DE8914777U1 - Capacitive deformation sensor - Google Patents

Description

• ftf ···· ····

"» ■••••«••»r·

. Marelli Autronica S.pA. Munich, 15 December 1989

1-20123 Milan, Italy JST-si 16 258

Capacitive communication sensor

The present invention relates to a capacitive deformation sensor, in particular for measuring the deformation of a structure.

In particular, the object of the invention is to provide a sensor with first and second, opposite poles, which are attached to two points of the structure, from which a relative displacement in an orthogonal direction to the said devices is to be determined on the basis of corresponding capacitance changes of the capacitor.

It is the aim of the present invention to provide a deformation sensor of the type described above which is simple, /cbust and reliable

According to the present invention, this object is achieved by a sensor, which consists of a first tubular body with an internal recess in which a first pole is located. In the first body, a second tubular body is arranged, which moves in relation to the first body in a direction orthogonal to the plane of the first pole depending on the deformation and to which the second pole is attached. The first and second bodies are each provided with anchoring pieces for connection to the two points of the structure mentioned, the relative displacement of which is to be determined.

Further details, features and advantages of the invention emerge from the following description of the drawing, which represents only a non-limiting example.

2 Show

Figure 1 shows a longitudinal section of a deformation sensor according to the present

Invention,

Figure 2 is a section along the line &Pgr;-&Pgr; in Figure 1, and Figure 3 is a block diagram of an electronic circuit connected to the

sensor according to the invention

In the drawing, the number 1 designates a deformation sensor, in particular for measuring the load resting on the axle of a commercial vehicle, based on the deformation of the axle under the action of the load. The sensor 1 consists of a first tubular body 2 with an inner recess 3, which is closed at one end by a bottom wall 4. Inside the recess 3 there is a first metal foil S which is fastened to the bottom wall 4 with the interposition of a layer 6 of electrically insulating material. Inside the body 2 there is a second tubular body 7 which can be moved relative to the first body, at one end of which there is a second metal foil 8 which lies opposite the foil S and is at a distance from it. The foil 8 is fastened to the body 7 by a layer 9 of an electrically insulating material. The body 7 also has a recess in its interior and inside it there is a support disk 10 on which the components of an electronic circuit 11 are arranged, as described below.

In the drawing, the radial distance between the body 2 and the body 7 is shown enlarged for better understanding. In reality, this distance is in the range of a tenth of a millimeter. Outside the bodies 2 and 7 there is a protective bellows 12 made of elastomeric material, the ends of which are each connected to the body 2 or the body 7 with fastening clamps 14.

The first body 2 and the second body 7 are each connected at their ends with

13 we Befeatitmno of Setunn 1 provided. Diea aemchl&ht

for example by soldering/welding at two points 16 of a construction 17, the deformation of which is determined based on the relative displacement of the two points

The bending deformations of the structure 17 in the directions indicated by the arrows A |

The directions indicated cause a relative displacement of the bodies 2 and 7 in a direction essentially orthogonal to the plane of the foils S and

8th . \

UUIVIi uiv &kgr; uiivu »&zgr; Uhu \J uvouiiuiitv ivipnciiat uvo nviiuviiauivia &agr;&ngr;&igr;&iacgr;&pgr;&ogr;&idiagr;&idiagr;&eegr;&igr;

accordingly depending on the deformation of the structure 17.

In order to prevent deformations of various magnitudes of the structure 17 and the bodies 2 and 7 due to temperature fluctuations, which can be interpreted as a change in the load acting on the structure 17, the bodies 2 and 7 are preferably made of the same material as the structure 17, for example of soft iron.

The foils 5 and 8 are connected by means of conductors 18 to an electronic circuit 11, which is carried by the plate 10 and provides a voltage signal as an indication of the capacitor capacity. Figure 3 shows a block diagram of a

Zicäcui kücü cätcK säiguctcü oCuäitüüg öTgcSiciit.

In the example shown, the circuit 11 comprises an oscillator 20 whose oscillation frequency depends on the capacitance of the capacitor 5.8 connected to it. The output of the oscillator 20 is connected to a monostable circuit 21 followed by low-pass filters 22 which together effect a frequency-voltage conversion. The output terminal of the monostable circuit 21, which exits through a hole 21 in the body 7 (Figures 1 and 2), supplies (with respect to ground) a voltage V indicative of the capacitance of the capacitor 5.8 and thus of the total deformation of the structure 17.

As an alternative to the embodiment shown in Figure 3, the electronic circuit 11 may consist of an oscillator with a fixed frequency followed by a modulating element whose time axis is a variable for changing the capacitance of the

capacitor. In this case too, a low-pass filter is connected to the output of the monostable element.

Claims (7)

• ·a 4 · t «4 ·· 4 4 44 4 · ( · · « Marelli Autronica S.p.A. Munich, December 15, 1989 1-20123 Milan, Italy JST-§i 16 258 Capacitive strain sensor A ttert &Lgr; K &Mgr;&Lgr; »7 ff 1. Deformation sensor, in particular for measuring the deformation of a structure (17) consisting of a capacitor (5, 8) with opposing first (5) and second poles (8) which are connected to two points of the structure (17), the relative displacement of which in an orthogonal direction to the poles (5, 8) can be determined on the basis of the corresponding capacitance changes of the capacitor, characterized in that that the sensor (1) consists of a first tubular body (2) with an inner recess (3) in which the first pole (5) is arranged, wherein a second tubular body (7) is located in the first body (2), uvi αr;&idiagr;&ngr;&igr;&idiagr; Ui i-ujuaiigtgnxiu tuii uvi Tciiin iiiiiiig in c»cz,ug aux ucu ciaicii ivuijTCi in a direction orthogonal to the plane of position of the pole and to which the second pole (8) is attached, the first (2) and the second body (7) each being provided with anchoring elements (15) for their connection to the two points of the structure (17) whose relative displacement is to be determined. 2. Deformation sensor according to claim 1, characterized in that the first body (2) is closed at one end by a wall (4) and that the first pole (5) is formed by a conductive foil attached to this wall (4). I « I · •III!· »I···«· · I ti 3. Deformation tensor according to claim 2, characterized in that that the second pole (8) consists of a conductive foil attached to the end of the second body (7) which extends into the interior of the first body (2). 4. Deformation sensor according to one of the preceding claims,
characterized, that the srsis '2^ and the second !conner '7^ consist of a single Mstsrisl?" which has essentially the same thermal expansion properties as the structure (17) whose deformation is to be determined. 5. Deformation sensor according to claim 1,
characterized, that an electronic circuit (11) is connected to the capacitor (5, 8) which has an oscillator (20) whose frequency depends on the capacitance of the capacitor (5, 8), as well as a frequency-voltage converter (21, 23) which is connected to the output of the oscillator (20). 6. Deformation sensor according to claim 1, that an electronic circuit (11) is connected to the capacitor (5, 8) ■ which has a fixed frequency oscillator which is connected to the input % of a monostable element whose time constant is a function of the capacitance of the capacitor (S, 8); a low-pass filter is connected to the output of the monostable element 7. Deformation sensor according to claim 5, characterized, that the components of the electronic circuit (11) are supported by a support device (10) which is arranged in a recess provided in the interior of the second body (7)