Apparatus and corresponding method for inspecting the surface of a transparent object

Abstract

The present invention relates to an apparatus for inspecting a thin-film-type transparent object (10) having an upper first surface (11) and a lower second surface (12), for measuring the distribution and size of particles on the upper or lower surface of the object, respectively. For this purpose, the device comprises a camera (40) and at least one light source (20), the light source (20) being arranged such that electromagnetic radiation emitted by the light source illuminates a linear area (15) of the first surface (11) from above or the second surface (12) from below of the object, the illumination being at a predetermined angle (α) with respect to the respective illuminated surface (11), the camera (40) being arranged to detect the intensity of the back-reflected electromagnetic radiation in at least a portion of the linear area (15). The predetermined angle (α) is less than or equal to 15°, and the electromagnetic radiation emitted by the light source (20) is mainly linear and s-polarized. A method of inspection is also provided.

Description

[Technical Field]

[0001] The present invention relates to the inspection of the surface of thin-film transparent objects, such as thin glass or transparent films, and a corresponding method therefor. [Background technology]

[0002] Thin glass or transparent films, typically 0.01 to several millimeters thick, are primarily used in the optical, electronics, and display industries, for example, in the production of liquid crystal displays or screens. Thin glass is also known as thin glass, display glass, or microsheet. Thin glass or films have a top surface and a bottom surface opposite the top surface, and they expand relatively significantly relative to the thickness of the object. In the production of such objects, the purity of their surfaces is an important criterion. Therefore, during the production of glass sheets, for example, the presence and distribution of particles on the glass surface is monitored. Such particles can be very small, i.e., only a few micrometers in diameter.

[0003] Optical inspection of glass and films has been known for some time. Typically, camera-based methods with strong dark-field illumination are used to detect contamination. This method simultaneously detects particles on the top and bottom of thin glass. This method is called AB-plane. However, it cannot distinguish between particles on the top and bottom surfaces.

[0004] However, for further processing of transparent objects, for example targeted cleaning of glass sheets, it is desirable to be able to target contamination to one of two surfaces, ie either the top or bottom surface. Summary of the Invention [Problem to be solved by the invention]

[0005] It is therefore an object of the present invention to provide an apparatus that can separately measure the size and distribution of particles on only one surface of a transparent object, i.e., either the top or bottom surface, and similarly to provide a corresponding method. [Means for solving the problem]

[0006] The above object is solved by a device having the features of claim 1 and a method having the features of claim 9.

[0007] The device according to the invention for inspecting a thin, transparent object having a first upper surface and a second lower surface comprises, inter alia, a camera and at least one light source. The thin, transparent object may have a thickness (dimension) of, for example, 0.1 mm to several millimeters. Here, the upper and lower surfaces of the transparent object are the two opposite surfaces that expand most. Thus, "above" refers to the space above the upper surface, and "below" refers to the space below the lower surface. The thickness is the material dimension of the object between the upper and lower surfaces.

[0008] The term "transparency" is used to describe the optical properties of an object's material, i.e., its transmittance to electromagnetic radiation. In particular, the present invention is applicable to objects whose transmittance to electromagnetic radiation is at least 50% in at least a subsection of the wavelength range from 300 nm to 3 μm, preferably in the wavelength range from 380 nm to 780 nm (visible light). The light source is arranged so that the electromagnetic radiation emitted by the light source irradiates a linear region on a first surface from above the object or a linear region on a second surface from below. The wavelength of the electromagnetic radiation used by the light source is, for example, in the wavelength range from 300 nm to 3 μm, preferably in the wavelength range from 380 nm to 780 nm (visible light). Thus, the light source irradiates the surface of the transparent object facing the light source within a linear region, which may have, for example, a dimension (length) along the line ranging from 1 cm to 10 m and a dimension (width) perpendicular to the line ranging from several μm to several mm. The linear area illuminated by the light source is slightly larger than or equal to the detection area of ​​the camera, which is designed, for example, as a line scan camera, to detect the electromagnetic radiation reflected from the linear area. In this case, the illumination is performed at a predetermined angle relative to each illuminated surface, and the camera is set up to detect the intensity of the electromagnetic radiation reflected onto at least one section of the linear area, i.e., the intensity of the electromagnetic radiation reflected in the direction of the light source. Therefore, the cameras are arranged on the same surface of the object, i.e., the surface facing the light source. Furthermore, the predetermined angle is defined to be 15° or less, and the electromagnetic radiation is primarily linearly s-polarized (i.e., electrically polarized transversely). Preferably, the predetermined angle is in the range of 3° to 12°, more preferably 5° to 10°. Here, the polarization direction of the electric field vector means that its oscillation direction is constant (linear polarization). Here, s-polarization means that the electric field of the electromagnetic radiation is perpendicular to the plane of incidence. The expression "predominantly s-polarized" means that the degree of polarization (fraction of s-polarized radiation) is at least 75%, preferably at least 90%, particularly preferably at least 95%.Because electromagnetic radiation reflected from a clean surface is reflected away from the light source, the camera detects only the intensity of electromagnetic radiation reflected from particles on the surface toward the camera or light source. Specifically, the camera detects the intensity of electromagnetic radiation reflected from an illuminated linear region of the surface toward at least one light source. If the camera detects a high back-reflection intensity in a subarea of ​​the linear region, it is determined that particles contaminating this surface are present on the surface.

[0009] The device according to the invention has the advantage that at very small illumination angles (predetermined angles of 15° or less), only a relatively small amount of light is transmitted through the transparent object. The proportion of light that is reflected depends on the illumination angle. At small illumination angles, most of the incident light is reflected away from the light source (and thus the camera), while only a small portion is transmitted through the transparent object. The same effect occurs on the side of the transparent object opposite the illuminated surface: only a very small portion of the incident light reaches the contamination particles located on the surface opposite the illuminated surface.

[0010] It is also known that electromagnetic radiation is partially reflected at the interface between two media (i.e., the illuminated surface of a transparent object in this case) and partially refracted within the second medium (here, the transparent material). Here, the proportion of reflected radiation, and therefore also the proportion of refracted radiation, is different for s-polarized light compared to p-polarized light. This principle is ingeniously used so that primarily s-polarized electromagnetic radiation is used for illumination. At small illumination angles—as in this case—a large proportion of s-polarized electromagnetic radiation is reflected, while a relatively small proportion is transmitted. For p-polarized light, this effect also appears, but only at extremely small angles, which, for space reasons, can only be achieved in practice with great effort. At smaller angles, the reflected portion of p-polarized light decreases very rapidly. When only s-polarized light is illuminated, the p-polarized portion of the incident electromagnetic radiation is very small, and the total illuminated portion refracted into the transparent material is very small. In contrast, the majority of the incident s-polarized radiation is reflected, and only a small portion is refracted into the transparent material. Thus, a negligible fraction of light reaches the surface of the transparent material opposite the illuminated surface.

[0011] Both of these effects result in a very small percentage of electromagnetic radiation passing through a transparent object. Therefore, very little light reaches the contamination on the opposite side of the illuminated surface. Therefore, in the corresponding camera image, each particle on the surface facing the camera is detected with a significantly stronger intensity than particles on the surface facing away from the camera, making it possible to distinguish contamination particles on the opposite side of the object. Light reflected in the direction of at least one light source is detected by the camera and provides a basis for determining the location and size of these surface contamination particles.

[0012] In one embodiment, the optical path of the camera at the object-side end adjacent to the illuminated linear region of each surface forms an angle of less than 20°, preferably less than 10°, and particularly preferably less than 5°, with the optical path of the electromagnetic radiation emitted by the light source. By arranging the light source and the camera in the same manner, i.e., at such a small angle, adverse effects on the inspection caused by changes in the position of the object's surface at the camera's focal point and in the illumination intensity are largely eliminated. Changes in the height of the object do not cause the illuminated linear region of the illuminated surface to move beyond the camera's detection range. In this embodiment, the optical path of the camera forms an angle of less than 5° with the optical path of the electromagnetic radiation emitted by the light source, i.e., the incident light ray. Preferably, the angle is less than 3°, more preferably less than 1°. In one embodiment, the optical path of the camera can be arranged to extend in the same plane as the optical path of the light source at the end adjacent to the illuminated linear region of each surface.

[0013] The device according to the invention and the method according to the invention are particularly applicable to objects made of glass (e.g. silicate glass) or plastic. The object may have a ribbon-like configuration, i.e. it may pass through the device according to the invention at a predetermined speed, or it may be inspected as a single piece.

[0014] In one embodiment, two or more light sources are provided. In another embodiment, one or two or more light sources are in the form of lasers with line optics, which expand the light beam emitted from the laser to form a line. The linear laser beam thus generated illuminates a linear area of ​​a first surface from above or a linear area of ​​a second surface from below with high intensity, e.g., optical power in the range of 1 mW to 10 mW per millimeter of line. The line optics expands the electromagnetic radiation emitted by the light source toward the object, so that the light source and the emitted radiation require only a small space on the surface facing the light source. For example, a laser with a frequency in the visible wavelength range (e.g., a diode laser) can be used as the laser, which has the advantage of emitting only polarized light. The light only needs to be aligned so that it is s-polarized relative to the direction of incidence on the surface.

[0015] In one embodiment, two light sources may be provided, each illuminating a portion of the linear region of the surface. In this embodiment, a single camera is provided to monitor both portions of the linear region. More than one camera may be provided.

[0016] In one embodiment, the object end of the camera's optical path is bounded on one end by a deflecting mirror and on the other end by the illuminated surface of the object. In other words, the object end of the camera's optical path is formed between the surface of the object facing the camera and a deflecting mirror angled into the camera's optical path at that point. The deflecting mirror deflects the camera's viewing direction by, for example, 90°, although other angles within the range of 20° to 170° are also contemplated. This allows for a space-saving placement of the camera and also allows for the deflecting mirror to be disposed within the camera's optical path.

[0017] A particularly simple structure of the device can be achieved by placing at least one light source next to the aforementioned deflection mirror disposed in the optical path of the camera. Here, "adjacent" means that the at least one light source is located a short distance away in a direction perpendicular to the optical path of the camera in a plane spanning the linear region of the illuminated surface and the optical path of the camera. This allows light from the at least one light source to pass laterally beyond the deflection mirror, and from the deflection mirror, the optical paths of the camera and light source extend in a common plane or at a small angle (less than 5°) as described above. Thus, the illumination direction of the light source and the viewing direction of the camera are the same. In a further embodiment, one light source is disposed next to each side of the deflection mirror.

[0018] Alternatively or additionally, the deflection mirror may be designed to be partially transparent, and at least one light source may be arranged behind the deflection mirror when viewed from the transparent object. The electromagnetic radiation emitted by the light source then passes through the deflection mirror and is then flush with the optical path of the camera. For example, the optical path of the camera is flush with the light source between the deflection mirror and the surface of the transparent object. Therefore, the illumination direction and the camera's viewing direction are the same in this case as well.

[0019] In one embodiment, the camera is designed as a line scan camera, which detects the intensity of reflected electromagnetic radiation pixel by pixel and along the illuminated linear area. The line scan camera may have a CCD, NMOS, InGaAs, and / or CMOS sensor. Line scan cameras are advantageous for the device according to the present invention compared to two-dimensional sensors with multiple lines. Line sensors have approximately the same pixel size as area sensors, but the line length can be much larger. Instead of the maximum pixel width of 1,000 to 4,000 pixels of area sensors, line scan cameras can have 17,000 pixels or more. Therefore, line scan cameras offer better spatial resolution for a given object field. Furthermore, lines can be read much faster than areas. In particular, it is advantageous to provide a higher-intensity light source to achieve clock speeds that are typically substantially faster than those of area scan cameras. Another major advantage is that the exact same illumination shape is used for the composite image of each line in the longitudinal direction (i.e., transverse to the line / width of the object).

[0020] The method according to the present invention for inspecting a thin-film transparent object having a first upper surface and a second lower surface is carried out by an apparatus including a camera and at least one light source. The electromagnetic radiation emitted by the at least one light source illuminates a linear region of the first surface of the object from above or a linear region of the second surface from below, with the illumination being at a predetermined angle relative to the respective illuminated surfaces. The camera then detects the intensity of the electromagnetic radiation reflected back to the at least one light source in at least a portion of the linear region, with the predetermined angle being 15° or less, and the electromagnetic radiation emitted by the light source being primarily linearly and s-polarized. The degree of contamination of the illuminated surface is determined based on the intensity of the reflected electromagnetic radiation detected by the camera (i.e., from the detected intensity data). This procedure is based on the inventor's findings above regarding the advantageous reflection behavior of electromagnetic radiation at small angles of incidence, whereby the electromagnetic radiation is primarily linearly and s-polarized.

[0021] In an exemplary embodiment having the advantages already mentioned above, the camera is oriented so that the optical path of the camera at the object-side end adjacent to the illuminated linear area of ​​each surface makes an angle of less than 5° with the optical path of the electromagnetic radiation emitted by the light source. The above-mentioned embodiments for arranging the optical paths of the light source and the camera apply analogously to the method according to the invention. In one exemplary embodiment, the intensity of the electromagnetic radiation reflected from the illuminated linear area of ​​the surface is detected pixel by pixel, for example by a line scan camera.

[0022] In a further embodiment, the position and / or size of the contaminating particles aligned on the illuminated surface of the transparent object are determined from the intensity data (i.e., data on the back-reflected intensity of electromagnetic radiation measured by the camera from the linear region) by a data processing device connected to the camera and transmitting the measured intensity data. For example, the camera measures a light intensity between a value of 0 and a maximum intensity value (e.g., a value of 255) for each pixel. Furthermore, each pixel of the camera can be assigned a position on the illuminated surface of the transparent object, i.e., the first or second surface. This can be achieved, for example, by defining two-dimensional coordinates and assigning them to corresponding positions on the object's surface. By corresponding calibration, the data processing device knows which positions have coordinates currently illuminated by the light source, and therefore, depending on which positions the back-reflected intensity of electromagnetic radiation is currently detected by the camera. This depends, in particular, on the arrangement of the light source and / or the camera, the (initial) position of the ribbon of the transparent object and its feed speed (in the case of inspecting a tape-like transparent object). Since the back-reflected electromagnetic radiation detected by the camera is in the illuminated area, each pixel can be assigned a location or coordinate on the surface of the object. If the intensity is detected to be above a first, predetermined intensity threshold, it is concluded that a particle contaminating the surface is present at the corresponding assigned location (represented by two-dimensional coordinates) on the surface relative to the light source and camera. The intensity of the back-reflected light can be evaluated to more accurately represent the size of the contaminant particle. For example, intensity subranges can be predefined, into which the intensity range between the first intensity threshold and the maximum intensity value is divided. For example, four intensity subranges can be defined. By assigning the measured intensity to each pixel, the size of each particle can be determined, with higher measured intensities assumed to be generated by larger contaminant particles. Therefore, a data processing device (e.g., a microprocessor) can determine the location and / or size of the contaminant particle on both surfaces. In this regard, a particle or a collection of particles can span multiple pixels.

[0023] When inspecting the surface of a thin, transparent object, such as a thin sheet of glass, over its entire length (i.e., transverse to the width of the object), the procedure involves, for example, moving the object relative to the device. In a direction perpendicular to the direction of object movement, the illuminated linear area is arranged so that the entire width of the object is covered, if possible. If necessary, multiple devices according to the present invention are arranged next to each other to cover the entire width of the transparent object. By moving the object, the entire surface of one side of the object is inspected. Alternatively, the device can move along the object for inspection.

[0024] By such inspection, flat objects, ie objects with continuously formed surfaces, can very well be inspected individually for contamination on each of their upper or lower surfaces.

[0025] Further advantages, features and possible applications of the present invention will be described below with reference to preferred embodiments and drawings, all features described and / or shown thereby constituting the subject matter of the present invention, notwithstanding their summary in the claims and their subsequent references. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a partial view in a perspective side view of a first embodiment of the device according to the invention during inspection of a thin-film transparent object; FIG. [Figure 2] 2 is a front perspective view of the embodiment according to FIG. 1; FIG. [Figure 3] 2 is a further perspective side view of the embodiment according to FIG. 1; [Figure 4] 2 is a side view of the optical paths of the camera and light source and the course of the transparent object in the embodiment according to FIG. 1; DETAILED DESCRIPTION OF THE INVENTION

[0027] 1 to 4 show a first embodiment of an apparatus according to the invention for inspecting a transparent object. The object, for example a transparent glass sheet 10, passes through the apparatus at a constant speed in a direction R in the form of an endless ribbon of width B, for example 1 m. The glass sheet 10 has an upper first surface 11 and a lower second surface 12. The thickness (dimension) D of the glass sheet 10 may be, for example, 0.1 mm to several millimeters.

[0028] To inspect the first surface 11 of the glass sheet for particle contamination, the apparatus includes two lasers 20 (e.g., diode lasers, with laser wavelengths in the visible light wavelength range, for example) arranged side by side with line optics to illuminate a 50 cm long linear region 15 on the first surface 11. The width of the linear region (perpendicular to the length) is within the range described above. Both lasers emit linearly polarized light, which is s-polarized. The lasers 20 are mounted on a support plate 17 attached to a frame that protrudes into the glass sheet ribbon. The line optics cause the light from each laser 20 to spread into a wide, linear light beam 22, so that when the light beam strikes the first surface 11 of the glass sheet 10, only the linear region 15 is illuminated. In this case, the two lasers 20 are arranged next to each other so that each laser 20 illuminates half the length of the linear region 15.

[0029] 4 shows that the light beam 22 of each light source 20 makes an angle α with the first surface 11 of the glazing, for example, less than 15°, preferably between 3° and 12°, and particularly preferably between 5° and 10°. The small angle α, combined with the s-polarization of the incident light 22, ensures that, in the absence of contaminant particles on the first surface 11, at least 85% of the incident electromagnetic radiation is reflected from the surface 11. Light 24 reflected away from the light source 20 also makes an angle α with the surface 11 of the glazing.

[0030] Only one device according to the invention may be provided to inspect the entire surface 11 of the glass sheet 10, or two or more devices according to the invention may be arranged side by side so that the glass sheet is detected over its entire width.

[0031] The two lasers 20 are further arranged so that their light in each case passes laterally past a deflection mirror 30. The deflection mirror 30 works in conjunction with a line scan camera 40 mounted on a support plate 17 above the first surface 11 of the glass sheet. The camera's field of view beam 41 is reflected by the deflection mirror 30, for example at an angle of 90°, so that its optical path now extends parallel to and in the same plane as the two light beams 22 of the light 20 and strikes the surface 11 of the glass sheet in the illuminated linear region. In other words, the camera 40 monitors the linear region 15 of the first surface 11 with the object-side end 42 of its optical path, which is in the same plane as the two light beams 22 of the light 20. Therefore, as shown in FIG. 4, the object-side end 42 also forms an angle α with the surface 11. Alternatively, the angle of the object-side end 42 of the camera 40 with the surface 11 may differ from the angle α by less than 5°. By placing the light source 20 and the camera 40 at the same or nearly the same angle, changes in the position of the surface 11 of the glass sheet 10 are largely prevented from adversely affecting the focus of the camera and the intensity of the laser 20 illumination.

[0032] If one or more contamination particles are present in the illuminated linear area 15 of the first surface 11, this / these will reflect the laser light towards the camera 40. The electromagnetic radiation reflected by the contamination particles towards the camera will be recognised by the camera as a bright spot and detected as brightness information (intensity of the reflected light) by at least one pixel of the camera.

[0033] A data processor 50 (see FIG. 2) connected to the camera 40 receives the intensity data detected by the camera, which is then transmitted to the line scan camera along with its pixel assignment. Furthermore, the data processor 50 determines the location of the illuminated linear region 15 on the first surface 11 of the glass sheet 10, from which the data processor calculates the location of dust particles belonging to the detected bright region of the line scan camera. For example, the detected intensity may range from 0 to 255 per camera pixel. For example, if the intensity is equal to or greater than a first intensity threshold of 21 for a pixel, the data processor 50 infers that the particle is located at the associated location of the illuminated linear region. Various intensities can be assigned to particle sizes of different sizes, as shown in the table below for illustrative purposes.

[0034] [Table 1]

[0035] A further possibility for evaluating the obtained intensity values ​​of the back-reflected electromagnetic radiation can alternatively or additionally be implemented in such a way that a particle is considered to be spread over two or more pixels if the neighboring pixels have a predetermined intensity value (e.g., within the above-mentioned range). The measured particle sizes of these neighboring pixels can then be summed, for example. If intensity values ​​above a first intensity threshold are measured in neighboring pixels in the direction R, the measured particle sizes can be added together. Other evaluations of the measured intensity values ​​of the back-reflected electromagnetic radiation are also possible. In this case, the scanning speed of the camera 40 is adapted to the speed of the glass sheet ribbon moving in the R direction, so that when the camera detects one line, the glass sheet ribbon has advanced in the R direction by exactly the width of the exposed linear region detected by the line scan camera, and so the next detection will detect a new linear region exactly adjacent to the previous linear region.

[0036] In an alternative embodiment, not shown, the lasers 20 are arranged behind the deflection mirror 30 instead of next to it. Their light passes through the deflection mirror 30 and reaches the first surface 11 through the deflection mirror 30. For this purpose, the deflection mirror is designed as a partially transparent mirror.

[0037] When measuring contamination on the second surface 12, the camera, deflecting mirror and light source are arranged in a mirror-reversed manner below the glass pane, and a linear field of illumination is realized at an angle α relative to the second surface 12. The camera's optical path extends above the second surface 12. The camera's optical path further extends to the edge of the object at an angle α relative to the second surface 12.

[0038] The device according to the invention makes it possible to measure contamination in particular on the surface of one side of a glass sheet or other thin, transparent object.

Claims

1. 1. An apparatus for inspecting a thin-film transparent object (10) having an upper first surface (11) and a lower second surface (12), comprising: a camera (40) and at least one light source (20); the light source (20) is configured such that the electromagnetic radiation emitted by the light source illuminates a linear area (15) of the first surface (11) from above or a linear area (15) of the second surface (12) from below of the slice-type transparent object, The irradiation is performed at a predetermined angle (α) with respect to the irradiated surface (11, 12), the camera (40) is arranged to detect an intensity of back-reflected electromagnetic radiation in at least a portion of the linear region (15); the predetermined angle (α) is in the range of 5° to 10°, and the electromagnetic radiation emitted by the light source (20) is predominantly linear and s-polarized; The device, characterized in that in the linear region of the illuminated surface (11, 12), the optical path (41, 42) of the camera (40) forms an angle of less than 20° with the optical path (22) of the electromagnetic radiation emitted by the light source (20).

2. 2. The apparatus according to claim 1, wherein a deflection mirror (30) is provided on the optical path of the camera (40), and the optical path is refracted by the deflection mirror (30) in a direction opposite to each of the surfaces (11, 12).

3. The light source (20) has two light sources (20) disposed on both sides of the deflection mirror (30), 3. The device according to claim 2, wherein the electromagnetic radiation from each light source (20) is directed onto the linear region (15) without passing through the deflection mirror (30).

4. 3. The device according to claim 2, wherein the deflection mirror is partially transparent and the at least one light source is arranged behind the deflection mirror as seen from the slice-type transparent object (10).

5. 5. Device according to any one of claims 1 to 4, characterized in that the light source (20) is a laser with line optics and capable of emitting visible light.

6. 6. Apparatus according to any one of claims 1 to 5, characterized in that the camera (40) is configured to detect the intensity of the reflected electromagnetic radiation pixel by pixel.

7. 7. The device according to claim 1, further comprising a data processing device (50) connected to the camera (40) and capable of transmitting intensity data measured by the camera (40), the data processing device (50) being configured to determine the position and / or size of particles aligned on the illuminated surface (11, 12) of the thin-film-type transparent object (10) from the intensity data.

8. 1. A method for inspecting a thin-film transparent object (10) having an upper first surface (11) and a lower second surface (12) by means of an apparatus, comprising: The device comprises a camera (40) and at least one light source (20); the electromagnetic radiation emitted by the light source (20) illuminates the linear area (15) of the first surface (11) of the flake-type transparent object from above or illuminates the second surface (12) from below, The irradiation is performed at a predetermined angle (α) with respect to the irradiated surface (11, 12), The camera (40) detects the intensity of the back-reflected electromagnetic radiation in at least a portion of the linear region (15); the predetermined angle (α) is in the range of 5° to 10°, and the electromagnetic radiation emitted by the light source (20) is predominantly linear and s-polarized; The method, wherein the degree of contamination of the illuminated surface (11, 12) is measured based on the intensity detected by the camera (40), The method, characterized in that in the linear region of each of the surfaces (11, 12), the optical path (41, 42) of the camera (40) makes an angle of less than 20° with the optical path (22) of the electromagnetic radiation emitted by the light source (20).

9. 9. The method of claim 8, wherein the intensity of the reflected electromagnetic radiation is detected by the camera on a pixel-by-pixel basis.

10. 10. The method according to claim 8 or 9, characterized in that the position and / or size of particles arranged on the illuminated surface (11, 12) of the thin-film-type transparent object (10) are determined from the measured intensities by a data processing device (50) connected to the camera (40) and to which the intensity data measured by the camera (40) are transmitted.

11. The optical path of the camera (40) is refracted in a direction opposite to each of the surfaces (11, 12) by a deflection mirror (30) provided on the optical path; 11. The method according to claim 8, wherein the linear region (15) is irradiated with electromagnetic radiation from two light sources (20) arranged on either side of the deflection mirror (30) without passing through the deflection mirror (30).

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