Development of a Force Control Strategy for Single Wheel Experiments in Soil Environments

Robust locomotion through rough, sandy terrain is essential for planetary exploration rovers. In order to test and evaluate the performance of wheel designs as well as t erramechanical models, single wheel experiments are widely used. Common test benches provide three degrees of freedom and therefore no complex scenarios, e.g cornering behavior, can be simulated. In order to circumvent these restrictions, the Terramechanics Robot ics Locomotion Lab of the DLR uses a robotic manipulator to provide additional degrees of freedom. The usage of a robotic manipulator to control th e contact force of the wheel-soil interaction poses new challenges for the force control system. In this thesis a force control concept for granular soil en vironments is developed to improve the currently implemented control system. To predict the performance of the developed system, a simulation framework for th e testbench is implemented. In order to replicate the occurring failure cause, a terramechanical model of the wheel-soil interaction was developed for this spec ific use-case. Using this framework, different approaches for the force control concept are tested and evaluated. The resulting Adaptive Admittance Control (AAC) scheme, adapts the admittance gain depending on force deviation, rotational velocity of the wheel and estimated environmental stiffness. The AAC is implemented, tes ted and evaluated on the testbench, showing superior performance for fixed slip single wheel experiments which were used as benchmark experiments.