A drift model of a strapdown electrostatic gyro and identification of its parameters

A.P.Buravlyov, B.Ye.Landau, S.L.Levin, S.G.Romanenko

Central Scientific and Research Institute “Elektropribor”

30 Malaya Posadskaya Str., St.Petersburg 197046, Russia

Introduction

The increase in accuracy of strapdown gyro systems for marine, ground, aviation and space applications has motivated the need for the most precise of the currently available sensors - electrostatically suspended gyros with a spherical rotor (ESG). This type of gyro complies with the idea of a classical free balanced gyro most.

Electrostatic gyros were designed and are in operation only in the USA, Russia and France. The first hollow-rotor ESGs intended for gimbaled systems proved to be highly accurate, the residual drift after auto-compensation and algorithmic compensation not exceeding 10^-4-10^-5 deg/h. More recently, the companies engaged in gyro development switched to the solid- and hollow-rotor ESGs for strapdown gyro systems.

The creation of strapdown ESGs called for further investigation and solution of a number of fundamentally new problems, the most sophisticated being as follows:

- Development of a gyro drift model for the subsequent algorithmic compensation for its errors;

- Development of a rotor readout system – a system capable of circular reading the information about the angular position of the rotor relative to the gyro case-fixed coordinate system in an unlimited angle range and an error model for this system, methods and procedures for identification of its parameters.

The equations given in paper formed the basis for the program of gyro motion simulation that takes into consideration different initial conditions.

Experimental and simulated relations for the polar, equatorial and vertical orientations of one of the gyros for the same drift model coefficients are presented. The differential process is of deterministic character and includes the following components: a constant component, growing in time, harmonic components with the frequencies multiple of the gyro precession motion frequency, and a white-noise component. The latter is mainly caused by the noises of the angular readout system, while the rest of them – by incompleteness of the drift model and errors in calculating model coefficients.

The calculated value of uncompensated drift determined from the differential values is . At the same time the potential accuracy of the gyro (estimated by the value of the average rate of equilibrium position change in 240 hr tests in the polar orientation) is that is substantially less than the estimation given above.

The further increase in accuracy by algorithmic drift compensation is made possible by:

- refining the gyro drift model;

- increasing the accuracy of the drift model coefficients identification;

- decreasing the errors of the rotor readout system.

When used in space conditions, the ESG can show the decrease in drift by two orders by:

- decreasing the reference voltage because of the extremely low level of effective accelerations;

- 15-fold reduction of the spacecraft orbital motion period as compared to the terrestrial conditions.

In conclusion it should be noted that the analysis of the contactless gyro behavior under the effect of error torques of a particular physical nature has been the subject matter of domestic and foreign researchers for a few decades. It can be said with confidence that the ESG under consideration is quite close in its characteristics to a free gyro and its behavior satisfies the general theory and physical concept and nature of effective forces to a high degree of certainty.