JP2010197737A - Fixing device, image forming apparatus, and magnetic field generating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a fixing device of an electromagnetic induction heating system, wherein the resistance and inductance of an electric circuit system for generating an AC magnetic field can be adjusted. <P>SOLUTION: A plurality of magnetic cores 84, which are arranged along a width direction of a fixing belt and form a magnetic of an AC magnetic field generated by an excitation coil 82, are supported by a support member 81 so as to be freely moved in the width direction of the fixing belt, and each of the plurality of magnetic cores 84 movably supported by the support member 81 is set and fixed to a predetermined position in the width direction of the fixing belt by a magnetic core-setting member 87. <P>COPYRIGHT: (C)2010,JPO&INPIT

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 electromagnetic induction heating type fixing device that directly heats the fixing roll is described.

JP 2003-186322 A

Here, in general, an electromagnetic induction heating type fixing device is designed to correspond to an image forming apparatus on which the size, arrangement position, mutual positional relationship, and the like of components constituting the fixing device are mounted. Therefore, the resistance and inductance of the electric circuit system for generating an alternating magnetic field are also different for different fixing devices. Accordingly, for example, a power source that supplies power to the electric circuit system is designed according to the configuration of the fixing device, and it is difficult to achieve compatibility of the power sources between fixing devices having different configurations.
An object of the present invention is to realize an electromagnetic induction heating type fixing device capable of adjusting the resistance and inductance of an electric circuit system for generating an alternating magnetic field.

  According to the first aspect of the present invention, there is provided a fixing member that has a conductive layer, the toner is fixed to the recording material by electromagnetically heating the conductive layer, and an alternating magnetic field that intersects the conductive layer of the fixing member. A magnetic field generating member to be generated; a plurality of magnetic path forming members that are arranged along a width direction of the fixing member and that form a magnetic path of an alternating magnetic field generated by the magnetic field generating member; and a plurality of the magnetic path forming members. A support member that is movably supported in the fixing member width direction and a plurality of the magnetic path forming members that are movably supported by the support member are set at predetermined positions in the width direction of the fixing member. A fixing device including a position setting member to be fixed.

According to a second aspect of the present invention, there is further provided an adjusting magnetic member that is arranged in a plurality along the width direction of the fixing member and adjusts an alternating magnetic field generated by the magnetic field generating member so as to equalize the fixing member width direction. The support member supports the adjustment magnetic member so as to be movable in the fixing member width direction, and the position setting member predetermines each of the adjustment magnetic members supported so as to be movable by the support member. The fixing device according to claim 1, wherein the fixing device is set and fixed at a position in a width direction of the fixing member.
According to a third aspect of the present invention, the support member includes a position setting surface for setting the magnetic field generating member at a position having a predetermined gap with the fixing member, and the magnetic path forming member with the position setting surface in advance. A position setting portion that is movably supported in the fixing member width direction while being set at a position having a predetermined gap, and the position setting portion of the support member is in a direction orthogonal to the movement direction of the fixing member. And a pair of convex portions arranged in parallel along the position, and further supports the magnetic path forming member movably back and forth in the moving direction of the fixing member along the position setting surface. The fixing device according to 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 support member 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 surface of the member.
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 plurality of magnetic field generating members for generating an alternating magnetic field intersecting the conductive layer of the fixing member, and a plurality of magnetic field generating members arranged along the width direction of the fixing member to form a magnetic path of the alternating magnetic field generated by the magnetic field generating member. Each of a magnetic path forming member, a support member that supports the plurality of magnetic path forming members movably in the fixing member width direction, and a plurality of the magnetic path forming members supported movably by the support member. Of the fixing member determined in advance. An image forming apparatus characterized by comprising a position setting member for fixing set direction position.

According to a seventh aspect of the present invention, a plurality of the fixing units are arranged along the width direction of the fixing member, and the AC magnetic field generated by the magnetic field generating member is adjusted so as to equalize in the fixing member width direction. The fixing member further includes an adjustment magnetic member, the support member of the fixing unit supports the adjustment magnetic member so as to be movable in the fixing member width direction, and the position setting member of the fixing unit is movable by the support member. The image forming apparatus according to claim 6, wherein each of the adjusting magnetic members supported by the fixing member is set and fixed at a predetermined position in the width direction of the fixing member.
According to an eighth aspect of the present invention, the support member of the fixing unit includes a position setting surface for setting the magnetic field generating member at a position having a predetermined gap from the fixing member, and the magnetic path forming member at the position. A position setting unit that supports the setting surface and a position having a predetermined gap so as to be movable in the fixing member width direction, and the position setting unit of the support member has a moving direction of the fixing member. It is composed of a pair of convex portions arranged in parallel along a direction orthogonal to each other, and further supports the magnetic path forming member movably back and forth in the moving direction of the fixing member along the position setting surface. The image forming apparatus according to claim 6.
According to a ninth aspect of the present invention, the fixing unit elastically deforms the magnetic field between the magnetic field generating member and the magnetic path forming member while pressing the magnetic field generating member toward the support member surface. 7. The image forming apparatus according to claim 6, further comprising an elastic support member for supporting the generating member on the surface of the support member.
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 the fixing member that fixes the toner to the recording material by electromagnetic induction heating. A plurality of magnetic path forming members arranged along the width direction of the fixing member and forming a magnetic path of an alternating magnetic field generated by the magnetic field generating member; and a plurality of the magnetic path forming members arranged in the fixing member width direction. And a position setting member for setting and fixing each of the plurality of magnetic path forming members movably supported by the support member at a predetermined position in the width direction of the fixing member. And a magnetic field generating device.

According to a twelfth aspect of the present invention, there is further provided an adjusting magnetic member that is arranged in a plurality along the width direction of the fixing member and adjusts an alternating magnetic field generated by the magnetic field generating member so as to equalize the fixing member width direction. The support member supports the adjustment magnetic member so as to be movable in the fixing member width direction, and the position setting member predetermines each of the adjustment magnetic members supported so as to be movable by the support member. 12. The magnetic field generating apparatus according to claim 11, wherein the fixing member is set and fixed at a position in a width direction of the fixing member.
According to a thirteenth aspect of the present invention, the support member has a position setting surface for setting the magnetic field generating member at a position having a predetermined gap from the fixing member, and the magnetic path forming member is connected to the position setting surface in advance A position setting portion that is movably supported in the fixing member width direction while being set at a position having a predetermined gap, and the position setting portion of the support member is in a direction orthogonal to the movement direction of the fixing member. And a pair of convex portions arranged in parallel along the position, and further supports the magnetic path forming member movably back and forth in the moving direction of the fixing member along the position setting surface. 11 is a magnetic field generation device according to 11.

According to the first aspect of the present invention, it is possible to realize an electromagnetic induction heating type fixing device capable of adjusting the resistance and inductance of an electric circuit system for generating an alternating magnetic field.
According to the second aspect of the present invention, compared to the case where the present invention is not adopted, the resistance and inductance of the electric circuit system for generating an alternating magnetic field between the fixing devices having different configurations are approximated, and the electric circuit system is supplied with electric power. Compatibility of power supply sources to be supplied can be achieved.
According to the third aspect of the present invention, even when the dimensional accuracy of the magnetic path forming member is relaxed, the magnetic field generating member and the magnetic path forming member, and further, between the magnetic field generating member and the fixing member are compared with the case where the present invention is not adopted. The positional accuracy is improved, and the approximate accuracy of resistance and inductance can be increased between fixing devices having different configurations.
According to the fourth aspect of the present invention, compared with the case where the present invention is not adopted, the occurrence of misalignment in the magnetic field generating member is suppressed, and the approximate accuracy of resistance and inductance between the fixing devices having different configurations can be improved. it can.
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 invention of claim 6, in the electromagnetic induction heating type fixing device mounted on the image forming apparatus, it is possible to realize a configuration in which the resistance and inductance of the electric circuit system for generating the alternating magnetic field can be adjusted.
According to the seventh aspect of the invention, the compatibility of the power supply source for supplying power to the electric circuit system by approximating the resistance and inductance of the electric circuit system for generating an alternating magnetic field between fixing devices having different configurations is provided. Can be planned.
According to the eighth aspect of the present invention, even when the dimensional accuracy of the magnetic path forming member is relaxed, the magnetic field generating member and the magnetic path forming member, and further, between the magnetic field generating member and the fixing member are compared with the case where the present invention is not adopted. The positional accuracy is improved, and the approximate accuracy of resistance and inductance can be increased between fixing devices having different configurations.
According to the ninth aspect of the present invention, compared to the case where the present invention is not adopted, the occurrence of misalignment in the magnetic field generating member is suppressed, and the approximation accuracy of resistance and inductance between the fixing devices having different configurations can be improved. it can.
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, it is possible to realize a configuration capable of adjusting the resistance and inductance of an electric circuit system for generating an alternating magnetic field in an electromagnetic induction heating type fixing device.
According to the invention of claim 12, the compatibility of the power supply source for supplying power to the electric circuit system by approximating the resistance and inductance of the electric circuit system for generating an alternating magnetic field between the fixing devices having different configurations. Can be planned.
According to the invention of claim 13, compared with the case where the present invention is not adopted, 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 further between the magnetic field generating member and the fixing member, The positional accuracy is improved, and the approximate accuracy of resistance and inductance can be increased between fixing devices having different configurations.

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. It is a perspective view explaining the state which a magnetic core setting member sets the longitudinal direction position of a magnetic core and an adjustment magnetic core. It is a figure which illustrated the tolerance range of the excitation circuit designed according to the dispersion | variation in resistance and inductance in the fixing unit from which a structure differs. It is the figure which showed the structural example of the IH heater. It is the figure which showed the structural example of the IH heater.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
<Description of Image Forming Apparatus>
FIG. 1 is a diagram illustrating a configuration example of an image forming apparatus to which the fixing device of the present embodiment is applied. An image forming apparatus 1 shown in FIG. 1 is a so-called tandem color printer, and includes an image forming unit 10 that forms an image based on image data and a control unit 31 that controls the operation of the entire image forming apparatus 1. Further, for example, a communication unit 32 that receives image data by communicating with a personal computer (PC) 3 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 auxiliary 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. For example, the fixing belt 61 has a diameter of 30 mm and a length in the width direction of 300 mm in the original shape (cylindrical shape). Further, as shown in FIG. 4 (cross-sectional layer configuration diagram of the fixing belt 61), the fixing belt 61 includes a base material layer 611, a conductive heat generating layer 612 laminated on the base material layer 611, and a toner image fixability. The belt member has a multilayer structure including an elastic layer 613 for improving the surface and a surface release layer 614 coated on the uppermost layer.

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

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

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

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

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

<Description of pressing pad>
The pressing pad 63 is 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 1.5 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 increased when the main switch of the image forming apparatus 1 is turned on and the fixing belt 61 is heated to the fixing set temperature. This is to prevent the temperature from flowing into the temperature-sensitive magnetic member 64 and shorten the warm-up time.

Further, the temperature-sensitive magnetic member 64 has a “permeability change start temperature” (see later stage) equal to or higher than a fixing set temperature at which each color toner image melts, and heat resistance of the elastic layer 613 and the surface release layer 614 of the fixing belt 61. It is composed of a material set within a temperature range lower than the temperature. That is, the temperature-sensitive magnetic member 64 is made of a material having a characteristic (“temperature-sensitive magnetism”) that reversibly changes between ferromagnetism and paramagnetism 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 close to the Curie point, which is the temperature at which the substance loses magnetism, but has a different concept from the Curie point.

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

<Description of induction member>
The induction member 66 is formed in an arc shape that follows the inner peripheral surface of the temperature-sensitive magnetic member 64, and has a predetermined gap (for example, 1.0 to 5.0 mm) from the inner peripheral surface of the temperature-sensitive magnetic member 64. Having a non-contact arrangement. The induction member 66 is made of a nonmagnetic metal having a relatively small specific resistance value, such as Ag, Cu, or Al. Then, when the temperature-sensitive magnetic member 64 rises to a temperature equal to or higher than the permeability change start temperature, an alternating magnetic field (line of magnetic force) generated by the IH heater 80 is induced, and the vortex is more vortexed than the conductive heating layer 612 of the fixing belt 61. A state in which the current I is easily generated is formed. Thereby, the thickness of the induction member 66 is a predetermined thickness (for example, 1.0 mm) 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 167. A bearing bearing portion 67c that is freely coupled is provided. Then, as shown in FIG. 2, the support portions 65a at both ends of the holder 65 are fixed to both ends of the casing 69 of the fixing unit 60, whereby the end cap member 67 is coupled to the support portion 65a. It is rotatably supported via the bearing bearing portion 67c.
As a material constituting the end cap member 67, so-called engineering plastics having high mechanical strength and heat resistance are used. For example, phenol resin, polyimide resin, polyamide resin, polyamideimide resin, PEEK resin, PES resin, PPS resin, LCP resin and the like are suitable.

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

Here, when the fixing belt 61 rotates by receiving a driving force directly from the end cap members 67 at both ends, a torque of about 0.1 to 0.5 N · m is generally applied. However, in the fixing belt 61 of the present embodiment, the base material layer 611 is made of, for example, nonmagnetic stainless steel having high mechanical strength. For this reason, even when a torsional torque of about 0.1 to 0.5 N · m acts on the entire fixing belt 61, buckling or the like hardly occurs in the fixing belt 61.
Further, the flange portion 67d of the end cap member 67 suppresses the deviation of the fixing belt 61. In general, the fixing belt 61 at that time is generally 1 to 5 in the axial direction from the end portion (flange portion 67d) side. A compressive force of about 5N works. However, even when the fixing belt 61 receives such a compressive force, since the base material layer 611 of the fixing belt 61 is made of nonmagnetic stainless steel or the like, occurrence of buckling or the like is suppressed.
As described above, the fixing belt 61 according to the present embodiment rotates by receiving a driving force directly from both end portions of the fixing belt 61, and thus stable rotation is performed. At that time, the base material layer 611 of the fixing belt 61 is made of, for example, non-magnetic stainless steel having high mechanical strength, thereby realizing a structure in which buckling or the like hardly occurs against torsion torque or compression force. is doing. Furthermore, since the base material layer 611 and the conductive heat generating layer 612 are formed 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 via the fixing belt 61 with a load of 20 kgf, for example, by a pressing spring 68 (see FIG. 2).

<Description of IH heater>
Next, the IH heater 80 that performs electromagnetic induction heating by applying an AC magnetic field to the conductive heat generating layer 612 of the fixing belt 61 will be described.
FIG. 6 is a cross-sectional view illustrating the configuration of the IH heater 80 of the present embodiment. As shown in FIG. 6, the IH heater 80 includes a support 81 as an example of a support member made of a non-magnetic material such as a heat-resistant resin, and an exciting coil as an example of a magnetic field generating member that generates an alternating magnetic field. 82. 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. Further, an adjustment magnetic core 100 as an example of an adjustment magnetic member that is arranged along the width direction of the fixing belt 61 and that equalizes the AC magnetic field generated by the excitation coil 82 in the longitudinal direction of the support 81, a magnetic core 84 and a magnetic core setting member 87 as an example of a position setting member for setting the position of the adjustment magnetic core 100 in the longitudinal direction of the support 81. Furthermore, a shield 85 that shields the magnetic field, a pressurizing member 86 that pressurizes the magnetic core 84 toward the support 81 side, and an excitation circuit 88 as an example of a power supply source that supplies an alternating current (electric power) to the excitation coil 82 are provided. Yes.

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 5 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 81b1 and 81b2 support the gap between the magnetic core 84 and the support surface 81a so as to keep constant. The magnetic core support portions 81b1 and 81b2 are formed with spaces in which the adjustment magnetic core 100 is disposed in the inner region.
Further, on both sides of the support surface 81a, there are arranged magnetic core restricting portions 81c for restricting movement of the magnetic core 84 supported by the magnetic core supporting portions 81b1 and 81b2 in the moving direction (arc direction) of the fixing belt 61.
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, which are bundled with, for example, 90 copper wires having a diameter of 0.17 mm and wound in a closed loop with a hollow shape such as an ellipse, an ellipse, or a rectangle. . Then, when an alternating current having a predetermined frequency is supplied to the exciting coil 82 from the exciting circuit 88, an alternating magnetic field centered around a litz wire wound in a closed loop is generated around the exciting coil 82. . Generally, the frequency of the alternating current supplied from the excitation circuit 88 to the excitation coil 82 is 20 k to 100 kHz generated by the general-purpose power source.
The elastic support member 83 is a sheet-like member made of an elastic body such as silicone rubber or fluorine rubber. The elastic support member 83 is set to press the excitation coil 82 against the support 81 so that the excitation coil 82 is fixed in close contact with the support surface 81a of the support 81.

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

Here, the magnetic core 84 is preferably made of a material having a small loss due to magnetic path formation. Specifically, the magnetic core 84 is desirably used in a form that reduces the eddy current loss (current path interruption or division by slits, thin plate bundling, etc.), and is preferably formed of a material having a small hysteresis loss.
Further, the length of the magnetic core 84 along the rotation direction of the fixing belt 61 is configured to be smaller than the length of the temperature-sensitive magnetic member 64 along the rotation direction of the fixing belt 61. Thereby, the leakage of magnetic lines of force to the periphery of the IH heater 80 is reduced, and the power factor is improved. Furthermore, electromagnetic induction to the metal member constituting the fixing unit is suppressed, and the heat generation efficiency in the fixing belt 61 (conductive heat generation layer 612) is increased.
The magnetic core 84 is supported by a pair of magnetic core support portions (convex portions) 81b1 and 81b2 disposed at the center of the support surface 81a, and the position of the support 81 in the longitudinal direction is set by the magnetic core setting member 87.

  The adjustment magnetic core 100 has a rectangular parallelepiped shape (block shape) made of a high permeability oxide or alloy material such as sintered ferrite, ferrite resin, amorphous alloy (amorphous alloy), permalloy, and magnetic shunt steel, for example. A ferromagnetic material is used. The adjusting magnetic core 100 is an adjusting magnetic member for equalizing the strength of the magnetic field in the longitudinal direction of the support 81 with respect to the AC magnetic field formed by the magnetic core 84 and the temperature-sensitive magnetic member 64 disposed around the exciting coil 82. Function as. By averaging the strength of the magnetic field generated in the longitudinal direction of the support 81, temperature unevenness in the width direction of the fixing belt 61 is reduced. The adjusting magnetic core 100 is disposed in a space formed in the inner region of the magnetic core support portions 81b1 and 81b2 (region surrounded by the inner walls of the magnetic core support portions 81b1 and 81b2), and the position in the longitudinal direction of the support 81 is a magnetic core setting member 87. Is set by

<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 heat generating layer 612 in the thickness direction, the magnetic field in the temperature-sensitive magnetic member 64 is increased. It is radiated toward the magnetic core 84 in a concentrated manner from the lower part. Therefore, the magnetic force lines H that cross the conductive heat generating layer 612 of the fixing belt 61 in the thickness direction are concentrated from the temperature-sensitive magnetic member 64 toward the magnetic core 84, and the magnetic flux density in the region R3 is also increased.

In the conductive heating layer 612 of the fixing belt 61 where the magnetic lines H cross in the thickness direction, an eddy current I proportional to the amount of change in the number of magnetic lines H per unit area (magnetic flux density) is generated. Thereby, as shown in FIG. 7, a large eddy current I is generated in the regions R1, R2 and R3 where the amount of change in magnetic flux density is large. The eddy current I generated in the conductive heat generation layer 612 generates Joule heat W (W = I ² R), which is the product of the specific resistance value R of the conductive heat generation layer 612 and the square of the eddy current I. Thereby, a large Joule heat W is generated in the conductive heat generating layer 612 where the large eddy current I is generated.
As described above, when the temperature of the fixing belt 61 is in the temperature range equal to or lower than the permeability change start temperature, large heat is generated in the regions R1 and R2 and the region R3 where the lines of magnetic force H cross the conductive heat generating layer 612. Thereby, the fixing belt 61 is heated.

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

<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, 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 magnetic member 64 and thus diffuse radially. As a result, the magnetic flux density (number of magnetic force lines H per unit area) of the magnetic field lines H crossing the conductive heat generating layer 612 of the fixing belt 61 in the thickness direction decreases. Further, even in the region R3 that crosses the conductive heat generating layer 612 in the thickness direction when the magnetic force line H returns to the magnetic core 84 again, the magnetic force line H returns to the magnetic core 84 from the diffused wide region. The magnetic flux density of the magnetic field lines H crossing 612 in the thickness direction decreases.
Therefore, when the temperature of the fixing belt 61 is in a temperature range exceeding the permeability change start temperature, the magnetic flux density of the magnetic field lines H 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. Therefore, for example, when a large amount of image formation is continuously performed, heat is accumulated in the temperature-sensitive magnetic member 64, and the temperature of the temperature-sensitive magnetic member 64 tends to increase even in the paper passing area (see FIG. 8). Presents. As a result, if the temperature-sensitive magnetic member 64 that has large eddy current loss and hysteresis loss and easily generates heat due to the passage of the magnetic field lines H is used, depending on the situation, even if the temperature of the fixing belt 61 does not exceed the magnetic permeability change start temperature, In some cases, the temperature-sensitive magnetic member 64 functions to suppress the temperature increase of the fixing belt 61 in the sheet passing region. 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 64s that divide the flow of the eddy current I generated by the lines of magnetic force H (see FIG. 10). Even if the material and thickness of the temperature-sensitive magnetic member 64 are selected so that induction heating is difficult, it is difficult to set the eddy current I generated in the temperature-sensitive magnetic member 64 to zero. Therefore, by dividing the flow of the eddy current I generated in the temperature-sensitive magnetic member 64 by the plurality of slits 64s, the eddy current I is reduced and the Joule heat W generated in the temperature-sensitive magnetic member 64 is kept low. .

  FIG. 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 magnetic field lines 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. Thereby, when the slit 64s is formed, the eddy current I flowing through the temperature-sensitive magnetic member 64 (solid line in FIG. 10 (b)) 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, magnetic core and adjusting magnetic core in IH heater>
Next, a method for fixing the exciting coil 82, the magnetic core 84, and the adjusting magnetic core 100 to the support 81 in the IH heater 80 of the present embodiment will be described.
FIG. 11 is a diagram for explaining a laminated structure of the IH heater 80 of the present embodiment. As shown in FIG. 11, in the exciting coil 82, the closed-loop hollow portion 82a of the exciting coil 82 is on the support surface 81a of the support 81 as an example of a support member, and the longitudinal center axis (axis) of the support surface 81a. 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 formed / set to a specified value (design value). Then, the exciting coil 82 is pressed against the support surface 81a of the support 81 by the elastic support member 83, thereby being closely attached and fixed to the support surface 81a.

  Further, each of the plurality of magnetic cores 84 arranged along the width direction of the fixing belt 61 is formed as an inner circumferential side arc surface 84b whose inner circumferential surface on the exciting coil 82 side is arc-shaped toward the moving direction of the fixing belt 61. Has been. In addition, the inner circumferential arc surface 84b of the magnetic core 84 is formed with such a length that the moving direction of the fixing belt 61 covers (wraps) the entire region where the exciting coil 82 is disposed. Each of the magnetic cores 84 is supported by the inner circumferential arc surface 84b of the magnetic core 84 supported by a pair of magnetic core support portions 81b1 and 81b2 disposed in parallel along the longitudinal central axis axis on the support surface 81a. The gap between the magnetic core 84 and the support surface 81a is set to be constant. Further, at that time, the magnetic core 84 is positioned along the moving direction of the fixing belt 61 on the magnetic core supporting portions 81b1 and 81b2 between the magnetic core restricting portions 81c arranged on both sides of the supporting surface 81a in the moving direction of the fixing belt 61. It is supported movably. The magnetic core 84 is supported on the magnetic core support portions 81b1 and 81b2 so as to be movable in the longitudinal direction of the support 81 (= the width direction of the fixing belt 61).

Here, the elastic support member 83 is made of a sheet-like elastic body such as silicone rubber or fluorine rubber having a low Young's modulus, and is disposed between the exciting coil 82 and the magnetic core 84. On the other hand, in the magnetic core 84, when the inner circumferential arc surface 84b is supported by the pair of magnetic core support portions 81b1 and 81b2 on the support surface 81a, the gap between the magnetic core 84 and the support surface 81a is set to a predetermined gap. (See also FIG. 6). In this case, the elastic support member 83 is formed thicker than the gap between the magnetic core 84 and the support surface 81a. On the other hand, each magnetic core 84 is pressed to the support 81 side via the magnetic core setting member 87 by the pressing member 86 provided on the lower surface of the shield 85 by attaching the shield 85 to the support 81. Therefore, the elastic support member 83 is elastically deformed (compressed) by receiving pressure applied to the support body 81 via the magnetic core 84, and presses the exciting coil 82 toward the support surface 81a by the elastic force generated thereby. In this way, the elastic support member 83 fixes the exciting coil 82 in close contact with the support surface 81a. Since the support surface 81a is formed / set so as to maintain a predetermined gap (design value) with the surface of the fixing belt 61, the exciting coil 82 has the entire exciting coil 82 and the predetermined gap with the surface of the fixing belt 61. Is set to keep.
As the pressure member 86, for example, an elastic member such as a spring may be used in addition to an elastic body such as silicone rubber or fluorine rubber.

  Subsequently, each of the plurality of magnetic cores 84 arranged along the width direction of the fixing belt 61 has an inner peripheral arcuate surface 84b installed and supported on the pair of magnetic core support portions 81b1 and 81b2, and then the magnetic core setting member 87. The position in the longitudinal direction of the support 81 is fixed. The magnetic core setting member 87 is pressed from the upper side toward the support 81 side by a pressing member 86 provided on the lower surface of the shield 85. Thereby, the magnetic core setting member 87 presses each magnetic core 84 toward the support body 81 side, and its position in the longitudinal direction of the support body 81 is fixed. As a result, each magnetic core 84 is pressed so as to be sandwiched between the pressure member 86 on the upper surface and the elastic support member 83 on the lower surface via the magnetic core setting member 87, so that the vertical direction is changed inside the IH heater 80. Fixed. Further, each magnetic core 84 in a state of being supported by the magnetic core setting member 87 pressurized from the upper side by the pressurizing member 86 movably in the longitudinal direction of the support body 81 on the pair of magnetic core support portions 81b1 and 81b2, The position in the longitudinal direction of the support 81 is fixed. The fixing method related to the position in the longitudinal direction of the support 81 for each magnetic core 84 will be described in detail later.

Further, each of the plurality of adjusting magnetic cores 100 arranged along the width direction of the fixing belt 61 is formed in a rectangular parallelepiped shape (block shape), and is arranged in a space formed in an inner region of the magnetic core support portions 81b1 and 81b2. The As a result, the position of the adjustment magnetic core 100 inside the IH heater 80 is set.
Each of the adjustment magnetic cores 100 is supported so as to be movable in the longitudinal direction of the support 81 (= the width direction of the fixing belt 61) when installed in the inner region of the magnetic core support portions 81b1 and 81b2. By installing the magnetic core setting member 87, the position of the adjustment core 100 in the longitudinal direction of the support 81 is set and fixed by the magnetic core setting member 87 together with each of the magnetic cores 84. The fixing method related to the position in the longitudinal direction of the support 81 for each adjustment magnetic core 100 will also be described in detail later.

  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 closely_contact | adheres to is 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, the plurality of magnetic cores 84 provided by being divided along the longitudinal direction of the excitation coil 82 presses the elastic support member 83 uniformly over the longitudinal direction. Thereby, the adhesiveness of the exciting coil 82 and the support surface 81a is improved over the longitudinal direction.
In addition, 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 to be 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 equally distributed between the front and back of the direction.

  On the other hand, the inner circumferential arc surface 84b of each magnetic core 84 has the same center 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 ( The support surface 81a is formed on a circle (cir2) in which a predetermined gap g2 is set.

  As a result, the inner circumferential arc surface 84b of each magnetic core 84 is separated from the support surface 81a by a gap g2 regardless of which position in the moving direction (arc direction) of the fixing belt 61 is supported by the pair of magnetic core support portions 81b1 and 81b2. Is set. That is, the inner circumferential arc surface 84b of each magnetic core 84 is configured as a part of a circle (cir2) passing through the vertex b1 of the outer wall of the magnetic core support portion 81b1 and the vertex b2 of the outer wall of the magnetic core support portion 81b2. The circle (cir2) is concentric with the support surface 81a (= cir1). Therefore, even if any position of the inner circumferential side arc surface 84b is supported by the pair of magnetic core support portions 81b1 and 81b2, the inner circumferential side arc surface 84b and the circle cil2 coincide with each other. A gap g2 is set between the surface 84b and the support surface 81a.

By the way, the ferrite constituting the magnetic core 84 is generally a material whose shape tends to vary due to the heat treatment after molding, and it is difficult to improve 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. However, the positional relationship between the magnetic core 84 and the exciting coil 82 greatly affects the AC magnetic field output from the IH heater 80. According to the experiment, for example, when the gap between the magnetic core 84 and the exciting coil 82 varies by 0.5 mm, the resistance (R) and inductance (L) of the electric circuit system constituted by the exciting coil 82 and the exciting circuit 88 are 10 % Changes. For this reason, when the positional accuracy between the magnetic core 84 and the exciting coil 82 is lowered, as in the case of the positional accuracy between the exciting coil 82 and the support 81 described above, a partial variation occurs in the amount of heat generated on the surface of the fixing belt 61. .
On the other hand, even if it is not possible to improve the dimensional accuracy of all the elements that determine the shape of the magnetic core 84 such as the length and thickness of the magnetic core 84, the inner circumferential arc that is a part of the magnetic core 84 can be obtained. It is possible to form only the surface 84b with high accuracy. Therefore, in the present embodiment, the position accuracy of the magnetic core 84 and the exciting coil 82 is increased by the above-described configuration using the inner circumferential arc surface 84b as the reference position of the magnetic core 84 and the inner circumferential arc surface 84b. .

  At this time, the inner circumferential arc surface 84b of the magnetic core 84 covers the entire region in which the length of the fixing belt 61 in the moving direction (see FIG. 12) is arranged with respect to the moving direction of the fixing belt 61. It is formed to wrap. If a region located outside the inner peripheral arcuate surface 84b 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 AC magnetic field generated by the exciting coil 82. The number of magnetic fluxes generated and induced inside the magnetic core 84 decreases. In that case, the heat generation efficiency in the fixing belt 61 (conductive heat generation layer 612) is lowered. Therefore, the length length of the inner circumferential arc surface 84b is formed so as to cover the entire arrangement region of the exciting coil 82.

  At this time, it is difficult to obtain high dimensional accuracy for the length length of the magnetic core 84 for the reason described above. However, each magnetic core 84 is longer than the length covering the entire region where the exciting coil 82 is disposed, and is longer than the length between the magnetic core restricting portions 81c disposed on both sides of the support surface 81a in the moving direction of the fixing belt 61. The dimensional accuracy in a relatively wide range of small can be easily realized. As a result, the length length of the magnetic core 84 is not less than the length covering the entire region where the exciting coil 82 is disposed and is smaller than the length between the magnetic core restricting portions 81c disposed on the support surface 81a. The magnetic core 84 is manufactured with the dimensional accuracy of The magnetic core 84 is movable along the moving direction of the fixing belt 61 between the magnetic core restricting portions 81c as an example of the restricting portions disposed on both sides of the support surface 81a by the pair of magnetic core supporting portions 81b1 and 81b2. To support.

Thereby, even if the dimensional accuracy of the length length of the magnetic core 84 is set in a relatively wide range, the magnetic core 84 is installed in a region sandwiched between the magnetic core restricting portions 81c disposed on the support surface 81a. The Then, the length length of the magnetic core 84 varies within a relatively wide range of dimensional accuracy, and any position of the inner circumferential arc surface 84b of each magnetic core 84 is supported by the pair of magnetic core support portions 81b1 and 81b2. As described above, the gap g2 is set between the inner circumferential arc surface 84b and the support surface 81a. Furthermore, the magnetic core 84 is installed so as to cover the entire arrangement region of the exciting coil 82.
As a result, the positional accuracy between the magnetic core 84 and the exciting coil 82 is increased, and the alternating magnetic field generated by the exciting coil 82 is efficiently induced inside the magnetic core 84. Further, since the positional accuracy between the magnetic core 84 and the exciting coil 82 is increased, the magnetic core 84 uniformly presses the elastic support member 83 in the longitudinal direction, so that the adhesion between the exciting coil 82 and the support surface 81a is longitudinal. It is further increased over time.
On the other hand, when the length 84 of the magnetic core 84 varies within the range of the length between the magnetic core restricting portions 81c, the magnetic core 84 is arranged at any position in the moving direction (arc direction) of the fixing belt 61. Even so, the positions of the regions R1 and R2 shown in FIG. 7 where the fixing belt 61 (conductive heat generating layer 612) is heated are only slightly moved in the arc direction. Therefore, there is little influence on the heat generation efficiency of the conductive heat generation layer 612.

<Description of Setting Method of Longitudinal Position of Magnetic Core and Adjustment Magnetic Core in IH Heater>
Next, a setting method related to the longitudinal position of the support body 81 of the magnetic core 84 and the adjustment magnetic core 100 in the IH heater 80 of the present embodiment will be described.
As described above, the position of the magnetic core 84 and the adjustment magnetic core 100 in the layer direction with respect to the exciting coil 82 is set by the support 81 (a pair of magnetic core support portions 81b1 and 81b2) as an example of a support member. On the other hand, when the magnetic core 84 is installed on the outer wall of the magnetic core support portion 81b1 and the outer wall of the magnetic core support portion 81b2, it is supported movably in the longitudinal direction of the support body 81. Similarly, when the adjustment magnetic core 100 is installed in the inner region of the magnetic core support portions 81b1 and 81b2 (the region surrounded by the inner wall of the magnetic core support portion 81b1 and the inner wall of the magnetic core support portion 81b2), the length of the support body 81 is increased. It is supported movably in the direction. For the magnetic core 84 and the adjustment magnetic core 100 that are supported movably in the longitudinal direction of the support 81, a magnetic core setting member 87 as an example of a position setting member sets and fixes the position in the longitudinal direction of the support 81. To do. That is, in a state where the magnetic core 84 and the adjustment magnetic core 100 are installed on the magnetic core support portions 81 b 1 and 81 b 2, the magnetic core 84 and the adjustment magnetic core 100 can freely move in the longitudinal direction, and the longitudinal position provided on the magnetic core setting member 87. The longitudinal positions of the magnetic core 84 and the adjusting magnetic core 100 are fixed to the arrangement position of the longitudinal position setting section according to the arrangement configuration of the setting section.

FIG. 13 is a perspective view illustrating a state in which the magnetic core setting member 87 sets the longitudinal positions of the magnetic core 84 and the adjustment magnetic core 100. As shown in FIG. 13, the magnetic core 84 is installed on the support 81 having the excitation coil 82 installed on the support surface 81 a with the elastic support member 83 interposed therebetween. Each magnetic core 84 is supported on the outer wall of the magnetic core support portions 81b1 and 81b2. At this stage, a member that restricts the movement of each magnetic core 84 in the longitudinal direction of the support 81 (solid arrow in the figure) is provided on the support 81. It is not done. Therefore, the magnetic core 84 is supported by the outer walls of the magnetic core support portions 81b1 and 81b2 in a state where it can freely move in the longitudinal direction.
Further, the adjustment magnetic core 100 is supported on the inner walls of the magnetic core support portions 81b1 and 81b2. At this stage, the member that regulates the movement of each adjustment magnetic core 100 in the longitudinal direction of the support 81 (solid arrow in the figure). Is not provided on the support 81. Therefore, the adjustment magnetic core 100 is supported on the inner walls of the magnetic core support portions 81b1 and 81b2 in a state where it can freely move in the longitudinal direction.

In this state, the magnetic core setting member 87 is installed from above the magnetic core 84 and the adjustment magnetic core 100 (broken arrows in the figure). A first longitudinal position setting portion 87a that defines the longitudinal position of the magnetic core 84 and a longitudinal position of the adjusting magnetic core 100 are defined on the lower surface of the magnetic core setting member 87 (the surface on the support 81 side). The two longitudinal direction position setting portions 87b are arranged in correspondence with the plurality of magnetic cores 84 and the plurality of adjustment magnetic cores 100 arranged in the IH heater 80, respectively.
Thereby, when the magnetic core setting member 87 is installed, each magnetic core 84 is set to a position where the longitudinal direction position is predetermined by the first longitudinal direction position setting portion 87a. Similarly, each of the adjustment magnetic cores 100 is set at a predetermined position in the longitudinal direction by the second longitudinal position setting unit 87b.
That is, by selecting the arrangement positions of the first longitudinal position setting portion 87a and the second longitudinal position setting portion 87b disposed on the magnetic core setting member 87, the longitudinal direction of each magnetic core 84 and each adjustment magnetic core 100 is selected. The position is not restricted by the support 81 and can be set freely. Furthermore, the number of each magnetic core 84 and each adjustment magnetic core 100 can be increased or decreased.

  In general, for example, the positional relationship between the components such as the fixing belt 61 and the exciting coil 82 and the arrangement position of the components such as the fixing belt 61 and the temperature-sensitive magnetic member 64 are allowed by design tolerances (allowable). Variation in manufacturing range). Accordingly, the resistance (R) and inductance (L) of the electric circuit system configured by the exciting coil 82 and the exciting circuit 88 have different variation regions corresponding to the configuration of the fixing unit 60. Therefore, when designing the excitation circuit 88 that supplies driving power to the excitation coil 82, circuit elements such as transistors that constitute the excitation circuit 88 in accordance with variations in resistance (R) and inductance (L) of the electric circuit system. The excitation circuit 88 is designed on the assumption of the withstand voltage and the short-circuit current. Therefore, normally, the excitation circuit 88 having different specifications is designed for each configuration of the fixing unit 60.

FIG. 14 is a diagram illustrating a tolerance range of the excitation circuit 88 designed in accordance with variations in resistance (R) and inductance (L) in the fixing unit 60 having different configurations.
As shown in FIG. 14, in the fixing unit 60 of type A, the excitation circuit having specifications corresponding to the range of resistance R variation from R_Amax to R_Amin and the range of inductance L variation from L_Amax to L_Amin. 88 is designed. In the type B fixing unit 60, the excitation circuit 88 having a specification corresponding to the variation range of the resistance R from R_Bmax to R_Bmin and the variation range of the inductance L from L_Bmax to L_Bmin is designed.
However, the excitation circuits 88 corresponding to the type A fixing unit 60 and the type B fixing unit 60 are not compatible because their specifications are different from each other. Further, the cost for designing and manufacturing the excitation circuit 88 having different specifications also increases.

Therefore, in the IH heater 80 of the present embodiment, the longitudinal direction of each magnetic core 84 and each adjustment magnetic core 100 is such that the variation range of the resistance R and the variation range of the inductance L are approximated to the fixing unit 60 having a different configuration. The positions are set freely, and further, the positions are set by increasing / decreasing the numbers of the magnetic cores 84 and the adjustment magnetic cores 100.
By changing the longitudinal position and number of each magnetic core 84 and each adjustment magnetic core 100, the resistance R and inductance L of the electric circuit system constituted by the excitation coil 82 and the excitation circuit 88 are adjusted. Therefore, if the longitudinal positions and the numbers of the magnetic cores 84 and the adjustment magnetic cores 100 of one or both of the fixing units 60 are changed so as to approximate the resistance R and the inductance L in the fixing units 60 having different configurations, excitation is performed. Mutual compatibility of the circuits 88 is achieved. For example, the variation range of the resistance R and the variation range of the inductance L in the fixing unit 60 of type B in FIG. 14 are made close to the variation range of the resistance R and the variation range of the inductance L in the fixing unit 60 of type A. If the longitudinal positions and the numbers of the magnetic cores 84 and the adjustment magnetic cores 100 are set, the excitation circuit 88 designed for the type A fixing unit 60 can be used in the type B fixing unit 60. Specifically, for example, if the number of adjusting magnetic cores 100 is increased, the resistance R and the inductance L tend to increase. Therefore, for example, by adjusting the longitudinal position and number of the adjusting magnetic core 100 in the type B fixing unit 60, for example, the variation range of the resistance R and the variation range of the inductance L of the type B fixing unit 60 can be reduced. The variation range of the resistance R and the variation range of the inductance L in the fixing unit 60 can be approached.

  Therefore, in the IH heater 80 of the present embodiment, the longitudinal positions of the magnetic cores 84 and the adjustment magnetic cores 100 can be freely set. Further, the number of the magnetic cores 84 and the adjustment magnetic cores 100 can be increased or decreased. It is configured so that it can be set. As a result, it is possible to use the common excitation circuit 88 by approximating the variation range of the resistance R and inductance L of the electric circuit system constituted by the excitation coil 82 and the excitation circuit 88 in the fixing unit 60 having a different configuration. Yes.

For example, FIGS. 15 and 16 show longitudinal positions of the magnetic core 84 and the adjusting magnetic core 100 so as to approximate the variation ranges of the resistance R and the inductance L of the electric circuit system constituted by the exciting coil 82 and the exciting circuit 88. It is the figure which showed the structural example of the IH heater 80 to which the number was set. 15 and 16, (b) is a plan view of the IH heater 80 with the shield 85 removed, and (a) is an XX cross-section of the magnetic core setting member 87 in FIG. 16 (b). .
First, in the IH heater 80 having the configuration shown in FIG. 15, the nine magnetic cores 84 having the width a1 are set so that the distance between the magnetic cores 84 is a2, and the seven adjusting magnetic cores 100 having the width b1 are formed. Between the magnetic core 84 and the magnetic core 84 is set so as to be b2. However, the interval between the magnetic cores 84 at the left end in the figure is set closer to the interval a2 in order to suppress a decrease in the magnetic field at the left end portion.
In order to set the longitudinal position of the magnetic core 84 and the adjusting magnetic core 100, the magnetic core setting member 87 is provided with a first longitudinal position setting portion 87a and a second longitudinal position setting portion 87b. Yes. That is, in the magnetic core setting member 87, the first longitudinal position setting portion 87a for setting the magnetic core 84 having the width a1 to be a2 apart from the magnetic core 84 at the left end in the drawing and the adjustment of the width b1. A second longitudinal position setting portion 87b for setting the magnetic core 100 between the magnetic core 84 and the magnetic core 84 so that the distance between the magnetic core 84 is b2 is disposed.

On the other hand, in the IH heater 80 having the configuration shown in FIG. 16, twelve magnetic cores 84 having a width a1 are arranged so that the distance between them is a3, and the adjusting magnetic core 100 is not arranged. However, as in the case of FIG. 15, the interval between the magnetic cores 84 at the left end in the drawing is closer to the interval a3 in order to suppress a decrease in the magnetic field at the left end portion.
In order to set such a longitudinal position of the magnetic core 84, the magnetic core setting member 87 is provided with the first longitudinal direction position setting part 87a and is not provided with the second longitudinal direction position setting part 87b. That is, the magnetic core setting member 87 is provided with only the first longitudinal position setting portion 87a for setting the magnetic cores 84 having the width a1 so that the mutual interval is a2, except for the magnetic core 84 at the left end in the drawing. .

In this case, in the IH heater 80 having the configuration shown in FIGS. 15 and 16, the longitudinal positions and the number of the magnetic cores 84 and the adjustment magnetic core 100, the presence / absence of the installation of the adjustment magnetic core 100, and the corresponding magnetic core Except for the arrangement configuration of the first longitudinal direction position setting portion 87a and the second longitudinal direction position setting portion 87b in the setting member 87, the IH heater 80 is configured similarly. That is, in the IH heater 80 having the configuration shown in FIGS. 15 and 16, the support 81, the excitation coil 82, the elastic support member 83, the shield 85, the pressurizing member 86, and the excitation circuit 88 are similarly configured. The shapes and sizes of the magnetic core 84 and the adjustment magnetic core 100 are also configured in the same manner.
Then, the variation range of the resistance R and the inductance L of the electric circuit system constituted by the exciting coil 82 and the exciting circuit 88 is approximated in correspondence with all or part of the configuration other than the IH heater 80 in the fixing unit 60. As described above, the longitudinal positions of the magnetic cores 84 and the adjustment magnetic cores 100 are set, and the numbers of the magnetic cores 84 and the adjustment magnetic cores 100 are set.
In order to realize such an arrangement setting of the magnetic cores 84 and the adjustment magnetic cores 100, in the IH heater 80 of the present embodiment, the longitudinal positions of the magnetic cores 84 and the adjustment magnetic cores 100 can be freely set. Further, the number of magnetic cores 84 and the number of adjusting magnetic cores 100 can be increased or decreased.

In the configuration example of the IH heater 80 shown in FIGS. 15 and 16, the case where the number of the magnetic cores 84 is different is shown. However, when approximating the variation range of the resistance R and the inductance L, the number of the magnetic cores 84 is the same. In some cases, only the presence or absence of the adjusting magnetic core 100 is different.
The longitudinal position and number of the adjustment magnetic core 100 are also set from the viewpoint of improving the uniformity of the alternating magnetic field generated by the IH heater 80 in the longitudinal direction of the support 81.

As described above, in the fixing unit 60 provided in the image forming apparatus 1 of the present embodiment, the temperature-sensitive magnetic member 64 is disposed in the vicinity of the inner peripheral surface of the fixing belt 61. As a result, the temperature rise of the non-sheet passing region is suppressed excessively.
Further, the IH heater 80 that electromagnetically heats the fixing belt 61 can freely set the longitudinal positions of the magnetic cores 84 and the adjustment magnetic cores 100, and further increase or decrease the number of the magnetic cores 84 and the adjustment magnetic cores 100. And can be set. As a result, it is possible to use the common excitation circuit 88 by approximating the variation range of the resistance R and inductance L of the electric circuit system constituted by the excitation coil 82 and the excitation circuit 88 in the fixing unit 60 having a different configuration. Yes.

  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 device, 61 ... Fixing belt, 62 ... Pressure roll, 64 ... Temperature-sensitive magnetic member, 80 ... IH heater, 81 ... Support part, 81a ... Support surface, 81b1, 81b2 ... Magnetic core support Part, 81c ... magnetic core regulating part, 82 ... excitation coil, 84 ... magnetic core, 87 ... magnetic core setting member, 87a ... first longitudinal direction position setting part, 87b ... second longitudinal direction position setting part, 611 ... base material layer 612 ... conductive heat generating 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;
A plurality of magnetic path forming members arranged along the width direction of the fixing member and forming a magnetic path of an alternating magnetic field generated by the magnetic field generating member;
A support member that movably supports the plurality of magnetic path forming members in the fixing member width direction;
A position setting member configured to set and fix each of the plurality of magnetic path forming members supported movably by the support member at a predetermined position in the width direction of the fixing member; apparatus. A plurality of adjusting magnetic members arranged along the width direction of the fixing member and adjusting the AC magnetic field generated by the magnetic field generating member so as to equalize the fixing member width direction;
The support member supports the adjustment magnetic member movably in the fixing member width direction,
2. The fixing according to claim 1, wherein the position setting member sets and fixes each of the adjustment magnetic members supported movably by the support member at a predetermined position in the width direction of the fixing member. apparatus. The support member sets the magnetic field generating member to a position having a predetermined gap from the fixing member, and sets the magnetic path forming member to a position having a predetermined gap from the position setting surface. While having a position setting unit that is movably supported in the fixing member width direction,
The position setting portion of the support member includes a pair of convex portions arranged in parallel along a direction orthogonal to the moving direction of the fixing member, and further extends the magnetic path forming member along the position setting surface. The fixing device according to claim 1, wherein the fixing device is supported so as to be movable forward and backward in the moving direction of the fixing member.   An elastic support member that elastically deforms and supports the magnetic field generation member on the surface of the support member while pressing the magnetic field generation member toward the surface of the support member 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;
A plurality of magnetic path forming members arranged along the width direction of the fixing member and forming a magnetic path of an alternating magnetic field generated by the magnetic field generating member;
A support member that movably supports the plurality of magnetic path forming members in the fixing member width direction;
And a position setting member for setting and fixing each of the plurality of magnetic path forming members supported movably by the support member at a predetermined position in the width direction of the fixing member. Forming equipment. The fixing unit further includes an adjustment magnetic member that is arranged in a plurality along the width direction of the fixing member and adjusts an alternating magnetic field generated by the magnetic field generation member so as to equalize the fixing member width direction.
The support member of the fixing unit supports the adjustment magnetic member so as to be movable in the fixing member width direction,
The position setting member of the fixing unit sets and fixes each of the adjustment magnetic members supported movably by the support member at a predetermined position in the width direction of the fixing member. 6. The image forming apparatus according to 6. The support member of the fixing unit has a position setting surface for setting the magnetic field generating member to a position having a predetermined gap from the fixing member, and a gap for setting the magnetic path forming member to the position setting plane. A position setting unit that supports the fixing member so as to be movable in the width direction while setting the position,
The position setting portion of the support member includes a pair of convex portions arranged in parallel along a direction orthogonal to the moving direction of the fixing member, and further extends the magnetic path forming member along the position setting surface. The image forming apparatus according to claim 6, wherein the image forming apparatus is supported so as to be movable forward and backward in the moving direction of the fixing member.   The fixing means is elastically deformed while pressing the magnetic field generating member toward the support member surface between the magnetic field generating member and the magnetic path forming member, and supports the magnetic field generating member on the support member surface. The image forming apparatus according to claim 6, further comprising an elastic support member.   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 having a conductive layer and generating an alternating magnetic field intersecting with the conductive layer of the fixing member that fixes the toner to the recording material by electromagnetic induction heating of the conductive layer;
A plurality of magnetic path forming members arranged along the width direction of the fixing member and forming a magnetic path of an alternating magnetic field generated by the magnetic field generating member;
A support member that movably supports the plurality of magnetic path forming members in the fixing member width direction;
A position setting member configured to set and fix each of the plurality of magnetic path forming members movably supported by the support member at a predetermined position in the width direction of the fixing member. Generator. A plurality of adjusting magnetic members arranged along the width direction of the fixing member and adjusting the AC magnetic field generated by the magnetic field generating member so as to equalize the fixing member width direction;
The support member supports the adjustment magnetic member movably in the fixing member width direction,
12. The magnetic field according to claim 11, wherein the position setting member sets and fixes each of the adjustment magnetic members supported movably by the support member at a predetermined position in the width direction of the fixing member. Generator. The support member sets the magnetic field generating member to a position having a predetermined gap from the fixing member, and sets the magnetic path forming member to a position having a predetermined gap from the position setting surface. While having a position setting unit that is movably supported in the fixing member width direction,
The position setting portion of the support member includes a pair of convex portions arranged in parallel along a direction orthogonal to the moving direction of the fixing member, and further extends the magnetic path forming member along the position setting surface. The magnetic field generation device according to claim 11, wherein the magnetic field generation device is supported so as to be movable forward and backward in the moving direction of the fixing member.

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