Abstract
Screw theory is used to establish the general kinematic prin ciples offully-in-series and fully-in-parallel devices. Through screw theory, we show that a workpiece grasped by a fully-in- series manipulator can only lose freedom while a workpiece grasped by a fully-in-parallel manipulator can only gain freedom. Multi-finger multi-freedom grippers or robot hands use a mixture of in-parallel and serial actuation, and so a workpiece grasped by such a device can both gain and lose freedom. These linkages belong to a class called composite serial/in-parallel manipulators. Using the well-established concepts of screw systems and reciprocity, we identify the general criteria that govern the gain and loss of workpiece freedoms. We illustrate how these gains and losses of work piece freedom arise, by considering the Stanford/JPL hand.