Ankatron: Design, Development, and Functional Evaluation of 2-DoF Robotic Transtibial Prosthesis

The growing population of transtibial amputees worldwide highlights the urgent need for functional and lightweight powered prostheses. In this study, we present Ankatron, a robotic transtibial prosthesis that integrates two complementary mechanisms to replicate the natural gait cycle during level walking. The dorsiflexion (DF) mechanism employs parallel springs that compress during mid-stance and release stored energy at push-off through a circular slot, thereby regulating the effective moment arm at the ankle joint. In parallel, the Extra Energy Storing (EES) mechanism uses a ball-screw actuator to accumulate energy throughout the gait cycle, except during push-off, and releases it at push-off to compensate for the torque and power demands of walking. Kinematic and kinetic simulations conducted in ADAMS initially confirm that the proposed design successfully reproduces the torque and power requirements of natural gait. Furthermore, adding a second degree of freedom in inversion/eversion (Inv/Ev) enhances balance control during walking on uneven and sloped terrain. The prototype, manufactured using composite 3D printing, results in a device that is 46% lighter than comparable prototypes reported in the literature. Functional evaluations with both a non-disabled subject and a transtibial amputee demonstrate that Ankatron generates more than the required torque for natural walking, exceeding biological demand by 31% in the able-bodied trials and 40% in the amputee trials. These findings demonstrate the feasibility of a lightweight, multi-DoF powered prosthesis capable of replicating natural ankle biomechanics while providing enhanced adaptability to varied terrains.