Preliminary design and evaluation of a multi-axis ankle-foot prosthesis

The human gait shows significant differences in the ankle movements during turning and sidestep cutting compared to straight walking, especially in frontal plane. This suggests that the next advancement in lower extremity assistive devices is to extend their design and control to the frontal plane. In this paper, the concept of a multi-axis powered ankle-foot prosthesis is introduced and its feasibility is shown by a proof of concept prototype of a cable-driven, multi-axis ankle-foot prosthesis. The design kinematics and its ankle joint's mechanical impedance in non-load bearing conditions are evaluated and discussed. It is shown that the developed prototype is capable of closely mimicking the ankle movements in both sagittal and frontal planes during turning and walking on straight path with passive mechanical impedance in sagittal and frontal planes comparable to the ones of the human ankle.