Patent ID: 8708172

Claim:
A multi-stage trolley for a crane, comprising: a first trolley movable in a longitudinal direction along a boom of the crane; a second trolley movable in a lateral direction perpendicular to the longitudinal direction on the first trolley; a hoisting wire provided in the longitudinal direction along the boom; a spreader connected to the hoisting wire through the first trolley and the second trolley and supported by the hoisting wire, the spreader being movable in a vertical direction according to a movement of the hoisting wire; a wire driving drum for winding or unwinding the hoisting wire to adjust a vertical level of the spreader; and a sheave block unit for changing a direction of the hoisting wire to maintain the vertical level of the spreader constant without operating the wire driving drum when the first trolley and the second trolley are moved, wherein the sheave block unit includes direction changing sheave blocks provided at the first trolley, at least one of the direction changing sheave blocks changing a direction of the hoisting wire provided thereto in the longitudinal direction into the lateral direction, wherein the direction changing sheave blocks include pairs of direction changing sheave blocks diagonally disposed at the first trolley, and at least one pair of the direction changing sheave blocks are coupled to each other by the hoisting wire.