ON THE CLOSURE-PROPERTIES OF ROBOTIC GRASPING

The form-closure and force-closure properties of robotic grasping are investigated. Loosely speaking, these properties are related To the ca pability 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) const raints, such as those applied on a workpiece by a mechanical fixture, while force-closure is related to the capability of the particular rob otic device being considered to apply forces through contacts. The con cepts of partial form- and force-closure properties are introduced and discussed, and art algorithm is proposed to obtain a synthetic geomet ric description of partial form-closure constraints. Although the lite rature abounds with form-closure tests, proposed algorithms for testin g force-closure are either approximate or computationally expensive. T his article proves the equivalence of force-closure analysis with the study of the equilibria of an ordinary differential equation, to which Lyapunov's direct method is applied. This observation leads to an eff icient algorithm for assessing the force-closure property of the grasp .