Patent attributes
Bins or other storage units contained within a three-dimensional grid structure are arranged in cells, each of which has multiple storage units surrounding a central void or space on different sides thereof. This void space is slightly larger than each storage unit, enabling the unit to be pulled into the void by mechanical means, and allowing access to the bins on all sides of the void. The storage units are stacked within the three-dimensional grid structure, which can be built or expanded to a predetermined footprint. The aligned voids of stacked cells create vertical shafts spanning between upper and lower tracks of the grid structure on which robotic retrieval vehicles can horizontally travel to and from any given shaft. The robotic retrieval vehicles can directly access any storage unit via the vertical shafts.