Mechanical Compliance and Dynamic Load Isolation Design of Lower Limb Exoskeleton for Locomotion Assistance

Improving the comfort and portability of exoskeleton structures for human locomotion assistance is challenging. Research shows that the misalignments between exoskeletons and human joints will lead to interference and undesired interaction forces in locomotion. Moreover, the weight and inertia of exoskeletons will lead to rapid changes in impact forces acting on the wearer. When the exoskeleton is tightly bound to the wearer's body, such forces are usually unavoidable. These issues not only reduce the comfort and portability of exoskeletons, but also increase the energy costs to wearers. To address these issues, we propose a novel lower limb exoskeleton with a constant-force suspension mechanism and self-adapting compliant joints. The constant-force suspension mechanism aims to isolate the impact force on the back of the wearer, while the self-adapting compliant joints aim to reduce the misalignments between the exoskeleton and the wearer. For the first time, a structure designed to isolate the impact force of exoskeletons is proposed. Moreover, compliant joints exhibiting comprehensive great performances in portability, flexibility, self-aligning, and weight-supporting ability have also been rarely reported. The experimental results demonstrate that the developed mechanisms can reduce the impact forces and misalignments in locomotion. Furthermore, the proposed exoskeleton can reduce the metabolic rate during walking at 5 km/h by 10.95 ± 4.40% and that during running at 9 km/h by 1.71 ± 4.54% compared with locomotion without the exoskeleton. These results confirm that the proposed designs can improve the performance of the exoskeleton in locomotion.