A gantry crane conventionally includes a vertically movable spreader (also referred to as a “grappler”) that is used for lifting a container, trailer, or other load. More particularly, a gantry crane typically includes a plurality of vertical columns, and vertically-movable front and rear stabilizer beams. Each of the stabilizer beams is horizontally disposed between a respective pair of the columns. Additionally, the crane includes front and rear trolleys that are movably mounted to the respective stabilizer beams for movement in a lateral direction. The spreader is suspended from hanger chains supported by the laterally movable trolleys.
The spreader is required to be positioned a significant distance below the stabilizer beams in some applications, thus requiring the hanger chains to be relatively long. For example, such a configuration is required for placing a container on the ground next to a loaded double-stack rail container car or a container on a chassis. A problem is that the spreader tends to sway in a pendulum-like manner when subjected to horizontal acceleration or deceleration, and the sway magnitude increases with length of the hanger chains. Such acceleration and deceleration can be caused by the motion of the trolleys or driving the crane in forward or reverse directions as necessary to position the load. Spreader sway presents difficulties and inefficiencies for handling loads, particularly when long hanger chains are used. Therefore, a need exists for an improved spreader that resists swaying.