This paper describes a wire-driven parallel robotic system for the maintenance of offshore wind turbines. This robotic system vertically climbs on towers or blades, and performs cleaning and inspection using waterjets and phased array ultrasonic testing (PAUT) devices, respectively. For a detailed mechanical design, mechanisms for (1) climbing towers or blades, (2) transition motion between towers and blades, (3) gripping blades, and (4) contact motion between PAUT devices and blade surfaces are proposed so that the robotic system can maneuver on towers and blades. For the motion analysis of the robotic system, nonholonomic constraints are analyzed and utilized in height and attitude control schemes, which are proposed to adapt varying nonholonomic constraints of blade surface and achieve the climbing motion on towers and blades. To validate these control schemes, we conduct experiment and analyze the performance of the proposed control schemes. The results show that the height and attitude control schemes for the robotic system do achieve the control goals and overcome the control challenges.

Recently, offshore plants are demanded to secure natural resources more and more and it is strongly required unmanned ones for safety of human operators and less running costs. In this paper, a practical multi-user teleoperation system is proposed for monitoring, inspection, operation, and maintenance of the unmanned offshore plants. The proposed system is developed to control mobile manipulator in a cooperative way among multiple human operators for better performance. For this, two control schemes, hand-eye coordination and disjoint axes were introduced for easier intuitive control of the mobile manipulator and for better cooperative control among multi-user, respectively. A well-known passivity-based approach, the time-domain passivity approach was, in addition, adopted to maintain system stability. And then, the proposed multi-user teleoperation system was evaluated via a human-centered method with several quantitative metrics regarding task completion time and interaction forces. Experimental results showed that the proposed multi-user teleoperation system has the benefit in tasks requiring less task completion time and interaction forces.