阅读说明：本技术 用于可动部的同轴电缆 (Coaxial cable for movable part ) 是由 黄得天 小林正则 塚本佳典 森山真至 于 2019-08-09 设计创作，主要内容包括：本发明提供一种用于可动部的同轴电缆,其具有适于长距离传输的电气特性且即使被施加使其减径的负荷时也难以发生断线等不良。用于可动部的同轴电缆(1)具有内部导体(2)、包覆内部导体(2)周围的绝缘体(3)、包覆绝缘体(3)周围的将胶带部件(41)卷绕成螺旋状而形成的磨损抑制层(4)、包覆磨损抑制层(4)的外周且由编织屏蔽层形成的外部导体(5)以及包覆外部导体(5)周围的护套(6),其中,磨损抑制层(4)的胶带部件(41)中面向绝缘体(3)的面以及面向外部导体(5)由氟树脂构成。(The invention provides a coaxial cable for a movable part, which has electrical characteristics suitable for long-distance transmission and is difficult to generate defects such as disconnection and the like even if a load for reducing the diameter is applied. A coaxial cable (1) for a movable part comprises an inner conductor (2), an insulator (3) covering the periphery of the inner conductor (2), a wear-inhibiting layer (4) covering the periphery of the insulator (3) and formed by winding a tape member (41) in a spiral shape, an outer conductor (5) covering the periphery of the wear-inhibiting layer (4) and formed by a braided shield layer, and a sheath (6) covering the periphery of the outer conductor (5), wherein the surface of the tape member (41) of the wear-inhibiting layer (4) facing the insulator (3) and the surface facing the outer conductor (5) are formed by a fluororesin.)

1. A coaxial cable for a movable part, comprising:

an inner conductor of the first and second conductors,

an insulator surrounding the inner conductor,

a wear-inhibiting layer formed by spirally winding a tape member around the insulator,

an outer conductor formed of a braided shield layer covering an outer periphery of the wear-suppressing layer, and

a jacket surrounding the outer conductor;

wherein, in the wear-suppressing layer, a surface of the tape member facing the insulator and a surface facing the external conductor are composed of a fluororesin.

2. The coaxial cable for a movable part according to claim 1, wherein in the wear-suppressing layer, the tape member is wound in an overlapping manner such that a part of the tape member in a width direction overlaps with each other, and the tape members overlapping with each other are movable with each other.

3. The coaxial cable for a movable part according to claim 1 or 2, wherein in the wear suppressing layer, a friction coefficient of a surface of the tape member is lower than a friction coefficient of a surface of the insulator.

4. The coaxial cable for a movable part according to any one of claims 1 to 3, wherein the insulator comprises:

a non-filled extruded layer disposed at an outer periphery of the inner conductor,

a foam layer non-adhesively disposed about the outer periphery of the non-filled extruded layer,

a non-foamed layer adhesively disposed on the periphery of the foamed layer;

the inner conductor and the non-filled extruded layer are capable of moving independently of each other.

5. The coaxial cable for a movable part according to any one of claims 1 to 4, wherein an air layer is formed between the outer conductor and the wear-suppressing layer at a part in a circumferential direction.

6. The coaxial cable for a movable part according to any one of claims 1 to 5, wherein the outer conductor is constituted by a multilayer lamination of braided shield layers, and a braid angle of a braided shield layer disposed innermost in a radial direction is smaller than a braid angle of a braided shield layer disposed outside thereof with respect to the braided shield layer.

7. The coaxial cable for a movable part according to any one of claims 1 to 6, wherein the outer conductor is formed of a braided shield layer braided from a bare metal wire having a tensile strength of 340MPa or more and an elongation of 5% or more.

8. The coaxial cable for a movable part according to claim 7, wherein the metal bare wire used in the outer conductor is formed of a tin-plated copper alloy.

9. The coaxial cable for a movable part according to claim 7 or 8, wherein the bare metal wire used in the outer conductor is coated with a lubricant.

10. The coaxial cable for a movable part according to any one of claims 1 to 9, wherein the conductor cross-sectional area of the inner conductor is 0.75mm²The above.

11. The coaxial cable for a movable part according to any one of claims 1 to 10, wherein the inner conductor is formed by twisting a plurality of metal bare wires to obtain a sub-strand, and further twisting a plurality of the sub-strands to obtain a composite strand.

Technical Field

The present invention relates to a coaxial cable for a movable portion.

Background

In recent years, as a measure for improving productivity, the market for human-cooperative robots and small-sized articulated robots is expanding. As the robot cable used in such a robot, a cable for a movable part wired to the movable part of the robot and a cable for a fixed part connecting the robot and the control device are used. Examples of the cable for the movable portion include a coaxial cable for the movable portion, which transmits a high-speed signal from a camera or the like.

As a conventional coaxial cable used for a movable portion, there is patent document 1. The coaxial cable for the movable portion of patent document 1 has a three-layer structure of the insulator, and thus improves high-speed signal transmission characteristics and improves bending resistance and twisting resistance.

Disclosure of Invention

Problems to be solved by the invention

In recent years, robots and the like having a wide movable range (moving range) have been put to practical use, and as a coaxial cable used for a movable part, it is also required to be capable of transmitting over a long distance of several tens of meters or more (for example, about 5 to 80 m). In order to reduce the amount of attenuation at the time of long-distance transmission, it is necessary to increase the cross-sectional area of the conductor, but when the cross-sectional area of the conductor is increased, the outer diameter of the coaxial cable for the movable portion is also increased.

When the outer diameter of the coaxial cable for the movable portion is increased, the coaxial cable for the movable portion is difficult to freely move in a limited wiring space, and a load for reducing the diameter (しごく) of the coaxial cable for the movable portion is likely to act on the coaxial cable when the robot or the like is moved. When a load for reducing the diameter of the coaxial cable used for the movable portion is applied, lateral pressure friction is generated between the braided shield layer used for the outer conductor and the insulator, the insulator is worn away locally, and there is a risk of deterioration in characteristics, short-circuiting or disconnection between the inner conductor and the outer conductor, and other problems.

Accordingly, an object of the present invention is to provide a coaxial cable for a movable portion, which has electrical characteristics suitable for long-distance transmission and in which a failure such as disconnection is less likely to occur even when a load for reducing the diameter is applied.

Means for solving the problems

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a coaxial cable for a movable part, which includes an inner conductor, an insulator covering the inner conductor, a wear-inhibiting layer formed by winding a tape member in a spiral shape around the insulator, an outer conductor covering the outer periphery of the wear-inhibiting layer and formed of a braided shield layer, and a sheath covering the outer conductor, wherein a surface of the tape member facing the insulator and a surface facing the outer conductor in the wear-inhibiting layer are formed of a fluororesin.

Effects of the invention

According to the present invention, it is possible to provide a coaxial cable for a movable portion, which has electrical characteristics suitable for long-distance transmission and in which a failure such as disconnection is unlikely to occur even when a load for reducing the diameter is applied.

Drawings

Fig. 1 is a view showing a coaxial cable for a movable part according to an embodiment of the present invention, in which (a) is a cross-sectional view showing a cross-section perpendicular to a length direction of the cable, and (b) is an enlarged view of a portion a thereof.

In fig. 2, (a) is a perspective view of the tape member, and (b) to (d) are cross-sectional views of the tape member.

Fig. 3 is a diagram illustrating a bending test.

Fig. 4 is a diagram illustrating a twist test.

Fig. 5 is a diagram illustrating a U-bend test.

Fig. 6 is a diagram illustrating a reducing test.

Description of the reference numerals

1 … coaxial cable for movable part, 2 … inner conductor, 3 … insulator, 31 … non-filled extrusion layer, 32 … foamed layer, 33 … non-foamed layer, 4 … abrasion suppression layer, 41 … tape member, 5 … outer conductor, 51 … inner braided shield layer, 52 … outer braided shield layer, 6 … sheath, 7 … air layer.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Fig. 1 is a diagram showing a coaxial cable for a movable part according to the present embodiment, in which (a) is a cross-sectional view showing a cross section perpendicular to a length direction of the cable, and (b) is an enlarged view of a portion a thereof.

As shown in fig. 1(a) and (b), the coaxial cable 1 for the movable portion is configured such that an insulator 3, a wear-inhibiting layer 4, an outer conductor 5, and a sheath 6 are provided in this order around an inner conductor 2. The coaxial cable 1 used for the movable portion is a member for internal or external wiring of a robot used in a factory, for example, and at least a part thereof is arranged to pass through the movable portion. The length of the coaxial cable 1 used for the movable portion is, for example, about 5 to 80 m. The coaxial cable 1 used for the movable portion is used for transmitting a high-frequency signal having a bandwidth of, for example, 10MHz to 6 GHz. The characteristic impedance of the coaxial cable 1 for the movable portion is, for example, 75 Ω.

(inner conductor 2)

The inner conductor 2 is formed of a composite twisted wire obtained by twisting a plurality of bare metal wires made of copper or the like to obtain a sub-twisted wire, and further twisting a plurality of sub-twisted wires. The sub-strands are formed by collectively twisting a plurality of bare metal wires, and the inner conductor 2 is formed by concentrically twisting a plurality of sub-strands. The composite twist of the inner conductor 2 can improve the flexibility of the coaxial cable 1 for the movable portion, thereby facilitating wiring, and can improve the bending resistance and the twisting resistance, since the bare metal wire is less likely to be broken even when repeated bending and twisting are applied to the movable portion. Further, the inner conductor 2 is formed as the above-described composite stranded wire, and even if a load for reducing the diameter of the coaxial cable 1 for the movable portion is applied, disconnection or the like is less likely to occur, which is effective.

In order to obtain sufficient bending resistance and twisting resistance, a material having an elongation strength of 220MPa or more and an elongation of 5% or more is used as the bare metal wire used for the inner conductor 2. In addition, in order to suppress the attenuation amount at the time of long-distance transmission, the conductor cross-sectional area of the inner conductor 2 may be made 0.75mm²The above. In the present embodiment, for example, as the bare metal wire used for the inner conductor 2, a tinned annealed copper wire having a bare wire diameter of 0.08mm is used, and a sub-strand obtained by twisting 30 tinned annealed copper wires is concentrically twisted by 7 pieces to form the inner conductor 2. The outer diameter of the inner conductor 2 at this time was approximately 1.41mm, and the conductor cross-sectional area was approximately 1.04mm²。

(insulator 3)

The insulator 3 is formed to cover the periphery of the inner conductor 2. As the insulator 3, a material having a low dielectric constant is preferably used in order to improve transmission characteristics of a high-frequency signal (more specifically, to make it difficult to attenuate a high-frequency signal having a bandwidth of, for example, 10MHz to 6GHz when the signal is transmitted over a long distance). In the present embodiment, a material having a 3-layer structure, that is,: a non-filled extruded layer 31 provided on the outer periphery of the inner conductor 2, a foamed layer 32 provided non-adhesively to the outer periphery of the non-filled extruded layer 31, and a non-foamed layer 33 provided adhesively to the outer periphery of the foamed layer 32.

The non-filled extruded layer 31 is formed by using a non-foamed resin material of a low dielectric constant and extruding through a tube. The non-filled extruded layer 31 is formed by tube extrusion, whereby the resin material does not enter between the metal bare wires of the inner conductor 2 when the non-filled extruded layer 31 is formed, and a gap is partially generated between the inner conductor 2 and the non-filled extruded layer 31. Thereby, the inner conductor 2 can be moved independently of the unfilled extruded layer 31, and the bending resistance and the twisting resistance can be further improved. As the non-filled extruded layer 31, a fluororesin material formed of, for example, FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), or the like can be used. In this embodiment, a non-filled extruded layer 31 made of FEP and having a thickness of 0.3mm may be formed.

The foamed layer 32 is a low dielectric constant layer ensuring good electrical characteristics at high frequencies, and is made of a foamed insulating resin material. The foaming degree of the foamed layer 32 may be 30% or more and 70% or less. This is because when the degree of foaming of the foamed layer 32 is less than 30%, the dielectric constant increases and the long-distance transmission characteristics of the high-frequency signal deteriorate, and when the degree of foaming exceeds 70%, the foamed layer 32 becomes too soft and easily crushed by an external force at the time of bending or the like, and the transmission characteristics of the high-frequency signal deteriorate. The foamed layer 32 is formed of a resin material having a lower melting point than the resin material used for the non-filled extruded layer 31, and is formed so as to be non-adhesive with the non-filled extruded layer 31. Thus, when the coaxial cable 1 for the movable portion moves following the movement of the robot, the lengthwise non-filled extruded layer 31 of the coaxial cable 1 for the movable portion can move independently of the foamed layer 32, and the bending resistance and the twisting resistance can be further improved. As the foamed layer 32, a material containing, for example, radiation-crosslinked foamed polyethylene, foamed polypropylene, or the like can be used. In this embodiment, a foamed layer 32 having a thickness of 1.15mm and made of radiation-crosslinked foamed polyethylene was formed.

The non-foamed layer 33 is a layer for protecting the foamed layer 32, and is formed by inflation extrusion using the same resin material as the foamed layer 32. The non-foamed layer 33 is formed by inflation extrusion, whereby foamed cells appearing on the surface of the foamed layer 32 are filled, and the non-foamed layer 33 is bonded to the foamed layer 32. As the non-foamed layer 33, a resin material containing a non-foamed insulating resin having an elongation of 300% or more, a tensile strength of 15MPa or more, and a dielectric constant of 2.5 or less can be used. By increasing the elongation percentage and tensile strength of the non-foamed layer 33 as the load in bending the coaxial cable 1 for the movable portion increases toward the outside in the radial direction, cracks are less likely to occur in the insulator 3 when the coaxial cable is repeatedly bent and twisted, and the bending resistance and twisting resistance are further improved. As the non-foamed layer 33, for example, a material containing non-foamed polypropylene, radiation-crosslinked polyethylene, or the like can be used. In the present embodiment, the non-foamed layer 33 having a thickness of 1.25mm may be formed of radiation crosslinked polyethylene. The outer diameter of the insulator 3 at this time was about 6.8 mm.

(wear-inhibiting layer 4)

The abrasion suppression layer 4 is formed by spirally winding a tape member 41 made of a fluororesin tape around the insulator 3. For example, it is conceivable to provide the wear-inhibiting layer 4 by extrusion molding, but in this case, the wear-inhibiting layer 4 is cylindrical and extremely hard, and is hard to bend, resulting in a decrease in flexibility of the coaxial cable 1 used for the movable portion. That is, in the present embodiment, in order to suppress the abrasion of the insulator 3 due to the lateral pressure abrasion generated between the outer conductor 5 formed of a plurality of bare metal wires and the insulator 3 formed of an insulating resin material when a load for reducing the diameter of the coaxial cable 1 for the movable portion is applied to the coaxial cable 1 for the movable portion while suppressing the reduction in flexibility of the coaxial cable 1 for the movable portion, the tape member 41 formed of a fluororesin tape is wound in a spiral shape around the insulator 3, and the abrasion suppression layer 4 is formed. The tape member 41 is wound in a manner to overlap a portion of the fluororesin tape in the width direction, and is wound spirally around the outer periphery of the insulator 3. At this time, when the coaxial cable 1 for the movable portion is moved so as to reduce the diameter thereof, the tape member 41 is wound in an overlapping manner so as to maintain the state in which the surface of the insulator 3 is not exposed from the overlapping portion of the tape member 41. The overlapping portions of the tape members 41 are not bonded, and the tape members 41 overlapping each other can slide when the cable 1 for the movable portion moves so as to reduce the diameter. The fluororesin tape constituting the tape member 41 preferably has a surface that is non-adhesive to the insulator 3 and the outer conductor 5, respectively. Here, the "tape member made of a fluororesin tape" means a tape formed of a uniform fluororesin. In order to achieve the above-described operation and effect, the tape member 41 is preferably wound so that the overlapping portion of the fluororesin tapes is 0.3 to 0.5 times the width (for example, 15 to 35mm) of the fluororesin tapes.

According to the coaxial cable 1 for the movable portion of the present embodiment, since the abrasion suppression layer 4 is provided between the insulator 3 and the outer conductor 5, when a load for reducing the diameter of the coaxial cable 1 for the movable portion is applied, the coaxial cable 1 for the movable portion receives a lateral pressure, but the abrasion of the insulator 3 due to the friction between the insulator 3 (particularly the surface of the non-foamed layer 33) and the outer conductor 5 due to the lateral pressure can be suppressed. That is, since the surface of the wear-inhibiting layer 4 in contact with the insulator 3 and the surface of the wear-inhibiting layer 4 in contact with the outer conductor 5 are less likely to be worn by lateral pressure by the wear-inhibiting layer 4, the durability of the coaxial cable 1 for the movable portion when a load for reducing the diameter thereof is applied (hereinafter, simply referred to as "durability against diameter reduction") can be improved.

The wear-resistant layer 4 is preferably smooth in surface (having a coefficient of friction lower than that of the insulator 3) so that the outer conductor 5 can slide relative to the wear-resistant layer 4 when a load for reducing the diameter of the coaxial cable 1 for the movable portion is applied thereto, and durability against the reduction can be improved. Examples of the fluororesin tape used for the tape member 41 include an ETFE (tetrafluoroethylene-ethylene copolymer) tape and a PTFE (polytetrafluoroethylene) tape.

In addition, as the tape member 41, a material having a dielectric constant as low as possible is preferably used in order to suppress the attenuation amount of the high-frequency signal. In the present embodiment, the tape member 41 made of PTFE having a smooth surface and a low dielectric constant can be used.

The thickness of the tape member 41 may be 25 μm to 150 μm. This is because if the thickness of the tape member 41 is less than 25 μm, the tape member is too thin and easily broken by abrasion back and forth, and if the thickness of the tape member 41 exceeds 150 μm, the abrasion prevention layer 4 becomes hard, and the flexibility of the coaxial cable 1 for the movable portion is reduced. In the present embodiment, the tape member 41 formed of, for example, a PTFE tape having a thickness of 100 μm can be used.

In the present embodiment, as shown in fig. 2(a) and (b), the tape member 41 is formed using a fluororesin tape having 1 fluororesin layer 411 (single layer), but the present invention is not limited thereto, as long as the tape member 41 has a surface 41a facing the insulator 3 and a surface 41b facing the outer conductor 5 made of a fluororesin. For example, as shown in fig. 2(c) and (d), the tape member 41 may have a multilayer structure having 2 or more layers. Fig. 2 c shows an example in which the fluororesin layers 411 are laminated in a plurality of layers (2 layers in the example of the figure) and both the surfaces 41a and 41b are made of fluororesin. The tape member 41 of fig. 2(c) can be formed by, for example, laminating a film made of a fluororesin. Fig. 2(d) shows an example in which fluororesin layers 411 are provided on both surfaces of a base 412, and both surfaces 41a and 41b are made of fluororesin. The tape member 41 of fig. 2(d) may be formed by applying a fluororesin to the entire surface of the substrate 412 and curing the fluororesin to form the fluororesin layer 411, or may be formed by bonding a film of a fluororesin to the entire surface of both sides of the substrate 412 and welding the film to the substrate 412.

(outer conductor 5)

The outer conductor 5 is a material for shielding external noise. The outer conductor 5 is formed of a braided shield layer formed by braiding a bare metal wire in order to cover the outer periphery of the wear-inhibiting layer 4 and secure flexibility of the coaxial cable 1 for the movable portion. In the present embodiment, the outer conductor 5 is formed by laminating a plurality of braided shield layers. Here, although the case where the braided shield layer is laminated in 2 layers to form the outer conductor 5 is described, the braided shield layer may be laminated in 3 or more layers to form the outer conductor 5. Hereinafter, the braided shield layer disposed radially inward is referred to as an inner braided shield layer 51, and the braided shield layer disposed radially outward is referred to as an outer braided shield layer 52.

According to the coaxial cable 1 for a movable part of the present embodiment, the air layer 7 can be formed between the outer conductor 5 (inner braided shield layer 51) and the wear-suppressing layer 4 at a part in the circumferential direction. In order to form the air layer 7, the inner diameter of the inner braided shield layer 51 may be larger than the outer diameter of the wear-suppressing layer 4. In the present embodiment, when forming the inner braided shield layer 51, for example, a rod-shaped spacer incorporated in a braided shield forming device is arranged along the cable longitudinal direction on the outer periphery of the wear-suppressing layer 4, a metal bare wire is braided on the spacer to form the inner braided shield layer 51, and the inner braided shield layer 51 formed is sequentially fed out from the braided shield forming device so as to be separated from the spacer, whereby the air layer 7 can be formed. Note that even when such a manufacturing method is not performed, a slight gap is generated between the step portion of the tape member 41 (step portion generated by overlapping a part of the tape member 41 in the width direction) and the bare metal wires of the inner braided shield layer 51, but the gap is not included in the air layer 7 of the present invention. In addition, the shape of the spacer is not limited to the rod shape. The size of the air layer 7 is in a range where the maximum distance from the surface of the wear-resistant layer 4 to the inner surface of the outer conductor 5 (the surface facing the surface of the wear-resistant layer 4) is 5 μm or more and 30 μm or less, and is referred to as a state where the outer conductor 5 floats from the surface of the wear-resistant layer 4 toward the jacket 6. The maximum distance is determined by the following method: after the coaxial cable 1 for the movable portion was cut at a predetermined position, the maximum value of the linear distance from the surface of the wear-inhibiting layer 4 to the inner surface of the outer conductor 5 was measured when the cross section of the cut portion (cross section perpendicular to the cable length direction) was observed by an optical microscope or an electron microscope.

By forming the air layer 7 between the outer conductor 5 (inner braided shield layer 51) and the wear-resistant layer 4, it is possible to suppress the outer conductor 5 from being pressed, and when the coaxial cable 1 for a movable portion is bent, shaken, or reduced in diameter, the outer conductor 5 (inner braided shield layer 51) and the wear-resistant layer 4 can be easily moved relative to each other, and it is possible to improve the bending resistance, the twisting resistance, and the durability against the reduction in diameter.

The outer braided shield layer 52 is formed by braiding a metal bare wire on the outer periphery of the inner braided shield layer 51, in the same manner as a method for producing a usual braided shield layer. This is because, when an air layer is formed between the inner braided shield layer 51 and the outer braided shield layer 52, contact resistance in the outer conductor 5 becomes high, and there is a risk of deterioration in characteristics.

In order to obtain sufficient bending resistance and twisting resistance, the bare metal wires used for the braided shield layers 51 and 52 are made of a material having a tensile strength of 340MPa or more and an elongation of 5% or more. In the present embodiment, as the bare metal wires used for the braided shield layers 51 and 52, a tin-plated copper alloy having a bare wire diameter of 0.08mm can be used. In addition, the density of the two braided shield layers 51,52 is about 90%. The bare metal wires used in the braided shield layers 51 and 52 may have the same or different diameters.

Further, in the present embodiment, a metal bare wire coated with a lubricant may be used for both the braided shield layers 51, 52. As the lubricant, for example, liquid paraffin may be used. This makes it easier for the outer conductor 5 and the wear-suppressing layer 4 to slide, and can further improve the bending resistance, the twisting resistance, and the durability against diameter reduction.

However, when the braiding angle of the inner braided shield layer 51 is large, there is a risk that friction with the wear-suppressing layer 4 becomes severe. In addition, when the braid angle of the outer braided shield layer 52 which is susceptible to bending is small, there is a risk that the bare metal wire becomes susceptible to breakage and the bending resistance is reduced. Further, when the braiding angles of the two braided shield layers 51,52 are the same, there is a risk that abrasion between the two braided shield layers 51,52 becomes large. Therefore, it is preferable that the braiding angle of the inner braided shield layer 51 is smaller than that of the outer braided shield layer 52. In the case where the outer conductor 5 has 3 or more braided shield layers, it is preferable that the braiding angle of the braided shield layer disposed on the innermost side in the radial direction is smaller than the braiding angle of the braided shield layer disposed on the outer side of the braided shield layer. The braid angle is an angle (absolute value) formed between the longitudinal direction of the bare metal wire and the longitudinal direction of the coaxial cable 1 for the movable portion.

(sheath 6)

The sheath 6 is formed to wrap around the outer conductor. As the sheath 6, for example, a material containing PVC (polyvinyl chloride) or polyurethane can be used. In the present embodiment, the sheath 6 having a thickness of 1.0mm is formed of PVC. Preferably, the sheath 6 is formed by tube extrusion so that the outer conductor 5 can move within the sheath 6. The outer diameter of the coaxial cable 1 for the movable portion after the sheath 6 is formed is about 10 mm.

(characteristics of coaxial Cable 1 for Movable part)

The coaxial cable 1 for the movable portion described above was produced as an example, and subjected to a bending resistance test, a twisting resistance test, a U-bend test, and a reducing test. In addition, as a comparative example, a coaxial cable for a movable part of a comparative example having the same structure as the coaxial cable 1 for a movable part of the example except that the abrasion suppressing layer 4 was omitted was prepared, and the same test was performed.

In the bending test, as shown in fig. 3, the upper end portion of the coaxial cable 1 for the movable portion is fixed so as not to move the center line, and a weight having a load W of 5N (500gf) is hung from the lower end portion of the coaxial cable 1 for the movable portion, and the coaxial cable 1 for the movable portion is bent by bending the coaxial cable 1 in the left-right direction by ± 90 ° along the bending jig 11 in a state where the bending jig 11 for bending the coaxial cable 1 for the movable portion in the left-right direction is attached. The bending radius R of the coaxial cable 1 for the movable portion is bent about 5 times the outer diameter of the coaxial cable 1 for the movable portion. The bending speed was 30 times/minute, and the number of bending times was 1 reciprocation in the left-right direction. Further, the bending of the coaxial cable 1 for the movable portion is repeated, the conduction detection of the inner conductor 2 is performed between both end portions of the coaxial cable 1 for the movable portion a suitable number of times, and the number of bending times when the attenuation amount from the initial or the change amount of the characteristic impedance is 10% or more is taken as the bending life. In the bending test, the bending life was regarded as being acceptable when 30 ten thousand cycles or more, and the bending life was regarded as being unacceptable when less than 30 ten thousand cycles.

In the twist test, as shown in fig. 4, the upper end portion of the coaxial cable 1 for the movable portion was fixed so that the center line thereof did not move, the fixed collet 12 was attached to one position of the coaxial cable 1 for the movable portion so as not to rotate, and the rotating collet 13 was attached to a position spaced apart from the upper portion by a distance d (twist length) of 500 mm. A weight with a load W of 5N (500gf) is hung from the lower end of the coaxial cable 1 used for the movable portion. In this state, the collet 13 is rotated to repeatedly apply a twist of ± 180 ° to the coaxial cable 1 for the movable portion. The twisting speed was 30 times/minute, and the number of twists was counted as 1 reciprocation in each direction. The detection of the conduction of the inner conductor 2 between the both ends of the coaxial cable 1 for the movable portion is performed a suitable number of times by repeating the winding of the coaxial cable 1 for the movable portion, and the number of times of winding when the attenuation from the initial or the change in the characteristic impedance is 10% or more is taken as the winding life. In the twist test, the product was judged as being acceptable when the twist life was 30 ten thousand or more, and the product was judged as being unacceptable when the twist life was less than 30 ten thousand.

In the U-bend test, as shown in fig. 5, one end portion of the coaxial cable 1 for the movable portion is fixed to the fixed plate 14, the coaxial cable 1 for the movable portion is extended in a direction parallel to the fixed plate 14, the extended coaxial cable 1 for the movable portion is folded back in a U shape, and then the other end portion of the coaxial cable 1 for the movable portion is fixed to the moving plate 15 arranged parallel to the fixed plate 14. In this state, the moving plate 15 is repeatedly reciprocated as follows: the moving plate 15 reciprocates with a stroke length L of 1m in a direction parallel to the extending direction of the coaxial cable 1 for the movable portion. The bending radius of the coaxial cable 1 for the movable portion is about 10 times the outer diameter of the coaxial cable 1 for the movable portion. The stroke speed was 25 times/minute, and the number of strokes was counted as 1 time for 1 round trip of the moving plate 15. The conduction of the inner conductor 2 between the both ends of the coaxial cable 1 for the movable portion is detected an appropriate number of times, and the number of strokes when the attenuation from the initial or the change in the characteristic impedance is 10% or more is referred to as the U-bend life. In the U-bend test, the condition that the U-bend life is more than 100 ten thousand times is regarded as qualified, and the condition that the U-bend life is less than 100 ten thousand times is regarded as unqualified.

In the diameter reduction test, as shown in fig. 6, the coaxial cable 1 for the movable portion is disposed to extend in the horizontal direction, and the two ends thereof are extended downward by the pulley 16, and the weight 17 having a load W of 5N (500gf) is hung from the two ends thereof. Further, the coaxial cable 1 for the movable portion between the pulleys 16 is passed through 2 pulleys 18a,18b provided on the carriage 18 and capable of reciprocating in the horizontal direction. One pulley 18a rotates the coaxial cable 1 for the movable portion introduced from the left side by 180 degrees and extends leftward, and the other pulley 18b rotates the coaxial cable 1 for the movable portion introduced from the pulley 18a by 180 degrees and extends rightward. The carriage 18 is repeatedly reciprocated in the left-right direction, thereby repeatedly reducing the diameter of the coaxial cable 1 used for the movable portion. The reduction speed was 10 times/minute, and the number of times of reduction was 1 time of 1 reciprocation of the carriage 18. The pulleys 18a,18b have a diameter of 160 mm. The conduction of the inner conductor 2 between the both ends of the coaxial cable 1 for the movable portion is detected an appropriate number of times, and the number of times of reduction when the attenuation from the initial or the change in characteristic impedance is 10% or more is referred to as the reduction life. In the reducing test, the case where the reducing life was 10 thousands of times or more was regarded as pass, and the case where the reducing life was less than 10 thousands of times was regarded as fail.

The results of the bending test, the twisting test, the U-bend test, and the reducing test are summarized in table 1.

TABLE 1