The mVSA-UT: A miniaturized differential mechanism for a continuous rotational variable stiffness actuator

In this paper, we present the mechanical design of the mVSA-UT, a miniaturized variable stiffness actuator. The apparent output stiffness of this innovative actuation system can be changed independently of the output position by varying the transmission ratio between the internal mechanical springs and the actuator output. The output stiffness can be tuned from zero to almost infinite by moving a pivot point along a lever arm. The mVSA-UT is actuated by means of two motors, connected in a differential configuration, which both work together to change the output stiffness and the output position. The output shaft can perform unbounded and continuous rotation. The design ensures high output torque capability, light weight and compact size to realize a multiple purpose actuation unit for a great variety of robotic and biomechatronic applications.