阅读说明：本技术 定影装置、图像形成装置 (Fixing device and image forming apparatus ) 是由 小柳圣 佐藤贵亮 井上彻 于 2019-03-07 设计创作，主要内容包括：本发明获得一种定影装置以及图像形成装置,与加热模式时包含在辊隙范围内的导热部的长度和定影模式时包含在辊隙范围内的导热部的长度相同的情况相比,能够在加热模式时缩短发热板达到规定温度所需的时间。移动部使加压部移动,以使加热模式时包含在辊隙范围内的导热部的长度比定影模式时包含在辊隙范围内的导热部的长度短。(The invention provides a fixing device and an image forming apparatus, which can shorten the time required for a heat generating plate to reach a specified temperature in a heating mode compared with the case that the length of a heat conducting part contained in a nip range in the heating mode is the same as the length of the heat conducting part contained in the nip range in the fixing mode. The moving section moves the pressing section so that the length of the heat-conducting section included in the nip range in the heating mode is shorter than the length of the heat-conducting section included in the nip range in the fixing mode.)

1. A fixing device, characterized by comprising:

an endless belt rotating in a circumferential direction and having an outer circumferential surface contacting the recording medium to be conveyed;

a heat generating plate formed with a heat generating portion that extends in an axial direction of the endless belt and generates heat so as to have a surface in contact with an inner peripheral surface of the endless belt and extend in the axial direction;

a heat conducting portion that is in contact with a back surface of the heat generating plate of a portion different from a portion where the heat generating portion is formed in a transport direction of the recording medium, and conducts heat generated by the heat generating portion in the axial direction;

a force application portion that applies a force to the heat conduction portion toward the heat generation plate;

a pressing section disposed on the opposite side of the heat generating plate with the endless belt therebetween, forming a nip with the endless belt, and pressing the recording medium to be conveyed to the endless belt; and

a moving section that moves the pressure section relative to the endless belt, and that narrows a nip width of the nip in a heating mode in which the endless belt is heated, compared to a fixing mode in which an image is fixed to a recording medium,

in the heating mode, a length of the heat generating portion that generates heat when included in a range of the nip in a conveying direction of the recording medium is set to L1, a length of the heat conducting portion included in the range of the nip in the conveying direction is set to S1,

in the fixing mode, L2 represents the length of the heat generating portion that generates heat when included in the range of the nip in the conveying direction, S2 represents the length of the heat conducting portion included in the range of the nip in the conveying direction, and the following formula (1) is satisfied,

L2-L1＜S2-S1……(1)。

2. a fixing device according to claim 1,

the length L1 is the same as the length L2.

3. The fixing device according to claim 1 or 2,

the plurality of heat generating portions having different lengths in the axial direction are arranged in the conveying direction,

in the heating mode, the heat generating portion that is longest in the axial direction is included in the range of the nip in the conveying direction, and in the heating mode, heat is generated by the heat generating portion that is longest in the axial direction.

4. A fixing device according to claim 3,

in the heating mode, all the heat generating portions are included in the range of the nip in the conveying direction, and in the heating mode, heat is generated by all the heat generating portions.

5. A fixing device according to claim 4,

the heat generating portion that is longest in the axial direction is a portion that is disposed on the center side of the nip in the conveying direction in the heating mode.

6. The fixing device according to claim 1 or 2,

the plurality of heat generating portions having different lengths in the axial direction are arranged in the conveying direction,

in the heating mode, the heat generating portion closest to the heat conductive portion in the conveying direction does not generate heat, and heat is generated by the heat generating portion different from the heat generating portion closest to the heat conductive portion.

7. A fixing device according to claim 6,

in the heating mode, heat is generated by the heat generating portion that is farthest from the heat conductive portion in the conveying direction.

8. The fixing device according to any one of claims 1 to 7,

the length S1 is zero.

9. An image forming apparatus, characterized by comprising:

a forming section that forms an image on a recording medium; and

the fixing device according to any one of claims 1 to 8, fixing the image formed on the recording medium to the recording medium.

Technical Field

The present invention relates to a fixing device and an image forming apparatus.

Background

Patent document 1 describes a fixing device that heats and fixes a developed image by passing a recording material and a fixing film (film) on which an unfixed developed image is placed through a nip (nip) between a heating body and a pressing member, wherein a highly heat conductive member is provided on the back surface of the heating body.

[ Prior art documents ]

[ patent document ]

Patent document 1: japanese patent laid-open No. H05-289555

Disclosure of Invention

[ problems to be solved by the invention ]

There is a fixing device including: an endless belt that rotates and has an outer circumferential surface that contacts the recording medium being conveyed; and a heat generating plate having a surface in contact with an inner circumferential surface of the endless belt and formed with a heat generating portion that generates heat to heat a part of the inner circumferential surface of the endless belt. Further, the fixing device includes: a heat conducting portion that is in contact with a back surface of the heat generating plate at a portion different from a portion where the heat generating portion is formed in a conveying direction of the recording medium, and that conducts heat generated by the heat generating portion in an axial direction; and a force application portion that applies force to the heat conduction portion toward the heat generation plate. Further, the fixing device includes a pressing portion that forms a nip with the endless belt and presses the recording medium to an outer peripheral surface of the endless belt.

In the above-described fixing apparatus, in a heating mode (start mode) in which the endless belt is heated by the movement of the pressure section, the nip width of the nip may be narrowed as compared with a fixing mode in which an image is fixed to a recording medium. Specifically, in the heating mode, the nip width is narrowed so as to prevent heat generated from the heat generating portion from being conducted to the pressing portion.

Here, in the heating mode, if the heat conductive portion is entirely included in the range of the nip, the heat transfer rate between the heat generating plate and the heat conductive portion is high, and the heat generated by the heat generating portion is transferred to the heat conductive portion. Therefore, the time required to heat the endless belt will become longer in the heating mode. In other words, the time required to heat the heat generating plate will become longer in the heating mode.

The present invention has an object to shorten the time required for a heat generating plate to reach a predetermined temperature in a heating mode, as compared with a case where the length of a heat conducting portion included in a nip range in the heating mode is the same as the length of a heat conducting portion included in the nip range in a fixing mode.

[ means for solving the problems ]

A fixing device according to embodiment 1 of the present invention includes: an endless belt rotating in a circumferential direction and having an outer circumferential surface contacting the recording medium to be conveyed; a heat generating plate formed with a heat generating portion that extends in an axial direction of the endless belt and generates heat so as to have a surface in contact with an inner peripheral surface of the endless belt and extend in the axial direction; a heat conducting portion that is in contact with a back surface of the heat generating plate of a portion different from a portion where the heat generating portion is formed in a transport direction of the recording medium, and conducts heat generated by the heat generating portion in the axial direction; a force application portion that applies a force to the heat conduction portion toward the heat generation plate; a pressing section disposed on the opposite side of the heat generating plate with the endless belt therebetween, forming a nip with the endless belt, and pressing the recording medium to be conveyed to the endless belt; and a moving section that moves the pressure section relative to the endless belt, and that, in a heating mode in which the endless belt is heated, narrows a nip width of the nip compared to a fixing mode in which an image is fixed to a recording medium. In the heating mode, a length of the heat generating portion included in a range of the nip in a transport direction of the recording medium to generate heat is set to L1, a length of the heat conductive portion included in the range of the nip in the transport direction is set to S1, and in the fixing mode, a length of the heat generating portion included in the range of the nip in the transport direction to generate heat is set to L2, and a length of the heat conductive portion included in the range of the nip in the transport direction is set to S2, and the following equation (1) is satisfied, where L2-L1 < S2-S1 … … (1).

A fixing device according to embodiment 2 of the present invention is the fixing device according to embodiment 1, wherein the length L1 is the same value as the length L2.

A fixing device according to embodiment 3 of the present invention is the fixing device according to embodiment 1 or 2, wherein the plurality of heat generating portions having different lengths in the axial direction are arranged in the conveying direction, and the heat generating portion that is longest in the axial direction is included in a range of the nip in the conveying direction in the heating mode. In the heating mode, heat is generated by the heat generating portion that is longest in the axial direction.

A fixing device according to embodiment 4 of the present invention is the fixing device according to embodiment 3, wherein all of the heat generating portions are included in the range of the nip in the conveying direction in the heating mode. In the heating mode, heat is generated by all the heat generating portions.

A fixing device according to embodiment 5 of the present invention is the fixing device according to embodiment 4, wherein the heat generating portion that is longest in the axial direction is a portion that is disposed on the center side of the nip in the conveying direction in the heating mode.

A fixing device according to embodiment 6 of the present invention is the fixing device according to embodiment 1 or 2, wherein the plurality of heat generating portions having different lengths in the axial direction are arranged in the conveying direction. In the heating mode, the heat generating portion closest to the heat conductive portion in the conveying direction does not generate heat, and heat is generated by the heat generating portion different from the heat generating portion closest to the heat conductive portion.

A fixing device according to embodiment 7 of the present invention is the fixing device according to embodiment 6, wherein heat is generated by the heat generating portion that is farthest from the heat conductive portion in the conveying direction in the heating mode.

A fixing device according to embodiment 8 of the present invention is the fixing device according to any one of embodiments 1 to 7, wherein the length S1 is zero.

An image forming apparatus according to embodiment 9 of the present invention includes: a forming section that forms an image on a recording medium; and the fixing device according to any one of embodiments 1 to 8, fixing the image formed on the recording medium to the recording medium.

[ Effect of the invention ]

According to the fixing device of embodiment 1 of the present invention, the time required for the heat generating plate to reach the predetermined temperature in the heating mode can be shortened as compared with the case where the length of the heat conductive portion included in the nip range in the heating mode is the same as the length of the heat conductive portion included in the nip range in the fixing mode.

According to the fixing device of embodiment 2 of the present invention, the time required for the heat generating plate to reach the predetermined temperature in the heating mode can be shortened as compared with the case where the length L1 of the heat generating portion is shorter than the length L2 of the heat generating portion.

According to the fixing device of embodiment 3 of the present invention, the time required for the heat generating plate to reach the predetermined temperature in the heating mode can be shortened as compared with the case where the heat generating portion that generates heat is shorter than other heat generating portions.

According to the fixing device of embodiment 4 of the present invention, the time required for the heat generating plate to reach the predetermined temperature can be shortened in the heating mode, as compared with the case where there is a heat generating portion that does not generate heat in the heating mode.

According to the fixing device of embodiment 5 of the present invention, the time required for the heat generating plate to reach the predetermined temperature in the heating mode can be shortened as compared with the case where the longest heat generating portion is arranged at the nip end side portion in the conveying direction in the heating mode.

According to the fixing device of embodiment 6 of the present invention, the time required for the heat generating plate to reach the predetermined temperature can be shortened in the heating mode, as compared with the case where heat is generated only by the heat generating portion closest to the heat conductive portion in the heating mode.

According to the fixing device of embodiment 7 of the present invention, the time required for the heat generating plate to reach the predetermined temperature in the heating mode can be shortened as compared with the case where heat is generated only by the heat generating portion different from the heat generating portion farthest from the heat conducting portion in the heating mode.

According to the fixing device of embodiment 8 of the present invention, the time required for the heat generating plate to reach the predetermined temperature in the heating mode can be shortened as compared with the case of having a length of S1 in the heating mode.

According to the image forming apparatus of embodiment 9 of the present invention, the time required for outputting the first sheet after the start can be shortened as compared with the case of providing a fixing apparatus in which the length of the heat transfer portion included in the nip range in the heating mode is the same as the length of the heat transfer portion included in the nip range in the fixing mode.

Drawings

Fig. 1 is an enlarged sectional view of a fixing device according to embodiment 1 of the present invention in a heating mode.

Fig. 2 is an enlarged cross-sectional view of the fixing device according to embodiment 1 of the present invention in a fixing mode.

Fig. 3 is a plan view showing a heat generating plate of the fixing device according to embodiment 1 of the present invention.

Fig. 4 is a sectional view of the fixing device according to embodiment 1 of the present invention in a heating mode.

Fig. 5 is a cross-sectional view of the fixing device according to embodiment 1 of the present invention in a fixing mode.

Fig. 6 is a sectional view of the fixing device according to embodiment 1 of the present invention in a heating mode.

Fig. 7 is a perspective view showing a heat-conducting member and a spring of the fixing device according to embodiment 1 of the present invention.

Fig. 8 is a block diagram showing a control system in a control unit of the fixing device according to embodiment 1 of the present invention.

Fig. 9 is a front view showing a fixing device according to embodiment 1 of the present invention.

Fig. 10 is a schematic configuration diagram showing an image forming apparatus according to embodiment 1 of the present invention.

Fig. 11 is an enlarged sectional view of a fixing device according to a comparative embodiment to embodiment 1 of the present invention in a heating mode.

Fig. 12 is an enlarged sectional view of a fixing device according to embodiment 2 of the present invention in a heating mode.

Fig. 13 is a plan view showing a heat generating plate of a fixing device according to embodiment 3 of the present invention.

Fig. 14 is an enlarged sectional view of a fixing device according to embodiment 3 of the present invention in a heating mode.

Fig. 15 is an enlarged cross-sectional view of a fixing device according to embodiment 3 of the present invention in a fixing mode.

[ description of symbols ]

10: image forming apparatus with a toner supply device

18: image forming unit (an example of forming part)

50: fixing device

52: pressure roller (one example of a pressurizing part)

62: endless belt

64: heating plate

76 a: resistance heating part (an example of heating part)

76 b: resistance heating part (an example of heating part)

84: spring (an example of a biasing part)

86: moving part

92: heat-conducting member (an example of a heat-conducting portion)

150: fixing device

250: fixing device

264: heating plate

276 a: resistance heating part (an example of heating part)

276 b: resistance heating part (an example of heating part)

276 c: resistance heating part (an example of heating part)

NF: roller gap

P: sheet member

P1: sheet member

P2: sheet member

P3: sheet member

Detailed Description

< embodiment 1 >

An example of a fixing device and an image forming apparatus according to embodiment 1 of the present invention will be described with reference to fig. 1 to 11. In the figure, arrow H indicates the vertical direction of the apparatus (vertical direction), arrow W indicates the width direction of the apparatus (horizontal direction), and arrow D indicates the depth direction of the apparatus (horizontal direction).

(integral constitution)

As shown in fig. 10, in the image forming apparatus 10 of the present embodiment, from the lower side toward the upper side in the vertical direction (the direction of arrow H), there are arranged in order: a housing portion 14 that houses a sheet member P as a recording medium; a conveying section 16 that conveys the sheet members P stored in the storage section 14; and an image forming section 20 for forming an image on the sheet member P conveyed from the storage section 14 by the conveying section 16.

[ storage section 14 ]

In the storage portion 14, a storage member 26 is disposed which can be drawn out from the apparatus main body 10A of the image forming apparatus 10 toward the near side in the apparatus depth direction, and the sheet member P is mounted on the storage member 26. Further, in the storage section 14, a delivery roller 30 is disposed, and the delivery roller 30 delivers the sheet member P loaded in the storage member 26 to the conveyance path 28 constituting the conveyance section 16.

[ carrying section 16 ]

The conveying section 16 is provided with a plurality of conveying rollers 32, and the plurality of conveying rollers 32 convey the sheet member P along a predetermined conveying path 28.

[ image forming section 20 ]

In the image forming portion 20, four image forming units 18Y, 18M, 18C, and 18K of Yellow (Yellow), Magenta (M), Cyan (C), and blacK (blacK, K) are arranged. In the following description, Y, M, C, K may be omitted when the specification Y, M, C, K need not be distinguished.

In the image forming unit 18 of each color, an image holder 36, a charging roller 38 that charges the surface of the image holder 36, and an exposure device 42 that irradiates the charged image holder 36 with exposure light are disposed. Further, in the image forming portion 20, a developing device 40 is disposed, and the developing device 40 develops the electrostatic latent image formed by exposing the charged image holding body 36 to the exposure device 42 and visualizes the electrostatic latent image as a toner image. The image forming unit 18 is an example of a forming portion.

Further, the image forming unit 20 includes: a ring-shaped transfer belt 22 which rotates in the direction of arrow a in the figure; and a primary transfer roller 44 that transfers the toner images formed by the image forming units 18 of the respective colors to the transfer belt 22. Further, the image forming unit 20 includes: a secondary transfer roller 46 that transfers the toner image of the transfer belt 22 to the sheet member P; and a fixing device 50 that heats and pressurizes the sheet member P to fix the toner image to the sheet member P. The fixing device 50 will be described in detail later.

(function of image Forming apparatus)

In the image forming apparatus 10, an image is formed in the following manner.

First, the charging rollers 38 of the respective colors to which the voltages are applied are brought into contact with the surfaces of the image holding bodies 36 of the respective colors, and the surfaces of the image holding bodies 36 are uniformly negatively charged at a predetermined potential. Then, based on data input from the outside, the exposure device 42 irradiates the surface of the charged image holding body 36 of each color with exposure light to form an electrostatic latent image.

Thereby, an electrostatic latent image corresponding to data is formed on the surface of the image holding body 36 of each color. Further, the developing devices 40 of the respective colors develop the electrostatic latent images to visualize them as toner images. The toner image formed on the surface of the image holding member 36 of each color is transferred to the transfer belt 22 by the primary transfer roller 44.

Therefore, the sheet member P fed out from the storage member 26 to the conveyance path 28 by the feeding-out roller 30 is fed out to the transfer position T where the transfer belt 22 contacts the secondary transfer roller 46. At the transfer position T, the sheet member P is sandwiched and conveyed by the transfer belt 22 and the secondary transfer roller 46, and thereby the toner image on the surface of the transfer belt 22 is transferred to the sheet member P.

The toner image transferred to the sheet member P is fixed to the sheet member P by the fixing device 50. Then, the sheet member P with the toner image fixed thereto is discharged to the outside of the apparatus body 10A by the conveying roller 32.

(major part constitution)

Next, the fixing device 50 will be explained.

The fixing device 50 is detachably mounted on the device main body 10A, and includes a pressure roller 52 and a heating section 60 facing the pressure roller 52 in the device width direction, as shown in fig. 5. The fixing device 50 further includes a motor 58 (see fig. 9) that rotates the pressure roller 52, a moving unit 86 (see fig. 9) that moves the pressure roller 52, and a control unit 102 (see fig. 8) that controls each unit.

[ pressure roller 52 ]

As shown in fig. 5, the pressure roller 52 includes a metal shaft 54 extending in the device depth direction, a cylindrical elastic layer 56 into which the shaft 54 is inserted, and a release layer, not shown, covering the elastic layer 56. The pressure roller 52 is an example of a pressurizing portion.

The shaft portion 54 is formed of a metal material such as steel, stainless steel, or aluminum, the elastic layer 56 is formed of a rubber material, and the release layer is formed of tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), for example.

In the above configuration, the pressure roller 52 is grounded and biased toward the heating section 60. Further, the pressure roller 52 is rotated in the direction of arrow R1 by transmitting a rotational force from the motor 58 (see fig. 9). Thereby, the rotating pressure roller 52 presses the sheet member P to which the toner image is transferred to the outer peripheral surface of the later-described endless belt 62. In the present embodiment, the pressure roller 52 is rotated so that the peripheral speed of the outer peripheral surface of the elastic layer 56 reaches 230 [ mm/sec ].

[ heating section 60 ]

As shown in fig. 5, the heating unit 60 includes: a cylindrical annular band 62 extending in the device depth direction; a heat generation plate 64 that generates heat to heat the endless belt 62; and a heat conduction member 92 that conducts heat of the heat generating plate 64 in the device depth direction (the axial direction of the endless belt 62). Further, the heating section 60 includes: a compression coil spring 84 (hereinafter referred to as "spring 84") that urges the heat conductive member 92 toward the heat generating plate 64; a holding member 90 that holds the heat generating plate 64; and a frame 80 supporting the holding member 90. The heating unit 60 includes a detection member 82 (see fig. 6) that detects the temperature of the heat generating plate 64.

Annular band 62-

As shown in fig. 5, the endless belt 62 is in contact with the pressure roller 52 at its outer circumferential surface. As described above, the endless belt 62 comes into contact with the pressure roller 52, thereby forming the nip NF (see fig. 2) that sandwiches the sheet member P being conveyed. The endless belt 62 is formed of, for example, polyimide resin coated with fluorine on the outer peripheral surface, and the thickness of the endless belt 62 is 100 [ μm ].

Further, cylindrical support members (not shown) that support the inner peripheral surface of the endless belt 62 are disposed at both ends of the endless belt 62 in the longitudinal direction, respectively. Further, a lubricating oil (e.g., silicone oil) is applied to the inner circumferential surface of the endless belt 62 to reduce frictional resistance with the heat generating plate 64.

In the above configuration, the endless belt 62 rotates (revolves) in the direction of the arrow R2 (counterclockwise direction) in the figure following the rotating pressure roller 52 while maintaining a circular shape.

Retaining member 90

As shown in fig. 5, the holding member 90 is disposed inside the endless belt 62. The holding member 90 is formed of a resin material such as Liquid Crystal Polymer (LCP), for example, and extends in the device depth direction. The cross section of the holding member 90 perpendicular to the longitudinal direction is U-shaped and opens opposite to the pressure roller 52 side. The thermal conductivity of the holding member 90 was set to 0.56 [ W/mK ].

Further, in the holding member 90, a concave mounting portion 90a for mounting the heat generating plate 64 with a mounting member such as an adhesive agent not shown is formed in a portion facing the pressure roller 52. In the mounting portion 90a, a through-hole 90b in which a part of the heat-conductive member 92 is disposed is formed in a portion on the downstream side in the conveying direction of the sheet member P so as to penetrate the holding member 90 in the device width direction (the direction in which the pressure roller 52 faces the heating portion 60). The mounting portion 90a and the through-hole 90b extend in the depth direction of the device.

Further, as shown in fig. 6, in the holding member 90, a plurality of through holes 90c for disposing the probe members 82 are formed at intervals in the device depth direction.

Frame 80-

As shown in fig. 5, the frame 80 is disposed inside the endless belt 62 on the opposite side of the pressure roller 52 with the holding member 90 interposed therebetween. The frame 80 is formed by bending a metal plate, and extends in the device depth direction. The frame 80 has a U-shape with a side opening of the holding member 90 in a cross section perpendicular to the longitudinal direction.

Further, the front end side portion of the holding member 90 is attached to the front end side portion of the U-shaped frame 80 by an attachment member such as an adhesive agent not shown, whereby the frame 80 supports the holding member 90. Thus, a region 94 surrounded by the holding member 90 and the frame 80 is formed inside the endless belt 62. Both ends of the frame 80 in the longitudinal direction protrude outward from the endless belt 62, and the protruding portions are fixed to a not-shown framework member.

Heating plate 64-

As shown in fig. 5, the heat generating plate 64 is disposed on the opposite side of the pressure roller 52 with the endless belt 62 interposed therebetween, and has a surface in contact with the inner circumferential surface of the endless belt 62. The heat generating plate 64 is a plate-shaped member having a plate surface facing the device width direction, and extends from one end side to the other end side in the device depth direction of the endless belt 62. For example, the thickness of the heat generating plate 64 is set to 0.7 [ mm ].

The heat generating plate 64 has a rectangular shape extending in the depth direction of the device as shown in fig. 3 when viewed from the plate thickness direction. The heat generating plate 64 includes: an electrically insulating base material 66; an insulating film 68 formed of a heat-resistant resin material; three electrodes 72a, 72b, and 72c for voltage application; and a conducting portion 74 for applying a voltage to the electrodes 72a, 72b, and 72c to flow a current. The conductive portion 74 has resistance heat generating portions 76a and 76b (hatched portions in the figure) which generate heat by flowing a current. Here, the term "insulating property" means that the conductivity is 1 × 10^-10(S/m) or less.

The substrate 66 is a molded body of alumina as an electrically insulating ceramic. The thermal conductivity of the base material 66 was set to 41 [ W/mK ]. The electrode 72a, the electrode 72b, the electrode 72c, and the conduction portion 74 are formed on the surface of the base material 66 (the surface on the inner circumferential surface side of the endless belt 62). Specifically, the electrodes 72a, 72b, and 72c are formed on the front side of the base material 66 in the device depth direction, and are arranged in order from the upstream side toward the downstream side in the sheet member P conveyance direction (vertical direction in the drawing, hereinafter referred to as "sheet conveyance direction").

The conductive portion 74 is covered with the insulating film 68, and has a first conductive portion 74a extending from the electrode 72a toward the back side in the device depth direction, a second conductive portion 74b extending from the electrode 72b toward the back side in the device depth direction, and a third conductive portion 74c extending from the electrode 72c toward the back side in the device depth direction. The conduction portion 74 further includes a coupling portion 74d that couples the distal end portions of the first conduction portion 74a, the second conduction portion 74b, and the third conduction portion 74c so as to extend in the sheet conveying direction, with the coupling portion 74 d.

The resistance heat generating portion 76a is formed in the first conduction portion 74a, and the resistance heat generating portion 76a is formed so as to include a range in which the sheet member P (P1 in the drawing) having the largest size to be conveyed passes in the depth direction of the apparatus (the width direction of the sheet member P1). The resistance heat generating portion 76b is formed in the second conduction portion 74b, and the resistance heat generating portion 76b is formed so as to include a range in which the sheet member P (P2 in the drawing) of the minimum size to be conveyed passes in the depth direction of the apparatus. The resistance heat generation portion 76a is longer than the resistance heat generation portion 76 b. The width of the resistance heat generation portion 76a (length in the sheet conveying direction) is the same as the width of the resistance heat generation portion 76b (length in the sheet conveying direction). The resistance heat generating portions 76a and 76b are examples of heat generating portions.

Further, in the image forming apparatus 10, a center alignment system is adopted in which the sheet members P are supported from both sides in the width direction and the positions are aligned with respect to the center in the width direction.

In the above configuration, in a heating mode (start mode) in which the endless belt 62 is heated to fix the toner image to the sheet member P, the control section 102 (see fig. 8) turns on a power switch (not shown) and applies a voltage to the electrode 72a and the electrode 72c regardless of the size of the sheet member P. Thus, in the heating mode, heat is generated in the resistance heat generating portions 76a formed in the first conduction portion 74a, and no heat is generated in the resistance heat generating portions 76b formed in the second conduction portion 74 b. In other words, in the heating mode, heat is generated by the resistance heat generation portion 76a that is farthest from the heat conductive member 92 in the sheet conveying direction, and no heat is generated by the resistance heat generation portion 76b that is closest to the heat conductive member 92 in the sheet conveying direction.

Heat conducting member 92

As shown in fig. 5, the heat transfer member 92 is disposed in a region 94 surrounded by the holding member 90 and the frame 80, and has a rectangular shape extending in the device width direction when viewed from the device depth direction. Further, the heat conductive member 92 is inserted into the through hole 90c of the holding member 90 at the heating plate 64 side portion. The heat conductive member 92 is an example of a heat conductive portion.

Further, in the heat transfer member 92, the end surface on the heat generation plate 64 side is in contact with a portion on the downstream side in the sheet conveyance direction (vertical direction in the drawing) of the rear surface of the heat generation plate 64. Specifically, as shown in fig. 2, the end face of the heat transfer member 92 is in contact with the back surface of the heat generating plate 64 in a portion different from the portions where the resistance heat generating portions 76a and 76b are formed in the sheet conveying direction. In other words, the end face of the heat conductive member 92 is in contact with the back surface of the heat generation plate 64 of a portion different from the portion where heat is generated in the sheet conveyance direction.

The heat conductive member 92 includes a rectangular parallelepiped main body 92a and a silicon sheet 92b stacked on the end surface of the main body 92a on the side of the heat generating plate 64. The main body 92a is made of copper, and the thermal conductivity of the main body 92a is 403 [ W/mK ]. As described above, the thermal conductivity of the body portion 92a is higher than the thermal conductivity of the base material 66 of the heat generation plate 64.

Here, as described above, the heat conductive member 92 is disposed at a different position from the resistance heat generation portions 76a and 76b in the sheet conveying direction. Thus, the heat generated by the resistance heat generation portions 76a and 76b flows toward the downstream side in the sheet conveyance direction in the base material 66, and is conducted to the heat guide member 92. Also, the heat conductive member 92 conducts heat in the device depth direction. As described above, the heat flowing toward the sheet conveyance direction downstream side in the base material 66 is conducted to the heat conductive member 92.

Detection means 82

The probe member 82 is provided in plurality at intervals in the device depth direction, and as shown in fig. 6, a part thereof is disposed in a through hole 90c formed in the holding member 90. The detection member 82 is in contact with a portion of the back surface of the heat generation plate 64 on the upstream side in the sheet conveyance direction (vertical direction in the drawing). Specifically, the detection member 82 is in contact with the back surface of the heat generation plate 64 in a portion where the resistance heat generation portions 76a and 76b (see fig. 3) are formed in the sheet conveyance direction.

In the above configuration, the detection means 82 detects the temperature of the heat generating plate 64. The control unit 102 (see fig. 8) controls on/off of a power switch (not shown) to apply or stop application of voltage to the electrodes 72a, 72b, and 72c (see fig. 3) so that the temperature of the heat generating plate 64 detected by the detection member 82 falls within a predetermined range.

Spring 84-

As shown in fig. 5, the spring 84 extends in the device width direction on the opposite side of the heat generating plate 64 across the heat conductive member 92. The spring 84 is interposed between the frame 80 and the heat conductive member 92. Further, as shown in fig. 7, a plurality of springs 84 are provided at intervals in the device depth direction.

In the above configuration, the plurality of springs 84 urge the heat conductive member 92 toward the heat generating plate 64. The spring 84 is an example of the urging portion.

[ moving part 86 ]

As shown in fig. 9, the moving portions 86 are disposed on both sides of the pressure roller 52 in the device depth direction, and are configured by combining known mechanical elements.

The moving unit 86 moves the pressure roller 52 in the apparatus width direction and the apparatus vertical direction so as to change the nip width of the nip NF (see fig. 1 and 2). Specifically, the moving portion 86 moves the pressure roller 52 to a first position (see fig. 2) that is a nip width when the sheet member P is sandwiched between the pressure roller 52 and the endless belt 62 and the toner image is fixed to the sheet member P, and a second position (see fig. 1) where the nip width is narrower than the first position. As described above, the moving section 86 functions as a nip width changing member that changes the nip width of the nip NF.

Specifically, the control portion 102 controls the moving portion 86 to move the pressure roller 52 to the second position at the time of a heating mode (start mode) in which the endless belt 62 is heated in order to fix the toner image to the sheet member P. In contrast, in the fixing mode in which the sheet member P on which the toner image is formed is heated and pressed to fix the toner image, the control unit 102 controls the moving unit 86 to move the pressure roller 52 to the first position.

As shown in fig. 1, the length of the resistance heat generation portion 76a included in the range of the nip NF in the sheet conveyance direction in the state where the pressure roller 52 is disposed at the second position in the heating mode is L1. As described above, heat is generated in the resistance heat generating portion 76a formed in the first conduction portion 74a in the heating mode. Then, the length of the heat-conductive member 92 included in the range of the nip NF in the sheet conveying direction in this state is set to S1. Specifically, in the state where the pressure roller 52 is disposed at the second position in the heating mode, a part of the resistance heat generating portion 76a and a part of the heat conductive member 92 are included in the range of the nip NF in the sheet conveying direction. In the range of the nip NF, a sheet in which pressure-detectable elements are arranged in a matrix is sandwiched by the nip NF, and a portion where a voltage equal to or higher than a threshold value is generated is determined as the nip NF.

Further, as shown in fig. 2, in a state where the pressure roller 52 is disposed at the first position in the fixing mode, the length of the resistance heat generation portion 76a included in the range of the nip NF in the sheet conveyance direction is L2. Further, it is assumed that heat is generated by the resistance heat generating portion 76a formed in the first conduction portion 74a in the fixing mode. Further, the length of the heat conductive member 92 included in the range of the nip NF in the sheet conveying direction in this state is set to S2. Specifically, in a state where the pressure roller 52 is disposed at the first position in the fixing mode, all of the resistance heat generation portions 76a and all of the heat conductive member 92 are included in the range of the nip NF in the sheet conveying direction. Thus, the second position of the pressure roller 52 and the first position of the pressure roller 52 are determined so that the following expression (1) holds.

L2-L1＜S2-S1……(1)

As can be seen from the above formula (1), the length of the heat-conductive member 92 included in the range of the nip NF varies in the sheet conveying direction. That is, the moving portion 86 functions as an intra-nip heat transfer length changing member that changes the length of the heat transfer member included in the range of the nip NF.

Specifically, in the heating mode, the length S1 (see fig. 1) of the heat-conductive member 92 included in the range of the nip NF in the sheet conveying direction is shorter than the length S2 (see fig. 2) of the heat-conductive member 92 included in the range of the nip NF in the sheet conveying direction in the fixing mode.

Therefore, the pressure contact force of the heat generation plate 64 and the heat conductive member 92 in the heating mode is smaller than the pressure contact force of the heat generation plate 64 and the heat conductive member 92 in the fixing mode. That is, the moving portion 86 functions as a pressure contact force changing member that changes the pressure contact force between the heat conductive member 92 and the heat generating plate 64.

Also, the pressure contact force of the heat generation plate 64 and the heat conductive member 92 in the heating mode is smaller than the pressure contact force of the heat generation plate 64 and the heat conductive member 92 in the fixing mode. In this way, the heat transfer rate between the heat generation plate 64 and the heat conductive member 92 in the heating mode is lower than the heat transfer rate between the heat generation plate 64 and the heat conductive member 92 in the fixing mode. In other words, the heat transfer rate between the heat generation plate 64 and the heat conductive member 92 in the fixing mode is higher than the heat transfer rate between the heat generation plate 64 and the heat conductive member 92 in the heating mode. That is, the moving portion 86 functions as a heat transfer rate changing member that changes the heat transfer rate between the heat transfer member 92 and the heat generating plate 64.

Further, according to the formula (1), the length of the resistance heat generation portion 76a included in the range of the nip NF in the sheet conveying direction changes. That is, the moving portion 86 functions as a nip heat generating portion length changing member that changes the length of the resistance heat generating portion included in the range of the nip NF.

[ control section 102 ]

As shown in fig. 8, the control unit 102 controls the application of voltage to the electrodes 72a, 72b, and 72c by controlling the on/off of a power switch, not shown, based on the detection result of the detection means 82. The control of each unit by the control unit 102 will be described together with the operation described later.

(action)

Next, the operation of the fixing device 50 will be described in comparison with the fixing device 550 of the comparative embodiment. First, the configuration of the fixing device 550 according to the comparative embodiment will be mainly described with respect to the portions different from the fixing device 50. The operation of the fixing device 550 will be mainly described with respect to the portion different from the fixing device 50. In addition, regarding the actions of the fixing device 50 and the fixing device 550, a case of fixing the toner image to the sheet member P1 of the maximum size will be described.

Composition of the fixing device 550

The fixing device 550 does not include a moving unit with respect to the structure of the fixing device 50. The fixing device 550 is similar to the fixing device 50 except that it does not include a moving part.

Further, in the fixing device 550, as shown in fig. 11, the nip width of the nip NF does not change in the heating mode and the fixing mode. Specifically, in the fixing device 550, the pressure roller 52 is always disposed at the first position. That is, in the sheet conveying direction, all of the resistance heat generating portions 76a and all of the heat conductive member 92 are included in the range of the nip NF.

In other words, in the fixing device 550, a value obtained by subtracting the length of the heat-conductive member 92 included in the range of the nip NF in the sheet conveyance direction in the fixing mode from the length of the heat-conductive member 92 included in the range of the nip NF in the sheet conveyance direction in the heating mode is zero. In other words, the length of the heat-conductive member 92 included in the range of the nip NF in the heating mode is the same as the length of the heat-conductive member 92 included in the range of the nip NF in the fixing mode.

The functions of the fixing device 50 and the fixing device 550

In a state before the operation of the fixing apparatus 50 shown in fig. 4, the application of voltage to the electrodes 72a, 72b, and 72c (see fig. 3) is stopped, and further, the pressure roller 52 is disposed at the second position, and the rotation of the pressure roller 52 is stopped.

On the other hand, in the state before the operation of the fixing device 550 shown in fig. 11, the application of voltage to the electrodes 72a, 72b, and 72c (see fig. 3) is stopped, and further, the pressure roller 52 is disposed at the first position, and the rotation of the pressure roller 52 is stopped.

When fixing the toner image transferred to the sheet member P, the control portion 102 (see fig. 8) shifts the fixing device 50 and the fixing device 550 to the heating mode. Specifically, the control unit 102 controls the motor 58 to transmit the rotational force to the pressure roller 52. The pressure roller 52 shown in fig. 4 and 11 rotates in the direction of arrow R1 in the figure. Thereby, the endless belt 62 in contact with the pressure roller 52 rotates in the direction of arrow R2 in the drawing, following the rotating pressure roller 52.

When the endless belt 62 rotates, the control unit 102 turns on a power switch (not shown) and starts voltage application to the electrodes 72a and 72c (see fig. 3). Thereby, heat is generated by the resistance heat generating portion 76a, and the heat generating plate 64 generates heat. The heat generating plate 64 heats the rotating endless belt 62 from the inner circumferential surface.

Here, in the fixing device 550 shown in fig. 11, the pressure roller 52 is always disposed at the first position. Therefore, the nip width of the fixing device 550 in the heating mode is wider than the nip width of the fixing device 50 in the heating mode.

Since the nip width of the fixing device 550 in the heating mode is widened, the amount of heat transferred from the heat generating plate 64 to the pressure roller 52 via the endless belt 62 is increased. Therefore, in the fixing device 550, it takes time for the heat generation plate 64 to reach a predetermined temperature, as compared with the case of using the fixing device 50.

In the fixing device 550, the heat-conductive member 92 is entirely included in the range of the nip NF in the sheet conveying direction in the heating mode. Therefore, in the fixing device 550, the heat transfer rate between the heat generation plate 64 and the heat conductive member 92 in the heating mode is higher than the heat transfer rate between the heat generation plate 64 and the heat conductive member 92 in the heating mode of the fixing device 50.

Further, in the fixing device 550, the heat transfer rate between the heat generation plate 64 and the heat conductive member 92 in the heating mode becomes high, so that the amount of heat transferred from the heat generation plate 64 to the heat conductive member 92 increases at the time of the heating mode as compared with the case of using the fixing device 50. In other words, in the fixing device 50, the amount of heat transferred from the heat generation plate 64 to the heat conductive member 92 is reduced at the time of the heating mode, as compared with the case of using the fixing device 550.

On the other hand, in the fixing device 50, the above equation (1) holds. That is, a value obtained by subtracting the length S1 of the heat-conductive member 92 included in the range of the nip NF in the heating mode from the length S2 of the heat-conductive member 92 included in the range of the nip NF in the fixing mode is set to "S2 to S1". Further, a value obtained by subtracting the length L1 of the resistance heat generating portion 76a included in the range of the nip NF in the heating mode from the length L2 of the resistance heat generating portion 76a included in the range of the nip NF in the fixing mode is set to "L2 to L1". Thus, "S2-S1" is larger than "L2-L1".

That is, the effect of reducing the length of the heat conductive member 92 included in the range of the nip NF is greater than the effect of reducing the length of the resistance heat generation portion 76a included in the range of the nip NF.

As described above, in the fixing device 50, the time required for the heat generation plate 64 to reach the predetermined temperature in the heating mode is shorter than that in the case of using the fixing device 550.

When the temperatures detected by all the detection means 82 (see fig. 6) reach 200 [ ° (an example of a predetermined temperature), the mode is changed from a heating mode (start mode) in which the endless belt 62 is heated to a fixing mode in which the toner image is fixed to the sheet member P.

Specifically, in the fixing apparatus 50, the control unit 102 controls the moving unit 86 to move the pressure roller 52 to the first position. Further, when shifting to the fixing mode for fixing the toner image to the sheet member P1 of the maximum size, the control portion 102 continues the application of the voltage to the electrodes 72a, 72 c.

Then, the heating section 60 and the pressure roller 52 are conveyed while sandwiching the sheet member P to which the toner image is transferred, and thereby the toner image is fixed to the sheet member P. Then, the heating section 60 and the pressure roller 52 are conveyed while sandwiching the sheet member P on which the toner image is transferred, and thereby the heat of the heat generating plate 64 in the portion through which the sheet member P passes is deprived of the sheet member P. Thereby, the temperature of the heat generating plate 64 is lowered. Therefore, for example, the control unit 102 controls on/off of a power switch, not shown, so that the temperature of the heat generating plate 64 becomes 190 [ ° c or more and 230 [ ° c or less.

When a series of operations for forming a toner image on the sheet member P is completed and the operation of the fixing device 50 and the fixing device 550 is stopped, the control unit 102 turns off a power switch (not shown) to stop the application of voltage to the electrodes 72a and 72c (see fig. 3). Further, the control unit 102 controls the motor 58 to stop the rotation of the pressure roller 52. In the fixing apparatus 50, the control unit 102 controls the moving unit 86 to move the pressure roller 52 to the second position.

When the toner image is fixed to the sheet member P2 having the smallest size, the control unit 102 controls the on/off of a power switch, not shown, to stop the voltage application to the electrodes 72a and 72c and start the voltage application to the electrodes 72b and 72c when the fixing mode is switched. Thereby, heat is generated by the resistance heat generating portion 76 b.

In the case of the sheet member P having a size larger than the minimum size sheet member P2, the control unit 102 continues to apply the voltage to the electrodes 72a and 72c when the fixing mode is switched.

(conclusion)

As described above, since the fixing device 50 satisfies the above equation (1), the time required for the heat generation plate 64 to reach the predetermined temperature in the heating mode is shorter than that in the case of using the fixing device 550.

In the fixing device 50, at least a part of the longest resistance heat generating portion 76a is included in the range of the nip NF in the sheet conveying direction in the heating mode. In the heating mode, heat is generated by the resistance heat generation portion 76 a. Therefore, the time required for the heat generating plate 64 to reach the predetermined temperature in the heating mode is shorter than in the case where the resistance heat generating portion that generates heat in the heating mode is shorter than the other resistance heat generating portions.

Further, in the fixing device 50, heat is generated by the resistance heat generating portion 76a different from the resistance heat generating portion 76b closest to the heat conductive member 92 in the sheet conveying direction at the time of the heating mode. In other words, heat is not generated only by the resistance heat generation portion 76b closest to the heat conductive member 92 in the sheet conveying direction. Therefore, in the heating mode, the amount of heat conducted from the resistance heat generating portion to the heat conducting member is reduced as compared with the case where only the resistance heat generating portion closest to the heat conducting member 92 generates heat in the heating mode, and therefore the time required for the heat generating plate 64 to reach a predetermined temperature is short.

In the fixing apparatus 50, heat is generated by the resistance heat generating portion 76a that is farthest from the heat conductive member 92 in the sheet conveying direction in the heating mode. Therefore, compared to the case where heat is generated only by the resistance heat generating portion different from the resistance heat generating portion farthest from the heat conductive member 92 in the heating mode, the amount of heat conducted from the resistance heat generating portion to the heat conductive member is reduced in the heating mode, and therefore the time required for the heat generating plate 64 to reach a predetermined temperature is short.

In addition, in the image forming apparatus 10, the time required for outputting the first sheet after the start is shorter than that in the case where the fixing device 550 is provided.

< embodiment 2 >

An example of a fixing device and an image forming apparatus according to embodiment 2 of the present invention will be described with reference to fig. 12. In addition, embodiment 2 will be described mainly with respect to the differences from embodiment 1. The fixing device 150 according to embodiment 2 differs from the fixing device 50 according to embodiment 1 only in the state where the pressure roller 52 is disposed at the second position.

Specifically, as shown in fig. 12, in a state where the pressure roller 52 is disposed at the second position, all of the resistance heat generation portions 76a are included within the range of the nip NF in the sheet conveying direction. That is, the length L1 of the resistance heat generation portion 76a included in the range of the nip NF in the sheet conveyance direction in the heating mode and the length L2 of the resistance heat generation portion 76a included in the range of the nip NF in the sheet conveyance direction in the fixing mode are the same values. The same value means that one value is 90 [% ] to 110 [% ] of the other value in consideration of assembly variation, movement variation, and the like.

Thus, the time required for the heat generation plate 64 to reach the predetermined temperature in the heating mode is shorter than when the length L2 of the resistance heat generation portion 76a is shorter than the length L1 of the resistance heat generation portion 76a in the fixing device 150.

< embodiment 3 >

An example of the fixing device and the image forming apparatus according to embodiment 3 of the present invention will be described with reference to fig. 13 to 15. In addition, embodiment 3 will be described mainly with respect to the differences from embodiment 1.

As shown in fig. 13, the heat generating plate 264 provided in the fixing device 250 according to embodiment 3 is rectangular and extends in the device depth direction. The heat generating plate 264 includes an electrically insulating base material 66, an insulating film 68 made of a heat-resistant resin material, four electrodes 272a, 272b, 272c, 272d for voltage application, and a conducting portion 274 for applying a voltage to the electrodes 272 to flow a current. The conductive portion 274 has a resistance heat generating portion 276a, a resistance heat generating portion 276b, and a resistance heat generating portion 276c (hatched portions in the figure) which generate heat by flowing a current.

The electrode 272a, the electrode 272b, the electrode 272c, and the electrode 272d are arranged in this order from the upstream side toward the downstream side in the sheet conveying direction.

The conductive portion 274 is covered with the insulating film 68, and has a first conductive portion 274a extending from the electrode 272a to the back side in the device depth direction, a second conductive portion 274b extending from the electrode 272b to the back side in the device depth direction, and a third conductive portion 274c extending from the electrode 272c to the back side in the device depth direction. The conductive portion 274 further includes a fourth conductive portion 274d extending from the electrode 272d toward the back side in the device depth direction, and a coupling portion 274e coupling the distal end portion of the first conductive portion 274a, the distal end portion of the second conductive portion 274b, the distal end portion of the third conductive portion 274c, and the distal end portion of the fourth conductive portion 274d so as to extend in the sheet conveying direction.

The resistance heat generation portion 276a is formed in the first conduction portion 274a, and the resistance heat generation portion 276a is formed so as to include a range in which the sheet member P (P3 in the drawing) having the largest size used in the image forming apparatus 10 passes in the apparatus depth direction (the width direction of the sheet member P3). Further, the resistance heat generating portion 276b is formed in the second conductive portion 274b, and the resistance heat generating portion 276b is formed so as to include a range through which the sheet member P1 having the largest size passes in the depth direction of the apparatus. Further, the resistance heat generating portion 276c is formed in the third conductive portion 274c, and the resistance heat generating portion 276c is formed so as to include a range through which the sheet member P2 having the smallest dimension passes in the device depth direction.

That is, the lengths of the resistance heat generating portion 276b, the resistance heat generating portion 276a, and the resistance heat generating portion 276c are sequentially shorter. Further, the width of the resistance heat generation portion 276a (length in the sheet conveying direction), the width of the resistance heat generation portion 276b (length in the sheet conveying direction), and the width of the resistance heat generation portion 276c (length in the sheet conveying direction) are the same. The resistance heat generating portions 276a, 276b, 276c are examples of heat generating portions.

As shown in fig. 15, the resistance heat generating portions 276a, 276b, and 276c are disposed upstream of the heat conductive member 92 in the sheet conveying direction.

In the above configuration, in a state where the pressure roller 52 is disposed at the first position in the fixing mode, as shown in fig. 15, all of the resistance heat generation portions 276a, 276b, and 276c are included within the range of the nip NF in the sheet conveying direction. Further, the heat conductive member 92 is entirely included within the range of the nip NF in the sheet conveying direction.

When the image is fixed to the sheet member P1 having the maximum size, a voltage is applied to the electrodes 272b and 272d in the fixing mode, and heat is generated by the resistance heat generation portion 276 b. Further, in the case of fixing the image to the sheet member P2 of the minimum size, in the fixing mode, a voltage is applied to the electrodes 272c and 272d, and heat is generated by the resistance heat generating portion 276 c. Further, when fixing an image to the sheet member P3 having the largest size, a voltage is applied to the electrodes 272a and 272d in the fixing mode, and heat is generated by the resistance heat generation portion 276 a. In the case of sheet members P of other sizes, heat is generated by the shortest resistance heat generating portion 276 including the sheet members P of the above-described size in the device depth direction (width direction of the sheet members P).

On the other hand, in the state where the pressure roller 52 is disposed at the second position in the heating mode, as shown in fig. 14, all of the resistance heat generating portions 276a, 276b, and 276c are included in the range of the nip NF in the sheet conveying direction. The resistance heat generating portion 276b longest in the device depth direction is a central portion of the nip NF disposed in the sheet conveying direction. Here, the central portion of the nip NF in the sheet conveying direction means a central portion obtained by equally dividing the nip NF in the sheet conveying direction.

Further, the heat conductive member 92 is not entirely included within the range of the nip NF in the sheet conveying direction. In other words, the length S1 of the heat-conductive member 92 included in the range of the nip NF in the sheet conveyance direction is zero at the time of the heating mode. Further, in other words, the length S1 of the heat conductive member 92 included in the range of the nip NF in the sheet conveyance direction does not exist.

In the heating mode, a voltage is applied to all of the electrodes 272a, 272b, 272c, and 272d, and heat is generated by all of the resistance heat generating portions 276a, 276b, and 276 c. That is, the length L1 of the heat generating resistance portion included in the range of the nip NF in the sheet conveying direction and generating heat is a value obtained by summing the illustrated length L1-1 of the heat generating resistance portion 276a, the length L1-2 of the heat generating resistance portion 276b, and the length L1-3 of the heat generating resistance portion 276c in the heating mode. Similarly, in the fixing mode, the length L2 of the resistance heat generating portion that is included in the range of the nip NF in the sheet conveying direction and generates heat is L2-1 shown in fig. 15 in the case where heat is generated by the resistance heat generating portion 276a, and is L2-2 shown in fig. 15 in the case where heat is generated by the resistance heat generating portion 276 b. When heat is generated by the resistance heat generating portion 276c, L2-3 shown in fig. 15 is obtained.

As described above, in the fixing device 250, all of the resistance heat generation portions 276a, 276b, and 276c are included in the range of the nip NF in the sheet conveying direction in the heating mode. Further, in the heating mode, all of the resistance heat generating portions 276a, 276b, and 276c generate heat. Therefore, the time required for the heat generation plate 64 to reach the predetermined temperature in the heating mode is shorter than in the case where there is a resistance heat generation portion that does not generate heat in the heating mode.

In the fixing device 250, the longest resistance heat generating portion 276b is arranged at the center side portion of the nip NF in the sheet conveying direction in the heating mode. Therefore, compared to the case where the resistance heat generating portions 276b are arranged at the end side portion of the nip NF, even if the relative positions of the pressure roller 52 and the endless belt 62 are deviated in the heating mode, the longest resistance heat generating portion 276b can be suppressed from deviating from the range of the nip NF. Thus, the time required for the heat generation plate 64 to reach the predetermined temperature in the heating mode is shorter than in the case where the resistance heat generation portion 276b is disposed at the end side portion of the nip NF.

Further, in the fixing device 250, the length S1 of the heat-conductive member 92 included in the range of the nip NF in the sheet conveying direction is absent (the length is zero) at the time of the heating mode. Therefore, the amount of heat transferred from the heat generation plate 64 to the heat conductive member 92 is reduced as compared with the case where the length S1 of the heat conductive member 92 included in the range of the nip NF exists in the sheet conveyance direction (the case of being larger than zero) at the time of the heating mode. Thus, the time required for the heat generation plate 64 to reach the predetermined temperature in the heating mode is shorter than in the case where the length S1 of the heat conductive member 92 included in the range of the nip NF exists in the sheet conveyance direction (the case where it is greater than zero) in the heating mode.

While the present invention has been described in detail with reference to the specific embodiments, it will be apparent to those skilled in the art that the present invention is not limited to the embodiments, and various other embodiments can be made within the scope of the present invention. For example, in the above embodiment, the heat conductive member 92 includes the silicon sheet 92b on the end surface on the heat generating plate 64 side, but the sheet may not be particularly provided.

Further, in the above embodiment, the resistance heat generation portion 76, the resistance heat generation portion 276, and the heat transfer member 92 are arranged in this order from the upstream side in the sheet conveying direction, but the heat transfer member and the resistance heat generation portion may be arranged in this order from the upstream side in the sheet conveying direction.

In the above embodiment, the nip width is changed by the movement of the pressure roller 52, but the nip width may be changed by the movement of at least one of the heating section 60 and the pressure roller 52.

In the above embodiment, the spring 84 is used as the biasing portion, but any other elastic member such as an elastic pad (pad) may be used as long as it biases the heat conductive member 92 toward the heat generating plate 64.

In the above embodiment, the center alignment method is described as an example, but a side edge alignment method may be used in which one end of the sheet member P in the width direction is used as a reference.