GB2031594A

GB2031594A - Monitoring forces in a load- handling boom

Info

Publication number: GB2031594A
Application number: GB7932113A
Authority: GB
Original assignee: Francaise du Ferodo SA
Current assignee: Valeo SE
Priority date: 1978-09-18
Filing date: 1979-09-17
Publication date: 1980-04-23
Also published as: FR2436376A1; FR2436376B1; DE2937735A1; GB2031594B

Abstract

An articulated handling boom 10 has a jib BII pivoted at B to a hoisting arm BI which in turn is pivoted at O to a chassis 11. The pivots B, O form force- sensors carrying strain gauges which are mounted so as to be sensitive only to shearing strains, and which are appropriately connected in the form of Wheatstone bridge circuits. The gauges are arranged to measure not the effects of a force FV in the plane of the mechanism but the bending of the jib BII and the bending and torsion of the arm BI which result from a lateral force at C. The strain gauges on pivot B are in planes parallel to the plane containing the axes of B and C. <IMAGE>

Description

SPECIFICATION Dynamometric device for monitoring stresses in a load-handling boom with articulated arms French Patent Application No. 75/33499 (published under No. 2,346,278) describes a dynamometric device for a load-handling boom-type assembly, which device employs an axle which serves as a pivot of articulation between two members and forms, by itself, a force sensor, this axle being fixed to one of the said members in a pre-determined angular orientation with respect to a given direction of measurement, and carrying, in essentially two parallel planes, two sets of strain gauges arranged to be sensitive only to shearing strains.

in the above mentioned French Patent Application, the boom of the unit in question is formed by a single hoisting arm; the load applied to this boom only acts along an approximately vertical axis, and the only purpose of the force-sensing axle employed is to make it possible to measure the torque reaction to which this unit is subjected because of this load.

The present invention relates generally to the application of a force-sensing axle of this type to the monitoring of at least some of the stresses to which a load-handling boom is subjected, which boom is formed successively of a hoisting arm, articulated on a chassis, and of a jib, which is articulated on the said arm, when this handling boom is coupled to a load which can act in any direction and, in practice, in a direction other than vertical.

In such a case, the force due to such a load has, overall, a component in a vertical plane and a component in a horizontal plane.

The first component causes a vertical bending of each of the constituent arms of the handling boom in question and, as is customary, it can be of value to monitor the torque reaction thereof, for example in order to employ limiting devices.

However, the second component causes a lateral bending, both of the jib and of the hoisting arm, and a twisting of the latter, which it is also of value to monitor in order to employ limiting devices.

According to the invention, with regard to the measurement of the lateral bending of the jib, a force-sensing axle forms the pivot of articulation between the hoisting arm and this jib, and this force-sensing axle is oriented so that the planes in which its strain gauges are located are approximately parallel to the plane which contains, on the one hand, the geometrical axis of the said force-sensing axle, and, on the other hand, the geometrical axis of the axle by means of which the handling boom is coupled to the load which is applied thereto.

By virture of this device and of the appropriate utilisation of the strain gauges, only the forces which are opposite in direction to one another, which result in the bending to be monitored, are taken into account; conversely, the forces which, on the other hand, are in the same direction are not taken into account.

Likewise, with regard to the measurement of the lateral bending of the hoisting arm, a force-sensing axle forms the pivot of articulation between this hoisting arm and the chassis, and this force-sensing axle is oriented so that the planes in which its strain gauges are located are approximately parallel to the plane which contains, on the one hand, the geometrical axis of the said force-sensing axle, and, on the other hand, the geometrical axis of the axle by means of which the hoisting arm is articulated on the jib.

Moreover, with regard to the measurement of the twisting of the hoisting arm, the corresponding force-sensing axle comprises, according to the invention, two other sets of strain gauges which are essentially arranged in planes which are approximately perpendicular to the above mentioned planes.

In fact, calculation shows that these strain gauges only take into account that component of the twisting force which does not result in simple lateral bending in the case of the hoisting arm.

Finally, with regard to the measurement of the torque reaction, this measurement is carried out, according to the invention, by monitoring, with the aid of a force-sensing axle forming a pivot of articulation, the total moment of the forces to which the handling boom in question is subjected, relative to the axle of articulation, on the chassis, of the jacking means acting on its hoisting arm, those planes of the said force-sensing axle in which its strain gauges are located being perpendicular to the plane which contains the geometrical axis of the axle by means of which the hoisting arm is articulated to the chassis.

Thus, according to the invention, three force-sensing axles suffice to monitor the lateral bending of each of the arms of the handling boom, the twisting the hoisting arm, and the torque reaction of the whole assembly.

In order that the invention may be more fully understood, embodiments in accordance therewith will now be described by way of example, with reference to the accompanying schematic drawings, in which Figure 1 is a view in elevation, of a load-handling boom to which a dynamometric device according to the invention is applied; Figure 2 is a longitudinal view, in section and to a different scale, of the jib of this boom taken along the line ll-ll of Figure 1; Figure 3 is a view, in transverse section and to a larger scale, of this boom taken along the line Ill-Ill of Figure 2; Figure 4 shows, on a larger scale, a detail of Figure 3; Figures 5 and 6 are views, in transverse section, along the lines V-V and VI-VI of Figure 3, respectively;; Figure 7 is an electrical diagram illustrating the connection of the strain gauges employed; Figure 8 is a view, in longitudinal section, of the hoisting arm of the handling boom in question, along the line VIII-VIII of Figure 1; Figure 9 is a simple diagram representing the handling boom in question; Figure 70 is an isolated view of one of the force-sensing axles employed, according to the invention, in this handling boom; Figure 11 is a view in transverse section, of this axle taken along the line Xl-Xl of Figure 10; and Figure 12 is a force diagram relating to the diagram of Figure 9.

Referring to the drawings, Figure 1 schematically illustrates a load-handling boom 10 which is articulated on a chassis 11 and is formed successively of a first arm Bl, referred to as the hoisting arm, which is articulated on the chassis 11 by means of an axle 0, and of a second arm B11, referred to as the jib, which is articulated on the above arm Bl by means of an axle B.

A handling boom 10 of this type can belong, for example, to any type of fixed or mobile unit having a bed which forms in this embodiment the chassis 11.

Various constructions of the handling boom 10 are possible and these do not form part of the present invention; the boom will not therefore be described in detail in this text.

It will suffice to specify that, for example, as shown, each of the arms B1 and B11 consists longitudinally of two parallel beams.

So that it can be operated, the handling boom 10 comprises, in the embodiment shown, a hoisting jack Vl, which is articulated on the chassis 11 by means of an axle A, and on the arm B1 by means of an axle D, and a jib jack Vll, which is articulated on the arm B1 by means of an axle E and on the jib Bll by means of an axle H.

It is simply for convenience that these jacks Vl and Vll are both considered as single jacks in the embodiment shown. In practice either or both of these jacks could be a multiple jack, for example a double jack, or could also be replaced by any other suitable jacking means.

At its free end, the jib Bll carries an axle C by means of which the handling boom 10 can be coupled to any load.

This results in the application, to this handling boom 10, of a force which can be resolved into a component FV, which is located in the mean vertical plane of this boom 10, in Figure land which possesses any orientation in this plane, and a component FH, which is located in the horizontal plane passing through the geometrical axis of the axle C, in Figure 2, and which itself possesses any orientation relative to the direction of elongation DLIl of the jib B11.

This horizontal component FH can itself be resolved into a lateral component FH1, which is approximately perpendicular to the direction of elongation D41 of the hoisting arm (sic) Bull, and a longitudinal component FH2, which extends approximately in this direction of elongation DL11.

Only the lateral horizontal component FH1 will be taken into account below, because it is this component which results in the bending to which the arms B11 and B1 are subjected, and in the twisting to which the arm B1 is subjected, as will become apparent below, the longitudinal horizontal component FH2 having no effect in this respect.

In order to measure the lateral bending to which the jib B11 is subjected because of the load applied to the axle C, the axle B, by means of which this jib B11 is articulated on the hoisting arm BI, forms, by itself, according to the invention, a force-sensing axle.

As shown in Figures 3 to 6, the axle B comprises, in the region of its ends, two lengths 13 and 13' of small diameter, each of these lengths of small diameter extending between two lengths having the same larger diameter, namely a median length 14 and two end lengths 15 and 15'.

By means of its median length 14, the axle B is engaged so as to pivot in a fork 16 which the beams FL, and FL'I of the hoisting arm B1 conjointly form at their ends.

By means of its end lengths 15 and 15', the axle B is fixed to the beams F41 and FL'II of the jib B", in a determined angular orientation specified below, by means of, for example, keys and keyways (which are not shown in the Figures).

Part of the fork 16 of the hoisting arm B, extends over the median length 14 of the axle B, and part extends above the lengths 13 and 13' of small diameter, of this axle; likewise, part of the beams FL and FL'11 of the jib B11 extends over the end lengths 15 and 15' of the axle B, and part extends above the lengths 13 and 13' of small diameter, of this axle.

At right-angles to its lengths 13 and 13' of small diameter, and approximately in two planes P1 and P2 parallel to its axial plane of symmetry P, which plane contains the geometrical axis of the axle C in addition to its own geometrical axis, in Figures 5 and 6, the axle B which forms a force sensor carries two sets of strain gauges J1 and J2, as explained in detail below.

For each plane P1 or P2, the sets of strain gauges J1 and J2 each comprise, in the embodiment shown, two groups of two strain gauges J and J', each group being respectively associated with the lengths 13 and 13' of smaller diameter, of the axle B.

Thus, in Figures 3 to 5, the end length 13 of this axle comprises, on a surface F, which extends approximately in the plane P1 and the ends of which (in the embodiment shown) overlap the lengths 15 and 14 of larger diameter, of the axle B, a group of two strain gauges J1A and J1B- The strain gauges are arranged so as to be sensitive only to shearing strains.

For example, as shown, the strain gauge J1A is inclined at 45", in a first direction, with respect to the plane which is perpendicular to the plane P and to the geometrical axis of the axle B, and the strain gauge J1B, which is also inclined at 45" with respect to the plane in question, but at 90 relative to the strain gauge J1A.

According to similar arrangements, the length 13, of small diameter, of the axle B carries, in the plane P2, a group of two strain gauges J2A and J2B arranged, in this case, on a surface F2 of this axle, and the length 13' of small diameter, of this axle carries, in this case on surfaces F'1 and F'2 respectively arranged in the planes P1 and P2, a group of two strain gauges J'1A and J'1B and a group of two strain gauges Jl2A and J'2B.

The surfaces F1, F2, F'1 and F'2 can be approximately plane; the surfaces can also be curved.

Regardless of the arrangements adopted above, it is evident that the strain gauges having the same index letter, namely A or B, have the same direction of inclination, and that the sets of strain gauges J1 and J2 are symmetrical relative to the axial plane of symmetry P.

The various strain gauges of the sets J1 and J2, explained in detail above, conjointly belong to one and the same Wheatstone bridge 18 on Figure 7.

Strain gauges working in the same manner must be arranged in the same arm of this bridge, whether a tensile stress or a bending stress is involved.

Thus, depending on the manner in which they are connected relative to one another, and/or on the direction of their inclination, which is imposed by the manner in which they are mounted on the axle B, these strain gauges can occupy various positions in the Wheatstone bridge 18.

In the embodiment shown, each arm of this Wheatstone bridge 18 comprises, in series, two strain gauges each belonging respectively to the two groups of one and the same set.

Thus, for example, in the case of any one of the arms of this Wheatstone bridge 18, the strain gauge J1A of a first group of the set J1 is in series with the strain gauge J'A which, since it belongs to the second group of this same set, is of opposite inclination, analogous arrangements being adopted for the other arms of this Wheatstone bridge.

As a result, if a reference tension V is applied to one of the diagonals of this Wheatstone bridge 18, a measurement tension M is obtained on the other diagonal of this bridge, which tension is in the image of the bending to which the jib B11 is subjected because of the load to which the handling boom 10 is coupled.

In fact, as is apparent from the force diagram shown in Figure 2, the lateral horizontal component FH1 of this load induces, at right-angles to the housings of the axle B at the surfaces FL11 and FL'II of the jib BII, reaction forces f1 which, since they are parallel to the direction of elongation D41 of this jib, are in opposite directions.

If the distance between these housings is denoted by el and the spacing between the geometrical axes of the axles B and C is denoted by 1 ll, it is possible to write:

As a result, the reaction force f11 at right-angles to one end of the axle B is directly proportional to the bending FH1 . 1it to which the jib B11 is subjected, and this bending can therefore be measured by measuring this force alone.

Now, from the arrangements adopted, it is apparent that the measurement tension M obtained on the Wheatstone bridge 18 is in the image of the reaction force fl; in fact, as illustrated in Figures 5 and 6, only the effects of those forces which are in opposite directions are taken into account, whilst the effects of those forces which are in the same direction are not taken into account.

Figures 5 and 6 show, by way of example, the reactions R11, due to the corresponding housings, of the vertical component FV of the load.

These reactions make the same angle 4 with the direction of elongation DL11 of the jib Bull.

Moreover, they are in the same direction.

In the equilibrium equation of the system, which is written as follows:

their effects cancel out.

In practice, taking account of the angular orientation, specificed above, which is adopted for the axle B forming a force sensor, the detection of lateral bending is optimal, the plane of symmetry P of this axle containing the direction of elongation Do11, parallel to which the shearing strains due to the reaction forces f1 are measured.

Via the axle B which forms their pivot of articulation, the jib B11 transmits the lateral horizontal component FH1 to the hoisting arm Ba, and this component is responsible, in the case of this hoisting arm Bl, not only for lateral bending, to which reaction forces fl correspond, as above, at right-angles to the housings of the axle 0 on the beams FL1 and FL'I of the hoisting arm B1, which forces, since they are parallel to the direction of elongation DL1 of this hoisting arm Bl, are in opposite directions, as shown in Figure 8, but also for a twisting torque due to the forces fil.

As illustrated in Figure 9, this twisting torque Cl can be resolved into two components C'l and C"1 having the following values:

in which equations ep is the angle made by the direction of elongation D41 of the jib Bll with the normal to the direction of elongation DLX of the hoisting arm BI, and ell is the spacing between the housings for the forces full.

The first component C'l creates, for the arm Bi, lateral bending which adds to the component.

According to the invention, the lateral bending to which the hoisting arm B, is thus subjected overall is monitored by converting the axle 0 to a force-sensing axle of the type described above, as illustrated in Figures 11 and 12, this axle 0, which therefore serves as a pivot of articulation between the hoisting arm B1 and the chassis 11, being fixed to the said hoisting arm as above, for example by means of keys which are not shown.

In other words, in order to measure this lateral bending, this axle 0 carries two sets of strain gauges J1 and J2 which are arranged so as to be sensitive only to the shearing strains, and which are essentially set up in two planes P1 and P2 of the axle 0, approximately parallel to the axial plane of symmetry of this axle, which plane contains, on the one hand, its geometrical axis, and, on the other hand, the geometrical axis of the axle B, each of the said sets of strain gauges comprising two groups of such gauges.

In Figures 10 and 11, the gauges in question of the sets J1 and J2 have been given the same references as previously.

Furthermore, also as previously, a force-sensing axle 0 of this type is associated with a Wheatstone bridge, each arm of which comprises, in series, two strain gauges each respectively belonging to the two groups of one and the same set (which is not shown in the Figures).

Moreover, according to the invention, in order to measure the component C"l, which forms, by itself, the twisting torque to which the hoisting arm Bll is subjected, the axle 0 comprises a further two sets of strain gauges K1 and K2 which are essentially arranged in planes Q, and Q2, approximately perpendicular to the above planes P1 and P2.

Since the arrangements adopted for this second system of strain gauges are analogous to the above arrangements, they will not be described in greater detail in this text, and the same will apply to the corresponding Wheatstone bridge.

However, Figures 10 and 11 schematically represent the positioning of the corresponding strain gauges K1A, K1B, K'1A, K'1B, K2A, K2B, K'2A and K'2B In addition, according to the invention, in order to measure the torque reaction, that is to say in order to measure the total moment due to the various forces acting on the handling boom 10, the axle A by means of which the hoisting jack Vl is articulated on the chassis 11 is itself an axle forming a force sensor.

The force diagram of Figure 12 shows the forces in question, which are as follows: FV; FG1, it being assumed that the mass of the hoisting arm B1 is concentrated at the centre of gravity G1 of this arm; and FG11, it being assumed that the mass of the jib B11 is concentrated at the centre of gravity G11 of this jib.

The equilibrium of the system about the geometrical axis of the axle A makes it possible to write the following relationship: FV.1 +Gl.1GI+G.l.1GIiFA.d=O in which 1 is the distance between the geometrical axis 0 and the component FV of the load, 1 G1 and 1 G11 are the horizontal distances between this axis and the corresponding centres of gravity G1 and Gull, d is the distance between the geometrical axes of the axles 0 and A, and FA is the component, in the direction perpendicular to the direction OA, of the reaction of the system at the point A.

From the above relationship, it is apparent that the total moment to be measured is directly proportional to the component FA of the reaction at A, and that it therefore suffices to estimate this component.

This estimation can be carried out by selecting a force-sensing axle, according to an arrangement described above, in the case of the axle A, the planes of this force-sensing axle in which its strain gauges are located being perpendicular to the plane which contains the geometrical axes of the axles 0 and A.

Preferably, according to an arrangement which is not shown, each force-sensing axle is provided, externally, with a reference mark such as a simple radial line on one of its corresponding end transverse edges, which makes it possible to monitor the angular orientation thereof.

Of course, the present invention is not restricted to the embodiments shown, but encompasses any modified embodiment, in particular as regards the strain gauges, which can each be double or multiple gauges.

Claims

1. A stress-monitoring dynamometric device for a handling boom comprising successively a hoisting arm, which is articulated to a chassis, and a jib, which is articulated to the said arm, which device is of the kind comprising an axle serving as an articulation pivot between two members and forming, by itself, a force sensor, said axle being fixed to one of the said members in a determined angular orientation with respect to a given direction of measurement, and carrying, in essentially two parallel planes, two sets of strain gauges which are arranged so as to be sensitive only to shearing strains, wherein for the measurement of the lateral bending of the jib due to the load to which the handling boom is coupled, said force-sensing axle forms the pivot of articulation between the hositing arm and the jib, and this force-sensing axle is oriented so that the planes in which its strain gauges are located are approximately parallel to the plane which contains, on the one hand, the geometrical axis of the said force-sensing axle, and, on the other hand, the geometrical axis of l 'le axle by means of which the handling boom is coupled to the load which is applied thereto.

2. A stress-monitoring dynamometric device for a handling boom comprising successively a hoisting arm which is articulated to a chassis, and a jib which is articulated to the said arm, which device is of the kind comprising an axle serving as an articulation pivot between two members and forming, by itself, a force sensor, the said axle being fixed to one of the said members in a determined angular orientation with respect to a given direction of measurement, and carrying, in essentially two parallel planes, two sets of strain gauges arranged so as to be sensitive only to shearing strains, wherein for the measurement of the lateral bending of the hoisting arm due to the load to which the handling boom is coupled, said force-sensing axle forms the pivot of articulation between this hoisting arm and the chassis, and this force-sensing axle is oriented so that the planes in which its strain gauges are located are approximately parallel to the plane which contains, on the one hand, the geometrical axis of the said force-sensing axle, and, on the other hand, the geometrical axis of the axle by means of which the hoisting arm is articulated to the jib.

3. A dynamometric device according to Claim 2, wherein for measuring the twisting of the hoisting arm, said force-sensing axle comprises two other sets of strain gauges which are essentially arranged in planes which are approximately perpendicular to the above-mentioned planes.

4. A dynamometric device according to any one of Claims 1 to 3, wherein for measuring the total moment of the forces to which the handling boom is subjected, relative to the axle of articulation on the chassis of the jacking means acting on its hoisting arm, this axle forming a force sensor, those planes of the said force-sensing axle in which its strain gauges are located are perpendicular to the plane which contains the geometrical axis of the said force-sensing axle and the geometrical axis of the axle by means of which the hoisting arm is articulated to the chassis.

5. A dynamometric device according to any one of Claims 1 to 4, wherein said force-sensing axle carries externally a reference mark which makes it possible to monitor the orientation thereof.

6. A stress monitoring dynamometric device substantially as hereinbefore described with reference to the accompanying drawings.