Abstract:
A sheet feeding roller is brought into contact with an uppermost sheet stacked on a hopper, and rotates to feed the uppermost sheet to the recording apparatus. A separation pad presses the uppermost sheet against the feeding roller so that the upper most sheet is separated from a next uppermost sheet. A first sheet returner pushes back a first part of the next uppermost sheet situated on the separation pad to the hopper. A second sheet returner pushes back a second part of the next uppermost sheet situated on the separation pad to the hopper. The sheet feeding roller, the separation pad and the first sheet returner are incorporated in a single unit which is disposed at a first position of a sheet feeding passage formed on the hopper. The second sheet returner is solely disposed at a second position of the sheet feeding passage.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a sheet feeder which feeds sheets of paper stacked within a hopper one by one from the uppermost one to an apparatus such as a printer etc.  
           [0002]    Some of the printers coupled to the personal computers are provided with sheet feeders. Such a sheet feeder supplies sheets of paper stacked on the hopper one by one from the uppermost one to a transferring roller of the printer by using a sheet feeding roller and a separation pad of a sheet feeding roller unit.  
           [0003]    Then, the transfer operation of the transferring roller and the recording operation of a recording head are alternately executed with respect to the sheet thus supplied to the transferring roller of the printer, thereby to record an image including characters on the sheet thus transferred, and the sheet thus recorded is ejected.  
           [0004]    A sheet returner and an idle roller are also provided at the sheet feeding roller unit. The sheet feeding roller unit operates after the rear end of the uppermost sheet moves away from a nipping portion between the separation pad and the idle roller to thereby return on the hopper the next-positioned sheet which leading end is located on the separation pad.  
           [0005]    However, a plurality of, usually, two sheet feeding roller units each configured in the aforesaid manner are provided in a sheet feeding passage. It is sufficient to provide the single sheet feeding roller unit in the sheet-width direction in order to supply the sheet to the printer by using the sheet feeding roller and the separation pad of the sheet feeding roller unit. In view of such a fact, it is not rational to provide a plurality of sheet feeding roller units in the width direction of the sheet feeding passage, and the provision of the plural sheet feeding roller units results in the increase of the number of the parts.  
           [0006]    However, it is necessary to dispose the plural sheet feeding roller units provided with the sheet returners in the width direction of the sheet feeding passage in order to return the sheet which leading end is located on the separation pad on the hopper without being skewed by the sheet returners.  
           [0007]    Further, the hopper of the sheet feeder is provided with an edge guide which is slidable in the width direction of the sheet. There is a sheet feeder which is configured in a manner that one of the sheet feeding roller units is coupled to the edge guide and slidable together with the edge guide in the width direction of the sheet. However, according to such a sheet feeder, the resistance (sliding load) caused at the time of sliding the edge guide becomes large and so the operability of the edge guide is degraded.  
           [0008]    On the other hand, when the sheet is nipped between the sheet feeding roller in the sheet feeding roller unit and the separation pad, a force from the separation pad toward the sheet feeding roller, that is, a force directed to a back face of a separation pad holder for supporting the separation pad acts. The nipping state between the sheet feeding roller and the separation pad becomes insufficient due to the action of the force in the back face direction, so that there may occur such a phenomenon that the sheets are not supplied well one by one by the sheet feeding roller and the separation pad.  
         SUMMARY OF THE INVENTION  
         [0009]    In view of the aforesaid circumstances, an object of the invention is to provide a sheet feeder which can return a sheet without being skewed, supply well a sheet to a sheet supply target from the hopper and realize the rationalization. Further, another object of the invention is to provide a sheet feeder which can secure preferably the pressure contact state between a sheet feeding roller and a separation pad and supply a sheet well to the sheet supply target from the hopper.  
           [0010]    In order to achieve the above objects, according to the present invention, there is provided a sheet feeder for feeding sheets of a recording medium to a recording apparatus comprising:  
           [0011]    a hopper, on which the sheets of recording medium are stacked;  
           [0012]    a sheet feeding roller, which is brought into contact with an uppermost sheet stacked on the hopper, and rotates to feed the uppermost sheet to the recording apparatus;  
           [0013]    a separation pad, which presses the uppermost sheet against the feeding roller so that the upper most sheet is separated from a next uppermost sheet;  
           [0014]    a first sheet returner, which pushes back a first part of the next uppermost sheet situated on the separation pad to the hopper; and  
           [0015]    a second sheet returner, which pushes back a second part of the next uppermost sheet situated on the separation pad to the hopper,  
           [0016]    wherein the sheet feeding roller, the separation pad and the first sheet returner are incorporated in a single unit which is disposed at a first position of a sheet feeding passage formed on the hopper, and the second sheet returner is solely disposed at a second position of the sheet feeding passage.  
           [0017]    In this configuration, since the required number of parts are decreased, not only the sheet can be returned without being skewed and supplied well to the recording apparatus from the hopper, but also the rationalization of the sheet feeder can be realized.  
           [0018]    Preferably, the first sheet returner and the second sheet returner are provided immovably in a widthwise direction of the sheet feeding passage.  
           [0019]    In this configuration, since none of the first sheet returner or the second sheet returner moves in the widthwise direction of the sheet feeding passage in cooperation with a slidable edge guide of the hopper, the resistance (sliding load) caused at the time of sliding the edge guide can be reduced and so the sliding operation of the edge guide can be performed smoothly.  
           [0020]    Preferably, the sheet feeder further comprises guide members which are separately provided in the vicinity of the first sheet returner and the second sheet returner, each of the guide members having a guide face which forms a part of the sheet feeding passage.  
           [0021]    In this configuration, as compared with the case where these guide members are formed continuously in the widthwise direction of the sheet feeding passage, even if the next uppermost sheet on the hopper which leading end is positioned at the separation pad is skewed or warped, the sheet is guided by the guide members by the operation of the first and second sheet returners and so the next uppermost sheet can be surely returned to the hopper. Therefore, in accordance with the forward rotation of the sheet feeding roller which is operated next, only the next uppermost sheet on the hopper can be supplied to the recording apparatus, and the sheets can be prevented from being supplied in a duplicated manner.  
           [0022]    Preferably, the hopper includes an edge guide member, on which one side edges of the stacked sheets are aligned. Here, the first position of the sheet passage is in the vicinity of the edge guide member. A distance between the edge guide member and the second position almost corresponds to a width of a sheet having a size in a range from A6 to B5.  
           [0023]    In this configuration, the sheet having the size equal to or smaller than almost A6 is returned to the hopper only by the first sheet returner, the sheet having the size in a range larger than almost A6 and to almost B5 is returned to the hopper only by the first sheet returner or by both the first and second sheet returners, and the sheet having the size larger than almost B5 is returned to the hopper by both the first and second sheet returners. In this manner, any sizes of the sheet can be surely returned to the hopper by these sheet returners without being skewed.  
           [0024]    Preferably, the second sheet returner includes a sheet returning lever, and a lever cam, which is integrally provided with a rotary shaft of the sheet feeding roller, for operating the sheet returning lever.  
           [0025]    In this configuration, the accuracy of the parts of the lever cam can be improved and the number of the parts thereof can be reduced.  
           [0026]    According to the present invention, there is also provided a sheet feeder for feeding sheets of a recording medium to a recording apparatus, comprising:  
           [0027]    a hopper, on which the sheets of recording medium are stacked;  
           [0028]    a sheet feeding roller, which is brought into contact with an uppermost sheet stacked on the hopper, and rotates to feed the uppermost sheet to the recording apparatus;  
           [0029]    a separation pad, which presses the uppermost sheet against the feeding roller so that the upper most sheet is separated from a next uppermost sheet; and  
           [0030]    a cover member, which covers the sheet feeding roller, and is secured to the recording apparatus such that a force acting from the separation pad to the sheet feeding roller when the uppermost sheet is fed is received by the recording apparatus.  
           [0031]    Here, it is preferable that the cover member is formed with a hook member engaged with a part of the recording apparatus so that the force is received by the recording apparatus through the hook member.  
           [0032]    In this configuration, the sheet feeding roller is prevented from moving to a direction to which the force is acted when the sheet is fed to the recording apparatus. As a result, the pressure contacting state between the sheet feeding roller and the separation pad is secured well and the sheet can be supplied well to the recording apparatus from the hopper. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]    The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein like reference numerals designate like or corresponding parts throughout the several views, and wherein:  
         [0034]    [0034]FIG. 1 is an entire perspective view showing a sheet feeder according to one embodiment of the invention;  
         [0035]    [0035]FIG. 2 is a front view of the sheet feeder of FIG. 1;  
         [0036]    [0036]FIG. 3 is a sectional view along a line III-III in FIG. 2;  
         [0037]    [0037]FIG. 4 is a sectional view along a line IV-IV in FIG. 2; and  
         [0038]    [0038]FIG. 5 is a schematic side sectional view showing the sheet feeder of FIG. 1 and a printer incorporating the same; 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0039]    One embodiment of the invention will be explained with reference to the accompanying drawings.  
         [0040]    As shown in FIG. 1, a sheet feeder  10  is configured by an apparatus frame  11 , a roller shaft  12  made of resin, for example, rotatably supported by the apparatus frame  11 , a sheet feeding roller unit  13  and a second sheet returner  15  provided at the roller shaft  12  as described later, and a hopper  16  rotatably attached to the apparatus frame  11 .  
         [0041]    As shown in FIG. 5, the sheet feeder  10  is assembled in a printer  17  (ink jet printer) to which sheets are supplied. The printer  17  has sheet guides  18 , a transferring roller pair  19 , a recording head  20  and a discharging roller pair  21 . When a sheet S is supplied to the printer  17  from the sheet feeder  10 , the sheet S thus supplied passes between the pair of the sheet guides  18  of the printer  17 . Then, the transfer operation of the transferring roller pair  19  and the recording operation of the recording head  20  are alternately executed thereby to record an image including characters on the sheet thus transferred, and the sheet thus recorded is ejected out of the printer  17  by the discharging roller pair  21 .  
         [0042]    In this respect, the sheet S is a cut sheet such as a plain sheet, a coated sheet, an OHP (overhead projector)sheet, a glossy sheet, a glossy film etc.  
         [0043]    The hopper  16  of the sheet feeder  10  is pivotally supported by the apparatus frame  11  through a shaft  22  so as to be rotatable and disposed in a skewed manner with respect to the printer  17 . A plurality of sheets S are stacked on the hopper  16 . In this case, the leading ends of the sheets S thus set abut against a back face  48  of a separation pad holder  32  and a back face  47  of guide members  44 ,  45  and then are aligned.  
         [0044]    As shown in FIG. 5, a hopper spring  23  is disposed between the leading end portion of the hopper  16  and the apparatus frame  11 . The hopper  16  serves to make the sheets S be able to contact with the sheet feeding roller  28  (described later) of the sheet feeding roller unit  13  due to the urging force of the hopper spring  23  at the time of the sheet supplying operation of the sheet feeding roller  28 . Further, as shown in FIG. 1, cam followers  24  are formed at the both sides of the leading end portion of the hopper  16 , respectively. When the cam followers  24  abut against the hopper cams  25  fixed at the both ends of the roller shaft  12 , respectively, the rotation of the hopper  16  due to the hopper spring  23  is restricted.  
         [0045]    Further, as shown in FIGS. 1 and 2, the hopper  16  is provided with an edge guide  26  which is slidable in the width direction of the sheet S. The edge guide  26  is operated so as to be slid to match with the width of the sheet S set in the hopper  26 . The sheet S to be supplied is positioned so as to abut at its one side edge Sa against a side wall  27  serving as the one end side of the apparatus frame  11  constituting a sheet feeding passage K and also positioned so as to abut at it&#39;s the other end side Sb against the edge guide  26 .  
         [0046]    As described above, in the sheet feeding passage K formed in the apparatus frame  11  for supplying the sheet S from the hopper  16  to the printer  17 , the sheet feeding roller unit  13  is disposed at the one end side of the width direction of the sheet S, and only the second sheet returner  15  is disposed at the other side thereof. As shown in FIG. 3, the sheet feeding roller unit  13  is configured to include the sheet feeding roller  28 , a separation pad  29 , an idle roller  30 , a first sheet returner  14  and a roller cover  31 .  
         [0047]    As shown in FIG. 3, the sheet feeding roller  28  includes an arcuate portion  28 A and a flat portion  28 B to thereby be formed in a D-character shape when viewed from the side face thereof. High-friction material (for example, rubber) is attached at least to the face of the arcuate portion  28 A. The sheet feeding roller  28  is integrally formed by a bush  36 , and the bush  36  is integrally fixed to the roller shaft  12  so as to be immovable in the axial direction (that is, the width direction of the sheet S).  
         [0048]    A not-shown gear is fixed to the one end portion of the roller shaft  12 . The roller shaft  12  is provided so as to be driven and rotatable in the forward and reverse directions by a driving member (not shown) through the gear. When the roller shaft  12  rotates by one revolution in the forward direction, the sheet feeding roller  28  contacts to the uppermost sheet S on the hopper  16  shown in FIG. 5 and rotates by one revolution (forward direction) thereby to make this sheet S possible to be supplied to the transferring roller pair  19  of the printer  17 .  
         [0049]    The separation pad  29  is fixed to the separation pad holder  32 . The separation pad  29  is formed by a material (for example, cork material etc.) having a friction coefficient with respect to the sheet S which is smaller than that of the sheet feeding roller  28 . Each of the sheet feeding roller  28  and the separation pad  29  is formed by material which friction coefficient is larger than that between the sheets S. That is, supposing that the friction coefficient between the sheet feeding roller  28  and the sheet S is μ1, the friction coefficient between the separation pad  29  and the sheet S is μ2, and the friction coefficient between the sheets S is μ3, these friction coefficients has a relation of μ1&gt;μ2&gt;μ3.  
         [0050]    As shown in FIGS. 3 and 5, the separation pad holder  32  is rotatably provided at the apparatus frame  11  through a shaft  33 . A pad spring  34  is disposed between the leading end portion of the separation pad holder  32  and the apparatus frame  11 . The separation pad holder  32  makes the separation pad  29  possible to contact with pressure to the sheet feeding roller  28  by means of the urging force of the pad spring  34 .  
         [0051]    Thus, the separation pad  29  sandwiches with pressure the uppermost sheet S on the hopper  16  between this separation pad and the sheet feeding roller  28 , whereby the uppermost sheet S can be separated from the next-positioned sheet S on the hopper  16  due to the aforesaid difference of the friction coefficients among μ1, μ2 and μ3.  
         [0052]    As shown in FIGS. 1 and 3, the idle roller  30  is pivotally supported by an idle roller holder  35 . The idle roller holder  35  is formed in a ring-shape for passing the roller shaft  12  therethrough and disposed at the inside of the roller cover  31 . The idle roller holder  35  is biased by a not-shown roller spring disposed also at the roller cover  31  to thereby make the idle roller  30  possible to abut against the separation pad  29 .  
         [0053]    Further, the idle roller holder  35  makes the idle roller  30  possible to contact to and separate from the separation pad  29  in accordance with the rotation of the roller shaft  12  due to the function of a not-shown cam. In other words, the uppermost sheet S on the hopper  16  is started to be supplied due to the rotation (forward rotation) of the sheet feeding roller  28  caused by the rotation of the roller shaft  12 , and the idle roller  30  is separated from the separation pad  29  just before the leading end of this sheet S passes between the idle roller  30  and the separation pad  29 . Further, the sheet S is continuously supplied while being sandwiched with pressure between the arcuate portion  28 A of the sheet feeding roller  28  and the separation pad  29 , and the idle roller  30  abuts against the separation pad  29  just before this sandwiching state is released.  
         [0054]    In the aforesaid supplying process of the uppermost sheet S, when the sheet S is sandwiched with pressure between the arcuate portion  28 A of the sheet feeding roller  28  and the separation pad  29 , the next-positioned sheet S on the hopper  16  is prevented from falling by the sandwiched portion. After the sandwiching state of the uppermost sheet S between the arcuate portion  28 A of the sheet feeding roller  28  and the separation pad  29  is released, the idle roller  30  abuts against the separation pad  29  through the uppermost sheet S, and the next-positioned sheet S on the hopper  16  is prevented from falling by the abutment portion.  
         [0055]    As shown in FIGS. 2 and 3, the first sheet returner  14  of the sheet feeding roller unit  13  is configured to have a lever cam  38  integrally formed with the bush  36  of the sheet feeding roller unit  13  and a sheet reversing lever  37  pivotally supported by the apparatus frame  11 . Since the bush  36  is fixed to the roller shaft  12  so as to rotate integrally therewith and is immovable in the axial direction, the sheet feeding roller unit  13  including the first sheet returner  14  is disposed so as to be immovable in the width direction of the sheet S in the sheet feeding passage K.  
         [0056]    As shown in FIG. 4, the second sheet returner  15  is configured to have a lever cam  40  integrally formed with the roller shaft  12  and a sheet reversing lever  39  pivotally supported by the device  11 . Thus, the second sheet returner  15  is disposed so as to be immovable in the width direction of the sheet S in the sheet feeding passage K formed in the apparatus frame  11 .  
         [0057]    The sheet reversing lever  37  of the first sheet returner  14  and the sheet reversing lever  39  of the second sheet returner  15  can be held at neutral positions by not-shown lever springs, respectively. That is, although these sheet reversing levers  37  and  39  are respectively positioned at the neutral positions when no external force (external force due to the lever cams  38 ,  40  or the sheet S while being supplied) acts thereon, these sheet reversing levers rotate clockwise or counterclockwise in FIGS. 3 and 4 against the urging force of the lever spring when the external force acts thereon. When the external force disappears, these sheet reversing levers restore the neutral positions due to the urging force of the lever springs, respectively.  
         [0058]    The lever cam  38  of the first sheet returner  14  and the lever cam  40  of the second sheet returner  15  have the same configuration and each of which is provided with a recess portion  41  at a portion in the circumferential direction of the disk as shown in FIG. 4. The lever cams  38 ,  40  are arranged in a manner that the sheet reversing levers  37 ,  39  disposed at the neutral positions come into the recess portions  41  thereof, respectively.  
         [0059]    Thus, when the roller shaft  12  rotates forwardly, the lever cams  38  and  40  also rotate forwardly, so that the corner portions  42  of these lever cams  38 ,  40  abut against the sheet reversing levers  37 ,  39  thereby to rotate these sheet reversing levers  37 ,  39  counterclockwise in FIGS. 3 and 4, respectively.  
         [0060]    In contrast, when the roller shaft  12  rotates backwardly, the lever cams  38  and  40  also rotate backwardly, so that the corner portions  43  of these lever cams  38 ,  40  abut against the sheet reversing levers  37 ,  39  thereby to rotate these sheet reversing levers  37 ,  39  clockwise in FIGS. 3 and 4, respectively. The separation pad  29  of the sheet feeding roller unit  13  is configured to separate from the idle roller  30  when the sheet reversing levers  37 ,  39  rotate clockwise.  
         [0061]    The clockwise rotation of the sheet reversing levers  37 ,  39  is performed at a predetermined timing (for example, once each time the uppermost sheet S is supplied or once each time uppermost seven sheets S are supplied) after the uppermost sheet S on the hopper  16  is supplied to the printer  17  side due to the action of the arcuate portion  28 A of the sheet feeding roller  28  and the separation pad  29  in the sheet feeding roller unit  13  and the rear end of the uppermost sheet S passes the nipping portion between the idle roller  30  and the separation pad  29 . Due to the clockwise rotation of the sheet reversing levers  37 ,  39 , the next-positioned sheet S on the hopper  16  which leading end is positioned on the separation pad  29  can be pushed back to the hopper  16 .  
         [0062]    Thus, when the roller shaft  12  is rotated forwardly after the aforesaid push-back operation of the sheet S is performed by the first sheet returner  14  and the second sheet returner  15 , the next uppermost sheet S on the hopper  16  is supplied one by one to the printer  17  side without being supplied in a duplicated (overlapped) manner.  
         [0063]    As shown in FIG. 2, in a case where the sheets S are set in the stacked state on the hopper  16 , then the sheet S is disposed in the sheet feeding passage K formed in the apparatus frame  11  and the one side edge Sa of this sheet S is positioned at the side wall  27  of the apparatus frame  11 , the sheet feeding roller unit  13  is disposed at the side of the other side edge Sb side of this sheet S when the sheet S has almost A6 size, and the second sheet returner  15  is disposed at the side of the other side edge Sb side of this sheet S when the sheet S has a size in a range larger than almost A6 and to almost B5. In this embodiment, the second sheet returner  15  is disposed at the side of the other side edge Sb side of this sheet S when the sheet S has almost B5 size.  
         [0064]    The reasons why the sheet feeding roller unit  13  and the second sheet returner  15  are disposed in the aforesaid manner are as follows. That is, first reason is to supply the uppermost sheet S on the hopper  16  to the printer  17  side in a good state without being skewed only by the sheet feeding roller unit  13 . Second reason is that although the sheet S equal to or smaller than A5 size can be returned to the hopper  16  in a good state without being skewed only by the first sheet returner  14  of the sheet feeding roller unit  13 , the sheet S equal to or larger than A5 size can not be returned to the hopper  16  without being skewed without using both the first sheet returner  14  of the sheet feeding roller unit  13  and the second sheet returner  15 .  
         [0065]    Thus, the sheet S smaller than the disposed position of the second sheet returner  15 , for example, the sheet S having the size of A5, A6 or smaller can be returned to the hopper  16  in a good state without being skewed only by the first sheet returner  14  of the sheet feeding roller unit  13 . In contrast, the sheet S equal to or larger than the disposed position of the second sheet returner  15 , for example, the sheet S having the size of B5 or A4 can be returned to the hopper  16  in a good state without being skewed by both the first sheet returner  14  of the sheet feeding roller unit  13  and the second sheet returner  15 .  
         [0066]    Further, in the apparatus frame  11  of the embodiment, the guide members  44 ,  45  constituting a part of the sheet feeding passage K for guiding the sheet S are formed in the vicinities of the first sheet returner  14  of the sheet feeding roller unit  13  and the second sheet returner  15 . Each of these guide members  44 ,  45  has a guide face  46  and a back face  47  as shown in FIGS. 2 and 4.  
         [0067]    The faces  46  of the guide members  44 ,  45  guide both the sheet S supplied to the printer  17  side by the sheet feeding roller  28  of the sheet feeding roller unit  13  and the sheet S returned to the hopper  16  by the first sheet returner  14  of the sheet feeding roller unit  13  and the second sheet returner  15 . The slanted angle of the guide face  46  is set to such an angle that the sheet S on the guide face  46  does not fall by its own weight. As described above, the back faces  47  of the guide members  44 ,  45  abut against the leading end of the sheets S stacked on the hopper  16  together with the back face  48  (FIG. 3) of the separation pad holder  32  of the sheet feeding roller unit  13  to thereby align the leading ends of the sheets.  
         [0068]    The reason why the guide members  44 ,  45  are not continuously formed in the width direction of the sheet S in the sheet feeding passage K but formed separately in the vicinities of the first sheet returner  14  and the second sheet returner  15 , respectively, as shown in FIG. 2, is as follows.  
         [0069]    That is, in the case where the guide members  44 ,  45  are continuously formed in the width direction of the sheet S in the sheet feeding passage K, if the sheet S is skewed or warped, at the time of the push-back operation of the sheet S by the first sheet returner  14  and the second sheet returner  15 , such a sheet S can not be returned surely on the hopper  16  by the first sheet returner  14  and the second sheet returner  15 . In the case where the guide members  44 ,  45  are disposed separately in the vicinities of the first sheet returner  14  and the second sheet returner  15 , respectively, even if the sheet S is skewed or warped, such a sheet S is guided on the faces  46  of the guide members  44 ,  45  by the push-back operation of the first sheet returner  14  and the second sheet returner  15  and so surely returned to the hopper  16 .  
         [0070]    As shown in FIGS.  1  to  3  (particularly FIG. 3), the roller cover  31  is provided as a part of the sheet feeding roller unit  13  so as to cover the sheet feeding roller  28 , the lever cam  38 , the idle roller holder  35  and the idle roller  30 . The top panel portion  49  of the roller cover  31  abuts against and is supported by a frame  50  bridged horizontally in the printer  17 . When the sheet feeding roller  28  of the sheet feeding roller unit  13  is made in contact with pressure to the separation pad  29  through the sheet S, an upward force P in the height direction of the printer  17  acting on the sheet feeding roller  28  from the separation pad  29  (the separation pad holder  32 ) is received by the frame  50 .  
         [0071]    Further, a hook-shaped engagement claw  52 , which protrudes in the forward direction of the printer  17  and is bent perpendicularly upward in the height direction of the printer  17 , is integrally provided with the front face portion  51  of the roller cover  31 . This engagement claw  52  is arranged to be engaged with or stopped by a main frame  53  extending to the scanning direction of the recording head  20  in the printer  17 . In the state where the engagement claw  52  is stopped by the main frame  53 , when the sheet feeding roller  28  of the sheet feeding roller unit  13  is made in contact with pressure to the separation pad  29  through the sheet S, a force F acting on the sheet feeding roller  28  from the separation pad  29  (the separation pad holder  32 ) in a direction shown by an arrow in FIG. 3 (toward the back face  48  of the separation pad holder  32 ) is received by the main frame  53 , so that the roller cover  31  is prevented from being rotated together with the roller shaft  12 .  
         [0072]    Since the force F is received by the main frame  53  through the engagement claw  52 , the pressure contact state between the arcuate portion  28 A of the sheet feeding roller  28  and the separation pad  29  is secured in a good state and the uppermost sheet S on the hopper  16  can be separated well from the next-positioned sheet S. Further, since the co-rotation of the roller cover  31  can be prevented, the idle roller  30  of the sheet feeding roller unit  13  is held at a suitable position with respect to the separation pad  29 . Thus, the abutment state between the idle roller  30  and the separation pad  29  becomes well, and the next-positioned sheet S on the hopper  16  is prevented from falling into the nipping portion between the idle roller  30  and the separation pad  29 .  
         [0073]    Advantageous effect which is able to be attained by the present invention will be summarized as follows.  
         [0074]    i) The sheet feeding roller unit  13  having the sheet feeding roller  28 , the separation pad  29 , the separation pad holder  32 , the idle roller  30 , the idle roller holder  35  and the first sheet returner  14  is disposed on the one end (the side wall  27 ) side in the width direction of the sheet S in the sheet feeding passage K of the apparatus frame  11 , and only the second sheet returner  15  is disposed on the other side thereof. Thus, the next-positioned sheet S on the hopper  16  which leading end is positioned on the separation pad  29  can be completely returned to the hopper  16  without being skewed by the first sheet returner  14  and the second sheet returner  15 . Therefore, in accordance with the forward rotation of the sheet feeding roller  28  which is operated next, the uppermost sheet S (that is, the aforesaid next-positioned sheet S) can be supplied well without being supplied in a duplicated manner from the hopper  16  to the printer  17 .  
         [0075]    ii) The sheet feeding roller unit  13  is disposed only at the one end (the side wall  27 ) side of the sheet feeding passage K of the apparatus frame  11  and only the second sheet returner  15  in place of the sheet feeding roller unit  13  is disposed at the other end side thereof. Thus, the number of parts of the sheet feeder  10  can be reduced, so that the rationalization can be realized.  
         [0076]    iii) The sheet feeding roller unit  13  and the second sheet returner  15  are disposed so as to be immovable in the width direction of the sheet S in the sheet feeding passage K of the apparatus frame  11 . Thus, since none of the sheet feeding roller unit  13  or the second sheet returner  15  moves in the width direction of the sheet S in cooperation with the edge guide  26  of the hopper  16 , the resistance (sliding load) caused at the time of sliding the edge guide  26  can be reduced and so the sliding operation of the edge guide  26  can be performed smoothly.  
         [0077]    iv) The guide members  44 ,  45  constituting the part of the sheet feeding passage K in the apparatus frame  11  for guiding the sheet S are separately formed in the vicinities of the first sheet returner  14  and the second sheet returner  15 , respectively. Thus, as compared with the case where the guide members  44 ,  45  are formed continuously in the width direction of the sheet S, even if the next-positioned sheet S on the hopper  16  which leading end is positioned at the separation pad  29  is skewed or warped, the sheet is guided by the guide members  44 ,  45  by the operation of the first sheet returner  14  and the second sheet returner  15  and so the next-positioned sheet S can be surely returned to the hopper  16 . Therefore, in accordance with the forward rotation of the sheet feeding roller  28  of the sheet feeding roller unit  13  which is operated next, only the uppermost sheet S (that is, the aforesaid next-positioned sheet S) on the hopper  16  can be supplied to the printer  17  and the sheets S can be prevented from being supplied in a duplicated manner.  
         [0078]    v) The second sheet returner  15  is disposed so as to be positioned on the other side edge Sb side of the sheet S having the size in a range larger than almost A6 and to almost B5 in the case where the sheet S is disposed in the sheet feeding passage K of the apparatus frame  11  and the one side edge Sa of this sheet S is positioned at the one end (the side wall  27 ) of the sheet feeding passage K. Thus, the sheet S having the size equal to or smaller than almost A6 is returned to the hopper  16  only by the first sheet returner  14  of the sheet feeding roller unit  13 , the sheet S having the size in a range larger than almost A6 and to B5 is returned to the hopper  16  only by the first sheet returner  14  or by both the first sheet returner  14  and the second sheet returner  15 , and the sheet S having the size larger than almost B5 is returned to the hopper  16  by both the first sheet returner  14  and the second sheet returner  15 . In this manner, any sizes of the sheet S can be returned to the hopper  16  by properly using the first sheet returner  14  and the second sheet returner  15  without being skewed.  
         [0079]    vi) Since the lever cam  40  of the second sheet returner  15  is integrally formed with the roller shaft  12  supporting the sheet feeding roller  28 , the accuracy of the parts of the lever cam  40  can be improved and the number of the parts thereof can be reduced.  
         [0080]    vii) At the time of supplying the sheet S by the sheet feeding roller  28  of the sheet feeding roller unit  13 , the roller cover  31  of the sheet feeding roller unit  13  is secured by the main frame  53  of the printer  17  through the engagement claw  52  so as to receive the force F acting on the sheet feeding roller  28  from the separation pad  29  while being directed toward the back face of the separation pad  29  (that is, the separation pad holder  32 ). Thus, the sheet feeding roller unit  13  can be prevented from moving toward the back face  48  of the separation pad holder  32  by the force F. As a result, the pressure contacting state between the sheet feeding roller  28  and the separation pad  29  is secured well and the sheet S can be supplied well to the printer  17  from the hopper  16 .  
         [0081]    Although the present invention has been shown and described with reference to specific preferred embodiments, various changes and modifications will be apparent to those skilled in the art from the teachings herein. Such changes and modifications as are obvious are deemed to come within the spirit, scope and contemplation of the invention as defined in the appended claims.  
         [0082]    For example, although the embodiment is described as to the case where the sheet is supplied to the printer  17 , the sheet may be supplied to another image forming apparatus such as a copy machine, a facsimile etc.