A new fiber braided soft bending actuator for singer exoskeleton

Abstract

This thesis presents a design, development and analysis of a novel bending-type pneumatic soft actuator as a drive source for a finger exoskeleton. Soft actuators are gaining momentum in robotic applications due to their simple structure, high compliance, high power-to-weight ratio and low production cost. Smaller and lighter soft actuator that can provide higher power transmission at lower operating air pressure will benefit finger actuation mechanism compared to motorized cable and pulley-driven finger rehabilitation devices. In this study, a soft actuator with new bending method is proposed. It is based on fibre reinforcement of two fibre braided angles of contraction and extension characteristics combined in a single-chamber cylindrical actuator. Another four design parameters identified that affect the bending motion and the actuating force were the air chamber diameter, position of fibre layer reinforcement, fibre reinforcement coverage angle, and silicone rubber materials. Geometrical and material parameters were varied in Finite Element Method (FEM) simulation for design optimization and some parameters were tested experimentally to validate the FEM models. The effects of fibre angles (contraction and extension) on the bending motion and force were analyzed. The optimized actuator can generate bending motion up to 131° bending angle and the end tip of the actuator can make contact with the other base tip at only 240 kPa given input pressure. Both displacement simulation and experimental testing results matched closely. Maximum bending force of 5.42 N was generated at 350 kPa. A wearable finger soft exoskeleton prototype with five optimized bending actuators was tested to drive finger flexion motion of eight healthy subjects with simulated paralysis conditions. The finger soft exoskeleton demonstrated the ability to provide gripping force of 3.61 ± 0.22 N, gained at 200 kPa given air pressure. The device can successfully provide assistance to weak fingers in gripping at least 240 g object. It shows potential in helping people with weakened finger muscle to be more independent in their finger rehabilitation exercise.