JP4858561B2 - 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 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, in Patent Document 1, an electromagnetic induction coil as a magnetic flux generating means is arranged inside a fixing roll made of a core metal cylinder made of magnetic metal, and an eddy current is induced in the fixing roll by an induced magnetic field generated by the electromagnetic induction coil. An induction heating type fixing device that directly heats the fixing roll is described.

JP 2003-186322 A

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

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 and an inner peripheral surface facing the magnetic field generating member are formed in an arc shape in the moving direction of the fixing member, and a magnetic field forming a magnetic path of an alternating magnetic field generated by the magnetic field generating member A path setting member, a position setting surface that is formed in an arc shape toward the moving direction of the fixing member, and sets the magnetic field generating member at a position having a predetermined gap from the fixing member; and the magnetic path forming member And a position setting member having a position setting portion for setting the position setting surface to a position having a predetermined gap, and the position setting portion of the position setting member extends in a direction orthogonal to the moving direction of the fixing member. Parallel along Consists of a pair of convex portions which Rutotomoni, the pair of convex portions, a height from the positioning surface of a portion that supports the magnetic path forming member is formed on the same, and the magnetic field generation The magnetic path forming member is supported so as to be movable back and forth in the moving direction of the fixing member along the position setting surface. The fixing device is characterized in that.

According to a second aspect of the present invention, the magnetic path forming member is configured to cover a region of the position setting member where the magnetic field generating member is disposed, and the position setting member is configured to move the fixing member. The fixing device according to claim 1, further comprising a restriction portion that restricts movement of the magnetic path forming member supported by the position setting portion on both sides in the direction.
The invention according to claim 3 is characterized in that the magnetic path forming member is formed in an arc shape in which a region supported by the position setting portion of the inner peripheral surface is concentric with the position setting surface. The fixing device according to claim 1.
According to a fourth aspect of the present invention, the magnetic field generating member is elastically deformed while pressing the magnetic field generating member toward the position setting surface between the magnetic field generating member and the magnetic path forming member. The fixing device according to claim 1, further comprising an elastic support member that supports the setting surface.
According to a fifth aspect of the present invention, the magnetic field generating member is disposed in a temperature range up to a magnetic permeability change starting temperature that is arranged to face the magnetic field generating member with the fixing member interposed therebetween and starts to decrease the magnetic permeability. And a second magnetic path forming member that forms a magnetic path of the alternating magnetic field and transmits the alternating magnetic field generated by the magnetic field generating member in a temperature range that exceeds the permeability change start temperature. 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 an inner peripheral surface that faces the magnetic field generating member is formed in an arc shape toward the moving direction of the fixing member, and generates the magnetic field. A magnetic path forming member that forms a magnetic path of an alternating magnetic field generated by the member, and a position that is formed in an arc shape in the moving direction of the fixing member, and the magnetic field generating member has a predetermined gap from the fixing member Position to set to A position setting member having a fixed surface and a position setting unit that sets the magnetic path forming member to a position having a predetermined gap with the position setting surface, and the position setting unit of the position setting member includes consists of a pair of convex portions which are arranged parallel along the direction orthogonal to the moving direction of the fixing member Rutotomoni, the pair of convex portions, the positioning surface of a portion that supports the magnetic path forming member And the magnetic path forming member is arranged along the position setting surface, and the magnetic path forming member is arranged along the position setting surface. An image forming apparatus, wherein the fixing member is supported so as to be movable in the front-rear direction.

According to a seventh aspect of the present invention, the magnetic path forming member of the fixing unit is configured to cover a region of the position setting member where the magnetic field generating member is disposed, and the position setting member of the fixing unit is The image forming apparatus according to claim 6 , further comprising a restricting portion that restricts movement of the magnetic path forming member supported by the position setting portion on both sides in the moving direction of the fixing member.
According to an eighth aspect of the present invention, the magnetic path forming member of the fixing unit is formed in an arc shape in which a region supported by the position setting portion on the inner peripheral surface is concentric with the position setting surface. The image forming apparatus according to claim 6.
According to a ninth aspect of the present invention, the magnetic field generating member is elastically deformed while pressing the magnetic field generating member toward the position setting surface between the magnetic field generating member and the magnetic path forming member, and the magnetic field generating member is moved to the position. The image forming apparatus according to claim 6, further comprising an elastic support member that supports the setting surface.
According to a tenth aspect of the present invention, the fixing unit is disposed opposite to the magnetic field generating member with the fixing member interposed therebetween, and the fixing unit is in a temperature range up to a magnetic permeability change starting temperature at which the magnetic permeability starts decreasing. A second magnetic path forming member that forms a magnetic path of the alternating magnetic field generated by the magnetic field generating member and transmits the alternating magnetic field generated by the magnetic field generating member in a temperature range that exceeds the permeability change start temperature; The image forming apparatus according to claim 6, wherein the image forming apparatus is provided.

According to an eleventh 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 a fixing member that fixes the toner on the recording material by electromagnetic induction heating. And an inner peripheral surface facing the magnetic field generating member is formed in an arc shape toward the moving direction of the fixing member, and forms a magnetic path of an alternating magnetic field generated by the magnetic field generating member, and A position setting surface that is formed in an arc shape toward the moving direction of the fixing member, sets the magnetic field generating member at a position having a predetermined gap from the fixing member, and the magnetic path forming member is the position setting surface. A position setting member having a position setting portion that sets a position having a predetermined gap, and the position setting portion of the position setting member is disposed in parallel along a direction orthogonal to the moving direction of the fixing member. Pair of convex shapes In configured Rutotomoni, the pair of convex portions, a height from the positioning surface of a portion that supports the magnetic path forming member is formed on the same, and the central axis and the position of the magnetic field generation member Magnetic field generation, characterized in that the magnetic path forming member is disposed at a position that is symmetrical with respect to an intersecting line with a setting surface, and the magnetic path forming member is movably supported along the position setting surface in the moving direction of the fixing member. Device.

According to a twelfth aspect of the present invention, the magnetic path forming member is configured to cover a region of the position setting member where the magnetic field generating member is disposed, and the position setting member is disposed on both sides of the fixing member in the moving direction. The magnetic field generation device according to claim 11 , further comprising a restricting portion that restricts movement of the magnetic path forming member supported by the position setting portion.
The invention according to claim 13 is characterized in that the magnetic path forming member is formed in an arc shape in which a region supported by the position setting portion of the inner peripheral surface is concentric with the position setting surface. A magnetic field generation apparatus according to claim 11 .

According to the first aspect of the present invention, the uniformity in the longitudinal direction of the fixing member of the AC magnetic field supplied to the fixing member in the induction heating type fixing device can be improved as compared with the case where the present invention is not adopted.
According to the second aspect of the present invention, even when the dimensional accuracy of the magnetic path forming member is relaxed, the magnetic field generating member, the magnetic path forming member, and the positional accuracy of the magnetic field generating member and the fixing member, compared with the case where the present invention is not adopted. In addition, the AC magnetic field generated by the magnetic field generating member can be efficiently induced inside the magnetic path forming member.
According to the first aspect of the present invention, compared with the case where the present invention is not adopted, the magnetic field generated by the magnetic field generating member can be evenly distributed to the front and rear in the moving direction of the fixing member.
According to the third aspect of the present invention, even if the shape of the magnetic path forming member varies as compared with the case where the present invention is not adopted, in the upstream region and the downstream region in the movement direction of the fixing member of the magnetic path forming member. The gap between the magnetic path forming member and the position setting surface can be set symmetrically and equally.
According to the invention of claim 4 , as compared with the case where the present invention is not adopted, the magnetic field generating member is brought into close contact with the position setting surface so that the positional accuracy between the magnetic field generating member and the magnetic path forming member and the magnetic field generating member and the fixing member is increased. While increasing, it can absorb the vibration which generate | occur | produces in a magnetic field generation member, and can suppress generation | occurrence | production of position shift in a magnetic field generation member.
According to the fifth aspect of the present invention, it is possible to suppress an excessive increase in temperature in the non-sheet passing region as compared with the case where the present invention is not adopted.

According to the sixth aspect of the present invention, the uniformity of the AC magnetic field supplied to the fixing member in the longitudinal direction of the fixing member is increased in the induction heating type fixing device mounted on the image forming apparatus as compared with the case where the present invention is not adopted. Can do.
According to the seventh aspect of the present invention, even if the dimensional accuracy of the magnetic path forming member is relaxed, the magnetic field generating member and the magnetic path forming member, and the positional accuracy between the magnetic field generating member and the fixing member, compared with the case where the present invention is not adopted. In addition, the AC magnetic field generated by the magnetic field generating member can be efficiently induced inside the magnetic path forming member.
According to the sixth aspect of the present invention, the magnetic field generated by the magnetic field generating member can be evenly distributed between the front and rear in the moving direction of the fixing member as compared with the case where the present invention is not adopted.
According to the eighth aspect of the present invention, even if the shape of the magnetic path forming member varies as compared with the case where the present invention is not adopted, the movement direction of the fixing member of the magnetic path forming member in the upstream region and the downstream region is different. The gap between the magnetic path forming member and the position setting surface can be set symmetrically and equally.
According to the ninth aspect of the present invention, as compared with the case where the present invention is not adopted, the magnetic field generating member is brought into close contact with the position setting surface so that the positional accuracy between the magnetic field generating member and the magnetic path forming member and the magnetic field generating member and the fixing member is increased. While increasing, it can absorb the vibration which generate | occur | produces in a magnetic field generation member, and can suppress generation | occurrence | production of position shift in a magnetic field generation member.
According to the tenth aspect of the present invention, it is possible to suppress an excessive increase in temperature in the non-sheet passing region as compared with the case where the present invention is not adopted.

According to the eleventh aspect of the present invention, the uniformity of the AC magnetic field supplied to the fixing member provided in the induction heating type fixing device in the longitudinal direction of the fixing member can be improved as compared with the case where the present invention is not adopted.
According to the twelfth aspect of the present invention, even if the dimensional accuracy of the magnetic path forming member is relaxed as compared with the case where the present invention is not adopted, the magnetic field generating member, the magnetic path forming member, and the positional accuracy between the magnetic field generating member and the fixing member In addition, the AC magnetic field generated by the magnetic field generating member can be efficiently induced inside the magnetic path forming member.
According to the thirteenth aspect of the present invention, even when the shape of the magnetic path forming member varies as compared with the case where the present invention is not adopted, the movement direction of the fixing member of the magnetic path forming member in the upstream region and the downstream region is different. The gap between the magnetic path forming member and the position setting surface can be set symmetrically and equally.

1 is a diagram illustrating a configuration example of an image forming apparatus to which a fixing device according to an exemplary embodiment is applied. FIG. 2 is a front view illustrating a configuration of a fixing unit of the present embodiment. FIG. 3 is an XX cross-sectional view of the fixing device in FIG. 2. FIG. 3 is a cross-sectional layer configuration diagram of a fixing belt. (a) is a side view of an end cap member, (b) is a top view of the end cap member seen from the Z direction. It is sectional drawing explaining the structure of an IH heater. It is a figure explaining the 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. It is a section lineblock diagram showing the state where a magnetic core is supported by a pair of magnetic core support parts. FIG. 5 is a cross-sectional configuration diagram illustrating a state in which a magnetic core is supported by a pair of magnetic core support portions when the curvature of an inner circumferential arc surface of the magnetic core is smaller than a design value. FIG. 6 is a cross-sectional configuration diagram illustrating a state in which a magnetic core is supported by a pair of magnetic core support portions when the curvature of an inner circumferential arc surface of the magnetic core is formed larger than a design value.

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 generation device 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 the fixing belt 61, and a peeling assisting member 173 that assists in peeling the paper P from the fixing belt 61.

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

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

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

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

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

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

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

  In the present embodiment, a peeling assisting member 173 is arranged on the downstream side of the nip portion N as a peeling assisting means by the pressing pad 63. The peeling auxiliary member 173 is supported by the holder 172 in a state where the peeling baffle 171 is close to the fixing belt 61 in a direction opposite to the rotational movement direction of the fixing belt 61 (so-called counter direction). The curled portion formed on the paper P at the outlet of the pressing pad 63 is supported by the peeling baffle 171 to suppress 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 2.5 mm) from the inner peripheral surface of the fixing belt 61. Although they are close to each other, they are arranged in a non-contact manner. The temperature-sensitive magnetic member 64 is disposed close to the fixing belt 61 because the temperature of the temperature-sensitive magnetic member 64 changes corresponding to the temperature of the fixing belt 61, that is, the temperature of the temperature-sensitive magnetic member 64 is changed. This is because the temperature is substantially the same as the temperature 61. Further, the temperature-sensitive magnetic member 64 is disposed in a non-contact manner with the fixing belt 61 because the heat of the fixing belt 61 is heated when the main switch of the image forming apparatus 1 is turned on and the fixing belt 61 is heated to the fixing 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 (second magnetic path forming member), and is generated by the IH heater 80 in a temperature range equal to or lower than the permeability change start temperature exhibiting ferromagnetism, and the fixing belt 61. A magnetic path passing through the inside of the temperature-sensitive magnetic member 64 is formed by guiding the magnetic force lines that have passed through the inside. As a result, the temperature-sensitive magnetic member 64 forms a closed magnetic path that encloses the fixing belt 61 and the exciting coil 82 of the IH heater 80 (see FIG. 6 at a later stage). On the other hand, in the temperature range exceeding the permeability change start temperature, the temperature-sensitive magnetic member 64 crosses the magnetic field lines generated by the IH heater 80 and transmitted through the fixing belt 61 in the thickness direction of the temperature-sensitive magnetic member 64. Make it transparent. Thereby, the magnetic lines of force generated by the IH heater 80 and transmitted through the fixing belt 61 form a magnetic path that passes through the temperature-sensitive magnetic member 64, passes through the inside of the guide member 66, and returns to the IH heater 80.
The “permeability change start temperature” here is a temperature at which the magnetic permeability (for example, the magnetic permeability measured by JIS C2531) starts to decrease continuously. For example, a member such as the temperature-sensitive magnetic member 64 This is the temperature point at which the amount of magnetic flux that passes through (the number of lines of magnetic force) starts to change. Therefore, the permeability change start temperature is a temperature close to the Curie point, which is the temperature at which magnetism disappears, but has a concept different from the Curie point.

As a material used for the temperature-sensitive magnetic member 64, a binary system temperature-sensitive magnetism such as an Fe-Ni alloy (permalloy) whose magnetic permeability change start temperature is set in a range of 140 (fixing set temperature) to 240 ° C., for example. A ternary temperature-sensitive magnetic alloy such as an alloy or Fe—Ni—Cr alloy is used. For example, in a Fe-Ni binary temperature-sensitive magnetic alloy, the magnetic permeability change start temperature can be set to around 225 ° C. by setting it to about Fe 64% and Ni 36% (atomic ratio). Such metal alloys such as permalloy and temperature-sensitive magnetic alloy are suitable for the temperature-sensitive magnetic member 64 because they are excellent in moldability and workability, have high 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 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 to 300 μm. The configuration and function of the temperature-sensitive magnetic member 64 will be described in further detail later.

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

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

<Description of Fixing Belt Drive Mechanism>
Next, a driving mechanism for the fixing belt 61 will be described.
As shown in FIG. 2 which is a front view, the fixing belt 61 is rotated in the circumferential direction while maintaining the cross-sectional shape of both ends of the fixing belt 61 in a circular shape at both axial ends of the holder 65 (see FIG. 3). An end cap member 67 to be driven is fixed. The fixing belt 61 directly receives the rotational driving force from both ends via the end cap member 67, and rotates and moves in the direction of arrow C in FIG. 3 at a process speed of 140 mm / s, for example.
5A is a side view of the end cap member 67, and FIG. 5B is a plan view of the end cap member 67 viewed from the Z direction. As shown in FIG. 5, the end cap member 67 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 the driving force directly from both ends of the fixing belt 61, so that stable rotation is performed. At that time, the base material layer 611 of the fixing belt 61 is made of, for example, non-magnetic stainless steel having high mechanical strength, thereby realizing a structure in which buckling or the like hardly occurs against torsion torque or compression force. is doing. Furthermore, since the base material layer 611 and the conductive heat generating layer 612 are formed in a thin layer to ensure the flexibility / flexibility of the fixing belt 61 as a whole, deformation and shape restoration following the nip portion N are prevented. Done.

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

<Description of IH heater>
Next, the IH heater 80 that performs electromagnetic induction heating by applying an AC magnetic field to the conductive heat generating layer 612 of the fixing belt 61 will be described.
FIG. 6 is a cross-sectional view illustrating the configuration of the IH heater 80 of the present embodiment. As shown in FIG. 6, the IH heater 80 includes a support 81 made of a non-magnetic material such as a heat resistant resin, and an exciting coil 82 as an example of a magnetic field generating member that generates an alternating magnetic field. In addition, a plurality of elastic support members 83 formed of an elastic body for fixing the excitation coil 82 on the support 81 and a magnetic path of an alternating magnetic field generated by the excitation coil 82 are arranged along the width direction of the fixing belt 61. Is formed. Furthermore, a 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). In addition, a pair of magnetic core support portions (convex portions) 81b1 and 81b2 that support the magnetic core 84 are arranged in parallel in the longitudinal direction at the center of the support surface 81a. The magnetic core support portions 81 b 1 and 81 b 2 keep the gap between the magnetic core 84 and the support surface 81 a constant and support the magnetic core 84 so as to be movable along the rotation direction of the fixing belt 61. Further, on both sides of the support surface 81a, magnetic core restricting portions 81c for restricting the movement of the magnetic core 84 supported by the magnetic core supporting portions 81b1 and 81b2 in the fixing belt 61 moving direction (arc direction) are arranged.
Examples of the material constituting the support 81 include heat-resistant resins such as heat-resistant glass, polycarbonate, polyethersulfone, and PPS (polyphenylene sulfide), or heat-resistant resins obtained by mixing glass fibers with these materials. A non-magnetic material is used.

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

For the magnetic core 84, for example, an arc-shaped ferromagnetic body made of a high-permeability oxide or alloy material such as sintered ferrite, ferrite resin, amorphous alloy (amorphous alloy), permalloy, or temperature-sensitive magnetic alloy is used. And functions as a magnetic path forming member. The magnetic core 84 induces a magnetic force line (magnetic flux) generated by the alternating magnetic field generated by the exciting coil 82, and crosses the fixing belt 61 from the magnetic core 84 toward the temperature-sensitive magnetic member 64. A path of magnetic lines of force (magnetic path) is formed so as to pass through and return to the magnetic core 84. That is, the AC magnetic field generated by the excitation coil 82 is configured to pass through the inside of the magnetic core 84 and the inside of the temperature-sensitive magnetic member 64 so that the magnetic lines of force wrap the fixing belt 61 and the excitation coil 82 inside. A closed magnetic circuit is formed. As a result, the magnetic field lines of the alternating magnetic field generated by the exciting coil 82 are concentrated in a region facing the magnetic core 84 of the fixing belt 61.
Here, the magnetic core 84 is preferably made of a material having a small loss due to magnetic path formation. Specifically, the magnetic core 84 is desirably used in a form that reduces the eddy current loss (current path interruption or division by slits, thin plate bundling, etc.), and is preferably formed of a material having a small hysteresis loss.
Further, the length of the magnetic core 84 along the rotation direction of the fixing belt 61 is configured to be smaller than the length of the temperature-sensitive magnetic member 64 along the rotation direction of the fixing belt 61. Thereby, the leakage of magnetic lines of force to the periphery of the IH heater 80 is reduced, and the power factor is improved. Furthermore, electromagnetic induction to the metal member constituting the fixing unit is suppressed, and the heat generation efficiency in the fixing belt 61 (conductive heat generation layer 612) is increased.

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

  FIG. 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 inside of the temperature-sensitive magnetic member 64 which is a ferromagnetic material. Be guided. Therefore, the magnetic field lines H crossing the conductive heat generating layer 612 of the fixing belt 61 in the thickness direction are concentrated so as to enter the inside of the temperature-sensitive magnetic member 64, and the magnetic flux density in the regions R1 and R2 increases. Further, even when the magnetic field lines H that have passed through the inside of the temperature-sensitive magnetic member 64 along the spreading direction return to the magnetic core 84 again, in the region R3 that crosses the conductive heating layer 612 in the thickness direction, the magnetic field in the temperature-sensitive magnetic member 64 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.

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

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

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

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

<Description of the configuration for suppressing the temperature rise of the temperature-sensitive magnetic member>
In order for the temperature-sensitive magnetic member 64 to perform the function of suppressing the excessive temperature rise in the non-sheet passing region Fb described above, the temperature of each region in the longitudinal direction of the temperature-sensitive magnetic member 64 is the longitudinal direction of the fixing belt 61 facing it. It is necessary to fulfill a function as a detection unit that detects the temperature of the fixing belt 61 and changes according to the temperature of each region.
Therefore, regarding the temperature-sensitive magnetic member 64 itself, a configuration that is difficult to be induction-heated by the magnetic field lines H is adopted. That is, even if the temperature of the fixing belt 61 is equal to or lower than the permeability change start temperature and the temperature-sensitive magnetic member 64 exhibits ferromagnetism, the temperature-sensitive magnetic member 64 is included in the magnetic force lines H from the IH heater 80. There is a magnetic field line H that crosses in the thickness direction. As a result, a weak eddy current I is generated inside the temperature-sensitive magnetic member 64, and a slight amount of heat is generated in the temperature-sensitive magnetic member 64 itself. For this reason, for example, when a large amount of image formation is continuously performed, the self-heat generated heat is accumulated in the temperature-sensitive magnetic member 64, and the temperature of the temperature-sensitive magnetic member 64 is also in the paper passing area (see FIG. 8). Shows an upward trend. Thus, when the self-heating due to eddy current loss is large, the temperature of the temperature-sensitive magnetic member 64 rises and unintentionally reaches the temperature at which the permeability change starts, and the magnetic characteristics of the paper passing area and the non-paper passing area are improved. The difference is almost eliminated and the temperature rise suppression effect may not be obtained sufficiently. Therefore, the correspondence between the temperature of the temperature-sensitive magnetic member 64 and the temperature of the fixing belt 61 is maintained, and the temperature-sensitive magnetic member 64 functions as a detection unit that detects the temperature of the fixing belt 61 with high accuracy. It is necessary to suppress the Joule heat W generated in the member 64 itself.

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

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

<Description of fixing method of exciting coil and magnetic core in IH heater>
Next, 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.
In the IH heater 80 of the present embodiment, the excitation coil 82 is pressed against the support surface 81a of the support 81 by the elastic support member 83, thereby being fixed so as to be in close contact with the support surface 81a. That is, the elastic support member 83 is formed of a sheet-like elastic body such as silicone rubber or fluorine rubber having a low Young's modulus. The 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 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 (84b in FIG. 11 in the subsequent stage) 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 pair of magnetic core support portions 81b1 and 81b2 (see FIGS. 11 and 12 in the subsequent stage) arranged in parallel along the longitudinal central axis on the support surface 81a. By supporting the surface, 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.
Then, after each of the magnetic cores 84 is supported by the pair of magnetic core support portions 81b1 and 81b2 on the inner circumferential side arc surface, the pressure member 86 provided on the lower surface of the shield 85 is directed from the upper side toward the support body 81 side. Pressure. Accordingly, each magnetic core 84 is fixed inside the IH heater 80 by being pressed so as to be sandwiched between the pressure member 86 on the upper surface and the elastic support member 83 on the lower surface.

  FIG. 11 is a diagram for explaining a laminated structure of the IH heater 80 of 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 installed so as to surround a pair of magnetic core support portions (convex portions) 81b1 and 81b2 as an example of a position setting portion arranged in parallel. 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 according to the present embodiment, the excitation coil 82 disposed on the support surface 81a of the support 81 is configured to be pressed toward the support surface 81a by the elastic support member 83. .
Specifically, when the magnetic core 84 is disposed above the exciting 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 (see also FIG. 6). In this case, the thickness of the elastic support member 83 disposed between the magnetic core 84 and the exciting coil 82 is the same as that of the magnetic core 84 when the inner circumferential arc surface 84b is supported by the magnetic core support portions 81b1 and 81b2. It is formed thicker than the gap with the surface 81a. Further, the magnetic core 84 is pressed toward the support 81 by a pressurizing member 86 provided on the lower surface of the shield 85 when the shield 85 is attached to the support 81. Thereby, the elastic support member 83 is elastically deformed (compressed) by receiving pressure from the pressure member 86 to the support 81 side via the magnetic core 84, and the exciting coil 82 is directed toward the support surface 81a by the elastic force generated thereby. Press. 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 excitation coil 82 and the fixing belt 61 is set to the design value.
As the pressure member 86, for example, an elastic member such as a spring may be used in addition to an elastic body such as silicone rubber or fluorine rubber.

  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, if the excitation coil 82 is fixed to the support 81 using a so-called rigid body (material having a high Young's modulus) such as an adhesive, vibration of the excitation coil 82 due to long-term cumulative use becomes a factor. Thus, 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 of the present embodiment, the elastic support member 83 made of an elastic body such as silicone rubber or fluorine rubber presses the excitation coil 82 against the support 81 to support the surface 81a. The structure which supports so that it may closely_contact | adhere to is employ | adopted. The elastic support member 83 formed of an elastic body elastically deforms itself according to the vibration of the excitation coil 82 while absorbing the vibration of the excitation coil 82. Accordingly, even if the cumulative number of vibrations of the excitation coil 82 becomes large due to the cumulative use of the fixing unit 60 over a long period of time, the elastic support member 83 and the excitation coil 82 are not separated, and the support 81 and the excitation coil are separated. 82 is maintained in the initial positional relationship.
Further, the elastic support member 83 can be managed so that the thickness (set value) is within a predetermined dimensional accuracy at the time of manufacture. Thereby, it is easy to set the pressing force for supporting 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 of the present embodiment, a plurality of magnetic cores 84 provided by being divided along the longitudinal direction of the exciting coil 82 causes the elastic support member 83 to extend in the longitudinal direction as will be described later. Press evenly. Thereby, the adhesiveness of the exciting coil 82 and the support surface 81a is improved over the longitudinal direction.
In addition, 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.

Next, each of the plurality of magnetic cores 84 arranged along the width direction of the fixing belt 61 has a pair of magnetic cores in which the inner circumferential arc surface 84b is arranged in parallel along the longitudinal center axis axis on the support surface 81a. It is supported by the support portions 81b1 and 81b2.
FIG. 12 is a cross-sectional configuration diagram illustrating a state in which the magnetic core 84 is supported by the pair of magnetic core support portions 81b1 and 81b2. As shown in FIG. 12, the pair of magnetic core support portions 81b1 and 81b2 are disposed on the support surface 81a of the support 81 formed / set so as to maintain a predetermined gap g1 from the surface of the fixing belt 61. Yes. Further, the pair of magnetic core support portions 81b1 and the magnetic core support portions 81b2 are disposed at positions symmetrical with respect to the longitudinal center axis axis (see also FIG. 11) of the support surface 81a. That is, the distance between the outer wall of the magnetic core support portion 81b1 and the longitudinal center axis axis and the distance between the outer wall of the magnetic core support portion 81b2 and the longitudinal center axis axis are set equal (= w). Further, the height of the outer wall of the magnetic core support portion 81b1 and the height of the outer wall of the magnetic core support portion 81b2 are set equal (= h).

  The longitudinal center axis axis is a straight line orthogonal to the moving direction of the fixing belt 61 as shown in FIG. In particular, if the longitudinal center axis axis is a straight line along the longitudinal direction where the center axis of the excitation coil 82 and the support surface 81 a intersect, the alternating magnetic field generated by the excitation coil 82 moves the fixing belt 61 of the magnetic core 84. It is easy to realize a configuration that equally distributes the upstream area and the downstream area in the direction.

On the other hand, the inner circumferential arc surface 84b of each magnetic core 84 has the same center (concentric circle) as the circle (cir1) formed by the support surface 81a when each magnetic core 84 is supported by the pair of magnetic core support portions 81b1 and 81b2. Therefore, the support surface 81a is designed to form a circle (cir2) in which a predetermined gap g2 is set.
As a result, the inner peripheral arcuate surface 84b of each magnetic core 84 is supported by the apex b1 of the outer wall of the magnetic core support portion 81b1 and the apex b2 of the outer wall of the magnetic core support portion 81b2, so that the shape of each magnetic core 84 varies. (See the latter stage), at least in the region where the pair of magnetic core support portions 81b1 and 81b2 are arranged, each magnetic core 84 is supported movably along a circle (cir2) passing through the apex b1 and the apex b2. . This circle (cir2) is a concentric circle set to the support surface 81a (= cir1) and the gap g2. Thereby, each magnetic core 84 is upstream in the moving direction of the fixing belt 61 around the central axis axis in the longitudinal direction between the magnetic core restricting portions 81c as an example of the restricting portions disposed on both sides of the support surface 81a. In the side region and the downstream region, the gap g2 between the inner circumferential arc surface 84b and the support surface 81a is set substantially symmetrical. That is, the gap g2 between the inner circumferential arc surface 84b and the support surface 81a is set to be substantially equal between the position of the upstream region and the position of the downstream region that are equal in distance from the longitudinal central axis axis. For example, in the upstream end E1 and the downstream end E2, the gap g2 between the inner circumferential arc surface 84b and the support surface 81a is substantially equal.

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 g2 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 symmetric in the upstream region and the downstream region centered on the longitudinal central axis axis. It is comprised so that.

FIG. 13 is a cross-sectional configuration diagram showing a state in which the magnetic core 84 is supported by the pair of magnetic core support portions 81b1 and 81b2 when the curvature of the inner circumferential arc surface 84b of the magnetic core 84 is formed smaller than the design value. is there.
As shown in FIG. 13, when the curvature of the inner circumferential arc surface 84b of the magnetic core 84 is smaller than the design value, the inner circumferential arc surface 84b of each magnetic core 84 is configured with the curvature of the design value. It is closer to the exciting coil 82 than the circle (cir2). However, even when the curvature of the inner circumferential arc surface 84b varies smaller than the design value due to the above-described support configuration using the pair of magnetic core support portions 81b1 and 81b2 and the inner circumferential arc surface 84b, the magnetic core A gap g (<g2) between the arcuate surface 84b on the inner circumferential side 84b and the support surface 81a that supports the exciting coil 82 is substantially symmetric between the upstream region and the downstream region centered on the longitudinal central axis axis. . As a result, the distribution of magnetic lines of force passing through the inside of the magnetic core 84 becomes substantially equal in the upstream region and the downstream region centered on the longitudinal center axis axis (see FIG. 8), and a partial amount of heat generated on the surface of the fixing belt 61 is obtained. Variation is reduced.

  In this case, the width L2 of the magnetic core 84 is shorter than the design value (width L1 in FIG. 12) because the curvature of the inner circumferential arc surface 84b is smaller than the design value. However, the interval between the magnetic core restricting portions 81 c as an example of the restricting portions disposed on both sides of the support surface 81 a is set assuming variation in the width of the magnetic core 84. Further, each magnetic core 84 is supported by a pair of magnetic core support portions 81b1 and 81b2 so as to be movable along a circle (cir2) passing through the apex b1 and the apex b2. Therefore, even when the curvature of the inner circumferential arc surface 84b varies smaller than the design value, the magnetic cores 84 are set in a region between the magnetic core restricting portions 81c.

FIG. 14 is a cross-sectional configuration diagram illustrating a state in which the magnetic core 84 is supported by the pair of magnetic core support portions 81b1 and 81b2 when the curvature of the inner circumferential arc surface 84b of the magnetic core 84 is formed larger than the design value. is there.
As shown in FIG. 14, when the curvature of the inner circumferential arc surface 84b of the magnetic core 84 is formed larger than the design value, the inner circumferential arc surface 84b of each magnetic core 84 is configured with the curvature of the design value. It leaves | separates from the exciting coil 82 rather than the made circle (cir2). However, even when the curvature of the inner peripheral arc surface 84b varies more than the design value due to the above-described support configuration using the pair of magnetic core support portions 81b1 and 81b2 and the inner peripheral arc surface 84b, the magnetic core The gap g (> g2) between the arcuate surface 84b on the inner circumferential side 84b 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. . As a result, the distribution of magnetic lines of force passing through the inside of the magnetic core 84 becomes substantially equal in the upstream region and the downstream region centered on the longitudinal center axis axis (see FIG. 8), and a partial amount of heat generated on the surface of the fixing belt 61 is obtained. Variation is reduced.

  In this case, the width L3 of the magnetic core 84 is longer than the design value (width L1 in FIG. 12) because the curvature of the inner circumferential arc surface 84b is larger than the design value. However, the interval between the magnetic core restricting portions 81 c as an example of the restricting portions disposed on both sides of the support surface 81 a is set assuming variation in the width of the magnetic core 84. Further, each magnetic core 84 is supported by a pair of magnetic core support portions 81b1 and 81b2 so as to be movable along a circle (cir2) passing through the apex b1 and the apex b2. Therefore, even when the curvature of the inner circumferential arc surface 84b varies more than the design value, the magnetic cores 84 are set in the region between the magnetic core restricting portions 81c.

  The width (L 1, L 2, L 3) 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. If a region located outside the magnetic core 84 exists in a part of the arrangement region of the exciting coil 82, a magnetic field line (magnetic flux) that is not induced in the magnetic core 84 is generated in the alternating magnetic field generated by the exciting coil 82, and the magnetic core is generated. The number of magnetic fluxes induced inside 84 is reduced. In that case, the heat generation efficiency in the fixing belt 61 (conductive heat generation layer 612) is lowered. Therefore, the length L of the inner circumferential arc surface 84b is formed so as to cover the entire arrangement region of the exciting coil 82.

As described above, in the fixing unit 60 provided in the image forming apparatus 1 of the present embodiment, the temperature-sensitive magnetic member 64 is disposed in the vicinity of the inner peripheral surface of the fixing belt 61. As a result, the temperature rise of the non-sheet passing region is suppressed excessively.
The IH heater 80 that electromagnetically heats the fixing belt 61 includes a plurality of magnetic cores 84 arranged along the width direction of the fixing belt 61, and the inner peripheral surface of the exciting coil 82 in the moving direction of the fixing belt 61. It is formed in a circular arc shape. Further, the inner circumferential arc surface 84b of the magnetic core 84 is formed so as to cover the entire region where the exciting coil 82 is disposed in the moving direction of the fixing belt 61. In each of the magnetic cores 84, the inner peripheral arc surface of the magnetic core 84 is supported by a pair of magnetic core support portions 81b1 and 81b2 disposed in parallel along the longitudinal central axis on the support surface 81a. 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.
As a result, even if the shape of each magnetic core 84 varies, the positional accuracy between the magnetic core 84 and the exciting coil 82 increases, and the alternating magnetic field generated by the exciting coil 82 is efficiently induced inside the magnetic core 84. The

  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 unit, 61 ... Fixing belt, 62 ... Pressure roll, 64 ... Temperature-sensitive magnetic member, 80 ... IH heater, 81 ... Support body, 81a ... Support surface, 81b1, 81b2 ... Magnetic core support Part, 81c ... magnetic core regulating part, 82 ... exciting coil, 84 ... magnetic core, 611 ... base material layer, 612 ... conductive heating layer

Claims (13)

A fixing member having a conductive layer and fixing the toner to the recording material by electromagnetic induction heating of the conductive layer;
A magnetic field generating member that generates an alternating magnetic field that intersects the conductive layer of the fixing member;
An inner peripheral surface facing the magnetic field generating member is formed in an arc shape in the moving direction of the fixing member, and forms a magnetic path of an alternating magnetic field generated by the magnetic field generating member; and
A position setting surface that is formed in an arc shape toward the moving direction of the fixing member, sets the magnetic field generating member at a position having a predetermined gap from the fixing member, and the magnetic path forming member is the position setting surface. A position setting member having a position setting unit that sets a position having a predetermined gap;
The position setting unit of the position setting member, along said direction orthogonal to the moving direction of the fixing member is composed of a pair of convex portions which are arranged parallel to Rutotomoni, the pair of convex portions, the magnetic The height from the position setting surface of the portion that supports the path forming member is formed to be the same, and is disposed at a position that is symmetric with respect to the intersecting line between the central axis of the magnetic field generating member and the position setting surface ,
The fixing device according to claim 1, wherein the magnetic path forming member is supported so as to be movable forward and backward along the position setting surface in the moving direction of the fixing member.   The magnetic path forming member is configured to cover a region of the position setting member where the magnetic field generating member is disposed, and the position setting member is provided on both sides of the fixing member in the moving direction by the position setting unit. The fixing device according to claim 1, further comprising a restricting portion that restricts movement of the supported magnetic path forming member.   The fixing device according to claim 1, wherein the magnetic path forming member is formed in an arc shape in which a region supported by the position setting portion on the inner peripheral surface is concentric with the position setting surface.   An elastic support member that elastically deforms and supports the magnetic field generation member on the position setting surface while pressing the magnetic field generation member toward the position setting surface between the magnetic field generation member and the magnetic path forming member. The fixing device according to claim 1, further comprising:   A magnetic path of an alternating magnetic field generated by the magnetic field generation member is formed in a temperature range up to a magnetic permeability change start temperature at which the magnetic permeability starts to decrease. The fixing device according to claim 1, further comprising a second magnetic path forming member that transmits an alternating magnetic field generated by the magnetic field generating member in a temperature range that exceeds the permeability change start temperature. . Toner image forming means for forming a toner image;
Transfer means for transferring the toner image formed by the toner image forming means onto a recording material;
Fixing means for fixing the toner image transferred onto the recording material to the recording material;
The fixing means is
A fixing member having a conductive layer and fixing the toner to the recording material by electromagnetic induction heating of the conductive layer;
A magnetic field generating member that generates an alternating magnetic field that intersects the conductive layer of the fixing member;
An inner peripheral surface facing the magnetic field generating member is formed in an arc shape in the moving direction of the fixing member, and forms a magnetic path of an alternating magnetic field generated by the magnetic field generating member; and
A position setting surface that is formed in an arc shape toward the moving direction of the fixing member, sets the magnetic field generating member at a position having a predetermined gap from the fixing member, and the magnetic path forming member is the position setting surface. A position setting member having a position setting unit that sets a position having a predetermined gap;
The position setting unit of the position setting member, along said direction orthogonal to the moving direction of the fixing member is composed of a pair of convex portions which are arranged parallel to Rutotomoni, the pair of convex portions, the magnetic The height from the position setting surface of the portion that supports the path forming member is formed to be the same, and is disposed at a position that is symmetric with respect to the intersecting line between the central axis of the magnetic field generating member and the position setting surface ,
The image forming apparatus, wherein the magnetic path forming member is supported so as to be movable forward and backward along the position setting surface in the moving direction of the fixing member. The magnetic path forming member of the fixing unit is configured to cover a region where the magnetic field generating member is disposed in the position setting member,
The position setting member of the fixing unit further includes a restricting portion that restricts movement of the magnetic path forming member supported by the position setting portion on both sides in the moving direction of the fixing member. 6. The image forming apparatus according to 6 . Wherein said magnetic path forming member of the fixing means, according to claim 6, wherein the area to be supported by the position setting part of the inner peripheral surface is formed in an arc shape which is the position setting surface concentric Image forming apparatus. An elastic support member that elastically deforms and supports the magnetic field generation member on the position setting surface while pressing the magnetic field generation member toward the position setting surface between the magnetic field generation member and the magnetic path forming member. The image forming apparatus according to claim 6, further comprising: The fixing unit is disposed opposite to the magnetic field generating member with the fixing member interposed therebetween, and an AC magnetic field generated by the magnetic field generating member in a temperature range up to a magnetic permeability change starting temperature at which the magnetic permeability starts decreasing. And a second magnetic path forming member that transmits an alternating magnetic field generated by the magnetic field generating member in a temperature range exceeding the permeability change start temperature. 6. The image forming apparatus according to 6 . 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 electromagnetically heating the conductive layer;
An inner peripheral surface facing the magnetic field generating member is formed in an arc shape in the moving direction of the fixing member, and forms a magnetic path of an alternating magnetic field generated by the magnetic field generating member; and
A position setting surface that is formed in an arc shape toward the moving direction of the fixing member, sets the magnetic field generating member at a position having a predetermined gap from the fixing member, and the magnetic path forming member is the position setting surface. A position setting member having a position setting unit that sets a position having a predetermined gap;
The position setting unit of the position setting member, along said direction orthogonal to the moving direction of the fixing member is composed of a pair of convex portions which are arranged parallel to Rutotomoni, the pair of convex portions, the magnetic The height from the position setting surface of the portion that supports the path forming member is formed to be the same, and is disposed at a position that is symmetric with respect to the intersecting line between the central axis of the magnetic field generating member and the position setting surface ,
The magnetic field generation device, wherein the magnetic path forming member is supported so as to be movable forward and backward along the position setting surface in the moving direction of the fixing member. The magnetic path forming member is configured to cover a region of the position setting member where the magnetic field generating member is disposed, and the position setting member is supported by the position setting unit on both sides in the moving direction of the fixing member. The magnetic field generation apparatus according to claim 11 , further comprising a restriction unit that restricts movement of the magnetic path forming member. The magnetic field generation device according to claim 11 , wherein the magnetic path forming member is formed in an arc shape in which a region supported by the position setting portion on the inner peripheral surface is concentric with the position setting surface.

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