On the Closure Properties of Robotic Grasping

Abstract

The form-closure and force-closure properties of robotic grasp ing are investigated. Loosely speaking, these properties are related to the capability of the robot to inhibit motions of the workpiece in spite of externally applied forces. In this article, form-closure is considered as a purely geometric property of a set of unilateral (contact) constraints, such as those applied on a workpiece by a mechanical fixture, while force-closure is related to the capability of the particular robotic device being considered to apply forces through contacts. The concepts of partial form- and force-closure properties are introduced and discussed, and an algorithm is proposed to obtain a synthetic geometric description of partial form-closure constraints. Al though the literature abounds with form-closure tests, proposed algorithms for testing force-closure are either approximate or computationally expensive. This article proves the equiva lence of force-closure analysis with the study of the equilibria of an ordinary differential equation, to which Lyapunov's di rect method is applied. This observation leads to an efficient algorithm for assessing the force-closure property of the grasp.