JP2005190728A - Heating device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heating device and an image forming device, in which the reliability, durability, and improvement of quality of images have been achieved, while the large-sizing of the devices and a cost increase are suppressed. <P>SOLUTION: This is a heating device which comprises magnetic flux generating means 3b, 3c; an induction exothermic body 1 that heats heated materials by electro-magnetic induction exotherm using the magnetic flux generated by the magnetic flux generating means; a magnetic flux shielding means 12 that shields a part of the acting magnetic flux supplied from the magnetic flux generating means onto the induction exothermic body; a movement means 15 that actuates the magnetic flux shielding means in accordance with the necessary region for shielding magnetic flux; and temperature detecting means 4, 5, 6 that detect temperatures of the induction exothermic body. The magnetic flux generating means, the magnetic flux shielding means, and the temperature detecting means are arranged on the opposite side of the face where the heated materials of the induction exothermic body are heated, while the temperature detecting means are arranged outside the movable region of the magnetic flux shielding means, and contacting the face of the induction exothermic body in order to detect the temperature. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heating device of an electromagnetic (magnetic) induction heating method, and an image forming apparatus provided with the heating device as an image heating device such as image fixing.

  For convenience, an image heating and fixing device as an image heating device in an image forming apparatus such as an electrophotographic copying machine, a printer, and a fax machine will be described as an example.

  An image heat fixing apparatus in an image forming apparatus is a toner (developer) made of heat-meltable resin or the like by an appropriate image forming process means such as electrophotography, electrostatic recording, magnetic recording, etc. ) Is used to heat and fix an unfixed toner image formed on the surface of the recording material as a heated material by a direct method or an indirect (transfer) method as a permanently fixed image on the recording material surface.

  FIG. 8 shows a cross-sectional model view of the main part of a heat fixing apparatus using an electromagnetic induction heating element as a heating element. In this fixing device, as described in, for example, Patent Document 1, a magnetic material is applied to an electromagnetic induction heating element by a magnetic field generation unit, and a material to be heated is generated by Joule heating based on eddy current generated in the electromagnetic induction heating element. In this apparatus, heat is applied to the sheet material and an unfixed toner image is heated and fixed on the surface of the sheet material.

  A pressure roller (pressure member) 2 is in contact with the fixing roller 1 serving as an induction heating element so as to be parallel and rotatable, thereby forming a nip portion N for fixing toner. The fixing roller 1 is a thin iron core metal roller 1 having a small heat capacity, and a fixing roller surface layer (fluororesin coating layer) 1a is applied to the outer surface in order to reduce power and wait time required for heating. The fixing roller 1 is rotatably supported by a fixing roller housing (not shown), and is given a rotational force by a driving mechanism (not shown). Further, the electromagnetic induction heating type heat source 3 as magnetic flux generating means in which the magnetic core 3b and the exciting coil 3c are held in the electromagnetic induction heating holder 3a inside the fixing roller 1 is prevented from rotating to a fixing roller housing (not shown). It is fixed to. The exciting coil 3c generates an alternating magnetic flux by an alternating current supplied from an exciting circuit (not shown), and the alternating magnetic flux is guided to the magnetic core 3b to generate an eddy current in the iron core roller 1b facing the nip portion N. . The eddy current generates Joule heat due to the specific resistance of the iron core roller 1b. That is, by supplying an alternating current to the exciting coil 3c, the fixing roller 1 is in an electromagnetic induction heat generation state in the fixing nip portion N. The fixing roller 1 is made uniform in surface temperature as it rotates.

  The temperature of the fixing roller 1 is detected by a main thermistor 4 as temperature detecting means arranged in contact with the fixing roller surface layer 1a, and the surface temperature is adjusted to an arbitrary temperature (fixing temperature) by a control device (not shown). As temperature detection means, in addition to the main thermistor 4, a sub-thermistor 5 for detecting abnormally high temperature and a thermo switch 6 are arranged in the longitudinal direction (frontward direction in the figure) at the same circumferential position as the main thermistor 4 described above. It is shifted and placed. Further, when using these contact-type temperature detecting means 4, 5, 6, which are given as an example here, in consideration of damage to the fixing roller surface layer 1 a due to contact, the temperature detecting means 4. In some cases, high durability is achieved by dispersing the contact surface between 5 and 6 and the fixing roller surface layer 1a. Alternatively, in the case of the temperature detecting means 5 and 6 for detecting abnormally high temperatures, the fixing roller is disposed in the longitudinal direction at the end of the fixing roller 1 which is a sheet material non-conveying region, and damage to the fixing roller surface layer 1a In some cases, even if this occurs, there is no effect on the image.

  Further, a movable magnetic flux shielding plate 12 as magnetic flux shielding means is disposed between the electromagnetic induction heating type heat source 3 and the iron core roller 1b, and the magnetic flux shielding is performed according to the size of the sheet material P to be conveyed. The plate 12 is operated. For example, as shown in FIG. 6, the magnetic flux shielding plate 12 changes its shape in a direction (longitudinal direction of the fixing roller 1) perpendicular to the sheet material conveyance direction so as to shield the non-conveyance region C of the small size sheet material. By adopting a simple shape, it is possible to prevent an excessive temperature rise at the end of the fixing roller 1 when the small-size sheet material is conveyed.

  That is, in FIG. 8A, the magnetic flux shielding plate 12 is in the magnetic flux shielding plate retracted position, and the alternating magnetic flux directed to the magnetic core 3b and directed toward the nip portion N is not shielded in the entire longitudinal direction (frontward direction in the drawing). The entire length of the fixing roller 1 in the longitudinal direction is heated by electromagnetic induction. In other words, the fixing roller 1 and the pressure roller 2 are rotated, and the large-size sheet material P on which the unfixed toner image t to be image-fixed is formed and carried between the rollers 1 and 2 of the fixing nip N is conveyed by the conveying belt 7. Is introduced through the pre-fixing guide 8 and is nipped and conveyed by both rollers, so that the heat of the fixing roller is applied to the large-size sheet material at the nip portion, and the unfixed toner image is applied to the sheet material surface by the applied pressure of the nip portion. Then, the sheet material is fed to the paper discharge roller 10 through the post-fixing guide 9.

  On the other hand, in FIG. 8B, the magnetic flux shielding plate 12 is in the shielding position, and a part of the alternating magnetic flux (longitudinal end region) guided to the magnetic core 3 b toward the nip portion N is shielded by the magnetic flux shielding plate 12. By doing so, it is possible to suppress heat generation in the end region in the longitudinal direction of the fixing roller 1. The operation of the magnetic flux shielding plate 12 is controlled by a rotational movement by a driving means (not shown). In other words, the fixing roller 1 and the pressure roller 2 are rotated, and the small-size sheet material P on which the unfixed toner image t to be image-fixed is formed and carried between the rollers 1 and 2 of the fixing nip N is conveyed by the conveying belt 7. Is introduced through a pre-fixing guide 8 and is nipped and conveyed by both rollers, so that the heat of the fixing roller is applied to the small-size sheet material at the nip portion, and the unfixed toner image is applied to the sheet material surface by the applied pressure of the nip portion. Then, the sheet material is fed to the paper discharge roller 10 through the post-fixing guide 9. Reference numeral 13 denotes a separation claw for preventing the sheet material P from being wound around the fixing roller 1.

  In the above fixing device, the sub-thermistor 5 described above may be used for controlling the magnetic flux shielding plate 12 by detecting the temperature rise at the end of the fixing roller 1 in addition to the use as a means for detecting abnormally high temperatures. is there.

Such an electromagnetic induction heating type fixing device can electromagnetically heat the vicinity of the nip portion of the fixing roller 1 and achieves a higher efficiency fixing process than a heat roller type fixing device using a halogen lamp as a heat source. doing. At the same time, it is possible to achieve high durability and high image quality by preventing excessive temperature rise in the non-conveying region (edge) of the sheet material by the magnetic flux shielding plate 12 as magnetic flux adjusting means.
Japanese Patent Laid-Open No. 9-171889

  However, in the case of the prior art as described above, the following problems have occurred.

  In recent years, image forming apparatuses are required to further improve the reliability and durability of the apparatus, improve image quality, reduce the size of the apparatus, and reduce the cost.

  When using the contact-type temperature detecting means (main thermistor 4, sub-thermistor 5, thermo switch 6) as shown in FIG. 8, as mentioned above, the damage to the fixing roller surface layer 1a due to contact is considered. High durability is achieved by dispersing the contact surfaces of the temperature detecting means 4, 5, 6 and the fixing roller surface layer 1a by a reciprocating mechanism (not shown).

  However, the use of the reciprocating mechanism of the contact-type temperature detecting means is a factor that contradicts the recent demand for cost reduction, such as an increase in the number of parts and the driving means. Even if the contact surface is dispersed by the reciprocating mechanism, the contact with the surface layer 1a of the fixing roller remains unchanged, and the wear of the surface layer 1a of the fixing roller proceeds most in this contact region, and the durability life is limited. It becomes the first factor to do.

  Further, a part of the developer (toner) that could not be fixed to the sheet material is adhered to the surface layer 1a of the fixing roller, and the cleaning roller 11 for cleaning the surface layer of the fixing roller is attached to the contact surface of the contact-type temperature detecting means. In some cases, the developer that could not be removed by adhesion adheres and accumulates. In some cases, the accumulated developer is detached from the contact surface due to some disturbance and adheres again to the surface of the sheet material being fixed and conveyed, thereby causing image smearing.

  As a means for solving these problems, it is conceivable to employ a non-contact type temperature detection means, but the non-contact type temperature detection means is inferior in response and does not directly detect the detection surface. It is difficult to achieve high accuracy. In recent years, with the reduction in power required for image forming apparatuses, the heat capacity of the fixing roller 1 has been reduced by reducing the thickness of the iron core roller 1b of the fixing roller 1. As a cause of the low heat capacity, the temperature change of the fixing roller 1 becomes abrupt, and it reacts sensitively to the influence of disturbance, and the responsiveness of the temperature detection means and high-precision detection are essential conditions. is there. However, the use of a highly responsive non-contact temperature detecting means that compensates for this leads to an increase in cost, and the increase in accuracy leads to an increase in the number of peripheral parts such as stable airflow, which also increases the cost. . Furthermore, the non-contact temperature detecting means needs to be separated from the fixing roller 1 that is the detection target by a certain distance, and in addition, the temperature of the detecting means itself needs to be increased. Since the occupied area needs to be large, the apparatus becomes large.

  The present invention has been made to solve the above-described problems of the prior art, and its object is to achieve improvement in reliability, durability, and image quality while suppressing increase in size and cost of the apparatus. Another object is to provide a heating device and an image forming apparatus.

  The heating device and the image forming apparatus according to the present invention are characterized by the following configurations.

(1) Magnetic flux generation means, an induction heating element that heats the material to be heated by electromagnetic induction heat generation by the magnetic flux generated by the magnetic flux generation means, and a part of the magnetic flux acting on the induction heating element from the magnetic flux generation means In a heating apparatus comprising magnetic flux shielding means, moving means for moving the magnetic flux shielding means according to a required magnetic flux shielding area, and temperature detecting means for detecting the temperature of the induction heating element,
The magnetic flux generation means, the magnetic flux shielding means, and the temperature detection means are disposed on the opposite side of the surface of the induction heating element that heats the material to be heated, and the temperature detection means is outside the movable region of the magnetic flux shielding means. The heating device is arranged so as to detect the temperature in contact with the surface of the induction heating element.

  (2) The induction heating element has a cylindrical shape, and the magnetic flux shielding means and the temperature detection means are arranged inside the cylindrical induction heating element. Heating device.

  (3) The heating according to (1) or (2), wherein the magnetic flux shielding means is movable so as to make the magnetic flux shielding area variable according to the size of the material to be heated introduced into the apparatus. apparatus.

  (4) In any one of (1) to (3), the temperature detection unit is arranged to detect a temperature in an area corresponding to a heated material conveyance area of the induction heating element. The heating device described.

  (5) The heating device according to any one of (1) to (4), wherein the temperature detection means is a thermistor.

  (6) The heating apparatus according to any one of (1) to (4), wherein the temperature detection means is a thermo switch.

  (7) The heating apparatus according to any one of (1) to (6), wherein the induction heating element is a thermal fixing unit that thermally fixes an unfixed developer image formed on a recording material.

  (8) Image forming means for forming and supporting an unfixed toner image on a recording material, and heat fixing means for fixing the unfixed toner image on the recording material, wherein the heat fixing means is (1) to (7) An image forming apparatus comprising the heating device according to any one of the above.

  That is, the temperature detecting means is disposed on the opposite side of the induction heating element from the surface to be heated and detects the temperature in contact with the surface of the induction heating element outside the movable region of the magnetic flux shielding means. Wear of the surface of the heating element that heats the heated material can be completely avoided, and as a result, the durability of the induction heating element can be dramatically improved without increasing the cost. Further, it is possible to avoid a failure due to the temperature detecting means coming into contact with the surface of the induction heating element that heats the material to be heated. For example, when the heating device is used as an image heating and fixing device, the developer (toner) does not accumulate on the temperature detecting means on the surface of the induction heating element that heats the material to be heated, resulting in image smearing. Occurrence is eliminated, and image quality can be improved at the same time.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.

(1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration model diagram of an image forming apparatus in this embodiment. The image forming apparatus of this example is a laser printer using a transfer type electrophotographic process, which includes an electromagnetic induction heating type heating apparatus according to the present invention as an image heating and fixing apparatus.

  Reference numeral 101 denotes a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier, which is driven to rotate in the clockwise direction indicated by an arrow at a predetermined peripheral speed.

  Reference numeral 102 denotes a charging roller as charging means, which uniformly charges the outer peripheral surface of the rotating photosensitive drum 101 to a predetermined polarity and potential.

  A laser scanner 103 outputs a laser beam modulated in accordance with a time-series electric digital pixel signal of image information, and scans and exposes the uniformly charged surface of the rotating photosensitive drum 101. As a result, an electrostatic latent image corresponding to the scanning exposure pattern is formed on the photosensitive drum surface.

  Reference numeral 104 denotes a developing device, which performs reverse development or normal development using the electrostatic latent image on the photosensitive drum surface as a toner image.

  Reference numeral 105 denotes a transfer roller as transfer means, which forms a transfer nip T by contacting the photosensitive drum 101 with a predetermined pressing force. A recording material P as a material to be heated is fed to the transfer nip T from a sheet feeding mechanism (not shown) at a predetermined control timing, and is nipped and conveyed through the transfer nip T. A predetermined transfer bias is applied to the transfer roller 105 at a predetermined control timing. As a result, the toner images on the photosensitive drum 101 surface side are sequentially electrostatically transferred onto the surface of the recording material P that is nipped and conveyed through the transfer nip T.

  The recording material P that has exited the transfer nip T is separated from the surface of the photosensitive drum 101 and is introduced into an image heating and fixing apparatus 100 using an electromagnetic induction heating method, which will be described later. The image heating and fixing apparatus 100 heat-fixes the unfixed toner image on the introduced recording material P as a permanently fixed image, and discharges and conveys the recording material P.

  A photosensitive drum cleaner 106 removes transfer residual toner on the photosensitive drum after separation of the recording material. The photosensitive drum surface, from which the transfer residual toner has been removed and cleaned, is repeatedly used for image formation.

(2) Image heating and fixing device 100
The image heating and fixing apparatus 100 of this example is a heating apparatus of an electromagnetic induction heating system according to the present invention, FIG. 2 is a front model view of the apparatus omitted in the middle, and FIG. 3 is a partially cutaway view thereof. FIG. 4 is an external perspective view of the drive end portion side of the magnetic shielding plate.

  In the fixing device 100 shown in this example, the same reference numerals are given to members / parts common to the conventional fixing device for the sake of simplicity.

  Reference numeral 20 denotes a fixing roller assembly as a heat fixing member, and 2 denotes a pressure roller as a pressure member. These two members 20 and 2 are arranged in parallel vertically and pressed to form a fixing nip portion N.

  The fixing roller assembly 20 includes a cylindrical fixing roller 1 as an induction heating element (heating body), and the fixing roller 1 is on the opposite side to the outer peripheral surface that heats the recording material P as a heated material, that is, on the inner side. An exciting coil assembly 30 as magnetic flux generating means is inserted and arranged.

  The fixing roller 1 has a fluororesin or the like on the outer peripheral surface of a cored bar roller 1a made of a magnetic metal (conductor) such as nickel, iron, ferromagnetic SUS, iron-nickel alloy, iron-nickel-chromium alloy, nickel-cobalt alloy. A cylindrical thin metal sleeve made of an induction heating element having a thickness of, for example, 50 μm to 2000 μm, or a composite layer sleeve including the metal layer, with the heat-resistant release layer 1b of The sliding rings 21a and 21b are fitted and fixed to the end portions on the side, and the sliding ring portions are rotatably supported by the main side plates 61a and 61b on the back side and the near side of the fixing device via bearing members 62a and 62b, respectively. Are arranged.

  An exciting coil assembly 30 inserted and disposed in the interior of the fixing roller 1 includes an electromagnetic induction heating holder (exterior case body) (hereinafter referred to as a holder) 3a, a magnetic core 3b as a magnetic flux generating means, and an exciting coil 3c. And an assembly of a magnetic shielding plate 12 or the like as magnetic shielding means. The exciting coil 3c and the magnetic core 3b are stored and held in the holder 3a, and the magnetic shielding plate 12 is rotated to the back end portion side of the holder 3a. It is freely assembled and supported. The exciting coil assembly 30 includes sub-side plates 63a and 63b in which end portions 3a1 and 3a2 on the back side and near side of the holder 3a are disposed outside the main side plates 61a and 61b on the back side and near side of the fixing device. A non-rotating support is provided at a predetermined angle between them, and a predetermined interval is provided in a non-contact manner on the inner surface of the fixing roller.

  The pressure roller 2 includes a cored bar 2a, a heat-resistant elastic layer 2b, and a releasable surface layer 2c. The pressure roller 2 is arranged in parallel to the fixing roller 1 below the fixing roller assembly 20, Ends 2a1 and 2a2 on the back side and the front side of the gold 2a are rotatably supported between the back side and the main side plates 61a and 61b on the front side via bearing members 64a and 64b. . The bearing members 64a and 64b are arranged so as to be movable in the direction toward the fixing roller 1 with respect to the main side plates 61a and 61b, respectively. The bearing members 64a and 64b are urged by a pressing spring or the like (not shown). By bringing the pressure roller 2 into the pushing-up biasing state, the pressure roller 2 is brought into pressure contact with the lower surface portion of the fixing roller 1 against the elasticity of the elastic layer 2b with a predetermined pressing force, so that a fixing nip portion (heating nip) having a predetermined width is obtained. Part) N is formed.

  G1 is a fixing roller driving gear, and is fitted and fixed to the inner end of the fixing roller 1. When the driving force is transmitted to the gear G1 from the first driving source 14 side, the fixing roller 1 is rotationally driven clockwise at a predetermined peripheral speed in FIG. As the fixing roller 1 is driven to rotate, a rotational torque acts on the pressure roller 2 by a frictional force with the fixing roller 1 in the fixing nip portion N, and the pressure roller is driven to rotate.

  In the exciting coil assembly 30, the holder 3 a has a semicircular cross-sectional shape having a slightly smaller outer diameter than the inner diameter of the fixing roller 1, and the exciting coil 3 c and the magnetic core 3 b are disposed and held inside the holder 3 a. is there. The rear end 3a1 of the holder 3a is a cylindrical shaft portion, and this cylindrical shaft portion is inserted and held in a circular hole formed in the sub-side plate 63a on the back side of the fixing device, and the front end 3a2 of the holder 3a is D As the cut shaft portion, this D cut shaft portion is inserted and held in a D-shaped hole provided in the sub-side plate 63b on the front side of the fixing device, so that the holder 3a, that is, the exciting coil assembly 30 is placed on the back side and the front side. Between the side plates 63a and 63b, the semi-cylindrical surface side is supported in a non-rotating manner with an angle posture with the semi-cylindrical surface side facing downward, and is arranged on the inner surface of the fixing roller 1 in a non-contact manner with a predetermined interval.

  The holder 3a of this example is a molded body obtained by adding glass to a PPS resin having both heat resistance and mechanical strength. Of course, it is non-magnetic. Non-magnetic materials such as PPS resin, PEEK resin, polyimide resin, polyamide resin, polyamideimide resin, ceramic, liquid crystal polymer, and fluorine resin are suitable for the holder 3a.

  The exciting coil 3c must generate an alternating magnetic flux sufficient for heating. For this purpose, it is necessary to make the resistance component low and the inductance component high. As a core wire of the exciting coil 3c, 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, an exciting coil 3c that is wound 8 to 12 times in a horizontally long boat shape in accordance with the shape of the inner bottom surface of the holder 3a so as to go around the core 3b is used. Reference numerals 3c1 and 3c2 denote two lead wires for the exciting coil 3c. The lead wires 3c1 and 3c2 are led to the outside of the holder 3a through the inside of the cylindrical end portion 3a1 of the holder 3a and connected to the high frequency power source 3.

  For the exciting core 3b, a plate member made of a magnetic material used for a transformer core, such as ferrite or permalloy, is used. In this example, it is composed of a single vertically long rectangular plate-shaped vertical core disposed at the center position of the exciting coil 3c and having a length dimension corresponding to a large-size sheet conveyance area (large-size paper passing width area) A. .

  G2 is a magnetic shielding plate driving gear, which is rotatably fitted and supported on the cylindrical shaft portion, which is the back end portion 3a1, of the holder 3a via the bearing member 22 inside the sub side plate 63a on the back side of the fixing device. It is.

  In the fixing roller 1, a movable magnetic flux shielding plate 12 is disposed between the exciting coil assembly 30 and the core metal roller 1 a. The magnetic flux shielding plate 12 includes a shielding portion 12a, a support portion 12b, a flange portion 12c, and the like, and is configured integrally. As shown in FIG. 4, the magnetic flux shielding plate 12 is fixedly supported integrally with the gear G2 by fixing the flange portion 12c provided at the inner end of the shielding plate to the inner surface of the magnetic shielding member drive gear G2 with screws b1 and b2. I'm allowed. In this embodiment, the shape is changed in a direction (longitudinal direction of the fixing roller 1) perpendicular to the conveying direction of the sheet material as the recording material P. Specifically, both end portions of the rear side end portion and the front side end portion connected and supported by the support portion 12b are extended in the circumferential direction of the fixing roller 1 in a protruding shape to form a shielding portion 12a. The shielding part 12a) shields the alternating magnetic flux. The longitudinal width / position of the shielding portion 12a is determined according to the sheet material size that is assumed to require magnetic flux shielding. The material of the magnetic shielding member 12 is a non-magnetic and highly conductive material, for example, an alloy such as aluminum, copper, magnesium, or silver.

  When the driving force is transmitted from the second driving source 15 side as the moving means to the magnetic shielding member driving gear G2, the gear G2 rotates, and the magnetic shielding member 12 integrated with the gear G2 is fixed to the fixing roller 1. Rotate along the inner peripheral surface of the.

  In this embodiment, the sheet material P is passed through the fixing device by central reference conveyance. In FIG. 2 and FIG. 3, O is the center conveyance reference line, and is set at approximately the center in the longitudinal direction of the fixing device. A is a conveyance area of a large-size sheet material, and corresponds to the maximum sheet passing width area where no temperature increase occurs in the non-sheet passing portion. B is a conveyance area (small size paper passing width area) of a small size sheet material whose width is smaller than that of the large size paper corresponding to the large size sheet material conveyance area A. C is a small-size sheet material non-conveying area (non-paper-passing area) that occurs when small-size paper is passed. The shielding portion 12a of the magnetic shielding plate 12 has a length dimension that covers the non-transport region C.

  As shown in FIG. 5A, the magnetic shielding plate 12 is normally held at this position with the upper position of the exciting coil assembly 30 in the fixing roller 1 as the magnetic shielding plate retracting position which is the home position. This retracted position is a position where the magnetic flux does not substantially act from the exciting coil assembly 30 to the fixing roller 1. Further, as shown in FIG. 5B, the magnetic shielding plate 12 is held in this position with the lower position of the exciting coil assembly 30 as a shielding position in the fixing roller 1. This shielding position is a working magnetic flux shielding position where the working magnetic flux from the exciting coil assembly 30 to the fixing roller 1 is partially shielded by the shielding portion 12a.

  As described above, by forming the magnetic flux shielding plate 12 so as to shield the non-conveying area of the small size sheet material, the end portion of the fixing roller 1 that is likely to occur when the small size sheet material is continuously conveyed. Overheating of the non-transport area C can be prevented. That is, in FIG. 5-A, the magnetic flux shielding plate 12 is in the magnetic flux shielding plate retracted position, and the alternating magnetic flux directed to the magnetic core 3b and directed to the nip portion is not shielded in the entire longitudinal direction (frontward direction in the drawing). The entire longitudinal direction of the fixing roller 1 is heated by electromagnetic induction. On the other hand, in FIG. 5-B, the magnetic flux shielding plate 12 is in the shielding position, and a part of the alternating magnetic flux (longitudinal end region) directed to the magnetic core 3b and directed to the nip portion is shielded by the shielding portion 12a. Thus, it is possible to suppress the heat generation in the end region in the longitudinal direction of the fixing roller 1. In the magnetic flux shielding plate 12, for example, the control circuit 7 drives the drive mechanism 15 to rotate based on a detection signal from a size detection sensor (not shown) that detects the size of the sheet material used to pass through the nip portion N. By controlling, it is rotationally moved from the retracted position to the shield position or from the shield position to the retract position.

(3) Arrangement Mode of Thermistor / Thermo Switch, etc. FIG. 5 is a cross-sectional enlarged model view of the main part of the fixing device 100. A is a state where the magnetic shielding plate is moved and held in the retracted position, and B is a magnetic shielding plate. Shows a state in which is moved and held at the shielding position. FIG. 6 is an appearance model diagram of the fixing roller and the pressure roller, and shows the form of the magnetic flux shielding plate in the fixing roller and the arrangement of the thermistor and the thermo switch.

  Reference numeral 4 denotes a main thermistor as temperature detecting means, which is provided in the non-movable region D of the magnetic flux shielding plate 12 in the fixing roller 1 as shown in FIG. As shown in FIG. 6, the main thermistor 4 is supported on the outer surface of the holder 3 a of the exciting coil assembly 30 via a spring plate 16 a serving as a temperature detecting means supporting member having spring elasticity in the non-movable region D. The spring plate is brought into contact with the inner peripheral surface of the fixing roller in the non-movable region by the spring elasticity of the spring plate.

  The main thermistor 4 detects the temperature of the fixing roller portion corresponding to the small size sheet material conveyance region B, which is a common conveyance region for the large size sheet and the small size sheet, and outputs the detection signal to the control unit 17. The controller 17 controls the high frequency power supply 18 to control the power supply to the excitation circuit 19 connected to the excitation coil 3c, thereby adjusting the temperature of the fixing roller to a predetermined temperature (fixing temperature).

  As shown in FIG. 6, as the temperature detecting means, in addition to the main thermistor 4, an abnormally high temperature detecting sub-thermistor 5 for detecting the end temperature corresponding to the small size sheet material non-conveying region C of the fixing roller 1. The thermo switch 6 serving as a heat-sensitive safety device is shifted in the longitudinal direction to the same position on the inner peripheral side as in the above-described main thermistor 4 and is brought into contact with the inner peripheral surface of the fixing roller 1. That is, the sub-thermistor 5 and the thermo switch 6 are each provided with a spring plate 16b as a temperature detecting means supporting member having spring elasticity on the outer surface of the holder 3a of the exciting coil assembly 30 in the shielding plate non-movable region D in the fixing roller 1. 16c, and is brought into contact with the inner peripheral surface of the fixing roller by the spring elasticity of the spring plate.

  The sub-thermistor 5 detects the temperature of the non-conveying area C of the fixing roller 1 and outputs a detection signal to the control unit 17. The control unit 17 controls the high-frequency power source 18 to control the power supply to the excitation circuit 19 so as to adjust the temperature of the fixing roller 1 to a predetermined temperature (fixing temperature) and to control the drive mechanism 15 to rotate. The position of the magnetic shielding plate 12 is controlled.

  The thermo switch 6 is configured to cut off the power supply to the excitation circuit 19 by being cut off when the fixing roller 1 exceeds a predetermined temperature (fixing temperature) and causes thermal runaway.

  In the fixing device of this embodiment, when a conventional halogen lamp is used as a heat source instead of the exciting coil assembly 30, temperature detection means such as the main thermistor 4, the sub-thermistor 5 and the thermo switch 6 in the fixing roller 1 are used. Since radiant heat is directly received from the halogen lamp, it is necessary to take measures for raising the temperature of these temperature detecting means 4, 5, 6 themselves. However, when the electromagnetic induction heating type exciting coil assembly 30 is employed as a heat source as in this embodiment, the heat generating portion of the fixing roller 1 is only the nip portion N of the cored bar roller 1b where eddy current is generated. For this reason, the above temperature detection means 4, 5, 6 itself have a relatively small temperature rise countermeasure, and the cost increase can be minimized.

  Further, the position of the temperature detection means 4, 5, 6 on the inner circumferential side of the fixing roller 1 is a non-movable region of the above-described magnetic flux shielding plate 12, as shown in FIG. On the other hand, in the longitudinal direction of the fixing roller 1 (the front-rear direction in FIG. 5), the temperature detecting means 4, 5, 6 are arranged in the large-size sheet material conveyance area A of the fixing roller 1. For this reason, the temperature detectors 4 and 5 can control the magnetic flux shielding plate 12 to prevent the temperature rise at the end of the fixing roller 1 and can detect sensitively the temperature change due to the conveyance of the sheet material without interfering with the effect.・ 6 arrangements are possible.

  As described above, the temperature detection means 4, 5, 6, which is a contact type, contacts the inner peripheral surface of the fixing roller 1 and detects the temperature. As a result, wear on the la can be completely avoided, and as a result, the durability of the fixing roller 1 can be drastically improved without increasing the cost. Further, the developer (toner) that could not be fixed as described above is not deposited on the temperature detecting means 4, 5, 6 and no image smearing is caused, and the image quality is improved at the same time. Can be achieved.

  Further, as shown in FIG. 7, the main thermistor 4 and the spring plate 16a, the sub-thermistor 5 and the spring plate 16b, and the thermo switch 6 and the spring plate 16c are respectively made of insulating coating materials 51, 52, and the like such as a heat-resistant resin film. If covered with 53, wear due to direct friction with the inner peripheral surface of the fixing roller of the main thermistor 4, sub-thermistor 5 and thermo switch 6 can be reduced, and long-term use becomes possible.

  In the present embodiment, the longitudinal position / width of the shielding portion 12a of the magnetic flux shielding plate 12 is constant and one type is given as an example. However, the shielding portion 12a has a stepped shape and a plurality of shielding ranges are provided. In some cases, a technique may be employed in which the position and width of the elongated portion of the shielding portion 12a are continuously changed in the circumferential direction of the fixing roller 1 so that the shielding range can be adjusted steplessly. When the magnetic flux shielding plate 12 has a plurality of shielding regions (shielding portions 12a) or steplessly, the control circuit 7 controls the rotational direction position of the magnetic flux shielding plate 12 according to the sheet material size.

  Further, in the magnetic flux shielding plate 12, the shielding portion 12a and the supporting portion 12b are integrally formed, but the supporting portion 12b may be separately provided as a magnetic flux shielding plate support member. When the magnetic flux shielding plate support member is provided separately, the temperature detecting means 4, 5, 6 are arranged outside the region including the movable region of the support member.

  Further, the thermo switch 6 is not limited to the small size sheet material non-transport area C, and may be disposed in the small size sheet material transport area B.

[Other]
1) The form of the induction heating element is not limited to the rotating roller body, and other rotation bodies such as an endless belt made of the induction heating element may be used. Alternatively, a long end film made of an induction heating element wound in a roll may be used, and this may be configured to run at a predetermined speed toward the winding shaft via the lower part of the magnetic flux generation means. Good.

  2) Although the apparatus of an Example is an apparatus structure which conveys a to-be-heated material (sheet material) with a center reference | standard, this invention can be applied effectively also to the apparatus of a structure conveyed with a one-side reference | standard.

  3) Although the apparatus of the present embodiment has an apparatus configuration corresponding to a material to be heated (sheet material) of two sizes, large and small, the present invention passes the material to be heated (sheet material) of three or more sizes. It can also be applied to devices.

  4) The electromagnetic induction heating type heating apparatus of the present invention is not limited to the image heating and fixing apparatus of the embodiment, but is assumed to be attached to the recording paper carrying the unfixed image, and the recording paper carrying the fixed image is reheated. Therefore, it is also effective as an image heating apparatus such as a surface modification apparatus for modifying the image surface properties such as gloss. In addition, for example, it is also effective to use as a heating device for heat-treating a sheet-like member, such as a heat press device for removing wrinkles such as banknotes, a heat laminating device, and a heating and drying device for evaporating moisture content such as paper. Of course.

Schematic configuration model diagram of an image forming apparatus Front model of the fixing device omitted in the middle Partial cut away view of the fixing device External perspective view of drive end side of magnetic shielding plate Cross-sectional model diagram showing a state where the magnetic shielding plate is moved and held in the retracted position in the fixing device, Cross-sectional model diagram showing the state where the magnetic shielding plate is moved and held at the shielding position in the fixing device External view of the fixing roller and pressure roller Explanatory drawing which shows the other example of the arrangement | positioning form of a main thermistor, a sub thermistor, and a thermo switch Cross-sectional model diagram showing a state where the magnetic shielding plate is moved and held in the retracted position in the conventional fixing device, Model diagram showing a state where the magnetic shielding plate is moved and held at the shielding position in the conventional fixing device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 .... Fixing roller 2 ... Pressure roller 3 ... Heat source 3a ... Electromagnetic induction heating holder 3b ... Magnetic core 3c ... Excitation coil 4 ... Main Thermistor (temperature detection means)
5. Sub-thermistor (temperature detection means)
6 ··· Thermo switch (temperature detection means)
12. Magnetic flux shielding plate

Claims (8)

Magnetic flux generation means, induction heating element that heats the material to be heated by electromagnetic induction heat generation by the magnetic flux generated by the magnetic flux generation means, and magnetic flux shielding means that shields part of the applied magnetic flux from the magnetic flux generation means to the induction heating element And a heating device comprising a moving means for moving the magnetic flux shielding means according to a necessary magnetic flux shielding area, and a temperature detecting means for detecting the temperature of the induction heating element.
The magnetic flux generation means, the magnetic flux shielding means, and the temperature detection means are disposed on the opposite side of the surface of the induction heating element that heats the material to be heated, and the temperature detection means is outside the movable region of the magnetic flux shielding means. The heating device is arranged so as to detect the temperature in contact with the surface of the induction heating element.   The heating apparatus according to claim 1, wherein the induction heating element has a cylindrical shape, and the magnetic flux shielding means and the temperature detection means are arranged inside the cylindrical induction heating element. .   The heating apparatus according to claim 1 or 2, wherein the magnetic flux shielding means is movable so as to make the magnetic flux shielding area variable according to the size of a material to be heated introduced into the apparatus.   The heating apparatus according to any one of claims 1 to 3, wherein the temperature detection unit is arranged to detect a temperature in an area corresponding to a heated material conveyance area of the induction heating element.   The heating apparatus according to claim 1, wherein the temperature detection unit is a thermistor.   The heating apparatus according to any one of claims 1 to 4, wherein the temperature detection means is a thermo switch.   7. The heating apparatus according to claim 1, wherein the induction heating element is a thermal fixing unit that thermally fixes an unfixed developer image formed on a recording material.   8. An image forming means for forming and carrying an unfixed toner image on a recording material, and an image heating means for fixing the unfixed toner image on the recording material, wherein the heat fixing means is any one of claims 1 to 7. An image forming apparatus characterized by being a heating apparatus.