Articulated Boom Lifting Arrangement

Abstract

A bell crank and a mechanical link are included in an aerial lift system to mechanically constrain motion of a two-boom aerial lift mechanism to prevent the aerial lift system from accessing unstable positions. Typically an aerial lift is coupled to a vehicle via a turntable. The turntable includes a counterweight on a rearward side of the turntable to balance the booms and associated hardware as they are extended in a forward direction. If the booms are in certain rearward, or even vertical positions, the counterweight can cause the vehicle to tip and such unstable positions are to be avoided. By providing the bell crank proximate the pivot joint between upper and lower booms, with the bell crank coupling at pivot joints with: the lower boom, the mechanical link, and an upper hydraulic cylinder, the booms of the aerial lift system are mechanically constrained to avoid vehicle tipping.

1 . A boom system, comprising:
 a support member;   a lower boom coupled to the support member at a first turntable pivot;   a lower linear actuator coupled between the support member and the lower boom;   a mechanical link coupled to the support member at a second support member pivot;   a bell crank comprising:
 a first bell-crank pivot coupled to the lower boom; 
 a second bell-crank pivot coupled to the mechanical link; and 
 a third bell-crank pivot; 
   an upper boom coupled to the lower boom via a boom-to-boom pivot; and   an upper linear actuator coupled to the bell crank at the third bell crank pivot and coupled to the upper boom.   
     
     
         2 . The boom system of  claim 1  wherein the bell crank is generally triangular with the first, second, and third bell crank pivots located near corners of the generally triangular bell crank. 
     
     
         3 . The boom system of  claim 1  wherein the support member is a rotatable turntable, the lower boom couples with the turntable proximate a first end of the lower boom, the lower boom couples with the upper boom and the bell crank proximate a second end of the lower boom, and the lower linear actuator couples with the lower boom at a point in between the first and second ends of the lower boom. 
     
     
         4 . The boom system of  claim 1  wherein the lower linear actuator is pivotally coupled to the lower boom at a coupling location and the coupling location is proximate a first end of the lower linear actuator and along the length of the lower boom. 
     
     
         5 . The boom system of  claim 4  wherein the support member is a turntable, a second end of the lower linear actuator extends through a slot in the turntable, the lower linear actuator is trunnion mounted to the turntable at a location away from the second end of the lower linear actuator, and the lower linear actuator is configured to pivot with respect to the turntable. 
     
     
         6 . The boom system of  claim 1  wherein the lower linear actuator is a lower hydraulic cylinder and the upper linear actuator is an upper hydraulic cylinder. 
     
     
         7 . The boom system of  claim 6 , further comprising:
 a lower hydraulic line coupled to the lower hydraulic cylinder;   an upper hydraulic line coupled to the upper hydraulic cylinder;   a lower operator-controlled actuator to control supply of hydraulic fluid in the lower hydraulic line; and   an upper operator-controlled actuator to control supply of hydraulic fluid in the upper hydraulic line.   
     
     
         8 . The boom system of  claim 1  wherein the support member is a turntable, the lower boom is coupled to the turntable at a first end of the lower boom and the boom-to-boom pivot is located proximate a second end of the lower boom and proximate a first end of the upper boom. 
     
     
         9 . The boom system of  claim 8 , further comprising a basket system coupled to the upper boom at a second end of the upper boom. 
     
     
         10 . A boom system, comprising:
 a turntable;   a lower boom pivotally coupled to the turntable;   a lower linear actuator pivotally coupled between the turntable and the lower boom;   a mechanical link pivotally coupled to the turntable;   a bell crank pivotally coupled to the lower boom and the mechanical link;   an upper boom pivotally coupled to the lower boom; and   an upper linear actuator pivotally coupled between the bell crank and the upper boom.   
     
     
         11 . The boom system of  claim 10  wherein the lower linear actuator comprises a hydraulic cylinder and the upper linear actuator comprises a hydraulic cylinder. 
     
     
         12 . The boom system of  claim 10  wherein the lower linear actuator is coupled to the turntable rearward of a coupling between the lower boom and the turntable, the system further comprising:
 a counterweight mounted on the turntable, the counterweight located rearward with respect to the coupling between the lower boom and the turntable. 
 
     
     
         13 . The boom system of  claim 10  wherein:
 the mechanical link is coupled to the turntable at a location that is rearward with respect to a coupling between the lower boom and the turntable; and 
 the lower linear actuator is coupled to the turntable at a location that is rearward with respect to a coupling between the mechanical link and the turntable. 
 
     
     
         14 . The boom system of  claim 10  wherein the mechanical link comprises two members and the lower linear actuator passes through the two members of the mechanical link. 
     
     
         15 . The boom system of  claim 10  wherein one end of the lower linear actuator extends through an opening in the turntable. 
     
     
         16 . The boom system of  claim 15  wherein the lower linear actuator is trunnion coupled to the turntable, the lower linear actuator is a hydraulic cylinder, and the upper linear actuator is a hydraulic cylinder. 
     
     
         17 . An aerial lift system, comprising:
 a vehicle;   a turntable rotably coupled to the vehicle;   a lower boom pivotally coupled to the turntable;   a mechanical link pivotally coupled to the turntable;   a bell crank pivotally coupled to the lower boom and the mechanical link; and   an upper boom pivotally coupled to the lower boom.   
     
     
         18 . The aerial lift system of  claim 17 , further comprising:
 a lower hydraulic cylinder pivotally coupled between the turntable and the lower boom; and   an upper hydraulic cylinder pivotally coupled between the bell crank and the upper boom.   
     
     
         19 . The aerial lift system of  claim 18  wherein the bell crank is generally triangular with a lower boom pivot proximate a first corner of the bell crank, a mechanical link pivot proximate a second corner of the bell crank, and an upper hydraulic cylinder pivot proximate a third corner of the bell crank. 
     
     
         20 . The aerial lift system of  claim 17 , further comprising:
 an extendible link coupled to the upper boom; and   a basket system coupled to the extendible link.