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Ankle Feedback Control in FES Assisted Standing and Walking


R. Nguyen

Master Thesis

Impairment in the ability to voluntarily rotate the ankle joint, such as from stroke or spinal cord injury, negatively affects gait and posture function. Although some subjects are able to recover partial function, problems such as drop foot can persist. Functional electrical stimulation has been shown to improve gait function in such patients. The majority of systems apply fixed patterns of stimulation to the muscles, triggered by a foot switch or push button to indicate a particular phase of the gait cycle. The stimulation patterns used have varied from simple on-off square patterns, to trapezoidal patterns that prevent problems such as spastic reactions, to even intensity profiles mimicking muscle activation observed during normal gait. Although such systems work well, they are all essentially open loop control systems that do not adapt to changing conditions. Here, we propose a novel control method based on estimates of muscle force and length. The idea is to apply stimulation to the ankle dorsiflexors and plantar flexors according to positive feedback of muscle force or length. Although direct measurement of such muscle parameters was not done, we demonstrate the possibility of coarse estimation using ground reaction force and goniometer measurements. We have implemented such a measurement system and show that the system is able to assist quiet standing and produce stimulation profiles during walking at various speeds that are similar to natural EMG activity. The results of this study suggest the possibility of providing for patients improved FES ankle control that delivers natural activation patterns and adapts to user need.

Further Information

Type of Publication:

(12)Diploma/Master Thesis

M. Morari

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% Autogenerated BibTeX entry
@PhdThesis { Xxx:2008:IFA_3193
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