Vibration Reduction of 6-DOF Hydraulic Parallel Robot Based on Robust Control

A method of robust control combined with compensation of feed-forward load force and feedback friction is presented to reduce the motion vibration of 6-DOF (six degree-of-freedom) hydraulic parallel robot. A mathematic model for the asymmetric hydraulic actuator controlled by symmetric valve is established and a Lugre friction observer is designed. The observed friction and ideal load force computed through the inverse dynamics of 6-DOF parallel robot are dynamically compensated. According to the mixed-sensitivity theory, a robust controller about the asymmetric hydraulic actuator system is developed. Simulation results show that the proposed method effectively reduces the system vibration which is caused by the parameter uncertainties and nonlinear friction during platforms reverse motion and enhances the motion precision of the system.