GB2169722A

GB2169722A - Manufacture of optical fibre cables using gas feed

Info

Publication number: GB2169722A
Application number: GB08529860A
Authority: GB
Inventors: Terence Hall
Original assignee: Telephone Cables Ltd
Current assignee: Telephone Cables Ltd
Priority date: 1985-01-11
Filing date: 1985-12-04
Publication date: 1986-07-16
Also published as: GB8500772D0; GB8529860D0

Abstract

In order to feed optical fibres 3 into channels 2 provided in the surface of an extruded core 1 at a controlled excess rate so that the optical fibres are loosely within their respective channels, each fibre is guided via a tube 4 such as a hyperdermic needle and a gas, such as air, is forced to flow through the tube so as to feed the fibre into the respective channel. The gas is shown being forced into a venturi head 5 via an inlet 6. <IMAGE>

Description

SPECIFICATION Manufacture of optical cables This invention relates to methods of manufacturing optical cables and more particularly to a method of manufacturing optical cables of the type having an extruded core with channels provided in the surface of the core, into which channels, one or more optical fibres are introduced so as to be loose within the channels.

This is achieved by overfeeding the fibres so that their length is greater than that of the extruded core, but this must obviously be precisely controlled and causes difficulty. The problem is compounded by the fact that the fibres are quite fragile and therefore must be handled with great care so that they enter the channels undamaged.

It is thus an object of the present invention to provide a method of manufacturing optical cables of the type described above in such a way that the fibres can be introduced into the channels undamaged and with a precise amount of overfeed.

Accordingly, the invention provides a method of manufacturing optical cables comprising the steps of extruding a core with at least one channel provided in the surface thereof, guiding at least one optical fibre into the or each channel via a tube and moving the fibre along the tube and into the channel by providing a flow of gas through the tube, the fibre being fed into the channel at a controlled rate.

The rate of feeding the fibre into the channel is preferably controlled by adjusting the rotation of a capstan which feeds the fibre into the tube, in relation to the line speed of the extruded core. However, in some cases it may be controlled by adjusting the rate of flow of gas through the tube.

The speed at which the fibre is fed into the channel is preferably greater than the speed at which the core is extruded such that in the completed cable the fibre has a length which is greater than that of the channel.

The invention will now be more fully described by way of example with reference to the drawing which shows part of a line for manufacturing optical cables.

An extruded plastics core 1 is arranged to move longitudinally from the extruder head (not shown) in the direction of arrow A. The core 1 may include a central strength member, if desired, and is extruded with several channels or grooves extending iongitudinally along the core and spaced at intervals around its diameter.

It is into these channels 2 that it is desired to feed optical fibres 3 in such a way that the fibres 3 have a precise and controllable amount of overfeed so that they are longer than, and therefore loose within, the respective channels, Thus each fibre 3, is guided into its respective channel 2 by means of a narrow flexible tube 4, of which only only one is shown. The tube 4, which may be similar to a hypodermic needle, is fixed at one end to the outlet of a venturi head 5, and its other end is cut at an obligue angle as shown so as to lie within the channel 2 and thus guide the fibre 3 into it.

Compressed air is forced into the venturi head 5 via an inlet 6 and is guided towards the tube 4 by a baffle 7, which is conically shaped and which forms the inlet for the optical fibre 3 which is drawn into the head 5 by the venturi effect.

The fibre 3 is fed into the head 5 from a capstan 8 which has a belt drive 9 to accurately control its rate of rotation and thus the rate of feeding of the fibre. Between the capstan 8 and the head 5, the fibre forms a catenary loop 10 which can be used for easily checking that the rate of feed of the fibre is correct in relation to the line speed of the core 1.

In this way the fibres 3 are fed into the channels 2 undamaged and with the correct amount of overfeed.

The rate of feed of the fibres into the grooves will depend upon the relationship between the length of fibre in the catenary and the rate of air flow and may be adjusted, if desired, by varying one or both of these parameters, adjustment of the catenary length being achieved by varying the speed of rotation of the capstan. Adjustment may be carried out automatically, if desired, in response to signals generated by one or more sensing devices responsive to changes in the catenary length, and/or the line speed of the core.

After their introduction into the respective grooves the fibres are retained in position by the provision of a retaining means over the grooves, for example in the form of a tape of any suitable material wound helically around the core.

The cable is then completed by providing, around the taped core assembly, a protective cover. This may comprise, for example, one or more sheaths of thermoplastics material extruded around the assembly, and may incorporate a lining of metal foil possibly with a plastics coating on one or both surfaces to act as a water barrier.

It will be understood that the invention includes within its scope apparatus for carrying out the method above described.

1. A method of manufacturing optical cables comprising the steps of extruding a core with at least one channel provided in the surface thereof, guiding at least one optical fibre into the or each channel via a tube and moving the fibre along the tube and into the channel by providing a flow of gas through the tube, the fibre being fed into the channel at a controlled

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Manufacture of optical cables This invention relates to methods of manufacturing optical cables and more particularly to a method of manufacturing optical cables of the type having an extruded core with channels provided in the surface of the core, into which channels, one or more optical fibres are introduced so as to be loose within the channels. This is achieved by overfeeding the fibres so that their length is greater than that of the extruded core, but this must obviously be precisely controlled and causes difficulty. The problem is compounded by the fact that the fibres are quite fragile and therefore must be handled with great care so that they enter the channels undamaged. It is thus an object of the present invention to provide a method of manufacturing optical cables of the type described above in such a way that the fibres can be introduced into the channels undamaged and with a precise amount of overfeed. Accordingly, the invention provides a method of manufacturing optical cables comprising the steps of extruding a core with at least one channel provided in the surface thereof, guiding at least one optical fibre into the or each channel via a tube and moving the fibre along the tube and into the channel by providing a flow of gas through the tube, the fibre being fed into the channel at a controlled rate. The rate of feeding the fibre into the channel is preferably controlled by adjusting the rotation of a capstan which feeds the fibre into the tube, in relation to the line speed of the extruded core. However, in some cases it may be controlled by adjusting the rate of flow of gas through the tube. The speed at which the fibre is fed into the channel is preferably greater than the speed at which the core is extruded such that in the completed cable the fibre has a length which is greater than that of the channel. The invention will now be more fully described by way of example with reference to the drawing which shows part of a line for manufacturing optical cables. An extruded plastics core 1 is arranged to move longitudinally from the extruder head (not shown) in the direction of arrow A. The core 1 may include a central strength member, if desired, and is extruded with several channels or grooves extending iongitudinally along the core and spaced at intervals around its diameter. It is into these channels 2 that it is desired to feed optical fibres 3 in such a way that the fibres 3 have a precise and controllable amount of overfeed so that they are longer than, and therefore loose within, the respective channels, Thus each fibre 3, is guided into its respective channel 2 by means of a narrow flexible tube 4, of which only only one is shown. The tube 4, which may be similar to a hypodermic needle, is fixed at one end to the outlet of a venturi head 5, and its other end is cut at an obligue angle as shown so as to lie within the channel 2 and thus guide the fibre 3 into it. Compressed air is forced into the venturi head 5 via an inlet 6 and is guided towards the tube 4 by a baffle 7, which is conically shaped and which forms the inlet for the optical fibre 3 which is drawn into the head 5 by the venturi effect. The fibre 3 is fed into the head 5 from a capstan 8 which has a belt drive 9 to accurately control its rate of rotation and thus the rate of feeding of the fibre. Between the capstan 8 and the head 5, the fibre forms a catenary loop 10 which can be used for easily checking that the rate of feed of the fibre is correct in relation to the line speed of the core 1. In this way the fibres 3 are fed into the channels 2 undamaged and with the correct amount of overfeed. The rate of feed of the fibres into the grooves will depend upon the relationship between the length of fibre in the catenary and the rate of air flow and may be adjusted, if desired, by varying one or both of these parameters, adjustment of the catenary length being achieved by varying the speed of rotation of the capstan. Adjustment may be carried out automatically, if desired, in response to signals generated by one or more sensing devices responsive to changes in the catenary length, and/or the line speed of the core. After their introduction into the respective grooves the fibres are retained in position by the provision of a retaining means over the grooves, for example in the form of a tape of any suitable material wound helically around the core. The cable is then completed by providing, around the taped core assembly, a protective cover. This may comprise, for example, one or more sheaths of thermoplastics material extruded around the assembly, and may incorporate a lining of metal foil possibly with a plastics coating on one or both surfaces to act as a water barrier. It will be understood that the invention includes within its scope apparatus for carrying out the method above described. CLAIMS

1. A method of manufacturing optical cables comprising the steps of extruding a core with at least one channel provided in the surface thereof, guiding at least one optical fibre into the or each channel via a tube and moving the fibre along the tube and into the channel by providing a flow of gas through the tube, the fibre being fed into the channel at a controlled rate.

2. A method of manufacturing optical cables according to Claim 1, wherein the rate of feeding the fibre into the channel is controlled by adjusting the rotation of a capstan, which feeds the fibre into the tube, in relation to the line speed of the extruded core.

3. A method of manufacturing optical cables according to Claim 1, wherein the rate of feeding the fibre into the channel is controlled by adjusting the rate of flow of gas through the tube.

4. A method of manufacturing optical cables according to Claim 1, 2 or 3 wherein the speed at which the fibre is fed into the channel is greater than the speed at which the core is extruded such that in the completed cable the fibre has a length which is greater than that of the channel.

5. A method of manufacturing optical cables substantially as herein described with reference to the accompanying drawing.

6. Apparatus for use in the manufacture of optical cables comprising an extruder head for extruding a thermoplastics core with at least one channel in its surface, a tube disposed so as to enable an optical fibre to be introduced into the formed channel, and means for producing a flow of gas through the tube so as to carry the fibre through the tube and into the channel.

7. Apparatus according to Claim 6 including a capstan for feeding the fibre into the tube, and means for controlling the speed of rotation of the capstan and/or the rate of flow of air through the tube.

8. Apparatus according to Claim 7 including means for sensing the length of fibre between the capstan and the tube, and/or for sensing the live speed of the core, and for generating control signals in response thereto, and means for automatically controlling the speed of rotation of the capstan and/or the rate of flow of air through the tube in response to said control signals.