A load, hanging stationary from an overhead crane hook, naturally begins to swing like a pendulum when the trolley above starts to move or comes to a stop. This is load sway.
For decades experienced crane operators have controlled load sway by timing crane movement, carefully driving into the sway and centering the crane over the load. But regardless of his or her skill level, a crane operator is often left with little choice but to wait for a load to stop its swing before setting it down.
Clearly, load sway not only cuts into productivity, but impacts crane safety as well, especially for inexperienced operators.
In recent years, technology solutions have been developed to counteract sway and help crane operators maintain control of loads while improving productivity and crane safety. Chief among these are variable frequency drives, which increase the time it takes cranes to reach full speed and to come to a stop, thereby reducing the forces that lead to sway. Soft start devices also help by preventing the abrupt starts and stops that further contribute to sway. The effectiveness of these solutions often depends on the height of the hook and load. A load just a few inches off the ground may be stable, but halfway up it could be subject to the forces of load sway.
The most recent advance in controlling load swing is sway control technology, a programmable logic control (PLC) solution. Konecranes’ PLC sway control, or anti-sway, technology prevents sway and can be programmed to factor in the variables that cause loads to swing. Examples of these variables include the height of the hook and the length of the sling–the distance from the hook to the bottom of the load.
To prevent sway, Konecranes anti-sway must be programmed and activated before the crane starts. While the current technology is unable to stop existing sway, Konecranes is working on solutions for existing load sway to incorporate into future anti-sway technology.
Konecranes’ anti-sway technology has been available for about 10 years, and many existing cranes can be updated with it. However, to be a candidate for an anti-sway retrofit, a crane must have a variable frequency drive, as opposed to contactor controls, and must have a feedback device to communicate hook height to the PLC.
For additional information about crane safety and sway control, contact your Konecranes representative.