Drive mechanism for jib cranes

Claim 1

In a crane having an elongated cantilevered main jib of the box type construction, an extendable and retractable elongate extension jib of uniform rectangular cross section telescopically mounted within the main jib, hydraulic power means including means for selectively energizing the power means for telescopically extending and retracting the extension jib, and securing means for holding the extension jib in place following telescopic movement, the improvement comprising: a U-shaped lever having the ends of the extending arms of the U hinged to the lateral sides of the main jib and the crossmember of the U passing transversely through the lateral sides of the main jib; a first roller mounted on a first shaft passing transversely through the lateral sides of the main jib and being journalled to the arms of the U-shaped lever, the first roller sitting on top of the extension jib; a second roller mounted on a second shaft passing transversely through and being journalled to the latteral sides of the main jib and supporting the bottom of the extension jib, the axis of the second shaft being vertically aligned with the axis of thE first shaft; a third roller spaced horizontally from and parallel with the second roller and being mounted on a third shaft passing transversely through and being journalled to the lateral sides of the main jib and supporting the bottom of the extension jib; a pulley wheel keyed to each shaft including a continuous belt means drivingly connecting the pulley wheels to the hydraulic power means for rotating the rollers in unison and telescopically moving the extension jib upon energization of the hydraulic power means; a brake shoe sitting on top of the extension jib in the space between the vertical planar axes of the second and third shafts; first and second hydraulic power ram means mounted on the main jib and each having first and second piston rod means respectively and being hydraulically connected to the hydraulic power means for simultaneous energization of the piston rod means with the power means, the first piston rod means being connected to the brake shoe for lifting the brake shoe from the extension jib upon energization thereof, the second piston rod means being connected to the cross-member of the U for swinging the arms of the U upon energization thereof and squeezing the extension jib between the rotating rollers; and spring means between the brake shoe and the first piston rod means for pressing the brake shoe against the top of the extension jib upon the simultaneous de-energization of the hydraulic power means and piston rod means for halting the movement of the extension jib.