WO2001068505A1

WO2001068505A1 - Apparatus for controlling tension in a cable

Info

Publication number: WO2001068505A1
Application number: PCT/GB2001/000996
Authority: WO
Inventors: Stephen William Bedford; Johnathan Ralph Manchester; Simon Vivian Ranulf Bateson
Original assignee: Soil Machine Dynamics Limited
Priority date: 2000-03-13
Filing date: 2001-03-08
Publication date: 2001-09-20
Also published as: AU2001240781A1; GB0005905D0

Abstract

An apparatus (100) for controlling tension in a cable (108) is disclosed. The apparatus comprises a drum body (104) rotatable about an axis (107). A plurality of staves (102) extend parallel to the axis (107) and are adapted to slide parallel to the axis (107) relative to the drum body (104). The cable (108) is under tension and at least partially coiled around the staves (102) such that the cable (108) touches the staves (102). A cam (110) displaces a major proportion of the staves (102) in a forward axial direction and, at a plurality of spaced apart locations on the outer surface of the apparatus (100), a minor proportion of the staves (102) in a reverse axial direction.

Description

APPARATUS FOR CONTROLLING TENSION IN A CABLE

The present invention relates to an apparatus for controlling tension in a cable, and relates particularly, but not exclusively, to an apparatus for controlling the tension in a telephone cable laid on the sea bed from a cable laying vessel.

Telephone cables laid on the sea bed connect most of the regions of the world. The cables are installed using specialised cable laying vessels. The cable is loaded into a large tank in the vessel in a continuous length, and as the vessel moves, the cable is fed out over a sheave at the stern of the vessel and falls to the sea bed. In order to accommodate changes in the topology of the sea bed, the tension in the cable laid on the sea bed varies. A cable tensioning device, fitted to the cable vessel, is used to control the amount of cable leaving the vessel. The cable tensioning device can also be used to lift a damaged cable from the sea bed to carry out repairs.

It is usual to use a cable tensioning device known as a linear cable engine to lay new cable, since it can operate at high speeds and does not cause damage to the telephone cable. However, to recover cable from the sea bed requires a tension greater than that achievable using a linear cable engine, and so most cable vessels are also fitted with a drum cable engine.

In a drum cable engine, the cable is wrapped around a drum in a number of non-overlapping turns, and a small linear cable engine known as a draw-off hold-back engine (which will be familiar to persons skilled in the art) keeps the turns of cable on the drum tight. The cable is wrapped around the drum in a sufficient number of turns that as the drum rotates, the friction between the coil of cable and the drum causes the coil to turn with the drum so that the tension in the cable can be controlled.

However, drum cable engines suffer from the drawback that in order to obtain the necessary friction between the cable and the drum, the cable must be coiled on to the drum in a number of non-overlapping turns, as a result of which, as the drum rotates, the helix of turns moves axially along the drum In the case of a long cable, this limits the number of rotations the drum can make before the helix of turns reaches one end of the drum

A solution to this problem has been proposed by moving the coil of cable along the drum by means of a knife or fleeting ring that continuously slides the coil of cable across the surface of the drum However, such prior art devices suffer from the drawback that high forces have to be applied to the cable to move the coil of cable along the drum which, in the case of fibre optic cables, can cause damage to the cable

A solution to this problem is disclosed in European Patent No 0159130, which describes an apparatus known as a self-fleeting drum cable engine, and which is described with reference to Figures 1 to 4 The cable engine 1 has a drum 2 mounted to a frame 3 for rotation about an axis 4, and the outer surface of the drum 2 is divided into a number of staves 5 which can slide parallel to the axis 4 across the width of the drum 2. A cam 6 (Figure 3) is fixed relative to the frame 3 and has a cam groove 7, and each of the staves 5 is provided with a cam follower (not shown) for location in the cam groove 7. The cam groove 7 is provided with a shallow part 8 and a relatively steep reset part 9, so that as the cam 6 rotates relative to the staves 5, the staves located in the shallow part 8 of the cam groove 7 gradually move in one axial direction across the drum 2, and the staves engaging the reset part 9 ( which are smaller in number than the staves 5 engaging the shallow part 8) are rapidly returned to their initial positions. A cable 10 wrapped around the drum in a number of non-overlapping turns rests on the majority of the staves 5, as a result of which, the coil of cable 10 is gradually carried across the drum 2 as it rotates, while the small number of staves 5 which are reset slide under the cable 10 without moving it appreciably because the cable is supported by a larger number of staves 5 moving in the other direction. By suitable arrangement of the cam profile, all of the staves 5 can be reset in this way, so that the cable never reaches the axial end of the drum.

This type of self-fleeting drum cable engine greatly reduces the forces applied to the cable, which makes the apparatus suitable for the installation of new telephone cable, whilst retaining the benefit of high tension capability to enable a deployed cable to be retrieved for repair operations However, the prior art self-fleeting drum cable engine suffers from the drawback that because the staves being reset are moved to their initial position in a single operation, the steepness of the reset part 9 of the cam groove 7 is such that significant forces are applied to the cam followers on the staves 5 if the cam 6 rotates at high speeds. This can cause significant wear on the apparatus, as a result of which the speed at which the cam can rotate is limited, which in turn makes the apparatus unsuitable for new cable installation in which large lengths of cable are to be installed.

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

According to the present invention there is provided an apparatus for controlling tension in a cable, the apparatus comprising:

a drum member adapted to be rotated about an axis;

a plurality of elongate sliding members extending substantially parallel to said axis on an outer surface of said drum member, wherein said sliding members are adapted to slide substantially parallel to said axis relative to said drum member, and said drum member and sliding members are adapted to receive a tensioned cable at least partially coiled around said drum member and said sliding members such that the cable touches said sliding members; and

displacing means for displacing a major proportion of said sliding members in a forward axial direction and, at a plurality of spaced apart locations on said outer surface, a minor proportion of said sliding members in a reverse axial direction.

By displacing a minor proportion of the sliding members in a reverse axial direction at a plurality of spaced apart locations on the outer surface of the drum member, this means that the forces imposed on the apparatus are less than in the case in which the sliding members are reset in a single operation. This provides the advantage that the apparatus can be operated at higher drum rotation speeds than in the case of the prior art.

In a preferred embodiment, the displacing means comprises a cam member adapted to move relative to said sliding members, and each said sliding member is provided with engaging means for engaging said cam member, wherein said cam member further comprises a plurality of first cam surfaces for engaging a said engaging means to displace the corresponding sliding member in a forward axial direction, and a plurality of second cam surfaces for engaging a said engaging means to displace the corresponding sliding member in a reverse axial direction

The second cam surfaces are preferably steeper than said first cam surfaces

In a preferred embodiment, the speed of movement of said cam member relative to said sliding members is adjustable

This provides the advantage that the rate of fleeting of the cable (i e the rate of movement of the cable along the drum) can be adjusted independently of the speed of rotation of the drum As a result, the advantage is achieved that the separation of adjacent turns of the coil of cable, and the point at which the cable exits the drum can be controlled

The engaging means may comprise at least two rollers

This provides the advantage that the engaging means may be arranged such that one roller engages the first cam surfaces and the other roller engages the second cam surfaces, as a result of which for each direction of rotation of the drum, each roller needs to rotate in one direction only This provides the advantage that the direction of rotation of the rollers in moving from the first to second cam surfaces does not need to be reversed, thus minimising the wear on the rollers

In a preferred embodiment, said rollers in use are maintained in contact with the said cam member

This provides the advantage of further minimising wear on the rollers, since the situation is avoided in which a roller comes into contact with the cam member and is accelerated from rest up to the speed of the cam member The engaging means preferably further comprises biassing means for biassing the rollers into contact with the cam member.

In a preferred embodiment, said cam member is arranged between said rollers and has said first and second cam surfaces on opposite sides thereof

In an alternative embodiment, the cam member comprises an internal track having opposed cam surfaces, and the rollers engage said opposed cam surfaces.

The apparatus may further comprise at least one roller between each said sliding member and said drum member.

This provides the advantage of minimising the force required to axially displace each said sliding member.

The apparatus may further comprise low friction guide means provided between pairs of adjacent sliding members.

The displacing means may be adapted to displace a minor proportion of said sliding members in a reverse axial direction at at least four said spaced apart locations.

In a preferred embodiment, said sliding members are spaced apart.

The apparatus preferably further comprises cable tensioning means for exerting a tension on the cable.

Preferred embodiments 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 is a schematic side elevation view of a prior art self-fleeting drum cable engine;

Figure 2 is an end elevation view of the cable engine of Figure 1, Figure 3 A is an end elevation view of a cam of the cable engine of Figures 1 and 2;

Figure 3B is a side elevation view of the cam of Figure 3 A;

Figure 4 shows the track of a cam groove of the cam of Figures 3 A and 3B over the circumference of the cam;

Figure 5A is a partial cross-section view of a self-fleeting drum cable engine of a first embodiment of the present invention;

Figure 5B is a view along the line A-A in Figure 5A;

Figure 6 is a view, corresponding to Figure 4, of the track of a cam groove of a cam of the cable engine of Figures 5A and 5B;

Figure 7 is a cross-sectional view of a pair of rollers of a stave of a cable engine of a second embodiment of the present invention;

Figure 8 is a cross-sectional view, corresponding to Figure 7, of a pair of rollers of a stave of a cable engine of a third embodiment of the present invention; and

Figure 9 is a schematic side elevational view of a cable engine of a fourth embodiment of the present invention.

Referring to Figure 5 A, a self-fleeting drum cable engine 100 has a drum 101, the surface of which is made up of a number of staves 102, each of which is supported on rollers 103 on a drum body 104 and is connected to the drum body by a link rod 105. The drum body 104 rotates on a bearing 106 so that it can be driven by a motor (not shown) for rotation about an axis 107. The staves are mounted on the rollers 103 so that they can slide relative to the drum body 104 in a direction generally parallel to axis 107, and the rollers 103 provide a reaction force to radial loads caused by a cable 108 under tension wrapped around the drum 101, and reduce the force required to move the staves 102 in the axial direction. Movement of the staves in the axial direction is also guided by low friction pads 109 as shown in Figure 5B.

A cam 110 is attached to a frame (not shown) of the drum cable engine 100 and comprises a continuous narrow track having four first cam surfaces 111 and four second cam surfaces 112, steeper than the first cam surfaces 111. Each of the staves 102 is provided with a pair of rollers 113, 114 in the vicinity of the cam 110, so that as the drum 101 rotates about axis 107, one of the rollers 113, 114 engages the cam and rolls along the cam 110 to cause the stave 102 to move axially relative to the drum body 104. In particular, as each stave 102 rotates with the drum 101, roller 113 rolls along each first cam surface 111 to gradually push the stave 102 axially across the width of the drum in one direction, and the other roller 114 alternately rolls along the second cam surfaces 112 to rapidly push the stave 102 back to start another cycle. This cycle is repeated four times for each revolution of the drum 101.

By having two cam rollers 113, 114 per stave 102, each roller rotates in the same direction. As a result, the direction of rotation of the rollers 113, 114 is not reversed, thus minimising the amount of wear on the cam and rollers since the situation is avoided in which a rotating roller 113,114 is engaged by a cam surface moving in the opposite direction, which leads to significant wear.

The shape of the second cam surfaces 112 is designed to minimise peak accelerations while returning only one of a group of staves to its start position. By having four cam cycles per revolution of the drum 101, the lift of the cam at each reset is reduced, thus reducing the peak accelerations of the staves and allowing the drum to rotate faster. Also, because the first cam surfaces 111 are longer than the second cam surfaces 112, at any particular time, the first cam surfaces will always engage more staves 102 than the second cam surfaces, as a result of which most of the staves 102 will be moving in the axially forward direction, and a small number of rollers will be moving in the reverse direction.

In operation, a cable 108 is wrapped around the drum to form a number of non-overlapping coils, typically from 4 to 6, and a draw-off hold-back machine (not shown) which will be familiar to persons skilled in the art maintains a low tension in the cable 108 to hold the cable wraps on to the drum The friction between the cable 108 and the surface of the drum formed by the staves 102 prevents the coils from slipping around the drum according to the relationship e^μθ which will be familiar to persons skilled in the art, and as the drum 101 rotates about the axis 107, the cable is either paid out or picked up, according to the direction of rotation. Because there is no slip between the cable 108 and drum 101, the speed and tension of the cable 108 passing through the apparatus 100 can be accurately controlled.

Referring to Figure 7, in which parts common to the embodiment of Figure 5 are denoted by like reference numerals but increased by 100, one of the rollers 213 is provided with a spring 220 so that the rollers 213, 214 nip the cam member 210 between them. As a result, contact between the rollers 213, 214 and the cam member210 is maintained at all times.

As the drum rotates, one of the rollers 213, 214 moves along the cam member 210 to cause the stave 202 to gradually traverse the surface of the drum, and the other roller 213, 214 resets the movement of the stave 202. The maintenance of contact between the rollers 213, 214 and cam member 210 at all times avoids the situation in which there is clearance between the rollers 213, 214 and the cam, as a result of which the roller not in contact with the cam can stop rotating. In such a situation, when the roller came back into contact with the cam, it would be accelerated up to the speed of the cam, thus causing wear. It can therefore be seen that the provision of a spring 220 minimises wear on the rollers. The further advantage is provided that noise at high rotational speed of the drum is minimised.

Figure 8 is a view corresponding to Figure 7 of a third embodiment of the invention, in which parts common to the embodiment of Figure 7 are denoted by like reference numerals but increased by 100. In this embodiment, the cam 310 is split into two separate cam components 330, 331 to provide internal cam surfaces 311, 312, and one of the cam components 330 is biassed by means of springs 320 towards the other cam component 331 so that contact between the cam components 330, 331 and rollers 313, 314 is maintained.

Figure 9 shows a schematic view of a cable engine of a fourth embodiment of the invention, in which parts common to the embodiment of Figure 5 are denoted by like reference numerals but increased by 300 The cam member 410 is mounted for rotation about axis 407 and can rotate independently of drum 401. As a result, the number of cycles that the staves 402 move through per revolution of the drum 401 can be adjusted independently by rotating the cam member 410 about the axis 407 at a different speed from the speed of rotation of the drum. Since the point at which the cable 108 is first fed to the surface of the drum 401 will usually be fixed since the cable is fed from the tank to the drum by means of a guide fixed in position relative to the drum, the spacing of adjacent turns of the coil of cable 108, and hence the point at which the cable leaves the drum, can be adjusted independently of the speed of rotation of the drum 401.

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

Claims

1. An apparatus for controlling tension in a cable, the apparatus comprising:

a drum member adapted to be rotated about an axis;

2. An apparatus according to claim 1, wherein the displacing means comprises a cam member adapted to move relative to said sliding members, and each said sliding member is provided with engaging means for engaging said cam member, wherein said cam member further comprises a plurality of first cam surfaces for engaging a said engaging means to displace the corresponding sliding member in a forward axial direction, and a plurality of second cam surfaces for engaging a said engaging means to displace the corresponding sliding member in a reverse axial direction.

3. An apparatus according to claim 2, wherein the second cam surfaces are steeper than said first cam surfaces.

4. An apparatus according to claim 2 or 3, wherein the speed of movement of said cam member relative to said sliding members is adjustable

5. An apparatus according to any one of claims 2 to 4, wherein the engaging means comprises at least two rollers

6 An apparatus according to claim 5, wherein said rollers in use are maintained in contact with the said cam member

7. An apparatus according to claim 6, further comprising biassing means for urging the rollers into contact with the cam member

8. An apparatus according to any one of claims 5 to 7, wherein said cam member is arranged between said rollers and has said first and second cam surfaces on opposite sides thereof.

9. An apparatus according to any one of claims 5 to 7, wherein said cam member comprises an internal track having opposed cam surfaces, and the rollers engage said opposed cam surfaces.

10. An apparatus according to any one of the preceding claims, further comprising at least one roller between each said sliding member and said drum member.

11. An apparatus according to any one of the preceding claims, further comprising low friction guide means provided between pairs of adjacent sliding members.

12. An apparatus according to any one of the preceding claims, wherein the displacing means is adapted to displace a minor proportion of said sliding members in a reverse axial direction at at least four said spaced apart locations.

13. An apparatus according to any one of the preceding claims, wherein the sliding members are spaced apart.

14. An apparatus according to any one of the preceding claims, further comprising cable tensioning means for exerting a tension on the cable

15 An apparatus for controlling tension in a cable, the apparatus substantially as hereinbefore described with reference to Figures 5 to 9 of the accompanying drawings