Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/8806—Specially adapted optical and illumination features
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
  • G01B11/25—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures by projecting a pattern, e.g. one or more lines, moiré fringes on the object
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/8806—Specially adapted optical and illumination features
  • G01N2021/8829—Shadow projection or structured background, e.g. for deflectometry

Definitions

• the present invention relates to a device for detecting surface defects, specifically on painted surfaces, according to the preamble of the main claim.
• the painted surfaces specifically the painted surfaces of metal components in the automotive field, have very high quality standards: a small painting defect has to be detected before the part is assembled and leaves the factory .
• the defects of painted surfaces, or however of surfaces being subjected to surface treatment comprise clots of paint or resin, dust or impurities that blended with the paint or resin.
• defects are three-dimensional, i.e. they are not simply local color variations, but ridges or however irregularities on the surface.
• defects also comprise defects such as bumps or lines being on the surface even before the painting operation or also a missed surface cleaning which can result in a paint ripple.
• a light source projecting a plurality of light and dark parallel lines on the surface to be inspected is used.
• a localized defect reflects the light in a different way and can thus be visualized as a sudden irregularity of the lines reflected by the test surface.
• the deflectometry requires glossy and highly reflective surfaces, since the surface roughness increases the light diffusion in all the directions and decreases the specular reflection.
• a video camera can capture the images reflected by the surface to be inspected and mathematical algorithms can allow an automated analysis thereof.
• the currently used techniques are based on the specular reflection of light by the surface to be inspected.
• deflectometry requires an accurate positioning of the video camera with respect to the light source and the surface to be inspected.
• Another issue is that the detection of the defects depends on the color of the paint and the condition thereof .
• a defect such as for example an orange peel effect painted surface, can hardly be detected by current techniques.
• Object of the present invention is therefore to realize a device and a process which allow overcoming the mentioned drawbacks .
• an object is to realize a device and a process for detecting defects on the surface of elements to be inspected, in particular on painted surfaces, which increases the reliability of the technique and the likelihood of detecting the defect.
• Another object is to realize a device and a process for detecting defects on painted elements, which works on all colors .
• Another object is to obtain a device simpler than the current ones, with larger freedom of positioning the components.
• Fig. 1A shows a perspective view of the device according to the invention with the projection of a plurality of high-intensity electromagnetic radiation lines, alternating with low-intensity electromagnetic radiation lines, on the surface to be inspected;
• Fig. IB shows the distribution of the electromagnetic radiation intensity on a line LI intersecting such high- intensity electromagnetic radiation lines and low- intensity electromagnetic radiation lines in the center part of the beam projected by the source on the surface to be inspected.
• Fig. 2 shows a perspective view of an embodiment of the device according to the invention with an electromagnetic radiation source to which two video cameras are connected;
• Fig. 3 shows a sectional view of the same source as Fig. 2;
• Fig. 4 shows a part of the electromagnetic spectrum with a first emission spectral band of the electromagnetic radiation source, a second spectral band wherein the video camera is sensitive and the spectral working band obtained by the intersection of the first and second spectral bands, said spectral working band coinciding in this case with the second spectral band.
• the human eye visible electromagnetic radiation ranges from about 400 nm (purple) to 750 nm (red) .
• the not-visible radiation beyond the red is named as infrared radiation.
• the infrared radiation is categorized in non-thermal infrared (from 750 nm to about 2000 nm) and thermal infrared (beyond 2000 nm) .
• a body being at room temperature (about 300 K) emits infrared radiation in the thermal infrared band, but not in the non-thermal infrared band, and thus under 2000 nm.
• Normal video cameras with CCD or CMOS sensor are sensitive in the 300 nm - 1100 nm band and can thus see in the non-thermal infrared region to which the human eye is not sensitive.
• This property is used to see in the dark, by using an infrared illuminator, for example a suitable led.
• an infrared source emits infrared radiation which is reflected by an object and then captured by the sensor of a video camera, such as in the visible.
• the room temperature bodies emit electromagnetic radiation and such emitted radiation is added to the possibly reflected radiation.
• the radiation emitted by a source and addressed to a surface to be inspected, is partly specularly reflected by the surface and partly and diffusely reflected in all the directions.
• the share of radiation diffusely reflected in all the directions increases as the surface roughness of the surface to be inspected increases.
• the deflectometric techniques are based on the radiation specularly reflected by the surface to be inspected, the radiation diffusely reflected in all the directions can allow detecting surface and painting defects with a better signal-to-noise ratio and thus a better likelihood of correctly detecting the defect.
• the device according to the invention for detecting defects on surfaces to be inspected preferably painted surfaces, is shown, comprising
• a source 1 adapted to emit electromagnetic radiation in at least one first spectral band Bl (Fig. 4), in order to project a beam of electromagnetic radiation onto at least one surface to be inspected 6, preferably a painted surface ;
• a video camera 2 sensitive in at least one second spectral band B2 (Fig. 4) and arranged so that to obtain images of said at least one surface to be inspected 6 in the zone wherein the electromagnetic radiation beam emitted by the source 1 is projected,
• a diffuser 3 adapted to intercept at least part of the electromagnetic radiation emitted by the source 1 and to make more homogeneous the spatial distribution of the intensity of said electromagnetic radiation on said at least one surface to be inspected 6.
• the source 1 can be a normal incandescent lamp or a neon or led lamp or any other source, such as for example a laser, emitting in a spectral band Bl which overlaps at least partly to the spectral band B2 wherein the video camera is sensitive.
• the intersection between said first band Bl and said second band B2 establishes a spectral working band BL wherein the device is operative.
• One of the first and second bands Bl or B2 can be completely comprised in the other one, whereby the spectral working band BL corresponds to one of the two bands.
• the second band B2 wherein the video camera is sensitive is completely comprised in the first band Bl wherein the source emits, whereby the spectral working band BL is corresponding to the second band B2 of the video camera.
• Said spectral working band can also comprise several bands, for example one in the visible and one in the non- thermal infrared.
• the video camera can comprise a normal black and white video camera with CCD (charge coupled device) or CMOS (complementary metal-oxide semiconductor) sensor which is sensitive in a spectral band from 300 to 1100 nm, thus also comprising a part of non-thermal infrared, to which a filter is put before in order to select the desired spectral working band.
• CCD charge coupled device
• CMOS complementary metal-oxide semiconductor
• the spectral working band has a bandwidth lower than or equal to 200 nm and is between 300 nm and 1100 nm.
• the diffuser 3 can comprise an opaline or a milky semitransparent element interposed between the source 1 and the surface 6 to be inspected. While a normal lamp or light source lightens a surface with non-homogeneous intensity, the device according to the invention obtains better results when the intensity of the emitted electromagnetic radiation is homogeneously distributed over the surface to be inspected.
• the diffuser 3 helps to make more homogeneous the distribution of the intensity of the electromagnetic radiation emitted by the source 1.
• the spectral working band BL is adequately narrow and has therefore a bandwidth lower than or equal to 50 nm, even better if said spectral working band BL has a bandwidth lower than or equal to 20 nm.
• a spectral working band BL is arranged in the non-thermal infrared, for example if the spectral working band BL is between 750 nm and 1050 nm.
• spectral working band BL is between 810 nm and 860 nm.
• the currently existing devices often project onto the surface to be inspected a plurality of light and dark lines, which alternate a high light intensity and a low light intensity .
• the device according to the invention comprises an intensity alternator 4 adapted to intercept, after the diffuser 3, the electromagnetic radiation emitted by the source 1 and to generate, on said at least one surface to be inspected 6, a spatial arrangement 5 of the electromagnetic radiation comprising high-intensity electromagnetic radiation zones alternating with low- intensity electromagnetic radiation zones.
• such a spatial arrangement 5 of the intensity distribution of the electromagnetic radiation emitted by the source comprises a plurality of high-intensity electromagnetic radiation lines Zl alternating with low-intensity electromagnetic radiation lines Z2, said lines Zl and Z2 being substantially parallel.
• the alternation of high- intensity electromagnetic radiation lines Zl with low- intensity electromagnetic radiation lines Z2 creates a repetitive figure, wherein the pitch PI (Fig. IB) of such a repetition is preferably small, lower than or equal to 20 mm, better if lower than or equal to 4 mm.
• the size of such a pitch PI also depends on the minimum size of the defect desired to be detected.
• the duty-cycle varies between 5% and 95%, i.e. that the thickness of the high- intensity electromagnetic radiation lines Zl is different from that of the low-intensity electromagnetic radiation lines Z2, specifically that the thickness of the high- intensity electromagnetic radiation lines Zl is smaller than that of the low-intensity electromagnetic radiation lines .
• the electromagnetic radiation emitted from the source is adequately diffused such that the passage from a high-intensity electromagnetic radiation zone to an adjacent low-intensity electromagnetic radiation zone is substantially stepped and the intensity of the electromagnetic radiation in the high-intensity electromagnetic radiation zone is homogeneous.
• the distribution of the electromagnetic radiation intensity over a line LI intersecting such high-intensity electromagnetic radiation zones (Zl) and low-intensity electromagnetic radiation zones (Z2) is preferably a substantially square wave function, with steep rising edge and falling edge and substantially uniform values in the high-intensity electromagnetic radiation zone Zl and in the low-intensity electromagnetic radiation zone Z2.
• the ambient lightning can create a decrease in contrast and saturation and, if not arranged homogeneously, can determine a lower homogeneity of the radiation intensity.
• the video camera is preferred not to reach the saturation, when observing the high-intensity electromagnetic radiation zone Zl on a defect-free surface to be inspected .
• the spectral working band may comprise two or more different spectral bands and the image acquisition may occur simultaneously on said spectral bands or in temporal succession (first on a band and then on another band) .
• the images obtained on different bands are overlapped or processed together in accordance with convenient mathematical algorithms, in order to improve the signal- to-noise ratio and increase the likelihood of detecting possible defects being on the surface to be inspected.
• the relative position of the source and the video camera is not relevant.
• source 1 and video camera 2 are close together and mutually constrained.
• the video camera and the source are preferably arranged along a direction normal to the surface to be inspected. Such an arrangement is not usually adopted in the deflectometric techniques since, in order to obtain better sensitivity, it is preferred that the electromagnetic radiation emitted by the source impinge onto the surface to be inspected with an angle of at least 45° with respect to the normal, whereas the video camera is arranged in the specular direction with respect to the incidence direction of the electromagnetic radiation .
• the source 1 projects onto the surface to be inspected a beam of electromagnetic radiation having homogeneous high-intensity electromagnetic radiation zones alternating with low-intensity electromagnetic radiation zones, for example a strip spatial arrangement 5.
• the video camera 2 captures the surface to be inspected in the center portion of the beam projected by the source 1.
• the presence of a defect locally alters the homogeneity of the radiation intensity or locally deforms the spatial arrangement, thus allowing the defect to be detected.
• the defect can appear as low intensity spots in the high-intensity electromagnetic radiation zones and/or as high intensity spots in the low-intensity electromagnetic radiation zones, or as a distortion of the edges wherein the passage between a high-intensity electromagnetic radiation zone and a low-intensity electromagnetic radiation zone occurs.
• the surface to be inspected runs with respect to the device according to the invention such that the scan of the whole surface to be inspected can be obtained quickly .
• An electronic device for image analysis can easily and automatically detect the defects with high reliability.
• the present invention also wants to protect a process for detecting defects on surfaces to be inspected, preferably on painted surfaces, comprising the following steps:
• the intensity alternator 4 so to intercept, after the diffuser 3, the electromagnetic radiation emitted by the source 1 so that to create, on the surface to be inspected, high-intensity electromagnetic radiation zones alternating with low- intensity electromagnetic radiation zones;
• the process comprises the image acquisition on different spectral working bands and the processing of said images by means of mathematical algorithms adapted to increase the signal-to-noise ratio and the likelihood of detecting a defect that might be on the surface to be inspected.
• the electromagnetic radiation being distributed homogeneously at least in the high-intensity electromagnetic radiation zones, the detection of the painting or geometric and aesthetic defects is made easier with respect to other today existing devices and the signal-to-noise ratio is improved, with higher reliability of the device.
• the inspection can of course be expected to be done in the visible spectrum by a human operator, thus without a video camera.
• the surfaces that can be inspected are not only painted surfaces, but also surfaces having been subjected or not to a surface treatment, such as resin deposition or even a transparent coating.
• the device according to the invention does not use an intensity alternator in order to have high-intensity electromagnetic radiation zones alternating with low- intensity electromagnetic radiation zones, but simply a diffuser in order to have an homogeneous distribution of the intensity of the electromagnetic radiation emitted by the source over the surface to be inspected.
• An adequate homogeneity of the electromagnetic radiation distribution over the surface to be inspected is often enough .
• An advantageous characteristic of the invention is that, conversely to the devices based on the deflectometric technique, the device according to the invention allows wide freedom in the arrangement of the video camera and the source.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Computer Vision & Pattern Recognition (AREA)
• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Health & Medical Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)

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Citations (6)

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• 2017
  • 2017-07-10 IT IT102017000077459A patent/IT201700077459A1/it unknown
• 2018
  • 2018-07-09 WO PCT/IB2018/055041 patent/WO2019012404A1/en not_active Ceased
  • 2018-07-09 US US16/629,530 patent/US11105614B2/en active Active
  • 2018-07-09 MA MA049568A patent/MA49568A/fr unknown
  • 2018-07-09 EP EP18749871.2A patent/EP3652524B1/en active Active
  • 2018-07-09 ES ES18749871T patent/ES2977710T3/es active Active
  • 2018-07-09 JP JP2020523065A patent/JP2020527728A/ja active Pending
• 2021
  • 2021-07-20 US US17/380,285 patent/US11629953B2/en active Active
• 2023
  • 2023-05-23 JP JP2023084317A patent/JP2023106529A/ja active Pending

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