Optical fiber cable

Abstract

To provide an optical fiber cable having excellent laying working efficiency and handling properties.SOLUTION: An optical fiber cable 1 is for example a slotless type cable without using any slots, and is constituted of a core 3, tension members 5, a covering 7, and the like. The core 3 comprises multiple optical fiber conductors. Multiple tension members 5 are provided around the core 3. The tension member 5 bears tension of the optical fiber cable 1. The covering 7 is provided in the outer periphery of the core 3 and the core 3 is covered with the covering 7. In a section vertical to the axial direction of the optical fiber cable 1, the outer shape of the covering 7 is nearly polygonal. In more detail, for the sectional shape of the optical fiber cable 1, the outer surface of the covering 7 between apexes of a polygon is in a concave shape in the center direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical fiber cable comprising a plurality of optical fiber core wires. [Background technology]

[0002] In order to efficiently lay optical fiber cables in ducts, etc., development of blown cables for pressure feeding is progressing. Such blown cables lay optical fiber cables in ducts by feeding the optical fiber cable into the duct with a pushing unit while sending compressed air into the duct.

[0003] For such optical fiber cables, a method has been proposed in which multiple protrusions are provided on the outer surface of the jacket to reduce the contact area with the inner surface of the duct and thereby reduce frictional resistance (Patent Document 1, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2020-075734 [Patent Document 2] Japanese Patent Publication No. 2021-018338 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when forming convex portions as in the past, if the height of the convex portions is too low, the effect of the convex portions is reduced, and if the height of the convex portions is too high, the cross-sectional area of ​​the concave portions becomes too large, which prevents air leakage from the concave portions and prevents the pumping distance from being extended.

[0006] Furthermore, in the conventional convex shape, a corner is formed at the boundary between the concave portion and the convex portion (at the base of the convex portion).

[0007] 6 is a diagram showing a conventional optical fiber cable 100. In the optical fiber cable 100, the core 103 and the tension members 105 are covered with the jacket 107, and as described above, the convex portions 111 and the concave portions 109 are formed alternately in the circumferential direction on the outer periphery of the jacket 107. In other words, the concave portions 109 are formed between the convex portions 111.

[0008] Here, the recess 109 excluding the protrusion 111 is substantially circular, and the protrusion 111 is formed to protrude from the outer periphery of this circle. Therefore, a corner (X in the figure) is formed at the boundary between the protrusion 111 and the recess 109 (the base of the protrusion 111). At such a corner (the intersection of curves in different directions, the concave direction and the convex direction, or a portion with a large change in curvature), stress is likely to concentrate when the optical fiber cable is bent. Therefore, if corners are continuous in the longitudinal direction, they can cause damage to the optical fiber cable.

[0009] The present invention has been made in view of the above problems, and has as its object to provide an optical fiber cable that is easy to install and handle. [Means for solving the problem]

[0010] In order to achieve the above-mentioned object, the present invention provides an optical fiber cable comprising a core or loose tube consisting of a plurality of optical fiber cores, an outer sheath covering the core or loose tube, and a tension member that bears tension, wherein in a cross section perpendicular to the axial direction, the outer sheath is approximately polygonal, and the outer surface of the outer sheath between the vertices of the polygon is concave toward the center.

[0011] It is desirable that the depth of the recessed shape be 0.1 mm or more relative to the straight line connecting the vertices of the polygon.

[0012] The vertices of the polygon are preferably curved.

[0013] It is desirable that the radius of curvature of the curved shape at the vertices of the polygon be 0.2 mm or more and 2.0 mm or less.

[0014] In a cross section perpendicular to the axial direction, it is desirable that the core be disposed at the center, and that a plurality of the tension members be disposed around the core, with the tension members being disposed at positions corresponding to the vertices of a polygon.

[0015] In a cross section perpendicular to the axial direction, the tension member may be disposed at the center, and a plurality of the loose tubes may be disposed around the tension member.

[0016] According to the present invention, the outer shape of the jacket is substantially polygonal, with the sides between the vertices being concave toward the center, thereby reducing the contact area with a duct, etc., and achieving the same effect as a conventional optical fiber cable with convex portions. Furthermore, with a simple polygonal shape, there is a risk of the optical fiber cable coming into surface contact with the duct, etc., when laid in a rectangular duct, etc., having a flat surface, but by forming the concave portions between the convex portions, it is possible to reliably reduce the contact area between the optical fiber cable and the duct, etc., and reduce frictional resistance.

[0017] Furthermore, by making the vertices of the polygon concave, there are no corners where the shape of the concave or convex portion changes significantly between the vertices, and the vertices are smoothly connected, which makes it difficult for stress to concentrate. This helps prevent damage to the optical fiber cable during installation and handling.

[0018] Furthermore, by making the depth of the recessed shape 0.1 mm or more relative to the straight line connecting the vertices of the polygon, it is possible to more reliably suppress surface contact with ducts, etc.

[0019] Furthermore, by making the vertices of the polygon curved, deformation and breakage of the tip of the vertex can be suppressed.

[0020] In particular, by setting the radius of curvature of the curved shape of the vertex of the polygon to be 0.2 mm or more and 2.0 mm or less, deformation or damage to the tip of the vertex can be more reliably suppressed, and an increase in the contact area with ducts, etc. can be efficiently suppressed.

[0021] Furthermore, by arranging the tension members at positions corresponding to the vertices of the polygon in a cross section perpendicular to the axial direction, it is possible to ensure a covering margin for the outer covering on the tension members.

[0022] Such an optical fiber cable may have a tension member disposed at the center in a cross section perpendicular to the axial direction, and a plurality of loose tubes disposed around the tension member. [Effects of the Invention]

[0023] According to the present invention, an optical fiber cable that is excellent in laying workability and handling ability can be provided. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a cross-sectional view of an optical fiber cable 1. FIG. [Figure 2] FIG. 2 is an enlarged view of a recessed portion 9 and a protruding portion 11. [Figure 3] FIG. 2 is a cross-sectional view of the optical fiber cable 1a. [Figure 4] 1 is a schematic diagram showing a method for performing a pressure test on an optical fiber cable 15. FIG. [Figure 5] FIG. 3 is a diagram showing the shape of a pipe 13. [Figure 6] 1 is a diagram showing the shape of a conventional optical fiber cable 100. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a cross-sectional view perpendicular to the axial direction of an optical fiber cable 1. The optical fiber cable 1 is, for example, a slotless cable that does not use slots, and is composed of a core 3, a tension member 5, an outer jacket 7, etc.

[0026] The core 3 is made up of a plurality of optical fiber cores. More specifically, a plurality of optical fiber cores are twisted together to form an optical fiber unit, and a plurality of optical fiber units are further twisted together to form the core 3. The optical fiber core may be, for example, an intermittently bonded optical fiber ribbon in which a plurality of optical fibers are arranged in parallel and bonded intermittently in the longitudinal direction.

[0027] A pressure winding member is provided on the outer periphery of the core 3. The pressure winding member is a tape-like member, a nonwoven fabric, or the like, and is wound longitudinally around the outer periphery of the core 3 so that, for example, its width direction coincides with the circumferential direction of the optical fiber cable 1. The pressure winding member is not necessarily required, and the core 3 may include the pressure winding member.

[0028] In a cross section perpendicular to the longitudinal direction of the optical fiber cable 1, a plurality of tension members 5 are provided around the core 3. The tension members 5 bear the tension of the optical fiber cable 1. There are no particular restrictions on the material of the tension members 5, but examples that can be used include fiber-reinforced plastics (FRP) made from aramid fiber, glass fiber, etc.

[0029] An outer sheath 7 is provided on the outer periphery of the core 3, and the core 3 is covered by the outer sheath 7. A tear cord (not shown) is provided at a circumferential position different from the tension members 5. In other words, the outer sheath 7 is provided so as to cover the core 3, the tension members 5, the tear cord, etc.

[0030] In a cross section perpendicular to the axial direction of the optical fiber cable 1, the outer shape of the jacket 7 is approximately polygonal. More specifically, the cross-sectional shape of the optical fiber cable 1 is such that the outer surface of the jacket 7 between the vertices of the polygon is concave toward the center. The number of vertices is not particularly limited, but it is preferable that the shape be, for example, hexagonal to dodecagonal. Furthermore, it is preferable that the vertices of the polygon are not perfectly angular, but that the vertices of the polygon are curved.

[0031] Here, the apex of the approximately polygonal shape is defined as a protrusion 11, and the curved portion between adjacent protrusions 11 facing the center is defined as a recess 9. That is, a plurality of recesses 9 and protrusions 11 are alternately formed in the circumferential direction on the outer circumferential surface of the jacket 7. The recesses 9 and protrusions 11 are formed continuously in the longitudinal direction of the optical fiber cable 1.

[0032] As described above, in a cross section perpendicular to the axial direction of the optical fiber cable 1, the core 3 is disposed at the center, and multiple tension members 5 are disposed around the core 3. In this case, each tension member 5 is disposed at a position corresponding to a protrusion 11 (a vertex of a polygon). In this way, the thickness of the jacket 7 that covers the tension members 5 can be ensured.

[0033] Furthermore, when a tear cord is provided, it is desirable to provide it approximately in the center of the recess 9. This allows the thickness of the outer jacket 7 to be torn by the tear cord to be thin, making the tearing operation easier.

[0034] The material of the outer jacket 7 is not particularly limited, but may be, for example, a polyolefin resin, such as LDPE (low density polyethylene) or HDPE (high density polyethylene). Considering the strength of the protrusions 11, the protrusions 11 may be made of a resin with an elastic modulus of 1000 MPa or more, and the material of the outer jacket 7 may be, for example, PP (polypropylene) or (PBT) polybutylene terephthalate.

[0035] 2 is an enlarged view of the outer periphery of the jacket 7. Assuming a straight line connecting the protrusions 11 (the vertices of the polygon), the depth of the recessed shape of the recess 9 relative to this line (A in the figure) is preferably 0.1 mm or more. The depth of the recess 9 is the maximum depth at the center between the protrusions 11.

[0036] In this way, by making the depth of the recess 9 0.1 mm or more, even if deformation of the protrusion 11 occurs, the contact area with the inner surface of the duct, etc. is reduced, and the effect of reducing frictional resistance can be reliably obtained.

[0037] It is desirable that the depth of the recess 9 be 0.9 mm or less. If the depth of the recess 9 is too deep, air may leak from the recess 9 during pumping, which may shorten the pumping distance.

[0038] As mentioned above, the apex of the polygon is not a perfect angle, but is curved at the tip. In this case, it is desirable that the radius of curvature of the curved apex of the polygon (B in the figure) be 0.2 mm or more and 2.0 mm or less. If the radius of curvature is too small, the strength of the tip of the protrusion 11 will be weakened, and there is a risk of damage to the protrusion 11. Furthermore, if the radius of curvature is too large, it will be difficult to ensure sufficient depth of the recess 9, and there is a risk of increasing the contact area with the inner surface of a duct, etc.

[0039] As described above, according to this embodiment, by forming multiple recesses 9 and protrusions 11 on the outer surface in a cross section perpendicular to the longitudinal direction of the optical fiber cable 1, the contact area with the inner surface of the duct can be reduced when laying the optical fiber cable in a duct, etc., thereby reducing the resistance to wiring.

[0040] In particular, the cross-sectional shape of the optical fiber cable 1 is approximately polygonal, and the spaces between the convex portions 11 are formed by recesses 9, which are gently concave curves. Therefore, except for the curved portions at the tops of the convex portions 11, the entire spaces between the convex portions 11 (recesses 9) are formed by approximately constant concave curves, and there is no clear boundary between the convex portions 11 and the recesses 9. In other words, there are no corners at the boundaries between the convex portions 11 and the recesses 9, as in the past, and stress concentration can be suppressed.

[0041] Furthermore, by making the cross-sectional shape of the convex portion 11, which is the apex of the polygon, a curved shape, it is possible to suppress damage to the convex portion 11. In particular, by setting the radius of curvature of the apex of the convex portion 11 within an appropriate range, the above effect can be reliably obtained.

[0042] Furthermore, by setting the depth of the recess 9 within an appropriate range, it is possible to more reliably perform long-distance pressure feeding.

[0043] Next, a second embodiment will be described. Fig. 3 is a cross-sectional view showing an optical fiber cable 1a according to the second embodiment. In the following description, components that have the same functions as those in the first embodiment are given the same reference numerals as those in Figs. 1 and 2, and redundant description will be omitted.

[0044] The optical fiber cable 1a has a configuration similar to that of the optical fiber cable 1, but has a different internal structure. In a cross section perpendicular to the axial direction of the optical fiber cable 1a, a tension member 5 is disposed at the center, and multiple loose tubes 3a are disposed around the tension member 5. Multiple optical fiber cores are housed in the loose tubes 3a.

[0045] The jacket 7 of the optical fiber cable 1a is formed so as to cover the plurality of loose tubes 3a and the tension members 5. The outer shape of the jacket 7 (the shape of the recesses 9 and protrusions 11) is substantially the same as that of the optical fiber cable 1.

[0046] According to the second embodiment, it is possible to obtain the same effects as those of the first embodiment. As described above, as long as the outer shape of the outer cover 7 is made substantially polygonal and the apexes are connected by gently sloping concave surfaces, the internal structure is not particularly limited. [Example]

[0047] A number of optical fiber cables were fabricated and subjected to a pressure-feeding test. Figure 4 is a conceptual diagram showing the method of the pressure-feeding test. First, a prototype optical fiber cable 15 is inserted into the conduit 13 from the pressure-feeding head 17 via a pair of caterpillar (registered trademark)-shaped propulsion units 19. While feeding high-pressure air into the propulsion head 17 (arrow D in the figure), the optical fiber cable 15 is sent out by the propulsion units 19, thereby enabling the optical fiber cable 15 to be pressure-fed into the conduit 13 (arrow C in the figure).

[0048] Figure 5 is a schematic diagram showing the path of the pipeline 13. The straight section E in the figure is approximately 9 m long, and the straight section F in the figure is approximately 38 m long. The curved section R1 in the figure has a radius of approximately 12 m. The straight section E and the straight section F are smoothly connected by two quarter circles with a radius R2 = 1 m in the figure.

[0049] The length of one lap of the conduit 13 was approximately 200 m, and the conduits 13 in the form shown in Figure 5 were connected in a continuous coil shape, with 10 laps making up a total length of 2000 m. The shape of each optical fiber cable 15 and the results of the pressure feeding test are shown in Table 1.

[0050] [Table 1]

[0051] The convex radius is the radius of the circumscribed circle of the convex portion (maximum radius of the cable). The concave amount is the depth of the concave portion (A in Figure 2). The vertex angle R is the radius of the curved portion at the tip of the convex portion (radius B in Figure 2). The minimum jacket thickness is the thickness of the jacket at the center of the concave portion 9. The internal structure of each optical fiber cable is generally the same as the structure in Figure 1.

[0052] The optical fiber cable was made by twisting together 12 12-fiber ribbons to form an optical fiber unit, and then wrapping a pressure winding member around the outer periphery of six optical fiber units to form a core. A tension member was placed around the core, and the jacket was extrusion coated. The amount of depression was adjusted by the resin temperature during extrusion, the shape of the mouthpiece, etc. Note that Comparative Example 2 has a conventional concave-convex shape, as shown in Figure 6.

[0053] In assessing stress concentration, those in which corners were formed between the convex and concave portions as described above were deemed to be at risk of stress concentration and were therefore rated as failing (×), whereas those in which there were no corners between the convex and concave portions and which had a smoothly continuous shape (a shape in which the entire space between the convex portions was composed of curves in the same direction (or a combination of curves in the same direction and partial straight lines)) were deemed to be passing (○) as they were deemed not to be at risk of stress concentration.

[0054] In addition, in the pressure feeding test, those that were able to pump 2000m were rated as passing (○), those that were unable to pump the optical fiber cable 15 along the way but the pumping distance was less than 2000m but 500m or more were rated as (△), and those that were less than 500m were rated as (×).

[0055] From the results in Table 1, in all of Examples 1 to 12, recesses were formed between the apexes of the polygons, so there were no corners at the boundary between the protrusions and recesses, and stress concentration was unlikely to occur, and so they were judged to pass. Also, Comparative Example 1 did not have a recessed shape, but the apexes were straight lines, so there were no corners at the boundary between the protrusions and recesses, and stress concentration was unlikely to occur, so it was judged to pass. In other words, unlike shapes in which protrusions are formed on parts of a substantially circle as in Patent Documents 1 and 2, corners are not formed at the boundary between the protrusions and recesses, so there is no risk of stress concentration.

[0056] In contrast, in Comparative Example 2, as described above, corners were formed at the boundaries between the convex and concave portions, which could cause stress concentration, and the sample was therefore rejected.

[0057] On the other hand, Comparative Example 1, which is a polygon with no concave shapes between vertices, had high friction resistance and was rated × in the pumping test. Also, Example 12 had a large concave amount and air leakage, which resulted in a somewhat shorter pumping distance and a △ in the pumping test.

[0058] Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the technical scope of the present invention is not limited to the above-described embodiments. It is clear that those skilled in the art can conceive of various modifications and alterations within the scope of the technical ideas described in the claims, and it is understood that these modifications and alterations also fall within the technical scope of the present invention. [Explanation of symbols]

[0059] 1, 1a....Optical fiber cable 3...Core 5...Tension member 7……Outer cover 9....Recess 11....Convex part 13……Pipeline 15....Optical fiber cable 17... Pumping head 19……Promotion Department 100....Optical fiber cable 103...Core 105...Tension member 107……Outer cover 109...recess 111....Convex part

Claims

1. a core or loose tube made of a plurality of optical fiber cores; an outer jacket covering the core or loose tube; A tension member that bears tension, Equipped with An optical fiber cable characterized in that, in a cross section perpendicular to the axial direction, the outer jacket is approximately polygonal, and the outer surface of the outer jacket between the vertices of the polygon is concave toward the center.

2. 2. The optical fiber cable according to claim 1, wherein the depth of the recessed shape relative to the straight line connecting the vertices of the polygon is 0.1 mm or more.

3. 2. The optical fiber cable according to claim 1, wherein the vertices of the polygon are curved.

4. 4. The optical fiber cable according to claim 3, wherein the radius of curvature of the curved shape at the vertices of the polygon is 0.2 mm or more and 2.0 mm or less.

5. 2. The optical fiber cable according to claim 1, characterized in that, in a cross section perpendicular to the axial direction, the core is positioned at the center, a plurality of the tension members are positioned around the core, and the tension members are each positioned at a position corresponding to the vertices of a polygon.

6. 2. The optical fiber cable according to claim 1, wherein, in a cross section perpendicular to the axial direction, the tension member is disposed at the center, and a plurality of the loose tubes are disposed around the tension member.

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