Robust three-finger three-parameter caging of convex polygons

Abstract

This paper studies cages of convex polygonal objects using three point fingers. The fingers are said to cage the object when it is impossible to move the object arbitrarily far from its initial placement without penetrating the fingers. We consider a three-parameter model of the relative position of the fingers, which gives complete generality for three point fingers in the plane. We consider robustness of caging grasps - what variations in the relative position of the fingers is allowed without breaking the cage. Using a simple decomposition of free space around the polygon, we present an algorithm which gives all caging placements of the fingers and a characterization of the robustness of these cages, albeit at the cost of significant computational complexity.