Robust trajectory tracking of mobile manipulators based on extended state observer and nonlinear control

Abstract

This doctoral thesis proposes and experimentally validates Extended State Observer(ESO) based nonlinear control strategies for real-time trajectory tracking of mobile manipulators (MMs) operating in uncertain and dynamic environments. The developed approaches aim to overcome the limitations of conventional control methods in handling nonlinear couplings, parameter uncertainties, and external disturbances, which significantly affect the stability and tracking precision of mobile manipulators. Mobile manipulators combine the dexterity of multi-link robotic arms with the mobility of wheeled platforms, thereby expanding their operational workspace and enabling applications in industrial automation, medical assistance, and planetary exploration. However, their complex coupled dynamics, characterized by nonholonomic constraints and interconnected subsystems, make trajectory tracking a highly challenging task. This research addresses these challenges by developing a unified observer–controller framework that guarantees robust, high-precision, and f ixed-time trajectory tracking performance. The first part of the research introduces a Nonlinear Active Disturbance Rejection Control (NADRC) scheme, in which a Nonlinear Extended State Observer (NESO) estimates the total disturbances arising from model uncertainties and external perturbations, while a nonlinear proportional-derivative (PD) controller ensures accurate trajectory tracking. The second contribution proposes an Extended State Observer-based Non-Singular Fast Terminal Sliding Mode Control (ESO-NFTSMC) for n-DoF coupled mobile manipulators. This design avoids singularities, enhances transient response, and compensates for lumped disturbances in real-time, achieving finite-time convergence with reduced chattering. Finally, the third and principal contribution develops a Fixed-Time Terminal Sliding Mode Control (FTSMC) integrated with a Fixed-Time Extended State Observer (FESO). This framework ensures convergence to the desired trajectory within a predefined time bound, independent of initial conditions, while maintaining robustness to uncertainties and measurement noise. All proposed approaches are mathematically analyzed using Lyapunov stability theory and experimentally validated on a 5-DoF mobile manipulator platform (Mob-ETS) developed at ÉTS. The real-time results demonstrate progressively sophisticated performance, from the smooth and robust tracking of the NADRC to the fast, finite-time convergence of the ESO-NFTSMC, and culminating in the verified fixed-time convergence of the FTSMC-FESO framework. All controllers show excellent tracking accuracy and strong robustness against external disturbances under a variety of operating conditions. Overall, this research establishes a comprehensive and experimentally verified control framework for robust and time-guaranteed trajectory tracking of mobile manipulators, providing a significant contribution to the field of nonlinear robotic control and laying the foundation for future extensions to multi-robot coordination and adaptive fixed-time observer designs.

Date	17 Feb 2026
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Maarouf Saad (Supervisor), Mohamad Saad (Co-supervisor) & Raouf Fareh (Co-supervisor)