JP2013152399A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of both reducing power consumption and reducing a possibility of generating a fixing failure in an induction heating type fixing device.SOLUTION: There is provided a fixing device which comprises: a fixing member (61) for fixing an image on a recording medium by heat generated from a heating layer; a pressure member (62) for forming a nip part (R1) through which the recording medium is passed together with the fixing part when being in contact with the fixing member; induction heating means (67) for induction-heating the heating layer; moving means (90) for moving a pressure member to the fixing part so that the pressure member is in contact with the fixing member or separated from the fixing member; and control means (110) which controls the state of heating of the heating layer and moves the pressure member so that the recording medium is separated from the fixing member during a period in which the recording medium is not passed through the nip part based on the timing when each of the recording media reaches the nip part and the timing when each of the recording media separates from the nip part when a plurality of recording media is sequentially passed through the nip part.

Description

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

  Various techniques have been proposed to reduce power consumption in a fixing device of an image forming apparatus. Japanese Patent Application Laid-Open No. 2004-151561 describes that power consumption is reduced by determining an image region and a non-image region from image information and setting a fixing temperature of the non-image region low.

JP 2003-307964 A

  An object of the present invention is to achieve both reduction in power consumption and reduction in the possibility of fixing failure in an induction heating type fixing device that fixes toner onto a recording medium using heat generated from a heat generating layer that is induction heated. It is to provide possible technology.

  In order to solve the above-described problem, a fixing device according to claim 1 of the present application includes a heat generating layer that generates heat by induction heating, and images are sequentially applied to a plurality of recording media that are sequentially supplied with heat generated from the heat generating layer. A fixing member for fixing the recording medium, and a pressure member capable of taking a state of being in contact with the fixing member and a state of being separated from the fixing member, and the recording medium together with the fixing member when in contact with the fixing member. A pressure member that forms a passing nip portion, induction heating means for induction heating the heat generating layer of the fixing member, and the pressure member is moved relative to the fixing member, the pressure member being the fixing member Moving means for contacting the recording medium or moving away from the fixing member, and when the plurality of recording media sequentially pass through the nip portion, the timing at which each recording medium reaches the nip portion Based on the timing of separation from the nip portion, the aspect of heating the heat generating layer of the fixing member by the induction heating means is controlled, and the plurality of recording media are removed from the fixing member during a period when the recording medium is not passing through the nip portion. Control means for controlling the moving means to move the pressure member so as to be separated.

  The fixing device according to a second aspect of the present invention is the fixing device according to the first aspect, wherein the control unit passes the recording medium through the nip portion more than a period during which the recording medium passes through the nip portion. In a non-medium period, the energy supplied from the induction heating means for reducing the heat generation layer of the fixing member is reduced.

  The fixing device according to a third aspect of the present invention is the fixing device according to the second aspect, wherein the control unit is configured to perform the heat generation of the fixing member by the induction heating unit during a period when the recording medium is not passing through the nip portion. The heating of the layer is stopped.

  According to a fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects, the control unit is configured to move away from the fixing member according to a state of the pressure member. Control of the moving means for moving the pressure member is stopped.

  A fixing device according to a fifth aspect of the present invention is the fixing device according to the fourth aspect, in which the control unit removes the fixing member from the fixing member when it is determined that the pressure member and the fixing member are in a thermal equilibrium state. Control of the said moving means for moving the said pressurizing member so that it may leave | separate is stopped, It is characterized by the above-mentioned.

  A fixing device according to a sixth aspect of the present invention is the fixing device according to the fifth aspect, wherein the pressure member is a cylindrical member that is driven to rotate about an axis, and the fixing member is the additional member. A driven rotating body that rotates by receiving a rotational driving force from the pressure member when in contact with the pressure member, and the fixing device includes a speed sensor that detects a rotation speed of the fixing member; The means controls the rotation speed of the pressure member so that the rotation speed of the fixing member detected by the speed sensor becomes a target rotation speed, and the rotation speed of the fixing member detected by the speed sensor and the target When the state where the difference from the rotation speed is within a predetermined range continues for a predetermined time or more, it is determined that the pressure member and the fixing member are in a thermal equilibrium state.

  A fixing device according to a seventh aspect of the present invention is the fixing device according to the fifth aspect, wherein the pressure member is a cylindrical member driven to rotate about an axis, and the fixing member is the additional member. A driven rotating body that rotates by receiving a rotational driving force from the pressure member when in contact with the pressure member, and the fixing device includes a speed sensor that detects a rotation speed of the fixing member; The means controls the rotation speed of the pressure member so that the rotation speed of the fixing member detected by the speed sensor becomes a target rotation speed, and changes in the control amount for controlling the rotation speed of the pressure member When the state where the width is equal to or less than a predetermined value continues for a predetermined time or more, it is determined that the pressure member and the fixing member are in a thermal equilibrium state.

  An image forming apparatus according to claim 8 of the present application performs exposure according to image data to 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. 8. A transfer unit that transfers a formed image to a recording medium, and a fixing device according to claim 1, wherein the image transferred to the recording medium is fixed on the recording medium.

According to the configurations of claims 1 and 8, in the induction heating type fixing device, it is possible to reduce both power consumption and the possibility of fixing failure.
According to the configuration of claim 2, heating of the heat generating layer of the fixing member is performed in a period in which the recording medium is not passing through the nip portion, compared to a period in which the recording medium is passing through the nip portion. Therefore, compared with the case where the energy supplied from the induction heating means is not reduced, the power consumption in the induction heating type fixing device is reduced.
According to the configuration of claim 3, compared to a case where heating of the heat generating layer of the fixing member by the induction heating unit is not stopped in a period in which the recording medium is not passing through the nip portion, the induction heating type is used. The power consumption in the fixing device is reduced.
According to the fourth aspect of the present invention, it is possible to prevent the pressure member from being unnecessarily moved away from the fixing member.
According to the configuration of the fifth aspect, it is possible to prevent the pressing member from being unnecessarily moved away from the fixing member.
According to the configuration of the sixth aspect, it is possible to determine whether the pressure member and the fixing member are in a thermal equilibrium state based on the rotation speed of the fixing member.
According to the configuration of the seventh aspect, it can be determined whether the pressure member and the fixing member are in a thermal equilibrium state based on a control amount for controlling the rotation speed of the pressure 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. The figure which shows the structure of a fixing | fixed part. The perspective view which shows the detail of a fixing | fixed part. The partial expansion perspective view seen in the arrow V direction in FIG. The partial expansion perspective view seen in the arrow VI direction in FIG. The block diagram which shows the function which a control part performs regarding control of a fixing part after completion | finish of warm-up of a fixing belt. 6 is a timing chart for explaining the operation of the fixing unit when a fixing process is sequentially performed on a plurality of sheets after the fixing belt is warmed up. FIG. 9 is a block diagram illustrating functions executed by a control unit according to Modification 1 regarding control of the fixing unit after the fixing belt has been warmed up.

[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. A section 7, a discharge section 8, and a sheet detection section 21.

  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. .

  The paper detection unit 21 is for detecting whether or not there is a paper at a certain position on the conveyance path B1 (presence / absence of paper). Hereinafter, a position where the paper detection unit 21 detects the presence or absence of paper is referred to as a “paper detection position”. The paper detection unit 21 is disposed so that the paper detection position is in the range from the transfer region to the fixing unit 7 in the transport path B1. The paper detection unit 21 is, for example, an optical sensor, and transmits light to the paper detection position and receives light from the paper detection position. The intensity of light received by the paper detection unit 21 differs depending on whether or not there is a paper at the paper detection position. For example, when the intensity is greater than or equal to a certain threshold, it is indicated that there is a sheet at the sheet detection position, and when it is less than the threshold, it is indicated that there is no sheet. The paper detection unit 21 supplies detection data indicating the detection result to the control unit 110. This detection data is data indicating the intensity of received light, for example. The control unit 110 detects the presence of a sheet at the sheet detection position when the intensity indicated by the detection data is equal to or greater than the threshold value, and detects the absence of the sheet when the intensity is less than the threshold value.

<Fixing part>
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>
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 a magnetic field induced by the induction heater 67, and a metal layer such as iron, cobalt, nickel, copper, aluminum, or chromium is about 1 to 80 μm thick. What was formed 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.

  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. In particular, the surface release layer 61d formed of a resin-based 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 of the present invention.

  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 plurality of transport rollers 5 are means for transporting the paper on which the image is formed to the nip portion R1, and are an example of the “transport means” according to the present invention. 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 of the fixing belt 61, and the pressure pad 63 is pressed over substantially the entire length in the longitudinal direction. The roll 62 is configured to pressurize.

  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.

  In this embodiment, a temperature-sensitive magnetic metal 65 such as an Fe—Ni alloy is fixed to the support member 64 inside the fixing belt 61. The temperature-sensitive magnetic metal 65 is located on the opposite side of the pressure pad 63 and is disposed opposite the fixing belt 61 inside the fixing belt 61 with a predetermined gap. The temperature-sensitive magnetic metal 65 itself has slits (not shown) formed at appropriate positions so as not to be induction-heated by the induction heater 67, and is heated by radiant heat from the fixing belt 61. As a result, the temperature of the temperature-sensitive magnetic metal 65 changes following the temperature of the fixing belt 61. When the temperature of the temperature-sensitive magnetic metal 65 rises and reaches the Curie point temperature, the magnetic permeability decreases and changes from a ferromagnetic material to a non-magnetic material. Therefore, when the temperature of the temperature-sensitive magnetic metal 65 reaches the Curie point temperature, induction heating of the fixing belt 61 by the induction heater 67 is suppressed, and overheating of the fixing belt 61 is prevented.

<Induction heater>
An induction heater 67 is disposed on the outside of the fixing belt 61 and facing the temperature-sensitive magnetic metal 65. The induction heater 67 is an example of the induction heating means of the present invention. 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 an excitation circuit 73 for supplying a high-frequency current to the excitation coil 69. have. 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.

  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 excitation circuit 73 to the excitation coil 69, the magnetic flux repeatedly generates and disappears around the excitation coil 69. 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.

  A temperature sensor 75 is provided in the gap between the temperature-sensitive magnetic metal 65 and the fixing belt 61. As shown in FIG. 3, in this example, the temperature sensor 75 contacts the inner periphery of the fixing belt 61 at the end of the heating region on the downstream side in the rotational direction A4, that is, at the end of heating the fixing belt 61. Is fixed. Accordingly, the temperature sensor 75 measures the temperature of the portion of the fixing belt 61 where the heating by the induction heater 67 has been almost completed. The temperature sensor 75 supplies data indicating the measured temperature to the control unit 110 shown in FIG. As will be described later, the control unit 110 controls the high-frequency current flowing through the exciting coil 69 based on the temperature of the fixing belt 61 measured by the temperature sensor 75 and the set target temperature. Note that a plurality of (for example, two) temperature sensors 75 may be provided and arranged at different positions in the axial direction of the fixing belt 61.

<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. 4 is a perspective view specifically showing the fixing unit, FIG. 5 is a partially enlarged perspective view seen from the direction of arrow V in FIG. 4, and FIG. 6 is seen from the direction of arrow VI 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 connected to a drive motor 81M (not shown in FIGS. 4 to 6) disposed on one side of the fixing unit 7 in the longitudinal direction. 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 81M 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 rotary rod 91 is rotated by a latch motor 90M (not shown in FIGS. 4 to 6), 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 of the present invention. 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. 4 and 6 detects the rotation speed of the fixing belt 61. In this example, the rotation detector 96 includes a detection gear 97 that rotates according to 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 the speed sensor of the present invention.

<Operation of fixing unit>
When the fixing unit 7 is operated to fix images on a plurality of sheets that are sequentially supplied, the control unit 110 drives the drive motor 81M to transmit the driving force from the drive motor 81M to the rotational drive transmission mechanism 81. 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 fixing belt 61 is heated. When it is detected by the output of the temperature sensor 75 that the temperature of the fixing belt 61 has risen to a predetermined temperature, the control unit 110 determines that the fixing belt 61 has been warmed up, and sends it to the rotational drive transmission mechanism 81. The clutch of the included gear 85 is disengaged. As a result, the driving force from the drive motor 81M is not transmitted to the fixing belt 61 through the rotational drive transmission mechanism 81, and the fixing belt 61 rotates following the pressure roll 62 when the pressure roll 62 is in contact. When the pressure roll 62 is not in contact, the rotation is continued due to inertia. Therefore, after the warm-up is completed, the rotation speed of the fixing belt 61 is determined by the peripheral speed (speed of the outer peripheral surface) of the pressure roll 62 and is controlled by controlling the rotation speed of the pressure roll 62.

  After the fixing belt 61 is warmed up, the sheet on which the unfixed toner image is placed is passed through the nip portion R1 in a state where the pressure roll 62 contacts the fixing belt 61 and the nip portion R1 is formed. The toner is fixed on the paper by the pressure.

  FIG. 7 is a block diagram illustrating functions executed by the control unit 110 regarding control of the fixing unit 7 after the warm-up of the fixing belt 61 is completed. As illustrated in FIG. 7, the control unit 110 includes a rotation control unit 111, a position control unit 112, a sheet presence / absence determination unit 113, a sheet passing timing calculation unit 114, a target temperature setting unit 115, and a heating control unit 116. The functions of these units of the control unit 110 are realized by the CPU executing a program stored in the memory of the control unit 110.

  The rotation control unit 111 controls a drive motor 81M that applies a rotational driving force to the rotational drive transmission mechanism 81. For example, when the drive motor 81M is a DC motor, the rotation control unit 111 controls the rotation speed of the drive motor 81M by controlling the voltage or current applied to the drive motor 81M. As described above, after the warm-up of the fixing belt 61 is completed, the rotational driving force of the drive motor 81M is transmitted to the pressure roll 62 through the rotational drive transmission mechanism 81, and the fixing belt 61 rotates following the pressure roll 62. . After the fixing belt 61 is warmed up, during the fixing operation of a plurality of sheets, the rotation control unit 111 has a target rotation speed determined based on a detection signal from the rotation detector 96 and a rotation speed of the fixing belt 61 determined. Thus, the voltage and current applied to the drive motor 81M are controlled, and the rotational speed of the pressure roll 62 is controlled. The voltage or current applied to the drive motor 81M is an example of a control amount for controlling the rotation speed of the pressure member of the present invention. The target rotation speed may be stored in advance in the storage unit 150, or may be set by the control unit 110 according to the conveyance speed when the conveyance speed of the paper is variable.

  The position control unit 112 controls the latch motor 90M according to the sheet passing timing sent from the sheet passing timing calculating unit 114, which will be described later, and drives the moving mechanism 90, whereby the pressure roll 62 is applied to the fixing belt 61. It is moved to a state where it is in contact or away from the fixing belt 61. The sheet passing timing is a timing at which each sheet reaches the nip portion R1 and a timing at which the respective sheets are separated from the nip portion R1. From the sheet passing timing, a period in which the sheet exists in the nip portion R1 (that is, a period in which the sheet is passing through the nip portion R1) and a period in which the sheet does not exist (that is, a period in which the sheet does not pass through the nip portion R1) are obtained.

  The paper presence / absence determination unit 113 determines whether there is a paper at the paper detection position based on the detection data from the paper detection unit 21. Specifically, the sheet presence / absence determination unit 113 determines that there is a sheet at the sheet detection position when the intensity of light indicated by the detection data is equal to or greater than the threshold value, and there is no sheet when the detection value is less than the threshold value. Is determined. The paper presence / absence determination unit 113 repeatedly performs this determination at a predetermined interval (for example, every 1 msec), and sends the determination result to the paper timing calculation unit 114.

  The sheet passing timing calculation unit 114 calculates the sheet passing timing at the nip portion R1 based on the determination result regarding the presence / absence of the sheet at the sheet detection position sent from the sheet presence / absence determination unit 113. In order to calculate the sheet passing timing at the nip portion R1, the storage unit 150 includes a first distance along the conveyance path B1 from the sheet detection position where the sheet detection unit 21 detects the presence or absence of the sheet to the nip portion R1, and The second distance obtained by adding the distance along the conveyance path B1 of the nip portion R1 to the first distance is stored. Specific processing performed by the sheet passing timing calculation unit 114 is as follows.

  First, when the determination result sent from the paper presence / absence determination unit 113 changes from the absence of paper to the presence of paper, the paper passage timing calculation unit 114 first detects the leading edge of the paper, that is, the paper conveyance direction. When it is detected that the edge portion on the front side of A2 has reached the paper detection position, and the determination result changes from the presence of paper to the absence of paper, the rear edge of the paper, that is, the paper transport direction A2 It is detected that the rear edge portion has reached the paper detection position. When the leading edge and the trailing edge of the sheet are detected, the sheet passing timing calculation unit 114 acquires the time when each detection is performed (referred to as the leading edge detection time and the trailing edge detection time, respectively).

  Subsequently, the sheet passing timing calculation unit 114 adds the time obtained by dividing the first distance by the currently set conveyance speed to the acquired leading edge detection time to the nip R1. Calculated as arrival time (referred to as arrival time). This arrival time is an example of arrival timing. The time added here indicates the time required for the leading edge of the sheet conveyed at this conveyance speed to reach the nip portion R1 after passing the sheet detection position. Further, the sheet passing timing calculation unit 114 adds the time obtained by dividing the second distance by the currently set conveyance speed to the acquired trailing edge detection time, and the sheet from the nip portion R1. Calculated as the time to leave (referred to as the time to leave). This leaving time is an example of the leaving timing. The time added here indicates the time required from the trailing edge of the sheet conveyed at this conveyance speed to the separation of the nip portion R1 after passing the sheet detection position. When the current time is included in the range from the arrival time calculated as described above to the departure time, it indicates that the sheet is passing through the nip R1 (that is, the sheet exists in the nip R1). If it is not included, it is indicated that the sheet is not passing through the nip portion R1 (that is, the sheet is not present in the nip portion R1). The sheet passing timing calculation unit 114 supplies the calculated arrival time and departure time to the position control unit 112 and the target temperature setting unit 115.

  The target temperature setting unit 115 sets the target temperature of the fixing belt 61 in accordance with the sheet passing timing sent from the sheet passing timing calculating unit 114. The heating control unit 116 controls the excitation circuit 73 of the induction heater 67 based on the temperature of the fixing belt 61 detected by the temperature sensor 75 and the target temperature set by the target temperature setting unit 115, and the excitation coil. The high-frequency current flowing through 69 is adjusted. More specifically, the heating control unit 116 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 temperature sensor 75 and the target temperature. Then, PID control is performed on the electric power supplied from the exciting coil 69 for heating the conductive layer (heat generating layer) 61b of the fixing belt 61. When the temperature of the fixing belt 61 detected by the temperature sensor 75 is higher than the target temperature, the heating control unit 116 controls the excitation circuit 73 to stop the supply of the high-frequency current to the excitation coil 69, and The conductive layer 61b is not heated by induction.

  FIG. 8 is a timing chart for explaining the operation of the fixing unit 7 when the fixing process is sequentially performed on a plurality of sheets after the warm-up of the fixing belt 61 is completed. The top graph in FIG. 8 shows the timing at which the paper passes through the nip portion R1 (paper passage timing). In this example, times t1, t3, and t5 indicate times when the paper reaches the nip portion R1, and times t2, t4, and t6 indicate times when the paper leaves the nip portion R1. That is, in this example, the period from time t1 to t2, from t3 to t4, and from t5 to t6 is a period during which the sheet passes through the nip portion R1 (hereinafter referred to as “passing period”). From t3 to t5, from t4 to t6, the period after t6 indicates that the sheet is not passing through the nip portion R1 (hereinafter referred to as “non-passing period”). As described above, the arrival times t1, t3, and t5 and the leaving times t2, t4, and t6 are calculated by the paper passing timing calculation unit 114 and supplied to the position control unit 112 and the target temperature setting unit 115.

  The second graph from the top in FIG. 8 shows the state of induction heating control performed by the heating control unit 116. The ON state indicates that high frequency current is supplied from the excitation circuit 73 to the excitation coil 69 and induction heating of the fixing belt 61 is performed, and the OFF state indicates that high frequency current is not supplied to the excitation coil 69 and induction heating of the fixing belt 61 is performed. Indicates that nothing will be done. As shown in the figure, induction heating is turned on during the passage period, and induction heating is turned off (stopped) during the non-passage period. Such induction heating control is performed based on the arrival times t1, t3, t5 and the detachment times t2, t4, t6 supplied from the paper passing timing calculation unit 114. Is set to a predetermined fixing temperature (for example, 160 ° C.), and the target temperature is set to a temperature (for example, 0 ° C.) lower than the temperature that the fixing belt 61 can take during the non-passing period. The temperature that can be taken by the fixing belt 61 during the non-passing period may be obtained by experiment, for example. When induction heating is on, the high-frequency current supplied to the exciting coil 69 so that the temperature of the fixing belt 61 detected by the temperature sensor 75 becomes the fixing temperature set by the target temperature setting unit 115. The power supplied from the exciting coil 69 for heating the conductive layer (heat generating layer) 61b of the fixing belt 61 may be controlled.

  The third graph from the top in FIG. 8 shows a control signal supplied from the position control unit 112 to the latch motor 90M. Below that, a contact state between the pressure roll 62 and the fixing belt 61 is shown. When the control signal is “ON”, the latch motor 90M rotates in a predetermined direction, and when the control signal is “OFF”, the latch motor 90M remains stationary. As described above, when the latch motor 90M rotates, the posture of the swing lever 93 of the moving mechanism 90 changes, and the position of the pressure roll 62 supported by the swing lever 93 with respect to the fixing belt 61 changes. Therefore, by controlling the rotation of the latch motor 90 </ b> M, the pressure roll 62 is moved to a position in contact with the fixing belt 61 or a position away from the fixing belt 61. The rotation direction of the latch motor 90M is not limited to one direction, and the rotation direction of the latch motor 90M is different between when the pressure roll 62 is brought into contact with the fixing belt 61 and when the pressure roll 62 is separated from the fixing belt 61. The latch motor 90M may be controlled to be reversed.

  In this embodiment, the position control unit 112 reaches the latch motor 90M so that the pressure roll 62 and the fixing belt 61 are in contact with each other during the passage and the pressure roll 62 is separated from the fixing belt 61 during the non-passing period. Driving is performed based on times t1, t3, and t5 and departure times t2, t4, and t6. As shown in the figure, in this example, the control signal of the latch motor 90M is turned on from the arrival time (for example, t1) before a predetermined time Δta, the latch motor 90M is driven, and the fixing belt 61 The pressure roll 62 is moved from a remote position to a position where it contacts the fixing belt 61. This is so that the contact between the pressure roll 62 and the fixing belt 61 is completed at the start of the passage period (that is, the arrival time). In addition, the control signal of the latch motor 90M is turned on from a time Δtb that is predetermined from the separation time (for example, t2), the latch motor 90M is driven, and contacts the fixing belt 61 from a position away from the fixing belt 61. The pressure roll 62 is moved to the position. This is because a normal image is not formed in the vicinity of the rear end of the paper, and therefore, even if the pressure roll 62 is moved away from the fixing belt 61 before the separation time, no fixing failure of the image occurs. You may adjust these time (DELTA) ta and (DELTA) tb suitably.

  Thus, according to the present embodiment, since the induction heating is turned off during the non-passing period, the power consumption of the fixing unit 7 is reduced as compared with the case where the induction heating is performed even during the non-passing period. In addition, since the latch motor 90M is driven so that the pressure roll 62 is separated from the fixing belt 61 during the non-passing period, the pressure roller 62 is in contact with the fixing belt 61 during the non-passing period. Further, heat is prevented from moving from the fixing belt 61 to the pressure roll 62 during the non-passing period. Accordingly, heat is transferred from the fixing belt 61 to the pressure roll 62 during the non-passing period, and the temperature of the fixing belt 61 is lowered to cause fixing failure or uneven gloss (brightness) of the image due to toner melting unevenness. Is less likely to occur. In addition, since the driving torque that needs to be generated by the drive motor 81M is reduced by separating the pressure roll 62 and the fixing belt 61 during the non-passing period, the power consumption of the fixing unit 7 is reduced accordingly. Reduced.

[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, when the fixing process is sequentially performed on a plurality of sheets after the fixing belt 61 is warmed up, the pressure roll 62 and the fixing belt 61 are in contact with each other during the passing period, and the pressure is applied during the non-passing period. The latch motor 90M was driven based on arrival times t1, t3, t5 and separation times t2, t4, t6 so that the roll 62 was separated from the fixing belt 61. However, if the pressure roll 62 biased toward the fixing belt 61 by the biasing means is frequently moved to move away from the fixing belt 61 during the non-passing period (referred to as a separation operation), The service life of the member of the fixing unit 7 can be shortened and the reliability of the operation of the fixing unit 7 can be reduced.

  FIG. 9 is a block diagram illustrating functions executed by the control unit 110a according to the first modification regarding the control of the fixing unit 7 after the fixing belt 61 is warmed up. In FIG. 9, the same reference numerals are given to portions common to FIG. 7, and detailed description is omitted. The control unit 110a illustrated in FIG. 9 is different from the control unit 110 illustrated in FIG. 7 in that the control unit 110a includes a separation operation necessity determination unit 117.

  When the fixing belt 61 is warmed up, the separation operation necessity determination unit 117 performs a fixing process on a plurality of sheets sequentially so that the pressure roll 62 is separated from the fixing belt 61 during the non-passing period. Whether or not an operation to move 62 (separation operation) is necessary is determined based on the state of the pressure roll 62, and the determination result is sent to the position control unit 112. When the determination result from the separation operation necessity determination unit 117 indicates that the separation operation is unnecessary, the position control unit 112 is a latch motor for the separation operation of the pressure roll 62 after the warm-up of the fixing belt 61 is completed. 90M drive control is not performed. When the determination result from the separation operation necessity determination unit 117 indicates that the separation operation is necessary, as described above, drive control of the latch motor 90M for the separation operation of the pressure roll 62 is performed.

  In this example, the separation operation necessity determination unit 117 determines the state of the pressure roll 62 based on information from the rotation control unit 111. The principle will be described below.

  When fixing a plurality of sheets after the warm-up of the fixing belt 61 is completed, heat is transferred from the fixing belt 61 to the pressure roll 62 via the sheet when the sheet is passing through the nip portion R1 during the passing period. Can do. Further, since the nip portion R1 has a length in the sheet conveyance direction, for example, the fixing belt 61 and the pressure roll are formed after the rear end of the sheet reaches the nip portion R1 and before the nip portion R1 is released. In some cases, the portion 62 directly contacts without passing through the paper. In this case, heat is transferred from the fixing belt 61 to the pressure roll 62. Therefore, after the start of the fixing operation, the temperature of the pressure roll 62 gradually increases, and the diameter of the pressure roll 62 increases due to thermal expansion. As the amount of heat stored in the pressure roll 62 increases due to heat transfer from the fixing belt 61 to the pressure roll 62, and the temperature of the pressure roll 62 approaches the temperature of the fixing belt 61, the pressure roll 62 and the fixing belt 61 come into contact with each other. The heat transfer from the fixing belt 61 to the pressure roll 62 during the operation becomes small, and eventually reaches a state where no heat transfer from the fixing belt 61 to the pressure roll 62 occurs (thermal equilibrium state). The rise and increase in diameter saturate. As described above, in a state where the fixing belt 61 and the pressure roll 62 reach the thermal equilibrium state, even if the pressure roll 62 is in contact with the fixing belt 61, heat transfer from the fixing belt 61 to the pressure roll 62 occurs. Therefore, the separating operation for moving the pressure roll 62 away from the fixing belt 61 during the non-passing period is unnecessary.

  As described above, after the warm-up of the fixing belt 61 is completed, the fixing belt 61 is rotated by being in contact with the outer peripheral surface of the pressure roll 62 and driven by the pressure roll 62, so that the rotation speed of the fixing belt 61 is controlled. This is done by controlling the rotation speed of the pressure roll 62 (or the drive motor 81M). At this time, before the fixing belt 61 and the pressure roll 62 reach the thermal equilibrium state, the rotation speed of the fixing belt 61 (corresponding to the increase in the diameter of the pressure roll 62 as the temperature of the pressure roll 62 increases) That is, it is necessary to control the rotation speed of the pressure roll 62 so that the circumferential speed of the pressure roll 62 becomes the target speed, whereas the fixing belt 61 and the pressure roll 62 have reached a thermal equilibrium state. In FIG. 3, since there is no change in diameter due to thermal expansion of the pressure roll 62, the fixing belt 61 (after the fixing belt 61 and the pressure roll 62 have reached the thermal equilibrium state is more than the state before the thermal equilibrium state is reached. Or the rotation speed control of the pressure roll 62) becomes more stable. Therefore, the state of the pressure roll 62 is indicated by the information indicating the stable state of the rotation speed control of the fixing belt 61 performed by the rotation control unit 111.

  In this example, as information indicating the stable state of the rotation speed control of the fixing belt 61, the difference Δp between the target rotation speed and the current rotation speed of the fixing belt 61 detected by the rotation detector 96 is the rotation control unit 111. To the separation operation necessity determination unit 117. The separation operation necessity determination unit 117 stabilizes the rotation speed control of the fixing belt 61 when the value of the difference Δp is within a predetermined range for a predetermined time, that is, with the fixing belt 61. It is determined that the pressure roll 62 has reached the thermal equilibrium state, and it is determined that the separation operation is unnecessary. On the other hand, when the condition that the value of the difference Δp is within a predetermined range for a predetermined time or more is not satisfied, the separation operation necessity determination unit 117 determines that the separation operation is necessary.

  As described above, in this example, unnecessary separation operation of the pressure roll 62 is prevented. Therefore, it is possible to prevent the life of the member of the fixing unit 7 from being shortened by an unnecessary separation operation and the reliability of the operation of the fixing unit 7 from being lowered.

(Modification 2)
In the first modification described above, information indicating the stable state of the rotational speed control of the fixing belt 61 (or the pressure roll 62) (that is, whether or not the fixing belt 61 and the pressure roll 62 have reached a thermal equilibrium state). The difference Δp between the target rotation speed of the fixing belt 61 and the current rotation speed of the fixing belt 61 detected by the rotation detector 96 is used, but the present invention is not limited to this. For example, a control amount such as a voltage applied to the drive motor 81M for rotationally driving the pressure roll 62 is sent from the rotation control unit 111 to the separation operation necessity determination unit 117, and the separation operation necessity determination unit 117 performs this control amount. From this value, the stable state of the rotation speed control of the fixing belt 61 may be determined. For example, when the state where the fluctuation range of the voltage applied to the drive motor 81M is equal to or less than a predetermined value continues for a predetermined time or more, the rotational speed control of the fixing belt 61 (or the pressure roll 62) is stable. That is, it may be determined that the fixing belt 61 and the pressure roll 62 have reached the thermal equilibrium state, and it may be determined that the separation operation is unnecessary.

  Or when the temperature sensor which detects the temperature (for example, surface temperature) of the pressurization roll 62 is provided, the separation operation necessity determination part 117 is based on the temperature of the pressurization roll 62 detected by this temperature sensor. The necessity of the separation operation may be determined. That is, when the temperature of the pressure roll 62 detected by the temperature sensor is higher than a predetermined temperature, or the difference between the temperature of the pressure roll 62 and the temperature of the fixing belt 61 detected by the temperature sensor 75 is in advance. When the value is smaller than the predetermined value, it may be determined that the fixing belt 61 and the pressure roll 62 have reached the thermal equilibrium state, and it may be determined that the separation operation is unnecessary.

(Modification 3)
In the embodiment described above, it takes a predetermined time to move the pressure roll 62 to a state where it is separated from the fixing belt 61 or to a state where it is in contact with the fixing belt 61. Therefore, for example, when the distance between the sheets is small and the non-passing period is short, when the pressure roll 62 is moved away from the fixing belt 61, the pressure roll 62 is moved until the next sheet reaches the nip portion R1. It may not be possible to return to the state in contact with the fixing belt 61. Accordingly, when the non-passing period obtained from the arrival time and the separation time is shorter than the determined time, the position control unit 112 may not perform the operation of moving the pressure roll 62 away from the fixing belt 61. Good.

(Modification 4)
In the above-described embodiment, the target temperature setting unit 115 sets the target temperature of the fixing belt 61 during the non-passing period to a low temperature (for example, 0 ° C.) at which induction heating is turned off. It is not limited to. The target temperature of the fixing belt 61 during the non-passing period may be equal to or lower than the target temperature during the passing period. For example, the target temperature setting unit 115 may set the target temperature during the non-passing period to be the same as the target temperature (fixing temperature) during the passing period. Even in such a case, the pressure roll 62 is separated from the fixing belt 61 by the control of the position control unit 112 during the non-passing period, so that the pressure roll 62 contacts the fixing belt 61 during the non-passing period. The outflow of heat from the fixing belt 61 is suppressed as compared with the case where it is kept. Therefore, even if induction heating in the non-passing period is not completely turned off, electric power for heating the heat generating layer 61b of the fixing belt 61 is maintained in order to keep the temperature of the fixing belt 61 at the target temperature in the non-passing period. Reduced.

(Modification 5)
In the embodiment described above, the target temperature setting unit 115 sets the target temperature of the fixing belt 61 during the non-passing period to a sufficiently low temperature (for example, 0 ° C.), thereby turning off the induction heating during the non-passing period. However, the induction heating during the non-passing period may be turned off by another method. For example, the arrival time and the detachment time calculated by the sheet passing timing calculation unit 114 are supplied to the heating control unit 116, and the heating control unit 116 in the non-passing period specified from the arrival time and the detachment time, The excitation circuit 73 may be controlled so that the high-frequency current supplied to the excitation coil 69 becomes zero.

(Modification 6)
The fixing unit 7 may have a heat storage plate in order to realize high productivity. Here, the heat storage plate is a member that is formed using, for example, a temperature-sensitive magnetic alloy as a material, and is in contact with the inner peripheral surface of the fixing belt 61. The heat storage plate is arranged in the heating region, and its thickness and material are adjusted so that heat is generated by electromagnetic induction in an alternating magnetic field generated by the induction heater 67. The heat generated by the heat storage plate is supplied to the fixing belt 61. In this way, by providing the heat storage plate, the fixing belt 61 is warmed by the heat generated by the heat storage plate in addition to the heat generated by the fixing belt 61, and thus the fixing is performed while increasing the efficiency of electromagnetic induction heating by the induction heater 67. It is possible to provide the fixing unit 7 that suppresses the temperature drop of the belt 61 and realizes high productivity.

(Modification 7)
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 8)
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 ... temperature-sensitive magnetic metal, 67 ... induction heater, 68 ... pedestal, 69 ... excitation coil, 70 ... magnetic flux holding member, 73 ... excitation circuit, 74 ... Shield, 75 ... Temperature 80, drive transmission mechanism, 81 ... rotational 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 DESCRIPTION OF SYMBOLS ... 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 detection 97 ... detection gear, 98 ... rotation detection plate, 99 ... optical sensor, 100 ... end cap, 110 ... control unit, 110a ... control unit, 111 ... rotation control unit, 112 ... position control unit, 113 ... paper presence / absence Determining unit, 114 ... paper passing timing calculating unit, 115 ... target temperature setting unit, 116 ... heating control unit, 117 ... separation operation necessity determination unit, 120 ... display unit, 130 ... operation unit, 40 ... communication unit, 150 ... storage unit, 160 ... image forming unit, B1 ... conveyance path, R1 ... nip

Claims (8)

A fixing member having a heat generating layer that generates heat by induction heating, and fixing images on a plurality of recording media that are sequentially supplied with heat generated from the heat generating layer;
A pressure member that can be in contact with the fixing member and separated from the fixing member, and forms a nip through which the recording medium passes when the fixing member is in contact with the fixing member. A pressure member;
Induction heating means for induction heating the heat generating layer of the fixing member;
Moving means for moving the pressure member relative to the fixing member so that the pressure member is in contact with the fixing member or separated from the fixing member;
When the plurality of recording media sequentially pass through the nip portion, the heating layer of the fixing member by the induction heating unit is based on the timing at which each recording medium reaches the nip portion and the timing at which the recording medium separates from the nip portion. And a control means for controlling the moving means to move the pressure member so as to move away from the fixing member during a period when the plurality of recording media are not passing through the nip portion. Fixing device. The control means may perform the induction heating for heating the heat generating layer of the fixing member during a period in which the recording medium is not passing through the nip portion than in a period during which the recording medium is passing through the nip portion. The fixing device according to claim 1, wherein energy supplied from the means is reduced. The fixing device according to claim 2, wherein the control unit stops heating the heat generating layer of the fixing member by the induction heating unit during a period when the recording medium is not passing through the nip portion. 4. The control unit according to claim 1, wherein the control unit stops control of the moving unit for moving the pressure member so as to move away from the fixing member according to a state of the pressure member. 5. The fixing device according to claim 1. The control means stops the control of the moving means for moving the pressure member away from the fixing member when it is determined that the pressure member and the fixing member are in a thermal equilibrium state. The fixing device according to claim 4. The pressure member is a cylindrical member that is driven to rotate about an axis,
The fixing member is a driven rotating body that rotates when a rotational driving force is transmitted from the pressure member when it is in contact with the pressure member;
The fixing device includes a speed sensor that detects a rotation speed of the fixing member,
The control means controls the rotation speed of the pressure member so that the rotation speed of the fixing member detected by the speed sensor becomes a target rotation speed, and the rotation speed of the fixing member detected by the speed sensor When the state where the difference from the target rotational speed is within a predetermined range continues for a predetermined time or more, it is determined that the pressure member and the fixing member are in a thermal equilibrium state. The fixing device according to claim 5. The pressure member is a cylindrical member that is driven to rotate about an axis,
The fixing member is a driven rotating body that rotates when a rotational driving force is transmitted from the pressure member when it is in contact with the pressure member;
The fixing device includes a speed sensor that detects a rotation speed of the fixing member,
The control means controls a rotation speed of the pressure member so that a rotation speed of the fixing member detected by the speed sensor becomes a target rotation speed, and a control amount for controlling the rotation speed of the pressure member. The pressure member and the fixing member are determined to be in a thermal equilibrium state when a state where the fluctuation range of the pressure is not more than a predetermined value continues for a predetermined time or longer. The fixing device described. 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