US3586841A

US3586841A - Boom load indicating system

Info

Publication number: US3586841A
Application number: US799379A
Authority: US
Inventors: Robert F Griffin
Original assignee: Warner and Swasey Co
Current assignee: Warner and Swasey Co
Priority date: 1969-02-14
Filing date: 1969-02-14
Publication date: 1971-06-22
Anticipated expiration: 1988-06-22
Also published as: DE2006722A1; FR2033339A1; GB1295341A; GB1295342A; GB1295343A; FR2033339B1; CA939780A

Abstract

A boom load indicating system for a self-supporting boom which determines the maximum bending stress on the boom and, in the case of a telescoping boom, determines the bending stress on each section of the boom. A strain transducer is mounted on the boom as close as possible to the pivot where the boom lift force is applied. Electrical analog circuitry indicates when bending stress is approaching or at a maximum permissible value. When the boom is operated at a substantial slewing angle, the predetermined maximum permissible tipping moment provides the standard against which the actual bending stress on the boom is compared.

Description

i United States Patent [72] Inven r Robert F- Grim" 3,079,080 H963 Mason 235/1502 South Euclid,Ohio 3,157,148 H964 Reed 73/88.5 X [21] AppliNo. 799,379 3,251,483 H966 Devol... 214/1 (B3) [22] Filed Feb. 14,1969 3,265,220 /1966 Knight 212/55 X P lenw J 2.1 3,338,091 /1967 Tatum 73/100 X [73] Asslgnee gr ggg g f Company Primary Examiner-Malcolm A. Morrison Assistant Examiner-Edward J. Wise AttorneyY0unt, Flynn and Tarolli [54] BOOM LOAD INDICATING SYSTEM 7 1 2 Claims [Drawing Figs ABSTRACT: A boom load indicating system for a self-sup- ".S. C porting boom which detennines the maximum stress 235/134 212/55, 73/100 on the boom and, in the case of a telescoping boom, deter- [5 1] hr. Cl G06g 7/12 mines the bending tress on each ection of the boom, A strain Field of Search ..235/15 1.33, transducer i unt d on th boom as close as possible to the I pivot where the boom lift force is applied. Electrical analog 177/21 1 circuitry indicates when bending stress is approaching or at a maximum permissible value. When the boom is operated at a (56] References cued substantial slewing angle, the predetermined maximum per- UNITED STATES PATENTS missible tipping moment provides the standard against which 2,935,213 /1960 Cellitti et a1. 73/885 X the actual bending stress on the boom is compared.

PATENTED JUNZZ 19m SHEET 1 UF 6 INVENTUR P75. 2

RUM HT lal wn'l IN PATENTEU JUH22 um SHEET 2 OF 6 INVENTUR RUBERT F. ERIFFlN PATENTEUJUN22 m1 SHEET [1F 6 5 If /4 I I2 I/ l A 4 V A A v E W M W W W W F 4 V 5 5 i J! x J 5 v13 53 \2 5 J 5 g v. fi W n MAW f o f a, 3 Q 6 k F F n T Q Lu M 0 f f aw a n INVENTUR RUBERT E GRIFFIN WW Afro/9N6 y;

PATENTED JUH22 um SHEET 5 BF 6 [NI/ENTER c. b a A Z Q m K M 5 l 6 RUBERT F GRIFFIN ATTORNEYS PATENTEU JUN22 ml SHEET 8 BF 6 INVENTUR RUBERT E ERJIFFIN BOOM LOAD INDICATING SYSTEM In the past, various crane boom load indicating and warning systems have been developed for indicating boom angle, boom radius, boom length, boom load, etc. Representative of these systems are U.S. Pat. No. 3,079,080, issued Feb. 26, 1963 to H. L. Mason and U.S. Pat. No. 2,858,070, issued on Oct. 28, 1958 to Leon Scharff, both of which relate to booms of the cable-supported type, as distinguished from self-supporting booms, particularly telescopic booms.

In the prior art systems for cablesupported booms, boom load transducers have been located in a number of places. One place has been in the boom support cable system as shown in U.S. Pat. No. 3,362,022, issued Jan. 2, 1968, to G. W. Mock et al. This arrangement has the disadvantage that the measured force is not a simple function of boom weight, load weight and boom angle, and therefore does not readily lend itself to use as an input signal to an analog computer.

Another place where load transducers have been located in systems for cable-supported booms is at the outer end of the boom, coupled to the lift line sheave. With this arrangement, the output signal is proportional to the weight of the load, but the eiectrical cable to the transducer is subject to mechanical abuse if mounted outside the boom, and if applied to a telescoping boom it would present playout and takeup problems.

Still another place where load transducers have been placed in systems for cable-supported booms is in the lift cable, right at the running block, or where the boom is single reeved, right at the hook swivel. This placement has all the disadvantages of the one last described, and in addition may subject the transducer to large impact forces.

Another significant practical disadvantage of both of these last-mentioned systems is that the readout indicates only the load weight, and the operator must refer to load charts to determine whether that load weight is safe for that particular boom length and boom angle, which leads to the possibility of human error or carelessness in the necessary correlation of this information.

The prior art systems have been primarily concerned with preventing rigid, cable-supported boom cranes from tipping over. In presentday cranes having self-supporting booms, particularly telescoping booms, the structural strength of the boom, which enables it to withstand the bending moment caused by the weight of the load and the weight and length of the boom itself may be the limiting factor, rather than tipping moment. The prior art systems do not adequately satisfy the need for a system that will indicate when a boom '5 structural limit is being approached, as well as when a tipping condition is being approached.

In telescoping boom cranes, each boom section usually has a different maximum allowable bending stress. Therefore, depending upon the particular way in which a telescoping boom is extended, the maximum allowable bending stress in one or the other of the several boom sections may be the limiting factor on the pen'nissible load. Therefore, it is desirable to have a load indicating system that is self-adjustable to indicate the maximum allowable load in accordance with the way the boom sections are extended.

A principal object of this invention is to provide a novel and improved boom load indicating system of improved accuracy for self-supporting booms, particularly telescoping booms.

Another object of this invention is to provide a novel and improved boom load indicating system for a self-supporting boom having a strain transducer mounted on the boom at a location which insures that the strain measured there is substantially linearly proportional to the total bending moment on the boom, regardless of the boom angle or, in the case of a telescoping boom, the boom length or the particular manner in which the boom is extended.

Another object of this invention is to provide a novel and improved boom load indicating system for a selfsupporting telescoping boom which responds to the bending moments in all ofthe individual sections ofthe telescoping boom.

Another object of this invention is to provide a novel and improved boom load indicating system for a self-supporting boom, especially a telescoping boom, which includes transducers connected to control the operation of analog computer circuitry whose output gives an indication of the permissible boom load for the particular conditions (e,g., boom angle and boom length) under which the boom is then operating.

Another object of this invention is to provide a novel and improved boom load indicating arrangement for a self-supporting boom in which a boom strain transducer is mounted in such a manner as to minimize the possibility of its being damaged.

Another object of this invention is to provide a novel and improved indicating system for self-supporting booms which operates automatically in accordance with either the permissible limit imposed by the strength of the boom or the permissible tipping moment due to slewing of the boom, depending upon which is the more critical for the then-existing conditions ofoperation.

Further objects and advantages of the present invention will be apparent from the following detailed description of certain presently preferred embodiments thereof, which are illustrated schematically in the accompanying drawings.

In the drawings:

FIG. I is a side elevational view of a vehicle-mounted, hydraulically operated crane boom with which the present indicating system is associated;

FIG. 2 is an elevational view of this vehicle-mounted crane boom, viewed from the right end of FIG. I and with the boom support cab and the boom turned from the FIG. 1 position and with the boom lowered from the FIG. 1 position;

FIG. 3 illustrates schematically the boom in an extended position and at a particular boom angle up from the horizontal;

FIG. 4 shows bending moment diagrams for the different boom sections with and without a load suspended from the boom;

FIG. 5 is a schematic electrical circuit diagram of analog circuitry for producing voltages proportional to the bending moments on the individual boom sections due to their own weights and extended lengths and for any boom angle, in the case ofa boom having all of its sections telescopable;

FIG. 6 is a similar diagram of analog circuitry for combining the voltages produced by the FIG. 5 circuitry with the output signal of the boom strain transducer to produce individual signals which are proportional to the total bending moments on the respective individual boom sections;

FIG. 7 is a schematic electrical circuit diagram showing analog circuitry for the same general purpose as the FIG. 5 circuitry, but for a boom in which not all of the boom sections are telescopable;

FIG. 8 shows a portion of the circuitry used to provide the signals proportional to the bending moments on the individual boom sections due to the weight of the load, which signals are to be combined with the output signals of FIG. 7 in the manner shown in FIG. 6;

FIG. 9 is a schematic electrical circuit diagram showing analog circuitry for determining the bending moment on a boom having the characteristic that the output signal of the boom strain transducer is substantially the same for different boom lengths and boom angles when the rated load for a certain length and boom angle is applied;

FIG. 9A illustrates schematically a switching circuit for selectively causing the FIG. 9 circuit to respond to the slewing angle of the boom so as to indicate the maximum tipping moment, instead of the maximum bending moment; and

FIG. 10 illustrates the preferred manner of mounting the strain transducer on the underside of the base section of the boom in accordance with the present invention.

Referring first to FIGS. l and 2, there are shown two views of a vehicle-mounted hydraulic crane with telescoping boom 15 of known construction. The boom has, in succession outwardly from the supporting vehicle, a base section 16, an inner midsection 17, and an outer midsection 18. If desired, the

boom may be provided with a fly section t9 and a jib 20, as shown in FIG. 3. The base section Ilti of the boom is pivotally supported near its lower end from the vehicle, as shown at P in FIG. 3.

The weight of the boom l5 plus the weight of any load hoisted by the crane results in bending moments on the boom. These moments are opposed by moments resulting from the weight of the vehicle 21 or other carrier for the boom and the usual counterweight. if the sum of the moments resulting from the weight of the boom and the load exceed the opposing moments, the crane will tip over. A discussion and analysis of tipping moment may be found in U.S. Pat. No. 3,079,080 to H. L. Mason.

Although tipping moment is a limitation that affects any mobile crane, it is often less of a limitation than is the structural strength of the boom. This is especially true with the selfsupported telescoping booms commonly used on hydraulic cranes. These crane booms have no supporting cable structure and, therefore, are limited in lifting ability by the magnitude of bending moment they can withstand. This being the case, it is desirable to accurately determine the bending moments in the boom so that the crane operator may be provided with an iridication when the structural limits of the boom are being approached.

An important aspect of the present invention is directed to the particular mounting ofa strain transducer on the boom for sensing the strain on the boom due to its own weight and the weight of the load. l have discovered that ideally the boom strain transducer should be mounted on the base section to of the boom near the pivot 22 where the boom-lift cylinder-andpiston units 23 operatively engage this base section. There may be two such boom-lift cylinder-andpiston units, one at each side of the base section of the boom, or on small size cranes there may be one centrally located boom-lift cylinderand-piston. The boom strain transducer is indicated generally by the reference character Tr in MG. 11, whereas this transducer is hidden in FlG. 2. The preferred arrangement for attaching this transducer to the boom is described in detail hereinafter with reference to H6. 10.

l have discovered that there are substantially no stress con centrations on the underside of the base section to of the boom in the immediate vicinity of the pivot 22 and that the strain measured in this region is substantially linearly propor tional, at all boom lengths and elevation angles, to the total bending moment resulting from the weight of the boom and the weight of the load.

In order to provide the crane operator with information in meaningful tenns, it is preferable to convert the output signal of the boom strain transducer Tr to a reading in units with which the operator is familiar, such as the percentage of rated load the boom is lifting at each boom length and boom angle. The present system includes electronic circuitry for performing certain analog operations on signals that are functions of boom length, angle, etc., in order to provide the crane operator with information which is most readily informative to him.

FIGS. 5 and 6 show schematically a system for this purpose, in accordance with the present invention, which perfomis these analog operations in the most general case under con sideration. The system of FIGS. 5 and 6 is adapted for a telescoping boom in which each boom section is telescopable, having a variable length, 1,,, measured from the end of the next lower section, where n is a number subscript denoting the particular boom section. With respect to the base section 36 of the boom, 1 is measured from the pivot 22, as shown in FIG. 3. With respect to the inner midsection 17 of the boom, 1 is measured from the outer end of the base section to, and so on. Each boom section to, 1'7, 18, 19 and 2% has weight, W which may be thought of as acting at the boom sections center of gravity. The center of gravity of each boom section l6, l7, l8, l9 and 20 is located a distance L,, from its outer end.

Each of the telescoping boom sections outwardly from the base section 16 has a respective upwardly facing shoe U on the top at its inner end. Each of the boom sections which telescopically receives another boom section has a respective upwardly facing shoe 0 on the bottom at its outer end. These shoes provide the support surfaces between successive boom sections, and from FIG. 3 it can be seen that the maximum bending moment in each telescoping boom section will occur directly above the shoe 0 at the outer end of the next boom section which receives it. in the base section to, the maximum bending moment will occur at the pivot 22. in the general solution, it is also assumed that the boom is at and angle 0 above the horizontal and is supporting a load having weight W Therefore, the vector components of the weights of the load and boom sections normal to the boom are W cos 0 and W cos 0, where the subscript n again refers to the particular boom section under consideration.

Thus, the maximum moment in thejib 20 of boom 15 occur ring at the point 24 of its attachment to the fly section H9 is:

it can be shown by superposition that the moment at any point in a system is equal to the sum of all the individual moments acting about that point. This is shown graphically in FIG. 4. Therefore, the moments caused by the weights of the load and boom sections may each be calculated separately. Letting the subscripts B and 1 refer to the boom and load respectively, the equation (1 may be rewritten as:

Considering now only the moments due to the weight of the boom sections, the maximum moment in the fly section 19 due to its own weight and the weight of the jib 20 will be:

Since, from equation (4-), the first term of the right side of equation (5) is equal to M it may be written:

it may also be shown that:

The moments in each boom section due to the weight of the load may be written as follows:

The strain transducer Tr mounted on the bottom of the base section to of the boom as close as possible to the pivot 22 generates an electrical signal that is a function of the strain to which it is subjected. The strain in the mounting area is proportional to the bending moment at this point on the boom. Letting the output of transducer Tr be represented by T, we can write T=KM where M, is the moment at pivot 22 and K is a constant of proportionality.

EEG. is a schematic diagram of an electrical analog circuit that will provide electrical signals representative of the m0- ments in the several boom sections due only to the weights of the boom sections themselves.

A regulated power supply (not shown) provides a power supply voltage of +5 for an amplifier 25 and also provides a power supply voltage of E,, for one end of a cosine potentiometer 26. The opposite end of potentiometer 26 is at a fixed reference potential E such as by being grounded to the crane chassis. The input shaft of the cosine potentiometer" 2b is coupled to the boom, as indicated schematically by the dashed line 27 in FIG. 5, so that it is rotated in accordance with the boom elevation angle 6 and the schematically illustrated adjustable potentiometer tap 28 is positioned in accordance with the cosine of 8. Therefore. the output E, of

potentiometer

26, 28 is equal to E,, c056.

This signal is amplified by the amplifier 25. having a gain of K,, which may be unity or higher to provide subsequent signals in a desired voltage range.

The output voltage Khd IE, from amplifier appears at point 29 in FIG. 5, and it is applied to a plurality of voltage dividers equal in number to the number of boom sections whose individual moments are to be determined. Each voltage divider is shown as consisting of a variable resistor and a potentiometer resistance connected in series between point 29, which is at the potential Khd 115,, and point 30, which is at the reference potential E The voltage divider for the fifth boom section 20 (the jib) includes variable resistor R and potentiometer resistance R,,; the voltage divider for the fourth boom section 19 (the fly section) includes variable resistor R and potentiometer resistance R; the voltage divider for the third boom section 18 (the outer midsection) includes variable resistor R and potentiometer resistance R;,,; the voltage divider for the second boom section 17 (the inner midsection) includes variable resistor R and potentiometer resistance R11; and the voltage divider for the first boom section 16 (the base section) includes variable resistor R and potentiometer resistance R Each of the variable resistors R R 30, R and R, is manually adjusted so that the voltage at its juncture with the respective potentiometer resistance R R R R or R in the same voltage divider is proportional to the sum of the normal forces due to the corresponding boom section and all boom sections supported thereby (i.e., all additional boom sections outward of this boom section That is:

It will be evident that since the input voltage to each voltage divider (at point 29) already includes the c056 factor, resistor R is adjusted manually to have an ohmic value inversely proportional to W which is the known weight of the fifth boom section 20. Similarly, resistor R is adjusted manually to have a resistance value inversely proportional to W,+W which is the sum of the known weight ofthe fourth and fifth boom sec tions 19 and 20. The same technique is used for determining the adjusted values of resistors R R and R The adjustable contact of each potentiometer R R R R and R is connected mechanically in any suitable manner to its respective boom section so that the position of the adjustable contact is proportional to the extended length, l,,, of its respective boom section. These mechanical connections are indicated schematically by the dashed lines leading from 1 to the adjustable contact of potentiometer R from I to the adjustable contact of potentiometer R and so on. Therefore, the voltages at the adjustable contacts of the respective potentiometers may be expressed as follows:

Five additional potentiometers R5 Ru. R R and R are also connected in parallel with each other across the aforementioned voltage dividers R ,+R R +R etc. Each of these potentiometers is set manually to provide a voltage at its adjustable contact which is proportional to (L,,W,, c056). Thus:

E -L ll cos 6 ('28) fi hll] cos 6 (29) As shown in FIG. 5, the voltage E at the adjustable contact on potentiometer R and the voltage IE at the adjustable contact on potentiometer R are applied to a summing amplifier 32 which subtracts them to provide an output voltage E as follows:

This, it will be recognized, is the expression developed previously for M From FIG. 5, it will be apparent that the summing amplifier 33 is connected to receive three input voltages, E E and E and to produce an output voltage E as follows:

E, =E +E ,E (31) which will be recognized as the expression developed for M Similarly from an inspection of FIG. 5, it will be evident that These signals, E E E E and E are applied as input signals to the correspondingly designated input terminals in FIG. 6, now to be described. In addition to these just-mentioned input signals, which are respectively proportional to the moments of force on the individual boom sections due to the weight of the boom itself, the FIG. 6 circuit also produces signals which are proportional respectively to the bending moments on the individual boom sections resulting from the weight of the load W,. The output signal T of the boom strain transducer which is proportional to M,=M, .+Mm. is amplified by a linear amplifier34. the output of which is labeled E,

The voltage E proportional to M,,,, is subtracted from E in summing amplifier A to provide as its output voltage E As already indicated, the voltage E is received from the cor respondingly labeled output terminal ofFIG. 5.

Referring to the moment diagrams of FIG. 4, the lowermost set of straight-line curves shows the bending moments due only to the weights of the individual boom sections for a given boom angle with respect to the horizontal. The upper set of curves shows the bending moments due to the weight of the load and the weights of the individual boom sections for this same boom angle.

Referring to the lower set of curves, the bending moment due solely to the weight of the outermost boom section, the jib 20, is designated by the line 58. The weight of this boom sec tion may be considered as concentrated at its center of gravi ty, designated by the point C.G.5 along the abscissa. The Support point for this boom section is designated by the point S along the abscissa. The respective centers of gravity and sup port points for the fourth, third, second and first boom sections are similarly designated, except that the support point for the base section 16 is designated by reference numeral 22 to correspond to FIG. 3.

It will be apparent that the bending moment due to the weight of the fifth section of the boom alone is a straight-line function, increasing from zero at C.G.5 to a maximum at the support point 22 for the base section of the boom. The slope of line 58 is proportional to the weight of the fifth boom section.

Line 48 in FIG. 4 shows the bending moment due solely to the weight of the fourth boom section 19 plus the weight of the fifth boom section. Line 4B is a straight-line function, intersecting the bending moment line 58 for the fifth section at C.G.4 (the center of gravity of the fourth section) and then sloping upwardly from line 58 to a maximum at the support point 22 for the base section of the boom. The difference between the slopes of lines 48 and 5B is proportional to the weight ofthe fourth boom section 19 alone.

Similarly, line 33 in the lower set of curves in FIG. 4 shows the bending moment due solely to the weights of the third, fourth and fifth boom sections l8, l9 and 20. Line 38 follows a straight-line function, having a minimum alue at its intersection with line 48 at C.G.3, the center of gravity of the third boom section 18, and increasing linearly to a maximum value at the support point 22 for the base section of the boom. The

difference between the slopes of lines 38 and 4B is proportional to the weight of the third boom section 18 alone.

A similar analysis holds true for the bending moments 2B and 1B for the second and

first boom sections

17 and 16.

When a weight is suspended from the outer end of the boom, at a point outward beyond the center of gravity C.G.5 for the outermost boom section, the entire set of curves is displaced to a position as shown by the upper set of curves in FIG. 5. The inclined base line z of this upper set of curves shows the bending moment at various points along the boom due solely to the weight of the load.

Referring again to FIG. 6, in order to derive signals proportional to the bending moments in each boom section due to the load, the output E, of summing device A,, which is proportional to M is fed to a voltage divider having five variable resistors R' R',,, R' R and R' The generic expression for these resistors will be called R',,,, where n corresponds to the final digit in the subscript of the individual resistor. Each resistor R in this voltage divider is mechanically coupled in any suitable manner to the corresponding boom section so that it has a resistance proportional to the instantaneous length 1,, of that boom section. This mechanical coupling is indicated schematically by dashed lines associated with these resistors in FIG. 6. If the constant of proportionality between the length 1,, of each boom section n and its associated variable resistor R is the same for all of these resistors, then the voltage E,,,, at the lower end of each resistor R will be propor tional to the bending moment in that boom section due to the load.

Thus, E,, is proportional to M and E E;,,,, E and E, are proportional to M M M and M respectively.

The FIG. 6 circuitry includes summing amplifiers A' A;,', A',, and A, in which the voltages E E E and E are respectively summed with voltages E E E and E which are proportional to M M M and M and are produced in the circuit of FIG. 5, as already described in detail. These summing operations produce voltages E E E and E at the respective outputs of amplifiers A A A', and A which are proportional to M M;,, M, and M,, respectively. These signals, along with the E, output of amplifier 34, which is proportional to M,, represent the maximum bending moments in the respective sections of the boom.

Each of these signals may be continuously or selectively monitored or scanned, or compared to another signal representing the maximum safe allowable bending moment in each boom section. For example, a voltage comparator S may be arranged to compare the E signal with an E reference signal which represents the maximum safe allowable moment in the second section of the boom. Similar signal comparators S S and S, are provided for comparing the actual bending moment signal, E E or E with a reference signal E E or E representing the maximum allowable bending moment for the same boom section. Each signal comparator may energize a respective warning lamp Q 0,, Q, or Q, when the actual bending moment signal for that boom section approaches the maximum permissible value, such as by exceeding 85 percent of that value. Also, each signal comparator may energize another indicator lamp P P P or F when the actual bending moment signal for that boom section reaches I00 percent of the maximum permissible value, and when any of lamps P P P or I is energized an audible alarm device X is also energized.

The E, output from amplifier 34 in FIG. 6, which is proportional to the bending moment on the base section I6 of the boom, is applied as one input signal to a voltage comparator S, where it is compared with a reference signal E When the boom extends substantially longitudinally of the vehicle (i.e.. not appreciably to one side or the other of the vehicle), this E reference signal is obtained from the adjustable contact of a potentiometer 35, whose manually adjusted setting produces an E, voltage that is proportional to the maximum allowable bending moment on the base section of the boom.

However, when the boom is at a significant slewing angle (to one side or the other of the vehicle) then the tipping moment may be more critical than the bending moment of the boom. That is, the crane may tend to tip over at a boom load ing much lower than would be critical to the structural strength of the boom itself under a bending moment. In that case, the E signal will be obtained for a second potentiometer 36 whose adjustable contact is positioned in accordance with the sine of the slewing angle by being mechanically coupled in any suitable manner to the boom slewing equipment. Desirably, potentiometer 36 may be a sine potentiometer.

The connections of the two alternatively used

potentiometers

35 and 36 to the comparator S, are such that the potentiometer whose adjustable contact is at the smaller voltage will be connected to provide the second input signal to comparator S,, for comparison therein against the E input signal. When the slewing angle is zero or small, then the potentiometer 35 will provide this second input signal to comparator 5,. When the slewing angle is large, then potentiometer 36 will provide this second input signal to comparator S,.

Comparator S, is arranged to turn on an indicator lamp 0, when the bending moment signal E approaches the E, signal, such as when it exceeds percent of E,,,. Also, comparator S, is arranged to turn on another indicator lamp P, and also to energize the audible alarm device X when the E,, signal reaches I00 percent ofthe E signal.

The analog circuit of FIGS. 5 and 6 is provided with a test arrangement which enables the operator to test it. The operator will position the crane boom at a predetermined length, boom angle and load and depress test switch C, which provides a voltage which when added to the strain transducer output signal T in the FIG. 6 circuit, should produce a response of lamp P, and the audible alarm device X.

The analog circuitry of FIGS. 5 and 6 is a general solution designed for use in conjunction with a boom having all of its boom sections telescopically arranged. Simplification of this circuitry is possible where the crane boom is as shown in FIG. 3, having a base section l6 of fixed length and having an outermost section orjib 20 which is not telescopable at all, but is arranged to be manually attached to or removed from the fly section 19. Therefore, for purposes of providing an electrical analog, the jib 20 is either present in its full length or it is abscnt. Likewise, the fly section I9, although it is telescopablc, may not be powered, and therefore it will be either in its fully retracted or its fully extended position, but not inbetween. When retracted, its length I is at a minimum but its weight W must still be accounted for in calculating the bending momerits due to the weights of the boom sections.

Therefore, an electrical analog for such a boom may be provided as shown in FIG. 7, which is simpler than that of FIGS. 5 and 6 in that variable resistors and potentiometers are replaced by fixed voltage sources. For example, as shown in FIG. 7, because the jib section of the boom is not telescopablc, R and R are eliminated and R is set so that it provides a voltage proportional to (I L )W cosO. A manually operated switch SW, may then be used to connect the E output of amplifier 32 to the positive input terminal of amplifier 33 when the jib 20 is attached to the fly section 19 and to disconnect the E output of amplifier 32 from this input terminal of amplifier 33 when the jib is detached.

In the voltage divider for the fourth boom section R is replaced by fixed resistances or a pair of potentiometers R' and R",,, as shown in FIG. 7, that may be manually set to provide voltages proportional to the extended and contracted positions, respectively, of the fly 19. A switch SW, may be provided to select between those two conditions.

Also, R and R,, are eliminated because the base section I6 of the boom is of fixed length, and R is set to provide a volt age proportional to Except for these simplifications the FIG. 7 circuit is essentially the same as that of FIG. 5 and therefore it is not necessary to repeat the detailed description of its operation.

FIG. 8 shows modified circuitry for use in place of the input side of the FIG. 6 circuit and in conjunction with the FIG. '7 circuit.

In FIG. 8, R,, is fixed, instead of adjustable, because the base section 16 of the boom has a fixed length.

Resistor R at the input side of FIG. 6 is replaced by a pair of series-connected fixed resistors R and R'}, in FIG. 8, and a switch SW is connected across resistor R";,. If fly section 19 of the boom is fully extended, then switch SW, is opened. If the fly section is fully retracted, then switch SW is closed.

In FIG. 8, R is fixed because the jib 20, if present on the boom, is not adjustable in length, and a switch SW is connected across R',,. If the jib 20 is present on the outer end of the boom, then switch SW is kept open. However, if the jib is not present, then switch SW is closed to shunt R In FIG. 8, the variable resistors R', and R' which are proportional to the lengths of the respective boom sections, may be provided by multiturn potentiometers driven by tag lines affixed to the

respective boom sections

17 and 18. However, if the crane boom of FIGS. 1 and 2 is operated so that the inner and outer midsections l7 and 18 are always extended and retracted equally, then a fixed relationship is established between 1 and l and therefore between R and R' so that only one tag line is required. That is, if l =l;,, then a single tag line affixed to the inner midsection 17 may adjust both R and R equally.

It will be apparent, in view of the foregoing description that the present analog circuitry may be modified to accommodate any number of telescoping or removable boom sections. Such circuitry is necessary to yield the desired information for the crane operator where failure may occur in different boom sections subjected to widely differing bending moments.

In one particular hydraulic crane, it was found that the output of the strain transducer, Tr, was approximately the same value for all boom lengths and boom angles when the rated load for the particular length and angle was applied to the hook. So long as this relationship holds true, a greatly simplified electrical analog may be constructed, as illustrated in FIG. 9.

The strain transducer Tr affixed to the boom as described with reference to FIG. 1 produces an output signal proportional to the total bending moment in the boom. This signal is amplified by an amplifier 40, which may be a solid state integrated circuit device. A zero adjust signal may also be introduced via line 400 into amplifier 40, which acts as a summing amplifier. In this manner, the signal from transducer Tr caused by its preload may be cancelled out, thereby providing a signal T at the output of amplifier so that is zero when the bending moment at the pivot 22 is zero, even though the transducer Tr is preloaded to some initial strain.

The output T of amplifier 40 will be a signal proportional to the total moment in the boom, In order to translate this signal into information meaningful to the operator, it is desirable to subtract the effects of boom weight. The moment due to the load may be represented by:

where:

M, total moment at the transducer M, moment due to weight of boom M, moment due to weight ofload The moment due to the weight of the boom may be represented by:

M =W L cos0 where:

W,, is the weight ofthe boom;

L is the distance from the pivot point 22 to the center of gravity of the boom; and

0 is the vertical angle the boom makes with the horizontal.

The circuit for generating the above relationship incorporates a cosine function potentiometer 411, the input shaft of which is rotated in accordance with the boom angle 0, as indicated by the dashed line 42 in FIG. 9. This may be done, for example, by a damped pendulum, as described in U.S. Pat.

No. 3,362,022, issued Jan. 2, 1968, to G.W. Mock et al. The output of cosine potentiometer 41 is equal to its input voltage multiplied by cost9. Because the weight of the boom is constant, the input voltage to cosine potentiometer 41 may be made proportional to boom weight W so that the output of cosine potentiometer 41 is proportional to W c050. This output may be multiplied by an amplifier 43.

The amplified signal from cosine potentiometer 41 provides the input to a boom length potentiometer 44, the shaft of which is rotated in accordance with boom length, as indicated by the dashed line 45, such that it is representative of the distance from pivot 22 to the center of gravity of the boom. A spring loaded reel having a tag line affixed to one of the telescoping boom sections may be used to rotate the shaft of potentiometer 44 to provide this relationship. Potentiometer 44 may be linear or it may be constructed to more closely approximate the movement of the center of gravity of the boom with boom extension.

The output of potentiometer 44 is proportional to M,,=W,,L cosl9, but because a potentiometer has a gain equal to or less than unity, preferably it is amplified by an amplifier 46 to provide a signal Y of the proper magnitude. In practice, the gains of

amplifiers

43 and 46 may be adjusted so that the output Y of amplifier 46 is of the proper magnitude.

Boom length will, of course, never be zero on a working crane. Therefore, so that the resistance proportional to boom length does not go to zero, a fixed resistor may be inserted in series with potentiometer 44. Alternatively, the same offset effect may be obtained by use of a separate signal L added into amplifier 46, as shown in FIG. 9.

The output Y of amplifier 46, which is proportional to W L cos6=M1w. is used along with the output T from amplifier 40 as the inputs to summing amplifier 47 to produce a signal T-Y which is proportional to M -M =M the moment due only to load.

This signal, T-Y, at the output of amplifier 47 may be operated upon by a network 48 having a l/cos transfer function generator to provide an indication on an indicating device 49 of load weight W However, networks with l/cos transfer functions are expensive, and even if the crane operator knew the weight of the load, he would still have to refer to load charts to determine whether he could safely move the boom to a more extended length.

As noted above, in the particular crane boom that was studied, the strain measured by transducer Tr was approximately the same for each boom elevation and length at the respective rated loads. This being the case, a maximum safe strain signal C may be used for all boom elevations and lengths. In the analog circuit of FIG. 9, C may be generated by a voltage divider 50 connected across a reference voltage source. Because C is proportional to the maximum safe strain, and therefore the maximum safe bending moment about pivot 22, a signal C-Y will be proportional to the maximum safe bending moment less the actual bending moment due to the weight of the boom, and this C-Y signal is proportional to the maximum bending moment that may be placed on the boom due to the load. The C-Y signal is provided by applying the C and Y signals to the opposite input terminals of a summing amplifier 51, as shown in FIG. 9, which subtracts them to provide the C-Y signal on its output line 52.

Since TY is proportional to the actual bending moment due to the load, and CY is proportional to the maximum safe bending moment which may be due to the load, the fraction TY/CY, expressed as a percentage, is an indication of how much of the booms capacity is being utilized. A signal proportional to T-Y/C-Y may be generated in a divider network of known design, represented schematically by the box 53 in FIG. 9. The outputs of

amplifiers

47 and 51 are connected to the two input terminals of network 53 to produce an output signal proportional to T-Y/C-Y, which output signal may be applied to any desired indicating device 54, such as a gal vanometer type meter.

There may also be provided an indication as to when a certain percentage, less than 100 percent, of the maximum safe bending moment has been reached. This may be in the form of a triggering circuit 55 that lights a lamp 56 when the signal proportional to T-Y/C-Y reaches a predetermined percent age. A second triggering circuit 57 may be adapted to light a second lamp 58 and sound an audible alarm device 59 when 100 percent of the maximum safe bending moment has been reached or exceeded.

In the FIG. 9 circuit, the value of the signal C obtained from potentiometer 50 may be adjusted in accordance with the slewing angle 4; of the boom, as indicated schematically by the dashed line 60. This may be done by changing the position of the adjustable contact of potentiometer 50 in accordance with an appropriate function of the slewing angle, 11, such as the sine of the slewing angle.

However, in accordance with the presently preferred embodiment of the circuit depicted in FIG. 9, the value C is either one of two values depending upon whether the slewing angle is small or large. For example as shown in H6. 9A, two alternatively used potentiometers 50' and 50" may be provided and a selector switch 61 is connected between the adjustable contact on one or the other of these potentiomcters and the input side of the summing amplifier 51. This switch 61 is suitably coupled to the boom to sense the slewing angle such that when a predetermined slew angle is exceeded the switch 61 abruptly disconnects potentiometer 50' and connects the other potentiometer 50" to the amplifier input. Thus, when the boom extends over the end of the carrier vehicle the signal C is established by potentiometer 50, but when the boom extends over the side of the carrier vehicle the signal C is established by potentiometer 50".

As already pointed out, the mounting of the strain transducer Tr on the boom, particularly its attachment to the base section 16 near the pivotal connection of the boom lift cylinder-and-piston units to the boom, is an important feature of the present invention.

FIG. shows the preferred structural arrangement for mounting the strain transducer Tr, which is utilized in the electrical analog circuits of the present invention as already described in detail. Atfixed to the bottom plate 62 of the base section 16 of the crane boom 15, preferably by welding, are a pair of support blocks 63 and 64, which are spaced apart lengthwise of the boom. A cylindrical hole 65 in block 63 is coaxial with a smaller cylindrical hole 66 in block 64, their common axis being parallel to the longitudinal axis of crane boom 15.

A transducer housing bolt 67 is slidably received in the block holes 65 and 66. The housing bolt 67 has a head 68, a proximal shank portion 69 adjacent the head that is slightly smaller than the block hole 65 so that it may easily fit therein, a mid shank portion 70 that is slightly smaller in diameter than hole 66, and a distal shank portion 71 approximately the same diameter as the mid shank portion 70. The proximal shank portion 69 is screw-threaded from the mid shank portion 70 approximately halfway to the head 68, and is adapted to threadedly receive a first nut 72 at the inner side of block 63. The distal portion 71 is screw-threaded to receive

nuts

73 and 74 at the inner and outer sides of block 64. Suitable lock washers 72a, 73a and 74a are engaged between the correspondingly numbered nuts and the adjacent sides of the respective blocks.

A small bore 75 extends through the head 68 and proximal shank portion 69 of the bolt into the mid shank portion 70. The boom strain transducer Tr is cemented or otherwise fixedly secured in this bore 75 at its inner end in such a manner that any strain on the bolt is imparted to the transducer Tr. The cross section of the mid shank portion 70 of the bolt in the vicinity of the transducer Tr is made precisely uniform to insure against erroneous signals that could be caused by nonuniform displacement under stress. The bolt head 68 may be provided with an electrical connector 76 adapted to seal the strain transducer within the bore 75 and to provide a convenient connection to an external cable for connecting the lead-in wires of the transducer into the electrical analog circuitry, as already described.

1n use, the distal portion 71 of bolt 67' is inserted through the block hole 65 and nut 72 slipped over this distal portion. Then nut 73 is screwed onto the distal portion 71 and all the way over to the midportion of the bolt. The distal portion is then inserted through the block hole 66. Next, nut 72 is screwed onto the proximal portion 69 of the bolt and is turned down tightly, locking the bolt 67 to block 63. Then nut 73 is turned to the right in FlG. 10 along the distal portion 71 of the bolt until it abuts tightly against block 64 to place the bolt shank between

nuts

72 and 73 in compression between

blocks

63 and 64. When the desired compressional preload has been achieved, nut 74 is screwed onto the projecting end of distal portion 71 and is tightened against the outer side of block 64.

The compressional preloading of bolt 67 is imparted to the strain transducer Tr so that the latter is preloaded under compression also. This compressional preload achieves two desira ble results. First, it prevents the output signal from the strain transducer Tr from ever going negative under any normally encountered boom conditions. This simplifies the electronic circuitry. Secondly, it avoids some small errors that can occur in the zero strain area due to internal stress in the bolt, blocks and boom.

While certain presently preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, it is to be understood that various modifications, omissions, refinements and adaptions which depart from the disclosed embodiments may be adopted without departing from the scope of the present invention. For example, any of the analog circuits disclosed herein may be modified by the use of different circuit components to perform the analog functions described.

: Having described my invention, l claim:

ll. ln combination with a boom which is subject to a substantial bending moment, a strain transducer, and means operatively connecting said transducer to the boom at a location effective to produce on the transducer a strain which is substantially a predetermined function of the bending moment on the boom, said predetermined function is a substantial linear function of the strain on the transducer with respect to the total bending moment on the boom due to its own weight and the weight of any load suspended from its outer end.

2. In combination with a self-supporting boom for supporting a load from its outer end, boom lift means operatively engaging the underside of the boom near its lower end for lifting and lowering the boom, a strain transducer, and means rigidly attaching said transducer to the underside of the boom in close proximity to the location thereon where said boom lift means engages the boom so that the strain measured by the transducer is substantially linearly proportional to the total bending moment on the boom due to the load and due to the weight of the boom itself.

3. The combination of claim 2, wherein said boom has a plurality of extensible sections which interfit in succession along its length.

4. The combination of claim 3, wherein said boom has telescoping sections.

5. The combination of claim 3, and further comprising cir cuit means operative in response to the output signal of said transducer and in response to the individual lengths and weights of the boom sections to determine the actual bending moment on each boom section.

6. The combination of claim 5, wherein said circuit means comprises electrical analog circuitry.

7. The combination of claim 5, wherein said circuit means comprises means for producing reference signals proportional respectively to predetermined maximum safe bending moments for each of the boom sections, and means for comparing each of said reference signals against a signal proportional to the actual bending moment on the corresponding boom section.

8. The combination of claim 7, and further comprising indicator means for each boom section operable by the comparison between each reference signal and the corresponding actual bending moment signal to provide an indication when the actual bending moment signal is at least a predetermined percentage of the respective reference signal.

9. An indicator system for use with a self-supporting boom having a plurality of boom sections in succession outwardly from its base and certain of which sections, at least, are extensible, said system comprising means for sensing the bending moment on the boom at a location thereon where the response of said sensing means is substantially linearly proportional to the actual bending moment at said location on the boom, an analog circuit including circuit elements operatively connected to provide signals which are substantially proportional to the lengths of the respective boom elements, the circuit ele ments which correspond to the extensible boom sections being variable in accordance with the individual extended lengths of the latter, said analog circuit also including circuit elements operatively connected to provide signals which are substantially proportional to the weights of the respective boom elements, and said analog circuit including means for combining the output signal of said sensing means and said boom section length signals and said boom section weight signals to provide for each boom section a signal substantially proportional to the actual bending moment thereon.

10. A system according to claim 11, and further Comprising means for producing reference signals proportional respectively to predetermined maximum safe bending moments for the individual boom elements, and means for comparing each of said reference signals against the signal representing the actual bending moment on the corresponding boom section.

11. In combination with a self-supporting boom having a base section and a plurality of additional sections in succession outwardly from the base section, at least certain of said sections of the boom being extensible, strain transducer means operatively coupled to the boom to determine the bending moment on the boom at a particular location thereon, and circuit means operable in accordance with the respective weights and extended lengths of the several boom sections and the output of said strain transducer means to produce a plurality of signals which individually are representative of the bending moments on respective sections of the boom.

12. The combination of claim ll, and further comprising boom lift means operatively engaging the base section of the boom from below for lifting and lowering the boom, and means rigidly coupling said strain transducer means to the underside of said base in close proximity to its operative engage ment by said boom lift means so that the strain measured by said strain transducer means is substantially linearly proportional to the total bending moment on the boom due to its own weight and the weight of any load suspended from its outer end.

13. The combination of claim 11, wherein said circuit means is an analog circuit including circuit elements operatively connected to provide signals which are substantially proportional to the lengths of the respective boom elements, the circuit elements which correspond to the extensible boom sections being variable in accordance with the individual variable lengths of the latter, said analog circuit also including circuit elements operatively connected to provide signals which are substantially proportional to the weights of the respective boom elements, and said analog circuit including means for combining the output signal of said strain transducer means and said boom section length signals and said boom section weight signals to provide for each boom section a signal which is substantially proportional to the actual bending moment thereon.

14. The combination of claim 13, and further comprising boom lift means operatively engaging the base section of the boom at a predetermined location for lifting and lowering the boom, and means operatively connecting said strain transducer means to the base section of the boom to measure the strain at the underside of the boom in close proximity to the location where said boom lift means is operatively connected to the base section of the boom.

15. The combination of claim l3, and further comprising means for producing reference signals proportional respectively to predetermined maximum safe bending moments for the respective boom sections, and means for comparing each of said reference signals against a signal proportional to the actual bending moment on the corresponding boom section.

to. The combination of claim 15, and further comprising means for producing a maximum safe tipping moment signal, and means for comparing said tipping moment signal against the signal proportional to the actual bending moment on the base section of the boom when the slewing angle of the boom exceeds a predetermined value while at the same time disabling the comparison between said actual bending moment signal for the base section and the corresponding reference signal which is proportional to the maximum safe bending load for the base section.

17. A method comprising the steps of changing the length of a boom for supporting an external load and having telescoping sections by varying the telescopic relationship between sections of the boom, sensing the length of the boom, changing the angular position of the boom relative to a support surface by moving the boom transversely to the support surface, sensing the angular position of the boom relative to the support surface, sensing bending moment induced in the boom under the combined effects of the external load and weight of the boom, and generating a load signal which is a function of the sensed bending moment in the boom, the sensed length of the boom and the sensed angle of the boom relative to the support surface.

18. A method comprising the steps of changing the length of a boom having telescoping sections by varying the telescopic relationship between sections of the boom with a resulting change in the bending moment in the sections of the boom, changing the angular position of the sections of the boom relative to a support surface by moving the sections of the boom transversely to the support surface with a resulting change in the bending moment in the sections of the boom, generating a plurality of load signals each of which is associated with a different one of the sections of the boom, and varying said load signals in response to and as a function of changes in the bending moment in the associated one of the boom sections resulting from changes in the length of the boom and changes in the angular position of the boom relative to the support surface.

19. A method as set forth in claim 18 further including the method steps of generating a reference signal corresponding to a predetermined maximum safe load, comparing said load and reference signals, and generating an output signal when said load signal exceeds a predetermined function of said reference signal.

20. A method as set forth in claim 18 further including the steps of changing the magnitude of an external load supported by the boom with a resulting change in the bending moment in each of the sections of the boom, and varying each of said load signals in response to changes in the bending moment in the associated one of the boom sections resulting from changes in the magnitude of the external load supported by the boom.

2ll. A method comprising the steps of changing the length of a boom for supporting an external load and having telescoping sections by varying the telescopic relationship between sections of the boom, changing the angular position of the sec tions of the boom relative to a support surface by moving the sections of the boom transversely to the support surface, sensing bending moment induced in a section of the boom under the combined influence of the external load and weight of the boom, generating as a function of the sensed bending moment a plurality of load signals each of which is associated with a different one of the sections of the boom and is representative of the bending moment induced in the as sociated section of the boom by the external load, generating a plurality of boom signals each of which is associated with a different one of the sections of the boom and is representative of the bending moment induced in the associated section of the boom by the weight of the boom, and producing a plurality of combined signals each of which is associated with a different one of the boom sections, each of said combined signals being a function of the load and boom signal associated with the same boom section as the combined signal and being representative of the bending moment induced in the associated boom section under the combined influence of the external load and weight of the boom.

22, An assembly comprising a boom having a plurality of telescoping sections, means for moving said telescoping sections of said boom relative to each other to thereby vary the telescopic relationship between said sections and the length of said boom, means for varying the angular relationship of said boom to the support surface by moving said boom toward and away from the support surface, and circuit means for producing a signal representative of the bending moment in said boom, said circuit means including means for varying said signal in response to changes in length of said boom and means for varying said signal in response to changes in the angular relationship of said boom to the support surface.

23. An assembly as set forth in claim 22 further including means operatively connected to said boom of engaging external loads of different magnitudes, said circuit means including means for varying said signal in response to changes in the magnitude of the load engaged by said means for engaging external loads.

24. An assembly comprising a boom having a plurality of telescoping sections, means for moving said telescoping sections of said boom relative to each other to thereby vary the telescopic relationship between said sections and the length of said boom, means for varying the angular relationship of said sections of said boom relative to a support surface by moving said boom toward and away from the support surface, and circuit means for generating a plurality of signals each ofwhich is associated with a different one of said sections of said boom and is representative of at least a portion of the bending mo ment in the associated one of said boom sections, said circuit means including means for varying at least some of said signals in response to changes in the length of said boom and means for varying at least some of said signals in response to variations in the angular relationship of said sections of said boom relative to the support surface.

25 An assembly as set forth in claim 24 further including means operatively connected to said boom for engaging external loads of different magnitudes, said circuit means including means for varying at least some of said signals in response to changes in the magnitude of the load engaged by said means for engaging external loads.

26. An assembly as set forth in claim 25 wherein said circuit means includes means for generating a plurality of reference signals each of which is associated with one of said boom sections and is representative of the magnitude of the maximum permissible bending moment in the associated one of said boom sections, and means for comparing each of said signals which is representative of the bending moment in an associated one of said boom sections with the reference signal which is associated with the same boom section and for providing an output signal when a predetermined relationship exists between the signal representative of the bending moment in one of said boom sections and the reference signal associated with the same boom section.

27. An assembly comprising a boom having a plurality of telescoping sections for supporting an external load, means for moving said telescoping sections of said boom relative to each other to thereby vary the telescopic relationship between said sections and the length of said boom, means for varying the angular relationship of said boom to a support surface by moving said boom toward and away from the support surface, a sensor means operatively connected with said boom for sensing bending moment induced in a section of said boom under the combined influence of the external load and weight of said boom, first circuit means operatively connected to said sensor means for generating a plurality of load signals each of which is associated with a different one of said sections of said boom and is representative of the bending moment induced in the associated section of said boom by an external load, second circuit means for generating a plurality of boom signals each of which is associated with a different one of said sections of said boom and is representative of the bending moment induced in the associated section of said boom by the weight of said boom, and third circuit means connected with said first and second circuit means for generating a plurality of combined signals each of which is associated with a different one of said boom sections and each of which is representative of the bending moment induced in the associated boom section under the influence of the external load and the weight of the boom.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,586,8 ll Dated June 22, 1971 Inventor(s) Robert F. Griffin It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column t, line 18, formula l) change M w cosg+fl L )W c0s9 to --M =l w cos9+( l -L )W cos9--;

Line 26, formula (2), change M +M to --M =M +M Line 28, formula (3), change M =A1 w cosG to z M =1 W cosQ--; Line 30, formula ?4) change M =Al W cosQ-L W cos9 to --M =l w cos9-L W cos9-; Lines 36,

3 7, 38 and 39 of formula (5) printed as:

=l cos9+( 1 -L )W o0s9+luWucos9-L W cos9 1 -1 )W cosQ+lu(W )cosQ-Lqqcosg should read:

1 -L )w cos9+l (Wa+W )cose-Lz w cosg Line 42, formula (6) M =AM +lMW )cosg-Lqw cos 9 should read "M -=1 +l (w +w )cosg-Luw cos -q Line ML, formula (7') M =AM +l (W +W5)cosG-L W cos9 should read -M3B=M) +1 (W3-l-W +W5) 3OS9-L W3COS9-; Line 45, formula (8), M =AM +1 (W W +W )cos9-L cos9 should read FORM 90-1050 USCOMM-DC 60376-F'B9 {I U S GOVEHNMENT PRINTING OFFICE 1989 0-365-334 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,5 Sbrl Dated ne 2 1971 Robert F. Griffin PAGE 2 Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

(Page 2) Column 4 line 46, formula (9) M =AM +l (W +W +W +W5)cosQL W cos9 should read: -M =M ?+l (w +w +w +w +w )cosG-L W cosO--; Line #9, formula 10) M =A1 W cos9 should read --M =l W cos9--;

Line 52, formula l3) M l +l +l aZl )W cosG shouki read:

--M2Z=( 1 +1 +1 +1 )Wzcos9--; Line 5 formula 1n) M 1 +1 +1 aZl +1 )w cosQ should read:

lZ l 2 3 L; z

- -M1Z$( )WZCOSQ- Column 5, lines 8 and l t, "Khd 1E should read Column 6, lines l7, l8 and 19, formulas (32), (33) and E 2 13 should readE =E +E -E =M Column 7, line 31, "M should read "M line 32 "A I should read --A line 38, "A A should read 3 -A A n, (Cont.

FORM P0-105O (\0-69! USCOMM-DC 50376-F e9 i u 5 GOVERNMENT PRINTING OFFICE 19? 0-36G-33 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,58 ,8 4]. Dated June 22, 1971 Robert F. Griffin PAGE 3 Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 9, line 56, M -M should read --M =M -M In the claims:

Claim 10, line L change 11" to read --9-- Signed and sealed this 2nd day of May 1972.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOITSCHALK Attesting Officer Commissioner of Patents FORM PO105OUO'697 LJSCOMM-OC GOS'I'S-PBQ U 5 GOVERNMENT PRINTlNG OFFICE 19.9 DJ55-534

Claims

1. In combination with a boom which is subject to a substantial bending moment, a strain transducer, and means operatively connecting said transducer to the boom at a location effective to produce on the transducer a strain which is substantially a predetermined function of the bending moment on the boom, said predetermined function is a substantial linear function of the strain on the transducer with respect to the total bending moment on the boom due to its own weight and the weight of any load suspended from its outer end.

4. The combination of claim 3, wherein said boom has telescoping sections.

5. The combination of claim 3, and further comprising circuit means operative in response to the output signal of said transducer and in response to the individual lengths and weights of the boom sections to determine the actual bending momenT on each boom section.

9. An indicator system for use with a self-supporting boom having a plurality of boom sections in succession outwardly from its base and certain of which sections, at least, are extensible, said system comprising means for sensing the bending moment on the boom at a location thereon where the response of said sensing means is substantially linearly proportional to the actual bending moment at said location on the boom, an analog circuit including circuit elements operatively connected to provide signals which are substantially proportional to the lengths of the respective boom elements, the circuit elements which correspond to the extensible boom sections being variable in accordance with the individual extended lengths of the latter, said analog circuit also including circuit elements operatively connected to provide signals which are substantially proportional to the weights of the respective boom elements, and said analog circuit including means for combining the output signal of said sensing means and said boom section length signals and said boom section weight signals to provide for each boom section a signal substantially proportional to the actual bending moment thereon.

12. The combination of claim 11, and further comprising boom lift means operatively engaging the base section of the boom from below for lifting and lowering the boom, and means rigidly coupling said strain transducer means to the underside of said base in close proximity to its operative engagement by said boom lift means so that the strain measured by said strain transducer means is substantially linearly proportional to the total bending moment on the boom due to its own weight and the weight of any load suspended from its outer end.

15. The combination of claim 13, and further comprising means for producing reference signals proportional respectively to predetermined maximum safe bending moments for the respective boom sections, and means for comparing each of said reference signals against a signal proportional to the actual bending moment on the corresponding boom section.

16. The combination of claim 15, and further comprising means for producing a maximum safe tipping moment signal, and means for comparing said tipping moment signal against the signal proportional to the actual bending moment on the base section of the boom when the slewing angle of the boom exceeds a predetermined value while at the same time disabling the comparison between said actual bending moment signal for the base section and the corresponding reference signal which is proportional to the maximum safe bending load for the base section.

21. A method comprising the steps of changing the length of a boom for supporting an external load and having telescoping sections by varying the telescopic relationship between sections of the boom, changing the angular position of the sections of the boom relative to a support surface by moving the sections of the boom transversely to the support surface, sensing bending moment induced in a section of the boom under the combined influence of the external load and weight of the boom, generating as a function of the sensed bending moment a plurality of load signals each of which is associated with a different one of the sections of the boom and is representative of the bending moment induced in the associated section of the boom by the external load, generating a plurality of boom signals each of which is associated with a different one of the sections of the boom and is representative of the bending moment induced in the associated section of the boom by the weight of the boom, and producing a plurality of combined signals each of which is associated with a different one of the boom sections, each of said combined signals being a function of the load and boom signal associated with the same boom section as the combined signal and being representative of the bending moment induced in the associated boom section under the combined influence of the external load and weight of the boom.

22. An assembly comprising a boom having a plurality of telescoping sections, means for moving said telescoping sections of said boom relative to each other to thereby vary the telescopic relationship between said sections and the length of said boom, means for varying the angular relationship of said boom to the support surface by moving said boom toward and away from the support surface, and circuit means for producing a signal representative of the bending moment in said boom, said circuit means including means for varying said signal in response to changes in length of said boom and means for varying said signal in response to changes in the angular relationship of said boom to the support surface.

24. An assembly comprising a boom having a plurality of telescoping sections, means for moving said telescoping sections of said boom relative to each other to thereby vary the telescopic relationship between said sections and the length of said boom, means for varying the angular relationship of said sections of said boom relative to a support surface by moving said boom toward and away from the support surface, and circuit means for generating a plurality of signals each of which is associated with a different one of said sections of said boom and is representative of at least a portion of the bending moment in the associated one of said boom sections, said circuit means including means for varying at least some of said signals in response to changes in the length of said boom and means for varying at least some of said signals in response to variations in the angular relationship of said sections of said boom relative to the support surface.

25. An assembly as set forth in claim 24 further including means operatively connected to said boom for engaging external loads of different magnitudes, said circuit means including means for varying at least some of said signals in response to changes in the magnitude of the load engaged by said means for engaging external loads.