Abstract
In order to improve the control quality of the active reflector system which is used in the 500 m aperture spherical radio telescope (FAST) project, a study on hydraulic actuator is proposed. 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 characteristics. Bond graph model is ideal for this task. In addition, conventional PID control strategy cannot achieve the required accuracy and precision, so we combine grey prediction with PID control. Furthermore, a new adjustment mechanism is presented to change the grey step size, which is simple, automatic, less time-consuming, and efficient. Simulations and experiments on the actuator are carried out to evaluate the effectiveness of the proposed control method. In experiments, the velocity error is less than 0.05mm/s and the position error is less than 0.2mm. It shows the actuator meets the astronomical observation requirement totally.
Highlights
Five hundred-meter aperture spherical radio telescope (FAST) project belongs to Chinese “megascience” project building in the unique karst area, which will be the largest single aperture radio telescope in the world [1,2,3]
In order to realize the active deformation characteristics of radio telescope, the supporting structure of active reflector adopts the cable net structure which consists of ring beam, main cable net, drop-down cable net, triangular reflector unit, hydraulic actuator, and anchor block
The triangular reflector unit is laid in the main cable net which is fixed on the beam, and the triangle vertices are connected by cable net nodes
Summary
Five hundred-meter aperture spherical radio telescope (FAST) project belongs to Chinese “megascience” project building in the unique karst area, which will be the largest single aperture radio telescope in the world [1,2,3] It is primarily composed of active reflector system, the supporting system, the measurement and control system, and the receiver and the terminal system. The actuator traces the observation target in a closed-loop position control In this situation, the position error is less than 0.25mm without velocity requirements. Based on the above requirements, the hydraulic actuator with the form of pumpcontrolled differential cylinder is adopted in this paper. The recent research on pump-controlled differential cylinder mainly focuses on two aspects of modeling and control strategy. A switching grey prediction PID control strategy is designed according to the working conditions of the hydraulic actuator in the active reflector system. In order to verify the effectiveness of the whole control strategy, is simulation carried out on the basis of the bond graph model, and a field experiment platform is built in FAST and field tests are conducted
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