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Research Papers

Design and Control of a Pneumatically Actuated Lower-Extremity Orthosis

[+] Author and Article Information
Xiangrong Shen

e-mail: xshen@eng.ua.edu
Department of Mechanical Engineering,
The University of Alabama,
290 Hardaway Hall,
Box 870276, Tuscaloosa, AL 35487

Manuscript received January 3, 2012; final manuscript received August 31, 2012; published online October 11, 2012. Assoc. Editor: Vijay Goel.

J. Med. Devices 6(4), 041004 (Oct 11, 2012) (9 pages) doi:10.1115/1.4007636 History: Received January 03, 2012; Revised August 31, 2012

Lower-extremity orthosis is a type of wearable mechanical device that serves a wide variety of important biomedical purposes, such as gait assistance and rehabilitative training. Due primarily to the constraints associated with actuation technology, the majority of current lower-extremity orthoses are either passive or tethered to external power sources, limiting the functionality of such devices. In this paper, the authors present the research results towards a fully mobile (i.e., untethered) powered lower-limb orthosis, leveraging the high power density of pneumatic actuators for the joint power generation. The design of the orthosis is presented, with the objectives of providing full locomotive assistance in multiple common locomotive modes and generating a minimum level of restriction to the wearer's daily activities. For the control of the orthosis, a finite-state impedance-based controller is developed, which simulates an artificial impedance in order to enable the natural interaction with the wearer. Preliminary testing on a healthy subject demonstrated that the orthosis was able to provide a natural gait and a comfortable user experience in the treadmill walking experiments.

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Figures

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Fig. 1

Metal-frame knee-ankle-foot orthosis

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Fig. 2

Actuation structures for the (a) knee and (b) ankle joints

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Fig. 3

Schematics of the actuation structures for the (a) knee and (b) ankle

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Fig. 4

Comparison of the torque capacity of powered orthotic joints versus the torque requirements of various locomotion modes: (a) knee joint, and (b) ankle joint. Note that the black lines indicate the torque capacities of the actuated joints.

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Fig. 5

Controller states and switching conditions

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Fig. 6

A healthy subject fitted with the powered lower-extremity orthosis

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Fig. 7

Comparison of the knee trajectories in walking, with and without power assist from the orthosis

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Fig. 8

Comparison of the ankle trajectories in walking, with and without power assist from the orthosis

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Fig. 9

(a) The knee joint assistive torque, and (b) power trajectories over a typical gait cycle

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Fig. 10

(a) The ankle joint assistive torque, and (b) power trajectories over a typical gait cycle

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