Friction compensation without a friction model

This paper presents the design of a position control system for plants that have nonlinear friction. The approach uses nested integral tracking loops: an inner velocity loop and an outer position loop. An additional component of the proposed approach is the nonstandard use of an observer, or reduced-order observer, in the inner loop to estimate the state of the velocity integrator. The designs of the inner loop, outer loop, and observer are accomplished using standard linear pole-placement techniques. The method does not require knowledge of any friction model, yet results in effective friction compensation over a certain bandwidth. The performance of the proposed approach is demonstrated using simulation results as well as hardware experiments with a belt-driven positioning system.