The Arithmetic Of SINS Initial Alignment On Azimuth Rotation And Large Misalignment Angles

Inertial navigation system has the characteristic of self-alignment, the alignment precision directly influences the navigation accuracy and the alignment time affects the response rapidity. So the alignment precision and speed are the two important parameters in the initial alignment of strap-down inertial navigation system (SINS). To further enhance the navigation performance of SINS, the algorithms which can improve the SINS'initial alignment precision.and speed are studied.Because of the poor observability in the initial alignment procedure of SINS on stationary base, a new alignment method of azimuth rotation is put forward. The observability analysis theory of piece wise constant system (PWCS) and the method of singular value decomposition (SVD) are applied to analyze the the influence of various maneuver of rotation on the observability, the observability degree in different alignment methods is also researched quantitatively. In the case of small misalignment angles after coarse alignment, the simulation study is carried out in different alignment methods by comparision, the results show that the estimation accuracy of the azimuth misalignment is approximately 2 times higher than that of the two-position alignment.In order to reduce the alignment time, the direct initial alignment method of lager misalignment angles is put forward, the nonlinear error modle and filter arithmetic are studied. Considering the attitude equations of SINS with lager misalignment angles, the system error equations based on addative quaternion error (AQE) is derived and the simulation results show that the nonlinear AQE equations is suitable for three misalignment angles. Considering the linear observation equation of SINS initial alignment, the unscented kalman filter (UKF) is simplified and compared with the extended kalman filter (EKF) in the procedure of initial alignment, the results indicate that the UKF is better than the EKF in the convergence rate and estimation precision.On the basis of the theory analysis and simulation validation, the SINS intial alignment software is developed by using the distributed structure, it can provide an effective research method and environment for studying and verifying the method of initial alignment.