Identification of Friction in the 50/80 cm ARIES Schmidt Telescope Using the LuGre Model

Abstract

In this paper, we discuss the LuGre model based parameter estimation of the friction present in the 50/80 cm Schmidt telescope at the Aryabhatta Research Institute of Observational sciencES (ARIES). Identification and compensation of friction in telescopes is essential to achieve sub-arcsec pointing and tracking accuracies at very low velocities. The six parameter LuGre model which is an extension of the Dahl model captures most of the observed dynamic behavior of friction. High accuracy encoders mounted on the telescope axes are capable of measuring micro and macro displacements useful for estimating the six parameters. A suitable PI controller was developed for performing experiments on the Schmidt telescope to estimate the friction. It was observed that the system exhibits the behaviour described by the LuGre friction model.