JPH03144403A - Optical cable for leading in by pneumatic force-feeding - Google Patents

Abstract

PURPOSE:To facilitate the leading in of the optical cable by pneumatic force-feeding by forming >=3 projecting lines extending in a longitudinal direction apart nearly equal circumferential intervals on the outer peripheral surface of a sheath to about the height at which the sheath does not longer comes into contact with the inside surface of the pipe. CONSTITUTION:The >=4 projecting lines 25 extending in the longitudinal direction apart nearly equal circumferential intervals are formed on the outer peripheral surface of the sheath 24 to about the height at which the sheath 24 does no longer comes into contact with the inside surface of the pipe. The optical cable 21 is brought into contact with the inside surface of the pipe 12 by the projecting lines 25 extending in the longitudinal direction and, therefore, the friction resistance at the time of leading in the optical cable 21 into the pipe 12 is decreased to about half the friction resistance of the conventional optical cables. The optical cable 21 is easily floated from the inside surface of the pipe 12 by the action of a wind pressure on the projecting lines 25 as well and the generation of a gap G between the sheath 24 and the inside surface of the pipe 12 and the flow of air therein. The leading in of the optical cable 21 by the pneumatic force-feeding is facilitated in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a relatively small diameter optical cable that is drawn into a pipe by pneumatic feeding.

[Prior art]

For example, when combining an optical cable with an electric cable, as shown in Figure 5, when twisting the electric cable core 11, an empty pipe I2 is twisted around the shoulder of the electric cable core 11, and later the optical cable is inserted into this pipe 12. A convenient method for drawing the optical cable into the pipe as described above is to use air pressure.

As shown in Figure 6, this method involves attaching a wind blowing member 14 to the tip of the optical cable 13, inserting it into the pipe 12, and then forcefully feeding air into the pipe 12 from behind the optical cable 13. 13. To carry out this method, an apparatus as shown in Figure 7 is used. This device stores a bobbin 16 on which an optical cable 13 is wound in a closed container 15, connects a compressor (or cylinder) 18 to the closed container 15 via a hose 17, and connects a pipe 12 to the outlet of the closed container 15. It is connected to send compressed air from the compressor 18.

By the way, the optical cable that is drawn into the pipe is a relatively small-diameter cable (with an outer diameter of about 1 to 10 mm), which is made by applying a sheath to the outer periphery of an optical fiber core unit consisting of one or more cored optical fibers. In order to increase the lifting force of the air flowing inside the pipe, conventionally, foamed polyethylene was used for the sheath to facilitate the passage of the pipe by air pressure.

〔assignment〕

However, since conventional optical cables have a circular cross section, even if the outer diameter is increased somewhat, the lifting force due to the circulating air does not increase significantly, and there is also a limit to increasing the outer diameter due to the relationship with the inner diameter of the pipe. Furthermore, since pipes usually have bends, the frictional resistance between the inner surface of the pipe and the sheath is also large. For these reasons, conventional optical cables have a problem in that there is a limit to the length that can be retracted by pneumatic feeding, and the retractable length cannot be increased beyond a certain level.

[Means for solving problems and their effects]

In order to solve the above-mentioned problems, the present invention provides an optical cable in which a sheath is applied to the outer periphery of an optical fiber core unit and is drawn into a pipe by pneumatic feeding, in which the outer periphery of the sheath is substantially equal to the outer periphery of the sheath in the circumferential direction. The pipe is characterized in that three or more protrusions extending in the longitudinal direction at intervals are formed at a height such that the sheath does not come into contact with the inner surface of the pipe.

The air flowing inside the pipe generally flows in the longitudinal direction of the pipe, but locally there is turbulence, so if the ridges described above are formed, wind pressure will also act on the ridges, causing the optical cable to The lift force increases.

Furthermore, since it comes into contact with the inner surface of the pipe through a protrusion extending in the drawing direction, the frictional resistance with the inner surface of the pipe is also reduced. Therefore, the optical cable can be easily pulled in by pneumatic feeding, and the length that can be pulled in can be increased.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the optical cable according to the present invention. This optical cable 21 is formed by applying a sheath 24 to the outer periphery of an optical fiber core unit 22 formed by collecting a plurality of optical fiber cores 22. The pipe is characterized by having four protrusions 25 extending in the longitudinal direction at a height such that the sheath 24 does not come into contact with the inner surface of the pipe.

When the outer diameter of the sheath 24 is about 3 mm, the height of the protrusion 25 is about 11, and the width is about 0.5 to 1.51. Projection 2
5 can be formed integrally with the sheath 24 during extrusion molding. The sheath 24 and the protrusions 25 may be made of polyethylene or polyvinyl chloride, and may be foamed or non-foamed.

2 shows the state in which the optical cable 21 of the present invention is drawn into the pipe 12, and FIG. 3 shows the state in which the conventional optical cable 13 is drawn into the pipe 12. The conventional optical cable 13 is in surface contact with the inner surface of the pipe 12, but the optical cable 21 of the present invention is in contact with the inner surface of the pipe 12 through a projection 25 extending in the longitudinal direction. As a result, in the optical cable of the present invention, the frictional resistance when being drawn into a pipe is reduced to about half that of conventional optical cables. In addition, wind pressure acts on the protrusion 25 and the sheath 2
4 and the inner surface of the pipe, and air flows through the gap G, making it easier for the optical cable to lift up from the inner surface of the pipe.

This shows the results of a wind tunnel experiment. It can be seen that the lift coefficient of the optical cable 21 of the present invention is approximately four times that of the conventional optical cable 13.

For these reasons, the optical cable of the present invention can be drawn into a pipe about 1.5 to 2 times longer than conventional optical cables, and the composite cable can be made longer.

〔Effect of the invention〕

As explained above, the optical cable according to the present invention has a protrusion on the outer periphery of the sheath, so when it is drawn into the pipe by air pressure, the lifting force due to wind pressure becomes large, and the protrusion does not meet the inner surface of the pipe. Since they are in contact with each other, the frictional resistance with the inner surface of the pipe is reduced. Therefore, there is an advantage that the length that can be drawn into the pipe can be made significantly longer than before.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of an optical cable according to an embodiment of the present invention.
Figure 2 shows the optical cable being pulled into the pipe: 1st L
Earth/rV Nakadai ζt between -01 to
4 is a graph showing the results of a wind tunnel experiment of the optical cable according to the present invention and a conventional optical cable, Figure 5 is a cross-sectional view of an electric cable combined with a pipe for pulling in an optical cable, and Figure 6 is a method for pulling an optical cable into a pipe using air pressure. FIG. 7 is an explanatory diagram of the apparatus used therein. 12: Pipe 13: Conventional optical cable 21; Optical cable of the present invention 22: Optical fiber core 23: Optical fiber core unit 24: Sheath 25: Protrusion diagram-3 Figure-2 Figure- Wind speed (m/sec)

Claims (1)

[Claims] 1. In an optical cable that is formed by applying a sheath to the outer periphery of an optical fiber core unit and is drawn into a pipe by pneumatic feeding, three or more strips extending in the longitudinal direction at approximately equal intervals in the circumferential direction are provided on the outer circumferential surface of the sheath. An optical cable for pneumatic feeding, characterized in that the protrusion is formed at a height such that the sheath does not come into contact with the inner surface of the pipe.