Fixing device

Abstract

To provide a fixing device that does not require exchange of a side guide even when a projection which is a swing fulcrum of the side guide is worn.SOLUTION: A fixing device comprises: a second fixing member 82 that forms a nip part between itself and a first fixing member; and an energizing mechanism that has an arm which energizes the second fixing member 82 toward the first fixing member. The second fixing member 82 comprises: a belt 130; a nip forming member N that nips at the belt 130 between itself and the first fixing member; a side guide SG that has a first guide surface guiding an inner peripheral surface 131 of the belt 130 and a second guide surface F12 guiding an end surface of the belt 130; a stay (210) that supports the nip forming member N; and a buffer member BF that is arranged on an opposite side of the belt 130 relative to the side guide SG, and at least a portion of which buffer member is nipped between the stay and the arm. The buffer member BF has a projection part BF4 that contacts with the side guide SG, the projection part BF4 supporting the side guide SG so as to be able to fluctuate.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a fixing device for fixing a developer image onto a sheet. [Background technology]

[0002] Conventionally, a fixing device is known that includes a heating roller, a belt, a pressure member that sandwiches the belt between the heating roller, a pressure arm that urges the pressure member against the heating roller, and a side guide that guides the end surface and inner peripheral surface of the belt (see Patent Document 1). In this technology, the side guide has a protrusion that protrudes toward the pressure arm. The side guide is swingable relative to the pressure arm, with the protrusion as a fulcrum. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-292793 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, since the side guide is usually made of a material softer than the pressure arm, the protrusions of the side guide wear out as the fixing device is used. When the protrusions wear out, the side guide needs to be replaced, but when the side guide is removed from the belt, the grease applied to the inner peripheral surface of the belt may adhere to the side guide and become reduced. When the grease on the inner peripheral surface of the belt becomes reduced in this way, the sliding properties of the inner peripheral surface of the belt change, which creates the problem of needing to replenish the grease on the inner peripheral surface of the belt.

[0005] SUMMARY OF THE PRESENTLY PREFERRED EMBODIMENTS In view of the above, an object of the present invention is to provide a fixing device in which it is not necessary to replace the side guide even if the protrusion that serves as the swing fulcrum of the side guide becomes worn. [Means for solving the problem]

[0006] In order to solve the above problem, the fixing device of the present invention includes a first fixing member having a roller, a second fixing member forming a nip portion between the first fixing member, and a biasing mechanism that biases the second fixing member toward the first fixing member.

[0007] The biasing mechanism includes an arm that supports the second fixing member and a spring that biases the arm toward the first fixing member.

[0008] The second fixing member includes a belt, a nip forming member that sandwiches the belt between the first fixing member, a side guide having a first guide surface that guides an inner surface of the belt and a second guide surface that guides an end surface of the belt, a stay that supports the nip forming member, and a buffer member that is positioned on the opposite side of the side guide to the belt and at least a portion of which is sandwiched between the stay and the arm.

[0009] The buffer member has a protrusion that comes into contact with the side guide and supports the side guide so as to be able to swing.

[0010] According to this configuration, when the protrusions wear out, it is only necessary to replace the buffer member without removing the side guide from the belt, making it unnecessary to replace the side guide. Therefore, when replacing the side guide, the grease is removed together with the side guide, which can prevent a change in the sliding property of the inner peripheral surface of the belt.

[0011] Furthermore, a contact surface of the protrusion with the side guide may be a curved surface that protrudes toward the side guide.

[0012] In addition, the stay may be positioned biased toward the downstream side of the nip portion in the direction of movement of the belt in the nip portion, and the contact point of the convex portion with the side guide may be located inside the orbit of the belt when viewed in the width direction of the belt, and upstream of the stay in the direction of movement.

[0013] According to this, the contact point can be disposed near the center of the nip portion in the direction of movement, so that the side guide can be swung in a well-balanced manner.

[0014] The Young's modulus of the buffer member may be equal to or greater than the Young's modulus of the side guide.

[0015] According to this, the side guide is less susceptible to wear than the buffer member, so replacement of the side guide becomes less necessary.

[0016] The buffer member may be made of resin.

[0017] The buffer member may be conductive.

[0018] This allows the stay to be grounded via the buffer member.

[0019] Further, the second fixing member may be a support member that supports the nip forming member and is supported by the stay, the support member having an upstream convex portion that protrudes upstream in the movement direction of the belt in the nip portion and a downstream convex portion that protrudes downstream in the movement direction of the belt in the nip portion, the side guide having an outer surface that is the surface opposite to the second guide surface, an upstream engagement portion having an upstream recess into which the upstream convex portion fits, and a downstream engagement portion having a downstream recess into which the downstream convex portion fits, and the upstream engagement portion and the downstream engagement portion may protrude on the opposite side of the second guide surface from the outer surface.

[0020] This prevents the upstream engagement portion and the downstream engagement portion from interfering with components located widthwise inward of the belt than the second guide surface, while the upstream recess and the downstream recess can be lengthened to prevent the side guide from rotating around an axis along the direction of movement.

[0021] Furthermore, the side guide may be an arc-shaped rib having the first guide surface, the rib extending from upstream to downstream of the nip portion in the movement direction of the belt in the nip portion, and at least one of both end faces of the rib in the movement direction may have an inclined surface that is inclined relative to the second guide surface.

[0022] According to this, when inserting the side guide into the belt during assembly of the fixing device, it is possible to prevent the rib from interfering with a member inside the belt, making it difficult to insert the side guide.

[0023] The inclined surface may be located at a position away from the second guide surface.

[0024] According to this, for example, compared to a configuration in which one end of the inclined surface is located on the second guide surface, the size of the first guide surface can be made larger, thereby suppressing buckling of the belt caused by the first guide surface being smaller.

[0025] The second fixing member may also include an upstream pad that sandwiches the belt between itself and the first fixing member, a downstream pad that is arranged downstream of the upstream pad in the sheet transport direction and sandwiches the belt between itself and the first fixing member, and a support member that supports the upstream pad and the downstream pad. Effect of the Invention

[0026] According to the present invention, even if the protruding portion that serves as the swing fulcrum of the side guide becomes worn, it is necessary to replace only the buffer member, making it unnecessary to replace the side guide. [Brief description of the drawings]

[0027] [Figure 1] 1 is a cross-sectional view showing an image forming apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view showing the fixing device. [Diagram 3]FIG. 2 is an exploded perspective view showing each member disposed on the inner side of the belt. [Figure 4] FIG. [Diagram 5] 1A is a cross-sectional view showing a pressure changing mechanism when the nip pressure is a first nip pressure, and FIG. 1B is a cross-sectional view showing a structure around the nip portion. [Figure 6] 4 is a perspective view showing a structure of one end side in the width direction of a second fixing member. FIG. [Figure 7] 1A and 1B are perspective views showing a side guide and a buffer member, and FIG. 1C is a perspective view showing the buffer member. [Figure 8] 1A is a view of the side guide as seen from a specific direction, FIG. 1B is a view of the side guide as seen from the direction of movement, and FIG. [Figure 9] FIG. 4A is a diagram showing a relationship between a side guide and a shock absorbing member, and FIG. 4B is a diagram showing a relationship between the side guide and the shock absorbing member and a first stay, etc. [Figure 10a] FIG. 4 is a cross-sectional view of the second fixing device as seen from the movement direction, showing the entire second fixing device in the width direction. [Figure 10b] FIG. 4 is a cross-sectional view of the second fixing device as seen from the movement direction, and is an enlarged view showing the structure of one end side of the second fixing device. [Figure 11] FIG. 2 is a conceptual diagram showing the relationship between the width directions of a belt, a sliding sheet, a pad, a roller base tube, and an elastic layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Hereinafter, an embodiment of the invention will be described in detail with reference to the drawings as appropriate.

[0029] 1, a fixing device 8 according to the embodiment is used in an image forming apparatus 1 such as a laser printer. The image forming apparatus 1 includes a main body housing 2, a sheet supply unit 3, an exposure device 4, a developer image forming unit 5, and the fixing device 8.

[0030] The sheet supply unit 3 is provided in the lower part of the main body housing 2, and includes a sheet tray 31 in which sheets S such as paper are stored, and a sheet supply mechanism 32. The sheets S in the sheet tray 31 are supplied to the developer image forming unit 5 by the sheet supply mechanism 32.

[0031] The exposure device 4 is disposed at the upper part inside the main body housing 2, and includes a light source device (not shown), a polygon mirror (shown without reference numerals), a lens, a reflecting mirror, etc. The exposure device 4 exposes the surface of the photoconductor drum 61 by scanning the surface of the photoconductor drum 61 at high speed with a light beam (see dashed line) based on image data emitted from the light source device.

[0032] The developer image forming unit 5 is disposed below the exposure device 4. The developer image forming unit 5 is configured as a process cartridge, and is detachable from the main body housing 2 through an opening formed when a front cover 21 provided at the front of the main body housing 2 is opened. The developer image forming unit 5 includes a photosensitive drum 61, a charger 62, a transfer roller 63, a developing roller 64, a supply roller 65, and a developer storage unit 66 that stores a developer made of dry toner.

[0033] The developer image forming unit 5 uniformly charges the surface of the photoconductor drum 61 using a charger 62. Thereafter, the surface of the photoconductor drum 61 is exposed to a light beam from an exposure device 4, so that an electrostatic latent image based on image data is formed on the surface. In addition, the developer image forming unit 5 supplies the developer in a developer container 66 to a development roller 64 via a supply roller 65.

[0034] Then, the developer image forming unit 5 supplies the developer on the developing roller 64 to the electrostatic latent image formed on the photosensitive drum 61. As a result, the electrostatic latent image is visualized and a developer image is formed on the photosensitive drum 61. Thereafter, the developer image forming unit 5 transfers (forms) the developer image on the photosensitive drum 61 onto the sheet S by transporting the sheet S supplied from the sheet supply unit 3 between the photosensitive drum 61 and the transfer roller 63.

[0035] The fixing device 8 is disposed behind the developer image forming section 5. The fixing device 8 will be described in detail later. The fixing device 8 thermally fixes the developer image to the sheet S by passing the sheet S onto which the developer image has been transferred. The image forming apparatus 1 discharges the sheet S onto which the developer image has been thermally fixed, by a conveying roller 23 and a discharge roller 24, onto a paper discharge tray 22 outside the main body housing 2.

[0036] 2, the fixing device 8 includes a heater 110, a first fixing member 81, a second fixing member 82, and a biasing mechanism 300A (see FIG. 4) described later. The second fixing member 82 is biased toward the first fixing member 81 by the biasing mechanism 300A (see FIG. 4) described later. In the following description, the direction in which the second fixing member 82 is biased toward the first fixing member 81 is referred to as a "predetermined direction." In this embodiment, the predetermined direction is a direction perpendicular to the width direction and movement direction described later, and is a direction in which the first fixing member 81 and the second fixing member 82 face each other.

[0037] The first fixing member 81 has a rotatable roller 120. The second fixing member 82 is a member that forms a nip portion NP between the first fixing member 81 and the second fixing member 82. The second fixing member 82 includes a belt 130, a nip forming member N, a holder 140 as an example of a support member, a stay unit 200, a belt guide G, and a sliding sheet 150. In the following description, the width direction of the belt 130 is simply referred to as the "width direction." The width direction is the direction in which the rotation axis of the roller 120 extends, that is, the axial direction of the roller 120. The width direction is perpendicular to a predetermined direction.

[0038] The heater 110 is a halogen lamp that emits light and generates heat when energized, and uses radiant heat to heat the roller 120. The heater 110 is disposed so as to pass through the inside of the roller 120 along the rotation axis of the roller 120.

[0039] Roller 120 is a cylindrical roller that is long in the width direction, and is heated by heater 110. Roller 120 has an element tube 121 made of metal or the like, and an elastic layer 122 that covers the outer peripheral surface of element tube 121. Elastic layer 122 is made of rubber such as silicone rubber. Roller 120 is rotatably supported by side frame 83 (see FIG. 4), which will be described later, and is rotated counterclockwise in FIG. 2 by input of driving force from a motor (not shown) provided in main body housing 2.

[0040] The belt 130 is a long cylindrical member and has flexibility. Although not shown, the belt 130 has a base material made of metal, resin, or the like, and a release layer covering the outer peripheral surface of the base material. When the roller 120 rotates, the belt 130 rotates clockwise in FIG. 2 due to friction with the roller 120 or the sheet S. A lubricant such as grease is applied to the inner peripheral surface 131 of the belt 130. A nip forming member N, a holder 140, a stay unit 200, a belt guide G, and a sliding sheet 150 are arranged inside the belt 130.

[0041] In other words, the nip forming member N, the holder 140, the stay unit 200, the belt guide G and the sliding sheet 150 are covered by the belt .

[0042] 2 and 3, the nip forming member N is a member that forms a nip portion NP by nipping the belt 130 between itself and the roller 120. The nip forming member N includes an upstream nip forming member N1 and a downstream nip forming member N2.

[0043] The upstream nip forming member N1 has an upstream pad P1 and an upstream fixed plate B1.

[0044] The upstream pad P1 is a rectangular parallelepiped member. The upstream pad P1 is made of rubber such as silicone rubber. The upstream pad P1 and the roller 120 sandwich the belt 130 to form an upstream nip portion NP1.

[0045] In the following description, the movement direction of the belt 130 in the upstream nip portion NP1 and the nip portion NP described later in detail is simply referred to as the "movement direction." In this embodiment, the movement direction is along the outer circumferential surface of the roller 120, but since this direction is roughly along a direction perpendicular to the predetermined direction and the width direction, it will be illustrated as a direction perpendicular to the predetermined direction and the width direction. The movement direction is the same as the conveyance direction of the sheet S in the nip portion NP.

[0046] The upstream pad P1 is fixed to the surface of the upstream fixed plate B1 on the side of the roller 120. The upstream fixed plate B1 is made of a material harder than the upstream pad P1, such as a metal.

[0047] The downstream nip forming member N2 is disposed downstream in the moving direction relative to the upstream nip forming member N1 with a gap therebetween. The downstream nip forming member N2 has a downstream pad P2 and a downstream fixed plate B2.

[0048] The downstream pad P2 is a rectangular parallelepiped member. The downstream pad P2 is made of rubber such as silicone rubber. The downstream pad P2 sandwiches the belt 130 between itself and the roller 120 to form a downstream nip portion NP2. The downstream pad P2 is separated from the upstream pad P1 in the rotation direction of the belt 130.

[0049] Therefore, between the upstream nip portion NP1 and the downstream nip portion NP2, there is an intermediate nip portion NP3 where the pressure from the second fixing member 82 does not directly act. In this intermediate nip portion NP3, the belt 130 contacts the roller 120, but there is no member that sandwiches the belt 130 between the roller 120 and the intermediate nip portion NP3, so almost no pressure is applied. Therefore, the sheet S passes through the intermediate nip portion NP3 while being heated by the roller 120 and almost without being pressurized. In this embodiment, the region from the upstream end of the upstream nip portion NP1 to the downstream end of the downstream nip portion NP2, that is, the entire region where the outer circumferential surface of the belt 130 and the roller 120 contact each other, is referred to as the nip portion NP. In other words, in this embodiment, the nip portion NP includes a portion to which the pressing forces from the upstream pad P1 and the downstream pad P2 are not applied.

[0050] The downstream pad P2 is fixed to the surface of the downstream fixed plate B2 on the side of the roller 120. The downstream fixed plate B2 is made of a material harder than the downstream pad P2, such as a metal.

[0051] The hardness of the upstream pad P1 is greater than the hardness of the elastic layer 122 of the roller 120. The hardness of the downstream pad P2 is greater than the hardness of the upstream pad P1.

[0052] Here, the hardness refers to the durometer hardness defined in ISO 7619-1. The durometer hardness is a value obtained from the depth of a specified indenter when the specified indenter is pressed into a test piece under specified conditions. For example, when the durometer hardness of the elastic layer 122 is 5, it is preferable that the durometer hardness of the upstream pad P1 is 6 to 10, and the durometer hardness of the downstream pad P2 is 70 to 90.

[0053] The holder 140 is a member that supports the nip formation member N. The holder 140 is made of a heat-resistant resin or the like. The holder 140 has a holder main body 141 and two engagement portions 142 and 143.

[0054] The holder body 141 is a portion that holds the nip formation member N. Most of the holder body 141 is disposed within the range of the belt 130 in the width direction. The holder body 141 is supported by the stay unit 200.

[0055] The engaging portions 142, 143 extend from each end in the width direction of the holder body 141. The engaging portions 142, 143 are disposed outside the range of the belt 130 in the width direction. The engaging portions 142, 143 engage with each end in the width direction of a first stay 210, which will be described later.

[0056] The stay unit 200 is a member that is located on the opposite side of the holder 140 from the nip forming member N and supports the holder 140. In other words, the stay unit 200 supports the nip forming member N via the holder 140. The stay unit 200 includes a first stay 210 as an example of a stay, and a second stay 220 that is connected to the first stay 210 by a connecting member CM.

[0057] The first stay 210 is a member that supports the holder main body 141 of the holder 140. The first stay 210 is made of metal or the like. The first stay 210 is disposed biased toward the downstream side of the nip portion NP in the movement direction. In other words, the distance from the downstream end of the nip portion NP to the first stay 210 in the movement direction is smaller than the distance from the upstream end of the nip portion NP to the first stay 210. The first stay 210 has a base portion 211 and a hemming bent portion HB that is bent by hemming.

[0058] The base portion 211 has a contact surface Ft at one end on the holder 140 side, which contacts the holder main body 141 of the holder 140. The contact surface Ft is a flat surface perpendicular to a predetermined direction.

[0059] The base portion 211 has load input portions 211A at both ends in the width direction, which receive a force from a biasing mechanism 300A (see FIG. 4) described later. The load input portions 211A are recesses that open on the side opposite the nip forming member N in a predetermined direction, and are formed at the end of the base portion 211 on the side opposite the nip forming member N in the predetermined direction.

[0060] A buffer member BF made of conductive resin is attached to the load input portion 211A. The buffer member BF is a member for suppressing friction between the metal base portion 211 and a metal arm 310 (see FIG. 4), which will be described later. The buffer member BF has a fitting portion BF1 that fits into the load input portion 211A, and a pair of legs BF2 that are disposed on the upstream and downstream sides in the movement direction with respect to the end of the width direction of the base portion 211. The fitting portion BF1 is sandwiched between the first stay 210 and the arm 310 (see FIG. 5(a)).

[0061] The belt guide G is a member that guides an inner circumferential surface 131 of the belt 130. The belt guide G is made of a heat-resistant resin or the like. The belt guide G has an upstream guide G1 and a downstream guide G2.

[0062] The sliding sheet 150 is a rectangular sheet for reducing frictional resistance between each of the pads P1, P2 and the belt 130. The sliding sheet 150 is sandwiched between the inner circumferential surface 131 of the belt 130 and each of the pads P1, P2 at the nip portion NP. The sliding sheet 150 is made of an elastically deformable material. Note that the sliding sheet 150 may be made of any material, but in this embodiment, a resin sheet containing polyimide is used.

[0063] As shown in FIG. 2, the upstream guide G1, the downstream guide G2 and the first stay 210 are fastened together by a screw SC.

[0064] 4, the fixing device 8 further includes a frame FL and a pressure change mechanism 300. The frame FL is a frame that supports the first fixing member 81 and the second fixing member 82, and is made of metal or the like. The frame FL includes side frames 83 and brackets 84 that are disposed on both sides in the width direction of the first fixing member 81 and the second fixing member 82, and connection frames 85 that are connected to each side frame 83.

[0065] The side frame 83 is a frame that supports the first fixing member 81 and the second fixing member 82. The side frame 83 has a spring engagement portion 83A that engages with one end of a first spring 320, which will be described later.

[0066] The bracket 84 is a member that supports the second fixing member 82 so as to be movable in a predetermined direction, and is fixed to the side frame 83. More specifically, the bracket 84 has a first elongated hole 84A that is long in the predetermined direction. The first elongated hole 84A supports the end of the first stay 210 via the engagement portions 142, 143 of the holder 140 so as to be movable in the predetermined direction.

[0067] The pressure change mechanism 300 is a mechanism for changing the nip pressure of the nip portion NP. More specifically, the pressure change mechanism 300 can change the nip pressure of the nip portion NP to a first nip pressure, a second nip pressure smaller than the first nip pressure, and a third nip pressure smaller than the second nip pressure. As shown in FIG. 4 and FIG. 5(a), the pressure change mechanism 300 includes a biasing mechanism 300A, a second spring 330, and a cam 340. The biasing mechanism 300A includes an arm 310 and a first spring 320 as an example of a spring. The arm 310, the first spring 320, the second spring 330, and the cam 340 are provided at one end side and the other end side in the width direction of the frame FL, respectively.

[0068] The arm 310 is a member for pressing the first stay 210 via the buffer member BF. The arm 310 supports the second fixing member 82, and is supported by the side frame 83 so as to be rotatable.

[0069] The arm 310 has an arm body 311 and a cam follower 350. The arm body 311 is an L-shaped plate-like member made of metal or the like.

[0070] The arm body 311 has one end 311A ​​rotatably supported by the side frame 83, the other end 311B to which the first spring 320 is connected, and an engagement hole 311C that supports the second fixing member 82. The engagement hole 311C is disposed between the one end 311A ​​and the other end 311B, and engages with the buffer member BF.

[0071] Moreover, the arm body 311 further has a guide protrusion 312 extending towards the cam 340. The guide protrusion 312 is disposed between the other end 311B and the engagement hole 311C in the direction from the other end 311B towards the engagement hole 311C.

[0072] Cam follower 350 is attached movably relative to guide protrusion 312 of arm body 311, and is capable of contacting cam 340. Cam follower 350 is made of resin or the like, and has a cylindrical portion 351 that fits into guide protrusion 312, a contact portion 352 provided at one end of cylindrical portion 351, and a flange portion 353 provided at the other end of cylindrical portion 351.

[0073] Cylindrical portion 351 is supported by guide protrusion 312 so as to be movable in the extending direction of guide protrusion 312. Contact portion 352 is a wall that closes an opening at the end portion of cylindrical portion 351 on the cam 340 side, and is disposed between cam 340 and the tip of guide protrusion 312. Flange portion 353 protrudes from the other end of cylindrical portion 351 in a direction perpendicular to the moving direction of cam follower 350.

[0074] In addition, a second spring 330 is disposed between the cylindrical portion 351 and the arm body 311. This allows the arm body 311 to be biased by the first spring 320 and also biased by the second spring 330.

[0075] The first spring 320 is a spring that applies a first biasing force to the second fixing member 82. In detail, the first spring 320 applies the first biasing force to the second fixing member 82 via the arm body 311 by biasing the arm body 311 toward the roller 120.

[0076] More specifically, the first spring 320 biases the upstream pad P1 and the downstream pad P2 toward the roller 120 via the arm body 311, the buffer member BF, the first stay 210, and the holder 140. The first spring 320 is a tension coil spring made of metal or the like, and has one end connected to the spring engagement portion 83A of the side frame 83 and the other end connected to the other end portion 311B of the arm body 311.

[0077] The second spring 330 is a spring capable of applying a second biasing force in a direction opposite to the first biasing force to the second fixing member 82. In detail, the second spring 330 is capable of applying the second biasing force to the second fixing member 82 via the arm main body 311. The second spring 330 is a compression coil spring made of metal or the like, and is disposed between the tubular portion 351 and the arm main body 311 with the guide protrusion 312 inserted in the space surrounded by the compression coil spring.

[0078] The cam 340 is a member that can change the expansion and contraction state of the second spring 330 to a first expansion and contraction state in which the second biasing force is not applied to the second fixing member 82, a second expansion and contraction state in which the second biasing force is applied to the second fixing member 82, and a third expansion and contraction state in which the second fixing member 82 is deformed more than the second expansion and contraction state. The cam 340 also has a function of moving the second fixing member 82 against the biasing force of the first spring 320. The cam 340 is supported by the side frame 83 so as to be rotatable between a first cam position corresponding to the first nip pressure, a second cam position corresponding to the second nip pressure, and a third cam position corresponding to the third nip pressure, as shown in FIG. 5(a). In detail, the cam 340 rotates from the first cam position to the third cam position by the forward rotation of a motor (not shown), and rotates from the third cam position to the first cam position by the reverse rotation of a motor (not shown).

[0079] The cam 340 is made of resin or the like and has an opposing surface F1, a first support surface F2, and a second support surface F3. The opposing surface F1, the first support surface F2, and the second support surface F3 are located on the outer circumferential surface of the cam 340.

[0080] The opposing surface F1 is a surface that faces the cam follower 350 when the cam 340 is located at the first cam position, that is, when the nip pressure is the first nip pressure. When the cam 340 is located at the first cam position, the opposing surface F1 is separated from the cam follower 350.

[0081] The first support surface F2 is a surface that supports the cam follower 350 so that the expansion / contraction state of the second spring 330 is maintained in the second expansion / contraction state. The first support surface F2 comes into contact with the cam follower 350 when the cam 340 is located at the second cam position, that is, when the nip pressure is the second nip pressure. More specifically, the first support surface F2 comes into contact with the cam follower 350 when the cam 340 rotates approximately 90 degrees clockwise from the first cam position. The distance from the first support surface F2 to the rotation center of the cam 340 is greater than the distance from the opposing surface F1 to the rotation center of the cam 340.

[0082] The second support surface F3 is a surface that supports the cam follower 350 so that the second spring 330 is maintained in a third extension / contraction state and the posture of the arm body 311 is maintained in a second posture different from the first posture shown in FIG. 5(a). The second support surface F3 contacts the cam follower 350 when the cam 340 is located at the third cam position, that is, when the nip pressure is the third nip pressure. More specifically, the second support surface F3 contacts the cam follower 350 when the cam 340 rotates about 270 degrees clockwise from the first cam position, in other words, when the cam 340 rotates about 180 degrees clockwise from the second cam position. The distance from the second support surface F3 to the rotation center of the cam 340 is greater than the distance from the first support surface F2 to the rotation center of the cam 340.

[0083] When the cam 340 is located at the first cam position, the cam 340 is separated from the cam follower 350, and the second spring 330 is in the first extended / contracted state. When the cam 340 causes the second spring 330 to be in the first extended / contracted state in this manner, the arm main body 311 is in the first posture shown in Fig. 5(a).

[0084] In detail, when the cam 340 sets the second spring 330 in the first extended / retracted state, the cam 340 is separated from the cam follower 350, and therefore the second biasing force of the second spring 330 is not applied to the second fixing member 82 via the arm body 311, and only the first biasing force of the first spring 320 is applied to the second fixing member 82 via the arm body 311. In this manner, when the first biasing force is applied to the second fixing member 82 by the first spring 320 and the second biasing force is not applied to the second fixing member 82 by the second spring 330, the nip pressure becomes the first nip pressure.

[0085] In this embodiment, when the cam 340 sets the second spring 330 in the first contraction state, the second spring 330 is disposed between the cam follower 350 and the arm body 311 in a deformed state. That is, in this embodiment, the second spring 330 is not in its natural length in the first contraction state, but in a state deformed from its natural length. Even if the second spring 330 is in a deformed state in the first contraction state, the cam 340 is separated from the cam follower 350, so that the second biasing force of the second spring 330 is not applied to the second fixing member 82. In the process of rotating from the first cam position to the second cam position shown in FIG. 5(a) , that is, in the process of changing the nip pressure from the first nip pressure to the second nip pressure, the cam 340 comes into contact with the cam follower 350 and moves the cam follower 350 by a predetermined amount relative to the arm body 311. As a result, the second spring 330 between the cam follower 350 and the arm body 311 is deformed, so that when the cam 340 is located at the second cam position, the second spring 330 enters a second expanded / contracted state that is more deformed than the first expanded / contracted state.

[0086] When cam 340 is located at the second cam position, cam follower 350 is supported by cam 340, and therefore the second biasing force of second spring 330 is applied to second fixing member 82 in the opposite direction to the first biasing force via arm body 311. Therefore, when the first biasing force is applied to second fixing member 82 by first spring 320 and the second biasing force is applied to second fixing member 82 by second spring 330, the nip pressure becomes a second nip pressure that is smaller than the first nip pressure.

[0087] When the cam 340 sets the second spring 330 in the second contraction state, the arm body 311 remains in the first position described above. Here, the downstream pad P2 is pressed against the roller 120, that is, when a load is applied to the downstream pad P2, it is not substantially deformed regardless of the magnitude of the load. Since the downstream pad P2 is not substantially deformed, the position of the stay unit 200 supporting the downstream pad P2 and the arm 310 supporting the stay unit 200 are also kept substantially constant regardless of the magnitude of the load. Furthermore, since the position of the upstream pad P1 is determined by the position of the downstream pad P2, when the downstream pad P2 is not substantially deformed and its position is not deformed, the position of the upstream pad P1 is not changed. Therefore, in both the strong nip (first nip pressure) and the weak nip (second nip pressure), the total nip width (the length from the entrance of the upstream nip portion NP1 to the exit of the downstream nip portion NP2) is not changed, and the position of the arm 310 is also kept substantially constant.

[0088] The reason why the downstream pad P2 does not deform is that the hardness of the downstream pad P2 is sufficiently higher than the hardness of the upstream pad P1 and the elastic layer 122 of the roller 120. More specifically, the downstream pad P2 has a hardness that is such that it is hardly deformed by a nip pressure within the range from the maximum nip pressure (downstream nip pressure at the time of strong nip) to the minimum nip pressure (downstream nip pressure at the time of weak nip) required at the downstream nip portion NP2.

[0089] In other words, the maximum nip pressure and the minimum nip pressure required at the downstream nip are set to a value that causes almost no deformation of the downstream pad P2.

[0090] Here, "the downstream pad P2 is almost not deformed" includes the downstream pad P2 deforming to an extent that the deformation amount of the nip width (length and position of the nip in the belt movement direction) of the downstream nip portion NP2 formed by the downstream pad P2 does not affect image quality or paper transport (the deformation amount of the downstream nip width is not zero).

[0091] In this way, whether the second spring 330 is in the first or second contraction state, the arm body 311 takes the first posture, so that in both states where the nip pressure is the first nip pressure and where the nip pressure is the second nip pressure, the upstream pad P1 and the downstream pad P2 sandwich the belt 130 between themselves and the roller 120. More specifically, in each state, the position of the second fixing member 82 relative to the roller 120 is substantially the same, so that the width (length in the movement direction) of the nip portion NP in each state is substantially the same.

[0092] In the process of rotating from the second cam position to the third cam position, that is, in the process of changing the nip pressure from the second nip pressure to the third nip pressure, cam 340 moves cam follower 350 further relative to arm body 311, thereby bringing cam follower 350 into contact with arm body 311. When cam 340 then rotates further, cam 340 presses arm body 311 via cam follower 350. As a result, the contraction state of second spring 330 becomes a third contraction state that is more deformed than the second contraction state, and arm body 311 rotates from the first posture to a second posture different from the first posture.

[0093] Specifically, in the first stage of the process of rotating the cam 340 from the second cam position to the third cam position, the cam follower 350 moves relative to the arm body 311 so that the contact portion 352 of the cam follower 350 approaches the tip of the guide protrusion 312. When the contact portion 352 comes into contact with the tip of the guide protrusion 312, the contracted state of the second spring 330 becomes the third contracted state. When the cam 340 makes the contracted state of the second spring 330 the third contracted state in this manner, the contact portion 352, which is a part of the cam follower 350, is sandwiched between the cam 340 and the guide protrusion 312. In other words, the contact portion 352 comes into contact with the cam 340 and also with the guide protrusion 312. Thereafter, when cam 340 is further rotated, cam 340 presses guide protrusion 312 via contact portion 352, so that arm body 311 rotates from the first position to the second position against the biasing force of first spring 320. In other words, cam 340 deforms first spring 320 via cam follower 350 and arm body 311.

[0094] As a result, when the arm body 311 is in the second position, the second fixing member 82 is disposed at a position farther away from the roller 120 than when the arm body 311 is in the first position. By changing the position of the second fixing member 82 relative to the roller 120 in this way, when the arm body 311 is in the second position, the width of the nip portion NP becomes smaller than when the arm body 311 is in the first position, and the nip pressure becomes a third nip pressure that is smaller than the second nip pressure. In other words, the position of the arm 310 is changed by the cam 340, so that the nip pressure and the nip width change. In detail, when the arm 310 is in the second position, the belt 130 is sandwiched only between the upstream pad P1 and the roller 120, and the belt 130 is not sandwiched between the downstream pad P2 and the roller 120. As a result, when the arm 310 is in the second position, the upstream nip pressure and the upstream nip width become smaller, and the downstream nip pressure disappears.

[0095] In this embodiment, when the nip pressure is the third nip pressure, the upstream pad P1 pinches the belt 130 between itself and the roller 120, but the present invention is not limited to this. For example, when the nip pressure is the third nip pressure, the upstream pad P1 does not need to pinch the belt 130 between itself and the roller 120. In this case, the third nip pressure is zero.

[0096] 6, the second fixing member 82 further includes side guides SG that guide the ends of the belt 130. The side guides SG are provided at one end and the other end of the belt 130. The side guides SG are supported by a holder 140 so as to be movable in the width direction, more specifically, so as to be swingable about an axis along a predetermined direction.

[0097] Specifically, the holder 140 has an upstream convex portion 144 and a downstream convex portion 145. The upstream convex portion 144 and the downstream convex portion 145 are provided at one end and the other end of the holder main body 141 in the width direction, respectively. The upstream convex portion 144 protrudes upstream from the upstream side surface of the holder main body 141 in the movement direction. The downstream convex portion 145 protrudes downstream from the downstream side surface of the holder main body 141 in the movement direction.

[0098] The side guide SG has an upstream recess C1 into which the upstream protrusion 144 fits, and a downstream recess C2 into which the downstream protrusion 145 fits. This allows the side guide SG to be supported by the holder 140 so as to be able to swing.

[0099] The buffer member BF is disposed on the opposite side of the side guide SG from the belt 130 in the width direction. The Young's modulus of the buffer member BF is equal to or greater than that of the side guide SG. The buffer member BF has the aforementioned fitting portion BF1 and a pair of legs BF2, and further has an extension portion BF3 extending from the fitting portion BF1 toward the upstream side in the moving direction, and a protrusion BF4 protruding from the extension portion BF3 toward the side guide SG.

[0100] The pair of legs BF2 sandwich the base portion 211 of the first stay 210 via a part of the holder 140. In other words, a part of the holder 140 is disposed between the legs BF2 and the base portion 211. In this manner, the cushioning member BF is attached to the holder 140 by sandwiching a part of the holder 140 and the base portion 211 between the pair of legs BF2.

[0101] The protrusion BF4 contacts the side guide SG in the width direction and supports the side guide SG so that it can swing. More specifically, the protrusion BF4 contacts the outer surface F11 of the side guide SG, which is the surface opposite to the belt 130, and serves as a fulcrum for the swinging of the side guide SG. As shown in FIG. 7(c), the contact surface F21 of the protrusion BF4 with the side guide SG is a curved surface that is convex toward the side guide SG. More specifically, the contact surface F21 is an arcuate shape that is convex toward the side guide SG in a cross section perpendicular to the predetermined direction, and is also an arcuate shape that is convex toward the side guide SG in a cross section perpendicular to the moving direction.

[0102] As shown in FIGS. 9(a) and 9(b), the contact point TP of the protrusion BF4 with the side guide SG is located inside the track of the belt 130 when viewed in the width direction, and is located upstream of the first stay 210 in the movement direction.

[0103] 7(a) and (b), the side guide SG has a plate-shaped portion SG1 having the outer surface F11 described above, an arc-shaped rib SG2, an upstream engagement portion SG3 having the upstream recess C1 described above, and a downstream engagement portion SG4 having the downstream recess C2 described above. The plate-shaped portion SG1 has a second guide surface F12 that guides the end surface of the belt 130. The second guide surface F12 is a surface that is perpendicular to the width direction together with the outer surface F11, and is located on the opposite side to the outer surface F11.

[0104] The rib SG2 has a first guide surface F13 that guides the inner circumferential surface 131 of the belt 130. The first guide surface F13 is the outer circumferential surface of the arc-shaped rib SG2. A reinforcing rib SG5 is provided on the inner circumferential surface of the rib SG2, and extends in the width direction from a portion of the plate-shaped portion SG1 that contacts the protruding portion BF4 of the buffer member BF.

[0105] 9(b), the rib SG2 extends from the upstream to the downstream of the nip portion NP in the moving direction. The rib SG2 is located on the opposite side of the nip forming member N across the first stay 210. In the rotation direction of the belt 130, the above-mentioned upstream guide G1 is disposed downstream of the rib SG2, and the above-mentioned downstream guide G2 is disposed upstream of the rib SG2.

[0106] 8(a) and (c), the rib SG2 has an upstream end face FU located at the upstream end in the moving direction, and a downstream end face FD located at the downstream end in the moving direction. The upstream end face FU has an orthogonal end face FU1 perpendicular to the second guide surface F12, and an inclined surface FU2 inclined with respect to the second guide surface F12. The orthogonal end face FU1 extends in the width direction from the second guide surface F12. The inclined surface FU2 extends from the end of the orthogonal end face FU1 opposite to the second guide surface F12 toward the upstream of the rotation direction of the belt 130 and in a direction away from the second guide surface F12.

[0107] As shown in Fig. 8(b) and (c), the downstream end face FD has an orthogonal end face FD1 perpendicular to the second guide face F12 and an inclined face FD2 inclined with respect to the second guide face F12. The orthogonal end face FD1 extends along the width direction from the second guide face F12. The inclined face FD2 extends from the end of the orthogonal end face FD1 opposite to the second guide face F12 toward the downstream of the rotation direction of the belt 130 and in a direction away from the second guide face F12. As shown in Fig. 8(a) and (b), each of the inclined faces FU2 and FD2 is located at a position away from the second guide face F12 in the width direction.

[0108] As shown in FIG. 6 and FIG. 7(a) and (b), the upstream engagement portion SG3 and the downstream engagement portion SG4 are formed in a U-shape that opens toward the holder 140. The upstream engagement portion SG3 and the downstream engagement portion SG4 are integrally formed with the plate-shaped portion SG1 so as to protrude from the outer surface F11 of the plate-shaped portion SG1 to the opposite side of the second guide surface F12, and to protrude from the second guide surface F12 of the plate-shaped portion SG1 to the opposite side of the outer surface F11. As a result, the upstream recess C1 and the downstream recess C2 extend from the outer surface F11 to the opposite side of the second guide surface F12, and to the opposite side of the outer surface F11 to the second guide surface F12. As shown in FIG. 7(a), the portion of the downstream engagement portion SG4 protruding from the second guide surface F12 has a shape in which the bottom of the U-shape is cut out, but this portion may also be formed in a U-shape, similar to the upstream engagement portion SG3.

[0109] The widthwise dimensions of the upstream engagement portion SG3 and the downstream engagement portion SG4 need to be a predetermined dimension so that the side guide SG does not come off the upstream convex portion 144 and the downstream convex portion 145 of the holder 140 when the side guide SG swings, and the side guide SG does not rotate about the axis center along the moving direction. Here, if the upstream engagement portion SG3 and the downstream engagement portion SG4, which require such a predetermined dimension, are provided only on the second guide surface F12 side without protruding from the outer surface F11, the protruding amount of the upstream engagement portion SG3 and the downstream engagement portion SG4 from the second guide surface F12 becomes large. In contrast, in this embodiment, since the upstream engagement portion SG3 and the downstream engagement portion SG4 are protruding from the outer surface F11, the protruding amount of the upstream engagement portion SG3 and the downstream engagement portion SG4 from the second guide surface F12 can be reduced.

[0110] 9(a) and (b), the upstream engagement portion SG3 overlaps with the upstream guide G1 when projected in the width direction. Also, the downstream engagement portion SG4 overlaps with the downstream guide G2 when projected in the width direction. As described above, in this embodiment, the upstream engagement portion SG3 and the downstream engagement portion SG4 have small protrusions from the second guide surface F12, so that the width dimensions of the upstream guide G1 and the downstream guide G2 can be made large, and the upstream guide G1 and the downstream guide G2 can guide the belt 130 well.

[0111] 10a, 10b, and 11, the length in the width direction of the elastic layer 122 of the roller 120 is shorter than the length in the width direction of the belt 130. And, the entire elastic layer 122 of the roller 120 in the width direction contacts the belt 130. In other words, the belt 130 has an area that does not contact the elastic layer 122 of the roller 120 at each end in the width direction.

[0112] The width of the sliding sheet 150 is shorter than the width of the belt 130. The entire sliding sheet 150 is disposed within the range of the belt 130. The width of the sliding sheet 150 is longer than the width of the upstream pad P1 and the downstream pad P2. The width of the sliding sheet 150 is longer than the width of the elastic layer 122 of the roller 120. The width of the elastic layer 122 of the roller 120 is longer than the width of the upstream pad P1 and the downstream pad P2.

[0113] When viewed from a predetermined direction, the rib SG2 overlaps with the upstream pad P1 and the downstream pad P2. One end face of the belt 130 in the width direction is located closer to the second guide surface F12 than the tip SG21 of the rib SG2. When viewed from a predetermined direction, the belt 130 is located so as to overlap with the upstream engagement portion SG3 of the side guide SG.

[0114] The width of the holder 140 is longer than the width of the upstream pad P1 and the downstream pad P2. Also, the width of the holder 140 is longer than the width of the sliding sheet 150.

[0115] Next, the effects of the fixing device 8 according to this embodiment will be described.

[0116] 6, when the fixing device 8 is in operation, if the belt 130 moves in the width direction, the side guide SG swings around the protruding portion BF4 of the buffer member BF as a fulcrum so as to follow the movement. This makes it possible to prevent the end of the belt 130 from strongly hitting the side guide SG and becoming worn.

[0117] When the protruding portion BF4 wears out due to long-term use of the fixing device 8, a repair person removes the buffer member BF on the outer side of the side guide SG from the holder 140 and replaces it with a new buffer member BF. At this time, since there is no need to remove the side guide SG from the belt 130, the grease is removed together with the side guide SG, and this saves the trouble of replenishing grease to prevent changes in the sliding properties of the inner circumferential surface 131 of the belt 130.

[0118] As described above, the following effects can be obtained in this embodiment.

[0119] When the protrusion BF4, which serves as the fulcrum for the swinging of the side guide SG, becomes worn, it is not necessary to replace the side guide SG, since only the buffer member BF needs to be replaced without removing the side guide SG from the belt 130. Therefore, problems that arise when replacing the side guide SG, specifically, changes in the sliding properties of the inner peripheral surface 131 of the belt 130, can be suppressed.

[0120] By positioning the contact point TP of the convex portion BF4 with the side guide SG inside the orbit of the belt 130 when viewed from the width direction and upstream of the first stay 210 in the movement direction, the contact point TP can be positioned near the center of the nip portion NP in the movement direction, so that the side guide SG can be oscillated in a balanced manner.

[0121] By setting the Young's modulus of the buffer member BF to be equal to or greater than the Young's modulus of the side guide SG, the side guide SG becomes less susceptible to wear than the buffer member BF, making replacement of the side guide SG less necessary.

[0122] Since the buffer member BF is conductive, the first stay 210 can be grounded via the buffer member BF.

[0123] By protruding the upstream engagement portion SG3 and the downstream engagement portion SG4 toward the opposite side of the second guide surface F12 from the outer surface F11, the upstream engagement portion SG3 and the downstream engagement portion SG4 can be prevented from interfering with the upstream guide G1 and the downstream guide G2, while the upstream recess C1 and the downstream recess C2 can be lengthened to prevent the side guide SG from rotating around an axis along the movement direction.

[0124] Since the upstream end face FU and downstream end face FD of the rib SG2 of the side guide SG have inclined faces FU2, FD2, when the side guide SG is inserted into the belt 130 during assembly of the fixing device 8, it is possible to prevent the rib SG2 from interfering with a component within the belt 130, such as the sliding sheet 150, making it difficult to insert the side guide SG.

[0125] By positioning the inclined surfaces FU2, FD2 at a position away from the second guide surface F12, the size of the first guide surface F13 can be made larger compared to, for example, a configuration in which one end of the inclined surface is located on the second guide surface, and buckling of the belt 130 caused by the first guide surface F13 being smaller can be suppressed.

[0126] Since belt 130 has an area at each end in the width direction that does not come into contact with elastic layer 122 of roller 120, when grease leaks from the end of belt 130, the grease can be prevented from adhering to elastic layer 122 of roller 120.

[0127] In the width direction, the entire sliding sheet 150 is positioned within the range of the belt 130, so that the grease is prevented from leaking along the sliding sheet 150 to the outside of the belt, and the amount of grease leaking from the ends of the belt can be reduced.

[0128] When viewed from a specific direction, the rib SG2 overlaps with the upstream pad P1 and the downstream pad P2. Therefore, compared to a case in which the rib SG2 does not overlap with the upstream pad P1 and the downstream pad P2, the widthwise size of the fixing device can be reduced while the widthwise length of the rib SG2 that guides the belt 130 can be increased, thereby suppressing buckling of the belt 130.

[0129] The present invention is not limited to the above-described embodiment, but can be used in various forms as exemplified below.

[0130] In the above embodiment, inclined surfaces FU2, FD2 are provided on both end faces (FU, FD) of the rib SG2 in the movement direction, but the present invention is not limited to this, and an inclined surface may be provided on only one of the end faces in the movement direction of the rib.

[0131] In the embodiment, the pressure change mechanism 300 is provided with the first spring 320 and the second spring 330, but the present invention is not limited to this, and the second spring 330 may be omitted. In this case, the cam follower 350 is not necessary either, and it is sufficient that the cam 340 is configured to directly press the arm body 311.

[0132] The image forming apparatus is not limited to a laser printer, but may be a printer, copier, multifunction machine, etc. that uses LEDs for exposure.

[0133] The first spring and the second spring are not limited to the coil spring described above, and may be, for example, a torsion spring, a leaf spring, or the like.

[0134] In the above embodiment, the fixing device 8 using the heater 110 is exemplified, but the present invention is not limited to this, and a fixing device without a heater may be used. The fixing device may be, for example, a device that fixes a developer image to a sheet by applying light to a nip portion.

[0135] In the above embodiment, a halogen lamp is used as the heater, but the heater may be, for example, a carbon heater.

[0136] In the above embodiment, the upstream pad P1 and the downstream pad P2 are made of rubber, but the present invention is not limited to this, and the pads may be made of a hard material such as resin or metal that does not elastically deform even when pressure is applied.

[0137] In the above embodiment, a cylindrical roller incorporating the heater 110 is exemplified as the first fixing member, but the present invention is not limited thereto. The first fixing member may be, for example, a pressure roller having a shaft and a rubber layer formed around the shaft, or an endless belt whose inner circumferential surface is heated by a heater. Alternatively, an external heating method in which a heater is disposed outside the first fixing member and the outer circumferential surface of the first fixing member is heated, or an induction heating method may be used. Alternatively, a heater may be provided on the second fixing member to indirectly heat the first fixing member that is in contact with the outer circumferential surface of the second fixing member. Alternatively, each of the first fixing member and the second fixing member may incorporate a heater. When the first fixing member is a pressure roller, the nip forming member may be a nip plate that sandwiches the belt between the pressure roller and the pressure roller, a flat heater, or the like.

[0138] The elements described in the above-mentioned embodiment and modified examples may be implemented in any combination. [Explanation of symbols]

[0139] 8 Fixing device 81 First fixing member 82 Second fixing member 120 Lola 130 Belt 131 Inner surface 210 1st Stay 300A biasing mechanism 310 Arm 320 First Spring BF Cushioning material BF4 convex part F12 Second guide surface F13 First guide surface N Nip forming member NP Nip SG Side Guide

Claims

1. a first fixing member having a roller; a second fixing member facing the first fixing member in a predetermined direction and forming a nip portion between the second fixing member and the first fixing member; a biasing mechanism that biases the second fixing member toward the first fixing member, The biasing mechanism includes: an arm supporting the second fixing member; a spring that biases the arm toward the first fixing member, The second fixing member is Belt and a nip forming member that sandwiches the belt between the first fixing member and the nip forming member; a side guide having a first guide surface that guides an inner peripheral surface of the belt and a second guide surface that guides an end surface of the belt; A stay supporting the nip forming member; a buffer member disposed on an opposite side of the side guide from the belt, at least a portion of which is sandwiched between the stay and the arm, The buffer member is A protrusion that comes into contact with the side guide and supports the side guide so that the side guide can swing, The fixing device, wherein the protrusion serves as a fulcrum for swinging the first guide surface and the second guide surface about an axis extending in the predetermined direction.

2. The fixing device according to claim 1 , wherein a contact surface of the protruding portion with the side guide is a curved surface that is convex toward the side guide.

3. a support member for supporting the nip forming member, the support member being supported by the stay; The stay is a contact surface located at one end in the predetermined direction and in contact with the support member; a load input portion located at the other end in the predetermined direction and in contact with the buffer member, the nip portion has a downstream side in a moving direction of the belt, 3. The fixing device according to claim 1, wherein the protrusion is located inside a path of the belt as viewed in a width direction of the belt and upstream of the load input portion in the moving direction.

4. 4. The fixing device according to claim 1, wherein the Young's modulus of the buffer member is equal to or greater than the Young's modulus of the side guide.

5. 5. The fixing device according to claim 1, wherein the buffer member is made of a resin.

6. 6. The fixing device according to claim 1, wherein the buffer member is conductive.

7. a first fixing member having a roller; a second fixing member that forms a nip portion between the first fixing member and a second fixing member; a biasing mechanism that biases the second fixing member toward the first fixing member, The biasing mechanism includes: an arm supporting the second fixing member; a spring that biases the arm toward the first fixing member, The second fixing member is Belt and a nip forming member that sandwiches the belt between the first fixing member and the nip forming member; a side guide having a first guide surface that guides an inner peripheral surface of the belt and a second guide surface that guides an end surface of the belt; A stay supporting the nip forming member; a buffer member disposed on an opposite side of the side guide from the belt, at least a portion of which is sandwiched between the stay and the arm; a support member that supports the nip forming member and is supported by the stay, The buffer member is A protrusion that comes into contact with the side guide and supports the side guide so that the side guide can swing, The support member is an upstream convex portion protruding toward an upstream side in a moving direction of the belt in the nip portion; a downstream protrusion protruding toward a downstream side of the nip portion in the moving direction of the belt, The side guide is an outer surface that is a surface opposite to the second guide surface; an upstream engagement portion having an upstream recess into which the upstream protrusion fits; a downstream engagement portion having a downstream recess into which the downstream protrusion fits, The upstream engagement portion and the downstream engagement portion are disposed on an opposite side to the second guide surface with respect to the outer surface. A fixing device characterized in that the fixing device protrudes toward the fixing member.

8. a first fixing member having a roller; a second fixing member that forms a nip portion between the first fixing member and a second fixing member; a biasing mechanism that biases the second fixing member toward the first fixing member, The biasing mechanism includes: an arm supporting the second fixing member; a spring that biases the arm toward the first fixing member, The second fixing member is Belt and a nip forming member that sandwiches the belt between the first fixing member and the nip forming member; a side guide having a first guide surface that guides an inner peripheral surface of the belt and a second guide surface that guides an end surface of the belt; A stay supporting the nip forming member; a buffer member disposed on an opposite side of the side guide from the belt, at least a portion of which is sandwiched between the stay and the arm, The buffer member is A protrusion that comes into contact with the side guide and supports the side guide so that the side guide can swing, The side guide is a circular arc-shaped rib having the first guide surface, the rib extending from the upstream side to the downstream side of the nip portion in a moving direction of the belt in the nip portion; the rib has two end faces in the moving direction, and at least one end face has an inclined surface inclined with respect to the second guide surface.

9. The fixing device according to claim 8 , wherein the inclined surface is located at a position away from the second guide surface.

10. The second fixing member is an upstream pad that sandwiches the belt between the upstream pad and the first fixing member; a downstream pad disposed downstream of the upstream pad in a sheet conveying direction and sandwiching the belt between the upstream pad and the first fixing member; The fixing device according to claim 1 , further comprising a support member supporting the upstream pad and the downstream pad.

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