Design and Evaluation of a Lightweight, Ligaments-Inspired Knee Exoskeleton for Walking Assistance

With proper assistance, knee exoskeletons can benefit humans with impaired leg function. Prior studies found that misalignment between the knee and the exoskeleton may cause harm and undermine assistance performance. Self-aligning mechanisms can reduce misalignment but implementing them with a simple and lightweight design remains a challenge. In this letter, we designed a lightweight (740 g) knee exoskeleton that can provide assistive torque for knee extension and flexion during walking. A compact elastic limiter was proposed to reduce misalignment using an integrated shock-absorbing slider. Drawing inspiration from the cruciate ligaments, springs were equipped to reduce the nonlinearities in the alignment process. With selected spring stiffness, preliminary pressure measurements between the frames and the human body showed the exoskeleton can reduce undesired interaction forces by 50.9% during walking assistance. Preliminary experimental results demonstrated the exoskeleton can achieve high torque control performance and reduce quadriceps activities during multiple gaits. For example, the activities of the rectus femoris, vastus medialis, and vastus lateralis were reduced by an average of 23.8%, 44.0%, and 34.0%, respectively during 8$^{\circ }$ uphill walking. The initial findings indicated the system's ability to provide effective gait assistance and made it promising for improving patients' mobility.