Real-time estimation algorithm for the center of mass of a bipedal robot with flexible inverted pendulum model

A closed-loop observer to extract the center of mass (CoM) of a bipedal robot is suggested. Comparing with the simple conversion equation of using just joint angle measurements, it enables to get more reliable estimates by using both joint angle measurements and F/T sensor outputs at the ankle joint. First, a nonlinear type observer is constructed in the extended Kalman filter framework to estimate the flexible rotational motion of biped. It is based on the inverted pendulum model with flexible beam which is to simply address the flexible behavior of a biped, specifically in the single support phase. Then, the predicted estimates of CoM by the flexible motion observer are combined with the outputs of the CoM conversion equation and the final estimates will be determined according to the weighting value which penalizes the flexible motion model and the CoM conversion equation. Simulation results are followed to show the effectiveness of the proposed scheme.