WO2003025524A1

WO2003025524A1 - Weight sensor

Info

Publication number: WO2003025524A1
Application number: PCT/ZA2002/000146
Authority: WO
Inventors: Rudiger Heinz Gebert
Original assignee: Gebert Ruediger Heinz
Priority date: 2001-09-19
Filing date: 2002-09-19
Publication date: 2003-03-27

Abstract

This invention provides a weight sensor (10) which includes a fibre optic element (12) having an optical transmittance which is affected when influenced by a downward force (100) exerted by a wheel of a vehicle passing over the element (12). The weight sensor (10) also includes a transmitter (14) for transmitting an optical signal along the element (12) and a receiver (16) for receiving the optical signal after the signal has passed along at least that part of the element (12) which is affected when influenced by the downward force (100). The weight sensor (10) further includes a converter (18) for converting at least one characteristic of the received signal into a weight measurement of the downward force (100). The at least one characteristic of the received signal is related to the affect on the optical transmittance of the fibre optic element (12) when influenced by the downward force (100).

Description

WEIGHT SENSOR

FIELD OF THE INVENTION

The present invention lies in the field of weighing. In particular, this invention relates to a weight sensor for weighing, and a casing for a weight sensor, a former for a weight sensor, and a converter for a weight sensor.

BACKGROUND TO THE INVENTION

The term weighing in motion" refers to weighing vehicles as they pass over a weight sensor. The Inventor is aware of weighing in motion pads which comprise a sandwich construction of three electrically conductive sheets, such as aluminium sheets, separated from each other by elastic strips, such as polyurethane (PU) or silicone strips, bonded between the inner sheet and the two outer sheets. A signal from a stable oscillator is applied between the inner sheet on the one hand and the two outer sheets on the other and a circuit measures the change of capacitance which results when a vehicle passes over the pad. The change in capacitance results from the sheets being compressed together by the weight of a vehicle wheel or wheels on a single axle or axis which may generically be termed an axle set. The change in capacitance is then converted electronically to produce a number related to the weight of the axle.

A disadvantage of such pads is that, in order to ensure that such pads produce an accurate and reliable weight reading, the PU elasticity of each pad must remain reasonably stable with temperature and age and the bond of the PU to the sheets must remain intact. The sandwich must also be impervious to entry of water between the sheets as this immediately causes leakage currents and adversely affects the security of the bond and the stability of the oscillator. Because it is necessary to measure weight of all axle sets of a vehicle which pass over a pad within milliseconds of each other when a vehicle is at speed the PU strips must elastically recover from compression very quickly.

Quality control in the manufacture of such pads is difficult and tends to be inconsistent. The weather at the time of the work causing greater or lesser humidity, impurities in the air of dust, oils or other workshop pollutants even only in parts per million which are normally not noticed affect the quality of the bonds, as well as errors by the artisans placing the release treated strips, etc. Bond quality is important because the compression of the PU strips causes shear forces at the bond so that any weakness in the bond results in partial or complete failure of the bond in service. Once failed the response characteristics are distorted and the pad becomes unserviceable.

Such pads are electrically and electromagnetically sensitive, that is, should the pads be subjected to external electricity or electromagnetic waves these cause inaccurate and unreliable weight readings and may even cause damage to the pads.

Furthermore, the Inventor is aware of piezo weight sensors. Such weight sensors are however vibration sensitive and tend, in certain conditions of road surface, vehicles and the like, to be subjected to vibration during weighing in motion which causes inaccurate and unreliable weight readings. The vibration may be caused by the vehicle being weighed or by other vehicles proximate the vehicle being weighed. This may make such weight sensors unsuitable for use on bridges, for example, where vibration is normally quite substantial.

In order to minimise at least some of the above disadvantages, such pads are relatively expensive to produce. SUMMARY OF THE INVENTION

The Inventor believes that optical fibre technology can be employed to produce a weight sensor which does not suffer from at least some of the above disadvantages.

According to an aspect of the invention there is provided a weight sensor which includes a fibre optic element having an optical transmittance which is affected when influenced by a downward force exerted by at least a part of an object present above the fibre optic element; a transmitter for transmitting an optical signal along the fibre optic element; a receiver for receiving the optical signal after the signal has passed along at least that part of the fibre optic element which is affected when influenced by the downward force exerted by at least a part of an object present above the fibre optic element; and a converter for converting at least one characteristic of the received signal into a weight measurement when the fibre optic element is influenced by a downward force exerted by at least a part of an object present above the fibre optic element, the at least one characteristic of the received signal being related to the affect on the optical transmittance of the fibre optic element when influenced by the downward force exerted by the at least a part of the object.

It is to be appreciated that the at least a part of the object may, in certain embodiments of the invention, include the entire object. The object may be a vehicle. The at least a part of the vehicle may be at least one wheel of the vehicle or at least one continuous track of the vehicle.

The at least one characteristic of the received signal may be selected from any one, or any combination, of the group including the amplitude of the signal, the frequency of the signal, the phase of the signal, the intensity of the signal, and the energy of the signal. The converter may include receiver measuring means for measuring the at least one characteristic of the received signal. The receiver measuring means may include an analogue to digital (A/D) converter for converting the at least one characteristic of the received signal into a digital form.

The converter may compare the at least one characteristic of the received signal with a corresponding at least one characteristic of the transmitted signal in order to produce a weight measurement of the downward force exerted by the at least a part of the object.

The converter may include transmitter measuring means for measuring the corresponding at least one characteristic of the transmitted signal so as to compare the at least one characteristic of the received signal with the corresponding at least one characteristic of the transmitted signal. The transmitter measuring means may include an analogue to digital (A/D) converter for converting the at least one characteristic of the transmitted signal into a digital form.

Otherwise, the at least one characteristic of the transmitted signal may be pre-stored in the converter so as to compare the at least one characteristic of the received signal with the corresponding at least one characteristic of the transmitted signal.

The converter may include circuitry facilitating conversion of the at least one characteristic of the received signal into the weight measurement. The circuitry may be designed according to results derived from a study of the correlation between the at least one characteristic of the received signal and the downward force exerted by at least a part of an object. The correlation may be obtained by way of a plurality of varying measurements of the at least one characteristic of the received signal as the downward force exerted by an at least a part of an object is varied. The correlation may be made by interpolation between the actual measured values. The interpolation may produce a correlation for a set range of weight measurements. The correlation may be in the form of a mathematical formula.

The circuitry typically includes at least one processor. The processor may be programmed with instructions based on the above correlation between the at least one characteristic of the received signal and the downward force exerted by an at least a part of an object.

The fibre optic element may be configured such that the element substantially covers a surface area at least the size of a footprint of the at least a part of the object in order that a part of the downward force which is to influence the element is not dissipated past the element without influencing the element. The fibre optic element may be configured such that the element bears the entire downward force exerted by the at least a part of the object. The fibre optic element may be configured to form a coil. The fibre optic element may be configured to form a series of S-type shapes.

It is to be appreciated that the weight sensor may be configured to receive a plurality of parts of the same object at substantially the same time thereon, in which case the weight sensor measures a weight measurement of the downward force exerted by a plurality of parts of the object.

The weight sensor may include a casing for the fibre optic element which casing is configured to transmit at least a portion of the downward force exerted by the at least a part of the object onto the fibre optic element. The casing may include at least one protrusion on an upper inner surface thereof, which protrusion facilitates transmission of at least a portion of the downward force exerted by the at least a part of the object onto the fibre optic element. The casing may include at least one protrusion on a lower inner surface thereof, which protrusion facilitates transmission of at least a portion of the downward force exerted by the at least a part of the object onto the fibre optic element. The at least one protrusion on the upper inner surface of the casing may be aligned with the at least one protrusion on the lower inner surface of the casing so that the fibre optic element is trapped between adjacent protrusions when the at least a part of the object is present above the casing. Each protrusion may be in the form of a rib.

Otherwise, the casing may be configured to cause the fibre optic element to bend when influenced by the downward force exerted by the at least a part of the object. The casing may be configured to cause the amount which the element bends to increase as the downward force exerted by the at least a part of the object increases. The casing may include at least one protrusion on an upper inner surface thereof, which protrusion facilitates bending of the fibre optic element when influenced by the downward force exerted by the at least a part of the object. The casing may include at least one protrusion on a lower inner surface thereof, which protrusion facilitates bending of the fibre optic element when influenced by the downward force exerted by the at least a part of the object. The at least one protrusion on the upper inner surface of the casing may be aligned with a gap adjacent the at least one protrusion on the lower inner surface of the casing. Each protrusion may be in the form of a rib.

The fibre optic element may be wound around an elongate former, which former is shaped so as to localise stress transmitted onto the fibre optic element by the downward force exerted by the at least a part of the object. The former may be shaped, in cross sectional view, so as to be multi- sided, typically triangular.

An upper surface of the casing may be shaped and configured to receive the entire footprint of the at least a part of the object thereon so that the entire downward force exerted by such at least a part of the object is exerted on the casing. This is to ensure that a part of the downward force which is to influence the element is not dissipated past the element without influencing the element. The upper surface of the casing may be shaped and configured to receive a plurality of entire footprints of a plurality of parts of the same object thereon so that the entire downward force exerted by such parts of the object is exerted on the casing.

It is to be appreciated that the fibre optic element may be replaced by a plurality of fibre optic elements. The rest of the weight sensor may then be altered accordingly so as to produce a weight measurement of the downward force exerted by the at least a part of the object to be weighed.

According to another aspect of the invention there is provided a casing as described above.

According to a further aspect of the invention there is provided a former as described. Furthermore, a converter as described above is also provided.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described, by way of non-limiting example, with reference to the following diagrammatic drawings (not to scale) in which Figure 1 shows, in part cross-sectional side view, one embodiment of a weight sensor in accordance with the invention;

Figure 2 shows, in part cross-sectional side view, another embodiment of a weight sensor in accordance with the invention;

Figure 3 shows, in part cross-sectional three-dimensional side view, yet another embodiment of a weight sensor in accordance with the invention; and Figure 4 shows, in three-dimensional view, still another embodiment of the invention wherein the fibre optic element is wound around an elongate former in accordance with the invention.

With reference to the Figure 1 , reference numeral 10 generally indicates a weight sensor in accordance with the invention. The weight sensor 10 includes a fibre optic element 12 having an optical transmittance which is affected when influenced by a downward force 100 exerted by a wheel of a vehicle passing over the fibre optic element 12. In this embodiment of the invention, the fibre optic element 12 is arranged in a straight line. The weight sensor 10 also includes a transmitter 14 for transmitting an optical signal along the fibre optic element 12 and a receiver 16 for receiving the optical signal after the signal has passed along at least that part of the fibre optic element 12 which is affected when influenced by the downward force 100 exerted by a wheel of a vehicle passing over the fibre optic element 12.

The weight sensor 10 further includes a converter 18 for converting at least one characteristic of the received signal, in these embodiments the amplitude of the received signal, into a weight measurement of the downward force 100 exerted by a wheel when present above the fibre optic element 12. The amplitude of the received signal is related to the affect on the optical transmittance of the fibre optic element 12 when influenced by the downward force 100 exerted by a wheel of a vehicle passing over the fibre optic element 12.

It is to be appreciated that, in other embodiments of the invention, the at least one characteristic of the received signal may be selected from any one, or any combination, of the group including the amplitude of the signal, the frequency of the signal, the phase of the signal, the intensity of the signal, and the energy of the signal.

In the embodiment shown in Figure 1 , the weight sensor 10 includes a casing 20 for the fibre optic element 12 which casing 20 is configured to transmit at least a portion of the downward force 100 exerted by the wheel onto the fibre optic element 12. The casing 20 includes a plurality of protrusions 22 on an upper inner surface 24 thereof and a plurality of protrusions 26 on a lower inner surface 28 thereof. The protrusions 22 are aligned with the protrusions 26 so that the fibre optic element 12 is trapped between adjacent protrusions when a wheel passes over the casing 20. Such trapping of the fibre optic element 12 between adjacent protrusions facilitates transmission of at least a portion of the downward force 100 exerted by the wheel onto the fibre optic element 12. The protrusions 22, 26 are in the form of ribs. It is to be appreciated that the greater the downward force 100 exerted by a wheel of a vehicle passing over the element 12 the more the optical transmittance of the element 12 is affected, and in particular, the more the amplitude of the received signal is reduced.

An upper surface 30 of the casing 20 is shaped and configured to receive the entire footprint of a wheel thereon so that the entire downward force 100 exerted by such wheel is exerted on the casing 20.

The converter 18 includes receiver measuring means (not shown) for measuring the amplitude of the received signal. The receiver measuring means includes a sample and hold circuit (not shown) which stores the measured value of the amplitude of the received signal when the amplitude of the received signal is different from the amplitude when no downward force 100 is present. The receiver measuring means also includes an analogue to digital (A/D) converter (not shown) for converting the amplitude of the received signal into a digital form.

In one embodiment of the invention, the converter 18 includes transmitter measuring means (not shown) for measuring the corresponding amplitude of the transmitted signal. The transmitter measuring means also includes an analogue to digital (A/D) converter (not shown) for converting the at least one characteristic of the transmitted signal into a digital form.

The converter 18 includes circuitry which then compares the amplitude of the received signal with the corresponding amplitude of the transmitted signal in order to produce the weight measurement. It is to be appreciated that the corresponding amplitude of the transmitted signal is not influenced by the downward force exerted by a wheel of a vehicle passing over the fibre optic element 12.

In another embodiment of the invention, the amplitude of the transmitted signal is pre-measured and then pre-stored in the converter 18 which converter 18 then compares the amplitude of the received signal with the corresponding pre-stored amplitude of the transmitted signal.

The circuitry is designed according to results derived from a study of the comparison of the amplitude of the received signal with the corresponding amplitude of the transmitted signal, a plurality of comparisons being made for a corresponding plurality of varying downward forces 100 exerted by a wheel of a vehicle so as to determine a correlation between the downward force 100 exerted by a wheel and the comparison of the received signal with the transmitted signal. The correlation is made by interpolation between the actual measured values. The interpolation produces a correlation for a set range of weight measurements. In some embodiments of the invention, the correlation is in the form of a mathematical formula.

The circuitry includes at least one processor which is programmed with instructions based on the above correlation between the downward force 100 exerted by a wheel and the comparison of the received signal with the transmitted signal.

The weight sensor 10 includes a display (not shown) connected to the circuitry. The display displays the weight measurement of the downward force 100 exerted by the wheel.

It is to be appreciated that the weight measurement of the downward force 100 exerted by the wheel can easily be related to a weight measurement of the entire vehicle.

In another embodiment of the invention, the amplitude of the received signal is not compared with the corresponding amplitude of the transmitted signal in order to produce the weight measurement. Accordingly, the converter 18 does not include transmitter measuring means. In this embodiment, the circuitry is designed according to results derived from a study of the correlation between only the amplitude of the received signal and the downward force 100 exerted by a wheel of a vehicle. The correlation is then obtained by way of a plurality of varying measurements of the amplitude of the received signal as the downward force 100 exerted by a wheel of a vehicle is varied. The correlation is typically made by interpolation between the actual measured values. The interpolation produces a correlation for a set range of weight measurements. In this embodiment, the circuitry typically includes at least one processor programmed with instructions based on the above correlation between the amplitude of the received signal and the downward force 100 exerted by a wheel of a vehicle. In some embodiments of the invention, the correlation is in the form of a mathematical formula.

It is to be appreciated that in still another embodiment of the invention, the weight sensor 10 is configured to receive a plurality of wheels of the same vehicle at substantially the same time in which case the weight sensor measures a weight measurement of the downward force 100 exerted by a plurality of wheels. Accordingly, the upper surface 30 of the casing 20 is then shaped and configured to receive a plurality of entire footprints of a plurality of wheels of the same vehicle thereon so that the entire downward force 100 exerted by such wheels is exerted on the casing 20.

It is to be appreciated that, in yet another embodiment of the invention, the fibre optic element 12 is replaced by a plurality of fibre optic elements 12. The rest of the weight sensor 10 is then altered accordingly so as to produce a weight measurement of the downward force 100 exerted by at least one wheel of a vehicle.

Figures 2, 3 and 4 show further embodiments of a weight sensor 10, in accordance with the invention. Like reference numerals have been used in the figures to indicate like features.

In Figure 2, the casing 20 is configured to cause the fibre optic element 12 to bend when influenced by the downward force 100 exerted by the at least a part of the object. The casing 20 is further configured to cause the amount which the element 12 bends to increase as the downward force 100 exerted by the at least a part of the object increases. Unlike the embodiment shown in Figure 1 , the protrusions 22 on the upper inner surface 24 of the casing 20 of the embodiment shown in Figure 2 are aligned with gaps 32 adjacent the protrusions 26 on the lower inner surface 28 of the casing 20 in order to cause the bending described above.

In Figure 3, the fibre optic element 12 is configured such that the element 12 substantially covers a surface area at least the size of a footprint of the wheel of the vehicle in order that a part of the downward force 100 which is to influence the element 12 is not dissipated past the element 12 without influencing the element 12. This is achieved by configuring the element 12 out in a series of S-type shapes within the casing 20. In another embodiment of the invention, this may be achieved by configuring the element 12 in the shape of a coil.

The element 12 preferably to be lain out so that the gaps between the element 12 are minimised and where possible non-existent. This is to ensure that the part of the downward force 100 which is to influence the element 12 is not dissipated past the element 12 without influencing the element 12. It is, however, to be appreciated that, as Figure 3 is not drawn to scale, the gaps between the element 12 are shown to be greater than that preferred.

Unlike the embodiments of Figures 1 and 2, the casing 20 shown in Figure 3 does not include a plurality of protrusions on the upper inner surface 24 thereof but does include a plurality of protrusions 26 on the lower inner surface 28 thereof. This configuration causes the fibre optic element 12 to bend when influenced by the downward force 100 exerted by the at least a part of the object.

Figure 4 shows an embodiment of the invention wherein the fibre optic element 12 is wound around an elongate former 40. Only a portion of the former 40 and element 12 wound around it is shown in Figure 4. The former 40 is shaped to have a triangular cross section so as to localise stress transmitted onto the fibre optic element 12 by the downward force 100 exerted by the at least a part of the object. Accordingly, the stress is localised on the edges 42 of the former 40.

Even though it is not indicated in a drawing, it is to be appreciated that, in this embodiment of the invention, the former 40 and element 12 wound around it are typically configured in a similar manner to the configuration of the element 12 shown in Figure 3 so that the element 12 substantially covers a surface area at least the size of a footprint of the wheel of the vehicle in order that a part of the downward force 100 which is to influence the element 12 is not dissipated past the element 12 without influencing the element 12. Unlike the embodiment shown in Figure 3, however, the casing 20 in this embodiment of the invention would not include a plurality of protrusions on the upper inner surface 24 thereof nor a plurality of protrusions 26 on the lower inner surface 28 thereof as the former 40 is shaped to have a triangular cross section so as to localise stress transmitted onto the fibre optic element 12 by the downward force 100 exerted by the at least a part of the object.

It is to be appreciated that, even though this detailed description of the invention has been drafted in respect to weighing in motion of vehicles, the weight sensor 10 is equally suitable for use as a static weight sensor, that is, a weight sensor for weighing a stationary vehicle or any other stationary object.

The Inventor believes the weight sensor according to this invention is advantageous in that it is simple and therefore easier and less expensive to manufacture than conventional weighing in motion weight sensors. The Inventor also believes that the simplicity of this weight sensor leads to a longer lasting and more durable weight sensor than conventional weighing in motion weight sensors. Furthermore, the Inventor believes that this weight sensor provides more accurate weight measurements than conventional weighing in motion weight sensors.

Claims

1. A weight sensor which includes a fibre optic element having, an optical transmittance which is affected when influenced by a downward force exerted by at least a part of an object present above the fibre optic element; a transmitter for transmitting an optical signal along the fibre optic element; a receiver for receiving the optical signal after the signal has passed along at least that part of the fibre optic element which is affected when influenced by the downward force exerted by at least a part of an object present above the fibre optic element; and a converter for converting at least one characteristic of the received signal into a weight measurement when the fibre optic element is influenced by a downward force exerted by at least a part of an object present above the fibre optic element, the at least one characteristic of the received signal being related to the affect on the optical transmittance of the fibre optic element when influenced by the downward force exerted by the at least a part of the object.

2. A weight sensor as claimed in claim 1, wherein the object is a vehicle.

3. A weight sensor as claimed in either one of claims 1 or 2, wherein the at least one characteristic of the received signal is selected from any one, or any combination, of the group including the amplitude of the signal, the frequency of the signal, the phase of the signal, the intensity of the signal, and the energy of the signal.

4. A weight sensor as claimed in any one of claims 1 to 3, wherein the converter includes receiver measuring means for measuring the at least one characteristic of the received signal.

5. A weight sensor as claimed in claim 4, wherein the receiver measuring means includes an analogue to digital converter for converting the at least one characteristic of the received signal into a digital form.

6. A weight sensor as claimed in any one of claims 1 to 5, wherein the converter compares the at least one characteristic of the received signal with a corresponding at least one characteristic of the transmitted signal in order to produce a weight measurement of the downward force exerted by the at least a part of the object.

7. A weight sensor as claimed in claim 6, wherein the converter includes transmitter measuring means for measuring the corresponding at least one characteristic of the transmitted signal so as to compare the at least one characteristic of the received signal with the corresponding at least one characteristic of the transmitted signal.

8. A weight sensor as claimed in claim 7, wherein the transmitter measuring means includes an analogue to digital converter for converting the at least one characteristic of the transmitted signal into a digital form.

9. A weight sensor as claimed in claim 6, wherein the at least one characteristic of the transmitted signal is pre-stored in the converter so as to compare the at least one characteristic of the received signal with the corresponding at least one characteristic of the transmitted signal.

10. A weight sensor as claimed in any one of claims 1 to 9, wherein the converter includes circuitry facilitating conversion of the at least one characteristic of the received signal into the weight measurement.

11. A weight sensor as claimed in claim 10, wherein the circuitry is designed according to results derived from a study of the correlation between at least the at least one characteristic of the received signal and the downward force exerted by at least a part of an object.

12. A weight sensor as claimed in claim 11 , wherein the correlation is obtained by way of a plurality of varying measurements of the at least one characteristic of the received signal as the downward force exerted by an at least a part of an object is varied.

13. A weight sensor as claimed in any one of claims 10 to 12, wherein the circuitry includes at least one processor programmed with instructions based on the correlation between the at least one characteristic of the received signal and the downward force exerted by an at least a part of an object.

14. A weight sensor as claimed in any one of claims 1 to 13, wherein the fibre optic element is configured such that the element substantially covers a surface area at least the size of a footprint of the at least a part of the object in order that a part of the downward force which is to influence the element is not dissipated past the element without influencing the element.

15. A weight sensor as claimed in claim 14, wherein the fibre optic element is configured such that the element bears the entire downward force exerted by the at least a part of the object.

16. A weight sensor as claimed in any one of claims 1 to 15, wherein the weight sensor includes a casing for the fibre optic element which casing is configured to transmit at least a portion of the downward force exerted by the at least a part of the object to the fibre optic element.

17. A weight sensor as claimed in claim 16, wherein the casing includes at least one protrusion on an upper inner surface thereof, which protrusion facilitates transmission of at least a portion of the downward force exerted by the at least a part of the object to the fibre optic element.

18. A weight sensor as claimed in claim 17, wherein the casing includes at least one protrusion on a lower inner surface thereof, which protrusion facilitates transmission of at least a portion of the downward force exerted by the at least a part of the object to the fibre optic element.

19. A weight sensor as claimed in claim 18, wherein the at least one protrusion on the upper inner surface of the casing is aligned with the at least one protrusion on the lower inner surface of the casing so that the fibre optic element is trapped between adjacent protrusions when the at least a part of the object is present above the casing.

20. A weight sensor as claimed in any one of claims 16 to 18, wherein the casing is configured to cause the fibre optic element to bend when influenced by the downward force exerted by the at least a part of the object.

21. A weight sensor as claimed in claim 20, wherein the casing is configured to cause the amount which the element bends to increase as the downward force exerted by the at least a part of the object increases.

22. A weight sensor as claimed in either one of claims 20 or 21 when claim 20 is dependent on at least claim 18, wherein the at least one protrusion on the upper inner surface of the casing is aligned with a gap adjacent the at least one protrusion on the lower inner surface of the casing.

23. A weight sensor as claimed in any one of claims 1 to 22, wherein the fibre optic element is wound around an elongate former, which former is shaped so as to localise stress transmitted to the fibre optic element by the downward force exerted by the at least a part of the object.

24. A weight sensor as claimed in claim 23, wherein the former is shaped, in cross sectional view, so as to be multi-sided.

25. A weight sensor as claimed in any one of claims 1 to 24, which is configured to receive a plurality of parts of the same object at substantially the same time thereon so that the weight sensor measures a weight measurement of the downward force exerted by a plurality of parts of the object.

26. A casing for a fibre optic element of weight sensor, which casing is configured to transmit at least a portion of a downward force exerted by at least a part of an object present above the fibre optic element to the fibre optic element.

27. A casing as claimed in claim 26, which includes at least one protrusion on an upper inner surface thereof, which protrusion facilitates transmission of at least a portion of the downward force exerted by the at least a part of the object to the fibre optic element.

28. A casing as claimed in claim 27, which includes at least one protrusion on a lower inner surface thereof, which protrusion facilitates transmission of at least a portion of the downward force exerted by the at least a part of the object to the fibre optic element.

29. A casing as claimed in claim 28, wherein the at least one protrusion on the upper inner surface of the casing is aligned with the at least one protrusion on the lower inner surface of the casing so that the fibre optic element is trapped between adjacent protrusions when the at least a part of the object is present above the casing.

30. A casing as claimed in any one of claims 26 to 28, which is configured to cause the fibre optic element to bend when influenced by the downward force exerted by the at least a part of the object.

31. A casing as claimed in claim 30, wherein the casing is configured to cause the amount which the element bends to increase as the downward force exerted by the at least a part of the object increases.

32. A casing as claimed in either one of claims 30 or 31 when claim 30 is dependent on at least claim 28, wherein the at least one protrusion on the upper inner surface of the casing is aligned with a gap adjacent the at least one protrusion on the lower inner surface of the casing.

33. A weight sensor or a casing as hereinbefore generally described.

34. A weight sensor or a casing as specifically described with reference to or as illustrated in the accompanying drawings.