Abstract:
The invention describes a sheet feed device having a sheet tray having a bottom plate defining a first portion of a storing portion that receives sheets therein, a feed roller, a separation plate, and a recessed portion formed in the separation surface. The feed roller moves to contact a sheet of the sheets, and to feed the sheet. The separation plate is disposed at a downstream end of the sheet tray and extends in a width direction. The separation plate has a separation surface which is inclined with respect to the bottom plate of the sheet tray, and defines at least a second portion of the storing portion. The recessed portion is formed in the separation surface and extends toward a downstream end of the separation surface. The separation plate is configured to separate the sheet from the sheets as the feed roller feeds the sheet.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority from Japanese Patent Application No. 2007-339615, which was filed on Dec. 28, 2007, the disclosure of which is incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates generally to sheet feed devices which comprise a sheet tray configured to receive a plurality of sheets, a feed roller configured to move with respect to the sheet tray, and an inclined separation plate which cooperates with the feed roller to feed an uppermost sheet from the sheet tray toward a recording unit. The invention also relates to image recording apparatus which comprise such a sheet feed device. 
         [0004]    2. Description of Related Art 
         [0005]    A known sheet feed device is used in a known image recording apparatus, such as a printer or a facsimile device, or both. The known sheet feed device comprises a sheet tray configured to receive a plurality of sheets therein and a feed roller configured to move with respect to the sheet tray and feed the sheets from the sheet tray toward a recording unit. The sheet tray comprises a single side guide or a pair of side guides configured to move in a sheet widthwise direction and guide sides edges of sheets stacked in the sheet tray. A linear mark, which is parallel to an upper surface of the stacked sheets, is engraved or printed on an inner side surface of the single side guide or one of the pair of side guides, or on an inner side surface of one of side walls of the sheet tray which extend along side edges of the stacked sheets. The linear mark is used to restrict a maximum permissible load of sheets in the sheet tray. 
         [0006]    However, when the sheet tray is configured to be detachably inserted into the image recording apparatus while the extending direction of the side walls of the sheet tray is parallel to the inserting direction, the linear mark may be difficult to be seen when viewed in the inserting direction. This may cause stacking of sheets in the sheet tray beyond the linear mark, which may result in an idle rotation of the feed roller, misfeeding of sheets, or paper jamming. 
       SUMMARY OF THE INVENTION 
       [0007]    Therefore, a need has arisen for sheet feed devices and image recording apparatus that overcome these and other shortcomings of the related art. A technical advantage of the present invention is that stacking of excessive sheets may be prevented and the sheets may be fed from the sheet tray in a stable manner. 
         [0008]    In an embodiment of the invention, a sheet feed device comprises a sheet tray comprising a bottom plate which defines at least a first portion of a storing portion, wherein the storing portion is configured to receive a plurality of sheets therein, a feed roller configured to move with respect to the storing portion, to contact an uppermost sheet of the plurality of sheets, and to feed the uppermost sheet in a sheet feed direction, a separation plate disposed at a downstream end of the sheet tray in the sheet feed direction and extending in a width direction of the sheet tray, wherein the separation plate comprises a separation surface which is inclined with respect to the bottom plate of the sheet tray, and defines at least a second portion of the storing portion, and a recessed portion formed in the separation surface and extending toward a downstream end of the separation surface in the sheet feed direction, wherein the separation plate is configured to separate the uppermost sheet from the plurality of sheets as the feed roller feeds the uppermost sheet in the sheet feed direction, and wherein the width direction is substantially perpendicular to the sheet feed direction. 
         [0009]    In another embodiment of the invention, a sheet feed device comprises a sheet tray comprising a bottom plate which defines at least a first portion of a storing portion, wherein the storing portion is configured to receive a plurality of sheets therein, a feed roller configured to move with respect to the storing portion, to contact an uppermost sheet of the plurality of sheets, and to feed the uppermost sheet in a sheet feed direction, a separation plate disposed at a downstream end of the sheet tray in the sheet feed direction and extending in a width direction of the sheet tray, wherein the separation plate comprises a separation surface which is inclined with respect to the bottom plate of the sheet tray, and defines at least a second portion of the storing portion, and a pair of recessed portions formed in the separation surface and disposed on the separation surface at positions corresponding to edges of a shorter-side dimension of the plurality of sheets, wherein the pair of recessed portions extend toward a downstream end of the separation surface in the sheet feed direction, wherein the separation plate is configured to separate the uppermost sheet from the plurality of sheets as the feed roller feeds the uppermost sheet in the sheet feed direction, and wherein the width direction is substantially perpendicular to the sheet feed direction. 
         [0010]    In still another embodiment of the invention, an image recording apparatus comprises a sheet feed device comprising a sheet tray comprising a bottom plate which defines at least a first portion of a storing portion, wherein the storing portion is configured to receive a plurality of sheets therein, a feed roller configured to move with respect to the storing portion, to contact an uppermost sheet of the plurality of sheets, and to feed the uppermost sheet in a sheet feed direction, a separation plate disposed at a downstream end of the sheet tray in the sheet feed direction and extending in a width direction of the sheet tray, wherein the separation plate comprises a separation surface which is inclined with respect to the bottom plate of the sheet tray, and defines at least a second portion of the storing portion, and a recessed portion formed in the separation surface and extending toward a downstream end of the separation surface in the sheet feed direction. The image recording apparatus also comprises a recording unit configured to record an image on the plurality of sheets fed by the feed roller, wherein the separation plate is configured to separate the uppermost sheet from the plurality of sheets as the feed roller feeds the uppermost sheet in the sheet feed direction, and wherein the width direction is substantially perpendicular to the sheet feed direction. 
         [0011]    Other advantages of the present invention will be apparent to persons of ordinary skill in the art in view of the following detailed description of the invention and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    For a more complete understanding of the present invention, and the needs satisfied thereby, reference now is made to the following descriptions taken in connection with the accompanying drawings. 
           [0013]      FIG. 1  is a perspective view of an image recording apparatus, according to an embodiment of the invention. 
           [0014]      FIG. 2  is a side, cross-sectional view of a recoding unit and a sheet feed device of the image recording apparatus of  FIG. 1 . 
           [0015]      FIG. 3  is a perspective view of a sheet tray of the sheet feed device of  FIG. 2 . 
           [0016]      FIG. 4  is a plan view of the sheet tray of the sheet feed device of  FIG. 2 . 
           [0017]      FIG. 5  is an enlarged perspective view of a mark portion of the sheet tray of  FIG. 3 . 
           [0018]      FIG. 6  is a cross-sectional view of the mark portion taken along line VI-VI of  FIG. 5 . 
           [0019]      FIG. 7  is a cross-sectional view of a side guide taken along line VII-VII of  FIG. 5 . 
           [0020]      FIG. 8A  is a front view of a mark portion according to another embodiment of the invention. 
           [0021]      FIG. 8B  is a front view of a mark portion according to yet another embodiment of the invention. 
           [0022]      FIG. 8C  is a front view of a mark portion according to still another embodiment of the invention. 
           [0023]      FIG. 8D  is a front view of a mark portion according to a further embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0024]    Embodiments of the present invention may be understood by referring to  FIGS. 1-8D , like numerals being used for like corresponding parts in the various drawings. 
         [0025]      FIG. 1  shows an image recording apparatus  1  according to an embodiment of the present invention. The image recording apparatus  1  may be a multi-function device (“MFD”) that has printing, copying, scanning, or facsimile functions, or any combination thereof. As shown in  FIG. 1 , the image recording apparatus  1  may comprise a housing  2 . An opening  2   a  may be formed in the front of the housing  2 . A sheet tray  3  may be mounted in the opening  2   a , such that the sheet tray  3  may be selectively inserted into and removed from the opening  2   a  in an X-axis direction with side plates  3   c  of the sheet tray  3  parallel to the inserting/removing direction. A discharge tray  33  is may be disposed on the sheet tray  3 . Hereinafter, a side in which the opening  2   a  is located is referred to as a “front” side of the image recording apparatus  1 , and a side opposite the opening  2   a  is referred to as a “rear” side of the image recording apparatus  1 . 
         [0026]    An image reading device  5  may be disposed, on an upper portion of the housing  2 , for reading a document during a copying and/or a facsimile operation of the image recording apparatus  1 . The image reading device  5  may be vertically pivotable about a pivot located at one end of the housing  2 . A glass plate may be disposed at the top of the image reading device  5 , and may be covered by a document cover  6  which may be vertically pivotable about a pivot located at a rear end of the image reading device  5 . A document may be disposed on the glass plate by opening the document cover  6  upward. A scanner, e.g., a contact image sensor, may read an image of the document while reciprocating under the glass plate in a main scanning direction, e.g., a Y-axis direction. 
         [0027]    An operation panel  7  may be disposed at the top of the housing  2 , on a front side of the image reading device  5 , and may comprise a plurality of operation buttons and a display device  8 , e.g., a liquid crystal display. The operation buttons may comprise a start button (not shown) and a stop button (not shown), which may be selected to execute various operations. The display device  8  may display setting conditions of the image recording apparatus  1  and operation messages. 
         [0028]    A memory slot  11  for receiving external memories may be disposed at the front of the housing  2 , on an upper side of the opening  2   a . The external memories may be, for example, a Compact Flash®, a Smart Media®, a Memory Stick®, a SD Card®, and/or a xD Card®. Data stored in an external memory inserted in the memory slot  11  may be read into an internal memory of the image recording device  1 , and may be printed on a sheet by a recording unit  10 . 
         [0029]    As shown in  FIG. 2 , the recording unit  10  may be defined by a main frame (not shown) having an upwardly open box structure, and a first guide member  15  and a second guide member  16  which comprise elongate plates which are supported by side plates of the main frame and extend in the main scanning direction. A carriage  13 , on which a recording head (not shown) of the recording unit  10  may be mounted, may be supported by the first guide member  15  disposed upstream of the carriage  13  in a sheet discharge direction (indicated by arrow B) and the second guide member  16  disposed downstream of the carriage  13 , such that the carriage  13  may be slidably movable on the first guide member  22  and the second guide member  23 . Thus, the carriage  13  may be reciprocally movable in the Y-axis direction. 
         [0030]    In order to reciprocally move the carriage  13 , a timing belt (not shown) may be disposed on an upper surface of the second guide member  16 . The timing belt extends in the Y-axis direction and may be wound around pulleys (not shown). A carriage motor (not shown) configured to drive the timing belt may be fixed to a lower surface of the second guide member  16 . 
         [0031]    A platen  17  may have a flat shape and may extend in the Y-axis direction to face an underside of the recording head on the carriage  13 . The platen  17  may be fixed above a bottom plate of the main frame between the first guide member  15  and the second guide member  16 . 
         [0032]    A pair of register rollers (convey rollers)  18  may be disposed upstream of the platen  17  in the sheet discharge direction to feed the sheet to the underside of the recording head, and a pair of discharge rollers  19  may be disposed downstream of the platen  17  to discharge the printed sheet to the discharge tray  33  disposed on the sheet tray  3 . The platen  17  supports the sheet conveyed by the register rollers  18 , such that a distance between the sheet and the recording head may be maintained constant. 
         [0033]    Sheet tray  3  may store various types of recording media, including, e.g., plain paper, cardboard postcards and envelopes, specialized paper, e.g., coated paper, resin films, and the like. In a sheet feed device  12 , the sheet tray  3  may be made of synthetic resin by injection molding and may comprise a first portion, e.g., an inner storing portion  3   b  and an outer storing portion  3   d  connected to the inner storing portion. The outer storing portion  3   d  may be moved closer to and away from the inner storing portion  3   b . When the outer storing portion  3   d  is moved away from the inner storing portion  3   b , e.g., to increase the X-axis dimension of the sheet tray  3 , a plurality of sheets, e.g., A3-sized sheets, may be stored in the inner sheet storing portion  3   b  and the outer sheet storing portion  3   d . In this configuration, the plurality of sheets may have their longer sides extending in the X-axis direction and their shorter sides extending in the Y-axis direction. 
         [0034]    When the outer storing portion  3   d  is moved toward the inner storing portion  3   b , e.g., to reduce the X-axis dimension of the sheet tray  3 , a plurality of sheets, e.g., A4-sized sheets may be stored in the sheet tray  3 . A pendulum-type feed unit  20  sequentially may feed the sheets one at a time from the sheet tray  3  toward the recording unit  10 . 
         [0035]    The inner storing portion  3   b  may be defined by a bottom plate  3   a , the opposed side plates  3   c  extending in the X-axis direction, and a separation plate  21  disposed at a downstream end of the sheet tray  3  in a sheet feed direction, e.g., the direction indicated by arrow C in  FIG. 2 . The separation plate  21  may extend in the Y-axis direction and may have a front surface which may be inclined with respect to the bottom plate  3   a , and which may face the inner storing portion  3   b . The outer storing portion  3   d  may be defined by a bottom plate (not shown), opposed side plates (not shown) and a handle portion  3   f  disposed at an upstream end of the sheet tray  3  in the sheet feed direction. The maximum permissible load of sheets in the sheet tray  3  may be about 150 sheets of plain paper, or a stack of sheets having a height of about 15 mm. 
         [0036]    The discharge tray  33  may be made of synthetic resin by injection molding, and may comprise an inner receiving portion  33   a  connected to the sides plates  3   c , such that the discharge tray may be vertically pivotable, and an outer receiving portion  33   b  may be connected to the inner receiving portion  33   a , such that the outer receiving portion  33   b  may move closer to and away from the inner receiving portion  33   a . As shown in  FIG. 3 , the outer receiving portion  33   b  may be horizontally disposed on the opposed side plates of the outer storing portion  3   d , and outer storing portion  3   d  and outer receiving portion  33   b  may be extendable together from the opening  2   a.    
         [0037]    As shown in  FIGS. 3 and 4 , the inner storing portion  3   b  of the sheet tray  3  may comprise a pair of side guides  41  and a tail guide (not shown). The side guides  41  extend in the sheet feed direction (X-axis direction), and may position and guide side edges of the sheets disposed in the sheet tray  3 . The tail guide may be movable in the X-axis direction so as to position trailing edges of the sheets. 
         [0038]    The side guides  41  may be slidable, such that the distance therebetween selectively is increased and decreased. Racks  46  connected to the side guides  41  may engage a pinion  47  disposed at a widthwise center (center in the Y-axis direction) of the sheet tray  3 . Thus, the distance between the side guides  41  may be adjusted, such that a widthwise centerline of the sheet tray  3  aligns with a widthwise centerline of the sheets. Each of the side guides  41  may comprise a slider  43  and a stopper  44 . Each slider  43  may be slidable in the Y-axis direction and supports a lower surface of the sheets. The stopper  44  stands upright, and may contact the side edges of the sheets. 
         [0039]    One of the side guides may comprise a lock member (not shown) with a handle  45 . The lock member may be configured to engage one of teeth formed in the upper surface of the bottom plate  3   a . When the handle  45  is operated, the lock member may be released from the bottom plate  3   a.    
         [0040]    As shown in  FIG. 2 , the feed unit  20  may comprise an arm  20   c  which may be vertically pivotable about a drive shaft  39 . The arm  20   c  may extend toward the separation plate  21 . A pair of feed rollers  20   a  may be disposed at a free end of the arm  20   c , and may be driven by the drive shaft  39  via a gear transmission mechanism  20   b . The feed rollers  20   a  may contact and feed the uppermost sheet of the sheets in the sheet tray  3 . 
         [0041]    A pair of friction members  25  may be fixed to an upper surface of the bottom plate  3   a  of the sheet tray  3  to receive the pair of feed rollers  20   a  when the arm  20   c  pivots downward. This prevents two or more sheets from being fed together by the feed rollers  20   a  when only a small number of sheets remain in the sheet tray  3 . 
         [0042]    Referring again to  FIG. 3 , a front surface of the separation plate  21  may have a convex shape, such that a widthwise center, e.g., a Y-axis center, thereof may project, e.g., extend, toward the leading edges of the sheets in the storing portion. Similarly, widthwise ends, e.g., Y-axis ends, thereof may retract away from the leading edges of the sheets in the storing portion. A separation member  21   a  may have a sawtooth shape, and may be disposed at the widthwise center (Y-axis center) of the front surface of the separation plate  21 . In this case, a widthwise center of the leading edge of the sheet fed by the feed rollers  20   a  contacts the separation member  21   a  before widthwise ends of the leading edge of the sheet contact the front surface of the separation plate  21 . This may ensure a reliable separation of the sheet. 
         [0043]    The feed rollers  20   a  may feed the sheets one at a time from the sheet tray  3  along with the separation member  21   a , which may be made from a metal spring. The sheets may be fed via the convey path member  40 , to the recording unit  10  located above the sheet feed tray  3 . The sheet may make a U-turn along the convey path member  40 . The sheet recorded thereon may be discharged toward the opening  2   a , with the recorded surface facing upward. 
         [0044]    The separation plate  21  may comprise a mark portion  50  which may be recessed in the front surface of the separation plate  21  and which may indicate the maximum permissible load of sheets in the sheet tray  3 , e.g., the maximum number of sheets that sheet tray  3  may be configured to receive. The maximum permissible load of sheets means a maximum number of sheets or a maximum height of a stack of sheets that may allow for the feed rollers  20   a  and the separation plate  21  to feed the sheets in a stable manner without causing a potential malfunction, e.g., an idle rotation of the feed rollers  20   a , feeding of no sheet, feeding of a plurality of sheets at a time, skewing of sheets, paper jamming, or the like. 
         [0045]    When excessive sheets are stored in the sheet tray  3 , an angle of inclination of the arm  20   c  with respect to an upper surface of the sheets may decrease, and a contact force applied by the feed rollers  20   a  on the sheets also may decrease. The contact force may drop such that a sheet drawing force associated with the feed rollers  20   a  also may decrease enough to result in an idle rotation of the feed roller, e.g., a failure to feed a sheet. The angle of inclination of the arm  20   c  may be formed between an upper surface of the sheets and a line which connects a point at which each of the feed rollers  20   a  contacts the upper surface of the sheets and the pivot center of the arm  20   c . The maximum permissible load of sheets in the sheet tray  3  may be selected to ensure a stable sheet feeding based on the configuration specifications of the printer. 
         [0046]    As shown in  FIGS. 3-6 , the mark portion  50  may be formed as a recessed portion  51  in the front surface of the separation plate  21  and may have a rectangular shape when viewed from an upstream side of the sheet tray  3  in the sheet feed direction. The recessed portion  51  may extend in a downstream side of the separation plate  21  until the recessed portion  51  reaches the downstream end of the separation plate  21 , and may extend by about one-third of the length of separation plate  21  in the sheet feed direction of the separation plate  21 . The recessed portion  51  may be enclosed by three side walls, and may be open at the downstream end of the separation plate  21 . A lower edge  51   a  of the recessed portion  51 , e.g. an upstream edge of the recessed portion  51  in the sheet feed direction, may be formed on the separation plate  21  at a position corresponding to the maximum permissible load of sheets in the sheet tray  3 . 
         [0047]    Recessed portion  51  may be disposed such that the position of the lower edge  51   a  may be at a height Hi from the bottom plate  3   a . The lower edge  51   a  may correspond to the lowest position of the recessed portion  51 . When the sheets are stacked within sheet tray  3 , if lower edge  51   a  is visible, the stacked sheets may not exceed the maximum permissible load of sheets in the sheet tray  3 , and malfunctions, e.g., misfeeding of sheets may be less likely to occur. 
         [0048]    As shown in  FIG. 5 , the recessed portion  51  may be formed at three levels, e.g., heights of sub-portions. Each of a pair of first level portions  51   b  may have a substantially right triangular shape, having the lower edge  51   a  as a lower side and one side of the recessed portion  51   a  as a vertical side. The pair of first level portions  51   b  may be symmetrical with respect to a centerline therebetween. A second level portion  51   c  may be formed between the pair of first level portions  51   b  and may have an acute angle which may form a point at the lower edge  51   a . A third level portion  51   d  may be formed above the first level portions  51   b  and the second level portion  51   c  and may have a substantially rectangular shape. 
         [0049]    As shown in  FIG. 6 , the depth from the front surface of the inclined separation panel  21  may increase toward the downstream end of the separation surface, e.g., the inclined surface, in the sheet feed direction, e.g., in the order of the first level portions  51   b , the second level portion  51   c , and the third level portion  51   d.    
         [0050]    The horizontal lower edge  51   a  and the acute angle of the second level portion  51   c  which may form the point at the horizontal lower edge  51   a , which may indicate the maximum permissible load of sheets in the sheet tray  3 , may easily be viewed by an operator when the operator supplies sheets into the sheet tray  3  while facing the front surface of the separation plate  21 . The horizontal lower edge  51   a  and the acute angle of the second level portion  51   c  which may form the point at the horizontal lower edge  51   a  also easily may be viewable when the operator inserts the sheet tray  3  into the housing  2  through the opening  2   a , with the front surface of the separation plate facing toward the opening  2   a.    
         [0051]    As shown in  FIG. 3 , a plurality of mark portions  50  may be formed in the front surface of the separation plate  21 . A pair of mark portions  50 , and another pair of mark portions  50  may be disposed closer to the widthwise ends, e.g., the Y-axis ends, of the front surface than to the widthwise center, e.g., the Y-axis center, of the front surface. In other words, a pair of mark portions  50  may be disposed to correspond to edges of a shorter-side dimension of the A4-sized sheet, and another pair of mark portions  50  may be disposed adjacent to inner surfaces of the side plates  3   c  of the sheet tray  3  to correspond to edges of a shorter-side dimension of an A3-sized sheet. 
         [0052]    The stopper of each of the pair of side guides  44  may have a contact surface which may face side edges of the sheets in the sheet tray  3 . As shown in  FIG. 7 , when the side guides  44  are moved in a sheet widthwise direction, e.g., the Y-axis direction, and the contact surface of the stopper  44  of each of the side guides  44  contacts side edges of the sheets, the stopper  44  may oppose a corresponding one of the mark portions  50  such that the contact surface is perpendicular to a horizontal line corresponding to the lower edge  51   a  of the mark portion  50 . If the length of the lower edge  51   a  is set to a predetermined length, e.g., about 20 mm, the pair of mark portions  50  may be disposed on the front surface of the separation plate  21  at positions corresponding to edges of a shorter-side dimension of A4-sized sheets and legal-sized sheets which are about 6 mm longer in the shorter-side dimension than A4-sized sheets. 
         [0053]    Although not shown in the figure, another pair of mark portions  50  may be formed at positions closer to the separation member  21   a , which may be located at the widthwise center of the front surface of the separation plate  21 , such that the another pair of mark portions  50  may correspond to edges of a shorter side dimension of smaller sheets than A4-sized sheets, e.g. postcards, L-sized photo paper, and the like. 
         [0054]    As shown in  FIG. 7 , even in instances in which the sheet P may have a corner curled upward or downward, or a corner having cutting burrs, and when the leading edge of the sheet P may abut the front surface of the separation plate  21 , the sheet P yet may be likely to be fed toward a convey path member  40  without interference between the curled portion or the burrs and the recessed portion  51 . This is because the mark portion  50 , and the recessed portion  51  may be recessed from the front surface of the separation plate  21 , and because the recessed portion  51  may extend to the downstream end of the front surface of the separation plate  21 . Accordingly, the mark portion  50  and the recessed portion  51  are unlikely to cause paper jamming. 
         [0055]    In addition, when the front surface of the separation plate  21  is convex, such that the widthwise center, e.g., the Y-axis center, thereof projects toward the storing portion of the sheet tray  3  and the widthwise ends, e.g., the Y-axis ends, thereof retract away from the storing portion, the corner of the sheet P may be less likely to interfere with the recessed portion  51 . 
         [0056]    When the separation plate  21  is made of synthetic resin by injection molding, the mark portions  50  and recessed portions  51  may be formed integrally and simultaneously with the separation plate  21 , thereby reducing the manufacturing cost of the mark portions  50  and recessed portions  51 . 
         [0057]      FIGS. 8A ,  8 B,  8 C, and  8 D show mark portions, e.g., recessed portions  52  according to other embodiments of the invention. In another embodiment of the invention, as shown in  FIG. 8A , a recessed portion  52  may have a half-ellipse shape when viewed from an upstream side of the sheet tray  3  in the sheet feed direction. The recessed portion  52  may gradually widen, e.g., increase in width, toward a downstream end of the front surface of the separation plate  21 . A lower edge  52   a  may be defined by a lower edge of a downward convex end of the half-ellipse. The height Hi from the bottom plate  3   a  of the sheet tray  3  to the lower edge  52   a  may correspond to the maximum permissible load of sheets in the sheet tray  3 , similarly to the above-described embodiment. An arrow mark  56  pointing the lower edge  52   a  and a letter mark  57  spelling “MAX” may be formed, e.g., engraved, on a recessed surface of the recessed portion  52  to indicate the maximum permissible load of sheets. These marks allow the operator to immediately recognize the maximum permissible load of sheets. 
         [0058]    As shown in  FIG. 9 , the recessed portion  52  may extend to a downstream end of the front surface of the separation plate  21 , and the marks  56 ,  57  may be recessed from the front surface of the separation plate  21 , such that the marks  56 ,  57  may not contact a leading edge of the sheet to be fed. Even when the sheet to be fed has a corner curled upward or downward, or a corner having cutting burrs, the sheet is likely to be fed toward the U-turn convey path  40  without interference between the curled portion or the burrs and the recessed portion  52 . Accordingly, similarly to the above-described recessed portion  51 , the recessed portion  52  is unlikely to cause paper jamming. 
         [0059]    As shown in  FIG. 8B , a recessed portion  53  also may have an inverted triangle shape when viewed from an upstream side of the sheet tray  3  in the sheet feed direction. The recessed portion  53  may gradually widen, e.g., increase in width, toward a downstream end of the front surface of the separation plate  21 . As shown in  FIG. 8C , a recessed portion  54  may have a trapezoid shape, having a lower side shorter than an upper side, when viewed from an upstream side of the sheet tray  3  in the sheet feed direction. As shown in  FIG. 8D , a recessed portion  55  may have a rectangular shape when viewed from an upstream side of the sheet tray  3  in the sheet feed direction. 
         [0060]    A lower edge, e.g., lower edge  53   a ,  54   a , or  55   a  may correspond to the maximum permissible load of sheets in the sheet tray  3 . An arrow mark  56  may point to the lower edge, e.g., lower edge  53   a ,  54   a , or  55   a , and a letter mark  57  spelling “MAX” may be formed, e.g., engraved on a recessed surface of the recessed portion, e.g., recessed portion  53 ,  54 , or  55 . The recessed portion, e.g., recessed portion  53 ,  54 , or  55 , may extend to a downstream end of the front surface of the separation plate  21 , and the marks  56 ,  57  may be recessed from the front surface of the separation plate  21  such that the marks may not contact a leading edge of the sheet to be fed. Accordingly, similarly to the above-described recessed portion  51 , the recessed portion, e.g., recessed portion  53 ,  54 , or  55 , may be unlikely to cause paper jamming. 
         [0061]    The recessed portion, e.g., recessed portions  52 ,  53 ,  54 , or  55 , may be formed in the front surface of the separation plate  21  such that when the side guide  41  is moved to be adjusted to a particular width of the sheets, the stopper  44  opposes the recessed portion, e.g., recessed portions  52 ,  53 ,  54 , or  55 , and the contact surface of the stopper  44  may be perpendicular to a horizontal line passing the lower edge, e.g., lower edge  52   a  or  53   a , of the recessed portion, e.g., recessed portion  52  or  53 , or may be perpendicular to the lower edge, e.g., lower edge  54   a  or  55   a  of the recessed portion, e.g., recessed portion  54  or  55 . 
         [0062]    The mark portions, e.g., the recessed portions, may be formed at more than four portions in pairs corresponding to widthwise ends of each size of sheets usable in the sheet tray. 
         [0063]    Alternatively, a single mark portion, e.g., the recessed portion, or a single pair of mark portions, e.g., the recessed portions, may be formed at a position or positions which may be relatively close to the widthwise center of the front surface of the separation plate. The mark portion(s) in such position(s) may be used commonly for small sheets and large sheets when the sheet tray is of a center registration type in which a widthwise centerline of the sheet tray may align with a widthwise centerline of the sheets. 
         [0064]    While the invention has been described in connection with preferred embodiments, it will be understood by those of ordinary skill in the art that other variations and modifications of the preferred embodiments described above may be made without departing from the scope of the invention. Other embodiments will be apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein. It is intended that the specification and the described examples only are considered as exemplary of the invention, with the true scope of the invention being defined by the following claims.