GB556287A - Improvements relating to electric follow-up mechanism - Google Patents

Abstract

556,287. Positional control systems. PRECISION DEVELOPMENTS CO., Ltd., and OLAH, G. April 29, 1942, No. 5727. [Class 40 (i)] [Also in Groups XXXIV and XXXVII] In a follow-up system, the servomotor is provided with an electromagnetic brake having a permanently energized winding normally applying the brake which is released by an opposing winding, or one of a pair of such windings in the case of a split field reversible motor, when the motor is started, the brake being controlled directly by the follow-up contacts. If the supply fails, the brake releases and the driven member, if spring biased, takes up an extreme position. In the arrangement shown in Fig. 2 the operating handle rotates shaft 6, sun-wheel 7, and planet gearing mounted on member 9 carrying a contact A1 into engagement with one or other of the fixed contacts C1, D2. The motor 1 rotates the controlled member, which may be a rudder shaft, and also the ring member 8 of the gearing which restores contact carrying member 9 to its normal position. The brake comprises pivoted arms B2, B3 normally urged against the shaft of the motor 1 by a permanently energized winding B, but contact member 9 connects an opposing winding BC or BD in parallel with field winding C3, D3 to release the brake. The motor may have a series shunt or compound field. Figs. 7 and 8 (not shown) comprise a modification using a follow-up switch described in Specification 556,288 but provided with a biasing spring to prevent undesired circuit connections. Fig. 9 (not shown) comprises a motor with a single field winding and a single " opposing " winding controlled by a combined follow-up and reversing switch also described in Specification 556,288. Brake construction, Figs. 4 and 5.-An extension 10 of the motor shaft carries a brake drum comprising a magnetic disc DM and friction discs DF1, DF2 of slightly larger diameter than DM to prevent reduction of the air-gap to zero and consequent adherence of the brake shoes due to remanent magnetism. The brake shoes BM of magnetic material carrying friction pads, not shown, are pivoted at P to members B4 forming part of the magnetic circuit carrying the windings B, BD, BC. The shoes are statically balanced on their pivots, slight bias towards the drums being' provided by springs SP. The friction pads may be of oil-impregnated porous metal or a mixture of graphite and metal whereas the discs DF1, 2 may be of non-metallic material such as phosphor bronze or an alloy of copper and nickel or beryllium. The friction surfaces may be bevelled or grooved.