Synthesis of grasps with four contact points including at least three force-closure grasps of three contact points

The paper presents a method to build force-closure grasps on polyhedral objects with four frictional contact points such that three of the fingers can individually lose the contact with the object without making the three finger remaining grasp losing the force-closure property. This type of grasps is useful to allow the object manipulation via regrasp using finger gating. A necessary and sufficient condition for the determination of these grasps is proposed, as well as the algorithm to compute them.