JP2013235088A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology for increasing temperature-increase speed during warm-up of a temperature-sensitive magnetic member which comes into contact with a fixing member during fixation, while preventing the temperature-sensitive magnetic member from being overheated during fixation.SOLUTION: A fixing device (7) comprises: a fixing member (61) having a first heat generating layer (61b); magnetic flux generation means (67) generating a magnetic flux for inductively heating the first heat generating layer of the fixing member; temperature-sensitive magnetic member (65) that includes a temperature-sensitive magnetic layer (65a) having temperature-sensitive characteristics and comes into contact with the fixing member during fixation; a second heat generating layer (65b) disposed on a surface of the temperature-sensitive magnetic layer on the side of the fixing member and formed of nonmagnetic metal inductively heated by the magnetic flux generated by the magnetic flux generation means, the second heat generating layer (65b) of which heat generation efficiency changes depending on a frequency of the magnetic flux; and a control means (110) that controls the magnetic flux generation means to change the frequency of the magnetic flux to be generated by the magnetic flux generation means so that the heat generation efficiency of the second heat generation layer during warm-up becomes higher than that during fixation.

Description

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

  An image forming apparatus including an induction heating type fixing device is known. An induction heating type fixing device usually has a heat generating layer that is induction-heated and has a fixing member (fixing belt) that fixes an image on a recording medium with heat generated from the heat generating layer. In addition, in order to prevent an excessive temperature rise of the fixing belt while increasing the heating efficiency of the fixing belt, when the temperature exceeds a predetermined temperature, the magnetic permeability decreases and the temperature sensitivity changes from a ferromagnetic material to a paramagnetic material. It is known to provide a temperature-sensitive magnetic member having characteristics near a fixing member (see, for example, Patent Document 1).

  In the fixing device described in Patent Document 1, the temperature-sensitive magnetic member includes a temperature-sensitive layer that has a temperature-sensitive characteristic and serves as a base layer, and a heat generation layer that is laminated on the surface of the temperature-sensitive layer. Further, the fixing device described in Patent Document 1 moves the temperature-sensitive magnetic member relative to the fixing belt so that the temperature-sensitive magnetic member is in contact with the fixing belt or the temperature-sensitive magnetic member is separated from the fixing belt. When the temperature of the temperature-sensitive magnetic member reaches the reference set temperature, the temperature-sensitive magnetic member is brought into contact with the inner peripheral surface of the fixing belt by the contact-and-separation mechanism, and heat is stored in the temperature-sensitive magnetic member. Heat energy is transferred to the fixing belt.

  Further, in Patent Document 1, in order to quickly raise the temperature of the temperature-sensitive magnetic member to the reference set temperature, a heating element that generates heat by the power supplied from the power storage unit is provided on the inner peripheral surface of the temperature-sensitive magnetic member (the fixing belt). It is described that it is provided on the opposite surface).

JP 2009-282413 A

  An object of the present invention is an induction heating type fixing device having a heat generating layer that is heated by induction and having a fixing member that fixes an image on a recording medium with heat generated from the heat generating layer. It is intended to provide a technique capable of both increasing the rate of temperature rise during the warm-up of the temperature-sensitive magnetic member in contact with the heater and suppressing overheating of the temperature-sensitive magnetic member during the fixing operation.

  In order to solve the above-described problem, a fixing device according to claim 1 of the present application includes a first heat generating layer that generates heat by induction heating, and fixes an image on a recording medium with heat generated from the first heat generating layer. A fixing member, a magnetic flux generating means arranged to face the fixing member and generating a magnetic flux for inductively heating the first heat generating layer of the fixing member, and when the temperature rises above a predetermined temperature A temperature-sensitive magnetic layer having a reduced magnetic permeability, disposed on the opposite side of the fixing member from the magnetic flux generating means, and contacting the fixing member during a fixing operation; and the temperature-sensitive magnetic layer A second heat generating layer provided on the surface of the fixing member and formed by a nonmagnetic metal that is induction-heated by the magnetic flux generated by the magnetic flux generating means, and the frequency of the magnetic flux generated by the magnetic flux generating means By heat generation efficiency The heat generation efficiency of the second heat generation layer changing and the heat generation efficiency of the second heat generation layer in the first period before the fixing operation are higher than the heat generation efficiency of the second heat generation layer in the second period of the fixing operation. And control means for controlling the magnetic flux generation means so as to change the frequency of the magnetic flux generated by the magnetic flux generation means between the first period and the second period.

  According to a second aspect of the present invention, in the fixing device according to the first aspect, the second heat generating layer is diffusion bonded to the temperature-sensitive magnetic layer so as to be exposed on the surface of the temperature-sensitive magnetic layer. Or is laminated on the surface of the temperature-sensitive magnetic layer by plating.

  An image forming apparatus according to claim 3 of the present application performs exposure according to image data on an image carrier, a charging unit for charging the image carrier, and an image carrier charged by the charging unit. An exposure means for forming an electrostatic latent image, a developing means for developing the electrostatic latent image formed by the exposure means to form an image on the surface of the image carrier, and a surface for the image carrier. The image forming apparatus includes: a transfer unit that transfers the formed image to a recording medium; and the fixing device according to claim 1 or 2, wherein the image transferred to the recording medium is fixed on the recording medium.

According to the first and third aspects of the present invention, the temperature rising speed of the temperature-sensitive magnetic member that contacts the fixing member during the fixing operation is increased, and the temperature-sensitive magnetic member is overheated during the fixing operation. It is possible to achieve both suppression.
According to the configuration of claim 2, the second heat generating layer is diffusion bonded so as to be exposed on the surface of the temperature-sensitive magnetic member, or is laminated on the surface of the temperature-sensitive magnetic member by plating. Therefore, the second heat generating layer is hardly peeled off from the temperature-sensitive magnetic member.

1 is a block diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention. The figure which shows the structure of an image formation part. FIG. 3 is a cross-sectional view illustrating a configuration of a fixing unit. Sectional drawing which shows the structure of a temperature-sensitive magnetic member. The perspective view which shows the detail of a fixing | fixed part. The partial expansion perspective view seen in the arrow VI direction in FIG. The partial expansion perspective view seen in the arrow VII direction in FIG. The block diagram which shows the function which a control part performs regarding control of alternating current magnetic flux. The graph which shows the example of the relationship between the frequency of the alternating current magnetic flux produced | generated by an exciting coil, and the heat generation efficiency of the heat generating layer of a thermosensitive magnetic member with respect to the different thickness of a heat generating layer. Sectional drawing which shows the structure of the temperature-sensitive magnetic member which concerns on the modification 2. As shown in FIG.

[Embodiment]
<Overall configuration of image forming apparatus>
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of an image forming apparatus 10 according to an embodiment of the present invention. The image forming apparatus 10 is an apparatus that forms an image according to image data. The image forming apparatus 10 includes a control unit 110, a display unit 120, an operation unit 130, a communication unit 140, a storage unit 150, and an image forming unit 160. The control unit 110 is a computer including an arithmetic device including a CPU (Central Processing Unit) and a memory. The arithmetic unit of the control unit 110 executes a program stored in the memory to control each unit of the image forming apparatus 10 and process data. The control unit 110 has a function of measuring time, acquires the time when these controls and processes are performed, and performs these controls and processes at a predetermined time. The control unit 110 is an example of a control unit of the present invention.

  The display unit 120 includes a liquid crystal display screen and a liquid crystal drive circuit, and displays the progress of processing, information for guiding operations to the user, and the like based on information supplied from the control unit 110. The operation unit 130 includes an operator such as a button, and supplies operation information representing the operation content to the control unit 110 in accordance with a user operation. The communication unit 140 is connected to a communication line such as a LAN (Local Area Network) and communicates with an external device connected to the communication line. For example, request data indicating that the image is to be formed on a recording medium (for example, paper) is transmitted from the external apparatus together with image data for forming the image. The communication unit 140 supplies the transmitted data to the control unit 110. The storage unit 150 includes a storage device such as an HDD (Hard Disk Drive), and stores, for example, the image data. The image forming unit 160 forms an image on a sheet by electrophotography using four color toners of yellow (Y), magenta (M), cyan (C), and black (K). The recording medium is not limited to paper but may be made of another material such as plastic.

<Configuration of image forming unit>
FIG. 2 is a diagram illustrating a configuration of the image forming unit 160. Among the reference numerals of the image forming unit 160 shown in FIG. 2, the alphabet attached to the end corresponds to the color of toner handled by the image forming apparatus. The configurations having different alphabets at the end of the codes are different in the color of the toner to be handled, but the configurations are common to each other. In the following description, when it is not necessary to distinguish between these components, the description will be made with the alphabet at the end of the reference numerals omitted. The image forming unit 160 includes image forming units 1Y, 1M, 1C, and 1K, an exposure device 2, an intermediate transfer belt 3, a paper feeding unit 4, a plurality of transport rolls 5, a secondary transfer roll 6, and a fixing unit. It has a part 7 and a discharge part 8.

  The exposure apparatus 2 outputs light (exposure light) corresponding to the image data of each color to each image forming unit 1 to form an electrostatic latent image that is the basis of the image of each color. The exposure apparatus 2 is an example of an exposure unit according to the present invention. The image forming units 1Y, 1M, 1C, and 1K develop the electrostatic latent image using toner and form images of respective colors. The configuration of the image forming unit 1 will be described by taking the configuration of the image forming unit 1K as an example. The image forming unit 1K includes a photoreceptor 11K, a charging device 12K, an exposure unit 13K, a developing device 14K, a primary transfer roll 15K, and a cleaning device 16K. The photoconductor 11K is a cylindrical member that rotates around an axis by laminating a photoconductive film on the surface, and holds an electrostatic latent image formed on the surface. The photoconductor 11K is an example of an image carrier according to the present invention.

  The charging device 12K charges the photoconductor 11K to a predetermined charging potential. The charging device 12K is an example of a charging unit according to the present invention. The exposure unit 13K forms a path for the exposure light output from the exposure apparatus 2 to reach the photoconductor 11K. Exposure light output from the exposure device 2 reaches the surface of the photoconductor 11K charged by the charging device 12K through the exposure unit 13K, and an electrostatic latent image corresponding to the image data is formed. The developing device 14K contains a developer having a toner that is a non-magnetic material and a carrier that is a magnetic material. The developing device 14K supplies the toner contained in the developer to the electrostatic latent image, develops the electrostatic latent image, and forms an image on the surface of the photoreceptor 11K. The developing device 14K is an example of a developing unit according to the present invention. The primary transfer roll 15K primarily transfers this image from the photoreceptor 11K to the intermediate transfer belt 3. The cleaning device 16K removes toner remaining on the surface of the photoconductor 11K after the primary transfer.

  The intermediate transfer belt 3 is stretched around a plurality of rolls including a drive roll 31 and is rotatably supported by these rolls. The drive roll 31 is driven by a drive mechanism (not shown) controlled by the control unit 110 and rotates at a rotation speed (rotation speed) determined by the control unit 110. The intermediate transfer belt 3 rotates in the rotation direction A1 indicated by the arrow when the drive roll 31 rotates. An image formed by each image forming unit is primarily transferred onto the outer peripheral surface of the intermediate transfer belt 3 so as to be superimposed. The paper feed unit 4 contains a plurality of sheets.

  The plurality of transport rolls 5 form a transport path B1 indicated by a broken arrow extending from the paper feed unit 4 to the discharge unit 8 via the secondary transfer roll 6 and the fixing unit 7, and this transport path B1 is indicated by an arrow. It is a transport means for transporting the paper in the transport direction A2 shown. These transport rolls 5 are driven by a drive mechanism (not shown) controlled by the control unit 110 and rotate at a rotation speed determined by the control unit 110. The secondary transfer roll 6 is in contact with the intermediate transfer belt 3 to form a transfer area which is an area for image transfer. The secondary transfer roll 6 secondarily transfers the image primarily transferred to the intermediate transfer belt 3 onto the sheet conveyed to the transfer area by the plurality of conveyance rolls 5. As a result of the secondary transfer of the image in this way, an image is formed on the paper. The primary transfer roll 15K, the intermediate transfer belt 3, and the secondary transfer roll 6 described above are examples of the transfer unit according to the present invention. The secondary transfer roll 6 is driven by a drive mechanism (not shown) controlled by the control unit 110 and rotates at a rotation speed determined by the control unit 110. The sheet that has passed through the transfer area is conveyed to the fixing unit 7 through the conveyance path B1.

  The paper feed roller 9 is driven at a timing determined by the control unit 110, and feeds the paper stored in the paper feed unit 4 one by one to the transport path B1. By controlling the operation timing of the paper feed roller 9, the distance between the sheets conveyed along the conveyance path B1 is adjusted. The distance between sheets includes, for example, the presence or absence of post-processing (for example, sorting, stapling, punching, and saddle stitching) in a finisher (post-processing device) (not shown), paper size, print mode (monochrome or color), and image quality It is adjusted according to. In addition to or instead of adjusting the distance between the sheets, the sheet conveyance speed may be adjusted. To change the conveyance speed, the operation of many members must be adjusted as described later. In general, only the distance between sheets is adjusted.

  The fixing unit 7 fixes the image on the paper by heating and pressurizing the image secondarily transferred onto the conveyed paper. The fixing unit 7 is controlled by the control unit 110 shown in FIG. The fixing unit 7 and the control unit 110 cooperate to function as a “fixing device” according to the present invention. The sheet on which the image is fixed is transported by a plurality of transport rolls 5 and discharged to a discharge unit 8.

  The sheet conveyance speed is determined by the rotation speeds of the plurality of conveyance rolls 5, the intermediate transfer belt 3, and the secondary transfer roll 6. These rotational speeds are determined by the controller 110 as described above. That is, the control unit 110 controls the sheet conveyance speed in the range of, for example, 150 mm / second to 200 mm / second by determining these rotational speeds. Specifically, the control unit 110 controls the drive mechanisms so that the paper is transported at the transport speed by supplying a control signal corresponding to the transport speed to each of the drive mechanisms described above. .

<Fixing part>
FIG. 3A is a cross-sectional view of the fixing unit 7. In the present embodiment, as shown in FIG. 3A, the fixing unit 7 includes a ring-shaped fixing belt 61 and a nip R <b> 1 between the fixing belt 61 and the outer peripheral surface of the fixing belt 61. A pressure roll 62 to be formed, a pressure pad 63 that is disposed on the back surface of the fixing belt 61 and presses the fixing belt 61 between the pressure roll 62 in the nip portion R1, and induction heating that induction heats the fixing belt 61. Instrument 67. Note that a peeling member for peeling the paper wound around the fixing belt 61 may be provided on the exit side of the nip portion R1 of the fixing belt 61. Hereinafter, the main elements of the fixing unit 7 will be described in detail.

<Fixing belt>
FIG. 3B is a cross-sectional view of the fixing belt 61. As shown in FIG. 3B, the fixing belt 61 includes, in order from the inner peripheral surface side, a base layer 61a made of a sheet-like member having high heat resistance, a conductive layer 61b laminated on the base layer 61a, and a conductive layer 61b. The elastic layer 61c laminated | stacked on the layer 61b and the surface mold release layer 61d laminated | stacked on this elastic layer 61c are provided. The fixing belt 61 is an example of a fixing member of the present invention.

  As the base layer 61a, a material having flexibility, excellent mechanical strength and heat resistance, such as fluororesin, polyimide resin, polyamide resin, polyamideimide resin, PEEK resin, PES resin, PPS resin, PFA resin, PTFE resin, FEP resin, etc. Are preferably used. A thickness of 10 to 150 μm is suitable. If the thickness is smaller than 10 μm, the strength as the fixing belt 61 cannot be obtained. If the thickness is larger than 150 μm, the flexibility is impaired, and the heat capacity increases and the temperature rise time becomes longer. is there.

  The conductive layer 61b is a layer (heat generation layer) that is induction-heated by an alternating magnetic field induced by the induction heater 67, and a metal layer such as iron, cobalt, nickel, copper, aluminum, or chromium has a thickness of about 1 to 80 μm. What was formed in is used. The material and thickness of the conductive layer 61b are appropriately selected so as to realize a specific resistance value that can generate sufficient heat by eddy current due to electromagnetic induction. In the present embodiment, the conductive layer 61b is made of copper and has a thickness of 10 μm. The conductive layer 61b is an example of a first heat generating layer of the present invention.

  The elastic layer 61c has a thickness of 10 to 500 μm and is made of silicone rubber, fluorine rubber, fluorosilicone rubber or the like having excellent heat resistance and heat conductivity.

  When printing a color image, particularly when printing a photographic image or the like, a solid image is often formed over a large area on a sheet. For this reason, when the surface of the fixing belt 61 (surface release layer 61d) cannot follow the unevenness of the paper or toner image, heating unevenness occurs in the toner image, and the fixed image has a portion with a large amount of heat transfer and a portion with a small amount of heat transfer. Uneven gloss occurs. That is, the glossiness is high in the portion where the heat transfer amount is large, and the glossiness is low in the portion where the heat transfer amount is small. Such a phenomenon is likely to occur when the thickness of the elastic layer 61c is smaller than 10 μm. Therefore, the thickness of the elastic layer 61c is preferably set to 10 μm or more. On the other hand, when the elastic layer 61c is larger than 500 μm, the thermal resistance of the elastic layer 61c increases, and the quick start performance of the fixing unit 7 decreases. Therefore, the thickness of the elastic layer 61c is preferably set to 500 μm or less.

  If the rubber hardness of the elastic layer 61c is too high, glossiness unevenness tends to occur in the fixed image because it cannot follow the unevenness of the paper or toner image. Accordingly, the rubber hardness of the elastic layer 61c is suitably 50 ° (JIS-A: JIS-KA type tester) or less.

Furthermore, with respect to the thermal conductivity λ of the elastic layer 61c, λ = 6 × 10 ⁻⁴ to 2 × 10 ⁻³ [cal / cm · sec · deg] is suitable. This is because the thermal resistance is large when the thermal conductivity λ is smaller than 6 × 10 ⁻⁴ [cal / cm · sec · deg], and the temperature rise in the surface layer (surface release layer 61 d) of the fixing belt 61 is slow. On the other hand, when the thermal conductivity λ is larger than 2 × 10 ⁻³ [cal / cm · sec · deg], the hardness becomes excessively high or the compression set is deteriorated.

  Since the surface release layer 61d is a layer that is in direct contact with the unfixed toner image transferred onto the paper, it is necessary to use a material having excellent release properties and heat resistance. Therefore, as the material constituting the surface release layer 61d, for example, tetrafluoroethylene perfluoroalkyl vinyl ether polymer (PFA), polytetrafluoroethylene (PTFE), fluororesin, silicone resin, fluorosilicone rubber, fluororubber, silicone Rubber or the like is preferably used.

  The thickness of the surface release layer 61d is preferably 5 to 50 μm. This is because, when the thickness of the surface release layer 61d is smaller than 5 μm, there is a problem that uneven coating occurs during coating and a region with poor release properties is formed, or durability is insufficient. Further, when the surface release layer 61d exceeds 50 μm, there arises a problem that heat conduction is deteriorated, and in particular, the surface release layer 61d formed of a resin material has too high hardness, and the elastic layer 61c. By reducing the function of the. In order to improve toner releasability in the surface release layer 61d, an oil application mechanism for applying oil (release agent) for preventing toner offset to the surface release layer 61d is brought into contact with the fixing belt 61. It may be arranged.

<Pressure roll>
The pressure roll 62 is made of a metal cylindrical roll member 62a as a core material (core), and heat resistance such as silicone rubber, foamed silicone rubber, fluororubber, or fluororesin provided on the surface of the cylindrical roll member 62a. An elastic layer 62b made of a material having a surface and a surface release layer 62c on the outermost surface. The pressure roll 62 is an example of a pressure member that contacts a fixing belt (fixing member) 61 and forms a nip portion through which a recording medium passes together with the fixing belt 61.

  As will be described later, the pressure roll 62 can be in contact with the fixing belt 61 or separated from the fixing belt 62. FIG. 3A shows a state where the pressure roll 62 is in contact with the fixing belt 61. In a state where it is in contact with the fixing belt 61, the pressure roll 62 is pressed against the fixing belt 61 with a predetermined load (nip load) by an urging means such as a spring (not shown), and a nip portion is formed between the pressing roll 62 and the fixing belt 61. R1 is formed. A sheet (indicated by reference numeral P1 in FIG. 3A) is conveyed through the conveyance path B1 to the nip portion R1 by the plurality of conveyance rollers 5 illustrated in FIG. The pressure roll 62 rotates in the rotation direction A3 indicated by the arrow in FIG. 3A, and the fixing belt 61 rotates in the rotation direction A4 indicated by the arrow. As the pressure roll 62 and the fixing belt 61 rotate in these directions, the paper P1 transported to the nip R1 passes through the nip R1 and is transported again along the transport path B1.

<Pressure pad>
The pressure pad 63 is formed of an elastic material such as silicone rubber or fluororubber, a heat resistant resin such as polyimide resin, polyphenylene sulfide (PPS), polyethersulfone (PES), or liquid crystal polymer (LCP). . The pressure pad 63 is disposed over a region that is slightly wider than the region through which the sheet passes in the width direction (that is, the axial direction) of the fixing belt 61. It is comprised so that the pressurization roll 62 may be pressurized over the full length.

  Further, in order to improve the slidability between the pressure pad 63 and the fixing belt 61 in the clamping portion (nip portion R1) of the fixing belt 61 between the pressure pad 63 and the pressure roll 62, the pressure pad 63 and Between the fixing belt 61, a sliding sheet (not shown) made of a polyimide film having excellent sliding properties and high wear resistance, a glass fiber sheet impregnated with a fluororesin, or the like is disposed. Further, a lubricant is applied to the inner peripheral surface of the fixing belt 61. As the lubricant, amino-modified silicone oil, dimethyl silicone oil, or the like is used. Accordingly, the frictional resistance between the fixing belt 61 and the pressure pad 63 is reduced, and the fixing belt 61 can be smoothly rotated.

<Supporting member>
A support member 64 that supports the pressure pad 63 is disposed inside the fixing belt 61. The support member 64 is formed in a rod shape extending along the longitudinal direction of the pressure pad 63, and the pressure pad 63 is held below the support portion 64. Here, the material of the support member 64 needs to have a predetermined rigidity or more so as to reduce the amount of deflection when receiving the pressure contact force from the pressure roll 62 (for example, 1 mm or less), such as iron, SUS, A metal such as aluminum is preferred.

<Temperature-sensitive magnetic member>
In the present embodiment, the temperature-sensitive magnetic member 65 is fixed to the support member 64 so as to always contact the inner peripheral surface of the fixing belt 61 inside the fixing belt 61. As shown in the cross-sectional view of FIG. 4, the temperature-sensitive magnetic member 65 includes a temperature-sensitive magnetic layer 65 a formed of a temperature-sensitive magnetic material such as an Fe—Ni alloy, and the fixing belt 61 side of the temperature-sensitive magnetic layer 65. And a heat generating layer 65b laminated on the surface of the substrate. The heat generating layer 65b is an example of a second heat generating layer of the present invention.

  The temperature-sensitive magnetic layer 65a is a ferromagnetic material when the temperature is lower than a predetermined set temperature (sometimes referred to as Curie temperature), and contributes to generation of magnetic flux for induction heating of the fixing belt 61. When the temperature rises and reaches the set temperature, the magnetic permeability decreases and changes from a ferromagnetic material to a paramagnetic material. Therefore, during the fixing operation, the temperature of the fixing belt 61 rises above a predetermined preferable operating temperature (also referred to as a fixing temperature) for some reason, and the temperature-sensitive magnetic layer 65a is transferred by heat transfer from the fixing belt 61. When the temperature reaches the set temperature, the magnetic permeability of the temperature-sensitive magnetic layer 65a decreases, and induction heating of the fixing belt 61 by the induction heater 67 is suppressed. Here, the set temperature of the temperature-sensitive magnetic layer 65a is fixed so that the temperature of the temperature-sensitive magnetic layer 65a reaches the set temperature before the temperature of the fixing belt 61 exceeds the upper limit of the allowable temperature of the fixing belt 61. It is preferably determined in consideration of the thermal conductivity from the belt 61 to the temperature-sensitive magnetic layer 65, the heat capacity of the temperature-sensitive magnetic layer 65a, and the like. The set temperature of the temperature-sensitive magnetic layer 65a is adjusted, for example, by changing the ratio of iron and nickel forming the temperature-sensitive magnetic layer 65a. Thus, the temperature-sensitive magnetic layer 65a of the temperature-sensitive magnetic member 65 serves to prevent the fixing belt 61 from overheating while contributing to the generation of magnetic flux and increasing the heating efficiency of the fixing belt 61.

  Further, when the image is fixed on the sheet, heat is transferred from the fixing belt 61 to the sheet, and the temperature of the fixing belt 61 is lowered. Therefore, in order to fix the image on the next sheet, it is necessary to wait for the temperature of the fixing belt 61 to rise to the fixing temperature. Accordingly, it is difficult to perform image fixing processing on a plurality of sheets at high speed only by heat generated by the conductive layer 61b of the fixing belt 61. In the present embodiment, when the temperature of the fixing belt 61 decreases because the temperature-sensitive magnetic member 65 is in contact with the fixing belt 61, the heat stored in the temperature-sensitive magnetic member 65 is transmitted to the fixing belt 61 and is fixed. A decrease in the temperature of the belt 61 is suppressed. Therefore, compared to the case where the temperature-sensitive magnetic member 65 is not in contact with the fixing belt 61 during the fixing operation, the fixing process is performed at a higher speed when images are continuously fixed on a plurality of sheets ( That is, the number of sheets to be fixed per unit time is large). Thus, the temperature-sensitive magnetic member 65 functions as a heat storage body that suppresses a decrease in the temperature of the fixing belt 61 during the fixing operation. The temperature-sensitive magnetic member 65 (temperature-sensitive magnetic layer 65a) preferably has a larger heat capacity than the fixing belt 61 in order to function as a heat storage body. In order to suppress a decrease in the temperature of the fixing belt 61 during the fixing operation, the temperature of the temperature-sensitive magnetic member 65 (temperature-sensitive magnetic layer 65a) is set to a predetermined temperature (that is, the temperature of the sheet in the fixing operation). It is necessary to reach a temperature higher than the temperature of the fixing belt 61 when the temperature is lowered by the contact.

  The heat generating layer 65 b provided on the surface of the temperature-sensitive magnetic layer 65 a on the fixing belt 61 b side is made of a nonmagnetic metal such as copper and is induction-heated by the alternating magnetic flux generated by the induction heater 67. Here, the nonmagnetic metal includes an alloy. If the heat generation layer 65b is made of a nonmagnetic metal and is made of a ferromagnetic material, the magnetic flux penetrating the conductive layer 61b of the fixing belt 61 even if the temperature-sensitive magnetic layer 65a becomes a paramagnetic material due to the temperature rise of the fixing belt 61. This is because heating of the conductive layer 61b is not suppressed. In the present embodiment, the heat generating layer 65b is made of copper and has a thickness of 15 μm. That is, the heat generating layer 65b has a thickness different from the thickness of the conductive layer 61b of the fixing belt 61 (10 μm in this example).

  The heat generating layer 65b has a rate of temperature increase when the temperature of the temperature-sensitive magnetic layer 65a is raised to a predetermined temperature in the warm-up before the start of the fixing operation (that is, the supply of paper to the nip portion R1). It works to speed up and reduce warm-up time. If the heat generating layer 65b is provided on the surface of the temperature-sensitive magnetic layer 65a opposite to the fixing belt 61b side, the thickness of the temperature-sensitive magnetic layer 65a is greater than the skin depth of the magnetic flux generated by the exciting coil 69. Since the magnetic flux passes through the temperature-sensitive magnetic layer 65a and does not reach the heat-generating layer 65b and the heat-generating layer 65b is not induction-heated, it is preferable to provide the heat-generating layer 65b on the surface of the temperature-sensitive magnetic layer 65a on the fixing belt 61b side. The heat generating layer 65b and the temperature sensitive magnetic layer 65a may be provided as a so-called clad material in which the boundary surface between the heat generating layer 65b and the temperature sensitive magnetic layer 65a is diffusion bonded (that is, an alloy layer is formed). Alternatively, depending on the material, the heat generating layer 65b may be formed on the temperature-sensitive magnetic layer 65a by plating.

<Induction heater>
Referring to FIG. 3A again, an induction heater 67 is disposed at a portion facing the temperature-sensitive magnetic member 65 outside the fixing belt 61. In this example, the induction heater 67 includes a pedestal 68 having a curved surface corresponding to the fixing belt 61, an excitation coil 69 supported by the pedestal 68, and a high frequency applied to the excitation coil 69 under the control of the control unit 110. And an excitation circuit 73 for supplying a current. The pedestal 68 is made of a material having insulating properties and heat resistance. For example, a phenol resin, a polyimide resin, a polyamide resin, a polyamideimide resin, a liquid crystal polymer resin, or the like may be used. The exciting coil 69 has a substantially cylindrical curved surface facing the fixing belt 61 so as to face the substantially cylindrical fixing belt 61 at a constant interval. The induction heater 67 is an example of the magnetic flux generation means of the present invention.

  Furthermore, in this example, a magnetic flux holding member 70 that is made of a material with high magnetic permeability (ferrite, permalloy, etc.) and holds the magnetic flux generated by the exciting coil 69 is provided on the back side of the pedestal 68. . A shield 74 is provided outside the magnetic flux holding member 70. The shield 74 shields the magnetic field and suppresses leakage to the outside.

  In such an induction heater 67, when a high frequency current is supplied from the exciting circuit 73 to the exciting coil 69, the magnetic flux repeatedly generates and disappears around the exciting coil 69 (AC magnetic flux). The frequency of the high frequency current is set to about 10 to 500 kHz, for example. When the generated magnetic flux crosses the conductive layer 61b of the fixing belt 61, an eddy current is generated in the conductive layer 61b so as to generate a magnetic field that hinders the change of the magnetic field, and power proportional to the skin resistance of the conductive layer 61b. Joule heat is generated. The region of the fixing belt 61 that is heated when an induction current flows through the conductive layer 61b when a high-frequency current flows through the exciting coil 69 may be referred to as a heating region. The heating area is determined by the shape of the exciting coil 69. In the present embodiment, the heat generation layer 65b provided on the surface of the temperature-sensitive magnetic layer 65a of the temperature-sensitive magnetic member 65 is also generated by the excitation coil 69 of the induction heater 67, like the conductive layer 61b of the fixing belt 61. Induction heating is performed by the generated magnetic flux.

<Temperature sensor>
In order to detect the temperature of the fixing belt 61, a first temperature sensor 75 is provided so as to contact the inner peripheral surface of the fixing belt 61 at a position downstream of the heating region. The first temperature sensor 75 may be a temperature sensor using a thermistor whose resistance value changes depending on the temperature, for example. The first temperature sensor 75 supplies data indicating the detected temperature of the fixing belt 61 to the control unit 110 shown in FIG. The controller 110 controls the high-frequency current flowing through the exciting coil 69 based on the temperature of the fixing belt 61 detected by the first temperature sensor 75 and the set target temperature. A plurality of (for example, two) first temperature sensors 75 may be provided and arranged at different positions in the axial direction of the fixing belt 61.

  Further, in order to detect the temperature of the temperature-sensitive magnetic member 65 (more specifically, the temperature-sensitive magnetic layer 65a), a second temperature sensor 76 is provided at one end in the circumferential direction of the temperature-sensitive magnetic member 65. Similarly to the first temperature sensor 75, the second temperature sensor 76 may be a temperature sensor using a thermistor whose resistance value changes depending on the temperature, for example. The second temperature sensor 76 supplies data indicating the detected temperature of the temperature-sensitive magnetic layer 65 a to the control unit 110. Based on the temperature of the temperature-sensitive magnetic layer 65a detected by the second temperature sensor 76, the controller 110 determines the timing for starting the supply of paper to the nip portion R1 (that is, completion of warm-up). The second temperature sensor 76 is not limited to one, and a plurality of second temperature sensors 76 may be provided.

<Fixer drive mechanism>
Next, the overall configuration of the drive transmission mechanism 80 of the fixing unit 7 will be described with reference to FIGS. 5 is a perspective view specifically showing the fixing unit, FIG. 6 is a partially enlarged perspective view seen from the direction of arrow VI in FIG. 5, and FIG. 7 is seen from the direction of arrow VII in FIG. FIG. As shown in these drawings, the drive transmission mechanism 80 includes a rotational drive transmission mechanism 81 that rotationally drives the fixing belt 61 and the pressure roll 62, a state in which the pressure roll 62 is in contact with the fixing belt 61, and the fixing belt 61. A moving mechanism 90 that moves the pressure roll 62 with respect to the fixing belt 61 is provided so as to be in a separated state.

  The rotational drive transmission mechanism 81 has a drive gear 82 that is disposed on one side in the longitudinal direction of the fixing unit 7 and is connected to a drive motor (not shown) controlled by the control unit 110. A drive transmission gear 83 for transmitting a driving force to the pressure roll 62 is engaged with the drive gear 82, whereby the pressure roll 62 is rotationally driven.

  The rotational drive transmission mechanism 81 has a drive transmission gear train 84 composed of a plurality of stages of drive transmission gears, and the drive gear 82 is engaged with the first-stage drive transmission gear 84 a of the drive transmission gear train 84. A gear 85 with clutch is engaged with the final stage drive transmission gear 84e of the drive transmission gear train 84, and a drive transmission gear 87 for fixing belt drive transmission is provided on the opposite side of the longitudinal direction of the fixing belt 61 with respect to the clutch-equipped gear 85. Arranged. The drive transmission gear 87 and the clutched gear 85 are connected by a connecting rod 86. An end cap 100 serving as a final drive transmission body is engaged with the drive transmission gear 87 via a drive transmission gear 88. Thus, the rotational driving force of the drive motor is transmitted to the fixing belt 61, and the fixing belt 61 is rotationally driven. The end caps 100 (specifically, 100a and 100b) are end cover covers that are inserted and attached to both ends of the fixing belt 61, and are formed at both ends of the support member 64 disposed inside the fixing belt 61. The shaft portion (not shown) is fitted to the shaft portion.

  The moving mechanism 90 has a rotatable rotating rod 91 extending along the axial direction of the pressure roll 62, and eccentric cams 92 are fixed to both sides of the rotating rod 91 in the axial direction. On the other hand, a swingable swing lever 93 is provided at a portion corresponding to the eccentric cam 92, and a roll-shaped cam follower 94 that contacts the cam surface of the eccentric cam 92 is provided at a part of the swing lever 93. It is done. The cam follower 94 is always pressed against the cam surface of the eccentric cam 92 by the urging force of the elastic spring 95. When the rotating rod 91 is rotated by a latch motor (not shown) controlled by the control unit 110, the cam surface of the eccentric cam 92 moves, and the posture of the swing lever 93 changes via the cam follower 94. The shaft portion (cylindrical roll member 62 a) of the pressure roll 62 is rotatably supported by a swing lever 93. Therefore, the position of the pressure roll 62 with respect to the fixing belt 61 depends on the posture of the swing lever 93. Instead, the pressure roll 62 comes into contact with or separates from the fixing belt 61. The moving mechanism 90 is an example of a moving unit that moves the pressure member (pressure roll 62) relative to the fixing member (fixing belt 61). The pressure roll 62 is constantly urged toward the fixing belt 61 by an urging means (not shown), and therefore the operation of moving the pressure roll 62 away from the fixing belt 61 is performed by the urging means. It will be done against the urging force by.

  The rotation detector 96 shown in FIGS. 5 and 7 detects the rotation speed of the fixing belt 61. In this example, the rotation detector 96 includes a detection gear 97 that rotates in accordance with the rotation of the end cap 100. A rotation detection plate 98 that rotates coaxially with the gear 97 is attached, and a rotation operation of the rotation detection plate 98 is detected by an optical sensor 99. That is, the rotation detector 96 is configured to function as a so-called rotary encoder. The rotation detector 96 is an example of a speed sensor that detects the rotation speed of the fixing belt 61.

<Operation of fixing unit>
When the fixing unit 7 is operated to fix the image on the paper conveyed along the conveyance path B1, the control unit 110 drives the drive motor to transmit the driving force from the drive motor to the rotational drive transmission mechanism 81. Then, the fixing belt 61 and the pressure roll 62 are driven to rotate. When the driving rotation starts and the rotation operation of the end cap 100 is detected by the optical sensor 99 as the rotation operation of the rotation detection plate 98 constituting the rotation detector 96, the control unit 110 controls the excitation circuit 73 to control the excitation coil 69. A high-frequency current is passed through. As a result, the conductive layer 61b of the fixing belt 61 and the heat generating layer 65b of the temperature-sensitive magnetic member 65 are induction-heated. When it is detected by the output of the first temperature sensor 75 that the temperature of the fixing belt 61 has risen to a predetermined temperature, the control unit 110 disengages the clutch-equipped gear 85 included in the rotational drive transmission mechanism 81, Further, the moving mechanism 90 is controlled to move the pressure roll 62 to contact the fixing belt 61. As a result, the fixing belt 61 rotates following the pressure roll 62.

  When it is detected by the output of the second temperature sensor 76 that the temperature of the temperature-sensitive magnetic member 65 (temperature-sensitive magnetic layer 65a) has risen to a preset temperature, the control unit 110 has finished warming up. Then, the conveyance roll 5 and the like are controlled to start conveyance of the sheet on which the unfixed toner image is placed to the nip portion R1. When the sheet passes through the nip portion R1, the toner is fixed on the sheet by heat and pressure.

  The control unit 110 also controls the excitation circuit 73 to switch the frequency of the alternating magnetic flux generated by the excitation coil 69 between the warm-up period and the fixing operation. FIG. 8 is a block diagram illustrating functions executed by the control unit 110 regarding the control of the alternating magnetic flux. As shown in FIG. 8, the control unit 110 includes a frequency setting unit 111 and a heating control unit 112. The frequency setting unit 111 and the heating control unit 112 are realized by the CPU executing a program stored in the memory of the control unit 110.

  The frequency setting unit 111 determines the frequency of the alternating magnetic flux generated from the exciting coil 69 based on the signal indicating the temperature of the temperature-sensitive magnetic layer 65a supplied from the second temperature sensor 76 (that is, from the exciting circuit 73 to the exciting coil 69). Set the frequency of the excitation current supplied to. Here, the relationship between the frequency of the alternating magnetic flux generated from the exciting coil 69 and the heat generation efficiency of the heat generating layer 65b of the temperature-sensitive magnetic member 65 (or the conductive layer 61b of the fixing belt 61) will be described.

  FIG. 9 is a graph showing an example of the relationship between the frequency of the alternating magnetic flux generated by the excitation coil 69 and the heat generation efficiency of the heat generation layer 65b of the temperature-sensitive magnetic member 65 with respect to different thicknesses of the heat generation layer 65b. In this example, the heat generating layer 65b is made of copper (Cu). Here, the heat generation efficiency means the ratio (power factor) of the power used for heating the heat generating layer 65b to the power supplied to the exciting coil 69 that generates the alternating magnetic flux.

  In FIG. 9, a solid line curve L1 indicates the heat generation efficiency when the thickness of the heat generation layer 65b is 10 μm, and a one-dot chain line curve L2 indicates the heat generation efficiency when the thickness of the heat generation layer 65b is 2 μm. Curve L3 shows the heat generation efficiency when the thickness of the heat generation layer 65b is 15 μm. As shown in the figure, the characteristic of the heat generation efficiency of the heat generating layer 65b with respect to the frequency of the applied AC magnetic flux varies depending on the thickness of the heat generating layer 65b. Specifically, when the thickness of the heat generating layer 65b is 10 μm, the heat generation efficiency of the heat generating layer 65b varies over a frequency range of about 20 kHz to about 100 kHz as compared with the case where the heat generating layer 65b has another thickness. Small and relatively high. When the thickness of the heat generation layer 65b is 2 μm, the heat generation efficiency of the heat generation layer 65b becomes a peak when the frequency of the AC magnetic flux is about 70 kHz, and shows a higher value than when the thickness of the heat generation layer 65b is 10 μm. The heat generation efficiency is greatly reduced in the region. When the thickness of the heat generating layer 65b is 15 μm, the heat generation efficiency of the heat generating layer 65b becomes a peak at the frequency of the AC magnetic flux of about 30 kHz and shows a higher value than when the thickness of the heat generating layer 65b is 10 μm. The heat generation efficiency is greatly reduced.

  As described above, the mode of change in the heat generation efficiency of the heat generation layer 65b with respect to the frequency of the AC magnetic flux generated by the exciting coil 69 varies depending on the thickness of the heat generation layer 65b. The thickness of the heat generation layer 65b having high (or low heat generation efficiency) changes. Specifically, when the frequency of the alternating magnetic flux is about 30 kHz, the heat generation efficiency is the highest when the thickness of the heat generation layer 65b is 15 μm, the second highest when the thickness of the heat generation layer 65b is 10 μm, and the heat generation layer 65b Is the lowest when the thickness is 2 μm. On the other hand, when the frequency of the AC magnetic flux is about 70 kHz, the heat generation efficiency is the highest when the thickness of the heat generation layer 65b is 2 μm, the second highest when the thickness of the heat generation layer 65b is 10 μm, and the thickness of the heat generation layer 65b. Is the lowest when the thickness is 15 μm.

  When the conductive layer 61b of the fixing belt 61 is made of copper, the heat generation efficiency of the conductive layer 61b has the same characteristics as shown in FIG.

  In this embodiment, the conductive layer 61b of the fixing belt 61 is a layer made of copper having a thickness of 10 μm, and the heat generating layer 65b of the temperature-sensitive magnetic member 65 is a layer made of copper having a thickness of 15 μm. Therefore, the conductive layer 61b exhibits a relatively high heat generation efficiency over a frequency range of about 20 kHz to about 100 kHz, and the heat generation layer 65b exhibits a high heat generation efficiency when the frequency of the AC magnetic flux is low (for example, about 30 kHz). When the frequency of magnetic flux is high (for example, about 70 kHz), low heat generation efficiency is exhibited.

  The frequency setting unit 111 is supplied from the second temperature sensor 76 based on the characteristics of the heat generation efficiency of the conductive layer 61b of the fixing belt 61 and the heat generation layer 65b of the temperature-sensitive magnetic member 65 with respect to the frequency of the AC magnetic flux. When the temperature of the temperature-sensitive magnetic layer 65a indicated by the signal is lower than a predetermined temperature (that is, when it is determined that the warm-up is not completed), the frequency of the AC magnetic flux is set to a low frequency (for example, 30 kHz). If the temperature of the temperature-sensitive magnetic layer 65a is equal to or higher than a predetermined temperature, the frequency of the AC magnetic flux is set to a high frequency (for example, 70 kHz). As a result, during the warm-up period when the temperature of the temperature-sensitive magnetic layer 65a is lower than a predetermined temperature, the heat generating layer 65b of the temperature-sensitive magnetic member 65 is heated with higher heat generation efficiency than the conductive layer 61b of the fixing belt 61. The temperature rise of the temperature magnetic layer 65a becomes faster and the warm-up period is shortened. In addition, when the temperature of the temperature-sensitive magnetic layer 65a becomes equal to or higher than a predetermined temperature and the supply of the sheet to the nip portion R1 (that is, the fixing operation) is started, the conductive layer 61b of the fixing belt 61 is heated with high heat generation efficiency. While heating, the heat generation efficiency of the heat generating layer 65b of the temperature sensitive magnetic member 65 is lowered, and the temperature sensitive magnetic member 65 is prevented from overheating. In the above, the period in which the temperature of the temperature-sensitive magnetic layer 65a is lower than the predetermined temperature is an example of a first period before the fixing operation of the present invention, and the temperature of the temperature-sensitive magnetic layer 65a is a predetermined temperature. The above period is an example of the second period of the present invention.

  The heating control unit 112 controls the excitation circuit 73 of the induction heater 67 on the basis of the temperature of the fixing belt 61 detected by the first temperature sensor 75 and a preset target temperature (fixing temperature). The high-frequency current flowing through the coil 69 is adjusted. More specifically, the heating control unit 112 controls the magnitude of the high-frequency current supplied to the exciting coil 69 according to the difference between the temperature of the fixing belt 61 detected by the first temperature sensor 75 and the target temperature. Then, PID control is performed on the power supplied from the exciting coil 69 for heating the conductive layer 61 b of the fixing belt 61. At this time, the heating control unit 112 controls the excitation circuit 73 so that the high-frequency current is supplied to the excitation coil 69 at the frequency set by the frequency setting unit 111.

[Modification]
The above embodiment may be modified as follows. The embodiments described above and the modifications described below may be implemented in combination as necessary.

(Modification 1)
In the above-described embodiment, the temperature-sensitive magnetic member 65 is always in contact with the inner peripheral surface of the fixing belt 61, but the present invention is not limited to this. A contact / separation mechanism for moving the temperature-sensitive magnetic member 65 relative to the fixing belt 61 may be provided so that the temperature-sensitive magnetic member 65 can be brought into contact with the fixing belt 61 and separated from the fixing belt 61. As such a contact / separation mechanism, for example, the contact / separation mechanism described in Patent Document 1 may be adopted.

  When a contact / separation mechanism for moving the temperature-sensitive magnetic member 65 with respect to the fixing belt 61 is provided, the control unit 110 determines that the temperature of the temperature-sensitive magnetic member 65 (temperature-sensitive magnetic layer 65a) detected by the second temperature sensor 76 is in advance. In the warm-up period lower than the predetermined temperature, the contact / separation mechanism is controlled so that the temperature-sensitive magnetic member 65 is separated from the fixing belt 61, and the temperature-sensitive magnetic member 65 is detected when the temperature reaches a predetermined temperature. The contact / separation mechanism may be controlled so that the warm magnetic member 65 contacts the fixing belt 61.

  Even in this case, by providing the heat generating layer 65b made of nonmagnetic metal on the surface of the temperature sensitive magnetic layer 65a of the temperature sensitive magnetic member 65 on the fixing belt 61 side, the heat generating layer 65b is not provided. Thus, the temperature increase rate of the temperature-sensitive magnetic member 65 is improved and the warm-up period is shortened (that is, the temperature-sensitive magnetic member 65 is brought into contact with the fixing belt 61 at an earlier timing). In addition, the heat generation efficiency of the heat generation layer 65b during the fixing operation after completion of the warm-up is generated by the excitation coil 69 by controlling the excitation circuit 73 by the control unit 110 so that the heat generation efficiency of the heat generation layer 65b during the warm-up period is lower. By changing the frequency of the magnetic flux applied, overheating of the temperature-sensitive magnetic member 65 during the fixing operation is suppressed.

(Modification 2)
In the embodiment described above, the heat generating layer 65b of the temperature-sensitive magnetic member 65 is laminated on the surface of the temperature-sensitive magnetic layer 65a, but the present invention is not limited to this. For example, as in the temperature-sensitive magnetic member 65A shown in FIG. 10, the heat-generating layer 65b is embedded in the temperature-sensitive magnetic layer 65a so that the heat-generating layer 65b is exposed (also referred to as inlay processing). May be provided. Compared to the case where the heat generating layer 65b is laminated on the surface of the temperature sensitive magnetic layer 65a by inlaying the heat generating layer 65b on the temperature sensitive magnetic layer 65a, the heat generating layer 65b in contact with the fixing belt 61 is separated from the temperature sensitive magnetic layer 65a. The possibility of peeling is reduced. Further, by providing the heat generation layer 65b only at a desired location of the temperature-sensitive magnetic layer 65a, the heat generation region is limited to a necessary region. For example, by providing the heat generating layer 65b only in a region overlapping with the exciting coil 69, the heat generating region is limited to that region. Alternatively, by providing the heat generating layer 65b inside the maximum value of the width of the paper fixed by the fixing unit 7, the region of the temperature-sensitive magnetic layer 65a outside the maximum value of the width of the paper to be fixed is heated unnecessarily. Is prevented.

(Modification 3)
The characteristics of the heat generation efficiency of the heat generating layer 65b (or the conductive layer 61b of the fixing belt 61) provided on the surface of the temperature-sensitive magnetic layer 65a of the present invention with respect to the frequency of the alternating magnetic flux are not limited to those shown in FIG. The characteristics of the heat generation efficiency of the heat generating layer 65b and the conductive layer 61b can vary depending on the material forming the heat generating layer 65b and the conductive layer 61b.

(Modification 4)
The control unit 110 may have an ASIC (Application Specific Integrated Circuit). In this case, the function of the control unit 10 may be realized by an ASIC, or may be realized by a CPU and an ASIC.

(Modification 5)
A program for realizing the function of the control unit 110 includes a magnetic recording medium (magnetic tape, magnetic disk (HDD, FD (Flexible Disk)), etc.), an optical recording medium (optical disk (CD (Compact Disc), DVD (Digital Versatile Disk)) )), And may be provided in a state stored in a computer-readable recording medium such as a magneto-optical recording medium or a semiconductor memory and installed in the image forming apparatus 10. Alternatively, it may be downloaded and installed via a communication line.

DESCRIPTION OF SYMBOLS 1Y, 1M, 1C, 1K ... Image forming unit, 2 ... Exposure apparatus, 3 ... Intermediate transfer belt, 4 ... Paper feed part, 5 ... Conveyance roll, 6 ... Secondary transfer roll, 7 ... Fixing part, 8 ... Discharge part , 9 ... paper feed roller, 10 ... image forming device, 11K ... photoconductor, 12K ... charging device, 13K ... exposure unit, 14K ... developing device, 15K ... primary transfer roll, 16K ... cleaning device, 21 ... paper detection unit, DESCRIPTION OF SYMBOLS 31 ... Drive roll, 61 ... Fixing belt, 61a ... Base layer, 61b ... Conductive layer, 61c ... Elastic layer, 61d ... Surface release layer, 62 ... Pressure roll, 62a ... Cylindrical roll member, 62b ... Elastic layer, 62c ... Surface release layer, 63 ... Pressure pad, 64 ... Support member, 65, 65A ... Temperature sensitive magnetic member, 65a ... Temperature sensitive magnetic layer, 65b ... Heat generation layer, 67 ... Induction heater, 68 ... Pedestal, 69 ... Excitation coil, 70 ... Magnetic flux holding member 73 ... Excitation circuit, 74 ... Shield, 75 ... First temperature sensor, 76 ... Second temperature sensor, 80 ... Drive transmission mechanism, 81 ... Rotary drive transmission mechanism, 81M ... Drive motor, 82 ... Drive gear, 83 ... Drive transmission Gear, 84 ... Drive transmission gear train, 85 ... Gear with clutch, 86 ... Connecting rod, 87 ... Drive transmission gear, 88 ... Drive transmission gear, 90 ... Moving mechanism, 90M ... Latch motor, 91 ... Rotating rod, 92 ... Eccentric Cam ... 93 ... Swing lever, 94 ... Cam follower, 95 ... Elastic spring, 96 ... Rotation detector, 97 ... Detection gear, 98 ... Rotation detection plate, 99 ... Optical sensor, 100 ... End cap, 110 ... Control part, DESCRIPTION OF SYMBOLS 111 ... Frequency setting part, 112 ... Heating control part, 120 ... Display part, 130 ... Operation part, 140 ... Communication part, 150 ... Memory | storage part, 160 ... Image formation part, B1 ... Conveyance path, R1 ... -Up unit

Claims (3)

A fixing member having a first heat generating layer that generates heat by induction heating, and fixing an image on a recording medium with heat generated from the first heat generating layer;
A magnetic flux generating means disposed opposite to the fixing member and generating a magnetic flux for inductively heating the first heat generating layer of the fixing member;
A temperature-sensitive magnetic layer whose magnetic permeability decreases when the temperature rises above a predetermined temperature is disposed on the opposite side of the fixing member from the magnetic flux generating means, and contacts the fixing member during a fixing operation. A temperature-sensitive magnetic member;
A second heat generating layer provided on a surface of the temperature-sensitive magnetic layer on the fixing member side and formed by a nonmagnetic metal that is induction-heated by a magnetic flux generated by the magnetic flux generating means; A second heat generating layer whose heat generation efficiency varies depending on the frequency of the generated magnetic flux,
The heat generation efficiency of the second heat generation layer in the first period before the fixing operation is higher than the heat generation efficiency of the second heat generation layer in the second period of the fixing operation. And a control means for controlling the magnetic flux generation means to change the frequency of the magnetic flux generated by the magnetic flux generation means in a period of 2. The second heat generating layer is diffusion bonded to the temperature-sensitive magnetic layer so as to be exposed on the surface of the temperature-sensitive magnetic layer, or is formed by being laminated on the surface of the temperature-sensitive magnetic layer by plating. The fixing device according to claim 1, wherein: An image carrier,
Charging means for charging the image carrier;
Exposure means for forming an electrostatic latent image by performing exposure according to image data on the image carrier charged by the charging means;
Developing means for developing the electrostatic latent image formed by the exposure means to form an image on the surface of the image carrier;
Transfer means for transferring an image formed on the surface of the image carrier to a recording medium;
An image forming apparatus comprising: the fixing device according to claim 1, wherein the image transferred to the recording medium is fixed on the recording medium.

Images