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This paper describes a real-time walking control system developed for the biped robots JOHNNIE and LOLA. Walking trajectories are planned on-line using a simplified robot model and modified by a stabilizing controller. The controller uses hybrid position/force control in task space based on a resolved motion rate scheme. Inertial stabilization is achieved by modifying the contact force trajectories. The paper includes an analysis of the dynamics of controlled bipeds, which is the basis for the proposed control system. The system was tested both in forward dynamics simulations and in experiments with JOHNNIE.

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To simplify the development of new trajectories for a humanoid robot with many joints, the ability to check for potential collisions is crucial. More importantly, to enable online generation of general motions, such as whole-body-motion, collision avoidance must be employed, which is usually more challenging. In this paper, a model-based and efficient on-line distance calculation between links of the robot is proposed. To avoid collisions the results are projected into the nullspace term of the inverse-kinematics which is based on the redundancy resolution framework of LIÉGEOIS. Additionally, a novel method to reduce the vertical angular momentum for a walking biped robot which uses the arm motion is proposed. It reduces the vertical angular momentum of the walking robot especially for larger steps. Since the method also works in the null-space, it can easily be combined with the proposed collision avoidance scheme. Finally, results for the proposed methods from simulations and experiments with the robot Lola are shown.

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