A Lightweight Wrist Exoskeleton with Equivalent-Input-Disturbance-Based Control for Pathological Tremor Suppression

Developing a wearable exoskeleton that effectively suppresses pathological tremor while remaining lightweight for daily use is a significant challenge. Furthermore, the complex and time-varying nature of wrist dynamics often limits the performance of conventional model-based control strategies. To address this, this study proposes a lightweight (less than 200 g) wrist exoskeleton. By employing a compact transmission architecture to amplify the torque of a miniature motor, the design achieves the high-fidelity force transmission required for active suppression while minimizing physical burden. Additionally, ergonomic sponge-lined fixtures are integrated to ensure user comfort and adaptability. To tackle the challenge of unmodeled wrist dynamics and time-varying tremor, an Equivalent-Input-Disturbance (EID) control strategy is developed. This method treats complex nonlinearities and tremor torque as a lumped disturbance, estimating and compensating for them in real-time without requiring precise patient-specific modeling. Pilot clinical validation with five patients (four with PD and one with ET) demonstrated significant tremor attenuation, with a power suppression ratio ranging from 89.37% to 96.37%. Furthermore, the root-mean-square error during voluntary motion tracking was reduced by 21.3%. These preliminary findings suggest the feasibility and potential efficacy of the proposed system.