AbsIrnct-Exoskeletons that enhance human strength, endurance, and speed while being transparent to the wearer are feasible. In order to he transparent, the exoskeleton must dctermlne the user's intent, apply forces when and where appropriate, and present low impedance to the wearer.We present a one degree of freedom exoskeleton called the RoboKnee which acbleves a b i b level of transparency. User intent is determined through the knee jolnt angle and ground reaction forces. Torque is applied across the knee in order to allow the user's quadriceps muscles to relax. Low impedance is achieved through the use of Series Elastic Actuators.The RoboKnet allows the wearer to climb stairs and perform deep knee bends while canying a slgniJ3cant load in a backpack. The device provides most of the energy required to work against gravity while the user sbys in control, deciding when and where to walk, as well as providing balance and control Videos, photographs, and more Information ahout the RohoKnee can he found at

Series elastic actuators provide many benefits in force control of robots in unconstrained environments. These benefits include high force fidelity, extremely low impedance, low friction, and good force control bandwidth. Series elastic actuators employ a novel mechanical design architecture which goes against the common machine design principal of “stiffer is better”. A compliant element is placed between the gear train and driven load to intentionally reduce the stiffness of the actuator. A position sensor measures the deflection, and the force output is accurately calculated using Hooke’s Law (F = Kx). A control loop then servos the actuator to the desired output force. The resulting actuator has inherent shock tolerance, high force fidelity and extremely low impedance. These characteristics are desirable in many applications including legged robots, exoskeletons for human performance amplification, robotic arms, haptic interfaces, and adaptive suspensions.