Pressure-sensitive sensor

Abstract

A pressure-sensitive sensor, includes a hollow tubular member including an elastic insulating material; and n electrode wires (n being an integer of not less than 3) arranged away from one another and held inside the tubular member, wherein when an external pressure is applied to the tubular member, the tubular member elastically deforms such that at least two of the n electrode wires contact with each other, and wherein the n electrode wires extend linearly and parallel to a central axis of the tubular member.

Claims

1. A pressure-sensitive sensor, comprising: a hollow tubular member comprising an elastic insulating material; and n electrode wires (n being an integer of not less than 3) arranged away from one another and held inside the tubular member, wherein when an external pressure is applied to the tubular member, the tubular member elastically deforms such that at least two of the n electrode wires contact with each other, wherein the n electrode wires extend linearly and parallel to a central axis of the tubular member, and wherein in a transversal cross-sectional view; each surface connecting between adjacent electrode wires comprises an arc shape.

2. The pressure-sensitive sensor according to claim 1, wherein each of the n electrode wires is partially embedded in the hollow tubular member.

3. The pressure-sensitive sensor according to claim 2, wherein the n electrode wires are free of damage due to scraping.

4. The pressure-sensitive sensor according to claim 2, wherein, in the transversal cross-sectional view, said each surface connecting between the adjacent electrode wires comprises a continuous curved shape.

5. The pressure-sensitive sensor according to claim 2, wherein each of the n electrode wires is partially embedded in the tubular member by an internal pressure applied to an internal space of the tubular member.

6. The pressure-sensitive sensor according to claim 5, wherein the internal pressure comprises a compressed gas injected into an internal space of the tubular member.

7. The pressure-sensitive sensor according to claim 2, wherein each of the n electrode wires is fused to an inner surface of the tubular member by an internal pressure applied to an internal space of the tubular member.

8. The pressure-sensitive sensor according to claim 7, wherein the internal pressure comprises a compressed gas injected into an internal space of the tubular member.

9. The pressure-sensitive sensor according to claim 2, wherein the tubular member deforms such that the at least two of the n electrode wires contact with each other, when external pressure is applied to the tubular member from any direction.

10. The pressure-sensitive sensor according to claim 2, wherein the elastic insulating material comprises a rubber-based composition obtained by cross-linking ethylene-propylene-diene copolymer mixed with a conductive filler.

11. The pressure-sensitive sensor according to claim 2, wherein the elastic insulating material comprises a ene-based thermoplastic elastomer composition.

12. The pressure-sensitive sensor according to claim 1, wherein the n electrode wires are free of damage due to scraping.

13. The pressure-sensitive sensor according to claim 1, wherein, in the transversal cross-sectional view, said each surface connecting between the adjacent electrode wires comprises a continuous curved shape.

14. The pressure-sensitive sensor according to claim 1, wherein each of the n electrode wires is partially embedded in the tubular member by an internal pressure applied to an internal space of the tubular member.

15. The pressure-sensitive sensor according to claim 14, wherein the internal pressure comprises a compressed gas injected into an internal space of the tubular member.

16. The pressure-sensitive sensor according to claim 1, wherein each of the n electrode wires is fused to an inner surface of the tubular member by an internal pressure applied to an internal space of the tubular member.

17. The pressure-sensitive sensor according to claim 16, wherein the internal pressure comprises a compressed gas injected into an internal space of the tubular member.

18. The pressure-sensitive sensor according to claim 1, wherein the tubular member deforms such that the at least two of the n electrode wires contact with each other, when external pressure is applied to the tubular member from any direction.

19. The pressure-sensitive sensor according to claim 1, wherein the elastic insulating material comprises a rubber-based composition obtained by cross-linking ethylene-propylene-diene copolymer mixed with a conductive filler.

20. The pressure-sensitive sensor according to claim 1, wherein the elastic insulating material comprises a styrene-based thermoplastic elastomer composition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Next, the present invention will be explained in more detail in conjunction with appended drawings, wherein:

(2) FIG. 1 is a cross sectional view showing a pressure-sensitive sensor in the first embodiment of the present invention;

(3) FIGS. 2A and 2B are explanatory diagrams illustrating the pressure-sensitive sensor deformed when pressure is applied in different directions from the outside of a tubular member;

(4) FIG. 3 is a cross sectional view showing a pressure-sensitive sensor in the second embodiment of the invention;

(5) FIG. 4 is a cross sectional view showing a pressure-sensitive sensor in the third embodiment of the invention;

(6) FIG. 5 is a cross sectional view showing a pressure-sensitive sensor in the fourth embodiment of the invention; and

(7) FIG. 6 is a cross section showing an extruder used to manufacture the pressure-sensitive sensor of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

(8) The first embodiment of the invention will be described below in reference to FIGS. 1 to 2B. Note that, the embodiments described below are only shown as preferred examples for implementing the invention. Although some part of the embodiments specifically illustrates various technically preferable matters, the technical scope of the invention is not limited to such specific aspects.

(9) FIG. 1 is a cross sectional view showing a pressure-sensitive sensor in the first embodiment of the invention. A pressure-sensitive sensor 1 is provided with a hollow tubular member 2 formed of an elastic insulating material having elasticity as well as insulating properties, and four electrode wires 3 arranged at a distance from one another and held inside the tubular member 2. Each electrode wire 3 is formed by covering a metal wire 4 with an elastic conductor 5, and the electrode wires 3 are separated by a space 6. The pressure-sensitive sensor 1 elastically deforms when the tubular member 2 is subjected to an external pressure, and at least any two of the four electrode wires 3 come into contact with each other (short-circuited). FIG. 1 shows the pressure-sensitive sensor 1 not under external pressure when viewed in a cross section orthogonal to the central axis of the tubular member 2.

(10) FIGS. 2A and 2B show the pressure-sensitive sensor 1 which is deformed due to pressure applied from the outside of the tubular member 2. In each of FIGS. 2A and 2B, a direction of pressure applied to the pressure-sensitive sensor 1 is indicated by an arrow. FIG. 2A shows the pressure-sensitive sensor 1 receiving pressure from above. In this state, a pair of electrode wires located on a diagonal comes into contact with each other (short-circuited). FIG. 2B shows the pressure-sensitive sensor 1 receiving pressure from right obliquely above (a direction inclined toward the right at 45° with respect to the vertical direction). In this state, two pairs of adjacent electrode wires come into contact each other (short-circuited).

(11) As such, in the pressure-sensitive sensor 1, at least any two of the four electrode wires 3 come into contact with each other (short-circuited) under pressure in any directions.

(12) Configuration of the Pressure-Sensitive Sensor

(13) The tubular member 2 has a circular shape when viewed in a cross section orthogonal to the central axis, and a length of the tubular member 2 in a longitudinal direction (a direction parallel to the central axis) is not limited and is, e.g., from 1 to several tens meters depending on the intended use. The outer diameter of the tubular member 2 is, e.g., 4 mm. The tubular member 2 can be formed of a material which has small compression set and is excellent in flexibility, cold resistance, water resistance, chemical resistance and weather resistance, etc., and it is possible to favorably use, e.g., a rubber-based composition obtained by cross-linking an ethylene-propylene-diene copolymer, or a styrene-based thermoplastic elastomer composition not requiring a cross-linking process.

(14) The electrode wires 3 extend linearly and parallel to the central axis of the tubular member 2. Each electrode wire 3 is composed of the metal wire 4 and the elastic conductor 5 covering the metal wire 4. The metal wire 4 can be, e.g., a twisted wire formed by twisting plural (seven in this example) strands of a highly conductive metal such as copper. Meanwhile, the elastic conductor 5 has elasticity and electrical conductivity. For example, a rubber-based composition obtained by cross-linking an ethylene-propylene-diene copolymer mixed with conductive fillers such as a carbon black, or a styrene-based thermoplastic elastomer composition not requiring a cross-linking process etc. can be suitably used to form the elastic conductor 5 which thus has elasticity and can deform with the tubular member 2 under an external pressure.

(15) Method for Manufacturing the Pressure-Sensitive Sensor

(16) To obtain the pressure-sensitive sensor 1, e.g., the following two types of manufacturing method can be used. In the first manufacturing method, firstly, the electrode wires 3 are made by covering the metal wires 4 with the elastic conductors 5 using an extruder. Next, four electrode wires 3 are arranged such that the respective centers are located on the vertices of a square. Then, as shown in FIG. 6, the electrode wires 3 are fed through a crosshead of the extruder while extruding a tubular elastic insulation 42 on the outer peripheral side (from a mouthpiece 41), thereby fusing the electrode wires 3 to the inner surface of the tubular member 2. At this time, to prevent the tubular member 2, the electrode wires 3 and the space 6 from losing the shape and alignment, a compressed gas 43 is injected to apply pressure from the inside of the tubular member 2. It is possible to maintain the size or arrangement by increasing the internal pressure and the pressure-sensitive sensor 1 is thereby obtained. To arrange the electrode wires 3 on the vertices of a square, there is a method in which the electrode wires 3 are fed through four holes formed on a core bar 44 of the extruder. Meanwhile, to inject the compressed gas 43 to apply pressure from the inside, there is a method in which one or plural holes are formed at, e.g., the center of the core bar 44 and the compressed gas 43 is supplied from the inner side of the core bar 44 toward an outlet. Suitable compressed gas 43 is the air or an inert gas such as nitrogen.

(17) In the second manufacturing method, the electrode wires 3 are formed by extruding the elastic conductors 5 around the metal wires 4 which are arranged such that the respective centers are located on the vertices of a square, and simultaneously, the tubular elastic insulation 42 is extruded from the outer peripheral side, thereby fusing the electrode wires 3 to the inner surface of the tubular member 2. A common co-extrusion technique is used for the simultaneous extrusion. In addition, to prevent the tubular member 2, the electrode wires 3 and the space 6 from losing the shape and alignment, the compressed gas 43 is injected to apply pressure from the inside of the tubular member 2, in the same manner as in the first manufacturing method. It is possible to maintain the size or arrangement by increasing the internal pressure and the pressure-sensitive sensor 1 is thereby obtained.

Effects of the First Embodiment

(18) In the first embodiment, since the electrode wires 3 are arranged linearly and parallel to the central axis of the tubular member 2 and are also fused to the inner surface of the tubular member 2 by injecting the compressed gas to apply pressure from the inside of the tubular member 2 during manufacturing of the pressure-sensitive sensor 1, it is not necessary to provide any spacer and it is possible to freely design the length of the finished pressure-sensitive sensor 1. In addition, since four electrode wires 3 are provided, sensitivity of the pressure-sensitive sensor 1 to pressure does not greatly decrease in any specific direction, which means that it is possible to detect pressure in any directions. Although the electrode wires 3 are arranged to be located on the vertices of a square in the configuration of the example described above, the configuration may be such that the electrode wires 3 are arranged to be located on the vertices of a regular n-sided polygon (n being an integer of not less than 3).

Other Embodiments

(19) Next, other embodiments of the invention will be described in reference to FIGS. 3 to 5.

(20) FIG. 3 is a cross sectional view showing a pressure-sensitive sensor 11 in the second embodiment of the invention. FIG. 4 is a cross sectional view showing a pressure-sensitive sensor 21 in the third embodiment of the invention. FIG. 5 is a cross sectional view showing a pressure-sensitive sensor 31 in the fourth embodiment of the invention.

(21) Each of the pressure-sensitive sensors 11, 21 and 31 in the second to fourth embodiments is provided with a tubular member 2 or 12 and four electrode wires 3 each formed by covering the metal wire 4 with the elastic conductor 5 and extending linearly and parallel to the central axis inside the tubular member 2 or 12 in the same manner as the pressure-sensitive sensor 1 in the first embodiment, but the configuration of the tubular member or the cross-sectional shape of the electrode wire 3 is different from the first embodiment. FIGS. 3 to 5 respectively show the pressure-sensitive sensors 11, 21 and 31 in the cross sections orthogonal to the tubular members 2 or 12.

(22) Next, the respective configurations of the pressure-sensitive sensors 11, 21 and 31 will be described in detail.

(23) The tubular member 12 of the pressure-sensitive sensor 11 in the second embodiment has a two-layer structure and is composed of an inner tubular member 7 and an outer tubular member 8. Providing the outer tubular member 8 in the tubular member 12 is effective particularly to increase strength of pressure-sensitive sensor or to enhance compatibility (adhesion, etc.) with other members (e.g., sealing members at end portions or a portion for attaching the pressure-sensitive sensor, etc.). Both the inner tubular member 7 and the outer tubular member 8 can be formed of an elastic insulating material. To form the inner tubular member 7, it is possible to use the same material as that used to form the tubular member 2 of the pressure-sensitive sensor 1. Meanwhile, to form the outer tubular member 8, it is possible to use, e.g., a thermoplastic urethane which is excellent in strength and abrasion resistance and has good adhesion to polyamide which is often used to form other members. To manufacture the pressure-sensitive sensor 11, it is possible to employ a method in which the structure covered with the inner tubular member 7 is manufactured by the same method as that used to manufacture the pressure-sensitive sensor 1 in the first embodiment and the outer tubular member 8 is then extruded as the outermost layer, or a method in which two layers, the inner tubular member 7 and the outer tubular member 8, are co-extruded instead of the process of extruding the tubular member 2 in manufacturing of the pressure-sensitive sensor 1 in the first embodiment.

(24) The pressure-sensitive sensors 21 and 31 in the third and fourth embodiments are configured that a hollow portion of the tubular member 2 has a circular shape in a cross section and the electrode wires 3 are formed along the inner surface of the hollow portion. In the pressure-sensitive sensor 21, the cross-sectional shape of the electrode wire 3 is substantially a semicircle, such that an arc portion 3a faces toward the central axis of the tubular member 2. In the pressure-sensitive sensor 31, the cross-sectional shape of the electrode wire 3 is substantially a triangle, such that one of vertex portions 3b faces toward the central axis of the tubular member 2. Since the cross-sectional shape of the electrode wire 3 is asymmetrical, a suitable manufacturing method is a method in which the electrode wires 3 are formed by extruding the elastic conductors 5 around the metal wires 4, and simultaneously, a tubular elastic insulating material is extruded from the outer peripheral side such that the electrode wires 3 are fused to the inner surface of the tubular member 2 and the positions thereof are fixed.

(25) Also for the pressure-sensitive sensors 11, 21 and 31 in the second to fourth embodiments, it is not necessary to provide any spacer, it is possible to freely design the length of the finished pressure-sensitive sensors 11, 21 and 31, and sensitivity of the pressure-sensitive sensors 11, 21 and 31 to pressure does not greatly decrease in any specific direction, which means that it is possible to detect pressure in any directions, in the same manner as the pressure-sensitive sensor 1 in the first embodiment.

(26) Technical ideas understood from the embodiments will be described below citing the reference numerals, etc., used for the embodiments. However, each reference numeral described below is not intended to limit the constituent elements in the claims to the members, etc., specifically described in the embodiments.

(27) [1] A pressure-sensitive sensor (1, 11, 21, 31), comprising: a hollow tubular member (2, 12) comprising an elastic insulating material (42); and n electrode wires (3) (n being an integer of not less than 3) arranged away from one another and held inside the tubular member (2, 12), wherein when an external pressure is applied to the tubular member (2, 12), the tubular member (2, 12) elastically deforms such that at least two of the n electrode wires (3) contact with each other, and wherein the n electrode wires (3) extend linearly and parallel to a central axis of the tubular member (2, 12).

(28) [2] A method for manufacturing a pressure-sensitive sensor (1, 11, 21, 31), the sensor (1, 11, 21, 31) comprising a hollow tubular member (2, 12) comprising an elastic insulating material (42), and n electrode wires (3) (n being an integer of not less than 3) arranged away from one another and held inside the tubular member (2, 12), wherein an external pressure is applied to the tubular member (2, 12), the tubular member (2, 12) elastically deforms such that at least two of the n electrode wires (3) contact with each other, the method comprising: forming the tubular member (2, 12) by extruding the elastic insulating material (42) to be the tubular member (2, 12) around the n electrode wires (3) while feeding the n electrode wires (3) linearly and parallel to each other; and injecting a compressed gas (43) inside the tubular member (2, 12).

(29) [3] A method for manufacturing a pressure-sensitive sensor (1, 11, 21, 31), the sensor (1, 11, 21, 31) comprising a hollow tubular member (2, 12) comprising an elastic insulating material (42), and n electrode wires (3) (n being an integer of not less than 3) arranged away from one another and held inside the tubular member (2, 12), wherein the electrode wires (3) each comprise a metal wire (4) and a conductive elastomer (5) formed around the metal wire (4), and wherein when an external pressure is applied to the tubular member (2, 12), the tubular member (2, 12) elastically deforms such that at least two of the n electrode wires (3) contact with each other, and the method comprising: forming the n electrode wires (3) and the tubular member (2, 12) by co-extruding the conductive elastomers (5) around each of the n metal wires (4) and the elastic insulating material (42) around the electrode wires (3) while feeding the n metal wires (4) linearly and parallel to each other; and injecting a compressed gas (43) inside the tubular member (2, 12).

(30) Although the embodiments of the invention have been described, the invention according to claims is not to be limited to the embodiments. Further, please note that all combinations of the features described in the embodiments are not necessary to solve the problem of the invention. The invention can be appropriately modified and implemented without departing from the gist thereof.