GB2180655A

GB2180655A - Acceleration or vibration sensing device

Info

Publication number: GB2180655A
Application number: GB08622335A
Authority: GB
Inventors: Orto Giuseppe Dell
Original assignee: MARELLI AUTRONICA; Marelli Autronica SpA
Current assignee: MARELLI AUTRONICA; Marelli Europe SpA
Priority date: 1985-09-17
Filing date: 1986-09-17
Publication date: 1987-04-01
Also published as: IT8553803V0; CH668651A5; GB2180655B; FR2587497A1; GB8622335D0; JPS6267264U; BE905452A; NL8602360A; IT206728Z2; FR2587497B1; PT83392B; DE3631651A1; PT83392A

Abstract

An acceleration or vibration sensing device comprises a support structure for fixing to the body 1 the acceleration or vibrations of which it is desired to measure, and including a substrate 2 which is resiliently deformable through the effect of an acceleration of the body, at least one thick-film resistor 3 being applied to the substrate so that, in use, it undergoes deformations univocally corresponding to the deformations of the substrate, and circuit means (e.g. a bridge circuit) connected to the at least one resistor and arranged to output electrical signals indicative of the variations in its resistance. The substrate may be mounted in an air-tight or liquid-tight casing. A mass M1 may be fixed to the substrate. <IMAGE>

Description

SPECIFICATION Accleration or vibration sensing device This invention relates to an acceleration or vibration sensing device.

An object of the invention is to provide an acceleration or vibration sensing device having a particularly strong and simple structure, which can be made simply and cheaply and has good accuracy and which is easy and simpleto install.

According to the invention there is provided an acceleration or vibration sensing device characterised in that it comprises a support structure for fixing to the body the acceleration or vibrations of which it is desired to measure, and including a substrate which is resiliently deformablethrough the effect of an acceleration ofthe body, at leastonethick-film resistor being applied to the substrate so that, in use, itun- dergoes deformations univocally corresponding to the deformations of the substrate, and circuit means connected to the at least one resistor and arranged to output electrical signals indicative of the variations in its resistance.

The substrate is preferably electrically insulating but may be electrically insulated from the thick-film resistor.

According to a further characteristic of the device according to the invention, a mass may be fixed to the substrate to increase its inertia and amplify its deformation.

Further characteristics and advantages of the sensing device according to the invention will become apparent from the detailed description which follows with reference to the appended drawings, provided purely by way of non-limiting example, in which: Figure lisa perspective view of a body the acceleration of which it is wished to measure, the body having a sensor according to the invention, shown schematically byway of example, Figure2 is an electrical circuit diagram, partially in block form, of the sensor according to the invention, Figures 3 and 5 show two different solutions of the assembly of the device according to the invention, Figures4and 6showcircuitarrangements relating to the assemblies of Figures 3 and 5, and Figure 7 is a sectioned elevational view of another sensing device according to the invention.

With reference to Figure 1,a bodywhoseaccelera- tion in a predetermined direction it is wished to detect is indicated 1. To this body is fixed a plate orsub strate 2, for example of ceramics material, which is rectangular in shape in the embodiment illustrated.

More particularly, the plate 2 is fixed along one edge to the body 1.

Athick-film resistor 2 is deposited on one face of the plate 2 by the known silk-screen process. Con ductivetracks4and 5 are also applied to this face and are connected to conductors 6,7forconnection two a processing and treatment circuit 8. This circuit, as indicated in Figure 2, may include, for example, a bridge circuit 9 of known type of which the thick-film resistor 3 constitutes one side. The circuit 9 is con necked to an amplifier 10.

When the body 1 is subjected to an acceleration, for example, in the direciton indicated by the arrow F1 in Figure 1,the support plate 2 is subjected to an acceleration in the opposite direction, as indicated by the arrow F2, and deforms to take up a configuration of the type shown, by way of example, in broken outline in Figure 1. The plate 2 is thus deformed to a greater extent the greaterthe acceleration of the body 1. As a result of the deformation of the substrate 2, the thick-film resistor 3 is also deformed and, by virtue of its piezo-resistive characteristics, there is a corresponding variation in its resistance. Consequ ently, the voltage signa l fed to the amplifier 10 by the bridge circuit 9varies and the signal output by the amplifier also varies.

The signal output by the circuit 8 is thus directly indicative ofthe acceleration to which the body 1 is subjected.

In orderto increase the inertia of the plate 2 and hence amplify its deformation, a mass such as that indicated M in Figure 1 may be attached to it.

Although the use of a single thick-film resistor is shown by way of example and schematically in Figures 1 and 2, it is clearthattwo or more thick-film resistors may be disposed on the substrate 2 in posi tions where the deformations ofthe substrate are particularly perceptible.

Thus, as shown in Figure 3, a respective thick-film resistor 3,3' may be applied to each of the two faces of the plate 2 of Figure 1, when one ofthese extends and the other is compressed as a resultofac- celerations orvibrations, and these resistors are suit- ably arranged in a circuit (forexample,the arrangement of Figure 4), it is possible to sum the effects to obtain a stronger electrical signal for a given acceleration.

Figure 5 shows a device according to the invention in which the support plate 2 has both its ends fixed to the body 1 whose accelerations or vibrations areto be detected. to the same face of the plate 2, there are applied thick-film resistors 3 int he central zone and 3' close to its attachments. If the mass M is applied to the centre of the other face of the plate 2, a force F2 acting in the direction illustrated tends to deform the plate in the manner shown in broken outline, compressing the resistors 3 and extending the resistors 3'. With the bridge circuit arrangement shown in Figure 6, it is also possible in this case to sum the effects ofthe deformations of the resistors 3 and 3'.

It is not necessaryforthe support plate 2 to be of ceramics material, it could be of steel, for example, and a thick-film resistors could be applied to previously insulated areas of the plate or sheet,orthick- film resistors which have previously been deposited on an insulating substrate, such as a ceramic, may be applied to the plate or sheet.

Furthermore, it is not necessaryforthe support plate 2 to be rectangular and it is even less necessary for it to be fixed by a portion only of its periphery.

Figure 3 shows an embodiment in which the support plate 2 is circular and its periphery is gripped between two half-shells 11 and 1 2togetherforming a closed casing.

In the embodiment illustrated, the optional mass M is preferably applied to the centre of the diaphram and the thick-film resistor or resistors must naturally be applied to it in positions in which the deformations are particularly perceptible, that is, preferably nearthe centre ofthe diaphram and the fixed periphery.

For use in conditions in which very small forces on the substrate are foreseen, it may be useful to evacuate the casing in which the substrate is fixed in orderto avoid damping dueto the air, as well as having recourseto an auxiliary mass.

If very high forces on the substrate are foreseen in the condition of use, however, it may be appropriate for the casing in which the substrate is mounted to be at least partly filled with an inert fluid, such as oil, freon, etc.

An acceleration sensor according to the invention maybeusedtoadvantageformeasuring ac- celerations of motor vehicles or commercial vehicles. It may also be used for detecting and measuring vibrations in a motorvehicle on more or less rough ground.

Claims

1. An acceleration or vibration sensing device, characterised in that it comprises a support structure forfixing to a body the acceleration or vibrations of which it is desired to measure, and including a such strate which is resiliently deformable through the effect of an acceleration of the body, at least one thickfilm resistor being applied to the substrate so that, in use, it undergoes deformations univocally corresponding to the deformation of the substrate, and, circuit means connected to the at least one resistor and arranged to output electrical signals indicative of the variations in its resistance.

2. Device according to Claim 1, characterised in that a mass is fixed to the substrate to increase its inertia and amplify its deformation.

3. Device according to Claim 1 orClaim 2, part- icularlyfor use in situations in which very modest forces act on the substrate, characterised in thatthe structure includes a casing which is airtight and undervacuum, and in which the substrate is mounted.

4. Deviceaccording to Claim 1 orClaim 2, part- icularlyfor use in situations in which forces greater than a predetermined value act on the substrate characterised in that the structure includes a casing which is liquid-tightand contains an inert liquid, and in which the substrate is mounted.

5. Device according to any one ofthe preceding claims, characterised in that the substrate is in the form of a diaphragm fixedtothe supportstructure around its periphery.

6. Device according to anyone of the preceding claims, characterised in that the substrate is of ceramics material.

7. Device according to any one of the preceding claims, characterised in that the support structure includes a metal plate to which a substrate of ceramics material carrying one or more thick-film resistors is applied.

8. Acceleration or vibration sensor device substantially as hereinbeofre described and illustrated with reference to Figures 1 and 2, Figures3 and 4, Figures 5 and 6 or Figure 7 ofthe accompanying drawings.