Design of Sliding Mode Controller Combined with Nonlinear Disturbance Observer for Trajectory Tracking of Mobile Robots in Mixed Terrain

Accurate trajectory tracking is a fundamental yet challenging requirement for mobile robots, especially when operating on surfaces with varying frictional characteristics (mixed terrain) and subjected to external disturbances as well as model uncertainties. This study presents the design and evaluation of an integrated control strategy aimed at enhancing trajectory tracking performance under these demanding conditions. A Sliding Mode Controller (SMC), known for robustness but prone to chattering, was integrated with a Nonlinear Disturbance Observer (NDO). The NDO was designed to estimate lumped disturbances encompassing varying friction, model errors, and other external disturbances; this estimate was then used for compensation within the SMC control law to reduce the switching component's amplitude. The effectiveness of the proposed SMC-NDO method was verified through simulations on a mobile robot model following a reference trajectory in a simulated mixed terrain environment under various disturbance conditions. Simulation results showed that the proposed SMC-NDO controller significantly improves trajectory tracking accuracy and reduces chattering compared to the traditional SMC controller and a PID controller. The integration of the NDO with SMC proves to be an effective approach for improving mobile robot trajectory tracking, enhancing accuracy and robustness while mitigating chattering in challenging environments with varying terrain and disturbances.