Azimuth Alignment Error Analysis and Process Optimization of Rate-Bias Laser-Gyroscope Inertial Measurement System

Rate-bias technology, as another way to solve the lock-in threshold problem, eliminates the extra random walk noise resulting from frequent dead-zone crossing of dithered-bias laser gyroscope. Currently, a rate-bias self-alignment method utilizing a forward and backward continuous rotational scheme has been employed to achieve rapid and high-precision north seeking. However, even under conditions of nearly horizontal placement and perfectly symmetrical bidirectional rotation, the scale-factor error along the rotation axis can still lead to significant heading alignment errors. The theoretical analysis in this article indicates that besides the equivalent east gyro bias and change rate of north specific force, the vertical gyro bias also contributes to heading alignment error. It is theoretically deduced and simulation-based validated that the primary error source of the reciprocating rotation rate-bias alignment is the angular velocity measurement error along the rotational axis caused by gyro scale-factor error and triad misalignment. An enhanced rotation scheme capable of error self-compensating instead of the scheme of estimating the scale factor by grating angle measurement is proposed to achieve high-precision alignment under conditions of angular swaying. Static and swaying alignment tests demonstrate the superiority of the proposed scheme compared to the traditional forward and backward rotational method. The alignment repeatability of the proposed scheme is better than $21^{\prime \prime }\text {(3}\sigma $ ) and $35^{\prime \prime }\text {(3}\sigma $ ) under static conditions and sway conditions, respectively.