Research On The Large Misalignment Angle Transfer Alignment Algorithm Of The Strapdown Inertial Navigation System For The Projectile

Inertial navigation system is completely autonomous, highly covert and has a high data frequency, it takes a very important place in modern guided munitions. For on-board INS, highly accurate initial alignment is very useful to improve the system's accuracy. As INS used in guided munitions often has a low accuracy, aircraft's high accuracy INS need to be used in transfer alignment.Traditional linear transfer alignment model suggest the misalignment angles are small. But for guided munitions, the plane's maneuvering or bad circumstance makes misalignment angles no longer small, so that the system becomes nonlinear. In this case, carry on using linear model will lead to decreasing accuracy, even makes the filter unstable.This paper researches transfer alignment algorithm for guided munitions when misalignment angles are large.First, the basic theory of strapdown inertial navigation system is introduced, gyro and accelerator error model is analysed and simplified. The error equation of strapdown inertial navigation system is inferred. Based on small and large misalignment angle, linear model and nonlinear model for transfer alignment is inferred.Then,KF,UKF,CKF and their advantages and disadvantages is discussed.The development in matching method and observability is briefly introduced.The observability of transfer alignment base on PWCS with SVD resolve is analysed, the result decides the matching method and aircraft movement for the following simulation.Then, level arm effect, flexure and time delay errors are analysed, compensation methods for each kind of these errors are researched and the result of simulation is given. After this, proceeding the simulation with all three kinds of errors and compensation.At last, as nonlinear filter has to do a large amount of calculation that limits its practical application, a reduced dimension CKF is designed to reduce calculation. Based on the simulation result, the performance of reduced dimension CKF and standard CKF is compared.