Patent Publication Number: US-9885985-B2

Title: Fixing device and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2016-005527 filed Jan. 14, 2016. 
     BACKGROUND 
     The present invention relates to a fixing device and an image forming apparatus. 
     SUMMARY 
     According to an aspect of the invention, a fixing device includes a first support portion, a first member, a second member, a first biasing member, a second support portion, a third support portion, a second biasing member, and a switching portion. The first support portion supports an endless belt, and presses the endless belt against a rotating body by relatively moving with respect to the rotating body. The first member is supported in the endless belt by the first support portion. The second member is supported in the endless belt so as to be capable of approaching and being separated from the first support portion. The first biasing member is provided in the first support portion, and biases the second member to a rotating body side. The second support portion supports the first support portion to be rotatable around a shaft portion. The third support portion supports the second support portion so that the second support portion is capable of relatively moving, rotates the first support portion in a direction of approaching the rotating body by pressing the first support portion to the rotating body side at a first position where the third support portion has moved in the direction of approaching the rotating body side, and is separated from the first support portion at a second position where the third support portion has moved in a direction of being separated from the rotating body. The second biasing member is provided in the third support portion, and biases the second support portion to the rotating body side. The switching portion switches between a first state and a second state. In the first state, the endless belt is pressed against the rotating body by the first member and the second member, by moving the third support portion to the first position. In the second state, the endless belt is pressed against the rotating body only by the second member among the first member and the second member, by moving the third support portion to the second position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a configuration view illustrating an image forming apparatus according to an exemplary embodiment of the invention; 
         FIG. 2  is a perspective view illustrating a fixing device according to a first exemplary embodiment which is used in the image forming apparatus illustrated in  FIG. 1 ; 
         FIG. 3  is a perspective view illustrating one end portion in the shaft direction of a fixing belt and a heating roll which are used in the fixing device illustrated in  FIG. 2 ; 
         FIG. 4  is a perspective view illustrating a configuration of a child lever which supports a guide member of the fixing belt illustrated in  FIG. 3 , and a parent lever which supports the child lever to be movable; 
         FIG. 5  is a sectional view illustrating a first state in which the fixing belt is pressed against the heating roll by a pad member and a block member which are used in the fixing device illustrated in  FIG. 3 ; 
         FIG. 6  is a sectional view illustrating a state where a part near the pad member, the block member, and the heating roll which are illustrated in  FIG. 5  is enlarged; 
         FIG. 7  is a sectional view taken through a different part from the part through which  FIG. 5  is taken and illustrates a state where the parent lever presses the guide member of the fixing belt against the heating roll side in the first state illustrated in  FIG. 5 ; 
         FIG. 8  is a sectional view taken through a different part from the parts through which  FIGS. 5 and 7  are taken and illustrates a state where the child lever is separated from the guide member of the fixing belt in the first state illustrated in  FIG. 5 ; 
         FIG. 9  is a sectional view illustrating a second state where the fixing belt is pressed against the heating roll only by the pad member among the pad member and the block member which are used in the fixing device illustrated in  FIG. 3 ; 
         FIG. 10  is a sectional view illustrating a state where a part near the pad member, the block member, and the heating roll which are illustrated in  FIG. 9  is enlarged; 
         FIG. 11  is a sectional view taken through a different part from the part through which  FIG. 9  is taken and illustrates a state where the parent lever is separated from the guide member of the fixing belt in the second state illustrated in  FIG. 9 ; 
         FIG. 12  is a sectional view taken through a different part from the part through which  FIG. 9  is taken and illustrates a state where the child lever holds the guide member of the fixing belt in the second state illustrated in  FIG. 9 ; 
         FIG. 13  is a sectional view illustrating a state where the fixing belt used in the fixing device illustrated in  FIG. 3  is separated from the heating roll; 
         FIG. 14  is a sectional view taken through a different part from the part through which  FIG. 13  is taken and illustrates a state where the parent lever is separated from the guide member of the fixing belt in a latch release state illustrated in  FIG. 13 ; 
         FIG. 15  is a sectional view taken through a different part from the part through which  FIG. 13 , is taken and illustrates a state where the child lever holds the guide member of the fixing belt, in the latch release state illustrated in  FIG. 13 ; 
         FIG. 16  is a sectional view illustrating a fixing device according to a second exemplary embodiment, and a sectional view illustrating the first state where the fixing belt is pressed against the heating roll by the pad member and the block member; 
         FIG. 17  is a sectional view illustrating the second state where the fixing belt is pressed against the heating roll only by the pad member among the pad member and the block member of the fixing device illustrated in  FIG. 16 ; 
         FIG. 18  is a sectional view illustrating a state where the fixing belt of the fixing device illustrated in  FIG. 16  is separated from the heating roll; and 
         FIG. 19  is a view illustrating a position of a shaft portion which supports the guide member and the child lever of the fixing belt to be relatively rotatable, in a fixing device according to a third exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments of a fixing device and an image forming apparatus of the invention will be described based on the drawings. In addition, in the drawings, the direction indicated by an arrow H is the apparatus height direction, and the direction indicated by an arrow W is the apparatus width direction. In the drawings, the direction which is indicated by an arrow D which is orthogonal to each of the apparatus height direction and the apparatus width direction, is the apparatus depth direction (arrow D indicates a near side in the apparatus depth direction). 
     Entire Configuration of Image Forming Apparatus 
     In  FIG. 1 , an example of a configuration of the image forming apparatus provided with the fixing device according to a first exemplary embodiment of the invention is described. As illustrated in  FIG. 1 , an image forming apparatus  10  includes a recording paper accommodating unit  12  which accommodates recording paper P which is an example of a recording medium, a toner image forming unit  14 , a transport unit  16 , a fixing device  70 , a discharge unit  20 , and a controller  22 . The toner image forming unit  14  is provided with four image forming units  24 Y,  24 M,  24 C, and  24 K, and a transfer unit  26 . Here, yellow (Y), magenta (M), cyan (C), and black (K) are examples of toner colors. Each of the image forming units  24 Y,  24 M,  24 C, and  24 K is provided with a photoconductor  28 , a charging device  30 , an exposure device  32 , a developing device  34 , and a removing device  36 . In each of the image forming units  24 Y,  24 M,  24 C, and  24 K, toner images of each color of yellow (Y), magenta (M), cyan (C), and black (K) are formed on an outer circumferential surface of each photoconductor  28 . 
     The photoconductor  28  has a function of holding the toner image developed by the developing device  34 . The photoconductor  28  is formed in a cylindrical shape, is provide with a photosensitive layer on a surface thereof, and is driven to rotate in the arrow direction by a driving unit (not illustrated). The developing device  34  develops a latent image formed in the photoconductor  28  as the toner image. 
     The transfer unit  26  is provided with a transfer belt  38 , a primary transfer roll  40  of each color, a driving roll  42 , and a secondary transfer roll  44 . A posture of the transfer belt  38  is determined by four rolls, including the primary transfer roll  40 , a support roll  46 , the driving roll  42 , and a tension applying roll  48 , which are in contact with the inner circumferential surface. In the transfer belt  38 , a cleaning device which is not illustrated is provided downstream of a secondary transfer portion which is in contact with the secondary transfer roll  44 . The outer circumferential surface of each photoconductor  28  disposed in each of the image forming units  24 Y,  24 M,  24 C, and  24 K, is in contact with the outer circumferential surface on the lower side of the transfer belt  38 . 
     The transport unit  16  is provided with a sending roll which is not illustrated and sends out the recording paper P from the recording paper accommodating unit  12 , and plural transport roll pairs which are not illustrated along a transport path, and transports the recording paper P sent out by the sending roll to the secondary transfer portion which is at a position at which the driving roll  42  and the secondary transfer roll  44  oppose each other. Furthermore, the transport unit  16  transports the recording paper P to the fixing device  70 . In the fixing device  70 , the toner image which is secondarily transferred to the recording paper P is fixed to the recording paper P, and further, the recording paper P is transported to the discharge unit  20  by the transport unit  16 . 
     In the image forming apparatus  10 , exposure light emitted in accordance with image data of each color from the exposure device  32  is incident on the outer circumferential surface of the photoconductor  28  charged by the charging device  30 , and the latent image which corresponds to the image data of each color is formed on the outer circumferential surface of each photoconductor  28 . The latent image formed on the outer circumferential surface of each photoconductor  28  is developed as the toner image of each color by each developing device  34 . The toner image of each color of the outer circumferential surface of each photoconductor  28  is primarily transferred to the outer circumferential surface of the transfer belt  38  by each primary transfer roll  40  which opposes each photoconductor  28 . 
     Meanwhile, in accordance with a timing at which the toner image of each color which is primarily transferred to the transfer belt  38  reaches the secondary transfer portion, the recording paper P is sent out of the recording paper accommodating unit  12 , and is transported to the secondary transfer portion provided with the secondary transfer roll  44 . In the secondary transfer portion, the toner image of each color on the transfer belt  38  is secondarily transferred to the recording paper P. Furthermore, after the recording paper P to which the toner image is transferred is transported toward the fixing device  70 , is heated in a contact portion between a heating roll  72  and a fixing belt  74  which will be described later, and is pressurized, and the toner image is fixed to the recording paper P, the recording paper P is output to the discharge unit  20 . 
     Configuration of Fixing Device 
     Next, the fixing device  70  will be described. In  FIG. 2 , the fixing device  70  is illustrated in a perspective view, and in  FIG. 3 , a state where one end portion side of the fixing device  70  in the longitudinal direction is illustrated in a perspective view. As illustrated in  FIGS. 2 and 3 , the fixing device  70  is provided with the heating roll  72  which is an example of a rotating body, and the fixing belt  74  which is an example of an endless belt that is in contact with or is separated from the heating roll  72 . The heating roll  72  and the fixing belt  74  are aligned in the apparatus width direction indicated by the arrow W. 
     The fixing device  70  is provided with a support member  76  and a support unit  78 . The support member  76  supports both end portions of the heating roll  72  to be rotatable. The support unit  78  supports both end portions of the fixing belt  74  to be rotatable, and presses the fixing belt  74  against the heating roll  72  by relatively moving to the support member  76 . The support members  76  are provided in both end portions of the heating roll  72  as a left and right pair, and the support units  78  are provided in both end portions of the fixing belt  74  as a left and right pair (refer to  FIG. 2 ). The heating roll  72  and the fixing belt  74  are disposed considering the apparatus depth direction indicated by the arrow D of the image forming apparatus  10  as the shaft direction (longitudinal direction). 
     The heating roll  72  has a multilayer structure provided with a thin cylindrical core bar made of a steel material, an elastic layer made of silicone rubber with which the surface of the core bar is coated, and a release layer including a fluororesin with which the surface of the elastic layer is coated. On the inside of the heating roll  72 , a heat source  73  configured with plural halogen lamps (three in the exemplary embodiment) is disposed at an interval with the inner circumferential surface of the heating roll  72  (refer to  FIGS. 2 and 5 ). 
     The fixing belt  74  has a shape of an endless belt, and the release layer including the fluororesin is provided on the outer circumferential surface of a thin cylindrical base member made of a synthetic resin, such as a polyimide resin or a polyamide-imide resin, as necessary. As illustrated in  FIG. 5 , on the inside of the fixing belt  74 , in order to press the outer circumferential surface of the fixing belt  74  against the outer circumferential surface of the heating roll  72 , a block member  120  which is an example of a first member and a pad member  122  which is an example of a second member are provided. The fixing belt  74  is configured to perform pressurizing by the heating roll  72  nipping the recording paper P (not illustrated), and the toner image on the recording paper P is fixed in the contact portion (nip portion) at which the outer circumferential surface of the heating roll  72  and the outer circumferential surface of the fixing belt  74  is in contact with each other. The configuration of the inside of the fixing belt  74  will be described later. 
     The support member  76  supports both end portions of the heating roll  72  to be rotatable via a bearing which is not illustrated. The support member  76  is supported by a bracket  100  in which an arc-like recessed portion  100 A to which the support member  76  is fitted is formed. 
     As illustrated in  FIGS. 2 to 4 , the support unit  78  is provided with a guide member  102  which is an example of a first support portion that supports the fixing belt  74 . Furthermore, the support unit  78  is provided with a child lever  80  which is an example of a second support portion that supports the guide member  102  to be relatively rotatable in the direction of approaching or being separated from the heating roll  72 , and a parent lever  82  which is an example of a third support portion that supports the child lever  80  to be relatively rotatable. 
     An upper portion  82 A of the parent lever  82  in a plan view of the fixing device  70  is formed in a U shape, and is open toward the support member  76  side of the heating roll  72 . An upper portion  80 A of the child lever  80  in a plan view of the fixing device  70  has a U shape, and is open toward the side opposite to the support member  76 . The width (width in the apparatus depth direction indicated by the arrow D) of the child lever  80  is configured to be smaller than the width (width in the apparatus depth direction indicated by the arrow D) of the parent lever  82 , and the child lever  80  is inserted into the parent lever  82 . In this state, the parent lever  82  and the child lever  80  relatively move. 
     More specifically, as illustrated in  FIGS. 3 and 4 , the child lever  80  is provided with an inner wall  80 B disposed on the inner side (fixing belt  74  side) in the apparatus depth direction indicated by the arrow D, and an outer wall  80 C disposed to oppose the outer side (a side opposite to the fixing belt  74 ) of the inner wall  80 B. On the inner wall  80 B of the child lever  80 , a recessed portion  81  which is recessed in the apparatus width direction (arrow W direction) is formed not to interfere with the fixing belt  74  (refer to  FIG. 4 ). The parent lever  82  is provided with an inner wall  82 B disposed on the inner side (fixing belt  74  side) in the apparatus depth direction indicated by the arrow D, and an outer wall  82 C disposed to oppose the outer side (a side opposite to the fixing belt  74 ) of the inner wall  82 B. The inner wall  82 B of the parent lever  82  is formed in an L shape not to interfere with the fixing belt  74  (refer to  FIG. 4 ). 
     The inner wall  80 B and the outer wall  80 C of the child lever  80  are disposed between the inner wall  82 B and the outer wall  82 C of the parent lever  82 , and a shaft portion  84  which is an example of a second shaft portion penetrates a through hole formed in a lower portion of the inner walls  82 B and  80 B and outer walls  80 C and  82 C. Accordingly, the child lever  80  and the parent lever  82  relatively move (in the exemplary embodiment, rotate) around the shaft portion  84 . In other words, the child lever  80  and the parent lever  82  move independently from the support member  76 . 
     In a wall  80 D along the apparatus depth direction (D direction) of the upper portion  80 A of the child lever  80 , a hole portion  80 E (refer to  FIG. 4 ) is formed, and in a state where a pin member  86  is inserted into the hole portion  80 E, a base end of the pin member  86  is fixed to the wall  80 D (refer to  FIGS. 4 and 5 ). The shaft direction of the pin member  86  is the direction intersecting the shaft direction of the shaft portion  84 . In a wall  82 D along the apparatus depth direction (D direction) of the upper portion  82 A of the parent lever  82 , a long hole  82 E is formed (refer to  FIG. 3 ). The long hole  82 E is formed in the wall  82 D so that a long diameter portion is in the apparatus height direction (H direction). The outer diameter of the shaft portion of the pin member  86  is configured to be smaller than a short diameter portion of the long hole  82 E, and in a state where the tip end portion side of the pin member  86  penetrates the long hole  82 E, the pin member  86  can move in the long hole  82 E. In other words, the tip end portion of the pin member  86  is not fixed to the wall  82 D of the parent lever  82 , and is a free end. 
     A spring  96  which is an example of a second biasing member which biases the wall  80 D of the child lever  80  to the support member  76  side of the heating roll  72  is attached to the wall  82 D of the parent lever  82 . The spring  96  is disposed around the pin member  86 , and in this state, one end of the spring  96  is fixed to the wall  82 D of the parent lever  82  by an attaching tool  88  (refer to  FIG. 4 ). 
     In addition, on an end surface on the guide member  102  side of the inner wall  82 B of the parent lever  82 , a projection portion  82 F which protrudes to the guide member  102  side is provided (refer to  FIG. 4 ). When the parent lever  82  moves in the direction of approaching the heating roll  72 , the guide member  102  is pressed by the projection portion  82 F. An operation of the parent lever  82  will be described later. 
     As illustrated in  FIGS. 2 and 3 , in an intermediate portion of the parent lever  82  in the vertical direction, a roll member  90  is disposed, and a shaft portion  90 A of the roll member  90  is supported to be rotatable by the inner wall  82 B and the outer wall  82 C. The roll members  90  are respectively provided to one left and right pair of the parent levers  82 . 
     On a wall  100 B on the roll member  90  side in the apparatus width direction (arrow W direction) of the bracket  100 , a cam  92  which is an example of a switching portion is supported to be rotatable. The cams  92  are provided as a left and right pair on both sides of the fixing device  70  in the longitudinal direction, and the left and right pair of cams  92  are configured to be linked to each other by a rotating shaft  94  and to integrally rotate. In the cam  92 , a radius of an outer circumferential surface  92 A from the center portion of the rotating shaft  94  continuously changes in the circumferential direction, and the outer circumferential surface  92 A of the cam  92  is in contact with the outer circumferential surface of the roll member  90 . The cam  92  is driven to rotate by a motor (not illustrated) linked to the end portion of the rotating shaft  94  in the shaft direction. 
     As the position of the roll member  90  changes according to the rotation of the cam  92 , the parent lever  82  relatively moves in the direction of approaching or being separated from the support member  76  of the heating roll  72  around the shaft portion  84 . 
     As illustrated in  FIGS. 3 and 5 , the guide member  102  is disposed in both end portions of the fixing belt  74 . The guide member  102  is provided with a main body portion  102 A disposed along the vertical direction on the outer side of both end portions of the fixing belt  74  in the longitudinal direction, and an arc-like outer guide portion  102 B formed along the outer circumferential surface of both end portions of the fixing belt  74  in the main body portion  102 A (in  FIG. 3 , only one end portion of the fixing belt  74  is illustrated, and the other end portion of the fixing belt  74  is omitted). Furthermore, the guide member  102  is provided with an extending portion  102 C which extends to a lower side in the vertical direction along the child lever  80  from the lower portion of the main body portion  102 A. 
     In the inner wall  80 B of the child lever  80  and the extending portion  102 C of the guide member  102 , a through hole (not illustrated) is provided, and a shaft portion  130  which is an example of a first shaft portion is provided in the through hole. The shaft portion  130  is disposed considering the longitudinal direction of the fixing belt  74  as the shaft direction. Accordingly, the guide member  102  is supported to be rotatable by the child lever  80  around the shaft portion  130 . In other words, the guide member  102  is rotatable with respect to the child lever  80  in the direction of approaching or being separated from the heating roll  72  around the shaft portion  130  disposed in the lower portion of the guide member  102 . In  FIGS. 5 and 6 , in order to easily grasp the position of the shaft portion  130 , a center  130 A of the shaft portion  130  is illustrated. 
     As illustrated in  FIG. 5 , on the inside of the fixing belt  74 , an ark-like sliding sheet  103  which is disposed along the inner circumferential surface of the fixing belt  74  and allows the fixing belt  74  to slide, is provided. The sliding sheets  103  are respectively attached to a first attaching member  104  and a second attaching member  106  which are fixed to the main body portion  102 A of the guide member  102 . In addition, in  FIG. 5 , the first attaching member  104  is a section, but in order to easily grasp the configuration, hatching is omitted. 
     The sliding sheet  103 , the first attaching member  104 , and the second attaching member  106  are disposed along the longitudinal direction of the fixing belt  74 . The first attaching member  104  is formed in an L shape in a sectional view, and a felt member  108  is fixed to one end portion of the first attaching member  104  by adhesion or the like to be in contact with the inner circumferential surface of the fixing belt  74 . Lubricating oil is impregnated into the felt member  108 , and when the felt member  108  contacts with the inner circumferential surface of the fixing belt  74 , the oil is supplied to the inner circumferential surface. 
     On the inside of the fixing belt  74 , a first holding portion  110  formed in an L shape in a sectional view is disposed along the first attaching member  104 , and the first holding portion  110  is fixed to the first attaching member  104  and the main body portion  102 A of the guide member  102 . In addition, in  FIG. 5 , the first holding portion  110  is a section, but in order to easily grasp the configuration, hatching is omitted. A hole portion  110 A is formed in one end portion (end portion on the heating roll  72  side) of the first holding portion  110 . In addition, on the inside of the fixing belt  74 , a second holding portion  112  formed in an L shape in a sectional view is disposed to configure the first holding portion  110  and a rectangular frame body. One end portion of the second holding portion  112  is inserted into the hole portion  110 A of the first holding portion  110 , and the other end portion of the second holding portion  112  is in contact with the other end portion of the first holding portion  110 . In this state, the second holding portion  112  is fixed to the first holding portion  110 . A part of the second attaching member  106  is in contact with the outer side of the other end portion of the second holding portion  112 , and the other end portion of the second holding portion  112  is fixed to the second attaching member  106 . 
     An attaching surface  112 A which opposes the heating roll  72  is formed on one end portion side of the second holding portion  112 , and the block member  120  is fixed to the attaching surface  112 A by adhesion or the like. Accordingly, the block member  120  is supported (fixed) to the guide member  102  via plural components, such as the first holding portion  110  and the second holding portion  112 . In the exemplary embodiment, the block member  120  is formed of a synthetic resin. 
     In the second attaching member  106 , an attaching portion  106 A having a U shape in a sectional view is formed on the center portion side of the fixing belt  74 , the attaching portion  106 A is disposed to be open to the heating roll  72  side. In the attaching portion  106 A, a spring  114  which is an example of a first biasing member is disposed, and one end portion of the spring  114  is fixed to a bottom surface of the attaching portion  106 A. A holding portion  116  having an L shape in a sectional view is attached to the other end portion of the spring  114 . A recessed surface  116 A is formed toward the heating roll  72  side in the holding portion  116 , and the pad member  122  is fixed to the recessed surface  116 A by adhesion or the like. Accordingly, the pad member  122  is biased to the heating roll  72  side by the spring  114  disposed in the attaching portion  106 A of the second attaching member  106 . The second attaching member  106  is fixed to the main body portion  102 A of the guide member  102 , and the pad member  122  is supported to approach and be separated from the main body portion  102 A of the guide member  102 . In the exemplary embodiment, the pad member  122  is formed of a foam resin, such as a silicone resin, and has a softer configuration than that of the block member  120 . In addition, in the exemplary embodiment, the pad member  122  has a two-layered structure in which the foam resins having different forming ratios are layered, but the configuration of the pad member  122  can be changed, and for example, may have a single layer structure. 
     In the fixing device  70 , the pad member  122  is disposed on an upstream side in the transport direction of the recording paper P ( FIG. 1 ) which passes through the contact portion (nip portion) between the heating roll  72  and the fixing belt  74 , and the block member  120  is disposed downstream of the pad member  122  in the transport direction of the recording paper P ( FIG. 1 ). In the exemplary embodiment, in the contact portion between the heating roll  72  and the fixing belt  74 , the transport path of the recording paper P is disposed along the vertical direction, the pad member  122  is disposed on the lower side of the vertical direction, and the block member  120  is disposed on the upper side of the vertical direction. The pad member  122  and the block member  120  are disposed at a position at which the pad member  122  and the block member  120  are near or adjacent to each other. 
     In addition, the guide member  102  can rotate around the shaft portion  130  disposed at a lower part of the guide member  102  with respect to the child lever  80 . In other words, the pad member  122  is disposed upstream of the block member  120  in the transport direction of the recording paper P ( FIG. 1 ) which passes through the contact portion between the heating roll  72  and the fixing belt  74 , and the shaft portion  130  is disposed upstream of the block member  120  in the transport direction of the recording paper P which passes through the contact portion between the heating roll  72  and the fixing belt  74 . Therefore, when the guide member  102  rotates around the shaft portion  130  with respect to the child lever  80 , the block member  120  which is disposed to be far from the shaft portion  130  is more largely displaced in the direction of approaching or being separated from the heating roll  72  than the pad member  122  which is positioned to be close to the shaft portion  130  (a displacement amount increases). 
     In addition, in the fixing device  70 , the child lever  80  is supported to be rotatable around the shaft portion  84  with respect to the parent lever  82 , and the shaft portion  84  is disposed upstream of the contact portion between the heating roll  72  and the fixing belt  74  in the transport direction of the recording paper P. In the exemplary embodiment, a length of a line segment L 1  that connects the center of the contact portion between the heating roll  72  and the fixing belt  74  in the transport direction of the recording paper P and the center  130 A of the shaft portion  130  is shorter than that of a line segment L 2  that connects the center of the contact portion between the heating roll  72  and the fixing belt  74  in the transport direction of the recording paper P and the center of the shaft portion  84  (refer to  FIG. 6 ). 
     In addition, in the fixing device  70 , a tension spring  132  which links an upper portion of the main body portion  102 A of the guide member  102  and the parent lever  82  is provided. In other words, one end of the tension spring  132  is locked to the upper portion of the main body portion  102 A of the guide member  102 , and the other end of the tension spring  132  is locked to the upper portion  82 A side of the parent lever  82 . 
     In the fixing device  70 , by the rotation of the cam  92 , the parent lever  82  of the support unit  78  and the heating roll  72  (support member  76 ) are relatively moved in the direction of approaching or being separated from each other. As illustrated in  FIGS. 5 and 6 , when a part having a large radius of the outer circumferential surface  92 A of the cam  92  comes into contact with the roll member  90 , as the parent lever  82  rotates (rotates clockwise indicated by the arrow A in  FIG. 5 ) around the shaft portion  84 , the parent lever  82  relatively moves in the direction of approaching the heating roll  72 . In other words, in  FIGS. 5 and 6 , the parent lever  82  moves to a first position which is close to the heating roll  72 . 
     In addition, as illustrated in  FIGS. 9 and 10 , when a part having a smaller radius of the outer circumferential surface  92 A than the radius of the outer circumferential surface  92 A, at the first position, of the cam  92  comes into contact with the roll member  90 , as the parent lever  82  rotates around the shaft portion  84 , the parent lever  82  relatively moves in the direction of being separated from the heating roll  72 . In other words, in  FIGS. 9 and 10 , the parent lever  82  moves to a second position where the parent lever  82  is separated from the heating roll  72 . 
     The cam  92  is configured to switch between a first state (refer to  FIGS. 5 and 6 ) and a second state (refer to  FIGS. 9 and 10 ), by moving the parent lever  82  of the support unit  78  between the first position and the second position. In the first state, the fixing belt  74  is pressed against the heating roll  72  by the block member  120  and the pad member  122 . In the second state, the fixing belt  74  is pressed against the heating roll  72  only by the pad member  122 . 
     More specifically, in the fixing device  70 , as illustrated in  FIGS. 5 and 6 , when the part having a large radius of the outer circumferential surface  92 A of the cam  92  comes into contact with the roll member  90 , a full latch mode is achieved, and the state of the full latch mode becomes the first state. In the first state, the parent lever  82  moves to the first position which is close to the heating roll  72 , and the child lever  80  moves in the direction of approaching the heating roll  72  by the spring  96  of the upper portion  82 A of the parent lever  82 . In addition, as illustrated in  FIG. 7 , when the parent lever  82  moves to the first position, the first holding portion  110  fixed to the guide member  102  is pressed by the projection portion  82 F of the parent lever  82 , and the guide member  102  rotates in the direction of approaching the heating roll  72  indicated by an arrow B against the force of the tension spring  132 . In addition, as illustrated in  FIG. 8 , when the parent lever  82  moves to the first position, the child lever  80  does not abut against the guide member  102 . In this state, the fixing belt  74  is pressed against the heating roll  72  by the block member  120  and the pad member  122  (refer to  FIGS. 5 and 6 ). 
     As illustrated in  FIG. 13 , when the part having the smallest radius of the outer circumferential surface  92 A of the cam  92  comes into contact with the roll member  90 , a latch release mode is achieved. In the latch release mode, as the parent lever  82  rotates around the shaft portion  84 , the parent lever  82  relatively moves in the direction of being separated from the heating roll  72 . In other words, the parent lever  82  moves to a third position which is the most separated from the heating roll  72 . The child lever  80  is biased to the heating roll  72  side by the spring  96  of the upper portion  82 A of the parent lever  82 , the child lever  80  moves to a position at which the tip end portion (head portion) of the pin member  86  comes into contact with the wall  82 D of the parent lever  82 . As illustrated in  FIG. 14 , when the parent lever  82  moves to the third position, the parent lever  82  does not abut against the guide member  102 . In addition, as illustrated in  FIG. 15 , when the parent lever  82  moves to the third position, as the recessed portion  81  of the child lever  80  abuts against the guide member  102 , the child lever  80  holds the guide member  102  against the force of the tension spring  132 . In this state, the block member  120  and the pad member  122  are separated from the heating roll  72 . 
     As illustrated in  FIGS. 9 and 10 , when a part (a part having a smaller radius than the radius of the first state and a larger radius than the radius of the latch release mode) at which the radius of the outer circumferential surface  92 A of the cam  92  is set to be an intermediate dimension comes into contact with the roll member  90 , a half latch mode is achieved, and a state of the half latch mode becomes the second state. In the second state, the parent lever  82  moves to the second position (a position which is close to the heating roll  72  than the third position) which is more separated from the heating roll  72  than the first position. The child lever  80  is biased to the heating roll  72  side by the spring  96  of the upper portion  82 A of the parent lever  82 , and the child lever  80  stops at a position at which a load of the spring  96 , a load of the spring  114 , and a pressing force of the block member  120  are balanced with respect to the parent lever  82 . As illustrated in  FIG. 11 , when the parent lever  82  moves to the second position, the parent lever  82  does not abut against the guide member  102 . In addition, as illustrated in  FIG. 12  when the parent lever  82  moves to the second position, as the recessed portion  81  of the child lever  80  abuts against the guide member  102 , the child lever  80  holds the guide member  102 . In this state, a fixing belt  74  is pressed against the heating roll  72  only by the pad member  122  among the block member  120  and the pad member  122 . 
     In the fixing device  70 , as the fixing belt  74  is pressurized to the heating roll  72  only by the pad member  122  in the second state, the length of the spring  114  and a stroke by which the pad member  122  moves are set. 
     In the image forming apparatus  10  provided with the fixing device  70 , an operation of the motor which rotates the cam  92  is controlled by the controller  22 . 
     The fixing device  70  is configured so that in the first state, a pressing load to the heating roll  72  by the block member  120  and the pad member  122  switch between a high load and a low load by changing the radius of the outer circumferential surface  92 A of the cam  92 . In other words, in the first state, the pressing load increases (high load) at the part having a large radius of the outer circumferential surface  92 A of the cam  92 , and the pressing load decreases (low load) at the part having a smaller radius of the high load of the outer circumferential surface  92 A of the cam  92  than that of the part. In addition, in the fixing device  70 , in the second state, by changing the radius of the outer circumferential surface  92 A of the cam  92 , the pressing load to the heating roll  72  by the pad member  122  is configured to change to the high load and the low load. In other words, in the second state, the pressing load increases (high load) at the part (a part having a smaller radius than that of the first state) having a large radius of the outer circumferential surface  92 A of the cam  92 , the pressing load decreases (low load) at the part having a smaller radius of the outer circumferential surface  92 A of the cam  92  than that of the part of the high load of the second state. 
     In accordance with the type of the recording paper P which passes through the contact portion (nip portion) between the heating roll  72  and the fixing belt  74 , the cam  92  is configured to switch the first state and the second state. In the exemplary embodiment, the type of the recording paper P is detected by a sensor which is not illustrated, but the type of the recording paper P may be manually input. For example, when thin paper (for example, a case of being less than 60 g/m 2 (GSN)) is used as the recording paper P, the cam  92  is switched to the high load in the first state, and when plain paper (for example, a case of being from 60 g/m 2 (GSN) to 120 g/m 2 (GSN)) is used as the recording paper P, the cam  92  is switched to the low load in the first state. In addition, for example, when thick paper (for example, a case of being greater than 170 g/m 2 (GSN)) is used as the recording paper P, the cam  92  is switched to the high load in the second state, and when an envelope (a case where of a double paper structure) is used as the recording paper P, the cam  92  is switched to the low load in the second state. In addition, the type of the recording paper P and the switching of the cam  92  are not limited to the above-described configuration, and can be changed. 
     Next, actions and effects of the exemplary embodiment will be described. 
     As illustrated in  FIGS. 5 and 6 , in the fixing device  70 , when the part having a large radius of the outer circumferential surface  92 A of the cam  92  comes into contact with the roll member  90 , the full latch mode is achieved, and the first state is achieved. As the parent lever  82  rotates around the shaft portion  84  by the cam  92 , the parent lever  82  moves to the first position where the parent lever  82  is close to the heating roll  72 . In the upper portion  80 A of the parent lever  82 , the spring  96  which biases the child lever  80  to the heating roll  72  side is provided, and the child lever  80  moves in the direction of approaching the heating roll  72  by the spring  96 . At this time, at the position at which the load of the spring  96 , the load of the spring  114 , and the pressing force of the block member  120  are balanced, the child lever  80  stops with respect to the parent lever  82 . 
     As illustrated in  FIG. 7 , when the parent lever  82  moves to the first position, the first holding portion  110  fixed to the guide member  102  is pressed by the projection portion  82 F of the parent lever  82 , and the guide member  102  rotates in the direction of approaching the heating roll  72  indicated by the arrow B against the force of the tension spring  132 . At this time, as illustrated in  FIG. 8 , the child lever  80  does not abut against the guide member  102 . 
     Accordingly, the fixing belt  74  is pressed against the heating roll  72  by the block member  120  supported by the guide member  102 . In addition, the pad member  122  is biased to the heating roll  72  side by the spring  114  disposed in the second attaching member  106  of the guide member  102 , and the fixing belt  74  is pressed against the heating roll  72  by the pad member  122 . Therefore, in the first state, the fixing belt  74  is pressed against the heating roll  72  by the block member  120  and the pad member  122 . In other words, the part at which the fixing belt  74  is pressed against the heating roll  72  by the block member  120  and the pad member  122  becomes the contact portion (nip portion), and as the recording paper P passes through the contact portion, the toner image on the recording paper P is fixed. 
     In addition, the fixing device  70  is configured so that in the first state, the pressing load to the heating roll  72  by the block member  120  and the pad member  122  is switched between the high load and the low load by changing the radius of the outer circumferential surface  92 A of the cam  92 . 
     As illustrated in  FIG. 13 , when the part (the part having a smaller radius than that of the first state and the second state) having the smallest radius of the outer circumferential surface  92 A of the cam  92  comes into contact with the roll member  90 , the latch release mode is achieved. As the parent lever  82  rotates around the shaft portion  84  by the cam  92 , the parent lever  82  moves to the third position which is the most separated from the heating roll  72 . The child lever  80  is biased to the heating roll  72  side by the spring  96  of the upper portion  82 A of the parent lever  82 , and by the force of the spring  96 , the child lever  80  moves to the position at which the tip end portion (head portion) of the pin member  86  comes into contact with the wall  82 D (refer to  FIG. 9 ) of the parent lever  82 . 
     When the parent lever  82  moves to the third position which is the most separated from the heating roll  72 , the parent lever  82  does not abut against the guide member  102  (refer to  FIG. 14 ), and as the recessed portion  81  of the child lever  80  abuts against the guide member  102 , the child lever  80  holds the guide member  102  (refer to  FIG. 15 ). At the position of the guide member  102 , the block member  120  fixed to the guide member  102  is separated from the heating roll  72 , and the pad member  122  attached to the second attaching member  106  of the guide member  102  via the spring  114  is also separated from the heating roll  72 . 
     As illustrated in  FIGS. 9 and 10 , when the part (the part having a radius smaller than that of the first state and a radius larger than that of the latch release state) at which the dimension of the outer circumferential surface  92 A of the cam  92  is set to be the intermediate dimension comes into contact with the roll member  90 , the half latch mode is achieved, and the second state is achieved. As the parent lever  82  rotates around the shaft portion  84  by the cam  92 , the parent lever  82  moves to the second position (a position which is closer to the heating roll  72  than the third position) where the parent lever  82  is more separated from the heating roll  72  than the first position. The child lever  80  is biased to the heating roll  72  side by the spring  96  of the upper portion  82 A of the parent lever  82 . In addition, the pad member  122  is biased to the heating roll  72  side by the spring  114  disposed in the second attaching member  106  of the guide member  102 . At the position at which the load of the spring  96 , the load of the spring  114 , and the pressing force of the block member  120  are balanced, the child lever  80  stops with respect to the parent lever  82 . 
     When the parent lever  82  moves to the second position, the parent lever  82  does not abut against the guide member  102  (refer to  FIG. 11 ), and as the recessed portion  81  of the child lever  80  abuts against the guide member  102 , the child lever  80  holds the guide member  102  (refer to  FIG. 12 ). The position of the guide member  102  moves in the direction of being more separated from the heating roll  72  than the position of the guide member  102  of the first state. At the position of the guide member  102 , the block member  120  fixed to the guide member  102  is separated from the heating roll  72 . 
     In addition, the pad member  122  is biased to the heating roll  72  side by the spring  114  disposed in the second attaching member  106  of the guide member  102 , and the fixing belt  74  is pressed against the heating roll  72  by the pad member  122 . Therefore, in the second state, the fixing belt  74  is pressed against the heating roll  72  only by the pad member  122  among the block member  120  and the pad member  122 . In other words, the part at which the fixing belt  74  is pressed against the heating roll  72  only by the pad member  122  becomes the contact portion (nip portion), and as the recording paper P passes through the contact portion, the toner image on the recording paper P is fixed. 
     In addition, in the fixing device  70 , in the second state, by changing the radius of the outer circumferential surface  92 A of the cam  92 , the pressing load to the heating roll  72  by the pad member  122  is changed to the high load and the low load. 
     The cam  92  switches four modes, such as the high load and the low load in the first state, and the high load and the low load in the second state, in accordance with the type of the recording paper P which passes through the contact portion (nip portion) between the heating roll  72  and the fixing belt  74 . 
     In the fixing device  70 , compared to a configuration in which the first support portion, the second support portion, and the third support portion are not provided, a load difference when performing the switching by the cam  92  increases. 
     In addition, in the fixing device  70 , the pad member  122  is disposed upstream of the block member  120  in the transport direction of the recording paper P which passes through the contact portion (nip portion) between the heating roll  72  and the fixing belt  74 , and the shaft portion  130  is disposed upstream of the block member  120  in the transport direction of the recording paper P which passes through the contact portion between the heating roll  72  and the fixing belt  74 . Therefore, in the fixing device  70 , compared to a configuration in which the first member is not disposed at a position which is farther from the shaft portion than the second member, in the second state, the block member  120  which is at a position farther from the shaft portion  130  than the pad member  122  is likely to move in the direction of being separated from the heating roll  72 . 
     In addition, in the fixing device  70 , the child lever  80  is supported to be rotatable around the shaft portion  84  with respect to the parent lever  82 , and the shaft portion  84  is disposed upstream of the contact portion between the heating roll  72  and the fixing belt  74  in the transport direction of the recording paper P. In the exemplary embodiment, the length of the line segment L 1  which connects the center of the contact portion between the heating roll  72  and the fixing belt  74  in the transport direction of the recording paper P and the center  130 A of the shaft portion  130  is shorter than that of the line segment L 2  which connects the center of the contact portion between the heating roll  72  and the fixing belt  74  in the transport direction of the recording paper P and the center of the shaft portion  84 . Therefore, compared to a case where the shaft portion and the other shaft portion match each other, since the rotation of the guide member  102  by the shaft portion  130  is generated in addition to the rotation of the guide member  102  by the child lever  80  and the shaft portion  84  of the parent lever  82 , the pressure on the downstream side in the transport direction of the pad member  122  (downstream side in the transport direction of the recording paper P) in the second state does not deteriorate, and the deterioration of the fixing properties of the toner is prevented. 
     Furthermore, according to the image forming apparatus  10  provided with the fixing device  70 , compared to a configuration in which the switching portion which switches the first state and the second state is not provided, an appropriate fixing load is switched in accordance with the type of the recording paper P which passes through the contact portion between the heating roll  72  and the fixing belt  74 . 
     Next, by using  FIGS. 16 and 18 , the fixing device according to the second exemplary embodiment of the invention will be described. In addition, configuration elements which are the same as those of the above-described first exemplary embodiment will be given the same reference numerals, and the description thereof will be omitted. 
     As illustrated in  FIG. 16 , in a fixing device  150 , on the inside of the fixing belt  74 , a first holding portion  152 , a second holding portion  154 , and a second attaching member  156  which are fixed to the main body portion  102 A of the guide member  102  are provided. The first holding portion  152  is formed in an L shape in a sectional view, is disposed along the first attaching member  104 , and is fixed to the first attaching member  104 . The L-shaped second holding portion  154  is fixed to the first holding portion  152 , and the second attaching member  156  is fixed to the second holding portion  154 . In addition, in  FIG. 16 , the first holding portion  152  is a section, and in order to easily grasp the configuration, hatching is omitted. 
     In the second attaching member  156 , an attaching portion  156 A in a U shape in a sectional view is formed on the center portion side of the fixing belt  74  to be open to the heating roll  72  side. In the attaching portion  156 A, the spring  114  is disposed, and the pad member  122  is biased to the heating roll  72  side by the spring  114 . 
     At the position which is adjacent to the attaching portion  156 A, a spring  158  which is an example of a third biasing member which biases the block member  120  to the heating roll  72  side is attached to the first holding portion  152 . More specifically, one end portion of the spring  158  is fixed to a wall surface on the felt member  108  side of the first holding portion  152 . A holding portion  160  is attached to the other end portion of the spring  114 , and the block member  120  is fixed to an attaching surface  160 A on the heating roll  72  side of the holding portion  160  by adhesion or the like. In other words, the first holding portion  152  is fixed to the main body portion  102 A of the guide member  102 , and the block member  120  is supported to approach and be separated from the main body portion  102 A of the guide member  102 . 
     In the fixing device  150 , as illustrated in  FIG. 16 , when the part having a large radius of the outer circumferential surface  92 A of the cam  92  comes into contact with the roll member  90 , the full latch mode is achieved, and the first state is achieved. As the parent lever  82  rotates around the shaft portion  84  by the cam  92 , the parent lever  82  moves to the first position where the parent lever  82  is close to the heating roll  72 . In the first state, the block member  120  is biased to the heating roll  72  side by the spring  158  supported by the guide member  102 , and the fixing belt  74  is pressed against the heating roll  72  by the block member  120 . In addition, the pad member  122  is biased to the heating roll  72  side by the spring  114  supported by the guide member  102 , and the fixing belt  74  is pressed against the heating roll  72  by the pad member  122 . Therefore, in the first state, the fixing belt  74  is pressed against the heating roll  72  by the block member  120  and the pad member  122 . 
     As illustrated in  FIG. 18 , when the part having the smallest radius of the outer circumferential surface  92 A of the cam  92  comes into contact with the roll member  90 , the latch release mode is achieved. In a latch release state, as the parent lever  82  rotates around the shaft portion  84 , the parent lever  82  moves to the third position which is the most separated from the heating roll  72 , and the block member  120  and the pad member  122  are separated from the heating roll  72 . 
     As illustrated in  FIG. 17 , when the part (the part having a radius smaller than that of the first state and a radius larger than that of the latch release state) at which the radius of the outer circumferential surface  92 A of the cam  92  is set to be the intermediate dimension comes into contact with the roll member  90 , the half latch mode is achieved, and the second state is achieved. As the parent lever  82  rotates around the shaft portion  84  by the cam  92 , the parent lever  82  moves to the second position (a position which is closer to the heating roll  72  than the third position) where the parent lever  82  is more separated from the heating roll  72  than the first position. When the parent lever  82  moves to the second position, the guide member  102  moves in the direction of being more separated from the heating roll  72  than the position of the guide member  102  of the first state. At the position of the guide member  102 , the block member  120  supported by the guide member  102  via the spring  158  is separated from the heating roll  72 . 
     The pad member  122  is biased to the heating roll  72  side by the spring  114  supported by the guide member  102 , and the fixing belt  74  is pressed against the heating roll  72  by the pad member  122 . Therefore, in the second state, the fixing belt  74  is pressed against the heating roll  72  only by the pad member  122  among the block member  120  and the pad member  122 . 
     In the fixing device  150 , the spring  158  which biases the block member  120  to the heating roll  72  side is provided. Therefore, compared to a configuration in which the spring  158  is not provided, the pressure by which the fixing belt  74  comes into contact with the heating roll  72  by the block member  120  is stabilized. 
     Next, by using  FIG. 19 , the fixing device according to the third exemplary embodiment of the invention will be described. In addition, configuration elements which are the same as those of the above-described first and second exemplary embodiments will be given the same reference numerals, and the description thereof will be omitted. 
     As illustrated in  FIG. 19 , in a fixing device  170 , the position at which the block member  120  (refer to  FIG. 5 ) and the pad member  122  (refer to  FIG. 5 ) are disposed is a region between an upper virtual line  172  and a lower virtual line  174 . In the fixing device  170 , the upper virtual line  172  and the lower virtual line  174  are disposed along the pressing direction of the block member  120  (refer to  FIG. 5 ) of the full latch state. In the fixing device  170 , the shaft portion  84  and the shaft portion  130  are disposed on the lower side in the vertical direction (upstream side in the transport direction of the recording paper P). The shaft portion  84  relatively rotates the parent lever  82  and the child lever  80 . The shaft portion  130  relatively rotates the child lever  80  and the guide member  102 . Furthermore, the length of the line segment L 1  which connects the center of the contact portion between the heating roll  72  and the fixing belt  74  in the transport direction of the recording paper P and the center  130 A of the shaft portion  130  is shorter than that of the line segment L 2  which connects the center of the contact portion between the heating roll  72  and the fixing belt  74  in the transport direction of the recording paper P and the center of the shaft portion  84 . Accordingly, in the fixing device  170 , compared to a case where the first shaft portion and the second shaft portion match each other, since the rotation of the guide member  102  by the shaft portion  130  is generated in addition to the rotation of the guide member  102  by the child lever  80  and the shaft portion  84  of the parent lever  82 , the pressure on the downstream side in the transport direction of the pad member  122  (downstream side in the transport direction of the recording paper P) in the second state does not deteriorate, and the deterioration of the fixing properties of the toner is prevented. 
     Here, in the fixing device  170 , the positions of the shaft portion  84  and the shaft portion  130  can be changed. At this time, in the region between the upper virtual line  172  and the lower virtual line  174 , since the displacement amount of the guide member  102  is small, the shaft portion  130  is not provided. Therefore, a configuration in which the shaft portion  84  which relatively rotates the parent lever  82  and the child lever  80 , and the shaft portion  130  which relatively rotates the child lever  80  and the guide member  102 , are provided further on the upper side of the upper virtual line  172  in the vertical direction (downstream of the upper virtual line  172  in the transport direction of the recording paper P), may be employed. At this time, it is preferable that the length of the line segment L 1  which connects the center of the contact portion between the heating roll  72  and the fixing belt  74  in the transport direction of the recording paper P and the center  130 A of the shaft portion  130  is shorter than that of a line segment L 2  which connects the center of the contact portion between the heating roll  72  and the fixing belt  74  in the transport direction of the recording paper P and the center of the shaft portion  84 . 
     In addition, in the fixing device  170 , a case where the shaft portion  130  is disposed on the upper side of the upper virtual line  172  in the vertical direction (upstream of the upper virtual line  172  in the transport direction of the recording paper P), it is preferable that the pad member  122  is disposed downstream of the block member  120  in the transport direction of the recording paper P which passes through the nip portion and that the shaft portion  130  is disposed upstream of the block member  120  in the transport direction of the recording paper P which passes through the nip portion. Accordingly, compared to a configuration in which the first member is not disposed at a position which is farther from the first shaft portion than the second member, in the second state, the block member  120  which is at a position farther from the shaft portion  130  than the pad member  122  is likely to move in the direction of being separated from the heating roll  72 . 
     In addition, in the first to third exemplary embodiments, the cam  92  is used as a switching portion, but the invention is not limited thereto. For example, a configuration in which a switching portion, such as a cylinder, an actuator, and a lack and pinion, is used, may be employed. 
     In addition, in the first to third exemplary embodiments, the tension spring  132  which links the upper portion of the main body portion  102 A of the guide member  102  and the parent lever  82  is provided, but a configuration in which the tension spring  132  is not provided may be employed. 
     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.