Design Feasibility of an Energy-efficient Wrist Flexion-Extension Exoskeleton using Compliant Beams and Soft Actuators

Passive and active exoskeletons have been used over recent decades. However, regarding many physiological systems, we see that the majority explore both active and passive elements to minimize energy consumption while retaining proper motion control. In light of this, we propose a design that combines compliant mechanisms as passive support for gravity balancing of the hand's weight and soft actuators as active support for wrist flexion-extension. Our approach offers a safe, lightweight solution that intrinsically complements and supports the wrist's degrees of freedom. We hypothesize that the proposed soft wearable device is able to increase the range of motion and reduce muscle fatigue while being energy-conservative by balancing of the passive and active subsystems. In this work, we perform a design feasibility study for such soft wrist exoskeletons, particularly focused on wrist flexion-extension rehabilitation. Through optimization, geometries for the required functionality of the compliant beam and soft actuator are obtained, and their performance as separate subsystems is evaluated by simulations and experiments. Under the appropriate inputs, we show that the system can introduce a controllable bifurcation. Through experiments, we investigate such bi-stability and explore its usefulness for rehabilitative support of wrist flexion-extension. In short, the proposed wearable can offer a viable, energy-efficient alternative to traditional rehabilitation technologies.