GB1121702A - Improvements relating to lift control systems - Google Patents

Abstract

1,121,702. Control of D.C. motors. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. 26 April, 1966 [26 April, 1965], No. 17524/65. Heading H2J. [Also in Division G3] In a Ward-Leonard control system for a lift, the stand-still energization of motor M is determined by the comparison of signals representing, on the one hand, the degree of unbalance between the car and counterweight and, on the other hand, the torque being exerted by the motor to counteract this unbalance. Before the lift is started, regulator R excites generator field winding F so that stalled armature current passing through resistor R1 produces a voltage which balances the output from load measuring circuit DT, the points MP2 and E being at equal potential in the state of balance. The circuit DT comprises a transformer with two secondary windings whose coupling to the primary is varied differentially by movement of a magnetic bar which is displaced by a load-bearing part of the lift structure. The secondary windings are connected to respective bridge rectifiers in series opposition to provide the signal representing the degree of unbalance. When loadbalancing is established, the brake is lifted and the system is converted to a speed regulator in which a reference voltage applied to point MP1 is compared with the output of tachometer generator TG. The acceleration full-speed, and initial deceleration operations of the lift are controlled by ramp function generator U associated with speed-selecting relays which drop out when the lift passes predetermined positions in the shaft. A pre-levelling speed is selected by applying a reference voltage determined by the resistor R4 to the point MP1, other pre-levelling speed relays being dropped out in turn as the lift approaches a floor. When the lift is travelling at a low speed, the system is returned to the load-balancing operation, whilst capacitor C is discharged into regulator R to force the field winding F in the " off " direction. The armature current is thus reversed to brake the motor. A suicide connection is made for the generator when the friction brake is applied by connecting the field winding across the armature. A similar arrangement is used for the regulator R which may comprise thyristors.