A Cosine-Fitting Self-Alignment Method of MEMS-Based Inertial Navigation System Consisting of a Skew FOG

MEMS inertial measurement unit (MIMU) has widely used in low-cost inertial navigation fields, such as pedestrian navigation system. However, the realization of self-alignment function and high-grade navigation performance are still uprising challenges. In present study, a novel MIMU/FOG compound system consisting of the MEMS inertial sensors and a skew fiber optic gyro (FOG) is proposed. The configuration which is based on the rotation modulation technology, realizes self-alignment function, and the skew FOG used as the redundant angular velocity measurement unit improves the navigation accuracy. During the rotation process, the projection of the fiber optic gyro sensitive axis is a direct current component, the earth rotation rate projected on the sensitive axis of the fiber optic gyro is a cosine component, and the initial phase is the yaw. Further, a cosine-fitting self-alignment method which requires no latitude information is introduced to calculate initial yaw alignment accuracy. The alignment time is adjustable by setting various rotation rate of rotary mechanism. When the rotary mechanism rate is fixed at 1°/s, the proposed method achieves better yaw alignment accuracy of 0.37° ($1\boldsymbol {\sigma }$ ) by using the 0.1°/h (100s, $1\boldsymbol {\sigma }$ ) fiber optic gyro. Our work opens up a new perspective to implement self-alignment of the MIMU/FOG compound system.