Passive Knee Exoskeleton Using Brake Torque to Assist Stair Ascent

Manipulating mechanical energy intelligently, passive exoskeletons can improve the energy efficiency of cyclic human motions. Aiming to reduce the energy cost of knee moment during stair ascent, this paper presents a concept of brake-torque support activated when the knee moment is required in the opposite direction to the angular velocity of the knee joint. Integrating an electromagnetic brake to a crossing four-bar knee joint with a compact design, the passive knee exoskeleton enables the polycentric knee center of rotation covering the wide range of knee angle during stair ascent. For preliminary validation, the surface electromyography (EMG) of rectus femoris (RF) and biceps femoris (BF) were studied on a healthy male volunteer wearing the exoskeleton on his right leg. The reduction of peak muscle activity is observed as the brake torque is applied during knee extension while the knee flexion moment is required.