Patent GB-1150324-A (GB)
Title: Compensating Errors in Gyroscopic Apparatus
IPC: G01C19/14
Filed: 1966-07-06
Abstract: 1,150,324. Gyroscopic apparatus. SPERRY RAND CORP. July 6, 1966 [July 21, 1965], No. 30329/66. Heading G1C. A gyroscope comprises a housing rotated about an axis A-A by a motor 30, and having a central cavity 19 containing a fluid which forms the gyro-rotor and is spun by the housing, angular differences between the spin axes of the fluid and the housing being detected by differential pressure transducers 11, 12 which communicate with the cavity 19 by way of ports 17, 18, 20, 21 and passages 13, 14, 15, 16 arranged in the form of a figure 8 for each transducer. This particular arrangement of the passages is designed to substantially eliminate or reduce spurious pressures caused by angular acceleration of the gyroscope or angular vibration at twice spin frequency. It is described in the Specification how the passages may be so dimensioned and arranged to substantially eliminate either of these particular sources of error, and in each case the effects of the other of the two errors will be reduced. In a described embodiment angular acceleration errors are eliminated by passage design and angular vibration at twice spin frequency subsequently eliminated using electronic circuitry. Each of the pressure transducers 11, 12 comprises a central diaphragm with an electrode on each side and functions as a capacitive microphone. The two stator electrodes of the transducer are fed with an alternating voltage at a frequency of e.g. 10 kc/s by way of a rotary transformer 35. If an angular difference between the axis A-A and that of spin of the fluid in the cavity 19 is present, then the pressure differences at the ports 17, 18 and 20, 21 will give rise to an output signal at the diaphragm of the pressure transducer which will be the carrier input frequency modulated at the spin frequency of the housing. This signal is picked-off by way of a rotary transformer 36. In the described embodiment two further pressure transducers are arranged at 90 degrees to the transducers 11, 12 and are fed with the input carrier frequency in quadrature phase using an R-C network. The outputs of all four transducers are summed and applied to the rotor 40 of the rotary transformer 36. The variations in the amplitue of the 0 degrees angle phase of the carrier frequency voltage are representative of the sum of the pressure variations acting on the transducers 11, 12, while the variations in the amplitude of the 90 degrees angle phase of the reference voltage are representative of the sum of the pressure variations acting the two transducers at 90 degrees to the transducers 11, 12. The signals from the transformer 36 are demodulated giving rise to two signals varying at spin frequency and relatively in quadrature phase. The phase rotation will have one sense for a steady input and the opposite sense for the undesirable output resulting from an angular vibration at twice spin frequency. This undesirable output can thus be eliminated by use of a suitable summing network D.C. output signals are than obtained by comparison of the signals from the summing network with those from a reference voltage generator 41. Errors may also be introduced due to modulation of the carrier frequency by the rotary transformers due to variation of the coupling coefficient between stator and rotor with angle, or of input impedance with angle. These errors are eliminated by use of a further coil in the rotary transformer stator coupled to a bridge network controlling the current in yet another rotary transformer coil generating an M.M.F. which cancels the effect of the required error voltage.