Mobile lift crane with variable position counterweight

摘要

A mobile lift crane (610) includes a carbody (612); moveable ground engaging menbers (614, 616); a rotating bed (620); a boom (622); a moveable counterweight unit (634); and a counterweight movement structure comprising a rack and pinion assembly (636). A method of operating the crane (610) comprises performing a pick, move and set operation, wherein the counterweight unit (634) is moved toward and away from the rotating bed (620) but is never supported by the ground during the operation, other than indirectly by the ground engaging members (614, 616).