Designing of a Dual-Degree-of-Freedom Passive Ankle Exoskeleton

The current passive spring-actuated ankle-foot exoskeleton draws inspiration from the muscle-tendon unit. However, it still faces challenges such as operational noise, reliability and overbinding due to the lack of freedom. This study presents a novel passive powered clutch-spring design, where disengagement is achieved through cable length control via a pre-tensioning mechanism. The exoskeleton features two rotational degrees of freedom in the sagittal and coronal planes, enabling ankle inversion and eversion. The efficacy of the exoskeleton was evaluated by analyzing lower limb joint angles, joint moment, and calf muscle activation during walking. Preliminary findings suggest that this exoskeleton can offer up to 25% of the natural ankle joint moment, assisting in reducing joint moments and calf muscle activation during walking. These results highlight the potential of this ankle-foot exoskeleton for enhancing daily human activities.