A method of coarse alignment for FOG based inertial platform system using rotation modulation

A platform inertial platform system (IPS) is a kind of independent navigation system. A fiber optic gyro (FOG) based IPS can stabilize its inertial measurement unit (IMU) in inertial space using its FOG readouts, and calculate its carrier's real-time displacement and velocity using its accelerometer readouts. Alignment is the initialization process of the IPS. During the coarse alignment of the FOG based IPS, the instrument errors, random noise and base vibration can cause decline of the alignment accuracy. To improve the precision of coarse alignment, the IMU rotation modulation is used to suppress the errors of inertial instruments by utilizing the equivalent integration process contained in the averaging computation. On the stationary base, calculate the attitude matrix of the rotating IMU in each sampling period, and averaging computation can compensate the errors caused by biases of inertial instruments. When the carrier is in vibration condition, the alignment coordinate frame (CF) is introduced to assist the rotation modulation. Carry out the attitude updating within the alignment CF in each sampling period to correct the estimated attitude matrix, and the rotation modulation based method can still improve the precision of coarse alignment in vibration condition.