A walking stability controller with disturbance rejection based on CMP criterion and Ground Reaction Force feedback

A novel controller using Center of Gravity (COG) planning based on the Centroidal Moment Pivot (CMP) criterion with Ground Reaction Force (GRF) feedback is presented. High level motion planning of the robot is done by planning a reference CMP trajectory that lies within the support polygon. In order to ensure rotational stability, the controller regulates the distance between the Zero Moment Point (ZMP) and the reference CMP through COG manipulation. A reference COG trajectory is generated from the measured GRF and a simplified model of the rotational dynamics of the robot. The reference COG is then decomposed into reference joint velocities via kinematic resolution of the COG Jacobian. Planar simulations show that modifying the COG trajectory using the CMP criterion with GRF feedback increases the controller´s robustness to external disturbances compared to a ZMP based controller. Additionally, the results show that the constant non-zero momentum generated by external disturbances can be regulated by minimizing the difference between the reference CMP and ZMP positions, without explicitly regulating the momentum about the COG.