Global Localization Based on Tether and Visual-Inertial Odometry With Adsorption Constraints for Climbing Robots

Localization in a large-scale three-dimensional scene is a key challenge faced by climbing robots on large workpieces. This article proposes a global localization method for climbing robots based on tether displacement sensor, visual-inertial odometry (VIO), and computer-aided design (CAD) model of workpieces. Tether displacement sensor measures the distance between robot and tether anchor with little drift, which enables robot to acquire global pose. Adsorption constraints on robot motion are extracted using CAD model to reduce the drift of VIO. The approach realizes global localization with high accuracy for the robots when climbing on large workpieces without other external locating equipment. The performance is verified with a prototype of climbing robot testing on real large workpieces. In all experiments, our method with adsorption constraints outperforms existing VIO. The largest drift of merged trajectory is as low as 0.51% in global localization on a wind turbine blade with length of 8 m.