GB2026210A - Motor speed control systems - Google Patents

Abstract

A driving arrangement has two drive members in the form of drums or pulleys required to drive separate ropes 3 at the same speed as each other, in which the drive members are connected to individual electric motors M1 M2, the arrangement including means TG for generating signals TG1 TG2 representative of the speeds of the individual drive members, together with means SC for combining the speed signals and a speed reference signal R to produce an error signal RO and means for controlling the input current to the motors in dependence upon the error signal in the sense which tends to produce substantially the same output torque from the motors, and maintain the sum of the speeds of the two motors constant ie at the reference value R. <IMAGE>

Description

SPECIFICATION Driving arrangements for conveyors and like equipment This invention relates to driving arrangements incorporating two or more drive members, and to control arrangements therefor.

Some types of equipment incorporate two drive members in the form of drums or pulleys which are used to drive separate ropes or cables, hereinafter referred to as ropes for simplicity. In many cases the ropes are required to be driven at the same speed as each other, but this cannot alays be achieved by rotating the drive members themselves at precisely the same speed, due for example to slight differences in their diameters, variations in the positions of the ropes on the members, or to other factors. For this reason it has been the custom to connect the drive members to a common electric motor, or possibly more than one motor, through a differential gear box.

However differential gear boxes tend to be bulky and expensive, and an object of the present invention is to provide an alternative form of driving arrangement which is especially suitable for such equipment.

According, therefore, to one aspect of the invention, in a driving arrangement incorporating two drive members in the form of drums or pulleys used to drive separate ropes, the drive members are coupled to individual electric motors and the arrangement includes means for generating signals representative of the speeds of the individual drive members, means for combining the speed signals and a speed reference signal to produce an error signal having a value which depends on the difference between the speed reference signal and the sum of the speeds of the drive members and a control means for controlling the input current to the motors in dependence upon the error signal, in the sense which tends to produce substantially the same output torque from the motors.

Such an arrangement has been found to produce an approximately equal tension in the ropes, giving effectively similar characteristics to a differential gearbox, but with improved accuracy of torque output, less losses and improved overall efficiency, in addition to being less bulky. It also controls the means speed of the drive members at a value corresponding to the reference signal.

The invention has particular application to rope driven belt conveyors, that is to say conveyors of the kind having a conveyor belt which is driven by frictional engagement with a pair of ropes separately driven by individual drums or pulleys, for causing the ropes to exert the same pull on the conveyor.

Conveniently the arrangement includes means for generating further signals representative of the E.M.F.'s of the individual motors, and means for combining these with said other signals for producing a modified error signal or signals, the control means being arranged to control the input current to one or both motors in dependence upon the modified error signal or signals in the sense which tends to reduce any slight differences in the motor torques and make them more nearly equal. By suitably combining the speed signals and E.M.F. signals it is possible to obtain a substantially exact balancing of the motor torques, as will be later described. Thus such an arrangement may be used to correct for variations in motor torques due to brush movement, hysteresis and other factors.

In an alternative arrangement in which the error signal is used to control the armature currents in both motors, means may be provided for generating further signals representative of the E.M.F.'s of the individual motors to provide a modified error signal or signals. Then by suitably combining the speed and E.M.F.

signals it is possible to vary the field currents of one or both motors to obtain a substantially exact balancing of the motor torques, as will be later described.

In a modification of the arrangements above described the speed feed-back signals can be combined in a greater speed selecting circuit, the output from which is a signal representative of the speed of the drive member having the greater speed, which signal is compared with the speed reference signal to produce said error signal. This arrangement prevents the speeding up of one or other drive member above the set speed reference speed, if any speed differences occur.

The speed signals may be derived from tachogenerators coupled to the motors or the drive members or in any other convenient manner; for example the speed signals may be derived from motor voltage signals, with or without IR compensation, as is common practice in other forms of driving arrangements.

Also in some cases the speed signals may be obtained by the use of sensing means responsive to the actual rope speeds.

The invention makes it readily possible to limit the torque applied to each of the drive members in use of the arrangement, and in some cases the maximum torque that can be applied when the arrangement is at rest can be arranged to differ from that which obtains when the drive is running.

Means may alternatively or additionally be provided for limiting the maximun speed at which the drive members are driven, and in some cases means may also be provided for controlling the rate of acceleration or deceleration of the drive members during starting or stopping of the arrangement or for controlling the rate of change of acceleration and deceleration to set values.

The arrangement can incorporate, if desired, a controlling arrangement for limiting any difference in speed between the drive members, or protection circuits for stopping the drive if, due to some fault arising, an excessive torque or speed difference occurs between them.

An exact control of the individual rope tensions can be achieved by the use of suitable tension measuring devices designed to produce tension signals dependent upon tensions in the ropes, and means for producing an over-riding signal which controls the output torque of the motors in response to the tension signals. By this means a substantially accurate balancing of the tension in the ropes can be achieved.

Conveniently means are provided for setting the motor current and hence the torque in proportion to the signals from the tension measuring devices. Such an arrangement is useful on driving arrangements which incorporate mechanical brakes acting on the driving members, the arrangement then enabling the motor torque to be set to a value which allows the brakes to be removed without the driving members moving, until a speed reference signal is applied.

In such an arrangement the current to the motors can be preset with the brakes on to a value which will just hold the drive members steady when the brakes are released.

An exact control of the movements of each rope can be provided by using devices to sense the positions of each rope, for example the proven system of magnetically striping ropes in use on mine winders.

These signals can ensure that both ropes move exactly the same distance if required.

A driving arrangement in accordance with the invention is applicable to both AC or DC motors, which can be direct coupled or geared to the respective drive members.

A driving arrangement in accordance with the present invention can readily be extended to the control of more than two drive members.

Several embodiments of the invention will now be described by way of example with reference to Figures 1 to 15 of the accompanying schematic drawing, in which Figures 1 and2 illustrate diagrammatically a plan view and a side view respectively of part of a rope-driven belt conveyor associated with a driving arrangement in accordance with the invention, Figure 3 shows one method of controlling the output torque of the electric motors utilised in the driving arrangement, Figures 4 to 15 show alternative ways of controlling the motor output torque.

The belt 1 of the conveyor illustrated in Figures 1 and 2 passes round end rollers 2 (only one of which is shown) and, between the end rollers, the upper and lower runs of the belt are supported by endless ropes 3, 4 disposed adjacent each side of the belt as shown, the ropes being themselves supported by idler rollers 5.

The belt carries on both surfaces longitudinally extending ridges 6 (Figure 2B) formed with guide grooves 7 which accommodate the ropes 3, 4. In use of the conveyor the ropes are arranged to be driven at substantially the same speed as will subsequently be described, the frictional contact between the ropes and the accommodating grooves imparting the drive to the belt.

At the driving end the ropes 3, 4 pass round appropriately positioned diverter pulleys 8 and then over respective drive pulleys 9, being held under tension by further, horizontal, pulleys as at 10.

It is desirable for the ropes 3,4 to be driven at the same speed as each other in use of the conveyor, and in order to achieve this, despite variations in the positions of the ropes on the drive pulleys 8, and for possible slight differences in the pulley diameters, it is at present usual to drive the ropes through a differential gear box. However such gear boxes are bulky and expensive.

In accordance with the present invention the drive pulleys 9, are coupled, either directly, or through simple reduction gears as at 11, to individual D.C. electric motors M1, M2, the output torque of which motors is controlled to provide the required equality of rope speed.

This can be achieved utilising the control arrangement illustrated in Figure 3.

For controlling the motor torque each motor M1, M2 is associated with a tachogenerator TG each arranged to produce an output signal TG1, TG2 respectively representative of the motor speed, and these signals are fed to a speed control circuit SC, which is used to generate an error signal RO; of the form RO = f (R - TG1 -TG2) where R is a speed reference signal.

The error signal R is used to control the input current to the motors M1, M2.

Such an arrangement produces an approximately equal tension in the ropes 3, 4, whilst avoiding the need for a differential gear box, and also controls the mean speed of the drive members at a value corresponding to the reference signal.

However for a simple D.C. motor with a fixed field the flux Q, is approximately constant and can be given by the expression = 4?n (1 + x) where on is the nominal flux and xis the degree of error. Now in a D.C.

machine the output torque T = I. < )A.K, (IA being armature current and K a constant) and if the armature current corresponds to a reference signal R the output torque T = R.n.K (1 + x) so that there is a limit to the degree of accuracy obtained with this simple circuit.

Instead of the tachogenerators TG being associated with the motors M1, M2, they may alternatively be associated with the drive pulleys.

An alternative arrangement which provides a more accurate control is illustrated in Figure 4. In this arrangement the armature current IA1 of the motor M1 is controlled by a current control circuit C1 in response to a speed reference signal R. A monitor device 12 provides a signal proportional to the armature current which signal is fed into a mixing circuit 13, into which is also fed the reference signal R. The output of the mixing circuit represents the difference between the armature current which is called for by the reference signal R and the actual armature current represented by the feed-back signal from the monitor device 12. The two signals are fed into the mixing circuit in opposite senses so that the output of the mixing circuit represents the difference between the current called for and the actual current. This resultant signal is fed into the current control circuit C1 with a sense and amplitude which tends to control and hold the armature current IA1 at a value which corresponds to the reference signal and thus maintains it at the set value. The device 12 could be in D.C. circuit or in A.C. supply lines for converter fed motors.

The reference signal R is also fed to a second current control circuit C2, through a torque balance circuit 14 which converts the reference signal to a further signal Rl,which is a modified error signal, and this further signal is fed into an associated current control circuit C2 controlling the value of the armature current IA2 of the second motor M2. A further monitor device 15 provides a signal representative of the armature current IA2 and this is combined with the further signal R1, in a second mixing circuit 16 the output of which corresponds to the difference between the actual armature current IA2 and that called for by the further modified error signal Rl,this being fed to the control circuit C2 in the sense which tends to maintain the armature current IA2 at the required value.The field currents 1f1 and lf2 of the motors M1 and M2 are maintained at substantially constant equal values.

Each motor M1, M2 is associated with a tachogenerator or other device 17, 18 respectively which provides an output signal N1, N2 which is representative of the motor speed, and also with a circuit 19, 20 which provides a further signal El, E2 representative of the E.M.F. of the motor. These signals are fed into the torque balance circuit 14 and are used to convert the reference signal R into the further signal R1 such that R1 = R.E1 .N2 (1) N1 E2 Now for a D.C. machine the motor E.M.F. is proportional to the product of the flux and the motor speed, which can be expressed as E = .N.Kl, where K1 is a constant.

Thus for the motor M1 T1 = < )1.1A.K = El . R.K (?) N1 Kl and for the motor M2 T2 = 2.1A2.K = E2 . R1.K = E2.El .N2R.K = El. R. K N2 K1 N2 N1 E2 K1 N1 K1 (3) ThusT1 =T2 Accordingly the output torque ofthe motors M1, M2 is the same, and hence the rope tension will be substantially the same.

The conversion of R into R1 is conveniently effected by means of standard multiplier and divider circuits as illustrated at 21 and 22 in Figure 5, in which the first circuit 21 converts the signals, R, El and N1 into a further signal equivalent to R.E1 N1 and the second circuit 22 converts this further signal into another which is equivalent to R.El .N2 N1 E2 that is to say the required signal R1.

The signals El and E2 are conveniently obtained by means of a circuit as illustrated in Figure 6.

In this circuit the armature of the motor M1 is connected in series with a compole winding of resistance RC and is shunted with a series combination of a diode D, and two resistors RA and RB as shown, the resistor R5 being variable.

One signal output terminal 23 is connected to the junction of the resistors RA, RB and the second signal output terminal 24 is connected to the junction of the armature and compole windings.

Now VB = (V - VD) R8 (4) RA + RB where VB is the voltage across the resistor RB, V is the applied voltage, and VD is the voltage across the diode D.

Vc = IARc (5) where Vc is the voltage across the compole winding.

V = E + IA( RAR + Rc) + VBR (6) where E is the motor E.M.F, RAR is the motor armature resistance and VBR is the motor brush volts drop. If the voltage of the output signal is El El =VB-Vc (7) El=(V-V0) RB -Ve (8) RA+RB = E.RB + IA- (RAR+Rc). R5 + VBR.RB - VD.RB -lARO (9) RA+RB RA+RB RA+RB RA+RB Now if VD is made equal to VBR by appropriate selection of the diode D (or diodes as a number of diodes can replace the single diode D if necessary), and RB RA+RB is made equal to Rc RAR+Rc by adjustment of the value of the resistor RB, then as E1 = E.RB + IA- (RAR+Rc) [ RB - Rc + RB [VBR-VD] (10) RA+RB RA+RB RAR+RC] RA+RB from 9, El = KE where K is a constant.

Accordingly the output signal El is proportional to the motor E.M.F. A similar circuit can be used for deriving an output signal E2 proportional to the E.M.F. of the motor M2. However other circuit arrangements may be used for obtaining the output signals El, E2 if desired.

If the differences in the speeds of the motors M1 and M2 are so small compared with their actual speeds so that it can be neglected N1 = N2, and equation (1) can be simplified to R1 = R.E1 E2 Accordingly a single multiply and divide circuit can replace the two circuits of Figure 5, to derive the signal R1 from R.

If the differences of El, E2 and N1, N2 are small then making R1 = R + R (E1-E2)+R (N2-N1) E1 N1 gives an approximate solution which needs less accurate circuits.

And again, if N1 and N2 can be ignored, R1 = R + R (E1-E2) provides an even simpler solution.

El If three or more motors are to be controlled the circuit of motor M1 stays the same and the circuits of motor M2 are repeated for each extra motor.

An alternative control arrangement for deriving an equal torque output from motors M1 and M2 is illustrated in Figure 7, which is similar to that illustrated in Figure 4, except that a circuit 14A is added, the circuit 14B being equivalent to the circuit 14 of the earlier figure.

The circuit of Figure 7 operates in a similar manner to that of Figure 4, and gives R1A=R.N1 = IA1 (11) E1 R1B=R.N2 =IA2 (12) E2 As El =1N1.Kl (13) E2 = #2N2.K1 (14) T1 = #1IA1.K (15) T2 = #2IA2.K (16) Then from (ll)to (16) T1 = El R.N1 K = R.K N1.K1 El K1 T2 = E2 .R.N2 K=R.K N2.K1 E2 K1 T1 =T2 The input and output of the circuits 14A and 14B are shown in Figure 8, as in the previous case a simplified equation can be used for small changes, and the system can be easily extended to three or more motors.

An alternative control arrangement for deriving an equal torque output from the motors M1 and M2 is illustrated in Figure 9.

In this arrangement the armature currents IA1 and IA2 of both motors M1 and M2 are controlled by feed-back circuits so as to correspond to the value of the same input signal R, and the field current lt2 of the motor M2 is controlled so that the output torque T2 of this motor equals that of the motor Ml, the field current If, of the latter being maintained constant.

For this purpose there is provided a field current control circuit 26 into which are fed signals El, E2 corresponding to the E.M.F.'s of the motors M1 and M2 and speed signals N1, N2 corresponding to the speed of the motors and derived in a manner similar to that described above.

The control circuit 26 is illustrated in more detail in Figure 10 and incorporates two divider circuits 27, 28 associated with the output from the motors M1, M2 respectively, to provide signals in the form E1 and E2.

N1 N2 These signals are combined in an amplifier 29 to provide a control signal S in the form El -E2, N1 N2 and this signal is fed, via a further high gain amplifier 30, to an output circuit 31 from which the excitation current lf2 of the motor M2 is derived, this being controlled by a current monitor and feed-back circuit so that its value varies with changes in the value of the signal S, in the sense to reduce S to zero, that is to say to make E2 =E1.

N2 N1 Now since T1 = #1.IA1.K = #1.R.K. (17) and T2 = #2.lA2.K = #2.R.K. (18) E2.R.K = E1.R.K = #1.R.K (19) N2 N1 Therefore the torque output T2 of the motor M2 is equal to the torque output T1 of the motor M1.

If the difference in the speeds of the motors is very small and can be ignored such that N1 is effectively equal to N2 the circuit shown in Figure 10 can be simplified to the form illustrated in Figure 11,theexcitation current lf2 of the motor M2 being controlled so that its value varies with changes in the value of the signal E1-E2 in the sense to reduce this to zero.

Then T2 = 4)2 1A2 K = E2.R.K = E2.R.K = E1.R.K = #1.R.K = T1 (20) N2 N1 N1 In either of the two circuits illustrated in Figures 10 or 11 the two amplifiers 29, 30 can be combined into one amplifier.

Another control circuit deriving a substantially equal torque output from the motors by controlling the field current of the motor M2, and which is suitable for use in cases where the difference in the motor speeds is so small that it can be ignored is illustrated in Figure 12.

In this arrangement the motors are connected in parallel and the sum of the motor armature currents i.e.

1A1 and IA2 is maintained at a value corresponding to reference signal R by a monitor 12 and feed-back circuit.

Signals dependent upon the two armature currents 1A1 IA2 are combined to form a signal IA,-IA2 which are fed into a circuit controlling the field current lf2 of the motor M2, the value of this current being arranged to vary with changes in the value of the signal IA,-IA2 in the sense to reduce this to zero.

Now V = El + IA1.RM1 + VBR1 (21) and V = E2 + IA2.RM2 + VBR2 (22) where V is the voltage across the motors, El and E2 the motor E.M.F.'s, RMl and RM2 the motor resistances, and VBR1 and VBR2 the motor brush drops.

Now as IA1.RM1 = lA2.RM2 and VBR1 = VBR2 then El = E2.

1.Nl = 2.N2 If N1 is effectively equal to N2 then 4) = But as T1 = IA1#1 and T2 = IA2.#2 = IA1.#1 so that T1 = T2.

In a further control arrangement illustrated in Figure 13 the motors M1, M2 are connected in series so that the armature currents IA1 and IA2 are equal, and means are provided for controlling the field current 1f1 or 1f2 of the motor M1 or M2 by any of the control arrangements illustrated in Figures 9 to 11.

The method illustrated in Figures 9 to 13 can easily be extended to three or more sectors.

An alternative control arrangement for deriving an equal torque output from the motors M1 and M2 is illustrated in Figure 14.

This circuit works in a similiar way to Figure 9 but in this case both field currents If, and lf2 are controlled by respective control circuits 26A, 26B, so that N1-E1 =OandN2-E2=O which, as in the arrangement of Figure 9, keeps the two torques balanced.

This arrangement can also be easily extended to any number of motors.

In the arrangement illustrated in Figure 15 which is otherwise similarto that of Figure 4, speed signals derived from the tachogenerators 17, 18 associated with the motors M1, M2 or the drive pulleys 9, 10 are fed to a comparator 31, and if any of these speed signals indicates that the speed of one or both ropes has attained a maximum permitted value, the comparator produces a limit signal which is fed back to the speed control circuit to prevent any further rise in speed. Alternatively the limit signal from the comparator may be arranged to switch off the motors if the speed of one or both of them reaches a predetermined level.

Aiternatively or in addition the speed comparator 31 may be arranged to generate a signal for switching off the motors if an excessive speed difference occurs between them.

A further circuit, as at 32, may be provided for limiting the rate at which the armature current of each of the motors M1, M2 varies.

In a further modification means (not shown) can be added to modify the speed reference to limit the acceleration or deceleration of the drive pulleys 9, 10, or to limit the rate of change of acceleration or deceleration to a required value.

In a futher modification means (not shown), which may be responsive to the force exerted on a diverter pulley associated with each rope, is provided for developing a signal representative of the tension in the rope, and this may be fed back to the torque control circuit to reduce the torque in the event of the tension in the rope reaching a permitted maximum value.

Similar modifications can be applied to any of the other control arrangements described with reference to Figures 7 to 14.

If the ropes are required to move exactly the same distance this could be achieved by utilising suitable position feed-back signals of the rope positions, for example by the provision of magnetic stripes uniformly spaced along the length of the ropes, together with appropriate sensing devices capable of generating output signals on the passage of the magnetic stripes.

Although the invention has particular application to rope driven conveyor it may also be used to advantage for other equipment in which two or more ropes are required to be driven at substantially the same speed, for equalising the tension in the ropes.

Claims (25)

1. A driving arrangement incorporating two drive members in the form of drums or pulleys used to drive separate ropes, wherein the drive members are coupled to individual electric motors, and the arrangement includes means for generating signals representative of the speeds of the individual drive members, means for combining the speed signals and a speed reference signal to produce an error signal having a value which depends on the difference between the speed reference signal and the sum of the speeds of the drive members, and a control means for controlling the input current to the motors in dependence upon the error signal, in the sense which tends to produce approximately the same output torque from the motors.

2. A driving arrangement according to Claim 1 including means for generating further signals representative of the E.M.F.'s of the individual motors, and means for combining these with said other signals for producing a modified error signal or signals, the control means being arranged to control the input current to one or both motors in dependence upon the modified error signal or signals in the sense which tends to reduce any slight difference in the motor torques and make them more nearly equal.

3. A driving arrangement according to Claim 1, wherein the error signal controls the armature currents in both motors, and which includes means for generating further signals representative of the E.M.F.'s of the individual motors, and means for combining these with said other signals for producing an additional error signal or signals, the additional error signal or signals being arranged to vary the field currents of one or both motors, in the sense which tends to reduce any slight differences in the motor torques and make them more nearly equal.

4. A modification of the driving arrangement according to Claim 1,2 or 3 incorporating a greater speed selecting circuit, into which the speed signals are arranged to be fed, and which is arranged to generate a signal representative of the speed of the drive member having the greater speed, and means for comparing said greater speed signal with a speed reference signal to produce said error signal for controlling the input current to the motors.

5. A driving arrangement according to any preceding claim wherein the speed signals are derived from tachogenerators coupled to the respective motors or drive members.

6. A driving arrangement according to any preceding claim wherein the speed signals are derived from motor voltage signals.

7. An arrangement according to any preceding claim incorporating means for limiting the maximum torque that is applied to each said drive member in use of the arrangement.

8. An arrangement according to Claim 7 wherein the torque limiting means is arranged to limit the amount of maximum torque that can be applied to a drive member to a first maximum when the arrangement is at rest, and to a different maximum when the arrangement is running.

9. An arrangement according to any preceding claim including means for limiting the maximum speed at which the drive members can be driven.

10. An arrangement according to any preceding claim incorporating means controlling the rate of acceleration and/or deceleration of the drive members during starting or stopping of the arrangement and/or for controlling the rate of change of accelerationg and/or deceleration to set values.

11. An arrangement according to any preceding claim incorporating a controlling arrangement arranged to limit any difference in speed between the drive members.

12. An arrangement according to any preceding claim incorporating means controlling the rate of change of motor current and hence the torque applied to the drive members.

13. An arrangement according to any preceding claim incorporating a protective arrangement for stopping the driving motors if the speed of one or both drive members reaches a permitted maximum value, or the difference in speeds reaches a permitted maximum value.

14. An arrangement according to any preceding claim incorporating a protective arrangement for stopping the driving motors if the torque of each drive members and/or the current of each motor reaches a permitted maximum value, or the difference in torque or currents reaches a permitted maximum value.

15. An arrangement according to any preceding claim incorporating tension measuring devices arranged to produce tension signals dependent upon the tensions in the individual ropes, and means for producing an over-riding signal which controls the torque applied to a respective drive member to achieve a substantially accurate balancing of the tension in the ropes.

16. An arrangement according to any preceding claim incorporation tension measuring devices arranged to produce tension signals dependent upon the tension in the individual ropes, and means for setting the motors current and hence the torque in proportion to the signals from the tension measuring devices.

17. An arrangement according to any preceding claim incorporating rope position measuring devices, e.g. magnetic rope striping, and means for using the signals from the rope position measuring devices to ensure each rope moves exactly the same distance.

18. An arrangement according to any preceding claim wherein the motors are D.C. motors, which can be direct coupled or geared.

19. An arrangement according to any one of Claims 1 to 17 wherein the motors are A.C. motors, which can be direct coupled or geared.

20. An arrangement according to Claim 2 incorporating D.C. electric motors and means for sensing the E.M.F. of the motors substantially as shown in and as hereinbefore described with reference to Figure 6 of the accompanying drawings.

21. A driving arrangement according to Claim 1, 2 or 3 having one or more additional drive members in the form of drums or pulleys arranged to drive separate ropes, wherein the drive members are coupled to individual electric motors, and are each associated with means for generating a signal representative of the speed of the drive member, the arrangement including means for combining the speed signals associated with all the drive members with the speed reference signal to produce said error signal.

22. A driving arrangement according to Claim 4 having one or more additional drive members in the form of drums or pulleys arranged to drive separate ropes, wherein the drive members are coupled to individual electric motors, and are each associated with means for generating a signal representative of the speed of the drive member, the arrangement including means for feeding the speed signals associated with all the drive members to said speed selecting circuit which is arranged to generate a signal representative of the speed of the drive member having the greatest speed, which greatest speed signal is arranged to be compared with said speed reference signal to produce said error signal.

23. A driving arrangement substantially as shown in and as hereinbefore described with reference to Figures 1,2 and 3, or Figures 1,2 and 4 to 6, or Figures 1,2 and 7 to 9 or Figures 1,2 and any of Figures 10 to 15 of the accompanying drawings.

24. A rope-driven belt conveyor in which the ropes are driven by individual electric motors controlled by a control arrangement according to any preceding claim.

25. Any mechanical equipment incorporating two or more drive members which are driven by individual electric motors, controlled by an arrangement according to any one of Claims 1 to 23.