Humanoid push recovery strategy for unknown input forces

Because of the high dimensional, non-linear, and hybrid features, humanoid push recovery is very difficult unlike animals and humans who are very adept on this. The topic is currently one of the exciting topics in robotics and existed research results have already provided significant methods to recover from push. However existed researches usually specify the range of the push magnitude which in real world is usually unknown and unexpected. Biomechanical studies evidence indicate that different strategies are prepared in advance, and the most appropriate response motion is launched when an unknown push occurs. Therefore the humanoid is expected to recover itself in different motions when the input pushes differ. Toward this problem, in this paper we propose a push recovery strategy dealing with such unknown magnitude input forces and it employs two recovery motions to different volume pushes.