The vsaUT-II: A novel rotational variable stiffness actuator

In this paper, the vsaUT-II, a novel rotational variable stiffness actuator, is presented. As the other designs in this class of actuation systems, the vsaUT-II is characterized by the property that the output stiffness can be changed independently of the output position. It consists of two internal elastic elements and two internal actuated degrees of freedom. The mechanical design of the vsaUT-II is such that the apparent output stiffness can be varied by changing the transmission ratio between the elastic elements and the output. This kinematic structure guarantees that the output stiffness can be changed without changing the potential energy stored internally in the elastic elements. This property is validated in simulations with the port-based model of the system and in experiments, through a proper control law design, on the prototype.