Mechanical design of a lightweight compliant and adaptable active ankle foot orthosis

The ankle joint is the main contributor in providing support to the body, ensuring forward progression and initiating the swing of the leg during the push-off phase of walking. However, its capability can be negatively altered by neuromuscular disorders. In these cases, an active ankle-foot orthosis (AAFO) can greatly enhance the rehabilitation of the affected patients. This paper presents the mechanical design of a lightweight and compliant AAFO, which can be used for rehabilitation purposes. The actuator is bidirectional, thus it can assist the ankle during both dorsiflexion and plantarflexion. With respect to most of the existing AAFOs, the presented one is adaptable to different subjects. The connections between the ankle actuator and the user's shank and foot are designed to fit the AAFO to different users and to align the human and the robot ankle joints, without the need of building customized versions of it. The implemented ankle actuator is a MACCEPA (Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator) and it can provide a peak torque of 25Nm. Due to a careful design of the actuator components, the total weight of the AAFO is only 1.7kg.