               ! "#$%  &$’!  $()*           ! "#$%$"$&’() &$  +   * + , )  - * ,* .!..% /’() ! ! 0  *        ! ’() $  ,#       1 22"22 &3)’)()  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 CO 2 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.  AFO Anklefoot orthosis. PPAFO Portable powered anklefoot orthosis. DE Direct event detection. CC Crosscorrelation state estimator.       Walking is a fundamental part of everyday life for most individuals, and greatly contributes to overall quality of life. Gait itself is a cyclic task, with one cycle defined as the initial ground contact of the foot to the following contact by the same foot. During a gait cycle the ankle joint performs four main functional tasks: deceleration of the foot during loading response, support for stability during early to midstance, propulsion during late stance, and motion control of the foot during swing [13]. The ability of the ankle joint to perform these functional tasks can be impaired by injury or neuromuscular pathologies. Sizeable populations exist in the United States alone with these types of impairments: stroke (8M), spinal cord injuries (1.3M), multiple sclerosis (1M), cerebral palsy (412K), and polio (272K) [4, 5]. Pathological gait can manifest in a variety of ways, but two common lowerleg symptoms are weakness in the plantarflexors (calf muscles) or in the dorsiflexors (shin muscles). Weakness in the dorsiflexor muscles affects both the loading response and swing phases of gait. This affect could present as an audible foot slap during weight acceptance or footdrop during swing. Weak plantarflexor muscles, on the other hand, primarily affect limb stability and propulsion [1]. Proceedings of the ASME 2011 Dynamic Systems and Control Conference DSCC2011 October 31 - November 2, 2011, Arlington, VA, USA 1 Copyright © 2011 by ASME DSCC2011-6170 Downloaded From: http://proceedings.asmedigitalcollection.asme.org/ on 09/19/2015 Terms of Use: http://www.asme.org/about-asme/terms-of-use