CABLES

The present invention relates to a method and apparatus for handling light weight fibre optic cables and relates particularly, but not exclusively, to a method and apparatus for handling light weight fibre optic cables containing bundles of optical fibres.

Fibre optic cables are presently used a variety of signal transmission applications, such as the underground transmission of telephone or cable television signals. The installation of such fibre optic cables involves introducing an end of the cable into a conduit such as an underground cable duct via a duct access chamber (e.g. a man hole) , and then pulling the end of the cable through the duct, for example by means of a wire, to the other end of the duct located in a second duct access chamber at a location remote from the first access chamber (for example 1km away) . This process is then repeated for successive lengths of duct, successive lengths of cable being spliced together.

This known method suffers from the drawback that each successive splicing of the cable causes undesirable attenuation of signals carried by the cable. It would therefore be highly desirable to install the cable in single sections of the maximum possible length. However, this gives rise to the difficultly that installation of a light weight or unreinforced fibre optic cable in sections of greater length subjects the cable to greater tension at the end by which the cable is pulled during pulling of the cable through the duct than in the case of shorter lengths of cable. This increases the risk of damage and / or breakage of the cable. On the other hand, the use of reinforced cable, while mitigating the problem of damage or breakage, considerably increases the difficulty in installation of the cable in a conduit because of the much higher installation power required.

A technique is known in which a light weight fibre optic bundle is blown along a conduit by means of compressed air such that the length of fibre optic bundle to occupy a first length of conduit can be blown down the first length of conduit, as

well as a further length to occupy one or more subsequent lengths of conduit. The subsequent length of fibre optic bundle on exiting the first length of conduit is then recoiled into a receptacle in preparation for a subsequent blowing operation.

It has been found that the operations of blowing the bundle and recoiling it into a receptacle cannot satisfactorily be carried out simultaneously because the large distance (typically 1km) between the blowing device and the coiling device causes considerable difficulties in synchronising the operation of the two devices.

Preferred embodiments of the present invention therefore seek to overcome the above disadvantages of the prior art .

According to an aspect of the present invention, there is provided a method of handling light weight fibre optic cable, the method comprising pulling a length of said cable out of a first receptacle adjacent a first end of a conduit by means of a pulling device adjacent a second end of the conduit, and simultaneously coiling a length of the cable into a second receptacle adjacent the second end of the conduit, wherein each turn of the cable coil in the second receptacle is laterally displaced relatively to the preceding turn.

In this way, the pulling device pulls a length of cable out of the first receptacle, through a conduit such as an underground duct or the like while a length of cable is simultaneously coiled into the second receptacle in such a manner as to minimise tangling of the cable as it is subsequently withdrawn from the second receptacle, for instance during subsequent installation into a further underground duct.

In a preferred embodiment, the turns of each successive pair of turns of the cable coil in the second receptacle are displaced relative to each other by substantially the same amount .

This provides the advantage of enabling the coiling process to be automated in synchronisation with the operation of the pulling device in a simple manner.

Preferably, each turn of the cable coil is substantially

circular .

In a preferred embodiment, the method further comprises the step of laterally displacing the cable as it enters the second receptacle, and simultaneously rotating the second receptacle relative to the outlet of the pulling device.

This provides the advantage of enabling automatic coiling of the cable into the second receptacle to be achieved in a simple manner.

The method may further comprise the step of directing the cable as it enters the second receptacle in response to rotation of the second receptacle relative to the outlet of the pulling device.

By synchronising rotation of the second receptacle and direction of the cable as it enters the receptacle, correct coiling of the cable in the second receptacle is maximised, even if the speed of rotation should vary.

The method preferably further comprises the step of controlling the pulling device in response to the tension in the cable.

This gives the advantage of preventing the tension in the cable from exceeding a predetermined limit, which may otherwise result in damage and / or breakage of the cable.

According to another aspect of the invention, there is provided a method of installing a light weight fibre optic cable into a conduit, the method comprising pulling an end of the cable from a first end of a length of the conduit to a second end thereof, handling a length of the cable at a second end of the length of conduit according to a method as defined above, and pulling the end of the cable from a first end of a further length of the conduit to a second end thereof.

In this way, the cable can be drawn through the first length of conduit, a length of cable can be drawn out of the first length of conduit at the second end thereof, and coiled into the second receptacle in such a manner as to minimise tangling thereof. By suitable construction of the second receptacle, access to the end of the cable can be obtained, in order to remove the cable from the second receptacle for

subsequent installation thereof, for instance into a further length of conduit .

A single length of fibre optic cable can thus be installed in successive manageable lengths by pulling a length of the cable through a first length of conduit and coiling the cable into a receptacle, and repeating the pulling and recoiling process for subsequent installation of the cable, in successive lengths of conduit.

According to a further aspect of the invention, there is provided an apparatus for handling light weight fibre optic cable, the apparatus comprising a pulling device for pulling a length of cable therethrough; and a coiling device arranged adjacent to the pulling device for simultaneously coiling cable received from the pulling device into a receptacle supported in use by the coiling device, wherein each turn of the cable coil in the receptacle is displaced relative to the preceding turn.

In this way, apparatus can be provided at a single location which can pull a cable through a first conduit and then coil a further length of the cable into a receptacle in a single operation. The provision of apparatus at a single location enables simplified synchronisation of the operation of the pulling coiling devices.

The pulling device may comprise an endless friction belt co-operating with a pulley, wherein the cable is driven in use between the belt and the pulley.

In a preferred embodiment, the pulling device further comprises tension sensor means for providing a sicfnal representing the tension in the cable during pulling thereof, and control means for controlling operation of the pulling device in response to said signal .

This provides the advantage of enabling operation of the pulling device to be controlled to prevent the tension in the cable from exceeding a level which would otherwise cause damage and / or breakage of the cable.

In a preferred embodiment, the coiling device comprises directing means arranged adjacent an outlet of the pulling

device for controlling the direction of movement of the cable at the outlet, and drive means for rotating the receptacle in use relative to the directing means.

In this way, coiling of the cable as it leaves the pulling device can be automatically carried out in a particularly convenient manner.

The apparatus preferably further comprises mechanical means interconnecting the guide means and drive means such that each turn of the cable coil is laterally displaced relative to the preceding turn.

The mechanical means may comprise a gear box.

Alternatively, the apparatus may further comprise electronic means interconnecting the drive means and guide means such that each turn of the cable coil is displaced relative to the preceding turn.

A preferred embodiment of the invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which:

Figure 1 shows a schematic diagram (not to scale) of an arrangement for installing a fibre optic cable by a method embodying the present invention;

Figure 2 shows a schematic elevational view of an apparatus embodying the present invention;

Figure 3 shows a plan view of the apparatus of Figure 2 without the fibre pan installed;

Figure 4 shows a detailed view of the apparatus of Figure 2; and

Figure 5 shows a detailed view of a fibre optic cable for use in the present invention.

Referring in detail to Figure 1, an arrangement is shown for installing a fibre optic cable 1 in an underground conduit 2 comprising successive lengths of cable duct 3 (typically 1km in length) interconnected by duct access chambers 4, 5 in the form of manholes.

In order to install cable 1 of length of several kilometres in conduit 2 comprising successive lengths of duct 3, the cable is first installed in the length of conduit 2

between access chambers 4, 5.

In order to install cable 1 into the length of duct 3 between access chamber 4, 5 and subsequently into a length of cable duct (not shown) in a subsequent portion 6 of the conduit 2, the cable 1 is drawn from a first receptacle, known as a fibre pan 7, over a pulley 8, through the duct 3 between access chambers 4, 5, over a pulley 9 and is coiled by means of a combined pulling and coiling apparatus 10 into a second fibre pan 11 supported by the apparatus 10.

This is achieved by first attaching an end of the cable 1 to a suitable pulling means such as a wire (not shown) extending along the cable duct 3. The end of the cable 1 is attached to the pulling means at the end of the duct 3 in access chamber 4, and is then pulled to the end of the duct 3 in access chamber 5, where the end of the cable 1 is mounted to the combined pulling and coiling apparatus 10. The combined pulling and coiling apparatus 10 is then actuated such that the length of cable 1 which is to be installed beyond access chamber 5 (i.e. passing through portion 6 of the conduit and beyond) is pulled through the apparatus 10 and coiled into the fibre pan 11.

By suitable construction of the fibre pan 11, after coiling of the cable 1, the fibre pan 11 can be turned over to allow access to the end of the cable 1, such that the process can be repeated at a subsequent duct access chamber (not shown) with a similar combined pulling and coiling apparatus 10 to that shown in Figure 1, and with the second fibre pan 11 taking over the role of the first fibre pan 7.

Figure 2 shows the combined pulling and coiling apparatus 10 shown in Figure 1. The apparatus 10 comprises a puller unit 12 and a coiling unit 13 mounted to an extruded aluminium frame 14 having feet 15.

As shown in greater detail in Figures 2 to 4 , the puller unit 12 comprises a guide pulley 16 over which the cable 1 passes, a free wheeling pulley 17, around generally 90° of which the cable 1 passes, and a drive means comprising an idling pulley 18 over which the cable 1 passes, and which co-

operates with an endless friction belt 19 passing around a timing pulley 20 driven by a 12 volt dc electric motor 21, an idling pulley 22 and a belt tensioning pulley 23. The tension of the belt 19 is manually adjustable for inserting the cable 1.

The puller unit 12 also includes a tension sensor 24 arranged co-axially with the free wheeling pulley 17 and which provides an electrical signal representative of the tension in the cable 1 at the free wheeling pulley 17. The electrical signal is passed to electrical control means 25 which in turn controls the electric motor 21 and timing pulley 20 to regulate the speed of operation of the puller unit 12. In this way, if the tension in the cable 1 exceeds a predetermined level, the speed of operation of the puller unit automatically slows down in a manner readily appreciated by persons skilled in the art to prevent the cable 1 from being damaged or broken.

In addition, the electrical control means 25 synchronises the operation of the puller unit 12 and coiling unit 13, as well as measuring the length of cable 1 passing through the puller unit 12 by means of an encoder (not shown) mounted on electric motor 21.

Downstream of the friction belt 19, the cable 1 passes through a guide tube 26 having a removable cover for allowing access thereto to enable fibres of the cable 1 to be changed during the coiling process. Thereafter, the cable 1 passes through a guide 27 mounted to the frame 14 by means of a pivot 28 such that movement of the guide 27 about pivot 28 adjusts the direction of cable 1 exiting the guide 27. The guide 27 also has a removable cover for inserting or demounting of cables midway through the coiling operation.

The coiling unit 13 has a rotatable platform 29 having three locating blocks 30 for receiving the fibre pan 11. The fibre pan has an annular channel 31 of width x and having inner diameter approximately 33cm and outer diameter approximately 50cm for receiving the cable 1 and disposed directly below the guide 27 such that pivoting of the guide 27 about pivot 28 adjusts the direction of the cable across the entire width x of

the annular channel 31.

The rotatable platform 29 is mounted to a vertical shaft 32 which forms part of a gear box 33, the gear box 33 also having a horizontal output shaft 34 to which a crank wheel 35 is mounted. In use, the gear box 33 is covered by a sheet metal box 37. A cable 36 is mounted to the radially outermost part of the crank wheel 35 and is supported by a block 38 adjacent its other end mounted to the frame 14. The end of the cable 36 remote from the crank wheel 35 is mounted via a coupling arm 39 to the guide 27 such that rotation of the crank wheel 35 through 360° causes a single oscillation of the guide 27 about pivot 28 such that the direction of the cable exiting the guide 27 scans the entire width x of annular channel 31.

The gear box 33 is driven by a 12 volt dc motor 40 having a helical gear in mesh with the gear on the vertical shaft 32 of the gear box, the ratio of the helical gear and gear on the vertical shaft 32 being 1 : 1. The gear box 33 has two helical gears, one on the vertical shaft 32 and one on the horizontal shaft 34, the ratio of the gears being 1 : 1.02.

The operation of the apparatus 10 shown in Figures 2 to 4 will now be described in detail .

As the cable 1 is pulled through the apparatus 10 by the puller unit 12, the coiling unit 13 rotates the fibre pan 11 as the cable 1 is fed into the fibre pan 11. At the same time, synchronisation of the movement of the guide 27 with that of the coiling unit 13 via vertical shaft 32, gear box 33, horizontal shaft 34, crank wheel 35 and cable 36 is such that as the fibre pan 11 rotates through 360°, a single loop of the cable coil is laid into annular channel 31. A single loop of the cable coil has diameter of approximately 41.5cm. The starting point of the subsequent turn of the cable coil is circumferentially off set by approximately 0.1° (which corresponds roughly to 20mm) relative to the preceding turn. As a result, the turns of the cable coil are progressively offset with respect to respective preceding turns, which minimises twisting of the fibres and tangling of the cable 1 as the cable 1 is subsequently removed from the fibre pan 11.

This also ensures that the risk of tangling is minimised when the cable coil in the fibre pan 11 is turned upside down in a manner known to persons skilled in the art to provide access to the leading end of the cable 1.

It will be understood by persons skilled in the art that the above embodiment has been described by way of example only, and not in any limitative sense, and that various modifications and alterations to the invention are possible without departure from the scope of the appended claims.