| 摘要 |
Heavy machinery comprising a lower support structure having an upper surface, and an upper structure having a generally horizontal lower surface facing the upper surface of the lower structure, the upper structure being supported above the lower structure for rotation relative to the lower structure about a generally vertical axis, and the lower surface of the upper structure having therein an upwardly extending recess surrounding the axis to provide space for a person working on the machinery, the recess being defined at least in part by an upper wall above and generally parallel to the lower surface, and by a plurality of generally planar facets surrounding the axis, each of the facets extending transversely to the upper wall and to the lower surface.
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