Litton Systems, Inc.

Daniel T Zaida

John Christopher Baker

Gregory M Johnson

Patrick A Toole

A vibratory sensor with a resonator for measuring angular rotation, such as for example a hemispherical resonator gyroscope (HRG) operating in force rebalance mode, includes circuitry to generate a virtual node and antinode in the resonator standing wave. Shifting a pair of pickoff electrodes from a position directly over an actual node in the HRG standing wave to an offset position where the primary and secondary harmonic contributions at the first pickoff electrode are equal to the primary and secondary harmonic contributions at the second pickoff electrode permits the elimination of secondary harmonics contribution. A virtual node is created by offsetting a pair of pickoff electrodes 22.5 degrees from the actual antinode such that each pickoff electrode includes an equal contribution of the secondary harmonic signal present in the standing wave. Differencing the two signals eliminates both the primary signal contribution as well as the secondary harmonic signal contribution, thereby reducing the signal below the actual node signal. The virtual node can then be amplified to a greater extent without the filtering and shifting that is ordinarily required of the signal processing at the actual node. While the virtual antinode includes contributions of the secondary harmonic signal at both pickoff electrodes, the peak amplitude of the secondary harmonic is typically only one percent of the primary vibration pattern and does not adversely affect the processing of the virtual antinode. Using a circuit which adds and differences the two inputs requires only two additional buffers and results in a vibratory sensor with significantly better accuracy.

Vibratory sensor with virtual node/antinode correction of secondary harmonics

A time based digital to analog converter is presented in which known reference voltages are used to create variable period waveforms which, when combined according to a desired computation, can convert digital words into a sinusoidal signal of a precision variable. To illustrate the application of the present invention, a hemispherical resonator gyroscope (HRG) operating in force rebalance is presented wherein a time based digital to analog converter with a variable period output controls the HRG electronics in nulling the standing wave. A rate of the standing wave is calculated, and a software component calculates the fraction of the maximum rate needed to oppose and null the initial rate of the standing wave. The fraction of the maximum rate is converted to digital words corresponding to the number of periods of a clock connected to the circuit. Using the digital words thus determined, a gate array using digital logic generates waveforms having variable periods, where the amplitude of the waveforms correspond to fixed reference voltage sources, and the period of the waveforms are determined by the digital words in the earlier calculation. Using the waveforms, the HRG rate controls can be maintained at a high level of precision.

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Goleta, CA, United States of America

Daniel T Zaida