US3517829A - Luffing crane - Google Patents

Description

June 30, 1970 H. TAX 3,517,829

LUFFING CRANE Filed Aug. 2, 1967 s Sheets-Sheet 1 Fig.1

lIVl/[iIV/UR Hans Bk 1 June 30, 1910 3,1 3,517,829

' 'LUFFING CRANE Filed Aug. 8, 1967 3 Sheets-Sheet :3

June 30, 1970 H. TAX

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3 sheets-sheet 3 Filed Aug. 8. 1967 INVENTOR- Hd s Tra I/QMM Bum 3,517,829 7 LUFFING CRANE Hans Tax, 3 Potsdamer Strasse, 8 Munich 23, Germany Filed Aug. 8, 1967, Ser. No. 659,102 Claims priority, applicatiglli sggmany, Aug. 12, 1966,

Int. Cl. 1266c 23/10 US. Cl. 212-8 1 Claim ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to cranes, and particularly to luifing cranes of the type commonly used in harbor in-. stallations, and usually mounted on revolving bases.

Such cranes normally have an upright post, a jib pivotally attached to the bottom end of the post, and a load rope or the like, one end of which is attached to a winch on the crane base. The rope passes over a guide pulley near the top of the post and an idler at the free end of the jib. Provisions must be made for moving a load suspended from the rope in an approximately horizontal path when the jib is pivoted on the post.

Approximately horizontal movement is desirable to facilitate visual control of load movement by the crane operator and to minimize the power required for pivotally moving the jib. It is furthermore advantageous that the path of the load have an initial slightly descending portion and a final slightly ascending portion in order to reduce the energy required for starting the horizontal movement of the load and to absorb most of this energy at the end of the movement.

The simplest known cranes which satisfy the aforeenumerated requirements have a load rope which is reeved over a three-sheaved block arrangement mounted between the free ends of the post and the jib. The triple rope strands necessarily sag and oscillate transversely. When the length of the jib is of the order of at least meters, as in many harbor cranes, the multiple ropes tend to tangle.

Numerous other devices have been proposed for controlling the movement of a load in the desired manner during angular displacement of the jib on the post. These known devices are either complex and correspondingly costly to build and maintain, or they can move a load only in a path which significantly deviates from the preferred path outlined above.

The object of the invention is the provision of a level lufiing crime which is simple, and hence inexpensive to build and maintain, and which permits the desired control of load movement.

SUMMARY OF THE INVENTION In one of its basic aspects, this invention resides in a crane of the general type described above in which a second pivot on the jib is offset in a direction toward the United States Patent 0 "Ice free jib end from the first-mentioned pivot connecting the jib and post. A third pivot is upwardly offset on the post from the first pivot. Two links are respectively attached to the second and third pivots and connected by a fourth pivot spaced from the second and third pivots so that the two links and the portion of the jib between the first and second pivots constitute three members of a four-bar linkage in which the portion of the post between the first and third pivots is the fourth member.

In addition to the afore-mentioned guide pulley at the top of the post, a second guide pulley is mounted on one of the three linkage members other than the post, and a third guide pulley on the top part of the post. A load rope, chain, or cable, hereinafter referred to as the load rope member, is trained from the first guide pulley in sequence over the second and third guide pulleys toward the idler at the free end of the jib.

Other features, additional objects, and many of the attendant advantages of this invention will readily be appreciated as the same becomes better understood by reference to the following detailed description of preferred embodiments when considered in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 shows a crane of the invention in fragmentary side elevation; and

FIG. 2 illustrates a modification of the crane of FIG. 1 in a corresponding view.

FIG. 3 shows the relative dimensions of a crane according to FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring initially to FIG. 1, there is seen a harbor crane having a base 10 provided with a turntable 12 on which an upright post 14 is mounted. The operators cabin and the power source of the crane form an integral part of the post and have not been shown in detail, nor has the winch been shown which is also installed in the bottom end of the post 14.

A first pivot 16 on the bottom part of the post attaches a jib 18 to the post. The free end of the jib, not seen in the drawing, is provided with an idler sheave in the usual manner. A link 20 is attached to the jib by a second pivot 22, and a link 24 is similarly attached to the post 14 by a third pivot 26. The links are connected by a fourth pivot 28. The four pivots have parallel axes and are spaced from each other so that the two links 20, 24 and respective portions 30, 32 of the jib and of the post form a plane four-bar linkage in which the jib portion 30 is much longer than any of the other three bars.

A guide pulley 34 is coaxially mounted on the fourth pivot 28. The load rope member 36 of the crane extends upward from the winch (not shown) to a guide pulley 38 on the top of the post 14, is then trained over the pulley 34, another guide pulley 40 coaxial with the pulley 38, and ultimately over the non-illustrated idler sheave on the jib from which the end of the rope member depends.

A screw jack 42 is fixedly mounted on the post 14 and its extensible member is attached to the link 24.

The crane illustrated in FIG. 2 is closely similar to that described above with reference to FIG. 1. Identical elements have been provided with the same reference numerals, and do not require separate description. The post 14 is modified to provide a slideway 46 for a counterweight 44 suspended from one end of a tension member 48, such as a rope, cable, or chain, which is trained over a pulley 50, coaxial with the afore-described pulleys 38, 40. The slideway slopes steeply, but is not vertical. The other end of the tension member 48 is attached by a fastener 52 to a link arranged in the manner of the aforedescribed link 20. The fastener 52 is equidistant from the pivots 22, 28, and the link 20 is wider than the link 20 to withstand the transverse stresses transmitted by the tension member 48.

Both embodiments of the invention operate similarly.

When the jib 18 is close to the horizontal position, and the moment produced by its weight is near its maximum value, the four-bar linkage acts in the manner of a toggle to apply the tension of the rope member 36 to the jib 18 under conditions of maximum torque to balance the moment produced by the weight of the jib. When the jib 18 approaches its terminal position near the post 14 (14), and the moment produced by its weight approaches a minimum value, the tension of the rope member is about equally transmitted to the links 20 (20'), 24 so that the moment applied to the jib by the rope member reaches its minimum.

The height of the post, the length of the jib, the location of the first pivot 16, and other dimensional characteristics of a luffing crane and the speed of its movement are normally determined by the intended application. The theory of four-bar linkages is well developed, and the locations of the pivots 22, 26, 28 and of the pulley 34 are readily determined by routine calculations to produce any desired movement of the load attached to the rope member, including a fiat path with terminal portions which slope upward from the substantially horizontal central portion of the path. A rise by about 0.7 times the horizontal sweep of the load is normally preferred.

The whipping movement of the crane jib is actuated by the jack 42 which may be replaced by any other connecting element whose length can be varied, such as a hydraulic motor or the like, and which is interposed between the post 14 (14') and one of the otherthree members of the four-bar linkage. It is advantageous hingedly to attach the connecting element to the link 24 because this arrangement requires only a single pivot pin to be released if it is desired completely to lower the jib 18.

The counterweight arrangement shown in FIG. 2 can readily balance the weight of the jib 18 in a very simple manner in practically any angular position of the jib. It is as effective as a counterweight mounted on an extension of the jib beyond the pivot 16 without requiring the com plex jib structure necessary when the jib is to extend beyond the post in two directions. It will be appreciated that the weight of the jib cannot be balanced uniformly, or even approximately uniformly in all angular positions of the jib, when a tension member carrying a counterweight is directly attached to the jib. The members of the fourbar linkage of this invention, and particularly the links 20', 24, move in very different individual paths. The point on one of the links to which the tension member 48 is to be attached to produce a desired result is readily calculated in a conventional manner.

The dimensional relationships of the four pivots in the four-bar linkage and the locations of the guide pulleys shown in the drawing are representative of successful practice of this invention in a crane having other dimenvention, and that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit of the invention.

FIG. 3 shows the relative dimensions of the crane according to the FIG. 1 and 2. The different dimensions have in one embodiment of this invention the following values:

a=100, 17:25, 0:9.6, 02:5, e=10, f=9,6, h: 10, i=4.3.

With these relative dimensions an approximately horizontal path of the suspended load is achieved when the jib is pivoted. Further this path of the load has a slightly descending portion at the one end and a slightly ascend ing portion at the other end.

What is claimed is:

1. In a level-luffing crane, the combination of an up wardly extending post, a first pivot on the bottom portion of said post, a jib having one end thereof attached to said first pivot and also having a free end, a second pivot on said jib offset from said first pivot, a third pivot on said post upwardly ofiset from said first pivot, two links respectively attached to said second and third pivots, a fourth pivot spaced from said second and third pivots and connecting said links together, actuating means for raising and lowering said jib about said first pivot, the distance between said first and second pivots being a substantially greater than that between the first and third pivots and also being substantially greater than the length of each of said links, a pair of guide pulleys mounted coaxially at the top of said post, a third guide pulley mounted on said fourth pivot, and a load rope member extending from a winch in the bottom portion of said post, said rope member being reeved consecutively around one of the pair of guide pulleys at the top of said post, around said third guide pulley on said fourth pivot, and around the other of the pair of guide pulleys at the top of the post before extending to an idler pulley at the free end of said jib.

References Cited UNITED STATES PATENTS HARVEY C. HORNSBY, Primary Examiner U.S. Cl. X.R, 212-48, 59

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