Multiple offset crane boom extension

A crane boom extension or jib is held on the nose of the boom by a single fixed length self-adjusting cable loop which extends around an arcuate guide attachable at several different locations to an inclined plane mounting bracket on the jib near its outer end. The mere repositioning of the guide on the inclined plane mounting bracket allows the jib to assume several different angularly offset positions relative to the axis of the boom without other adjustments. The inclined plane mounting bracket establishes the plane in which the cable loop lies in all adjusted positions of the jib. The arrangement is convenient, safe and simplified.

BACKGROUND OF THE INVENTION 
As noted in the above-referenced prior application, existing arrangements 
which permit angular offsetting of crane boom extensions or jibs are 
varied and not entirely satisfactory from the standpoint of convenience of 
use, simplicity of construction and safety. Accordingly, the main 
objective of this invention is to improve on all known devices which 
enable angular offsetting of boom jibs particularly in these areas of 
convenience of installation and operation, simplicity of construction and 
safety of the operator or installer of the means which supports the jib in 
its several offset positions. 
More particularly, it is an object of the invention to provide an 
offsettable extension or jib for crane booms which is held in each of its 
several offset positions by a single fixed length self-adjusting cable 
loop or guy. The loop or guy has its ends attached to the nose assembly of 
the boom and extends around a fixed arcuate guide mounted on an inclined 
plane bracket which is attached to the jib relatively close to its outer 
end, the inclination of the mounting bracket relative to the axis of the 
jib defining the plane occupied by the cable loop in all adjusted 
positions of the jib and also establishing a constant angle between the 
cable loop and the jib axis in all offset positions of the jib. 
A major feature of the device is the ability of the jib to assume its 
several different angular positions relative to the boom axis merely by 
repositioning the cable loop guide and fixing it in a corresponding number 
of positions on the inclined plane bracket. 
The device is safer than prior art devices for the same general purpose 
inasmuch as the use and installation of separable jib support links and 
guy cables is eliminated. These prior art components have generally 
required the installer or operator to climb onto the crane boom while it 
is in a depressed position to install links or cables associated with the 
jib. The present device does not require this because of the fact that the 
inclined plane bracket on which the multiple position cable loop guide is 
held is located near the forward end of the jib and consequently is very 
close to ground level when the crane boom is in its maximum depressed 
position. Therefore, an installer standing on the ground can place the 
cable loop around the arcuate guide and can also adjust the position of 
the guide on the inclined plane guide mounting bracket with complete 
safety. 
Other features and advantages of the invention will become apparent during 
the course of the following detailed description.

DETAILED DESCRIPTION 
Referring to the drawings in detail, wherein like numerals designate like 
parts, a conventional telescoping crane boom 10, FIG. 1, includes a nose 
assembly 11 having parallel side plates 12, FIGS. 2 and 2A. A boom 
extension or jib 13 according to the present invention is of the general 
type shown in U.S. Pat. No. 3,366,250. Such a jib has spaced bifurcated 
inner end mounting extensions 14 which straddle the nose assembly side 
plates 12 and pivotally engage a cross shaft 15 of the nose assembly, the 
extensions 14 being detachably connected to the cross shaft 15 by 
removable pins 16. 
Jibs of this type, when detached from the boom nose assembly, may be stowed 
on support brackets along the bottom of the crane boom or may be swung on 
the shaft 15 to such a bottom stowed position as shown in U.S. Pat. No. 
3,366,250. However, the present invention is not intended to be limited to 
a bottom stowable jib and could be employed with other forms of jibs and 
boom extensions, such as swing-around side stowable jib of the type shown 
in the above-referenced prior application. 
In accordance with the invention, the jib 13 near its forward end and on 
its upper side has fixed thereto an inclined plane wedge-like mounting 
bracket 17, preferably of inverted U-cross section, including an attached 
base plate 18 which rests directly on the jib 13. The parallel side walls 
19 of the inclined plane mounting bracket each contain three spaced pairs 
of apertures 20, whose purpose will be fully described. 
A cable guide member 21, preferably a casting, rests on the upper face of 
the bracket 17 and includes a pair of spaced depending side bars 22 which 
straddle the bracket 17, as best shown in FIG. 4. The bars 22 each have a 
pair of apertures 23 in alignment with the apertures of the opposite bar 
22 and spaced apart to register with any of the three pairs of apertures 
20 of inclined plane bracket 17. A pair of sturdy removable locking pins 
24 is utilized to secure the guide 21 to the bracket 17 in any of the 
three possible positions of the guide on the bracket 17. The locking pins 
24 are equipped near their corresponding ends with detachable retainer 
pins 25. 
The cable guide 21 in its forward side with relation to the jib 13 has an 
arcuate preferably semi-circular cable seating groove 26 formed by flanges 
27. This arcuate groove terminates at the rear edges of side flange 
extensions 28 which edges lie on a common line through the center of the 
arcuate groove 26, FIG. 3. The main web 29 of cable guide 21 is spaced 
slightly above the top face of bracket 17, FIGS. 4 and 5 and may have a 
rear profiled edge 30, as depicted in FIG. 3, forming spaced rear 
extensions 31 on the web 29. 
In accordance with a key feature of the invention, a single fixed length 
self-adjusting cable loop or guy 32 has a pair of end clevis connectors 33 
fixed thereon which are attached by pins 34 to the two side plates 12 of 
boom nose assembly 11 at the front upper corner thereof, FIG. 1. The cable 
loop 32 is trained around the guide 21, as shown in the drawings, and lies 
in the arcuate groove 26 thereof defined by the flanges 27. 
The cable loop is retained in the arcuate groove 26 by preferably three 
retainer bolts 35, one pair at the sides of the guide through apertures of 
the flange extensions 28 and a single bolt at the front and center of the 
guide through apertures of flange extensions 36. The retainer bolts 35 are 
spaced from and do not bind the cable loop 32 in the arcuate groove 26 so 
that, when under tension, the cable loop can be self-adjusting with 
respect to the guide 21 and its groove. 
The boom nose assembly 11 on its opposite sides is provided with fixed 
backstops 37 engageable with coacting backstops 38 on the rear of the jib 
13 near its base. These contacting backstops positively limit the rearward 
or upward swing of the jib 13 to the position shown in full lines in FIG. 
1. In this fully raised position of the jib, the axis of the jib assumes 
an angle of approximately 0.degree.-5.degree. above the axis of the boom 
10. As shown in broken lines in FIG. 1, this invention enables offsetting 
the jib 13 to two angular positions below the position shown in full 
lines, namely, to positions 15.degree. and 30.degree. below the full line 
position in FIG. 1. In accordance with the invention, these offset 
positions of the jib are obtained merely by relocating the cable loop 
guide 21 on the inclined plane bracket 17, utilizing the several pairs of 
apertures 20 in the bracket. 
As stated, the three illustrated positions of the jib 13 are obtained with 
the use of the one fixed length cable loop 32 and the described simple 
adjustment of the guide 21. The upper face of the bracket 17 defines the 
plane in which the cable loop lies and defines the angle of convergence of 
the cable loop forwardly with the axis of the jib 13, which angle of 
convergence remains constant in all adjusted positions of the jib. The 
angle of convergence defined by the top face of the inclined plane bracket 
17 is preferably about 71/2.degree. as illustrated. 
The operation of the invention can be briefly summarized as follows: 
The crane boom 10 is depressed to the lowermost possible position, usually 
a few degrees below horizontal. With the jib 13 in place on the boom nose 
assembly in accordance with prior art techniques and projecting forwardly 
of the depressed boom 10, the forward end of the jib may rest on the 
ground or on a solid support close to ground level. An installer, standing 
on the ground, may then place the cable loop guide 21 on the bracket 17 
and adjust it thereon by means of the apertures 20 and locking pins 24 to 
achieve the desired offset position of the jib. The cable loop 32 is 
engaged with the adjustable guide 21 at the time that the adjustments of 
the guide on the bracket 17 are made. As illustrated in FIG. 1, the guide 
21 is placed in its forwardmost position on the bracket 17 to position the 
jib 13 in its uppermost position shown in full lines where the backstops 
37 and 38 are in contact. In essence, the effective length of the cable 
loop is shortened in this position to hold the jib in its most elevated 
position. 
With the guide 21 adjusted to the intermediate position, the effective 
length of the cable loop 32 is increased and the degree of increase 
enables the taut loop to hold the jib 13 at the 15.degree. position, FIG. 
1. Finally, when the guide 21 is in the rearmost position on the bracket 
17, the jib will be held by the cable loop 32 in the 30.degree. offset 
position. 
When each required adjustment of the guide 21 is made substantially at 
ground level, the crane boom 10 is elevated and the weight of the jib will 
be picked up by the cable loop in the desired offset position as soon as 
the loop becomes taut by transfer of the jib weight thereto. At this 
point, the forward end of the jib will rise from the ground or other low 
temporary support. 
The device is characterized by extreme simplicity, ease of installation and 
adjustment, and economy of manufacturing. The cable loop 32 is 
self-adjusting with respect to its passage around the arcuate groove of 
the guide 21 so that equal tension will be imparted to both branches of 
the cable loop which attach through their connectors 33 to the nose 
assembly side plates 12. 
The terms and expressions which have been employed herein are used as terms 
of description and not of limitation, and there is no intention, in the 
use of such terms and expressions, of excluding any equivalents of the 
features shown and described, or portions thereof, but it is recognized 
that various modifications are possible within the scope of the invention 
claimed.