The optimal object posture that minimizes contact forces in grasping

Because of the ill-posedness of grasping, one feasible method must be selected from possible strategies. Among many factors, this paper focuses on the posture of an object: which object direction is best when it is grasped. Then, the object is assumed to be held with three points where the contact forces can be generated in any directions. To evaluate the object posture, the norm of contact force vector consisting of the normal and tangential forces is selected. Consequently, the contact force becomes minimal when the center of mass of the grasped object and the centroid of the triangle composed by three contact points are aligned in the gravitational direction.