Iterative learning control of drop foot stimulation with array electrodes for selective muscle activation

Abstract

Disorders of the central nervous system like stroke often lead to a paresis of the muscles responsible for dorsiflexion and eversion of the foot during swing phase. Functional electrical stimulation (FES) is commonly used to improve the foot movement. A precise placement of two single surface electrodes on the shank as well as a manual tuning of heelswitch triggered stimulation is required when using standard drop-foot stimulators. In this work, the use of automatically tuned array electrodes for selective nerve/muscle stimulation and the application of iterative learning control for adjusting stimulation intensities are investigated with the aim to obtain an optimal foot movement. The stimulation effect is observed by means of two inertial measurement units mounted on the foot and shank, respectively. Two array electrodes are placed over the areas covering the peroneal nerve and the muscle tibialis anterior. A fast identification procedure finds three suitable sets of array elements, forming so-called virtual electrodes, in both arrays. Two stimulation channels are established over the three virtual electrodes. Both channels produce dorsiflexion, but one promotes eversion and the other inversion. A decoupling matrix is applied to the stimulation intensities of both channels in order to obtain independent control over dorsiflexion and eversion. Finally, two independent iterative learning controllers are employed to achieve desired angle profiles. The proposed stimulation and control scheme is initially tested on a healthy person sitting on a table with the shank and foot free to swing. A tracking RMS error of less than one degree is achieved within six walking steps.

A decision support system for electrode shaping in multi-pad FES foot drop correction

“…Currently available commercial systems stimulate dorsiflexion only; they do not compensate for eversion (EV) or inversion (IV) and do not support push-off due to the complexity of proper electrode positioning [11, 14–16]. …”

RehaMovePro: A versatile mobile stimulation system for transcutaneous FES applications

“…3 Electrode arrays are used in an increasing number of research contributions, since they can help to increase the selectivity of muscle activation and to delay muscle fatigue. Electrode arrays consist of multiple small elements, which can be combined to form virtual electrodes of various sizes and shapes.…”

Feedback control of foot eversion in the adaptive peroneal stimulator

“…Recent research has therefore focused on the use of array electrodes which allow for quick manipulations of the stimulation site without the need for repositioning the array. In particular, it was demonstrated recently that both the dorsiflexion angle trajectory and the eversion angle trajectory of a healthy seated subject can be controlled by FES via array electrodes using ILC methods [12].…”