Friction Compensation in Servo Systems Using a Local Control Design Approach

Nonlinearities degrade considerably performances in motion control systems. Nonlinear friction is a major source of many serious problems such as wear, tracking errors and limit cycles. There has been an extensive research activity dealing with the design of compensating techniques. The approaches cited in the litterature can be divided into: free model compensation or model based compensation strategy. In the present work, a dynamic fuzzy modeling approach of a servo system with friction is developed. The main idea is to take advantage of the linear form of the resulting dynamics to design: 1- a friction observer used as a compensating term of friction effects, 2- a stable tracking controller that allows the system to achieve a trajectory involving slow motions and velocity reversal. The proposed control method is relatively simple to design and efficient for the compensation of friction induced errors. The experimental tests on a robot joint control have demonstrated precise motion control and smoother velocity reversal in the presence of significant level of friction.