A Climbing Machining Robot for Large Components With Variable Curvature Surface

Abstract

This article proposes a climbing machining robot that can adsorb and move on the variable curvature surface of large and complex components to perform machining tasks. Active compliance suction units, which consist of twofold innovation, are proposed for this robot to overcome the bottleneck involving adsorption on the variable curvature surface. To solve the dilemma between high vacuum tolerance and surface compliance capability, we designed a novel trachea-inspired anisotropic stiffness sealing lip for the suction chamber, and it showed flexibility in the adsorption direction for adoption to complex surfaces and presented a high stiffness that can withstand large vacuum forces at its sides. Furthermore, to avoid vacuum leaks due to overstretching and overcompressing of the sealing lip, we developed an active compliance actuator to align the axis direction of the suction chamber with the normal direction of the adsorbed surface and maintain a suitable distance. To meeting strict weight and dimension demands, the actuator innovatively combines cable-driven units and 3-revolute-revolute-spherical parallel mechanism to reach a high load/weight ratio. The prototype of the climbing machining robot was developed and tested on a real large wind-turbine blade with variable curvatures ranging from 1 to 15 m. The experimental results show that the 10 kg-weight climbing machining robot with three ACSUs can provide over 1000 N adsorption force in total, and the fluctuation of adsorption forces can be reduced by 96% compared with that of robots with traditional pure passive compliance suction units. A comparative polishing experiment was executed on different curvature regions of the wind turbine blade, and the results prove that the proposed method can apply uniform polishing. In addition, a polishing-quality verification experiment was realized using the proposed climbing machining robot with a force-controlled polisher. These polishing experiments proved the machining capability of the proposed climbing robot.