ELSA: A Foot-Size Powered Prosthesis Reproducing Ankle Dynamics During Various Locomotion Tasks

Powered ankle–foot prostheses offer the potential to emulate natural locomotion dynamics, thereby addressing the issues related to uneven gait and insufficient propulsion typically experienced by individuals with lower limb amputation wearing a passive prosthetic device. Despite significant progress, existing powered prostheses are often hindered by their substantial build height, bulky design, excessive weight, and noise level, limiting their widespread adoption. This work presents ELSA (Efficient and Lightweight Spring Ankle), a lightweight (1.15 kg) and compact (11 cm high) powered ankle–foot prosthesis fitting within the volume of a shoe and capable of providing a net positive mechanical energy over the gait cycle. This level of integration is achieved through an innovative arrangement of a spring and actuator mechanisms operating in synergy. This hybrid architecture offers users the choice to walk actively, with propulsive energy assistance; regeneratively, potentially allowing for energy harvesting to recharge the device battery; or completely turned off (passive). This prototype has been validated during benchtop experiments and through trials involving four amputated participants. These tests encompassed various scenarios, including treadmill walking and everyday ambulation tasks. In addition, a sensitivity analysis was conducted to assess how different control parameters impacted the provided mechanical energy and resulting gait performance.