Patent Publication Number: US-9423742-B1

Title: Image forming apparatus and fixing device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2015-028307 filed Feb. 17, 2015. 
     BACKGROUND 
     Technical Field 
     The present invention relates to an image forming apparatus and a fixing device. 
     SUMMARY 
     According to an aspect of the present invention, there is provided an image forming apparatus including: an image forming portion that forms a developer image on a recording medium; and a fixing device that is removably mounted to an image forming apparatus body and that fixes the developer image formed by the image forming portion to the recording medium, in which the fixing device includes a first rotator, a second rotator that contacts the first rotator to form an interposition region in which the recording medium is interposed between the first rotator and the second rotator, and a pressing mechanism that presses the first rotator and the second rotator against each other, the image forming apparatus further includes a change mechanism that changes a force with which the pressing mechanism presses the first rotator and the second rotator against each other, and the change mechanism is mounted to the image forming apparatus body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  illustrates a schematic configuration of an image forming apparatus according to an exemplary embodiment of the present invention; 
         FIG. 2  is a plan view illustrating a fixing device of the image forming apparatus illustrated in  FIG. 1 ; 
         FIG. 3  is a vertical sectional view illustrating the fixing device illustrated in  FIG. 2 ; 
         FIG. 4  illustrates a section of the image forming apparatus illustrated in  FIG. 1  taken along the line IV-IV of  FIG. 1 ; 
         FIG. 5  is a perspective view illustrating a tie plate of the image forming apparatus illustrated in  FIG. 1 ; 
         FIG. 6  illustrates the configuration and operation of a change mechanism of the image forming apparatus illustrated in  FIG. 1 ; 
         FIG. 7A  illustrates operation of the change mechanism of the image forming apparatus illustrated in  FIG. 1 , illustrating a state of the fixing device at the time when a developer image is fixed to regular paper; 
         FIG. 7B  illustrates operation of the change mechanism of the image forming apparatus illustrated in  FIG. 1 , illustrating a state of the fixing device at the time when a developer image is fixed to an envelope; and 
         FIG. 7C  illustrates operation of the change mechanism of the image forming apparatus illustrated in  FIG. 1 , illustrating a state of the fixing device in which a force of pressing a first rotator and a second rotator against each other has been canceled. 
     
    
    
     DETAILED DESCRIPTION 
     Now, an exemplary embodiment of the present invention will be described with reference to the drawings.  FIG. 1  illustrates an image forming apparatus  10  according to an exemplary embodiment of the present invention. As illustrated in  FIG. 1 , the image forming apparatus  10  includes an image forming apparatus body  20 . An ejection port  22  that ejects paper used as a recording medium is formed in the image forming apparatus body  20 . The upper surface of the image forming apparatus body  20  is used as an ejection portion  24  to which a recording medium to which a developer image has been fixed is ejected. The term “recording medium” refers to a member to which a developer image may be fixed for recording. Specific examples of the recording medium include regular paper and an envelope. 
     The image forming apparatus body  20  includes a tie plate  30  used as a fixed portion to which a fixing device  200  to be discussed later is fixed. With the fixing device  200  fixed to the tie plate  30 , the fixing device  200  is accurately positioned in the image forming apparatus body  20 , and reinforced. 
     An open/close portion  90  is mounted to the left side (left side in  FIG. 1 ) of the image forming apparatus body  20  so as to be rotatable about a hinge  92  to be openable/closable with respect to the image forming apparatus body  20 .  FIG. 1  illustrates a state in which the open/close portion  90  is closed with respect to the image forming apparatus body  20 . The open/close portion  90  is opened with respect to the image forming apparatus body  20  by rotating the open/close portion  90  about the hinge  92  in the direction of the arrow a indicated in  FIG. 1  from the state illustrated in  FIG. 1 . 
     An image forming portion  100  that forms a developer image on paper is disposed in the image forming apparatus body  20 . The image forming portion  100  includes a photosensitive drum  102 , a charging device  104 , a latent image forming device  106 , a developing device  110 , a transfer device  122 , and a cleaning device  124 . The photosensitive drum  102  is used as an image holding element that holds an image. The charging device  104  uniformly charges a surface of the photosensitive drum  102 . The latent image forming device  106  forms an electrostatic latent image on the surface of the photosensitive drum  102  uniformly charged by the charging device  104 . The developing device  110  develops the latent image formed by the latent image forming device  106  using a developer. The transfer device  122  transfers the developer image, which has been formed on the surface of the photosensitive drum  102  by the developing device  110  developing the latent image, to paper. The cleaning device  124  cleans the developer or the like remaining on the surface of the photosensitive drum  102  after the developer image is transferred to the paper by the transfer device  122 . 
     All or some of the photosensitive drum  102 , the charging device  104 , the latent image forming device  106 , the developing device  110 , and the cleaning device  124  may be accommodated in a single structure to be used as a so-called process cartridge. The process cartridge may be mounted to and removed from the image forming apparatus body  20 . 
     The developing device  110  includes a developing device body  112  and a developing roller  114  that holds the developer and that supplies the developer to the photosensitive drum  102 . In the exemplary embodiment, a so-called two-component developing device is used as the developing device  110 . The developing device  110  develops a latent image using a two-component developer composed of a non-magnetic toner and a magnetic toner. More specifically, the developing device  110  electrostatically moves the toner in a charged state in the developer to the photosensitive drum  102  to develop the latent image. 
     A toner replenishment device  150  is disposed in the image forming apparatus body  20 . The toner replenishment device  150  replenishes the developing device  110  with the toner in the case where the concentration of the toner in the developer accommodated in the developing device body  112  has been lowered, for example. The toner replenishment device  150  includes a toner accommodation container  154 , a toner replenishment device body  156 , and a transport path  158 . The toner accommodation container  154  accommodates the toner. The toner accommodation container  154  is mounted to and removed from the toner replenishment device body  156 . The toner is transported to the developing device  110  through the transport path  158 . A toner transport member (not illustrated) that is rotatable to transport the toner, for example, is disposed in the transport path  158 . 
     The fixing device  200  which fixes the developer image formed on the paper by the image forming portion  100  to the paper is disposed in the image forming apparatus body  20 . The fixing device  200  is mountable to and removable from the image forming apparatus body  20 , and fixed to the tie plate  30  with the fixing device  200  mounted to the image forming apparatus body  20 . 
     To mount the fixing device  200  to the image forming apparatus body  20 , the open/close portion  90  is opened with respect to the image forming apparatus body  20 , and an operator inserts the fixing device  200  into the image forming apparatus body  20  in the direction of the arrow b indicated in  FIG. 1  from the outside of the image forming apparatus body  20  toward the tie plate  30 . To detach the fixing device  200  from the image forming apparatus body  20 , the open/close portion  90  is opened with respect to the image forming apparatus body  20 , and the fixing device  200  which has been fixed to the tie plate  30  is drawn out of the image forming apparatus body  20  in the direction of the arrow c indicated in  FIG. 1 . 
     The fixing device  200  is mounted to and removed from the image forming apparatus body  20  to replace the fixing device  200  which has been used so far with another fixing device  200 , for example, because a fixing roller  204  to be discussed later or a fixing belt  230  to be discussed later has been degraded along with use, for example. The fixing device  200  will be discussed in detail later. 
     A paper feed device  610  and a paper feed device  620  are disposed in the image forming apparatus body  20 . The paper feed device  610  supplies paper such as regular paper and an envelope (hereinafter referred to as “paper etc.”), for example, to the image forming portion  100 . The paper feed device  620  also supplies paper etc. to the image forming portion  100 . The paper feed device  610  includes a paper accommodation portion  612  and a feeding device  614 . The paper accommodation portion  612  accommodates paper etc. in a stacked state. The feeding device  614  feeds the paper etc. accommodated in the paper accommodation portion  612  to a transport path  500  to be discussed later. The paper feed device  620  includes a paper accommodation portion  622  and a feeding device  624 . The paper accommodation portion  622  accommodates paper etc. in a stacked state. The feeding device  624  feeds the paper etc. accommodated in the paper accommodation portion  622  to the transport path  500  to be discussed later. 
     The paper accommodation portion  612  and the paper accommodation portion  622  may accommodate paper etc. of different types or sizes. Examples of the paper etc. of different types include paper of different thicknesses. Additional examples of the paper etc. of different types include regular paper and an envelope. To fix the developer to paper of different types such as paper of different thicknesses, it is desirable to employ different fixing conditions under which the fixing device  200  fixes a developer image to the paper. 
     The transport path  500  for transport of the paper etc. is formed in the image forming apparatus body  20 . The transport path  500  includes a principal transport path  502  and a reverse transport path  504 . The paper feed device  620  discussed earlier, the paper feed device  610  discussed earlier, a resist roller  510 , the transfer device  122  discussed earlier and the photosensitive drum  102  discussed earlier, the fixing device  200  discussed earlier, and an ejection roller  520  are disposed along the principal transport path  502  in this order from the upstream side in the direction of transport of the paper etc. through the principal transport path  502 . 
     The resist roller  510  temporarily stops movement of the distal end portion of the paper etc. supplied from one of the paper feed device  610  and the paper feed device  620 , and resumes movement of the distal end portion of the paper etc. to a transfer portion formed by the photosensitive drum  102  and the transfer device  122  so as to match the timing when a toner image is formed on the surface of the photosensitive drum  102 . 
     The transfer device  122  is applied with a transfer bias to electrostatically transfer the toner image, which has been formed on the surface of the photosensitive drum  102 , to the paper etc. 
     The ejection roller  520  ejects the paper etc., to which the toner image has been fixed by the fixing device  200 , toward the ejection portion  24  through the ejection port  22 . To form a developer image on the other surface of paper etc., on one surface of which a developer image has been formed, the ejection roller  520  starts rotating in the opposite direction at the timing when a portion near the rear end portion of the paper etc. reaches the ejection roller  520 , and the ejection roller  520  rotates in the opposite direction to feed the paper etc., on one surface of which a developer image has been formed, to the reverse transport path  504  from the rear end portion side. 
     Two transport rollers  530  and  532 , for example, are disposed along the reverse transport path  504  in this order from the upstream side in the direction of transport of paper etc. in the reverse transport path  504 . The transport roller  530  and the transport roller  532  transport the paper etc., on one surface of which a toner image has been formed, toward the resist roller  510  with the paper turned over. 
     An operation panel  130  used as an operation portion for operating the image forming apparatus  10  is attached to the front surface, for example, of the image forming apparatus body  20 . The operation panel  130  is used by the operator to input information about image formation such as which of the paper feed device  610  and the paper feed device  620  supplies paper, for example. 
     A change mechanism  300  and a motor  360  are disposed in the image forming apparatus body  20 . The change mechanism  300  changes a force with which the fixing roller  204  to be discussed later and the fixing belt  230  to be discussed later are pressed against each other. The motor  360  is used as a drive source that drives the change mechanism  300 . The change mechanism  300  will be discussed in detail later. 
     A drive mechanism  162  that drives the toner transport member (not illustrated) disposed in the transport path  158  is disposed in the image forming apparatus body  20 . A drive force is transmitted from the motor  360 , which serves as the drive source for the change mechanism  300 , to the drive mechanism  162 . In this way, the drive source which drives the change mechanism  300  is also used as the drive source for the transport member which transports the toner from the toner replenishment device  150  to the developing device  110 . 
     The fixing device  200  is illustrated in  FIGS. 2 and 3 . As illustrated in  FIGS. 2 and 3 , the fixing device  200  includes a rear side plate  202 R, a front side plate  202 F, and the fixing roller  204 . The rear side plate  202 R is a side plate positioned on the rear side. The front side plate  202 F is a side plate positioned on the front side. The fixing roller  204  is used as a first rotator. The fixing roller  204  is supported such that the rear end portion side thereof is rotatable with respect to the rear side plate  202 R via a bearing  206 R. The fixing roller  204  is supported such that the front end portion side thereof is rotatable with respect to the front side plate  202 F via a bearing  206 F. 
     A drive source  208  such as a motor, for example, is coupled to the fixing roller  204 . The fixing roller  204  receives a drive force transmitted from the drive source  208  to be rotated in the direction of the arrow d indicated in  FIG. 3 . The fixing roller  204  has a cylindrical shape. A heat source  210  is disposed in a hollow portion of the fixing roller  204 . A halogen lamp or the like may be used as the heat source  210 . 
     The fixing device  200  includes the fixing belt  230 . The fixing belt  230  is used as a second rotator that contacts the fixing roller  204  to form an interposition region N in which paper is interposed between the fixing roller  204  and the fixing belt  230 . The fixing belt  230  is a flexible endless belt-like member, and is rotatably supported by a belt support portion  244  disposed inside the fixing belt  230 . The fixing belt  230  is driven by rotation of the fixing roller  204  in the direction of the arrow d to be rotated in the direction of the arrow e indicated in  FIG. 4 . 
     The fixing device  200  includes a pressing mechanism  240  that presses the fixing roller  204  and the fixing belt  230  against each other. The pressing mechanism  240  includes a rear lever member  242 R, a front lever member  242 F, and the belt support portion  244  discussed earlier. The rear lever member  242 R and the front lever member  242 F are used as a movable member that is movable by the action of the change mechanism  300  (see  FIG. 1 ). 
     The rear lever member  242 R is supported so as to be rotatable with respect to the rear side plate  202 R by a rear shaft member  246 R. The front lever member  242 F is attached so as to be rotatable with respect to the front side plate  202 F by a front shaft member  246 F. The belt support portion  244  supports the fixing belt  230 . The rear end portion of the belt support portion  244  is fixed to the rear lever member  242 R. The front end portion of the belt support portion  244  is fixed to the front lever member  242 F. 
     With the configuration described above, the belt support portion  244 , the fixing belt  230 , the rear lever member  242 R, and the front lever member  242 F are integrally rotatable and swingable in the direction of the arrow f indicated in  FIG. 3  and the direction of the arrow g indicated in  FIG. 3  about the rear shaft member  246 R and the front shaft member  246 F with respect to the rear side plate  202 R and the front side plate  202 F. 
     The pressing mechanism  240  includes a first torsion spring  248 R (i.e., rear torsion spring) used as a first urging unit and a second torsion spring (i.e., front torsion spring that is not illustrated) also used as the first urging unit. The pressing mechanism  240  also includes a first coil spring  252 R (i.e., a rear coil spring) used as a second urging unit and a second coil spring (i.e. a front coil spring that is not illustrated) also used as the second urging unit. The first torsion spring  248 R, the second torsion spring, the first coil spring  252 R, and the second coil spring are members that press one of the fixing roller  204  and the fixing belt  230  against the other of the fixing roller  204  and the fixing belt  230 . In the exemplary embodiment, the members are used to press the fixing belt  230  against the fixing roller  204 . 
     One end portion of the first torsion spring  248 R is coupled to the rear lever member  242 R. The other end portion of the torsion first spring  248 R is fixed to a fixing portion  254 R. The fixing portion  254 R is formed on a member (not illustrated) mounted to the rear side plate  202 R, and has a projected shape, for example. The torsion first spring  248 R urges the rear lever member  242 R etc. so as to rotate in the direction of the arrow f. One end portion of the second torsion spring is coupled to the front lever member  242 F. The other end portion of the second torsion spring is fixed to another fixing portion (not illustrated). The other fixing portion is formed on another member (not illustrated) mounted to the front side plate  202 F, and has a projected shape, for example. The second torsion spring urges the front lever member  242 F etc. so as to rotate in the direction of the arrow f. 
     One end portion of the first coil spring  252 R is coupled to the rear lever member  242 R. The other end portion of the first coil spring  252 R is fixed to the rear side plate  202 R. The first coil spring  252 R urges the rear lever member  242 R etc. so as to rotate in the direction of the arrow f. One end portion of the second coil spring is coupled to the front lever member  242 F. The other end portion of the second coil spring is fixed to the front side plate  202 F. The second coil spring urges the front lever member  242 F etc. so as to rotate in the direction of the arrow f. 
     The rear lever member  242 R, the front lever member  242 F, the belt support portion  244 , and the fixing belt  230  are integrally urged by at least one of the first torsion spring  248 R and the second torsion spring and the first coil spring  252 R and the second coil spring so as to be rotated in the direction of the arrow f indicated in  FIG. 4  so that the fixing belt  230  is pressed against the fixing roller  204 . 
     In  FIG. 2  which is a plan view illustrating the fixing device  200 , in order to illustrate the positional relationship between the fixing device  200  and the other members with the fixing device  200  mounted to the image forming apparatus body  20  (see  FIG. 1 ), a rear cam member  310 R to be discussed later which is a member of the change mechanism  300 , a front cam member  310 F to be discussed later which is also a member of the change mechanism  300 , and the image forming apparatus body  20  are illustrated by the phantom lines (double-dashed lines). 
       FIG. 4  illustrates a section of the image forming apparatus  10  taken along the line IV-IV of  FIG. 1  with the fixing device  200  detached from the image forming apparatus body  20 . In  FIG. 4 , in order to illustrate the positional relationship between the change mechanism  300  and the fixing device  200 , a part of the fixing device  200  is illustrated by the phantom lines (double-dashed lines). 
     As illustrated in  FIG. 4 , the image forming apparatus body  20  forms an outer frame of the image forming apparatus  10 , and includes an outer covering portion  40  manufactured by shaping a resin or the like, for example. The image forming apparatus body  20  includes a rear frame portion  50 R and a front frame portion  50 F. The rear frame portion  50 R is disposed on the rear side in a space surrounded by the outer covering portion  40 , and made of metal, for example. The front frame portion  50 F is disposed on the front side in the space surrounded by the outer covering portion  40 , and made of metal, for example. The tie plate  30  discussed earlier is fixed to the rear frame portion  50 R and the front frame portion  50 F to be supported by the rear frame portion  50 R and the front frame portion  50 F. 
     As illustrated in  FIG. 4 , the change mechanism  300  includes the rear cam member  310 R (also see  FIG. 6 ) and the front cam member  310 F. The rear cam member  310 R is positioned on the rear side in the image forming apparatus body  20 . The front cam member  310 F is positioned on the front side in the image forming apparatus body  20 . The rear cam member  310 R and the front cam member  310 F are fixed to a coupling shaft  312 , and coupled to each other by the coupling shaft  312 . 
     The position at which the rear cam member  310 R is fixed to the coupling shaft  312  is determined such that the rear cam member  310 R and the rear lever member  242 R may contact each other (also see  FIG. 6 ). The position at which the front cam member  310 F is fixed to the coupling shaft  312  is determined such that the front cam member  310 F and the front lever member  242 F may contact each other. 
     The rear end portion side of the coupling shaft  312  is rotatably supported by the rear frame portion  50 R. The front end portion side of the coupling shaft  312  is rotatably supported by the front frame portion  50 F. Therefore, the rear cam member  310 R, the front cam member  310 F, and the coupling shaft  312  are rotatable with respect to the image forming apparatus body  20  in the direction of the arrow i indicated in  FIG. 6  and the direction of the arrow j indicated in  FIG. 6 . 
     As illustrated in  FIG. 4 , the change mechanism  300  which is composed of the rear cam member  310 R and the front cam member  310 F is disposed between the tie plate  30  and the ejection portion  24  in the direction indicated by the arrow f in  FIG. 4  in which the paper is ejected to the ejection portion  24 . As illustrated in  FIG. 4 , the change mechanism  300  is disposed on the outer side with respect to the ejection portion  24  in the direction of the width of the ejection portion  24  which crosses the direction indicated by the arrow f in which the paper is ejected to the ejection portion  24 . 
     The motor  360  is attached to the rear frame portion  50 R of the image forming apparatus body  20 . The motor  360  is coupled to the coupling shaft  312  via a drive transmission mechanism  370  such as a gear train, for example. The motor  360  transmits a drive force to integrally rotate the rear cam member  310 R, the front cam member  310 F, and the coupling shaft  312  with respect to the image forming apparatus body  20 . 
     As with the motor  360 , the drive transmission mechanism  370  is attached to the rear frame portion  50 R. Although the drive transmission mechanism  370  is composed of a gear train etc. as discussed earlier, the drive transmission mechanism  370  is illustrated schematically in  FIG. 4  with gears etc. composing the gear train discussed above not illustrated. 
     The tie plate  30  includes a rear opening portion  32 R formed at a position on the rear side and a front opening portion  32 F formed at a position on the front side (also see  FIG. 5 ). The rear lever member  242 R is disposed to pass through the rear opening portion  32 R to project from the side of the fixing device  200  with respect to the tie plate  30  to the side of the change mechanism  300  with respect to the tie plate  30 . The front lever member  242 F is disposed to pass through the front opening portion  32 F to project from the side of the fixing device  200  with respect to the tie plate  30  to the side of the change mechanism  300  with respect to the tie plate  30 . 
       FIG. 5  illustrates the tie plate  30 . As discussed earlier, the tie plate  30  includes the rear opening portion  32 R formed on the rear side and the front opening portion  32 F formed on the front side. 
       FIG. 6  illustrates the configuration and operation of the change mechanism  300 . The change mechanism  300  operates with the motor  360  controlled by a controller  140 , for example, on the basis of an input from the operation panel  130 , for example. 
     The controller  140  includes a control circuit including a central processing unit (CPU), for example, and determines a fixing condition on the basis of which of the paper feed device  610  and the paper feed device  620  is selected by the input to the operation panel  130 , and controls the motor  360  on the basis of the determined fixing condition. That is, in the case where the paper feed device  610  is selected, the motor  360  is controlled so as to achieve a fixing condition that is suitable for the paper accommodated in the paper feed device  610 . In the case where the paper feed device  620  is selected, the motor  360  is controlled so as to achieve a fixing condition that is suitable for the paper accommodated in the paper feed device  620 . 
     The motor  360  is rotated on the basis of the control by the controller  140  to rotate the rear cam member  310 R and the front cam member  310 F (see  FIG. 2 ) in the direction of the arrow i or the direction of the arrow j indicated in  FIG. 6 . When the rear cam member  310 R and the front cam member  310 F are rotated, the right end side of the rear lever member  242 R and the front lever member  242 F (see  FIG. 2 ) is moved in the direction of the arrow k indicated in  FIG. 6  or the direction of the arrow l indicated in  FIG. 6 . 
     Instead of the motor  360  rotating the rear cam member  310 R and the front cam member  310 F in the direction of the arrow i or the direction of the arrow j indicated in  FIG. 6 , the motor  360  may rotate the rear cam member  310 R and the front cam member  310 F only in the direction of the arrow i or the direction of the arrow j indicated in  FIG. 6 . 
     The direction of the arrow k and the direction of the arrow l, in which the change mechanism  300  moves the right end portion side of the rear lever member  242 R and the right end portion side of the front lever member  242 F, cross the direction of the arrow b and the direction of the arrow c (also see  FIG. 1 ), in which the fixing device  200  is mounted to and removed from the image forming apparatus body  20 . 
       FIGS. 7A to 7C  illustrate operation of the change mechanism  300 .  FIG. 7A  illustrates a state of the fixing device  200  at the time when a developer image is fixed to regular paper.  FIG. 7B  illustrates a state of the fixing device  200  at the time when a developer image is fixed to an envelope.  FIG. 7C  illustrates a state of the fixing device  200  in which a force of pressing the fixing roller  204  and the fixing belt  230  against each other has been canceled. 
     As illustrated in  FIGS. 7A to 7C , the position of the rear lever member  242 R is different among the state illustrated in  FIG. 7A , the state illustrated in  FIG. 7B , and the state illustrated in  FIG. 7C . The rear lever member  242 R is moved by the action of the rear cam member  310 R which receives a drive force transmitted from the motor  360  as discussed earlier. Although the front lever member  242 F is not illustrated in  FIGS. 7A to 7C , the front lever member  242 F is moved in the same manner as the rear lever member  242 R together with the rear lever member  242 R. 
     In the state illustrated in  FIG. 7A , the rear cam member  310 R is not in contact with the rear lever member  242 R. The fixing belt  230  is pressed against the fixing roller  204  by the action of both the first torsion spring  248 R and the second torsion spring (not illustrated) and the first coil spring  252 R and the second coil spring (not illustrated). 
     In the state illustrated in  FIG. 7B , the rear lever member  242 R has been moved in the direction of the arrow g and the arrow l from the position illustrated in  FIG. 7A  by the action of the rear cam member  310 R, and the front lever member  242 F has been moved in the same manner as the rear lever member  242 R. In the state illustrated in  FIG. 7B , the force with which the first coil spring  252 R presses the fixing belt  230  against the fixing roller  204  has been canceled by the movement of the rear lever member  242 R, and the force with which the second coil spring presses the fixing belt  230  against the fixing roller  204  has been canceled by the movement of the front lever member  242 F. 
     In the state illustrated in  FIG. 7B , the fixing belt  230  is pressed against the fixing roller  204  by only the first torsion spring  248 R and the second torsion spring. Therefore, in the state illustrated in  FIG. 7B , the force with which the fixing belt  230  is pressed against the fixing roller  204  is small compared to the state illustrated in  FIG. 7A . 
     In the state illustrated in  FIG. 7C , the rear lever member  242 R has been further moved in the direction of the arrow g and the arrow l from the position illustrated in  FIG. 7B  by the action of the rear cam member  310 R, and the front lever member  242 F has been moved in the same manner as the rear lever member  242 R. In the state illustrated in  FIG. 7C , the force with which the first torsion spring  248 R presses the fixing belt  230  against the fixing roller  204  has been canceled by the movement of the rear lever member  242 R, and the force with which the second torsion spring presses the fixing belt  230  against the fixing roller  204  has been canceled by the movement of the front lever member  242 F. 
     Therefore, in the state illustrated in  FIG. 7C , the fixing belt  230  is not pressed against the fixing roller  204  by any of the first torsion spring  248 R and the second torsion spring and the first coil spring  252 R and the second coil spring. In  FIG. 7C , for convenience of illustration, the fixing belt  230  and the fixing roller  204  are illustrated as contacting each other. However, it is desirable that the fixing roller  204  and the fixing belt  230  should not contact each other in a state in which a force of pressing the fixing roller  204  and the fixing belt  230  against each other has been canceled. 
     With the image forming apparatus  10  configured as described above, the fixing roller  204  and the fixing belt  230  are replaced by replacing the fixing device  200 . However, the change mechanism  300  and the motor  360  which are mounted to the image forming apparatus body  20  are not replaced together with the fixing device  200 , and are continuously used also after a new fixing device  200  is mounted to the image forming apparatus body  20 . 
     As has been described above, the present invention may be applied to an image forming apparatus such as a copier, a facsimile device, and a printer, for example, and a fixing device for use in such an image forming apparatus. 
     The foregoing description of the exemplary embodiment of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiment was chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.