Self-alignment of strapdown inertial navigation systems incorporating micro-electromechanical systems (MSINS) is a great challenge for marine applications. In this paper, a self-alignment method for a rotating MEMS strapdown compass is proposed with the aim of solving this problem. First, based on an analysis of biaxial rotation modulation and initial alignment of the strapdown compass, a selfalignment method is presented and verified. Second, by analyzing the effects of biaxial rotation modulation, the proposed method is improved by speeding up the rotation and reducing the stop time of the biaxial rotation mechanism to shorten the initial alignment time, which effectively suppresses the influence of MEMS noise on the initial alignment error angle. The influence of ship swinging on the initial alignment error angle is also analyzed. The efficiency of the method is verified by experiments on a swinging base. Finally, a parameter adjustment approach is presented that allows the proposed method to be used with different types of MEMS. This approach is validated by experiments. All the experimental results demonstrate the efficiency and precision of the proposed method.

Introduction

An MEMS strapdown inertial navigation system (MSINS) is a combination of a strapdown inertial navigation system (SINS) and micro-electro-mechanical systems (MEMS) technology. Such systems are at the forefront of navigation research and are already in use for moderate to low-precision navigation of ships, owing to their advantages of, among other things, high reliability, low cost, and capability of miniaturization. Obtaining the initial alignment that determines the initial attitude is a prerequisite for navigational computation in a SINS [1]. This initial self-alignment relies on the inertial measurement unit (IMU) itself to complete the initial alignment without the aid of external information. Normally, the MEMS initial alignment depends on the MEMS accelerometer and magnetometer to determine horizontal attitude and heading attitude [2]. However, this method can determine the attitude only on a static base and in the absence of magnetic interference. It is not suitable for marine applications, where there are swinging motion and strong magnetic interference [3]. To remove the limitation imposed by the use of a magnetometer, a single-antenna method is adopted in [4]. However, it is only used on a moving base. To allow both swinging and static bases, a double-antenna method is adopted in [5], although this method is not suitable for use in bad weather. In [6], transmission alignment methods are adopted to avoid interference with GPS signals.