Vibration suppression method for dual-flexible manipulator considering bearing friction based on nonlinear disturbance observer

A manipulator that contains both flexible joints and flexible loads is called a dual-flexible manipulator, whose vibration is affected by bearing friction torque and 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. First, a mechanical model of the dual-flexible manipulator considering bearing frictions was established. Then, the adaptive law of the PI controller was proposed by the Lyapunov stability theorem. The optimal values of controller parameters were 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 results show that the nonlinear DOB can effectively identify the friction torque in the manipulator servo system and the adaptive PI control strategy can effectively reduce the tracking error by changing the controller parameters. The experimental results of the physical prototype show that the adaptive PI control strategy using a nonlinear DOB control strategy can reduce the acceleration in the vibration sensitive direction of manipulators by 41.78 % compared with the PI control strategy. Therefore, the experimental results prove the effectiveness of the proposed control strategy for reducing the vibration of dual-flexible manipulators.