Wearable exoskeleton upper limb device based on soft actuators: design, characterization, and preliminary testing

This article presents the development of a wearable exoskeleton robotic device designed for the motor recovery of the upper limbs following stroke, in which the possibility of integrating soft actuators was explored. The device is designed for multi-joint assistance, with the ability to help patients in recovery training with sequential movements of the elbow, wrist, and fingers in flexion/extension and adduction/abduction. Based on the specific characteristics of each target area, the device integrates three different types of soft actuators, whose force and range of motion (ROM) characteristics were analyzed using numerical and experimental methods. The relatively low force/torque characteristics in the targeted areas of the limb have made it possible to develop a compact, lightweight system that offers comfort during long periods of use. The device is made entirely of soft materials and textiles, and the soft actuators have been designed based on average anthropometric characteristics. The force development and their ROM were the defining characteristics analyzed of the three different types of soft actuators (bellows-type textile actuator, McKibben-type artificial muscles, and PneuNets multi-segment actuators-MSA). The device integrates a closed-loop control, increasing performance as well as patients' adaptability. According to the results, the actuators develop sufficient force for recovery training, and preliminary analysis regarding ROM shows an error of 2.29% for finger flexion, 4% and 10.5% for adduction/abduction, for forearm flexion: 4.4%, and higher for hand flexion/extension. In accordance with these results, future directions concentrate on investigating the device on stroke patients and augmenting the portability of the mechanism.