Differential flatness-based robust control of mobile robots in the presence of slip

Slip between the ground and wheel often cannot be avoided in most applications of mobile robots. However, a majority of controllers developed so far make a no-slip assumption with non-holonomic constraints. To achieve desired performance in the presence of slip, controllers that are robust to slip are required. In this paper, we discuss robust trajectory-tracking control for a differentially driven two-wheeled mobile robot. The structure of a differential flatness controller, which has shown distinctive advantages providing an integrated framework for planning and control, is extended to account for slip disturbances. It is shown that the differential flatness framework can be extended to develop a robust controller based on a dynamic as well as a kinematic model with slip. Simulation results for both kinematic and dynamic controllers are presented to demonstrate the effectiveness of the robust controllers. Experiments with the kinematic controller which is suited to typical laboratory and field mobile robots were conducted to validate the proposed robust controller. The simulation and experimental results show that the proposed robust controllers are effective in the presence of slip.