In particular, the present invention is particularly intended for use in cable reeling applications. However, it is to be appreciated that the present invention is of much wider applicability and the scope of the present application is in no way to be restricted by its specific application to cable reeling.

Firstly, let us consider the forces involved in recovering and paying out cable. These forces, for convenience, will be expressed as TORQUE (which is cable tension times radius of reel) .

Some reels (mostly radials) have a varying radius but the forces applying to them are basically the same as for a drum (or p&rallel) type reel. Considering firstly the recovery torques, let: Tl = Torque to accelerate the reel from rest T2 = Torque to accelerate the cable on the reel from rest T3 = Torque to overcome vertical lift of cable T4 = Torque due to internal friction in reel due to bearings and seals, layering mechanism (if used) and sliprings. T5 = Torque required to overcome out of balance forces due to tangential entry of cable on to reel. T6 = Torque required to overcome eccentricity of load on

reel. T7 = Torque to overcome friction in roller guides for cable (if used) T8 = Torque required to flex cable around guides and reel. T9 = Torque required to overcome wind forces in cable.

TIO = Torque required to overcome friction in guides due to mud or clay on the cable If: TR = Torque to recover cable into reel then:

TR = T1+ T2+ T3+ T4+ T5+ T6+ T7+ T8+ T9+ TIO (1 ^: ) TR can vary between a full reel and an empty reel so that calculations are required to determine the maximum value. If all the values Tl to TIO are accurately assessed, it will not be necessary to have any additions to TR except perhaps a small allowance for increased friction due to wear.

Consider payout torque TP. Ideally TP would be such that the cable Would have zero tension induced but this is virtually impossible as tension due to T3 (vertical lift), T5 (out of balance forces), T7 (roller guide friction), part of T8 (cable flex), T9 (wind forces) and TIO (mud/clay friction) cannot be designed out. Attempts have been made to remove cable tension due to the other torques, Tl (cable acceleration), T2 (reel acceleration), T4 (reel friction), T5 (out of balance forces) and T6 (load eccentricity) by driving the reel in the payout and recovery modes at varying torques to keep cable tension to a minimum. Accurate cable tension

monitoring is needed and because of the quick response to changes in torque required the drives have to be fairly highly powered. This has been accomplished (at a high cost penalty) by using a micro processor coupled to a variable speed drive with continuous cable tension monitoring. The system must be maintained at a high level not usual to most sites as any failure in the system will almost certainly result in damage to the cable due to uncontrolled inertia of the drive being transmitted to the cable, in addition to all the previously listed torques. When a reel carrying three tonnes of cable of 60 mm diameter and rotating at speed is stopped suddenly by the cable tension, damage is inevitable, especially when the maximum tension of the cable can be as low as 150 kg force. When a slipping interface drive is used as a torque regulating device to control the cable tension, most applications can be covered by limiting the torque to the safe working load of the cable or if possible to a lower value. Power failures and emergency stops of the machine do not effect the torque limiter and the cable is protected.

However in the case of high voltage cables, which have a very low working tension, and used in large reels with high accelerations, problems occur in keeping working tensions - below the allowable.

Consider a single slipping interface drive when cable is recovered under power. Thus:

TR = Tl + T2+ T3 + T4 + T5 + T6 + T7 + T8 + T9 + TIO (1) The slipping interface is adjusted to give a torque setting

equal to TR.

However, on payout, all of the factors causing tension in the cable with the exception of the vertical lift torque T3 are repeated. If the cable drives the reel on payout against the slipping interface, the cable must work against the torque limiting device. The total payout torque TP becomes:

TP = TR + T1+ T2- T3+ T4+ T5+ T6+ T7+ T8+ T9+ TIO (2)

From equation (1) : TP = 2TI + 2T2+ 2T4+ 2T5+ 2T6+ 2T7+ 2T8+ 2T8+ 2T10 (3)

This value of TP was attained with a torque regulating device which had a 1:1 payout to recovery ratio.

Torque regulating devices can be built to give a 1:1 payout to a recovery ratio. but for reasons of cost and ease of maintenance, are normally supplied to give a 2:1 payout to recovery ratio on a cold start, i.e. when the reel has stopped.

The payout to recovery ratio is introduced, not by the torque regulating device but in any gear train which the torque regulating device precedes.

Equation (3) then becomes:

TP = 2TR + T1+ T2- T3+ T4+ T5+ T6+ T7+ T8+ T9+ TIO (4) from equation (1)

TP = 3T1+ 3T2+ T3+ 3T4+ 3T5+ 3T6+ 3T7+ 3T8+ 3T9+ 3T10 (5) The effect of a slipping interface using steel or bronze as friction material and having a payout to recovery torque of

5:1 can be easily seen.

Generally TP falls within the allowable tension of the cable. However, in cases of high values of T3 (vertical

lift) coupled with high values of Tl (cable acceleration) and T2 (reel acceleration), the value of TP will often exceed the allowable tension.

SUMMARY OF THE INVENTION The present invention provides a torque regulating system in which the payout torque is within the allowable cable tension limit.

In accordance with one aspect of the present invention there is provided a torque regulating system for cable reeling applications comprising a shaft arranged to rotate -a reel, two or more torque regulating devices coupled to the shaft and a respective motor means coupled to each torque regulating device, each motor means being arranged to drive the shaft through its respective torque regulating device, characterised in that a first torque regulating device is arranged to apply a torque equivalent to that required to accelerate the reel from rest and to accelerate a cable on the reel from rest, and a second torque regulating device is arranged to apply a torque equivalent to that required to maintain the reel at a constant speed, means being provided for de-energising the motor coupled to the first torque regulating device when the reel and the cable have been accelerated to a desired constant speed. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic plan view of a first embodiment of a torque regulating system in accordance with the present

invention; and

Figure 2 is a schematic plan view of a second embodiment of a torque regulating system in accordance with the present invention. DESCRIPTION OF THE INVENTION

In the context of the present invention, ^' if a motor is said to run "forward", this shall be taken to mean the motor rotates to recover cable. Similarly, if the motor is said to run "backward" , this shall be taken to means the motor rotates to payout cable.

Shown in Figure 1 is a torque regulating system 10 comprising a shaft 12 having at one end thereof a load in the form of a cable reel 14 having a cable (not shown) wound thereon. Rotation of the shaft 12 results in corresponding rotation of the reel 14. Coupled to the shaft 12 is a first torque regulating device A. Coupled to the torque regulating device A is a first motor 16. The motor 16 is typically a three phase electric motor. The motor il6 is arranged to drive the shaft 12 through the torque regulating device A. The torque regulating device A limits the torque the motor 16 can apply to the shaft 16. A second torque regulating device B similar to the torque regulating device A is coupled to the shaft 12. A second motor 18, similar to the motor 16, is coupled to the torque regulating device B; The motor 18 drives the shaft 12 in a similar manner to the motor 16. The torque regulating device B limits the torque the.motor 18 can apply to the shaft 12. The motor 16 has a brake device 19. When the brake device

19 is activated shaft 21 of the motor 16 is locked and may not rotate. The brake device 19 could be used on either motor 16 or 18 or both of them depending on the application of the apparatus. Each torque regulating device A and B has typically a slipping interface incorporated in the helical gear wheel of a helical worm gear unit. The gear wheel may be driven by a pinion fixed to the output shaft of a gear motor or fixed directly to the output shaft of a motor depending on the required reel speed. The gear motor may be a helical type and the motor can be an electric motor, both of which can be back driven without developing any significant resistance torque. Preferably, the torque regulating devices A and B are of the type described and claimed in co-pending International Patent Application No.

PCT/AU90/00142 in the name of the present applicant. The brake 19 described above prevents a motor from back running when power is turned off. The brake 19 is conveniently released by external power and is applied automatically when power is turned off or fails.

In relation to the motor 18 which does not have a brake, the torque from the cable reel paying out will drive the motor 18 backwardly against very small resistance if the motor 18 is not energised. When the motor 18 is energised in the forward (recovery) direction to the torque (limited by the slipping interface) of the torque regulator B is added to the torque developed by the motor 16 (also limited by the slipping interface). De-energising the motor of the torque regulator A motor 18

allows it to be driven backward (payout direction), by the cable, with a neglible torque requirement. In this case, it is practical to consider that the motor 18 produces zero torque. 5. Upon energising the motor 18 in reverse (payout direction) the torque developed is effectively subtracted from the torque produced by the motor 16.

Thus, by simply energising, de-energising or reversing an electric motor, three different controlled torques can be 10 obtained with the apparatus of the present invention.

The motor 16 with the brake 19 cannot free wheel when the motor is de-energised.

Even further, the motor 18 is preferably equipped with a timer (not shown) which turns off the motor 18 after a 15 predetermined period (to be described).

In use, on the start of recovery of cable, both motors 16 and 18 are driven forward to rotate the shaft 12 to recover cable.

If: i 20 TA = torque setting of torque regulating device A

TB = torque setting of torque regulating device B

Then:

TR = TA + TB (6) [during recovery]

It is to be noted that TA and TB are not necessarily equal 25 as will be described.

Now let:

TB = Tl + T2 (7)

Then, from equations (1) , (6) and (7)

TA = T3 + T4+ T5 + T6 + T7 + T8 + T9 + TIO (8)

On the start of recovery both motors 16 and 18 are energised. Once the cable reel 14 and the cable on the reel 14 have been accelerated to a desired speed, the motor 18 is de-energised by the timer. Generally, this will happen after a predetermined or calculated period.

In this situation the de-energised motor 18 runs backwards so that the device B does not apply any torque to the shaft

12.

The torque setting TB may be thought of as an inertia component of the total torque TR, due to the mass of the cable reel 14 and cable. The torque setting TA may be thought of as a vertical lift, friction and windage component. Thus once the cable and reel 14 have been accelerated to speed, only sufficient torque (TA) is required to maintain that speed.

Thus, on recovery, there are two phases:

Phase Total torque applied to shaft 12 acceleration TA + TB (=TR) constant speed TA When the cable is stationary, the brake device of the torque regulating device A is actuated. This prevents the weight of the vertical lift of cable from unwinding the cable from the reel 14. In use, when paying out cable, the motor 16 is either run forward or is stopped and the brake device activated. In either case, the torque applied to the shaft 12 is TA. The motor 18 is run backward to payout cable from the reel 14.

Thus, the sign of TB changes in equation (6). Equation (6) then becomes:

TR= TA - TB (9) [during payout] Then, from equation (4): TP = 2(TA-TB) + T1+ T2- T3+ T4+ T5+ T6+ T7+ T8+ T9+ TIO (10) and, from equations (7) and (8)

TP = -(T1+T2) + T3+ 3T4+ 3T5+ 3T6+ 3T7+ 3T8+ 3T9+ 3T10 (11)

By comparing equations (5) and (11), the torque applied to the cable during payout has been reduced by a factor of

4(T1 + T2). . .

A typical example of a cable reeling application which illustrates the advantages of the system 10 is set out below: EXAMPLE

Figures from a typical reel application :

Radius of reel = 1.033m

Length reel = 3.500m voltage= 11KV

Diameter of cable = 66mm length reeling = 510 M Mass/m cable = 5.47kg Acceleration =0.15m/sec/sec

Max allowable tension in cable = 180 kg force max operating

= 300 kg force max allowable

From calculations:

Tl = 88 Nm T2 = 441 Nm T3 = 1003 Nm - T4 = 180 Nm T6 = 66 Nm T6 = 54 Nm T7 = 153 Nm

T8 = 20 Nm T9 = 0 T10 = 60Nm

From equation (1) :

TR = T1+ T2+ T3+ T4+ T5+ T6+ T7+ T8+ T9+ T10 = 2065 NM

Cable tension = 2065 Nm = 1999N = 204 kg force

1.033m This is within the maximum allowable force and is acceptable

A single torque regulating device set at 2065 NM maximum torque will be suitable. From equation (5)

TP = 3T1+ 3T2+ T3+ 3T4+ 3T5+ 3T6+ 3T7+ 3T8+ 3T9+ 3T10 = 4189 NM

-Cable tension = 4189 NM =4055N = 413 kg force

1.033 M This is well above the maximum allowable force and is not acceptable.

Now using the embodiment of Figure 1: From equation (7) : TB = Tl + T2

= 529 Nm = torque setting of torque regulating device B From equation (8) :

TA = T3+ T4+ T5+ T6+ T7+ T8+ T9+ T10

= 1536 Nm = torque setting of torque regulating device A from equation (11) :

TP = -(Tl + T2) +T3+ 3T4+ 3T5+ 3T6+ 3T7+ 3T8+ 3T9+ 3T10 = 2073-Nm

Cable tension = 2073Nm = 2007N = 205 Kg force

1.003 m This is well within the maximum allowable force and is

acceptable.

Figure 2 shows a torque regulating system 20, similar to the torque regulating system 10, like numerals denoting like features. The torque regulating device A is coupled to the shaft 12 through a gearing arrangement which typically comprises a first sprocket 22 attached to the shaft 12, a second sprocket 24 attached to the torque regulating device A and a drive chain 26 connecting the sprockets 22 and 24. Preferably, the sprocket 22 has more teeth than the sprocket 24. Typically, the sprocket 22 has up to five times as many teethes the sprocket 24. This gearing arrangement has the effect of reducing the torque setting of the device A. This is of benefit where extremely high torque, low speed reels which are occasionally encountered. In use, the system 20 functions in a similar manner to the system 10. However, due to the gearing arrangement, the torque regulating device A rotates at a much faster speed when compa'red to the embodiment of Figure 1. Thus, the torque setting of Device A has a mechanical advantage due to the gearing arrangement. The system 20 gives the apparatus a greater combination of torques for different applications. Whilst the embodiments of Figures 1 and 2 have been shown with two torque regulating devices, it is envisaged that more than two torque regulating devices may be used, if this is considered necessary.

Modifications and variations such as would be apparent to a skilled addressee are deemed within the scope of the

present invention. For example, the torque settings TA and TB may be set to equal any combination of the individual torque components Tl to TIO.