Cooperative motion control for biped locomotion robots

Biped walking is an attractive locomotion method in our living environment because of its high mobility. To realize stable biped walking, the robot is controlled to keep its unstable equilibrium state dynamically. However, the decisive control strategy for achieving the objective is not mapped out. Paying attention to the fact that the animals' walking motion is realized according to the locomotion rhythm generated in the central nervous system, we proposed the rhythm based control method for biped walking. Then, we refined the method by introducing the compliance characteristics to realize more stable walking. In these studies, the compliance controller was designed under the assumption that the motion in the frontal plane was realized due to the reference rhythm. However, the motion in the sagittal plane interferes with the one in the frontal plane during walking, so the assumption was not necessarily satisfied. The biped walking should be realized under the cooperation between the motions in the frontal and sagittal plane. To realize stable biped waking, the robot should be necessarily controlled so that the motion in the frontal plane may be coordinated with the motion in the sagittal plane. We propose the cooperative motion control between the frontal and sagittal planes based on the compliance concept. In the method, the motion in the frontal plane is approximated with the inverted pendulum model, and the interference of the motions in the sagittal and frontal planes is regarded as the external force. Then, the compliance controller of the motion in the frontal plane is designed to keep the supporting leg contacting with the surface at multiple points on its foot. The effectiveness of the proposed method for realizing stable biped walking with multiple-point contact state is confirmed from some simulation results.