JPH04317010A - Optical fiber cable for press feeding - Google Patents

Abstract

PURPOSE:To provide the optical fiber unit having the structure suitable for pneumatically feeding into a spiral tube line. CONSTITUTION:Total 7 pieces of cords consisting of six pieces of optical fibers 1 and one piece of tear cord are twisted. An inside layer coating 3 and an outside layer coating 4 are clad thereon, by which the optical fiber unit is constituted. The twisting direction of the optical fibers is reversed from the twisting direction of the tube line into which this unit is to be inserted. The pitch of the twists is set smaller than the pitch of the twists of the tube line. The twists are relieved and the bending rigidity is lowered, by which the insertion characteristic is improved when this unit is inserted into the spiral tube line.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a pressure-feeding optical fiber cable constructed by forcing and inserting an optical fiber unit into a tube using air flow, and particularly to the structure of the optical fiber unit used in the installation method. It is.

0002

2. Description of the Related Art A method of constructing an optical fiber cable by inserting an optical fiber unit or a single optical fiber into a pre-installed tube using air flow is described in Japanese Patent Publication No. 2-22921. However, this publication does not consider the relationship between the conduit form of the tube and the structure of the optical fiber unit inserted therein. After that, as described in "Preliminary Papers of the 1990 Institute of Electronics, Information and Communication Engineers National Conference" B-667, and "Air Blown Transmission to Twisted Pipe" by Kanzaki et al., it was used as a conduit through which an optical fiber unit was inserted. Although there are reports using a spiral conduit, the relationship with the structure of the optical fiber unit is not considered in this case either.

[0003] Conventional optical fiber units for pneumatic transport are:
It was developed on the premise that it would be pumped into a tube conduit that has a straight line and several curved sections, so it is possible that the tubes assembled in a spiral have curved sections with a radius of curvature of 200 cm or less. When used in a tube conduit, there was a problem in that the insertion ability was significantly reduced.

[0004] The reason for this is that the optical fiber unit is bent into a spiral shape during the process of insertion, which consumes a large amount of pumping energy even in the portion where the conduit is laid straight. Therefore, it can be said that the conventional type optical fiber unit, which has a large bending rigidity, is disadvantageous for a spiral conduit.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide an optical fiber having a structure suitable for pneumatically feeding a spiral tube conduit. The purpose is to realize the unit.

[0006]

[Means for Solving the Problems] The present invention provides a pressure-feeding optical fiber cable in which an optical fiber unit consisting of a plurality of optical fibers is inserted into a conduit in which a plurality of tubes are twisted, using an air flow. In the optical fiber unit, the optical fibers constituting the optical fiber unit or a subunit consisting of a plurality of optical fibers are twisted at a twisting pitch shorter than the twisting pitch of the tube, and the twisting direction is opposite to the twisting direction of the tube. It is characterized by its orientation.

[0007]

[Operation] When inserted into a tube, the optical fiber unit is bent in the helical direction of the tube as it is inserted. At this time, the smaller the bending rigidity of the optical fiber unit, the higher the insertion ability. As the optical fiber unit according to the present invention is inserted into a tube,
As the tip gradually rotates in the direction of twisting the tube,
The twist of the optical fiber or subunit becomes loose and the bending rigidity decreases.

On the other hand, when the optical fiber or subunit is twisted in the same direction as the tube, the tip of the optical fiber unit rotates in the tube's twisting direction, tightening the twist, increasing the bending rigidity, and improving the insertion capacity. causing a decline. In addition, in an optical fiber unit in which the optical fibers or subunits are not twisted, when the optical fibers or subunits are bent, the outer optical fibers or subunits are stretched and strained, so the bending rigidity increases, and the insertion ability is similarly reduced. It is disadvantageous because it decreases.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of an embodiment of an optical fiber unit of the present invention. In the figure, 1 is an optical fiber, 2 is a tear string, 3 is an inner layer coating, and 4 is an outer layer coating. In this embodiment, an optical fiber unit is constructed by twisting a total of seven optical fibers, six optical fibers 1 and one tearing string 2, covering them with an inner layer coating 3, and then coating them with an outer layer coating 4. has been done. The twist direction is opposite to the twist direction of the tube conduit through which this unit is inserted, and the twist pitch is smaller than the twist pitch of the tube conduit.

FIG. 2 is a sectional view of another embodiment of the optical fiber unit of the present invention. In the figure, 1 is an optical fiber, 2 is a tear string, 3 is an inner layer coating, 4 is an outer layer coating, 5 is a subunit, and 6 is an inner layer coating. In this embodiment, the optical fiber unit is composed of three subunits 5. Each subunit 5 is composed of a total of seven optical fibers, six optical fibers 1 and one tear string 2, similar to that explained in FIG. The optical fiber 1 and tear string 2 in the subunit are twisted together as in FIG. 1, but they do not necessarily need to be twisted. The three subunits 5 are twisted in a direction opposite to the twisting direction of the tube conduit through which this unit is inserted, and the twisting pitch is smaller than the twisting pitch of the conduit.

FIG. 3 shows an example of a conduit. In the figure, 7 is a tube, 8 is a coating, and 9 is a power cable. The tube 7 with the covering 8 is twisted together with a three-phase power cable 9. A suitable coating may also be applied over these.

[0012] The optical fiber unit described in FIG. 1 or 2 is inserted into such a conduit to construct an optical fiber cable. In order to insert the optical fiber unit into the tube 7, it is necessary to reduce the bending rigidity in the helical direction of the tube. For this purpose, it is effective to twist the optical fibers or optical fiber subunits constituting the optical fiber unit. Moreover, since the twisting pitch is shorter than the twisting pitch of the tube and the twisting direction is opposite to the twisting direction of the tube, the rigidity during insertion can be reduced.

In order to confirm the effects of the present invention, ten types of optical fiber units shown in FIG. 4 were fabricated as prototypes, and insertion experiments were conducted. The conduit used was a spiral polyethylene tube with an outer diameter of 8 mm and an inner diameter of 6 mm. The spiral shape of the tube was such that the twisting pitch was 830 mm, the core diameter of the tube was 46 mm, and the twisting direction was right.

Among the 10 types of optical fiber units, N
o. 1~No. 5, coated optical fibers with an outer diameter of 250 μm are arranged in a total of 7 fibers, one in the center and six around it, and coated with polypropylene as an inner layer coating to form a fiber with an outer diameter of 1 m.
The structure was similar to that shown in FIG. 1, with an outer diameter of 2 mm and an outer layer coated with high-density foamed polyethylene. The twist pitch of optical fiber is shown in Figure 4.
As shown below.

[0015]No. 6~No. In No. 10, three of the above-mentioned polypropylene inner layer coatings were used as subunits. This was twisted at the pitch shown in FIG. 4, an inner layer of polypropylene was layered thereon to give a diameter of 2.5 mm, and the outer diameter was made to be 4 mm by covering it with high-density foamed polyethylene. The structure is similar to that shown in FIG.

FIG. 5 shows the insertion characteristics of the ten types of optical fiber units shown in FIG. 4 tested in the above-mentioned spiral tube conduit. The compression pressure of the air used for insertion was 5 kg/cm2 in gauge pressure. The length of the tube that was pumped was No. 1~No. 600m for 5, No.
．． 6~No. 10 is 300m.

As can be seen from this result, it was confirmed that the insertion ability is particularly high when the tube and the optical fiber or subunit are twisted in opposite directions and the twisting pitch is less than or equal to the twisting pitch of the tube. did it.

[0018] The present invention can be applied to conduits where the tubes are twisted, such as when an optical fiber unit is inserted after the tubes have been installed as a combination of a power cable or the like, as explained in Fig. 3. Effective for conduits. In addition, not only when tubes are combined with other cables, but also when cables are made by bundling only multiple tubes.
Tubes are often twisted to increase the flexibility of cables. The optical fiber unit according to the present invention is also effective for such conduits.

[0019]

As is clear from the above description, according to the present invention, the optical fibers or subunits constituting an optical fiber unit are twisted in the opposite direction to the tube, and the twisting pitch is set to less than the twisting pitch of the tube. By doing so, it is possible to provide an optical fiber unit with improved insertion ability.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of an optical fiber unit of the present invention.

FIG. 2 is a sectional view of another embodiment of the optical fiber unit of the present invention.

FIG. 3 is an example of a conduit to which the present invention is applied.

FIG. 4 is an explanatory diagram of the characteristics of the optical fiber unit used in the experiment.

FIG. 5 is an explanatory diagram of experimental results.

[Explanation of symbols]

1 Optical fiber 2 Tear string 3 Inner layer coating 4 Outer layer coating 5 Subunit 6 Inner layer coating

Claims (1)

[Claims] 1. A pressure-feeding optical fiber cable in which an optical fiber unit consisting of a plurality of optical fibers is inserted into a conduit in which a plurality of tubes are twisted, using an air flow, wherein the optical fiber unit is The optical fiber or subunit consisting of a plurality of optical fibers constituting the tube is twisted at a twisting pitch shorter than the twisting pitch of the tube, and the twisting direction is opposite to the twisting direction of the tube. Optical fiber cable for pressure feeding.