Grasp and manipulation of multiple objects

This paper discusses grasp and manipulation of multiple objects initially placed on a table. We show the kinematically necessary and sufficient condition for lifting up two cylindrical objects from a table by finger links in contact with them. It is guaranteed that if pushing points between a finger link and object is lower than the contact point between objects, two objects are detached from the table. For two grasped objects, we further show a sufficient condition for producing a small relative displacement between objects. This sufficient condition given as the function of joint torques enables us to achieve a primitive manipulation of two objects within the hand. The basic idea is also experimentally verified by using a three-fingered robot hand.