Rigid body analysis of the indeterminate grasp force in power grasps

The grasp force in power grasps is not necessarily determined uniquely by joint torques when Coulomb friction is assumed in the contact points between a grasped object and finger links. This paper analyzes the indeterminate grasp force with their rigid body models. This paper shows that contact sliding directions are constrained in power grasps. The frictional force acts only in the opposite direction of sliding. This characteristic of friction restricts the grasp force in power grasps although it is indeterminate in general. First the authors show an example to illustrate this restriction imposed on a grasp force. A special case where it is unique is shown