JP2008282037A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably heat an electromagnetic induction heating type fixing device due to a problem of deterioration of a coil due to a rise in coil temperature and a Curie point of a core material. Furthermore, the generated magnetic field has influenced the outside.
SOLUTION: An air-core coil is used as a magnetic field generating means and is sandwiched between a heating roller and a magnetic material. The magnetic material provided at a position corresponding to the end of the heating roller in the rotation axis direction is moved to change the distance from the air core coil.
[Selection] Figure 17

Description

  The present invention relates to a fixing device using an induction heating method.

2. Description of the Related Art Conventionally, a heating roller type fixing device includes a heating roller that heats a sheet carrying a developer image made of a powder developer, and a pressure roller that conveys the sheet while applying pressure. When the sheet passes through a fixing point which is a pressure contact portion (nip portion), the developer on the sheet is fused and pressure-fixed.
In a conventional fixing device of an electrophotographic apparatus, a halogen lamp or the like is installed as a heating source inside a metal roller, the roller is heated by radiant heat, and the object to be fixed is brought into pressure contact with the roller. A method is generally used in which elastic rollers are pressed and these rollers are rotated to pass the material to be fixed as described above. In addition, various types such as a flash heating method, an oven heating method, and a hot plate heating method are put into practical use. Has been.

  In a fixing device using a halogen lamp, light from the halogen lamp is emitted in the entire circumferential direction of the heating roller to heat the whole. In this case, considering the loss when light is converted into heat and the efficiency when heating the air in the roller to transfer heat to the roller, the heat conversion efficiency is 60 to 70%, the heat efficiency is low, It was disadvantageous for energy saving. In addition, since the thermal efficiency is low, there is a problem that the warm-up time becomes long.

  For these reasons, in recent years, a heating type fixing device using a cylindrical heat-resistant film material has been put into practical use. It has a heat-resistant film that moves in close contact with the heating body and the heating body. The material to be heated is brought into close contact with the heating body through this film and moved together with the film, and the thermal energy of the heating body is transferred through the film. And a heating device applied to the object to be heated. In this case, it is necessary to uniformly manage the temperature in the longitudinal direction of the line-shaped heating element of the heating element, and in the case of actual production, such as uniformity during production and high-precision temperature control during operation are required. The obstacle is great. Further, a high-speed copying machine requires a heating element having a high calorific value, which causes a problem in reducing power consumption.

In order to solve the above problems and the like, there are JP-A-9-258586, JP-A-8-76620, and the like as fixing devices using an induction heating method. Japanese Patent Application Laid-Open No. 9-258586 is a system in which a coil is wound around a core provided along the rotation shaft of a fixing roller and an eddy current is passed through the roller to heat it. Japanese Patent Laid-Open No. 8-76620 is an apparatus for fixing a recording medium in which a conductive film is heated and adhered by a magnetic field generating means, and a heating belt is sandwiched between a member that assembles the magnetic field generating means and a heating roller. Not forming a nip.
JP-A-9-258586 JP-A-8-76620

  However, the electromagnetic induction heating apparatus as described above has the following problems. That is, although a heating coil is used as the magnetic field generating means, the induction heating coil uses a core material to concentrate the magnetic flux at the fixing nip portion and its periphery. As the core material, iron or ferrite material is used. Since the heating coil and the core are disposed inside the roller or the heat generating belt, the heat applied to the roller and the heat generating belt is trapped inside, causing the core and the coil to rise in temperature. If continuous operation for a long time exceeds the heat resistance temperature of the coil, and if the coil is damaged, or if a ferrite material is used as the core material, it will exceed the Curie temperature and the core characteristics will deteriorate rapidly, resulting in magnetic flux There was a problem that it was impossible to concentrate. In order to alleviate the above problem, there is a patent that maintains the core and coil temperatures by air-cooling the air inside the roller and the heat generating belt with a fan, but it is a well-known fact that the heat generation efficiency decreases by air cooling.

  In order to solve the above-mentioned problems, there is one in which a coil is arranged on the outer peripheral surface of a heating roller as disclosed in JP-A-7-295414. In this case, since the heat generated in the coil is radiated to the outer peripheral surface of the coil, the temperature rise of the coil can be suppressed. However, in the case of the fixing device having this configuration, the coil is disposed outside the heating roller and the magnetic flux is not concentrated in a certain direction by the core material or the like. Instead of acting only on the surface, a magnetic field is generated in the direction facing the roller. This becomes a noise that leaks out of the fixing device or heats other metal members. Further, since the magnetic flux is not concentrated, the efficiency is also lowered.

  Further, when it is desired to adjust the heat generation amount in the longitudinal direction of the roller, the shape of the coil and the core material around which the coil is wound has to be changed. When the core material is integrally formed, it cannot be adjusted, and the shape of the core material must be changed again to be rewound. In order to solve the above problems, it is necessary to increase the assembly accuracy and processing accuracy of the core material and the coil and to perform positioning with dimensional accuracy. Furthermore, since the temperature detecting means is installed on the roller, it is difficult to adjust the amount of heat generated locally, such as taking into account the temperature drop at that portion.

  There is a patent that divides the core material around which the coil is wound and adjusts the amount of heat generation so that it can move. In this case, in order to adjust the position of the core material, the coil must be removed and adjusted individually. Therefore, adjustment takes time. Moreover, in order to adjust the heat generation amount of the local portion, it is necessary to increase the number of divisions of the core material. However, in order to make the heat generation amount constant, the core material must be positioned one by one. In other words, uniform heating itself becomes difficult.

  The present invention has been made in view of solving the above-described problems, and provides a fixing device in which it is easy to make the temperature of the heating roller uniform due to a problem caused by a temperature rise of the fixing device.

The present invention has been made based on the above problems,
The fixing device according to claim 1 is formed in a coil shape with a heat generating member that rotates and heats and fixes an image formed on a sheet, and a conductive wire, and generates a generated magnetic field on the outer surface side of the heat generating member. A magnetic field generating member that generates heat by causing the heat generating member to generate eddy currents, a side opposite to the heat generating member via the magnetic field generating member, and a rotation axis direction of the heat generating member A first magnetic member fixedly arranged at a position corresponding to the central portion, and a position opposite to the heat generating member via the magnetic field generating member and at a position corresponding to an end portion in the rotation axis direction of the heat generating member. A second magnetic member; a second magnetic member; and a position adjusting member that moves the second magnetic member to change a distance from the magnetic field generating member. To do.

  According to the present invention, it has been possible to provide a fixing device in which the magnetic field generated from the coil does not affect the outside while preventing the coil from being deteriorated due to the temperature rise of the coil. Furthermore, the heat generation amount of the heating roller can be adjusted without changing the shape and position of the coil and the core material.

Hereinafter, a first embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a simplified diagram showing the overall configuration of the fixing device. The fixing device 1 includes a heating roller 2 (φ40 mm) and a pressure roller 3 (φ40). The pressure roller 3 is pressed against the heating roller 2 by a pressure mechanism (not shown) and is maintained to have a constant nip width. The heating roller 2 is a drive motor (not shown). The pressure roller 3 is driven to rotate in the direction of the arrow. The heating roller 2 is made of iron and has a thickness of 1 mm. The roller surface is coated with a release layer such as Teflon. In this embodiment, iron is used as the roller material. However, stainless steel, aluminum, a composite material of stainless steel and aluminum, or the like may be used.

  The pressure roller 3 is configured by covering the cored bar with silicon rubber, fluorine rubber or the like. When the paper P passes through a fixing point which is a pressure contact portion (nip portion) between the heating roller 2 and the pressure roller 3, the developer on the paper is fixed by fusing and pressing.

  On the circumference of the heating roller 2, on the peeling claw 5 for peeling the paper P from the heating roller 3 on the downstream side in the rotation direction from the contact position (nip portion) between the heating roller 2 and the pressure roller 3, There are provided a cleaning member 6 for removing dust such as toner and paper scraps offset from the toner, a release agent application device 8 for applying an offset prevention release agent, and a thermistor 9 for detecting the temperature of the heating roller 2.

  As the heating principle, an induction heating device (magnetic field generating means) 10 is used. The induction heating device 10 includes an exciting coil 11 and is disposed on the outer peripheral surface of the heating roller 2. The exciting coil 11 uses a linear 0.5 mm copper wire, and is configured as a litz wire in which a plurality of wires insulated from each other are bundled. By using a litz wire, the wire diameter can be made smaller than the penetration depth, and an alternating current can be effectively passed. In this embodiment, 16 pieces of φ0.5 mm are bundled. The coated wire of the coil uses heat-resistant polyamideimide. The magnetic field generating means does not use a core material (core member) used for concentrating the magnetic flux of the coil, but uses an air-core coil. Since an air core coil is used, a core material having a complicated shape is not used, so that the production is relatively easy. Also, a simple excitation circuit is sufficient.

Magnetic flux and eddy current are generated in the heating roller 2 so as to prevent the magnetic field from being changed by magnetic flux generated by a high frequency current applied to the exciting coil 11 from an excitation circuit (inverter circuit) (not shown). Joule heat is generated by the eddy current and the heating roller resistance, and the heating roller 2 is heated. In this embodiment, a high frequency current having a frequency of 20 kHz and an output of 900 W was passed through the exciting coil 11. The surface temperature of the heating roller 2 is set to 180 ° C. and controlled. The surface temperature is detected by the thermistor 9, and the heating roller 2 is heated by feedback control. At this time, the heating roller 2 and the pressure roller 3 are rotating in order to make the temperature distribution of the entire roller uniform.
A certain amount of heat is given to the entire roller surface by rotating the roller. When the surface temperature of the heating roller reaches 180 ° C., the copying operation starts, and the sheet P passes through a fixing point where the sheet P is a pressure contact portion (nip portion) between the heating roller 2 and the pressure roller 3. The above developer is fixed by fusion bonding. The current to the excitation circuit is supplied through a thermostat 13 which is a temperature fuse pressed against the surface of the heating roller. In this thermostat, the surface temperature of the heating roller 2 is preset, and when the temperature reaches an abnormal temperature, the current supplied to the circuit is cut off.

FIG. 2 is a perspective view schematically showing the heating roller 2 and magnetic field generating means of the present embodiment. As shown in FIG. 2, an air-core coil 11 (indicated by a dotted line) is disposed on the outer peripheral surface of the heating roller. The distance between the heating roller 2 and the air-core coil 11 is set to 1 mm.
A magnetic field shielding material 16 is disposed on the opposite side of the heating roller 2 via the air core coil 11. The magnetic shielding material 16 is preferably made of a magnetic material. In this embodiment, a ferrite material having a high magnetic permeability and hardly generating heat is used.

  The distance between the air core coil 11 and the magnetic shielding material 16 is set to 5 mm. By disposing the magnetic field shielding material 16, even if an air core coil is disposed on the outer periphery of the heating roller, the magnetic field leaking outside is shielded, so that problems such as noise can be solved. Further, since the magnetic field shielding material 16 is arranged so that the coil itself generates a magnetic field on the side other than the roller side, there is no problem, and an air core coil without a core material that can be easily formed can be used. When there is no shielding member and the magnetic field generating means is arranged outside the roller, a core material that does not have a magnetic field outside must be used, and the shape is limited or the core material is made complex. There must be. In the present embodiment, the magnetic field shielding material 16 may be arranged completely separately from the magnetic field generating means and does not depend on the magnetic field generating means. Moreover, since it is not necessary to use a complicated shape, there is no cost. In this embodiment, it has a circumferential surface, but a shielding effect can be obtained even with a flat plate.

  3 and 4 show the results of magnetic field analysis performed for examining the effect of the magnetic field shielding material. FIG. 3 shows how the magnetic flux is generated when the magnetic field shielding member is not used. In order to simplify the calculation, the flat plate is heated. From this result, it can be clearly seen that the magnetic flux 22 is generated on the opposite side of the flat plate 21 via the coil 20 in addition to the magnetic flux applied to the flat plate. That is, the magnetic flux 22 leaks to the outside, which may cause problems such as noise and circuit malfunction. On the other hand, in FIG. 4, it can be seen that the magnetic field shielding material 23 shields the magnetic field generated on the opposite side of the flat plate 21 via the coil 22. By arranging the magnetic field shielding material by this analysis, the magnetic field does not leak outside even if the air-core coil is arranged outside the roller. This eliminates the need to put the magnetic field generating means inside the heating roller, thereby solving the problem that the coil generates heat and deteriorates due to the radiant heat in the roller, or the core material generates heat and the characteristics are deteriorated to lower the thermal efficiency. I was able to. In this embodiment, the ferrite material is used as the magnetic field shielding member, but the same effect can be obtained even if other magnetic members are used. In the present embodiment, the distance between the magnetic shielding material and the air core coil is set to 5 mm, but it goes without saying that the effect can be obtained even when the magnetic shielding material is in contact with the air core coil.

  Next, a second embodiment according to the present invention will be described. Since the outline of the fixing device is the same as that of the first embodiment, description thereof is omitted. FIG. 5 is a perspective view schematically showing the heating roller and magnetic field generating means of this embodiment. As shown in FIG. 5, the air-core coil 11 is arranged on the outer peripheral surface of the heating roller. The distance between the heating roller 2 and the air-core coil 11 is set to 1 mm. A magnetic field shielding material 32 is disposed on the opposite side of the heating roller 2 via the air-core coil 11. As shown in FIG. 5, the magnetic shielding material 32 is divided perpendicularly to the longitudinal direction (roller longitudinal direction). In the present embodiment, the further divided magnetic field shielding materials 32 are arranged at a constant interval (Y).

  In the first embodiment, the magnetic field shielding member is integrally configured to cover the entire air-core coil, but in the present embodiment, a configuration in which a plurality of magnetic field shielding materials 32 are arranged at regular intervals is employed. The reason for this is that in an actual fixing device, a magnetic field is generated on the opposite side of the roller via the air-core coil. When shielding this magnetic field, the entire air-core coil is made to use a member having a high magnetic permeability. Even if it is not completely covered, the magnetic flux is controlled by the shielding materials by arranging them at a certain interval, and it is possible to prevent leakage through the shielding material to the outside. Although the interval varies depending on the characteristics of the shielding material, in this embodiment, the shielding material interval is set to 20 mm with respect to the shielding material width of 15 mm. Under these conditions, the magnetic field did not leak outside the fixing device, and noise and other problems could be solved. Thereby, since it is not necessary for a shielding material to cover the whole coil, since each shielding material can be made small, mold shaping became easy. Moreover, since the shielding material can be made smaller, it is easier to obtain dimensional accuracy than a large one. Since there is a certain interval, the material of the shielding material can be reduced.

  Next, a third embodiment according to the present invention will be described. Since the outline of the fixing device is the same as that of the first embodiment, description thereof is omitted. FIG. 6 is a diagram (top view) showing an arrangement configuration of the heating roller and the magnetic shielding material. As shown in FIG. 6, the air core coil 11 is disposed on the outer periphery of the heating roller, and a plurality of magnetic field shielding materials 32 are disposed on the opposite side of the heating roller 2 via the air core coil 11. In this embodiment, the arrangement conditions of the magnetic field shielding material pieces 42a and 42b arranged at the end of the air-core coil 11 (near the end in the roller longitudinal direction) are changed from those of other magnetic field shielding members. This is because the method of generating the magnetic flux at the end portion is different from other places, so that the magnetic field can be efficiently shielded by using the magnetic field shielding material pieces 42a and 42b according to the magnetic flux generation form at the end portion. it can. Further, the same effect can be obtained even if the split pieces 43 parallel to the longitudinal direction are performed as shown in FIG.

  Although the magnetic field shielding material of the third embodiment is composed of a single material, the same effect can be obtained by shielding the magnetic flux at the coil end using a plurality of materials. In the second embodiment, it goes without saying that the respective effects can be obtained even if a plurality of materials are used for the magnetic field shielding means.

  In the second embodiment, the magnetic field is divided perpendicularly to the longitudinal direction (roller longitudinal direction). However, since a plurality of magnetic field shielding materials are molded by molding, the draft is taken into consideration. Thus, they may be arranged in the roller longitudinal direction with a certain angle.

Next, a fourth embodiment according to the present invention will be described. Since the outline of the fixing device is the same as that of the first embodiment, description thereof is omitted. FIG. 8 is a perspective view schematically showing the heating roller and the magnetic field generating means. As shown in FIG. 8, an air core coil is disposed on the outer peripheral surface of the heating roller, and a magnetic field shielding material 51 is disposed on the opposite side of the heating roller 2 via the air core coil.
The magnetic field shielding member is formed by laminating and bonding a plurality of magnetic field shielding member elements 52a, 52b... In the longitudinal direction (roller rotation axis direction). In this embodiment, a ferrite material is used as the material of the magnetic field shielding material 51.

  In the fourth embodiment, ferrite is used as the material of the shielding member, but iron, silicon steel plate, permalloy, or the like may be used. In the case of iron, silicon steel plate, and permalloy, unlike the ferrite used in this embodiment, it is a conductive member. For this reason, when the material itself is manufactured by integral molding, an eddy current is generated in the shielding member and heat loss is likely to occur. However, when they are laminated and integrated as in the fourth embodiment, the eddy current is difficult to draw a closed loop, and the generation of eddy current can be prevented. Further, since the laminated members are bonded, the mechanical strength of the shielding member is equivalent to that of the integrally molded member, and it is not necessary to hold the shielding material in a special case or the like. Furthermore, if the ferrite material is formed by integral molding, it is difficult to obtain accurate dimensional accuracy. This causes warpage in the longitudinal direction. Even if dimensional accuracy is maintained, it causes a significant cost increase in manufacturing. However, if integrated by laminating adhesion as in this embodiment, the individual shielding material elements can be relatively easily dimensional accuracy. The cost can be suppressed by integrating the core elements. The above embodiment is effective when there is a large leakage of magnetic flux outside the roller of the magnetic field generating means and it is necessary to cover the entire coil.

  Next, a fifth embodiment according to the present invention will be described. FIG. 9 is a simplified cross-sectional view showing the overall configuration of the fixing device. Since the shape and basic configuration of the fixing device are the same as those in the first embodiment, a description thereof will be omitted. Only magnetic field generating means having different configurations will be described below. As the heating principle, an induction heating device (magnetic field generating means) 60 is used. The induction heating device 60 includes the exciting coil 11 and is disposed on the outer peripheral surface of the heating roller 2. The exciting coil 11 uses a linear 0.5 mm copper wire, and is configured as a litz wire in which a plurality of wires insulated from each other are bundled. By using a litz wire, the wire diameter can be made smaller than the penetration depth, and an alternating current can be effectively passed. In this embodiment, 16 pieces of φ0.5 mm are bundled. The coated wire of the coil uses heat-resistant polyamideimide. In this embodiment, the magnetic field generating means does not use the core material used to concentrate the magnetic flux of the coil, but uses an air-core coil. However, a type in which the magnetic flux is concentrated using the core material 63 as shown in FIG. 10 may be used.

  Magnetic flux and eddy current are generated in the heating roller so as to prevent the magnetic field from being changed by magnetic flux generated by a high frequency current applied to the exciting coil 11 from an excitation circuit (inverter circuit) (not shown). Joule heat is generated by the eddy current and the heating roller resistance, and the heating roller is heated. In this embodiment, a high frequency current having a frequency of 20 kHz and an output of 900 W was passed through the coil.

  The magnetic field generating means of the present embodiment will be described with reference to sectional views schematically showing the heating roller and the magnetic field generating means. As shown in FIG. 11, a plurality of magnetic materials 72 are arranged on the opposite side of the heating roller 2 via the exciting coil 11. This is used to adjust the heat generation amount with respect to the longitudinal direction of the heating roller 2. That is, in this embodiment, since the temperature detection means are attached to the a part and b part inside the overheating roller, heat is transmitted to the temperature detection means of parts a and b by heat conduction, and the surface temperature of the heating roller 2 is lowered. Resulting in. In order to adjust the local heat generation amount, a plurality of magnetic materials 72 are arranged. In the present embodiment, the magnetic field at the place where the magnetic material 72 is disposed becomes stronger, and the amount of heat generated at that portion can be increased. As a result, the amount of heat reduced by the temperature detecting means can be compensated. Thus, by arranging a plurality of magnetic materials in the longitudinal direction, temperature adjustment at a local location can be performed.

  A modification of the fifth embodiment will be described. When heating the heating roller, the temperature distribution at the end of the heating roller tends to be lower than that at the center of the roller. This is because the heat radiation to the outside of the roller end is greater than that in the central portion of the roller. That is, the heat escapes into the air and the heat is taken away from the support member that supports the end portion. For this reason, in the modification of the fifth embodiment, a magnetic material 80 is disposed as shown in FIG. The magnetic flux received by the end of the heating roller 2 is increased by making the distance between the magnetic material 81a, 81b at the end and the exciting coil 11 closer than the magnetic material 82 at the center, so that the amount of heat applied to the end can be increased. . As described above, since the heat generation amount in the longitudinal direction of the heating roller 2 can be easily changed without changing the shape of the coil itself, the adjustment can be made efficiently.

  As a method for supporting the magnetic material, as shown in FIG. 13, the magnetic material is supported by a case 86 for keeping the distance from the exciting coil 11 constant. Case 86 is formed of a heat-resistant resin material. Since the material of the case 86 is nonmagnetic, it does not affect the magnetic material 80 that controls the magnetic flux. A spacer 88 is used as a mechanism for adjusting the positions of the magnetic material 80 and the exciting coil 11. When the distance from the exciting coil 11 is increased, a spacer 88 is inserted under each magnetic material. The material of the spacer 88 is the same as that of the case. In order to reduce the distance between the coil and the magnetic material, a positioning mechanism for bringing the entire case 86 close to the exciting coil 11 is provided. When the magnetic material 72 is disposed only at a local portion as shown in FIG. 14, the magnetic material 72 may be adhered to the case 86, or a spacer may be inserted between the magnetic materials. In this embodiment, it is bonded to the case 86.

In the sixth embodiment of the present invention, the magnetic members 95 are arranged at regular intervals as shown in FIG. When the magnetic material is spaced at a certain interval, a difference occurs between the roller temperature at which the magnetic material 72 is present and the roller temperature at which the magnetic material 72 is not present. The number of bodies themselves is reduced to reduce costs and weight. Since it reduces the transmitted magnetic material each other by that heat to the heat conduction be spaced a predetermined distance, heating efficiency is obtained an effect of improving and good heat dissipation. Further, as shown in FIG. 16, a heat radiating member 97 can be attached on the upper side of the magnetic material 72 to further improve the heat radiating effect.

  Further, each of the above-described embodiments is arranged for the purpose of adjusting the heat generation amount in the longitudinal direction of the roller by controlling the magnetic flux, but with the effect as a shielding member for shielding the magnetic field by the magnetic material. It can also be used as a role.

  Next, a seventh embodiment according to the present invention will be described. Since the shape and basic configuration of the fixing device are the same as those of the fifth embodiment, the description thereof is omitted. Only the magnetic field generating means having a different structure will be described below. The magnetic field generating means is arranged on the outer periphery of the heating roller as in the embodiment. A plurality of magnetic materials for controlling the magnetic flux are disposed on the opposite side of the heating roller via the coil. The plurality of magnetic materials are housed in a heat-resistant resin case in order to maintain a certain distance from the coil. A cross-sectional view of the coil and magnetic material described above is shown in FIG. In the seventh embodiment, the distance between the magnetic material 100 and the exciting coil 11 can be varied according to the paper size sent to the fixing device. In this embodiment, as an example, the positions of the magnetic material 100 and the excitation coil 11 are varied when A4 vertical size paper and A4 horizontal size paper are inserted. As a configuration, the case supporting the magnetic material 100 is divided into three. The case 102a in the center portion substantially matches the size of the A4 vertical size. The magnetic material 100 accommodated in cases 102b and 102c corresponding to A4 horizontal size is arranged on both sides. The cases 102a and 102b on both sides are provided with a mechanism 103 (position adjustment member) for moving the case itself in the vertical direction. This is a mechanism in which the slide portion 105 moves up and down in accordance with the rotation of the shaft 104. The rotation of the shaft 104 is connected by cases on both sides and is driven by a drive source (not shown). For this reason, it moves up and down simultaneously, and the positional relationship between the coil 101 and the magnetic material 100 can be varied.

  When the A4 landscape size is passed, there is no difference in the amount of heat taken from the roller in the longitudinal direction of the roller, so that the temperature distribution in the longitudinal direction of the roller is unlikely to occur. In this case, the temperature distribution of the rollers can be maintained by keeping all three cases at the same position. On the other hand, when A4 vertical size paper is continuously passed, the heat consumption of the roller portion in the A4 vertical size area is larger than that at the end portion. The temperature will rise. As a result, the bush or the like that supports the roller end is damaged or deteriorated due to the temperature rise of the roller. In addition, temperature unevenness occurs on the roller, and fixing performance cannot be maintained.

  Therefore, by attaching a moving mechanism for changing the magnetic material position as in this embodiment, when the A4 vertical size is continuously passed and the temperature rise at the end of the roller begins to occur, the cases 102b and 102c are removed from the coil. Move away (moves upward, FIG. 18). When the magnetic material 100 of the cases 102b and 102c is separated from the coil 11, the magnetic flux reaching the roller in that portion is weakened, so that eddy currents generated at the roller ends are reduced, and the temperature rise at the ends can be suppressed. By making the positions of the magnetic material and the coil variable in this way, it is possible to prevent the occurrence of temperature unevenness in the longitudinal direction of the roller due to the difference in the sheet passing size, and to obtain good fixing performance. In the present embodiment, the A4 size is changed by the size of the side, but it goes without saying that it can be changed according to the postcard size and the like.

1 is a cross-sectional view of a fixing device according to the present invention. The perspective view which showed the positional relationship of a heating roller and a magnetic field generator. The figure which showed the magnetic field analysis result when not using a magnetic field shielding member. The figure which showed the magnetic field analysis result at the time of using a magnetic field shielding member. The perspective view which showed the positional relationship of the heating roller and magnetic field generator in 2nd Example of this invention. The figure which showed the positional relationship of the exciting coil and magnetic field shielding material in the 3rd Example of this invention. The figure which showed the division | segmentation method of a magnetic field shielding material. The figure which showed the positional relationship of the heating roller and magnetic field shielding material in the 4th Example of this invention. Sectional drawing of the fixing apparatus which concerns on the 5th Example of this invention. Sectional drawing of the fixing device which concerns on the 5th Example at the time of using a core material. The figure which showed the example of arrangement | positioning of the magnetic material which concerns on a 5th Example. The figure which showed the example of arrangement | positioning of the magnetic material which concerns on a 5th Example. The figure which showed the case instruction | indication method of the magnetic material. The figure which showed the case instruction | indication method of the magnetic material. The figure which showed the example of arrangement | positioning of the magnetic material of the fixing device which concerns on the 6th Example of this invention. The figure which showed the example which attached the heat sink. FIG. 10 is a cross-sectional view illustrating a moving mechanism of a fixing device according to a seventh embodiment of the present invention. The figure which showed the example of a movement of a magnetic material.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixing device 2 Heating roller 3 Pressure roller 5 Peeling claw 6 Cleaning member 8 Release agent application device 9 Thermistor 10 Induction heating device 11 Excitation coil 13 Thermostat 16 Magnetic shielding material 20 Coil 21 Flat plate 22 Magnetic flux 32 Magnetic shielding material 42 Magnetic shielding Material piece 43 Division piece 52 Magnetic shielding member element 60 Induction heating device 63 Core material 72 Magnetic material 80 Magnetic material 86 Case 88 Spacer 97 Heat dissipation member

Claims (4)

A heating member that rotates and heats and fixes the image formed on the paper;
A magnetic field generating member that is formed in a coil shape by a conductive wire and generates an eddy current by causing the generated magnetic field to act on the heat generating member from the outer surface side of the heat generating member,
A first magnetic member fixedly disposed at a position opposite to the heat generating member via the magnetic field generating member and at a position corresponding to the central portion in the rotation axis direction of the heat generating member;
A second magnetic member provided on the opposite side of the heat generating member via the magnetic field generating member and at a position corresponding to the rotation axis direction end of the heat generating member;
A second magnetic member, and a position adjusting member that moves the second magnetic member to change a distance from the magnetic field generating member;
A fixing device. A temperature detection member that detects the temperature of the end portion in the rotation axis direction of the heat generating member on which the second magnetic member is disposed;
A control unit for controlling the movement of the position adjustment member;
The control unit controls the position adjusting member to detect the second magnetic property when the temperature detecting member detects that the temperature of the end portion in the rotation axis direction of the heat generating member has increased as the sheet is continuously passed. The fixing device according to claim 1, wherein the member is moved away from the magnetic field generating member.   The fixing device according to claim 1, wherein the first and second magnetic members are a plurality of magnetic members arranged along the magnetic field generating member with a gap therebetween.   The first and second magnetic members are a plurality of magnetic members that are arranged with a gap between each other along the magnetic field generating member and shield the magnetic field from the magnetic field generating member. The fixing device according to claim 1.