Emergent stop for humanoid robots

This paper describes a real-time gait change for a walking humanoid robot. We propose a control method to change the gait motion by modifying a pre-defined Zero Moment Point (ZMP) trajectory in real time. 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 is 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 between the ZMP modification and the timing of command for stable gate modification. The robot executes the best motion referring to the map. In this method, the humanoid robot can stop immediately within one 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 mode; single leg stop motion and double leg stop motion. The stop mode and the next landing position are decided according to the command time of the stop signal. The validity of the proposed method is confirmed by experiment using a humanoid robot HRP-2.