Multi-articular passive exoskeleton for reducing the metabolic cost during human walking

Ankle passive exoskeleton has been demonstrated to enhance walking economy and reduce the metabolic cost during walking. How to develop multi-articular passive exoskeleton to further reduce the metabolic cost during human walking still remains a challenge. In this paper, we develop a hip-knee passive exoskeleton that uses springs to assist both hip extension and knee flexion. Springs in the exoskeleton are firstly stretched to store some of the negative mechanical power of knee joint during the late swing phase, then the stored energy in the springs is released to assist hip extension during the early stance phase. The whole process is controlled by a mechanical clutch. The experiment results show that the metabolic cost was reduced by 7.6^% compared to walking without the exoskeleton. To our knowledge, this is the first multi-articular passive exoskeleton that can reduce the metabolic cost of walking. This paper also discusses the possibility for the passive exoskeleton to exploit heel-strike energy for further reducing the metabolic cost of walking.