Motion Planning of Emergency Stop for Humanoid Robot by State Space Approach

A motion planner of emergency stop must make an operating humanoid robot to a stationary state under the emergency signal. It plays an important role in prevention of falling over because humanoid robots fall over easily. Immediately after the emergency signal, it must generate the emergency stop motion in real-time. We modeled a humanoid robot as a simple dynamic system consists of ZMP (zero-moment point) and COG (center of gravity) as its states. The emergency stop motion is generated by a state feedback. We determined optimal feedback gains in terms of the initial conditions and the pole assignment. The proposed method realized a reliable emergency stop with low computational cost. Furthermore, it can easily predict the possibility of the successful emergency stop at any time. The validity of the proposed method is confirmed by an experiment using humanoid robot HRP-2