JPH0822206A - Heating device and image forming device - Google Patents

Abstract

PURPOSE:To provide a device of high reliability capable of controlling a temperature with stability and high accuracy and without causing overshooting and also capable of securing safety, as to a magnetic induction heating system heating device. CONSTITUTION:As for the magnetic induction heating system heating device, a material to be heated 12 is heated by a heat generated by a magnetic metallic member 7 due to an eddy current generated in the magnetic metallic member 7 when a magnetic field is applied on the magnetic metallic member 7 by a magnetic field generating means 6, the device is provided with a current measuring circuit for measuring the exciting current waveform of an exciting coil of the magnetic field generating means 6 and a circuit for measuring a cycle based on an induction voltage induced by the exciting coil.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic (electromagnetic) induction heating type heating device and an image forming apparatus provided with the heating device as an image heating device.

[0002]

2. Description of the Related Art Conventionally, a recording material heating device for heating and fixing an image, that is, an image of a copying machine, a laser beam printer, a facsimile, a microfilm reader printer, an image display (display) device, a recording machine, etc. In the forming device, a recording material (electrofax sheet, electrostatic recording sheet, transfer material sheet, transfer material sheet A visible image (unfixed toner image) corresponding to the target image information formed on the surface of the printing paper or the like by a direct method or an indirect (transfer) method as a permanently fixed image on the surface of the recording material carrying the image. A heat roller type device is widely used as an image heating and fixing device (image heating device) for performing heat fixing processing.

This heat roller type apparatus basically comprises a roller pair of a heating roller (fixing roller) and a pressure roller which are pressed against each other and rotate, and a recording in which an unfixed toner image is supported in a pressure contact nip portion of the roller pair. An unfixed image is heated and pressure-fixed on the surface of the recording material by introducing the material and nip-conveying it.

The heating roller generally comprises an aluminum metal roller as a base, a heat-resistant rubber is coated on the outer periphery of the base as an upper layer, and a halogen heater is disposed inside as a heat source.
The electric power supplied to the halogen heater, which is a heat source, causes the heater to generate heat and emit light, and the heat radiates and convects the aluminum metal roller that is the base of the heating roller. The aluminum metal roller, which is the roller base, serves to conduct the received heat to the entire roller without any temperature difference.

The roller having a uniform temperature distribution in this way heats and melts the unfixed toner on the recording material via the heat-resistant rubber coated on the upper layer, so that the unfixed toner is impregnated into the recording material medium and fixed. It is a thing.

Generally, a halogen heater which is a heat source is a glass-sealed elongated rod-shaped halogen heater, which is passed through the hollow portion in the center of the roller.
This is a configuration in which an alternating current power supply (line input power supply) supplies a current through a switching control element to heat the roller.

Therefore, the heating roller temperature control is performed by detecting the roller temperature by a temperature detecting element arranged in the vicinity of the roller, generally a thermistor thermosensitive element, and by a switching element provided between the AC power source and the halogen heater, for example, a triac. The on / off control is performed so that the target constant temperature can be obtained.

FIG. 15 shows a general schematic structure of an image heating and fixing device as such a heating device of a heat roller type.

From the image forming mechanism side (not shown), the conveyor belt 13
As a result, the recording material 12 as a material to be heated, which supports the unfixed toner image, becomes the heating roller 10 and the pressure roller 11 of the apparatus.
It is conveyed and introduced into a pressure contact nip portion (fixing nip portion).

The heating roller 10 and the pressure roller 11 start to rotate when the recording material 12 is conveyed by the conveyor belt 13 and the motor 15 starts driving based on the signal detected by the sensor 16.

Then, the recording material 12 is conveyed to the pressure contact nip portion between the heating roller 10 and the pressure roller 11, is heated and pressed in the nip portion, is discharged, and passes through the sensor 17. After that, the signal of the sensor 17 changes from on to off, and the driving of the motor 15 is stopped.

The heating of the recording material 12 at the nip portion is performed by supplying electric power to the halogen heater H contained in the heating roller 10 to generate heat, and the heating roller 10 is heated by the heat.

The energization of the halogen heater H is controlled so that the resistance value of the thermistor 9, which is a temperature detecting element provided in contact with the surface of the heating roller, is constant with respect to a reference value. As a result, the heating roller 10 maintains the temperature necessary for fixing and is configured to perform good fixing.

However, if the temperature of the heating roller 10 is constantly maintained at the temperature required for fixing, power consumption increases and abnormal heating of the roller may occur. Therefore, in the above apparatus, when the roller is stopped. The temperature is controlled to be lower than that during rotation.

This temperature control will be described. FIG. 16 shows an example of the temperature control circuit and the roller drive circuit of the heating roller 10.

Reference numeral 6 denotes a first A / D converter, which is a voltage VT obtained by the voltage dividing ratio of the thermistor 9 and the resistor R1.
To obtain the digital value S11.

Reference numeral 27 is a second A / D converter for obtaining a digital value S12 from the control target voltage Vref1.

Reference numeral 28 is a third A / D converter for obtaining a digital value S13 from the control target voltage Vref2.

That is, the first A / D converter 6 detects the actual temperature of the heating roller 10, the second A / D converter 27 detects the reference temperature of the fixing device, and the third A / D converter 28 detects the roller. This is for detecting the reference temperature when stopped.

The first A / D converter 6 and the second A / D
Digital values S11, S12, and S13 output by the converter 27 and the third A / D converter 28 are input to the control unit 21.

As shown in Table 1, the controller 21 controls the sensor 1
The motor 15 is controlled to be turned on / off by the control signal S11 according to the input of 6/17, and the digital value S12 /
By selectively selecting and inputting S13, the halogen heater H is turned on / off.

The control of the halogen heater H is performed via the power supply pattern generator 3. The power energization pattern generator 3 outputs a heater control signal S4 to the heater drive circuit 4 based on the energization pattern signal S3 of the control unit 21, and the heater drive circuit 4 outputs the halogen heater H based on the heater control signal S5. AC drive.

[0023]

[Table 1] Next, the operation of the above control circuit will be described. First, when the recording material 12 is not conveyed to the apparatus, the sensors 16 and 17 are in the off state, and the control unit 21
Turns off the control signal S10 of the motor 15 as shown in Table 1, and outputs the signal S12 from the second A / D converter 27.
The temperature is controlled with reference to.

The signal S12 is a control target voltage Vre corresponding to a temperature lower than a temperature suitable for fixing the recording material 12.
This is a digital value of f1, and the temperature of the heating roller 10 is maintained at the temperature T1 as shown in FIG.

When the recording material is conveyed to the apparatus,
First, the sensor 16 is turned on, but the control unit 21 turns on the signal S10 to the motor 15 as shown in Table 1, and the third
The temperature control is performed with reference to the signal S13 from the A / D converter 28.

This signal S13 is a digital value of the control target voltage Vref2 corresponding to the temperature suitable for fixing, and the temperature of the heating roller 10 becomes the temperature T2 as shown in FIG.

Further, while the sensor 16 or 17 is on, the recording material is in the vicinity of the roller, so that the control unit 21
Turns on the signal S10 to the motor 15 as shown in Table 1 and uses the signal S13 from the third A / D converter 28 as a reference. As a result, the temperature of the heating roller 10 becomes T2 above.
And good fixing is realized.

The above operation will be described with reference to the flowchart of FIG. First, the states of the sensors 16 and 17 are judged (step 201), and the sensor 16 or the sensor 1 is detected.
When any one of 7 is on or both sensors are on, the signal S10 to the motor 15 is turned on (steps 201 to 201).
202).

Then, S13 is selected as a signal serving as a reference for temperature control (step 203).

On the other hand, when both the sensors 16 and 17 are off, the signal S10 to the motor 15 is turned off (steps 201 to 204), and S12 is selected as a reference signal for temperature control (step). 205).

After the reference signal for temperature control is selected as described above, temperature control is performed based on the selected signal (step 206).

However, since the heating roller 10 of the above-mentioned conventional heating roller type heating device is constructed so that the heating roller 10 is heated by the rod-shaped halogen heater H contained therein, the control method is the switching provided between the AC power source and the heater. An on / off control method is adopted by a control element such as a triac.

Therefore, when such a configuration is performed, first,
Since the heating roller 10 is lower than the target temperature when the power is turned on, the control circuit turns on the switching element to supply the maximum power.

When such control is performed, the temperature control feedback circuit is in a state in which the triac is on while the detected value is lower than the target temperature, so that the temperature rises and reaches the vicinity of the target temperature. Even if it happens, since the control circuit keeps the switching control element on-hold, it continues to supply the same maximum power as when starting up.

In such a control system, even if the switch is turned off when the temperature reaches the target temperature, the large electric power supplied up to that point far exceeds the target temperature and causes an overshoot. It has been reported that such overshooting occurs at about 5% of the target temperature when the above-mentioned simple control means is performed.

Assuming that the overshoot of 5% (the temperature is 7
(About 8 degrees) is not a serious problem in a normal electrophotographic process, but, for example, in a color electrophotographic process, a fixing device performs mixed color development of toners of different colors, which is a large factor in image quality. It has been confirmed that accurate temperature control is an essential technical issue.

Further, since the high-temperature halogen heater H is used, it is required that the high-temperature support member and the heat insulation be properly performed when the structure for supporting and fixing the high-temperature halogen heater H is used, which is expensive and highly accurate. It becomes a design.

Regarding the temperature overshoot, for example, the well-known PI is known from the temperature information from the temperature sensor.
It is considered that the overshoot can be practically prevented by obtaining the control amount by the operation of the D control method and obtaining the obtained result as the conduction time of the switching element.

However, due to the constitution of the fixing device as described above, and the heater H is arranged at a central portion which is considerably distant from the base roller metal of the heating roller to which heat is to be transferred, the thermal resistance before reaching the roller is high. Also, due to the heat capacity of the roller, the heat model has a very complicated structure and the analysis becomes difficult. At least not at the level of simple primary transmission.

This is a structure in which heat is introduced to a recording material as a material to be heated through a path such as heater → heater glass tube → internal space (radiation, convection) → roller base → heat resistant rubber. It is considered that this is due to the presence of a plurality of temporary heat storage systems (roller base and heat resistant rubber).

When temperature control is performed by detecting the temperature of the heating roller surface with the above configuration, since the transfer function until heat is conducted to the roller surface, the heater and the roller surface temperature are turned on with a temperature difference of several hundred degrees. The control is performed so that the roller surface temperature is kept constant as a result.

In such a model, the control is established by one cycle of the heat transfer path: heater → heater glass tube → tube inner space (radiation, convection) → roller base → heat resistant rubber fulfill a sufficient time integration function. As a result, the result is that the input power is operated so as to obtain a constant temperature even if the input power is controlled at a relatively slow level.

However, regarding the controlled object as described above,
In order to perform ideal temperature control, it is necessary to change the control method each time due to various factors related to the model when not passing the normal paper, during the paper passing, paper quality, ambient temperature, and other temperature. Will end up. That is, there is a technical problem that high-precision control cannot be performed unless conditions such as printing, standby, paper quality control, and ambient temperature are constantly sensed and complicated control is performed while operating control parameters. .

Further, since it is basically on / off control, if the relationship between the heat storage system of the roller, the heater power, and the set temperature cannot be matched, suppression of temperature ripple cannot be expected.

On the other hand, there is also a magnetic induction heating type heating device. Japanese Patent Publication No. 5-9027 proposes to generate eddy current (eddy current) in a heating roller (fixing roller) as a heating member by magnetic flux to generate heat by Joule heat.

By utilizing the generation of the eddy current as described above, the heat generation position can be brought closer to the toner, and the warm-up time can be shortened as compared with the heat roller system using the halogen lamp.

Further, the present inventors have a heating body and a heat resistant film (heat resistant carbon material etc.) that moves in close contact with the heating body. The material to be heated is brought into close contact with the heating body through this film. Is a film heating type heating device that moves the position of the heating element together with the film to apply the heat energy of the heating element to the material to be heated through the film. The heating element is a magnetic metal member (induction magnetic material, magnetic field absorption) Conductive material, conductive material)
And a magnetic field generation coil, a high-frequency switching current is applied to the magnetic field generation coil, the generated high-frequency magnetic field is magnetically coupled to the magnetic metal member, and the eddy current loss caused by magnetism causes the magnetic metal member to generate heat. We have been researching magnetic induction heating type and film heating type heating devices that transfer heat to the material to be heated through the film.

Further, the film itself as a heating member is made of a magnetic metal member to generate heat by magnetic induction heating, so that the film does not become a thermal resistance so that the thermal efficiency is improved and thus the magnetic induction heating system / film heating system. Have been researching heating devices.

This is to change the magnetic field generated by a magnetic field generating means, for example, a magnetic material by combining an exciting coil with a core material which is a magnetic body. That is, an eddy current is generated in the magnetic metal layer in the film by applying a high frequency to the coil and repeating the generation and disappearance of the magnetic field in the film as a magnetic metal member that moves in the generated magnetic field. This eddy current is converted into heat (Joule heat) by the electric resistance of the magnetic metal layer, and as a result, only the film as a heating member that comes into close contact with the material to be heated generates heat, and the thermal efficiency is excellent.

That is, when a fluctuating magnetic field traverses the conductor, an eddy current is generated in the magnetic metal member (conductive layer) of the film so as to generate a magnetic field that prevents the change of the magnetic field. Due to the skin resistance of the magnetic metal member of the film, this eddy current causes the magnetic metal member of the film to generate heat with power proportional to the skin resistance.

As described above, since heat is directly generated near the surface layer of the film as the heating member, there is an advantage that heating can be performed rapidly regardless of the thermal conductivity and heat capacity of the film base layer. In addition, rapid heating that does not depend on the film thickness can be realized.

As a result, it is possible to increase the thickness and rigidity of the film base layer without impairing the energy saving and quick start properties, and to cope with the durability and speeding up.

[0053]

The present invention enables stable and highly accurate temperature control without overshoot and secures safety, especially in the latter magnetic induction heating type heating device. It is intended to provide a highly reliable device.

[0054]

The present invention is a heating device and an image forming apparatus characterized by the following configurations.

(1) A magnetic induction heating type heating device in which a magnetic field is applied to the magnetic metal member by the magnetic field generating means to heat the material to be heated by the heat generated in the magnetic metal member by the eddy current generated in the magnetic metal member. A heating device having a current measuring circuit for measuring an exciting current waveform of an exciting coil of a magnetic field generating means and a circuit for measuring a cycle from an induced voltage induced in the exciting coil.

(2) A comparison circuit for comparing the current measurement value detected by the current measurement circuit with a predetermined set value, the period obtained from the induced voltage, and the excitation voltage waveform according to each value. Is characterized by changing (1)
The heating device according to.

(3) At least one of the members used in the magnetic path forming means has a Curie point lower than that of the member having the lowest heat resistant temperature. The heating device according to (1) or (2), characterized in that

(4) The heating device according to any one of (1) to (3), wherein the magnetic metal member is a fixed member, or a rotating member or a traveling / moving end member.

(5) The heating device according to any one of (1) to (4), wherein the magnetic metal member is a laminated member including a magnetic metal layer, or a member of magnetic metal itself.

(6) The heating device according to any one of (1) to (5), which has a pressing member for directly or indirectly adhering the material to be heated to the magnetic metal member.

(7) The pressing member is a pressing rotary member that is rotationally driven or driven to rotate (6)
The heating device according to.

(8) The material to be heated is a recording material carrying an image to be heat-treated, and is an image heating device for heating the image on the material to be recorded (1) to (7). )
The heating device according to any one of 1.

(9) An image forming apparatus comprising the heating device according to any one of (1) to (8) as an image heating device.

[0064]

According to the present invention, the magnetic induction heating type heating device enables stable and highly accurate temperature control without control temperature ripples and overshoots, and ensures safety and high reliability. Can be obtained.

That is, in the present invention, since the amount of magnetic flux is controlled as a control target, the ripple of the control temperature is minimized by making the power control linear and stepless by the switching pulse control method. .

Further, the direct heating method in which heat is generated by the high frequency induction magnetic field is adopted, and as a result, the response of the temperature of the heating body (magnetic metal member) can be said to be the response of the primary component. Therefore, when feedback control is performed based on the temperature information from the temperature detection (for example, thermistor), the temperature control process of the system is extremely stable, and the stability is improved by the simple configuration (proportional + integral control by operational amplifier etc.). It is possible to obtain a control result of high (less temperature ripple).

By the control method performed as described above, it becomes possible to provide a control means for the heating element temperature that is faithful to the target temperature.

Therefore, if the image heating (fixing) control is performed in such a system having a good followability, the theme is to shorten the warm-up time, which is the most required function of the fixing device. Will come.

Therefore, by heating the metal foil or the like vapor-deposited on the film and supplying the temperature to the heating medium, high-speed rising characteristics can be realized.

On the other hand, since the speed is too fast, even if for some reason, for example, foreign matter or the like is mixed into the film and the exciting circuit, and a gap is generated,
Although this should not be the case, a cycle detection circuit that monitors the resonance state even when the temperature sensor is separated from the detection body, and the temperature value by the temperature sensor and the value of the switching current are detected. A highly reliable heating device can be realized by providing a corresponding exciting voltage waveform to the exciting coil.

Since the heating method is based on the magnetic induction of the magnetic metal member, it is possible to realize a very monotonous structure of the heat transfer model from the heat source. Moreover, the high-speed heating when used in the film heating method or the like can be performed immediately. It is necessary to make an abnormality determination, and based on the abnormality determination, the circuit was stopped in advance to ensure safety.

Further, as a temperature detecting method, a method of detecting the temperature dependence of resistivity of metal by magnetic field coupling is used, so that the temperature can be controlled without providing a sensor or wiring on the high heat element (magnetic metal member). Thus, it is possible to obtain a stable fixing temperature without overshoot by improving the reliability and detecting voltage of the element as it is by feedback control constituted by an operational amplifier.

Further, since the controlled object is the magnetic flux and therefore continuous control can be performed by the switching pulse control, it is possible to obtain a highly accurate temperature control result with a simple feedback system.

Further, the magnetic material has a temperature dependency of magnetic permeability, which means that even if any unexpected situation occurs, a magnetic flux is generated only at a temperature below a specific Curie temperature, so that a heater is used. It is possible to provide an extremely safe heating means when compared to existing systems.

[0075]

【Example】

<Embodiment 1> (FIGS. 1 to 7) (1) Overall schematic configuration of apparatus FIG. 1 shows a magnetic induction heating type / film heating type image heating fixing apparatus (image heating apparatus) as a heating apparatus of the present embodiment. )
FIG. 2 is a side view of the schematic configuration of one example, and FIG. 2 is a perspective view of the device.

This apparatus is disclosed in JP-A-4-44075-440.
This is a so-called tensionless type device disclosed in Japanese Patent Publication No. 83, Japanese Patent Publication No. 4-204980-204984 and the like. In this tensionless type device, an endless belt-shaped or cylindrical film is used as a heat resistant film (fixing film), and at least a part of the circumference of the film is always tension-free (a state where no tension is applied). Is a device that is rotationally driven by the rotational driving force of the pressing member.

Reference numeral 1 denotes an endless (cylindrical) heat-resistant film, which comprises a field (excitation) coil unit 6 and a magnetic metal member (hereinafter referred to as a heating body metal) 7 which is a heating portion, as described later. It is fitted onto a film inner surface guide (stay) 3 including a heating body 5 which is a magnetic induction heating structure.

The inner peripheral length of the endless heat-resistant film 1 and the outer peripheral length of the guide 3 including the heating body 5 are larger than those of the film 1 by, for example, 3 mm. It fits loosely with a margin.

The film 1 has a film thickness of 100 in order to reduce the heat capacity and improve the quick start property.
A single-layer film of PTFE, PFA, FEP or the like having heat resistance of μm or less, preferably 50 μm or less and 20 μm or more, or holimide, polyamideimide, PEEK,
PTFE, P on the outer peripheral surface of the film such as PES, PPS
A composite layer film coated with FA, FEP or the like can be used.

The heating element 5 is the heating element metal 7 which is the heating section.
The side is exposed downward, and it is attached by fitting along the length of the guide to the approximate center of the lower surface of the film inner surface guide 3 with a rigid and heat-resistant cross-section made of thermosetting resin, etc. I'm holding it.

Reference numeral 2 is a pressure roller as a pressure member for forming the pressure contact nip portion (fixing nip portion) N by sandwiching the film 1 with the heating body 5 and rotating the film 1 (pressure). Member drive system).

The pressure roller 2 is composed of a core metal 2a and a heat-resistant rubber layer 2b having good releasability such as silicon rubber, and holds the film 1 with a predetermined pressing force by bearing means and biasing means (not shown). It is sandwiched and arranged in pressure contact with the lower surface of the heating element metal 7 of the heating element 5. Then, it is rotationally driven by the drive means M in the counterclockwise direction indicated by the arrow.

The rotating force of the pressure roller 2 causes a frictional force between the roller and the film outer surface to exert a rotating force on the film 1, so that the film 1 comes into close contact with the lower surface of the heating body metal 7 of the heating body 5. Sliding and rotating.

Then, in a state where the temperature of the heating element 5 rises to a predetermined level and the rotational peripheral speed of the film 1 due to the rotation of the pressure roller 2 is stabilized, the heating element 5 and the pressure roller are sandwiched with the film 1 interposed therebetween. A recording material 12 to be image-fixed as a material to be heated, which is a material to be heated, is introduced between the film 1 and the pressure roller 2 in the pressure contact nip portion N formed by the image forming portion (not shown) and together with the film 1. The heat of the heating element metal 7 of the heating element 5 is applied to the recording material 12 through the film 2 by being nipped and conveyed in the pressure contact nip portion N, and the unfixed toner image T on the recording material 12 is transferred to the recording material 12 surface. It is heated and fixed. The recording material 12 passing through the pressure nip portion N is separated from the surface of the film 1 and conveyed.

Not limited to the image heating and fixing device, for example, a device for heating a recording material carrying an image to modify the surface property such as gloss, a hypothetical wearing device, etc., and a wide range of sheet-shaped materials to be heat-treated. It can be used as a means / device for

(2) Heating Body 5 The heating body 5 is a magnetic induction heating structure composed of the field coil unit 6 and the heating body metal 7 as the heating portion. The heating body 5 is a recording material 12 as a heated material that is passed through the apparatus.
Is a laterally elongated member having a maximum width or a length dimension longer than that.

The field coil unit 6 may have various configurations, but in this embodiment, five sets of heating field (excitation) coils 100 to 104 are connected in series as shown in FIG. 1
Reference numeral 05 is a temperature detecting field coil, which will be described later. In FIG. 2, reference numeral 20 is a high frequency converter for supplying a high frequency current to the coils 100 to 105 of the field coil unit 6.

When a high-frequency current generated by the high-frequency converter 20 is applied to the field coils 100 to 104, the heating element metal 7 below the field coil unit 6 on the opposing surface.
High frequency magnetic field acts on.

When the high frequency magnetic field is applied to the heating metal 7, the magnetic flux forms a minimum magnetic resistance route in a loop loop starting from the center of the coil that gives the magnetomotive force and returning to the center of the coil. That is, a path that traces the space (μ ₀ ) and the nonmagnetic metal portion to the minimum is formed. Therefore, FIG.
Although not shown in FIG. 3, a magnetic circuit, that is, a magnetic path made of a high-permeability material through which magnetic flux is efficiently coupled to and penetrates the heating metal 7, is formed inside.

The high frequency magnetic field generated from the field coils 100 to 104 of the field coil unit 6 is applied to the heating metal 7
The heat-resistant film 1 in which the recording material 12 as a material to be heated closely adheres to the heating metal 7 by heating the heating metal 7 by magnetically coupling to the heating metal 7 by the eddy current loss caused by magnetism. Is heated through.

(3) Temperature Control System FIG. 4 shows how the high frequency converter 20 supplies the switching power to the model having such a configuration. In the figure, a commercial alternating current input from a line is double-wave rectified by a rectifier (rectifying bridge) 200 and supplied to one end of a field coil. Switching semiconductor (FET) 201 in which the supplied power is connected to the other end of the coil
Perform higher frequency switching.

Since the heating element metal 7 is magnetically coupled as described above, it can be represented by the same equivalent circuit as the switching transformer of the power supply. FIG. 5 shows the state in more detail. In FIG. 5, reference numeral 206 denotes a control IC, and a part of the circuit configuration is shown for explaining the operation.

A copper metal ring (copper ring) 106 (FIG. 3) is embedded in the surface portion of the heating metal 7 facing the temperature detecting coil 105 of the field coil unit 6. When the magnetic flux from the coil 105 is coupled to the copper ring 106,
Eddy current is generated inside the copper ring 106, and its voltage can be detected as a voltage drop of the coil 105.

Voltage detection (measurement) by the temperature detection coil 105
FIG. 4 shows the circuit A that does. An AC sine wave constant current is applied to the coil 105, and the resulting voltage drop in the coil 105 is detected as a DC voltage by the waveform rectifier circuit.

The detected voltage is compared and amplified with a reference voltage corresponding to a temperature reference, which will be described later, and an error signal is output to the control IC 20.
6 is inputted as a control signal, and as a result, the control IC 206
Operates to change the waveform (switching duty, frequency, etc.) applied to the heating field coils 100 to 104 and control the supplied power to keep the temperature of the heating element metal 7 constant.

More specifically with reference to FIG. 5, the heating element metal 7 is excited and heated by the heating field coils 100 to 104. The generated temperature of the excited heating element metal 7 is proportional to the voltage drop due to the current of the copper ring 106 on the facing surface of the temperature detecting field coil 105 shown in FIG. 3, that is, the resistor 205 shown in FIG.

Therefore, the pair of transistors 208 and 209 to which the voltage of the AC voltage 207 is complementarily connected.
After sufficiently amplifying the amplitude by means of a coil, a constant current is made by a coil 211 through a coupling capacitor 210 for cutting a direct current component, and then a temperature detecting field coil 105 is provided.
Is supplied to.

The magnetic field of the coil 105 is combined with the copper ring 106 attached to the surface of the heating element metal 7 to flow a ring current. Since the super power required for this ring current is supplied from the coil 105, when the coil 105 is driven with the constant current as described above, a voltage value corresponding to the voltage drop is generated across the coil 105.

Therefore, the voltage of the coil 105 is rectified and peak-charged by the rectifier circuit by the operational amplifier 215 to convert it into DC voltage.

This converted DC voltage is a voltage drop generated by the copper ring 106 of the heating element metal 7, that is, if the resistivity of copper changes depending on the temperature of the heating element metal 7, a voltage obtained proportionally. Information.

The change in resistivity of copper with respect to temperature is established in the following relationship.

R = R ₁ (1+ (t−t ₂ ) / (234.5 + t ₁ )) R: Copper resistance value (Ω) at temperature t R ₁ : Copper resistance value (Ω) t at temperature t ₁ : Copper temperature (° C.) t ₁ : Copper temperature (° C.) t ₂ : Ambient temperature (° C.) Since the field coil 105 is driven by a constant current, it is expressed as a voltage drop, and V = V ₁ ( 1+ (t−t _a ) / (234.5 + t ₁ )) V: voltage drop (V) at temperature t V ₁ : voltage drop (V) at temperature t ₁ does not change its essence, Are exactly equivalent.

Therefore, by measuring the detection voltage (V ₁ ) at the known temperature (t ₁ ), the metal temperature (= t) of the heating element can be uniquely known from the detection value (V) of the voltage drop. .

Therefore, when the detected voltage is input to the terminal 31 as the temperature, it is compared and amplified with the target temperature 218, and the pulse width modulation is performed by the comparator 32 according to the voltage input. This pulse width modulation is applied to the heating field coils 100-1.
It drives the gate of the FET 201 that is switching-driving 04, and changes the supplied power (switching waveform).

With the above-described structure, the control is performed by the drive waveform (high frequency) modulation of the field coil, so that the linear temperature control is achieved in the target temperature range.

The reason why the linear control can be promoted as an important function is that the heat roller type fixing device uses a high-power halogen heater which exceeds the specified temperature with respect to the target value temperature as described in the conventional example. Depending on whether or not it is turned on or off, a configuration is adopted that leads to a specified temperature by performing ON / OFF control (control of commercial AC in 1/2 cycle units). Even if the rate of temperature rise or overshoot is managed and the switching state is changed in a complicated manner, it is impossible to eliminate the temperature ripple determined by the transfer element due to the heat capacity of the heating element. Therefore, the temperature control by the waveform control of the switching state at the high frequency level works effectively as a solution to the above problem.

Further, a resistor 219 attached to the error amplifier
Since the capacitor 220 corrects the phase of the detected voltage (temperature) and performs the proportional-plus-integral operation in combination with the operational amplifier, the error-detected signal is optimal for the target temperature and achieves high-speed loop control. Therefore, it is possible to realize a system which does not necessarily require the control via the CPU as in the conventional case and can converge the temperature (FIG. 7) with higher accuracy than the conventional configuration.

FIG. 6 shows operation waveforms in the above configuration. 25
0 is a commercial AC power supply waveform, 251 is a waveform output through the rectification bridge 200, and 252 is a flyback waveform when the rectification waveform 251 is high-frequency switched by the switching control element (FET) 201. Reference numeral 253 shows a switching state waveform at a high voltage in the rectification lip.

Thus, the input voltage waveform (commercial AC voltage)
The reason that the switching cycle is modulated according to the value of the voltage is to flow a sine wave current as much as possible in order to improve the power factor of the input current waveform of the power supply.

To achieve this purpose, the voltage divided by the resistors 221 and 222 shown in FIG. 5 is monitored, and the capacitor 35 and the discharge current that determine the oscillation frequency are defined according to the voltage. It has a configuration for controlling the resistor 34.

When the high-frequency switching element 201 performs switching control on the rectified wave ripple voltage input to one end of the field coil, electric power is magnetically stored in the exciting inductance of the field winding and heating corresponding to the load is performed. Magnetically coupled to the body metal 7, an eddy current due to magnetism flows, Joule heat is generated due to resistance loss of the metal, and as a result, the heating body metal 7 is heated.

As described above, since the heating element is the heating element metal 7 itself with which the film 1 is in direct contact, a very monotonous structure of the heat transfer model from the heat source can be realized.
Since the voltage drop detection value of the copper ring 106 due to the induction coil is directly used for feedback control constituted by an operational amplifier, a stable fixing temperature without overshoot as shown in FIG. 7 is obtained, and a temperature detecting element is connected to the heating element. Without, it is possible to have a simple structure (no wiring) around the heating element.

(4) Safety circuit As described above, the direct heating method using the magnetic induction heating method and the fact that the directly heated heating metal is a film-shaped metal has a low specific heat. Shows a rapid temperature rise in a very short time.

Therefore, a safety circuit for preventing overheating becomes indispensable along with the performance requirement of the temperature detection system that follows this rapid temperature rise.

What kind of situation may occur in the equipment, for example, when an improper excessive voltage is input as the input voltage, or when the field coil of the fixing unit is mechanically damaged (cracks, cracks, foreign matters are mixed in the magnetic path). Etc.) Even if there is a problem from the standpoint of use, safety (especially fire safety) is an absolutely indispensable condition for equipment without exceeding a certain temperature.

In the circuit of FIG. 5, the drain voltage of the FET, that is, one end of the exciting coil is detected, and the zero cross detection circuit 219 detects the zero cross of the flyback voltage waveform.
The detected timing is used as a synchronization signal, and the capacitor of the timing generation circuit is charged / discharged as a start signal of the ON width control circuit according to the temperature information obtained by the temperature detection to switch the circuit in synchronization with the flyback waveform. ing.

In FIG. 6, 254 is, for example, as described above.
There was a problem from the standpoint of use, such as input of an unreasonable excessive voltage as the input voltage, or further mechanical damage to the field coil of the fixing unit (cracks, cracks, contamination of foreign matter into the magnetic path, etc.). In this case, the on-time width is the width determined by the temperature detection voltage, and the off-width, that is, the flyback waveform, is the cycle that is uniquely determined by the inductance of the coil and the resonance capacitor.

[0118]

[Outside 1] Is. 255 is a current waveform flowing in the field coil.

Therefore, if a problem occurs due to breakage of the magnetic circuit, inclusion of foreign matter, or the like due to any of the above reasons, it can be achieved by monitoring the period and current waveform because the circuits are synchronized.

Therefore, a reference voltage to be compared with a predetermined value is input to the signal of the current detection circuit 220 shown in FIG. 5 as an abnormality determination, overcurrent is detected, and temperature information and a flyback detection waveform are used. The zero crossing and the period information by a timer or the like are measured, and the above information is input to the abnormality determination circuit 224 to determine the abnormality.

As an example of the determination method here, The period is high 2. Current value is over 2. The detected value of the temperature sensor exceeds the specified value. Furthermore, as combination judgment. There is little increase in temperature, but there is a large amount of current.

Any of the above phenomena indicates an abnormality in the magnetic circuit of the induction heating unit or the temperature detection system. Immediately when the converter is stopped, the information is sent to the sequence controller, and the control circuit is set in advance. It was possible to stop and to ensure safety.

The magnetic material as the heating metal 7 has temperature dependence of magnetic permeability, and the Curie temperature (temperature at which magnetism is impaired) is, for example, about 230 ° C. for ferrite and about 450 for permalloy metal. ℃. This is
No matter what kind of unexpected situation occurs, magnetic flux is generated only at a temperature lower than that, so it is possible to provide an extremely safe heating means when compared with a system using a heater. is there.

Example 2 (FIGS. 8 to 11) FIGS. 8 to 1
Reference numeral 1 describes the second embodiment.

The control circuit of FIG. 8 is almost the same as the circuit of FIG. 5 of the first embodiment. Reference numeral 300 denotes, for example, a processing CP for performing the print sequence processing of the printer which is the apparatus
U and 301 are temperature sensors connected to the processing CPU.

For example, in a printer device using an electrophotographic system, the characteristics are greatly influenced by the surrounding environment because of the relationship of the image reproduction by the charging process of the toner and the photosensitive drum. Naturally, it is possible to overcome environmental fluctuations by strictly controlling the accuracy of parts and the latitude of standard values, but in multicolor printers, etc., there are too many control parameters and high image quality. In many cases, a temperature / humidity sensor is attached because of processing requirements. It is calibrated so that the target voltage (fixing temperature) of the temperature detection circuit and the sensor are calibrated based on the data from the temperature and humidity sensor.

FIG. 9 is a flowchart showing the contents of the fixing temperature control processing. First, assuming that the fixing device is not heated, after turning on the power of the device, the ambient temperature is measured by the environmental temperature sensor 301 and the measured temperature is set to t ₁ . At this time, the temperature reference voltage is 0 V from the CPU 300 to the control circuit.
Are instructed. That is, the heating field coil 10
No current flows in 0 to 104. Next, the detection circuit (OP
The output voltage from the AMP 215) is read at the CPU port, and the voltage is set to V ₁ . By the measurement values _{V 1, t 1 V = V} 1 (1+ (t-t a) / (234.5 + t 1)) obtains a target reference voltage as the fixing target temperature t.

For example, measured value t: 160 ° C., V ₁ : 2 :.
5V, t ₁ : 25 ° C., v = 2.5 (1+ (160-25) / (234.5 + 2)
5)) = 3.8 [V].

FIG. 10 shows the relationship between the fixing temperature and the detected voltage under the above conditions. That is, the reference voltage of the control circuit is 3.
By supplying and setting 8 V from the CPU, the heating element metal 7 rapidly starts heating toward the target temperature of 160 ° C.

The heating element is successively compared and amplified with the voltage value (temperature of the heating element metal) of the voltage drop monitor circuit of the copper ring 106,
The gate waveform of the FET 201 switching the heating field coils 100 to 104 is controlled to bring it to the target temperature.

By the above-described operation, the external circuit can realize the rising at a high speed and without overshoot without performing special complicated control.

In the above description, the voltage drop of the copper ring 106 has been mainly described, but the present invention is not limited to copper, and this method is all effective as long as the temperature coefficient of resistivity is clear. Further, although the copper metal is ring-shaped for the sake of easy explanation, it is possible to detect sheet metal in the same manner.

Based on the thus detected temperature value, in the circuit of FIG. 8, the drain voltage of the FET 201, that is, one end of the exciting coil is detected to detect the zero cross detection circuit 21.
The zero cross of the flyback voltage waveform is detected at 9, and a reference voltage to be compared with a predetermined value is input to the signal of the current detection circuit 220 as an abnormality determination, overcurrent is detected, and from the flyback detection waveform, Measured as the cycle information of zero cross and timer etc., and the above information is C
Each is input to the PU 300 to make an abnormality determination.

Examples of the determination method here are: The period is high 2. Current value is over 2. The detected value of the temperature sensor exceeds the specified value. Furthermore, as combination judgment. There is little increase in temperature, but there is a large amount of current.

Any of the above phenomena indicates an abnormality in the magnetic circuit of the induction heating section or in the temperature detection system. The converter is stopped immediately and the information is sent to the sequence controller, and the control circuit is in advance. It is essential to stop and secure safety. FIG. 11 shows a control flow for abnormality determination.

<Embodiment 3> (FIG. 12) FIG. 12 is a schematic structural model view of the apparatus of this embodiment. In the apparatus of this example, the film itself in the apparatus of Example 1 or FIG. 2 is a magnetic metal member (a film member provided with a magnetic metal layer,
This is a device in which a film member itself made of a magnetic metal material (hereinafter referred to as a magnetic metal film) is used to generate heat by magnetic induction heating, and a material to be heated that is brought into close contact with this is heated.

Reference numeral 6 denotes a field coil unit as a magnetic field generating means formed by winding an exciting coil around an E-shaped core material (core, magnetic material), and transports the magnetic metal film 1A and recording material (heated material) 12 ( It is a laterally long member whose longitudinal direction is a direction intersecting (orthogonal) with the (moving) direction.

Reference numeral 3.3 is a stay for supporting the field coil unit 6 and for keeping the magnetic metal film 1A running, and is made of liquid crystal polymer, phenol resin or the like, and a rubbing plate is provided on a portion in contact with the film. Is attached.

The stays 3 and 3 are the field coil unit 6
The E-shaped core member is a laterally long member disposed so that the three legs thereof face downward and both longitudinal sides thereof are sandwiched.

Reference numeral 4 denotes a film sliding plate (sliding plate) provided on the downward surface of the E-shaped core member of the field coil unit 6, which is glass or the like having a small friction resistance with the magnetic metal film 1A.
Further, it is preferable to apply a lubricant such as grease or oil to the surface thereof. Alternatively, the film sliding portion may be configured as a smooth surface with the core material of the field coil unit 6.

The above field coil unit 6, stay 3,
Endless (cylindrical, seamless) on the outside of the assembly (magnetic induction heating structure) consisting of the film sliding plate 4 etc.
The heat-resistant magnetic metal film 1A of 1 is loosely fitted on the outside.

Reference numeral 2 is a pressure roller, which is constructed by coating the core metal with silicone rubber, fluororubber or the like. The pressure roller 2 is pressed against the lower surface of the film sliding plate 4 of the assembly 6, 3 and 4 with a magnetic metal film 1A interposed therebetween by a predetermined pressing force by bearing means and biasing means (not shown). Therefore, the magnetic metal film 1A is sandwiched between the film sliding plate 4 and the lower surface thereof to form a pressure contact nip portion (fixing nip portion) N.

The pressure roller 2 is rotationally driven in the counterclockwise direction indicated by the arrow by the driving means. A rotational force acts on the magnetic metal film 1A by a frictional force between the pressure roller 2 and the outer surface of the film due to the rotational driving of the pressure roller 2, and the magnetic metal film 1A comes into close contact with the lower surface of the film sliding plate 4 to slide. Rotate the outer circumference of the assembly 6, 3, 4.

The magnetic metal film 1A has a thickness of 10 μm to 1
00μm polyimide, polyimide amide, PEEK
A heat resistant resin such as PES / PPS / PFA / PTFE / FEP is used as the base layer 1a, and the magnetic metal layer 1b is provided on the outer periphery (the pressure contact surface side of the material to be heated) of the base layer 1a with Fe or Co, such as Ni.
-Metal such as Cu and Cr is formed with a thickness of 1 μm to 100 μm by a process such as plating. Further, as a surface layer on the free surface of the magnetic metal layer 1b, for example, PFA / PTFE is used.
A three-layer structure in which a release layer 1c is formed by mixing or independently coating a heat-resistant resin having a good toner release property such as FEP / silicone resin. In this example, the film base layer 1a and the magnetic metal layer 1b are separate layers, but the film base layer 1a itself may be the magnetic metal layer.

When a current is applied to the exciting coil of the field coil unit 6 from an exciting circuit (not shown), the magnetic metal layer 1b of the magnetic metal film 1A generates heat by magnetic induction heating.

Then, the magnetic metal film 1A is rotated by the rotation of the pressure roller 2, and a current is applied to the exciting coil of the field coil unit 6 from the exciting circuit, whereby the magnetic metal layer 1b of the magnetic metal film 1A. In the state where the heat is generated, the recording material 12 as the material to be heated is introduced into the pressure contact nip portion N, adheres closely to the surface of the magnetic metal film 1A, and passes through the pressure contact nip portion N together with the magnetic metal film 1A. The unfixed toner image T provided with the heat of the magnetic metal film 1A thus applied to the recording material 12 is heated and fixed.

Since heat is generated directly near the surface layer of the magnetic metal film 1A, there is an advantage that heating can be performed rapidly regardless of the thermal conductivity and heat capacity of the film base layer 1a. Further, since it does not depend on the thickness of the magnetic metal film 1A, the rigidity of the magnetic metal film 1A is improved for speeding up, and thus even if the base layer 1a of the magnetic metal film 1A is thickened, it can be quickly heated to the fixing temperature. . Furthermore, since the film base layer 1a is a resin having a low thermal conductivity, it has good heat insulating properties, and can insulate heat from a large heat capacity such as a coil inside the film, so that heat loss is small even when continuous printing is performed, and energy efficiency is improved. good. In addition, heat is not transmitted to the coil inside the film, and the performance of the coil does not deteriorate. As the thermal efficiency is improved, the temperature rise in the apparatus is suppressed, and the influence on the image forming unit of the image forming apparatus such as the electrophotographic apparatus using the heating apparatus as the image heating and fixing apparatus can be reduced.

As described above, the heating device having the structure in which the film 1A is used as the magnetic metal member to heat the film itself by the magnetic induction heating and the material 12 to be heated adhered thereto is heated is the same as in the first or second embodiment. Similarly, the field coil unit 6 as the magnetic field generating means is provided with the temperature detecting field coil (105), and the surface portion on the film 1A side corresponding to the position of the field coil is arranged in the circumferential direction of the cylindrical film. By providing the copper ring (106), the same temperature control as in Example 1 or 2 can be performed to obtain the same effect.

<Embodiment 4> (FIG. 13) FIGS. 13 (a), (b) and (c) show another example of the configuration of a magnetic induction heating system / film heating system heating device. is there.

(A) is a film 1 (1A) in the form of an endless belt between three members of the lower surface of the magnetic field generating means 6 and 7 (or 6), the driving roller 61, and the driven roller (tension roller) 62. Is stretched around and the film 1 (1A) is rotationally driven by the drive roller 61. 63 is a magnetic field generating means 6 with the film 1 (1A) interposed therebetween.
A pressure roller pressed against the lower surface of 7 (or 6) and driven to rotate with the rotational movement of the film 1 (1A).

In the case of (b), the endless belt-shaped film 1 (1A) is suspended and stretched between the lower surface of the magnetic field generating means 6 and 7 (or 6) and the two members of the drive roller 61. It is configured to be rotationally driven by.

In the case of (c), as the film 1 (1A), not the endless belt-like one but a long end film wound in a roll is used, and this is taken out from the feeding shaft 64.
From the side, the magnetic field generating means 6 and 7 (or 6) are made to travel through the lower surface to the winding shaft 65 side at a predetermined speed.

In each of the above embodiments, the direction of the magnetic field is configured to enter perpendicularly to the magnetic metal member 7.1b, but the magnetic field may be applied parallel to the layer surface.

Although the film heating has been described, the heating member (magnetic metal member) may be a heat roller.

<Embodiment 5> (FIG. 14) In this embodiment, for example, an outline of an example of an image forming apparatus in which the heating apparatus of the magnetic induction heating system of the above-described Embodiment 1 is used as an image heating fixing apparatus (image heating apparatus) 85 It is a block diagram. The image forming apparatus of this example is a laser beam printer using an electrophotographic process.

Reference numeral 71 is a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image supporting member (first image supporting member). The photosensitive drum 71 is rotationally driven in the clockwise direction of the arrow at a predetermined peripheral speed (process speed), and in the course of the rotation, the primary charging device 72 uniformly charges the negative dark potential V _D.

Reference numeral 73 denotes a laser beam scanner, which emits a laser beam L modulated in accordance with a time series electric digital pixel signal of target image information input from a host device such as an image reading device, a word processor and a computer (not shown). Then, the surface of the photosensitive drum 71, which is negatively and uniformly charged by the primary charger 72 as described above, is scanned and exposed by the laser beam, so that the potential absolute value of the exposed portion becomes small and becomes the bright potential V _L , and the exposed portion rotates. An electrostatic latent image corresponding to target image information is formed on the surface of the photosensitive drum 71.

Next, the latent image is subjected to reversal development with the powder toner negatively charged by the developing device 74 (laser exposure portion V
Toner is attached to _L ) to make it visible.

The developing device 74 has a developing sleeve 74a which is rotationally driven, and the outer peripheral surface of the developing sleeve 74 is coated with a thin layer of toner having a negative charge to face the surface of the photosensitive drum 71. Absolute value is photosensitive drum 7
By applying the developing bias voltage _VDC which is smaller than the dark potential V _{D of} 1 and larger than the bright potential V _L , the toner on the sleeve 74 a is transferred only at the bright potential V _L portion of the photosensitive drum 71. The latent image is visualized (reversal development).

On the other hand, the recording material (second image carrier, transfer paper) P stacked and set on the paper feed tray 75 is fed out and fed one by one by the paper feed roller 76, and the conveyance guide 7
A nip portion (transfer portion) 82 between the photosensitive drum 71 and the transfer roller 80 as a transfer member which is brought into contact with the photosensitive drum 71 and a transfer bias is applied by the power source 81 via the registration roller pair 78 and the pre-transfer guide 79. The toner images on the surface of the photosensitive drum 71 are sequentially transferred to the surface of the fed recording material 12 by being fed at an appropriate timing synchronized with the rotation of the photosensitive drum 71. Transfer roller 80 as transfer member
A resistance value of 10 ⁸ to 10 ⁹ Ωm is suitable.

The recording material 12 that has passed through the transfer portion 82 is separated from the surface of the photosensitive drum 71, and is fixed by the conveyance guide 84 to the fixing device 85.
Then, the transferred toner image is fixed and is output to the paper discharge tray 86 as an image formed product (print). The surface of the photosensitive drum 71 after separation of the recording material is a cleaning device 83.
Then, the residual toner on the surface of the photosensitive drum such as residual toner after transfer is removed, and the surface is cleaned to be repeatedly used for image formation.

[0162]

As described above, according to the present invention, in the magnetic induction heating type heating device, stable and highly accurate temperature control without overshoot is possible, and safety is ensured and high reliability is achieved. Can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a heating device (image heating and fixing device of magnetic induction heating system / film heating system) according to a first embodiment.

FIG. 2 is a perspective view of the device.

FIG. 3 is a perspective view of magnetic field generating means (field coil unit and heating body metal).

[Fig. 4] Control circuit diagram

FIG. 5 is a more detailed control circuit diagram.

[Figure 6] Various waveform diagrams

[Figure 7] Temperature change diagram

FIG. 8 is a control circuit diagram of the apparatus according to the second embodiment.

FIG. 9: Temperature control flow chart

FIG. 10 is a graph showing the relationship between fixing temperature and detection voltage.

FIG. 11 is a control flow chart for abnormality determination.

FIG. 12 is a schematic structural model diagram of the apparatus of Example 3.

13 (a), (b), and (c) are schematic views of another example of the configuration of a magnetic induction heating type / film heating type heating device (Example 4).

FIG. 14 is a schematic configuration diagram of an example of an image forming apparatus (Example 5).

FIG. 15 is a schematic view of a heating roller type heating device (fixing device).

FIG. 16: Temperature control circuit for heating roller and roller driving circuit

FIG. 17: Temperature control graph

FIG. 18 Control flowchart

[Explanation of symbols]

 1 Film 2 Pressure Roller 3 Film Inner Surface Guide (Stay) 5 Heating Body 6 Field Coil Unit 7 Magnetic Metal Member (Heating Body Metal) 12 Recording Material (Heating Material) 20 High Frequency Converter 100-104 Heating Field (Excitation) Coil 105 Temperature detecting field coil 106 Copper ring 206 Control IC

Claims (9)

[Claims] 1. A heating apparatus of a magnetic induction heating system, wherein a magnetic field is applied to a magnetic metal member by a magnetic field generating means to heat a material to be heated by heat generation of the magnetic metal member by an eddy current generated in the magnetic metal member. A heating device comprising: a current measuring circuit for measuring an exciting current waveform of an exciting coil of the magnetic field generating means; and a circuit for measuring a period from an induced voltage induced in the exciting coil. 2. A comparison circuit for comparing a current measurement value detected by the current measurement circuit with a preset setting value, a period obtained from the induced voltage, and an excitation voltage waveform according to each value. It is changed, It is characterized by the above-mentioned.
The heating device according to. 3. At least one of the members used in the magnetic path forming means has a Curie point lower than that of the member having the lowest heat resistant temperature. The heating device according to claim 1 or 2. 4. The heating device according to any one of claims 1 to 3, wherein the magnetic metal member is a fixed member, or a rotating body or a traveling / moving end member. 5. The heating device according to claim 1, wherein the magnetic metal member is a laminated member including a magnetic metal layer, or a member made of a magnetic metal itself. 6. The heating device according to claim 1, further comprising a pressure member for directly or indirectly adhering the material to be heated to the magnetic metal member. 7. The heating device according to claim 6, wherein the pressurizing member is a pressurizing rotary member that is rotationally driven or driven to rotate. 8. The heating target material is a recording material carrying an image to be heat-treated, and an image heating device for heating the image on the recording material. The heating device according to claim 1. 9. An image forming apparatus comprising the heating device according to any one of claims 1 to 8 as an image heating device.