Balance Recovery for Humanoid Robot in the Presence of Unknown External Push

It is known that for an external push a humanoid robot can take three strategies, i.e. ankle strategy, hip strategy and step strategy, to recover balance. For the limited joint torque, the response strategy depends on the external push applied. This paper proposes a criterion for balance recovery based on initial phase plane by using inverted pendulum mode including angular moment. The step length and step amount are especially considered in step strategy. Furthermore step-one-out strategy is presented for balance recovery planning based on analytical method, which is divided into four phase and takes vertical CoM (Center of Mass) motion into account. The simulation results verify the effectiveness of the proposed method under strong external push.