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