JP2003215958A - Image heating device and image forming device used for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image heating device by which a specified heating value is obtained by a small current. <P>SOLUTION: An image heating device is constituted by using a heat generating roller 1 having magnetism and conductivity and an exciting coil 5 arranged opposed to the outer peripheral surface of the heat generating roller 1 and to make the heat generating roller 1 generate heat by electromagnetic induction. The exciting coil 5 is formed by stretching a wire bundle obtained by bundling 60 wire rods whose surface is insulated, whose outer diameter is 0.2 mm and which is made of copper and also circulating it in the peripheral direction of the heat generating roller 1. Also the exciting coil 5 is arranged so that the wire bundle is mutually brought into close contact along the peripheral direction of the heat generating roller 1 so as to cover the upper half of the heat generating roller 1. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image heating device suitable for a fixing device for fixing an unfixed image, which is used in an image forming device such as an electrophotographic device or an electrostatic recording device, and an image forming device using the same. Regarding the device.

[0002]

2. Description of the Related Art As an image heating apparatus of this type, there is known one using electromagnetic induction as disclosed in Patent Document 1, Patent Document 2, and the like.

Patent Document 1 describes an exciting coil in which a coil is wound around a core, as an exciting means applied to electromagnetic induction. FIG. 26 shows a sectional view of the image heating apparatus disclosed in this publication.

In FIG. 26, 310 is a coil for generating a high-frequency magnetic field, and 311 is a metal sleeve that is heated by induction heating and rotates. Also, 31
Reference numeral 2 is an internal pressure member provided inside the metal sleeve 311. Reference numeral 313 is an external pressure member provided outside the metal sleeve 311.
3 forms a nip portion by being pressed against the internal pressing member 312 via the metal sleeve 311. External pressure member 313
Rotates in the direction of arrow a in the figure, and the metal sleeve 311 rotates with the rotation of the external pressure member 313.

A recording paper 314 as a recording material carrying an unfixed toner image is conveyed to a nip portion as shown by an arrow in the figure. Then, due to the heat of the metal sleeve 311 and the pressure of the pressure members 312 and 313, the recording paper 314
The upper unfixed toner image is fixed.

The coil 310 comprises a plurality of separate windings 3
It is provided with 10a and 310b. These winding parts 310
The a and 310b are formed by winding a conductive wire a plurality of times around the leg portions 315b and 315d of the core 315 having a large number of leg portions 315a to 315e via an insulating member (not shown). Here, the core 315 is made of ferrite, which is a magnetic material, and forms a magnetic path of a magnetic flux generated by an alternating current applied to the coil 310.

By the way, the following problems can be considered in the image heating apparatus disclosed in the above-mentioned Patent Document 1.

That is, in the structure of the exciting means, the conductor wire is wound around the leg portion of the core 315, so that the arrangement of the conductor wire is restricted by the position of the leg portion of the core. Therefore, the degree of freedom in designing the conductor wires is limited, and it becomes difficult to dispose the conductor wires widely along the circumferential surface of the metal sleeve 311 in the circumferential direction.

On the other hand, Patent Document 2 discloses an exciting means having a structure in which a conductive coil is spirally arranged on an insulating support. FIG. 27 shows a sectional view of the image heating apparatus disclosed in this publication, and FIG. 28 shows a perspective view of a heating coil used in this image heating apparatus.

As shown in FIG. 27, the heating roller 201.
Is driven to rotate in the direction of the arrow in the figure while being in contact with the pressure roller 202, and the pressure roller 202 rotates as the heating roller 201 rotates. Further, the pressure roller 202 is pressed by the heating roller 201 and is driven to rotate. Then, the recording paper 203 carrying the unfixed toner image and conveyed between the rollers 201 and 202 is
It is heated and pressed between the two, so that the unfixed toner image on the recording paper 203 is fixed.

The heating coil 204 is arranged in a buried state inside the insulating support 205. As shown in FIG. 27 and FIG. 28, the heating coil 204 has a thin conductive film extending along the curved surface of the semi-cylindrical insulating support 205 and has a spiral shape over the entire width of the insulating support 205 as a whole. It is arranged in. An alternating current is applied to the heating coil 204 from an induction heating power source. And the heating coil 2
An alternating magnetic flux is generated by the alternating current applied to 04,
The heating roller 201 is excited, and an eddy current in the direction opposite to the alternating current flowing through the heating coil 204 is generated in the heating roller 201. When this eddy current is generated in the heating roller 201, Joule heat is generated in the heating roller 201 and the heating roller 201 generates heat.

According to the structure of the exciting means described in this patent document 2, the degree of freedom in designing the arrangement of the conducting wire is less restricted as compared with the structure of the exciting means of the above patent document 1. Therefore, it is possible to widely dispose the conductive wire along the circumferential surface of the heating roller 201 in the circumferential direction.

[0013]

[Patent Document 1] Japanese Patent Laid-Open No. 10-74007

[Patent Document 2] JP-A-7-295414

[0014]

However, the image heating device disclosed in the above-mentioned Patent Document 2 has the following problems.

That is, since the heating coil 204 is formed by spirally disposing the conductive film, there is a space in which no current flows between the circulating currents. Therefore, as shown by the broken line S in FIG. 27, the magnetic flux passes between the coils to form a small loop. In this case, the magnetic flux cannot be efficiently guided to the heating roller 201, and the magnetic flux that does not penetrate the heating roller 201 increases. Therefore, in order to obtain the electric power required to heat the heating roller 201, it is necessary to flow a large current through the heating coil 204.
Then, in order to pass a large current through the heating coil 204, it is necessary to use a component having a large withstand current for the induction heating power source, which makes the induction heating power source expensive.

The present invention has been made to solve the above-mentioned problems in the prior art, and provides an image heating apparatus and an image forming apparatus using the same, which can obtain a predetermined heat generation amount with a small current. With the goal.

[0017]

In order to achieve the above object, the image heating apparatus according to the present invention has a structure in which a heating member made of a rotating body having conductivity and a wire member are provided along the peripheral surface of the heating member. An exciting coil that is formed so as to circulate and that heats the heat generating member, a magnetic permeability portion that faces the peripheral surface of the heat generating member via the exciting coil, and a magnetic field facing the peripheral surface of the heat generating member without the exciting coil. A plurality of cores made of a magnetic material having a facing portion, and the plurality of cores are arranged with a space therebetween, and the magnetically permeable portion and the facing portion are arranged in a rotational axis direction of the heat generating member. Characterized by different widths.

According to this structure of the image heating apparatus, since the magnetic flux generated by the alternating current (coil current) flowing through the exciting coil passes between the facing portion and the heat generating member, most of the magnetic path has high magnetic permeability. It can be composed of materials. Therefore, the air portion having a low magnetic permeability through which the magnetic flux generated by the coil current passes is only the narrow gap portion between the heat generating member and the core. Therefore, the inductance of the exciting coil increases, and the magnetic flux generated by the coil current is almost completely guided to the heat generating member. As a result, the electromagnetic coupling between the heat generating member and the exciting coil is further improved, and it becomes possible to apply more power to the heat generating member even with the same coil current. Further, since the magnetic path is defined by the facing portion and the heat generating member, the magnetic circuit can be freely designed. Further, the heat generation distribution can be freely designed by changing the arrangement of the cores. Further, the heat can be released from the gap between the cores, and at the same time, the surface area of the core itself is increased, so that the heat release can be promoted.

Further, in the configuration of the image heating apparatus of the present invention, it is preferable that the plurality of cores are arranged at non-uniform intervals. Further, in this case, the plurality of cores are arranged at intervals in the end portion and the central portion in the rotation axis direction of the heat generating member, and the spacing at the end portion may be narrower than the spacing at the central portion. preferable. According to this preferable example, the temperature distribution of the heat generating member can be made uniform to prevent defective fixing. In this case,
It is preferable that the plurality of cores have a shape in which the magnetic permeability portion is asymmetric with respect to a center line of the exciting coil parallel to the rotation axis of the heat generating member. According to this preferable example, the heat generation distribution in the rotation axis direction of the heat generating member can be made uniform with a smaller number of cores. On the contrary, if the cores have the same amount, the heat generation distribution can be made more uniform. In this case, further, in the plurality of cores, it is preferable that an interval between the magnetically permeable parts is wider than an interval between the facing parts. According to this preferable example, it is possible to reduce the usage amount of the material of the magnetic permeability portion while securing the length of the core of the facing portion that determines the range of the heat generating portion. Even with the configuration, the heat generation distribution can be made uniform. In this case, it is preferable that at least some of the cores are connected to each other. According to this preferable example, even if a gap is provided in the core of the magnetically permeable portion and the core is unevenly distributed,
The magnetic field can be made uniform in the rotation axis direction. As a result, it is possible to make the heat generation distribution of the heat generating member uniform in the portion through which the recording material passes while reducing the number of cores in the magnetically permeable portion, so that the temperature distribution in the fixing portion becomes uniform. Therefore, a stable fixing action can be obtained. Further, since the core of the magnetically permeable portion can be reduced while making the heat generation distribution of the heat generating member uniform, it is possible to reduce the size of the device and reduce the cost.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below with reference to embodiments.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a fixing device as an image heating device in the embodiment, and FIG. 2 is a partially cutaway plan view showing a heat generating portion of the fixing device.

In FIGS. 1 and 2, 1 is a heat generating roller as a heat generating member, 2 is a supporting side plate made of a galvanized steel plate, 3 is fixed to the supporting side plate 2, and the heat generating roller 1 is rotatably supported at both ends. Bearing. Heat roller 1
Is rotatably driven by a drive means of the apparatus body (not shown). The heating roller 1 is made of a magnetic material which is an alloy of iron, nickel and chromium, and has a Curie point of 30.
It is adjusted to be 0 ° C or higher. The heat generating roller 1 is formed in a pipe shape having a thickness of 0.3 mm.

The surface of the heat roller 1 is coated with a release layer (not shown) made of a fluororesin having a thickness of 20 μm in order to impart releasability. As the release layer,
Resins and rubbers having good releasability such as PTFE, PFA, FEP, silicone rubber, and fluororubber may be used alone or in combination. When the heating roller 1 is used for fixing a monochrome image, only releasability is required to be secured, but when the heating roller 1 is used for fixing a color image, it is desirable to impart elasticity. In that case, Needs to form a thicker rubber layer.

Reference numeral 4 is a pressure roller as a pressure means.
The pressure roller 4 is made of silicone rubber having a hardness of JIS A65 degrees, and is pressed against the heat generating roller 1 with a pressing force of 20 kgf to form a nip portion. Then, in this state, the pressure roller 4 rotates as the heat generating roller 1 rotates. The pressure roller 4 may be made of other heat resistant resin such as fluororubber or fluororesin, or rubber. Further, in order to improve wear resistance and releasability, it is desirable that the surface of the pressure roller 4 be coated with a resin or rubber such as PFA, PTFE, FEP, etc., alone or in a mixture. Further, in order to prevent heat dissipation, the pressure roller 4
Is preferably composed of a material having low thermal conductivity.

Reference numeral 5 is an exciting coil as an exciting means.
The exciting coil 5 has an outer diameter of 0.2 mm with its surface insulated.
The wire bundle formed by bundling 60 copper wire rods is formed in such a manner that it extends in the rotation axis direction of the heat generating roller 1 and circulates along the circumferential direction of the heat generating roller 1. The cross-sectional area of the wire bundle is about 7 mm ² including the insulating coating of the wire.

The cross section of the exciting coil 5 perpendicular to the rotation axis of the heat generating roller 1 is arranged such that the wire bundles are closely attached to each other along the circumferential direction of the heat generating roller 1 so as to cover the upper half of the heat generating roller 1. It has a double-layered shape. in this case,
Adjacent line bundles of the line bundles from one end to the other end of the heat generating roller 1 are in close contact, and adjacent line bundles of line bundles from the other end of the heat generating roller to the one end are in close contact.

It should be noted that the winding order of the wire bundle that is extended and wound in the direction of the rotation axis of the heat generating roller 1 does not have to be from the one closer to the center of the winding, but may be changed in the middle.

The exciting coil 5 has a total of 18 turns, and the wire bundles are adhered to each other by an adhesive agent on the surface, so that the shapes shown in FIGS. 1 and 2 are maintained. The exciting coil 5 is connected to the outer peripheral surface of the heat roller 1 by about 2
They are facing each other with a space of mm. The range in which the exciting coil 5 faces the outer peripheral surface of the heat generating roller 1 is a wide range in which the angle is about 180 degrees about the rotation axis of the heat generating roller 1.

An alternating current of 30 kHz is applied to the exciting coil 5 from an exciting circuit 6 which is a semi-resonant inverter.
The alternating current applied to the exciting coil 5 is controlled by the temperature signal obtained by the temperature sensor 7 provided on the surface of the heat roller 1 so that the surface of the heat roller 1 reaches a predetermined fixing temperature of 170 ° C. It Excitation coil 5
The alternating current applied to is also called "coil current".

In the present embodiment, A4 size (width 210 mm) recording paper is used as the maximum width recording paper, and the length of the heat generating roller 1 in the rotation axis direction is 270 m.
m, the length of the outer peripheral portion of the exciting coil 5 along the rotation axis direction of the heating roller 1 is 230 mm, and the length of the inner peripheral portion of the exciting coil 5 along the rotation axis direction of the heating roller 1 is 2.
It is set to 00 mm.

In the fixing device constructed as described above, the recording paper 8 as the recording material having the toner 10 carried on the surface is
The toner 10 on the recording paper 8 is fixed by being inserted from the direction of the arrow in FIG. 1.

In this embodiment, the exciting coil 5 causes the heat generating roller 1 to generate heat by electromagnetic induction. Hereinafter, the mechanism will be described with reference to FIG.

The magnetic flux generated by the exciting coil 5 by the alternating current from the exciting circuit 6 (see FIG. 2) is the heating roller 1
Due to the magnetism of No. 2, as shown by a broken line M in FIG. 3, the heat roller 1 penetrates the inside in the circumferential direction and repeats generation and disappearance. The induced current generated in the heat generating roller 1 due to the change of the magnetic flux flows almost only on the surface of the heat generating roller 1 due to the skin effect, and generates Joule heat.

In the present embodiment, the exciting coil 5
However, the adjacent line bundles of the line bundles from the one end to the other end of the heat generating roller 1 are in close contact with each other, and the adjacent line bundles of the line bundles from the other end to the one end of the heat generating roller 1 are in close contact with each other. Therefore, the magnetic flux does not pass between the flux. Further, since there is no bundle of rays in the central portion of the exciting coil 5 and a gap is provided so that the magnetic flux can pass through, the magnetic flux is large around the exciting coil 5 as shown by the broken line M in FIG. Form a loop. Furthermore, the exciting coil 5
Is provided in the circumferential direction of the heat generating roller 1 so as to face the heat generating roller 1 over a wide range of an angle of about 180 degrees about the rotation axis of the heat generating roller 1, so that the heat generating roller 1
The magnetic flux penetrates in a wide range in the circumferential direction. As a result, since the heat generating roller 1 generates heat in a wide range, it is possible to apply a predetermined electric power to the heat generating roller 1 even if the coil current is small and the generated magnetic flux is small.

As described above, since there is no magnetic flux passing between the wire bundles without penetrating the heat generating roller 1, the electromagnetic energy applied to the exciting coil 5 is transmitted to the heat generating roller 1 without leakage. Therefore, even if the coil current is small, it is possible to efficiently apply the predetermined power to the heat generating roller 1.
Further, the exciting coil 5 can be downsized by bringing the wire bundles into close contact with each other.

Further, the wire bundle of the exciting coil 5 is the heating roller 1
The magnetic flux generated by the coil current is efficiently transmitted to the heat generating roller 1 since it is located in the vicinity of. The eddy current generated in the heat generating roller 1 by this magnetic flux flows so as to cancel the change in the magnetic field due to the coil current. In this case, since the coil current and the eddy current generated in the heat generation roller 1 are close to each other, the effect of canceling each other is great, and the magnetic field generated in the peripheral space by the entire current is suppressed.

Further, since there is nothing that hinders heat radiation from the outer circumference of the exciting coil 5, it is possible to prevent the insulating coating of the wire from being melted and the resistance value of the exciting coil 5 from increasing due to the temperature rise due to heat accumulation. You can

FIG. 4 shows an equivalent circuit of the exciting coil and the heat generating roller when the exciting coil is opposed to the heat generating roller. In FIG. 4, r is the resistance of the exciting coil 5 itself,
R is the resistance due to the exciting coil 5 facing the heat roller 1 and electromagnetically coupled, and L is the impedance of the entire circuit. In r, the exciting coil 5 is removed from the heat roller 1, and the electric resistance of the exciting coil 5 alone is LCR at a predetermined angular frequency ω.
It is obtained by measuring with a meter. R is obtained as a value obtained by removing r from the electric resistance when the exciting coil 5 is opposed to the heat generating roller 1. L is not much different from the inductance of the exciting coil 5 alone. When the current I flows through this circuit, the product of the square of the current I and the resistance value is consumed as effective power, and heat is generated. The exciting coil 5 generates heat by the power consumed by r, and the heat generating roller 1 generates heat by the power consumed by R. This relationship is expressed by the following (Equation 1) when the input power to the heat generating roller 1 is W.

W = (R + r) × I ² (Equation 1) When the voltage applied to the exciting coil 5 is V, the following (Equation 2) is established.

I = V / {(R + r) ² + (ωL) ² } (Formula 2) As can be seen from the above (Formula 2), when L and R are excessive, a sufficient current is maintained under a constant voltage V. I can't get it.
Therefore, as can be seen from the above (Equation 1), the input power W is insufficient and a sufficient amount of heat generation cannot be obtained. On the contrary, if R is too small, the effective power is not consumed even if the current I flows, and a sufficient amount of heat generation cannot be obtained. If L is too small,
The excitation circuit 6 which is a semi-resonant inverter does not operate sufficiently. When the frequency of the alternating current applied from the exciting circuit 6 to the exciting coil 5 is in the range of 25 kHz to 50 kHz, R is 0.5Ω or more and 5Ω or less and L is 10 μH or more and 5
It may be 0 μH or less. In this case, the excitation circuit 6
Can be configured by a circuit element whose current resistance and withstand voltage are not so high, and sufficient input power and heat generation amount can be obtained. If the values of R and L are within this range, the same effect can be obtained even if the specifications of the exciting coil 5 such as the number of turns of the exciting coil 5 and the distance between the exciting coil 5 and the heat roller 1 are changed.

In the present embodiment, as described above, the wire bundle of the exciting coil 5 is formed by bundling 60 wire rods having an outer diameter of 0.2 mm. The configuration of the wire bundle is not necessarily limited to this configuration, but the outer diameter is 0.1 mm.
It is desirable that 50 to 200 wire rods having a size of 0.3 mm or more be bundled. If the outer diameter of the wire is less than 0.1 mm, the wire may break due to a mechanical load. On the other hand, when the outer diameter of the wire exceeds 0.3 mm, the electric resistance (r in FIG. 4) to a high-frequency alternating current becomes large, and the heat generation of the exciting coil 5 becomes excessive. Further, when the number of wires constituting the wire bundle is 50 or less, the cross-sectional area is small, so that the electric resistance becomes large and the heat generation of the exciting coil 5 becomes excessive.
On the other hand, if the number of wire rods constituting the wire bundle is 200 or more, it becomes difficult to wind the exciting coil 5 into an arbitrary shape because the wire bundle becomes thick, and it is difficult to obtain a predetermined number of turns in a predetermined space. Becomes Generally, the outer diameter of the wire bundle is 5 mm
These conditions can be satisfied by the following. As a result, the number of turns of the exciting coil 5 can be increased in a narrow space, so that the required power can be supplied to the heat generating roller 1 while the exciting coil 5 is downsized.

The magnetic fluxes of the exciting coil 5 that circulate may be partially spaced apart from each other, but it is more efficient if most of them are in close contact with each other. Further, the winding wire bundle of the exciting coil 5 may be configured by partially changing the stacking manner, but the lower the exciting coil 5 is, the more current is supplied to the heat generating roller 1 with a smaller current. be able to. The exciting coil 5 may have any shape as long as the width (circumferential length) of the exciting coil 5 is larger than the height (laminated thickness) of the exciting coil 5.

When the length of the exciting coil 5 in the rotation axis direction of the heat generating roller 1 is longer than the length of the heat generating roller 1, the magnetic flux penetrates the conductive member at the end of the heat generating roller 1 such as the side plate 2. Will be done. Therefore, the surrounding constituent members generate heat, and the transmission rate of the electromagnetic energy to the heat generating roller 1 decreases. In the present embodiment, since the length of the heat generating roller 1 is longer than the length of the exciting coil 5 in the rotation axis direction of the heat generating roller 1, the magnetic flux generated by the coil current reaches the peripheral components such as the side plate 2. Almost all reach the heat generating roller 1 without doing so. Thereby, the electromagnetic energy applied to the exciting coil 5 can be efficiently transmitted to the heat generating roller 1. In particular, when the magnetic flux passes from the end surface of the heat generating roller 1 in the rotation axis direction, the eddy current density on the end surface of the heat generating roller 1 increases. In this case, there is a problem that the heat generated at the end surface of the heat roller 1 becomes too large.

In the present embodiment, as described above, the inner peripheral portion of the exciting coil 5, the recording paper with the maximum width, the outer peripheral portion of the exciting coil 5, The heating roller 1 is provided, and the exciting coil 5 is a portion through which the recording paper 8 passes, and is parallel to the rotational axis direction of the heating roller 1 and evenly wound in the rotational axis direction.
Therefore, the heat generation distribution of the heat generation roller 1 can be made uniform in the portion where the recording paper 8 passes. As a result, the temperature distribution in the fixing unit can be made uniform, and a stable fixing action can be obtained.

(Second Embodiment) FIG. 5 shows a second embodiment of the present invention.
FIG. 6 is a cross-sectional view showing a heat generating part of a fixing device as an image heating device in the embodiment, and FIG. 6 is a bottom view showing the heat generating part of the fixing device excluding a heat generating roller. The members having the same functions as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

In the present embodiment, the wire bundles are wound in the circumferential direction of the heating roller 1 without being overlapped with each other, and a pair of back cores 9 are provided on the back surface of the exciting coil 5 in the first embodiment.
This is different from the embodiment.

The material of the back core 9 has a relative magnetic permeability of 1
000-3000, saturation magnetic flux density is 200-300m
T, ferrite having a volume resistivity of 1 to 10 Ω · m is used. As the material of the back core 9, other than ferrite, a material such as permalloy having a high magnetic permeability and a high resistivity can be used.

The cross section of the back core 9 has an outer diameter of 36 mm and a thickness.
Cut a 5mm cylinder at an angle of about 90 degrees in the axial direction.
It has a curved shape. Therefore, the cross-sectional area of the back core 9 is
243 mm²Becomes The cross-sectional area of the exciting coil 5 is 7
mm²126mm x 9 rolls x 2 ²Becomes

The heating roller 1 is formed in a pipe shape having an outer diameter of 20 mm and a thickness of 0.3 mm. For this reason, the cross-sectional area of the surface inside the heat roller 1 perpendicular to the rotation axis is about 2
It becomes 95 mm ² . Therefore, the cross-sectional area of the exciting coil 5 including the back core 9 is larger than the cross-sectional area of the surface inside the heat roller 1 which is perpendicular to the rotation axis. The distance between the back core 9 and the heat generating roller 1 is 5.5 mm.

Further, in the present embodiment, the recording paper of A4 size (width 210 mm) is used as the recording paper of the maximum width, and the length of the heating roller 1 in the rotation axis direction is 24.
0 mm, the length of the outer circumference of the rotating excitation coil 5 along the rotation axis direction of the heat generation roller 1 is 200 mm, the length of the inner circumference of the excitation coil 5 along the rotation axis direction of the heat generation roller 1 is 170 mm, and the back surface The length of the core 9 along the rotation axis direction of the heat generating roller 1 is set to 220 mm.
The bearing 3 (see FIG. 2), which is a support member of the heat generation roller 1, is made of steel, which is a magnetic material. The distance between the bearing 3 and the back core 9 is 10 mm,
It is larger than the distance between the back core 9 and the heat generating roller 1.

The other structure is the same as that of the first embodiment.

The operation of the fixing device having the above structure will be described below.

By providing the back core 9, the inductance of the exciting coil 5 is increased, the electromagnetic coupling between the exciting coil 5 and the heat roller 1 is improved, and R in the equivalent circuit of FIG. 4 is increased. Therefore, it is possible to apply a large amount of power to the heat generating roller 1 even with the same coil current. Therefore, it is possible to realize a fixing device having a short warm-up time by using the inexpensive exciting circuit 6 (see FIG. 2) having low withstand current and withstand voltage.

Further, as shown by a broken line M in FIG. 5, all the magnetic flux on the back side of the exciting coil 5 passes through the inside of the back core 9, so that the magnetic flux can be prevented from leaking backward. As a result, it is possible to prevent the peripheral conductive member from generating heat due to electromagnetic induction, and also to prevent unnecessary electromagnetic wave radiation.

Further, since the revolving wire bundles are not overlapped, all the wire bundles of the exciting coil 5 are located near the heat generating roller 1. Therefore, the magnetic flux generated by the coil current is more efficiently transmitted to the heat generating roller 1.

In this embodiment, since the exciting coil 5 and the back core 9 are installed outside the heat generating roller 1 (heat generating portion), the exciting coil 5 and others are heated by the influence of the temperature of the heat generating portion. Can be prevented. For this reason,
The calorific value can be kept stable. In particular, the heat roller 1
Since the exciting coil 5 and the back core 9 having a cross-sectional area larger than the cross-sectional area of the surface perpendicular to the rotation axis inside the are used, the heat generating roller 1 having a small heat capacity, the exciting coil 5 having a large number of turns, Appropriate amount of ferrite (back core 9)
And can be used in combination. Therefore, it is possible to apply a large amount of electric power to the heat generating roller 1 with a predetermined coil current while suppressing the heat capacity of the fixing device.

In the present embodiment, as described above, the inner peripheral portion of the exciting coil 5, the outer peripheral portion of the exciting coil 5, the recording paper having the maximum width, It is a back core 9 and a heat generating roller 1. In this way, the length of the outer peripheral portion of the exciting coil 5 along the rotation axis direction of the heat generation roller 1 is made smaller than the width of the recording paper having the maximum width, while the rotation axis direction of the heat generation roller 1 of the rear core 9 is decreased. Since the length along the line is made larger than the width of the maximum width of the recording paper, even if the winding of the exciting coil 5 is somewhat uneven, the magnetic field reaching the heat generating roller 1 from the exciting coil 5 is directed in the rotation axis direction. Can be uniform. Therefore, the heat generation distribution of the heat generation roller 1 can be made uniform in the portion where the recording paper passes. As a result, the temperature distribution in the fixing section can be made uniform, and a stable fixing action can be obtained. Further, while making the heat distribution of the heat roller 1 uniform,
Since the length of the heating roller 1 in the rotation axis direction and the length of the exciting coil 5 along the rotation axis of the heating roller 1 can be shortened, it is possible to reduce the size of the device and reduce the cost. Furthermore, since the length of the rear surface core 9 along the rotation axis direction of the heat generation roller 1 is shorter than the length of the heat generation roller 1 in the rotation axis direction, the eddy current density on the end surface of the heat generation roller 1 becomes high and It is possible to prevent excessive heat generation at the end faces.

Further, as described above, as the bearing 3 (see FIG. 2) which is a supporting member of the heat generating roller 1, in order to guarantee the mechanical strength, steel having magnetism is generally used. Therefore, the magnetic flux generated by the coil current is easily attracted to the bearing 3, and when the magnetic flux penetrates the bearing 3, heat is generated. For this reason, the rate of transmission of electromagnetic energy to the heat generating roller 1 decreases, and the temperature of the bearing 3 rises, resulting in a shorter life. In the present embodiment, as described above, the distance between the bearing 3 and the end surface of the back core 9 is set to be larger than the facing distance between the back core 9 and the heat generating roller 1, so that the back core 9 is penetrated. Most of the generated magnetic flux penetrates the heat generating roller 1 without being guided to the bearing 3. As a result, the electromagnetic energy applied to the exciting coil 5 can be efficiently transmitted to the heat generating roller 1, and heat generation of the bearing 3 can be prevented.

The distance between the bearing 3 and the back core 9 (10 mm in this embodiment) is equal to the distance between the back core 9 and the heating roller 1.
It suffices if the distance is larger than the facing interval (5.5 mm in the present embodiment), but it is preferably twice or more.

Further, since the thickness of the back core 9 is uniform, heat is not locally accumulated inside the back core 9. Further, since there is nothing to prevent heat radiation from the outer periphery of the back core 9, it is possible to prevent the saturation magnetic flux density of the back core 9 from being lowered by the temperature rise due to heat storage, and to prevent the magnetic permeability as a whole to sharply decrease. it can. Thereby, the heat generating roller 1 can be stably maintained at a predetermined temperature for a long time.

(Third Embodiment) FIG. 7 shows a third embodiment of the present invention.
FIG. 3 is a cross-sectional view showing a heat generating portion of a fixing device as an image heating device in the embodiment. The members having the same functions as those in the second embodiment are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, as shown in FIG. 7, the back core 9 is extended to a range where the exciting coil 5 does not exist, and the "opposing portion F" is opposed to the heat generating roller 1 without the exciting coil 5 interposed therebetween. Is provided, which is different from the second embodiment. Hereinafter, the portion of the back core 9 that faces the heat generating roller 1 via the exciting coil 5 is referred to as a "magnetic permeability portion T". In addition, the cross section of the back core 9 has a cylindrical shape of 180 degrees in the axial direction.
The shape is cut at an angle of degrees.

In this case, the magnetic path can be formed by more ferrite (back surface core 9). Therefore, the air portion having a low magnetic permeability through which the magnetic flux generated by the coil current passes is only the narrow gap portion between the heat generating roller 1 and the back core 9. Therefore, the inductance of the exciting coil 5 is increased, and the magnetic flux generated by the coil current is almost completely guided to the heat generating roller 1. as a result,
The electromagnetic coupling between the heating roller 1 and the exciting coil 5 is further improved, and R in the equivalent circuit of FIG. 4 is further increased. This makes it possible to apply more power to the heat generating roller 1 even with the same coil current.

Further, as indicated by a broken line M in FIG. 7, the magnetic flux guided from the back core 9 to the heat generating roller 1 passes through the facing portion F. The length of the facing portion F along the rotation axis direction of the heat generating roller 1 is the same as the length of the back core 9 along the rotation axis direction of the heat generating roller 1, and is longer than the width of the recording paper. For this reason,
The magnetic flux uniformly enters from the facing portion F to the portion where the recording paper passes. Therefore, it is possible to uniformly heat the range required for fixing the heat generating roller 1.

In the present embodiment, the back core 9 is
The exciting coil 5 is arranged on the side opposite to the heat generating roller 1, but as shown in FIG. 8, the heat generating roller 5 is wound around the back core 9 having a semi-cylindrical shape while the wire bundle is extended in the axial direction and circulated. It is also possible to form the exciting coil 5 by making a turn along the circumferential direction of 1. In this case, the magnetic flux generated by the coil current is generated not only on the circumference of the heating roller 1 on the side of the exciting coil 5 but
The pressure roller side also penetrates (broken line M ′ in FIG. 8). As a result, the entire circumference of the heat generating roller 1 is heated, so that the amount of heat generated can be increased even with the same coil current. Moreover, since the cross-sectional area through which the magnetic flux passes becomes large, even if more magnetic flux penetrates the heat generating roller 1, the saturation magnetic flux density of the heat generating roller 1 is not exceeded. Therefore, it is possible to prevent the magnetic flux from passing through the space other than the heat generating roller 1, so that the heat generating roller 1 can be heated more efficiently by electromagnetic induction.

(Fourth Embodiment) FIG. 9 shows a fourth embodiment of the present invention.
FIG. 10A is a cross-sectional view showing an image forming apparatus using the image heating apparatus as a fixing apparatus according to the fourth embodiment of the present invention.
11 is a sectional view showing a fixing device as an image heating device in the embodiment of the present invention, FIG. 11 is a projection view of the heat generating portion viewed from the direction of arrow G in FIG. 10A, and FIG. It is sectional drawing of the heat generating part in the surface containing.

In FIG. 9, 11 is an electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum"). The photosensitive drum 11 is
While being rotationally driven in the direction of the arrow at a predetermined peripheral speed, the surface thereof is uniformly charged to a negative dark potential V0 by the charger 12. Reference numeral 13 denotes a laser beam scanner, which outputs a laser beam 14 modulated in accordance with a time series electric digital pixel signal of image information input from a host device such as an image reading device or a computer (not shown). The surface of the charged photosensitive drum 11 is the laser beam 14
Scanned and exposed by. As a result, the photosensitive drum 11
In the exposed part of, the absolute value of the electric potential is lowered to the bright electric potential VL,
An electrostatic latent image is formed. This latent image is developed by the negatively charged toner of the developing device 15 and visualized.

The developing device 15 has a developing roller 16 which is driven to rotate. The developing roller 16 is the photosensitive drum 11.
And a thin layer of toner is formed on the outer peripheral surface thereof. A developing bias voltage whose absolute value is smaller than the dark potential V0 of the photosensitive drum 11 and larger than the bright potential VL is applied to the developing roller 16, whereby the toner on the developing roller 16 becomes bright on the photosensitive drum 11. The latent image is visualized by being transferred only to the portion of the potential VL.

On the other hand, the recording papers 8 are fed one by one from the paper feed unit 17, and pass through the registration roller pair 18 to the nip portion between the photosensitive drum 11 and the transfer roller 19 and the photosensitive drum 1
It is sent at an appropriate timing synchronized with the rotation of 1. Then, the toner image on the photosensitive drum 11 is sequentially transferred to the recording paper 8 by the transfer roller 19 to which the transfer bias is applied. After the recording paper 8 is separated, the residual material such as transfer residual toner on the surface of the photosensitive drum 11 is removed by the cleaning device 20, and is repeatedly used for the next image formation.

A fixing paper guide 21 guides the movement of the recording paper 8 after transfer to the fixing device 22 by the fixing paper guide 21. After the recording paper 8 is separated from the photosensitive drum 11, the recording paper 8 is conveyed to the fixing device 22, and the toner image transferred onto the recording paper 8 is fixed thereby. Reference numeral 23 is a paper ejection guide, and the paper ejection guide 23 is used to fix the fixing device 22.
The recording paper 8 that has passed through is guided to the outside of the apparatus. The fixing paper guide 21 and the paper discharge guide 23 are made of resin such as ABS. The fixing paper guide 21 and the paper discharge guide 23 may be made of a non-magnetic metal material such as aluminum. The recording paper 8 after the toner image is fixed is discharged to the paper discharge tray 24.

Reference numeral 25 is a bottom plate of the main body of the apparatus, 26 is a top plate of the main body of the apparatus, and 27 is a chassis of the main body. These together serve as the strength of the main body of the apparatus. These members are
It is composed of a zinc-plated material with steel as a base material being a magnetic material.

28 is a cooling fan, and this cooling fan 28 generates an air flow in the apparatus. Reference numeral 29 denotes a coil cover as a shielding member made of a non-magnetic metal material such as aluminum. The coil cover 29 is configured to cover the back core 9 of the exciting coil 5 (see FIG. 10A).

Next, the fixing device as the image heating device of this embodiment will be described in detail.

In FIG. 10A, the thin fixing belt 31
Is an endless belt whose base material is made of polyimide resin and has a diameter of 50 mm and a thickness of 100 μm. Fixing belt 3
The surface of 1 is coated with a release layer (not shown) made of a fluororesin and having a thickness of 20 μm in order to impart releasability. As the material of the base material, a very thin metal such as nickel produced by electroforming can be used in addition to heat-resistant polyimide resin, fluororesin, and the like. Further, as the release layer, resins and rubbers having good release properties such as PTFE, PFA, FEP, silicone rubber, and fluororubber may be used alone or in combination. When the fixing belt 31 is used for fixing a monochrome image, only releasability is required to be secured, but when the fixing belt 31 is used for fixing a color image, it is desirable to impart elasticity, and in that case. Needs to form a thicker rubber layer.

The exciting coil 5 serving as an exciting means extends a wire bundle, which is a bundle of 60 copper wires whose outer diameter is 0.2 mm and whose outer diameter is insulated, in the rotation axis direction of the heat roller 1, and It is formed so as to circulate along the circumferential direction of.
The cross-sectional area of the wire bundle is about 7 mm ² including the insulating coating of the wire.

As shown in FIGS. 10A to 12, the exciting coil 5 has a sectional shape that covers the fixing belt 31 wound around the heat roller 1. In this case, the exciting width of the exciting coil 5 in the moving direction of the fixing belt 31 is the contact range (wrapping range) between the fixing belt 31 and the heat roller 1.
It is below. The fixing belt 31 of the heat generating roller 1
When the portion where heat is not taken away generates heat, there is a problem that the temperature of the heat generating roller 1 easily rises beyond the heat resistant temperature of the material of the fixing belt 31. However, with the configuration of the present embodiment, it is possible to prevent the temperature of the heat generating roller 1 from rising abnormally because only the area of the heat generating roller 1 that contacts the fixing belt 31 generates heat. it can. Further, the wire bundles overlap only at both ends of the exciting coil 5 (both ends in the rotation axis direction of the heat generating roller 1), and the heat generating roller 1
It makes nine turns along the circumferential direction in close contact with each other. Both ends of the exciting coil 5 in the rotation axis direction of the heat generating roller 1 are raised in a state where the wire bundles are overlapped in two rows. That is, the exciting coil 5 is formed in a saddle-like shape as a whole. Therefore, a wider range of the heating roller 1 in the rotation axis direction can be uniformly heated.
It should be noted that since the wire bundles that are overlapped at both ends of the exciting coil 5 have a large distance from the heat generating roller 1, eddy currents are not concentrated in this part and the temperature does not become too high.

The back core 9 includes a C-shaped core 32 and a central core 3.
3 and 3. The C-shaped core 32 has a width of 10
7 mm and are arranged at intervals of 25 mm in the rotation axis direction of the heat generating roller 1. As a result, the magnetic flux leaking to the outside can be captured. The central core 33 is located at the center of the winding of the exciting coil 5 and has a convex shape with respect to the C-shaped core 32. That is, the central core 33 is a portion N of the facing portion F of the back core 9 that is close to the heat generating roller 1 (see FIG. 13).
The cross sectional area of the central core 33 is 3 mm × 10 mm.

The central core 33 may be divided into several pieces in the direction of the rotation axis of the heat roller 1 so that ferrite can be easily manufactured. Further, the central core 33 may have a shape integrally combined with the C-shaped core 32, and further has a shape integrally combined with the C-shaped core 32, and
The heating roller 1 may be divided into several parts in the rotation axis direction.

Reference numeral 34 is a heat insulating member having a thickness of 1 mm and made of a resin having a high heat resistance temperature such as PEEK material or PPS. At both ends of the heat insulating member 34, both-end holding portions 34a for holding the raised portions of both ends of the exciting coil 5 in the rotation axis direction of the heat generating roller 1 are provided. As a result, it is possible to prevent the swelling at both ends of the exciting coil 5 from collapsing, and the position outside the exciting coil 5 is regulated.

The material of the back core 9 is the same as that of the second embodiment. C-shaped core 32 except for the central core 33
The cross-sectional shape of the back core 9 and the shape of the heat generating roller 1 in the cross section including the same are the same as those in the second embodiment. Therefore, the point that the cross-sectional area of the exciting coil 5 including the back core 9 is larger than the cross-sectional area of the surface inside the heat roller 1 that is perpendicular to the rotation axis is also the same as in the second embodiment.

From the exciting circuit 6 (see FIG. 2) to the exciting coil 5
The alternating current applied to is similar to that in the first embodiment. The alternating current applied to the exciting coil 5 is controlled by the temperature signal obtained by the temperature sensor provided on the surface of the fixing belt 31 so that the surface of the fixing belt 31 reaches a predetermined fixing temperature of 190 ° C. .

As shown in FIG. 10A, the fixing belt 31
Has a surface with a low hardness (JIS A 30 degrees) and is made of a silicone rubber which is a foamed material having a diameter of 2
Fixing roller 35 with low thermal conductivity of 0 mm and diameter of 20 mm
It is suspended with a predetermined tension on the heat generating roller 1 and is rotatable in the direction of arrow B. Here, ribs (not shown) for preventing the fixing belt 31 from meandering are provided at both ends of the heat roller 1. Further, the pressure roller 4 as a pressure unit is provided with the fixing belt 31.
The pressure roller is pressed against the fixing roller 35 via the, thereby forming a nip portion.

In the present embodiment, A4 size (width 210 mm) recording paper is used as the maximum width recording paper, the width of the fixing belt is 230 mm, and the length of the heat generating roller 1 in the rotation axis direction is 260 mm. The length between the outermost ends of the back core 9 in the rotation axis direction of the heat generating roller 1 is 225 m.
m, the length of the outer circumference of the revolving excitation coil 5 along the rotation axis direction of the heat generating roller 1 is 245 mm, and the heat insulating member 3
The length of the heating roller 1 of No. 4 along the rotation axis direction is 250 m.
It is set to m.

In the present embodiment, the exciting coil 5,
The back core 9 and the heat generating roller 1 are configured as described above, and the exciting coil 5 causes the heat generating roller 1 to generate heat by electromagnetic induction. The mechanism will be described below with reference to FIG.

As shown in FIG. 13, the magnetic flux generated by the coil current flows from the facing portion F of the back core 9 to the heat generating roller 1.
Enter In this case, the magnetic flux generated by the coil current is
Due to the magnetism of the heat generating roller 1, the heat generating roller 1 penetrates the inside of the heat generating roller 1 in the circumferential direction as indicated by a broken line M in the figure. Then, this magnetic flux forms a large loop from the central core 33, which is the proximity portion N of the back surface core 9 to the heat generating roller 1, through the magnetic permeable portion T, and repeats the generation and disappearance. The point that the induced current generated by the change of the magnetic flux generates Joule heat is
This is the same as the embodiment.

In the present embodiment, as shown in FIG. 11, a plurality of narrow C-shaped cores 32 are arranged at equal intervals in the rotation axis direction of the heat roller 1, but this configuration is the only one. Then, the magnetic flux flowing in the circumferential direction on the back surface of the exciting coil 5 is concentrated in the portion of the C-shaped core 32 and hardly flows into the air between the adjacent C-shaped cores 32. Therefore, the magnetic flux entering the heat generating roller 1 tends to concentrate on the portion where the C-shaped core 32 exists. Therefore, the heat generation of the heat generation roller 1 is likely to increase at the portion facing the C-shaped core 32. However, in the present embodiment, since the central core 33 forming the proximity portion N at the center of the winding of the exciting coil 5 is continuously provided in the rotation axis direction of the heat generating roller 1, the C-shaped core 32 faces each other. The magnetic flux that has entered the heat generating roller 1 from the portion F flows in the heat generating roller 1 also in the direction of the rotation axis, and the distribution is made uniform. Therefore, the non-uniformity of the heat generation amount of the heat generation roller 1 is alleviated.

The magnetic flux of the magnetically permeable portion T is applied to the facing portion F of the C-shaped core 32.
The function of guiding the magnetic field to another facing portion F is not directly related to the distribution of the magnetic flux incident on the heat generating roller 1. Therefore, it is very effective to optimize the shape of the back core 9 by separately configuring the magnetically permeable portion T and the facing portion F. The magnetic permeable portion T does not need to be uniform in the axial direction, and the facing portion F may be made uniform in the axial direction as much as possible.

Since the central core 33 is formed in a convex shape with respect to the C-shaped core 32 to provide the proximity portion N to the heat generating roller 1, the magnetic path can be formed by a larger amount of ferrite. Therefore, the air portion having a low magnetic permeability through which the magnetic flux generated by the coil current passes is only the narrow gap portion between the heat generating roller 1 and the back core 9. Therefore, the inductance of the exciting coil 5 is further increased,
Since more magnetic flux generated by the coil current is guided to the heat generating roller 1, electromagnetic coupling between the heat generating roller 1 and the exciting coil 5 is improved. This makes it possible to apply more power to the heat generating roller 1 even with the same current.
In particular, since the magnetic flux generated by the coil current always passes through the center of the circumference of the exciting coil 5, the proximity portion N formed by the central core 33 continuous in the rotation axis direction of the heat generating roller 1 is provided at this portion. The magnetic flux generated by the current can be efficiently guided to the heat generating roller 1.

The cross-sectional area in the circumferential direction of the magnetically permeable portion T of the C-shaped core 32 is set so that the density of the magnetic flux guided from the exciting coil 5 does not exceed the maximum magnetic flux density as a material. This magnetic flux density is set to be about 80% of the saturation magnetic flux density of ferrite at the maximum. The ratio of the maximum magnetic flux density to the saturated magnetic flux density may be 100% or less, but practically it is desirable to set it in the range of 50% to 85%. If this ratio is too high, the maximum magnetic flux density may exceed the saturation magnetic flux density due to variations in the environment and members. In this case, the magnetic flux flows on the back surface of the back surface core 9 and heats the rear member. On the other hand, if this ratio is too low, expensive ferrite is used more than necessary, and the device becomes expensive.

The C-shaped core 32 has a uniform width,
Since a plurality of heat-dissipating rollers 1 are arranged at large intervals in the rotation axis direction of the heat-generating roller 1, heat is not accumulated in the back core 9 and the exciting coil 5. Furthermore, since there is nothing that hinders heat radiation from the outer periphery of the back core 9 and the excitation coil 5, the saturation magnetic flux density of the ferrite of the back core 9 is lowered by the temperature rise due to heat storage, and the overall magnetic permeability is sharply reduced. Can be prevented. In addition, it is possible to prevent the insulating coatings of the wires from melting and short-circuiting the wires. Thereby, the heat generating roller 1 can be stably maintained at a predetermined temperature for a long time.

Further, since both ends of the exciting coil 5 in the direction of the rotation axis of the heat roller 1 are formed by overlapping the wire bundles, the exciting coil 5 is uniformly extended in the direction of the rotation axis of the heat roller 1 over a wider range. be able to. Thereby, the heat generation distribution of the heat generation roller 1 can be made uniform. On the contrary, the exciting coil 5 while ensuring a uniform heating area
Since the width of both ends of the heat generating roller 1 in the rotation axis direction can be reduced, the overall size of the apparatus can be reduced.

Further, in this embodiment, the recording paper having the largest width, the back core 9, the fixing belt 31, the outer peripheral portion of the exciting coil 5, and the heat insulating member 34 are arranged in the order of increasing length in the rotation axis direction of the heat generating roller 1. , The heating roller 1. That is, the heat insulating member 34 is longer than the exciting coil 5 and the back core 9. Since the back core 9 and the heat generating roller 1 and the fixing belt 31 face each other via the heat insulating member 34, even when the back core 9 is brought close to the heat generating roller 1, the temperature rise of the back core 9 increases. Can be prevented. Further, it is possible to prevent the cooling airflow from contacting the fixing belt 31 and cooling the fixing belt 31.

Further, since the width of the fixing belt 31 is longer than the length of the rear core 9 in the direction of the rotation axis of the heat generating roller 1, the heat generating roller 1 which is not in contact with the fixing belt 31 is not heated. It is possible to prevent the temperature of the heat generating roller 1 in this portion from rising too high.

Further, by providing the coil cover 29, it is possible to prevent the magnetic flux slightly leaking to the back surface of the back core 9 and the high-frequency electromagnetic wave generated from the exciting coil 5 from propagating inside and outside the device. As a result, it is possible to prevent the electric circuits inside and outside the device from malfunctioning due to electromagnetic noise.

Further, the coil cover 29 and the heat insulating member 34
Since the airflow from the cooling fan 28 flows through the space surrounded by and as a ventilation path, the heat generating roller 1 and the fixing belt 3
It is possible to cool the exciting coil 5 and the back core 9 without cooling 1.

The magnetic members constituting the device such as the bottom plate 25, the top plate 26, and the main body chassis 27 of the main body of the apparatus are set to 20 mm, which is closest to the exciting coil 5. As a result, it is possible to prevent the magnetic flux passing through the inside of the back core 9 from being radiated to the outside of the exciting coil 5 from a portion other than the facing portion F and entering the magnetic member such as the main body chassis 27. As a result, the electromagnetic energy applied to the exciting coil 5 can be efficiently supplied to the heat generating roller 1 without unnecessarily heating the constituent members of the apparatus. Although the minimum value of the distance between the exciting coil 5 and the magnetic member such as the main body chassis 27 is set to 20 mm, the distance between the back core 9 and the magnetic member such as the main body chassis 27 is set to the back core 9 and the heat generating roller 1. If the distance is equal to or larger than the distance, preferably 1.5 times the distance, the leakage of the magnetic flux to the back surface of the exciting coil 5 can be prevented. In the present embodiment, since the fixing paper guide 21 and the paper discharge guide 23, which must be closest to the fixing device 22, are made of resin, a sufficient space is provided between the back core 9 and other magnetic members. The space can be easily secured.

Further, in the present embodiment, the heat generating roller 1 (heat generating portion) is installed inside the fixing belt 31, while the exciting coil 5 and the back core 9 are installed outside the fixing belt 31. Therefore, it is possible to prevent the exciting coil 5 and the like from being heated by the influence of the temperature of the heat generating portion. Therefore, the calorific value can be kept stable. In particular, the exciting coil 5 and the back core 9 having a cross-sectional area larger than the cross-sectional area of the surface inside the heat roller 1 perpendicular to the rotation axis.
The heat generating roller 1 having a small heat capacity is used because
The exciting coil 5 having a large number of turns and a suitable amount of ferrite (back surface core 9) can be used in combination. Therefore, while suppressing the heat capacity of the fixing device 22,
It becomes possible to apply a large amount of electric power to the heat generating roller 1 with a predetermined coil current. As a result, the fixing device 22 having a short warm-up time can be realized by using the inexpensive exciting circuit 6 (see FIG. 2) having low withstand current and withstand voltage.
In the present embodiment, the alternating current from the excitation circuit 6 was able to supply 800 W of electric power to the heating roller 1 with an effective value voltage of 140 V (voltage amplitude 500 V) and an effective value current of 22 A (peak current 55 A).

Since the exciting coil 5 located outside the heat generating roller 1 heats the surface of the heat generating roller 1, the fixing belt 31 comes into contact with the portion of the heat generating roller 1 having the largest heat generation amount. Therefore, the maximum heat generating portion serves as a heat transfer portion to the fixing belt 31, and the generated heat can be transferred to the fixing belt 31 without heat conduction in the heat generating roller 1. In this way, since the heat transfer distance is small, it is possible to perform a quick response control with respect to the temperature fluctuation of the fixing belt 31.

A temperature sensor (not shown) is provided near the position where the heating roller 1 has passed the contact portion with the fixing belt 31.
Is provided. By controlling the temperature of this portion to be constant, the temperature of the fixing belt 31 when entering the nip portion between the fixing roller 35 and the pressure roller 4 can be always kept constant. As a result, a plurality of recording papers 8
Even when fixing is performed, the fixing can be stably performed.

Further, since the exciting coil 5 and the back core 9 cover almost half of the circumference of the heat generating roller 1, the entire area of the contact portion between the fixing belt 31 and the heat generating roller 1 generates heat. Therefore, more heating energy transmitted from the exciting coil 5 to the heat generating roller 1 by electromagnetic induction can be transmitted to the fixing belt 31.

Further, in the present embodiment, the material, thickness, etc. of the heat roller 1 and the fixing belt 31 can be independently set. Therefore, as the material and thickness of the heat generating roller 1, it is possible to select the optimum material and thickness for heating the exciting coil 5 by electromagnetic induction. Further, as the material and thickness of the fixing belt 31, an optimum material and thickness for fixing can be selected.

In the present embodiment, in order to achieve the purpose of shortening the warm-up time, the heat capacity of the fixing belt 31 is set as small as possible, and the thickness and the outer diameter of the heat generating roller 1 are made small so that the heat capacity can be reduced. Is set small. Therefore, it was possible to reach the predetermined temperature in about 15 seconds from the start of the temperature rise for fixing with the applied power of 800 W.

In this embodiment, the C-shaped core 3
2 are arranged at equal intervals in the rotation axis direction of the heat roller 1, but the intervals do not necessarily have to be equal. By adjusting the interval depending on the heat radiation condition and the presence or absence of a contact member such as a temperature sensor, it is possible to freely design the heat generation distribution so that the temperature distribution becomes uniform.

Further, in the present embodiment, the rear surface core 9 is composed of a plurality of C-shaped cores 32 having a uniform thickness and made of ferrite and arranged at intervals in the rotation axis direction of the heat roller 1.
And a central core 33 which is also made of ferrite, but is not necessarily limited to this configuration. For example, a configuration in which a plurality of holes are provided in the back core 9 that is continuous and continuous in the rotation axis direction of the heat generating roller 1 may be used. Further, a plurality of blocks made of ferrite may be separately distributed on the back surface of the exciting coil 5.

Further, although the base material of the fixing belt 31 is made of resin in the present embodiment, it may be made of ferromagnetic metal such as nickel instead of resin. In this case, part of the heat generated by electromagnetic induction is generated in the fixing belt 31, and the fixing belt 31 itself is also heated, so that heating energy is applied to the fixing belt 3.
It is possible to convey to 1 more effectively.

Further, in the present embodiment, the bottom plate 25 of the apparatus main body, the top plate 26 of the apparatus main body, and the main body chassis 27 are made of a magnetic material, but a resin material is used instead of the magnetic material. You can also In this case, the members responsible for the strength of the apparatus main body do not affect the lines of magnetic force, so these members can be arranged in the vicinity of the back core 9. As a result, the size of the entire device can be reduced.

Further, in the present embodiment, both ends of the heat generating roller 1 are supported by the bearings 3, but as shown in FIG. 14, the heat generating roller 1 is provided at both ends of the heat generating roller 1 and is made of bakelite or the like. Flange 36 made of heat-resistant resin having low heat conductivity, and both flanges 36
It may be configured to be supported by the central shaft 37 penetrating through. If this configuration is adopted, leakage of heat and magnetic flux from both ends of the heat generating roller 1 can be suppressed.

Further, in the present embodiment, the exciting width of the exciting coil 5 in the moving direction of the fixing belt 31 is set to be equal to or less than the contact range (wrapping range) between the fixing belt 31 and the heat roller 1, but it is not always necessary. The configuration is not limited to this. For example, as shown in FIG. 10B, the exciting width of the exciting coil 5 in the moving direction of the fixing belt 31 is extended from the contact range (wrapping range; boundary line b) between the fixing belt 31 and the heat generating roller 1 to the fixing roller 35 side. May be. According to this configuration, as compared with the configuration of FIG. 10A, it is possible to generate heat in a wider range of the heat generation roller 1 (range of a in FIG. 10B), and thus a sufficient amount of heat generation can be obtained even with a small coil current. it can. Further, in this case, after the exciting coil 5 is formed by circling the wire bundle and then the exciting coil 5 is compressed, the circling wire bundle has a substantially quadrangular cross section, and the wire bundles are further brought into close contact with each other.
As a result, the volume occupied by the exciting coil 5 can be reduced, and the number of turns of the exciting coil 5 can be increased. As a result, the current density of the coil current increases, so the density of the eddy current generated in the heat generating roller 1 also increases, and the amount of heat generation increases. For this reason, it becomes possible to reduce the required coil current and to reduce the diameter of the heat generating roller 1. Furthermore, since the distance between the back core 9 and the exciting coil 5 can be increased, heat dissipation of the back core 9 can be promoted and the temperature rise of the back core 9 can be prevented. Further, since the wire bundles are in close contact with each other, the adhesion between the wire bundles is strong, and the exciting coil 5 alone can maintain its shape. Therefore, the assembly process of the fixing device 22 is simplified.

(Fifth Embodiment) FIG. 15 is a sectional view showing a heat generating portion of a fixing device as an image heating device according to a fifth embodiment of the present invention. The members having the same functions as those in the fourth embodiment are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 15, in the present embodiment, unlike the above-described fourth embodiment, the portion of the facing portion F of the back core 9 facing the heat generating roller 1 is the heat generating roller 1.
Is formed in a convex shape so as to be close to.

The other structure is similar to that of the fourth embodiment.

According to the structure of this embodiment, the magnetic path can be formed almost completely of ferrite. Therefore, the air portion having a low magnetic permeability through which the magnetic flux generated by the coil current passes is only the narrow gap portion between the heat generating roller 1 and the back core 9. Therefore, the inductance of the exciting coil 5 is further increased, and the magnetic flux generated by the coil current is almost completely guided to the heat generating roller 1. As a result, the electromagnetic coupling between the heat roller 1 and the exciting coil 5 is improved, and R in the equivalent circuit of FIG. 4 is increased. Therefore, even if the same coil current is used, more power is generated by the heat generating roller 1.
It is possible to input to. In this embodiment, 800 W at an effective current of 20 A (peak current of 50 A)
It was possible to apply the power of 1 to the heat generating roller 1.

Further, since the rear surface core 9 faces the heat generating roller 1 and the fixing belt (not shown) via the heat insulating member 34, even when the rear surface core 9 is brought close to the heat generating roller 1, It is possible to prevent the temperature of the back core 9 from rising.

(Sixth Embodiment) FIG. 16 is a sectional view showing a heat generating portion of a fixing device as an image heating device according to a sixth embodiment of the present invention. FIG. 17 shows the heat generating portion in the direction of arrow A in FIG.
It is a projection view seen from the direction. The members having the same functions as those in the fifth embodiment are designated by the same reference numerals,
The description is omitted.

As shown in FIGS. 16 and 17, in the present embodiment, unlike the fifth embodiment, as the facing portion F of the back core 9, a facing core continuous in the rotation axis direction of the heat generating roller 1 is provided. 38 are provided. A4 size (width 210 mm) recording paper is used as the maximum width recording paper, and the length of the heat roller 1 in the rotation axis direction is 240.
mm, the length between the outermost ends of the C-shaped core 32 excluding the facing core 38 in the rotation axis direction of the heat generating roller 1 is 200 mm,
The length of the inner circumference of the exciting coil 5 along the rotation axis direction of the heat generating roller 1 is set to 210 mm, and the length of the opposing core 38 along the rotation axis direction of the heat generating roller 1 is set to 220 mm.

The other structure is similar to that of the fifth embodiment.

In the present embodiment, the length of the magnetic permeability portion T of the exciting coil 5 along the rotation axis direction of the heat generating roller 1 (along the rotation axis direction of the heat generating roller 1 at the inner peripheral portion of the exciting coil 5). While the length is made smaller than the width of the recording paper having the maximum width, the length of the facing portion F of the back core 9 along the rotation axis direction of the heat generation roller 1 (the rotation axis direction of the heat generation roller 1 of the opposite core 38). Since the length (along the length) is made larger than the width of the recording paper having the maximum width, even if the back core 9 in the magnetic permeability portion T is provided with a gap and is unevenly distributed, the magnetic field reaching the heat generating roller 1 from the facing portion F is reduced. It can be made uniform in the rotation axis direction. As a result, the heat distribution of the heat roller 1 can be made uniform in the portion through which the recording paper passes while reducing the number of rear cores 9 in the magnetically permeable portion T, so that the temperature distribution in the fixing portion becomes uniform. Therefore, a stable fixing action can be obtained.
Further, since the back core 9 in the magnetically permeable portion T can be reduced while making the heat generation distribution of the heat generating roller 1 uniform, it is possible to reduce the size of the apparatus and reduce the cost.

In the present embodiment, the back core 9 is
The facing core 38 as the facing portion F is continuously provided in the rotation axis direction of the heat generating roller 1, but is not necessarily limited to this configuration. For example, as shown in FIG. 18, the opposing core 38 is divided, and the back core 9 is configured such that the opposing portion F is wider than the magnetically permeable portion T in the rotation axis direction of the heat roller 1. You may. According to this configuration, the back core 9 in the facing portion F is reduced, so that the weight of the back core 9 can be reduced. Further, since the surface area of the facing portion F where the temperature tends to rise can be increased, cooling by heat radiation can be promoted.

(Seventh Embodiment) FIG. 19 is a sectional view showing a heat generating portion of a fixing device as an image heating device according to a seventh embodiment of the present invention. FIG. 20 shows the heat generating portion in the direction of arrow A in FIG.
It is a projection view seen from the direction. The members having the same functions as those in the fifth embodiment are designated by the same reference numerals,
The description is omitted.

As shown in FIGS. 19 and 20, in the present embodiment, unlike the fifth embodiment, the C-shaped core 38 covers a range of approximately 90 degrees with respect to the rotation axis of the heat roller 1. It is shaped like a cover, and has a different installation orientation.
The shaped cores 38a and 38b are arranged in a zigzag pattern in the rotation axis direction of the heat generating roller 1. That is, the facing portion F of the back core 9 is arranged at an asymmetric position with respect to the center line of the exciting coil 5 in the rotation axis direction of the heat roller 1.

In the fifth embodiment described above, since the same circumferential portion of the heat generating roller 1 rotates facing the two facing portions F of the C shaped core 32, the C shaped core 32 of the heat generating roller 1 is rotated. There is a large difference in the amount of heat generated between the portion opposite to and the other portion, and large unevenness in the temperature distribution is likely to occur. On the other hand, in the present embodiment, the same circumferential portion of the heat generating roller 1 is C
Since it rotates in opposition to one facing portion F of the shaped core 38, there is no great difference in the amount of heat generated between the portion of the heat generating roller 1 facing the C shaped core 38 and the other portion. Further, when the heating roller 1 rotates while reducing the volume of the back core 9 to be used, the interval of the loci of the portion of the surface of the heating roller 1 facing the facing portion F of the back core 9 becomes shorter. That is, the length of the facing portion F along the rotation axis direction of the heat generating roller 1 is 220 m as in the sixth embodiment.
When set to m, the pitch is 44 mm because five C-shaped cores 38 are arranged in one row, but since the two rows of C-shaped cores 38a and 38b are arranged in a staggered pattern, the heat-generating roller is arranged. When 1 rotates, the pitch of the portion facing the staggered facing portion F becomes apparently half, that is, 22 mm, on the surface of the heat generating roller 1. As described above, in the present embodiment, there is no large difference in the amount of heat generated between the portion of the heat generating roller 1 facing the C-shaped core 38 and the portion other than that, and the heat generated by the facing portion F is concentrated. Since the interval becomes smaller,
The heat generation distribution can be made uniform. As a result, it is possible to suppress temperature unevenness of the heat generating roller 1 and the fixing belt.

Further, since the back core 9 in the facing portion F is reduced, the weight of the back core 9 can be reduced. Furthermore, since the surface area of the back core 9 can be increased, cooling by heat dissipation can be promoted.
Therefore, heat is not locally accumulated inside the back core 9. As a result, it is possible to prevent the saturation magnetic flux density of the back core 9 from decreasing due to the temperature rise due to heat storage, and the magnetic permeability as a whole to suddenly decrease. As a result, the heat generating roller 1 can be stably maintained at a predetermined temperature for a long time.

(Eighth Embodiment) FIG. 21 is a sectional view showing a heat generating portion of a fixing device as an image heating device according to an eighth embodiment of the present invention. FIG. 22 shows the heat generating portion in the direction of arrow A in FIG.
It is a projection view seen from the direction. The members having the same functions as those in the fourth embodiment are designated by the same reference numerals,
The description is omitted.

As shown in FIGS. 21 and 22, the fourth embodiment is different from the fourth embodiment in that the interval between the adjacent C-shaped cores 32 is changed along the rotation axis direction of the heat generating roller 1. This is different from the embodiment. In FIG. 22, d1 = 21 m
m, d2 = 21 mm and d3 = 18 mm. Therefore,
The relationship is d1 = d2> d3. That is, the heat roller 1
The interval between the back cores 9 adjacent to each other at the end of the is narrow.
In addition, 5 mm at the same position in the axial direction as the position where the temperature sensor 7 for contacting the surface of the fixing belt and measuring the temperature is installed.
A block 40 made of square ferrite is installed.

By the way, if the intervals between the adjacent back cores 9 are made uniform, the temperatures of the end portions of the heat generating roller 1 and the fixing belt may become low. The temperature unevenness in the rotation axis direction of the heat generating roller 1 causes defective fixing.

In the present embodiment, as described above, the distance between the back cores 9 adjacent to each other at the end portion is narrower than at the center portion of the heat roller 1, so that the magnetic flux generated by the coil current generates heat. The end portion of the roller 1 is slightly larger than the central portion. Therefore, the amount of heat generation increases at the end of the heat generation roller 1. On the other hand, in the end portion of the heat generating roller 1, more heat is more easily removed than in the central portion due to heat conduction to the bearing and the like. Therefore, both effects are canceled out, and the temperature distributions of the heat generating roller 1 and the fixing belt are made uniform, so that defective fixing can be prevented.

Further, since the temperature sensor 7 is in contact with the surface of the fixing belt, the temperature sensor 7 may remove heat from the fixing belt. For this reason, the temperature tends to be low in the circumferential direction of the fixing belt only in the portion in contact with the temperature sensor 7.

In the present embodiment, as described above, since the block 40 made of ferrite is installed in this portion, the magnetic flux is more likely to be concentrated in this portion than in other portions. Therefore, the amount of heat generated in this portion is larger than that in other portions. As a result, the heat taken by the temperature sensor 7 can be complemented and the temperature distribution on the surface of the fixing belt can be made uniform, so that defective fixing can be prevented.

In the present embodiment, a uniform temperature distribution is obtained by narrowing the interval between the back cores 9 adjacent to each other at the end of the heat roller 1, but the structure is not limited to this. It is not something that will be done. For example, the intervals between the adjacent back cores 9 may be made uniform, and the width of the back core 9 located at the end of the heat roller 1 may be made wider than the width of the back core 9 located at the center of the heat roller 1. Similarly, a uniform temperature distribution can be obtained. Also,
For example, a uniform temperature distribution can be obtained also by making the intervals between the adjacent back cores 9 uniform and disposing the blocks made of ferrite in an isolated manner in a range near the end of the heat generating roller 1.

(Ninth Embodiment) FIG. 23 is a projection view showing a heat generating portion of a fixing device as an image heating device in a ninth embodiment of the present invention, and FIG. 24 is a ninth embodiment of the present invention. FIG. 3 is a cross-sectional view showing a heat generating portion of a fixing device as an image heating device in the embodiment. The members having the same functions as those in the fourth embodiment are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIGS. 23 and 24, in the present embodiment, unlike the fourth embodiment, the C-shaped core 32a of the back core 9 located near the end of the heat roller 1 is located. , 32b are movably held. Furthermore, in this embodiment, A3 size (width 297 m
The recording paper of m) is used as the recording paper with the maximum width.
The C-shaped core 32a is located outside the area through which A4 size (width 210 mm) recording paper passes.
As indicated by a ′, the C-shaped core 32 a moves in the radial direction of the heat generating roller 1 and away from the heat generating roller 1. When a recording paper of a smaller size is used, the C-shaped core 32 located inside the C-shaped core 32a
Similarly, b is moved.

The other structure is the same as that of the fourth embodiment.

In the present embodiment, the C-shaped core 32 outside the region through which the recording paper passes moves, and only this portion increases the air portion with low magnetic permeability through which the magnetic flux generated by the coil current passes. . Therefore, the magnetic flux in this portion is reduced, and the heat generation amount of the heat generating roller 1 in the opposing portion is reduced. As a result, it is possible to prevent the temperature in the range where the recording paper does not pass from rise excessively and prevent the temperature of members such as the fixing belt and the bearing at the end from exceeding the heat resistant temperature. Furthermore, even if a recording paper of a large size is used after continuously using a recording paper of a small size, it is possible to prevent hot offset from occurring because the temperature of the fixing unit is appropriate. Therefore, a large size recording paper can be used immediately after using a small size recording paper.

In the present embodiment, the C-shaped core 3
The case where only 2 is movable has been described as an example, but the configuration is not necessarily limited to this. For example, in FIG.
As shown in FIG. 5, even if the C-shaped core 32a and the central core 33 are integrated and moved as indicated by a broken line 9 ′, the same effect can be obtained.

Further, in each of the above-mentioned embodiments, the exciting coil 5 and the back core 9 are brought into contact with each other, but the same effect can be obtained even when a gap of about 1 mm is provided between them. be able to. By thus providing the gap between the exciting coil 5 and the back core 9, the exciting coil 5
It is possible to prevent the temperature from rising at the contact portion between the back core 9 and the back core 9.

Further, in each of the above embodiments, the heat insulating member 34 and the exciting coil 5 are brought into contact with each other, but the present invention is not necessarily limited to this configuration. For example, when the heat insulating member 34 and the exciting coil 5 are separated from each other and the airflow passes between them, the heat dissipation of the exciting coil 5 can be further promoted.

The structures of the exciting coil 5, the back core 9 and the heat generating roller 1 are not limited to those of the above-mentioned respective embodiments. In the equivalent circuit of FIG. 4, the inductance L is 10 μH or more and 50 μH or less, and the resistance component R is 0.5 Ω.
If it is 5Ω or less, there is no practical problem.

In each of the above embodiments, the case where the exciting coil 5 excites the heat generating roller 1 (heat generating member) from the outside has been described as an example. However, the heat generating roller 1
The configuration may be such that the inside of the (heating member) is excited.

[0139]

As described above, according to the present invention,
It is possible to realize an image heating apparatus that can obtain a predetermined amount of heat generation with a small current and an image forming apparatus using the image heating apparatus.

[Brief description of drawings]

FIG. 1 is a sectional view showing a fixing device as an image heating device according to a first embodiment of the present invention.

FIG. 2 is a partially cutaway plan view showing a heat generating portion of a fixing device as an image heating device according to the first embodiment of the invention.

FIG. 3 is a sectional view showing a heat generating portion of a fixing device as an image heating device according to the first embodiment of the invention.

FIG. 4 is an equivalent circuit diagram of a heat generating portion of a fixing device as an image heating device according to the first embodiment of the invention.

FIG. 5 is a sectional view showing a heat generating portion of a fixing device as an image heating device according to a second embodiment of the invention.

FIG. 6 is a bottom view showing a heat generating portion of the fixing device as the image heating device according to the second embodiment of the present invention, excluding a heat generating roller.

FIG. 7 is a sectional view showing a heat generating portion of a fixing device as an image heating device according to a third embodiment of the invention.

FIG. 8 is a sectional view showing a heat generating portion of another example of a fixing device as an image heating device according to the third embodiment of the invention.

FIG. 9 is a sectional view showing an image forming apparatus using an image heating device as a fixing device according to a fourth embodiment of the present invention.

FIG. 10A is a sectional view showing a fixing device as an image heating device according to a fourth embodiment of the present invention, and B is another fixing device as an image heating device according to the fourth embodiment of the present invention. Sectional view showing an example

FIG. 11 is a projection view of the heat generating portion viewed from the direction of arrow G in FIG. 10A.

FIG. 12 is a cross-sectional view of a heat generating portion on a surface including a rotation shaft of a heat generating roller and a center of an exciting coil of a fixing device as an image heating device according to a fourth embodiment of the present invention.

FIG. 13 is a sectional view showing a heat generating portion of a fixing device as an image heating device according to a fourth embodiment of the invention.

FIG. 14 is a cross-sectional view showing a heat generating roller of a fixing device as an image heating device according to a fourth embodiment of the present invention.

FIG. 15 is a sectional view showing a heat generating portion of a fixing device as an image heating device according to a fifth embodiment of the present invention.

FIG. 16 is a sectional view showing a heat generating portion of a fixing device as an image heating device according to a sixth embodiment of the invention.

FIG. 17 is a projection view of a heat generating portion of a fixing device as an image heating device according to a sixth embodiment of the present invention, as viewed in the direction of arrow A in FIG.

FIG. 18 is a projection view showing another example of the heat generating portion of the fixing device as the image heating device in the sixth embodiment of the invention.

FIG. 19 is a sectional view showing a heat generating portion of a fixing device as an image heating device according to a seventh embodiment of the invention.

FIG. 20 is a projection view of a heat generating portion of a fixing device as an image heating device according to a seventh embodiment of the present invention, as viewed in the direction of arrow A in FIG.

FIG. 21 is a sectional view showing a heat generating portion of a fixing device as an image heating device according to an eighth embodiment of the invention.

FIG. 22 is a projection view of a heat generating portion of a fixing device as an image heating device according to an eighth embodiment of the present invention, as viewed in the direction of arrow A in FIG.

FIG. 23 is a projection view showing a heat generating portion of a fixing device as an image heating device according to a ninth embodiment of the invention.

FIG. 24 is a sectional view showing a heat generating portion of a fixing device as an image heating device according to a ninth embodiment of the invention.

FIG. 25 is a sectional view showing another example of the heat generating portion of the fixing device as the image heating device in the ninth embodiment of the invention.

FIG. 26 is a cross-sectional view showing an image heating device in the related art.

FIG. 27 is a cross-sectional view showing another example of the image heating apparatus in the prior art.

FIG. 28 is a perspective view showing a heating coil used in another example of the image heating apparatus in the related art.

[Explanation of symbols]

1 Heat roller 2 Support side plate 3 bearings 4 pressure roller 5 Excitation coil 6 Excitation circuit 7 Temperature sensor 8 recording paper 9 Back core 10 toner 11 Photosensitive drum 12 Charger 13 Laser beam scanner 14 laser beam 15 Developer 16 developing roller 17 Paper feeder 18 Registration roller pair 19 Transfer roller 20 Cleaning device 21 Fixing paper guide 22 Fixing device 23 Paper ejection guide 24 Output tray 28 Cooling fan 29 coil cover 31 fixing belt 32 C type core 33 core 34 Thermal insulation member 35 fixing roller 36 flange 37 central axis 38 Opposing core

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masaru Imai             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Hideki Tatematsu             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 2H033 AA32 BA11 BA25 BA26 BA27                       BB23 BE06                 3K059 AA08 AD05 AD07 CD52

Claims (9)

[Claims] 1. A heat-generating member made of a conductive rotating body, an exciting coil formed by winding a wire along a peripheral surface of the heat-generating member, and causing the heat-generating member to generate heat, and via the exciting coil. A plurality of cores made of a magnetic material having a magnetically permeable portion facing the peripheral surface of the heat generating member and a facing portion facing the peripheral surface of the heat generating member without the excitation coil interposed therebetween; The image heating device is characterized in that the cores are arranged at intervals, and the width of the heat generating member in the rotation axis direction is different between the magnetically permeable portion and the facing portion. 2. The image heating apparatus according to claim 1, wherein the exciting coil is arranged to face an outer peripheral surface of the heat generating member. 3. The image heating apparatus according to claim 1, wherein the plurality of cores are arranged at non-uniform intervals. 4. The plurality of cores are arranged at an end portion and a central portion in the rotation axis direction of the heat generating member with a space therebetween, and a gap at the end portion is narrower than a gap at the central portion. The image heating device according to claim 1. 5. The image according to claim 1, wherein the plurality of cores have a shape in which the magnetic permeability portion is asymmetric with respect to a center line of the exciting coil parallel to the rotation axis of the heat generating member. Heating device. 6. The image heating apparatus according to claim 1, wherein in the plurality of cores, an interval between the magnetically permeable parts is wider than an interval between the facing parts. 7. The image heating apparatus according to claim 1, wherein at least some of the plurality of cores are connected to each other. 8. The image heating apparatus according to claim 7, wherein a part of the plurality of cores connected to each other is located at an inner peripheral portion of a wire forming the exciting coil. 9. The image heating apparatus according to claim 7, wherein a part of the plurality of cores connected to each other is located on an outer peripheral portion of a wire forming the exciting coil.