JP6969323B2 - Fixing device and image forming device - Google Patents

Description

The present invention relates to a fixing device for fixing a developer on a recording medium and an image forming device for forming an image on a recording medium.

Conventionally, as a fixing device used in an image forming device, a fixing device using an endless belt is known. For example, in Patent Document 1, as a pressure belt type fixing device, a heating roller, a pressure pad for sandwiching an endless belt between the heating rollers, and a cam for pressing the pressure pad toward the heating roller are provided. Things are known.

Japanese Unexamined Patent Publication No. 2005-189746

However, in the prior art, since the reaction force of the pressing force applied to the cam from the pressure pad is supported only by the camshaft, the camshaft bends and the nip pressure at the center of the fixing nip in the rotation axis direction is higher than that at the end. It may become smaller.

Therefore, an object of the present invention is to prevent the nip pressure at the center in the rotation axis direction from becoming smaller than that at the end due to the reaction force applied to the cam from the pressurizing member such as the pressurizing pad or the nip forming member. ..

In order to solve the above problems, the fixing device according to the present invention is in contact with the heater, the facing member heated by the heater, the endless belt, and the inner peripheral surface of the endless belt, and is between the facing member. A pressurizing member that sandwiches the endless belt to form a nip portion, a cam member that presses the pressurizing member toward the facing member, and a cam member that sandwiches the cam member and is arranged on the opposite side of the pressurizing member. A stay that supports the cam member is provided.
The cam member includes a center cam that presses the central portion of the pressurizing member in the width direction of the endless belt toward the facing member, and a center cam having a smaller outer peripheral length than the center cam and the pressurizing member in the width direction. It has a side cam that presses the end portion thereof toward the facing member.
The center cam comes into contact with the stay.

According to this configuration, since the center cam comes into contact with the stay, it is suppressed that the nip pressure at the center of the nip portion in the rotation axis direction becomes smaller than the nip pressure at the end due to the reaction force applied to the cam member from the pressurizing member. can do.

Further, the center cam may be in constant contact with the stay regardless of the rotation angle of the cam member.

According to this, regardless of the rotation angle of the cam member, it is possible to prevent the nip pressure at the center of the nip portion in the rotation axis direction from becoming smaller than the nip pressure at the end portion.

Further, when the rotation angle of the cam member is the first angle, the side cam may come into contact with the stay.

According to this, when the cam member is at the first angle, the center cam and the side cam come into contact with the stay, so that it is possible to suppress the camshaft of the cam member from bending. Further, since the center cam and the side cam are supported by the stay, a strong pressing force can be applied to the entire width direction of the pressurizing member, and the nip pressure is satisfactorily applied to a relatively wide paper such as plain paper. Can be added.

Further, when the major axis of the center cam and the major axis of the side cam are equal to each other and the rotation angle of the cam member is the first angle, the major axis of the center cam and the major axis of the side cam are pressurized with the facing member. The members may be along opposite directions.

According to this, in a state where the pressing force of each cam is maximum, each cam is supported by the stay, so that the maximum pressing force can be satisfactorily generated.

Further, when the rotation angle of the cam member is the second angle, the side cam may be separated from the stay.

According to this, since the side cam is separated from the stay at the second angle, the pressing force applied to the end portion of the pressurizing member from the side cam can be reduced, and a high nip pressure distribution at the center can be obtained. Further, by separating the side cam from the stay, the drive torque of the cam member can be suppressed to a small size.

Further, the cam member has a cam shaft, and when the rotation angle of the cam member is the second angle, the center working radius is a dimension from the action point of the center cam to the rotation center of the cam shaft. Is the first dimension, and the side action radius, which is the length from the action point of the side cam to the rotation center, may be the second dimension smaller than the first dimension.

According to this, by making the side working radius smaller than the center working radius, the pressing force applied to the end of the pressurizing member from the side cam can be reduced, so that a high nip pressure distribution at the center can be obtained. .. Further, by reducing the pressing force applied to the end portion of the pressurizing member from the side cam, the driving torque of the cam member can be suppressed to a small size.

Further, when the rotation angle of the cam member is the third angle, the center working radius and the side working radius may have a third dimension smaller than the first dimension.

According to this, by making each radius of action smaller than the first dimension, for example, the nip pressure distribution having a high center can be lowered as a whole as compared with the case where the rotation angle of the cam member is the first angle. Therefore, good nip pressure can be applied to relatively thick paper such as thick paper and envelopes.

Further, the fixing device is located at the center of the endless belt in the width direction, is provided between the pressurizing member and the center cam, and urges the pressurizing member toward the facing member. A side having a center urging member, located at the end of the endless belt in the width direction, provided between the pressurizing member and the side cam, and urging the pressurizing member toward the facing member. Further including a urging member, the urging force of the side urging member may be smaller than the urging force of the center urging member.

According to this, by making the urging force of the side urging member smaller than the urging force of the center urging member, a high nip pressure distribution at the center can be obtained, so that relatively wide paper such as plain paper can be obtained. The nip pressure can be applied satisfactorily.

Further, the center urging member has a predetermined number of springs arranged in the width direction, and the center is more than the pitch of two springs arranged on one end side or the other end side in the width direction of the center cam. The pitch of the two springs arranged on the center side of the cam in the width direction may be smaller.

According to this, since the urging force can be increased at the center in the width direction of the center cam and the urging force can be decreased at both ends, a high nip pressure distribution at the center can be obtained even in the range of the center cam.

Further, the fixing device is sandwiched between the center urging member and the center cam, and the center moves in the opposite direction in which the facing member and the pressurizing member face each other in conjunction with the rotational operation of the cam member. A moving member and a side moving member sandwiched between the side urging member and the side cam and moving in the opposite direction in conjunction with the rotational operation of the cam member may be further provided.

According to this, since the cam member is in sliding contact with the moving member which is a member different from the urging member, the cam member can be smoothly rotated.

Further, the stay is located upstream of the cam member and extends toward the facing member in the moving direction of the endless belt in the nip portion, and is located downstream of the cam member. With a downstream side wall extending towards the opposing member,
The center moving member and the side moving member may be sandwiched between the upstream side wall and the downstream side wall.

According to this, since each moving member can be movably supported by the upstream side wall and the downstream side wall of the stay, for example, as compared with a structure in which the member that movably supports each moving member is a separate member from the stay. It is possible to suppress an increase in the number of parts.

Further, the center moving member and the side moving member each extend from the first wall to which the cam member slides and the upstream end of the first wall in the moving direction along the upstream side wall of the stay. It may have a wall and a third wall extending along the downstream side wall of the stay from the downstream end of the first wall in the moving direction.

According to this, since the second wall and the third wall of each moving member come into surface contact with the upstream side wall and the downstream side wall of the stay, the contact position between the cam member and each moving member is moved by the endless belt due to the rotation of the cam member. It is possible to suppress the change in the orientation of each first wall even if the first wall is displaced in the direction. Further, the movement of each moving member in the opposite direction can be satisfactorily guided by the stay.

Further, the center moving member and the side moving member may be configured to be rotatable around the upstream end portion in the moving direction of the endless belt in the nip portion, respectively.

According to this, for example, as compared with a structure in which each moving member moves in parallel in the facing direction, the amount of fluctuation in the nip pressure on the inlet side of the nip portion between the facing member and the pressurizing member can be reduced, so that the paper nips. It is possible to suppress printing distortion caused by slippage when plunging into the portion.

Further, the center urging member and the side urging member may each have a plurality of springs arranged in the moving direction of the endless belt in the nip portion.

Further, the cam member may have a camshaft, and the camshaft may be located upstream of the center of the pressurizing member in the moving direction of the endless belt in the nip portion.

Further, the side cams may be arranged one by one at positions corresponding to both ends of the pressurizing member in the width direction.

Further, the image forming apparatus according to the present invention is an image forming apparatus for forming an image on a recording medium, and is formed on an endless belt, an opposing member in contact with the outer peripheral surface of the endless belt, and an inner peripheral surface of the endless belt. A nip forming member that comes into contact and sandwiches the endless belt between the facing member, a cam member that presses the nip forming member toward the facing member, and a side opposite to the nip forming member that sandwiches the cam member. It is provided with a stay which is arranged in and supports the cam member.
The cam member includes a center cam that presses the central portion of the nip forming member in the width direction of the endless belt toward the facing member, and a center cam having a smaller outer peripheral length than the center cam and having the width direction of the nip forming member. Has a side cam that presses the end portion of the above-mentioned facing member toward the facing member.
The center cam comes into contact with the stay.

According to this configuration, since the center cam comes into contact with the stay, it is suppressed that the nip pressure at the center of the nip portion in the rotation axis direction becomes smaller than the nip pressure at the end due to the reaction force applied to the cam member from the nip forming member. can do.

According to the present invention, it is possible to prevent the nip pressure at the center in the rotation axis direction from becoming smaller than that at the end due to the reaction force applied to the cam from the pressure member such as the pressure pad or the nip forming member.

It is sectional drawing which shows the laser printer which concerns on one Embodiment of this invention. It is sectional drawing which shows the fixing device. It is an exploded perspective view which shows the pressurizing unit. It is sectional drawing which cut the fixing device by the plane orthogonal to the front-rear direction. It is a figure (a) which looked at the cam member from the width direction when the cam member is a 1st angle, and is the cross-sectional view (b) which shows the one end side in the width direction of a cam member enlarged. It is a figure (a) which looked at the cam member from the width direction when the cam member is a 2nd angle, and is the cross-sectional view (b) which shows the one end side in the width direction of a cam member enlarged. It is a figure (a) which looked at the cam member from the width direction when the cam member is a 3rd angle, and is the cross-sectional view (b) which shows the one end side in the width direction of a cam member enlarged. It is a figure (a) which looked at the cam member from the width direction when the cam member is a 4th angle, and is the cross-sectional view (b) which shows the one end side in the width direction of a cam member enlarged. It is a graph which shows the nip pressure distribution according to the angle of a cam member. It is a figure (a)-(c) which shows the modification of the moving member. It is a figure which shows the state when the cam member of FIG. 10 is a 4th angle. It is a figure (a)-(c) which shows the modification of the cam member. It is a figure which shows the state when the cam member of FIG. 12 is a 4th angle.

Next, an embodiment of the present invention will be described in detail with reference to the drawings as appropriate. In the following description, the direction is "front" when facing the paper in FIG. 1, "rear" when facing the paper, "left" when facing the paper, and front toward the paper. The side is "right". In addition, the vertical direction is defined as "up and down" toward the paper surface.

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

The paper feed unit 3 is provided in the lower part 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, and a paper feed mechanism 33. There is. The paper S housed in the paper feed tray 31 is moved upward by the paper pressing plate 32 and supplied to the process cartridge 5 by the paper feed mechanism 33.

The exposure device 4 is arranged in the upper part of the housing 2 and includes a light source device (not shown), a polygon mirror, a lens, a reflector, and the like, which are indicated by omitting reference numerals. In the exposure apparatus 4, the light beam based on the image data emitted from the light source apparatus is scanned at high speed on the surface of the photoconductor drum 61 to expose the surface of the photoconductor drum 61.

The process cartridge 5 is arranged below the exposure apparatus 4, and is removable from the housing 2 through an opening formed when the front cover 21 provided in 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 photoconductor drum 61, a charger 62, and a transfer roller 63. Further, the developing unit 7 is removable from the drum unit 6, and mainly includes a developing roller 71, a supply roller 72, a layer thickness regulating blade 73, and an accommodating portion 74 for accommodating toner. ..

In the process cartridge 5, the surface of the photoconductor drum 61 is uniformly charged by the charger 62 and then exposed by the light beam from the exposure apparatus 4, so that the surface of the photoconductor drum 61 is static electricity based on image data on the photoconductor drum 61. An electro-latent image is formed. Further, 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 blade 73, and enters the developing roller 71 as a thin layer having a constant thickness. Be carried. The toner supported on the developing roller 71 is supplied from the developing roller 71 to the electrostatic latent image formed on the photoconductor drum 61. As a result, the electrostatic latent image is visualized and a toner image is formed on the photoconductor drum 61. After that, the paper S is conveyed between the photoconductor drum 61 and the transfer roller 63, so that the toner image on the photoconductor drum 61 is transferred onto the paper S.

The fixing device 8 is arranged behind the process cartridge 5. The paper S on which the toner image is transferred passes through the fixing device 8 to fix the toner image. The paper S on which the toner image is fixed is discharged onto the paper output tray 22 by the transport rollers 23 and 24.

As shown in FIG. 2, the fixing device 8 includes a heating roller 81 as an example of the facing member, a heater 82, an endless belt 83, and a pressurizing unit 84. In the following description, the width direction of the endless belt 83 is also simply referred to as “width direction”, and the moving direction of the portion of the endless belt 83 that comes into contact with the heating roller 81 is also simply referred to as “moving direction”. The facing direction in which the pressurizing unit 84 (specifically, the pressurizing pad 85 described later) faces is also simply referred to as "opposing direction". In the present embodiment, the width direction is along the left-right direction, the movement direction is along the front-back direction, and the opposite direction is along the up-down direction.

The heating roller 81 is a cylindrical member, and as an example, it is configured by forming a mold release layer made of fluororesin or the like on the outer peripheral surface of a raw tube made of a metal such as aluminum. As shown in FIG. 4, the heating roller 81 is rotatably supported by the frame F of the fixing device 8, and the gear G1 is provided at the end thereof. The heating roller 81 is rotationally driven counterclockwise in FIG. 2 by inputting a driving force from the first motor M1 to the gear G1 at the end. The heating roller 81 is in contact with the outer peripheral surface of the endless belt 83.

The heater 82 is a heater that heats the heating roller 81, and is arranged inside 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 radiant heat can be used.

The endless belt 83 is a tubular member and has flexibility. As an example, the endless belt 83 is configured by forming a mold release layer made of 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 a polyimide resin. The endless belt 83 is provided so as to rotate clockwise in FIG. 2 by the rotation of the heating roller 81.

A lubricant such as grease is arranged on the inner peripheral surface 83A of the endless belt 83. As a result, the slidability between the inner peripheral surface 83A of the endless belt 83 and the pressure unit 84 can be improved, so that the endless belt 83 can be rotated satisfactorily.

As shown in FIG. 3, the pressure unit 84 mainly includes a pressure pad 85, a holder 86, a cam member 9, a camshaft 87, and a stay 88. Further, the pressure unit 84 has a center urging member 100, a first side urging member 110, a second side urging member 120, and a center moving member 200 between the holder 86 and the cam member 9. A first side moving member 210 and a second side moving member 220 are provided. In this embodiment, the pressure pad 85 and the holder 86 correspond to the pressure member or the nip forming member.

As shown in FIG. 2, the pressure pad 85 is in contact with the inner peripheral surface 83A of the endless belt 83, sandwiches the endless belt 83 with the heating roller 81, and forms a nip portion. As shown in FIG. 3, the pressure pad 85 is a rectangular parallelepiped and is formed in a long shape long in the width direction. The pressure pad 85 is elastically deformable because it is formed of an elastic material such as rubber.

The holder 86 is a frame for supporting the pressure pad 85. The holder 86 is made of resin or metal. The holder 86 has a base 86A, an upstream wall 86B, a downstream wall 86C, and an intermediate wall 86D. The base portion 86A is a portion to which the pressure pad 85 is fixed, and is formed in a long shape long in the width direction. A recess A1 into which the pressure pad 85 is fitted is formed on the upper surface of the base portion 86A.

The upstream wall 86B extends away from the pressure pad 85 from the upstream end of the base 86A in the moving direction. The downstream wall 86C extends away from the pressure pad 85 from the downstream end of the base 86A in the moving direction. The intermediate wall 86D extends from the substantially central portion of the base portion 86A in the moving direction in a direction away from the pressure pad 85.

The intermediate wall 86D is located closer to the upstream wall 86B than the downstream wall 86C. The space between the upstream wall 86B and the intermediate wall 86D and the space between the intermediate wall 86D and the downstream wall 86C are spaces in which the urging members 100, 110, and 120 described later are arranged. Specifically, the upstream springs 101, 111, 121 described later are arranged between the upstream wall 86B and the intermediate wall 86D, and the downstream springs 102, 112, 122 described later are arranged between the intermediate wall 86D and the downstream wall 86C. Be placed.

The cam member 9 is a member for pressing the pressure pad 85 toward the heating roller 81, and is made of resin or metal. The cam member 9 has a center cam 90 that presses the central portion of the pressure pad 85 in the width direction toward the heating roller 81, and a first one that presses one end portion of the pressure pad 85 in the width direction toward the heating roller 81. It has a side cam 91 and a second side cam 92 that presses the other end of the pressure pad 85 toward the heating roller 81 in the width direction. The shapes of the cams 90 to 92 will be described in detail later.

The camshaft 87 is made of resin or metal and has a cam member 9. The camshaft 87 is located upstream of the center of the holder 86 in the moving direction of the endless belt 83 at the nip portion. Both ends of the camshaft 87 are supported by a slotted hole F11 as a bearing shown in FIG. 4 so as to be rotatable and movable in the opposite direction. The major axis of the slot F11 is along the facing direction. A gear G2 is provided at the end of the camshaft 87, and the driving force of the second motor M2 is input to the gear G2. Since the gear G2 moves with the movement of the camshaft 87 in the opposite direction, the gear for transmitting the driving force to the gear G2 can transmit the driving force to the gear G2 regardless of the position of the gear G2. It can be a gear (for example, a swing gear). The cam member 9 and the camshaft 87 may be integrally formed or may be formed separately.

As shown in FIG. 3, the stay 88 is made of resin or metal. The stay 88 is formed in a U shape in a cross-sectional view, and has a support wall 88A, an upstream side wall 88B, and a downstream side wall 88C.

The support wall 88A is arranged on the side opposite to the pressure pad 85 with the cam member 9 interposed therebetween, and supports the cam member 9. The upstream side wall 88B extends upward from the front end of the support wall 88A. In other words, the upstream side wall 88B is located upstream of the cam member 9 in the moving direction of the endless belt 83 at the nip portion and extends toward the heating roller 81.

The downstream side wall 88C extends upward from the rear end of the support wall 88A. In other words, the downstream side wall 88C is located downstream of the cam member 9 in the moving direction of the endless belt 83 at the nip portion and extends toward the heating roller 81.

The upstream side wall 88B and the downstream side wall 88C of the stay 88 sandwich the holder 86, the center moving member 200, the first side moving member 210, and the second side moving member 220 in the moving direction. As a result, the holder 86, the center moving member 200, the first side moving member 210, and the second side moving member 220 are movably supported by the upstream side wall 88B and the downstream side wall 88C in the opposite direction. Both ends of the stay 88 in the width direction are supported by the frame F of the fixing device 8 as shown in FIG.

As shown in FIG. 3, the center urging member 100 is a member that urges the pressurizing pad 85 and the holder 86 toward the heating roller 81, and is located at the center of the endless belt 83 in the width direction to pressurize. It is provided between the pad 85 (specifically, the holder 86) and the center cam 90. The center urging member 100 has five upstream springs 101 arranged in the width direction and five downstream springs 102 arranged in the width direction.

Each upstream spring 101 and each downstream spring 102 are arranged in the moving direction. Each downstream spring 102 is arranged on the downstream side in the moving direction with respect to each upstream spring 101. The downstream spring 102 is configured to have a larger urging force than the upstream spring 101.

As shown in FIG. 4, the five downstream springs 102 are arranged so as to be symmetrical in the width direction with respect to the line CL passing through the center in the width direction of the heating roller 81. Here, the line CL coincides with the center of the maximum width of the paper S that can be conveyed by the fixing device 8 in the width direction.

The middle downstream spring 102 of the five is arranged at a position corresponding to the line CL in the width direction, and the two downstream springs 102 adjacent to the middle downstream spring 102 are respectively from the middle downstream spring 102 to the second pitch PC2. Have been placed. The two outermost downstream springs 102 are arranged from the two downstream springs 102 adjacent to the middle downstream spring 102 at a first pitch PC1 larger than the second pitch PC2. That is, the two arranged on the center side in the width direction of the center cam 90 from the first pitch PC1 which is the pitch of the two downstream springs 102 arranged on one end side or the other end side in the width direction of the center cam 90. The second pitch PC2, which is the pitch of the downstream spring 102, is smaller. As shown in FIG. 3, the upstream spring 101 is also arranged at the same pitch PC1 and PC2 as the downstream spring 102.

The first side urging member 110 is a member that urges the pressure pad 85 and the holder 86 toward the heating roller 81, and is located at one end of the endless belt 83 in the width direction. , Holder 86) and the first side cam 91. The first side urging member 110 has an upstream spring 111 and a downstream spring 112 arranged in the moving direction. The downstream spring 112 is arranged on the downstream side in the moving direction with respect to the upstream spring 111. The downstream spring 112 is configured to have a larger urging force than the upstream spring 111.

The second side urging member 120 is a member that urges the pressure pad 85 and the holder 86 toward the heating roller 81, and is located at the other end of the endless belt 83 in the width direction. Is provided between the holder 86) and the second side cam 92. The second side urging member 120 has an upstream spring 121 and a downstream spring 122 arranged in the moving direction. The downstream spring 122 is arranged on the downstream side in the moving direction with respect to the upstream spring 121. The downstream spring 122 is configured to have a larger urging force than the upstream spring 121.

The urging force of the first side urging member 110 and the urging force of the second side urging member 120 are smaller than the urging force of the center urging member 100. Specifically, in the present embodiment, the magnitude of the urging force is adjusted mainly by adjusting the number of springs. The method of making a difference in the magnitude of the urging force is not limited to this, and for example, the magnitude of the urging force may be made different by setting the magnitude of the spring constant to a different value.

The center moving member 200 is a member that moves in the opposite direction in conjunction with the rotational operation of the cam member 9, and is sandwiched between the center urging member 100 and the center cam 90. The center moving member 200 is formed in a U shape in cross section. The center moving member 200 has a plate-shaped first wall 201 orthogonal to the vertical direction, a second wall 202 extending downward from the front end portion of the first wall 201, and a second wall extending downward from the rear end portion of the first wall 201. It has three walls 203.

The first wall 201 has a sliding contact surface TF0 (see FIG. 4) with which the center cam 90 slides. The second wall 202 extends from one end of the first wall 201 in the moving direction, specifically, the upstream end along the upstream side wall 88B of the stay 88. The third wall 203 extends from the other end of the first wall 201 in the moving direction, specifically, from the downstream end along the downstream side wall 88C of the stay 88.

The first side moving member 210 is a member that moves in the opposite direction in conjunction with the rotational operation of the cam member 9, and is sandwiched between the first side urging member 110 and the first side cam 91. The first side moving member 210 is formed in a U shape in cross-sectional view. The first side moving member 210 has a plate-shaped first wall 211 orthogonal to the vertical direction, a second wall 212 extending downward from the front end portion of the first wall 211, and a downward portion from the rear end portion of the first wall 211. It has a third wall 213 that extends.

The first wall 211 has a sliding contact surface TF1 (see FIG. 4) with which the first side cam 91 slides. The second wall 212 extends from one end of the first wall 211 in the moving direction along the opposite direction. The third wall 213 extends from the other end of the first wall 211 in the moving direction along the opposite direction.

The second side moving member 220 is a member that moves in the opposite direction in conjunction with the rotational operation of the cam member 9, and is sandwiched between the second side urging member 120 and the second side cam 92. The second side moving member 220 is formed in a U shape in cross-sectional view. The second side moving member 220 includes a plate-shaped first wall 221 orthogonal to the vertical direction, a second wall 222 extending downward from the front end portion of the first wall 221 and a downward portion from the rear end portion of the first wall 221. It has a third wall 223 that extends.

The first wall 221 has a sliding contact surface TF2 (see FIG. 4) with which the second side cam 92 slides. The second wall 222 extends from one end of the first wall 221 in the moving direction along the opposite direction. The third wall 223 extends from the other end of the first wall 221 in the moving direction along the opposite direction.

The second walls 202, 212, 222 of the moving members 200, 210, 220 are in surface contact with the inner surface of the upstream side wall 88B of the stay 88. Further, the third walls 203, 213, 223 of the moving members 200, 210, 220 are in surface contact with the inner surface of the downstream side wall 88C of the stay 88.

As shown in FIGS. 5 to 7, the cam member 9 is configured to be rotated in one direction, specifically in the counterclockwise direction shown in the figure, by the second motor M2 shown in FIG. The first motor M1 and the second motor M2 shown in FIG. 1 are controlled by the control unit CT. The center cam 90 is configured to be in constant contact with the support wall 88A of the stay 88. In other words, the center cam 90 is configured to come into contact with the support wall 88A regardless of the rotation angle of the cam member 9.

The center cam 90 and the center moving member 200 are always in contact with each other by moving up and down while the center moving member 200 is supported by the center cam 90 regardless of the angle of the cam member 9. Similarly, the side cams 91 and 92 are always in contact with the side moving members 210 and 220 regardless of the angle of the cam member 9.

The peripheral surface of the center cam 90 has an arcuate first portion 90A in which the distance from the rotation center 9A of the cam member 9 is the maximum radius RB of the cam member 9, and the distance from the rotation center 9A is the minimum radius of the cam member 9. It has a second part 90B that becomes an RS, and a third part 90C that connects the first part 90A and the second part 90B with a smooth curved surface. The angle range from one end to the other end in the circumferential direction of the first portion 90A is set to an angle larger than 180 °. The major axis DL1 of the center cam 90 is twice as long as the maximum radius RB of the cam member 9, and the minor axis DS1 is the sum of the maximum radius RB and the minimum radius RS of the cam member 9. There is.

The first side cam 91 has a smaller outer peripheral length than the center cam 90 and has an elliptical shape. The major axis DL2 of the first side cam 91 is twice as long as the maximum radius RB of the cam member 9, and the minor axis DS2 is twice as long as the minimum radius RS of the cam member 9. The orientation of the first side cam 91 is fixed with respect to the center cam 90 so that the major axis DL2 coincides with the major axis DL1 of the center cam 90 and the minor axis DS2 coincides with the minor axis DS1 of the center cam 90. ing. Since the second side cam 92 has the same structure as the first side cam 91, the description thereof will be omitted. Further, in the following description, the rotation angle of the cam member 9 shown in FIG. 5A is referred to as a first angle, and the rotation angle of the cam member 9 in a state of being rotated counterclockwise by about 20 ° from the first angle is referred to as a first angle. The rotation angle of the cam member 9 in a state of being rotated counterclockwise by about 90 ° from the first angle, which is called the second angle, is called the third angle, and is in a state of being rotated counterclockwise by about 180 ° from the third angle. The rotation angle of the cam member 9 is referred to as a fourth angle.

As shown in FIG. 5A, when the rotation angle of the cam member 9 is the first angle, each major axis DL1 and DL2 of the center cam 90, the first side cam 91 and the second side cam 92 are along the facing directions. .. When each major axis DL1 and DL2 are along the opposite direction in this way, the upper end and the lower end of each cam 90 to 92 are at the same position in the opposite direction. Therefore, when the rotation angle of the cam member 9 is the first angle, the center cam 90, the first side cam 91, and the second side cam 92 are in contact with the support wall 88A of the stay 88.

At this time, as shown in FIG. 5B, the moving members 200, 210, and 220 are arranged at the uppermost positions. Specifically, the moving members 200, 210, and 220 are arranged at a distance of twice the maximum radius RB from the support wall 88A of the stay 88.

As shown in FIG. 6A, when the rotation angle of the cam member 9 is the second angle, the first portion 90A of the peripheral surface of the center cam 90 is in contact with the center moving member 200. That is, when the rotation angle of the cam member 9 is the second angle, the center action radius RA1 which is the dimension from the action point P1 of the center cam 90 to the rotation center 9A of the cam member 9 is the maximum radius RB as the first dimension. Is set to. Here, the point of action P1 is a portion where the force of the center cam 90 acts on the center moving member 200, and is a contact portion of the center cam 90 with the center moving member 200. Similarly, the points of action P2 and P3, which will be described later, are the portions where the forces of the side cams 91 and 92 act on the side moving members 210 and 220, and the forces of the side cams 91 and 92 with the side moving members 210 and 220. It is a contact part.

Further, when the rotation angle of the cam member 9 is the second angle, the first portion 90A of the peripheral surface of the center cam 90 is in contact with the support wall 88A of the stay 88. That is, when the rotation angle of the cam member 9 is the second angle, the dimension from the contact point of the center cam 90 with the support wall 88A to the rotation center 9A of the cam member 9 is the maximum radius RB. Therefore, when the rotation angle of the cam member 9 is the second angle, the center moving member 200 is arranged at a distance of twice the maximum radius RB from the support wall 88A, so that the nip pressure at the center in the width direction of the nip portion is reached. Is the same value as for the first angle.

When the rotation angle of the cam member 9 is the second angle, the major axis of the first side cam 91 is inclined with respect to the facing direction. As a result, when the rotation angle of the cam member 9 is the second angle, the first side working radius RA2, which is the length from the working point P2 of the first side cam 91 to the rotation center 9A, is the maximum radius which is the first dimension. It has a second dimension smaller than RB. In other words, when the rotation angle of the cam member 9 is the second angle, the upper end of the first side cam 91 is located below the upper end of the center cam 90. Therefore, when the rotation angle of the cam member 9 is the second angle, as shown in FIG. 6B, the first side moving member 210 supported by the first side cam 91 is supported by the center cam 90. It is located below the moving member 200. Specifically, assuming that the angle of the straight line connecting the point of action P2 of the first side cam 91 and the center of rotation 9A with respect to the opposite direction is θ, the distance D from the first side moving member 210 to the support wall 88A is calculated by the following equation (1). ) Can be expressed.
D = RB + RA2 ・ cosθ) ・ ・ ・ (1)

The rotation amount θ is preferably set to 45 ° or less.

Further, as shown in FIG. 6A, when the rotation angle of the cam member 9 is the second angle, the major axis of the first side cam 91 is tilted with respect to the facing direction, so that the first side cam 91 has a support wall. It is separated from 88A.

Similarly, the second side working radius RA3, which is the length from the working point P3 of the second side cam 92 to the rotation center 9A, is set to a second dimension smaller than the maximum radius RB, which is the first dimension. Further, when the rotation angle of the cam member 9 is the second angle, the second side cam 92 is separated from the support wall 88A.

As shown in FIG. 7A, when the rotation angle of the cam member 9 is the third angle, the second portion 90B of the peripheral surface of the center cam 90 faces upward, and the center cam 90 and the first side cam 91 And each minor axis DS1 and DS2 (see FIG. 5) of the second side cam 92 are along the opposite direction. In this way, when the second portion 90B faces upward and the minor diameter DS1 and DS2 are along the facing direction, the upper ends of the cams 90 to 92 are at the same position in the facing direction. Therefore, when the rotation angle of the cam member 9 is the third angle, the moving members 200, 210, and 220 are arranged at the same position in the facing direction as shown in FIG. 7B. Further, as shown in FIG. 7A, when the rotation angle of the cam member 9 is the third angle, the center working radius RA1, the first side working radius RA2, and the second side working radius RA3 have the first dimension. It has a third dimension smaller than a certain maximum radius RB, and more specifically, a minimum radius RS (see FIG. 5).

Further, when the rotation angle of the cam member 9 is the third angle, the lower ends of the side cams 91 and 92 are arranged above the lower ends of the center cam 90. As a result, when the rotation angle of the cam member 9 is the third angle, the first portion 90A of the center cam 90 is in contact with the support wall 88A, and the side cams 91 and 92 are separated from the support wall 88A.

When the rotation angle of the cam member 9 is the third angle, the first portion 90A of the center cam 90 comes into contact with the support wall 88A, so that the moving members 200, 210, and 220 are RB + RS from the support wall 88A. It is arranged at a position separated by the distance of, that is, a position lower than that at the first angle and the second angle.

As shown in FIG. 8A, when the rotation angle of the cam member 9 is the fourth angle, the second portion 90B of the peripheral surface of the center cam 90 faces downward, and the center cam 90 and the first side cam 91 And each minor axis DS1 and DS2 (see FIG. 5) of the second side cam 92 are along the opposite direction. In this way, when the second portion 90B faces downward and the minor diameter DS1 and DS2 are along the facing direction, the lower ends of the cams 90 to 92 are at the same position in the facing direction. As a result, when the rotation angle of the cam member 9 is the fourth angle, each cam 90 to 92 comes into contact with the support wall 88A, and the distance from the contact portion of each cam 90 to 92 with the support wall 88A to the rotation center 9A. Is the minimum radius RS. That is, the camshaft 87 is moving downward in the process of rotating from the third angle to the fourth angle.

Further, when the rotation angle of the cam member 9 is the fourth angle, the upper ends of the side cams 91 and 92 are arranged below the upper ends of the center cam 90. As a result, when the rotation angle of the cam member 9 is the fourth angle, the center working radius RA1 is larger than the first side working radius RA2 and the second side working radius RA3. Specifically, when the rotation angle of the cam member 9 is the fourth angle, the center working radius RA1 is the maximum radius RB, and the side working radii RA2 and RA3 are the minimum radius RS.

As a result, the distance from the center moving member 200 to the support wall 88A is RB + RS, and the distance from each side moving member 210, 220 to the support wall 88A is twice the minimum radius RS. That is, when the rotation angle of the cam member 9 is the fourth angle, the position of the center moving member 200 in the facing direction is the same as that of the third angle, and the side moving members 210 and 220 are at the third angle. It is located below the time.

Next, the action and effect of the cam member 9 will be described in detail.
As shown in FIG. 5A, when the cam member 9 has the first angle, the major diameters DL1 and DL2 of the cams 90 to 92 are along the opposite directions, so that the moving members 200, 210 and 220 are located. Is placed at the uppermost position, so that the nip pressure can be maximized as shown by the solid line in FIG. Here, the nip pressure is distributed so that the biasing members 100, 110, and 120 are configured as described above, so that the center is the highest and the nip pressure becomes lower toward the end in the width direction. Therefore, when the cam member 9 is set to the first angle, the nip is satisfactorily applied to the paper S having the maximum width Wmax (see FIG. 4) that can be printed by the laser printer 1, regardless of the width of the paper S. Pressure can be applied.

When the cam member 9 is rotated counterclockwise by about 20 ° from the first angle to the second angle, the position of the upper end of the center cam 90 does not change as shown in FIGS. 6A and 6B. , The upper ends of the side cams 91 and 92 are located slightly below the upper ends of the center cam 90. As a result, the side moving members 210 and 220 move below the center moving member 200. Therefore, as shown by the broken line in FIG. 9, at the second angle, the nip pressure at the end in the width direction becomes the first angle. It becomes smaller than the nip pressure at the time of. Thereby, for example, when printing on the paper S having a width narrower than the width of the center moving member 200 (for example, the minimum width Wmin: see FIG. 4), the width while applying a good nip pressure to the paper S. By reducing the nip pressure outside the paper passing range of the paper S in the direction, the driving torque of the heating roller 81 can be reduced as compared with the case where the cam member 9 has the first angle.

When the cam member 9 is rotated counterclockwise by about 70 ° from the second angle to the third angle, the upper ends of the cams 90 to 92 are the second, as shown in FIGS. 7A and 7B. It is placed below the angle. As a result, the moving members 200, 210, and 220 move lower than at the second angle. Therefore, as shown by the alternate long and short dash line in FIG. 9, the nip pressure is applied to the second angle at the third angle. It can be smaller than it is. Further, at the third angle, the moving members 200, 210, and 220 are arranged at the same positions in the facing directions as in the case of the first angle, so that the nip pressure at the first angle is generally applied. The distribution can be offset downwards. As a result, when printing on thick paper S such as an envelope or thick paper, it is possible to suppress the occurrence of wrinkles and curls on the paper S while applying a good nip pressure to the paper S. ..

When the cam member 9 is rotated counterclockwise by about 180 ° from the third angle to the fourth angle, the position of the upper end of the center cam 90 is the third angle as shown in FIGS. 8A and 8B. The position of the upper end of each side cam 91, 92 moves lower than that at the third angle, as in the case of. As a result, at the fourth angle, the nip pressure at the center in the width direction remains equal to that at the third angle, and the nip pressures at both ends in the width direction are smaller than the nip pressure at the third angle. As a result, when printing on narrow and thick paper S such as a postcard, the nip pressure outside the paper passing range of the paper S in the width direction is applied while applying a good nip pressure to the paper S. By further reducing the torque, the driving torque of the heating roller 81 can be reduced as compared with the case where the cam member 9 has the third angle.
When the cam member 9 is rotated counterclockwise by about 180 ° from the third angle to the fourth angle, the camshaft 87 moves downward along the elongated hole F11 as a bearing. After that, when the cam member 9 is rotated counterclockwise by about 90 ° from the fourth angle to return to the first angle, the camshaft 87 moves upward along the slotted hole F11. As a result, the cam member 9 can be rotated without applying a load to the camshaft 87.

As described above, according to the present embodiment, the following effects can be obtained in addition to the above-mentioned effects.
Since the center cam 90 is in constant contact with the support wall 88A, it is possible to suppress the camshaft 87 from bending due to the reaction force applied to the cam member 9 from the pressure pad 85.

By making the urging force of each side urging member 110, 120 smaller than the urging force of the center urging member 100, a high nip pressure distribution can be obtained at the center, so that relatively wide paper such as plain paper can be obtained. The nip pressure can be applied satisfactorily to S.

Two upstream springs arranged on the center side of the center cam 90 in the width direction rather than the pitch of the two upstream springs 101 or the two downstream springs 102 arranged on one end side or the other end side of the center cam 90 in the width direction. Since the pitch of the 101 or the downstream spring 102 is made smaller, the urging force can be increased at the center of the center cam 90 in the width direction and the urging force can be decreased at both ends. Therefore, even in the range of the center cam 90, a high nip pressure distribution at the center can be obtained.

Since the cam member 9 is in sliding contact with the moving members 200, 210, 220 which are different members from the urging members 100, 110, 120, the cam member 9 can be smoothly rotated.

Since the moving members 200, 210, and 220 are movably supported by the stay 88 that receives the reaction force from the cam member 9, for example, compared with the structure in which the member that movably supports each moving member is a separate member from the stay. , The increase in the number of parts can be suppressed.

Since the second walls 202, 212, 222 and the third walls 203, 213, 223 of the moving members 200, 210, 220 come into surface contact with the upstream side wall 88B and the downstream side wall 88C of the stay 88, each of them is caused by the rotation of the cam member 9. Even if the contact positions between the cams 90 to 92 and the moving members 200, 210, 220 deviate in the moving direction, it is possible to suppress the tilting of the first walls 2011, 211,221. Further, the stay 88 can satisfactorily guide the movement of the moving members 200, 210, 220 in the opposite direction.

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

In the above-described embodiment, the moving members 200, 210, and 220 are slid and moved in opposite directions, but the present invention is not limited thereto. For example, as shown in FIGS. 10 and 11, the center moving member 300, the first side moving member 310, and the second side moving member 320 are configured to be rotatable around the upstream end in the moving direction. You may. Specifically, in this structure, the rotation centers of the moving members 300, 310, and 320 are arranged upstream of the upstream spring 101 in the moving direction.

According to this, as compared with the structure of the above-described embodiment, the amount of fluctuation in the nip pressure on the inlet side of the nip portion between the heating roller 81 and the pressure pad 85 can be reduced regardless of the rotation angle of the cam member 9. Therefore, it is possible to suppress print distortion caused by slippage when the paper S rushes into the nip portion.

The center moving member 300, the first side moving member 310, and the second side moving member 320 are rotatably supported by, for example, a shaft fixed to a frame F of the fixing device 8 or a wall formed on the stay 88. be able to. Specifically, holes communicating in the width direction are formed near the upstream ends of the moving members 300, 310, and 320. A shaft 340 extending in the width direction is inserted into each of the holes of the moving members 300, 310, and 320. The shaft 340 rotatably supports each of the moving members 300, 310, and 320, and both ends thereof are fixed to the frame F.

Further, in this structure, the camshaft 87 is located on the downstream side in the moving direction with respect to the upstream spring 101 located on the most upstream side in the moving direction. In other words, in the moving direction, the rotation axis of the camshaft 87 is located downstream of the center of the holder 86. According to this, for example, as compared with the structure in which the camshaft is arranged near the rotation center of each moving member, the force for pressing each moving member 300, 310, 320 by the cam member 9 can be reduced, so that the cam member can be reduced. The durability of 9 can be improved.

In the above embodiment, the side cams 91 and 92 have an elliptical shape, but the present invention is not limited thereto. For example, as shown in FIGS. 12A to 12C, each side cam 491 and 492 are always in contact with the support wall 88A while the cam member 409 rotates from the first angle to the third angle. The shapes of the side cams 491 and 492 may be changed. Specifically, in this structure, the side cams 491 and 492 have a half portion on the second portion 90B side of the center cam 90 with respect to the major axis DL2 having the same shape as the elliptical side cams 91 and 92 in the above embodiment. The half portion of the center cam 90 opposite to the second portion 90B of the major axis DL2 has the same shape as the first portion 90A of the center cam 90.

That is, the major axis DL2 of the side cams 491 and 492 has the same length (2 × RB) as the embodiment, but the minor axis DS2 has the same length as the minor axis DS1 of the center cam 90, unlike the embodiment. It is (RB + RS). According to this, while the cam member 409 rotates from the first angle to the third angle, the side cams 491 and 492 are always in contact with the support wall 88A, so that the bending of the camshaft 87 can be further suppressed. Further, in this embodiment, each cam 90, by appropriately switching the rotation direction of the second motor M2 for moving the cam member 409 so as to move the cam member 409 only in the range from the first angle to the third angle. The 491 and 492 can always be in contact with the support wall 88A. Further, in this embodiment, as shown in FIG. 13, each cam 90, 491, 492 comes into contact with the support wall 88A even when the cam member 409 is at the fourth angle.

In the above embodiment, the center cam 90 is always in contact with the support wall 88A, but the present invention is not limited to this, and the center cam comes into contact with the support wall at least when the developer image is fixed on the paper. You just have to.

In the above embodiment, the moving members 200, 210, and 220 are provided, but the present invention is not limited to this, and the urging member may be directly pressed by the cam without providing the moving member. Further, the holder may be directly pressed by the cam without providing the urging member, or the pressure pad may be directly pressed by the cam without providing the holder.

In the above embodiment, the nip pressure adjusting mechanism of the present invention is applied to the fixing device 8, but the present invention is not limited to this, and the nip pressure adjusting mechanism of the present invention is also applied to a paper transport system other than the fixing device. be able to. For example, in a paper transport system including a paper transport belt for transporting paper between a transport roller and a transport roller, the nip pressure adjusting mechanism of the present invention may be provided in the paper transport belt.

In the above embodiment, the pressure pad 85 is a rectangular parallelepiped, but the present invention is not limited to this, and the pressure pad may have any shape.

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

In the above embodiment, the heating roller 81 having a built-in heater 82 as the facing member is exemplified, but the present invention is not limited to this, and for example, even an endless heating belt in which the inner peripheral surface is heated by the heater. good. Further, an external heating method in which the heater is arranged outside the facing member to heat the outer peripheral surface of the facing member, or an IH (Induction Heating) method may be used. Further, a heater may be arranged inside the endless belt to indirectly heat the facing member. Further, the facing member and the endless belt may each have a built-in heater.

Further, the nip pressure adjusting mechanism of the present invention can be applied not only to the fixing device 8 as in the above embodiment but also to various fixing devices. For example, a pressurizing roller that forms a fixing nip between the fixing roller and the fixing roller, and a heating unit that heats the fixing roller by contacting the fixing roller with a predetermined nip pressure are provided, and the fixing nip is on paper. In the fixing device for fixing the toner image to the surface, the nip pressure adjusting mechanism of the present invention may be provided in the heating unit. Specifically, when the heating unit includes an endless belt and a heating member that sandwiches the endless belt between the fixing rollers, the heating member may be pressed toward the fixing roller by the cam member or the like of the present invention. good. That is, the cam member or the like of the present invention may be provided in the rotating body that forms the nip at a position different from the fixing nip.

In the above embodiment, the elongated hole F11 formed in the frame F is exemplified as the bearing, but the present invention is not limited to this, and for example, a bearing separate from the frame of the fixing device may be used.

In the above embodiment, the stay 88 is formed in a U shape in a cross-sectional view, but the present invention is not limited to this, and the stay may have any shape as long as it has a support wall. Further, the moving member is not limited to the U shape in cross-sectional view, and may have any shape.

In the above embodiment, the present invention is applied to the laser printer 1, but the present invention is not limited to this, and the present invention may be applied to other image forming devices such as a copier and a multifunction device.

Further, each element described in the above-described embodiment and modification may be arbitrarily combined and carried out.

8 Fixing device 9 Cam 81 Heating roller 82 Heater 83 Endless belt 83A Inner peripheral surface 85 Pressurizing pad 87 Camshaft 88 Stay 88A Support wall 90 Center cam 91 1st side cam 92 2nd side cam F11 Long hole

Claims (17)

With a heater
The facing member heated by the heater and
With an endless belt,
A pressure member that comes into contact with the inner peripheral surface of the endless belt and sandwiches the endless belt with the facing member to form a nip portion.
A cam member that presses the pressurizing member toward the facing member, and
It is provided with a stay, which is arranged on the side opposite to the pressurizing member with the cam member in between and supports the cam member.
The cam member is
A center cam that presses the central portion of the pressurizing member in the width direction of the endless belt toward the facing member, and
A side cam having a smaller outer peripheral length than the center cam and pressing the end portion of the pressurizing member in the width direction toward the facing member.
Have,
The center cam is a fixing device characterized in that it comes into contact with the stay. The fixing device according to claim 1, wherein the center cam is in constant contact with the stay regardless of the rotation angle of the cam member. The fixing device according to claim 2, wherein the side cam comes into contact with the stay when the rotation angle of the cam member is the first angle. The major axis of the center cam and the major axis of the side cam are equal,
When the rotation angle of the cam member is the first angle, the major axis of the center cam and the major axis of the side cam are along the facing directions in which the facing member and the pressurizing member face each other. The fixing device according to claim 3. When the rotation angle of the cam member is the second angle,
The fixing device according to any one of claims 2 to 4, wherein the side cam is separated from the stay. The cam member has a camshaft and has a camshaft.
When the rotation angle of the cam member is the second angle,
The center radius of action, which is the dimension from the point of action of the center cam to the center of rotation of the camshaft, is the first dimension.
The fixing device according to claim 5, wherein the side working radius, which is the length from the working point of the side cam to the center of rotation, has a second dimension smaller than the first dimension. When the rotation angle of the cam member is the third angle,
The fixing device according to claim 6, wherein the center working radius and the side working radius have a third dimension smaller than the first dimension. A center urging member located at the center of the endless belt in the width direction, provided between the pressurizing member and the center cam, and urging the pressurizing member toward the facing member.
Further, a side urging member located at the end of the endless belt in the width direction, provided between the pressurizing member and the side cam, and urging the pressurizing member toward the facing member. Prepare,
The fixing device according to any one of claims 1 to 7, wherein the urging force of the side urging member is smaller than the urging force of the center urging member. The center urging member has a predetermined number of springs arranged in the width direction.
The pitch of the two springs arranged on the center side of the center cam in the width direction is smaller than the pitch of the two springs arranged on one end side or the other end side of the center cam in the width direction. The fixing device according to claim 8. A center moving member that is sandwiched between the center urging member and the center cam and moves in the opposite direction in which the facing member and the pressurizing member face each other in conjunction with the rotational operation of the cam member.
8. Item 9. The fixing device according to item 9. The stay has an upstream side wall located upstream of the cam member and extending toward the facing member in the moving direction of the endless belt in the nip portion, and the facing member located downstream of the cam member. With a downstream side wall that extends towards
The fixing device according to claim 10, wherein the center moving member and the side moving member are sandwiched between the upstream side wall and the downstream side wall. The center moving member and the side moving member have a first wall to which the cam member slides and a second wall extending from the upstream end of the first wall in the moving direction along the upstream side wall of the stay, respectively. 11. The fixing device according to claim 11, further comprising a third wall extending from the downstream end of the first wall in the moving direction along the downstream side wall of the stay. According to claim 10, the center moving member and the side moving member are configured to be rotatable around an upstream end portion in the moving direction of the endless belt in the nip portion, respectively. Item 12. The fixing device according to any one of Items 12. 13. The fixing device described. The cam member has a camshaft and has a camshaft.
The one according to any one of claims 1 to 14, wherein the camshaft is located on the upstream side of the center of the pressurizing member in the moving direction of the endless belt in the nip portion. Fixing device. The fixing device according to any one of claims 1 to 15, wherein one side cam is arranged at a position corresponding to both ends of the pressurizing member in the width direction. An image forming apparatus that forms an image on a recording medium.
With an endless belt,
With the facing member in contact with the outer peripheral surface of the endless belt,
A nip forming member that contacts the inner peripheral surface of the endless belt and sandwiches the endless belt between the facing member and the nip forming member.
A cam member that presses the nip forming member toward the facing member, and a cam member.
It is provided with a stay that is arranged on the side opposite to the nip forming member across the cam member and supports the cam member.
The cam member is
A center cam that presses the central portion of the nip forming member in the width direction of the endless belt toward the facing member, and
A side cam having a smaller outer peripheral length than the center cam and pressing the end portion of the nip forming member in the width direction toward the facing member.
Have,
The center cam is an image forming apparatus that comes into contact with the stay.

Images