CA1093504A

CA1093504A - Equalization system for overhead cranes

Info

Publication number: CA1093504A
Application number: CA330,910A
Authority: CA
Inventors: Felim P. Mccaffrey
Original assignee: Hatch Associates Ltd
Current assignee: Hatch Associates Ltd
Priority date: 1978-07-03
Filing date: 1979-06-29
Publication date: 1981-01-13
Also published as: JPS5511496A; IT7924072A0; AU4833979A; DE2926321A1; IT1122553B; SE7905724L; BE877436A; JPS5827194B2; FR2430386A1; FR2430386B1; ZA793198B; GB2028753A; SE428915B; GB2028753B; BR7904185A; AU526721B2; NL7905048A

Abstract

Abstract In a bridge crane, a rigid rectangular crane bridge frame is supported on a main runway by a truck at each corner, and in order to eliminate loadings on the trucks due to distortion of the run-way, the trucks on one side of the bridge support the bridge frame through interlinked levers forming part of an equalizing linkage

Description

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E~ualization system for ov rhead cranes This invention relates to overhead c:ranes of the kind in which a bridge ~rame carrying a laterally moveable trolley supporting the hoisting machinery is supported on al main runway by means o~ a truck at each ¢oxner.

A problem affecting such overhead cranes i~ local de~lection or subsidence of the runway or its supports. If the bridge ~rame o~
the crane is rigid9 and ~he trucks directly support the frame, any resulting lack of alignment of ~he track can result in gross in-equality of the loads ransmitted through the diffexent trucks. :~
This result~ in increased stresses being applied to the runway9those trucks whose loadi.ng is increased, and the frame. In ex-treme cases, even quite small runway deflections can result in the : ~ :

. .'~ `~" . ~ ' load applied to one or even two of the trucks being reduced to zero.
Various approaches to this problem have been adopted. One solution is to render the bridge frame sufficiently flexible to accommodate deflections and subsidences of the runway, typically either by forming th~ frame of wo sp~ced but linked members ~r by p~acing a flexible link in the periphery of the frame. Such techniques permit distortions in the frame which would otherwise give rise to very high torsional stresses. Dis~dvantages of these solutions are that a distortion of tha bridge frame will also rssult in distor-10 tion of the secondary run~ay provid2d on the frame for the trolley,which must therefore itself be designed to accommodate such dis-tortion . Furthermore the tracking of such a frame as it moves along the main runway is inferior to that of a rigid f rame, with the result that the frame may tend to become misaligned on th2 run-15 way. If a rigid f rame is retaîned, problems in maintaining align-ment of the trolley runway are elLmi.nated,and tracking problems are reduced. On ~he oth~r hand, the transfer of loads between the trucks upporting the frame on the main runway will re~ult in very high torsional stresses being applied to the frame. Thus the de-20 signexs of the crane and the runway must consider the interactionbetween the s~ iffness ~haracteristics of the frame, and the prob-able degree of ubs idence and deflection likely to occur in the runway. It is of course often difficult to estimate the likely de-gree of suksidence of a runway in advance; although it should in 25 theory be pO9~ ible to des ign foundations for the runway ~tructure which in most cases will be free of subsidence, in practice an ~3~9~

unpredictable amount of subsidence often tends to occur.

According to the invention an overhead crane comprising a rigid generally rectangular bridge frame, a truck beneath each corner of the frame for supporting the latter on parallel rails of a main runway for longitudinal movement, a trolley carxying hoisting machinery and movable laterally of the rectangular frame, opposi-tely acting levers forming the connections be-tween the trucks on one side only of the frame and the frame itself, and a link interconnecting the levers independently of the frame to equalize the l~ads on the trucks so connected, the levers each having a generally vertically extending lever arm and horizontally spaced longitudinally inner and outer trunnions forming a second longitudinally extending lever arm at the base of said vertically extending lever arm, the bridge frame being supported by the longitudinally outer trunnions of the two levers, and the trucks supporting the longitudinally inner trunnions of the two levers, the top ends of the verti-cally extending lever arms being connected by a link extending between the arms, the vertical extent of each vertically ex-tending lever arm being very large compared to the horizontalextent of the longitudinally extending lever arms formed by the spacing of the axes of the trunnions.

Further features of the invention will be apparent from the following description of a preferred embodiment.

Figure l is a perspective view from above, one end and one side of an overhead crane in accordance with the in~ention.

Figure 2 is an end elevation, partially broken away, of the same crane, Fi~ure 3 is an exploded detail of the lever system shown connec-ting the trucks to the frame in Figure 2.
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Referring to Figure 1, a crane is shown having a rigid rectan-gular perimeter frame 2 having lateral members 4 and end member 6 and 8. The lateral members 4 carry rails 10 forming a secondary runway for a trolley 12. The trolley 12 supports crane hoisting machinery indicated generally at 14. The frame

2 is supported on a main runway formed by longitudinal rails j 16 by means of trucks 18, 20. The trucks 20 are located be-.~ neath the ends of the end member 8 by conventional means (not :~ shown), but the trucks 18 are located beneath the ends of the 1 10 end member 6 by trunnion assemblies forming parts of bell-crank -i levers 22. These trunnion assemblies are best seen in Figure . 3, and each comprises two sets of trunnions 24, 26 space lon-gitudinally of the main runway with one set longitudinally . inward and one set longitudinally outward of the base of a ,~. 15 generally vertically extending lever arm 28. The vertical extend of each lever arm is large compared with the horizontal . spacing between the axes of the associated trunnions, which spacing forms the horizontal lever arm of the bell crank lever.
The longitudinally outer trunnions 26 are received in saddles 30 beneath the ends of the member 6, whilst the longitudinally inner trunnions 24 rests in saddles 32 on the truc]cs 18. Thus . the application of loads by the beam 6 through the trunnion assembly to the trucks 18 will tend to cause the levers 22 to . act in opposition and the lever arms 28 to move apart. Such movement is rPstrained by means of a link in the form of a tie bar 34 extending between clevises 36 at the upper ends of the lever arms 28 above the ~runnions 24 and 26. Since the turning moments applied to the lever arms 28 by the tie bar 34 will be equal and opposite, the loads applied to the trucks 18 through the trunnions 24 must also ~

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he equal and opposite provided that the angular movement of the lever assembly is small. This entails that the loadings applied to the trucks 18 must be equal, which in turn implies that no loadings can ~e applied to the trucks 20 as a result of distox-tion of the m~in runway. The levers 22 will thus move in a co-ordinated manner about the trunnions 26 so as to move the trucks 18 relative to the mem~er 6 to elLminate the loads on all four trucks due to runway distortion.

A small amount of suspension movement may also be introduced into the system by incorporating an extensible element 36 into the har 34. This member would normally be a compression spring with separate portions of the bar 34 actLng on its ends in such a manner as to compress thP spring.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An overhead crane comprising a rigid generally rectangular bridge frame, a truck beneath each corner of the frame for supporting the latter on parallel rails of a main runway for longitudinal movement, a trolley carrying hoisting machinery and movable laterally of the rectangular frame, oppositely acting levers forming the connections between the trucks on one side only of the frame and the frame itself, and a link inter-connecting the levers independently of the frame to equalize the loads on the trucks so connected, the levers each having a generally vertically extending lever arm and horizontally spaced longitudinally inner and outer trunnions forming a second longitudinally extending lever arm at the base of said vertically extending lever arm, the bridge frame being suppor-ted by the longitudinally outer trunnions of the two levers, and the trucks supporting the longitudinally inner trunnions of the two levers, the top ends of the vertically extending lever arms being connected by a link extending between the arms, the vertical extent of each vertically extending lever arm being very large compared to the horizontal extent of the longitudinally extending lever arms formed by the spacing of the axes of the trunnions.

2. A crane according to Claim 1, wherein the link incorporates a resilient element.

3. A crane according to Claim 1, wherein said vertically extending lever arms and said link are accommodated within said one side of the frame above said trucks.