JP2012047957A - Optical fiber drop cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber drop cable capable of preventing a galloping phenomenon through optimizing sizes of a support line portion, a cable portion and a neck portion.SOLUTION: An optical fiber drop cable 1 comprises a cable portion 10 which is rectangular in cross section, a support line portion 20 and a neck portion 30. A size a on a short side 10Y of the cable portion is 2.0±0.2 mm, and a size b on a long side 10X thereof is 3.1±0.2 mm. When an overall height of the cable from the cable portion 10 to the support line portion 20 is defined as x, and a height of the neck portion is defined as y, a conditional expression y≤0.7524x-3.98292 is satisfied. Furthermore, the support line portion has an external diameter of at most 3.0 mm, and the neck portion has a height of at most 1.0 mm.

Description

  The present invention relates to an optical fiber drop cable used when an optical fiber is pulled from an overhead optical fiber cable to each user's house.

  In recent years, with the development of FTTH (Fiber To The Home), optical fiber wiring to each user's home has been frequently performed. At that time, an optical fiber drop cable as described in Patent Document 1 is mainly used for wiring from an aerial closure disposed in the vicinity of the telephone pole to each user's house.

  FIG. 8 is a cross-sectional view showing an example of the structure of an optical fiber drop cable. The optical fiber drop cable 101 has a long side parallel to the first direction X (also referred to as “major axis”) and a short side parallel to the second direction Y orthogonal to the first direction X (commonly known as “ A cable section 110 having a substantially rectangular cross section having a short diameter), a support line section 120 having a circular cross section disposed in parallel to the cable section 110 and supporting the cable section 110, and the cable section 110 and the support line section. The neck portion 130 has a constricted neck portion 130 that is formed thinner than 120 and connects the cable portion 110 and the support wire portion 120 together.

  The cable unit 110 includes an optical fiber core 111, strength members 112 arranged along the longitudinal direction of the optical fiber core 111 on both sides in the first direction X of the optical fiber core 111, and an optical fiber core wire. 111 and a sheath 113 made of resin that covers the strength member 112. The support wire portion 120 includes a support wire (generally a steel wire) 122 having a circular cross section as a strength member, and a resin sheath 113 that covers the support wire 122.

  The sheath 113 of the cable part 110 and the sheath 113 and the neck part 130 of the support line part 120 are made of an integrally molded resin. In addition, notches 118 are formed on both outer side surfaces of the sheath 113 of the cable portion 110 to break the sheath 113 and facilitate the drawing of the optical fiber core wire 111 therein. Further, the optical fiber core wire 111, the two strength members 112, the neck portion 130, and the support wire 122 are arranged on a straight line in a cross section in a plane perpendicular to the cable longitudinal direction.

  By the way, this type of optical fiber drop cable 101 is aerial wired in a posture in which the support wire portion 120 is located on the upper side and the cable portion 110 is hung down on the lower side as in the posture shown in FIG. When a strong wind blows from the side, galloping phenomenon may occur like when the snow is attached to the electric wire.

  Galloping is a phenomenon in which the transmission line vibrates violently up and down when strong wind blows with snow or ice attached to the transmission line. When a galloping phenomenon occurs in an optical fiber drop cable, vibrations that cannot occur in normal strong winds continue, so there are concerns about cable breakage due to over tension, deterioration in transmission characteristics, damage due to hitting surrounding objects, and the like. The presence or absence of the possibility of galloping can be determined by the D value (described later) of the Den-Hartog judgment formula. When the D value becomes negative, galloping does not occur.

  As examples of optical fiber drop cables that take measures against wind pressure, Patent Documents 2 and 3 describe cable structures for reducing wind pressure load.

JP 2004-69900 A JP 2003-227984 A Japanese Patent No. 3854164

  However, although those shown in Patent Document 2 and Patent Document 3 may be able to reduce the wind pressure load, there is no possibility of preventing the occurrence of the galloping phenomenon because no consideration is given to galloping. Is big.

  In view of the above circumstances, an object of the present invention is to provide an optical fiber drop cable in which the galloping phenomenon does not occur after laying by optimizing the dimensions of the support wire portion, the cable portion, and the neck portion.

The invention according to claim 1 is a cable portion having a rectangular cross section having a long side and a short side, a support line portion arranged in parallel to the cable portion and supporting the cable portion, the cable portion, and the support A constricted neck portion integrally connecting the cable portion and the support wire portion, wherein the cable portion includes an optical fiber core and the optical fiber on both sides of the optical fiber core. A tension member disposed along a longitudinal direction of the core wire, and a resin sheath covering the optical fiber core wire and the strength member, and the support wire portion includes a support wire as a strength member and the support. In an optical fiber drop cable provided with a resin sheath covering the wire, the short side dimension of the cable part is 2.0 ± 0.2 mm, the long side dimension is 3.1 ± 0.2 mm, From the cable part to the support line part When the total height of the cable at x is x and the height of the neck is y,
y ≦ 0.7524x−3.998292
In addition, the outer diameter of the support wire portion is 3.0 mm or less and the height of the neck portion is 1.0 mm or less.

According to the optical fiber cable of the present invention, the short side dimension of the cable part having a rectangular cross section is 2.0 ± 0.2 mm, the long side dimension is 3.1 ± 0.2 mm, and from the cable part to the support line part. Where x is the total height of the cable and y is the height of the neck in the first direction,
y ≦ 0.7524x−3.998292
Since the values of x and y are set so as to satisfy the conditional expression, and the outer diameter of the support wire portion is regulated to 3.0 mm or less and the height of the neck portion is regulated to 1.0 mm or less, the D value of the galloping determination formula Can be made negative, and the galloping phenomenon can be prevented from occurring.

It is sectional drawing of the optical fiber drop cable of embodiment of this invention. It is explanatory drawing of the galloping phenomenon which occurs in the power transmission line to which ice and snow adhered at the time of a strong wind. It is an enlarged view which shows the relationship of force when a galloping phenomenon may occur in a power transmission line. It is a graph which shows the relationship between the total height x from the cable part of a fiber-optic drop cable from which the D value of a galloping judgment formula becomes negative, and the support line part, and the height y of a neck part. It is sectional drawing of the optical fiber drop cable of Example 1 of this invention. It is sectional drawing of the optical fiber drop cable of Example 2 of this invention. It is sectional drawing of the optical fiber drop cable of Example 3 of this invention. It is sectional drawing of the conventional optical fiber drop cable.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view of an optical fiber drop cable according to the embodiment, FIG. 2 is an explanatory diagram of a galloping phenomenon that occurs in a transmission line, and FIG. 3 is an enlarged view that shows the relationship of forces when a galloping phenomenon may occur in the transmission line. It is.

  As shown in FIG. 1, the optical fiber drop cable 1 of the present embodiment has a long side parallel to a first direction (height direction in a normal laid state) X (also referred to as “major axis”). A cable portion 10 having a rectangular cross section having a short side (also referred to as “short diameter”) 10Y parallel to a second direction Y orthogonal to the first direction X, and the first portion of the cable portion 10 A support line part 20 having a circular cross section that is disposed in parallel to the cable part 10 and supports the cable part 10 at a position adjacent to the direction X, and is formed thinner than the cable part 10 and the support line part 20 to support the cable part 10. It has a constricted neck portion 30 that connects the wire portions 20 together.

  The cable unit 10 includes an optical fiber core wire 11, strength members 12 disposed along the longitudinal direction of the optical fiber core wire 11 on both sides in the first direction X of the optical fiber core wire 11, and an optical fiber core wire. 11 and a resin sheath 13 that covers the strength member 12. The support wire portion 20 includes a support wire (generally a steel wire) 22 having a circular cross section as a strength member, and a resin sheath 13 covering the support wire 22.

  The sheath 13 of the cable portion 10 and the sheath 13 and the neck portion 30 of the support wire portion 20 are made of an integrally molded resin. In addition, notches 18 are formed on both outer side surfaces of the sheath 13 of the cable portion 10 to make it easier to pull out the optical fiber core wire 11 by breaking the sheath 13. The optical fiber core wire 11, the two strength members 12, the neck portion 30, and the support wire 22 are arranged on a straight line in a cross section in a plane perpendicular to the cable longitudinal direction.

The dimension a of the short side 10Y of the cable portion 10 is set to 2.0 ± 0.2 mm, and the dimension b of the long side 10X is set to 3.1 ± 0.2 mm. Further, when the total height of the cable in the first direction X from the cable portion 10 to the support wire portion 20 is x, and the height in the first direction X of the neck portion 30 is y,
y ≦ 0.7524x−3.998292
The total height x of the cable, in particular, the diameter c of the support line portion 20 that influences the total height x and the height y of the neck portion 30 are set so as to satisfy the conditional expression. Moreover, the diameter c of the support wire portion 20 is set to 3.0 mm or less, and the height y of the neck portion 30 is set to 1.0 mm or less.

  When such a condition is satisfied, even when a wind with a wind speed of 40 m / s is received, since the D value (described later) of the galloping determination formula becomes negative, the galloping phenomenon does not occur.

  Here, the generation principle of the generally known transmission line galloping phenomenon will be described with reference to FIGS. As shown in FIG. 2, the galloping phenomenon is a phenomenon in which when the icing snow 52 is attached to the electric wire 50 and a strong wind force (wind pressure) F acts thereon, the vertical vibration is repeated with a large amplitude and a low frequency.

  As shown in FIG. 3, when a wind force (wind pressure) F is received from the side with the icing snow 52 attached to the electric wire 50, a drag FD and a lift force FL are generated on the electric wire 50. When the electric wire 50 has a circular cross section without the icing snow 52, only the drag FD in the horizontal direction against the wind is generated, and no lift FL is generated, and therefore no vertical vibration is generated. However, when the icing snow 52 is attached to the electric wire 50, the electric wire apparently has a non-circular cross section, so that when the wind is received, a lift FL is generated in addition to the drag FD on the electric wire. The vibration generated by the lift FL becomes self-excited vibration and develops into a galloping phenomenon. This is expressed by the Den-Hartog judgment formula, and the present invention applies this formula.

  In general, when this type of optical fiber drop cable 1 receives wind in the state after laying, the support wire 22 swings around its axis (swing center), and the support wire portion 20 is located on the windward side. 10 is a posture that is swept to the leeward side. However, the highest point of the cable portion 10 does not exceed the highest point of the support wire portion 20 due to the influence of gravity. Here, the state in which the cable unit 10 hangs down vertically (cable state shown by a solid line in FIG. 1) is 90 °, and the state in which it is raised horizontally (cable state shown by a two-dot chain line in FIG. 1) is 0 °. An angle formed by the cable portion 10 with respect to is β [deg].

  A calculation method for calculating the drag value FD [N] and the lift force FL [N] generated in the optical fiber drop cable 1 when the wind speed V [m / s] is received from the horizontal direction by the finite element method is as follows. Shown in

First, the drag coefficient CD and the lift coefficient CL are obtained from the following equations. Where ρ is the air density [kg / m3], and An is the projected area [m2] of the cable viewed from the direction of the wind.

When T is the air temperature [° C.], the air density ρ is obtained by the following equation. However, in general, the air temperature T is calculated at 25 ° C.

Also, the angle α

And the Den-Hartog galloping judgment formula is obtained as follows, with the angle β as the attack angle of the wind.

  When the D value in this expression is positive, there is a possibility of galloping, and when the D value is negative, it is determined that there is no possibility of galloping.

For example, Table 1 shows the calculation result of the D value when the size a × b of the cable portion is 2.0 × 3.1 mm and the height y of the neck portion 30 and the diameter c of the support wire portion 22 are changed. Table 1 shows the maximum value of the D value when the optical fiber drop cable 1 receives wind and swings in the range of 0 ° to 90 °. The shaded area has a positive D value, and the unshaded area has a negative D value.

Table 2 summarizes the conditions under which D values are negative in Table 1.

  The relationship between the neck height y and the total cable height x in Table 2 is shown in the graph of FIG.

From this relationship,
y ≦ 0.7524x−3.998292
The conditional expression is derived. A region indicated by diagonal lines in FIG. 4 represents a region where the D value is negative.

  In order to satisfy the above conditions, the following optical fiber drop cables are provided.

  FIG. 5 is a cross-sectional view of the optical fiber drop cable according to the first embodiment. The optical fiber drop cable 1A of Example 1 uses a single optical fiber core wire as the optical fiber core wire 11, and the size of the short diameter a × long diameter b of the cable portion 10 is 2.0 × 3.1 mm. It has become. Further, the height y of the neck portion 30 is 0.2 mm, the outer diameter c of the support wire portion 20 is 2.8 mm, the diameter of the support wire 22 is 1.2 mm, and the total height x of the cable is 6.1 mm. The material is PO (polyolefin), and the strength member 12 is K-FRP (Kevlar fiber).

  FIG. 6 is a cross-sectional view of the optical fiber drop cable according to the second embodiment. The optical fiber drop cable 1B of Example 2 uses a single optical fiber core wire as the optical fiber core wire 11, and the size of the short diameter a × long diameter b of the cable portion 10 is 1.9 × 3.0 mm. It has become. Further, the height y of the neck portion 30 is 0.7 mm, the outer diameter c of the support wire portion 20 is 2.6 mm, the diameter of the support wire 22 is 1.2 mm, and the total cable height x is 6.3 mm. And the sheath 13 of the support wire portion 20 has a two-layer structure of an outer layer 13A made of PO and an inner layer 13B made of HDPE (high density polyethylene), and the material of the tensile body 12 was K-FRP (Kevlar fiber). Is.

  FIG. 7 is a cross-sectional view of the optical fiber drop cable according to the third embodiment. The optical fiber drop cable 1C of Example 3 uses a two-core optical fiber as the optical fiber core 11, and the size of the short diameter a × long diameter b of the cable portion 10 is 2.1 × 3.2 mm. It has become. Further, the height y of the neck portion 30 is 0.1 mm, the outer diameter c of the support wire portion 20 is 2.2 mm, the diameter of the support wire 22 is 0.95 mm, and the overall cable height x is 5.5 mm. The material is HDPE, and the material of the strength member 12 is K-FRP (Kevlar fiber).

  In the above embodiment, the case where the sheath 13 covering the optical fiber core wire 11, the strength member 12 and the support wire 22 is composed of one layer or two layers is shown. The following is desirable.

  In the above embodiment, the case where the number of the optical fiber cores 11 is one or two is shown. However, an optical fiber drop cable having two or more cores and not more than eight cores may be used.

  INDUSTRIAL APPLICABILITY The present invention can be used for an optical fiber cable suitable for drawing an optical fiber from an aerial wired optical fiber cable to each user's house.

1A, 1B, 1C: Optical fiber drop cable 10: Cable portion 10X: Long side (long diameter)
10Y ... Short side (minor axis)
DESCRIPTION OF SYMBOLS 11 ... Optical fiber core wire 12 ... Strength body 13 ... Sheath 22 ... Support line

Claims (1)

A cable portion having a rectangular cross section having a long side and a short side, a support wire portion arranged in parallel to the cable portion and supporting the cable portion, and formed thinner than the cable portion and the support wire portion. A constricted neck that integrally connects the support portion and the support wire portion,
The cable part is made of an optical fiber core, a tensile body disposed on both sides of the optical fiber core along the longitudinal direction of the optical fiber core, and a resin coating the optical fiber core and the tensile body. With a sheath of
In the optical fiber drop cable, the support line portion includes a support line as a tensile body and a resin sheath covering the support line.
The short side dimension of the cable part is 2.0 ± 0.2 mm, the long side dimension is 3.1 ± 0.2 mm, the total height of the cable from the cable part to the support line part is x, and the neck part Where y is the height of
y ≦ 0.7524x−3.998292
The optical fiber drop cable is characterized in that the outer diameter of the support wire portion is 3.0 mm or less and the height of the neck portion is 1.0 mm or less.

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