Offsetting link assembly for folding luffing jib

A crane boom and luffing jib assembly, comprising:

• (a) a crane boom having a boom top;
• (b) a luffing jib, comprising a jib butt section pivotally secured to the boom top, a jib boom section pivotally secured to the jib butt section, and a jib top section secured to the jib boom section, each jib section having a longitudinal neutral axis and each jib section having upper and lower chords in relation to a ground surface when the crane boom is raised and the luffing jib is extended parallel to the ground surface;
• and
• (c) an offsetting link structure connecting chords of the jib boom section to chords of the jib butt section, the offsetting link being capable of holding the jib boom and butt sections in both a fixed operational relationship and a folded set-up relationship in which the longitudinal neutral axis of the jib boom section is offset relative to the longitudinal neutral axis of the jib butt section.

An offsetting link pivotally connecting two sections of a luffing jib together so that the sections are able to move between an operational relationship and an offset relationship each section having upper and lower chords, the link comprising a pair of side brackets connected by cross-braces, each side bracket comprising a pair of plates spaced to receive an end of a jib section chord therebetween, the chords being retained in the brackets by pins, wherein:

• (a) each side bracket has a hole in a lower end of the bracket aligned with holes in an end of the lower chords of the jib sections, and axle pins extending through the holes in the side brackets and through the holes in the lower chords of the jib sections to secure the jib sections to each other and to the offsetting link;
• (b) each side bracket has two holes in an upper end of the bracket, one of the holes being aligned with holes in an end of the upper chords of each of the jib sections;
• (c) the upper chords of one jib section are secured to the offsetting link by a hinge pin, the upper chords of the other jib section are secured to the offsetting link by a second pin;
• and
• (d) a stop lug is positioned between the plates at the upper end of each bracket to engage an abutment member on the end of the upper members of one of the jib sections to limit the degree of offset allowable when the hinge pins are removed.

A crane comprising:

• (a) an upper works rotatably mounted upon a mobile lower works, the upper works rotatable about a vertical swing axis;
• (b) a boom having a longitudinal neutral axis and upper and lower chords spaced outwardly from the boom longitudinal neutral axis to provide buckling strength to the boom, and a luffing jib connection pivot being near enough to the boom longitudinal neutral axis so that the axis of the connection pivot is between two planes, each of which is parallel to the boom longitudinal neutral axis and defined respectively by upper and lower faces of the boom;
• (c) a luffing jib pivotally connected to the boom at the luffing jib connection pivot, the luffing jib also having a longitudinal neutral axis and upper and lower chords spaced outwardly from the jib longitudinal neutral axis to provide buckling strength to the jib, with the jib connection pivot being near enough to the jib longitudinal neutral axis when the jib is in an operational configuration so that the axis of the connection pivot is between two planes, each of which is parallel to the jib longitudinal neutral axis and defined respectively by upper and lower faces of the luffing jib;
• (d) said jib including a hinge longitudinally spaced from said luffing jib connection pivot to allow the longitudinal neutral axis of the boom or the jib to be offset relative to the jib connection pivot.

A method of assembling a crane boom and luffing jib, the boom having a boom top, a longitudinal neutral axis and a jib connection pivot on the boom top, the luffing jib having a jib butt section, a jib boom section having a longitudinal neutral axis, a jib top section and a hinged connection connecting the jib butt section and jib boom section, comprising the steps of:

• (a) assembling the luffing jib and boom, the luffing jib being pivotally attached to the jib connection pivot, the luffing jib also being folded back and under the boom along a ground surface, the hinged connection allowing the neutral axis of the jib boom section to be offset relative to the boom connection pivot;
• (b) attaching the boom to a crane;
• (c) raising the boom top upwardly, causing the jib top section to travel along the ground surface until the luffing jib is lifted off the ground surface;
• (d) causing the neutral axis of the jib boom section to be aligned with the jib connection pivot;
• and
• (e) inserting pins into the hinged connection to lock the jib boom section in axial alignment with the jib connection pivot.