GB2080553A - Weighing apparatus - Google Patents

Abstract

Apparatus for weighing a load comprises a composite member in which a strain gauge is located so as to be subjected to a strain induced in the composite member by the load. Signals from strain gauges A1, A2, etc are sent to receiver means, such as analogue-to- digital converter 84 which converts the signal for transmission to display means, such as a micro-processor 81, which provides a visual or audible indication of the applied load on the composite member. The composite member may be, or form part of a suspension spring of a vehicle so that the signals represent the load on an axle of the vehicle, which is then registered on the display means. Individual indication of the load applied to each of several composite members may be provided, or a selected combination of the loads may be indicated. <IMAGE>

Description

SPECIFICATION Weighing of loads This invention relates to the weighing of loads and comprehends the use of a member of composite material, that is to say a member which is manufactured from two or more materials which are combined to form the member.

The present invention consists in apparatus for weighing a load comprising, in combination, a composite member which in use is subjected to a load which induces a strain in at least a part thereof, a strain responsive member located and held within the part thereof in which a strain is induced and orientated so as to be subjected to the strain, signalling means adapted to communicate a signal from the strain responsive member to receiver means, which signal is a function of a strain detected by the strain responsive member consequent on the application of a load to the composite member, and means to communicate the said signal to a display means which display means provides an indication of the load applied to the composite member.

The strain responsive member may be located and held within the member of composite material (hereafter referred to as "the composite member") so as to respond, for example, to a tensile, compressive or torsional strain (or any combination of these) in the composite member.

In a composite member which in use is subjected to a load which induces a bending moment in a part thereof resulting in a strain over that part, the strain responsive member is located and held within the part in which a bending moment is induced and arranged so that it does not lie on the neutral plane of the composite member when loaded.

The composite member may have a second strain responsive member located and held within it in proximity to the strain responsive member (the first strain responsive member), and second signalling means may be provided to communicate to the receiver means a signal (the second signal) from the second strain responsive member such that the resultant or summation of the first and second signals taken together is a function of a strain detected by the first strain responsive member, or of strains detected by the first and second strain responsive members. The first and second strain responsive members may comprise strain gauges spaced longitudinally of the composite member in the same longitudinal plane through the composite member and oriented in the same direction.

The strain gauges may be mounted on a carrier strip or incorporated in a printed circuit whereby they are accurately located relative to one another and the carrier strip or printed circuit is bonded into the composite member.

The receiver means may be arranged to amplify the said signal or the resultant signal, as the case may be, for transmission to the display means.

The composite member may be made of, or may include curved fibre reinforced resin. It may comprise three or more elements which are bonded tonofhor tz/n ni itpr aIamRnfSt and an inner element between them. Each, or one of the, outer elements may, for example, be a metal leaf spring or may comprise fibres of metal, carbon, glass orthermoplastic material (or any combination of these) incorporated in a matrix of cured resin. The inner element may be of cured fibre reinforced resin, for example glass or jute fibre. The three elements may be co-extensive over all, or most, of their length.

The composite member may be encased in a thermoplastic or resilient covering for protective purposes. This cover may, for example, be of rubber or polyurethane, in paint or plastic form, polyethylene or polypropylene. If metal spring leaves are used in the composite member they may be exposed, or embedded in a protective covering.

Where two or more strain responsive members are contained within the composite member they may be in the same plane, for example horizontally or vertically, or in different planes, and they may be orientated in the same direction or in different directions.

Preferably the strain responsive member or members are orientated in the direction of strain in the composite member.

The receiver means may be arranged to receive signals from the strain responsive member or members in a plurality of composite members whereby the indication represents a summation of the loads applied to each of the composite members.

When the receiver means is arranged to receive signals from strain responsive members in a plurality of composite members selection means are preferably provided whereby individual indication of the load applied to each composite member, or to a selected combination of the composite members, may be obtained.

The composite member may be relatively flexible, for example in the form of a spring, or relatively inflexible as in, for example, a press tool or a replacement for a conventional load cell.

The indication provided by the display means may be visual or audible.

Apparatus in accordance with the invention may be included in a vehicle. The or each composite member of the apparatus may then, for example, be, or form part of, a suspension spring of the vehicle, such that a load on the spring can be measured by the strain induced in the or each composite member by the load.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a side elevation of a flexible composite member in the form of a single leaf vehicle spring, Figure2 is a plan view from above of the spring of Figure 1, Figure 3 is a section through the spring showing two strain responsive members which are in the same longitudinal plane and in the same orientation.

Figure 4 is a section on line A-A of Figure 3, Figure 5 is a section through a connecting block, Figure 6 is an electrical circuit diagram, and Figure 7 is a further electrical circuit diagram.

Referring to Figures 1 to 5 of the drawings, the spring comprises a composite member 1 with an eye end fitting 2, which may be of forged steel, secured to the upper surface at one end 3 by through bolts 4 and nuts 5 which clamp against a steel pressure plate 6 on the lower surface of the member.

Intermediate the ends of the member 1 acetal bearing pads 7 are located by a bolt 8 and nut 9 on the upper and lower surfaces of the member. A hardened steel rubbing plate 11 is bonded to the upper surface of the composite member 1 at its other end 12.

The composite member 1 may be made of three elements in a known manner. These comprise upper and lower elements of one or more superimposed strips of pre-impregnated longitudinally extending carbon fibres, or a mix of carbon and glass fibres, and an inner element of one or more superimposed strips of pre-impregnated glass fibres. During laying up of the pre-impregnated strips two strain gauges 13, 14 and their leads 13a, 13b, 14a, 14b are introduced into the active length of the spring, that is to say in that part of the spring which experiences a bending moment on the application of a load. The gauges 13, 14 are positioned at a predetermined distance apart and away from the neutral axis 15 of the member 1. The leads 13a, 13b, 14a, 14b extend to the end 12 of member 1.

The laid-up composite member is cured in known manner by hot press moulding with the plate 11 located in the tool so that it is bonded to the composite member during curing. Alternatively, this plate may be secured by adhesive after curing.

A connector socket, not shown, is secured to each wire after curing of the composite member and an insulating block 16 is fitted to retain these sockets whereby a plug connector with multicore cable may be inserted to carry signals from the strain gauges to display means which may comprise indicating or monitoring apparatus. The block 16 may be cast in a plastics material, may be moulded in rubber or may be fitted and secured to the end 12 of the composite member with the aid of adhesive.

In a spring having two strain gauges in the same orientation and in which the load applied to the spring is to be gauged by measuring the difference in strain between the gauges, the latter should be sufficiently close to one another to minimise temperature differences between them but sufficiently far apart to obtain a satisfactory measurable difference in strain. From the difference in strain over a set known length of the spring the load applied to the spring can be determined. In this type of construction the two strain gauges may be mounted on or be integral with a carrier strip so that their linear spacing is accurately maintained during moulding.

Alternatively they may, together with their signalling leads, be incorporated in a printed circuit which is introduced during laying up of the composite member.

In the design of a flexible composite member such as the leaf spring herein described it will be appreciated that the operating strain of a gauge must not be exceeded in use or it will be broken. Similarly, the elastic limit of the signalling wires must not be exceeded.

It will be appreciated that provision may be required in apparatus to which two or more gauges are connected to compensate for different lengths of leads from the gauges and for a change of gauge resistance occurring during moulding. If two gauges are provided which are vertically separated, that is one above the other, for example, one on either side of the neutral axis, this may save any requirement for lead length compensation. It can provide a satisfactory signal of difference in strain between the two gauges due to one being in compression and the other in tension. There will be a small separation between them and consequently any requirement for temperature compensation may also be avoided.

Springs of composite material generally fail suddenly and without prior warning following an overload. In the composite member one or more strain responsive members may be adapted, in conjunction with receiving means and display means, to give a warning when the design load (or any other predetermined load) is applied to the member so that over-loading may be avoided. This may be faciiitated by providing one or more strain responsive members in a high strain region of the composite member.

The number of strain responsive members to be incorporated in the composite member will depend on a number of factors, including space availability, the way in which it is desired to measure a load applied to the composite member and the degree of accuracy of measurement which is required. For example, the strain in a single strain gauge may be used to provide the required measurement. Alternatively the difference between strains in two or more strain gauges may be used, or an average of these strains. The strains in two or more gauges may be compared, or averaged and compared, with the strain in one or more other gauges.

Referring now to Figure 6 of the drawings, an electrical circuit is shown for a tractor and drawbar trailer combination in which the trailer has four springs as described with reference to Figures 1 to 5, each spring having two strain gauges Al, A2; B1, B2; Cl, C2 and Dl, D2 as 13,14. These springs are respectively associated with wheels W1, W2, W3 and W4 atthe front, W1 and W3 being on the left hand side and W2 and W4 on the right hand side.

A battery (not shown) is connected by conductors 21, to a regulator 23 which, in combination with - the capacitors 24, 25 and the resistor 26, reduces the battery voltage to a stabilised value of 15 volts from a 24 volt battery. The stabilised voltage is applied by conductors 27, 22 across the strain gauge pairs, their associated resistors (to be described) and a summing amplifier 28. An output conductor 29 from the amplifier 28 is connected to one terminal of a meter 31,for example a milliammeter, in a tractor cab, the other terminal of the meter being connected to the conductor 22 by way of a resistor 32 which has a capacitor 33 connected across it.

A battery, not shown, but which may be the same as the battery already referred to, is connected by conductors 34, 22 to a regulator 35, similar to regulator 23, whereby a stabilised reduced voltage is applied to a bank of switches S1 taS9 by a conductor 36. As with the regulator 23, the regulatorXi is associated with capacitors 37, 38 and a resistor 39 which are connected between conductors 34, 22 and conductors 36, 22 as shown in the drawing. Conductor 36 is connected to the conductor 22 by way of a resistor 41 and the resistor 32.

The pair of strain gauges A1,A2 have a common connection to the cursor of a potentiometer 42 and this potentiometer is connected in series with resistors 43,44 across the conductors 27, 22. The common connection is connected by a conductor 45 to one terminal of an analogue switch 46. The other terminal of switch 46 is connected to the amplifier 28 through a conductor 47, potentiometer 48, resistor 49 and conductor 51. The other pairs of strain gauges B1, B2; C1,C2; D1, D2 are similarly connected to analogue switches 52, 53, 54 respectively.

The output from each of these switches similarly passes to the amplifier 28 by way of a potentiometer, a resistor and conductor 51.

A resistor 50, conductor 55 and resistor 56 are connected in series between the conductors 27, 22 and the conductor 55 is connected to the amplifier 28 by a conductor 57. A capacitor 58 is connected across the resistor 56. Conductors 59, 61 connect the conductors 27, 22 respectively to the amplifier 28. A resistor 62 and capacitor 63 connected in parallel are connected across the amplifier 28 between the conductors 51,29.

The switch S1 is connected to the analogue switch 53 to supply a digital signal to operate it through a conductor 64, diode 65 and conductor 66. Conductor 66 is connected to the conductor 22 by way of the tractor chassis through a conductor 67 and resistor 68. Switches S5, S6 and S9 are also connected to the conductor 66 by way of conductors 69,71,72 and diodes 73, 74,75 respectively. In a similar manner the switches S2, S6, S7 and S9 are connected to analogue switch 54; switches S3, S5, S8 and S9 are connected to the analogue switch 52; and switches S4,S7,S8 and S9 are connected to the analogue switch 46. These switches are also similarly connected to conductor 22 by way of a resistor and the tractor chassis.

The weighing system is calibrated by jacking up the trailer so that the running gear is suspended free in air by the springs. Each strain gauge pair is then selected in turn by the appropriate switches S1 to S4 and its associated potentiometer is adjusted so that a zero reading is obtained on the meter. Thus, considering gauges Al, A2, the switch S4 is closed to switch on the analogue switch 46. Any current reading now showing on the meter 31 is reduced to zero by adjustment of the potentiometer 42.

The trailer is then lowered so that it is supported by its running gear and the same load is applied to each spring in turn. The potentiometers, as 48, are adjusted so as to obtain the same meter reading from each spring and corresponding with a load calibration on the meter 31. If the accuracy required is such that the weight of the running gear needs to be compensated for this can be taken into account in the load which is applied to the springs in turn.

When the trailer is loaded it will be seen that indication of the load on each spring can be selected bv operation of the appropriate switch S1 to S4 for reading from the meter. Operation of the switch S5 will give the combined loads applied to the springs on the left hand side of the trailer whilst switch S7 will give the corresponding loads on the right hand side. Switches S6 and S8 will give the combined loads on the front springs and the rear springs respectively. Operation of switch S9 will result in a meter reading of the combined loads on all four springs.

It will be seen that the circuit described requires six conductors between the tractor and trailer. In a more complex system requiring a larger number of selectable indications the number of conductors can be reduced by binary coding of signals from the switches as S1 to S9 on the tractor for transmission to the trailer and decoding signals on the trailer for feeding to the analogue switches. The number of conductors could be further reduced by known microchip technology using serial data exchange between tractor and trailer.

Referring now to Figure 7, a battery (not shown) is connected by conductors 34, 22 to a regulator 35 which, in combination with capacitors 37,38 and resistor 39, reduces the battery voltage to a stabilised value of say 15 volts from a 24 volt battery. The stabilised voltage is applied by conductors 36,22 to a microprocessor and display unit 81. This is shown in Figure 7 as having a display window and selector buttons for selecting the loads to be displayed. It will be understood that the selection and display may be arranged in any convenient manner. when the microprocessor 81 is switched on it connects the voltage from the trailer battery across regulator 23, as has been described with reference to Figure 6 via connectors 82, 83. As before, the output from regulator 23 is applied across pairs of strain gauges A1,A2; B1,B2; C1,C2 and soon.The common connection between strain gauges A1,A2 is taken to receiver means 84 in which the potentiometer 42 is incorporated and the cursor for the potentiometer is connected, within the receiver means, to an analogue to digital converter indicated at 85. The cursor of the potentiometer to which the common connection between strain gauges B1,B2 is connected is also connected to the converter 85. A bus 86 connects converter 85 to micro-processor 81. Receiver means similar to 84 will provide an output signal to indicate the front axle load or the load on the individual wheels mounted thereon and subsequent receiver means provide signals in respect of subsequent axles and their wheels. A common bus 86 connects all the output signals to the microprocessor. If desired individual receiver means may be provided for each spring. The calibration and weighing of loads is substantially as has already been described with reference to Figure 6. A selection (of axle or wheel load) on the micro-processor causes a coded digital signal to be passed along the bus connection. This is decoded at the individual receiver means so as to accept, convert and transmit a signal from the selected strain gauge pairs - all of which have been energised via conductors 82,83.

The signal output from the convertor or convertors is received and decoded by the micro-processor 81 which then displays the weight of the selected load.

If no battery supply is available on the trailer then conductors, as 82,83, can be used to carry stabilised voltage from regulator 35 via the micro-processorto the strain gauges and receiver means. The resistor networks and potentiometer, as 42, shown in the receiver means 84 may alternatively be incorporated in a programme in the micro-processor. Provision may be made for continuous energisation of the strain gauges, a continuous sequence of energisation or pulsing at programmed or selected intervals through the micro-processor. A circuit of this type using digital signals between cab and trailer has the advantage of reducing the possibility of obtaining spurious signals.

Provision may be made for recording and printing of read-outs of weighings, continuous monitoring of loads and visual and/or audible warnings on attainment of predetermined loads.

Claims (15)

1. Apparatus for weighing a load comprising, in combination, a composite member which in use is subjected to a load which induces a strain in at least a part thereof, a strain responsive member located and held within the part thereof in which a strain is induced and orientated so as to be subjected to the strain, signalling means adapted to communicate a signal from the strain responsive member to receiver means, which signal is a function of a strain detected by the strain responsive member consequent on the application of a load to the composite member and means to communicate the said signal to a display means which display means provides an indication of the load applied to the composite member.

2. Apparatus as claimed in Claim 1 wherein the composite member includes a second strain responsive member located and held within it in proximity to the first mentioned strain responsive member, second signalling means adapted to communicate to the receiver means a signal (the second signal) from the second strain responsive member such that the resultant or summation of the first and second signals taken together is a function of a strain detected by the first strain responsive member or of strains detected by the first and second strain responsive members and such resultant signal is communicated to the display means.

3. Apparatus as claimed in Claim 1 or 2 in which the receiver means is arranged to amplify the said signal or the resultant signal, as the case may be, for transmission to the display means.

4. Apparatus as claimed in Claim 3 in which the receiver means is arranged to receive signals from the strain responsive member or members in a plurality of composite members whereby the indication represents a summation of the loads applied to each of the composite members.

5. Apparatus as claimed in Claim 4 including means to select the signal from one composite member or the signals from a selected combination of composite members for transmission to the display means whereby the display means is enabled to indicate the load applied to an individual composite member or the sum of the loads applied to a selected combination of composite members.

6. Apparatus as claimed in Claim 1 or 2 in which the receiver means is arranged to convert the said signal, or the resultant signal as the case may be, to a digital signal for transmission to the display means which comprises a micro-processor which processes the signal received so as to display an indication of the load applied to the composite member.

7. Apparatus as claimed in Claim 6 in which thesaid signal or resultant signal as the case may be from each of a plurality of composite members is transmitted to the display means and means associated with the display means adapted to select the signal emanating from an individual composite member or from a selected combination of composite members for display so as to indicate the load applied to an individual selected composite member or the sum of the loads applied to a selected combination of composite members.

8. Apparatus as claimed in Claim 6 or Claim 7 in which the receiver means comprises an individual analogue to digital converter fitted to the or each composite member.

9. A vehicle incuding apparatus according to any preceding claim.

10. A vehicle according to Claim 9 wherein the or each composite member is orforms part-of a suspension spring of the vehicle.

11. A vehicle according to Claim 9 having at least one axle located in position by means of two suspension springs, and wherein the apparatus is in accordance with any one of Claims 1 to 7, said two suspension springs being, or including, composite members, and a single receiver means being connected to receive signals from said composite members.

12. Apparatus substantially as described herein with reference to Figures 1 to 6 of the accompanying drawings.

13. Apparatus substantially as described herein with reference to Figures 1 to 5 and 7 of the accompanying drawings.

14. A vehicle including apparatus substantially as described herein with reference to Figures 1 to 6 of the accompanying drawings.

15. A vehicle including apparatus substantially as described herein with reference to Figures 1 to 5 and 7 of the accompanying drawings.