Contact-responsive high-gain robot motion controllers using a constrained disturbance observer

Abstract High-gain robot controllers are well known for their robustness against unknown disturbances, ensuring high control accuracy. However, this robustness makes handling unexpected contacts challenging, particularly in the absence of joint torque sensors (JTSs). This paper presents a contact-responsive high-gain motion controller (CRMC) that ensures accurate tracking in free motion while adapting to unknown interactions, even without joint torque sensing. To achieve CRMC, we propose a constrained disturbance observer (CDOB), an extension of the DOB framework designed to optimize the nominal robot’s motion. The real robot follows this optimized motion using an inner-loop high-gain disturbance compensator that reduces the deviation between the nominal and real robot motions. The optimization of CDOB allows the user to impose various motion constraints, enabling contact-responsive behavior and broader task-specific designs. The proposed method is subjected to rigorous stability analysis and extensive experimental validation on a collaborative robot without JTSs, demonstrating its effectiveness in real-world contact scenarios.