A high performance wire device for an elbow prosthesis

New requirements for human powered prostheses are energetic autonomy, low production cost and human like behavior. Several teams are developing new solutions for bionic arms, usually based on serial mechanisms. On the scientific panorama very few examples of parallel device are available. We present an alternative device, with a simple mechanical hardware, to simulate human elbow movements. The parallel architecture avoids the requirement of a full size actuator to perform flexion/extension movement. The wire transmission architecture allows two linear actuators to control the motion of the forearm among two degrees of freedom in an improved work volume. The device, indeed, is designed to provide also pronation/supination movement, that is usually provided by the wrist in common commercial products. The choice of power source is oriented to a mixed fluid actuation, in which pressurized gas transfer power to incompressible fluid, in order to get a non-back power transmission. To increase energetic autonomy, a "hydro-pneumatic" circuit is set up with capability to recover energy coming by passive movements. Energetic recover is never tried in arm prosthesis at the state of the art and it could be a future innovative feature.