GB2087826A - Controlled torque apparatus for cables - Google Patents

Abstract

A cable drum 10 is provided with apparatus which allows for a constant pull on the cable. The apparatus includes a prime mover 12 which drives the drum 10 and also, through reduction/differential gearing 13, a fluid pump 14 or compressor which is fed from a reservoir 15 through a control valve 16. Torque generated by the pump balances the torque on the cable drum shaft 20 by altering resistance to pump fluid flow, either by manual adjustment of the control valve or by pre-setting the valve to regulate at a given pressure. The apparatus can be incorporated on a cable drum with the gearing located in the drum in a bath of oil; alternatively, the apparatus can be separate from and connectible to a drum located alongside the apparatus. The apparatus can be used on winches and hoists. <IMAGE>

Description

SPECIFICATION Controlled torque apparatus for cables This invention relates to a controlled torque apparatus for a cable drum, and is applicable to winches and hoists for many varied uses such as lifting work pieces in machine shops, cranes and specialised winches for driving, mooring or towing and as a back-tension control on drills in the oil/gas production industry. In short, any application where a constant pull is desirable.

Presently used apparatus for these purposes have some or all of the following disadvantages: (a) Apparatus comprises compensating devices separate and additional to the hoist or load sustaining devices.

(b) Control of compensating devices is often positional by means of a feedback control loop leading to problems of instability and hunting due to out of phase conditions.

(c) Less sophisticated apparatus may depend on a prime mover such as a pneumatic motor which can be stalled or run in reverse as a pump. These devices are difficult to regulate so as to provide uniform torque recordals of the operating conditions.

An object of the invention is to provide apparatus which in use will assist maintaining a constant pull on a load-carrying cable.

According to the present invention there is provided a controlled torque apparatus for a winch drum, said drum being coupled to a prime mover through a differential gear, the other output of which is coupled to a pump, said pump being connected to a reservoir of fluid through said pump and means to vary the pressure of said fluid to vary the torque reaction of the differential gear and thus the torque applied to the winch drum.

Preferably, said pump has a fixed displacement and a regulating valve is provided to vary the pressure of the fluid.

Alternatively, the pump has a variable displacement.

Preferably also, a second prime mover is incorporated in the fluid line from the variable displacement pump and gear to feed back power thereto to tandem with the first prime mover.

Preferably also, the differential gear is enclosed within the cable drum.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which Figure 1 is a sectional elevation of a cable drum incorporating one embodiment controlled torque apparatus according to the invention; Figure2 is a sectional elevation of a cable drum incorporating a second embodiment; Figure 3 is a diagrammatic elevation of back tension or controlled torque apparatus according to another embodiment; Figure 4 is a detail; and Figure 5 is an alternative detail.

Referring firstly to Figures 1 and 3, a cable drum 10 is carried on a mounting 11 and incorporates a controlled torque apparatus which comprises a prime mover 12, which drives the drum 10, and through a combined reduction/differential gear 13 drivesafluid pump 14 or compressor which is supplied with fluid from a reservoir 15 via a valve 16.

The reduction/differential gear is housed within the drum and immersed in oil and comprises a ring gear 17 in the form of an epicyclic gear having a central gear 17A and three planets 17B which are coupled to a plate 18. A brake drum 19 is integral with late 18 and has shoes (not shown) which actuate by a minimum hydraulic pressure thus providing a fail-safe feature.

The prime mover 12, eg. a belt drive, provides input power which is divided by the reduction/ differential gear 13 between the drum shaft 20 and the fluid pump 14, the drive to the shaft being in the direction tending to wind on the cable 21 of the drum the reduction may be 8:1. The torque reaction of the pump 14 and hence the torque applied to constantly revolving drum shaft 20 can then be regulated by altering the resistance to pump fluid flow via valve 16. The valve 16 which may be a needle valve can be set to regulate at a given pressure to vary the fluid flow or it can be manually operated.

When the torque generated is relatively small it may be acceptable to dissipate the energy supplied by a fixed displacement pump 14, in the form of heat, and if hydraulic oil is the medium used, a radiator or cooler 22 (Figure 4) may be fitted into the fluid line.

In a modification (Figure 5) where the torque generated is relatively high, the energy supplied by a second variable displacement hydraulic pump 30 is used to drive a second prime mover 31 which thus recirculates power back to the input in tandem with the belt drive 12.

For very sensitive requirements an additional feedback loop can be introduced into the control circuit.

In use for tensioning a control line or instrument cable the cable drum shaft 20 is rotated in the direction tending to rewind the cable, i.e. against the travel of the cable as it is lowered. At the same time, fluid is pumped through the pump 14.

The tension in the cable is kept substantially constant because, as the cable is pulled offthe drum 10 the speed of pump 14 increases and the regulating valve 16 opens to allow increased flow at constant pressure thus maintaining the torque reaction of the pump constant and consequently the cable tension constant.

When the load is to be suspended, the torque generated by the pump equals that on the drum shaft. To lift the load, the torque generated by the pump is increased relative to the torque on the drum shaft.

Referring to Figure 2, the drum 10 has side plates 40 so that the gearing 13 is located in oil within the drum. The gearing in this embodiment comprises spur gears 41 to 44. Gears 41,42 are driven by the prime mover (belt drive) 45, gears 42 and 43 are coupled through this drum and gear 43 drives gear 44 which via gears 46,47 located outside the drum drive the pump 48. Thus, the prime mover 45 provides input power which is divided by the gearing 13 between driving the drum gears 41,42 and driving the pump 41-44 and 46,47. The torque is controlled in the same way as described hereinbefore with reference to Figure 1.

Where the apparatus is incorporated in a crane or derrick, the second prime mover 31 E is operated by the variable displacement pump 30 to provide extra drive to the differential input. Thus is a situation where the cable is subjected to snatch loads, e.g. in view of heavy seas, cable tension cannot rise above that determined by the control of the variable delivery pump 30.

The differing features of Figures 1 and 2 may be used in any combination and the actual device would be made to suitthe application and constructionai considerations of the winch itself.

The arrangement of the Figure 1 embodiment would be suitable for applications requiring maximum precision of torque control as the continuously revolving shaft would eliminate static friction.

The Figure 2 arrangement is particularly suited to applications where a robust and rigid construction is desired.

The embodiments of Figures 1 and 2 illustrate the reduction/differential gearing combined and housed within the drum. In Figure 3 the gearing is shown separate and outside the drum, being in a unitto which a drum can be brought and coupled up.

The apparatus as hereinbefore described has many applications. It can be used to lift work pieces in machine shops, a work piece being suspended over a machine using the apparatus then finally positioned manually, the weight of the work piece being balanced by the controlled hoist torque.

Other uses include controlling the torque on winches used in driving, mooring, towing or lifting, i.e. compensating for heave or snatch loads where a constant manual control of the pump valve will provide equalising torque generated by the pump and thus a constant pull on the cable. Another use is as a back-tension control on cable attached to a drill string.

Advantages of the apparatus hereinbefore described are: (a) Tension in the cable is limited and closely controlled art a preset value.

(b) The apparatus automatically follows motions of moving loads, paying out and rereeling as necessary to keep cable load constant.

(c) In constant tension applications load is pre cisely maintained once the correct tension has been preset.

(d) In hoisting applications operator is free to control lifting in the desired manner as the apparatus automatically compensates for motions imposed on the load from other sources.

(e) As no feedback loop is involved in the main hoist control, the possibility of hunting introduced by cyciical loads is eliminated.

Claims (6)

1. A controlled torque apparatus for a winch drum, said drum being coupled to a prime mover thrugh a differential gear, the other output of which is coupled to a pump, said pump being connected to a reservoir of fluid through said pump and means to vary the pressure of said fluid to vary the torque reaction of the differential gear and thus the torque applied to the winch drum.

2. Apparatus as claimed in claim 1, in which said pump has a fixed displacement and a regulating valve is provided to vary the pressure of the fluid.

3. Apparatus as claimed in claim 1, in which the pump has a variable displacement.

4. Apparatus as claimed in claim 3 in which a second prime mover is incorporated in the fluid line from the variable displacement pump and gear to feed back power thereto in tandem with the first prime mover.

5. Apparatus as claimed in any one of claims 1 to 4, in which the differential gear is enclosed within the cable drum.

6. Controlled torque apparatus for a winch drum substantially as hereinbefore described with reference to the accompanying drawings.