Patent Publication Number: US-11385577-B2

Title: Transport device, fixing device, and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of International Application No. PCT/JP2019/31499 filed on Aug. 8, 2019, and claims priority from Japanese Patent Application No. 2019-047499 filed on Mar. 14, 2019. 
    
    
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a transport device, a fixing device, and an image forming apparatus. 
     Related Art 
     JP-A-2006-259223 discloses a fixing device including: a fixing roll pair including a first fixing roll and a second fixing roll arranged as a pair, at least one of which is a heating roll, and a surface layer of at least one of which is replaceable; a sticking means provided with a sticking member; a charger for charging at least one of a recording medium and the sticking means; and a securing means for physically securing a tip end portion of the recording medium in a transport direction to the sticking means by a gripping part, and in the fixing device, the charger electrostatically attracts the sticking member and the recording medium, the securing means secures the recording medium to the sticking means, and then the fixing roll pair transports the recording medium together with the sticking means while sandwiching the recording medium, thus fixing an image. 
     SUMMARY 
     It is considered that a transport device such as the fixing device has a configuration including a first nipping part such as a heating roll; a second nipping part such as a pressure roll that forms, with the first nipping part, a nip region in which the recording medium is nipped and that is relatively movable between a first position at which a distance from the first nipping part is a distance at which the nip region is formed and a second position at which a distance from the first nipping part is longer than the distance at the first position; and a transport part that transports the recording medium by moving a holder that holds a front end side of the recording medium and causes the holder to pass through the nip region. 
     In this configuration, when a middle point of a period from when a relative movement of the second nipping part from the first position to the second position is started until when the second nipping part is relatively moved to the first position coincides with a middle point of a period during which a holding position where the holder holds the recording medium passes through the nip region, a timing at which the recording medium is nipped by the first nipping part and the second nipping part is delayed. 
     Aspects of non-limiting embodiments of the present disclosure relate to advancing the timing at which the recording medium is nipped by the first nipping part and the second nipping part, as compared with the configuration in which the middle point of the period from when the relative movement of the second nipping part from the first position to the second position is started until when the second nipping part is relatively moved to the first position coincides with the middle point of the period during which the holding position passes through the nip region. 
     Aspects of certain non-limiting embodiments of the present disclosure address the above advantages and/or other advantages not described above. However, aspects of the non-limiting embodiments are not required to address the advantages described above, and aspects of the non-limiting embodiments of the present disclosure may not address advantages described above. 
     According to an aspect of the present disclosure, there is provided a transport device including: a first nipping part having an outer surface; a second nipping part having an outer surface, the second nipping part being configured to form, with the first nipping part, a nip region in which a recording medium is nipped by bringing the outer surface of the second nipping part into contact with the outer surface of the first nipping part, the second nipping part being relatively movable between a first position at which a distance from the second nipping part to the first nipping part is a first distance at which the nip region is formed and a second position at which the distance from the second nipping part to the first nipping part is longer than the first distance; a transport part including a holder that holds a front end side of the recording medium, the transport part being configured to move the holder to transport the recording medium to pass through the nip region together with the holder while the recording medium is being held by the holder; and a moving mechanism configured to relatively move the second nipping part such that a middle point of a period from when a relative movement of the second nipping part from the first position to the second position is started before a holding position of the recording medium by the holder enters the nip region to when the second nipping part is relatively moved to the first position after the holding position enters the nip region precedes a middle point of a period during which the holding position passes through the nip region. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Exemplary embodiment(s) of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a schematic diagram showing an image forming apparatus according to the present exemplary embodiment; 
         FIG. 2  is a perspective view showing a secondary transfer body according to the present exemplary embodiment; 
         FIG. 3  is an enlarged side view showing a secondary transfer portion of the image forming apparatus according to the present exemplary embodiment; 
         FIG. 4  is a front view showing a part of a fixing device according to the present exemplary embodiment; 
         FIG. 5  is a side view showing a part of the fixing device according to the present exemplary embodiment; 
         FIG. 6  is a perspective view showing a part of the fixing device according to the present exemplary embodiment; 
         FIG. 7  is a front view showing a state in which a heating roll is located at a retracted position in the fixing device shown in  FIG. 4 ; 
         FIG. 8  is a perspective view showing grippers according to the present exemplary embodiment; 
         FIG. 9  is a front view schematically showing a positional relationship between the heating roll and a pressure roll according to the present exemplary embodiment; 
         FIG. 10  is a front view schematically showing a positional relationship between the heating roll and the pressure roll according to the present exemplary embodiment; 
         FIG. 11  is a front view schematically showing a positional relationship between the heating roll and the pressure roll according to the present exemplary embodiment; 
         FIG. 12  is a front view schematically showing a positional relationship between the heating roll and the pressure roll according to the present exemplary embodiment; 
         FIG. 13  is a diagram showing a cam according to the present exemplary embodiment; 
         FIG. 14  is a diagram showing a relationship between an elapsed time (horizontal axis) and the positional relationship between the heating roll and the pressure roll (vertical axis); and 
         FIG. 15  is a front view schematically showing a positional relationship between a heating roll and a pressure roll according to a modification. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an example of an exemplary embodiment according to the present disclosure will be described with reference to the drawings. 
     (Image Forming Apparatus  10 ) 
     A configuration of an image forming apparatus  10  according to the present exemplary embodiment will be described.  FIG. 1  is a schematic diagram showing the configuration of the image forming apparatus  10  according to the present exemplary embodiment. 
     The image forming apparatus  10  shown in  FIG. 1  is an example of an image forming apparatus that forms an image on a recording medium. Specifically, the image forming apparatus  10  is an electrophotographic image forming apparatus that forms a toner image (an example of an image) on a recording medium P. More specifically, the image forming apparatus  10  includes an image forming unit  14  and a fixing device  16 . Hereinafter, each part (the image forming unit  14  and the fixing device  16 ) of the image forming apparatus  10  will be described. 
     (Image Forming Unit  14 ) 
     The image forming unit  14  has a function of forming a toner image on the recording medium P. Specifically, the image forming unit  14  includes a toner image forming unit  22  and a transfer device  17 . 
     (Toner Image Forming Unit  22 ) 
     The toner image forming unit  22  shown in  FIG. 1  has a function of forming a toner image. Plural toner image forming units  22  are provided so as to form toner images for each color. In the present exemplary embodiment, toner image forming units  22  of a total of four colors of yellow (Y), magenta (M), cyan (C), and black (K) are provided. The (Y), (M), (C), and (K) shown in  FIG. 1  show constituent portions corresponding to the respective colors. 
     Since the toner image forming unit  22  of each color has the same configuration except for the toner to be used, on behalf of the toner image forming unit  22  of each color, each part of the toner image forming unit  22 (Y) is designated by a reference numeral in FIG.  1 . 
     Specifically, the toner image forming unit  22  of each color includes a photoconductor drum  32  (photoconductor) that rotates in one direction (for example, in a counterclockwise direction in  FIG. 1 ). Further, the toner image forming unit  22  of each color includes a charging unit  23 , an exposure device  36 , a developing device  38 , and a removing device  40 . 
     In the toner image forming unit  22  of each color, the charging unit  23  charges the photoconductor drum  32 . The exposure device  36  exposes the photoconductor drum  32  charged by the charging unit  23  to light, so as to form an electrostatic latent image on the photoconductor drum  32 . The developing device  38  develops the electrostatic latent image that is formed on the photoconductor drum  32  by the exposure device  36 , to form a toner image. Then, the removing device  40  removes toner remaining on the photoconductor drum  32  after the toner image is transferred to a transfer belt  24  to be described later. 
     (Transfer Device  17 ) 
     The transfer device  17  shown in  FIG. 1  is a device that transfers the toner image formed by the toner image forming unit  22  to the recording medium P. Specifically, the transfer device  17  primarily transfers the toner image of the photoconductor drum  32  of each color onto the transfer belt  24  as an intermediate transfer body in a superimposed manner, and secondarily transfers the superimposed toner images onto the recording medium P at a secondary transfer position T 2  (a transfer nip region  28 A to be described later). More specifically, as shown in  FIG. 1 , the transfer device  17  includes the transfer belt  24 , primary transfer rolls  26 , a secondary transfer body  27 , and a charging unit  60 . 
     (Primary Transfer Roll  26 ) 
     The primary transfer roll  26  shown in  FIG. 1  is a roll that transfers the toner image of the photoconductor drum  32  of each color to the transfer belt  24  at a primary transfer position T 1  between the photoconductor drum  32  and the primary transfer roll  26 . In the present exemplary embodiment, the toner image formed on the photoconductor drum  32  is transferred to the transfer belt  24  at the primary transfer position T 1  by applying a primary transfer electric field between the primary transfer roll  26  and the photoconductor drum  32 . 
     (Transfer Belt  24 ) 
     The toner image is transferred from the photoconductor drum  32  of each color to an outer circumferential surface of the transfer belt  24  shown in  FIG. 1 . Specifically, the transfer belt  24  is configured as follows. As shown in  FIG. 1 , the transfer belt  24  has an annular shape. The transfer belt  24  wraps around plural rolls  42  including a driving roll  42 D and wrap rolls  42 E,  42 F, and a posture of the transfer belt  24  is determined thereby. For example, the driving roll  42 D among the plural rolls  42  is rotationally driven by a driving unit (not shown), and thus the transfer belt  24  rotates in a predetermined direction indicated by an arrow A (hereinafter, referred to as a belt rotation direction A). A specific configuration of the wrap rolls  42 E,  42 F will be described later. 
     (Secondary Transfer Body  27 ) 
     The secondary transfer body  27  is an example of a transfer unit that transfers an image onto a recording medium. Specifically, as shown in  FIG. 2 , the secondary transfer body  27  includes a transfer cylinder  28  and a pair of sprockets  29 . As shown in  FIG. 3 , the transfer cylinder  28  has a transfer nip region  28 A as a nip region in which the recording medium P is nipped between the transfer cylinder  28  and the outer circumferential surface of the transfer belt  24 . In  FIG. 3 , the recording medium P is simplified and a part thereof is shown. 
     The transfer nip region  28 A is formed by wrapping the transfer belt  24  around the transfer cylinder  28 . The transfer nip region  28 A may also be referred to as a contact region where the transfer belt  24  and the transfer cylinder  28  are in contact with each other. Further, the transfer nip region  28 A is set as the secondary transfer position T 2  at which the toner image is transferred from the transfer belt  24  onto the recording medium P. The transfer cylinder  28  transports the recording medium P while sandwiching the recording medium P between the transfer cylinder  28  and the transfer belt  24  in the transfer nip region  28 A. 
     As shown in  FIG. 2 , the pair of sprockets  29  are arranged on both end sides of the transfer cylinder  28  in an axial direction thereof. In other words, the transfer cylinder  28  is provided between the pair of sprockets  29 . Further, the pair of sprockets  29  is arranged coaxially with the transfer cylinder  28  and rotates integrally with the transfer cylinder  28 . The secondary transfer body  27  is rotationally driven by a driving unit (not shown). 
     On an outer circumference of the transfer cylinder  28 , one recess  28 D in which grippers  54  and an attachment member  55 , which are to be described later, of a transport part  15  are accommodated is formed. Plural recesses  28 D may be formed according to an arrangement interval of the grippers  54  along a rotation direction C of a chain  52  to be described later. 
     (Charging Unit  60 ) 
     As shown in  FIG. 3 , the charging unit  60  is arranged on an inner side of the transfer belt  24  so as to face the transfer cylinder  28 . Specifically, the charging unit  60  is a charger (so-called corotron charging unit) that transfers the toner image on the transfer belt  24  by corona discharge. 
     More specifically, the charging unit  60  includes a discharge wire  60 A and a case  62  (housing). The discharge wire  60 A has a linear shape with a length along the axial direction of the transfer cylinder  28 . 
     The case  62  surrounds the discharge wire. Specifically, the case  62  is formed in a box shape, and has an opening  62 C on a transfer cylinder  28  side (that is, a lower side). 
     Specifically, the case  62  has a first wall  62 A arranged on a side opposite the transfer cylinder  28  with respect to the discharge wire  60 A, and a pair of second walls  62 B arranged upstream and downstream of the discharge wire  60 A in the belt rotation direction A. Further, the case  62  has third walls (not shown) arranged on both end sides of the discharge wire  60 A in a length direction thereof. 
     In the charging unit  60 , a voltage is applied to the discharge wire  60 A and the discharge wire  60 A discharges, so that the recording medium P is electrostatically attracted to the transfer belt  24  and the transfer cylinder  28 . Further, in the charging unit  60 , the transfer belt  24  is charged due to the discharge of the discharge wire  60 A, and the toner images superimposed on the transfer belt  24  are transferred from the transfer belt  24  to the recording medium P in the transfer nip region  28 A (secondary transfer position T 2 ). 
     (Wrap rolls  42 E,  42 F) 
     The wrap rolls  42 E,  42 F shown in  FIGS. 1 and 3  are a pair of wrap rolls on the inner side the transfer belt  24 , around which the transfer belt  24  wraps. Specifically, the wrap rolls  42 E,  42 F are arranged upstream and downstream of the charging unit  60  in the belt rotation direction A. Further, wrapping portions  43 E,  43 F in the transfer belt  24  that wrap around the wrap rolls  42 E,  42 F are both separated from the transfer cylinder  28 . 
     (Fixing Device  16 ) 
     The fixing device  16  shown in  FIG. 1  is a device that fixes the toner image, which is transferred to the recording medium P by the transfer cylinder  28 , on the recording medium P. More specifically, as shown in  FIG. 1 , the fixing device  16  includes a pressing body  67  serving as a pressure member, a heating roll  68  serving as a heating member, the transport part  15 , a support body  70  (see  FIGS. 4 and 5 ), and a moving mechanism  80  (see  FIGS. 4 and 5 ). 
     (Pressing Body  67 ) 
     As shown in  FIG. 6 , the pressing body  67  includes a pressure roll  69  and the pair of sprockets  19 . The pressure roll  69  is an example of a first nipping part. The pressure roll  69  has a function of pressing the recording medium P by sandwiching the recording medium P between the pressure roll  69  and the heating roll  68 . Specifically, as shown in  FIGS. 4, 5, and 6 , the pressure roll  69  includes a shaft portion  69 A and a roll portion  69 B formed on an outer circumference of the shaft portion  69 A. 
     As shown in  FIG. 6 , the pair of sprockets  19  are arranged on both end sides of the pressure roll  69  in an axial direction thereof. In other words, the pressure roll  69  is provided between the pair of sprockets  19 . Further, the pair of sprockets  19  are arranged coaxially with the pressure roll  69 , and are configured to rotate integrally with the pressure roll  69 . 
     Specifically, as shown in  FIG. 5 , the pair of sprockets  19  are fixed to the shaft portion  69 A on axial outer sides of the roll portion  69 B of the pressure roll  69 . The axial outer side refers to a direction side from a center in the axial direction toward both ends in the axial direction. In  FIG. 5 , only one sprocket  19  in the pair of sprockets  19  is shown. In  FIGS. 4 and 7 , illustration of the sprockets  19  is omitted. 
     The pressure roll  69  is, for example, rotationally driven, via the shaft portion  69 A, in a direction indicated by an arrow E shown in  FIGS. 4 and 6  by a driving unit (not shown). Further, as shown in  FIG. 6 , on an outer circumference of the pressure roll  69 , one recess  69 D in which the grippers  54  and the attachment member  55  of the transport part  15  are accommodated is formed. As shown in  FIGS. 4 and 6 , the recess  69 D is opened to an radial outer side of the pressure roll  69 . The recess  69 D has a corner portion  69 F (hereinafter, referred to as a front end edge  69 F) at a downstream end in the rotation direction of the pressure roll  69 . Further, the recess  69 D has a corner portion  69 R (hereinafter, referred to as a rear end edge  69 R) at an upstream end in the rotation direction of the pressure roll  69 . 
     Plural recesses  69 D may be formed according to an arrangement interval of the grippers  54  along the rotation direction C of the chain  52  to be described later. 
     (Heating Roll  68 ) 
     The heating roll  68  shown in  FIG. 4  is an example of a second nipping part. The heating roll  68  has a function of heating the recording medium P. Specifically, as shown in  FIGS. 4, 5, and 6 , the heating roll  68  includes a shaft portion  68 A and a roll portion  68 B formed on an outer circumference of the shaft portion  68 A. 
     By bring an outer circumferential surface (an example of an outer surface of the second nipping part) of the roll portion  68 B of the heating roll  68  into contact with an outer circumferential surface (an example of an outer surface of the first nipping part) of the roll portion  69 B of the pressure roll  69 , a fixing nip region  61  (an example of a nip region) in which the recording medium P is nipped is formed by the heating roll  68  and the pressure roll  69 . 
     (Support Body  70 ) 
     The support body  70  shown in  FIG. 5  has a function of supporting the pressing body  67  and the heating roll  68 . Specifically, as shown in  FIG. 5 , the support body  70  has a first frame  71 , a pair of second frames  72 , and a bottom wall  73 . In  FIG. 5 , only one second frame  72  in the pair of second frames  72  is shown. 
     The bottom wall  73  is arranged below the pressing body  67 . The bottom wall  73  is formed in a plate shape having a thickness in an upper-lower direction. 
     The first frame  71  has a pair of side walls  71 A and a coupling wall  71 B. The pair of side walls  71 A are arranged on both end sides of the heating roll  68  in the axial direction thereof. In  FIG. 5 , only one side wall  71 A in the pair of side walls  71 A is shown. 
     As shown in  FIG. 4 , the side wall  71 A is arranged above the pressure roll  69 . Further, as viewed in the axial direction of the heating roll  68 , the side wall  71 A extends along the chain  52  toward an upstream side of the fixing nip region  61  in the transport direction (see  FIG. 6 ), and extends along a circumferential direction of the pressure roll  69  toward a downstream side of the fixing nip region  61  in the transport direction (see  FIG. 4 ). 
     As shown in  FIG. 5 , the coupling wall  71 B extends from one of the pair of side walls  71 A to the other of the pair of side walls  71 A along the axial direction of the heating roll  68 . The coupling wall  71 B couples upper portions of the pair of side walls  71 A to each other. 
     The pair of side walls  71 A rotatably support the heating roll  68 . A cam follower  82  to be described later is provided on an outer surface  71 G of each of the pair of side walls  71 A. The outer surface  71 G of the side wall  71 A is a surface opposite an inner surface  71 N at which the pair of side walls  71 A face each other. 
     The pair of second frames  72  are provided on an outer side of the pair of side walls  71 A and on the bottom wall  73  so as to extend upward from the bottom wall  73 . The outer side of the pair of side walls  71 A is a side opposite a side (an arrow TA in  FIG. 5 ) on which the pair of side walls  71 A face each other. In other words, the pair of second frames  72  are arranged on both end sides of the pressing body  67  and the heating roll  68  in the axial direction thereof. The second frame  72  is formed in a plate shape having a thickness in the axial direction of the pressure roll  69 . 
     The pair of second frames  72  rotatably support the pressure roll  69 . Specifically, the pair of second frames  72  rotatably support the shaft portion  69 A of the pressure roll  69  on both end sides in the axial direction. More specifically, the pair of second frames  72  rotatably support the shaft portion  69 A of the pressure roll  69  on axial outer sides of the roll portion  69 B (specifically, axial outer sides to be described later). 
     Further, the pair of second frames  72  support the first frame  71  via a rotation shaft  75  such that the first frame  71  is rotatable around the rotation shaft  75 . As shown in  FIG. 4 , the rotation shaft  75  is arranged upstream of the fixing nip region  61  in the transport direction. The “upstream of the fixing nip region  61  in the transport direction” is an example of “a first side in the transport direction with respect to the nip region”. 
     Specifically, the pair of second frames  72  support the first frame  71  upstream of the fixing nip region  61  in the transport direction such that the heating roll  68  is movable between a nip position (an example of a first position) shown in  FIGS. 4 and 9  and a retracted position (an example of a second position) shown in  FIGS. 7 and 10 . 
     That is, the heating roll  68  is movable between the nip position shown in  FIGS. 4 and 9  and the retracted position shown in  FIGS. 7 and 10  around a fulcrum upstream of the fixing nip region  61  in the transport direction. The nip position is a position at which a distance between the heating roll  68  and the pressure roll  69  is a distance at which the fixing nip region  61  is formed. The retracted position is a position at which the distance between the heating roll  68  and the pressure roll  69  is longer than the distance at the nip position. Specifically, the distance between the pressure roll  69  and the heating roll  68  means an inter-axis distance between the pressure roll  69  and the heating roll  68 . 
     The first frame  71  is pushed or pulled by an elastic force of an elastic member such as a spring so as to locate the heating roll  68  to the nip position. That is, the heating roll  68  is pushed toward or pulled from the nip position. 
     In the fixing device  16 , by heating and pressing the recording medium P by the heating roll  68  and the pressure roll  69 , the toner image formed on the recording medium P is fixed on the recording medium P. 
     (Transport Part  15 ) 
     The transport part  15  shown in  FIGS. 1 to 3 and 6  has a function of transporting the recording medium P. Specifically, the transport part  15  has a function of transporting the recording medium P to pass through the transfer nip region  28 A (see  FIG. 3 ) and the fixing nip region  61 . 
     More specifically, as shown in  FIGS. 1 and 2 , the transport part  15  includes a pair of chains  52  and the grippers  54 . The grippers  54  are an example of a holder that holds a front end side of the recording medium. In  FIGS. 1 and 3 , the chains  52  and the grippers  54  are shown in a simplified manner. 
     As shown in  FIG. 1 , the pair of chains  52  each are formed in an annular shape. As shown in  FIGS. 2 and 6 , the pair of chains  52  are arranged at an interval in an apparatus depth direction (direction D in  FIG. 2 ). The pair of chains  52  respectively wraps around the pair of sprockets  29  (see  FIG. 2 ) provided on the secondary transfer body  27  and the pair of sprockets  19  (see  FIG. 6 ) provided on the pressing body  67 . Further, by rotating the secondary transfer body  27  including the pair of sprockets  29  and the pressing body  67  including the pair of sprockets  19 , the chains  52  are configured to rotate in the rotation direction C (direction indicated by an arrow C in  FIGS. 1, 2, and 6 ). 
     As shown in  FIGS. 2 and 6 , the attachment member  55  to which the grippers  54  are attached is stretched across the pair of chains  52  along the apparatus depth direction. Plural attachment members  55  are fixed to the pair of chains  52  at predetermined intervals along the circumferential direction (rotation direction C) of the chain  52 . 
     As shown in  FIGS. 2 and 6 , plural grippers  54  are attached to the attachment member  55  at predetermined intervals along the apparatus depth direction. In other words, the grippers  54  are attached to the chains  52  via the attachment members  55 . The grippers  54  have a function of holding the front end portion of the recording medium P. Specifically, as shown in  FIG. 8 , the gripper  54  includes a claw  54 A and a claw base  54 B. The grippers  54  are configured to hold the recording medium P by sandwiching the front end portion of the recording medium P between the claws  54 A and the claw bases  54 B. In other words, the grippers  54  are an example of a holder that grips the recording medium P in the thickness direction. 
     More specifically, the grippers  54  hold the front end portion of the recording medium P outside an image region of the recording medium P. The image region of the recording medium P is a region in the recording medium P onto which the toner image is transferred. In the gripper  54 , for example, the claw  54 A is pressed against the claw base  54 B by a spring or the like, and the claw  54 A is opened and closed with respect to the claw base  54 B by an action of a cam or the like. 
     As shown in  FIG. 8 , the transport part  15  holds, by the grippers  54 , the front end portion of the recording medium P sent from an accommodating part (not shown) in which the recording medium P is accommodated. In the transport part  15 , the chains  52  rotate in the rotation direction C in a state in which the grippers  54  hold the front end portion of the recording medium P, thus the grippers  54  are moved to transport the recording medium P, and the recording medium P passes through the transfer nip region  28 A together with the grippers  54  while the recording medium P is being held by the grippers  54 . 
     In a portion of the chain  52  which wraps around the sprocket  29 , the grippers  54  are moved in the rotation direction of the transfer cylinder  28  integrally with the transfer cylinder  28  in a state of being accommodated in the recess  28 D of the transfer cylinder  28 . 
     Further, after transport the recording medium P to pass through the transfer nip region  28 A, the transport part  15  further transports the recording medium P to pass through the fixing nip region  61  together with the grippers  54  while the recording medium P is being held by the grippers  54 . In the portion of the chain  52  which wraps around the sprocket  19 , the grippers  54  are moved in the rotation direction of the pressure roll  69  integrally with the pressure roll  69  in a state where the grippers  54  are accommodated in the recess  69 D of the pressure roll  69 . 
     (Moving Mechanism  80 ) 
     The moving mechanism  80  shown in  FIGS. 4 and 5  is an example of a moving mechanism that moves the heating roll  68  relative to the pressure roll  69 . Specifically, the moving mechanism  80  is a mechanism that moves the heating roll  68 . More specifically, as shown in  FIGS. 4 and 5 , the moving mechanism  80  includes the cam followers  82  and cams  84 . 
     The cam follower  82  is provided on the outer surface  71 G of each of the pair of side walls  71 A of the first frame  71 . Specifically, as shown in  FIG. 5 , the cam follower  82  is rotatably supported by a front end portion of a shaft portion  83  that protrudes from the outer surface  71 G of the side wall  71 A to an outside of the side wall  71 A. 
     More specifically, the cam follower  82  is provided downstream of the fixing nip region  61  in the transport direction. The “downstream of the fixing nip region  61  in the transport direction” is an example of “a second side in the transport direction with respect to the nip region”. In other words, the cam follower  82  is arranged downstream of the heating roll  68  in the rotation direction of the pressure roll  69 . That is, the cam follower  82  is deviated downstream of the heating roll  68  in the rotation direction of the pressure roll  69  by a predetermined rotation angle of the pressure roll  69 . 
     As shown in  FIG. 4 , the cam follower  82  is formed in a circular disk shape as viewed in the axial direction of the heating roll  68 . The cam follower  82  has an outer diameter smaller than an outer diameter of the heating roll  68  and an outer diameter of the pressure roll  69 . In  FIGS. 4 and 5 , only one cam follower  82  of the pair of cam followers  82  is shown. 
     As shown in  FIGS. 4 and 5 , the cams  84  are provided on the pressure roll  69 . Specifically, the cams  84  are provided at both end portions of the shaft portion  69 A of the pressure roll  69 . More specifically, as shown in  FIG. 5 , the cam  84  is fixed between the sprocket  19  in the shaft portion  69 A of the pressure roll  69  and the second frame  72 . In  FIGS. 4 and 5 , only one cam  84  of the pair of cams  84  is shown. 
     The cam  84  is arranged downstream of the recess  69 D of the pressure roll  69  in the rotation direction of the pressure roll  69 . That is, the cam  84  is deviated downstream of the recess  69 D of the pressure roll  69  in the rotation direction of the pressure roll  69  by a predetermined rotation angle of the pressure roll  69 . The deviation amount corresponds to the deviation amount of the cam follower  82  with respect to the heating roll  68 . 
     The cam  84  is rotated integrally with the pressure roll  69 , and is brought into contact with the cam follower  82  at a position facing the cam follower  82  (a position on an obliquely upper left side in  FIG. 4 ). As shown in  FIG. 13 , the cam  84  has a cam surface  84 X to which a distance from a rotation axis  69 P of the pressure roll  69  varies. 
     In a portion  84 B, the cam surface  84 X has a longest distance from the rotation axis  69 P of the pressure roll  69 . That is, in the portion  84 B, the cam surface  84 X protrudes furthest to the radial outer side of the pressure roll  69 . 
     In addition, the distance from the rotation axis  69 P of the pressure roll  69  gradually decreases from the portion  84 B toward a portion  84 A. The portion  84 A is positioned downstream of the portion  84 B in the rotation direction of the pressure roll  69 . Further, the distance from the rotation axis  69 P of the pressure roll  69  gradually decreases from the portion  84 B toward a portion  84 C. The portion  84 C is positioned upstream of the portion  84 B in the rotation direction of the pressure roll  69 . A length along the circumferential direction of the pressure roll  69  from the portion  84 B to the portion  84 C is shorter than a length along the circumferential direction of the pressure roll  69  from the portion  84 B to the portion  84 A. Therefore, an average of inclination from the portion  84 B to the portion  84 C of the cam surface  84 X is smaller than an average of inclination from the portion  84 B to the portion  84 A of the cam surface  84 X. Between the portion  84 C and a portion  84 D, the distance from the rotation axis  69 P of the pressure roll  69  is constant. The portion  84 D is positioned upstream of the portion  84 C in the rotation direction of the pressure roll  69 . 
     Then, as the pressure roll  69  rotates, the cam surface  84 X comes into contact with the cam follower  82 , and the cam  84  moves the heating roll  68  between the nip position and the retracted position. Specifically, the heating roll  68  operates as follows when a contact position of the cam  84  with respect to the cam follower  82  changes. 
     The heating roll  68  starts to move from the nip position to the retracted position before the recess  69 D of the pressure roll  69  enters the fixing nip region  61  (hereinafter, this time point is referred to as a start time point A 1 ).  FIG. 9  shows a positional relationship between the heating roll  68  and the pressure roll  69  at the start time point A 1 . At the start time point A 1 , the cam  84  comes into contact with the cam follower  82  at the portion  84 A in  FIG. 13 . 
     At the start time point, as shown in  FIG. 9 , the grippers  54  are also in a state before entering the fixing nip region  61 . Therefore, it may be said that the heating roll  68  starts to move from the nip position to the retracted position before the grippers  54  enter the fixing nip region  61 . 
     Further, when the recess  69 D starts to enter the fixing nip region  61 , the heating roll  68  is located at the retracted position (see  FIG. 10 ). That is, when the front end edge  69 F of the recess  69 D starts to enter the fixing nip region  61 , the heating roll  68  is located at the retracted position. 
       FIG. 10  shows a positional relationship between the heating roll  68  and the pressure roll  69  at a time point (hereinafter, referred to as an entry time point B 1 ) at which the recess  69 D starts to enter the fixing nip region  61 . At the entry time point B 1 , the cam  84  comes into contact with the cam follower  82  at the portion  84 B in  FIG. 13 . The fixing nip region  61  in a state where the heating roll  68  is not in contact with the pressure roll  69  means a place or a range where the fixing nip region  61  is formed in a case where the heating roll  68  is in contact with the pressure roll  69 . 
     Since the grippers  54  enter the fixing nip region  61  later than the recess  69 D, the grippers  54  are in a state before entering the fixing nip region  61  at the entry time point B 1 , as shown in  FIG. 10 . 
     Further, as shown in  FIG. 11 , after the recess  69 D enters the fixing nip region  61 , the heating roll  68  moves to the nip position (hereinafter, this time point is referred to as an end time point C 1 ). Specifically, the heating roll  68  moves to the nip position before the recess  69 D leaves the fixing nip region  61 . More specifically, the heating roll  68  moves to the nip position after the front end edge  69 F of the recess  69 D leaves the fixing nip region  61  and before the rear end edge  69 R enters the fixing nip region  61 . 
     As shown in  FIG. 11 , the heating roll  68  moves to the nip position after the grippers  54  enter the fixing nip region  61 . Specifically, the heating roll  68  moves to the nip position before the grippers  54  leave the fixing nip region  61 . 
     At this nip position, the heating roll  68  is not in contact with the grippers  54  accommodated in the recess  69 D. That is, the heating roll  68  moves to the nip position at which the heating roll  68  is not in contact with the grippers  54  located in the fixing nip region  61 . 
       FIG. 11  shows a positional relationship between the heating roll  68  and the pressure roll  69  at the end time point C 1 . At the end time point C 1 , the cam  84  comes into contact with the cam follower  82  at the portion  84 C in  FIG. 13 . 
     Further, the heating roll  68  maintains the state of being located at the nip position. Therefore, from entry of the rear end edge  69 R of the recess  69 D into the fixing nip region  61  to leaving the fixing nip region  61 , the heating roll  68  is located at the nip position. 
     Further, it may be said that the heating roll  68  is located at the nip position when the grippers  54  leave the fixing nip region  61 . 
       FIG. 12  shows a positional relationship between the heating roll  68  and the pressure roll  69  at a time point (hereinafter, referred to as a leaving time point D 1 ) when the rear end edge  69 R of the recess  69 D leaves the fixing nip region  61 . At the leaving time point D 1 , the cam  84  comes into contact with the cam follower  82  at the portion  84 D in  FIG. 13 . 
       FIG. 14  shows a relationship between an elapsed time and the positional relationship between the heating roll  68  and the pressure roll  69  (specifically, the inter-axis distance between the heating roll  68  and the pressure roll  69 ). In  FIG. 14 , the elapsed time is shown on a horizontal axis, and the positional relationship between the heating roll  68  and the pressure roll  69  is shown on a vertical axis. In  FIG. 14 , “R 1 ”, “R 2 ”, “x”, and “y” indicate a “radius of the heating roll  68 ”, a “radius of the pressure roll  69 ”, a “retraction distance”, and a “compression amount of an elastic layer of the heating roll  68 ”, respectively. An arrow A 1  and an arrow C 1  in  FIG. 14  indicate the start time point A 1  and the end time point C 1 , respectively. Further, an arrow B 1  and an arrow D 1  in  FIG. 14  indicate the entry time point B 1  and the leaving time point D 1 , respectively. The horizontal axis in  FIG. 14  may be regarded as a change in rotation angle of the pressure roll  69 . 
     As the heating roll  68  moves as shown in  FIGS. 9 to 12 , a middle point  100 A of a period  100  from the start time point A 1  to the end time point C 1  precedes a middle point  200 A of a period  200  during which the recess  69 D passes through the fixing nip region  61  as shown in  FIG. 14 . 
     In other words, in the present exemplary embodiment, the heating roll  68  moves such that the middle point  100 A of the period  100  from the start time point A 1  to the end time point C 1  precedes the middle point  200 A of the period  200  during which the recess  69 D passes through the fixing nip region  61 . 
     Further, in the present exemplary embodiment, the heating roll  68  moves such that the middle point  100 A of the period  100  from the start time point A 1  to the end time point C 1  precedes a middle point  300 A of a period  300  during which the grippers  54  pass through the fixing nip region  61 . 
     Further, an amount of relative movement of the heating roll  68  from the retracted position to the nip position per unit time is smaller than an amount of relative movement of the heating roll  68  from the nip position to the retracted position per unit time. That is, in  FIG. 14 , inclination of a line LB from the arrow B 1  to the arrow C 1  is smaller than inclination of a line LA from the arrow A 1  to the arrow B 1 . 
     (Operation According to Present Exemplary Embodiment) 
     In the present exemplary embodiment, as described above, the heating roll  68  moves such that the middle point  100 A of the period from the start time point A 1  to the end time point C 1  precedes the middle point  200 A of the period during which the recess  69 D passes through the fixing nip region  61 . 
     Here, in a configuration (first comparative example) in which the middle point  100 A of the period from the start time point A 1  to the end time point C 1  coincides with the middle point  200 A of the period during which the recess  69 D passes through the fixing nip region  61 , for example, the heating roll  68  moves to the nip position after the rear end edge  69 R of the recess  69 D leaves the fixing nip region  61 , so that the timing at which the recording medium P is nipped between the pressure roll  69  and the heating roll  68  is delayed. 
     In contrast, in the present exemplary embodiment, since the heating roll  68  moves such that the middle point  100 A precedes the middle point  200 A, for example, the heating roll  68  moves to the nip position before the rear end edge  69 R of the recess  69 D leaves the fixing nip region  61 . Therefore, the timing at which the recording medium P is nipped between the pressure roll  69  and the heating roll  68  is advanced as compared with the first comparative example. As a result, since the toner image is fixed from the front end side of the recording medium P, a range in which the toner image is fixable on the recording medium P is widened as compared with the first comparative example. In other words, according to the present exemplary embodiment, the range in which the toner image is to be formed on the recording medium P is widened as compared with the first comparative example. 
     In the present exemplary embodiment, the heating roll  68  moves such that the middle point  100 A of the period from the start time point A 1  to the end time point C 1  precedes the middle point  300 A of the period during which the grippers  54  pass through the fixing nip region  61 . 
     Here, in a configuration (second comparative example) shown in  FIG. 15  in which the middle point  100 A of the period from the start time point A 1  to the end time point C 1  coincides with the middle point  300 A of the period during which the grippers  54  pass through the fixing nip region  61 , for example, the heating roll  68  moves to the nip position after the rear end edge  69 R of the recess  69 D leaves the fixing nip region  61 , so that the timing at which the recording medium P is nipped between the pressure roll  69  and the heating roll  68  is delayed. 
     In contrast, in the present exemplary embodiment, since the heating roll  68  moves such that the middle point  100 A precedes the middle point  300 A, for example, the heating roll  68  moves to the nip position before the rear end edge  69 R of the recess  69 D leaves the fixing nip region  61 , so that the timing at which the recording medium P is nipped between the pressure roll  69  and the heating roll  68  is advanced as compared with the second comparative example. 
     Further, in the present exemplary embodiment, since the heating roll  68  moves to the nip position before the rear end edge  69 R of the recess  69 D leaves the fixing nip region  61 , the range in which the recording medium P is nipped between the pressure roll  69  and the heating roll  68  is widened as compared with a configuration in which the heating roll  68  moves to the nip position after the rear end edge  69 R of the recess  69 D leaves the fixing nip region  61 . 
     Further, in the present exemplary embodiment, since the heating roll  68  moves to the nip position before the grippers  54  leave the fixing nip region  61 , the range in which the recording medium P is nipped between the pressure roll  69  and the heating roll  68  is widened as compared with a configuration in which the heating roll  68  moves to the nip position after the grippers  54  leave the fixing nip region  61 . 
     In the present exemplary embodiment, the heating roll  68  moves to the nip position at which the heating roll  68  is not in contact with the grippers  54  located in the fixing nip region  61 . Therefore, interference between the heating roll  68  and the grippers  54  is prevented as compared with a configuration in which the heating roll  68  is in contact with the grippers  54  located in the fixing nip region  61  at the nip position. 
     In the present exemplary embodiment, the heating roll  68  is movable around a fulcrum upstream of the fixing nip region  61  in the transport direction, and the cam follower  82  is provided downstream of the fixing nip region  61  in the transport direction. 
     Therefore, as compared with a configuration in which the fulcrum and the cam follower  82  are arranged on the first side in the transport direction with respect to the fixing nip region  61 , since the fulcrum and a force point are separated from each other, the heating roll  68  is moved with a smaller load. Further, as compared with a configuration in which the cam follower  82  is provided upstream of the fixing nip region  61  in the transport direction, the cam follower  82  is prevented from interfering with a member arranged upstream of the fixing nip region  61  in the transport direction. 
     Further, in the present exemplary embodiment, the amount of relative movement of the heating roll  68  from the retracted position to the nip position per unit time is smaller than the amount of relative movement of the heating roll  68  from the nip position to the retracted position per unit time. 
     Accordingly, as compared with a configuration in which the amount of relative movement of the heating roll  68  from the retracted position to the nip position per unit time is larger than the amount of relative movement of the heating roll  68  from the nip position to the retracted position per unit time, the heating roll  68  is quickly separated from the pressure roll  69 , and the heating roll  68  is slowly brought close to the pressure roll  69 . As a result, vibration due to contact between the heating roll  68  and the pressure roll  69  is prevented. 
     (Modification of Operation of Heating Roll  68 ) 
     In the exemplary embodiment described above, as shown in  FIG. 11 , the heating roll  68  moves to the nip position after the recess  69 D enters the fixing nip region  61 , but the present disclosure is not limited thereto. 
     For example, as shown in  FIG. 15 , the heating roll  68  may move to the nip position after the holding position  54 P of the recording medium P by the grippers  54  enters the fixing nip region  61 . In this configuration, the heating roll  68  moves to the nip position before the holding position  54 P leaves the fixing nip region  61 . 
     In the present configuration, as shown in  FIG. 14 , a time point E 1  at which the heating roll  68  moves to the nip position is later than the end time point C 1 . 
     Further, as shown in  FIG. 14 , a middle point  500 A of a period  500  from the start time point A 1  to the time point E 1  precedes a middle point  400 A of a period  400  during which the holding position  54 P of the recording medium P by the grippers  54  passes through the fixing nip region  61 . 
     In other words, in the present exemplary embodiment, the heating roll  68  moves such that the middle point  500 A of the period  500  from the start time point A 1  to the time point E 1  precedes the middle point  400 A of the period  400  during which the holding position  54 P of the recording medium P by the grippers  54  passes through the fixing nip region  61 . 
     As described above, in the present modification, since the heating roll  68  moves such that the middle point  500 A precedes the middle point  400 A, for example, the timing at which the recording medium P is nipped between the pressure roll  69  and the heating roll  68  is advanced as compared with a configuration (third comparative example) in which the middle point  500 A and the middle point  400 A coincide with each other. As a result, according to the present exemplary embodiment, since the toner image is fixed from the front end side of the recording medium P, the range in which the toner image is fixable on the recording medium P is widened as compared with the third comparative example. In other words, according to the present exemplary embodiment, the range in which the toner image is fixable on the recording medium P is widened as compared with the third comparative example. 
     (Other Modifications) 
     In the present exemplary embodiment, the heating roll  68  is configured to move, but the pressure roll  69  may be configured to move. That is, the heating roll  68  and the pressure roll  69  may be configured to move relative to each other. 
     In the present exemplary embodiment, as shown in  FIG. 4 , the rotation shaft  75  is positioned upstream of the fixing nip region  61  in the transport direction, but the present disclosure is not limited thereto. For example, the rotation shaft  75  may be positioned downstream of the fixing nip region  61  in the transport direction. In this case, the cam follower  82  is arranged, for example, upstream of the fixing nip region  61  in the transport direction. 
     Further, in the present exemplary embodiment, the grippers  54  hold the front end portion of the recording medium P, but the present disclosure is not limited thereto. For example, the grippers  54  may be configured to hold the front end side of the recording medium P from a lateral end side of the recording medium P. The front end side of the recording medium is a portion downstream (forward) of a center of the recording medium in the transport direction. 
     Further, in the present exemplary embodiment, a case has been described in which an example of the transport device is a fixing device having a transporting function of transporting the recording medium P and a fixing function of fixing an image onto the recording medium P, but the present disclosure is not limited thereto. The transport device may be, for example, a device having only the transporting function, or a device having a function other than the fixing function and the transporting function. 
     The foregoing description of the exemplary embodiments 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 embodiments were 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.