WO2023274458A1

WO2023274458A1 - Normal stress sensor system

Info

Publication number: WO2023274458A1
Application number: PCT/DE2022/200084
Authority: WO
Inventors: Siegfried Reck
Original assignee: Contitech Luftfedersysteme Gmbh
Priority date: 2021-06-30
Filing date: 2022-05-02
Publication date: 2023-01-05
Also published as: DE102021206816A1

Abstract

The present invention relates to a normal stress sensor system having at least one normal stress sensor (1) having at least one first resonator (11a) with a first natural frequency, which is, preferably at least substantially linearly, dependent on a first normal mechanical stress (F) to be recorded, having at least one second resonator (11b) with a second natural frequency, which is, preferably at least substantially linearly, dependent on a second normal mechanical stress (F) to be recorded, the normal stress sensor (1) being designed to be arranged between two objects in such a way that normal mechanical stresses (F) acting between the objects are able to alter the natural frequencies of the resonators (11a, 11b), and having at least one control unit designed to excite the resonators (11a, 11b) of the normal stress sensor (1) to produce oscillations at the natural frequencies thereof and to record the oscillations thereof, the control unit further being designed to determine the normal mechanical stresses (F) from the recorded oscillations of the resonators (11a, 11b).

Description

description

normal stress sensor system

The present invention relates to a normal stress sensor system according to patent claim 1, a normal stress sensor for use in such a normal stress sensor system according to patent claim 14 and a control unit for use in such a normal stress sensor system according to patent claim 15.

In order to measure mechanical normal and shear stresses, the transducers must be integrated into the component in such a way that they can record the force flow to be measured. If this power flow is inhomogeneous, flat sensors are usually required. Elastomer-based pressure measuring foils, which are inserted into the component for each measurement, depict the distribution of the maximum stresses that have occurred by means of color changes. However, this is usually imprecise, cannot be recorded electronically and an unused pressure measuring foil must be installed, removed again and evaluated for each measurement, which makes this type of recording of normal and shear stresses unattractive.

With the help of electronic pressure measuring foils, normal stress distributions can be measured continuously and electronically. For example, a matrix of piezoresistive transducers supplies the data for a spatially resolved image. Alternatively, dielectric elastomer sensors (DES) can be suitable for measuring mechanical normal stresses.

With the exception of the dielectric elastomer sensors, however, such known sensors are only suitable to a limited extent for measuring mechanical stresses in elastomeric bodies, because the dielectric elastomer sensors cannot follow relatively large strains. In addition, piezoresistive pressure sensing foils are expensive, so they are preferably used for discontinuous measurements.

DE 102020216234.4 (unpublished) discloses a device for detecting mechanical normal stresses in an elastomeric component, with an elastomeric component having at least one normal stress sensor, the normal stress sensor having at least one resonator whose natural frequency depends, preferably at least essentially, on the mechanical normal stresses to be detected linear, dependent, wherein at least the resonator is embedded in the elastomer component in such a way that mechanical normal stresses acting on the elastomer component can change the natural frequency of the resonator, and with at least one control unit which is designed to excite the resonator to oscillate at its natural frequency and its To detect vibrations, wherein the control unit is further designed to determine the mechanical normal stresses of the elastomeric component from the detected vibrations of the resonator.

In other words, a normal force sensor for elastomeric components is described, which consists of a so-called symmetrical microwave stripline, which is designed as a resonator. A dielectric is located along the longitudinal axis above and below a conductor strip, which is covered on its outer surface with a conductive layer and is electrically at ground potential. The normal force to be measured compresses the strip line along the longitudinal axis and thus reduces the distance between the centrally arranged conductor strip and the two outer ground planes along the longitudinal axis, which changes the wave impedance and the return loss of the arrangement. When measuring the force, the strip line is connected to an impedance spectrometer that Evaluates the wave impedance and the return loss and uses this to calculate the measurement result.

A disadvantage of the device of DE 102020216234.4 is that in this way only the average normal stress can be detected, which acts in the middle of the surface of the normal stress sensor.

One object of the present invention is to improve the possibilities for measuring normal stresses of the type described in the introduction. In particular, different normal stresses, i.e. different value ranges, should be able to be measured. At the very least, an alternative to known options for measuring normal stresses should be created.

The object is achieved according to the invention by a normal stress sensor system having the features of patent claim 1, by a normal stress sensor having the features of patent claim 14 and by a control unit having the features of patent claim 15. Advantageous developments are described in the dependent claims.

The invention thus relates to a normal stress sensor system with at least one normal stress sensor with at least one first resonator with a first natural frequency which is dependent, preferably at least essentially linearly, on a mechanical first normal stress to be detected, with at least one second resonator with a second natural frequency which is a mechanical second normal stress to be detected, preferably at least essentially linearly, wherein the normal stress sensor is designed to be arranged between two objects in such a way that mechanical normal stresses acting between the objects can change the natural frequencies of the resonators, and with at least one control unit , which is formed, the resonators of the normal stress sensor to excite oscillations in its natural frequencies and to detect its oscillations, the control unit also being designed to determine the mechanical normal stresses of the elastomer component from the detected oscillations of the resonators.

In other words, according to the invention, the mechanical normal stresses of a plurality of differently designed resonators or designed with regard to their natural frequencies can be detected by sensors. The resonators can thus detect mechanical normal stresses in the form of compressive forces and/or tensile forces, in that the forces influence the vibration behavior of the resonators in such a way that the vibration behavior of the respective resonator can be characteristic of the acting mechanical normal stresses. If the resonators are excited to oscillate and the oscillating behavior of the resonators is recorded and evaluated, conclusions can be drawn about the mechanical normal stresses that are present. As a result, mechanical normal stresses can be continuously detected by sensors. In this way, different value ranges of the normal voltages can be detected by the two different resonators, and not just a single value range of a usually mean normal voltage, as was previously known. Thus, the normal stresses that occur can be detected by sensors in a larger value range of their amplitudes or strengths than previously known.

It is particularly advantageous here that resonators of this type can be produced simply, quickly, accurately in position and/or robustly, for example by vulcanization, by printing or by gluing. Such resonators can also be made comparatively flat. Furthermore, such resonators or a corresponding normal voltage sensor can be made available as a simple component at comparatively low cost. According to one aspect of the invention, the resonators of the normal stress sensor are elastic, preferably in the form of a conductive liquid. In this way, the resonators can flexibly adapt to the movements of the objects between which the normal stresses are to be measured, and as a result can record the mechanical normal stresses comparatively precisely. The resonators or the corresponding normal stress sensor can also follow significantly greater expansions than rigid measuring transducers due to their elastic construction.

According to a further aspect of the invention, the resonators of the normal voltage sensor are designed as high-frequency resonators. A high-frequency resonator is understood to mean a resonator which can work in the frequency range of high-frequency oscillations. Flier are understood to mean frequencies in the frequency range from 1 to 300 GFIz.

The advantage here is that such high frequencies have correspondingly small wavelengths and the resonators can thus be realized with comparatively small dimensions. In this way, the comparatively small resonators can also be integrated in a very small normal voltage sensor. Overall, a small resonator may favor being embedded within a material.

Another advantage of this is that due to the high frequency, no interaction between the electromagnetic field of the resonators and a surrounding material can occur, which could have a negative effect on the functionality.

Another advantage of this is that due to its high operating frequency, the resonators can be very sensitive to the measured value signal and thus to normal force or pressure. This can increase the measurement sensitivity. According to a further aspect of the invention, the resonators of the normal stress sensor are arranged on a preferably elastic carrier layer, preferably a carrier film. This can favor implementation, especially as a flexible design.

According to a further aspect of the invention, the resonators of the normal stress sensor are arranged in a ring around a longitudinal axis, the longitudinal axis corresponding to the direction of the mechanical normal stresses acting between the objects. This can favor an arrangement of the multiple resonators that is as uniform as possible relative to the axis of the normal stresses to be detected along the longitudinal axis and make it possible for the same normal stresses to act equally on all resonators and thus to be able to be detected by them in the same way.

According to a further aspect of the invention, the resonators of the normal stress sensor are each arranged perpendicular to the direction of the mechanical normal stresses between at least one pair of electrically conductive conductor layers and embedded in a dielectric, with at least one feed line being arranged in the dielectric and extending parallel to the resonators. This can represent an easy way to implement the resonators with the properties and advantages described here.

According to a further aspect of the invention, the normal voltage sensor has at least one connection which is electrically conductively connected in parallel to the resonators and to the feed line. This can allow access, in particular for the control unit, to the detected sensor values.

According to a further aspect of the invention, the dielectric of the normal stress sensor is elastic. This can implement the allow corresponding properties described above on the part of the dielectric.

According to a further aspect of the invention, the resonators of the normal stress sensor are designed to extend over a surface, preferably in a U-shape, the resonators being embedded in the dielectric with their surface plane of extension perpendicular to the direction of the mechanical normal stresses. This can make it possible to implement the resonators with a sufficiently long extension while at the same time having a compact design. This can favor a large-scale sensory detection of the mechanical normal stresses, which can improve the quality of the sensory values.

According to a further aspect of the invention, the control unit is designed to excite the resonators of the normal stress sensor to oscillate at their natural frequencies using broadband pulses, to detect their impulse responses and to determine the mechanical normal stresses from the detected impulse responses. This can represent a mode of operation in which the resonators are excited to oscillate at their respective natural frequencies and the corresponding signals from the resonators are recorded or received.

According to a further aspect of the invention, the control unit is designed to continuously excite the resonators of the normal stress sensor with oscillations of variable frequency to oscillate at their natural frequency, to detect their oscillations, to determine the transmission parameters from the resonant frequency of the detected oscillations and to determine the mechanical normal stresses from the determined transmission parameters to determine. This can represent an alternative mode of operation to excite the resonators to oscillate at their respective natural frequency and to detect or receive the corresponding signals of the resonators. According to a further aspect of the invention, the normal stress sensor also has at least one third resonator with a third natural frequency which is dependent, preferably at least essentially linearly, on a mechanical third normal stress to be detected. This can correspondingly extend the possibilities described above to a third resonator.

According to a further aspect of the invention, the normal stress sensor has a housing which is designed to be arranged between the two objects, the housing being designed to transmit mechanical normal stresses acting between the objects partially in parallel past the resonators. In other words, the normal stress sensor according to the invention can be designed in this way in a manner comparable to a force measuring electrode, so that the normal stresses can be detected by sensors as described above, but without having a complete effect on the elements of the normal stress sensor and possibly overloading or damaging them as a result .

The present invention also relates to a normal stress sensor for use in a normal stress sensor system as described above. A normal stress sensor can thereby be provided to implement a normal stress sensor system as described above and to use its properties and advantages.

The present invention also relates to a control unit for use in a normal stress sensor system as described above. In this way, a control unit can be created in order to implement the device described above and to be able to use its properties and advantages. The control unit can also be used universally, for example for similar devices or measuring systems, with appropriate adjustment of the software implementation of the functions described above for the respective application.

In other words, the object of the present invention can be seen in particular as creating a force-measuring device that can record several individual forces simultaneously in order to determine the force distribution in its measuring area.

The task can be solved in particular by a force-measuring device with at least two resonators, which are tuned to different frequencies due to their geometric dimensions and can be excited by field coupling from a common feed line. The entire structure consisting of the feed line and the coupled resonators can be implemented as a symmetrical strip line. While conventional strip lines consist of rigid materials, the force measuring device according to the invention can consist of elastic materials. In particular, the striplines can be created with conductive ink that is based on metallic nanoparticles and can therefore allow for expansions of around 1% before the structures printed with it lose their conductivity. An elastic foil can be used as a carrier for the conductor structures.

A coaxial high-frequency cable can preferably be connected to a connector of the force-measuring device and connected to a transceiver as a control unit. The outer conductor of the connector can be electrically at ground potential. The transceiver can be designed as a so-called "Software Defined Radio", whose integrated programmable computing unit can calculate the forces acting on the individual resonators from the changes in the individual resonance frequencies or the return losses. The force-measuring device according to the invention can be characterized by a low overall height of 2 mm<h<10 mm. By specifying the maximum permissible compression, the measuring range can be predetermined with the help of the modulus of elasticity of the dielectric. The outer, grounded ground surfaces of the dielectric can protect the force-measuring device from interference from electromagnetic influences. Due to its elasticity, the measuring device can also be used for curved surfaces.

The force-measuring device according to the invention can preferably be implemented for a round cross-section with three measuring points distributed around the circumference. The dimensions of the traces, i.e. their length and width, as well as their spacing, can be determined using a simulation calculation for the return loss. The dimensions can be tuned so that the resonances in the frequency response are distinguishable from each other. If necessary, the feed line can be terminated with an ohmic resistor.

In order to improve the quality of the resonators, the conductor structures can be printed on both sides of the carrier film so that they run congruently.

In order to avoid damage to the elastomeric dielectric due to mechanical overload, the force measuring device can be integrated into a metal housing that takes over part of the power flow ("shunt").

Normal stress sensor systems according to the invention can be used in particular in the case of elastomeric components such as belts, air springs, hoses, belts, bearings, etc., and in measurement technology in general.

An exemplary embodiment and further advantages of the invention are explained below in connection with the following figures. It shows: Fig. 1 is a schematic representation of an inventive

Normal stress sensor considered along the longitudinal axis;

FIG. 2 shows the representation of FIG. 1 cut open and viewed unrolled along the longitudinal axis; FIG. Figure 3 is a section A-A through Figures 1 and 2 perpendicular to the longitudinal axis; and FIG. 4 shows the representation of FIG. 3 with the housing.

The above figures are described in cylindrical coordinates with a longitudinal axis X, a radial direction R perpendicular to the longitudinal axis X and a circumferential direction U running around the longitudinal axis X. The longitudinal axis X, the radial direction R and the circumferential direction U together can also be defined as spatial directions X, R, U or as cylindrical spatial directions X, R, U. A normal stress sensor 1 according to the invention has an elastic

Carrier layer 10, which can also be referred to as carrier film 10. The carrier film 10 is essentially circular with a radial projection. Along the longitudinal axis X from above, a feed line 12 is printed onto the carrier film 10, which runs in a ring around the longitudinal axis X and ends at one end on the projection of the carrier film 10 and is electrically conductively connected there to a connection 13 in the form of a plug 13. Radially outside the feed line 12, offset by 90° to the plug 13 in the circumferential direction U, a first U-shaped resonator 11a is applied on the same side as the feed line 12 by means of printed electrically conductive ink. This is followed by a second resonator 11b and a third resonator 11c of the same type, offset by a further 90°, but each of which is designed to become larger with regard to its extent in the circumferential direction U, see Figures 1 and 2. The carrier film 10 is along the longitudinal axis X with the resonators 11a, 11b, 11c and the feed line 12 on both sides in a flexible dielectric 14 embedded, see FIG. 3. The dielectric 14 is arranged on both sides along the longitudinal axis X between electrically conductive conductor layers 15 in the form of ground planes 15 . The carrier foil 10 is arranged exactly in the middle between the two ground surfaces 15 along the longitudinal axis X, so that a distance h from the carrier foil 10 to each of the two ground surfaces 15 is the same when the normal voltage sensor 1 is in the unloaded state.

The normal stress sensor forms a normal stress sensor system together with a control unit (not shown). The control unit can excite the resonators 11a, 11b, 11c of the normal stress sensor 1 to oscillate at the respective natural frequency and these oscillations can be detected by the control unit 1. The control unit can determine the mechanical normal stresses F along the longitudinal axis X from the detected vibrations of the resonators 11a, 11b, 11c.

In other words, if the distance h between the ground surfaces 15 and the resonators 11a, 11b, 11c is reduced by the acting normal voltage F, this affects the natural frequency of the resonators 11a, 11b, 11c, ie the natural frequencies are detuned . This can be detected or recognized by the control unit and the applied normal mechanical stress F along the longitudinal axis X can be determined from this. In this case, different strong normal voltages F can lead to different significant detunings of the resonators 11a, 11b, 11c, which can each be designed for a value range of the normal voltages F. Correspondingly, depending on the applied normal stress F, one of the resonators 11a, 11b, 11c can be detuned more than the other two resonators 11a, 11b, 11c and then exactly its sensor values can be used to determine the applied mechanical normal stress F along the longitudinal axis X. This can increase the measurement accuracy, since one of the three resonators 11a, 11b, 11c can be designed to be correspondingly sensitive over the value range of the normal voltages F to be detected for all three resonators 11a, 11b, 11c in order to to cover or detect the entire range of values of the normal stresses F to be detected with greater accuracy than is previously known from such normal stress sensors with only one resonator. In order to reduce the normal stresses F acting on the normal stress sensor 1, the normal stress sensor 1 can be arranged in a housing 16 comparable to a load cell. The connection to objects (not shown), between which the normal stresses F are to be detected by sensors as described above, can be made along the longitudinal axis X on one side via a housing base 16a and on the opposite side via a housing cover 16b. The normal voltages F can be conducted parallel to the normal voltage sensor 1 via the housing walls 16c of the housing 16, see Figure 4.

List of reference symbols (part of the description)

A-A section F mechanical normal stresses or direction of the mechanical

Normal stresses h Distance between carrier layer 10 and ground planes 15

R radial direction

U circumferential direction X longitudinal axis

I normal stress sensor

10 backing layer; carrier film

I I a first resonator 11 b second resonator

11 c third resonator

12 feed line

13 connector; plug

14 dielectric 15 electrically conductive conductor layers; ground planes

16 housing

16a caseback

16b housing cover

16c housing walls

Claims

patent claims

1. Normal stress sensor system with at least one normal stress sensor (1) with at least one first resonator (11a) with a first natural frequency, which is dependent on a mechanical first normal stress (F) to be detected, preferably at least essentially linearly, with at least one second resonator ( 11b) with a second natural frequency, which is dependent on a mechanical second normal stress (F) to be detected, preferably at least essentially linearly, the normal stress sensor (1) being designed to be arranged between two objects such that between the objects acting mechanical normal stresses (F) can change the natural frequencies of the resonators (11a, 11b), and with at least one control unit which is designed to excite the resonators (11a, 11b) of the normal stress sensor (1) to oscillate at its natural frequencies and its To detect vibrations, wherein the control unit further is designed to determine the mechanical normal stresses (F) from the detected vibrations of the resonators (11a, 11b).

2. Normal stress sensor system according to claim 1, characterized in that the resonators (11a, 11b) of the normal stress sensor (1) are elastic, preferably designed as a conductive liquid.

3. Normal stress sensor system according to claim 1 or 2, characterized in that the resonators (11a, 11b) of the normal voltage sensor (1) are designed as high-frequency resonators (10).

4. Normal stress sensor system according to one of the preceding claims, characterized in that the resonators (11a, 11b) of the normal stress sensor (1) are arranged on a preferably elastic carrier layer (10), preferably carrier film (10).

5. Normal stress sensor system according to one of the preceding claims, characterized in that the resonators (11a, 11b) of the normal stress sensor (1) are arranged in a ring around a longitudinal axis (X), the longitudinal axis (X) being the direction of the mechanical normal stresses acting between the objects (F) corresponds.

6. Normal stress sensor system according to one of the preceding claims, characterized in that the resonators (11a, 11b) of the normal stress sensor (1) are each perpendicular to the direction of the mechanical normal stresses (F) between at least one pair of electrically conductive conductor layers (15) and in a dielectric (14) are arranged embedded, wherein in the dielectric (14) at least one feed line (12) is arranged, which extends parallel to the resonators (11a, 11b).

7. Normal voltage sensor system according to claim 6, characterized in that the normal voltage sensor (1) has at least one connection (13) which is electrically conductively connected in parallel to the resonators (11a, 11b) and to the feed line (12).

8. Normal stress sensor system according to claim 6 or 7, characterized in that the dielectric (14) of the normal stress sensor (1) is elastic.

9. Normal stress sensor system according to one of the preceding claims, characterized in that the resonators (11a, 11b) of the normal stress sensor (1) are designed to extend over a surface area, preferably in a U-shape, the resonators (11a, 11b) with their surface plane of extension are embedded in the dielectric (14) perpendicular to the direction of the mechanical normal stresses (F).

10. Normal stress sensor system according to one of the preceding claims, characterized in that the control unit is designed to excite the resonators (11a, 11b) of the normal stress sensor (1) by means of broadband pulses to oscillate at their natural frequencies, to record their impulse responses and from the recorded impulse responses to determine the mechanical normal stresses (F).

11 . Normal stress sensor system according to one of the preceding claims, characterized in that the control unit (2) is designed to continuously stimulate the resonators (11a, 11b) of the normal stress sensor (1) with oscillations of variable frequency to oscillate at their natural frequency, to detect their oscillations to determine the transmission parameters from the resonant frequency of the detected vibrations and to determine the mechanical normal stresses (F) from the determined transmission parameters.

12. Normal stress sensor system according to one of the preceding claims, characterized in that the normal stress sensor (1) also has at least one third resonator (11c) with a third natural frequency, which depends on a third mechanical normal stress (F) to be detected, preferably at least essentially linearly. is dependent.

13. Normal stress sensor system according to one of the preceding claims, characterized in that the normal stress sensor (1) has a housing (16) which is designed to be arranged between the two objects, the housing (16) being designed to act between the objects to transfer mechanical normal stresses (F) partially parallel to the resonators (11a, 11b) past.

14. Normal stress sensor (1) for use in a normal stress sensor system according to any one of claims 1 to 13.

15. Control unit for use in a normal stress sensor system according to any one of claims 1 to 13.