Highly precise dynamic simulation environment for humanoid robots

In this paper we present a simulation environment for humanoid robots with a precise and efficient method of handling ground contact, and experiments empirically validating the simulator. Highly accurate dynamic simulation is an essential tool for research and development in humanoid robotics, and a simulator should ideally provide a transparent interface with pathways for control and sensing information identical to those of the actual robot(s) it models. We identified ground contact as the chief source of divergence from reality in work to date and have tackled this problem by developing an algorithm for resolving ground contact for humanoid robots. Our objective was to produce an algorithm that is accurate, efficient and easy to implement. The algorithm is general with respect to the complexity of the foot model; is based on empirically measurable characteristics of the foot-ground interaction, i.e., friction, which we have obtained using experiments described; provides an exact implementation of the Coulomb friction model (avoiding polyhedral approximation of the friction cone); runs in real-time; is also amenable to a straightforward accuracy-speed trade-off; and is relatively easy to implement as a constraint selection method. The simulation environment embodies generality, and we have applied it to two different humanoid robots, Hoap-2 and CB. We present experiments comparing the results of simulation with identical motions performed by real robots, and comparing the full contact resolution algorithm, the modification trading accuracy for computational speed and a penalty-based method.