Optical fiber cable

An optical fiber cable includes: a cable main body including a core that includes optical fibers, at least a pair of tension members that face each other with the core interposed therebetween, and an inner sheath that covers the core and the tension members; a cylindrical outer sheath that accommodates the cable main body; a reinforcing sheet provided between the cable main body and the outer sheath; and a rip cord provided between the reinforcing sheet and the cable main body. The reinforcing sheet surrounds an entire circumference of the cable main body, the reinforcing sheet includes an overlapping portion in which portions of the reinforcing sheet overlap each other in a portion in a circumferential direction of the cable main body, and the reinforcing sheet is formed of a metal.

TECHNICAL FIELD

The present invention relates to an optical fiber cable.

Priority is claimed on Japanese Patent Application No. 2015-201276, filed on Oct. 9, 2015, the content of which is incorporated herein by reference.

BACKGROUND ART

With an increase in the use of optical fiber cables, there have been cases where optical fibers within the optical fiber cable are damaged due to the cable being bitten by an animal, such as a rat or a squirrel. In response, measures such as the provision of a protection structure, for example, a metal tape, which surrounds optical fibers have been taken (for example, see Patent Document 1 and Patent Document 2).

PATENT DOCUMENTS

SUMMARY

However, in the optical fiber cable, there has been a difficulty in cutting off an outer sheath due to the protection structure in an operation of cutting off the outer sheath by a rip cord and taking out the optical fibers.

One or more embodiments of the present invention provide an optical fiber cable which is capable of preventing optical fibers from being damaged due to animals' bites and has an excellent workability in an operation of taking out the optical fibers.

An optical fiber cable according one or more embodiments of the present invention includes a cable main body including a core including optical fibers, at least a pair of tension members disposed so as to face each other with the core interposed therebetween, and an inner sheath covering the core and the tension members, a cylindrical outer sheath accommodating the cable main body, a reinforcing sheet provided between the cable main body and the outer sheath, the reinforcing sheet surrounding an entire circumference of the cable main body, the reinforcing sheet having an overlapping portion in which portions of the reinforcing sheet overlap each other in a portion in a circumferential direction of the cable main body, the reinforcing sheet being formed of a metal, and a rip cord provided between the reinforcing sheet and the cable main body. The overlapping portion of the reinforcing sheet and the rip cord are provided at different positions in the circumferential direction of the cable main body.

According to one or more embodiments, a side edge of the reinforcing sheet disposed on an outer circumference in the overlapping portion of the reinforcing sheet and the tension members may be provided at different positions in the circumferential direction of the cable main body.

According to one or more embodiments, the overlapping portion of the reinforcing sheet and the tension members may be provided at different positions in the circumferential direction of the cable main body.

According to one or more embodiments, one of the tension members may be disposed within a region surrounded by a first virtual line passing through a center of the cable main body and a center of the rip cord and a second virtual line which is inclined at 30° or less with respect to the first virtual line and extends toward an outside in a radial direction, in the cable main body.

According to one or more embodiments, the optical fiber cable may further include at least a pair of rip cords, in which an angle between a third virtual line passing through a center of the cable main body and a center of a first rip cord in the pair of rip cords and a fourth virtual line passing through the center of the cable main body and a center of a second rip cord in the pair of rip cords may be 120° or more.

According to one or more embodiments, a difference between an outer diameter of the cable main body and an inner diameter of the reinforcing sheet may be smaller than twice an outer diameter of the rip cord.

According to one or more embodiments, a pull-out force of the rip cord may be 2.94 N or more.

According to one or more embodiments, the outer sheath may be formed to have a corrugated shape.

According to one or more embodiments, the positions of a rip cord and an overlapping portion of a reinforcing sheet in a cable circumferential direction are different from each other, and thus the rip cord is disposed at a location where the reinforcing sheet is configured as a single layer. For this reason, it is possible to reliably cut off the reinforcing sheet by the rip cord. Accordingly, the workability of an operation of taking out the optical fibers is improved because of intermediate post-branching or the like.

According to one or more embodiments, the reinforcing sheet surrounding the cable main body is provided, and thus it is possible to prevent the optical fibers from being damaged due to feeding damage caused by animals.

DETAILED DESCRIPTION

Hereinafter, one or more embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1is a cross-sectional view showing an optical fiber cable10according to a first example of one or more embodiments of the present invention.FIG. 1is a cross-sectional view perpendicular to the longitudinal direction of the optical fiber cable10.FIG. 2is a perspective view showing the structure of the optical fiber cable10.FIG. 3is a perspective view showing an example of a core5which is used for the optical fiber cable10.

Note that the longitudinal direction of the optical fiber cable10may be referred to as a “cable longitudinal direction”.

InFIG. 1, the cable longitudinal direction is a direction perpendicular to a paper surface. In addition, the circumferential direction (circumferential direction in a surface perpendicular to the cable longitudinal direction) of the cable main body1may be referred to as a “cable circumferential direction”.

As shown inFIG. 1, the optical fiber cable10includes a cable main body1, an outer sheath2, a reinforcing sheet3, and a pair of rip cords4(tear strings).

The cable main body1includes a core5, a tension member6, and an inner sheath7.

As shown inFIG. 3, the core5is constituted by assembling a plurality of optical fibers8. The plurality of optical fibers8constituting the core5are, for example, bundled, and can be configured to be wound by a binding material9(identification thread).

As shown inFIG. 1, the cross-sectional shape of the core5is a circular shape. The cross-sectional shape of the core5does not need to be a complete circular shape, or may be an elliptical shape. The optical fiber8is an optical fiber core wire, and may be an optical fiber strand, an optical fiber tape core wire, or the like.

Note that the core5may be constituted by assembling a plurality of units each including the plurality of optical fibers8.

The tension member6is constituted by, for example, a metal wire (a steel wire or the like), a tension fiber (aramid fibers or the like), FRP, or the like.

Regarding the tension member6, at least a pair of tension members is provided so as to interpose the core5. In the optical fiber cable10shown inFIG. 1, the cable main body1includes a first pair of tension members6A and6A that are disposed at positions rotationally symmetrical to each other about a center axis C1of the cable main body1, and a second pair of tension members6B and6B that are disposed at positions rotationally symmetrical to each other about the center axis C1of the cable main body1.

One tension member6A1of the first pair of tension members6A and6A and one tension member6B1of the second pair of tension members6B and6B are close to each other. Similarly, the other tension member6A2of the first pair of tension members and the other tension member6B2of the second pair of tension members are close to each other.

In one or more embodiments, the tension members6A1and6B1have the same mechanical characteristics (for example, flexural rigidity). Similarly, the tension members6A2and6B2have the same mechanical characteristics (for example, flexural rigidity).

In addition, in one or more embodiments, the tension members6A and6A have the same mechanical characteristics (for example, flexural rigidity) and the tension members6B and6B have the same mechanical characteristics (for example, flexural rigidity).

Since the tension member6A1and the tension member6B1are close to each other, the tension member6A1and the tension member6B1are regarded as one tension member and are referred to as a first tension member11. Similarly, the tension member6A2and the tension member6B2are regarded as one tension member and are referred to as a second tension member12.

The first tension member11and the second tension member12are disposed so as to face each other with the core5interposed therebetween.

A difference in position in the cable circumferential direction between a center axis CA1of the tension member6A1and a center axis CB1of the tension member6B1can be an angle of, for example, 20° or less. In other words, an angle between a virtual line passing through the center of the cable main body1and the center of the tension member6A1and a virtual line passing through the center of the cable main body1and the center of the tension member6B1can be 20° or less.

Similarly, a difference in position in the cable circumferential direction between a center axis CA2of the tension member6A2and a center axis CB2of the tension member6B2can be an angle of, for example, 20° or less. In other words, an angle between a virtual line passing through the center of the cable main body1and the center of the tension member6A2and a virtual line passing through the center of the cable main body1and the center of the tension member6B2can be 20° or less.

The center of an arc a1connecting the center axis CA1of the tension member6A1and the center axis CB1of the tension member6B1is referred to as C2, and the center of an arc a2connecting the center axis CA2of the tension member6A2and the center axis CB2of the tension member6B2is referred to as C3.

A straight line passing through the center C2and the center C3is referred to as a neutral line L1. Note that the arcs a1and a2are arcs having the center axis C1as the center thereof.

The neutral line L1may be parallel to a straight line connecting the center axes CA1and CB2of the tension members6A1and6B2and a straight line connecting the center axes CB1and CA2of the tension members6B1and6A2.

In a cross-section (seeFIG. 1) which is perpendicular to the longitudinal direction of the cable main body1, a direction (vertical direction inFIG. 1) which is perpendicular to the neutral line L1is a direction in which the expansion and contraction of the tension member6are reduced during the bending of the cable main body1, as compared to another direction, and thus it is relatively easy to bend the cable main body1in this direction.

The inner sheath7collectively covers the core5and the tension member6. As a material of the inner sheath7, a resin such as polyethylene (PE) or polyvinyl chloride (PVC) can be used.

The reinforcing sheet3is formed of a metal such as stainless steel, copper, or a copper alloy. In particular, stainless steel is used. The reinforcing sheet3has, for example, a tape shape, and is provided such that the longitudinal direction thereof is consistent with the longitudinal direction of the cable main body1.

The thickness of the reinforcing sheet3can be, for example, 0.1 to 0.3 mm. The thickness of the reinforcing sheet3is in a range from 0.1 to 0.3 mm, and thus it is possible to prevent the optical fibers8from being damaged due to feeding damage caused by animals and to easily perform an operation of cutting off the reinforcing sheet3by the rip cord4.

The reinforcing sheet3surrounds the entire circumference of the cable main body1, and has portions overlapping each other in a portion in the cable circumferential direction. The portions overlapping each other of the reinforcing sheet3are referred to as an overlapping portion13.

The overlapping portion13is a portion where a side region (first side region)14aincluding one side edge (first side edge)3aof the reinforcing sheet3and a side region (second side region)14bincluding the other side edge (second side edge)3boverlap each other. In one or more embodiments, the side region14aand the side region14bare bounded to each other by using an adhesive or the like.

In one or more embodiments, the overlapping portion13has a constant width along the longitudinal direction of the reinforcing sheet3.

In one or more embodiments, the position of the overlapping portion13in the cable circumferential direction is constant in the cable longitudinal direction.

In one or more embodiments, the side edge (side edge in the outer circumference)3aof the reinforcing sheet3(side region14a) on the outer circumference side in the overlapping portion13and the tension member6differ from each other in the position in the cable circumferential direction.

A difference in the position in the cable circumferential direction between the side edge3aof the reinforcing sheet3and the tension member6refers to a difference between the position of the side edge3aof the reinforcing sheet3in the cable circumferential direction and the positions of a formation region (first formation region)11aof the first tension member11and a formation region (second formation region)12aof the second tension member12in the cable circumferential direction.

The formation region11aof the first tension member11is constituted by formation ranges15A1and15B1of the tension members6A1and6B1and an intermediate range15C1corresponding to a region between the tension member6A1and the tension member6B1. The formation region12aof the second tension member12is constituted by formation ranges15A2and15B2of the tension members6A2and6B2and an intermediate range15C2corresponding to a region between the tension member6A2and the tension member6B2.

As described above, it is relatively easy to bend the cable main body1in a direction (vertical direction inFIG. 1) which is perpendicular to the neutral line L1.

In the optical fiber cable10, the side edge3aof the reinforcing sheet3and the tension member6differ from each other in the position in the cable circumferential direction, and thus relative positions of the side edge3aand the outer sheath2are not likely to fluctuate even when the cable main body1is bent. Accordingly, it is possible to avoid the damage of the outer sheath2due to the side edge3a.

In one or more embodiments, the overlapping portion13and the tension member6differ from each other in the position in the cable circumferential direction. A position of the overlapping portion13and a position of the tension member6are made different from each other in the cable circumferential direction, and thus it is possible to reliably avoid the damage of the outer sheath2due to side edge3aeven when the cable main body1is bent.

In one or more embodiments, a difference between an outer diameter A1of the cable main body1and an inner diameter A2of the reinforcing sheet3is smaller than twice an outer diameter A3of the rip cord4. That is, the following Expression (1) is satisfied.
A2−A1<2A3  (1)

As the difference between the outer diameter of the cable main body1and the inner diameter of the reinforcing sheet3becomes larger, a tendency to cause a positional deviation of the rip cord4becomes stronger (seeFIG. 5). However, the difference between the outer diameter of the cable main body1and the inner diameter of the reinforcing sheet3is in the range (range in which Expression (1) mentioned above is satisfied), and thus it is possible to increase a frictional force of the rip cord4between the outer surface of the cable main body1and the inner surface of the reinforcing sheet3. Accordingly, it is possible to reliably hold the rip cord4by the cable main body1and the reinforcing sheet3and to prevent a positional deviation in the cable circumferential direction of the rip cord4.

The difference between the outer diameter A1of the cable main body1and the inner diameter A2of the reinforcing sheet3can be equal to or greater than 1.5 times the outer diameter A3of the rip cord4.

A cord formed of synthetic fiber, such as polyester or aramid, can be used as the rip cord4. The rip cord4is required to have such a mechanical strength (for example, tensile strength) as to be capable of cutting off the reinforcing sheet3and the outer sheath2. The outer diameter of the rip cord4may be, for example, 0.2 to 0.5 mm.

The rip cord4and the overlapping portion13differ from each other in the position in the cable circumferential direction.

Since the rip cord4and the overlapping portion13differ from each other in the position in the cable circumferential direction, the position in the cable circumferential direction of the rip cord4is a location where the reinforcing sheet3is a single layer. The location where the reinforcing sheet3is a single layer has a lower mechanical strength than that of the overlapping portion13, and thus it is possible to reliably cut off the reinforcing sheet3by the rip cord4.

On the other hand, in a case where the position of at least one rip cord4and the position of the overlapping portion13in the cable circumferential direction are consistent with each other as an optical fiber cable10A shown inFIG. 4, it is not easy to cut off the overlapping portion13by the rip cord4, which results in poor workability.

As shown inFIG. 1, the two rip cords4,4are provided at positions facing each other with the cable main body1interposed therebetween. A difference in the position in the cable circumferential direction between the two rip cords4,4is 120° or more. In other words, an angle between a third virtual line passing through the center of the cable main body1and the center of a first rip cord4A in the pair of rip cords4A and4B and a fourth virtual line passing through the center of the cable main body1and the center of a second rip cord4B in the pair of rip cords4A and4B is 120° or more. The difference in the position in the cable circumferential direction between the two rip cords4,4(4A,4B) is in the range (120° or more), and thus it is easy to take the cable main body1out of the divided outer sheath2. In the optical fiber cable10shown inFIG. 1, the two rip cords4,4are disposed at positions rotationally symmetrical to each other with the center axis C1as the center thereof, and thus a difference in the position in the cable circumferential direction therebetween is 180°.

On the other hand, as in an optical fiber cable10B shown inFIG. 5, as a difference D1in the position in the cable circumferential direction between the two rip cords4,4becomes smaller, the width of an open portion of the divided outer sheath2having a C-shaped cross-section becomes smaller, and thus it is not easy to take out a cable main body1.

Note that the difference in the position in the cable circumferential direction between the two rip cords4,4refers to a smaller angle in angles in the cable circumferential direction which are formed by the center axis of one rip cord4and the center axis of the other rip cord4.

The following test was performed on the difference in the position in the cable circumferential direction between the two rip cords4,4.

The optical fiber cable10was manufactured in which the difference in the position in the cable circumferential direction between the two rip cords4,4was values shown in Table 1.

An operation was performed of cutting off the reinforcing sheet3and the outer sheath2by the two rip cords4,4and taking the cable main body1out of the divided outer sheath2.

In this test, the take-out workability of the cable main body1was evaluated as any of A, B, and C. The “A” means that the workability is excellent. The “B” means that the cable main body1can be taken out, but it can be said that the workability is not excellent. The “C” means that the cable main body1cannot be taken out. The results are shown in Table 1.

TABLE 1Difference in position in cable circumferentialdirection between two rip cords (°)Take-out workability30B60B90B120A150A180A

According to Table 1, it can be understood that the take-out workability is improved by setting the difference in the position in the cable circumferential direction between the two rip cords4,4to be 120° or more.

A pull-out force (pull-out force per meter of the length of the optical fiber cable10) of the rip cord4is 300 gf or more (2.94 N or more). Note that 1 gf is approximately 9.81×10−3N.

The following text was performed on the pull-out force of the rip cord4.

The optical fiber cable10was manufactured in which the pull-out force (pull-out force per meter of the length of the optical fiber cable10) of the rip cord4was values shown in Table 2, by adjusting the outer diameter of the cable main body1or the inner diameter of the outer sheath2, and a bending test and a twisting test were performed on the optical fiber cable10. The pull-out force of the rip cord4was examined by a pull-out test (pull-out speed of 200 mm/min).

A bending test device30shown inFIG. 7was used for the bending test. The bending test device30includes two rollers21and22that are disposed in parallel.

The optical fiber cable10was in a state of being bent at +90° along the first roller21(solid line), and was then in a state of being bent at −90° along the second roller22(virtual line). In this manner, an operation of performing bending at ±90° was repeated in 25 cycles.

In the twisting test, the optical fiber cable10was twisted at +180° per meter of the length thereof, and was then twisted at −180°. In this manner, an operation of performing twisting at ±180° was repeated in 10 cycles.

The presence or absence of a positional deviation of the rip cord4was examined with respect to the optical fiber cable10having been subjected to the bending test and the twisting test. The results are shown in Table 2.

TABLE 2Pull-out force of rip cord (gf)Positional deviation of rip cord100Present200Present300Absent500Absent1000Absent3000Absent

As shown in Table 2, it was possible to prevent a positional deviation of the rip cord4by setting the pull-out force of the rip cord4to be 300 gf or more (2.94 N or more).

In one or more embodiments, the position of the rip cord4and the position of the tension member6in the cable circumferential direction are close to each other.

InFIG. 1, a center axis C4A of one rip cord (first rip cord)4A in the pair of rip cords4,4is positioned in the formation region11aof the tension member6in the cable circumferential direction. Similarly, a center axis C4B of the other rip cord (second rip cord)4B is positioned in the formation region12aof the tension member6in the cable circumferential direction. For this reason, it can be understood that the position of the rip cord4and the position of the tension member6are close to each other in the cable circumferential direction.

The center axis of the rip cord4and the tension member6may differ from each other in the position in the cable circumferential direction, but a difference in the position in the cable circumferential direction between the center axis of the rip cord4and the tension member6is 30° or less.

When the optical fiber cable10shown inFIG. 1is taken as an example, the difference in the position in the cable circumferential direction between the center axis C4A of the rip cord4A and the formation region11ais 30° or less. In other words, in one or more embodiments, one (tension member6A1) of the tension members6A is disposed in a region surrounded by a first virtual line passing through the center of the cable main body1and the center of the rip cord4(4A) and a second virtual line which is inclined at 30° or less with respect to the first virtual line and extends toward the outside in the radial direction, in the formation range11ain the cable main body1. Similarly, regarding the tension member6B1, in one or more embodiments, one (tension member6B1) of the tension members6B is disposed in a region surrounded by the first virtual line passing through the center of the cable main body1and the center of the rip cord4(4A) and a second virtual line which is inclined at 30° or less with respect to the first virtual line and extends toward the outside in the radial direction, in the formation range11ain the cable main body1.

Similarly, a difference in the position in the cable circumferential direction between the center axis C4B of the rip cord4B and the formation region12ais 30° or less. In other words, in one or more embodiments, one (tension member6B2) of the tension members6B is disposed in a region surrounded by a first virtual line passing through the center of the cable main body1and the center of the rip cord4(4B) and a second virtual line which is inclined at 30° or less with respect to the first virtual line and extends toward the outside in the radial direction, in the formation range12ain the cable main body1. Similarly, regarding the tension member6A2, in one or more embodiments, one (tension member6A2) of the tension members6A is disposed in a region surrounded by a first virtual line passing through the center of the cable main body1and the center of the rip cord4(4B) and a second virtual line which is inclined at 30° or less with respect to the first virtual line and extends toward the outside in the radial direction, in the formation range12awithin the cable main body1.

The position of the rip cord4and the position of the tension member6in the cable circumferential direction are brought close to each other, and thus it is possible to align an open direction of the semi-cylindrical outer sheath2, which is divided by the rip cord4, and a direction in which the cable main body1tends to bend, when the cable main body1is taken out of the semi-cylindrical outer sheath2.

Accordingly, it is easy to perform an operation of taking the cable main body1out of the outer sheath2.

The outer sheath2is formed in a cylindrical body that accommodates the cable main body1. As a material of the outer sheath2, a resin such as polyethylene (PE) or polyvinyl chloride (PVC) can be used.

The inner diameter of the outer sheath2is larger than the outer diameter of the cable main body1. InFIG. 1, the cross-section of the outer sheath2is formed to have a circular shape concentric with the cross-section of the cable main body1.

As shown inFIG. 2, in one or more embodiments, the outer sheath2is formed to have a shape in which protrusions2aextending in the circumferential direction and grooves2bextending in the circumferential direction are alternately formed in the cable longitudinal direction, that is, a corrugated shape.

The outer sheath2is formed to have a corrugated shape, and thus it is possible to enhance the strength of the outer sheath2and to enhance a function of protecting the cable main body1.

Note that a direction in which the protrusions2aand the grooves2bextend may not strictly be the circumferential direction of the outer sheath2, or may be inclined with respect to the circumferential direction of the outer sheath2.

When an intermediate post-branching operation is performed on the optical fiber cable10, the reinforcing sheet3and the outer sheath2are cut off by the rip cord4. The outer sheath2is divided into two parts by being cut off by the rip cord4, and thus the outer sheath2has a semi-cylindrical shape.

The cable main body1is taken out of the outer sheath2, and the inner sheath7is cut off using a rip cord (not shown) which is provided in the inner sheath7of the cable main body1, thereby exposing the core5.

The optical fiber8is partially cut out and is connected to an optical fiber provided in a branch destination.

In the optical fiber cable10, the rip cord4and the overlapping portion13differ from each other in the position in the cable circumferential direction, and thus the position of the rip cord4in the cable circumferential direction is a location where the reinforcing sheet3is a single layer. For this reason, it is possible to reliably cut off the reinforcing sheet3by the rip cord4. Accordingly, the workability of an operation of taking out the optical fibers8is improved because of intermediate post-branching or the like.

In addition, it is possible to reliably cut off the reinforcing sheet3by the rip cord4, and thus it is not necessary to set a high strength (for example, tensile strength) of the rip cord4. Accordingly, it is possible to achieve a reduction in cost.

The optical fiber cable10includes the reinforcing sheet3surrounding the cable main body1, and thus it is possible to prevent the optical fibers8from being damaged due to feeding damage caused by animals.

The present invention is not limited to the above-described embodiments and can be appropriately modified without departing from the scope of the invention.

For example, in the optical fiber cable10shown inFIG. 1and the like, four tension members6are used. However, the number of tension members is not particularly limited and can be applied in the scope in which the inventor is generally conceivable.

FIG. 6is a cross-sectional view showing an optical fiber cable20according to a second example of one or more embodiments of the present invention. The optical fiber cable20has the same structure as that of the optical fiber cable10shown inFIG. 1except that two tension members16(16A and16B) facing each other with a core5interposed therebetween are used Instead of the tension members6. Note that the number of pair of tension members may be two or may be three or more.

In the optical fiber cable10shown inFIG. 1and the like, the core5is an assembly of the optical fibers8, but the core may be constituted by a single optical fiber (optical fiber core wire or the like).

1Cable main body

3aSide edge (side edge of reinforcing sheet on outer circumference side)

10,20Optical fiber cable

11First tension member

12Second tension member