JP2013114035A - Image heating device and image forming apparatus having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image heating device A of an electromagnetic induction heating system, capable of reducing change of temperature distribution in a longer direction of an image heating member, reducing electric power consumption, down-sizing the device, and efficiently heating the image heating member.SOLUTION: When a direction orthogonal to a recording material conveyance direction a is defined as a width direction in a plane of a conveyance path of recording material, magnetic flux adjustment means 6 comprises: a housing 6a for housing magnetic fluid 12; magnetic fluid regulation members 8L, 8R which can move in the width direction of the housing, and which regulate existence area width of the magnetic fluid in the housing; and regulation member movement means 17 for moving the magnetic fluid regulation members. A control circuit part controls the regulation member movement means so that the existence area width of the magnetic fluid in the housing is regulated by the magnetic fluid regulation members according to width size of the recording material made to pass through the device.

Description

  INDUSTRIAL APPLICABILITY The present invention is suitable for use as a fixing device mounted on an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multi-function machine for performing image formation by an image forming process such as electrophotography, electrostatic recording, and magnetic recording. The present invention relates to an image heating apparatus using an electromagnetic induction heating method. The present invention also relates to an image forming apparatus equipped with the image heating apparatus.

  Examples of the image heating device include a fixing device that fixes or presupposes an unfixed image on the recording material, and a gloss increasing device that increases the gloss of the image by heating the image fixed on the recording material. In addition, an image heating apparatus or the like may be used to quickly dry ink in an image forming apparatus that forms an image with a liquid containing a dye or a pigment, such as an ink jet method.

  Hereinafter, the fixing device will be described as an example. 2. Description of the Related Art Conventionally, in an image forming apparatus employing an electrophotographic method, various types of fixing devices have been proposed as a fixing device that heats and fixes an unfixed toner image. One such fixing device is an electromagnetic induction heating type fixing device.

  In this fixing device, as a means for heating a fixing member (image heating member) that heats and fixes an unfixed toner image, a conductive layer is provided on the fixing member, and the conductive layer is heated by electromagnetic induction heating. It has been. In electromagnetic induction heating, an exciting coil that generates a variable magnetic field is disposed opposite to a conductive layer, and a magnetic flux is applied to the conductive layer. Thereby, an eddy current is generated in the conductive layer and heat is generated. According to the electromagnetic induction heating, the conductive layer can generate heat in a very short time, and the fixing member can be directly heated.

  Therefore, the apparatus can be warmed up more efficiently than when a heating element such as a halogen lamp is used as a heating source. Further, the exciting coil can be arranged either inside or outside the fixing member so as to face the conductive layer, and the degree of freedom in design is increased.

  However, in the conventional fixing device of the electromagnetic induction heating method, the following problem of temperature rise of the non-sheet passing portion is remarkable. Non-sheet-passing temperature rises when a recording material with a width smaller than the maximum sheet-feeding width that can be introduced and used in the machine is continuously fed and heat-fixed to form a fixing nip. This is a phenomenon in which the temperature of the non-sheet passing portion of the fixing member and the pressure member for nipping and conveying the recording material is higher than that of the sheet passing portion.

  This is because the heat consumed for heating the recording material is compensated by the temperature control system at the sheet passing portion in the fixing member and the pressure member and maintained at a predetermined temperature, whereas in the non-sheet passing portion, the recording is performed. Since heat is not consumed by heating the material, heat is accumulated. For this reason, the temperature of the non-sheet passing portion is higher than that of the sheet passing portion that is maintained at a predetermined temperature. When the temperature rise due to the temperature rise of the non-sheet passing portion is significant, the fixing member surface layer, the elastic layer, the pressure member, and other components around the temperature raising portion are likely to be thermally damaged.

  In order to save energy, the heat capacity of the fixing member is reduced, the fixing member is formed into a so-called film, and the sheet passing speed is increased to maintain the fixing member at a predetermined temperature when the sheet is passed. The power of will increase. Then, the temperature rise in the non-sheet passing portion becomes more remarkable. Therefore, when the recording material having the maximum sheet passing width is passed, the temperature rise of the non-sheet passing portion outside the sheet passing area may become a problem.

  As a countermeasure against such a temperature increase in the non-sheet passing portion, there is an example shown in Patent Document 1. The fixing device includes a demagnetizing coil that overlaps with one bent portion of the exciting coil and has an extending portion that substantially overlaps a part of the extending portion of the exciting coil to cancel the magnetic flux generated by the exciting coil. It is. Further, in Patent Document 2, the temperature rise control of the non-sheet passing portion region is performed by dividing the exciting coil into a center coil at the center and side coils at both ends.

JP 2005-321642 A JP 2008-258163 A

  However, according to the above-described prior art, there are the following problems. Since the demagnetizing coil and the split coil described in Patent Documents 1 and 2 have a constant length in the longitudinal direction, they cannot cope with a variety of paper sizes. That is, when a paper size that is longer than or equal to the longitudinal length of the degaussing coil is passed, the longitudinal temperature distribution in the paper passing area cannot be kept constant, and the end sag or the non-sheet passing portion rises. Warmth occurs.

  In order to cope with the paper size, a countermeasure of arranging a degaussing coil corresponding to the non-sheet passing portion area of each paper size is also conceivable. However, according to the above-described prior art, the number of turns of the degaussing coil is said to be 1/2 or more of the number of turns of the exciting coil, and arranging many degaussing coils increases the size of the fixing device. There is a problem of inviting.

  Furthermore, since the power applied to the degaussing coil is inversely proportional to the number of turns of the degaussing coil, there is a trade-off between the problem of increasing the size of the fixing device due to the number of turns of the degaussing coil and the increase in power consumption. In the above prior art, the number of turns of the degaussing coil is ½ or more of the number of turns of the exciting coil. Therefore, the power applied to the degaussing coil is equivalent to the power applied to the exciting coil. The amount is considered necessary. As a result, the energy consumed by the electromagnetic induction heating device increases, and as a result, the electromagnetic induction heating device originally used for energy saving may have a contradictory result that the energy saving performance is impaired.

  The present invention has been made in view of the above circumstances. An object of the present invention is to reduce fluctuations in the longitudinal temperature distribution of an image heating member that generates electromagnetic induction heat for heating a recording material carrying an image in an electromagnetic induction heating type image heating apparatus. Another object of the present invention is to efficiently heat an image heating member while enabling reduction in power consumption and downsizing of the apparatus in the image heating apparatus.

  In order to achieve the above object, a typical configuration of the image heating apparatus according to the present invention includes a coil that generates a magnetic flux and a recording material that generates heat by the action of the magnetic flux and carries the image and is conveyed. In an image heating apparatus having a rotatable image heating member to be heated, a magnetic flux adjusting means for adjusting a magnetic flux acting on the image heating member, and a control means, the recording material is transported in a direction perpendicular to the recording material conveyance direction. When the direction parallel to the width direction is the width direction, the magnetic flux adjusting means is movable in the width direction of the housing containing the magnetic fluid and the width of the magnetic fluid existing in the housing. A magnetic fluid regulating member for regulating, and a regulating member moving means for moving the magnetic fluid regulating member, wherein the control means corresponds to the width of the recording material passed through the image heating device. In the housing of Kicking existence region width and controls the regulating member moving means so as to be restricted by the magnetic fluid restricting member.

  According to the present invention, in an electromagnetic induction heating type image heating apparatus, it is possible to reduce fluctuations in the longitudinal temperature distribution of an image heating member that generates electromagnetic induction heat for heating a recording material carrying an image. In addition, the image heating member can be efficiently heated while reducing power consumption and downsizing the apparatus.

1 is a structural model diagram of an example of an image forming apparatus equipped with an electromagnetic induction heating type image heating apparatus according to the present invention as an image fixing apparatus. Expanded cross-sectional side view of main part of fixing device and block diagram of control system Schematic diagram showing the dimensional relationship in the longitudinal direction of various members constituting the fixing device Cross-sectional schematic diagram showing the layer structure of the fixing belt (A) is an external perspective view of a magnetic flux adjustment unit, (b) is an external perspective view of a built-in mechanism part. (A) is a schematic diagram of the top surface of the magnetic flux adjustment unit, (b) is a schematic diagram of the bottom surface. (A) And (b) is a schematic diagram explaining operation | movement of a built-in mechanism part. Distribution diagram of magnetic field generated from coil in paper passing area Distribution map of magnetic field generated from coil in non-paper passing area Example of specific control flow of magnetic flux adjustment unit in embodiment 1 The figure which shows the SIM result of the temperature rising suppression effect in Example 1 The figure which shows the heat_generation | fever change of the magnetic fluid area | region in Example 1. The schematic diagram which shows the structure of the magnetic flux adjustment unit in Example 2. FIG.

  Hereinafter, the present invention will be described more specifically with reference to examples. Although these examples are examples of the best mode of the present invention, the present invention is not limited to these examples.

[Example 1]
(1) Example of Image Forming Apparatus FIG. 1 is a structural model diagram of an example of an image forming apparatus in which an electromagnetic induction heating type image heating apparatus according to the present invention is mounted as a fixing device (image fixing means) A. This image forming apparatus is a color image forming apparatus using an electrophotographic system.

  Y, C, M, and K are four image forming portions that form yellow, cyan, magenta, and black color toner images, respectively, and are arranged in order from the bottom to the top. Each of the image forming units Y, C, M, and K includes an electrophotographic photosensitive drum 21, a charging device 22, a developing device 23, a cleaning device 24, and the like. The developing devices 23 of the image forming units Y, C, M, and K each have a developer of yellow (Y color), cyan (C color), magenta (M color), and black (K color) as a developer. Toner is contained.

  Each drum 21 is rotationally driven in a counterclockwise direction indicated by an arrow at a predetermined speed. An optical system 25 that forms an electrostatic latent image by exposing each of the drums 21 is provided corresponding to the four-color image forming portions Y, C, M, and K. A laser scanning exposure optical system is used as the optical system. In each of the image forming units Y, C, M, and K, the drum 21 uniformly charged by the charging device 22 is subjected to scanning exposure based on image data from the optical system 25, thereby scanning exposure on the drum surface. An electrostatic latent image corresponding to the image pattern is formed.

  Those electrostatic latent images are developed as toner images by the developing device 23. That is, a Y-color toner image is stored on the drum 21 of the image forming unit Y, a C-color toner image is stored on the drum 21 of the image forming unit C, and an M-color toner image is stored on the drum 21 of the image forming unit M. A K toner image is formed on each of the K drums 21. The color toner images formed on the drums 21 of the image forming units Y, C, M, and K are in a predetermined position on the intermediate transfer body 26 that rotates at a substantially constant speed in synchronization with the rotation of the drums 21. In the combined state, the images are sequentially superimposed and transferred primarily. As a result, an unfixed full-color toner image is synthesized and formed on the intermediate transfer member 26.

  In this embodiment, an endless intermediate transfer belt is used as the intermediate transfer member 26. The belt 26 is stretched around three rollers including a driving roller 27, a secondary transfer counter roller 28, and a tension roller 29. The belt 26 is circulated and driven by the drive roller 27 in the clockwise direction of the arrow at a speed substantially equal to the speed of the drum 21.

  A primary transfer roller 30 is used as a primary transfer unit of the toner image from the drum 21 to the belt 26 of each of the image forming units Y, C, M, and K. A primary transfer bias having a polarity opposite to that of the toner is applied to the primary transfer roller 30 from a bias power source (not shown). As a result, the toner images are primarily transferred from the drums 21 of the image forming units Y, C, M, and K to the belt 26. After the primary transfer from the drum 21 to the belt 26 in each of the image forming units Y, C, M, and K, the toner remaining as a transfer residue on the drum 21 is removed by the cleaning device 24.

  The above process is performed for each of the colors Y, C, M, and K in synchronization with the rotation of the belt 26, and the primary transfer toner images of the respective colors are sequentially stacked on the belt 26. It should be noted that the above process is performed only for the target color during image formation of only a single color (monochromatic mode).

  On the other hand, the recording material P in the recording material cassette 31 is separated and fed by the feeding roller 32. The fed recording material P is fed to a secondary transfer nip portion, which is a pressure contact portion between the belt 26 portion wound around the secondary transfer counter roller 28 and the secondary transfer roller 34 at a predetermined timing by the registration roller 33. Be transported.

  The primary transfer composite toner image formed on the belt 26 is collectively transferred onto the recording material P at the secondary transfer nip portion by a bias having a reverse polarity to the toner applied to the secondary transfer roller 34 from a bias power source (not shown). The The secondary transfer residual toner remaining on the belt 26 after the secondary transfer is removed by the intermediate transfer belt cleaning device 35.

  The above is the image forming means for forming an unfixed image on the recording material P. The unfixed toner image secondarily transferred to the recording material P is fused and mixed (fixed) as a fixed image on the recording material P by the fixing device A, which is an image heating device, and passes through the paper discharge path 36 as a full-color print. Then, it is sent out to the paper discharge tray 37.

(2) Fixing device A
In the following description, the longitudinal direction or the width direction of the fixing device (image fixing unit) A or a member constituting the fixing device A is a direction parallel to the direction orthogonal to the recording material conveyance direction a in the recording material conveyance path surface. is there. The short direction is a direction parallel to the recording material conveyance direction. Regarding the fixing device, the front means the surface of the apparatus viewed from the recording material inlet side, the rear surface is the opposite surface (recording material outlet side), and the left and right are the left or right when the apparatus is viewed from the front. The upstream side and the downstream side are the upstream side and the downstream side in the recording material conveyance direction.

  FIG. 2 is an enlarged cross-sectional side view of a main part of a fixing device A as an image heating device of an electromagnetic induction heating method in this embodiment and a block diagram of a control system. FIG. 3 is a schematic diagram showing a dimensional relationship in the longitudinal direction (width direction) of various members constituting the fixing device A.

  In electromagnetic induction heating, an exciting coil that generates a variable magnetic field is disposed opposite to a conductive layer, and a magnetic flux is applied to the conductive layer, thereby generating an eddy current in the conductive layer and generating heat. According to the electromagnetic induction heating, the conductive layer can generate heat in a very short time, and the fixing member can be directly heated. Therefore, the apparatus can be warmed up more efficiently than when a heating element such as a halogen lamp is used as a heating source. Further, the exciting coil can be arranged either inside or outside the fixing member so as to face the conductive layer, and the degree of freedom in design is increased.

  Referring to FIGS. 2 and 3, the fixing device A in this embodiment is a fixing belt unit in which both ends in the longitudinal direction are held between left and right device side plates of a fixing device frame (device frame, chassis) (not shown). (Hereinafter referred to as a belt unit) 20 is provided. An elastic pressure roller 2 as a pressure member is disposed below the belt unit 20 with both ends rotatably supported between the left and right device side plates. On the upper side of the belt unit 20, the induction heating device 4 is disposed such that both ends in the longitudinal direction are held between the left and right device side plates.

1) Belt unit 20
The belt unit 20 is disposed inside the belt 1 and a cylindrical fixing belt (endless belt: hereinafter referred to as a belt) 1 that is long in the left-right direction as an image heating member that generates electromagnetic induction heat by the action of magnetic flux. The pressing member 3 is long in the left-right direction. The pressing member 3 is a member that presses the belt 1 toward the pressure roller 2, and includes a nip forming member 3a and a stay 3b that supports the nip forming member 3a. Moreover, it has the inner side magnetic body core 6b arrange | positioned so that the outer side of the stay 3b may be covered.

  In the present embodiment, the length L1 of the belt 1 is 350 mm. FIG. 4 is a model diagram of the layer structure of the belt 1. The belt 1 has a nickel base layer (conductive layer, dielectric, metal layer: hereinafter referred to as a metal layer) 1a, which has an inner diameter of 30 mm and is manufactured by electroforming, as an electromagnetic induction heat generating layer. The thickness of the metal layer 1a is 40 μm.

  For the metal layer 1a, iron alloy, copper, silver or the like can be appropriately selected in addition to nickel. Moreover, the structure of laminating | stacking these metals on a resin base layer may be sufficient. The thickness of the metal layer 1a may be adjusted according to the frequency of a high-frequency current flowing through an exciting coil, which will be described later, and the permeability / conductivity of the metal layer, and may be set between about 5 and 200 μm.

  A heat-resistant silicone rubber layer is provided as an elastic layer 1b on the outer periphery of the metal layer 1a. The thickness of the silicone rubber layer is preferably set within a range of 100 to 1000 μm. In this embodiment, in consideration of shortening the warm-up time by reducing the heat capacity of the belt 1 and obtaining a suitable fixed image when fixing a color image, the thickness of the silicone rubber layer 1b is set to 300 μm. Yes. This silicone rubber has a hardness of JIS-A 20 degrees and a thermal conductivity of 0.8 W / mK.

  Further, on the outer periphery of the elastic layer 1b, a fluororesin layer (for example, PFA or PTFE) is provided as a surface release layer 1c with a thickness of 30 μm. On the inner surface side of the base layer 1a, in order to reduce sliding friction with the temperature sensors TH1 and TH2 disposed in elastic contact with the inner surface of the belt, a resin layer (sliding layer) 1d such as fluororesin or polyimide is used. 10 to 50 μm may be provided. In this example, 20 μm of polyimide was provided as the layer 1d.

  The nip forming member 3a is, for example, a heat-resistant resin molded product, and is a member having a cross-sectional arch shape in which the lower surface is a convex curved surface having the same curvature as the curvature of the inner peripheral surface of the belt 1 and the upper surface is a plane. The stay 3b is made of metal because it needs rigidity to press the nip forming member 3a against the pressure roller 2 via the belt 1. In the present embodiment, the stay 3b is a U-shaped iron member having a transverse cross section that faces downward, and is bonded to the upper surface of the nip forming member 3a to support the nip forming member 3a.

  The inner magnetic core 6b is a C-shaped member having a downward cross section and is disposed outside the stay 3b so as to cover the stay 3b. The inner magnetic core 6b has convex curved surfaces facing along the inner peripheral surface of the substantially upper half of the belt 1. That is, the inner magnetic body core 6b is opposed to the inner peripheral surface of the belt 1 in the circumferential direction and the longitudinal direction corresponding to the coil 5 of the induction heating device 4 described later.

  As will be described later, the nip forming member 3a is pressed against the pressure roller 2 via the belt 1 by the pressure applied by the stay 3b to form the fixing nip portion N. The length of the fixing nip portion N is 320 mm which is the same as the length L2 of the pressure roller 2. The length of the fixing nip portion N is longer than the maximum sheet passing area width Wmax = 300 mm in this embodiment.

  The length L3a of the nip forming member 3a is set to be longer than the maximum sheet passing area width Wmax = 300 mm and shorter than the length L2320 mm of the pressure roller 2. The length L3b of the stay 3b is 360 mm. The length L6b of the inner magnetic core 6b is 320 mm, which is the same as the length of the fixing nip portion N. The belt 1 is loosely fitted to the assembly of the pressing member 3 and the core 6b.

  Here, in this embodiment, the recording material P is fed (conveyed) to the fixing device A based on the central reference at the center of the recording material width. That is, recording media of various sizes of large, medium, and small sizes that can be passed through the apparatus pass through the central portion in the longitudinal direction of the belt 1 in the central portion in the width direction. O is the central reference transport line O (virtual line). In the recording material, the width size is a dimension in a direction orthogonal to the recording material conveyance direction a in the recording material conveyance path surface.

  Wmax is a width (maximum sheet passing area width) of a sheet passing area (sheet passing portion) of a recording material having a maximum width size (large size recording material) that can be used in the fixing device A. Wmin is a width (minimum sheet passing area width) of a sheet passing area (sheet passing part) of a recording material having a minimum width size (small size recording material) that can be used for the fixing device A. Accordingly, the fixing device A uses a large-size recording material, a small-size recording material, and medium-size recording materials of various width sizes having a width smaller than that of the large-size recording material and larger than that of the small-size recording material. I can do it.

  B is the width of a non-sheet passing region (non-sheet passing portion) which is a difference width portion between a sheet passing region width and a maximum sheet passing region width Wmax when a small size recording medium or a medium size recording material is passed. In this embodiment, since the recording material passing is center reference conveyance, the non-sheet passing region B is generated on both left and right sides of the small size recording material or medium size recording material. The width of the non-sheet passing region B is the largest in the case of a small size recording material, and in the case of a medium size recording material, the width varies depending on the width of the medium size recording material used for paper passing.

  A first temperature sensor (temperature detection element) TH1 such as a thermistor is connected to the position of the center of the nip forming member 3a and the end (right end) on one side via the elastic support member 14, respectively. Temperature sensor TH2 is disposed. The temperature sensors TH1 and TH2 are elastically brought into contact with the inner surface of the belt 1 due to the elasticity of the elastic support member 14, and detect the temperature at the longitudinal center (width direction center) and the end of the belt 1, respectively.

  The first temperature sensor TH1 detects the temperature of the belt portion serving as a sheet passing portion for recording materials of large, medium, and small width sizes. For this purpose, the belt 1 is positioned at the longitudinal center (within the minimum sheet passing area width Wmin: in the present embodiment, the belt portion substantially corresponding to the position of the center reference transport line O). The second temperature sensor TH2 detects the temperature of the belt portion that becomes the non-sheet passing portion B when the small size recording material or the medium size recording material is passed. For this purpose, the belt portion is positioned slightly inside the boundary line on one side (right side) of the maximum sheet passing area width Wmax.

  The detected temperature information (electrical information related to temperature) of each of the first and second temperature sensors TH1 and TH2 is input to the control circuit unit 100. Since the first and second temperature sensors TH1 and TH2 are supported by the elastic support member 14 in elastic contact with the inner surface of the belt 1, position fluctuations such as undulation of the contact surface of the rotating belt 1 occur. Even if it occurs, a good contact state is maintained following this.

  End members 7L and 7R having flange portions 7a, which are heat-resistant resin molded products, are fitted to both left and right ends of the stay 3b. The left and right terminal members 7L and 7R are held so as to be slidable in the vertical direction with respect to the left and right device side plates, respectively. Terminal member shift mechanisms 19L and 19R as pressure urging means for the terminal members 7L and 7R are disposed on the outer surface sides of the left and right device side plates, respectively.

  The shift mechanisms 19L and 19R include, for example, a cam mechanism connected to a motor, and are controlled by the control circuit unit 100 to have a function of moving the terminal members 7L and 7R upward or downward. As the terminal members 7L and 7R move downward, the pressing member 3 is pushed down, and the nip forming member 3a is predetermined against the upper surface of the pressing roller 2 via the belt 1 against the elasticity of the pressing roller 2. In this embodiment, a pressure of 490 N (50 kgf) is applied (wearing state). As a result, a fixing nip portion N having a predetermined width is formed between the belt 1 and the pressure roller 2 in the recording material conveyance direction a.

  Further, the terminal members 7L and 7R move upward, whereby the pressing member 3 is lifted and the nip forming member 3a is separated from the upper surface of the pressure roller 2 (disengaged state). As a result, the pressure contact between the belt 1 and the pressure roller 2 is released. By doing so, it is possible to prevent the elastic layer 2b of the pressure roller 2 and the belt 1 from being permanently deformed.

2) Pressure roller 2
The pressure roller 2 is an elastic roller having an outer diameter of 30 mm in which a core rubber 2a is provided with a silicone rubber layer as an elastic layer 2b. The cored bar 2a is a tape-shaped crown-shaped cored bar made of an iron alloy having a diameter in the center in the longitudinal direction of 20 mm and a diameter at both ends of 19 mm. The surface of the elastic layer 2b is provided with a fluororesin layer (for example, PFA or PTFE) with a thickness of 30 μm as the release layer 2c. The hardness at the center in the longitudinal direction of the pressure roller 2 is ASK-C 70 degrees.

  The pressure roller 2 is disposed such that the left and right ends of the cored bar 2a are rotatably supported by left and right device side plates via bearing members (not shown). The pressure roller 2 is driven to rotate at a predetermined peripheral speed in the counterclockwise direction indicated by an arrow R2 in FIG. 2 when a driving force is transmitted from a driving device (driving means: motor) M1 via a driving transmission means (not shown). Is done.

  The cored bar 2a is tapered because the fixing formed by the belt 1 and the pressure roller 2 even when the pressure member 3 is bent when the pressure member 3 is pressed against the pressure roller 2 via the belt 1. This is for making the pressure in the nip portion N uniform over the longitudinal direction of the nip portion.

  In this embodiment, the length of the pressure roller 2 (length of the elastic layer 2b) L2 is 320 mm. Further, depending on the shift mechanisms 19L and 19R, a fixing nip portion N formed between the belt 1 and the pressure roller 4 in a state where the pressure member 3 is pressed against the pressure roller 2 with a predetermined pressure. The width in the recording material conveyance direction a is about 8 mm at both ends in the longitudinal direction. In the central part, it is about 7.5 mm. This has the advantage that paper wrinkles (recording material wrinkles) are less likely to occur because the conveyance speed at both ends in the width direction of the recording material P is faster than the central portion.

3) Induction heating device 4
The induction heating device 4 is a heating source (induction heating means) for inductively heating the belt 1 (metal layer 1a), and the upper side of the belt unit 20 has a longitudinal direction substantially parallel to the longitudinal direction of the belt unit 20 and between the device side plates. The position is fixed.

  The induction heating device 4 has an exciting coil (hereinafter referred to as a coil) 5 that opposes the outer peripheral surface of substantially the upper half of the belt 1 and generates a magnetic flux to heat the belt 1 with the magnetic flux. The coil 5 is formed by using, for example, a litz wire as an electric wire, which is horizontally long and shaped like a ship bottom and is opposed to a part of the peripheral surface and side surface of the belt 1. The length L5 of the coil 5 is 350 mm.

  Further, a magnetic flux adjusting unit 6 using a magnetic fluid 12 as a heating element external magnetic flux adjusting means (external magnetic core) is provided outside the coil 5. The length L6 of the magnetic flux adjustment unit 6 is 350 mm. The magnetic flux adjusting unit 6 is opposed to the outer peripheral surface of the belt 1 in the circumferential direction and the longitudinal direction corresponding to the coil 5. Details of the magnetic flux adjustment unit 6 will be described later in section (3).

  The induction heating device 4 includes first and second sub magnetic cores 6e and 6f. The first sub-magnetic core 6e is disposed on the recording material entrance side of the fixing nip N so as to be close to the front edges of both the coil 5 and the magnetic flux adjusting unit 6 and along the longitudinal length of the front edge. It is a rectangular magnetic core. The second sub magnetic core 6f is disposed along the longitudinal length of the rear edge of the fixing nip N on the recording material outlet side, close to the rear edge of both the coil 5 and the magnetic flux adjusting unit 6. This is a magnetic core having a rectangular cross section.

  The coil 5, the magnetic flux adjusting unit 6, and the first and second sub magnetic cores 6e and 6f are integrally molded with an electrically insulating resin (mold member) 6c. The molded product is covered with a magnetic flux shielding housing 15 except for the inner surface facing the outer peripheral surface of the belt 1. The magnetic flux shielding housing 15 prevents the magnetic field generated by the coil 5 from substantially leaking except for the metal layer (conductive layer) 1 a of the belt 1.

  The induction heating device 4 is disposed with its inner surface facing the outer peripheral surface of the upper surface of the belt 1 with a predetermined gap (gap). In this embodiment, the coil 1 of the belt 1 and the induction heating device 4 is electrically insulated by a 0.5 mm mold, and the distance between the belt 1 and the coil 5 is 1.5 mm (the distance between the mold surface and the fixing belt surface). Is constant at 1.0 mm), and the belt 1 is heated uniformly.

4) Fixing Operation The fixing operation of the fixing device A will be described. Based on the input of the image formation start signal, the control circuit unit 100 switches the shift mechanisms 19L and 19R from the detached state to the worn state at least during execution of image formation. As a result, the pressing member 3 is pushed down, and the nip forming member 3 a is pressed against the upper surface of the pressure roller 2 through the belt 1 with a predetermined pressure against the elasticity of the pressure roller 2. A fixing nip N having a predetermined width is formed between the belt 1 and the pressure roller 2 in the recording material conveyance direction a.

  The control circuit unit 101 turns on the driving device M1 and turns on the power supply device (excitation circuit) 101. When the driving device M1 is turned on, the pressure roller 2 is rotationally driven at a predetermined speed in the counterclockwise direction of the arrow R2 in FIG. By the rotation of the pressure roller 2, a rotational force acts on the belt 1 by the frictional force between the surface of the pressure roller 2 and the surface of the belt 1 in the fixing nip portion N. The inner surface of the belt 1 is in close contact with the lower surface of the nip forming member 3a at the nip portion N and slides around the outer periphery of the pressing member 3 and the inner magnetic core 6b in the clockwise direction indicated by the arrow R1. Followed rotation at almost the same speed.

  The pressing member 3 and the inner magnetic core 6b also serve as a guide member for the rotating belt 1. Since the rotating belt 1 has a base layer 1a made of a metal, as a means for restricting the shift in the length direction even in the rotating state, the belt 1 simply receives the end of the belt 1. It is sufficient to provide a flange member. In this embodiment, the terminal members 7L and 7R fitted to the left and right ends of the stay 3b are respectively provided with flange portions 7a to receive the left and right ends of the belt 1 so that the left or right side of the belt 1 is received. The movement to the side is regulated. Thereby, there is an advantage that the configuration of the fixing device A can be simplified.

  Further, when the power supply device 101 is turned on, a high frequency current (alternating current) of 20 to 50 kHz is applied to the coil 5, and the metal layer 1 a of the belt 1 is inductively heated by the magnetic field generated by the coil 5. The heat generated by the metal layer 1a raises the temperature of the rotating belt 1. The control circuit unit 100 adjusts the temperature so that the temperature of the belt 1 becomes substantially constant at a predetermined target temperature (fixing temperature). That is, the temperature is adjusted by controlling the power input from the power supply device 101 to the coil 5 based on the temperature detected by the first temperature sensor TH1 that detects the temperature of the longitudinal center of the belt 1.

  In this embodiment, the temperature is adjusted so that the temperature of the belt 1 is substantially constant at 180 ° C. The first temperature sensor TH <b> 1 detects the temperature of the belt portion that is the sheet passing area of the recording material, and the detected temperature information is fed back to the control circuit unit 100. The control circuit unit 100 controls the electric power input from the power supply device 101 to the coil 5 so that the detected temperature input from the first temperature sensor TH1 is maintained at a predetermined target temperature. That is, when the detected temperature of the belt 1 is raised to a predetermined temperature, the energization to the coil 5 is interrupted.

  As described above, the pressure roller 2 is driven, and the belt 1 rises to a predetermined fixing temperature and is temperature-controlled. In this state, the recording material P having the unfixed toner image T is introduced into the fixing nip portion N while being guided by the guide member 16 with the toner image carrying surface side facing the belt 1 side. The recording material P is in close contact with the outer peripheral surface of the belt 1 at the fixing nip portion N, and is nipped and conveyed along the fixing nip portion N together with the belt 1. As a result, the heat of the belt 1 is mainly applied to the recording material P, and the image T is fixed to the surface of the recording material P by receiving pressure from the fixing nip N.

  The recording material P that has passed through the fixing nip N is self-separated from the outer peripheral surface of the belt 1 due to deformation of the exit portion of the fixing nip N, and is conveyed outside the fixing device. The belt 1 is driven and rotated at a peripheral speed substantially the same as the conveying speed of the recording material P carrying the image T, which is conveyed from the image transfer unit side, by the pressure roller 2 being rotationally driven by the driving device M1. To do. In the case of this embodiment, the surface rotation speed of the belt 1 rotates at 210 mm / sec, and 50 full-color images can be fixed in A4 size (lateral feed) per minute.

  Since the induction heating device 4 including the coil 5 is disposed not on the inside of the belt 1 that is at a high temperature but on the outside, the temperature of the coil 5 is not likely to be high, the electrical resistance does not increase, and a high-frequency current is allowed to flow. Loss due to heat generation can be reduced. In addition, the arrangement of the coil 5 on the outside contributes to a reduction in the diameter (reduction in heat capacity) of the belt 1. As a result, it can be said that it is also excellent in energy saving.

  Since the warming-up time of the fixing device A of this embodiment has a very low heat capacity, for example, when 1200 W is input to the exciting coil 5, it can reach the target temperature of 180 ° C. in about 15 seconds. And since the heating operation in standby is unnecessary, it is possible to keep power consumption very low.

(3) Magnetic flux adjusting unit 6 and its control In the fixing device A, a small-size recording material or a medium-size recording material having a width smaller than that of a large-size recording material having a maximum paper passing width that can be introduced and used in the apparatus is continuously passed. Then, when heat fixing is executed, the non-sheet passing portion temperature rises. That is, the temperature of the non-sheet passing portion B is higher than that of the sheet passing portion that is maintained at a predetermined temperature. When the temperature rise due to the temperature rise of the non-sheet passing portion is significant, the surface layer and elastic layer of the belt 1 as a fixing member, the pressure roller 2, and other components around the temperature raising portion are likely to be thermally damaged. For this reason, a measure for mitigating the temperature rise of the non-sheet passing portion is required.

  In this embodiment, the second temperature sensor TH2 detects the temperature rise of the non-sheet passing portion B of the belt 1 when a small size recording material or a medium size recording material is passed through the fixing device A. The control circuit unit 100 controls the magnetic flux adjustment unit 6 based on the detected temperature information of the second temperature sensor TH2 to perform control for alleviating the temperature rise of the non-sheet passing portion. Hereinafter, the magnetic flux adjusting unit 6 using the magnetic fluid 12 in the present embodiment as the magnetic flux adjusting means and its control will be described.

1) Magnetic flux adjustment unit 6
5A is an external perspective view of the magnetic flux adjustment unit 6, and FIG. 5B is an external perspective view of the built-in mechanism. 6A is a schematic diagram of the upper surface of the magnetic flux adjustment unit 6, and FIG. 6B is a schematic diagram of the lower surface. FIGS. 7A and 7B are schematic diagrams for explaining the operation of the built-in mechanism. The magnetic flux adjustment unit 6 has a housing 6 a for accommodating the magnetic fluid 12. The housing 6a is a downwardly saddle-like thin hollow body that is curved along the outer arc surface of the coil 5 (on the side opposite to the side facing the belt 1) in the cross section. The length L6a is 350 mm. That is, the housing 6 a has a cross-sectional shape and a length that covers the outside of the coil 5.

  An upper bulging portion serving as a magnetic fluid pool 6d is formed on the upper surface plate of the housing 6a along the upper surface plate length at a substantially central portion in the upper surface plate short direction. Narrow tube portions 6h, 6i, and 6j as ventilation portions are provided upward at the longitudinal central portion, left end portion, and right end portion of the magnetic fluid pool 6d, respectively.

  A lower bulging portion 6g serving as a central core portion is formed on the lower surface plate of the housing 6a along the lower surface plate length at a substantially central portion in the lower surface plate short direction. The downward bulging portion 6g is positioned so as to be fitted into the space portion 5a at the center of the coil 5 as shown in FIG. 2 in a state where the magnetic flux adjusting unit 6 is disposed on the outside of the coil 5 in a predetermined manner.

  The inside of the housing 6a has a cylinder structure and has a pair of left and right pistons 8L and 8R as magnetic fluid regulating members. The outer shapes of the pistons 8L and 8R correspond to the cross-sectional shape of the inner space of the housing 6a, respectively, and can slide in the left-right direction (the width direction of the housing).

  A shaft portion 10L is disposed on the inner surface side of the left piston 8L (on the side facing the piston 8R) supported by a guide member (not shown) in parallel with the longitudinal direction of the housing 6a. Further, on the inner surface side of the right piston 8R (the surface facing the piston 8L), a shaft portion 10R is disposed in parallel with the longitudinal direction of the housing 6a and supported by a guide member (not shown). Each shaft portion 10L and 10R is provided with rack teeth 10a along the length.

  A gear (pinion gear) 11 having a diameter of 15 mm with a shaft portion 11a in the vertical direction is held by a bearing portion (not shown) at a central portion in the longitudinal direction (width direction central portion) inside the housing so as to be rotatable. ing. The two shaft portions 10L and 10R are positioned forward and backward with the gear 11 interposed therebetween, and the rack teeth 10a of the shaft portions 10L and 10R mesh with the gear 11.

  The shaft 11 a of the gear 11 extends through the upper surface plate of the housing 6 a and is driven forward and backward by a driving device M 2 controlled by the control circuit unit 100. As a result, the left and right pistons 8L and 8R move in a symmetrical manner in the left-right direction within the housing in a direction that widens the distance from each other with respect to the central reference or a direction that narrows the distance from each other. That is, the left and right pistons 8L and 8R can be moved in both longitudinal directions inside the casing.

  In the above, the shaft portions 10L and 10R having the rack teeth 10a, the gear 11, the shaft portion 11a, and the driving device M2 constitute the restricting member moving means 17 that moves the left and right pistons 8L and 8R that are magnetic fluid restricting members. Yes. The housing 6a and the internal mechanism are made of a nonmagnetic member or a magnetic member.

  In the present embodiment, the gear 11 is driven to rotate in the forward direction so that the distance between the left and right pistons 8L and 8R can be set to the maximum corresponding to the maximum sheet passing area width Wmax as shown in FIG. . Further, by rotating the gear 11 in the reverse direction, the distance between the left and right pistons 8L and 8R can be made the minimum corresponding to the minimum sheet passing area width Wmax as shown in FIG. Further, by controlling the number of rotations of the gear 11, the distance between the left and right pistons 8L and 8R is an interval corresponding to the width of various medium size recording materials between the maximum sheet passing area width Wmax and the minimum sheet passing area width Wmax. Can be.

  A space between the left and right pistons 6L and 6R inside the housing 6a accommodates a colloidal magnetic fluid (magnetic colloid solution) 12 containing magnetic powder. The magnetic fluid 12 used in this example uses magnetic powder (soft magnetic fine particles) in which soft ferrite having an initial permeability of 2000 μi at 25 ° C. and an initial permeability of 4500 μi at 200 ° C. is made into fine particles having a diameter of 10 nm. And

  The magnetic fluid 12 is a simple liquid without magnetism when the applied magnetic field is zero (the AC power supply to the coil 5 is off), but is magnetized and hardened by applying a magnetic field from the outside (AC power supply on). However, when the external magnetic field is removed again, the magnetization of the magnetic fluid disappears again. Such a magnetic fluid having a magnetic property called “superparamagnetism” does not have characteristics such as remanent magnetization and hysteresis, and therefore can achieve higher heat generation efficiency than a ferrite core or the like.

  As described above, the characteristics of the magnetic fluid 12 that changes liquefaction / curing and character by turning on / off the applied magnetic field are utilized. In the present embodiment, the magnetic fluid 12 is included in the magnetic flux adjusting unit 6 that is disposed so as to cover the coil 5 so that the magnetic field generated by the coil 5 does not leak to the outside and the magnetic field efficiently flows into the belt 1. .

  The magnetic fluid 12 accommodated in the space between the left and right pistons 8L and 8R inside the housing 6a is prevented from leaking into the housing outside the pistons 8L and 8L due to the movement of the pistons 8L and 8R. Therefore, for example, by arranging the permanent magnet 9 in a rubber material having a high sealing property in the cross section of the pistons 8L and 8R, the pistons 8L and 8R are not leaked from the housing space between the pistons 8L and 8R. Can be moved.

  Due to the fluidity of the magnetic fluid 12 in the state where no external magnetic field is applied, the width of the region where the magnetic fluid 12 exists inside the casing is widened corresponding to the distance between the left and right pistons 8L and 8R. Be changed.

  That is, as shown in FIG. 7A, when the interval between the left and right pistons 8L and 8R is set to the interval corresponding to the maximum sheet passing region width Wmax, the region width of the magnetic fluid 12 in the housing is as follows. The width corresponds to the maximum sheet passing area width Wmax. Further, as shown in FIG. 7B, when the interval between the left and right pistons 8L and 8R is set to the interval corresponding to the minimum sheet passing region width Wmax, the region width of the magnetic fluid 12 in the housing is as follows. The width corresponds to the minimum sheet passing area width Wmax.

  When the distance between the left and right pistons 8L and 8R is a distance corresponding to the width of various medium size recording materials between the maximum sheet passing area width Wmax and the minimum sheet passing area width Wmax, The existence area width of the magnetic fluid 12 is the sheet passing area width of the medium size recording material.

  That is, when the recording material to be passed is a small size recording material or a medium size recording material, the magnetic fluid 12 is disposed in a portion corresponding to the paper passing portion inside the housing of the magnetic flux adjustment unit 6. The magnetic fluid 12 is not disposed in a portion corresponding to the non-sheet passing portion.

  Therefore, in the paper passing portion, as shown in FIG. 8A, the magnetic fluid 12 in which the magnetic field generated from the coil 5 exists corresponding to the paper passing portion in the magnetic flux adjusting unit 6 functions as an external magnetic core. And converges on the belt 1 and flows in. Thereby, the part corresponding to the paper passing part of the belt 1 generates heat efficiently.

  On the other hand, the magnetic fluid 12 does not exist in a portion corresponding to the non-sheet passing portion of the magnetic flux adjusting unit 6. Therefore, as shown in FIG. 8B, the magnetic field generated from the coil 5 is not converged on the belt 1, and the magnetic field flowing into the belt 1 is reduced. Thereby, the calorific value of the part corresponding to the non-sheet passing part B of the belt 1 can be significantly reduced. That is, the non-sheet passing portion temperature rise is effectively mitigated. The magnetic field that is not converged on the belt 1 in the non-sheet passing portion B is shielded by the magnetic flux shielding housing 15 of the induction heating device 4.

  The magnetic flux adjustment unit 6 as the magnetic flux adjustment means is summarized as follows. The bundle adjustment unit 6 includes a housing 6 a that contains the magnetic fluid 12. It has magnetic fluid regulating members 8L and 8R that are movable in the width direction of the casing 6a and regulate the width of the region where the magnetic fluid 12 is present in the casing. Moreover, it has the control member moving means 17 which moves a magnetic fluid control member. Then, the control means 100 controls the restricting member moving means 17 so that the width of the region where the magnetic fluid 12 is present in the housing is restricted by the magnetic fluid restricting members 8L and 8R corresponding to the width size of the recording material passed through the apparatus. To control.

  The recording material P is conveyed by the center reference, and the existence area width of the magnetic fluid 12 in the housing is regulated by the magnetic fluid regulating member that is moved by the center reference corresponding to the width size of the recording material passed through the fixing device A. Is done.

  FIG. 9 is a specific control flow example of the magnetic flux adjustment unit 6 in the present embodiment. The left and right pistons 8L and 8R of the magnetic flux adjustment unit 6 are normally stopped with the position at an interval corresponding to the maximum sheet passing area width Wmax as shown in FIG. Therefore, the width of the region where the magnetic fluid 12 exists inside the housing is substantially the width corresponding to the maximum sheet passing region width Wmax.

  The control circuit unit 100 is inputted with size information of the recording material used for passing the sheet through the apparatus. The size information of the recording material is input from the operation unit by the user. Or it inputs from the size detection means which detects automatically the size of the recording material which passed the apparatus.

  Step S1: Upon receiving the recording material size information, the control circuit unit 100 performs the following calculation according to the width size of the recording material to be passed. That is, the number of rotations of the gear 11 necessary for moving the left and right pistons 8L and 8R of the magnetic flux adjustment unit 6 to the position corresponding to the width size of the recording material passed from the home position is calculated ( Longitudinal magnetic flux control width selection).

  Step S2: Next, the control circuit unit 100 turns on the driving device M1 of the fixing device A. Further, the power supply device 101 is turned on and a high frequency current of 20 to 50 kHz is passed through the coil 5. Accordingly, the metal layer (conductive layer) 1a of the rotating belt 1 is inductively heated by the magnetic field generated by the coil 5. That is, the temperature of the belt 1 increases.

  In this case, the left and right pistons 8L and 8R of the magnetic flux adjusting unit 6 are positioned at home positions that are spaced at intervals corresponding to the maximum sheet passing area width Wmax, and the width of the area where the magnetic fluid 12 exists inside the housing. Is a width corresponding to the maximum sheet passing area width Wmax. The magnetic fluid 12 receives a magnetic field generated from the coil 5 and is magnetized and hardened to form a magnetic path equivalent to that of soft ferrite, for example. The full length area corresponding to the maximum sheet passing area width Wmax of the belt 1 is heated evenly.

  The control circuit section 100 receives the detected temperature above the belt 1 from the first and second temperature sensors TH1 and TH2. Based on the temperature information detected by the first temperature sensor TH1, the control circuit unit 100 raises the temperature of the belt 1 to a predetermined target temperature (fixing temperature), which is 180 ° C. in this embodiment, and maintains that temperature. Adjust the temperature.

  In this state, the recording material is passed and printing is started. When the recording material to be passed is a large size recording material having a width corresponding to the maximum paper passing area width Wmax, the temperature rise of the non-sheet passing portion does not occur, and therefore the belt detected by the second temperature sensor TH2. 1 is approximately the same as the temperature of the belt 1 detected by the first temperature sensor TH1.

  Accordingly, when the recording material to be passed is a large size recording material, the predetermined set number of sheets are maintained while the interval between the left and right pistons 8L and 8R is maintained at the interval corresponding to the maximum sheet passing area width Wmax. All the printing operations are executed and printing is completed.

  Steps S3 to S5: When the recording material to be passed is a small size recording material or a medium size recording material and is continuously passed, a non-sheet passing portion temperature rise occurs in the non-sheet passing portion B of the apparatus A. The temperature of the belt portion corresponding to the non-sheet passing portion B is detected by the second temperature sensor TH2 and input to the control circuit portion 100. When the detected temperature (edge temperature) input from the second temperature sensor TH2 becomes T> 200 ° C. during the continuous printing (S3), the control circuit unit 100 is applied to the coil 5 from the power supply device 101. The high frequency current that has been stored is turned off (S4). Thereby, the magnetic fluid 12 contained in the magnetic flux adjusting unit 6 is softened and becomes a colloidal liquid without magnetism.

  Along with this step S4, the driving device M2 is controlled so as to reversely rotate the gear 11 by the number of rotations calculated in step S1. As a result, the width size of the small-size recording medium or medium-size recording material being passed from the home position where the left and right pistons 8L and 8R of the magnetic flux adjusting unit 6 are spaced from each other corresponding to the maximum sheet passing area width Wmax. Is moved to the position of the interval corresponding to. That is, the magnetic fluid 12 does not exist in the portion corresponding to the non-sheet passing portion of the magnetic flux adjusting unit 6.

  Step S6: In this state, the control circuit unit 100 turns on the power supply device 101 to continue printing. The magnetic fluid 12 receives a magnetic field generated from the coil 5, is magnetized and hardened, and forms a magnetic path equivalent to, for example, soft ferrite. Then, the entire length region corresponding to the sheet passing portion of the belt 1 is heated uniformly and adjusted to a predetermined fixing temperature.

  On the other hand, the magnetic fluid 12 does not exist in a portion corresponding to the non-sheet passing portion of the magnetic flux adjusting unit 6. Therefore, the magnetic field generated from the coil 5 is not converged on the belt 1, the magnetic field flowing into the belt 1 is reduced, and the amount of heat generated in the portion corresponding to the non-sheet passing portion B of the belt 1 is greatly reduced. The temperature detected at the belt end portion input from the temperature sensor TH2 to the control circuit portion 100 is lowered.

  Steps S7 to S9: When the detected temperature (edge temperature) input from the second temperature sensor TH2 becomes T <180 ° C. (S7), the control circuit unit 100 is applied to the coil 5 from the power supply device 101. The high frequency current that has been stored is turned off (S8). Thereby, the magnetic fluid 12 contained in the magnetic flux adjusting unit 6 is softened and becomes a colloidal liquid without magnetism.

  Along with this step S8, the left and right pistons 8L and 8R of the magnetic flux adjusting unit 6 control the driving device M2 so as to return to the home position at an interval corresponding to the maximum sheet passing area width Wmax, thereby rotating the gear 11 forward. (S9). As a result, the width of the region where the magnetic fluid 12 exists inside the housing is returned to the width corresponding to the maximum sheet passing region width Wmax.

  Step S10: In this state, the control circuit unit 100 turns on the power supply device 101 to continue printing. The magnetic fluid 12 receives a magnetic field generated from the coil 5, is magnetized and hardened, and forms a magnetic path equivalent to, for example, soft ferrite. Then, the full length area corresponding to the maximum sheet passing area width Wmax of the belt 1 is heated uniformly, and the temperature of the non-sheet passing part B rises.

  Step S11: In steps S2 to S10 described above, the detection temperature input to the control circuit 100 from the second temperature sensor TH2 is 180 ° C. <T <200 ° C. in continuous feeding of a small size recording medium or medium size recording material. This is done until the end of all printing so that the range is constant.

  Step S12: When all the printing is completed, if the left and right pistons 8L and 8R of the magnetic flux adjustment unit 6 are not positioned at the home position, the control circuit unit 100 controls the driving device M2 to return to the home position. Wait for input of the print start signal.

  FIG. 10 is a diagram showing SIM results of the temperature rise suppression effect in this example. FIG. 11 is a diagram showing a heat generation change in the magnetic fluid region in the present embodiment. By the above control, it is possible to effectively mitigate the temperature rise in the non-sheet passing portion in continuous passing of small size recording materials or medium size recording materials. In addition, with the above-described apparatus configuration, it is possible to reduce the fluctuation of the temperature distribution in the longitudinal direction of the heat generating rotating body that generates heat by electromagnetic induction for heating the recording material carrying the image. In addition, the heat generating rotating body can be efficiently heated while reducing power consumption and downsizing the apparatus.

  By providing the magnetic fluid pool 6d in the housing 6a that accommodates the magnetic fluid 12 in the magnetic flux adjusting unit 6, the magnetic fluid 12 can be disposed even in the region of the small size recording material. The magnetic fluid pool 6d not only has an effect of “escape” of the magnetic fluid 12, but also the magnetic fluid 12 is disposed in the magnetic fluid pool 6d, thereby improving the magnetic flux density around the belt as shown in FIG. It has a function to make it.

  As described above, the magnetic fluid 12 is arranged in the sheet passing area, so that the temperature rise in the non-sheet passing area can be suppressed and the heat generation efficiency in the sheet passing area can be greatly improved. As a result, when the magnetic fluid 12 is disposed in the paper passing area and the magnetic fluid pool 6d, the high-frequency current applied to the coil 5 can be reduced, and the power consumption can be suppressed.

  The setting of the home positions of the left and right pistons 8L and 8R is not limited to the position of the width corresponding to the substantially maximum sheet passing area width Wmax in the above embodiment. For example, the left end position and the right end position in the housing 6a may be set. You may set to the position of the width | variety corresponding to the minimum paper passing area | region width Wmax. Without setting the home position, the current position of the left and right pistons 8L and 8R is used as a base point. Then, the movement direction and the movement amount of the left and right pistons 8L and 8R corresponding to the width size of the recording material passed through the apparatus are calculated to control the movement of the left and right pistons 8L and 8R. It can also be.

[Example 2]
The inner magnetic core 6b is used as a heating element internal magnetic flux adjustment means, and a unit using the magnetic fluid 12 is used in the same manner as the magnetic flux adjustment unit 6 as a heating element external magnetic flux adjustment means, thereby adjusting the magnetic flux between the paper passing portion and the non-paper passing portion. By doing so, it is also possible to have a device configuration that suppresses the temperature rise in the non-sheet passing region.

  FIG. 12 is a schematic diagram when the inner magnetic core 6 b is a magnetic flux adjustment unit using the magnetic fluid 12. An internal mechanism similar to that of the magnetic flux adjusting unit 6 and the magnetic fluid 12 are included in the hollow housing 6b. Operation and control are the same as those of the magnetic flux adjustment unit 6.

  In the inner magnetic core 6b, if the core is moved, the inner side of the belt 1 may be touched, and the belt may be damaged, causing problems from the viewpoint of temperature control and durability. However, this embodiment is advantageous in that the magnetic flux density in the longitudinal non-sheet passing region can be controlled without moving the core. Either or both of the outer magnetic core and the inner magnetic core can be configured as a magnetic flux adjusting unit using the magnetic fluid 12.

[Other matters]
1) The heating rotator 1 is not limited to a roller body. A flexible endless belt body that is suspended and stretched between a plurality of stretching members and can be circulated is also possible.

  2) The pressure member 2 that forms the nip portion N with the heating rotator 11 is not limited to a roller body. A rotatable endless belt body can also be used. Further, it may be in the form of a non-rotating member (such as a pressure pad) having a small friction coefficient on the surface (the contact surface with the heating rotator 1 or the recording material P). The pressure member 2 can also be heated.

  3) The passing (conveying) of the recording material P to the apparatus is not limited to the central reference. It is also possible to adopt a one-side reference apparatus configuration that passes (conveys) paper on the basis of one side in the width direction of the recording material. In this case, in the magnetic flux adjustment unit, the width of the region where the magnetic fluid is present in the housing is regulated by the magnetic fluid regulating member that is moved on the one-side basis corresponding to the width size of the recording material that is passed through the image heating device. .

  4) The image heating apparatus of the present invention is not limited to use as a fixing apparatus that heats and fixes an unfixed image formed on a recording material as a fixed image as in the embodiment. It is also effective as a heat treatment apparatus that adjusts the surface properties of an image such as improving the glossiness by heating and pressurizing an image (fixed image or semi-fixed image) once fixed or presupposed to a recording material.

  5) The image forming unit of the image forming apparatus is not limited to the electrophotographic system. The image forming unit may be an electrostatic recording system or a magnetic recording system. Further, the present invention is not limited to the transfer method, and an unfixed image may be formed on the recording material by a direct method.

  5 .. Coil, t ... Image, P recording material, 1 .... Image heating member, 6 .... Magnetic flux adjusting means, Chiyoda-ku, Tokyo, ... Control means, A ... Image heating device, a ... Recording material conveyance Direction, 12 ... Magnetic fluid, 6a ... Housing, 8L, 8R ... Magnetic fluid regulating member, 17 ... Restricting member moving means

Claims (9)

A coil that generates magnetic flux, a rotatable image heating member that generates heat by the action of the magnetic flux, and that heats the recording material that is carried while carrying the image, and a magnetic flux that adjusts the magnetic flux that acts on the image heating member In an image heating apparatus having an adjustment unit and a control unit,
When the width direction is a direction parallel to the direction perpendicular to the recording material conveyance direction in the recording material conveyance path surface, the magnetic flux adjusting means is movable in the width direction of the case and the case containing the magnetic fluid. The magnetic fluid regulating member for regulating the width of the region where the magnetic fluid is present in the housing, and the regulating member moving means for moving the magnetic fluid regulating member, and the control means is a recording that is passed through the apparatus. An image heating apparatus, wherein the restricting member moving means is controlled so that an existing region width of the magnetic fluid in a housing is restricted by the magnetic fluid restricting member in accordance with a width size of the material.   2. The image heating apparatus according to claim 1, wherein the magnetic fluid is a magnetic colloid solution containing soft magnetic fine particles having a diameter of 10 nm.   The image heating apparatus according to claim 1, wherein the magnetic fluid regulating member is configured using a permanent magnet.   The image heating apparatus according to any one of claims 1 to 3, wherein the magnetic flux adjusting means is outside the image heating member.   The image heating apparatus according to any one of claims 1 to 3, wherein the magnetic flux adjusting means is provided inside the image heating member.   The image heating apparatus according to any one of claims 1 to 3, wherein the magnetic flux adjusting means is provided outside and inside the image heating member.   The magnetic material is conveyed by the central reference, and the magnetic fluid regulating member is moved by the central reference in accordance with the width size of the recording material in which the existence area width of the magnetic fluid in the housing passes through the image heating device. The image heating apparatus according to any one of claims 1 to 6, wherein the image heating apparatus is regulated.   The recording material is conveyed on a one-sided basis, and the magnetic fluid regulating member is moved on the one-sided reference in accordance with the width size of the recording material in which the existence area width of the magnetic fluid in the housing is passed through the image heating device. The image heating apparatus according to any one of claims 1 to 6, wherein the image heating apparatus is regulated.   An image forming apparatus comprising: an image forming unit that forms an unfixed image on a transported recording material; and an image fixing unit that fixes the unfixed image by heating the recording material transported from the image forming unit. The image forming apparatus according to claim 1, wherein the image fixing unit is the image heating apparatus according to claim 1.