Model-free fast integral terminal sliding mode control with improved disturbance observer for robust trajectory tracking of omnidirectional mobile robots

This paper introduces a robust model-free fast integral terminal sliding mode control (MFFITSMC) that incorporates an improved disturbance observer for three-wheeled omnidirectional mobile robots (TWOMRs) operating in dynamic urban search and rescue (USAR) environments. Tailored to manage dynamic conditions with variable parameters and unknown disturbances, including uneven terrain, slippery surfaces, and changing payloads, the MFFITSMC ensures precise tracking and adaptability. The approach incorporates an improved fast terminal sliding mode observer (IFTSMO) based on an ultra-local model (ULM). The ULM approximates the complex TWOMR dynamics within a brief sliding time window, enabling the MFFITSMC to achieve rapid convergence of errors. Meanwhile, the IFTSMO effectively identifies and eliminates lumped disturbances, enhancing steady-state accuracy, robustness, and disturbance rejection. Numerical simulations of the TWOMRs system using the proposed MFFITSMC strategy are conducted in a MATLAB/Simulink environment, and the findings demonstrate that the proposed method achieves superior performance, reducing the maximum orientation tracking error by 66.7% and improving the settling time by 75% compared to conventional model-free sliding mode control (MFSMC).