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Mechanical Design and Experimental Validation of a Variable Stiffness Ankle Exoskeleton

The ankle joint plays an important role in providing propulsion and absorbing ground impact through dynamic stiffness adjustment. In comparison, the present ankle exoskeleton has no or limited ability in stiffness adjustment which constrains the compliant performance of the exoskeleton. Inspired by the stiffness characteristics of the human ankle joint during walking, this paper proposes an ankle exoskeleton allowing a wide range of stiffness adjustments. A bi-directional spring mechanism is designed to reproduce the ankle stiffness characteristics of the healthy person. Experimental results show that the proposed exoskeleton can provide the required stiffness without interfering with walking and it is effective in absorbing the ground impact as human ankle does.