Visualization of Force-Closure Grasps for Objects Through Contact Force Decomposition

Abstract

This article presents an analysis of the mechanics for grasps of solid objects. The main feature in the approach followed in this article is the decomposition of the contact finger forces. At each grasp point, a contact force is resolved into components along the normal and tangential directions. This concept of force decomposition results in a new formulation relating the contact forces and the geometry of contact points. Mathemati cally, under the assumption of a frictional point contact model, this formulation motivates the need of forming degenerate (es sentially planar) and general solid object grasps with three and four contact points, respectively. Simple rules for testing the feasibility of a set of contact points are developed based on the closed-form expression for the internal contact forces, which is expressed in terms of the geometrical quantities of the con tact points and their relative orientations. The functions of the normal and tangential contact force components for manipu lating an object are easily visualized as squeezing and twisting through this new formulation.