Composite Adaptive Dynamic Surface Control for a Multi-DOF Hydraulic Manipulator With Disturbance Observer

This paper presents an adaptive dynamic surface control strategy based on composite adaptive method for a multi-DOF hydraulic manipulator with the unknown disturbance and uncertainties. The manipulator is driven by multiple hydraulic actuators so that the system can have the advantages of the hydraulic system such as the high-power density. Dynamic characteristics of the hydraulic system have a non-negligible impact on the performance of the manipulator. Considering the hydraulic actuator dynamics, the mathematical model of the hydraulic manipulator is derived at first. The dynamic model is high nonlinear, and has unmatched and matched disturbances and parameter uncertainties such as the mass and length of each articulated arm and the elastic modulus of hydraulic oil. Then, a composite adaptive control law is designed to estimate the uncertain parameters of the hydraulic manipulator, and a disturbance observer is explored to compensate the unknown disturbances without acceleration measurement that generally introduces the high noise into the system. Besides, the dynamic surface controller is proposed to account for the system nonlinearity and stabilize the closed-loop system. Finally, comparative experiments of the position tracking of the hydraulic manipulator are performed to verify the effectiveness of the proposed control strategy.