Research On High Precision LOS Stabilization Technology Based On Fast Steering Mirror

The stabilization technology of line of sight is very important for application of long distance surveillance for EO/IR systems, laser-guided bombs, laser communication. The technology can significantly attenuate the disturbance of the vehicle angular motion, the vehicle vibration and the wind resistance for the line of sight. This technology has been applied for almost sixty years and developed for five stages: passive isolation stabilization, passive mechanical balance stabilization, active gyro stabilization for two-axis-gimbal, active gyro stabilization for four-axis-gimbal, active six-axis-gimbal stabilization based on fast steering mirror.Active six-axis-gimbal stabilization technology has been widely applied in US’s military high-end EO/IR systems since the end of the 20 th century. Such as DB110 pod, MTS-A/B systems, MX series stabilization platform, Sniper pod, F35-EOTS systems. This super fast stabilization technology benefits from the development for the fast steering mirror. Fast steering mirror stabilization technology is different from the traditional mechanical stable technology.The fast steering mirror is arranged in imaging optical path, and the residuals of gyro mechanical stability can be adjusted and compensated through the optical path. Since the fast steering mirror has high position accuracy and bandwidth, which can achieve high accuracy of line of sightstabilization, traditional mechanical stability is often regarded as coarse line of sight stabilization,and fast steering mirror stabilization is regarded as fine optical stabilization on the basis of the technique.Active six-axis-gimbal stabilization technology now is on the state of research in China.Under the development of "11th Five-Year plan", some breakthrough of active six-axis-gimbal stabilization technology has been made. Such as the optical system design for the fast steering mirror, the image motion compensation by fast steering mirror. This article firstly puts forward the suitable optical design for the classical application of fast steering mirror and fine optical compensation principle by fast steering mirror. Subsequently several algorithms for coarse LOS stabilization are discussed which focuses on the application environment of fast steering mirror.According to the fast steering mirror’s angle travel is very small, these algorithms should have significantly effect on attenuating the disturbance. If the accuracy of the coarse stabilization can’t match the requirements, the fine stabilization won’t achieve the goal. The fast steering mirror can be actuated by piezoelectric ceramics or voice coil motor. In the subsequent chapter the mechanical design and control method for different fast steering mirror will be discussed. By comparing the two different drive methods for fast steering mirrors, we choose fast steering mirror driven by voice coil motor as the control object. The fast steering mirror itself has a position sensor and driving mechanism to form a single closed loop system, so two-stage stabilization control usually treats fast steering mirror as an independent control unit which receives the residual signal of mechanical stability as the input to achieve closed-loop LOS stabilization control. Such control is similar with traditional closed loop control without disturbance modeling which limits the improvement of Los stability.This paper firstly established the open-loop transfer function for fast steering mirror, while the low frequency and high frequency perturbation of the open-loop transfer function respectively stands for the coarse stabilization residuals and aircraft vibration. By modeling the low frequency and the high frequency perturbation, combined with the open loop model and gyro sensor data of fast steering mirror, we can get a new line of sight(LOS) stabilization control equation of state. Through the analysis of observability and controllability of it, the controllable state variables are controlled to achieve the purpose of line of sight stabilization.At the end of the article, the development for EO/IR systems will be presented. The new mechanical design, the new actuating method, the new angle sensor design for the inner gimbals will be discussed. The bandwidth of coarse stabilization will be improved by the new design of EO/IR systems. So the fast steering mirror will be designed for smaller angle travel and higher bandwidth will be achieved. The overall accuracy for stabilization of LOS in EO/IR systems will be better.