GB400723A - Improvements in or relating to electro-magnetic driving mechanism particularly suitable for actuating a rheostat switch - Google Patents

Abstract

400,723. Electromagnetic switches. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London, and TUPPEN, E. B., 54, Hillmorton Road, Rugby. June 29, 1932, No. 18402. [Class 38 (v).] An intermittently-operating electromagnetic driving mechanism which may be used in the control of a rheostat comprises a toothless double-acting ratchet device actuated to rotate a shaft in either direction by electromagnetic solenoid-operating means. The toothless double-acting ratchet mechanism comprising a rotatable member having a cylindrical inner surface, and a cam member for each direction of rotation pivoted about the axis of the rotatable member having a curved working surface co-operating with the inner surface of the cylindrical member so that a spring-pressed roller or ball locks the rotatable member and cam together for at least part of the forward movement, a fixed stop being provided so that the rotatable member is unlocked during return movement of the cam member. As shown in Fig. 6, two solenoids 14, 15 have their cores 16, 17 connected by links to arms 2, 3, Fig. 2, loosely mounted on a shaft 18. When either solenoid is energized the movement of the core causes a cam surface carried by the arm 2 or 3 to wedge a roller 7 or 8 against a flange of an outer drum keyed to the shaft, so stepping round the drum and shaft. When the electromagnet is de-energized the core returns under spring action and the roller is released, the drum remaining in its displaced position and the roller being returned by a spring 9 or 10 and distance piece 11 or 12 to rest against a stop 5 or 6 in readiness for a subsequent operation. Each electromagnet may be provided with a snap action switch in its energizing circuit so that while a corresponding pushbutton is maintained depressed a continuous stepping round of the shaft 18 takes place in one or other direction and a contact arm mounted thereon may be moved intermittently across contact studs connected to sections of resistance. The snap action switches for interrupting the electromagnet circuits may be of the type shown in Figs. 3 and 4, in which the movement of a rod 23 connected to the solenoid core brings two pivoted arms 28, 29 across the line of action of springs 24 connecting their outer ends so snapping them across to their opposite positions in which they rest against fixed stops 22, 22a, an insulated bridging contact 26 being thereby moved rapidly out of contact with posts 21 acting as contacts in the corresponding electromagnet circuit. Other forms of quick-action switches may, however, be employed. When used for operating a rheostat the contacts may be arranged in a circle, the movable contact arm being driven from the shaft 18 either directlv or through gearing, or, alternatively, the contacts may be arranged in line, the movable contact being driven by screw or nut mechanism or by sprockets and a chain. In this form limit switches may be provided at the ends of the movement of the movable contact.