A Novel Rotating Beam Link for Variable Stiffness Robotic Arms

In this paper, we present a novel design concept for a robot arm link with variable stiffness. Variable stiffness links are intended to grant a robot the safety benefits of compliance and the performance benefits of stiffness. Our compact design actively modulates stiffness via parallel, rotating beams actuated by simple servomotors. It achieves a lateral stiffness ratio greater than ten with a minimum stiffness under 0.2 N/mm. Our novel design offers many benefits over existing variable stiffness link solutions in its compactness, simplicity, and speed of actuation. One challenge of this research lies in the mechanics modeling of variable stiffness. Here we propose a comprehensive mechanics model that considers mechanical compliances due to deflections of parallel guided beams, column buckling, and bearing at the beam roots. By comparing with experimental testing data, we show that our analytical model accurately predicts the lateral stiffness of the robotic link. This model can be used as a design tool in future iterations, including for scaling the design.