US2579262A - Level luffing jib crane - Google Patents

Description

Dec. 18, 1951 I; KAY

LEVEL LUFFING JIB CRANE 2 SHEETS-SHEET 1 Filed April 50. 1947 Dec. 18, 1951 KAY 2 2,579,262

LEVEL LUFFING JIB CRANE Filed April 30. 1947 v 2 SI-lEETS-Sl-IEET 2 Patented Dec. 18, 1951 UNITED S E S IEIN T ZQZF'FICE 2,579,262 I I LEVELLUFFEN G JIB CRANE Ignatius Kay, Lon'den, England assignoi" tcv The Wellman Sinith Gwen Engineer ingllorpora- .tion Limited,..London, England,..a companyiof Great Britain "Application April 30, 1947;Serial Noi745,033 1 In Great B'ritainMay 3, 1946 1 Glaim.

lufiing jibcrane comprises a frame, a balanced jib with free ends and a pivot intermediate such ends, connectingimeansbetween-the jib and the frame constraining the said .pivot to move .in .an arcuate path, furtherconnecting means between the jib and the frame constraininga pOiIltDILthB jib offset from its longitudinal axis tomove .in-a path directed substantially radially with respect to the said arcuatepath, the said paths .being such that the lufiing of the jib-produces substantially horizontal movement of its centrelof gravity and substantially verticalmovementof its end remote from :the load, .a..pulley .at the saidjibend, a secondfipulley on the framesubstantially vertically beneath the first pulley and 1a hoisting rope passing. froma winding drum on the-frame over the second. and firstlpulleysand;over:a;hoistingpulley at ithe'load-carryingzend of the jib. In

such a crane the hoisting ropepulls actingon the jib are arranged to have anequal moment about the centre-ofigravity of thejib, the ratio between the length of the jib forward of thersaidcentre and. thelengthiofthe remainder of the jib being equal to the .ratio between the 'number'of parts of hoisting rope at the rearjib-endand the :num-

vber of .parts of. the same. repeat the forward jib-end.

The connecting vmeans between the jib and frame comprised a;pair.of.links, each pivoted at one end-to'the frameand at the other end :to the jib, so disposed that .if extended beyond their 'pivots on the jib they wouldmeet onithe intersection of a transverse vertical plane. containing the centre of gravity of thejiband a horizontal plane containing the rear i jib-end. The, upper link extended from a point on'the. frame .horizontally opposite the centre of gravity of the jib toa point-on the latter spacedzbothfromttherrear jib-end and from theicentre .of. gravity :by an amount equal to "the :length of the linkywhereas the lower link extended froni anpoint Jon the frame verticallybeneath 'the'rear ijib-endi to :a

point on the jib offset downwards from'tthe point 'of attachment of the upper linkuto .the..;jib, the

distance-between the 'two. pivotsonthe jib being equal to the-length ofthe upper link. fl' orepracticalreasons, thesaid upper 'link was generally rebladbyan equivalent but siiorterilink having one end pivoted to the frame ;at;.a.point lying on a-l-ine joining the pivot on.the;jib for the lower link-to the .point atwhich the frame-connected -end of the upper 'linkwouldlotherwisebe disposed. The shorter link extended incthe direction of the intersection point for the upper and lower links (when extended) and was pivoted to the jib at a point lying on a line joining the jib-connected end of the lower link to the point at which the upper link would otherwise be connected to the jib.

.Insuch cranes there is a point on the jib (referred to hereinaftenas the reference point) -which:subdivides the length .-of the jib into two parts, a head portion and aitail portion, the lengths ,of which bear the samerelationship to each other asthe number of parts of the hoisting ropeat the tail of the jib :bears-to the ,numberlof 'parts of .thesame repeat thehead ,of .the jib. Hence, if there is .one -.part of rope atboth the head ,and the tail of .the jib, the reference point is (located mid-way of the length of the jib, whereas if thereisone part of-ropeat the head and three parts at the tail, the reference point. is located at one quarter of the lengthof the jib from the tailsendthereof. The referencepoint in the cranes accordingto thesaid earlier invention has :been constrained to ,move horizontally during the lufiing' of the jib .(by reason of the linkage arrangements describedland it has there- .fore been considered essential ,toarrange that the centre'of gravity of the jibshouldcoincidewith the said reference point, as will have become clear from qtheabove brief descriptionsof the earlier in- :vention. The pathof travelof the reference point .being horizontal, .the rear jib-end-was necessarily arranged to move vertically and thepartorparts .of hoisting rope-extending from the, pulley at this end to that on the crane frame was .or werealso vertically directed.

Now it frequently happens that the. ,practical requirements-in the construction. of alevel lufling gjib crane make. it inconvenient either toarrange the centre of gravity ofztheljib to-coincide with the reference pointer. to ,arrangethe pulleyon the-crane frame vertically beneath that on .the rear jib-end. Forie x-ample, in theearlier speci ficationtof United States Patent No. 2,386,475 there is shown andrdescribed -a construction having the reference-;poi11t;located :mid-way-of the length? of the jib. .;Ina practical construction this :.would entail counterweighting, the forward; end of J the. jib tor ,2 employing ,-Il ight-;metal inthe -..con- -.str.uction;'of the rear-end-of the jib,.or the-useof both expedients, in orderrto cause the' centraof gravity of the jib to coincide with the reference point.

The object of the present invention is to provide modifications in the said earlier invention which shall enable'the effect of non-coincidence of the centre of gravity of the jib and the reference point to be overcome without such use of forward counterpoise or other undesirable expedient.

According to the invention, in a level lufiing jib crane substantially in accordance with the invention claimed in the said earlier specification but having the centre of gravity of the jib disposed rearward of the reference point, the hoisting rope pulley at the tail-end of the jib is disposed so that a line joining the axis of the pulley to the reference point is canted upwards with relation to the line joining the reference point to the axis of the hoisting rope pulley at the head of the jib through a predetermined angle a, and the connecting means between the crane frame and the jib are arranged to cause the reference point to travel along a path inclined upwards and rearwards to the horizontal at an angle which is equal to where n is the number of parts of hoisting rope at the head of the jib and n1 is the number of parts of the hoising rope at the tail of the jib, so that the pulley at the tail-end will move along a path inclined downwards and rearwards to the vertical at the angle a and passing through the axis of a hoisting rope pulley mounted on the crane frame, the centre of gravity of the jib thereby being constrained to move horizontally.

The nature of the invention will be more clearly understood from the following description of some examples of the way in which it may be carried into eifect and the theoretical considerations which apply, reference being made to the accompanying drawings which are mainly diagrammatic.

Fig. l is a line diagram illustrating the linkage arrangement which constitutes the main feature of the earlier invention referred to above and which is fully described in the specification of United States Patent No. 2,386,47 5,

Fig. 2 is a similar line diagram illustrating the modified arrangement of the present invention,

Fig. 3 is a diagrammatic side elevation of one form of crane embodying a practical example of the linkage arrangement shown in Fig. 2, there being one part of hoisting rope at the head and tail of the jib, and

Fig. 4 is a similar view of another form of crane according to the invention in which a different location of the reference point on the jib is necessitated by an alteration in the reeving of the ropes, there being one part of hoisting rope at the head of the jib and three parts of the same rope at the tail of the jib.

In Figs. 3 and 4 only the parts essential to a clear understanding of the present invention have been indicated, the main members of the jib being shown in heavy lines and the main members of the frame by double lines. Many of the bracing members and other known constructional details, including means permitting of slewing the crane or traversing it along rails when desired, have not been illustrated as their arrangement or construction will beobvious to those skilled in the art.

Referring first to the construction forming the subject-matter of the earlier United States Patent No. 2,386,475, shown in Fig. 1, a pivoted jib A, B (represented by its longitudinal centre-line) is suspended from a crane frame (not shown) by a pair of links, the pivotal point of the jib being at C. A downwardly extending arm D is rigidly fixed to the jib at the point C, is equal in length to the tail portion C2 of the jib, and has its lower end pivoted at E to the forward end of a thrust link F which has its rear end pivoted at C on the crane frame vertically beneath the end 2 of the tail portionCZ. A second link H is pivoted at its upper end on the crane frame at a point J vertically above the tail end Z of the jib, is of a length equal to that of the arm D and is pivoted at its lower end to the jib at the point C. The links F and H, when extended, meet at the point K which during the movement is constantly vertically beneath a reference point L on the jib. The hoisting rope pulls acting on the jib A, B, are represented by, the arrows M and N. The reference point is spaced from C by a distance equal to CZ and subdivides the jib into the head portion A and tail portion B. Due to the fact that the lengths of CZ, CL and CJ are all equal the angle ZJL is a right angle and the point J is horizontally opposite to the point L.

It has been demonstrated in the earlier specification referred to that luffing of the jib A, B, when thus supported from the crane frame, results in the reference point L always moving in a horizontal path, the tail end of the jib always moving in a vertical path, and the reduction or increase in the distance between the tail end of the jib and the point G always bearing a definite ratio to the lift or fall of the head end of the jib. The numerical value of this ratio depends on the relation between the lengths of the head and tail portions, A and B, respectively, of the jib and this relation is the same as that between the number of parts of hoisting rope at the tail of the jib and the number of parts of this rope at the head of the jib. With the center of gravity of the jib arranged to coincide with the reference point L and with the hoisting rope pulls, M and N, arranged to have an equal moment about the same point, the jib is in balance for any position of the point L along its horizontal path of travel. Moreover, the load supported from the head end of the jib A, B, will travel in a horizontal path during lufling of the jib, provided that the hoisting rope at the tail end of the jib runs vertically downwards to a pulley mounted on the crane frame at or near to the pivot G.

For practical constructional reasons it is preferred to replace the link H by an equivalent link 0, this being pivoted on the crane frame at a point P lying on a line EJ and pivoted on the arm D at a point Q lying on a line PK. The link H is removed when the link 0 is fitted.

As has been indicated above, it has heretofore been considered essential to arrange that the centre of gravity of the jib A, B, should coincide with the reference point L, and the part or parts of the hoisting rope extending from the tail end of the jib to the pulley on the crane frame was or were necessarily directed vertically. The rectangle JLKZ thus had its sides LK and JZ disposed vertically.

According to the present invention, the limitations and disadvantages of the earlier. linkage arrangement may be removed by making some modifications therein, as shown in Fig. 2. In this .figure, parts or points corresponding to thoseof Fi r are-indicatedby the'same fferenoe characters ashave been used i describing Fig The example chosen*has" the referencepoint L disposed mid-way of the 1efigtn-or the ji-bA, B, (the lin'eB (or-LY) representingthe normal position-of the tail portion) and the centre or gravity'CG ofthe jib is disp'o'sedrearward of the reference-point L. If the diagonalLZ (of-the rectangle ULKZ) passingthroughthe centre" of gravity CG were to coincidewith the continua- "tion B of the upper'part of the jib as in-tlie'con- *struction of Fig. L-lufiing of thisjibwould'cause the centre of "gravity CG to 'rise' and'fa-ll as the "point L travelled horizontally. This is preverited with the "construction-of- FigrZ-in'which the reference-point L is arranged to move along-apath 'LJ that is inclinedupwards andrearwards with respectto the horizontal at an angle 18 such-that the" centre of gravity CG will always move along -a horizontal pah. The'value of the angle ,8 is readily determinedby plotting the extreme positions of the jib (assuming horizontal movement of the reference point L) --measuring the fall of the centre -of-gravity- CG from the one 'positionto the other, and thenarrahging-for the reference point -L to rise by acorresponding amount 'for the same displacement of the jib. The-angle 3 is generally about-8 -for cases'where the reference pointL-is -at the centre of length of the jib. Due to the inclination of the path LJ' the rectangle -JLKZ which fixes the positions of the points K andJ-is swung about its corner L through the angle 15. The pivotal-point C of the jib is now disposed on the' 'second diagonal LZ of the rectangle (JKbei-ng the first'diagonal) and this diagonal LZ inclines upwards with relation to the continuation-B of the centre-line of the upper partofthejib, --at ananglefi. --The geometrical construction determining the positions and lengths of the links and- F and of the arm-Dis otherwise the-sameasin Fig. 1, the link D being shown as terminating at the'line B for convenience but obviously being of the efizective length EC.

Again due to the inclination-0f the path LJ,

the rear jib-end no longer-moves vertically nor does' its extent-of travel bear the constant defi- "n'ite'relationship to the rise and fall of the head "of-the-jib which is necessary to secure level lufilng of the load. In order to secure this action, therefore, the hoisting rope pulley which would normally be disposed at the point Y on the tail portion of the jib is raised above the said point to an extent such thata line -B joining its axis X to-the reference point Lmakes an angle (7. with the continuation B of the upper part of the centre line and is of the same length as said line B. The-pulley now travels along a path (the disposition of which is shown by arrow N) also making an angle a. with the vertical, as the jib is luffed. It can be demonstrated that the dis- 'tance h"travell'ed by the "pulley albn'g'thisp'ath always bears a desired constdhfileitibns'liip"to the verticaldistance-h -through which the head of the 'jib is displaced at the same time. For the example illustrated the; distances h and'h are equal, as the nurnber of parts of hoisting rope at the head and the tail of the jib are also the same.

="given by the expression where n is the number of parts of rope at the angle" {3 is three qnarters' of the angle a.

"jib at the position or -ma xim'u'm -rea'ch is then decided andthe position rormimmum reach is "also selected. j

The jibis then drawn in -its'=two and positions movewverucany. The'vertical fall 'in the positidnbf the centreof'fg'ravity-in -the movelnent "from" the one positionto' the' other' is thn'ineas- "ured'and the line *joining the' two-locations of L "is inclined upwards to the horizontal *from the maximum reach position of L at an'angle "fl su'ch that n at the minim m-reach position wi u have risen vertically through -the same distance as the'centre of gravity fell. A-n anglewiis then calculated'from "and the tail pdi'tion'foff the .jiaextenamg'irrom the reference point L? is ineimedtpwardsat this angle 'a with res ect to 'ltshii'g'inal position. In

addition, the puneypn' thecrane frame ispfo'sihoned on'a linemak'ing "an'angle d'with" the vertical] from the friew position "of the A tail 'Iid of'the jib. V

The "rectangle J ISKZ' is then constructed with the side JL'atanangle 8 to the horizontal and 'ql'lal in length to the" product 6f the length of the tailend 0f the jib and' th (B'O'Sine'Of trieangle 0. The'side LK'is 'inade equar to the"pr'odilctof the length of the tail end of "the "j ib and the 'sine' of the angle 0. The intersection "of the'diago'nals of the rectangle fixes "the position "of the point C, "and the appropriate position for the point C for thefiosition or the jib in ithe minimum reach setting is also determined'by 'dr'alwing'the 'jibtiiith the diagonal LZ in the correctrelativ'e position Strikingan 81rd from ect LZ'at C1. Arcs J with arafdiiis to are struck from c andbfwi'th a'ra'dius 'J'Gand their intersection fixes" the position "of" the point E. KEfiiroducedgivesthe "dir'eiition of the link position of-Q is cnos'enon EC ('gen'erallyas the result ofp'ractical ex erience) so that 'KQ 'p'ro- I diled 'will intersect J E E at P appropriatel close to the generalpositioii ofthe'ta'ilbf' the "j ib"wh"e'n The positions andler'igthsbf thearm Derid the linksFand O are "now fixed to give "the"co'rrect motion "of the will move in the direction N.

A"practieairorm oftonstructmn of a crane corresponding to the diagram" of Fig. '2 is illus- 'trated by" Fig. 3. Here thebraneframeis indiplatform X" which'h'iayhe driven in any suitable "manner for sl'eWing-the'ora fie and may in turn be mounted on rails in amanner,peimitting of the crane being displaodhodlly. The parts of the crane which correspond to the elements of the diagram of Fig. 2 are indicated by the reference characters also used in that diagram. Only .to the frame.

the main outer members of the jib have been shown in heavy lines, the bracing members and other known constructional parts being omitted for claritys sake. Additionally illustrated are a pulley R at the head of the jib, a pulley S at the tail-end of the jib, a load hook T, a run U of the hoisting rope extending from the pulley U on the crane frame (to which the part N of the rope passes from the pulley S) to the winding drum V, and lumng gear comprising a screw Y" pivotally attached at Y to the link and engaged in a motor-driven nut Z which is pivotally mounted at Z on the crane frame W.

In operation, the jib is luffed by rotation of the nut Z". The screw Y" passes through the nut Z and thus draws the link 0 towards the pivot Z. Since the point P is fixed on the frame, the movement of the link 0 towards the pivot Z produces arcuate movement of the free end of the link 0. The jib-pivot Q is at this free end and is thus moved arcuately when the nut Z is turned. The jib-pivot Q is rigidly connected to the arm D, which at its other end is pivoted at E to the forward end of a thrust link F, which in turn is pivoted at its rear end G Thus the pivot E- is constrained to move on an arcuate path having its centre at G. Since the link F is relatively long and the movement of the pivot E relatively short, this arcuate path approximates to a straight line normal to the link F, that is to say, along the line PE. The arcuate movement of the jib-pivot Q and the movement of the pivot E approximately' along the line PE causes the arm D to pivot about E in an anticlockwise direction. Since the arm D is rigidly connected to the jib, this will also pivot about E in an anticlockwise direction, so that the pulley R at the head of the jib will swing upwards and inwards.

Owing to the construction of the crane and as explainedin relation to the diagram of Fig. 2, the reference point L will move upwardly and inwardly along a line lying at an angle ,8 to the horizontal, the tail-end of the jib will move downwardly towards the frame along a line lying at an angle a to the vertical, and the centre of gravity G will move inwardly along a horizontal line.

Fig. 4 shows another construction in which, as far as possible, corresponding parts are again indicated by like reference characters.

In this case, the centre of gravity of the jib (not indicated) is located somewhat lower down the jib than the reference point L which is itself at a distance from the pulley S of one-quarter of the length of the jib A, B, suitable counterweighting being resorted to, as will be understood, but the counter-poise (not shown) being arranged on the canted up tail-end of the jib. Hence a single part M of the hoisting rope at the upper end R. of the jib requires three parts of the same rope at the lower end S of the jib, and this is ensured by suitably reeving the rope, as shown at N before it passes at U to the drum V. The operation of this crane is substantially as already described above, each of the three parts of rope N releasing or taking up one third of the total rope required when the jib is luffed.

.It is to be understood that the theoretically correct arrangement according to this invention is, as stated above, with the centre of gravity located on the diagonal LZ of the rectangle JLKZ but in practice some slight departure from this condition is sometimes unavoidable due to manufacturing difficulties.

What I claim is:

A level luffing jib crane comprising a supporting frame, a balanced jib, a hoisting pulley at the load-carrying end of the jib, a first counterloading pulley at the end of the jib remote from the load carrying end and so disposed that a line joining its axis to a point along the length of the jib located between the centre of gravity of the latter and the hoisting pulley is canted upwards through a predetermined angle a. with relation to a line joining the said point to the axis of the said hoisting pulley, a pivot for the jib located between the said ends thereof, a second counter-loading pulley so located on the supporting frame beneath and rearwards of the first counter-loading pulley that a line joining the axes of the counter-loading pulleys will make the angle a. with the vertical, a winding drum on the said frame, a hoisting rope passed over said hoisting pulley and over said first and second counter-loading pulleys and attached to the said winding drum, the number n of parts of the said rope at the load-carrying end of the jib bearing the same ratio to the number m of parts of the said rope at the other end of the jib as the distance between the said point of the jib and the said other end bears to the distance between the said point and the load-carrying end of the jib, means mounting the jib-pivot on the said frame for arcuate movement about a point thereon, a rigid part on the jib extending at an angle downwards away from the longitudinal axis ,of the jib with its upper end proximate to the jib-pivot and its lower end spaced from the said jib-pivot by approximately the distance between the latter and the first counter-loading pulley, means connecting the lower end of the said jib-part to the frame for movement substantially along a line joining the said lower end and the point on the frame about which the jib-pivot moves, and means for luifing the jib and thereby simultaneously producing displacement of both the jib-pivot and the lower end of the said jib-part so that the said point in the length of the jib moves along a path inclined upwards and rearwards to the horizontal at an angle 13 which is equal to n-l-m and the first counter-loading pulley moves along the line joining the axes of the two counterloading pulleys, the centre of gravity of the jib thereby being constrained to move horizontally.

IGNATIUS KAY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,036,386 Andersen Apr. 7, 1936 2,386,475 Kay Oct. 9, 1945 FOREIGN PATENTS Number Country Date 500,459 Germany June 21, 1930

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