Patent GB-461424-A (GB)
Title: Improvements relating to gyroscopic compasses
IPC: G01C19/38
Filed: 1935-05-15
Abstract: 461,424. Gyroscopic compasses. SPERRY GYROSCOPE CO., Ltd., HARDING, W. G., and NISBET, R. H. May 15, 1935, No. 14255. [Class 97 (iii)] A device for correcting the reading of a gyro compass or repeater for speed and course error comprises a mechanical calculator of the formula tan E = S cos C/V cos L + S sin C where E is the error, C the course angle and S the speed of the ship, V the surface speed at the equator due to the earth's rotation, and L the latitude of the ship. The adjustment of the device for the speed S and latitude L is effected manually or automatically and the adjustment for C automatically from the relative movement of parts of the compass during changes of course. In the diagram, Fig. 2, the vector OC represents the ship's velocity due to the earth's rotation and the vector CP the velocity due to the ship's speed over the earth, so that the angle COP represents the speed and course error. In the two embodiments shown in Figs. 3 and 7, the triangle OCP is mechanically reproduced, the side OC being, however, of fixed length and the side CP proportional to S/V cos L. The correction angle COP is applied as a rotation of the lubber ring. In Fig. 3, 3 is the rotor casing and 4 the vertical ring suspended at 5 from a stem 6 which carries the phantom ring 7, compass card 11, and azimuth gear 9 and is supported in bearings 2-2 in the main frame 1. The compass card is read opposite a lubber mark on the lubber ring 13 which rests on the rim of the frame 1 and is rotatably mounted in bearings 14. The fixed distance OC is represented on the lubber ring 13 by the distance from the vertical axis of the compass to the axis of a shaft 27 rotatably mounted in the ring 13. The shaft 27 carries a gear-wheel 30 with a depending diametrical flange 30<11> on which slides a carriage 35 having a toothed rack 37 and a pin 36 representing the point P. The pin 36 may be moved from the axis C of the shaft 27 by rotation of a spindle 39 which is journalled in the shaft 27 and carries a gear-wheel 38 engaging the rack 37. The rotation of the spindle 39 necessary to bring the distance CP to the value S/V cos L is indicated by speed and and latitude graduations on a disc 28 on the shaft 27 which is viewed through a window in a disc 40 at the top of the spindle 39. The gear 30 is driven from an equal gear 31 fixed to the azimuth gear 9 by means of an idler gear 32 on a shaft 33 journalled in the lubber ring so that the rotation of the gear 30 relative to the ring 13 equals the rotation of the gear 31 relative to the ring 13, i.e. the course angle of the ship. The pin P slides in a radial slot in a bracket 46 fixed to the frame 1 so that the lubber ring 13 is pushed round to maintain the angle between the line OC on the lubber ring and the line of the slot, viz. OP, equal to the error angle. In the form shown in Fig. 7, the vertical axis of the compass represents the point C and the point P is represented by the centre of a circular cam 49 with bosses 50, 51, 52. A guide rod 53 fixed to the compass card 11 passes through bores in the bosses 50, 51 and a threaded rod 59 rotatably mounted in the compass card engages a threaded bore in the boss 52 so that by rotating the rod 59 by means of gearing 61, 62, and a knob 60, the distance of the cam 49 from the central axis may be varied. A rack bar 64 fixed to the cam 49 engages a toothed sector 65 to which is fixed an arm 67 graduated in terms of latitude and moving over a plate 68 marked with speed curves so that the distance CP may be accurately set. The point O is represented at the periphery of the lubber ring 13 by the pivot axis of a lever 74 which has a rectangular aperture with sides 77, 78 engaging the cam 49 through the intermediary of shoes 79, 80, one of which may have a spring-pressed face. The axis of the lever 74, representing the side OP, is thus caused to rotate relatively to the side OC fixed in the lubber ring 13 through the error angle. The lubber ring 13 is caused to rotate through the error angle by the engagement of a toothed sector 89 on the lever 74 with a gear-wheel 90 and toothed sector 95 which is normally fixed to the main frame 1, but may be angularly adjusted to correct the latitude damping error by an arm 102 moved by the tangent screw 99 through angles indicated by the scale 97. In a modification, the correction angle may be introduced as a relative movement between the phantom ring and the azimuth gear as described in Specification 433,494. Specification 15679 /11, [Class 97 (iii)], also is referred to.