Crane sensor to detect out of plumb lift cable

Claim 1

A safety device for hoisting apparatus of the type having a pivoted elevated boom mounted for rotary slewing and vertical jib motion, said safety device adapted to indicate an out of plumb lift cable as attached to a load comprising, said boom having a head, a pulley carried by said head, a powered lift cable sheaved about said pulley, said lift cable having a lowermost portion provided with attachment means adapted to engage a load, a sensor assembly attached adjacent said pulley, said sensor assembly including a single pendulum arm suspended from said boom head adjacent said lift cable, a multi-pole switch carried by said pendulum arm, a deflectable switch actuating member extending from said switch and provided with a unitary lift cable engageable element substantially encircling said lift cable, said pendulum arm including an upper end pivotally attached to said boom head to allow swinging of said arm solely in the tilting plane of said boom during vertical jib motion, normal pendulum action of said arm maintaining said cable engageable element in a substantially non-biasing relationship with respect to said lift cable as encircled therewithin when said lift cable is plumb, a panel unit observable by the operator of said hoisting apparatus, activatable signal means in said panel unit, and electrical circuit means joining said multi-pole switch and signal means whereby, upon engagement between said cable attachment means and a load with said lift cable out of plumb, said switch actuating member cable engageable element is radially deflected by the encircled lift cable to activate said switch and a portion of said circuit means and said signal means to indicate to the operator in which direction said boom head is out of plumb relative to the attached load.