Patent GB-1175863-A (GB)
Title: Improvements relating to meridian seeking instruments
Inventor: AMBROSINI LEONARD RALPH
IPC: G01C19/38
Filed: 1967-02-20
Abstract: 1,175,863. Gyroscopic apparatus. LEAR SIEGLER Inc. Feb. 20, 1967 [Feb. 23, 1966], No. 7960/67. Heading G1C. A meridian seeking gyroscopic instrument comprises a gyroscope unit 25 having a horizontal spin axis 27 and mounted in an inner casing 30 for angular movement about a vertical axis 16, the inner casing 30 being pendulously suspendedby a band 55 inside an outer casing 15, pick-offs 22 for providing an electrical signal proportional to the relative angular displacement between the casings 30, 15 from a reference position in which no torsional strain is imposed on the suspension band 55 the signals from the pick-offs 22 being used to control a servomotor 20 which rotates the outer casing 15 so that it is slowed to the movements of the inner casing, the rate of rotation of the motor being sensed by a generator 46 thus developing a signal proportional to the rate of rotation of the inner casing about the vertical axis 16, this signal being fed to a torquer 36 which generates a torque about the axis 16 opposing and damping the movement of the inner casing so that the spin axis 27 brings itself into alignment with the meridian with substantially zero velocity and zero overshoot. The outer casing 15 is mounted for rotation in bearings 12, 13, the motor 20 driving it through bevel gearing 17, 18. A caging piston 52, which may for example be actuated by a solenoid, may be released to engage a caging sent 51 on the outer casing 15 under the action of a spring 57 when it is desired to cage the gyroscope 25. The suspension band 55 is secured at its upper end to a disc 56 mounted in a cylinder 58 which is itself mounted in bearings 59 in the outer casing 15. If misalignment of the casings 15, 30 occurs during transport this may be corrected before subsequent use by connecting the output from the pick-offs 22 by way of a switch 68 to a motor 63 which, by way of bevel gearing 60, 62, rotates the cylinder 58 and disc 56 to bring the casings 30, 15 back into alignment. This calibration is effected with the gyroscope rotor at rest and when carried out the cylinder 58 is keyed in its set position and the motor 63 pivoted to separate the gears 60, 62. The motor 20 which slows the casing 15 to the inner casing 30 is mechanically coupled to the rate generator 46. The torquer 36 comprises two orthogonal annular coils, 37, 39, are inside the other, one, 39, being carried by an arm 41 on the outer casing 15, and the other being fixedly mounted on the inner casing 30. Electrical power for the gyro spin motor and the pick-offs 22 is conducted to the casing 30 by way of two semicircular spring bands 29 Symmetrically arranged about the vertical axis 16 and contained in a plane also containing this axis. The gyroscope is mounted in a shield 80 of mu metal to eliminate magnetic effects and the bearing races 83 for the rotor spin shaft 81 are carried by flexible diaphragms 84 which ensure that a constant load is applied to the rotor bearings in spite of temperature variations. The case 11 for the instrument is peferably carried by tripod legs in such a way that displacement of the case 11 does not cause displacement of the suspension point 8 of the band 55 and gyroscope unit 25.