cable

Abstract

To provide a cable having a small outer diameter and good transmission characteristics.SOLUTION: A cable 1 includes: a cable core 3 with a plurality of electric wires 2 including a plurality of signal lines 21; a bind layer 4 disposed around the cable core 3; and a sheath 6 disposed around the bind layer 4. Each of the signal lines 21 includes a conductor 211, and a non-foaming insulator 212 that covers a circumference of the conductor 211. The bind layer 4 includes a foam layer 411 composed of expanded polypropylene.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a cable.

Background Art

[0002] As a cable wired in an automobile or an industrial robot, for example, there is one including a cable core formed by twisting a plurality of electric wires including a plurality of signal lines, a shield layer provided around the cable core, and a sheath provided around the shield layer. As such a cable, in order to obtain good transmission characteristics, a cable using a foamed resin such as foamed polyethylene as an insulator of the electric wire is known (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when a foamed resin is used as the insulator of the electric wire, when the cable core is twisted or when the cable is bent and wired with a small bending radius (for example, a bending radius of 6 times or less the outer diameter of the cable), the insulator made of the foamed resin may be crushed, and the transmission characteristics may deteriorate.

[0005] In order to suppress the crushing of the insulator, for example, it is conceivable to cover the periphery of the foamed resin with a non-foamed skin layer. However, in this case, the outer diameter of the cable core may increase, and the cable may become larger in diameter.

[0006] Therefore, an object of the present invention is to provide a cable having a small outer diameter and good transmission characteristics.

Means for Solving the Problems

[0007] The present invention aims to solve the above problems and provides a cable comprising a cable core having a plurality of electric wires including a plurality of signal wires, a binding layer provided around the cable core, and a sheath provided around the binding layer, wherein the signal wires have a conductor and a non-foamed insulator covering the conductor, and the binding layer has a foamed layer made of foamed polypropylene. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a cable with a small outer diameter and good transmission characteristics. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view showing a section perpendicular to the longitudinal direction of a cable according to one embodiment of the present invention. [Figure 2] (a) is a cross-sectional view of the tape member, and (b) and (c) are cross-sectional views showing modified examples of the tape member. [Figure 3] This is a cross-sectional view showing a cross-section perpendicular to the longitudinal direction of a cable according to one modified example of the present invention. [Modes for carrying out the invention]

[0010] [Embodiment] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0011] Figure 1 is a cross-sectional view showing a cross-section perpendicular to the longitudinal direction of the cable 1 according to this embodiment. The cable 1 is used, for example, as wiring for automobiles or industrial robots.

[0012] As shown in Figure 1, the cable 1 comprises a cable core 3 having multiple electric wires 2 including multiple signal lines 21, a binding layer 4 formed by wrapping a tape member 41 around the cable core 3, a shield layer 5 provided to cover the binding layer 4, and a sheath 6 provided to cover the shield layer 5.

[0013] (Cable core 3) The cable core 3 is constructed by twisting together multiple wires 2. In this embodiment, the cable core 3 has two signal lines 21 for signal transmission and two power lines 22 for power supply, and is constructed by twisting together a total of four wires 2. However, the number of wires 2 constituting the cable core 3 is not limited to this, and the number of signal lines 21 and power lines 22 is not limited to two. High-speed signals, such as 10 GHz, are transmitted through the signal lines 21.

[0014] The signal line 21 has a conductor 211 and a non-foamed insulator 212 surrounding the conductor 211. The power line 22 has a conductor 221 and a non-foamed insulator 222 surrounding the conductor 221. The conductors 211 and 221 are stranded conductors made by twisting together multiple metal strands made of copper or copper alloy. The insulators 212 and 222 are made of non-foamed insulating resin, such as non-foamed polypropylene or polyethylene. Considering the recent regulations on PFAS (perfluoroalkyl and polyfluoroalkyl substances), it is preferable to use non-fluororesin as the insulators 212 and 222. The signal line 21 may have an outer conductor made of multiple metal strands surrounding the insulator 212. Alternatively, a covering may be provided to surround the outer conductor.

[0015] The signal lines 21 and power lines 22 are arranged alternately in the circumferential direction of the cable, with the signal lines 21 and power lines 22 facing each other across the cable center. The signal lines 21 have a larger outer diameter than the power lines 22. In this embodiment, the two signal lines 21 are in contact at the center of the cable, and the power lines 22 are positioned in the valleys between the two signal lines 21. However, the signal lines 21 may not be in contact at the center of the cable and may be spaced apart. If the signal lines 21 are spaced apart, it is preferable that the shortest distance between the signal lines 21 is smaller than the outer diameter of the power lines 22. This prevents the insulator 212 from being crushed at the center of the cable.

[0016] (Bind Layer 4) The binding layer 4 serves to hold the cable core 3 in place so that the twist does not unravel, to improve the transmission characteristics (attenuation), and to adjust the characteristic impedance of the cable 1. Generally, the characteristic impedance is controlled by the thickness and material (such as using foamed resin) of the insulator 212 of the signal line 21, but in this embodiment, the characteristic impedance is adjusted by the thickness and material of the tape material 41 used in the binding layer 4, and the number of layers wrapped around it (i.e., the number of layers in the binding layer 4).

[0017] The tape member 41 has a foamed layer 411 made of foamed polypropylene. Because foamed polypropylene is relatively resistant to crushing, even when the cable is bent with a small bending radius (for example, a bending radius of 6 times or less the outer diameter of the cable), it is possible to suppress the crushing of the foamed layer 411 and suppress the deterioration of transmission characteristics. Furthermore, by constructing the tape member 41 from foamed resin, dielectric loss is suppressed and good transmission characteristics (good attenuation) can be obtained. Moreover, by constructing the tape member 41 from foamed resin, it becomes possible to make the insulator 212 of the signal line 21 thinner while maintaining good transmission characteristics, which also contributes to the weight reduction and miniaturization of the cable 1.

[0018] In this embodiment, as shown in Fig. 2(a), as the tape member 41, a tape member composed entirely of a foam layer 411 was used. The foaming ratio (degree of foaming) of the tape member 41 is preferably about 40%, and more specifically, it is preferably 30% or more and 50% or less. By setting the foaming ratio to 30% or more, the degradation of transmission characteristics can be sufficiently suppressed, and by setting the foaming ratio to 50% or less, it is possible to suppress the tape member 41 from being easily crushed. Also, the thickness of the tape member 41 is preferably 35 μm or more and 100 μm or less. By setting the thickness of the tape member 41 to 35 μm or more, breakage of the tape member 41 can be suppressed. By setting the thickness of the tape member 41 to 100 μm or more, the difference in thickness between the overlapping portion (lap portion) of the tape member 41 and the non-overlapping portion can be reduced, the variation in characteristic impedance can be suppressed, and the transmission characteristics can be stabilized.

[0019] The tape member 41 is configured by spirally winding the tape member 41 around the cable core 3 such that a part in the width direction overlaps. Thereby, a gap is formed in the vicinity of the overlapping portion of the tape member 41, and the thickness of the entire binding layer 4 can be increased, so that the distance between the conductor 211 of the signal line 21 and the shield layer 5 can be increased, and the transmission characteristics can be stabilized. A gap 7 (air layer) is formed between the adjacent electric wires 2 and the binding layer 4 (tape member 41) in the circumferential direction without any intervening material filled.

[0020] The winding direction of the tape member 41 is preferably opposite to the twisting direction of the cable core 3. Thereby, it is possible to suppress the tape member 41 from falling between the adjacent electric wires 2 in the circumferential direction of the cable, and it is possible to make the outer diameter of the entire cable 1 closer to a circular shape. As a result, the symmetry of the cross-sectional shape of the cable 1 can be maintained, and the transmission characteristics can be stabilized.

[0021] In addition, in this embodiment, the case where the entire tape member 41 is a foamed layer 411 has been described. However, the present invention is not limited to this, and at least one of the front and back surfaces of the tape member 41 may be made of the foamed layer 411. For example, as shown in FIG. 2(b), the tape member 41 may have a structure in which foamed layers 411 are provided on the front and back surfaces of the non-foamed layer 412, respectively. The non-foamed layer 412 may be made of a material different from polypropylene (for example, polyethylene). Further, as shown in FIG. 2(c), a configuration in which foamed layers 411 having different degrees of foaming are combined may also be used. In the illustrated example, the second foamed layer 411b having a lower foaming ratio than the first foamed layer 411a is provided on the front and back surfaces of the first foamed layer 411a having a large foaming ratio. By configuring as shown in FIGS. 2(b) and 2(c), it becomes possible to adjust the cushioning property of the binding layer 4 or to adjust the characteristic impedance.

[0022] Also, in this embodiment, the binding layer 4 is provided as a single layer. However, a plurality of binding layers 4 may be provided between the cable core 3 and the shield layer 5. This makes it possible to increase the distance between the conductor 211 of the signal line 21 and the shield layer 5 and to make the transmission characteristics more stable. In this case, the winding directions of the tape members 41 of the binding layers 4 adjacent to each other in the cable diameter direction are preferably opposite to each other. This makes it possible to suppress the influence of the step at the overlapping portion of the tape member 41, further suppress the variation in characteristic impedance, and make the transmission characteristics more stable. When providing a plurality of binding layers 4, a structure may be adopted in which a binding layer 4 formed by extrusion coating a resin made of foamed polypropylene is provided around the binding layer 4 composed of the tape member 41 made of foamed polypropylene. This makes it possible to increase the thickness of the entire binding layer 4, so that the distance between the conductor 211 of the signal line 21 and the shield layer 5 can be increased, and the transmission characteristics can be stabilized. Also, a layer for suppressing the collapse of the binding layer 4 may be provided between the binding layer 4 and the shield layer 5 around the binding layer 4. This layer is made of, for example, a non-foamed tape member or an extrusion coating member.

[0023] (Shield layer 5) The shield layer 5 is composed of a braided shield made by braiding together multiple metal wires, for example, made of copper or a copper alloy. However, it is not limited to this, and the shield layer 5 may also be a horizontally wound shield made by spirally winding multiple metal wires.

[0024] Incidentally, in industrial robots used in factories and the like, the cables wired to the industrial robot are repeatedly bent and twisted as they operate. When a cable 1 is wired to the movable parts (parts that bend and twist) of such an industrial robot, it is necessary to suppress the breakage of the metal wires of the shield layer 5 when the cable 1 is repeatedly bent and twisted, and to suppress the deterioration of the shielding characteristics (noise shielding effect) of the shield layer 5. In this embodiment, since the binding layer 4 that serves as the base for the shield layer 5 is made of a tape member 41 having a foam layer 411, the binding layer 4 acts as a cushioning layer. That is, the binding layer 4 can alleviate the stress applied to the shield layer 5 and cable core 3 when the cable 1 is bent and twisted, thereby suppressing the breakage of the metal wires of the shield layer 5 and damage to the electric wires 2 that make up the cable core 3.

[0025] (Sheath 6) Sheath 6 is made of, for example, PVC (polyvinyl chloride).

[0026] (modified version) In this embodiment, the two signal lines 21 are in contact at the center of the cable. However, the cable core 3 may be constructed by providing a fiber intervening 8 at the center of the cable and twisting the wires 2 (two signal lines 21 and two power lines 22) around the fiber intervening, as shown in Figure 3, when the outer diameters of the signal lines 21 and power lines 22 are the same. Since the transmission characteristics will deteriorate if the fiber intervening 8 absorbs moisture, it is preferable to use resin fibers made of nylon, polyethylene, or other materials that do not easily absorb moisture as the fiber intervening 8. In order to suppress the deterioration of transmission characteristics, it is preferable to leave a gap 7 (air layer) between adjacent wires 2 and the binding layer 4 (tape member 41) in the circumferential direction without filling it with fiber intervening 8. In this embodiment, the binding layer 4 is made of a tape member 41 made of foamed polypropylene. However, the binding layer 4 may be made by extruding a resin made of foamed polypropylene around the cable core 3. However, the bind layer 4, which is made of a tape member 41 made of foamed polypropylene, is easier to obtain the effects and advantages of this embodiment than the bind layer 4 which is made by extrusion coating, and the bind layer 4 is also easier to form.

[0027] (Operation and Effects of the Embodiment) As described above, in the cable 1 according to this embodiment, the insulator 212 of the signal line 21 is non-foamed, and the tape member 41 constituting the binding layer 4 has a foamed layer 411 made of foamed polypropylene.

[0028] The presence of a foamed layer 411 in the tape member 41 allows for good transmission characteristics even when the insulator 212 of the signal line 21 is not foamed, enabling the realization of a cable 1 with a small outer diameter and good transmission characteristics. Furthermore, since the foamed layer 411 is made of foamed polypropylene, it is less prone to crushing, making it possible to maintain good transmission characteristics even when the cable 1 is bent at a small bending radius (for example, a bending radius of 6 times or less the outer diameter of the cable). In addition, the presence of a foamed layer 411 in the tape member 41 makes it possible to achieve a desired characteristic impedance while making the insulator 212 thin. As a result, a cable 1 suitable for long-distance transmission of high-speed signals, such as 10 GHz, can be realized.

[0029] Furthermore, Cable 1 does not require complex manufacturing processes and can be manufactured with simple processes, resulting in low cost and high productivity. In addition, Cable 1 reduces the use of fluororesin, thus reducing the environmental impact. Conventionally, when fluororesin was not used for the insulator 212 of the signal line 21, foamed irradiated cross-linked polyethylene was sometimes used as the insulator 212 of the signal line 21. In this case, the insulator 212 was prone to crushing, which tended to degrade the transmission characteristics at high frequencies. In this embodiment, since a tape member 41 made of foamed polypropylene is used, the degradation of transmission characteristics due to crushing can be suppressed.

[0030] Furthermore, the binding layer 4 acts as a cushioning layer, which helps to prevent breakage of the metal wires in the shielding layer 5 and damage to the electric wires 2 that make up the cable core 3 when the cable 1 is repeatedly bent or twisted.

[0031] (Summary of the embodiments) Next, the technical concept understood from the embodiments described above will be described using the reference numerals and other symbols from the embodiments. However, the reference numerals and other symbols in the following description are not limited to the components in the claims that are specifically shown in the embodiments.

[0032] [1] A cable (1) comprising a cable core (3) having a plurality of electric wires (2) including a plurality of signal lines (21), a binding layer (4) provided around the cable core (3), and a sheath (6) provided around the binding layer (4), wherein the signal lines (21) have a conductor (211) and a non-foamed insulator (212) covering the conductor (211), and the binding layer (4) has a foamed layer (411) made of foamed polypropylene.

[0033] [2] The binding layer (4) is made by wrapping a tape member (41) around the cable core, as described in [1].

[0034] [3] The cable (1) according to [2], wherein the tape member (41) has at least one of its front and back surfaces made of the foam layer (411).

[0035] [4] The cable (1) according to [2], wherein the tape member (41) is entirely made of the foam layer (411).

[0036] [5] The cable (1) according to [4], wherein the thickness of the tape member (41) is 35 μm or more and 100 μm or less.

[0037] [6] The binding layer (4) is configured by spirally wrapping the tape member (41) around the cable core (3) such that a portion of the tape member (41) in the width direction overlaps, as described in [2], the cable (1).

[0038] [7] The cable (1) according to [2], wherein the cable core (3) is made up of a plurality of electric wires (2) twisted together, and the twisting direction of the cable core (3) and the winding direction of the tape member (41) are in opposite directions.

[0039] [8] The cable (1) according to [1], wherein a plurality of the binding layers (4) are laminated around the cable core (3), and each of the plurality of the binding layers (4) is made by winding a tape member (41) in the longitudinal direction of the cable, and the winding direction of the tape member (41) of adjacent binding layers (4) in the radial direction of the cable is opposite.

[0040] (Note) Although embodiments of the present invention have been described above, the embodiments described above do not limit the invention as defined in the claims. Furthermore, it should be noted that not all combinations of features described in the embodiments are necessarily essential for solving the problem of the invention. In addition, the present invention can be implemented with appropriate modifications without departing from its spirit. [Explanation of Symbols]

[0041] 1… Cable 2...Electric wire 21... Signal line 211... Conductor 212...Insulator 22…Power line 3… Cable core 4…Binding layer 41... Tape component 411... Foam layer 5…Shield layer 6...Sheath 7…Gap

Claims

1. A cable core having multiple wires including multiple signal lines, A binding layer provided around the cable core, The binding layer comprises a sheath provided around the binding layer, The signal line comprises a conductor and a non-foamed insulator covering the conductor. Multiple binding layers are stacked around the cable core. Each of the multiple binding layers is formed by wrapping a tape member around the cable in the longitudinal direction. The winding directions of the tape members of the binding layers adjacent to each other in the cable radial direction are opposite. The multiple binding layers each have a foamed layer made of foamed polypropylene. cable.

2. The tape member has at least one of its front and back surfaces made of the foam layer. The cable according to claim 1.

3. The tape member is entirely made of the foam layer. The cable according to claim 1.

4. The thickness of the tape member is 35 μm or more and 100 μm or less. The cable according to claim 3.

5. The plurality of binding layers are formed by spirally wrapping the tape member around the cable core such that a portion of the tape member in the width direction overlaps. The cable according to claim 1.

6. The cable core is constructed by twisting together the multiple electric wires. The cable according to claim 1.

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