Variable Stiffness Actuation via 3D-Printed Nonlinear Torsional Springs

Variable Stiffness Actuators (VSAs) are promising for advanced robotic systems, offering benefits such as improved energy efficiency, impact safety, stiffness adaptability, mechanical robustness, and dynamic versatility. However, traditional designs often rely on complex mechanical assemblies to achieve nonlinear torque-deflection characteristics, increasing system intricacy and introducing potential points of failure. This letter presents the design, implementation, and validation of a novel antagonistic VSA that drastically simplifies complexity of the mechanisms by utilizing 3D-printed progressive nonlinear torsional springs (3DNS). By directly 3D-printing springs, we enable precise control over nonlinear behavior through strategic variation of their geometry. Empirical testing and finite element simulations demonstrate that our springs exhibit low hysteresis, low variance across samples, and a strong correlation between simulated and measured behavior. Integrating these springs into an antagonistic setup demonstrates the feasibility of achieving VSAs with low damping, minimal hysteresis, and stiffness that aligns well with modeled predictions. Our findings suggest that this approach offers a cost-effective and accessible solution for the development of high-performance VSAs.