GB844234A - Automatic control systems for lifts and the like - Google Patents

Abstract

844,234. Control of A.C. motors. ALLMANNA SVENSKA ELEKTRISKA A.B. Feb. 25, 1958 [March 2, 1957], No. 6012/58. Class 38 (3). [Also in Group XXXV] A lift-car is started by energizing an asynchronous driving motor 14 and lifting brake 20, the car being accelerated with substantially constant torque by a regulator 16 which adjusts the rotor resistance 15 according to the stator current. With change-over switch 29 and sliding contact 34 in the positions shown, the whole voltage of source 31 is utilized as a reference voltage which exceeds the output voltage of tachometer generator 23. A rectifier 22 blocks the current to brake solenoid 21, so that the brake is disengaged. When the car reaches a predetermined distance from a desired stopping- position, a magnetic clutch 24 is engaged whereby contact arm 38 follows the movement of the car to reduce the reference voltage, and the brake solenoid is energized to produce a braking torque which increases as the difference between the tachometer and reference voltages increases. At the landing, a switch 18 is opened and the brake 20 fully engaged, the magnetic clutch 24 being de-energized. During the retardation period the sliding contacts 34, 35 interchange positions so that a new retardation operation may be initiated without returning the arm 38 to its initial position, by changing- over switch 29 to disconnect contact strip 36 and to connect contact strip 37 in the control circuit of the brake.