JP2020166222A - Fixing device - Google Patents

Abstract

To prevent rubber pads from being deformed by an endless belt into an unintended shape.SOLUTION: A fixing device 8 comprises: an upstream rubber pad P1; a downstream rubber pad P2; a holder 140 that holds the rubber pads P1, P2; an upstream guide 160 that has a guide surface Fg for guiding an endless belt 130 on an upstream side of the upstream rubber pad P1; and an urging member that urges the holder 140 in a predetermined direction. The upstream rubber pad P1 has an opposing surface Fp1 that is opposite to an inner peripheral surface 131 of the endless belt 130. An upstream end Ep of the opposing surface Fp1 is separated from a center of rotation X1 of a rotating body 120 compared with a downstream end Eg of a guide surface Fg in the predetermined direction. The opposing surface Fp1 has an upstream portion Fp11 that includes the upstream end Ep and does not sandwich the endless belt 130 with the rotating body 120, and a downstream portion Fp12 that is located on the downstream side of the upstream portion Fp11 and sandwiches the endless belt 130 with the rotating body 120 to form an upstream nip part NP1.SELECTED DRAWING: Figure 3

Description

The present invention relates to a fixing device that heat-fixes a toner image transferred to a sheet to the sheet.

Conventionally, the fixing device includes a heating roller, an endless belt, a rubber pad for sandwiching the endless belt between the heating rollers, and an upstream guide surface for guiding the endless belt on the upstream side in the paper transport direction with respect to the rubber pad. Is known (see Patent Document 1). In this technique, in the direction in which the rubber pad is pressed by the heating roller, the downstream end of the upstream guide surface is arranged at a position farther from the rotation center of the heating roller than the upstream end of the rubber pad.

JP-A-2010-230711

However, in the prior art, the endless belt guided by the upstream guide surface pushes the upstream end of the rubber pad in the downstream direction, so that the rubber pad is deformed into an unintended shape and the nip width does not become a desired width. There is a risk.

Therefore, an object of the present invention is to prevent the rubber pad from being deformed into an unintended shape by the endless belt.

In order to solve the above problems, the fixing device according to the present invention forms an upstream nip portion by sandwiching the endless belt between the heater, the rotating body heated by the heater, the endless belt, and the rotating body. The upstream rubber pad and the upstream rubber pad are arranged on the downstream side of the upstream nip portion in the moving direction of the endless belt, and the endless belt is sandwiched between the upstream rubber pad and the rotating body to form a downstream nip portion. An upstream guide having a rubber pad, a holder for holding the upstream rubber pad and the downstream rubber pad, and a guide surface for guiding the inner peripheral surface of the endless belt on the upstream side of the upstream rubber pad in the moving direction, the rotating body and the rotating body and the above. It includes an urging member that urges one of the holders toward the other along a predetermined direction.
The upstream rubber pad is located on the rotating body side and has a facing surface facing the inner peripheral surface of the endless belt.
The upstream end of the facing surface in the moving direction is farther from the rotation center of the rotating body than the downstream end of the guide surface in the moving direction in the predetermined direction.
The facing surface is located on the upstream portion including the upstream end and does not sandwich the endless belt with the rotating body, and on the downstream side in the moving direction with respect to the upstream portion, and the rotation. It has a downstream portion that sandwiches the endless belt with the body and forms the upstream nip portion.

According to this configuration, the upstream end of the upstream rubber pad is farther from the center of rotation than the downstream end of the guide surface, and an upstream nip portion is formed between the downstream portion of the upstream rubber pad and the rotating body. Unintentional deformation of the upstream rubber pad can be suppressed, and fluctuations in the nip width can be suppressed. Further, since the upstream nip portion is formed by using only a part (downstream portion) of the upstream rubber pad, the durability of the rubber pad can be improved as compared with the case where the entire upstream rubber pad is used. Further, by forming the downstream nip portion with the downstream rubber pad, as compared with the case where the downstream nip portion is formed by using a hard member such as resin as the pad, the shape of the pad does not need to be processed with high accuracy. An appropriate nip pressure can be obtained.

Further, the downstream rubber pad has a facing surface that is located on the rotating body side and faces the inner peripheral surface of the endless belt, and the facing surface of the downstream rubber pad is the endless belt with the rotating body. An upstream portion that forms the downstream nip portion with the above portion sandwiched between the two, and a downstream portion that is located on the downstream side in the moving direction with respect to the upstream portion and does not sandwich the endless belt with the rotating body. You may have.

Further, when the rotating body is separated from the endless belt, the downstream portion of the upstream rubber pad is arranged at a position closer to the rotation center of the rotating body than the upstream portion of the downstream rubber pad in the predetermined direction. It may have been.

According to this, when the rotating body and each rubber pad are pressed against each other, the downstream portion of the upstream rubber pad can be crushed before the upstream portion of the downstream rubber pad, so that the upstream nip portion can be stably formed. it can.

Further, the upstream rubber pad may be separated from the downstream rubber pad in the moving direction.

According to this, the nip width can be widened without increasing the size of the pad. In addition, each rubber pad is not easily affected by each other's heat.

Further, the upstream guide may be separated from the upstream rubber pad in the moving direction.

According to this, it is possible to suppress the heat of the upstream rubber pad from being transferred to the upstream guide.

Further, the fixing device further includes a downstream guide that guides the inner peripheral surface of the endless belt on the downstream side of the downstream rubber pad in the moving direction, and the downstream guide is separated from the downstream rubber pad in the moving direction. You may be.

According to this, it is possible to suppress the heat of the downstream rubber pad from being transferred to the downstream guide.

Further, in the predetermined direction, the downstream guide may be farther from the rotation center of the rotating body than the downstream rubber pad.

According to this, it is possible to prevent the endless belt that has passed through the downstream rubber pad from being caught by the downstream guide and being worn.

Further, the holder has an upstream support surface that supports the upstream rubber pad and a downstream support surface that supports the downstream rubber pad, and has the upstream support surface and the downstream support surface in a cross section orthogonal to the width direction of the endless belt. The downstream support surface may be perpendicular to the predetermined direction.

According to this, for example, compared to a structure in which the support surface of the downstream pad is slanted with respect to the support surface of the upstream pad and substantially the entire surface of each pad is pressed against the rotating body, the tangent line of the rotating body at the downstream end of the downstream nip portion Since the angle between the surface of the downstream rubber pad and the surface of the downstream rubber pad on the rotating body side is increased, the peelability of the sheet passing through the downstream nip portion from the rotating body can be improved.

Further, when viewed from the moving direction, the upstream support surface and the downstream support surface may be arranged at a position where the center in the width direction is closer to the rotating body than the end portion.

According to this, it is possible to prevent the nip pressure at the center in the width direction from becoming too low.

Further, the fixing device further includes a stay that transmits the force of the urging member to the holder, and the distance from the stay to the downstream rubber pad in the moving direction is larger than the distance from the stay to the upstream rubber pad. May be small.

According to this, since the stay that receives the force from the urging member is arranged near the downstream rubber pad, the nip pressure of the downstream nip portion can be set to an appropriate pressure.

Further, the upstream guide includes an outer peripheral wall having the guide surface and ribs protruding from a surface of the outer peripheral wall opposite to the guide surface, and a downstream end portion of the outer peripheral wall in the moving direction is provided. , May project to the downstream side in the moving direction from the rib.

According to this, for example, as compared with a structure in which the downstream end of the outer peripheral wall does not protrude downstream from the rib, the downstream end of the outer peripheral wall can be made less likely to hit the endless belt, so that the endless belt is the downstream end of the outer peripheral wall. It is possible to suppress the strong pressing against the portion, and it is possible to suppress the wear of the endless belt.

Further, the downstream end portion of the outer peripheral wall has an inner surface facing the holder side in the predetermined direction, and the inner surface is the upstream end of the facing surface of the upstream rubber pad in the predetermined direction. It may be away from the center of rotation of the rotating body.

According to the present invention, it is possible to prevent the upstream rubber pad from being deformed into an unintended shape by the endless belt.

It is sectional drawing of the image forming apparatus provided with the fixing apparatus which concerns on embodiment. It is sectional drawing of the fixing device. It is an enlarged cross-sectional view around the nip part, and is the figure which shows the state which the pressurizing unit is located at the pressure contact position. It is an enlarged cross-sectional view around the nip part, and is the figure which shows the state which the pressurizing unit is located at the nip release position. It is a figure which shows that each support surface and stay of a holder have a mid-convex shape. It is sectional drawing (a), (b) which shows the modification of the upstream guide. It is a perspective view which shows the upstream guide of FIG.

Hereinafter, an embodiment of the invention will be described in detail with reference to the drawings as appropriate.
As shown in FIG. 1, the fixing device 8 according to the embodiment is used in an image forming device 1 such as a laser printer. The image forming apparatus 1 includes a main body housing 2, a sheet supply unit 3, an exposure apparatus 4, a developer image forming unit 5, and a fixing device 8.

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

The exposure device 4 is arranged in the upper part of the main body housing 2 and includes a light source device (not shown), a polygon mirror shown by omitting a reference numeral, a lens, a reflector, and the like. The exposure apparatus 4 exposes the surface of the photoconductor drum 61 by scanning a light beam (see one-point chain line) based on image data emitted from the light source device on the surface of the photoconductor drum 61 at high speed.

The developer image forming unit 5 is arranged below the exposure apparatus 4. The developer image forming unit 5 is configured as a process cartridge, and is removable from the main body housing 2 through an opening formed when the front cover 21 provided at the front portion of the main body housing 2 is opened. The developer image forming unit 5 includes a photoconductor drum 61, a charger 62, a transfer roller 63, a developing roller 64, a supply roller 65, and a developer accommodating unit 66 accommodating a developer composed of dry toner. I have.

The developer image forming unit 5 uniformly charges the surface of the photoconductor drum 61 by the charger 62. After that, the surface of the photoconductor drum 61 is exposed by the light beam from the exposure apparatus 4, so that an electrostatic latent image based on the image data is formed on the surface. Further, the developer image forming unit 5 supplies the developer in the developer accommodating unit 66 to the developing roller 64 via the supply roller 65.

Then, the developer image forming unit 5 supplies the developer on the developing roller 64 to the electrostatic latent image formed on the photoconductor drum 61. As a result, the electrostatic latent image is visualized, and a developer image is formed on the photoconductor drum 61. After that, the developer image forming unit 5 conveys the sheet S supplied from the sheet supply unit 3 between the photoconductor drum 61 and the transfer roller 63, so that the developer image on the photoconductor drum 61 is transferred to the sheet S. Transfer.

The fixing device 8 is arranged behind the developer image forming unit 5. Details of the fixing device 8 will be described later. The fixing device 8 heat-fixes the developer image to the sheet S by passing the sheet S on which the developer image is transferred. The image forming apparatus 1 discharges the sheet S on which the developer image is heat-fixed onto the paper discharge tray 22 outside the main body housing 2 by the transport roller 23 and the discharge roller 24.

As shown in FIG. 2, the fixing device 8 includes a heating unit 81, a pressurizing unit 82, and an urging member SP. The pressurizing unit 82 is urged toward the heating unit 81 by the urging member SP along a predetermined direction. The predetermined direction is a direction orthogonal to the width direction and the moving direction described later, and is a direction in which the heating unit 81 and the pressurizing unit 82 face each other.

In the present embodiment, the urging member SP is simply illustrated as a compression coil spring, but the present invention is not limited thereto. For example, the urging member may be a tension coil spring that pulls the end of an arm that is rotatably supported by the frame of the fixing device 8. In this case, the tension coil spring urges the pressurizing unit 82 toward the heating unit 81 via the arm.

The heating unit 81 includes a heater 110 and a rotating body 120. Further, the pressurizing unit 82 includes an endless belt 130, an upstream rubber pad P1, a downstream rubber pad P2, a holder 140, a stay 150, an upstream guide 160, a downstream guide 170, and a sliding sheet 180. .. In the following description, the width direction of the endless belt 130 is simply referred to as the "width direction". The width direction is the direction in which the rotation axis of the rotating body 120 extends.

Here, in the present embodiment, it is assumed that the holder 140, the upstream guide 160, and the downstream guide 170 are assembled to the stay 150. The present invention is not limited to this, and both ends of the holder 140, the stay 150, the upstream guide 160, and the downstream guide 170 in the width direction may be supported by side guides (not shown).

The heater 110 is a halogen lamp, which emits light when energized and generates heat, and heats the rotating body 120 by radiant heat. The heater 110 is arranged so as to pass inside the rotating body 120 along the rotation axis of the rotating body 120.

The rotating body 120 is a cylindrical roller long in the width direction, and is heated by the heater 110. The rotating body 120 has a raw tube 121 made of metal or the like, and an elastic layer 122 that covers the outer peripheral surface of the raw tube 121. The elastic layer 122 is made of rubber such as silicon rubber. In the present embodiment, the rotating body 120 has a concave shape in which the outer diameters at both ends in the width direction are larger than the outer diameter at the center in the width direction, and the outer diameter gradually increases from the center in the width direction toward both ends. have. However, the shape of the rotating body is not limited to this. The rotating body may have, for example, a cylindrical shape having a uniform outer diameter in the width direction. Further, the rotating body may have a crown shape in which the outer diameter gradually decreases from the center in the width direction toward both ends.

The rotating body 120 is rotatably supported by a frame (not shown) of the fixing device 8, and rotates counterclockwise in FIG. 2 when a driving force is input from a motor (not shown) provided in the main body housing 2. Drive.

The endless belt 130 is a long tubular member and has flexibility. Although not shown, the endless belt 130 has a base material made of metal, resin, or the like, and a release layer that covers the outer peripheral surface of the base material. When the rotating body 120 rotates, the endless belt 130 is driven and rotated clockwise in FIG. 2 due to friction with the rotating body 120 or the seat S. A lubricant such as grease is applied to the inner peripheral surface of the endless belt 130. An upstream rubber pad P1, a downstream rubber pad P2, a holder 140, a stay 150, an upstream guide 160, a downstream guide 170, and a sliding sheet 180 are arranged inside the endless belt 130.

The upstream rubber pad P1 is a rectangular parallelepiped member long in the width direction. The upstream rubber pad P1 is made of rubber such as silicon rubber. The upstream rubber pad P1 forms an upstream nip portion NP1 with an endless belt 130 sandwiched between the upstream rubber pad P1 and the rotating body 120.

In the following description, the moving direction of the endless belt 130 in the upstream nip portion NP1 is simply referred to as "moving direction". In the present embodiment, the moving direction is a direction along the outer peripheral surface of the rotating body 120, but since this direction is a direction substantially orthogonal to the predetermined direction and the width direction, the moving direction is the predetermined direction. It is shown as a direction orthogonal to the width direction. The moving direction is the same as the transporting direction of the sheet S at the nip portion NP.

The downstream rubber pad P2 is a rectangular parallelepiped member long in the width direction. The downstream rubber pad P2 is made of rubber such as silicon rubber. The downstream rubber pad P2 forms the downstream nip portion NP2 with the endless belt 130 sandwiched between the downstream rubber pad P2 and the rotating body 120.

The downstream rubber pad P2 is arranged on the downstream side in the moving direction with respect to the upstream rubber pad P1. The downstream rubber pad P2 is separated from the upstream rubber pad P1 in the moving direction.

Therefore, between the upstream nip portion NP1 and the downstream nip portion NP2, there is an intermediate nip portion NP3 in which the pressure from the pressurizing unit 82 does not directly act. In this intermediate nip portion NP3, although the endless belt 130 comes into contact with the rotating body 120, almost no pressure is applied because there is no member sandwiching the endless belt 130 with the rotating body 120. Therefore, the sheet S passes through the intermediate nip portion NP3 while being heated by the rotating body 120 and being substantially not pressurized. In the present embodiment, the region from the upstream end of the upstream nip portion NP1 to the downstream end of the downstream nip portion NP2, that is, the entire region where the outer peripheral surface of the endless belt 130 and the rotating body 120 come into contact with each other is referred to as a nip portion NP. That is, in the present embodiment, the nip portion NP includes a portion to which the pressing force from the upstream rubber pad P1 and the downstream rubber pad P2 is not applied.

The hardness of the upstream rubber pad P1 is larger than the hardness of the elastic layer 122 of the rotating body 120. Further, the hardness of the downstream rubber pad P2 is larger than the hardness of the upstream rubber pad P1.

Here, the hardness is the durometer hardness defined in ISO7619-1. The durometer hardness is a value obtained from the pressing depth of the pressing needle when the specified pressing needle is pressed into the test piece under the specified conditions. For example, when the durometer hardness of the elastic layer 122 is 5, the durometer hardness of the upstream rubber pad P1 is preferably 6 to 10, and the durometer hardness of the downstream rubber pad P2 is preferably 70 to 90.

The hardness of the silicon rubber can be adjusted by changing the ratio of the additives (silica-based filler and carbon-based filler) added at the time of production. Specifically, the hardness of the rubber increases as the ratio of the additives increases. Further, the hardness can be reduced by adding a silicone-based oil. As a rubber manufacturing method, liquid injection molding or extrusion molding can be adopted. In general, low-hardness rubber is suitable for liquid injection molding, and high-hardness rubber is suitable for extrusion molding.

The upstream guide 160 has a guide surface Fg that guides the inner peripheral surface 131 of the endless belt 130 on the upstream side of the upstream rubber pad P1 in the moving direction. The upstream guide 160 is separated from the upstream rubber pad P1 in the moving direction. The upstream guide 160 is made of a heat-resistant resin or the like.

The downstream guide 170 is a member that guides the inner peripheral surface 131 of the endless belt 130 on the downstream side of the downstream rubber pad P2 in the moving direction. The downstream guide 170 is separated from the downstream rubber pad P2 in the moving direction. The downstream guide 170 is separated from the rotation center X1 of the rotating body 120 by the downstream rubber pad P2 in a predetermined direction. More specifically, the upstream end Ed in the moving direction of the guide surface Fd of the downstream guide 170 that guides the inner peripheral surface 131 of the endless belt 130 is the rotating body 120 in a predetermined direction rather than the facing surface Fp2 of the downstream rubber pad P2 described later. It is arranged at a position farther than the rotation center X1. The downstream guide 170 is made of a heat-resistant resin or the like.

The sliding sheet 180 is a rectangular sheet for reducing the frictional resistance between the rubber pads P1 and P2 and the endless belt 130. The sliding sheet 180 is sandwiched between the inner peripheral surface 131 of the endless belt 130 and the rubber pads P1 and P2. One end of the sliding sheet 180 is fixed to the inner wall surface of the upstream guide 160. The inner wall surface is a surface opposite to the guide surface Fg of the upstream guide 160, and is a surface away from the inner peripheral surface 131 of the endless belt 130 than the guide surface Fg. The sliding sheet 180 is wound so as to cover the guide surface Fg of the upstream guide 160, and the other end is arranged between the downstream guide 170 and the inner peripheral surface 131 of the endless belt 130.

In the present embodiment, the other end of the sliding sheet 180 is free, but the present invention is not limited to this, and the other end may be fixed to the downstream guide 170. The material of the sliding sheet 180 may be any material, but in the present embodiment, a resin sheet containing polyimide is used.

The holder 140 is a member that holds the upstream rubber pad P1 and the downstream rubber pad P2, and is made of a heat-resistant resin or the like. The holder 140 is formed long in the width direction. The holder 140 has a support wall 141, an upstream wall 142, a central wall 143, and a downstream wall 144.

The support wall 141 has an upstream support surface F1 that supports the upstream rubber pad P1 and a downstream support surface F2 that supports the downstream rubber pad P2. In the cross section orthogonal to the width direction, the upstream support surface F1 and the downstream support surface F2 are perpendicular to a predetermined direction. The upstream support surface F1 and the downstream support surface F2 are arranged at the same position in a predetermined direction.

The upstream wall 142, the central wall 143, and the downstream wall 144 project from the support wall 141 toward the rotating body 120. The upstream wall 142 is arranged at the upstream end of the support wall 141.

The downstream wall 144 is arranged at the downstream end of the support wall 141. The central wall 143 is arranged between the upstream wall 142 and the downstream wall 144 and away from the upstream wall 142 and the downstream wall 144 in the moving direction.

The upstream support surface F1 described above is arranged between the upstream wall 142 and the central wall 143. Further, the downstream support surface F2 described above is arranged between the central wall 143 and the downstream wall 144.

The upstream rubber pad P1 is in contact with the upstream wall 142 and is arranged at a position away from the central wall 143. The downstream rubber pad P2 is in contact with the downstream wall 144 and is arranged at a position away from the central wall 143.

The stay 150 is a member that transmits the force of the urging member SP to the holder 140. The stay 150 is made of metal or the like. The stay 150 is formed long in the width direction. The stay 150 has a contact surface Ft that contacts the surface F3 on the side opposite to the support surfaces F1 and F2 of the support wall 141.

The stay 150 is arranged at a position closer to the downstream rubber pad P2 in the moving direction. Specifically, as shown in FIG. 4, the distance D2 from the stay 150 to the downstream rubber pad P2 is smaller than the distance D1 from the stay 150 to the upstream rubber pad P1 in the moving direction. Specifically, the distance D2 from the center of the stay 150 in the moving direction of the contact surface Ft to the upstream end of the downstream rubber pad P2 in the moving direction is from the center of the contact surface Ft in the moving direction to the downstream end of the upstream rubber pad P1 in the moving direction. It is smaller than the distance D1. In the present embodiment, the stay 150 is arranged so that the stay 150 projected in a predetermined direction overlaps with the downstream rubber pad P2.

As shown in FIG. 5, the contact surface Ft of the stay 150 has an arcuate cross-sectional view (middle convex) so that the center in the width direction is arranged closer to the rotating body 120 than the end when viewed from the moving direction. Shape) is formed. Further, urging members SP are arranged at both ends of the stay 150 in the width direction.

When both ends of the stay 150 are urged toward the rotating body 120 by each urging member SP, the central portion of the stay 150 in the width direction receives a reaction force from the rotating body 120 and separates from the rotating body 120. Deforms in the direction. In this case, if the contact surface Ft of the stay 150 is flat, the nip pressure at the center in the width direction may become too low. However, since the contact surface Ft is formed in the mid-convex shape as described above, it is possible to prevent the nip pressure at the center in the width direction from becoming too low.

In a state where both ends of the stay 150 are urged toward the rotating body 120 by each urging member SP, the support wall 141 of the holder 140 is deformed so as to follow the contact surface Ft of the stay 150. Therefore, in this state, the upstream support surface F1 and the downstream support surface F2 of the support wall 141 are arranged at positions where the center in the width direction is closer to the rotating body 120 than the end portion when viewed from the moving direction.

As shown in FIGS. 3 and 4, the upstream rubber pad P1 has a facing surface Fp1 located on the rotating body 120 side and facing the inner peripheral surface 131 of the endless belt 130. Specifically, the facing surface Fp1 faces the inner peripheral surface 131 of the endless belt 130 via the sliding sheet 180.

The upstream end Ep of the facing surface Fp1 in the moving direction is farther from the rotation center X1 of the rotating body 120 than the downstream end Eg of the guide surface Fg of the upstream guide 160 in the moving direction in a predetermined direction. In other words, when the pressurizing unit 82 is located at the pressure contact position shown in FIG. 3, the distance Dp from the rotation center X1 to the upstream end Ep of the upstream rubber pad P1 in a predetermined direction is the downstream end of the upstream guide 160 from the rotation center X1. The distance to Eg is greater than Dg. Further, even when the pressurizing unit 82 is located at the nip release position shown in FIG. 4, the distance Ds from the rotation center X1 to the upstream end Ep of the upstream rubber pad P1 is the distance Ds from the rotation center X1 to the upstream guide 160 in a predetermined direction. It is larger than the distance Dg to the downstream end Eg.

The facing surface Fp1 has an upstream portion Fp11 and a downstream portion Fp12.
The upstream portion Fp11 is a portion including the upstream end Ep of the facing surface Fp1. The upstream portion Fp11 is separated from the sliding sheet 180. That is, the upstream portion Fp11 does not sandwich the endless belt 130 and the sliding sheet 180 with the rotating body 120.

The downstream portion Fp12 is located on the downstream side in the moving direction with respect to the upstream portion Fp11. The downstream portion Fp12 forms an upstream nip portion NP1 with an endless belt 130 and a sliding sheet 180 sandwiched between the downstream portion Fp12 and the rotating body 120.
The upper surface of the upstream wall 142 of the holder 140 is separated from the rotation center X1 in a predetermined direction from the downstream end Eg of the upstream guide 160 and the facing surface Fp1 of the upstream rubber pad P1. As a result, the upstream guide 160 moves from the upstream rubber pad P1 in the moving direction with an interval equal to or larger than the thickness of the upstream wall 142 in the moving direction, at least in a state where no force is applied to the rubber pads P1 and P2 (state in FIG. Placed apart in.

The downstream rubber pad P2 has an opposing surface Fp2 located on the rotating body 120 side and facing the inner peripheral surface 131 of the endless belt 130. Specifically, the facing surface Fp2 faces the inner peripheral surface 131 of the endless belt 130 via the sliding sheet 180.

The facing surface Fp2 has an upstream portion Fp21 and a downstream portion Fp22. The upstream portion Fp21 is a portion including the upstream end of the facing surface Fp2. The upstream portion Fp21 forms a downstream nip portion NP2 with an endless belt 130 and a sliding sheet 180 sandwiched between the upstream portion Fp21 and the rotating body 120.

The downstream portion Fp22 is located on the downstream side in the moving direction with respect to the upstream portion Fp21. The downstream portion Fp22 is separated from the sliding sheet 180. That is, the downstream portion Fp22 does not sandwich the endless belt 130 and the sliding sheet 180 with the rotating body 120.
The upper surface of the downstream wall 144 of the holder 140 is separated from the rotation center X1 in a predetermined direction from the upstream end Ed in the moving direction of the guide surface Fd of the downstream guide 170 and the facing surface Fp2 of the downstream rubber pad P2. As a result, the downstream guide 170 moves from the downstream rubber pad P2 in the moving direction with a distance equal to or larger than the thickness of the downstream wall 144 in the moving direction at least in a state where no force is applied to the rubber pads P1 and P2 (state in FIG. 4). Placed apart in.

As shown in FIG. 4, when the rotating body 120 is separated from the endless belt 130, that is, when no force is applied to the rubber pads P1 and P2, the size of the upstream rubber pad P1 in a predetermined direction is the size of the downstream rubber pad P2. It is larger than the size in the predetermined direction. As a result, when the rotating body 120 is separated from the endless belt 130, the downstream portion Fp12 of the upstream rubber pad P1 is arranged at a position closer to the rotation center X1 of the rotating body 120 than the upstream portion Fp21 of the downstream rubber pad P2 in a predetermined direction. Has been done.

The pressurizing unit 82 can be moved between the pressure contact position shown in FIG. 3 and the nip release position shown in FIG. 4 by a cam (not shown) and the urging member SP. Here, for example, the cam may be arranged at a position where both ends of the stay 150 in the width direction can be pressed against the urging force of the urging member SP.

Next, the operation and effect of the fixing device 8 according to the present embodiment will be described.
When the pressurizing unit 82 is moved from the nip release position shown in FIG. 4 to the pressure contact position shown in FIG. 3, the downstream portion Fp12 of the upstream rubber pad P1 is crushed more than the upstream portion Fp21 of the downstream rubber pad P2. As a result, the upstream nip portion NP1 can be stably formed between the downstream portion Fp12 of the upstream rubber pad P1 and the rotating body 120.

As shown in FIG. 2, when the fixing device 8 is driven, the rotating body 120 rotates counterclockwise as shown, and the endless belt 130 rotates clockwise as shown. At this time, the upstream end Ep of the upstream rubber pad P1 is farther from the rotation center X1 than the downstream end Eg of the guide surface Fg of the upstream guide 160, and the endless belt 130 is located between the upstream end Ep of the upstream rubber pad P1 and the rotating body 120. Etc. are not sandwiched, so that the endless belt 130 does not push the upstream end Ep of the upstream rubber pad P1 via the sliding sheet 180. As a result, it is possible to prevent the upstream rubber pad P1 from being deformed into an unintended shape.

Based on the above, the following effects can be obtained in the present embodiment.
Since it is possible to prevent the upstream rubber pad P1 from being deformed into an unintended shape, it is possible to prevent the nip width (length in the moving direction) of the nip portion NP from fluctuating. Further, since the upstream nip portion NP1 is formed by using only a part of the upstream rubber pad P1 (downstream portion Fp12), the durability of the upstream rubber pad P1 can be improved as compared with the case where the entire upstream rubber pad P1 is used, for example. Further, by forming the downstream nip portion NP2 with the downstream rubber pad P2, the shape of the pad does not need to be processed with high accuracy as compared with the case where the downstream nip portion is formed by using a hard member such as resin as a pad. However, an appropriate nip pressure can be obtained.

When the rotating body 120 and the rubber pads P1 and P2 are pressed against each other, the downstream portion Fp12 of the upstream rubber pad P1 can be crushed before the upstream portion Fp21 of the downstream rubber pad P2, so that the upstream nip portion NP1 can be stably crushed. Can be formed.

Since the upstream rubber pad P1 is separated from the downstream rubber pad P2 in the moving direction, the nip width of the nip portion NP can be widened without increasing the pad size. Further, the rubber pads P1 and P2 are not easily affected by each other's heat.

Since the upstream guide 160 is separated from the upstream rubber pad P1 in the moving direction, it is possible to suppress the heat of the upstream rubber pad P1 from being transferred to the upstream guide 160.

Since the downstream guide 170 is separated from the downstream rubber pad P2 in the moving direction, it is possible to suppress the heat of the downstream rubber pad P2 from being transferred to the downstream guide 170.

Since the downstream guide 170 is farther from the rotation center X1 of the rotating body 120 than the downstream rubber pad P2 in the predetermined direction, it is possible to prevent the endless belt 130 passing through the downstream rubber pad P2 from being caught by the downstream guide 170 and being worn. be able to.

Since the upstream support surface F1 and the downstream support surface F2 are perpendicular to the predetermined direction in the cross section orthogonal to the width direction, for example, the support surface of the downstream pad is slanted with respect to the support surface of the upstream pad, and each pad The angle formed by the tangent line of the rotating body 120 at the downstream end of the downstream nip portion NP2 and the facing surface Fp2 of the downstream rubber pad P2 is larger than that of the structure in which substantially the entire surface of the above is pressed against the rotating body. Therefore, the peelability of the sheet S that has passed through the downstream nip portion NP2 from the rotating body 120 can be improved.

When viewed from the moving direction, the center of the upstream support surface F1 and the downstream support surface F2 in the width direction is arranged at a position closer to the rotating body 120 than the end portion, so that the nip pressure at the center in the width direction becomes too low. It can be suppressed.

Since the stay 150 that receives the force from the urging member SP is arranged closer to the downstream rubber pad P2, the nip pressure of the downstream nip portion NP2 can be set to an appropriate pressure.

The present invention is not limited to the above embodiment, and can be used in various forms as illustrated below. In the following description, members having substantially the same structure as that of the above embodiment are designated by the same reference numerals, and the description thereof will be omitted.

The upstream guide is not limited to the shape as in the above embodiment, and may have any shape. For example, an upstream guide 260 having a shape as shown in FIG. 6A may be adopted. Specifically, the upstream guide 260 according to this embodiment includes an outer peripheral wall 261 and ribs 262. The outer peripheral wall 261 has a guide surface Fg similar to that of the above embodiment. Further, the outer peripheral wall 261 has an inner peripheral surface Fb which is a surface opposite to the guide surface Fg.

As shown in FIG. 7, the rib 262 protrudes from the inner peripheral surface Fb of the outer peripheral wall 261. A plurality of ribs 262 are provided at intervals in the width direction.

Returning to FIG. 6A, the downstream end portion 261A of the outer peripheral wall 261 in the moving direction projects to the downstream side in the moving direction with respect to the rib 262. In other words, the outer peripheral wall 261 has a base portion 261B formed from the upstream end to the downstream end of the rib 262 in the rotation direction of the endless belt 130, and a downstream end portion 261A protruding downstream from the rib 262. ing.

As shown in FIG. 6B, the thickness T1 of the downstream end portion 261A is smaller than the thickness T2 of the base portion 261B and smaller than the thickness T2 of the base portion 261B in this embodiment. The downstream end portion 261A has a tapered shape in which the thickness gradually decreases toward the downstream side in the moving direction.

The downstream end portion 261A has an outer surface Fo facing the heater 110 side and an inner surface Fi facing the holder 140 side in a predetermined direction. The outer surface Fo is formed in a substantially arc shape in cross-sectional view, and is connected to the downstream end of the inner surface Fi in the moving direction.

The inner surface Fi is formed in a plane shape that is substantially perpendicular to a predetermined direction. The inner surface Fi is separated from the rotation center X1 of the rotating body 120 from the upstream end Ep of the facing surface Fp1 of the upstream rubber pad P1 in a predetermined direction.

According to this form, for example, as compared with a structure in which the downstream end of the outer peripheral wall does not protrude downstream from the rib, the tapered downstream end 261A can be made less likely to come into contact with the sliding sheet 180. The wear of 180 can be suppressed.
The sliding sheet 180 may not be used, but in that case as well, the tapered downstream end portion 261A can be made difficult to hit the endless belt 130. Therefore, it is possible to prevent the endless belt 130 from being strongly pressed against the tapered downstream end portion 261A, and it is possible to suppress the wear of the endless belt 130.

In the above embodiment, the holder 140 is urged toward the rotating body 120 by the urging member SP, but the present invention is not limited to this, and the rotating body is urged toward the holder by the urging member. May be good. Further, the urging member SP is not limited to the compression coil spring, and may be, for example, a tension coil spring, a leaf spring, a torsion spring, or the like.

In the above embodiment, the halogen lamp is exemplified as the heater, but the heater may be, for example, a carbon heater.

In the above embodiment, a cylindrical roller having a built-in heater 110 is exemplified as a rotating body, but the present invention is not limited to this, and for example, an endless belt in which the inner peripheral surface is heated by the heater. May be good. Further, an external heating method in which the heater is arranged outside the rotating body to heat the outer peripheral surface of the rotating body, or an IH (Induction Heating) method may be used. Further, a heater may be arranged inside the endless belt to indirectly heat the rotating body in contact with the outer peripheral surface of the endless belt. Further, the rotating body and the endless belt may each have a built-in heater.

Each element described in the above-described embodiment and modification may be arbitrarily combined and implemented.

8 Fixing device 110 Heater 120 Rotating body 130 Endless belt 131 Inner peripheral surface 140 Holder 160 Upstream guide Eg Downstream end Ep Upstream end Fg Guide surface Fp1 Opposing surface Fp11 Upstream part Fp12 Downstream part NP1 Upstream nip part NP2 Downstream nip part P2 Upstream rubber pad Downstream rubber pad SP urging member X1 rotation center

Claims (12)

With a heater
The rotating body heated by the heater and
With an endless belt,
An upstream rubber pad that forms an upstream nip portion with the endless belt sandwiched between the rotating body and the rotating body.
A downstream rubber pad that is arranged on the downstream side of the upstream nip portion in the moving direction of the endless belt with respect to the upstream rubber pad and forms a downstream nip portion with the endless belt sandwiched between the upstream rubber pad and the rotating body.
A holder that holds the upstream rubber pad and the downstream rubber pad,
An upstream guide having a guide surface for guiding the inner peripheral surface of the endless belt on the upstream side of the upstream rubber pad in the moving direction,
A urging member that urges one of the rotating body and the holder toward the other along a predetermined direction is provided.
The upstream rubber pad has a facing surface that is located on the rotating body side and faces the inner peripheral surface of the endless belt.
The upstream end of the facing surface in the moving direction is farther from the rotation center of the rotating body than the downstream end of the guide surface in the moving direction in the predetermined direction.
The facing surface is
An upstream portion that includes the upstream end and does not sandwich the endless belt with the rotating body.
Fixing characterized by having a downstream portion located on the downstream side in the moving direction with respect to the upstream portion and forming the upstream nip portion with the endless belt sandwiched between the rotating body and the rotating body. apparatus. The downstream rubber pad has a facing surface that is located on the rotating body side and faces the inner peripheral surface of the endless belt.
The facing surface of the downstream rubber pad is
An upstream portion that sandwiches the endless belt with the rotating body to form the downstream nip portion, and an upstream portion.
The fixing device according to claim 1, further comprising a downstream portion located on the downstream side in the moving direction with respect to the upstream portion and not sandwiching the endless belt with the rotating body. .. When the rotating body is separated from the endless belt, the downstream portion of the upstream rubber pad is closer to the rotation center of the rotating body than the upstream portion of the downstream rubber pad in the predetermined direction. The fixing device according to claim 2. The fixing device according to any one of claims 1 to 3, wherein the upstream rubber pad is separated from the downstream rubber pad in the moving direction. The fixing device according to any one of claims 1 to 4, wherein the upstream guide is separated from the upstream rubber pad in the moving direction. A downstream guide for guiding the inner peripheral surface of the endless belt on the downstream side of the downstream rubber pad in the moving direction is further provided.
The fixing device according to any one of claims 1 to 5, wherein the downstream guide is separated from the downstream rubber pad in the moving direction. The fixing device according to claim 6, wherein the downstream guide is farther from the rotation center of the rotating body than the downstream rubber pad in the predetermined direction. The holder has an upstream support surface that supports the upstream rubber pad and a downstream support surface that supports the downstream rubber pad.
The aspect according to any one of claims 1 to 7, wherein the upstream support surface and the downstream support surface are perpendicular to the predetermined direction in a cross section orthogonal to the width direction of the endless belt. The fixing device described. The fixing device according to claim 8, wherein the upstream support surface and the downstream support surface are closer to the rotating body at the center in the width direction than at the end when viewed from the moving direction. Further provided with a stay for transmitting the force of the urging member to the holder.
The fixing device according to any one of claims 1 to 9, wherein the distance from the stay to the downstream rubber pad in the moving direction is smaller than the distance from the stay to the upstream rubber pad. .. The upstream guide
The outer peripheral wall having the guide surface and
The outer peripheral wall is provided with ribs protruding from a surface opposite to the guide surface.
The fixing device according to any one of claims 1 to 10, wherein the downstream end portion of the outer peripheral wall in the moving direction protrudes toward the downstream side in the moving direction from the rib. The downstream end of the outer peripheral wall has an inner surface facing the holder side in the predetermined direction.
The fixing device according to claim 11, wherein the inner surface is separated from the rotation center of the rotating body by the upstream end of the facing surface of the upstream rubber pad in the predetermined direction.

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