Development of an unpowered ankle exoskeleton for walking assist

Abstract

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 Rehabilitation

• The 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.

Keywords:

• Unpowered ankle exoskeleton
• pneumatic artificial muscle
• assistive device

Disclosure statement

No potential conflict of interest was reported by the authors.