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A novel control method for biped locomotion on rugged terrain is introduced, assuming an ideal robot model which has massless legs. By applying constraint control to the robot body so that it moves on a particular straight line and rotates at a constant angular velocity, the dynamics of the center of mass of the body becomes completely linear. Such motion of the ideal model is called the linear inverted pendulum mode, and it is used to develop the control scheme of the biped walking on rugged terrain. Under the control method in the linear inverted pendulum mode, walking on a particular rugged ground is shown to be equivalent to walking on a level ground. It is also shown that the additional use of the ankle torque makes the proposed control scheme robust and applicable to a real biped robot with mass legs. Simulation results are presented.>
Kajita et al. (Tue,) studied this question.