Robotic Grasp Optimization from Contact Force Analysis

The ability to quantitatively assess grasp performance is essential both in off-line planning of grasps for robotic manipulation as in evaluating on-line executed grasps. Until now most existing metrics rely on force-closure tests that are limited in scope. We propose a grasp quality metric that provides sensible performance criteria even in non-force-closure grasps. It is based in two improvements with respect to existing metrics: a patch contact model, providing smoothness properties, and a bimodal wrench space analysis that provides continuity in the transition from non-force-closure to force-closure grasps. It is experimentally demonstrated, in a series of simulations, that the developed metric outperforms existing ones. We also show empirically that optimal points are invariant to the choice of reference frame, which allows its application on-line in nonmodel based approaches.