Development And Performance Analysis Of The Hydraulic Actuator Used In The Active Reflector System Of The FAST Project

In order to improve the control quality of the active reflector system which is used in the five hundred meter aperture spherical radio telescope(FAST)project,a study on hydraulic actuator was proposed.The article presents a significant aspect of an integrated study of the function realization process,dynamic characteristics,control strategy and regulation mechanism of the hydraulic actuator,which is specially applied to the FAST project.The dynamic performance of hydraulic actuator is due to the interaction of several physical phenomena.Modeling of such a system needs a unified approach to represent the nonlinear behavior model in a generic and systematic way.Bond graph model is well suited for this task.In this paper,the nonlinear mathematical model of the hydraulic actuator is established by using the bond graph method,while the whole system is decomposed into several energy exchange subsystems.Combining the pump controlled differential cylinder with a motor circuit,the dynamic response of the closed-loop system is analyzed.Furthermore,the state space expression of the system is derived,and the main factors affecting the performance of the system are studied.In addition,the mathematical model of the closed-loop system is further simplified,which provides a guarantee and theoretical basis for the subsequent computer processing.It is difficult to obtain the ideal accuracy by using the conventional PID control strategy.In order to achieve the desired performance of the system with respect to the changing the target source condition and the scanning tracking condition,close-loop control system is designed with a suitable controller,namely SGPID.Furthermore,a new adjustment mechanism was presented to change the grey step size,which is very convenient,simple,automatic,less time-consuming and efficient for engineering application.In conclusion,simulations and experiments on the actuator are carried out to evaluate the effectiveness of the proposed control method to achieve the control precision in normal working state.The research results validate the effectiveness of the proposed model and the adjustment mechanism of SGPID.It can well guide the work of the application of the hydraulic actuators using in the active reflector system,which has obvious engineering practical significance for the FAST project.