Load control apparatus for cranes

Claim 1

In a hoisting apparatus having a superstructure, a boom pivotally supported on said superstructure at a hinge point spaced from the center of gravity of said hoisting apparatus, said boom being movable in a vertical plane about said hinge point, a variable length boom support means connected at one end to the free end of said boom and at its other end to an anchor point adjacent said superstructure for moving said boom into different angular positions in said vertical plane, a rigid cantilever beam having a longitudinal centerline substantially colinear with the line between said anchor point and said hinge point, said beam being rigidly connected at one end to said superstructure adjacent said hinge point the other end of said beam extending free from said superstructure and being connected to said other end of said boom support means for constituting said anchoring point, hoisting means connected to the free end of said boom for supporting a load therefrom, and means mounted adjacent said anchor point end of said cantilever beam and independently thereof, responsive to the deflection of said cantilever beam at the anchor point end thereof said means for sensing the deflection of the rigid beam at the anchor point is an electrical switch secured to the superstructure and positioned adjacent the anchor point end of the beam, said switch having operator means in contact with the anchor point End of the beam whereby the switch contacts are closed when the deflection of the beam is less than a fixed predetermined value and the switch contacts are opened when the deflection of said beam exceeds the predetermined value, the opening of said switch contact operating to render inoperative the hoisting means to prevent further increase of the pitching moment.