Research On Initial Alignment Technology Of Fog Strapdown Inertial Navigation System

Initial alignment technology is one of key technologies of SINS, which is a research focus in the field of inertial navigation at home and abroad. For the purpose of improving SINS initial alignment accuracy, this paper takes shipboard FOG SINS as the research object and divides the initial alignment process into two stages:coarse alignment and fine alignment. According to the size of initial misalignment angle, a comparative study of fine alignment based on SINS linear error model and nonlinear error model respectively is implemented.Firstly, the SINS coarse alignment technology is studied. The principles of analytic coarse alignment, inertial-frame coarse alignment, solidification-method coarse alignment and quaternion-method alignment are presented. Then the error equations and the application conditions of these methods are deduced and analyzed. Finally, the simulation experiment results verify the effectiveness of these methods in the corresponding environment.Secondly, the SINS fine alignment technology with small misalignment angle is studied. SINS linear error model is introduced. Then the gyrocompass alignment method based on classical feedback control theory, the parameter recognition alignment based on least-square estimation, and Kalman alignment are elaborated. In order to improve alignment speed and precision, the principles of fast least-square recognition, optimal double-position alignment and drift measurement and two-position Kalman alignment are derived in detail. Finally, the simulation experiment validates the correctness of these alignment methods, and the modified methods are really beneficial to improving alignment accuracy.Thirdly, the SINS fine alignment technology with large misalignment angle is studied. The SINS nonlinear error model based on Euler platform error angle is introduced. The EKF, UKF and CKF are deduced under the Bayesian filtering theory when the error state meets Gaussian distribution. Finally, the simulation experiment verifies the validity of the nonlinear error model, the performance of each filtering algorithm with large misalignment angle and the equivalence of Kalman filtering algorithm with small misalignment angle.Fourthly, FOG SINS initial alignment experiment based on Windows operation system. The multi-task programing theory and navigation platform with Windows are introduced. Then the conditions and contents of three-axis turntable experiment and vehicle experiment are stated. Finally, the FOG SINS real-time initial alignment experiment is implemented, and the experiment results verify the correctness and effectiveness of the designed methods.