JP2020042143A - Image forming apparatus and fixing device - Google Patents

Abstract

To provide an image forming apparatus capable of preventing a part of an induction heating unit from coming into contact with detection means when attaching the induction heating unit to a housing using a fixing device with the induction heating unit.SOLUTION: The image forming apparatus includes: a magnetic flux shielding member 80 that is disposed between a fixing film 21 and an exciting coil, is movable in a rotation axis direction D2 of the fixing film 21, and is capable of shielding a magnetic flux; and a detected part 84 that is movable in conjunction with the magnetic flux shielding member 80. The image forming apparatus also includes: an induction heating unit 30 that is attached in a detachable manner in a vertical direction D1 with respect to a housing; and a moving mechanism 81 for moving the magnetic flux shielding member 80. A control part 70 is configured so as to, when the power is off, control the moving mechanism 81 so that the detected part 84 is positioned in a retracted position P2 which is different from the home position with respect to the rotation axis direction D2.SELECTED DRAWING: Figure 8

Description

  The present invention relates to an image forming apparatus and a fixing device that use a fixing device to fix a toner image transferred to a recording material by an electrophotographic method, an electrostatic recording method, or the like.

  2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic method, a developing device develops an electrostatic latent image formed on a photosensitive drum as an image carrier with toner to form a toner image, and this toner image is used as a recording material. After that, the image is fixed on the recording material by a fixing device. The fixing device has, for example, a heating rotator such as a fixing film and a pressing rotator such as a pressing roller, forming a fixing nip therebetween, and heating and pressing the recording material in the fixing nip. The unfixed toner image is fixed on the recording material. For example, as a heating means in a film fixing system using a fixing film, an induction heating system in which an induction heating device is arranged to face a film provided with a metal layer and induction heating is performed by an alternating magnetic flux has been put to practical use.

  In recent years, there has been a tendency to increase the size of the product, and an image forming apparatus has been developed which allows the magnetic flux shielding member to move outward in the rotation axis direction from a position where the fixing flange regulates the end of the fixing film (Patent) Reference 1). According to this image forming apparatus, when an image is formed on a large-sized recording material, it is possible to uniformly heat the fixing film over a wide range in the fixing device.

  In such an induction heating type fixing device, it is possible to suppress the temperature rise in the non-sheet passing portion by adjusting the heating range by moving the pair of magnetic flux shielding members in the rotation axis direction of the heating rotator. . Here, when a pair of movable magnetic flux shielding members is provided, since the position where the temperature of the non-sheet passing portion rises depends on the size of the recording material being conveyed, the magnetic flux shielding member is moved to an appropriate position. Detecting means for detecting the position of the member is required. As the detecting means, for example, a photointerrupter having a low-cost and simple configuration is used. The photointerrupter has, for example, a photosensor including a light emitting unit and a light receiving unit fixedly provided to a housing of the fixing device, and a detected unit that can move integrally with the magnetic flux shielding member to block the photosensor. In this case, for example, the position of the magnetic flux shielding member in a state where the detected part blocks the photosensor is set as a home position, and the magnetic flux shielding member is moved to a desired position by controlling a moving distance of the magnetic flux shielding member from the home position. Let it.

  On the other hand, the fixing film and the pressure roller of the fixing device are detachable from the housing of the fixing device so that they can be replaced when their life is approaching. When exchanging these fixing films and pressure rollers, it is necessary to remove an induction heating device having a magnetic flux shielding member (hereinafter referred to as an induction heating unit). ing. Here, when attaching and detaching the induction heating unit to replace the fixing film and the pressure roller, the power supply of the apparatus main body is usually turned off. At this time, the magnetic flux shielding member is located at the home position in consideration of the response of rising after the induction heating unit is mounted on the housing again and the power is turned on.

JP 2014-52454 A

  However, in the image forming apparatus described in Patent Document 1, when the induction heating unit is attached to and detached from the housing, the magnetic flux shielding member is located at the home position. For this reason, after replacing the fixing film or the pressure roller, when the induction heating unit is mounted on the housing of the fixing device, the detected part of the magnetic flux shielding member is inserted between the light emitting part and the light receiving part of the photo sensor. Need to be Here, the induction heating unit is fixed to the housing at a predetermined distance so that the magnetic flux shielding member does not contact the fixing film, but since the magnetic flux shielding member is held so as to be movable in the rotation axis direction, the fixing unit is fixed. The device has slight backlash in the rotation axis direction and the circumferential direction with respect to the housing of the device. Therefore, when the induction heating unit is mounted on the housing after replacing the fixing film or the pressure roller, if the induction heating unit is attached to the housing with an unintended inclination, a part of the induction heating unit There is a possibility of contact with the photo interrupter. Further, the same applies to not only the photointerrupter but also a detection unit that detects the position of the magnetic flux shielding member.

  The present invention provides an image forming apparatus and a fixing device that can prevent a part of an induction heating unit from contacting a detection unit when the induction heating unit is mounted on a housing by using a fixing device having the induction heating unit. It is intended to provide a device.

  The image forming apparatus of the present invention includes an image forming unit that forms an unfixed toner image on a recording material, a fixing device that fixes the toner image formed by the image forming unit on the recording material, and a control unit. An image forming apparatus, wherein the fixing device includes a housing, a heating rotator that is rotatable by induction heating with a magnetic flux incident thereon, and an induction device that is disposed to face the outside of the heating rotator to generate the magnetic flux. Heating means, provided between the heating rotator and the induction heating means, movable in the rotation axis direction of the heating rotator, a magnetic flux shielding member capable of blocking the magnetic flux, and the magnetic flux shielding member A detection unit movable in conjunction with the induction heating unit detachably mounted in a predetermined direction with respect to the housing, a moving mechanism for moving the magnetic flux shielding member, and And providing the induction heating unit with the housing A detection unit that is located at a position overlapping with the detected part with respect to the predetermined direction when mounted, and that can detect that the detected part is positioned at a predetermined position in the rotation axis direction; Is characterized in that the moving mechanism is controlled so that the detected part is located at a position different from the predetermined position in the rotation axis direction when the power is off.

  Further, the fixing device of the present invention is a fixing device that fixes a toner image formed by an image forming unit that forms an unfixed toner image on a recording material to a recording material, wherein the housing and a magnetic flux are incident. A heating rotator that is rotatable by induction heating, an induction heating unit that is disposed to face the outside of the heating rotator to generate the magnetic flux, and is provided between the heating rotator and the induction heating unit, A magnetic flux shielding member that can move in the rotation axis direction of the heating rotator and that can shut off the magnetic flux, and a detected part that can move in conjunction with the magnetic flux shielding member; An induction heating unit detachably mounted in a predetermined direction, a moving mechanism for moving the magnetic flux shielding member, and a moving mechanism provided on the housing, wherein the induction heating unit is mounted on the housing and the induction heating unit is mounted on the housing. Position that overlaps with the detected part Detecting means for detecting that the detected part is located at a predetermined position in the direction of the rotation axis, wherein when the power is off, the detected part is in the predetermined position with respect to the direction of the rotation axis. It is characterized by being located at a position different from the above.

  According to the present invention, it is possible to prevent a part of the induction heating unit from coming into contact with the detection unit when the induction heating unit is mounted on the housing using the fixing device having the induction heating unit.

FIG. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment. FIG. 2 is a control block diagram of the image forming apparatus according to the embodiment. FIG. 2 is a cross-sectional view illustrating the fixing device according to the exemplary embodiment. FIG. 2 is a cross-sectional view illustrating a fixing film according to the exemplary embodiment. FIG. 3 is a side view illustrating a pressing mechanism of the fixing device according to the exemplary embodiment. It is an exploded perspective view showing the induction heating unit concerning this embodiment. FIGS. 3A and 3B are diagrams illustrating a state in which a magnetic flux shielding member is located at a home position in the fixing device according to the exemplary embodiment, wherein FIG. 3A is a plan view and FIG. 4A and 4B are diagrams illustrating a state in which a magnetic flux shielding member is located at a retracted position in the fixing device according to the exemplary embodiment, wherein FIG. 4A is a plan view and FIG. 9 is a flowchart illustrating a processing procedure when the magnetic flux shielding member is moved using the fixing device according to the exemplary embodiment. 4A and 4B are diagrams illustrating a state in which a part of a moving mechanism of an induction heating unit in a fixing device interferes with a photo sensor, wherein FIG. 4A is a front view and FIG.

  Hereinafter, an embodiment of an image forming apparatus as an example of the present invention will be described in detail with reference to FIGS. In the present embodiment, a tandem-type full-color printer is described as an example of the image forming apparatus 1. However, the present invention is not limited to being mounted on the tandem type image forming apparatus 1 and may be mounted on another type of image forming apparatus, and is not limited to being full color. Alternatively, it may be monochrome or monochrome. Alternatively, the present invention can be implemented for various uses such as a printer, various printing machines, a copying machine, a FAX, and a multifunction machine.

  As shown in FIG. 1, the image forming apparatus 1 includes an apparatus main body 10, a sheet feeding unit (not shown), an image forming unit 40, a control unit 70, and an operation unit 11. The image forming apparatus 1 can form a four-color full-color image on a recording material according to an image signal from a host device such as a document reading device or a personal computer (not shown) or an external device such as a digital camera or a smartphone. . The sheet S, which is a recording material, is a member on which a toner image is formed, and specific examples include plain paper, a sheet made of synthetic resin that is a substitute for plain paper, thick paper, and a sheet for an overhead projector.

[Image forming unit]
The image forming unit 40 can form an image as an unfixed toner image on the sheet S fed from the sheet feeding unit based on the image information. The image forming unit 40 includes image forming units 50y, 50m, 50c, and 50k, toner bottles 41y, 41m, 41c, and 41k, exposure devices 42y, 42m, 42c, and 42k, an intermediate transfer unit 44, and a secondary transfer unit. 45 and the fixing device 20. The image forming apparatus 1 according to the present embodiment corresponds to full color, and the image forming units 50y, 50m, 50c, and 50k include yellow (y), magenta (m), cyan (c), and black (k). ) Are separately provided in the same configuration for each of the four colors. For this reason, in FIG. 1, each component of the four colors is shown with the same reference numeral followed by a color identifier, but in the specification, there may be a case where only the reference numeral is used without a color identifier.

  The image forming unit 50 includes a photosensitive drum 51 that carries a toner image and moves, a charging roller 52, a developing device 53, and a cleaning blade 55. The image forming unit 50 is integrally unitized as a process cartridge, is configured to be detachable from the apparatus main body 10, and forms a toner image on an intermediate transfer belt 44b described later.

  The photosensitive drum 51 is rotatable and carries an electrostatic latent image used for image formation. In the present embodiment, the photosensitive drum 51 is a negatively chargeable organic photosensitive member (OPC) having an outer diameter of 30 mm, and is rotationally driven by a motor (not shown) in a direction indicated by an arrow at a predetermined process speed (peripheral speed). Each of the charging rollers 52y, 52m, 52c, and 52k uses a rubber roller that contacts the surface of each of the photosensitive drums 51 and rotates by being driven, and uniformly charges the surface of the photosensitive drum 51. The exposure device 42 is a laser scanner, and emits a laser beam according to the image information of the separated color output from the control unit 70.

  The developing devices 53y, 53m, 53c, and 53k have developing sleeves 54y, 54m, 54c, and 54k, and develop an electrostatic latent image formed on the photosensitive drum 51 by applying a developing bias with toner. The developing device 53 accommodates the developer supplied from the toner bottle 41 and develops the electrostatic latent image formed on the photosensitive drum 51. The developing sleeve 54 is made of a non-magnetic material such as aluminum or non-magnetic stainless steel, and is made of aluminum in the present embodiment. Inside the developing sleeve 54, a roller-shaped magnet roller is fixedly installed in a non-rotating state with respect to the developing container. The developing sleeve 54 carries a developer having a non-magnetic toner and a magnetic carrier, and transports the developer to a developing area facing the photosensitive drum 51.

  The toner image developed on the surface of the photosensitive drum 51 is primarily transferred to the intermediate transfer unit 44. That is, the photosensitive drum 51 can carry a toner image by supplying toner to the intermediate transfer belt 44b. The cleaning blades 55y, 55m, 55c, and 55k are of a counter blade type, and are in contact with the photosensitive drum 51 with a predetermined pressing force. After the primary transfer, the toner remaining on the photosensitive drum 51 without being transferred to the intermediate transfer unit 44 is removed by a cleaning blade 55 provided in contact with the photosensitive drum 51 to prepare for the next image forming step.

  The intermediate transfer unit 44 includes a plurality of rollers such as a drive roller 44a, a driven roller 44d, and primary transfer rollers 47y, 47m, 47c, and 47k, and an intermediate transfer belt that is wound around these rollers and moves while carrying a toner image. 44b. The driven roller 44d is a tension roller that controls the tension of the intermediate transfer belt 44b to be constant. A force is applied to the driven roller 44d such that the intermediate transfer belt 44b is pushed to the front side by the urging force of an urging spring (not shown). The primary transfer rollers 47y, 47m, 47c, and 47k are disposed to face the photosensitive drums 51y, 51m, 51c, and 51k, respectively, abut the intermediate transfer belt 44b, and transfer the toner image on the photosensitive drum 51 to the intermediate transfer belt 44b. Transcribe. That is, the intermediate transfer belt 44b moves (rotates) while carrying the toner image.

  The intermediate transfer belt 44b contacts the photosensitive drum 51 to form a primary transfer portion with the photosensitive drum 51, and applies a primary transfer bias to transfer the toner image formed on the photosensitive drum 51 to the primary transfer portion. Primary transfer. By applying a primary transfer bias of positive polarity to the intermediate transfer belt 44b by the primary transfer roller 47, the respective toner images having negative polarity on the photosensitive drum 51 are sequentially multiplex-transferred to the intermediate transfer belt 44b. The intermediate transfer belt 44b is provided with a belt cleaning device 56 that cleans transfer residual toner on the intermediate transfer belt 44b.

  The secondary transfer section 45 includes a secondary transfer inner roller 45a and a secondary transfer outer roller 45b. The outer secondary transfer roller 45b is in contact with the intermediate transfer belt 44b, and a secondary transfer bias having a polarity opposite to that of the toner is applied at a nip portion between the intermediate transfer belt 44b and the intermediate transfer belt 44b. As a result, the secondary transfer outer roller 45b collectively secondary-transfers the toner image carried on the intermediate transfer belt 44b onto the sheet S supplied to the nip.

  The fixing device 20 includes a fixing film 21 and a pressure roller 22. When the sheet S is sandwiched between the fixing film 21 and the pressure roller 22 and is conveyed in the sheet conveying direction, the toner image formed by the image forming unit 40 and transferred to the sheet S is heated and pressed to form a sheet. Fixed to S. The fixing device 20 is driven by drive motors M1, M2, M3 (see FIG. 2) housed in the fixing device 20. Details of the fixing device 20 will be described later.

[Control unit]
As shown in FIG. 2, the control unit 70 is constituted by a computer, for example, a CPU 71, a ROM 72 for storing a program for controlling each unit, a RAM 73 for temporarily storing data, and an input / output for inputting and outputting signals to and from the outside. And a circuit (I / F) 74. The CPU 71 is a microprocessor that controls the entire control of the image forming apparatus 1 and is a main body of the system controller. The CPU 71 is connected to the operation unit 11, the sheet feeding unit, the image forming unit 40, and the like via the input / output circuit 74, exchanges signals with each unit, and controls the operation. The control unit 70 is connected to the drive motors M1, M2, M3 of the fixing device 20 and the excitation coil 31, and can control the operation of the fixing device 20. The drive motor M1 is provided for driving the pressure roller 22, the drive motor M2 is provided for driving the pressure mechanism 60 described later, and the drive motor M3 is provided for driving the movement mechanism 81 described later. The ROM 72 stores an image formation control sequence and the like for forming an image on the sheet S. The operation unit 11 includes, for example, a liquid crystal touch panel 11a. The operation unit 11 is provided so as to be capable of inputting information such as the type of the sheet S to be used to the CPU 71 from the outside when a user operates and inputs data. I have.

[Image forming operation]
Next, an image forming operation in the image forming apparatus 1 configured as described above will be described. When the image forming operation is started, first, the photosensitive drum 51 rotates and the surface is charged by the charging roller 52. Then, a laser beam is emitted from the exposure device 42 to the photosensitive drum 51 based on the image information, and an electrostatic latent image is formed on the surface of the photosensitive drum 51. When the toner adheres to the electrostatic latent image, it is developed and visualized as a toner image, and is transferred to the intermediate transfer belt 44b.

  On the other hand, the sheet S is supplied in parallel with such a toner image forming operation, and the sheet S is transported to the secondary transfer unit 45 via the transport path in synchronization with the timing of the toner image on the intermediate transfer belt 44b. . Further, an image is transferred from the intermediate transfer belt 44b to the sheet S, and the sheet S is conveyed to the fixing device 20, where the unfixed toner image is heated and pressed to be fixed on the surface of the sheet S. Is discharged from

[Fixing device]
Next, the fixing device 20 will be described in detail with reference to FIGS. As shown in FIG. 3, the fixing device 20 is a heating device of a film heating type, and is formed in a cartridge shape detachable from the apparatus main body 10. The fixing device 20 includes a housing 20a (see FIG. 5), a rotatable endless belt-shaped cylindrical fixing film (heating rotator) 21, a pressure roller 22 pressed against the fixing film 21, and a fixing film. And an induction heating unit 30 for heating 21. The fixing film 21 is an endless belt having a metal layer, and a magnetic flux is incident on the fixing film 21 by an induction heating unit 30, which will be described later, and is heated by induction. The pressure roller 22 is disposed so as to be in contact with the outer periphery of the fixing film 21, forms a fixing nip N with the fixing film 21, and is capable of nipping and transporting the sheet S between the fixing nip N. is there. As a result, the fixing device 20 fixes the toner image by applying heat and pressure to the sheet S carrying the toner image by nipping and conveying the sheet S at the fixing nip portion N.

  The fixing device 20 has a pad support member 23, a fixing pad 24, a stay 25, and an internal core 26 described below on the inner peripheral side of the fixing film 21, and both ends of the fixing film 21 in the rotation axis direction. The portion has a flange 27. The pad support member 23 is a nip forming member for forming a fixing nip N by applying a pressing force between the fixing film 21 and the pressing roller 22, and is held by a metal stay 25. The stay 25 is arranged on the inner peripheral side of the fixing film 21 in order to secure the strength of the pad support member 23. The fixing film 21 and the pressing roller 22 form a fixing nip N by applying a pressing force between the pad supporting member 23 provided inside the fixing film 21 and the pressing roller 22. The pad support member 23 is made of a heat-resistant resin, and holds the fixing pad 24 on the pressure roller 22 side. The fixing pad 24 is made of a material having high hardness such as a metal such as stainless steel or ceramics, and has a thickness of, for example, about 1 mm and extends in the rotation axis direction of the fixing film 21. The flanges 27 are provided so as to hold both ends of the stay 25 and regulate each end of the fixing film 21 in the rotation axis direction.

[Fixing film]
The fixing film 21 is a rotating body that comes into contact with the surface of the sheet S having the unfixed toner image passing through the fixing nip portion N, and transfers the heat obtained by the induction heating to the toner image on the sheet S to transfer the toner. It is a heat-resistant cylindrical member that heats an image. The fixing film 21 is fitted around the flange 27 and held rotatably. As shown in FIG. 4, the fixing film 21, which is an endless belt, has a smooth layer 21a, a base layer 21b, an elastic layer 21c, and a release layer 21d in this order from inside to outside.

The base layer 21b is a metal layer having an inner diameter of about 20 to 40 mm. As the base layer 21b of the fixing film 21, an iron alloy, a nickel alloy, copper, silver, or the like can be appropriately selected. As an example, the fixing film 21 of the present embodiment has an outer diameter of 30 mm and an inner diameter of the base layer 21b of about 29.6 mm. The elastic layer 21c provided on the outer periphery of the base layer 21b is a heat-resistant rubber layer. The thickness of the rubber layer is preferably set in the range of 100 to 800 μm. In the present embodiment, the thickness of the rubber layer is, for example, 200 μm in consideration of reducing the heat capacity of the fixing film 21 to shorten the warm-up time and obtaining a suitable fixed image when fixing a color image. . A release layer 21d is provided as a surface layer on the outer periphery of the elastic layer 21c, and the surface resistance of the fixing film 21 is 1.0 × 10 ⁶ (Ω) or more. The release layer 21d is a fluororesin (for example, PFA (perfluoroalkoxy fluororesin) or PTFE (polytetrafluoroethylene)) layer. The release layer 21d is a surface layer of the fixing film 21 and enhances the releasability of the toner. The thickness of the release layer 21d is, for example, 40 μm. Note that the release layer 21d may be configured to contain carbon black in addition to the fluororesin as long as the above-described surface resistance is satisfied.

[Pressure roller]
As shown in FIG. 3, both ends of the pressure roller 22 are rotatably supported by a front plate 28 (see FIGS. 7A and 7B) and a rear plate 29 (see FIG. 5). The pressure roller 22 forms a fixing nip portion N with the fixing film 21, and includes a metal core 22a having an outer diameter of 30 mm, an elastic layer 22b of a rubber layer, and a release layer 22c. I have. The release layer 22c is a surface layer of the pressure roller 22, and is a fluororesin layer (for example, PFA or PTFE).

[Pressure mechanism]
As shown in FIG. 5, the flange 27 and the pressure roller 22 are detachably attached to the front plate 28 (see FIGS. 7A and 7B) and the rear plate 29 of the housing 20a in the vertical direction D1. Have been. The fixing device 20 includes a pressing mechanism 60 that presses the pad support member 23 toward the pressing roller 22 in order to form the fixing nip N. The pressure mechanism 60 includes a pressure cam 61, a pressure plate rotation shaft 62, a pressure cam rotation shaft 63, a pressure plate 64, a pressure adjustment screw 65, a pressure support plate 66, And a spring 67.

  The pressurizing support plate 66 is supported by the pressurizing plate rotating shaft 62 penetrating the front side plate 28 (see FIGS. 7A and 7B) and the rear side plate 29 fixed to the housing 20a. ing. The pressure support plate 66 is screwed or the like to each of the front plate 28 and the rear plate 29 at a distal end opposite to the pressure plate rotation shaft 62. Thus, the pressure support plate 66 is fixed to the front plate 28 and the rear plate 29.

  The pressure plate 64 is pivotally supported by the pressure plate rotation shaft 62, and is provided rotatably about the pressure plate rotation shaft 62 with respect to the pressure support plate 66. The pressure spring 67 is, for example, a compression coil spring that applies a load to the pressure plate 64. A pressure adjusting screw 65 is fastened to the pressure supporting plate 66. The bearing surface of the pressure adjusting screw 65 reduces the spring length of the pressure spring 67 and applies a load to the pressure plate 64. Since the pressure plate 64 is rotatably supported by the pressure support plate 66, a moment is generated around the pressure plate rotation shaft 62 by the compression force of the pressure spring 67.

  The pressing plate 64 is disposed so as to contact the flange 27 from above, and the moment generated in the pressing plate 64 pushes the flange 27 downward in the direction of the pressing roller 22, that is, in the vertical direction D <b> 1. A stay 25 is held on the flange 27, and the stay 25 presses the pad support member 23 in the direction of the pressure roller 22. As described above, the pressing mechanism 60 applies the pressing force to the flange 27 by the pressing spring 67, and the fixing nip portion N is formed between the pressing roller 22 and the fixing film 21.

  The pressing force applied by the pressing plate 64 to the flange 27 can be released by the pressing cam 61 pushing up the pressing plate 64. When the pressing force is released, the pressing cam 61 having a predetermined eccentric amount rotates about the pressing cam rotation shaft 63 to push up the pressing plate 64 and release the contact between the pressing plate 64 and the flange 27. The pressing force is released by rotating the pressing plate 64 until the pressing is performed. The pressing force is applied (for example, 550 N) by rotating the pressing cam 61 from the state in which the pressing force is released and bringing the pressing plate 64 into contact with the flange 27.

[Induction heating unit]
As shown in FIG. 6, the induction heating unit 30 is a heating source for induction heating the fixing film 21. The induction heating unit 30 is detachably attached to the front side plate 28 (see FIGS. 7A and 7B) and the rear side plate 29 (see FIG. 5) D1 of the housing 20a in a vertical direction (predetermined direction) D1. ing. The induction heating unit 30 has an excitation coil (induction heating means) 31, an outer magnetic core 32, a coil holding member and a power supply device (not shown). The exciting coil 31 is formed by using, for example, a litz wire as an electric wire, and making it horizontally long and in a ship bottom so as to face a part of a peripheral surface and a side surface of the fixing film 21. The power supply (excitation circuit) applies a high-frequency current of 20 to 60 kHz to the excitation coil 31 while the fixing film 21 is rotating. That is, the exciting coil 31 is arranged to face the outside of the fixing film 21 to generate a magnetic flux. The metal layer (conductive layer) of the fixing film 21 generates induced heat by the magnetic flux generated by the exciting coil 31 with the high-frequency current.

  The outer magnetic core 32 covers the excitation coil 31 so that the magnetic flux generated by the excitation coil 31 does not substantially leak to a portion other than the metal layer (conductive layer) that is the base layer 21b of the fixing film 21. The outer magnetic core 32 is made of a material having a high magnetic permeability such as ferrite that shields the magnetic flux so that the magnetic flux generated by applying a high-frequency current to the exciting coil 31 is used for heating the fixing film 21 more efficiently. Consists of The coil holding member is an electrically insulating resin having a thickness of about 2 mm that supports the exciting coil 31 and the outer magnetic core 32. The induction heating unit 30 is disposed on the upper surface of the outer peripheral surface of the fixing film 21 with a predetermined gap (gap) in the fixing film 21.

  Inside the fixing film 21, an inner core 26 (see FIG. 3) is provided on the coil side of the stay 25 in order to more effectively perform induction heating. The inner core 26 is made of a material having a high magnetic permeability such as ferrite that shields the magnetic flux so that the magnetic flux generated by applying a high-frequency current to the exciting coil 31 is used for heating the fixing film 21 more efficiently. .

  As shown in FIGS. 7A and 7B, the induction heating unit 30 includes a magnetic flux shielding member 80 and a moving mechanism 81 that moves the magnetic flux shielding member 80. The magnetic flux shielding member 80 is provided between the fixing film 21 and the exciting coil 31 (see FIG. 3). In the present embodiment, the magnetic flux shielding member 80 faces both ends of the fixing film 21 in the rotation axis direction D2. It is provided. It can move in the rotation axis direction D2 of the fixing film 21 and can interrupt magnetic flux. The magnetic flux shielding member 80 used a copper plate, and the thickness of the copper plate was 0.5 mm in consideration of the skin depth at 20 kHz to 50 kHz. However, the magnetic flux shielding member 80 is not limited to being made of copper, and may be, for example, a nonmagnetic metal such as aluminum, copper, silver, gold, or brass or an alloy thereof, and a high magnetic permeability member such as ferrite or permalloy. Material may be used.

  The moving mechanism 81 includes a holding member 82 that holds the magnetic flux shielding member 80, a feed screw 83 that can move the holding member 82 in the rotation axis direction D2, and a drive motor M3. The pair of magnetic flux shielding members 80 are held by the holding member 82 so as not to contact the fixing film 21. A spiral groove is formed in the feed screw 83, and the holding member 82 engaged with the groove is moved in the rotation axis direction D2 by rotation. The drive motor M3 is connected to the feed screw 83. When the drive motor M3 is driven, the feed screw 83 is driven to rotate, and moves the magnetic flux shielding member 80 in the rotation axis direction D2. The control unit 70 is connected to the drive motor M3, and controls rotation and stop of the drive motor M3.

  A photo interrupter (detection means) 90 is provided on the front side plate 28. The photo interrupter 90 includes a light emitting unit 91 capable of emitting light, and a light receiving unit 92 capable of receiving light emitted from the light emitting unit 91. The light emitting section 91 has a light emitting body such as an LED, for example, and the light receiving section 92 has a photo sensor, for example. On the other hand, a detection section 84 is provided on the holding member 82. The detected part 84 is movable in conjunction with the magnetic flux shielding member 80. The output signal from the light receiving unit 92 differs depending on whether or not the detected unit 84 is located between the light emitting unit 91 and the light receiving unit 92. Whether or not it is located between the parts 92 can be detected. The photo interrupter 90 is also provided on the rear plate 29 so that the position of the detected portion 84 on the rear plate 29 can be detected.

  Further, as shown in FIGS. 7A and 7B, the position when the magnetic flux shielding member 80 is located at the end of the fixing film 21 in the rotation axis direction D2 is defined as a home position (predetermined position) P1. That is, the home position P1 corresponds to the end of the movable range of the detected portion 84. At this time, the respective members are arranged such that the detected part 84 is located between the light emitting part 91 and the light receiving part 92 and detected by the photo interrupter 90. That is, the photo interrupter 90 is provided in the housing 20a, and is located at a position overlapping the detected portion 84 in the vertical direction D1 when the induction heating unit 30 is mounted on the housing 20a, and the detected portion 84 is rotated in the rotation axis direction. It can be detected that it is located at the home position P1 of D2.

[Removal of induction heating unit]
Next, for example, when exchanging the pressure roller 22, a procedure for removing the fixing roller 20 from the fixing device 20 and attaching it again will be described. Since the life of the pressure roller 22 is set shorter than that of the fixing device 20, replacement by a service person in the market occurs during the life of the fixing device 20. As shown in FIG. 5, the pressure roller 22 is disposed so as to engage with the front plate 28 (see FIGS. 7A and 7B) and the rear plate 29, and the pressure roller 22 is engaged. The flange 27 of the fixing film 21 is engaged with the front plate 28 and the rear plate 29 above the groove. The induction heating unit 30 is connected by a connecting member (not shown) while being positioned with respect to the flange 27. Therefore, when the pressure roller 22 is replaced, the pressure roller 22 is removed from the housing 20a after the induction heating unit 30 and the fixing film 21 connected to each other are removed from the housing 20a of the fixing device 20. Next, after the pressure roller 22 is replaced and mounted, when the induction heating unit 30 is mounted on the housing 20a of the fixing device 20, the induction heating unit 30 and the connected heating unit 30 are connected in the reverse order to the removal. The fixing film 21 is mounted on the housing 20a.

  Here, when mounting the induction heating unit 30 and the fixing film 21 to the housing 20a, it is necessary to engage the flanges 27 at both ends with the front side plate 28 and the rear side plate 29 while supporting them by hand. However, since the induction heating unit 30 and the fixing film 21 are connected and integrated, the weight is heavy, and there is a possibility that the induction heating unit 30 and the fixing film 21 are attached obliquely to the front side plate 28 and the rear side plate 29. On the other hand, assuming that the magnetic flux shielding member 80 is controlled to be at the home position P1 in preparation for the movement of the feed screw 83 in the rotation axis direction D2 in the next image forming job, the holding member 82 is moved from the home position P1. It may shift. In this case, for example, as shown in FIGS. 10A and 10B, there is a possibility that a part 82 a of the holding member 82 of the magnetic flux shielding member 80 abuts on the upper surface of the photo interrupter 90. Alternatively, there is a possibility that the detected portion 84 may come into contact with the upper surface of the photo interrupter 90 without entering between the light emitting portion 91 and the light receiving portion 92. That is, there is a possibility that the magnetic flux shielding member 80, the moving mechanism 81, and the detected portion 84 may interfere with the photo interrupter 90. In these cases, the positions of the induction heating unit 30 and the fixing film 21 need to be corrected so that the induction heating unit 30 and the fixing film 21 cannot be normally assembled to the housing 20a and do not interfere with the upper surface of the photointerrupter 90. And the workability is reduced. Therefore, in the present embodiment, when the induction heating unit 30 and the fixing film 21 are removed from the housing 20a, the magnetic flux shielding member 80 is retracted to the retracted position P2 on the center side in the rotation axis direction D2, and the photo interrupter 90 is mounted at the time of assembly. Prevent interference.

  Next, the movement of the magnetic flux shielding member 80 when removing the induction heating unit 30 and the fixing film 21 from the housing 20a will be described in detail with reference to FIGS. As shown in FIGS. 7A to 8B, the pair of magnetic flux shielding members 80 are moved in the rotation axis direction of the fixing film 21 by a moving mechanism 81 using a feed screw 83 arranged in parallel with the fixing film 21. It is arranged keeping a positional relationship symmetrical to D2. Accordingly, the pair of magnetic flux shielding members 80 can move in the rotation axis direction D2 of the fixing film 21.

  The replacement of the pressure roller 22 or the fixing film 21 is performed when the power of the image forming apparatus 1 is off. In the present embodiment, a power switch that can switch the power between an on state and an off state is provided, and the power off state is realized by turning off the power switch. However, in the power-off state, in addition to the case where the power switch is turned off, for example, when the front door of the apparatus main body 10 is opened to replace the fixing apparatus 20, or when the operation unit 11 is operated, the fixing apparatus 20 is turned off. The case where the exchange mode is performed is also included.

  At this time, when the pressure roller 22 is replaced, the magnetic flux shielding member 80 is moved by a predetermined amount toward the center in the rotation axis direction D2 to be located at the retracted position P2 different from the home position P1. This prevents the magnetic flux shielding member 80, the moving mechanism 81, and the detection unit 84 from interfering with the photointerrupter 90 even when the serviceman is mounted obliquely during replacement work, thereby preventing the workability of the mounting work from deteriorating. be able to. In the present embodiment, the retreat position P2 is a position 20 mm closer to the center side from the home position P1. The position of the retreat position P2 is not limited to this.

  Next, a processing procedure for moving the magnetic flux shielding member 80 in the image forming apparatus 1 of the present embodiment will be described with reference to a flowchart shown in FIG. When the control unit 70 receives the energization command and turns on the power switch of the image forming apparatus 1 (step S1), the process proceeds to start-up control (step S2). At this time, the detection operation at the initial position of the magnetic flux shielding member 80 is also performed, and the magnetic flux shielding member 80 is moved so as to be located at the home position P1. After the transition to the start-up control, the apparatus enters a state of waiting for input of an image forming job. The image forming job is executed by, for example, a print start instruction input from the operation unit 11 or an external personal computer by the user, or a copy start instruction input from the operation unit 11 by the user.

  The control unit 70 determines whether or not an operation of turning off the power switch has been performed (step S3). When determining that the operation of turning off the power switch has not been performed (NO in step S3), control unit 70 determines whether an image forming job has been input (step S4). When determining that the image forming job has not been input (NO in step S4), control unit 70 determines whether an operation of turning off the power switch has been performed again (step S3). If the control unit 70 determines that the image forming job has been input (YES in step S4), the information corresponding to the type, size, and basis weight of the sheet material of the sheet S on which the toner image is to be formed in the image forming job (Step S5). These pieces of information are input from the operation unit 11 or an external personal computer as instructions from the user.

  The control unit 70 determines whether or not to move the magnetic flux shielding member 80 by referring to the table based on the acquired information, and moves the magnetic flux shielding member 80 as necessary (step S6). Thereafter, the image forming job is executed, and the control unit 70 determines whether the image forming job has been completed (step S7). If the control unit 70 determines that the image forming job has not been completed (NO in step S7), the control unit 70 acquires sheet information including information corresponding to the type, size, and basis weight of the sheet material again (step S5). . When the control unit 70 determines that the image forming job is completed (YES in step S7), the magnetic flux shielding member 80 is returned to the home position P1 (step S8), and an operation of turning off the power switch again is performed. It is determined whether or not it has been performed (step S3). That is, when the power is on, the control unit 70 moves the detection target unit 84 to the home position P1 after the end of the image formation.

  On the other hand, when it is determined that the operation of turning off the power switch has been performed (YES in step S3), the control unit 70 shifts to the end control, and moves the magnetic flux shielding member 80 to the retreat position P2 during the end control. It is moved (step S9). That is, the control unit 70 controls the moving mechanism 81 so that the detected unit 84 is located at the retreat position P2 different from the home position P1 in the rotation axis direction D2 when the power is off. At this time, in the fixing device 20, when the power is off, the detected portion 84 is located at the retracted position P2 different from the home position P1 in the rotation axis direction D2. After the end control, the power of the image forming apparatus 1 is completely turned off. By driving the moving mechanism 81 of the magnetic flux shielding member 80 during the end control of the image forming apparatus 1 as described above, the pair of magnetic flux shielding members 80 can be moved to the retreat position P2 when the pair is removed from the fixing device 20.

  As described above, according to the image forming apparatus 1 of the present embodiment, when the induction heating unit 30 and the fixing film 21 are removed from the housing 20a, the magnetic flux shielding member 80 is moved to the retreat position P2 on the center side in the rotation axis direction D2. Evacuate to Thereby, it is possible to prevent interference with the photointerrupter 90 during assembly. For this reason, it is possible to prevent a part of the induction heating unit 30 from contacting the photointerrupter 90 when the induction heating unit 30 is mounted on the housing 20a by using the fixing device 20 having the induction heating unit 30.

  In the above-described image forming apparatus 1 of the present embodiment, the home position P1 is a position when the magnetic flux shielding member 80 is located at the end of the movable range in the rotation axis direction D2, but is not limited thereto. Absent. For example, the position may be a predetermined amount from the end of the movable range toward the center.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 20 ... Fixing apparatus, 20a ... Housing | casing, 21 ... Fixing film (heating rotary body), 30 ... Induction heating unit, 31 ... Excitation coil (Induction heating means), 40 ... Image forming part, 70 ... Control section, 80: magnetic flux shielding member, 81: moving mechanism, 84: detected section, 90: photo interrupter (detecting means), 91: light emitting section, 92: light receiving section, P1: home position (predetermined position), P2 ... Evacuation position (different position), S: sheet (recording material).

Claims (6)

An image forming apparatus comprising: an image forming unit that forms an unfixed toner image on a recording material; a fixing device that fixes the toner image formed by the image forming unit on the recording material; and a control unit,
The fixing device includes:
A housing,
A heating rotator to which a magnetic flux is incident and is induction-heated and rotatable;
Induction heating means for generating the magnetic flux, which is disposed facing the outside of the heating rotator, provided between the heating rotator and the induction heating means, and is movable in a rotation axis direction of the heating rotator. An induction heating unit having a magnetic flux shielding member capable of shutting off the magnetic flux, and a detected part movable in conjunction with the magnetic flux shielding member, and being detachably attached to the housing in a predetermined direction. When,
A moving mechanism for moving the magnetic flux shielding member,
When the induction heating unit is provided in the housing, the induction heating unit is located at a position overlapping the detected portion with respect to the predetermined direction, and the detected portion is positioned at a predetermined position in the rotation axis direction. Detecting means that can detect that
The control unit controls the moving mechanism so that the detected unit is located at a position different from the predetermined position with respect to the rotation axis direction when the power is off.
An image forming apparatus comprising: The predetermined position is an end of a movable range of the detected part,
The image forming apparatus according to claim 1, wherein: The control unit, when the power supply is in an on state, positions the detected unit at the predetermined position after the end of image formation,
The image forming apparatus according to claim 1, wherein: A power switch that can switch the power supply between an on state and an off state,
The power-off state is realized by turning off the power switch.
The image forming apparatus according to claim 1, wherein: The detecting means has a light emitting unit capable of emitting light, and a light receiving unit capable of receiving light emitted from the light emitting unit, and whether the detected part is located between the light emitting unit and the light receiving unit. The output signal from the light receiving unit is a different photo interrupter depending on whether or not,
The image forming apparatus according to claim 1, wherein: A fixing device that fixes a toner image formed by an image forming unit that forms an unfixed toner image on a recording material to the recording material,
A housing,
A heating rotator to which a magnetic flux is incident and is induction-heated and rotatable;
Induction heating means for generating the magnetic flux, which is disposed facing the outside of the heating rotator, provided between the heating rotator and the induction heating means, and is movable in a rotation axis direction of the heating rotator. An induction heating unit having a magnetic flux shielding member capable of shutting off the magnetic flux, and a detected part movable in conjunction with the magnetic flux shielding member, and being detachably attached to the housing in a predetermined direction. When,
A moving mechanism for moving the magnetic flux shielding member,
When the induction heating unit is provided in the housing, the induction heating unit is located at a position overlapping the detected portion with respect to the predetermined direction, and the detected portion is positioned at a predetermined position in the rotation axis direction. Detection means capable of detecting that
When the power is off, the detected part is located at a position different from the predetermined position with respect to the rotation axis direction,
A fixing device characterized by the above-mentioned.

Images