WO2007054539A1

WO2007054539A1 - Weighing device

Info

Publication number: WO2007054539A1
Application number: PCT/EP2006/068296
Authority: WO
Inventors: Sergio Biffi
Original assignee: Biffi, Marco; Giovanetti, Marilena
Priority date: 2005-11-09
Filing date: 2006-11-09
Publication date: 2007-05-18
Also published as: ITMI20052133A1

Abstract

A weighing device is described, comprising: a transducer; a frame accommodating said transducer and supporting a load to be weighed; a device for receiving signals from the transducer and transforming them into weighing result. The frame comprises: a rigid upper loading plate; a rigid lower supporting plate; a flexible membrane in intermediate position between the two upper and lower plates; there are provided in the frame protuberances which engage corresponding grooves for the connection of at least some of said upper plate, lower plate or flexible membrane.

Description

Weighing device

DESCRIPTION FIELD OF THE INVENTION

The present invention relates to a weighing device. DESCRIPTION OF THE PRIOR ART

The need for a low-cost weighing device which is capable of accurately measuring loads of considerable weight, for example up to 3500 kg in high temperature environments, also up to 400⁰C and over, has arisen.

Numerous weighing devices are known in the prior art, none of which however appears indicated to meet both the high load and the high temperature requirements. Furthermore, the known devices which most approach the requirements above, for example of the load cell type, are costly. SUMMARY OF THE INVENTION

It is therefore the object of the present invention to overcome all the aforesaid drawbacks and indicate a low-cost weighing device which is capable of measuring, with a high degree of accuracy, loads of considerable weight, in high temperature environments, and which exploits the low cost and the accuracy of electronic devices.

The object of the present invention is a weighing device comprising: a transducer; a frame which accommodates said transducer and supports the load to be weighed; a device which receives the transducer signals and transforms them into weighing result, characterised in that said transducer is of the strain type and said frame comprises: a rigid flat upper plate; a rigid lower supporting plate; a flexible membrane in intermediate position between the two upper and lower plates; being envisaged in said frame protuberances which engage corresponding grooves for the connection of at least some of said upper plate, lower plate or flexible membrane; said flexible membrane flexing under the application of said load to be weighed, and determining a deformation of said transducer so as to determine said weighing result. The particular object of the present invention is a weighing device as better described in the claims, which form an integral part of the present description. BRIEF DESCRIPTION OF THE DRAWINGS

Objects and advantages of the present invention will be apparent from the detailed description that follows of an example of embodiment of the same (and of variants thereof) and the accompanying drawings by way of mere illustrative and non-limitative example, in which: figures from 1 to 7 show examples of embodiment variants of the weighing device object of the present invention. The same numbers in the figures indicate the same components or functionally equivalent components. DESCRIPTION OF THE PREFERRED EMBODIMENTS The device object of the invention consists of the following main elements:

- an electronic transducer; - a frame accommodating the transducer and supporting the load to be weighed;

- a measuring device, preferably of the electronic type, which receives the signals from the transducer and transforms them into weighing results.

The described variants include the following main components of the frame, which may be made of stainless steel: a rigid upper loading plate; a rigid lower supporting plate; a flexible membrane in intermediate position between the two upper and lower plates.

In a first variant (figure 1 ), a peripheral protuberance V preferably with round section is made on the lower surface of upper plate 1.

The upper surface of intermediate membrane 2 displays a first round section peripheral groove 2' positioned so as to engage protuberance V of the upper plate.

The lower surface of intermediate membrane 2 displays a second preferably round section peripheral groove 2".

The upper surface of lower plate 3 displays a first round section peripheral protuberance 3' positioned so as to engage second peripheral groove 2" of the intermediate membrane.

Between the lower surface of intermediate membrane 2 and the upper surface of lower plate 3 a transducer 4 is positioned, for example of the silicon type, adapted to be elastically deformed by compression to detect a deformation of thickness which is transformed into an electrical signal and sent to the electronic device (not shown) which detects the indication and determines the measurement of the load.

A protuberance 5 in relief on the lower surface of membrane 2, in contact with transducer 4, is provided to ensure coupling with the transducer.

The operating principle is that of the lever, by offsetting the contact points of the two plates and the central membrane with respect to the centre of the frame and the thickness of the membrane, which bends by effect of the load placed on the upper plate, thus pressing on the transducer. The entity of the flexing is proportional to the weight of the load.

The variables involved are the dimensional relationships between contact points between the two loading and supporting plates and the flexible membrane, the radiuses of curvature of the peripheral grooves and protuberances, and the thickness of the intermediate membrane, which determine the entity of the flexing of the membrane at equivalent weight to be measured, and which also allow to leave a certain freedom of choice of the type of stainless steel and the type of transducer.

In this variant, the distance from the centre of the frame of protuberance 3' and corresponding peripheral groove 2" between flexible membrane 2 and supporting plate 3 is higher than that of protuberance V and corresponding peripheral groove 2' between flexible membrane 2 and loading plate 1 , thus creating an offset capable of bending the membrane towards supporting plate 3 lower than the application of the load to be measured, pressing against the transducer. The round section of the peripheral grooves assures a regular pattern of flexion by deformation of the membrane, avoiding punctual contact between the plates and the membrane, which would risk altering the measurement or damaging the frame itself.

The frame reduces the load applied to the transducer. This load reduction is essential for operation. If the maximum load were directly applied to the transducer, this would sink into the steel thus making the system unusable. The load measurement is obtained from the compression of the transducer.

In a second variant (figure 2), with respect to the first, upper plate 1 and flexible membrane 2 are integrated into a single element, providing an equivalent operation. Central part 1 of the single element performs the function of rigid upper plate while external part 2 performs the function of flexible membrane.

The upper surface of the external edge of the single element is shaped as an open groove 2'" which engages against protuberance 3'" of the upper edge of rigid lower plate 3.

The external part of the single element bends by effect of the load resting on the rigid central part, thus pressing on transducer 4.

The entity of the flexing is proportional to the weight of the load.

The variables involved are the dimensional relationships between the width of the rigid central part and the distance from the contact edge with the protuberance of the lower plate, and furthermore the thickness of the part constituting the flexible membrane, which determine the entity of the flexion of the membrane at equal load to be measured.

In a third variant (figure 3) with respect to the first variant, the protuberance in relief on the lower surface of the flexible membrane is not present, while transducer 4 is in contact with the lower edge of membrane 2 and distanced with respect to the lower plate. In this case, the flexural deformation of the membrane following the positioning of the load on the loading plate, determines a corresponding flexural deformation on the transducer. The extent of the strain of the transducer provides the measurement of the load.

In a fourth variant (figure 4) with respect to the first variant, a recess 6 is made on the upper edge of lower plate 3, over which transducer 4 is positioned. A protrusion 7 which is in contact with transducer 4 is made on the lower edge of flexible membrane 2. By applying the load on upper plate 1 , membrane 2 flexes and protrusion 7 presses on transducer 4, which is flexurally deformed towards the recess. The entity of flexion of the transducer provides the measurement of the load. In a fifth variant (figure 5) with respect to the first variant, the protuberance in relief on the lower surface of the flexible membrane is not present, while flat armature capacitors 8, 9 are used as transducers and positioned in the gaps between upper plate 1 and membrane 2 and between membrane 2 and lower plate 3. When the load to be measured is applied, the flexion of membrane 2 causes a deformation by variation of the distance between the two armatures of the capacitors, in particular a closing of lower capacitor 9 and an opening of upper capacitor 8, and therefore a variation of capacitance of the capacitors themselves. The load measurement is obtained by the variation of capacitance.

Only one capacitor may be applied in one of the two gaps, instead of in both. The variant with capacitors in both gaps is preferable, because by detecting the respective variations of thickness in independent fashion, a measuring error compensation effect due to the opposite pattern of the deformations may be obtained.

The transducer may be either an integrated circuit, or a passive component of the type used in the first to fourth variant, or of the armature capacitor type with dielectric constituted, for example, by air or other suitable material. Electrical wires may be arranged to connect the transducer to the electronic device which may pass through appropriate side channel envisaged in the grooves or protuberances or by drilling the lower plate or the membrane. In sixth variant (fig. 6), with respect to the second variant (fig. 2), upper plate

1 and flexible membrane 2 are divided in two elements.

The rigid upper plate 1 has raised lateral edges 1 ' as a protuberance, engaging in suitable recesses 2' or grooves, obtained in the upper central part of the flexible membrane 2. The lower surface of the external edge of the flexible membrane 2 is shaped as an open groove 2'", engaging against the protuberance 3'" of the upper edge on the lower rigid plate 3.

The flexible membrane 2 bends by effect of the load resting on the upper plate 1 , thus pressing or deforming the transducer 4. The amount of bending is proportional to the weigh of the load. In a seventh variant (fig. 7), with respect to the first variant (fig. 1 ), the upper rigid plate 1 is shaped as an internally empty ring , having a groove V on the internal lower surface; the intermediate flexible membrane 2 is shaped with a greek-pi like section with upper 2' and lower 2" edges shaped as an overhanging protuberance, divided by vertical lateral walls; the transsducer 4 is placed on the upper surface of the orizontal side of the membrane 2; the rigid lower plate 3 has a groove 3'" on the internal upper surface;

The overhanging protuberances 2' and 2" of the flexible membrane 2 engage respectively with the grooves V and 3" of the upper and lower plates. The load is placed on the upper edge of the ring of the upper plate 1 . The upper overhanging protuberance 2' of the flexible membrane 2 bends due to the load, letting the orizontal side of the membrane curve upwards, pressing or deforming the transducer 4 against the lower side of the load. The amount of bending is proportional to the weight of the load. Other possible variants of the non-limitative example described are possible, without departing from the scope of protection of the present invention, comprising all equivalent implementations for a person skilled in the art.

In all variants, the protuberances and the corresponding peripheral grooves may either have a continuous development along the various parts of the frame or be developed in segments.

Furthermore, the peripheral protuberances, as the corresponding peripheral grooves, may be made either on the flexible membrane or on the upper and lower rigid plates.

The upper and lower plates and the flexible membrane may be either round or have another shape.

The offset between upper and lower grooves and protuberances may be reversed, and the transducer may be positioned between the upper plate and the flexible membrane.

More in detail, especially but not exclusively with reference to the first four variants, the distance from the centre of the frame of the groove and the corresponding peripheral protuberance between flexible membrane 2 and supporting plate 3 may be smaller than that of the groove and the respective peripheral protuberance between flexible membrane 2 and loading plate 1 , thus creating an offset capable of bending the membrane towards the supporting plate higher than the application of the load to be measured, pressing against the transducer.

From the description above, a person skilled in the art will be capable of implementing the object of the invention without introducing further constructive details.

Claims

1. A weighing device, comprising:

- a transducer (4);

- a frame (1 ,2,3) accommodating said transducer and supporting a load to be weighed;

- a device for receiving signals from the transducer and transforming them into weighing result; characterised in that said transducer (4) is of the strain type and said frame comprises: a rigid upper loading plate (1 ); a rigid lower supporting plate (3); a flexible membrane (2) in intermediate position between the two upper and lower plates, protuberances being envisaged in said frame, which engage corresponding grooves for the connection of at least some of said upper plate, lower plate or flexible membrane, said flexible membrane (2) flexing under the application of said load to be weighed, and determining a deformation of said transducer (4) so as to determine said weighing result.

2. A weighing device according to claim 1 , characterised in that said protuberances and said grooves have a round section.

3. A weighing device according to claim 1 , characterised in that said protuberances and said grooves are of the open type.

4. A weighing device according to claim 1 , characterised in that said protuberances and grooves connect said upper plate to said flexible membrane and said flexible membrane to said lower plate in a reciprocally offset manner.

5. A weighing device according to claim 1 , characterised in that said upper plate and said flexible membrane are integrated in a single element, said single element being connected to said lower plate by means of protuberances and grooves.

6. A weighing device according to claim 4, characterised in that said offset is such so as to determine a flexion of said flexible membrane (2) towards said lower plate and in that said transducer (4) is positioned between said lower plate and said flexible membrane.

7. A weighing device according to claim 6, characterised in that said transducer (4) is positioned in contact between said lower plate and said flexible membrane by means of a protuberance (5).

8. A weighing device according to claim 6, characterised in that said transducer (4) is positioned in contact with said flexible membrane and being distanced with respect to said lower plate.

9. A weighing device according to claim 6, characterised in that it comprises:

- a groove (6) on the upper edge of the lower plate (3) over which said transducer (4) is positioned;

- a protrusion (7) on the lower edge of the flexible membrane 2, in contact with the transducer.

10. A weighing device according to claim 4, characterised in that said offset is such so as to determine a flexion of said flexible membrane (2) towards said upper plate and in that said transducer (4) is positioned between said upper plate and said flexible membrane.

11. A weighing device according to any one of the proceeding claims, characterised in that said transducer is of the integrated circuit or passive component type.

12. A weighing device according to claim 4, characterised in that said transducer comprises one or more flat armature capacitors (8, 9) positioned in at least one of the gaps between upper plate 1 and membrane 2, and between membrane 2 and lower plate 3.

13. A weighing device according to any one of the preceding claims, characterised in that said peripheral protuberances and said grooves are either continuously developed along the various parts of the frame, or are developed in segments.

14. A weighing device according to any one of the preceding claims, characterised in that said upper and lower plates and said flexible membrane have a round peripheral shape.

15. A weighing device according to claim 2 or 4, characterised in that the dimensional relationships between the contact points between said loading and supporting plates and said flexible membrane, the radiuses of curvature of said peripheral grooves and protuberances, and the thickness of the intermediate membrane, determine the entity of flexion of the membrane given equal load to be measured.

16. A weighing device according to claim 2 or 5, characterised in that the dimensional relationships between the width of the rigid central part and the distance from the contact edge with the protuberance of the lower plate, and furthermore the thickness of the part constituting the flexible membrane, determine the entity of the flexion of the membrane at equal load to be measured.

17. A weighing device according to claim 1 , characterised in that: said upper rigid plate (1 ) is shaped as an internally empty ring, having a groove (1 ') on the internal lower surface; said intermediate flexible membrane (2) is shaped with a greek-pi like section with upper (2') and lower (2") edges shaped as an overhanging protuberance, divided by vertical lateral walls; said transducer (4) being placed on the upper surface of the orizontal side of the membrane (2); said rigid lower plate (3) has a groove (3'") on the internal upper surface; said overhanging protuberances (2', 2" ) of the flexible membrane (2) engage respectively with the grooves (1 ', 3") of the upper and lower plates.