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FES Ankle Control for the Lokomat


R. Nguyen, S. Perala, S. Micera, M. Morari

ZNZ Symposium, Zurich, Switzerland

Conventional therapy is unable to restore functional gait for many patients. Functional electrical stimulation (FES) can be used for such patients to exogenously activate muscles. Function can be improved, even after therapy in the absence of stimulation. Another rehabilitation technology is treadmill training with the automated gait orthosis Lokomat. To improve training, a closed-loop control system was developed to control the ankle angle with FES during gait training using the Lokomat. The controller modulated stimulation amplitude, based on proportional-integral-derivative (PID) feedback of ankle angle, to contract the tibialis anterior and triceps surae muscles. Feedforward control and phase correction were further added to improve performance. The system was evaluated healthy volunteers. At a stride time of 2.0 seconds, the phase shift between the desired and measured ankle angle converged in as few as seven steps with an RMS error of 3.1 degrees. Although the phase shift was not affected by decreasing the stride time to more typical 1.5 and 1.0 seconds, an increase of the RMS error was observed: 3.5 and 4.2 degrees respectively. We conclude that the developed system was able to provide FES of the ankle appropriate for gait therapy with the Lokomat.


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