An estimation model for footstep modifications of biped robots

Pushing, soft ground contact and other unknown large disturbances can cause humanoid robots to fall. In order to face such problems, an accurate and fast model of the robot is necessary to estimate the state at a certain time in the future using only current measurements. We approximate the robot by a three-mass model with two degrees of freedom. Unilateral compliant contacts and a closed-loop control similar to the one used on the real robot are included additionally. Utilizing this model it is possible to predict the robot's behavior and calculate compensating motions for different disturbance cases. Furthermore, it is possible to integrate the estimation results into the real-time control system of our biped LOLA. Simulation and experimental results demonstrate the effectiveness and the advantages of the proposed method.