Decoupled and Closed-Loop Motion and Stiffness Control for Articulated Soft Robots Driven by a Class of Electromechanical Variable Stiffness Actuators

Controlling articulated soft robots (ASRs) driven by variable stiffness actuators (VSAs) remains an open challenge from the model-based control perspective, where the key difficulties are due to: 1) the coupling between motion and stiffness dynamics; 2) highly nonlinear dynamics; and 3) sensitivity to the model accuracy. Herein, we contribute to: 1) by achieving decoupling through shifting the eigenvalues of the actuator matrix to avoid singularity, followed by the compensation of such shift through the integral action. To address; 2) we design a cascade-based control that formally proves convergence of the motion and stiffness tracking errors to zero. Finally, our contribution resolves; and 3) by ensuring robustness to uncertain dynamics parameters through adaptive approach. Notably, this methodology enables independent motion and stiffness control design, allowing the application of diverse control strategies. The proposed solution is validated in simulation and on an ASR hardware setup. The results prove that the method is capable of controlling motion and stiffness in a decoupled manner, while the adaptive strategy ensures improved tracking performance.