In this paper, we report the model of an original actuation concept for a transfemoral prosthesis, relying on the combination of a single power motor, a compliant element (a spring), a mechanical differential, and two infinitely variable transmissions. It allows to manage the mechanical power flows through the device in both directions (i.e. when energy should be produced or dissipated by the knee and ankle), so that the power motor does not face the sharp load power fluctuations. The paper further reports a preliminary approach to synthesize a closed-loop controller for this device, and simulation results of this closed-loop behavior for three locomotion tasks: level-ground walking and stair ascent/descent. These results illustrate the capacity of this actuation principle to filter the load power profile, and further highlight the necessity to maximize the mechanical efficiency of each part of this actuation scheme.
