METHOD AND DEVICE FOR THERMOGRAPHIC AND TOPOGRAPHIC CHARACTERIZATION OF INOMOGENEITIES IN THE LAYER STRUCTURE OF COATED SUBSTRATES

Abstract

The invention relates to a method and a device for the thermographic characterisation of the surface (2) of a workpiece (1), in particular a coated workpiece, in which method a thermogram is produced of one or more first surface portions (3, 4) of the surface (2), and an image is produced of one or more illuminated second surface portions of the surface (2), at least some of the one or more first and second surface portions (3, 4) extending over a common region of the surface (2). In order to provide additional information for the characterisation, in particular for a topographical characterisation of inhomogeneities in the layer structure of coated metal substrates, the invention proposes that, in addition to the spatial extent of an inhomogeneity in the layer structure determined using the thermogram, a height profile of the surface (2) is also determined. To this end, the illuminated region of the surface (2), of which a thermogram and an image are created, is illuminated such that the image provides a height profile of the surface (2).

Description

1 / 12 “METHOD AND DEVICE FOR THERMOGRAPHIC AND TOPOGRAPHIC CHARACTERIZATION OF INOMOGENEITIES IN THE LAYER STRUCTURE OF COATED SUBSTRATES” Technical Field

[001] The present invention relates to a method for the thermographic characterization of the surface of a workpiece, in particular a coated one, in which a thermogram is created from one or more first surface sections of the surface and an image is created from one or more illuminated second surface sections of the surface, wherein at least some of the one or more first and second surface sections extend over a common area of ​​the surface.

[002] The invention further relates to a device for performing the method with a thermographic device having an energy radiator and a sensor for creating a thermogram, with a light source for illuminating the surface of the workpiece, with a sensor arrangement for recording an image of the illuminated surface and with a device for moving the workpiece relative to the sensor arrangement and the thermographic device. State of the Art

[003] Document DE 10 2017003 175 A1 describes an automated method and device for assessing corrosion damage on coated surfaces of metallic substrates. The metallic substrates are coated with a layer of lacquer. The lacquer layer is damaged in defined locations. Specifically, an artificial lesion in the form of a scratch line is created in the paint layer using a scratching tool. The pre-treated part is then placed in a corrosive atmosphere for a predetermined time, for example, by spraying it with salt water. During this treatment, corrosion forms in the damaged area, which spreads under the lacquer layer over time. Petition 870250080870, dated 09 / 09 / 2025, page 34 / 55 2 / 12 po. This leads to heterogeneities in the lacquer layer structure, for example, in the form of delamination between the lacquer layer and the substrate. In most cases, this also results in a bulging of the lacquer surface, detectable by sensitive optical methods. A standardized method used to determine the extent of these inhomogeneities involves the mechanical removal of the lacquer layer, for example, with a steel brush. The widths of the visible inhomogeneities are measured at intervals of a few millimeters along the marking line. An average value is then calculated. The aforementioned document describes an automated method for automatically measuring heterogeneity in the layer structure using pulse thermography. Furthermore, the measurement range for pulse thermography hn is defined based on a visual image generated by a camera.To draw conclusions about the type of corrosion, the color values ​​of each individual pixel in the visual image are also determined and compared with the thermogram to classify inhomogeneities in the layer structure, such as corrosion damage. In practice, corrosion damage assessment is carried out in accordance with the EN ISO 6428-8 standard.

[004] In addition, the state of the art includes methods that can be used to measure non-contact, reflective, or at least sufficiently light-reflective surfaces. These include, in particular, photometry, radiometry, photogrammetry, laser scanning, reflectometry, deflectometry, and dark-field illumination. This method can be used to determine the height profile of a surface. Summary of the Invention

[005] The invention is based on the objective of developing the generic method in a way that is advantageous for use. The invention aims to provide additional information for the characterization, in particular for the topographic characterization, of inhomogeneities in the structure of ca Petition 870250080870, dated 09 / 09 / 2025, page 35 / 55 3 / 12 layers of coated substrates, particularly metallic substrates.

[006] The problem is solved by the invention specified in the claims. The dependent claims represent not only advantageous developments of the invention specified in the independent claims, but also their own solutions to the problem.

[007] Firstly, it is proposed that, in addition to the spatial extent of an inhomogeneity in the layer structure of a coated substrate, for example, a glass substrate, a concrete substrate or, preferably, a metal substrate, determined by the thermogram, a surface height profile is also determined. The method according to the invention is particularly suitable for analyzing corrosion damage in lacquer samples. For this purpose, a substrate, particularly a metallic one, is coated with a layer of lacquer. The lacquer layer is damaged at a defined location; the sample prepared in this way is exposed to a corrosive atmosphere, for example, salt water, for a predetermined period of time. The resulting corrosion, which infiltrates the lacquer layer, is examined by pulsed thermography. Using an energy beam, particularly a laser beam, the surface is heated at high power for a few milliseconds in the initial surface sections.The heat flow to the substrate is influenced by the corrosion layer formed between the substrate surface and the lacquer layer. As a result, the temperature of the first section of the surface, measured with a sensor such as an infrared sensor, an infrared thermal camera, or a thermal imaging sensor, can be used to determine if there is corrosion under the lacquer layer. The infrared sensor can detect an array of pixels. The array should preferably have at least 8 x 16 pixels. The energy beam can be applied to the lacquer surface in pulses. For example, temperatures can be measured... Petition 870250080870, dated 09 / 09 / 2025, page 36 / 55 4 / 12 of the successive measurements are taken in different sections of the first surface after the pulsed application of the laser beam. It is also possible to move a continuous or pulsed laser beam rapidly over the surface to simultaneously measure the temporal progression of the temperature at the respective exposure point using an infrared camera that takes a large number of images successively. According to the invention, this method is complemented by recording a height profile of the surface. For this purpose, a height profile is determined in two sections of the surface. The second surface sections contain at least some or more of the first surface sections. The height profile is also determined in an area of ​​the surface where the thermographic examination is also performed. The height profile can be recorded simultaneously with the thermographic examination. However, it can also be recorded before or after.A device according to the invention, which has a thermographic device for this purpose, has an additional set of sensors and a light source. The light source illuminates the surface of the workpiece in such a way that the height profile can be determined using the associated additional sensor set. A computing device, which includes in particular an image recognition device, can spatially correlate the height profile with the thermogram. The elevation values ​​of the elevation profile are spatially assigned to the temperature values ​​of the thermogram. The elevation profile and the thermogram are recorded on a variety of first and second surfaces, respectively, wherein, for some, preferably all, surface sections where a thermogram was created, i.e., a temperature was measured, a surface height value is also optically determined.The workpiece can be automatically moved relative to a measuring device. For this purpose, the measuring device preferably comprises... Petition 870250080870, dated 09 / 09 / 2025, page 37 / 55 5 / 12 The invention comprises the energy radiator, the temperature detection sensor, the light source, and the sensor array for recording an image of the illuminated surface. According to the invention, the type of illumination is selected to provide information on the extent of non-homogeneity, for example, the bulging of a paint layer in the area damaged by corrosion. For this purpose, the optovisual methods used are mainly PSD (Phase Shifting Deflectometry), laser triangulation, or dark-field illumination. To this end, a visual image of the coated surface can be generated using a camera, where the type of illumination and the evaluation of the visual image of the coated surface allow the thermal image to be correlated with color values ​​and a height profile. The color values ​​can be captured with a camera that captures a visual image and allows conclusions to be drawn about the type of heterogeneity.For example, rust or the formation of aluminum oxide can be detected based on color. A coated metallic substrate, especially one containing iron, is preferred as a substrate. A key factor for the thermographic process is the difference in thermal capacity and / or thermal conductivity between the coating and the substrate; therefore, the process can also be applied to coated substrates made of other materials. Brief Description of the Drawings

[008] The embodiments of the invention are explained below with reference to the accompanying drawings:

[009] Figure 1 shows a schematic perspective view of an early embodiment of a device for performing the method in which the height profile is determined by laser triangulation,

[0010] Figure 2 shows a two-dimensional schematic representation of a second embodiment of a device in which the height profile (shown enlarged in the drawings) is also determined. Petition 870250080870, dated 09 / 09 / 2025, page 38 / 55 6 / 12 swimming by laser triangulation,

[0011] Figure 3 is a representation similar to Figure 1 of a third embodiment in which the height profile is determined using deflectometry,

[0012] Figure 4 is a two-dimensional representation of the device shown in Figure 3 and

[0013] Figure 5 is a representation of a fourth embodiment in which the height profile is determined using dark-field illumination. Description of the Implementations

[0014] A support 15 is fixed to a frame 16, which can be arranged in a stationary manner, for example in a laboratory, and carries an infrared laser 8, which generates a laser beam 9 that strikes a workpiece 1 in a first surface section 3. A sensor 13 that is fixed to the support 15 and which can be a thermal imaging sensor with which a section of the surface 2 of the workpiece 1 located in a detection area 19 is detected can be used to record a thermal image of this detection area 19. The infrared laser 8 generates a laser beam 9 with a wavelength that is outside the sensitivity range of the sensor 13, so that the temperature of the first surface section 3 heated by the application of energy can be determined with the sensor 13.

[0015] The heat flow from the surface to the volume of the workpiece influences the temperature.

[0016] Support 15 also has a camera 14, with which a visual image of the surface 2 of the workpiece 1 can be recorded, including, in particular, color values. In the exemplary embodiment, the detection range 18 of the camera 14 is slightly greater than the detection range 19 of the sensor 13.

[0017] A second surface section 4 of surface 2 is illuminated Petition 870250080870, dated 09 / 09 / 2025, page 39 / 55 7 / 12 nothing by an additional laser 10. An additional sensor arrangement 12 can be used to determine the height of the surface section 4 by means of laser triangulation.

[0018] The following method can be performed with this device: A metal part 1 previously coated with a layer of lacquer 5 is damaged, for example, by injecting a scratch line into the lacquer layer 5, extending to the metal surface 1'. Part 1 is then exposed to a corrosive environment in a climatic chamber for a predetermined time. Corrosive damage 7 forms in the area of ​​the damage 20 and also migrates down the lacquer layer 5 (see Figure 2).

[0019] The workpiece 1 thus pre-treated is placed on a support 17, which can be moved relative to the frame 16 by an automated control device (not shown). According to the method described in the aforementioned document DE 102017003 175 A1, a thermogram is recorded on a plurality of predetermined first surface sections 3, which can be used to draw conclusions about the delamination of the lacquer. In detail, a sensor 13, in particular a thermographic camera, is used to examine the temperature to which the first surface section exposed by the laser beam 9 heats up during exposure or how the temperature changes after exposure.

[0020] At the same time, a height profile is recorded on the same surface sections or on other surface sections, which are referred to below as second surface sections 4. Values ​​are determined that indicate the respective height of the lacquer layer surface 5 or its distance from the metal surface 1'. The computer (not shown), which may include an image recognition device, correlates the thermographic measurement points with the height measurement points, so that height values ​​are also available for some, preferably Petition 870250080870, dated 09 / 09 / 2025, pp. 40 / 55 8 / 12 mind all, the measurement locations where temperatures were measured using thermography.

[0021] Workpiece 1 can be moved in the X direction and / or Y by stepper motors relative to support 15. However, it is also possible that support 15 can be moved, for example, in the X direction relative to frame 16, and support 17 can be moved in the Y direction relative to frame 16. By properly controlling the stepper motors, the laser beam 9 can be moved line by line across the workpiece 1. Along with this, the measuring point or measuring location of the sensor array 12 also moves across the surface of the workpiece 1. Using this method, a surface contour of the corrosion damage 7 can then be determined.

[0022] The optical axis of the laser beam 11 can be perpendicular to the surface 2.

[0023] The embodiment shown in Figures 3 and 4 differs from the embodiment described previously essentially in the method of determining the height profile. The height profile is determined here using the deflectometry method. A two-dimensional image 21 of a defined structure is generated on a screen, which moves in a manner defined across the screen, so that an area of ​​the surface 1 on which the moving image 21 is reflected can be observed with an array of sensors, which here consists of an optical camera 22. With an ideally flat surface, the structures moving across the screen would be captured without distortion by the optical camera 22. However, a surface that deviates from ideal flatness distorts the image captured by the optical camera 22 and thus exhibits distortions compared to the moving image 21.Through a comparison calculation with an image recognition device, in which the image recorded by the 22-sensor array is compared with the two-dimensional image 21, conclusions are drawn about the topology of the su. Petition 870250080870, dated 09 / 09 / 2025, page 41 / 55 9 / 12 of the profile 2 can be taken from deviations attributable to distortion. The height profile can be calculated from these images.

[0024] The embodiment shown in Figure 5 differs from the embodiments described previously essentially in the method of determining the height profile. The height profile is generated here using dark-field illumination. Using light sources 23, surface 2 is illuminated at a shallow angle. Camera 14 captures an image of the exposed area. The image is evaluated using the image recognition device. The height profile can be calculated from the image.

[0025] The optical axis of camera 14 can be perpendicular to surface 2. The height profile can be recorded using visible light. However, it is also possible to record the height profile using non-visible light, for example, infrared or ultraviolet light.

[0026] In all the embodiments described above, it can also be foreseen that visual images of surface 2 are recorded. This can be done, in particular, with visual camera 14. Visual camera 14 can be sensitive to visible light. However, it can also be sensitive to infrared or ultraviolet light. The images obtained preferably contain color information so that the color of the corrosion damage 7 can be analyzed. This allows conclusions to be drawn about the type of heterogeneity in the layer structure.

[0027] The above statements serve to explain the inventions covered by the application as a whole, which also independently develop the state of the art at least by the following combinations of features, whereby two, several or all of these combinations of features may also be combined, namely:

[0028] A method characterized by the fact that the area is illuminated in such a way that the image provides a height profile of the surface. Petition 870250080870, dated 09 / 09 / 2025, page 42 / 55 10 / 12

[0029] A method characterized by the fact that the thermogram and the height profile are placed in a spatial correlation.

[0030] A method characterized by the fact that the height profile is determined using the laser triangulation method, dark field illumination or deflectometry.

[0031] A method that is characterized in that the workpiece 1 has a lacquer layer 5 applied to a surface 1' of a substrate and is exposed to a corrosive environment for a predetermined time such that inhomogeneities 6, 7 are formed in the layer structure, wherein the first and second surface sections 3, 4 are in the inhomogeneity region 6, 7, wherein the inhomogeneity is, in particular, a delamination of the lacquer layer 5 and the substrate or other compromise of the lacquer layer 5.

[0032] A method that is characterized by the fact that images with color values ​​are generated from at least the surface area 2, which are placed in spatial correlation with the height profile.

[0033] A device characterized by the fact that the light source 10, 21, 23 is designed and arranged so that the image provides a height profile of the surface area.

[0034] A device characterized by an image recognition device with which the thermogram recorded by the thermography device 8, 13 and the image recorded by the sensor array 12, 22, 14 are automatically placed in a spatial correlation.

[0035] A device characterized in that the light source comprises one or more lasers 10 and the sensor array comprises one or more sensors 12 sensitive to laser light reflected from the surface, or in that the sensor array 22 provides a time-varying two-dimensional image and the sensor array is a camera 22 that captures the reflected image from the surface, or in that the Petition 870250080870, dated 09 / 09 / 2025, page 43 / 55 11 / 12 light source 23 illuminates surface 2 at a shallow angle and sensor array 14 is a camera that captures a visual image.

[0036] A device that is characterized in that the sensor arrangement comprises a camera 14 with which images with color values ​​are generated from at least the illuminated area of ​​the surface 2, and the image recognition device is configured in such a way that the images with the color values ​​can be placed in a spatial correlation with the height profile.

[0037] All the features described are (individually, but also in combination with each other) essential to the invention. The application disclosure fully incorporates the content of the associated priority documents / annexes (copy of the prior application), also for the purpose of incorporating features from those documents into the claims of the present application. Dependent claims characterize, even without the features of a referenced claim, independent inventive developments of the prior art with their features, in particular to make divisional applications based on those claims. The invention specified in each claim may additionally comprise one or more of the features indicated in the description above, in particular with reference numerals and / or in the list of reference numerals.The invention also relates to designs in which the individual features mentioned in the description above are not implemented, particularly to the extent that they are clearly unnecessary for the intended use or can be replaced by other technically equivalent means. List of Reference Numerals Workpiece Metallic surface Surface Petition 870250080870, dated 09 / 09 / 2025, pages 44 / 55 12 / 12 First section of the surface Second section of the surface Lacquer layer height structure Corrosion damage Infrared laser Laser beam Light source, laser Laser beam Sensor arrangement Sensor Camera Support Frame Support Detection area Detection area Damage Two-dimensional image Sensor arrangement, camera Light source Petition 870250080870, dated 09 / 09 / 2025, pages 45 / 55

Claims

1 / 2 CLAIMS 1. Method for the thermographic characterization of the surface (2) of a particularly coated workpiece (1), in which a thermogram and an image are created from an illuminated area of ​​the surface (2), characterized in that the area is illuminated in such a way that the image provides a height profile of the surface.

2. Method, according to claim 1, characterized in that the thermogram and the height profile are placed in a spatial correlation.

3. A method, according to any of the preceding claims, characterized in that the height profile is determined using the laser triangulation method, dark-field illumination, or deflectometry.

4. Method, according to any of the preceding claims, characterized in that the workpiece (1) has a lacquer layer (5) applied over a surface (1') of a substrate and is exposed to a corrosive environment for a predetermined time, that inhomogeneities (6, 7) are formed in the layer structure, wherein the first and second surface sections (3, 4) are in the inhomogeneity region (6, 7), wherein the inhomogeneity is, in particular, a delamination of the lacquer layer (5) and the substrate or other impairment of the lacquer layer (5).

5. Method, according to any of the preceding claims, characterized in that images with color values ​​are generated from at least the surface area (2), which are placed in spatial correlation with the height profile.

6. Device for performing a method, as defined in any of the preceding claims, with a thermography device (8, 13) having an energy radiator (8) and a sensor (13) for creating a thermogram, with a light source (10, 21, 23) for Petition 870250080870, dated 09 / 09 / 2025, page. 46 / 55 2 / 2 illuminate at least one area of ​​the surface (2) of the workpiece (1), with an arrangement of sensors (12, 22, 14) to record an image of the illuminated area of ​​the surface (2) and with a device (17) to move the workpiece (1) relative to the arrangement of sensors (12, 22, 14) and the thermography device (8, 13), characterized in that the light source (10, 21, 23) is designed and arranged so that the image provides a height profile of the surface area.

7. Device according to claim 6, characterized in that an image recognition device with which the thermogram recorded by the thermography device (8, 13) and the image recorded by the sensor array (12, 22, 14) are automatically placed in a spatial correlation.

8. Device according to claim 6 or 7, characterized in that the light source comprises one or more lasers (10) and the sensor arrangement comprises one or more sensors (12) sensitive to laser light reflected from the surface or that the sensor arrangement (22) provides a time-varying two-dimensional image and the sensor arrangement is a camera (22) capturing the image reflected on the surface or that the light source (23) illuminates the surface (2) at a shallow angle and the sensor arrangement (14) is a camera capturing a visual image.

9. Device, according to any one of claims 6 to 8, characterized in that the sensor arrangement comprises a camera (14) with which images with color values ​​are generated from at least the illuminated area of ​​the surface (2), and the image recognition device is configured in such a way that the images with the color values ​​can be placed in a spatial correlation with the height profile.

10. Method or device, characterized in that it has one or more of the characterizing features, according to any of the preceding claims. Petition 870250080870, dated 09 / 09 / 2025, p. 47 / 55

Images