Velocity Reversal Systems: A Simple Friction Model for Telescopes

In this paper we experimentally characterize friction in an astronomical telescope and introduce a new model for capturing the observed behavior of friction in both the micro and macro displacement regimes of motion. The model is a modification of the LuGre model and is developed for velocity reversal systems like an astronomical telescope. The proposed model is represented with a pair of masses separated by a linear spring. This model is then employed to synthesize a feedback linearizable controller for the system. The simulation results for the proposed friction model in open loop are presented and validated with the experimental results. The stability aspects of the closed loop system with the modified friction model is then investigated. For estimating the unmeasurable states of the system used in feedback linearization, we discuss the observability of the system with the new model for friction.