Grasping and Fixturing with Customized Effectors

We have been interested in using curved, i.e., planar, cylindrical, or spherical, effectors for robotic grasping tasks. We have realized that every polyhedral object can be immobilized and caged with at most three such effectors. As one application of the theory, we are implementing "whole-arm grasping": in the figure, the virtual rock (as well as the "real" rock in the small figure at the lower right corner) cannot move, i.e., the two cylindrical effectors of the manipulator are immobilizing it; then, other contacts from the two arms or the torso can be added without losing stability. The two-armed robot is thus performing whole-arm grasping, which can be useful for a wide range of large, bulky objects, without special-purpose end-effectors.