Biped Walking of a Humanoid Robot on Loose Soil

Humanoid robots have been expected to work as an alternative to human in severe working conditions. In order for humanoid robots to work in the field of civil engineering, construction or disaster-relief, humanoid robots must have ability of walking on uneven terrain such as sand, clay and snow. However, most of studies on biped walking on even or uneven terrain have assumed stiff ground. Biped walking on loose soil has been considered as a great challenge. This research aims to realize biped walking on loose soil. As the first step of this research, we develop a simulation environment which can estimate behavior of a biped robot on loose soil. This simulator consists of a usual dynamics simulator and a loose soil model proposed in this research. The proposed loose soil model provides sinkage of a foot, slippage of a sole and reactive force acting on feet from loose soil. The sinkage of the foot and slippage of the sole are calculated by using terramechanics model, which are important characteristics for biped robots to walk on loose soil. The reactive force acting on feet from loose soil is calculated using a spring-damper model between the foot and the deformed ground. In order to verify the simulation result, experiments were carried out using a humanoid robot as shown in Fig. 1. The developed simulator enables us to develop a stable walking algorithm on loose soil safely and efficiently.