JP2010231006A - Image forming device, controller, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To protect the fixing components and the presser of the image fixing unit from damaging in the image forming device when the power supply is suspended. <P>SOLUTION: This image forming device includes a toner image forming section to form toner images, a transfer section to transfer the toner image formed in the toner image forming section to the recording material, a fixing component forming a pressing section between a turning drive presser and the presser and pressing the recording material carried to the pressing section at the pressing section, a fixing section to fix the toner on the recording material, and a contact means to press the presser to the fixing component of the fixing section when fixing the toner on the recording material by supplying power from the power supply supplying power to various sections, and to press the presser to the fixing component with a pressure smaller than at the fixing when the power from the power supply is suspended. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and the like.

  In a fixing device provided in an image forming apparatus such as a copying machine using an electrophotographic system, a heat fixing method is widely adopted. As a fixing device using this heat fixing method, for example, a belt clamping system has been developed in which an endless belt is pressed against a fixing roll to form a pressure contact area (a clamping area) in which a sheet is sandwiched (see Patent Document 1).

Japanese Patent No. 3298354

  An object of the present invention is to prevent damage to a fixing member and a pressure member of a fixing device in an image forming apparatus in a state where power supply is stopped.

The invention according to claim 1 is a toner image forming unit that forms a toner image, a transfer unit that transfers a toner image formed by the toner image forming unit onto a recording material, a pressure member that is rotated, A fixing unit that forms a pressing part between the pressing member and presses the recording material conveyed to the pressing unit by the pressing unit, and fixes the toner to the recording material; At the time of fixing in which the power is supplied from the power supply unit that supplies the toner to the recording material and the toner is fixed, the pressure member is pressed against the fixing member of the fixing unit, and the power supply is stopped from the power supply unit In the state, the image forming apparatus includes: a contact / separation unit that presses the pressure member against the fixing member at a pressure smaller than that at the time of fixing.
According to a second aspect of the present invention, the contacting / separating means is positioned according to a signal for stopping the power supply output from the accepting means for receiving an instruction from the switching section for switching the power supply state / supply stop state of the power supply section. The image forming apparatus according to claim 1, wherein the driving source is driven and the positioning driving source keeps the pressing member in pressure contact with the fixing member at a pressure smaller than that at the time of fixing.
According to a third aspect of the present invention, the fixing member of the fixing unit is an endless belt having a conductive layer that is heated by electromagnetic induction, and the fixing unit is an AC magnetic field that intersects the conductive layer of the endless belt. The image forming apparatus according to claim 1, further comprising a magnetic field generating member that generates

  According to a fourth aspect of the present invention, when an image forming apparatus including a fixing unit that fixes toner on a recording material is brought into a state where power supply from a power supply unit that supplies power to each component unit is stopped. In response to the power supply stop instruction signal output from the accepting unit that has received the instruction of the switching unit that switches between the power supply state and the supply stop state of the power supply unit, the pressure member is attached to the fixing member at a pressure smaller than that at the time of fixing. Drive instruction means for driving the positioning drive source so as to make pressure contact, and the drive instruction means controls to stop the power supplied from the power supply unit after the pressure member is brought into contact with the fixing member. And a stop control means.

  According to a fifth aspect of the present invention, a power supply state for supplying power to each component of an image forming apparatus including a fixing unit for fixing toner on a recording material is in a power supply state or a supply stop state performed by an operator. In response to the function of acquiring the power supply stop instruction signal output from the receiving means for receiving the instruction and the power supply stop instruction signal, the pressure member is brought into pressure contact with the fixing member of the fixing unit at a pressure smaller than that at the time of fixing. And a function of stopping the power supplied from the power supply unit after the pressure member is brought into contact with the fixing member. .

  According to the first aspect of the present invention, damage to the fixing member and the pressure member of the fixing device is prevented in the image forming apparatus in the power supply stop state as compared with the case where the present invention is not adopted.

  According to the second aspect of the present invention, as compared with the case where the present invention is not adopted, the fixing member and the pressure member are reliably positioned in the image forming apparatus in the power supply stop state.

  According to the third aspect of the present invention, as compared with the case where the present invention is not adopted, in the image forming apparatus including the electromagnetic induction heating type fixing device, the deformation of the fixing belt left in the power supply stop state is prevented.

  According to the fourth aspect of the present invention, the positioning of the fixing member and the pressure member in the power supply stop state is controlled according to the power supply stop instruction signal of the image forming apparatus as compared with the case where the present invention is not adopted.

  According to the fifth aspect of the present invention, the positioning of the fixing member and the pressure member is controlled in accordance with the power supply stop instruction signal of the image forming apparatus as compared with the case where the present invention is not adopted.

1 is a diagram illustrating a configuration example of an image forming apparatus to which a fixing device according to an exemplary embodiment is applied. FIG. 4 is a diagram illustrating a driving mechanism of a pressure roll and a fixing belt in the fixing unit of the present embodiment. FIG. 3 is a cross-sectional view taken along line XX of the fixing unit in FIG. 2. FIG. 3 is a cross-sectional layer configuration diagram of a fixing belt. (A) is a side view of an end cap member, (b) is a top view of the end cap member seen from the Z direction. It is a figure explaining the half nip state arrange | positioned to the position which pressurizes a pressure roll to a fixing belt weakly than the time of fixing. FIG. 6 is a diagram illustrating a latch OFF state in which the pressure roll is not physically in contact with the fixing belt. It is sectional drawing explaining the structure of an IH heater. It is a figure explaining the laminated structure of an IH heater. It is a figure explaining the state of a line of magnetic force in case the temperature of a fixing belt exists in the temperature range below the magnetic permeability change start temperature. FIG. 6 is a diagram illustrating an outline of a temperature distribution in a width direction of a fixing belt when small-size paper is continuously passed. FIG. 6 is a diagram for explaining a state of magnetic lines of force when the temperature of the fixing belt in a non-sheet passing region is in a temperature range exceeding the permeability change start temperature. It is the figure which showed the slit formed in a temperature sensitive magnetic member. 6 is a timing chart illustrating an example of a fixing operation in the image forming apparatus. It is a control block diagram of the control part shown in FIG. 6 is a flowchart illustrating a flow of processing of an operation of the image forming apparatus after a signal for stopping power supply from a power supply unit is input.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
<Description of Image Forming Apparatus>
FIG. 1 is a diagram illustrating a configuration example of an image forming apparatus to which the fixing device of the present embodiment is applied. An image forming apparatus 1 shown in FIG. 1 is a so-called tandem color printer, and includes an image forming unit 10 that forms an image based on image data and a control unit 31 that controls the operation of the entire image forming apparatus 1. Further, for example, a communication unit 32 that receives image data by communicating with a personal computer (PC) 3, an image reading device (scanner) 4, and the like. An image processing unit 33 that performs image processing is provided.

The image forming unit 10 includes four image forming units 11Y, 11M, 11C, and 11K (also collectively referred to as “image forming unit 11”), which are examples of toner image forming units that are arranged in parallel at regular intervals. I have. Each image forming unit 11 forms an electrostatic latent image and a photosensitive drum 12 as an example of an image holding body that holds a toner image, and charging that uniformly charges the surface of the photosensitive drum 12 with a predetermined potential. 13, an LED (Light Emitting Diode) print head 14 that exposes the photosensitive drum 12 charged by the charger 13 based on each color image data, and a developer that develops an electrostatic latent image formed on the photosensitive drum 12. 15. A drum cleaner 16 for cleaning the surface of the photosensitive drum 12 after transfer is provided.
Each of the image forming units 11 is configured in substantially the same manner except for the toner stored in the developing device 15, and each forms a toner image of yellow (Y), magenta (M), cyan (C), and black (K). To do.

  The image forming unit 10 also receives the intermediate transfer belt 20 onto which the color toner images formed on the photosensitive drums 12 of the image forming units 11 are transferred, and the color toner images formed on the image forming units 11. A primary transfer roll 21 that sequentially transfers (primary transfer) to the intermediate transfer belt 20 is provided. Further, a secondary transfer roll 22 that batch-transfers (secondary transfer) each color toner image transferred and superimposed on the intermediate transfer belt 20 onto a sheet P that is a recording material (recording paper), and each color toner that is secondarily transferred. A fixing unit 60 is provided as an example of a fixing unit (fixing device) that fixes the image on the paper P. In the image forming apparatus 1 of the present embodiment, the intermediate transfer belt 20, the primary transfer roll 21, and the secondary transfer roll 22 constitute a transfer unit.

  In the image forming apparatus 1 of the present embodiment, under the operation control by the control unit 31, image forming processing is performed by the following process. That is, the image data from the PC 3 or the scanner 4 is received by the communication unit 32, subjected to predetermined image processing by the image processing unit 33, and then sent to each image forming unit 11 as image data for each color. It is done. For example, in the image forming unit 11K that forms a black (K) color toner image, the photosensitive drum 12 is uniformly charged at a predetermined potential by the charger 13 while rotating in the direction of arrow A, and the image processing unit The LED print head 14 scans and exposes the photosensitive drum 12 based on the K-color image data transmitted from 33. As a result, an electrostatic latent image relating to the K color image is formed on the photosensitive drum 12. The K-color electrostatic latent image formed on the photosensitive drum 12 is developed by the developing unit 15, and a K-color toner image is formed on the photosensitive drum 12. Similarly, yellow (Y), magenta (M), and cyan (C) toner images are formed in the image forming units 11Y, 11M, and 11C, respectively.

  Each color toner image formed on the photosensitive drum 12 of each image forming unit 11 is sequentially electrostatically transferred (primary transfer) onto the intermediate transfer belt 20 that moves in the direction of arrow B by the primary transfer roll 21, and each color toner is superimposed. A superimposed toner image is formed. The superimposed toner image on the intermediate transfer belt 20 is conveyed to a region (secondary transfer portion T) where the secondary transfer roll 22 is disposed as the intermediate transfer belt 20 moves. When the superimposed toner image is conveyed to the secondary transfer unit T, the paper P is supplied from the paper holding unit 40 to the secondary transfer unit T in accordance with the timing. The superimposed toner image is collectively electrostatically transferred (secondary transfer) onto the conveyed paper P by the transfer electric field formed by the secondary transfer roll 22 in the secondary transfer portion T.

Thereafter, the sheet P on which the superimposed toner image is electrostatically transferred is conveyed to the fixing unit 60. The toner image on the paper P conveyed to the fixing unit 60 receives heat and pressure by the fixing unit 60 and is fixed on the paper P. Then, the paper P on which the fixed image is formed is conveyed to a paper stacking unit 45 provided in the discharge unit of the image forming apparatus 1.
On the other hand, the toner (primary transfer residual toner) adhering to the photosensitive drum 12 after the primary transfer and the toner (secondary transfer residual toner) adhering to the intermediate transfer belt 20 after the secondary transfer are respectively drum cleaner 16. , And the belt cleaner 25.
In this way, the image forming process in the image forming apparatus 1 is repeatedly executed for the number of cycles corresponding to the number of prints.

<Description of fixing unit configuration>
Next, the fixing unit 60 of this embodiment will be described. In this embodiment, an example using an electromagnetic induction heating method will be described.
2 and 3 are diagrams showing the configuration of the fixing unit 60 of the present embodiment. FIG. 2 is a diagram illustrating a driving mechanism for the pressure roll and the fixing belt in the fixing unit 60. A front view of a fixing operation, that is, a state in which the pressure roll 62 is in a latched ON state (a state in which the fixing belt 61 and the pressure roll 62 are pressed against each other, details will be described later) is shown. 3 is a cross-sectional view taken along the line XX in FIG.
As shown in FIG. 3, the fixing unit 60 is an example of an IH (Induction Heating) heater 80 as an example of a magnetic field generating member that generates an alternating magnetic field, and an example of a fixing member that is electromagnetically heated by the IH heater 80 to fix a toner image. A fixing belt 61, a pressure roll 62 as an example of a pressure member disposed so as to face the fixing belt 61, and a pressure pad 63 pressed from the pressure roll 62 via the fixing belt 61. .
Further, the fixing unit 60 is a temperature-sensitive magnetic member 64 as a magnetic path forming member that forms a magnetic path by inducing an alternating magnetic field generated by the holder 65 and the IH heater 80 that support components such as the pressing pad 63. In addition, a guide member 66 that guides the lines of magnetic force that have passed through the temperature-sensitive magnetic member 64 and a peeling assisting member 70 that assists in peeling the paper P from the fixing belt 61 are provided.

  In the fixing unit 60 according to the present embodiment, as will be described later, when the pressure roll 62 is in the latched ON state, the pressure roll 62 is driven, and the fixing belt 61 is driven to rotate as the pressure roll 62 rotates. It is like that. In this embodiment, the fixing belt 61 and the pressure roll 62 can be brought into contact with and separated from each other as needed, and the amount of pressure contact (the amount of biting) between the fixing belt 61 and the pressure roll 62 can be adjusted. ing. For this reason, the fixing unit 60 includes an contacting / separating mechanism 200 as an example of an contacting / separating unit that fixes the attaching position on the fixing belt 61 side and contacts / separates the pressure roll 62 with respect to the fixing belt 61. Yes.

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

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

The conductive heating layer 612 is an example of a conductive layer, and is an electromagnetic induction heating element layer that is electromagnetically heated by an alternating magnetic field generated by the IH heater 80. That is, the conductive heat generating layer 612 is a layer that generates an eddy current when the AC magnetic field from the IH heater 80 passes in the thickness direction.
In general, a general-purpose power source that can be manufactured at low cost is used as a power source for an excitation circuit that supplies an alternating current to the IH heater 80 (see also FIG. 10 below). Therefore, the frequency of the alternating magnetic field generated by the IH heater 80 is generally 20 k to 100 kHz by a general-purpose power source. Thereby, the conductive heat generating layer 612 is configured such that an alternating magnetic field having a frequency of 20 k to 100 kHz enters and passes therethrough.

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

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

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

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

  In the present embodiment, the peeling assisting member 70 is disposed on the downstream side of the nip portion N as a peeling assisting means by the pressing pad 63. The peeling assisting member 70 is supported by the holder 72 in a state in which the peeling baffle 71 is close to the fixing belt 61 in a direction facing the rotational movement direction of the fixing belt 61 (so-called counter direction). Then, the curled portion formed on the paper P at the outlet of the pressing pad 63 is supported by the peeling baffle 71, and the paper P is prevented from moving toward the fixing belt 61.

<Description of temperature-sensitive magnetic member>
The temperature-sensitive magnetic member 64 is formed in an arc shape that follows the inner peripheral surface of the fixing belt 61. The temperature-sensitive magnetic member 64 is disposed close to the inner peripheral surface of the fixing belt 61 so as to have a predetermined gap (for example, 0.5 mm to 1.5 mm) and is not contacted.
By arranging the temperature-sensitive magnetic member 64 close to the fixing belt 61, the temperature of the temperature-sensitive magnetic member 64 changes corresponding to the temperature of the fixing belt 61. For this reason, the temperature of the temperature-sensitive magnetic member 64 is substantially the same as the temperature of the fixing belt 61.
Further, when the main switch of the image forming apparatus 1 is turned on and the fixing belt 61 is heated to the fixing set temperature, the heat of the fixing belt 61 is suppressed from flowing into the temperature-sensitive magnetic member 64, and the warm-up time is shortened. To do.

  Further, the temperature-sensitive magnetic member 64 is made of a material having a “permeability change start temperature” (see the subsequent stage), which is a temperature at which the magnetic permeability of the magnetic characteristics changes suddenly. The permeability change start temperature is a temperature at which the permeability of the magnetic characteristics changes suddenly. In the present embodiment, the temperature change start temperature of the material constituting the temperature-sensitive magnetic member 64 is equal to or higher than the fixing set temperature at which each color toner image is melted, and the elastic layer 613 and the surface release layer of the fixing belt 61. It is set within a temperature range lower than the heat resistant temperature of 614. That is, the temperature-sensitive magnetic member 64 is made of a material having a characteristic (“temperature-sensitive magnetism”) that reversibly changes between ferromagnetic and non-magnetic (paramagnetic) in a temperature range including the fixing set temperature. . The temperature-sensitive magnetic member 64 functions as a magnetic path forming member in a temperature range that is equal to or lower than the permeability change start temperature exhibiting ferromagnetism, and induces magnetic field lines generated by the IH heater 80 and transmitted through the fixing belt 61 to the inside. Thus, a magnetic path passing through the inside of the temperature-sensitive magnetic member 64 is formed. As a result, the temperature-sensitive magnetic member 64 forms a closed magnetic path that encloses the fixing belt 61 and the exciting coil 82 (see FIG. 10 at a later stage) of the IH heater 80 inside.

On the other hand, in the temperature range exceeding the permeability change start temperature, the temperature-sensitive magnetic member 64 transmits the magnetic field lines generated by the IH heater 80 and transmitted through the fixing belt 61 so as to cross the thickness direction of the temperature-sensitive magnetic member 64. Let Thereby, the magnetic lines of force generated by the IH heater 80 and transmitted through the fixing belt 61 form a magnetic path that passes through the temperature-sensitive magnetic member 64, passes through the inside of the guide member 66, and returns to the IH heater 80.
The “permeability change start temperature” here is a temperature at which the magnetic permeability (for example, the magnetic permeability measured by JIS C2531) starts to decrease continuously. For example, the temperature-sensitive magnetic member 64 or the like The temperature point at which the amount of magnetic flux (number of lines of magnetic force) passing through the member starts to change. Therefore, the permeability change start temperature is a temperature close to the Curie point, which is the temperature at which magnetism disappears, but has a concept different from the Curie point.

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

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

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

  Further, end cap members 67 (see FIG. 2) that maintain the cross-sectional shape of both ends of the fixing belt 61 in a circular shape are fixed to both ends in the axial direction of the holder 65. The fixing belt 61 is supported by end cap members 67 at the inner peripheral surfaces of both ends, and rotates and moves in the direction of arrow C in FIG. 3 at a process speed of, for example, 140 mm / s while maintaining a substantially circular shape.

Here, FIG. 5A is a side view of the end cap member 67, and FIG. 5B is a plan view of the end cap member 67 viewed from the Z direction. As shown in FIG. 5, the end cap member 67 is formed with a fixing portion 67 a fitted inside the both ends of the fixing belt 61 and has an outer diameter larger than that of the fixing portion 67 a, and when the end cap member 67 is attached to the fixing belt 61. A flange portion 67d formed so as to protrude radially from the fixing belt 61, a gear portion 67b to which a rotational force is transmitted, a support portion 65a formed at both ends of the holder 65, and a coupling member 166 are rotatable. The bearing bearing part 67c couple | bonded with is provided. Then, as shown in FIG. 2, the support portions 65a at both ends of the holder 65 are fixed to both ends of the casing 69 of the fixing unit 60, whereby the end cap member 67 is coupled to the support portion 65a. It is rotatably supported via the bearing bearing portion 67c.
As a material constituting the end cap member 67, so-called engineering plastics having high mechanical strength and heat resistance are used. For example, phenol resin, polyimide resin, polyamide resin, polyamideimide resin, PEEK resin, PES resin, PPS resin, LCP resin and the like are suitable.

Here, when the fixing belt 61 rotates while being supported by the end cap members 67 at both ends, generally a torque of about 0.1 N · m to 0.5 N · m acts.
In the fixing belt 61 of the present embodiment, the base material layer 611 is made of high mechanical strength, for example, nonmagnetic stainless steel. Therefore, even when a torsional torque of about 0.1 N · m to 0.5 N · m is applied to the entire fixing belt 61, buckling or the like hardly occurs in the fixing belt 61.

Further, the flange portion 67 d of the end cap member 67 suppresses the deviation of the fixing belt 61. The fixing belt 61 at that time generally has a compressive force of about 1N to 5N from the end (flange portion 67d) side in the axial direction. In the present embodiment, even when the fixing belt 61 receives such a compressive force, the base material layer 611 of the fixing belt 61 is made of nonmagnetic stainless steel or the like, so that buckling or the like occurs. It is suppressed.
As described above, in this embodiment, the base material layer 611 of the fixing belt 61 is made of, for example, non-magnetic stainless steel having high mechanical strength, so that buckling or the like occurs with respect to torsion torque or compression force. A difficult configuration is realized. Furthermore, since the base material layer 611 and the conductive heat generating layer 612 are formed as thin layers to ensure the flexibility and flexibility of the fixing belt 61 as a whole, deformation and shape restoration following the nip portion N are prevented. Done.

The pressure roll 62 is disposed so as to face the fixing belt 61, and rotates in the direction of arrow D in FIG. 3 at a process speed of, for example, 140 mm / s. Then, a nip portion N is formed in a state where the fixing belt 61 is sandwiched between the pressure roll 62 and the pressing pad 63, and the sheet P holding the unfixed toner image is passed through the nip portion N, so that the heat and pressure To fix the unfixed toner image on the paper P.
The pressure roll 62 includes, for example, a solid aluminum core (cylindrical metal core) 621 having a diameter of 18 mm, and a heat-resistant elastic body layer 622 such as a silicone sponge having a thickness of 5 mm, which is coated on the outer peripheral surface of the core 621. Further, for example, a release layer 623 made of a heat-resistant resin coating such as PFA containing carbon having a thickness of 50 μm or a heat-resistant rubber coating is laminated. Then, the contact / separation mechanism 200 is pressed against the fixing belt 61 so as to press the pressing pad 63 with a load of 25 kgf, for example.
In the present embodiment, the pressure roll 62 supplies power to each component shown in FIG. 6 to be described later by the contact / separation mechanism 200 in addition to the position of the latch ON state during the normal fixing operation shown in FIG. The position is controlled in a half-nip state in a state where power supply from the power supply unit is stopped (when the main power supply is OFF) and a latch OFF state in warm-up shown in FIG.

<Description of drive mechanism for pressure roll and fixing belt>
Returning to FIG. 2, the driving mechanism for the pressure roll 62 and the fixing belt 61 in the fixing unit 60 of the present embodiment will be described.
Here, it is assumed that the fixing unit 60 is set in a nip released state before the fixing operation as shown in FIG. In a standby state before the fixing operation, the pressing roll 62 is placed at a warm-up position away from the fixing belt 61 by the contact / separation mechanism 200. This warm-up position is a position where the pressure roll 62 is disposed at the time of warm-up, and a so-called latch OFF state in which the pressure roll 62 does not physically contact the fixing belt 61 is brought about.

  As shown in FIG. 2, in the fixing unit 60, the rotational driving force from the drive motor 90 is transmitted to the shaft 97 via the transmission gear 92 fixed to the rotation shaft 91 and the transmission gears 93, 94, 95, 96. Is done. Thereby, the rotational driving force is transmitted to the pressure roll 62 and the pressure roll 62 is rotationally driven.

  Next, the rotational driving force from the drive motor 90 is transmitted to the shaft 103 via the transmission gear 101 fixed to the rotation shaft 91 coaxially with the transmission gear 92 and the one-way clutch 102 as an example of a rotation transmission limiting member. The gears 67 b (see FIG. 5) of both end cap members 67 are transmitted from the transmission gears 104 and 105 coupled to the shaft 103. As a result, a rotational driving force is transmitted from the end cap member 67 to the fixing belt 61, and the end cap member 67 and the fixing belt 61 are integrally rotated. At this time, the fixing belt 61 rotates by receiving a driving force directly from both ends of the fixing belt 61.

  Next, when the fixing unit 60 performs a fixing operation as shown in FIG. 3, the pressing roll 62 is placed in a latch-on state in which the pressing roll 62 is pressed against the fixing belt 61 by the contact / separation mechanism 200. At this time, the one-way clutch 102 is operated, and the transmission of the rotational driving force from the drive motor 90 to the shaft 97 is stopped. The fixing belt 61 rotates following the rotation of the pressure roll 62.

Note that the fixing unit 60 of the present embodiment detects the rotation speed of the fixing belt 61 in the latch-on state by the rotation detector 107, and an output signal is input to the control unit 31. The rotation of the drive motor 90 is controlled via the motor driver 910 that has received a control signal from the control unit 31.
The contact / separation mechanism 200 (see FIG. 3) includes a latch motor 201 serving as a positioning drive source, a rotating shaft 202, transmission gears 203 and 204, a shaft 205, and a shaft cam 206 on the shaft 205. For example, the rotational position of the shaft 205 is detected by the photo sensor 207, and the output signal is input to the control unit 31. The operation of the latch motor 201 is controlled via the motor driver 210 that receives the control signal from the control unit 31.

<Description of IH heater>
The IH heater 80 that performs electromagnetic induction heating by applying an alternating magnetic field to the conductive heat generating layer 612 of the fixing belt 61 will be described below.
FIG. 8 is a cross-sectional view illustrating the configuration of the IH heater 80 in the present embodiment. As shown in FIG. 8, the IH heater 80 includes a support 81 made of a nonmagnetic material such as a heat resistant resin, and an exciting coil 82 that generates an alternating magnetic field. Further, an elastic support member 83 made of an elastic body that fixes the excitation coil 82 on the support 81 and a magnetic core 84 that forms a magnetic path of an alternating magnetic field generated by the excitation coil 82 are provided. Furthermore, a shield 85 that shields the magnetic field, a pressure member 86 that pressurizes the magnetic core 84 toward the support 81, and an excitation circuit 88 that supplies an alternating current to the excitation coil 82 are provided.

The support 81 is formed in a shape whose cross section is curved along the surface shape of the fixing belt 61, and an upper surface (supporting surface) 81 a that supports the exciting coil 82 has a predetermined gap (for example, 0) from the surface of the fixing belt 61. 0.5 mm to 2 mm). Moreover, as a material which comprises the support body 81, heat resistance, such as heat resistant resins, such as heat resistant glass, a polycarbonate, polyether sulfone, PPS (polyphenylene sulfide), or the glass fiber mixed with these, for example. Some non-magnetic materials are used.
The exciting coil 82 is formed by winding, for example, 90 litz wires, which are bundled with, for example, 90 copper wires having a diameter of 0.17 mm, which are insulated from each other, into a closed loop with a hollow space such as an ellipse, an ellipse, or a rectangle. Configured. Then, when an alternating current having a predetermined frequency is supplied to the exciting coil 82 from the exciting circuit 88, an alternating magnetic field centered around a litz wire wound in a closed loop is generated around the exciting coil 82. . Generally, the frequency of the alternating current supplied from the excitation circuit 88 to the excitation coil 82 is 20 kHz to 100 kHz generated by the general-purpose power source.

The magnetic core 84 functions as a magnetic path forming unit. Examples of the material of the magnetic core 84 include a ferromagnetic material made of an oxide or alloy material having a high magnetic permeability such as soft ferrite, ferrite resin, amorphous alloy (amorphous alloy), permalloy, and magnetic shunt steel. .
The magnetic core 84 forms a path (magnetic path) for lines of magnetic force. This magnetic line of force (magnetic path) induces a magnetic line of force (magnetic flux) generated by the alternating magnetic field generated by the exciting coil 82, and crosses the fixing belt 61 from the magnetic core 84 toward the temperature-sensitive magnetic member 64. It passes through the warm magnetic member 64 and returns to the magnetic core 84.
That is, the AC magnetic field generated by the exciting coil 82 is configured to pass through the inside of the magnetic core 84 and the inside of the temperature-sensitive magnetic member 64, and the magnetic lines of force wrap the fixing belt 61 and the exciting coil 82 inside. A closed magnetic circuit is formed. As a result, the magnetic field lines of the alternating magnetic field generated by the exciting coil 82 are concentrated in a region facing the magnetic core 84 of the fixing belt 61.
Here, the magnetic core 84 is preferably made of a material having a small loss due to magnetic path formation. Specifically, the magnetic core 84 is desirably used in a form that reduces the eddy current loss (current path interruption or division by slits, thin plate bundling, etc.), and is preferably formed of a material having a small hysteresis loss.
Further, the length of the magnetic core 84 along the rotation direction of the fixing belt 61 is configured to be smaller than the length of the temperature-sensitive magnetic member 64 along the rotation direction of the fixing belt 61. Thereby, the leakage of magnetic lines of force to the periphery of the IH heater 80 is reduced, and the power factor is improved. Furthermore, electromagnetic induction to the metal member constituting the fixing unit 60 is suppressed, and the heat generation efficiency in the fixing belt 61 (conductive heat generation layer 612) is increased.

<Description of fixing method of excitation coil>
Next, a method for fixing the exciting coil 82 to the support 81 in the IH heater 80 of the present embodiment will be described.
In the IH heater 80 of the present embodiment, the elastic support member 83 that is an example of an elastic support member that supports the excitation coil 82 on the support 81 is made of an elastic body such as silicone rubber or fluorine rubber. The elastic support member 83 is elastically deformed while pressing the excitation coil 82 against the support 81, thereby supporting the excitation coil 82 on the support surface of the support 81. That is, the elastic support member 83 is made of a material having a low Young's modulus, and when the elastic support member 83 presses the exciting coil 82 against the support 81, the elastic support member 83 with a low Young's modulus is elastically deformed, The exciting coil 82 is supported on the support body 81.

  FIG. 9 is a view for explaining the laminated structure of the IH heater 80 of the present embodiment. As shown in FIG. 9, in the exciting coil 82, on the support surface 81a of the support 81, the closed loop hollow portion 82a of the exciting coil 82 surrounds the convex portion 81b provided on the central axis in the longitudinal direction of the support surface 81a. Installed. The support surface 81a is supported by the above-described end cap member 67 (see FIG. 5), and the position setting is such that the distance from the fixing belt 61 that rotates while drawing a substantially circular locus is set to a specified value (design value). It is formed as a surface. As a result, the exciting coil 82 is disposed in close contact with the support surface 81a, whereby the distance between the exciting coil 82 and the fixing belt 61 is set to a design value.

Therefore, in the IH heater 80 of the present embodiment, the excitation coil 82 disposed on the support surface 81a of the support 81 is configured to be pressed toward the support surface 81a by the elastic support member 83. . That is, the magnetic core 84 disposed on the upper portion of the exciting coil 82 is attached to the support rail portions 81c provided at both end portions 84a of the support body 81 (see also FIG. 8). Thereby, the elastic support member 83 disposed on the lower surface of the magnetic core 84 (the side surface on the support body 81 side) is placed in contact with the upper surface of the exciting coil 82. On the other hand, when the shield 85 is attached to the support body 81, the magnetic core 84 is pressed to the support body 81 side by the pressing member 86 provided on the lower surface of the shield 85. Thereby, the exciting coil 82 receives the elastic force from the elastic support member 83 that receives the pressure from the magnetic core 84, and is supported while being pressed toward the support surface 81a by the elastic support member 83 that is elastically deformed by the pressure. It is supported on the surface 81a. As a result, the exciting coil 82 comes into close contact with the support surface 81a, and the distance between the exciting coil 82 and the fixing belt 61 is set to a design value.
As the pressure member 86, for example, an elastic member such as a spring may be used in addition to an elastic body such as silicone rubber or fluorine rubber.

  In general, when an alternating magnetic field is generated by the exciting coil 82, the magnetic core 84 disposed in the vicinity of the exciting coil 82, the temperature-sensitive magnetic member 64 disposed on the inner peripheral surface side of the fixing belt 61, etc. Magnetic force acts, and vibration (magnetostriction) is generated in the exciting coil 82 itself. For this reason, when the excitation coil 82 is fixed to the support 81 using a so-called rigid body (a material having a high Young's modulus) such as an adhesive, the vibration of the excitation coil 82 is caused by the cumulative use of the fixing unit 60 over a long period of time. As a result, the rigid body such as an adhesive and the exciting coil 82 are easily separated. When the exciting coil 82 is peeled off from a rigid body such as an adhesive, the exciting coil 82 is displaced on the support surface 81a, or the exciting coil 82 is deformed. Then, the distance between the exciting coil 82 and the fixing belt 61 deviates from the initial design value, and the density of magnetic lines of force (magnetic flux density) passing through the fixing belt 61 via the magnetic core 84 partially varies on the surface of the fixing belt 61. Become. For this reason, the magnitude of the eddy current I generated in the fixing belt 61 may be uneven, and a state may be formed in which the amount of heat generated on the surface of the fixing belt 61 varies partially.

  Further, when the excitation coil 82 is fixed to the support 81 using a rigid body such as an adhesive, the entire surface of the excitation coil 82 is displaced from the support 81 until the adhesive or the like is solidified. It is necessary to fix so that there is no. However, since the exciting coil 82 is, for example, a litz wire bundled in a closed loop and bonded, the deformation is likely to occur. For this reason, it is difficult to fix the exciting coil 82 with the support 81 so as not to be displaced until the adhesive or the like is solidified, and the positional accuracy of the exciting coil 82 with respect to the support 81 tends to be lowered. When the positional accuracy of the exciting coil 82 with respect to the support 81 is lowered, a state in which a partial variation occurs in the amount of heat generated on the surface of the fixing belt 61 is formed as described above.

Therefore, in the IH heater 80 according to the present embodiment, the elastic support member 83 made of an elastic body such as silicone rubber or fluorine rubber presses the excitation coil 82 against the support 81 to thereby support the support body. The support surface 81a of 81 is comprised so that it may support. The elastic support member 83 formed of an elastic body elastically deforms itself in accordance with the vibration of the excitation coil 82 while absorbing the vibration of the excitation coil 82. Accordingly, even if the cumulative number of vibrations of the excitation coil 82 becomes large due to the cumulative use of the fixing unit 60 over a long period of time, the elastic support member 83 and the excitation coil 82 are not separated, and the support 81 and the excitation coil are separated. 82 is maintained in the initial positional relationship.
Further, the elastic support member 83 is managed so that the thickness (set value) falls within a predetermined dimensional accuracy at the time of manufacture. Therefore, the pressing force in the longitudinal direction for supporting the exciting coil 82 on the support surface 81a is set to be substantially equal. In particular, in the IH heater 80 according to the present embodiment, a plurality of magnetic cores 84 divided and provided along the longitudinal direction of the excitation coil 82 press the excitation coil 82 uniformly along the longitudinal direction. Thereby, the adhesion between the exciting coil 82 and the support surface 81a is enhanced in the longitudinal direction, and the positions of the exciting coil 82 and the fixing belt 61 are set in the longitudinal direction.
Further, when the IH heater 80 is manufactured, the exciting coil 82 is attached in a short time without requiring time for the adhesive or the like to solidify.

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

  FIG. 10 is a diagram for explaining the state of the lines of magnetic force (H) when the temperature of the fixing belt 61 is in a temperature range equal to or lower than the permeability change start temperature. As shown in FIG. 10, when the temperature of the fixing belt 61 is in a temperature range equal to or lower than the permeability change start temperature, the magnetic field lines H of the alternating magnetic field generated by the IH heater 80 pass through the fixing belt 61, A magnetic path passing through the inside of the temperature-sensitive magnetic member 64 along the spreading direction (direction orthogonal to the thickness direction) is formed. Therefore, the number of magnetic field lines H (magnetic flux density) per unit area in the region crossing the conductive heat generating layer 612 of the fixing belt 61 increases.

  That is, after the magnetic force line H is radiated from the magnetic core 84 of the IH heater 80 and passes through the regions R1 and R2 crossing the conductive heat generating layer 612 of the fixing belt 61, the magnetic force line H enters the inside of the temperature-sensitive magnetic member 64 which is a ferromagnetic material. Be guided. Therefore, the magnetic field lines H crossing the conductive heat generating layer 612 of the fixing belt 61 in the thickness direction are concentrated so as to enter the inside of the temperature-sensitive magnetic member 64, and the magnetic flux density in the regions R1 and R2 increases. Further, even when the magnetic field lines H that have passed through the inside of the temperature-sensitive magnetic member 64 along the spreading direction return to the magnetic core 84 again, in the region R3 that crosses the conductive heating layer 612 in the thickness direction, the magnetic field in the temperature-sensitive magnetic member 64 is increased. It is concentrated toward the magnetic core 84 from the lower part. Therefore, the magnetic force lines H that cross the conductive heat generating layer 612 of the fixing belt 61 in the thickness direction are concentrated from the temperature-sensitive magnetic member 64 toward the magnetic core 84, and the magnetic flux density in the region R3 is also increased.

In the conductive heating layer 612 of the fixing belt 61 where the magnetic lines H cross in the thickness direction, an eddy current I proportional to the amount of change in the number of magnetic lines H per unit area (magnetic flux density) is generated. Accordingly, as shown in FIG. 10, a large eddy current I is generated in the regions R1, R2 and R3 where the amount of change in magnetic flux density is large. The eddy current I generated in the conductive heat generation layer 612 generates Joule heat W (W = I ² R), which is the product of the specific resistance value R of the conductive heat generation layer 612 and the square of the eddy current I. Thereby, a large Joule heat W is generated in the conductive heat generating layer 612 where the large eddy current I is generated.
As described above, when the temperature of the fixing belt 61 is in a temperature range equal to or lower than the permeability change start temperature, large heat is generated in the regions R1 and R2 and the region R3 where the lines of magnetic force H cross the conductive heat generating layer 612. Thereby, the fixing belt 61 is heated.

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

<Description of function for suppressing temperature rise of non-sheet passing portion of fixing belt>
Next, the function of suppressing the temperature rise at the non-sheet passing portion of the fixing belt 61 will be described.
First, a case where small-size paper P (small-size paper P1) is continuously passed through the fixing unit 60 will be described. FIG. 11 is a diagram showing an outline of the temperature distribution in the width direction of the fixing belt 61 when the small size paper P1 is continuously fed. In FIG. 11, the maximum sheet passing area which is the maximum size width (for example, A3 width) of the sheet P used in the image forming apparatus 1 is Ff, and the small size sheet P1 (for example, the width is smaller than the maximum size sheet P). , A4 (vertical feed) passes through the area (small size paper passing area) as Fs, and the non-sheet passing area through which the small size paper P1 does not pass is Fb. In the image forming apparatus 1, it is assumed that the sheet is passed based on the center position.

  As shown in FIG. 11, when the small size paper P1 is continuously passed, heat for fixing is consumed in the small size paper passing area Fs through which the small size paper P1 passes. Therefore, the temperature adjustment control at the fixing set temperature is performed by the control unit 31 (see FIG. 1), and the temperature of the fixing belt 61 in the small size paper passing area Fs is maintained within the range near the fixing set temperature. On the other hand, temperature adjustment control similar to that of the small-size paper passing area Fs is performed also in the non-paper passing area Fb. However, heat for fixing is not consumed in the non-sheet passing area Fb. For this reason, the temperature of the non-sheet passing area Fb is likely to rise to a temperature higher than the fixing set temperature. Then, when the continuous passage of the small size paper P1 is continued in this state, the temperature of the non-sheet passing region Fb rises, for example, higher than the heat resistance temperature of the elastic layer 613 and the surface release layer 614 of the fixing belt 61, 61 may be damaged.

  Therefore, as described above, in the fixing unit 60 of the present embodiment, the temperature-sensitive magnetic member 64 is equal to or higher than the preset fixing temperature and is, for example, equal to or lower than the heat resistance temperature of the elastic layer 613 and the surface release layer 614 of the fixing belt 61. For example, an Fe—Ni alloy or the like having a magnetic permeability change start temperature set within the temperature range is used. That is, as shown in FIG. 11, the magnetic permeability change start temperature Tcu of the temperature-sensitive magnetic member 64 is equal to or higher than the fixing set temperature Tf, for example, a temperature equal to or lower than the heat resistance temperature Tlim of the elastic layer 613 and the surface release layer 614. It is set in the area.

Accordingly, when the small size paper P1 is continuously passed, the temperature in the non-sheet passing region Fb of the fixing belt 61 exceeds the magnetic permeability change start temperature of the temperature-sensitive magnetic member 64. Accordingly, the temperature in the non-sheet passing region Fb of the temperature-sensitive magnetic member 64 adjacent to the fixing belt 61 also exceeds the permeability change start temperature in the same manner as the fixing belt 61 corresponding to the temperature of the fixing belt 61. For this reason, the temperature-sensitive magnetic member 64 in the non-sheet-passing region Fb has a relative magnetic permeability close to 1, and the properties as a ferromagnetic material disappear. The relative magnetic permeability of the temperature-sensitive magnetic member 64 decreases and approaches 1 so that the magnetic field lines H in the non-sheet-passing region Fb are not guided into the temperature-sensitive magnetic member 64 but pass through the temperature-sensitive magnetic member 64. become. Therefore, in the non-sheet passing region Fb of the fixing belt 61, the magnetic field lines H after passing through the conductive heat generating layer 612 are diffused, and the magnetic flux density of the magnetic field lines H crossing the conductive heat generating layer 612 is reduced. Thereby, the eddy current I generated in the conductive heat generation layer 612 is reduced, and the heat generation amount (Joule heat W) in the fixing belt 61 is reduced. As a result, an excessive temperature rise in the non-sheet passing area Fb is suppressed, and damage to the fixing belt 61 is suppressed.
As described above, the temperature-sensitive magnetic member 64 functions as a detection unit that detects the temperature of the fixing belt 61 and suppresses an increase in temperature that suppresses an excessive temperature increase of the fixing belt 61 according to the detected temperature of the fixing belt 61. It also has a function as a department.

  The lines of magnetic force H after passing through the temperature-sensitive magnetic member 64 reach the guide member 66 (see FIG. 3) and are guided into this. When the magnetic flux reaches the induction member 66 and is induced therein, more eddy current I flows toward the induction member 66 where the eddy current I flows more easily than the conductive heat generation layer 612. Therefore, the amount of eddy current flowing in the conductive heat generating layer 612 is further suppressed, and the temperature rise in the non-sheet passing region Fb is suppressed.

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

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

  FIG. 12 is a diagram for explaining the state of the lines of magnetic force H when the temperature of the fixing belt 61 in the non-sheet-passing region Fb is in a temperature range exceeding the permeability change start temperature. As shown in FIG. 12, when the temperature of the fixing belt 61 is in the temperature range exceeding the magnetic permeability change start temperature in the non-sheet passing area Fb, the temperature-sensitive magnetic member 64 in the non-sheet passing area Fb has a ratio. Magnetic permeability decreases. Therefore, the magnetic field lines H of the alternating magnetic field generated by the IH heater 80 change so as to easily pass through the temperature-sensitive magnetic member 64. Accordingly, the magnetic field lines H of the alternating magnetic field generated by the IH heater 80 (excitation coil 82) are radiated so as to diffuse from the magnetic core 84 toward the fixing belt 61 and reach the induction member 66.

That is, in the regions R1 and R2 where the magnetic force lines H are radiated from the magnetic core 84 of the IH heater 80 and cross the conductive heat generating layer 612 of the fixing belt 61, the magnetic force lines H are difficult to be guided to the temperature-sensitive magnetic member 64 and thus diffuse radially. As a result, the magnetic flux density (number of magnetic force lines H per unit area) of the magnetic field lines H crossing the conductive heat generating layer 612 of the fixing belt 61 in the thickness direction decreases. Further, even in the region R3 that crosses the conductive heat generating layer 612 in the thickness direction when the magnetic force line H returns to the magnetic core 84 again, the magnetic force line H returns to the magnetic core 84 from the diffused wide region. The magnetic flux density of the magnetic field lines H crossing 612 in the thickness direction decreases.
Therefore, when the temperature of the fixing belt 61 is in a temperature range exceeding the permeability change start temperature, the magnetic flux density of the magnetic field lines H crossing the conductive heating layer 612 in the thickness direction in the regions R1, R2, and R3 decreases. It becomes. As a result, the eddy current I generated in the conductive heating layer 612 where the magnetic field lines H cross in the thickness direction is reduced, and the Joule heat W generated in the fixing belt 61 is reduced. As a result, the temperature of the fixing belt 61 decreases.

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

<Description of the configuration for suppressing the temperature rise of the temperature-sensitive magnetic member>
In order for the temperature-sensitive magnetic member 64 to perform the function of suppressing an excessive temperature rise in the non-sheet-passing region Fb, the temperature of each region in the longitudinal direction of the temperature-sensitive magnetic member 64 is the length of the fixing belt 61 facing it. It changes in accordance with the temperature of each region in the direction, and needs to function as a detection unit that detects the temperature of the fixing belt 61 described above.
Therefore, regarding the temperature-sensitive magnetic member 64 itself, a configuration that is difficult to be induction-heated by the magnetic field lines H is adopted. That is, even if the temperature of the fixing belt 61 is equal to or lower than the permeability change start temperature and the temperature-sensitive magnetic member 64 exhibits ferromagnetism, the temperature-sensitive magnetic member 64 is included in the magnetic force lines H from the IH heater 80. There is a magnetic field line H that crosses in the thickness direction. As a result, a weak eddy current I is generated inside the temperature-sensitive magnetic member 64, and a slight amount of heat is generated in the temperature-sensitive magnetic member 64 itself. For this reason, for example, when a large amount of image formation is continuously performed, the self-heat generation heat is accumulated in the temperature-sensitive magnetic member 64, and the temperature of the temperature-sensitive magnetic member 64 also in the paper passing area (see FIG. 11). Shows an upward trend. Thus, if the self-heating due to eddy current loss is large, the temperature rises and unintentionally reaches the temperature at which the permeability change starts, and there is no difference in the magnetic characteristics between the paper passing area and the non-paper passing area. The suppression effect may stop working. Therefore, the correspondence between the temperature of the temperature-sensitive magnetic member 64 and the temperature of the fixing belt 61 is maintained, and the temperature-sensitive magnetic member 64 functions as a detection unit that detects the temperature of the fixing belt 61 with high accuracy. It is necessary to suppress the Joule heat W generated in the member 64 itself.

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

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

  FIG. 13 is a view showing slits 64 s formed in the temperature-sensitive magnetic member 64. FIG. 13A is a side view showing a state in which the temperature-sensitive magnetic member 64 is installed in the holder 65, and FIG. 13B is a plan view seen from above (a direction). As shown in FIG. 13, in the temperature-sensitive magnetic member 64, a plurality of slits 64 s are formed orthogonal to the direction in which the eddy current I generated by the lines of magnetic force H flows. Therefore, when there is no slit 64s, the eddy current I (broken line in FIG. 13B) that flows as a large eddy over the entire longitudinal direction of the temperature-sensitive magnetic member 64 is divided by the slit 64s. Thereby, when the slit 64s is formed, the eddy current I flowing through the temperature-sensitive magnetic member 64 (solid line in FIG. 13A) becomes a small vortex in the region between the slit 64s and the slit 64s, The amount of eddy current I as a whole is reduced. As a result, the amount of heat generated by the temperature-sensitive magnetic member 64 (Joule heat W) is reduced, and a configuration that hardly generates heat is realized. Therefore, the plurality of slits 64 s function as an eddy current dividing unit that divides the eddy current I.

In the temperature-sensitive magnetic member 64 illustrated in FIG. 13, the slit 64 s is formed perpendicular to the direction in which the eddy current I flows. However, if the flow of the eddy current I is divided, for example, the eddy current I flows. You may form the slit inclined with respect to the direction. In addition to the configuration in which the slits 64 s as shown in FIG. 13 are formed over the entire region in the width direction of the temperature-sensitive magnetic member 64, the slit 64 s may be formed in a part in the width direction of the temperature-sensitive magnetic member 64. Further, the number, position, inclination angle, and the like of the slits may be set according to the amount of heat generated in the temperature-sensitive magnetic member 64.
Moreover, as a state where the inclination angle of the slit is maximized, the temperature-sensitive magnetic member 64 may be a small piece divided group in which the temperature-sensitive magnetic member 64 is divided into small pieces at the slit portion. The effect of is obtained similarly.

  Fourthly, the heat-sensitive magnetic member 64 heat-transfers heat generated by the temperature-sensitive magnetic member 64 toward the inner side of the temperature-sensitive magnetic member 64 (direction of the induction member 66). A heat dissipation path as an example of the means is formed. In this case, it is desirable that the temperature of the temperature-sensitive magnetic member 64 is maintained at substantially the same temperature as that of the fixing belt 61 because of the function of the temperature-sensitive magnetic member 64 described above. Therefore, the heat dissipation path is configured such that the temperature-sensitive magnetic member 64 and other members (for example, the induction member 66) disposed inside the temperature-sensitive magnetic member 64 are maintained in a non-contact state. That is, an air layer is interposed in a part of the heat dissipation path, thereby suppressing an excessive outflow of heat from the temperature-sensitive magnetic member 64 via the heat dissipation path. Accordingly, for example, when a situation occurs in which heat generated by the temperature-sensitive magnetic member 64 is accumulated, such as when a large amount of image formation is continuously performed, the amount of heat that exceeds the temperature of the fixing belt 61 is generated. The heat dissipation path is made to function so that the heat quantity of the heat-sensitive magnetic member 64 is easily dissipated.

Next, the fixing operation in the fixing unit 60 will be described.
In the fixing unit 60 to which the exemplary embodiment is applied, when the toner image forming operation in the image forming apparatus 1 is started, the latch motor 201 is operated, and the pressure roller 62 is set at a predetermined temperature by the contact / separation mechanism 200. The fixing belt 61 is strongly pressed against the heated fixing belt 61 and is disposed at a fixing position. As shown in FIG. 3, this fixing position is a so-called latch ON state in which the pressure roll 62 is in close contact with the fixing belt 61 by the pressing pad 63. At this time, the fixing belt 61 in the vicinity of the nip portion N is deformed along the shape of the pressing pad 63. At this time, as described above, the one-way clutch 102 is operated, the transmission of the rotational driving force from the drive motor 90 to the shaft 97 is stopped (see FIG. 3), and the pressure roll 62 is rotationally driven from the drive motor 90. The fixing belt 61 is driven to rotate in the direction of the arrow C as the pressure roll 62 is rotated.
At this time, the control unit 31 outputs a control signal to the excitation circuit 88 (see FIG. 8) of the IH heater 80 and supplies a high-frequency current (electric power) to the excitation coil 82 (see FIG. 8), thereby fixing the fixing belt. 61 induction heating is started and a warm-up operation for heating to a predetermined temperature is performed.

Next, in a state where the pressure roller 62 is pressed against the fixing belt 61, the paper P is fed into the nip portion N formed by the fixing belt 61 and the pressure roller 62 and heated by the IH heater 80. 61 and the pressure roll 62 are heated and pressed. Then, the toner image is melt-pressed on the surface of the paper P and fixed.
When the paper P is sent out from the nip portion N formed by the fixing belt 61 and the pressure roll 62, the paper P tries to go straight in the direction sent out due to its rigidity, and the leading end of the paper P is bent from the fixing belt 61 to be bent. The separation assisting member 70 enters between the leading end of the sheet P and the fixing belt 61, and the sheet P is separated from the surface of the fixing belt 61. Thereafter, the paper P is conveyed to a paper stacking unit 45 provided in the discharge unit of the image forming apparatus 1.

In the present embodiment, as shown in FIG. 7, in the latch OFF state where the pressure roll 62 before the fixing operation is not in physical contact with the fixing belt 61, the rotation from the drive motor 90 is performed as described above. The pressure roller 62 and the fixing belt 61 that are separated from each other are rotated by the driving force (the pressure roller 62 is in the direction of arrow F. The fixing belt 61 is in the direction of arrow E).
At this time, the control unit 31 outputs a control signal to the excitation circuit 88 (see FIG. 8) of the IH heater 80 and supplies a high-frequency current (electric power) to the excitation coil 82 (see FIG. 8). Induction heating is started. Thereby, a warm-up operation for heating the fixing belt 61 to a predetermined temperature is executed. By separating the fixing belt 61 and the pressure roll 62, the warm-up time is shortened without the heat of the fixing belt 61 being taken away by the pressure roll 62. Further, by rotating the fixing belt 61 and the pressure roll 62, it is possible to prevent temperature unevenness from occurring in the rotation direction.
Further, in the electromagnetic induction heating type fixing unit 60 according to the present embodiment, the induction coil 82 side of the fixing belt 61 is mainly subjected to electromagnetic induction heating, so that the temperature can be made uniform while the fixing belt 61 is moved. is necessary.

  Next, FIG. 14 is a timing chart for explaining an example of the fixing operation in the image forming apparatus 1. As shown in FIG. 14, an image forming motion signal (Print signal) is input in a state where the drive motor 90 of (A) is driven (drive motor ON), and the pressure roll 62 is applied to the fixing belt 61 in (B). The latch motor 201 is driven by a signal to press strongly (nip signal ON), and the latch ON state is set. Next, together with the input of the image signal in (C), the driving of the latch motor 201 is stopped in (D), and the latch ON state is maintained.

  Subsequently, in (E), a cycle down signal for completing a series of fixing operations is input, and at the same time, input of an image signal is ended in (F). In (G), the latch motor 201 is driven by a signal for separating the pressure roller 62 from the fixing belt 61 (nip signal ON) to release the latch ON state, and in (H), the driving of the latch motor 201 is stopped ( The nip signal is OFF) and the latch is OFF. In (I), the drive motor 90 stops (drive motor OFF).

  In the present embodiment, thereafter, in (J), a signal (POWER OFF signal) for stopping power supply from a power supply unit (not shown) that supplies power to each component of the image forming apparatus 1 is input. Then, in (K), the latch motor 201 is driven by a signal (nip signal ON) that presses the pressure roll 62 weakly against the fixing belt 61 than at the time of fixing, and a half-nip state is set. In (L), the latch motor is set. The driving of 201 is stopped (nip signal OFF), and then the process of stopping the supply of current to the image forming apparatus 1 (power OFF process) is performed, and the half-nip state is maintained and the image forming apparatus 1 Operation stops.

  FIG. 6 is a diagram for explaining a half-nip state in the fixing unit 60 of the present embodiment. In the present embodiment, after a process for stopping the supply of current to the image forming apparatus 1 (power OFF process) is performed, the operation of the image forming apparatus 1 is stopped, and the fixing unit 60 continues to be in a half-nip state. Retained. As shown in FIG. 6, the pressure roll 62 is disposed at a position where it is brought into pressure contact with the fixing belt 61 with a pressure smaller than that during fixing (half-nip position). At the position where the pressure roll 62 is disposed, the pressure roll 62 is brought into pressure contact with the fixing belt 61 so that the fixing belt 61 contacts the peeling nip region 63b of the pressure pad 63 provided on the outlet side of the nip portion N. Arrangement position. In this case, the fixing belt 61 in the vicinity of the nip portion N is in a half-nip state that does not deform along the shape of the pressing pad 63.

Next, the operation and control of the image forming apparatus 1 after a signal for stopping power supply from the power supply unit (POWER OFF signal) is input will be described.
FIG. 15 is a control block diagram of the control unit 31 shown in FIG. The control unit 31 has a function of controlling the entire image forming apparatus 1, but only blocks related to the operation of the contact / separation mechanism 200 are shown here. A CPU (Central Processing Unit) of the control unit 31 executes processing while exchanging data with a RAM (Random Access Memory) in accordance with a program stored in a ROM (Read Only Memory). Instruction information from the switch 2 serving as a switching unit that switches between a power supply state and a supply stop state of the power supply unit 150 is input to the control unit 31 via the input / output interface 50. On the other hand, the control unit 31 outputs a control signal to the power supply unit 150 that supplies power to the components of the contact / separation mechanism 200 and the image forming apparatus 1 via the input / output interface 50.

FIG. 16 is a flowchart for explaining a processing flow of the operation of the image forming apparatus 1 after a signal (POWER OFF signal) for stopping power supply from the power supply unit 150 is input.
The control unit 31 determines whether or not a signal for stopping the power supply supplied from the power supply unit 150 (power supply stop instruction signal: POWER OFF signal) is input from the switch 2 (step 101).
When the input of the power supply stop instruction signal (POWER OFF signal) is detected in Step 101 (Yes), the contact / separation mechanism 200 is operated next, and the pressure roller 62 is fixed by driving the latch motor 201. The position is moved to a position (half nip position) that is weakly pressed against the fixing belt 61 (step 102).
Subsequently, the control unit 31 determines whether or not the pressure roll 62 has been moved to the half nip position by the contact / separation mechanism 200 (step 103).
In step 103, when it is detected that the pressure roll 62 has moved to the half nip position, the power supply unit 150 performs a process of stopping power supply to each component of the image forming apparatus 1 ( Step 104).

The reason why the fixing unit 60 according to the present embodiment is in a half-nip state in which the pressure roll 62 is disposed at a position where the pressure roller 62 is pressed against the fixing belt 61 weaker than when fixing when the power is turned off will be described.
Generally, a fixing device used in the heat fixing method is in a latch-on state in which the pressure roll 62 is in close contact with the fixing belt 61 during a fixing operation. At this time, the fixing belt 61 in the vicinity of the nip portion N is deformed along the shape of the pressing pad 63. Therefore, if the latch-on state is left in the power-off state after the fixing operation is finished, the pressure roll 62 is likely to be deformed. In the case of the heat fixing method, after the fixing operation is completed, it is also necessary to separate the fixing belt 61 and the pressure roll 62 to prevent temperature unevenness generated in the pressure roll 62.
Here, when vibration or the like is applied to the fixing belt 61 and the pressure roll 62 arranged in such a separated state, the pressure roll 62 is not fixed, so that damage, scratches, and the like are caused by contact between the two.
Therefore, in the fixing unit 60 of the present embodiment, as shown in FIG. 6, when the power roll is turned off, the pressure roll 62 is placed in a half-nip state at a position where it is pressed to the fixing belt 61 weaker than at the time of fixing. Even when subjected to vibration or impact, the pressure roll 62 and the fixing belt 61 are prevented from being damaged or scratched.

  As described above, in the fixing unit 60 provided in the image forming apparatus 1 according to the present embodiment, the pressure roller 62 is fixed to the fixing belt 61 in a state where the power supply from the power supply unit 150 is stopped than when fixing to the fixing belt 61. It is in a half-nip state where it is placed at a position where it is weakly pressed. Thereby, even if the fixing unit 60 receives vibration or impact, the pressure roll 62 and the fixing belt 61 are prevented from being damaged or scratched.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 60 ... Fixing apparatus, 61 ... Fixing belt, 62 ... Pressure roll, 64 ... Temperature-sensitive magnetic member, 66 ... Induction member, 80 ... IH heater, 82 ... Excitation coil, 84 ... Magnetic core, 200 ... Contact / separation mechanism, 611 ... base material layer, 612 ... conductive heating layer

Claims (5)

A toner image forming unit for forming a toner image;
A transfer unit that transfers the toner image formed by the toner image forming unit onto a recording material;
A pressure member that rotates, and a fixing member that forms a pressing portion between the pressure member and presses the recording material conveyed to the pressing portion at the pressing portion. A fixing unit for fixing;
At the time of fixing in which power is supplied from a power supply unit that supplies power to each component unit and toner is fixed to a recording material, the pressure member is pressed against the fixing member of the fixing unit, and power is supplied from the power supply unit. A contacting / separating means for bringing the pressure member into contact with the fixing member at a pressure smaller than that at the time of fixing in the stopped state;
An image forming apparatus comprising:   The contact / separation means drives a positioning drive source in response to a signal for stopping power supply output from a receiving means that receives an instruction from a switching section that switches between a power supply state / supply stop state of the power supply section, and the fixing 2. The image forming apparatus according to claim 1, wherein the positioning driving source keeps the pressure member in pressure contact with the member at a pressure smaller than that at the time of fixing.   The fixing member of the fixing unit is an endless belt having a conductive layer that is heated by electromagnetic induction, and the fixing unit further includes a magnetic field generating member that generates an alternating magnetic field that intersects the conductive layer of the endless belt. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. When an image forming apparatus including a fixing unit that fixes toner on a recording material is put into a state where power supply from a power supply unit that supplies power to each component unit is stopped, the power supply state of the power supply unit In response to the power supply stop instruction signal output from the receiving means that has received the instruction of the switching unit for switching between the supply stop state and the supply stop state, the positioning drive source is set so that the pressure member is brought into pressure contact with the fixing member at a pressure smaller than that at the time of fixing. Drive instruction means for driving;
Stop control means for controlling the power supplied from the power supply unit to stop after the drive instructing means brings the pressure member into contact with the fixing member;
A control device comprising: A power supply unit that supplies power to each component of the image forming apparatus including a fixing unit that fixes toner on the recording material is output from a reception unit that receives an instruction of a power supply state or a supply stop state performed by an operator. A function to acquire a power supply stop instruction signal,
In response to the power supply stop instruction signal, a function of driving a positioning drive source so that the pressure member is pressed against the fixing member of the fixing unit at a pressure smaller than that at the time of fixing;
A function of stopping the power supplied from the power supply unit after bringing the pressure member into contact with the fixing member;
A program characterized by realizing.

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