Fixing device

Abstract

To make it possible to efficiently correct a curl in a sheet even in a fixing device in which a peeling member is not arranged.SOLUTION: A fixing device 8 comprises: a roller 81; a fixing member 180; a pair of conveying rollers 85; and a sheet guide 86. The fixing member 180 sandwiches a sheet S with the roller 81 to form a first nip part NP1. The pair of conveying rollers 85 sandwich and convey the sheet S at a second nip part NP2. The sheet guide 86 is located between the first nip part NP1 and the second nip part NP2, and has a first guide 86A that guides a surface of the sheet S facing the roller 81. On a cross-section orthogonal to the axis of rotation 81X of the roller 81, the first guide 86A intersects with a tangent line L1 of the roller 81 at an exit P2 of the first nip part NP1. On a cross-section orthogonal to the axis of rotation 81X of the roller 81, an extension line L2 of the first guide 86A intersects with a line segment L3 connecting the exit P2 of the first nip part NP1 and an entrance P3 of the second nip part NP2 with each other.SELECTED DRAWING: Figure 5

Description

[Technical field]

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

[0002] 2. Description of the Related Art Conventionally, among fixing devices using a heat roller and a pressure belt, there is known one having a peeling member that comes into contact with the heat roller to peel off a sheet from the heat roller (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-109583 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, since the peeling member comes into contact with the heating roller, there is a risk of damaging the heating roller, but if the peeling member is not provided, the position where the sheet is peeled off from the pressure roller is far from the nip position, which causes a problem that the sheet curls more strongly.

[0005] Therefore, an object of the present invention is to suppress curling of a sheet even in a fixing device that does not have a peeling member. [Means for solving the problem]

[0006] In order to solve the above problems, the fixing device according to the present invention includes a roller, a fixing member, a heater, a pair of conveying rollers, and a sheet guide. The fixing member conveys a sheet by sandwiching it between the roller and the fixing member. The fixing member has an endless belt and a nip forming member that sandwiches the belt and the sheet between the roller and the fixing member to form a first nip portion. The heater heats the roller or the fixing member. The pair of conveying rollers are located downstream of the first nip portion in the sheet conveying direction, and convey the sheet by sandwiching it in the second nip portion. The sheet guide is located between the first nip portion and the second nip portion, and has a first guide that guides the surface of the sheet facing the roller. The first guide intersects with a tangent to the roller at the outlet of the first nip portion in a cross section perpendicular to the rotation axis of the roller. An extension line of the first guide intersects with a line segment connecting the exit of the first nip portion and the entrance of the second nip portion in a cross section perpendicular to the rotation axis of the roller.

[0007] According to this configuration, in a cross section perpendicular to the rotation axis of the roller, the first guide intersects with a tangent to the roller at the exit of the first nip, so that the sheet coming out of the first nip comes into contact with the first guide and is peeled off from the roller. Then, in a cross section perpendicular to the rotation axis of the roller, an extension line of the first guide intersects with a line segment connecting the exit of the first nip and the entrance of the second nip, so that the sheet is guided by the first guide in a curled manner and conveyed to the second nip. This makes it possible to straighten the curl of the sheet coming out of the first nip.

[0008] In addition, in the above-mentioned configuration, the sheet guide may further have a second guide located farther from the first nip portion than the first guide, guiding the roller side of the sheet, and the extension line of the second guide may be configured not to intersect with the line segment in a cross section perpendicular to the rotation axis of the roller.

[0009] According to this configuration, the sheet can be stably guided to the second nip portion by the second guide.

[0010] In addition, in the above-mentioned configuration, in a cross section perpendicular to the rotation axis of the roller, the angle between a straight line connecting the rotation axis of the roller and the outlet of the first nip portion and a straight line connecting the rotation axis of the roller and the upstream end of the first guide may be greater than 45°.

[0011] According to this configuration, the upstream end of the first guide is sufficiently far from the exit of the first nip portion, so that the leading edge of the sheet is likely to hit the first guide while slightly spaced from the roller, and the sheet is likely to peel off from the roller.

[0012] In the above-mentioned configuration, the sheet conveying speed by the pair of conveying rollers may be faster than the sheet conveying speed by the roller.

[0013] According to this configuration, slack in the sheet between the first nip portion and the second nip portion can be suppressed, and tension can be applied to the sheet to correct curls.

[0014] In the above-described configuration, the conveying force of the second nip portion may be smaller than the conveying force of the first nip portion.

[0015] According to this configuration, in a state in which the sheet is sandwiched between both the first nip portion and the second nip portion, it is possible to prevent the sheet from being pulled by the second nip portion more than necessary.

[0016] Furthermore, in the above-described configuration, the roller may have an elastic layer on its surface, and the nip forming member may be a first elastic pad that forms a first nip portion with the elastic layer at the outlet of the first nip portion, the first elastic pad having a larger elastic modulus than the elastic layer, and when the roller and the first elastic pad are pressed against each other, the deformation amount of the elastic layer may be smaller than the deformation amount of the first elastic pad.

[0017] In addition, in the above-mentioned configuration, the nip forming member may be a second elastic pad located upstream of the first elastic pad in the sheet transport direction, forming the first nip portion, and having a smaller elastic modulus than the elastic layer.

[0018] In the above-described configuration, the first elastic pad and the second elastic pad may be arranged with a gap therebetween in the sheet transport direction.

[0019] In the above-mentioned configuration, the heater may be disposed inside the roller. Effect of the Invention

[0020] According to the present invention, it is possible to suppress curling of a sheet even in a fixing device that does not include a peeling member. [Brief description of the drawings]

[0021] [Figure 1] 1 is a diagram showing an image forming apparatus including a fixing device according to an embodiment of the present invention; [Diagram 2] FIG. [Diagram 3] FIG. 2 is an enlarged cross-sectional view of the vicinity of a heating roller and a fixing member. [Figure 4] 4A and 4B are diagrams illustrating a nip pressure adjusting mechanism. [Diagram 5] FIG. 4 is an enlarged cross-sectional view of the vicinity of a nip portion. [Figure 6] 13A and 13B are diagrams showing a sheet guide in another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings as appropriate. 1, the image forming apparatus 1 is configured to be capable of forming images on both sides of a sheet S, and includes a main body housing 2, and a supply section 3, an image forming section 4, a fixing device 8, and a conveying section 9 that are arranged inside the main body housing 2. In this embodiment, the image forming apparatus 1 is a color printer.

[0023] The main body housing 2 has a discharge tray 21 on the top surface.

[0024] The supply unit 3 is provided in the lower part inside the main body housing 2, and includes a supply tray 31 that stores sheets S, and a supply mechanism 32 that supplies the sheets S in the supply tray 31 to the image forming unit 4.

[0025] The image forming section 4 has a function of transferring a toner image onto a sheet S to form an image, and includes an exposure device 5, four process cartridges 6, and a transfer unit .

[0026] The exposure device 5 is disposed at the upper part of the main body housing 2, and includes a light source, a polygon mirror, and the like (not shown). The exposure device 5 exposes the surface of the photoconductor drum 61 by scanning a light beam based on image data, indicated by a dashed dotted line, over the surface of the photoconductor drum 61 at high speed.

[0027] Each process cartridge 6 includes a photosensitive drum 61, a charger 62, and a developing roller 63. The four process cartridges 6 contain toner of each of the colors yellow, magenta, cyan, and black.

[0028] The transfer unit 7 includes a drive roller 71 as an example of a belt roller, a driven roller 72, a conveyor belt 73, four transfer rollers 74, and a belt frame 75. The conveyor belt 73 is an endless belt. The conveyor belt 73 conveys the sheet S on which the toner image is formed to a guide surface 151 of a chute 150 of the fixing device 8 (see FIG. 2). The belt frame 75 rotatably supports the drive roller 71 and the driven roller 72. A conveyor belt 73 is wound around the drive roller 71 and the driven roller 72. The upper surface of the conveyor belt 73 is a sheet conveying surface 73A that conveys the sheet S. A transfer roller 74 is disposed on the inner side of the conveyor belt 73 so as to sandwich the conveyor belt 73 between itself and the corresponding photosensitive drum 61.

[0029] The charger 62 charges the surface of the photoconductor drum 61. The exposure device 5 exposes the charged surface of the photoconductor drum 61 to light, and forms an electrostatic latent image on the surface of the photoconductor drum 61 based on image data.

[0030] The developing roller 63 supplies toner to the electrostatic latent image formed on the photosensitive drum 61. As a result, a toner image is formed on the photosensitive drum 61. When the sheet S is transported between the photosensitive drum 61 and the transfer roller 74 by the transport belt 73, the toner image on the photosensitive drum 61 is transferred to the sheet S.

[0031] The fixing device 8 is a device that thermally fixes the toner image onto the sheet S. The fixing device 8 will be described in detail later.

[0032] The conveying section 9 is configured to convey the sheet S discharged from the fixing device 8 to the outside of the main body housing 2 or again toward the image forming section 4. The conveying section 9 includes a first conveying path 91, a second conveying path 92, a re-conveying path 93, a first conveying roller 94, a second conveying roller 95, a first switchback roller SR1, a second switchback roller SR2, a plurality of re-conveying rollers 96, and a rotatable first flapper FL1 and a second flapper FL2.

[0033] The first transport path 91 is a path that guides the sheet S discharged from the fixing device 8 toward the discharge tray 21. The second transport path 92 is a path that guides the sheet S discharged from the fixing device 8 toward the discharge tray 21 via a route different from the first transport path 91. The re-transport path 93 is a path that guides the sheet S drawn into the main body housing 2 by a first switchback roller SR1 (to be described later) or the like, to the supply mechanism 32 upstream of the image forming unit 4. The re-transport roller 96 is a roller that transports the sheet S in the re-transport path 93 toward the supply mechanism 32, and is provided in the re-transport path 93.

[0034] The first conveying roller 94 is provided in the fixing device 8. The first conveying roller 94 conveys the sheet S on which the toner image has been thermally fixed, toward the second flapper FL2.

[0035] The second conveying roller 95, the first switchback roller SR1, and the second switchback roller SR2 are rollers that can rotate forward and backward. The second conveying roller 95, the first switchback roller SR1, and the second switchback roller SR2 convey the sheet S to the outside of the main body housing 2, specifically, toward the discharge tray 21, when rotating forward, and pull the sheet S into the main body housing 2 when rotating reversely.

[0036] The second conveying roller 95 and the first switchback roller SR1 are provided on the first conveying path 91. The first switchback roller SR1 is disposed closer to the discharge tray 21 than the second conveying roller 95. The second switchback roller SR2 is provided on the second conveying path 92.

[0037] In the conveying section 9, the positions of the first flapper FL1 and the second flapper FL2 can be appropriately switched to convey the sheet S from the fixing device 8 toward the first conveying path 91 or the second conveying path 92, or to convey the sheet S from the first conveying path 91 or the second conveying path 92 to the re-conveying path 93.

[0038] As shown in FIG. 2, the fixing device 8 includes two heaters H, a roller 81, a fixing member 180, a chute 150, a fixing frame 88, a nip pressure adjustment mechanism 200 (see FIG. 4), a pair of conveying rollers 85, a sheet guide 86, and the above-mentioned first flapper FL1.

[0039] As shown in FIG. 3, the roller 81 has a base tube 81A and an elastic layer 81B. The base tube 81A is a metal pipe. The roller 81 is supported by a fixing frame 88 via a bearing (not shown) so as to be rotatable about a rotation axis 81X. The roller 81 is driven to rotate by a motor (not shown) provided in the image forming apparatus 1. The elastic layer 81B is provided on the outer periphery of the blank tube 81A. In other words, the roller 81 has the elastic layer 81B on the surface. The elastic layer 81B has elasticity.

[0040] The two heaters H are heaters for heating the roller 81, and are disposed inside the base tube 81A of the roller 81. In other words, the heaters H are disposed inside the roller 81.

[0041] Fixing member 180 is a member that forms a first nip portion NP1 between itself and roller 81, and conveys sheet S by nipping it between roller 81. Fixing member 180 includes an endless belt 181, two nip forming members 182 and 183, a support member 184, an upstream belt guide 185, a downstream belt guide 186, a stay 187, a sliding sheet 188, and a side guide 189.

[0042] The belt 181 is an endless belt made of heat-resistant resin etc. The belt 181 has a width larger than the width of the maximum sheet S transported by the image forming apparatus 1. The belt 181 transports the sheet S by nipping it between itself and the roller 81.

[0043] The nip forming members 182 and 183 are members that form the first nip portion NP1 by sandwiching the belt 181, the sliding sheet 188, and the sheet S between themselves and the roller 81. The entrance of the first nip portion NP1 is designated as P1, and the exit of the first nip portion NP1 is designated as P2.

[0044] The nip forming member 183 has a support plate 183A and a first elastic pad 183B. The first elastic pad 183B is fixed to the support plate 183A. The nip forming member 182 has a support plate 182A and a second elastic pad 182B. The second elastic pad 182B is fixed to the support plate 182A.

[0045] The first elastic pad 183B and the second elastic pad 182B are disposed with a gap therebetween in the conveying direction of the sheet S. Specifically, the first elastic pad 183B is located downstream of the second elastic pad 182B in the conveying direction of the sheet S. The second elastic pad 182B is located upstream of the first elastic pad 183B in the conveying direction of the sheet S. The first elastic pad 183B forms the first nip portion NP1 with the elastic layer 81B at the exit P2 of the first nip portion NP1. The second elastic pad 182B forms the first nip portion NP1 with the elastic layer 81B at the entrance P1 of the first nip portion NP1.

[0046] The first elastic pad 183B has elasticity and is elastically deformable. In this embodiment, the first elastic pad 183B is made of a material having a higher elastic coefficient than the elastic layer 81B. However, since the first elastic pad 183B is thicker than the elastic layer 81B, when the roller 81 and the first elastic pad 183B are pressed against each other, the deformation amount of the elastic layer 81B is smaller than the deformation amount of the first elastic pad 183B.

[0047] Specifically, the thickness of the first elastic pad 183B is 8 to 12 times the thickness of the elastic layer 81 B. When the roller 81 and the first elastic pad 183B are pressed against each other, the deformation amount of the elastic layer 81B is 0.45 to 0.55 times the deformation amount of the first elastic pad 183B.

[0048] The second elastic pad 182B has elasticity and is elastically deformable. The second elastic pad 182B has a smaller elastic coefficient than the first elastic pad 183B. In this embodiment, the second elastic pad 182B has a smaller elastic coefficient than the elastic layer 81B. The second elastic pad 182B is thicker than the elastic layer 81B. When the roller 81 and the nip forming member 182 are pressed against each other, the deformation amount of the elastic layer 81B is smaller than the deformation amount of the second elastic pad 182B. When the roller 81 and the nip forming members 182, 183 are pressed against each other, the deformation amount of the second elastic pad 182B is larger than the deformation amount of the first elastic pad 183B.

[0049] The support member 184 is a member that supports the nip forming members 182 and 183.

[0050] The upstream belt guide 185 is a member that guides the movement of the belt 181 upstream of the first nip portion NP1 in the conveying direction of the sheet S. The upstream belt guide 185 has a curved surface that allows the endless belt 181 to rotate smoothly. In the following description, the conveying direction of the sheet S will be simply referred to as the “conveying direction.” The conveying direction is the traveling direction of the sheet S along the conveying path of the sheet S shown in FIG.

[0051] The downstream belt guide 186 is a member that guides the movement of the belt 181 downstream of the first nip portion NP1 in the conveying direction of the sheet S. The upstream belt guide 185 has a curved surface that allows the endless belt 181 to rotate smoothly.

[0052] The stay 187 is a member that supports the support member 184, the upstream belt guide 185, the downstream belt guide 186, and the side guide 189. The stay 187 is formed by pressing a metal plate.

[0053] The sliding sheet 188 is a sheet-like member disposed between the upstream belt guide 185, the nip forming members 182 and 183, the downstream belt guide 186, and the belt 181. The sliding sheet 188 is made of a material with excellent sliding properties, and has an uneven shape on the surface facing the belt 181 to make it easier to hold grease.

[0054] The side guides 189 are disposed at both ends of the belt 181 in the axial direction along which the rotation axis 81X of the roller 81 extends (hereinafter simply referred to as the "axial direction"). The side guides 189 have an inner circumferential guide 189A that is arc-shaped when viewed from the axial direction and that fits inside the belt 181, and a flange 189B that extends from the inner circumferential guide 189A in a direction perpendicular to the rotation axis 81X. The flange 189B restricts the belt 181 from moving in the axial direction.

[0055] 4, the nip pressure adjustment mechanism 200 includes a swing arm 210, a first spring 220, a second spring 230, a cam 240, and a cam follower 250. Although the nip pressure adjustment mechanism 200 disposed on one axial side of the fixing frame 88 is shown in Fig. 4, a nip pressure adjustment mechanism of a similar configuration is also provided on the other axial side of the fixing frame 88.

[0056] The swing arm 210 is disposed at both ends of the fixing frame 88 in the axial direction. One end 210A of the swing arm 210 is swingably supported by a shaft 88F provided on the fixing frame 88. One end of a first spring 220 is hooked to the other end 210B. The first spring 220 is a tension spring. The other end of the first spring 220 is hooked to a spring hook portion 88A provided on the fixing frame 88, and always biases the swing arm 210 in the counterclockwise direction in FIG. 5. The swing arm 210 supports the stay 187 of the fixing member 180 via several members, thereby swingably supporting the fixing member 180 with respect to the fixing frame 88.

[0057] The swing arm 210 has a guide protrusion 212 extending toward the cam 240. A cam follower 250 is slidably engaged with the guide protrusion 212. A second spring 230, which is a compression spring, is disposed between the cam follower 250 and a base portion of the swing arm 210 from which the guide protrusion 212 extends.

[0058] The cam 240 is disposed opposite the cam follower 250 and is rotated by a motor (not shown). When the cam 240 rotates, the cam follower 250 is pushed and the swing arm 210 swings, whereby the fixing member 180 moves relative to the roller 81, and the nip pressure between the roller 81 and the fixing member 180 is adjusted. Specifically, when the cam 240 rotates, the nip pressure can be adjusted between a strong nip state where the nip pressure is the greatest and suitable for fixing, for example, plain paper, a weak nip state where the nip pressure is greater and suitable for fixing thicker paper than the strong nip state, and a nip release state where the nip pressure is the smallest and suitable for removing a sheet S stuck in the fixing device 8.

[0059] As shown in FIG. 5, the pair of conveying rollers 85 is located downstream of the first nip portion NP1 in the conveying direction. The pair of conveying rollers 85 is a roller that conveys the sheet S that has been thermally fixed in the first nip portion NP1 toward the conveying section 9. The pair of conveying rollers 85 is arranged in a line in the axial direction. The pair of conveying rollers 85 is composed of a first roller 85A and a second roller 85B facing the first roller 85A. The first roller 85A forms a second nip portion NP2 with the second roller 85B. The entrance of the second nip portion NP2 is designated as P3, and the exit of the second nip portion NP2 is designated as P4.

[0060] The pair of conveying rollers 85 convey the sheet S by nipping it at the second nip portion NP2. The conveying speed of the sheet S by the pair of conveying rollers 85 is faster than the conveying speed of the sheet S by the rollers 81.

[0061] The surface of the first roller 85A is made of rubber and rotates by receiving a driving force from a motor (not shown). The surface of the second roller 85B is made of resin and rotates following the rotation of the first roller 85A. The conveying force of the second nip portion NP2 is smaller than the conveying force of the first nip portion NP1.

[0062] The sheet guide 86 is located between the first nip portion NP1 and the second nip portion NP2. The sheet guide 86 guides the roller 81 side of the sheet S and is not in contact with the roller 81. In this embodiment, the sheet guide 86 is located above the sheet S being conveyed.

[0063] Although not shown in the figure, the sheet guide 86 is made up of ribs extending in the conveying direction of the sheet S, and is arranged in a line in the axial direction. The sheet guide 86 has a first guide 86A and a second guide 86B. The first guide 86A and the second guide 86B are each made up of the edges of a plurality of ribs. In other words, the first guide 86A and the second guide 86B guide the roller 81 side of the sheet S with the edges of the plurality of ribs.

[0064] The first guide 86A is the guide closest to the roller 81, and guides the sheet S coming out of the first nip portion NP1. The first guide 86A extends straight from an upstream end T1 in the conveying direction of the first guide 86A. The first guide 86A intersects with a tangent L1 of the roller 81 at the exit P2 of the first nip portion NP1 in a cross section perpendicular to the rotation axis 81X of the roller 81.

[0065] Further, an extension line L2 of the first guide 86A intersects with a line segment L3 connecting the exit P2 of the first nip portion NP1 and the entrance P3 of the second nip portion NP2 in a cross section perpendicular to the rotation axis 81X of the roller 81. The extension line L2 is a straight line extending the first guide 86A downstream in the conveying direction of the sheet S.

[0066] In addition, in a cross section perpendicular to the rotational axis 81X of the roller 81, the angle θ1 between a straight line L4 connecting the rotational axis 81X of the roller 81 and the outlet P2 of the first nip portion NP1 and a straight line connecting the rotational axis 81X of the roller 81 and the upstream end T1 of the first guide 86A in the conveying direction is greater than 45°.

[0067] The second guide 86B is located downstream of the first guide 86A in the conveying direction, and guides the sheet S in a direction different from that of the first guide 86A. In other words, the second guide 86B is located farther away from the first nip portion NP1 than the first guide 86A. The second guide 86B extends linearly in a cross section perpendicular to the rotation axis 81X. The first guide 86A and the second guide 86B are connected by a rib having an arc-shaped edge. The angle of the second guide 86B with respect to the line segment L3 is smaller than the angle of the first guide 86A with respect to the line segment L3. In other words, the second guide 86B faces in a direction along the conveying path of the sheet S than the first guide 86A. In other words, the extension line L6 of the second guide 86B downstream in the conveying direction does not intersect with the line segment L3 connecting the exit P2 of the first nip portion NP1 and the entrance P3 of the second nip portion NP2 in a cross section perpendicular to the rotational axis 81X of the roller 81.

[0068] The effects of the fixing device 8 configured as above will be described below. After the toner image is transferred onto the sheet S, the sheet S is conveyed to the fixing device 8 and thermally fixed at the first nip portion NP1. In this embodiment, since there is no peeling member that contacts the roller 81, the sheet S is discharged from the exit P2 of the first nip portion NP1 while slightly wrapping around the roller 81. Then, the leading edge of the sheet S peels off from the roller 81 before reaching the first guide 86A, and the leading edge hits the first guide 86A. Then, the sheet S is guided by the first guide 86A to be conveyed toward the second nip portion NP2. Since the extension line of the first guide 86A intersects with the line segment L3 connecting the exit P2 of the first nip portion NP1 and the entrance P3 of the second nip portion NP2, the sheet S is conveyed to the second nip portion NP2 while being guided by the first guide 86A so as to be warped toward the fixing member 180 side. This makes it possible to correct the curl of the sheet S that has come out of the first nip portion NP1.

[0069] Moreover, the sheet guide 86 further includes a second guide 86B, and an extension line L6 of the second guide 86B does not intersect with a line segment L3 connecting the exit P2 of the first nip portion NP1 and the entrance P3 of the second nip portion NP2 in a cross section perpendicular to the rotation axis 81X of the roller 81. Therefore, the sheet S that has passed through the first guide 86A can be stably guided to the second nip portion NP2 by the second guide 86B.

[0070] In addition, in a cross section perpendicular to the rotation axis 81X of roller 81, an angle θ1 formed by a line L4 connecting the rotation axis 81X of roller 81 and the exit P2 of first nip portion NP1 and a line L5 connecting the rotation axis 81X of roller 81 and the upstream end T1 of first guide 86A is greater than 45°. Therefore, the distance between first guide 86A and the exit P2 of first nip portion NP1 becomes large, and the leading edge of sheet S is likely to hit first guide 86A in a state slightly separated from roller 81, and sheet S is likely to peel off from roller 81.

[0071] Furthermore, the conveying speed of the sheet S by the pair of conveying rollers 85 is faster than the conveying speed of the sheet S by the rollers 81. Therefore, the sheet S is prevented from becoming loose between the first nip portion NP1 and the second nip portion NP, and tension is applied to the sheet S to correct curls.

[0072] In addition, the conveying force of the second nip portion NP2 is smaller than the conveying force of the first nip portion NP1, so that when the sheet S is sandwiched between both the first nip portion NP1 and the second nip portion NP2, it is possible to prevent the second nip portion NP2 from pulling the sheet S more than necessary.

[0073] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and can be used in various forms as exemplified below.

[0074] In the embodiment, the sheet guide 86 has the first guide 86A and the second guide 86B, but is not limited to this, and may have only the first guide 86A as shown in Fig. 6(a). Also, the first guide 86A and the second guide 86B are not limited to being straight in a cross section perpendicular to the rotation axis 81X, but may extend in a curved shape as shown in Fig. 6(b). For example, the first guide 86C may be curved and recessed away from the conveying path of the sheet S, and the second guide 86D may be curved and protruding toward the conveying path.

[0075] In the embodiment, the roller 81 is heated by the heater H, but the present invention is not limited to this, and the belt 181 of the fixing member 180 may be heated by the heater H. Also, the nip forming members 182, 183 of the fixing member 180 are configured to have fixed elastic bodies, but may be rollers. Also, the nip forming members may be entirely configured from a single elastic pad.

[0076] In the above embodiment, two heaters H are provided, but the number of heaters may be one, or three or more.

[0077] In the above embodiment, the heater H is disposed inside the roller, but the heater H may be disposed outside the roller.

[0078] The elements described in the above-mentioned embodiment and modified examples may be implemented in any combination. [Explanation of symbols]

[0079] 8 Fixing device 9. Conveyor Section 81 Lola 81X Rotation axis 85 Transport roller 86 Seat guide 86A 1st Guide 86B 2nd Guide 180 Fixing member 181 Belt 182 Nip forming member 182B 2nd Elastic Pad 183 Nip forming member 183B First Elastic Pad H Heater L1 tangent L2 extension line L3 line segment L4 Straight line L5 straight line L6 extension line NP1 First nip section NP2 Second nip section

Claims

1. A roller having an elastic layer on its surface; a fixing member for conveying a sheet by nipping it between the fixing member and the roller, the fixing member including an endless belt and a nip forming member for nipping the belt and the sheet between the fixing member and the roller to form a first nip portion; a heater disposed inside the roller and configured to heat the roller; a pair of conveying rollers located downstream of the first nip portion in a sheet conveying direction and configured to sandwich and convey the sheet in a second nip portion; a sheet guide having a first guide located between the first nip portion and the second nip portion, the first guide guiding a surface of the sheet facing the roller and having a toner image thermally fixed thereon, The nip forming member is a first elastic pad that forms the first nip portion together with the elastic layer at an outlet of the first nip portion, the first elastic pad having an elastic modulus greater than that of the elastic layer; When the roller and the first elastic pad are pressed against each other, a deformation amount of the elastic layer is smaller than a deformation amount of the first elastic pad, the pair of conveying rollers includes a first roller located on the belt side of a sheet conveying path, and a second roller located on the roller side of the sheet conveying path, the first guide intersects with a tangent to the roller at an outlet of the first nip portion in a cross section perpendicular to a rotation axis of the roller, A fixing device characterized in that an extension line of the first guide intersects with a line segment connecting the exit of the first nip portion and the entrance of the second nip portion, and also intersects with the first roller, in a cross section perpendicular to the rotation axis of the roller.

2. the sheet guide further includes a second guide extending continuously from a downstream end of the first guide to the first guide and positioned farther away from the first nip portion than the first guide, the second guide guiding the roller side of the sheet; 2. The fixing device according to claim 1, wherein an extension line of the second guide does not intersect with the line segment in a cross section perpendicular to the rotation axis of the roller.

3. 3. The fixing device according to claim 1, wherein in a cross section perpendicular to the rotation axis of the roller, an angle between a straight line connecting the rotation axis of the roller and the outlet of the first nip portion and a straight line connecting the rotation axis of the roller and the upstream end of the first guide is greater than 45°.

4. a conveying speed of the sheet by the pair of conveying rollers is higher than a conveying speed of the sheet by the roller; The first roller has a surface made of rubber, 4. The fixing device according to claim 1, wherein the second roller has a surface made of resin and is rotated by the first roller.

5. 5. The fixing device according to claim 1, wherein a conveying force of the second nip portion is smaller than a conveying force of the first nip portion.

6. The nip forming member is A fixing device as described in any one of claims 1 to 5, characterized in that it has a second elastic pad located upstream of the first elastic pad in the sheet transport direction, forming the first nip portion, the second elastic pad having an elastic coefficient smaller than that of the elastic layer.

7. 7. The fixing device according to claim 6, wherein the first elastic pad and the second elastic pad are disposed at an interval in the conveying direction of the sheet.

Images