Research On High Precision Pointing Control Delay Compensation Method For Large Radio Telescope

Large aperture and high frequency are the development trend of radio telescope nowadays.With the expansion of the antenna aperture,the natural frequency of the structure becomes lower and the damping becomes smaller,which leads to the narrowing of the servo bandwidth.Meanwhile,the high frequency band puts forward higher requirements for the pointing accuracy of the system.In addition,the adverse effects of large aperture antennas will be increased when subjected to external environmental disturbances such as gust,which will make the tracking control of the antenna system more difficult.At the same time,the friction moment,un-modeled geometric nonlinear dynamic characteristics and large inertia in the pitch motion result in the delaying the output.These will further reduce the tracking accuracy of the system,increase the terminal vibration which even leads to instability of the system.Therefore,high-precision pointing control has become a key problem in engineering implementation.This paper takes the large radio telescope as the research object.In view of the contradiction between the rapidity and the stability of the system,on the basis of the original dual-loop compound control scheme,the Pareto front optimization is proposed to optimize the parameters of the inner loop robust controller and the outer loop PID controller,so as to achieve the purpose of finding suitable controller parameters.This method mainly aims at the contradiction between the rapidity and the terminal vibration.Large inertia,gap,friction and disturbance are existed in the large radio telescope system.These factors cause the system to time delay.The existence of hysteresis makes the control performance of the system worse.If the delay time is too large,it will even cause oscillation and instability of the system.In this paper,Smith predictor is designed to compensate the delay time and model.The principle of this method is to move the delay link outside the closed loop system,thereby improving the dynamic performance of the system.However,in the actual working process of large radio telescope,the delay time is usually not fixed,the result of identification is not accurate,and there is a serious model mismatch problem for the Smith predictor method.Therefore,the time delay is equivalent to disturbance,and a self-structuring fuzzy network method is proposed to estimate the above disturbance online,and the output of self-structuring fuzzy is regarded as a compensation added into control system.The rationality and applicability of the method are verified by simulation.Finally,the large aperture radio telescope is equivalent to a three inertia system.The flexible ruler is used to simulate the structural flexibility of the large antenna,and the corresponding experimental platform is built.On the platform,dual-loop compound controller parameters optimization experiment and self-structuring fuzzy feed forward compensator experiment are platform,respectively.In order to connect the algorithm to the hardware interface,the C MEX S function is used in the experiment of self-structuring fuzzy feed forward compensator.The experimental results are consistent with the simulation results.The system can effectively control the vibration while the control accuracy is satisfied.