Biped walk based on vertical pivot motion of linear inverted pendulum

Typical human walking patterns include extended-knee postures. Humanoid robots, however, walk with bended knees in order to avoid controlling motion in the presence of kinematic singularities, appearing at the extended-knee postures. Hence, the walking motion patterns of humanoid robots are not as natural and as efficient as those of humans. We have addressed the problem in previous works and shown that, for a static walking pattern, it is possible to include the extended-knee postures, provided control is based on the singularity-consistent (SC) approach, which can ensure stable control in the neighborhood of kinematic singularities. In this paper, we propose a method to generate a dynamic walking pattern including up-and-down waist motion, such that the support leg enters the singularity neighborhood in the middle of each support phase. The basic motion pattern is generated with the help of a linear inverted pendulum model, whose pivot is controlled in the vertical direction to ensure the up-and-down waist motion, independently of the horizontal motion of the pendulum. Experimental results show the effectiveness of our approach.