Design and structural analysis of a passive ankle-foot prosthesis with manually adjustable stiffness and having two degrees of freedom

Abstract

The majority of commercial Below Knee Prosthetics are Passive Prosthetics as they are lightweight, affordable, durable and require less maintenance. Since the human ankle is a set of highly integrated joints, ankle design is the most crucial aspect of a Below Knee (transtibial) prosthesis design process. This research work focuses on developing and analysing a Passive Ankle-Foot Prosthesis to attain 2 DOF, i.e., plantarflexion-dorsiflexion and inversion-eversion motions of a foot, such that it could mimic the behaviour of a natural lost limb. Further, this study presents the integration of manual ankle stiffness modulation into the same design for dorsiflexion-plantarflexion which can be altered by the amputee to a preferred stiffness for various ambulation requirements. The design proposed in this study also assimilates the features of an ESR and a SACH foot to a significant level. The structural analysis demonstrates that the device can sustain a vertical load of 800 N with the Factor of Safety (FOS) of 1.5. The deflection analysis of the leaf spring used in the design shows the exponential increase in stiffness as the slider moves beyond 70% of the length of the leaf spring towards its free end.