A smart harvester for capturing energy from human ankle dorsiflexion with reduced user effort

Scavenging energy from human motion is a potential way to meet the increasing requirement of electrical power supply for portable electronics. However, since the conventional energy harvesters may collect both positive and negative work, the users have to pay extra efforts. This work aims at developing a smart energy harvester to accurately identify and capture the negative work of human ankle motion. During normal walking, only the dorsiflexion at stance phase performs negative work. Thus, one-way clutch is employed to filter ankle plantarflexion and mechanical contact switch array is used to disconnect electrical load, avoiding capturing positive work when ankle dorsiflexion is at swing phase. With the one-way clutch and mechanical contact switch array, the energy harvester can effectively target negative work as energy scavenged without consuming electrical energy. A wearable and light prototype is built to test its power output and users' metabolic expenditure during walking. The energy harvesting system is also modeled and analyzed. The experimental results show that the energy harvester produces an average power of 0.35 W at 4.9 km h ^-1 while reducing metabolic expenditure by 0.84 W, so as to achieve lower cost of harvesting compared with the previous work.