Patent Publication Number: US-9403650-B2

Title: Sheet feeding device and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Preferred embodiments of the present invention relate to a sheet feeding device configured to feed sheets and an image forming apparatus including the sheet feeding device. 
     2. Description of the Related Art 
     This type of sheet feeding device includes a sheet feed tray to be loaded with sheets, a sheet feed roller, and a separation member to contact the sheet feed roller. Sheets are drawn from the sheet feed tray to be forwarded onto a sheet conveying path through a nip region between the sheet feed roller and the separation member. In a case where a stack of a plurality of sheets is drawn from the sheet feed tray, the sheets are separated one by one when the sheets pass through the nip region between the sheet feed roller and the separation member, for conveyance. 
     JP 2004-137021 A teaches that a guide film is placed in an area from the sheet feed tray to the surface of the separation member. The guide film acts to guide the sheets smoothly to the surface of the separation member, so as to prevent the sheets from being stuck in the middle of conveyance from the sheet feed tray to the separation member, thus eliminating sheet feed errors. 
     In a case where a guide film is disposed in an area from the sheet feed tray to the surface of the separation member as in JP 2004-137021 A, laying an elongated guide film over a wide area on the surface of the separation member decreases the area of contact of the surface of the separation member with respect to the sheets, which invites a multi-sheet feed in which a plurality of sheets is conveyed while being stacked. Shortening the guide film increases the area of contact of the surface of the separation member with respect to the sheets, which suppresses the occurrence of the multi-sheet feed. On the other hand, a curled leading end of a sheet may be hooked on the surface of the separation member, which hinders proper conveying of sheets, and the sheets are liable to experience sheet feed errors. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention were made in view of the foregoing circumstances, in order to provide a sheet feeding device and an image forming apparatus. A sheet feeding device according to a preferred embodiment of the present invention includes a sheet guide member including, for example, a guide film located in an area along a surface of a separation member and operable to significantly reduce or prevent multi-sheet feeds and sheet feed errors. 
     A sheet feeding device according to a preferred embodiment of the present invention includes a sheet feed tray configured to be loaded with sheets, a sheet guide member, a sheet feed roller configured to convey the sheets, and a separation member configured to separate the sheets in case of a multi-sheet feed. The sheets are adapted to be guided from the sheet feed tray along the sheet guide member to a nip region between the sheet feed roller and the separation member such that the sheets are forwarded through the nip region onto a sheet conveying path. A projected end portion and a recessed end portion are arranged on a leading end portion of the sheet guide member in a direction perpendicular or substantially perpendicular to a direction of conveyance of the sheets. The sheet guide member is directed toward a downstream side in the direction of conveyance. The projected end portion projects toward the downstream side in the direction of conveyance. The recessed end portion is recessed from the projected end portion toward an upstream side in the direction of conveyance. 
     In such a preferred embodiment of the present invention, the sheet guide member is disposed to guide the sheets drawn from the sheet feed tray to the nip region between the sheet feed roller and the separation member. The projected end portion and the recessed end portion are arranged on the leading end portion of the sheet guide member in the direction perpendicular or substantially perpendicular to the direction of conveyance of the sheets, the projected end portion projecting toward the downstream side in the direction of conveyance of the sheets, the recessed end portion being recessed toward the upstream side in the direction of conveyance of the sheets. Thus, the leading end of the sheet is guided in contact with the projected end portion to the vicinity of the nip region, and a sheet feed error is prevented. Further, since the recessed end portion is recessed away toward the upstream side in the direction of conveyance of the sheets, the distance from the recessed end portion to the nip region is longer, and the leading end of the sheet is in contact with the separation member for a longer time right after passing the recessed end portion until reaching the nip region. Thus, even though a plurality of sheets is stacked, the sheets are reliably separated one by one by the separation member, and a multi-sheet feed is prevented. 
     In the sheet feeding device according to a preferred embodiment of the present invention, projected end portions identical to the projected end portion are preferably arranged on two sides of the leading end portion of the sheet guide member in the direction perpendicular or substantially perpendicular to the direction of conveyance. 
     In this case, the leading end of the sheet is guided to the nip region with two portions of the leading end of the sheet that is in contact with the corresponding projected end portions. Thus, the sheets are prevented from veering off course, and a sheet feed error is more favorably prevented. 
     Moreover, in the sheet feeding device according to a preferred embodiment of the present invention, the projected end portion is preferably opposite to a lateral end of the separation member, the lateral end extending in the direction perpendicular or substantially perpendicular to the direction of conveyance. 
     In this case, even though the leading end of the sheet is curled, the leading end of the sheet is guided to the nip region without being hooked at, for example, a lateral end of the separation member. Thus, a sheet feed error is even more reliably prevented. 
     In the sheet feeding device according to a preferred embodiment of the present invention, the projected end portion is preferably opposite to a central portion of the sheet feed roller, the central portion being located in the direction perpendicular or substantially perpendicular to the direction of conveyance. 
     In this case, even though the leading end of the sheet is curled, a central portion of the leading end of the sheet contacts the projected end portion, such that the curling degree at the central portion of the leading end of the sheet is reduced. Thus, the curling at two sides of the central portion of the leading end is also reduced approximately equally, and the sheet is guided to the nip region with the two sides of the central portion of the leading end approximately straightened out, such that the sheets are less likely to veer off the course, and sheet feed errors are even more favorably prevented. 
     Moreover, in the sheet feeding device according to a preferred embodiment of the present invention, the projected end portion preferably has a smaller width in the direction perpendicular or substantially perpendicular to the direction of conveyance toward the nip region. 
     In this case, the area of contact of the leading end of the sheet with the separation member is increased after passing the recessed end portion, thus more favorably preventing a multi-sheet feed. 
     An image forming apparatus according to another preferred embodiment of the present invention includes a sheet feeding device according to one of the preferred embodiments of the present invention described above, and a printer configured to form an image on a sheet forwarded by the sheet feeding device. 
     Such an image forming apparatus according to a preferred embodiment of the present invention also provides similar effects to those of the sheet feeding device according to other preferred embodiments of the present invention. 
     According to various preferred embodiments of the present invention, the sheet guide member is provided to guide sheets drawn from the sheet feed tray to the nip region between the sheet feed roller and the separation member. The leading end portion of the sheet guide member is provided with a projected end portion projecting toward the downstream side in the direction of conveyance of the sheets and a recessed end portion recessed toward the upstream side in the direction of conveyance of the sheets, alternately in the direction perpendicular or substantially perpendicular to the direction of conveyance of the sheets. Thus, the leading end of the sheet is guided in contact with the projected end portion to the vicinity of the nip region, and sheet feed errors are prevented. Further, the recessed end portion is recessed away toward the upstream side in the direction of conveyance of the sheets. Thus, the distance from the recessed end portion to the nip region is longer, and the leading end of the sheet is in contact with the separation member for a longer time right after passing the recessed end portion until reaching the nip region. Accordingly, even though a plurality of sheets is stacked, the sheets are separated one by one by the separation member, and occurrence of multi-sheet feeds is reliably prevented. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view depicting an image forming apparatus applied with a manual bypass device which is a first preferred embodiment of a sheet feeding device according to the present invention. 
         FIG. 2  is a side view schematically depicting the manual bypass device of the first preferred embodiment of the present invention. 
         FIG. 3  is a front view of a sheet feed roller, a separation roller, and a sheet guide member of the manual bypass device of  FIG. 2  as viewed from the upstream side in a direction of sheet conveyance. 
         FIG. 4A  is a plan view depicting the sheet guide member, and  FIG. 4B  is a plan view depicting a variation of the sheet guide member. 
         FIG. 5  is a side view schematically depicting the periphery of the sheet guide member of the manual bypass device of  FIG. 2  in an enlarged manner. 
         FIG. 6  is a plan view depicting a sheet guide member of a manual bypass device which is a second preferred embodiment of the sheet feeding device according to the present invention. 
         FIG. 7  is a side view schematically depicting a sheet feeding device according to a third preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention are described in detail below with reference to the drawings. 
       FIG. 1  is a cross-sectional view depicting an image forming apparatus applied with a first preferred embodiment of a sheet feeding device according to the present invention. This image forming apparatus  1  has a copying function of reading a document and printing the document on a recording sheet. The image forming apparatus  1  includes, for example, a document reader  2 , an automatic document feeder (ADF)  3 , a printer  4 , a sheet feeding device  5 , a manual bypass device (a sheet feeding device according to a first preferred embodiment)  7 , and a sheet conveyor  8 . The document reader  2  and the automatic document feeder  3  are mounted on the upper side of the main body of the image forming apparatus  1 . The printer  4 , the sheet feeding device  5 , and the sheet conveyor  8  are incorporated in the main body of the image forming apparatus  1 . The manual bypass device  7  is attached to a sidewall of the main body of the image forming apparatus  1 . 
     The image forming apparatus  1  handles image data corresponding to a color image using colors of black (K), cyan (C), magenta (M), and yellow (Y), or corresponding to a monochrome image using a single color, e.g., black. Thus, in the printer  4 , for example, four developing devices  12 , four photosensitive drums  13 , four drum cleaning devices  14 , and four charging devices  15 , each one of which are associated with black, cyan, magenta, and yellow, respectively, are preferably provided so as to form four kinds of toner images that correspond to each color, thus configuring four image stations Pa, Pb, Pc, and Pd. 
     In each of the image stations Pa, Pb, Pc, and Pd, the drum cleaning device  14  removes and recovers residual toner on the surface of the photosensitive drum  13 , then the charging device  15  uniformly charges the surface of the photosensitive drum  13  to a predetermined potential, an optical scanning device  11  exposes the surface of the photosensitive drum  13  so as to form an electrostatic latent image thereon, and the developing device  12  develops the electrostatic latent image on the surface of the photosensitive drum  13  to form a toner image on the surface of the photosensitive drum  13 . In this manner, a toner image of each color is formed on the surface of each photosensitive drum  13 . 
     After that, a belt cleaning device  22  removes and recovers residual toner on an intermediate transfer belt  21 , and the toner image of each color formed on the surface of each photosensitive drum  13  is transferred on the intermediate transfer belt  21 , so as to form a color toner image on the intermediate transfer belt  21 , with the intermediate transfer belt  21  being moved in a circulating manner in the direction of arrow C. 
     A nip region is provided between the intermediate transfer belt  21  and a transfer roller  23   a  of a secondary transfer device  23 . Color toner images on the surface of the intermediate transfer belt  21  are transferred on recording sheets with the recording sheets conveyed along an S-shaped sheet conveying path R 1  being nipped in the nip region for conveyance. Then, the recording sheets are nipped between a heating roller  24  and a pressing roller  25  in a fixing device  17  so as to be subjected to heat and pressure thereon, such that color toner images are fixed on the recording sheets. 
     Meanwhile, in the sheet conveyor  8 , recording sheets are forwarded from the sheet feeding device  5  and the manual bypass device  7  to be conveyed along the sheet conveying path R 1 , and the recording sheets are delivered past the secondary transfer device  23  and the fixing device  17  to a sheet discharge tray  37  by way of sheet discharge rollers  36 . For example, registration rollers  34 , conveyance rollers  35 , and the sheet discharge rollers  36  are arranged on the sheet conveying path R 1 . The registration rollers  34  cause the recording sheets to stop once for registration of the recording sheets at the leading ends thereof, and then to start conveyance of the recording sheets at the timing where toner images are transferred at the nip region between the intermediate transfer belt  21  and the transfer roller  23   a . The conveyance rollers  35  assist conveyance of the recording sheets. 
     The sheet feeding device  5  includes, for example, a cassette  51  that is positioned in a lower portion of the image forming apparatus  1 , a sheet feed tray  52  to be loaded with recording sheets, a pickup roller  53  that is disposed on the upper side of one end of the sheet feed tray  52 , a sheet feed roller  54  that is positioned downstream of the pickup roller  53  in the direction of sheet conveyance, and a separation roller  55  that is in pressing contact with the sheet feed roller  54 . In the sheet feeding device  5 , recording sheets are drawn by the pickup roller  53  from the sheet feed tray  52  and are guided to the sheet feed roller  54 , and the recording sheets are passed in between the sheet feed roller  54  and the separation roller  55  to separate the sheets one by one, so as to forward the individual sheets onto the sheet conveying path R 1 . 
     The manual bypass device  7  is positioned on the sidewall of the main body of the image forming apparatus  1 . The manual bypass device  7  includes, for example, a manual feed tray  71  to be loaded with recording sheets, a sheet feed roller  72  disposed on the upper side of one end of the manual feed tray  71 , a separation roller  73  that is in pressing contact with the sheet feed roller  72 , and a sheet guide member  74  that is positioned upstream of a nip region between the sheet feed roller  72  and the separation roller  73  in the direction of conveyance of the recording sheets. In the manual bypass device  7 , recording sheets are guided from the manual feed tray  71  past the sheet guide member  74  to the nip region between the sheet feed roller  72  and the separation roller  73 , such that the recording sheets are passed through the nip region to separate the recording sheets one by one, so as to forward the individual sheets onto the sheet conveying path R 1 . 
     Next, detailed description is given of the manual bypass device  7  in the first preferred embodiment of the sheet feeding device according to the present invention.  FIG. 2  is a side view schematically depicting the manual bypass device  7 .  FIG. 3  is a front view of the sheet feed roller  72 , the separation roller  73 , and the sheet guide member  74  in the manual bypass device  7  as viewed from the upstream side in a direction E of sheet conveyance, i.e., from the manual feed tray  71  side. 
     As depicted in  FIGS. 2 and 3 , the manual feed tray  71  is disposed at an angle such that a leading end portion  71   a  is directed downward. The leading end portion  71   a  is provided with a first slant contacting portion  71   b , a second slant contacting portion  71   c , and a third slant contacting portion  71   d  sequentially from the upstream side in the direction E of sheet conveyance of the recording sheets. A pair of guide plates  75  configured to nip and guide recording sheets is disposed on the upper surface of the manual feed tray  71 . The guide plates  75  are movably disposed in a direction perpendicular or substantially perpendicular to the direction E of sheet conveyance and are moved by a mechanism (not shown) in conjunction with each other in a symmetrical manner with respect to the center of the manual feed tray  71 , such that the center of the recording sheets held between the guide plates  75  is aligned with the center of the manual feed tray  71 . 
     The sheet feed roller  72  is positioned above the third slant contacting portion  71   d  of the leading end portion  71   a  of the manual feed tray  71 . The separation roller  73  is positioned below the sheet feed roller  72 . The separation roller  73  includes a shaft  73   a  that is parallel or substantially parallel with a drive shaft  72   a  of the sheet feed roller  72 . A spring (not shown) urges a bearing (not shown) of the shaft  73   a  of the separation roller  73  toward the sheet feed roller  72  such that the separation roller  73  is made to pressingly contact the sheet feed roller  72 , so as to provide a nip region H between the sheet feed roller  72  and the separation roller  73 . 
     For example, the sheet feed roller  72  and the separation roller  73  are preferably made of a cylindrical rubber. The sheet feed roller  72  preferably has a diameter φa of approximately 30 mm, whereas the separation roller  73  preferably has a diameter φb of approximately 16 mm, for example. The sheet feed roller  72  preferably has a width J 1  that is approximately the same, i.e., approximately 40 mm, as a width J 2  of the separation roller  73  in the lengthwise direction of the drive shaft  72   a  of the sheet feed roller  72 . 
     The third slant contacting portion  71   d  includes a contacting surface  71   e  and a slant surface  71   f  that is bent and inclined toward the nip region H at the upper end of the contacting surface  71   e . The sheet guide member  74  is fixedly attached to the slant surface  71   f . The sheet guide member  74  extends to the surface of the sheet feed roller  72 . The sheet guide member  74  includes a leading end that is in contact with the surface of the sheet feed roller  72  or is slightly spaced apart from the surface. 
       FIG. 4A  is a plan view depicting the sheet guide member  74 . As depicted in  FIG. 4A , the sheet guide member  74  preferably has a rectangular or approximately rectangular shape, for example. A leading end portion  74   a  of the sheet guide member  74  that faces downstream side in the direction E of sheet conveyance is provided with projected end portions  74   b  and recessed end portions  74   c  alternately in the direction perpendicular or substantially perpendicular to the direction E of sheet conveyance. The projected end portions  74   b  project toward the downstream side in the direction E of sheet conveyance. The recessed end portions  74   c  are recessed from the projected end portion  74   b  toward the upstream side in the direction E of sheet conveyance. 
     As depicted in  FIG. 3 , two projected end portions  74   b  are arranged on two sides of the leading end portion  74   a  of the sheet guide member  74  in the lengthwise direction of the drive shaft  72   a  of the sheet feed roller  72 . One of the projected end portions  74   b  is positioned at the center of the leading end portion  74   a  of the sheet guide member  74 . The two projected end portions  74   b  arranged on the two sides of the leading end portion  74   a  of the sheet guide member  74  oppose two lateral ends of the sheet feed roller  72  lengthwise of the drive shaft  72   a , in a direction perpendicular or substantially perpendicular to the lengthwise direction. More specifically, the two projected end portions  74   b  on both of the two sides of the leading end portion  74   a  continuously extend in the lengthwise direction of the drive shaft  72   a  from the respective inner sides of the lateral ends of the sheet feed roller  72 , i.e., from within the sheet feed roller  72  region, to the respective outer sides of the lateral ends of the sheet feed roller  72 , i.e., to the outside of the sheet feed roller  72  region. The two projected end portions  74   b  on both of the two sides of the leading end portion  74   a  oppose the lateral ends of the sheet feed roller  72  in the direction perpendicular or substantially perpendicular to the lengthwise direction. The projected end portion  74   b  at the center of the leading end portion  74   a  of the sheet guide member  74  opposes a central portion of the sheet feed roller  72  lengthwise of the drive shaft  72   a , in the direction perpendicular or substantially perpendicular to the lengthwise direction. 
     The sheet guide member  74  is a flexible film preferably made of a synthetic resin such as polyethylene-telephthalate (PET) and preferably has a thickness of approximately 188 μm, for example. The sheet guide member  74  preferably has a width J 3  of approximately 45 mm, for example, which is wider than the width J 1  of the sheet feed roller  72  and the width J 2  of the separation roller  73  in the lengthwise direction of the drive shaft  72   a  of the sheet feed roller  72 . The projected end portions  74   b  preferably have a width jb of approximately 7 mm, for example. The recessed end portions  74   c  preferably have a width jc of approximately 12 mm, for example. Moreover, the sheet guide member  74  preferably has a length L of approximately 11 mm in the direction E of sheet conveyance, for example. The projected end portions  74   b  project from the recessed end portions  74   c  preferably by approximately 0.6 mm, for example, toward the downstream side, i.e., toward the surface of the sheet feed roller  72 , in the direction E of sheet conveyance. In contrast, the recessed end portions  74   c  are recessed from the projected end portions  74   b  preferably by approximately 0.6 mm, for example, toward the upstream side, i.e., in a direction away from the surface of the sheet feed roller  72 , in the direction E of sheet conveyance. 
     It is to be noted that the sheet guide member  74  may be made of a stainless panel on the order of about 50 μm in thickness, for example. Alternatively, as depicted in  FIG. 4B , a flexible film  77  made of a synthetic resin such as PET may be placed over and applied to a stainless panel  76  such that the film  77  sticks out from the stainless panel  76  toward the downstream side in the direction E of sheet conveyance. 
     In the manual bypass device  7  thus configured, as depicted in  FIG. 5 , a sheet bundle of recording sheets P is loaded on the manual feed tray  71 , and the sheet bundle of the recording sheets P is held by the guide plates  75  on the upper surface of the manual feed tray  71 , such that the center of the recording sheets P is aligned with the center of the manual feed tray  71 . Further, the sheet bundle of the recording sheets P slides off downward along the inclination of the manual feed tray  71 , or is slid off by the user downward along the inclination of the manual feed tray  71 . An end surface of the sheet bundle passes over the first slant contacting portion  71   b  and the second slant contacting portion  71   c  of the manual feed tray  71 , so as to butt the contacting surface  71   e  of the third slant contacting portion  71   d . Moreover, the end surface of the sheet bundle butts the sheet guide member  74  to be aligned thereby, and the recording sheet P at the uppermost layer of the sheet bundle slides over the surface of the sheet guide member  74 , such that the leading end of the recording sheet P at the uppermost layer is guided by the surface of the sheet feed roller  72  to be in contact therewith. 
     In this state, upon rotationally driving the sheet feed roller  72  in the direction of arrow F, the recording sheet P at the uppermost layer is drawn by the sheet feed roller  72  and slides over the surface of the sheet guide member  74  to be guided to the nip region H. At this time, as depicted in an enlarged manner in  FIG. 5 , the sheet guide member  74  flexes along the recording sheets P, and the leading end of the sheet guide member  74  touches the separation roller  73  to be directed toward the nip region H. The leading end of the recording sheet P is guided to the nip region H along the leading end portion  74   a  of the sheet guide member  74  and also in contact with the surface of the separation roller  73 . The recording sheet P passes through the nip region H to be forwarded onto the sheet conveying path R 1 . With the drawing and conveyance of the recording sheet P at the uppermost layer, a following recording sheet P is guided to the surface of the sheet feed roller  72  to be in contact therewith, and the following recording sheet P comes to the uppermost layer. This recording sheet P passes through the nip region H according to the same procedure to be forwarded onto the sheet conveying path R 1 . 
     A torque limiter (not shown) is preferably disposed on the shaft  73   a  of the separation roller  73 . When the separation roller  73  is in direct pressing contact with the sheet feed roller  72 , or when the separation roller  73  is pressed against the sheet feed roller  72  with one recording sheet interposed therebetween, the turning force of the sheet feed roller  72  is transmitted to the separation roller  73  as it is, which magnifies the torque to act on the torque limiter on the separation roller  73 . As a result, the separation roller  73  comes into an idling state, such that the separation roller  73  is driven into rotation by the sheet feed roller  72 . 
     Thus, in case where the recording sheets P are sequentially drawn one by one from the manual feed tray  71 , when a recording sheet P is guided to and nipped in the nip region H between the sheet feed roller  72  and the separation roller  73 , the separation roller  73  comes into an idling state to be driven into rotation, such that the recording sheet P is conveyed by the sheet feed roller  72 . 
     When a plurality of recording sheets P is drawn simultaneously from the manual feed tray  71 , even though the recording sheet that directly touches the sheet feed roller  72  is conveyed by the sheet feed roller  72 , the torque that acts on the torque limiter on the separation roller  73  does not increase, for the recording sheets interposed between the sheet feed roller  72  and the separation roller  73  shift from each other. Thus, the separation roller  73  comes to a halt and is not driven into rotation, such that the other recording sheets that do not directly touch the sheet feed roller  72  are stopped from being conveyed, and the other recording sheets are separated from the recording sheet that is being conveyed by the sheet feed roller  72 . 
     It is to be noted here that as depicted in  FIGS. 3 and 4A , the projected end portions  74   b  project from the recessed end portions  74   c  preferably by approximately 0.6 mm, for example, toward the downstream side in the direction E of sheet conveyance, and that in contrast, the recessed end portions  74   c  are recessed from the projected end portions  74   b  preferably by approximately 0.6 mm, for example, toward the upstream side in the direction E of sheet conveyance. Thus, in guiding the leading end of a recording sheet P to the nip region H along the leading end portion  74   a  of the sheet guide member  74  and also in contact with the surface of the separation roller  73 , the leading end of the recording sheet P moves while sliding on the surfaces of the projected end portions  74   b  to be guided to the vicinity of the nip region H, and the leading end of the recording sheet P quickly passes through the nip region H. Hence, a sheet feed error is less likely to occur. Further, since the distance from the recessed end portions  74   c  to the nip region H is longer, and the leading end of the recording sheet P is in contact with the separation roller  73  for a longer time right after passing the recessed end portions  74   c  until reaching the nip region H, the recording sheets P are separated one by one by the separation roller  73  even though a plurality of recording sheets P is stacked, and a multi-sheet feed is less likely to occur. 
     Further, since the projected end portions  74   b  are provided on the two sides of the leading end portion  74   a  of the sheet guide member  74 , the leading end of the recording sheet P is guided to the nip region H with two portions at the leading end being in contact with the projected end portion  74   bs  on the two sides, which two portions are equidistant from the center of the leading end of the recording sheet P. Thus, the recording sheets P are less likely to veer off course, and sheet feed errors are more reliably prevented. 
     Further, since the projected end portions  74   b  oppose the two lateral ends of the sheet feed roller  72 , even though the leading end of the recording sheet P curls down, the leading end of the recording sheet is guided to the nip region H without being hooked at a lateral end or a corner of the separation roller  73 , and sheet feed errors are more favorably prevented. 
     Further, since a projected end portion  74   b  is positioned at the center of the leading end portion  74   a  of the sheet guide member  74 , even though the leading end of the recording sheet P curls up or down, a central portion of the leading end of the recording sheet P is held between the projected end portion  74   b  at the center and the sheet feed roller  72 ; hence, the curling degree at the central portion of the leading end of the recording sheet P is significantly reduced, and the curling at two sides of the central portion of the leading end is also reduced equally or approximately equally. Accordingly, the recording sheet P is guided to the nip region H with the two sides of the central portion of the leading end of the recording sheet P approximately straightened out, such that the recording sheets P are less likely to veer off course, and sheet feed errors are even more reliably prevented. 
     Next, detailed description is given of a manual bypass device  7  which is a second preferred embodiment of the sheet feeding device according to the present invention.  FIG. 6  is a plan view depicting a sheet guide member  81  in the manual bypass device  7  of the second preferred embodiment. 
     The manual bypass device  7  of the second preferred embodiment is, like the manual bypass device  7  depicted in  FIG. 1 , disposed on a sidewall of the main body of the image forming apparatus  1  and is configured to forward recording sheets P onto the sheet conveying path R 1 . The manual bypass device  7  of the second preferred embodiment is however different from the manual bypass device  7  of the first preferred embodiment in that the sheet guide member  81  depicted in  FIG. 6  is provided in place of the sheet guide member  74  depicted in  FIG. 4A . 
     The sheet guide member  81  depicted in  FIG. 6  is, like the sheet guide member  74  depicted in  FIG. 4A , fixedly attached to the slant surface  71   f  of the third slant contacting portion  71   d , extends to the surface of the sheet feed roller  72 , and includes a leading end that is in contact with the surface of the sheet feed roller  72  or is slightly spaced apart from the surface. 
     The sheet guide member  81  preferably has a rectangular or approximately rectangular shape, for example. A leading end portion  81   a  of the sheet guide member  81  that faces downstream side in the direction E of sheet conveyance is provided with projected end portions  81   b  and recessed end portions  81   c  alternately in a direction perpendicular or substantially perpendicular to the direction E of sheet conveyance. Two projected end portions  81   b  are arranged on two sides of the leading end portion  81   a  in the lengthwise direction of the drive shaft  72   a  of the sheet feed roller  72 . One of the projected end portions  81   b  is positioned at the center of the leading end portion  81   a . The two projected end portions  81   b  arranged on the two sides of the leading end portion  81   a  oppose two lateral ends of the sheet feed roller  72  lengthwise of the drive shaft  72   a , in the direction perpendicular or substantially perpendicular to the lengthwise direction. More specifically, the two projected end portions  81   b  on both of the two sides of the leading end portion  81   a  continuously extend in the lengthwise direction of the drive shaft  72   a  from the respective inner sides of the lateral ends of the sheet feed roller  72 , i.e., from within the sheet feed roller  72  region, to the respective outer sides of the lateral ends of the sheet feed roller  72 , i.e., to the outside of the sheet feed roller  72  region. The two projected end portions  81   b  on both of the two sides of the leading end portion  81   a  oppose the lateral ends of the sheet feed roller  72  in the direction perpendicular or substantially perpendicular to the lengthwise direction. The projected end portion  81   b  at the center of the leading end portion  81   a  opposes a central portion of the sheet feed roller  72  lengthwise of the drive shaft  72   a , in the direction perpendicular or substantially perpendicular to the lengthwise direction. 
     The projected end portion  81   b  at the center of the leading end portion  81   a  preferably has an isosceles trapezoidal shape with the two lateral edges thereof inclined with respect to the direction E of sheet conveyance. The projected end portion  81   b  at the center of the leading end portion  81   a  preferably has a width jb 1  that is gradually reduced toward the upstream side in the direction E of sheet conveyance, i.e., closer to the nip region H. Moreover, the projected end portions  81   b  on two sides of the leading end portion  81   a  each preferably have a trapezoidal shape with the inner edge thereof inclined with respect to the direction E of sheet conveyance. The projected end portions  81   b  on two sides of the leading end portion  81   a  preferably have a width jb 2  that is gradually reduced toward the upstream side in the direction E of sheet conveyance, i.e., closer to the nip region H. Thus, the projected end portions  81   b  have a distance M in between that is gradually increased toward the upstream side in the direction E of sheet conveyance, i.e., closer to the nip region H. 
     The sheet guide member  81  preferably is a flexible film made of a synthetic resin such as PET and preferably has a thickness of approximately 188 μm, for example. The sheet guide member  81  preferably has a width J 3  of approximately 45 mm, for example, which is wider than the width J 1  of the sheet feed roller  72  and the width J 2  of the separation roller  73 . The projected end portions  81   b  preferably have maximum widths jb 1  and jb 2  of approximately 7 mm, for example. The recessed end portions  81   c  preferably have a width jc of approximately 12 mm, for example. Moreover, the sheet guide member  81  preferably has a length L of approximately 11 mm, for example, in the direction E of sheet conveyance. The projected end portions  81   b  project from the recessed end portions  81   c  preferably by approximately 0.6 mm, for example, toward the downstream side in the direction E of sheet conveyance, i.e., toward the surface of the sheet feed roller  72 . 
     It is to be noted that the sheet guide member  81  may be made of a stainless panel on the order of about 50 μm in thickness, for example. Alternatively, a film made of a synthetic resin may be applied to stainless such that the film sticks out from the stainless panel toward the downstream side in the direction E of sheet conveyance. 
     In the manual bypass device  7  thus configured, a sheet bundle of recording sheets P is loaded on the manual feed tray  71 , an end surface of the sheet bundle passes over the first slant contacting portion  71   b  and the second slant contacting portion  71   c  of the manual feed tray  71  to butt the contacting surface  71   e  of the third slant contacting portion  71   d . The end surface of the sheet bundle butts the sheet guide member  81  to be aligned thereby, and the recording sheet P at the uppermost layer of the sheet bundle slides over the surface of the sheet guide member  81 , such that the leading end of the recording sheet P at the uppermost layer is guided by the surface of the sheet feed roller  72  to be in contact therewith. 
     In this state, upon rotationally driving the sheet feed roller  72  in the direction of arrow F, the recording sheet P at the uppermost layer is drawn by the sheet feed roller  72  and slides over the surface of the sheet guide member  81  to be guided to the nip region H. At this time, as depicted in  FIG. 5 , the sheet guide member  81  flexes along the recording sheets P, and the leading end of the sheet guide member  81  touches the separation roller  73  to be directed toward the nip region H. The leading end of the recording sheet P is guided to the nip region H along the leading end portion  81   a  of the sheet guide member  81  and also in contact with the surface of the separation roller  73 . The recording sheet P passes through the nip region H to be forwarded onto the sheet conveying path R 1 . 
     Then, the leading end of the recording sheet P moves while sliding on the surfaces of the projected end portions  81   b  to be guided to the vicinity of the nip region H. Thus, the leading end of the recording sheet P quickly passes through the nip region H, and sheet feed errors are significantly reduced or prevented. 
     Further, since the leading end of the recording sheet P is in contact with the separation roller  73  for a longer time right after passing the recessed end portions  81   c  until reaching the nip region H, even though a plurality of recording sheets P is stacked, the recording sheets P are separated one by one by the separation roller  73 , and a multi-sheet feed is less likely to occur. 
     And besides, since the distance M between the projected end portions  81   b  is gradually increased toward the upstream side in the direction E of sheet conveyance, i.e., closer to the nip region H, the area of contact of the recording sheet P with the surface of the separation roller  73  is increased as the leading end of the recording sheet P approaches the nip region H, and thus the separation roller  73  provides an enhanced effect of preventing multi-sheet feeds of recording sheets P. 
     Next, detailed description is given of a sheet feeding device  5  according to a third preferred embodiment of the present invention.  FIG. 7  is a side view schematically depicting the sheet feeding device  5  according to the third preferred embodiment. 
     In the sheet feeding device  5  according to the third preferred embodiment, support pieces  52   b  are disposed in a projecting manner on two sides of a rear end portion  52   a  of the sheet feed tray  52 . Shafts  51   a  that are disposed in a projecting manner on inner walls (not shown) on two sides of the cassette  51  are passed through openings in the support pieces  52   b , thus supporting the sheet feed tray  52  such that the sheet feed tray  52  is freely rotatable with respect to the shafts  51   a  in the direction of arrow D. 
     A conical coil spring  56  is fixedly attached to a bottom portion  51   b  of the cassette  51 . The conical coil spring  56  is held between a leading end portion  52   c  of the sheet feed tray  52  and the bottom portion  51   b  of the cassette  51 , such that the leading end portion  52   c  of the sheet feed tray  52  is urged upward by the conical coil spring  56 . In a case where recording sheets P are placed on the sheet feed tray  52 , the leading end portion  52   c  of the sheet feed tray  52  is urged upward by the conical coil spring  56 , such that the pickup roller  53  pressingly contacts the recording sheets P on the sheet feed tray  52 . 
     A drive shaft  54   a  of the sheet feed roller  54  is passed through an opening in a first end portion of a rocking support piece  57 , so as to rotatably support the rocking support piece  57 . A drive shaft  53   a  of the pickup roller  53  is passed through an opening in a second end portion of the rocking support piece  57  for support. The pickup roller  53  is rotatably driven in the direction of arrow F in the same manner as the sheet feed roller  54 . The separation roller  55  has a shaft  55   a  that is in parallel or substantially in parallel with the drive shaft  54   a  of the sheet feed roller  54 . The separation roller  55  is in pressing contact with the sheet feed roller  54 , so as to provide a nip region H between the sheet feed roller  54  and the separation roller  55 . The shaft  55   a  of the separation roller  55  is preferably provided with a torque limiter (not shown) to prevent a multi-sheet feed of recording sheets P. 
     A sidewall  51   c  of the cassette  51  is located below the separation roller  55 , and an upper end portion  51   d  of the sidewall  51   c  is bent and inclined into the direction E of sheet conveyance. The sheet guide member  74  depicted in  FIG. 4A or 4B  is applied and fixed to an inner slant surface of the upper end portion  51   d . The sheet guide member  74  extends to the surface of the sheet feed roller  54 . The sheet guide member  74  includes a leading end that is in contact with the surface of the sheet feed roller  54  or is slightly spaced apart from the surface. 
     In the sheet feeding device  5  thus configured, the rocking support piece  57  is urged in the direction of arrow G with respect to the drive shaft  54   a  of the sheet feed roller  54 , and the pickup roller  53  is made to pressingly contact the recording sheet P at the uppermost layer of a sheet bundle on the sheet feed tray  52 . In this state, upon rotationally driving the pickup roller  53  and the sheet feed roller  54  in the directions of arrow F, the recording sheet P at the uppermost layer of the sheet bundle on the sheet feed tray  52  is drawn by the pickup roller  53 , and the sheet guide member  74  flexes along the recording sheets P. The leading end of the sheet guide member  74  touches the separation roller  55 , the leading end of the recording sheet P is guided to the nip region H along the leading end portion  74   a  of the sheet guide member  74  in contact with the surface of the separation roller  55 . The recording sheet P passes through the nip region H to be forwarded onto the sheet conveying path R 1 . 
     At this time, the leading end of the recording sheet P slides and moves on the surfaces of the projected end portions  74   b  to be guided to the vicinity of the nip region H. Thus, the leading end of the recording sheet P quickly passes through the nip region H, and a sheet feed error is much less likely to occur. 
     Further, since the leading end of the recording sheet P is in contact with the separation roller  55  for a longer time right after passing the recessed end portions  74   c  until reaching the nip region H, even though a plurality of recording sheets P is stacked, the recording sheets P are separated one by one by the separation roller  55 , and thus a multi-sheet feed is much less likely to occur. 
     It is to be noted that the sheet guide member  81  depicted in  FIG. 6  is applicable in the third preferred embodiment shown in Fi.  7  in place of the sheet guide member  74 . In this case, the area of contact of the recording sheet P with the surface of the separation roller  55  is increased toward the upstream side in the direction E of sheet conveyance, i.e., closer to the nip region H; thus, the separation roller  55  provides an enhanced effect of preventing multi-sheet feeds of recording sheets P. 
     It is to be noted that preferred embodiments of the present invention are not limited to the foregoing first to third preferred embodiments and may be modified in various ways. For example, in place of the separation roller  73  (or  55 ), a separation pad may be made to pressingly contact the sheet feed roller  72  (or  54 ), so as to provide a nip region between the sheet feed roller  72  (or  54 ) and the separation pad. Recording sheets may be passed through the nip region, thus preventing multi-sheet feeds of recording sheets. In this case, the sheet guide member is disposed such that the leading end portion of the sheet guide member overlaps an end of the surface of the separation pad that faces upstream in the direction E of sheet conveyance. In this manner, the leading end of the recording sheet is guided along the sheet guide member to the nip region in sliding contact with the surface of the separation pad. 
     While preferred embodiments of the present invention and variations thereof have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.