Advanced crane motion control

The ship to shore container crane is essentially a rail track suspended up to 50m above the quay, which runs from the quay, out over the ship. Containers are picked up using a hooking device called a spreader, which is suspended by cables from a trolley that runs along this track. The supporting structure is mounted on bogies that run along the dock side on rails set into the quay. All the motions are driven by DC electric motors which can be up to 1000kW. The use of flexible cables suspending the container makes the system behave in a pendulum like fashion. This swinging of the load hampers the operator in placing the container accurately. As a result, loading ships quickly requires highly skilled operators, who can often only operate efficiently for two or three hours. These factors have produced a requirement for a driver assistance system capable of measuring and controlling load sway, while still allowing the driver to position containers accurately. Four years ago to meet this need Cutler Hammer Crane Controls began development of its sway control system. The package was developed using computer simulation and crane development trials to produce an effective and user friendly system. Two generations of the system have been developed using different types of sway measurement