US3079080A - Crane warning system - Google Patents

Description

Feb. 26, 1963 Filed Feb. 12, 1960 FORE H. L. M'AdN CRANE WARNING SYSTEM 2 Sheets-Sheet 1 I RIGHT LEFT BYV

ATTORNEY Feb. 26, 1963 Filed Feb. 12, 1960 H. L.- MASON CRANE WARNING SYSTEM I 2 Sheets-Sheet 2 Iii 1" DJ:

HENRY LEA MASON BY M91 ATTORNEY tts 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 payment 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 such as cranes.

Heretofore the operation of certain types of material handling equipment under heavy load has been hazardous to both human life and property. One of the primary hazards of heavy load operation of such equipment is the danger of overturning or tipping over the equipment. This hazard is present in any equipment which is constructed to support a load to be lifted at a distance from the center of gravity of the equipment, such as a crane.

Accidents have frequently occurred when a heavily loaded crane boom has been elevated or lowered to a certain position relative to the earth. The weight on the crane boom is seldom known by the operator, consequently an overturning accident may occur should a certain combination of load weight and boom length be reached or v exceeded in excess of the moment created by the counterbalancing weight of the body of the crane.

Numerous attempts have been made to eliminate, or partially eliminate, the foregoing hazards of operation of certain types of material handling equipment. example of a crane warning system, otherwise known as a moment computing and indicating system, is described in U.S. Patent No. 2,858,070, issued on October 28, 1958, to Leon Schartf. This patent provides an excellent rsum of the prior art.

As will be pointed out more fully hereinafter, my invention outlines a system for gauging crane stability which does not impose restrictions on the orientation of the crane counterweight, boom, and load relative to the supporting truck. Instruments heretofore developed for this purpose have gauged stability relative to the least stable condition only; this is usually the configuration in which the horizontal projection of the crane boom is perpendicular to the edge of the fulcrum least distant from the machinery table center of rotation.

Some of the prior art systems, which are essentially analog computers with angle-sensing resolvers and adding amplifiers responding to a load-force transducer, have been found to have the following disadvantages: (a) the 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 of the carrier as might be due to uneven or soft ground or to fiexure of the carrier frarne, has also been found 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 A good angle is defined as the horizontal angle ,0 between the axis of the moving part of the crane and that of the carrier, whether the latter be an automotive truck for road and field use, or locomotive type crane for use on railroad tracks or a floating 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 cable failure.

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

Other and further objects and advantages of my inven tion will appear in conjunction with the following description and drawings wherein:

FIGURE 1 is a schematic side elevation of a typical automotive type crane disclosing the factors involved in the moment computation in accordance with the present invention;

FIG. 2 is a schematic plan vew of the crane disclosing further factors used in moment computation; and

FIG. 3 shows the circuitry for my improved analog computer.

In the preliminary planning stages leading to my invention, two basic concepts were carefully considered and examined. The first of these concepts warns the operator at a fixed percent tip, i.e., fixed ratio between overturning moment and righting moment, computed for instantaneous variates of load L, vertical boom angle 0 and horizontal slewing angle 30 of FIGS. 1 and 2. The second concept limits the load L at all slewing angles to of that sufiicient to cause overturn at any given radiusi-I-l cos 0-in the least stable direction, presumably at =90 or 270. This least stable requirement further provides backward stability for the unloaded crane by requiring a minimum force on specified sets of wheels. This latter requirement permits a relatively simple warning system but limits unnecessarily the loads which could be handled safely while working at slewing angles distan from the least stable position.

The second of the above concepts appeared to be productive of more fruitful results, hence my invention is based on the assumptions (1) that at any combination of slewing angle, boom length, and vertical boom angle, loads are permitted up to 85% tip for that combination and (2) that counterweights will not cause backward overturn 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 W =26,400 lbs. for cab plus counterweights W =27,900 lbs. for carrier truck W =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 gravity of truck i=2.5 feet, distance from axis of cab rotation to pivot point P of boom 1:15.5 feet j =5.l67 feet k =k =3.193 feet No values are given for 1 the length of the boom, and

it is assumed that 0, the vertical angle of elevation of the boom, never exceeds 90".

For further purposes of our computation, let us propose a definition which is based on, the second concept mentioned above. This definition is:

Tipping Load (without outriggers set). At any given radiusfor truclomouted types of cranes, the tipping load with tires resting on a firm, level, and even supporting surface shallbe that load which overcomes the stability of the crane in the least stable direction to the H extent that the tires opposite the load leave the supporting surface.

Since it is expected that the least stable direction is at =90 or 270, consider sidewise tipping of the entire crane structure due. to load L about either of the two fulcrum lines S S or S S in FIG. 2. The net sidewise tipping moment, M with load L suspended outside S S or S S will be:

where sinrb maybe taken as an absolute numerical'value without regard to sign. Tipping will occurwhen sin 31 ,13, 1' cos 0, and load safety factor fnbeeome so large that M ordinarily negative, becomes zero. Under our; sec ondconcept, we take, f O .8 5, i.e., the lifting capacity in pounds shall not exceed 85% of the tipping loadat any given radius in the least stable position. We interpret this .lastphrase to mean the position in which sin r//=d:1. However, the value of M, can readily be instrumented for values of sin 9 lying between 0 and :1. This would 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 ping load for the instantaneous position.

Consider next the possibility of tipping-sidewise due to counterweight overhang beyond S S or S ,,without outtriggers set and without load. The definitiomhere, may be stated:

Backward Stability (without outriggers set). In apply- .ingthe following values, the boom is to be at its recommended minimum radius, (usually 10 feet), the crane is to be unloaded, the cooling system full and the fueI tank half full. Then, minimum load onall wheels on the side on which the boom is located, with the axis of the boom at .right angles to the axis of the truck and using the minimum recommended length of boom, shall not'be less than 15% of the total weight of. the crane and truck in operating condition without load.

'I'heco-rresponding general expression M for sidewise tipping, in the absence of load and due to the counterweight positions in the vicinity of either 90or 270,",- is:

Wstis niw 10 6 -Ho The corresponding minimum wheelloading, for some factor. f applied to the sum of W; and W maybe expressed as a sidewise restraining moment, M

sr=fw[ 1+ 2l 2k By the Backward Stability definition above, the quantity M, =M }-M must be kept negative, with sin t: 1 and f =0.15. For the prototype crane with boom vertical,

This shows that the counterweighting will not be dangerous even under these conditions of operation, i.e., with boom vertical and with no load to couterbalance the crane counterweights.

However, it may be necessary at times to remove the boom completely and there is no danger if W stands inside or between the fulcrum lines 8; 5 -8 S i.e., if g M' =+39,600-89,000=49,000 ft.-lb.

In this case, the value of M has passed the required safety margin with the specified countcrweighting, so that a warning signal will be necessary. This need is made more important by the fact that a new operator coming on the job has no guarantee that the counterweights have not been changed. Provision will be made in my invention for automatic readjustment of the warning system for the case where removal of the boom or reduction of the load causes the value of M to become dangerous. This will be done without interposing switches, with their potential unreliability, in the normal operating channels for the large forces L, W and W Consider now the danger of tipping about the aft axle AA. The aft tipping moment, M due to load, L, is:

Mm=fe t cos a cos 0 cos r -i2].

+W [i cos 30+0.5 1 cos 6 cos 0- 3] ett=fLL 008 t -b 0 P-Ih] This condition is most dangerous for 11 :0, i.e., when the boom is extending rearwardly perpendicular to the aft axle AA, and a warning signal seems advisable when the net negative M 'becomes numerically small. The danger decreases as L is swung inward (with increasing \i/ and 0) and vanishes when as L swings inside, i.e., forward, of line AA. In the prototype crane, g is less than so there is little danger from the counterweighting. For other models in which we might find g greater than i the simplest procedure would be to instrument a condition for backward stability by requiring a minimum load on the front wheels.

Lastly, consider the danger of tipping aboutthe-front or fore axle FF. 'The forward tipping moment due to load L, M with cos b-understood as an absolute value without regard to sign, is:

This is most dangerous for yl1=180 and a warning signal may be needed when the net negative M becomes numerically small. However, if j is. approximately equal to; Bi as in the prototype crane, there is little danger. Also, the danger of tipping decreases as L is swung inward, i.e., rearward of FF, and vanishes when as L swings inside or rearward of the line FF. There is no danger from the counterweighting because g is less than 1' and this condition is likely to he so for most cranes. I

We now see that overturn or tipping might occur ('1) about S 8 or S S due either to L or to W; and (2) about AA or FF due to L. 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 indicator 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 be provided for setting up the system, and checking its performance.

Simplicity and reliability-should be thecontrolling characteristics for a crane warningsystem. To minimize the number of components necessary to compute allot the above tipping moments, it-will be desirable to form inter- 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:

Using for intermediate sums the notations:

1= 1+ 2+ B+fL z=fL o+' B o 3 [fL +W ]iIS cos 6W g these moment equations reduce to:

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 computer art. It is assumed in that figure that amplifiers have a gain of 1; that resolvers have a gain of +1; that voltage dividers represent factors less than unity; and that all components have sufiicient adjustability to accommodate a range of material handling equipment including, but not necessarily limited to, power cranes and power shovels. Conceivably, certain types of firefighting equipment, tree surgery equipment, mobile concrete conveyers for high buildings and other similar equipment could be equipped with such a warning system.

Conventional analog computer components, either A.C. or DC, may be used and only the load transducer might be considered a special item. Amplifiers may contain vacuum tubes, transistors or magnetic amplifier elements. Resolvers may be inductive or resistive. Voltage dividing resistors may be either wire-wound or carbon-film type. No manual switching is required and automatic switching is arranged for maximum reliability. Two variable resistors are used for representing the value of 1 in order to avoid loading eifects on the voltage dividers.

In normal operation, both visual indicator and audible signal are simultaneously effective for Mm, M and M where danger comes from large values of L. On the other hand, where L is small, the danger of overturn comes from the counterweight, and M should govern with L acting as a stabilizing efifect. The transition takes place automatically via coil and normally open magnetic relay contacts 1, according to the value V set on the voltage dividing resistor. For any lower value of L, including zero and not excluding the possibility of W =0, the relay 1 closes and the warning system operates under M 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 association with an automotive crane, it is to be understood that the inventive concept is not so limited. The inventive concept disclosed herein may be advantageously employed in any installation or equipment in which a computation of moments is desired. Difierently expressed, it may be stated further that the present invention can be employed to advantage in connection with any equipment which is subject to variable loads at various angles between 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 the supporting structure of said portion of equipment.

Further, while the invention has been particularly described in connection with a warning system for material handling equipment whereby the operator thereof may be warned of an incipient overturn condition for all positions 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 modifications may be made without departing from the scope and spirit of the invention as defined by the claims appended hereto.

I claim:

1. In material handling equipment having a boom pivotally mounted on a substantially horizontal relatively stationary structure for elevation, depression, and horizontal slewing and capable of suspending weights of various magnitudes from the free end thereof, said boom being movable to assume an infinite number of inclined positions in a vertical plane between positions of maximum depression and maximum elevation and to assume an infinite number of positions in a horizontal plane with reference to the horizontal longitudinal axis of said supporting 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 responsive to the load on the boom and connected across 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 output of said load transducer, a sine-cosine potentiometer mechanically connected to said boom for adjustment in accordance with the horizontal slewing angle of said boom with relation to said structure and connected in series with said cosine potentiometer, means electrically connected to the outputs of said load transducer and said series connected potentiometers for producing output signals having magnitudes proportional to the moments created by the various loads on the equipment, means for visually indicating the magnitudes of said signals and means for audible indication when any one of said plurality of moments exceeds a predetermined fraction of that maximum moment which would caus said equip ment to overturn.

2. In material handling equipment having a substantially horizontal supporting structure and a horizontally rotating structure pivotally mounted on said supporting structure, said rotating structure consisting of portions including a motive machinery containing cab, counterweights attached to said cab, and a boom capable of vertical elevation and lifting a variable load, said supporting structure, portions, and load having weights acting vertically downward with respect to the pivot between said supporting and rotating structures, a moment computing and indicating system for continuously computing and indicating moments aiiecting said equipment comprising a source of electrical power, a first plurality of means for predeterminedly entering the moments of the weights of 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 relation to said supporting structure, means electrically connecting said first and second plurality of means with said source of power for producing an output signal having a magnitude proportional to the moments created by the various weights on the equipment and means for audible indication of said output signal when any one of the said moments affecting said equipment exceeds a predetermined eaovaeeo fraction of that maximum moment which would'cause :saidequipinent to .ojverturn.

' 3; A moment computfng and indicating s'ystem'as' described in .cIaimZWherein said moments afiectingfsaid equipment include afirst sideways tipping moment about -a horizontal longitudinal axis of said supporting structure where said first moment 'resu'lts principally from the weight of the variable load lifted by said boom, a second sideways tippingmornent due principally to the weights of said ,counterweig'hts and said cab, and a third ,set of t-moom'ents' acting to tip said equipment about a horizontal transverse axis'oflsaid supportingrstructure.

=4.A fmoment computing and indicating system as claimed inclaim 2 further characterized by producing three output signals responsive respectively to the tipping 1'" effect of the load forwardly and aftly with respect to a horizontal transverse axis of said supporting structure and the 8, combined tipping effectstof the load and the moments-of weightsof said portions with respect to the horizontal longitudinal axisjof said supporting structure and switching 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'signa'l becomes proportional mainly to the sideways tipping effect of the eights of said counterweights and cab.

References Cited in the file of this patent UNITED STATES PATENTS 1,614,575 Siebs Jan. 18, 1927 1,775,435 Lichtenberg Sept. 9, 1930 2,858,070 Scharit Oct. 28, 1953

Claims (1)

1. IN MATERIAL HANDLING EQUIPMENT HAVING A BOOM PIVOTALLY MOUNTED ON A SUBSTANTIALLY HORIZONTAL RELATIVELY STATIONARY STRUCTURE FOR ELEVATION, DEPRESSION, AND HORIZONTAL SLEWING AND CAPABLE OF SUSPENDING WEIGHTS OF VARIOUS MAGNITUDES FROM THE FREE END THEREOF, SAID BOOM BEING MOVABLE TO ASSUME AN INFINITE NUMBER OF INCLINED POSITIONS IN A VERTICAL PLANE BETWEEN POSITIONS OF MAXIMUM DEPRESSION AND MAXIMUM ELEVATION AND TO ASSUME AN INFINITE NUMBER OF POSITIONS IN A HORIZONTAL PLANE WITH REFERENCE TO THE HORIZONTAL LONGITUDINAL AXIS OF SAID SUPPORTING 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 RESPONSIVE TO THE LOAD ON THE BOOM AND CONNECTED ACROSS 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 OUTPUT OF SAID LOAD TRANSDUCER, A SINE-COSINE POTENTIOMETER MECHANICALLY CONNECTED TO SAID BOOM FOR ADJUSTMENT IN ACCORDANCE WITH THE HORIZONTAL SLEWING ANGLE OF SAID BOOM WITH RELATION TO SAID STRUCTURE AND CONNECTED IN SERIES WITH SAID COSINE POTENTIOMETER, MEANS ELECTRICALLY CONNECTED TO THE OUTPUTS OF SAID LOAD TRANSDUCER AND SAID SERIES CONNECTED POTENTIOMETERS FOR PRODUCING OUTPUT SIGNALS HAVING MAGNITUDES PROPORTIONAL TO THE MOMENTS CREATED BY THE VARIOUS LOADS ON THE EQUIPMENT, MEANS FOR VISUALLY INDICATING THE MAGNITUDES OF SAID SIGNALS AND MEANS FOR AUDIBLE INDICATION WHEN ANY ONE OF SAID PLURALITY OF MOMENTS EXCEEDS A PREDETERMINED FRACTION OF THAT MAXIMUM MOMENT WHICH WOULD CAUSE SAID EQUIPMENT TO OVERTURN.

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