Compensation Control Of Servo Systems With Friction

Friction is widely present in servo systems. It depends not only on the normal forces in contact and relative velocity, but also on the lag time, leading to the friction memory and rising static friction, which may result in stick-slip in low speed, increasing steady-state errors and reducing stability of system. In order to eliminate or reduce the effect of friction, and increase the system performance, appropriate methods must be carried out. This dissertation focuses on the following work:Firstly, a mathematic model for X-Y table with dynamic LuGre friction model is established. And an nonlinear observer is designed to estimate the unknown friction parameters and other disturbances for adaptive friction compensation and disturbances rejection. A backstepping control law is derived with Lyapunov stability theory to ensure astringency of parameter estimation and global stability of servo systems with friction. Simulation results show that system robustness and tacking accuracy are improved with proposed method than that with traditional PID control.Finally, a one-step method for LuGre friction model parameter identification is presented. With the proper selected objective function, four static parameters and two dynamic parameters are obtained at one time. Thus, the complex and time-consuming constant velocity experiments, which are necessary for the two-step method, is avoided that makes the proposed method more practical.