Extendible boom with locking mechanism having equalizer arrangement

摘要

A extendible boom incorporates a locking mechanism that mechanically engages an extended boom section in response to the loss of hydraulic fluid pressure to the lift cylinder for that boom section so as to prevent unintended boom lowering. The locking mechanism includes locking devices, such as toothed cams, that are located on opposite sides of the boom and that are configured to move, 1) from a disengaged position permitting unobstructed movement of the extended section relative to the adjacent section, 2) to an engaged position in which the locking devices engage opposite sides of the extended section to prevent unintended boom lowering. In order to prevent the imposition of unequal locking forces that could occur if only the locking device on one side of the extended boom section were to engage that section, an equalizer arrangement mechanically couples the locking devices on opposite sides of the extended boom section to one another so that both locking devices always move through essentially the same stroke at essentially the same time. The equalizer arrangement preferably comprises an equalizer bar that mechanically couples pivot shafts of the two locking devices together so that rotation of one pivot shaft drives the other pivot shaft to simultaneously rotate through a pivot stroke that at least substantially equals a pivot stroke of the one shaft.