Hammerhead crane with plural shuttle trolleys, a load trolley and

Abstract

A hammerhead type of crane has a structural tower with opposed structural cantilevers extending horizontally therefrom and there is a horizontal track along which a load carrying trolley may move through the tower between limits near the outer ends of the cantilevers and a second horizontal track along which a counterweight may travel at the same speed and distance but in the opposite direction and with the load trolley and counterweight passing each other as they move through the tower from one cantilever to the other. The counterweight is moved by means of a cable that has its opposite ends attached to the counterweight and which between its ends is wound about a reversible drum arranged to selectively move the counterweight in one direction or the other. For moving the load trolley in a direction opposite to but at the same speed, a system of cables connected with the counterweight is provided which includes a shuttle trolley on each cantilever arranged to move in the same direction as the load trolley but at half the speed, while other cables transmit motion between the load trolley and the slower-moving shuttle trolleys. This arrangement (a) avoids many long unbroken spans of cables otherwise commonly used and reduces the hazards of an accident, (b) provides the opportunity of direct reeving of the bucket hold and close lines, and (c) reduces sag tension at the bucket, thereby reducing the bucket weight requirements and thus permitting greater payload.