External pendant pay-out system with anti-droop control

A pendant pay-out system for maintaining the working angle of a pendant supported extensible boom substantially constant when the boom is being extended or retracted, said boom being pivoted to support means and including a pivotally supported base section having at least one section telescopically received therein, a live mast supported for pivotal movement relative to said support means and having rotatable pendant supporting means on the free end thereof, and means for pivoting the mast between a lowered position and one of a plurality of raised working positions with one position defining a predetermined mast-boom angle, the improvement which comprises:

• a pendant trained over said rotatable means on said mast and having one end connected to said one boom section and the other end portion supportively connected to said base section, reversible power operated means for taking up or paying out pendant, control means responsive to extension of the boom for actuating said power means to pay out sufficient pendant and responsive to retraction of the boom for actuating said power means to haul in sufficient pendant to maintain said mast boom angle substantially constant during extension and retraction of the boom, said reversible power operated means being directly connected to said boom, said reversible power means includes hydraulic motor means;
• and wherein said control means comprises electrical control means including a first potentiometer responsive to linear changes in the amount of pendant being taken in or payed out, a second potentiometer responsive to linear changes due to extension and retraction of the boom, and a comparator for receiving signals from said potentiometers;
• and wherein said control means also includes a hydraulic valve and a servo mechanism for receiving signals from said comparator for shifting said valve;
• said potentiometers being preset to provide a predetermined output ratio when said mast-boom angle is at said predetermined working angle, said servo mechanism being responsive to changes in said output ratio from said predetermined ratio due to extension or retraction of the boom to shift the hydraulic valve into positions which drive said motor in a direction which pays out or hauls in pendant until said output ratio returns to said predetermined output ratio.