Control and Implementation of a Fluidic Elastomer Actuator for Active Suppression of Hand Tremor

Active exoskeletons for tremor suppression show potential for treatment of pathological tremor thanks to their non-invasive nature. However, the active force was only used for the voluntary movement following. As a potential alternative, fluidic elastomer actuators (FEAs) possess compliance and flexibility that is important for wearable devices. In this letter, we introduce the control implementation for a FEA to the application of active suppression of hand tremor, which allows a wearable FEA actively exerting force on the finger against tremor and meanwhile following the voluntary motion. The proposed pressure control algorithm could push the closed-loop pressure control to 19 Hz cutoff frequency. A combination neural network of Gated Recurrent Unit-Multilayer Perceptron (GRU-MLP) was proposed to identify and control a fiber-reinforced FEA following the voluntary movement of hand. The active tremor suppression effectiveness of the proposed method was tested on a bench-top tremor simulator, and such method could suppress the hand tremor from the original amplitude of more than 5$^\circ$ to less than 1$^\circ$. The proposed method paves a new way for tremor suppression exoskeletons.

I. Introduction

Approximately 60% of those people affected by pathological tremor (PT) experience movement disability in their activities of daily living because of the involuntary, rhythmic oscillations of body parts [1], [2]. Amid the treatments for PT, exoskeletons for tremor suppression have shown advantages and application potentials due to their relatively low cost and the non invasive nature [3], [4]. Recent studies in this field are classified into three major strategies: active methods that apply active force on the human body [5], [6], [7], [8], passive methods that utilize mechanical dampers with a fixed value of damping [9], and semi-active methods utilizing mechanical dampers with an adjustable value of damping [10]. Active methods possess superiority such as their full suppression of tremors due to their abilities to exert active force on the body against tremors. However, these active methods did not exert active force on finger for resisting against tremor and instead only utilized the active force to follow the voluntary movement and relied on the passive resistance of exoskeletons to achieve tremor suppression.