AVASTT: A New Variable Stiffness Actuator with Torque Threshold

Variable Stiffness Actuators (VSAs) emerged as an alternative to conventional actuators in a variety of applications, such as walking robots and service robotics. New requirements, which were obviated in the design of rigid actuators, must be accounted for during the mechanical design of such new devices. Among them, we find the possibility of tunning the natural frequency of the mechanical system or damage reduction in case of impacts A multitude of solutions have been already proposed in the literature, each characterized by the kind of mechanism in charge of implementing the equilibrium position and the stiffness of the joint. With this work, we introduce a new actuator design based on tendon transmission, where a main motor controls the equilibrium position of the link while a secondary motor is in charge of modifying the joint stiffness. Unlike existing actuators, our proposal achieves a wide range of stiffness values, from close to zero up to completely rigid. Another distinguishing feature of the new design is the existence of a torque threshold, such that variable stiffness only becomes effective once the load is above a certain predefined threshold.