Design and development of a lightweight ankle exoskeleton for human walking augmentation

Abstract

Most of powered ankle exoskeletons add considerable distal mass to the user which limit their capacity in reducing the metabolic energy of walking. The objective of the work presented in this paper is to develop an ankle exoskeleton with a minimum added distal mass compared to existing autonomous powered ankle exoskeletons while it can provide at least 30 Nm of assistive plantarflexion torque. The proposed exoskeleton uses Bowden cables to transmit the mechanical force from the actuation unit attached to the waist to the carbon fiber struts fixed on the boot. As the struts are pulled, they create an assistive ankle plantarflexion torque. A 3d-printed brace was attached to the shin to adjust the direction of the cables. A design optimization study was performed to minimize the mass of the struts, thereby limiting the total added distal mass, attached to the shin and foot, to only 348 g. The main result obtained from walking tests was the reduction of the soleus and gastrocnemius muscles activity by a maximum of 37% and 44% respectively when walking with the exoskeleton compared to normal walking. This result shows the potential of the proposed exoskeleton to reduce the metabolic cost of walking and emphasizes the importance of minimizing the distal mass of ankle exoskeletons. Tests with more subjects will be carried in the future to confirm this result.