Multivariable control of foot motion during gait by peroneal nerve stimulation via two skin electrodes

Foot drop appears, for example, in stroke patients and is characterized by the limited ability to lift (the lateral and/or medial edge of) the foot, which leads to a pathological gait. We consider treatment of this syndrome via Functional Electrical Stimulation (FES) of the peroneal nerve during the swing phase of the paretic foot. We introduce a novel stimulation pulse waveform modification technique that allows us to manipulate the recruitment of m. tibialis anterior and m. fibularis longus almost independently via two single surface electrodes without violating the zero net current requirement. A piecewise linear controller output mapping is applied in order to cope with the nonlinearities in patients' stimulation intensity tolerance. The pitch and roll angle of the foot are estimated by means of an Inertial Measurement Unit (IMU) and controlled via a decentralized Iterative Learning Control (ILC) scheme. We demonstrate the effectiveness of our approach in experimental trials with stroke patients walking on a treadmill. Starting from conventional stimulation parameters, the controller automatically achieves physiological foot pitch and roll angle trajectories within only two strides.