Invariance controlled balance of legged robots

A balance control approach for legged robots is presented that is based on Zero Moment Point manipulation. Therefore the invariance control method is used, where an output of the system is kept in an admissible region by switching between two controllers, the nominal controller and the corrective controller. The nominal controller is designed to achieve the main control objective whereas the corrective controller is used to keep the system in the admissible region whenever a constraint violation is about to occur. The corrective control signal is chosen as close as possible to the nominal control signal to enable the return to the nominal task after correction is not necessary any more. The control system for balance control comprises the mechanical robot model and a simplified model of the motor dynamics. The method is demonstrated in simulation experiments of a single joint robot and a planar eight degree of freedom legged robot.