Coil assembly of LVDT sensor, LVDT sensor and preparation method of coil assembly of LVDT sensor

Abstract

The invention discloses a coil assembly of an LVDT sensor, the LVDT sensor and a preparation method of the coil assembly of the LVDT sensor, and relates to the technical field of sensors, the coil assembly of the LVDT sensor comprises a framework tube, a flexible long-strip-shaped circuit board, a plurality of first coils and a plurality of second coils, the multiple first coils and the multiple second coils are arranged on the flexible long-strip-shaped circuit board, the first coils and the second coils are arranged in a spaced mode, and the inner diameter of the first coils and the inner diameter of the second coils are both larger than the outer diameter of the framework pipe. The plurality of first coils and the plurality of second coils are arranged on the framework pipe in a sleeving manner, and the plurality of first coils and the plurality of second coils are coaxially arranged. Through the design, the linear precision and the mass production consistency of the coil assembly of the LVDT sensor are improved.

Description

Technical Field

[0001] This application relates to the field of sensor technology, and in particular to a coil assembly of an LVDT sensor, an LVDT sensor, and a method for fabricating the coil assembly of an LVDT sensor. Background Technology

[0002] As a high-precision linear displacement sensor, the LVDT sensor is widely used in many fields such as industrial automation control, aerospace, precision instrument manufacturing, and automotive industry due to its advantages such as simple structure, wide measurement range, high resolution, and strong stability. In these fields, it plays a crucial role in the accurate detection and control of displacement. Simply put, the LVDT sensor connects an excitation voltage to both ends of the primary coil and outputs an induced voltage in the secondary coil. When the magnetic core moves, the induced voltage changes, and this voltage change is used to represent the distance moved.

[0003] The primary and secondary coils are important components of LVDT sensors, but the linearity and mass production consistency of the coil assemblies in existing LVDT sensors are not high. Summary of the Invention

[0004] The purpose of this application is to provide a coil assembly for an LVDT sensor, an LVDT sensor, and a method for fabricating the coil assembly for an LVDT sensor, thereby improving the linear accuracy and mass production consistency of the coil assembly for the LVDT sensor.

[0005] This application discloses a coil assembly for an LVDT sensor. The coil assembly includes a skeleton tube, a flexible elongated circuit board, a plurality of first coils and a plurality of second coils. The plurality of first coils and the plurality of second coils are respectively disposed on the flexible elongated circuit board. The first coils and the second coils are spaced apart. The inner diameter of the first coils and the inner diameter of the second coils are both larger than the outer diameter of the skeleton tube. The plurality of first coils and the plurality of second coils are sleeved on the skeleton tube and are coaxially arranged.

[0006] Optionally, the flexible elongated circuit board includes an external portion, multiple carrier portions, and multiple connecting portions. The two ends of the connecting portions are respectively connected to two adjacent carrier portions. The external portion is connected to the carrier portion at the edge. Multiple first coils and multiple second coils are respectively disposed on multiple carrier portions, with the first coils located on the front side of the carrier portion and the second coils located on the back side of the carrier portion.

[0007] Optionally, the number of the first coil includes three, and the number of the second coil includes three.

[0008] Optionally, the skeleton tube is provided with an elongated opening that penetrates the inner wall and the outer wall of the skeleton tube, and the elongated opening extends from the upper end to the lower end of the skeleton tube.

[0009] Optionally, the height of the first coil is equal to the height of the second coil, and the length of the connecting portion is greater than or equal to the height of the first coil.

[0010] Optionally, the supporting part is circular in shape and has a circular through hole, the diameter of which is larger than the inner diameter of the skeleton tube; the width of the connecting part is less than 1 / 5 of the diameter of the supporting part.

[0011] Optionally, concave notches are provided on both sides of the connection between the connecting part and the bearing part.

[0012] This application also discloses an LVDT sensor, which includes an iron core and a coil assembly of the LVDT sensor, wherein the iron core is located inside the skeleton tube.

[0013] This application also discloses a method for fabricating a coil assembly of an LVDT sensor. The method for fabricating the coil assembly of an LVDT sensor includes the following steps:

[0014] S1: Provides a flexible elongated circuit board, a standard sleeve, and a bobbin tube;

[0015] S2: A winding machine is used to wind wire on the standard bushing to obtain multiple first coils and second coils;

[0016] S3: The first coil and the second coil are disposed on the flexible elongated circuit board, and the first coil and the second coil are disposed at intervals;

[0017] S4: Sequentially mount multiple first coils and multiple second coils onto the skeleton tube.

[0018] Compared to existing LVDT sensor coil assembly solutions, this application first sets multiple first coils and multiple second coils on a flexible elongated circuit board. Since the flexible elongated circuit board is flexible and foldable, the multiple first coils and multiple second coils can be fitted onto the skeleton tube by folding the flexible elongated circuit board. In this way, each first coil and each second coil can be formed by winding separately, without the need to set multiple slots on the skeleton tube, and will not be affected by the different parameters of different slots. This ensures the consistency of each first coil and each second coil, thereby improving the linear accuracy and mass production consistency of the LVDT sensor coil assembly. Attached Figure Description

[0019] The accompanying drawings, which form part of the specification, are used to provide a further understanding of the embodiments of this application and illustrate the implementation methods of this application, together with the textual description, to explain the principles of this application. Obviously, the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings:

[0020] Figure 1 This is a schematic diagram of a coil assembly of an LVDT sensor according to an embodiment of this application;

[0021] Figure 2 This is a schematic diagram of a flexible elongated circuit board according to an embodiment of this application;

[0022] Figure 3 This is a schematic diagram of an embodiment of the present application in which both the number of the first coil and the number of the second coil are three;

[0023] Figure 4 This is a schematic diagram of an embodiment of the present application in which the first coil and the second coil are both disposed on the same side of a flexible elongated circuit board;

[0024] Figure 5 This is a partial schematic diagram of a flexible elongated circuit board according to an embodiment of this application;

[0025] Figure 6 This is a schematic diagram of a skeleton tube according to an embodiment of this application;

[0026] Figure 7 This is a schematic diagram of an LVDT sensor according to an embodiment of this application;

[0027] Figure 8 This is a schematic diagram of a method for fabricating a coil assembly of an LVDT sensor according to an embodiment of this application;

[0028] Figure 9 This is a schematic diagram of a standard sleeve according to an embodiment of this application.

[0029] Among them, 10 is the LVDT sensor; 20 is the iron core; 30 is the coil assembly of the LVDT sensor; 100 is the skeleton tube; 110 is the elongated opening; 200 is the flexible elongated circuit board; 210 is the external part; 220 is the bearing part; 221 is the circular through hole; 230 is the connecting part; 231 is the concave notch; 310 is the first coil; 320 is the second coil; 400 is the retaining ring; and 500 is the standard sleeve. Detailed Implementation

[0030] It should be understood that the terminology, specific structural and functional details used herein are merely for describing particular embodiments and are representative. However, this application may be implemented in many alternative forms and should not be construed as being limited to the embodiments set forth herein.

[0031] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating relative importance or implying the number of technical features indicated. Therefore, unless otherwise stated, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature; "multiple" means two or more. The term "comprising" and any variations thereof mean non-exclusive inclusion, where one or more other features, integers, steps, operations, units, components, and / or combinations thereof may be present or added.

[0032] In addition, terms such as “center,” “horizontal,” “up,” “down,” “left,” “right,” “vertical,” “horizontal,” “top,” “bottom,” “inner,” and “outer” that indicate orientation or positional relationship are based on the orientation or relative positional relationship shown in the accompanying drawings. They are only for the purpose of simplifying the description of this application and do not indicate that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0033] Furthermore, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0034] The present application will now be described in detail with reference to the accompanying drawings and optional embodiments.

[0035] Figure 1This is a schematic diagram of a coil assembly of an LVDT sensor according to an embodiment of this application. Figure 2 This is a schematic diagram of a flexible elongated circuit board according to an embodiment of this application, as shown below. Figures 1-2 As shown, this application discloses a coil assembly 30 for an LVDT sensor. The coil assembly 30 includes a skeleton tube 100, a flexible elongated circuit board 200, a plurality of first coils 310 and a plurality of second coils 320. The plurality of first coils 310 and the plurality of second coils 320 are respectively disposed on the flexible elongated circuit board 200. It is understood that the flexible elongated circuit board 200 is provided with pads, and the plurality of first coils 310 and the plurality of second coils 320 are connected to the pads on the flexible elongated circuit board 200.

[0036] The first coil 310 and the second coil 320 are arranged at intervals, and the inner diameter of the first coil 310 and the inner diameter of the second coil 320 are both larger than the outer diameter of the skeleton tube 100.

[0037] A plurality of first coils 310 and a plurality of second coils 320 are sleeved on the skeleton tube 100, and the plurality of first coils 310 and the plurality of second coils 320 are coaxially arranged.

[0038] The first coil 310 can be a primary coil and the second coil 320 can be a secondary coil; alternatively, the first coil 310 can be a secondary coil and the second coil 320 can be a primary coil.

[0039] The existing LVDT sensor coil assembly is made by directly creating multiple slots on the skeleton tube and then winding the wire directly in the slots. In order to improve linearity, a multi-slot structure is made. Theoretically, the more slots there are, the higher the linearity can be adjusted. However, in order to keep the shape of the LVDT sensor coil assembly 30 from changing too much, the width of the slots must be narrowed when there are more slots, and the number of coil layers in each slot will be more. Due to manufacturing issues, the parameters of different slots will be inconsistent, so each slot will not be exactly the same. This makes the overall flatness of the coil assembly formed by winding the wire directly in the slot worse, resulting in poorer linearity and poorer consistency during mass production.

[0040] Compared to existing LVDT sensor coil assembly solutions, this application first sets multiple first coils 310 and multiple second coils 320 on a flexible elongated circuit board 200. Since the flexible elongated circuit board 200 is flexible and foldable, it can be folded to allow multiple first coils 310 and multiple second coils 320 to be fitted onto the skeleton tube 100. In this way, each first coil 310 and second coil 320 can be formed by winding separately, eliminating the need to set multiple slots on the skeleton tube 100 and avoiding the influence of different slot parameters. This ensures the consistency of each first coil 310 and second coil 320, thereby improving the linearity and mass production consistency of the LVDT sensor coil assembly 30.

[0041] Furthermore, the thinner thickness of the flexible elongated circuit board 200 allows for further miniaturization of the coil assembly 30 of the LVDT sensor.

[0042] For example, the number of first coils 310 includes five, and the number of second coils 320 includes five. The coil assembly 30 of the LVDT sensor may further include two retaining rings 400, which are respectively disposed at both ends of the skeleton tube 100. The two retaining rings 400 are used to limit the multiple first coils 310 and multiple second coils 320 sleeved on the skeleton tube 100 along the length of the skeleton tube 100, thereby preventing different gaps between the multiple first coils 310 and multiple second coils 320, thus improving the yield of the coil assembly 30 of the LVDT sensor.

[0043] For example, the flexible elongated circuit board 200 includes an external portion 210, a plurality of carrier portions 220 and a plurality of connecting portions 230. The two ends of the connecting portions 230 are respectively connected to two adjacent carrier portions 220. The external portion 210 is connected to the edge of the carrier portion 220. A plurality of first coils 310 and a plurality of second coils 320 are respectively disposed on the plurality of carrier portions 220, and the first coils 310 are located on the front side of the carrier portion 220, and the second coils 320 are located on the back side of the carrier portion 220.

[0044] Compared to a scheme in which all first coils 310 and all second coils 320 are disposed on the same side of the support portion 220, a scheme in which the first coils 310 are disposed on the front side of the support portion 220 and the second coils 320 are disposed on the back side of the support portion 220 can ensure a more uniform gap between any two adjacent first coils 310 and second coils 320.

[0045] Figure 3 This is a schematic diagram of an embodiment of the present application, showing that both the first coil and the second coil consist of three coils. Figure 3 As shown, for example, the number of the first coil 310 includes three, and the number of the second coil 320 includes three. That is, the number of the first coil 310 and the second coil 320 can be determined according to needs and is not limited here.

[0046] Figure 4 This is a schematic diagram of an embodiment of the present application, in which the first coil and the second coil are both disposed on the same side of a flexible elongated circuit board, as shown. Figure 4 As shown, the first coil 310 and the second coil 320 can also be disposed on the same side of the support portion 220. Compared with the scheme of disposing of the first coil 310 on the front side of the support portion 220 and the second coil 320 on the back side of the support portion 220, the scheme of disposing of the first coil 310 and the second coil 320 on the same side of the support portion 220 can reduce the assembly difficulty of the first coil 310, the second coil 320 and the flexible elongated circuit board 200.

[0047] Figure 5 This is a partial schematic diagram of a flexible elongated circuit board according to an embodiment of this application, combined with... Figure 1 , Figure 2 and 5 As shown, this application uses the example of the first coil 310 being disposed on the front side of the support portion 220 and the second coil 320 being disposed on the back side of the support portion 220 for explanation and description.

[0048] The height of the first coil 310 is equal to the height of the second coil 320, and the length of the connecting portion 230 is greater than or equal to the height of the first coil 310. Thus, when the first coil 310 and the second coil 320 are fitted onto the skeleton tube 100, the flexible elongated circuit board 200 can be folded firstly, so that the side of the second coil 320 facing away from the support portion 220 is attached to the side of the support portion 220 below the adjacent first coil 310 facing away from the first coil 310. This allows all the first coils 310 and the second coil 320 to be arranged in a stacked manner, making it easier to fit the first coils 310 and the second coil 320 onto the skeleton tube 100.

[0049] For example, to avoid squeezing the first coil 310 and the second coil 320 when assembling them onto the skeleton tube 100, the supporting part 220 of this application is circular in shape, and the supporting part 220 is provided with a circular through hole 221, the diameter of which is larger than the inner diameter of the skeleton tube 100; thus, when assembling the first coil 310 and the second coil 320 onto the skeleton tube 100, the supporting part 220 can be directly supported and pushed forward, thereby avoiding squeezing the first coil 310 and the second coil 320.

[0050] The width of the connecting part 230 is less than 1 / 5 of the diameter of the supporting part 220. This makes the width of the connecting part 230 smaller when the flexible elongated circuit board 200 is folded, so that the connecting part 230 does not occupy a lot of space, thereby facilitating the miniaturization of the coil assembly 30 of the LVDT sensor.

[0051] Furthermore, concave notches 231 are provided on both sides of the connection between the connecting part 230 and the supporting part 220. In this way, when folding the flexible elongated circuit board 200, a folding line can be formed along the concave notches 231 on both sides, so that the first coil 310 and the second coil 320 are in the same direction after folding, without being offset, thereby improving assembly efficiency.

[0052] Figure 6 This is a schematic diagram of a skeleton tube according to an embodiment of this application, as shown below. Figure 6 As shown, if the inner diameters of the first coil 310 and the second coil 320 are equal to the outer diameter of the skeleton tube 100, it is inconvenient to fit the first coil 310 and the second coil 320 onto the skeleton tube 100, thus increasing the assembly difficulty. If, in order to facilitate fitting the first coil 310 and the second coil 320 onto the skeleton tube 100, the inner diameters of the first coil 310 and the second coil 320 are set to be larger than the outer diameter of the skeleton tube 100, then the axes of the multiple first coils 310 and the multiple second coils 320 after assembly will not be on the same straight line, thus reducing the measurement accuracy.

[0053] Therefore, this application also provides an elongated opening 110 on the skeleton tube 100, the elongated opening 110 penetrating the inner wall and the outer wall of the skeleton tube 100, and the elongated opening 110 extending from the upper end of the skeleton tube 100 to the lower end of the skeleton tube 100.

[0054] In other words, the elongated opening 110 forms a through channel in the axial direction of the skeleton tube 100, and the through design of its inner and outer walls allows the skeleton tube 100 to produce a certain elastic deformation when subjected to external force.

[0055] By providing an elongated opening 110 on the skeleton tube 100, the skeleton tube 100 becomes elastic, allowing its outer diameter to be compressed and reduced and then restored. When the first coil 310 and the second coil 320 need to be fitted onto the skeleton tube 100, radial pressure can be applied to the skeleton tube 100, and the presence of the elongated opening 110 temporarily reduces the outer diameter of the skeleton tube 100, thus facilitating the coil fitting operation. After fitting, once the external force is removed, the skeleton tube 100 will return to its original shape due to its elasticity. At this time, its outer wall can fit tightly against the inner wall of the first coil 310 and the second coil 320, thereby ensuring that the axes of the multiple first coils 310 and second coils 320 remain on the same straight line. This effectively solves the problems of assembly difficulties and decreased measurement accuracy caused by the mismatch between the inner diameter of the first coil 310 and the second coil 320 and the outer diameter of the skeleton tube 100.

[0056] Figure 7 This is a schematic diagram of an LVDT sensor according to an embodiment of this application, as shown below. Figure 7 As shown, this application also discloses an LVDT sensor 10, which includes an iron core 20 and a coil assembly 30 of the LVDT sensor, wherein the iron core 20 is located inside the skeleton tube 100.

[0057] Figure 8 This is a schematic diagram illustrating a method for fabricating a coil assembly of an LVDT sensor according to an embodiment of this application. Figure 9 This is a schematic diagram of a standard sleeve according to an embodiment of this application, as shown below. Figure 8 and Figure 9 As shown, this application also discloses a method for fabricating a coil assembly 30 of an LVDT sensor, characterized in that the method for fabricating the coil assembly 30 of the LVDT sensor includes the following steps:

[0058] S1: Provides a flexible elongated circuit board, a standard sleeve, and a bobbin tube;

[0059] S2: A winding machine is used to wind wire on the standard bushing to obtain multiple first coils and second coils;

[0060] S3: The first coil and the second coil are disposed on the flexible elongated circuit board, and the first coil and the second coil are disposed at intervals;

[0061] S4: Sequentially mount multiple first coils and multiple second coils onto the skeleton tube.

[0062] Compared to existing LVDT sensor coil assemblies 30, which directly create multiple slots on the skeleton tube 100 and then wind wires directly within these slots, this application fabricates multiple first coils 310 and second coils 320 separately on a standard sleeve 500. These first coils 310 and second coils 320 are then mounted on a flexible elongated circuit board 200. Since the flexible elongated circuit board 200 is flexible and foldable, it can be folded to allow the multiple first coils 310 and second coils 320 to be fitted onto the skeleton tube 100. This allows each first coil 310 and second coil 320 to be individually wound, eliminating the need for slots on the skeleton tube 100 and preventing interference from different slot parameters. This ensures the consistency of each first coil 310 and second coil 320, thereby improving the linear accuracy and mass production consistency of the LVDT sensor coil assembly 30.

[0063] Furthermore, in order to avoid the axes of the multiple first coils 310 and the multiple second coils 320 being not on the same axis, this application may also provide an elongated opening 110 on the skeleton tube 100. The elongated opening 110 penetrates the inner wall and the outer wall of the skeleton tube 100, and the elongated opening 110 extends from the upper end of the skeleton tube 100 to the lower end of the skeleton tube 100.

[0064] The outer diameter of the skeleton tube 100 is made flexible, so that the outer diameter of the skeleton tube 100 can be reduced before the first coil 310 and the second coil 320 are fitted onto the skeleton tube 100, and the outer diameter of the skeleton tube 100 can be restored after the first coil 310 and the second coil 320 are fitted onto the skeleton tube 100. This allows the outer wall of the skeleton tube 100 to be tightly attached to the inner wall of the first coil 310 and the inner wall of the second coil 320, so that the axes of all the first coil 310 and all the second coil 320 are on the same line.

[0065] Accordingly, step S4: sequentially sleeves a plurality of first coils 310 and a plurality of second coils 320 onto the skeleton tube 100 further includes:

[0066] S41: Controls the shrinkage of the outer diameter of the skeleton tube;

[0067] S42: Sequentially sleeve multiple first coils and multiple second coils onto the skeleton tube;

[0068] S42: Control the outer diameter of the skeleton tube to restore, so that the outer wall of the skeleton tube and the inner wall of the first coil and the inner wall of the second coil are in contact.

[0069] For example, since the skeleton tube 100 is made of non-magnetic insulating material, the outer diameter of the skeleton tube 100 can be reduced by first controlling the width of the elongated opening 110 on the skeleton tube 100 to be smaller. For example, a clamp is used to apply radial pressure to the skeleton tube 100, and then a thin thread is used to wrap around the outer wall of the skeleton tube 100, so that the outer diameter of the skeleton tube 100 is kept in a reduced state. Then, after multiple first coils 310 and multiple second coils 320 are sleeved on the skeleton tube 100, the thin thread is removed, so that the outer diameter of the skeleton tube 100 is restored, so that the inner wall of the first coil 310 and the inner wall of the second coil 320 on the outer wall of the skeleton tube 100 are in contact.

[0070] It should be noted that the limitations on each step involved in this solution are not considered as limiting the order of steps, provided that they do not affect the implementation of the specific solution. The steps listed first can be executed first, later, or even simultaneously. As long as this solution can be implemented, it should be considered to fall within the scope of protection of this application.

[0071] It should be noted that the inventive concept of this application can form many embodiments, but due to the limited space of the application documents, they cannot all be listed. Therefore, without conflict, the embodiments described above or the technical features can be arbitrarily combined to form new embodiments. After the embodiments or technical features are combined, the original technical effect will be enhanced.

[0072] The above description, in conjunction with specific optional embodiments, provides a further detailed explanation of this application and should not be construed as limiting the specific implementation of this application to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of this application, and all such modifications or substitutions should be considered within the scope of protection of this application.

Claims

1. A coil assembly for an LVDT sensor, characterized in that, The coil assembly of the LVDT sensor includes a skeleton tube, a flexible elongated circuit board, a plurality of first coils and a plurality of second coils. The plurality of first coils and the plurality of second coils are respectively disposed on the flexible elongated circuit board. The first coils and the second coils are spaced apart. The inner diameter of the first coil and the inner diameter of the second coil are both larger than the outer diameter of the skeleton tube. The plurality of first coils and the plurality of second coils are sleeved on the skeleton tube and are coaxially arranged.

2. The coil assembly of the LVDT sensor according to claim 1, characterized in that, The flexible elongated circuit board includes an external portion, multiple carrier portions, and multiple connecting portions. The two ends of the connecting portions are respectively connected to two adjacent carrier portions. The external portion is connected to the carrier portion at the edge. Multiple first coils and multiple second coils are respectively disposed on multiple carrier portions, with the first coils located on the front of the carrier portion and the second coils located on the back of the carrier portion.

3. The coil assembly of the LVDT sensor according to claim 2, characterized in that, The number of the first coil includes three, and the number of the second coil includes three.

4. The coil assembly of the LVDT sensor according to claim 1, characterized in that, The skeleton tube has an elongated opening that penetrates both the inner and outer walls of the skeleton tube and extends from the upper end to the lower end of the skeleton tube.

5. The coil assembly of the LVDT sensor according to claim 2, characterized in that, The height of the first coil is equal to the height of the second coil, and the length of the connecting portion is greater than or equal to the height of the first coil.

6. The coil assembly of the LVDT sensor according to claim 5, characterized in that, The supporting part is circular in shape and has a circular through hole, the diameter of which is larger than the inner diameter of the skeleton tube; the width of the connecting part is less than 1 / 5 of the diameter of the supporting part.

7. The coil assembly of the LVDT sensor according to claim 6, characterized in that, Both sides of the connection between the connecting part and the bearing part are provided with concave notches.

8. An LVDT sensor, characterized in that, The LVDT sensor includes an iron core and a coil assembly of the LVDT sensor as described in any one of claims 1-7, wherein the iron core is located inside the skeleton tube.

9. A method for fabricating a coil assembly of an LVDT sensor, characterized in that, The method for fabricating the coil assembly of the LVDT sensor is used to fabricate the coil assembly of the LVDT sensor as described in any one of claims 1-7, and the method for fabricating the coil assembly of the LVDT sensor includes the following steps: S1: Provides a flexible elongated circuit board, a standard sleeve, and a bobbin tube; S2: A winding machine is used to wind wire on the standard bushing to obtain multiple first coils and second coils; S3: The first coil and the second coil are disposed on the flexible elongated circuit board, and the first coil and the second coil are disposed at intervals; S4: Sequentially mount multiple first coils and multiple second coils onto the skeleton tube.

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