GB590060A - Improvements in and relating to electric control systems employing limit switches for electric and other motors - Google Patents

Abstract

590,060. Fluid-pressure servomotorcontrol systems. SIMMONS, J. D., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Nov. 10, 1943, No. 18713. Drawings to Specification. [Class 135] [Also in Group XXXVII] In a system for controlling a hydraulic motor in which the operation of a limit switch gives rise to a torque dependent on the speed of the motor and in opposition to the movement of the motor, a rectifier is arranged so that when the motor is reversed the opposition torque is eliminated or reduced. In the arrangement described a reversible hydraulic motor is controlled by a throttle valve operated by a moving coil electromagnetic device, the moving element of which has a main and an auxiliary winding. In normal operation, the direction and amount of opening of the valve is dependent on the direction and magnitude of the current supplied to the main winding through any suitable control means from a source of constant voltage. At each limit of motor travel, the auxiliary winding is energized through a limit switch and rectifier from a tachometer generator coupled to the motor so as to oppose the main winding and thereby reduce motor torque. Thus, the motor may be held against limit stops by a torque of low value. On reversal of the motor, the rectifier is no longer conductive and the motor moves away from the stop with full acceleration. Two pairs of limit. switches may be used so that only one rectifier is necessary. In a modification, the throttle valve may be manually operated and a byepass valve, which is spring-biassed to its closed position, opened electromagnetically, to reduce motor torque at the limits of motor travel, by a winding corresponding to the auxiliary winding above.