Characterisation of a soft exosuit for assistance of the elbow joint

The use of fabric-based frames and Bowden cables to transmit forces and torques to the human body allows to design active assistive devices that are lighter, more comfortable and cosmetically less invasive than traditional exoskeletons. This approach has been shown to be successful in reducing the metabolic cost and muscular effort of human movements and in assisting impaired subject in daily activities. Yet still very little is known about how to optimise the transmission of forces at the interface between the suit and the human body, with significant implications for comfort, efficiency and safety of the device. This work outlines the design and characterisation of a soft, textile-based exosuit for assistance of flexion/extension of the elbow joint, with emphasis on a data-driven design for optimising the efficiency of the transmission and the distribution of forces at the human-suit interface. Quantifying and understanding how design choices such as the materials used for transmitting power and the structure of the functional components of the suit affect these parameters can help us to improve the ergonomics, safety and effectiveness of such devices. Results obtained by comparing different Bowden cables constructions show that the ones with a linear-strand construction offer the highest efficiency and stiffness, lowest backlash and lowest viscous friction. Combining semi-rigid components with fabric at the anchor points of the suit allows for a more homogeneous distribution of force at the human-suit interface, avoiding peaks of pressure that can disrupt subcutaneous blood flow and cause tissue damage.