CN110967955B - Fixing device - Google Patents

Abstract

A fixing device, comprising: a heater; a rotating body heated by the heater; an endless belt; an upstream nip forming member that forms an upstream nip with the rotating body by sandwiching the endless belt; a first restriction member that is in contact with the upstream nip forming member and restricts movement of the upstream nip forming member in a movement direction of the endless belt at the upstream nip portion; a first urging member urging the upstream nip forming member in the moving direction toward the first restricting member so that the upstream nip forming member contacts the first restricting member; a downstream nip forming member which is disposed downstream in the moving direction with respect to the upstream nip forming member and forms a downstream nip with the rotating body by sandwiching the endless belt; a second restriction member that contacts the downstream nip forming member and restricts movement of the downstream nip forming member in the movement direction; and a second urging member urging the downstream nip forming member in the moving direction toward the second restricting member so that the downstream nip forming member contacts the second restricting member.

Description

Fixing device

Technical Field

The present invention relates to a fixing device having an endless belt.

Background

Conventionally, a belt-type fixing device is known in which an upstream pad and a downstream pad are disposed with a gap between them in order to prevent wrinkles from occurring in a recording medium such as an envelope. More specifically, in the inner space formed by the endless belt, an upstream pad in contact with the inner peripheral surface of the endless belt, a support plate supporting the upstream pad, and a holding portion supporting the support plate are provided.

The holding portion integrally has a downstream pad in contact with an inner peripheral surface of the endless belt. By fitting the support plate into the recess formed in the holding portion, the upstream pad is positioned relative to the downstream pad in the moving direction of the endless belt at the nip portion.

Disclosure of Invention

However, if there is a gap between the upstream pad and the downstream pad or between the upstream pad and the holding portion, there is a possibility that the fixing nip region may be changed due to a manufacturing error of the upstream pad itself or an installation error with the support plate, etc., which adversely affects the fixing property, the conveyance property of the recording medium, etc. In particular, since the contact and separation operation (nip state, unclamped state) of the heating roller and the endless belt is repeated, the position of each pad in the moving direction of the endless belt is changed, which adversely affects the fixability, the conveyance property of the recording medium, and the like.

In view of the above, an object of the present invention is to suppress a change in the position of each clamping portion due to a manufacturing error of each pad (clamping forming member), repeated clamping, unclamping, or the like.

In order to achieve the above object, the present invention provides a fixing device including: a heater; a rotating body heated by the heater; an endless belt; an upstream nip forming member that nips the endless belt between the upstream nip forming member and the rotating body to form an upstream nip; a first restriction member that contacts the upstream nip forming member for restricting movement of the upstream nip forming member in a movement direction of the endless belt at the upstream nip portion; a first urging member urging the upstream nip forming member in the moving direction toward the first restricting member so that the upstream nip forming member contacts the first restricting member; a downstream nip forming member disposed on a downstream side in the moving direction with respect to the upstream nip forming member, the downstream nip forming member and the rotating body sandwiching the endless belt therebetween to form a downstream nip portion; a second restriction member that contacts the downstream nip forming member for restricting movement of the downstream nip forming member in the movement direction; and a second urging member urging the downstream nip forming member in the moving direction toward the second restricting member so that the downstream nip forming member contacts the second restricting member.

According to the above configuration, since the respective pinching forming members are biased toward the respective restricting members so as to be brought into contact with the respective restricting members, even if the respective pinching forming members have a manufacturing error, repeatedly assume a pinching state, release a pinching state, or the like, the positions of the pinching portions can be stabilized.

Further, the first urging member and the second urging member are integrally formed.

According to the above structure, the number of components can be reduced, and the cost can be reduced.

Further, the first restriction member is disposed on an upstream side in the moving direction with respect to the upstream nip forming member, and the second restriction member is disposed on a downstream side in the moving direction with respect to the downstream nip forming member.

According to the above configuration, for example, a single compression coil spring or the like can be used as the first urging member and the second urging member, and the device can be simplified.

Further, the fixing device further includes a holding portion that supports the upstream nip forming member and the downstream nip forming member, the first urging member and the second urging member being constituted by a single plate spring including: a first arm portion in contact with the downstream nip forming member; a second arm portion in contact with the upstream nip forming member; and a base portion connecting the first arm portion and the second arm portion, the holding portion including: a base portion supporting the upstream nip forming member and the downstream nip forming member; and a protruding portion that is located between the upstream nip forming member and the downstream nip forming member in the moving direction, protrudes from the base portion of the holding portion in the width direction of the endless belt, and comes into contact with the base portion of the leaf spring to thereby restrict movement of the leaf spring.

According to the above configuration, the leaf springs as the first urging member and the second urging member can be restrained from being separated from the upstream sandwiching formation member and the downstream sandwiching formation member.

Further, the first restriction member is disposed on a downstream side in the moving direction with respect to the upstream nip forming member, and the second restriction member is disposed on an upstream side in the moving direction with respect to the downstream nip forming member.

According to the above configuration, for example, a single tension coil spring or the like can be used as the first urging member and the second urging member, and the device can be simplified.

Further, the first restriction member is disposed on a downstream side in the moving direction with respect to the upstream nip forming member, and the second restriction member is disposed on a downstream side in the moving direction with respect to the downstream nip forming member.

According to the above structure, the nip forming member can be restrained from moving against the force exerted by the spring member due to friction with the endless belt.

Further, the upstream nip forming member includes: a first pressurizing pad sandwiching the endless belt between the first pressurizing pad and the rotating body; and a first fixing member that is harder than the first pressing pad, the first pressing pad being fixed to the first fixing member, the downstream nip forming member including: a second pressurizing pad sandwiching the endless belt between the second pressurizing pad and the rotating body; and a second fixing member that is harder than the second pressing pad, the second pressing pad being fixed to the second fixing member, the first urging member urging the first fixing member, the second urging member urging the second fixing member.

According to the above configuration, since the pressing members are biased by the fixing members which are harder than the pressing pads, the positions of the pressing pads, that is, the positions of the clamping portions can be stabilized further.

Further, the first urging member is disposed at a distance from the first pressurizing pad in the width direction of the endless belt, and the second urging member is disposed at a distance from the second pressurizing pad in the width direction of the endless belt.

According to the above configuration, since the urging members are disposed with a gap therebetween in the width direction, the operation of attaching the urging members can be easily performed.

Further, the first urging member and the second urging member are leaf springs.

According to the above configuration, for example, when the first urging member and the second urging member are integrally formed, it is easy to integrally form the first urging member and the second urging member from a single leaf spring.

Further, the fixing device further includes a holding portion that supports the upstream nip forming member and the downstream nip forming member, the first restricting member and the second restricting member being integrally configured with the holding portion.

According to the above structure, the number of components can be reduced, and the cost can be reduced.

Further, the upstream nip forming member includes a first pressure pad sandwiching the endless belt between the first pressure pad and the rotating body, the downstream nip forming member includes a second pressure pad sandwiching the endless belt between the second pressure pad and the rotating body, and the holding portion includes: an upstream wall disposed on an upstream side of the first pressing pad in the moving direction, the upstream wall facing the first pressing pad in the moving direction; and a downstream wall disposed on a downstream side of the second pressing pad in the moving direction, the second pressing pad being opposed in the moving direction, a distance from the upstream wall to the downstream wall in the moving direction being larger than a sum of a length of the upstream nip forming member in the moving direction and a length of the downstream nip forming member in the moving direction.

According to the above configuration, the work of attaching each of the grip forming members to the holding portion can be easily performed.

The present invention is not limited to the fixing device, but may be applied to a conveying device having an endless belt in which a recording medium is conveyed between the endless belt and a rotating body.

According to the present invention, it is possible to suppress a change in the position of each of the clamping portions due to a manufacturing error of each of the clamping forming members, repeated clamping, unclamping, or the like.

Drawings

Fig. 1 is a sectional view showing a laser printer according to an embodiment of the present invention.

Fig. 2 is a sectional view showing the fixing device.

Fig. 3 is a sectional view showing the pressing unit.

Fig. 4 is an exploded perspective view showing the pressing unit.

Fig. 5 is a perspective view showing the pressing unit.

Fig. 6 is a sectional view showing a pressing unit according to a first modification.

Fig. 7 is a perspective view showing a pressing unit according to the first modification.

Fig. 8 is a sectional view showing a pressing unit according to a second modification.

Fig. 9 is a perspective view showing a pressing unit according to a second modification.

Fig. 10 (a) is a cross-sectional view showing a pressing unit according to a third modification, and (b) is a top view.

Fig. 11 (a) is a sectional view showing a pressing unit according to a fourth modification, and (b) is a perspective view showing a structure around a compression coil spring.

Fig. 12 is a sectional view showing a pressing unit according to a fifth modification.

Fig. 13 (a) is a sectional view showing a pressing unit according to a sixth modification, and (b) is a perspective view showing a structure around a leaf spring.

Fig. 14 (a) is a cross-sectional view showing a pressing unit according to a seventh modification, and (b) is a perspective view showing a structure around a leaf spring.

Detailed Description

Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In the following description, the direction is "front" on the left side facing the paper surface, the "rear" on the right side facing the paper surface, the "left" on the deep side facing the paper surface, and the "right" on the near front side facing the paper surface in fig. 1. Further, the up-down direction when facing the paper surface is "up-down".

As shown in fig. 1, the laser printer 1 mainly includes a paper feed section 3, an exposure device 4, a process cartridge 5, and a fixing device 8 in a housing 2.

The paper feed section 3 is provided in a lower portion of the housing 2, and mainly includes: a paper feed tray 31 for accommodating paper S as an example of a recording medium; a paper pressing plate 32; a paper feed mechanism 33. The sheet S accommodated in the sheet feed tray 31 is lifted up by the sheet pressing plate 32 and fed to the process cartridge 5 by the sheet feed mechanism 33.

The exposure device 4 is disposed at an upper portion in the housing 2, and includes a light source device not shown, and a polygon mirror, a lens, a reflecting mirror, and the like, which are omitted from the drawing. In the exposure device 4, the light beam emitted from the light source device based on the image data scans the surface of the photosensitive drum 61 at a high speed, thereby exposing the surface of the photosensitive drum 61.

The process cartridge 5 is disposed below the exposure device 4, and the process cartridge 5 can be attached to and detached from the housing 2 by opening an opening formed when the front cover 21 provided on the housing 2 is opened. The process cartridge 5 includes a drum unit 6 and a developing unit 7. The drum unit 6 mainly includes a photosensitive drum 61, a charger 62, and a transfer roller 63. The developing unit 7 is attachable to and detachable from the drum unit 6, and mainly includes a developing roller 71, a supply roller 72, a layer thickness regulating blade 73, and a housing portion 74 for housing toner.

In the process cartridge 5, the surface of the photosensitive drum 61 is uniformly charged by the charger 62 and then exposed by the light beam from the exposure device 4, thereby forming an electrostatic latent image based on image data on the photosensitive drum 61. The toner in the accommodating portion 74 is supplied to the developing roller 71 via the supply roller 72, enters between the developing roller 71 and the layer thickness regulating sheet 73, and is carried on the developing roller 71 as a thin layer having a certain thickness. The toner carried on the developing roller 71 is supplied from the developing roller 71 to the electrostatic latent image formed on the photosensitive drum 61. Thereby, the electrostatic latent image is visualized, and a toner image is formed on the photosensitive drum 61. Then, the sheet S is conveyed between the photosensitive drum 61 and the transfer roller 63, whereby the toner image on the photosensitive drum 61 is transferred onto the sheet S.

The fixing device 8 is disposed behind the process cartridge 5. The sheet S to which the toner image is transferred passes through the fixing device 8, thereby fixing the toner image. The sheet S having the toner image fixed thereon is discharged onto the discharge tray 22 by the conveying rollers 23, 24.

As shown in fig. 2, the fixing device 8 includes a heating roller 81 as one example of a rotating body, a heater 82, an endless belt 83, and a pressing unit 84. By urging one of the heating roller 81 and the pressing unit 84 toward the other, a nip NP is formed between the heating roller 81 and the endless belt 83.

In the following description, the width direction of the endless belt 83 is also simply referred to as "width direction", the moving direction of the endless belt 83 at the nip portion NP is also simply referred to as "moving direction", and the facing direction in which the heating roller 81 and the pressing unit 84 (specifically, the respective nip forming members 85, X described later) face is also simply referred to as "facing direction". In the present embodiment, the width direction is along the left-right direction, the movement direction is along the front-rear direction, and the facing direction is along the up-down direction.

The heating roller 81 is a roller having a cylindrical base body, and is formed by forming a release layer made of a fluororesin or the like on the outer peripheral surface of a tube body made of a metal such as aluminum. By inputting a driving force from a motor not shown in the drawing, the heating roller 81 is rotated counterclockwise in fig. 2. The heating roller 81 is in contact with the outer peripheral surface of the endless belt 83.

The heater 82 is a heater for heating the heating roller 81, and is disposed radially inward of the heating roller 81. As the heater 82, for example, a halogen lamp that emits light when energized and heats the heating roller 81 by heat radiation can be used.

The endless belt 83 is a cylindrical member, and has flexibility. The endless belt 83 is formed by forming a release layer made of a fluororesin or the like on the outer peripheral surface of a base material made of a metal such as stainless steel or a resin such as polyimide resin, for example. The endless belt 83 is provided to be driven to rotate clockwise in fig. 2 with the rotation of the heating roller 81. Thereby, the endless belt 83 conveys the sheet S between it and the heating roller 81.

The inner peripheral surface 83A of the endless belt 83 is coated with a lubricant such as grease. Thus, the sliding property between the inner peripheral surface 83A of the endless belt 83 and the pressing unit 84 can be improved, and thus the endless belt 83 can be rotated well.

The pressing unit 84 mainly includes a downstream nip forming member 85, an upstream nip forming member X, a holding portion 186 for supporting each nip forming member 85, X, a leaf spring S5 as one example of a first urging member and a second urging member, and a supporting portion 87 for supporting the holding portion 186. Each of the nip forming members 85, X (specifically, each of the pressing pads 88, Y described later) protrudes toward the heating roller 81 side than the surface of the holding portion 186 on the heating roller 81 side in a state of being supported by the holding portion 186.

As shown in fig. 3, the downstream nip forming member 85 is a member that forms a downstream nip portion NPd between the heating roller 81 and the endless belt 83 by sandwiching the endless belt 83 between the downstream nip forming member and the heating roller 81, and is located inside the endless belt 83. The upstream nip forming member X is a member that forms an upstream nip portion NPu between the heating roller 81 and the endless belt 83 by sandwiching the endless belt 83 between the upstream nip forming member X and the heating roller 81, and is located inside the endless belt 83. The upstream nip forming member X is located upstream in the moving direction with respect to the downstream nip forming member 85. Thus, by forming the upstream nip NPu and the downstream nip NPd by the pressing unit 84, the sheet S is heated and pressed while passing through the nip NP, and the toner image is fixed on the sheet S.

In the present embodiment, the upstream nip forming member X is arranged to be separated from the downstream nip forming member 85 in the moving direction. Therefore, between the upstream nip NPu and the downstream nip NPd, there is an intermediate nip NPi in which the pressure from the pressurizing unit 84 does not directly act. At the intermediate nip NPi, although the endless belt 83 contacts the heating roller 81, since there is no member that sandwiches the endless belt 83 together with the heating roller 81, little pressure is applied. Therefore, the sheet S passes through the intermediate nip portion NPi while being heated by the heating roller 81, with little pressurization. In the present embodiment, a region from the upstream end of the upstream nip portion NPu to the downstream end of the downstream nip portion NPd, that is, the entire region where the outer peripheral surface of the endless belt 83 contacts the heating roller 81, is referred to as a nip portion NP. That is, in the present embodiment, the nip NP includes a portion to which no pressure from the pressurizing pads 88, Y is applied.

The downstream nip forming member 85 includes: a second pressurizing pad 88, the second pressurizing pad 88 sandwiching the endless belt 83 between it and the heating roller 81; and a plate-like second fixing member 89 to which the second pressurizing pad 88 is fixed.

As shown in fig. 4, the second pressing pad 88 is a cube formed in an elongated shape long in the width direction. The second pressing pad 88 is formed of an elastic material such as rubber, and is elastically deformable. Since the pressing unit 84 has a laterally symmetrical shape, in fig. 4, a right side portion of the pressing unit 84 is enlarged and described, and a left side portion thereof is omitted because it has the same structure.

The second fixing member 89 is a member made of a harder material than the second pressing pad 88, specifically, a metal plate. The second fixing member 89 includes: a base 89A, the second pressurizing pad 88 being engaged at the base 89A; and an extension portion 89B extending from an end portion of the base portion 89A in the width direction to the outside in the width direction.

The length of the base 89A in the moving direction is longer than the length of the second pressurizing pad 88. The region where the second pressurizing pad 88 is engaged is provided at a position apart from the upstream and downstream ends of the base 89A. Thus, the second fixing member 89 has a convex portion C that protrudes further toward the downstream side in the moving direction than the second pressing pad 88 in a state where the second pressing pad 88 is fixed to the base portion 89A.

The length of the base 89A in the width direction is longer than the length of the second pressurizing pad 88. The region where the second pressing pad 88 is joined is provided at a position apart from each end portion in the width direction of the base portion 89A.

The extension portion 89B has a length in the moving direction shorter than that of the base portion 89A, and is disposed so as to be offset toward the end portion on the downstream side of the base portion 89A.

The upstream nip forming member X includes: a first pressing pad Y sandwiching an endless belt 83 between it and the heating roller 81; and a plate-shaped first fixing member Z to which the first pressurizing pad Y is fixed. The first pressurizing pad Y is constructed in substantially the same manner as the second pressurizing pad 88.

The first fixing member Z is constructed in substantially the same manner as the second fixing member 89. Specifically, the first fixing member Z is a member made of a harder material than the first pressurizing pad Y, and specifically, is made of a metal plate. The first fixing member Z includes a convex portion CA, a base portion ZA, and an extension portion ZB, which are substantially the same as the convex portion C, the base portion 89A, and the extension portion 89B of the second fixing member 89. The extension portion ZB of the first fixing member Z is arranged to be offset toward the upstream-side end portion of the base portion ZA.

The holding portion 186 is made of resin or metal. The holding portion 186 includes a base portion 186A, an upstream wall 186B as an example of a first restriction member, a downstream wall 86C as an example of a second restriction member, a first support portion engaging wall 86E, and a second support portion engaging wall 86F. That is, in the present embodiment, the first restricting member and the second restricting member are integrally formed with the holding portion 186. The base 186A is a plate-like portion having a support surface FS perpendicular to the facing direction, and is formed in a long shape long in the width direction. The support surface FS slidably supports the fixing members 89 and Z in the moving direction.

As shown in fig. 2, the upstream wall 186B protrudes from the upstream end portion of the base 186A in the moving direction toward the direction approaching the heating roller 81. The surface on the upstream side in the moving direction of the upstream wall 186B is a curved surface for guiding the inner peripheral surface 83A of the endless belt 83. The upstream wall 186B is disposed on the upstream side in the moving direction with respect to the first pressurizing pad Y in a state where the upstream nip forming member X is attached to the holding portion 186. The upstream wall 186B faces the first pressurizing pad Y in the moving direction.

The downstream wall 86C protrudes from the downstream end portion of the base 186A in the moving direction toward the heating roller 81. The surface on the downstream side in the moving direction of the downstream wall 86C is a curved surface for guiding the inner peripheral surface 83A of the endless belt 83. The downstream wall 86C is disposed on the downstream side in the moving direction with respect to the second pressurizing pad 88 in a state where the downstream sandwiching formation member 85 is attached to the holding portion 186. The downstream wall 86C faces the second pressurizing pad 88 in the moving direction.

As shown in fig. 3 and 4, the downstream wall 86C has a contact surface FT that contacts the second pressurizing pad 88 on the upstream side in the moving direction, and a concave portion G that is concave from the contact surface FT toward the downstream side in the moving direction. The contact surface FT is a surface that contacts the second pressing pad 88 in the moving direction, is perpendicular to the moving direction, and faces the upstream side in the moving direction.

The interval from the contact surface FT to the upstream wall 186B (contact surface FTA described later) in the moving direction is larger than the total length of the base 89A, ZA of each of the fixing members 89, Z in the moving direction. This makes it possible to easily perform a work of placing the base 89A, ZA on the support surface FS through between the upstream wall 186B and the downstream wall 86C.

The concave portion G is a groove into which the convex portion C of the second fixing member 89 can enter, and is formed so as to penetrate the downstream wall 86C in the width direction. The length of the concave portion G in the moving direction is longer than the length of the convex portion C in the moving direction. In other words, the depth of the concave portion G is larger than the protruding amount of the convex portion C from the second pressurizing pad 88 in the moving direction.

Further, a side surface of the concave portion G on the opposite side to the heating roller 81 is formed flush with the support surface FS of the base 186A. The side surface of the concave portion G on the opposite side to the heating roller 81 may also be located farther from the heating roller 81 than the support surface FS.

The upstream wall 186B has a contact surface FTA that contacts the first pressing pad Y on the downstream side in the moving direction and a concave portion GA that is concave from the contact surface FTA toward the upstream side in the moving direction. The contact surface FTA is a surface that contacts the first pressing pad Y in the moving direction, is perpendicular to the moving direction, and faces the downstream side in the moving direction.

The concave portion GA is a groove into which the convex portion CA of the first fixing member Z can enter, and is formed so as to penetrate the upstream wall 186B in the width direction. The relationship between the depth of the concave portion GA and the protruding amount of the convex portion CA in the moving direction is the same as the relationship between the concave portion G and the convex portion C.

The base 186A has a concave portion CP recessed from an end surface in the width direction, and a protruding portion PP provided in the concave portion CP and protruding in the width direction.

The space in the concave portion CP is a space in which the leaf spring S5 is disposed. The protruding portion PP is a portion for restricting upward movement of the leaf spring S5.

The plate spring S5 is made of metal or resin. The leaf spring S5 is disposed at a position spaced apart from the pressing pads 88, Y in the width direction. The leaf spring S5 has a base S51, a first arm S52, and a second arm S53. The base S51 is a portion for connecting the two arm portions S52 and S53. The base S51 is disposed below the protruding portion PP.

The first arm S52 is a portion that mates with the extension portion 89B of the second fixing member 89. The first arm S52 extends from an end portion on the downstream side in the moving direction of the base S51 toward the downstream side in the moving direction and obliquely upward with respect to the base S51.

The second arm portion S53 is a portion that mates with the extension portion ZB of the first fixing member Z. The second arm portion S53 extends from an end portion on the upstream side in the moving direction of the base portion S51 toward the upstream side in the moving direction and obliquely upward with respect to the base portion S51.

The leaf spring S5 is disposed in a compressed state between the extension portion 89B of the second fixing member 89 and the extension portion ZB of the first fixing member Z. Thereby, the plate spring S5 biases the second fixing member 89 toward the downstream wall 86C in the moving direction, and biases the first fixing member Z toward the upstream wall 186B. That is, in the present embodiment, the second urging member that urges the second fixing member 89 and the first urging member that urges the first fixing member Z are integrally constituted by a single leaf spring S5.

When the plate spring S5 is compressed between the extension portion 89B of the second fixing member 89 and the extension portion ZB of the first fixing member Z, the plate spring S5 tends to move upward due to its own restoring force. However, since the base portion S51 of the leaf spring S5 is in contact with the protruding portion PP, upward movement of the leaf spring S5 is restricted, and detachment of the leaf spring S5 from the second fixing member 89 and the first fixing member Z is suppressed.

The first support portion engaging wall 86E is a wall that engages with an end portion of an upstream side wall 87B (see fig. 2) of the support portion 87 on the heating roller 81 side, and is provided in two so as to sandwich the upstream side wall 87B in the moving direction. Each first support portion engagement wall 86E protrudes from the base portion 186A toward the support portion 87.

The second support portion engaging wall 86F is a wall that engages with an end portion of a downstream side wall 87C (see fig. 2) of the support portion 87 on the heating roller 81 side, and is provided in two so as to sandwich the downstream side wall 87C in the moving direction. Each second support portion engagement wall 86F protrudes from the base portion 186A toward the support portion 87.

As shown in fig. 2, the supporting portion 87 is made of resin or metal. The support portion 87 is formed in a U-shape in cross section, and has a bottom wall 87A, an upstream side wall 87B, and a downstream side wall 87C. The bottom wall 87A is a plate-like portion having a surface perpendicular to the facing direction, and is formed in an elongated shape long in the width direction.

The upstream side wall 87B extends from an upstream-side end of the bottom wall 87A toward the holding portion 186. The downstream side wall 87C extends from the end portion on the downstream side of the bottom wall 87A toward the holding portion 186.

Next, the function and effect of the fixing device 8 according to the present embodiment will be described.

As shown in fig. 3, in a clamped state in which the endless belt 83 is sandwiched between the heating roller 81 and the clamp forming members 85, X, the fixing members 89, Z are biased toward the walls 86C, 186B by the plate spring S5, so that the pressing pads 88, Y come into contact with the walls 86C, 186B, and movement of the clamp forming members 85, X is restricted. In the unclamped state in which the endless belt 83 is not sandwiched between the heating roller 81 and the respective nip forming members 85, X, similarly, the respective pressing pads 88, Y are in contact with the respective walls 86C, 186B, and the movement of the respective nip forming members 85, X is restricted. Therefore, even if the clamped state and the unclamped state are repeated, the positions of the respective clamp forming members 85, X with respect to the holding portion 186 can be kept constant, and therefore, the positions of the upstream clamp portion NPu and the downstream clamp portion NPd, that is, the positions of the entire clamp portion NP can be stabilized. Further, even if the respective clamp forming members 85, X have manufacturing errors, for example, mounting errors occur when the respective pressing pads 88, Y are joined to the respective fixing members 89, Z, the respective pressing pads 88, Y are in contact with the respective walls 86C, 186B due to the force exerted by the leaf springs S5, and therefore the positions of the respective pressing pads 88, Y with respect to the holding portions 186 can be kept constant, and the positions of the respective clamp portions NPu, NPd can be stabilized.

Further, since the first urging member and the second urging member are integrally constituted by a single leaf spring S5, the number of components can be reduced, and the cost can be reduced.

In addition to the above effects, the present embodiment can obtain the following effects.

Since the plate spring S5 biases the fixing members 89 and Z harder than the pressing pads 88 and Y, the positions of the pressing pads 88 and Y, that is, the positions of the clamping portions NPu and NPd can be further stabilized.

Since the convex portions C, CA of the fixing members 89, Z enter the concave portions G, GA formed in the walls 86C, 186B, the separation of the clamp forming members 85, X from the holding portion 186 can be suppressed.

By making the length of the concave portion G, GA in the moving direction longer than the length of the convex portion C, CA in the moving direction, the tip end of the convex portion C, CA does not contact the bottom surface of the concave portion G, GA, and therefore, the force exerted by the leaf spring S5 can be used more effectively as the force to press the respective pressing pads 88, Y against the contact surfaces FT, FTA.

Since the leaf spring S5 is disposed at a position spaced apart from the pressing pads 88, Y in the width direction, the work of attaching the leaf spring S5 can be easily performed.

The present invention is not limited to the above-described embodiments, and can be utilized in various modes as exemplified below. In the following description, members having substantially the same structures as those of the above-described embodiments are given the same reference numerals, and the description thereof is omitted.

In the above embodiment, the leaf spring S5 was exemplified as the first urging member and the second urging member, but the present invention is not limited to this, and the first urging member and the second urging member may be heat-resistant rubber or the like.

The structure in which the first urging member and the second urging member are integrated is not limited to the above embodiment. For example, the first urging member and the second urging member may be integrally constituted by a leaf spring S6 shown in fig. 6 and 7.

Specifically, the plate spring S6 is made of metal or resin. The leaf spring S6 has a base portion S61, a first spring portion S62, a second spring portion S63, and a fixing portion S64. The base S61 is a portion for connecting the two spring portions S62 and S63. The base S61 is disposed below the protruding portion PP.

The first spring portion S62 is a portion that biases the second fixing member 89 toward the downstream wall 86C. The first spring portion S62 is formed in a U-shape in cross section, which opens downward. The first spring portion S62 extends upward from the downstream end of the base portion S61, then is curved in an arc shape, and extends downward. The portion of the first spring portion S62 disposed downstream extends downward from the base portion S61. The first spring portion S62 is arranged between the second fixing member 89 and the protruding portion PP in a state compressed in the moving direction. The first spring portion S62 is an example of the second urging member.

The second spring portion S63 is a portion that biases the first fixing member Z toward the upstream wall 186B. The second spring portion S63 is formed in a U-shape in cross section, which opens downward. The second spring portion S63 extends upward from the upstream end of the base portion S61, then is curved in an arc shape, and extends downward. The second spring portion S63 is arranged between the first fixing member Z and the protruding portion PP in a state compressed in the moving direction. The second spring portion S63 is an example of the first urging member.

The fixing portion S64 is a portion fixed to the holding portion 186. The fixing portion S64 protrudes downstream from the lower end of the first spring portion S62. The downstream wall 86C has a recess CP1, and the fixing portion S64 is fitted in the recess CP 1. In this embodiment, the downstream sandwiching formation member 85 can be biased toward the downstream wall 86C as well as the upstream sandwiching formation member X toward the upstream wall 186B by the plate spring S6.

The compression coil spring S7 shown in fig. 8 or 9 may be disposed between the second fixing member 89 and the first fixing member Z in a contracted state. The compression coil spring S7 is an example of a first urging member and an example of a second urging member. In this embodiment, the downstream sandwiching formation member 85 can be biased toward the downstream wall 86C as well as the upstream sandwiching formation member X toward the upstream wall 186B by the compression coil spring S7. In this embodiment, the protruding portion PP is not required, and thus the holding portion 186 may be configured to have no protruding portion PP. In order to hold the compression coil spring S7 between the fixing members 89 and Z, the fixing members 89 and Z may be provided with protrusions C3 and C4 that enter the space inside the compression coil spring S7 in the radial direction.

In the above embodiment, the two pinching forming members 85, X are biased in the direction to separate from each other, but the present invention is not limited to this. For example, as shown in (a) and (b) in fig. 10, the two pinching forming members 585, X1 may be biased toward each other.

Specifically, in the present embodiment, the downstream nip forming member 585 has the second pressurizing pad 88 identical to the above embodiment, and a second fixing member 589 slightly different in structure from the above embodiment. The second fixing member 589 has a base portion 89A and an extension portion 89B substantially the same as the above embodiment, but unlike the above embodiment, the extension portion 89B is offset toward the end portion on the upstream side of the base portion 89A.

The upstream nip forming member X1 has the same first pressing pad Y as the above embodiment, and a first fixing member Z1 slightly different in structure from the above embodiment. The first fixing member Z1 has the base portion ZA and the extension portion ZB substantially the same as the above embodiment, but is different from the above embodiment in that the extension portion ZB is offset toward the end portion on the downstream side of the base portion ZA.

The protruding portion PP1 protrudes upward from the support surface FS of the holding portion 186, and extends from one end to the other end of the holding portion 186 in the width direction. The protruding portion PP1 has a recess GB into which the upstream end of the second fixing member 589 enters, and a recess GC into which the downstream end of the first fixing member Z1 enters. In a state where the second pressing pad 88 is in contact with the protruding portion PP1, the second pressing pad 88 is arranged with respect to the second fixing member 589 such that the upstream end of the second fixing member 589 is separated from the bottom of the recess GB. In addition, in a state where the first pressurizing pad Y is in contact with the protruding portion PP1, the first pressurizing pad Y is arranged with respect to the first fixing member Z1 such that the downstream end of the first fixing member Z1 is separated from the bottom of the concave portion GC.

The two pinching forming members 585 and X1 are biased toward the protruding portion PP1 by the leaf spring S8. Here, the protruding portion PP1 is one example of the first restriction member and the second restriction member. The protruding portion PP1 is disposed downstream in the moving direction with respect to the upstream pinching forming member X1, and is disposed upstream in the moving direction with respect to the downstream pinching forming member 585. In the present embodiment, the first restriction member and the second restriction member are integrally constituted by the single protrusion PP1, but the present invention is not limited thereto, and the first restriction member and the second restriction member may be separately constituted.

The leaf spring S8 has a base portion S81, a first spring portion S82, and a second spring portion S83.

The base S81 is a portion for connecting the two spring portions S82 and S83. The base S81 includes a long strip portion extending in the moving direction, a portion extending obliquely upward from a downstream end of the long strip portion toward the downstream side, and a portion extending obliquely upward from an upstream end of the long strip portion toward the upstream side. The base S81 is disposed below the protruding portion PP 1.

The first spring portion S82 is a portion for biasing the second fixing member 589 toward the protruding portion PP 1. The first spring portion S82 is formed in a U-shape in cross section, which opens downward. The first spring portion S82 extends upward from the downstream end of the base portion S81, is curved in an arc shape, and extends downward. The first spring portion S82 is arranged between the second fixing member 589 and the downstream wall 86C in a state compressed in the moving direction. The first spring portion S82 is an example of the second urging member.

The second spring portion S83 is a portion for biasing the first fixing member Z1 toward the protruding portion PP 1. The second spring portion S83 is formed in a U-shape in cross section, which opens downward. The second spring portion S83 extends upward from the upstream end of the base portion S81, is curved in an arc shape, and extends downward. The second spring portion S83 is arranged between the first fixed member Z1 and the upstream wall 186B in a state compressed in the moving direction. The second spring portion S83 is an example of the first urging member. In the present embodiment, too, the pressing pads 88, Y can be brought into contact with the protruding portion PP1 by biasing the two pinching forming members 585, X1 toward the protruding portion PP1, and therefore the same effects as those of the above-described embodiments can be obtained.

The means for urging the two pinching forming members 585, X1 toward the protruding portion PP1 is not limited to the above-described leaf spring S8. For example, the two clamp forming members 685 and X2 may be biased toward the protruding portion PP1 by the tension coil spring S9 shown in (a) and (b) of fig. 11. The tension coil spring S9 is an example of a first urging member and an example of a second urging member.

Specifically, in this embodiment, the downstream nip forming member 685 has the same second pressurizing pad 88 as the embodiment of fig. 10, and a second fixing member 689 slightly different in structure from the embodiment of fig. 10. The second fixing member 689 has a base 89A substantially identical to the embodiment of fig. 10, and a first extension 689B and a second extension 689C.

The first extension 689B is a portion to which one end of the tension coil spring S9 is fitted. The first extending portion 689B protrudes from an end portion of the base portion 89A in the width direction.

The second extension 689C is a portion for suppressing the one end of the tension coil spring S9 from being separated from the first extension 689B. The second extending portion 689C protrudes from the head end of the first extending portion 689B toward the upstream side and the downstream side.

The upstream nip forming member X2 includes a first pressurizing pad Y identical to the embodiment of fig. 10, and a first fixing member Z2 slightly different in structure from the embodiment of fig. 10. The first fixing member Z2 includes a base ZA, a first extension Z21, and a second extension Z22, which are substantially the same as the embodiment of fig. 10. The first and second extending portions Z21 and Z22 have substantially the same structure as the first and second extending portions 689B and 689C of the second fixing member 689. That is, the other end of the tension coil spring S9 is engaged with the first extension Z21, and the second extension Z22 serves to suppress the other end of the tension coil spring S9 from being separated from the first extension Z21. In the present embodiment, the two sandwiching members 685 and X2 can be biased toward the protruding portion PP1 as well.

Further, the two sandwiching members 785 and X3 may be biased toward the protruding portion PP1 by the plate spring S10 shown in fig. 12.

Specifically, in the present embodiment, the downstream nip forming member 785 has the same second pressurizing pad 88 as the embodiment of fig. 11, and a second fixing member 789 slightly different in structure from the embodiment of fig. 11. The second fixing member 789 has a base portion 89A, a first extending portion 689B, and a second extending portion 689C (not shown) substantially the same as the embodiment of fig. 11, but unlike the embodiment of fig. 11, the first extending portion 689B is offset toward an end portion on the upstream side of the base portion 89A.

The upstream nip forming member X3 has the same first pressing pad Y as the embodiment of fig. 11, and a first fixing member Z3 slightly different in structure from the embodiment of fig. 11. The first fixing member Z3 has a base portion ZA, a first extension portion Z21, and a second extension portion Z22 (not shown) which are substantially the same as those of the embodiment of fig. 11, but unlike the embodiment of fig. 11, the first extension portion Z21 is offset toward the end portion on the downstream side of the base portion ZA.

The leaf spring S10 is a substantially U-shaped leaf spring in cross section. One end of the leaf spring S10 is fitted to the downstream end of the first extension portion 689B of the second fixing member 789, and the other end is fitted to the upstream end of the first extension portion Z21 of the first fixing member Z3. The leaf spring S10 is an example of a first urging member and an example of a second urging member. In the present embodiment, the two sandwiching members 785 and X3 can be biased toward the protruding portion PP1 as well.

Further, both of the two sandwiching members 885, X1 may be biased toward the downstream side by the leaf spring S11 shown in fig. 13 (a) and (b). Specifically, in the present embodiment, the downstream sandwiching forming member 885 slightly different from the structure of the embodiment of fig. 4 and the upstream sandwiching forming member X1 substantially the same as the embodiment of fig. 10 are biased toward the downstream side by the plate spring S11.

Here, in the present embodiment, the downstream wall 86C corresponds to the second restriction member, and the protruding portion PP2 corresponds to the first restriction member. The downstream wall 86C is disposed downstream in the moving direction with respect to the downstream pinching forming member 885, and the protruding portion PP2 is disposed downstream in the moving direction with respect to the upstream pinching forming member X1.

The downstream nip forming member 885 has a second pressing pad 88 identical to the embodiment of fig. 4, and a second fixing member 889 slightly different in structure from the embodiment of fig. 4. The second fixing member 889 has a base 89A and an extension 89B substantially identical to the embodiment of fig. 4. The extension portion 89B of the second fixing member 889 is located at a position different from the extension portion ZB of the first fixing member Z1 in the width direction.

The protruding portion PP2 is formed in a long strip shape long in the width direction like the protruding portion PP1 of fig. 10, but is different from the protruding portion PP1 of fig. 10 in that a slit PP21 is formed at an end portion in the width direction. The notch PP21 is a notch for avoiding interference with the base S111 of the leaf spring S11 described later.

Further, the protruding portion PP2 has substantially the same concave portion GC as the embodiment of fig. 10, but is different from the embodiment of fig. 10 in that it does not have the concave portion GB. The leaf spring S11 has a base portion S111, a first spring portion S112, and a second spring portion S113.

The first spring portion S112 is a portion that biases the second fixing member 889 toward the downstream wall 86C. The first spring portion S112 is formed in a U-shape in cross section, which is open upward. The first spring portion S112 is arranged between the protruding portion PP2 and the extension portion 89B of the second fixing member 889 in a state compressed in the moving direction. The first spring portion S112 is an example of the second urging member.

The second spring portion S113 is a portion for biasing the first fixing member Z1 toward the protruding portion PP 2. The second spring portion S113 is formed in a u-shape in cross section, which is open upward. The second spring portion S113 is disposed between the upstream wall 186B and the extension portion ZB of the first fixing member Z1 in a state compressed in the moving direction. The second spring portion S113 is an example of the first urging member.

The base S111 is a portion for connecting the spring portions S112 and S113. The base portion S111 extends from the second spring portion S113 to the downstream side, then extends in the width direction toward the opposite side from the second pressing pad 88, then extends to the upstream side, and is coupled to the first spring portion S112.

According to the present embodiment, the two pinching forming members 885, X1 can be biased toward the downstream wall 86C and the protruding portion PP2 to bring the pressing pads 88, Y into contact with the downstream wall 86C and the protruding portion PP2, and therefore the same effects as those of the above embodiment can be obtained. In the present embodiment, since both the pinching forming members 885, X1 are biased toward the downstream side, the pinching forming members 885, X1 can be restrained from moving against the force applied by the leaf spring S11 due to friction with the endless belt 83.

Further, both of the two sandwiching members 985 and X4 may be biased toward the downstream side by the leaf spring S12 shown in fig. 14 (a) and (b).

Specifically, in the present embodiment, the downstream nip forming member 985 has the same second pressurizing pad 88 as the embodiment of fig. 13, and a second fixing member 989 slightly different in structure from the embodiment of fig. 13. The second fixing member 989 has a base portion 89A substantially identical in structure to the embodiment of fig. 13, and an extension portion 989B extending from an end portion of the base portion 89A in the width direction to the upstream side. A slit 989C is formed at the upstream end of the extension 989B.

The upstream nip forming member X4 has a first pressurizing pad Y substantially identical to the embodiment of fig. 13, and a first fixing member Z4 slightly different in structure from the embodiment of fig. 13. The first fixing member Z4 has a base portion ZA substantially identical in structure to the embodiment of fig. 13. At an upstream end of the base ZA in the width direction, a notch Z41 is formed. The notch Z41 of the first fixing member Z4 is arranged between the notch 989C of the second fixing member 989 and the first pressurizing pad Y in the width direction.

The first fixing member Z4 is disposed below the second fixing member 989. Specifically, the holding portion 186 has a first support surface FS1 and a second support surface ES2, the first support surface FS1 supporting the second fixing member 989 so as to be movable in the moving direction, and the second support surface FS2 supporting the first fixing member Z4 so as to be movable in the moving direction. The first support surface FS1 is located above the second support surface FS 2.

The leaf spring S12 has a base portion S121, a first spring portion S122, and a second spring portion S123.

The first spring portion S122 is a portion that biases the second fixing member 989 toward the downstream wall 86C. The first spring portion S122 is formed in a U-shape in cross section, which is open upward. The first spring portion S122 is disposed between the upstream wall 186B and the extension portion 989B (the slit 989C) of the second fixing member 989 in a state compressed in the moving direction. The first spring portion S122 is an example of the second urging member.

The second spring portion S123 is a portion that biases the first fixing member Z4 toward the same protruding portion PP2 as in fig. 13. In the present embodiment, the notch PP21 of the protruding portion PP2 is a notch formed to avoid interference with the extension portion 989B of the second fixing member 989. The second spring portion S123 is formed in a U-shape in cross section, which is open upward. The second spring portion S123 is disposed between the upstream wall 186B and the first fixing member Z4 (the slit Z41) in a state compressed in the moving direction. The second spring portion S123 is an example of the first urging member.

The base S121 is a portion for connecting the spring portions S122 and S123. The base S121 connects the upper ends of the spring portions S122 and S123 to each other.

In the present embodiment, the two pinching forming members 985 and X4 can be biased toward the downstream wall 86C and the protruding portion PP2 as well.

In the above embodiment, both ends of the fixing member are biased by the two biasing members, but the present invention is not limited thereto, and for example, the center of the fixing member in the width direction may be biased by a single biasing member. Further, the first urging member and the second urging member may be configured as separate members.

In the above embodiment, the pressing pads 88, Y are in contact with the inner peripheral surface 83A of the endless belt 83, but the present invention is not limited thereto, and for example, a slide sheet may be provided between the inner peripheral surface of the endless belt and the pressing pad.

In the above embodiment, the nip forming members 85, X are constituted by the pressing pads 88, Y and the fixing members 89, Z, but the present invention is not limited thereto, and the nip forming members may be constituted by, for example, only the pressing pads. The pressing pad may be made of a hard material such as a resin or a metal that does not elastically deform even when pressed. In this case, the pressurizing pad may be directly biased by the spring member.

In the above embodiment, the restricting member is provided integrally with the holding portion 186, but the present invention is not limited thereto, and for example, the restricting member may be a member separate from the holding portion.

In the above embodiment, the fixing members 89, Z are formed in a plate shape, but the present invention is not limited thereto, and the fixing members may be, for example, thick members instead of plate-shaped members.

In the above-described embodiment, the structure for forming the nip of the present invention is applied to the fixing device 8, but the present invention is not limited to this, and the structure of the present invention may be applied to a conveying device other than the fixing device. For example, in a conveying apparatus having a conveying roller and a sheet conveying belt, the structure of the present invention may be provided in the sheet conveying belt, in which the sheet is conveyed between the sheet conveying belt and the conveying roller.

In the above embodiment, the pressing pads 88, Y are cubes, but the present invention is not limited thereto, and the pressing pads may have any shape.

In the above embodiment, the halogen lamp is exemplified as the heater 82, but the present invention is not limited thereto, and the heater may be, for example, a carbon heater.

In the above embodiment, the heating roller 81 having the heater 82 incorporated therein is illustrated as the rotating body, but the present invention is not limited to this, and for example, an endless heating belt in which the inner peripheral surface is heated by the heater may be used. Further, an external heating system in which a heater is disposed outside the rotating body to heat the outer peripheral surface of the rotating body or an IH (Induction Heating ) system may be used. Further, a heater may be disposed inside the endless belt to indirectly heat the rotating body that is in contact with the outer peripheral surface of the endless belt. Further, the rotating body and the endless belt may be respectively built-in with heaters.

The structure for forming the nip portion of the present invention is not limited to the fixing device 8 of the above embodiment, and may be applied to various fixing devices. For example, the structure of the present invention may be provided in a heating unit of a fixing device having: a fixing roller; a pressure roller forming a fixing nip between the pressure roller and the fixing roller; and a heating unit that contacts the fixing roller at a predetermined nip pressure to heat the fixing roller. Specifically, in the case where the heating unit has an endless belt and a heating member that sandwiches the endless belt between the fixing rollers, the heating member may be biased by a biasing member.

In the above-described embodiment, the present invention is applied to the laser printer 1, but the present invention is not limited thereto, and may be applied to other image forming apparatuses such as a copying machine, a multifunction machine, and the like.

The present invention can be implemented by arbitrarily combining the elements described in the above embodiments and modifications.

Claims (11)

1. A fixing device, comprising:

A heater;

a rotating body heated by the heater;

an endless belt;

An upstream nip forming member that nips the endless belt between the upstream nip forming member and the rotating body to form an upstream nip;

A first restriction member that contacts the upstream nip forming member for restricting movement of the upstream nip forming member in a movement direction of the endless belt at the upstream nip portion;

A first urging member urging the upstream nip forming member in the moving direction toward the first restricting member so that the upstream nip forming member contacts the first restricting member;

A downstream nip forming member disposed on a downstream side in the moving direction with respect to the upstream nip forming member, the downstream nip forming member and the rotating body sandwiching the endless belt therebetween to form a downstream nip portion;

A second restriction member that contacts the downstream nip forming member for restricting movement of the downstream nip forming member in the movement direction; and

And a second urging member urging the downstream nip forming member in the moving direction toward the second restricting member so that the downstream nip forming member contacts the second restricting member.

2. The fixing device according to claim 1, wherein the first urging member and the second urging member are integrally constituted.

3. The fixing device according to claim 1 or 2, wherein the first regulating member is disposed on an upstream side in the moving direction with respect to the upstream nip forming member,

The second restriction member is disposed on a downstream side in the moving direction with respect to the downstream nip forming member.

4. A fixing device according to claim 3, further comprising a holding portion that supports the upstream nip forming member and the downstream nip forming member,

The first urging member and the second urging member are constituted by a single leaf spring,

The leaf spring includes: a first arm portion in contact with the downstream nip forming member; a second arm portion in contact with the upstream nip forming member; and a base portion connecting the first arm portion and the second arm portion,

The holding portion includes: a base portion supporting the upstream nip forming member and the downstream nip forming member; and a protruding portion located between the upstream nip forming member and the downstream nip forming member in the moving direction, protruding from the base portion of the holding portion in the width direction of the endless belt,

The protrusion contacts the base of the leaf spring to limit movement of the leaf spring.

5. The fixing device according to claim 1 or 2, wherein the first regulating member is disposed on a downstream side in the moving direction with respect to the upstream nip forming member,

The second restriction member is disposed on an upstream side in the moving direction with respect to the downstream nip forming member.

6. The fixing device according to claim 1 or 2, wherein the first regulating member is disposed on a downstream side in the moving direction with respect to the upstream nip forming member,

The second restriction member is disposed on a downstream side in the moving direction with respect to the downstream nip forming member.

7. The fixing device according to any one of claims 1 to 6, wherein the upstream nip forming member includes: a first pressurizing pad sandwiching the endless belt between the first pressurizing pad and the rotating body; and a first fixing member, the first fixing member being harder than the first pressing pad, the first pressing pad being fixed to the first fixing member,

The downstream nip forming member includes: a second pressurizing pad sandwiching the endless belt between the second pressurizing pad and the rotating body; and a second fixing member, the second fixing member being harder than the second pressing pad, the second pressing pad being fixed to the second fixing member,

The first urging member urges the first fixing member,

The second urging member urges the second fixing member.

8. The fixing device according to claim 7, wherein the first urging member is disposed with a space from the first pressing pad in a width direction of the endless belt,

The second urging member is disposed with a space from the second pressurizing pad in the width direction of the endless belt.

9. The fixing device according to any one of claims 1 to 8, wherein the first urging member and the second urging member are leaf springs.

10. The fixing device according to any one of claims 1 to 9, further comprising a holding portion that supports the upstream nip forming member and the downstream nip forming member,

The first restricting member and the second restricting member are integrally formed with the holding portion.

11. The fixing device according to claim 10, wherein the upstream nip forming member includes a first pressing pad sandwiching the endless belt between the first pressing pad and the rotating body,

The downstream nip forming member includes a second pressurizing pad sandwiching the endless belt between the second pressurizing pad and the rotating body,

The holding portion includes: an upstream wall disposed on an upstream side of the first pressing pad in the moving direction, the upstream wall facing the first pressing pad in the moving direction; and a downstream wall disposed downstream of the second pressing pad in the moving direction, facing the second pressing pad in the moving direction,

The interval from the upstream wall to the downstream wall in the moving direction is larger than the sum of the length of the upstream nip forming member in the moving direction and the length of the downstream nip forming member in the moving direction.