A Robust Observer-Based Control Strategy for n-DOF Uncertain Robot Manipulators with Fixed-Time Stability

Area of Science:

• Robotics
• Control Systems Engineering
• Nonlinear Control Theory

Background:

• Robot manipulators are susceptible to uncertainties and external disturbances, complicating precise control.
• Traditional sliding mode control (SMC) methods often suffer from singularity issues and control signal chattering.
• Achieving rapid and guaranteed convergence to a stable state (fixed-time stability) remains a challenge in uncertain systems.

Purpose of the Study:

• To develop a robust observer-based control strategy for n-Degree-of-Freedom (n-DOF) uncertain robot manipulators.
• To achieve global fixed-time stability, ensuring rapid convergence of control errors to zero.
• To mitigate singularity issues and reduce chattering inherent in conventional control methods.

Main Methods:

• Design of a novel fixed-time nonsingular sliding mode surface for fast error convergence without singularity.
• Development of a fixed-time disturbance observer using a uniform robust exact differentiator to handle uncertainties and disturbances.
• Formulation of a robust observer-based control strategy integrating the novel sliding mode control and the disturbance observer.

Main Results:

• The proposed observer accurately approximates uncertain system terms within a fixed time.
• Significant reduction in chattering compared to traditional sliding mode control was achieved.
• The control strategy demonstrated global fixed-time stabilization for n-DOF uncertain robot manipulators.

Conclusions:

• The developed robust observer-based control strategy guarantees global fixed-time stability for uncertain robot manipulators.
• The novel fixed-time nonsingular sliding mode surface and disturbance observer effectively address system uncertainties and disturbances.
• Simulation results on an industrial robot manipulator validate the observer's approximation capability, sliding surface convergence, and overall control strategy effectiveness.