Patent Publication Number: US-8113506-B2

Title: Sheet supply apparatus and image forming apparatus

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The present invention relates to a sheet supply apparatus and an image forming apparatus. 
     A conventional sheet supply tray is provided in an image forming apparatus, and the conventional sheet supply tray includes a side guide member movably attached to a bottom plate thereof for guiding both of left and right edges or one edge of a print medium in a transportation direction according to a size of the print medium. The side guide member is arranged to be movable and fixed at a position corresponding to a width of a standard print medium such as the A4-size sheet and the A5-size sheet (refer to Patent Reference).
     Patent Reference: Japanese Patent Publication No. 2003-276868   

     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, a sheet supply apparatus is provided with a print medium storage device for storing a print medium. The print medium storage device includes a guide member for guiding the print medium thus stored; an engaging portion for engaging the guide member at a specific position; an engaged portion for engaging the engaging portion; an operation portion disposed to be movable for separating the engaging portion from the engaged portion; and an abutting portion for abutting against the operation portion to move the operation portion when the print medium storage device is situated at a first position, and for separating from the operation portion when the print medium storage device is situated at a second position. 
     According to a second aspect of the present invention, an image forming apparatus is provided with a sheet supply apparatus, and the sheet supply apparatus is provided with a print medium storage device for storing a print medium. The print medium storage device includes a guide member for guiding the print medium thus stored; an engaging portion for engaging the guide member at a specific position; an engaged portion for engaging the engaging portion; an operation portion disposed to be movable for separating the engaging portion from the engaged portion; and an abutting portion for abutting against the operation portion to move the operation portion when the print medium storage device is situated at a first position, and for separating from the operation portion when the print medium storage device is situated at a second position. 
     With the sheet supply apparatus of the present invention, it is possible to stably supply the print medium without paper jam even when the print medium thus stored has a variance in a width thereof. With the image forming apparatus of the present invention, it is possible to stably form an image without paper jam even when the print medium thus stored has a variance in a width thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional view showing a configuration of a printer according to a first embodiment of the present invention; 
         FIG. 2  is a perspective view showing a sheet supply tray according to the first embodiment of the present invention; 
         FIG. 3  is a bottom side view showing the sheet supply tray according to the first embodiment of the present invention; 
         FIG. 4  is a plan view showing the sheet supply tray according to the first embodiment of the present invention; 
         FIG. 5  is a schematic partially enlarged view of a portion A shown in  FIG. 4  showing a first engaging groove group and a second engaging groove group of the sheet supply tray according to the first embodiment of the present invention; 
         FIG. 6  is a schematic sectional view showing the first engaging groove group taken along a line  6 - 6  in  FIG. 5  according to the first embodiment of the present invention; 
         FIG. 7  is a schematic sectional view showing the second engaging groove group taken along a line  7 - 7  in  FIG. 5  according to the first embodiment of the present invention; 
         FIG. 8  is a perspective view showing an L-side sheet guide of the sheet supply tray according to the first embodiment of the present invention; 
         FIG. 9  is a side view showing the L-side sheet guide of the sheet supply tray according to the first embodiment of the present invention; 
         FIG. 10  is a schematic sectional view showing the L-side sheet guide of the sheet supply tray in a state that a second engaging claw engages the second engaging groove group taken along a line  10 - 10  in  FIG. 8  according to the first embodiment of the present invention; 
         FIG. 11  is a schematic sectional view showing the L-side sheet guide of the sheet supply tray in a state that the second engaging claw is disengaged from the second engaging groove group taken along the line  10 - 10  in  FIG. 8  according to the first embodiment of the present invention; 
         FIG. 12  is a schematic sectional view showing the L-side sheet guide of the sheet supply tray in another state that the second engaging claw is disengaged from the second engaging groove group taken along the line  10 - 10  in  FIG. 8  according to the first embodiment of the present invention; 
         FIGS. 13(   a ) and  13 ( b ) are schematic enlarged views showing the first engaging claw in a first state that the first engaging claw engages the first engaging groove group and a second state that the first engaging claw is disengaged from the first engaging groove group taken along a line  13 ( a )- 13 ( a ) in  FIG. 8  according to the first embodiment of the present invention; 
         FIGS. 13(   c ) and  13 ( d ) are schematic enlarged views showing the second engaging claw in a third state that the second engaging claw engages the second engaging groove group and a fourth state that the second engaging claw is disengaged from the second engaging groove group taken along a line  13 ( c )- 13 ( c ) in  FIG. 8  according to the first embodiment of the present invention; 
         FIG. 14  is a perspective view showing an expansion sheet supply apparatus according to the first embodiment of the present invention; 
         FIG. 15  is a sectional view showing the expansion sheet supply apparatus in a state that the sheet supply tray is inserted to the expansion sheet supply apparatus taken along a line  15 - 15  in  FIG. 14  according to the first embodiment of the present invention; 
         FIG. 16  is a sectional view showing the expansion sheet supply apparatus in another state that the sheet supply tray is inserted to the expansion sheet supply apparatus taken along the line  15 - 15  in  FIG. 14  according to the first embodiment of the present invention; 
         FIG. 17  is a sectional view showing the expansion sheet supply apparatus in a state that the sheet supply tray is attached to the expansion sheet supply apparatus taken along the line  15 - 15  in  FIG. 14  according to the first embodiment of the present invention; 
         FIG. 18  is a perspective view showing a modified example of the sheet supply tray according to the first embodiment of the present invention; 
         FIG. 19  is a side view showing the modified example of the sheet supply tray according to the first embodiment of the present invention; 
         FIG. 20  is a bottom side view showing a sheet supply tray according to a second embodiment of the present invention; 
         FIG. 21  is a schematic enlarged view of a portion G shown in  FIG. 20  showing the sheet supply tray according to the second embodiment of the present invention; 
         FIG. 22  is a schematic enlarged view showing a guide groove portion of the sheet supply tray according to the second embodiment of the present invention; 
         FIG. 23  is a plan view showing a sheet supply tray according to a third embodiment of the present invention; and 
         FIG. 24  is a schematic enlarged view of a portion H shown in  FIG. 23  showing the sheet supply tray according to the third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereunder, embodiments of the present invention will be explained with reference to the accompanying drawings. Note that the present invention is not limited to the embodiments, and the embodiments may be modified within scope of the present invention. 
     First Embodiment 
     A first embodiment of the present invention will be explained. First, a printer  400  as an image forming apparatus will be explained. The printer  400  is provided with a sheet supply tray  101  as a print medium storage device. The sheet supply tray  101  and an expansion sheet supply apparatus  103  will be explained. The sheet supply tray  101  is detachably attached to the expansion sheet supply apparatus  103 . 
       FIG. 1  is a schematic sectional view showing a configuration of the printer  400  according to the first embodiment of the present invention. The printer  400  may be a color printer of an electro-photography type, and is capable of printing an image on a print medium according to print data input thereto. 
     In the embodiment, the printer  400  includes the sheet supply tray  101  as the print medium storage device for placing a sheet P as the print medium; the expansion sheet supply apparatus  103  to which the sheet supply tray  101  is detachably attached; a sheet supply roller  401  for transporting the sheet P in an arrow direction X; a hopper  402  for pressing the sheet P against the sheet supply roller  401 ; transport rollers  403 L and  403 U for correcting skew of the sheet P and transporting the sheet P to an image forming unit  404 ; the image forming unit  404  for forming a developer image according to the print data thus input; a fixing unit  407  for heating and pressing the developer image on the sheet P formed with the image forming unit  404  to fix the developer image; a discharge roller  408  for discharging the sheet P to a medium discharge portion  409  after the sheet P passes through the fixing unit  407 ; the medium discharge portion  409  for discharging the sheet P to outside the printer  400 ; a medium stacker  410  for placing the sheet P discharged from the medium discharge portion  409 ; and a sheet transportation path S formed in an S character shape relative to a lower frame of the printer  400 . 
     In the embodiment, the sheet supply tray  101  stores the sheet P therein in a stacked state, and is detachably attached to a lower portion of the printer  400 . The sheet supply roller  401  is disposed at an upper portion of the sheet supply tray  101  for separating and picking up the sheet P one by one. Further, the sheet supply tray  101  is detachably attached to the expansion sheet supply apparatus  103  functioning as an adapter of the sheet supply tray  101  with respect to the printer  400 . Note that the sheet supply tray  101  and the expansion sheet supply apparatus  103  will be explained in more detail later. 
     In the embodiment, a drive source (not shown) drives the sheet supply roller  401  to rotate, so that the sheet supply roller  401  transports the sheet P picked up from the sheet supply tray  101  to the transport rollers  403 L and  403 U. The hopper  402  is provided with an urging member (not shown) for pressing the sheet P against the sheet supply roller  401 . 
     In the embodiment, the transport rollers  403 L and  403 U are provided for correcting skew of the sheet P. Further, a drive source (not shown) drives the transport rollers  403 L and  403 U to rotate, so that the transport rollers  403 L and  403 U transport the sheet P to the image forming unit  404 . 
     In the embodiment, the image forming unit  404  includes developing portions  405  for developing with developer corresponding to four colors, i.e., black, yellow, magenta, and cyan, so that the developer image is formed according to the print data thus input. The developing portions  405  are detachably attached to the printer  400  along the sheet transportation path S. After the developing portions  405  form the developer image, transfer units  406  transfer the developer image to the sheet P. 
     In the embodiment, after the developer image is transferred to the sheet P, the fixing unit  407  applies heat and pressure to the sheet P when the sheet P passes through a nip portion between a heating roller  407   a  and a fixing belt  407   b , so that the developer image is fixed to the sheet P. 
     In the embodiment, after the sheet P passes through the fixing unit  407 , a drive source (not shown) drives the discharge roller  408  to rotate, so that the discharge roller  408  transports the sheet P to the medium discharge portion  409 . The medium discharge portion  409  includes a plurality of rollers and a guide member, and discharges the sheet P to the medium stacker  410  after the sheet P passes through the fixing unit  407 . The medium stacker  410  is formed of a housing outer surface of the printer  400  for placing the sheet P discharged from the medium discharge portion  409 . 
     In addition to the components described above, the printer  400  further includes a print control unit having a microprocessor, an ROM (Read Only Memory), an RAM (Random Access Memory), an input/output port, a timer, and the likes; an interface control unit for receiving the print data and a control command and controlling an entire sequence of the printer  400  to perform a printing operation; a display unit having a display unit such as an LCD (Liquid Crystal Display) for displaying a state of the printer  400 ; an operation unit having an input device such as a touch panel for inputting an instruction from an operator; various sensors such as a temperature/humidity sensor, a density sensor, and the likes for monitoring an operation state of the printer  400 ; a head drive control unit for controlling drive of a print head portion (not shown); a temperature control unit for controlling a temperature of the fixing unit  407 ; a sheet transport motor control unit for controlling a drive motor as a drive source for rotating the various rollers to transport the sheet P; a drive control unit for controlling a drive motor to rotate the rollers disposed in the developing portions  405 ; and various power sources for applying voltages to the rollers. 
     With the configuration described above, the printer  400  is capable of forming an image on the sheet P according to the print data input thereto. 
     Next, the sheet supply tray  101  and the expansion sheet supply apparatus  103  to which the sheet supply tray  101  is detachably attached will be explained.  FIG. 2  is a perspective view showing the sheet supply tray  101  according to the first embodiment of the present invention.  FIG. 3  is a bottom side view showing the sheet supply tray  101  according to the first embodiment of the present invention.  FIG. 4  is a plan view showing the sheet supply tray  101  according to the first embodiment of the present invention. 
     As shown in  FIGS. 2 to 4 , the sheet supply tray  101  includes an L-side (left side) sheet guide  104 ; an R-side (right side) sheet guide  105 ; side guide slide grooves  106 ; an L-side rack  107 ; an R-side rack  108 ; a pinion gear  109 ; a tail guide  110 ; and a tail guide slide groove  111 . 
     As shown in  FIG. 2 , the sheet supply tray  101  has a box shape with an upper opening portion, and is configured to be detachable relative to the expansion sheet supply apparatus  103  (described later). The L-side sheet guide  104  and the R-side sheet guide  105  are disposed inside the sheet supply tray  101  as guide members formed of a plastic for aligning the sheet P at a position in a width direction thereof perpendicular to a transportation direction of the sheet P. The L-side sheet guide  104  and the R-side sheet guide  105  are fitted in the side guide slide grooves  106  formed in a backside surface of the sheet supply tray  101  and extending in a direction perpendicular to the transportation direction of the sheet P. 
     In the embodiment, the L-side rack  107  is attached to the L-side sheet guide  104 , and the R-side rack  108  is attached to the R-side sheet guide  105 . The pinion gear  109  connects the L-side rack  107  and the R-side rack  108 . The tail guide  110  is fitted in the tail guide slide groove  111  formed at a rear end portion of the sheet supply tray  101  in the transportation direction of the sheet P for aligning a trailing edge of the sheet P. A sheet separation member  112  having a roller shape formed of a rubber is disposed at a position facing the sheet supply roller  401 . 
     As shown in  FIG. 4 , engaging groove groups are formed in a bottom surface portion of the sheet supply tray  101  as engaged portions for engaging the L-side sheet guide  104 . The engaging groove groups includes two types of engaging groups two of each type disposed in two rows, thereby totaling four rows. More specifically, second engaging groove groups  114  are disposed on both sides of the side guide slide groove  106  in a direction perpendicular to a direction that the side guide slide groove  106  extends, and first engaging groups  113  are disposed outside the second engaging groove groups  114 . 
       FIG. 5  is a schematic partially enlarged view of a portion A shown in  FIG. 4  showing the first engaging groove group  114  and the second engaging groove group  113  of the sheet supply tray  101  according to the first embodiment of the present invention. 
     As shown in  FIG. 5 , the first engaging group  113  includes an A4-size sheet groove  115  for engaging the L-side sheet guide  104  at a position such that the L-side sheet guide  104  and the R-side sheet guide  105  contact with side edges of a sheet having the A4-size. Similarly, the first engaging group  113  includes a letter size sheet groove  116  for engaging the L-side sheet guide  104  at a position such that the L-side sheet guide  104  and the R-side sheet guide  105  contact with side edges of a sheet having a letter size. Further, the first engaging group  113  includes first irregular size grooves  117  with a pitch t in between at positions corresponding to irregular sizes of the sheet P other than the standard size such as the A4-size and the letter size. 
     In the embodiment, the pitch t is set to 1 mm. The second engaging group  114  includes second irregular size grooves  118  situated away from the first engaging group  113  by a half of the pitch t (½t=0.5 mm) in a width direction of the sheet P. 
     In the embodiment, the second engaging groove group  114  is situated away from the first engaging group  113  by a half of the smallest pitch t of the first engaging group  113 . When a plurality of engaging claws and a plurality of engaging groove groups are provided in an n number of stages, i.e., an n-stage system, an n-th engaging groove group may be situated away from the first engaging groups  113  by a 1/n of the smallest pitch of the first engaging groups  113 , thereby making it possible to set the L-side sheet guide  104  with a fine pitch. The pitch may be adjustable, and is not limited to 1/n. 
       FIG. 6  is a schematic sectional view showing the first engaging groove group  113  taken along a line  6 - 6  in  FIG. 5  according to the first embodiment of the present invention.  FIG. 7  is a schematic sectional view showing the second engaging groove group  114  taken along a line  7 - 7  in  FIG. 5  according to the first embodiment of the present invention. 
     In the embodiment, the A4-size sheet groove  115  and the letter size sheet groove  116  of the first engaging group  113  for the standard size sheet have a depth greater than that of the first irregular size grooves  117  of the first engaging group  113  and the second irregular size grooves  118  of the second engaging groove group  114 . Accordingly, it is easy to guide the L-side sheet guide  104  at the position for the standard size sheet. 
     Further, when the A4-size sheet groove  115  and the letter size sheet groove  116  for the standard size sheet have a greater depth, it is possible to securely position the L-side sheet guide  104  at the position for the standard size sheet used more frequently. Note that the R-side sheet guide  105  moves along with the L-side sheet guide  104  through the L-side rack  107 , the pinion gear  109 , and the R-side rack  108 . Accordingly, the engaging groove group is not formed on the R (right) side of the sheet supply tray  101 . 
     A configuration of the L-side sheet guide  104  will be explained next.  FIG. 8  is a perspective view showing the L-side sheet guide  104  of the sheet supply tray  101  according to the first embodiment of the present invention.  FIG. 9  is a side view showing the L-side sheet guide  104  of the sheet supply tray  101  according to the first embodiment of the present invention. 
     As shown in  FIGS. 8 and 9 , the L-side sheet guide  104  includes a lock release lever  119  as a first operation portion; a lock release lever rotational shaft  120  (described later); hanging pins  121 ; fixing portions  122 ; first engaging claws  123  as an engaging portion for engaging the first engaging groups  113 ; second engaging claws  124  as an engaging portion for engaging the second engaging groove groups  114 ; a first engaging claw pushing spring  125 ; a pushing spring holding portion  126 ; a second engaging claw pushing spring  127 ; a lock release bar  128  as a second operation portion; a rotational shaft  129 ; a pushing portion  130 ; a bar pushing portion  131 ; and a claw position fixing groove  132 . 
     In the embodiment, when the lock release lever  119  is griped or pushed in an arrow direction P in  FIG. 8 , it is possible to disengage the first engaging claws  123  and the second engaging claws  124  from the first engaging groups  113  and the second engaging groove groups  114 , respectively, so that the L-side sheet guide  104  can move to a specific position. When the lock release lever  119  is released and returns to an original position, the first engaging claws  123  and the second engaging claws  124  engage the first engaging groups  113  and the second engaging groove groups  114 , respectively. 
     In the embodiment, the lock release lever  119  is formed of a material capable of deforming elastically such as polypropylene and the likes, and is attached to the lock release lever rotational shaft  120  provided on the L-side sheet guide  104 . The hanging pin  121  formed of a metal bar member is fitted into the lock release lever  119 . The fixing portions  122  are disposed on one end portion of the hanging pins  121  to prevent the first engaging claws  123  from being disengaged when the lock release lever  119  is griped. 
     In the embodiment, each of the first engaging claws  123  is formed of a plate member having an H character shape, and has a lower end portion having a sharp claw shape. Long holes  123   a  and  123   b  are formed in upper portions of the first engaging claws  123 , so that the first engaging claws  123  are attached to the hanging pins  121  in a hanging state. The first engaging claw pushing spring  125  is disposed at an upper center portion of the first engaging claws  123  for engaging the first engaging claws  123  with the first engaging groups  113 . The pushing spring holding portion  126  is formed as a part of the L-side sheet guide  104  above the first engaging claw pushing spring  125  for fixing the first engaging claw pushing spring  125 . 
     Similar to the first engaging claws  123 , each of the second engaging claws  124  is formed of a plate member having an H character shape, and has a lower end portion having a sharp claw shape. Long holes  124   a  and  124   b  are formed in upper portions of the second engaging claws  124 , so that the second engaging claws  124  are attached to the hanging pins  121  in a hanging state. The second engaging claw pushing spring  127  is disposed at an upper center portion of the second engaging claws  124  for engaging the second engaging claws  124  with the second engaging groove groups  114 . The pushing spring holding portion  126  is disposed above the second engaging claw pushing spring  127  for fixing the second engaging claw pushing spring  127 . The first engaging claws  123  and the second engaging claws  124  are arranged linearly in a direction in parallel to the transportation direction of the sheet P. 
     In the embodiment, when the lock release bar  128  rotates, it is possible to disengage the first engaging claws  123  and the second engaging claws  124  from the first engaging groups  113  and the second engaging groove groups  114 , respectively, so that the L-side sheet guide  104  can move to a specific position. When the lock release bar  128  is released and returns to an original position, the first engaging claws  123  and the second engaging claws  124  engage the first engaging groups  113  and the second engaging groove groups  114 , respectively. 
     The lock release bar  128  is disposed to be rotatable around the rotational shaft  129 . Further, the lock release bar  128  includes the pushing portion  130  at one end portion thereof, i.e., a position where the pushing portion  130  abuts against lower center portions of the first engaging claws  123  and the second engaging claws  124 , and the bar pushing portion  131  having a gentle slope shape at the other end portion thereof. 
     In the embodiment, the claw position fixing groove  132  has a claw width the same as that of the first engaging claws  123  and the second engaging claws  124 . Further, the claw position fixing groove  132  is disposed at a lower portion of the L-side sheet guide  104 , so that the first engaging claws  123  and the second engaging claws  124  do not move in a direction perpendicular to the transportation direction of the sheet P. 
       FIG. 10  is a schematic sectional view showing the L-side sheet guide  104  of the sheet supply tray  101  in a state that the second engaging claw  124  engages the second engaging groove group  114  taken along a line  10 - 10  in  FIG. 8  according to the first embodiment of the present invention. As shown in  FIG. 10 , the second engaging claw  124  engages the second engaging groove group  114 , so that the L-side sheet guide  104  is fixed. 
       FIG. 11  is a schematic sectional view showing the L-side sheet guide  104  of the sheet supply tray  101  in a state that the second engaging claw  124  is disengaged from the second engaging groove group  114  taken along the line  10 - 10  in  FIG. 8  according to the first embodiment of the present invention. As shown in  FIG. 11 , when the second engaging claw  124  is disengaged from the second engaging groove group  114 , it is possible to move the L-side sheet guide  104  to a specific position. 
       FIG. 12  is a schematic sectional view showing the L-side sheet guide  104  of the sheet supply tray  101  in another state that the second engaging claw  124  is disengaged from the second engaging groove group  114  taken along the line  10 - 10  in  FIG. 8  according to the first embodiment of the present invention. As shown in  FIG. 12 , when the lock release lever  119  is gripped or pushed in the arrow direction P in  FIG. 8 , it is possible to disengage the second engaging claws  124  from the second engaging groove groups  114 , so that the L-side sheet guide  104  can move to a specific position. When the lock release lever  119  is released and returns to an original position, the first engaging claws  123  and the second engaging claws  124  engage the first engaging groups  113  and the second engaging groove groups  114 , respectively. 
       FIGS. 13(   a ) and  13 ( b ) are schematic enlarged views showing the first engaging claw  123  in a first state that the first engaging claw  123  engages the A4-size sheet groove  115  of the first engaging groove group  113  and a second state that the first engaging claw  123  is engaged from the A4-size sheet groove  115  of the first engaging groove group  113  taken along a line  13 ( a )- 13 ( a ) in  FIG. 8  according to the first embodiment of the present invention. 
       FIGS. 13(   c ) and  13 ( d ) are schematic enlarged views showing the second engaging claw  124  in a third state that the second engaging claw  124  engages the second irregular size grooves  118  of the second engaging groove group  114  and a fourth state that the second engaging claw  124  is disengaged from the second irregular size grooves  118  of the second engaging groove group  114  taken along a line  13 ( c )- 13 ( c ) in  FIG. 8  according to the first embodiment of the present invention. 
     As shown in  FIGS. 13(   a ) to  13 ( d ), when the first engaging claws  123  engages the A4-size sheet groove  115 , the second engaging claw  124  doe not engage the second irregular size grooves  118 . On the other hand, when the second engaging claws  124  engages the second irregular size grooves  118 , the first engaging claw  123  does not engage the A4-size sheet groove  115 . As described above, the first engaging group  113  is disposed away from the second engaging groove group  114  by ½ t in the width direction of the sheet P. Accordingly, the first engaging claws  123  and the second engaging claws  124  arranged linearly do not engage simultaneously in the direction in parallel to the transportation direction of the sheet P. 
     Next, the expansion sheet supply apparatus  103  to which the sheet supply tray  101  is detachably attached will be explained with reference to  FIGS. 13 to 17 .  FIG. 14  is a perspective view showing the expansion sheet supply apparatus  103  according to the first embodiment of the present invention.  FIG. 15  is a sectional view showing the expansion sheet supply apparatus  103  in a state that the sheet supply tray  101  is inserted to the expansion sheet supply apparatus  103  taken along a line  15 - 15  in  FIG. 14  according to the first embodiment of the present invention. 
       FIG. 16  is a sectional view showing the expansion sheet supply apparatus  103  in another state that the sheet supply tray  101  is inserted to the expansion sheet supply apparatus  103  taken along the line  15 - 15  in  FIG. 14  according to the first embodiment of the present invention.  FIG. 17  is a sectional view showing the expansion sheet supply apparatus  103  in a state that the sheet supply tray  101  is attached to the expansion sheet supply apparatus  103  taken along the line  15 - 15  in  FIG. 14  according to the first embodiment of the present invention. 
     As shown in  FIGS. 14 and 15 , the expansion sheet supply apparatus  103  has a pushing member  133  as an abutting portion having a protruded shape with a gentle slope. The pushing member  133  is situated at a position to contact with the lock release bar  128  when the sheet supply tray  101  is inserted into the expansion sheet supply apparatus  103 . The pushing member  133  extends in a direction perpendicular to the transportation direction of the sheet P, and has a lateral length corresponding to a moving range of the L-side sheet guide  104  in a width direction thereof. 
     In the embodiment, the pushing member  133  has a longitudinal length corresponding to a half of the moving range of the L-side sheet guide  104  in a longitudinal direction thereof. When it is necessary to release the engagement for placing a sheet having a specific size, it is sufficient that the L-side sheet guide  104  is fixed at a position corresponding to a width of the sheet. 
     As shown in  FIGS. 15 to 17 , when the sheet supply tray  101  is inserted into the expansion sheet supply apparatus  103 , the pushing member  133  contacts with the lock release bar  128 . When the sheet supply tray  101  is completely attached to the expansion sheet supply apparatus  103 , the pushing member  133  does not contact with the lock release bar  128 . 
     In the embodiment, the lock release bar  128  is configured to push up the pushing portion  130  by 4.5 mm when the pushing member  133  pushes down the bar pushing portion  131  by 5.5 mm. Note that a position of the sheet supply tray  101  where the pushing member  133  pushes down the lock release bar  128  is a first position, and a position of the sheet supply tray  101  when the sheet supply tray  101  is completely inserted is a second position. 
     A printing operation of the printer  400  having the sheet supply tray  101  and the expansion sheet supply apparatus  103  described above will be explained next. 
     According to a print instruction from the print control unit (not shown), when the drive source (not shown) drives the sheet supply roller  401  to rotate, the hopper  402  pushes up the sheet P from the sheet supply tray  101 , so that the sheet supply roller  401  transports the sheet P to the transport roller  403 L. At this moment, even when a plurality of sheets is picked up due to friction between the sheets, the sheet separation member  112  separates the sheets, so that it is possible to transport the sheet P one by one. 
     When the sheet supply roller  401  transports the sheet P, the transport rollers  403 L and  403 U transport the sheet P along the transportations path S to the image forming unit  404  while correcting skew of the sheet P. Then, the image forming unit  404  forms the developer image on the sheet P according to the print data input thereto. After the developer image is formed on the sheet P, the sheet P is transported to the fixing unit  407 . 
     When the sheet P is transported to the fixing unit  407 , the fixing unit  407  applies heat and pressure to the sheet P when the sheet P passes through the nip portion between the heating roller  407   a  and the fixing belt  407   b , so that the developer image is fixed to the sheet P. 
     After the sheet P passes through the fixing unit  407 , the sheet P is transported to the discharge roller  408 . The drive source (not shown) drives the discharge roller  408  to rotate, so that the discharge roller  408  transports the sheet P to the medium discharge portion  409 . Then, the medium discharge portion  409  discharges the sheet P to the medium stacker  410 , thereby completing the printing operation of the printer  400 . 
     An operation of the sheet supply tray  101  and the expansion sheet supply apparatus  103  will be explained next. First, an operation of setting the sheet P in the sheet supply tray  101  will be explained. 
     When the sheet P is set in the sheet supply tray  101 , first, the sheet supply tray  101  is detached from the expansion sheet supply apparatus  103 . Then, the L-side sheet guide  104  and the R-side sheet guide  105  move along the side guide slide grooves  106  according to the size of the sheet P. At this moment, the L-side rack  107  fixed to the L-side sheet guide  104  is connected to the R-side rack  108  fixed to the R-side sheet guide  105 . Accordingly, the R-side sheet guide  105  moves together with the L-side sheet guide  104 . 
     In the embodiment, the lock release lever  119  is gripped or pushed in the arrow direction P in  FIG. 8 , so that the second engaging claws  124  are disengaged from the second engaging groove groups  114  to move the L-side sheet guide  104 . At this moment, as shown in  FIG. 10 , the lock release lever  119  elastically deforms at a portion C and a portion D around the lock release lever rotational shaft  120 , so that the hanging pins  121  fixed to the lock release lever  119  move vertically. When the hanging pins  121  move upward, the hanging pins  121  contact upper portions of the long holes  123   a  and  123   b  formed in the first engaging claws  123 , thereby lifting the first engaging claws  123 . Similar to the first engaging claws  123 , the second engaging claws  124  are lifted as well. 
     When the first engaging claws  123  and the second engaging claws  124  are lifted, the first engaging claws  123  are disengaged from the first engaging groups  113 , and the second engaging claws  124  are disengaged from the second engaging groove groups  114 . While maintaining the state, the L-side sheet guide  104  and the R-side sheet guide  105  move to the positions corresponding to the size of the sheet P, and the lock release lever  119  is released when the distance between the L-side sheet guide  104  and the R-side sheet guide  105  becomes equal to the width of the sheet P. 
     When the lock release lever  119  is released and the elastic deformation at the portion C and the portion D returns to an original state, the hanging pins  121  fixed to the lock release lever  119  move downward. Accordingly, the first engaging claws  123  and the second engaging claws  124  engage the first engaging groups  113  and the second engaging groove groups  114 , respectively. At this moment, the hanging pins  121  do not contact upper portions of the long holes  123   a ,  123   b ,  124   a , and  124   b . Accordingly, when the lock release lever  119  is released, the first engaging claws  123  and the second engaging claws  124  do not move. 
     An operation of setting the sheet supply tray  101  to the expansion sheet supply apparatus  103  will be explained next.  FIG. 15  is a sectional view showing the expansion sheet supply apparatus  103  in a state that the sheet supply tray  101  is inserted to the expansion sheet supply apparatus  103  taken along a line  15 - 15  in  FIG. 14  according to the first embodiment of the present invention. In the state shown in  FIG. 15 , the lock release bar  128  is situated at a front position relative to a position F where the lock release bar  128  contacts with the pushing member  133 . 
       FIG. 16  is a sectional view showing the expansion sheet supply apparatus  103  in another state that the sheet supply tray  101  is inserted to the expansion sheet supply apparatus  103  taken along the line  15 - 15  in  FIG. 14  according to the first embodiment of the present invention. In the state shown in  FIG. 16 , the lock release bar  128  contacts with the pushing member  133 . 
       FIG. 17  is a sectional view showing the expansion sheet supply apparatus  103  in a state that the sheet supply tray is attached to the expansion sheet supply apparatus taken along the line  15 - 15  in  FIG. 14  according to the first embodiment of the present invention. In the state shown in  FIG. 17 , the lock release bar  128  is situated at a rear position relative to the position F where the lock release bar  128  contacts with the pushing member  133 . 
     The state shown in  FIG. 13(   a ), in which the first engaging claws  123  engage the first engaging groups  113 , will be explained. When the hanging pins  121  move downward, the first engaging claw pushing spring  125  pushes down the first engaging claws  123 . In this case, the first engaging claws  123  engage the A4-size sheet grooves  115  of the first engaging groups  113 . At this moment, the second engaging claw pushing spring  127  pushes down the second engaging claws  124  as well. As described above, the first engaging groups  113  are disposed away from the second engaging groove groups  114  by the distance ½ t. Accordingly, when the first engaging claws  123  engage the first engaging groups  113 , the second engaging claws  124  does not fit in and engage the second engaging groove groups  114 . 
     In the state described above, the sheet P is set in the sheet supply tray  101 , and the sheet supply tray  101  is inserted into the expansion sheet supply apparatus  103  as shown in  FIG. 15 . Then, as shown in  FIG. 16 , the sheet supply tray  101  is inserted further into the expansion sheet supply apparatus  103 , and the lock release bar  128  contacts with the pushing member  133  at the position F, so that the bar pushing portion  131  is pushed down. At this moment, the lock release bar  128  rotates around the rotational shaft  129 , so that the pushing portion  130  rotates upward. Accordingly, the pushing portion  130  pushes up the center portions of the first engaging claws  123  and the second engaging claws  124 , thereby disengaging the L-side sheet guide  104 . 
     In this state, when the distance between the surfaces of the L-side sheet guide  104  and the R-side sheet guide  105  contacting with the edges of the sheet P is smaller than the width of the sheet P, the L-side sheet guide  104  and the R-side sheet guide  105  are pushed sideway in the width direction of the sheet P due to rigidity of the sheet P. Accordingly, the L-side sheet guide  104  automatically moves according to the width of the sheet P until the L-side sheet guide  104  is situated at an appropriate position by an interval of the distance ½ t. As described above, the L-side rack  107  fixed to the L-side sheet guide  104  is connected to the R-side rack  108  fixed to the R-side sheet guide  105  through the pinion gear  109 . Accordingly, when the L-side sheet guide  104  moves, the R-side sheet guide  105  moves as well. 
     When the lock release bar  128  passes the position F as shown in  FIG. 17  to become the state shown in  FIG. 13(   b ), the first engaging claw pushing spring  125  pushes down the first engaging claws  123 , and the second engaging claw pushing spring  127  pushes down the second engaging claws  124 . Accordingly, ones of the first engaging claws  123  and the second engaging claws  124  engage the first engaging groups  113  or the second engaging groove groups  114 , thereby completing the operation of setting the sheet P in the sheet supply tray  101 . 
     As described above, in the embodiment, the standard size includes the A-4 size and the letter size. When the first engaging claws  123  and the second engaging claws  124  are provided according to other sizes of the sheet P, it is possible to apply the configuration to other standard sizes. 
     Further, as described above, in the embodiment, when the lock release bar  128  contacts with the pushing member  133 , the first engaging claws  123  and the second engaging claws  124  are lifted and disengaged from the first engaging groups  113  and the second engaging groove groups  114 , respectively. The present invention is not limited to the embodiment, and may be modified. 
       FIG. 18  is a perspective view showing a modified example of a sheet supply tray  101 ′ according to the first embodiment of the present invention.  FIG. 19  is a side view showing the modified example of the sheet supply tray  101 ′ according to the first embodiment of the present invention. 
     As shown in  FIGS. 18 and 19 , in the modified example, a grip portion of a lock lease lever  128 ′ partially extends in a height direction thereof. When the sheet supply tray  101 ′ is set to an expansion sheet supply apparatus  103 ′, the grip portion contact with a pushing member  133 ′ disposed on the expansion sheet supply apparatus  103 ′. The lock lease lever  128 ′ has an inclined portion  128 ′ a  at a distal end portion thereof. The inclined portion  128 ′ a  is bent in a direction the same as that the lock lease lever  128 ′ moves upon being gripped. 
     With the configuration described above, when the sheet supply tray  101 ′ is set to the expansion sheet supply apparatus  103 ′, the inclined portion  128 ′ a  of the lock lease lever  128 ′ contacts with the pushing member  133 ′. Accordingly, the lock lease lever  128 ′ moves in an inclined direction of the inclined portion  128 ′ a , i.e., the direction that the lock lease lever  128 ′ is gripped with a finger. As a result, similar to the case that the lock lease lever  128 ′ is gripped, first engaging claws  123 ′ and second engaging claws  124 ′ are lifted and disengaged. Accordingly, in the modified example, it is possible to obtain an effect similar to that in the first embodiment while reducing a number of parts. 
     In the embodiment described above, the expansion sheet supply apparatus  103  is explained as an example of the sheet supply apparatus, and the sheet supply apparatus may be applied to a sheet supply apparatus disposed in a main body of an image forming apparatus. Further, in the embodiment, the first engaging groups  113 , the second engaging groove groups  114 , the first engaging claws  123 , and the second engaging claws  124  are formed of a plurality of groups. Further, the first engaging claws  123  and the second engaging claws  124  have a thickness the same as that of one group, and the first engaging groups  113  and the second engaging groove groups  114  have the width the same as that of one group. Accordingly, as compared to one group, it is possible to engage with a fine pitch without reducing a locking force. 
     As described above, in the embodiment, when the sheet supply tray  101  is set to the expansion sheet supply apparatus  103 , the L-side sheet guide  104  of the sheet supply tray  101  is disengaged. Then, the L-side sheet guide  104  moves to the position corresponding to the width of the sheet P, and is locked at the position. Accordingly, when a sheet having a size larger than the position where the L-side sheet guide  104  is set in the sheet supply tray  101 , it is possible to automatically reset the L-side sheet guide  104  to the position where the L-side sheet guide  104  does not interfere with the transportation of the sheet. Further, when the L-side sheet guide  104  is set to the position corresponding to the standard size, and a sheet having a size slightly larger than the standard size, it is possible to reset the L-side sheet guide  104  to the position where the L-side sheet guide  104  does not interfere with the transportation of the sheet. 
     Further, in the embodiment, when the L-side sheet guide  104  is set to the standard sheet size, the L-side sheet guide  104  moves to the position corresponding to the actual width of the sheet P. Accordingly, even when the sheet P has a variance in the width thereof, it is possible to stably supply the sheet P without paper jam due to excessive friction between the contact surface of the L-side sheet guide  104  and the edge of the sheet P during the transportation of the sheet P. 
     Second Embodiment 
     A second embodiment of the present invention will be explained next. In the second embodiment, the printer  400 , a sheet supply tray  201 , and the expansion sheet supply apparatus  103  have configurations similar to those in the first embodiment. Accordingly, similar components are designated with the same reference numerals, and only differences from the first embodiment will be explained. 
       FIG. 20  is a bottom side view showing the sheet supply tray  201  according to the second embodiment of the present invention.  FIG. 21  is a schematic enlarged view of a portion G shown in  FIG. 20  showing the sheet supply tray  201  according to the second embodiment of the present invention. 
     As shown in  FIGS. 20 and 21 , an L-side rack  207  is attached to the L-side sheet guide  104  of the sheet supply tray  201 , and includes a cut portion with a U character shape at a position where the L-side rack  207  abuts against the sheet supply tray  201 . A guide protrusion  206  is formed at one end portion of the cut portion with the U character shape, and has a triangular shape capable of deforming elastically. A guide spring  205  is disposed inside the cut portion with the U character shape as an urging member with respect to the cut portion for urging the cut portion in a widening direction. A guide groove portion  202  with a triangular shape is formed in the sheet supply tray  201  at a position where the sheet supply tray  201  abuts against the guide protrusion  206 . The guide protrusion  206  and the guide groove portion  202  constitute a guide portion. 
       FIG. 22  is a schematic enlarged view showing the guide groove portion  202  of the sheet supply tray  201  according to the second embodiment of the present invention. As shown in  FIG. 22 , the guide groove portion  202  includes a groove as a deepest portion at a position where the distance between the contact surfaces of the L-side sheet guide  104  and the R-side sheet guide  105  becomes equal to the standard size of the sheet P, and the guide protrusion  206  becomes a second shape to engage each groove portion when the L-side sheet guide  104  moves. 
     In the embodiment, as shown in  FIG. 21 , the guide groove portion  202  includes an A4-size guide groove  203  and a letter size guide groove  204 . In the A4-size guide groove  203  and the letter size guide groove  204 , the guide protrusion  206  becomes a first shape as a deformation state from where the guide protrusion  206  is pushed and deformed to a largest extent to the deepest portion. 
     As shown in  FIG. 22 , the A4-size guide groove  203  and the letter size guide groove  204  have butting surfaces such that a distance between the guide protrusion  206  and an outer distance e of the abutting surface becomes greater than an inner distance f thereof with a top portion thereof as a center in the width direction of the sheet P. 
     In the embodiment, the guide groove portion  202  includes a first inclined portion  204   a  and a second inclined portion  204   b . More specifically, as shown in  FIG. 22 , the guide groove portion  202  includes the first inclined portion  204   a  inclined up to the letter size guide groove  204  within the outer distance e. Further, the guide groove portion  202  includes the second inclined portion  204   b  inclined up to the letter size guide groove  204  within the inner distance f. The first inclined portion  204   a  has a length greater than that of the second inclined portion  204   b . In the embodiment, the outer distance e is 1.5 mm (e=1.5 mm), and the inner distance f is 1.0 mm (f=1.0 mm) 
     An operation of setting the sheet P in the sheet supply tray  201  will be explained next. 
     When the sheet P is set in the sheet supply tray  201 , similar to the first embodiment, the L-side sheet guide  104  and the R-side sheet guide  105  move according to the size of the sheet P. At this moment, in the second embodiment, when the L-side sheet guide  104  approaches the standard size position, the guide protrusion  206  urged with the guide spring  205  enters the guide groove portion  202 . Further, the top portion of the triangular shape forming the guide protrusion  206  is urged with the guide spring  205 , and is pulled into a direction matching to the top portion of the triangular shape of the guide groove portion  202 . 
     In the embodiment, as described above, it is configured that the outer distance e becomes greater than the inner distance f. Accordingly, with respect to the standard size, the L-side sheet guide  104  is pulled in a wider effective range at a wider position (outer distance) than a narrower position (inner distance). 
     As described above, in the embodiment, when the L-side sheet guide  104  is set, the L-side sheet guide  104  is pulled to the standard size position at a position near the standard size, thereby making it possible to prevent the L-side sheet guide  104  from being set at a wrong position. Further, when the L-side sheet guide  104  is set and pulled to the standard size position, an operator can sense the pulled feeling, thereby making it possible to notify the operator that the L-side sheet guide  104  is set at the standard size position. 
     Further, in the embodiment, a force is generated in the direction that the guide protrusion  206  is pulled into the guide groove portion  202 . Accordingly, when an impact is applied in a direction that the sheet supply tray  201  is inserted into the expansion sheet supply apparatus  103 , it is possible to prevent the distance between the L-side sheet guide  104  and the R-side sheet guide  105  from increasing with respect to the sheet size. Further, the guide spring  205  generates friction. Accordingly, at the irregular size position where the guide groove portion  202  is not formed, it is possible to prevent the distance between the L-side sheet guide  104  and the R-side sheet guide  105  from increasing due to an impact. 
     Third Embodiment 
     A third embodiment of the present invention will be explained next. In the third embodiment, the printer  400 , a sheet supply tray  301 , and the expansion sheet supply apparatus  103  have configurations similar to those in the first and second embodiments. Accordingly, similar components are designated with the same reference numerals, and only differences from the first and second embodiments will be explained. 
       FIG. 23  is a plan view showing the sheet supply tray  301  according to the third embodiment of the present invention.  FIG. 24  is a schematic enlarged view of a portion H shown in  FIG. 23  showing the sheet supply tray  301  according to the third embodiment of the present invention. 
     As shown in  FIGS. 23 and 24 , the sheet supply tray  301  includes a first engaging groove group  302 . The first engaging groove group  302  is configured such that the distance between the contact surfaces of the L-side sheet guide  104  and the R-side sheet guide  105  contacting with the edges of the sheet P becomes slightly smaller than the standard size by a distance 2s. In other words, the L-side sheet guide  104  and the R-side sheet guide  105  engage at a distance smaller than a size that an operator intends by the distance 2s. In the embodiment, the distance s is 1 mm (s=1 mm), and may be adjusted according to an accuracy of the sheet. 
     In the embodiment, the first engaging groove group  302  includes an A4-size sheet groove  304  for setting the A4-size sheet and a letter size sheet groove  305  for setting the letter size sheet. Further, a second engaging groove group  303  is disposed away from the letter size sheet groove  305  by a distance ½ t. In the embodiment, the distance ½ t is 1 mm. 
     An operation of setting the sheet P in the sheet supply tray  301  will be explained next. In the embodiment, it is assumed that the sheet P has the A4-size with the width of 209 mm, slightly smaller than the standard width of 210 mm. 
     When the sheet P is set in the sheet supply tray  301 , the L-side sheet guide  104  moves to a position where the first engaging claws  123  engages the A4-size sheet groove  304 . At this moment, the L-side rack  107  fixed to the L-side sheet guide  104  is connected to the R-side rack  108  fixed to the R-side sheet guide  105  through the pinion gear  109 . Accordingly, when the L-side sheet guide  104  moves, the R-side sheet guide  105  moves together with the L-side sheet guide  104 , so that the contact surfaces thereof contacting with the edges of the sheet P becomes 208 mm. 
     In this state, when the sheet P with the width of 209 mm is set in the sheet supply tray  301 , the L-side sheet guide  104  and the R-side sheet guide  105  are pushed sideway in the width direction of the sheet P due to rigidity of the sheet P. When the sheet supply tray  301  is inserted into the expansion sheet supply apparatus  103  in this state, similar to the first embodiment, the L-side sheet guide  104  is disengaged, so that the L-side sheet guide  104  and the R-side sheet guide  105  automatically move to the positions corresponding to the width of the sheet P, and then engage once again. 
     In the embodiment, the sheet P has the width of 209 mm. Accordingly, the second engaging claws  124  engages one of engaging grooves of the second engaging groove group  303  outside the A4-size sheet groove  304 . At this moment, the distance between the L-side sheet guide  104  and the R-side sheet guide  105  becomes 209 mm. 
     As described above, in the third embodiment, the distance between the contact surfaces of the L-side sheet guide  104  and the R-side sheet guide  105  contacting with the edges of the sheet P becomes slightly smaller than the standard size by the distance 2s. Accordingly, even when the sheet P has a size smaller than that standard side due to a dryness or a cutting variance of the sheet P, it is possible to set the sheet P without creating a gap between the L-side sheet guide  104  and the sheet P simply through setting the L-side sheet guide  104  at the standard size. 
     In the embodiments described above, the color printer of the electro-photography type is explained as an example, and the present invention is not limited thereto. The present invention is applicable to a sheet supply apparatus and an image forming apparatus such as a facsimile, a copier, and a multi-function product, in which a sheet supply tray is provided with a sheet guide. 
     The disclosure of Japanese Patent Application No. 2008-217028, filed on Aug. 26, 2008, is incorporated in the application by reference. 
     While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.