DGPS Positioning and Automatic Steering of Gantry Cranes (RTGs)
With the, in general use, Global Positioning System (GPS) it is possible to determine a geographical position. The commonly used standard GPS provide an accuracy of approx. 20 m. With the aid of additional equipment and under certain area conditions it is possible to achieve a geographic position with an accuracy of up to ±3 cm.
Due to the achievable positional determination of approx. ±3 cm, that in addition is refreshed every 100 ms, it is possible to track a vehicles movements. Consequently by using a series of measurements along with the geographical positional data it is possible to determine the vehicles direction of travel and velocity.
With the aid of these functions it is possible to automatically steer a RTG over a predetermined route within the container yard. This means, that apart from the free mov- ability that the rubber tired vehicles provide, they like the rail mounted vehicles can be used within the container storage area with- out disrupting the drivers attentiveness, with unnecessary requirement to control the tracking and manually steer the crane. A special advantage of this system is that for both functions there is absolutely no requirement to mount equipment within the track surface of the container yard.
All these points serve to aid the operational safety and therefore remove some of the stress placed on the driver, which in turn reduces the error rate. A looped memory stores all relevant information so that in the event of a disruption with the systems function or during testing, a quick and easy error diagnoses is available. For special or emergency uses all these functions are manually operable so that a complete operational shut down can be avoided.
Sideways sway of less than 5 cm of the RTG are allowed; in any other case is the use of an additional slope controller necessary.
Container Location Tracking
The temporary storage of containers by use of visual means with manual confirmation leads to an error rate in the storage handling, which disrupts the efficient turn over time of the container ships. Therefore it is better to use GPS to control the positioning and documentation of containers within the container port environment.
Now the Rubber Tired Gantry Cranes (RTG), working on container transport within a seaport, communicate with the controlling container management system, via a data Radio Transceiver, when they pick up or set down a container at a predesignated position within the container yard. This takes some of the load off of the driver as well as it reduces the error rate — complicated and time exhaustive container searches are no longer necessary.