On the Constrained Walking of the NAO Humanoid Robot

The legs of the NAO humanoid robot have only 11 DOF; consequently, the motion of the pelvis and the free foot cannot be entirely specified in order to fully controlling the zero moment point (ZMP) in the contact area of the support foot. Thus, constraints on motion of both the pelvis and free foot must be appropriately taken into account in the motion planning process in order to specify suitable stable gaits. Specifically, the take-off and landing of the free foot have to be achieved in such a way that undesirable forces in the contact point with the floor be avoided. In this paper, a procedure is proposed to planning suitable walks in such a way that contact between the foot and the floor produces a stable behavior of the robot. To the knowledge of the authors, this problem has not be previously studied in the literature. The proposed method is applied in a study case to show its efficacy to get a stable gait.