Research Of Low-rate Stability Of O-E Tracking System

With the development of precise tracking technology, focus on performance and stability of O-E tracking systems is increasingly high by concern of scholars. In many areas, theodolite is need to work in long-time at low-speed situations, such as theodolite used in the field of deep space exploration. In this case, the more requirements would be put to low-speed stability for O-E tracking system. After research and analysis,the key factors that affect the low-speed stability and the low-speed tracking precision are friction torque disturbance caused by the mechanical structure of turntable and the accuracy of signal of speed feedback.Firstly, the paper discussed the main methods of commonly getting signals of speed feedback used O-E tracking system. It is approximate differential method based on optical encoder. Analyzing the method showed that position signal acquired by optical encoder will appear jumps, because that the system will appear creeping phenomenon at low speed. Meanwhile, due to a larger sampling frequency, the errors brought by creeping phenomenon would be amplified after using differential method to approximate the differential. To solve these problems, the paper proposes three methods to obtain high-precision speed feedback, and it is Kalman filter, the state observer and the nonlinear tracking-differentiator in velocity estimation. Firstly, the paper analyze these three methods, and verify its effectiveness through simulation and experiments, then draw conclusions by comparing three methods to quantify the simulation results.Secondly, the paper analyzed the impact of nonlinear friction torque for optical tracking systems. Static friction model and dynamic friction model are established. Through analysis, dynamic LuGre friction model is close to the actual friction torque for turntable models. Simulation analyzing the parameters of dynamic LuGre friction model how to affect the accuracy and the stability of O-E tracking system. Then the paper propose the new compensation control method- adaptive fuzzy PID control method for Servo Control System added friction model, comparing to traditional PID control. Finally, the simulation results show that the adaptive fuzzy PID compensation for the disturbance caused by the friction torque has a good effect.In this paper, two main factors affecting the low-speed stability for O-E tracking system were analyzed. Through simulation, several algorithms are proposed to solve those two factors, and the good results are got. It is meaningful that laid the theoretical basis and practical reference to improve the low-speed stability for O-E tracking system.