Manipulation
Form Closure
Form closure is a grasp or fixture property in which an object's mobility is completely constrained by the geometry of frictionless contacts alone, so no motion is possible regardless of applied wrenches. Because it assumes no friction, form closure is a stronger condition than force closure and generally requires more contacts, at least four in the plane and seven in space for a rigid body. It underlies fixture and caging design.
Why it matters for physical AI
Geometry-only immobilization offers robustness that does not depend on uncertain friction estimates, informing caging grasps and fixture strategies that make manipulation reliable when surface properties are unknown.
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