Fluid-Power Harvesting by Under-Foot Bellows During Human Gait

Pneumatic and hydraulic bellows were investigated for under-foot power harvesting during human walking. Placement under the heel allows the bellow to be compressed during the heel strike of the gait cycle, whereas placement under the metatarsal allows compression during the mid-stance and toe-off phases. In either case, body weight is used as the power source for a self-contained fluid power circuit. Once unweighted, air is drawn into the bellow through a one-way valve allowing the bellow to recharge as it expands during the swing phase of the gait cycle. A collapsible spring was placed inside the bellow to ensure full opened conditions for this phase. To evaluate this concept, experimental studies were conducted on two circular bellows with outside diameters of 4.13 cm and 6.35 cm placed under the heel or the metatarsal of the foot, on a person walking on a treadmill. These pressure profiles were then reproduced on a compression testing machine to investigate the power generated per cycle. During normal walking, the pneumatic bellows generated peak power levels of 20–25 W and maximum pressures of 450 kPa. The average power available over a single cycle was 1.5 and 4.5 W for the small and large bellows, respectively. This novel use of bellows demonstrates the ability to use these devices for regenerative fluid power harvesting capabilities during walking.