A robotic forearm orthosis using soft fabric-based helical actuators

Abstract

This article outlines the design, construction, and preliminary human-subject evaluation of a robotic forearm orthosis. The robotic forearm orthosis integrates an antagonistic pair of soft fabric-based helical actuators, which provide active pronation and supination torques. The pneumatic fabric-based helical actuators are fabricated with a knit elastic band, strain limiting nylon fabric, and internal bladder. Empirical isometric loading characteristics show that the actuators can provide up to 1.7 Nm of torque when inflated to an internal pressure of 690 kPa (100 psi). The effectiveness of torque assistance provided by the robotic forearm orthosis was assessed during a preliminary (N=6) human-subjects evaluation. Subjects completed pronation and supination reaching tasks, while varying levels of assistive torque were applied to the users. Subject effort was evaluated with surface electromyography. Results indicate that the assistive torques provided by the proposed robotic orthosis significantly decreased subjects' efforts during both reaching tasks. On average, the proposed robotic orthosis reduced the effort by 59% and 24%, for supination and pronation respectively. This work demonstrates the practical implementation of a tunable fabric-based robotic forearm orthosis, that can reduce user effort during a manipulation task.