Conceptual design of a novel variable stiffness actuator for use in lower limb exoskeletons

A novel modular variable stiffness actuator (VSA), for use in the knee joint of lower limb exoskeletons, is presented. The actuator consists of a combination of a spindle-driven MACCEPA (Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator) and a spring acting in parallel, (dis)engaged by means of a simple on/off mechanism depending on the phase of the gait cycle. Such design approach is inspired by two clearly distinctive gait phases of a knee joint, one with a high velocity and low torque, and another one with low velocity and high torque profiles. By tackling each of these two phases separately, energy consumption and torque requirements of an active part of the actuator have been decreased, while keeping the size and the weight of the actuator at a reasonable size for use in wearable robots (WR).