FlexCVA: A Continuously Variable Actuator for Active Orthotics

Active orthotic devices require actuators with high torque, a free movement mode, high efficiency, and small size and weight. The FlexCVA is a new type of actuator that addresses these requirements in a unique way. It provides continuously varying torque through the use of two belts alternately deflected by cams. The belts alternate in supplying output torque with one belt pulling the output while the slack is removed from the other belt. The drive ratio is automatically adjusted in response to the load by varying the deflection distance of the belts. The resulting actuator prototype has been demonstrated to supply up to 34 Nm of output torque, and its free movement mode allows it to be backdriven at speeds greater than 400 deg/sec