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Closed Loop Positive Feedback for Functional Electrical Stimulation Assisted Gait


R. Nguyen, H. Geyer, M. Morari

Recent Advances in Neuro-Robotics Symposium: Sensorimotor Control, Freiburg, Germany

Gait function can be severely affected by various impairments such as spinal cord injury and hemiplegia due to stroke. Although some patients are able recover partial function, problems such as drop foot can persist. Functional electrical stimulation has been shown to improve gait function in these 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 to improve gait, they are all essentially open loop control systems that do not adapt to changing conditions. Here, we propose a novel control method based on positive feedback for closed loop control of the ankle during walking. 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 is not possible, we demonstrate the possibility of coarse estimation using ground reaction force and goniometer measurements. We have implemented such a measurement system and show the predicted stimulation profiles calculated during a normal walking trial of a healthy subject. The preliminary results reveal that this control method is able to provide dynamic stimulation patterns that better mimic the activation patterns observed during normal gait.


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