Isotropic Design Method of Suspension System of Dithered RLG Strapdown Inertial Measurement Unit

Abstract

The dithered ring laser gyro (DRLG) strapdown inertial navigation system (SINS) is widely used in many applications, including military and commercial systems for the advantages such as high accuracy, wide dynamic range and bandwidth, outstanding scale factor stability over temperature, compactness and lower cost. However, the dither motion introduced to eliminate the lock-in error which is the inherent phenomena in the ring laser gyro also brought the adverse disturbance to the inertial measurement unit (IMU). Meanwhile, the installation environment of the SINS may also bring undesirable vibration and shock. For these reasons, a feasible and reliable suspension system is required to provide decoupling of the translational and rotational vibrations of the inertial sensor assembly (ISA) and attenuating the outside vibration and shock. Based on this, the isotropic design method of suspension system of DRLG strapdown IMU is proposed in this paper. The method consists four principles: 1) the input axes of sensors should be placed symmetrically along the ISA symmetric axes which are also the principle inertial axes; 2) the mass center of ISA is also the center of the geometric structure; 3) the elastic center of the suspension system is overlapped on the mass center by placing mounting isolators in the ISA structure corner in the isotropic manner and 4) the first mode frequency of ISA structure should be twice or more higher than the maxim mechanical dither frequency of DRLG triad. Following these principles, a design practice is implemented. The simulation and the experiment result show that the IMU using isotropic design method is proved to be feasible and reliable even in the extreme temperature ambiance.