Autonomous leg exoskeleton. (A) The autonomous exoskeleton applies torque about the human ankle joint during walking, adding positive mechanical power to the wearer during the push-off portion of stance phase. During the swing phase, the device applies negligible forces on the wearer by allowing small amounts of slack into the cord. The mechanism consists of a winch actuator and fiberglass struts that directly apply a resultant torque about the ankle. (B) The winch actuator provides a torque on the ankle by winding the cord around the spool. As the cord is tightened, a force is applied to the struts on either side of the leg. The winch actuator’s brushless motor applies the torque to the ankle joint through a transmission that consists of the belt transmission stage in series with the geometric transmission stage comprising spool, idler roller and strut.