Note: Descriptions are shown in the official language in which they were submitted.
3.~
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
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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
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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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