Principle of operation of RotWWC-VSA, a multi-turn rotational variable stiffness actuator

This work presents the principle of operation of RotWWC-VSA, a Variable Stiffness Actuator (VSA) characterized by no rotational stroke limits, conversely to the vast majority of rotational VSAs, typically characterized by restrictions in the angular range of motion. The possibility to perform an unlimited number of turns is a characteristic taken for granted for standard motors, but it is not for VSA rotational motors. It features two antagonist nonlinear equivalent springs, each of them made up of a tension spring, a cam and a wire which, properly configured, realize a torsion spring characterized by a customizable non-linear stiffness characteristic. Theoretical aspects of the actuator are accompanied by numerical simulations. Design guidelines are drawn and a concept design is presented.