Fluid-power harvesting by pneumatic bellow during human gait

In this paper, we describe power and pressure characteristics of bellows designed for under-foot power harvesting during human walking for a single cycle. This single cycle corresponds to the typical human gait cycle (heel-strike and stance on the floor to toe-off and free swing to subsequent recontact with the floor, with a total duration of about one second). A bellow can be placed in a shoe insole and compressed during initial heel strike or during the mid-stance portion of the gait cycle. The compressed fluid can then be used for power applications during the remaining portion of the cycle. A collapsible spring was placed inside the bellow to extend it when the foot is off the ground, yet allow the bellow to be compressed. 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. Thus, body weight is used as the power source for a self-contained pneumatic circuit. Experimental studies were conducted on two circular bellows with outside diameters of 1.625 in and 2.5 in (4.13 cm and 6.35 cm) and stroke lengths of approximately 1.4 cm. The pressure dynamics of the bellows placed under the heel of the foot or under the ball of the foot were investigated while walking on a treadmill. These pressure profiles were then reproduced on a compression testing machine to investigate the power generated per gait cycle. The results indicate that the bellows generated a peak power during normal walking of approximately 25-30 W and a maximum pressure of 450 kPa. The average power available over a single gait cycle is on the order of 1 W. This novel use of bellows demonstrates the ability to use these devices for regenerative fluid power harvesting capabilities during walking.