Patent GB-885947-A (GB)
Title: Gyro-compass
Inventor: CAMPBELL MARK ERVIN
IPC: G01C19/38
Filed: 1960-10-24
Abstract: 885,947. Gyroscopic apparatus. NORTH AMERICAN AVIATION Inc. Oct. 24, 1960, No. 36381/60. Class 97(3). A gyrocompass comprises a rotor 20 soinning about axis 21 in a gimbal 24 which is rotatably mounted about an output axis 50 in a case 29 which is itself pivoted about an input axis 15 in a frame 35 the arrangement being such that when the rate of rotation of the case 29 relative to frame 35 about the input axis 15, due to the rotation of 'the earth, is zero the axis 15 is accurately aligned with the E-W direction. Such a gyrocompass may have a mirror 68 on axis 15 on which an optical instrument is sighted as in Specification 885,946. To set up the gyrocompass, screws 44-46 are adjusted so that axis 36 is vertical as shown by levels 47, 48. A "coarse bias adjustment" is then made by moving switch 26 to position 1 and thus energizing all portions of the gyrocompass except the rotor 20, whose motor 25 is supplied with three-phase current from source A, B, C, two of the phases passing through switch levels 26c and 26d respectively. Direct current from source 65, adjusted by potentiometer 66 is fed to torquer 67 acting about output axis 50 and is so arranged that a recorder 59 gives a null indication, the recorder 59 being acted on by a signal which originates from a power supply 51, pick-off 49, amplifier 52 and demodulator 53 and is thus indicative of the displacement of gimbal 24 with respect to case 29. In this condition the torque exerted by torquer 67 balances the internal torques acting on axis 50 due to fluid forces, electrical conductors, magnetic fields and the like. During this adjustment a pin 75 locks the case 29 in a vertical position. Next, the switch 26 is moved to position 2 so that the rotor 20 is energized and the signal from pick-off 49 and demodulator 53 is fed to a torquer 54 acting on case 29 about axis 15 whilst the signal from demodulator 58 and pick-off 55, indicating the displacement of case 29 with respect to frame 35, is fed to recorder 59. The screw 42 is actuated to adjust frame 35 in increments about axis 36 until recorder 59 shows no change in angular displacement between case 29 and frame 35. Axis 15 is then approximately E-W. Account must now be taken, of. the error torques acting when the rotor 20 is energized e.g. those caused by vibration and thermal changes and this is done by modulating the rotor velocity, conveniently by changing its direction of rotation. So with switch 26 in position 3 and thus rotor 20 spinning in one direction, a potentiometer 70 is controlled to adjust the supply from a direct current source 69 to torquer 67 until recorder 59 shows zero change in rotational displacement of case 29 relative to frame 35. The position of potentiometer 70 is noted. Switch 26 is then moved to position 4 so that through switch levels 26c, 26d the rotor 20 is caused to rotate in the opposite direction and potentiometer 70 again adjusted and its position noted. On setting the potentiometer 70 to the average of the two positions the error torques are cancelled out. Screw 42 is finally adjusted until recorder 59 detects no change and axis 15 is then accurately E-W. To determine latitude the gyro case is rotated through exactly 90 degrees in azimuth and the new setting required on potentiometer 70 to achieve zero relative rate of rotation of the case 29 relative to the frame 35 is determined, the current being proportional to the cosine of the latitude.