Induction heating device

Abstract

An induction heating device (10) comprises: an induction coil (1) that includes at least two coils; a high-frequency power supply (2) that supplies currents of mutually different phases to each of the at least two coils; and a conveyance device (3) that conveys a heating subject (4). When a current is supplied to the induction coil (1), a shifting magnetic field is formed on the surface of the heating subject (4), and the shifting direction (Y) of the shifting magnetic field is different from the conveyance direction (X) of the heating subject (4).

Description

induction heating device

[0001] The present disclosure relates to induction heating devices.

[0002] Drying furnaces are used to heat objects to be heated (hereinafter also referred to as workpieces) in drying processes such as drying paint on metal plates and drying coatings on battery electrodes. One drying method used in drying furnaces is the induction heating (IH) method. Induction heating devices that use induction heating for drying pass a high-frequency current through a coil placed close to the workpiece, inducing eddy currents inside the workpiece, and heat the workpiece using Joule heat from the eddy currents. The induction heating device disclosed in Patent Document 1 has multiple coils with different shapes arranged at different positions in the workpiece transport direction. This allows heating power to be applied to different locations as the workpiece is transported.

[0003] Japanese Unexamined Patent Publication No. 63-175374

[0004] However, with conventional techniques, the distribution of heating power applied by each coil is uneven, making it difficult to achieve a sufficiently uniform temperature distribution in the workpiece.

[0005] An object of the present disclosure is to provide an induction heating device that can heat an object to be heated so that the temperature distribution of the object is uniform.

[0006] An induction heating device according to one aspect of the present disclosure comprises an induction coil including at least two coils, a high-frequency power supply that supplies currents of different phases to each of the at least two coils, and a transport device that transports an object to be heated, wherein when the current is supplied to the induction coil, a moving magnetic field is formed on the surface of the object to be heated, and the moving direction of the moving magnetic field is different from the transport direction of the object to be heated.

[0007] According to the present disclosure, it is possible to provide an induction heating device that can heat an object to be heated so that the temperature distribution of the object is uniform.

[0008] FIG. 1 is a diagram schematically showing the configuration of an induction heating device according to a first embodiment; FIG. 2 is a cross-sectional view schematically showing an induction coil and a workpiece viewed from the transport direction; FIG. 3 is a diagram schematically showing the distribution of eddy currents generated in a workpiece by a current flowing through an induction coil; FIG. 4 is a diagram schematically showing the time-averaged distribution of heating power applied to a workpiece; FIG. 5 is a cross-sectional view schematically showing a cross section of an induction heating device according to a second embodiment (specifically, an induction coil and a workpiece) perpendicular to the transport direction of the workpiece; FIG. 6 is a cross-sectional view schematically showing a cross section of an induction heating device according to a third embodiment (specifically, an induction coil and a workpiece) perpendicular to the transport direction of the workpiece; and FIG. 7 is a cross-sectional view schematically showing a cross section of an induction heating device according to a fourth embodiment (specifically, an induction coil and a workpiece) perpendicular to the transport direction of the workpiece.

[0009] Hereinafter, an induction heating device according to an embodiment will be described in detail with reference to the drawings.

[0010] 1 is a diagram showing a schematic configuration of an induction heating device 10 according to embodiment 1. The induction heating device 10 includes an induction coil 1, a high-frequency power supply 2, a transport device 3, a temperature sensor 5, and a controller 6.

[0011] The induction coil 1 is disposed above the workpiece 4 at a predetermined distance. The workpiece 4 is an object to be heated in the induction heating device 10. The workpiece 4 is, for example, a flat plate-shaped workpiece or a thin foil-shaped workpiece.

[0012] The transport device 3 transports the workpiece 4 at a predetermined speed in a transport direction X. The transport direction X is also referred to as a "first direction."

[0013] The induction coil 1 includes at least two coils. In the example shown in Fig. 1, the induction coil 1 is composed of a first coil 1A, a second coil 1B, and a third coil 1C. The first coil 1A, the second coil 1B, and the third coil 1C partially overlap each other. A current of a predetermined frequency is supplied from a high-frequency power supply 2 to each of the first coil 1A, the second coil 1B, and the third coil 1C.

[0014] The temperature sensor 5 measures the temperature of the measurement area 7, which is the measurement target on the workpiece 4. The measurement results measured by the temperature sensor 5 are transmitted to the controller 6, which acquires the measurement results. Specifically, a sensor signal S1 indicating the measurement results is transmitted from the temperature sensor 5 to the controller 6. The controller 6 receives the sensor signal S1 from the temperature sensor 5. The measurement results are, for example, the temperature of a portion of the measurement area 7 or the temperature distribution of the measurement area 7.

[0015] The controller 6 controls the current supplied to the first coil 1A, the second coil 1B, and the third coil 1C from the high frequency power supply 2. Specifically, the controller 6 receives a sensor signal S1 obtained from the temperature sensor 5, and transmits a control signal S2 to the high frequency power supply 2 based on the sensor signal S1 to control the high frequency power supply 2.

[0016] For example, the controller 6 controls the high frequency power supply 2 so as to change the phase of the current supplied to at least one of the at least two coils in accordance with the measurement result.

[0017] FIG. 2 is a cross-sectional view schematically showing the induction coil 1 and the workpiece 4 as viewed from the conveying direction X. The induction coil 1 is disposed at a predetermined distance d from the workpiece 4. In the example shown in FIG. 2, the distance d is the shortest distance from the workpiece 4 to each coil. The first coil 1A, the second coil 1B, and the third coil 1C are offset from one another in the width direction Y of the workpiece 4. In the cross-section shown in FIG. 2, a portion of the first coil 1A is disposed adjacent to a portion of the third coil 1C, and the second coil 1B is disposed across the first coil 1A and the third coil 1C. The winding densities of the coils may be uniform or may differ.

[0018] The high-frequency power supply 2 supplies currents of different phases to at least two coils. When the high-frequency power supply 2 supplies currents to the first coil 1A, the second coil 1B, and the third coil 1C, the current supplied to the second coil 1B has a phase lead or lag of 90 degrees relative to the phase of the current supplied to the first coil 1A and the phase of the current supplied to the third coil 1C. For example, with respect to the phase of the first coil 1A, a current with a phase lag of 90 degrees is supplied to the second coil 1B, and a current with a phase lag of 180 degrees is supplied to the third coil 1C. The amplitudes of the currents supplied to each coil may be the same, or currents with different amplitudes may be supplied to each coil. When the amplitudes of the currents supplied to each coil are the same, each current is a quadrature two-phase AC current.

[0019] 3 is a diagram showing a schematic diagram of the distribution of eddy currents generated in the workpiece 4 by the current flowing through the induction coil 1. The phase of the current flowing through the second coil 1B lags behind the phase of the current flowing through the first coil 1A by 90 degrees, and the phase of the current flowing through the third coil 1C lags behind the phase of the current flowing through the first coil 1A by 180 degrees. Therefore, if K is the amplitude of the current, f is the frequency, and t is time, the current flowing through the first coil 1A can be expressed as Ia = K cos(2πft), the current flowing through the second coil 1B can be expressed as Ib = K cos(2πft - π / 2), and the current flowing through the third coil 1C can be expressed as Ic = K cos(2πft - π).

[0020] When a current is supplied to the induction coil 1, a moving magnetic field is formed on the surface of the workpiece 4. Specifically, when currents of different phases are passed through the first coil 1A, the second coil 1B, and the third coil 1C, a moving magnetic field that advances in the width direction Y of the workpiece 4 is formed on the surface of the workpiece 4. The width direction Y of the workpiece 4 is a direction different from the transport direction X of the workpiece 4. In other words, the moving direction of the moving magnetic field is a direction different from the transport direction X of the workpiece 4. The width direction Y is also referred to as the "moving direction Y" or the "second direction."

[0021] In the example shown in FIG. 1, the direction of movement of the moving magnetic field is perpendicular to the transport direction X.

[0022] When the phase of the current in the first coil 1A is 0 degrees, the distribution of eddy currents shown by the solid line in Fig. 3 is generated in the workpiece 4. As time passes, when the phase of the current flowing in the first coil 1A becomes 90 degrees, the distribution of eddy currents generated in the workpiece 4 becomes the distribution shown by the dashed line in Fig. 3. In this way, the distribution of eddy currents becomes a traveling wave that moves in the width direction Y of the workpiece 4 over time.

[0023] The phase velocity of the moving magnetic field is faster than the transport speed of the workpiece 4. The transport speed of the workpiece 4 is the speed at which the transport device 3 transports the workpiece 4. Since the frequency f of the current supplied to each coil from the high-frequency power supply 2 is typically about 1 kHz to 20 MHz, the phase velocity of this traveling wave is sufficiently faster than the transport speed. Therefore, when the time average is taken, the distribution of the magnitude of the eddy current is uniform in the width direction Y, which is the direction of the traveling wave.

[0024] Fig. 4 is a diagram showing a schematic diagram of the time-averaged distribution of the heating power applied to the workpiece 4. As described above, the distribution of eddy currents becomes a traveling wave, which repeatedly moves at high speed in the width direction Y, thereby realizing a uniform time-averaged distribution of the heating power in the width direction Y, as shown by the solid line in Fig. 4. Furthermore, the distribution of the heating power can be changed by changing the phase difference between the first coil 1A and the second coil 1B.

[0025] The dashed line in Figure 4 shows a schematic diagram of the heating power distribution when the phase difference between the first coil 1A and the second coil 1B is 45 degrees. Compared to when the phase difference is 90 degrees, the heating power distribution is larger on the first coil 1A side and smaller on the third coil 1C side. On the other hand, when the phase difference between the first coil 1A and the second coil 1B is 135 degrees, the heating power distribution is smaller on the first coil 1A side and larger on the third coil 1C side.

[0026] In this way, the distribution of heating power can be controlled by controlling the phase of the current in the second coil 1B. The controller 6 controls the phase of the current in the second coil 1B based on information (e.g., temperature distribution) of the measurement area 7 measured by the temperature sensor 5, and controls the distribution of heating power, thereby maintaining the uniformity of the temperature distribution of the workpiece 4.

[0027] As described above, by passing currents of different phases through the first coil 1A, second coil 1B, and third coil 1C that make up the induction coil 1, traveling waves of a moving magnetic field and eddy current distribution that progress in the width direction Y of the workpiece 4 are formed, thereby making it possible to uniformly heat the workpiece 4 in the width direction Y. Furthermore, by having the controller 6 control the phase of the second coil 1B based on information about the workpiece 4 measured by the temperature sensor 5 (for example, temperature distribution), it is possible to maintain the uniformity of the temperature distribution of the workpiece 4.

[0028] As described above, according to the first embodiment, it is possible to provide the induction heating device 10 capable of heating the workpiece 4 so that the temperature distribution of the workpiece 4 is uniform.

[0029] Embodiment 2 Figure 5 is a cross-sectional view that schematically shows a cross section of an induction heating device 10 (specifically, the induction coil 1 and the workpiece 4) according to embodiment 2, which is perpendicular to the conveying direction X of the workpiece 4. In the example shown in Figure 5, the cross section perpendicular to the conveying direction X of the workpiece 4 is also a cross section along the moving direction Y of the moving magnetic field.

[0030] In the second embodiment, the arrangement of each coil of the induction coil 1 differs from that of the first embodiment. In the induction coil 1, the first coil 1A and the third coil 1C are adjacent to each other, and the second coil 1B is arranged so as to straddle a part of the first coil 1A and a part of the third coil 1C. The winding densities of these coils may be uniform or may differ.

[0031] The current supplied to the second coil 1B has a phase lead or lag of 90 degrees relative to the phase of the current supplied to the first coil 1A and the phase of the current supplied to the third coil 1C. For example, a current with a phase lag of 90 degrees relative to the phase of the first coil 1A is supplied to the second coil 1B, and a current with a phase lag of 180 degrees relative to the phase of the first coil 1A is supplied to the third coil 1C. The amplitudes of the currents supplied to each coil may be the same, or currents of different amplitudes may be supplied to each coil. When the amplitudes of the currents supplied to each coil are the same, the currents are quadrature two-phase AC currents.

[0032] Each coil of the induction coil 1 is positioned away from the workpiece 4. The distance from the first coil 1A to the workpiece 4, the distance from the second coil 1B to the workpiece 4, and the distance from the third coil 1C to the workpiece 4 are different from one another. In the example shown in FIG. 5 , in a cross section of the induction heating device 10 perpendicular to the conveyance direction X of the workpiece 4, the distance between the end of the induction coil 1 (first coil 1A in FIG. 5 ) and the workpiece 4 in the movement direction Y of the moving magnetic field is defined as d1, the distance between the center of the induction coil 1 (the boundary between the first coil 1A and the third coil 1C in FIG. 5 ) and the workpiece 4 in the movement direction Y is defined as d3, and the distance between the center of the induction coil 1 in the movement direction Y and the end of the induction coil 1 in the movement direction Y (second coil 1B in FIG. 5 ) and the workpiece 4 in the movement direction Y is defined as d2. The relationships between the distances d1, d2, and d3 satisfy d1 > d2 and d3 > d2.

[0033] In the example shown in Figure 5, distance d1 is the shortest distance between the end of the induction coil 1 (first coil 1A in Figure 5) and the workpiece 4, distance d2 is the shortest distance between the middle part of the induction coil 1 between the end and the workpiece 4 (second coil 1B in Figure 5), and distance d3 is the shortest distance between the center of the induction coil 1 (the boundary between the first coil 1A and third coil 1C in Figure 5) and the workpiece 4.

[0034] This weakens the eddy currents at the ends and center of the workpiece 4 where eddy currents flow easily, and strengthens the eddy currents in the middle area where eddy currents do not flow easily, thereby achieving a more uniform distribution of heating power.

[0035] 6 is a cross-sectional view schematically illustrating a cross section of an induction heating device 10 (specifically, the induction coil 1 and the workpiece 4) according to a third embodiment, which crosses orthogonally to the conveying direction X of the workpiece 4. In the example shown in Fig. 6, the cross section orthogonal to the conveying direction X of the workpiece 4 is also a cross section along the moving direction Y of the moving magnetic field.

[0036] In the third embodiment, the arrangement of each coil of the induction coil 1 differs from that of the first embodiment. The first coil 1A, second coil 1B, and third coil 1C are arranged in this order in the width direction Y of the workpiece 4. The first coil 1A is arranged so as to straddle a part of the second coil 1B and a part of the third coil 1C. The second coil 1B is arranged so as to straddle a part of the first coil 1A and a part of the third coil 1C. The third coil 1C is arranged so as to straddle a part of the first coil 1A and a part of the second coil 1B.

[0037] The current supplied to each coil of the induction coil 1 is a three-phase AC current. The current supplied to the second coil 1B has a phase lead or lag of 120 degrees relative to the phase of the current supplied to the first coil 1A and the phase of the current supplied to the third coil 1C. For example, a current with a phase lag of 120 degrees relative to the phase of the first coil 1A is supplied to the second coil 1B, and a current with a phase lead of 120 degrees relative to the phase of the first coil 1A is supplied to the third coil 1C. The amplitude of the current supplied to each coil may be the same, or currents of different amplitudes may be supplied to each coil. By supplying three-phase AC current to coils that are offset from each other in the width direction Y, a moving magnetic field that moves in the width direction Y is formed.

[0038] Each coil of the induction coil 1 is positioned away from the workpiece 4. In the example shown in Fig. 6 , in a cross section of the induction heating device 10 perpendicular to the conveying direction X of the workpiece 4, when the distance between the end of the induction coil 1 (first coil 1A and third coil 1C in Fig. 6 ) in the width direction Y and the workpiece 4 is d1, the distance between the center of the induction coil 1 (boundary between the first coil 1A and the third coil 1C in Fig. 6 ) in the width direction Y and the workpiece 4 is d3, and the distance between the center of the induction coil 1 in the width direction Y and the end of the induction coil 1 in the width direction Y and the workpiece 4 (second coil 1B in Fig. 6 ) is d2, the relationships among the distances d1, d2, and d3 satisfy d1 > d2 and d3 > d2.

[0039] In the example shown in Figure 6, distance d1 is the shortest distance between the end of the induction coil 1 (in Figure 6, the first coil 1A and the third coil 1C) and the workpiece 4, distance d2 is the shortest distance between the intermediate portion between the center of the induction coil 1 and the end of the induction coil 1 in the width direction Y (in Figure 6, the second coil 1B) and the workpiece 4, and distance d3 is the shortest distance between the center of the induction coil 1 (in Figure 6, the boundary between the first coil 1A and the third coil 1C) and the workpiece 4.

[0040] In a cross section of the induction heating device 10 perpendicular to the transport direction X of the workpiece 4, the winding density of the central part of the induction coil 1 in the movement direction Y of the moving magnetic field (in Figure 6, the part where the first coil 1A and the third coil 1C face each other) is smaller than the winding density of the intermediate part between the central part of the induction coil 1 in the movement direction Y of the moving magnetic field and the end part of the induction coil 1 in the movement direction Y of the moving magnetic field (in Figure 6, the second coil 1B).

[0041] 6, the winding density of the first coil 1A and the third coil 1C is smaller than the winding density of the second coil 1B. This weakens the eddy currents at the ends and center of the workpiece 4, where eddy currents tend to flow, and strengthens the eddy currents in the middle portion (second coil 1B in FIG. 6), where eddy currents tend not to flow, thereby achieving a more uniform distribution of heating power.

[0042] According to the third embodiment, a uniform distribution of heating power can be achieved by a moving magnetic field using three-phase AC.

[0043] 7 is a cross-sectional view schematically illustrating a cross section of an induction heating device 10 (specifically, the induction coil 1 and the workpiece 4) according to a fourth embodiment, the cross section being perpendicular to the conveying direction X of the workpiece 4. In the example shown in FIG. 7, the cross section perpendicular to the conveying direction X of the workpiece 4 is also a cross section along the moving direction Y of the moving magnetic field.

[0044] In the fourth embodiment, the arrangement of each coil of the induction coil 1 differs from that of the first embodiment. As in the above-described embodiments, the induction coil 1 has a first coil 1A, a second coil 1B, and a third coil 1C. In the moving direction Y of the moving magnetic field, the end of the first coil 1A and the end of the third coil 1C face each other. When viewed in a direction perpendicular to the moving direction Y of the moving magnetic field and the transport direction X, the center of the second coil 1B in the moving direction Y of the moving magnetic field is located midway between the center of the first coil 1A in the moving direction Y of the moving magnetic field and the center of the third coil 1C in the moving direction Y of the moving magnetic field.

[0045] 7, the first coil 1A and the third coil 1C are adjacent to each other in the movement direction Y of the moving magnetic field, and the second coil 1B is disposed on the opposite side of the workpiece 4 from the first coil 1A and the third coil 1C. The winding densities of these coils may be uniform or may be different.

[0046] The current supplied to the second coil 1B has a phase lead or lag of 90 degrees relative to the phase of the current supplied to the first coil 1A and the phase of the current supplied to the third coil 1C. For example, a current with a phase lag of 90 degrees relative to the phase of the first coil 1A is supplied to the second coil 1B, and a current with a phase lag of 180 degrees relative to the phase of the first coil 1A is supplied to the third coil 1C. The amplitudes of the currents supplied to each coil may be the same, or currents of different amplitudes may be supplied to each coil. When the amplitudes of the currents supplied to each coil are the same, the currents are quadrature two-phase AC currents.

[0047] In this way, a moving magnetic field is formed as in the first embodiment, the eddy current distribution becomes a traveling wave, and a uniform heating power distribution can be generated as a time average. Furthermore, since the second coil 1B does not have any intersections with other coils, the induction coil 1 can be easily positioned.

[0048] The features of the above-described embodiments can be combined with each other, and the components of each embodiment can be modified or omitted.

[0049] Various aspects of the present disclosure are summarized below as appendices. (Appendix 1) An induction heating device comprising: an induction coil including at least two coils; a high-frequency power supply supplying currents of different phases to each of the at least two coils; and a transport device for transporting an object to be heated, wherein when the current is supplied to the induction coil, a moving magnetic field is formed on the surface of the object to be heated, and the moving direction of the moving magnetic field is different from the transport direction of the object to be heated. (Appendix 2) The induction heating device according to Appendix 1, wherein the moving direction of the moving magnetic field is perpendicular to the transport direction. (Appendix 3) The induction heating device according to Appendix 1 or 2, wherein the phase speed of the moving magnetic field is faster than the transport speed of the object to be heated. (Appendix 4) The induction heating device according to any one of Appendixes 1 to 3, further comprising: a temperature sensor for measuring the temperature of the object to be heated; and a controller for acquiring a measurement result measured by the temperature sensor, wherein the controller controls the high-frequency power supply to change the phase of the current supplied to at least one of the at least two coils in accordance with the measurement result. (Supplementary Note 5) The induction heating device according to any one of Supplementary Notes 1 to 4, characterized in that, in a cross section of the induction heating device orthogonal to the transport direction, when a distance between an end of the induction coil in the movement direction and the object to be heated is d1, a distance between a center of the induction coil in the movement direction and the object to be heated is d3, and a distance between an intermediate portion between the center of the induction coil in the movement direction and the end of the induction coil in the movement direction and the object to be heated is d2, the following relationships are satisfied: d1 > d2 and d3 > d2. (Supplementary Note 6) The induction heating device according to any one of Supplementary Notes 1 to 5, characterized in that, in a cross section of the induction heating device orthogonal to the transport direction of the object to be heated, a winding density of a central portion of the induction coil in the movement direction is smaller than a winding density of a central portion between the central portion of the induction coil and the end of the induction coil in the movement direction.(Supplementary Note 7) The induction heating device according to any one of Supplementary Notes 1 to 6, characterized in that the induction coil has a first coil, a second coil, and a third coil, an end of the first coil and an end of the third coil face each other in the movement direction, and when viewed in a direction perpendicular to the movement direction and the conveying direction, a center of the second coil in the movement direction is located midway between a center of the first coil in the movement direction and a center of the third coil in the movement direction. (Supplementary Note 8) The induction heating device according to Supplementary Note 7, characterized in that the second coil is arranged on the opposite side of the object to be heated from the first coil and the third coil. (Supplementary Note 9) The induction heating device according to Supplementary Note 7 or 8, characterized in that the current supplied to the second coil has a 90-degree leading phase or a 90-degree lagging phase based on the phase of the current supplied to the first coil and the phase of the current supplied to the third coil. (Supplementary Note 10) The induction heating device according to Supplementary Note 7 or 8, wherein the current supplied to the second coil has a phase lead of 120 degrees or a phase lag of 120 degrees based on the phase of the current supplied to the first coil and the phase of the current supplied to the third coil.

[0050] REFERENCE SIGNS LIST 1 induction coil, 1A first coil, 1B second coil, 1C third coil, 2 high frequency power supply, 3 conveying device, 4 work (object to be heated), 5 temperature sensor, 6 controller, 7 measurement area, 10 induction heating device, S1 sensor signal, S2 control signal, X conveying direction, Y width direction (movement direction of moving magnetic field)

Claims

1. An induction heating device comprising: an induction coil including at least two coils; a high-frequency power supply that supplies currents having different phases to each of the at least two coils; and a conveying device that conveys an object to be heated, wherein when the current is supplied to the induction coil, a moving magnetic field is formed on the surface of the object to be heated, and a moving direction of the moving magnetic field is different from a conveying direction of the object to be heated.

2. The induction heating device according to claim 1, wherein the moving direction of the moving magnetic field is perpendicular to the conveying direction.

3. The induction heating device according to claim 1 or 2, wherein a phase velocity of the moving magnetic field is faster than a conveying velocity of the object to be heated.

4. The induction heating device according to any one of claims 1 to 3, further comprising: a temperature sensor that measures a temperature of the object to be heated; and a controller that acquires a measurement result measured by the temperature sensor, wherein the controller controls the high-frequency power supply to change a phase of a current supplied to at least one of the at least two coils according to the measurement result.

5. In a cross section of the induction heating device perpendicular to the conveying direction, when a distance between an end portion of the induction coil in the moving direction and the object to be heated is d1, a distance between a center of the induction coil in the moving direction and the object to be heated is d3, and a distance between an intermediate portion between the center of the induction coil in the moving direction and the end portion of the induction coil in the moving direction and the object to be heated is d2, the induction heating device according to any one of claims 1 to 4, characterized in that d1 > d2 and d3 > d2 are satisfied.

6. In a cross section of the induction heating device perpendicular to the conveying direction of the object to be heated, a winding density of a central portion of the induction coil in the moving direction is smaller than a winding density of an intermediate portion between the central portion of the induction coil and an end portion of the induction coil in the moving direction, the induction heating device according to any one of claims 1 to 5.

7. The induction coil has a first coil, a second coil, and a third coil. In the moving direction, the ends of the first coil and the ends of the third coil face each other. When viewed in a direction orthogonal to the moving direction and the conveying direction, the center of the second coil in the moving direction is located midway between the center of the first coil in the moving direction and the center of the third coil in the moving direction. The induction heating device according to any one of claims 1 to 6, characterized in that.

8. The induction heating device according to claim 7, characterized in that the second coil is arranged on the side opposite to the first coil and the third coil with respect to the object to be heated.

9. The induction heating device according to claim 7 or 8, characterized in that the current supplied to the second coil has a phase advanced by 90 degrees or a phase delayed by 90 degrees with reference to the phase of the current supplied to the first coil and the phase of the current supplied to the third coil.

10. The induction heating device according to claim 7 or 8, characterized in that the current supplied to the second coil has a phase advanced by 120 degrees or a phase delayed by 120 degrees with reference to the phase of the current supplied to the first coil and the phase of the current supplied to the third coil.

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