Elevator motor control system for a.c. induction motor

Claim 1

An elevator motor control system in which a three phase A.C. induction motor with fast and slow speed stator windings is accelerated by having its fast speed windings appropriately connected by switching apparatus to the supply lines of a three phase A.C. voltage source in at least two lines of which are current regulating devices for regulating the magnitude of alternating current applied to said fast speed windings in accordance with a signal representing the difference between a reference speed signal and the output signal of a tachometer generator driven in response to the rotation of said motor, wherein said switching apparatus operates in response to the location of said car at a predetermined distance from a landing at which a stop is to be made to disconnect said fast speed windings from and to connect said slow speed windings to said current regulating devices to receive three phase alternating current from said source in a phase sequence different from that by which said current was applied to said fast speed windings, said switching apparatus in operating also switching the control of said current regulating devices from said difference signal to an error signal derived by comparing said tachometer generator signal with a deceleration pattern signal produced by a function generator in response to the distance the car is calculated to be from said landing at which it is to stop, said calculated distance being represented by a continuously decreasing signal generated by an integrating circuit which integrates the signal produced by said tachometer generator after said car arrives at said predetermined distance and subtracts that integrated signal from a signal representing said predetermined distance.