JP2023155616A - Fixing device - Google Patents

Abstract

To reduce, in an area between a first pressure pad and a second pressure pad, a ratio of a portion of an endless belt not pressed by the pressure pads.SOLUTION: A fixing device 8 comprises a heating roller 81, an endless belt 130, a first pressure pad P1, and a second pressure pad P2. The second pressure pad P2 is located on the downstream side in a conveyance direction of the first pressure pad P1. The first pressure pad P1 has a base part P11, and an extension part P12 extending from the base part toward the downstream side in the conveyance direction. In a state in which the first pressure pad P1 is not deformed, a dimension S2 in the direction of movement of the extension part P12 is smaller than a dimension S1 in the direction of movement of the base part P11.SELECTED DRAWING: Figure 3

Description

The present invention relates to a fixing device for thermally fixing a toner image on a sheet.

Conventionally, a fixing device is known that thermally fixes a sheet by nipping it with a heating roller and an endless belt. A pressure pad is arranged inside the endless belt, and the pressure pad presses the endless belt toward the heating roller. In Patent Document 1, two pressure pads (a first pressure pad and a second pressure pad) separated in the sheet conveyance direction are provided in order to enlarge the nip area.

JP 2017-021068 Publication

However, in a fixing device in which a first pressure pad and a second pressure pad are provided as two pressure pads, the endless belt is not applied in the area between the first pressure pad and the second pressure pad. The proportion of the area that is not pressed by the pressure pad is large.

Therefore, an object of the present disclosure is to reduce the proportion of the portion of the endless belt that is not pressed by the pressure pad in the region between the first pressure pad and the second pressure pad.

A fixing device for solving the above problem includes a heating roller, an endless belt, a first pressure pad, a second pressure pad, and an intermediate pressure pad.
The endless belt contacts the heating roller, nips the sheet together with the heating roller, and transports the sheet in the transport direction. The first pressure pad is made of an elastic body and presses the endless belt against the heating roller. The second pressure pad is located downstream of the first pressure pad in the conveyance direction. The second pressure pad is made of an elastic body and presses the endless belt against the heating roller.
The first pressure pad and the second pressure pad are movable relative to the heating roller in a direction of movement toward the heating roller.
The first pressure pad has a base portion and an extension portion extending from the base portion toward the downstream side in the conveyance direction.
When the first pressure pad is not deformed, the dimension of the extending portion in the moving direction is smaller than the dimension of the base portion in the moving direction.

According to such a configuration, since the first pressure pad has the extending portion, the endless belt is not pressed against the pressure pad in the area between the first pressure pad and the second pressure pad. The proportion of parts can be reduced.

The fixing device described above may include a pad holder that has a first holding surface that holds the first pressure pad and a second holding surface that holds the second pressure pad, and is movable in the movement direction. Good too.

According to this configuration, since the fixing device includes the pad holder, the first pressure pad and the second pressure pad can be moved without changing their relative positions and movement amounts.

In the fixing device described above, when the first pressure pad is not deformed, the first pressing surface that presses the endless belt on the base part and the second pressing surface that presses the endless belt on the extension part are moved. A configuration in which the positions in the directions are the same may be used.

According to such a configuration, the first pressure pad can be continuously pressed against the inner circumferential surface of the endless belt.

In the fixing device described above, the pad holder may have a support surface that protrudes from the first holding surface toward the heating roller and supports the extending portion from the side opposite to the heating roller in the moving direction.

According to such a configuration, since the extending portion is supported by the support surface, an appropriate nip pressure can be generated between the heating roller and the extending portion.

In the fixing device described above, when the first pressure pad is not deformed, the support surface does not contact the extension part, and when the first pressure pad is deformed, the support surface does not contact the extension part. It is also possible to have a structure in which it comes into contact with the part.

In the fixing device described above, the second pressure pad is harder than the first pressure pad, and when the first pressure pad and the second pressure pad are not deformed, the second pressure pad moves from the first holding surface to the first pressure surface. The dimension in the moving direction from the first holding surface to the second pressing surface may be larger than the dimension in the moving direction from the first holding surface to the second pressing surface.

In the fixing device described above, the first bottom surface may be located on the same plane as the second bottom surface of the extension portion on the opposite side of the heating roller in the moving direction.

According to such a configuration, it is possible to prevent the pad holder from having a complicated shape.

In the fixing device described above, the lowest value of the pressure with which the extending portion presses the endless belt is smaller than the highest value of the pressure with which the base portion presses the endless belt, and the highest value of the pressure with which the second pressure pad presses the endless belt. It may be configured to be smaller than the value.

According to such a configuration, the pressure with which the extending portion presses the endless belt can be suppressed from becoming greater than the pressure with which the base portion and the second pressure pad press the endless belt.

According to the present invention, it is possible to reduce the proportion of the portion of the endless belt that is not pressed by the pressure pad in the region between the first pressure pad and the second pressure pad.

1 is a cross-sectional view of an image forming apparatus including a fixing device according to the present disclosure. 1 is a cross-sectional view showing a fixing device according to an embodiment. FIG. 3 is a cross-sectional view of the fixing device in a non-nipped state. They are an enlarged view (a) of the vicinity of the pressure pad in FIG. 3, an enlarged view (b) of the vicinity of the pressure pad in FIG. 2, and a graph (c) showing the distribution of the pressing force of the pad in the conveyance direction. FIGS. 4A, 4B, and 4C are diagrams corresponding to FIG. 4 in the second embodiment. 4A, 4B, and 4C are diagrams corresponding to FIG. 4 in the third embodiment. FIGS. 4A, 4B, and 4C are diagrams corresponding to FIG. 4 in the fourth embodiment. FIGS. 4A, 4B, and 4C are diagrams corresponding to FIG. 4 in the fifth embodiment. 4A, 4B, and 4C are diagrams corresponding to FIG. 4 in a comparative example.

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

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

The exposure device 4 is disposed in the upper part of the main body casing 2, and includes a light source device (not shown), a polygon mirror, a lens, a reflector, etc., which are shown without reference numerals. The exposure device 4 exposes the surface of the photoreceptor drum 61 by scanning the surface of the photoreceptor drum 61 at high speed with a light beam (see the dashed line) based on the image data emitted from the light source device.

The developer image forming section 5 is arranged below the exposure device 4 . The developer image forming section 5 is configured as a process cartridge, and is removable from the main body casing 2 through an opening formed when a front cover 21 provided at the front of the main body casing 2 is opened. The developer image forming section 5 includes a photosensitive drum 61, a charger 62, a transfer roller 63, a developing roller 64, a supply roller 65, and a developer storage section 66 that stores a developer made of dry toner. We are prepared.

The developer image forming section 5 uniformly charges the surface of the photoreceptor drum 61 using a charger 62 . Thereafter, the surface of the photoreceptor drum 61 is exposed to a light beam from the exposure device 4, so that an electrostatic latent image based on the image data is formed on the surface. Further, the developer image forming section 5 supplies the developer in the developer storage section 66 to the developing roller 64 via the supply roller 65 .

Then, the developer image forming section 5 supplies the developer on the developing roller 64 to the electrostatic latent image formed on the photoreceptor drum 61. As a result, the electrostatic latent image is visualized, and a developer image is formed on the photoreceptor drum 61. Thereafter, the developer image forming section 5 transfers the developer image on the photoreceptor drum 61 to the sheet S by conveying the sheet S supplied from the sheet supply section 3 between the photoreceptor drum 61 and the transfer roller 63. Transcribe.

The fixing device 8 is arranged behind the developer image forming section 5. Details of the fixing device 8 will be described later. The fixing device 8 thermally fixes the developer image onto the sheet S by passing the sheet S onto which the developer image has been transferred. The image forming apparatus 1 discharges the sheet S on which the developer image has been thermally fixed onto a paper discharge tray 22 outside the main body housing 2 by means of a conveyance roller 23 and a discharge roller 24 .

The fixing device 8 includes a heating roller 81, a pressure unit 82, and a moving mechanism 83.

The moving mechanism 83 is a known mechanism that moves the pressure unit 82 linearly and changes the distance between the heating roller 81 and the pressure unit 82. Specifically, the pressurizing unit 82 is moved by the moving mechanism 83 to the nip position shown in FIG. 2 and the release position shown in FIG. 3. As shown in FIG. 2, when the pressure unit 82 is located at the nip position, the pressure unit 82 is urged toward the heating roller 81 by the moving mechanism 83. As shown in FIG. 3, when the pressure unit 82 is located at the release position, the pressure unit 82 is not urged toward the heating roller 81 by the moving mechanism 83.
In the following description, the direction in which the pressure unit 82 moves toward the heating roller 81 will be referred to as a "moving direction." In this embodiment, the moving direction is the direction in which the heating roller 81 and the pressure unit 82 face each other.

As shown in FIG. 2, the heating roller 81 includes a heater 110 and a rotating body 120. The pressure unit 82 also includes an endless belt 130, a pad holder 140, a pressure pad P, a sliding sheet 150, a belt guide 160, and a stay 170. In addition, 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 X1 of the rotating body 120 extends. The width direction is perpendicular to the movement direction.

Heater 110 heats at least one of rotating body 120 and endless belt 130. In this embodiment, the heater 110 is arranged inside the rotating body 120 and heats the rotating body 120.

The rotating body 120 is a cylindrical roller and includes a raw tube 121 and an elastic layer 122. The raw pipe 121 is a metal pipe. The elastic layer 122 is rotatable around the rotation axis X1. The rotating body 120 is driven by a motor (not shown) provided in the image forming apparatus 1 and rotates counterclockwise in FIG. 2 . The elastic layer 122 is provided around the outer periphery of the raw tube 121 . In other words, the rotating body 120 has the elastic layer 122 on its surface. The elastic layer 122 has elasticity.

The endless belt 130 is an endless belt made of metal or the like. The endless belt 130 has a width greater than the width of the largest sheet S conveyed by the image forming apparatus 1 . The endless belt 130 contacts the outer peripheral surface of the heating roller 81. The endless belt 130 and the heating roller 81 nip the sheet S and transport it in the transport direction. The endless belt 130 rotates clockwise in FIG. 2 due to friction with the rotating body 120 or the seat S when the rotating body 120 rotates.

As shown in FIG. 4(a), the pad holder 140 is a member that holds the pressure pad P. Pad holder 140 has a first holding surface 141 , a second holding surface 142 , and a support surface 143 .

The first holding surface 141 and the second holding surface 142 are located on the same plane. The support surface 143 protrudes from the first holding surface 141 toward the heating roller 81 . That is, the support surface 143 is located closer to the conveyance path of the sheet S than the first holding surface 141 and the second holding surface 142. The support surface 143 is a surface that supports the extension portion P12, which will be described later, from the side opposite to the heating roller 81 in the moving direction. In this embodiment, the first holding surface 141, the second holding surface 142, and the supporting surface 143 are surfaces perpendicular to the moving direction.

The pressure pad P is a member that forms a nip portion NP with the rotating body 120 by sandwiching the endless belt 130, the sliding sheet 150, and the sheet S. Note that in the following description, the direction in which the sheet S is conveyed in the nip portion NP is simply referred to as the "conveyance direction." The conveyance direction is perpendicular to the width direction.

The pressure pad P includes a first pressure pad P1 and a second pressure pad P2. The second pressure pad P2 is located downstream of the first pressure pad P1 in the transport direction.

In a state where the first pressure pad P1 and the second pressure pad P2 are not elastically deformed, there is a gap G1 between the first pressure pad P1 and the second pressure pad P2 in the transport direction.

The second pressure pad P2 has a higher durometer hardness than the first pressure pad P1. That is, the second pressure pad P2 is harder than the first pressure pad P1. Durometer hardness is specified in ISO7619-1. Durometer hardness is the value obtained from the depth of penetration of a specified indenter into a test piece under specified conditions. For example, when the durometer hardness of the elastic layer 122 is 5, it is preferable that the durometer hardness of the first pressure pad P1 is 6 to 10 and the durometer hardness of the second pressure pad P2 is 70 to 90.

The first pressure pad P1 is made of an elastic body and is elastically deformable. For example, the first pressure pad P1 is made of rubber such as silicone rubber. The first pressure pad P1 has a base portion P11 and an extending portion P12.

The base portion P11 has a rectangular parallelepiped shape. The base portion P11 has a first pressing surface PM1 and a first bottom surface QM1. The first pressing surface PM1 is a surface that presses the endless belt 130. The first pressing surface PM1 is in contact with the sliding sheet 150 in a state where the first pressing pad P1 is deformed (see FIG. 4(b)). The first bottom surface QM1 is a surface held by the first holding surface 141.

Since the base portion P11 is thicker than the elastic layer 122, when the rotating body 120 and the first pressure pad P1 are pressed against each other, the amount of deformation of the elastic layer 122 is smaller than the amount of deformation of the base portion P11. The base portion P11 forms a first nip portion NP1 with the rotating body 120 across the endless belt 130. The base portion P11 presses the endless belt 130 against the heating roller 81.

The extending portion P12 is a portion extending from the base portion P11 toward the downstream side in the conveyance direction. The extending portion P12 has a rectangular parallelepiped shape smaller than the base portion P11. When the first pressure pad P1 is not deformed, the dimension D2 of the extending portion P12 in the moving direction is smaller than the dimension D1 of the base portion P11 in the moving direction.

The extending portion P12 has a second pressing surface PM2 and a second bottom surface QM2. The second pressing surface PM2 is a surface that presses the endless belt 130. In a state where the first pressure pad P1 is not deformed, the first pressure surface PM1 and the second pressure surface PM2 are continuous and on the same plane. That is, in a state where the first pressure pad P1 is not deformed, the first pressure surface PM1 and the second pressure surface PM2 are at the same position in the movement direction.

The second pressing surface PM2 is in contact with the sliding sheet 150 in a state where the first pressing pad P1 is deformed (see FIG. 4(b)). The second bottom surface QM2 is a surface supported by the support surface 143. In a state where the first pressure pad P1 is not deformed, the first bottom surface QM1 and the second bottom surface QM2 are not continuous and on the same plane. When the first pressure pad P1 is not deformed, the first bottom surface QM1 and the second bottom surface QM2 have different positions in the moving direction. Specifically, in the moving direction, the second bottom surface QM2 is located closer to the heating roller 81 than the first bottom surface QM1.

Since the extending portion P12 is thicker than the elastic layer 122, when the rotating body 120 and the first pressure pad P1 are pressed against each other, the amount of deformation of the elastic layer 122 is greater than the amount of deformation of the extending portion P12. small. The extending portion P12 forms a second nip portion NP2 with the rotating body 120 sandwiching the endless belt 130 (see FIG. 2). The extending portion P12 presses the endless belt 130 against the heating roller 81.

When the first pressure pad P1 is not deformed, the support surface 143 is not in contact with the extension portion P12.
As shown in FIG. 4(b), when the first pressure pad P1 is deformed, the support surface 143 contacts the extension portion P12.

The second pressure pad P2 is a rectangular parallelepiped member. The second pressure pad P2 is made of an elastic body and is elastically deformable. For example, the second pressure pad P2 is made of rubber such as silicone rubber.

As shown in FIG. 2, the second pressure pad P2 has a higher durometer hardness than the elastic layer 122, but since the second pressure pad P2 is thicker than the elastic layer 122, the second pressure pad P2 has a higher durometer hardness than the elastic layer 122. When the first pressure pads P1 are pressed against each other, the amount of deformation of the elastic layer 122 is smaller than the amount of deformation of the second pressure pad P2. The second pressure pad P2 forms a second nip portion NP2 with the rotating body 120 across the endless belt 130. The second pressure pad P2 presses the endless belt 130 against the heating roller 81.

As shown in FIG. 4(a), the second pressure pad P2 has a third pressing surface PM3 and a third bottom surface QM3. The third pressing surface PM3 is a surface that presses the endless belt 130. The third bottom surface QM3 is a surface supported by the support surface 142.

In a state where the first pressure pad P1 and the second pressure pad P2 are not elastically deformed, the dimension D3 in the movement direction from the second holding surface 142 to the third pressing surface PM3 is from the first holding surface 141 to the first It is smaller than the dimension D1 in the direction of movement up to the pressing surface PM1.
Further, in a state where the first pressure pad P1 and the second pressure pad P2 are not elastically deformed, the dimension D3 in the movement direction from the second holding surface 142 to the third pressure surface PM3 is the dimension D3 from the second bottom surface QM2 to the third pressure surface PM3. It is larger than the dimension D2 in the moving direction up to the second pressing surface PM2.

Here, the pad holder 140 is movable in the moving direction by the moving mechanism 83. Therefore, the first pressure pad P1 and the second pressure pad P2 are movable relative to the heating roller 120 in the movement direction.

Returning to FIG. 2, the sliding sheet 150 is sandwiched between the inner circumferential surface 131 of the endless belt 130 and the pressure pad P. The sliding sheet 150 is in contact with the inner peripheral surface 131 of the endless belt 130. When the rotating body 120 rotates, the sliding sheet 150 is always in contact with the endless belt 130. On the other hand, when the rotating body 120 rotates, each part of the inner peripheral surface 131 of the endless belt 130 alternately repeats a state in which it is in contact with the sliding sheet 150 and a state in which it is not in contact with the sliding sheet 150.

The belt guide 160 is a member that guides the movement of the endless belt 130. The belt guide 160 has a curved surface that allows the endless belt 130 to rotate smoothly.

The stay 170 is a member that supports the pad holder 140 and the belt guide 160. The stay 170 is formed by press-molding a metal plate.

Here, the pressures (nip pressures) at the first nip portion NP1, the second nip portion NP2, and the third nip portion NP3 are shown by solid lines in the graph of FIG. 4(c). Note that the broken line in the graph of FIG. 4C indicates the pressure (nip pressure) in a conventional fixing device that does not have an extending portion (see FIG. 8).

As shown in FIG. 4(c), the pressures at the first nip portion NP1 and the third nip portion NP3 are not significantly different from those in the configuration shown in FIG. On the other hand, in the second nip part NP2, the pressure is higher than in the form of FIG. 9, and the pressure in the second nip part NP2 and the pressure in the first nip part NP1 and the third nip part NP3 are The difference is smaller than that in the embodiment shown in FIG. As an example, the lowest value K3 of the pressure at which the extending portion P12 presses the endless belt 130 is higher than the lowest pressure K8 in the form of FIG. 9 .
Further, the lowest value K3 of the pressure with which the extending portion P12 presses the endless belt 130 is smaller than the highest value K1 of the pressure with which the base portion P11 presses the endless belt 130, and the second pressure pad P2 presses the endless belt 130. is smaller than the maximum value K2 of the pressure.

According to the above, the following effects can be obtained in this embodiment.
As shown in FIG. 8A, some fixing devices are provided with two pressure pads spaced apart in the sheet conveyance direction in order to enlarge the nip area. In this case, as shown in FIGS. 8(b) and 8(c), the endless belt 110 covers two areas between the two pressure pads (the first pressure pad P1 and the second pressure pad P2). The proportion of the area that is not pressed by the pressure pad is large. If the proportion of the area that is not pressed by the pressure pad is large, the image quality may deteriorate due to the sheet S being conveyed in the nip area slipping or becoming wrinkled in the nip area. there were.
However, in the fixing device 8 of this embodiment, since the first pressure pad P1 has the extension part P12, the extension part P12 is attached to the endless belt in the area between the base part P11 and the second pressure pad P2. 130 is pressed against the heating roller 81. Therefore, in the region between the first pressure pad and the second pressure pad, it is possible to reduce the proportion of the portion of the endless belt that is not pressed by the pressure pad. Further, as shown in FIG. 4(c), the lowest pressure value K3 in the second nip portion NP2 is larger than the lowest pressure value K8 in the form of FIG. Furthermore, as shown in FIG. 4(c), compared to the form of FIG. 8 (broken line), the nip pressure in the area between the first pressure pad P1 and the second pressure pad P2 is suppressed from becoming weaker. can. Therefore, changes in pressure can be suppressed in the region between the first pressure pad P1 and the second pressure pad P2.
As a result, it is possible to suppress deterioration in image quality due to the sheet S being conveyed in the nip area slipping or being wrinkled in the nip area.

Moreover, since the pad holder 140 has the first holding surface 141 and the second holding surface 142, the first pressure pad P1 and the second pressure pad P2 can be moved without changing their relative positions and movement amounts.

Further, in a state where the first pressure pad P1 is not deformed, the first pressing surface PM1 of the base portion P11 and the second pressing surface PM2 of the extending portion P12 are at the same position in the moving direction. Therefore, the first pressure pad P1 can be continuously pressed against the inner circumferential surface 131 of the endless belt 130.

The pad holder 140 also has a support surface 143 that protrudes from the first holding surface 141 toward the heating roller and supports the extension P12 from the side opposite to the heating roller in the moving direction. Therefore, an appropriate nip pressure can be generated between the heating roller and the extending portion.

Further, the lowest value K3 of the pressure with which the extending portion P12 presses the endless belt 130 is smaller than the highest value K1 of the pressure with which the base portion P11 presses the endless belt 130, and the second pressure pad P2 presses the endless belt 130. is smaller than the maximum value K2 of the pressure. Therefore, the pressure with which the extending portion P12 presses the endless belt 130 can be suppressed from becoming greater than the pressure with which the base portion P11 and the second pressure pad P2 press the endless belt 130.

Note that the present disclosure is not limited to the embodiments described above, and can be utilized in various forms as exemplified below.

In the embodiment described above, as shown in FIG. 4(a), when the first pressure pad P1 is not deformed, the support surface 143 is not in contact with the extension portion P12. This disclosure is not limited thereto.

For example, the first pressure pad P101 shown in FIGS. 5A and 5B includes a base portion P11 and an extension portion P112. In this form, as shown in FIG. 5A, the support surface 143 is in contact with the extension portion P112 when the first pressure pad P101 is not deformed. As shown in FIG. 5(b), even when the first pressure pad P101 is deformed, the support surface 143 contacts the extension portion P112.
Also in this embodiment, it is possible to reduce the proportion of the portion of the endless belt that is not pressed by the pressure pad in the region between the first pressure pad and the second pressure pad. Furthermore, as shown in FIG. 5(c), the difference between the pressure in the second nip portion NP2 and the pressures in the first nip portion NP1 and the third nip portion NP3 is smaller than in the form of FIG. .

In the embodiment described above, as shown in FIG. 4(a), when the first pressure pad P1 is not deformed, the first pressing surface PM1 and the second pressing surface PM2 are continuous and the same plane, Although the first bottom surface QM1 and the second bottom surface QM2 are not continuous and on the same plane, the present disclosure is not limited thereto.

For example, the first pressure pad P201 shown in FIGS. 6(a) and 6(b) has a base portion P11 and an extending portion P212. In this form, as shown in FIG. 6(a), when the first pressure pad P301 is not deformed, the first bottom surface QM1 and the second bottom surface QM2 are continuous and the same plane, and the first pressing surface PM1 and the second pressing surface PM2 are not continuous and on the same plane. Also in this form, in the area between the first pressure pad and the second pressure pad, the endless belt is not pressed by the pressure pad. The ratio can be reduced. Furthermore, as shown in FIG. 6(c), the difference between the pressure in the second nip portion NP2 and the pressures in the first nip portion NP1 and the third nip portion NP3 is smaller than in the form of FIG. .

For example, the first pressure pad P301 shown in FIGS. 7(a) and 7(b) has a base portion P11 and an extending portion P312. In this form, as shown in FIG. 7(a), when the first pressure pad P301 is not deformed, the first pressing surface PM1 and the second pressing surface PM2 are not continuous and the same plane, but the first pressing surface PM1 and the second pressing surface PM2 are The bottom surface QM1 and the second bottom surface QM2 are also not continuous and the same plane.
Also in this embodiment, it is possible to reduce the proportion of the portion of the endless belt that is not pressed by the pressure pad in the region between the first pressure pad and the second pressure pad. Further, as shown in FIG. 7(c), the difference between the pressure in the second nip portion NP2 and the pressures in the first nip portion NP1 and the third nip portion NP3 is smaller than in the form of FIG. .

The pad holder 340 in the form of FIGS. 6 and 7 does not have a support surface protruding from the first holding surface 341, and has a simpler shape than the embodiment described above. Therefore, it is possible to prevent the pad holder 340 from having a complicated shape.

In the embodiment described above, as shown in FIG. 4(a), the extending portion P12 has a rectangular parallelepiped shape when the first pressure pad P1 is not deformed. Not limited.

For example, the first pressure pad P401 shown in FIGS. 8(a) and 8(b) has a base portion P11 and an extending portion P412. In this form, as shown in FIG. 8A, the extending portion P412 does not have a rectangular parallelepiped shape when the first pressure pad P401 is not deformed. The second bottom surface QM2 of the extending portion P412 in this form is a plane that is inclined so as to approach the second pressing surface PM2 as it goes downstream in the conveyance direction.
Also in this embodiment, it is possible to reduce the proportion of the portion of the endless belt that is not pressed by the pressure pad in the region between the first pressure pad and the second pressure pad. Furthermore, as shown in FIG. 8(c), the difference between the pressure in the second nip portion NP2 and the pressures in the first nip portion NP1 and the third nip portion NP3 is smaller than in the embodiment of FIG. .
Furthermore, although the second bottom surface QM2 shown in FIG. 8(a) is a flat surface, it may have a curved surface configuration.

In the embodiment described above, the moving mechanism 83 moves the pressure unit 82, but the moving mechanism may move the heating roller or both the heating roller and the pressure unit. . That is, the moving mechanism can be configured to move at least one of the heating roller and the pressure unit in the movement direction and change the distance between the heating roller and the pressure unit (pad holder 140).

In the embodiment described above, the first holding surface 141 and the second holding surface 142 are surfaces perpendicular to the moving direction, but the first holding surface 141 and the second holding surface 142 are surfaces perpendicular to the moving direction. You don't have to.

In the embodiment described above, when the first pressure pad P1 and the second pressure pad P2 are not elastically deformed, the dimension D3 in the moving direction from the second holding surface 142 to the second pressing surface PM3 is equal to the second bottom surface. Although the configuration was larger than the dimension D2 in the moving direction from QM2 to the second pressing surface PM2, the dimension D3 in the moving direction from the second holding surface 142 to the second pressing surface PM3 is larger than the dimension D2 in the moving direction from the second bottom surface QM2 to the second pressing surface It may be smaller than the dimension D2 in the moving direction up to PM2.

In the above-described embodiment, a cylindrical roller with a built-in heater 110 is illustrated as the rotating body, but the present disclosure is not limited to this, and for example, an endless belt whose inner circumferential surface is heated by a heater may also be used. good. Alternatively, an external heating method or an IH (induction heating) method may be used in which a heater is disposed outside the rotating body to heat the outer circumferential surface of the rotating body. Alternatively, a heater may be disposed inside the endless belt to indirectly heat the rotating body that contacts the outer peripheral surface of the endless belt. Further, the rotating body and the endless belt may each have a built-in heater.

The elements described in the embodiments and modifications described above may be implemented in any combination.

8 Fixing device 81 Heating roller 82 Pressure unit 83 Moving mechanism 130 Endless belt 140 Pad holder 141 First holding surface 142 Second holding surface 143 Support surface 150 Sliding sheet 160 Belt guide 170 Stay P Pressure pad P1 First pressure Pad P11 Base part P12 Extension part P2 Second pressure pad PM1 First pressing surface PM2 Second pressing surface PM3 Third pressing surface QM1 First bottom surface QM2 Second bottom surface QM3 Third bottom surface

Claims (8)

heating roller;
an endless belt that contacts the heating roller and nip the sheet together with the heating roller to convey the sheet in the conveying direction;
a first pressure pad that is made of an elastic body and presses the endless belt against the heating roller;
a second pressure pad that is located downstream of the first pressure pad in the conveying direction, is made of an elastic body, and presses the endless belt against the heating roller;
The first pressure pad and the second pressure pad are movable relative to the heating roller in a direction of movement toward the heating roller,
The first pressure pad has a base portion and an extension portion extending from the base portion toward the downstream side in the conveyance direction,
A fixing device characterized in that, when the first pressure pad is not deformed, a dimension of the extending portion in the moving direction is smaller than a dimension of the base portion in the moving direction. The pad holder has a first holding surface that holds the first pressure pad, and a second holding surface that holds the second pressure pad, and is movable in the moving direction. The fixing device according to claim 1.
In a state where the first pressure pad is not deformed, a first pressing surface of the base portion that presses the endless belt and a second pressing surface of the extension portion that presses the endless belt are connected to each other during the movement. The fixing device according to claim 2, characterized in that the positions in the directions are equal. 2. The pad holder has a support surface that protrudes from the first holding surface toward the heating roller and supports the extending portion from a side opposite to the heating roller in the moving direction. The fixing device described in . When the first pressure pad is not deformed, the support surface does not contact the extension part,
The fixing device according to claim 4, wherein the support surface contacts the extending portion when the first pressure pad is deformed. The second pressure pad is harder than the first pressure pad,
When the first pressure pad and the second pressure pad are not deformed, the dimension in the moving direction from the first holding surface to the first pressing surface is equal to the distance from the first holding surface to the second pressing surface. The fixing device according to claim 3, wherein the fixing device is larger than the dimension in the moving direction up to the pressing surface. The base portion has a first bottom surface that is held by the first holding surface,
3. The fixing device according to claim 2, wherein the first bottom surface is located on the same plane as a second bottom surface of the extension part on the opposite side of the heating roller in the moving direction. The minimum value of the pressure with which the extending portion presses the endless belt is:
less than the maximum pressure with which the base presses the endless belt,
The fixing device according to any one of claims 1 to 7, wherein the pressure of the second pressure pad is smaller than the maximum pressure with which the endless belt is pressed.

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