Abstract
In this paper, we consider a landing motion control problem of 4-link robots which imitates a standing human. We note in this work that when both of the toe and the heel touch the ground, the robot becomes a fully actuated system. That is, it is possible to decouple the position of the center of mass (CoM) and the angular momentum about CoM by input transformation. Then, we can consider only three terms about CoM, vertical position, horizontal position, and angular momentum for motion control. First of all, vertical position control of CoM is built based on trajectory design to keep floor reaction force as weak as possible. Secondly, we introduce a Zero Moment Point (ZMP), and control the horizontal position of CoM to keep ZMP within the sole range. Thirdly, the angular momentum is controlled to be gradually converged to zero so that the robot stops after landing motion. Finally, we confirm the effectiveness of the present method by simulations.
