Stability and Gait Switching of Underactuated Biped Walkers

This paper introduces a new gait switching approach for underactuated biped walkers. The switching condition relies on a reduced region of attraction - that of the unactuated dynamics - which is shown to be sufficient to predict falls. A gait transition is accordingly stable (as in “the robot does not fall if the biped's state is within the reduced region of attraction of the switched-in gait when switching takes place. Two- and five-link biped models complete a sequence of random gait transitions using the switching logic. The condition is also used to enlarge the full region of stability of the five-link model by embedding feedback-stabilized trajectories from a gait library in a mapping. The mapping stitches stable trajectories to the orbit of the desired gait based on each gait's reduced region of attraction. This improves the robustness of the five-link model walking on uneven terrain without ground perception regardless of the size of the gait library.