Compliant Variable Stiffness Actuator and Robust Interactive Torque Control: Principle Mechanism Design and Experimental Verification

The development of Variable Stiffness Actuators (VSAs) represents a promising approach for enhancing intrinsic safety in physical human-robot interaction. This study introduces an innovative VSA design employing an epicyclic-lever mechanism to modulate stiffness through spiral spring preload adjustment. The centrosymmetric lever configuration significantly expands the stiffness tuning range, while the transmission ratio between gear displacement and spring deflection is governed by the lever mechanism, thereby enabling customization of the stiffness profile and adjustment range. The stiffness model of the VSA is established, and its design parameters and driving characteristics related to the stiffness are analyzed. To ensure precise torque tracking in the case of unexpected disturbance, a modified disturbance observer is developed for arbitrary disturbance estimation. Then, a novel robust interactive torque controller for the VSA is proposed. The stiffness identification test, collision experiment, trajectory tracking tests under unload and load conditions, and cyclic movement experiments have validated the superiority of the novel VSA and the developed controller.