Fuel efficiency of a portable powered ankle-foot orthosis

Morgan K. Boes, Mazharul Islam, Yifan David Li, Elizabeth T. Hsiao-Wecksler

Research output: Chapter in Book/Report/Conference proceedingConference contribution


A Portable Powered Ankle-Foot Orthosis (PPAFO) has been designed for gait assistance. The PPAFO can supply assistive torque at the ankle joint in plantarflexion and dorsiflexion using a bidirectional pneumatic actuator. Two control schemes have been developed to regulate timings of the assistive torques during different phases in the gait cycle. The Direct Event (DE) controller uses heel and toe force sensors to detect the start and end of key phases using specific events (e.g., heel strike and toe-off). The State Estimation (SE) controller finds the least-square-error between real-time sensor data and a reference model from training data to estimate the gait state and to detect phases based on this estimate. A pneumatic recycling scheme for improved fuel efficiency was also implemented. This scheme regenerates energy from plantarflexion exhaust gas to power dorsiflexion actuation. The objective of this study was to assess the fuel efficiency of these two controllers and pneumatic recycling scheme, as measured by fuel consumption and work output. Data were collected from 3 minute walking trials with the PPAFO by five healthy young control subjects. The SE with recycling (SER) scheme had an average fuel savings of 25% compared to the SE control scheme, and 24% compared to the DE controller. The SER controller allowed for comparable net work output to the SE controller which both did more net work than the DE controller. These observations can be applicable to other portable fluid-powered orthotics, prosthetics, and robotics in terms of potential impact of controller choice and energy regeneration on fuel consumption.

Original languageEnglish (US)
Title of host publication2013 IEEE 13th International Conference on Rehabilitation Robotics, ICORR 2013
StatePublished - 2013
Event2013 IEEE 13th International Conference on Rehabilitation Robotics, ICORR 2013 - Seattle, WA, United States
Duration: Jun 24 2013Jun 26 2013

Publication series

NameIEEE International Conference on Rehabilitation Robotics
ISSN (Print)1945-7898
ISSN (Electronic)1945-7901


Other2013 IEEE 13th International Conference on Rehabilitation Robotics, ICORR 2013
Country/TerritoryUnited States
CitySeattle, WA


  • ankle-foot orthosis
  • efficiency
  • exoskeleton
  • fluid power
  • gait assistance
  • pneumatic recycling
  • powered orthosis
  • regenerative

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Electrical and Electronic Engineering
  • Rehabilitation


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