A Robotic Transtibial Prosthesis With Equilibrium-Adjustable Parallel Springs to Improve Energy Efficiency in Slope Walking

Energy efficiency is crucial in developing transtibial prostheses, encompassing two main aspects: amputee metabolic cost and prosthetic energy consumption. The parallel elastic structure is commonly used to enhance power efficiency, but usually with a fixed balanced angle. However, it can be demonstrated that the energy efficiencies in both aspects are related to this balanced angle when walking on different slopes. Therefore, we developed a powered transtibial prosthesis with adjustable parallel springs to change the equilibrium position. Slope adaptation strategies in both aspects are proposed based on theoretical and dataset analysis. The effectiveness is experimentally illustrated through multiple unilateral transtibial amputees walking on various slopes. The results demonstrate that the proposed prosthesis can effectively increase the peak torque, and substantially impact the energy consumption and the metabolic cost by adjusting the equilibrium position. We also confirm that the optimal positions in the metabolic cost and the prosthetic energy consumption are different in the same slope condition.