JP2022023503A - Optical fiber cable - Google Patents

Abstract

To provide an optical fiber cable capable of attaining suppression of occurrence of buckling while maintaining bending directivity.SOLUTION: An optical fiber cable 1 comprises: a cable body part 10; a tubular external sheath 20 housing the cable body part 10; a pair of first tension members 31 that are embedded in the external sheath 20 and arranged so as to face each other with the cable body part 10 held therebetween on a first imaginary line L1 passing through a center C1 of the cable body part 10; and a pair of second tension members 32 that are embedded in the external sheath 20 and arranged so as to face each other with the cable body part 10 held therebetween on a second imaginary line L2 passing through the center C1 of the cable body part 10. The first imaginary line L1 and the second imaginary line L2 are substantially orthogonal to each other, and the first tension members 31 is thicker than the second tension members 32.SELECTED DRAWING: Figure 1

Description

The present invention relates to an optical fiber cable.

The optical fiber cable includes an optical fiber core wire, a tensile strength fiber layer provided on the outer periphery of the optical fiber core wire, an outer skin provided on the outer periphery of the tensile strength fiber layer, and a pair of tensile strength bodies embedded in the outer skin. (See, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2005-208430

For an optical fiber cable as described above, in order to protect the optical fiber from tension during laying and to set a direction in which the optical fiber cable is easily bent (to give bending direction) to facilitate laying workability. Is provided with a pair of tensile strength bodies.

Further, in such an optical fiber cable laying process, a part of the optical fiber cable is usually laid with a surplus in preparation for future expansion or the like. This surplus portion may be bundled in an annular shape by being bent in the above-mentioned flexible direction, and may be stored in an upright state inside a manhole or the like. However, when the temperature of the storage environment becomes high, the outer skin of the optical fiber cable may soften and the bundle may be crushed by its own weight. At this time, the load is concentrated on the portion of the optical fiber cable having a large curvature. As a result, there is a problem that the optical fiber cable buckles and the outer skin is cracked, or the transmission quality of the optical fiber cable is deteriorated due to a sharp bending applied to the optical fiber.

An object of the present invention is to provide an optical fiber cable capable of suppressing the occurrence of buckling of the optical fiber cable while maintaining the bending direction.

[1] The optical fiber cable according to the present invention is embedded in a cable main body having an optical fiber, a tubular outer sheath accommodating the cable main body, and the outer sheath, and passes through the center of the cable main body. A pair of first tensile strength bodies arranged so as to face each other with the cable body portion interposed therebetween on a first virtual straight line, and a second one embedded in the outer sheath and passing through the center of the cable body portion. The first virtual straight line and the second virtual straight line are substantially provided with a pair of second tensile strength bodies arranged so as to face each other with the cable main body portion interposed therebetween on the virtual straight line of the above. The first tensile strength body is an optical fiber cable thicker than the second tensile strength body.

[2] In the above invention, the following equation (2) may be satisfied.
0.09 ≤ I _x / I _y ≤ 0.36 ... (2)
However, in the above equation (2), I _x is the moment of inertia of area with respect to the first virtual straight line of the optical fiber cable, and I _y is the moment of inertia of area with respect to the second virtual straight line of the optical fiber cable. The next moment.

[3] In the above invention, an optical fiber cable satisfying the following equation (3).
0.09 ≤ S ₂ / S ₁ ≤ 0.36 ... (3)
However, in the above equation (3), S ₁ is the cross-sectional area of the first tensile strength body, and S ₂ is the cross-sectional area of the second tensile strength body.

[4] In the above invention, the cross-sectional shapes of the first and second tensile strength bodies are perfect circles, and the following equation (4) may be satisfied.
0.3 ≤ d ₂ / d ₁ ≤ 0.6 ... (4)
However, in the above equation (4), d ₁ is the diameter of the first tensile strength body, and d ₂ is the diameter of the second tensile strength body.

[5] In the above invention, the cross-sectional shape of the first and second tensile strength bodies may be elliptical or rectangular.

In the optical fiber cable of the present invention, the first tensile strength body is thicker than the second tensile strength body. Therefore, the optical fiber cable is easier to bend in the direction in which the first virtual straight line is bent in the neutral line than in the case where the second virtual straight line is bent in the bending neutral line. That is, the optical fiber cable has bending directionality in the direction in which the first virtual straight line is the neutral line for bending.

Further, even if the outer sheath softens at a high temperature, the second tensile strength body can prevent the optical fiber cable from excessively bending in the direction in which the first virtual straight line is a bending neutral line. Further, since the second tensile strength body is embedded in the outer sheath, the second tensile strength body does not shift in the circumferential direction of the optical fiber cable. Therefore, the occurrence of buckling of the optical fiber cable can be suppressed by the second tensile strength body.

From the above, the optical fiber cable of the present invention can suppress the occurrence of buckling of the optical fiber cable while maintaining the bending direction.

FIG. 1 is a cross-sectional view showing an optical fiber cable according to an embodiment of the present invention. FIG. 2 is a perspective view showing an optical fiber unit according to an embodiment of the present invention. FIG. 3 is a perspective view showing an intermittently fixed optical fiber tape core wire according to the embodiment of the present invention. FIG. 4 is a cross-sectional view showing a modified example of the optical fiber cable according to the embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an optical fiber cable according to the present embodiment. FIG. 2 is a perspective view showing an optical fiber unit according to the present embodiment. FIG. 3 is a perspective view showing an intermittently fixed optical fiber tape core wire in the present embodiment.

As shown in FIG. 1, the optical fiber cable 1 includes a cable main body portion 10, an external sheath 20, a first tensile strength body 31, and a second tensile strength body 32.

The cable main body 10 in the present embodiment is a member extending linearly along the longitudinal direction of the optical fiber cable 1. The cable main body 10 is covered with an external sheath 20 and is located substantially in the center of the optical fiber cable 1. The cable main body 10 has an optical fiber assembly 11 and a presser winding tape 17.

The optical fiber assembly 11 is an assembly in which a plurality of optical fibers 14 are assembled. Specifically, in the present embodiment, the optical fiber assembly 11 is formed by bundling a plurality of optical fiber units 12. Further, as shown in FIG. 2, each optical fiber unit 12 includes a plurality of optical fiber tape core wires 13 and a bundle material 16.

As shown in FIG. 3, each optical fiber tape core wire 13 is an intermittent adhesive type optical fiber in which a plurality of (four in this example) optical fibers (optical fiber strands) 14 are connected in parallel and intermittently connected. It is a tape. Specifically, the optical fibers 14 (optical fiber strands) adjacent to each other are intermittently bonded by the bonding portion 15 at predetermined intervals. The adhesive portion 15 is formed of, for example, an ultraviolet curable resin or a thermoplastic resin. The adhesive portions 15 are arranged so as to be offset from each other with respect to the longitudinal direction of the optical fiber tape core wire 13.

As shown in FIG. 2, the optical fiber unit 12 is composed of a plurality of optical fiber tape core wires 13 bundled by a bundle material 16. The bundle material 16 is a member wound around the outer circumference of a bundle of optical fiber tape core wires 13. Although not particularly shown, as the bundle material 16, a string-shaped member wound spirally or SZ-shaped around the outer circumference of the bundle of the optical fiber tape core wire 13 may be used. The bundle material 16 may be one or a plurality of bundles. The configuration of the bundle material 16 is not particularly limited as long as the bundled state of the plurality of optical fibers can be maintained.

Then, as shown in FIG. 1, a plurality of optical fiber units 12 are twisted together to form an optical fiber aggregate 11. Specific examples of the method of twisting the optical fiber unit 12 include SZ twisting and unidirectional twisting. The SZ twist is a twisting method in which a plurality of linear bodies are twisted while reversing the twisting direction at predetermined intervals. The unidirectional twist is a twisting method of a plurality of linear bodies having a twisting direction of only one direction, that is, a twisting method of twisting a plurality of linear bodies in a spiral shape.

The configuration of the optical fiber tape core wire 13 is not limited to the above. For example, the optical fibers 14 may not be intermittently bonded to each other, but the entire optical fibers 14 may be bonded to each other. Further, the configuration of the optical fiber unit 12 is not particularly limited to the above configuration. For example, the optical fiber unit 12 may be configured by simply bundling a plurality of optical fiber strands 14 without using the optical fiber tape core wire 13. Further, the configuration of the optical fiber assembly 11 is not particularly limited to the above configuration. For example, the optical fiber assembly 11 may be configured by simply twisting a plurality of optical fiber strands 14 without using the optical fiber unit 12. Further, the optical fiber assembly 11 may be formed of a loose tube accommodating the optical fiber.

The periphery of the optical fiber assembly 11 is covered with a presser winding tape 17. In the present embodiment, the longitudinal direction of the presser winding tape 17 substantially coincides with the axial direction of the optical fiber cable 1, and the width direction of the presser winding tape 17 substantially coincides with the circumferential direction of the optical fiber cable 1. As such, the presser winding tape 17 is vertically attached to the outer periphery of the optical fiber assembly 11. By winding the presser winding tape 17 vertically, the workability of taking out the optical fiber 14 from the optical fiber cable 1 is improved. The method of winding the presser winding tape 17 is not limited to vertical winding, and may be, for example, horizontal winding (spiral winding).

The presser winding tape 17 is made of a non-woven fabric or a film. Specific examples of the nonwoven fabric constituting the presser winding tape 17 are not particularly limited, and examples thereof include a nonwoven fabric made of fibers such as polyester, polyethylene, and polypropylene. Specific examples of the film constituting the presser foot tape 17 are not particularly limited, but for example, a resin such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), or nylon. A film consisting of. A water-absorbent member may be used as the presser foot tape 17. Although the presser-wrapping tape 17 is not an essential configuration, the optical fiber 14 can be protected by arranging the presser-wrapping tape 17.

As shown in FIG. 1, the outer sheath 20 is a tubular member that covers the outer periphery of the presser winding tape 17. The external sheath 20 houses the cable main body 10 inside. The outer sheath 20 is made of a resin material such as polyvinyl chloride (PVC), polyethylene (PE), nylon, ethylene fluoride, or polypropylene (PP).

The pair of first tensile strength bodies 31 are tensile strength wires extending substantially parallel to the cable main body 10. The cross section of the first tensile strength body 31 in the width direction has a perfect circular shape. The pair of first tensile strength bodies 31 have substantially the same diameter d1 from _each other. The first tensile strength body 31 is thicker than the second tensile strength body 32. In the present embodiment, "thick" means that the maximum width of the first tensile strength body 31 is larger than the maximum width of the second tensile strength body 32. In the present embodiment, the maximum width of the first and second tensile strength bodies 31, 32 is the diameter.

The first tensile strength body 31 is embedded in the outer sheath 20. Further, the center C ₂ of the first tensile strength body 31 is separated from the center C ₁ of the cable main body portion 10 by a distance _R1 . The center C ₂ of the first tensile strength body 31 is located on the first virtual straight line L ₁ . Further, the pair of first tensile strength bodies 31 are provided so as to be line-symmetric with respect to the _second virtual straight line L2 substantially orthogonal to the _first virtual straight line L1. Therefore, the pair of first tensile strength bodies 31 face each other so as to sandwich the cable main body 10 from both sides of the cable main body 10.

The _first virtual straight line L1 in the present embodiment is a straight line passing through the center C1 of the cable main body ₁₀ and the center _C2 of the pair of first tensile strength bodies 31 in the widthwise cross section of the optical fiber cable 1. The second virtual straight line L ₂ in the present embodiment is a straight line passing through the center C ₁ of the cable main body 10 and the center C ₃ of the pair of second tensile strength bodies 32 (described later) in the widthwise cross section of the optical fiber cable 1. Is.

As the material constituting the first tensile strength body 31, a non-metallic material or a metallic material can be exemplified. Specific examples of the non-metallic material are not particularly limited, but for example, glass fiber reinforced plastic (GFRP), aramid fiber reinforced plastic (KFRP) reinforced with Kevlar (registered trademark), polyethylene fiber reinforced plastic reinforced with polyethylene fiber, and the like. Further, fiber reinforced plastics (FRP) such as carbon fiber reinforced plastics (CFRP) reinforced with carbon fibers can be mentioned. Specific examples of the metallic material are not particularly limited, and examples thereof include metal wires such as steel wires.

The pair of second tensile strength bodies 32 are tensile strength wires extending substantially parallel to the cable main body 10. The cross section of the second tensile strength body 32 in the width direction has a perfect circular shape. The pair of second tensile strength bodies 32 have substantially the same diameter d ₂ from each other.

The second tensile strength body 32 is a member independent of the first tensile strength body 31. The optical fiber cable 1 of the present embodiment includes a total of four tensile strength bodies 31 and 32. The second tensile strength body 32 is embedded in the outer sheath 20. Further, the center C ₃ of the second tensile strength body 32 is separated from the center C ₁ of the cable main body portion 10 by a distance _R2 . The distance R ₂ is not particularly limited, but is substantially the same as the above-mentioned distance R ₁ (R ₁ = R ₂ ). The center C ₃ of the second tensile strength body 32 is located on the second virtual straight line L ₂ substantially orthogonal to the first virtual straight line L ₁ . Further, the pair of second tensile strength bodies 32 are provided so as to be line-symmetric with respect to the _first virtual straight line L1. Therefore, the pair of second tensile strength bodies 32 face each other so as to sandwich the cable main body 10 from both sides of the cable main body 10 described above. As the material constituting the second tensile strength body 32, the same material as the material constituting the first tensile strength body 31 can be used.

The diameter d ₂ of the second tensile strength body 32 is smaller than the diameter d ₁ of the first tensile strength body 31 as shown in the following equation (5). The diameter d ₁ of the tensile strength body is appropriately designed by adjusting the material and thickness of the tensile strength body according to the allowable tension required for the optical fiber cable 1. For example, in an optical fiber cable having a core number in the range of 48 cores to 10368 cores, a glass FRP having a tensile elastic modulus of 50 GPa can be used as the optical fiber. The diameter d ₁ of the first tensile strength body 31 can be, for example, larger than 1.5 mm and 3.0 mm or less (1.5 mm <d ₁ ≦ 3.0 mm). The diameter d ₂ of the second tensile strength body 32 can be, for example, 0.25 mm or more and less than 3.0 mm (0.25 mm ≦ d ₂ <3.0 mm).
d ₁ > d ₂ ... (5)

In the optical fiber cable 1 in the present embodiment as described above, as described in the above equation (5), the diameter d ₂ of the second tensile strength body 32 is smaller than the diameter d ₁ of the first tensile strength body 31. Therefore, the optical fiber cable has bending directionality in the direction (first direction D ₁ ) in which the first virtual straight line L ₁ is the neutral line for bending.

Further, in the optical fiber cable 1 bundled in the state of being bent in the _first direction D1, when the outer sheath 20 is softened at a high temperature, the second tensile strength body located outside the bending of the optical fiber cable 1 Tensile stress is applied to 32, and compressive stress is applied to the second tensile strength body 32 located inside the bending of the optical fiber cable 1. At this time, since the second tensile strength body 32 located inside the bending of the optical fiber cable 1 withstands the compressive stress, it is possible to prevent the optical fiber cable ₁ from being excessively bent in the first direction D1. .. As a result, it is possible to suppress the occurrence of buckling of the optical fiber cable 1.

Further, when the second tensile strength body is not fixed to the outer sheath, when the optical fiber cable is bent in the first direction, the second tensile strength body approaches the first virtual straight line of the optical fiber cable. It will shift. As described above, if the second tensile strength body is displaced, it is not possible to prevent the optical fiber cable from being excessively bent in the first direction. On the other hand, in the present embodiment, the second tensile strength body 32 is embedded in the outer sheath 20, so that when the optical fiber cable 1 is bent in the _first direction D1, the second tensile strength body 32 is embedded. 32 does not shift. Therefore, the second tensile strength body 32 can suppress the occurrence of buckling of the optical fiber cable 1.

From the above, the optical fiber cable 1 in the present embodiment can suppress the occurrence of buckling of the optical fiber cable 1 while maintaining the bending direction, and the occurrence of cracks in the external sheath 20 and the optical fiber cable. It is possible to suppress the deterioration of the transmission quality of 1.

Further, as shown in the above equation (5), the diameter d ₂ of the second tensile strength body 32 is smaller than the diameter d ₁ of the first tensile strength body 31. Therefore, the moment of inertia of area I _x with respect to the first virtual straight line L ₁ of the optical fiber cable 1 is smaller than the moment of inertia of area I _y with respect to the second virtual straight line L ₂ of the optical fiber cable 1 (I). _x <I _y ).

The bendability of the optical fiber cable 1 in a specific direction is determined by the moment of inertia of area of the optical fiber cable 1. Here, the elastic modulus of the outer sheath 20 is smaller than the elastic modulus of the first and second tensile strength bodies 31 and 32, and should be sufficiently ignored when calculating the moment of inertia of area of the optical fiber cable 1. Can be done. Therefore, in the present embodiment, the moment of inertia of area I _x , I _y of the optical fiber cable 1 is described below (6) when the first tensile strength body 31 and the second tensile strength body 32 are made of the same material. As shown in the equation and the equation (7), it can be represented by the moment of inertia of area of the first tensile strength body 31 and the second tensile strength body 32, and the diameters d ₁ of the first and second tensile strength bodies 31, 32, It depends heavily _on d2.

In the present embodiment, the ratio I _x / I _y of the moment of inertia of area preferably satisfies the following equation (8). By setting the ratio I _x / I _y to 0.09 or more, even if the outer sheath 20 of the optical fiber cable 1 is softened, the optical fiber cable ₁ is excessively bent in the first direction D1. Since it can be suppressed, the occurrence of buckling of the optical fiber cable 1 can be further suppressed. Further, when the ratio I _x / I _y is set to 0.36 or less, the optical fiber cable 1 is bent in the direction (second direction D ₂ ) in which the second virtual straight line L ₂ is the bending neutral line. In comparison, the optical fiber cable ₁ is more easily bent in the first direction D1.
0.09 ≤ I _x / I _y ≤ 0.36 ... (8)

Further, the ratio I _x / I _y of the moment of inertia of area in the present embodiment is the ratio S ₂ / S ₁ of the cross-sectional area S ₂ of the second tensile strength body 32 to the cross-sectional area S ₁ of the first tensile strength body 31. Can be approximated. In the above equation (6) showing the moment of inertia of area I _x , since R ₂ is a sufficiently large value with respect to d ₁ and d ₂ , the first and second terms on the right side can be ignored. Therefore, the moment of inertia of area I _x can be expressed as the following equation (9). Similarly, since R ₂ has the same value as R ₁ , the moment of inertia of area I _y can be expressed as the following equation (10) by ignoring the first and second terms on the right side. Therefore, the ratio I _x / I _y of the moment of inertia of area can be expressed as the following equation (11) from the following equations (9) and (10).

Here, the ratio S2 / S1 of the cross _- sectional area S2 of the _second tensile strength body 32 to the cross _- sectional area S1 of the _first tensile strength body 31 can be expressed by the following equation (12). Therefore, from the above equation (11) and the following equation (12), the following equation (13) showing that the ratio I _x / I _y and the ratio S ₂ / S ₁ are close can be derived.

Therefore, from the above equations (8) and (13), it is preferable that the ratio S ₂ / S ₁ satisfies the following equation (14) as in the case of I _x / I _y .
0.09 ≤ S ₂ / S ₁ ≤ 0.36 ... (14)

Further, in the present embodiment, it is preferable that the ratio d ₂ / d ₁ of the diameter d ₂ of the second tensile strength body 32 to the diameter d ₁ of the first tensile strength body 31 satisfies the following equation (15). By setting the ratio d ₂ / d ₁ to 0.3 or more, even if the outer sheath 20 of the optical fiber cable 1 is softened, the optical fiber cable 1 is excessively bent in the first direction D ₁ . Since it can be suppressed, the occurrence of buckling of the optical fiber cable 1 can be further suppressed. Further, by setting the ratio d ₂ / d ₁ to 0.6 or less, the optical fiber cable 1 is twisted in the first direction D ₁ as compared with the case where the optical fiber cable 1 is bent in the second direction D ₂ . It becomes easy to bend.
0.3 ≤ d ₂ / d ₁ ≤ 0.6 ... (15)

It should be noted that the embodiments described above are described for facilitating the understanding of the present invention, and are not described for limiting the present invention. Therefore, each element disclosed in the above-described embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

Further, the outer shape of the cable main body 10 is not particularly limited as long as it does not deviate from the gist of the present application. For example, the outer shape of the cable body 10 may be round, flat, irregular, or irregular. Further, the cable main body portion 10 may have a center tube structure including an internal sheath. Further, the optical fiber cable 1 may include a ripcord for tearing the outer sheath 20.

Further, in the above embodiment, the cross-sectional shapes of the first and second tensile strength bodies 31 and 32 are perfect circles, but the cross-sectional shapes may be elliptical or rectangular. When the cross-sectional shape is an ellipse, the length of the long axis, which is the maximum width of the ellipse, is larger than that of the second tensile strength body 32 when the first tensile strength body 31 is larger than the second tensile strength body 32. However, it can be said that the first tensile strength body 31 is thicker. Further, when the cross-sectional shape is rectangular, the second tensile strength body 31 is larger than the second tensile strength body 32 when the length of the long side, which is the maximum width of the ellipse, is larger than that of the second tensile strength body 32. It can be said that the first tensile strength body 31 is thicker than the 32.

FIG. 4 is a cross-sectional view showing a modified example of the optical fiber cable in the present embodiment. In this modification, the case where the cross-sectional shapes of the first and second tensile strength bodies 31B and 32B of the optical fiber cable 1B are elliptical will be described.

As shown in FIG. 4, the cross-sectional shape of the first tensile strength body 31B is an ellipse having a major axis length of d _1y and a minor axis length of d _1x . The cross-sectional shape of the second tensile strength body 32B is an ellipse having a major axis length of d _2x and a minor axis length of d _2y . Since the major axis d _1y is longer than the major axis d _2x (d _1y > d _2x ), the first tensile strength body 31B is thicker than the second tensile strength body. Further, the short axis d _1x is also longer than the length d _2y of the short axis (d _1x > d _2y ).

The first tensile strength body 31B is arranged so that the long axis is substantially perpendicular to the _first virtual straight line L1 and the short axis is substantially parallel to the _first virtual straight line L1. There is. The second tensile strength body 32B is arranged so that the long axis is substantially perpendicular to the _second virtual straight line L2 and the short axis is substantially parallel to the _second virtual straight line L2. There is. By making the minor axis direction of the first and second tensile strength bodies 31B and 32B substantially parallel to the thickness direction of the outer sheath 20, the outer sheath 20 can be made thinner, so that the alignment of the optical fiber cable 1B becomes more linear. Can be made thinner.

Further, the moment of inertia of area I _x , I _y of the optical fiber cable 1B is the following equation (16) and (17) when the first tensile strength body 31B and the second tensile strength body 32B are made of the same material. As shown in the formula, it can be represented by the moment of inertia of area of the first tensile strength body 31B and the second tensile strength body 32B. Also in this case, as in the above embodiment, it is preferable that the ratio I _x / I _y of the moment of inertia of area satisfies the relationship of the above equation (8).

Further, also in this modification, the ratio I _x / I _y of the moment of inertia of area is the ratio S ₂ / S of the cross-sectional area S ₂ of the second tensile strength body 32B to the cross-sectional area S ₁ of the first tensile strength body 31B. It can be approximated by ₁ . Also in the above equations (16) and (17) showing the moment of inertia of area, R ₁ and R ₂ are sufficiently large values with respect to d _1x , d _1y , d _2x , and d _2y , so that they are on the right side. The first and second terms can be ignored. Therefore, the ratio I _x / I _y of the moment of inertia of area can be expressed as the following equation (18). Here, the cross-sectional area ratio S ₂ / S ₁ can be expressed by the following equation (19) using the area formula of the ellipse. Therefore, from the following equations (18) and (19), the following equation (20) showing that the ratio I _x / I _y and the ratio S ₂ / S ₁ are close can be derived.

Therefore, even in this modification, the ratio S2 _/ S1 satisfies the above equation ₍ 14). In this modification, the above equation (14) holds regardless of the direction in which the minor axis and the major axis of the ellipse extend. Therefore, it can be said that the bending direction and buckling resistance of the optical fiber cable do not depend on the directions of the long axis and the short axis of the ellipse, but depend on the ratio of the cross-sectional areas. Therefore, also in this modification, the same bending direction and buckling resistance of the optical fiber cable as in the above embodiment can be obtained. Even when the cross-sectional shape of the tensile strength body is rectangular, it is self-evident that the same bending direction and buckling resistance of the optical fiber cable as in the above embodiment can be obtained within the range satisfying the equation (14). ..

Hereinafter, examples and comparative examples in this embodiment will be described. In the following Examples and Comparative Examples, an optical fiber cable was produced, and the bending direction and buckling resistance of the optical fiber cable were evaluated.

(Examples 1 to 9)
The diameter d ₂ of the second tensile strength body 32 was changed in a range less than the diameter d ₁ of the first tensile strength body 31 to produce an optical fiber cable 1 as shown in FIG. Then, the bending directionality of the produced optical fiber cable 1 was evaluated, and the buckling resistance under high temperature was evaluated. At this time, the outer shape of the optical fiber cable 1 was set to 34 mm. The thickness of the outer sheath 20 was set to 3 mm. Further, the distance _R1 between the center C1 of the cable main body 10 and the center _C2 of the _first tensile strength body 31 is set to 16 mm. Further, the distance R ₂ between the center C ₁ of the cable main body 10 and the center C ₃ of the second tensile strength body 32 is also set to 16 mm.

The bending direction was evaluated as follows. That is, the optical fiber cable 1 is bent in the first direction D ₁ and the second direction D ₂ shown in FIG. 1, respectively, and is bent in the first direction D ₁ and in the second direction D ₂ . We evaluated whether we felt a difference in some cases. In Table 1 below, the case where the difference is clearly felt is judged as "◎". In addition, the case where a difference was felt was judged as "○". In addition, the case where a slight difference was felt was judged as "Δ". In addition, the case where no difference was felt was determined as "x".

The buckling resistance was evaluated as follows. That is, first, the optical fiber cable ₁ was bent in the first direction D1 and bundled in an annular shape. At this time, the diameter of the bundle was set to 1.5 m. Then, the bundled optical fiber cable 1 was left standing for 24 hours in an environment of 70 ° C. in an upright state. After that, it was visually confirmed whether or not the bundle of the optical fiber cable 1 was deformed into an elliptical shape due to its own weight, and whether or not the outer sheath 20 was cracked. In Table 1 below, the case where the bundle of the optical fiber cables 1 is not deformed or cracked is judged as “◯”. Further, the case where the optical fiber cable 1 was deformed but buckling and cracking did not occur was determined as “Δ”. Further, the case where the optical fiber cable 1 is greatly deformed and buckling and cracking occur is determined as “x”. Here, when the height of the bundle of the optical fiber cable 1 is less than 80% of the initial bundle diameter, it is determined that "deformation has occurred".

(Comparative Example 1)
An optical fiber cable was produced in the same manner as in Examples 1 to 9, except that the optical fiber cable was not provided with a pair of second tensile strength bodies. Then, in the same manner as in the examples, the bending directionality of the produced optical fiber cable was evaluated, and the buckling resistance at high temperature was evaluated.

(Comparative Example 2)
An optical fiber cable was produced by setting the diameter d ₂ of the second tensile strength body 32 to the same value as the diameter d ₁ of the first tensile strength body 31. Then, in the same manner as in the examples, the bending directionality of the produced optical fiber cable was evaluated, and the buckling resistance at high temperature was evaluated.

表１に示すように、実施例１～９では、光ファイバケーブルの束の座屈が生じることがなかった。なお、実施例１，２において、光ファイバケーブルの束が若干変形したが、この光ファイバケーブルは品質上問題のないものであった。これに対して、比較例１では、光ファイバケーブルが大きく変形して座屈し、外部シースに割れが生じてしまった。

As shown in Table 1, in Examples 1 to 9, buckling of the bundle of the optical fiber cable did not occur. In Examples 1 and 2, the bundle of the optical fiber cables was slightly deformed, but the optical fiber cables had no problem in terms of quality. On the other hand, in Comparative Example 1, the optical fiber cable was greatly deformed and buckled, and the outer sheath was cracked.

Further, in Examples 1 to 9, a difference could be felt when the optical fiber cable was bent in the _first direction D1 and when it was bent in the _second direction D2. On the other hand, in Comparative Example 2, the difference could not be felt.

Therefore, in Examples 1 to 9, it was confirmed that the bending direction of the optical fiber cable can be maintained and the occurrence of buckling of the optical fiber cable can be suppressed.

Further, as described above, since the deformation hardly occurred in Examples 3 to 6, it was confirmed that the occurrence of buckling could be surely suppressed as compared with Examples 1 and 2. Further, in Examples 3 to 6, the difference between the case where the optical fiber cable is bent in the _first direction D1 and the case where the optical fiber cable is bent in the _second direction D2 is clearer than that in Examples 7 to 9. I could feel it. Therefore, in Examples 3 to 6, it was confirmed that the bending direction of the optical fiber cable can be clarified and that the occurrence of buckling of the optical fiber cable can be surely suppressed. It is self-evident that the same results as in Table 1 above can be obtained even when the cross-sectional shapes of the first and second tensile strength bodies are elliptical or rectangular.

1,1B ... Optical fiber cable 10 ... Cable body C ₁ ... Center 11 ... Optical fiber aggregate 12 ... Optical fiber unit 13 ... Optical fiber tape core wire
14 ... Optical fiber
15 ... Adhesive part 16 ... Bundle material 17 ... Presser winding tape 20 ... External sheath 31, 31B ... First tensile strength wire C ₂ ... Center R ₁ ...
32, 32B ... Second tensile strength line C ₃ ... Center L ₁ ... First virtual straight line L ₂ ... Second virtual straight line

Claims (5)

The cable body with optical fiber and
A cylindrical outer sheath that houses the cable body, and
A pair of first tensile strength bodies embedded in the outer sheath and arranged so as to face each other across the cable body on a first virtual straight line passing through the center of the cable body.
A pair of second tensile strength bodies embedded in the outer sheath and arranged so as to face each other across the cable main body on a second virtual straight line passing through the center of the cable main body are provided. ,
The first virtual straight line and the second virtual straight line are substantially orthogonal to each other.
The first tensile strength body is an optical fiber cable thicker than the second tensile strength body. The optical fiber cable according to claim 1.
An optical fiber cable that satisfies the following formula (2).
0.09 ≤ I _x / I _y ≤ 0.36 ... (2)
However, in the above equation (2), I _x is the moment of inertia of area with respect to the first virtual straight line of the optical fiber cable, and I _y is the moment of inertia of area with respect to the second virtual straight line of the optical fiber cable. The next moment. The optical fiber cable according to claim 1 or 2.
An optical fiber cable that satisfies the following formula (3).
0.09 ≤ S ₂ / S ₁ ≤ 0.36 ... (3)
However, in the above equation (3), S ₁ is the cross-sectional area of the first tensile strength body, and S ₂ is the cross-sectional area of the second tensile strength body. The optical fiber cable according to claim 1 or 2.
The cross-sectional shape of the first and second tensile strength bodies is a perfect circle.
An optical fiber cable that satisfies the following equation (4).
0.3 ≤ d ₂ / d ₁ ≤ 0.6 ... (4)
However, in the above equation (4), d ₁ is the diameter of the first tensile strength body, and d ₂ is the diameter of the second tensile strength body. The optical fiber cable according to any one of claims 1 to 3.
An optical fiber cable having an elliptical or rectangular cross-sectional shape of the first and second tensile strength bodies.

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