rotate in the direction of arrow B in a state of abutting the second cam followers  44 . On the other hand, when the presser plate  14  falls, the second cams  38  rotate in the direction resisting the urging forces of the springs  74  (i.e., in the direction of arrow C) due to the second cams  38  abutting the second cam followers  44 .  
         [0073]     In this way, by the simple structure of providing the springs  74  which urge the second cams  38 , the behavior of the second cams  38  at times when the presser plate  14  is moving upward and downward can be stabilized.  
       THIRD EMBODIMENT  
       [0074]     Hereinafter, a third embodiment of a sheet supplying device relating to the present invention will be described briefly with reference to  FIGS. 9A, 9B ,  10 A, and  10 B.  
         [0075]     Note that the same reference numerals are applied to members and portions which were described in the first and second embodiments, and repeat description will be appropriately omitted.  
         [0076]     In a sheet supplying device  80  shown in  FIG. 9B , second cams  82  are rotatably supported at the presser plate  14  via the rotating shafts  39 . Springs such as in the second embodiment are not provided at the second cams  82 .  
         [0077]     Second cam followers  84 , which abut the second cams  82  and rotate the second cams  82  in a given direction, are provided beneath the concave portions  42  of the first cam followers  40 .  
         [0078]     Third cam followers  86  are provided at positions which oppose the second cam followers  84 , with the second cams  82  therebetween. The third cam followers  86  restrict rotation of the second cams  82  in the direction of moving away from the second cam followers  84 .  
         [0079]     The surfaces of the third cam followers  86  which surfaces abut the second cams  82  have configurations which curve along the loci of rotation of the second cams  82 . The third cam followers  86  can make the second cams  82  rotate continuously in the given direction.  
         [0080]     The second cam follower  84  and the third cam follower  86  are formed as an integral part and mounted to the base (see  FIG. 1 ).  
         [0081]     Next, operation of the present sheet supplying device  80  will be described.  
         [0082]     As shown in  FIG. 9A , the second cams  82  abut the second cam followers  84  and the third cam followers  86  at the both sides. The portions of the second cams  82  where the eccentric radii are large abut the portions of the first cams  30  where the eccentric radii are large. At this time, the presser plate  14  is positioned at its lowermost position against the urging forces of the springs  20 .  
         [0083]     When the first cams  30  rotate in the direction of arrow A due to the rotation of the supporting shaft  22 , components of force in the direction opposite to the direction of rotation of the first cams are applied to the second cams  82 . The second cams  82  rotate in the direction of arrow B while abutting the second cam followers  84 . At this time, because the abutment surfaces of the third cam followers  86  are formed in configurations which curve along the loci of rotation of the second cams  82 , the second cams  82  rotate continuously without joggling. As the second cams  82  rotate, the presser plate  14  rises smoothly.  
         [0084]     As shown in  FIG. 9B , due to the rising of the presser plate  14 , the second cams  82  separate from the second cam followers  84 . At this time, the rotation of the second cams  82  is restricted by the pins and the receiving portions (which are not illustrated) (see  FIG. 2 ). Then, due to the rotation of the first cams  30 , the presser plate  14  rises up to its uppermost position.  
         [0085]     As shown in  FIG. 10A , when the first cams  30  rotate further in the direction of arrow A, the first cams  30  abut the first cam followers  40  and push the presser plate  14  downward. Due to the lowering of the presser plate  14 , the second cams  82  abut the second cam followers  84 , and the second cams  82  rotate in the direction of arrow C (see  FIG. 10B ).  
         [0086]     As shown in  FIG. 10B , as the presser plate  14  is lowered, the second cams  82  abut the third cam followers  86 , and rotation of the second cams  82  in the direction of arrow C is restricted. Due to the first cams  30  separating from the first cam followers  40  and abutting the second cams  82 , the presser plate  14  is lowered to its lowermost position.  
         [0087]     In this sheet supplying device  80 , the third cam followers  86  are disposed at positions opposing the second cam followers  84  with the second cams  82  therebetween. Therefore, rotation of the second cams  82  in the direction of moving away from the second cam followers  84  can be restricted. As a result, the second cams  82  rotate so as to smoothly follow the second cam followers  84 . Due to such a structure, even if the springs  74  (see  FIGS. 8A, 8B ) of the second embodiment are not provided, similar effects can be achieved.  
         [0088]     Note that, instead of mounting the second cam follower  84  and the third cam follower  86  as an integral part to the base (see  FIG. 1 ), the second cam follower and the third cam follower may be structured as separate parts, and the third cam follower may be mounted to the presser plate  14 .  
       FOURTH EMBODIMENT  
       [0089]     Hereinafter, a fourth embodiment of a sheet supplying device relating to the present invention will be described in detail with reference to  FIGS. 11 through 13 C.  
         [0090]     Note that the same reference numerals are applied to members and portions which were described in the first embodiment, and repeat description will be appropriately omitted.  
         [0091]     As shown in  FIGS. 11 and 12 A, in a sheet supplying device  160 , a supporting shaft  166  is rotatably provided at a main body frame  301 . Oval first cams  150  and rod-shaped members  156 , which are longer than the portions of the first cams  150  where the eccentric radii are large, are fixed to the supporting shaft  166 . As shown in  FIG. 11 , the free end of the rod-shaped member  156  is bent inwardly and forms an abutment portion  156 a which abuts the first cam follower  40  of the presser plate  14 .  
         [0092]     Oval second cams  154  are rotatably supported at the presser plate  14  by the rotating shafts  39 . The second cams  154  abut second cam followers  164  which are mounted to the main body frame  301  (not shown in  FIGS. 12A through 12C ), and are urged in the direction of arrow B by unillustrated springs.  
         [0093]     As shown in  FIG. 11 , long holes  159 ,  161  which extend in the vertical direction are formed in the first cam follower  40  and the main body frame  301 . A rotating shaft  158  of an oval third cam  152  is slidable in the vertical direction along the long holes  159 ,  161 . The third cams  152  can abut second cam followers  162  which are mounted to the main body frame  301  (not shown in  FIGS. 12A through 12C ). The third cams  152  are urged in the direction of arrow C by springs which are not shown.  
         [0094]     The first cams  150  are driven to rotate in the direction of arrow A due to the rotation of the supporting shaft  166 . The third cams  152  and the second cams  154  are driven cams which rotate following the rotation of the first cams  150 .  
         [0095]     As shown in  FIG. 12A , the supporting shaft  166  of the first cams  150  and the rod-shaped members  156  is a different shaft than the supporting shaft  22  of the feed roller  24 , and can be driven to rotate separately from the feed roller  24 .  
         [0096]     Next, operation of the present sheet feeding device  160  will be described with reference to  FIGS. 12A through 12C  and  FIGS. 13A through 13C .  
         [0097]     As shown in  FIG. 12A , the presser plate  14  is pushed downward to its lowermost position due to respective portions of the first cams  150 , the third cams  152 , and the second cams  154 , at which portions the eccentric radii are large, abutting one another and the abutment portions  156   a  of the rod-shaped members  156  abutting the first cam followers  40 .  
         [0098]     As shown in  FIG. 12B , when the first cams  150  rotate in the direction of arrow A, accompanying this rotation, the rod-shaped members  156  also rotate, and the abutment portions  156 a separate from the first cam followers  40 . As the first cams  150  rotate, the third cams  152  rotate followingly in the direction of arrow C (which is the urging direction of the unillustrated springs) while abutting the second cam followers  162 . As the third cams  152  rotate, the rotating shafts  158  begin to slide along the long holes  159 .  
         [0099]     As the third cams  152  rotate, the second cams  154  rotate in the urging direction of the unillustrated springs (the direction of arrow B) while abutting the second cam followers  164 . Due to such rotation of the first cams  150  and the third cams  152  and the second cams  154 , the presser plate  14  rises upward due to the urging forces of the springs  20 .  
         [0100]     As shown in  FIG. 12C , when the first cams  150  rotate further in the direction of arrow A, the third cams  152  rotate further in the direction of arrow C, and the rotating shafts  158  slide in the long holes  159 . Accompanying this, the second cams  154  also rotate in the direction of arrow B. When the third cams  152  and the second cams  154  have respectively rotated 90°, rotation thereof is restricted due to the unillustrated pins and receiving portions.  
         [0101]     Due to the portions of the first cams  150 , the third cams  152 , and the second cams  154 , at which portions the eccentric radii are small, abutting one another, the presser plate  14  rises to its topmost position. At this time, the first cam followers  40  do not interfere with the abutment portions  156   a  of the rod-shaped members  156  and the supporting shaft  166  of the first cams  150 . When the presser plate  14  is raised, the sheets P are supplied by the feed roller  24  (see  FIG. 1 ).  
         [0102]     Thereafter, as shown in  FIG. 13A , when the first cams  150  rotate in the direction of arrow A, the abutment portions  156   a  of the rod-shaped members  156  abut the first cam followers  40 , and push the presser plate  14  downward against the urging forces of the springs  20 .  
         [0103]     As shown in  FIG. 13B , when the first cams  150  rotate further in the direction of arrow A, the first cams  150  abut the third cams  152 , and the third cams  152  abut the second cam followers  162 , and the third cams  152  rotate in the direction of arrow E which is opposite to the urging forces of the springs (not shown). Together therewith, the rotating shafts  158  of the third cams  152  are slid along the long holes  159 . The second cams  154 , which are abutting the third cams  152 , abut the second cam followers  164  and rotate in the direction of arrow D which is opposite to the urging forces of the springs (not shown).  
         [0104]     As shown in  FIG. 13C , when the first cams  150  have rotated one time in the direction of arrow A, the rotating shafts  158  of the third cams  152  slide along the long holes  159 , and the portions of the first cams  150 , the third cams  152 , and the second cams  154 , at which portions the eccentric radii are large, abut one another. In this way, the presser plate  14  falls to its lowermost position.  
         [0105]     In the present sheet supplying device  160 , the presser plate  14  is raised and lowered by the combination of the three cams. Therefore, even if the eccentric radii of the respective cams  150 ,  152 ,  154  are not made to be large, the stroke of the presser plate  14  can be made to be large. Therefore, the sheet P accommodating capacity can be increased, and the device can be made compact overall.  
       FIFTH EMBODIMENT  
       [0106]     Hereinafter, a fifth embodiment of a sheet supplying device relating to the present invention will be described in detail with reference to  FIGS. 14A, 14B  and  FIGS. 15A, 15B .  
         [0107]     Note that the same reference numerals are applied to members and portions which were described in the first and fourth embodiments, and repeat description will be appropriately omitted.  
         [0108]     As shown in  FIG. 14A , first cams  170  are provided so as to be rotatable by a supporting shaft  176  at the main body frame (not illustrated) of a sheet supplying device  180 . The supporting shaft  176  is driven to rotate separately from the supporting shaft  22  of the feed roller  24 . Second cams  174  are rotatably supported by rotating shafts  182  at the presser plate  14 . The second cams  174  can abut the second cam followers  164 . Springs for urging in a given direction are not provided at the second cams  174 .  
         [0109]     Third cams  172  are rotatably supported by rotating shafts  178  between the first cams  170  and the second cams  174 , so as to abut the first cams  170  and the second cams  174 . The rotating shafts  178  can slide vertically along long holes (not illustrated) provided in the main body frame. The third cams  172  can abut the second cam followers  162 . Springs for urging in a given direction are not provided at the third cams  172 .  
         [0110]     The first cams  170  are driven to rotate  900  in opposite directions (the direction of arrow A and the direction of arrow D), due to the rotation of the supporting shaft  176 . The third cams  172  and the second cams  174  are driven cams which rotate followingly accompanying the rotation of the first cams  170 .  
         [0111]     Next, operation of the present sheet supplying device  180  will be described.  
         [0112]     The presser plate  14  is pushed downward to its lowermost position due to the respective portions of the first cams  170 , the third cams  172 , and the second cams  174 , at which portions the eccentric radii are large, abutting one another.  
         [0113]     As shown in  FIG. 14A , when the first cams  170  rotate in the direction of arrow A, the third cams  172  rotate followingly in the direction of arrow C while abutting the second cam followers  162 . Together therewith, the rotating shafts  178  start to slide. Due to the rotation of the third cams  172 , the second cams  174  rotate followingly in the direction of arrow B while abutting the second cam followers  164 . Due to the rotation of the first cams  170  and the third cams  172  and the second cams  174 , the presser plate  14  rises upward due to the urging forces of the springs  20 .  
         [0114]     As shown in  FIG. 14B , at the time when the first cams  170  rotate  90 ° in the direction of arrow A due to the rotation of the supporting shaft  176 , when the third cams  172  followingly rotate  90 ° in the direction of arrow C, the rotation of the third cams  172  is restricted due to the pins and the receiving portions which are not shown. Accompanying the rotation of the third cams  172 , the second cams  174  also followingly rotate  90 ° in the direction of arrow B, and the rotation of the second cams  174  is restricted due to the pins and the receiving portions which are not shown.  
         [0115]     Due to respective portions of the first cams  170 , the third cams  172 , and the second cams  174 , at which portions the eccentric radii are small, abutting one another, the presser plate  14  rises to its topmost position. When the presser plate  14  is raised, the sheets P are supplied by the feed roller  24  (see  FIG. 1 ).  
         [0116]     Thereafter, as shown in  FIG. 15A , when the first cams  170  are driven to rotate in the direction of arrow D (the direction opposite to the direction of arrow A) by the supporting shaft  176 , the lowering of the presser plate  14  due to the rotation of the first cams  170  begins. At this time, the third cams  172  and the second cams  174  remain stopped because their rotation is restricted.  
         [0117]     As shown in  FIG. 15B , when the first cams  170  rotate further in the direction of arrow D, the third cams  172  abut the second cam followers  162 , and thereby rotate followingly in the direction of arrow E.  
         [0118]     Moreover, due to the second cams  174  abutting the second cam followers  164 , the second cams  174  rotate followingly in the direction of arrow F, and push the presser plate  14  downward.  
         [0119]     The presser plate  14  moves downward to its lowermost position due to the first cams  170  rotating further in the direction of arrow D, and the portions of the first cams  170 , the third cams  172 , and the second cams  174 , at which portions the eccentric radii are large, abutting one another.  
         [0120]     In the present sheet supplying device  180 , the presser plate  14  can be moved upward and downward by the combination of the three cams. Therefore, even if the eccentric radii of the respective cams  170 ,  172 ,  174  are not made to be large, the stroke of the presser plate  14  can be made to be large. Therefore, the sheet P accommodating capacity can be increased, and the device can be made compact overall.  
       EMBODIMENT OF THE IMAGE FORMING DEVICE  
       [0121]     Lastly, an embodiment of an image forming device, to which the sheet supplying device  10  of the first embodiment is applied, will be described in detail with reference to  FIG. 7 .  
         [0122]     The process cartridge  204 , in which an image forming section has been integrally formed into a unit, is provided in the present image forming device  200 . A photosensitive body drum  216 , which rotates in a given direction, is provided at the interior of the process cartridge  204 . A charging roller  218 , which charges the photosensitive drum, a developing roller  220 , which develops an electrostatic latent image formed on the photosensitive body drum, and a transfer roller  222 , which transfers the developed toner image on the photosensitive body drum onto the sheet P, are disposed at the periphery of the photosensitive body drum  216  from the rotating direction upstream side. A cleaning member  224 , which cleans the surface of the photosensitive body drum after transfer, is provided at the downstream side of the transfer roller  222  in the rotating direction of the photosensitive body drum  216 . An exposure device  214 , which illuminates image light onto the photosensitive body drum  216 , is provided in the image forming device  200  between the charging roller  218  and the developing roller  220 .  
         [0123]     The sheet supplying devices  10  of the present invention, in which the sheet-shaped sheets P are stacked, are provided in two levels, one above the other, at the lower portion of the image forming device  200 . Feeding cassettes  206 ,  208 , in which the sheets P of respectively different sizes can be accommodated, are disposed at the sheet feeding devices  10  so as to be able to be pulled out to the exterior thereof. The feed rollers  24 , which remove and convey the sheets P one-by-one as described above, are provided at the sheet P removing positions of the feeding cassettes  206 ,  208 .  
         [0124]     Two sets of conveying rollers  210 ,  211  and conveying rollers  212 ,  213  are provided which convey the sheets P, which have been supplied from the feed rollers  24 , to a position opposing the photosensitive body drum  216  and the transfer roller  222 . A fixing unit  250 , which is provided with a heat roller  252  and a pressure roller  254 , is installed at the downstream side of the transfer roller  22  in the conveying direction of the sheets P. A discharged sheet tray  230 , to which the sheets P are discharged after fixing, is provided at the downstream side of the fixing unit  250 .  
         [0125]     An opening/closing cover  232  is provided at the image forming device  200 . By opening the opening/closing cover  232 , the fixing unit  250  can be installed in the image forming device  200 . When the fixing unit  250  is installed in the image forming device  200 , simultaneously therewith, a connector of the fixing unit  250  and a connector of the image forming device  200  are joined together. By closing the opening/closing cover  232 , the image forming device  200  is set in a state in which operation is possible.  
         [0126]     In this image forming device, an electrostatic latent image is formed on the surface of the photosensitive body drum  216  due to the photosensitive body drum  216  being charged by the charging roller  218  and image light being illuminated thereon from the exposure device  214 . The electrostatic latent image is developed by the developing roller  220 , such that a toner image is formed on the photosensitive body drum  216 .  
         [0127]     The sheet P is supplied from the feeding cassette  206  of the sheet supplying device  10  due to the rotation of the feed roller  24 , and the sheet P is conveyed by the conveying rollers  210 ,  211  and the conveying rollers  212 ,  213  to the position opposing the photosensitive body drum  216  and the transfer roller  222 . Then, the toner image on the photosensitive body drum  216  is transferred onto the sheet P by the transfer roller  222 . Due to the application of heat and pressure between the heat roller  252  and the pressure roller  254  of the fixing unit  250 , the toner image on the sheet P is fused such that the image is fixed on the sheet P. Thereafter, the sheet P on which the image has been formed is discharged out to the discharged sheet tray  230 .  
         [0128]     In the image forming device  200  in which the sheet supplying device  10  of the first embodiment is incorporated, when the presser plate  14  is raised up and the sheet P is supplied by the rotation of the feed roller  24 , the presser plate  14  and the supporting shaft  22  of the feed roller  24  do not interfere with one another, and the accommodating capacity of the sheets P can be increased even if the first cams  30  are not made to be large. Namely, the sheet supplying device  10 , and accordingly, the image forming device  200 , can be made to be compact.  
         [0129]     Note that, instead of the sheet supplying device  10  of the first embodiment, any of the sheet supplying devices of the second through fifth embodiments can be incorporated into the image forming device. In this way, the sheet P accommodating capacity can similarly be increased, and the image forming device can be made to be compact.