Vibration Suppression Method for Dual-flexible Manipulator Considering Bearing Friction Based on Adaptive PI Control Strategy with Nonlinear Disturbance Observer

Abstract A manipulator that contains both flexible joints and flexible loads is called a dual-flexible manipulator. The vibration of dual-flexible manipulators is affected by the bearing friction torque and the double flexibilities. This vibration phenomenon will reduce the motion accuracy in dual-flexible manipulators. In this study, an adaptive PI control strategy using a nonlinear disturbance observer (DOB) is proposed to reduce speed fluctuations of the servo system, thereby suppressing the vibration. Firstly, the mechanical model of the dual-flexible manipulator considering bearing frictions is established. Then, the adaptive law of the PI controller is proposed by the Lyapunov stability theorem. The optimal values of controller parameters are obtained by the adaptive law. Finally, the numerical simulation and control experiments of the dual-flexible manipulator prove that the control strategy can powerfully reduce the vibration. The experimental results show that the control strategy can reduce the acceleration in the vibration sensitive direction of the flexible manipulator by 41.78% compared with the PI control strategy.