Stable dynamic walking of a quadruped robot “Kotetsu” using phase modulations based on leg loading/unloading

In this study, we intend to show the basis of a general legged locomotion controller with the ability to integrate both posture and rhythmic motion controls and shift continuously from one control method to the other according to the walking speed. The rhythmic motion of each leg in the sagittal plane is generated by a single leg controller which controls the swing-to-stance and stance-to-swing phase transitions using respectively leg loading and unloading information. Since rolling motion induced by inverted pendulum motion during the two-legged stance phases results in the transfer of the load between the contralateral legs, leg loading/unloading involves posture information in the frontal plane. As a result of the phase modulations based on leg loading/unloading, rhythmic motion of each leg is achieved and leg coordination (resulting in a gait) emerges, even without explicit coordination among the leg controllers, allowing to realize dynamic walking in the low- to medium-speed range. But an additional ascending coordination mechanism between ipsilateral leg controllers helps to improve the stability. In this paper, we report the result of experiments using a newly constructed quadruped robot “Kotetsu” in order to verify the results of simulations. Details of trajectory generation and movies can be seen at: http://robotics.mech.kit.ac.jp/kotetsu/.