JP2003140499A - Induction heating device and image forming apparatus using induction heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heating device and an image forming apparatus in which the transport speed of recording material is not decreased even when the thickness of the recording material is large and optimum fixation that temperature rise at the end of a heating roller or the like and the rise of in-machine temperature caused by such temperature rise are restrained even when size is changed is realized. SOLUTION: This image forming apparatus is equipped with the induction heating device having a heating member to generate heat by an induction current, a pressure member to form a nip by press-contacting with the heating member, and an induction coil to generate magnetic flux supplied to the heating member, and heating the recording material carrying an unfixed toner image and passing through the nip part by the heating member. The image forming apparatus has a mechanism capable of switching a distance between the induction coil and the heating member according to the thickness of the recording material after detecting the thickness of the recording material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an electrophotographic image forming apparatus, and more specifically, an induction heating device for heating and fixing a toner image on a recording material by using electromagnetic induction, and the induction heating. The present invention relates to an image forming apparatus having a device.

[0002]

2. Description of the Related Art In the case of a heating roller type fixing device using an infrared heater, a nichrome wire heater, etc., which has been used in an electrophotographic image forming apparatus, a fixing device of
When the thickness of paper or the like as a recording material is large, fixing is insufficient, and in order to fix this sufficiently, it is necessary to take measures such as slowing the conveying speed.
Also, when the thickness of the paper is changed, the temperature of the heating roller can be adjusted by switching the power, but there are many problems such as the temperature response speed due to the power switching is slow and it is not possible to respond quickly. It was

Another problem of the fixing device using the above-mentioned ordinary heating roller is that of a small size such as A5,
When a sheet of A6 or the like is passed, there is a phenomenon that the end temperature of the heating roller rises and overheats. As a countermeasure against the overheating, a method of cooling the end with a fan or the like has been used. However, even if a method of supplying air with a fan is adopted, the temperature inside the machine rises, the toner melts, and the like due to the warm air exhausted during cooling, causing problems.

A fixing device utilizing electromagnetic induction usually has a heating means utilizing electromagnetic induction and a pressurizing means for rotating in pressure contact with the heating means. The recording medium carrying the image is nipped and conveyed to fix the recording medium. The heating means has a spring-shaped coil or a longitudinally wound coil (induction coil) and optionally a core inside a roller- or belt-shaped rotating heating element, and the coil preferably receives a high-frequency alternating current of 5 kHz or more. Supply to generate an alternating magnetic flux to induce an eddy current in the heating element,
It is a means for heating and fixing by heat generation due to the eddy current loss, and the toner image is fixed on the recording material by heat while being elastically pressed against the pressing means.

Therefore, the fixing device utilizing the electromagnetic induction is smaller and lighter than the conventional fixing device using the infrared heater, the nichrome wire heater, etc., and is free from the danger of fire and consumes no electric power. There is no waste, and it has excellent characteristics such as high-frequency alternating current supply and quick fixing by heating. Recently, research and development on a fixing device using electromagnetic induction have been advanced, and for example, Japanese Patent Laid-Open No. 11-25105.
3, JP-A-2000-29336, JP-A-2000-1
No. 3,1981, various technologies related to a fixing device using electromagnetic induction are proposed.

The present invention takes advantage of the characteristics of a fixing device utilizing electromagnetic induction, such as quick startup, small size and light weight, and provides a solution to the above problems.

That is, unlike a fixing device using a conventional infrared heater or a nichrome wire heater, the fixing device can cope with recording materials having different thicknesses without changing the conveying speed, etc. Even when the recording material is passed, a fixing device capable of fixing in a short time without causing a problem due to overheating can be obtained.

[0008]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to prevent the temperature of the end portion of a heating roller or the like from decreasing the conveying speed of the recording material even if the recording material is thick and changing the size. An object of the present invention is to provide an induction heating device and an image forming apparatus capable of performing optimum fixing while suppressing an increase in temperature and a rise in internal temperature due to the increase.

[0009]

The above objects of the present invention can be achieved by the following means.

1. A heating member that generates heat by induced current,
A recording material having a pressure member that presses against the heating member to form a nip, and an induction coil that generates a magnetic flux to be supplied to the heating member, and carries an unfixed toner image that passes through the nip portion. An image forming apparatus including an induction heating device for heating with a heating member, having a mechanism capable of switching the distance between the induction coil and the heating member according to the thickness of the recording material after detecting the thickness of the recording material. Image forming apparatus.

2. 2. The image forming apparatus as described in 1 above, wherein the heating member is made of a ferromagnetic material.

3. 2. The image forming apparatus according to 1 above, wherein the heating member is a film member, a contact member made of a ferromagnetic material is provided on the film member, and the contact member faces the induction coil. .

4. A heating member that generates heat by induced current,
A recording material having a pressure member that presses against the heating member to form a nip, and an induction coil that generates a magnetic flux to be supplied to the heating member, and carries an unfixed toner image that passes through the nip portion. An induction heating apparatus for heating with a heat from a heating member, characterized by having a mechanism capable of switching the distance between the induction coil and the heating member according to the thickness of the recording material after detecting the thickness of the recording material. apparatus.

5. A heating member that generates heat by induced current,
The recording material passing through the nip portion is heated by the heat from the heating member, which has a pressing member that presses against the heating member to form a nip, and an induction coil that generates a magnetic flux to be supplied to the heating member. In an image forming apparatus equipped with an induction heating device, two or more induction units having different lengths in a direction orthogonal to a recording material conveyance direction are provided in the vicinity of a heating member on a side of a recording material facing a toner image. An image forming apparatus having a coil.

6. 6. The image forming apparatus according to 5, wherein the heating member facing the toner image on the recording material is made of a ferromagnetic material.

7. A heating member facing the toner image on the recording material is a film member, and an abutting member made of a ferromagnetic material is provided on the back surface of the film member, and the abutting member and one of the induction coils are opposed to each other. 5 characterized in that
Or the image forming apparatus according to item 6.

8. 8. The image forming apparatus according to any one of 5 to 7 above, wherein a structure is adopted in which no voltage is applied to each induction coil at the same time.

9. 9. The image forming apparatus as described in any one of 5 to 8 above, wherein each induction coil is movable with respect to a facing fixing member.

10. 10. The image forming apparatus according to any one of 5 to 9 above, wherein each induction coil is arranged in parallel with a facing heating member.

11. 11. The image forming apparatus according to any one of 5 to 10 above, further comprising a unit that switches the induction coil according to the width of the recording material.

12. An unfixed toner having a heating member that generates heat by an induced current, a pressure member that presses against the heating member to form a nip, and an induction coil that generates a magnetic flux to be supplied to the heating member, and passes through the nip portion. In an induction heating device that heats and fixes a recording material carrying an image with heat from the heating member, the recording material is orthogonal to the conveying direction of the recording material in the vicinity of the heating member on the side facing the toner image on the recording material. An induction heating device comprising two or more induction coils having different lengths in different directions.

The present invention will be described in detail below. The image forming apparatus of the present invention includes a heating member that generates heat by an induced current, and a pressing member that presses against the heating member to form a nip.
And an induction coil that generates a magnetic flux to be supplied to the heating member. When a recording material (for example, paper) carrying an unfixed toner image passes through the nip portion, the toner image is fixed by the heat from the heating member heated by the alternating magnetic flux generated by the induction coil. The nip portion where the fixing is performed is formed between a heating member (for example, a heating roller) and a pressure member (for example, a pressure roller) that presses against the heating member, and the recording material (paper) is introduced into the nip portion. The heat of the heating member is applied to the recording material to heat and fix the toner image on the recording material.

In the image forming apparatus of the present invention, when the toner image is fixed on the recording material by heat, the thickness of the recording material is detected in advance to detect the thickness of the recording material.
It has a mechanism capable of switching the distance between the induction coil and the heating member. Accordingly, even when the thickness of the recording material changes, the distance between the induction coil and the heating member can be adjusted according to the recording material to heat the heating member to the optimum temperature required for fixing.

The heating member typically has a thickness of 0.
A conductive core metal cylinder (heating rotor) made of a ferromagnetic material having a thickness of 5 to 5 mm and good thermal conductivity, and a cylindrical heating roller having a heat insulating material therein are used. The heating roller is heated by forming an AC magnetic field inside the heating rotator by the magnetic flux emitted from the induction coil. That is, the heating rotator is a magnetic field generating means (induction coil and magnetic core) by passing an electric current through the induction coil
The magnetic flux generated from the magnetic field causes an AC magnetic field of about 0.5 to 50 kHz to be formed in the ferromagnetic material forming the core metal cylinder, and the heating roller is heated by the eddy current generated inside the ferromagnetic material generated by the AC magnetic field. It

A heating belt is included as another heating member. Although the belt system will be described later, it is an endless (cylindrical, seamless) heat-resistant belt, in which an endless film member made of a heat-resistant resin has a conductive contact member (conductive layer) made of a ferromagnetic material. Is provided so that the abutting member and one of the induction coils face each other. Further, it may have a three-layer structure in which a release layer is formed on the surface of the conductive layer. Of course, the present invention is not limited to this. For example, the belt base layer and the conductive layer may not be separate layers, and the film substrate itself may be a ferromagnetic material. Also in this case, an AC magnetic field is formed in the heating belt conductive layer by the magnetic flux generated by passing an electric current through the induction coil, and the heating belt is heated by the eddy current inside generated by the AC magnetic field.

An induction coil and optionally a magnetic core are used as the magnetic field generating means. In the present invention, the induction coil is designed so that the distance to the heating roller or heating belt facing the induction coil can be changed. When it is small, the change in the magnetic flux generated by the induction coil is greatly affected to increase the eddy current flowing in the ferromagnetic material forming the heating member to form the surface layer of the heating member. (Layer) is heated strongly to generate a high temperature. In addition, it is possible to suppress the heat generation of the heating member by adjusting the strength by separating the distance.

Therefore, the means for separately detecting the thickness of the recording member by means of the sensor and the magnetic field generating means comprising the induction member and the magnetic core, etc. facing the heating member by previously detecting the thickness of the recording member by the sensor. By using the fixing device or the image forming apparatus equipped with the means for adjusting the distance, the image forming apparatus can cope with recording materials of various thicknesses.

The magnetic field generating means of the present invention is typically composed of an induction coil, a magnetic core and a high frequency power source for applying a high frequency alternating current to the induction coil.
As long as the AC magnetic field H of about Hz is formed, various configurations are used and the form is not limited.

As the magnetic field generating means, a magnetic core wound with a litz wire coil as an induction coil is preferably used.

Iron is mainly used for the magnetic core,
In order to increase the heat generation of the heating rotor, use materials with high magnetic permeability and low residual magnetic flux density, such as ferrite and permalloy.
Strengthens the magnetic flux generated by the induction coil. Alternatively, the current flowing through the heating rotor is increased by increasing the change in magnetic flux. The magnetic core 22 shown in FIG.
1 is an E shape having one central wall and two side walls, but an I shape having one central wall and a U shape having two side walls are also applicable.

As the pressing member paired with the heating member, a pressing roller is mainly used, and a soft roller is formed by forming an elastic layer made of a sponge-like thick rubber layer on the outer peripheral surface of a metal cored bar. It Further, a coating layer may be formed on the outer side in order to obtain releasability. By using an elastic rubber roller having a high heat insulating property as the pressure roller, it is possible to prevent diffusion of heat from the heating member and to secure a wide nip width. The toner is fixed by the planar fixing nip portion N formed between the heating member and the pressing member.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an image forming apparatus and an induction heating apparatus of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross sectional view showing an example of the induction heating device of the present invention. The heating roller 1 includes a metal cylinder 11 which is a heating member, and a heat insulating material 12 inside the cylinder (for example, as the heat insulating material, resin, rubber, foamed materials of these materials, non-woven fabric, or the like is used. Is a rubber with a high foaming rate). The cylinder has a thickness of 0.5 to 5 mm and mainly uses an iron cored bar cylinder that transmits magnetic flux and has good heat conductivity. The surface of the cylinder is coated with a perfluoroacrylate (PFA) tube having a thickness of 20 to 100 μm or a polytetrafluoroethylene (PTFE) tube in order to improve the releasability from the toner, or a fluororesin ( 20-100 PFA or PTFE paint
The one having a thickness of 20 μm to 500 μm and the one having a layer thickness of 20 to 500 μm molded with silicone rubber or fluororubber have a thermal conductivity of (3
-10) × 10 ⁻³ J / cm · s · K surface layer may be provided.

A magnetic field generating means 2 is provided so as to face the heating roller and comprises an induction coil 21 and a magnetic core 22. Although not shown in the figure, the induction coil is coupled to a high frequency AC power source via a conductor.

An AC magnetic field of about 0.5 to 50 kHz is formed inside the metal cylinder 11 by the magnetic flux generated from the magnetic core by passing a current through the induction coil.
The metal cylinder is heated by the eddy current generated by this alternating magnetic field.

In the figure, L represents the distance between the induction coil and the heating roller. By adjusting the distance, the eddy current generated inside the metal cylinder can be adjusted to adjust the surface temperature of the heating roller. For example, in the case of a thick recording material, for example, the temperature of the heating roller is raised by reducing the distance between the induction coil and the heating roller, that is, the value of L is reduced. For example, by setting the value of L to be larger and setting the temperature of the heating roller to be slightly lower by increasing the distance, it becomes possible to control the fixing conditions (in the figure, a means for changing the position of the induction coil 21 is shown. Not). Since the response of the induction heating by the magnetic flux is fast, the optimum heating temperature can be automatically set according to the thickness of the recording material by combining with a mechanism for detecting the thickness of the recording material (recording paper) and linking it.

The pressure roller 3 forming a pair with the heating roller includes, for example, a core metal 31 made of aluminum and a silicone rubber layer or a fluororubber layer on the outer peripheral surface of the core metal, or a foamed material of silicone rubber. Sponge-shaped, thickness (wall thickness) 5-20mm, rubber hardness 10Hs-40H
It is configured as a soft roller having an outer diameter of about 25 to 50 mm formed with an elastic layer 32 made of a thick rubber layer of s (JIS, A rubber hardness). On the outer side of the elastic layer 32, a coating layer 33 that covers a tube made of heat-resistant fluororesin such as PFA or PTFA having releasability is formed. By using an elastic rubber roller having a high heat insulating property for the lower pressure roller, it is possible to prevent heat from being diffused from the upper heating roller and to secure a wide nip width. The toner is fixed by the planar fixing nip portion N formed between the heating roller and the pressure roller.

In order to prevent the influence of magnetic flux on other parts of the image forming apparatus (for electromagnetic shielding), the fixing device is covered with a shield member 4 formed of a conductive member such as metal such as aluminum. Preferably.
The two guide rollers 5 eject the recording material after fixing.
Further, a temperature detecting element TS for detecting the surface temperature of the metal cylinder is arranged near the outer peripheral surface of the metal cylinder.
The temperature sensing element may be arranged near the magnetic core or the induction coil. As the temperature detecting element, an infrared non-contact temperature sensor, a thermistor, a thermocouple or the like can be used.
The temperature detecting element is also preferably covered with an electromagnetic shield member, and the electromagnetic shield member is any one of ferrite, nickel fiber and permalloy. This enables accurate temperature detection without the influence of magnetic flux.

FIG. 2 shows an AC magnetic field H generated in the induction coil, the magnetic core, and the metal cylinder 11 of the heating roller generated by the magnetic core. The magnetic field generating means 2 is composed of an E-shaped induction coil 21 having one central wall and two side walls and a magnetic core 22, and indicates an AC magnetic field H generated in the magnetic core and the metal cylinder. . 1
3 is a polytetrafluoroethylene (PTFE), a fluororesin (PFA or PTF) provided on the surface of the heating roller for improving the releasability from the toner.
E) or a surface layer (release layer) of silicone rubber or fluororubber, and 12 is a heat insulating material.

Although iron is used for the magnetic core 22, in order to increase the heat generation of the metal cylinder, a material having a high magnetic permeability and a small residual magnetic flux density such as ferrite or permalloy is used, and the magnetic flux generated by the induction coil is strengthened. Or by increasing the change in magnetic flux, the current flowing through the metal cylinder of the heating roller is increased.

With such a structure, a high-frequency alternating current is passed through an induction coil outside the heating roller to generate an alternating magnetic flux,
The roller is heated and fixed by Joule heat generated by the eddy current generated in the heating roller. However, when the thickness of the paper is different and, for example, 110 kg of paper is passed, the distance L between the roller and the induction coil is set to For example, it is heated closer than when 55 kg paper is used. As a result, the heat generation efficiency is increased, and the fixability can be improved even on thick paper.

FIGS. 3 and 4 are sectional structural views showing another embodiment of the induction heating apparatus of the present invention. As in the induction heating apparatus shown in FIG. 1, the toner held on the recording material is heated and melted. And is fixed to the recording material, and is composed of a ferromagnetic material in an endless film member of a heat-resistant resin having a releasing layer (not shown in the figure) having a releasing property for toner. Conductive contact member (conductive layer)
Is used with a heating belt provided so that the contact member and one of the induction coils face each other.

A magnetic field generating means such as an induction coil and a magnetic core is installed on the side of the ferromagnetic material layer or on the side opposite thereto so that the distance to the heating belt can be adjusted. It is preferable to provide an abutting member of the ferromagnetic material on the pressure-contact surface side of the material to be heated, because the side of the recording material on which the toner image is carried is fixed to the layer made of the ferromagnetic material. It is preferable that the induction coil is installed closer to the ferromagnetic material layer side (that is, on the outer side) because heating efficiency is higher, but when the film member has a small thickness, the belt substrate itself is also used. When is made of a ferromagnetic material, it is preferably installed inside from the viewpoint of compact design of the induction heating device.

FIG. 3 shows a heating belt 6 provided with a conductive layer of the ferromagnetic material, a driving roller 7 and a tension roller 8 for driving the heating belt, and an induced current is generated in the conductive layer of the heating belt 6. Magnetic field generating means 2 (provided inside the heating belt) for inductively heating the heating belt, a high-frequency AC power supply unit (omitted) for supplying electric power to the magnetic field generating means 2, and holding and heating the magnetic field generating means 2. It is an induction heating device provided with means (not shown in the figure) for adjusting the distance between the outer surface of the belt 6 and the magnetic field generating means 2. The recording material holding the unfixed toner has a pressure roller 3 that rotates together with the heating belt 6 while sandwiching it between the heating roller 6 and a portion N (nip portion) where the heating belt 6 is in pressure contact with the heating belt 6. It is fixed by passing. Temperature detecting elements TS are arranged in front of and behind the nip portion to detect the temperature of the heating belt.

The magnetic field generating means can achieve the object of the present invention by adjusting and controlling the distance according to the thickness of the recording material detected in advance by means for adjusting the distance from the heating belt.

The respective parts will be described in detail below.
If the surface resistance of heat-resistant resin (for example, polyimide, polyether, polyamide or tetrafluoroethylene / perfluorovinyl ether copolymer) is 10 ¹⁴ Ω or more,
A high resistance film having a thickness of about 20 μm is used as a base material of the endless belt, and a conductive layer (for example, nickel or the like) having a surface resistance of 10 ⁵ to 10 ⁸ Ω on the outer periphery of the base material (the pressure contact surface side of the material to be heated). Thin film), and further on the surface of the conductive layer,
It has a three-layer structure in which a release layer made of fluorine-based or silicon-based resin is formed. Of course, the present invention is not limited to this, and for example, a release layer having a thickness of ⁵ to 15 μm and having a surface resistance of 10 ⁵ to 10 ⁸ Ω by adding a conductive agent to a fluorine-based or silicon-based resin on a base material. It may have a two-layer structure provided, or the belt base material itself may be the conductive layer.

The magnetic field generating means is the induction coil 2 as in the above.
It is composed of an E-shaped magnetic core 22 having one and one central walls and two side walls.

The magnetic field generating means 2 is a laterally long member having a length in a direction intersecting (orthogonal to) the moving direction of the heating belt 6.

Although not shown in the figure, the magnetic field generating means is held by the control means which detects the thickness of the recording material and then controls and changes the distance to the heating belt according to the thickness.

The driving roller 7 is rotatably held via bearings, and sliding bearings are formed at both ends of the driving roller 7 and are rotatably attached.
A drive gear is fixed to one end, and is rotationally driven by a drive source such as a motor and a speed reducer connected to the drive gear.

The tension roller 8 is rotatable according to the drive of the driving roller 7, and is rotatably attached to a fixing device unit frame (not shown) by a shaft. Other reference numerals have the same meaning as in FIG.

Although the temperature detecting element TS is arranged inside the heating belt before and after the nip portion of the pressure roller in the present embodiment, the temperature detecting element TS is arranged at a position depending on the structure of the fixing device. Differently, it may be appropriately arranged outside or inside the heating belt before and after the nip portion of the pressure roller. Although not shown in the figure, the temperature detecting element TS is fixed to the fixing device unit frame by a supporting member made of heat resistant resin.

With the above structure, after the thickness of the recording material is detected in advance, the distance L between the induction coil and the heating belt can be controlled to the optimum position set by the thickness of each recording material to perform the optimum fixing. .

Further, by disposing the temperature detecting element TS for the temperature before the nip of the heating element and the temperature detecting element TS for the temperature after the nip of the heating element, the nip is removed from the temperature detecting element disposed before the nip. Information about the amount of heat lost in other parts, the amount of heat lost in the nip part is obtained from the temperature sensing element arranged after the nip, and this information and the control temperature according to the thickness of the recording material are stored in advance in the memory. The CPU of the control means can perform an analysis process based on the information from the CPU, and the corrected amount of the supplied power can be accurately determined by the CPU and fed back through the CPU to be calculated in advance between the induction heating device and the heating belt. By controlling the optimum amount of electric power at different distances, optimum heat fixing can be performed according to the thickness of each recording material.

In the temperature control of the heating element of the present invention, the optimum amount of heat can be rapidly supplied to the temperature to be corrected, so that the overshoot can be reduced.

Also in an induction heating apparatus using a heating belt in which an endless film member of the heat resistant resin is provided with a conductive contact member (conductive layer) made of a ferromagnetic material, the conductive layer of the heating belt is also used. The magnetic field generating means may be arranged on the side. Since the induction coil and the conductive layer are close to each other, heating efficiency is good. FIG. 4 is a cross-sectional configuration diagram showing another example of such an induction heating device.

The magnetic field generating means used in the present invention is preferably cooled by a cooling device. As the cooling device, an air blowing device is used such that air is continuously fed by rotation of an impeller or air is continuously fed by rotation of a rotor (above, JIS standard). Alternatively, a cooling device in which cooling means is connected to the blower to send out cool air is also applicable.

The magnetic field generating means is cooled by the air or cold air that has been fed under pressure to lower the surface temperature of the induction coil and the magnetic core. Further, it is possible to prevent a temperature rise due to radiant heat from the heating member.

Magnetic core 2 such as ferrite which is a ferromagnetic material
When the temperature of 2 becomes near the Curie temperature, the magnetic permeability sharply decreases and the heat generation efficiency decreases. Moreover, since the inductance of the magnetic core changes greatly, the output of the high frequency power supply decreases.

In order to prevent these problems, when the temperature of the magnetic core approaches the Curie temperature, the magnetic core is forcibly cooled. However, the Curie temperature differs depending on the material of the magnetic core such as ferrite, and even the same product has variations during manufacturing, so the temperature difference between the Curie temperature of the magnetic core and the temperature of the magnetic core is constant. When it is detected that the value becomes, the driving of the cooling device may be started, and the magnetic core and the induction coil may be cooled by blowing air.

FIG. 5 is a sectional view showing an example of an image forming apparatus using the induction heating device according to the present invention.

The image forming apparatus shown in FIG.
01 is provided with a charging means 102, an exposure means 103, a developing means 104, a transfer means 105, a charge eliminating means 105A, a separating means 106, and a cleaning means 107. After the charging unit 102 uniformly charges the surface of the photoconductor 101, the laser of the exposure unit 103 irradiates light based on the image data read from the original to form a latent image, and the latent image is formed. Inverse development is performed by the developing unit 104 to which a bias is applied, and the photoconductor 10
A toner image is formed on the surface of 1.

On the other hand, the recording material (paper) P fed from the paper storage means 108 is sent to the transfer position, and the toner image is transferred onto the paper P by the transfer means 105 at the transfer position. After that, the charge on the back surface of the sheet P is erased by the charge eliminating unit 105A, and the photoconductor 1 is separated by the separating unit 106.
Separated from 01 and conveyed by the intermediate conveying section 109,
Subsequently, it is heated and fixed by the induction heating device 110 of FIG. 1 of the present invention, and is discharged to the discharge tray. On the other hand, the photoconductor 10
On the surface of No. 1, the developer remaining on the surface is removed by the cleaning unit 107 downstream of the separating unit 106 to prepare for the next image formation. Although the means for detecting the thickness of the recording material and the means for adjusting the position of the magnetic field generating means such as the induction coil are omitted in FIG. 5, the recording material is fixed after the paper is fed from the paper storage means. Optimum fixing can be obtained by detecting the thickness of the sheet at any position on the transport path and changing the distance between the induction coil of the induction heating device and the heating roller according to the detection result.

With the induction heating apparatus of the present invention, optimum fixing can be performed on recording materials having different thicknesses according to the thickness of the recording materials. Another aspect of the present invention will be described below.

In another aspect of the present invention, it is possible to obtain a fixing device capable of optimally fixing a plurality of recording materials having different sizes.

That is, in another image forming apparatus of the present invention, a heating member that generates heat by an induced current, a pressing member that presses against the heating member to form a nip, and a magnetic flux that is supplied to the heating member is generated. The recording material is introduced into a fixing nip portion formed of a heating member and a pressure member that is in pressure contact with the heating member, and the heating member that generates heat by an induction current heats the toner image on the recording material. As an induction heating device for fixing the recording material carrying the unfixed toner image passing through the nip portion, the outer periphery of the heating member on the side facing the toner image on the recording material. In the vicinity of the surface, two or more (a plurality depending on the type of recording material of different sizes) induction coils having different lengths in the direction orthogonal to the recording material conveyance direction, and a magnetic core if necessary Magnetic field generating means It is to use an induction heating apparatus provided.

The plurality of magnetic field generating means have different lengths, and it is preferable that the lengths correspond to different recording material (paper) widths. By switching and using the magnetic field generating means corresponding to the paper width, the hollow rotating body (heating roller) can generate heat only with the desired paper width, and the end of the heating roller heats up depending on the size of the paper (recording material). , It is not necessary to provide a fan for cooling this.
It suffices to provide a magnetic field generating means corresponding to several commonly used sizes.

Since the other components of the image forming apparatus are the same as those of the image forming apparatus described above, the induction heating apparatus provided with the magnetic field generating means having several sizes corresponding to the sizes of a plurality of recording materials will be described here. , Detailed.

In this embodiment, by arranging a plurality of induction coils (and magnetic cores) having different lengths in the circumferential direction of the heating roller or heating belt, the size of the paper (recording material) can be improved.
For example, an induction coil having a length corresponding to the paper width is used, a high-frequency alternating current is passed through the induction coil to generate an alternating magnetic flux, and the heating roller or the heating belt is heated by Joule heat due to eddy current. That is, after the image recording device or the induction heating device detects the width of the recording material (paper), the induction heating device composed of the induction coil and the magnetic core corresponding to the width is moved immediately before the nip for heat fixing. Then, if a high-frequency alternating current is passed through this to generate an alternating magnetic flux, the heating roller or the heating belt can generate heat only with the desired paper width. By using such an induction heating device, it is possible to prevent an increase in the end temperature of the heating roller or the heating belt and the like, and to prevent an increase in the temperature inside the machine and the melting of the toner.

Embodiments of the image forming apparatus and the induction heating apparatus will be described below with reference to the drawings.

[0071]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 6 shows an induction heating apparatus 1 according to this embodiment.
It is a section lineblock diagram showing an example.

A heating roller 1 serving as a heating member, a pressure roller 3 forming a nip facing the heating roller, a shield member 4 for shielding a magnetic field, a guide roller 5 for discharging a recording material after fixing, etc. 3 but with a different length in the axial direction of the roller facing the heating roller.
Magnetic field generating means R1 comprising a seed induction coil and a magnetic core
The rollers R3 to R3 are rotated in the circumferential direction of the roller and are respectively arranged at positions facing the roller so that they can be switched and used. Although not understood from the figure, for example, R1 has a width corresponding to B4, R2 has a width corresponding to A4, R3 has a width corresponding to the width of the recording material, such as B5. The generating means is in the axial direction of the roller.

Although not shown in the figure, the induction coils are each coupled to a high frequency power source through a conductor. By applying an electric current to the induction coil, the alternating magnetic flux generated from the magnetic core causes 0.5 to 5 inside the metal cylinder 11.
An AC magnetic field of about 0 kHz is formed, and the eddy current generated by this AC magnetic field heats the metal cylinder.

When the induction heating apparatus or the image forming apparatus of the present invention detects the width of the recording material (paper) in advance, any of the magnetic field generating means R1 to R3 composed of an induction coil and a magnetic coil corresponding to the size of the recording material. Moves to a position facing the metal cylinder just before the nip. Then, the heating roller is caused to generate heat only with the desired paper width. A plurality of magnetic field generation means are connected in parallel to the AC power supply, and after detecting the paper width,
It has a mechanism to be connected to the corresponding induction coil. Therefore, it is preferable that the plurality of magnetic field generating means have a structure in which a high frequency voltage is not applied simultaneously.

FIG. 7 is a schematic perspective view showing the heating roller and the magnetic field generating means facing the heating roller, in which only the relationship between the heating roller and the magnetic field generating means is taken out.
On the other hand (an induction coil is omitted in the figure), another magnetic field generating means R2 used for recording materials of different sizes is on standby. A plurality of magnetic field generating means are arranged in parallel and are on standby, and any means may be used as long as it is a mechanism for switching these according to the size of the recording material. 6 and 7,
Although the magnetic field generating means, that is, the means for switching the induction coil is not shown, by combining with a mechanism for detecting the width of the recording material (recording paper) and linking it, the optimum induction coil according to the size of the recording material is automatically generated. You can select and switch the size.

In this way, by arranging the sizes of the magnetic field generating means (induction coils) according to the type of recording material, only the portion necessary for fixing can be provided without applying excessive heating to the end portion of the heating roller. It can be heated. In addition, since the induction heating response by the magnetic flux is fast, quick switching is possible.

FIG. 8 shows an example of a heating belt type, which is similar to FIG. 3 except that the magnetic field generating means is used by switching the size.

By using the fixing device with the induction heating device whose size can be switched in place of the induction heating device shown in FIG. 5, for example, the induction heating device can be switched depending on the size of the recording material (paper) to form an image. The device can be obtained as well.

In the fixing device of the present invention, a color image is formed on the photoconductor or the intermediate transfer member by the image forming means, the color toner image is transferred onto the paper by the transferring means, and then the color toner image is formed by the fixing device. It can also be applied to a color image forming apparatus of a fixing processing type.

[0080]

EFFECTS OF THE INVENTION Even when the recording material (paper) is thick, the conveying speed of the recording material is not reduced, and even if the size is changed, the temperature rise in the end portion of the heating roller or the inside of the machine can be suppressed. Thus, it was possible to provide a fixing device capable of optimal fixing.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram showing an example of an induction heating device of the present invention.

FIG. 2 is a diagram showing an AC magnetic field H generated in a metal cylinder 11 of a heating roller.

FIG. 3 is a cross-sectional configuration diagram showing another aspect of the induction heating device of the present invention.

FIG. 4 is a cross-sectional configuration diagram showing another aspect of the induction heating device of the present invention.

FIG. 5 is a cross-sectional configuration diagram showing an example of an image forming apparatus using the induction heating device of the present invention.

FIG. 6 is a cross-sectional configuration diagram showing an example of an induction heating device having a plurality of induction coils.

FIG. 7 is a schematic perspective view showing a heating roller and a magnetic field generating unit facing the heating roller.

FIG. 8 is a cross-sectional configuration diagram showing an example of an induction heating device of a heating belt type having a plurality of induction coils.

[Explanation of symbols]

1 heating roller 2 Magnetic field generating means 3 pressure roller 4 Shield material 5 Guide roller 6 heating belt 7 drive roller 8 tension roller 11 Metal cylinder 12 Insulation 13 Surface layer (release layer) 21 induction coil 22 Magnetic core 31 core metal 32 elastic layer 33 Heat-resistant coating layer 101 photoconductor 102 charging means 103 exposure means 104 developing means 105 transfer means 105A static eliminator 106 separation means 107 cleaning means 108 paper storage means 109 Intermediate transport section 110 Induction heating device H AC magnetic field N fixing nip TS temperature sensing element

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H027 DC02 DC10 DE07 EA12 EC06                       EC18 ED17 ED25 EE01 EF09                       ZA07                 2H033 AA24 AA47 BA11 BA12 BA26                       BA27 BB03 BB06 BB13 BB14                       BB21 BB23 BE03 BE06 CA16                       CA17 CA30                 3K059 AA08 AB19 AB28 AC37 AC38                       AD03 AD05 AD13 AD15 AD19                       AD40 CD52 CD53 CD64 CD66                       CD72 CD75 CD77 CD79

Claims (12)

[Claims] 1. A heating member that generates heat by an induced current, and a pressure member that presses against the heating member to form a nip.
An image forming apparatus having an induction heating device for heating a recording material carrying an unfixed toner image passing through a nip portion with an induction coil, the induction coil generating a magnetic flux supplied to the heating member, An image forming apparatus having a mechanism capable of switching the distance between the induction coil and the heating member according to the thickness of the recording material after detecting the thickness of the recording material. 2. The image forming apparatus according to claim 1, wherein the heating member is made of a ferromagnetic material. 3. The heating member is a film member, and an abutting member made of a ferromagnetic material is provided on the film member, and the abutting member and the induction coil are opposed to each other. The image forming apparatus according to item 1. 4. A heating member that generates heat by an induced current, and a pressure member that presses against the heating member to form a nip.
In an induction heating device having an induction coil for generating a magnetic flux supplied to the heating member and heating an unfixed toner image passing through a nip portion with heat from the heating member, An induction heating apparatus having a mechanism capable of switching the distance between the induction coil and the heating member according to the thickness of the recording material after the thickness is detected. 5. A heating member that generates heat by an induced current, and a pressing member that presses against the heating member to form a nip.
In an image forming apparatus having an induction heating device for generating a magnetic flux to be supplied to the heating member, the induction heating device heating the recording material passing through the nip portion with the heat from the heating member. An image forming apparatus characterized in that two or more induction coils having different lengths are provided in a direction orthogonal to a recording material conveyance direction in the vicinity of a heating member on a side facing a toner image. 6. The image forming apparatus according to claim 5, wherein the heating member facing the toner image on the recording material is made of a ferromagnetic material. 7. A heating member facing a toner image on a recording material is a film member, and an abutting member made of a ferromagnetic material is provided on the back surface of the film member, and the abutting member and one of the induction coils are provided. 6. Opposed to each other.
Or the image forming apparatus according to item 6. 8. The image forming apparatus according to claim 5, wherein the induction coil has a structure in which no voltage is applied to the induction coils at the same time. 9. The image forming apparatus according to claim 5, wherein each induction coil is movable with respect to a fixing member facing the induction coil. 10. The image forming apparatus according to claim 5, wherein the induction coils are arranged in parallel with the facing heating member. 11. The image forming apparatus according to claim 5, further comprising means for switching the induction coil according to the width of the recording material. 12. A heating member which generates heat by an induced current,
A recording material having a pressure member that presses against the heating member to form a nip, and an induction coil that generates a magnetic flux to be supplied to the heating member, and carries an unfixed toner image that passes through the nip portion. In an induction heating device that heats and fixes with heat from a heating member, the length differs in the direction orthogonal to the recording material conveyance direction in the vicinity of the heating member on the side facing the toner image on the recording material. An induction heating device comprising one or more induction coils.