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Actuation Timing Strategies for a Portable Powered Ankle Foot Orthosis

[+] Author Affiliations
Emily A. Morris, K. Alex Shorter, Yifan Li, Elizabeth T. Hsiao-Wecksler, Timothy Bretl

University of Illinois, Urbana-Champaign, Urbana, IL

Geza F. Kogler

Georgia Institute of Technology, Atlanta, GA

William K. Durfee

University of Minnesota, Minneapolis, MN

Paper No. DSCC2011-6170, pp. 807-814; 8 pages
  • ASME 2011 Dynamic Systems and Control Conference and Bath/ASME Symposium on Fluid Power and Motion Control
  • ASME 2011 Dynamic Systems and Control Conference and Bath/ASME Symposium on Fluid Power and Motion Control, Volume 2
  • Arlington, Virginia, USA, October 31–November 2, 2011
  • Conference Sponsors: Dynamic Systems and Control Division
  • ISBN: 978-0-7918-5476-1
  • Copyright © 2011 by ASME


Ankle-foot orthoses (AFOs) are used to assist persons with lower-limb neuromuscular impairments. We have developed the portable powered AFO (PPAFO). This device uses a bidirectional pneumatic actuator powered by a CO2 bottle to provide dorsiflexor and plantarflexor torque assistance. The PPAFO operates tether-free, allowing for use outside of the laboratory. This system has been tested on one impaired and multiple healthy subjects. Timing of the assistance provided by the PPAFO has been determined by: 1) direct event detection using sensor feedback with threshold triggers, and 2) state estimation in which gait events are estimated using a cross-correlation based algorithm. Direct event detection, while simple to implement, can be unreliable for subjects with certain gait impairments. State estimation, while more complicated to implement, provides access to state information that cannot be directly measured by the AFO, which allows for greater flexibility in assistance timing. Current hardware limitations and future work are also discussed.

Copyright © 2011 by ASME
Topics: Orthotics



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