GB594397A - Improvements in and relating to limit switch arrangements - Google Patents

Abstract

594,397. Control of D.C. motors. SPERRY GYROSCOPE CO., Inc. Dec. 17, 1943, No. 21219. Convention date, Dec. 26, 1942. [Class 38(iii)] [Also in Group XXXVIII] In a control system, a controlled object, driven by a motor to some desired position, operates a limit switch when it approaches a limiting position in one direction, thus bringing into circuit a unidirectionally conducting device controlling power supply to the motor so that it can only be energised to return the controllable object from the limiting position. In the follow-up system shown, the controlled object 4 is driven by motor 12 and on approaching a limiting position cam 29 opens the contacts 24, 24<1>, and brings into circuit the rectifiers 22, the flow of power being from 14 to 15. Current tending to drive the object further in the same direction produces a high voltage drop across the 'rectifiers which energises the relay 17 thus closing contacts 18, 18<1> and short circuiting the armature of the motor to effect braking. Current flowing in the opposite sense will find a short circuit path between 15 and 14 and the object will move away from the limiting position. The direction and speed of the motor may be controlled by a signal voltage indicative of the displacement of the object from the desired position modified if necessary by other factors such as its speed. The circuit between the points 14, 15 can be in the circuit of the control signal instead of the circuit of the motor.