Friction Compensation in Servo Applications

For servo positioning, consideration of the friction effect is very important when high precision is required. Friction not only reduces positioning accuracy but also induces lots of problems. Static lubrication is able to partially solve some of the problems, while dynamic compensation can give better solutions in general. Since, in most of the manufacturing applications, the friction effect cannot be precisely modeled and its actual value might be time dependent with unknown variation bounds, traditional robust designs or adaptive controls do not properly apply. In this paper, a function approximation based adaptive compensator is found to cover the friction effect in a servo system to improve positioning accuracy. Rigorous mathematical proof based on the Lyapunov-like technique is employed to justify closed loop stability and boundedness of internal variables. An experimental setup is constructed to evaluate the performance of the proposed strategy.