US Patent 10010126 Protective helmet with integrated rotational limiter

A helmet is disclosed for protection during an impact. An outer liner and an inner liner slidably coupled to an interior surface of the outer liner through at least one return spring. The outer liner includes an interior surface with a shelf extending inward. The shelf includes an arresting surface. The inner liner has an exterior surface, an interior surface and an edge connecting the exterior surface to the interior surface. The edge faces the arresting surface of the shelf. The inner liner is slidably movable relative to the outer liner between a first position in which the edge of the inner liner is separated from the arresting surface of the shelf by a gap, and an arrested position in which a portion of the edge of the inner liner is in contact with a portion of the arresting surface of the shelf.