Design of an energy efficient transfemoral prosthesis using lockable parallel springs and electrical energy transfer

Over the last decade, active lower-limb prostheses demonstrated their ability to restore a normal gait for transfemoral amputees by supplying the required positive energy balance [1]. However, the added-value of such devices is significantly impacted by their limited energetic autonomy preventing their full appropriation by the patients. There is thus a strong incentive to reduce the overall power consumption of active prostheses. Addressing this need requires to revisit the electromechanical design. For both the ankle and the knee, the present paper demonstrates that both the use of a lockable parallel spring and the transfer of electrical energy between joints can significantly improve the energetic performance for overground walking. A simulation model of such a prosthesis was implemented in order to quantify the energy gain being achievable when augmenting a classical series elastic actuator (SEA) with different parallel spring topologies. Simulations predict that adding a lockable parallel spring (LPS) to the SEA reduces the ankle motor consumption by 24% and allows the knee (naturally dissipative) to produce 38% more electrical energy. Moreover, the total energy consumption of the device is reduced to 22J/stride when the harvested electrical energy from the knee is stored and transfered to the ankle.