JP4715942B2 - Fixing apparatus, image forming apparatus, and magnetic field generating apparatus - Google Patents

Description

  The present invention relates to a fixing device, an image forming apparatus, and a magnetic field generation 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, Patent Document 1 describes an electromagnetic induction heating type fixing device that forms a magnetic path by inserting a fixing belt having a copper heat generation layer and an excitation coil with two magnetic members to electromagnetically heat the copper heat generation layer. Has been.

JP 2008-152247 A

In general, in an electromagnetic induction heating type fixing device, an exciting coil that generates an alternating magnetic field that intersects the conductive layer of the fixing member and a magnetic core that forms a magnetic path of the alternating magnetic field generated by the exciting coil are rigid with an adhesive or the like. It is fixed by the body. When the fixing device is used for a long period of time, a rigid body such as an adhesive is peeled off or a ferrite magnetic core is damaged, and the magnetic field generating member is displaced.
SUMMARY OF THE INVENTION An object of the present invention is to prevent misalignment of a magnetic field generating member due to long-term use in an electromagnetic induction heating type fixing device.

The invention according to claim 1 includes a conductive layer, and the conductive layer is heated by electromagnetic induction to generate a fixing member that fixes toner on the recording material, and an alternating magnetic field that intersects the conductive layer of the fixing member. A magnetic field generating member, a magnetic path forming member that forms a magnetic path of an alternating magnetic field generated by the magnetic field generating member, a support member that supports the magnetic field generating member, the magnetic field generating member, and the magnetic path forming member, And is arranged so as to be in contact with the plurality of magnetic path forming members, and is elastically deformed while pressing the magnetic field generating member toward the support member to fix the magnetic field generating member on the support member. A fixing device comprising: a sheet-like elastic support member; and a pressing member that presses the magnetic path forming member toward the magnetic field generating member.
In the invention according to claim 2, the magnetic path forming member is pressed toward the support member by the pressing member and is pressed so as to be sandwiched between the pressing member and the sheet-like elastic support member. The fixing device according to claim 1, wherein the fixing device is fixed by the fixing device.
In the invention according to claim 3, the sheet-like elastic support member presses the magnetic field generating member toward the support member by an elastic force generated by the applied pressure received from the pressing member through the magnetic path forming member. The fixing device according to claim 1, wherein the fixing device is a fixing device.
The invention according to claim 4 is characterized in that the pressing force of the pressing member is larger than the elastic force generated in the sheet-like elastic support member by the pressing force received from the pressing member. The fixing device according to Item 1.
The invention according to claim 5 further includes a shielding member attached to the support member so as to shield the alternating magnetic field generated by the magnetic field generating member and sandwich the magnetic path forming member and the pressing member, 5. The fixing device according to claim 1, wherein the magnetic path forming member is pressed toward the support member by the pressing member. 6.
The invention according to claim 6 is the fixing device according to any one of claims 1 to 5, wherein the pressing member is made of a nonmagnetic material.
The invention according to claim 7 is the fixing device according to any one of claims 1 to 6, wherein the sheet-like elastic support member and the pressing member are made of a rubber-like elastic body. is there.

The invention according to claim 8 is a toner image forming portion that forms a toner image, a transfer portion that transfers a toner image formed by the toner image forming portion onto a recording material, and a toner image that is transferred to the recording material. A fixing unit that fixes the toner onto the recording material, the fixing unit having a conductive layer, and the conductive layer is heated by electromagnetic induction,
A magnetic field generating member that generates an alternating magnetic field that intersects the conductive layer of the fixing member, a magnetic path forming member that forms a magnetic path of an alternating magnetic field generated by the magnetic field generating member, and a support that supports the magnetic field generating member A member, arranged between the magnetic field generating member and the magnetic path forming member and arranged to contact the plurality of magnetic path forming members, and elastic while pressing the magnetic field generating member toward the support member An image forming comprising: a sheet-like elastic supporting member that deforms and fixes the magnetic field generating member on the supporting member; and a pressing member that presses the magnetic path forming member toward the magnetic field generating member. Device.
According to a ninth aspect of the present invention, the magnetic path forming member of the fixing unit is fixed by being pressed so as to be sandwiched between the pressing member and the sheet-like elastic support member, and the sheet-like elastic support is provided. The image forming apparatus according to claim 8, wherein the member presses the magnetic field generating member toward the support member by an elastic force generated by the applied pressure received from the pressing member.

  According to a tenth aspect of the present invention, there is provided a magnetic field generating member that has a conductive layer and generates an alternating magnetic field that intersects the conductive layer of the fixing member that fixes the toner to the recording material by electromagnetic induction heating. A magnetic path forming member that forms a magnetic path of an alternating magnetic field generated by the magnetic field generating member, a support member that supports the magnetic field generating member, and provided between the magnetic field generating member and the magnetic path forming member; And a sheet-like elastic support member that is arranged so as to be in contact with the plurality of magnetic path forming members and elastically deforms the magnetic field generating member while pressing the magnetic field generating member toward the supporting member and fixes the magnetic field generating member on the supporting member. And a pressing member that presses the magnetic path forming member toward the magnetic field generating member.

  According to the first aspect of the present invention, as compared with the case where the present invention is not adopted, the electromagnetic induction heating type fixing device prevents the magnetic field generating member from being displaced due to long-term use.

  According to the invention of claim 2, the magnetic path forming member is securely sandwiched and fixed between the two members as compared with the case where the present invention is not adopted.

  According to the invention of claim 3, the magnetic field generating member is more reliably fixed as compared with the case where the present invention is not adopted.

  According to the invention of claim 4, each member can be positioned more reliably than in the case where the present invention is not adopted.

  According to the fifth aspect of the present invention, pressurization via the pressing member is more possible than when the present invention is not adopted.

  According to invention of Claim 6, compared with the case where this invention is not employ | adopted, an electromagnetic induction heating system is not affected.

  According to the seventh aspect of the present invention, the vibration of the magnetic field generating member such as the exciting coil is absorbed in the electromagnetic induction heating system as compared with the case where the present invention is not adopted.

  According to the eighth aspect of the present invention, as compared with the case where the present invention is not adopted, the electromagnetic induction heating type fixing device prevents the magnetic field generating member from being displaced due to long-term use.

  According to the ninth aspect of the present invention, the magnetic path forming member and the magnetic field generating member are more reliably fixed in the electromagnetic induction heating type fixing device as compared with the case where the present invention is not adopted.

  According to the tenth aspect of the present invention, as compared with the case where the present invention is not adopted, in the electromagnetic induction heating type magnetic field generating device, the magnetic field generating member is prevented from being displaced due to long-term use.

1 is a diagram illustrating a configuration example of an image forming apparatus including a fixing device to which the exemplary embodiment is applied. FIG. 3 is a front view illustrating a configuration of a fixing unit to which the exemplary embodiment is applied. FIG. 3 is an XX 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 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. It is a figure explaining the laminated structure of an IH heater.

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, an image reading device (scanner) 4, and the like. An image processing unit 33 that performs image 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”) that are examples of toner image forming units that are arranged in parallel at regular intervals. 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) color toner image, the photosensitive drum 12 is uniformly charged at a predetermined potential by the charger 13 while rotating in the direction of arrow A, and the image processing unit The LED print head 14 scans and exposes the photosensitive drum 12 based on the K-color image data transmitted from 33. 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) 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 cycles corresponding to the number of prints.

<Description of fixing unit configuration>
Next, the fixing unit 60 of this embodiment will be described.
2 and 3 are diagrams showing a configuration of the fixing unit 60 to which the exemplary embodiment is applied. FIG. 2 is a front view, and FIG. 3 is a sectional view taken along line XX in FIG.
As shown in FIG. 3, the fixing unit 60 is an example of an IH (Induction Heating) heater 80 as an example of a magnetic field generating member that generates an alternating magnetic field, and an example of a fixing member that is electromagnetically heated by the IH heater 80 to fix a toner image. A fixing belt 61, a pressure roll 62 disposed so as to face the fixing belt 61, and a pressing pad 63 pressed from the pressure roll 62 via the fixing belt 61.
Further, the fixing unit 60 is a temperature-sensitive magnetic member 64 as a magnetic path forming member that forms a magnetic path by inducing an alternating magnetic field generated by the holder 65 and the IH heater 80 that support components such as the pressing pad 63. 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. For example, the fixing belt 61 has a diameter of 30 mm and a length in the width direction of 370 mm when the original shape (cylindrical shape) is used. 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. It is formed. 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 μm to 200 μm (preferably 50 to 150 μm), a resin material having a thickness of 60 μm 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 kHz 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 kHz to 100 kHz enters and passes therethrough.

The region where the alternating magnetic field can enter the conductive heating 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). In the equation (1), f is the frequency of the alternating magnetic field (for example, 20 kHz), ρ is the specific resistance (Ω · m), and μr 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) so that an alternating magnetic field having a frequency of 20 kHz 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, as the conductive heat generating layer 612, a nonmagnetic metal such as Cu having a thickness of 2 μm to 20 μm and a specific resistance of 2.7 × 10 ⁻⁸ Ω · m or less (a paramagnetic material having a relative permeability of approximately 1). Is used.
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.

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. Thus, for example, a silicone rubber having a thickness of 100 μm 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, tetrafluoroethylene perfluoroalkyl vinyl ether polymer (PFA), polytetrafluoroethylene (PTFE), silicone copolymer, or a composite layer thereof is used. If the thickness of the surface release layer 614 is excessively thin, the wear resistance is not sufficient, and the life of the fixing belt 61 tends to be shortened. When the thickness of the surface release layer 614 is excessively large, the heat capacity of the fixing belt 61 increases and the warm-up time tends to be long. In the present embodiment, the thickness of the surface release layer 614 is preferably 1 μm to 50 μm in consideration of the balance between wear resistance and heat capacity.

<Description of pressing pad>
The pressing pad 63 is made of 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 assisting member 70 is supported by the holder 72 in a state in which the peeling baffle 71 is close to the fixing belt 61 in a direction facing the rotational movement direction of the fixing belt 61 (so-called counter direction). Then, the curled portion formed on the paper P at the outlet of the pressing pad 63 is supported by the peeling baffle 71, and the paper P is prevented from moving toward the fixing belt 61.

<Description of temperature-sensitive magnetic member>
The temperature-sensitive magnetic member 64 is formed in an arc shape that follows the inner peripheral surface of the fixing belt 61. The temperature-sensitive magnetic member 64 is disposed close to the inner peripheral surface of the fixing belt 61 so as to have a predetermined gap (for example, 0.5 mm to 1.5 mm) and is not contacted.
By arranging the temperature-sensitive magnetic member 64 close to the fixing belt 61, the temperature of the temperature-sensitive magnetic member 64 changes corresponding to the temperature of the fixing belt 61. For this reason, the temperature of the temperature-sensitive magnetic member 64 is substantially the same as the temperature of the fixing belt 61.
Further, 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, the heat of the fixing belt 61 is suppressed from flowing into the temperature-sensitive magnetic member 64, and the warm-up time is shortened. To do.

Further, the temperature-sensitive magnetic member 64 is made of a material having a “permeability change start temperature” (see the subsequent stage), which is a temperature at which the magnetic permeability of the magnetic characteristics changes suddenly. The permeability change start temperature is a temperature at which the permeability of the magnetic characteristics changes suddenly. In the present embodiment, the temperature change start temperature of the material constituting the temperature-sensitive magnetic member 64 is equal to or higher than the fixing set temperature at which each color toner image is melted, and the elastic layer 613 and the surface release layer of the fixing belt 61. It is set within a temperature range lower than the heat resistant temperature of 614. 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 in a temperature range that is equal to or lower than the permeability change start temperature exhibiting ferromagnetism, and induces magnetic field lines generated by the IH heater 80 and transmitted through the fixing belt 61 to the inside. 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 transmits the magnetic field lines generated by the IH heater 80 and transmitted through the fixing belt 61 so as to cross the thickness direction of the temperature-sensitive magnetic member 64. Let 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, the temperature-sensitive magnetic member 64 or the like The temperature point at which the amount of magnetic flux (number of lines of magnetic force) passing through the member 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, for example, a magnetic permeability change start temperature is set in a range of 140 ° C. (fixing set temperature) to 240 ° C., for example, a Fe—Ni alloy (permalloy) or the like. A ternary thermosensitive magnetic alloy such as a ternary thermosensitive magnetic alloy or an Fe—Ni—Cr alloy is used. For example, in a Fe-Ni binary temperature-sensitive magnetic alloy, the 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, metal alloys made of Fe, Ni, Si, B, Nb, Cu, Zr, Co, Cr, V, Mn, Mo, or the like are used.
Further, the temperature-sensitive magnetic member 64 is formed with a thickness greater 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 μm 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 is a predetermined gap (for example, 1.0 mm to 5.0 mm) from the inner peripheral surface of the temperature-sensitive magnetic member 64. It is arranged in a non-contact manner so as to have. In addition, the guide member 66 is made of a nonmagnetic metal having a relatively small specific resistance value such as Ag, Cu, or Al. 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 an eddy current is generated from the conductive heating layer 612 of the fixing belt 61. A state in which I is likely to occur is formed. Thereby, the thickness of the induction member 66 is formed with a thickness (for example, 1.0 mm) sufficiently thicker than the skin depth δ (see the above formula (1)) so that the eddy current I flows easily. .

<Description of Fixing Belt Drive Mechanism>
Next, a driving mechanism for the fixing belt 61 will be described.
As shown in FIG. 2, end cap members that rotationally drive the fixing belt 61 in the circumferential direction while maintaining the circular cross-sectional shape of both ends of the fixing belt 61 at the axial ends of the holder 65 (see FIG. 3). 67 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 is formed with a fixing portion 67 a fitted inside the both ends of the fixing belt 61 and has an outer diameter larger than that of the fixing portion 67 a, and when the end cap member 67 is attached to the fixing belt 61. Rotating through a flange portion 67d formed so as to project radially from the fixing belt 61, 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 166. A bearing bearing portion 67c that is freely coupled is provided. 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, generally a torque of about 0.1 N · m to 0.5 N · m acts.
In the fixing belt 61 of the present embodiment, the base material layer 611 is made of high mechanical strength, for example, nonmagnetic stainless steel. Therefore, even when a torsional torque of about 0.1 N · m to 0.5 N · m is applied to the entire fixing belt 61, buckling or the like hardly occurs in the fixing belt 61.
Further, the flange portion 67 d of the end cap member 67 suppresses the deviation of the fixing belt 61. The fixing belt 61 at that time generally has a compressive force of about 1N to 5N from the end (flange portion 67d) side in the axial direction. In the present embodiment, even when the fixing belt 61 receives such a compressive force, the base material layer 611 of the fixing belt 61 is made of nonmagnetic stainless steel or the like, so that buckling or the like occurs. It 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 and 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 in the present embodiment. As shown in FIG. 6, the IH heater 80 includes, for example, a support body 81 as a support member made of a nonmagnetic material such as a heat resistant resin, and an excitation coil 82 as a magnetic field generation member that generates an alternating magnetic field. ing. In addition, a sheet-like elastic support member 83 formed of an elastic body that fixes the excitation coil 82 on the support 81, and a magnetic core 84 as a magnetic path forming member that forms a magnetic path of an alternating magnetic field generated by the excitation coil 82. It has. Further, a pressing member 86 that presses the magnetic core 84 toward the support 81, a magnetic core hold 87 as a cover material for the magnetic core 84, and a shield as a shielding member that shields the magnetic field while pressing the pressing member 86 by being attached to the support 81. 85, an excitation circuit 88 for supplying an alternating current to the excitation coil 82 is provided. As will be described later, the sheet-like elastic support member 83 is formed in a sheet shape that is provided between the exciting coil 82 and the magnetic core 84 and is continuous in the axial direction of the fixing belt 61 so as to be in contact with the plurality of magnetic cores 84. Are arranged.

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 mm 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 formed by winding, for example, 90 litz wires, which are bundled with, for example, 90 copper wires having a diameter of 0.17 mm, which are insulated from each other, into a closed loop with a hollow space such as an ellipse, an ellipse, or a rectangle. Configured. 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 kHz to 100 kHz generated by the general-purpose power source.

The magnetic core 84 functions as a magnetic path forming unit. Examples of the material of the magnetic core 84 include ferromagnetic materials composed of oxides or alloy materials having high magnetic permeability such as soft ferrite, ferrite resin, amorphous alloy (amorphous alloy), permalloy, and temperature-sensitive magnetic alloy. It is done.
The magnetic core 84 forms a path (magnetic path) for lines of magnetic force. This magnetic line of force (magnetic path) induces a magnetic line of force (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. It passes through the warm magnetic member 64 and returns to the magnetic core 84.
That is, the AC magnetic field generated by the exciting coil 82 is configured to pass through the inside of the magnetic core 84 and the inside of the temperature-sensitive magnetic member 64, and the magnetic lines of force wrap the fixing belt 61 and the exciting 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. Further, 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.

<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 magnetic 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 ° C. ˜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. 7 is a diagram for explaining the state of the lines of magnetic force (H) when the temperature of the fixing belt 61 is in the temperature range equal to or lower than the permeability change start temperature. As shown in FIG. 7, 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 temperature-sensitive magnetic member 64 that 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 generating layer 612 generates Joule heat W (W = I2R), which is the product of the specific resistance value R of the conductive heat generating 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 a 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. 8 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. 8, 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. 8, when the 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. 8, 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.

Accordingly, 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 induction member 66 are selected so that the induction member 66 induces most of the magnetic field lines H from the exciting coil 82 and suppresses leakage of the magnetic field 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. 9 is a diagram illustrating 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 the temperature range exceeding the permeability change start temperature. As shown in FIG. 9, when the temperature of the fixing belt 61 is in the temperature range exceeding the 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 magnetic 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 crossing the conductive heating layer 612 in the thickness direction in the regions R1, R2, and R3 decreases. 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. 8). It shows an upward trend. When self-heating due to eddy current loss is large in this way, 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, and the temperature rises. 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, first, for the temperature-sensitive magnetic member 64, a material having physical properties (specific resistance value and magnetic permeability) that is difficult to be induction-heated by the magnetic field lines H 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 reduce 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. Yes.

  FIG. 10 is a view showing slits formed in the temperature-sensitive magnetic member 64. FIG. 10A is a side view showing a state in which the temperature-sensitive magnetic member 64 is installed on the holder 65, and FIG. 10B is a plan view seen from above (a direction). As shown in FIG. 10, 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. 10B) that flows as a large eddy over the entire longitudinal direction of the temperature-sensitive magnetic member 64 is divided by the slit 64s. Accordingly, when the slit 64s is formed, the eddy current I flowing through the temperature-sensitive magnetic member 64 (solid line in FIG. 10A) 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. 10, 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. 10 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.

  Fourthly, the heat-sensitive magnetic member 64 heat-transfers heat generated by the temperature-sensitive magnetic member 64 toward the inner side of the temperature-sensitive magnetic member 64 (direction of the induction member 66). A heat dissipation path as an example of the means is formed. In this case, it is desirable that the temperature of the temperature-sensitive magnetic member 64 is maintained at substantially the same temperature as that of the fixing belt 61 because of the function of the temperature-sensitive magnetic member 64 described above. Therefore, the heat dissipation path is configured such that the temperature-sensitive magnetic member 64 and other members (for example, the induction member 66) disposed inside the temperature-sensitive magnetic member 64 are maintained in a non-contact state. That is, by allowing an air layer to intervene in a part of the heat dissipation path, the outflow of heat from the temperature-sensitive magnetic member 64 via the heat dissipation path is suppressed. Accordingly, for example, when a situation occurs in which heat generated by the temperature-sensitive magnetic member 64 is accumulated, such as when a large amount of image formation is continuously performed, the amount of heat that exceeds the temperature of the fixing belt 61 is generated. The heat dissipation path is made to function so that the heat quantity of the heat-sensitive magnetic member 64 is easily dissipated.

<Description of fixing method of exciting coil and magnetic core in IH heater>
Next, returning to FIG. 6, a method for fixing the exciting coil 82 and the magnetic core 84 to the support 81 in the IH heater 80 of the present embodiment will be described.
As shown in FIG. 6, in the IH heater 80 of the present embodiment, the exciting coil 82 is provided between the magnetic core 84 and the exciting coil 82, and is supported on the support surface 81 a of the support 81 by the sheet-like elastic support member 83. By being pressed, it is fixed so as to be in close contact with the support surface 81a. Here, as will be described later, the sheet-like elastic support member 83 has a sheet shape continuously formed in the axial direction of the fixing belt 61 and is disposed so as to be in contact with the plurality of magnetic cores 84. That is, the sheet-like elastic support member 83 is made of a sheet-like elastic body having a low Young's modulus, such as silicone rubber or fluororubber. The sheet-like elastic support member 83 is disposed so as to press the excitation coil 82 toward the support surface 81 a of the support 81. Accordingly, the sheet-like elastic support member 83 fixes the exciting coil 82 in close contact toward the support surface 81a. In this case, the support surface 81a is formed / set to maintain a predetermined gap (design value) with the surface of the fixing belt 61. Therefore, the excitation coil 82 is set so that the entire excitation coil 82 maintains a predetermined gap from the surface of the fixing belt 61.

Further, each of the plurality of magnetic cores 84 arranged along the width direction of the fixing belt 61 has an inner peripheral surface on the exciting coil 82 side formed in an arc shape (an inner peripheral arc surface) toward the moving direction of the fixing belt 61. Has been. Further, the inner circumferential arc surface (rear stage, 84 b in FIG. 11) of the magnetic core 84 is formed so as to cover (wrap) 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 has a circular arc surface on the inner peripheral side of the magnetic core 84 on a pair of magnetic core support portions 81b1 and 81b2 (see later, see FIG. 11) disposed in parallel along the longitudinal central axis on the support surface 81a. By being supported, the gap between the magnetic core 84 and the support surface 81a is set to be kept constant. Further, at that time, the magnetic core 84 is supported so as to be movable along the moving direction of the fixing belt 61 between the magnetic core restricting portions 81c disposed on both sides of the supporting surface 81a in the moving direction of the fixing belt 61.
Each of the magnetic cores 84 is supported by a pair of magnetic core support portions 81b1 and 81b2 on the inner circumferential side arc surface, and then a sponge-like pressing member 86 provided on the lower surface of the shield 85 via the magnetic core hold 87. Pressure is applied from the upper side toward the support 81 side. Accordingly, each magnetic core 84 is fixed inside the IH heater 80 by being pressed so as to be sandwiched between the pressing member 86 on the upper surface and the sheet-like elastic support member 83 on the lower surface.

  FIG. 11 is a diagram for explaining the laminated structure of the IH heater 80 in the present embodiment. As shown in FIG. 11, the exciting coil 82 is configured such that the closed loop hollow portion 82 a of the exciting coil 82 is on the longitudinal center axis (axis) of the supporting surface 81 a on the supporting surface 81 a of the supporting body 81 as an example of the position setting member. ) Are arranged so as to surround a pair of magnetic core support portions (convex portions) 81b1 and 81b2 as an example of a position setting portion disposed in parallel with each other. 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 set to a specified value (design value). As a result, the exciting coil 82 is disposed in close contact with the support surface 81a, so that the gap between the exciting coil 82 and the fixing belt 61 is set to a design value.

Therefore, in the IH heater 80 of the present embodiment, the exciting coil 82 disposed on the support surface 81a of the support 81 is supported by the sheet-like elastic support member 83 formed in the longitudinal direction of the support 81. It is configured to be pressed toward the side.
Specifically, when the magnetic core 84 is disposed above the excitation coil 82, the inner peripheral arcuate surface 84b of the magnetic core 84 is supported by a pair of magnetic core support portions 81b1 and 81b2 provided on the support surface 81a. The Thereby, the gap between the magnetic core 84 and the support surface 81a is set to a predetermined gap. In this case, the thickness of the sheet-like elastic support member 83 disposed between the magnetic core 84 and the excitation coil 82 is such that the magnetic core 84 when the inner circumferential arc surface 84b is supported by the magnetic core support portions 81b1 and 81b2. And a gap thicker than the gap between the support surface 81a.
Further, the magnetic core 84 is pressed to the support 81 side by the pressing member 86 provided on the lower surface of the shield 85 when the shield 85 is attached to the support 81. As a result, the sheet-like elastic support member 83 is elastically deformed (compressed) by receiving pressure from the pressing member 86 to the support 81 side via the magnetic core hold 87 and the magnetic core 84, and the exciting coil 82 is deformed by the elastic force generated thereby. Pressing toward the support surface 81a. Thereby, the exciting coil 82 is brought into close contact with and fixed to the support surface 81a. Since the support surface 81a is formed / set to maintain a predetermined gap (design value) with the surface of the fixing belt 61, the distance between the exciting coil 82 and the fixing belt 61 is set to the design value.
Here, in the present embodiment, the pressing force of the pressing member 86 is preferably made larger than the elastic force by the sheet-like elastic support member 83. Thereby, positioning by fixing the magnetic core 84 and the exciting coil 82 can be performed reliably. As the pressing 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 fluororubber.

  In general, when an alternating magnetic field is generated by the exciting coil 82, the magnetic core 84 disposed in the vicinity of the exciting coil 82, the temperature-sensitive magnetic member 64 disposed on the inner peripheral surface side of the fixing belt 61, etc. When the magnetic force acts, vibration (magnetostriction) is generated in the exciting coil 82 itself. Therefore, when the exciting coil 82 is fixed to the support 81 using a so-called rigid body (a material having a high Young's modulus) such as an adhesive, vibration of the exciting coil 82 due to long-term cumulative use is a factor. Further, peeling between the exciting coil 82 and a rigid body such as an adhesive that fixes the exciting coil 82 is likely to occur. When the exciting coil 82 is peeled off from the adhesive or the like, the position of the exciting coil 82 on the support surface 81a is shifted or the exciting coil 82 is deformed. As a result, the distance between the exciting coil 82 and the fixing belt 61 deviates from the original design value, and the density of magnetic lines of force (magnetic flux density) passing through the fixing belt 61 via the magnetic core 84 varies partially on the surface of the fixing belt 61. Arise. As a result, the magnitude of the eddy current I generated in the fixing belt 61 may be non-uniform, and the amount of heat generated on the surface of the fixing belt 61 may vary in the longitudinal direction, resulting in uneven fixing.

  Further, when the excitation coil 82 is fixed to the support 81 using a rigid body such as an adhesive, the entire surface of the excitation coil 82 is displaced from the support 81 until the adhesive or the like is solidified. It is necessary to fix so that there is no. However, since the exciting coil 82 is, for example, a litz wire bundled in a closed loop and bonded, the deformation is likely to occur. For this reason, the exciting coil 82 may be deformed or displaced until the adhesive or the like is solidified, and the positional accuracy of the exciting coil 82 with respect to the support 81 may be lowered. When the positional accuracy of the excitation coil 82 with respect to the support 81 is lowered, the amount of heat generated on the surface of the fixing belt 61 is partially varied as described above.

Therefore, in the IH heater 80 according to the present embodiment, a pressing member 86 is provided on the lower surface of the shield 85, and a sheet-like elasticity formed in a sheet shape in the longitudinal direction of the support 81 between the magnetic core 84 and the excitation coil 82. A support member 83 is disposed, and a shield 85 is attached to the support body 81. Thereby, the pressing member 86 and the sheet-like elastic support member 83 are pressed toward the support body 81 side. Thus, the pressing member 86 is elastically deformed (compressed) by receiving pressure on the supporting member 81 side, and the sheet-like elastic supporting member 83 is further moved from the pressing member 86 to the supporting member 81 side through the magnetic core hold 87 and the magnetic core 84. Under pressure, it is elastically deformed (compressed). And the structure which the sheet-like elastic support member 83 supports so that it may closely_contact | adhere to the support surface 81a by pressing the exciting coil 82 with respect to the support body 81 with the elastic force which arises by that is employ | adopted. The sheet-like elastic support member 83 made of a rubber-like elastic body elastically deforms itself in accordance with the vibration of the excitation coil 82 while absorbing the vibration of the excitation coil 82. As a result, 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 sheet-like elastic support member 83 and the exciting coil 82 are not separated from each other. The initial positional relationship between the exciting coil 82 and the exciting coil 82 is maintained.
Further, the pressing member 86 and the sheet-like elastic support member 83 can be managed so that the thickness (set value) is within a predetermined dimensional accuracy at the time of manufacture. Accordingly, it is easy to set the pressing force for supporting the magnetic core 84 and the exciting coil 82 on the support surface 81a so as to be substantially uniform over the longitudinal direction. Furthermore, in the IH heater 80 according to the present embodiment, the plurality of magnetic cores 84 provided by being divided along the longitudinal direction of the exciting coil 82 press the sheet-like elastic support member 83 uniformly over the longitudinal direction. Thereby, the adhesiveness of the exciting coil 82 and the support surface 81a is improved over the longitudinal direction.
In addition to the above, when the IH heater 80 is manufactured, the exciting coil 82 is attached in a short time without requiring time until the adhesive or the like is solidified.

In general, the ferrite constituting the magnetic core 84 is a material that tends to vary in shape due to heat treatment after molding, and it is difficult to increase the dimensional accuracy. Therefore, if it is going to set the position of the magnetic core 84 and the exciting coil 82 based on the shape of the magnetic core 84 which was shape | molded and heat-processed, the positional accuracy between both will fall. The variation in the positional relationship between the magnetic core 84 and the excitation coil 82 causes the AC magnetic field output from the IH heater 80 to be greatly affected. According to the experiment, for example, when the gap between the magnetic core 84 and the excitation coil 82 varies by 0.5 mm, the resistance and inductance of the electric circuit composed of the excitation coil 82 and the excitation circuit 88 change by about 10%. For this reason, when the positional accuracy between the magnetic core 84 and the exciting coil 82 is lowered, for example, the distribution of magnetic lines of force passing through the inside of the magnetic core 84 varies in the upstream region and the downstream region centered on the longitudinal center axis axis. There is a partial variation in the amount of heat generated on the 61 surface.
In that case, in particular, the curvature of the inner circumferential arc surface 84b of the magnetic core 84 is likely to vary. Therefore, in the present embodiment, even when the curvature of the inner circumferential arc surface 84b of the magnetic core 84 varies, the above-described configuration using the pair of magnetic core support portions 81b1 and 81b2 and the inner circumferential arc surface 84b. With this support configuration, the gap between the inner circumferential arc surface 84b of the magnetic core 84 and the support surface 81a that supports the exciting coil 82 is substantially symmetrical between the upstream region and the downstream region centered on the longitudinal central axis axis. It is comprised so that it may become.

As described above, in the fixing unit 60 provided in the image forming apparatus 1 of the present embodiment, the exciting coil 82 and the magnetic core 84 are formed in a sheet shape in the longitudinal direction of the pressing member 86 and the support 81. The elastic support member 83 is fixed. Then, the support member 81 is positioned by the pressure of the pressing member 86. Further, by making the pressure of the pressing member 86 larger than the reaction force by the sheet-like elastic support member 83, positioning by fixing is ensured.
As a result, compared to the conventional case where the exciting coil 82 and the magnetic core 84 are fixed using an adhesive or the like, problems such as cracking and peeling of the magnetic core 84 due to the peeling of the adhesive are eliminated, and the use for a long time The displacement of the excitation coil 82 and the magnetic core 84 due to is prevented. Further, the bonding equipment is not required, and the manufacturing cost is reduced.

  In the present embodiment, the fixing unit 60 is described in which the temperature-sensitive magnetic member 64 is disposed in a non-contact manner with the fixing belt 61 and the temperature-sensitive magnetic member 64 itself does not easily generate heat. The IH heater 80 can be applied to the fixing unit 60 in which the temperature-sensitive magnetic member 64 is disposed in contact with the fixing belt 61 and the temperature-sensitive magnetic member 64 itself generates heat.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 60 ... Fixing apparatus (fixing unit), 61 ... Fixing belt, 62 ... Pressure roll, 64 ... Temperature-sensitive magnetic member, 66 ... Induction member, 80 ... IH heater, 81 ... Support body, 82 ... Excitation coil, 83 ... sheet-like elastic support member, 84 ... magnetic core, 86 ... pressing member, 611 ... base material layer, 612 ... conductive heating layer

Claims (10)

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;
A magnetic path forming member that forms a magnetic path of an alternating magnetic field generated by the magnetic field generating member;
A support member for supporting the magnetic field generating member;
It is provided between the magnetic field generating member and the magnetic path forming member and is disposed so as to contact the plurality of magnetic path forming members, and elastically deforms while pressing the magnetic field generating member toward the support member. A sheet-like elastic support member for fixing the magnetic field generating member on the support member;
A pressing member that presses the magnetic path forming member toward the magnetic field generating member;
A fixing device comprising:   The magnetic path forming member is fixed by being pressed toward the support member by the pressing member and pressed so as to be sandwiched between the pressing member and the sheet-like elastic support member. The fixing device according to claim 1.   2. The sheet-like elastic support member presses the magnetic field generating member toward the support member by an elastic force generated by a pressurizing force received from the pressing member via the magnetic path forming member. Or the fixing device according to 2;   4. The fixing device according to claim 1, wherein the pressing force of the pressing member is larger than an elastic force generated in the sheet-like elastic support member due to the pressing force received from the pressing member. 5.   The AC magnetic field generated by the magnetic field generating member is shielded, and further includes a shielding member attached to the support member so as to sandwich the magnetic path forming member and the pressing member. The fixing device according to claim 1, wherein the fixing member is pressed against the support member side by a member.   The fixing device according to claim 1, wherein the pressing member is made of a nonmagnetic material.   The fixing device according to claim 1, wherein the sheet-like elastic support member and the pressing member are made of a rubber-like elastic body. A toner image forming unit for forming a toner image;
A transfer unit that transfers the toner image formed by the toner image forming unit onto a recording material;
A fixing unit for fixing the toner image transferred to the recording material on the recording material,
The fixing unit includes:
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;
A magnetic path forming member that forms a magnetic path of an alternating magnetic field generated by the magnetic field generating member;
A support member for supporting the magnetic field generating member;
It is provided between the magnetic field generating member and the magnetic path forming member and is disposed so as to contact the plurality of magnetic path forming members, and elastically deforms while pressing the magnetic field generating member toward the support member. A sheet-like elastic support member for fixing the magnetic field generating member on the support member;
A pressing member that presses the magnetic path forming member toward the magnetic field generating member;
An image forming apparatus comprising:   The magnetic path forming member of the fixing unit is fixed by being pressed so as to be sandwiched between the pressing member and the sheet-like elastic support member, and the sheet-like elastic support member is received from the pressure member. The image forming apparatus according to claim 8, wherein the magnetic field generating member is pressed toward the support member by an elastic force generated by the applied pressure. A magnetic field generating member that generates an alternating magnetic field that intersects the conductive layer of the fixing member that has a conductive layer and is heated by electromagnetic induction to fix the toner on the recording material;
A magnetic path forming member that forms a magnetic path of an alternating magnetic field generated by the magnetic field generating member;
A support member for supporting the magnetic field generating member;
Provided between the magnetic field generating member and the magnetic path forming member, and disposed so as to contact the plurality of magnetic path forming members, and elastically deform while pressing the magnetic field generating member toward the support member. A sheet-like elastic support member for fixing the magnetic field generating member on the support member;
A pressing member that presses the magnetic path forming member toward the magnetic field generating member;
A magnetic field generation apparatus comprising:

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