Two-level variable impedance control for internal/External forces tracking of dual-arm manipulators under uncertainties.

Coordinated operation of dual-arm manipulators is essential for enhancing the load capacity and adaptability of robotic systems. However, the precise control of the internal and external forces during the coordinated operation of dual-arm manipulators can pose considerable challenges owing to factors such as force interactions, kinematic constraints, positional inaccuracies, and external disturbances. This study focused on precise force-tracking control for a dual-arm manipulator system in the presence of external disturbances and uncertainties. The proposed approach adopted a two-level adaptive variable impedance control system to regulate the internal and external forces, thereby enhancing the flexibility and compliance of dual-arm manipulators. An object-level hybrid impedance controller was designed to address external disturbances arising from unknown environments by adaptively adjusting the object's trajectory to ensure compliance with the surrounding environment. The internal force was regulated by a manipulator-level force feedback variable impedance controller (FFVIC), where the damping coefficient was adjusted based on feedback force sensor signals. This system could achieve internal force tracking even in the presence of positional errors and uncertain stiffness. Theoretically, the asymptotic stability of the system was demonstrated using the Routh stability criterion, and the boundaries of the adaptive law parameters were established. To validate the effectiveness and superiority of the proposed two-level control scheme, a series of cooperative experiments was conducted using two redundant manipulators. The results unequivocally demonstrate the successful regulation of internal and external forces using the proposed control scheme. According to the experimental results, the force-tracking ability of the FFVIC exceeded that of the traditional impedance controller.