JP4194530B2 - Fixing device - Google Patents

Description

  The present invention relates to a recording material (transfer sheet, electrofax sheet, electrostatic recording paper) by a heating device for heating the material to be heated and appropriate image forming process means such as an electrophotographic process, an electrostatic recording process, and a magnetic recording process. -The heating device is provided as a heating means for heating and fixing an unfixed image (toner image) formed and supported on a recording material by a transfer method or a direct method on an OHP sheet, printing paper, format paper, etc. as a permanently fixed image. The present invention relates to an image forming apparatus and a temperature control method in a heating apparatus.

  As a heating device of an image forming apparatus, a film heating type fixing device has been put into practical use from the viewpoint of quick start and energy saving. A film heating type fixing device forms a fixing nip by sandwiching a heat-resistant thin fixing film between a ceramic heater as a heating means and a pressure roller as a pressure member, and pressurizes the fixing film. By rotating the rollers together, the unfixed toner image is fixed by applying heat and pressure while conveying the recording material.

  In the film heating type fixing device, the heat capacity of the fixing film, which is a heating member, is very small compared to the heat roller method that has been widely adopted so far, so the heat energy from the heating means is efficiently used for fixing the toner image. Can be used. For this reason, the temperature rise rate of the fixing film is overwhelmingly faster than that of the heat roller system, and the waiting time from the power-on of the image forming apparatus to the printable state can be shortened (quick start). Furthermore, since it is not necessary to preheat the heating member during printing standby, the power consumption of the image forming apparatus can be kept low (energy saving).

  In recent years, induction heating type fixing devices have begun to be put into practical use as a more efficient heating type fixing device (for example, see Patent Document 1). As an example of an induction heating type fixing device, a fixing device including a fixing film provided with a conductive member as a heat generating layer and an exciting coil as a magnetic field generating unit has been put into practical use. The exciting coil generates an alternating magnetic flux by an alternating current supplied from a switching power supply serving as an induction heating power supply. The alternating magnetic flux substantially forms a closed magnetic path by a heat generating layer or a magnetic core provided in the fixing film, and generates an eddy current in the heat generating layer of the fixing film. The heat generating layer provided on the fixing film generates Joule heat due to its own specific resistance, and as a result, the fixing film can generate heat.

  In this induction heating method, since the fixing film itself can generate heat, the heat energy from the heating means can be used for fixing the toner image more efficiently than the film heating method using a ceramic heater.

JP-A-10-301415

  In the temperature control (temperature control) of the induction heating type fixing device as described in Patent Document 1, the alternating frequency of the alternating current supplied to the exciting coil is variable in order to perform power control with high controllability. Thus, a method of varying the power supplied to the fixing device has been put into practical use. This is to increase or decrease the power to the fixing device by controlling the alternating current flowing in the excitation coil by increasing or decreasing the ON state time (control amount) of the switching means provided in the excitation circuit of the induction heating power supply. It is. As a result, the switching cycle of the alternating current changes, so that the alternating frequency of the alternating current flowing through the exciting coil increases and decreases, and the alternating frequency of the alternating magnetic flux generated from the exciting coil increases and decreases accordingly. Such a power control method for making the alternating frequency variable is the optimum power always in accordance with the control amount calculated from the difference between the detected temperature of the fixing film output from the temperature detecting means and the target temperature using a PID control arithmetic expression or the like. Can be supplied to the fixing device, so that highly accurate temperature control can be realized.

  However, in the control method described above, when the alternating frequency of the alternating current matches or approaches the natural frequency of the fixing film, the fixing film resonates due to vibration of the fixing film due to electromagnetic force according to the alternating frequency. There is. In particular, a highly flexible fixing film tends to resonate because the rigidity of the fixing film itself is low. When the fixing film resonates, there is a problem that the unfixed toner on the recording material immediately before entering the fixing nip is scattered by the vibration, and the sharpness of the fixed image is lowered. Furthermore, when the resonance frequency of the fixing film is in the human audible range, there is a problem that the resonance sound is heard as an abnormal sound, making the user uncomfortable.

Therefore, according to the present invention, in the induction heating type fixing device, by controlling the temperature without causing the heating member to resonate, it is possible to prevent noise from the fixing device and improve the image quality of the fixed image at low cost. It is an object to provide a fixing device.

The present invention includes a heating member having a heat generation layer, an excitation coil that generates magnetic flux for generating eddy currents in the heat generation layer, and a switching element that switches an energization on state and an energization off state to the excitation coil. Based on a power source that supplies an alternating current having a frequency determined by an on-state time and an energization-off state time to the exciting coil, a temperature detection unit that detects the temperature of the heating member, and a detection temperature of the temperature detection unit And a temperature control means for controlling the temperature of the heating member by controlling the frequency, and fixing the toner image on the recording material to the recording material by using heat generated in the heat generating layer. In the apparatus, a specific frequency band that is not set regardless of the detected temperature of the temperature detecting means is set between the maximum value and the minimum value of the frequency controlled by the temperature control means. If the detected temperature of the temperature detecting means is a detected temperature corresponding to the specific frequency band, currents having a frequency higher and lower than the frequency of the specific frequency band are alternately supplied to the exciting coil. By controlling in this way, a current corresponding to the detected temperature is supplied to the exciting coil .

The present invention also includes a heating member having a heat generating layer, an excitation coil that generates a magnetic flux for generating an eddy current in the heat generating layer, and a switching element that switches an energization on state and an energization off state to the excitation coil. A power source for supplying an alternating current having a frequency determined by the energization-on time and the energization-off time to the exciting coil, temperature detection means for detecting the temperature of the heating member, and detection temperature of the temperature detection means Temperature control means for controlling the frequency of the heating member by controlling the frequency based on the temperature, and heating the toner image on the recording material to the recording material using heat generated in the heat generating layer In the fixing device for fixing, a specific frequency that is not set between the maximum value and the minimum value of the frequency controlled by the temperature control unit regardless of the temperature detected by the temperature detection unit. When a band is provided and the detected temperature of the temperature detecting means is a detected temperature corresponding to the specific frequency band, the energized off state time is set as the time corresponding to the detected temperature. By changing so that a current having a frequency outside the specific frequency band is supplied to the exciting coil, a current corresponding to the detected temperature is supplied to the exciting coil .

In the induction heating type fixing device, it is possible to prevent noise due to resonance of the heating member by performing temperature control without causing the heating member to resonate. Further, for example, it is possible to improve the image quality of a fixed image in an image forming apparatus using such a fixing device at a low cost.

<First embodiment>
(1) Schematic Configuration of Image Forming Apparatus FIG. 17 is a diagram illustrating a schematic configuration of an example of the image forming apparatus according to the present embodiment. The image forming apparatus of this embodiment is a color laser printer using an electrophotographic process.

  In such an image forming apparatus, first, a photosensitive drum 101, which is a latent image carrier formed of an organic photoreceptor or an amorphous silicon photoreceptor, rotates at a predetermined conveyance speed (circumferential speed) in the counterclockwise direction indicated by an arrow. Driven. The photosensitive drum 101 is subjected to a uniform charging process with a predetermined polarity and potential by a charging device 102 such as a charging roller during its rotation.

  Next, the charged surface is subjected to a scanning exposure process according to target image information by a laser beam 103 output from a laser optical box (laser scanner) 110. The laser optical box 110 outputs a modulated laser beam 103 that is switched on or off in response to a time-series electric digital pixel signal of target image information from an image signal generation device such as an image reading device (not shown), The surface of the drum 101 is scanned and exposed. Thereby, an electrostatic latent image corresponding to the target image information is formed on the surface of the photosensitive drum 101. At this time, the output laser light from the laser optical box 110 is deflected to the exposure position of the photosensitive drum 101 by the mirror 109.

  In the case of full-color image formation, scanning exposure and latent image formation are performed on a first color separation component image, for example, a yellow component image, in a target full-color image. The yellow toner image is developed by the operation of 104Y. The yellow toner image is transferred to the surface of the intermediate transfer drum 105 at the primary transfer portion T1 which is a contact portion (or proximity portion) between the photosensitive drum 101 and the intermediate transfer drum 105. The surface of the photosensitive drum 101 after the transfer of the toner image to the surface of the intermediate transfer drum 105 is cleaned by the cleaner 107 after removal of adhered residues such as transfer residual toner.

  The process cycle of charging, scanning exposure, development, primary transfer, and cleaning as described above is the second color separation component image of the target full color image (for example, the magenta component image, the magenta developer 104M is activated), the third color An intermediate transfer drum is sequentially executed for each color separation component image of the separation component image (for example, cyan component image, cyan developing device 104C is activated) and the fourth color separation component image (for example, black component image, black developing device 104Bk is activated). The four color toner images of yellow toner image, magenta toner image, cyan toner image, and black toner image are sequentially superimposed and transferred onto the surface 105, and a color toner image corresponding to the target full-color image is synthesized and formed.

  The intermediate transfer drum 105 is provided with a middle resistance elastic layer and a high resistance surface layer on a metal drum. The intermediate transfer drum 105 is in the clockwise direction indicated by an arrow at the same peripheral speed as the photosensitive drum 101 in contact with or close to the photosensitive drum 101. And a bias potential is applied to the metal drum of the intermediate transfer drum 105, and the toner image on the photosensitive drum 101 side is transferred to the surface of the intermediate transfer drum 105 by the potential difference with the photosensitive drum 101.

  The color toner image formed on the surface of the intermediate transfer drum 105 is fed to the secondary transfer portion T2 (not shown) in the secondary transfer portion T2 which is a contact nip portion between the intermediate transfer drum 105 and the transfer roller 106. The image is transferred to the surface of the recording material P fed from the portion at a predetermined timing. The transfer roller 106 supplies a charge having a polarity opposite to that of the toner from the back surface of the recording material P, thereby sequentially transferring the combined color toner images sequentially from the surface of the intermediate transfer drum 105 to the recording material P side.

  The recording material P that has passed through the secondary transfer portion T2 is separated from the surface of the intermediate transfer drum 105 and introduced into a fixing device (image heating device) 100 as a heating device, and an unfixed toner image is fixed by heat fixing processing. It becomes a toner image and is discharged to a discharge tray (not shown) outside the apparatus. The configuration and temperature control of the fixing device 100 will be described later.

  The intermediate transfer drum 105 after the color toner image is transferred to the recording material P is cleaned by the cleaner 108 after removal of residual residues such as transfer residual toner and paper dust. The cleaner 108 is always held in a non-contact state with the intermediate transfer drum 105, and is kept in contact with the intermediate transfer drum 105 during the secondary transfer of the color toner image from the intermediate transfer drum 105 to the recording material P. The

  Also, the transfer roller 106 is always held in a non-contact state with the intermediate transfer drum 105, and the recording material P is transferred from the intermediate transfer drum 105 to the intermediate transfer drum 105 during the secondary transfer of the color toner image to the recording material P. It is held in contact via

(2) Schematic configuration of heating device (2-A) Overall configuration The heating device in this example is a pressure roller driving system using an electromagnetic induction heat generating cylindrical fixing film (fixing belt) as a heating member, This is an induction heating type fixing device 100. FIG. 1 is a cross-sectional side view of a main part of a fixing device 100 as a heating device in the present embodiment, FIG. 2 is a front view of the main part, and FIG. 3 is a front cross-sectional front view of the main part.

  The fixing device 100 is roughly divided into a film guide member 16 as a cylindrical support member, and a cylindrical electromagnetic induction exothermic fixing film 10 as a heating member loosely fitted on the film guide member 16. And a pressure roller 30 as a pressure member in which a nip portion N is formed with the fixing film 10 sandwiched between the film guide member 16 and the film guide member 16.

  The cylindrical film guide member (film support member) 16 is configured as a cylindrical body by combining a pair of left and right cross-sectional substantially semicircular arc shaped saddle-shaped halves 16a and 16b with openings facing each other. . In FIG. 1, magnetic cores 17 a, 17 b, 17 c as magnetic field generating means and an excitation coil 18 are disposed and held inside the right film guide member half 16 a.

  The pressure roller 30 includes a cored bar 30a and a heat-resistant elastic material layer 30b made of silicone rubber, fluororubber, fluororesin, or the like that is concentrically and integrally molded around the cored bar. Both ends of the core metal 30a are rotatably supported between the chassis side metal plates (not shown) of the apparatus.

  The film guide member 16 on which the fixing film 10 is externally fitted is disposed on the upper side of the pressure roller 30, and both ends of the pressure rigid stay 22 inserted through the film guide member 16 and spring receivers on the apparatus chassis side. By pressing the pressure springs 25a and 25b between the members 29a and 29b, a pressing force is applied to the pressure rigid stay 22, respectively. As a result, the lower surface of the film guide member 16 and the upper surface of the pressure roller 30 are pressed against each other with the fixing film 10 interposed therebetween, so that a fixing nip portion N having a predetermined width is formed.

  The pressure roller 30 is rotationally driven in the counterclockwise direction indicated by the arrow by the driving means M (FIG. 1). By the rotational driving of the pressure roller 30, a rotational force acts on the fixing film 10 by the frictional force between the pressure roller 30 and the outer surface of the fixing film 10 in the fixing nip portion N, and the inner peripheral surface of the fixing film 10 becomes the fixing nip. While rotating closely in contact with the lower surface of the film guide member 16 at the portion N, the outer periphery of the film guide member 16 is rotated in the clockwise direction indicated by the arrow at a peripheral speed substantially corresponding to the peripheral speed of the pressure roller 30 (pressure roller). Drive system).

  In order to reduce the mutual sliding frictional force between the lower surface of the film guide member 16 and the inner surface of the fixing film 10 in the fixing nip portion N, the surface portion corresponding to the fixing nip portion N on the lower surface of the film guide member 16 is heat resistant. A low-friction sliding member 40 is provided. The sliding member 40 is preferably made of, for example, polyimide resin, glass, alumina, alumina coated glass, or the like. In this example, an alumina substrate coated with glass is disposed.

  The sliding member 40 is a strip-like or tape-like member having a length and width corresponding to at least the length and width of the fixing nip portion N, and is provided along the length on the lower surface of the film guide member 16 in this example. It is positioned and held in the fitted groove portion. Furthermore, it is good to fix with a heat resistant adhesive.

  Further, a lubricant is interposed between the sliding member 40 and the inner peripheral surface of the fixing film 10 to reduce the sliding resistance of the fixing film 10. In this embodiment, fluorine grease is used as the lubricant.

  Further, as shown in FIG. 4, the peripheral surface of the film guide member half 16a on the right side in FIG. 1 is provided with convex rib portions 16e at predetermined intervals in the longitudinal direction thereof. The contact sliding resistance between the peripheral surface of the half body 16a and the inner surface of the fixing film 10 is reduced, and the rotational load of the fixing film 10 is reduced. Such a convex rib portion 16e can be similarly formed on the left half 16b of the film guide member in the drawing.

  Reference numerals 23a and 23b denote flange members which are fitted and arranged on the front and back end portions of the cylindrical film guide member 16, and receive the end portions of the fixing film when the fixing film 10 rotates. It serves to regulate the movement of the ten film guide members 16 along the length. The flange members 23 a and 23 b may be configured to rotate by the rotation of the fixing film 10.

  Reference numeral 26 denotes a thermistor as temperature detecting means, which is a temperature sensor for detecting the temperature of the fixing film 10. The temperature of the fixing film 10 is controlled so that a predetermined temperature is maintained by controlling the current supply to the exciting coil 18 by a temperature control system including a thermistor 26 described later.

  50 is a thermo switch. In this embodiment, the thermo switch 50 is provided at a position facing the exciting coil 18 with the fixing film 10 interposed therebetween. Further, the fixing film 10 is disposed in a non-contact manner on the outer surface of the fixing film 10 so as not to damage the fixing film 10. The thermo switch 50 is connected in series to a later-described relay switch and a DC power supply (not shown). When the thermal switch 50 is detected and the thermo switch 50 is opened, the power supply to the relay switch is cut off. The relay switch is operated so that power supply to an excitation circuit 307 described later is cut off.

  Thus, the pressure roller 30 is driven to rotate, and the fixing film 10 is rotated accordingly, and is heated by the action of a magnetic field generated by power supply from the excitation circuit 307 (FIG. 4) as an induction heating power source to the excitation coil 18. The fixing film 10 as a member generates heat by electromagnetic induction, and the fixing nip N rises to a predetermined temperature, and the temperature is controlled. In this state, the recording material P on which the unfixed toner image t conveyed from the image forming unit (not shown) is formed is introduced between the fixing film 10 and the pressure roller 30 in the fixing nip N and fixed. In the nip portion N, the image surface is brought into close contact with the outer surface of the fixing film and is nipped and conveyed together with the fixing film 10. At this time, the toner image t is fixed to the recording material P by the heat of the fixing film 10 and the pressure by the pressure roller 30.

  When the recording material P passes through the fixing nip portion N, it is separated from the outer surface of the fixing film 10 and discharged and conveyed. The heat-fixed toner image t on the recording material P passes through the fixing nip N and is then cooled to become a permanently fixed image.

(2-B) Configuration of magnetic field generating means The magnetic cores 17a, 17b, and 17c are members of high magnetic permeability, and materials used for transformer cores such as ferrite and permalloy are good. More preferably, even at an alternating frequency of 100 kHz or higher. It is better to use ferrite with less loss.

  The exciting coil 18 constituting the magnetic field generating means uses a bundle (bundled wire) of a plurality of thin copper wires each coated with an insulation coating as a conducting wire (electric wire) constituting the coil (wire ring). The exciting coil 18 is formed by winding this several times. In this example, the exciting coil is formed by 12 turns.

As the covering member for performing the insulating coating, it is preferable to use a coating having heat resistance in consideration of heat conduction due to heat generation of the fixing film 10. For example, a coating such as amideimide or polyimide may be used. In this embodiment, a polyimide coating is used and the heat resistant temperature is 220 ° C.
The excitation coil 18 may improve the density by applying pressure from the outside.

  An insulating member 19 is disposed between the magnetic field generating means 17a, 17b, 17c and 18 and the pressurizing rigid stay 22. As a material of the insulating member 19, a material having excellent insulating properties and good heat resistance is preferable. For example, a phenol resin, a fluororesin, a polyimide resin, a polyamide resin, a polyamideimide resin, a polyether ketone resin, a polyether sulfone resin, a polyphenylene sulfide resin, a PFA resin, a PTFE resin, an FEP resin, an LCP resin, or the like may be selected.

  FIG. 5 schematically shows how the alternating magnetic flux generated by the magnetic field generating means is generated. A magnetic flux C represents a part of an alternating magnetic flux generated by the exciting coil 18 driven by the exciting circuit 307. The alternating magnetic flux C guided to the magnetic cores 17a, 17b, and 17c generates eddy currents in the heat generating layer 1 of the fixing film 10 between the magnetic cores 17a and 17b and between the magnetic cores 17a and 17c. generate. This eddy current causes Joule heat (eddy current loss) to be generated in the heat generating layer 1 by the specific resistance of the heat generating layer 1.

  The calorific value Q is determined by the density of the magnetic flux C passing through the heat generating layer 1, and shows a distribution as shown in the graph of FIG. In the graph shown in FIG. 5, the vertical axis indicates the circumferential position in the fixing film 10 represented by an angle θ with the center of the magnetic core 17 a being 0, and the horizontal axis is the amount of heat generated in the heat generating layer 1 of the fixing film 10. Q is indicated. Here, the heat generation region H is defined as a region where the maximum heat generation amount is Q and the heat generation amount is Q / e or more (e is the base of the natural logarithm). This is a region where the amount of heat generated for the fixing process can be obtained.

(2-C) Configuration of Fixing Film 10 FIG. 6 is a layer configuration model diagram of the fixing film 10 in this embodiment.
The fixing film 10 of this embodiment is a composite structure of a heat generating layer 1 made of an electromagnetic induction heat generating metal film or the like as a base layer, an elastic layer 2 laminated on the outer surface, and a release layer 3 laminated on the outer surface. belongs to.

  For adhesion between the heat generating layer 1 and the elastic layer 2 and adhesion between the elastic layer 2 and the release layer 3, a primer layer (not shown) may be provided between the respective layers.

  In the fixing film 10 having a substantially cylindrical shape, the heat generating layer 1 is on the inner surface side in contact with the sliding member 40, and the release layer 3 is on the outer surface side in contact with the pressure roller or the recording material (heated material). .

  As described above, when the alternating magnetic flux acts on the heat generating layer 1, an eddy current is generated in the heat generating layer 1 and the heat generating layer 1 generates heat. This heat is transmitted to the elastic layer 2 and the release layer 3 so that the entire fixing film 10 is heated, and the recording material P passed through the fixing nip portion N is heated to fix the toner t image by heat. .

a. Heat generation layer 1
As the heat generating layer 1, magnetic and nonmagnetic metals can be used, but magnetic metals are preferably used. As such a magnetic metal, a ferromagnetic metal such as nickel, iron, ferromagnetic stainless steel, nickel-cobalt alloy or permalloy is preferably used. Further, in order to prevent metal fatigue due to repeated bending stress received when the fixing film 10 rotates, a member in which manganese is added to nickel may be used.

The thickness of the heat generating layer 1 is preferably thicker than the skin depth σ represented by the following formula and 200 μm or less. If the thickness of the heat generating layer 1 is within this range, the heat generating layer 1 can efficiently absorb electromagnetic waves, and therefore heat can be generated efficiently.
σ = (ρ / πfμ) ^1/2 (1)
Here, f is the frequency of the excitation circuit, μ is the magnetic permeability of the heat generating layer 1, and ρ is the specific resistance of the heat generating layer 1.

  This skin depth σ indicates the depth of absorption of electromagnetic waves used for electromagnetic induction, and the intensity of the electromagnetic waves is 1 / e or less deeper than this. Conversely, most of the energy is absorbed up to this depth (see the relationship between the heat generation layer depth and the electromagnetic wave intensity shown in FIG. 8).

  The thickness of the heat generating layer 1 is more preferably 1 to 100 μm. When the thickness of the heat generating layer 1 is thinner than the above range, the efficiency is deteriorated because most of the electromagnetic energy cannot be absorbed. On the other hand, if the heat generating layer 1 is thicker than the above range, the rigidity of the heat generating layer 1 becomes too high, and the flexibility becomes poor, making it unrealistic to use as a rotating body.

b. Elastic layer 2
The elastic layer 2 is preferably made of a material having good heat resistance and thermal conductivity, such as silicone rubber, fluorine rubber, and fluorosilicone rubber.

  The thickness of the elastic layer 2 is preferably 10 to 500 μm in order to guarantee the fixed image quality. When a color image is printed, a solid image is formed over a large area on the recording material P, particularly in a photographic image. In this case, if the heating surface (release layer 3) cannot follow the unevenness of the recording material P or the unevenness of the toner layer t, uneven heating occurs, and uneven gloss occurs in the image where the heat transfer amount is large and small. . That is, the glossiness is high in the portion where the heat transfer amount is large, and the glossiness is low in the portion where the heat transfer amount is small. When the thickness of the elastic layer 2 is smaller than the above range, the release layer 3 cannot follow the unevenness of the recording material P or the toner layer t, and image gloss unevenness occurs. On the other hand, when the elastic layer 2 is too larger than the above range, the thermal resistance of the elastic layer 2 becomes too large, making it difficult to realize a quick start. The thickness of the elastic layer 2 is more preferably 50 to 500 μm.

  If the elastic layer 2 is too hard, it cannot follow the unevenness of the recording material P or the toner layer t, and image gloss unevenness occurs. Therefore, the hardness of the elastic layer 2 is preferably 60 ° (JIS-A) or less, more preferably 45 ° (JIS-A) or less.

The thermal conductivity λ of the elastic layer 2 is preferably 2.5 × 10 ^{−1 to} 8.4 × 10 ⁻¹ W / m · ° C. When the thermal conductivity λ is smaller than the above range, the thermal resistance is too large, and the temperature rise in the surface layer (release layer 3) of the fixing film 10 is delayed. When the thermal conductivity λ is larger than the above range, the hardness of the elastic layer 2 becomes too high or compression set tends to occur. More preferably, it is 3.3 × 10 ^{−1 to} 6.3 × 10 ⁻¹ W / m · ° C.

c. Release layer 3
The release layer 3 is preferably made of a material having good release properties and heat resistance such as fluororesin, silicone resin, fluorosilicone rubber, fluororubber, silicone rubber, PFA, PTFE, and FEP.

  The thickness of the release layer 3 is preferably 1 to 100 μm. If the thickness of the release layer 3 is thinner than the above range, uneven coating of the coating film occurs, causing a problem that a part having poor release property is generated or durability is insufficient. Moreover, when the thickness of the release layer 3 is thicker than the above range, the heat conduction is deteriorated. In particular, when a resin material is used for the release layer 3, the hardness of the release layer 3 becomes too high and the effect of the elastic layer 2 is lost.

d. Insulation layer 4
As shown in FIG. 7, in the configuration of the fixing film 10, the heat insulating layer 4 may be provided on the contact surface side of the heat generating layer 1 with the sliding member 40. The heat insulating layer 4 is preferably a heat resistant resin such as a fluororesin, a polyimide resin, a polyamide resin, a polyamideimide resin, a PEEK resin, a PES resin, a PPS resin, a PFA resin, a PTFE resin, or an FEP resin.

  As thickness of the heat insulation layer 4, 10-1000 micrometers is preferable. When the thickness of the heat insulation layer 4 is less than 10 μm, the heat insulation effect cannot be obtained and the durability is insufficient. On the other hand, if it exceeds 1000 μm, the distances from the magnetic cores 17a, 17b, 17c and the exciting coil 18 to the heat generating layer 1 become large, and the magnetic flux is not sufficiently absorbed by the heat generating layer 1.

  Since the heat insulating layer 1 can insulate the heat generated in the heat generating layer 1 so as not to go to the inside of the fixing film 10, the heat supply efficiency to the recording material P is improved as compared with the case without the heat insulating layer 1. Therefore, power consumption can be suppressed.

  Further, if the heat insulating layer 10d is made of a material having good slipperiness, the sliding resistance between the sliding member 40 and the fixing film 10 can be reduced.

(3) Schematic Configuration of Induction Heating Power Supply (3-A) Overall Configuration FIG. 9 is a block diagram of the overall configuration of the induction heating power supply 300 including the heating device 100 and the temperature control means 400.

  Reference numeral 300 denotes an entire induction heating power source, 100 denotes an entire fixing device as a heating device, and 400 denotes an entire temperature control means. 301 is a power line input terminal, 302 is a breaker, 303 is a relay switch, 304 is a rectifier circuit composed of a bridge rectifier circuit and a capacitor for performing both-wave rectification, 305 and 306 are gate control transformers of switching elements described later, and 307 is Excitation circuit. 401 is a feedback control circuit, and 402 is a driver circuit.

  Input from the power line input terminal 301. C. Current enters rectifier circuit 304 through breaker 302 and relay contact 303. Here, the relay switch 303 is turned on via the contact point of the thermo switch 50 that is opened when the temperature of the fixing device 100 exceeds a specified temperature and the temperature rises abnormally. If the temperature of the fixing device 100 is abnormally increased due to a trouble, the relay switch 303 is turned off by opening the contact of the thermo switch 50, and further, the input from the power source of the excitation circuit 307 is cut off, thereby preventing thermal runaway. The safety of the fixing device 100 is ensured. Next, A. C. The current is supplied to the D.C. C. Converted to current. On the other hand, the temperature of the fixing film 10 of the fixing device 100 is detected by the thermistor 26, and the detection result is input to the feedback control circuit 401. The feedback control circuit 401 performs PID (proportional / integral / differential) calculation and the like while comparing with the target temperature based on the detection result of the thermistor 26. Although details will be described later, data for controlling the switching element of the excitation circuit 307 (On time and / or off time of the switching element) is calculated. The feedback control circuit 401 includes a CPU that calculates data for controlling the switching elements of the excitation circuit 307, a ROM that stores a calculation program for the CPU, and a RAM that provides a work area for the CPU.

  The driver circuit 402 receives the signal having data for controlling the switching element from the feedback control circuit 401 and drives the gate control transformers 305 and 306 with a control signal suitable for the voltage resonance control of the power supply, and the excitation circuit 307. The output to the exciting coil 18 is controlled.

(3-B) Excitation Circuit FIG. 10 is a diagram illustrating a main part of the excitation circuit 307 of the induction heating power supply 300. The excitation circuit 307 of this embodiment is a voltage resonance method.

  Reference numeral 201 denotes a first switching element, and 205 denotes a second switching element. The first switching element 201 as a switching means performs a main switching operation and controls a current flowing through the exciting coil 18. The second switching element 205 performs a switching operation in synchronization with the first switching element 201 to reduce a load during the switching operation. As a specific operation of these switching elements, voltage resonance is performed by turning on and off the first switching element 201 by opening the second switching element 205. The second switching element 205 is turned on when the flyback voltage finishes rising while the first switching element 201 is turned off, and turned off when the flyback voltage falls. The soft switching which does not apply an electrical load to one switching element 201 is realized. These switching elements 201 and 205 have a small loss during normal operation and a small switch loss, and preferably have a high breakdown voltage and a large current type. Generally used are switching elements such as MOSFETs and IGBTs.

  Reference numeral 18 denotes an exciting coil. In this embodiment, as described above, the exciting coil 18 is provided in the fixing device 100 together with the fixing film 10. The fixing film 10 can be represented by an equivalent circuit including an inductance component L and a resistance component R with respect to the excitation circuit 307. The fixing film 10 generates heat due to Joule heat generated by the resistance component R due to an induced current flowing in an equivalent circuit of the fixing film 10 due to an electromagnetic induction effect between the high-frequency magnetic field generated from the exciting coil 18 and the fixing film 10.

  202 is a first reverse conducting diode, and 206 is a second reverse conducting diode. During the period in which the amplitude of the flyback voltage is large and the voltage on the collector terminal 201C side of the first switching element 201 is lower than the voltage on the emitter terminal 201E side, the first reverse conducting diode 202 is turned on and the current is excited. Flow into. During this period, the voltage on the collector terminal 201C side of the first switching element 201 is clamped to 0V. It is generally known that if the first switching element 201 is turned on during such a period, the switch can be turned on without burdening the voltage. With such a driving method, the loss associated with switching of the first switching element 201 can be minimized, and switching with high efficiency and low noise is possible.

Reference numeral 204 denotes a first resonance capacitor, and 207 denotes a second resonance capacitor. When the first switching element 201 is turned off, the exciting coil 18 keeps flowing current, and therefore a high voltage called a flyback voltage is generated by the sharpness of the resonance circuit determined by the resonance capacitors 204 and 207 and the exciting coil 18. To do. This voltage oscillates about the power supply voltage V _B, converges as it idea keeping the OFF state supply voltage V _B.

  The peak value of the current flowing through the exciting coil 18 increases with the ON time of the first switching element 201. Therefore, the excitation energy stored in the excitation coil 18 can be increased as the on-time is longer. That is, the electric power supplied to the fixing device 100 can be controlled by changing the alternating frequency of the alternating current flowing through the exciting coil 18. On the other hand, the off time of the first switching element 201 is constant in accordance with the oscillation period of the flyback voltage in this embodiment.

(4) Temperature Control Hereinafter, temperature control of the fixing device 100 that is a feature of the present invention will be described.

  In FIG. 9, the detection result of the thermistor 26 is input to the feedback circuit 401. The feedback circuit 401 performs PID calculation based on the detection result, and calculates the ON time of the first switching element 201 that can output the optimum power for maintaining the temperature of the fixing film 10 at the target temperature. The calculation result is output to the driver circuit 402 (in this embodiment, the off time is fixed by hardware).

In this embodiment, as described above, the power supply to the fixing device 100 is controlled by fixing the off time of the first switching element 201 and varying the on time. Here, when the on-time of the first switching element 201 is t _on , the off-time is t _off , and the alternating frequency of the alternating current flowing through the exciting coil 18 is f, these relationships are expressed by equation (1). .
f = 1 / (t _on + t _off ) (1)

FIG. 18 shows the relationship between the on-time t _on of the first switching element 201 and the alternating frequency f in the conventional temperature control. t _on max and t _on min respectively indicate the maximum on-time and the minimum on-time of the first switching element 201 used in the temperature control of this embodiment. Further, f max and f min indicate a maximum alternating frequency corresponding to the minimum on-time t _on min and a minimum alternating frequency corresponding to the maximum on-time t _on max, respectively.

As described above, the power supplied to the fixing device 100 increases as the on-time t _on of the first switching element 201 increases. In other words, the power supplied to the fixing device 100 increases as the alternating frequency f decreases. In this embodiment, the maximum on-time t _on max is 25 μsec, the minimum on-time t _on min is 1.5 μsec, and the on-time t _on is PWM controlled by the driver circuit 402 in 256 stages. The switch-off time t _off of the first switching element 201 is fixed at 17 μsec. If replaced with the alternating frequency of the alternating current, the minimum alternating frequency f min is 23.8 kHz, and the maximum alternating frequency f max is 54.1 kHz, and these frequencies are controlled to be variable in 256 steps.

  In the shaded area, when power is supplied to the fixing device 100 at an alternating frequency included in this frequency band, resonance of the fixing film 10 occurs, resulting in an image defect level or abnormal noise level. Indicates a frequency band that is problematic in practice. This shaded area is referred to herein as a resonance frequency band. The resonance frequency band in the fixing device configuration of the present embodiment was 29 to 31 kHz centering on about 30 kHz.

  FIG. 19 is a schematic diagram showing, in time series, changes in the alternating frequency of the alternating current during the image forming operation in the case of conventional temperature control. The hatched area indicates the resonance frequency band in which the fixing film 10 resonates, as in FIG.

  “Warm-up” refers to a state where the temperature of the fixing film 10 is raised to a target temperature at which the fixing film 10 can be fixed after the image forming operation is started, and it is necessary to supply maximum power in order to quickly raise the temperature of the fixing film 10. The induction heating power source 400 outputs an alternating current having the maximum on-time of the first switching element 201, that is, the minimum alternating frequency fmin, in accordance with the calculation result of the feedback control circuit 401 as the temperature control means. After the temperature of the fixing film 10 reaches the vicinity of the target temperature, the induction heating power source 400 reduces the on-time of the first switching element 201 to an appropriate value according to the calculation result of the feedback control circuit 401, that is, the alternating frequency is appropriately set. Increase the value so that the temperature of the fixing film 10 does not overshoot.

  “During printing” refers to a state in which a medium as a recording material is actually passed through the fixing device 100, and in order to maintain the fixing film 10 at a target temperature, appropriate power supply is required as needed. According to the calculation result of the feedback control circuit 401 as the temperature control means, an alternating current having an optimal frequency is appropriately output in the range of fmax to fmin. Actually, the power necessary for the fixing process gradually decreases as components such as the pressure roller 30 of the fixing device 100 are warmed as the number of passing sheets advances, and as a result, they are used. The alternating frequency f also tends to increase gradually with time.

  During the image forming operation, the alternating frequency f used changes with time. In this process, when the alternating frequency f reaches the resonance frequency band indicated by diagonal lines, the fixing film 10 is subjected to electromagnetic force corresponding to the alternating frequency. Resonance occurs. In the temperature control of the conventional example, when the alternating frequency enters the resonance frequency band, a sound wave having a frequency that is ½ of the alternating frequency may be generated. When the frequency of this sound wave is in the human audible range, the fixing film 10 may cause the user to be uncomfortable as an abnormal sound. In this example, when the alternating frequency reached 30 kHz, a relatively high-pitched sound wave of 15 kHz was heard. In addition, under conditions where the electrostatic adsorption force of unfixed toner to the paper cannot be sufficiently secured, the unfixed toner may be scattered due to resonance of the fixing film 10 and the image may be disturbed, resulting in a decrease in image quality. It was. In particular, the longer the time during which the alternating frequency f stays in this alternating frequency band, the worse the phenomenon.

  In order to solve the above problems, the present invention is characterized in that the temperature of the fixing film 10 is controlled at an alternating frequency f excluding the resonance frequency band. Hereinafter, temperature control of the fixing film 10 in this embodiment will be described.

FIG. 11 shows the relationship between the on-time t _on of the first switching element 201 and the alternating frequency f in the temperature control of this embodiment. The horizontal axis represents the on time t _on of the first switching element 201, and the vertical axis represents the alternating frequency f.

f1 is a frequency slightly lower than the resonance frequency band. Below this frequency, f1 indicates a frequency at which image defects or abnormal sounds due to resonance of the fixing film 10 do not cause a problem in practice. Similarly, f2 is a frequency that is slightly higher than the resonance frequency band. Above this frequency, f2 indicates a frequency at which image defects or abnormal sounds due to resonance of the fixing film 10 do not cause a problem in practice. t _on 1 and t _on 2 are ON times of the switching elements corresponding to the alternating frequencies f1 and f2, respectively.

  In the temperature control of the present invention, in order to avoid resonance of the fixing film 10, the alternating frequency of the alternating current is varied while avoiding the frequency band from f1 to f2 including the resonance frequency band. That is, the alternating frequency f of the alternating current output from the induction heating power source in this embodiment is a frequency from fmin to f1 and a frequency from f2 to fmax.

In the region where the alternating frequency f is less than f1 and the region where the alternating frequency is more than f2, the temperature is changed by changing the alternating frequency f by changing the on time t _on with the off time t _off constant as in the conventional temperature control. Take control. However, the alternating frequency f between f1 and f2 is not used for the temperature control of this embodiment. Simply removing the alternating frequency between f1 and f2 from the temperature control makes it impossible to output the power corresponding to the alternating frequency f between f1 and f2, and the controllability of the temperature control deteriorates. Therefore, this embodiment is characterized in that power corresponding to a frequency between f1 and f2 is pseudo-output by performing duty control by alternately using two types of alternating frequencies f1 and f2.

In this embodiment, the maximum on time t _on max is 25 μsec, the minimum on time t _on min is 1.5 μsec, and the off time t _off is fixed at 17 μsec. If replaced with an alternating frequency of the alternating current, the minimum alternating frequency f min is 23.8 kHz, and the maximum alternating frequency f max is 54.1 kHz. The alternating frequency is controlled to be variable between the maximum and minimum frequencies except for the frequency band between f1 and f2. Further, t _on 1 was set to 19 μsec and t _on 2 was set to 14 μsec as the on time corresponding to the frequencies f1 and f2 used for duty control. If these are converted to frequencies, f1 is 27.8 kHz, f2 is 32.3 kHz, and the resonance frequency band around 29 to 31 kHz is set not to be used.

FIG. 12 shows a schematic diagram of duty control using two types of alternating frequencies. The horizontal axis represents time, and the vertical axis represents alternating frequency. T _f1 indicates the time for output at the alternating frequency f1, and T _f2 indicates the time for output at the alternating frequency f2.

By alternately outputting the alternating frequencies f1 and f2 every T _f1 time and T _f2 time, respectively, it is possible to artificially output the power of the frequency corresponding to the middle between f1 and f2.
It is better to set the duty cycle T _f1 + T _f2 to be shorter in order to ensure more accurate controllability. However, it is necessary to set the duty cycle T _f1 + T _f2 so that the frequency (1 / T _f1 + T _f2 ) of the duty control itself does not enter the resonance frequency band.

Further, in the power control method of this embodiment in which power is controlled by the on-time of the switching element, the output time T _f1 of the alternating frequency _f1 and the time T _f2 of the alternating frequency f2 are shorter than the switching period of each alternating frequency. It is better not to. That is, T _f1 must be set at least t _on 1 + t _off of the switching period of f1, and T _f2 must be set at least t _on 2 + t _off of the switching period of f2.

In this embodiment, T _f1 is set to 20 msec, T _f2 is set to 20 msec, and the duty ratio is set to 1: 1. That is, the frequency by the duty control is 25 Hz. Therefore, at the time of duty control, it is possible to output power substantially in the middle of the power of f1 and f2.

  A plurality of duty ratios may be set. As the number of set duty ratios increases, finer power settings can be made, so that the controllability of temperature control can be improved.

Further, the duty cycle T _f1 + T _f2 is not limited to a fixed value. When a plurality of duty ratios are set, the duty cycle may be variable within a range in which the frequency of the duty control itself does not enter the resonance frequency band.

  Further, two or more alternating frequencies used for duty control may be set. In the duty control of this embodiment, two types of alternating frequencies f1 and f2 are used. However, the frequency is not limited to two types, and two or more types of alternating frequencies may be used as long as the frequency is outside the resonance frequency band. good.

  FIG. 13 is a schematic diagram showing, in time series, changes in the alternating frequency of the alternating current during the image forming operation in the case of the temperature control of this embodiment. A hatched area indicates a resonance frequency band in which the fixing film 10 resonates.

  When the alternating frequency used for temperature control reaches the region between f1 and f2 including the resonance frequency band, duty control is activated, and temperature control is performed by alternately outputting the frequencies f1 and f2 deviating from the resonance frequency. . Compared with FIG. 19 in the case of the conventional temperature control, the alternating frequency used for the temperature control does not stay within the resonance frequency band, and the temperature is always controlled outside the resonance frequency band. Can be suppressed.

  In the conventional example, a high-pitched sound in the vicinity of 15 kHz was heard in the early stage of “printing”, but when the temperature control of this embodiment was applied, no abnormal sound from the fixing device was heard from the start to the end of printing. It was confirmed. Further, it was confirmed that there was no image defect in which the toner image was scattered.

When the alternating frequency transitions from f1 or less to f2 or more, or conversely, in the process of transition from f2 or more to f1 or less, the resonant frequency band is instantaneously traversed. Since it is short, problems such as abnormal sounds and image defects do not occur substantially.
By the above control, resonance of the fixing film 10 due to the alternating current can be suppressed, so that abnormal noise and image defects due to resonance can be prevented at low cost.

<Second embodiment>
The second embodiment of the present invention will be described below. Since the schematic configuration of the image forming apparatus and the schematic configuration of the heating device in the present embodiment are the same as those in the first embodiment, description thereof will be omitted. Further, regarding the induction heating power source and the temperature control, the description of the same parts is omitted.

  Regarding the induction heating power source of the present embodiment, the difference from the first embodiment is that the off time of the first switching element 201 is fixed in the first embodiment, but is variable in the present embodiment. Is a point. That is, the alternating frequency of the alternating current can be changed by both the on time and the off time of the first switching element 201.

Next, temperature control of the present embodiment will be described.
FIG. 14 shows the relationship between the on-time t _on of the first switching element 201 and the alternating frequency f in the temperature control of this embodiment. The horizontal axis represents the on time t _on of the first switching element 201, and the vertical axis represents the alternating frequency f.

f1 is a frequency slightly lower than the resonance frequency band, and indicates a frequency at which an image defect or abnormal noise due to resonance of the fixing film 10 does not cause a problem in practice below this frequency. Similarly, f2 is a frequency slightly higher than the resonance frequency band. Above this frequency, f2 indicates a frequency at which image defects or abnormal noise due to resonance of the fixing film 10 does not cause a problem in practice. t _on 1 and t _on 2 are ON times corresponding to the alternating frequencies f1 and f2, respectively.

In the temperature control of this embodiment, in order to avoid the resonance of the fixing film 10, the alternating frequency of the alternating current is varied by avoiding the frequency band from f1 to f2 including the resonance frequency band. When the alternating frequency f is equal to or less than f1, and when the alternating frequency is equal to or greater than f2, the alternating frequency f is changed by changing the on time t _on with the off time t _off constant as in the conventional temperature control. In between alternating frequency f from f1 f2, by off-time t _off is also changed, and controls the switching period as an alternating frequency f does not fall within the resonance frequency band. In this embodiment, control is performed so as to avoid the resonance frequency band by adjusting the change amount of the on time with the off time t _off and keeping the alternating frequency at f1.

For example, when the on time is decreased from the state of t _on 1 indicated by the arrow A, if the off time t _off is fixed as in the temperature control of the conventional example, the frequency is higher than f1 from the equation (1). It increases and enters the resonance frequency band. Therefore, the increase in the alternating frequency can be suppressed by extending the off time by the amount by which the on time is decreased from t _on 1. Since the ON time t _on for determining the power supply amount to the fixing device 100 can be varied as in the conventional example over the entire frequency from fmin to fmax, it is controlled rather than the duty control as in the first embodiment. Sex is good.

In this embodiment, the maximum on-time t _on max of the first switching element is 25 μsec, the minimum on-time t _on min is 1.5 μsec, and this is 17 μsec in the region where the off time t _{off is} constant. When replaced with the alternating frequency of the alternating current, the minimum alternating frequency f min is 23.8 kHz, and the maximum alternating frequency f max is 54.1 kHz, and these frequencies are controlled to be variable. In addition, t _on 1 was set to 19 μsec and t _on 2 was set to 14 μsec as a region in which the off time is variable. That the off time t _off is variable between from 27.8kHz alternating frequency f1 to the 32.3kHz of f2, in this period are made variable in the off-time t _off from 17μsec to 22Myusec.

Next, FIG. 15 shows the control state of the switching elements having alternating frequencies indicated by arrows A and B in FIG. The horizontal axis represents time, and the vertical axis represents the switch state of the first switching element 201. The on-times of the switching elements corresponding to the alternating frequencies f1 and f2 are t _on 1 and t _on 2, respectively, and the switch-off time, that is, the off-time is t _off 1 and t _off 2. Here, there is a relationship of t _on 1> t _on 2.
The switching period of the alternating frequency f1 indicated by the arrow A in FIG. 14 is t _on 1 + t _off 1. This is shown in FIG. Further, the switching cycle of the alternating frequency f1 indicated by the arrow B in FIG. 14 is t _on 2 + t _off 2. This is shown in FIG.

Since the alternating frequencies of arrow A and arrow B are the same at f1, the relationship of equation (2) is established.
t _on 1 + t _off 1 = t _on 2 + t _off 2 (2)
Here, if the difference between t _on 1 and t _on 2 is Δt and t _on 2 = t _on 1−Δt, the relationship between t _off 1 and t _off 2 is expressed by equation (3) from equation (2). Be represented
t _off 2 = t _off 1 + Δt (3)

  That is, by adding a decrement of the on-time to the off-time, or conversely, reducing the increment of the on-time from the off-time, the switching period can be made constant and the alternating frequency can be kept constant. Therefore, even if the on-time of the first switching element 201 is changed, temperature control is performed with an alternating current having a frequency that avoids the resonance frequency band by simultaneously changing the off-time so that the alternating frequency becomes a frequency other than the resonance frequency band. can do.

  In this embodiment, control is performed so that the frequency is constant in a region where the alternating frequency does not enter the vicinity of the resonance frequency band, but it is not necessary to be constant, and even if the alternating frequency is out of the resonance frequency band, it may be variable. good.

  FIG. 16 is a schematic diagram showing, in time series, changes in the alternating frequency of the alternating current during the image forming operation in the case of the temperature control of the present embodiment. A hatched area indicates a resonance frequency band in which the fixing film 10 resonates.

  When the alternating frequency used for temperature control reaches the region between f1 and f2 including the resonance frequency band, the off time becomes variable, and the temperature control is performed at the alternating frequency f1 outside the resonance frequency band. Compared with FIG. 18 in the case of the conventional temperature control, the alternating frequency used for the temperature control does not stay within the resonance frequency band, and the temperature is always controlled when it deviates from the resonance frequency band. Therefore, temperature control can be performed while suppressing resonance of the fixing film 10.

  In the conventional example, a high-pitched sound in the vicinity of 15 kHz was heard in the early stage of “printing”, but when the temperature control of this embodiment was applied, no abnormal sound from the fixing device was heard from the start to the end of printing. It was confirmed. Further, it was confirmed that there was no image defect in which the toner image was scattered.

  The alternating frequency instantaneously crosses the resonance frequency band in the process of transition from a frequency of f1 or lower to a frequency of f2 or higher, and vice versa. Since the frequency transition time of the switching element is short, problems such as abnormal sounds and image defects did not occur substantially.

In this embodiment, since the ON time t _on of the switching element can be continuously variable as before, the accuracy is higher than that of the first embodiment in which the ON time t _on of the switching element is controlled discontinuously by duty control. High temperature control can be performed.

  By the above control, the resonance of the fixing film 10 due to the alternating current can be suppressed, so that noise and image defects due to the resonance can be prevented at low cost without impairing the controllability of the temperature control.

<Other embodiment examples>
1) The electromagnetic induction heat-generating fixing film 10 may be in a form in which the elastic layer 2 is omitted in the case of heat fixing such as a monochrome or one-pass multi-color image. The heat generating layer 1 can also be configured by mixing a metal filler into a resin. It can also be a member of a single heating layer.
2) The fixing film 10 is not an endless rotating member. For example, the fixing film 10 may be a long end web member wound in a roll, and the apparatus may be configured such that the fixing film 10 is fed and moved.
3) The pressure member 30 is not limited to a roller body, and may be a member of another form such as a circular belt type. Further, in order to supply thermal energy from the pressing member 30 side to the recording material, a heating unit such as electromagnetic induction heating is also provided on the pressing member 30 side to control the heating temperature to a predetermined temperature. You can also.
4) The heating device of the present invention is not limited to the image heating and fixing device of the embodiment, but is assumed to be an image heating device that heats a recording material carrying an image to improve the surface properties such as gloss. It can be widely used as a means / device for heat-treating a material to be heated, such as an image heating device, a heating / drying device for a heated member, a heating laminating device, a heating / pressurizing wrinkle removing device.

It is a cross-sectional side model figure of the principal part of the heating apparatus of a 1st Example. It is a front model figure of the principal part. It is the longitudinal front model figure of the principal part. It is a perspective model figure of the half body of the film guide member of the right side which arrange | positioned and supported the magnetic field generation | occurrence | production means inside. It is the figure which showed the relationship between a magnetic field generation means and the emitted-heat amount Q. It is a layer structure model figure of an electromagnetic induction exothermic fixing film. It is a layer structure model figure of an electromagnetic induction exothermic fixing film. It is the graph which showed the relationship between the heat generating layer depth and electromagnetic wave intensity. It is a whole block diagram of an induction heating power supply including a heating device and temperature control means. It is a figure which shows the principal part of the excitation circuit of an induction heating power supply. It is a figure which shows the relationship between the ON time t _on of the switching element in the temperature control of a 1st Example, and the alternating frequency f. It is a figure which shows the duty control using the two types of alternating frequency in a 1st Example. It is the schematic diagram which showed the change of the alternating frequency at the time of image formation operation | movement in the temperature control of 1st Example in time series. It is a figure which shows the relationship between the ON time t _on of the switching element in the temperature control of a 2nd Example, and the alternating frequency f. It is a figure which shows the control state of the switching element of the alternating frequency shown by the arrow A and arrow B in FIG. It is the schematic diagram which showed the change of the alternating frequency at the time of image formation operation | movement in the temperature control of 2nd Example in time series. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to a first embodiment. It is a figure which shows the relationship between the ON time t _on of the switching element in the temperature control of a prior art example, and the alternating frequency f. It is the schematic diagram which showed the change of the alternating frequency at the time of image formation operation | movement in the temperature control of a prior art example in time series.

Explanation of symbols

1 Heat generation layer 10 Fixing film (heating member)
18 Excitation coil (magnetic field generating means)
26 Thermistor (temperature sensing element)
30 Pressure roller (Pressure member)
100 Fixing device (heating device)
201 1st switching element (switching means)
205 Second switching element 300 Induction heating power supply 307 Excitation circuit 400 Temperature control means 401 Feedback circuit 402 Drive circuit N Fixing nip P Recording material

Claims (2)

A heating member having a heat generation layer; an excitation coil that generates magnetic flux for generating eddy currents in the heat generation layer; and a switching element that switches an energization on state and an energization off state to the excitation coil. A power supply for supplying an alternating current having a frequency determined by a time and a time of the energization off state to the exciting coil, a temperature detecting means for detecting the temperature of the heating member, and the frequency based on the detected temperature of the temperature detecting means. A temperature control means for controlling the temperature of the heating member by controlling, and a fixing device that heat-fixes the toner image on the recording material on the recording material using heat generated in the heat generating layer.
A specific frequency band that is not set regardless of the detected temperature of the temperature detecting means is provided between the maximum value and the minimum value of the frequency controlled by the temperature control means, and the detected temperature of the temperature detecting means is When the detected temperature corresponds to a specific frequency band, the current corresponding to the detected temperature is controlled by controlling so that currents having a frequency higher and lower than the frequency of the specific frequency band are alternately supplied to the exciting coil. Is supplied to the exciting coil . A heating member having a heat generation layer; an excitation coil that generates magnetic flux for generating eddy currents in the heat generation layer; and a switching element that switches an energization on state and an energization off state to the excitation coil. A power supply for supplying an alternating current having a frequency determined by a time and a time of the energization off state to the exciting coil, a temperature detecting means for detecting the temperature of the heating member, and the frequency based on the detected temperature of the temperature detecting means. A temperature control means for controlling the temperature of the heating member by controlling, and a fixing device that heat-fixes the toner image on the recording material on the recording material using heat generated in the heat generating layer.
A specific frequency band that is not set regardless of the detected temperature of the temperature detecting means is provided between the maximum value and the minimum value of the frequency controlled by the temperature control means, and the detected temperature of the temperature detecting means is When the detected temperature corresponds to a specific frequency band, a current having a frequency outside the specific frequency band is obtained by changing the time in the energized off state while setting the time in the energized on state as the time corresponding to the detected temperature. A fixing device, wherein a current corresponding to the detected temperature is supplied to the exciting coil by performing control so as to be supplied to the exciting coil .

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