Patent GB-612916-A (GB)
Title: Improvements in or relating to control systems for electric motors driving elevators
IPC: B66B1/36
Filed: 1946-06-06
Abstract: 612,916. Push-button lifts. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. June 6, 1946, No. 17191. Convention date, June 9, 1945. [Class 40 (i)] [Also in Group XXXVII] A control system for an electric lift-motor comprises means for levelling the lift-car at a desired floor, means responsive to the levelling means for increasing the motor torque until the car is started and means responsive to the starting of the car for reducing the motor torque. Excessive levelling-speed is prevented. A lift-car is driven by a three-phase induction motor 21 which is provided with stator windings 23, 24 and 25. The system comprises an electromagnetically-operated brake B, and an inductor relay Q which is mounted on the car and is adapted to open contacts for stopping the car when the relay-coil is influenced by plates of magnetic material which are mounted on the walls of the lift-shaft. When the car is standing at the lowest floor, operation for example, of a third floor button 3F energizes a relay 3R and an up-direction relay W. A cam-switch IS prevents operation of a down-direction relay X. A relay 80 is energized thereby de-energizing a levelling-relay L and timing-relays 11T and 12T. An up-direction switch U and'a car-running relay M are closed. A coil B1 is energized to remove the brake. The motor stator windings are connected to the supply and the motor starts upwardly. Accelerating contactors 11, 12, 13 and 14, which are controlled by timing-relays 11T, 12T and 13T and are provided with holding relays 12A, 13A and 14A, are progressively energized to remove a stator winding resistance in steps. As the car approaches the third floor an arm of a selector switch 28 opens the contacts 45 to de-energize the relays 3R and W. The relay Q and a field winding TGF of a tachometer generator are energized and the tachometer armature is connected to energize a low-speed relay V and a high-speed relay Y. A resistor R21 is inserted in series with the relay V to render it more sensitive to decrease of tachometer speed. As the car moves towards the third floor, contacts QUS of the relay Q are opened to de-energize relays LU, U and M. The lift-motor is disconnected and the brakes are applied. The relay 80 is deenergized to prepare the levelling-relay L for operation and the motor stator winding resistors are inserted in circuit. When the carspeed drops to a pre-determined value the relay Y drops out and de-energizes a relay YA to short-circuit resistors R14 and R15 in the brake-coil circuit. When the car stops, the tachometer generator ceases to supply the relay V which is de-energized together with a relay VA. A resistor R21 is short-circuited to render the relay V more sensitive. The relay L is energized to short-circuit protective resistors R20 and R23 in the circuits of relays V and Y. A discharge resistor R17 is connected across the brake-coil. The timing relays 11T and 12T are re-energized before they drop out under the opening action of the relay VA. Assuming that the lift-car has halted above the desired floor level, contacts QDL of the relay Q will close to energize relays LD, D and M. The motor stator windings are energized and the brake removed. The timing relay 11T is de-energized to energize the contactor 11 and increase the motor torque. Thereafter other accelerating contactors 12 and 13 are energized and the motor torque is sufficient to re-start the lift. As soon as the car starts the tachometer generator re-energizes the relay V, VA, 12T, 13T and 14T. Thereupon the contactor 13 is de-energized, since the contactor 14 had not been energized at the time the car started, and a, portion of the accelerating resistance is re-inserted to reduce the motor torque to a desired value for levelling. If the levelling speed becomes too great the relays Y and YA are re-energized to introduce resistors R14 and R15 in the brake-coil circuit and partially apply the brake. As soon as the levelling speed falls sufficiently the relay Y drops out. When the car reaches the desired position, the contacts QDL are opened.. The motor is disconnected and the brakes applied. If the car stalls during a levelling operation the tachometer generator 'ceases operation and the relay V is de-energized to re-operate the relay 13 and decrease the motor stator resistance until the car again starts. A safety switch 40 is provided to prevent operation of the lift when the car door is open. A time-delay relay 70T permits the car to be levelled and the door opened before the car is prepared to move to another floor. An additional contact of the relay 40 may be provided to allow the relay Q to be maintained energized while the car is at a floor. A higher discharge resistor is permanently connected in shunt with the brake coil B 1 to effect rapid flux decay when the coil is disconnected. The resistor R17 is inserted in shunt with the brake coil when it is being deenergized during levelling operation to prevent rough operation. A series resistor R18 ensures full operation of the brake when the car is running at high speeds and prevents overheating of the coil. Resistors R15 and R16 are controlled by a brake-operated switch BK to ensure that the brake picks up quickly prior to levelling. The switch BK is opened by the brake when it is partially applied so that the brake may be quickly re-set.