Induction heating device

Abstract

The present invention provides a transverse-type induction heating device with a simplified structure that suppresses overheating at both ends of the material being heated. [Solution] A transverse induction heating device 10 for induction heating a plate-shaped material to be heated S, wherein a plurality of coils 2 are stacked in the thickness direction D of the material to be heated S so as to face at least one side surface S1 of the material to be heated S, and the plurality of coils 2 are powered by an AC power supply 4, and at least one end 211 in the width direction of the plurality of coils 2 at least one coil 21 is positioned differently from the width direction ends 221 and 231 of the other coils 22 and 23 of the plurality of coils 2 when viewed from the one side surface S1 of the material to be heated S.

Description

Technical Field

[0001] The present invention relates to an induction heating device.

Background Art

[0002] Induction heating devices are generally classified into two types: solenoid type and transverse type. The solenoid type generates a magnetic flux in a direction perpendicular to the thickness of a thin plate that is the material to be heated, thereby generating eddy currents in the material to be heated for heating. Here, in the case of a solenoid type induction heating device, when the material to be heated is a thin plate of a non-magnetic material typified by austenitic stainless steel, it is difficult to generate eddy currents because the penetration depth is large. Therefore, it is difficult to heat such a material to be heated. Thus, when heating a thin plate of a non-magnetic material, a transverse type induction heating device as shown in Patent Document 1, in which a coil is installed so as to face one side or both sides of the thin plate, is used.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] In transverse induction heating devices, such as the one shown in Patent Document 1, the size of the coil ring can be changed to match the width of the thin plate, but there is a problem that both ends of the thin plate become overheated. For this reason, as shown in Patent Documents 2 and 3, there are devices that generate magnetic flux in opposite directions at both ends of the coil to cancel out the magnetic force and suppress overheating at both ends of the thin plate. However, in the case of a root-type coil like the one in Patent Document 2, due to the structure of the coil, there are places where the conductor is at an acute angle, raising concerns about heat concentration at those parts, and there are also problems that the method of manufacturing the coil is limited. Furthermore, in the case of a coil that combines an M shape and a V shape, as in Patent Document 3, there is a problem that the heating efficiency is poor when the width of the thin plate is small.

[0005] Therefore, the present invention aims to provide a transverse-type induction heating device with a simplified structure while suppressing overheating at both ends of the material to be heated. [Means for solving the problem]

[0006] The present invention relates to a transverse type induction heating device for induction heating a plate-shaped material to be heated, Multiple coils are stacked in the thickness direction of the material to be heated so as to face at least one side of the material to be heated. The aforementioned multiple coils are powered by an AC power source. At at least one end of the material to be heated in the width direction, the end of at least one coil of the plurality of coils in the width direction is configured to be positioned differently from the ends of the other coils of the plurality of coils when viewed from the one side surface of the material to be heated.

[0007] According to the above configuration, a simple structure is used in which multiple coils are stacked so as to oppose at least one side of the material to be heated, and the position of the widthwise end of at least one coil is different from the position of the widthwise end of the other coils, thereby suppressing overheating of the widthwise end of the material to be heated. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a transverse-type induction heating device with a simplified structure while suppressing overheating at both ends of the material to be heated. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic side view of an induction heating device according to an embodiment of the present invention. [Figure 2] This is a top view of multiple coils 2. [Figure 3] This is a side perspective view of multiple coils 2 and 3. [Figure 4] This is a schematic diagram showing multiple coils 2 adjusted in the width direction. [Figure 5] This is a top view of a case where multiple coils have a rectangular shape with rounded corners. [Figure 6] This is a schematic side view of an induction heating device according to a different embodiment of the present invention. [Modes for carrying out the invention]

[0010] (First Embodiment) Figure 1 is a schematic side view of an induction heating device 10 according to an embodiment of the present invention. As shown in Figure 1, the induction heating device 10 is a transverse type induction heating device that induces heating of a thin plate-shaped material S by high-frequency current, wherein a plurality of coils 2 are stacked in the thickness direction D of the material S so as to face one side surface S1 of the material S, and further, a plurality of coils 3 are stacked in the thickness direction D of the material S so as to face the other side surface S2 of the material S.

[0011] Figure 2 is a top view of multiple coils 2, and Figure 3 is a side perspective view of multiple coils 2 and 3. As shown in Figures 1 to 3, multiple coils 2 are powered by an AC power supply 4 with high-frequency current, and multiple coils 3 are powered by an AC power supply 5 with high-frequency current.

[0012] The multiple coils 2 are comprised of coils 21, 22, and 23, starting from the side closest to the material to be heated S. In this embodiment, the multiple coils 2 are constructed by stacking three coils 21, 22, and 23, but the number of stacked coils is not limited to three; any number of two or more is acceptable. Coils 21, 22, and 23 have a rounded rectangular shape with semicircles attached to both ends of the long side of the rectangle, and are similar in shape. As shown in Figure 3, the multiple coils 2 are wired together by electric wires 6, and when a high-frequency current is supplied by an AC power supply 4, the direction of the current flowing through coils 21, 22, and 23 is the same, and they are insulated by an insulating part A. Coils 21, 22, and 23 are connected by wiring, and this wiring is detachable. That is, by detaching the wiring, coils 21, 22, and 23 can be replaced.

[0013] In the multiple coils 2, the ends 211 of coil 21, 221 of coil 22, and 231 of coil 23 are configured to be positioned at different locations when viewed from one side surface S1 of the material S to be heated, at one end W1 in the width direction W of coil 21, coil 22, and coil 23, respectively. Here, the width direction W is the direction perpendicular to the transport direction of the material S to be heated. Specifically, end 221 protrudes outward in the width direction W relative to end 231, and end 211 protrudes outward in the width direction W relative to end 221. That is, the ends 211, 221, and 231 of coil 2 in the width direction W protrude outward in the width direction W as they approach one side surface S1 of the material S to be heated. Furthermore, the amount of protrusion T2 of end 221 protruding outward in the width direction W relative to end 231 is equal to the amount of protrusion T1 of end 211 protruding outward in the width direction W relative to end 221. Furthermore, the positions of the ends 211 of coil 21, 221 of coil 22, and 231 of coil 23 are adjustable in the width direction W. Therefore, as shown in Figure 4, the positions of the ends 211 of coil 21, 221 of coil 22, and 231 of coil 23 can be moved by any distance in the width direction W from the state shown in Figure 1. On the other hand, at the other end W2 of coil 2 in the width direction W, the ends 212 of coil 21, 222 of coil 22, and 232 of coil 23 are configured to be positioned so as to overlap or sufficiently exceed the other end W2 of the material to be heated, when viewed from one side surface S1 of the material to be heated S.

[0014] The distances (distances in the thickness direction D) of coils 21, 22, and 23 from one side surface S1 of the material S to be heated are adjustable. As shown in Figure 3, the distance X1 between coil 21 and surface S1 is greater than the distance X2 between coil 21 and coil 22, and the distance X3 between coil 22 and coil 23. Note that the distances X2 between coil 21 and coil 22, and the distances X3 between coil 22 and coil 23 are equal. Also, coils 21, 22, and 23 may be in contact vertically (X2=X3=0).

[0015] The multiple coils 3 are comprised of coils 31, 32, and 33, starting from the side closest to the material to be heated S. In this embodiment, the multiple coils 3 are constructed by stacking three coils, 31, 32, and 33, but the number of stacked coils is not limited to 3; any number of 2 or more is acceptable. Coils 31, 32, and 33 have a rounded rectangular shape with semicircles attached to both ends of the long side of the rectangle, and are similar in shape. As shown in Figure 3, the multiple coils 3 are wired together by electric wires 6, and when a high-frequency current is supplied by an AC power source 5, the direction of the current flowing through coils 31, 32, and 33 is the same, and they are insulated by an insulating part A. Coils 31, 32, and 33 are connected by wiring, and this wiring is detachable. That is, by detaching the wiring, coils 31, 32, and 33 can be replaced.

[0016] The plurality of coils 3 are generally point-symmetrical with the plurality of coils 2 about the center of the heated material S as the center of symmetry. Specifically, in the plurality of coils 3, at one end portion W1 in the width direction W of the heated material S, the end portion 311 in the width direction W of the coil 31, the end portion 321 in the width direction W of the coil 32, and the end portion 331 in the width direction W of the coil 33 are each configured to be disposed at a position that overlaps or a position that sufficiently exceeds the one end portion W1 of the heated material S when viewed from the other surface S2 of the heated material S. On the other hand, at the other end portion W2 in the width direction W of the heated material S, the end portion 312 in the width direction W of the coil 31, the end portion 322 in the width direction W of the coil 32, and the end portion 332 in the width direction W of the coil 33 are each configured to be disposed at different positions when viewed from the other surface S2 of the heated material S. More specifically, the end portion 322 protrudes outward in the width direction W with respect to the end portion 332, and the end portion 312 protrudes outward in the width direction W with respect to the end portion 322. That is, the end portions 312, 322, 332 in the width direction W of the coil 3 protrude outward in the width direction W as they approach the other surface S2 of the heated material S. Further, the protruding amount T4 by which the end portion 322 protrudes outward in the width direction W with respect to the end portion 332 is equal to the protruding amount T3 by which the end portion 312 protrudes outward in the width direction W with respect to the end portion 322. That is, the protruding amounts T1 to T4 that protrude outward in the width direction W of the coils 2 and 3 are equal to each other. Note that the positions of the end portion 312 of the coil 31, the end portion 322 of the coil 32, and the end portion 332 of the coil 33 are adjustable in the width direction W.

[0017] The distances (distances in the thickness direction D) of the coils 31, 32, 33 from the other surface S2 of the heated material S are configured to be changeable. As shown in FIG. 3, the distance X4 between the coil 31 and the surface S2 is larger than the distance X5 between the coil 31 and the coil 32 and the distance X6 between the coil 32 and the coil 3⑶. Note that the distance X5 between the coil 31 and the coil 32 and the distance X6 between the coil 32 and the coil 33 are equal to each other. That is, the distance X1 and the distance X4 are equal, and the distances X2, X3, X5, X6 are equal to each other. Also, the coils 31, 32, and 33 may be in contact with each other vertically (X5 = X6 = 0).

[0018] In each of the plurality of coils 2 and 3, the coils 21, 22, and 23 may be connected by a bus bar or a water-cooled cable, and the coils 31, 32, and 33 may also be connected by a bus bar or a water-cooled cable. The bus bar is a conductor that conducts a large-capacity current. By connecting between the plurality of coils with a bus bar, a large-capacity current can be efficiently supplied to each coil. Copper is mainly used for the bus bar.

[0019] According to the induction heating device 10 having the above configuration, the following effects can be exhibited.

[0020] (1) Since a plurality of coils 2 and 3 are laminated in the thickness direction D of the heated material S, and the end portions 211, 221, 231, 312, 322, and 332 in the width direction W of the plurality of coils 2 and 3 are respectively arranged at different positions when viewed from the surfaces S1 and S2 of the heated material S, by simply laminating the plurality of coils 2 and 3 and changing the positions of the end portions in the width direction W, overheating of the end portions W1 and W2 in the width direction W of the heated material S can be suppressed.

[0021] (2) Since the end portions 211, 221, 231, 312, 322, and 332 in the width direction W of the plurality of coils 2 and 3 protrude in the width direction W as they approach the surfaces S1 and S2 of the heated material S, concentration of magnetic flux at the end portions W1 and W2 in the width direction W of the heated material S can be suppressed, and overheating can be further suppressed.

[0022] (3) Since the positions of the end portions 211, 221, 231, 312, 322, and 332 in the width direction W of each of the plurality of coils 2 and 3 are configured to be changeable, by adjusting the positions of the end portions 211, 221, 231, 312, 322, and 332 in the width direction W of the coils 2 and 3, the heating amount of the end portions W1 and W2 in the width direction W of the heated material S can be adjusted.

[0023] (4) Since the wiring of the multiple coils 2 and 3 can be detached, the overall configuration of the coil can be freely adjusted by replacing them with coils of different windings and shapes. In addition, since the coils can be easily removed individually, the coils can be easily disassembled and cleaned.

[0024] (5) In two adjacent coils, the amount of protrusion in the width direction of one coil closer to the surfaces S1 and S2 of the material to be heated S is equal to that of the other coil further away from the surfaces S1 and S2 of the material to be heated S. This makes it possible to make the magnetic flux at the end of the material to be heated S in the width direction W more uniform.

[0025] (6) Multiple coils 2 and 3 are provided as a pair in the thickness direction D of the material to be heated S, sandwiching the material to be heated S, and each of the multiple coils 2 and 3 is displaceable in the width direction and the vertical direction, so that the position of each of the multiple coils 2 and 3 provided to sandwich the material to be heated S can be adjusted according to the width direction length of the material to be heated S and its temperature distribution.

[0026] In this embodiment, multiple stacked coils 2 are arranged facing the surface S1 of the material to be heated S, and multiple stacked coils 3 are arranged facing the surface S2 of the material to be heated S. However, it is not necessary for multiple stacked coils to be arranged facing each of the surfaces S1 and S2 of the material to be heated S; it is sufficient for multiple stacked coils to be arranged facing at least one of the surfaces S1 and S2 of the material to be heated S.

[0027] In this embodiment, each coil 2 and 3 has the shape of a rounded rectangle with semicircles attached to both ends of the longer side of the rectangle when viewed from the surfaces S1 and S2 of the material to be heated. However, as shown in Figure 5, coils 2 and 3 may have a rectangular shape with rounded corners, or they may have a circular or elliptical shape.

[0028] In this embodiment, multiple coils 2 are supplied with high-frequency current by an AC power supply 4, and multiple coils 3 are supplied with high-frequency current by an AC power supply 5. However, multiple coils 2 and multiple coils 3 may be supplied with high-frequency current from a single AC power supply, and multiple coils 2 may be supplied with high-frequency current by different AC power supplies, and multiple coils 3 may be supplied with high-frequency current by different AC power supplies.

[0029] In this embodiment, the end 211 in the width direction W of coil 21, the end 221 in the width direction W of coil 22, and the end 231 in the width direction W of coil 23 are all positioned differently from the ends in the width direction W of the other coils. However, in the present invention, it is sufficient that at least one coil, for example, the end 211 of coil 21, is positioned differently from the end 221 of coil 22 and the end 231 of coil 23. For example, the ends 221 and 231 may be positioned at the same location (T2=0).

[0030] In this embodiment, the end 312 in the width direction W of coil 31, the end 322 in the width direction W of coil 32, and the end 332 in the width direction W of coil 33 are all positioned differently from the ends in the width direction W of the other coils. However, in the present invention, it is sufficient that at least one coil, for example, the end 312 of coil 31, is positioned differently from the end 322 of coil 32 and the end 332 of coil 33. For example, the ends 322 and 332 may be positioned at the same location.

[0031] In this embodiment, the amount of protrusion T2 of end 221 protruding outward in the width direction W relative to end 231 is equal to the amount of protrusion T1 of end 211 protruding outward in the width direction W relative to end 221. However, since the positions of end 211 of coil 21, end 221 of coil 22, and end 231 of coil 23 are adjustable in the width direction W, the protrusion amounts T1 and T2 can be set arbitrarily. For example, the amount of protrusion may increase as it moves away from one side surface S1 of the material to be heated, that is, the amount of protrusion T1 may be set to be smaller than the amount of protrusion T2.

[0032] In this embodiment, the amount of protrusion T4 of end 322 protruding outward in the width direction W relative to end 332 is equal to the amount of protrusion T3 of end 312 protruding outward in the width direction W relative to end 322. However, since the positions of end 312 of coil 31, end 322 of coil 32, and end 332 of coil 33 are adjustable in the width direction W, the protrusion amounts T3 and T4 can be set arbitrarily. For example, the amount of protrusion may increase as it moves away from the other side surface S2 of the material to be heated, that is, the protrusion amount T3 may be set to be smaller than the protrusion amount T4.

[0033] In this embodiment, the ends 211, 221, and 231 of coil 2 in the width direction W protrude outward in the width direction W as they approach one side surface S1 of the material to be heated S, and the ends 312, 322, and 332 of coil 3 in the width direction W protrude outward in the width direction W as they approach the other side surface S2 of the material to be heated S. However, as shown in Figure 6, the ends 211, 221, and 231 of coil 2 in the width direction W may protrude outward in the width direction W as they move away from one side surface S1 of the material to be heated S, and the ends 312, 322, and 332 of coil 3 in the width direction W may protrude outward in the width direction W as they move away from the other side surface S2 of the material to be heated S. By configuring in this way, the concentration of magnetic flux at the ends W1 and W2 of the material to be heated S in the width direction W can be suppressed, and overheating can be further suppressed.

[0034] In this embodiment, the distance X1 between coil 21 and surface S1 is larger than the distance X2 between coil 21 and coil 22 and the distance X3 between coil 22 and coil 23, and is equal to the distance X2 between coil 21 and coil 22 and the distance X3 between coil 22 and coil 23. However, since the distances of coils 21, 22, and 23 from one side surface S1 of the material to be heated S are configured to be changeable, distances X1 to X3 can be set arbitrarily, and the distances may decrease as they move away from one side surface S1 of the material to be heated S, that is, distance X1 may be set to be larger than distance X2 and distance X2 to be larger than distance X3, or the distances may increase as they move away from one side surface S1 of the material to be heated S, that is, distance X1 may be set to be smaller than distance X2 and distance X2 to be smaller than distance X3.

[0035] In this embodiment, the distance X4 between coil 31 and surface S2 is larger than the distance X5 between coil 31 and coil 32 and the distance X6 between coil 32 and coil 33, and is equal to the distance X5 between coil 31 and coil 32 and the distance X6 between coil 32 and coil 33. However, since the distances of coils 31, 32, and 33 from the other side surface S2 of the material to be heated S are configured to be changeable, distances X4 to X6 can be set arbitrarily, and the distance may decrease as it moves away from the other side surface S2 of the material to be heated S, that is, distance X4 may be set to be larger than distance X5 and distance X5 to be larger than distance X6, or the distance may increase as it moves away from the other side surface S2 of the material to be heated S, that is, distance X4 may be set to be smaller than distance X5 and distance X5 to be smaller than distance X6.

[0036] The present invention and its embodiments are summarized as follows.

[0037] (1) One embodiment of the present invention is a transverse type induction heating device for induction heating a plate-shaped material to be heated, Multiple coils are stacked in the thickness direction of the material to be heated so as to face at least one side of the material to be heated. The aforementioned multiple coils are powered by an AC power source. At at least one end of the material to be heated in the width direction, the end of at least one coil of the plurality of coils in the width direction is configured to be positioned differently from the ends of the other coils of the plurality of coils when viewed from the one side surface of the material to be heated.

[0038] According to the above configuration (1), a simple structure is used in which multiple coils are stacked so as to face at least one side of the material to be heated, and the position of the widthwise end of at least one coil is different from the position of the widthwise end of the other coils, thereby suppressing overheating of the widthwise end of the material to be heated.

[0039] (2) In the above configuration (1), the ends of the plurality of coils in the width direction protrude in the width direction as they approach the one side surface of the material to be heated.

[0040] According to the above configuration (2), by making the ends of the coil in the width direction protrude as it approaches the surface of the material to be heated, the magnetic flux is gradually weakened towards the edge of the material to be heated, thereby suppressing the concentration of magnetic flux at the ends in the width direction of the material to be heated and further suppressing overheating.

[0041] (3) In the above configuration (1), the ends of the plurality of coils in the width direction protrude in the width direction as they move away from the one side surface of the material to be heated.

[0042] According to the above configuration (3), by causing the ends of the coil in the width direction to protrude as they move away from the surface of the material to be heated, the magnetic flux is gradually weakened towards the end of the material to be heated. This suppresses the concentration of magnetic flux at the ends of the material in the width direction, and further suppresses overheating.

[0043] (4) In any one of the above configurations (1) to (3), the position of each of the ends of the plurality of coils in the width direction is configured to be changeable.

[0044] According to the above configuration (4), the amount of heating at the ends of the material to be heated in the width direction can be adjusted by adjusting the position of the ends of the coil in the width direction.

[0045] (5) In any one of the above configurations (1) to (4), the wiring of the plurality of coils is detachable.

[0046] According to the above configuration (5), the overall configuration of the coil can be freely adjusted by replacing it with a coil of a different number of turns or shape. In addition, since the coils can be easily removed individually, the coils can be easily disassembled and cleaned.

[0047] (6) In the above configuration (2), in any two adjacent coils, the amount of protrusion in the width direction of one coil that is closer to the one side surface of the material to be heated is equal to that of the other coil that is further away from the one side surface of the material to be heated.

[0048] According to the above configuration (6), by making the amount by which the coil closer to the surface of the material to be heated protrudes in the width direction equal to that of the coil further away from the adjacent surface of the material to be heated, the magnetic flux is proportionally and gradually weakened toward the edge of the material to be heated, thereby making the magnetic flux at the edges in the width direction of the material to be heated more uniform.

[0049] (7) In the above configuration (3), in any two adjacent coils, the amount of protrusion in the width direction of the other coil, which is farther from the one side surface of the material to be heated, is equal to the amount of protrusion of the other coil, which is farther from the one side surface of the material to be heated, relative to the one coil, which is closer to the one side surface of the material to be heated.

[0050] According to the above configuration (7), by making the amount by which the coil furthest from the surface of the material to be heated protrudes in the width direction equal to that of the adjacent coil closer to the surface of the material to be heated, the magnetic flux is proportionally and gradually weakened toward the edge of the material to be heated, thereby making the magnetic flux at the edges in the width direction of the material to be heated more uniform.

[0051] (8) In any one of the above configurations (1) to (7), the plurality of coils are provided as a set in the thickness direction of the material to be heated, sandwiching the material to be heated. Each of the aforementioned coils is displaceable in the width direction and the vertical direction.

[0052] According to the above configuration (8), the heating effect occurs on both sides of the material to be heated, resulting in a faster temperature rise. In addition, the positions of the set of multiple coils, which are arranged to sandwich the material to be heated, can be adjusted according to the width of the material to be heated and its temperature distribution.

[0053] Various modifications and alterations can be made without departing from the spirit and scope of the invention as described in the claims. [Industrial applicability]

[0054] This invention provides a transverse-type induction heating device with a simplified structure that suppresses overheating at both ends of the material being heated, thus having great industrial value. [Explanation of Symbols]

[0055] 10 Induction heating device 2 coils 21 coils 211 End 212 End 22 coils 221 End 222 End 23 coils 231 End 232 End 3 coils 31 coils 311 End 312 End 32 coils 321 End 322 End 33 coils 331 End 332 End 4 AC power supply 5 AC power supply 6 electric wire A Insulation part S Heated material S1 One side S2 Other side T1 Overhang amount T2 Overhang amount T3 Overhang amount T4 Overhang amount X1~X6 distance W (width direction) W1 End in the width direction W2 End in the width direction D thickness direction

Claims

1. A transverse-type induction heating device for inductively heating a plate-shaped material to be heated, Multiple coils are stacked in the thickness direction of the material to be heated so as to face at least one side of the material to be heated. The aforementioned multiple coils are powered by an AC power source. At one end of the material to be heated in the width direction, the end of at least one coil of the plurality of coils in the width direction is configured to be positioned differently from the ends of the other coils of the plurality of coils when viewed from the one side surface of the material to be heated. An induction heating device in which, at the other end of the material to be heated in the width direction, the ends of the plurality of coils in the width direction are arranged in a position that overlaps when viewed from the one side surface of the material to be heated.

2. The induction heating apparatus according to claim 1, wherein at one end of the material to be heated in the width direction, the ends of the plurality of coils in the width direction protrude in the width direction as they approach the surface of the material to be heated on that one side.

3. The induction heating device according to claim 1, wherein at one end of the material to be heated in the width direction, the ends of the plurality of coils in the width direction protrude in the width direction as they move away from the surface of the material to be heated on that one side.

4. The induction heating apparatus according to claim 1, wherein the plurality of coils are wired to be detachable.

5. The induction heating apparatus according to claim 2, wherein in any two adjacent coils, the amount of protrusion in the width direction of one coil closer to the one side surface of the material to be heated is equal to that of the other coil further away from the one side surface of the material to be heated.

6. The induction heating apparatus according to claim 3, wherein in any two adjacent coils, the amount of protrusion in the width direction of the other coil, which is farther from the one side surface of the material to be heated, is equal to the amount of protrusion in the width direction of the other coil, which is farther from the one side surface of the material to be heated, relative to the one coil, which is closer to the one side surface of the material to be heated.

7. The aforementioned plurality of coils are arranged as a set in the thickness direction of the material to be heated, sandwiching the material to be heated. The induction heating apparatus according to any one of claims 1 to 6, wherein each of the plurality of coils is displaceable in the vertical direction.

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