Model-Based Chassis Control of a Wheeled Mobile Robot on Soft Ground Using the Example of the ExoMars Planetary Exploration Rover

This thesis addresses the question whether a chassis controller can be designed for the control allocation of an exploration rover, such that its degrees of freedom are exploited for improving the rover’s locomotion in soft sand. Although this work is derived with the example of the Rosalind Franklin rover of the European ExoMars mission, it is transferable to the field of mobile robots on rough terrain in general.

The approach of this thesis is a comprising model development of the robotic rover system and the wheel-ground interaction for soft sand, called terramechanics. A fully model-based chassis controller is then synthesized, which, at the same time, allows for explicit computation of the actuator trajectories and exploitation of the full solution space of the over-actuation. For managing these conflicting goals, the full model is divided into dynamic, but determined, sub-systems and a linear, static, underdetermined system of equations with several necessary model modifications. The nonlinear control methods feedback linearization and dynamic extension are used for the dynamic sub-systems, whereas the general solution to the

underdetermined system of equations is used for the allocation itself. It consists of the least-squares solution with a pseudo-inverse of the allocation matrix and the homogeneous solution with a base of its null-space.

The performance of the designed chassis controller is evaluated in a co-simulation with a high-fidelity model of the rover and the robustness of the approach is investigated by the injection of different disturbances.