JP2011141564A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve uniformity of a calorific value of a fixing member in a longitudinal direction in an electromagnetic induction heating type fixing device. <P>SOLUTION: The fixing device includes a fixing belt 61, an end cap member, a pressure roll 62, a pressing pad 63 pressing the pressure roll 62 through the fixing belt 61, an IH heater, a thermosensitive magnetic member 64, and a holder 65. The pressing pad 63 is formed so that pressing force for pressing the pressure roll 62 is stronger on a downstream side than on an upstream side in a movement direction of the fixing belt 61, and the thermosensitive magnetic member 64 is attached to the holder 65 so that the position of an end near to a downstream side in the movement direction of the fixing belt 61 of the pressing pad 63 in the movement direction of the fixing belt 61 of a curved portion 64a is displaced from a longitudinal direction both end sides to a central part direction in a direction away from the fixing belt 61 in comparison with the position of an end near to an upstream side in the movement direction of the fixing belt 61 of the pressing pad 63. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

As a fixing device mounted on an image forming apparatus such as a copying machine or a printer using an electrophotographic system, an apparatus using an electromagnetic induction heating system is known.
For example, in Patent Document 1, an electromagnetic induction coil as a magnetic flux generating means is arranged inside a fixing roll made of a core metal cylinder made of magnetic metal, and an eddy current is induced in the fixing roll by an induced magnetic field generated by the electromagnetic induction coil. An electromagnetic induction heating type fixing device that directly heats the fixing roll is described.

JP 2003-186322 A

Here, in general, for example, the fixing member heated by the electromagnetic induction heating method is constituted by a belt member having a small heat capacity, so that the time required to raise the fixing member to the fixing set temperature (warm-up time) is shortened. However, on the other hand, since the fixing member constituted by the belt member has a small heat capacity, the amount of heat generation tends to vary in the longitudinal direction of the fixing member.
SUMMARY OF THE INVENTION An object of the present invention is to improve the longitudinal uniformity of the heat generation amount of a fixing member in an electromagnetic induction heating type fixing device.

The invention according to claim 1 has a conductive layer, and the conductive layer is heated by electromagnetic induction to support the fixing belt for fixing the toner to the recording material and the vicinity of both end portions in the width direction of the fixing belt. An end cap member formed in a substantially elliptical shape, a pressure roll that conveys the recording material between the fixing belt, and an inside of the fixing belt, and the pressure applied via the fixing belt A pressing member that presses the roll; a magnetic field generation member that generates an alternating magnetic field that intersects the conductive layer of the fixing belt; and an arc-shaped portion that is disposed to face the magnetic field generation member across the fixing belt. A magnetic path forming member that forms a magnetic path of the alternating magnetic field generated by the magnetic field generating member and transmits the alternating magnetic field generated by the magnetic field generating member; and a support member that supports the magnetic path forming member. Comprising The pressure member is formed such that the pressing force for pressing the pressure roll is stronger on the downstream side than the upstream side in the fixing belt moving direction, and the magnetic path forming member is the fixing belt moving direction of the arc-shaped portion. The position of the end portion of the pressing member close to the downstream side in the fixing belt movement direction is closer to the center portion direction from both ends in the longitudinal direction than the position of the end portion of the pressing member close to the upstream side in the fixing belt movement direction. The fixing device is attached to the support member so as to be displaced in a direction away from the fixing belt.

The invention according to claim 2 is that, in the magnetic path forming member, the upstream end position at the longitudinal center portion of the arc-shaped portion is more circular than the upstream end position at both longitudinal end portions. The fixing device according to claim 1, wherein the fixing unit is attached to the support member so as to be displaced in a downstream end direction of the shape portion in the fixing belt moving direction and away from the magnetic field generation member. is there.
The invention according to claim 3 is the fixing device according to claim 1, wherein the magnetic path forming member is divided into a plurality of parts along the width direction of the fixing belt.
According to a fourth aspect of the present invention, in the fixing device according to the first aspect, the magnetic path forming member is formed with a plurality of notches perpendicular to the longitudinal direction along the longitudinal direction.
The invention according to claim 5 is the fixing device according to claim 1, wherein the magnetic path forming member is disposed in a non-contact manner with the fixing belt.

According to a sixth aspect of the present invention, there is provided a toner image forming unit that forms a toner image, a transfer unit that transfers the toner image formed by the toner image forming unit onto a recording material, and a toner image that is transferred onto the recording material. Fixing means for fixing the toner image to the recording material, the fixing means having a conductive layer, and fixing belt for fixing the toner to the recording material by electromagnetically heating the conductive layer; An end cap member formed in a substantially oval shape that supports the vicinity of both end portions in the width direction of the fixing belt, a pressure roll that conveys the recording material between the fixing belt, and a fixing belt. A pressing member that is disposed inside and presses the pressure roll through the fixing belt, a magnetic field generation member that generates an alternating magnetic field that intersects the conductive layer of the fixing belt, and the magnetic field sandwiched by the fixing belt. A magnetic path forming member having an arc-shaped portion disposed opposite to the generating member, forming a magnetic path of an alternating magnetic field generated by the magnetic field generating member, and transmitting the alternating magnetic field generated by the magnetic field generating member And a support member that supports the magnetic path forming member, and the pressing member is formed such that the pressing force for pressing the pressure roll is stronger on the downstream side than the upstream side in the fixing belt moving direction, In the magnetic path forming member, the position of the end portion of the arc-shaped portion close to the downstream side in the fixing belt movement direction of the pressing member in the fixing belt movement direction is close to the upstream side of the pressing member in the fixing belt movement direction. An image forming apparatus, wherein the image forming apparatus is attached to the support member so as to be displaced in a direction away from the fixing belt from the both ends in the longitudinal direction toward the center as compared with the position of the end. .

According to a seventh aspect of the present invention, in the magnetic path forming member of the fixing unit, the upstream end position at the longitudinal center of the arc-shaped portion is the upstream end position at both longitudinal ends. 7. The mounting member according to claim 6, wherein the arcuate portion is attached to the support member so as to be displaced in a downstream end direction in the fixing belt moving direction and away from the magnetic field generating member. This is an image forming apparatus.
According to an eighth aspect of the present invention, in the image forming apparatus according to the sixth aspect, the magnetic path forming member of the fixing unit is divided into a plurality of parts along the width direction of the fixing belt. It is.
  According to a ninth aspect of the present invention, in the magnetic path forming member of the fixing unit, a plurality of notches perpendicular to the longitudinal direction are formed along the longitudinal direction. Device.
According to a tenth aspect of the present invention, in the image forming apparatus according to the sixth aspect, the magnetic path forming member of the fixing unit is disposed in a non-contact manner with the fixing belt.
According to an eleventh aspect of the present invention, there is provided a fixing member that has a conductive layer, the toner is fixed to a recording material by electromagnetic induction heating of the conductive layer, and an alternating magnetic field that intersects the conductive layer of the fixing member. A magnetic field generating member to be generated, and an arcuate portion disposed opposite the magnetic field generating member with the fixing member interposed therebetween, forming a magnetic path of an alternating magnetic field generated by the magnetic field generating member, and the magnetic field A magnetic path forming member that transmits an alternating magnetic field generated by the generating member; and a support member that supports the magnetic path forming member, wherein the arc-shaped portion of the magnetic path forming member extends in the width direction of the fixing member. A plurality of cutout portions are formed along the longitudinal direction, which are integrally formed from at least one end portion to the central portion of the fixing member with respect to the longitudinal direction along the longitudinal direction. The longitudinal direction The upstream end position in the moving direction of the fixing member on the magnetic field generating member side at the center is downstream in the fixing member moving direction of the arc-shaped portion from the upstream end position at both ends in the longitudinal direction. A fixing device, wherein the fixing device is attached to the support member so as to be displaced toward a side end position side and away from the magnetic field generation member.
According to a twelfth aspect of the present invention, a toner image forming unit that forms a toner image, a transfer unit that transfers the toner image formed by the toner image forming unit onto a recording material, and a toner image that is transferred onto the recording material. Fixing means for fixing the toner image to the recording material, the fixing means including a conductive layer, and a fixing member for fixing the toner to the recording material by electromagnetically heating the conductive layer. A magnetic field generating member that generates an alternating magnetic field that intersects with the conductive layer of the fixing member; and an arc-shaped portion that is disposed to face the magnetic field generating member across the fixing member. A magnetic path forming member that forms a magnetic path of the generated AC magnetic field and transmits the AC magnetic field generated by the magnetic field generating member; and a support member that supports the magnetic path forming member. The arc-shaped portion of the The longitudinal direction along the width direction of the fixing member is integrally formed from at least one end portion to the central portion of the fixing member, and a notch that intersects with the longitudinal direction at an angle has the longitudinal direction. The upstream end position in the moving direction of the fixing member on the magnetic field generating member side at the center in the longitudinal direction is more than the upstream end position at both ends in the longitudinal direction. An image forming apparatus, wherein the arcuate portion is attached to the support member so as to be displaced toward the downstream end position side in the moving direction of the fixing member and away from the magnetic field generating member.

According to the first aspect of the present invention, the uniformity in the longitudinal direction of the heat generation amount of the fixing belt can be improved in the electromagnetic induction heating type fixing device as compared with the case where the present invention is not adopted.
According to the second aspect of the present invention, compared to the case where the present invention is not adopted, the arc-shaped portion is kept in the arc-shaped portion while keeping the fluctuation amount of the gap between the fixing belt and the magnetic path forming member on the downstream side in the fixing belt moving direction small. The upstream end position of the shape portion can be displaced in a direction away from the fixing belt from both longitudinal end portions toward the central portion.
According to the invention of claim 3, compared with the case where the present invention is not adopted, the length in the longitudinal direction of the magnetic path forming member can be made shorter, and the deformation in the longitudinal direction in the magnetic path forming member can be easily generated. Can do.
According to the fourth aspect of the present invention, compared with the case where the present invention is not adopted, it is possible to configure that stress is not easily accumulated in the magnetic path forming member, and to suppress the influence on the magnetic path passing through the inside of the magnetic path forming member. it can.
According to the invention of claim 5, compared to the case where the present invention is not adopted, when the fixing belt is heated to the fixing set temperature, the heat of the fixing belt is suppressed from flowing into the magnetic path forming member, and the fixing belt is fixed. The time to reach the set temperature can be shortened.

According to the sixth aspect of the present invention, compared to the case where the present invention is not adopted, in the electromagnetic induction heating type fixing device mounted on the image forming apparatus, the uniformity of the heat generation amount of the fixing belt in the longitudinal direction can be improved. .
According to the seventh aspect of the present invention, compared with the case where the present invention is not adopted, the arc-shaped portion is maintained in the arc-shaped portion while keeping the fluctuation amount of the gap between the fixing belt and the magnetic path forming member on the downstream side in the fixing belt moving direction small. The upstream end position of the shape portion can be displaced in a direction away from the fixing belt from both longitudinal end portions toward the central portion.
According to the eighth aspect of the present invention, the length of the magnetic path forming member in the longitudinal direction can be made shorter than in the case where the present invention is not adopted, and the longitudinal deformation of the magnetic path forming member is easily caused. Can do.
According to the ninth aspect of the present invention, compared with the case where the present invention is not adopted, it is possible to configure that the stress is less likely to be accumulated inside the magnetic path forming member, and to suppress the influence on the magnetic path passing through the inside of the magnetic path forming member. it can.
According to the tenth aspect of the present invention, compared to the case where the present invention is not adopted, when the fixing belt is heated to the fixing set temperature, the heat of the fixing belt is suppressed from flowing into the magnetic path forming member, thereby fixing the fixing belt. The time to reach the set temperature can be shortened.
According to the eleventh aspect of the present invention, compared with the case where the present invention is not adopted, in the electromagnetic induction heating type fixing device, the uniformity of the heat generation amount of the fixing member in the longitudinal direction can be improved.
According to the invention of claim 12, compared with the case where the present invention is not adopted, in the electromagnetic induction heating type fixing device mounted on the image forming apparatus, the uniformity of the heat generation amount of the fixing member in the longitudinal direction can be improved. .

1 is a diagram illustrating a configuration example of an image forming apparatus to which a fixing device according to an exemplary embodiment is applied. FIG. 2 is a front view illustrating a configuration of a fixing unit of the present embodiment. FIG. 3 is an XX cross-sectional view of the fixing device in FIG. 2. FIG. 3 is a cross-sectional layer configuration diagram of a fixing belt. (a) is a side view of an end cap member, (b) is a top view of the end cap member seen from the Z direction. It is sectional drawing explaining the structure of an IH heater. It is a figure explaining the laminated structure of an IH heater. It is a figure explaining the state of a line of magnetic force in case the temperature of a fixing belt exists in the temperature range below the magnetic permeability change start temperature. FIG. 6 is a diagram illustrating an outline of a temperature distribution in a width direction of a fixing belt when small-size paper is continuously passed. FIG. 6 is a diagram for explaining a state of magnetic lines of force when the temperature of the fixing belt in a non-sheet passing region is in a temperature range exceeding the permeability change start temperature. It is the figure which showed the slit formed in a temperature sensitive magnetic member. FIG. 3 is a perspective view showing a schematic configuration inside a fixing belt. It is a figure explaining the track | orbit of the fixing belt in the center part area | region away from the end cap member of both ends. It is a figure explaining the attachment position to the holder of the temperature-sensitive magnetic member in the width direction center position. (A) The top view which looked at the thermosensitive magnetic member of the state attached to the holder from upper direction, (b) The enlarged view of the area | region Y. FIG. 6 is a perspective view showing a configuration example in which a temperature-sensitive magnetic member is divided into two in the width direction of the fixing belt.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
<Description of Image Forming Apparatus>
FIG. 1 is a diagram illustrating a configuration example of an image forming apparatus to which the fixing device of the present embodiment is applied. An image forming apparatus 1 shown in FIG. 1 is a so-called tandem color printer, and includes an image forming unit 10 that forms an image based on image data and a control unit 31 that controls the operation of the entire image forming apparatus 1. Further, for example, a communication unit 32 that receives image data by communicating with a personal computer (PC) 3 or an image reading device (scanner) 4, and a predetermined image for the image data received by the communication unit 32. An image processing unit 33 that performs processing is provided.

The image forming unit 10 includes four image forming units 11Y, 11M, 11C, and 11K (also collectively referred to as “image forming unit 11”), which are examples of toner image forming units arranged in parallel at a predetermined interval. I have. Each image forming unit 11 forms an electrostatic latent image and a photosensitive drum 12 as an example of an image holding body that holds a toner image, and charging that uniformly charges the surface of the photosensitive drum 12 with a predetermined potential. 13, an LED (Light Emitting Diode) print head 14 that exposes the photosensitive drum 12 charged by the charger 13 based on each color image data, and a developer that develops an electrostatic latent image formed on the photosensitive drum 12. 15. A drum cleaner 16 for cleaning the surface of the photosensitive drum 12 after transfer is provided.
Each of the image forming units 11 is configured in substantially the same manner except for the toner stored in the developing device 15, and each forms a toner image of yellow (Y), magenta (M), cyan (C), and black (K). To do.

  The image forming unit 10 also receives the intermediate transfer belt 20 onto which the color toner images formed on the photosensitive drums 12 of the image forming units 11 are transferred, and the color toner images formed on the image forming units 11. A primary transfer roll 21 that sequentially transfers (primary transfer) to the intermediate transfer belt 20 is provided. Further, a secondary transfer roll 22 that batch-transfers (secondary transfer) each color toner image transferred and superimposed on the intermediate transfer belt 20 onto a sheet P that is a recording material (recording paper), and each color toner that is secondarily transferred. A fixing unit 60 is provided as an example of a fixing unit (fixing device) that fixes the image on the paper P. In the image forming apparatus 1 of the present embodiment, the intermediate transfer belt 20, the primary transfer roll 21, and the secondary transfer roll 22 constitute a transfer unit.

  In the image forming apparatus 1 of the present embodiment, under the operation control by the control unit 31, image forming processing is performed by the following process. That is, the image data from the PC 3 or the scanner 4 is received by the communication unit 32, subjected to predetermined image processing by the image processing unit 33, and then sent to each image forming unit 11 as image data for each color. It is done. For example, in the image forming unit 11K that forms a black (K) toner image, the photosensitive drum 12 is uniformly charged at a predetermined potential by the charger 13 while rotating in the arrow A direction, and the image processing unit 33 is charged. The LED print head 14 scans and exposes the photosensitive drum 12 based on the K-color image data transmitted from. As a result, an electrostatic latent image relating to the K color image is formed on the photosensitive drum 12. The K-color electrostatic latent image formed on the photosensitive drum 12 is developed by the developing unit 15, and a K-color toner image is formed on the photosensitive drum 12. Similarly, yellow (Y), magenta (M), and cyan (C) color toner images are formed in the image forming units 11Y, 11M, and 11C, respectively.

  Each color toner image formed on the photosensitive drum 12 of each image forming unit 11 is sequentially electrostatically transferred (primary transfer) onto the intermediate transfer belt 20 that moves in the direction of arrow B by the primary transfer roll 21, and each color toner is superimposed. A superimposed toner image is formed. The superimposed toner image on the intermediate transfer belt 20 is conveyed to a region (secondary transfer portion T) where the secondary transfer roll 22 is disposed as the intermediate transfer belt 20 moves. When the superimposed toner image is conveyed to the secondary transfer unit T, the paper P is supplied from the paper holding unit 40 to the secondary transfer unit T in accordance with the timing. The superimposed toner image is collectively electrostatically transferred (secondary transfer) onto the conveyed paper P by the transfer electric field formed by the secondary transfer roll 22 in the secondary transfer portion T.

Thereafter, the sheet P on which the superimposed toner image is electrostatically transferred is conveyed to the fixing unit 60. The toner image on the paper P conveyed to the fixing unit 60 receives heat and pressure by the fixing unit 60 and is fixed on the paper P. Then, the paper P on which the fixed image is formed is conveyed to a paper stacking unit 45 provided in the discharge unit of the image forming apparatus 1.
On the other hand, the toner (primary transfer residual toner) adhering to the photosensitive drum 12 after the primary transfer and the toner (secondary transfer residual toner) adhering to the intermediate transfer belt 20 after the secondary transfer are respectively drum cleaner 16. , And the belt cleaner 25.
In this way, the image forming process in the image forming apparatus 1 is repeatedly executed for the number of printed sheets.

<Description of fixing unit configuration>
Next, the fixing unit 60 of this embodiment will be described.
2 and 3 are views showing the configuration of the fixing unit 60 of the present embodiment, FIG. 2 is a front view, and FIG. 3 is a sectional view taken along line XX in FIG.
First, as shown in FIG. 3, which is a cross-sectional view, the fixing unit 60 is heated by electromagnetic induction by an IH (Induction Heating) heater 80 and an IH heater 80 as an example of a magnetic field generating member that generates an alternating magnetic field, thereby generating a toner image. A fixing belt 61 as an example of a fixing member to be fixed, a pressure roll 62 disposed so as to face the fixing belt 61, and a pressure pad 63 pressed from the pressure roll 62 via the fixing belt 61 are provided.
Further, the fixing unit 60 includes a holder 65 as an example of a support member that supports components such as the pressing pad 63, and a temperature-sensitive magnetic member 64 that induces an alternating magnetic field generated by the IH heater 80 to form a magnetic path. In addition, a guide member 66 that guides the lines of magnetic force that have passed through the temperature-sensitive magnetic member 64 and a peeling assisting member 70 that assists in peeling the paper P from the fixing belt 61 are provided.

<Description of fixing belt>
The fixing belt 61 is formed of an endless belt member having an original cylindrical shape, and has a diameter of 30 mm and a length in the width direction of 370 mm in the original shape (cylindrical shape), for example. Further, as shown in FIG. 4 (cross-sectional layer configuration diagram of the fixing belt 61), the fixing belt 61 includes a base material layer 611, a conductive heat generating layer 612 laminated on the base material layer 611, and a toner image fixability. The belt member has a multilayer structure including an elastic layer 613 for improving the surface and a surface release layer 614 coated on the uppermost layer.

The base material layer 611 is composed of a heat-resistant sheet-like member that supports the thin conductive heat generating layer 612 and forms the mechanical strength of the fixing belt 61 as a whole. In addition, the base material layer 611 is made of a material having a physical property (relative magnetic permeability, specific resistance) that allows the magnetic field to pass therethrough so that the AC magnetic field generated by the IH heater 80 acts to the temperature-sensitive magnetic member 64, and the thickness. Formed with. On the other hand, the base material layer 611 itself is configured not to generate heat or hardly generate heat due to the action of a magnetic field.
Specifically, as the base material layer 611, for example, a nonmagnetic metal such as nonmagnetic stainless steel having a thickness of 30 to 200 μm (preferably 50 to 150 μm), a resin material having a thickness of 60 to 200 μm, or the like is used.

The conductive heating layer 612 is an example of a conductive layer, and is an electromagnetic induction heating element layer that is electromagnetically heated by an alternating magnetic field generated by the IH heater 80. That is, the conductive heat generating layer 612 is a layer that generates an eddy current when the AC magnetic field from the IH heater 80 passes in the thickness direction.
In general, a general-purpose power source that can be manufactured at low cost is used as a power source for an excitation circuit that supplies an alternating current to the IH heater 80 (see also FIG. 6 below). Therefore, the frequency of the alternating magnetic field generated by the IH heater 80 is generally 20 k to 100 kHz by a general-purpose power source. Thereby, the conductive heat generating layer 612 is configured such that an alternating magnetic field having a frequency of 20 k to 100 kHz enters and passes therethrough.

The region where the alternating magnetic field can enter the conductive heat generating layer 612 is defined as “skin depth (δ)”, which is a region where the alternating magnetic field attenuates to 1 / e, and is derived from the following equation (1). (1) In the equation, f is the AC magnetic field frequency (e.g., 20 kHz), [rho is resistivity (Omega · m), the mu _r is the relative permeability.
Therefore, the thickness of the conductive heat generating layer 612 is determined by the skin depth (δ) of the conductive heat generating layer 612 defined by the equation (1) such that an alternating magnetic field having a frequency of 20 k to 100 kHz penetrates and passes through the conductive heat generating layer 612. It is configured in a thinner layer. Further, as a material constituting the conductive heat generating layer 612, for example, a metal such as Au, Ag, Al, Cu, Zn, Sn, Pb, Bi, Be, Sb, or a metal alloy thereof is used.

Specifically, a nonmagnetic metal such as Cu having a thickness of 2 to 20 μm and a specific resistance of 2.7 × 10 ⁻⁸ Ω · m or less (relative magnetic permeability is approximately 1) is used as the conductive heating layer 612.
Further, from the viewpoint of shortening the time required for the fixing belt 61 to be heated to the fixing set temperature (hereinafter referred to as “warm-up time”), the conductive heat generating layer 612 is preferably formed as a thin layer.

Next, the elastic layer 613 is composed of a heat-resistant elastic body such as silicone rubber. The toner image held on the sheet P to be fixed is formed by laminating each color toner as powder. Therefore, in order to supply heat uniformly to the entire toner image at the nip portion N, it is preferable that the surface of the fixing belt 61 is deformed following the unevenness of the toner image on the paper P. Therefore, for example, silicone rubber having a thickness of 100 to 600 μm and a hardness of 10 ° to 30 ° (JIS-A) is suitable for the elastic layer 613.
Since the surface release layer 614 is in direct contact with the unfixed toner image held on the paper P, a material having a high release property is used. For example, PFA (tetrafluoroethylene perfluoroalkyl vinyl ether polymer), PTFE (polytetrafluoroethylene), silicone copolymer, or a composite layer thereof is used. If the thickness of the surface release layer 614 is too thin, it is not sufficient in terms of wear resistance, and the life of the fixing belt 61 is shortened. On the other hand, if it is too thick, the heat capacity of the fixing belt 61 becomes too large and the warm-up time becomes long. Therefore, the thickness of the surface release layer 614 is preferably 1 to 50 μm in consideration of the balance between wear resistance and heat capacity.

<Description of pressing pad>
The pressing pad 63 is an example of a pressing member, and is constituted by an elastic body such as silicone rubber or fluorine rubber, and is supported by the holder 65 at a position facing the pressure roll 62. Then, it is arranged in a state of being pressed from the pressure roll 62 via the fixing belt 61, and a nip portion N is formed with the pressure roll 62.
The pressing pad 63 includes a pre-nip region 63a on the inlet side of the nip portion N (upstream side in the conveyance direction of the paper P) and a peeling nip region 63b on the outlet side of the nip portion N (downstream side in the conveyance direction of the paper P). Different nip pressures are set. That is, in the pre-nip region 63 a, the surface on the pressure roll 62 side is formed in an arc shape that substantially follows the outer peripheral surface of the pressure roll 62, thereby forming a uniform and wide nip portion N. Further, the peeling nip region 63b is formed so as to be locally pressed from the surface of the pressure roll 62 with a large nip pressure so that the radius of curvature of the fixing belt 61 passing through the peeling nip region 63b becomes small. As a result, a curl (down curl) in a direction away from the surface of the fixing belt 61 is formed on the paper P passing through the peeling nip region 63b to promote the peeling of the paper P from the surface of the fixing belt 61.

  In the present embodiment, the peeling assisting member 70 is disposed on the downstream side of the nip portion N as a peeling assisting means by the pressing pad 63. The peeling auxiliary member 70 is supported by the holder 72 in a state where the peeling baffle 71 is close to the fixing belt 61 in a direction (so-called counter direction) opposite to the rotational movement direction of the fixing belt 61. The curled portion formed on the paper P at the outlet of the pressing pad 63 is supported by the peeling baffle 71, thereby suppressing the paper P from moving toward the fixing belt 61.

<Description of temperature-sensitive magnetic member>
Next, the temperature-sensitive magnetic member 64 is formed in an arc shape (arc-shaped portion) that follows the inner peripheral surface of the fixing belt 61, and a predetermined gap (for example, 0.5 mm) from the inner peripheral surface of the fixing belt 61. ˜1.5 mm), but in close contact but arranged in a non-contact manner. The temperature-sensitive magnetic member 64 is disposed close to the fixing belt 61 because the temperature of the temperature-sensitive magnetic member 64 changes corresponding to the temperature of the fixing belt 61, that is, the temperature of the temperature-sensitive magnetic member 64 is changed. This is because the temperature is substantially the same as the temperature 61. Further, the temperature-sensitive magnetic member 64 is disposed in a non-contact manner with the fixing belt 61 because the heat of the fixing belt 61 is increased when the main switch of the image forming apparatus 1 is turned on and the fixing belt 61 is heated to the fixing set temperature. This is to prevent the temperature from flowing into the temperature-sensitive magnetic member 64 and shorten the warm-up time.

Further, the temperature-sensitive magnetic member 64 has a “permeability change start temperature” (see below), which is a temperature at which the magnetic permeability of the magnetic characteristics changes suddenly, equal to or higher than a fixing set temperature at which each color toner image is melted. The elastic layer 613 and the surface release layer 614 are made of a material set in a temperature range lower than the heat resistant temperature. That is, the temperature-sensitive magnetic member 64 is made of a material having a characteristic (“temperature-sensitive magnetism”) that reversibly changes between ferromagnetic and non-magnetic (paramagnetic) in a temperature range including the fixing set temperature. . The temperature-sensitive magnetic member 64 functions as a magnetic path forming member, and induces magnetic lines of force that are generated by the IH heater 80 and transmitted through the fixing belt 61 in a temperature range equal to or lower than the magnetic permeability change start temperature exhibiting ferromagnetism. Thus, a magnetic path passing through the inside of the temperature-sensitive magnetic member 64 is formed. As a result, the temperature-sensitive magnetic member 64 forms a closed magnetic path that encloses the fixing belt 61 and the exciting coil 82 of the IH heater 80 (see FIG. 6 at a later stage). On the other hand, in the temperature range exceeding the permeability change start temperature, the temperature-sensitive magnetic member 64 crosses the magnetic field lines generated by the IH heater 80 and transmitted through the fixing belt 61 in the thickness direction of the temperature-sensitive magnetic member 64. Make it transparent. Thereby, the magnetic lines of force generated by the IH heater 80 and transmitted through the fixing belt 61 form a magnetic path that passes through the temperature-sensitive magnetic member 64, passes through the inside of the guide member 66, and returns to the IH heater 80.
The “permeability change start temperature” here is a temperature at which the magnetic permeability (for example, the magnetic permeability measured by JIS C2531) starts to decrease continuously. For example, a member such as the temperature-sensitive magnetic member 64 This is the temperature point at which the amount of magnetic flux that passes through (the number of lines of magnetic force) starts to change. Therefore, the permeability change start temperature is a temperature close to the Curie point, which is the temperature at which magnetism disappears, but has a concept different from the Curie point.

As a material used for the temperature-sensitive magnetic member 64, a binary system feeling such as an Fe-Ni alloy (permalloy), for example, in which the magnetic permeability change start temperature is set in a range of 140 ° C. to 240 ° C. used as the fixing set temperature, A ternary thermosensitive magnetic alloy such as a thermomagnetic alloy or an Fe—Ni—Cr alloy is used. For example, in a Fe-Ni binary temperature-sensitive magnetic alloy, the magnetic permeability change start temperature can be set to around 225 ° C. by setting it to about Fe 64% and Ni 36% (atomic ratio). Such metal alloys such as permalloy and temperature-sensitive magnetic alloy are suitable for the temperature-sensitive magnetic member 64 because they are excellent in moldability and workability, have high heat conductivity, and are inexpensive. As other materials, a metal alloy made of Fe, Ni, Si, B, Nb, Cu, Zr, Co, Cr, V, Mn, Mo or the like is used.
Further, the temperature-sensitive magnetic member 64 is formed with a thickness larger than the skin depth δ (see the above formula (1)) with respect to the AC magnetic field (lines of magnetic force) generated by the IH heater 80. Specifically, for example, when an Fe—Ni alloy is used, the thickness is set to about 50 to 300 μm. The configuration and function of the temperature-sensitive magnetic member 64 will be described in further detail later.

<Description of holder>
The holder 65 that supports the pressing pad 63 is made of a material having high rigidity so that the amount of bending in a state where the pressing pad 63 receives the pressing force from the pressing roll 62 becomes a certain amount or less. Thereby, the uniformity of the pressure in the longitudinal direction (nip pressure N) at the nip portion N is maintained. Furthermore, since the fixing unit 60 according to the present embodiment employs a configuration in which the fixing belt 61 is heated using electromagnetic induction, the holder 65 is made of a material that does not affect or hardly gives influence to the induced magnetic field. It is made of a material that is not affected or hardly affected by the induced magnetic field. For example, a heat-resistant resin such as glass-mixed PPS (polyphenylene sulfide) or a nonmagnetic metal material such as Al, Cu, or Ag is used.

<Description of induction member>
The induction member 66 is formed in an arc shape that follows the inner peripheral surface of the temperature-sensitive magnetic member 64, and has a predetermined gap (for example, 1.0 to 5.0 mm) from the inner peripheral surface of the temperature-sensitive magnetic member 64. Having a non-contact arrangement. The induction member 66 is made of a nonmagnetic metal having a relatively small specific resistance value, such as Ag, Cu, or Al. Then, when the temperature-sensitive magnetic member 64 rises to a temperature equal to or higher than the permeability change start temperature, an alternating magnetic field (line of magnetic force) generated by the IH heater 80 is induced, and the vortex is more vortexed than the conductive heating layer 612 of the fixing belt 61. A state in which the current I is easily generated is formed. Thereby, the thickness of the induction member 66 is a predetermined thickness (for example, 1.0 mm) sufficiently thicker than the skin depth δ (see the above formula (1)) so that the eddy current I can easily flow. It is formed.

<Description of Fixing Belt Drive Mechanism>
Next, a driving mechanism for the fixing belt 61 will be described.
As shown in FIG. 2 which is a front view, the fixing belt 61 is rotated in the circumferential direction while maintaining the cross-sectional shape of both ends of the fixing belt 61 in a circular shape at both axial ends of the holder 65 (see FIG. 3). An end cap member 67 to be driven is fixed. The fixing belt 61 directly receives the rotational driving force from both ends via the end cap member 67, and rotates and moves in the direction of arrow C in FIG. 3 at a process speed of 140 mm / s, for example.
5A is a side view of the end cap member 67, and FIG. 5B is a plan view of the end cap member 67 viewed from the Z direction. As shown in FIG. 5, the end cap member 67 has a circular fixed section 67 a fitted inside the both ends of the fixing belt 61 and has a larger outer diameter than the fixed section 67 a. A flange portion 67d formed so as to project radially from the fixing belt 61 when attached, a gear portion 67b to which rotational driving force is transmitted, a support portion 65a formed at both ends of the holder 65, and a coupling member The bearing bearing portion 67c is rotatably coupled via the 166. Then, as shown in FIG. 2, the support portions 65a at both ends of the holder 65 are fixed to both ends of the casing 69 of the fixing unit 60, whereby the end cap member 67 is coupled to the support portion 65a. It is rotatably supported via the bearing bearing portion 67c.
As a material constituting the end cap member 67, so-called engineering plastics having high mechanical strength and heat resistance are used. For example, phenol resin, polyimide resin, polyamide resin, polyamideimide resin, PEEK resin, PES resin, PPS resin, LCP resin and the like are suitable.

As shown in FIG. 2, in the fixing unit 60, the rotational driving force from the drive motor 90 is transmitted to the shaft 93 via the transmission gears 91 and 92, and both are transmitted from the transmission gears 94 and 95 coupled to the shaft 93. It is transmitted to the gear portion 67b (see FIG. 5) of the end cap member 67. As a result, a rotational driving force is transmitted from the end cap member 67 to the fixing belt 61, and the end cap member 67 and the fixing belt 61 are integrally rotated.
Thus, the fixing belt 61 rotates by receiving the driving force directly from both ends of the fixing belt 61, so that the fixing belt 61 rotates stably.

Here, when the fixing belt 61 rotates by receiving a driving force directly from the end cap members 67 at both ends, a torque of about 0.1 to 0.5 N · m is generally applied. However, in the fixing belt 61 of the present embodiment, the base material layer 611 is made of, for example, nonmagnetic stainless steel having high mechanical strength. For this reason, even when a torsional torque of about 0.1 to 0.5 N · m acts on the entire fixing belt 61, buckling or the like hardly occurs in the fixing belt 61.
Further, the flange portion 67d of the end cap member 67 suppresses the displacement of the fixing belt 61. In general, the fixing belt 61 at that time is generally 1 to 5 in the axial direction from the end portion (flange portion 67d) side. A compressive force of about 5N works. However, even when the fixing belt 61 receives such a compressive force, since the base material layer 611 of the fixing belt 61 is made of nonmagnetic stainless steel or the like, occurrence of buckling or the like is suppressed.
As described above, the fixing belt 61 according to the present embodiment rotates by receiving the driving force directly from both ends of the fixing belt 61, so that stable rotation is performed. At that time, the base material layer 611 of the fixing belt 61 is made of, for example, non-magnetic stainless steel having high mechanical strength, thereby realizing a structure in which buckling or the like hardly occurs against torsion torque or compression force. is doing. Furthermore, since the base material layer 611 and the conductive heat generating layer 612 are formed in a thin layer to ensure the flexibility / flexibility of the fixing belt 61 as a whole, deformation and shape restoration following the nip portion N are prevented. Done.

Returning to FIG. 3, the pressure roll 62 is arranged so as to face the fixing belt 61, and rotates in the direction of arrow D in FIG. 3 at a process speed of 140 mm / s, for example, following the fixing belt 61. Then, a nip portion N is formed in a state where the fixing belt 61 is sandwiched between the pressure roll 62 and the pressing pad 63, and the sheet P holding the unfixed toner image is passed through the nip portion N, so that the heat and pressure To fix the unfixed toner image on the paper P.
The pressure roll 62 includes, for example, a solid aluminum core (cylindrical metal core) 621 having a diameter of 18 mm, and a heat-resistant elastic body layer 622 such as a silicone sponge having a thickness of 5 mm, which is coated on the outer peripheral surface of the core 621. Further, for example, a release layer 623 made of a heat-resistant resin coating such as PFA containing carbon having a thickness of 50 μm or a heat-resistant rubber coating is laminated. Then, the pressing pad 63 is pressed through the fixing belt 61 with a load of 25 kgf, for example, by a pressing spring 68 (see FIG. 2).

<Description of IH heater>
Next, the IH heater 80 that performs electromagnetic induction heating by applying an AC magnetic field to the conductive heat generating layer 612 of the fixing belt 61 will be described.
FIG. 6 is a cross-sectional view illustrating the configuration of the IH heater 80 of the present embodiment. As shown in FIG. 6, the IH heater 80 includes a support 81 made of a nonmagnetic material such as a heat resistant resin, and an exciting coil 82 that generates an alternating magnetic field. In addition, a plurality of elastic support members 83 formed of an elastic body for fixing the excitation coil 82 on the support 81 and a magnetic path of an alternating magnetic field generated by the excitation coil 82 are arranged along the width direction of the fixing belt 61. Is formed. Furthermore, a plurality of adjustment cores 87 are provided along the width direction of the fixing belt 61 and for equalizing the alternating magnetic field generated by the excitation coil 82 in the longitudinal direction of the support 81. Furthermore, a shield 85 that shields the magnetic field, a pressure member 86 that pressurizes the magnetic core 84 toward the support 81, and an excitation circuit 88 that supplies an alternating current (electric power) to the excitation coil 82 are provided.

The support 81 is formed in a shape whose cross section is curved along the surface shape of the fixing belt 61, and an upper surface (supporting surface) 81 a that supports the exciting coil 82 has a predetermined gap (for example, 0) from the surface of the fixing belt 61. 0.5 to 2 mm). Moreover, as a material which comprises the support body 81, heat resistance, such as heat resistant resins, such as heat resistant glass, a polycarbonate, polyether sulfone, PPS (polyphenylene sulfide), or the glass fiber mixed with these, for example. Some non-magnetic materials are used.
The exciting coil 82 is configured by winding, for example, 90 litz wires, which are bundled with, for example, 90 copper wires having a diameter of 0.17 mm and wound in a closed loop with a hollow shape such as an ellipse, an ellipse, or a rectangle. . Then, when an alternating current having a predetermined frequency is supplied to the exciting coil 82 from the exciting circuit 88, an alternating magnetic field centered around a litz wire wound in a closed loop is generated around the exciting coil 82. . Generally, the frequency of the alternating current supplied from the excitation circuit 88 to the excitation coil 82 is 20 k to 100 kHz generated by the general-purpose power source.

The exciting coil 82 is configured by winding, for example, 90 litz wires, which are bundled with, for example, 90 copper wires having a diameter of 0.17 mm and wound in a closed loop with a hollow shape such as an ellipse, an ellipse, or a rectangle. . Then, when an alternating current having a predetermined frequency is supplied to the exciting coil 82 from the exciting circuit 88, an alternating magnetic field centered around a litz wire wound in a closed loop is generated around the exciting coil 82. . Generally, the frequency of the alternating current supplied from the excitation circuit 88 to the excitation coil 82 is 20 k to 100 kHz generated by the general-purpose power source.
The elastic support member 83 is a sheet-like member made of an elastic body such as silicone rubber or fluorine rubber. The elastic support member 83 is set to press the excitation coil 82 against the support 81 so that the excitation coil 82 is fixed in close contact with the support surface 81a of the support 81.

  For the magnetic core 84, for example, an arc-shaped ferromagnetic body made of a high-permeability oxide or alloy material such as sintered ferrite, ferrite resin, amorphous alloy (amorphous alloy), permalloy, or temperature-sensitive magnetic alloy is used. And functions as a magnetic path forming member. The magnetic core 84 induces a magnetic force line (magnetic flux) generated by the alternating magnetic field generated by the exciting coil 82, and crosses the fixing belt 61 from the magnetic core 84 toward the temperature-sensitive magnetic member 64. A path of magnetic lines of force (magnetic path) is formed so as to pass through and return to the magnetic core 84. That is, the AC magnetic field generated by the excitation coil 82 is configured to pass through the inside of the magnetic core 84 and the inside of the temperature-sensitive magnetic member 64 so that the magnetic lines of force wrap the fixing belt 61 and the excitation coil 82 inside. A closed magnetic circuit is formed. As a result, the magnetic field lines of the alternating magnetic field generated by the exciting coil 82 are concentrated in a region facing the magnetic core 84 of the fixing belt 61.

Here, the magnetic core 84 is preferably made of a material having a small loss due to magnetic path formation. Specifically, the magnetic core 84 is desirably used in a form that reduces the eddy current loss (current path interruption or division by slits, thin plate bundling, etc.), and is preferably formed of a material having a small hysteresis loss.
Further, the length of the magnetic core 84 along the rotation direction of the fixing belt 61 is configured to be smaller than the length of the temperature-sensitive magnetic member 64 along the rotation direction of the fixing belt 61. Thereby, the leakage of magnetic lines of force to the periphery of the IH heater 80 is reduced, and the power factor is improved. Furthermore, electromagnetic induction to the metal member constituting the fixing unit is suppressed, and the heat generation efficiency in the fixing belt 61 (conductive heat generation layer 612) is increased.
The magnetic core 84 is supported by a pair of magnetic core support portions (convex portions) 81b1 and 81b2 disposed in the center of the support surface 81a.

  The adjusting magnetic core 87 has a rectangular parallelepiped shape (block shape) made of a high permeability oxide such as sintered ferrite, ferrite resin, amorphous alloy (amorphous alloy), permalloy, magnetic shunt steel, or alloy material. A ferromagnetic material is used. The adjustment magnetic core 87 is a magnetic field adjustment member for equalizing the strength of the magnetic field in the longitudinal direction of the support 81 in an AC magnetic field formed by the magnetic core 84 and the temperature-sensitive magnetic member 64 disposed around the excitation coil 82. Function as. By averaging the strength of the magnetic field generated in the longitudinal direction of the support 81, temperature unevenness in the width direction of the fixing belt 61 is reduced. The adjusting magnetic core 87 is disposed in a space (region surrounded by the inner walls of the magnetic core support portions 81b1 and 81b2) formed in the inner region of the magnetic core support portions 81b1 and 81b2.

  Here, FIG. 7 is a diagram for explaining a laminated structure of the IH heater 80 of the present embodiment. As shown in FIG. 7, in the exciting coil 82, the closed loop hollow portion 82a of the exciting coil 82 is arranged in parallel along the longitudinal center axis (axis) of the supporting surface 81a on the supporting surface 81a of the supporting body 81. Is installed so as to surround the pair of magnetic core support portions (convex portions) 81b1 and 81b2. The support surface 81a is formed as a position setting surface in which a gap with the fixing belt 61 that rotates and moves while drawing a substantially circular path is formed / set to a specified value (design value). Then, the exciting coil 82 is pressed against the support surface 81a of the support 81 by the elastic support member 83, thereby being closely attached and fixed to the support surface 81a.

  Each of the plurality of magnetic cores 84 arranged along the width direction of the fixing belt 61 has an inner peripheral surface 84 b on the exciting coil 82 side that is formed in an arc shape toward the moving direction of the fixing belt 61. In addition, the inner peripheral surface 84b of the magnetic core 84 is formed with a length that covers (wraps) the entire region where the exciting coil 82 is disposed in the moving direction of the fixing belt 61. Each of the magnetic cores 84 is supported by the inner peripheral surface 84b of the magnetic core 84 supported by a pair of magnetic core support portions 81b1 and 81b2 disposed in parallel along the longitudinal central axis axis on the support surface 81a. 84 and the support surface 81a are set to be kept constant.

The elastic support member 83 is made of a sheet-like elastic body such as silicone rubber or fluorine rubber having a low Young's modulus, and is disposed between the exciting coil 82 and the magnetic core 84. Further, when the inner peripheral surface 84b of the magnetic core 84 is supported by the pair of magnetic core support portions 81b1 and 81b2 on the support surface 81a, the gap between the magnetic core 84 and the support surface 81a is set to a predetermined gap (FIG. (See also 6). In this case, the elastic support member 83 is formed thicker than the gap between the magnetic core 84 and the support surface 81a. On the other hand, each magnetic core 84 is pressed toward the support 81 by a pressing member 86 provided on the lower surface of the shield 85 by attaching the shield 85 to the support 81. Therefore, the elastic support member 83 is elastically deformed (compressed) by receiving pressure applied to the support body 81 via the magnetic core 84, and presses the exciting coil 82 toward the support surface 81a by the elastic force generated thereby. In this way, the elastic support member 83 fixes the exciting coil 82 in close contact with the support surface 81a. Since the support surface 81a is formed / set so as to maintain a predetermined gap (design value) with the surface of the fixing belt 61, the exciting coil 82 has the entire exciting coil 82 and the predetermined gap with the surface of the fixing belt 61. Is set to keep. Further, even if the cumulative number of vibrations of the exciting coil 82 becomes large due to the cumulative use of the fixing unit 60 over a long period of time, the elastic support member 83 and the exciting coil 82 are not separated, and the support 81 and the exciting coil 82 are not separated. The initial positional relationship between the two is maintained.
As the pressure member 86, for example, an elastic member such as a spring may be used in addition to an elastic body such as silicone rubber or fluorine rubber.

Subsequently, each of the plurality of magnetic cores 84 disposed along the width direction of the fixing belt 61 is provided on the lower surface of the shield 85 in a state where the inner peripheral surface 84b is supported on the pair of magnetic core support portions 81b1 and 81b2. The pressure member 86 is pressurized from the upper side toward the support 81 side. Thereby, each magnetic core 84 is pressed so as to be sandwiched between the pressure member 86 on the upper surface and the elastic support member 83 on the lower surface, so that the position in the vertical direction is fixed inside the IH heater 80.
Further, each of the plurality of adjustment magnetic cores 87 arranged along the width direction of the fixing belt 61 is formed in a rectangular parallelepiped shape (block shape), and the inner sides of the magnetic core support portions 81b1 and 81b2 between the magnetic core 84 and the magnetic core 84. Arranged in the space formed in the region. Then, pressure is applied from the upper side toward the support body 81 side by a pressure member 86 provided on the lower surface of the shield 85. Accordingly, each adjustment magnetic core 87 is pressed so as to be sandwiched between the upper pressure member 86 and the inner region of the lower magnetic core support portions 81b1 and 81b2, so that the inner sides of the magnetic core support portions 81b1 and 81b2 are pressed. Fixed to the area.

<Description of the state in which the fixing belt generates heat>
Subsequently, a state in which the fixing belt 61 generates heat by the alternating magnetic field generated by the IH heater 80 will be described.
First, as described above, the permeability change start temperature of the temperature-sensitive magnetic member 64 is within a temperature range that is not less than the set fixing temperature for fixing each color toner image and not more than the heat resistance temperature of the fixing belt 61 (for example, 140 to 240 ° C.). When the temperature of the fixing belt 61 is equal to or lower than the magnetic permeability change start temperature, the temperature of the temperature-sensitive magnetic member 64 adjacent to the fixing belt 61 is also started corresponding to the temperature of the fixing belt 61. Below temperature. Therefore, since the temperature-sensitive magnetic member 64 exhibits ferromagnetism, the magnetic field lines H of the alternating magnetic field generated by the IH heater 80 pass through the fixing belt 61 and then pass through the inside of the temperature-sensitive magnetic member 64 along the spreading direction. To form a magnetic path. Here, the “spreading direction” means a direction orthogonal to the thickness direction of the temperature-sensitive magnetic member 64.

  FIG. 8 is a diagram for explaining the state of the lines of magnetic force (H) when the temperature of the fixing belt 61 is in a temperature range equal to or lower than the permeability change start temperature. As shown in FIG. 8, when the temperature of the fixing belt 61 is in a temperature range equal to or lower than the permeability change start temperature, the magnetic field lines H of the alternating magnetic field generated by the IH heater 80 are transmitted through the fixing belt 61. A magnetic path passing through the inside of the temperature-sensitive magnetic member 64 along the spreading direction (direction orthogonal to the thickness direction) is formed. Therefore, the number of magnetic field lines H (magnetic flux density) per unit area in the region crossing the conductive heat generating layer 612 of the fixing belt 61 increases.

  That is, after the magnetic field lines H are radiated from the magnetic core 84 of the IH heater 80 and pass through the regions R1 and R2 across the conductive heat generating layer 612 of the fixing belt 61, the magnetic field lines H enter the inside of the temperature-sensitive magnetic member 64 which is a ferromagnetic material. Be guided. Therefore, the magnetic field lines H crossing the conductive heat generating layer 612 of the fixing belt 61 in the thickness direction are concentrated so as to enter the inside of the temperature-sensitive magnetic member 64, and the magnetic flux density in the regions R1 and R2 increases. Further, even when the magnetic field lines H that have passed through the inside of the temperature-sensitive magnetic member 64 along the spreading direction return to the magnetic core 84 again, in the region R3 that crosses the conductive heating layer 612 in the thickness direction, the magnetic field in the temperature-sensitive magnetic member 64 is increased. It is concentrated toward the magnetic core 84 from the lower part. Therefore, the magnetic force lines H that cross the conductive heat generating layer 612 of the fixing belt 61 in the thickness direction are concentrated from the temperature-sensitive magnetic member 64 toward the magnetic core 84, and the magnetic flux density in the region R3 is also increased.

In the conductive heating layer 612 of the fixing belt 61 where the magnetic lines H cross in the thickness direction, an eddy current I proportional to the amount of change in the number of magnetic lines H per unit area (magnetic flux density) is generated. Thereby, as shown in FIG. 8, a large eddy current I is generated in the regions R1, R2 and R3 where the amount of change in magnetic flux density is large. The eddy current I generated in the conductive heat generation layer 612 generates Joule heat W (W = I ² R), which is the product of the specific resistance value R of the conductive heat generation layer 612 and the square of the eddy current I. Thereby, a large Joule heat W is generated in the conductive heat generating layer 612 where the large eddy current I is generated.
As described above, when the temperature of the fixing belt 61 is in the temperature range equal to or lower than the permeability change start temperature, large heat is generated in the regions R1 and R2 and the region R3 where the lines of magnetic force H cross the conductive heat generating layer 612. Thereby, the fixing belt 61 is heated.

  By the way, in the fixing unit 60 of the present embodiment, the temperature-sensitive magnetic member 64 is disposed in the vicinity of the fixing belt 61 on the inner peripheral surface side of the fixing belt 61. As a result, the magnetic core 84 that guides the magnetic force lines H generated by the exciting coil 82 to the inside and the temperature-sensitive magnetic member 64 that guides the magnetic force lines H transmitted through the fixing belt 61 in the thickness direction are close to each other. The configuration is realized. For this reason, the AC magnetic field generated by the IH heater 80 (excitation coil 82) forms a loop with a short magnetic path, so that the magnetic flux density and the magnetic coupling degree in the magnetic path increase. Accordingly, when the temperature of the fixing belt 61 is in a temperature range equal to or lower than the magnetic permeability change start temperature, heat is more efficiently generated in the fixing belt 61.

<Description of function for suppressing temperature rise of non-sheet passing portion of fixing belt>
Next, the function of suppressing the temperature rise at the non-sheet passing portion of the fixing belt 61 will be described.
First, a case where small-size paper P (small-size paper P1) is continuously passed through the fixing unit 60 will be described. FIG. 9 is a diagram showing an outline of the temperature distribution in the width direction of the fixing belt 61 when the small size paper P1 is continuously fed. In FIG. 9, the maximum sheet passing area which is the maximum size width (for example, A3 width) of the sheet P used in the image forming apparatus 1 is Ff, and the small size sheet P1 (for example, smaller than the maximum size sheet P) (for example, , A4 (vertical feed) passes through the area (small size paper passing area) as Fs, and the non-sheet passing area through which the small size paper P1 does not pass is Fb. In the image forming apparatus 1, it is assumed that the sheet is passed based on the center position.

  As shown in FIG. 9, when small-size paper P1 is continuously passed, heat for fixing is consumed in the small-size paper passing area Fs through which the small-size paper P1 passes. Therefore, the temperature adjustment control at the fixing set temperature is performed by the control unit 31 (see FIG. 1), and the temperature of the fixing belt 61 in the small size paper passing area Fs is maintained within the range near the fixing set temperature. On the other hand, temperature adjustment control similar to that of the small-size paper passing area Fs is performed also in the non-paper passing area Fb. However, heat for fixing is not consumed in the non-sheet passing area Fb. For this reason, the temperature of the non-sheet passing area Fb is likely to rise to a temperature higher than the fixing set temperature. Then, when the continuous passage of the small size paper P1 is continued in this state, the temperature of the non-sheet passing region Fb rises, for example, higher than the heat resistance temperature of the elastic layer 613 and the surface release layer 614 of the fixing belt 61, and the fixing belt. 61 may be damaged.

  Therefore, as described above, in the fixing unit 60 of the present embodiment, the temperature-sensitive magnetic member 64 is equal to or higher than the preset fixing temperature and is, for example, equal to or lower than the heat resistance temperature of the elastic layer 613 and the surface release layer 614 of the fixing belt 61. For example, an Fe—Ni alloy or the like having a magnetic permeability change start temperature set within the temperature range is used. That is, as shown in FIG. 9, the magnetic permeability change start temperature Tcu of the temperature-sensitive magnetic member 64 is equal to or higher than the fixing set temperature Tf, for example, a temperature equal to or lower than the heat resistance temperature Tlim of the elastic layer 613 and the surface release layer 614. It is set in the area.

Thereby, when the small size paper P1 is continuously passed, the temperature in the non-sheet passing region Fb of the fixing belt 61 exceeds the magnetic permeability change start temperature of the temperature-sensitive magnetic member 64. Accordingly, the temperature in the non-sheet passing region Fb of the temperature-sensitive magnetic member 64 adjacent to the fixing belt 61 also exceeds the permeability change start temperature in the same manner as the fixing belt 61 corresponding to the temperature of the fixing belt 61. For this reason, the temperature-sensitive magnetic member 64 in the non-sheet-passing region Fb has a relative magnetic permeability close to 1, and the properties as a ferromagnetic material disappear. The relative magnetic permeability of the temperature-sensitive magnetic member 64 decreases and approaches 1 so that the magnetic field lines H in the non-sheet-passing region Fb are not guided into the temperature-sensitive magnetic member 64 but pass through the temperature-sensitive magnetic member 64. become. Therefore, in the non-sheet passing region Fb of the fixing belt 61, the magnetic field lines H after passing through the conductive heat generating layer 612 are diffused, and the magnetic flux density of the magnetic field lines H crossing the conductive heat generating layer 612 is reduced. Thereby, the eddy current I generated in the conductive heat generation layer 612 is reduced, and the heat generation amount (Joule heat W) in the fixing belt 61 is reduced. As a result, an excessive temperature rise in the non-sheet passing area Fb is suppressed, and damage to the fixing belt 61 is suppressed.
As described above, the temperature-sensitive magnetic member 64 functions as a detection unit that detects the temperature of the fixing belt 61 and suppresses an increase in temperature that suppresses an excessive temperature increase of the fixing belt 61 according to the detected temperature of the fixing belt 61. It also has a function as a department.

  The lines of magnetic force H after passing through the temperature-sensitive magnetic member 64 reach the guide member 66 (see FIG. 3) and are guided into this. When the magnetic flux reaches the induction member 66 and is induced therein, more eddy current I flows toward the induction member 66 where the eddy current I flows more easily than the conductive heat generation layer 612. Therefore, the amount of eddy current flowing in the conductive heat generating layer 612 is further suppressed, and the temperature rise in the non-sheet passing region Fb is suppressed.

  At this time, the thickness, material, and shape of the guiding member 66 are selected so that the guiding member 66 guides most of the magnetic force lines H from the exciting coil 82 and suppresses leakage of the magnetic force lines H from the fixing unit 60. . Specifically, the guide member 66 may be made of a material having a sufficiently thick skin depth δ. Thereby, even if the eddy current I flows through the induction member 66, the amount of heat generation is also minimized. In the present embodiment, the guide member 66 is made of Al (aluminum) having a substantially circular shape with a thickness of 1 mm along the temperature-sensitive magnetic member 64, and is not in contact with the temperature-sensitive magnetic member 64 (an average distance of, for example, 4 mm). ). As other materials, Ag and Cu are suitable.

  By the way, when the temperature in the non-sheet-passing region Fb of the fixing belt 61 becomes lower than the magnetic permeability change start temperature of the temperature-sensitive magnetic member 64, the temperature in the non-sheet-passing region Fb of the temperature-sensitive magnetic member 64 is also permeable. It becomes lower than the change start temperature. As a result, the temperature-sensitive magnetic member 64 changes to ferromagnetic again, and the magnetic field lines H are induced inside the temperature-sensitive magnetic member 64, so that a large amount of eddy current I flows through the conductive heating layer 612. Therefore, the fixing belt 61 is heated again.

  FIG. 10 is a diagram for explaining the state of the lines of magnetic force H when the temperature of the fixing belt 61 in the non-sheet-passing region Fb is in a temperature range exceeding the permeability change start temperature. As shown in FIG. 10, when the temperature of the fixing belt 61 is in the temperature range exceeding the magnetic permeability change start temperature in the non-sheet passing area Fb, the temperature-sensitive magnetic member 64 in the non-sheet passing area Fb has a ratio. Magnetic permeability decreases. Therefore, the magnetic field lines H of the alternating magnetic field generated by the IH heater 80 change so as to easily pass through the temperature-sensitive magnetic member 64. Accordingly, the magnetic field lines H of the alternating magnetic field generated by the IH heater 80 (excitation coil 82) are radiated so as to diffuse from the magnetic core 84 toward the fixing belt 61 and reach the induction member 66.

That is, in the regions R1 and R2 where the magnetic force lines H are radiated from the magnetic core 84 of the IH heater 80 and cross the conductive heat generating layer 612 of the fixing belt 61, the magnetic force lines H are difficult to be guided to the temperature sensitive member 64 and thus diffuse radially. As a result, the magnetic flux density (number of magnetic force lines H per unit area) of the magnetic field lines H crossing the conductive heat generating layer 612 of the fixing belt 61 in the thickness direction decreases. Further, even in the region R3 that crosses the conductive heat generating layer 612 in the thickness direction when the magnetic force line H returns to the magnetic core 84 again, the magnetic force line H returns to the magnetic core 84 from the diffused wide region. The magnetic flux density of the magnetic field lines H crossing 612 in the thickness direction decreases.
Therefore, when the temperature of the fixing belt 61 is in a temperature range exceeding the permeability change start temperature, the magnetic flux density of the magnetic field lines H that cross the conductive heating layer 612 in the thickness direction decreases in the regions R1, R2, and R3. It becomes. As a result, the eddy current I generated in the conductive heating layer 612 where the magnetic field lines H cross in the thickness direction is reduced, and the Joule heat W generated in the fixing belt 61 is reduced. As a result, the temperature of the fixing belt 61 decreases.

As described above, when the temperature of the fixing belt 61 in the non-sheet-passing area Fb is in the temperature range equal to or higher than the magnetic permeability change start temperature, the magnetic field lines H are induced inside the temperature-sensitive magnetic member 64 in the non-sheet-passing area Fb. The magnetic field lines H of the alternating magnetic field generated by the exciting coil 82 cross the conductive heat generating layer 612 of the fixing belt 61 while diffusing in the thickness direction. Therefore, the magnetic path of the alternating magnetic field generated by the exciting coil 82 forms a long loop, and the magnetic flux density in the magnetic path passing through the conductive heating layer 612 of the fixing belt 61 decreases.
Thereby, for example, in the non-sheet passing region Fb where the small size paper P1 is continuously passed and the temperature rises, the eddy current I generated in the conductive heat generating layer 612 of the fixing belt 61 is reduced and the fixing belt 61 is not passed. The amount of heat generation (joule heat W) in the paper region Fb is reduced. As a result, an excessive temperature rise in the non-sheet passing area Fb can be suppressed.

<Description of the configuration for suppressing the temperature rise of the temperature-sensitive magnetic member>
In order for the temperature-sensitive magnetic member 64 to perform the function of suppressing the excessive temperature rise in the non-sheet passing region Fb described above, the temperature of each region in the longitudinal direction of the temperature-sensitive magnetic member 64 is the longitudinal direction of the fixing belt 61 facing it. It is necessary to fulfill a function as a detection unit that detects the temperature of the fixing belt 61 and changes according to the temperature of each region.
Therefore, regarding the temperature-sensitive magnetic member 64 itself, a configuration that is difficult to be induction-heated by the magnetic field lines H is adopted. That is, even if the temperature of the fixing belt 61 is equal to or lower than the permeability change start temperature and the temperature-sensitive magnetic member 64 exhibits ferromagnetism, the temperature-sensitive magnetic member 64 is included in the magnetic force lines H from the IH heater 80. There is a magnetic field line H that crosses in the thickness direction. As a result, a weak eddy current I is generated inside the temperature-sensitive magnetic member 64, and a slight amount of heat is generated in the temperature-sensitive magnetic member 64 itself. For this reason, for example, when a large amount of image formation is continuously performed, the heat-sensitive magnetic member 64 accumulates heat generated by itself, and the temperature of the temperature-sensitive magnetic member also increases in the paper passing area (see FIG. 9). It shows an upward trend. Thus, if the self-heating due to eddy current loss is large, the temperature rises and unintentionally reaches the temperature at which the permeability change starts, and there is no difference in the magnetic characteristics between the paper passing area and the non-paper passing area. The suppression effect may stop working. Therefore, the correspondence between the temperature of the temperature-sensitive magnetic member 64 and the temperature of the fixing belt 61 is maintained, and the temperature-sensitive magnetic member 64 functions as a detection unit that detects the temperature of the fixing belt 61 with high accuracy. It is necessary to suppress the Joule heat W generated in the member 64 itself.

Therefore, in order to reduce the eddy current loss and hysteresis loss in the temperature-sensitive magnetic member 64, first, the temperature-sensitive magnetic member 64 has physical properties (specific resistance value and magnetic permeability) that are difficult to be induction-heated by the lines of magnetic force H. Selected material is selected.
Second, the thickness of the temperature-sensitive magnetic member 64 exhibits ferromagnetism so that the magnetic field lines H are difficult to cross in the thickness direction of the temperature-sensitive magnetic member 64 at least in the temperature range below the permeability change start temperature. It is formed thicker than the skin depth δ in the state.

  Third, the temperature-sensitive magnetic member 64 is formed with a plurality of slits 64 s that divide the flow of the eddy current I generated by the lines of magnetic force H. Even if the material and thickness of the temperature-sensitive magnetic member 64 are selected so that induction heating is difficult, it is difficult to set the eddy current I generated in the temperature-sensitive magnetic member 64 to zero. Therefore, by dividing the flow of the eddy current I generated in the temperature-sensitive magnetic member 64 by the plurality of slits 64s, the eddy current I is reduced and the Joule heat W generated in the temperature-sensitive magnetic member 64 is kept low. .

  FIG. 11 is a view showing slits formed in the temperature-sensitive magnetic member 64. FIG. 11A is a side view showing a state in which the temperature-sensitive magnetic member 64 is installed in the holder 65, and FIG. 11B is a plan view seen from above (a direction). As shown in FIG. 11, in the temperature-sensitive magnetic member 64, a plurality of slits 64 s are formed orthogonal to the direction in which the eddy current I generated by the lines of magnetic force H flows. Therefore, when there is no slit 64s, the eddy current I (broken line in FIG. 11B) that flows as a large eddy over the entire length of the temperature-sensitive magnetic member 64 is divided by the slit 64s. Thereby, when the slit 64s is formed, the eddy current I flowing through the temperature-sensitive magnetic member 64 (solid line in FIG. 11 (a)) becomes a small eddy in the region between the slit 64s and the slit 64s, The amount of eddy current I as a whole is reduced. As a result, the amount of heat generated by the temperature-sensitive magnetic member 64 (Joule heat W) is reduced, and a configuration that hardly generates heat is realized. Therefore, the plurality of slits 64 s function as an eddy current dividing unit that divides the eddy current I.

In the temperature-sensitive magnetic member 64 illustrated in FIG. 11, the slit 64s is formed perpendicular to the direction in which the eddy current I flows. However, if the flow of the eddy current I is divided, for example, the eddy current I flows. You may form the slit inclined with respect to the direction. In addition to the configuration in which the slits 64 s as shown in FIG. 11 are formed over the entire region in the width direction of the temperature-sensitive magnetic member 64, the slit 64 s may be formed in a part in the width direction of the temperature-sensitive magnetic member 64. Further, the number, position, inclination angle, and the like of the slits may be set according to the amount of heat generated in the temperature-sensitive magnetic member 64.
Moreover, as a state where the inclination angle of the slit is maximized, the temperature-sensitive magnetic member 64 may be a small piece divided group in which the temperature-sensitive magnetic member 64 is divided into small pieces at the slit portion. The effect of is obtained similarly.

<Explanation for mounting temperature-sensitive magnetic member to holder>
As described with reference to FIGS. 2 and 5 above, the fixing belt 61 rotates and moves in the circumferential direction while maintaining a substantially circular cross-sectional shape at both ends by the end cap members 67 provided at both ends. On the other hand, in a region other than both ends of the fixing belt 61, the substantially circular cross-sectional shape set by the end cap member 67 is maintained by the rigidity of the fixing belt 61 itself. However, the fixing belt 61 passes through a peeling nip region 63b that locally forms a large nip pressure. In the peeling nip region 63b, the fixing belt 61 is deformed so that the radius of curvature of the surface of the fixing belt 61 becomes small in order to form a large nip pressure locally. Accordingly, the fixing belt 61 receives a pulling force toward the peeling nip region 63b, and a force toward the temperature-sensitive magnetic member 64 acts on the fixing belt 61 on the downstream side after passing through the peeling nip region 63b.
For this reason, in the longitudinal region other than both end portions that maintain the substantially circular cross-sectional shape due to the rigidity of the fixing belt 61 itself, the track of the fixing belt 61 is circular in the downstream region after passing through the peeling nip region 63b. It becomes a flat thing close to the temperature-sensitive magnetic member 64.

FIG. 12 is a perspective view showing a schematic configuration inside the fixing belt 61. In FIG. 12, the fixing belt 61 is cross-sectioned by a fixing portion 67a of the end cap member 67 in both end regions near end cap members 67 (not shown in FIG. 12, see FIGS. 2 and 5) provided at both ends. It rotates and moves in the circumferential direction while maintaining a substantially circular shape. That is, the line of intersection of the end side plane D1 and the end side plane D2 orthogonal to the width direction of the fixing belt 61 and the fixing belt 61 is substantially circular.
However, for example, in the center region away from the end cap members 67 at both ends, the circular cross section set by the end cap member 67 rotates while maintaining the rigidity of the fixing belt 61 itself. For this reason, the fixing belt 61 rotates while drawing a trajectory approaching the temperature-sensitive magnetic member 64 side by receiving a pulling force toward the peeling nip region 63b due to a locally large nip pressure in the peeling nip region 63b. That is, the intersection line between the center plane Dc perpendicular to the width direction of the fixing belt 61 and the fixing belt 61 becomes a flat ellipse on the downstream side after passing through the peeling nip region 63b.

FIG. 13 is a view for explaining the trajectory of the fixing belt 61 in the center region away from the end cap members 67 at both ends. In FIG. 13, the solid line shows the trajectory of the fixing belt 61 in the center region, and the broken line shows the trajectory of the fixing belt 61 in both end regions.
The fixing belt 61 receives a large nip pressure Np locally in the peeling nip region 63b. In this case, the fixing belt 61 is configured such that the base material layer 611 is not easily buckled or the like due to torsional torque or compression force due to, for example, nonmagnetic stainless steel having high mechanical strength (see FIG. 4). Therefore, in the downstream region Q1 immediately after passing through the peeling nip region 63b, the fixing belt 61 is outside (Fb1) so as to follow the shape of the pressing pad 63 in the peeling nip region 63b due to the high rigidity of the fixing belt 61 itself. Draw a trajectory that swells in the direction). As a result, in the downstream region Q2, as a reaction, the fixing belt 61 moves toward the temperature-sensitive magnetic member 64 side (Fb2 direction). That is, since it is difficult for the fixing belt 61 to be stretched, in the region Q2, the fixing belt 61 passes along a track closer to the temperature-sensitive magnetic member 64 side than the circular shape by the circumferential length swelled outward in the region Q1. As a result, in a region away from both ends in the width direction of the fixing belt 61, an elliptical orbit flattened on the downstream side after passing through the peeling nip region 63b (solid line in the figure).
On the other hand, the above-described action also works in a region near both ends of the fixing belt 61 in the width direction. However, a force that maintains the shape of the end cap member 67 acts on this region. Therefore, the fixing belt 61 passes through a substantially circular track by the end cap member 67 in a region close to both end portions in the width direction (broken line in the figure).

As a result, in the region downstream of the pressing pad 63 of the fixing belt 61 (region Q2), the gap g between the fixing belt 61 and the temperature-sensitive magnetic member 64 is separated from both ends of the fixing belt 61 in the width direction, for example. The gap g1 in the central region is smaller than the gap g0 at both ends in the width direction of the fixing belt 61 (g1 <g0). That is, the gap g between the fixing belt 61 and the temperature-sensitive magnetic member 64 decreases from both ends (gap g0) toward the center (gap g1).
As described above, if the gap g between the fixing belt 61 and the temperature-sensitive magnetic member 64 differs in the position in the width direction of the fixing belt 61, the region R2 (= region Q2 in FIG. 13) crossing the fixing belt 61 shown in FIG. The density of the lines of magnetic force H in the region corresponding to (1) also varies depending on the position of the fixing belt 61 in the width direction. For this reason, the heat generation amount of the fixing belt 61 changes from both ends in the longitudinal direction toward the center, and the fixability varies depending on the position in the width direction.

  A similar tendency occurs in the track of the fixing belt 61 in the region upstream of the pressing pad 63, that is, in the region Q3 facing the region Q1 and the region Q2. However, since these regions are separated from the peeling nip region 63b, the influence of the swelling of the fixing belt 61 in the region Q1 is not large, and the deviation of the track is small. Therefore, in the region Q3, the difference in the position in the width direction of the fixing belt 61 in the gap g2 between the fixing belt 61 and the temperature-sensitive magnetic member 64 is small (g2 = g0). Therefore, the difference in the density of the lines of magnetic force H in the region R1 crossing the fixing belt 61 shown in FIG. 8 (= the region corresponding to the region Q3 in FIG. 13) is small regardless of the position in the width direction of the fixing belt 61. .

  As described above, in the region Q2 on the downstream side of the pressing pad 63 of the fixing belt 61, the gap g between the fixing belt 61 and the temperature-sensitive magnetic member 64 is directed from both ends (gap g0) to the center (gap g1). Become smaller. Therefore, in the fixing unit 60 of the present embodiment, the gap g between the fixing belt 61 and the temperature-sensitive magnetic member 64 extends in the width direction of the fixing belt 61 in the region Q2 downstream of the pressing pad 63 of the fixing belt 61. The temperature-sensitive magnetic member 64 is displaced and attached to the holder 65 so as to correspond to the change in the width direction of the gap g.

FIG. 14 is a view for explaining the attachment position of the temperature-sensitive magnetic member 64 to the holder 65 at the center position in the width direction. As shown in FIG. 14, the temperature-sensitive magnetic member 64 is attached to the holder 65 in a region (region Q2) on the downstream side of the pressing pad 63 of the fixing belt 61 and a region (region Q3) on the upstream side. . The temperature-sensitive magnetic member 64 is attached to the holder 65 in the downstream region (region Q2) at the center of the fixing belt 61 in the width direction (longitudinal direction of the temperature-sensitive magnetic member 64 itself). The position (upstream end position) of the upstream end E1 of the curved portion (arc-shaped portion) 64a of the member 64 is the inner side direction (S1 direction: downstream end E3 direction) than both ends in the width direction, And it is set to the position displaced downward (S2 direction: the direction away from the IH heater 80). As a result, the gap g between the fixing belt 61 and the temperature-sensitive magnetic member 64 that is smaller than both ends in the width direction of the fixing belt 61 (gap g0 = g2) in the region Q2 downstream of the pressing pad 63 of the fixing belt 61 is For example, the gap g2 (= g0) also spreads in the central region. As a result, the gap g between the fixing belt 61 and the temperature-sensitive magnetic member 64 becomes substantially constant over the width direction of the fixing belt 61.
Note that the temperature-sensitive magnetic member 64 and the curved end portion 64a upstream end E1 ′ indicated by broken lines in FIG. 14 are at both end portions in the width direction.

  Here, the position where the upstream end E1 of the curved portion 64a is displaced downward (in the S2 direction) is set to the gap g between the fixing belt 61 and the temperature-sensitive magnetic member 64 narrowed in the downstream region Q2. It is to spread. On the other hand, when the upstream end E1 is displaced downward (S2 direction), the temperature-sensitive magnetic member 64 in the upstream region Q3 is also displaced downward (S2 direction), and the fixing belt 61 and the temperature-sensitive magnetic member 64 are displaced. The gap g is widened. Therefore, the upstream end E1 of the bending portion 64a is set to a position displaced in the inner direction (S1 direction), and adjustment is made so that the bending portion 64a of the temperature-sensitive magnetic member 64 swells upward (S3 direction). Thereby, the position (for example, position E2) of the temperature-sensitive magnetic member 64 in the upstream region Q3 displaced downward (S2 direction) by displacing the upstream end E1 downward (S2 direction) is upward (S3). Direction). As a result, the fluctuation amount of the gap g between the fixing belt 61 and the temperature-sensitive magnetic member 64 in the upstream region Q3 is extremely small, and the gap g2 (= g0) is maintained.

15A is a plan view of the temperature-sensitive magnetic member 64 attached to the holder 65 as viewed from above, and FIG. 15B is an enlarged view of the region Y shown in FIG.
In the temperature-sensitive magnetic member 64, the upstream end E1 of the curved portion 64a of the temperature-sensitive magnetic member 64 is in the inner direction (S1 direction) than the both ends in the longitudinal direction at the center position (center) in the longitudinal direction. The holder 65 is set by being displaced in the (S2 direction). As a result, as shown in FIG. 15A, the temperature-sensitive magnetic member 64 has a shape that enters the inner side direction (S1 direction) from both ends in the longitudinal direction toward the center position (center) in the downstream region Q2. Set to Accordingly, the gap g corresponds to the change in the longitudinal direction (width direction of the fixing belt 61) of the gap g between the fixing belt 61 and the temperature-sensitive magnetic member 64 in the downstream region Q2. It becomes substantially constant over the direction.
On the other hand, the shape of the temperature-sensitive magnetic member 64 does not change in the upstream region Q3. As a result, the gap g is substantially constant over the width direction of the fixing belt 61 even in the upstream region Q3 where the amount of change in the longitudinal direction of the gap g between the fixing belt 61 and the temperature-sensitive magnetic member 64 is small.

  In this case, the upstream end E1 of the curved portion (arc-shaped portion) 64a of the temperature-sensitive magnetic member 64 is set in the holder 65 by being displaced in the inner direction (S1 direction) and downward (S2 direction). At this time, the deformation (displacement) in the longitudinal direction of the temperature-sensitive magnetic member 64 mainly occurs in the arrangement portion of the slit 64s as an example of the notch portion provided in the curved portion 64a of the temperature-sensitive magnetic member 64. That is, as shown in FIG. 15B, the deformation in the longitudinal direction of the temperature-sensitive magnetic member 64 mainly occurs due to the positional shift that occurs on both sides of the slit 64s. Therefore, stress is not easily accumulated in the temperature-sensitive magnetic member 64, and the influence on the magnetic field lines H passing through the temperature-sensitive magnetic member 64 is suppressed to be small.

  As described above, in the fixing unit 60 according to the present embodiment, when the temperature-sensitive magnetic member 64 is attached to the holder 65, the sensitivity is adjusted in accordance with the change in the width direction of the gap g between the fixing belt 61 and the temperature-sensitive magnetic member 64. The position (upstream end position) of the upstream end E1 of the curved portion (arc-shaped portion) 64a of the warm magnetic member 64 is displaced. As a result, the gap g between the fixing belt 61 and the temperature-sensitive magnetic member 64 is substantially constant in the width direction of the fixing belt 61 also in the region Q2 on the downstream side of the pressing pad 63 of the fixing belt 61. The density of the lines of magnetic force H in the region R2 (= the region corresponding to the region Q2 in FIG. 13) crossing the fixing belt 61 is made uniform in the width direction of the fixing belt 61.

In the present embodiment, the case where the temperature-sensitive magnetic member 64 is integrally formed over the entire width of the fixing belt 61 is shown. In addition to such a configuration, the temperature-sensitive magnetic member 64 may be divided in the width direction of the fixing belt 61.
FIG. 16 is a perspective view showing a configuration example in which the temperature-sensitive magnetic member 64 is divided into two in the width direction of the fixing belt 61. In the configuration example shown in FIG. 16, two temperature-sensitive magnetic members 64 </ b> A and 64 </ b> B are arranged from the widthwise end of the fixing belt 61 to the center (center). Each of the temperature-sensitive magnetic members 64A and 64B is attached to the holder 65 at the end portion in the width direction and the center portion (center) of the fixing belt 61 in the downstream region Q2. When each of the temperature-sensitive magnetic members 64A and 64B is attached to the holder 65 at the center (center), similarly to the above, the curved portion 64a upstream end E1 of the temperature-sensitive magnetic member 64 has both ends in the width direction. The position is set to a position displaced inward (S1 direction) from the position and downward (S2 direction) (see FIG. 14).
If the temperature-sensitive magnetic member 64 is divided in the width direction of the fixing belt 61 as described above, the lengths of the divided temperature-sensitive magnetic members 64 in the longitudinal direction can be shortened. The deformation in the longitudinal direction becomes easy.

As described above, in the fixing unit 60 provided in the image forming apparatus 1 of the present embodiment, the temperature-sensitive magnetic member 64 is disposed in the vicinity of the inner peripheral surface of the fixing belt 61. As a result, the temperature rise of the non-sheet passing region is suppressed excessively.
Further, when the temperature-sensitive magnetic member 64 is attached to the holder 65, the curved portion (arc-shaped portion) of the temperature-sensitive magnetic member 64 corresponding to the change in the width g of the gap g between the fixing belt 61 and the temperature-sensitive magnetic member 64. The position (upstream end position) of the upstream end E1 of 64a is displaced. As a result, the gap g between the fixing belt 61 and the temperature-sensitive magnetic member 64 is substantially constant in the width direction of the fixing belt 61 also in the region Q2 on the downstream side of the pressing pad 63 of the fixing belt 61. As a result, the density of the lines of magnetic force H in the region crossing the fixing belt 61 is made uniform in the width direction of the fixing belt 61. As a result, the heat generation amount of the fixing belt 61 becomes substantially constant along the width direction, and the occurrence of uneven fixing is suppressed.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 60 ... Fixing apparatus, 61 ... Fixing belt, 62 ... Pressure roll, 64 (64A, 64B) ... Temperature-sensitive magnetic member, 64s ... Slit, 65 ... Holder, 80 ... IH heater, 81 ... Support Body, 82 ... exciting coil, 84 ... magnetic core, 611 ... base material layer, 612 ... conductive heating layer

Claims (12)

A fixing belt having a conductive layer and fixing the toner to the recording material by electromagnetic induction heating of the conductive layer;
An end cap member formed in a substantially oval shape for supporting the vicinity of both end portions in the width direction of the fixing belt;
A pressure roll that conveys the recording material with the fixing belt interposed therebetween;
A pressing member disposed inside the fixing belt and pressing the pressure roll through the fixing belt;
A magnetic field generating member that generates an alternating magnetic field that intersects the conductive layer of the fixing belt ;
An alternating current generated by the magnetic field generation member having an arc-shaped portion disposed opposite to the magnetic field generation member across the fixing belt , forming a magnetic path of an alternating magnetic field generated by the magnetic field generation member A magnetic path forming member that transmits a magnetic field ;
A support member for supporting the magnetic path forming member,
The pressing member is formed such that the pressing force for pressing the pressure roll is stronger on the downstream side than the upstream side in the fixing belt moving direction,
The magnetic path forming member, the position of the fixing belt moving direction downstream side closer to the end portion of the pressing member in the fixing belt moving direction of the arc-shaped portion is closer to the fixing belt moving direction upstream side of the pressing member A fixing device, wherein the fixing device is attached to the support member so as to be displaced in a direction away from the fixing belt from both end portions in the longitudinal direction toward a central portion as compared with the position of the end portion . In the magnetic path forming member, the upstream end position at the center in the longitudinal direction of the arc-shaped portion is more in the fixing belt movement direction of the arc-shaped portion than the upstream end position at both ends in the longitudinal direction. The fixing device according to claim 1, wherein the fixing device is attached to the support member so as to be displaced in a downstream end direction and in a direction away from the magnetic field generation member. The fixing device according to claim 1, wherein the magnetic path forming member is divided into a plurality of parts along a width direction of the fixing belt .   The fixing device according to claim 1, wherein the magnetic path forming member includes a plurality of cutout portions perpendicular to the longitudinal direction along the longitudinal direction. The fixing device according to claim 1, wherein the magnetic path forming member is disposed in non-contact with the fixing belt . Toner image forming means for forming a toner image;
Transfer means for transferring the toner image formed by the toner image forming means onto a recording material;
Fixing means for fixing the toner image transferred onto the recording material to the recording material;
The fixing means is
A fixing belt having a conductive layer and fixing the toner to the recording material by electromagnetic induction heating of the conductive layer;
An end cap member formed in a substantially oval shape for supporting the vicinity of both end portions in the width direction of the fixing belt;
A pressure roll that conveys the recording material with the fixing belt interposed therebetween;
A pressing member disposed inside the fixing belt and pressing the pressure roll through the fixing belt;
A magnetic field generating member that generates an alternating magnetic field that intersects the conductive layer of the fixing belt ;
An alternating current generated by the magnetic field generation member having an arc-shaped portion disposed opposite to the magnetic field generation member across the fixing belt , forming a magnetic path of an alternating magnetic field generated by the magnetic field generation member A magnetic path forming member that transmits a magnetic field ;
A support member for supporting the magnetic path forming member,
The pressing member is formed such that the pressing force for pressing the pressure roll is stronger on the downstream side than the upstream side in the fixing belt moving direction,
The magnetic path forming member, the position of the fixing belt moving direction downstream side closer to the end portion of the pressing member in the fixing belt moving direction of the arc-shaped portion is closer to the fixing belt moving direction upstream side of the pressing member An image forming apparatus, wherein the image forming apparatus is attached to the support member so as to be displaced in a direction away from the fixing belt from the both ends in the longitudinal direction toward the center as compared with the position of the end . In the magnetic path forming member of the fixing means, the upstream end position at the longitudinal central portion of the arc-shaped portion is more fixed to the arc-shaped portion than the upstream end position at both longitudinal end portions. The image forming apparatus according to claim 6, wherein the image forming apparatus is attached to the support member so as to be displaced in a downstream end direction in a belt moving direction and in a direction away from the magnetic field generating member. The image forming apparatus according to claim 6, wherein the magnetic path forming member of the fixing unit is divided into a plurality of parts along a width direction of the fixing belt .   The image forming apparatus according to claim 6, wherein the magnetic path forming member of the fixing unit includes a plurality of notches perpendicular to the longitudinal direction along the longitudinal direction. The image forming apparatus according to claim 6, wherein the magnetic path forming member of the fixing unit is disposed in non-contact with the fixing belt . A fixing member having a conductive layer and fixing the toner to the recording material by electromagnetic induction heating of the conductive layer;
A magnetic field generating member that generates an alternating magnetic field that intersects the conductive layer of the fixing member;
An alternating current generated by the magnetic field generating member having an arc-shaped portion disposed opposite to the magnetic field generating member across the fixing member, forming a magnetic path of an alternating magnetic field generated by the magnetic field generating member A magnetic path forming member that transmits a magnetic field ;
A support member for supporting the magnetic path forming member,
The arc-shaped portion of the magnetic path forming member is integrally formed from at least one end portion to the center portion of the fixing member with respect to the longitudinal direction along the width direction of the fixing member, and the longitudinal direction. A plurality of cutout portions that intersect with the longitudinal direction are formed along the longitudinal direction, and the upstream end position in the moving direction of the fixing member on the magnetic field generating member side at the central portion in the longitudinal direction is the longitudinal direction. The support member is displaced from the upstream end position at both ends to the downstream end position side of the arc-shaped portion in the fixing member moving direction and away from the magnetic field generating member. A fixing device characterized in that it is attached to a fixing device. Toner image forming means for forming a toner image;
Transfer means for transferring the toner image formed by the toner image forming means onto a recording material;
Fixing means for fixing the toner image transferred onto the recording material to the recording material;
The fixing means is
A fixing member having a conductive layer and fixing the toner to the recording material by electromagnetic induction heating of the conductive layer;
A magnetic field generating member that generates an alternating magnetic field that intersects the conductive layer of the fixing member;
An alternating current generated by the magnetic field generating member having an arc-shaped portion disposed opposite to the magnetic field generating member across the fixing member, forming a magnetic path of an alternating magnetic field generated by the magnetic field generating member A magnetic path forming member that transmits a magnetic field ;
A support member for supporting the magnetic path forming member,
The arc-shaped portion of the magnetic path forming member is integrally formed from at least one end portion to the center portion of the fixing member with respect to the longitudinal direction along the width direction of the fixing member, and the longitudinal direction. A plurality of cutout portions that intersect with the longitudinal direction are formed along the longitudinal direction, and the upstream end position in the moving direction of the fixing member on the magnetic field generating member side at the central portion in the longitudinal direction is the longitudinal direction. The support member is displaced from the upstream end position at both ends to the downstream end position side of the arc-shaped portion in the fixing member moving direction and away from the magnetic field generating member. An image forming apparatus attached to the image forming apparatus.

Images