Patent Publication Number: US-7722040-B2

Title: Sheet carrying device and sheet carrying method for image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from U.S. Provisional Application 60/969,593 filed on Aug. 31, 2007, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present invention relates to a sheet carrying device for an image forming apparatus, which stably carries a recording medium without causing image blur in a copier, a printer or the like. 
     In an image forming apparatus such as a copier or a printer, when image formation is performed by using a thick paper having a large weighing capacity, image blur is liable to occur. In general, when the trailing edge of a thick paper passes through a registration roller pair, it is flipped by the registration rollers and the thick paper is instantaneously accelerated. As a result, the thick paper deforms, for example, a transfer belt by its firmness, and the image blur is caused. This is caused because, when the trailing edge of the thick paper passes through the registration rollers, the registration roller pair abruptly returns to the contact state. 
     Thus, hitherto, a delay mechanism is provided in the registration roller pair, and when the trailing edge of the thick paper passes through, the return of the registration roller pair to the contact state is delayed. This adjustment mechanism is such that a cam is axially attached to one of the registration rollers, and the cam is made to intervene between the shafts of the registration roller pair. By the operation of this cam, when the trailing edge of the sheet passes through, the return of the registration roller pair to the contact state is delayed. That is, after the trailing edge of the sheet passes through the cam, the cam is rotated together with the shaft of the other registration roller, and the registration roller pair slowly returns to the contact state. By this, it is suppressed that the thick paper is accelerated, and the image blur at the time of image formation is prevented. 
     However, in the conventional adjustment mechanism, even at the time of image formation on a standard paper, the shaft of the registration roller for rotating the cam together is always in contact with a specific position of the cam. Accordingly, the specific position of the cam made of, for example, POM (polyacetal) is worn away by the shaft made of, for example, metal. When the specific portion of the cam is worn away as stated above, the original operation of the cam cannot be obtained, and the cam cannot smoothly rotate during the passage of the thick paper, and besides, after the thick paper passes through, it becomes impossible to smoothly return the registration roller pair to the contact state. Thus, there is a fear that the exchange frequency of the cam increases, and the maintenance property is degraded. 
     Then, it is desired to develop a sheet carrying device for an image forming apparatus, which prevents a cam of an adjustment mechanism from being worn away, prolongs the life of the cam, and is excellent in maintenance property. 
     SUMMARY 
     An aspect of the invention is to prevent wear of a cam caused by a shaft of a registration roller at the time of image formation on a standard paper, to prolong the life of the cam, and to improve the maintenance property. 
     According to an embodiment of the invention, a sheet carrying device for an image forming apparatus includes a registration roller pair to carry a recording medium to a transfer position of an image carrier, a contact delay mechanism to set a pitch between the registration roller pair in accordance with a thickness of the recording medium passing through the registration roller pair and to hold the pitch when the recording medium passes through the registration roller pair, and a movement member to dispose the contact delay mechanism at an adjustment position at a time of carrying a thick paper recording medium and to eject the contact delay mechanism from the adjustment position at a time of carrying a standard paper recording medium. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic structural view showing a color copier of an embodiment of the invention; 
         FIG. 2  is a schematic side view showing a registration roller unit of the embodiment of the invention; 
         FIG. 3  is a schematic perspective view showing a pitch adjustment mechanism of the embodiment of the invention; 
         FIG. 4  is a schematic side view showing the pitch adjustment mechanism of the embodiment of the invention; 
         FIG. 5  is a front side partial explanatory view showing a state where the pitch adjustment mechanism of the embodiment of the invention is ejected from an adjustment position; 
         FIG. 6  is a rear side partial explanatory view showing a state where the pitch adjustment mechanism of the embodiment of the invention is ejected from the adjustment position; 
         FIG. 7  is a front side partial explanatory view showing a state where the pitch adjustment mechanism of the embodiment of the invention is disposed at the adjustment position; 
         FIG. 8  is a rear side partial explanatory view showing a state where the pitch adjustment mechanism of the embodiment of the invention is disposed at the adjustment position; and 
         FIG. 9  is a schematic explanatory view showing a separation mechanism of the embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an embodiment of the invention will be described in detail with reference to the accompanying drawings.  FIG. 1  is a schematic structural view showing a four-tandem color copier  1  as an image forming apparatus of the embodiment of the invention. The color copier  1  includes a scanner unit  2  and an in-body paper discharge unit  3  which are disposed on an upper side. The color copier  1  includes an image forming unit  11  having four sets of image forming stations  11 Y,  11 M,  11 C and  11 K of yellow (Y), magenta (M), cyan (C) and black (K) disposed in parallel along the lower side of an intermediate transfer belt  10 . 
     The respective image forming stations  11 Y,  11 M,  11 C and  11 K include photoconductive drums  12 Y,  12 M,  12 C and  12 K, respectively. Charging chargers  13 Y,  13 M,  13 C and  13 K, developing devices  14 Y,  14 M,  14 C and  14 K, and photoreceptor cleaning devices  16 Y,  16 M,  16 C and  16 K are disposed respectively around the photoconductive drums  12 Y,  12 M,  12 C and  12 K along rotation directions of arrow m directions. Exposure lights are irradiated by a laser exposure device  17  between the charging chargers  13 Y,  13 M,  13 C and  13 K and the developing devices  14 Y,  14 M,  14 C and  14 K around the photoconductive drums  12 Y,  12 M,  12 C and  12 K, and electrostatic latent images are formed on the photoconductive drums  12 Y,  12 M,  12 C and  12 K. 
     The developing devices  14 Y,  14 M,  14 C and  14 K respectively have two-component developers made of toners of yellow (Y), magenta (M), cyan (C) and black (K) and carriers. 
     An intermediate transfer belt  10  as an image carrier is stretched by a backup roller  21 , a driven roller  20 , and the first to the third tension rollers  22  to  24 . The intermediate transfer belt  10  is opposite to and in contact with the photoconductive drums  12 Y,  12 M,  12 C and  12 K. Primary transfer rollers  18 Y,  18 M,  18 C and  18 K for primarily transferring toner images on the photoconductive drums  12 Y,  12 M,  12 C and  12 K to the intermediate transfer belt  10  are provided at positions of the intermediate transfer belt  10  opposite to the photoconductive drums  12 Y,  12 M,  12 C and  12 K. 
     A secondary transfer roller  27  is disposed in a secondary transfer unit at a transfer position of the intermediate transfer belt  10  supported by the backup roller  21 . In the secondary transfer unit, a specified secondary transfer bias is applied to the backup roller  21 . When a sheet paper as a recording medium passes through between intermediate transfer belt  10  and the secondary transfer roller  27 , the toner images on the intermediate transfer belt  10  are secondarily transferred onto the sheet paper. After the secondary transfer is ended, the intermediate transfer belt  10  is cleaned by a belt cleaner  10   a.    
     A paper feed cassette  4  for feeding sheet papers in a direction toward the secondary transfer roller  27  is provided below the laser exposure device  17 . A manual feed mechanism  31  for manually feeding sheet papers is provided on the right side of the color copier  1 . 
     A pickup roller  4   a , a separation roller  28   a , a carrying roller  28   a  and a registration roller pair  36  are provided between the paper feed cassette  4  and the secondary transfer roller  27 . A manual feed pickup roller  31   b  and a manual feed separation roller  31   c  are provided between a manual feed tray  31   a  of the manual feed mechanism  31  and the registration roller pair  36 . 
     Further, a medium sensor  39  for detecting the kind of sheet paper is disposed on a vertical carrying path  34  for carrying the sheet paper in the direction toward the secondary transfer roller  27  from the paper feed cassette  4  or the manual feed tray  31   a . The medium sensor  39  detects the thickness of various sheet papers by using, for example, a contact-type detection terminal. The color copier  1  can control the carrying speed of sheet paper, a transfer condition, a fixing condition and the like from the detection result of the medium sensor  39 . Besides, a fixing device  30  is provided downstream of the secondary transfer unit along the direction of the vertical carrying path  34 . 
     The sheet paper taken out from the paper feed cassette  4  or fed from the manual feed mechanism  31  is carried along the vertical carrying path  34  through the registration roller pair  36  and the secondary transfer roller  27  to the fixing device  30 . The fixing device  30  fixes the toner image transferred on the sheet paper by a heat treatment in the secondary transfer unit. A gate  33  is provided downstream of the fixing device  30 , and changes over the direction toward a paper discharge roller  41  and the direction toward a re-carrying unit  32 . The sheet paper guided to the paper discharge roller  41  is discharged to the in-body paper discharge unit  3 . Besides, the sheet paper guided to the re-carrying unit  32  is again guided in the direction toward the secondary transfer roller  27 . 
     The image forming station  11 Y integrally includes the photoconductive drum  12 Y and process means, and is provided to be attachable to and detachable from the image forming apparatus body. The process means represents at least one of the charging charger  13 Y, the developing device  14 Y and the photoreceptor cleaning device  16 Y. The image forming stations  11 M,  11 C and  11 K have the same structure as the image forming station  11 Y, and each of the image forming stations  11 Y,  11 M,  11 C and  11 K may be attachable to and detachable from the image forming apparatus, or they may be attachable to and detachable from the image forming apparatus as an integral image forming unit  11 . 
     Next, the registration roller pair  36  will be described in detail with reference to a registration roller unit  35  of  FIG. 2 . Reference numerals  35   a  and  35   b  denote carrying guides of sheet paper. The registration roller pair  36  includes a first roller  37  and a second roller  38 . A pitch adjustment mechanism  42  as a contact delay mechanism shown in  FIG. 3  is provided at the front side and the rear side of a first shaft  37   a  of the first roller  37 . The pitch adjustment mechanism  42  includes a cam  42   a  axially attached to the first shaft  37   a . As shown in  FIG.4  the cam  42   a  is formed such that a distance (r) between the first shaft  37   a  and the outer periphery of the cam  42   a  becomes (r 1 )&gt;(r 2 ). Besides, the pitch adjustment mechanism  42  has a cam spring  42   b  as a first urging member for urging the cam  42   a  in an arrow w direction. 
     While the pitch adjustment mechanism  42  is disposed at an adjustment position, the posture of the cam  42   a  is controlled by the pitch between the first shaft  37   a  and a second shaft  38   a  and the cam spring  42   b . Besides, while the pitch adjustment mechanism  42  is disposed at the adjustment position, the cam  42   a  is in slide contact with the second shaft  38   a  of the second roller  38 . The cam  42   a  is rotated together with the second shaft  38   a  by the rotation of the second shaft  38   a , and can be rotated in an arrow v direction. 
     Further, the pitch adjustment mechanism  42  has a stopper  43  for regulating the rotation range of the cam  42   a . The stopper  43  is provided at an end of a registration front guide  44  for guiding the sheet paper to the registration roller pair  36 . The stopper  43  comes in contact with a regulation lever  45   b , and regulates the rotation range of the cam  42   a  in the arrow v direction by the second shaft  38   a . Besides, the stopper  43  comes in contact with a lower corner part  45   a  of the cam  42   a  and regulates the rotation range of the cam  42   a in an arrow w direction by the cam spring  42   b.    
     The cam  42   a  is rotated in the arrow w direction by the cam spring  42   b  according to the thickness of the sheet paper as the recording medium during the passage through the registration roller pair  36 . After the sheet paper passes through the registration roller pair  36 , the cam  42   a  is rotated in the arrow v direction by the second shaft  38   a.    
     The urging force of the cam spring  42   b  for rotating the cam  42   a  in the arrow w direction varies according to the arrangement position of the cam  42   a . That is, the urging force of the cam  42   a  when the cam  42   a  is disposed at the adjustment position described later is larger than the urging force of the cam  42   a  when the cam  42   a  is ejected from the adjustment position. 
     A movement spring  47  as a second urging member and a plunger  48   a  of a solenoid  48 , which constitute a movement member, are attached to the cam  42   a . The other end of the movement spring  47  and the solenoid  48  are attached to a unit frame. The movement spring  47  urges the cam  42   a  at the front side in an arrow x 1  direction, urges the cam  42   a  at the rear side in an arrow x 2  direction, slides the cam  42   a  along the first shaft  37   a , and can eject the cam  42   a  from the adjustment position to a standby position. An opposite part  38   b  to the standby position is formed to be cut out so that, when the cam  42   a  is ejected to the standby position, the second shaft  38   a  does not come in slide contact with the cam  42   a.    
     The solenoid  48  extends the plunger  48   a  at the front side in an arrow y 1  direction at the time of power application, extends the plunger  48   a  at the rear side in an arrow y 2  direction at the time of power application, and holds the cam  42   a  at the adjustment position. The cam  42   a  is in slide contact with the second shaft  38   a  while it is held at the adjustment position. 
     Next, the operation of the pitch adjustment mechanism  42  will be described. When the power source of the color copier  1  is off, in the registration roller unit  35 , the first roller  37  and the second roller  38  of the registration roller pair  36  are separate from each other. Besides, when the power source of the color copier  1  is off, since the solenoid  48  is off, the cam  42   a  is pulled in the arrow x direction by the urging force of the movement spring  47 , and is ejected from the adjustment position to the standby position as shown in  FIG. 5  and  FIG. 6 . That is, the cam  42   a  is separate from the second shaft  38   a . Also during this, the urging force to cause rotation in the arrow w direction is given to the cam  42   a  by the cam spring  42   b . However, since the regulation lever  45   b  comes in contact with the stopper  43 , the rotation range of the cam  42   a  is regulated. 
     When the power source is turned on in such a state, first, the solenoid  48  is turned on, and the plunger  48   a  is extended. By this, the cam  42   a  is slid in an arrow yl direction at the front side and is slid in an arrow y 2  direction at the rear side along the first shaft  37   a  against the urging force of the movement spring  47 , and is set in the initial state where it is disposed at the adjustment position as shown in  FIG. 7  and  FIG. 8 . By this, the cam  42   a  is brought into slide contact with the first shaft  37   a.    
     Next, the rotation of the registration roller pair  36  is started, and when the second shaft  38   a  is rotated, the cam  42   a  is rotated together with the second shaft  38   a , and is rotated in the arrow v direction. Accordingly, the pitch between the first shaft  37   a  and the second shaft  38   a  regulated by the cam  42   a  is reduced. By this, the first roller  37  and the second roller  38  are brought into contact with each other by the urging force to urge both the rollers  37  and  38  in the contact direction. Incidentally, when the corner part  45   a  of the cam comes in contact with the stopper  43 , the rotation of the cam  42   a  in the arrow v direction is regulated irrespective of the rotation together with the second shaft  38   a.    
     Thereafter, when the color copier  1  is placed in a ready state, the solenoid  48  is turned off. By this, the cam  42   a  is pulled in the arrow x 1  direction at the front side and is pulled in the arrow x 2  direction at the rear side, by the urging force of the movement spring  47 , and is ejected from the adjustment position to the standby position as shown in  FIG. 5  and  FIG. 6 . By this, the cam  42   a  is separated from the second shaft  38   a.    
     Next, in the color copier  1 , an image formation process onto a standard paper P 1  as a standard paper recording medium having a weighing capacity of, for example, about 64 to 80 g/m 2  is started. At this time, the pitch adjustment mechanism  42  does not perform any operation on the registration roller pair  36 . By the start of the image formation process, in the image forming unit  11 , toner images are formed on the photoconductive drums  12 Y,  12 M,  12 C and  12 K in the image forming stations  11 Y,  11 M,  11 C and  11 K. The toner images on the respective photoconductive drums  12 Y,  12 M,  12 C and  12 K are multiply transferred onto the intermediate transfer belt  10  in sequence, and a full-color toner image is formed on the intermediate transfer belt  10  and reaches the secondary transfer roller  27 . 
     At this time, synchronously with the full-color toner image on the intermediate transfer belt  10 , the standard paper P 1  is carried to between the intermediate transfer belt  10  and the secondary transfer roller  27 . For example, the standard paper P 1  is taken out from the paper feed cassette  4  by the pickup roller  4   a , and is fed to the registration roller pair  36  through the separation roller  28   a  and the carrying roller  28   b . After the leading edge of the standard paper P 1  is aligned, the registration roller pair  36  starts to rotate, and feeds the standard paper P 1  to the secondary transfer unit. Thereafter, the toner image on the intermediate transfer belt  10  is transferred to the standard paper P 1  in the secondary transfer unit, and is heated, pressed and fixed by the fixing device  30 , and the fixed toner image is completed. After the fixing, when a single-sided image is formed, the standard paper P 1  is directly discharged to the in-body paper discharge unit  3  by the discharge roller  41  through the gate  33 . When both-sided image or multiple printing is performed, the standard paper is re-carried to the secondary transfer unit through the re-carrying unit  32 . 
     As stated above, while the standard paper P 1  is being fed, the cam  42   a  of the registration roller pair  36  is set at the standby position and is separate from the second shaft  38   a , and therefore, the cam is not worn away by the slide contact with the second shaft  38   a.    
     Next, in the color copier  1 , an image forming process onto a thick paper P 2  as a thick paper recording medium having, for example, a weighing capacity of 80 g/m.sup.2 or more will be described. When an image is formed on the thick paper P 2 , first, the mode of the color copier  1  is changed to a thick paper mode through the control panel of the color copier  1 . By this, the first roller  37  and the second roller  38  of the registration roller pair  36  are separated from each other. The separation between the first roller  37  and the second roller  38  is performed by, for example, a separation mechanism  50  shown in  FIG. 9  and provided at the front side and the rear side of the second roller  38 . The separation mechanism  50  moves the second shaft  38   a  in the direction of separating from the first roller  37  by moving a plunger  52  in the arrow z direction. 
     That is, when the image forming process is changed to the thick paper mode, one end  52   a  of the plunger  52  is urged in the arrow z direction by the cam  51 . The cam  51  is normally located at a position indicated by a solid line, and an urging force is not applied to the second shaft  38   a . When the image forming process is changed to the thick paper mode, the cam  51  is rotated as indicated by a dotted line. By this, the plunger  52  moves in the arrow z direction, and an end  52   b  of the plunger gives the urging force in the arrow z direction to the second shaft  38   a . As a result, the first roller  37  and the second roller  38  of the registration roller pair  36  are separated from each other. 
     As stated above, when the solenoid  48  is turned on while the first roller  37  and the second roller  38  are separate from each other, the cam  42   a  is slid in the arrow y 1  direction at the front side, and is slid in the arrow y 2  direction at the rear side by the extension of the plunger  48   a . By this, the cam  42   a  is disposed at the adjustment position shown in  FIG. 7  and  FIG. 8 . By this, the cam  42   a  is brought into slide contact with the first shaft  37   a . Thereafter, the cam  51  is again rotated to the position indicated by the solid line, and the urging force to the second shaft  38   a  by the plunger  52  is released. 
     Next, the rotation of the registration roller pair  36  is started, and when the second shaft  38   a  is rotated, the cam  42   a  is rotated together with the second shaft  38   a  and is rotated in the arrow v direction. By this, the first roller  37  and the second roller  38  come in contact with each other. Incidentally, when the corner part  45   a  of the cam comes in contact with the stopper  43 , the rotation of the cam  42   a  in the arrow v direction is regulated irrespective of the rotation together with the second shaft  38   a.    
     In order to start the image forming process on the thick paper P 2  in such a state, the thick paper P 2  is fed from, for example, the manual feed tray  31   a . The fed thick paper P 2  synchronizes with the full-color toner image on the intermediate transfer belt  10 , and the leading edge is aligned by the registration roller pair  36 , and then, the thick paper is fed to the secondary transfer unit. At the time of feeding the thick paper P 2 , when the thick paper P 2  is inserted into the registration roller pair  36 , the pitch between the first roller  37  and the second roller  38 , that is, the pitch between the first shaft  37   a  and the second shaft  38   a  is widened according to the thickness of the thick paper P 2 . By this, the cam  42   a  is urged by the cam spring  42   b , and is rotated in the arrow w direction by the increase of the pitch between the first shaft  37   a  and the second shaft  38   a.    
     While the thick paper P 2  passes through the registration roller pair  36 , the cam  42   a  is not rotated together with the second shaft  38   a  irrespective of the slide contact with the second shaft  38   a . The posture of the cam  42   a  is controlled between the first shaft  37   a  and the second shaft  38   a  so as to hold the pitch widened by the thick paper P 2 . When the trailing edge of the thick paper P 2  passes through the registration roller pair  36  and the force to widen the pitch between the first shaft  37   a  and the second shaft  38   a  is released, the cam  42   a  is rotated together with the slide-contacted second shaft  38   a  and is rotated in the arrow v direction. By this, the first roller  37  and the second roller  38  are brought into contact with each other. That is, when the trailing edge of the thick paper P 2  passes through the registration roller pair  36 , the first roller  37  and the second roller  38  are slowly returned to the contact state by the operation of the cam  42   a  rotated together with the second shaft  38   a.    
     By the contact delay operation as stated above, although the thick paper P 2  has high firmness, when the thick paper P 2  passes through the resister roller pair  36 , the trailing edge of the thick paper P 2  is not flipped by the registration roller pair  36 , and is not instantaneously accelerated. As a result, it is possible to prevent the image blur caused by the transfer blur in the secondary transfer unit when the thick paper P 2  passes through the registration roller pair  36 . 
     Thereafter, the thick paper P 2  on which the toner image is transferred without causing the image blur is heated, pressed and fixed by the fixing device  30 , and the fixed toner image is completed. Further, the thick paper P 2  is discharged to the in-body paper discharge unit  3  by the paper discharge roller  41  through the gate  33 , or is re-carried to the secondary transfer unit through the re-carrying unit  32 . In the registration roller unit  35 , until the image formation process to a specified number of thick papers P 2  is ended in this way, the contact delay operation of the registration roller pair  36  by the pitch adjustment mechanism  42  is repeated. 
     After the image formation process onto the thick paper P 2  is completed, next, the paper feed cassette  4  is selected by, for example, the control panel, and when it is recognized that the image formation process onto the standard paper P 1  is to be performed, the color copier  1  is changed to the standard paper mode, and the solenoid  48  is turned off in the registration roller unit  35 . By this, the cam  42   a  is pulled in the arrow x 1  direction at the front side and is pulled in the arrow x 2  direction at the rear side by the urging force of the movement spring  47 , and is discharged from the adjustment position to the standby position, and the cam  42   a  is separated from the second shaft  38   a . Thereafter, the image forming process to the standard paper P 1  is started by the operation of a start button on the control panel. 
     In this standard paper mode, the pitch adjustment mechanism  42  at the standby position does not perform any operation on the registration roller pair  36 . Besides, since the cam  42   a  of the registration roller pair  36  is separate from the second shaft  38   a , it is not worn away by the slide contact with the second shaft  38   a.    
     According to this embodiment, the pitch adjustment mechanism  42  can be moved between the adjustment position and the standby position, which prevents that, when the trailing edge of the sheet paper passes through the registration roller pair  36 , the sheet paper is flipped by the registration roller pair  36  because of the motion in which the registration roller pair  36  returns to the contact state, and the image blur occurs. That is, when the sheet P is the standard paper P 1 , the solenoid  48  is turned off, and the pitch adjustment mechanism  42  is ejected from the adjustment position by the urging force of the movement spring  47  and is moved to the standby position. When the sheet P is the thick paper P 2 , the solenoid  48  is turned on, the plunger  48   a  is extended, and the pitch adjustment mechanism  42  is disposed at the adjustment position. 
     By this, at the time of the image forming process to the standard paper P 1  in which there is no fear of occurrence of image blur when the paper passes through the registration roller pair  36 , the cam  42   a  is separated from the second shaft  38   a , and it is prevented that a specific portion of the cam  42   a  is worn away by the second shaft  38   a . As a result, the rotation of the cam  42   a  by the urging force of the cam spring  42   b  can be smoothly performed, and the rotated operation of the cam  42   a  caused by the second shaft  38   a  can be smoothly performed. On the other hand, at the time of the image forming process to the thick paper P 2 , the contact delay operation between the first roller  37  and the second roller  38  after the thick paper P 2  passes through can be performed by the operation of the pitch adjustment mechanism  42 . As a result, it is possible to prevent the image blur from being caused when the thick paper P 2  passes through the registration roller pair  36 , and the image quality can be improved. 
     Incidentally, the invention is not limited to the above embodiment, and can be variously modified within the scope of the invention. For example, the carrying path for carrying the sheet paper through the registration roller pair may not be the vertical carrying path but may be the horizontal carrying path for carrying the sheet paper in the horizontal direction. Besides, the shape of the cam member of the contact delay mechanism and the attachment position of the first urging member are not limited. Further, when the contact delay mechanism is disposed at the adjustment position and when it is disposed at the standby position, the distribution of the urging force to the cam member by the first urging member is not limited. However, when the contact delay mechanism is at the standby position, the urging force of the first urging member is not originally required, and accordingly, it is preferable that the urging force of the first urging member is made smaller. Besides, the structure of the movement member or the timing of the movement of the contact delay mechanism by the movement member is not limited. Further, in this embodiment, although the change of the mode is performed by input from the control panel, when the medium sensor detects the thick paper, the change to the thick paper mode may be automatically performed.