JP2010224035A - Fixing device, image forming apparatus, and temperature sensor for induction heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device of an induction heat system that suppresses an excessive increase in the temperature of a fixing member by making the fixing member less likely to be heated excessively by an electromagnetic induction coil, and to provide the others. <P>SOLUTION: A fixing unit 60 includes: a fixing belt 61 that has a conductive layer and fixes toner to a recording material by subjecting the conductive layer to electromagnetic induction heating; an IH heater 80 that generates an AC magnetic field intersecting the conductive layer of the fixing belt 61; and a temperature sensor 100 that is disposed in contact with the fixing belt 61 and has a bimetal deformed at predetermined temperature, a switching section turned on or off by deformation of the bimetal, and a temperature increase suppressing member for suppressing a temperature increase resulting from the electromagnetic induction heating of the bimetal. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fixing device, an image forming apparatus, and a temperature sensor for an induction heating device.

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 is provided with a heat generation control member that includes a temperature-sensitive magnetic metal material having a Curie point and is disposed to face a magnetic field generator via a fixing belt having a heat generation layer. There is described a fixing device that controls the heat generation of the heat generating layer by utilizing the magnetism and non-magnetization at the Curie point of the temperature-sensitive magnetic metal material constituting the control member.
Patent Document 2 discloses a heating element that generates heat by the action of a magnetic field on the inner peripheral side of the fixing belt, and is opposed to the magnetic field generator via the fixing belt and is in contact with the inner peripheral surface of the fixing belt. A fixing device is described in which a heating element is provided and the heating element has a thickness exceeding the skin depth and includes a magnetic metal material.

JP 2008-152247 A JP 2008-129517 A

Here, in general, the fixing member heated by the magnetic field generating member is composed of a member having a small heat capacity, so that the time required for raising the fixing member to a fixable temperature (warm-up time) is shortened. However, in the process of raising the temperature to the fixable temperature, for example, excessive heating occurs due to electromagnetic induction heating, and as a result of the temperature of the fixing member increasing beyond the fixable temperature, the inside of the fixing device may be damaged.
SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device or the like that suppresses excessive heating of a fixing member by an electromagnetic induction coil and suppresses an excessive increase in the temperature of the fixing member in an induction heating type fixing device. To do.

  According to the first aspect of the present invention, there is provided a fixing member that has a conductive layer, the toner is fixed to the recording material by electromagnetically heating 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, a bimetal that is disposed in contact with the fixing member and that is deformed at a predetermined temperature, a switch part that is turned on and off by the deformation of the bimetal, and a temperature due to electromagnetic induction heating of the bimetal And a temperature detection unit having a temperature increase suppressing member that suppresses the increase.

According to a second aspect of the present invention, in the fixing device according to the first aspect, the surface of the temperature detecting unit that contacts the fixing member has a shape that follows the shape of the inner surface of the fixing member. .
According to a third aspect of the present invention, the temperature rise suppressing member of the temperature detection unit is disposed adjacent to or in contact with the bimetal, and the temperature is prevented by inhibiting passage of the magnetic path of the alternating magnetic field to the bimetal. The fixing device according to claim 1, wherein rising is suppressed.
According to a fourth aspect of the present invention, in the fixing device according to the third aspect, the temperature rise suppressing member is made of a nonmagnetic material having a skin depth of 0.5 mm to 10 mm.
According to a fifth aspect of the present invention, the temperature rise suppression member of the temperature detection unit is disposed in contact with the bimetal, and suppresses the temperature rise by absorbing heat generated from the bimetal by heat transfer. The fixing device according to claim 1.

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 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 the conductive layer of the fixing member, and a magnetic path blocking member that is disposed in contact with the fixing member and that inhibits the penetration of the alternating magnetic field into the interior. An image forming apparatus comprising: a temperature detection unit that includes:
The invention according to claim 7 further includes a bimetal that deforms at a predetermined temperature, and a switch unit that is turned on and off by deformation of the bimetal,
The image forming apparatus according to claim 6, wherein the magnetic path blocking member is disposed adjacent to or in contact with the bimetal and blocks passage of the magnetic path of the alternating magnetic field to the bimetal. It is.

The invention according to claim 8 is a bimetal that is deformed at a predetermined temperature, a switch part that is turned on and off by the deformation of the bimetal, and a magnetic path to the bimetal that is disposed adjacent to or in contact with the bimetal. It is a temperature sensor for induction heating devices provided with a magnetic path inhibition member which inhibits passage of.
The invention according to claim 9 is the temperature sensor for an induction heating apparatus according to claim 8, wherein the magnetic path inhibiting member is made of a nonmagnetic material having a skin depth of 0.5 mm to 10 mm. It is.

According to the first aspect of the present invention, in comparison with the case where the present invention is not adopted, the fixing member of the induction heating type is less likely to cause excessive heating of the fixing member by electromagnetic induction heating, and the temperature of the fixing member is excessively increased. Can be suppressed.
According to the second aspect of the present invention, it is possible to provide a fixing device having a temperature detection function capable of measuring the temperature of the fixing member with higher responsiveness than when the present invention is not adopted.
According to the third aspect of the present invention, it is possible to provide a fixing device having a temperature detection function capable of suppressing the temperature rise of the bimetal as compared with the case where the present invention is not adopted.
According to the fourth aspect of the present invention, it is possible to provide a fixing device having a temperature detection function that achieves both responsiveness and suppression of temperature rise of the bimetal as compared with the case where the present invention is not adopted.
According to the fifth aspect of the present invention, it is possible to provide a fixing device having a temperature detection function capable of suppressing the temperature rise of the bimetal with a simpler structure than when the present invention is not adopted.
According to the sixth aspect of the present invention, it is possible to provide an image forming apparatus provided with a fixing device that performs a more stable operation than when the present invention is not adopted.
According to the seventh aspect of the present invention, it is possible to provide an image forming apparatus that employs a bimetallic temperature detection unit.
According to the eighth aspect of the present invention, it is possible to provide a temperature sensor for an induction heating device that is less likely to cause a malfunction due to electromagnetic induction heating compared to a case where the present invention is not adopted.
According to invention of Claim 9, compared with the case where this invention is not employ | adopted, the temperature sensor for induction heating apparatuses which made compatible both responsiveness and temperature rise suppression of a bimetal can be created.

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 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 (H) in case the temperature of a fixing belt exists in the temperature range below the magnetic permeability change start temperature. It is a figure explaining the schematic structure of a temperature sensor. FIG. 6 is a diagram illustrating the relationship between the time and temperature of a fixing belt when a temperature sensor is disposed in a non-contact manner on the inner surface of the fixing belt. It is sectional drawing explaining the 1st example of the internal structure of the temperature sensor for induction heating apparatuses with which this Embodiment is applied. It is sectional drawing explaining the 2nd example of the internal structure of the temperature sensor for induction heating apparatuses with which this Embodiment is applied.

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 that supports constituent members such as the pressure pad 63, a temperature-sensitive magnetic member 64 that induces an alternating magnetic field generated by the IH heater 80 to form a magnetic path, and a temperature-sensitive magnetic member 64. A guide member 66 that guides the lines of magnetic force that have passed through, a peeling auxiliary member 70 that assists in peeling the paper P from the fixing belt 61, and a temperature detector that measures the temperature of the fixing belt 61 and is disposed in contact with the fixing belt 61 As an example, a temperature sensor 100 is 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 300 mm in the original shape (cylindrical shape). 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, as the conductive heat generating layer 612, 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 (a paramagnetic material having a relative permeability of about 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.

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 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 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 that follows the inner peripheral surface of the fixing belt 61, and a predetermined gap (for example, 0.5 to 1.5 mm) from the inner peripheral surface of the fixing belt 61. Are arranged close to each other but 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 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 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 the magnetism of the substance disappears, but has a concept different from the Curie point.

As a material used for the temperature-sensitive magnetic member 64, a binary magnetic shunt steel such as an Fe—Ni alloy (permalloy) whose permeability change start temperature is set in a range of 140 (fixing set temperature) to 240 ° C., for example. And ternary shunt steels such as Fe—Ni—Cr alloy are used. For example, in the Fe-Ni binary magnetic shunt steel, the permeability change start temperature can be set around 225 ° C. by setting it to about Fe 64% and Ni 36% (atomic ratio). Such metal alloys such as permalloy and magnetic shunt steel are suitable for the temperature-sensitive magnetic member 64 because they are excellent in moldability and workability, have high thermal 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 smaller 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.

<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 paramagnetic 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) that is sufficiently thicker than the skin depth δ (see the above formula (1)) so that the eddy current I can easily flow. Formed with.

<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 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, 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 deviation 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 a driving force directly from both end portions of the fixing belt 61, and thus 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 as thin layers 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 via the fixing belt 61 with a load of 20 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. Further, an elastic support member 83 made of an elastic body that fixes the excitation coil 82 on the support 81 and a magnetic core 84 that forms a magnetic path of an alternating magnetic field generated by the excitation coil 82 are provided. 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 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 magnetic core 84 is made of, for example, a ferromagnetic material made of an oxide or alloy material having a high magnetic permeability such as soft ferrite, ferrite resin, amorphous alloy (amorphous alloy), permalloy, and magnetic shunt steel. It functions as a forming means. 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.

  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 the 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 cross the fixing belt 61. A magnetic path that passes through and passes 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 heat generating layer 612 in the thickness direction, the magnetic field in the temperature-sensitive magnetic member 64 is increased. It is radiated toward the magnetic core 84 in a concentrated manner 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. 7, 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.

<Explanation of temperature sensor>
Next, the temperature sensor 100 will be described in detail.
FIG. 8 is a diagram illustrating a schematic structure of the temperature sensor 100.
The temperature sensor 100 shown in FIG. 8 includes a head portion 101 provided on the temperature detection side and an attachment portion 102 for attaching the temperature sensor 100 to a predetermined location. In addition, the head unit 101 includes a heat receiving unit 103 that receives heat from a location where the temperature is to be measured, and a sensor unit 104 that receives heat received by the heat receiving unit 103 by heat transfer and turns on / off the conductive state at a predetermined temperature. Prepare.
As shown in FIG. 3, the temperature sensor 100 is disposed in the vicinity of the upstream side of the fixing nip N and in contact with the inner surface of the fixing belt 61. That is, the heat receiving portion 103 of the temperature sensor 100 and the fixing belt 61 come into contact with each other. The temperature sensor 100 functions as a hard switch (thermostat) for cutting off power when the fixing belt 61 is abnormally heated.

  Conventionally, the temperature sensor 100 is disposed on the inner surface of the fixing belt 61 in a non-contact manner. This is because the contact with the inner surface of the fixing belt 61 is easily affected by electromagnetic induction generated by the IH heater 80. That is, the temperature sensor 100 itself tends to generate heat due to the influence of electromagnetic induction. As a result, a malfunction due to heat generation is induced. However, if the fixing belt 61 is excessively heated when it is disposed in a non-contact manner, the temperature of the fixing belt 61 is detected because there is a gap between the fixing belt 61 and the temperature sensor 100. Is delayed. As a result, the inside of the fixing unit 60 may be excessively heated to cause damage.

FIG. 9 is a diagram illustrating the relationship between the time and temperature of the fixing belt 61 when the temperature sensor 100 is disposed on the inner surface of the fixing belt 61 in a non-contact manner. In this case, the temperature sensor 100 is separated from the inside of the fixing belt by about 10 mm.
FIG. 9 shows the relationship between the time and temperature of the fixing belt 61 when the fixing unit 60 is started. Here, the horizontal axis represents time in seconds (s), and the vertical axis represents the temperature of the fixing belt 61 in degrees (° C.).
The temperature sensor 100 is set to operate at 230 ° C., and when this temperature is exceeded, the power of the IH heater 80 is cut off. Here, the fixing unit 60 is adjusted so that excessive electromagnetic induction occurs in the IH heater 80 depending on the setting.
As shown in FIG. 9, with the start of the fixing unit 60, the fixing belt 61 suddenly increased in temperature and reached 460 ° C. after 30 seconds. At this time, the temperature sensor 100 is activated and the power of the IH heater 80 is cut off. As a result, the temperature of the fixing belt 61 is subsequently lowered.
As described above, when the temperature sensor 100 is disposed in contact with the fixing belt 61 in a non-contact manner, when an abnormal temperature rise occurs in the fixing belt 61, the operation of the temperature sensor 100 is delayed and the power of the IH heater 80 is delayed. Prone to results.

  Therefore, in this embodiment, the temperature sensor 100 is disposed in contact with the fixing belt 61. At this time, the shape of the surface of the heat receiving portion 103, which is the surface in contact with the fixing belt 61 of the temperature sensor 100 that is in direct contact with the fixing belt 61, is preferably a shape along the shape of the inner surface of the fixing belt 61. As a result, the contact area between the fixing belt 61 and the heat receiving portion 103 increases. Therefore, heat conduction from the fixing belt 61 to the heat receiving unit 103 is more likely to occur. As a result, the temperature of the fixing belt 61 can be detected more quickly, and the inner surface of the fixing belt 61 is less likely to be damaged by the end of the heat receiving portion 103. More specifically, it is preferable that the surface of the heat receiving portion 103 on the side in contact with the fixing belt 61 has an arc shape.

  By arranging the temperature sensor 100 in contact with the fixing belt 61 in this way, the temperature sensor 100 can detect the temperature of the fixing belt 61 more quickly. In the present embodiment, in addition to this, the temperature sensor 100 is provided with a temperature rise suppressing function. Next, the structure of the temperature sensor 100 for realizing this temperature rise suppression function will be described.

[First Embodiment]
Hereinafter, in the present embodiment, a first embodiment for providing the temperature sensor 100 with a temperature rise suppression function will be described.

FIG. 10 is a cross-sectional view illustrating a first example of the internal structure of temperature sensor 100 for an induction heating apparatus to which the present embodiment is applied.
In the temperature sensor 100a shown in FIG. 10, a bimetal 112, a pin 113 attached to the lower side of the bimetal 112 in FIG. 10, a leaf spring 114 driven by the pin 113, and a leaf spring are provided in the case 111. The contact 115a attached to one end of the contact 114, the terminal 116 disposed in contact with the end opposite to the end to which the contact 115a of the leaf spring 114 is attached, and the contact 115a are opened and closed. Thus, the contact 115b for performing the on / off operation of the temperature sensor 100a, the terminal 117 arranged in contact with the contact 115b, and the upper portion of the case 111 as seen in FIG. And a heat receiving portion 103 arranged to form a gap g.

In the temperature sensor 100 a, the heat generated from the fixing belt 61 is first transferred to the heat receiving unit 103. Then, the heat is further transferred to the bimetal 112 disposed under the heat receiving portion 103.
The bimetal 112 has a shape that protrudes upward as shown in FIG. 10 below a predetermined temperature. In this state, the contact 115a and the contact 115b are in contact with each other. Further, the terminal 116, the leaf spring 114, and the contact 115a are in contact with each other, and the contact 115b and the terminal 117 are in contact with each other. Therefore, the terminal 116 and the terminal 117 are in a conductive state. That is, the conductive state is on.

  On the other hand, the bimetal 112 is designed so that when the temperature exceeds a predetermined temperature, the shape is inverted upside down and protrudes downward. When the bimetal 112 changes to a shape that protrudes downward beyond the predetermined temperature in this way, the pin 113 moves downward in the direction seen in FIG. 10 and generates a force that pushes the leaf spring 114 downward. To do. The leaf spring 114 deflects the portion of the contact 115a downward by this force, so that the contact 115a is separated from the contact 115b. Therefore, the terminal 116 and the terminal 117 are brought out of electrical conduction. That is, the conductive state changes to an off state. Therefore, in this embodiment, the contact 115a and the contact 115b can be grasped as a switch unit that is turned on and off by deformation of the bimetal 112.

In this way, the contact 115a and the contact 115b are opened and closed by changing the shape of the bimetal 112 at the predetermined temperature. Therefore, the temperature sensor 100a can be turned on / off. In the present embodiment, temperature sensor 100a performs an operation that is on at or below a predetermined temperature and that is off when the temperature exceeds a predetermined temperature.
That is, in this case, when the fixing belt 61 is equal to or lower than a predetermined temperature, the temperature sensor 100a is on and the fixing unit 60 performs a normal operation. On the other hand, when the fixing belt 61 exceeds a predetermined temperature, the temperature sensor 100a is turned off, and the fixing unit 60 performs an operation such as cutting off the energization of the IH heater 80.

Here, the heat receiving portion 103 is made of aluminum which is a non-magnetic metal. And the thickness is about 0.5 mm normally. However, at this thickness, the AC magnetic field from the IH heater 80 easily penetrates the heat receiving portion 103 and enters the temperature sensor 100a. Electromagnetic induction heating acts on the bimetal 112. Therefore, the bimetal 112 itself generates heat, and when the temperature reaches a predetermined temperature, the shape of the bimetal 112 is reversed as described above. That is, even if the fixing belt 61 does not reach a predetermined temperature, the temperature sensor 100a operates and changes from an on state to an off state. That is, a malfunction is induced.

  Therefore, in the present embodiment, the heat receiving unit 103 is provided with a magnetic path blocking function. That is, the heat receiving unit 103 functions as a magnetic path blocking member and inhibits the penetration of an alternating magnetic field into the temperature sensor 100. This obstructs the passage of the magnetic path to the bimetal 112. As a result, the effect of electromagnetic induction generated by the IH heater 80 is less likely to occur inside the temperature sensor 100a. That is, the heat generation of the bimetal 112 is suppressed, and as a result, it is difficult to induce a malfunction of the temperature sensor 100a due to the heat generation of the bimetal 112.

  More specifically, a nonmagnetic material such as aluminum having a skin depth of 0.5 mm to 10 mm determined by the above equation (1) is used as the heat receiving portion 103. When the skin depth is 0.5 mm or more, the heat receiving portion 103 can sufficiently inhibit the AC magnetic field from entering the temperature sensor 100a. As a result, a temperature increase due to electromagnetic induction heating of the bimetal 112 inside the temperature sensor 100a can be suppressed. That is, in this case, the heat receiving portion 103 can be grasped as a temperature rise suppressing member. If the skin depth is 10 mm or more, heat transfer from the heat receiving portion 103 to the bimetal 112 is delayed, and as a result, the temperature of the fixing belt 61 cannot be measured quickly with good responsiveness. It becomes difficult to suppress an excessive rise.

  In the temperature sensor 100a illustrated in FIG. 10, the bimetal 112 is disposed adjacent to the heat receiving unit 103 in a non-contact manner with the gap g, but may be disposed in contact therewith. In this case as well, the temperature rise due to electromagnetic induction heating of the bimetal 112 can be suppressed as in the non-contact case described above.

[Second Embodiment]
Next, in the present embodiment, a second embodiment for providing the temperature sensor 100 with a temperature rise suppression function will be described.

FIG. 11 is a cross-sectional view illustrating a second example of the internal structure of temperature sensor 100 for the induction heating apparatus to which the present embodiment is applied.
The internal structure of the temperature sensor 100b shown in FIG. 11 basically has the same structure as the temperature sensor 100a described in FIG. However, the difference is that the bimetal 112 and the heat receiving portion 103 are arranged in contact with each other.

  In the case of this temperature sensor 100b, it is not necessary for the heat receiving portion 103 to have a function as a magnetic path blocking member. That is, the AC magnetic field generated by the IH heater 80 may enter the temperature sensor 100b. And when it invades, electromagnetic induction heating is caused in the bimetal 112. However, since the bimetal 112 and the heat receiving part 103 are arranged in contact with each other, the heat generated by the electromagnetic induction heating is transferred to the heat receiving part 103 and further to the fixing belt 61. In other words, in this case, the temperatures of the fixing belt 61, the heat receiving portion 103, and the bimetal 112 are held substantially the same. Therefore, even if the bimetal 112 generates heat by electromagnetic induction heating, the temperature rise due to the electromagnetic induction heating of the bimetal 112 can be suppressed. As a result, it becomes difficult to induce a malfunction of the temperature sensor 100b due to heat generated by the bimetal 112. In this case, the heat receiving unit 103 can be grasped as a heat transfer member that absorbs heat generated from the bimetal 112 by heat transfer.

  The temperature sensor 100 (100a, 100b) described in detail above is used to detect the temperature of the fixing belt 61 with respect to the electromagnetic induction heating type fixing unit 60, but is not limited thereto. That is, it can be used for other purposes as a temperature sensor for measuring the temperature of an induction heating type apparatus. For example, it can be applied to temperature measurement of an IH cooker (electromagnetic cooker) or the like.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 60 ... Fixing unit, 61 ... Fixing belt, 62 ... Pressure roll, 64 ... Temperature-sensitive magnetic member, 66 ... Induction member, 80 ... IH heater, 82 ... Excitation coil, 84 ... Magnetic core, 100, DESCRIPTION OF SYMBOLS 100a, 100b ... Temperature sensor, 103 ... Heat receiving part, 104 ... Sensor part, 112 ... Bimetal, 115a, 115b ... Contact, 611 ... Base material layer, 612 ... Conductive heating layer

Claims (9)

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 temperature rise suppression that suppresses a temperature rise due to electromagnetic induction heating of the bimetal that is disposed in contact with the fixing member and that is deformed at a predetermined temperature, a switch portion that is turned on and off by the deformation of the bimetal, and the bimetal. A temperature detector having a member;
A fixing device comprising:   The fixing device according to claim 1, wherein a surface of the temperature detection unit that contacts the fixing member has a shape that follows a shape of an inner surface of the fixing member.   The temperature rise suppression member of the temperature detection unit is disposed adjacent to or in contact with the bimetal, and suppresses the temperature rise by inhibiting the passage of the magnetic path of the AC magnetic field to the bimetal. The fixing device according to claim 1.   The fixing device according to claim 3, wherein the temperature increase suppressing member is made of a nonmagnetic material having a skin depth of 0.5 mm to 10 mm.   The temperature rise suppression member of the temperature detection unit is disposed in contact with the bimetal, and suppresses the temperature rise by absorbing heat generated from the bimetal by heat transfer. 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;
A temperature detection unit disposed in contact with the fixing member and having a magnetic path inhibition member that inhibits the penetration of the alternating magnetic field into the interior;
An image forming apparatus comprising: The temperature detection unit further includes a bimetal that deforms at a predetermined temperature, and a switch unit that is turned on and off by the deformation of the bimetal.
The image forming apparatus according to claim 6, wherein the magnetic path blocking member is disposed adjacent to or in contact with the bimetal and blocks passage of the magnetic path of the alternating magnetic field to the bimetal. . A bimetal that deforms at a predetermined temperature;
A switch part that is switched on and off by deformation of the bimetal;
A magnetic path inhibiting member that is disposed adjacent to or in contact with the bimetal and inhibits passage of the magnetic path to the bimetal;
A temperature sensor for an induction heating device.   The temperature sensor for an induction heating apparatus according to claim 8, wherein the magnetic path blocking member is made of a nonmagnetic material having a skin depth of 0.5 mm to 10 mm.

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