An Ankle Foot Orthosis with Insertion Point Eccentricity Control

A prototype active Ankle Foot Orthosis has been developed to control and assist plantar flexion and dorsiflexion using an innovative series elastic actuator integrated into a standard passive AFO. A motor controls the moment arm (Insertion Point Eccentricity Control or IPEC) of a pretensioned spring, and though the magnitude of the spring force remains relatively constant, the changing moment arm produces torque about the ankle. The IPEC AFO is able to provide 3.51 Nm about the ankle in dorsiflexion and 3.88 Nm in plantar flexion with a spring modulus of 3110 N/m and an initial tension of 77 N. The torque was sufficient to prevent toe-drag during swing phase. This technology may benefit users with drop-foot or other ankle disorders, including those who have suffered stroke or spinal cord injury.