Development of Wearable Cyborg HAL Ankle Joint Unit to improve ankle joint function during gait

Stroke, spinal cord injury, and cerebral palsy are central nervous system disorders that impair voluntary movement due to dysfunctions in the brain, nervous system, and muscles. Cybernics treatment of HAL is being promoted as a treatment for these diseases. Besides, patients with central nervous system disorders who have symptoms of equinus, drop foot, and spasticity experience difficulties improving their ankle joint function during gait because the ankle joint of HAL is a passive mechanism, which cannot reflect the wearer's intention. Thus, it is hypothesized that ankle joints can be improved by dorsiflexion and plantar flexion during gait of HAL based on the wearer's intention, serving as a treatment for abnormal gait in patients with these disorders. Therefore, the purpose of this study is to propose and develop the ankle joint unit that can be attached to a HAL to enable plantarflexion and dorsiflexion of the ankle joints based on the wearer's intention and we clarify the applicability of the developed unit for improving gait function through experiments involving individuals with spinal cord injury. We developed a unit consisted of a four-bar linkage mechanism with a parallelogram structure and a control method that utilizes bioelectrical signals obtained from the activation of the gastrocnemius and tibialis muscles, as well as ground reaction forces. To clarify the applicability of the ankle joint unit for improving gait function, we carried out intervention trials with spinal cord injury, involving two weeks of training using the developed system, conducted four times per week. For the individual with spinal cord injury, the results indicated 1.47 times increase in gait speed and 1.34 times increase in stride length following two weeks of intervention using the developed unit. In conclusion, we clarified the applicability of the ankle joint unit for improving gait function through experiments with spinal cord injury.