Comparative Research On Fast North-finding Algorithm For Constant-rate Biased Ring Laser Gyroscope North-finder

Research on high precision north- finder technology plays an important role in the civil and military areas. With the development of ring laser gyroscope(RLG) technology, manufacture of high precision north- finder based on RLG has been possible. Rotation- modulation constant-rate biased RLG north-finding scheme avoids the influence of random walk error caused by “rapidly-crossing lock-in” method in dither RLG, improving the precision and rapid convergence observably. Domestic scholars have made some progress on the research of rotation- modulation constant-rate biased RLG north-finding system of 3-gyros and 3-accelerations, successfully developing north-finding prototypes. But in the respect of reducing cost, research on the feasibility and limitation of rotation- modulation constant-rate biased RLG north-finding system of 1-gyro and 1-acceleration has an importance significant.The advantage of north- finder of 1 or 2-gyros and 1- acceleration is lower cost. And the weakness is that the precision is limited because of measurement information reducing, and on the other hand with the poor anti disturbance capacity, the SINS is generally used under the conditions of static base. The study object of this paper is high precision north- finder based on constant-rate biased RLG which is independently made by inertial technology lab. The north- finding scheme of d ummy gyro, asynchronism multi-position measurement with 1 or 2 gyros based on Kalman filter is proposed, and error characteristics is analysed. According to the fast convergence degree, the Kalman filter rapid convergence is analysed, and the practice experiment is done to validate the analysis. A north- finding with 1, 2, or 3 gyros algorithm based on sinusoid orthogonal detection technology is proposed. It is directly explained that d ue to the coning movement, the periodic instability of the shaft rate and angle measurement error of the turntable, azimuth sensitive error will be introduce into the north-finding results and influences heading angle accuracy of 1 or 2 gyros north- finder. The azimuth sensitive error is measured by the practice experiment to analyse the produce reason and error effect degree quantificationally.Main researches are as the follows:1. The error propagation property of constant-rate biased RLG north- finder is analysed, based on the math model of the north- finder and the state equation of 12 states. The north-finding algorithm of Kalman filter under constant-rate biased state is introduced, and the rapid convergence is analysed. On the basis of above content, the 1 or 2 gyros north-finding algorithms is studied.2. Dummy gyro north- finding algorithm with single gyro is introduced. The IMU of this algorithm is made up of single gyro and single acceleration, and the other 2 gyros and 2 accelerations are replaced by dummy gyro a nd acceleration. With this IMU of 3-gyros and 3-accelerations, the improved Kalman filter can be used to seek north.3. Asynchronism multi-position measurement north- finding algorithm is introduced. It’s analysed that how the periodic error of the shaft rate effect the results of asynchronism multi-position measurement north-finding algorithm. Using the fast convergence degree, the Kalman filter rapid convergence is analysed. The cost of SINS with 1 or 2 gyros and 1-acceleration come down. Because of measure information reducing, the precision fall down compared with the 3-gyros north-finding algorithm on chapter 2, and it can be used in low precision field.4. A north- finding algorithm based on sinusoid orthogonal detection technology is proposed. A single-axis continuous rotation gyroscopic north- finder is studied. Due to the coning movement, the periodic instability of the shaft rate and angle measurement error of the turntable, azimuth sensitive error will be introduced into the north-finding result and influences heading angle accuracy greatly when using orthogonal detection technology. According to theoretical analysis and practical tests, it is concluded that north-finding algorithm utilizing single or two gyroscopes cannot compensate the azimuth sensitive error completely, however the azimuth sensitive error can be compensated completely when utilizing three gyroscopes. Experiments are done on an independently designed constant-rate biased RLG north- finder on stationary base to validate the proposed algorithm.