JP2002270356A - Heating equipment, fixing equipment, and image forming equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain heating equipment of an induction heating, fixing equipment, and image forming equipment, in which a magnetic flux generating coil does not become high temperature, and a body of revolution can be uniformly heated in its length direction and also can be almost uniformly heated in its circumference direction of the body of revolution. SOLUTION: The heating equipment constitutes of the body of revolution 11 having an induction heating body, a pressurizing component 13, which is cramped with pressure to the body of revolution 11, and a magnetic flux generating means 12 arranged facing the perimeter of the body of revolution 11, and heats up the heated body by making the heated body pass through between the body of revolution and the pressurizing component 13. The magnetic flux generating means 12 has a core 21, which consists of a high magnetic permeability material, and a conductive wire rod 30, which is wound on the core 21 in parallel in the length direction of the body of revolution 11, and supplies frequency current. The core 21 approaches the body of revolution 11 to the closest distance in the both-sides end of the core 21 or its near in a direction perpendicular to a plane made by a torus, which the conductive wire rod 30 makes. The distance of the core 21 and the body of revolution 11 in the closest approaching position is constant in the longer direction of the body of revolution 11, and the conductive wire rod 30 is wound around the core 21 avoiding the above closest approach position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating apparatus for generating eddy currents by electromagnetic induction and heating the same, and also relates to a recording apparatus such as a copying machine, a facsimile, and an electrophotographic printer for recording paper or the like. A heat-fixing device for fixing an image formed of a heat-fusible toner formed on a medium surface as a permanent fixed image by heating and pressing on a recording material surface, and an image provided with the heat-fixing device as image heating means The present invention relates to a forming apparatus.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer, and a facsimile, an unfixed toner image is formed on a sheet-shaped recording medium by a transfer method or a direct method by an image forming process mechanism such as an electrophotographic method. Let it. Since the toner of the unfixed toner image is easily peeled off, it is necessary to permanently fix the toner on the surface of the sheet-shaped recording medium by applying heat, pressure, or both heat and pressure to the toner. This step is called a fixing process. The material of the sheet-shaped recording medium is not limited as long as the sheet-shaped recording medium can fix a toner image.
As an example of the sheet-shaped recording medium, plain paper or an OHP sheet cut into A4 size, A3 size, or the like is generally used. There are various ways to achieve the fusing process, but applying both heat and pressure is the most common. As a heating method at that time, a contact heat fixing method such as a heat roller fixing method or a film heat fixing method has been generally used.

A fixing device of a heat roller fixing type and a film heat fixing type is composed of a rotatable hollow or solid cylindrical member (hereinafter referred to as a rotator) and a sheet-shaped recording medium pressed against the rotator. (In the case of a hollow or solid cylindrical shape, referred to as a pressure roller). The rotating body may be heated by a heating element disposed in contact with or in the vicinity of the rotating body, or may be self-heating, with a part or all of the rotating body being a heating element. In the heat roller fixing method, the above-mentioned rotating body and a heating element for heating the rotating body are collectively referred to as a fixing roller. Alternatively, only the rotating body may be called a fixing roller.

The main difference between the heat roller fixing method and the film heat fixing method is that in the former, the rotating body has a certain thickness, and the rotating body is hardly deformed even when pressure is applied from the outside, but in the latter, pressure is applied. The more easily it deforms, the thinner the rotating body is. The sheet-shaped recording medium is conveyed between the rotating body and the pressing body following the rotation of the rotating body or the pressing body. Then, at a pressure contact portion (hereinafter, referred to as a nip portion) between the rotating body and the pressing body, the toner on the sheet-shaped recording medium is melted by the heat of the rotating body, and is pressed by the pressure applied by the rotating body and the pressing body. The image is fixed on the recording medium.

In the heat roller fixing method, a rod-shaped heating heater such as a halogen lamp or a nichrome wire heater is disposed on the center axis of the rotating body, and a predetermined voltage is applied to the heater to generate heat. Generally, the rotating body is heated. The outer surface of the rotating body is heated until its temperature becomes a temperature suitable for fixing. A temperature sensor is attached to the outer surface of the rotating body so that the temperature of the outer surface of the rotating body can be measured, so that the temperature of the rotating body is maintained at a temperature suitable for fixing. The power supply is controlled.

[0006] In the film heat fixing method, generally, a heating element on an elongated plate, which is disposed so that its longitudinal direction coincides with the direction of rotation of the film as a rotating body, is brought into contact with the film and heated. It is.

Conventionally, in the fixing device of the heat roller fixing method, it takes a long time to heat the rotating body, and a time period from when the power is turned on to when the temperature of the surface of the rotating body reaches a temperature suitable for fixing (hereinafter, referred to as a "fixing device"). Warm-up time), but it was relatively long. During that time, the user cannot use the copier, and there is a problem that the user has to wait for a long time. Also, in order to shorten the waiting time from standby to the ready state, the heating element is energized in order to keep the rotating body at a relatively high temperature even during standby. Was consuming. If a large amount of power is supplied to the rotating body, the warm-up time can be reduced, but the power consumption of the fixing device increases, which is not desirable from the viewpoint of energy saving. In order to achieve both energy saving (low power consumption) of the fixing device and user operability (quick print), it is desired to shorten the warm-up time without increasing power consumption.

On the other hand, in the fixing device of the film heat fixing system, although the heat capacity of the film-shaped rotating body is small, the warm-up time is short, but the amount of heat that can be held by the rotating body is small. Heat must be supplied from the heating element to the toner via the rotating element, and if the sheet-shaped recording medium is conveyed at a high speed to fix it, the heat cannot be supplied to the toner. Can not cope with a good fixation. Further, since the rotating body is liable to meander or break, the recording medium is inferior to the heat roller fixing system in terms of stability and durability of conveyance.

In view of the above, there has been proposed an induction heating type fixing device utilizing a heat generation phenomenon by an electromagnetic induction effect as a heating source of a rotating body. In this method, when a conductor is placed in an alternating magnetic field, an eddy current flows in the conductor due to electromagnetic induction, and the rotating body is heated using the phenomenon that the conductor generates heat due to Joule heat generated by the eddy current. is there. That is, a part or all of the rotating body is made of a conductor, a magnetic flux generating coil is arranged inside or outside the rotating body, and an alternating magnetic field generated by applying an alternating current to the magnetic flux generating coil generates a conductive body in the rotating body. An induced eddy current is generated in the rotator, and the rotator itself is heated by Joule heat by the eddy current and the resistance of the conductor itself in the rotator. This induction heating fixing device can greatly improve the conversion efficiency from electricity to heat, and can generate heat only in a thin layer near the surface of the rotating body even when the rotating body has a large thickness. Uptime can be reduced.

Among the conventional techniques of the induction heating type fixing device,
As placing the magnetic flux generating coil outside the rotating body,
JP-A-7-295414, JP-A-10-74007
JP-A-10-63126, JP-A-11-2974
No. 62, JP-A-11-297463, JP-A-2000-
No. 131981, JP-A-2000-172098 and JP-A-2000-181258.
As described in these publications, arranging the magnetic flux generating coil outside the rotating body has the following advantages as compared with arranging it inside the rotating body. That is, since the portion of the rotating body near the outer surface used for fixing can be concentratedly heated, the warm-up time can be reduced, and the heat generated by the electric resistance of the magnetic flux generating coil can be easily radiated, so that the magnetic flux generating coil is used. It is easy to prevent the heat generation efficiency from dropping due to high temperature and the coil coating material is broken, the assembly process is easy, and the magnetic flux generating coil is easy to remove when it needs to be replaced due to an accident or life. And so on.

[0011]

In the prior art in which the above-mentioned magnetic flux generating coils are arranged outside the rotating body, roughly two types of coils are used. One is JP-A-7-
295414, JP-A-10-63126, JP-A-11-
297462, JP-A-11-297463, JP-A-200
0-131981, JP-A-2000-172098, and JP-A-2000-181258. As shown in FIG. 18, a conductive material is formed on a two-dimensional curved surface curved along the surface of a cylindrical rotating body. This is a coil 87 which has a shape in which a conductive wire is routed and does not use a core. This will be referred to as a first shape coil. First
When using the coil 87 having the shape of, a magnetic body is disposed facing the surface of the coil 87 opposite to the rotating body to prevent the magnetic field from leaking to the periphery of the rotating body. I have.

The other one is used in Japanese Patent Application Laid-Open Nos. 10-74007 and 2000-131981. As shown in FIG. 19, the cross section perpendicular to the longitudinal direction, that is, the cross section, has a shape. , A coil having an E-shape, that is, a core 85 having a shape having three parallel projections, and a conductive wire 86 wound around a central projection among the three projections of the core 85. This will be referred to as a second shape coil.

When the coil 87 of the first shape is used,
There is a problem that it is difficult to uniformly heat the rotating body in the longitudinal direction. That is, since the heating value of the rotating body changes depending sensitively on the distance between the coil and the conductor layer of the rotating body, in the case of the coil 87 having the shape in which the conductive wire is routed on the two-dimensional curved surface as described above, In order to heat uniformly in the longitudinal direction of the rotating body, the distance between the coil 87 and the conductor layer of the rotating body must be kept constant in the longitudinal direction of the rotating body, and high assembly accuracy is required. For example, in a coil 87 curved so that the distance between the coil surface and the surface of the rotating body becomes uniform in the circumferential direction of the rotating body, as shown by a solid line 87A in FIG. Assuming that the curvature of the curvature of the coil surface is smaller than that, the distance between the coil and the rotating body 88 at the coil end in the circumferential direction of the rotating body 88 becomes larger at that location, as shown in FIG. The calorific value is smaller than in other places. In addition, since the amount of heat generated at each location of the rotating body depends on the density of the conductive wire at that location of the coil facing the location, in order to heat uniformly in the longitudinal direction of the rotating body, Also, the density of the conductive wire constituting the coil must be kept constant in the longitudinal direction of the rotating body, and high manufacturing accuracy is required.

According to the coil of the second shape, in order to uniformly heat the rotating body in the longitudinal direction, the gap between the rotating body and the core 85 may be made constant in the longitudinal direction. It is easier to heat the rotating body uniformly in the longitudinal direction than the coil of the first shape. However, since the coil 86 is sandwiched between the protruding portions of the core 85, there is a problem that self-heating of the coil 86 is trapped in the core 87, and the temperature of the coil 86 tends to be high. In addition, since heat is concentrated in a narrow range in the circumferential direction of the rotating body, when the rotating body is maintained at the standby temperature during standby, only a part of the rotating body in the circumferential direction becomes high in temperature. There is also a disadvantage that the rotating body needs to be rotated at a relatively high speed sometimes.

As a modification of the second shape coil,
Japanese Patent Application Laid-Open No. H10-74007 proposes a method of heating a wide range in the circumferential direction of a rotating body by increasing the number of protruding portions of a core and increasing the number of winding portions of a conductive wire to a plurality. However, there remains a problem that the manufacturing cost is increased by the complexity of the shape, and the coil is easily heated to a high temperature due to self-heating of the coil because the coil is sandwiched between the protruding portions of the core. Further, Japanese Patent Application Laid-Open No. H10-74
Japanese Patent Application Publication No. 007 discloses a modified example of the second shape coil.
A U-shaped core having no U-shaped core having a central protruding portion and a conductive wire wound around a central portion has been proposed. However, it has been proposed as a low-cost alternative to the second-shaped coil. It cannot heat a wide area in the circumferential direction of the body.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and the magnetic flux generating coil does not become high in temperature, the rotating body can be heated uniformly in the longitudinal direction, and the rotating body can be heated uniformly. It is an object of the present invention to provide an induction heating type heating device, a fixing device, and an image forming device that can be heated relatively uniformly even in the circumferential direction.

[0017]

According to the first aspect of the present invention,
A rotating body having an induction heating element that generates heat by the action of magnetic flux, a pressurizing member pressed against the rotating body, and magnetic flux generation means disposed opposite to the outer peripheral surface of the rotating body; In the heating device for heating the object to be heated by passing the object to be heated between the pressure member and the pressure member, the magnetic flux generating means includes a core made of a highly magnetically permeable material, and the core being parallel to the longitudinal direction of the rotating body. Having a conductive wire that is wound and supplied with a high-frequency current,
The core is closest to the rotating body at or near both ends of the core in a direction perpendicular to the plane formed by the ring formed by the conductive wire, and the distance between the core and the rotating body at the closest position is determined by this rotation. The conductive wire is wound around the core so as to be constant in the longitudinal direction of the body and to avoid the closest position.

According to a second aspect of the present invention, in the first aspect of the invention, the distance of the space separating the conductive wire and the rotating body at the closest position is the closest position between the core and the rotating body. Is characterized by being larger than the distance of the space separating the core and the rotating body. According to a third aspect of the present invention, in the first aspect, the core is curved substantially concentrically with the surface of the rotating body.

According to a fourth aspect of the present invention, in the first aspect, the core is formed on both ends or both sides of the core in a direction perpendicular to the plane formed by the loop formed by the conductive wire wound around the core. In the vicinity of the end, a protruding portion protruding toward the rotating body is provided. According to a fifth aspect of the present invention, in the first aspect of the present invention, the core is formed by bending a flat plate into a mountain shape, and the conductive wire is wound in parallel with the ridge direction.

According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the angle of the angle is bent at a right angle. According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, the gap forming member for securing a constant gap between the core and the rotating body at the closest position is the largest size. It is characterized in that it is provided in contact with the surface position of the rotating body outside the passing position of the heating body.

According to an eighth aspect of the present invention, in the first aspect, the core is formed by cutting out a part of a quadrangular prism including a full length of one side extending from the hollow quadrangular prism in the longitudinal direction of the quadrangular prism. A conductive wire is wound in parallel with its longitudinal direction, a pressing member comes into contact with two surfaces of the quadrangular pillar-shaped core that do not include the cutout portion, and a movement preventing material contacts the remaining two surfaces. Are in contact with each other.

According to a ninth aspect of the present invention, in the invention according to any one of the first to eighth aspects, a member made of a non-magnetic material having a high thermal conductivity is provided in the core near the closest position between the core and the rotating body. It is characterized by being in contact. Claim 10
According to the invention described in any one of claims 1 to 9, a cleaning member for cleaning the surface of the rotating body is provided so as to face the outer peripheral surface of the rotating body, and the cleaning member is arranged in the rotating direction of the rotating body. Is characterized in that a magnetic flux generating coil is provided on the downstream side.

According to an eleventh aspect of the present invention, there is provided a fixing device for an electrophotographic apparatus using the heating device according to any one of the first to tenth aspects, wherein the rotating body is a fixing roller of the fixing device. The present invention relates to a fixing device that heats a recording medium carrying an attached image with the fixing roller to fix the image on the recording medium.

According to a twelfth aspect of the present invention, there is provided an image forming apparatus comprising: an image forming means for forming and carrying a toner image on a sheet-like recording medium; and an image fixing means for heating the recording medium carrying the toner image. An image forming apparatus comprising the fixing device according to claim 11 as an image fixing unit.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a heating device, a fixing device, and an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of an image forming apparatus according to the present invention. The image forming apparatus can obtain an image by executing a well-known electrophotographic process, and has a photoconductive photosensitive member 1 formed in a cylindrical shape as an image carrier. Around the photoconductor 1, a charging roller 2 as a charging unit, a developing device 4,
A transfer roller 5, a cleaning device 7, and a charge removing device 8 are provided. Also, in addition to them, the image forming apparatus
An optical scanning device 3 and a fixing device 6 are provided. As the charging means, a corona charger can be used. The optical scanning device performs exposure by optical scanning on the photoconductor surface between the charging roller and the developing device.

When performing image formation, the photosensitive member 1 is
After the surface is uniformly charged by the charging roller 2, an electrostatic latent image is formed on the surface of the photoconductor 1 by exposure of the optical scanning device 3. The electrostatic latent image is reversely developed by the developing device 4 to form a toner image on the surface of the photoconductor 1. This toner image is superimposed on the recording medium 9 sent to the transfer section by a paper feed mechanism (not shown) at the same time as the toner image on the photoconductor 1 moves to the transfer position. The image is electrostatically transferred to the medium 9. The recording medium 9 to which the toner image has been transferred is discharged outside the apparatus after the toner image is fixed by the fixing device 6. After the transfer of the toner image, the cleaning device 7 removes residual toner and paper dust from the surface of the photoreceptor 1, and the charge is removed by the charge removing device 8.

Next, a specific example of a fixing device provided in the image forming apparatus will be described. Specific Example 1 of Fixing Device FIG. 2 shows a cross section perpendicular to the longitudinal direction of the fixing device.
In FIG. 2, reference numeral 11 denotes a fixing roller, 12 denotes a magnetic flux generating coil, 13 denotes a pressing roller as a pressing member, 14 denotes an arrow indicating the direction of rotation of the fixing roller, and 9 denotes a sheet carrying an unfixed toner image. Recording medium, 16 is a temperature detector, 1
Reference numeral 7 denotes a cleaning member, and reference numeral 18 denotes a separation claw for separating the recording medium from the fixing roller. FIG.
In FIG. 1, the cross section of the magnetic flux generating coil 12 as the magnetic flux generating means is displayed as a thick circular arc shape, but this shows the approximate size and position of the magnetic flux generating coil 12. Is composed of a core (core material) and a coil wound around the core, and its cross-sectional shape is not a mere thick arc shape. The shape of the magnetic flux generating coil will be described later in detail.

The fixing roller 11 corresponds to a rotating body referred to in the claims, and has a thickness of 1.0 mm.
US (stainless steel) circular tube with a thickness of 1
It is provided with a release layer made of 5 μm Teflon (trade name). The outer diameter of the fixing roller 11 is 40 mm.
However, the present invention is not limited to the fixing roller having the size and the layer configuration, and is applicable to a fixing roller having an arbitrary layer configuration, a diameter, and a thickness. For example, the core metal layer is not limited to SUS, and any magnetic material can be used. For example, iron,
Nickel, cobalt, or alloys thereof can be used. Further, the core metal layer is not limited to one layer, and may have a two-layer structure of a layer made of a non-magnetic material such as aluminum or copper and a layer made of a magnetic material, or one or more other layers. May be added. The material of the release layer is not limited to Teflon. The magnetic layer forms an induction heating element that generates heat by the action of magnetic flux.

The pressure roller 13 has a thickness of 5 m around the cored bar.
m silicone rubber layer, and the outside of the
The structure is covered with a 0 μm Teflon cap. The outer diameter of the pressure roller 13 is 40 mm. The fixing roller 11 and the pressing roller 13 are pressed by a pressing mechanism (not shown) so that the nip width becomes 4 mm. However, the application object of the present invention is not limited to this pressure roller, but can be applied to a pressure roller having an arbitrary layer configuration, diameter and thickness. Also, the nip width is not limited to 4 mm. The fixing roller 11
The driving unit (not shown) is driven to rotate in the direction of arrow 4 in FIG. 2, and the pressure roller 13 is driven to rotate with the rotation. 1 and 2 are drawn from opposite sides of the fixing roller 11 and the pressure roller 13 in the axial direction.

A sheet-shaped recording medium 9 carrying an unfixed toner image is conveyed to a pressure contact portion (nip portion) between the fixing roller 11 and the pressure roller 13 while the recording medium 9 passes through the pressure contact portion. Then, the toner image is fixed on the recording medium 9 by heat and pressure. A temperature detector 16 is attached to the fixing roller 11, and based on the temperature, power supplied to the magnetic flux generating coil 12 is adjusted by a control mechanism (not shown).
The temperature of the fixing roller 11 is controlled to a predetermined temperature. In order to detect the temperature after the fixing roller 11 has been heated by passing through the position facing the magnetic flux generating coil 12, the temperature detector 1
Reference numeral 6 is provided downstream of the magnetic flux generating coil 12 in the direction in which the fixing roller 11 rotates.

The fixing roller 11 is provided with a cleaning member 17 for removing unfixed toner, paper dust and the like attached thereto. The cleaning member 17 is provided upstream of the magnetic flux generating coil 12 in the direction in which the fixing roller 11 rotates so that unfixed toner, paper dust, and the like do not become clogged between the magnetic flux generating coil 12 and the fixing roller 11. I have. Outside the exit of the nip between the fixing roller 11 and the pressure roller 13, there is provided a separation claw 18 for separating the recording medium 9 that has passed through the nip from the fixing roller 11. Note that an oil application mechanism (not shown) for applying oil for preventing offset to the fixing roller 11 may be provided.

As the magnetic flux generating coil 12, a coil formed by winding a litz wire as a conductive wire around a ferrite core (core material) is used. The core is not limited to ferrite, and may be made of a material having high magnetic permeability such as iron or permalloy. The litz wire is a bundle of a plurality of thin copper wires whose outer circumference is insulated. FIG. 3 shows the shape of the core. In FIG. 3, the core 21 is curved with a curvature adapted to the curvature of the outer peripheral surface of the fixing roller 11 so that the distance between the outer peripheral surface of the fixing roller 11 and the core 21 is constant in the circumferential direction of the fixing roller 11. Further, protrusions 22 and 23 projecting toward the fixing roller 11 are provided at both ends in the circumferential direction. That is,
The core 21 has a curved U-shaped cross section perpendicular to the longitudinal direction (transverse cross section).

FIG. 4 is a view showing how to wind a litz wire around the core 21. In FIG. 4, reference numerals 24, 25, 26
Shows three parts of one litz wire, and 21 shows a core. Reference numerals 24 and 25 indicate visible portions of the litz wire as viewed from the viewpoint direction in the drawing, and reference numeral 26 indicates a portion of the litz wire hidden by the core 21. In FIG. 4, arrows 27 and 28 indicate the directions in which the litz wire is bent at both ends in the length direction of the core 21. As shown in FIG. 4, the litz wire is wound around the core 21 in parallel with the longitudinal direction of the core 21. FIG. 4 shows a state in which the litz wire is wound at intervals of one and a half turns so as to make it easy to understand how to wind the litz wire. It is.

FIG. 5 shows an enlarged cross section perpendicular to the longitudinal direction of the magnetic flux generating coil. In FIG. 5, 21 indicates a core, and 30 indicates a litz wire. In FIG. 5, the litz wire 30 is wound around the core 21 in a single layer, but may be wound more than once. Also, the number of turns is not limited to the number of turns shown in FIG. As can be seen from FIG. 5, the loop formed by the litz wire 30 which is a conductive wire has its surface orthogonal to the paper surface and the core surface, and is provided at both ends of the core 21 in a direction perpendicular to the plane formed by the ring. Protrusions 22, 23 are formed. The tips of the protrusions 22 and 23 are fixed to the fixing roller 1.
Closest to the surface of 1.

FIG. 6 is a cross-sectional view of the case where the litz wire 30 is wound twice around the core 21. The length of the core 21 in the longitudinal direction is substantially equal to the width of the largest size recording medium that can be used in the image forming apparatus. The length along the direction perpendicular to the longitudinal direction of the core 21, that is, the curvature in the curved direction is 90 mm. The length of the protruding portions 22 and 23 of the core 21 indicated by a solid line 29 with arrows at both ends in FIG.
5 mm.

FIG. 7 is a sectional view showing the positional relationship between the magnetic flux generating coil 30 and the fixing roller 11. In FIG.
11 is a fixing roller, 13 is a pressure roller, 21 is a core of a magnetic flux generating coil, 30 is a litz wire of the magnetic flux generating coil 12,
Reference numerals 31 and 32 denote gaps between the protruding portions 22 and 23 of the core 21 and the outer surface of the fixing roller 11. In FIG. 7, the dimensions of each part are illustrated differently from the actual ones for easy understanding. Further, the cross section of the litz wire 30 is omitted, and only eight sections are drawn.

The magnetic flux generating coil 12 is disposed on the fixing roller 11 as shown in FIG. That is,
The magnetic flux generating coil 12 is provided with the protruding portions 22 and 23 of the core 21 facing the fixing roller 11 such that the core 21 covers a portion of the outer peripheral surface of the fixing roller 11 other than the nip portion near the nip portion entrance. Have been. Further, they are arranged so that the distance between the protrusions 22 and 23 of the core 21 and the outer surface of the fixing roller 11 is constant. Projecting portion 22 of core 21,
The closer the roller 23 is to the outer surface of the fixing roller 11, the more efficiently the fixing roller 11 can be heated. In this embodiment, the distance between the protrusions 22 and 23 of the core 21 and the outer surface of the fixing roller 11 is 1 mm.

The distance between the litz wire 30 and the outer peripheral surface of the fixing roller 11 is longer than the distance between the protrusions 22 and 23 of the core 21 and the outer surface of the fixing roller 11. The height of the protrusions 22 and 23 is ensured. By doing so, the protruding portions 22, 2
When a gap is secured between the fixing roller 3 and the outer surface of the fixing roller 11, the litz wire 30 does not touch the outer peripheral surface of the fixing roller 11, so that the fixing roller 11 is not damaged. Therefore, the magnetic flux generating coil 12 and the fixing roller 11
It is easy to prevent the contact with the contact.

The gap between the protrusions 22 and 23 of the core 21 and the outer surface of the fixing roller 11 is preferably held by a gap holding mechanism as shown in FIG. In FIG. 8, reference numeral 21 denotes a core, and reference numerals 41, 42, 43
Indicates three of the four support rollers provided at both ends in the length direction of the protruding portions 22 and 23 of the core 21. Another support roller is hidden by the core 21 and is not shown. These supporting rollers 41, 42, 43 are made of silicone rubber, and the metal cores 3 projecting outward in the longitudinal direction of the core 21 from both ends in the longitudinal direction of the projecting portions 22, 23 of the core 21.
It is mounted so as to freely rotate around 5, 36, 37.

The support rollers 41, 42, and 43 are provided in FIG.
As shown in FIG. 2, when the core 21 is pressed toward the fixing roller 11 by a pressing mechanism (not shown), the core 21 is rotatably brought into contact with the outer peripheral surface of the fixing roller 11 and the protrusions 22 and 23 of the core 21 and the fixing roller 11 are fixed. 11 plays a role in maintaining a constant gap with the outer surface. FIG. 9 is a view of the fixing roller 11, the core 21, and the supporting rollers 41 and 42 viewed from the axial end of the fixing roller 11. These support rollers 41,
The metal cores 35 of the support rollers 41, 42, and 43 are provided so as to be in contact with the fixing roller 11 at positions outside the range through which the recording medium of the maximum usable size passes.
Adjust the length of 36 and 37.

If the length of the core 21 in the longitudinal direction is substantially equal to the width of the recording medium having the maximum size, the support rollers 41, 4
The length of the cores 35, 36, 37 of 2, 43 is as short as 1 cm or less. The support rollers 41, 42, and 43 have a radius of 4 mm, and the support rollers 41, 42, and 43 have an axial thickness of 5 mm. However, the protrusions 22 and 23 of the core 21 and the outer surface of the fixing roller 11 are desired. The radius is not limited to 4 mm, as long as the distance is only required. Further, the thickness of the support rollers 41, 42 and 43 in the axial direction is set to 5 m within a range where the strength of the support rollers 41, 42 and 43 can be maintained.
m. If the length of the fixing roller 11 is longer than the length of the core 21 as much as the axial thickness of the support rollers 41, 42, and 43 can be allowed,
The axial thickness of 42 and 43 may be greater than 5 mm.

A high frequency current of 30 kHz is applied to the magnetic flux generating coil 12 by a power supply (not shown). The alternating magnetic field generated in the magnetic flux generating coil 12 by the high frequency current generates an eddy current in the induction heating element layer of the fixing roller 11. Joule heat is generated in the induction heating element layer due to the eddy current and electric resistance of the induction heating element layer, and the induction heating element layer generates heat. The induction heating element layer is made of a magnetic material. Since the magnetic material has a significantly higher magnetic permeability than the non-magnetic material, it is easier to generate a large eddy current than when a non-magnetic material is used for the heat generating layer. In addition, since heat is generated due to hysteresis loss, heating is easier than when a nonmagnetic material is used for the heat generating layer. Based on the surface temperature of the fixing roller 11 detected by the temperature detector indicated by reference numeral 16 in FIG. 2, the application of the high-frequency current is controlled so that the surface temperature of the fixing roller 11 is maintained at a predetermined temperature.

FIG. 10 shows the state of the lines of magnetic force generated by the magnetic flux generating coil 12. In FIG. 10, reference numeral 11 denotes a fixing roller, reference numeral 21 denotes a core of a magnetic flux generating coil, and thick lines 44 and 45 indicate lines of magnetic force. A projecting portion 22 facing the fixing roller 11 on the core 21;
23, the majority of the magnetic flux
3 and enters the magnetic layer of the fixing roller 11. That is, the number of lines of magnetic force passing through the protrusions 22 and 23 as indicated by the line 44 is overwhelmingly greater than the number of lines of magnetic force extending from the coil to the fixing roller 11 via the space as indicated by the line 45. . Therefore, a solid line 46 with arrows at both ends is shown in FIG.
In the range indicated by, the magnetic flux density in the fixing roller 11 becomes relatively uniform in the circumferential direction.

On the other hand, FIG.
23 shows the lines of magnetic force when 23 is removed. If the core 21 does not have the protruding portions 22 and 23, the fixing roller 11 reaches the fixing roller 11 via a space from the middle of the coil, not from both ends of the coil in the circumferential direction of the fixing roller 11 as indicated by lines 47 and 48. The ratio of lines of magnetic force increases. Therefore, in the range indicated by the solid line 46 with arrows at both ends in FIG. Since the calorific value is high where the magnetic flux density is high, the core 2
If the projections 1 do not have the projections 22 and 23, the heat generation distribution in the circumferential direction in the fixing roller 11 also has a mountain shape with a sharp center. On the other hand, if the core 21 has the protruding portions 22 and 23, the magnetic flux density becomes relatively uniform as described above, so that the heat generation distribution in the circumferential direction in the fixing roller 11 becomes more gentle and uniform. Close distribution.

FIG. 12 shows the heat generation distribution in the circumferential direction of the fixing roller 11 when the core 21 has the protrusions 22 and 23 and when it does not. The positions indicated by A and B in FIG. 12 are the closest points between the protruding portions 22 and 23 of the core 21 and the fixing roller 11, and the position of the fixing roller 11 in a range sandwiched between the two protruding portions 22 and 23 of the core 21. Heat is generated in the area. If this heat generation range is narrow, the rotating fixing roller 11
While passing through the area between the two protruding portions 22 and 23, the user will experience a rapid rise in temperature, but a rapid temperature change is not preferable from the viewpoint of durability. It is preferable that the temperature of the fixing roller 11 be as uniform as possible in the circumferential direction when the fixing roller 11 is preheated. Therefore, the core 21
It is preferable that the positions where the two protruding portions 22 and 23 are close to the fixing roller 11 are separated as much as possible in the circumferential direction. For example, it is preferable that the distance between the fixing roller 11 and the circumferential length of the surface of the fixing roller 11 is about 1/4 to 1/3. Also,
Since it is desirable that the heated fixing roller 11 enters the nip before it cools down, the magnetic flux generating coil 12 is preferably installed on the entrance side of the nip, not on the exit side.

In the case of the magnetic flux generating coil 12 of this embodiment,
Since most of the magnetic flux enters the fixing roller 11 via the protruding portions 22 and 23 of the core 21, the magnetic flux density in the fixing roller 11 depends on the protruding portions 22 and 23 of the core 21 and the fixing roller 11.
If the distance of the gap from the outer surface is constant, the portion of the coil 12 other than the protrusions 22 and 23 of the core 21 and the fixing roller 11
Does not greatly depend on the distance between Therefore, when the distance between the protrusions 22 and 23 of the core 21 and the outer surface of the fixing roller 11 is constant, the amount of heat generated by the fixing roller 11 is fixed to the portion of the coil 12 other than the protrusions 22 and 23 of the core 21. It does not largely depend on the distance from the roller 11. for that reason,
Even if the distance between the coil 12 and the fixing roller 11 is different in the circumferential direction, for example, in FIG.
Even if the distance between the core 21 and the fixing roller 11 indicated by 53 and 53 is different from each other, the heat generation of the fixing roller 11 does not become uneven unlike the conventional magnetic flux generating coil.
Similarly, solid lines 51, 52 and 5 with double-ended arrows in FIG.
Even if the distance between the core 21 and the fixing roller 11 indicated by 3 or the like slightly fluctuates in the longitudinal direction of the fixing roller 11,
There is no heat generation unevenness in the longitudinal direction of the fixing roller 11. Therefore, the dimensional accuracy at the time of manufacturing can be loosened, and the manufacturing cost can be kept low.

The temperature of the litz wire and the core 21 rises due to the heat generated by the litz wire due to the electrical resistance of the litz wire and the heat radiation from the fixing roller 11. The rise in the temperature of the litz wire causes a relative increase in the calorific value of the litz wire with respect to the calorific value of the fixing roller due to an increase in the resistance value, and lowers the heating efficiency of the fixing roller 11. It can also cause destruction of the magnetic flux generating coil. In the case of the magnetic flux generating coil 12 of this embodiment, the heating efficiency of the fixing roller 11 is
1 depends largely on the distance between the protrusions 22 and 23 and the outer surface of the fixing roller 11 and does not depend greatly on the distance between the portion of the core 21 where the litz wire is wound and the fixing roller 11. By increasing the heights of the projecting portions 22 and 23 of FIG.
The distance between the portion of the core 21 around which the litz wire indicated by 2 and 53 is wound and the fixing roller 11 can be increased.
As a result, the heat received by the litz wire from the fixing roller 11 is reduced, and the heat generated by the litz wire is also easily radiated. Is easy to prevent.

The core 21 shown in FIG. 7 is curved so that the distance between the outer peripheral surface of the fixing roller 11 and the core 21 is constant in the circumferential direction of the fixing roller 11, that is, concentrically with the fixing roller 11. When curved, the distance between the magnetic flux generating coil 12 and the fixing roller 11 can be suppressed to a small value, which is advantageous when there is no room in the space around the fixing roller 11. If there is room in the space around the fixing roller 11, the core need not be curved concentrically with the fixing roller 11. FIG. 14 shows an example in which the core is not curved concentrically with the fixing roller 11. In FIG. 14, reference numeral 11 denotes a fixing roller, 55 denotes a core,
Reference numeral 6 denotes a litz wire. Each of these members is shown in a cross-section at the middle in the longitudinal direction. The litz wire 56 is shown only partially. The core 55 shown in FIG. 14 is formed in a substantially semi-cylindrical shape. In the case of such a cross-sectional shape of the core 55, since both ends in the circumferential direction of the core 55 are closest to the fixing roller 11, it is not necessary to provide the core 55 with a protrusion.

To prevent the temperature of the magnetic flux generating coil from becoming high, a cooling mechanism for the magnetic flux generating coil may be added.
FIG. 15 shows an example in which a cooling mechanism is added to the magnetic flux generating coil of the above embodiment. In FIG. 15, the fixing roller, the pressure roller, the core, the litz wire, and the like have the same configuration as those in the embodiment shown in FIG. The hatched portions in FIG. 15 are the cooling mechanisms 57 and 58 added to the magnetic flux generating coil of the above embodiment. This cooling mechanism 5
Numerals 7 and 58 denote plate-shaped members with aluminum fins, as shown in FIG.
Are bonded along the outer end surfaces of the protrusions 22 and 23 on both sides in the circumferential direction. The reason why the material is aluminum is that it has a high thermal conductivity and is a non-magnetic material. These cooling mechanisms 57, 58
Is the core 2 of the magnetic flux generating coil having the cross-sectional shape shown in FIG.
1 extends over the entire length of the core 21 in the longitudinal direction.
By adding the cooling mechanisms 57 and 58, the core 2
1 increases the heat radiation area, conducts heat from the protruding portions 22 and 23 of the core 21 to the cooling mechanisms 57 and 58, and
By radiating the heat from the fixing roller 8, the protrusions 22 and 23 of the core 21 that are particularly easily heated by the heat transfer from the fixing roller 11 can be effectively cooled. The number of fins is
It is not limited to two leaves as shown in FIG.

Second Embodiment of the Fixing Device Next, a second embodiment of the fixing device will be described. This embodiment is the same as Embodiment 1 except for the magnetic flux generating coil. Ferrite is difficult to mold into complex shapes. Therefore, when ferrite is used as the material of the core, it is desirable to make the core as simple as possible. In this embodiment, the core has a shape obtained by combining rectangular parallelepipeds.

FIG. 16 shows this embodiment, in which the magnetic flux generating coil, the fixing roller and the pressure roller are cut in a section perpendicular to their longitudinal direction. In FIG. 16, reference numeral 61 denotes a core made of ferrite, 62 denotes a litz wire, 1
3 is a pressure roller, 11 is a fixing roller, 68 and 69 are core projections, 70 and 71 are magnetic flux generating coil movement preventing mechanisms, and 72 and 73 are magnetic flux generating coil pressing mechanisms. The cross section of the litz wire 62 shows only eight of them.
The cross section of the part where the litz wire 62 of the core 61 is wound is
It is composed of two orthogonal rectangles, and the lengths of two sides indicated by two straight lines 66 and 67 with double-ended arrows in FIG. 16 are substantially equal. The protruding portions 68 and 69 of the core 61 extending from the portion where the litz wire 62 is wound toward the fixing roller 11 intersect at right angles with the portion where the litz wire 62 of the core 61 is wound. I have.

The movement of the magnetic flux generating coil in the downward direction in FIG. Also,
The movement to the right as viewed in FIG. 16 is restricted by the movement prevention mechanism 71. Therefore, the core 61 of the magnetic flux generating coil does not contact the fixing roller 11. The movement preventing mechanisms 70 and 71 are aluminum plates fixed to side plates of the fixing device. These also have the function of radiating the heat of the core 61. The core 61 of the magnetic flux generating coil is pressed against the movement preventing mechanisms 70 and 71 by pressing mechanisms 72 and 73 urged by springs. The magnetic flux generating coil of the present embodiment does not require the support rollers as shown in FIGS. 8 and 9 for the first embodiment.

In the magnetic flux generating coil of this embodiment, since the core 61 can be formed by bonding a rectangular parallelepiped ferrite, the manufacturing cost can be reduced. Further, it is easy to install the magnetic flux generating coil at an appropriate distance from the fixing roller 11.

Incidentally, as shown in FIG.
The core 61 without 8, 69 may be used. In FIG. 17, 61 is a core made of ferrite, 62 is a litz wire,
11 is a fixing roller, 13 is a pressure roller, 70 and 71 are movement preventing mechanisms of a magnetic flux generating coil, and 72 and 73 are magnetic flux generating coil pressing mechanisms. The fixing device of FIG. 17 is the same as the fixing device of FIG. 16 except that the core 61 does not have the protrusions 68 and 69 in the example shown in FIG. 16 and the distance between the core 61 and the fixing roller 11 is different. . The magnetic flux generating coil of FIG. 17 is different from the magnetic flux generating coil of FIG.
Since the whole 1 is close to the fixing roller, the position where the litz wire 62 is wound is limited, but the manufacturing cost can be reduced by the simpler shape of the core 61. In FIG. 17, the core 61 is bent at a right angle.
The angle of the bend shown by is not limited to 90 degrees.

[0055]

According to the first aspect of the present invention, as long as the distance between the core and the rotating body is kept constant in the longitudinal direction of the rotating body at the closest position between the core and the rotating body, the magnetic flux generating coil can be obtained. Even if the distance between the remaining part and the rotating body slightly fluctuates in the longitudinal direction of the rotating body, or even if the distance between the conductive wires slightly fluctuates in the longitudinal direction of the rotating body, No uneven heat generation in the direction. Therefore, the dimensional accuracy at the time of manufacturing the magnetic flux generating coil and the installation accuracy to the heating device can be reduced, and the manufacturing cost can be reduced. In addition, since a wide range can be relatively uniformly heated in the circumferential direction of the rotating body, a rapid temperature change in the circumferential direction of the rotating body can be avoided, and the durability of the rotating body is increased.
Also, when performing preliminary heating to maintain the temperature of the rotating body at a predetermined temperature when the heating device is on standby, the rotating body can be rotated at a high speed because a wide range can be relatively uniformly heated in the circumferential direction of the rotating body. You don't have to.

According to the second aspect of the present invention, if the positions of the core and the rotating body can be controlled so that the core and the rotating body do not come into contact with each other at the closest position between the core and the rotating body, the conductive wire can be applied to the rotating body. The rotating body is not damaged by touching. That is,
It is easy to prevent the magnetic flux generating coil from contacting the fixing roller.

According to the third aspect of the present invention, the distance between the magnetic flux generating coil and the rotating body can be suppressed to a small value, so that the magnetic flux generating coil is installed even when there is little room in the space around the rotating body. be able to.

According to the fourth aspect of the present invention, no matter what shape the portion other than the protruding portion of the core has, the core and the rotating body can be extended without increasing the distance between them at the closest position. Can be separated from the rotating body by the amount of protrusion of the protruding portion, so that the distance between the conductive wire and the rotating body can be lengthened, and a rise in the temperature of the conductive wire can be suppressed. Even if a part other than the protruding part of the core is separated from the rotating body, the distance between the core and the rotating body at the closest position can be kept small by increasing the protruding amount of the protruding part, without sacrificing heat generation efficiency. The distance between the conductive wire and the rotating body can be increased. When the distance between the conductive wire and the rotating body can be increased, the temperature rise of the conductive wire due to heat transfer from the rotating body can be suppressed, and the coating material of the conductive wire can be prevented from being broken by high temperature. In addition, if the distance between the conductive wire and the rotating body is increased, there is a space margin to increase the thickness of the conductive wire, so using a thick conductive wire can also suppress the heat generation of the conductive wire. Become. Further, a space is provided for inserting a heat insulating material between the conductive wire and the rotating body.

According to the fifth aspect of the present invention, since the shape of the core is simple, even when the core is made of a hard-to-process material such as ferrite, the manufacturing cost of the core can be suppressed.

According to the sixth aspect of the present invention, since the core can be formed by bonding two rectangular parallelepiped materials, the fabrication is extremely easy.

According to the seventh aspect of the present invention, the distance between the core and the rotating body can be ensured without damaging the passage of the heated body on the surface of the rotating body and without obstructing the passage of the heated body.

According to the eighth aspect of the present invention, since the core can be formed by bonding the rectangular parallelepiped ferrite, the manufacturing cost can be reduced. Further, since the cross section of the core is rectangular, it is easy to fix the core, and it is easy to install the magnetic flux generating coil at an appropriate distance from the fixing roller.

According to the ninth aspect of the present invention, the core is particularly susceptible to heat from the rotating body at the position where the core is closest to the rotating body, but the heat of the core can be radiated at that position. This prevents the core from exceeding the Curie temperature and losing ferromagnetism, thereby preventing the magnetic flux from entering the rotating body.

According to the tenth aspect, dust and the like can be prevented from being clogged between the magnetic flux generating coil and the fixing roller.

According to the eleventh aspect, heat generation unevenness is less likely to occur in the longitudinal direction of the fixing roller. Also, since a wide range can be relatively uniformly heated in the circumferential direction of the fixing roller,
A sudden temperature change in the circumferential direction of the fixing roller can be avoided, and the durability of the fixing roller increases. Also, when performing preliminary heating to maintain the temperature of the fixing roller at a predetermined temperature during standby of the fixing device, the fixing roller can be rotated at a high speed because a wide range can be relatively uniformly heated in the circumferential direction of the fixing roller. You don't have to.

According to the twelfth aspect of the present invention, since the image forming apparatus is provided with the heating device having the effects of the eleventh aspect, it is possible to obtain an image processing apparatus having a high fixing ability.

[Brief description of the drawings]

FIG. 1 is a front view illustrating an embodiment of a heating device, a fixing device, and an image forming apparatus according to the present invention.

FIG. 2 is a rear view showing a fixing unit in the embodiment.

FIG. 3 is a perspective view showing a core of a magnetic flux generating means used in the embodiment.

FIG. 4 is a perspective view conceptually showing how a coil is wound around the core.

FIG. 5 is a cross-sectional view showing an example in which a coil is wound around the core.

FIG. 6 is a cross-sectional view showing another example in which a coil is wound around the core.

FIG. 7 is a cross-sectional view illustrating another example of the fixing unit.

FIG. 8 is a perspective view showing another example of the magnetic flux generating means core that can be used in the present invention.

FIG. 9 is a cross-sectional view showing an arrangement relationship between the core and the fixing roller.

FIG. 10 is a cross-sectional view showing a state of a magnetic flux generated by a magnetic flux generating means used in the embodiment of the present invention.

FIG. 11 is a cross-sectional view showing a state of a magnetic flux generated by a conventional magnetic flux generating means in comparison with FIG.

12 is a graph showing a difference in heat value between the magnetic flux shown in FIG. 10 and the magnetic flux shown in FIG. 11;

FIG. 13 is a cross-sectional view of the fixing unit shown in FIG. 7 for explaining the effect obtained by the embodiment of the present invention.

FIG. 14 is a cross-sectional view illustrating another example of a fixing unit that can be used in the present invention.

FIG. 15 is a cross-sectional view showing still another example of a fixing unit that can be used in the present invention.

FIG. 16 is a cross-sectional view showing still another example of a fixing unit that can be used in the present invention.

FIG. 17 is a cross-sectional view showing still another example of a fixing unit that can be used in the present invention.

FIG. 18 is a perspective view illustrating an example of a magnetic flux generating unit of a heating device used in a conventional image forming apparatus.

FIG. 19 is a cross-sectional view showing another example of the magnetic flux generating means of the heating device used in the conventional image forming apparatus.

FIG. 20 is a cross-sectional view for explaining a problem of the magnetic flux generating means shown in FIG.

[Explanation of symbols]

 Reference Signs List 6 Fixing unit 9 Recording medium as a heated object 11 Fixing roller as a rotating body 12 Magnetic flux generating coil as a magnetic flux generating unit 13 Pressure roller 17 Cleaning member 21 Core 22 Projecting portion 23 Projecting portion 30 Litz wire as a conductive material 41 Roller as a gap forming member 42 Roller as a gap forming member 43 Roller as a gap forming member 61 Core 62 Litz wire

Claims (12)

[Claims] 1. A rotating body having an induction heating element that generates heat by the action of a magnetic flux, a pressing member pressed against the rotating body, and a magnetic flux generating means disposed to face an outer peripheral surface of the rotating body. A heating device for heating the object to be heated by passing the object to be heated between the rotating body and the pressing member, wherein the magnetic flux generating means includes a core made of a highly magnetically permeable material, A conductive wire that is wound in parallel with the longitudinal direction of the rotating body and is supplied with a high-frequency current, wherein the core has two ends or both ends of the core in a direction perpendicular to a plane formed by a ring formed by the conductive wire. In the vicinity of both ends, the rotor comes closest to the rotating body, and the distance between the core and the rotating body at the closest position is constant in the longitudinal direction of the rotating body. A heating device characterized in that the wire is wound . 2. The distance of the space separating the conductive wire and the rotating body at the closest position between the core and the rotating body is greater than the distance of the space separating the core and the rotating body at the closest position between the core and the rotating body. 2. The heating device according to claim 1, wherein the heating device is also large. 3. The heating device according to claim 1, wherein the core is curved substantially concentrically with the surface of the rotating body. 4. A protruding portion protruding toward the rotating body at both ends or near both ends of the core in a direction perpendicular to a plane formed by a loop formed by the conductive wire wound around the core. The heating device according to claim 1, further comprising: 5. The heating device according to claim 1, wherein the core has a shape obtained by bending a flat plate into a mountain shape, and a conductive wire is wound in parallel with a ridge direction of the core. 6. The heating device according to claim 5, wherein the angle of the angle is bent at a right angle. 7. A gap forming member for securing a constant gap between the core and the rotating body at the closest position is provided in contact with the surface of the rotating body outside the position where the largest size heating body passes. 7. The method according to claim 1, wherein
The heating device according to any one of the above. 8. The core has a shape obtained by cutting out a part of a quadrangular prism including a full length of one side extending from a hollow quadrangular prism in the longitudinal direction of the quadrangular prism. 2. The winding member, wherein the pressing member contacts two surfaces of the quadrangular prism-shaped core that do not include the cutout portion, and the movement preventing material contacts the remaining two surfaces. Heating equipment. 9. The core according to claim 1, wherein a member made of a non-magnetic material having a high thermal conductivity is in contact with the core in the vicinity of the closest position between the core and the rotating body. Heating equipment. 10. A cleaning member for cleaning a surface of a rotating body facing an outer peripheral surface of the rotating body, and a magnetic flux generating coil is provided downstream of the cleaning member in a rotating direction of the rotating body. The heating device according to any one of claims 1 to 9, wherein 11. A fixing device for an electrophotographic apparatus using the heating device according to any one of claims 1 to 10, wherein
The rotating body is a fixing roller of a fixing device, and the fixing device fixes the image on the recording medium by heating the recording medium carrying the unfixed image with the fixing roller. 12. An image forming apparatus comprising: an image forming means for forming and carrying a toner image on a sheet-like recording medium; and an image fixing means for heat-treating the recording medium carrying the toner image. An image forming apparatus comprising the fixing device according to claim 11 as means.