Multimuscle Functional-Electrical-Stimulation-Based Wrist Tremor Suppression Using Repetitive Control

Wrist motion is produced by a group of muscles acting in a coordinated way. However, existing functional electrical stimulation (FES)-based wrist tremor suppression methods just stimulate one pair of muscles, which can limit the tremor suppression performance and cause muscle fatigue. To address these problems, this article proposes a multimuscle FES-based wrist tremor suppression method by fully considering the properties of wrist motion. First, with the consideration of the mainly involved two pairs of muscles in wrist flexion and extension motion, a multimuscle wrist musculoskeletal model with a Hammerstein structure is developed, and the parameters are identified. Then, a feedback repetitive controller combined with a feedforward linearization controller is proposed for tremor suppression. A frequency-modified inverse repetitive control algorithm and a gradient-based repetitive control algorithm are put forward to regulate the FES level properly. Finally, experiments on both unimpaired subjects and intention tremor patients verify that compared to the existing single-muscle-pair FES-based methods, the proposed methods can substantially improve the performance of tremor suppression and effectively reduce the level of electrical stimulation significantly, thereby reducing muscle fatigue.