BACKGROUND ART Load sensors of various kinds are well-known. Typically, they incorporate a so-called "load sensing gauge", which is essentially a length of resistive wire having a predetermined resistance. The gauge is placed in such a manner that it may be stressed either in tension or in compression. When stressed in tension, the resistivity of the wire increases. When placed in compression the resistivity of the wire decreases.

The principles of such load sensors have been well- known for many years. Such load sensors are used in many applications. The load sensing gauges themselves may be relatively small, typically having dimensions of perhaps one centimetre square. However, the incorporation of such load sensing gauges in a piece of equipment, which is capable of being stressed by a weight or mass, and the electrical connection of such load sensor sensing gauges, so that they produce meaningful information presents certain problems. In many cases, the entire load sensor comprising the gauges themselves, and the mounting upon which they are mounted must be so arranged that it can be placed in a position where it is subjected to the stress or weight of the mass, without interfering with the operation of the equipment for which it is designed. In addition, for example, if such load sensor should fail, it is essential that it be so designed that the equipment itself can function even though the load sensor itself is no longer operating.

Preferably, such a load sensor should be provided with a large excess capacity in terms of stress or mass, so that the likelihood of failure is extremely low. This in turn

imposes certain limitations on the design of such a load sensor, since the objective is to permit the load sensor mounting to move in response to the stress or mass, in proportion to the actual intensity of the stress or the weight of the mass, and thus provide a progressive measurement of the actual stress or mass. Consequently, the design of such a load sensor unit becomes a matter of in the first place designing a unit which is strong enough to resist stresses or masses substantially in excess of the rated or normal duty cycle, and which will yet yield, in response to stresses or masses within the normal duty cycle, so as to produce an effect on the load sensing gauges themselves, which can be detected and read out on measuring equipment. These various problems become intensified, when it is necessary to incorporate such a load sensing unit in a restricted space, and in a piece of equipment with a predetermined existing design which substantially cannot be changed. For example, a load carrying apparatus,such as a pallet lift truck is typically used in industry for moving pallets loaded with goods from place to place. The two forks of the pallet truck are inserted into a space underneath a pallet. Typically, this space is no more than about 8.5 to 9 centimetres (about 3.5 inches). The forks must be adapted to be inserted beneath such a pallet, and must at the same time be strong enough to lift the pallet and its load of goods, and transport it to wherever it is required. Such load carrying apparatus is usually designed simply to lift a predetermined maximum load and move it. Weighing the load is usually performed on some kind of weigh scale, which involves another operation.

For all of these reasons, it is desirable to provide such a pallet truck or other load lifting apparatus with a load sensing system, which is capable of weighing the load on the forks, so that the operator can obtain an accurate

reading of the weight of the load, directly from the forks of the apparatus.

Some pallet trucks are manually operated to move relatively small loads. However, other load lifting apparatus may be operated by prime movers, and move much heavier loads. In all these cases it is desirable to incorporate an accurate form of load sensing for the operator to weigh the load on that particular apparatus, without moving to, and from, a separate weigh scale. As explained above however such forks must fit within the space provided beneath a pallet. The design of load sensing units to fit into such forks, without increasing the vertical height of the forks, presents substantial problems. The forks themselves must be designed and structured to have sufficient strength to lift a predetermined load. In order to provide such strength, the forks must have certain dimensions. For example in typical cases the forks will have dimensions equal to about 7.5 to 7.75 centimetres in height. Bearing in mind that the clearance beneath a typical pallet is between 8 and 8.5 centimetres, it will be appreciated that there is only a restricted space in which to incorporate additional equipment, such as load sensors, in the forks.

It is thus apparent that in order to provide load sensors, particularly load sensors designed for use in such low clearance equipment, the design of the load sensor must be highly refined so that it may be fitted within the existing equipment without increasing its dimensions.

DISCLOSURE OF THE INVENTION With a view to overcoming the various problems described above, the invention comprises a load sensing unit which in turn comprises a plate portion adapted to be secured in position, in a load supporting apparatus, a tongue portion connected to said plate portion, a plurality of load sensing gauges secured to said tongue portion, at

least two of said gauges being adapted to be placed in tension by a load on said tongue portion, and at least two of said gauges being adapted to be placed in compression by a said load on said tongue portion, electrical connection means connecting said gauges, whereby said gauges in tension, are connected in series with said gauges in compression on opposite sides of a bridge circuit, load bearing means on said tongue portion, whereby a load may be applied to said tongue portion, to cause deflection thereof, deflection of said tongue portion in turn placing at least two of said strain gauges in tension, and at least two of said strain gauges in compression, and electrical circuit means connected to said bridge circuit, whereby to receive signals from said strain gauges, and signal responsive means responsive to signals from said strain gauges in tension, and to signals from said strain gauges in compression, and to generate load signals responsive thereto.

The invention further comprises the provision of a load sensing assembly comprising an elongated bar of metal, said elongated bar of metal having a load sensing unit as aforesaid located at each end thereof.

The invention further comprises such a load sensing unit and incorporating groove means formed in said tongue portion transversely thereof, and electrical connection means extending between said strain gauges, running in said groove means, and further incorporating connection groove means in a portion of said plate means, for containing electrical connections from said strain gauges, to said signal responsive means.

The invention further comprises such a load sensing unit and wherein there are two said groove means extending transversely of said tongue portion, and wherein there are four said load sensing gauges, a first pair of said load sensing gauges being located in a first one of said groove means and a second pair of said load sensing gauges being located in a second one of said groove means, and connection channel means extending between said first and

second groove means, for connecting said first and second pairs of strain gauges.

The invention further comprises such a load sensing unit and further including an abutment device connected to said tongue portion, and adapted to extend upwardly of said tongue portion, for engagement by a load or mass.

The invention further comprises such a load sensing unit and wherein said tongue portion, when subjected to a load, is adapted to flex downwardly whereby to place said first pair of strain gauges in tension, and is adapted to place said second pair of strain gauges in compression, when subjected to a load on said tongue portion.

The invention further comprises a load carrying apparatus, adapted to lift a load, and wherein said apparatus incorporates at least carrying means (eg forks) adapted to be inserted under a pallet, and including load sensing units as aforesaid incorporated in said forks.

The invention further comprises such an apparatus and wherein the carrying means are formed of generally channel- shaped construction, having webs with upper and under sides, and side walls extending downwardly from said webs, and wherein said load sensing units are secured to said undersides of said webs between said channel walls, and including opening means in said webs, and said abutment devices on said load sensing units extending upwardly through said webs, whereby to receive a load on said forks. The invention further comprises such an apparatus, and wherein the forks have a predetermined length, and including load sensing assemblies extending for a substantial portion of said length, and having said load sensing units and abutment devices on each end of each of said load sensing assemblies, whereby there are four said load sensing units, and four said abutment devices extending upwardly through said webs, thereby engaging a said load at four points.

The invention further comprises such an apparatus and wherein said forks are made of sheet metal, and wherein said load sensing assemblies are formed of rigid elongated

bars of metal, said rigid elongated bars of metal being bolted to the underside of respective said webs, thereby substantially reinforcing the same, and reducing flexing of said forks due to loads placed thereon. The invention further comprises such an apparatus, and including instrument panel means supported at one end thereof, and electrical connection means connected between said load sensing units and said instrument panel means, whereby said instrument panel means is adapted to provide a visual indication of the load on said forks, when a load is supported thereon.

The invention further comprises such an apparatus and including a tongue member which when subjected to a load, is adapted to deflect and place a first pair of gauges, in compression and to place a second pair of gauges, in tension.

The invention further comprises such an apparatus, and including bar spacer means formed on one side of an elongated bar of metal, said spacer means terminating short of said load sensing unit, and further including tongue spacer means on said tongue, on a side thereof opposite to said bar spacer means, said tongue spacer means being located at the free end of said tongue, and fastening means securing said free end of said tongue, and said tongue spacer means against movement, while leaving the remainder of said tongue portion free to deflect, whereby a load placed on said bar means will cause deflection of said bar means and of said tongue.

The invention further comprises such an apparatus and wherein the tongue spacer means is located below the tongue at a free end thereof, thereby restraining the free end against deflection, while permitting the remainder of the tongue to deflect, deflection of the tongue by a load placing a first pair of gauges, in first groove means, in compression, and said second pair of gauges, in said second groove means in tension.

The invention further provides a load carrying apparatus of the type described, and wherein there is a

load sensing assembly on each of the forks thereof, each having load sensing units at each end thereof, and spacer means located beneath respective said tongue members of each of said load sensing assemblies, spacing the same above respective said forks, and intermediate spacer members located above said plate portions of said load sensing assembly, and cover means fastened over said intermediate spacer means, whereby a load placed on said cover means is transmitted through said intermediate spacer means to said plate members intermediate said tongue members, thereby causing said load to be applied to said plate members intermediate said load sensing assemblies, and causing downward flexing of said plate members, and portions of said tongue members, while said ends of said tongue members supported on said lower spacers are maintained stationary.

The various features of novelty which characterize the invention are pointed out with more particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an upper perspective view of a load sensing assembly, having two load sensing units in accordance with the invention;

Figure 2 is an upper perspective illustration of one of the load sensing unit of Figure 1;

Figure 3 is an electrical circuit diagram illustrating the circuits of the load sensing gauges of one of the load sensing units of Figures 2;

Figure 4 is a schematic perspective illustration of the operation of the load sensing unit of Figure 2 when subjected to a load;

Figure 5 is a perspective illustration of a hand operated load carrying apparatus (partially cut away) and incorporating the load sensing assemblies of Figure 1;

Figure 6 is a section along the lines 6-6 of Figure 5; Figure 7 is an exploded perspective illustration of a fork of an alternate form of load carrying apparatus;

Figure 8 is a section along the line 8-8 of Figure 9;

Figure 9 is a section along the line 9-9 of Figure 8;

Figure 10 is a section along the line 9-9, showing the loaded position;

Figure 11 is a perspective of the load cell of Figure 10, also in the loaded position, and,

Figure 12 is a perspective of a further alternate form of load sensing unit. MODES OF CARRYING OUT THE INVENTION

Referring first of all to Figure 1, a load sensing assembly is indicated generally as 10. It will be seen to comprise an elongated rigid bar of metal 12. Preferably the metal is of high tensile steel at least one half inch in thickness, in the case of the present application, and having a plurality of securement holes 14 therealong whereby it may be secured in position where desired.

At each end of the bar 12 there is located a load sensing unit 16-16. This form of construction is particularly suited to incorporation in the forks of a typical pallet truck (Figure 5) as will be described later.

Referring now to Figure 2, a load sensing unit 16 will be seen to comprise two side mounting plates 20-22, and a central tongue 24. The side mounting plates 20 and 22 and the tongue 24 in this embodiment are formed out of a single piece of bar stock and are partially separated from one another by two severance slots 26-26, terminating in generally cylindrical recesses 28-28.

In this way, the tongue 24 is rendered movable relative to the mounting plates 20-22 and bar 12.

Referring now to Figure 2, the tongue 24 will be seen to be provided with two generally transverse recesses or grooves 30-32. The grooves are parallel to one another, an

extend into the mounting plates 20-22 merely for the sake of convenience in machining.

An axial junction-groove 34 extends between transverse grooves 30-32. A load bearing spacer 35 (Figure 4) is secured at the end of tongue 24.

An electrical connection groove 36 in plate 22 communicates with one end of groove 30 for reasons to be described below. Within the groove 30 of the tongue 24, there are located two load sensing gauges 38-40.

Within the groove 32 in the tongue 24 there are located a further two load sensing gauges 42-44.

In this embodiment, the two gauges 38-40 are adapted to be placed in tension, and the two gauges 42-44 are adapted to be placed in compression as will be described below.

These four gauges are connected, substantially as shown in Figure 3, so as to provide what is known as a "wheatstone bridge" circuit 45.

This type of electrical circuit 45 has been well-known for many years. It consists of four resistances, arranged in pairs in series with one another, and at the connections between one pair of resistance an electrical current is supplied, and at the connection between the opposite pair of resistances the negative side of the same electrical circuit is connected.

Between the two pairs of resistances in each case, connections are made to some form of signal reading device. Such a signal reading device may be a digital read out, or for example maybe a moving coil device, having a swinging needle.

When all of the resistances are equal, on all four sides of the circuit, then current will flow from one side to the other, but there will be no signal supplied to the signalling device which will then read zero.

However, when the resistances change, then current will flow to one side of the signalling circuit, and

current will return from the other side of the signalling circuit. This will then cause the signalling device to deliver a reading.

Such circuits have been known for very many years and are fully described in text books of electrical engineering, and require no special understanding for the purposes of the invention.

In the present case, electrical current is supplied to the gauges 38, 40, 42, 44, in the bridge circuit 45, of Figure 3, through connecting wires 46 and 48.

The signal device is connected to the gauges 38, 40, 42, 44, by the wires 50 and 52.

The load sensing gauge 38 is thus connected in series with the load sensing gauge 44, and the load sensing gauge 42 is thus connected in series with the load sensing gauge 40 to the electrical current connections 46, 48.

The respective bridge circuits for the respective units 16 are connected in parallel to a signal readout instrument described below. Referring now to Figure 4, this is a pictorial illustration of the deflection of a tongue, when subjected to a load.

It will be seen that the two grooves 30-32 are spaced apart from one another and extend transversely from side to side of the tongue 24.

It will be seen that, as illustrated, when subjected to a load, the tongue 24 is deflected in an S-shape in section. The tongue 24 behaves in this way due to the characteristics of the metal, and the formation of the grooves 30 and 32, which, in effect, restrict the deflection into two axes, or an S-shaped curve. It will of course be appreciated that the degree of deflection of the tongue, shown in Figure 4 would generally not occur in practice. The limit of deflection will be reached much earlier as will be described below. However, for the purposes of illustrating the operation of the invention, the deflection of the tongue in Figure 4 has been greatly exaggerated.

- li ¬ lt will be seen that the two strain gauges 38-40 in the groove 30, when subjected to a load are placed in tension. It will also be seen that the two strain gauges 42-44 located in the groove 32 when subjected to a load, are placed in compression.

From the explanation already given in the Figure 3, and from an understanding of Figure 4, it will now be seen that when a load is applied to the tongue 24, the two strain gauges 38 and 44 on the one side of the bridge, will be place respectively in tension and in compression. At the same time the two strain gauges 42 and 40 on the other side of the bridge will be placed respectively in compression and in tension.

It will thus be understood that the resistance of the strain gauge 38 increases whereas the resistance of the strain gauge 44 decreases. It will also be understood that the resistance of the strain gauge 42 decreases while the resistance of the strain gauge 40 increases.

Since the current through the strain gauges connects from 46 to 48, it will thus be seen that current will flow through the strain gauge 42, and will be resisted by the strain gauge 38, since the resistance of the strain gauge 38 is higher and the resistance of the strain gauge 42 is lower. Similarly, it will be seen that the return current through the wire 48, will flow through the strain gauge 44, having a lower resistance and will be resisted by the strain gauge 40 having a higher resistance.

Thus current will flow in the signal connection wire 50 and 52.

It will of course be appreciated that the nominal resistances of the strain gauges themselves may be in the region of, for example 350 ohms. A change of one or two ohms upwardly, and one or two ohms downwardly, between respective gauges 38 and 42, and between respective gauges 40 and 44, will be proportional to the degree of deflection of the tongue 24 in response to the force.

However, in the design of such strain gauges, even these relatively minor changes in resistance, will provide a direct read out of the actual load applied to the tongue. Signal reading equipment such as digital read out devices or moving coil devices, at the present time, are entirely adequate to detect such changes, and will provide an accurate read out of the actual load, over all reasonable working ranges of a particular device.

Referring now to Figures 5 and 6, it will be seen that the load sensing assembly as illustrated in Figure 1, may be incorporated in a load carrying apparatus, such as the forks of a pallet truck indicated generally as 60 so as to function as a weigh scale. Typically such a pallet truck will have a pair of forks 62-62, connected to a cross-frame 64. The cross-frame 64 may be connected to a heavy duty pallet truck and prime mover (not shown) . However, in the present case the cross member 64 is connected simply to an operating handle 66. Wheels 68-68 are located underneath the forks 62-62, and further wheels 72 are located underneath the cross members 64. By use of suitable controls on the handle 66 (not shown) the forks may be first of all inserted underneath the clearance beneath a typical pallet (not shown) and the forks may then be raised, so that they lift the pallet off the floor. The pallet is then rendered mobile, and can be dragged or pushed by operation of a handle 66, while being supported on the forks 62.

All of this is well-known in the art, and requires no special description. For the purposes of the present invention however load sensing assemblies 10, as illustrated in Figure 1, are incorporated in each of the forks 62 for weighing a load.

Reference may be made to Figure 6, showing the cross- section of one of the forks 62. It will be seen to comprise a first channel portion, comprising side walls 74- 74, and a cross-member 76, and a second channel comprising side walls 78-78 and a cross-member 80.

The side walls 74-74 support the wheels 68 (Figure 5) .

Located beneath the cross wall 76, extending between the side walls 74, there is located the load sensing assembly 10. The load sensing assembly 10 is secured by bolts 82 or other suitable attachment devices, and extends the length of the cross wall 76.

Cross wall 76, is formed with openings 84, at each end registering with spacers 35 on tongues 24.

The tops of spacers 35 register with and extend through respective openings 84 (Figure 6) and engage the undersides of cross walls 80.

Thus when a load is applied to the forks 62 of the pallet truck, the load first of all sits on the cross walls 80. Since there are four load sensing units 16, one at each end of each bar 10, the load is thus shared between the four load sensing units.

At the same time, it will be appreciated that the load sensing assemblies 10, extend substantially the full length of the cross walls 76, and substantially reinforce the same rendering them rigid from end to end. This is an important feature of the invention, since if any flexing takes place, when a load is applied to the forks, the load sensing units will not provide an accurate read out.

For the sake of the convenience of the operator, a pedestal 86 is secured on cross member 64 of the pallet truck 60. On top of the pedestal 86, there is an instrument panel 88. The instrument panel 88 will contain any suitable signal responsive equipment indicated generally as 90. The operator of the pallet truck will thus immediately be given an accurate reading of the load. The operation of the devices is believed to be self- evident from the foregoing description.

In this way the load carrying apparatus, in this case the pallet truck can thus serve as a mobile weigh scale, enabling pallet loads to be weighed and replaced, or moved , in one operation.

While the invention has been illustrated in the embodiment described above, in the case where the plate member 12 is held secured, and the tongue members 24 are

free to move, it will be appreciated that an essentially reverse situation will also be capable of producing similar results.

Thus, it is permissable to leave the plate portions 12 of the load sensing assembly 10 free to flex, and to secure only the end portions of the tongues 24. This alternate embodiment is illustrated with respect to Figures 7, 8, 9, and 10.

In this embodiment, a fork of a typical load carrying apparatus (not shown) is illustrated generally as 100. In this case, for reasons of construction, it is considered desirable to locate the plate member 102 (only one of which is shown) , above the forks 100, rather than underneath, as was illustrated in the case of Figures 5 and 6 above. A cover channel 104 is located over the plate member 102 on respective forks 100.

Referring now to Figures 8 and 9, it will be seen that each plate member 102 has load sensing units 106-106 at each end similar to the load sensing units 16 of the embodiment of Figures 1 through 6. Between the two load sensing assemblies 106, the plate member 102 extends, similar to the plate member 12 in the embodiment of Figures 1 through 6.

The load sensing units 106-106 are formed with tongue members 110 (Figure 7) similar to the tongue members 24 of the embodiment of Figures 1 through 6.

Each of the tongue members has grooves and strain gauges located therein, wired in the form of a bridge circuit, all as described in the embodiment of Figures 1 through 6. The various grooves and strain gauges in the tongue members 110, may therefore be assumed to have the same references as the grooves and strain gauges in the embodiments of Figure 1 through 6, and the details are therefore omitted, since it would amount to duplication of the description. Further description of these members is omitted from this description for the sake of clarity.

As explained, however in this embodiment, the flexing of the tongue members 110 of the load sensing units 116

takes place in essentially the opposite manner from that described in association with Figures l through 6.

For this purpose each of the load sensing units 106- 106 has tongues 110, and side plate portions 112-112 (Figures 9 and 10) .

The end portions of the tongues 110 are supported from beneath by respective tongue spacer members 114-114, which are in turn secured on the upper surface of each of the forks 100, in spaced apart relation. It will thus be seen, that a force applied to the centre of the plate or bar portion 102, will be unsupported by the fork 100, and will thus cause the centre of the plate or bar 102 to bow downwardly (as shown in phantom in Figure 8) . In order to apply force to the portion of the plate or bar member 102, between the two load sensing units 106-106, upper bar spacer members 116 are secured on top of plate member 102. Bar spacers 116 are the same length of plate member 102, and but they do not overlap the tongues 110, for reasons to be described below. Bars 116 extend along either side of tongues 110, over side plate portions 112.

The cover 104, which is typically of generally channel shaped cross section is secured by bolts 118 which pass through cover 104 and spacers 116 and into the intermediate portion of plate member 102.

Bolts 120 pass through the ends of tongue members 110 and tongue spacers 114 into the forks 100.

The operation of this device is best understood with reference to Figures 8, 9, 10, and 11. It will be seen that in Figures 8 and 9, the

"unloaded" position is illustrated.

In this case the plate member 102 is planar, and is spaced, unsupported, above the respective fork 100.

In the loaded condition, illustrated in phantom in Figure 8, and also illustrated in section in Figure 10,and in Figure 11 the plate member 102 will be seen to be bowed downwardly, between the two lower tongue spacers 114-114. In the exaggerated position shown in Figures 10 and 11, the

cover channel can be seen almost contacting the tongues 110, although this position would seldom occur in practice. It will be appreciated that in this case, each tongue flexes in an upwardly curved shape rather than downwardly. In this case, again, one pair of strain gauges will be placed in tension and the other pair of strain gauges will be placed in compression, although the pairs in fact will be the opposite way around as compared with the illustration in Figure 4. The placing of the pairs of strain gauges respectively in tension and in compression, will cause current to flow in the respective bridge circuits, in the manner described above, and this in turn will provide a readout of the load, also in the manner described above. It will thus be seen that the load sensing assembly of the invention may be used as it were "either way round", that is to say, either with the tongues being flexed downwardly by the load, or alternatively with the plate portions being depressed downwardly and the ends of the tongues held rigid. In either case a reading of the load is provided.

A further form of load sensing unit 130 is shown in Figure 12. In this case the tongue 132 comprises the full width of bar 134. Grooves 136-136 extend from side to side of tongue 132, and are connected, by groove 138. In this example, an upper spacer 140 is secured to the end of tongue 132. The bar 134 would be secured against flexing (by means not shown) , and the full width of tongue 132 would deflect under load. However this embodiment could be reversed as in Figures 8,9,10, and 11. The foregoing is a description of a preferred embodiment of the invention which is given here by way of example only. The invention is not to be taken as limited to any of the specific features as described, but comprehends all such variations thereof as come within the scope of the appended claims.