Closed-Loop Correction for Slowly Varying Tracking Error at the AIMS Coudé Focal Plane

“Accurate Infrared Magnetic Field Measurements of the Sun” project (AIMS) requires a tracking accuracy of 1″/30min (RMS) for objectives observed on the solar disk. Since AIMS's terminal scientific instruments are positioned at the Coudé focus, the telescope and guiding optical path introduce slowly varying nonlinear tracking errors during solar tracking, which degrade the long-duration tracking accuracy. To address this issue, this paper first analyzes the mechanisms and characteristics of these slowly varying tracking errors at the Coudé focus based on AIMS's optical-mechanical structure and motion principles, and conducts actual measurements of the tracking errors. Next, a closed-loop correction scheme is designed in conjunction with AIMS's optical-mechanical mechanisms, detailing both hardware and software implementations. Finally, after more than a year of testing and trial use on AIMS, the results demonstrate that the system can stably perform closed-loop tracking of solar observation targets for over 30 minutes, the tracking error is less than 1.0″, and both the tracking duration and error value meet AIMS's tracking accuracy requirements.