Method and apparatus for characterizing non-uniform portions of the layer structure of coated substrates using thermography and topography.

Abstract

The present invention relates to a method and apparatus for thermographic characterization of a workpiece (1), particularly a surface (2) of a coated workpiece, wherein a thermogram is generated of one or more first surface sections (3,4) of the surface (2), and an image is generated of one or more irradiated second surface sections of the surface (2), and at least some of the one or more first and second surface sections (3,4) extend into a common area of ​​the surface (2). To provide further information for characterization, particularly for topographic characterization of heterogeneous portions in the layer structure of a coated metal substrate, the present invention also determines the height profile of the surface (2) in addition to the spatial extent of the heterogeneous portions of the layer structure determined using the thermogram. For this purpose, the image provides the height profile of the surface (2) by illuminating the irradiated area of ​​the surface (2) where the thermogram and image are generated.

Description

Technical Field

[0001] The present invention relates to a method for characterizing a workpiece, particularly a coated workpiece, by thermography of the surface, in which a thermogram of one or more first surface sections of the surface is generated, an image of one or more irradiated second surface sections of the surface is generated, and at least some of the one or more first and second surface sections extend into a common area of the surface.

[0002] The present invention further relates to an apparatus for carrying out the method, comprising a thermography apparatus having an energy emitter and a sensor for generating a thermogram, a light source for irradiating the surface of the workpiece, a sensor assembly for recording an image of the irradiated surface, and an apparatus for measuring the relative movement of the workpiece with respect to the sensor assembly and the thermography apparatus.

Background Art

[0003] Patent Document 1 describes an automated method and apparatus for evaluating corrosion damage to the coated surface of a metal substrate. The metal substrate is provided with a coating layer. The coating layer is damaged at a predetermined location. In particular, the coating layer is artificially scratched in the form of scratch lines using a scratching tool. Next, the workpiece pretreated in this manner is placed in a corrosion environment, for example, an environment where salt water is sprayed, for a predetermined time. During this treatment, corrosion occurs in the damaged area that spreads under the coating layer as the treatment period progresses. As a result, non-uniform portions, for example, in the form of peeling of the coating layer and the substrate, occur in the structure of the coating layer. In many cases, this causes the painted surface to swell, which can be identified using high-sensitivity optical methods. Conventional standardization methods for determining the extent of these non-uniform areas involve mechanically removing the paint layer, for example, using a wire brush. The width of the visible non-uniform area is measured transversely to the scratch line at predetermined points at a distance of several millimeters. An average value is then calculated from these measurements. The aforementioned literature specifies an automated method that allows for the automatic measurement of non-uniform areas within a layered structure using pulsed thermography. Furthermore, the measurement area of ​​the pulsed thermography is defined using a visual image generated by a camera. To derive conclusions regarding the type of corrosion, the color value of each individual pixel in the visual image is determined and compared with the thermogram to classify non-uniform areas, such as corrosion damage, in the layered structure. In practice, the EN ISO 6428-8 standard is used to evaluate corrosion damage. Furthermore, the prior art includes methods for measuring reflective surfaces, or at least surfaces that reflect light sufficiently, in a non-contact manner. These include, in particular, photometry, radiometry, photogrammetry, laser scanning, reflectometry, deflectometry, and dark-field illumination. These methods enable the acquisition of height profiles of the surface under determination. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] German Patent Application Publication No. 102017003175 Specification [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The object of the present invention is to further develop a general-purpose method in a manner that is advantageous in use. The present invention provides complementary information for characterizing heterogeneous portions in the layer structure of coated substrates, particularly metal substrates, especially for topographic characterization. [Means for solving the problem]

[0006] This problem is solved by the invention defined in the claims. The dependent claims constitute not only advantageous further embodiments of the invention defined in the dependent claims, but also clear means of solving the problem.

[0007] First and foremost, it is proposed that, in addition to the spatial extent of heterogeneous areas determined by thermography in the layered structure of a substrate, such as a glass substrate, a cement substrate, or preferably a metal substrate, the surface height profile is also determined. The method according to the present invention is particularly suitable for the analysis of corrosion damage to painted samples. For this purpose, a painted layer is provided on a substrate, especially a metal substrate. The painted layer is damaged at a specified location. The sample prepared in this manner is exposed to a corrosive atmosphere, such as saltwater, for a predetermined time. The resulting corrosion penetrates the painted layer and is examined by pulsed thermography. The surface is heated at high power for several milliseconds in the first surface section by an energy beam, particularly a laser beam. Heat dissipation to the substrate is affected by the corrosion layer formed between the substrate surface and the coating layer. Consequently, conclusions about corrosion located beneath the coating layer can be drawn from the temperature of the first surface section measured by a sensor, such as an infrared sensor, an infrared thermography camera, or a thermal imaging sensor. The infrared sensor can measure an "array" of pixels, preferably containing at least 8 × 16 pixels. The application of the energy beam to the coating layer may be pulsed, for example, allowing for continuous measurement of the temperature after applying pulses of the laser beam to different first surface sections. However, by passing a continuous or high-speed pulsed laser beam across a surface, it is also possible to simultaneously measure the temperature profile over time at individual irradiation points using an infrared camera that records multiple images in succession. According to the present invention, the method is complemented by recording the height profile of the surface. For this purpose, individual height profiles are determined in a second surface section. The second surface section includes at least several, i.e., multiple, first surface sections. Thus, the height profile is also determined in the area of ​​the surface where thermographic inspection is being performed. The height profile can be recorded simultaneously with the thermographic inspection. However, it may be recorded before or after. The apparatus according to the present invention for this purpose includes a thermographic apparatus, which has an additional sensor assembly and a light source. The surface of the workpiece is illuminated by the light source in such a manner that the height profile can be determined using the associated additional sensor assembly. The height profile can be spatially correlated with the thermogram, particularly using a computing device with an image recognition device. In this regard, the height values ​​in the height profile are locally related to the temperature values ​​in the thermogram. The height profile and thermogram are recorded on a plurality of first or second surface sections. For some, preferably all, of those surface sections from which the thermogram was generated, i.e., from which the temperature was measured, the surface height values ​​are also optically determined. In this regard, the workpiece can be automatically moved relative to the measuring device. For this purpose, the measuring device preferably includes an energy emitter, a temperature sensing sensor, a light source, and a sensor assembly for recording an image of the irradiated surface. According to the present invention, the type of irradiation is selected so that the height of non-uniform areas, such as the expansion of the coating layer in a corrosion-damaged area, can be predicted. For this purpose, in particular, phase-shift deflectometry (PSD), laser triangulation, or in practice, dark-field illumination are also used as optical / visual methods. For this purpose, a visual image of the coated surface can be generated by a camera, and by evaluating the type of irradiation and the visual image of the coated surface, it is possible to correlate the thermal image with color values ​​and height profiles. Color values ​​are recorded by a camera capable of capturing visual images and drawing conclusions about the type of non-uniformity. For example, the formation of rust or aluminum oxide can be detected using color. Preferably, painted metal substrates, and especially those containing iron, are considered as substrates. The key factor in thermography is the difference in heat capacity and / or thermal conductivity between the coating and the substrate; therefore, this method is also applicable to coated substrates made from other materials. [Brief explanation of the drawing]

[0008] The present invention will be described in further detail below with reference to exemplary embodiments with reference to the attached drawings. [Figure 1] Figure 1 shows a schematic perspective view of a first exemplary embodiment of an apparatus for performing a method by which a height profile is determined by laser triangulation. [Figure 2] Figure 2 shows a two-dimensional image of a second exemplary embodiment of a device in which the height profile (shown in a large magnified view in the figure) is also determined by laser triangulation. [Figure 3] Figure 3 shows a diagram similar to Figure 1 of a third exemplary embodiment in which the height profile is determined by deflectometry. [Figure 4] Figure 4 shows a two-dimensional view of the apparatus shown in Figure 3. [Figure 5] Figure 5 shows a diagram of a fourth exemplary embodiment in which the height profile is determined by dark-field illumination. [Modes for carrying out the invention]

[0009] The support unit 15 is attached to a frame 16 that can be fixed in a predetermined position, for example, in a laboratory. The support unit 15 carries an infrared laser 8 that generates a laser beam 9. The laser beam 9 strikes the first surface section 3 of the workpiece 1. A thermal image of the capture region 19 can be recorded by a sensor 13 attached to the support unit 15, and the sensor 13 may be a thermal imaging sensor. Using the sensor 13, it is possible to measure a portion of the surface 2 of the workpiece 1 located in the capture region 19. Since the infrared laser 8 generates a laser beam 9 with a wavelength outside the sensitivity range of the sensor 13, the temperature of the first surface section 3, which is heated by the application of energy, can be determined using the sensor 13.

[0010] The dissipation of heat from the surface to the interior of a workpiece affects its temperature.

[0011] Furthermore, the support unit 15 includes a camera 14 capable of recording a visual image of the surface 2 of the workpiece 1, particularly a visual image including color values. In an exemplary embodiment, the capture area 18 of the camera 14 is slightly larger than the capture area 19 of the sensor 13.

[0012] The second surface section 4 of surface 2 is illuminated by an additional laser 10. In the laser triangulation process, the height of surface section 4 can be determined by an additional sensor assembly 12.

[0013] The following method can be performed using this device. For example, damage 20 is caused in a metal workpiece 1 pre-coated with paint layer 5 by introducing scratch lines that penetrate into the paint layer 5 and reach the metal surface 1'. The workpiece 1 is then exposed to a corrosive environment in a climate chamber for a predetermined time. This creates corrosion damage 7 that penetrates beneath the paint layer 5 in the area of ​​damage 20 (see Figure 2).

[0014] The workpiece processed in this way is placed on a support 17 movable with respect to the frame 16 by an automatic control device not shown here. Corresponding to the method described in the above-mentioned Patent Document 1, thermograms are recorded at a plurality of predetermined first surface sections 3, and conclusions regarding the peeling of the coating can be derived using them. Specifically, the sensor 13, particularly a thermal imaging camera, is used to examine how much the first surface section irradiated with the laser beam 9 is heated during irradiation or how the temperature changes after irradiation.

[0015] At the same time, a height profile is recorded at the same surface section or at other surface sections hereinafter referred to as the second surface section 4. Values giving the individual heights of the surface of the coating layer 5, i.e., the distances from the metal surface 1', are determined. Using an arithmetic unit not shown which may have an image recognition device, the thermography measurement points are correlated with the measurement points for height measurement. Thereby, several, preferably all, of the measurement points where the temperature is measured by thermography are also given height values.

[0016] Here, the workpiece 1 is movable in the x-direction and / or the y-direction with respect to the support 15 by a stepping motor. However, it is also possible for the support 15 to move with respect to the frame 16, for example, in the x-direction, and for the support 17 to move with respect to the frame 16, for example, in the y-direction. Using appropriate control of the stepping motor, the laser beam 9 can be moved in rows on the workpiece 1. Along with this, the measurement points or measurement locations of the sensor assembly 12 can also be moved on the surface of the workpiece 1. Thereafter, the surface profile of the corrosion damage 7 can be determined by this method.

[0017] The optical axis of the laser beam 11 can be perpendicular to the surface 2 here.

[0018] The exemplary embodiments shown in FIGS. 3 and 4 are essentially different from the exemplary embodiments described above in the method for determining the height profile. Here, the height profile is determined using the deflectometry method. A two-dimensional image 21 with a defined structure is generated on the display screen, and by moving the image in a defined manner across the display screen, here using a sensor assembly, which is an optical camera 22, the surface area of the surface 1 that reflects the movable image 21 can be observed. In the case of an ideal flat surface, the structure moving across the display screen would be captured without distortion by the optical camera 22. However, a surface deviating from an ideal flat surface will distort the image recorded by the optical camera 22 and contain distortion compared to the movable image 21. By a comparison calculation by an image recognition device that compares the image recorded by the sensor assembly 22 with the two-dimensional image 21, conclusions regarding the surface topology of the surface 2 can be drawn from the deviation due to distortion. The height profile can be calculated from these images.

[0019] The exemplary embodiment shown in FIG. 5 is different from the exemplary embodiments described above in the method for determining the height profile. Here, the height profile is generated using the dark-field illumination method. The surface 2 is illuminated at a flat angle using a light source 23. An image of the area illuminated in this way is recorded by the camera 14. The image is evaluated by an image recognition device. The height profile can be calculated from this image.

[0020] The optical axis of the camera 14 can here be perpendicular to the 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, such as infrared or ultraviolet light.

[0021] Furthermore, in all the exemplary embodiments described above, a visual image of surface 2 can be recorded. In particular, this can be done using a visual camera 14. The visual camera 14 may be sensitive to visible light. However, it may also be sensitive to infrared or ultraviolet light. The image recorded in this manner preferably includes color information, thereby allowing for the analysis of the color of the corrosion damage 7. This allows for the drawing of conclusions regarding the type of heterogeneity in the layer structure.

[0022] The foregoing is intended to describe the invention covered by this application as a whole, and the present invention independently develops the prior art by at least a combination of the following features, and any combination of two, some, or all of these features may be combined.

[0023] A method characterized in that an area is illuminated in such a manner that the image provides a height profile of the surface.

[0024] A method characterized by spatially correlating a thermogram with a height profile.

[0025] A method characterized by determining the height profile using laser triangulation, dark-field illumination, or deflectometry.

[0026] A method characterized in that a workpiece 1 has a coating layer 5 applied to the surface 1' of a substrate and is exposed to a corrosive environment for a predetermined time in such a manner that non-uniform portions 6 and 7 are formed in the layer structure, the first surface section 3 and the second surface section 4 are located in the regions of the non-uniform portions 6 and 7, and in particular the non-uniform portions are peeling of the coating layer 5 and the substrate or further damage to the coating layer 5.

[0027] A method characterized in that an image containing color values ​​is generated from at least a region of surface 2, and this image is spatially correlated with a height profile.

[0028] An apparatus characterized in that light sources 10, 21, and 23 are constructed and arranged in such a manner that the image provides a height profile of the surface region.

[0029] An apparatus characterized by having an image recognition device, which is used to automatically spatially correlate thermograms recorded by thermography devices 8 and 13 with images recorded by sensor assemblies 12, 22, and 14.

[0030] An apparatus characterized in that the light source has one or more lasers 10 and the sensor assembly has one or more sensors 12 that are sensitive to light from the lasers reflected from the surface, or the light source 22 is a camera 22 that provides a two-dimensional image that changes over time and the sensor assembly is a camera 22 that captures the image reflected from the surface, or the light source 23 is a camera that illuminates the surface 2 at a flat angle and the sensor assembly 14 is a camera that captures a visual image.

[0031] The apparatus is characterized in that the sensor assembly has a camera 14, and an image recognition device is constructed such that an image including color values ​​in at least the illuminated area of ​​surface 2 is generated using the camera, and the image including color values ​​can be spatially correlated with a height profile.

[0032] All disclosed features are essential to the present invention (both for themselves and in combination with each other). The disclosures of this application encompass the entirety of the disclosures of any related / additional priority documents (copies of earlier applications), and it is also intended to incorporate the features of those documents into the claims of this application. Dependent claims feature independent inventive further developments of the prior art, even without the features of the cited claims, particularly for the purpose of filing a divisional application based on these claims. The invention specified in each claim may have one or more additional functions, particularly those specified in the preceding description, especially those to which reference numerals are assigned, and / or specified in the descriptions of the reference numerals. The present invention also relates, in particular, to design configurations in which individual features described above are not implemented, insofar as they are obviously unnecessary for their respective intended use or can be replaced by other means having the same technical effect. [Explanation of Symbols]

[0033] 1 workpiece 1' metal surface 2 surface 3. First Surface Section 4. Second Surface Section 5. Paint layer 6 Height structure 7. Corrosion damage 8. Infrared Laser 9 Laser beam 10 Light sources, lasers 11 Laser beam 12 Sensor Assembly 13 Sensors 14 Cameras 15 Support part 16 frames 17 Support part 18 Capture area 19 Capture area 20 damage 21 Two-dimensional images 22 Sensor assemblies, camera 23 Light source

Claims

1. A method for generating a thermogram and an image of an irradiated area of ​​a workpiece (1), particularly a coated workpiece surface (2), for thermographic characterization of the surface (2), characterized in that the area is irradiated in such a manner that the image provides a height profile of the surface.

2. The method according to claim 1, characterized in that the thermogram and the height profile are spatially correlated.

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

4. The workpiece (1) has a coating layer (5) applied to the surface (1') of the substrate, and is exposed to a corrosive environment for a predetermined time such that non-uniform portions (6, 7) are formed in the layer structure. The method according to any one of the preceding claims, wherein the first section (3) and the second section (4) are located in the region of the non-uniform portion (6, 7), and in particular the non-uniform portion is peeling of the coating layer (5) and the substrate or further damage to the coating layer (5).

5. A method characterized in that an image including color values ​​is generated from at least the region of the surface (2), and the image is spatially correlated with the height profile.

6. An apparatus for performing the method described in any of the preceding claims, A thermography apparatus (8, 13) having an energy emitter (8) and a sensor (13) for generating a thermogram; a light source (10, 21, 23) for illuminating at least one region of the surface (2) of the workpiece (1); a sensor assembly (12, 22, 14) for recording an image of the illuminated region of the surface (2); and a device (17) for measuring the relative movement of the workpiece (1) with respect to the sensor assembly (12, 22, 14), wherein The apparatus is characterized in that the light source (10, 21, 23) is constructed and arranged in such a manner that the image provides a height profile of the region on the surface.

7. The apparatus according to claim 6, characterized in that it has an image recognition device that automatically performs spatial correlation between the thermogram recorded by the thermography device (8, 13) and the image recorded by the sensor assembly (12, 22, 14).

8. The light source has one or more lasers (10) and the sensor assembly has one or more sensors (12) that are sensitive to light from the lasers reflected off the surface, or The light source (22) provides a two-dimensional image that changes over time, and the sensor assembly is a camera (22) that captures the image reflected from the surface, or The apparatus according to claim 6 or 7, characterized in that the light source (23) irradiates the surface (2) at a flat angle, and the sensor assembly (14) is a camera that captures a visual image.

9. The sensor assembly has a camera (14) used to generate an image including color values ​​in at least the illuminated area of ​​the surface (2), and The apparatus according to any one of 6 to 8, characterized in that the image recognition device is configured to spatially correlate a height profile with respect to the image, which includes color values.

10. A method or apparatus that has one or more of the characteristics described in any one of the above claims as characteristics.

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