JP2003091186A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a fixing member from being excessively locally heated in a fixing device where an unfixed toner image carried on a recording medium is heated and melted by an electromagnetic induction heating device and fixed on the recording medium. SOLUTION: In this fixing device, a pressure roll 23 is made to press-contact with a heating rotating body 21 having a conductive layer 21a, and the electromagnetic induction heating device 22 is provided to be opposed to the peripheral surface of the rotating body 21. As soon as the roll 23 starts driving and the rotating body 21 is submissively starts rotation at the time of warming-up, an AC current is supplied to an exciting coil 22c from an excitation circuit 22d and the conductive layer 21a generates heat. At such a time, power equal to or under set maximum power is supplied to the coil 22c, and then supplied to increase stepwise with the lapse of time. Therefore, the rotating body 21 is gradually heated until reaching a specified rotating speed without being excessively heated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in image recording devices such as printers, copiers and facsimiles.
The present invention relates to a fixing device in which an unfixed toner image carried on a recording medium is heated and melted by an electromagnetic induction heating device and fixed on the recording medium.

[0002]

2. Description of the Related Art Generally, in a process of fixing a toner image in an image forming apparatus using powdery toner, a toner image is electrostatically transferred onto a recording medium and then the toner image is melted on the recording medium by a fixing device. The crimping method is widely adopted.

The above-mentioned fixing device comprises a fixing member and a pressure member pressed against the fixing member. A recording medium carrying an unfixed toner image is sandwiched between the fixing member and the pressure member. It is heated and pressed to fuse the toner image to the recording medium to form a fixed image. As the fixing member, a heating element such as a halogen lamp is placed inside a cylindrical cored bar, and an elastic layer and a release layer are provided on the surface of the cored bar, or a heat resistance that is supported in a tension-free state. An endless belt or film having a heating element and an internal pressure member is generally used.

When power is applied to the heating element, the surface of the fixing member is heated to a temperature suitable for heating and melting the toner image due to radiant heat or contact heat of the heating element. However, when a heating element such as a halogen lamp is used as a heating source, it takes time for the heat of the heating element to be transferred to the surface of the fixing member after power is applied to the heating element and the fixing member reaches a predetermined temperature. . For this reason, it takes a long time to warm up the fixing member when the apparatus is started or when returning from the standby state, and power consumption increases.

Under these circumstances, for example, Japanese Patent Laid-Open No.
In JP-A-240049, JP-A-2000-221830, and JP-A-2000-330404, a conductive layer is provided on the fixing member as means for heating the fixing member.
It has been proposed to heat the conductive layer by electromagnetic induction heating. In electromagnetic induction heating, an exciting coil that generates a fluctuating magnetic field is arranged so as to face a conductive layer, and a magnetic flux that penetrates the conductive layer is generated to generate an eddy current in the conductive layer and generate heat. . According to the electromagnetic induction heating, the conductive layer can be heated in a very short time, and the fixing member can be directly heated. For this reason,
As compared with the case where a heating element such as a halogen lamp is used as a heating source, the device can be warmed up more efficiently.

[0006]

In such a fixing means, in general, the fixing member is heated to a temperature suitable for heating and fusing the toner image before starting the fixing operation at the time of starting or returning from the standby state. Is preheated, so-called warm-up is performed. In warming up, as shown in FIG. 5, an AC current is applied from the exciting circuit to the exciting coil almost at the same time when the fixing member starts driving, and the conductive layer of the fixing member instantly generates heat and becomes high in temperature. .

However, when the frictional force between the fixing member and the pressure contact member is large, the load on the drive motor for driving the fixing member is large, and the rotation speed of the motor does not reach a predetermined value instantaneously. Acceleration in rotary drive may be delayed. On the other hand, when the fixing member is in the form of a belt or a film, the pressure member that is in pressure contact with the fixing member is usually driven by the motor, and the fixing member is driven to rotate by the rotational driving of the pressure member. However, due to the frictional force between the fixing member and the pressure contact member, the fixing member may slip and the predetermined rotation speed may not be reached immediately.

When the fixing member is heated by the electromagnetic induction heating device in such a state, only the portion of the fixing member facing the electromagnetic induction heating device is continuously heated, and the fixing member may be overheated and damaged. . On the other hand, if an alternating current is applied to the exciting coil after confirming that the fixing member has started to rotate normally, it is possible to prevent the fixing member from generating excessive heat, but it takes a long time to warm up.

Further, in the fixing device described in Japanese Patent Laid-Open No. 2000-330404, the electric power supply to the electromagnetic induction heating device is controlled by an inverter, and the minimum electric power is supplied so that the fixing member maintains a constant temperature during standby of the device. It supplies power and supplies less power when the device is re-powered than when it was started.
In this device, by supplying power to the electromagnetic induction heating device even during standby, the power supply amount at the time of re-driving can be suppressed. However, even if the power supply is controlled as described above, if the fixing member is not driven normally, the fixing member may be excessively heated and damaged.

The present invention has been made in view of the above circumstances, and an object thereof is to heat and melt an unfixed toner image carried on a recording medium by an electromagnetic induction heating device, and fix it on the recording medium. In the fixing device, the fixing member is prevented from being locally overheated at the time of starting or returning from the standby state, and damage to the fixing member is prevented.

[0011]

In order to solve the above problems, the invention according to claim 1 has an endless peripheral surface,
A rotating body which is driven so that the peripheral surface revolves, and a pressure which is arranged so as to face the outer peripheral surface of the rotating body and presses a recording medium carrying an unfixed toner image against the outer peripheral surface of the rotating body. A member, a heating device that heats the rotating body, and a power supply device that supplies electric power to the heating device, and the rotating body has a conductive layer along a circumferential surface,
The heating device is located opposite to the peripheral surface of the rotating body,
The power supply device has an exciting coil that generates an alternating magnetic field to induce an eddy current in the conductive layer, and the power supply device increases stepwise with the passage of time at the same time as or after the drive start of the rotating body. As described above, there is provided a fixing device which supplies electric power to the exciting coil.

Simultaneously with or after the driving of the rotating body is started, electric power is supplied to the exciting coil of the heating device, and the alternating magnetic field is repeatedly generated and extinguished around the exciting coil. When such a fluctuating magnetic field crosses the conductive layer of the rotating body, an eddy current is generated in the conductive layer so as to generate a magnetic field that prevents the change of the magnetic field. Due to the skin effect, this eddy current mostly flows concentratedly on the surface of the conductive layer on the side of the exciting coil, and heat is generated with power proportional to the skin resistance of the conductive layer and the magnitude of the current flowing through the conductive layer. . Electric power is supplied to the exciting coil by the power supply device so as to increase stepwise with the passage of time. Then, as the supply power increases, the current flowing through the conductive layer of the rotating body increases, and the amount of heat generated by the rotating body increases. Therefore, when the rotating body does not drive normally, or when the rotation speed is slow before the driving of the rotating body becomes stable, the portion of the rotating body facing the heating device is excessively heated, and the rotating body is It can be prevented from being damaged.

According to a second aspect of the present invention, in the fixing device according to the first aspect, there is provided an orbital speed detecting means for detecting an orbital drive speed of the rotating body, and after the orbital drive of the rotating body is started, Before the orbiting speed is detected by the orbiting speed detecting means, the power supplied from the power supply device to the exciting coil is set to a predetermined value or less, and when it is detected that the orbiting speed is a normal value, the electric power is supplied to the exciting coil. It is assumed that the power to be used is set to be equal to or higher than the predetermined value.

In the fixing device, the electric power supplied from the power supply device to the exciting coil is below a predetermined value before the orbital speed detecting means detects that the orbital speed of the rotating body is a normal value. . For this reason, when the rotating speed of the rotating body is low or the rotating body is not driven, the amount of heat generated by the conductive layer of the rotating body is small, and the rotating body is prevented from excessive heat generation and damage. Then, when the orbital speed detecting means detects that the orbital speed of the rotating body is a normal value, the exciting coil is supplied with electric power of a predetermined value or more, and the rotating body is heated to a predetermined temperature. In addition, since the rotating body is already heated before the exciting coil is supplied with electric power of a predetermined value or more, compared to the case where the electric power of a predetermined value or more is supplied at the same time when the driving of the rotating body is started, The time for warming up is almost never long.

According to a third aspect of the present invention, in the fixing device according to the second aspect, the rotating body is an endless belt member, and the rotating body is detected when the rotating speed is detected by the rotating speed detecting means. Within 0.5 seconds after the start of driving, the electric power supplied to the exciting coil is 5 before the detection of the revolution speed.
It is assumed that the setting is set to 00 W or less.

Before the orbital speed detecting means detects that the orbital speed of the rotating body is a normal value, the power supplied to the exciting coil is 500 W or less. Has a small amount of heat generated by the conductive layer of the rotating body. The orbital speed of the rotating body is detected by the orbital speed detecting means within 0.5 seconds after the driving of the rotating body is started, and the exciting coil is supplied with electric power of a predetermined value or more, so that the warming-up time is hardly affected. Does not reach.

According to a fourth aspect of the present invention, in the fixing device according to the second or third aspect, the orbital speed detecting means irradiates the peripheral surface of the rotating body with light, and the peripheral surface of the rotating body is irradiated with light. It is assumed that the orbital speed is detected by detecting the light reflected by the reflector provided on the surface.

In the fixing device, the driving speed of the heated rotating body can be easily detected in a non-contact manner, and the amount of electric power supplied to the exciting coil can be easily controlled based on the detected value.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image forming apparatus that can use a fixing device according to an embodiment of the present invention. This image forming apparatus includes a cylindrical photosensitive drum 1 on the surface of which a latent image due to a difference in electrostatic potential is formed by irradiating image light after uniform charging. A charging device 2 for uniformly charging the surface of the photoconductor drum 1, and the photoconductor drum 1
An exposure device 3 for forming a latent image on the surface by irradiating the surface with image light;
A developing unit 4 for selectively transferring toner to a latent image on the photoconductor drum to form a toner image, and an intermediate transfer body in the form of an endless belt which faces the photoconductor drum 1 and whose circumferential surface is rotatably supported. 5, a cleaning device 6 for removing the toner remaining on the photoconductor drum 1 after the transfer of the toner image, and a destaticizing exposure device 7 for destaticizing the surface of the photoconductor drum 1.

Inside the intermediate transfer body 5, a transfer charger 8 for transferring the toner image formed on the photosensitive drum to the intermediate transfer body 5 and two support rolls 9a, 9b.
And a transfer facing roll 10 for performing secondary transfer, and the intermediate transfer member 5 is stretched around these by a roll. The transfer facing roll 10 and the intermediate transfer member 5
A transfer roll 11 for transferring the toner image on the intermediate transfer member to a recording sheet is disposed at a position opposed to each other via a sheet tray (a sheet tray ( The recording paper is fed from (not shown). On the downstream side of the pressure contact portion, a fixing device 12 that heats and melts the toner image on the recording paper and press-bonds it to the recording paper, and a cleaning device 13 that removes the toner remaining on the intermediate transfer member along the intermediate transfer member 5. And are provided.

Next, the details of the structure of the image forming apparatus will be described. The photoconductor drum 1 has a photoconductor layer made of various inorganic photosensitive materials such as Se, a-Si, a-SiC, and Cds, organic photosensitive materials, amorphous selenium-based photosensitive materials, and amorphous silicon-based photosensitive materials on the drum surface. Those that have can be used.

The charging device 2 is made of stainless steel,
The roll is made of a conductive metal such as aluminum and is coated with a high resistance material. The roll is brought into contact with the photosensitive drum 1 and driven to rotate. Then, when a predetermined voltage is applied, a continuous discharge is generated in a minute gap near the contact portion between the roll and the photoconductor drum 1, and the surface of the photoconductor drum 1 is almost uniformly charged. Is.

The exposure device 3 generates a blinking laser beam based on an image signal and scans the laser beam in the main scanning direction of the photoconductor drum 1 by a polygon mirror, whereby the surface of the photoconductor drum 1 is scanned. An electrostatic latent image is formed on.

In the developing unit 4, four developing units containing yellow, magenta, cyan, and black toners are rotatably supported, and the developing units are sequentially arranged close to and opposite to the photosensitive drum 1. The toner is transferred to the latent image corresponding to each color to form a visible image.

The belt-shaped intermediate transfer member 5 has a two-layer structure of a base layer and a surface layer. The base layer is made of polyimide, polyamide, polyamide in consideration of heat resistance, strength and surface smoothness. A heat-resistant resin such as imide or a metal such as aluminum or stainless steel is used, and the surface layer is made of silicone rubber, fluororubber, or the like, which has high heat resistance and releasability from toner.

The transfer charger 8 transfers the toner image on the photosensitive drum 1 to the intermediate transfer member 5 efficiently.
By applying a voltage, charges are applied to the back surface of the intermediate transfer member 5.

The transfer roll 11 is composed of a conductive or semi-conductive roll-shaped member, and when a voltage is applied between the transfer roll 11 and the transfer counter roll 10, the toner images on the intermediate transfer member are collectively transferred onto the recording paper. To do.

Details of the structure of the fixing device 12 will be described with reference to FIG. This fixing device 1
Reference numeral 2 denotes an endless belt-shaped heating rotator 21, an electromagnetic induction heating device 22 supported at a position facing the peripheral surface of the heating rotator 21, and a pressure roll 23 pressed against the heating rotator 21.
And the pressure roller 2 supported on the inner peripheral surface of the heating rotator 21.
Pressure pad 24 for sandwiching heating rotor 21 between
And a peeling member 25 supported near the downstream side of the pressure contact portion between the pressure roll 23 and the pressure pad 24. Further, in the vicinity of the heating rotator 21, a non-contact type temperature sensor 26 for measuring the surface temperature of the heating rotator 21 and a revolution speed sensor 27 are provided.

The heating rotator 21 is composed of a belt-shaped conductive layer 21a as a base layer and a surface release layer 21b laminated thereon. The conductive layer 21a is made of, for example, iron, magnetic stainless steel, magnetic metal such as nickel, or alloys mainly of these, non-magnetic stainless steel, aluminum,
A non-magnetic metal such as copper, or an alloy mainly composed of these and having a thickness of 0.05 μm to 50 μm is used, and the material is selected so that the specific resistance value is sufficient to generate sufficient heat by electromagnetic induction. To be done. The surface release layer 21b has a thickness of 3
A sheet or coat layer having a high releasability of about 0 μm is preferable, and for example, a fluororesin layer can be used. Further, a sheet-shaped member having high heat resistance represented by polyester, polyethylene terephthalate, polyimide amide, etc. may be used as a base layer, a conductive layer may be formed thereon, and a surface release layer may be further laminated thereon. In the outermost layer of the heating rotor 21, that is, the surface release layer 21b, the orbital speed sensor 27 detects the orbital speed of the heating rotor. A plurality of reflectors are provided.

The pressure roll 23 has a metallic cylindrical core bar 23a as a core material, and an elastic layer 23b such as sponge or rubber on the surface of the core bar 23a. The pressure roll 23 is rotationally driven by a drive motor (not shown), and the heating rotator 21 is driven to rotate accordingly.

The electromagnetic induction heating device 22 has a gap between the outer peripheral surface of the heating rotor 21 and the outer peripheral surface of 1 to 1.
It is arranged so as to have a thickness of 3 mm and causes the conductive layer of the heating rotator 21 to generate heat. The electromagnetic induction heating device 22 includes a magnetic core 22b made of ferrite or the like supported by a pedestal 22a, an exciting coil 22c wound around the magnetic core 22b, and the exciting coil 22c.
An exciting circuit 22d for supplying an alternating current to the main part constitutes a main part. The pedestal 22a is non-magnetic and has heat resistance, and is made of heat resistant resin such as polycarbonate or PPS (polyphenylene sulfide), heat resistant glass or liquid crystal polymer. As the magnetic core 22b, a single core block or a plurality of core blocks are continuously arranged.

The pressure pad 24 includes an elastic member 24b curved in a shape along the peripheral surface of the pressure roll 23, a pressure applying member 24c having a protrusion on the process downstream side of the elastic member 24b, and heating. A belt running guide 24d arranged along the inner peripheral surface of the rotating body 21 is supported by a holder 24a made of metal or heat resistant resin.

In the portion of the metallic holder 24a facing the electromagnetic induction heating device 22, a magnetic body 24f for collecting the magnetic flux passing through the conductive layer 21a of the heating rotator 21,
On the magnetic body 24f, a guide pad 24g for guiding the heating rotary body is provided along the inner peripheral surface of the heating rotary body. The magnetic body 24f is made of iron, cobalt, nickel,
Made of magnetic material such as ferrite, guide pad 24g
Is made of a material having a low thermal conductivity in which heat is hardly transferred from the heating rotator 21.

Since the elastic member 24b is in pressure contact with the pressure roll 23 and has a concave shape following the peripheral surface of the pressure roll 23, the elastic member 24b has a sufficient space between the elastic member 24b and the pressure roll 23 via the heating rotor 21. It is possible to obtain a wide pressure contact width. Further, the low friction layer 24e is provided on the surface of the elastic member 24b, and the friction with the inner peripheral surface of the heating rotor 21 can be reduced.

The pressure applying member 24c is the pressure roll 2
3 is made of a material harder than the elastic body layer 23b, and the pressure contact portion between the pressure applying member 24c and the pressure roll 23 is
Strain occurs in the elastic layer 23b of the pressure roll 23.
In the distorted portion, a difference occurs between the moving speed of the recording paper P sandwiched between the heating rotator 21 and the pressure roll 23 and the orbital speed of the heating rotator 21, and the recording paper P and the heating roll are rotated. The adhesive force with the body 21 is reduced, and the recording paper P is easily peeled off.

The belt running guide 24d is a material having a low friction coefficient because it slides on the inner peripheral surface of the heating rotator 21, and has a low thermal conductivity in order to reduce the amount of heat transfer from the heating rotator 21. Those consisting of are desirable.

The temperature sensor 26 measures the temperature of the heating rotator 21 in a non-contact state with the heating rotator 21. For example, infrared rays radiated from the heating rotator 21 are detected to measure the temperature. An infrared sensor that measures can be used. Then, according to the detected value, the heating rotator 21
Excitation circuit 2 so that the surface temperature of
The amount of power supplied from 2d to the exciting coil 22c is controlled.

The orbital speed sensor 27 is the heating rotor 2
Light is irradiated toward the peripheral surface of No. 1 and the light reflected by the reflector provided on the peripheral surface of the heating rotator 21 is detected. Then, from the circumference of the heating rotator, or the distance between the reflectors when a plurality of reflectors are provided, and the time from the detection of the first reflected light to the detection of the next reflected light, The rotating speed of the heating rotator 21 is detected.

In the peeling member 25, the peeling sheet 25b supported by the supporting member 25a is the heating rotator 2
1 and the heating roller 21 on the downstream side of the pressure contact portion of the pressure roll 23.
The release sheet 2 is disposed so as to be close to or in contact with the heating sheet 21 and the recording sheet P that has passed through the pressure contact portion.
5b enters and peels the recording paper P from the heating rotator 21.

The toner used in the image forming apparatus is composed of a thermoplastic binder containing a yellow, magenta, cyan or black dye, and can be formed of a known material.

Next, the image forming apparatus and the fixing device 12 described above.
The operation of will be described. First, the surface of the photosensitive drum 1 is almost uniformly charged by the charging device 2, and then the exposure device 3
Is irradiated with image light to form a latent image on the surface of the photosensitive drum 1 due to the difference in electrostatic potential. Then, the photosensitive drum 1
Is rotated to move to a position facing one developing device 4a of the developing unit 4, the toner of the first color is transferred from the developing device 4a, and a toner image is formed. This toner image is conveyed to a position facing the intermediate transfer body 5 by the circular movement of the photosensitive drum 1, and is electrostatically primary-transferred onto the intermediate transfer body.

On the other hand, the toner remaining on the photoconductor drum 1 after the primary transfer is removed by the cleaning device 7, the surface of the photoconductor drum 1 is initialized to a potential by the neutralization exposure device 8, and the surface of the photoconductor drum 1 is again charged with the charging device 2. Move to the opposite position. After that, the three developing devices 4b, 4c, and 4d of the developing unit 4 are sequentially moved to positions facing the photoconductor drum 1, and similarly, 2
Toner images of the third, fourth, and fourth colors are sequentially formed and transferred onto the intermediate transfer member 5 in an overlapping manner.

Toner image T superimposed on the intermediate transfer member
Is conveyed to a position where the transfer roll 11 and the transfer counter roll 10 face each other by the orbital movement of the intermediate transfer member 5, and is brought into contact with the recording paper P fed from the paper tray. A transfer bias voltage is applied between the transfer roll 11 and the intermediate transfer member 5, and the toner image T is secondarily transferred onto the recording paper.

The recording paper P carrying the unfixed toner image T is conveyed to the fixing device 12 and sent between the heating rotator 21 and the pressure roll 23 of the fixing device 12. Then, the recording paper P is heated and pressed by the heating rotator 21 heated to a predetermined temperature by the electromagnetic induction heating device 22 and the pressure roll 23, and the toner image T is fused and pressure-bonded to the recording paper P. The recording paper P is the elastic layer 23b of the pressure roll 23.
Is in a state of being easily peeled off from the heating rotator 21 at a portion deformed by the pressure applying member 24c, and further peeled off from the heating rotator 21 by the peeling member 25.

The fixing device 12 performs so-called warm-up, in which the heating rotator 21 is preheated to a temperature suitable for heating and melting the toner image before starting the fixing operation from the start-up state and the standby state. . The operation of the fixing device 12 during warm-up will be described based on FIG. An alternating current is supplied from the exciting circuit 22d of the electromagnetic induction heating device 22 to the exciting coil 22c almost at the same time as or immediately after the pressurizing roll 23 starts driving and the heating rotator is driven to start the revolution. To be done. At this time, the exciting coil 22c is supplied with electric power smaller than a preset maximum electric power. On the other hand, immediately after the heating rotator 21 starts to circulate, the orbiting speed of the heating rotator 21 is low because it does not reach a sufficient speed due to a load such as friction resistance with the pressure roll 23.

When an alternating current is supplied to the exciting coil 22c, the magnetic flux indicated by the arrow H is repeatedly generated and extinguished around the exciting coil 22c. Then, when the magnetic flux H crosses the conductive layer 21a of the heating rotor 21, an eddy current is generated in the conductive layer 21a so that a magnetic field that hinders the change of the magnetic field is generated. Heat is generated in proportion to the skin resistance and the magnitude of the current flowing through the conductive layer 21a.
On the other hand, the magnetic flux penetrating the conductive layer 21a is generated by the pressure pad 2
4 to form a closed path toward the magnetic body 24f.

Immediately after the rotation of the heating rotator 21 is started, the rotation speed is small, and the time for passing the position facing the exciting coil 22c, that is, the time for heating is long. However, since the amount of electric power supplied to the exciting coil 22c is kept low, the heating rotator 21 is gradually heated without the temperature rising excessively. This allows
It is possible to prevent the heating rotor 21 from being damaged due to overheating.

Thereafter, as shown in FIG. 3, electric power that increases stepwise with the passage of time is supplied to the exciting coil 22c. When the orbital speed of the heating rotator 21 reaches a predetermined speed and this is detected by the orbital speed sensor 27, the excitation coil 22c is supplied with the maximum power.
The electric power supplied to the exciting coil 22c is 500 W or less until the revolution speed of the heating rotator 21 reaches a predetermined value.

In this fixing device 12, the time from when the heating rotor 21 starts to orbit until the orbital speed reaches the predetermined speed is within 0.5 seconds after the heating rotor 21 starts to orbit. Has become. In addition, as described above, the exciting coil 2
The heating rotor is already heated before the maximum power is supplied to 2c. For this reason, the heating rotor 21 reaches a temperature suitable for heating and melting the toner image in about the same time as when the heating coil 21c starts to rotate and at the same time as the maximum power is supplied to the exciting coil 22c. It can be heated.

Further, the heating rotor 21 slips,
When the drive motor of the pressure roll 23 is out of order and the heating rotor does not normally rotate, the orbital speed sensor 27 does not detect the orbital speed of the heating rotor 21. Therefore, the maximum power is not supplied to the exciting coil 22c, and the heating rotator 21 is prevented from generating excessive heat.

FIG. 4 is a schematic sectional view showing another embodiment of the fixing device that can be used in the image forming apparatus shown in FIG. This fixing device includes a cylindrical heating rotator 31,
Between the electromagnetic induction heating device 32 supported at a position facing the peripheral surface of the heating rotator 31, a pressure pad 33 pressed against the heating rotator 31, and between the heating rotator 31 and the pressure pad 33. The endless belt 34, which is sandwiched and wound around the pressure pad 33 in a state where tension is not introduced, and the heating rotator 31.
Peeling member 35 installed in the vicinity of the temperature sensor 3
6 and a revolution speed sensor 37. The electromagnetic induction heating device 32, the peeling member 35, the temperature sensor 36, and the circulation speed sensor 37 are the same as those of the fixing device shown in FIG.

The heating rotator 31 is composed of a cylindrical metal core 31a made of metal, a conductive layer 31b laminated thereon, and a surface release layer 31c which is the uppermost layer. It is rotationally driven by (not shown). A metal having magnetism is used for the cylindrical cored bar 31a, and in consideration of cost and strength, for example, iron, magnetic stainless steel, nickel or the like is used. The conductive layer 31b has a thickness of 1 μm
Non-magnetic stainless steel, which is a non-magnetic metal of about 15 μm,
Aluminum, copper, etc. are used. Surface release layer 31c
Is preferably a sheet or coat layer having a thickness of about 0.1 μm to 30 μm and high releasability, and for example, a fluororesin layer can be used.

An alternating current is applied to the exciting coil 32a of the electromagnetic induction heating device 32, and the magnetic flux H repeatedly generated and extinguished around the exciting coil penetrates the conductive layer 31b and reaches the cylindrical cored bar 31a. . This cylindrical core metal 31a
Since it is made of magnetic metal, the magnetic flux H forms a closed path toward the magnetic core 32b without penetrating deeply into the cylindrical cored bar.

For the endless belt 34, a heat-resistant resin such as polyimide, polyamide, polyamide-imide, or a metal such as aluminum or stainless is used in consideration of heat resistance, strength, and surface smoothness.

In the fixing device, as in the fixing device shown in FIG. 2, the exciting coil 32 is provided immediately after the start of warming up and before the heating rotor reaches a predetermined revolution speed.
A low power is supplied to a, and the maximum power is supplied to the exciting coil 32a when a predetermined speed is reached. Therefore, the heating rotator 31 is prevented from being overheated and damaged.

[0056]

As described above, in the image forming apparatus according to the invention of the present application, the exciting coil included in the heating device is provided with the passage of time at the same time as or after the driving of the rotating body is started. Electric power is supplied so as to increase stepwise. Then, as the supply power increases, the current flowing through the conductive layer of the rotating body increases, and the amount of heat generated by the rotating body increases. Therefore, when the rotating body does not drive normally, or when the rotation speed is slow before the driving of the rotating body becomes stable, the portion of the rotating body facing the heating device is excessively heated, and the rotating body is It can be prevented from being damaged.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an image forming apparatus that can use a fixing device according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing a fixing device used in the image forming apparatus shown in FIG.

FIG. 3 is a diagram showing the relationship between the orbital speed of the heating rotating body of the fixing device shown in FIG. 2 and the amount of power supplied to the electromagnetic induction heating device.

FIG. 4 is a schematic cross-sectional view showing another embodiment of a fixing device that can be used in the image forming apparatus shown in FIG.

FIG. 5 is a diagram showing a relationship between a revolution speed of a heating rotating body included in a conventional fixing device and a power supply amount to an electromagnetic induction heating device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Charging device 3 Exposure device 4 Developing unit 5 Intermediate transfer member 6 Cleaning device 7 Discharge exposure device 8 Transfer charger 9 Support roll 10 Transfer facing roll 11 Transfer roll 12 Fixing device 21 Heating rotor 22 Electromagnetic induction heating device 23 Pressure Roll 24 Pressure Pad 25 Peeling Member 26 Temperature Sensor 27 Orbital Speed Sensor

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasutaka Naito             430 Green, Sakai, Nakai-cho, Ashigaragami-gun, Kanagawa Prefecture             Inside of Fuji Xerox Co., Ltd. (72) Inventor Baba Kibun             430 Green, Sakai, Nakai-cho, Ashigaragami-gun, Kanagawa Prefecture             Inside of Fuji Xerox Co., Ltd. (72) Inventor Hideaki Ohara             430 Green, Sakai, Nakai-cho, Ashigaragami-gun, Kanagawa Prefecture             Inside of Fuji Xerox Co., Ltd. (72) Inventor Kanji Oka             430 Green, Sakai, Nakai-cho, Ashigaragami-gun, Kanagawa Prefecture             Inside of Fuji Xerox Co., Ltd. (72) Inventor Shigehiko Hasenami             430 Green, Sakai, Nakai-cho, Ashigaragami-gun, Kanagawa Prefecture             Inside of Fuji Xerox Co., Ltd. F-term (reference) 2H033 AA25 BA11 BA12 BA25 BA31                       BA32 BB03 BB05 BB14 BB18                       BB29 BB30 BB37 BB39 BE03                       BE06 CA07 CA13 CA14 CA21                       CA28 CA30 CA40 CA44                 3K059 AA02 AA08 AB19 AB20 AB28                       AC35 AC47 AD08 AD34 CD07                       CD14 CD16 CD32 CD64 CD65                       CD66 CD73 CD75

Claims (4)

[Claims] 1. A rotating body having an endless peripheral surface, which is driven so as to rotate, and an unfixed toner image, which is arranged so as to face the outer peripheral surface of the rotating body. The rotating body has a pressing member that presses the recording medium against the outer peripheral surface of the rotating body, a heating device that heats the rotating body, and a power supply device that supplies electric power to the heating device. Along with a conductive layer, the heating device, the facing is located on the peripheral surface of the rotating body,
The power supply device has an exciting coil that generates an alternating magnetic field to induce an eddy current in the conductive layer, and the power supply device increases stepwise with the passage of time at the same time as or after the drive start of the rotating body. A fixing device for supplying electric power to the exciting coil. 2. An orbiting speed detecting means for detecting an orbiting speed of the rotating body is provided, and after the orbiting speed of the rotating body is started and before the orbiting speed is detected by the orbiting speed detecting means, from the power supply device. The power supplied to the exciting coil is set to a predetermined value or less, and when it is detected that the revolution speed is a normal value, the power supplied to the exciting coil is set to be the predetermined value or more. The fixing device according to claim 1, wherein: 3. The rotating body is an endless belt-shaped member, and when the orbiting speed is detected by the orbiting speed detecting means, it is within 0.5 seconds after the driving of the rotating body is started. Before detection, the power supplied to the exciting coil was 50
The fixing device according to claim 2, wherein the fixing device is set to 0 W or less. 4. The orbital speed detecting means irradiates the peripheral surface of the rotating body with light, detects light reflected by a reflector provided on the peripheral surface of the rotating body, and detects the orbital speed. The fixing device according to claim 2, wherein the fixing device comprises: