Dual mirror shearing interferometer

Abstract

The present invention relates to a measuring device (10) for non-destructive measurement of a surface of an object (22) by means of interferometry, the measuring device (10) comprising a diaphragm (20) having an aperture (21), a mirror arrangement (30) having two mirrors (32), each having a mirror surface (38), one of the two mirrors (32) being a partially transparent partial mirror (34) and one of the two mirrors (32) being a perfect mirror (36), the perfect mirror (36) being arranged behind the partially transparent partial mirror (34) in the radial direction (S), a camera lens (42) and a camera (40), an incident light beam passes through the diaphragm (20), and the mirror arrangement (30) comprises a mirror lens (42) and a camera (40), the incident light beam passes through the diaphragm (20), and the mirror arrangement (30) comprises two mirrors (32), each having a mirror surface (38), one of the two mirrors (32) being a partially transparent partial mirror (34) and one of the two mirrors (32) being a perfect mirror (36), the perfect mirror (36) being arranged behind the partially transparent partial mirror (34) in the radial direction (S), In the process, the light beam (100) is diffracted and strikes a mirror mechanism (30) where it is split and deflected into two partial beams (110, 120), the two partial beams (110, 120) then reach a camera (40) and interfere within the camera (40), the light beam (100) passes through a camera lens (42) in front of the camera (40) in a beam direction (S), one of the mirrors (32) of the mirror mechanism (30) is rotatable with respect to the other mirror (32) such that the two mirrors (32) include a non-zero angle β in a plane perpendicular to the mirror surface (38), the camera (40) includes a camera chip with a local sampling frequency, and the design of the diaphragm (20) is such that the incoming light beam (100) is diffracted as it passes through the diaphragm (20) to produce a spatial frequency f _light is at most the maximum local sampling frequency f _max_camera This is done to be consistent with the

Description

Technical Field

[0001] The present invention relates to a measuring device for non-destructively measuring the surface of an object using an interference measurement method. This device includes a diaphragm, a mirror mechanism, and a camera.

Background Art

[0002] Non-destructive measurement of an object surface by an interference measurement method is known in principle and has been established as a reliable method. For example, an interferometer is used for this purpose. An interferometer based on the principle of shearography is also known.

[0003] Shearography is also a non-destructive laser inspection method for non-contact high-sensitivity defect detection of a surface. This is particularly suitable for measuring modern lightweight materials made of fiber-reinforced plastics. Shearography is playing an increasingly central role in quality assurance in the aerospace industry and also in the automotive industry. In these fields, reduction of energy consumption and related utilization of resources will determine future trends.

[0004] Modern shearography measuring devices operate with a freely adjustable "shear". This is a decisive parameter for setting the sensitivity according to the measurement task. Furthermore, a so-called phase shift method is currently used for typical data processing of qualitative and quantifiable results in shearography component analysis.

[0005] A measuring device based on the principle of shearography and spatial phase shift is described in WO 2020 / 164667 A1, where a Mach-Zehnder interferometer is used. The laser light reflected from the measured object irradiated with the laser light hits a first beam splitter and is split into two components. Each component is directed towards a separate mirror and reflected by them. One mirror is tilted by an angle β from a 45° position, thereby creating the desired "shear" required for shearography. These two components then each pass through one diaphragm, whereby one of the diaphragms is displaced from the optical central axis. These two components are then merged again at a second beam splitter to obtain the desired interference result. This is imaged by a camera, enabling shearography measurements to be carried out. However, the construction of such a measurement system is complex and expensive.

[0006] Other well-known shearography measuring devices are also very sensitive to environmental influences and are difficult to use in industrial applications. In particular, temperature fluctuations, vibrations, or disturbing ambient light often cause disturbances that prevent the measurement or distort the measurement results to an unusable level. To ensure the reliable use of these systems, either a low-speed measuring device is used or high-stabilization efforts are carried out. In the former case, however, multiple measurements are required, and the latter efforts are carried out, for example, by using a measuring table that insulates vibrations or a special foundation that cancels out the vibrations of the measurement room. In many cases, the use of a powerful light source (for example, the use of a powerful laser) is also necessary for the measurement, which inevitably involves a strong need to increase the laser safety class and the high cost for a powerful laser. Furthermore, these measurement systems are not only expensive for the measurements performed, but also lack flexibility, have limited mobility, require a large setup, and take time to use. Moreover, these systems are often not user-friendly and can only be used limitedly in industrial environments.

[0007] The measurement setups and systems described in German Patent Invention No. 4231578C2, US Patent No. 6,606,160B1, Japanese Patent Application Laid-Open No. 63009802A, and European Patent Application Publication No. 0189482A1 show optical sensor setups for shearography in which the necessary phase information is obtained over time during measurement. All of these have at least one mirror that must be moved laterally during measurement, or an optical transmission element that must be controlled with respect to its optical refractive index during measurement. In addition to the high cost of these special, high-precision electromechanical or optoelectronic components, they require constant control to obtain phase information for each measurement, significantly reducing the robustness of the measurement.

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, the problem is to propose an improved measuring device that overcomes the disadvantages of the current state of the art, is user-friendly, and cost-effective.

Means for Solving the Problems

[0009] This problem is solved by a measuring device having the features described in claim 1 and a method having the features described in claim 15.

[0010] In one aspect, the present invention relates to a measuring device for non-destructively measuring a measurement object or the surface of an object using an interference measurement method, to which light as a light beam reflected from the surface is incident. The measuring device according to the present invention includes a diaphragm having an aperture, a mirror mechanism, a camera lens, and a camera. The mirror mechanism has two mirrors, each of the two mirrors has a mirror surface, one of the two mirrors is a partially transparent partial mirror, and one of the two mirrors is a total mirror, and the total mirror is arranged radially behind the partially transparent partial mirror.

[0011] The incident light beam passes through the diaphragm, is diffracted, hits the mirror mechanism, where it is split into two partial beams and deflected, and then reaches the camera. The partial beams of the light beam interfere with each other inside the camera. The light beam passes through the camera lens in front of the camera in the beam direction. In this device, one of the mirrors of the mirror mechanism is rotatable relative to the other mirror such that the two mirrors enclose a non-zero angle β in a plane perpendicular to the mirror surface.

[0012] In the measuring device according to the invention, the camera has a camera chip with a local sampling frequency. The local sampling frequency of the camera chip is the distance between the photosensitive pixels of the chip. The pixels are preferably square. Preferably, light having a spatial frequency of up to one oscillation per two pixels of the camera can be detected. The physical unit of the local sampling frequency is [1 / m].

[0013] The use of a diaphragm is essential for implementing the spatial phase shift. According to the invention, the diaphragm is designed such that the reflected light beam is diffracted in a desired manner when passing through the diaphragm. The diffraction of the light beam is such that its spatial frequency f light (i.e., the spatial frequency of the light) is, at most, equal to the maximum local sampling frequency f max camera of the camera chip during detection on the camera chip. The term spatial frequency of the optical signal means a sequence of bright and dark parts on the spatial axis, and this also has the unit [1 / m]. Therefore, the generation of light diffraction by the diaphragm is performed such that, at most, one bright interference peak or one dark interference valley of the light hitting the camera is imaged onto a camera pixel.

[0014] Therefore, it is preferably the case that the following equation applies. f light ≦f max camera or f light ≦1 / (2×b pixel ) (where b pixel = the pixel width of the camera chip)

[0015] In another aspect, the invention relates to a measurement system having such a measuring device and an evaluation unit, the evaluation unit receiving and processing the measurement signals generated by the camera, whereby the measurement variable characteristics of the surface of the object to be measured are determined from the measurement signals of the interfering partial beams, and this measurement variable characteristic enables statements to be made about the characteristics of the surface. As characteristics of the surface, there may be mentioned the texture, quality, deformation, strain, and defects (if any), or the uniformity of the surface of the object. The quality of the surface connection may also be determined.

[0016] Another aspect of the invention relates to a corresponding method, a computer program product, and a storage medium, the computer program product including program code for performing each step of the method when the program code is executed on a computer, and the storage medium storing a computer program that causes a computer to execute the method described herein when executed on the computer.

[0017] The dependent claims describe preferred embodiments of the invention. Of course, the features described above, as well as the features to be described later, may be used not only in the combinations shown in each case, but also in other combinations or alone, without departing from the scope of the invention. Specifically, the method and the computer program product may be implemented according to the embodiments described with respect to the measuring device in the dependent claims.

[0018] In the context of the present invention, it has been found that in a measuring device based on a Mach-Zehnder setup, in which the optical path from the entry of light into the measuring device to the camera includes two beam splitters, the optical path is very long, and as a result, shadows occur in the camera image. That is, it is not easy to capture a large measurement object and several measurement steps are required. This is because the measurement range at a typical measurement distance of about 400 mm corresponds only to the size of a DIN A4 page. The same problem occurs because the optical path of light is only slightly shorter in the case of a Michelson setup device.

[0019] Furthermore, when light passes through two beam splitters, unwanted light reflection and absorption are caused, which leads to a decrease in the laser measurement light. Therefore, a powerful laser source must be used to illuminate the object, thereby increasing the cost of the laser and incurring additional costs for raising the laser safety class. Furthermore, the quality of the result is degraded by the reflection.

[0020] As part of the present invention, it has also been found that the shift of two light beams required for shearography can be generated in another way. For this purpose, as revealed by the research, the light beam reflected by the measurement object first passes through a diaphragm and then directly hits a mirror mechanism, where the light beam is split into two partial beams. By tilting or screwing one of the mirrors to branch the partial beams so that they can interfere in the camera, it is possible to generate the necessary shear. That is, there is no intervening component that diffracts, splits, or reflects the light beam reflected by the measurement object.

[0021] Therefore, the mirror mechanism is designed such that the light beam hitting the mirror mechanism is split into a first partial beam and a second partial beam at the partial mirror, and the first partial beam is reflected and directed towards the camera. The second partial beam passes through the partial mirror, is reflected by the full mirror, and is directed towards the camera. The second light beam passes through the partial mirror again, but this time it passes through in another direction without being deflected.

[0022] As an advantage of the measuring device according to the present invention, an independent beam splitter can be omitted, and the optical path in the measuring device can be shortened. By shortening the optical path, the effect of forming shadows during measurement is reduced, and thereby a measurement range twice as wide as that of the Mach-Zehnder setup can be measured. The losses due to reflection and absorption are minimized, which is particularly significantly less than in the case of known setups, enabling the use of a low-power laser with the lowest laser safety class, thereby reducing costs and eliminating the high requirements for laser safety and protection.

[0023] Unlike the prior art, according to the present invention, the phase information is generated using the principle of "spatial phase shift". Furthermore, standard components (specially adjusted and specially arranged) can be used. As a central advantage, this optical setup does not include components that move or are continuously controlled during the measurement. Components that do not move during the measurement significantly increase the robustness of the measurement (by approximately a factor of 10). This means that this measuring device and measuring method can be used for the first time even in a harsh industrial environment.

[0024] According to the present invention, such a mechanism also serves as the basis for a double mirror shearing interferometer, specifically a small double mirror shearing interferometer that can be set up in a very narrow space and provides very good and reliable measurement results. This mechanism can be realized with only a few components, and thus is low-cost and very robust against environmental influences. Furthermore, the installation and adjustment work is reduced. This system is movable and can be easily deployed at the desired measurement location.

[0025] In a preferred embodiment of the measuring device according to the present invention, one mirror of the mirror mechanism is aligned such that the light beam hitting the mirror mechanism is reflected at an angle α in the direction of the camera and hits the camera. The angle α is preferably at least 70°, very preferably at least 80°, and particularly preferably 90°. Furthermore, the angle α is at most 110°, preferably at most 100°. Ideally, the angle α is 90°. However, acceptable measurement results that are actually useful can still be achieved within an angular range of ±20°.

[0026] In another preferred embodiment, each mirror of the mirror mechanism is designed such that the mirror surfaces where reflection or partial reflection occurs are spaced apart from each other. This distance is not zero, whereby the two partial beams formed in the mirror mechanism are offset. The distance x between the two mirror surfaces is defined as the distance perpendicular to the mirror surface between the mirror surfaces directed towards the incident light beam. Therefore, the mirror surface is regarded as the surface of the mirror where reflection or partial reflection of the incident light beam occurs. In a preferred embodiment, this distance x between the mirror surfaces is 70% or more of the width of the aperture of the diaphragm used. Furthermore, according to the results of practical research, the distance x must not be greater than 7 times the aperture of the diaphragm.

[0027] Therefore, it is preferable that the following equation is applicable. b max diaphragm ×cos(45°)≦x≦10×b max diaphragm ×cos(45°)

[0028] Under these conditions, a virtual double slit can be seen from the viewing direction of the camera, which provides a sufficiently good spatial frequency for spatial phase shift or for spatial frequency sampling for the purpose of optical phase determination.

[0029] In another similarly preferred embodiment of the measuring device according to the present invention, the angle by which one mirror of the mirror mechanism rotates with respect to the other mirror of the mirror mechanism is in the range of 0.001° to 20°. Preferably, the range of this angle β is 0.01° to 10°, and more preferably, the angle β is in the range of 0.1° to 5°. In actual use, a very robust and effective measurement value was obtained when the angle β was in the range of 0.2° to 1°. The range of 0.5° to 1° for the angle β was determined as the optimal operating range in various measurements for determining the surface characteristics of an object.

[0030] In principle, either mirror of the mirror mechanism can be made rotatable and either mirror can be designed as a fixed mirror. However, in actual applications, it has been shown that it is advantageous when the full mirror of the mirror mechanism is rotatable with respect to the partial mirror. Therefore, the partial mirror is fixed and the full mirror is rotatable.

[0031] In a preferred embodiment of the measuring device, in order to generate good measurement results, the camera lens may be arranged in front of the diaphragm in the direction of the beam. Alternatively, it is possible to arrange the camera lens between the mirror mechanism and the camera. In either case, good measurement results are achieved in the same way. Therefore, depending on the use and design of the camera, the arrangement method of the lens is different.

[0032] In a similarly preferred embodiment of the measuring device according to the present invention, the diaphragm includes a slit having a slit width of b, and the maximum value of the slit width b is the wavelength λ of the light beam, the focal length f of the camera lens lens and the maximum local sampling frequency f of the camera chip max camera and their product.

[0033] Therefore, it is preferable that the following equation is applied to the maximum gap width of the diaphragm. b max diaphragm ≦λ×f×f max camera Or b max diaphragm ≦λ×f×1 / 2b pixel

[0034] In another preferred embodiment of this measuring device, the diaphragm includes a circular aperture having a diameter of d. This leads to an improvement in the spatial resolution of the camera image, that is, an improvement in the lateral measurement accuracy. The maximum value of the diameter d is preferably 1.22 times the wavelength λ of the light beam, the focal length f of the camera lens lens and the maximum local sampling frequency f of the camera chip max camera and their product.

[0035] Therefore, it is preferable that the following equation is applied to the maximum circular diameter of the diaphragm. d max diaphragm ≦1.22×λ×f×f max camera Or d max diaphragm ≦1.22×λ×f×1 / 2b pixel

[0036] In another preferred embodiment of the present invention, the aperture of the diaphragm of the present measuring device includes a polarizing filter, and thus allows only light or light components having a specific polarization among the light beams to pass through. This enables the application of an additional coating and the discrimination of individual wavefronts. As a result, simultaneous additional phase evaluation is possible. Also preferably, the diaphragm has two apertures or slits, each having a polarizing filter and preferably aligned orthogonally.

[0037] In another preferred embodiment of the present invention, the aperture of the diaphragm of the present measuring device has a frequency filter that allows only a specific wavelength to pass through the diaphragm. This also enables the application of an additional coating (especially in the case of multi-wavelength irradiation) and the discrimination of individual wavefronts. As a result, simultaneous additional phase evaluation is possible, for example, for so-called in-plane deformation measurement.

[0038] Preferably, the present measuring device may have a plurality of diaphragms, and these diaphragms are designed in various ways, for example, combinations of the diaphragms described above.

[0039] The present measuring device may preferably include other mirrors in addition to the mirror mechanism having two mirrors. For example, the mirror mechanism may include two partial mirrors and one complete mirror.

[0040] The camera of the present measuring device may preferably be a CCD camera, a polarizing camera, or a color camera. Other types of cameras are also conceivable.

[0041] In a preferred embodiment of the present measuring device, the diaphragm is designed as a grating diaphragm. Using a grating diaphragm allows more light to reach the camera chip, thereby reducing the exposure time compared to measurements with a single aperture diaphragm and making the overall measurement more robust. Particularly preferred for a grating diaphragm is to have specific aperture slit widths in two dimensions, and preferably those slit widths have the same dimension. Of course, the slit widths may have different dimensions.

[0042] Another preferred embodiment enables the partial mirror to be polarized such that the first partial beam is reflected and the second partial beam, which is orthogonally polarized, is transmitted. The second partial beam then reaches the camera after being reflected by a total mirror. The partial mirror is passed through again. Since the light reflected by the total mirror has the "correct" polarization, it can pass through the mirror unhindered. For example, a polarized partial mirror may be used to prevent occasional multiple reflections between the two mirrors.

[0043] When using a polarized partial mirror, it is preferred to arrange a depolarizing element between the mirror mechanism and the camera. The depolarizing element makes the two polarized partial beams from the double mirror mechanism unpolarized again, that is, it cancels the polarization so that the partial beams can interfere with each other.

[0044] Another preferred embodiment of the present measuring device has a partial mirror with different reflectivity and transmittance. It is particularly preferred that the transmittance is higher than the reflectivity. In principle, the reflectivity and transmittance can vary in the range of 1% to 99%, and in practice, it is considered appropriate that the reflectivity is 40% and the transmittance is 60% (±10% in both cases). It is also possible that the reflectivity and transmittance are the same.

[0045] In a preferred embodiment, the present measuring device has an evaluation unit, and the evaluation unit receives and processes the measurement signals generated by the camera. In this way, using the measurement signals of the interfered partial beams, the measurement variables, which are the characteristics of the surface of the object to be measured, are determined. Thereby, it is possible to make statements regarding the characteristics of the surface.

[0046] In another preferred embodiment, the present measuring device may include a housing having an opening through which the light beam can pass. The housing preferably houses each element of the present measuring device, specifically, the diaphragm, the mirror mechanism, the camera lens, and the camera. In this case, the diaphragm is preferably arranged behind the opening. The camera lens may preferably be arranged between the diaphragm and the opening, within the opening, or in front of the opening.

[0047] Using the measuring device and / or system described herein, preferably also including an evaluation unit, it is possible to perform a number of measurements to draw conclusions regarding the characteristics of the object and the object surface. Such measurements include, for example, roughness measurement, flatness measurement, surface shape gradient measurement, and relative measurements (e.g., relative thickness measurement, relative gradient measurement, and relative strain measurement). Deformation measurement by a predetermined stimulus is also possible. Thereby, it is possible to make statements regarding defects such as cracks, inhomogeneities, delamination, foreign matter inclusion, air bubbles, etc. on or under the surface. Therefore, such measurements mean non-destructive inspection. Another measurement method is vibration analysis. In that case, each component is subjected to stress by a vibration load. From here, a more detailed description and explanation of this description will be given with respect to some selected embodiments related to the accompanying drawings. The drawings are as follows.

Brief Description of the Drawings

[0048]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0049] The measuring device 10 according to the present invention includes a diaphragm 20 having an aperture 21, a mirror mechanism 30 having two mirrors 32, a camera 40, and a camera lens 42.

[0050] One mirror 32 of the mirror mechanism 30 is designed as a partially transparent partial mirror 34, and the other mirror 32 is a total mirror 36. The total mirror 36 is arranged behind the partial mirror 34 in the radiation direction (arrow) S of the incident light beam 100. In the embodiment shown here, the partial mirror 34 is rotated by an angle β with respect to the total mirror 36, whereby the arrangement of the two mirrors 32 is no longer parallel. The two mirrors 32 are arranged at a distance from each other, and the distance is x. The distance x is the distance between the mirror surfaces 38 of the mirrors 32 when the two mirrors 32 are arranged parallel to each other.

[0051] When the light beam 100 hits the measuring device 10, it first passes through the diaphragm 20 and then is directed straight towards the mirror mechanism 30. This is preferably done without any other optical elements intervening. The light beam 100 hits the mirror surface 38 of the partial mirror 34, and a part of it is reflected therefrom to become a first partial beam 110 and is deflected in the direction of the camera. The partial beam 110 passes through the camera lens 42 and reaches the camera 40, where it hits a camera chip (not shown here).

[0052] A part of the light beam 100 passes through the partial mirror 34 and hits the mirror surface 38 of the total mirror 36. This part of the light beam 100 is reflected therefrom and reaches the camera 40 as the second partial beam 120. The two partial beams 110 and 120 interfere with each other within the camera 40, whereby these two partial beams are not parallel to each other when hitting the camera 40. The carrier frequency required for the spatial phase shift is generated by the distance x between the two mirrors 32. As a result, the beam direction is shifted laterally. By rotating one of the mirrors 32, the distance between the two mirrors and the shear angle of the two mirror surfaces relative to each other also change simultaneously. Therefore, the adjustment for measurement can be carried out very finely and is variable or possible in small steps. The fine adjustment of the device can be easily implemented.

[0053] The measuring device shown in FIG. 1 enables the partial mirror 34 to rotate relative to the total mirror 36. In the embodiment shown here, the light beam 100 incident on the total mirror 36 is reflected from the total mirror 36 at an angle α and reaches the camera 40 as the second partial beam 120. In the example shown here, the angle α is 90° or approximately 90°.

[0054] Alternatively, and particularly preferably, the partial mirror 34 is fixed and the total mirror 36 is rotatable, whereby the angle α between the light beam 100 incident on the partial mirror 34 and the reflected first light beam 110 is in the range of 70 to 110°, preferably 90° ± 2°, due to the appropriate arrangement of the partial mirror 34.

[0055] FIG. 2 shows a measurement system 12, which has the measuring device 10 of FIG. 1, a housing 14 for the measuring device 10, a light source in the form of a laser 16, and a control / evaluation unit 18. The control / evaluation unit 18 can, on the one hand, control and adjust the laser 16 and, on the other hand, receive a measurement signal from the camera 40, process it, and characterize the measurement variable of the surface of the object 22 to be measured.

[0056] The laser beam generated by laser 16 is directed towards the surface 24 of the object to be measured, where it is reflected in the direction of the measuring device. The reflected light beam 100 enters the housing 14 through the aperture 15, first passes through the diaphragm 20 of the measuring device 10, and then hits the mirror mechanism 30. Here, the light beam 100 is split into a first partial beam 110 and a second partial beam 120 as described above, and the two partial beams are not parallel to each other when they hit the camera 40 and interfere with each other there. By rotating the two mirrors 32 relative to each other and by the offset caused by the distance x between the two mirrors 32, the necessary "shear" is generated, which is necessary for the shearography evaluation.

[0057] Therefore, the measuring device of the present invention has the advantages of being very low-cost and having a simple design. All that is required other than the camera 40 having a camera lens 42 is a diaphragm and a dual mirror mechanism having a partially transparent partial mirror 34 (for example, a semi-transparent semi-mirror) and a full mirror 36. Shear is generated because one of the mirrors 32, for example, the partial mirror 34 as shown here, is tilted by an angle β with respect to the full mirror 36, which is necessary for shearography. Therefore, in this exemplary embodiment, the partial mirror is rotated out of the "45° position" where the full mirror 36 is located. The two reflected components (the first partial beam 110 and the second partial beam 120 from the partial mirror 34 or the full mirror 36) are merged on the way towards the camera, but at least merged inside the camera, so that the desired interference occurs. The resulting interference pattern is imaged by the camera, enabling the shearography measurement to be carried out. From the perspective of the camera, a virtual double slit is generated by the lateral offset (distance x) between the two mirrors. As a result, the superposition of the two light components (the first partial beam, the second partial beam) includes an additional carrier frequency used for the spatial phase shift.

[0058] Since very few components are used, a very small and compact design is possible. As a whole, this measuring device is very robust and highly mobile, so it can be easily used in various places.

[0059] Figure 2 shows an optional filter 44, which is arranged in the beam path in front of the diaphragm 20. The filter 44 is an optical filter and may be, for example, a color filter or a polarization filter. The filter 44 may also optionally be arranged between the diaphragm 20 and the mirror mechanism 30, or between the mirror mechanism 30 and the camera 40. However, there should be no components between the diaphragm and the mirror mechanism that diffract, split, or reflect the measurement light. The measurement light is the laser light reflected by the measurement object, and this is interference-superimposed within the camera.

[0060] The present invention has been comprehensively described and explained with reference to the drawings and the description. This description and explanation are intended to be illustrative rather than restrictive. The present invention is not limited to the disclosed embodiments. Those skilled in the art will, by using the present invention and by analyzing the drawings, the present disclosure, and the following claims in detail, be able to clarify other embodiments or variants.

[0061] In the claims, the terms "comprising" and "with" do not exclude other elements or steps. The indefinite article "a" or "an" does not exclude a plurality. The functions of the plurality of items described in the claims may be realized by a single element or unit. Some or all of the elements, units, devices, and systems may be implemented by corresponding hardware and / or software. The mere fact that specific means are described in different dependent claims does not indicate that these means cannot be used advantageously in combination.

[0062] The reference signs in the claims should not be construed restrictively.

Explanation of Signs

[0063] 10 Measuring device 12 Measuring system 14 Housing 15 Aperture 16 Laser 18 Control / Evaluation Unit 20 Diaphragm 21 Aperture 22 Object 24 Surface 30 Mirror Mechanism 32 Mirror 34 Partial Mirror 36 Full Mirror 38 Mirror Surface 40 Camera 42 Camera Lens 44 Filter 100 Light Beam 110 First Sub - beam 120 Second Sub - beam S Direction of the Light Beam X Distance

Claims

1. A measuring device for performing non-destructive measurement of the surface of an object (22) using an interference measurement method, the measuring device (10) on which light as an incident light beam (100) reflected by the surface (24) hits, a diaphragm (20) having an aperture (21), a mirror mechanism (30) having two mirrors (32), each of the two mirrors (32) having a mirror surface (38), one of the two mirrors (32) being a partially transparent partial mirror (34), one of the two mirrors (32) being a total mirror (36), the total mirror (36) being arranged behind the partially transparent partial mirror (34) in the radial direction (S), the mirror mechanism (30), a camera lens (42) and a camera (40), including, the incident light beam passes through the diaphragm (20), is diffracted, then hits the mirror mechanism (30), where it is split and deflected into two partial beams (110, 120), and the two partial beams (110, 120) then reach the camera (40) and interfere within the camera (40), the incident light beam (100) passes through the camera lens (42) in front of the camera (40) in the beam direction (S), one of the mirrors (32) of the mirror mechanism (30) is rotatable relative to the other of the mirrors (32) such that the two mirrors (32) include a non-zero angle β in a plane perpendicular to the mirror surface (38), The camera (40) includes a camera chip having a local sampling frequency, and the design of the diaphragm (20) is such that when the incident light beam (100) passes through the diaphragm (20), it is diffracted so that the spatial frequency f ＿ｌｉｇｈｔ of the incident light beam (100) is at most equal to the maximum local sampling frequency f ＿ｍａｘ＿ｃａｍｅｒａ of the camera chip during detection on the camera chip, the two mirror surfaces (38) of the mirrors (32) of the mirror mechanism (30) have a distance x therebetween, the distance x is the distance perpendicular to the mirror surface (38) between the mirror surfaces (38) of the two mirrors (32) directed towards the incident light beam (100), the distance x is 70% or more of the width of the aperture (21) of the diaphragm (20) and less than 7 times the width of the aperture (21) of the diaphragm (20) measuring device.

2. The incident light beam (100) incident on the mirror mechanism (30) is reflected at an angle α in the direction of the camera (40) and hits the camera (40), and one of the mirrors (32) of the mirror mechanism (30) is aligned such that the angle α is at least 70° and at most 110°. The measuring device according to claim 1.

3. The measuring device according to claim 2, wherein the angle α is at least 80° and at most 100°.

4. The measuring device according to claim 1, characterized in that the angle β is in the range of 0.001° to 20°.

5. The measuring device according to claim 4, characterized in that the angle β is in the range of 0.5° to 1°.

6. The measuring device according to claim 1, characterized in that the total mirror (36) of the mirror mechanism (30) is rotatable with respect to the partially transparent partial mirror (34).

7. The measuring device according to claim 1, characterized in that the camera lens (42) is arranged in front of the diaphragm (20) in the beam direction (S) or between the mirror mechanism (30) and the camera (40).

8. The diaphragm (20) includes a slit having a slit width of b, and a maximum value of the slit width b is the wavelength λ of the incident light beam, the focal length f of the camera lens ｌｅｎｓ and the maximum local sampling frequency f of the camera chip ＿ｍａｘ＿ｃａｍｅｒａ The measuring device according to claim 1, characterized in that it is not more than the product thereof.

9. The diaphragm (20) has a circular aperture with a diameter d, and the maximum value of the diameter d is 1.22 times the wavelength λ of the incident light beam, the focal length f of the camera lens ｌｅｎｓ and the maximum local sampling frequency f of the camera chip ＿ｍａｘ＿ｃａｍｅｒａ The measuring device according to any one of claims 1 to 7, characterized in that it is not more than the product of

10. The measuring device according to any one of claims 1 to 7, characterized in that the diaphragm (20) is a grating diaphragm or the diaphragm (20) includes a polarizing filter or a frequency filter.

11. The measuring device according to claim 1, characterized in that the partially transparent partial mirror (34) is designed to perform polarization, whereby a first partial beam (110) is reflected and a second partial beam (120) that is orthogonally polarized is transmitted, and the second partial beam (120) reaches the camera (40) after being reflected by the total mirror (36).

12. The measuring device according to claim 11, characterized in that a depolarizing element is arranged between the mirror mechanism (30) and the camera (40) to enable interference of the first partial beam (110) of the light and the orthogonally polarized second partial beam (120) with respect to the camera (40).

13. The measuring device according to claim 1, characterized in that the partially transparent partial mirror (34) has different reflectance and transmittance.

14. The control / evaluation unit (18) receives and processes the measurement signal generated by the camera (40), whereby the measurement variable characteristics of the surface (24) of the object (22) to be measured are determined from the measurement signals of the interfering partial beams (110, 120), and the measurement variable enables a statement regarding the characteristics of the surface (24) to be made. The measuring device according to claim 1, characterized in that.

15. The evaluation unit receives and processes the measurement signal generated by the camera, whereby the measurement variable characteristics of the surface of the object to be measured are determined from the measurement signal of the interfering partial beams, and the measurement variable characteristics enable a statement to be made about the characteristics of the surface. The measuring device according to claim 1.

16. A method for non-destructively measuring the surface (24) of an object (22) by an interference measurement method and for determining the characteristics of the surface (24) of the object (22), comprising: Providing a measuring device (10), the step of providing the measuring device (10) having a diaphragm (20) and a mirror mechanism (30) having two mirrors (32) arranged behind the diaphragm (20), each of the two mirrors (32) having a mirror surface (38), one of the two mirrors (32) being a partially transparent partial mirror (34), one of the two mirrors (32) being a total mirror (36), the total mirror (36) being arranged behind the partially transparent partial mirror (34) in the radial direction (S), the mirror mechanism (30), a camera lens (42), and a camera (40) having a camera chip with a local sampling frequency; Generating an incident light beam and irradiating the surface (24) of the object (22) to be measured; Guiding the incident light beam (100) such that the incident light beam (100) reflected by the surface (24) passes through the diaphragm (20) and directly hits the mirror mechanism (30) arranged behind the diaphragm (20); Adjusting a desired angle β between the partially transparent partial mirror (34) and the total mirror (36) by rotating one of the mirrors (32) such that the incident light beam (100) is split into two partial beams (110, 120) and both are directed towards the camera (40); Adjusting the two mirror surfaces (38) of the mirror (32) of the mirror mechanism (30), wherein the distance between the two mirror surfaces (38) is x, and the distance x is the distance between the mirror surfaces (38) of the two mirrors (32) directed at the incident light beam (100), which is perpendicular to the mirror surfaces (38), and the distance x is at least 70% of the width of the aperture (21) of the diaphragm (20) and less than 7 times the width of the aperture (21) of the diaphragm (20); Recording the two partial beams (110, 120) by the camera (40) and generating a measurement signal of their interference superposition; When the incident light beam (100) passes through the diaphragm (20), it is diffracted, and the spatial frequency f of the incident light beam (100) ＿ｌｉｇｈｔ is at most equal to the maximum local sampling frequency f of the camera chip during detection on the camera chip ＿ｍａｘ＿ｃａｍｅｒａ and adjusting the diaphragm (20) so as to match; Evaluating the measurement signal to determine a measured variable characteristic of the surface (24) that enables a statement regarding the characteristic of the surface (24) of the object (22) to be measured; A method comprising.

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