Application of active disturbance rejection controller for high precision servo system

Friction is a key factor that influences the low velocity performance of high precision servo systems. It usually causes the steady-state error of servo systems and results in the creeping phenomenon in low velocity motions. Friction is complicated nonlinear process with time-varying uncertainties. The traditional PID controller of servo systems with friction was not satisfactory in control precision and response time. In this paper,the model of servo system is obtained through open-loop U - Ω curve and the compensating voltage for friction torque is estimated so as to eliminate the friction disturbance via feedforward compensation.A new algorithm that combines the advantages of ADRC´(active disturbance rejection controller) and friction torque feedforward compensation is proposed Comparison experiments with the new ADRC technique and the common PID algorithm are carried out on the servo system. The result demonstrates that the improved ADRC technique could reduce steady-state error to only one third of the one using the PID algorithm.