Pseudo-linear Variable Lever Variable Stiffness Actuator: Design and Evaluation

This paper presents the design, mathematical model, and evaluation of a novel variant of a variable stiffness actuator. The actuator combines a cam and a variable lever mechanism. The lever length changes through the rotation of the follower and results in the change of the mechanism stiffness. The design of the actuator results in a nearly linear torque-deflection characteristic, earning it its name: pseudo-linear variable lever variable stiffness actuator (PLVL-VSA). The paper outlines the differences to other similar types of variable stiffness mechanisms, namely the pseudo-linear torque-deflection characteristics, no pretensioning of the elastic element and a fast rate of stiffness variation. Provided are the details on the mechanical design and the derivation of the mathematical model. The theoretically calculated pseudo-linear torque-deflection characteristic is shown on a real-world PLVL-VSA built using rapid prototyping, which also displays the rapid rate of stiffness change.