Title: On Functionality of a New Mechanical Hand
Author: prof. Alberto Rovetta N. AA-3

Functionality of a new mechanical hand, able to grasp objects of generic shape. In its morphology it is similar to the human hand; in its functionality it is adaptable as a robot extremity or, with some specific devices, as a prosthesis. The mechanical aspects of this mechanism point out some basic characteristics. Its properties might be considered for a development of its adaptability to multiple functions, in robotics and maybe in orthopaedics.

Different principles of grasping are performed, with respect to the system, which is made of linkages with rods, springs, and a platform, with functions similar to the fingers and to the palm of the human land. The study of the mechanics of prehension shows that elastic energy stored in the system represents a term of stabilization of the grasping process. The joint (at the upper extremity of the hand) which reproduces the hyperextension is here used as prototype in a mechanical extremity, with analogy to the human hand functionality. It constitutes an element of stabilization, also for a prosthesis, because, when forces exceed a threshold value, the hand enlarges its amplitude and the object is grasped with greater efficiency.

By dynamic equations, torques applied at every joint may be determined, and the geometrical configuration of the system is obtained. The elastic torque in every joint is function of the relative angular rotations. It must be considered that. while in grasping systems with rigid connections the grasping force is exerted directly by an actuator, in the mechanical hand here presented the force to be applied is consequence of the obtained configuration of the system, and may be determined by means of the dynamic basic equations. The configuration is defined by a set of angles and by the position of the palm.

Future possible developments
The new mechanical hand here examined in its functionality shows its adaptability to prehension of objects of generic shape. Principles of biomechanics and of mechanical optimisation, considered in robotics and in prosthetics. might cause developments in the mechanics and in the hierarchic control.