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

The Accurate Infrared Magnetic Field Measurements of the Sun (AIMS) project requires a root-mean-square tracking accuracy of 1″/30min to observe targets on the solar disk. Since the terminal scientific instruments in AIMS are positioned at the Coudé focus, the telescope and guiding optical path introduce slowly varying nonlinear tracking errors during solar tracking, which degrade long-duration tracking accuracy. To address this issue, we first analyze the mechanisms and characteristics of these slowly varying tracking errors at the Coudé focus, based on the optical-mechanical structure of AIMS and motion principles, and conduct actual measurements of the tracking errors. We have designed a closed-loop correction scheme in conjunction with the optical-mechanical mechanisms of AIMS, detailing both hardware and software implementations. Following over a year of testing and trial use on AIMS, results demonstrate that the system can stably perform closed-loop tracking of solar observation targets for over 30 minutes, with a tracking error of less than 1.0″. Both the tracking duration and error value meet tracking accuracy requirements.