Research On Modeling And Robust Control Of Slant-Axis Telescopes Servo System

The slant-axis telescope is a new type of telescope with a special structure that is benefited to for long-term operation in harsh environments such as the polar regions.The Dome A 5 m Terahertz Explorer(DATE5)is designed with this type of structure.At present,there is a lack of detailed servo system modeling and control design for the slant-axis telescope due to the telescopes at home and abroad being mainly horizontal and equatorial structure types.In this paper,the modeling and robust control of the slant-axis telescope servo system are discussed in detail by means of model derivation,simulation analysis and experimental verification.The specific research of this paper is as follows:First of all,a detailed model of the telescope servo system with a slant-axis is presented.A 2-degree-of-freedom rigid body model is established which is the abstract of the slant-axis structure.The Lagrange method is used for the dynamic modeling of the model.The model can be used to quantitatively analyze the coupling degree between the slant axis and azimuth axis of the telescope.The LuGre friction model is used to describe the influence of nonlinear friction disturbance.Moreover,the telescope servo system is also affected by random wind load.Based on the measured data of the Dome A environment,the Davenport wind velocity spectrum model is used for the simulation of wind-borne disturbance torque.Finally,a numerical simulation model describing the whole process of the slant-axis telescope servo system is established in the MATLAB/Simulink simulation software.According to the established mathematical model,a sliding mode controller with an integral sliding mode surface is designed to realize robust control of the system.The effectiveness of the model is verified in the simulation environment.To solve the chattering problem of the sliding mode controller,a disturbance observer-based adaptive sliding mode controller is designed.The method consists of two parts:the disturbance observer is responsible for estimating the external disturbance which is usually the lowfrequency part of it,and the residual disturbance is compensated by the sliding mode controller.The simulation results show that the composite controller has strong robustness in the nonlinear friction disturbance and external wind load disturbance,and can realize the pointing control index of the complete telescope in a complex environment.Finally,based on the above research,an experimental platform for the telescopic scale of the inclined axis is built,and the software and hardware of the control system were designed for it.The system verification experiments were carried out on the experimental platform,and compared with the simulation experiments.In Conclusion,the proposed robust control algorithm is feasible and effective,and the pointing accuracy can reach the hardware limit of the system.