Piezoelectric sensor wire

Abstract

This piezoelectric sensor wire comprises a core wire, an organic piezoelectric layer, and an electrode region. The core wire includes: steel wire; and a coating layer that is made of copper or a copper alloy and that coats the steel wire. The core wire has a diameter of 30-200 μm. The organic piezoelectric layer covers the outer peripheral surface of the core wire so as to contact the outer peripheral surface. The average thickness of the organic piezoelectric layer is 2.5-7.5 μm. The electrode region is in contact with the organic piezoelectric layer, and surrounds the core wire in a state of being separated from the core wire. The diameter of the piezoelectric sensor wire is 300 μm or less. The coating layer is in contact with the entirety of a first outer peripheral surface that is the outer peripheral surface of the steel wire.

Description

Piezoelectric sensor wire

[0001] This disclosure relates to a piezoelectric sensor wire. This application claims priority based on Japanese Application No. 2024-207615 filed on November 28, 2024, and incorporates all the descriptions described in the above application.

[0002] A piezoelectric sensor wire including a core wire, an organic piezoelectric layer covering the core wire, and a conductor layer covering the organic piezoelectric layer is known (see, for example, Patent Document 1 below). The core wire of the piezoelectric sensor wire described in Patent Document 1 includes a resin wire and a metal foil wound around the resin wire in a helical shape. Patent Document 1 describes that the thickness of the organic piezoelectric layer is 40 μm. Each of Patent Document 2 and Patent Document 3 describes that the thickness of the organic piezoelectric layer is 50 μm.

[0003] Japanese Unexamined Patent Application Publication No. 2020-043138, Japanese Unexamined Patent Application Publication No. 2021-170022, Japanese Unexamined Patent Application Publication No. 2019-67969

[0004] The piezoelectric sensor wire according to the present disclosure includes a core wire, an organic piezoelectric layer, and an electrode region. The core wire includes a steel wire and a coating layer made of copper or a copper alloy covering the steel wire. The wire diameter of the core wire is 30 μm or more and 200 μm or less. The organic piezoelectric layer covers the outer peripheral surface so as to contact the outer peripheral surface of the core wire. The average thickness of the organic piezoelectric layer is 2.5 μm or more and 7.5 μm or less. The electrode region contacts the organic piezoelectric layer and surrounds the core wire away from the core wire. The wire diameter of the piezoelectric sensor wire is 300 μm or less. The coating layer contacts the entire first outer peripheral surface which is the outer peripheral surface of the steel wire.

[0005] FIG. 1 is a cross-sectional view of an embodiment of a piezoelectric sensor wire. FIG. 2A is a cross-sectional view for explaining a first step in a method for manufacturing a piezoelectric sensor wire. FIG. 2B is a cross-sectional view for explaining a second step in a method for manufacturing a piezoelectric sensor wire. FIG. 2C is a cross-sectional view for explaining a third step in a method for manufacturing a piezoelectric sensor wire. FIG. 3A is a perspective view for explaining the third step in a method for manufacturing a piezoelectric sensor wire. FIG. 3B is a perspective view for explaining a fourth step in a method for manufacturing a piezoelectric sensor wire.

[0006] A piezoelectric sensor wire is required that has high detection accuracy and high response speed.

[0007] This disclosure provides a piezoelectric sensor wire with high detection accuracy and high response speed.

[0008] The piezoelectric sensor wire in accordance with this disclosure has high detection accuracy and high response speed.

[0009] (1) A piezoelectric sensor wire according to the present disclosure comprises a core wire, an organic piezoelectric layer, and an electrode region. The core wire includes a steel wire and a copper or copper alloy coating layer covering the steel wire. The diameter of the core wire is 30 μm or more and 200 μm or less. The organic piezoelectric layer covers the outer surface of the core wire so as to be in contact with the outer surface of the core wire. The average thickness of the organic piezoelectric layer is 2.5 μm or more and 7.5 μm or less. The electrode region is in contact with the organic piezoelectric layer and surrounds the core wire away from it. The diameter of the piezoelectric sensor wire is 300 μm or less. The coating layer is in contact with the first outer surface, which is the outer surface of the steel wire, over its entire area.

[0010] In the piezoelectric sensor wire described in Patent Document 1, the resin wire corresponds to the steel wire of this disclosure. The metal foil through which the current mainly flows in the core wire corresponds to the coating layer of this disclosure. In the piezoelectric sensor wire described in Patent Document 1, since the metal foil is wound around the resin wire, the metal foil does not contact the outer surface of the resin wire, and a gap may be formed between the metal foil and the outer surface. As a result, the detection accuracy of the piezoelectric sensor wire decreases due to this gap. In contrast, in the core wire of the piezoelectric sensor wire according to this disclosure, the coating layer through which the current mainly flows in the core wire is in contact with the first outer surface of the steel wire over its entire length, so the above-mentioned gap is not formed. Therefore, the piezoelectric sensor wire has high detection accuracy.

[0011] In the piezoelectric sensor wire described in Patent Document 1, the organic piezoelectric layer is thick at 40 μm, resulting in a low response speed. In contrast, the piezoelectric sensor wire according to this disclosure has a thin organic piezoelectric layer with an average thickness of 2.5 μm to 7.5 μm. Therefore, the piezoelectric sensor wire has a high response speed. As a result, the piezoelectric sensor wire according to this disclosure has high detection accuracy and high response speed.

[0012] (2) In the above (1), the piezoelectric sensor wire may further include an insulating layer that covers the electrode region. This configuration allows the electrode region to be insulated from the outside. Therefore, the detection accuracy of the piezoelectric sensor wire can be increased.

[0013] (3) In (2) above, the minimum thickness of the insulating layer may be 18 μm or more and 22 μm or less. This configuration makes it possible to achieve both high detection accuracy and miniaturization of the piezoelectric sensor wire.

[0014] (4) In any one of (1) to (3) above, the electrode region may include multiple electrode wires arranged in the circumferential direction. This configuration stabilizes the detection accuracy of the piezoelectric sensor wire.

[0015] (5) In (4) above, the electrode wire may be wound in a helical shape around the organic piezoelectric layer. Compared to a configuration in which the electrode wire is wound around the organic piezoelectric layer parallel to the axis of the core wire (i.e., a configuration in which the axis of the electrode wire and the axis of the core wire are parallel), this configuration reduces the contact area between the electrode wire and the organic piezoelectric layer, and increases the pressure on the organic piezoelectric layer relative to the apparent pressure. Therefore, the amount of power generated is improved in this configuration. In addition, this configuration allows for reliable contact of the conductor with an organic piezoelectric layer with low wettability, and is suitable for the manufacture of long piezoelectric sensor wires.

[0016] (6) In any one of (1) to (5) above, the coating layer may be a plating layer. With this configuration, the inner surface of the coating layer can be reliably in contact with the first outer surface over its entire area. Therefore, the detection accuracy of the piezoelectric sensor wire can be increased.

[0017] (7) In any one of (1) to (6) above, with respect to the vertical cross section, which is a cross section perpendicular to the longitudinal direction of the core wire, the area ratio of the coating layer on the core wire may be 30% or more and 60% or less. This configuration makes it possible to increase both the conductivity and mechanical strength of the core wire. As a result, this piezoelectric sensor wire has high detection accuracy and high mechanical strength.

[0018] (8) In any one of the above (1) to (7), the steel wire may be made of stainless steel. This configuration improves the corrosion resistance of the steel wire.

[0019] (9) In (8) above, the stainless steel may be austenitic stainless steel. Austenitic stainless steel is suitable for the steel wire of the piezoelectric sensor wire.

[0020] (10) In any one of the above (1) to (9), the steel wire may be made of carbon steel. This configuration can improve the mechanical strength of the steel wire.

[0021] [Details of an Embodiment of the Present Disclosure] An embodiment of the piezoelectric sensor wire according to the present disclosure will be described with reference to Figure 1. Figure 1 is a cross-sectional view of an embodiment of the piezoelectric sensor wire. In the following drawings, the same or corresponding parts are given the same reference numerals and their descriptions will not be repeated.

[0022] As shown in Figure 1, the piezoelectric sensor wire 1 has a circular shape in its vertical cross-section, which is a cross-section perpendicular to the longitudinal direction. The wire diameter R1 of the piezoelectric sensor wire 1 is 50 μm or more, and may be 100 μm or more. The wire diameter R1 of the piezoelectric sensor wire 1 is 300 μm or less, and may be 250 μm or less, 200 μm or less, or 150 μm or less. The piezoelectric sensor wire 1 comprises a core wire 2, an organic piezoelectric layer 3, an electrode region 4, and an insulating layer 5.

[0023] [Core wire 2] Core wire 2 has a circular shape in a vertical cross-section. Core wire 2 has an axis C1. Core wire 2 includes a steel wire 21 and a coating layer 22. Steel wire 21 has a circular shape in a vertical cross-section. Steel wire 21 has a first outer surface 211 which is the outer surface (circumferential surface). Steel wire 21 is made of stainless steel or carbon steel. Examples of stainless steel include austenitic stainless steel and ferritic stainless steel. Austenitic stainless steel is suitable for the steel wire 21 of the piezoelectric sensor wire 1.

[0024] The coating layer 22 covers the steel wire 21. The coating layer 22 has an annular shape in a vertical cross-section. The coating layer 22 is in contact with the first outer surface 211 over its entire surface. In other words, the coating layer 22 is in close contact with the first outer surface 211. The coating layer 22 has an inner surface 221 and a second outer surface 222. The inner surface 221 is in contact with the first outer surface 211 of the steel wire 21 over its entire surface. The second outer surface 222 is an outer surface located away from the first outer surface 211 of the steel wire 21. The coating layer 22 is made of copper or a copper alloy. Examples of copper alloys include copper-silver alloys. The coating layer 22 may contain unavoidable impurities. The coating layer 22 is a plating layer. With respect to the vertical cross-section, the area ratio of the coating layer 22 on the core wire 2 is 30% or more, and may be 40% or more. With respect to the vertical cross-section, the area ratio of the coating layer 22 on the core wire 2 is 60% or less, and may be 55% or less. The area ratio of the coating layer 22 on the core wire 2 approximates the conductivity of the core wire 2. That is, the area ratio of the coating layer 22 on the core wire 2 can be defined as %IACS (International Annealed Copper Standard). The wire diameter R2 of the core wire 2 is 30 μm or more, may be 40 μm or more, and may be 50 μm or more. The wire diameter R2 of the core wire 2 is 200 μm or less, may be 150 μm or less, may be 100 μm or less, and may be 70 μm or less.

[0025] [Organic piezoelectric layer 3] The organic piezoelectric layer 3 covers the outer surface of the core wire 2 so as to be in contact with the outer surface of the core wire 2. In other words, the organic piezoelectric layer 3 covers the second outer surface 222 of the coating layer 22 so as to be in contact with the second outer surface 222 of the coating layer 22. The organic piezoelectric layer 3 has a second inner surface 31 and a third outer surface 32. The second inner surface 31 is an inner surface that is in contact with the second outer surface 222 of the coating layer 22 over its entire length. The third outer surface 32 is an outer surface located away from the second outer surface 222. The third outer surface 32 has a shape that follows the outer shape of the electrode region 4. The third outer surface 32 has a plurality of recesses 321 and a plurality of connecting portions 322. In the circumferential direction, the recesses 321 and the connecting portions 322 are arranged alternately. The circumferential direction is the circular direction centered on the axis C1 of the core wire 2. Multiple recesses 321 are arranged at intervals in the circumferential direction. Each of the multiple recesses 321 is recessed toward the core wire 2. The connecting portion 322 connects adjacent recesses 321. In a vertical cross-section, the connecting portion 322 has an arc shape relative to the axis C1.

[0026] The average thickness t of the organic piezoelectric layer 3 (see Figure 2B) is 2.5 μm or more, may be 3 μm or more, or 4 μm or more. The average thickness t of the organic piezoelectric layer 3 (see Figure 2B) is 7.5 μm or less, may be 7 μm or less, or 6 μm or less. The ratio of the average thickness t of the organic piezoelectric layer 3 to the wire diameter R1 of the piezoelectric sensor wire 1 (t / R1) is 0.001 or more, may be 0.005 or more, or 0.008 or more. The ratio of the average thickness t of the organic piezoelectric layer 3 to the wire diameter R1 of the piezoelectric sensor wire 1 (t / R1) is 0.15 or less, may be 0.1 or less, or 0.08 or less. The organic piezoelectric layer 3 is relatively flexible and pliable. The average thickness t of the organic piezoelectric layer 3 is the average of the thickness that varies at multiple points in the organic piezoelectric layer 3 in the circumferential direction. The average thickness t of the organic piezoelectric layer 3 can also be determined by stripping the electrode region 4 (electrode wire 41), described later, and taking the average value of three points in the organic piezoelectric layer 3 that are equally spaced apart in the circumferential direction (Calculation Method A). The average thickness t of the organic piezoelectric layer 3 can be determined from the wire diameter R2 of the core wire 2 and the cross-sectional area of ​​the organic piezoelectric layer 3 (Calculation Method B). Examples of materials for the organic piezoelectric layer 3 include polyvinylidene fluoride, a copolymer of vinylidene fluoride and trifluoroethylene, a copolymer of vinylidene fluoride and tetrafluoroethylene, and silicone resin.

[0027] [Electrode Region 4] The electrode region 4 is in contact with the organic piezoelectric layer 3 and surrounds the core wire 2, away from the core wire 2. The electrode region 4 includes a plurality of electrode wires 41. Specifically, the electrode region 4 is composed of a plurality of electrode wires 41. The plurality of electrode wires 41 are arranged in the circumferential direction. In this disclosure, two circumferentially adjacent electrode wires 41 are located apart from each other. Although not shown, two circumferentially adjacent electrode wires 41 may be in contact with each other. A portion of each of the plurality of electrode wires 41 is embedded in the organic piezoelectric layer 3. The electrode wires 41 are wound around the organic piezoelectric layer 3 in a helical shape. The electrode wires 41 have a circular shape in a cross section perpendicular to the longitudinal direction of the electrode wire 41. Each of the plurality of electrode wires 41 also has an axis C2. The axis C2 is located away from the axis C1 of the core wire 2. The electrode wires 41 have a fourth outer surface 42. The fourth outer surface 42 is the outer surface (circumferential surface) of the electrode wire 41. The first portion 421, which is part of the fourth outer surface 42, is in contact with a part of the third outer surface 32. Although not shown, the electrode region 4 may be an electrode plate (electrode foil). The length (width) of the electrode plate in the circumferential direction is longer than the length (thickness) of the electrode plate in the radial direction. There may be a single electrode plate.

[0028] [Insulating Layer 5] As shown in Figure 1, the insulating layer 5 covers the electrode region 4. Specifically, the insulating layer 5 is in contact with the second portion 422. The second portion 422 is the portion of the fourth outer surface 42 of the electrode wire 41 that is not in contact with the third outer surface 32. The insulating layer 5 may also be in contact with the connecting portion 322. The insulating layer 5 has an outer surface (circumferential surface) 51. The outer surface 51 corresponds to the outer surface of the piezoelectric sensor wire 1. The minimum thickness L of the insulating layer 5 is 10 μm or more, and may be 18 μm or more. The minimum thickness L of the insulating layer 5 is 25 μm or less, and may be 22 μm or less. The minimum thickness L is the distance between the point in the second portion 422 closest to the outer surface 51 and the outer surface 51. Examples of materials for the insulating layer 5 include resin. Examples of resins include polyester resin, polyolefin resin, fluororesin, silicone resin, ethylene-vinyl acetate copolymer, and rubber. The insulating layer 5 may be a tape 52 (see Figure 3B) that is spirally wrapped around the organic piezoelectric layer 3 and the electrode region 4. The tape 52 is made of the resin described above.

[0029] [Method for Manufacturing the Piezoelectric Sensor Wire 1] The method for manufacturing the piezoelectric sensor wire 1 will be described with reference to Figures 2A to 3B. Figures 2A to 2C are cross-sectional views illustrating the method for manufacturing the piezoelectric sensor wire 1. Figure 2A shows the first step in the method for manufacturing the piezoelectric sensor wire. Figure 2B is a cross-sectional view illustrating the second step in the method for manufacturing the piezoelectric sensor wire. Figure 2C is a cross-sectional view illustrating the third step in the method for manufacturing the piezoelectric sensor wire. Figures 3A and 3B are perspective views illustrating the method for manufacturing the piezoelectric sensor wire 1. Figure 3A is a perspective view illustrating the third step in the method for manufacturing the piezoelectric sensor wire. Figure 3A corresponds to Figure 2C. Figure 3B is a perspective view illustrating the third step in the method for manufacturing the piezoelectric sensor wire. Figure 3B corresponds to Figure 1.

[0030] The method for manufacturing the piezoelectric sensor wire 1 comprises a first step, a second step, a third step, and a fourth step. In the method for manufacturing the piezoelectric sensor wire 1, the first step, the second step, the third step, and the fourth step are carried out in this order.

[0031] [First Step] As shown in Figure 2A, the first step involves preparing the core wire 2. In the first step, a coating layer 22 is formed on the first outer surface 211 of the steel wire 21. The coating layer 22 is formed by plating. The coating layer 22 is in contact with the entire first outer surface 211 of the steel wire 21.

[0032] [Second Step] As shown in Figure 2B, in the second step, an organic piezoelectric layer 3 is formed on the outer surface (second outer surface 222) of the core wire 2. The organic piezoelectric layer 3 is formed, for example, by applying and drying a coating composition containing the above-mentioned material. The organic piezoelectric layer 3 may also be formed by extruding the above-mentioned material (extrusion molding). The third outer surface 32 has a circular shape in a vertical cross-section. The third outer surface 32 shares an axis C1 (see Figure 1) with the first outer surface 211.

[0033] [Third Step] As shown in Figures 2C and 3A, the electrode region 4 is formed to be in contact with the organic piezoelectric layer 3. Specifically, a plurality of electrode wires 41 are wound spirally around the organic piezoelectric layer 3. At this time, the electrode wires 41 move from the outside of the organic piezoelectric layer 3 toward the core wire 2 (see Figure 2C). On the other hand, the electrode wires 41 are spaced apart from the core wire 2. In other words, the electrode wires 41 do not come into contact with the core wire 2. The third outer surface 32 of the organic piezoelectric layer 3 follows the external shape of the plurality of electrode wires 41 as they move. In other words, the third outer surface 32 of the organic piezoelectric layer 3 is deformed by the third step. A recess 321 is formed on the third outer surface 32. In addition, a portion of each of the plurality of electrode wires 41 is embedded in the organic piezoelectric layer 3. Therefore, as shown in Figures 2B and 2C, the average thickness t of the organic piezoelectric layer 3 corresponds to the thickness t of the organic piezoelectric layer 3 before the electrode wires 41 are embedded, that is, before the electrode wires 41 are embedded.

[0034] [Fourth Step] As shown in Figures 1 and 3B, in the fourth step, the insulating layer 5 is positioned to cover the electrode region 4. A resin tape 52 is wound spirally around the electrode region 4. The tape 52 is wound around the electrode region 4 such that parts of the tape 52 (the ends in the width direction) overlap. The piezoelectric sensor wire 1 is manufactured by this fourth step.

[0035] [How to use the piezoelectric sensor wire 1] The piezoelectric sensor wire 1 is used in pressure sensors and the like. For example, the piezoelectric sensor wire 1 is attached to an object. When the object deforms, an external force is applied to the piezoelectric sensor wire 1. This causes the organic piezoelectric layer 3 to deform. As a result, a potential difference is generated between the core wire 2 and the electrode region 4. The current based on the potential difference is detected by a detection device. The detection device is electrically connected to the core wire 2 or the electrode region 4. The detection device determines the external force corresponding to the detected current.

[0036] [Modification of piezoelectric sensor wire] The electrode wires 41 may be bundled parallel to the axis C1 of the core wire 2 with respect to the organic piezoelectric layer 3.

[0037] The embodiments disclosed herein should be understood to be illustrative in all respects and not restrictive in any way. The scope of the invention is defined by the claims and not by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. It should also be understood that at least one configuration described in the embodiments can be combined or modified in various ways as appropriate.

[0038] 1 Piezoelectric sensor wire, 2 Core wire, 3 Organic piezoelectric layer, 4 Electrode area, 5 Insulating layer, 21 Steel wire, 22 Coating layer, 31 Second inner surface (organic piezoelectric layer), 32 Third outer surface (organic piezoelectric layer), 41 Electrode wire, 42 Fourth outer surface (electrode wire), 51 Outer surface (insulating layer), 52 Tape, 211 First outer surface (steel wire), 221 Inner surface (coating layer), 222 Second outer surface (coating layer), 321 Recess, 322 Connecting part, 421 First part (fourth outer surface), 422 Second part (fourth outer surface), R1 Wire diameter (piezoelectric sensor wire), R2 Wire diameter (core wire), t Average thickness (organic piezoelectric layer).

Claims

1. A piezoelectric sensor wire comprising: a core wire having a diameter of 30 μm or more and 200 μm or less, including a steel wire and a copper or copper alloy coating layer covering the steel wire; an organic piezoelectric layer covering the outer surface of the core wire so as to be in contact with the outer surface of the core wire and having an average thickness of 2.5 μm or more and 7.5 μm or less; and an electrode region in contact with the organic piezoelectric layer and surrounding the core wire away from the core wire, wherein the diameter of the piezoelectric sensor wire is 300 μm or less, and the coating layer is in contact with the first outer surface, which is the outer surface of the steel wire, over its entire area.

2. The piezoelectric sensor wire according to claim 1, further comprising an insulating layer covering the electrode region.

3. The piezoelectric sensor wire according to claim 2, wherein the minimum thickness of the insulating layer is 18 μm or more and 22 μm or less.

4. The piezoelectric sensor wire according to any one of claims 1 to 3, wherein the electrode region includes a plurality of electrode wires arranged in the circumferential direction.

5. The piezoelectric sensor wire according to claim 4, wherein the electrode wire is wound in a helical shape around the organic piezoelectric layer.

6. The piezoelectric sensor wire according to any one of claims 1 to 5, wherein the coating layer is a plating layer.

7. With respect to a vertical cross section which is a cross section perpendicular to the longitudinal direction of the core wire, the area ratio of the coating layer on the core wire is 30% or more and 60% or less, according to any one of claims 1 to 6.

8. The piezoelectric sensor wire according to any one of claims 1 to 7, wherein the steel wire is made of stainless steel.

9. The piezoelectric sensor wire according to claim 8, wherein the stainless steel is austenitic stainless steel.

10. The piezoelectric sensor wire according to any one of claims 1 to 9, wherein the steel wire is made of carbon steel.

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