Design and Tests of Muti-motors Hydromantic Position Control System of Primary Mirror Based on Large Telescope

Abstract

The primary mirror hydromantic position control system requires multi-motors and hydromantic components are controlled synchronously, and the control forces of different motors are changed with the position of primary mirror changing. At the same time, the control system also be required to support the mirror weight. According to the requirement of the hydromantic position control system of the large telescope. This paper provides a high integrated level control system based on open embedded controller and Ether cat technology, in order to control five different hydromantic Oil Volume Adjustment Component(OVAc)which is driven by five linear Actuator, constituting five permanent magnet synchronous motors and Roller screws. The whole control system including correction mode (CM), close-loop control using displacement sensors mode (CLDM), close-loop control using encoder position mode (CLCPM), close-loop control using encoder velocity mode (CLCVM), monitoring mode (MM), and halting mode (HM), in order to satisfy different working requirements. Position control strategy adopts three close-loop structures, including the inner current loop is PI controller with fiction compensation, the speed closed-loop is PI controller with two-order filter and the position closed-loop is P controller with Speed feed forward compensation in order to guarantee the accuracy of control system. Experiments are carried on the OVAC of 4m telescope and hydromantic position control system of 1.23m mirror. The results show that the accuracy of OVAC can achieve 1um when it bears 2700N load which equivalent each OVAC should bear of 4m mirror. At same time, the accuracy of 1.23m mirror at different pitch angle and different velocity can be always controlled less than 4.4um. This control system play an important role in the active optics correction, it can guarantee the image to stabilize one image unit in the field of view, so the control system meets the requirement the image accuracy.