英语翻译Fig.2 shows the INS process..There are two main phases f

英语翻译
Fig.2 shows the INS process..There are two main phases for INS operation:the alignment phase and the navigation phase.The navigation phase starts from the initial velocity,position and attitude.The process for determining these INS initial conditions is called alignment.Any errors in either the alignment phase or the navigation phase will be integrated and will propagate over time.These errors determine the performance and the navigation accuracy of the INS.INS error models serve for the error analysis and the implementation of a data fusion filter in the INS algorithms [10].In the literature there are two approaches to the derivation of INS error models [11]:the phi-angle approach (or the true frame approach) and the psi-angle approach (or the computer approach).It has been shown that the models from these two approaches are equivalent and yield identical results [12–14].Most of the literature for INS modeling makes the assumption that all perturbation attitude errors are small angles.However,in many cases,this small angle assumption will not hold.For low cost inertial measurement whose sensitivity is not enough to measure the earth rate,the corresponding attitude error in both the phi-angle model and the psi-angle model could be up to ±180°making the small angle approximation not valid.Consequently,the INS error models with small angle assumption make the navigation system of low cost IMU inaccurate and unstable.This motivated the development of INS error model and navigation algorithm for low cost IMU in this paper.