Robust Tracking Control of Wheeled Mobile Robot Subject to Uncertainties

Abstract

The paper suggests a compound control that combines nonlinear flatness, active disturbance rejection control (ADRC), and sliding mode control (SMC). By employing the differential flatness methodology, the standard under-actuated wheeled mobile robot model is converted into a fully actuated one. Utilizing this model as a basis, a sliding feedback controller is suggested to address the issue of uncertainties associated with wheel slip and wind. However, as the uncertainties increase, a higher control input is required, resulting in an undesired chattering phenomenon. To reduce chattering in SMC, a boundary layer surrounding the switching surface is employed, and a continuous law is implemented within the boundary. The boundary layer width plays an important role in improving robustness and eliminating chatter. Indeed, increasing the thickness of the boundary layer significantly reduces chattering, but it may lead to a loss of robustness performance achieved by the discontinuous control provided by SMC. To resolve this problem, active disturbance rejection control is combined with boundary layer sliding mode control. When utilizing the ADRC method, the lumped uncertainties are estimated via an extended state observer and eliminated within the feedback loop. The newly obtained feedback control combines the advantages of boundary layer SMC and ADRC to achieve practical control and robust tracking performance. The stability properties exhibited by the closed-loop system are rigorously established through the application of Lyapunov theory. In conclusion, a series of simulations has been conducted to compare and evaluate the efficiency of the presented robust tracking controller against other existing control methods.