Knee energy harvester with variable transmission to reduce the effect on the walking gait

Harvesting energy from human motions is a promising solution to the power issue for wearable electronics. Recently, various energy harvesters were developed to capture the motion of the lower limbs such as the rotary motion of the knee and ankle joints to generate electricity. However, these devices would increase the users' burden for walking and at the same time alter the users' walking gait. It may also induce potential harm to the users' bodies. In this paper, we develop a lightweight human knee energy harvester to capture energy from the knee motion. To reduce the effect of the harvester on the users' gaits, a variable radius drum-cable mechanism with variable transmission ratio is employed to allow the generated torque to match the torque of the human knee joint. Experimental results indicate that when walking with the harvester, the changes to the users' walking gait are small, compared with normal gait. The Pearson's coefficient and root mean square error between the angle curves of the knee joint when walking with and without the device are over 0.96 and less than 5.96 , respectively. Metabolic cost testing shows no statistically significant difference between harvesting and normal walking.