In this project for a wind turbine gearbox manufacturing company, two overhead cranes running on a single track, both equipped with a trolley, were fitted with a sophisticated protection system. The cranes can operate separately or in tandem, and the workplace includes a restricted zone over which the trolleys are not allowed to pass.
To safeguard the restricted zone, approaching cranes must have their trolley positioned at the right side to gain permission to enter. If this is not the case, the crane will automatically slow down and stop as it approaches the zone. If the crane is positioned above the restricted zone, the trolley is not given permission to move into the zone – it will automatically slow down and stop as it approaches.
In tandem mode, the control units communicate with each other via a radio frequency (RF) signal to synchronize the protections for the cranes and trolleys. If one of the cranes has to slow down or stop, the other crane will automatically do the same. Cranes and trolley zone restrictions will also be shared. Commands to slow down or stop when a crane or trolley approaches the restricted zone will automatically be duplicated on the other crane, even if the latter is some distance from the zone. The tandem mode can only be activated if both cranes are beyond, and on the same side of, the restricted zone.
Tandem mode includes an additional protection in laser distance monitoring. The position of the cranes relative to each other, and the position of the trolleys relative to each other, are not allowed to deviate too much from the initial values recorded when the tandem mode was activated. This protection system is based on three laser distance measurements: one on the first crane measuring distance to the second crane, and one on both cranes to identify the position of the trolley.