TIP Model: A Combination of Unstable Subsystems for Lateral Balance in Walking Balancing or postural stability is one of important locomotor subfunctions in bipedal gaits. The inverted pendulum and virtual pivot point (VPP) are common modeling approaches to analyze balance control in human and robot walking. In this paper, we employ the VPP concept to investigate posture control in the frontal plane. The outcomes demonstrate that unlike posture control in the sagittal plane, the VPP in the frontal plane is place below center of mass. This finding explains a novel hybrid strategy for lateral stability in human walking. The here proposed model shows that switching between unstable inverted virtual pendulums generate stable posture control in the frontal plane. This outcome is consistent within a group of seven human subjects walking at normal and slow speeds.

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 xe2x80x94 that of the unactuated dynamics xe2x80x94 which is shown to be sufficient to predict falls. A gait transition is accordingly stable (as in xe2x80x9cthe robot does not fall if the bipedxe2x80x99s state is within the reduced region of attraction of the switchedin gait when switching takes place. Two and fivelink 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 fivelink model by embedding feedbackstabilized trajectories from a gait library in a mapping. The mapping stitches stable trajectories to the orbit of the desired gait based on each gaitxe2x80x99s reduced region of attraction. This improves the robustness of the fivelink model walking on uneven terrain without ground perception regardless of the size of the gait library.