Patent Publication Number: US-8991814-B2

Title: Sheet feed device and image forming apparatus including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims the benefit of priority from Japanese Patent Application No. 2013-94420, filed on Apr. 26, 2013, filed in the Japanese Patent Office. All disclosures of the document(s) named above are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present disclosure relates to a sheet feed device used to stock beforehand a multitude of sheets, such as paper sheets, to be supplied to an image forming apparatus and to feed the sheets thus stocked one by one, and the image forming apparatus incorporating the sheet feed device. 
     In an image forming apparatus represented by a copy machine or a printer, a paper feed cassette is used for feeding paper such as cut paper. The paper feed cassette is stocked beforehand with a multitude of paper sheets before printing and supplies, from an uppermost layer of a stack of the paper sheets stacked in the cassette, the paper sheets one by one separately from each other. 
     The paper feed cassette is provided with a sheet stacking plate having an upper surface on which paper sheets are placed. The paper sheets are stacked on the sheet stacking plate that is biased upward, and at a cassette mounting position in the image forming apparatus, a pickup roller provided on an image forming apparatus main body side comes in contact with an upper surface of an uppermost one of the paper sheets. Then, the pickup roller turns, causing the paper sheets to be fed out in order in a feed direction by a frictional force between the pickup roller and the uppermost one of the paper sheets. 
     By the way, in a paper feed device in which a paper feed cassette is disposed such that an insertion/pull-out direction thereof is orthogonal to a feed direction of a paper sheet, in a case where, when the paper feed cassette is inserted/pulled out for the purpose of paper sheet replenishment or the like, paper sheets stacked therein come in contact with a pickup roller while the insertion/pulling out of the paper feed cassette is in progress or have been in contact therewith prior to the insertion/pulling out of the paper feed cassette, the contact with the pickup roller causes an uppermost one of the paper sheets to be misaligned in the cassette insertion/pull-out direction, resulting in a problem that a paper sheet is fed out in an obliquely oriented state. Moreover, problems such as causing a paper sheet to be flawed or torn or causing a paper sheet to fall off from the paper feed cassette also are likely to occur. Also, the contact between the pickup roller and the paper sheets interferes with the insertion/pulling out of the cassette. In addition, there may occur sagging of a paper sheet between a width alignment cursor that regulates a paper sheet position in the direction orthogonal to the feed direction and the pickup roller, resulting in bending of the paper sheet at its end portion or a paper jam. 
     As a measure to solve these problems, there is known, for example, a paper feed, device including a pickup roller support body that supports a pickup roller to an apparatus main body such that the pickup roller is swingable in such a direction as to approach/separate from an upper surface of a paper sheet and a swing control body that is mounted to the apparatus main body such that it is movable substantially integrally with a cassette in accordance with insertion/pulling out of the cassette and controls a swing position of the pickup roller support body (position to which the pickup roller support body is swung). In the paper feed device, in accordance with insertion/pulling out of the cassette, the pickup roller is made to swing to be positioned as follows. That is, at the time of inserting the cassette, as the cassette approaches a mounting position of the cassette, the pickup roller swings to be positioned so as to increasingly come into contact with an upper surface of a paper sheet, and at the time of pulling out the cassette, as the cassette separates from the mounting position, the pickup roller swings to be positioned so as to increasingly separate from the upper surface of the paper sheet. 
     SUMMARY OF THE INVENTION 
     A sheet feed device according to a first aspect of the present disclosure includes a sheet housing portion, a sheet stacking plate, a pickup roller, a feed mechanism, a first bracket, an arm, and a feed roller mounting shaft. The sheet housing portion can be inserted in and pulled out from an image forming apparatus main body. The sheet stacking plate is pivotably supported, at an end portion thereof on an upstream side in a sheet feed direction, to a bottom surface of the sheet housing portion, and an end portion thereof on a downstream side in the sheet feed direction moves up and down between a placement position at which sheets are set and a feed position at which the sheets are fed. The pickup roller comes in contact with an upper surface of a plurality of sheets stacked on the sheet stacking plate and feeds out, one by one, an uppermost one of the sheets in a direction orthogonal to an insertion direction or a pull-out direction of the sheet housing portion. The feed mechanism feeds, by using a feed roller disposed on the downstream side in the sheet feed direction with respect to the pickup roller, a sheet fed out by the pickup roller. The first bracket has a first rotary shaft to which the pickup roller is supported so as to be slidable in an axial direction thereof, and is swingably supported to the image forming apparatus main body. The arm is mounted to the image forming apparatus main body and is movable together with the sheet housing portion in the insertion direction or the pull-out direction in accordance with insertion or pulling out of the sheet housing portion. Further, the arm makes the first bracket swing between a feed position where, when the sheet housing portion is at a first position at which mounting of the sheet housing portion in the image forming apparatus main body is completed, the arm makes sliding contact with the first bracket, and the pickup roller comes into contact with an upper surface of the sheets housed in the sheet housing portion, and a separation position where, when the sheet housing portion is at a second position to which the sheet housing portion has moved from the first position to a downstream side in the pull-out direction, the pickup roller separates from the upper surface of the sheets. The feed roller mounting shaft drives the feed roller to rotate and functions as a swing center of the first bracket. Then, at the time of pulling out the sheet housing portion from the image forming apparatus main body, when the sheet housing portion moves from the first position to the second position, the pickup roller moves on the first rotary shaft, through frictional contact with the upper surface of the sheets, to a position on an upstream side in the insertion direction, and at the time of inserting the sheet housing portion in the image forming apparatus main body, when the sheet housing portion moves from the second position to the first position, the pickup roller moves on the first rotary shaft, through frictional contact with the upper surface of the sheets, to a position on a downstream side in the insertion direction. A movable area of the pickup roller in a direction of the first rotary shaft is equal to or larger than a movement amount of the pickup roller between the position on the upstream side and the position on the downstream side. 
     Still other objects of the present disclosure and specific advantages provided by the present disclosure will be made further apparent from the following description of an embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a sectional side view showing an internal structure of an image forming apparatus  100  incorporating a sheet feed device  1  of the present disclosure. 
         FIG. 2  is a perspective view, as seen from above, of the sheet feed device  1  according to one embodiment of the present disclosure. 
         FIG. 3  is a perspective view of a first bracket  10 , a second bracket  16 , and an arm  12  as constituent components of the sheet feed device  1  of this embodiment. 
         FIG. 4  is a partially enlarged view, as seen from a lower direction in  FIG. 3 , of a vicinity of the first bracket  10  and the second bracket  16 . 
         FIG. 5  is a view showing a relationship between respective dispositions of a pickup roller  6  and a paper press roller  14  and an insertion/pull-out position of a paper feed cassette  2  in a case where the paper feed cassette  2  is at an insertion start position or a pull-out completion position. 
         FIG. 6  is a view showing a relationship between respective dispositions of the pickup roller  6  and the paper press roller  14  and an insertion/pull-out position of the paper feed cassette  2  in a case where the paper feed cassette  2  has been inserted in an X 1  direction by a prescribed amount from a position shown in  FIG. 5 . 
         FIG. 7  is a view showing a relationship between respective dispositions of the pickup roller  6  and the paper press roller  14  and an insertion/pull-out position of the paper feed cassette  2  in a case where the paper feed cassette  2  has been inserted in the X 1  direction by a prescribed amount from a position shown in  FIG. 6 . 
         FIG. 8  is a view showing a relationship between respective dispositions of the pickup roller  6  and the paper press roller  14  and an insertion/pull-out position of the paper feeing cassette  2  in a case where the paper feed cassette  2  has been inserted to a second position. 
         FIG. 9  is a view, as seen from an upstream side in an insertion direction of the paper feed cassette  2 , of a positional relationship of the pickup roller  6  and the paper press roller  14  with a sheet stacking plate  9 , which is shown in  FIG. 8 . 
         FIG. 10  is a view showing a relationship between respective dispositions of the pickup roller  6  and the paper press roller  14  and an insertion/pull-out position of the paper feed cassette  2  in a case where the paper feed cassette  2  has reached a first position. 
         FIG. 11  is a view, as seen from a rear surface side of the first bracket  10 , of the pickup roller  6  and a feed roller  18 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     With reference to the appended drawings, the following describes in detail an embodiment of the present disclosure.  FIG. 1  is a sectional side view showing an internal structure of an image forming apparatus  100  incorporating a paper feed cassette  2  as a constituent component of a sheet feed device  1  according to one embodiment of the present disclosure. Solid line arrows in the figure indicate conveying routes and conveying directions of a paper sheet. 
     In  FIG. 1 , at a lower portion in the image forming apparatus  100 , a cassette-type paper feed portion  101  is disposed. The cassette-type paper feed portion  101  is provided with a plurality of (herein, three) paper feed cassettes  2 . Inside each of the paper feed cassettes  2 , sheets of paper P before printing such as cut paper are housed in a stacked manner, and by a pickup roller  6  and a paper feed roller pair  115  composed of a feed roller  18  and a retardation roller  19 , the sheets of paper P are fed out one by one separately from each other. 
     A manual paper feed portion  102  is provided outside an upper portion of a right side surface of the image forming apparatus  100 . On the manual paper feed portion  102 , a recording medium to be fed one by one, such as a sheet of paper P of a type different in size and/or thickness from the paper P housed in the cassette-type paper feed portion  101 , an OHP sheet, an envelope, a postcard, or an invoice, is placed. 
     In the image forming apparatus  100 , a paper sheet conveying portion  103  is disposed. The paper sheet conveying portion  103  is positioned, with respect to the cassette-type paper feed portion  101 , on a right side that is a downstream side in a paper feed direction and, with respect to the manual paper feed portion  102 , on a left side that is a downstream side in the paper feed direction. By the paper sheet conveying portion  103 , a sheet of the paper P fed out from the cassette-type paper feed portion  101  is conveyed perpendicularly upward along the side surface of a main body of the image forming apparatus  100 , while a sheet of the paper P fed out from the manual paper feed portion  102  is conveyed horizontally. 
     On an upper surface of the image forming apparatus  100 , an original document conveying device  104  is disposed, below which an image reading portion  105  is disposed. In a case of performing copying of an original document, a plurality of original documents on which images such as characters, graphics, and patterns are drawn are stacked on the original document conveying device  104 . In the original document conveying device  104 , the original documents are fed out one by one separately from each other, and by the image reading portion  105 , the images on the original documents are read. The images thus read are converted into image data. 
     On a downstream side in a paper sheet conveying direction of the paper sheet conveying portion  103  and below the image reading portion  105 , an image forming portion  106  and a transfer portion  107  are disposed. In the image forming portion  106 , based on image data of an image on an original document read by the image reading portion  105 , an electrostatic latent image is formed, which then is developed into a toner image. On the other hand, in synchronization with a timing at which the toner image is formed in the image forming portion  106 , a sheet of the paper P is conveyed from the cassette-type paper feed portion  101  to the transfer portion  107  via the paper sheet conveying portion  103 . The toner image formed in the image forming portion  106  is transferred onto the sheet of the paper P in the transfer portion  107 . 
     On a downstream side with respect to the transfer portion  107 , a fixing portion  108  is disposed. The sheet of the paper P onto which the toner image in an unfixed state thus has been transferred in the transfer portion  108  is conveyed to the fixing portion  108 , where it passes through a nip portion between a fixing roller pair composed of a heating roller and a pressing roller, and thus the unfixed toner image on the sheet of the paper P is fixed into a permanent image. 
     On a downstream side with respect to the fixing portion  108  and in a neighborhood of a left side surface of the image forming apparatus  100 , an ejection • branching portion  109  is disposed. In a case where double-sided printing is not performed, the sheet of the paper P after being ejected from the fixing portion  108  is ejected from the ejection branching portion  109  onto a paper sheet ejection tray  111  provided on an outer side of the left side surface of the image forming apparatus  100 . 
     Below a portion extending from the image forming portion  106  over to the ejection • branching portion  109  and above the cassette-type paper feed portion  101 , a double-sided printing unit  110  is disposed. In a case where double-sided printing is performed, the sheet of the paper P after being ejected from the fixing portion  108  is sent to the double-sided printing unit  110  via the ejection • branching portion  109 . The sheet of the paper P sent to the double-sided printing unit  110  is turned upside down by switching back, and again passing through the paper sheet conveying portion  103  to be conveyed, with a surface thereof on which no image has yet been formed facing upward, to the transfer portion  107 . 
       FIG. 2  is a perspective view, as seen from above, of the sheet feed device  1  according to one embodiment of the present disclosure. Furthermore,  FIG. 3  is a perspective view of a first bracket  10 , a second bracket  16 , and an arm  12  as constituent components of the sheet feed device  1  of this embodiment, and  FIG. 4  is a partially enlarged view, as seen from a lower direction in  FIG. 3 , of a vicinity of the first bracket  10  and the second bracket  16 . With reference to  FIGS. 2 to 4 , a description is given of a detailed configuration of the sheet feed device  1  of the present disclosure. 
     The sheet feed device  1  includes the paper feed cassette  2  that is provided in the main body of the image forming apparatus  100  (see  FIG. 1 ) such that it can be inserted and pulled out, respectively, in directions indicated by arrows X 1  and X 2 , a sheet stacking plate  9  that is pivotably supported, at an end portion thereof on an upstream side in the paper feed direction, to a bottom surface of the paper feed cassette  2  and has an upper surface on which a stack of paper sheets (not shown) are placed, the pickup roller  6  that, in a state where the paper feed cassette  2  is mounted in the main body of the image forming apparatus  100 , comes in contact with an upper surface of the stack of paper sheets stacked on the sheet stacking plate  9  and feeds out, one by one, an uppermost one of the paper sheets in a direction (arrow Y direction) orthogonal to an insertion/pull-out direction (arrow X 1  and X 2  directions), the first bracket  10  that is swingably supported to a feed roller mounting shaft  8  extending in the insertion/pull-out direction of the paper feed cassette  2  in the main body of the image forming apparatus  100  and is a support body supporting the pickup roller  6 , and the arm  12  that is mounted to the main body of the image forming apparatus  100  such that it is movable together with the paper feed cassette  2  in accordance with insertion/pulling out of the paper feed cassette  2  and controls a swing position of the first bracket  10 . 
     The paper feed cassette  2  is configured in the shape of a flat box having an open upper surface, and from a direction of the upper surface, paper sheets are housed therein in a stacked manner. Inside the image forming apparatus  100 , the pickup roller  6  is disposed above the paper feed cassette  2 , and the paper sheets are supplied in the arrow Y direction shown in  FIG. 2 . At a front wall portion (wall portion on a near side in an insertion direction) X 1 )  2   a  of the paper feed cassette  2 , a housing cover  3  is formed integrally therewith and constitutes part of a housing at a lower portion of a front surface of the image forming apparatus  100 . The housing cover  3  is provided with a handle  3   a  used for an insertion/pull-out operation. At a left wall portion  2   b  and a right wall portion  2   c  of the paper feed cassette  2 , rails  4   a  and  4   b  for supporting the paper feed cassette  2  in the main body of the image forming apparatus  100  such that it can be inserted therein/pulled out therefrom are provided, respectively. 
     On an inner side on the bottom surface of the paper feed cassette  2 , the sheet stacking plate  9  on which paper sheets are stacked is mounted. The sheet stacking plate  9  is supported on the inner side on the bottom surface of the paper feed cassette  2 , with one end thereof on the upstream side in the paper feed direction used as a pivotal fulcrum  9   a,  and thus is swingable up and down, with an end portion thereof on a downstream side in the paper feed direction (end portion thereof on a pickup roller  6  side) used as a free end. The sheet stacking plate  9  is biased upward in a swing direction by a compression spring (not shown). The sheet stacking plate  9  is a plate-shaped member having notches provided correspondingly to movement regions of a width regulation cursor  30  and a back end regulation cursor  50 , which will be described later. 
     At both sides of the sheet stacking plate  9  in a direction orthogonal to the paper feed direction, a pair of the width regulation cursors  30  are provided so as to stand along the paper feed direction (arrow Y direction). The width regulation cursors  30  make contact, from both sides in a paper sheet width direction orthogonal to the paper feed direction, with side surfaces of a stack of paper sheets stacked on the sheet stacking plate  9 , thereby performing alignment of the paper sheets in a width direction thereof so that the paper sheets are positioned at a paper feed position at which the paper sheets are fed by the pickup roller  6  and the paper feed roller pair  115 . The width regulation cursors  30  are movable along a width regulation cursor movement groove  31  provided on the inner side on the bottom surface of the paper feed cassette  2  and extending in the paper sheet width direction. 
     At an upper end portion of the width regulation cursors  30  on a swing end side of the sheet stacking plate  9 , a lug portion  30   a  protruding to a sheet stacking plate  9  side is provided to prevent the level of a top end of a stack of paper sheets stacked on the sheet stacking plate  9  from increasing beyond a prescribed level, thereby controlling an upper limit position of an upper surface of the stack of paper sheets. 
     On the upstream side in the paper feed direction inside the paper feed cassette  2 , the back end regulation cursor  50  is provided. The back end regulation cursor  50  makes contact, from the upstream side in the paper feed direction, with a side surface of a stack of paper sheets stacked on the sheet stacking plate  9 , thereby performing alignment of the paper sheets in the paper feed direction so that the paper sheets are positioned at the paper feed position at which the paper sheets are fed by the pickup roller  6  and the paper feed roller pair  115 . The back end regulation cursor  50  is movable along a back end regulation cursor movement groove  51  provided on the inner side on the bottom surface of the paper feed cassette  2  and extending in the paper feed direction. 
     Furthermore, at the right wall portion  2   c  of the paper feed cassette  2 , there is provided a lock release member  53  that protrudes to an outer side of the right wall portion  2   c  by a biasing force of a spring (not shown) in the paper feed cassette  2 . The lock release member  53  has an anchor lug (not shown) for pressing a swing end (right end in  FIG. 2 ) of the sheet stacking plate  9 , and when the sheet stacking plate  9  is pressed against the bottom surface of the paper feed cassette  2 , the anchor lug presses the swing end of the sheet stacking plate  9 , thus bringing the sheet stacking plate  9  to a locked state. In this state, the paper feed cassette  2  is inserted into the main body of the image forming apparatus  100 , and upon a tip end portion of the lock release member  53  coming in contact with a contact piece (not shown) provided on a main body side, the lock release member  53  is once pressed to be retracted to an inner side of the right wall portion  2   c.  At this time, the anchor lug and the sheet stacking plate  9  are disengaged from each other, so that the locked state of the sheet stacking plate  9  is released. 
     The above-described paper feed device is configured so that, in accordance with insertion/pulling out of the paper feed cassette  2 , the pickup roller  6  swings in such a direction as to approach or separate from a paper sheet, and so that, in order to prevent, at the time of inserting/pulling out the paper feed cassette  2 , the pickup roller  6  from rubbing against an upper surface of the paper sheet, the pickup roller  6  is movable in a rotational axis direction thereof. The position of the pickup roller  6  in the rotational axis direction, therefore, is unfixed. 
     To be specific, in a state where the paper feed cassette  2  is mounted in an image forming apparatus  100  main body, the pickup roller  6  is being pressed by a paper sheet or the sheet stacking plate  9 , and hence, when the paper feed cassette  2  is pulled out from the image forming apparatus  100  main body, the pickup roller  6  necessarily moves, following the paper feed cassette  2 , to a near side with respect to the image forming apparatus  100  main body (downstream side in a pull-out direction). Accordingly, after the paper feed cassette  2  has been pulled out, the position of the pickup roller  6  is on a side closer to the near side. 
     Furthermore, in a case where the paper feed cassette  2  is inserted, with the sheet stacking plate  9  not being locked and thus being in a raised state, rubbing occurs between a paper sheet or the sheet stacking plate  9  and the pickup roller  6 , causing the pickup roller  6  to move to a depth side of the image forming apparatus  100  main body (downstream side in an insertion direction), in which case, depending on a magnitude of a force with which the paper feed cassette  2  is inserted, the position of the pickup roller  6  somewhat varies. 
     Pulling out the paper feed cassette  2  from the image forming apparatus  100  main body in a state where the pickup roller  6  is on a side closer to the near side, however, renders it meaningless to have the configuration in which the pickup roller  6  is movable in the rotational axis direction, and may cause a paper sheet to be misaligned or damaged due to the pickup roller  6  rubbing against an upper surface of the paper sheet. For these reasons, pulling out of the paper feed cassette  2  from the image forming apparatus  100  main body should not be performed in a state where the position of the pickup roller  6  is on a side closer to the near side. 
     Next, with reference to  FIGS. 3 and 4 , a description is given of the pickup roller  6  and the first bracket  10  supporting the pickup roller  6 . In the paper feed cassette  2 , the first bracket  10  is arranged above a stack of paper sheets stacked on the sheet stacking plate  9  on a tip end portion side thereof (downstream side in the paper feed direction). The first bracket  10  is pivotably supported to the feed roller mounting shaft  8  mounted on the main body side of the image forming apparatus  100 . 
     In the first bracket  10 , at a side closer to a pivotal end thereof (a side closer to the upstream side in the paper feed direction), there is provided a first rotary shaft  11  parallel to the feed roller mounting shaft  8 , to which the pickup roller  6  is mounted such that the pickup roller  6  is slidable only in an axial direction of the first rotary shaft  11 . Furthermore, the feed roller mounting shaft  8  is provided additionally with a drive output gear  8   a,  and the first rotary shaft  11  is provided additionally with a drive input gear  11   a.  The drive output gear  8   a  is in mesh with the drive input gear  11   a  via an idle gear  25 . When a rotary drive force from a drive motor (not shown) is inputted to the feed roller mounting shaft  8 , the pickup roller  6 , together with the feed roller  18 , is driven to turn. 
     At the pivotal end (end portion on the upstream side in the paper feed direction) of the first bracket  10 , there is formed a swing control portion  10   a  that is U-shaped in cross section when seen from a direction of the pivotal end. Moreover, by a tension coil spring  22 , the first bracket  10  is elastically biased upward, i.e. in such a direction as to separate from a stack of paper sheets P stacked on the sheet stacking plate  9 . In consequence thereof, the swing control portion  10   a  is in elastic contact with a guiding surface  20  (which will be described later) formed in the arm  12  and extending in a direction of the feed roller mounting shaft  8 . Further, when the swing control portion  10   a  moves up and down along the guiding surface  20 , the pickup roller  6  supported by the first bracket  10  also moves up and down. 
     As shown in  FIG. 4 , in an axial direction of the feed roller mounting shaft  8 , the first bracket  10  supporting the pickup roller  6  is provided, at one end portion (right end portion in  FIG. 4 ) thereof, with the swing control portion  10   a  that makes sliding contact with the guiding surface  20  of the arm  12 , and the pickup roller  6  is provided at a center portion thereof. Furthermore, the tension coil spring  22  that biases the first bracket  10  upward is engaged with the other end portion (left end portion in  FIG. 4 ) of the first bracket  10 . Thus, an upward (downward in  FIG. 4 ) biasing force F 1  from the tension coil spring  22  acts on the other end portion of the first bracket  10 , and an upward (downward in  FIG. 4 ) biasing force F 2  from the sheet stacking plate  9  (see  FIG. 2 ) acts on the center portion of the first bracket  10  via the pickup roller  6 . 
     Herein, when an attempt is made to receive the biasing forces F 1  and F 2  by the swing control portion  10   a  at the one end portion of the first bracket  10 , a biased load trying to torsionally deform the first bracket  10  acts on the first bracket  10 . 
     In order to avoid this, in this embodiment, there is provided a sliding contact portion  10   b  shaped similarly (U-shaped in cross section) to the swing control portion  10   a . The sliding contact portion  10   b  is provided at a portion on a pivotal end portion side, which is away in the direction of the feed roller mounting shaft  8  from the swing control portion  10   a  and lies between acting points of the biasing forces F 1  and F 2  so as to be close to the acting point of the biasing force F 1 . In consequence thereof, the upward biasing forces F 1  and F 2  acting on the first bracket  10  are received at two locations, i.e., by the swing control portion  10   a  and the sliding contact portion  10   b , and thus no biased load acts on the first bracket  10 , so that the first bracket  10  can be prevented from being torsionally deformed. 
     The sheet feed device  1  further includes a paper press roller  14  and the second bracket  16  that is a support body supporting the paper press roller  14 . The second bracket  16  supporting the paper press roller  14  is formed in a shape similar to that of the first bracket  10  supporting the pickup roller  6 , and is pivotably supported to the feed roller mounting shaft  8  adjacently to the first bracket  10 . In the second bracket  16 , there is provided a second rotary shaft  15  orthogonal to an extending direction of the feed roller mounting shaft  8 , and the paper press roller  14  is turnably mounted to the second rotary shaft  15 . The paper press roller  14  rotates while being in contact with an upper surface of a stack of paper sheets at the time of an operation to insert the paper feed cassette  2  or at the time of an operation to pull it out, thereby preventing a paper sheet from being positionally misaligned in a width direction thereof. 
     The paper press roller  14  is only required to be able to rotate while being in contact with an upper surface of a stack of paper sheets. The paper press roller  14  may be made of an appropriate material such as, for example, plastic, rubber, or metal. In order to facillitate contact with an upper surface of a stack of paper sheets even in a case where the second bracket  16  is swung to be inclined or the stack of paper sheets are inclined due to the sheet stacking plate  9  being inclined, the paper press roller  14  is formed to have an annular roll surface  14   a  (see  FIG. 9 ) that is circular arc-shaped in cross section on one side (sheet stacking plate  9  side) thereof. 
     At a pivotal end (end portion on the upstream side in the paper feed direction) of the second bracket  16 , similarly to the first bracket  10 , there is formed a swing control portion  16   a  formed to be U-shaped in cross section. Moreover, by a tension coil spring  23 , the second bracket  16  is elastically biased upward, i.e., in such a direction as to separate from a stack of paper sheets stacked on the sheet stacking plate  9 . In consequence thereof, the swing control portion  16   a  is in elastic contact with the guiding surface  20  formed in the arm  12  and extending in the axial direction of the feed roller mounting shaft  8 . Further, when the swing control portion  16   a  moves up and down along the guiding surface  20 , the paper press roller  14  supported by the second bracket  16  also moves up and down. 
     The arm  12  is a rod-shaped member extending, in the insertion/pull-out direction (X 1  and X 2  directions) of the paper feed cassette  2 , to a length shorter than a width between the front wall portion  2   a  and a back wall portion  2   d  of the paper feed cassette  2 . The arm  12  includes a strip plate-shaped top plate portion  12   a,  a protruding portion  12   b  that protrudes from one end of the top plate portion  12   a  toward the paper feed cassette  2  and faces an outer side of the back wall portion  2   d,  and the guiding surface  20  that is formed at a lower surface of the top plate portion  12   a.    
     The arm  12  is mounted to the main body of the image forming apparatus  100  such that the top plate portion  12   a  is slidable in the insertion/pull-out direction (arrow X 1  and) X 2  directions), and a tension coil spring  26  is mounted between an engagement portion  12   c  provided at the top plate portion  12   a  and the main body of the image forming apparatus  100 . In consequence thereof, the arm  12  is elastically biased in a pull-out direction (arrow X 2  direction) of the paper feed cassette  2 . Further, when the protruding portion  12   b  is in contact with the outer side of the back wall portion  2   d  (see  FIG. 2 ) of the paper feed cassette  2 , in conjunction with insertion/pulling out of the paper feed cassette  2 , the arm  12  moves, together with the paper feed cassette  2 , in the insertion/pull-out direction. 
     The guiding surface  20  extends in a longitudinal direction of the arm  12  and includes, in order from a protruding portion  12   b  side (left side in  FIG. 5 ), a first guiding surface  20   a  that is substantially the same flat surface as the lower surface of the top plate portion  12   a,  a second guiding surface  20   b  that is smoothly inclined in such a direction as to separate from the first guiding surface  20   a,  a third guiding surface  20   c  that is continuous with the second guiding surface  20   b  and has a protruding arc shape, a fourth guiding surface  20   d  that is smoothly inclined from the third guiding surface  20   c  in such a direction as to approach the top plate portion  12   a,  and a fifth guiding surface  20   e  that is continuous with the fourth guiding surface  20   d  and has a height from the lower surface of the top plate portion  12   a,  which is larger than that of the first guiding surface  20   a  and smaller than that of the third guiding surface  20   c.  Furthermore, at the guiding surface  20 , there is formed a guiding portion  13  with which the sliding contact portion  10   b  of the first bracket  10  makes sliding contact. The guiding portion  13  has an inclined surface having the same shape as that of the guiding surface  20  and is formed at a position misaligned with the guiding surface  20  in the paper feed direction (up-down direction in  FIG. 4 ) and the insertion/pull-out direction (left-right direction in  FIG. 4 ). 
     As will be described later, the respective shapes and dispositions of the guiding surfaces  20   a  to  20   e  and the guiding portion  13  are determined based on a relationship between a timing at which the pickup roller  6  and the paper press roller  14 , which are swingably mounted, come in/out of contact with an upper surface of a stack of paper sheets in the paper feed cassette  2  and an insertion/pull-out position of the paper feed cassette  2  to which the paper feed cassette  2  is inserted or pulled out, in conjunction with which the arm  12  moves. 
       FIGS. 5 to 8  and  FIG. 10  are explanatory views, as seen from the upstream side in the paper feed direction (left depth side in  FIG. 2 ), showing a relationship between respective dispositions of the pickup roller  6  and the paper press roller  14  and the insertion/pull-out position of the paper feed cassette  2 .  FIG. 5  shows an insertion start position or a pull-out completion position of the paper feed cassette  2 ,  FIG. 10  shows a position (hereinafter, referred to as a first position) of the paper feed cassette  2  at which mounting of the paper feed cassette  2  in the main body of the image forming apparatus  100  is completed, and  FIGS. 6 to 8  show positions of the paper feed cassette  2  at different stages in the process of being mounted therein.  FIG. 9  is a view, as seen from an upstream side in the insertion direction (X 1  direction) of the paper feed cassette  2 , of a positional relationship of the pickup roller  6  and the paper press roller  14  with the sheet stacking plate  9 , which is shown in  FIG. 8 . 
     As shown in  FIG. 5 , when the paper feed cassette  2  is at the insertion start position or the pull-out completion position, the swing control portion  10   a  of the first bracket  10  supporting the pickup roller  6  and the swing control portion  16   a  of the second bracket  16  supporting the paper press roller  14  are each in contact with the first guiding surface  20   a  of the arm  12 , and the pickup roller  6  and the paper press roller  14  are disposed at their respective positions most distant from an upper limit position S (indicated by an alternate long and short dashed line in the figures) of a stack of paper sheets P (or the sheet stacking plate  9 ). The upper limit position S refers to a position (paper feed position) of an uppermost surface of a stack of paper sheets when the sheet stacking plate  9  is in an raised state. In a state shown in  FIG. 5 , as a result of an operation to pull out the paper feed cassette  2 , the pickup roller  6  is disposed on a most upstream side in the insertion direction (X 1  direction). Furthermore, before being inserted in the main body of the image forming apparatus  100 , the paper feed cassette  2  is in a state where the sheet stacking plate  9  is locked with respect to the bottom surface by use of the anchor lug of the lock release member  53  (see  FIG. 2 ). 
     When the paper feed cassette  2  is inserted, from the position shown in  FIG. 5 , by a prescribed amount in a direction of a depth-side wall  100   a  (X 1  direction) of the main body of the image forming apparatus  100 , the back wall surface  2   d  of the paper feed cassette  2  comes in contact with the protruding portion  12   b  of the arm  12 , and then the arm  12  moves, together with the paper feed cassette  2 , in the X 1  direction against a biasing force of the tension coil spring  26 . As a result, as shown in  FIG. 6 , the swing control portion  10   a  of the first bracket  10  stays in contact with the first guiding surface  20   a , and the swing control portion  16   a  of the second bracket  16  comes in contact with the second guiding surface  20   b.  Further, the paper press roller  14  swings in such a direction as to approach the upper limit position S more closely than the pickup roller  6  does. Though not described below, the sliding contact portion  10   b  of the first bracket  10  comes in contact with the guiding portion  13  and thus also swings up and down at the same timing as that of the swing control portion  10   a.    
     When the paper feed cassette  2  is inserted further, from the position shown in  FIG. 6 , by a prescribed amount in the X 1  direction, the arm  12  also moves further, together with the paper feed cassette  2 , in the X 1  direction. As a result, as shown in  FIG. 7 , the swing control portion  10   a  of the first bracket  10  comes in contact with the second guiding surface  20   b,  and the swing control portion  16   a  of the second bracket  16  comes in contact with a tip end of the third guiding surface  20   c  having the protruding arc shape. Further, the paper press roller  14  is disposed at such a position as to come in contact with the upper limit position S, and the pickup roller  6  is disposed at a position slightly separated from the upper limit position S. 
     When the paper feed cassette  2  is inserted further, from the position shown in  FIG. 7 , by a prescribed amount in the X 1  direction, the arm  12  also moves further, together with the paper feed cassette  2 , in the X 1  direction. As a result, as shown in  FIGS. 8 and 9 , the swing control portion  10   a  of the first bracket  10  comes in contact with the third guiding surface  20   c  having the protruding arc shape, and the swing control portion  16   a  of the second bracket  16  comes in contact with the fifth guiding surface  20   e.  On the other hand, the lock release member  53  (see  FIG. 2 ) is pressed to be retracted into the paper feed cassette  2 , so that the locked state of the sheet stacking plate  9  with respect to the bottom surface of the paper feed cassette  2  is released to bring the sheet stacking plate  9  to a raised state, and thus an uppermost surface of the stack of paper sheets reaches the upper limit position S. As a result, the pickup roller  6  is disposed at such a position as to come in contact with the uppermost surface of the stack of paper sheets at the upper limit position S, and the paper press roller  14  is disposed at a position separated from the upper limit position S. In a state shown in  FIGS. 8 and 9 , the paper feed cassette  2  has not yet reached the first position. Hereinafter, such a position of the paper feed cassette  2  that the pickup roller  6  comes in contact with the upper limit position S, which is shown in  FIGS. 8 and 9 , is referred to as a second position. 
     When the paper feed cassette  2  is inserted further, from the second position shown in  FIG. 8 , by a prescribed amount in the X 1  direction, while a state is maintained where the swing control portion  10   a  of the first bracket  10  is in contact with the third guiding surface  20   c,  and the swing control portion  16   a  of the second bracket  16  is in contact with the fifth guiding surface  20   e,  the arm  12  moves further, together with the paper feed cassette  2 , in the X 1  direction. As a result, as shown in  FIG. 10 , the paper feed cassette  2  reaches the first position. Since the paper feed cassette  2  moves in the X 1  direction in a state where the pickup roller  6  is in contact with the upper limit position S, by friction between the pickup roller  6  and an upper surface of the stack of paper sheets (or the sheet stacking plate  9 ), the pickup roller  6  moves along the first rotary shaft  11  to a downstream side in the insertion direction (left side in  FIG. 10 ). 
     In a case where the paper feed cassette  2  is pulled out from the main body of the image forming apparatus  100 , the pickup roller  6  and the paper press roller  14  swing in an order reverse to that in the above-described case. That is, from the first position shown in  FIG. 10 , the paper feed cassette  2  moves, together with the arm  12 , in the pull-out direction (X 2  direction) in a state where the pickup roller  6  is in contact with the upper limit position S, so that, as shown in  FIG. 8 , by friction between the pickup roller  6  and an upper surface of a stack of paper sheets (or the sheet stacking plate  9 ), the pickup roller  6  moves along the first rotary shaft  11  to the upstream side in the insertion direction (right direction in  FIG. 10 ). 
     Moreover, after the second position shown in  FIG. 8  has been reached, the swing control portion  10   a  moves upward along the second guiding surface  20   b,  so that the pickup roller  6  separates from the upper limit position S, and as shown in  FIG. 7 , the paper feed cassette  2  moves, together with the arm  12 , in the pull-out direction (X 2  direction) in a state where the paper press roller  14  is in contact with the upper limit position S. After that, via a state shown in  FIG. 6 , as shown in  FIG. 5 , the paper feed cassette  2  is pulled out in a state where the pickup roller  6  and the paper press roller  14  are both separated from the upper limit position S. 
     While the paper feed cassette  2  described herein is of a type in which, at the time of pulling out the paper feed cassette  2  from the main body of the image forming apparatus  100 , the sheet stacking plate  9  is not brought to a lowered state, a configuration may be adopted in which, at the time of pulling out the paper feed cassette  2 , the sheet stacking plate  9  is brought to a lowered state and locked to the bottom surface of the paper feed cassette  2 . In this case, a configuration could be adopted in which the sheet stacking plate  9  is brought to a lowered state at a timing at which the pickup roller  6  separates from the upper limit position S and, at a point in time when the paper feed cassette  2  has been pulled out by a prescribed amount, the sheet stacking plate  9  is locked to the bottom surface of the paper feed cassette  2 . 
     In this embodiment, a timing at which the pickup roller  6  comes in/out of contact with the upper limit position S is adjusted so that a movement amount D 1  of the paper feed cassette  2  between the second position (indicated by a broken line in  FIG. 10 ) and the first position (indicated by a solid line in  FIG. 10 ) is substantially equal to a movable area D 2  of the pickup roller  6  in a direction of the first rotary shaft  11 . 
     According to this configuration, at the time of an operation to insert the paper feed cassette  2 , the pickup roller  6  moves, together with a stack of paper sheets, always to a most downstream side in the insertion direction (most upstream side in the pull-out direction) of the first rotary shaft  11 . Furthermore, at the time of an operation to pull out the paper feed cassette  2 , the pickup roller  6  moves, together with a stack of paper sheets, always to the most upstream side in the insertion direction (most downstream side in the pull-out direction). This eliminates a possibility that, at the time of an operation to insert or pull out the paper feed cassette  2 , an upper surface of a stack of paper sheets is rubbed against by the pickup roller  6 , and thus misalignment of a paper sheet and damage to a paper sheet can be effectively suppressed. Furthermore, movement of the pickup roller  6  in the axial direction during paper feeding is considerably reduced, and thus a constant positional relationship with the feed roller  18  is established, so that a stable paper feed operation can be performed. 
     While in this embodiment, the movement amount D 1  of the paper feed cassette  2  is set to be substantially equal to the movable area D 2  of the pickup roller  6 , the movable area D 2  of the pickup roller  6  in the direction of the first rotary shaft  11  may be set to be larger than the movement amount D 1  of the paper feed cassette  2 . This can suppress misalignment of a paper sheet and damage to a paper sheet due to interference between the pickup roller  6  and an upper surface of a stack of paper sheets. In the case, however, where the movable area D 2  of the pickup roller  6  is larger than the movement amount D 1  of the paper feed cassette  2 , at the time of an operation to insert the paper feed cassette  2 , the pickup roller  6  does not necessarily move to the most downstream side in the insertion direction. 
     As a solution to this, as shown in  FIG. 11 , the first rotary shaft  11  of the pickup roller  6  is inclined in such a direction as to approach the feed roller  18  from the upstream side in the insertion direction (near side with respect to the image forming apparatus main body, namely, a right side in  FIG. 11 ) toward the downstream side in the insertion direction (depth side of the image forming apparatus main body, namely, a left side in  FIG. 11 ) so that parallelism between the feed roller  18  and the pickup roller  6  is lost. With this configuration, every time paper feeding is performed, by drag (frictional force) the pickup roller  6  receives from a paper sheet P, the pickup roller  6  moves to be increasingly closer to the downstream side in the insertion direction, and thus it is possible to, after a prescribed number of sheets have been fed, make the pickup roller  6  automatically move to the most downstream side in the insertion direction. 
     Even with the above-described configuration, however, in which the pickup roller  6  is made to automatically move to the most downstream side in the insertion direction, there may be a case where, at a start of paper feeding, misalignment has occurred between positions of the pickup roller  6  and the feed roller  18  in a main scanning direction. Such a case leads to movement of the pickup roller  6  in the axial direction during paper feeding, and it, therefore, cannot be said that the above-described configuration is beneficial to paper feed performance. From this viewpoint, more preferable is the configuration of this embodiment in which the movement amount D 1  of the paper fed cassette  2  is set to be substantially equal to the movable area D 2  of the pickup roller  6  so that, when the paper feed cassette  2  is inserted, the pickup roller  6  is disposed always on the most downstream side in the insertion direction. 
     In addition to the above, without being limited to the foregoing embodiment, the present disclosure can be variously modified within the spirit of the present disclosure. For example, while the foregoing embodiment includes the paper press roller  14  along with the pickup roller  6 , in a case where the degree of misalignment of a paper sheet caused by a frictional force between a sheet of the paper P and the pickup roller  6  in the cassette insertion/pull-out direction is permissible, it is not necessary that the paper press roller  14  be provided. 
     Furthermore, while in the foregoing embodiment, in the arm  12  as a swing control body, the first bracket  10  as a pickup roller support body and the second bracket  16  as a paper press roller support body are in elastic contact with the guiding surface  20  by biasing forces of the tension coil springs  22  and  23 , instead of configuring the first bracket  10  and the second bracket  16  so that they make elastic contact with the guiding surface  20 , for example, a configuration may be adopted in which the arm  12  is provided with a guiding groove extending in the insertion/pull-out direction of the paper feed cassette  2 , and the pivotal ends of the first bracket  10  and the second bracket  16  are engaged therewith so that guiding is performed based on this engagement. 
     Furthermore, while in the foregoing embodiment, the first bracket  10  and the second bracket  16  are biased in their swing directions by the tension coil springs  22  and  23 , respectively, instead of using a tension coil spring, a twist spring may be mounted to the feed roller mounting shaft  8 . 
     Furthermore, in the paper feed cassette  2 , without any limitation to paper sheets, various types of sheets such as OHP sheets and label sheets can be housed. 
     The present disclosure is applicable to a sheet feed device that can be mounted in/demounted from an image forming apparatus and includes a sheet housing portion that is stocked beforehand with a multitude of sheets such as paper sheets and a pickup roller that feeds, one by one, the sheets thus stocked in the sheet housing portion. The use of the present disclosure provides a sheet feed device that can prevent, with increased reliability compared with conventional techniques and by using a simple configuration, positional misalignment of a sheet and damage to a sheet due to contact between a pickup roller and an uppermost sheet at the time of an operation to mount/demount a sheet housing portion in/from an image forming apparatus main body.