JP4321386B2 - Excitation coil for induction heating, fixing device including the same, and image forming apparatus - Google Patents

Description

The present invention is a fixing device including an induction heating excitation coil and the induction heating excitation coil as a pressure heat means, the image forming apparatus (electrophotographic apparatus or an electrostatic recording system of a copying machine having the fixing device, a facsimile And a printer) .

  In general, in order to save energy and increase the speed of these fixing devices for image forming apparatuses such as printers and copiers, electromagnetic induction heating type fixing devices are widely adopted as heating sources to replace halogen lamps and the like. It has become to. In such an electromagnetic induction heating type fixing device, a magnetic field generated by a magnetic field generating means is applied to a heating element, and the heating element is caused to generate Joule heat by this eddy current. For example, the heating device can be used as a fixing device of an image forming apparatus that heats an unfixed image formed on a recording medium such as transfer paper or an OHP sheet by an image forming unit.

By the way, the fixing device using such a heating device of the electromagnetic induction heating method has a configuration in which an eddy current is generated in a conductive layer provided on the surface of the cylindrical heating roller by a magnetic field generated by an exciting coil to joule the heating element. In order to achieve uniform temperature in the entire longitudinal direction and to support recording of different recording materials, and to reduce the size of the apparatus, there was a configuration in which a single excitation coil was used and adjustment was performed with magnetic parts (for example, patents) Reference 1).
JP 2002-43049 A

  However, in order to process different recording materials (Patent Document 1), a single exciting coil is used, and a magnetic component is used for adjusting the temperature distribution in order to make the temperature uniform in the longitudinal direction of the heating element. The structure is controlled by moving it closer to or away from the coil, which is effective for downsizing in the longitudinal direction. It wasn't. Moreover, in order to adjust the temperature distribution, the magnetic component is moved closer to or away from the coil, so that the inductance of the exciting coil fluctuates at every adjustment. In some cases, the electric power required for electromagnetic induction heating cannot be sufficiently supplied because the circuit cannot be matched.

In order to solve this problem, an induction heating excitation coil according to the present invention is an induction heating excitation coil that is disposed along a cylindrical heating element and generates heat by electromagnetic induction. Effective use of the longitudinal portion, the second longitudinal portion, the two transition portions connecting the first longitudinal portion and the second longitudinal portion, and the magnetic field of the longitudinal width of the two transition portions. In order to shorten the width in the longitudinal direction of the crossover portion and suppress the thickness, a coil is formed by laminating and winding the two crossover portions in the direction away from the heat generating body side while starting to wind from the heat generating body side and increasing the width in the longitudinal direction. A plurality of the coils are arranged such that the longitudinal direction thereof is aligned with the axial direction of the heating element, and the coils between the juxtaposed coils are reinforced in order to reinforce magnetic flux reduction at both transition parts between the juxtaposed coils. one magnetic spanning both of the connecting portions only It was configured to provide the wood.

According to the present invention, it is possible to form an optimum magnetic field for induction heating while effectively using a magnetic field having a longitudinal width of a coil transition portion while shortening a longitudinal width of the coil transition portion and suppressing a thickness of the laminated portion. In addition, the temperature distribution can be made uniform even with different recording materials, and the temperature drop due to the decrease in the magnetic flux at both transitions between the coils arranged side by side can be reinforced. An exciting coil can be provided.

An induction coil for an induction heating device according to claim 1 is an induction heating excitation coil that is disposed along a cylindrical heating element, and generates heat by electromagnetic induction. The first longitudinal portion, The two longitudinal portions, the two transition portions connecting the first longitudinal portion and the second longitudinal portion, and the longitudinal direction of the transition portions while effectively utilizing the magnetic field of the longitudinal width of the two transition portions In order to shorten the width and suppress the thickness, the coil has a coil that is formed by laminating and winding the two transition portions from the heating element side, stacking them in a direction away from the heating element side while giving a width in the longitudinal direction. In order to reinforce the reduction of magnetic flux in both transition portions between the juxtaposed coils , a plurality of the longitudinal portions are aligned in the axial direction of the heating element. adopted a configuration in which one magnetic member spanning only .

According to this configuration, in order to effectively use the magnetic field of the longitudinal width of the two transition portions of the coil while reducing the longitudinal width of the transition portion and suppressing the thickness, the two transition portions of the coil are separated from the heating element side. Since winding is started in the longitudinal direction and laminated in a direction away from the heating element side, the width of the coil connecting portion in the heating element axial direction is shortened while increasing the thickness toward the outer periphery of the heating element. It is possible to form an optimum magnetic field for induction heating by effectively using the magnetic field of the longitudinal width of the portion while shortening the longitudinal width of the coil connecting portion and suppressing the thickness of the laminated portion. Further, by arranging a plurality of coils with the longitudinal direction thereof aligned with the axial direction of the heating element, and selecting and energizing the plurality of coils, the temperature distribution can be made uniform even with different recording materials. Furthermore, in order to reinforce magnetic flux reduction at both transition portions between the juxtaposed coils, a magnetic member is provided across both transition portions between the juxtaposed coils. It is possible to reinforce the temperature drop due to the decrease in magnetic flux at the transition part. Therefore, it is possible to provide a small and highly accurate induction coil for induction heating.

The induction heating excitation coil according to claim 2 is the induction heating apparatus excitation coil according to claim 1 , wherein the magnetic member has a length equal to or greater than the combined length of the two transition portions .

According to this configuration, since the magnetic member having a length equal to or greater than the combined length of both the connecting portions is provided, the magnetic field generated from the longitudinal direction can be effectively collected on the magnetic member.

According to a third aspect of the present invention, there is provided an induction heating apparatus exciting coil according to any one of the first to second aspects, wherein the plurality is an odd number .

According to this configuration, it is possible to obtain a symmetrical temperature distribution of the heating element by a combination of the excitation coil disposed in the center and a plurality of excitations disposed on both sides thereof.

According to a fourth aspect of the present invention, there is provided a fixing device using the induction heating exciting coil according to any one of the first to third aspects as a heating means for heating an unfixed image formed on a recording medium.

With this configuration, it is possible to provide a fixing device that can uniformly heat and fix an unfixed image formed on a recording medium over the entire rotation direction by the heating unit .

According to a fifth aspect of the present invention, there is provided an image forming apparatus including the fixing device according to the fourth aspect .

  According to this configuration, it is possible to provide an image forming apparatus capable of uniformly heating and fixing an unfixed image formed on a recording medium over the entire heating width in the rotation axis direction by the fixing device.

  The gist of the present invention shows a configuration in which a temperature distribution can be made uniform in the longitudinal direction of a heating element in a fixing device that fixes a plurality of recording materials by combining a plurality of exciting coils.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, components having the same configuration or function and corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

(Embodiment 1)
FIG. 1 is an example of a cross-sectional view showing an image forming apparatus using an exciting coil according to Embodiment 1 of the present invention as a fixing device. In FIG. 1, reference numeral 11 denotes an electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”). The surface of the photosensitive drum 11 is uniformly charged to a negative dark potential V0 by the charger 12 while being rotated at a predetermined peripheral speed in the direction of the arrow. A beam scanner 13 outputs a laser beam 14 modulated in accordance with a time-series electric digital pixel signal of an image device input from a host device such as an image reading device or a computer (not shown). The surface of the charged photosensitive drum 11 is scanned and exposed by the laser beam 14. As a result, the absolute value of the potential of the exposed portion of the photosensitive drum 11 decreases to become a bright potential VL, and an electrostatic latent image is formed. This latent image is developed and visualized by the negatively charged toner of the developing device 15.

  The developing device 15 includes a developing roller 16 that is rotationally driven. The developing roller 16 is disposed to face the photosensitive drum 11, and a thin layer of toner is formed on the outer peripheral surface thereof. A developing bias whose absolute value is smaller than the dark potential V0 of the photosensitive drum 11 and larger than the bright potential VL is applied to the developing roller 16, so that the toner on the developing roller 16 is transferred to the light potential of the photosensitive drum 11. The latent image is visualized by being transferred only to the VL.

  On the other hand, the recording material 205 is fed one by one from the paper feeding unit 17 and passes through the registration roller pair 18 to the nip portion of the photosensitive drum 11 and the transfer roller 19 at an appropriate timing synchronized with the rotation of the photosensitive drum 11. Sent. The toner image on the photosensitive drum 11 is sequentially transferred to the recording material 205 by the transfer roller 19 to which a transfer bias is applied. The photosensitive drum 11 from which the recording material 205 has been separated is subjected to the subsequent image formation by removing the residual toner such as transfer residual toner on the surface thereof by the cleaning device 20.

  A fixing guide 21 guides the movement of the recording material 205 after transfer to the fixing device 22 by the fixing guide 21. The recording material 205 is separated from the photosensitive drum 11 and then conveyed to the fixing device 22, whereby the toner image transferred onto the recording material 205 is fixed. A paper discharge guide 23 guides the recording material 205 that has passed through the fixing device 22 to the outside of the apparatus. The fixing paper guide 21 and the paper discharge guide 23 are made of resin such as ABS. Note that the fixing guide 21 and the paper discharge guide 23 may be made of a non-magnetic metal such as aluminum. The recording material 205 after the toner image is fixed is guided to the paper discharge tray 24.

  Reference numeral 25 denotes a bottom plate of the apparatus main body, 26 denotes a top plate of the apparatus main body, and 27 denotes a main body chassis, which integrally take on the strength of the entire apparatus. These members are made of a galvanized material made of steel, which is a magnetic material, as a base material.

  Reference numeral 28 denotes a cooling fan, and this cooling fan 28 generates an air flow in the apparatus. Reference numeral 29 denotes a coil cover as a shielding member containing a nonmagnetic metal such as aluminum. The coil cover 29 is configured to cover the back surfaces of the exciting coil 105 and the arch core 106.

  Next, a fixing device as a heating device according to an example of the present embodiment will be described in detail.

  FIG. 2 is an explanatory view showing the fixing device according to the embodiment of the present invention.

The fixing device shown in FIG. 2 is an electromagnetic induction heating type fixing device used in an image forming apparatus,
A heating roller (first rotating body) 201 heated along the outer peripheral surface by electromagnetic induction of the induction heating unit 100, a fixing roller 202 arranged in parallel to the heating roller 201, the heating roller 201, and the fixing roller 202 An endless belt-like heat generating belt (second rotating body) 203 that is stretched around and heated by electromagnetic induction and rotates in the direction of arrow A by the rotation of the fixing roller 202, and the heat generating belt 203 is contacted to form a nip portion. Then, a pressure roller (pressure member) 204 that is pressed against the fixing roller 202 and rotates in the forward direction with respect to the heat generating belt 203, and an opposed core that faces the excitation coil 105 with the heat generating belt 203 and the heat generating roller 201 interposed therebetween. 110. As the material of the opposed core 110, a ferromagnetic material such as ferrite or permalloy can be used. In the opposed core 110, most of the magnetic flux generated by the exciting coil passes through the opposed core 110, so that there is little leakage magnetic flux to the outside of the exciting coil, and the magnetic flux of the exciting coil can be used effectively.

  The heat roller 201 is made of a hollow cylindrical ferromagnetic metal member made of, for example, Fe, Ni, and alloys thereof (SUS, etc.), and has an outer diameter of, for example, 20 mm and a wall thickness of, for example, 0.1 mm to 0.2 mm. It has a low heat capacity and high temperature rise.

  The fixing roller 202 includes, for example, a metal cored bar 202a such as SUS, and an elastic member 202b covered with a cored bar 202a in a solid or foamed heat-resistant silicone rubber. And, in order to form a contact portion (nip portion N) with a predetermined width between the pressure roller 204 and the pressing force from the pressure roller 204, the outer diameter is about 30 mm, which is larger than the heating roller 201. The elastic member 202b has a thickness of about 3 to 8 mm and a hardness of about 15 to 50 ° (Asker C).

  With such a configuration, the heat capacity of the heat generating roller 201 is smaller than the heat capacity of the fixing roller 202, so that the heat generating roller 201 is rapidly heated and the warm-up time is shortened.

  The heat generating belt 203 stretched between the heat generating roller 201 and the fixing roller 202 is heated by the induction heating means 100 disposed on the outer peripheral surface of the heat generating roller 201 and is in contact with the heated heat generating roller 201. The heat conduction is heated. Then, the inner surface of the heat generating belt 203 is continuously heated by the rotation of the heat generating belt 203 accompanying the rotation of the fixing roller 202 by the driving means (not shown), and as a result, the entire belt is heated.

  The heat generating belt 203 is composed of a thin endless belt having a diameter of 50 mm and a thickness of 50 μm, in which a conductive layer is formed by dispersing silver powder in a polyimide resin having a glass transition point of 360 (° C.). The conductive layer may have a structure in which two to three silver layers having a thickness of 10 μm are stacked. Further, the surface of the heat generating belt 203 may be covered with a 5 μm-thick release layer (not shown) containing a fluororesin in order to impart release properties. The glass transition point of the base material of the heat generating belt 203 is desirably in the range of 200 (° C.) to 500 (° C.). Further, as the release layer on the surface of the heat generating belt 203, a resin or rubber having good release properties such as PTFE, PFA, FEP, silicone rubber, and fluorine rubber may be used alone or in combination.

  In addition to the polyimide resin described above, a heat-resistant resin such as a fluororesin, or a metal such as a nickel thin plate and a stainless thin plate by electroforming can be used as the material for the base material of the heat generating belt 203. For example, the heat generating belt 203 has a structure in which a surface of SUS430 (magnetic) or SUS304 (nonmagnetic) having a thickness of 40 μm is plated with copper of 10 μm, or a nickel electroformed belt having a thickness of 30 to 60 μm. It may be.

  In addition, when the heat generating belt 203 is used as an image heating body for heating and fixing a monochrome image, it is only necessary to ensure releasability. However, the heat generating belt 203 is used as an image heating body for heating and fixing a color image. In some cases, it is desirable to provide elasticity by forming a rubber layer.

  The pressure roller 204 includes a cored bar 204a including a cylindrical member made of metal such as SUS or Al, and an elastic member 204b provided on the surface of the cored bar 204a and having high heat resistance and high toner releasability. It consists of and.

  As shown in FIG. 2, the induction heating unit 100 that heats the heat generating roller 201 by electromagnetic induction includes an exciting coil unit, a heat generating roller, and a heat generating belt. The exemplary coil unit includes an exciting coil 105 that is a magnetic field generating unit and a coil holding member 109. Here, the coil holding member 109 has a semicircular arc shape disposed close to the outer peripheral surface of the heat generating roller 201, functions as a heat insulating member between the heat generating roller and the exciting coil 105, the fixing of the exciting coil 105, and the arch core. 106, the center core 107, and the side core 108 are configured as members for fixing. That is, since the temperature of the heat generating roller portion of the coil holding member 109 reaches the fixing temperature, for example, 170 ° C., the radiant heat is blocked to the adjacent excitation coil 105 and the heat generation of the excitation coil 105 can be suppressed.

  The conducting wire used for the exciting coil 105 is formed by combining 1 to 10 litz wire bundles obtained by bundling wires having diameters of φ0.05 to φ0.2. The outer diameter of the Litz wire bundle is a combination of wire bundles having an outer diameter of 2 mm at the maximum, and the coil thickness can be 2 mm. Furthermore, in order to cope with a thinner coil thickness, the number of twists of one bundle of litz wire can be constituted by 10 to 40. The outer diameter of the litz wire can be calculated by (Equation 1) according to JIS C3005.

  (Here, D: outer diameter of litz wire, d: outer diameter of strand of litz wire, n: number of strands).

  Therefore, by combining a plurality of litz wire bundles and winding them at the same time, a thick portion of the exciting coil and a thin portion of the exciting coil can be wound in accordance with the winding. On the other hand, when the wire diameter is larger than φ0.2, the electric resistance due to the high-frequency AC current increases, and the heat generation of the exciting coil becomes excessive.

  FIG. 3 is a diagram showing an exciting coil unit according to the embodiment of the present invention.

  As in the excitation coil unit shown in FIG. 3, on the outside of the excitation coil 105, an arch core 106 formed in an arch shape that covers the back surface of the excitation coil 105, and a center core 107 disposed at the winding center of the excitation coil 105. And the side cores 108 disposed at both ends of the winding bundle of the exciting coil 105. Ferromagnetic materials such as ferrite and permalloy can be used as the core material. The exciting coil 105 is composed of three coils of the central portions 105a, 105b, and 105c, and is configured so as to be compatible with different recording materials. In addition, a magnetic component 121 is disposed in a transition portion between the exciting coils 105.

  The center core 107 and the side core 108 form a magnetic path together with the arch core 106. For this reason, outside the heat generating belt, most of the magnetic flux generated by the exciting coil 105 passes through these three types of cores to reduce the leakage magnetic flux to the outside of the core. Note that not all of these three types of cores are necessarily required, and there may be one type, some may be combined, or some may not.

Here, the center core 107 and the side core 108 may be integrated with the arch core 106 or may be combined with different members.

  The excitation coil 105 is fed with a high frequency alternating current of 10 kHz to 1 MHz, preferably a high frequency alternating current of 20 kHz to 800 kHz, from a drive power supply (not indicated). An alternating magnetic field is generated between the opposed cores 110. The drive power supply is configured to energize 105a to handle a narrow recording material, and to energize 105a, 105b, and 105c when processing a wide recording material. The alternating magnetic field acts on the heat generating roller 201 in the contact area L between the heat generating roller 201 and the heat generating belt 203 and the vicinity thereof, and an eddy current flows in the direction in which the change of the magnetic field is prevented.

  This eddy current generates Joule heat according to the resistance of the heat generating roller 201, and the heat generating roller 201 is heated by electromagnetic induction heat mainly in the contact area between the heat generating roller 201 and the heat generating belt 203 and in the vicinity thereof.

  The heat generating belt 203 heated in this way has its inner surface temperature detected by the temperature detecting means 112 including a temperature sensitive element such as a thermistor on the inlet side of the fixing nip N.

  As a result, since the temperature detecting unit 112 does not damage the surface of the heat generating belt 203, the fixing performance is continuously secured and the temperature immediately before entering the fixing nip portion N of the heat generating belt 203 is detected. Then, the temperature of the heat generating belt 203 is stably maintained at, for example, 170 ° C. by controlling the input power to the induction heating unit 100 based on a signal output based on this temperature information.

  When the toner image 206 formed on the recording material 205 is introduced into the fixing nip portion N in an image forming portion (not shown) disposed on the upstream side of the fixing device, the toner image 206 is heated by the heating unit 100. The sheet is fed into the fixing nip N in a state where the difference between the surface temperature and the back surface temperature of the heat generating belt 203 becomes small. Therefore, the belt surface temperature becomes excessively higher than the set temperature, so-called overshoot can be suppressed and stable temperature control can be performed.

  Next, the exciting coil according to the present embodiment will be described.

  FIG. 4A is a perspective view of an exciting coil of the heating device according to the present embodiment.

  FIG.4 (b) is a front view of the exciting coil of the heating apparatus which concerns on this Embodiment, FIG.4 (c) is a side view of an exciting coil.

  Each of the exciting coils 105a, 105b, and 105c includes a first longitudinal portion 301a and a second longitudinal portion 301b, and two transition portions 402 that connect the first longitudinal portion and the second transition portion. The distance between the longitudinal part and the second longitudinal part is set to a distance G1 in the range of 5 mm to 30 mm. The magnetic field generated from the longitudinal portions of the portion where the gap G is narrower than 5 mm has less influence on the heating element, and if it is larger than 30 mm, the exciting coil 105 must be formed larger.

The crossover portion 402 has a thickness T of 3 to 10 mm, and is provided with a recess 401 at the center. If the thickness T is set to be larger than φ2 which is the maximum outer shape of the conductor bundle, an increase in the shape of the transition portion can be prevented. The exciting coil is wound by a winding mold (not shown), the transition portion 402 is wound from the heating element side, and the winding end is separated from the heating element. As shown in FIG. 10, they are not necessarily stacked and wound in order from the beginning of the winding, but are stacked and wound according to the winding from the heating element side. The connecting portion of the conventional exciting coil is wound with the inner and outer shapes substantially equal to the longitudinal portion, and the thickness of the exciting coil 105 is substantially equal to the longitudinal portion winding. Therefore, by winding thicker than the coil thickness longitudinal part of the transition part, the thickness T in the longitudinal direction of the transition part can be shortened, and the entire excitation coil 105 can be shortened.

  The width G2 of the recess is substantially equal to the gap G1 between the longitudinal portions, and the height D of the recess is set to a height lower than 10 mm. If it is higher than 10 mm, the outer shape of the transition portion 402 of the exciting coil 105 becomes large, and the fixing device also becomes large. The thickness T of the transition portion is set as thin as possible in order to combine a plurality of excitation coils. However, when the thickness is less than 3 mm, the diameter of the transition portion 402 is increased. The effective magnetic field component that heats the body is reduced and temperature unevenness occurs.

  A magnetic component 121 is disposed between the transition portions 402 of the exciting coils 105, for example, below the recesses between the exciting coils 105a and 105b. The shape of the magnetic component 121 is a substantially rectangular parallelepiped shape, and the length of the magnetic component 121 is equal to or longer than the combined length of both transition portions. Further, the thickness is determined to be substantially equal to the thickness of the concave portion or in the range of 0 to 10 mm in consideration of the temperature distribution of the heating element. Moreover, as a material of the magnetic component, ferrite, Fe, or an Fe alloy (permalloy or the like) can be used. In the configuration in which the concave portion is provided, the configuration of the crossover portion 402 can be applied even when the winding end portion is not separated from the heating element from the winding start.

  The shape of the magnetic component 121 is not limited to a rectangular parallelepiped, but may be arbitrarily selected from a semi-cylindrical shape, a triangular prism shape, a kamaboko shape, and the like.

  As shown in FIG. 3, in the configuration in which the center core is disposed in the longitudinal direction, the magnetic component 121 is disposed separately from the center core 107 in the transition portion 402.

  The magnetic component 121 may not be disposed in the state of the temperature distribution in the longitudinal direction, and may be omitted when the length of the transition portion 402 is about 3 to 10 mm in the longitudinal direction.

  The exciting coil 105 and the magnetic component are fixed to the coil holding member 109 with an adhesive, for example. As the adhesive, a material having high heat resistance is desirable. For example, a silicon-based adhesive can be used.

  It is desirable that the exciting coil 105 is used in the range of 1 to 9 and is composed of an odd number. If the number is set to an odd number, the left and right symmetry of the heating element is easier to obtain, but of course, even if it is configured with an even number, the temperature of the heating element can be made uniform and symmetrical.

  FIG. 9 shows the temperature distribution of the heating element of the heating device composed of a plurality of exciting coils 105. As an example of the embodiment, an excitation coil 105a disposed at the center in the longitudinal direction corresponding to an A4 size recording material and excitation coils 105b and 105c are disposed on both sides thereof, and 105a, 105b and 105c are connected to each other, and an A3 size is provided. The temperature of the heating element in the case of the exciting coil 105 corresponding to the recording material is shown. With this configuration, the temperature distribution of A3 size and A4 size recording materials can be adjusted.

  In the embodiment, an example of three exciting coils has been described, but it goes without saying that adjustment can be made by combining a plurality of exciting coils in order to cope with various recording material sizes.

  FIG. 5 illustrates the shape of the exciting coil in the heating device of the present invention.

As shown in FIG. 5B, the FF vertical cross-sectional shape in the longitudinal direction of the exciting coil 105 is a shape along the heat generating belt 203, and includes a curved portion C, a flat portion H1, and a curved portion H2 formed by arcs. The belt 203 rotates in the direction of the arrow in the figure. The end of the excitation coil 105 is configured to extend along the shape of the heat generating belt 203 from the center of the arc toward the heat generating roller.

  By configuring the exciting coil 105 to extend along the heat generating belt 203, the area where the eddy current flowing through the conductive layer on the surface of the heat generating belt 203 is generated is increased, and the heat generation amount of the heat generating belt 203 is increased. Can do. In the embodiment of the present invention, 5 mm was extended along the heat generating belt 203 from the origin O of the curved portion C, and the time for the belt to rise to 170 ° C. was shortened by about 2 seconds. The length of the excitation coil 105 extending along the heat generating belt 203 is preferably in the range of 0 to 10 mm, and if it exceeds 10 mm, the effect of coupling with the opposed core 110 disposed in the heat generating roller 201 is reduced.

  Further, in the embodiment of FIG. 5B, an example in which the arc is formed by the curved portion C and the flat portion H1 and the curved portion H2 is shown. However, when the heat generating belt 203 is bulged or extended. In consideration of the above, both ends connected from the arc as shown in FIG. 5 (c) can be configured by flat portions, and the part connected from the arc as shown in FIG. 5 (d) is configured as an arc. May be.

  6 shows the coil angle and heat generation distribution when the coil thickness is uniform, and FIG. 7 shows the heat generation distribution when the coil thickness is partially reduced. Therefore, since the temperature of the heating element can be adjusted by adjusting the thickness of the coil, the amount of eddy current on the heating element is reduced, and the temperature of the heating element can be finely adjusted over the entire longitudinal direction. .

  The exciting coil is constituted by a saddle type coil, but the transition part at both ends has a flat part 401 at a center part away from the inner diameter. By comprising a saddle type coil, the heating element can have a long length in the longitudinal direction, and the entire length can be shortened.

  In order to cope with different recording materials as shown in FIG. 4, it is configured by combining a plurality of excitation coils, but in order to correct a magnetic field drop at the transition portion between the excitation coils when configured with a plurality of excitation coils, By adding a magnetic component inside the flat portion, the temperature distribution in the entire heating element can be made uniform.

  FIG. 8 is a diagram showing another configuration of the embodiment of the present invention.

  In the present embodiment, the two-axis type configuration in which the heat generating roller and the fixing roller are stretched by a heat generating belt has been described. However, the heating device of the present invention has a one-axis configuration in which the heat generating roller and the fixing roller are integrated. Conceivable. By adopting a uniaxial configuration, it is possible to reduce the size.

The exciting coil for induction heating according to the present invention can be used for a fixing device provided with the exciting coil for induction heating and an image forming apparatus provided with the fixing device .

Sectional drawing which shows the image forming apparatus which used the exciting coil concerning Embodiment 1 of this invention as a fixing device. Explanatory drawing which shows the fixing device which concerns on embodiment of this invention. The figure which shows the exciting coil unit concerning embodiment of this invention The figure which shows the exciting coil concerning embodiment of this invention The figure which shows the heating apparatus concerning embodiment of this invention (A) A sectional view of a heating device having a uniform coil thickness according to an embodiment of the present invention, and (b) a graph showing a heat generation amount on a fixing roller corresponding to the sectional views of (a). (A) Cross-sectional view of heating device with changed coil thickness according to an embodiment of the present invention, (b) Graph showing heat generation amount on fixing roller corresponding to cross-sectional view of (a) The figure which shows another structure of embodiment of this invention The figure which shows the temperature distribution of the heat generating body of the heating apparatus comprised with the several excitation coil Cross section of the crossover Conventional coil configuration diagram

Explanation of symbols

DESCRIPTION OF SYMBOLS 22 Fixing apparatus 100 Induction heating means 105 Excitation coil 106 Arch core 107 Center core 108 Side core 109 Coil holding member 110 Opposite core 121 Magnetic component 201 Heating roller 202, 202a, 202b Fixing roller 203 Heating belt 204, 204a, 204b Pressure roller 401 Concavity 402 Crossing

Claims (5)

An induction heating excitation coil that is arranged along a cylindrical heating element and generates heat by electromagnetic induction, and includes a first longitudinal part, a second longitudinal part, and the first longitudinal part. In order to shorten the width in the longitudinal direction and suppress the thickness of the two transition portions while effectively utilizing the magnetic field of the width in the longitudinal direction of the two transition portions , A coil is formed by laminating and winding the crossing portion in the direction away from the heating element side while starting to wind the transition part from the heating element side and having a width in the longitudinal direction,
A plurality of the coils are arranged such that the longitudinal direction thereof is aligned with the axial direction of the heating element, and both coils between the juxtaposed coils are reinforced in order to reinforce magnetic flux reduction at both transition parts between the juxtaposed coils. An exciting coil for induction heating, characterized in that a single magnetic member is provided that spans only the transition part. The exciting coil for induction heating according to claim 1, wherein the magnetic member has a length equal to or longer than a total length of both transition portions. The induction heating exciting coil according to claim 1, wherein the plurality is an odd number. The fixing device using the induction heating exciting coil according to claim 1 as a heating means for heating and fixing an unfixed image formed on a recording medium. An image forming apparatus comprising the fixing device according to claim 4.

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