Design and Simulation of a Pneumatic, Stored-energy, Hybrid Orthosis for Gait Restoration

[+] Author and Article Information
William K. Durfee, Adam Rivard

Department of Mechanical Engineering,  University of Minnesota, Minneapolis, MN 55439

J Biomech Eng 127(6), 1014-1019 (Jul 14, 2005) (6 pages) doi:10.1115/1.2050652 History: Received April 07, 2005; Revised July 14, 2005

Loss of mobility due to lower limb paralysis is a common result of thoracic level spinal cord injury. Functional electrical stimulation (FES) can restore primitive gait in the vicinity of a wheelchair by using electrical stimulation to generate muscle contractions. A new concept for FES-assisted gait is presented that combines electrical stimulation with an orthosis that contains a fluid power system to store and transfer energy during the gait cycle. The energy storage orthosis (ESO) can be driven through a complete gait cycle using only stimulation of the quadriceps muscles. The conceptual design of the ESO was completed and implemented in a dynamic simulation model and in a benchtop prototype for engineering measurements. No studies were conducted with human subjects. The results demonstrate the potential of the ESO concept for a feasible gait-assist system and the validity of the simulation model as a means for designing the system.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

Stored energy orthosis concept: (a) biased equilibrium position, (b) stimulation of quadriceps and storage of excess energy, and (c) discharge of stored energy

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Figure 2

Realization of ESO. Gas springs at the hip and knee bias joints in flexion. Pneumatic cylinders at the hip and knee convert mechanical to fluid power. Compressed air stored in accumulator tubing that couples hip and knee cylinders.

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Figure 3

Bench model physical prototype. The gas springs are on the back side.

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Figure 4

ADAMS dynamic simulation model. Head-arm-trunk loads were simulated with a controlled, moving “floor” that applied equal and opposite loads to the bottom of the leg linkage.

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Figure 5

Simulation model: hip and knee trajectories for one gait cycle

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Figure 6

Simulation model: force (top) and displacement (bottom) for hip (left) and knee (right) air cylinders for one gait cycle. Gas springs force leg to equilibrium during t=0–0.9s; knee extends during t=5.5–6.6s; pneumatic system forces hip extension during t=10.0–11.25s; leg returns to equilibrium during t=11.25–11.8s.

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Figure 7

Simulation model of knee extending at constant angular velocity: (a) t=2.0s; 60deg knee flexion, (b) t=4.0s; knee fully extended, (c) knee torque versus time. Required energy is 8.9J.

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Figure 8

Force-displacement properties of hip and knee air cylinders. Measured (markers) and two simulation results (lines). The dashed line accounts for dead volume between the cylinder and the valve.

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Figure 9

Prototype (markers) and simulation (line): hip (a) and knee (b) knee angle trajectories as joints move from full extension to equilibrium



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