Stacker cranes run on two rails; one mounted on the floor and one mounted on the roof. Between these rails spans a frame on which a carrying unit can move up and down. This setup allows much greater precision when placing and removing goods from the racking and it vastly reduces lean. The elimination of sway means that stacker cranes can operate much higher than MHE only supported by the ground (up to 45m). One carrying unit can support a payload of up to 8.5 tonnes.
This system can be operated by humans or be fully automated.
There are no onerous floor flatness requirements for this crane as it’s fully supported by guidance rails. However, the system is very sensitive to a change in level on either of the rails; therefore differential settlement of the floor can lead to serious operational problems.
Because they are very expensive to install, it is only cost effective to build these systems in very high warehouses (e.g. clad rack structures) where rapid movement of goods is required 24/7.