Whole-Body Stability for a Humanoid Robot: Analysis, Control Design, and Experimental Evaluation

Abstract

Future service robots have to be able to act compliantly in unstructured, dynamic environments and in the presence of humans residing in their workspace. Torque control methods such as the well-established impedance algorithms are suitable in this context. In order to provide mobility of the robotic system, it has to be equipped with legs or wheels. In case of nonholonomic wheeled platforms, position or velocity control methods are commonly applied. An admittance interface can be used to incorporate the kinematically controlled mobile platform to the torque controlled whole-body control framework. While the kinematic controller compensates the inertia and Coriolis/centrifugal couplings from the upper body to the moving base, inertia and Coriolis/centrifugal couplings from the base to the upper body remain in the system dynamics. Depending on the choice of control parameters, deteriorated performance or even a loss of stability of the overall system can be observed due to those remaining couplings. In this master’s thesis, the effects of inertia and Coriolis/centrifugal couplings on the overall system dynamics of impedance controlled robots with a kinematically controlled mobile platform are addressed. Initially, the general problem is analyzed using simple linear and nonlinear model systems. Building on the findings of that analysis, an approach for the compensation of the inertia and Coriolis/centrifugal couplings is presented and a proof of stability for the resulting system dynamics is given. Experiments with DLR’s humanoid robot Rollin’ Justin validate the approach.