Impedance control for running of biped robots

In this paper, a running cycle is divided into a stance phase and a flight phase, and impedance control algorithms for each phase are proposed. In the stance phase, under the assumption that the foot of supporting leg must be fixed on the ground, the impedance of the swing foot, which is to be controlled, is defined such that it dictates the characteristics of the swing foot. Thus, the impedance of the hip link is defined by the relationship between the velocity of the hip link and the force. Next, two feet of the flight phase are in the air. The swing foot is compressed into following the desired trajectory on the basis of the hip link. Thus, the impedance of two feet, which is to be controlled, is defined from the hip link. In the actual application, the modified impedance is used in order to increase the compliance about the environment and absorb the impact force at landing moment in the flight phase. And the desired trajectories of hip link and two feet are derived from the inverted pendulum mode and mass-spring model in the stance phase, and the ballistic motion in the flight phase. The effectiveness and the performance of the proposed control algorithms are shown in computer simulations with a 19-DOF biped robot and a 6-DOF elastic pad model.