JP2011145511A - Image heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize heat generation of a fixing roller (heating rotary body) 1 and to prevent temperature increase inside a machine due to abnormal temperature increase (temperature increase at ends, temperature increase at paper non-passing parts) at regions of the fixing roller other than paper passing regions or heat degradation of fixing device constituting members, in an electromagnetic induction heating type fixing device, thus achieving an excellent fixing image. <P>SOLUTION: A core holder 7 has a shape meeting the diameter surface of the fixing roller 1 and has an approximately symmetrical shape in relation to the diameter surface. Coil holders 81, 82 are positioned by the core holder 7 at least three places at both ends in the axial direction of the fixing roller and the vicinity of the center. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image fixing apparatus mounted on an image forming apparatus such as a copying machine, a facsimile, a printer, or a multi-function machine for forming an image on a recording material by an appropriate image forming process such as an electrophotographic system or an electrostatic recording system. The present invention relates to an image heating apparatus of an electromagnetic induction heating system suitable for use as an image forming apparatus.

  As an image heating device, a fixing device that heats an unfixed image on a recording material to fix or presuppose it as a fixed image, and a gloss increasing device that increases the gloss of the image by heating the image fixed on the recording material Can be mentioned. In addition, an image heating apparatus for quickly drying 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, can be used.

  As shown in Patent Document 1, an electromagnetic induction heating type fixing device using high frequency induction as a heating source has been proposed. In this apparatus, coils are concentrically arranged inside a hollow fixing roller made of a metal conductor (induction heating element) as a heating rotator (heating member). An induction eddy current is generated in the fixing roller by a high-frequency magnetic field generated by applying a high-frequency current to the coil, and the fixing roller itself generates Joule heat by the skin resistance of the fixing roller itself. According to this apparatus, since the electrical-thermal conversion efficiency is extremely improved, it is possible to improve the energy saving performance. By using the generation of the induced current, the fixing roller can directly generate heat, and a higher-efficiency fixing process than that of a heat roller type fixing device using a halogen lamp as a heat source is achieved.

  In general, a core unit using a ferrite core is used as a magnetic flux generating means of such a device. For example, in Patent Documents 2 and 3, there are proposals for fixing a plurality of cores with an adhesive or a resin in order to improve manufacturing efficiency.

  Even in such an apparatus, since the entire area of the recording material of the maximum width size that can be used to pass through the apparatus is operated at the fixing temperature to fix the image, it is more than the actual fixing of the toner. It consumes energy. Further, the power control for adjusting the temperature of the paper passing area is controlled by changing the current and frequency. For this reason, if a large amount of power is supplied when the temperature of the paper passing portion is suddenly lowered due to heat radiation from the recording material, an area (non-passing area) that is not the paper passing area of the fixing roller depends on the width size of the recording material. More power than necessary is supplied to the paper portion area. As a result, the temperature of the region is abnormally increased, which may cause the temperature increase in the apparatus or the thermal deterioration of the fixing device constituent members. As a countermeasure for this, as disclosed in Patent Document 2, it is effective to adjust the Curie temperature of the magnetic shunt alloy as a heating element to approximately the fixing temperature and fix the supply current value by the current supply means.

JP 59-033787 Japanese Patent No. 4087498 JP 2006-145949 A

  However, in the fixing devices of Patent Documents 2 and 3, the core is fixed by an adhesive or resin, and the fixing holder is warped in the longitudinal direction due to the difference in thermal expansion, and the distance between the fixing roller and the coil is stabilized. Therefore, there is a problem that the heat generation of the roller is not stable. Also, if the holder is warped due to thermal expansion because the core is fixed, the core may be overstressed, and the core may be cracked or chipped (the ferrite core is brittle and easy to wear) There is a problem that the heat generation of the roller is not stable.

  Also, in general, the outer diameter shape of the fixing roller is formed by machining a metal hollow pipe into an inverted crown shape by outer diameter cutting as shown in the model diagram of FIG. Yes. Reference numeral 1 denotes a fixing roller, and the model diagram shows a thick section along the length of the fixing roller 1. dx is the reverse crown amount dx. Reference numeral 5 denotes a plurality of magnetic cores arranged inside the fixing roller 1 along the length of the roller. g1 is a distance (gap) between the inner surface of the roller and the core 5. Since the inner diameter of the fixing roller 1 processed in the reverse crown shape by outer diameter cutting is straight along the longitudinal direction of the roller, the wall thickness gradually decreases from the longitudinal end portion to the central portion of the fixing roller 1 (d3 <d2 <d1). ). In the case of the fixing roller 1 made of a magnetic shunt alloy, the calorific value Pc (= calorific value of the non-sheet passing portion) equal to or higher than the Curie temperature is inversely proportional to the wall thickness, so that it is a cut product as shown in FIG. There is a problem that the effect of raising the temperature of the non-sheet passing portion is not sufficiently obtained (because the thickness of the non-sheet passing portion is reduced to the outside).

  The present invention solves the above-mentioned problems in an electromagnetic induction heating type image heating apparatus. In other words, even in an apparatus using a heating rotor made of a magnetic shunt alloy, the heat generated by the heating rotor is stabilized, and the inside of the machine is caused by abnormal temperature rise (edge temperature rise, non-paper feed temperature rise) in an area that is not a paper passing area. An object is to obtain good image heating performance by preventing temperature rise and thermal deterioration of apparatus constituent members.

  In order to achieve the above object, the image heating apparatus according to the present invention includes a cylindrical heating rotator that generates electromagnetic induction heat by the action of magnetic flux, and is disposed inside the heating rotator to generate magnetic flux. An image heating apparatus for heating an image carried on a recording material by heat of the heating rotator, wherein the magnetic flux generating means A plurality of magnetic cores arranged along the axial direction, a core holder that holds the magnetic core, a coil that is arranged outside the core holder, and a coil that is arranged outside the coil and holds the coil The core holder has a shape along the diameter surface of the heating rotator and is symmetrical with respect to the diameter surface, and the coil holder extends along the inner peripheral surface of the heating rotator. Half circle Has a shape, characterized in that it is positioned by the core holder at least three positions of the both ends and the central portion with respect to the axis direction of the heating rotator.

  According to the present invention, even in an apparatus using a heating rotating body made of a magnetic shunt alloy, the heat generation of the heating rotating body is stabilized, the temperature rise in the apparatus due to abnormal temperature rise in a region that is not a sheet passing area, and the thermal deterioration of apparatus constituent members And the like, and good image heating performance can be obtained.

(A) is a structural model diagram of an example of an image forming apparatus, and (b) is an enlarged cross-sectional model diagram of the main part of the fixing device. FIG. 3 is a model view of the main part of the fixing device as viewed from the recording material introduction side. (A) is an external perspective view of a coil assembly (magnetic flux generating means), and (b) is an exploded perspective view thereof. (A) is an exploded perspective view of a core holder and a core, (b) is an enlarged cross-sectional model view of the core holder in a state where the core is mounted. (A) is explanatory drawing of the play of a core, (b) is explanatory drawing of the positioning structure (snap fit) of the coil holder by a core holder. (A) is explanatory drawing of the fixing roller which formed the reverse crown shape by the bulge process, (b) is explanatory drawing of the fixing roller which formed the reverse crown shape by cutting, (c) is explanatory drawing of a comparative experiment example.

[Example]
(1) Example of Image Forming Apparatus FIG. 1A is a structural model diagram of an example of an image forming apparatus 100 provided with an electromagnetic induction heating type image heating apparatus according to the present invention as an image heating fixing apparatus 114. The apparatus 100 of this example is a transfer type electrophotographic process-use, laser scanning exposure type image forming apparatus (copying machine, printer, facsimile, combined function machine thereof).

  Reference numeral 101 denotes a document reading device (image scanner), and 102 denotes an area designation device (digitizer), both of which are arranged on the upper surface side of the device 100. The apparatus 101 scans a document by a scanning illumination optical system including a light source or the like provided inside a document surface placed on the document table of the apparatus, and reads reflected light from the document surface by an optical sensor such as a CCD line sensor. The image information is converted into a time series electric digital electric signal. The apparatus 102 sets a document reading area and outputs a signal. Reference numeral 104 denotes a control unit (CPU) that receives signals from the apparatus 101, the apparatus 102, the print controller 103, and the like, and performs signal processing for sending commands to each unit of the image forming apparatus and various image forming sequence controls.

  The following is a description of the image forming mechanism (image forming mechanism). Reference numeral 105 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a drum) as an image carrier, which is rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed. In the rotation process, the drum 105 is uniformly charged with a predetermined polarity and potential by the charging device 106, and the uniformly charged surface is subjected to image exposure L by the image writing device 107. As a result, the potential of the exposed bright portion of the uniformly charged surface is attenuated, and an electrostatic latent image corresponding to the exposure pattern is formed on the surface of the drum 105. In this example, the apparatus 107 is a laser scanner, which outputs laser light L modulated in accordance with image data signal-processed by the control unit 104, scans and exposes the uniformly charged surface of the rotating drum 105, and outputs image information. An electrostatic latent image corresponding to is formed.

  Next, the electrostatic latent image is developed as a toner image by the developing device 108. At the position of the transfer charging device 109, the toner image is transferred from the sheet feeding mechanism unit side to the recording material P to which the drum 105 is fed to the transfer unit T, which is the opposite part of the drum 105 and the device 109, at a predetermined control timing. Electrostatic transfer from the surface. In the case of this example, the sheet feeding mechanism unit is separated and fed by one sheet from the first cassette sheet feeding unit 110 or the second cassette sheet feeding unit 111 in which recording materials P having different width sizes are stacked and accommodated. A recording material conveyance path 112 that conveys the recording material P to the transfer portion T at a predetermined timing is provided. The width size of the recording material P is a dimension in a direction orthogonal to the conveyance direction of the recording material. The first cassette paper supply unit 110 stores and accommodates a recording material (large size paper) having a maximum width size that can be used in the apparatus. A recording material (small size paper) having a smaller width is stacked and accommodated in the second cassette paper supply unit 110.

  The recording material P that has received the transfer of the toner image from the surface of the drum 105 at the transfer unit T is separated from the surface of the drum 105, conveyed to the fixing device 114, and subjected to a fixing process for the unfixed toner image. The paper is discharged onto the paper tray 115. On the other hand, the surface of the drum 105 after separation of the recording material is cleaned by the cleaning device 113 after removal of adhering contaminants such as transfer residual toner, and is repeatedly used for image formation.

(2) Fixing Device FIG. 1B is an enlarged schematic cross-sectional view of the main part of the fixing device 114, and FIG. 2 is a model view of the main part of the device 114 as viewed from the recording material introduction side. The driving side of the device 114 is the back side, and the driven side is the front side. The device 114 is a heating roller type and is an electromagnetic induction heating type image heating device. The device 114 includes a heating roller 1 as a cylindrical heating rotating body that performs electromagnetic induction heating by the action of magnetic flux. Further, a pressure roller 2 as a pressure rotator that forms a fixing nip portion N as a contact portion (heating portion) that heats and presses the image t by sandwiching and conveying the recording material P with the heating roller 1. Have The coil assembly 3 is disposed inside a heating roller (hereinafter referred to as a fixing roller) 1 and serves as magnetic flux generating means for electromagnetically heating the fixing roller 1.

  The fixing roller 1 is a roller having a cylindrical (hollow) cored bar (metal layer, conductive layer) 1a as an induction heating element, and the outer peripheral surface of the cored bar 1a is coated with a fluororesin or the like to be heat resistant. A release layer (heat transfer material) 1b is formed. The metal core 1a is a magnetic metal (conductor, magnetic material) such as iron, nickel, SUS430, iron-nickel alloy, iron-nickel-chromium alloy, nickel-cobalt alloy, for example. Or it is a magnetic shunt alloy which adjusted Curie point temperature as desired, as disclosed by Unexamined-Japanese-Patent No. 2000-39797 etc. The core bar 1a of the fixing roller 1 of this embodiment is made of a magnetic shunt alloy, has a thickness of 0.05 mm to 1.5 mm, and has a Curie point temperature higher than the temperature at which the toner image t can be fixed to the recording material P. It is set higher than the heat resistance temperature of the exciting coil 6 (61, 62) described later. In this embodiment, since the fixing temperature is set to 195 ° C. and the above heat-resistant temperature is set to 230 ° C., the Curie point temperature is set to 205 ° C.

  The fixing roller 1 is disposed such that both ends thereof are rotatably supported via bearings 23 between front and back side plates (fixing device frames) 21 and 22 of the fixing device. In the inner space, a coil assembly 3 as a magnetic flux generating means for inserting a high frequency magnetic field for inducing an induced current (eddy current) in the metal core 1a to generate Joule heat is inserted and disposed.

  The pressure roller 2 is formed on a shaft core 2a, a silicon rubber layer (elastic body layer) 2b, which is a heat-resistant rubber layer concentrically and integrally formed around the shaft core 2a, and an outer peripheral surface thereof. It is an elastic roller having a release layer 2c. If the elastic layer 2b has surface releasability, the release layer 2c can be omitted. The pressure roller 2 is arranged in parallel below the fixing roller 1 and both end portions of the shaft core 2a are rotatably held via bearings 26 between the front and back side plates 21 and 22 of the fixing device. Has been. The pressure roller 2 is pressed against the lower surface of the fixing roller 1 with a predetermined pressing force against the elasticity of the elastic layer 2b by an urging means (not shown). Thus, a fixing nip portion N having a predetermined nip length (nip width) in the recording material conveyance direction a is formed between the fixing roller 1 and the pressure roller 2.

  The coil assembly 3 is a cylindrical member as a whole, and includes a magnetic core (core material) 5 made of a magnetic material, an excitation coil (induction coil, induction heat source) 6 (61, 62), and a core holder made of an insulating member. 7. An assembly of coil holders 81 and 82, etc. The outer diameter of the assembly 3 is a predetermined smaller than the inner diameter of the fixing roller 1, and the length is a predetermined longer than the length of the fixing roller 1. The assembly 3 is inserted substantially concentrically into the inner space of the fixing roller 1, and the front and back end portions are fixedly supported non-rotatably between the front and back support members 24 and 25 of the fixing device, respectively. Has been. As a result, the assembly 3 is disposed in the fixing roller 1 at a predetermined angle and posture with a predetermined interval (gap) in a non-contact manner on the inner surface of the fixing roller 1. The core 5 is inserted and held in a through hole 7 a formed in the core holder 7. The coil 6 (61 · 62) is formed by winding a copper wire around the core holder 7. In the present embodiment, the coil 6 includes two coils, a first coil 61 and a second coil 62, and the two coils 61 and 62 heat almost the entire circumference of the fixing roller 1. The coil 6 is accommodated in the assembly 3 so as not to be exposed to the outside of the fixing roller 1. The core 5 is preferably made of a material having a large magnetic permeability and a small self-loss. For example, ferrite, permalloy, sendust, etc. are suitable. The coil 6 must generate an alternating magnetic flux that sufficiently heats the fixing roller 1. For this purpose, the resistance component must be low and the inductance component must be high. As the core wire of the coil 6, a litz wire in which about 80 to 160 fine wires having a diameter of 0.1 to 0.3 are bundled is used. Insulated coated wires are used for the thin wires. Further, the core 5 is wound into a horizontal boat shape a plurality of times in accordance with the shape of the core holder 7 so as to circulate, thereby forming a coil 61.62. The coils 61 and 62 are wound in the longitudinal direction of the fixing roller 1. Reference numerals 6 a and 6 b denote two outward lead wires (coil supply wires) of the coil 6, which are led out from the back end of the assembly 3. The coil 6 (61.62) includes a current supply means for supplying a high frequency current, a constant current supply means for supplying a constant current, and a coil drive power supply (frequency variable control section, Constant current circuit) 116.

  Reference numeral 13 denotes a separation claw that serves to prevent the recording material P introduced into the nip portion N from being wound around the fixing roller 1 and separated from the fixing roller 1. The holder 7, the separation claw 13, and the coil holders 81 and 82 are made of heat-resistant and electrically insulating engineering plastic such as liquid crystal polymer, polyimide, polyphenylene sulfide, and the like. A fixing roller drive gear G is concentrically fixed to the end of the fixing roller 1 on the back side. When the rotational force is transmitted from the drive source M to the gear G via a transmission system (not shown), the fixing roller 1 is coiled at a predetermined peripheral speed in the clockwise direction indicated by the arrow A in FIG. -It is driven to rotate around the outside of the assembly 3. The pressure roller 2 rotates in the counterclockwise direction B indicated by the arrow following the rotational driving of the fixing roller 1.

  Reference numeral 14 denotes a fixing roller cleaner. The cleaner 14 has a web feeding shaft portion 14b that holds a cleaning web 14a as a cleaning member in roll form, and a web winding shaft portion 14c. Further, a pressing roller 14 d that presses the web portion between the shaft portions 14 b and 14 c against the outer surface of the fixing roller 1 is provided. At the web portion pressed against the fixing roller 1 by the roller 14d, the toner offset to the surface of the fixing roller 1 is wiped and the surface of the fixing roller is cleaned. The web portion pressed against the fixing roller 1 is gradually updated by feeding the web 14a little by little from the shaft portion 14b side to the shaft portion 14c side.

  Reference numeral 15 denotes a thermostat (temperature detecting means for detecting the temperature of the fixing roller 1), which is provided in contact with or close to the fixing roller 1 as a countermeasure when the fixing roller temperature rises abnormally (during thermal runaway). When the thermostat 15 reaches a preset temperature, the thermostat 15 opens the contact and cuts off the power supply to the coil 6. As a result, the fixing roller 1 is prevented from becoming a high temperature above a predetermined temperature. In the present embodiment, the sheet passing is performed based on the central reference. C is the central reference. That is, in any recording material of any width size that can be used for paper passing through the apparatus, the central portion of the recording material passes through the central portion in the axial direction of the fixing roller 1. In the apparatus 100 of this embodiment, the maximum width size (large size paper) of the recording material that can be passed is A4 landscape. The minimum size of the recording material that can be passed is B5R. P1 is a sheet passing area width of the large size paper, and P2 is a sheet passing area width of the small size paper whose width size is smaller than that of the large size paper.

  The first thermistor 11 (temperature detection means) is a central temperature detection device for the fixing roller 1 and detects the temperature of the central portion of the fixing roller corresponding to the substantially central portion of the sheet passing area width P2 of the small size paper. The thermistor 11 is arranged so as to be elastically pressed against the surface of the fixing roller 1 by an elastic member 16 so as to face the coil 6 across the fixing roller 1 at the center portion of the fixing roller. The second thermistor 12 (temperature detecting means) serves as a temperature detecting device for the end portion of the fixing roller 1 and generates a non-sheet passing portion temperature rise and a large size paper passing region width P1 and a small size paper passing region. The temperature at the end of the fixing roller corresponding to the difference area with the width P2 is detected. The thermistor 12 is disposed in an elastic contact with the elastic roller 16 against the surface of the fixing roller 1 at the end of the fixing roller.

  The control unit 104 activates the apparatus by turning on a main power switch (not shown) of the apparatus to start predetermined image forming sequence control. The fixing device 114 starts to rotate the fixing roller 1 when the drive source M is activated. The pressure roller 2 also rotates following the rotation of the fixing roller 1. Further, the control unit 104 activates the coil driving power source 116 and causes a high frequency current to flow through the coil 6. As a result, a high-frequency alternating magnetic flux is generated around the coil 6, and the fixing roller 1 generates heat by electromagnetic induction, and the temperature rises toward a predetermined fixing temperature, which is 195 ° C. in this embodiment. The temperature rise of the fixing roller 1 is detected by the first and second thermistors 11 and 12, and the detected temperature information is input to the control unit 104. The control unit 104 uses the first thermistor 11 as temperature detection means for temperature adjustment, and the electric power supplied from the power source 116 to the coil 6 so that the fixing roller detection temperature input from the thermistor 11 rises and is maintained at the fixing temperature. To control. In a state where the fixing roller 1 is adjusted to the fixing temperature, the recording material P carrying the unfixed toner image t is introduced from the image forming unit side to the nip portion N, and the nip portion N is nipped and conveyed. As a result, the unfixed toner image t is fixed on the surface of the recording material P by the heat of the fixing roller 1 and the pressing force of the nip portion N.

  When the recording material P to be passed is a small size paper, a difference area between the large size paper passing area width P1 and the small size paper passing area width P2 of the nip N is a non-sheet passing area. When the small size paper is continuously passed, the temperature of the fixing roller portion corresponding to the small size paper passing area width P2 which is the paper passing area is maintained at a predetermined fixing temperature of 195 ° C. The temperature of the fixing roller portion corresponding to the paper passing area increases. That is, since the heat of the fixing roller portion corresponding to the non-sheet passing portion area is not consumed for heating the recording material or the toner image, the temperature is raised beyond a predetermined fixing temperature of 195 ° C. (temperature raising of the non-sheet passing portion). To go. In this embodiment, since a magnetic shunt alloy is used for the fixing roller core metal, when the temperature of the non-sheet passing portion is raised and the temperature of the fixing roller end reaches the Curie temperature, the magnetism of the fixing roller end rapidly decreases. As a result, the amount of generated heat is reduced and the temperature of the fixing roller does not rise above the Curie temperature. In other words, when the fixing roller 1 reaches the Curie temperature, the power factor decreases, and accordingly, the power consumption of the coil 6 decreases, and the fixing roller 1 works in a direction to suppress heat generation, so that self-temperature control is possible.

  That is, in this embodiment, the heat generation amount P of electromagnetic induction heating is proportional to the skin resistance Rs of the fixing roller as shown in <Equation 1> and is proportional to the square of the eddy current i. The eddy current i is proportional to the magnetic field H generated by the coil. Further, since the magnetic field H is proportional to the number of turns N of the coil and the coil current I, the heat generation amount P when the fixing roller is less than the Curie temperature is expressed by Equation 3. When the temperature is equal to or higher than the Curie temperature, δ >> d (d: core thickness of the fixing roller core) is satisfied, so the heat generation amount Pc is expressed by Equation 4 and the non-sheet passing portion region where the fixing roller is equal to or higher than the Curie temperature. Then, from <Formula 4>, the calorific value does not depend on the frequency, but is proportional to the coil current I and inversely proportional to the core metal thickness d.

(3) Coil assembly 3
The configuration of the assembly 3 will be described in detail. 3A is an external perspective view of the assembly 3, and FIG. 3B is an exploded perspective view of the assembly 3. 4A is an exploded perspective view of the core holder 7 and the core 5, and FIG. 4B is an enlarged cross-sectional model view of the core holder 7 with the core 5 attached thereto. As described above, the assembly 3 is disposed inside the fixing roller 1 which is a cylindrical heating rotating body that performs electromagnetic induction heating by the action of magnetic flux, and is a magnetic flux generating means that generates the magnetic flux and heats the fixing roller 1. . The assembly 3 is a cylindrical member as a whole, and includes a core 5, a core holder 7 that holds the core 5, an excitation coil 6 (61, 62) positioned outside the core holder 7, This is an assembly of coil holders 81 and 82 that are located outside and hold the coil 6.

  The core holder 7 is a member that is long in the axial direction of the fixing roller 1 (longitudinal direction of the fixing roller 1). The core holder 7 has a shape along the diameter surface of the fixing roller 1 and is substantially symmetrical with respect to the diameter surface. In this embodiment, the core holder 7 holds a plurality of magnetic cores 5 adjacent to each other along the longitudinal direction (the axial direction of the fixing roller 1). In this embodiment, the core holder 7 holds ten cores 5 having substantially the same shape at substantially the same interval. More specifically, as shown in FIG. 4, the core holder 7 has ten holes 7a for core insertion formed at substantially the same intervals along the longitudinal direction, and the cores 5 are respectively inserted into the holes 7a. It is inserted evenly. Concave grooves 5 a are provided on both side surfaces of each core 5. In the individual cores 5 inserted into the holes 7a, the claw portions 7b formed on the core holder 7 side are fitted into the grooves 5a by snap fitting. As a result, each core 5 is held and retained in each hole 7 a of the core holder 7. A pair of coils 61 and 62 having a substantially semicircular cross section are arranged so as to surround and surround the outside of the ten cores 5 held by the core holder 7. Further, a pair of semi-cylindrical coil holders 81 and 82 are disposed so as to sandwich the coils 61 and 62 so as to surround the outside of the pair of coils 61 and 62. The coil holders 81 and 82 have a semi-cylindrical shape along the inner peripheral surface of the fixing roller 1 in the cross section. The coil holders 81 and 82 arranged with the coils 61 and 62 sandwiched between them are screwed at both longitudinal ends to fix each other. As a result, a generally cylindrical assembly 3 as shown in FIG. 3A is assembled.

  In the assembly 3, the core 5 is snap-fitted to the claw portion 7b formed in the core holder 7, and as shown in FIG. 5A, the core fixing surface 82a of the coil holder 82 and the claw portion 7b are connected. It is sandwiched between. A gap α is provided between the core 5 and the core fixing surface 82a, and the core 5 has some play (play). In this embodiment, the gap α is set to 0.5 mm. Therefore, even if the accuracy of parts such as the core holders 81 and 82 and the core 5 varies or expands due to heat, the shape is stabilized because it is absorbed by play. As a result, excessive stress is not applied to the core 5, so that no chipping or cracking occurs. Therefore, the positional accuracy of the core 5 is improved and the heat generation of the fixing roller 1 is stabilized.

  In the assembly 3, the coil holders 81 and 82 are positioned by the core holder 7 in at least three positions, that is, both end sides and the center portion with respect to the axial direction of the fixing roller 1. More specifically, FIG. 5B shows the front F, the center C, the back R, and the cross section of each part of the assembly 3 in FIG. A plurality of claw portions 81a, 82a, and 7d are provided at the semicircular arc end portions of the coil holders 81 and 82 and the left and right end portions of the core holder 7 that are substantially symmetrical in the vertical direction. The claw portions 81 a and 82 a of the coil holders 81 and 82 are fixed by snapping the coil holders 81 and 82 into the claw portions 7 d of the core holder 7. That is, the coil holders 81 and 82 are positioned by the core holder 7. With the above configuration, even when heat is applied and the assembly 3 expands in the longitudinal direction, the coil holders 81 and 82 are less likely to warp in the longitudinal direction following the core holder 7. Therefore, the distance between the fixing roller 1, the coil 6 (61, 62), and the core 5 can be ensured, and the heat generation of the fixing roller 1 is stabilized. That is, since the core holder 7 is symmetrical with respect to the diameter surface, heat is applied and the core holder 7 is unlikely to warp even when the assembly 3 expands in the longitudinal direction. The coil holders 81 and 82 positioned (fixed) on the core holder 7 are less likely to warp in the longitudinal direction than the core holder 7 which is less likely to warp. Therefore, even if the heat is applied and the assembly 3 expands in the longitudinal direction, the coil holders 81 and 82 do not warp in the longitudinal direction following the core holder 7 and the distance between the fixing roller 1 and the coils 6 (61 and 62) and the core 5 is ensured. And the heat generation of the fixing roller 1 is stabilized. Further, it is more preferable that the core holder 7 is not easily warped when the cores 7 are not fixed with an adhesive or resin.

  Further, as shown in FIG. 1B, the core holder 7 is provided with reinforcing ribs 7c (reinforcing portions) on the opposite side to the thermistors 11 and 12 and the thermostat 15 as temperature detecting means. In other words, in the configuration having the temperature detection means for detecting the temperature of the roller disposed in contact with or close to the outer surface of the fixing roller, the core holder 7 is provided with the temperature detection means with respect to the circumferential cross section of the fixing roller. A reinforcing portion 7c is provided on the semicircular surface side opposite to the semicircular surface side on the other side. Therefore, even if the assembly 3 is along the longitudinal direction due to thermal expansion, the assembly 3 is always warped in the direction of the temperature detecting means 11 and 12 and the thermostat 15. As a result, when the distance between the coil 6 and the core 5 and the fixing roller 1 is shortened, the roller temperature increases, so that the roller temperature on the warped side increases. In this embodiment, since the temperature detection means 11 and 12 and the thermostat 15 are warped, even if the temperature rises during an abnormality, it is possible to reliably prevent the temperature of the fixing device from rising.

(4) Fixing roller 1
The outer diameter shape of the fixing roller 1 is processed in a reverse crown shape to prevent paper wrinkles due to the ironing effect. In this embodiment, when the core 1a of the fixing roller 1 is provided with the reverse crown shape, the reverse crown is formed with a uniform thickness in the longitudinal direction of the fixing roller 1 by bulge processing proposed in Japanese Patent Laid-Open No. 8-123231. The shape is formed ((a) of FIG. 6). Therefore, since the core bar strength can be improved, it is possible to apply a higher pressure than the conventional cutting fixing roller (FIG. 6B) having the same thickness.

  A magnetic shunt alloy is used for the cored bar 1a. As a result, according to the above formula 4, the thickness of the non-sheet passing portion is reduced in the reverse crown processing by the conventional cutting, whereas the thickness of the fixing roller 1 of this embodiment is constant because the thickness is constant. It is possible to efficiently prevent the temperature rise of the paper section. In this embodiment, the wall thickness d1 = 1.0 mm and the reverse crown amount dx is 0.3 mm. Therefore, the thickness of the non-sheet passing portion region of the fixing roller 1 by conventional cutting is 0.8 to 0.9 mm, whereas the thickness of the non-sheet passing portion region of the fixing roller 1 in this embodiment is uniform. Therefore, it is 1.0 mm. Therefore, the heat generation amount Pc in the non-sheet passing portion region of the fixing roller according to the present embodiment is 10% to 20% less than that of the conventional cutting product from the above-described <Formula 4>. Therefore, it is possible to efficiently prevent the temperature increase at the non-sheet passing portion.

  In the present embodiment, the gap between the fixing roller 1 whose outer diameter is formed in a reverse crown shape by bulging and the coil and the core is separated from the end portion of the fixing roller 1 in the longitudinal direction. In addition, the distribution of the core arrangement in the longitudinal direction is made uniform. That is, g1> g2> g3 → magnetic flux strength: g1 part <g2 part <g3 part → heat generation amount: g1 part <g2 part <g3 part. Therefore, it is possible to prevent the temperature rise of the non-sheet passing portion of the fixing roller 1.

  The fixing roller 1 of the present embodiment has a constant thickness in the longitudinal direction, so that a pressing force 10% higher than that of a conventional machined product is applied. Therefore, it is possible to ensure higher fixability than conventional cutting products.

  With this configuration, in this embodiment, the longitudinal core distribution can be made uniform, the longitudinal temperature distribution can be made uniform, and the maximum width size paper can be fixed.

  As a comparative experiment, as shown in FIG. 6 (c), the core longitudinal arrangement was changed in the cut product of the fixing roller 1, and measures for increasing the temperature of the end portion were performed by making the center portion in the longitudinal direction dense and the end portion sparse. . As a result, the edge temperature could be increased, but edge temperature sagging occurred, and fixing failure occurred on the maximum width size paper.

  114 .. Image heating device, 1 .. Heating rotating body, 2 .. Magnetic flux generating means, 5 .. Magnetic body core, 6 .. Excitation coil, 7 .. Core holder, 81. Recording material, t ・ ・ Image

Claims (7)

A cylindrical heating rotator that generates electromagnetic induction heat by the action of magnetic flux; and a magnetic flux generating means that is disposed inside the heating rotator and generates the magnetic flux to heat the heating rotator. An image heating apparatus for heating an image carried on a recording material by the heat of
The magnetic flux generation means includes a plurality of magnetic cores arranged along the axial direction of the heating rotator, a core holder that holds the magnetic core, a coil that is disposed outside the core holder, The coil holder is disposed outside the coil and holds the coil. The core holder has a shape along the diameter surface of the heating rotator and is symmetrical with respect to the diameter surface. A semi-cylindrical shape along the inner peripheral surface of the heating rotator, and the core holder is positioned at at least three locations on both ends and the center with respect to the axial direction of the heating rotator. Features. Image heating device.   The temperature detecting means is disposed in contact with or in proximity to the outer surface of the heating rotator, and detects the temperature of the heating rotator, and the core holder has the temperature detecting means with respect to a circumferential cross section of the heating rotator. The image heating apparatus according to claim 1, further comprising a reinforcing portion on a semicircular surface side in a direction opposite to the semicircular surface side on the side where the lens is disposed.   The image heating apparatus according to claim 1, wherein the coil holder is positioned by a snap fit by the core holder.   The image heating apparatus according to any one of claims 1 to 3, wherein the plurality of magnetic cores are not fixed with an adhesive or a resin between the cores.   5. The pressurizing rotator which forms a contact portion for sandwiching and conveying the recording material between the heating rotator and heating and pressurizing an image. 6. The image heating apparatus according to item.   The image heating apparatus according to any one of claims 1 to 5, wherein the heating rotator is a magnetic shunt alloy.   The image heating apparatus according to any one of claims 1 to 6, wherein the heating rotator is processed in an inverted crown shape by bulge processing.