Glossary · Control
ZMP balance
Also known as: zero moment point
In brief
The Zero Moment Point (ZMP) is the point on the ground where the net horizontal moment from the robot's weight and inertia equals zero. Keeping the ZMP inside the robot's support polygon (its feet) is a classical sufficient condition for not falling over.
ZMP-based control was the dominant humanoid balance method through the early 2020s. Honda's ASIMO, the early Boston Dynamics PETMAN, and most Japanese research humanoids used some flavor of ZMP planning: pick foot placements, plan a trajectory for the center of mass that keeps the ZMP inside the support polygon, execute via inverse-kinematics joint commands.
ZMP control is conservative and robust on flat ground but struggles with dynamic motions (running, recovery from large pushes) where the support polygon is tiny or absent. Modern humanoids (Atlas Electric, Figure, Optimus) tend to use whole-body model-predictive control or learned policies that subsume ZMP as a special case.
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