Modeling and Force Control of a Terramechanical Wheel-Soil Contact for a Robotic Manipulator Used in the Planetary Rover Design Process

The German Aerospace Center (DLR) has developed the Terramechanics Robotics Locomotion Lab (TROLL) to provide a feasible testing facility for developing planetary exploration rovers, as well as validating terramechanical models. A robotic manipulator is used to provide the required degrees of freedom to the mounted wheel or subsystem, making it necessary to actively control the interaction force of the wheel-soil contact. This paper is concerned with the development of a feasible force control strategy for the testbench wheel-soil contact during single-wheel experiments. For this purpose, a terramechanical model has been developed to accurately map the dynamic processes relevant for the force control design, which is later used in a testbench simulation framework to predict and evaluate the performance of control strategies. The Adaptive Admittance Control (AAC) scheme developed is adapting the gain based on the current control deviation, the rotational velocity of the wheel and an estimated soil stiffness during the experiment. The AAC is evaluated using a benchmark single-wheel experiment and shows superior performance compared to standard admittance control.