Patent GB-1217957-A (GB)
Title: A method of and apparatus for regulating the operation of a machine, especially and ore-cutting machine
IPC: H02P29/40
Filed: 1968-01-23
Abstract: 1,217,957. Automatic control systems. CHARBONNAGES DE FRANCE. Jan.23, 1968 [Jan.23, 1967], No.3449/68. Heading G3R. An automatic control system for regulating a parameter comprises means to compare at least one feedback signal representing the parameter with a reference signal representing, at each instant, the value of a regulating quantity, the feedback signal being transmitted, if the parameter exceeds a first threshold value for a time dependent on the excess, with a time delay also dependent on the excess, and being transmitted instantaneously if the parameter exceeds a second threshold value higher than the first. The control system is applied to an ore-cutting machine comprising an electric motor 1 driving the cutting member 3 and a variable delivery hydraulic pump 4 connected in closed circuit with a constant volume hydraulic motor 5 driving a towing cable drum 6 engaging the towing chain 7 of the machine. The lateral speed of movement of the machine is the regulating quantity and is controlled by a jack 8 which varies the inclination of the barrel 41 of the pump 4 to determine its delivery and hence the rotational speed of the motor 5. This speed is made dependent on the current taken by the motor 1 to maintain the current, and hence the power and driving torque, substantially constant. To this end, a feedback signal representative of motor current is obtained from a current transformer 15 and applied to threshold circuits Fig. 3 (not shown) which respectively include the potentiometers P7, P8 and produce signals U<SP>1</SP>b7 and U<SP>1</SP>b8. The former signal is applied to an RC circuit 19 whose output signal U<SP>11</SP>b7, together with the signal U<SP>1</SP> b8, is applied to a comparator X controlling the jack 8 via a valve 9 and multi-vibrators T4-T7. The comparator X is also supplied with a signal Ur representative of the inclination of the barrel 41 and hence of the machine speed, which is initially set by adjustment of a potentiometer 14. controlling a signal Ua applied to the comparator X. Normally the machine runs at the set speed and a rated current, for which conditions the control system is inoperative. Should the motor current exceed a first value I 1  a signal U<SP>1</SP>b7 is produced and a corresponding signal U<SP>11</SP>b7 is applied to the comparator X increasing at a rate determined by the amount by which the current I 1  is exceeded. If the signal U<SP>11</SP>b7 reaches a value sufficient to actuate one of the multi-vibrators, the valve 9 is operated to reduce the machine speed and hence the motor current, stabilization occurring when the signals Ur U<SP>11</SP>b7 become equal corresponding to a new speed/current condition which continues until the next control operation. If the amount and duration of the excess current (over I 1 ) is below a predetermined value (set by choice of the circuit parameters) the signal U<SP>11</SP>b7 does not reach a value sufficient to operate the valve 9 and the machine continues undisturbed. If the motor current exceeds a second value I 2  (greater than I 1 ) a signal U<SP>1</SP>b8 is produced which is applied instantaneously to the comparator X to reduce the machine speed until the condition Ur U<SP>1</SP>b8 is reached. If this condition corresponds to a current between I 1  and I 2 , the signal U<SP>11</SP>b7 then takes over to reduce the speed and current further. A typical operating cycle for the machine is discussed, Fig.4 (not shown). The machine speed is also controlled by a system 20-23 responsive to the pressure in the hydraulic circuit and corresponding in function to the current feedback system, a discharge valve 20 operating in response to a high pressure P2 (equivalent to I 2 ) and the members 21, 23 operating in response to the excess and duration of pressure over a value P 1  (equivalent to I 1  ). The current and pressure feedback circuits, the comparator X and the control circuit for the valve 9 are described, Fig.3 (not shown) and include a transistor comparator, transistor multi-vibrators or Schmitt triggers, RC circuits and resistor-potentiometerdiode arrangements. The valve 9 is the symmetrical type, with two control windings and automatic return of the slide-valve to a central position. The control system may also be responsive to the temperature of the motor 1, for example by adding a temperature representative signal U# to the current signal from transformer 15. The machine speed can also be controlled (during inactive periods of the current-pressure control system) by a signal from a remote control unit 25 applied to the comparator X.