Objective  The extinction tube of the 2.5-meter large-field and high-resolution telescope receives thermal radiation from the main focal point, heats the air in the lens barrel, generates random turbulence, reduces the astronomical seeing, and affects the imaging quality of the telescope. In order to solve this problem and meet the temperature control index requirements of temperature control, the Smith-Active Disturbance Rejection Controller (ADRC-Smith) is designed.

  Methods  The designed ADRC-Smith controller uses the automatic disturbance rejection control combined with the Smith predictor method, which adds a Smith estimation module to the ESO signal input of the linear ADRC, uses the Smith predictor to cancel the time delay term in the closed-loop characteristic equation, and uses the automatic disturbance rejection controller to improve the response speed and robustness of the temperature control system to achieve accurate control of the extinction cylinder wall temperature. Firstly, the mechanism modeling and model parameter identification of the extinction cylinder temperature control system are carried out (Fig.3), the model of the extinction cylinder temperature control system is established, and the structure (Fig.5) as well as the parameter adjustment method of the ADRC-Smith controller are given. Secondly, according to the system model, the temperature control system of the matting cylinder is simulated when the model is accurate and the model is out of alignment to analyze the feasibility of the controller (Fig.6-7). Finally, the temperature control system of the matting cylinder at the main focus is set up for carrying out stability and reliability test to verify the practicality of the controller (Fig.1-2).

  Results and Discussions  The experiment results of the stability test show that the ADRC-Smith controller can quickly track the ambient temperature, control the temperature of the extinction cylinder wall within 2 ℃ of the ambient temperature, and the corresponding response time and settling time are about 59 s and 173 s respectively, and the following error is about 0.14 ℃ (Fig.9, Tab.1). After that, the reliability test of the controller is carried out, and the reliability of the controller is further verified by introducing heat source interference to cause large fluctuations in the ambient temperature (Fig.10). The results show that the ADRC-Smith controller can improve the performance of the extinction tube temperature control system of the 2.5-meter large-field and high-resolution telescope.

  Conclusions  Aiming at the temperature control research of the 2.5-meter large-field and high-resolution telescope extinction tube, the control goal is to control the temperature of its outer wall within 2 ℃ of the ambient temperature. The temperature control system of the extinction cylinder was designed and built. The temperature control system model was established through mechanism analysis and model parameter identification. According to the characteristics of the controlled object, the ADRC-Smith controller is designed by combining Smith predictor and active disturbance rejection controller. The controller has no system deviation, which can overcome the large lag of the system, has fewer parameters and can be easy to get the parameters. On the basis of the simulation results which verify the feasibility of the controller, the stability and reliability test are carried out respectively, and it is verified that the controller can be applied to the extinction cylinder temperature control system of 2.5-meter large-field and high-resolution telescope, and the system performance can be improved. The research results can also provide guidance for the design of the temperature control system of its primary mirror and reflecting diaphragm.