GB2235475A - Making twisted cables - Google Patents

Abstract

To make twisted cables, e.g. telephone cables Fig. 1, a twister 7 rotates bodily between a die plate 6 and a haul through capstan 1 feeding drum 8. The twister 7 comprises two parallel plates and guide wheels 12 to 15, Fig 1B, between the plates and feeding the cable in a zig-zag path. The spacing between the twister and the die plate is much greater than the spacing between the twister and the capstan. The cable is permanently twisted. A station may be provided to fill the cable with a water-resisting jelly. <IMAGE>

Description

METHOD AND APPARATUS FOR MAKING TWISTED CABLES.

This invention relates to communications cables, particularly but not exclusively cables made up from groups of twisted insulated copper pairs.

During the operation of laying up insulated cable conductors for multi stranded telephone cables, groups of twinned insulated cores from e.g. 10 pairs to e.g. 100 pairs (in 10 pair groups) are laid up in one operation.Presently, the twinned insulated conductors are fed via an oscillator and then bound to retain the 10 pair group. Up to 10 groups are formed instantaneously. They are then fed, in the same operation, to make up to a 100 pair groups on a drum twister take-up unit, which adds a twist to the completed cable per revolution of the drum twister.

Generally the throughput speed of this operation is limited to the rotational speed of the drum twister, which may be about 1 rotation per second.

With the introduction of a twinned core continual feed as described in our co-pending application 8829533.2 not yet published for input to the laying up operation, since the take-up bobbin would require replacement, this cannot be carried out whilst the machine is in operation.

An alternative arrangement would be to use a planetary strander which rotates the bobbins which supply the insulated conductors. There is then no need to rotate the drum twister, which is simply a haul off capstan. This is complicated and expensive equipment.

It is an object of the present invention to enable a continual process and to increase throughput speeds in the manufacture of such cables.

According to the present invention there is provided a method of making a telecommunications cable in which a plurality of conductor elements are drawn from respective supply bobbins by a haul through capstan and wound onto a take up drum and wherein the conductor elements are drawn through a twisting station before reaching the capstan whereby to twist together the conductor elements so that they are permanently twisted together on the take up drum, without rotating either the capstan or the drum about the cable manufacturing axis.

Preferably the conductor elements each comprise an insulated twisted copper pair or a group of such pairs.

The twisting is preferably imparted by a planar assembly of guide wheels over which the plurality of conductor elements are guided along a double-Z or double-S shaped path, and the assembly is rotated about the axis of entry to and exit from the assembly.

According to another aspect of the present invention there is provided apparatus for making a telecommunications cable comprising a haul-through capstan for hauling a plurality of the conductor elements, means for supporting a plurality of supply bobbins for supplying said conductor elements, a die plate for receiving said elements from the supply bobbins and a twist creator located intermediate the die plate and the haul-through capstan, said twist creator having a common entrance and a common exit for the conductors and being rotatable so as to twist the element together as they are hauled through the twist creator by the capstan.

In order that the invention can be clearly understood reference will now be made to the accompanying drawings in which: Fig. l shows schematically cable making apparatus according to an embodiment of the invention; Fig. 2 is a graph showing the output twist and back twist created in one mode of operation of the apparatus of Fig. 1, and Fig. 3 shows the output twist for different ratios R, in the form of a graph.

Referring to Fig. 1 of the drawings the apparatus comprises a take-up drum 1 and a support stand 2 for supporting a plurality of supply bobbins 3. The bobbins 3 rotate about an axial 4 of the support stand 2. Each bobbin carries an insulated twisted copper telephone pair 5.

The capstan 1 hauls the telephone pairs first through a die plate 6 and thence through a twist creator 7. The twist creator 7 is much closer to the capstan 1 than it is to the die plate 6. As a typical example the twist creator would be 14 metres from the die plate and about 1 metre from the capstan 1.

Finally the twisted pairs which themselves have been twisted together by the twist creator, are drawn around the capstan 1 and fed onto a take-up drum 8. The capstan 1 rotates only about its axis 1A and likewise the take-up drum 8 only rotates about its axis 8A.

The twister 7 and the capstan 1 are driven by a motor M1 and as an example the twister would complete one revolution for each metre of cable drawn through by the capstan 1. The take-up drum 8 is driven by a motor M2.

The twist creator 7 is shown in more detail on the right hand side of Fig. 1. It comprises a pair of side plates 10 and 11 and four guide wheels 12, 13, 14 and 15. This is shown in Fig. 1B somewhat schematically and with the plate 10 removed for clarity.

An entrance 16 and an exit 17 are formed by tubular die-like parts. They are aligned with the axis of manufacture of the cable A-A shown in Fig. lB.

The guide wheels 12 and 13 define a generally Z-shaped tortuous path on the inlet side and wheels 14 and 15 define a second Z-shaped path and it can be clearly seen that if the twister is rotated about the axis A-A then the cable components in the form of twisted pairs 5 entering the entrance 16 will become twisted together as they pass through the twister and out through the exit 17. The distance between the guide plate 6 and the bobbin stand 2 is approximately 4 metres.

Referring now to Fig. 2 there is shown in the form of curves on a graph the results of a test carried out using the apparatus of Fig. 1. In Fig. 2 curve X represents the number of twists between the die plate 6 and the twister 7 and curve Y shows the number of twists actually achieved on the take-up drum 8. This test was carried out with the twister being rotated about the axis A-A once for every metre of cable drawn through it by the capstan.

Referring to curve X, it can be seen that this curve is assymptotic to the horizontal line representing approximately 7.7 turns on the input side. It is thus clear that this apparatus can be run continuously without the back twist increasing and increasing beyond a certain limit (7.7 turns in this particular case).

The output twists measured in the cable are represented by the curve Y and it can be seen that this curve too is assymptotic to a horizontal line representing approximately 0.42 turns per metre of cable on the take-up drum 8.

In order to set the apparatus up for manufacture it is necessary to "pre-twist" the twister 7 a certain number of times in the same direction as it will be running during manufacture, so that most of the cable throughput has the desired amount of twist imparted to its components.

Contrary to previous belief, where it was thought that either the supply bobbins need to be rotated (planetary strander) or the take-up capstan and drum need to be rotated (drum twister) it has now been found that the pull through capstan and the take-up drum and the supply bobbins can each rotate about a stationary axis while still achieving the desired twist in the cable.

Clearly the twister can take a variety of forms, only one of which is taken in Fig. 1B. For example there could be more than 4 pulley wheels in a more sophisticated version or there could indeed be only 3 pulley wheels, two of them positioned at the entrance and exit like pulley 12 and 15 and one pulley either 13 or 14 off-axis A-A. However we have found that it is preferable for the twister to be dynamically balanced and so the same number of wheels on each side of the axis A-A is preferable in this reSpect.

The apparatus which has only been described in a schematic fashion in Fig. 1 can be modified in a number of ways. For example a binding head can be inserted between the twister 7 and the haul-through capstan 1 in order to provide a binding around the twisted conductors. Furthermore and preferably there would be a circular die between the die plate 6 and the bobbins 3 in order to draw the conductors smoothly towards the axis of the cable-making apparatus prior to entry into the die plate 6. As shown in Fig. 1A the die plate 6 has five holes each hole receiving a respective twisted pair from the bobbin 3, the holes being designated 6A.

Clearly more than five conductors can be mounted on the supply bobbin stand 2. Furthermore, the stand 2 can be replaced by a continuous feed arrangement as disclosed in our co-pending patent application 8829533.2 so that twisted pairs can be continually fed into the apparatus shown in Fig. 1. In order to take full advantage of this the take up drum 8 could be replaced by a dual arrangement in which there are two take up drums, and take up is automatically transferred from one drum 8 to the next drum 8 when the first drum is full of cable.

The apparatus of Fig. I can be further modified to include a water block filling station to fill the intersticies of the cable components with a water blocking compound such as petroleum jelly.

In order to understand how the twist creator can in fact create a finite twist in the cable when apparently it is imparting an equal and opposite back twist between the die plate and the twist creator, the following explanation is given.

Taking a ratio distance of 1 : 14 distance between capstan and twist creator = 1 metre distance between twist creator and die plate = 14 metres then for one revolution of the twist creator (say clockwise) and moving the cable linearly by 1 metre, the 1st metre of cable output would contain 1 twist (clockwise).

During this revolution of the twist creator in a clockwise direction, one back twist (anti-clockwise) is set up over the 14 metres between twist creator and die plate and hence this portion of cable would contain 1/14 twists/metre.

On the 2nd metre of cable produced, for one revolution of the twist creator (clockwise) the resultant twist in this metre of cable would be: 1 Tw. (clockwise) - Backtwist (anti-clockwise) = 1 -1/14 Tw/metre.

= 0.929 Tw (Clockwise) Taking this a step further:3rd metre of cable produced for 1 revolution (clockwise) of the twist creator would be: Backtwist this time would be 13/14 Tw/metre (anti-clockwise) from 14 the previous operation plus 1/14 Tw/metre from this rotation of the twist creator.

Hence the total backtwist would be: 13/14 + 1 Tw/metre 14 14 So the resultant twist in the 3rd metre of cable produced would be: 1 - 13/14 + 1 Tw/metre 14 14 = 1 - 0.138 = 0.862 Tw. (Clockwise) and so on.

The following table shows the progression of output twists per metre and completed cable twists as the manufacture proceeds.

EACH OUTPUT NUMBER OF LENGTH METRE TWIST/METRE TWISTS IN COMPLETED CABLE 1ST 1 1 1M 2ND 0.928 1.928 2M 3RD 0.862 2.790 3M 4TH 0.801 3.591 4M 5TH 0.745 4.336 5M 6TH 0.694 5.030 6M 7TH 0.648 5.678 7M 8TH 0.608 6.286 8M 9TH 0.573 6.859 9M 10TH 0.543 7.402 10M 11TH 0.515 7.917 llM 12TH 0.495 8.412 12M 13TH 0.480 8.892 13M 14TH 0.469 9.361 14M 15TH 0.464 9.825 15M 16TH 0.464 10.289 16M The twist imparted into the finished cable is dependent upon the ratio of the space between the die plate 6 and the twister 7 on the one hand and the twister 7 and the take up capstan on the other hand. As shown in Fig. 1 this spacing is fourteen metres to one metre.Different spacing can be used to achieve different output twists but in any practical apparatus we believe the twister needs to be closer to the capstan than it is to the die plate and then preferably by at least a ratio of 3 to 1 in order to achieve a sufficient twist in the cable components.

It was found that the output twist from the twist creator conformed to the following formula: Output twists per metre = 1 - ER + (R - 1) + (R - 2) + (R - 3) + etc] R2 where R is the ratio of the distances between the capstan and the twist creator and the twist creator and the input guide plate.

Example Taking a ratio R of 1 : 5 where distance between capstan and twist creator = 1 metre, and distance between twist creator and input guide plate = 5 metres .-. . assuming 1 metre linear throughput for each revolution of the twist creator then:1st metre throughput contains 1 twist = lTw.

2nd metre throughput contains (1 - 5/25) twist = 0.8 Tw.

3rd metre throughput contains (1 - 5 + 4) = twist 0.64 Tw. ( 25 4th metre throughput contains (1 - 5 + 4 + 3) twist = 0.52 Tw. ( 25 5th metre throughput contains (1 - 5 + 4 + 3 + 2) twist = 0.44 Tw. ( 25 6th metre throughput contains (1 - 5 + 4 + 3 + 2 + 1) twist = 0.4 Tw. ( 25 7th metre throughput contains (1 - 5 + 4 + 3 + 2 + 1) twist = 0.4 Tw. 25 and so on for each succeeding metre of cable throughput.

Figure 3 of the accompanying drawings illustrates the output twist per unit length of cable for three different ratios R, as the length of cable manufactured is increased from zero. Curve a represents R = 1:14, curve b represents R = 1:10 and curve c represents R = 1:5.

Curve a reaches a constant output twist after about 13 metres of cable have been hauled through, whereas curve b stabilises around 11 metres and curve c about 6 metres. It can be seen that as the ratio R gets longer, so the net steady-state output twist decreases.

Where R = 1:14, the steady state output twist is 0.47 Tw/m, where R = 1:10 the steady state output twist is 0.46 Tw/m, and where R = 1:5 the steady state output twist is 0.4 Tw/m. Thus by adjusting the ratio R, the steady state output twist can be varied for a given set of operating conditions i.e. speed of haul-through and speed of rotation of the twist creator.

Claims (12)

CLAIMS.

1. A method of making a telecommunications cable in which a plurality of conductor elements are drawn from respective supply bobbins by a haul through capstan and wound onto a take up drum and wherein the conductor elements are drawn through a twisting station before reaching the capstan whereby to twist together the conductor elements so that they are permanently twisted together on the take up drum, without rotating either the capstan or the drum about the cable manufacturing axis.

2. A method as claimed in claim 1 where each conductor element comprises an insulated twisted copper pair or group of such copper pairs.

3. A method as claimed in claim 1 or claim 2 wherein the twisting station comprises a pair of parallel plates and a series of guide pulleys between the plates defining a tortuous path, the method including drawing the cable conductors along this tortuous path while rotating the pulleys about an axis parallel to the axis along which the conductors are drawn in the cable making process.

4. A method as claimed in any preceding claim wherein the conductor elements pass through a fixed die plate having one discrete aperture for each conductor element or group of conductor elements.

5. A method of manufacturing a telecommunications cable substantially as hereinbefore described with reference to the accompanying drawings.

6. Apparatus for making a telecommunications cable comprising a haul-through capstan for hauling a plurality of the conductor elements, means for supporting a plurality of supply bobbins for supplying said conductor elements, a die plate for receiving said elements from the supply bobbins and a twist creator located intermediate the die plate and the haul through capstan, said twist creator having a common entrance and a common exit for the conductors and being rotatable so as to twist the elements together as they are hauled through the twist creator by the capstan.

7. Apparatus as claimed in claim 6 wherein the twist creator comprises a pair of spaced apart parallel frames supporting a series of guide wheels defining a tortuous path for the conductor elements and means for rotating the twist creator about an axis coincident with or parallel to the axis of cable manufacture.

8. Apparatus as claimed in claim 6 or claim 7, wherein there are an even number of guide wheels in the twist creator some of which are located on one side of the cable making axis and the others of which are located on the opposite side of said axis.

9. Apparatus as claimed in claim 8 wherein the twist creator comprises four guide wheels, a first pair located to one side of the cable making axis adjacent the entrance to the twister, and a second pair on the opposite side of said axis adjacent the exit of said twister, said wheels together defining a double Z or double S tortuous path.

10. Apparatus as claimed in any of claims 6 to 9, comprising a binding head located between the haul through capstan and the twister for applying a binder to the cable elements.

11. Apparatus for making a telecommunications cable and substantially as hereinbefore described with reference to the accompanying drawings.

12. A telecommunications cable made by a method or apparatus according to any preceding claim.