Passive hydraulic prosthetic foot to improve the push-off during walking

Passive prosthetic feet struggle to reproduce the human biological ankle range of motion and push-off. We propose the Hybrid-Hydraulic Ankle Prosthesis (H2AP), a prosthetic foot that provides a greater range of motion and push-off support compared to regular carbon feet. This novel prosthesis comprises a carbon foot and a hydraulic unit that includes a plantar flexion damper, a dorsiflexion damper, and a unidirectional spring that engage at specific phases of the gait cycle. The dampers are designed to enable an increased range of motion, and the unidirectional spring is used to store and release increased energy in late dorsiflexion and push-off. This paper focuses on the details of the mechanical design of the H2AP, its working principles, and the parameter tuning process. The design target is to replicate human ankle behavior in unimpaired walking, which is optimized using mathematical analyses and a simulation model. Pilot walking experiments with one transtibial amputee subject on level ground and a treadmill demonstrate the usability of the developed device and its acceptance in providing the intended functionality. The proposed design methodology can be used in the development and parameterization of the other assistive devices.