Patent GB-682803-A (GB)
Abstract: 682,803. Electric repeater systems. BENDIX AVIATION CORPORATION. June 6, 1950 [July 14, 1949], No. 14128/50. Class 40 (i) [Also in Groups XIX and XXIV] Errors in a master indicator operating repeater indicators through Selsyn or like follow-up systems are compensated by driving each of the repeater indicators from its servo-motor through a mechanical linkage including a cam and follower mechanism which is preadjusted to effect the correction. The invention is described as applied to a repeater compass system wherein the master compass 10, Fig. 1; drives the master indicator 14 directly and, through a Selsyn system 18, 24, controls a two phase servo-motor 28 which drives a repeater indicator 32 through a compensator 29. The stator of the Selsyn receiver is adjusted through a knob 36 in accordance with the magnetic variation indicated by a pointer 34 and the cam in the compensator 29 is adjusted to compensate for magnetic deviation. Compensator construction. Fig. 2. The control motor 28 drives the repeater indicator 32 through gearing 42, 44 and shaft 52. The cam comprises a normally fixed annular spring 62 with which co-operates a follower roller 79 carried by a stirrup 80 pivoted to a sleeve 78 rigid with the gear 46. A rod 84 forming with the stirrup 80 a bellcrank lever passes through an elongated slot in the gear 46 into an anchorage hole 88 in the gear 44. The gears 44, 46 are connected by a biasing spring 90 which-through the bell-crank urges the follower roller 79 into engagement with the cam track, and also permits limited relative rotational movement with the cam track, and also permits limited relative rotational movement of the gears 44, 46. The motor 28 thus drives the repeater pointer 32 through gearing 42, 44 and shaft 52 but drives the Selsyn receiver rotor shaft 40 from the gear 44 through the cam and follower mechanism, gear 46 and pinion 48. The cam is carried coaxially with, and by a normally stationary gear 56 by means of screws 60 spaced angularly at 30 degree intervals around the gear, the screws being selectively rotatable in the gear 56 to adjust the cam 62 axially to effect the desired correction. This is effected by swinging the craft carrying the master compass successively through 30 degree intervals. At each such position of the craft the Selsyn receiver stator 22 is rotated through a corresponding angle manually by turning the knob 36. This rotates the gear 56 through gears 106, 108 into such a position that subsequent retraction of the knob 37 engages the pinion 68 thereon with one of the gears 64, 65, 66 &c. fixed to the appropriate screw 60. Rotation of the knob 37 then rotates the operative screw 60 to adjust the cam track 62 at the associated point until the indicator 32 reads the true heading. The screws 60 are adjusted successively in this manner in the successive 30 degree positions of the craft. A detent 76 co-operates with a toothed wheel 110 on shaft 100 and with the shaft 70 to ensure locking of the shaft 40 in each adiustment position. Finally, after the cam track has been adjusted at each of its twelve angularly spaced points the stator is adjusted in accordance with the variation error. A screw 114, and a split nut 120 thereon co-operate with a fixed plate 118 to prevent rotation of the receiver stator through more than 180 degrees either way, from a zero position.