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Патент USA US3079087

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Feb. 26, 1963
H. L. M'AédN
3,079,080
_
CRANE WARNING SYSTEM
Filed Feb. 12, 1960
2 Sheets-Sheet 1
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JNVENTOR.
HENRY LEA MAsoN
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ATTORNEY
Feb. 26, 1963
H. L.- MASON
CRANE WARNING SYSTEM
Filed Feb. 12, ‘1960
I 2 Sheets-Sheet 2
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HENRY LEA MASON
BY M91“
ATTORNEY
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3,979,080
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Patented Feb. 26, 1963
2
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3,079,986
angle is de?ned as the horizontal angle ,0 between the axis
of the moving part of the crane and that of the carrier,
Henry L. Mason, Chevy Chase, Md, assignor to the
?eld use, or locomotive type crane for use on railroad
CRANE WARNING SYSTEM
whether the latter be an automotive truck for road and
United States of America as represented by the Secre
tary of the Navy
Filed Feb. 12, 1960, Ser. No. 8,468
4- Claims. (*Jl. 235-151)
(Granted under Title 35, U.S. Code (1952), see. 266)
The invention described herein may be manufactured
and used by or for the Government of the United States
of America for governmental purposes without the pay
ment of any royalties thereon or therefor.
The present invention relates to moment computing and
indicating systems and more particularly to such systems
as applied to certain types of material handling equipment
tracks or a ?oating crane installed on a marine hull.
Another object of this invention is to provide a crane
warning system that, while it consists essentially of an
analog computer responding to resolvers and a load-force
transducer, will be simpler and less power-consuming than
prior art systems.
Still another object of this invention is to provide a crane
warning system that will be operable to indicate danger
of overturn because of the counterweights when the boom
is removed or the load is suddenly dropped as by hoist
15 cable failure.
such as cranes.
A further object of my invention is to provide a crane
warning system which will obviate the disadvantages of
the prior art systems mentioned above.
I
Heretofore the operation of certain types of material
Other and further objects and advantages of my inven‘
handling equipment under heavy load has been hazardous
to both human life and property. One of the primary 20 tion will appear in conjunction with the following descrip
hazards of heavy load operation of such equipment is the
tion and drawings wherein:
'
danger of overturning or tipping over the equipment.
FIGURE 1 is a schematic side elevation of a typical
This hazard is present in any equipment which is con
automotive type crane disclosing the factors involved in
structed to support a load to be lifted at a distance from
the moment computation in accordance with the present
the center of gravity of the equipment, such as a crane. 25
Accidents have frequently occurred when a heavily
invention;
loaded crane boom has been elevated or lowered to a
further factors used in moment computation; and
,
FIG. 2 is a schematic plan vew of the crane disclosing
FIG. 3 shows the circuitry for my improved analog
computer.
an overturning accident may occur should a certain com 30
In the preliminary planning stages leading to my inven
certain position relative to the earth. The weight on the
crane boom is seldom known by the operator, consequently
bination of load weight and boom length be reached or v
tion, two basic concepts were carefully considered and
examined. The ?rst of these concepts warns the operator
balancing weight of the body of the crane.
at a ?xed “percent tip,” i.e., ?xed ratio between overturning
Numerous attempts have been made to eliminate, or
moment and righting moment, computed for instantaneous
partially eliminate, the foregoing hazards of operation of 35 variates of load L, vertical boom angle 0 and horizontal
certain types of material handling equipment. A good _ slewing angle 30 of FIGS. 1 and 2. The second concept
example of a crane warning system, otherwise known as
limits the load L at all slewing angles 31/ to 85% of that
a moment computing and indicating system, is described
su?icient to cause overturn at any given radius
in U.S. Patent ‘No. 2,858,070, issued on October 28, 1958,
i-I-lo cos 0-—in the least stable direction, presumably at
to Leon Schartf. This patent provides an excellent résumé 40 ¢=90° or 270°. This “least stable” requirement further
of the prior art.
provides “backward stability” for the unloaded crane by
As will be pointed out more fully hereinafter, my inven
requiring a minimum force on speci?ed sets of wheels.
tion outlines a system for gauging crane stability which
This latter requirement permits a relatively simple warning
does not impose restrictions on the orientation of the crane
system but limits unnecessarily the loads which could be
counterweight, boom, and load relative to the supporting
handled safely while working at slewing angles distan
truck. Instruments heretofore developed for this purpose
from the least stable position.
'
have gauged stability relative to the least stable condition
The second of the above concepts appeared to be pro~
only; this is usually the con?guration in which the hori
ductive of more fruitful results, hence my invention is
zontal projection of the crane boom is perpendicular to
based on the assumptions (1) that at any combination of
the edge of the fulcrum least distant from the machinery 50 slewing angle, boom length, and vertical boom angle, loads
table center of rotation.
are permitted up to 85% tip for that combination and
Some of the prior art systems, which are essentially
‘(2) that counterweights will not cause backward overturn
exceeded in excess of the moment created by the counter
analog computers with angle-sensing resolvers and adding
ampli?ers responding to a load-force transducer, have
been found to have the following disadvantages: (a) the 55
system is undesirably complicated and confusing to the
crane operator; ([2) the system power requirements are
excessive since great numbers of vacuum tubes are used;
(c) the system does not warn of incipient overturn in the
counterweight direction; (d) the inclusion of the effects
of load-swing, either fore-and-aft or sidewise, have been
found to be unnecessary complications as such effects are
generally negligible; (e) the inclusion of the effect of tilt
even if load and boom are removed.
In view of the above, our further computations may
be considered based on the following numerical values
which are taken from a prototype crane, where
W1=26,400 lbs. for cab plus counterweights
W2=27,900 lbs. for carrier truck
WB=4,025 lbs. for boom plus ‘rigging
g=4.7 feet, distance from axis of rotation of cab to center
of gravity of weight of cab plus counterweights
n=4.43 feet, distance from axis of rotation of cab to center
of the carrier as might be due to uneven or soft ground
of gravity of truck
or to ?exure of the carrier frarne, has also been found 65
unnecessary; (f) the inclusion of the stabilizing effect of
outriggers has been found unnecessary; and such prior art
systems employed a confusing number of indicators, all
being part of the crane warning system.
The principal object of my invention, therefore, is to
provide a crane Warning system that will be operable for
all angles of slew of the crane boom, where the slewing
i=2.5 feet, distance from axis of cab rotation to pivot
point P of boom
11:15.5 feet
j2=5.l67 feet
k1=k2=3.193 feet
No values are given for 10, the length of the boom, and
350793.80
3
4
it is assumed that 0, the vertical angle of elevation of the
boom, never exceeds 90".
sin it is less than k. When g sin ¢=k for the prototype
crane with neither boom nor load,
For further purposes of our computation, let us propose
a de?nition which is based on, the second concept men
M'Sm=+39,600-89,000=—49,000 ft.-lb.
tioned above. This de?nition is:
Tipping Load (without outriggers set). At any‘ given
radiusfor truclomouted types of cranes, the tipping load
a warning signal will be necessary. This need is made
with tires resting on a ?rm, level, and even supporting sur
more important by the fact that a new operator coming on
In this case, the value of Mstc has passed the required
safety margin with the speci?ed countcrweighting, so that
the job has no guarantee that the counterweights have
crane in the least stable direction to the H extent that the 10 not been changed. Provision will be made in my inven
tion for automatic readjustment of the warning system
tires opposite the load leave the supporting surface.
Since it is expected that the least stable direction is at
for the case where removal of the boom or reduction of
¢=90° or 270°, consider sidewise tipping of the entire
the load causes the value of Mm to become dangerous.
crane structure due. to load 7L about either of the two ful
This will be done without interposing switches, with their
crum lines S1 S1 or S2 S2 in FIG. 2. The net sidewise 15 potential unreliability, in the normal operating channels
face shallbe that load which overcomes the stability of the
tipping moment, Ms“. with load L suspended outside S1 S1
for the large forces L, W1 and W2.
or S2 S2 will be:
Consider now the danger of tipping about the aft axle
AA. The aft tipping moment, Man, due to load, L, is:
20
Mm=feLti cos ¢+1a cos 0 cos try-i2].
+WB[i cos 30+0.5 10 cos 6 cos 50-13]
Mett=fLL [i 008 til-b10605- 9’ C93, lP-Ih]
This condition is most dangerous for 114:0, i.e., when the
where sinrb. maybe taken as an absolute numerical'value
without regard to sign. Tipping will» occurwhen sin 311,13,
1'0 cos 0, and load safety factor fnbeeome so large that
Ms“, ordinarily negative,v becomes zero. ‘_Under our; sec—
ondconcept, we take, fL_—_vO_.8v,5, i.e., the lifting capacity in
boomfis extending rearwardly perpendicular to the aft
axle AA, and a warning signal‘ seems advisable when the
net negative Mau'becomes numerically small. The dan
ger decreases as ‘L is swung inward? (with increasing \i/ and
pounds shall not exceed, 85% of the tipping load- “at any
0)
and vanishes when
given radius in the least stable position.” We interpret this
.last- phrase to mean the position in which sin r//=d:1. 30
However, the value of M,“ can readily be instrumented
as L swings inside, i.e., forward, of line AA. In the proto
for values of sin, 39 lying between 0 and :1. This would
type crane, g is less than 1'2, so there is little danger from
permit lifting heavier loads safely over wide sectors on
each’ side of the 90° and 270° positions while retaining
the restriction that the liftingcapacity be 85% of the tip 35
ping load for the instantaneous position.
{Consider next the possibility of tipping-sidewise due to
counterweight overhang beyond S1 S1 or $2 S2,,without out
’
For other models in which we
might ?nd g greater than i2, the simplest procedure would
be to instrument a condition for backward stability by re
quiring a minimum load on the front wheels.
Lastly, consider the danger of tipping about‘the-front
or fore axle FF. 'The forward tipping moment due to
load L, Mm, with cos ib-understood as an absolute value
triggers set and without load. The de?nitiomhere, may
be stated:
the counterweighting.
.
40 without regard to sign, is:
.ingthe following values, the boom is to be at its recom
mended minimum radius, (usually 10 feet), the crane is
to be unloaded,>the cooling system full and the fueIItank
halfgfull. Then, minimum load onall wheels on the side 45 This is most dangerous for yl1=180° and a warning signal
on which the boom is located, with the axis of the boom at
may be needed when the net negative Mm becomes nu
v.right angles to the axis of the truck and using the minimum
merically small. However, if jl is. approximately equal
recommended length of boom, shall not'be less than 15%
to; Big, as in the prototype crane, there is little danger.
of the total weight of. the crane and truck in operating con
Also, the danger of tipping decreases as L is swung in
dition without load.
50 ward, i.e., rearward of FF, and vanishes when
'I'heco-rresponding general expression M’Sbc for sidewise
tipping, in the absence of load and due to the counter
weight positions in the vicinity of either 90°or 270,",- is:
as L swings inside or rearward of the line FF. There is
Backward Stability (without outriggers set). ‘In apply
no danger from the counterweighting because g is less
eWstisiniwo-i 10 0.0.5‘ 6 Sing-Ho
55 than 1'1 and this condition is likely to the so for most
The corresponding minimum wheelloading, for some
factor. fw applied to the sum ofrW; and W2, maybe ex
pressed as, a sidewise restraining moment, M5,:
We now see that overturn or tipping might occur ('1)
about‘ S181 or S2 S2 due either to L or to W; and ‘(2)
Msr=fw[W1+W2l 2k
By the Backward Stability de?nition above, the quantity
M,m=M’Sm—}-M5r must be kept negative, with sin it: 1 and
fw=0.15. For the prototype craneywith boom vertical,
This shows that the counterweighting will not be danger
cranes.
about AA or FF due to L.
60
I
Overturn moment. about a
single wheel, where these fulcrum lines intersect, is smaller
and, this behavior being physically unlikely, will be
neglected. Because it seems probable that an experienced
crane operator will instinctively move his controls toward
safety, regardless of the direction of the tipping tendency,
it seems unnecessary to supply a compound visual indi
cator for his use. Such an indicator would only distract
his attention from the loading area which he should be
watching. An audible signal is much to be preferred.
However, a group of simple visual indicators‘ might well
ous even under these conditions of operation, i.e., with 70 be provided for setting up thepsystem, and checking its
boom vertical and with no load ‘to couterbalance the crane
performance.
counterweights.
However, it may be necessary at times to remove the
boom completely and there is no danger if W1 stands in
Simplicity and reliability-should be thecontrolling char
acteristics for a crane warningsystem. To minimize the
number of components necessaryjto compute allot the
side or between the fulcrum lines 8; 51-82 S2, i.e., if g 75 above tipping moments, it-willrbe ‘desirable to form inter
8,079,080
J
mediate sums wherever possible. It has been helpful to
reformulate the overturn or tipping moment equations as
follows, so that for each situation the safe operating limit
is reached when --M approaches zero:
6
which is subject to variable loads at various angles be
tween a portion of the equipment and the vertical and its
various horizontal angles between the said portion of
equipment and the generally longitudinal axis through
UK the supporting structure of said portion of equipment.
Further, while the invention has been particularly de
scribed in connection with a warning system for material
handling equipment whereby the operator thereof may
be warned of an incipient overturn condition for all posi
10 tions of the load handling equipment, including the weights
of the loads, it will be apparent to those skilled in the
art that further embodiments and modi?cations may be
made without departing from the scope and spirit of the
invention as de?ned by the claims appended hereto.
I claim:
15
1. In material handling equipment having a boom piv
otally mounted on a substantially horizontal relatively
Using for intermediate sums the notations:
S1=W1+W2+ WB+fLL
Sz=fLL1o+'0-5WB1o
S3: [fLL+WB]i—I—S2 cos 6—W1g
these moment equations reduce to:
stationary structure for elevation, depression, and hori
zontal slewing and capable of suspending weights of vari
20 ous magnitudes from the free end thereof, said boom be
ing movable to assume an in?nite number of inclined posi
tions in a vertical plane between positions of maximum
depression and maximum elevation and to assume an in
?nite number of positions in a horizontal plane with ref
25 erence to the horizontal longitudinal axis of said support
ing structure, a moment computing and indicating system
for continuously computing and indicating a plurality of
moments affecting the equipment comprising a source of
electrical power, a computer including a load transducer
30 responsive to the load on the boom and connected across
FIG. 3 shows a block diagram of a warning system
based on these reduced equations and using a minimum
number of conventional components from the analog com
said source of power, said computer further including a
cosine potentiometer mechanically connected to the boom
for adjustment in accordance with the vertical angular
attitude of said boom and electrically connected to the
puter art. It is assumed in that ?gure that ampli?ers have
a gain of —1; that resolvers have a gain of +1; that volt 35 output of said load transducer, a sine-cosine potentiom
eter mechanically connected to said boom for adjustment
age dividers represent factors less than unity; and that all
in accordance with the horizontal slewing angle of said
components have su?‘icient adjustability to accommodate
boom with relation to said structure and connected in
a range of material handling equipment including, but
series with said cosine potentiometer, means electrically
not necessarily limited to, power cranes and power shovels.
Conceivably, certain types of ?re?ghting equipment, tree 40 connected to the outputs of said load transducer and said
series connected potentiometers for producing output sig
surgery equipment, mobile concrete conveyers for high
nals having magnitudes proportional to the moments cre
buildings and other similar equipment could be equipped
with such a warning system.
Conventional analog computer components, either A.C.
ated by the various loads on the equipment, means for
visually indicating the magnitudes of said signals and
or DC, may be used and only the load transducer might 45 means for audible indication when any one of said plu
rality of moments exceeds a predetermined fraction of
be considered a special item. Ampli?ers may contain
that maximum moment which would cause said equip
vacuum tubes, transistors or magnetic ampli?er elements.
ment to overturn.
Resolvers may be inductive or resistive. Voltage dividing
2. In material handling equipment having a substan
resistors may be either wire-wound or carbon-?lm type.
No manual switching is required and automatic switching 50 tially horizontal supporting structure and a horizontally
rotating structure pivotally mounted on said supporting
is arranged for maximum reliability. Two variable re
structure, said rotating structure consisting of portions in
sistors are used for representing the value of 1D in order
cluding a motive machinery containing cab, counter~
to avoid loading eifects on the voltage dividers.
weights attached to said cab, and a boom capable of ver
In normal operation, both visual indicator and audible
tical elevation and lifting a variable load, said supporting
signal are simultaneously effective for Mm, Man, and
structure, portions, and load having weights acting ver
Ms“, where danger comes from large values of L. On the
other hand, where L is small, the danger of overturn comes
tically downward with respect to the pivot between said
from the counterweight, and Mm should govern with L
supporting and rotating structures, a moment computing
acting as a stabilizing e?fect. The transition takes place
and indicating system for continuously computing and in
automatically via coil and normally open magnetic relay 60 dicating moments aiiecting said equipment comprising a
contacts 1, according to the value V set on the voltage
source of electrical power, a ?rst plurality of means for
dividing resistor. For any lower value of L, including
zero and not excluding the possibility of WB=0, the relay
1 closes and the warning system operates under Mstc.
Contactor 2, normally closed, represents a switch in the
bearing for the boom foot; when open it removes the
stabilizing effect of the boom.
Although the present invention has been disclosed in
predeterminedly entering the moments of the weights of
inventive concept disclosed herein may be advantageously
source of power for producing an output signal having a
magnitude proportional to the moments created by the
said supporting structure and portions with respect to said
pivot, a second plurality of means for entering the weights
of said variable load, the cosine of the angle of elevation
of said boom, and the sine and cosine of the angle of
horizontal rotation of said rotating structure with rela
tion to said supporting structure, means electrically con
association with an automotive crane, it is to be under
stood that the inventive concept is not so limited. The 70 necting said ?rst and second plurality of means with said
employed in any installation or equipment in which a
it may be stated further that the present invention can be
various weights on the equipment and means for audible
indication of said output signal when any one of the said
employed to advantage in connection with any equipment
moments affecting said equipment exceeds a predetermined
computation of moments is desired. Di?erently expressed,
eaovaeeo
7
‘fraction of that ‘maximum moment which would'cause
:saidequipinent to .ojverturn.
'
_
3; A moment computfng and indicating s'ystem'as' de
scribed in‘ .cIaim‘ZWherein said moments a?ectingfsaid
equipment include a?rst ‘sideways tipping moment about
-a horizontal longitudinal axis of said supporting ‘structure
where said ?rst moment 'resu'lts‘ principally from ‘the
weight of the variable load lifted by said boom, a second
8,
combined tipping effectstof the load and the moments-of
weightsof said portions with respect to the horizontal
longitudinal axisjof said supporting structure and switch
ing means associated ‘with said load and said 'boom for
automatically introducing the effectsof low load, loss of
load, and removal of boom into the circuitry producing
the third output signal whereby the latter'si’gna'l‘ becomes
proportional mainly to the sideways tipping effect of the
’
sideways tippingmornent due principally to the weights '
Weights of said counterweights and cab.
of '4 said ,counterweig'hts and said cab, and a third ,set of 10
t-moom'ents' acting to tip said equipment about a horizontal
References Cited in the ?le of this patent
transverse axis'oflsaid supportingrstructure.
‘=4.‘A‘ fmoment computing and ‘indicating system as
claimed in- claim‘ 2 further‘ characterized ‘by producing
three output signals responsive respectively to the tipping 1'"0
effect of the load forwardly and aftly with respect to a hor
izontal transverse axis of said supporting structure and the
UNITED STATES PATENTS
1,614,575
1,775,435
2,858,070
Siebs ___>_____-_ ______ __ Jan. 18, 1927
Lichtenberg _________ __ Sept.>9, 1930
Scharit _______ _,_.___-__>__ Oct.’ 28, 1953
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