Caging Polygonal Objects Using Formationally Similar Three-Finger Hands

Caging offers a robust strategy for grasping objects with robot hands. This letter describes an efficient caging-to-grasping algorithm for polygonal objects using minimalistic three-finger robot hands. This letter describes how to cage and then grasp polygonal objects, using single actuator triangular three-finger formations, whose shape is determined by any desired immobilizing grasp of the polygonal object. While the hand's configuration space is four-dimensional, the algorithm uses the hand's two-dimensional contact space, which represents all two- and three-finger contacts along the grasped object boundary. This letter describes how the problem of computing the critical cage formation that allows the object to escape the hand is reduced to a search along a caging graph constructed in the hand's contact space. Starting from a desired immobilizing grasp, the graph is searched for the critical cage formation, which is used to determine the caging regions surrounding the immobilizing grasp. Any three-finger placement within these regions guarantees robust object grasping. The technique is demonstrated with a detailed computational example and a video clip, which shows caging experiments with a single actuator three-finger robot hand.