A fast compass alignment method for SINS based on saved data and repeated navigation solution

Abstract

Compared with Gimbaled Inertial Navigation System (GINS), there are two differences in the compass alignment process for Strapdown INS (SINS) as follows: (1) the input signal is the projected sensor data from body frame to calculated navigation frame, not the sensor data; (2) the output control signal participates in navigation solution rather than driving navigation frame directly. Considering these characteristics, a fast compass alignment method based on iterative calculation is designed for SINS in this paper. With the help of high performance computer, the iterative process can be finished fast and the alignment time can be shortened obviously. However, there exist two problems in the new method, one of which is how to use the saved data, and the other is how to ensure the real-time property of alignment result. For the first problem, our simulation result shows that the forward–forward navigation solution method is more effective for compass alignment than the backward–forward one. And to solve the second problem, Multi-tasking method combined with Real Time Multi-tasking Operating System (RTOS) is used to trace the change of body frame and update the body frame of attitude matrix when the alignment is finished. The car test on a type of fiber-optic gyro SINS indicates that the alignment accuracy of the proposed method processed for 142s is as precise as that of the classical compass alignment method for 720s.