Development of an unpowered ankle exoskeleton for walking assist.

Aim: Assistive technologies traditionally rely on either powered actuation or passive structures to provide increased strength, support or the ability to perform specific functions. At one end of the spectrum are powered exoskeletons, which significantly increase a user's strength, but require powerful actuators, complex control systems and heavy power sources. At the other end are orthoses, which are generally unpowered and light in weight, relying on the mechanical properties of passive mechanical elements. Ideally, assistive technologies should combine the benefits of both systems and enhance human motion while remaining lightweight and efficient. This paper presents the development of a lightweight unpowered ankle exoskeleton that relies on the spring-like properties of a Pneumatic Artificial Muscle, which is inflated and sealed.Methods: This flexible air-spring is used to harness gait energy and compliment the human ankle torque at push-off. To mechanically validate the proposed exoskeleton design, a prototype was fabricated and experimentally tested.Results: Unlike other existing devices, the proposed unpowered exoskeleton was able to store a significant amount of energy and release it all at once. The timing mechanism worked as intended and triggered the release of 115 N m of torque when the ankle reached a pre-determined angle.Conclusion: Overall, the device demonstrated the ability to provide significant contribution to the ankle torque, timed to release precisely at the push-off phase of the gait cycle.Implications for RehabilitationThe currently proposed ankle exoskeleton makes use of an unpowered, fully mechanical system to provide walking assistance to users by providing additional torque to the ankle joint.The newly developed assistive device is devised as a solution for persons struggling with mobility issues, and can be used both as a means for rehabilitation or as a permanent assistive devices for patients struggling with long-term disabilities.The device also has potential to be used as a performance enhancing device for ablebodied users by reducing muscle fatigue during extended physical exertion.

Design and characterization of a hyperelastic tubular soft composite.

Research in the field of human mobility assistive devices, aiming to reduce the metabolic cost of daily activities, is seeing the benefits of the exclusive use of passive actuators to store and release energy during the gait cycle. Current devices commonly employ either mechanical springs or Pneumatic Artificial Muscles as the primary method of passive actuation. The Pneumatic Artificial Muscle has proven to be a superior actuation choice for these devices, when compared to its alternatives. However, challenges regarding muscle pressure loss and limited elongation potential have been identified. This paper presents a hyperelastic tubular Soft Composite that replicates the distinctive mechanical behaviour of the Pneumatic Artificial Muscle without the need for internal pressurization. The proposed Soft Composite solution is achieved by impregnating a prefabricated polyethylene terephthalate braided sleeve, held at a high initial fibre angle, with a silicone prepolymer. A comprehensive experimental evaluation is achieved on numerous prototypes for a variety of customizable design parameters including: the initial fibre angle, the silicone stiffness, and the braided sleeve style. This research has successfully developed, tested, and validated a novel Soft Composite that can achieve the desired nonlinear stiffness and elongation potential for optimal use as passive actuation in human mobility assistive devices.