WO2015043583A1

WO2015043583A1 - Measurement system and measurement method for measuring a surface deflection by means of a plasmonic reflector

Info

Publication number: WO2015043583A1
Application number: PCT/DE2014/200351
Authority: WO
Inventors: Andreas Schiffler; Jürgen GIERL; Frank Benkert
Original assignee: Schaeffler Technologies AG & Co. KG
Priority date: 2013-09-24
Filing date: 2014-07-25
Publication date: 2015-04-02
Also published as: DE102013219149A1

Abstract

The invention relates to a measurement system and to a measurement method for measuring a surface deflection on a machine part (41). In order to improve previous methods of the prior art, according to the invention, an optical approach is pursued which includes the generating of a test light beam (45) and uses a plasmonic reflector (31, 32, 33, 40) having a periodic structure (10, 11, 12) to generate plasmons. In dependence on the distortion of the periodic structure (10, 11, 12), which is substantially a nanostructure (11), which can be embedded in a microstructure (10, 12) as applicable, a part of an energy of each interacting photon is output to the periodic structure (10, 11, 12) to generate a plasmon. The reflected response beam (44) thus contains photons which are different in nature in comparison to the photons of the test light beam (45). Based on said discrepancy, a change in the periodic structure (10, 11, 12) can be recognized and thus the deflection or even a torque of the machine component (14) can be identified.

Description

Name of the invention

Measuring system and measuring method for measuring a surface strain using a plasmonic reflector

description

The invention relates to a measuring system for measuring a surface strain on a machine part. Furthermore, the invention relates to a measuring method for said measurement.

Scope of the Invention Strain gauges are widely used to monitor force loading or torsion loading of various components or machines. The problem usually lies in the fact that such an expansion is not readily apparent, in particular in an optical way can rarely be made statements on the strain of a component. For a sustained monitoring of loaded components, it is therefore necessary to first of all use a suitable sensor, whereby the measured values of the sensor must be monitored accordingly.

Background of the invention

Strain measurements are usually performed on surfaces, where the surface strain of the component can be determined by a variety of methods. Typical sensors for strain measurements on surfaces are so-called strain gauges, which can assume a wide variety of shapes and are widely used today. The technique of the strain gauges is exemplified by DE 10 2006 012 831 A1, in which the Linearis did and the Khechverhalten a strain gauge are made the subject of improvement.

For measuring non-metallic machine components, the state of the art also knows other transducers for detecting high local surface expansions, as are known, for example, from EP 0 227 036 A2. Strains are measured here by means of a tube filled with mercury, wherein the mercury column is electrically connected to connecting wires and thus can be integrated into an electrical circuit.

A problem with the methods mentioned by way of example from the prior art is the electrical wiring which accompanies the respective sensor and therefore leads to design problems if the strains or the surface expansions of movable machine parts are to be determined.

What applies to an electrical cable-based connection also applies accordingly to a connection via optical fibers, as used in optical strain gauges (fiber-Bragg-grating, FBG). In other words, the previous optical measuring methods provide in the case of a movable machine part no meaningful solution. By way of example, DE 10 2005 030 751 A1 may be mentioned here. In its teaching, the use of a Bragg grating is proposed, which can be optically interrogated by glass fiber, whether a deformation body, such as a component area, a voltage or torsion subject.

OBJECT OF THE INVENTION It is the object of the invention to enable a non-contact measurement of the surface strain of a machine part, the method being cost-efficient and easy to implement. Description of the invention

This object is achieved in a measuring system of the type mentioned at the beginning by having the following:

a light source for generating a test light beam,

a plasmonic reflector on the machine part for generating plasmons by an interaction of photons of the test light beam with a periodic structure of the plasmonic reflector, wherein a part of an energy of each interacting photon is delivered to a plasmon, and

an analyzer for spectral analysis of a reflected from the plasmonic reflector response beam, wherein the response steel is formed from participating in the interaction photons.

Photons are light quanta, which have no rest mass but are clearly defined by their energy and can be assigned in vacuum to a certain wavelength of the electromagnetic light. Plasmons are quantized vibrations of an electron gas, as occurs approximately in crystals or solids and, according to the invention, also in the periodic structure of the plasmonic reflector. Here, an electron gas is to be regarded as a physical model, which describes the group behavior of electrons in a solid. For plasmon formation, it is necessary that the periodic structure, like the atoms in a metal lattice, be able to form a conduction band for plasmons so that they can be optically excited and propagated within the periodic structure. The periodic structure consists, for example, of a polymer, but this polymer must have been doped with particles of at least one conductor or otherwise enriched, so that sufficient electrons are available to form at least approximately an electron gas. The term "electron gas" refers to a model of the behavior of groups of electrons, which, after an optical excitation, together carry out a coordinated movement and thus form the plasmon. This is not a free electron gas, but an electron gas, which exists within a conduction band for plasmons, as provided by the periodic structure.

The light source generates a test light beam which is directed to the periodic structure of the plasmonic reflector. The light cone of the test light detects the periodic structure over at least one or two periods. The test light excites plasmons in the periodic structure, with the interacting photons giving off part of their energy. This energy is absorbed by the plasmon and dissipated within the periodic structure. As a result, a response beam reflected from the plasmonic reflector contains photons which have given off some of their energy to plasmon and thus have a different frequency or a different wavelength. This can be determined by an analyzer, which performs a spectral analysis of the response beam and detects a spectral shift of the reflected light. This spectral shift can be related to the dimensions of the periodic structure.

For example, by means of a calibration or by a theoretical calculation, a periodic quantity or a periodic position can now be investigated on the basis of the measured spectral shift for a specific periodic structure. Effects on the periodic structure or the periodic size allow conclusions about the surface strain of the machine part or its torsional state. Advantageously, it can be determined without contact by means of the measuring system according to the invention whether a change has taken place in the periodic structure, which in turn suggests a surface expansion of the machine part. The surface strain is different in different ways to couple indirectly or indirectly with the periodic structure. This can be done for example via an adhesive or welding process or the like. Advantageously, the periodic structure of the plasmonic reflector is connected or coupled to the surface of the machine part such that the surface strain affects at least one periodic size or periodic position of the periodic structure. This change can be recognized in the periodic structure by the optical readout, which detects a spectral shift in comparison between the test light and the response beam.

In an advantageous embodiment, the periodic structure is formed at least partially from periodically arranged microstructures. Microstructures are structures that are smaller than 10 ^"3 meters and larger than 10 ^{" 6} meters. By the periodic arrangement of the microstructures, for example, a rotary measurement can be carried out, which determines a rotation angle of a rotatable machine part. In an advantageous embodiment, the microstructures are formed from nanostructures. The nanostructures are in the range of 10 ^"6 to 10 ^{" 9} meters. Since the nanostructures are significantly smaller than the microstructures, it is possible to detect even very small strains and possibly to combine them with a rotation angle measurement. Thus, the nanostructure allows the strain measurement and the microstructure allows the measurement of a rotation angle or a rotation speed.

In an advantageous embodiment, the microstructures and / or the nanostructures form periodically spaced-apart cylinders. In this way, it is comparatively easy to select as the periodic size of the distances or the spaced-apart cylinder, wherein the distance or distances is to bring in the simplest way with a wavelength shift in combination. So finds a surface strain on the machine Instead, the cylinders of the periodic structure are at least locally pulled apart or pushed together, so that the associated wavelength shift is detectable. It may well be that elsewhere the distance or the distances between the cylinders also adapt accordingly. Thus, attention must be paid to the size of the light cone of the test beam, so that one can ensure a reliable local assignment of the observed strain.

In an advantageous embodiment, the machine part is a movable, in particular rotatable, machine part. First, it is worth the use of the invention in fixed machine parts that are difficult to access, such as machine parts which are arranged in a vacuum or otherwise difficult to reach places. Alternatively, the non-contact measuring technology also offers an advantage for movable or even rotating machine parts, as they occur, for example, in industry or automotive technology.

Advantageously, the machine part is a shaft, a hub or a rolling element. All machine parts mentioned are subject to a certain load, which is well worth a measurement of the surface strain in one or the other application.

In an advantageous embodiment, the plasmonic reflector is formed on the machine part, in particular applied as a coating, or fixed on the machine part, in particular glued. In this case, it is intended that a corresponding coupling transfers the surface expansion of the machine part to the periodic structure such that a periodic variable or a periodic position or its changes remain spectrally recognizable. Advantageously, there is a wide range of application possibilities.

Advantageously, the periodic structure includes a first and a second coding. For example, a microstructure could vary depending on the NEN position show a slightly modified variant of another microstructure, so that for example in a wave on the basis of the partial beam illuminated microstructure is immediately apparent in which state of rotation is the wave. Thus, it is not necessary for a rotational position determination to keep the shaft running, but you can determine the position of the shaft based on the non-moving machine part. At the same time, the nanostructure could be used to perform the strain measurement by observing periodic sizes of the nanostructure from time to time, or in different microstructures, which allows two measurement methods to be combined in one measurement system. In principle, other codings are conceivable which relate, for example, to characteristic features of a machine or of the machine part. For example, it is conceivable that a microstructure or a nanostructure is made of a bar code or a two-dimensional point code.

The problem is further solved by a measuring method for measuring a surface strain on a machine part, which includes measuring method:

a generation of a test light beam,

a plasmonic reflection on a periodic structure on the machine part, wherein a part of an energy of each interacting photon is delivered to a plasmon by an interaction of photons of the test light beam with the periodic structure, and a spectral analysis of a response beam originating from the plasmonic reflection consisting of the photons involved in the interaction.

Further advantageous embodiments and preferred developments of the invention are to be taken from the description of the figures and / or the subclaims.

In the following the invention will be described and explained in more detail with reference to the embodiments illustrated in the figures. Brief description of the drawings

Show it:

FIG. 1A shows periodically arranged microstructures with integrated nanostructure, FIG.

FIG. 1B shows a simple microstructure, FIG.

1 C shows a second microstructure,

1 D shows a third microstructure, FIG. 1 E shows a simple nanostructure, FIG.

2 shows a doubly coded periodic structure,

3 shows a cylindrical roller bearing with periodic structures mounted on the end face of the cylindrical rollers,

4 shows a measuring system with light source and analyzer, and

5 shows a diagram with a spectrum of the test light beam in comparison to the spectrum of a corresponding reflected response beam.

Detailed description of the drawings

1A shows a periodic structure 10, 1 1 or at least part of a periodic structure in the micro-region (10 ^"6 ) .Together, 16 of the microstructures 10 are periodically arranged in two directions. consists of a nanostructure 1 1, both of which can be used for a separate coding.

In the exemplary embodiment shown, the nanostructure 1 1 is used for a strain measurement or an indirect torsion measurement by monitoring periodic variables within the nanostructure 1 1 and thus in some way changing a property of the back-reflected photons. In addition to a spectral shift, this may alternatively or additionally include a change in the amplitude and the phase position. Thus, there are three parameters available for evaluation, which may optionally indicate a surface strain that occurs on a machine part on which the microstructure 10 and the nanostructure 1 1 are applied. Figures 1 B, 1 C, 1 D show examples of microstructures suitable for a double encoding. The microstructures, such as the microstructures 12 of Figure 1 B, consist of a further, not shown, nanostructure and indicate by a slight modification of the macrostructure, for example, to a specific position or a certain angle of rotation of the machine part, wherein the information content the nanostructure of which can be read untouched.

FIG. 1E shows a nanostructure of the simplest type, wherein the distance A forms a periodic quantity which can be measured by the optical measuring method. The distance A changes with a spectral shift in comparison of the test light with the response beam. If the dependence between the distance A and the spectral shift is known, then this dependence can be used as a calibration curve. In the nanostructure shown, it is possible to excite plasmons, with which part of the photon energy of the test light beam can be dissipated. The plasmons absorb the energy, with the amount of energy depending on the structure in which the plasmons have been generated. In this way lets the energy loss of each photon or the associated wavelength shift close to a very specific distance A. The distance A may typically be on the order of 200 to 300 nanometers.

FIG. 2 shows a microstructure based on stars, wherein a Y-permutation PY can be distinguished from an X-permutation PX. As a result, it can be recognized at which point of the XY grid the measurement takes place. It is given an absolute information to the reading position, wherein a strain measurement based on a star shown, or by its nanostructure, is possible at any time.

Figure 3 shows a cylindrical roller bearing with differently loaded cylindrical rollers during a rotation D. In the lower region between the inner ring 35 and the outer ring 34 is the load zone in which the elastic load of the cylindrical rollers is highest. Depending on the position of the cylindrical roller, the load on its force F1, F2 or F3 increases. Thus, F1 <F2 <F3. On the end face of the cylindrical rollers shown thus sets in response to the forces acting on the cylindrical roller force F1, F2 or F3, a different surface strain. On the end faces of the cylindrical rollers shown periodic structures are attached, each forming a plasmonic reflector. A periodic quantity, such as the distance between cylindrical elements in the nanostructure, can be used to detect a surface strain. The periodic variable changes as a function of the position of the cylindrical roller or as a function of the force F1, F2 or F3 acting on it. Since the propagation conditions of plasmons change due to different strains in the periodic structure, the plasmon energy required for plasmone production also changes. Consequently, an interacting photon of the test light beam has to give off more or less energy and thus undergoes a different spectral shift. Each participating periodic structure 31, 32, 33 can thus be assigned a corresponding spectral shift as a function of the load state of the associated cylindrical roller. In this way, it is recognized to which load the respective cylindrical rollers are exposed. Therefore, for example, after a corresponding calibration, the forces F1, F2 and F3 have become optically readable. It is important that the periodic structure, which may, for example, be glued to the end face, is the same on each cylindrical roller, so that individual cylindrical rollers do not have to be distinguished per se.

FIG. 4 shows a measuring system with a light source 43, which radiates a test light beam 45 onto a plasmonic reflector 40 and spectrally analyzes the back-reflected response beam 44 in an analyzer 42 and possibly otherwise.

The plasmonic reflector 40 has a periodic structure which is intended to characterize the surface tension on the shaft 41 by being applied thereto, for example by gluing. Thanks to the nano-structure applied to the plasmonic reflector 40, a strain measurement is possible, whereby the torque of the shaft 41 can also be directly closed. This measurement can be accomplished by a prior calibration, where each surface tension is assigned the corresponding torsion or torque.

The shaft 41 is mounted with the roller bearings 38 and rotates about the axis of rotation R. Also in this application, it is conceivable information about external loads (kinetics) and kinematic states such as the angular position or a speed of the shaft 41 query.

The wavelengths of the test light beam 45 can be in the range of visible light, but also in the infrared and / or on frequencies of the gigahertz and Terrazertzbereiches lie. Accordingly, the nanostructure must be adapted so that the generation of a plasmone is possible.

FIG. 5 shows by way of example a spectral shift of approximately 80 nanometers, wherein the spectrum 50 is the spectrum of the test light beam 45 and the spectrum 51 is the spectrum of the response beam 44 of FIG. By means of a function fit, for example, the exact spectral difference of the respective center wavelength can be determined and a corresponding change of the periodic variable can be assigned.

In summary, the invention relates to a measuring system and a measuring method for measuring a surface strain on a machine part 41. To improve upon prior art methods, it is proposed to follow an optical approach involving the generation of a test light beam 45 and to generate a plasmonic reflector 40 having a periodic structure 10, 1, 12 for generating plasmons. Depending on the distortion of the periodic structure 10, 1, 12, which is formed by a nanostructure 1 1, which may optionally be embedded in a microstructure 10, 12, part of an energy of each interacting photon is used to generate a plasmone the periodic structure 10,1 1, 12 delivered. Thus, the reflected response beam 45 contains photons that are different from the photons of the test light beam 44. Based on this discrepancy, it is possible to detect a change in the periodic structure 10, 1, 12 and thus to determine the surface expansion or even a torque of the machine component 41. LIST OF REFERENCE NUMBERS

A distance, periodic size

F1, F2, F3 forces in the load zone

I intensity

D direction of rotation

R rotation axis

PX X permutation

PY Y permutation

X, Y coordinate

λ wavelength

10 microstructure

1 1 Nanostructure

12 microstructure

30 cylindrical roller bearings

31, 32,33 plasmonic reflector

34 outer ring

35 inner ring

38 rolling bearings

40 plasmonic reflector

41 wave

42 analyzer

43 light source

44 response beam

45 test light beam

50 spectrum of the test light beam

51 spectrum of the response beam

Claims

Patent claims

Measuring system for measuring a surface strain on a machine part (41).

- a light source (43) for generating a test light beam (45),

- a plasmonic reflector (31,32,33,40) on the machine part (41) for generating plasmons through an interaction of photons of the test light beam (45) with a periodic structure (10,1,1,12) of the plasmonic reflector (31 ,32,33,40), where a portion of an energy of each interacting photon is released to a plasmon, and

- an analyzer (42) for the spectral analysis of a response beam (44) reflected by the plasmonic reflector (31, 32, 33, 40), the response beam (44) being formed from photons involved in the interaction.

Measuring system according to claim 1, wherein the periodic structure (10,1 1,12) of the plasmonic reflector (31,32,33,40) is connected or coupled to the surface of the machine part (41) in such a way that the surface strains have at least one periodic quantity (A) or a periodic position of the periodic structure (10,1 1 ,12).

Measuring system according to claim 1 or claim 2, wherein the periodic structure (10,1 1,12) is at least partially formed from periodically arranged microstructures (10,12) and/or periodically arranged nanostructures (1 1).

Measuring system according to claim 3, wherein the microstructures (10,12) are formed from the nanostructures (1 1).

Measuring system according to one of the preceding claims, wherein the microstructures (10, 12) and/or the nanostructures (1 1) form periodically spaced apart cylinders.

6. Measuring system according to one of the preceding claims, wherein the machine part (41) is a movable, in particular rotatable, machine part (41).

7. Measuring system according to claim 6, wherein the machine part (41) is a shaft (41), a hub or a rolling body of a rolling bearing.

8. Measuring system according to one of the preceding claims, wherein the plasmonic reflector (31, 32, 33, 40) is formed on the machine part (41), in particular applied as a coating, or is attached, in particular glued, to the machine part (41).

9. Measuring system according to one of the preceding claims, wherein the periodic structure (10,1 1,12) contains a first and a second coding.

10. Measuring method for measuring a surface strain on a machine part (41).

- generating a test light beam (45),

- a plasmonic reflection on a periodic structure

(10,1 1,12) on the machine part (41), whereby a portion of the energy of each interacting photon is released to a plasmon through an interaction of photons of the test light beam (43) with the periodic structure (10,1 1,12). , and

- a spectral analysis of a response beam (44) originating from the plasmonic reflection, consisting of photons involved in the interaction.