Mobile lift crane with variable position counterweight

  • US 7,546,928 B2
  • Filed: 04/09/2007
  • Issued: 06/16/2009
  • Est. Priority Date: 10/27/2006
  • Status: Active Grant
First Claim
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1. A method of operating a mobile lift crane, the lift crane comprising a carbody having moveable ground engaging members;

  • a rotating bed rotatably connected to the carbody such that the rotating bed can swing with respect to the ground engaging members;

    a boom pivotally mounted on a front portion of the rotating bed, with a hoist line extending therefrom a mast mounted at its first end on the rotating bed; and

    a moveable counterweight unit;

    the method comprising;

    a) positioning the counterweight forward of a point directly below the top of the mast when no load is on the hoist line; and

    b) positioning the counterweight rearward of the top of the mast when the hoist line is supporting a load;

    c) wherein the moveable counterweight is never supported by the ground during crane pick, move and set operations other than indirectly by the moveable ground engaging members on the carbody; and

    wherein the top of the mast is defined as the furthest back position on the mast from which any line or tension member supported from the mast is suspended, and if no line or tension member is supported from the mast, then the top of the mast is the position to which any backhitch is attached; and

    wherein the position of the counterweight unit is defined as the center of gravity of the combination of all counterweight elements and any holding tray to which the counterweights are attached, or otherwise move in conjunction with, with all counterweight units on a crane that are tied together so as to always move simultaneously being treated as a single counterweight for purposes of determining the center of gravity.

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