US Patent 7455492 Multi-trolley container crane with bi-level track switching capability

The invention relates to a multiple trolley container crane having at least two trolley tracks (6, 7) disposed one on top of the other, on which trolleys (8) having running wheels, drive devices, and lifting devices move. Characterized in thatrunning wheels (20) that can be laterally retracted and extended, andan integrated lifting system (21, 22, 24, 25, 26) are disposed on the trolleys (8) on the trolley tracks (6, 7), with which they support themselves on or next to the trolley tracks (6, 7) and thereby get from the lower to the upper trolley tracks (6, 7) and vice versa.