Object manipulation by a multifingered gripper: on the transition from precision to power grasp

Whereas the emphasis of precision grasping only using the fingertips is placed on dexterity and sensitivity, power grasps guarantee high security and stability. But even if the task requires a power grasp, in the initial configuration the complete enveloping by the fingers is often impossible due to the position of the object in the workspace and only a fingertip grasp can be applied. Then a transition from precision to power grasping has to be performed. Based on an experimental study this paper discusses several possibilities to realize this transition by using a three-fingered dextrous hand mounted on a 6DOF robot. In particular it is distinguished between strategies requiring a coordination of robot and hand and strategies performing the transition only by the fingers like humans do