GB2028753A

GB2028753A - Equalisation system for overhead crane supports

Info

Publication number: GB2028753A
Application number: GB7922926A
Authority: GB
Original assignee: Hatch Associates Ltd
Current assignee: Hatch Associates Ltd
Priority date: 1978-07-03
Filing date: 1979-07-02
Publication date: 1980-03-12
Also published as: AU4833979A; NL7905048A; BE877436A; DE2926321A1; FR2430386B1; FR2430386A1; AU526721B2; CA1093504A; IT7924072A0; ZA793198B; GB2028753B; SE428915B; BR7904185A; JPS5511496A; IT1122553B; JPS5827194B2; SE7905724L

Abstract

In a bridge crane, a rigid rectangular crane bridge frame is supported on a main runway by a truck (18) at each corner, and in order to eliminate loadings on the trucks due to distortion of the runway, the trucks on one side of the bridge support the bridge frame through interlinked levers (22) forming part of an equalizing linkage. In a preferred arrangement the interlinked levers (22) support bearings (30) of the bridge frame on trunnions (26) and are supported by bearings (32) on the trucks via trunnions (24). <IMAGE>

Description

SPECIFICATION Equalization system for overhead cranes This invention relates to overhead cranes of the kind in which a bridge frame carrying a laterally moveable trolley supporting the hoisting machinery is supported on a main runway by means of a truck at each corner.

A problem affecting such overhead cranes is local deflection or subsidence of the runway or its supports. If the bridge frame of the crane is rigid, and the trucks directly support the frame, any resulting lack of alignment of the track can result in gross inequality of the loads transmitted through the different trucks. This results in increased stresses being applied to the runway, those trucks whose loading is increased, and the frame. In extreme 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 the frame of two spaced but linked members or by placing 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. Disadvantages of these solutions are that a distortion of the bridge frame will also result in distortion of the secondary runway provided on the frame for the trolley, which must therefore itself be designed to accommodate such distortion. Furthermore the tracking of such a frame as it moves along the main runway is inferior to that of a rigid frame, with the result that the frame may tend to become misaligned on the runway. If a rigid frame is retained, problems in maintaining alignment of the trolley runway are eliminated, and tracking problems are reduced. On the other hand, the transfer of loads between the trucks supporting the frame on the main runway will result in very high torsional stresses being applied to the frame.Thus the designers of the crane and the runway must consider the interaction between the stiffness characteristics of the frame, and the probable degree of subsidence and deflection likely to occur in the runway. It is of course often difficult to estimate the likely degree of subsidence of a runway in advance; although it should in theory be possible to design foundations for the runway structure which in most cases will be free of subsidence, in practice an unpredictable amount of subsidence often tends to occur.

According to the invention an overhead crane comprises a generally rectangular bridge frame, a truck beneath each corner of the frame for supporting the latter on parallel rails of a main runway, a trolley carrying hoisting machinery and moveable laterally of the rectangular frame, oppositely acting levers forming the connections between the trucks on one side of the frame and the frame itself, and a link interconnecting the levers to equalize the loads on the trucks so connected. In practice, this entails that the loads on the remaining two trucks are unaffected by distortions of the main runway.

Preferably the levers are bell-cranks with horizontally spaced longitudinally inner and outertrunnions and a vertically extending lever arm, the bridge frame resting on the longitudinally outertrunnions of the two levers, and the tracks supporting the longitudinally inner trunnions of the two levers, the lever arms being connected by a link extending between points on the arms spaced upwardly from the trunnions. The link may include a resilient element, whereby to provide some resiliency to the support for the frame.

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

Figure 1 is a perspective view from above, one end and one side of an overhead crane in accordance with the invention.

Figure2 is an end elevation, partially broken away, of the same crane, Figure 3 is an exploded detail of the lever system shown connecting the trucks to the frame in Figure 2.

Referring to Figure 1, a crane is shown having a rigid rectangular perimeter frame 2 having lateral members 4 and end members 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 16 by means of trucks 18,20. The trucks 20 are located beneath the ends of the end member 8 by conventional means (not shown), but the trucks 18 are located beneath the ends of the end member 6 bytrunnion assemblies forming parts of levers 22. These trunnion assemblies are best seen in Figure 3, and each comprises two sets of horizontally spaced longitudinally inner and outer trunnions 24,26 one set on either side of the base of a lever arm 28.The longitudinally outer trunnions 26 are received in saddles 30 beneath the ends of the member 6, whilst the longitudinally more closely spaced trunnions 24 rest in saddles 32 on the trunks 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 restrained by means of a link in the form of a tie bar 34 extending between devises 36 at the upper ends of the lever arms 28 above the trunnions 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 be 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 be applied to the trucks 20 as a result of distortion of the main 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 member 6 to eliminate 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 37 into the bar 34. This member would normally be a compression spring with separate portions of the bar 34 acting on its ends in such a manner as to compress the spring.

Claims

CLAIMS 1. An overhead crane comprising a generally rectangular bridge frame, a truck beneath each corner of the frame for supporting the latter on parallel rails of a main runway, a trolley carrying machinery and movable laterally of the rectangular frame, oppositely acting levers forming the connections between the trucks on one side of the frame and the frame itself, and a link interconnecting the levers to equalize the loads on the trucks so connected. 2. A crane according to claim 1, wherein the levers are bell-cranks with horizontally spaced longitudinally inner and outer trunnions and a vertically extending lever arm, the bridge frame resting on the longitudinally outer trunnions of the two levers, and the trucks supporting the longitudinally inner trunnions of the two levers, the lever arms being connected by a link extending between points on the arms spaced upwardly from the trunnions. 3. A crane according to claim 2, wherein the link incorporates a resilient element. 4. An overhead crane substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawing. New claims or amendments to claims filed on 8-11-79. Superseded claims 1-4. New or amended claims:

1. An overhead crane comprising a generally rectangular bridge frame, a truck beneath each corner of the frame for supporting the latter on parallel rails of a main runway, a trolley carrying hoisting machinery and movable laterally of the rectangular frame, oppositely acting bell-crank levers forming the connections between the trucks on one side of the frame and the frame itself, one lever arm of each bell-crank lever being large compared to the other lever arm of the respective bell-crank lever and a link interconnecting the longer arms of the two bell-crank levers to equalize the loads on the trucks so connected.

2. A crane according to claim 1, wherein the shorter arm of each bell-crank lever is defined by horizontally spaced longitudinally inner and outer trunnions and the longer arm of each bell-crank lever extends vertically.

3. A crane according to claim 2, wherein the bridge frame rests on the two longitudinally outer trunnions of the two bell-crank levers, and each truck supports a different one of the two longitudinally inner trunnions of the two bell-crank levers, the longer lever arms of the two bell-crank levers being connected by a tie bar.

4. A crane according to claim 3, wherein the tie bar incorporates a resilient element.

5. An overhead crane substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawing.