JP2002260836A - Heating device and image forming device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make uniform in the axis direction the temperature rising speed and temperature distribution of the heating roller in accordance with the dimensions of the heated material by a heating roller of simple structure. SOLUTION: The heating device comprises a heating roller 2 that has a tubular conductive layer 8 made of a material having conductivity, a pressuring roller 3 that is provided opposed to the heating roller 2 and transfers the heated material 5 compressed between the heating roller 2, and a magnetic field generating means 4 that impresses alternating field on the conductive layer 8 and makes it generate heat. The thickness of the layer t1 in axis direction in the vicinity of both end parts of the conductive layer 8 provided at the heating roller 2 is made thinner than the thickness of the layer t2 in the other portions of the conductive layer 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating device suitably implemented as a fixing device in a dry electrophotographic device, a drying device in a wet electrophotographic device, a drying device in an ink jet printer, and a heating device for a rewritable media erasing device. The present invention relates to an image forming apparatus having the same.

[0002]

2. Description of the Related Art In a heating device, for example, a fixing device used in an electrophotographic copying machine and a printer,
A configuration in which a halogen lamp is provided inside a heating roller having a hollow metal core such as aluminum and the heating roller is heated by the halogen lamp has been widely used.

However, the fixing device having such a configuration has a problem that the time required for sufficiently heating the heating roller (rise time) is long.

In recent years, attention has been paid to an induction heating type fixing device having a heating roller made of a conductive material on its surface. In this fixing device, an alternating magnetic field is applied to the heating roller to generate Joule heat, so that the heating roller itself is heated.

For example, in a fixing device disclosed in Japanese Patent Application Laid-Open No. H10-207269, a heating roller is formed by combining a plurality of metal rollers having different axial lengths.

[0006] The heating roller in the prior art includes an iron metal sleeve having an axial length longer than the axial length of the copper metal sleeve on the outer periphery of the copper metal sleeve. In this configuration, the fitting is performed so that the centers match. A magnetic field generating means is provided radially inward of the copper metal sleeve, and the magnetic field generating means can generate magnetic fields having two different frequencies.

The features of the technology disclosed in the prior art are as follows.
It is as follows. When fixing a material to be heated having a large width, which is a length in a direction perpendicular to the conveying direction of the material to be heated, an alternating magnetic field having a low frequency is generated by the magnetic field generating means, and the specific permeability of iron is higher than that of copper. By utilizing the high magnetic susceptibility, eddy current is generated only in the iron sleeve to generate heat. Thus, only the iron sleeve whose axial length is longer than the copper sleeve can be heated according to the size of the material to be heated having a large width.

On the other hand, when fixing a material to be heated having a small width, a high frequency alternating magnetic field is generated by a magnetic field generating means, and the fact that the relative magnetic permeability of copper is smaller than that of iron is used to make copper. An eddy current is generated only in the sleeve to generate heat. Thereby, according to the size of the material to be heated having a small width, only the copper sleeve having a shorter axial length than the iron sleeve can be heated.

Further, when fixing a material to be heated having a small width corresponding to the axial length of the copper sleeve, the heat generated in the copper sleeve is transmitted to the surface of the heating roller through the iron sleeve. Even if temperature unevenness occurs in the axial direction of the, the temperature unevenness is absorbed by the iron sleeve. In the case of fixing a material to be heated having a large width, the length of the iron sleeve in the axial direction is set to be longer than the width of the material to be heated, thereby suppressing the influence of temperature unevenness in the axial direction.

As described above, the length of the heat generating area in the axial direction of the heating roller can be adjusted according to the size of the material to be heated to be fixed, so that the heating roller can be uniformly spread over the entire length in the axial direction. Compared with the case of generating heat, the power consumption can be reduced and the fixing cost can be reduced.

[0011]

This prior art has the following problems. The magnetic field generating means generates a low-frequency alternating magnetic field, and the fact that iron has a higher relative magnetic permeability than copper. Part of the eddy current flows through the copper sleeve made of copper having a smaller volume resistivity than iron, so that the calorific value of the iron sleeve is reduced.

On the other hand, a high frequency alternating magnetic field is generated by the magnetic field generating means, and by utilizing the fact that copper has a lower relative magnetic permeability than iron, an eddy current is generated only in the copper sleeve to generate heat. Since the relative magnetic permeability of copper is too small, it is difficult to concentrate magnetic flux on the copper sleeve,
An eddy current required to obtain a sufficient heat generation cannot be generated. Further, since copper has a small volume resistivity, even if eddy current can be generated, the calorific value is small, and it is difficult to efficiently generate heat only from the copper sleeve. Therefore, even with a heating roller having a composite conductive layer formed by fitting different metal sleeves, an area where heat is generated in the axial direction is adjusted according to the size of the material to be heated, so that a uniform temperature distribution in the axial direction is obtained. It is difficult to get.

An object of the present invention is to provide a heating device which can make the heating rate and the temperature distribution of the heating roller uniform in the axial direction according to the size of the material to be heated by using a heating roller having a simple structure. That is.

[0014]

SUMMARY OF THE INVENTION The present invention relates to a heating roller provided with a cylindrical conductive layer made of a conductive material, wherein the thickness t1 of the conductive layer near both ends in the axial direction is equal to the thickness of the conductive layer. A heating roller formed so as to be thinner than the layer thickness t2 of the other portion, and provided opposite to the heating roller,
A heating apparatus comprising: a pressure roller that conveys a material to be heated while being pressed between the heating roller and a magnetic field generating unit that generates heat by applying an alternating magnetic field to a conductive layer.

According to the present invention, the layer thickness t1 near both ends in the axial direction of the conductive layer provided on the heating roller is formed so as to be smaller than the layer thickness t2 in other portions. As a result, the heat capacity near both ends in the axial direction formed at the layer thickness t1 of the conductive layer becomes smaller than the heat capacity at other portions formed at the layer thickness t2, and the heat capacity formed at the layer thickness t2 of the conductive layer is also reduced. The transfer of heat from the portion to be formed to the vicinity of both ends in the axial direction formed at the layer thickness t1 is suppressed. Therefore, when the conductive layer is induction-heated by the alternating magnetic field, it is possible to improve the delay of the heating rate near both ends in the axial direction of the conductive layer, and the heating rate and the temperature distribution in the axial direction of the conductive layer are uniform. Be transformed into Furthermore, when the pressing roller is pressed against the heating roller, the bending of the heating roller in the axial direction can be reduced.

Further, in the present invention, the length in the axial direction of the portion where the layer thickness of the conductive layer is formed at t2 is set to be equal to or longer than the length in the direction perpendicular to the conveying direction of the material to be heated. Features.

According to the present invention, the axial length of the portion where the thickness of the conductive layer is formed at t2 is set to be equal to or greater than the length in the direction perpendicular to the conveying direction of the material to be heated. When heating by pressing the material between the heating roller and the pressure roller,
The material to be heated can be uniformly heated in a direction perpendicular to the transport direction.

Further, in the present invention, the layer thickness t1 near both ends in the axial direction of the conductive layer is an inequality t1 ≦ √ (2 / ωσμ) where ω: angular frequency of the alternating magnetic field (= 2πf) f: alternating magnetic field Frequency [Hz] σ: electric conductivity of conductive layer [S / m] μ: selected so as to satisfy magnetic permeability of conductive layer.

According to the present invention, the layer thickness t1 near both ends in the axial direction of the conductive layer is selected so as to satisfy the inequality t1 ≦ √ (2 / ωσμ). Thus, when the conductive layer is induction-heated by the alternating magnetic field, heat is generated by the eddy current in the vicinity of both ends in the axial direction formed at the layer thickness t1 of the conductive layer, where the layer thickness t1 is equal to or less than the skin depth. Since the layer has only the thickness, the layer thickness t1 is effectively used for heat generation, and the time required to raise the temperature to a predetermined temperature is reduced due to the small heat capacity. On the other hand, the portion where the layer thickness of the conductive layer is formed at t2 is the thickness of the portion where the layer thickness t2 is larger than the skin depth, the thickness of the portion that generates heat due to the eddy current, and the heat load portion that is heated by heat conduction from the heat generation portion Including the thickness of
The heat capacity increases, and the time required to raise the temperature to a predetermined temperature increases. Therefore, the rate of temperature rise in the axial direction of the conductive layer is made uniform.

After the temperature is raised to a predetermined temperature, the thickness of the conductive layer near the opposite ends in the axial direction formed at the thickness t1 is t1.
Although the entire thickness of 1 is effectively used for heat generation, the heat dissipation is large, and the portion formed to have a thickness t2 of the conductive layer has less heat dissipation than the vicinity of both ends, but has the heat load portion. The temperature distribution in the axial direction of the layer is homogenized.

Further, according to the present invention, the magnetic field generating means includes control means for controlling a frequency of an alternating magnetic field, and the control means comprises:
The frequency of the alternating magnetic field is controlled according to the length in the direction perpendicular to the conveying direction of the material to be heated so that the temperature of the heating roller becomes uniform.

According to the present invention, the magnetic field generating means controls the frequency of the alternating magnetic field so as to make the temperature of the heating roller uniform according to the length in the direction perpendicular to the conveying direction of the material to be heated. including. Thereby, when heating the material to be heated whose length in the direction perpendicular to the transport direction is longer than the length in the axial direction of the portion formed with the layer thickness t2 of the conductive layer, the frequency of the alternating magnetic field is set higher. By generating heat under the condition that the layer thickness t1 near both ends in the axial direction of the conductive layer becomes the skin depth, it is possible to uniform the temperature rising rate and the temperature distribution over the entire length of the conductive layer in the axial direction.

Further, when heating a short material to be heated whose length in the direction perpendicular to the carrying direction is equal to or less than the length in the axial direction of the portion formed at the layer thickness t2 of the conductive layer, the frequency of the alternating magnetic field is increased. By setting the temperature to a low level, heat is mainly generated in a portion of the conductive layer formed at the layer thickness t2, and heat generation near both ends in the axial direction formed at the layer thickness t1 is suppressed, so that the temperature rising time to a predetermined temperature can be reduced. And power consumption can be reduced.

Further, the present invention further comprises a plurality of temperature detecting means which are arranged at predetermined intervals in the axial direction of the heating roller and detect the temperature of the heating roller, and the control means includes an output of each temperature detecting means. And controlling the frequency of the alternating magnetic field so that the temperature of the heating roller becomes uniform.

According to the present invention, the control means is arranged at a predetermined interval in the axial direction of the heating roller, responds to outputs of a plurality of temperature detecting means for detecting the temperature of the heating roller, and controls the frequency of the alternating magnetic field. Is controlled so that the temperature of the heating roller becomes uniform. Accordingly, when the temperature difference between the vicinity of both ends in the axial direction formed at the layer thickness t1 of the heating roller and the portion formed at the other layer thickness t2 is larger than a predetermined value, each temperature detecting means , The frequency of the alternating magnetic field can be controlled, so that the temperature distribution in the axial direction of the heating roller can be made uniform.

That is, the temperature near both ends in the axial direction formed at the layer thickness t1 of the heating roller is changed to the other layer thickness t2.
If the temperature is higher than a predetermined value than the temperature of the portion formed in the heating roller, the frequency of the alternating magnetic field is lowered, and the temperature near both ends in the axial direction formed in the layer thickness t1 of the heating roller is other than that. When the temperature of the portion formed at the layer thickness t2 is lower than a predetermined value by more than a predetermined value, the temperature distribution in the axial direction of the heating roller is made uniform by increasing the frequency of the alternating magnetic field, and the material to be heated is reduced. Heating can be performed so that the temperature becomes uniform in the direction perpendicular to the transport direction.

The present invention also provides any one of the above-mentioned heating devices, a toner image forming means for forming a toner image on a material to be heated, and a heating roller having a toner image formed on a surface thereof, which is heated and pressed by a heating roller. An image forming apparatus comprising: a conveying unit configured to convey the sheet between the roller and a roller.

According to the present invention, since the image forming apparatus includes any one of the above-described heating devices, it is possible to form an image of good quality without uneven heating in a direction perpendicular to the conveying direction of the material to be heated. it can.

[0029]

FIG. 1 is a cross-sectional view showing a simplified structure of a heating roller 2 included in a fixing device 1 which is a heating device according to an embodiment of the present invention, and FIG. FIG. 3 is a schematic cross-sectional view schematically illustrating the entire configuration of the fixing device 1 including the heating roller 2, and FIG. 3 is a plan view of an induction coil 20 included in the fixing device 1.

The fixing device 1 generally includes a heating roller 2,
Pressure roller 3 and magnetic field generating means 4 for generating an alternating magnetic field
(Here, the alternating magnetic field means that the N pole and the S pole constituting the magnetic field are periodically inverted, or the strength of one of the N pole and the S pole of the DC magnetic field periodically changes. If you say). The heating roller 2 is a roller having a hollow structure, and heats the recording paper 5 as a material to be heated. The pressure roller 3 can be pressed against the heating roller 2.
It is arranged so as to face the heating roller 2. Magnetic field generating means 4
Is disposed outside the heating roller 2. In the fixing device 1 having this configuration, the recording paper 5 carrying the toner image is nipped and conveyed between the heating roller 2 and the pressure roller 3 so that the toner transferred to the recording paper 5 is heated and melted. Recording paper 5
To be established. FIG. 2 shows that the toner 6 before fixing has changed to the toner 7 after fixing.

The heating roller 2 includes a cylindrical conductive layer 8 made of a conductive material, and a release layer 9 covering the outer periphery of the conductive layer 8. The conductive layer 8 has a cylindrical shape with an outer diameter of 40 mm, and is made of stainless steel SUS430. The layer thickness of the conductive layer 8 changes along the axial direction, the layer thickness t1 near both ends in the axial direction is formed to be 0.2 mm, and the layer thickness t2 of the other portions of the conductive layer 8 is set to 0.2 mm. It is formed to 5 mm. Hereinafter, the other portion of the conductive layer 8 formed with the layer thickness t2 is referred to as an axial center portion. Thus, in the present embodiment, the layer thickness t1 near both ends in the axial direction of the conductive layer 8 is:
It is formed so as to be thinner than the layer thickness t2 at the central part in the axial direction.

In the present embodiment, the layer thickness t1 near both ends in the axial direction of the conductive layer 8 is formed to be 0.2 mm, and the layer thickness t2 in the central portion in the axial direction is formed to be 0.5 mm. The layer thickness of the conductive layer to be set is not always constant but depends on the electric conductivity and magnetic permeability of the material of the conductive layer, and also depends on the frequency of the alternating magnetic field. Therefore, the thickness of the conductive layer needs to be selected according to the material of the conductive layer to be used and the frequency of the alternating magnetic field.

The axial length L11 near the one axial end portion 16 formed at the layer thickness t1 of the conductive layer 8 and the axial length L12 near the other axial end portion 34 are formed to be equal. Length W1 of the central portion in the axial direction formed at layer thickness t2
Is set to be equal to or longer than the length in the direction perpendicular to the transport direction of the recording paper 5. Hereinafter, the length in the direction perpendicular to the transport direction of the recording paper 5 conveyed by the pressure between the heating roller 2 and the pressure roller 3 is referred to as the width of the recording paper 5. In the present embodiment, the length W1
Is set, for example, to 210 mm, which is the length in the short direction of row A No. 4 defined in Japanese Industrial Standard P0138.
Accordingly, when the recording paper 5 is nipped and conveyed between the heating roller 2 and the pressure roller 3 to perform the fixing process, the longitudinal direction of the recording paper dimension A column No. 4 is set as the conveyance direction. Heating can be performed uniformly in the width direction, that is, in the width direction. The regions 10 and 11 where the layer thickness transitions between t1 and t2 are formed in a tapered shape, near the axial end portions formed at the layer thickness t1 and at the axial center portion formed at the layer thickness t2. Connected to The length L in the axial direction of the conductive layer 8
10 is formed equal to the length of the heating roller 2.

The conductive layer 8 is a heat generating member that generates heat by induction heating in an alternating magnetic field formed by the magnetic field generating means 4. As a material of the conductive layer 8, a material having magnetism and conductivity, particularly a material having a high relative permeability is desirable. Besides the above-described stainless steel SUS430, a silicon steel plate, an electromagnetic steel plate, a nickel steel, and the like can also be used. . Further, even if the material is non-magnetic such as stainless steel SUS304, any material having a large volume resistivity can be subjected to induction heating, and thus can be used as the conductive layer 8. Furthermore, even when a non-magnetic material such as ceramic is used as the base material, the above-described material having a high relative permeability is disposed on the base material so as to maintain conductivity. For example, it can be used as the conductive layer 8.

In the present embodiment, the thickness of the conductive layer 8 in the axial direction is changed by using an integral material.
Without being limited to this, the thickness of the conductive layer in the axial direction may be changed by stacking a plurality of sleeves having different lengths in the axial direction. Further, the conductive layer may be composed of a plurality of materials having different properties. In this case, the layer thickness of the material having the smaller magnetic permeability μ or the material having the higher electric conductivity σ is changed to another material. It is necessary to set the thickness to be smaller than the layer thickness. For example, iron or SUS4 on the first layer
When copper or aluminum is used for the second layer, copper or aluminum having a smaller magnetic permeability μ is set to be thinner than iron or SUS430.
The lamination of a plurality of materials is not limited to the lamination of the sleeve, but may be realized by vapor deposition, sputtering, or the like.

The release layer 9 covers the outer periphery of the conductive layer 8,
In the contact nip portion 12 formed by the contact between the heating roller 2 and the pressure roller 3, the toner whose viscosity has been reduced by heating is prevented from adhering to the heating roller 2. As a material of the release layer 9, polytetrafluoroethylene (PT
Fluorine-based materials such as FE) or a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether (PFA), silicon rubber and fluorine rubber are used. In this embodiment, PTFE having a thickness of 20 μm is used.
Is coated on the outer periphery of the conductive layer 8.

The axial length W2 of the outer periphery of the conductive layer 8 covered with the release layer 9 is longer than the axial center length W1 of the conductive layer 8 formed at the layer thickness t2. The length is set to include a part near both ends in the axial direction formed at t1. In the present embodiment, the axial length W2 of the release layer 9
Is set to 310 mm, which is slightly longer than the length in the longitudinal direction of the recording paper dimension A row 4. As a result, the fixing device 1 can perform the fixing process by selecting both the short direction and the long direction of the recording paper dimension A row No. 4 as the transport direction. The fixing device 1 of the present embodiment includes a recording paper 5
Is the center 35 of the heating roller 2 in the axial direction.
It is configured to be conveyed according to.

The heating roller 2 includes first and second bearings 1.
The fixing device 1 is rotatably supported by the housing 15 of the fixing device 1. One end 16 of heating roller 2 in the axial direction
, A gear 17 is mounted, for example, and the gear 17 is driven to rotate by an electric motor (not shown) or the like.

The pressure roller 3 has a columnar or cylindrical shape, and is a member in which a heat-resistant elastic layer such as silicon rubber is provided on the outer peripheral surface of a metal core made of iron, stainless steel or aluminum. PT on the outer peripheral surface of the heat-resistant elastic layer
A release layer made of FE or PFA for preventing toner adhesion may be provided. The pressure roller 3 is provided with a rotation shaft 19, and the rotation shaft 19 is rotatably supported by the body of the fixing device 1 by a bearing (not shown). The bearing is provided with a spring member (not shown) for applying a pressing force to the pressure roller 3.
Is pressed against the heating roller 2 with a force of approximately 100N. The contact between the heating roller 2 and the pressure roller 3 causes the contact nip 1
2 are formed. The contact nip portion 12 is hereinafter simply referred to as the nip portion 12. Nip portion 1 in the transport direction of recording paper 5
The nip width, which is the length of 2, is formed to be about 3.5 mm.

The magnetic field generating means 4 includes an induction coil 20, an excitation circuit 21 for supplying a high-frequency current to the induction coil 20, and a first temperature detector 22 as a temperature detection means for the surface of the heating roller 2.
And The induction coil 20 is formed by forming a wire into a coil shape whose plane shape is an ellipse, and includes a pair of extending coil portions 23 and 24 extending along the axial direction of the heating roller 2, and both ends of the heating roller 2 in the axial direction. Located near the department,
Connected to both ends of each of the extended coil portions 23 and 24,
Each extending coil portion 2 extends along the circumferential direction of the heating roller 2.
3 and 24 have a pair of bent coil ends 25 and 26 that connect one end and the other end of each other.

The induction coil 20 is made of a single aluminum wire having a surface insulating layer made of, for example, an oxide film. The material of the induction coil 20 is not limited to a single aluminum wire, and may be a copper wire or a copper-based composite material wire, or may be a litz wire obtained by twisting an enamel wire. Good. In any case of using any of the aforementioned materials, the total resistance value of the induction coil 20 is preferably 0.5Ω or less, more preferably, in order to suppress energy loss due to heat generation of the induction coil 20 itself. It is 0.1Ω or less.

Since the induction coil 20 is disposed so as to surround the heating roller 2 and is formed in a shape having a curvature, the magnetic flux concentrates on the center side of the induction coil 20 and the amount of eddy current generated is large. Thus, the surface temperature of the heating roller 2 can be increased in a short time. A plurality of induction coils 20 may be arranged according to the size of the recording paper 5 on which the fixing process is performed.

FIG. 4 is a block diagram showing a simplified electrical configuration of the excitation circuit 21. As shown in FIG. The excitation circuit 21 controls the frequency of the high-frequency current flowing through the induction coil 20.
(Single End Push Pull) type circuit. Excitation circuit 2
1, a rectifier circuit 27 for rectifying an AC current obtained from an AC power supply 32 into a DC current, first and second switching elements 28 and 29, a switching element control circuit 30,
And a capacitor 31.

The switching element control circuit 30, which is a control means, is a processing circuit realized by a microcomputer comprising a CPU (Central Process Unit) and the like. The switching element control circuit 30 alternately turns the first and second switching elements 28 and 29 ON-OF.
By performing F, the frequency of the current flowing through the excitation circuit 21 can be controlled, and a current having an arbitrary frequency can flow through the induction coil 20. The switching element control circuit 30 controls the frequency of the current flowing through the induction coil 20, that is, the frequency of the alternating magnetic field, and responds to the output of the first temperature detector 22 to turn on / off the high-frequency current oscillation by the excitation circuit 21.
It also controls the FF.

The first temperature detector 22 is a thermometer composed of a thermistor or the like. The first temperature detector 22 is located near the entry side of the recording paper 5 of the nip portion 12 and at the axis line formed at the layer thickness t1 of the conductive layer 8. It is arranged near the other end 34 in the direction. Also,
The first temperature detector 22 is connected to a switching element control circuit 30 included in the excitation circuit 21, detects the surface temperature of the heating roller 2, and provides a detection output to the switching element control circuit 30.

As described above, in the present embodiment, the layer thickness t1 near both ends in the axial direction of the conductive layer 8 provided on the heating roller 2 is formed to be smaller than the layer thickness t2 in the central portion in the axial direction. Is done. FIG. 5 is a diagram showing the relationship between the frequency f of the alternating magnetic field and the skin depth t. Referring to FIG.
The reason why the layer thickness t1 near both ends in the axial direction is formed to be smaller than the layer thickness t2 in the central portion in the axial direction will be described.

The skin depth t shown in FIG. 5 is given by the following equation. t = √ (2 / ωσμ) (1) where ω: angular frequency of the alternating magnetic field (= 2πf) f: frequency of the alternating magnetic field [Hz] σ: electric conductivity of the conductive layer [S / m] μ: Magnetic permeability of conductive layer

The curve 33 in FIG. 5 shows that the material of the conductive layer 8 is stainless steel SUS430 having a relative magnetic permeability of 100 and a volume resistivity corresponding to the electric conductivity of 60 μΩ · cm, and the frequency f of the alternating magnetic field is The result of obtaining the relationship between the skin depth and the skin depth t is shown. As shown by a curve 33 in FIG. 5, the skin depth t decreases with an increase in the frequency f of the alternating magnetic field, and SU
In S430, when the frequency f of the alternating magnetic field is 20 kHz, the skin depth t is 0.27 mm, and when the frequency f of the alternating magnetic field is as high as 40 kHz, the skin depth t is approximately 0.
Reduce to 2 mm.

The frequency of the current flowing through the induction coil 20;
That is, when the frequency f of the alternating magnetic field generated by the magnetic field generating means 4 is 40 kHz, the skin depth t at which the eddy current flows through the conductive layer 8 provided on the heating roller 2 is approximately 0.2.
mm. As described above, the layer thickness t1 near both ends in the axial direction of the conductive layer 8 is set to 0.2 mm.
1 is when the frequency f of the alternating magnetic field is 40 kHz (1)
It is formed substantially equal to the skin depth t obtained by the equation. Therefore, near the both ends in the axial direction of the conductive layer 8, eddy current flows over the entire layer thickness t1 set to 0.2 mm, so that all of the layer thickness t1 contributes to heat generation and heat is efficiently generated. it can.

On the other hand, the layer thickness t at the center of the conductive layer 8 in the axial direction is
2 is 0.5 mm, which means that the frequency of the alternating magnetic field is 4 mm.
It is thicker than the skin depth of 0.2 mm at 0 kHz, and the excess thickness is 0.3 mm more than the skin depth. Heat generation in the conductive layer 8 is caused by a skin depth of 0.2 m through which an eddy current flows.
m, a portion of 0.3 mm corresponding to the excess thickness hardly contributes to the heat generation of the conductive layer 8, and is heated by heat conduction from the heat generating portion up to 0.2 mm in thickness. Heat load.

Therefore, in the vicinity of both ends in the axial direction of the conductive layer 8, although there is a heat loss through the first and second bearings 13, 14, etc., the layer thickness t 1 all contributes to heat generation and generates heat efficiently, and At the center in the direction, although the heat loss is smaller than near both ends in the axial direction, since the layer thickness t2 is larger than the skin depth, the heat load portion must be heated. Thus, the vicinity of both ends in the axial direction where the layer thickness t1 of the conductive layer 8 is formed to be 0.2 mm, and the layer thickness t1
2 is 0.5 mm, the heating rate during warm-up and the temperature after heating are substantially equal, and the heating rate and the temperature distribution are uniform in the axial direction of the heating roller 2. Can be

Next, the fixing device 1 configured as described above is used.
Will be described. First, at the time of warm-up, the excitation circuit 21 operates, the induction coil 20 is excited, an eddy current is induced in the conductive layer 8 of the heating roller 2, and heat is generated by Joule heat. The calorific value at this time is about 800
W. Further, at the same time as the energization of the induction coil 20 by the excitation circuit 21 is started, the heating roller 2 is rotationally driven by an electric motor or the like, and the pressure roller 3 pressed by the heating roller 2 is driven to rotate. The surface temperature of the heating roller 2 is constantly detected by the first temperature detector 22. When the surface temperature of the heating roller 2 reaches a predetermined set temperature, for example, 180 ° C., the warm-up is completed. Thereafter, energization of the induction coil 20 by the excitation circuit 21 is performed by the first
In response to the detection output of the temperature detector 22, the control is switched to the ON-OFF control, and the surface temperature of the heating roller 2 is maintained at the predetermined set temperature.

By passing the recording paper 5 onto which the image of the unfixed toner 6 has been transferred through the nip portion 12 of the fixing device 1 in a state where the warm-up is completed, the unfixed toner 6
Receives the heat from the heating roller 2 and receives the pressure caused by the pressing of the heating roller 2 and the pressure roller 3, and is fused and fixed on the recording paper 5 to form a robust image.

FIG. 6 is a schematic sectional view showing a simplified configuration of an image forming apparatus 41 provided with the fixing device 1 shown in FIG. The image forming apparatus 41 of the present embodiment including the above-described fixing device 1 houses four sets of toner image forming units 41Y, 41M, 41C, and 41B for forming a toner image on the recording paper 5, and stores the recording paper 5. A recording paper tray 51, and a conveying means 52 for conveying the recording paper 5 between the heating roller 2 and the pressure roller 3.
And The recording paper tray 51 is arranged at the most upstream side in the conveying direction of the recording paper 5 indicated by an arrow 53, and stores and stores the recording paper 5, and separates the recording paper 5 one by one when forming an image. To send.

Four sets of toner image forming means 41Y, 41M,
41C and 41B are yellow (Y), magenta (M),
This is a unit for forming toner images of each color of cyan (C) and black (B), and is provided along the conveying unit 52 in this order from the upstream side to the downstream side in the conveying direction of the recording paper 5 indicated by an arrow 53. Can be

The yellow toner image forming means 41 Y includes a photosensitive member 42, a charging roller 43, and a laser irradiating means 44.
, A developing device 45, a transfer roller 46, and a cleaner 47. The photoconductor 42 is rotatably supported by the body of the image forming apparatus 41, and an electrostatic latent image is formed on the surface. The charging roller 43 is disposed to face the photoconductor 42,
Is uniformly charged. The laser irradiation unit 44 performs laser exposure on the surface of the photoconductor 42 according to the image information to form an electrostatic latent image.

The developing device 45 is arranged to face the photoconductor 42 at a predetermined interval, supplies toner to the photoconductor 42, develops the electrostatic latent image, and visualizes the electrostatic latent image. The transfer roller 46 is
A toner image formed on the surface of the photoconductor 42 is transferred onto the recording paper 5 by applying a bias voltage opposite to that of the toner and disposed opposite the photoconductor 42 via an endless belt 54 described later. After the toner image is transferred from the photoconductor 42 onto the recording paper 5, the cleaner 47 removes the toner remaining on the surface of the photoconductor 42 and cleans the surface of the photoconductor 42 in preparation for the next development. Other toner image forming means 41M, 41
C and 41B have the same configuration as the toner image forming unit 41Y except that the color of the toner is different.

The transport means 52 includes a driving roller 55, an idling roller 56, and a rotatable endless belt 54 stretched over the driving roller 55 and the idling roller 56. The driving roller 55 is driven to rotate by an electric motor or the like around an axis perpendicular to the paper surface of FIG. Although the idling roller 56 does not have a driving source, the rotational driving force of the driving roller 55 is transmitted by the endless belt 54, and is driven to rotate around an axis parallel to the axis of the driving roller 55. Endless belt 54 stretched between drive roller 55 and idling roller 56
Is a predetermined speed, for example, 134 mm /
The recording paper 5 is rotated in seconds, and the recording paper 5 is conveyed while being electrostatically attracted.

In the image forming apparatus 41, an image is formed as follows. The recording paper 5 fed one by one from the recording paper tray 51 is supplied with an arrow 53 by an endless belt 54.
Conveyed in the direction. First, in the toner image forming means 41Y,
The surface of the photoconductor 42 is uniformly charged by the charging roller 43, and then the surface of the photoconductor 42 is
Is subjected to laser exposure according to the image information to form an electrostatic latent image. A developing device 45 develops a toner image on the electrostatic latent image on the photoconductor 42, and the developed toner image is endlessly formed by a transfer roller 46 to which a bias voltage having a polarity opposite to that of the toner is applied. The image is transferred onto the recording paper 5 on the belt 54.

While the recording paper 5 is being conveyed in the direction indicated by the arrow 53, the other toner image forming means 41M, 41C and 41B arranged downstream in the conveyance direction cause
The toner of each color is sequentially transferred in a multiplex manner. After the transfer by the four toner image forming units 41Y, 41M, 41C, and 41B is completed, the recording paper 5 is separated from the endless belt 54 by the curvature formed on the driving roller 55, and the fixing device 1
Transported to In the fixing device 1, the recording paper 5 carrying the toner image is nipped between the heating roller 2 and the pressure roller 3 and given an appropriate temperature and pressure, and the toner is heated in the width direction of the recording paper 5. The toner is melted without unevenness and fixed on the recording paper 5 to form a robust image.

FIG. 7 is a sectional view showing a simplified configuration of the heating roller 2 included in the fixing device 61 according to the second embodiment of the present invention. The fixing device 61 of the present embodiment
Similar to the fixing device 1 according to the first embodiment, corresponding portions are denoted by the same reference numerals and description thereof will be omitted.

It should be noted that a plurality of temperature detecting means, that is, a second temperature detector 62 is provided in addition to the first temperature detector 22. The second temperature detector 62 is located near the other axial end portion 34 formed at the layer thickness t1 so as to be located at the axial center portion formed at the layer thickness t2 of the conductive layer 8. From the vessel 22 in the axial direction. The second temperature detector 62 is connected to the switching element control circuit 30 included in the excitation circuit 21 similarly to the first temperature detector 22, detects the surface temperature of the central portion in the axial direction of the heating roller 2, and outputs the detection output. It is given to the switching element control circuit 30. Switching element control circuit 30
Responds to the respective outputs of the first and second temperature detectors 22 and 62 to control the frequency of the alternating magnetic field so that the temperature in the width direction of the heating roller 2 becomes uniform.

Next, the reason why a plurality of temperature detecting means are provided will be described. For example, at the time of warm-up, the frequency of the alternating magnetic field is set as high as 40 kHz. However, when the temperature of the heating roller 2 is controlled only by the first temperature detector 22 under this driving condition, for example, the heat capacity is large like thick paper. When a large recording sheet is continuously passed through the heating roller 2, there is a problem that heat is deprived of the recording sheet and the temperature of the central portion of the heating roller 2 in the axial direction decreases. This is because, during warm-up, in order to equalize the temperature of the heating roller 2, heat generated in the central portion in the axial direction where heat loss is small is suppressed from both ends in the axial direction. This is a problem that occurs because the temperature near the other end 34 in the axial direction is detected. That is, the first temperature detector 22 is provided near the other end 34 of the heating roller 2 in the axial direction even though the temperature of the central portion in the axial direction of the heating roller 2 is low. The temperature drop cannot be detected. Also, since the frequency of the alternating magnetic field remains high, when replenishing the heat taken by the recording paper,
A large amount of heat is generated near both ends of the heating roller 2 in the axial direction, and a small amount of heat is generated at the central portion in the axial direction. Therefore, the temperature of the central portion in the axial direction of the heating roller 2 in which the temperature has decreased cannot be recovered to the temperature required for the fixing process.

According to the present embodiment, such a problem is solved, and the temperature distribution in the axial direction of the heating roller 2 becomes uniform in response to the outputs of the first and second temperature detectors 22 and 62. By controlling the frequency of the alternating magnetic field in this manner, the toner can be fixed on the recording paper 5 in the width direction without heating.

FIG. 8 is a flowchart showing the operation of the switching element control circuit 30 for controlling the frequency of the alternating magnetic field. The frequency control of the alternating magnetic field will be described with reference to FIG. In step s1, the heating of the heating roller 2 is started at the set frequency of the alternating magnetic field, for example, 40 kHz. In step s2, the surface temperature T1 near the other end portion 34 in the axial direction of the heating roller 2 detected by the first temperature detector 22 and the center temperature in the axial direction of the heating roller 2 detected by the second temperature detector 62 A temperature difference ΔT from the surface temperature T2 (= T1−T2) is calculated, and the absolute value of ΔT is 10 ° C.
It is determined whether or not: If the determination is affirmative, the process proceeds to step s6. If the determination is negative, the process proceeds to step s3. Here, although the temperature T1 is the surface temperature near the other end portion 34 in the axial direction, the temperature distribution in the axial direction of the heating roller 2 can be considered to be substantially line-symmetric with respect to the center in the axial direction. Hereinafter, the temperature T1 is referred to as a surface temperature near both ends in the axial direction.

In step s6, the heating of the heating roller 2 is continued with the frequency of the set alternating magnetic field kept at 40 kHz, and thereafter, the process returns to step s2 and the temperature difference ΔT
Is again determined whether or not the absolute value of is less than or equal to 10 ° C.
In step s3, the surface temperature T2 at the central portion in the axial direction of the heating roller 2 detected by the second temperature detector 62 is changed to the surface temperature near both ends in the axial direction of the heating roller 2 detected by the first temperature detector 22. It is determined whether it is lower than T1. If the determination is affirmative, the process proceeds to step s4. If the determination is negative, the process proceeds to step s5.

In step s4, the switching element control circuit 30 lowers the oscillation frequency of the excitation circuit 21 to lower the frequency of the alternating magnetic field. By lowering the frequency of the alternating magnetic field, the skin depth increases, the heat generation in the central portion in the axial direction where the thickness t2 of the conductive layer 8 is large is promoted, the temperature rises, and the temperature distribution in the axial direction of the heating roller 2 decreases. Be uniformed. After decreasing the frequency of the alternating magnetic field in step s4, the process returns to step s2, and the absolute value of the temperature difference ΔT becomes 1
It is determined again whether the temperature is 0 ° C. or less.

In step s5, the switching element control circuit 30 increases the oscillation frequency of the excitation circuit 21 to increase the frequency of the alternating magnetic field. By increasing the frequency of the alternating magnetic field, the skin depth is reduced, the heat generation near the axial end portions of the heating roller 2 having a small thickness t1 of the conductive layer 8 is promoted, the temperature is increased, and the axis of the heating roller 2 is increased. The temperature distribution in the direction is made uniform. In step s5, after increasing the frequency of the alternating magnetic field, the flow returns to step s2, where the temperature difference ΔT
Is again determined whether or not the absolute value of is less than or equal to 10 ° C.

As described above, the first and second temperature detectors 22, 22 are provided at predetermined intervals in the axial direction of the heating roller 2.
The temperature distribution in the axial direction of the heating roller 2 can be made uniform by controlling the frequency of the alternating magnetic field in response to the output of each temperature detector.

The fixing device 61 having the structure shown in FIG.
The width of the recording paper 5 passing through the heating roller 2 can be indirectly detected by the first and second temperature detectors 22 and 62, and the frequency of the alternating magnetic field can be controlled according to the detection result. For example, as described above, the frequency of the
Hz and the heating of the heating roller 2 is started. After the warm-up is completed, when the recording paper 5 having the same or smaller width as the axial length W1 at the axial center formed at the layer thickness t2 of the conductive layer 8 is passed through the heating roller 2, the recording paper 5 Heat is taken away by the passage of the heat roller 2, and the surface temperature T2 at the central portion in the axial direction of the heating roller 2 decreases.

Although the surface temperature T2 at the central portion in the axial direction of the heating roller 2 is lowered, the set alternating magnetic field is 40 k
Hz and a small skin depth, the heating of the heating roller 2 in the vicinity of both ends in the axial direction is promoted more than in the central portion in the axial direction. Therefore, when the recording paper 5 having the same or smaller width than the length W1 is continuously passed through the heating roller 2, the surface temperature T2 at the central portion in the axial direction of the heating roller 2 decreases, and the temperature required for the fixing process decreases. Will not recover until. As a result, in step s2, it is determined that the absolute value of the temperature difference ΔT between the surface temperature T2 at the center in the axial direction of the heating roller 2 and the surface temperature T1 near both ends in the axial direction exceeds 10 ° C., and then step s3 In, it is determined that the surface temperature T2 at the center in the axial direction is lower than the surface temperature T1 near both ends in the axial direction. Thus, the width of the recording paper 5 is regarded as being equal to or smaller than the length W1.

When the width of the recording paper 5 is regarded as being equal to or smaller than the length W1, the process proceeds to step s4.
In step s4, the frequency of the alternating magnetic field is reduced to, for example, 20 kHz as described above, and the length W1
Is controlled to the frequency of the alternating magnetic field corresponding to the recording paper 5 having the same or smaller width than that of the recording paper 5, so that the heat generation at the central portion in the axial direction of the heating roller 2 is promoted, and the temperature at the central portion in the axial direction becomes the temperature required for the fixing process. And the recording paper 5 can be uniformly heated in the width direction.

After the recording paper having the same width as the length W1 or a width smaller than the length W1 is passed through the heating roller 2, the frequency of the alternating magnetic field is controlled to be reduced to, for example, 20 kHz. When a recording sheet having a width larger than the length W1 is passed through the heating roller 2 instead of the recording sheet having a small width, heat is taken away by the passage of the recording sheet, and the surface near the both ends in the axial direction of the heating roller 2 is removed. The temperature T1 decreases.

Although the surface temperature T1 near both ends of the heating roller 2 in the axial direction decreases, the frequency of the set alternating magnetic field is low and the skin depth is large. Heating in the axial center is promoted. Therefore, when recording paper having a width greater than the length W1 is continuously passed through the heating roller 2, the surface temperature T1 near both ends of the heating roller 2 in the axial direction decreases, and the temperature is restored to a temperature required for the fixing process. Disappears. As a result, in step s2, it is determined that the absolute value of the temperature difference ΔT between the surface temperature T2 at the center in the axial direction of the heating roller 2 and the surface temperature T1 near both ends in the axial direction exceeds 10 ° C., and then step s3 , The surface temperature T at the center in the axial direction
2 is higher than the surface temperature T1 near both ends in the axial direction. Thus, the width of the recording paper is considered to be larger than the length W1.

When the width of the recording paper is considered to be greater than the length W1, the process proceeds to step s5. In step s5, the frequency of the alternating magnetic field is increased to, for example, 40 kHz as described above, and the length W1 is increased. Since the frequency of the alternating magnetic field is controlled according to the larger width of the recording paper, heat generation near both ends in the axial direction of the heating roller 2 is promoted, and the temperature near both ends in the axial direction recovers to a temperature required for the fixing process. Thus, the recording paper can be uniformly heated in the width direction.

The width of the recording paper is the same as or smaller than the length W1, and the frequency of the alternating magnetic field is, for example, 20 kHz.
When the temperature is set low, such as z, the width of the recording paper and the portion where the heating of the heating roller 2 is promoted match, so that the temperature difference between the center in the axial direction of the heating roller 2 and the vicinity of both ends thereof The heating of the heating roller 2 and the conveyance of the recording paper to the heating roller 2 are continued at the set frequency without ΔT exceeding 10 ° C. That is, the operations of step s2 and step s6 shown in FIG. 8 are repeated.

The width of the recording paper is greater than the length W1,
When the frequency of the alternating magnetic field is set to a high value, for example, 40 kHz, the width of the recording paper and the portion where the heating of the heating roller 2 is promoted match, so that steps s2 and s6 are performed in the same manner as described above. Are repeated.

As described above, the surface temperature T1 near both ends in the axial direction of the heating roller 2 and the surface temperature T
The indirect detection of the width of the recording paper is performed by determining whether the absolute value of the temperature difference ΔT from the recording medium 2 exceeds 10 ° C. and determining whether the surface temperature T1 or T2 is lower. The heating roller 2 can be uniformly heated in the width direction by controlling the frequency of the alternating magnetic field according to the width of the heating roller 2.

When the width of the recording paper is equal to or smaller than the length W1, the frequency of the alternating magnetic field is set low, and the heat generated at the center in the axial direction formed at the thickness t2 of the conductive layer 8 is reduced. It is desirable to promote. As a result, the central portion in the axial direction of the heating roller 2 corresponding to the width of the recording paper is:
Since the temperature is raised faster than the vicinity of both ends in the axial direction, the warm-up time is shortened and power consumption can be reduced.

Further, by controlling the frequency of the alternating magnetic field in accordance with the width of the recording paper and making the temperature distribution in the axial direction of the heating roller 2 uniform, the occurrence of hot offset can be prevented. Further, the width of the recording paper is equal to the length W1.
The heating roller 2 is heated while the frequency of the alternating magnetic field is set high, even though it is the same or smaller than that of the heating roller 2, so that heat from the vicinity of both ends in the axial direction of the heating roller 2 to the first and second bearings 13 and 14 is increased. When the amount of conduction increases, the first and second bearings 13 and 14 may be damaged by heat. However, the frequency of the alternating magnetic field is controlled in accordance with the width of the recording paper to reduce the temperature distribution in the axial direction of the heating roller 2. The uniformity can prevent the first and second bearings 13 and 14 from being damaged.

In the conventional fixing device, in order to detect the width of the recording paper passed through the fixing device, input means for inputting the width of the recording paper from the operation panel, or the width of the recording paper is optically detected, for example. According to the present embodiment, the surface temperatures T1 and T2 near both ends in the axial direction and the center of the heating roller 2 are set to the first and second temperatures.
By detecting using the temperature detectors 22 and 62,
It is possible to indirectly detect the width of the recording paper. Therefore, it is not necessary to provide a recording paper width input means on the operation panel, and it is not necessary to provide a recording paper width detecting means, so that the number of components can be reduced and the manufacturing cost can be reduced.

FIG. 9 is a sectional view showing a simplified configuration of a heating roller 63 according to a third embodiment of the present invention.
The heating roller 63 according to the present embodiment is similar to the heating roller 2 according to the first embodiment, and corresponding portions are denoted by the same reference numerals and description thereof is omitted.

The heating roller 63 of this embodiment has an axial length L13 near one axial end 16 formed at the thickness t1 of the conductive layer 64 and an axial length near the other axial end 34. Unlike the length L14, the length L13 is formed to be longer than the length L14. In the present embodiment,
Although the length L13 is larger than the length L14, the length L13 is not limited to this, and the length in the axial direction near the other end portion 34 in the axial direction is longer than the length in the axial direction near the one end portion 16 in the axial direction. May be done.

In the heating roller 63 according to the present embodiment, the length of the central portion in the axial direction formed at the layer thickness t2 of the conductive layer 64 and the portion near the other axial end portion 34 formed at the layer thickness t1 are determined. Is set to, for example, the length W3 in the short direction of the fourth row of row A defined in Japanese Industrial Standard P0138. The heating roller 63 has a configuration suitable for a case where the center of the recording paper in the width direction is fed from the axial center of the heating roller 63 to the other end 34.

As described above, in the first to third embodiments, the layer thickness of the conductive layer is configured in two steps: the layer thickness t1 near both ends in the axial direction and the layer thickness t2 at the center. However, the thickness of the conductive layer is adjusted so that the axial length that is uniformly heated is set to three or more stages, corresponding to the skin depth obtained according to the frequency of the set alternating magnetic field frequency. Even if the configuration differs in three or more stages in the axial direction, the gist of the present invention is the same.

FIG. 10 is a schematic sectional view showing a simplified structure of a fixing device 65 according to a fourth embodiment of the present invention. FIG. 11 is a sectional view of an induction coil 66 included in the fixing device 65 shown in FIG. It is a perspective view which shows a structure simplified. The fixing device 65 according to the present embodiment is similar to the fixing device 1 according to the first embodiment, and corresponding portions are denoted by the same reference numerals and description thereof is omitted.

In the fixing device 65 of the present embodiment, the induction coil 66 is provided radially inward of the conductive layer 8. The induction coil 66 is formed in a spiral shape by winding a single wire of aluminum around the axis of the heating roller 2. By providing the induction coil 66 inside the conductive layer 8 in the radial direction, the size of the fixing device 65 can be further reduced.

FIG. 12 is a schematic sectional view showing a simplified structure of a fixing device 67 according to a fifth embodiment of the present invention. FIG. 13 is a sectional view showing an induction coil 68 and a fixing device 67 included in the fixing device 67 shown in FIG. FIG. 7 is a simplified perspective view showing a configuration of a magnetic flux adjusting member 69. The fixing device 67 according to the present embodiment is similar to the fixing device 1 according to the first embodiment, and corresponding portions are denoted by the same reference numerals and description thereof is omitted.

In the fixing device 67 of the present embodiment, the induction coil 68 and the magnetic flux adjusting member 69 are provided inside the conductive layer 8 in the radial direction. The magnetic flux adjusting member 69 includes the heating roller 2
Is a member made of a magnetic material having an E-shaped cross section perpendicular to the axis. Magnetic flux adjusting member 6
As the material of No. 9, it is desirable to have a high magnetic permeability, and ferrite, a silicon steel sheet, an electromagnetic steel sheet and the like are suitable.
The magnetic flux adjusting member 69 includes a flat base 70 extending along the axis of the heating roller 2 and first to third bases that rise substantially perpendicularly from the base 70 and extend along the axis of the heating roller 2 almost in parallel with each other. Projecting pieces 71, 72, 73.

The induction coil 68 is formed by winding a single wire of aluminum around the second protruding piece 72 of the magnetic flux adjusting member 69 in one direction, faces the inner peripheral surface of the conductive layer 8, and forms the conductive layer 8 and the release layer. The pressure roller 3 is disposed so as to face the pressure roller 3. When the magnetic flux adjusting member 69 made of a magnetic material exists,
The magnetic flux generated by the current flowing through the induction coil 68 concentrates on the magnetic flux adjusting member 69. Magnetic flux adjusting member 6
By providing 9, the concentrated magnetic flux can be linked to the conductive layer 8, so that the magnetic flux density passing through the conductive layer 8 can be reduced as compared with the case where the magnetic flux passes through the atmosphere without the magnetic flux adjusting member 69. As a result, the heating efficiency of the conductive layer 8 can be improved.

As described above, the first to fifth embodiments of the present invention are described.
In the embodiment, the fixing device has one induction coil, but is not limited thereto, and may have a configuration having a plurality of induction coils. Further, the conductive layer is composed of one layer, but is not limited to this, and may be composed of a plurality of layers. Further, the temperature detecting means is constituted by two of the first and second temperature detectors 22, 62, and the frequency of the alternating magnetic field is controlled in response to each detection output of the first and second temperature detectors 22, 62. However, without being limited to this, the temperature detecting means
It may be configured to include three or more temperature detectors, and control the frequency of the alternating magnetic field in response to the output of each temperature detector.

[0092]

According to the present invention, the layer thickness t1 near both ends in the axial direction of the conductive layer provided on the heating roller is formed so as to be smaller than the layer thickness t2 in other portions. As a result, the heat capacity near both ends in the axial direction formed at the layer thickness t1 of the conductive layer becomes smaller than the heat capacity at the portion formed at the other layer thickness t2, and the layer thickness t2 of the conductive layer is obtained.
The transfer of heat from the portion formed at the bottom to the vicinity of both ends in the axial direction formed at the layer thickness t1 is suppressed. Therefore, when the conductive layer is induction-heated by the alternating magnetic field, it is possible to improve the delay of the heating rate near both ends in the axial direction of the conductive layer, and the heating rate and the temperature distribution in the axial direction of the conductive layer are uniform. Be transformed into Furthermore, when the pressing roller is pressed against the heating roller, the bending of the heating roller in the axial direction can be reduced.

According to the present invention, the thickness of the conductive layer is t2
The length of the portion formed in the axial direction is set to be equal to or greater than the length in the direction perpendicular to the transport direction of the material to be heated, so that the material to be heated is sandwiched between the heating roller and the pressure roller to be heated. In this case, the material to be heated can be uniformly heated in a direction perpendicular to the transport direction.

Further, according to the present invention, the layer thickness t1 near both ends in the axial direction of the conductive layer is inequality t1 ≦ √ (2 / ωσμ)
Are chosen to satisfy Thus, when the conductive layer is induction-heated by an alternating magnetic field, the thickness t of the conductive layer
In the vicinity of both ends in the axial direction formed at 1, the layer thickness t1 has a thickness equal to or less than the skin depth, that is, only the thickness that generates heat by eddy current, so that the layer thickness t1 is effectively used for heat generation and the heat capacity is small. In some cases, the time required to raise the temperature to a predetermined temperature is reduced. On the other hand, the portion where the layer thickness of the conductive layer is formed at t2 is the thickness of the portion where the layer thickness t2 is larger than the skin depth, the thickness of the portion that generates heat due to the eddy current, and the heat load portion that is heated by heat conduction from the heat generation portion , The heat capacity increases, and the time required to raise the temperature to a predetermined temperature increases. Therefore, the rate of temperature rise in the axial direction of the conductive layer is made uniform.

After the temperature is raised to the predetermined temperature, the layer thickness t1 is formed near both ends in the axial direction formed at the layer thickness t1 of the conductive layer.
Although the entire thickness of 1 is used effectively for heat generation, heat dissipation is large, and the portion formed to have a layer thickness t2 of the conductive layer has less heat dissipation than the vicinity of both ends, but has the heat load portion. The temperature distribution in the axial direction of the layer is homogenized.

Further, according to the present invention, the magnetic field generating means controls the frequency of the alternating magnetic field so that the temperature of the heating roller becomes uniform according to the length in the direction perpendicular to the conveying direction of the material to be heated. Including means. By this, when heating the material to be heated whose length in the direction perpendicular to the transport direction is longer than the length in the axial direction of the portion formed with the layer thickness t2 of the conductive layer,
By setting the frequency of the alternating magnetic field high and generating heat under the condition that the layer thickness t1 near both ends in the axial direction of the conductive layer becomes the skin depth, the temperature rising rate and the temperature distribution over the entire axial length of the conductive layer are made uniform. be able to. Further, when heating a short material to be heated whose length in the direction perpendicular to the transport direction is equal to or less than the length in the axial direction of the portion formed with the layer thickness t2 of the conductive layer, the frequency of the alternating magnetic field is set low. By mainly generating heat in a portion of the conductive layer formed at the layer thickness t2 and suppressing heat generation near both ends in the axial direction formed at the layer thickness t1, the heating time to a predetermined temperature is reduced, Power consumption can be reduced.

Further, according to the present invention, the control means is arranged at a predetermined interval in the axial direction of the heating roller, responds to the outputs of a plurality of temperature detecting means for detecting the temperature of the heating roller, and controls the alternating magnetic field. The frequency is controlled so that the temperature of the heating roller becomes uniform. Accordingly, when the temperature difference between the vicinity of both ends in the axial direction formed at the layer thickness t1 of the heating roller and the portion formed at the other layer thickness t2 is larger than a predetermined value, each temperature detecting means Responds to the output of
Since the frequency of the alternating magnetic field can be controlled, the temperature distribution in the axial direction of the heating roller can be made uniform.

That is, the temperature near both ends in the axial direction formed at the layer thickness t1 of the heating roller is changed to the other layer thickness t2.
If the temperature is higher than a predetermined value than the temperature of the portion formed in the heating roller, the frequency of the alternating magnetic field is lowered, and the temperature near both ends in the axial direction formed in the layer thickness t1 of the heating roller is other than that. When the temperature of the portion formed at the layer thickness t2 is lower than a predetermined value by more than a predetermined value, the frequency of the alternating magnetic field is increased to make the temperature distribution in the axial direction of the heating roller uniform and to convey the heating roller. Heating can be performed so that the temperature becomes uniform in a direction perpendicular to the direction.

Further, according to the present invention, since the image forming apparatus includes any one of the above-mentioned heating devices, it is possible to form an image of good quality without uneven heating in a direction perpendicular to the conveying direction of the material to be heated. Can be.

[Brief description of the drawings]

FIG. 1 is a simplified cross-sectional view showing a configuration of a heating roller 2 included in a fixing device 1 which is a heating device according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view schematically showing the entire configuration of a fixing device 1 including a heating roller 2 shown in FIG.

FIG. 3 is a plan view of an induction coil 20 included in the fixing device 1.

FIG. 4 is a simplified block diagram showing an electrical configuration of an excitation circuit 21;

FIG. 5 is a diagram showing a relationship between a frequency f of an alternating magnetic field and a skin depth t.

6 is an image forming apparatus 4 including the fixing device 1 shown in FIG.
1 is a schematic cross-sectional view showing a simplified configuration of FIG.

FIG. 7 shows a fixing device 61 according to a second embodiment of the present invention.
FIG. 3 is a cross-sectional view showing a simplified configuration of a heating roller 2 included in the embodiment.

FIG. 8 is a flowchart showing an operation of the switching element control circuit 30 for controlling the frequency of the alternating magnetic field.

FIG. 9 shows a heating roller 6 according to a third embodiment of the present invention.
3 is a simplified cross-sectional view showing the configuration of FIG.

FIG. 10 shows a fixing device 6 according to a fourth embodiment of the present invention.
5 is a schematic cross-sectional view showing a simplified configuration of FIG.

11 is a simplified perspective view showing a configuration of an induction coil 66 included in the fixing device 65 shown in FIG.

FIG. 12 shows a fixing device 6 according to a fifth embodiment of the present invention.
7 is a schematic cross-sectional view showing a simplified configuration of FIG.

FIG. 13 is a perspective view showing a simplified configuration of an induction coil 68 and a magnetic flux adjusting member 69 included in the fixing device 67 shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing apparatus 2 Heating roller 3 Pressure roller 4 Magnetic field generating means 8 Conductive layer 41 Image forming apparatus

Claims (6)

[Claims] 1. A heating roller provided with a cylindrical conductive layer made of a conductive material, wherein the layer thickness t1 near both ends in the axial direction of the conductive layer is the layer thickness t of other portions of the conductive layer.
A heating roller formed so as to be thinner than 2, a pressure roller provided opposite to the heating roller and for conveying the material to be heated while being pressed between the heating roller, and applying an alternating magnetic field to the conductive layer And a magnetic field generating means for generating heat by heating. 2. An axial length of a portion where the thickness of the conductive layer is formed at t2 is set to be equal to or longer than a length in a direction perpendicular to a conveying direction of a material to be heated. The heating device according to claim 1. 3. A layer thickness t1 near both ends in the axial direction of the conductive layer.
Is the inequality t1 ≦ √ (2 / ωσμ) where ω: angular frequency of the alternating magnetic field (= 2πf) f: frequency of the alternating magnetic field [Hz] σ: electric conductivity of the conductive layer [S / m] μ: conductive 3. The heating device according to claim 1, wherein the heating device is selected so as to satisfy the magnetic permeability of the layer. 4. The magnetic field generating means includes control means for controlling a frequency of an alternating magnetic field, wherein the control means heats the frequency of the alternating magnetic field in accordance with a length in a direction perpendicular to a conveying direction of the material to be heated. The heating device according to any one of claims 1 to 3, wherein the temperature of the roller is controlled to be uniform. 5. A heating roller further comprising a plurality of temperature detecting means disposed at predetermined intervals in an axial direction of the heating roller and detecting a temperature of the heating roller, wherein the control means responds to an output of each temperature detecting means. 5. The heating device according to claim 4, wherein the frequency of the alternating magnetic field is controlled so that the temperature of the heating roller becomes uniform. 6. A heating device according to any one of claims 1 to 5, a toner image forming means for forming a toner image on a material to be heated, and a material to be heated having a toner image formed on a surface thereof. An image forming apparatus, comprising: a conveying unit that conveys between a heating roller and a pressure roller.