Patent Publication Number: US-2016246230-A1

Title: Image forming apparatus, fixing device, and image forming method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2015-030205 filed Feb. 19, 2015. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to an image forming apparatus, a fixing device, and an image forming method. 
     SUMMARY 
     According to an aspect of the invention, there is provided an image forming apparatus including an image forming unit, a rotary member, a nipping area forming member, an assisting member, and a supporting unit. The image forming unit forms an image. The rotary member rotates while in contact with a recording medium, to which the image formed by the image forming unit is transferred. The nipping area forming member forms a nipping area for nipping the recording medium between the nipping area forming member and the rotary member. The assisting member assists the recording medium to peel off the rotary member and forms a gap between the assisting member and the rotary member. The supporting unit supports the assisting member to be movable in a direction of separating from the rotary member and a transport path used to transport the recording medium. 
    
    
     
       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  is a diagram illustrating a schematic configuration of an image forming apparatus according to the exemplary embodiment of the invention; 
         FIG. 2  is a diagram illustrating a schematic configuration of a fixing device included in the image forming apparatus illustrated in  FIG. 1 ; 
         FIG. 3  is a plan view illustrating a configuration of the fixing device illustrated in  FIG. 2 , in which a fixing roller, a fixing belt, and a peeling assisting member are attached to side plates; 
         FIG. 4  is a diagram illustrating the fixing device illustrated in  FIG. 2  in the direction of arrow IV in  FIG. 3 ; 
         FIG. 5  is a diagram illustrating the fixing roller and the peeling assisting member included in the fixing device illustrated in  FIG. 2 , as viewed from a left surface side; 
         FIG. 6  is a plan view illustrating a configuration of the fixing device illustrated in  FIG. 2 , in which changing members included in a changing mechanism are attached to the side plates in addition to the fixing roller, the fixing belt, and the peeling assisting member; 
         FIG. 7  is a diagram illustrating the fixing device illustrated in  FIG. 2  in the direction of arrow VII in  FIG. 6 ; and 
         FIGS. 8A to 8C  are diagrams illustrating operations of the fixing device illustrated in  FIG. 2 ,  FIG. 8A  being a diagram illustrating the fixing device in a state for fixing an image on plain paper,  FIG. 8B  being a diagram illustrating the fixing device in a state for fixing an image on thick paper, and  FIG. 8C  being a diagram illustrating the fixing device in a state in which force for pressing the fixing belt against the fixing roller is cancelled. 
     
    
    
     DETAILED DESCRIPTION 
     An exemplary embodiment for implementing the present invention will now be described with reference to the drawings.  FIG. 1  illustrates an image forming apparatus  10  according to an exemplary embodiment of the invention. As illustrated in  FIG. 1 , the image forming apparatus  10  includes an image forming apparatus body  20  formed with an exit port  22  through which a recording medium is discharged. Further, an upper surface of the image forming apparatus body  20  is used as an exit unit  24  onto which the recording medium having a toner image fixed thereon is discharged. Herein, the recording medium is a medium on which an image is fixed to be recorded. Specific examples of the recording medium include sheets and envelopes of various thicknesses, for example. A case in which a sheet such as plain paper is used as the recording medium will be described below as an example. 
     In the image forming apparatus body  20 , an image forming unit  100  is disposed which forms a toner image, that is, an image, on a sheet. The image forming unit  100  includes a photoconductor drum  102 , a charging device  104 , a latent image forming device  106 , a developing device  110 , a transfer device  112 , and a cleaning device  114 . The photoconductor drum  102  is used as an image carrier that carries the image. The charging device  104  uniformly charges a surface of the photoconductor drum  102 . The latent image forming device  106  forms an electrostatic latent image on the surface of the photoconductor 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  with a developer formed of a mixture of toner and carrier, for example. The transfer device  112  transfers to a sheet a toner image formed on the surface of the photoconductor drum  102  through the development of the latent image by the developing device  110 . The cleaning device  114  cleans off the toner and so forth remaining on the surface of the photoconductor drum  102  after the transfer of the toner image to the sheet by the transfer device  112 . 
     In the image forming apparatus body  20 , a fixing device  200  is further disposed which fixes on the sheet the toner image formed on the sheet by the image forming unit  100 . Details of the fixing device  200  will be described later. 
     In the image forming apparatus body  20 , sheet feed devices  610  and  620  are further disposed. The sheet feed device  610  supplies a sheet to the image forming unit  100 . The sheet feed device  620  similarly supplies a sheet to the image forming unit  100 . The sheet feed device  610  includes a sheet storage unit  612  that stores stacked sheets and a feeding device  614  that feeds the sheets stored in the sheet storage unit  612  to a later-described transport path  500 . Further, the sheet feed device  620  includes a sheet storage unit  622  that stores stacked sheets and a feeding device  624  that feeds the sheets stored in the sheet storage unit  622  to the later-described transport path  500 . 
     Each of the sheet storage units  612  and  622  is capable of storing different types of sheets in different sizes. The different types of sheets may be different in thickness, for example. When fixing toner images on different types of sheets different in thickness, for example, it is desirable to set a fixing condition, under which the fixing device  200  fixes a toner image on a sheet, to be different between the different types of sheets. 
     In the image forming apparatus body  20 , the transport path  500  for transporting a sheet is further formed. The sheet feed device  620 , the sheet feed device  610 , registration rollers  510 , the transfer device  112 , the photoconductor drum  102 , the fixing device  200 , and exit rollers  520  are disposed along the transport path  500  in this order from the upstream side in a transport direction of the sheet on the transport path  500 . 
     The registration rollers  510  temporarily stop the movement of a leading edge portion of the sheet supplied from one of the sheet feed devices  610  and  620 , and resume the movement of the leading edge portion of the sheet toward a transfer area formed by the photoconductor drum  102  and the transfer device  112  in synchronization with the formation of the toner image on the surface of the photoconductor drum  102 . 
     The transfer device  112  is applied with a transfer bias, and electrostatically transfers the toner image formed on the surface of the photoconductor drum  102  onto the sheet. 
     The exit rollers  520  discharge the sheet having the toner image fixed thereon by the fixing device  200  toward the exit unit  24  through the exit port  22 . 
     Further, an operation panel  30  used as an operation unit for operating the image forming apparatus  10  is attached to, for example, a front surface of the image forming apparatus body  20 . The operation panel  30  is used to input information related to image formation, such as an input by an operator as to which one of the sheet feed devices  610  and  620  should be caused to supply the sheet, for example. 
       FIG. 2  illustrates a schematic configuration of the fixing device  200 . As illustrated in  FIG. 2 , the fixing device  200  includes a fixing roller  210 , a fixing belt  230 , a peeling assisting member  250 , and a changing mechanism  300 . The fixing roller  210  is used as a rotary member that rotates while in contact with the sheet, to which the toner image formed by the image forming unit  100  (see  FIG. 1 ) is transferred. Further, the fixing roller  210  is connected to a drive source  260 , such as a motor, for example, via a drive transmission mechanism  262 , such as a gear train, for example, and is rotated in the direction of arrow a illustrated in  FIG. 2  by drive transmitted from the drive source  260 . 
     The fixing roller  210  has a cylindrical shape, and includes a core rod member  212  made of aluminum, for example, and an elastic layer  214  made of rubber, for example, and covering the core rod member  212 . A surface of the elastic layer  214  is coated with and protected by a resin or the like. The resin coating also makes it easy for the sheet having the toner image formed thereon to peel off a surface of the fixing roller  210 . 
     The fixing device  200  further includes a heat source  216 , which may be a halogen lamp, for example. The heat source  216  is disposed in a hollow space inside the core rod member  212 . 
     The fixing roller  210  includes the elastic layer  214 , as described above, and thus is compressed as the fixing belt  230  and so forth are pressed against the fixing roller  210 , and expands as the pressed fixing belt  230  and so forth separate from the fixing roller  210 . Further, the fixing roller  210  is compressed as the force for pressing the fixing belt  230  and so forth against the fixing roller  210  is increased, and expands as the force for pressing the fixing belt  230  and so forth against the fixing roller  210  is reduced. 
     The fixing belt  230  is used as a nipping area forming member that forms a nip part N, which is a nipping area for nipping the sheet, between the fixing belt  230  and the fixing roller  210 . The fixing belt  230  is an endless band-shaped member made of a flexible material, and is rotated in the direction of arrow b illustrated in  FIG. 2  by the rotation of the fixing roller  210 . Further, the fixing belt  230  is rotatably supported and pressed rightward (rightward in  FIGS. 1 and 2 ) against the fixing roller  210  by a fixing belt supporting member  240  disposed inside the fixing belt  230 . The fixing belt supporting member  240  is one of members forming a nipping area forming member supporting unit. 
     The fixing belt  230  may be replaced by a pad member, for example, which serves as the nipping area forming member that forms the nipping area (the nip part N) between the nipping area forming member and the fixing roller  210 . As described above, the nipping area forming member may or may not be moved by the rotation of the fixing roller  210 . 
     The peeling assisting member  250  is used as an assisting member for assisting the sheet to peel off the surface of the fixing roller  210 , and forms a gap G between the peeling assisting member  250  and the fixing roller  210 . When the toner image is formed on the sheet, the toner image is not formed on a leading edge portion in the transport direction of the sheet in many cases. Further, a part of the leading edge portion of the sheet not formed with the toner image (hereinafter referred to as the leading edge margin) is unlikely to adhere to the fixing roller  210 , and thus is often separated from the fixing roller  210 . 
     The peeling assisting member  250  assists the sheet to peel off the fixing roller  210  by guiding the leading edge margin separated from the fixing roller  210  onto the peeling assisting member  250 . The peeling assisting member  250  is thus capable of guiding and assisting the sheet to peel off the fixing roller  210  despite the gap G formed between the peeling assisting member  250  and the fixing roller  210 . Further, due to the gap G formed between the peeling assisting member  250  and the fixing roller  210 , the peeling assisting member  250  does not come into contact with and degrade the surface of the fixing roller  210 . 
     The changing mechanism  300  is used as a changing unit that changes the force for pressing the fixing belt  230  against the fixing roller  210 . Further, the changing mechanism  300  is connected to a drive source  302 , such as a motor, for example, and is driven by drive transmitted from the drive source  302 . The changing mechanism  300  may be operated by direction operation by the operator instead of the use of the drive source  302 . 
     The changing mechanism  300  is further connected to the fixing belt supporting member  240  and the peeling assisting member  250 . Further, the peeling assisting member  250  moves to change the size of the gap G in accordance with the change by the changing mechanism  300  of the force for pressing the fixing belt  230  against the fixing roller  210 . More specifically, the peeling assisting member  250  moves in a direction of approaching the fixing roller  210  in accordance with an increase by the changing mechanism  300  of the force for pressing the fixing belt  230  against the fixing roller  210 . In this case, the fixing roller  210  is compressed owing to the increase in the force for pressing the fixing belt  230  against the fixing roller  210 , raising the possibility that the gap G may exceed a desirable value. Since the peeling assisting member  250  moves in the direction of approaching the fixing roller  210 , however, the gap G is unlikely to exceed the desirable value. 
     Further, the peeling assisting member  250  moves in a direction of separating from the fixing roller  210  and the transport path  500  in accordance with a reduction by the changing mechanism  300  of the force for pressing the fixing belt  230  against the fixing roller  210 . In this case, the fixing roller  210  expands owing to the reduction in the force for pressing the fixing belt  230  against the fixing roller  210 , raising the possibility that the peeling assisting member  250  may come into contact with the fixing roller  210 . The peeling assisting member  250 , however, moves in the direction of separating from the fixing roller  210 , and thus does not come into contact with the fixing roller  210 . 
     Further, if the peeling assisting member  250  moves toward the transport path  500 , there arises the possibility that the peeling assisting member  250  may interfere with the transport path  500  and obstruct the transport of the sheet on the transport path  500 . In the present image forming apparatus  10 , however, the peeling assisting member  250  moves in the direction of separating from the transport path  500 , and thus does not obstruct the transport of the sheet on the transport path  500 . 
     Herein, the reduction of the force for pressing the fixing belt  230  against the fixing roller  210  includes the cancellation of the force for pressing the fixing belt  230  against the fixing roller  210 . As described above, in the present image forming apparatus  10 , the peeling assisting member  250  moves in the direction of separating from the fixing roller  210  and the transport path  500  in accordance with the expansion of the fixing roller  210 . 
     The fixing roller  210 , the fixing belt  230 , and the peeling assisting member  250  described above are supported by later-described support side plates  280 F and  280 R included in the fixing device  200  (see  FIG. 3 ). Details of the changing mechanism  300  will be described later. 
       FIG. 3  illustrates the support side plates  280 F and  280 R included in the fixing device  200 , and also illustrate a configuration in which the fixing roller  210 , the fixing belt  230 , and the peeling assisting member  250  are supported by the support side plates  280 F and  280 R. 
     As illustrated in  FIGS. 3 and 4 , a shaft bearing  218 F is attached to an end portion of the fixing roller  210  on the front side (the lower side in  FIG. 3  and the near side of paper in  FIG. 4 ), and a shaft bearing  218 R is attached to an end portion of the fixing roller  210  on the rear side (the upper side in  FIG. 3  and the depth side of paper in  FIG. 4 ). Further, the shaft bearing  218 F is fixed to the support side plate  280 F, and the shaft bearing  218 R is fixed to the support side plate  280 R. Thereby, the fixing roller  210  is installed to be rotatable relative to the support side plates  280 F and  280 R. In  FIG. 4 , a part of the shaft bearing  218 F is indicated by an imaginary line (dashed double-dotted line) to clearly illustrate members disposed behind the shaft bearing  218 F. 
     The fixing belt  230  is supported by a fixing belt supporting unit  232 , which is used as the nipping area forming member supporting unit that supports the fixing belt  230 , to be swingable relative to the support side plates  280 F and  280 R. The fixing belt supporting unit  232  includes the aforementioned fixing belt supporting member  240  (see also  FIG. 2 ), swing members  234 F and  234 R, and a regulation plate  242 . 
     In the fixing belt supporting unit  232 , a front end portion of the fixing belt supporting member  240  disposed inside the fixing belt  230  is fixed to the swing member  234 F, and a rear end portion of the fixing belt supporting member  240  is fixed to the swing member  234 R. Further, the swing member  234 F is supported by a shaft member  236 F to be rotatable relative to the support side plate  280 F in the directions of arrows c 1  and c 2  illustrated in  FIG. 4 . The swing member  234 R is supported by a shaft member  236 R to be rotatable relative to the support side plate  280 R in the directions of arrows c 1  and c 2 . 
     With the above-described structure, the fixing belt  230  is supported to be rotatable and swingable relative to the support side plates  280 F and  280 R around the shaft members  236 F and  236 R in the directions of arrows c 1  and c 2  illustrated in  FIG. 4  integrally with the fixing belt supporting unit  232 . 
     The regulation plate  242  has a front side attached to an upper portion of the swing member  234 F, a rear side attached to an upper portion of the swing member  234 R, and a right end portion projecting toward a later-described supporting member  252 . The regulation plate  242  comes into contact with and stops the supporting member  252  to regulate the position of the supporting member  252 . Although the regulation plate  242  is illustrated in  FIG. 4 , the illustration of the regulation plate  242  is omitted in FIG.  3  for convenience of illustration. 
     The swing member  234 F is attached with one end portion of a biasing member  238 F formed of an elastic body, such as a coil spring, for example, and the other end portion of the biasing member  238 F is attached to a later-described changing member  310 F. The swing member  234 R is attached with one end portion of a biasing member  238 R formed of an elastic body, such as a coil spring, for example, similarly to the biasing member  238 F, and the other end portion of the biasing member  238 R is attached to a later-described changing member  310 R. The fixing belt  230  is biased by the biasing members  238 F and  238 R to rotate in the direction of arrow c 1  around the shaft members  236 F and  236 R integrally with the fixing belt supporting unit  232 . Further, biased by the biasing members  238 F and  238 R, the fixing belt  230  is pressed against the fixing roller  210 . 
     As described above, the fixing belt supporting unit  232  used as the nipping area forming member supporting unit is biased in the direction in which the fixing belt  230  used as the nipping area forming member is pressed against the fixing roller  210  used as the rotary member. 
     The peeling assisting member  250  is supported by the supporting member  252 , which is used as a supporting unit and also as an assisting member supporting member included in the supporting unit. The peeling assisting member  250  and the supporting member  252  are supported to be integrally swingable and rotatable relative to the support side plates  280 F and  280 R. More specifically, a front side of the supporting member  252  is supported by a shaft member  254 F to be rotatable relative to the support side plate  280 F in the directions of arrows d 1  and d 2  illustrated in  FIG. 4 , and a rear side of the supporting member  252  is supported by a shaft member  254 R to be rotatable relative to the support side plate  280 R in the directions of arrows d 1  and d 2  illustrated in  FIG. 4 . 
     Further, the front side of the supporting member  252  is attached with a biasing member  256 F formed of an elastic body, such as a torsion spring, for example, and the rear side of the supporting member  252  is attached with a biasing member  256 R (not illustrated) formed of an elastic body, such as a torsion spring, for example, similarly to the biasing member  256 F. Further, the supporting member  252  is biased by the biasing members  256 F and  256 R to rotate around the shaft members  254 F and  254 R in the direction of arrow d 1 . The peeling assisting member  250  is thus biased to move in the direction of separating from the fixing roller  210  integrally with the supporting member  252 . 
     Further, the position of the supporting member  252  is regulated by the regulation plate  242  of the fixing belt supporting unit  232 . More specifically, the supporting member  252  comes into contact with the lower surface of the regulation plate  242  to be stopped against the biasing of the biasing members  256 F and  256 R. With the position of the supporting member  252  regulated by the regulation plate  242 , the position of the peeling assisting member  250  is regulated. 
     Herein, when O 1  represents the rotation center of the peeling assisting member  250  and the supporting member  252 , O 2  represents the rotation center of the fixing roller  210 , and L 1  represents a line connecting the rotation center O 2  and an end portion of the peeling assisting member  250  on the side of the fixing roller  210 , the rotation center O 1  is located downstream of the line L 1  in the transport direction in which the sheet is transported. When the supporting member  252  rotates in the direction of arrow d 1 , therefore, the peeling assisting member  250  moves in the direction of separating from the fixing roller  210 , unlike a case in which the rotation center O 1  is located upstream of the line L 1 . 
     Further, the rotation center O 1  is located upstream in the sheet transport direction of the end portion of the peeling assisting member  250  on the side of the fixing roller  210 , that is, upstream in the sheet transport direction of a line L 2  illustrated in  FIG. 4 . When the supporting member  252  rotates in the direction of arrow d 1 , therefore, the peeling assisting member  250  moves in the direction of separating from the transport path  500 , unlike a case in which the rotation center O 1  is located downstream of the line L 2 . 
       FIG. 5  illustrates the fixing roller  210 , the peeling assisting member  250 , and the supporting member  252 , as viewed from a left surface side. As illustrated in  FIG. 5 , the peeling assisting member  250  is attached to the supporting member  252  with plural, such as five, for example, fasteners  258  aligned in the longitudinal direction of the peeling assisting member  250  (the horizontal direction in  FIG. 5 ). The fasteners  258  may be screws, for example. With the fasteners  258  adjusted, the gap G (see  FIG. 2 ) between the peeling assisting member  250  and the fixing roller  210  is adjusted at respective positions of the fasteners  258  in the longitudinal direction. 
     Further, as illustrated in  FIG. 5 , the supporting member  252  has end portions  253  respectively in contact with areas  220 , which are located at opposite ends of the fixing roller  210  and do not come into contact with the sheet. Accordingly, the supporting member  252  and the peeling assisting member  250  are accurately positioned relative to the fixing roller  210 . Instead of the configuration in which the end portions  253  are placed in contact with the areas  220 , the front end portion  253  may be placed in contact with the shaft bearing  218 F, and the rear end portion  253  may be placed in contact with the shaft bearing  218 R. 
       FIGS. 6 and 7  illustrate the changing mechanism  300 . As illustrated in  FIGS. 6 and 7 , the changing mechanism  300  includes the aforementioned changing members  310 F and  310 R (see also  FIG. 3 ) and cam members  320 F and  320 R. 
     The changing member  310 F is supported by the shaft member  236 F to be rotatable and swingable relative to the support side plate  280 F in the directions of arrows c 1  and c 2  illustrated in  FIG. 7 . The changing member  310 R is supported by the shaft member  236 R to be rotatable and swingable relative to the support side plate  280 R in the directions of arrows c 1  and c 2  illustrated in  FIG. 7 . Further, as described above, the changing member  310 F is connected to the other end portion of the biasing member  238 F, the one end portion of which is connected to the swing member  234 F. Further, as described above, the changing member  310 R is connected to the other end portion of the biasing member  238 R, the one end portion of which is connected to the swing member  234 R. 
     The cam members  320 F and  320 R are connected by a connecting shaft  322 . As the connecting shaft  322  is rotated by the drive transmitted from the drive source  302 , the cam members  320 F and  320 R rotate at the same phase integrally with the connecting shaft  322 . Further, the cam member  320 F is in contact with and presses the changing member  310 F in a direction of rotating the changing member  310 F around the shaft member  236 F in the direction of arrow c 1  against the biasing of the biasing member  238 F. Further, the cam member  320 R is in contact with and presses the changing member  310 R around the shaft member  236 R in a direction of rotating the changing member  310 R in the direction of arrow c 1  against the biasing of the biasing member  238 R. 
     If the changing members  310 F and  310 R rotate in the direction of arrow d 1  in accordance with the operation of the cam members  320 F and  320 R, the biasing members  238 F and  238 R deform to contract. Thereby, the force for biasing the fixing belt supporting unit  232  to rotate in the direction of arrow c 1  is increased, and the force for rotating the fixing belt supporting unit  232  in the direction of arrow c 1  is increased. Consequently, the force for pressing the fixing belt  230  against the fixing roller  210  is increased. 
     Meanwhile, if the changing members  310 F and  310 R rotate in the direction of arrow d 2  in accordance with the operation of the cam members  320 F and  320 R, the biasing members  238 F and  238 R deform to expand. Thereby, the force for biasing the fixing belt supporting unit  232  to rotate in the direction of arrow c 1  is reduced, and the force for rotating the fixing belt supporting unit  232  in the direction of arrow c 1  is reduced. Consequently, the force for pressing the fixing belt  230  against the fixing roller  210  is reduced. 
     The phase between the cam members  320 F and  320 R is controlled by a controller  32  in accordance with the input from the operation panel  30 . That is, in accordance with the thickness of the sheet stored in the sheet storage unit  612  or  622  and specified by the operation of the operation panel  30 , the controller  32  calculates the phase between the cam members  320 F and  320 R to meet the fixing condition suitable for the specified sheet, and controls the drive source  302  such that the phase between the cam members  320 F and  320 R matches the calculated phase. 
       FIGS. 8A to 8C  are diagrams illustrating operations of the fixing device  200 .  FIG. 8A  is a diagram illustrating the fixing device  200  in a state for fixing a toner image on plain paper.  FIG. 8B  is a diagram illustrating the fixing device  200  in a state for fixing a toner image on thick paper thicker than the plain paper.  FIG. 8C  is a diagram illustrating the fixing device  200  in a state in which the force for pressing the fixing belt  230  against the fixing roller  210  is cancelled. To clearly illustrate the operations of the fixing device  200 ,  FIGS. 8A to 8C  exaggeratingly illustrate changes in position of the peeling assisting member  250  and the fixing belt  230  between the respective states. 
     In a shift from the state illustrated in  FIG. 8A  for fixing a toner image on plain paper to the state illustrated in  FIG. 8B  for fixing a toner image on thick paper, the cam members  320 F and  320 R rotate in accordance with the control of the controller  32 . Thereby, the changing members  310 F and  310 R rotate in the direction of arrow c 2 . Accordingly, the fixing belt supporting unit  232  and the fixing belt  230  rotate in the direction of arrow c 2 , and the force for pressing the fixing belt  230  against the fixing roller  210  is reduced. 
     Further, the regulation plate  242  of the fixing belt supporting unit  232  moves, and the supporting member  252  regulated in movement by the regulation plate  242  is biased by the biasing members  256 F and  256 R to rotate in the direction of arrow d 1 . As the supporting member  252  rotates in the direction of arrow d 1 , the peeling assisting member  250  moves in the direction of separating from the fixing roller  210  and the transport path  500 . 
     Also in a shift from the state illustrated in  FIG. 8B  for fixing a toner image on thick paper to the state illustrated in  FIG. 8C , in which the force for pressing the fixing belt  230  against the fixing roller  210  is cancelled, the cam members  320 F and  320 R rotate in accordance with the control of the controller  32 . Thereby, the changing members  310 F and  310 R rotate in the direction of arrow c 2 . Accordingly, the fixing belt supporting unit  232  and the fixing belt  230  rotate in the direction of arrow c 2 , and the force for pressing the fixing belt  230  against the fixing roller  210  is further reduced. 
     Further, the regulation plate  242  of the fixing belt supporting unit  232  moves to separate from the supporting member  252 . Separated from the regulation plate  242 , the supporting member  252  is biased by the biasing members  256 F and  256 R to rotate in the direction of arrow d 1 . As the supporting member  252  rotates in the direction of arrow d 1 , the peeling assisting member  250  further moves in the direction of separating from the fixing roller  210  and the transport path  500 . 
     As described above, the invention is applicable to an image forming apparatus, such as a copier, a facsimile machine, or a printer, for example, and a fixing device used 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.