The ship rolling prevents a gyroscope from reliably measuring the angular velocity of the earth's rotation (Ω). Consequently,the strapdown compass system based on fiber optic gyroscopes (FOG) cannot compute the heading of the carrier based on the outputs of gyroscopes and the accelerometers. To address this issue, a new north finding algorithm was proposed. By taking the inertial frame as the reference coordinate frame, this algorithm established the transitional inertial frame and the initial-time strapdown compass body inertial frame. The direction of vector Ω was then calculated according to the projection of the accelerometer sensitive to grivity in the initial-time body inertial frame. And this in turn recovers the true north of geographic direction. The proposed north finding algorithm consists of three steps. It established the initial-time body inertial frame. Then it obtained a stable level frame via the initial-time body frame and the outputs of gyroscope and accelerometer. By projecting the output of accelerometer from the strapdown compass body frame to the initial-time body inertial frame, the direction of vector Ω was calculated by the space circle fitting method. Then the true north was recovered by projecting the vector parallel with Ω from the initial-time body inertial frame to the stable level frame. The simulation result shows that the error of azimuth can be reduced to as low as 0.23°(1σ) .
Napolitano F,Gaiffe T.PHINS: the first high performances inertial navigation system based on fiber optic gyroscopes //9th Inter-national Conference on Integrated Navigation Systems.Saint Petersburg,Russia: ,2002:296-304
Gaiffe T,Cottreau Y,Faussot N,et al.Highly compact fiber optic gyrocompass for applica-tions at depths up to 3�~000 meters //IEEE Underwater Technology,Proceedings of the Inter-national Symposium.Tokyo,Japan: ,2000:155-160
Rawlings A L.The theory of the gyroscopic compass and its deviations [M].New York:The Macmillan Company,1994
�Ϲ���,����Ԫ,������,��.һ��������SINS��������ʼ�������㷨[J].ϵͳ��������Ӽ���, 2009, 31(3):634-637 Yan Gongmin,Qin Yongyuan,Wei Yuxin, et al.New initial alignment algorithm for SINS on moving base [J].Systems Engineering and Electronics,2009,31(3):634-637(in Chinese)
Gaiffe T. From R&D brassboards to navigation grade FOG-based INS:the experience of photo-netics/ixsea //IEEE 15th Optical Fiber Sensors Conference Technical Digest,Vol 1. Portland:IEEE,2002:1-4
����,������,�����.�����ߵ�ϵͳ�����Զ�[J].�й����Լ���ѧ��,2008,16(4):386-389 Li Yao,Xu Xiaosu,Wu Bingxiang.Gyro-compass self-alignment of SINS[J].Journal of Chinese Inertial Technology,2008,16(4):386-389(in Chinese)
Ali J,Fang Jiancheng.SINS/ANS/GPS integration using federated Kalman filter based on optimized information-sharing coefficients //AIAA Guidance,Navigation,and Control Conference and Exhibit.San Francisco,California:AIAA,Inc,2005:6030-6033