Design and Evaluation of a Bidirectional Ankle Exoskeleton System

Patients with foot-drop are unable to dorsiflexion during the swing phase, resulting in toe dragging and increasing the risk of falling. Ankle-foot-orthoses (AFOs) can reduce foot-drop of patients but limit their ankle plantarflexion. Assistive exoskeletons have a significant improvement on walking economy and the assistance can enhance human mobility. Here, we developed a bidirectional ankle exoskeleton to provide passive dorsiflexion assistance during the swing phase and active plantarflexion assistance during the stance phase. The performance of our exoskeleton was tested based on experiments of one healthy subject. We changed the front passive assistive materials and evaluated the kinematics and biological efforts of the subject with different assistive conditions. Results showed that the maximum ankle dorsiflexion angles were increased during the swing phase and ankle joint torques were reduced under assistance. The root mean square (RMS) of the soleus and tibialis anterior muscle activities were decreased by 21.8% and 17.9% under the assistance of elastic ropes condition. Our design expected to provide assistance for individuals with impaired dorsiflexion and plantarflexor muscle strength, which can enhance their locomotion ability.