Design of compact switchable magnetic grippers for the HyReCRo structure-climbing robot

Steel structures require inspection and maintenance tasks which are too dangerous for human workers, due to the risk of falling from heights. These tasks can be safely performed with the help of inchworm-like climbing robots, which use magnetic grippers to adhere, climb, and explore steel structures. This paper presents the design and implementation of novel magnetic grippers for the HyReCRo robot, which is a biped robot to climb and explore steel structures. Each gripper carries three switchable magnets and three rubber pads to increase friction and prevent slippage, and they are designed in two steps. Firstly, the notion of the Zero Moment Point is applied to guarantee that the grippers will not detach from the structure. Secondly, a static friction analysis is performed, determining the impending motion of the robot on the onset of slippage and the minimum friction coefficient necessary to prevent it. The developed grippers are very compact and offer an adhesion force of 33 kg on 3 mm-thick steel plates, which ensures a firm and stable adhesion to steel structures in all postures, as the experiments demonstrate.