Title: Fast Trajectory Optimization for Legged Robots using Vertex-based ZMP Constraints,
Abstract: This paper combines the fast Zero-Moment-Point (ZMP) approaches that work
well in practice with the broader range of capabilities of a Trajectory
Optimization formulation, by optimizing over body motion, footholds and Center
of Pressure simultaneously. We introduce a vertex-based representation of the
support-area constraint, which can treat arbitrarily oriented point-, line-,
and area-contacts uniformly. This generalization allows us to create motions
such quadrupedal walking, trotting, bounding, pacing, combinations and
transitions between these, limping, bipedal walking and push-recovery all with
the same approach. This formulation constitutes a minimal representation of the
physical laws (unilateral contact forces) and kinematic restrictions (range of
motion) in legged locomotion, which allows us to generate various motion in
less than a second. We demonstrate the feasibility of the generated motions on
a real quadruped robot.