Experimental identification of friction and its compensation in precise, position controlled mechanisms

The authors present methodologies developed for experimentally determining accurate models for the nonlinear friction inherent in most mechanisms. The second objective is to present alternative closed-loop controller strategies for decoupling the effect of friction in order to improve positioning accuracy. The identification methodology is novel in the manner in which it extracts the nonlinear friction properties from the closed-loop errors via an iterative signal processing technique. The present work is based on both theoretical modeling and a practical position control problem which was substantially resolved in developing the methodologies. The application was a robotic gripper with highly preloaded rack and pinion mechanism. The authors provide both measurement and control design methodologies to help systematically circumvent the problems of nonlinear friction in precise, position controlled mechanisms.<>