GB638916A - Improvements relating to automatic switches of the kind used in telephone systems - Google Patents

Abstract

638,916. Electric motors. SIEMENS BROS. & CO., Ltd., and CHRISTIAN, D. A. July 9, 1947, No. 12669. [Class 35] [Also in Groups XXXIV and XXXIX] In an automatic selector switch of the type individually driven by an electromotor, the rotor is brought to rest at the end of the setting movement by a magnetic braking device which acts at a time when the stator of the electromotor is exerting little or no driving torque on the rotor. In Fig. 1, a rotor R, a cam K, a braking switch wiper W and the armature of the braking device AR are securely attached to a shaft DS which also drives a wiper shaft through gearing G. With the rotor R in the position shown, winding I of driving electromagnet N, relay NR and relay CM are energized when relay A (not shown) responds to each incoming impulse, the relay CM ensuring that the circuit to winding 1 of the driving electromagnet M is held open when the cam K moves away. The electromagnet N and relay NR are locked up over winding II of N. Rotation of the shaft DS through 90 degrees due to the energization of N mechanically operates contacts CNS, thus energizing the relay CN and brings the wiper W to the next contact segment WS, thus energizing the coil BW via contact ring WF and attracting the ends of the flexible armature AR to the pole BF to provide friction braking. An air gap BG ensures quick release. In the embodiment, Fig. 4 (not shown), a permanent magnet PM which attracts the armature for braking purposes is neutralized during rotation by a coil energized over intermediate contact segments of the braking switch. In a third embodiment, Fig. 5 (not shown), four portions of the pole face BF are cut away so as to leave four isolated braking pole faces corresponding to the positions in which stopping is required and the braking is effected alternately by one of two coils wound to give opposite directions of magnetization. The reversals are retarded by a copper collar which enables the brake armature to move clear of its last braking polepiece before the reversed magnetization becomes effective.