Patent ID: 6109463
Filing Date: 2000-08-29
Classification: B66C,B66F

Abstract:
A lifting device comprising:a frame;an elongated boom having a first end pivotally connected to the frame along a pivot axis;a counterweight connected to the first end of the boom and a center of gravity that moves in response to the pivoting of the boom about the pivot axis;the frame having a turret rotatably mounted thereon and the boom being pivotally connected to the turret and rotatable therewith;the counterweight being pivotally connected to the first end of the boom by linkage means, the linkage means also being pivotally connected to the turret;a fixed pivot shaft extending horizontally within the turret;the counterweight pivotally resting directly on the fixed pivot shaft;the linkage means pivotally rotating the counterweight about the pivot shaft in response to the boom being pivoted;the linkage means comprising three substantially rigid elongated arms, the first elongated arm having one end connected to the first end of the boom, the second arm having one end pivotally connected to the counterweight, and the third arm having one end pivotally connected to the turret and another end pivotally connected to the first arm, the third arm having a central portion pivotally connected to a second end of the second arm.