Design and Evaluation of a Self-Aligning Knee Exoskeleton for Knee Extension Assistance During Walking

Exoskeletons can help people with impaired knee extensor function by providing assistance. Previous studies have shown that adding passive degrees of freedom to the knee exoskeleton can help reduce unwanted load on the knee joint. However, the problem of achieving passive degrees of freedom with low-weight structures has not been resolved. We designed and built a self-aligning knee exoskeleton which weighs 1.76kg and uses a slider-rail structure to add a passive degrees of freedom in the kinematic chain. The device was actuated by an off board motor to apply knee extension assist torque during walking. A magnetic connection device was designed to quickly connect the thigh and calf segments of the exoskeleton. The exoskeleton was evaluated on a healthy subject walking uphill at 0°, 2°, 4° and 6° slope with a setup assistance profile. The results indicated a decrease in rectus femoris, vastus medialis and vastus lateralis activity under assistance. The root mean squared (RMS) of the vastus medialis muscle activity decreased 21%, 25%, 24%, and 33% in each of the four conditions. These preliminary results show that the device has the capability to explore more assistance strategies to improve gait rehabilitation.