JP2000056603A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To concentrate magnetic flux on the comparatively narrow area of a fixing roller by making a magnetic substance core have nearly E-shaped cross section, oppositely arranging the top sides of the projection parts of the magnetic substance core along the axial direction of the fixing roller and winding an exciting coil round the center projection part of the magnetic substance core. SOLUTION: A temperature sensor 3 is arranged to abut on the surface of the fixing roller 1 and power supply to the exciting coil 8 is increased/ decreased by a control means and a high-frequency converter based on a detection signal from a temperature sensor 3. The winding of the coil 8 has such structure that a conductor is wound round the center projection part of the long-length magnetic substance core 9 whose cross section is nearly E-shaped. Therefore, the coil 8 is constituted of the projection parts 9a and 9b on both sides, the center projection part 9c and a base part 9d where the projection parts 9a to 9c project. The tops of the projection parts 9a to 9c are separated from the inside wall surface of the roller 1 through a specified space and has shape (round shape) to follow the inner peripheral wall surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fixing device for fusing and fixing a toner image on a transfer material in an image forming apparatus.

[0002]

2. Description of the Related Art An image forming apparatus using an electrophotographic method is:
Normally, a transfer material and a toner made of a resin, a magnetic material, a colorant, and the like, which are electrostatically carried on the transfer material, are pressed and rotated at a pressure contact portion (nip portion) of a fixing roller and a pressure roller which are pressed and rotated with each other. It has a fixing device that fuses and fixes by applying heat and pressure while nipping and conveying.

In such a fixing device, as a means for heating, an electromagnetic induction heating system is used in which an eddy current is generated in a conductive layer (heat generating source) provided on the inner surface of the fixing roller by magnetic flux from an exciting coil and heat is generated by Joule heat. Things have been suggested.

In this method, since the heat generating source can be arranged very close to the toner carried on the transfer material, the surface of the fixing roller is activated when the fixing device is started, as compared with the conventional heat roller method using a halogen lamp. This is characterized in that the time required for the temperature to reach an appropriate temperature for fixing can be shortened.

Another feature is that the heat transfer path from the heat source to the toner is short and simple, so that the heat efficiency is high.

[0006]

However, in the fixing device of the electromagnetic induction heating type in which an eddy current is generated in the conductive layer provided on the inner surface of the fixing roller by the magnetic flux generated by the exciting coil and heat is generated by Joule heat as in the above-described conventional example. In order to efficiently generate heat with limited electric power, it is better to concentrate the magnetic flux in a narrow area and flow a high density induced current.

For this reason, for example, in a configuration in which an exciting coil is wound around an I-shaped magnetic core, there is a disadvantage that the magnetic flux generated by the exciting coil is diffused in a relatively wide area and the heat generation efficiency is deteriorated. Was.

[0008] Further, when the configuration in which the magnetic core and the exciting coil are disposed outside the fixing roller is selected, there is a disadvantage that the magnetic field generated by the exciting coil leaks from the fixing device and adversely affects the image forming apparatus main body.

Further, when a large amount of small-sized transfer material is continuously fixed, the temperature of the non-sheet passing portion of the fixing roller may become a problem, or the fixing may be performed due to heat radiation from both ends of the fixing roller. In order to solve the problem such as the temperature drop at both ends of the roller, a method has been proposed in which the magnetic core and the excitation coil are divided in the longitudinal direction of the fixing roller and the power supplied to the excitation coil is independently controlled. However, each magnetic core
There is also a problem that the magnetic flux density penetrating the conductive layer of the fixing roller is lowered in a gap formed between the exciting coils, and the temperature of the fixing roller is lowered in that portion.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art. It is an object of the present invention to concentrate magnetic flux in a relatively narrow area of a fixing roller and to generate magnetic flux by an exciting coil. The purpose is to make the magnetic field contribute to the heat generation of the conductive layer of the fixing roller without leakage.

Another object of the present invention is to improve the degree of freedom in temperature control in the axial direction of the fixing roller and to make the temperature distribution uniform.

Another object of the present invention is to reduce the power loss by reducing the size of the fixing device or preventing the temperature from rising.

[0013]

According to the present invention, an eddy current is generated in a conductive layer provided on a fixing roller by an induction heating means having a magnetic core and an exciting coil. In a fixing device of an electromagnetic induction heating type for generating heat, the magnetic core has a substantially E-shaped cross section, and a tip end side of a protrusion of the magnetic core is opposed to the fixing roller along an axial direction of the fixing roller. Is characterized in that it is wound around a central projection of the magnetic core.

Thus, the magnetic flux generated by the exciting coil is concentrated in the space between the tips of the protrusions of the magnetic core having a substantially E-shaped cross section, and the magnetic circuit is composed of the magnetic core and the conductive layer of the fixing roller. Of the magnetic field from the outside to the outside.

It is also preferable that the induction heating means includes a plurality of magnetic cores divided in the axial direction, and a magnetic member extended in the axial direction to the projections of the divided magnetic cores.

Thus, the magnetic field acting on the conductive layer of the fixing roller can be changed in the axial direction.

The induction heating means includes an excitation coil in each of the plurality of magnetic path forming portions divided in the axial direction,
It is also preferable to provide control means for individually controlling the amount of power supply to the excitation coil according to the heat generation distribution in the axial direction.

This makes it possible to change the heat generation distribution of the fixing roller in the axial direction or to make it constant.

It is also preferable that the magnetic member is magnetically coupled to the protrusion of the magnetic core.

It is also preferable that the distance between the projections of the magnetic core in the width direction perpendicular to the axial direction is different in the axial direction.

As a result, the magnetic flux density in the axial direction of the magnetic core changes, and acts to change the amount of heat generated in the axial direction of the fixing roller.

It is also preferable that the distance between the protrusions of the magnetic core in the width direction perpendicular to the axial direction is smaller at both ends in the axial direction than at the center.

The magnetic flux density at both ends in the axial direction of the fixing roller increases, and the eddy current density in that portion also increases, so that the amount of heat generated at both ends in the axial direction of the fixing roller increases.

It is also preferable that the induction heating means is provided inside a fixing roller. Thereby, the volume of the fixing device can be reduced and the space can be saved.

Preferably, the induction heating means is provided outside the fixing roller.

Thus, the heat generated by the magnetic core and the exciting coil can be quickly radiated, and the power loss due to the temperature rise can be reduced.

It is also preferable that the protrusion of the magnetic core or the tip of the magnetic member opposed to the fixing roller has a shape following the peripheral wall surface of the opposed fixing roller.

As a result, the distance between the tip of the magnetic core and the conductive layer of the fixing roller can be reduced, and the magnetic flux density can be increased.

The image forming apparatus is provided with the above-described fixing device through which the transfer material on which the toner image is formed by the image forming means is passed.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIG. 1 is a drawing that best illustrates the features of the present invention, and is a schematic diagram of a cross-sectional configuration of a fixing device TS1 according to a first embodiment of the present invention.

The fixing roller 1 is provided with an iron core cylinder having an outer diameter of 40 (mm) and a thickness of 0.7 (mm), for example, PTFE of 10 to 50 (μm) in order to enhance the surface releasability.
Alternatively, a layer of PFA 10 to 50 (μm) may be provided.

As another material of the fixing roller 1, for example, a magnetic material (magnetic metal) such as magnetic stainless steel having a relatively high magnetic permeability μ and an appropriate resistivity ρ may be used.

Further, among the non-magnetic materials, a conductive material such as a metal can be used by thinning the material.

The pressure roller 2 is formed on the outer periphery of an iron core having an outer diameter of 20 (mm) by a layer of Si rubber having a thickness of 5 (mm) and, similarly to the fixing roller 1, in order to enhance the releasability of the surface. PTF
E10 to 50 (μm) and PFA10 to 50 (μm) layers are provided, and the outer diameter is 30 (mm).

The fixing roller 1 and the pressure roller 2 are rotatably supported, so that only the fixing roller 1 is driven. The pressure roller 2 is in pressure contact with the surface of the fixing roller 1 and is arranged so as to be driven to rotate by a frictional force at a pressure contact portion (nip portion).

The pressure roller 2 is pressed by a mechanism (not shown) using a spring or the like in the rotation axis direction of the fixing unit 1.

In this embodiment, the pressure roller 2 is about 3
The load is 0 (kg weight), and in this case, the width (nip width) of the press contact portion is about 6 (mm). However, depending on circumstances, the nip width may be changed by changing the load.

The temperature sensor 3 is disposed so as to be in contact with the surface of the fixing roller 1, and the power supply to the exciting coil 8 is increased or decreased by control means (not shown) and a high-frequency converter based on the detection signal of the temperature sensor 3. Is automatically controlled so that the surface temperature of the fixing roller 1 becomes a predetermined constant temperature.

The transport guide 4 is arranged at a position for guiding the transfer material 6 transported while carrying the unfixed toner image 5 formed by the image forming means to the nip portion between the fixing roller 1 and the pressure roller 2. Is done.

The separation claw 7 is disposed in contact with the surface of the fixing roller 1, and is provided after the transfer material 6 has passed through the nip portion.
If it sticks to the, it is forcibly separated to prevent jam.

As shown in FIG. 2, the winding of the exciting coil 8 has a structure in which a conductive wire is wound around a central projection of a long magnetic core 9 having a substantially E-shaped cross section.

The exciting coil 8 is therefore provided with the projections 9 on both sides.
a, 9b, a central projection 9c, and projections 9a, 9b, 9
c is composed of a protruding base 9d. And
The tips of the protrusions 9a, 9b, 9c are separated from the inner peripheral wall surface of the fixing roller 1 by a predetermined gap, and have a shape (R shape) following the inner peripheral wall surface.

The exciting coil 8 is a high-frequency converter 1
0, and 100-2000 (W) high-frequency power is supplied. Therefore, a thin wire made of several litz is used. It was used.

The magnetic core 9 has a high magnetic permeability and a low loss. In the case of an alloy such as permalloy, the eddy current loss in the magnetic core 9 increases at high frequencies, so that a laminated structure may be used. The magnetic core 9 is used for increasing the efficiency of the magnetic circuit and for shielding the magnetic field. The magnetic circuit portion of the exciting coil 8 and the magnetic core 9 may be air-core if there is a means capable of sufficiently shielding the magnetic field.

The exciting coil 8 includes a high-frequency converter 1
By 0, an alternating current of 10 to 100 (kHz) is applied. The magnetic flux induced by the alternating current passes through the inside of the E-shaped magnetic core 9 without leaking to the outside, and leaks to the outside of the magnetic body for the first time between the projections, penetrates the conductive layer of the fixing roller 1, and the eddy current flows to conduct. The layer itself generates Joule heat.

In order to increase the amount of heat generated, it is sufficient to concentrate the magnetic flux and flow an eddy current at a high density. In the case of the present embodiment, the protrusions 9a, 9b, 9c of the E-shaped magnetic core 9 are formed. It is effective to shorten the distance.

However, it is not necessary to simply shorten the widthwise distance between the projections 9a, 9b, and 9c (the distance in the widthwise direction perpendicular to the axial direction). It is preferable to set the distance between the tip of the protrusion and the conductive layer of the fixing roller 1 to be at least twice, for example, at least about three times.

As shown in FIG. 3, the distance between the projections 9a, 9b and 9c of the magnetic core 9 having the E-shaped cross section is shorter at both ends than at the center in the axial direction (the longitudinal direction in the figure). As a result, the magnetic flux density at both ends is increased, the eddy current density is increased, and the amount of heat generated is also increased. Therefore, heat escaping from both ends of the fixing roller 1 can be compensated, and the axial temperature distribution of the fixing roller 1 can be compensated. Can be made uniform.

As described above, in the present embodiment, the magnetic flux generated by winding the exciting coil 8 around the central projection 9 c of the magnetic core 9 having the E-shaped cross section allows the magnetic flux to be generated between the magnetic core 9 and the fixing roller 1. The magnetic flux is hardly leaked to a portion other than the conductive layer, and the magnetic flux is concentrated in a relatively narrow region of the conductive layer of the fixing roller 1.
It can generate heat efficiently.

The protrusion 9 of the magnetic core 9 having an E-shaped cross section
By shortening the distance between a, 9b, and 9c at both ends as compared with the central portion in the axial direction, the axial temperature distribution of the fixing roller 1 can be made uniform without a complicated configuration.

(Embodiment 2) In the second embodiment,
As shown in FIG. 4, a magnetic core having an E-shaped cross section and an exciting coil are divided into three in the axial direction. Each of the magnetic cores 11, 12, and 13 has a rod-shaped magnetic core 14, 15, or 16 as a magnetic member at the tip of the projection so that the magnetic flux density does not decrease between the divided magnetic cores and the amount of heat generation does not decrease. It is passed over and magnetically coupled.

The temperature drop due to the escape of heat at both ends of the fixing roller 1 often causes a problem. In the present embodiment, the power supply to the divided excitation coils 17, 18, and 19 is controlled individually. Can be avoided.

More specifically, the ratio of the power supplied to the exciting coils 17, 18, and 19 is set to 5: 3: 5, and a total of 100 to 200
When it is set to 0 (W), the temperature distribution becomes uniform in the longitudinal direction of the fixing roller.

When a small-sized transfer material is continuously fixed, for example, when the temperature is controlled based on the temperature detected by the temperature sensor 3 at the central portion in the axial direction of the fixing roller 1 in contact with the transfer material, the fixing roller At both ends in the axial direction that do not contact the transfer material, the temperature becomes considerably higher than a predetermined temperature regulation temperature, and problems such as promotion of thermal deterioration of peripheral members and hot offset of toner to the fixing roller occur. I will.

Therefore, in such a case, the exciting coil 1
The ratio of the power supplied to 7, 18, and 19 is preferably 3: 5: 3. A temperature sensor is provided in an area corresponding to each of the exciting coils 17, 18, and 19, and each of the exciting coils 17, 1 and 19 is arranged in accordance with an axial heat generation distribution (temperature distribution) of the fixing roller 1.
The power supplied to 8, 19 may be controlled individually.

In the present embodiment, the magnetic core / excitation coil is divided in the axial direction of the fixing roller 1 and the power supplied to the divided excitation coil is controlled independently, so that the axial direction of the fixing roller 1 can be controlled. The degree of freedom in temperature control can be improved.

(Embodiment 3) In the third embodiment,
As shown in FIG. 5, the magnetic core 9 and the exciting coil 8 are provided outside the fixing roller 1.

The configuration of the magnetic core 9 and the exciting coil 8 is such that the shape of the projection is changed to a shape following the outer peripheral wall surface of the fixing roller 1, but other configurations are the same as those of the first and second embodiments. A configuration similar to the configuration of the embodiment is adopted.

In the present embodiment, the magnetic core 9 and the exciting coil 8 are disposed outside the fixing roller 1 to prevent the temperature of the magnetic core 9 and the exciting coil 8 from rising and depend on the temperature. Power loss can be reduced.

[0060]

According to the present invention described above, the magnetic flux generated by the exciting coil is concentrated in the space between the tips of the protrusions of the magnetic core having a substantially E-shaped cross section, It is possible to reduce the leakage of the magnetic field from the magnetic circuit composed of the conductive layer of the fixing roller to the outside,
The region where the magnetic flux penetrates the conductive layer of the fixing roller becomes relatively narrow, and it becomes possible to efficiently generate Joule heat in the conductive layer of the fixing roller.

Since the induction heating means is divided in the axial direction and magnetically coupled by a magnetic member, the heat generation distribution of the fixing roller can be changed in the axial direction to improve the fixing property.

By varying the axial distance between the projections of the magnetic core in the axial direction, the magnetic flux density in the axial direction of the magnetic core changes and the amount of heat generated in the axial direction of the fixing roller changes. be able to. By making the distance in the width direction between the protrusions narrower at both ends in the axial direction than at the center, it is possible to increase the amount of heat generated at both ends in the axial direction of the fixing roller. Heat dissipation can be compensated and the temperature distribution in the longitudinal direction of the fixing roller can be made uniform.

By disposing the induction heating means inside the fixing roller, the volume of the fixing device can be reduced and the space can be saved.

By disposing the induction heating means outside the fixing roller, the heat generated by the magnetic core and the exciting coil can be quickly radiated, and the power loss due to the temperature rise can be reduced. .

By forming the protrusion of the magnetic core or the front end of the magnetic member facing the fixing roller into a shape following the peripheral wall surface of the fixing roller, the front end of the magnetic core and the conductive layer of the fixing roller are formed. , And the magnetic flux density can be increased.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a cross-sectional configuration of a fixing device according to a first embodiment.

FIG. 2 is a diagram illustrating a magnetic core part.

FIG. 3 is a view showing a magnetic core part.

FIG. 4 is an explanatory diagram of a cross-sectional configuration of a fixing device according to a second embodiment.

FIG. 5 is an explanatory cross-sectional configuration diagram of a fixing device according to a third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing roller 2 Pressure roller 3 Temperature sensor 4 Transport guide 5 Toner image 6 Transfer material 7 Separation claw 8 Excitation coil 9 Magnetic core 9a, 9b, 9c Projection 10 High frequency converter 11,12,13,14,15,16 Magnetic core 17, 18, 19 Excitation coil

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomoichiro Ota 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Gaku Fujita 3-30-2 Shimomaruko, Ota-ku, Tokyo Kyano 2H033 AA21 BB18 BE06 3K059 AA08 AA14 AB00 AB04 AB27 AB28 AC09 AC33 AC73 AD03 AD05 AD07 AD25 AD27 AD28 AD32 BD02 CD02 CD52 CD64 CD66 CD72 CD75 CD77

Claims (10)

[Claims] 1. An electromagnetic induction heating type fixing device in which an induction heating means having a magnetic core and an exciting coil generates an eddy current in a conductive layer provided on a fixing roller to generate heat, wherein the magnetic core has a substantially cross-sectional shape. E-shaped, wherein a tip end side of the projection of the magnetic core is arranged to face along the axial direction of the fixing roller, and the exciting coil is wound around a central projection of the magnetic core. Fixing device. 2. The induction heating means includes: a plurality of magnetic cores divided in an axial direction; and a magnetic member extending in an axial direction over a projection of the divided magnetic core. The fixing device according to claim 1. 3. The induction heating means includes an excitation coil in each of the plurality of magnetic path forming portions divided in the axial direction, and individually supplies power to the excitation coil in accordance with an axial heat generation distribution. The fixing device according to claim 2, further comprising control means for controlling the fixing device. 4. The fixing device according to claim 2, wherein the magnetic member is magnetically coupled to a protrusion of the magnetic core. 5. The fixing device according to claim 1, wherein the distance between the protrusions of the magnetic core in the width direction orthogonal to the axial direction is different in the axial direction. . 6. The magnetic head according to claim 5, wherein the distance between the protrusions of the magnetic core in the width direction orthogonal to the axial direction is smaller at both ends in the axial direction than at the center. Fixing device. 7. The fixing device according to claim 1, wherein the induction heating unit is disposed inside a fixing roller. 8. The fixing device according to claim 1, wherein the induction heating unit is disposed outside a fixing roller. 9. The fixing device according to claim 1, wherein the protrusion of the magnetic core or the front end of the magnetic member facing the fixing roller has a shape following the peripheral wall surface of the fixing roller facing the fixing roller. The fixing device according to claim 1. 10. An image forming apparatus comprising the fixing device according to claim 1, wherein a transfer material on which a toner image is formed by the image forming means is passed.