Multiple Model Switched Repetitive Control with Application to Tremor Suppression

Tremor is a debilitating oscillation of the limbs that affects millions of people worldwide. Functional electrical stimulation (FES) can reduce tremor by artificially activating opposing muscles, and when mediated by repetitive control (RC), has potential to provide complete suppression. However, all previous RC applications have limited performance due to fatigue, spasticity and modelling error. This paper first applies gap metric analysis to derive robust stability margins for RC subject to model uncertainty. It then formulates a multiple model switched repetitive control (MMSRC) scheme with guaranteed robust performance bounds. Simulation results demonstrate that MMSRC effectively suppresses tremor with realistic levels of identification error, fatigue and spasticity, whereas conventional RC FES schemes are unstable.