Dynamic Modeling and Robust Force-Position Control of a Variable Stiffness Gripper

Variable Stiffness Grippers (VSGs) represent a groundbreaking advancement in robotic manipulation, embodying the seamless integration of flexibility and rigidity to meet the multifaceted challenges of modern automation. These devices leverage the adaptability of compliant modes for handling a wide range of objects yet can switch to a rigid mode for tasks requiring high strength and precision. The management of variable stiffness poses significant challenges, especially in achieving precise control over the gripper's adaptability to objects of varying compliance. This paper proposes a method to provide a combination of position control and force control of a VSG by exploiting the dynamic model and the different stiffness levels. Our research examines active disturbance rejection control (ADRC) and deterministic robust control (DRC), demonstrating their advantages over PID in managing stiffness variations in robotic grippers. We highlight ADRC and DRC's enhanced robustness and adaptability through a comparative analysis, at different stiffness levels and grasping processes. These efforts highlight the importance of sophisticated control systems, in distinguishing between stiff and rigid modes effectively, enabling VSGs to handle objects ranging from fragile.