Maintenance Robot for 5-MW Offshore Wind Turbines and its Control

This paper presents a novel gigantic robotic system for the operation and maintenance (O&M) of 5-MW offshore wind turbines. The robotic system consists of a mobile platform and two manipulators. The mobile platform performs vertical climbing on the turbines' towers and blades using a wire-driven parallel mechanism, while the manipulators perform cleaning and inspection using phased array ultrasonic testing (PAUT) devices, which require normal directional contact with the blade. For achieving the vertical climbing motion, height, and attitude control schemes are proposed, which overcome limitations such as varying nonholonomic constraints and unknown initial positions. For the manipulators' tasks, hybrid position/force control schemes using the linear least-squares method are proposed for achieving the conditions of the PAUT devices that allow inspection images to be captured under wind disturbance. To validate the robustness of our robotic system and control schemes in the environment of the 5-MW offshore wind turbines, we conducted a highly realistic experiment that involved part of a full-size tower and blade, and a wind velocity of 6.51 m/s. The results of this experiment show that the proposed robotic system and control schemes have sufficient robustness against wind disturbance to allow the O&M of 5-MW offshore wind turbines.