Color confocal measurement device comprising camera
By designing a color confocal measuring device including a light pen with axial color difference and a camera with partially blocked light beam, the problem of difficulty in making the measurement points on the surface of the sample in the prior art is solved, and an efficient and accurate measurement effect is achieved.
Patent Information
- Application Number
- CN202380054139.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-05-19
- Filing Date
- 2023-05-19
- Publication Date
- 2025-05-06
AI Technical Summary
Existing optical comparators are difficult to make the measurement point visible when measuring the height and/or thickness of the sample surface, especially when the surface is small or the light beam is invisible, and traditional solutions are costly and bulky.
A color confocal measuring device is designed, including a light source, a light pen with axial color difference, and a camera close to the output end of the light pen, which partially blocks the light beam to ensure that a portion of the light beam reaches the sample surface and makes the measurement point visible.
It realizes that the measurement points on the surface to be studied can be easily, effectively and accurately made visible at reasonable cost and size, and improves measurement accuracy and sensitivity.
Smart Images
Figure CN119948310A_ABST
Abstract
Description
Technical Field
[0001] The present application relates generally to the field of inspection and optical control of components, and more particularly to the use of optical devices to measure height and / or point orientation of a sample surface. Background Art
[0002] Currently, there are optical comparator measurement devices including light pens that can measure the height, thickness and / or local orientation of a sample surface at one point and without contact. Depending on the objective lens selected, the diameter of the light beam at the sample surface (usually expressed by the term "spot") is typically between 1.5 μm and 50 μm.
[0003] In particular, such a comparator can be based on the principle of chromatic confocal coding, in which light, usually polychromatic, is focused on the surface to be investigated by a light pen comprising an objective with axial chromatic aberration. The spectral distribution of the light beam is subsequently analyzed in order to determine the wavelength of the light source of the sharp image obtained on the surface, which enables the distance between the objective and the surface to be deduced.
[0004] Some of these optical comparators require that the measurement point on the sample surface to be investigated be visible. However, when measuring with a chromatic confocal objective, the measurement point is materialized by a very small luminous spot which, moreover, may not be visible, depending on the type of surface to be measured. Furthermore, the surface to be investigated is itself very small and optical aids may be required in order to position the measurement spot correctly at the desired position on the surface.
[0005] Therefore, it has been proposed to use a camera in order to correctly position the light pen relative to the surface to be studied. For example, it has been proposed to mount the light pen and the camera on a robot configured so as to successively place the camera and then the light pen above the surface to be studied in order to adjust the position of the light pen relative to the surface. However, this solution requires a motorized measurement station, which implies high costs and significantly increases the size of the installation.
[0006] It has also been proposed to place the camera on the side of the light pen. However, in the case of rough surfaces, the measurement area may be obscured by the protrusions.
[0007] Finally, it has been proposed to use a splitter cube placed between the light source and the objective to deflect part of the light beam towards a camera placed close to the light pen. However, the image obtained by means of a chromatic confocal objective is only sharp for a given wavelength, which corresponds to the wavelength focused on the surface to be measured. Moreover, since the light pen is optimized at the center of the field of view, the image obtained includes significant aberrations, which makes it difficult to exploit the image. Moreover, the system is bulky and expensive. Summary of the invention
[0008] The object of the present application is therefore to propose a measuring device, for example for measuring the height and / or thickness of a sample surface, making it possible to visualize the measuring points on the surface to be studied in a simple, effective and precise manner, the measuring device having reasonable costs and dimensions.
[0009] To this end, a first aspect proposes a chromatic confocal measurement device for parameters of a sample surface, the device comprising:
[0010] - a light source configured to generate a light beam;
[0011] - a light pen comprising an objective lens with axial chromatic aberration, the objective lens with axial chromatic aberration being configured to apply a light beam onto a sample surface, the light pen having an input end connected to a light source and an output end configured to be placed close to the sample surface; and
[0012] - A camera is fixed near the output end of the light pen and is located between the objective lens with axial chromatic aberration and the sample surface, so that a part of the light beam originating from the light source and emitted from the objective lens with axial chromatic aberration is blocked by the camera at the output end of the light pen, and another part of the light beam bypasses the camera and reaches the sample surface.
[0013] Some preferred but non-limiting features of the measuring device are as follows, taken alone or in combination:
[0014] - the light pen comprises a lens placed close to the output end of the light pen, a first area corresponding to an orthogonal projection of the lens in a first plane perpendicular to the propagation axis of the light beam passing through the lens being larger than a second area corresponding to an orthogonal projection of the camera in the first plane, so that the camera only partially blocks the light field of the lens;
[0015] - the first area is at least two times larger than the second area, preferably at least four times larger;
[0016] - a through passage is formed in the lens, and the camera is at least partially accommodated in the through passage;
[0017] - the lens has axial chromatic aberration and forms part of an objective having axial chromatic aberration;
[0018] the lens is achromatic and is placed between the objective lens with axial chromatic aberration and the camera, a through passage is formed in the achromatic lens, and the camera is at least partially accommodated in the through passage;
[0019] -The camera is placed between the light pen and the surface to be measured;
[0020] - the measuring device further comprises an additional camera, which is fixed near the output end of the light pen and is located between the objective lens with axial chromatic aberration and the sample surface, so that a part of the light beam originating from the light source and emitted from the objective lens with axial chromatic aberration is also blocked by the additional camera at the output end of the light pen, and another part of the light beam also bypasses the additional camera and reaches the sample surface;
[0021] - The depth of field of the camera is between 2mm and 100mm;
[0022] - the measuring device further comprises a light emitting element fixed to the light pen and configured to illuminate the sample surface;
[0023] - the light source is integrated into the camera, or attached and fixed to the light pen near the output end; and / or
[0024] The measuring device further comprises a spectral analysis system configured to determine the spectral distribution of the light beam reflected by the sample surface. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Other characteristics, objectives and advantages of the invention will become apparent from reading the following detailed description, with reference to the accompanying drawings, given by way of non-limiting examples, in which:
[0026] Figure 1 is a schematic diagram of a first exemplary embodiment of an optical pen of a measuring device according to an embodiment of the present invention;
[0027] Figure 2 is a schematic diagram of a second exemplary embodiment of a light pen of a measuring device according to an embodiment of the present invention;
[0028] Figure 3 is a schematic diagram of a third exemplary embodiment of a light pen of a measuring device according to an embodiment of the present invention;
[0029] Figure 4 is a schematic diagram of a fourth exemplary embodiment of a light pen of a measuring device according to an embodiment of the present invention; and
[0030] Figure 5 A measuring device according to an embodiment of the invention is shown very schematically and comprises a fifth example of a light pen.
[0031] Similar elements have the same reference numerals throughout the drawings. DETAILED DESCRIPTION
[0032] The chromatic confocal measurement device 1 according to the present invention comprises: a light source 2 configured to generate a light beam 3; a light pen 4 comprising an objective lens 5 with axial chromatic aberration, the objective lens being configured to apply the light beam 3 to a sample surface 6; and a camera 7. The measurement device 1 further comprises: a spectral analysis system 8 (such as a spectrometer 8) configured to determine the spectral distribution of the light beam 3 reflected after passing through the light pen 4; and a signal processing device 9 enabling analysis of the spectral distribution in order to calculate the axial position of the surface 6.
[0033] The light pen 4 has an input end 10 connected to the light source 2 and an output end 11 configured to be placed close to the sample surface 6. The objective lens 5 with axial chromatic aberration is housed in the light pen 4 and comprises a series of lenses with known axial chromatic aberrations, which are placed in the objective lens 5 so that their optical axes are coaxial. Where applicable, the light pen 4 may further comprise a window 12 (in other words, a flat protective slide without chromatic aberration) mounted at its output end 11, downstream of the objective lens 5 with axial chromatic aberration ("upstream" and "downstream" are defined according to the propagation direction of the light incident into the light pen 4), in other words, between the objective lens 5 and the sample surface 6.
[0034] The light source 2, the light pen 4 and the spectrometer 8 may be connected by means of at least one optical fiber 13. The light source 2 and the spectrometer 8 may be housed in an optronics housing, which may be connected to the light pen 4 by means of at least one optical fiber 13 and to the processing device 9 via a cable. Where applicable, the light pen 4 and / or the processing device 9 may also be housed in the optronics housing. It should be noted that in this case, the optical fiber 13 is optional.
[0035] The light source 2 is configured to generate a light beam 3, which is preferably polychromatic (in contrast to a monochromatic light source 2 such as a laser). The use of a polychromatic light beam 3 allows chromatic confocal measurements and in particular may have axial chromatic aberration along the measurement axis, which allows distances to be measured without any movement of the measuring device 1. The light source 2 may in particular comprise white light, such as one or more light emitting diodes.
[0036] Furthermore, unlike a laser beam which is spatially and temporally coherent, the light beam 3 has low (spatial and temporal) coherence.
[0037] In a first embodiment, the measuring device 1 is a "point sensor". The light source 2 is polychromatic and the light pen 4 forms a set of monochromatic images of the light source 2 (or, more specifically, of the end of an optical fiber 13 used as a pinhole). These images define a rectilinear observation segment in space, each image of the light source being defined by its wavelength and its focal length relative to the light pen 4. The same light pen 4 also collects the backscattered light beam 3 to form a common polychromatic image of all the monochromatic images at the end of the optical fiber 13 used as a spatial filter. This polychromatic image consists of the wavelengths of the different interfaces encountered by the light beam 3 in the sample.
[0038] The polychromatic image is then transmitted to the spectrometer 8 via the optical fiber 13. The spectrum measured in this spectrometer then shows one or more peaks corresponding to the interfaces encountered by the light beam 3 when the sample is placed in a space covered by chromatic aberrations (ie observing straight line segments). For example, if the sample comprises an opaque surface 6, only one wavelength of the light source 2 obtains a clear image on the surface 6. The processing means 9 of the signal then make it possible to deduce the distance between the light pen 4 and the surface 6 based on the wavelength recognized by the spectrometer 8.
[0039] In a second embodiment, the measuring device 1 is a "line sensor" and is capable of measuring simultaneously a set of points aligned along a line. Unlike a point sensor, a line sensor comprises a series of optical fibers 13 configured to guide the light generated by the light source 2 to the input of the light pen 4 and return it from the light pen 4 to the spectrometer 8. More precisely, the ends of these optical fibers 13 are spatially organized to define a transverse measurement field of view (in particular a line). In an embodiment, the light beam emitted by each of these optical fibers 13 then propagates in the light pen 4 via a splitter to the surface 6, whereby the beam is dispersed along the optical axis. In a manner similar to that of a point sensor, each wavelength that is perfectly focused for each point of the transverse field of view is reflected by the sample surface 6, propagates in the light pen 4 in the opposite direction and is guided to the input of the spectrometer 8 via the splitter and the optical fibers 13. Therefore, the spectrometer 8 comprises a light detector in order to make visible the spectrum corresponding to each measurement point of the line.
[0040] In a third embodiment, the device is a "multipoint sensor". It is a sensor in which a plurality of light sources are arranged in an ordered manner, but not necessarily aligned as in the case of a line sensor. For example, the sensor may include three points in a triangle, four points in a square or rectangle, N points distributed on a circle, and generally N points distributed according to a geometric pattern. These source points may be the ends of optical fibers 13, each originating from a single point controller, or the ends of optical fiber bundles 13, where the points are not necessarily aligned.
[0041] In order to make the surface 6 to be investigated, and in particular the measuring points, visible, a camera 7 is fixed close to the output end 11 of the light pen 4, between the downstream part of the objective 5 with axial chromatic aberration and the sample surface 6, so that a part of the light beam 3 originating from the light source 2 and emerging from the objective 5 with axial chromatic aberration is blocked by the camera 7 at the output end 11 of the light pen 4, and another part of the light beam 3 bypasses the camera 7 and reaches the sample surface 6. Therefore, the size of the camera 7 is selected so that it only partially blocks the light beam 3, so as not to hinder the synchronous measurement of the measuring device 1.
[0042] The camera 7 is placed in the downstream part of the objective 5 with axial chromatic aberration, and the image obtained by the camera 7 is clear and not distorted by the aberrations of the light pen 4 or by the axial chromatic aberration of the objective 5. Moreover, since the measuring device 1 operates on the principle of chromatic confocal encoding, a partial blocking of the light beam 3 does not hinder the measurement and does not significantly reduce the performance of the measuring device 1. On the contrary, it is obvious that a partial blocking of the light beam 3 can reduce certain optical aberrations and improve the measurement accuracy of transparent objects with a large thickness or a very obvious shape, such as thick transparent tubes. Therefore, the only effect of the presence of the camera 7 is to reduce the luminous intensity of the light beam 3, which does not hinder the measurement performance of the measuring device 1. Finally, the camera 7 is placed in the light beam 3 of the light pen 4, and its field of view 21 is optimally positioned with respect to the measurement spot.
[0043] The camera 7 can be fixed in the light pen 4 or outside the light pen 4 at the output end 11 of the light pen.
[0044] The camera 7 can be centered on the propagation axis X of the light beam 3 ( Figure 1 , Figure 3 and Figure 4 Alternatively, the camera 7 may be off-center relative to the propagation axis X of the light beam 3 ( Figure 2 ) and, where applicable, are positioned so that their line of sight is inclined relative to the propagation axis X ( Figure 5 ).
[0045] In order not to block all of the light beam 3 and to allow the performance to be measured, the cross section of the light beam 3 occupied by the camera 7 is smaller than the total cross section of the light beam 3 emitted from the light pen 4. For this purpose, the area S1 of the lens 14 most downstream of the light pen 4 (see Figure 1 The cross section in FIG. 1 , which area may correspond to the most downstream lens 14 of the objective 5 with axial chromatic aberration or to the window 12 of the light pen 4) is larger than the area of the camera 7. The term "area S1 of the lens 14" should be understood here as the orthogonal projection of the lens 14 in a first plane P1 perpendicular to the propagation axis X of the light beam 3 passing through the lens 14. Similarly, the term "area S2 of the camera 7" should be understood here as the orthogonal projection of the camera 7 in the first plane P1.
[0046] The camera 7 itself is chosen such that its area S2 is smaller than the area of the lens 14, preferably at least two times smaller, for example at least four times smaller, in order to limit the loss of the optical signal during the measurement.
[0047] Thus, the camera 7 may be a miniature camera 7. This type of camera 7 is used in particular in the field of medical endoscopy. Typically, there is a camera 7 whose area (in the sense of the definition given above) is approximately 3.0 mm 2 and 30.0mm 2 (ie, if the camera 7 is substantially tubular, the diameter is between about 1.0 mm and about 3.1 mm).
[0048] An example of a camera 7 that can be used in the measuring device 1 is sold by MIKROP, which uses an omnidirectional Ominivision sensor (reference OV6946) with the following characteristics: resolution 400×400 pixels; optical size: 1 / 18"; progressive scan mode; frame rate 160Kpixel (400x400): 30fps; dimensions: 950μm x 940μm. A camera 7 sold by MIKROP containing this sensor then includes an objective lens with the following characteristics: aperture between 5.80 and 6.40; field of view between 90° and 140°; diameter of 1.50 mm; length of 8.9 mm; minimum working distance of 2 mm, and depth of field between 2 mm and 100 mm.
[0049] The use of a miniature camera 7 makes it possible to keep the conventional dimensions of the lenses of the light pen 4 and the objective 5 with axial chromatic aberration. In particular, it is not necessary to use lenses that are larger than those typically used in current chromatic confocal measurement devices. Typically, in small diameter devices, the lens 14 may have a diameter of about 3 mm to 10 mm. In general, the diameter of the lens 14 is preferably at least twice the diameter of the camera.
[0050] Preferably, the camera 7 has a depth of field suitable for producing a sharp image over the entire working range of the measuring device 1. Therefore, cameras 7 of this type usually do not have a manual or automatic ("autofocus") focusing device. The working range of the measuring device 1 (covering all distance measurements that can be performed by the measuring device 1) can be between 2 mm and 100 mm. Therefore, the camera 7 is selected to have a depth of field covering at least the interval between 2 mm and 100 mm.
[0051] It should be noted that the device may include a plurality of cameras 7 (see for example Figure 2) in order to obtain images from different viewpoints, or in order to obtain stereoscopic vision capable of creating a three-dimensional image of the sample. Subsequently, each camera 7 is placed in the beam 3 so as to partially block the beam while allowing a portion of the beam to pass through to reach the sample surface 6. Thus, the sum of the areas S2 of the cameras 7 (as described above) remains smaller than the area S1 of the lens 14. Preferably, the sum of the areas S2 of the cameras 7 is smaller than half of the area S1 of the lens 14, preferably one quarter of the area S1 of the lens 14.
[0052] In the first embodiment, the camera 7 is fixed to the output end 11 of the optical sensor.
[0053] For example, the light pen 4 may include an achromatic lens placed at the output end 11 of the light pen 4. The achromatic lens may, for example, correspond to the window 12 of the light pen 4. Subsequently, the camera 7 may be fixed, for example, by gluing, on one of the faces of the achromatic lens 12, for example, the downstream face (the output face of the incident light beam) (see, for example, Figure 4 ).
[0054] Alternatively, the camera 7 may be fixed on an achromatic lens which is attached and fixed on the output end 11 of the light pen 4 , for example by a screw connection or a snap fit.
[0055] This first embodiment has the advantage of being simple to manufacture and not requiring any modification of the light pen 4, apart from taking into account the possible addition of an achromatic lens (which has an impact on the optical path of the light beam 3) in the optical calculations performed by the processing means 9. On the other hand, placing the camera 7 outside the light pen 4 reduces the available working distance.
[0056] In the second embodiment, the through passage 19 is formed in one of the lenses of the light pen 4 and the camera 7 is at least partially accommodated in the through passage. Thus, the lens is penetrated to receive the camera 7, which enables the axial dimensions of the measuring device 1 to be reduced and in particular does not affect its working distance.
[0057] The pierced lens may correspond to the most downstream lens 14 of the objective 5 with axial chromatic aberration, in other words, to the last lens of the objective 5 closest to the output end 11 of the light pen 4. The selection of this lens 14 may avoid that the objective 5 with axial chromatic aberration distorts the image obtained by the camera 7.
[0058] Alternatively, the pierced lens may correspond to an achromatic lens placed downstream of the objective 5 with axial chromatic aberration (typically the window 12 of the light pen 4 ).
[0059] According to yet another alternative, both the most downstream lens 14 of the objective 5 with axial chromatic aberration and the achromatic lens (typically the window 12 ) can be permeable in order to receive the camera 7 .
[0060] In practice, the choice of one or more penetration lenses 12, 14 depends on the configuration of the measuring device 1, the size of the camera 7 in the direction of the propagation axis X of the light beam 3, and the desired working distance. In practice, when the distance between the most downstream lens 14 of the objective 5 and the window 12 is less than the length of the camera 7, and when it is desired to maximize the working distance, the lens 14 and the window 12 will be able to be penetrated so as to accommodate the camera 7 as a whole. On the other hand, when this distance is less than the length of the camera 7, or when the available working distance is adjustable, only the window 12 can be penetrated. Finally, when the light pen 4 has no window 12 or when the configuration of the objective 5 is assessed to accommodate the camera 7 in these two downstream lenses, it is also possible to penetrate only the lens 14 or the two most downstream lenses.
[0061] It should be noted that, where applicable, one or more lenses 12, 14 may also be pierced to allow the passage of a cable 20 for power supply and / or data transmission from the camera 7 to the processing device 9. Alternatively, an aperture may be formed in the body of the light pen 4 to allow one or more cables 20 to be led out from the camera 7 to the processing device 9.
[0062] The lenses 12, 14 may be penetrated by any known means, for example by optical coring, typically by diamond machining or even by drilling.
[0063] The spectrometer 8 comprises an optical sensor configured to measure the total energy (in J) of the light beam 3 through the projection objective 5 reflected by the sample surface 6 during an integration interval (in seconds). The signal processing device 9 comprises a processing unit 15, for example a computer or a server with processing means suitable for performing the chromatic confocal measurement method. The processing unit 15 may comprise, for example, a memory in which code instructions for performing the chromatic confocal measurement method are stored, and a processor, a microprocessor, a microcontroller type computer, etc. configured to execute these instructions. The device also comprises control means (touch screen, keyboard, mouse, buttons, etc.).
[0064] The camera 7 may be connected, for example, by a cable, to the processing device 9 or to two dedicated processing devices 9. The processing device 9 comprises in particular an acquisition system 16 configured to receive the images acquired by the camera 7 and to display the images on a display device 17, such as a screen, so as to allow the position of the measurement points on the surface 6 to be visible to a user in real time.
[0065] In case the camera 7 blocks a portion of the light beam 3, the measuring device 1 may further comprise a lighting element 18 which is fixed to the light pen 4 and is configured to illuminate the sample surface 6. The illumination of the sample surface 6 makes it possible to improve the quality of the image, in particular when the ambient lighting is insufficient or when the measuring device 1 blocks the ambient lighting.
[0066] The lighting 18 may be incorporated into the camera 7. For example, the camera 7 may have a ring of light emitting diodes mounted around its optical elements.
[0067] Alternatively, the light emitting member 18 may be attached and fixed to the light pen 4 at a position close to the output end 11 (see Figure 5 ). For example, the measuring device 1 may comprise a circular ring with light emitting diodes, which is attached and fixed around the output end 11 of the light pen.
[0068] It should be noted that the optical principle of the chromatic confocal microscope is essentially insensitive to ambient light. In particular, the measurement accuracy and sensitivity of the measuring device 1 are generally not affected by the presence of illumination by the light emitting element 18. Therefore, the measuring device 1 can be used normally without being disturbed by the illumination.
[0069] Where applicable, when the surface 6 to be measured is very reflective, the presence of the light 18 may interfere with the measurement. In this case, the processing unit may be configured to modulate the illumination of the light 18 (particularly when the light comprises addressable light emitting diodes) so as to synchronize measurement and illumination by shifting the light in time.
Claims
1. A chromatic confocal measurement device (1) for measuring parameters of a sample surface (6), the device comprising: - a light source (2) configured to generate a light beam (3); - a light pen (4), comprising an objective lens (5) with axial chromatic aberration, the objective lens with axial chromatic aberration being configured to apply the light beam (3) to the sample surface (6), the light pen (4) having an input end (10) connected to the light source (2) and an output end (11) configured to be placed close to the sample surface (6); as well as - a camera (7) which is fixed close to the output end (11) of the light pen (4) and is located between the objective lens (5) with axial chromatic aberration and the sample surface (6), so that a part of the light beam (3) originating from the light source (2) and emitted from the objective lens (5) with axial chromatic aberration is blocked by the camera (7) at the output end (11) of the light pen (4), and another part of the light beam (3) bypasses the camera (7) and reaches the sample surface (6).
2. The measuring device (1) according to claim 1, wherein: The light pen (4) comprises a lens (12, 14) placed near an output end (11) of the light pen (4), a first area (S1) corresponding to an orthogonal projection of the lens (12, 14) in a first plane (P1) perpendicular to a propagation axis (X) of a light beam (3) passing through the lens (12, 14) being larger than a second area (S2) corresponding to an orthogonal projection of the camera (7) in the first plane (P1), so that the camera (7) only partially blocks the light field of the lens (12, 14).
3. The measuring device (1) according to claim 2, wherein: The first area (S1) is at least two times larger than the second area (S2), preferably at least four times larger.
4. The measuring device (1) according to any one of claims 2 and 3, wherein: A through passage (19) is formed in the lens (12, 14), and the camera (7) is at least partially accommodated in the through passage (19).
5. The measuring device (1) according to claim 4, wherein: The lens (14) has axial chromatic aberration and forms a part of the objective lens (5) having axial chromatic aberration.
6. The measuring device (1) according to any one of claims 2 to 4, wherein: The lens (12) is achromatic and is placed between the objective lens (5) with axial chromatic aberration and the camera (7), a through passage (19) is formed in the achromatic lens (14), and the camera (7) is at least partially accommodated in the through passage (19).
7. The measuring device (1) according to any one of claims 1 to 3, wherein: The camera (7) is placed between the light pen (4) and the surface (6) to be measured.
8. The measuring device (1) according to any one of claims 1 to 7, further comprising an additional camera (7), which is fixed close to the output end (11) of the light pen (4) and is located between the lens (5) with axial chromatic aberration and the sample surface (6), so that a part of the light beam (3) originating from the light source (2) and emitted from the objective lens (5) with axial chromatic aberration is also blocked by the additional camera (7) at the output end (11) of the light pen (4), and another part of the light beam (3) also bypasses the additional camera (7) and reaches the sample surface (6).
9. The measuring device (1) according to any one of claims 1 to 8, wherein: The depth of field of the camera (7) is between 2 mm and 100 mm.
10. The measuring device (1) according to any one of claims 1 to 9, further comprising a lighting element (18) fixed to the measuring device (1) and configured to illuminate the sample surface (6).
11. The measuring device (1) according to claim 10, wherein: The light emitting element (18) is integrated into the camera (7), or is attached and fixed to the light pen (4) near the output end (11).
12. The measuring device (1) according to any one of claims 1 to 11, further comprising a spectral analysis system (8) configured to determine a spectral distribution (8) of the light beam (3) reflected by the sample surface (6).