Vibration suppression method for flexible link underwater manipulator considering torsional flexibility based on adaptive PI controller with nonlinear disturbance observer

Abstract

Achieving stable and high-precision control of underwater manipulators in complex ocean environments is one of the biggest challenges faced by the research of marine robotics at present. Flexible link manipulators can be installed on unmanned underwater vehicles to realize underwater operations such as underwater cable inspection, deep sea rescue, and marine organizational collections. The flexible link underwater manipulator will vibrate due to the influence of torsional flexibility and water flow disturbance during rotation, which will seriously affect the motion accuracy of the end actuator. In this paper, a control strategy combining the adaptive proportional-integral (PI) controller and the nonlinear disturbance observer is proposed, which indirectly suppresses vibration by improving the speed control accuracy. Firstly, according to the assumed mode method, a dynamic model of the flexible link underwater manipulator considering torsional flexibility and external disturbance is established. Next, the overload compensation control law is proposed to meet the closed-loop stability of the flexible link underwater manipulator. In addition, the PI controller's adaptive law is designed according to the Lyapunov theorem. Finally, the effectiveness of the adaptive PI controller with a nonlinear disturbance observer is proved by the simulation and control experiments of different control strategies. The results show that the proposed controller can achieve stable speed tracking and has a better vibration suppression effect.