The Comparison of Postural Stability Analysis of Biped Robot IWR-Ⅲ

초록

This paper presents the stability analysis of a biped robot IWR-III. We use a foot-rotation indicator (FRI) concept to reveal the degree of stability. The foot rotation can be a barometer of postural instability, which should be carefully treated in implementing a dynamically stable walk and avoided altogether in performing a statically stable walk. The conventionally mentioned zero moment point (ZMP) criterion may not be sufficient to express the stability of a biped robot. ZMP equation needs an assumption that the supporting foot is fixed firmly to the ground during the walking. Therefore, applying the FRI concept is more desirable when a biped robot is falling down. In order to simplify the stability analysis, first we consider the robot as a simplified inverted pendulum, which consists of a triangular foot, an ankle joint, and a massive link. The static and dynamic stability equation for this model is derived and the FRI, ZMP and Center of Gravity (COG) are then investigated. Finally, we expand it to the real IWR-III biped robot. The simulation result shows the FRI concept is valid as an indicator of stability.