GB2252286A

GB2252286A - Improved cable-handling engine

Info

Publication number: GB2252286A
Application number: GB9026127A
Authority: GB
Inventors: Kenneth Henderson
Original assignee: Northern Engineering Industries PLC
Current assignee: Rolls Royce Power Engineering PLC
Priority date: 1990-11-30
Filing date: 1990-11-30
Publication date: 1992-08-05
Anticipated expiration: 2010-11-30
Also published as: GB2252286B; GB9026127D0

Abstract

A drive mechanism for applying a movement to a submarine cable (10) in the direction of its length, comprises a pair of driven endless belts (14) which are moved about wheels mounted one at each end of a frame (12) which is pivotally mounted at (18) about an axis transverse to the length of the cable (10). The frames (12) are interconnected e.g. by a lever arrangement whereby movements of the frames, and thus the belts (14) to each side of the cable are equal. The belts (14) are preferably urged into contact with the cable by hydraulic means. A plurality of drive mechanisms are provided along the cable length. The arrangement is such that changing cable diameters do not lead to lateral displacement of the cable. <IMAGE>

Description

IMPROVED CABLE-HANDLING ENGINE This invention relates to engines for handling cables and more particularly to such engines for paying out and recovering submarine cables.

It is well established practice to provide linear cable engines on cable ships for laying submerged cable systems, these engines being of modular form, each module including a series of pairs of large pneumatic tyred wheels driven by hydraulic power to feed the cable therebetween.

The wheels of each pair of wheels are urged towards one another to contact the cable and to drive the cable in the desired direction, said wheels being movable away from one another to accommodate therebetween the increased diameter repeater units or joints that are provided periodically along the length of the cable.

However, such an arrangement has a number- of disadvantages. As-well as being extremely expensive and very bulky, there is only very small area contact of each tyre with the cable whereby it is not possible to maintain a constant compressive load on the cable as it passes through the engine. Furthermore, and in particular when the difference in diameter between the main length of cable and the repeater units is significant, there is no guarantee that movement of the two tyres of a pair of tyres one to each side of the line of action of the cable will be equal, and this can lead to decentralisation of the cable.

This latter point is of particular significance in relation to recently-introduced fibre optic cables which are of relatively small diameter, typically between 11.2 and 15.8mm, whereas the connectors spaced therealong are of generally tapering shape having a maximum diameter of, typically, 164mm. Thus the difference in diameter between the main length of cable and the joint is substantial. If the aforementioned engines are used with such-cables, there is a marked tendency for the component parts of each module to undergo unequal movements subsequent to the passage therebetween of a joint and as contact with the main length of cable is remade, and whereby the cable becomes misaligned from its central position.

It would be desirable to provide a cable-handling engine more able to maintain a constant compression on the cable than heretofore and in which the movement of the component parts thereof was controlled to ensure constant centralisation of the cable during passage therethrough.

According to the present invention there is provided a cable-handling engine comprising a plurality of engine modules axially spaced along the centreline of the cable, each module including a pair of opposed drive elements one to each side of said centreline of the cable, each drive element comprising a driven endless belt urged into driving engagement with the associated side of the cable, said drive elements each being pivotally mounted on an associated fixed axis extending transversely of the centreline of the cable in such a manner that, on passage therebetween of the cable, the endless belts follow the external contours of the cable to maintain driving engagement therewith, the drive elements of each pair being interconnected with one another whereby the movements of the elements to each side of the centreline of the cable are equal.

Thus it will be appreciated that, with such an arrangement, more extensive area contact with the cable is achieved than heretofore because of the provision of the plurality of opposed driven belts, while the interconnection of the two elements of each module to ensure equal movement thereof prevents any displacement of the cable from its preferred line of action and regardless of any significant variations in the diameter of the cable as it passes through the engine.

Conveniently the endless belts of a module are urged into driving engagement with the cable by hydraulic means reacting between a fixed point and the drive elements.

In a preferred embodiment of the invention, the drive elements of each module are interconnected by at least one linkage comprising a lever pivotal about an axis extending transversely of the engine through the centreline of the cable, and a pair of arms one pivotally mounted to each end of said lever, the ends of said arms remote from the lever being pivotally mounted to associated ones of said drive elements.

Preferably the hydraulic means comprises a hydraulic piston-cylinder assembly reacting between a fixed point and one end of the or each lever.

Conveniently there are two linkages associated with each module, one to each side thereof, and two hydraulic piston-cylinder assemblies, one associated with . each linkage.

Each driving element may comprise, within the endless belt, a powered driving wheel at one end thereof and an adjustable driven wheel at the other end thereof, and a plurality of idler wheels between said driving and driven wheels arranged to maintain the belt in driving engagement with the cable along the full length of the driving element.

Preferably a groove is formed centrally along the length of each endless belt to receive therein the cable and to improve the driving engagement of the belt with the cable.

By way of example only, an embodiment of the invention will now be described in greater detail with reference to the accompanying drawings of which: Fig. 1 is a side view of an engine according to the invention; Fig. 2 shows a module of the engine of Fig. 1 with a length of cable being driven therethrough, and Fig. 3 shows the module of Fig. 2 with the drive elements displaced to accommodate a cable joint therebetween.

The engine of the invention is particularly suited to the handling of high density polyethylene coated fibre optic cable of relatively small diameter, typically between 11.2mm and 15.8mm, and in which are provided joints, typically every 30 kilometres of cable.

The joints are of relatively substantial size and may be 2.4 metres long and of generally tapering shape, increasing to a maximum diameter of typically 164mm. Thus it will be appreciated that the dimensions of the overall cable to be handled by the engine vary considerably over the length of the cable, while the engine must also be capable df enabling the cable to pass therethrough at considerable speeds of up to 6 knots for extended periods of up to 10 days.

Referring to Fig. 1, there is shown a cable-handling engine for mounting on a cable-laying ship and capable of providing the aforementioned facilities. The engine comprises a main frame 2 adapted to be secured to the deck of the ship and having a pair of sidewalls between which are mounted four axially aligned modules each indicated generally at 4. The modules are substantially identical and only one will be described in detail.

Referring to Figs. 2 and 3, the module 4 comprises a pair of opposed drive elements 6,8 one to each side of a transverse plane that is to contain the cable 10 to be handled by the engine.

Each drive element 6,8 includes a fabricated frame 12 in which is located an endless toothed belt 14 manufactured from polymer composite rubber reinforced with man-made fibres for added strength and wear resistance. A groove is machined centrally along the length of the belt to accommodate the cable 10.

The belt 14 is driven by a bronze toothed driving wheel directly coupled to a slow speed hydraulic motor 15 fitted with a failsafe, spring-applied brake at one end of the element 6,8, an adjustable driven wheel being provided at the other end of the element 6,8 to enable the belt tension to be varied.

Five small diameter toothed bronze idler wheels are located between said driving wheel and said driven wheel whereby a compressive load is applied to the cable 10 over substantially the whole length of the belt 14 in contact with the cable 10.

All wheels except the driving wheel are supported and rotate on sealed frictionless bearings on static shafts, while the driving wheel is supported at one end by the hydraulic motor shaft and at the other end by a stub shaft and sealed frictionless bearing.

Each frame 12 is pivotally mounted at 16 to one end of a bracket 18 the other end of which is pivotal about a fixed axle 20 extending transversely of the main frame 2.

Thus it will be appreciated that each drive element 6,8 can undergo substantially universal pivoting movement in a vertical plane therethrough and can move upwardly and downwardly relative to the main frame 2 whilst undergoing pivotal movements about the points 16 and 20.

The two driving elements 6,8 are interconnected by means of a pair of opposed linkages one to each side of the frames 12. Each linkage includes a lever 22 pivotal about a central fixed axis 24 extending transversely of the element 6,8 through the centreline of the module.

Pivotally mounted to the opposed ends of the lever 22 at points 26,28 are the one ends of a pair of arms 30,32 one extending upwardly and one extending downwardly from said lever 22. The other- ends of the arms 30,32 are pivotally mounted to the brackets 18 at points 34,36 between the points 16 and 20.

It will thus be appreciated that, with such a linkage, and on any pivoting movement of the lever 22 about the fixed axis 24, any movement of the element 6 will be mirrored in the element 8 and the two elements move by equal amounts relative to the centreline of the module.

A pair of hydraulic piston-cylinder assemblies 38, one to each side of the main frame 2, react between fixed points 40 on said frame 2 and one end of each lever 22 to pivot said lever in a clockwise direction as viewed in Figs. 2 and 3 and thereby to urge the driving elements 6,8 towards one another such that a compressive load is applied by the belts 14 to the cable 10 located therebetween.

In order to draw a cable 10 through the described engine, the eight hydraulic motors 15, which are connected in parallel with one another, are powered whereby the eight belts 14 are driven under the same torque. The cable 10 incorporates joints 42 which are of a generally tapered nature increasing in diameter to a maximum of 164mm and, as these joints are drawn between the drive elements 6,8 of a module, the elements 6,8 pivot about the points 16,20 to accommodate therebetween the joints with the belts 14 following the external profile of the joint to maintain driving engagement therewith.

In order to ensure said driving engagement, the hydraulic piston-cylinder assemblies 38 are connected to a hydraulic supply and accummulator system sized to ensure rapid response of the assemblies 38 to any movement of the drive elements 6,8 towards and away from the centreline of the cable 10, which movement is transmitted to the piston of the assemblies by way of the levers 22.

Once the joint 42 has passed through a module, the drive elements return to their normal drive positions shown in Fig. 2 to re-engage the main cable length, the linkage between the two elements ensuring that the return movements are equal and whereby the cable 10 remains centrally disposed between the elements on its optimum line of action.

Conveniently a shaft encoder is fitted to one of the drive elements to monitor the length of cable deployed, while the engine is preferably anchored to a separate deck bolted sub-frame by means of two pin type load cells which measure the horizontal reaction of the engine and thus the cable tension.

Power for the engine is provided through an electrohydraulic power pack including a 24 cubic inch per revolution variable delivery axial piston pump fitted with a horse power limit control and a remote hydraulic stroker and coupled to two fixed delivery gear pumps. These pumps are driven by a 140 kwatt 1760 r.p.m. electric motor, while the variable delivery pump provides hydraulic power in a closed loop system to the eight motors 15 connected in parallel with one another via maximum flow bidirectional control valves.

One of the gear pumps prdvides replenishment flow for the closed loop system, while the other gear pump provides hydraulic power for the eight assemblies 38 and the failsafe brakes of the motors 15.

Full system cross line relief valves are fitted across the main lines to give system protection, while two 20 litre accummulators are connected into the lines to the assemblies 38 to ensure said rapid response to cable diameter variations.

A control console for the engine consists of a control pedestal in which are fitted a hydraulic single axis lever controller initial movement of which in either direction will release the brakes, while further movement away from and towards the operator will cause the engine to pay out and heave in respectively, a digital display unit to show cable tension, and a digital display unit to show cable length deployed.

Claims

1. cable-handling engine comprising a plurality of engine modules axially spaced along the centreline of the cable, each module including a pair of opposed drive elements one to each side of said centreline of the cable, each drive element comprising a driven endless belt urged into driving engagement with the associated side of the cable, said drive elements each being pivotally mounted on an associated fixed axis extending transversely of the centreline of the cable in such a manner that, on passage therebetween of the cable, the endless belts follow the external contours of the cable to maintain driving engagement therewith, the drive elements of each pair being interconnected with one another whereby the movements of the elements to each side of the centreline of the cable are equal.

2. An engine as claimed in claim 1 in which the endless belts of a module are urged into driving engagement with the cable by hydraulic means reacting between a fixed point and the drive elements.

3. An engine as- claimed in claim 1 or claim 2 in which the drive elements of each module are interconnected by at least one linkage comprising a lever pivotal about an axis extending transversely of the engine through the centreline of the cable, and a pair of arms one pivotally mounted to each end of said lever, the ends of said arms remote from the lever being pivotally mounted to associated ones of said drive elements.

4 An engine as claimed in claim 4 in which the hydraulic means comprises a hydraulic piston-cylinder assembly reacting between a fixed point and one end of the or each lever.

5. An engine as claimed in claim 3 or claim 4 in which there are two linkages associated with each module, one to each side thereof, and two hydraulic piston-cylinder assemblies, one associated with each linkage..

6. An engine as claimed in any one of claims 1 to 5 in which each driving element comprises, within the endless belt, a powered driving wheel at one end thereof and an adjustable driven wheel at the other end theredf, and a plurality of idler wheels between said driving and. driven wheels arranged to maintain the belt in driving engagement with the cable along the full length of the driving element.

7. An engine as claimed in any one pf claims 1 to 6 in which a groove is formed centrally along the length of each endless belt to receive therein the cable and to improve the driving engagement of the belt with the cable.

8. A cable-handling engine substantially as described with reference to and as illustrated by - the accompanying drawings.