Research On Attitude Measurement Systems Based On Hemispherical Resonator Gyro

Hemispherical resonance gyroscope (HRG) is very suitable to be used in long-term working occasions such as space vehicles due to the high accuracy andreliability, good impact and radiation resistance properties, as well as long life.Hence, the design of long life attitude measurement systems is of great significanceto the development of space technology, especially to the engineer construction ofsatellites in China. In order to develop a high performance attitude measurementsystem, this thesis researches several key technologies of restricting theperformance improvement of attitude measurement systems, including the gyrodrift mechanism and the drift compensation technology of HRG, the initialalignment technology of inertial measurement systems, and the technology ofintegrated attitude measurement systems based on HRG and star sensors. The maincontents of this thesis are as follows:The biggest error source of attitude measurement systems is the drift of HRGin the level of inertial instruments, so the most efficient way for improving thesystem performance is to explore the mechanism, modeling and compensation ofparameter drift. Two error sources of gyro drift are studied in the thesis and theresearch are focused on the following two parts: The influence of gyro’s structureerrors to its performance is studied. Since structure errors induce gyro drift byaffecting the vibration detecting system, the structure of pickoff and the capacitorgap is analyzed firstly, and a simulation model of the HRG’s vibration detectingsystem is built by incorporating the deformation dynamic equation of the resonatorin second-order free resonant condition. And a simulation model of the forcingsystem is also obtained by analyzing the dynamic characteristics of the resonator inthe action of multiple electrodes and the coupling between the amplitude controlsystem and the precession angle control system. Then, a compensation method forcalibratable errors and a quantitative evaluation model for uncalibratable errors areproposed, respectively, by simulation research, and this provides theoretical basisfor the determination of machining and assembly accuracy indexes. The driftmechanism of HRG under accumulation is studied. The analytical form of theresonator’s deformation under low frequency accumulation is obtained by solving its dynamic equation firstly. Then, the influence of the deformation to the vibrationdetecting system and the forcing system is analyzed. Finally, a vibration detectingscheme and a resonator exciting scheme are proposed, respectively, which canweaken the influence of accumulation greatly. Additionally, a static error model ofdrift caused by accumulation is founded, which is verified by rolling experiment ofHRG in gravitational field. And some improvement measures for gyro machiningand assembly are provided by analyzing the residual error of test data.In order to improve the alignment accuracy of the system and shorten thealigning time, the initial alignment problem of stationary base with large azimuthmisalignment angles is researched and an initial alignment approach based onGauss-Hermite Filter (GHF) is proposed in the level of inertial attitudemeasurement system. Then, the multi-variable nonlinear Gauss integration of themean and the covariance is addressed. Since the nonlinearity of the alignment errorequation is induced by a large azimuth misalignment angle, the so called“dimension problem” in the application of GHF to alignment is solved without lossof accuracy, by converting multi-variable integration to single variable integration.The proposed alignment approach is applied to a practical system lastly, and thealignment accuracy under a large azimuth misalignment angle condition isimproved and the aligning time is decreased, compared with Extended KalmanFilter (EKF) and Unscented Kalman Filter (UKF).An integrated attitude measurement system based on HRG and a star sensor isdeveloped in the level of integrated systems. A method of fast star patternrecognition is proposed firstly, and both a construction form and a filteringapproach of tightly-coupled integrated systems are given, in order to solve the datefusion problem in the case where the number of navigation stars is smaller thanthree in loosely-coupled integrated systems. Then, the integrated system is tested,and the result implies that the tightly-coupled integrated systems can solve thisproblem well, and hence enhances the adaptability for celestial sphere field.At last, all the above technologies are applied to an engineering prototype ofthe attitude measurement system based on HRG. The prototype is tested by a semi-physical simulation platform whose primary component is a three-axis turntable,and the test result shows that the accuracy, adaptability and reliability of theprototype are improved greatly. Especially, its accuracy attains the usage standard of high precision satellite attitude control systems.