A Scalable Variable Stiffness Revolute Joint Based on Layer Jamming for Robotic Exoskeletons

Abstract

Robotic exoskeletons have been a focal point of research due to an ever-increasing ageing population, longer life expectancy, and a desire to further improve the existing capabilities of humans. However, their effectiveness is often limited, with strong rigid structures poorly interfacing with humans and soft flexible mechanisms providing limited forces. In this paper, a scalable variable stiffness revolute joint is proposed to overcome this problem. By using layer jamming, the joint has the ability to stiffen or soften for different use cases. A theoretical and experimental study of maximum stiffness with size was conducted to determine the suitability and scalablity of this technology. Three sizes (25 mm, 18.75 mm, 12.5 mm diameter) of the joint were developed and evaluated. Results indicate that this technology is most suitable for use in human fingers, as the prototypes demonstrate a sufficient torque (0.054 Nm) to support finger movement.

A Novel Continuum Robot With Stiffness Variation Capability Using Layer Jamming: Design, Modeling, and Validation

“…The stiffness reinforcement capability of a jamming sheath is determined by the force F required to detach the contact layers. According to the research in [22], [28], this force can be calculated as F = μnPS, where μ is the COF of the flaps, n is the layer overlap number, P is the applied pressure, and S is the overlap area which is determined by the overlap width and length of the flap. From this equation, two variables can be adjusted to vary stiffness once the flap pattern is set.…”

“…In [27], a stiffness-tuneable segment for continuum soft robots with vertebrae was presented. A revolute joint based on layer jamming for robotic exoskeletons was developed [28]. In [29], stiffening sheaths based on layer jamming were built for continuum robots.…”