Nonorthogonality of mean platform frame for Electrostatically Supported Gyro on turntable

Case rotational auto-compensation is an effective technique to enhance the accuracy of Electrostatically Supported Gyro (ESG). However, the usage of such technique will introduce additional case rotational signal in the measured readout when ESG is tested on servo turntable. To accurately identify the constant and random drift coefficients of ESG, it is necessary to smooth the measured readout by filtering the case rotational signal. More importantly, one should check whether or not the mean platform frame is orthogonal after smoothing the readout, because nonorthogonality could introduce errors and therefore degrade the estimation precision of ESG's drift model. In this paper, we propose a framework to check the nonorthogonality of mean platform frame for electrostatically supported gyro on turntable. Specifically, we firstly formulate the mean platform frame by measured readout and analyze the orthogonality of the frame by checking if the dot product of the three axes of the frame is equal to zero. We find that nonorthogonality is mainly determined by case mis-alignment angle between the case rotational axis and momentum axis of ESG. Furthermore, we carry out some numerical study to characterize the relationship between case mis-alignment angle and the accuracy of gyro drift coefficient identification. Our simulation result shows that the magnitude of case mis-alignment angle will affect the identification accuracy of drift coefficient of ESG, which may imply the dependence between nonorthogonality and the identification accuracy.