Fixed-Time Sliding Mode Adaptive Control of Hydraulic Manipulator With Shutoff Deadzone and Uncertain Nonlinearity

There exist general model uncertainty and shutoff deadzone in hydraulic-driving plant due to unknown model parameters of mechanical structure and physical feature of electrohydraulic actuator, which will degrade the motion performance and stability. In this study, a fixed-time sliding mode adaptive control is presented in 2-DOF hydraulic manipulator to address these issues. First, the dynamic manipulator with two degree-of-freedom joint driving by hydraulic servo valve is setup via Lagrangian method. Then, a sliding mode disturbance observer is designed to approximate uncertain nonlinearity to ensure the lumped uncertainties convergence in a practical finite time. Furthermore, a parametric adaptive estimation is used to estimate unknown shutoff deadzone parameters. According to backstepping technique, a fixed-time convergence control is adopted to ensure all the system state errors converge into a zero neighborhood in a constant time not related to any initial condition. Finally, the fixed-time sliding mode adaptive controller has been verified in an experimental bench of 2-DOF manipulator.