Patent GB-1093550-A (GB)
Title: Gyroscopic inertial instruments and guidance systems
IPC: G01P9/04
Filed: 1966-05-20
Abstract: 1, 093, 550. Gyroscopic apparatus; accelerometers. LITTON INDUSTRIES Inc. May 20, 1966 [May 21, 1965], No.29232/67. Divided out of 1, 093, 549. Headings G1C and G1K. A gyroscopic inertial instrument comprises two inertial ring-like elements 26, 26' mounted for rotation on a common shaft 20 at a rotational frequency N by means of a synchrous motor 16, each of the elements 26, 26' being also mounted for vibratory motion at a frequency N about torsion bars 28, 28', the torsion bars 28 being orthogonal to the bars 28', and both sets of bars being orthogonal to the shaft 20. E-shaped sensors 40, 40' are positioned to detect the vibratory motions of the inertial elements 26, 26'. It is shown in the Specification that the equation of motion for the inertial elements demonstrates that the angular displacement of the element about its torsional oscillation axis is proportional to the rotational displacement of the shaft 20 multiplied by a cosine term representing the vibrations. This cosine term contains phase information which can be extracted by means of a timing signal to yield the angle between the axis of the rotational displacement of the shaft 20 and a fixed co-ordinate system in the gyroscope casing. In practice this timing signal is generated by a signal generator 51 positioned a slightly ellipsoidal member 36 on the shaft 20. Electronic circuitry is described which enables the required displacement information to be obtained. It has been found that spurious output signals can be derived from an inherent shaft wobble of the shaft 20 at a frequency 2N due to bearing tolerances. These are eliminated in the construction of Fig. 1 since the torsion bars 28, 28' are orthogonal so that the error signals from the two inertial elements 26, 26' are out of phase and cancel each other. When these instruments are used in an inertial guidance system the vibratory motion is nulled by torquing the platform back to its stabilized attitude. However, when mounted fixedly in an aircraft the vibratory motion must be nulled in order that the sensing signal can be utilized. Torquers 62, 62' are provided to effect this and these are fed back from the above mentioned electronic circuitry. It has also been found that if the centre of mass of one of the inertial elements 26, 26' is displaced slightly from the oscillation axis defined by the torsion bar 28 or 28', then linear acceleration along an axis orthogonal to the axis of the shaft 20 produces a moment on the inertial element causing vibration of the element about its torsional axis. This will produce a further term in the equation of motion of the element, which can be resolved by electronic circuitry as before, for example by comparing the signals generated by two inertial elements as 26, 26' with their torsion bars 28, 28' disposed parallel, and only one of which has its centre of mass displaced from the torsional oscillation axis. Various forms of inertial element are described which enable both angular displacement and linear acceleration terms to be resolved, and a complete inertial guidance system is described utilizing three orthogonally disposed inertial instruments of the type referred to above and serving to completely stabilize the platform.