Force Directed Design of a Voluntary Closing Hand Prosthesis

Abstract This paper presents the design of a body powered voluntary closing prosthetic hand. It is argued that the motion of the fingers before establishing a grip is much less relevant for good control of the object held than the distribution of forces once the object has been contacted. Based on this notion, the configurations of forces on the fingers and the force transmission through the whole mechanism were taken as point of departure for the design, rather than motion characteristics. For a good distribution of pinching forces on the object and a natural behavior, the prosthesis is made adaptive and flexible. To achieve good force feedback, the disturbing influences of the cosmetic glove are strongly reduced by a compensation mechanism. To further improve the transmission of forces, friction is reduced by furnishing the whole mechanism with rolling links. This force directed design approach has led to a simple mechanism with low operating force and good feedback of the pinching force.