GB1309134A - Electric motor control system - Google Patents

Abstract

1309134 Automatic speed control WESTINGHOUSE ELECTRIC CORP 12 June 1970 [30 June 1969] 28554/70 Heading G3R [Also in Division H2] A lift motor 1 is supplied from a Ward Leonard generator 3 which is driven by an A. C. motor 13, the generator field being excited by a S. C.R. amplifier 17 associated with A. C. source 19. A drag magnet regulator 21 produces a signal representing the difference between the desired and actual speeds of the lift-motor, the reference signal being derived from a pattern generator 22 which is coupled to a drum 23 rotated by tape 25. The tape is driven from the lift-car, and the pattern generator develops a signal which varies in accordance with the distance travelled during acceleration and with the distance remaining to be travelled during deceleration. The pattern generator receives signals from controller 29 to determine the stopping-floors and to initiate acceleration and deceleration. A unit 31 indicates when the car is to run, and the unit 33 determines the direction. If the system is operating on automatic control, a circuit 35 causes network 37 to apply a bias signal to amplifier 17 to initiate movement of the car and to compensate for lag in in response of the lift to the pattern signal. A circuit 39 disables the network 37 during levelling. A hand control pattern circuit 41 positions the car at points other than level with a landing; the pattern generator 22 then being inoperative. The maximum speed on hand controls is limited by circuit 43 which reduces the potential of the A. C. supplied from source 19 to the amplifier 17. If the car receives a start signal when it is on automatic control and the car is not in a levelling zone adjacent to a floor, a synchronizing circuit 45 causes the limiter 43 to reduce the voltage of the source 19. The car operates at reduced speed and acceleration until it stops at another landing and the system is resynchronized. The car will not begin to operate if the limiter is not in its effective position. Immediately prior to movement, a signal from the circuit 45 removes the limiting signal if the car is starting from within a levelling zone under automatic control. Feedback circuits associated with the amplifier 17 comprise a stabilization network and residual suppressor circuit which reduces the loop current when the car stops. Negative feedback reduces the effect of the error signal when the car runs out of synchronization to further limit the speed and to prevent saturation of the amplifier. Since the error signal is not used when the car is operating on hand control, a feedback signal proportional to the back electro-motive force of the motor is applied to the amplifier for comparison purposes. A loop current monitor 49 detects high loop current at a predetermined time after the car has come to a stop and disconnects the A. C. source 15 from the motor 13. Power cannot be restored until the system is reset. The monitor 49 receives the stop-signal from brake 50.