Patent GB-1111456-A (GB)
Title: Inertial navigational and positional sytems
IPC: G01C19/56
Filed: 1965-07-14
Abstract: 1,111,456. Gyroscopic apparatus. LITTON INDUSTRIES Inc. July 14, 1965 [July 31, 1964], No.29963/65. Headings G1C and G1N. The attitude of, e. g. a vehicle, is determined by a vibrating rotor gyroscope mounted on the vehicle, associated with a pick-up, stationary with respect to the rotor, which senses vibration of the rotor when its spin axis is displaced by a change in attitude of the vehicle. The vibration signals are analyzed with respect to amplitude and phase to determine the magnitude and direction of the displacement. As shown, Fig. 1, a vibrating rotor gyroscope comprises an inertial ring 26 driven by rotor 18 of a synchronous motor 6 at a frequency N about a stationary shaft 12. The ring 26 is attached to the rotor 18 by torsion bars 28 and diaphragms 30 and vibrates about a horizontal axis when the assembly is displaced about a perpendicular horizontal axis, the frequency of vibration being its natural resonant frequency, which is adjusted to be equal to N. Vibration of the ring is detected by an electromagnetic sensor 40, attached to the stationary outer case 10 of the gyroscope, which comprises an E-shaped ferrite core whose central leg carries a coil 43 excited by an A. C. generator 44 of frequency much greater than N. The resulting A. C. fields in the outer legs are detected by coils 47. Vibration of the ring 26, which may be constructed wholly of a low reluctance material, e. g. iron or steel, or may be of titanium and surrounded by an iron or steel ring 32, changes the reluctance of the magnetic paths producing an output signal of the frequency of generator 46 which is amplitude modulated at a frequency of 2N. The output signal of the sensor 40 together with a signal from generator 44, is then fed to a demodulator 46, whose output signal of frequency 2N is transmitted through an amplifier 48, a filter 49, tuned to the frequency 2N, to a further demodulator 50, to which a timing signal is also fed, and which resolves the sensing signal into two components along two orthogonal axes, X, Y (defined subsequently). In a modification the sensor 40 may utilize a D. C. field generated by coupling a D. C. generator to the coil 43 or by having a permanent magnet as the central leg. The output signal of frequency 2N is then directly representative of the vibration of the ring and is fed to the demodulator 50, via amplifier 48 if necessary. The timing signal is generated by a sensor 51 comprising a C-shaped core mounted on the casing 10 which detects a circular ring 36, of low reluctance material, asymmetrically mounted on the bottom surface of a magnetic shield 24, rotating with the ring 26. A further screening disc 34 is provided between the ring 36 and shield 24. As the reluctance of the magnetic path of the sensor 51 changes between two maxima and two minima for one revolution of the ring 26, the timing signal thus generated has a frequency of 2N. By varying the position of the sensor 51 around the spin axis the two maxima (or minima) of the signal can be arranged to occur when the torsion bars 28 point in the direction of a case-reference orthogonal axis X or Y (defined subsequently). Alternatively the signal can be resolved into two components along two orthogonal axes which are brought into coincidence with the case-reference axes X, Y by shifting the phase of the signals. In the embodiment, the timing signal is fed into a phase shifter 54 which provides two signals, one shifted in phase by 90 degrees from the other. Alternatively two sensor devices may be employed, one displaced circumferential by 45 degrees from the other. The vibration of the ring is then nulled by applying torquing forces directly to the inertial ring 26. Two torquer arrangements 62, (64), see also Fig. 2 (not shown), are mounted on the case 10 and define the case-reference orthogonal axes X, Y. These arrangements comprise E- shaped ferrite cores, having D. C. energized coils wound round their central legs, or alternatively having permanent magnets as their central legs. The X and Y components of the sensing signal from the demodulator 50 are then transmitted through X and Y command consoles 74, 76, to windings arranged on the two outer legs of the torquer arrangements 62, (64). If the gyroscope is operated in an earthreferenced co-ordinate system, a large part of the output signal is due to the earth's rate. This is suppressed by introducing signals, e. g. from generators (112, 114), Fig. 3 (not shown), into the command consoles 74, 76 through terminals 75, 77. The gyroscope can be used as a gyrocompass, Fig. 4 (not shown), to indicate true north and the east-west rotation of the earth or, by combining two gyroscopes, arranged with their spin axes perpendicular, as an altitude indicator, Fig. 5 (not shown), in aircraft or finally for stabilizing a platform, Figs. 6, 7 (not shown).