Soft ankle exoskeleton to counteract dropfoot and excessive inversion

Area of Science:

• Biomedical Engineering
• Rehabilitation Technology
• Biomechanics

Background:

• Dropfoot, a common post-stroke gait pathology, impairs foot clearance and necessitates compensatory movements.
• Existing assistive devices often lack multi-DOF (degrees of freedom) support for the ankle.
• Wearable exoskeletons offer a promising avenue for movement assistance and rehabilitation.

Purpose of the Study:

• To develop and evaluate a soft ankle exoskeleton capable of assisting two degrees of freedom simultaneously: dorsiflexion and eversion.
• To assess the exoskeleton's efficacy in normalizing gait parameters in individuals with simulated dropfoot.

Main Methods:

• A soft ankle exoskeleton with a novel actuation and transmission system using Bowden cables was designed.
• The system allowed simultaneous assistance of dorsiflexion and eversion, coupled with a force-free controller.
• Proof-of-concept experiments included seated movement tests and walking trials on non-disabled individuals simulating dropfoot.

Main Results:

• Seated tests demonstrated low angular errors (<1.5° for dorsiflexion/plantarflexion, <1.4° for eversion).
• The force-free controller effectively compensated for device resistance during plantarflexion.
• Gait tests showed normalization of ankle joint and foot segment kinematics, including foot inclination, ankle inversion at initial contact, and swing phase clearance.

Conclusions:

• The developed soft ankle exoskeleton is feasible for simultaneously assisting two ankle degrees of freedom.
• The device shows significant potential for assisting individuals with dropfoot and excessive inversion, improving gait normalcy.