Patent GB-631794-A (GB)
Title: Improvements in gyroscopic instruments
IPC: G01C19/36
Filed: 1944-01-19
Abstract: 631,794. Gyroscopic apparatus. SPERRY GYROSCOPE CO., Inc. Jan. 19, 1944, Nos. 1085, 1086 and 1087. Convention dates, Jan. 19, 1943. [Class 97 (iii)] [Also in Group XXXV] A gyroscope is precessed by a torque exerting device to correct, automatically, variations in relative angular position of a frame of the gyroscope and a controlling member, the torque exerting device being controlled through a heat responsive arrangement. In Fig. 1, the rotor-bearing case 41 of a gyromagnetic compass is mounted on trunnions 42, 43 for movement about a horizontal axis within a gimbal ring 31 mounted for movement about a vertical axis within a case 40. Compass card 34 is operated through crown and bevel gears 37, 38. Air drawn through filter 50, passage 52 and hollow trunnion 43 by suction means attached to outlet 49 spins the gyro rotor (not shown) which is of the non-inductive type described in Specification 574,848 and is mounted within case 41 with its axis perpendicular to that of case 41 and, normally, horizontal. Exhaust air leaves case 41 through nozzles 60, 61, the reaction torques of which about the axis of case 41 are normally equal and opposite. A compass magnet 63 acting as azimuth standard controlling the gyro has a vane 66, Fig. 5, attached, which normally allows equal air flow, adjustable by valve 71, through nozzles 68, 69, in the top of case 41, which are small and close to the axis of case 41 so that reaction effects are negligible. Air from the interior of case 41 to nozzles 68, 69 passes through separate passages 72, 73, respectively in which are mounted electrically heated wires 81, 80, having a high coefficient of expansion, attached to pivoted vanes 87, 85 controlling the openings of nozzles 61, 60. The arrangement is such that relative movement between magnet 63 and case 41 is corrected by the resulting unequal flow of air over wires 80, 81 the changes in length of which move vanes 85, 87 to unbalance the reaction effects of nozzles 60, 61 and thus produce the correcting torque about the axis of case 41 which precesses the gyro. In a modification, Fig. 11, the heated wires 103, 104 control the position of weights 90, 91 to apply correcting torque to the rotor bearing case gravitationally, the air passing over the wires being controlled by a vane 101 attached to magnet 63 co-operating with nozzles in the top of case 41 which give no resultant reaction effect. Magnet 63 is shielded from the nozzles by shield 100. In a modification, Fig. 13, the rotor-bearing case 24 of a gyro compass, which may be controlled by a magnet compass, is mounted as in Fig. 1 but the rotor is spun electrically by a three-phase squirrel-cage induction motor (not shown). A two-phase reversible torque motor 34 having its wound rotor 35 attached to gimbal ring 21 and its inductive stator 36 attached to case 20 applies torque about the vertical axis to correct tilt of case 24 about its horizontal axis. An electrically heated wire 46, Fig. 21, mounted in a reflector 42 attached to a lug 43 on case 24 moves, on tilt of case 24, relatively to a bimetallic snap action changeover switch 41 mounted on gimbal 21. Operation of switch 41 by heat radiated by reflector 42 reverses the torque motor by reyersal of one phase of its supply and the arrangement is such that the gyro rotor is maintained horizontal as in Fig. 13 with the top of reflector 42 opposite switch 41. Construction of the bimetallic switch 41 which is compensated for ambient temperature changes is described. In a modification, Fig. 23 (not shown), similar to that of Fig. 13, the heat radiator-bimetallic switch combination is replaced by a drum 50, Fig. 24, mounted on a trunnion 25 of the rotorbearing case, which is filled with two liquids of different specific gravity and heat conductivity, e.g. oil and air, arranged so that tilt of the case immerses one or other of two electricallyheated resistors 42, 43, of high temperature coefficient, in a fluid of different heat conductivity thereby unbalancing an A.C. Wheatstone bridge the output of which supplies one phase of the correcting torque motor. In a further modification a bridge arrangement is also employed but the temperature variable resistors 58, 59, Fig. 27, are mounted on an insulating disc 55 arranged to tilt with the rotor-bearing case and move relatively to a heat shield 57 which unbalances the bridge when, through tilt, it is not symmetrical with respect to the common junction 60 of the resistors. In this arrangement the controlled phase of the correcting torque motor is centretapped to provide the other arms of the bridge. In the final application, Fig. 30, to the erection control of the gyro vertical of an artificial horizon instrument, a rotor-bearing case 69 is mounted for movement about an athwartship axis within a ring 66 mounted for movement about a fore-and-aft axis within case 65. Torque motors 72, 73 correct tilt of case 69 about the athwartship and fore-and-aft axes respectively. These motors are controlled after the manner of Fig. 24, four sets of resistors 76, 77, 78, 79, Fig. 31, being mounted in grooves in the cover 80 of a cup-shaped member 89 fixed to the underside of case 69. Member 89 contains a fluid on the surface of which is a bubble of a fluid of different heat conductivity. Tilt of the case about either axis causes the bubble to move relative to one or other of the pairs of resistances 76, 77 and 78, 79 associated with two Wheatstone bridge circuits controlling the respective torque motors.