Design Of Active Optics Force Actuator Control System

Active optics is one of the key technologies in modern large telescope, which belongs to the intersection of mechanics, optics, computer, precision machinery and auto control. The main idea of active optics technology is to detect and correct mirror surface distortion in real-time. The object that active optics aims to correct is the mirror deformation caused by heat and gravity, as well as the mirror processing error. These errors change slowly, so 10-2 ~ 1Hz calibration frequency can meet the requirements. Active optics uses wavefront sensor(typically Shack-Hartmann) to detect mirror surface distortion, and accordingly calculates the correction force and coordinate. Then the force is transmitted to the appropriate actuators through feild-bus from master computer, and used to correct the mirror surface error by the force actuators. The main content of this paper is the design of the force actuator control system, as well as the control method study of the force actuator.This paper is composed of four segments:The first segment: This part introduces the force actuator’s mechanical structure and working principle firstly. And on this basis, the force actuator control system overall design is completed, and the scheme of the establishment of a distributed control system using CAN bus is proposed, then the system’s hardware and software requirements are analyzed. Furthermore, the system performance target, what is expected to achieve, is given.The second segment: In this part, all the needed hardware circuits are designed, including the force actuator control circuit, the drive circuit of stepper motor, the force signal acquisition circuit, and the power supply circuit. Using all these circuits, we have built an experimental platform for the force actuator control system.The third segment: Firstly, this part has studied force actuator control algorithm. The advantages and disadvantages of the open-loop and closed-loop control strategy in force actuator control system have been carefully analyzed, and a PID controller with dead-zone was designed. Secondly, the software design method of force actuator control system was introduced. The implementation methods of each function module were analyzed, and a detailed program flow chart was given.The fourth segment: The performance tests of the force actuator control system were completed, which included the force actuator performance test, the calibration and transfer accuracy test of the force signal acquisition circuit, force actuator control experiments. Then, results of the tests were analyzed. Experimental results showed that the system can work in accordance with the desired manner, and meet the accuracy requirement of active optics surface shape correction force, and has good response performance. This proved that the control system has certain practical value.