

Monitoring of Friction Condition Using a System Identification Technique
Abstract
ï€ In this paper, the effect of friction force on a feed-drive mechanism is analyzed. The feed-drive mechanism is controlled by a commercial servo control system which consists of position and velocity feedback loops. To characterize the relationship between the friction forces and the sliding velocities, the LuGre friction model is adopted and experiments under constant sliding velocities are performed to identify the parameters associated with the static friction force, the Coulomb friction force, the viscous friction force and the Stribeck effect. To verify the identified parameters, the torque commands obtained in the experiments are compared with the simulation results. It is found that since the friction forces are the functions of sliding velocities, they form a feedback loop in the velocity loop and will interact with the PI servo controller. Besides, the linear effect of friction forces including the Coulomb friction force and the viscous friction force can be captured and compensated by the PI servo controller. However, the nonlinear Stribeck effect could not be well compensated via the PI control architecture and it needs auxiliary compensation technique to achieve high moving accuracy. The simulation results in this paper could provide a fundamental basis for further development about the compensation technique for the nonlinear effect of friction forces.