Inspection system for very thin and fragile surfaces, based on a pair of wall climbing robots with magnetic wheels

In this paper describes a pair of wall climbing robots that use magnetic wheels for adhesion. They are designed for inspecting the interior surfaces of gas-tanks in oversea ships. Environments like this were impossible to access by previous climbing robots, as they are made out of very thin sheet metal that cannot support a high robot mass and contain several types of difficult obstacles. In order to master these challenges, the system described in this work uses two robots in a "mother-child"-structure: the smaller robot is built very lightweight and simple, without the ability to steer or climb vertically. It just moves horizontally and uses ridges in the gas tank surface as guidance rails. In order to pass from one ridge to the next one, the smaller robot docks to the bigger "mother"-robot. This robot always stays in an area where the sheet metal is thicker and never enters the extremely fragile surfaces. Thus, its mass is not critical for the structural stability of the environment and the robot can hence be built big enough to be able to climb in all directions of gravity and to pass difficult obstacles along its path. In the present paper, the basic concept, the mechanical design of all important components and the proposed control strategy are described briefly, followed by test results of the most critical components. An outlook to similar applications to which the basic idea of this work can be successfully transferred concludes this article.