In the case of a three-axis automatic or process crane, besides the lifting movement the crane gantry and the carriage also move.
The span width and travel path of the automatic crane units can be flexibly adapted. On average the travel path is around 30 to 70 metres, and up to 200 metres in special cases. Until now automatic cranes with span widths of up to 23 metres have been installed.
The necessary movement speed of the gantry, carriage and lifting mechanism are determined by H+H having regard to the material flow plan and the logistical performance requirements derived from that. With the three-axis variant nowadays 2 to 3 m/s (120 to 180 m/min) are considered as standard for the gantry. Those values can be exceeded, as for example with the Spanish company Metales Extroidos in Valladolid with 3.3 m/s. The highest value realised until now is 3.9 m/s (AluMenziken). For data on the carriage and lifting speeds, see the section on two-axis automatic cranes.
The three-axis automatic or process crane is designed as a two-support gantry crane with four track wheels, of which as a rule two are driven. For extreme requirements the crane can have “all-wheel drive”.
As the drive unit for “master/slave operation” specially designed asynchronous synchro-geared brake motors are used. Mechanical crane bridge guiding on one side takes place by means of laterally adjustable lateral guide rollers, electric synchronisation control by means of a synchronous positioning system with two laser distance measuring devices. Special provisions are made for synchronisation control when running hot. Length extensions of the crane tracks related to the building are compensated.
Other features: The speed at the end positions is controlled and additional security is provided by hydraulic buffers at the ends of the crane track.