Characterizing successful robotic insertion and removal from a dry storage cask using peg-like jamming and wedging analysis

This paper describes the derivation and experimental validation of geometric equations that govern insertion and extraction of a robotic inspection system that operates in gaps around vertical dry storage casks. During insertion, a robotic system may become jammed due to unbalanced forces acting on the robot, or wedged due to over-sized robot geometry. The robot must be removable by a tether in the event of power loss. Assuming simplified geometry and a quasi-static approach, the problem is modeled using a two-dimensional representation in which the robot is assumed to be rigid with equal weight distribution and a constant friction coefficient between surfaces. Equilibrium equations are derived from a modified peg-insertion formulation, allowing calculation of the maximum size of the robot and angle of insertion as a function of inspection gap geometry and friction. Experimentation tested the derived relationships using varying robot dimensions in a 1:1 scale mock-up of the overpack-to-canister gap space of a nuclear dry storage container. Experimental data confirmed that the modifications of the typical peg-insertion predicted successful insertion and extraction better than unmodified equations. The error between the model and experimentation had a mean and standard deviation of 4.4 and +/-0.53 degrees.