GB2245432A

GB2245432A - Optical fibre cable installation

Info

Publication number: GB2245432A
Application number: GB9113310A
Authority: GB
Inventors: Georg Maltz; Wolfgang Wenski
Original assignee: Kabelmetal Electro GmbH
Current assignee: Kabelmetal Electro GmbH
Priority date: 1990-06-21
Filing date: 1991-06-20
Publication date: 1992-01-02
Anticipated expiration: 2011-06-20
Also published as: GB2245432B; GB9113310D0; DE4019692A1

Abstract

A process for the overhead installation of optical fibre cables is described, in which the optical fibre cable 1 is mounted at specific spacings on structures such as buildings, masts 3, etc., and clamped by means of clamping elements. In order to form an excess length of the glass fibre(s) and to create a spare length for a branching connection, a specific length of the cable is taken up at specific spacings onto a reel or a core 4. The reel may be suitable for bifilar winding (Figs 3a, 3b). <IMAGE>

Description

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DESCRIPTION

OPTICAL FIBRE CABLE INSTALLATION The Invention relates to a process for the overhead Installation of optical fibre cables, preferably those having unstranded loose buffers or multifibre units and stress members, in which the optical fibre cable is mounted at specific spacings on structures such as buildings. masts. etc., and clamped by means of clamping elements.

Aerial optical fibre cables comprising loose buffers or multifibre units have the disadvantage of a low effective fibre excess length. The fibre excess length is required in order to protect the fibres from excessive stresses during installation and in operation is 1 despite the cable strain due to tensile forces and temperature change. Moreover,, due to continuous stress of the stress members long-term creepage can occur which leads to cable elongation and further reduces the fibre excess length.

However, the above-mentioned aerial optical fibre cables comprising unstranded loose buffers and/or multifibre units have the advantage that they are extremely thin. They are light, highly flexible, and therefore easy to install.

It is the object of the present invention to specify a process which enables a rapid and simple installation and an easy reclamping of such aerial cables. Moreover, a possibility is to be created of providing a cable reserve for a subsequent splice point. In particular, a fibre excess length reserve is to be created by the installation process.

This object is achieved when in accordance with the invention a specific length of the optical fibre cable is taken up at specific spacings, preferably at the clamping points, onto a reel or a core. Although it is possible in the case of aerial cables which, for example, are strapped to a messenger to attach the windings at any point between the masts, it is preferred to provide the reel or the core at the clamping point. The excess length reserve is provided due to the fact that the sensitive glass fibre or,,. in the case of a multif ibre unit, the glass fibres, which extend in a virtually freely moveable fashion inside a plastic tube, are taken up with a larger radius than the region, facing the winding core or the reel, of the plastic tube, that is to say the inside radius thereof. In the case of tensile stress, the winding diameter of the glass fibres can be reduced, until the glass fibre bears against the inside surface of the plastic tube.

The excess length c is computed according to the equation..

r ' FrIA 2':: Y 4 4.r 1T IZ + + CZ-5,-) L R where R winding radius &r r, r,, = pitch = ri - r,, = inside radius of the loose buffer = radius of the fibre Whereas the magnitude rf is not variable and ri is variable only within narrow limits, the magnitude of e can be influenced by R and S. S is dependent on the outside diameter of the optical fibre cable, and cannot become smaller than the outside diameter of the optical fibre cable.

According to a particularly advantageous development of the invention, the longitudinal axis of the helix or of the reel or of the core extends transversely to the longitudinal direction of the optical fibre cable.

It has proved to be particularly advantageous for the optical fibre cable to be taken up with the smallest possible pitch and/or the smallest possible winding diameter. As described earlier, a maximum excess length can be achieved hereby.

It is expedient for the optical fibre cable to be taken up in a bif ilar fashion. As a result, when the optical fibre cable is taken up no torsion is produced in the cable.

In a development of the invention it has proved to be advantageous that the optical fibre cable is clamped on both sides, eg by spring sheath clips, and the region free of tensile force between the working points of the spring sheath clip is taken up onto a reel or a core. As a result, windings reach into the region of the mast and are therefore easily accessible or easy to produce.

The invention further relates to a device for clamping optical fibre cables or other thin cables, which is also outstandingly suitable for carrying out the process according to the teaching of the invention. The device consists of a bifilar-wound reel provided in the clamping points. In this bifilar-wound reel, the reel core expediently has a channel of yin-yang shape, through which the optical fibre cable is led. The channel extends 1 is somewhat obliquely relative to the longitudinal axis of the reel, so that single-layer winding is possible. The yin-yang shape of the channel provides a simple way of enabling bifilar winding free of kinks.

The reel is advantageously secured by a rewind stop. Reels having such rewind stops are known per se, but have not so far been used for the said purpose. The taking up and the clamping of the optical fibre cable is simplified when the reel contains a crank receptor. Inserting the optical fibre cable into the channel is simplified when the reel or the core is divided transversely to the longitudinal axis.

The invention is explained in more detail with reference to the exemplary embodiments represented diagrammatically in Figures 1 to 4.

An optical fibre cable 1 for overhead instal lation, which is strapped to a messenger 2, is shown in Figure 1. The messenger 2 is, for example, mounted on a mast 3. The optical fibre cable 1 is a so-called aerial optical fibre cable comprising unstranded loose buffers and multifibre units. Regions of "discontinuous strand ing 11 4 and 5 are provided between the mounting points of the cable 1 in order to create a fibre excess length. It is expedient to undertake the I'discon tinuous stranding" during installation of the cable 1.

For this purpose, the cable 1 is taken up onto a core or a reel.

Figure 2 shows a section of a-reel or of a core 18, onto which an aerial optical fibre cable 1 is taken up helically. The aerial optical fibre cable consists of a loose buffer having a glass fibre 6 which is arranged inside a plastic tube 7 of substantially larger diameter. An outer sheath 8 protects the sensitive loose buffer and contains tensile load members (not represented in more detail). With such cables there is the danger that when tensile stress occurs, eg due to wind, ice or the like, the cable can stretch despite the tensile load members, since the material of the tensile load members is mostly not ageing-resistant. Since, however, the optical fibre is cannot participate in an elongation, it is necessary to create an excess length for the optical fibre or the glass fibre.

This problem Is solved in the process according to the invention when the glass f ibre 6, which is normally located in the centre of the plastic tube 7. as shown at top left in Figure 2, is displaced. Since the interior of the plastic tube 7 is usually filled with a vaseline-like compound. the diameter of the helix for the glass fibre 6 can be reduced until the helix or winding bears against the inner wall of the plastic tube 7 (see Figure 2. second turn at the top).

Figures 3a and 3b show a reel 9, onto which the cable 1 can be taken up in a bifilar fashion. For this purpose, the reel 9 has a channel 10 of yin-yang shape, which enables taking up to be free of kinks.

The channel 10 extends, matched to the cable diameter, somewhat obliquely through the body of the reel, in order to facilitate single-layer winding. It is expedient for the reel 9 to be transversely divided in the region of the channel 10, so that inserting the cable 1 into the channel 10 is simplified. In addition, due to the bifilar winding the advantage is achieved that the clamping process can be accelerated. Moreover, a sufficient cable reserve can be taken up onto the reel 9, so that the clamping point can be configured as a branch cable closure. The reel 9 further has a crank 11 and a rewind stop 12.

Figure 4 shows a clamping element 13 on which a bifilar-wound reel 9 is arranged. The clamping element 13 is mounted as a unit on a mast 3. Two guide rollers are denoted by 14. The middle piece of a cable length located on the reel 9 is led into a branch cable closure 15, from which a buried or aerial cable 16 Is led out which, for example, connects one or more subscribers to the network. Fixing of the cable 1 takes place by means of a conventional cable clamp 17.

1 m - 6 It will be understood that the invention has been described above purely by way of example, and that various modifications of detail can be made within the ambit of the invention.

Vme_tLne Lj c- re-aLsl-e-reC( 1 rale- Mn-r k.

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Claims

1. A method of carrying out the overhead installation of optical fibre cables comprising unstranded "loose buffer" single fibres or multifibre units and stress members, or of other optical fibre cables, the optical fibre cable being mounted at predetermined spacings on one or more buildings, masts or other operable supporting structures, and being clamped by means of clamping elements, in which method a predetermined length of the optical fibre cable is wound up, at the clamping points or at other cab le-run-subdividing points, onto a reel or core.

2. A method according to claim 1, in which the longitudinal axis of the winding or of the reel or core extends transversely to the longitudinal direction of the optical fibre cable.

3. A method according to claim 1 or 2, in which the optical fibre cable is wound up with the smallest pitch, and/or the smallest winding radius, permitted by the dimensioning of the cable and the reel or core.

4. A method according to Claim 1, 2 or 3, in which the optical fibre cable is wound up in a bifilar mode.

5. A method according to any of Claims 1 to 4, in which the optical fibre cable is clamped, on both sides of a predetermined point, by spring sheath-clips or other clamping means, and the region free of tensile stress which occurs between the points engaged by the clamping means is wound up onto a reel or core.

6. Means f or carrying out a method according to any of Claims 1 to 5, characterised by the provision, at the clamping points, of a reel or core designed for winding in a bifilar mode.

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7. Means according to Claim 6. wherein the reel or core has a channel of a yin-yang defining serpentine configuration, being so designed as to permit the relevant optical fibre cable to be passed through it.

8. Means according to Claim 6 or 7, wherein the reel is securable by means of a stop against undesired unwinding.

9. means according to any of Claims 6 to 8, wherein the reel is provided with a crank operable in the clamping procedure.

10. Means according to any of Claims 6 to 9, wherein the reel or core is divided transversely with respect to the longitudinal axis.

11. A method according to Claim 1, substantially as described with reference to any Figure or Figures of the accompanying drawings.

12. Means according to Claim 6, substantially as described with reference to any Figure or Figures of the accompanying drawings.

0 Published 1991 at rlbe Patent Office. Concept House. Cardiff Road, Newport. Gwent NP9 I RH. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point. Cwmfeltlffach, Cross Keys. Newport. NPI. 7HZ. Printed by Multiplex techniques ltd, St Mary Cray. Kent.