Wrench resistant multi-finger hand mechanisms

The classical definition and analysis of force closure in robotic grasping focuses only on the fingertip bodies and their contacts with the grasped object. However, the kinematic properties of the hand mechanism can have a non-trivial effect on the actual type of force closure which can be realized at a given grasp. This paper takes a new look at this classical problem, and introduces technical results on force closure, or wrench resistance, which incorporate the hand mechanism's kinematics in this important grasp security measure. Based on a decomposition of the finger contact forces into canonical subspaces, the paper introduces a division of the finger contact forces into active and passive forces, as well as a dual division into resistant and internal contact forces. The paper develops new formal definitions of these concepts, and describes their mutual orthogonality relationships. Based on these definitions, the paper introduces new theorems of wrench resistant grasps which factor the hand mechanism's structure into the analysis of a given grasp. Examples illustrate how the hand mechanism's structure affects its ability to maintain secure wrench resistant grasps.