阅读说明：本技术 加热装置及图像形成装置 (Heating device and image forming apparatus ) 是由 关贵之 于 2020-11-18 设计创作，主要内容包括：本发明涉及的加热装置及图像形成装置目的在于抑制因导体图案的发热引起的加热部件的温度的不均所导致的不良情况。该加热装置包括环状的定影带(20)、与定影带(20)接触形成定影夹持部(N)的加压辊(21)、加热定影带(20)的长条状的加热器(22),以及对定影带(20)或加压辊(21),用于在该定影带(20)和加压辊(21)之间形成定影夹持部(N)的加压机构(80A),(80B),加压机构(80A),(80B)使加热器(22)的长度方向的发热量大的一侧的加压力相对地小于发热量小的一侧的加压力。(The invention relates to a heating device and an image forming apparatus, which aim to restrain the defect caused by the temperature unevenness of a heating component caused by the heat generation of a conductor pattern. The heating device comprises an endless fixing belt (20), a pressure roller (21) which is in contact with the fixing belt (20) to form a fixing nip portion (N), a heater (22) which is long and heats the fixing belt (20), and pressurizing mechanisms (80A, 80B) for forming the fixing nip portion (N) between the fixing belt (20) and the pressure roller (21) or the pressure roller (21), wherein the pressurizing mechanisms (80A, 80B) make the pressurizing force on the side with large heat generation amount in the length direction of the heater (22) relatively smaller than the pressurizing force on the side with small heat generation amount.)

1. A heating device, comprising:

a rotating member;

an opposing member that forms a nip portion in contact with the rotating member;

a heating member for heating the rotating member, and

a pressing mechanism that presses at least one of the rotating member and the opposing member against the other member,

the heating device is characterized in that the pressurizing mechanism makes the pressurizing force on the side with larger heat generation amount in the length direction of the heating component relatively smaller than the pressurizing force on the side with smaller heat generation amount.

2. A heating device, comprising:

a rotating member;

an opposing member that forms a nip portion in contact with the rotating member;

a heating member for heating the rotating member, and

a pressing mechanism that presses at least one of the rotating member and the opposing member against the other member,

the heating device is characterized in that,

the pressing mechanism presses at least one of the rotating member and the opposing member such that a side of the heating member having a larger heat generation amount is relatively smaller than a side of the heating member having a smaller heat generation amount when the nip pressure of the nip portion is in the longitudinal direction of the heating member.

3. A heating device, comprising:

a rotating member;

an opposing member that forms a nip portion in contact with the rotating member;

a heating member for heating the rotating member, and

a pressing mechanism that presses at least one of the rotating member and the opposing member against the other member,

the heating device is characterized in that,

the pressing mechanism presses at least one of the rotating member and the opposing member such that a width of the nip portion in a direction orthogonal to the longitudinal direction of the heating member, that is, a nip portion width is relatively smaller on a side where a heat generation amount of the heating member is larger than on a side where the heat generation amount is smaller in the longitudinal direction of the heating member.

4. The heating device according to any 1 of claims 1 to 3, characterized in that the heating means comprises:

a first heat-generating part including at least 1 resistance heat-generating body;

a second heat generating portion including at least two resistance heat generating bodies located closer to both longitudinal end sides of the heating member than the first heat generating portion;

a plurality of conductors;

a first electrode connected to the first heat-generating portion through the conductor;

a second electrode commonly connected to the first and second heat generating portions through the conductor, an

And a third electrode connected to the second heat generating portion through the conductor.

5. A heating device, comprising:

a rotating member;

an opposing member that forms a nip portion in contact with the rotating member;

a heating member for heating the rotating member, and

a pressing mechanism that presses at least one of the rotating member and the opposing member against the other member,

the heating device is characterized in that the heating component comprises,

a first heat-generating part including at least 1 resistance heat-generating body;

a second heat generating portion including at least two resistance heat generating bodies located closer to both longitudinal end sides of the heating member than the first heat generating portion;

a plurality of conductors;

a first electrode connected to the first heat-generating portion through the conductor;

a second electrode commonly connected to the first and second heat generating portions through the conductor, an

A third electrode connected to the second heat generating portion through the conductor,

the pressurizing mechanism reduces a pressurizing force on a side opposite to a side where the first electrode is disposed in a longitudinal direction of the heating member relative to a pressurizing force on a side where the first electrode portion is disposed in a state where both the first and second heat generating portions are energized,

the pressurizing mechanism reduces a pressurizing force on a side where the first electrode is arranged relative to a pressurizing force on an opposite side to the side where the first electrode portion is arranged in a longitudinal direction of the heating member in a state where only the first heat-generating portion is energized among the first heat-generating portion and the second heat-generating portion.

6. The heating device according to any one of claims 1 to 5, wherein:

the pressing mechanism relatively reduces a pressing force on a side where a heat generation amount in a longitudinal direction of the heating member is large, relative to a pressing force on a side where the heat generation amount is small, after an image forming operation of the image forming apparatus is started.

7. The heating device according to claim 6, characterized in that:

the pressing mechanism reduces a pressing force on a side where a heat generation amount in a longitudinal direction of the heating member is large relative to a pressing force on a side where the heat generation amount is small after an image forming operation is performed on a predetermined number of recording media from an image forming apparatus.

8. The heating device according to claim 6, characterized in that:

the pressing mechanism reduces a pressing force on a side where a heat generation amount in a longitudinal direction of the heating member is large relative to a pressing force on a side where the heat generation amount is small after a predetermined time has elapsed from a start of an image forming operation of the image forming apparatus.

9. The heating device according to any one of claims 1 to 8, wherein:

after the image forming operation of the image forming apparatus is completed, the pressing mechanism changes the pressing force of one side and the pressing force of the other side in the longitudinal direction to be the same.

10. A heating device, comprising:

a rotating member;

an opposing member that forms a nip portion in contact with the rotating member;

a heating member that heats the rotating member;

a pressing mechanism that presses at least one of the rotating member and the opposing member against the other, and

a temperature detection mechanism arranged opposite to the rotating component and arranged at one side and the other side of the heating component in the length direction,

the heating device is characterized in that:

when the temperature difference detected by the temperature detection means on the one side and the other side is equal to or greater than a predetermined value, the pressurizing means reduces the pressurizing force on the side where the temperature detected by the temperature detection means is high relative to the pressurizing force on the side where the temperature is low.

11. The heating device according to any one of claims 1 to 10, wherein:

when a direction perpendicular to a longitudinal direction of the heat generating component and a direction different from a thickness direction of the heat generating component are taken as a short-side direction,

the ratio of the short-side direction dimension of the resistance heating element to the short-side direction dimension of the heating member is 25% or more.

12. The heating device according to any one of claims 1 to 10, wherein:

when a direction orthogonal to the longitudinal direction of the heating member is a direction different from the thickness direction of the heating member and is a short-side direction,

the ratio of the short-side direction dimension of the resistance heating element to the short-side direction dimension of the heating member is 40% or more.

13. The heating device according to any one of claims 1 to 12, wherein:

the toner on the recording medium is fixed by heat.

14. An image forming apparatus, characterized by comprising:

the heating device of any one 1 of claims 1 to 13.

Technical Field

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

Background

As a heating device mounted in an image forming apparatus such as a copying machine or a printer, a fixing device that fixes toner on a sheet by heat, a drying device that dries ink on the sheet, and the like are known.

For example, a fixing device disclosed in patent document 1 includes a heating member (heater) in which a heating element, an electric contact, a conductor pattern for electrically connecting them, and the like are provided on a long substrate.

However, in the heating member having such a conductor pattern provided on the substrate, when the heating element generates heat, the conductor pattern generates slight heat due to the current flowing through the conductor pattern. Therefore, strictly speaking, the heat generation distribution of the entire heating member is affected by the heat generation of the conductor pattern.

Therefore, depending on the heat generation distribution of the conductor pattern, there is a possibility that the temperature distribution of the heating member may vary due to the heat generation distribution. Therefore, in the device having such a heating member, a measure for suppressing the problem caused by the temperature variation of the heating member due to the heat generation of the conductor pattern is required.

[ patent document 1 ] Japanese patent laid-open No. 2016-

Disclosure of Invention

In order to solve the above problem, an aspect of the present invention relates to a heating device including: a rotating member; an opposing member that forms a nip portion in contact with the rotating member; and a pressing mechanism that presses at least one of the rotating member and the opposing member against the other member, wherein the pressing mechanism relatively reduces a pressing force on a side where a heat generation amount in a longitudinal direction of the heating member is large, to a pressing force on a side where the heat generation amount is small.

According to the present invention, it is possible to suppress a problem caused by a temperature deviation between one side and the other side in the longitudinal direction of the heating member.

Drawings

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

Fig. 2 is a schematic configuration diagram of the fixing apparatus.

Fig. 3 is a perspective view of the fixing device.

Fig. 4 is an exploded perspective view of the fixing device.

Fig. 5 is a perspective view of the heating unit.

Fig. 6 is an exploded perspective view of the heating unit.

Fig. 7 is a plan view of the heater.

Fig. 8 is an exploded perspective view of the heater.

Fig. 9 is a perspective view showing a state where the connector is connected to the heater.

Fig. 10 is a diagram showing power supply to the heater.

Fig. 11 is a diagram showing a normal energizing path.

Fig. 12 is a diagram showing an energization path when an unexpected shunt occurs.

Fig. 13 is a diagram showing the amount of heat generated by the power supply line for each block when an unexpected branching occurs.

Fig. 14 is a diagram showing the total heat generation amount of the power supply lines for each block in the case of fig. 13.

Fig. 15 is a diagram showing the amount of heat generated by the power feed line for each block when all heat generating portions are energized.

Fig. 16 is a diagram showing the total heat generation amount of the power supply lines for each block in the case of fig. 15.

Fig. 17 is a view showing the pressing force of the pressing mechanism under the equal pressing condition.

Fig. 18 is a diagram showing a state when a small-sized sheet passes through a sheet, in which the upper side is a positional relationship diagram in the longitudinal direction of the fixing device with respect to the heater, the center is a temperature distribution diagram in the longitudinal direction of the fixing belt.

Fig. 19 is a diagram showing how large-size paper passes, where the upper side shows a positional relationship in the longitudinal direction of the fixing device with respect to the heater and the center, and the lower side shows a temperature distribution in the longitudinal direction of the fixing belt.

Fig. 20 is a flowchart showing the timing of changing the pressurization conditions.

Fig. 21 is a flowchart showing the timing of changing the pressurizing conditions in the embodiment different from fig. 20.

Fig. 22 is a diagram of a fixing device in which a plurality of temperature detection mechanisms are provided in the longitudinal direction, the upper side is a diagram of a positional relationship in the longitudinal direction of the fixing device with respect to a heater and the center, and the lower side is a diagram showing a temperature distribution in the longitudinal direction of a fixing belt.

Fig. 23 is a flowchart showing the timing of changing the pressurizing conditions based on the detection result of the temperature detecting means.

Fig. 24 is a diagram of a fixing device in which a plurality of temperature detection mechanisms are provided in the longitudinal direction, the upper side is a diagram of a positional relationship in the longitudinal direction of the fixing device with respect to a heater and the center, and the lower side is a diagram showing a temperature distribution in the longitudinal direction of a fixing belt.

Fig. 25 is a flowchart showing the timing of changing the pressurizing conditions based on the detection result of the temperature detecting means.

Fig. 26(a) and 26(b) show a pressing mechanism under equal pressing conditions.

Fig. 27(a) and 27(b) show the pressing mechanism under the first pressing condition.

Fig. 28(a) and 28(b) are views showing the pressing mechanism under the second pressing condition.

Fig. 29(a) and 29(b) show a pressing mechanism according to a different embodiment.

Fig. 30 is a view showing another pressing mechanism according to a different embodiment.

Fig. 31 is a diagram showing a fixing device provided with a pressing mechanism for pressing a pressing roller.

FIG. 32 is a plan view showing the dimension of the heater in the short side direction and the dimension of the resistance heating element in the short side direction.

Fig. 33(a) and 33(b) are plan views showing modifications of the heater.

Fig. 34 is a view showing another fixing apparatus.

Fig. 35 is a view showing the structure of another fixing device.

Fig. 36 is a view showing the structure of still another fixing device.

Fig. 37 is a diagram showing power supply to a heater having a different configuration.

Fig. 38 is a diagram showing the amount of heat generated by the power supply line for each block when an unexpected branching occurs in the heater of fig. 37.

Fig. 39 is a diagram showing the total heat generation amount of the power supply lines for each block in the case of fig. 38.

Fig. 40 is a diagram showing the amount of heat generated by the power supply line for each block when all the heat generating portions are energized in the heater of fig. 37.

Fig. 41 is a diagram showing the total heat generation amount of the power supply lines for each block in the case of fig. 40.

Detailed Description

Embodiments according to the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding portions are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate. Hereinafter, in the description of the respective embodiments, a fixing device that fixes toner by heat will be described as a heating device.

In the image forming apparatus 1 for a single color shown in fig. 1, a photosensitive drum 10 is provided. The photosensitive drum 10 is a drum-shaped rotary body capable of bearing toner as a developer on its surface, and rotates in the direction of the arrow in the figure. Around the photosensitive drum 10, a charging roller 11 for uniformly charging the surface of the photosensitive drum 10, a developing device 12 having a developing roller 7 for supplying toner to the surface of the photosensitive drum 10, and the like, and a cleaning blade 13 for cleaning the surface of the photosensitive drum 10 are configured.

An exposure unit 3 is disposed above the processing unit 2. The exposure portion 3 irradiates the surface of the photosensitive drum 10 with laser light Lb emitted based on image data via a mirror 14.

Further, a transfer mechanism 15 having a transfer charger is disposed at a position facing the photosensitive drum 10. The transfer mechanism 15 transfers the image on the surface of the photosensitive drum 10 to the paper P.

The paper feeding unit 4 is located below the image forming apparatus 1, and includes a paper feeding cassette 16 that stores paper P as a recording medium, a paper feeding roller 17 that feeds the paper P from the paper feeding cassette 16 to the conveyance path 5, and the like. A registration roller 18 is disposed on the downstream side of the paper feed roller 17 in the conveyance direction.

The fixing device 9 includes a fixing belt 20 heated by a heating member described later, a pressure roller 21 capable of pressing the fixing belt 20, and the like.

Next, the basic operation of the image forming apparatus 1 will be described with reference to fig. 1.

When a printing operation (image forming operation) is started, the photoreceptor drum 10 is first charged on its surface by the charging roller 11. Then, the laser beam Lb is irradiated from the exposure portion 3 according to the image data, and the potential of the irradiated portion is lowered to form an electrostatic latent image. In the photoreceptor drum 10 on which the electrostatic latent image is formed, toner is supplied from the developing device 12 to the surface portion, and is visualized as a toner image (developer image). Then, the toner and the like remaining in the photoreceptor drum 10 after transfer are removed by the cleaning blade 13.

On the other hand, when the printing operation is started, the paper P accommodated in the paper feed cassette 16 is fed out to the conveyance path 5 by the rotational driving of the paper feed roller 17 of the paper feed unit 4 in the lower portion of the image forming apparatus 1.

The paper P fed into the conveyance path 5 is timed by the registration roller 18, conveyed toward the transfer section, which is the facing section of the transfer mechanism 15 and the photoreceptor drum 10, at a timing facing the toner image on the surface of the photoreceptor drum 10, and transferred by the application of a transfer bias of the transfer mechanism 15.

The sheet P on which the toner image is transferred is conveyed to the fixing device 9, and after being heated and pressed by the heated fixing belt 20 and the pressing roller 21, the toner image is fixed on the sheet P. Then, the paper P on which the toner image is fixed is separated from the fixing belt 20, conveyed by a conveying roller pair provided on the downstream side of the fixing device 9, and then discharged toward a paper discharge tray provided outside the apparatus.

Next, a more detailed configuration of the fixing device 9 will be described.

As shown in fig. 2, the fixing device 9 according to the present embodiment includes a fixing belt 20 as a rotating member or a fixing member, a pressure roller 21 as a facing member or a pressure member which is in contact with an outer peripheral surface of the fixing belt 20 and forms a nip portion N, and a heating unit 19 which heats the fixing belt 20. The heating unit 19 includes a planar heater 22 as a heating member, a heater supporter 23 as a holding member for holding the heater 22, and a supporter 24 as a supporting member for supporting the heater supporter 23.

The fixing belt 20 is formed of an endless belt member, and has a cylindrical base body made of Polyimide (PI) having an outer diameter of 25mm and a thickness of 40 to 120 μm, for example. In order to improve durability and ensure releasability, a release layer having a thickness of 5 to 50 μm made of a fluorine-based resin such as PFA or PTFE is formed on the outermost layer of the fixing belt 20. An elastic layer made of rubber or the like having a thickness of 50 to 500 μm may be provided between the base and the release layer. The substrate of the fixing belt 20 is not limited to polyimide, and may be a heat-resistant resin such as PEEK or a metal substrate such as nickel (Ni) or SUS. Polyimide, PTFE, or the like may be applied as a sliding layer to the inner circumferential surface of the fixing belt 20.

The pressure roller 21 is composed of, for example, a solid iron core 21a having an outer diameter of 25mm, an elastic layer 21b formed on the surface of the core 21a, and a release layer 21c formed outside the elastic layer 21 b. The elastic layer 21b is formed of silicone rubber and has a thickness of, for example, 3.5 mm. In order to improve the releasability, it is preferable to form a release layer 21c made of a fluororesin layer having a thickness of, for example, about 40 μm on the surface of the elastic layer 21 b.

The fixing belt 20 is pressed toward the pressure roller 21 by a pressing mechanism described later, and is pressed against the pressure roller 21. Thereby, a nip portion N is formed between the fixing belt 20 and the pressure roller 21. The pressure roller 21 functions as a drive roller that is rotationally driven after being transmitted as a driving force from a drive mechanism provided in the image forming apparatus main body. On the other hand, the fixing belt 20 is configured to rotate following the rotation of the pressure roller 21. Since the fixing belt 20 slides with respect to the heater 22 when the fixing belt 20 rotates, a lubricant such as oil or grease may be interposed between the heater 22 and the fixing belt 20 in order to improve the sliding mobility of the fixing belt 20.

The heater 22 is provided in a long shape in a rotational axis direction or an entire length direction of the fixing belt 20 (hereinafter also referred to as a "belt length direction"), and contacts an inner peripheral surface of the fixing belt 20 at a position corresponding to the pressure roller 21. The heater 22 is a member for heating the fixing belt 20 as a heated member and heating the fixing belt 20 to a predetermined fixing temperature.

Unlike the present embodiment, the heat generating portion 60 may be provided on the opposite side of the substrate 50 from the fixing belt 20 (on the heater supporter 23 side). At this time, since the heat of the heat generating portion 60 is transmitted to the fixing belt 20 through the base member 50, the base member 50 is preferably made of a material having high thermal conductivity such as aluminum nitride. In the configuration of the heater 22 according to the present embodiment, an insulating layer may be further provided on the surface of the substrate 50 opposite to the fixing belt 20 (on the heater stay 23 side).

The fixing belt 20 may be indirectly in contact with the heater 22 through a non-contact or low friction sheet, but in order to improve the heat transfer efficiency to the fixing belt 20, it is preferable to directly contact the heater 22 with the fixing belt 20 as in the present embodiment. Further, although the heater 22 may be in contact with the outer peripheral surface of the fixing belt 20, the outer peripheral surface of the fixing belt 20 may be in contact with the heater 22, which may cause damage, and therefore, the fixing quality may be lowered, and therefore, the surface in contact with the heater 22 is preferably the inner peripheral surface of the fixing belt 20.

The heater stay 23 and the stay 24 are disposed inside the fixing belt 20. The stay 24 is made of a metal tunnel material, and both end portions thereof are supported by both side wall portions of the fixing device 9. The surface of the heater supporter 23 opposite to the heater 22 side is supported by the supporter 24, the pressing force of the heater 22 and the heater supporter 23 against the pressing roller 21 is kept without large bending, and a nip N is formed between the fixing belt 20 and the pressing roller 21.

The heater supporter 23 is preferably formed of a heat-resistant material since it is easily heated to a high temperature by the heat of the heater 22. For example, when the heater supporter 23 is formed of a heat-resistant resin with low thermal conductivity such as LCP, heat transfer from the heater 22 to the heater supporter 23 can be suppressed, and the fixing belt 20 can be heated efficiently.

When the printing operation is started, the heat generating portion 60 generates heat by supplying power to the heater 22, and the fixing belt 20 is heated. The pressure roller 21 is rotationally driven, and the fixing belt 20 starts to rotate. Then, in a state where the temperature of the fixing belt 20 reaches a predetermined target temperature (fixing temperature), as shown in fig. 2, the sheet P bearing the unfixed toner image is conveyed (in the direction of arrow a in fig. 2) between the fixing belt 20 and the pressing roller 21 (nip portion N), and the unfixed toner image is heated and pressed to be fixed on the sheet P.

Fig. 3 is a perspective view of the fixing device, and fig. 4 is an exploded perspective view thereof.

As shown in fig. 3 and 4, the apparatus housing 40 of the fixing apparatus 9 includes a first apparatus housing 25 including a pair of side wall members 28 and a front wall member 27, and a second apparatus housing 26 including a rear wall member 29. The pair of side wall members 28 are disposed on one end side and the other end side in the belt longitudinal direction, and support both end sides of the fixing belt 20, the pressure roller 21, and the heating unit 19 by the two side wall members 28. A plurality of engaging projections 28a are provided on each side wall member 28, and the first device housing 25 and the second device housing 26 are assembled by engaging each engaging projection 28a with an engaging hole 29a provided in the rear wall member 29.

Each side wall member 28 is provided with an insertion groove 28b through which a rotary shaft of the pressure roller 21 or the like is inserted. The insertion groove 28b is open on the rear wall member 29 side, and is a non-open abutting portion on the opposite side. A bearing 30 for supporting the rotation shaft of the pressure roller 21 is provided at an end portion on the side of the abutting portion. Both ends of the rotation shaft of the pressure roller 21 are rotatably supported by the side wall members 28 by being attached to bearings 30.

Further, a drive transmission gear 31 as a drive transmission member is provided on one end side of the rotation shaft of the pressure roller 21. In a state where the pressure roller 21 is supported by the side wall members 28, the drive transmission gear 31 is disposed in a state of being exposed to the outside of the side wall members 28. Thus, when the fixing device 9 is mounted in the image forming apparatus main body, the drive transmission gear 31 is connected to a gear provided in the image forming apparatus main body, and a state in which the driving force from the driving source can be transmitted is achieved. The drive transmission member for transmitting the driving force to the pressure roller 21 may be a pulley, a coupling, or the like for tensioning the drive transmission belt, in addition to the drive transmission gear 31.

A pair of flanges 32 that support the fixing belt 20, the heater stay 23, the stay 24, and the like are provided at both ends of the heating unit 19 in the longitudinal direction. Each flange 32 is provided with a guide groove 32 a. The flange 32 is assembled to the side wall member 28 by entering the guide groove 32a along the edge of the insertion groove 28b of the side wall member 28.

Further, a pair of springs 33 as biasing members are in contact with the respective flanges 32. The stay 24 and the flange 32 are biased toward the pressure roller 21 by the springs 33, so that the fixing belt 20 is pressed against the pressure roller 21, and a nip portion is formed between the fixing belt 20 and the pressure roller 21. The end of the spring 33 opposite to the side in contact with the flange 32 is pressed by a pressing rod described later.

As shown in fig. 4, a hole 29b as a positioning portion is provided on one end side in the longitudinal direction of the rear wall member 29 constituting the second apparatus housing 26, and positions the fixing apparatus main body with respect to the image forming apparatus main body. On the other hand, a protrusion 101 as a positioning portion is provided in the image forming apparatus main body. The projection 101 is inserted into the hole 29b of the fixing device 9, and the projection 101 is fitted into the hole 29b, whereby the fixing device main body is positioned in the belt longitudinal direction with respect to the image forming apparatus main body. Further, no positioning portion is provided on the end side of the rear wall member 29 opposite to the end side where the hole portion 29b is provided. Thus, the expansion and contraction of the fixing device main body in the belt length direction accompanying the temperature change is not limited.

Fig. 5 is a perspective view of the heating unit 19, and fig. 6 is an exploded perspective view thereof.

As shown in fig. 5 and 6, a rectangular housing recess 23a for housing the heater 22 is provided in a surface of the heater stay 23 on the fixing belt side (a surface on the near side in fig. 5 and 6). The housing recess 23a is formed in substantially the same shape and size as the heater 22, but the longitudinal dimension L2 of the housing recess 23a is set slightly longer than the longitudinal dimension L1 of the heater 22. Since the housing recess 23a is formed slightly longer than the heater 22 in this manner, even if the heater 22 is elongated in the longitudinal direction due to thermal expansion, the heater 22 and the housing recess 23a do not interfere with each other. The heater 22 is held in the accommodating recess 23a by being sandwiched and held together with the heater holder 23 by a connector described later as a power supply member.

The pair of flanges 32 includes a C-shaped belt supporting member 32b inserted into the fixing belt 20 to support the fixing belt 20, a flange-shaped belt regulating member 32C contacting an end surface of the fixing belt 20 to regulate movement (deviation) in the belt longitudinal direction, and a supporting recess 32d inserted into both end sides of the heater supporter 23 and the supporter 24 to support them. By inserting the belt supporting members 32b into both end portions of the fixing belt 20, tension in the circumferential direction (belt rotation direction) is not substantially generated at the time of non-rotation of the endless belt, that is, the endless belt is supported by a so-called free belt system.

As shown in fig. 5 and 6, a positioning recess 23e as a positioning portion is provided in one end side in the longitudinal direction of the heater supporter 23. The heater stay 23 and the flange 32 are positioned in the belt longitudinal direction by fitting the fitting portion 32e of the flange 32 into the positioning recess 23e as shown on the left side of fig. 5 and 6. On the other hand, the flange 32 shown on the right side in fig. 5 and 6 is not provided with the fitting portion 32e, and is not positioned in the tape longitudinal direction with respect to the heater stay 23. By positioning the heater supporter 23 with respect to the flange 32 only on one side in the belt longitudinal direction in this manner, even if the heater supporter 23 expands and contracts in the belt longitudinal direction with a change in temperature, the expansion and contraction thereof are not restricted.

As shown in fig. 6, stepped portions 24a are provided at both ends of the stay 24 in the longitudinal direction to regulate the movement of the stay 24 with respect to the flanges 32. Each step portion 24a restricts the movement of the stay 24 in the longitudinal direction with respect to the flange 32 by the abutment with the flange 32. However, at least one of the stepped portions 24a is arranged with respect to the flange 32 via a gap (play). In this way, since at least one of the step portions 24a is disposed with respect to the flange 322 via a gap, even if the bracket 24 expands and contracts in the longitudinal direction with a temperature change, the expansion and contraction thereof are not restricted.

Fig. 7 is a plan view of the heater 22, and fig. 8 is an exploded perspective view thereof.

As shown in fig. 8, the heater 22 has a base 50, a first insulating layer 51 provided on the base 50, a conductor layer 52 having a heat generating portion 60 and the like provided on the first insulating layer 51, and a second insulating layer 53 covering the conductor layer 52. In the present embodiment, the base member 50, the first insulating layer 51, the conductor layer 52 (heat generating portion 60), and the second insulating layer 53 are laminated in this order toward the fixing belt 20 (nip portion N side), and heat generated from the heat generating portion 60 is transmitted to the fixing belt 20 via the second insulating layer 53 (see fig. 2).

The base member 50 is a long plate member made of a metal material such as stainless steel (SUS), iron, or aluminum. As the material of the base 50, ceramics, glass, or the like may be used in addition to the metal material. In the case where an insulating material such as ceramic is used for the base material 50, the first insulating layer 51 between the base material 50 and the conductor layer 52 may be omitted. On the other hand, since a metal material has excellent durability against rapid heating and is easy to process, it is suitable for achieving a reduction in cost. Among metal materials, aluminum and copper are particularly preferable because they have high thermal conductivity and are less likely to cause temperature unevenness. In addition, stainless steel has an advantage that it can be manufactured at low cost compared to them.

The insulating layers 51 and 53 are made of a material having insulating properties such as heat-resistant glass. As these materials, ceramics, Polyimide (PI), or the like can also be used.

The conductor layer 52 is composed of a heat generating component 60 having a plurality of resistive heating elements 59, a plurality of electrodes 61, and a plurality of conductive feeder wires 62 electrically connecting these components. Each of the resistance heating elements 59 is electrically connected in parallel to any two of the three electrodes 61 via a plurality of power feeding lines 62 provided on the base 50.

The heat generating member 60 is formed by applying paste prepared from silver palladium (AgPd), glass powder, or the like to the base material 50 by screen printing or the like, and then sintering the base material 50. As the material of the heat generating member 60, a resistance material of silver alloy (AgPt) or ruthenium oxide (RuO2) may be used in addition to these.

The power feed line 62 is made of a conductor having a smaller resistance value than the heat generating portion 60. The feeder line 62 and the electrode 61 may be formed by screen printing or the like using silver (Ag), silver palladium (AgPd), or the like as a material for the feeder line 62 and the electrode 61.

Fig. 9 is a perspective view showing a state where the connector 70 is connected to the heater 22.

As shown in fig. 9, the connector 70 includes a housing 71 made of resin, and a plurality of contact terminals 72 provided on the housing 71. Each contact terminal 72 is formed of a plate spring and is connected to a power supply harness 73.

As shown in fig. 9, the connector 70 is attached so as to sandwich the heater 22 and the heater supporter 23 together from the front side and the back side. In this state, the contact portions 72a provided at the tips of the contact terminals 72 are brought into elastic contact (pressure contact) with the corresponding electrodes 61, and the heat generating portion 60 is electrically connected to a power supply provided in the image forming apparatus via the connector 70. This allows power to be supplied from the power supply to the heat generating unit 60. In order to secure connection with the connector 70, at least a part of each electrode 61 is exposed without being covered with the second insulating layer 53 (see fig. 7).

As shown in fig. 10, in the present embodiment, among the plurality of resistive heat generators 59 arranged in the longitudinal direction of the base 50, a first heat generating portion (first resistive heat generator group) 60A including the resistive heat generators 59 except for both ends and a second heat generating portion (second resistive heat generator group) 60B including the resistive heat generators 59 on both ends can be configured to perform heat generation control independently. Specifically, the impedance heating elements 59 other than the two ends constituting the first heating element 60A are connected to the first electrode 61A provided at one end in the longitudinal direction of the base 50 via the first power feeding line 62A. Each of the resistive heating elements 59 constituting the first heating unit 60A is connected to a second electrode 61B provided on the opposite end side to the first electrode 61A via a second power feeding line 62B. On the other hand, each resistive heating element 59 constituting both ends of the second heat generating member 60B is connected to a third electrode 61C (other than the first electrode 61A) provided at one end in the longitudinal direction of the base 50 via a third feeder line 62C or a fourth feeder line 62D. The resistance heating elements 59 at both ends are connected to the second electrode 61B via the second power feeding line 62, similarly to the resistance heating elements 59 of the first heating unit 60A.

The electrodes 61A to 61C are connected to the power supply 64 via the connector 70, and are supplied with power from the power supply 64. A switch 65A as a switching means is provided between the electrode 61A and the power supply 64, and the application of voltage can be switched by turning ON and OFF the switch 65A. Similarly, a switch 65C as a switching means is provided between the electrode 61C and the power supply 64, and the application of voltage can be switched by turning ON and OFF the switch 65C. Further, the ON/OFF of these switches 65A, 65C and the timing of supplying power to the heater 22 are controlled by the control circuit 66. The control circuit 66 performs these controls based on the detection results of various sensors in the image forming apparatus. For example, the timing of paper passage can be determined based on the detection result of a sensor provided at the entrance or exit of the fixing nip N, and whether or not to supply power to the heater 22 and the switches 65A and 65C can be switched.

When a voltage is applied to the first electrode 61A and the second electrode 61B, the resistance heating elements 59 other than the both ends are energized, whereby only the first heating element 60A generates heat. On the other hand, when a voltage is applied to the second electrode 61B and the third electrode 61C, electricity is passed through the resistive heating elements 59 at both ends, and only the second heat generating portion 60B generates heat. Further, if a voltage is applied to all of the electrodes 61A to 61C, both (all) of the resistive heating elements 59 of the first and second heat generating portions 60A and 60B can be caused to generate heat. For example, when a sheet of a relatively small width size of a4 size (passing width: 210mm) or less is passed through the sheet, the heat generation region corresponding to the sheet width can be formed by causing only the first heat generating portion 60A to generate heat, and when a sheet of a relatively large width size exceeding a4 size (passing width: 210mm) is passed through the sheet, causing the second heat generating portion 60B to generate heat in addition to the first heat generating portion 60A.

However, in order to further reduce the size of the image forming apparatus and the fixing apparatus, it is important to reduce the size of a heater, which is one of the members disposed inside the fixing belt. That is, the diameter of the fixing belt can be reduced by reducing the heater short side direction (the direction of arrow Y in fig. 10: the direction crossing the longitudinal direction on the surface where the heat generating portions 60A and 60B of the heater 22 are provided, or the direction orthogonal to the longitudinal direction of the heater 22 and different from the direction orthogonal to the paper surface of fig. 10, that is, the direction of thickness of the heater 22), and the fixing device and the image forming apparatus can be further reduced in size. Specifically, as a method of reducing the heater in the short side direction, for example, the following three methods are given.

One method is to reduce the length of the heating portion (resistance heating element) in the short side direction. However, when the heating region short side direction is reduced, the width of the heating region to be heated by the fixing belt is reduced, and therefore, when it is necessary to secure the amount of heat to be applied to the fixing belt, there is a problem that the peak temperature rise value is increased. When the temperature rise peak increases, the temperature of an excessive temperature rise detection device such as a thermostat or a fuse provided on the back surface of the heater may exceed the heat-resistant temperature, or the excessive temperature rise detection device may malfunction. When the temperature rise peak becomes high, the heat transfer efficiency from the heater to the fixing belt also decreases, and therefore, this is not preferable from the viewpoint of energy efficiency. Thus, it may be difficult to adopt a method of making the heat generating portion smaller in the short-side direction.

As a second method, the length in the short-side direction is reduced for a portion where no heat generating portion, no electrode, and no power supply line are provided. However, in this method, the distance between the heat generating portion and the power supply line and the distance between the electrode and the power supply line are reduced, and therefore, there is a possibility that insulation cannot be secured. In view of the structure of the conventional heater, it is difficult to further reduce the distance between the heat generating portion and the power feed line and between the electrode and the power feed line.

As a remaining third method, a method of making the feed line smaller in the short side direction is used. This method has room for realization, compared with the above two methods. However, when the length of the power feed line in the short-side direction is reduced, the resistance value of the power feed line increases, and thus unintended shunting may occur in the conductive path of the heater. In particular, when the resistance value of the heat generating portion is reduced by increasing the amount of heat generated by the heat generating portion in order to cope with the increase in speed of the image forming apparatus, the resistance value of the power feeding line and the resistance value of the heat generating portion are relatively close to each other, and thus unintended shunt is likely to occur. As a method of avoiding such unexpected branching, it is conceivable to secure a cross-sectional area and suppress an increase in the resistance value of the feeder line by reducing the feeder line in the short-side direction by an amount to increase the thickness direction (the direction intersecting the longitudinal direction and the short-side direction) accordingly. However, in this case, it becomes difficult to screen-print the feeder line, and a method of forming the feeder line is forcibly changed. Therefore, it is difficult to adopt a solution of thickening the power supply line. Therefore, in order to reduce the heater in the short-side direction, it is necessary to reduce the length of the power feed line in the short-side direction in addition to anticipating an increase in resistance value, and to take measures to cope with unexpected branching that may occur in response to the increase.

Next, the unexpected branching and the adverse effect thereof will be described by taking the heater 22 as an example.

In the heater 22 shown in fig. 11, when a voltage is applied to the first electrode 61A and the second electrode 61B in order to generate heat only in the resistive heating elements 59 of the first heat generating portion 60A, a normal current flows through the first feeder line 62A, and flows through the resistive heating elements 59 other than both ends to the second feeder line 62B.

However, when the difference in the resistance value between the feeder line and the heat generating portion is small due to the increase in the resistance value of the feeder line and the decrease in the resistance value of the heat generating portion due to the increase in the heat generating amount due to the above-described downsizing, as shown in fig. 12, a shunt of an unexpected path occurs. That is, a part of the current passing through the second resistance heating element 59 from the left in fig. 12 flows toward the opposite side to the second electrode 61B side at the branch portion X of the second power feeding line 62A in front. The divided current passes through the resistance heating element 59 on the left end in fig. 12, further passes through the third feeder line 62C, the third electrode 61C, the fourth feeder line 62D, and the resistance heating element 59 on the right end in this order, and then merges into the second feeder line 62B.

As described above, in the heater 22 shown in fig. 12, the second power supply line 62B includes the portion extending leftward from the branch portion X, the resistive heating elements 59 forming the two ends of the second heat generating portion 60B, and the portions of the third electrode 61C, the third power supply line 62C, and the fourth power supply line 62D, and the branch conductive path E3 through which current flows through an unexpected path is formed.

In addition, if the electrically conductive path of the heater 22 is a path having at least a first electrically conductive portion E1 connecting the first heat generating portion 60A and the first electrode 61A, a second electrically conductive portion E2 extending from the first heat generating portion 60A in a first direction S1 (right side in fig. 12) in the longitudinal direction of the heater 22 and connected to the second electrode 61B, and a branched electrically conductive path E3 branched from the second electrically conductive portion E2 in a second direction S2 (left side in fig. 12) opposite to the first direction S1 and connected to the second electrically conductive portion E2 or the second electrode 61B without passing through the first electrically conductive portion E1, such an unexpected branching may occur when the first heat generating portion 60A is energized. In the present embodiment, the second heat generating portion 60B and the third electrode 61C are provided on the branched conductive path E3, but an unexpected branch may occur in a conductive path in which the second heat generating portion 60B and the third electrode 61C are not provided or even in a conductive path in which other conductive members are provided.

When the unexpected branch occurs, the current flows through an unexpected path, and therefore, the temperature distribution of the heater 22 varies due to heat generation of the power supply line. For example, in the heater 22 shown in fig. 13, when 20% of current flows uniformly from the first electrode 61A to each resistance heating element 59 of the first heat generating portion 60A, and the current flowing through the second resistance heating element 59 from the left in the figure is branched 5% in the branch portion X in front thereof, the heat generation amount of the power supply line generated in each block divided for each resistance heating element 59 is as shown in the table in the figure.

Here, since the portion of each power supply line extending in the short side direction of the heater 22 is short and the amount of heat generation is small in this portion, the amount of heat generation is ignored and only the amount of heat generation occurring in the portion of each power supply line extending in the long side direction of the heater 22 is calculated. Specifically, the amounts of heat generation generated in the portions of the first feeder line 62A, the second feeder line 62B, and the fourth feeder line 62D extending in the longitudinal direction of the respective heaters 22 are calculated. Since the heat generation amount (W) is expressed by the following expression (1), the heat generation amount shown in the table of fig. 13 is calculated as the square of the current (I) flowing through each power supply line for convenience. Therefore, the numerical value of the heat generation amount shown in the table of fig. 13 is simply a calculated value, and is different from the actual heat generation amount.

W (heating value) R (resistance) x I²(Current) · (1)

Specifically describing the method of calculating the calorific value with reference to fig. 13, in the first block, since the current flowing through the first feeder line 62A is 100% and the current flowing through the fourth feeder line 62D is 5%, the sum of the squares 10025(10000+25) of the respective currents becomes the total calorific value of the feeder lines in the first block. In the second block, since the current flowing through the first feeder line 62A is 80%, the current flowing through the second feeder line 62B is 5%, and the current flowing through the fourth feeder line 62D is 5%, the sum 6450(6400+25+25) of the squares thereof becomes the total amount of heat generation of the feeder lines in the second block. In addition, in other blocks, the calorific value is calculated in the same manner.

Next, fig. 14 is a diagram showing the total heat generation amount of each block shown in the table of fig. 13. As shown in fig. 14, the total heat generation amount of each block is asymmetrical to the left and right with respect to the fourth block in the center of the heat generation region due to the influence of the unexpected branching.

Even when electricity is applied to all the heat generating portions, the amount of heat generated in the longitudinal direction of the heater 22 is asymmetrical due to the difference in the magnitude of the current flowing through the conductive portions. That is, as described above, when the heater 22 is downsized, since the arrangement of the electrodes and the conductive portions is also restricted, it is also difficult to make the heat generation amount in the longitudinal direction of the heater 22 symmetrical to each other. Further, as described above, when the speed of the device is increased, the value of the current flowing through the conductive portion is increased, and the difference between the left and right sides is also increased, so that the difference cannot be ignored. Hereinafter, a case where current is supplied to all the heat generating portions will be described.

As shown in fig. 15, when current is passed through all the heat generating portions, a current of 20% flows through the resistive heating elements 59 at both the left and right ends and the power feeding lines 62C and 62D connected thereto, which is different from the above case. In this regard, the value of the current flowing to the power supply line 62A is the same as before. At this time, in the first block, since the current flowing through the first power feed line 62A is 100% and the current flowing through the fourth power feed line 62D is 20%, the total square value 10400(10000+400) becomes the total heat generation amount of the power feed lines in the first block. In the second block, since the current flowing through the first feeder line 62A is 80%, the current flowing through the second feeder line 62B is 20%, and the current flowing through the fourth feeder line 62D is 20%, the sum 7200(6400+400+400) of the squares thereof becomes the total amount of heat generated by the feeder lines in the second block. In addition, in other blocks, the calorific value is calculated in the same manner.

Then, as shown in fig. 16, the total heat generation amount of each block is asymmetric to the left and right with reference to the fourth block at the center of the heat generation region. In particular, the current value increases to 120% in the seventh block, which is the downstream side of the second power feeding line 62B connected to all the resistance heating elements 59, and a difference occurs in the amount of heat generation on the left and right sides.

Such variation in the amount of heat generated by the asymmetric power supply lines causes variation in the temperature in the longitudinal direction of the heater 22. When the temperature of the heater 22 varies in the longitudinal direction, the gloss of the image fixed on the paper is high in a portion where the temperature is high, and conversely the gloss is low in a portion where the temperature is low, so that there is a possibility that the gloss varies as a whole, and the image quality may be degraded. In the present embodiment, the length of each block is set to be the same so that the small-size paper and the large-size paper can be heated equally.

In the present embodiment, the following measures are taken to suppress the defects (for example, uneven gloss or uneven image gloss) caused by the temperature unevenness in the longitudinal direction of the heater 22 when the above-described partial energization is performed (when small-sized paper is passed) and when all the heat generating portions are energized (when large-sized paper is passed).

As shown in fig. 17, the flanges 321 and 322 supporting the end portion on one side and the end portion on the other side in the longitudinal direction of the fixing belt 20 are pressed by separate pressing mechanisms, and the fixing belt 20 is pressed against the pressing roller 21 by the pressing to form the nip portion N.

When the pressurizing condition does not need to be changed (to be described later in detail), the pressurizing force F is applied to the flange 321_LAnd a pressing force F against the flange 322_RThe same setting is performed (hereinafter, the setting of the pressurizing force is referred to as an equal pressurizing condition).

Fig. 18 is a diagram showing a positional relationship in the longitudinal direction between the heater 22 and other members in the fixing device 9, the upper side of the diagram showing the heater 22, and the middle showing the members in the fixing device 9, showing the positional relationship in the longitudinal direction. In addition, the lower side of the figure shows the distribution of the temperature (temperature T) of the fixing belt 20 in each longitudinal position. The sheet P passing through fig. 18 is a small-sized sheet corresponding to the heater 22, and is, for example, a 4-sized sheet.

As shown in the upper side of fig. 18, only the first heat generation portion 60A is energized in the heater 22 corresponding to the small-sized paper. At this time, as described above, the amount of heat generated by the heater 22 increases on one side in the longitudinal direction (the left side in the figure), and as shown on the lower side in fig. 18, the temperature T of the fixing belt 20 also increases on the left side in the figure. Here, "the heat generation amount of one side in the longitudinal direction of the heater 22 is large" means that the heat generation amount is large when measured with a single heater 22.

In the present embodiment, the pressure applied to the flanges 321 and 322 by the pressure applying mechanism can be changed from the above-described pressure applying conditions or the like, and the pressure can be changed in accordance with the distribution of the temperature T of the fixing belt 20 (or the distribution of the amount of heat generated by the heater 22). Specifically, as shown in the middle of fig. 18, the pressing force applied to the flange 321 supporting one end of the fixing belt 20 in the longitudinal direction is changed to be lower than the pressing force F_LSmall applied pressure F_L1And a pressure force applied to the other flange 322 is set as a pressure force F_RThe pressure force is not changed (hereinafter, the setting of the pressure force is referred to as a first pressure condition). That is, the pressing force against flange 321 is set to be smaller than the pressing force against flange 322. Thereby, the nip pressure of the nip portion N on the side where the heat generation amount in the longitudinal direction of the heater 22 is large (the pressure contact force between the fixing belt 20 and the pressure roller 21 at the nip portion) becomes relatively small. Further, a direction orthogonal to the longitudinal direction of the heater 22 (also the conveying direction of the sheet P at the nip portion)The width of the upper nip portion N (hereinafter, nip portion width) is relatively smaller on the side where the amount of heat generation in the longitudinal direction of the heater 22 is large. Therefore, it is possible to suppress a problem caused by a temperature deviation between one side and the other side in the longitudinal direction of the heater 24. That is, the difference in fixability between one side and the other side in the longitudinal direction can be suppressed, and the gloss deviation in the longitudinal direction can be suppressed. Therefore, image unevenness and gloss unevenness of the paper can be suppressed.

As shown in fig. 19, when a large-size sheet (for example, a 3-size sheet) passes through, that is, when all the heat generating portions are energized, the temperature T (the amount of heat generated by the heater 22) on the other side in the longitudinal direction is higher than that on the one side. At this time, the pressing force applied to the flange 321 is set to the pressing force F without changing from the equal pressing condition_LAnd the pressure force applied to the flange 322 is changed to a specific pressure force F_RSmall applied pressure F_R1(hereinafter, the setting of the pressurizing force is referred to as a second pressurizing condition). That is, the pressing force against flange 322 is set to be smaller than the pressing force against flange 321. This relatively reduces the clamping pressure on the side of the heater 22 having a large heat generation amount in the longitudinal direction. Further, the width of the nip portion on the side where the amount of heat generation in the longitudinal direction of the heater 22 is large is relatively small. Therefore, it is possible to suppress a problem caused by a temperature deviation between one side and the other side in the longitudinal direction of the heater 24. That is, the difference in fixability between one side and the other side in the longitudinal direction can be suppressed, and the gloss deviation in the longitudinal direction can be suppressed.

The pressing force and the clamping pressure can be measured for surface pressure using a pressure distribution measuring system, and calculated by dividing the weight in the pressed region by the area. Specifically, a surface pressure distribution measuring system (manufactured by Neda: I-SCAN) or the like can be used.

The method for measuring the nip width is to forcibly stop the fixing device for 10 seconds while the solid black image previously created by another image forming apparatus is passing through the sheet in the fixing device, and then form a glossy portion of the nip width on the solid black image from which the solid black image has been extracted.

By measuring the width of the glossy portion, the nip width can be known. In the method of measuring the nip width, the OHP sheet may be passed through the nip, the OHP sheet may be extracted after a contact state is continued for a certain period of time, and the nip width may be obtained by measuring the width of the formed trace of the nip.

Next, a specific example of the timing of switching the pressurization conditions described above will be described with reference to fig. 20.

As shown in fig. 20, when power is first turned on in the image forming apparatus 1 (step S0), power is supplied to the fixing device. At this time, the pressing mechanism is operated, and the fixing belt 20 is pressed against the pressing roller 21 under the equal pressing condition (step S1).

When the image forming apparatus 1 receives the print command (step S2), the image forming apparatus 1 recognizes the size of the printed paper and starts the printing operation (image forming operation) (step S3). The printing operation (image forming operation) mentioned here means that, as described above, after the printing command reaches the image forming apparatus and various operations for printing (heating of the fixing belt to the fixing temperature, rotation of various rollers for conveying the paper, and the like) are started, the printing command is discharged to the outside of the apparatus after the printing on the last paper is completed, and the various operations for printing are completed.

When the printing operation is started, the fixing belt 20 is heated to and maintained at the target temperature by the heater 22, and the fixing operation is enabled. After the printing operation is started, the pressing condition of the pressing mechanism for pressing the fixing belt 20 is changed according to the size of the paper to be printed (step S4). Specifically, as described above, the first pressing condition is set in the case of the small-size sheet, and the second pressing condition is set in the case of the large-size sheet (steps S5A, 5B). In the present embodiment, either the first pressing condition or the second pressing condition is set, and the pressing condition may be set to be equal according to the printing condition such as the size of the paper. The timing of changing the pressure condition after the start of the printing operation may be set to, for example, a predetermined timing immediately after the start of the printing operation or before the first sheet enters the fixing device.

Then, the pressing mechanism passes through the sheet in the fixing device under the pressing conditions set in steps S5A and 5B. Then, when the fixing operation for all the sheets is ended and the printing operation is ended (step S6), the pressing mechanism is changed to the equal pressing condition (step S7).

As described above, changing the pressing conditions according to the size of the paper passing through the paper can align the fixing performance of the paper at the time of fixing action on one side and the other side in the length direction of the fixing belt, and can suppress gloss unevenness or gloss unevenness of an image formed on the paper. Further, by setting the pressure conditions to be equal to each other except when the printing operation is performed, it is possible to extremely reduce the time required for the left-right deviation of the pressure force, and to suppress the left-right deviation of the abrasion of the fixing belt 20 and the pressure roller 21.

Next, an example in which the timing of switching the pressurization conditions is set to be different from the above-described timing will be described in order.

In the embodiment of the flowchart shown in fig. 21, after the printing operation is started (step S3), the pressing conditions are set to be equal until B sheets of paper pass through the fixing device without changing the pressing conditions (steps S11 a and S11B). Note that, when B sheets of paper are passed through the fixing device, the timing when the sensor provided on the exit side of the fixing nip N detects the trailing edge of the B-th sheet of paper is referred to. After B sheets of paper have passed, the pressing conditions are changed according to the paper size (steps S5A and 5B). After that, the same procedure is followed such that the pressure conditions are changed again after the printing operation is completed. In addition, fig. 21 shows a case where the number of printed sheets is B or more, and in a case where the number of printed sheets is less than B, the printing operation is terminated without changing the pressing conditions.

Immediately after the printing operation is started, the temperature deviation between the heater 22 and the fixing belt 20 is small. Therefore, as in the present embodiment, by setting the pressing conditions to the equal pressing conditions until B sheets pass, it is possible to press the sheets in a time zone in which the gloss unevenness or the gloss unevenness of the image is less likely to occur under the equal pressing conditions. Therefore, as compared with the case where the pressing condition is changed immediately after the printing operation is started, the time during which the pressing deviation occurs can be further reduced, and the lateral deviation of the abrasion of the fixing belt 20 and the pressing roller 21 can be further suppressed.

In the above embodiment, the pressing conditions are changed after the B-th sheet is passed through the fixing device, but the present invention is not limited to this, and these timings can be selected by providing a sensor at a position corresponding to the B-th sheet after it is discharged to the outside of the apparatus, or after it passes through the inlet side of the fixing device. Further, the pressing condition may be changed according to the paper size after a predetermined time C has elapsed after the printing operation is started. Even in this case, the time zone in which the image gloss is not uniform or the fixing is not easily uniform is set to the same pressing condition, and the lateral variation in the abrasion between the fixing belt 20 and the pressing roller 21 can be further suppressed. The time C is not limited to the time from the start of the printing operation, and may be selected from the time when the first sheet passes through a predetermined registration roller, the time from the arrival at the fixing device, or the like. The time B or C may be selected to be an optimum value according to productivity of the image forming apparatus, heat capacity of the fixing belt, linear velocity of the sheet, sheet thickness, or the like, and may be set to, for example, 2 sheets B or 10 seconds C.

Next, a case where the pressurizing condition is changed according to the temperature detected by the temperature detecting means will be described.

As shown in fig. 22, in the present embodiment, temperature detection means 41a and 41b for detecting the surface temperature of the fixing belt 20 are provided on one side and the other side of the fixing belt 20 in the longitudinal direction (i.e., the direction orthogonal to the longitudinal direction of the heater 22 and the paper conveying direction) so as to face the fixing belt 20. As the temperature detection means 41a and 41b, for example, a thermistor can be used, and a known temperature detection means can be used as appropriate.

In the present embodiment, the temperature detection mechanisms 41a and 41b are provided at positions corresponding to one end and the other end in the longitudinal direction of the small-size paper P passing through the fixing nip, in other words, at positions corresponding to the second block and the sixth block, respectively, in the longitudinal direction of the heater 22.

The presence or absence of the change in the pressurizing condition is determined based on whether or not the difference between the temperature Tb and the temperature Ta detected by the temperature detection means 41a and 41b exceeds the temperature difference T1 of the set threshold value. In the present embodiment, the temperature detection results of the temperature detection means 41a and 41b are used for determining the pressing conditions when the small-size paper passes.

Specifically, as shown in fig. 23, when a print command is issued and a printing operation for small-sized paper is started (steps S2 and S3), the temperatures Ta and Tb are detected by the temperature detection means 41a and 41b at predetermined time intervals. When the temperature Ta is higher than the temperature Tb by a temperature T1 or higher (step S41), the pressing mechanism is changed to the first pressing condition, and the pressing force on the one side in the longitudinal direction is decreased. That is, the pressurizing force on the side where the temperature detected by the temperature detection means 41a and 41b is high is made small. After that, the same procedure is followed such that the pressure conditions are changed again after the printing operation is completed. When the temperature difference does not exceed T1 during the printing operation, the printing operation is terminated as it is (step S43).

In addition, the temperature detection mechanism may be provided in a position corresponding to the width direction end of the large-size paper. For example, as shown in fig. 24, the temperature detection mechanisms 41a, 41b are provided at positions corresponding to one end and the other end in the longitudinal direction of the large-size sheet P, in other words, at positions corresponding to the first block and the seventh block, respectively. In the present embodiment, the temperature detection results of the temperature detection mechanisms 41a, 41b are used for determination of the pressing conditions when the large-size paper is passed.

Specifically, as shown in fig. 25, when the printing operation for the large-size paper is started (steps S2 and S3), the temperatures Ta and Tb are detected by the temperature detection means 41a and 41b at predetermined time intervals. When the temperature Tb is higher than the temperature Ta by the temperature T2 or higher (step S42), the pressing mechanism is changed to the second pressing condition, and the pressing force at the other end in the longitudinal direction is decreased. That is, the pressurizing force on the side where the temperature detected by the temperature detection means 41a and 41b is high is made small.

As described above, by detecting the temperature of the fixing belt 20 by the temperature detection means 41a and 41b, the pressure condition can be changed at a more appropriate timing, and a problem caused by a temperature deviation between one side and the other side in the longitudinal direction of the heater 24 can be suppressed. That is, the gloss unevenness or the gloss unevenness of the image can be effectively suppressed. Further, the time for which the pressing deviation occurs can be further reduced, and the lateral deviation of the abrasion of the fixing belt 20 and the pressing roller 21 can be further suppressed.

In order to effectively prevent the unevenness of the gloss and the unevenness of the fixability of the image, it is preferable to set the temperatures T1, T2 to 20deg or less. Further, the temperatures T1 and T2 need to be set in consideration of the temperature detection errors and the arrangement errors of the temperature detection mechanisms 41a and 41b, the deviation of the paper conveyance position from the fixing nip, and the arrangement errors of the resistance heating elements 59. That is, in order to suppress erroneous detection due to these factors, it is more preferable to set the temperatures T1 and T2 to about 10 deg.

As described above, the pressing conditions can be changed at each timing for each of the large-size paper and the small-size paper. In the image forming apparatus, the condition for changing to the first pressurization condition and the condition for changing to the second pressurization condition may be common or different. For example, in the case of a small-size sheet, the first pressing condition is changed immediately after the printing operation is started, but in the case of a large-size sheet, the second pressing condition may be changed after B sheets of paper are passed, and the method of generating the temperature deviation may be appropriately selected according to the method of generating the temperature deviation. Further, the pressing conditions may be changed only for a certain size of paper.

As a timing different from the above timing, the pressurizing condition may be changed only when the sheet passes through the fixing device (when the sheet P passes through the fixing nip N in fig. 2). This can prevent the uneven gloss or uneven fixing property of the image from being adversely affected, and further reduce the time required for the occurrence of pressure deviation.

In the above embodiment, the pressurizing force is reduced for the flange of the fixing belt 20 holding the heater 22 on the side where the heat generation amount in the longitudinal direction is large, as compared with the case of the equal pressurizing condition, but the pressurizing force may be increased on the side where the heat generation amount in the longitudinal direction of the heater 22 is small.

Further, in the above embodiment, the timing of returning the pressing conditions to the pressing conditions is after the printing operation is completed, but may be immediately after the last sheet is discharged from the image forming apparatus main body (immediately after the sheet is discharged outside the image forming apparatus 1 of fig. 1) or immediately after the last sheet passes through the fixing device (immediately after the trailing edge of the sheet P passes through the fixing nip N of fig. 2). This can prevent the uneven gloss or uneven fixing property of the image from being adversely affected, and further reduce the time required for the occurrence of pressure deviation.

Next, a pressing mechanism for pressing the flanges 321 and 322 and changing the pressing force thereof will be described.

As shown in fig. 26(a), the fixing device 9 has a pressing mechanism 80A for pressing a flange 321 provided on one side in the longitudinal direction of the fixing belt 20. The pressing mechanism 80A includes a spring 33 as an urging member, a pressing lever 81 as a pressing mechanism, a cam 82 as a pressing force adjusting mechanism, and the like.

One end of the spring 33 is connected to the flange 321, and the other end is connected to the pressure lever 81.

The pressing lever 81 has a fulcrum 81a at one end in the longitudinal direction thereof. The fulcrum 81a is fixed to a frame portion (for example, the side wall portion 28 in fig. 3) of the fixing device 9, and the pressing lever 81 is provided to be rotatable about the fulcrum 81a (see the double arrows in fig. 26 a). The other end side in the longitudinal direction of the pressure lever 81 abuts on the cam 82, and the surface opposite to the side (right side in fig. 26 a) abutting on the cam 82 is connected to the spring 33.

The cam 82 is provided to be rotatable about a cam shaft 82 a. The camshaft 82a is connected to a drive control mechanism 83.

The drive control mechanism 83 includes a motor 84 for applying a rotational drive force to the cam shaft 82a, and a control unit 85 for controlling the motor.

One end side of the pressing lever 81 is pressed by the cam 82, and thus the pressing force is transmitted to the flange 321 via the spring 33, and the fixing belt 20 is pressed toward the pressing roller 21 side.

As shown in fig. 26(B), similarly to the pressing mechanism 80A of the pressing flange 321, a pressing mechanism 80B of the pressing flange 322 is provided on the other end side in the longitudinal direction of the fixing belt 20. The pressing mechanism 80B has substantially the same structure as the pressing mechanism 80A. The cams 82 provided in the pressurizing mechanisms 80A, 80B have a common camshaft 82a, and are rotated only in the same phase by being applied with a driving force by a common drive control mechanism 83. In the present embodiment, the two cams 82,82 are shifted in phase by 120 degrees. The drive control mechanism for rotating the camshaft 82a is constituted by a pulse motor drive mechanism that is driven at 120-degree intervals. Each pressurizing lever 81 is provided to be independently rotatable about a fulcrum 81 a.

The pressing mechanism 80A presses the flange 321, the pressing mechanism 80B presses the flange 322, and the fixing belt 20 is pressed against the pressing roller 21 to form the fixing nip N.

The cam shaft 82a is rotated by the drive control mechanism 83 to change the pressing force applied to the flanges 321, 322. That is, the surface that abuts against the pressurizing rod 81 is changed by the rotation of each cam 82 about the cam shaft 82a, and the pressurizing force is changed.

Under the same pressing conditions, as shown in fig. 26(a) and 26(B), the cams 82 of both the pressing mechanisms 80A and 80B are set such that the longer diameter side (radius R1 side) thereof faces the pressing lever 81 and the pressing forces are the same, i.e., the pressing force F_L、F_R. The cam 82 of the pressurizing mechanism 80A and the cam 82 of the pressurizing mechanism 80B are different in rotational phase, and the short diameter side is brought into contact with the pressurizing rod 81 at different timings. Fig. 26(a) and 26(b) are views seen from the same direction.

As shown in fig. 27 a and 27 b, the first pressurizing condition can be changed by rotating the cam shaft 82a by a predetermined rotation amount (in the present embodiment, 120 degrees clockwise from the phase of fig. 26 a). Specifically, the cam 82 of the pressing mechanism 80A has the short diameter side (radius R2 side) in contact with the pressing lever 81, and the cam 82 of the pressing mechanism 81B has the long diameter side in contact with the pressing lever 81. By making the cam 82 of the pressurizing mechanism 80A and the pressurizingWhen the surface against which the lever 81 abuts changes from the longer diameter side to the shorter diameter side, the pressing force of the cam 82 against the pressing lever 81 becomes small, and accordingly, the spring load of the spring 33 against the flange 321 becomes small. That is, the force pressing the flange 321 is reduced. On the other hand, the pressing force on the pressing mechanism 80B side does not change. Thus, each pressurizing force is set as the pressurizing force F_L1、F_R. In fig. 26(a) to 27(a), the amount of expansion and contraction of the spring 33 changes in accordance with displacement of the pressure lever 81 in the lateral direction of the drawing.

As shown in fig. 28a and 28b, the camshaft 82a is rotated by a predetermined amount different from that in the case of changing to the first pressurizing condition (in the present embodiment, 240 degrees clockwise from the phase of fig. 26 a), so that the second pressurizing condition can be changed. Specifically, the cam 82 of the pressurizing mechanism 80A brings the long diameter side into contact with the pressurizing rod 81, and the cam 82 of the pressurizing mechanism 81B brings the short diameter side into contact with the pressurizing rod 81, thereby setting each pressurizing force to a pressurizing force F_L、F_R1。

By shifting the phases of the cams 82,82 of the pressurizing mechanisms 80A, 80B in this way, the cams 82,82 can be rotated by the common cam shaft 82a, and the pressurizing conditions can be changed, whereby the driving force of the pressurizing mechanisms 80A, 80B can be reduced, and the cams 82,82 can be prevented from shifting in rotational phase.

In the above description, the pressurizing mechanism configured to reduce the pressurizing force on the side where the heat generation amount in the longitudinal direction is large is shown, but the pressurizing mechanism configured to increase the pressurizing force on the side where the heat generation amount is small may be used. That is, the pressurizing force of the pressurizing mechanism 80B may be increased under the first pressurizing condition, and the pressurizing force of the pressurizing mechanism 80A may be increased under the second pressurizing condition.

As an example, the pressing mechanisms 80A and 80B shown in fig. 29(a) and 29(B) can be used. Unlike the above-described pressing mechanism, the cam 82 has a large range on the short diameter side (radius R2 side) and a small range on the long diameter side (radius R1 side). The pressing mechanism 80A and the pressing mechanism 80B are identical in phase difference of 120 degrees. FIGS. 29(a) and 29(b) show the case of the equal pressurization conditionWhen the pressing mechanism 80B is rotated 120 degrees clockwise from the state shown in the figure, the cam 82 of the pressing mechanism 80B changes the pressing force F of the pressing mechanism 80B to the pressing force F by bringing the long diameter side into contact with the pressing lever 81_RPressure F of pressurizing mechanism 80A_LLarge conditions. Further, by rotating 240 degrees clockwise from the state of the drawing, the cam 82 of the pressurizing mechanism 80A is changed to the pressurizing force F of the pressurizing mechanism 80A with the major diameter side abutting against the pressurizing lever 81_LPressure F of pressurizing mechanism 80B_RLarge conditions.

In the above embodiment, the case where only the pressing forces of the pressing mechanisms 80A and 80B are changed is shown, but the pressing forces of the pressing mechanisms 80A and 80B may be changed to change the pressing amount of the fixing belt 20 into the pressing roller 21 and change the fixing nip width.

For example, as shown in fig. 30, in the pressing mechanism 80A of the present embodiment, a pressing portion 81b that protrudes toward the flange 321 side and comes into contact with the flange 321 is provided on the pressing lever 81 in place of the spring 33. The pressing mechanism 80B also has substantially the same structure.

In the configuration using the spring 33, even if the position of the pressure lever 81 changes, the amount of change is absorbed by the change in the amount of compression of the spring 33. In contrast, in the present embodiment, the flange 321 moves by an amount corresponding to the movement of the pressing lever 81 in the left-right direction in the figure, and the pressing state of the fixing belt 20 against the pressing roller 21 changes. That is, the width of the fixing nip N varies.

Further, although fig. 30 illustrates the case of the cam 82 having a narrow range on the short diameter side, as shown in fig. 29, the cam 82 having a narrow range on the long diameter side may be employed, and the width of the fixing nip portion N on the side where the amount of heat generation in the longitudinal direction is small may be increased.

As described above, in the present invention, by relatively reducing the pressing force of the pressing mechanism on the side where the heat generation amount in the longitudinal direction of the heater 22 is large, it is possible to suppress a problem caused by temperature variation in the longitudinal direction of the heater 22 or the fixing belt 20. That is, the gloss unevenness or the gloss unevenness of the image can be suppressed. Therefore, the image forming apparatus can also be adapted to high-speed and small-sized image forming apparatuses.

In the above embodiment, the example in which the pressing mechanism presses the flange supporting the fixing belt is shown, but the pressing mechanism may press the shaft 21d of the pressing roller 21 and press the pressing roller 21 against the fixing belt 20 as shown in fig. 31. In fig. 31, the pressing mechanism is shown as pressing the shaft 21d of the pressure roller 21, but may be configured to press a bearing that supports the shaft of the pressure roller 21.

In addition, the present invention is particularly suitable for a heater miniaturized in the short side direction. Specifically, the present invention is preferably applied to the heater 22 shown in fig. 32 in which the ratio (R/Q) of the short-side direction dimension R of the resistance heat generating element 59 to the short-side direction dimension Q of the heater 22 (base material 50) is 25% or more. Further, the present invention is more preferably applied to the heater 22 having the dimension ratio (R/Q) in the short side direction of 40% or more. By applying the present invention to such a small-sized heater 22, a greater effect can be expected.

In order to suppress the temperature variation of the heater 22, a resistance heating element having PTC characteristics may be used. The PTC characteristic is a characteristic in which the resistance value becomes high when the temperature becomes high (the heater output power decreases when a constant voltage is applied). By using the heat generating portion having PTC characteristics, the temperature can be raised quickly at a low temperature by a high output, and an excessive temperature rise can be suppressed at a high temperature by a low output. For example, if the TCR coefficient of the PTC characteristic is about 300 to 4000 ppm/degree, the resistance required for the heater can be ensured and the cost can be reduced. More preferably, the TCR factor is 500 to 2000 ppm/degree.

The Temperature Coefficient of Resistance (TCR) can be calculated using the following formula (2). T0 in the formula (2) is a reference temperature, T1 is an arbitrary temperature, R0 is a resistance value at the reference temperature T0, and R1 is a resistance value at the arbitrary temperature T1. For example, in the above-described heater 22 shown in fig. 7, when the resistance value between the first electrode 61A and the second electrode 61B is 10 Ω (resistance value R0) at 25 ℃ (reference temperature T0), and 12 Ω (resistance value R1) at 125 ℃ (arbitrary temperature T1), the temperature coefficient of resistance calculated from the following equation (2) is 2000ppm/° c.

Temperature Coefficient of Resistance (TCR) ═ R1-R0)/R0/(T1-T0) × 10⁶···(2)

The heater to which the present invention is applied is not limited to the heater 22 having the block-shaped (rectangular) resistance heating element 59 as shown in fig. 7 and the like, and may be applied to, for example, the heater 22 having the resistance heating element 59 folded linearly as shown in fig. 33(a) or 33(b), or a heater having a resistance heating element of another shape. In the figure, the colored portion represents the resistance heating element 59. In fig. 33(a), the feeder lines 62A and 62D are formed along the longitudinal direction of the heater 22, and extend partially in the direction intersecting the longitudinal direction. On the other hand, fig. 33(b) shows an example in which a region bent in a direction intersecting the longitudinal direction from the feeder lines 62A and 62D formed along the longitudinal direction of the heater 22 is also formed as the resistance heating element 59.

The present invention is also applicable to the fixing apparatuses shown in fig. 34 to 36, in addition to the fixing apparatuses described above. The following briefly describes the structure of each fixing device shown in fig. 34 to 36.

First, the fixing device 9 shown in fig. 34 is configured such that a pressing roller 90 is disposed on the opposite side of the fixing belt 20 from the pressing roller 21 side, and the fixing belt 20 is heated by the pressing roller 90 and the heater 22 being sandwiched therebetween. On the other hand, on the pressure roller 21 side, a nip forming member 91 is disposed on the inner periphery of the fixing belt 20. The nip forming member 91 is supported by the stay 24, and the nip N is formed by the nip forming member 91 and the pressure roller 21 sandwiching the fixing belt 20.

As described in the above embodiment, the fixing device 9 shown in fig. 34 is also provided with a pressing mechanism that presses at least one of the fixing belt 20 and the pressing roller 21 against the other, so that the pressing force on the side where the heat generation amount in the longitudinal direction of the heater 22 is large is relatively smaller than the pressing force on the side where the heat generation amount is small. This relatively reduces the clamping pressure on the side of the heater 22 having a large heat generation amount in the longitudinal direction. Further, the width of the nip portion on the side where the heat generation amount in the longitudinal direction of the heater 22 is large is relatively small. Therefore, it is possible to suppress a problem caused by a temperature deviation between one side and the other side in the longitudinal direction of the heater 24. That is, the difference in fixability between one side and the other side in the longitudinal direction can be suppressed, and the gloss deviation in the longitudinal direction can be suppressed. Therefore, image unevenness and gloss unevenness of the paper can be suppressed.

Next, in the fixing device 9 shown in fig. 35, the aforementioned pressing roller 90 is omitted, and the heater 22 is formed in an arc shape along the curvature of the fixing belt 20 in order to secure the circumferential contact length between the fixing belt 20 and the heater 22. The other configuration is the same as that of the fixing device 9 shown in fig. 34.

Finally, the fixing device 9 shown in fig. 36 will be explained. The fixing device 9 includes a heating unit 92, a fixing roller 93 serving as a rotating member (fixing member), and a pressing unit 94 serving as an opposing member. The heating unit 92 includes the heater 22, the heating unit 19, and the heating belt 120 described in the above embodiments. The fixing roller 93 is composed of a solid iron core rod 21a, an elastic layer 21b formed on the surface of the core rod 21a, and a release layer 21c formed outside the elastic layer 21 b. Further, a pressing member 94 is provided on the opposite side of the heating member 92 from the fixing roller 93. The pressing assembly 94 is provided with a nip forming member 95 and a support 96, and the pressing belt 97 is rotatably arranged so as to include these nip forming member 95 and support 96. Then, the paper P is passed through a fixing nip N2 between the pressure belt 97 and the pressure roller 93, and the image is fixed by heating and pressing the paper P.

In the fixing device 9 shown in fig. 36, since the heating unit 92 heats the fixing roller 93, when there is a deviation in the amount of heat generated from one side and the other side in the longitudinal direction (depth direction in the drawing) of the heater 22 as described above, a temperature deviation also occurs in the fixing roller 93 from one side and the other side in the longitudinal direction.

Then, in the fixing device 9 shown in fig. 36, a pressing mechanism is provided that presses at least one of the fixing roller 93 as a rotating member (fixing member) and the pressing member 94 as a facing member against the other member, so that the pressing force on the side where the heat generation amount in the longitudinal direction of the heater 22 is large is relatively smaller than the pressing force on the side where the heat generation amount is small. This relatively reduces the clamping pressure on the side of the heater 22 having a large heat generation amount in the longitudinal direction. Further, the width of the nip portion on the side where the heat generation amount of the heater 22 is large is relatively small. Therefore, it is possible to suppress a problem caused by a temperature deviation between one side and the other side in the longitudinal direction of the heater 24. That is, the difference in fixability between one side and the other side in the longitudinal direction can be suppressed, and the gloss deviation in the longitudinal direction can be suppressed. Therefore, image unevenness and gloss unevenness of the paper can be suppressed.

The layout of the electrodes and the like disposed on the base 50 of the heater 22 is not limited to the above-described embodiment, and the present invention can be applied to a heater in which temperature variation occurs between one side and the other side in the longitudinal direction.

For example, as an example of another heater to which the present invention is applied, the heater 22 shown in fig. 37 is different from the foregoing embodiment in that all the electrodes are provided on one side in the longitudinal direction. That is, compared with the heater 22 of fig. 10 and the like, the difference is that the second electrode 61B is provided on one side in the longitudinal direction. Further, as shown in fig. 37, since the second electrode 61B is provided on one side in the longitudinal direction, the power feed line directly connected to the second electrode 61B extends to the other side in the longitudinal direction, and is folded back and connected to each of the resistance heating elements 59. In the present embodiment, the portion of the feeder line connecting the second electrode 61B and each of the resistive heating elements 59 from the portion connecting each of the resistive heating elements 59 to the other folded portion in the longitudinal direction is referred to as a second feeder line 62B, and the portion extending from the folded portion to one side in the longitudinal direction to the second electrode 61B is referred to as a fifth feeder line (conductor) 62E.

In such a heater 22, even when electricity is applied only to the first heat generating portion 60A and electricity is applied to the first heat generating portion 60A and the second heat generating portion 60B, the temperature deviation in the longitudinal direction as described above occurs.

First, when only the first heat generation unit 60A is energized, as shown in fig. 38 and 39, an unexpected branch occurs toward the third power feed line 62C. Therefore, the total amount of heat generation of the respective blocks is asymmetrical in the left-right direction with respect to the fourth block at the center of the heat generation region, and the amount of heat generation at one side in the longitudinal direction is larger than that at the other side. When current is passed to the first heat generating portion 60A and the second heat generating portion 60B, as shown in fig. 40 and 41, the total amount of heat generated based on the fourth block is asymmetrical in the left-right direction, and the amount of heat generated on the other side in the longitudinal direction is larger than that on the one side.

Then, as in the above-described embodiment, by making the pressing force generated by the pressing mechanism on the side of the heater 22 having the larger heat generation amount relatively smaller than the side having the smaller heat generation amount in the longitudinal direction of the heater 22, the nip pressure and the nip width in the nip N on the side of the heater 22 having the larger heat generation amount can be reduced, and the occurrence of a problem due to a temperature deviation between the one side and the other side in the longitudinal direction of the heater 22 can be suppressed. That is, the difference in fixability between one side and the other side in the longitudinal direction can be suppressed, and the gloss deviation in the longitudinal direction can be suppressed. Therefore, image unevenness and gloss unevenness of the paper can be suppressed.

The present invention is not limited to the fixing device described above, and can be applied to a drying device for drying ink applied to paper, and further can be applied to a heating device such as a laminator for thermally pressing a film material as a covering member to a surface of a sheet such as paper, or a thermal pressing device such as a heat sealing machine for thermally pressing a sealing portion of a packaging material. By applying the present invention to such a device, it is possible to suppress a problem caused by a temperature deviation between one side and the other side in the longitudinal direction of the heater 24.

The recording medium includes thick paper, postcards, envelopes, thin paper, coated paper (coated paper, and the like), tracing paper, OHP sheets, and the like, in addition to the paper P (plain paper).