Patent Publication Number: US-10787330-B2

Title: Recording apparatus

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a recording apparatus provided with an urging member that urges a recording medium placed on a placement unit toward a feeder. 
     2. Related Art 
     A known example of the recording apparatus of this type is an apparatus disclosed, for example, in JP-A-2004-331345. The recording apparatus of this type includes a paper cassette, a feed roller disposed in a region above the paper cassette, an intermediate plate that is disposed inside the paper cassette and on which sheets of paper are stacked, and first to third springs that urge the intermediate plate upward. A spring cap is disposed on the top face of the second spring. Inside the paper cassette, a pair of side regulation plates and a spring lock member are provided. A pair of the side regulation plates are movable so as to fit the size of sheets placed on the intermediate plate. The spring lock member engages the side regulation plates and is movable in a direction of transporting a sheet. 
     The spring lock member moves between a first position and a second position. The first position is a position at which the spring lock member is separated from the spring cap due to a balance between an urging force of a tension spring and a pressing force generated in conjunction with movement of the side regulation plates, and the spring lock member thereby permits the second spring to impart an urging force to the intermediate plate. The second position is a position at which the spring lock member engages the spring cap and thereby restrains the second spring from imparting the urging force to the intermediate plate. When the side regulation plates are moved to a position so as to fit large size sheets, the intermediate plate is pushed upward by the urging forces of the first spring, the second spring, and the third spring, which thereby generates a relatively large feed pressure (i.e., a contact pressure between the sheets and the feed roller). On the other hand, when the side regulation plates are moved to a position so as to fit small size sheets, the intermediate plate is pushed upward by the urging forces of the first spring and the third spring, which thereby generates a relatively small feed pressure. 
     However, in the recording apparatus described above, if the engagement state between the spring lock member and the spring cap is terminated due to, for example, an external force while the spring lock member stays at the second position, the second spring, which is disposed in an exposed and unprotected state, may be bent in an unexpected direction by the spring lock member. This may lead to breakage of the second spring. 
     SUMMARY 
     An advantage of some aspects of the invention is that a recording apparatus that can protect an urging member that imparts an urging force to a placement unit is provided. 
     Implementation and advantageous effects will be described. A recording apparatus according to an aspect of the invention includes a placement unit on which a recording medium on which recording is performed in a recording section is placed, a feeder that feeds the recording medium toward the recording section, a thrust mechanism that pushes up the placement unit toward the feeder, and an edge guide that is disposed in the placement unit and defines a position of a side of the recording medium in a direction intersecting a transport direction of the recording medium. In the recording apparatus, the thrust mechanism includes an urging member that imparts an urging force to the placement unit, a first accommodation body that is mounted on the placement unit and receives the urging member from an end thereof and accommodates the urging member, and a second accommodation body that is disposed so as to partially overlap the first accommodation body and receives the urging member from another end thereof and accommodates the urging member. In addition, the first accommodation body and the second accommodation body are movable relative to each other in an urging direction of the urging member and are rotatable together in a circumferential direction of the first accommodation body and the second accommodation body. The recording apparatus also includes a protrusion that is disposed in the first accommodation body and that rotates the first accommodation body in conjunction with movement of the edge guide, and a restrained portion that is disposed in the second accommodation body, that rotates together with the second accommodation body in conjunction with rotation of the first accommodation body, and that is displaced between a first position at which the restraining portion restrains the restrained portion and a second position at which the restraining portion does not restrain the restrained portion. In the recording apparatus, in a case in which the restrained portion is at the first position, the second accommodation body is restrained from moving relative to the first accommodation body, and the urging member is thereby restrained from imparting the urging force to the placement unit. 
     With this configuration, the urging member that imparts an urging force to the placement unit is covered by the first accommodation body and the second accommodation body, and thereby the urging member can be protected. It is preferable that the recording apparatus include a second urging member that urges the placement unit and the recording medium placed on the placement unit toward the feeder. 
     With this configuration, the urging forces imparted to the placement unit can be set suitably to fit recording media of a plurality of sizes. It is preferable that the recording apparatus further include two thrust mechanisms and a slide member that moves in conjunction with movement of the edge guide and is able to come into contact with the respective protrusions of the two thrust mechanisms, and that the slide member selectively restrain the respective urging members of the two thrust mechanisms from imparting the urging forces to the placement unit in accordance with a position to which the slide member has been moved. 
     With this configuration, a single slide member can selectively restrain two thrust mechanisms from functioning, which leads to a reduction in the number of parts. In the recording apparatus, it is preferable that the placement unit be configured to be rotatable around a pivot shaft, that the two thrust mechanisms be arranged adjacent to each other in a direction orthogonally intersecting an axial direction of the pivot shaft, and that in a case in which a pair of the edge guides are moved from positions that are away from each other to positions that are closer to each other, the urging member of one of the two thrust mechanisms that is located further away from the pivot shaft in the direction orthogonally intersecting the axial direction of the pivot shaft be restrained from imparting the urging force to the placement unit before the urging member of another one of the two thrust mechanisms that is located closer to the pivot shaft in the direction orthogonally intersecting the axial direction of the pivot shaft is restrained from imparting the urging force to the placement unit. 
     With this configuration, when the thrust mechanisms push up the placement unit and the recording medium placed thereon toward the feeder, the push-up forces can be adjusted appropriately in accordance with the size of the recording medium. 
     In the recording apparatus, it is preferable that the placement unit be configured to be rotatable around the pivot shaft, that the two thrust mechanisms be arranged adjacent to each other in the direction orthogonally intersecting the axial direction of the pivot shaft, and that the urging member of one of the two thrust mechanisms that is located further away from the pivot shaft in the direction orthogonally intersecting the axial direction of the pivot shaft provide a larger urging force than the urging member of another one of the two thrust mechanisms that is located closer to the pivot shaft in the direction orthogonally intersecting the axial direction of the pivot shaft. 
     With this configuration, when the placement unit is rotated around the pivot shaft, the urging members can impart the urging forces to the placement unit efficiently. It is preferable that the recording apparatus further include an abutment portion with which the second accommodation body comes into contact in a case in which the urging member imparts the urging force to the placement unit, and that the second accommodation body have a contact portion that is shaped like a hemisphere and comes into contact with the abutment portion. 
     With this configuration, even if the contact angle of the second accommodation body against the abutment portion changes slightly, changes in the urging force of the urging member that acts on the placement unit can be suppressed. In the recording apparatus, it is preferable that in a state in which the placement unit and the recording medium placed thereon are pushed up toward the feeder by the thrust mechanism, a pair of the edge guides be permitted to move in a direction away from each other. 
     With this configuration, when a recording medium is jammed between a pair of the edge guides, a pair of the edge guides can be moved in the direction away from each other so that the jammed recording medium can be removed easily. 
     In the recording apparatus, it is preferable that in a state in which the placement unit and the recording medium placed thereon are pushed up toward the feeder by the thrust mechanism, the restraining portion restrain the restrained portion from rotating, and a pair of the edge guides be thereby restrained from moving in a direction closer to each other. 
     With this configuration, after the second accommodation body moves relative to the first accommodation body, the restraining portion and the restrained portion are restrained from overlapping each other in the relative movement direction of the second accommodation body, which can restrain the second accommodation body from failing to return to the original position prior to the relative movement. 
     In the recording apparatus, it is preferable that the first accommodation body have a first engagement portion that extends in an urging direction of the urging member, and that the second accommodation body have a second engagement portion that extends in the urging direction of the urging member and engages the first engagement portion. 
     With this configuration, the first accommodation body and the second accommodation body can rotate together in the rotation direction of the protrusion while causing the first accommodation body and the second accommodation body to move relative to each other in the urging direction of the urging member. Thus, the protrusion of the first accommodation body and the restrained portion of the second accommodation body are restrained from being shifted in phase in the rotation direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a perspective view illustrating an ink jet type printer according to an embodiment. 
         FIG. 2  is a cross-sectional view illustrating the ink jet type printer in  FIG. 1 . 
         FIG. 3  is an exploded perspective view illustrating a medium feed mechanism. 
         FIG. 4  is a rear view illustrating a placement unit. 
         FIG. 5  is a cross-sectional view illustrating the vicinity of the placement unit when viewed from behind. 
         FIG. 6  is a cross-sectional view illustrating the vicinity of the placement unit when viewed from behind. 
         FIG. 7  is an exploded perspective view illustrating the placement unit when viewed from behind. 
         FIG. 8  is an enlarged view illustrating part of the placement unit in  FIG. 4 . 
         FIG. 9  is a perspective view illustrating a slide member. 
         FIG. 10  is a schematic diagram illustrating actions of a first thrust mechanism, a second thrust mechanism, and the slide member. 
         FIG. 11  is a schematic diagram illustrating actions of the first thrust mechanism, the second thrust mechanism, and the slide member. 
         FIG. 12  is a schematic diagram illustrating actions of the first thrust mechanism, the second thrust mechanism, and the slide member. 
         FIG. 13  is a schematic diagram illustrating actions of the first thrust mechanism, the second thrust mechanism, and the slide member. 
         FIG. 14  is a schematic diagram illustrating actions of the first thrust mechanism, the second thrust mechanism, the slide member, and edge guides. 
         FIG. 15  is a schematic diagram illustrating actions of the first thrust mechanism, the second thrust mechanism, the slide member, and the edge guides. 
         FIG. 16  is a schematic diagram illustrating actions of the first thrust mechanism, the second thrust mechanism, the slide member, and the edge guides. 
         FIG. 17  is a schematic diagram illustrating actions of the first thrust mechanism, the second thrust mechanism, the slide member, and the edge guides. 
         FIG. 18  is a schematic diagram illustrating actions of the first thrust mechanism, the second thrust mechanism, the slide member, and the edge guides. 
         FIG. 19  is a schematic diagram illustrating actions of the first thrust mechanism, the second thrust mechanism, the slide member, and the edge guides. 
         FIG. 20  is a cross-sectional view illustrating a state in which fifteen or less large-size sheets of paper are placed on the placement unit. 
         FIG. 21  is a cross-sectional view illustrating a state in which thirty large-size sheets of paper are placed on the placement unit. 
         FIG. 22  is a cross-sectional view illustrating a state in which the predetermined number or less of medium-size sheets of paper are placed on the placement unit. 
         FIG. 23  is a cross-sectional view illustrating a state in which thirty medium-size sheets of paper are placed on the placement unit. 
         FIG. 24  is a cross-sectional view illustrating a state in which small-size sheets of paper are placed on the placement unit. 
         FIG. 25  is a cross-sectional view illustrating a state in which the placement unit is at a standby position. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     An embodiment of a recording apparatus will be described with reference to the drawings. As illustrated in  FIG. 1 , an ink jet type printer  11 , which is an example of a recording apparatus, includes a casing  12  that has a predetermined height, a predetermined depth, and a predetermined width when placed on a horizontal placement surface. The ink jet type printer  11  also includes a document reader  13  disposed on the casing  12  and an auto document feeder  14  disposed on the document reader  13 . 
     The auto document feeder  14  includes a document-setting section  15  in which a plurality of documents G can be stacked and a discharge section  16  that is disposed under the document-setting section  15 . A plurality of the document G stacked in the document-setting section  15  is fed one by one to a document transport path (not illustrated) in which each document G is inverted. The document G is subsequently read by a reading section (not illustrated) that is disposed inside the document reader  13  and transported to the discharge section  16 . 
     Disposed on the front side of the casing  12  are, in order from the bottom upward, an openable/closable cover  17 , an installation opening  19 , and a discharge opening  20 . A paper cassette  18  that accommodates sheets of paper P, which are examples of recording media, is detachably installed in the installation opening  19 . Each sheet P on which recording (printing) has been performed is discharged from the discharge opening  20 . A discharge tray  22  that supports the sheets P discharged from the discharge opening  20  is detachably attached to the discharge opening  20  so as to protrudes frontward. An operation section  21  with which various operations are performed is provided on the front side of the document reader  13 . Note that the front side of the casing  12  and the front side of the document reader  13  are sides that have heights and widths and face a user that operates the ink jet type printer  11  normally. 
     As illustrated in  FIGS. 1 and 2 , a mounting section  23 , a paper accommodation section  24 , and a recording section  25  are disposed at respective positions behind the cover  17 , the installation opening  19 , and the discharge opening  20  inside the casing  12 . A container  88  that contains ink packs with ink (i.e., an example of liquid) filled therein is detachably mounted on the mounting section  23 . The paper accommodation section  24  is a portion of the paper cassette  18  that accommodates sheets of paper P. The recording section  25  performs recording onto each sheet P. The cover  17  openably covers the front side of the mounting section  23 . 
     Note that in the present embodiment, the depth direction X is defined as the direction from the front side of the casing  12  toward the opposite side (i.e., rear side) or from the rear side toward the front side. The width direction Y is defined as the direction that orthogonally intersects both the depth direction X and the vertical direction Z. The width direction Y and the depth direction X are substantially parallel to a horizontal plane. 
     A support platform  26  that supports a sheet P is disposed in a region above the paper accommodation section  24  in the casing  12 . Sheets P that are stacked in the paper accommodation section  24  are inverted one by one and transported onto the support platform  26  by a first transport section  27  that includes various types of transport rollers. Flexible tubes (not illustrated) are also disposed inside the casing  12 . The ink in the container  88  that is mounted in the mounting section  23  is supplied to the recording section  25  through the flexible tubes by actuating a supply pump (not illustrated). 
     The recording section  25  includes a recording head  28  that ejects ink supplied from the container  88  via flexible tubes (not illustrated) and a carriage  29  that supports the recording head  28 . The carriage  29  is supported by a guide shaft  30  that is suspended in the casing  12  and extends in the width direction Y, and the carriage  29  is able to move reciprocally. In other words, the carriage  29  is configured to move reciprocally in the width direction Y. 
     Recording (printing) is performed onto a sheet P in such a manner that while the carriage  29  moves reciprocally in the width direction Y along the guide shaft  30 , the recording head  28  ejects ink onto a sheet P that is transported onto the support platform  26 . The sheet P on which recording has been performed is discharged from the discharge opening  20  onto the discharge tray  22  by a discharge roller  31 . 
     As illustrated in  FIGS. 2 and 3 , a medium feed mechanism  32  is provided in an upper rear region in the casing  12  for supporting and transporting sheets P for so-called manual feed printing. The medium feed mechanism  32  includes a medium support unit  34  that can support a plurality of sheets P and a medium feed unit  36 . The medium feed unit  36  includes a feed roller  35 , which is an example of a feeder. The medium feed unit  36  feeds each of a plurality of sheets P supported by the medium support unit  34  toward the recording section  25 . 
     The medium support unit  34  and the medium feed unit  36  are separate units, but are detachably assembled into one unit. A second transport section  37  is disposed between the support platform  26  and the medium feed unit  36  in the casing  12 . The second transport section  37  includes various transport rollers that transport a sheet P that has been fed one by one by the medium feed unit  36  toward the support platform  26 . 
     As illustrated in  FIGS. 2 and 4 , the medium support unit  34  includes a housing  38  of which the top end is open and a lid member  39  that openably covers the top end opening of the housing  38 . Inside the housing  38 , a placement unit  33 , an accommodation portion  40  disposed behind the placement unit  33 , and an auxiliary tray  41  accommodated in the accommodation portion  40  are disposed. The placement unit  33  is shaped like a board on a front side of which a plurality of sheets P can be stacked. The auxiliary tray  41  can be drawn upward from the accommodation portion  40  when the lid member  39  is open. The auxiliary tray  41  is drawn out of the accommodation portion  40  and supplementally supports a portion of the sheet P that protrudes upward from the placement unit  33 . 
     Pivot shafts  42 , which form a pair, are provided at respective upper ends of the placement unit  33  in the width direction Y so as to protrudes outward in the width direction Y. A pair of the pivot shafts  42  are supported rotatably inside the housing  38 . Accordingly, the placement unit  33  is configured to be rotatable around a pair of the pivot shafts  42 . The bottom end of the front side of the placement unit  33 , which is the side on which sheets P are placed, opposes the feed roller  35  in the depth direction X. 
     A pair of torsion coil springs  43 , which are examples of second urging members, are disposed on a pair of the respective pivot shafts  42 . A pair of the torsion coil springs  43  urge the placement unit  33  in a direction in which the bottom end of the rotatable placement unit  33  comes closer toward the feed roller  35 . In other words, a pair of the torsion coil springs  43  urge the placement unit  33  and the sheets P placed on the placement unit  33  toward the feed roller  35 . 
     A pressing mechanism (not illustrated) is disposed inside the housing  38 . The pressing mechanism includes a cam (not illustrated) that rotates in conjunction with rotation of the feed roller  35 . In accordance with the rotating position of the cam, the placement unit  33  is pressed or not pressed by the cam against urging forces of a pair of the torsion coil springs  43  in a direction of the bottom end of the placement unit  33  moving away from the feed roller  35 . 
     When the pressing force from the pressing mechanism (not illustrated) does not act, the placement unit  33  is rotated by the urging forces of a pair of the torsion coil springs  43  to a feed position at which the sheets P placed on the placement unit  33  come into contact with the feed roller  35 . On the other hand, when the pressing force by the pressing mechanism (not illustrated) acts, the placement unit  33  is rotated, by the pressing force acting against the urging forces of a pair of the torsion coil springs  43 , to a standby position (i.e., home position) at which the sheets P placed on the placement unit  33  are separated from the feed roller  35 . 
     As illustrated in  FIGS. 4 and 5 , two thrust mechanisms  44  are provided on the back side of the placement unit  33  in a lower region at the center in the width direction Y. The thrust mechanisms  44  push up the placement unit  33  and the sheets P placed on the front side thereof toward the feed roller  35 . Two thrust mechanisms  44  are arranged on the back side of the placement unit  33  with a spacing therebetween in a direction that orthogonally intersects the axial direction of the pivot shafts  42 . In other words, two thrust mechanisms  44  are arranged vertically with a spacing therebetween. 
     One of the two thrust mechanisms  44  that is located at an upper position is denoted by a first thrust mechanism  45 , while the other one of the thrust mechanisms  44  that is located at a lower position is denoted by a second thrust mechanism  46 . In other words, the first thrust mechanism  45  is disposed at a position closer to the pivot shafts  42  in a direction orthogonally intersecting the axial direction of the pivot shafts  42  than the second thrust mechanism  46 , whereas the second thrust mechanism  46  is disposed at a position further away from the pivot shafts  42  in a direction orthogonally intersecting the axial direction of the pivot shafts  42  than the first thrust mechanism  45 . 
     On the front side of the placement unit  33 , a pair of edge guides  47  are disposed so as to be reciprocally movable in the width direction Y. The edge guides  47  regulate the positions of respective edges of a sheet P in the width direction Y, which is the direction intersecting the direction of transporting the sheet P. A pair of the edge guides  47  are moved in the width direction Y to respective positions that correspond to the length of a sheet P in the width direction Y. The edge guides  47  thereby guide both edges of the sheet P in the width direction Y. A pair of racks  48  that extend in the width direction Y are arranged vertically adjacent to each other with a spacing therebetween on the back side of the placement unit  33  at positions above the first thrust mechanism  45 . Each of a pair of the racks  48  is disposed so as to be movable in the width direction Y. 
     Between a pair of the racks  48  on the back side of the placement unit  33 , a pinion  49  is disposed so as to be rotatable around an axis extending in the direction perpendicular to the back side of the placement unit  33 . In the state in which a pair of the edge guides  47  are positioned furthest away from each other in the width direction Y, an end of one of the racks  48  is connected to one of the edge guides  47  and the other end intermeshes with the pinion  49 . Simultaneously, an end of the other one of the racks  48  intermeshes with the pinion  49  and the other end is connected to the other one of the edge guides  47 . 
     Accordingly, when one of the edge guides  47  is caused to move in the width direction Y, the force to move the edge guide  47  is transmitted to the other edge guide  47  via a pair of the racks  48  and the pinion  49 , which causes the other edge guide  47  to move in the width direction Y. In other words, a pair of the edge guides  47  are caused to move closer to each other or away from each other in the width direction Y synchronously. 
     A slide member  50  that extends straight in the width direction Y is disposed between the first thrust mechanism  45  and the second thrust mechanism  46  on the back side of the placement unit  33 . The slide member  50  is movable in the width direction Y so as to be able to come into contact with the first thrust mechanism  45  and the second thrust mechanism  46 . Note that the first thrust mechanism  45  and the second thrust mechanism  46  are configured to be the same substantially and to be shaped in line symmetry with respect to the slide member  50 . 
     In the state in which a pair of the edge guides  47  are positioned furthest away from each other in the width direction Y, a leading end  50   a  of the slide member  50  is positioned between the two thrust mechanisms  44 . A base end  50   b  of the slide member  50  is connected to one of the edge guides  47 . Accordingly, the slide member  50  moves in the width direction Y in synchronization with the edge guides  47 . 
     As illustrated in  FIGS. 6 and 7 , the first thrust mechanism  45  includes a first coil spring  51 , a first upper case  52 , and a second upper case  53 . The first coil spring  51  is an example of an urging member that imparts an urging force to the placement unit  33 . The first upper case  52  is an example of a first accommodation body that accommodates the first coil spring  51  of which one end in the axial direction is inserted into the first accommodation body. The second upper case  53  is an example of a second accommodation body that accommodates the first coil spring  51  of which the other end in the axial direction is inserted into the second accommodation body. Each of the first upper case  52  and the second upper case  53  is shaped like a closed-end cylinder with one end open. 
     The first upper case  52  is rotatably attached to a cylindrically shaped first boss  54  in such a manner that the closed-end of the first upper case  52 , which is opposite to the open end, is attached by a first screw  55  to the first boss  54  disposed on the back side of the placement unit  33 . The second upper case  53  is disposed such that a portion of the second upper case  53  overlaps the first upper case  52 . In other words, the open end of the first upper case  52  is inserted into the open end of the second upper case  53 . 
     An end of the first coil spring  51  in the axial direction thereof abuts the inside surface of the bottom wall of the first upper case  52 , whereas the other end of the first coil spring  51  in the axial direction abuts the inside surface of the bottom wall of the second upper case  53 . In this case, the first coil spring  51  is completely covered by the first upper case  52  and the second upper case  53 , and in this state, the first coil spring  51  continuously urges the first upper case  52  and the second upper case  53  in directions of separating from each other. 
     A first upper elongated protrusion  56 , which is an example of a first engagement portion, is formed on the outer periphery of the first upper case  52  so as to extend in an urging direction of the first coil spring  51 . A second upper groove  57 , which is an example of a second engagement portion, is formed on the inner periphery of the second upper case  53  so as to extend in the urging direction of the first coil spring  51  and to be able to receive the first upper elongated protrusion  56 . 
     In the state in which the first upper case  52  is inserted in the second upper case  53  with the first upper elongated protrusion  56  being inserted in the second upper groove  57 , the first upper elongated protrusion  56  and the second upper groove  57  are slidable relative to each other in the urging direction of the first coil spring  51 , while the first upper elongated protrusion  56  and the second upper groove  57  engage each other in the circumferential direction of the first upper case  52  and the second upper case  53 . Accordingly, the first upper case  52  and the second upper case  53  are movable relative to each other in the urging direction of the first coil spring  51  and are rotatable together in the circumferential direction. 
     As illustrated in  FIGS. 7 and 8 , a first upper rotating protrusion  58  and a second upper rotating protrusion  59  are disposed on the outer periphery of the first upper case  52  at the end near the placement unit  33  so as to protrude in radial directions. The first upper rotating protrusion  58  and the second upper rotating protrusion  59  are examples of a protrusion. The first upper rotating protrusion  58  and the second upper rotating protrusion  59  are disposed so as to be separated from each other by an acute angle (e.g., 70 degrees) in the circumferential direction and to have a slight distance between each other in the axial direction of the first upper case  52 . The first upper rotating protrusion  58  and the second upper rotating protrusion  59  come into contact with the slide member  50 , which is moved in conjunction with movement of the edge guides  47  (see  FIG. 4 ). The first upper rotating protrusion  58  and the second upper rotating protrusion  59  thereby cause the first upper case  52  to rotate. 
     A pair of first restrained plates  60 , which are examples of a restrained portion, are disposed on the outer periphery of the second upper case  53  at the end near the placement unit  33  so as to protrude in radial directions. A pair of the first restrained plates  60  are disposed on opposite sides of the second upper case  53  with the central axis of the second upper case  53  interposed therebetween. A pair of the first restrained plates  60  rotate together with the second upper case  53  in conjunction with rotation of the first upper case  52 . Note that as illustrated in  FIG. 10 , a first mortise  61  is provided at the end of the outer periphery of the second upper case  53  near the placement unit  33  in such a manner that the second upper rotating protrusion  59  of the first upper case  52  protrudes out of the second upper case  53  in a radial direction when the second upper case  53  covers the first upper case  52 . 
     As illustrated in  FIGS. 7 and 8 , a pair of first restraining portions  62  are disposed on the back side of the placement unit  33  at positions straddling the first thrust mechanism  45  in the width direction Y. The first restraining portions  62  are examples of a restraining portion. Each of the first restraining portions  62  is formed as a plate shaped like a letter L and extends in the axial direction of the first coil spring  51 . First restraining surfaces  63  are formed at respective base ends of the first restraining portions  62 . The first restraining surfaces  63  can engage the respective first restrained plates  60  in the axial direction of the first coil spring  51  due to rotation of the second upper case  53 . 
     Due to the rotation of a pair of the first restrained plates  60  in conjunction with rotation of the second upper case  53 , a pair of the first restrained plates  60  engage respective first restraining surfaces  63  of a pair of the first restraining portions  62  in the axial direction of the first coil spring  51 . As a result, the urging force of the first coil spring  51  restrains the first upper case  52  and the second upper case  53  from moving relative to each other in the axial direction of the first coil spring  51 . In other words, the first restrained plates  60  rotate together with the second upper case  53  in conjunction with rotation of the first upper case  52 , and thereby the first restrained plates  60  are displaced to a first position (a position illustrated in  FIG. 12 ) at which the first restrained plates  60  are restrained by the first restraining portions  62  and to a second position (a position illustrated in  FIG. 10 ) at which the first restrained plates  60  are not restrained by the first restraining portions  62 . 
     As illustrated in  FIGS. 5 and 6 , the second thrust mechanism  46  includes a second coil spring  64 , a first lower case  65 , and a second lower case  66 . The second coil spring  64  is an example of an urging member that imparts an urging force to the placement unit  33 . The first lower case  65  is an example of the first accommodation body that accommodates the second coil spring  64  of which one end in the axial direction is inserted into the first accommodation body. The second lower case  66  is an example of the second accommodation body that accommodates the second coil spring  64  of which the other end in the axial direction is inserted into the second accommodation body. Each of the first lower case  65  and the second lower case  66  is shaped like a closed-end cylinder with one end open and is elongated slightly more compared with each of the first upper case  52  and the second upper case  53 . 
     The first lower case  65  is rotatably attached to a cylindrically shaped second boss  67  in such a manner that the closed-end of the first lower case  65 , which is opposite to the open end, is attached by a second screw  68  to the second boss  67  disposed on the back side of the placement unit  33 . The second boss  67  and the second screw  68  are longer in length compared with the first boss  54  and the first screw  55 . The second lower case  66  is disposed such that a portion of the second lower case  66  overlaps the first lower case  65 . In other words, the open end of the first lower case  65  is inserted into the open end of the second lower case  66 . 
     An end of the second coil spring  64  in the axial direction thereof abuts the inside surface of the bottom wall of the first lower case  65 , whereas the other end of the second coil spring  64  in the axial direction abuts the inside surface of the bottom wall of the second lower case  66 . In this case, the second coil spring  64  is completely covered by the first lower case  65  and the second lower case  66 , and in this state, the second coil spring  64  continuously urges the first lower case  65  and the second lower case  66  in directions of separating from each other. Moreover in this case, compared with the first coil spring  51 , the second coil spring  64  is slightly longer in the axial direction and the urging force of the second coil spring  64  is larger. 
     A first lower elongated protrusion  69 , which is an example of the first engagement portion, is formed on the outer periphery of the first lower case  65  so as to extend in the urging direction of the second coil spring  64 . A second lower groove  70 , which is an example of the second engagement portion, is formed on the inner periphery of the second lower case  66  so as to extend in the urging direction of the second coil spring  64  and to be able to receive the first lower elongated protrusion  69 . 
     In the state in which the first lower case  65  is inserted in the second lower case  66  with the first lower elongated protrusion  69  being inserted in the second lower groove  70 , the first lower elongated protrusion  69  and the second lower groove  70  are slidable relative to each other in the urging direction of the second coil spring  64 , while the first lower elongated protrusion  69  and the second lower groove  70  engage each other in the circumferential direction of the first lower case  65  and the second lower case  66 . Accordingly, the first lower case  65  and the second lower case  66  are movable relative to each other in the urging direction of the second coil spring  64  and are rotatable together in the circumferential direction. 
     As illustrated in  FIGS. 6 and 8 , a first lower rotating protrusion  71  and a second lower rotating protrusion  72  are disposed on the outer periphery of the first lower case  65  at the end near the placement unit  33  so as to protrude in radial directions. The first lower rotating protrusion  71  and the second lower rotating protrusion  72  are examples of a protrusion. The first lower rotating protrusion  71  and the second lower rotating protrusion  72  are disposed so as to be separated from each other by an acute angle (e.g., 70 degrees) in the circumferential direction and to have a slight distance between each other in the axial direction of the first lower case  65 . The first lower rotating protrusion  71  and the second lower rotating protrusion  72  come into contact with the slide member  50 , which is moved in conjunction with movement of the edge guides  47 . The first lower rotating protrusion  71  and the second lower rotating protrusion  72  thereby cause the first lower case  65  to rotate. 
     A pair of second restrained plates  73 , which are examples of the restrained portion, are disposed on the outer periphery of the second lower case  66  at the end near the placement unit  33  so as to protrude in radial directions. A pair of the second restrained plates  73  are disposed on opposite sides of the second lower case  66  with the central axis of the second lower case  66  interposed therebetween. A pair of the second restrained plates  73  rotate together with the second lower case  66  in conjunction with rotation of the first lower case  65 . Note that as illustrated in  FIG. 10 , a second mortise  74  is provided at the end of the outer periphery of the second lower case  66  near the placement unit  33  in such a manner that the second lower rotating protrusion  72  of the first lower case  65  protrudes out of the second lower case  66  in a radial direction when the second lower case  66  covers the first lower case  65 . 
     As illustrated in  FIGS. 6, 7, and 8 , a pair of second restraining portions  75  are disposed on the back side of the placement unit  33  at positions straddling the second thrust mechanism  46  in the width direction Y. The second restraining portions  75  are examples of the restraining portion. Each of the second restraining portions  75  is formed as a plate shaped like a letter L and extends in the axial direction of the second coil spring  64 . Second restraining surfaces  76  are formed at respective base ends of the second restraining portions  75 . Rotation of the second lower case  66  can cause the second restraining surfaces  76  to engage the respective second restrained plates  73  in the axial direction of the second coil spring  64 . 
     Due to the rotation of a pair of the second restrained plates  73  in conjunction with rotation of the second lower case  66 , a pair of the second restrained plates  73  engage respective second restraining surfaces  76  of a pair of the second restraining portions  75  in the axial direction of the second coil spring  64 . As a result, the urging force of the second coil spring  64  restrains the first lower case  65  and the second lower case  66  from moving relative to each other in the axial direction of the second coil spring  64 . In other words, the second restrained plates  73  rotate together with the second lower case  66  in conjunction with rotation of the first lower case  65 , and thereby the second restrained plates  73  are displaced to a first position (a position illustrated in  FIG. 12 ) at which the second restrained plates  73  are restrained by the second restraining portions  75  and to a second position (a position illustrated in  FIG. 10 ) at which the second restrained plates  73  are not restrained by the second restraining portions  75 . 
     As illustrated in  FIGS. 8 and 9 , the slide member  50  has an upper projection  77  that is shaped like a block and disposed on the top side of the slide member  50  in an intermediate portion in the width direction Y. The slide member  50  also has a lower projection  78  that is shaped like a block and disposed on the bottom side thereof in an intermediate portion in the width direction Y. The upper projection  77  and the lower projection  78  are disposed with a spacing therebetween in the width direction Y. In other words, the upper projection  77  is disposed at a position closer to the base end  50   b  of the slide member  50  than the lower projection  78 , whereas the lower projection  78  is disposed at a position closer to the leading end  50   a  of the slide member  50  than the upper projection  77 . 
     Each of the upper projection  77  and the lower projection  78  has two side surfaces opposite to each other in the width direction Y. A side surface of the upper projection  77  near the leading end  50   a  is denoted by a first upper face  79 , whereas the other side surface of the upper projection  77  near the base end  50   b  is denoted by a second upper face  80 . A side surface of the lower projection  78  near the leading end  50   a  is denoted by a first lower face  81 , whereas the other side surface of the lower projection  78  near the base end  50   b  is denoted by a second lower face  82 . 
     As illustrated in  FIGS. 4 and 8 , when the slide member  50  moves in conjunction with movement of a pair of the edge guides  47  from positions that are furthest away from each other to positions that are closest to each other, the first lower face  81  is first brought into contact with the first lower rotating protrusion  71 , which causes the first lower rotating protrusion  71  to rotate. Subsequently, the first upper face  79  is brought into contact with the first upper rotating protrusion  58 , which causes the first upper rotating protrusion  58  to rotate. 
     On the other hand, when the slide member  50  moves in conjunction with movement of a pair of the edge guides  47  from positions that are closest to each other to positions that are furthest away from each other, the second upper face  80  is first brought into contact with the second upper rotating protrusion  59 , which causes the second upper rotating protrusion  59  to rotate. Subsequently, the second lower face  82  is brought into contact with the second lower rotating protrusion  72 , which causes the second lower rotating protrusion  72  to rotate. 
     As illustrated in  FIGS. 2 and 6 , an abutment plate  83  is fixed in the housing  38  at a position opposing the first thrust mechanism  45  and the second thrust mechanism  46  in the depth direction X. A first projection  84  that is shaped like a hemisphere is disposed at a center portion on the outside surface of the bottom wall of the second upper case  53  of the first thrust mechanism  45 . A second projection  85  that is shaped like a hemisphere is disposed at a center portion on the outside surface of the bottom wall of the second lower case  66  of the second thrust mechanism  46 . 
     As illustrated in  FIGS. 6 and 21 , the abutment plate  83  includes a first abutment surface  86  and a second abutment surface  87 , both of which are examples of an abutment portion and are formed as flat surfaces. When the first coil spring  51  imparts an urging force to the placement unit  33 , the first projection  84  of the second upper case  53  abuts the first abutment surface  86 . When the second coil spring  64  imparts an urging force to the placement unit  33 , the second projection  85  of the second lower case  66  abuts the second abutment surface  87 . In this case, the first projection  84 , which is shaped like a hemisphere, is a portion of the second upper case  53  that comes into contact with the first abutment surface  86 . The second projection  85 , which is shaped like a hemisphere, is a portion of the second lower case  66  that comes into contact with the second abutment surface  87 . 
     Next, operation of the first thrust mechanism  45  will be described with reference to  FIGS. 10 to 13 . Note that the slide member  50  illustrated in  FIGS. 10 to 13  are cross sections that are cut along line X,XI,XII,XIII-X,XI,XII,XIII in  FIG. 9 . As illustrated in  FIG. 10 , in the state in which a pair of the first restrained plates  60  of the second upper case  53  of the first thrust mechanism  45  do not engage respective first restraining surfaces  63  of a pair of the first restraining portions  62  in the axial direction of the first coil spring  51 , movement of the first upper case  52  and the second upper case  53  relative to each other in the axial direction of the first coil spring  51  is not restrained by the urging force of the first coil spring  51 . As a result, the urging force of the first coil spring  51  acts on the placement unit  33  due to the first projection  84  of the second upper case  53  abutting the first abutment surface  86 . In this case, the first upper rotating protrusion  58  stays at a position at which the first upper rotating protrusion  58  is ready to come into contact with the slide member  50 , whereas the second upper rotating protrusion  59  stays at a position away from the moving path of the slide member  50 . 
     Subsequently, if a pair of the edge guides  47  are moved in the direction to be closer to each other, the slide member  50  is caused to move in a first direction B that is parallel to the width direction Y. As a result, as illustrated in  FIG. 11 , the first upper face  79  of the upper projection  77  of the slide member  50  comes into contact with the first upper rotating protrusion  58  of the first upper case  52 . Further movement of the edge guides  47  in the direction of moving closer to each other causes the slide member  50  to move further in the first direction B. 
     As a result, as illustrated in  FIG. 12 , the first upper rotating protrusion  58 , the first upper case  52 , and the second upper case  53  rotate together in a forward direction. A pair of the first restrained plates  60  of the second upper case  53  are thereby rotated to the position at which the first restrained plates  60  engage the respective first restraining surfaces  63  of a pair of the first restraining portions  62  in the axial direction of the first coil spring  51 . The relative movement of the first upper case  52  and the second upper case  53  in the axial direction of the first coil spring  51  is thereby restrained due to the urging force of the first coil spring  51 . 
     As a result, the urging force of the first coil spring  51  does not act on the placement unit  33  irrespective of whether the first projection  84  of the second upper case  53  abuts the first abutment surface  86  or not. In this case, the first upper rotating protrusion  58  is rotated to a position away from the moving path of the slide member  50 , whereas the second upper rotating protrusion  59  is rotated to a position at which the second upper rotating protrusion  59  is ready to come into contact with the slide member  50 . 
     Subsequently, if a pair of the edge guides  47  are moved in the direction away from each other, the slide member  50  is caused to move in a second direction C that is opposite to the first direction B. As a result, as illustrated in  FIG. 13 , the second upper face  80  of the upper projection  77  of the slide member  50  comes into contact with the second upper rotating protrusion  59  of the first upper case  52 . Further movement of a pair of the edge guides  47  in the direction of moving away from each other causes the slide member  50  to move further in the second direction C. 
     As a result, as illustrated in  FIG. 10 , the second upper rotating protrusion  59 , the first upper case  52 , and the second upper case  53  rotate together in a backward direction that is opposite to the forward direction. A pair of the first restrained plates  60  of the second upper case  53  are thereby rotated to positions of not engaging the first restraining surfaces  63  of a pair of the first restraining portions  62  in the axial direction of the first coil spring  51 . As a result, the relative movement of the first upper case  52  and the second upper case  53  in the axial direction of the first coil spring  51  is not restrained by the urging force of the first coil spring  51 . 
     Accordingly, the first projection  84  of the second upper case  53  abuts the first abutment surface  86 , and thereby the urging force of the first coil spring  51  acts on the placement unit  33 . In this case, the first upper rotating protrusion  58  stays at a position at which the first upper rotating protrusion  58  is ready to come into contact with the slide member  50 , whereas the second upper rotating protrusion  59  stays at a position away from the moving path of the slide member  50 . 
     Note that operation of the second thrust mechanism  46  is the same as the operation of the first thrust mechanism  45  described above, and thus a repetitive description will be omitted. In other words, the description of operation of the second thrust mechanism  46  will be such that on the basis of the description of operation of the first thrust mechanism  45 , reference numerals of the members will be merely replaced with those provided in brackets in  FIGS. 10 to 13 . 
     Next, operation of the first thrust mechanism  45  and the second thrust mechanism  46  will be described in the case in which a pair of the edge guides  47  are moved from positions that are closest to each other to positions that are furthest away from each other. As illustrated in  FIGS. 6, 8, and 14 , when a pair of the edge guides  47  are closest to each other, the first restrained plates  60  of the second upper case  53  engage the first restraining portions  62  in the axial direction of the second upper case  53 , which restrains the second upper case  53  from moving in the axial direction thereof. As a result, the urging force of the first coil spring  51  does not act on the placement unit  33 . In other words, a push-up force by the first thrust mechanism  45  does not act on the placement unit  33 . 
     Similarly, the second restrained plates  73  of the second lower case  66  engage the second restraining portions  75  in the axial direction of the second lower case  66 , which restrains the second lower case  66  from moving in the axial direction thereof. As a result, the urging force of the second coil spring  64  does not act on the placement unit  33 . In other words, a push-up force by the second thrust mechanism  46  does not act on the placement unit  33 . 
     As illustrated  FIGS. 8 and 15 , movement of the edge guides  47  in the direction away from each other causes the second upper face  80  of the slide member  50  to abut the second upper rotating protrusion  59  and to start rotating the first restrained plates  60  together with the second upper rotating protrusion  59 . The first restrained plates  60  are caused to rotate counterclockwise when viewed from behind the placement unit  33 . 
     As illustrated in  FIGS. 8 and 16 , further movement of the edge guides  47  in the direction away from each other causes the first restrained plates  60  to rotate counterclockwise together with the second upper rotating protrusion  59  when viewed from behind the placement unit  33 . Consequently, the state of engagement between the first restrained plates  60  and the first restraining portions  62  in the axial direction of the second upper case  53  is terminated. 
     As a result, the urging force of the first coil spring  51  urges the second upper case  53  toward the first abutment surface  86 , which causes the first projection  84  of the second upper case  53  to abut the first abutment surface  86 . The urging force of the first coil spring  51  thereby acts on the placement unit  33 . In other words, the push-up force by the first thrust mechanism  45  acts on the placement unit  33 . 
     In this case, the placement unit  33  and the sheets P placed thereon are pushed up toward the feed roller  35  by the push-up force of the first thrust mechanism  45 . In this state, even if a pair of the edge guides  47  are moved in the direction away from each other, the first thrust mechanism  45  is not brought into contact with the slide member  50 . A pair of the edge guides  47  are thereby permitted to move in the direction away from each other. 
     On the other hand, in the state in which the placement unit  33  and the sheets P placed thereon are pushed up toward the feed roller  35  by the push-up force of the first thrust mechanism  45 , if a pair of the edge guides  47  are made to move in the direction closer to each other, the first upper face  79  of the slide member  50  abuts the first upper rotating protrusion  58 . As a result, the first restrained plates  60  are made to rotate clockwise together with the first upper rotating protrusion  58  when viewed from behind the placement unit  33 . 
     In this case, however, the first restrained plates  60  engage the first restraining portions  62  in this rotation direction (i.e., clockwise when viewed from behind the placement unit  33 ), and the first restraining portions  62  restrain the first restrained plates  60  from rotating further in this rotation direction. A pair of the edge guides  47  are thereby restrained from moving in the direction closer to each other. 
     Subsequently, movement of the edge guides  47  in the direction further away from each other, as illustrated  FIGS. 8 and 17 , causes the second lower face  82  of the slide member  50  to abut the second lower rotating protrusion  72  and to start rotating the second restrained plates  73  together with the second lower rotating protrusion  72 . The second restrained plates  73  are caused to rotate clockwise, when viewed from behind the placement unit  33 . 
     Further movement of the edge guides  47  in the direction away from each other, as illustrated in  FIGS. 8 and 18 , causes the second restrained plates  73  to rotate clockwise together with the second lower rotating protrusion  72  when viewed from behind the placement unit  33 . Consequently, the state of engagement between the second restrained plates  73  and the second restraining portions  75  in the axial direction of the second lower case  66  is terminated. 
     As a result, the urging force of the second coil spring  64  urges the second lower case  66  toward the second abutment surface  87 , which causes the second projection  85  of the second lower case  66  to abut the second abutment surface  87 . The urging force of the second coil spring  64  thereby acts on the placement unit  33 . In other words, a push-up force by the second thrust mechanism  46  acts on the placement unit  33 . 
     In this case, the placement unit  33  and the sheets P placed thereon are pushed up toward the feed roller  35  by the push-up force of the second thrust mechanism  46 . In this state, even if a pair of the edge guides  47  are moved in the direction away from each other, the second thrust mechanism  46  is not brought into contact with the slide member  50 . A pair of the edge guides  47  are thereby permitted to move in the direction away from each other. 
     On the other hand, in the state in which the placement unit  33  and the sheets P placed thereon are pushed up toward the feed roller  35  by the push-up force of the second thrust mechanism  46 , if a pair of the edge guides  47  are made to move in the direction closer to each other, the first lower face  81  of the slide member  50  abuts the first lower rotating protrusion  71 . As a result, the second restrained plates  73  are made to rotate counterclockwise together with the first lower rotating protrusion  71  when viewed from behind the placement unit  33 . 
     In this case, however, the second restrained plates  73  engage the second restraining portions  75  in this rotation direction (i.e., counterclockwise when viewed from behind the placement unit  33 ), and the second restraining portions  75  restrain the second restrained plates  73  from rotating further in this rotation direction. A pair of the edge guides  47  are thereby restrained from moving in the direction closer to each other. Subsequently, as illustrated in  FIG. 19 , further movement of a pair of the edge guides  47  in the direction away from each other causes a pair of the edge guides  47  to move to positions that are furthest away from each other. 
     When a pair of the edge guides  47  are moved from positions that are furthest away from each other to positions that are closest to each other, operation of the first thrust mechanism  45  and the second thrust mechanism  46  will be the reverse of the above described operation of the first thrust mechanism  45  and the second thrust mechanism  46  when a pair of the edge guides  47  are moved from the positions that are closest to each other to the positions that are furthest away from each other. 
     In the case in which a pair of the edge guides  47  are moved from the positions that are furthest away from each other to the positions that are closer to each other, the second thrust mechanism  46  restrains the urging force of the second coil spring  64  from acting on the placement unit  33  before the first thrust mechanism  45  restrains the urging force of the first coil spring  51  from acting on the placement unit  33 . 
     Note that when the placement unit  33  is at the standby position, a pair of the edge guides  47  move from the positions that are furthest away from each other to the positions that are closest to each other. As illustrated in  FIG. 25 , when the placement unit  33  is at the standby position, the first thrust mechanism  45  and the second thrust mechanism  46  are compressed by the abutment plate  83  against respective urging forces of the first coil spring  51  and the second coil spring  64 . In this state, the second upper case  53  of the first thrust mechanism  45  and the second lower case  66  of the second thrust mechanism  46  are maintained so as to be able to rotate freely. 
     As described above, in the present embodiment, the slide member  50  moves in conjunction with the movement of the edge guides  47  when the edge guides  47  are adjusted so as to fit the width of sheets P. In this process, the slide member  50  comes into contact with the first thrust mechanism  45  and with the second thrust mechanism  46  successively. In accordance with the position to which the slide member  50  has been moved, the first thrust mechanism  45  and the second thrust mechanism  46  selectively restrain the urging forces of the first coil spring  51  and the second coil spring  64  from acting on the placement unit  33 . 
     In other words, due to the slide member  50  coming into contact with the first thrust mechanism  45 , the first restrained plates  60  are caused to rotate to a first position at which the first restrained plates  60  engage the first restraining portions  62  in the axial direction of the second upper case  53 . As a result, the second upper case  53  is restrained from moving relative to the first upper case  52 , and the urging force of the first coil spring  51  is thereby restrained from acting on the placement unit  33 . 
     On the other hand, due to the slide member  50  coming into contact with the second thrust mechanism  46 , the second restrained plates  73  are caused to rotate to the first position at which the second restrained plates  73  engage the second restraining portions  75  in the axial direction of the second lower case  66 . As a result, the second lower case  66  is restrained from moving relative to the first lower case  65 , and the urging force of the second coil spring  64  is restrained from acting on the placement unit  33 . 
     When sheets P are placed on the placement unit  33 , a change in the length of the sheets P in the width direction Y affects the total weight of the sheets P. Accordingly, in a case in which the urging forces of only a pair of the torsion coil springs  43  urges the placement unit  33  and the sheets P placed thereon toward the feed roller  35 , the urging force may not be sufficient to provide the sheets P with an appropriate contact pressure against the feed roller  35 . Insufficient contact pressure of the sheets P against the feed roller  35  may lead to a problem that the feed roller  35  does not feed the sheets P properly. 
     According to the present embodiment, however, the first thrust mechanism  45  and the second thrust mechanism  46  can selectively impart the urging forces of the first coil spring  51  and the second coil spring  64  to the placement unit  33  in accordance with the distance between a pair of the edge guides  47  that corresponds to the length (in the width direction Y) of the sheets P placed on the placement unit  33 . 
     More specifically, when the size of sheets P placed on the placement unit  33  is large, the urging forces of a pair of the torsion coil springs  43  are backed by both of the urging forces of the first coil spring  51  of the first thrust mechanism  45  and the second coil spring  64  of the second thrust mechanism  46 . When the size of sheets P placed on the placement unit  33  is medium, the urging forces of a pair of the torsion coil springs  43  are backed only by the urging force of the first coil spring  51  of the first thrust mechanism  45 . When the size of sheets P placed on the placement unit  33  is small, the urging forces of a pair of the torsion coil springs  43  are not backed by the urging forces of the first coil spring  51  of the first thrust mechanism  45  and the second coil spring  64  of the second thrust mechanism  46 . 
     With this configuration, according to the present embodiment, even if the size of the sheets P placed on the placement unit  33  changes, the contact pressure of the sheets P against the feed roller  35  can be maintained appropriately simply by adjusting the distance between a pair of the edge guides  47  so as to fit the width of the sheets P. Excessively high contact pressure of the sheets P against the feed roller  35  may lead to a problem that for example, the feed roller  35  feeds two or more sheets P at a time in an overlapped state. 
     Moreover in the present embodiment, as illustrated in  FIG. 20 , if the number of the sheets P placed on the placement unit  33  is less than or equal to a predetermined number, the placement unit  33  is configured to be pushed up only by the urging forces of the torsion coil springs  43  even if the size of the sheets P is large. With this configuration, the first thrust mechanism  45  and the second thrust mechanism  46  are separated from the abutment plate  83  even though they are in operation, and the push-up forces of the first thrust mechanism  45  and the second thrust mechanism  46  stop acting on the placement unit  33 . 
     More specifically, in a case of large size sheets P of a basis weight of 80 g/m 2  being placed on the placement unit  33 , when the number of sheets P placed thereon becomes fifteen or less, the first thrust mechanism  45  and the second thrust mechanism  46  are configured to be separated from the abutment plate  83  even when they are in operation. This configuration is adopted because even if the size of the sheets P placed on the placement unit  33  are large, the total weight of the sheets P decreases as the number of the sheets P decreases, and when the number of the sheets P on the placement unit  33  becomes small, the contact pressure of the sheets P against the feed roller  35  becomes excessively high. 
     For example, as illustrated in  FIG. 21 , in a case in which thirty large size sheets P of a basis weight of 80 g/m 2  are placed on the placement unit  33 , the first thrust mechanism  45  and the second thrust mechanism  46  in operation abut the abutment plate  83 , and the respective push-up forces act on the placement unit  33 . 
     In the present embodiment, as illustrated in  FIG. 22 , if the number of the sheets P placed on the placement unit  33  is less than or equal to a predetermined number, the placement unit  33  is configured to be pushed up only by the urging forces of the torsion coil springs  43  even if the size of the sheets P is medium. With this configuration, the first thrust mechanism  45  in operation is separated from the abutment plate  83 , and the push-up force of the first thrust mechanism  45  stops acting on the placement unit  33 . In this case, the second thrust mechanism  46  does not operate. 
     For example, as illustrated in  FIG. 23 , in a case in which thirty medium size sheets P of a basis weight of 80 g/m 2  are placed on the placement unit  33 , the first thrust mechanism  45  in operation abuts the abutment plate  83 , and the push-up force thereof acts on the placement unit  33 . In this case, the second thrust mechanism  46  does not operate. 
     In the present embodiment, as illustrated in  FIG. 24 , if the size of the sheets P placed on the placement unit  33  is small, the placement unit  33  is pushed up only by the urging forces of the torsion coil springs  43 . In this case, the first thrust mechanism  45  and the second thrust mechanism  46  do not operate and are separated from the abutment plate  83 . Note that in the present embodiment, as illustrated in  FIG. 25 , when the placement unit  33  stays at the standby position, the first thrust mechanism  45  and the second thrust mechanism  46  do not operate and are in contact with the abutment plate  83 . 
     According to the embodiment described in detail above, the following advantageous effects can be provided. In the ink jet type printer  11 , the first coil spring  51  that imparts an urging force to the placement unit  33  is covered by the first upper case  52  and the second upper case  53 , whereas the second coil spring  64  that imparts an urging force to the placement unit  33  is covered by the first lower case  65  and the second lower case  66 . With this configuration, the first coil spring  51  and the second coil spring  64  can be protected. 
     The ink jet type printer  11  includes the torsion coil springs  43  that urge the placement unit  33  and the sheets P placed thereon toward the feed roller  35 . With this configuration, the urging forces imparted to the placement unit  33  can be set suitably to fit sheets P of a plurality of sizes. 
     The ink jet type printer  11  causes the first thrust mechanism  45  and the second thrust mechanism  46  selectively restrain the first coil spring  51  and the second coil spring  64  from imparting the urging forces to the placement unit  33  in accordance with the position to which the slide member  50  has been moved. With this configuration, a single slide member  50  can selectively restrain two thrust mechanisms  44  (i.e., the first thrust mechanism  45  and the second thrust mechanism  46 ) from functioning, which leads to a reduction in the number of parts. 
     In the ink jet type printer  11 , in the case in which a pair of the edge guides  47  are moved from the positions away from each other to the positions closer to each other, the second thrust mechanism  46 , which is one of the two thrust mechanisms  44  that is located further away from the pivot shafts  42  in the direction orthogonally intersecting the axial direction of the pivot shafts  42 , restrains of the second coil spring  64  from imparting the urging force to the placement unit  33  before the first thrust mechanism  45 , which is one of the thrust mechanisms  44  that is closer to the pivot shafts  42  in the direction orthogonally intersecting the axial direction of the pivot shafts  42 , restrains the first coil spring  51  from imparting the urging force to the placement unit  33 . With this configuration, when the first thrust mechanism  45  and the second thrust mechanism  46  push up the placement unit  33  and the sheets P placed thereon toward the feed roller  35 , the push-up forces can be adjusted appropriately in accordance with the size of the sheets P. 
     In the ink jet type printer  11 , the second coil spring  64  of the second thrust mechanism  46 , which is one of the two thrust mechanisms  44  that is located further away from the pivot shafts  42  in the direction orthogonally intersecting the axial direction of the pivot shafts  42 , provides a larger urging force than the first coil spring  51  of the first thrust mechanism  45 , which is one of the thrust mechanisms  44  that is closer to the pivot shafts  42  in the direction orthogonally intersecting the axial direction of the pivot shafts  42 . With this configuration, when the placement unit  33  is rotated around the pivot shafts  42 , the urging force of the second coil spring  64  in particular can be imparted to the placement unit  33  efficiently because of the leverage effect. 
     In the ink jet type printer  11 , the first projection  84  that is a portion of the second upper case  53  that comes into contact with the first abutment surface  86  is shaped like a hemisphere, and the second projection  85  that is a portion of the second lower case  66  that comes into contact with the second abutment surface  87  is also shaped like a hemisphere. With this configuration, even if respective contact angles of the first projection  84  and the second projection  85  against the first abutment surface  86  and the second abutment surface  87  change slightly, changes in the respective urging forces of the first coil spring  51  and the second coil spring  64  that act on the placement unit  33  can be suppressed. 
     In the ink jet type printer  11 , in the state in which the placement unit  33  and the sheets P placed thereon are pushed up toward the feed roller  35  by the push-up forces of the first thrust mechanism  45  and the second thrust mechanism  46 , a pair of the edge guides  47  are permitted to move in the direction away from each other. With this configuration, when a sheet P is jammed between a pair of the edge guides  47 , a pair of the edge guides  47  can be moved in the direction away from each other so that the jammed sheet P can be removed easily. 
     In the ink jet type printer  11 , in the state in which the placement unit  33  and the sheets P placed thereon are pushed up toward the feed roller  35  by the push-up forces of the first thrust mechanism  45  and the second thrust mechanism  46 , the first restraining portions  62  and the second restraining portions  75  restrain the first restrained plates  60  and the second restrained plates  73  from rotating, respectively, and a pair of the edge guides  47  are thereby restrained from moving in the direction closer to each other. With this configuration, after the second upper case  53  and the second lower case  66  move relative to the first upper case  52  and the first lower case  65 , respectively, the first restrained plates  60  and the second restrained plates  73  can be restrained from overlapping the first restraining portions  62  and the second restraining portions  75  in the relative movement direction. This restrains the second upper case  53  and the second lower case  66  from failing to return to the original positions before the relative movement. 
     In the ink jet type printer  11 , the first upper case  52  has the first upper elongated protrusion  56 , which extends in the urging direction of the first coil spring  51 , whereas the second upper case  53  has the second upper groove  57 , which extends in the urging direction of the first coil spring  51  and engages the first upper elongated protrusion  56 . In addition, the first lower case  65  has the first lower elongated protrusion  69 , which extends in the urging direction of the second coil spring  64 , whereas the second lower case  66  has the second lower groove  70 , which extends in the urging direction of the second coil spring  64  and engages the first lower elongated protrusion  69 . With this configuration, the second upper case  53  can move relative to the first upper case  52  in the urging direction of the first coil spring  51 , while the first upper case  52  and the second upper case  53  can rotate together in the rotation direction of the first upper rotating protrusion  58 . In addition, the second lower case  66  can move relative to the first lower case  65  in the urging direction of the second coil spring  64 , while the first lower case  65  and the second lower case  66  can rotate together in the rotation direction of the first lower rotating protrusion  71 . This restrains the first upper rotating protrusion  58  of the first upper case  52  from being shifted in phase in the rotation direction from the first restrained plates  60  of the second upper case  53 , and also restrains the first lower rotating protrusion  71  of the first lower case  65  from being shifted in phase in the rotation direction from the second restrained plates  73  of the second lower case  66 . 
     Modification Examples 
     Note that the embodiments described above may be modified as follows. The first upper case  52  and the first lower case  65  may be provided with the second upper groove  57  and the second lower groove  70 , respectively, while the second upper case  53  and the second lower case  66  may be provided with the first upper elongated protrusion  56  and the first lower elongated protrusion  69 . 
     The second upper groove  57  and the second lower groove  70  may be replaced with a first notch and a second notch that engage the first upper elongated protrusion  56  and the first lower elongated protrusion  69 , respectively. The second upper case  53  and the second lower case  66  may be provided with the first upper elongated protrusion  56  and the first lower elongated protrusion  69 , respectively, while the first upper case  52  and the first lower case  65  may be provided with a first notch and a second notch that engage the first upper elongated protrusion  56  and the first lower elongated protrusion  69 . 
     In the state in which the placement unit  33  and the sheets P placed thereon are pushed up toward the feed roller  35  by the first thrust mechanism  45  and the second thrust mechanism  46 , a pair of the edge guides  47  need not be restrained from moving in the direction closer to each other. 
     In the state in which the placement unit  33  and the sheets P placed thereon are pushed up toward the feed roller  35  by the first thrust mechanism  45  and the second thrust mechanism  46 , a pair of the edge guides  47  need not be permitted to move in the direction away from each other. 
     The first projection  84  that is a portion of the second upper case  53  that comes into contact with the first abutment surface  86  need not be shaped like a hemisphere, and the second projection  85  that is a portion of the second lower case  66  that comes into contact with the second abutment surface  87  need not be shaped like a hemisphere, either. 
     The second coil spring  64  of the second thrust mechanism  46  need not provide a larger urging force than the first coil spring  51  of the first thrust mechanism  45 . In the case in which a pair of the edge guides  47  are moved from the positions away from each other to the positions closer to each other, the second thrust mechanism  46  need not restrain the second coil spring  64  from imparting the urging force to the placement unit  33  before the first thrust mechanism  45  restrains the first coil spring  51  from imparting the urging force to the placement unit  33 . 
     Two slide members  50  may be provided in the placement unit  33  so as to engage the first thrust mechanism  45  and the second thrust mechanism  46 , and the two slide members  50  may selectively restrain the first coil spring  51  of the first thrust mechanism  45  and the second coil spring  64  of the second thrust mechanism  46  from imparting the urging forces to the placement unit  33  in accordance with respective positions to which the two slide members  50  have been moved. 
     The slide member  50  may be omitted. In this case, the edge guides  47  are configured to directly engage the first thrust mechanism  45  and the second thrust mechanism  46  and accordingly to have the same functions as the slide member  50 . 
     The entire disclosure of Japanese Patent Application No. 2018-035275, filed Feb. 28, 2018 is expressly incorporated by reference herein.