A proposed method of calibration of micromachined vibratory gyroscopes would make it unnecessary to test the gyroscopes at known rates of rotation. At present, calibration entails inertial tests in which the gyroscopes are exposed to tumble and rotation maneuvers on multiaxis precise rotation tables, which are expensive. By eliminating the need for the rotation tables, the proposed method could reduce the cost of calibration. Moreover, inasmuch as the number of gyroscopes that a rotation table can hold is limited, the elimination of the rotation tables method would make it possible to test more gyroscopes simultaneously.
The proposed method is based on the unique principle of operation of a micromachined vibratory microscope. This principle involves electrostatic excitation, capacitive sensing, and feedback control of vibrations of a microscopic body designed so that its vibrational modes are affected by the Coriolis force. One of the feedback control signals is a negative feedback signal for generating an electrostatic actuation force that compensates for the Coriolis force. In the proposed method, one would superimpose a simulated Coriolis-force signal on the electrostatic actuation signal.
Because signals representing the real and simulated Coriolis forces would be at the same frequency and phase, the gyroscope circuitry would respond to the simulated Coriolis force in the same way in which it would respond to the real Coriolis force. Hence, rotational testing would not be necessary because one could simply inject the simulated Coriolis-force signal into the feedback control loop to make the vibrations and the associated electronic signals behave as though the gyroscope were undergoing rotation.
The figure is a block diagram of an electronic system for implementing the method. The drive-motion excitation circuit would measure the drive motion (one of two vibratory motions involved in the basic principle of operation) and would provide an excitation force to sustain this motion. The sensing-motion closed loop would provide electrical damping of the sensing motion (the other vibratory motion involved in the basic principle of operation). The feedback control signal, τsense, would produce an electrostatic actuation force equal to the real Coriolis force plus the simulated (rotation-simulating) Coriolis force. The demodulation circuit would demodulate a sensing-motion force-rebalancing signal with the drive-motion signal to generate a signal proportional to the rate of rotation. During the simulation of rotation, the sensing-motion closed loop and the demodulation circuit would respond as though to a real rotation signal.
Of course, the value of this method of calibration would depend on the accuracy with which the simulated Coriolis-force signals could be made to duplicate the effects of the real Coriolis force. It would be necessary to perform conventional inertial calibration to verify the proposed method.
This work was done by Roman Gutierrez and Tony K. Tang of Caltech for NASA's Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
Technology Reporting Office, JPL, Mail Stop 122-116, 4800 Oak Grove Drive, Pasadena, CA 91109; (818) 354-2240.
Refer to NPO-20659
This Brief includes a Technical Support Package (TSP).
Non-Inertial Calibration of Vibratory Gyroscopes
(reference NPO20659) is currently available for download from the TSP library.
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