JP4728855B2 - Electromagnetic induction heating fixing device and image forming apparatus provided with the same - Google Patents

Description

  The present invention relates to an electromagnetic induction heating and fixing device including an induction heating unit that generates heat by electromagnetic induction of a roller or a belt that is a heating body for thermally fixing toner on an image forming medium, and an image forming apparatus including the same. is there.

  In an image forming apparatus (such as a printer, a facsimile machine, a copying machine, and a multi-function machine) that forms an image on recording paper by an electrophotographic process, unfixed toner transferred from the photosensitive member onto the recording paper is recorded by heat and pressure. There is provided a fixing device for fixing the toner. In this fixing device, in recent years, an electromagnetic induction heating method in which a heating medium such as a heating roller is heated by Joule heat generated by an electromagnetic induction action has attracted attention from the viewpoint of energy saving.

  On the other hand, in the fixing device, it is desired to make the temperature distribution in the axial direction uniform so that the fixing is performed uniformly over the entire surface of the recording paper. Since the temperature at the end in the axial direction is lower than that at the center, it is necessary to make the heat generation at the end in the axial direction larger than that at the center in the axial direction to make the temperature distribution in the axial direction uniform. .

The request for uniform temperature distribution is the same in the above-mentioned electromagnetic induction heating type fixing device. In order to make the amount of heat generated at the end in the axial direction larger than the central portion in the axial direction, the peripheral wall of the roller and the magnetic body There is known a configuration in which a magnetic core is provided so that a gap (air gap) between the core and the core is narrower at the axial end than at the axial center (see Patent Document 1). Further, a configuration is known in which the arrangement density of the magnetic cores at the axial end is higher than that at the central portion of the axial direction (see Patent Document 2). The temperature distribution in the axial direction can be made uniform by making it larger than the central portion in the direction.
Japanese Patent Laid-Open No. 9-62132 (FIGS. 9, 10, and 11) Japanese Patent Laying-Open No. 2005-203272 (FIGS. 2 and 7)

  However, in the prior art, since the magnetic core for adjusting the amount of heat generation is accommodated in the roller, the structure and shape of the roller are restricted, and the design freedom regarding the form and arrangement position of the magnetic core is free. There is a disadvantage that the degree of adjustment becomes low and adjustment for obtaining an appropriate temperature distribution becomes difficult. In addition, since the amount of heat generation is greatly affected by the mounting position of the magnetic core, it is necessary to assemble the magnetic core with high accuracy. However, it is not easy to fix the magnetic core inside the roller with high accuracy, and manufacturing is difficult. There is a difficult point.

  The present invention has been devised to solve such problems of the prior art, and its main purpose is to provide a high degree of freedom in design related to the form and arrangement position of the magnetic core and to provide an appropriate temperature distribution. It is an object of the present invention to provide an electromagnetic induction heating and fixing device configured so as to be easily adjusted and to be easily manufactured, and an image forming apparatus including the same.

  An electromagnetic induction heating fixing device and an image forming apparatus according to the present invention include a roller provided as a heating body for thermally fixing toner on an image forming medium, or a roller provided to support a belt serving as the heating body, An electromagnetic induction heating unit disposed opposite to the outer peripheral side of the roller to generate heat by the electromagnetic induction action, the electromagnetic induction heating unit including an excitation coil extending in the axial direction of the roller, and the excitation A magnetic core extending in the circumferential direction of the roller on the outside opposite to the roller across the coil, and the magnetic core has a magnetic path length passing through a non-magnetic substance at an axial end. In comparison, the circumferential length is changed according to the axial position so as to be longer at the axial center.

  According to the present invention, by providing the magnetic core with the circumferential length changed according to the axial position, the amount of heat generated at the axial center is made smaller than the axial end, and the temperature distribution of the heating body is reduced. It can be made uniform. And since the magnetic core is arranged on the outer side opposite to the roller across the exciting coil, there is a high degree of design freedom regarding the form and arrangement position of the magnetic core, and adjustment for obtaining an appropriate temperature distribution is easy. Furthermore, manufacture becomes easy.

  A first invention made to solve the above problems includes a roller provided as a heating body for thermally fixing toner on an image forming medium, or a roller provided to support a belt serving as the heating body, An electromagnetic induction heating unit disposed opposite to the outer peripheral side of the roller to generate heat by the electromagnetic induction action. The electromagnetic induction heating unit includes an excitation coil extending in the axial direction of the roller, A magnetic core extending in the circumferential direction of the roller on the outer side opposite to the roller across the exciting coil, and the magnetic core has a magnetic path length passing through a non-magnetic material at an axial end. Compared to the above, the circumferential length is changed according to the axial position so as to be longer at the axial center.

  According to this, by providing the magnetic core with the circumferential length changed according to the axial position, the amount of heat generation at the axial center is smaller than the axial end, and the temperature distribution of the heating element is made uniform can do. And since the magnetic core is arranged on the outer side opposite to the roller across the exciting coil, there is a high degree of design freedom regarding the form and arrangement position of the magnetic core, and adjustment for obtaining an appropriate temperature distribution is easy. Furthermore, manufacture becomes easy.

  In this case, in order to reduce the amount of heat generated in the central portion in the axial direction, it is only necessary to form the gap in the circumferential length of the magnetic core so that the gap passes through the nonmagnetic air. Since the magnetic path length becomes long, the ratio of leakage magnetic flux increases and the amount of heat generation decreases. Moreover, the structure which filled the space | gap with nonmagnetic materials, such as a synthetic resin material, is also possible.

  The second invention made to solve the above-mentioned problems is that, in the first invention, the magnetic core has a plurality of core members arranged in the axial direction of the roller, and the plurality of core members However, the core member is composed of a plurality of types having different circumferential lengths, the core member having a long circumferential length is disposed at an axial end, and the core member having a short circumferential length is disposed at an axial central portion. can do.

  According to this, it is possible to easily and accurately adjust the temperature distribution by variously changing the arrangement number and arrangement position of the plurality of types of core members having different circumferential lengths.

  According to a third aspect of the present invention for solving the above problem, in the first aspect, the core member is arranged in an axial direction in accordance with a temperature distribution state of the heating body along the axial direction of the roller. It can be set as the structure provided so that fine adjustment was possible.

  According to this, since the arrangement position of the core member can be finely adjusted, the arrangement of the core member can be arranged according to the actual temperature distribution of the heating element even when the manufacturing accuracy and assembly accuracy of the component parts such as the excitation coil are low. By finely adjusting the position, an appropriate temperature distribution can be set without being affected by the manufacturing accuracy and assembly accuracy of the component parts.

  In this case, the supporting member that supports the core member may be formed in an equal cross section along the axial direction of the roller so that the core member can be fixed at any axial position. In addition, the core member is of a plurality of types having different circumferential lengths. If the core member is held by a holding member having the same outer shape and then attached to the support member, it is bothered by the difference in the form of the core member itself. The core member can be disposed at an appropriate position.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing a schematic configuration of an image forming apparatus to which the present invention is applied. The image forming apparatus includes an image forming unit 1 that forms a required image on a recording paper (image forming medium) S with toner based on image data input from an image reading device (not shown) or a host device such as a PC; Here, a fixing unit (fixing device) 2 for fixing the toner image formed on the recording paper S is provided, and the recording paper S of the paper feeding unit 3 is supplied to the image forming unit 1 via the registration roller 4. Then, the image forming process is performed, and then the sheet is conveyed along the fixing guide 5 to the fixing unit 2 and subjected to the fixing process, and then conveyed along the sheet discharge guide 6 and discharged onto the sheet discharge tray 7.

  In the image forming unit 1, the photosensitive drum 12 uniformly charged by the charger 11 is irradiated with laser light from the laser scanning unit 13 to form an electrostatic latent image on the image forming surface of the photosensitive drum 12. After that, the toner in the developing device 14 is supplied to the photosensitive drum 12 through the developing roller 15 to develop the electrostatic latent image on the image forming surface, and the toner image formed thereby is transferred. The image is transferred onto the recording paper by the roller 16. Further, the cleaning device 17 removes the residue on the surface of the photosensitive drum 12.

  The fixing unit 2 is in pressure contact with the heating roller 22 by a heating belt (heating member) 21 for thermally fixing the toner on the recording paper S, a heating roller 22 and a fixing roller 23 around which the heating belt 21 is wound, and a spring (not shown). A pressure roller 24 biased in the direction to be heated, and an electromagnetic induction heating unit 25 disposed opposite to a portion where the heating belt 21 is wound around the heating roller 22 and generating heat by the electromagnetic induction action. The recording paper S is fed into the nip portion of the heating roller 21 and the pressure roller 24 around the fixing roller 23, and the toner on the recording paper S is applied to the recording paper S by the action of heat and pressure. It is fixed. A cooling fan 26 is provided in the vicinity of the fixing unit 2.

  FIG. 2 is a cross-sectional view showing the fixing unit shown in FIG. 1 in detail. The electromagnetic induction heating unit 25 includes an exciting coil 31 that generates an alternating magnetic flux interlinking with the heating belt 21 and the heating roller 22, and a center core as a magnetic core that increases the alternating magnetic flux interlinking with the heating belt 21 and the heating roller 22. 32, a side core 33, and an arch core (core member) 35. The center core 32, the side core 33, and the arch core 35 are formed of a ferromagnetic material such as ferrite or permalloy. Here, a thermistor 39 for detecting the temperature of the heating belt 21 is provided.

  The exciting coil 31 is held by the coil guide 36 so as to cover the outer peripheral side of the heating roller 22 over a substantially semicircular cross-sectional area centering on the heating roller 22. The coil guide 36 protrudes outward from both side edges of the hook-shaped portion 41 and hook-shaped portions 41 formed in a cross-sectional shape curved along the outer surface of the heating belt 21 bent in an arc shape by the heating roller 22. In order to prevent heat generation due to electromagnetic induction action, the pair of flange-shaped portions 42 are formed of a heat resistant resin.

  The coil guide 36 holds the center core 32, the side core 33, and the arch core 35 in addition to the excitation coil 31. The excitation coil 31 is supported on the outer peripheral surface of the bowl-shaped portion 41, and the center core is placed on the top of the bowl-shaped portion 41. 32 is supported, and the side core 33 is supported by the hook-shaped portion 42. The center core 32 and the side core 33 are fixed to the coil guide 36 with an adhesive.

  The arch core 35 extends in the circumferential direction of the heating roller 22 on the outer side opposite to the heating roller 22 with the excitation coil 31 interposed therebetween, and bridges the center core 32 and the side core 33 extending in the axial direction of the heating roller 22 in the circumferential direction. To do. The arch core 35 is fixed to the center core 32 with an adhesive while being accommodated in a core holder (holding member) 44. The core holder 44 is formed of a heat-resistant resin in order to prevent heat generation due to electromagnetic induction as with the coil guide 36. Note that the core holder 44 can be integrally formed with the arch core 35 by insert molding.

  A housing 37 is attached to the coil guide 36 so as to cover the exciting coil 31, the center core 32, the side core 33, and the arch core 35. The housing 37 is a magnetic shielding material capable of interrupting an alternating magnetic field generated by the exciting coil 31. (For example, aluminum alloy).

  FIG. 3 is an exploded perspective view of the electromagnetic induction heating unit 25 shown in FIG. The exciting coil 31 extends over substantially the entire length in the longitudinal direction of the coil guide 36 having dimensions corresponding to the widths of the heating belt 21 and the heating roller 22, and a litz wire 47 having a configuration in which a large number of coated conducting wires are bundled. It is formed by extending around the center core 32 so as to extend in the axial direction along the outer peripheral surface of the 36 ridge portions 41 and to be folded back at the end in the axial direction.

  The center core 32 extends to the top of the flanged portion 41 of the coil guide 36, and the side core 33 extends to the flanged portion 42 over substantially the entire length of the coil guide 36 in the longitudinal direction.

  FIG. 4 is a sectional view showing in detail the electromagnetic induction heating unit 25 shown in FIG. The arch core 35 shown in FIG. 2 includes a plurality of types having different circumferential lengths. In particular, as shown in FIG. 4A, the arch core 35a has a long circumferential length, and FIG. 2, there are two types of arch cores 35 b having a short circumferential length, and these two types of arch cores 35 a and 35 b are accommodated in a core holder 44 to constitute arch core assemblies 45 a and 45 b, respectively.

  As shown in FIG. 3, the arch core assemblies 45a and 45b are arranged at predetermined intervals in the axial direction, and in particular, an arch core assembly 45a having an arch core 35a having a long circumferential length shown in FIG. Is disposed at the axial end, and an arch core assembly 45b having an arch core 35b with a short circumferential length shown in FIG. 4B is disposed at the axial center.

  The coil guide (support member) 36 has a main portion formed in a substantially equal cross section along the axial direction, and two types of arch cores 35a and 35b having different circumferential lengths are accommodated in a core holder 44 having the same outer contour. Since there is no difference in the outer shape of the arch core assemblies 45a and 45b, as shown in FIG. 3, the mounting boss 48 provided on the top of the hook-shaped portion 41 for fixing the housing 37 to the coil guide 36. The arch core assemblies 45a and 45b can be attached at any axial position except for the above-described arrangement positions.

  In the electromagnetic induction heating unit 25 configured as described above, when the exciting coil 31 is energized, as shown in FIG. In this case, in the arch core 35b having a short circumferential length shown in FIG. 4B, a gap 52 is defined in the core holder 44 at the circumferential end 51, and this gap 52 minutes is formed. However, since the length of the magnetic path passing through the nonmagnetic air becomes longer than in the case of the arch core 35a shown in FIG. 4A, the ratio of the leakage magnetic flux increases, and the heating belt 21 and the heating roller 22 The magnetic flux density is lowered and the amount of heat generation is reduced.

  Therefore, by arranging the arch core assembly 45a including the arch core 35a having a long circumferential length at the axial end portion and arranging the arch core assembly 45b including the arch core 35b having a short circumferential length at the axial center portion, The amount of heat generated at the axial center can be made smaller than that at the axial end. Since the number of the arch core assemblies 45a and 45b and the adjustment of changing the arrangement position can be easily performed, the arch core assemblies 45a and 45b can be adjusted according to the actual temperature distribution of the heating belt 21 and the heating roller 22. By finely adjusting the arrangement position, the temperature distribution can be adjusted easily and accurately.

  The arch core 35b having a short circumferential length shown in FIG. 4B can be configured to fill the gap 52 by insert molding with a synthetic resin material or filling the gap 52 with a synthetic resin material. In this case as well, since the synthetic resin material is non-magnetic, the ratio of the leakage magnetic flux increases and the amount of heat generation decreases.

  5 and 6 show the temperature distribution in the axial direction of the heating belt 21 and the heating roller 22 shown in FIG. FIG. 5A shows an example of a configuration in which the arch core 35 is omitted. In this case, the magnetic flux passing through the heating belt 21 and the heating roller 22 is uniform in the axial direction, and the heating belt 21 and the heating roller 22 are axial. Although heat is generated uniformly in the direction, heat is radiated from the end portion in the axial direction via the support member of the heating roller 22, so that the temperature at the end portion in the axial direction is lower than that in the central portion in the axial direction.

  FIG. 5B shows an example of a configuration in which the arch core 35 is provided. In particular, here, the arrangement interval of the arch cores 35 is set to be smaller at the axial end portion than at the axial central portion. Yes. In this case, the calorific value is increased at the axial end where the arrangement interval of the arch core 35 is set to be small, and the problem that the temperature at the axial end is lowered as compared with the central portion in the axial direction is improved. There arises a problem that the fluctuation range of the temperature becomes large at the axially central portion where the arrangement interval is large.

  In the example of FIG. 6 (A), as shown in FIG. 4, two types of long and short arch cores 35a and 35b are used, the arch core 35b having a short circumferential length is at the axial center and the arch core 35a having a long circumferential length. Are arranged at the axial ends. In this case, the amount of heat generation in the axial center portion where the arch core 35b having a short circumferential length is arranged is reduced, and the temperature fluctuation range is reduced compared to the example of FIG. The distribution is made uniform and a good temperature distribution is obtained.

  In the example of FIG. 6 (B), various types of arch cores 35 having different circumferential lengths are used, and from the axial end to the axial center according to the temperature distribution curve shown in FIG. 5 (A). Thus, the arch cores 35 are arranged so that the circumferential length is gradually shortened, and the arrangement interval of the arch cores 35 is also set short. In this case, compared with the example of FIG. 6A, the temperature fluctuation range becomes smaller, and the temperature distribution in the axial direction is made more uniform.

  FIG. 7 shows the temperature distribution state in the axial direction of the heating belt 21 and the heating roller 22 according to another example of the arch core 35 shown in FIG. Here, the arch core 35 is continuous in the axial direction, and the circumferential length gradually decreases from the axial end toward the axial center according to the temperature distribution curve shown in FIG. Is formed. In this configuration, the temperature distribution in the axial direction is further uniformed as compared with the example of FIG. 6B, and an optimum temperature distribution is obtained.

  FIG. 8 is a cross-sectional view illustrating another example of the fixing unit illustrated in FIG. 1. Here, unlike the above example, the heating roller 82 that generates heat by the electromagnetic induction action of the exciting coil 81 is a heating element that directly contacts the recording sheet S and heat-fixes the toner on the recording sheet S. Then, the recording paper S is fed into the nip portion formed by the heating roller 82 and the pressure roller 83, and the toner on the recording paper S is fixed to the recording paper S by the action of heat and pressure.

  As in the above example, the exciting coil 81 is held by the coil guide 84 so as to cover the periphery of the heating roller 82 over a substantially semicircular cross-sectional area centering on the heating roller 82, and the heating roller 82. A center core 85, a side core 86, and an arch core 87 are provided as magnetic cores that increase alternating magnetic fluxes that are linked to each other. A plurality of types of arch cores 87 having different circumferential lengths are used. The arch core 87 is accommodated in a core holder 89 to form an arch core assembly 90. The arch core assembly 90 including the arch core 87 having a short circumferential length includes the arch core 87 having a long circumferential length at the center in the axial direction. Arch core assemblies 90 are respectively disposed at axial ends.

  In the above example, the configuration in which the center core and the side core are provided is shown. However, the center core and the side core are not essential, and a configuration in which the center core and the side core are omitted is also possible.

  The electromagnetic induction heating and fixing apparatus according to the present invention and the image forming apparatus including the same have a high degree of design freedom regarding the form and arrangement position of the magnetic core, can be easily adjusted to obtain an appropriate temperature distribution, and can be manufactured. Electromagnetic induction heating and fixing device including an induction heating unit that heats a roller or a belt, which is a heating body for heat fixing toner on an image forming medium, by electromagnetic induction, and an image including the same It is useful as a forming apparatus, for example, a printer, a copying machine, a facsimile machine, a multi-function machine.

Schematic sectional view showing a schematic configuration of an image forming apparatus to which the present invention is applied Sectional drawing which shows the fixing | fixed part shown in detail in FIG. 2 is an exploded perspective view of the electromagnetic induction heating unit shown in FIG. Sectional drawing which shows the electromagnetic induction heating unit shown in FIG. 2 in detail The figure which shows the temperature distribution state of the axial direction of the heating roller shown in FIG. The figure which shows the temperature distribution state of the axial direction of the heating roller shown in FIG. The figure which shows the temperature distribution state of the axial direction of the heating roller by another example of the arch core shown in FIG. Sectional drawing which shows another example of the fixing | fixed part shown in FIG.

Explanation of symbols

2 Fixing portion 21 Heating belt 22 Heating roller 23 Fixing roller 24 Pressure roller 25 Electromagnetic induction heating unit 31 Excitation coil 32 Center core 33 Side core 35 / 35a / 35b Arch core (core member)
36 Coil guide 44 Core holder 45 / 45a / 45b Arch core assembly 52 Air gap 81 Excitation coil 82 Heating roller 83 Pressure roller 84 Coil guide 85 Center core 86 Side core 87 Arch core S Recording paper (image forming medium)

Claims (4)

A roller provided as a heating body for heat-fixing the toner on the image forming medium, or a roller provided to support a belt as the heating body, and an outer peripheral side of the roller, the heating body is electromagnetically disposed. An electromagnetic induction heating unit that generates heat by induction,
The electromagnetic induction heating unit includes an excitation coil extending in the axial direction of the roller, and a magnetic core extending in the circumferential direction of the roller on the outer side opposite to the roller across the excitation coil,
This magnetic core is provided with the circumferential length changed according to the axial position so that the magnetic path length passing through the non-magnetic substance is longer at the axial center than at the axial end. An electromagnetic induction heating fixing device. The magnetic core has a plurality of core members arranged in the axial direction of the roller,
The plurality of core members are made of a plurality of types having different circumferential lengths, the core member having a long circumferential length is at an axial end, and the core member having a short circumferential length is at an axial center. The electromagnetic induction heating fixing device according to claim 1, wherein the electromagnetic induction heating fixing device is disposed.   3. The electromagnetic induction according to claim 2, wherein the core member is provided so that an arrangement position in the axial direction can be finely adjusted according to a temperature distribution state of the heating body along the axial direction of the roller. Heat fixing device. An image forming apparatus comprising the electromagnetic induction heating fixing device according to any one of claims 1 to 3.