Hand prosthesis design: Enhancing grasping capabilities through mechanical features

Prosthetic hand devices present the following limitations: low functionality, low cosmetics and low controllability. In order to overcome the main weaknesses generally associated with commercial prostheses the following criteria should be addressed: the prosthetic device should perform a stable power grasp with a wide variety of object with complex shapes; the prosthesis should have the same weight and dimensions of the human hand; and furthermore, the grasping movements should result as natural as possible and finally, the prosthesis should be easy to operate.
This thesis presents two different approaches aiming at solving the listed weaknesses and illustrates the differences in design approaches between active and passive adaptive grasp: the first one is based on the increase of the active degrees of freedom through the adoption of micro-electromagnetic actuators. The second approach is based on the exploitation of underactuated mechanisms that performs a passive adaptive grasping. Underactuated mechanisms allow reproducing most of the grasping behaviors of the human hand without augmenting the mechanical and the control complexity. The complexity of an underactuated finger can be further reduced applying the concept of compliant mechanisms that represents a further reduction of mechanical complexity and a strategic feature for prosthetic hand design.