Disturbance Observer-Based Nonlinear Friction Compensation in Servo Drive System

Solid friction in various machines is one of dominant nonlinearities limiting the control performance of servo drive systems. Nonlinear friction gives tracking errors and undesired stick-slip motion due to stiction (breakaway friction) and/or Stribeck effect. A wide variety of studies have been reported, which formulated nonlinear friction models, identified its parameters, and compensated for the friction. Those compensation schemes can significantly improve the conventional control performance, however, deterioration of the control accuracy is still the problems due to the inaccurate friction model and/or the restricted bandwidth of the compensation control loop.This paper presents the disturbance observer-based compensation for nonlinear friction in servo drive systems to improve the control performance. The proposed scheme uses a new disturbance observer which is designed on the basis of Coulomb friction characteristics. This scheme can realize the precise speed/position control without response delay which is caused by the restricted bandwidth in the conventional compensation scheme. Experimental results and analytical studies show the distinct performance improvement of the proposed scheme, comparing to the conventional compensation schemes.