Patent GB-460491-A (GB)
Abstract: 460,491. Gyro - magnetic compasses. ALKAN, R. June 12, 1936, No. 16427. Convention date, July 30, 1935. [Classes 97 (ii) and 97 (iii)] A gyro-magnetic compass is provided with follow-up mechanism adapted to drive the bowl of the magnetic element, cam-operated means for compensating for the deviation of the magnetic element, and repeating mechanism. As shown, the gyro casing 4, Fig. 1, carries a solenoid coil 5 coaxial with the rotor and pivots on a horizontal axis 10 in a vertical ring 3 carrying a compass card 2 and a pair of solenoid coils 6, 13 coaxial with the vertical axis of the ring 3. The coils 6, 13 which are supplied with current under the control of the magnetic compass, co-operate with the coil 5, which, together with the electrically driven rotor, is supplied with current through the gimbal pivots, as described in Specification 441,439, to provide a torque about the horizontal axis causing the gyro to process into alignment with the magnetic compass. The rotor axis is maintained in the horizontal plane by erecting torques provided by jets 8 which are supplied with air by a centrifugal fan comprising vanes 11 on the rotor and are differentially obscured by screens 7, 9 fixed to the vertical ring 3 when the rotor axis tilts. Rollers 15 on arms 14 fixed to the ring 3 co-operate with two insulated conducting half rings on a disc 16 to control a follow-up motor which drives a shaft 21 through gearing 22, 23. The disc 16 may be caused to follow the gyro by being directly connected to the shaft 21 but preferably it is given a small permanent oscillation relative to the shaft 21 by a lever 19 rocked by a return spring 17 and cam 18 driven through gearing 20 by an auxiliary motor 34, as described in Specification 458,090, [Group XXXV]. The magnetic compass, Fig. 2, comprises magnets 48 secured to a float 47 which is connected to a vertical spindle 46 by a cardan suspension 49. The spindle 46 is supported by a bearing 50 at the bottom of the bowl 40 which is filled with damping liquid, and extends through a tube 37, which supports a diaphragm 39 dividing the bowl into two compartments communicating through the annulus passage 45, to an upper bearing 35 in the free air. To the upper end of the spindle 46 is fixed a pointer 43 with flexible ends which are periodically clamped against a rail 42 formed of two semicircular insulated parts by a cylinder 44 surrounding the bowl 40 and intermittently given an axial movement by the lever 54. The latter is connected bv a link 51 to a lever 27, Fig. 1, rocked by a cam 29 geared at 24 to the auxiliary motor 34. Preferably, the pointer 43 is released between successive clampings for a time equal to one quarter of the period of the magnetic system. To avoid deterioration of the contacts 42, 43, which control the current to the coils 6, 13, Fig. 1, the circuit includes contacts 30, 31, which are closed and separated again by a cam 32 on the shaft of the cam 29 during the period that the pointer 43 is clamped. The contact rail 42 and compass bowl 40 are connected to the follow-up shaft 21 through a device which compensates for the errors and declination of the magnetic compass. A casing 63, Fig. 3, fixed to the shaft 21 but adjustable in accordance with the declination, carries on a horizontal trunnion a pinion 64 engaging a pinion 65 fixed to the compass bowl 40. A lever fixed to the pinion 64 terminates in a roller 66 resting on the edge of a drum cam 67 shaped according to the errors of the compass, the arrangement being such that the compass bowl 40 rotates with the shaft 21 except when the drum 67 rocks the lever and pinion 64 to modify the connection. The shaft 22, the rotation of which is proportional to the difference between the azimuth direction of the craft and the geographical north, may be connected through a differential gear 59, the intermediate shaft 58 of which may be adjusted to a set course as indicated on a dial, to a shaft 60, the rotations of which then indicate departures of the craft from a set course.