In-motion alignment of navigation-grade strapdown inertial navigation system (SINS) combined with odometer (OD) is one of the challenging issues for the land vehicle navigation, while most current in-motion alignment methods still rely on the measurements of the global positioning system or only aim at improving the attitude alignment, thus neglecting the position alignment. Thus, one of the main obstacles during the in-motion alignment for SINS/OD is to autonomously and simultaneously obtain the high-precision attitude and position within specified time. In this paper, an in-motion alignment scheme based on the backtracking scheme is presented to solve this problem. The proposed method consists of two steps. First, an improved optimization-based coarse alignment (IOBCA) is employed to obtain the attitude and position with reasonable precision, and the gravity deflexion error projection in inertial frame caused by the positioning error is diminished, which contributes to better alignment results for the subsequent process. Second, initialized with the alignment results provided by IOBCA, a backtracking-scheme-based fine alignment combined with the Kalman filter is investigated to make a further improvement in the precision of attitude and position, during which the known initial binding position and zero velocity have been utilized again. The car-mounted field experimental results illustrate that the proposed method can not only autonomously improve the precision of attitude within a short time but also simultaneously achieve the position with high precision. INDEX TERMS In-motion alignment, strapdown inertial navigation system (SINS), odometer (OD), backtracking.
In recent years, the applications of rotating inertial navigation systems (INSs) have been developed rapidly. By controlling the rotation of the inertial measurement unit, the drift error of an inertial device can be modulated and the divergence of INS errors can be suppressed. However, attitude errors and velocity errors accumulate as the result of the scale factor asymmetry of gyros based on a forward–reverse rotating system, which offers better performance than single-axis rotational navigation systems. In this paper, the error mechanism of scale factor asymmetry in forward–reverse rotating systems is discussed in detail. Based on a system-level fitting method, error deduction of the scale factor asymmetry of a gyro under different conditions, including the level and tilt environments, are introduced, respectively. Thus, a self-calibration and compensation method based on scale factor asymmetry is proposed. The simulation and experiment results show that the iterative calibration and compensation method has a positive effect on eliminating scale factor asymmetry, and the precision of initial alignment and navigation can be improved after compensation.
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