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Flows in Complex Systems

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

[+] Author and Article Information
Robin Chin

 Department of Mechanical Science and Engineering, University of Illinois, Urbana, IL 61801; Tippie School of Management, University of Iowa, Iowa City, IA 52242

Elizabeth T. Hsiao-Wecksler

 Department of Mechanical Science and Engineering, University of Illinois, Urbana, IL 61801

Eric Loth1

 Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, VA 22902

1

Corresponding author.

J. Fluids Eng 134(8), 081101 (Jul 27, 2012) (7 pages) doi:10.1115/1.4005725 History: Received April 29, 2010; Revised June 05, 2011; Published July 27, 2012; Online July 27, 2012

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.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the circular bellows (front view and isometric view) and placement at the heel of an insole. Black convoluted bellow and collapsible spring are visible through the transparent polycarbonate top plate.

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Figure 2

Treadmill gait data of pneumatic pressure from the small bellow mounted under the heel as a function of time. Each pressure build up represents a step.

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Figure 3

Treadmill gait data of pneumatic pressure from the small bellow mounted under the foot as a function of time. The bellows were mounted under the heel and metatarsal.

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Figure 4

The measured pneumatic pressures in the small (SB) and large (LB) bellows obtained from treadmill walking were matched to create similar pressure profiles on the MTS machine. One gait cycle is approximately one second.

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Figure 5

Static volume ratio measurement as a function of the initial charge pressure of the small bellow with no spring

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Figure 6

System schematic of bellow (B) doing work onto a piston cylinder (C)

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Figure 7

Maximum pneumatic pressure output as a function of the initial charge pressure of the bellows. The data were obtained from the machine testing experiment for the system with the bellow directly connected to a pressure transducer. Also shown are the isothermal predictions for the small bellow with no spring.

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Figure 8

Pneumatic pressure profile of the small bellow (SB) obtained from the machine testing experiment, with the bellow directly connected to a pressure sensor, compared to isothermal predictions from the static volume ratio and 75% of the static volume ratio

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Figure 9

Power output as a function of time for the pneumatic system with the bellows doing work on a piston cylinder

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Figure 10

(a) Linear displacement (solid) and pneumatic pressure (dash) in the piston cylinder and (b) power output as a function of time calculated from the displaced volume and the pressure in the piston cylinder

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Figure 11

Treadmill gait data of hydraulic pressure from the small bellow mounted under the heel as a function of time, which can be compared to Fig. 3 for the pneumatic under-heel system

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Figure 12

Treadmill gait data of hydraulic pressure from the small bellow mounted under the heel as a function of time. Each pressure build up represents a step, and the result can be compared to Fig. 2 for the pneumatic system.

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Figure 13

Maximum hydraulic pressure output as a function of the initial charge pressure for the water-filled bellows. The data were obtained from the machine testing experiment for the system with the bellow directly connected to a pressure sensor. See Fig. 7 legend.

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