Research On Inflencing Factors And Their Mechanism Of Accuracy And Rapidity For Constant-rate Biased Ring Laser Gyro North-finding System

Traditional pendulous gyroscope north-finder is generally only used in a fully stationary state. Although the accuracy of pendulous gyroscope north-finder is generally in a few arcseconds region, it takes up much time and behaves poor anti-disturbance performance. In recent years, advances in high-precision ring laser gyro technology and high-precision quartz flexible accelerometer technology have been achieved. Thus, the high-precision autonomous strapdown north-finding systems are increasingly become a hotspot in the field of inertial technology.Improveing the north-finding accuracy and shortening the reaction time are core tasks in the development of a north finding system. In order to meet the needs of high-precision and rapid north-finding, this paper focuses on inflencing factors and their mechanisms of accuracy and rapidity for continuous rotary north-finding system, which include gyro random errors, IMU rotation modulation schemes, system errors, and typical environments. Detailed analyses regarding corresponding engineering practical applications have been done, and simulations and practical tests have been carried out to verify the effectiveness of the proposed algorithms.1. An experimental method based on the fast orthogonal search algorithm for separating turntable dynamics and other periodic signals from the measurement output of the constant-rate biased ring laser gyro is proposed. By taking difference operation between random error records, turntable random errors are removed and the gyro noise error difference data record is extracted. Then, average angle random walk coefficient of the constant-rate biased ring laser gyro can be estimated effectively by reducing grouping interval of the resultant gyro noise error difference data record in Allan variance calculation. Practical tests have demonstrated that angle random walk error in the constant-rate biased ring laser gyro is smaller than that in the mechanically dithered ring laser gyro, which have laid the foundations for integrated design of the north-finding system and device selection.2. An analytic approach utilizing stochastic linear system theory is proposed. After establishing initial alignment Kalman filtering model for the north-finding system on stationary base, the concept of stochastic controllability can be used to perform quantitative analysis of the effects of gyro noise errors on the state estimation accuracy under turntable rotation condition, and observability degree based on the stochastic observability can be used to perform quantitative analysis of the effects of velocity measurement error, angular velocity measurement error and turntable rotation rate on state convergence rate. Practical tests are done on the single-axis contant-rate biased ring laser gyro north-finding postulate system, and the mechanism of north-finding accuracy is higher when utilizing the constant-rate biased ring laser gyro than utilizing the mechanically dithered ring laser gyro is revealed.3. An observation model with augmented linear measurement state is proposed. By analyzing error characteristics of the IMU measurement output in the azimuth continuous rotary north-finding system, a linear equality constraint is derived and used to improve the traditional initial alignment Kalman filtering model for the north-finding system on stationary base. Therefore, the azimuth estimation accuracy is improved and convergence rate is sped. Practical tests have been done on stationary base at fixed position. The experimental results show that, when the total alignment time is 600 s, the traditional filtering model has achieved a north-finding accuracy of 24.83 "(1σ), while the improved filtering model has achieved a north-finding accuracy of 6.78"(1σ).4. A mathematic model which treats the main system errors that have influences on the heading-sensitive error in stationary initial alignment as a whole was set up. Through analying the mechanism of the heading-sensitive error, the problem that system error parameters cannot be determined separately under field test conditions is overcome without external reference and removing device. The least square algorithm was carried out to compensate the heading-sensitive error online. Multi-position practical tests have been done on stationary base. When the total alignment time is 600 s and the improved filtering model is utilized and the tilting angle of north-finding system is within 3o, the north-finding accuracy is 16.19 "(1σ) without heading-sensitive error compensation, while the north-finding accuracy is 8.97"(1σ) with heading-sensitive error compensation.5. An observation noise covariance estimation method by residual velocity error sequences during initial alignment through a moving window is proposed. The decorrelation treatments to measurement information are made, and a measurement decorrelation modified velocity residual based adaptive filtering algorithm is derived. Compared with the standard Kalman filtering, the adaptive filtering algorithm does not need to predetermine the statistics characteristics of observation noise. The proposed method has improved engineering practicality and robustness of the north-finding system and has overcome the limitation of utilizing the standard Kalman filtering for initial alignment on rocking base effectively.