Emergent walking stop using 3-D ZMP modification criteria map for humanoid robot

Abstract

Real-time emergent stop walking motion is necessary for humanoid robots. We propose a new emergent stop method using modification criteria map. The stable gait change is generated by adjusting the amount of the ZMP modification according to the timing of stop command. The modified ZMP trajectory is given so that the humanoid robot can change the current motion without falling down. The modification criteria are defined from the relation between the predicted ZMP trajectory using a preview controller and the support polygon. The preview controller employs table-cart model and it derives center of mass (CoM) trajectory from ZMP reference in real-time. We make the map of relation among the ZMP modification length, the modification timing and the timing of the stop command for stable gait modification. The robot can execute the best motion referring to the predefined map. In this method, the humanoid robot can stop immediately within one step or zero step to avoid a collision, if humans or objects appeared unexpectedly in front of the walking humanoid robot. The stop motion is typically divided two phase: single leg support phase and double leg support phase. In the single leg support phase, the next landing position and timing are decided according to command time of the stop signal. In the double leg support phase, the humanoid robot can stop anytime without changing standing position. The validity of the proposed method is confirmed by experiment using a humanoid robot HRP-2.