Image analysis – Applications – Surface texture or roughness measuring
Reexamination Certificate
1999-02-18
2001-12-04
Johns, Andrew W. (Department: 2621)
Image analysis
Applications
Surface texture or roughness measuring
Reexamination Certificate
active
06327374
ABSTRACT:
FIELD OF INVENTION
The invention relates to inspection of strip-like or sheet-like surfaces, such as surfaces of rolled metal products, by an optoelectronic measuring arrangement.
BACKGROUND OF INVENTION
DE 19 511 534 A1 teaches a prior art method and arrangement in which the 3D characteristics of a moving surface are inspected by illuminating the surface from at least two different illumination directions with light sources, the light sources of each illumination direction illuminating the surface with a light of a different color than the other illumination directions. The object's surface is illuminated simultaneously from the different illumination directions, and the so illuminated surface is imaged with a camera to provide image information for analysis. The analysis of the 3D characteristics of the object's surface is based on color classification, with which the color values detected on the surface are compared.
The prior art method and arrangement allow the inspection of the 3D characteristics of the object's surface but not of the glossiness and reflectivity of the surface, since symmetrical dark field illumination from two illumination directions is used in the method. The fact that the 3D analysis is based on color classification impairs the method: for example, the method is not able to adjust to a change in the surface material of the object's surface, in which the surface material changes either completely or changes to a different variety of the same surface material or both, and neither is it able to adjust to changes in the illumination. This causes false alarms, which poses a major problem particularly in production processes.
On account of the above, the prior art method thus has a very limited ability to differentiate between different anomalies on the object's surface.
BRIEF DESCRIPTION OF INVENTION
The object of the invention is to provide a method and an arrangement implementing the method, simultaneously solving the above problems. The object is achieved with a method of the invention for automatic inspection of the surface of a moving object, the method comprising the steps of illuminating a region on the object's surface with light sources from different illumination directions, and imaging the object's illuminated surface region with a camera to provide image information for analysis. The light sources in the different illumination directions are pulsed to illuminate the object's surface region at different times, the pulsing frequency being >1 kHz. Further, the object's illuminated surface region is imaged as lines with a line scan camera in sync with the above pulsing. If colors are not considered relevant, the line scan camera used can be a monochrome camera. If colors are also to be measured, the line scan camera used is a color camera.
The invention also relates to an arrangement for inspecting the surface of a moving object, the arrangement comprising at least two light sources in at least two different illumination directions, i.e. at least one light source in each illumination direction used, for illuminating a surface region of the object under inspection; a camera for imaging the object's surface region; and an image analyzer for analyzing the image information acquired from the object's surface by imaging. As regards the light sources, the arrangement comprises light sources that illuminate the object's surface at different times from different illumination directions. To take images from the surface, the arrangement comprises at least one line scan camera. The arrangement also comprises a timing controller for synchronous pulsing of the light sources and the at least one line scan camera, the pulsing frequency being >1 kHz.
The preferred embodiments of the invention are claimed in the dependent claims.
The invention is based on the idea that the light sources in the different illumination directions are pulsed to illuminate the object's surface region at different times, the pulsing frequency being >1 kHz, and that the object's illuminated surface region is imaged as lines with a line scan camera in sync with the pulsing.
Various advantages are achieved with the method and arrangement of the invention. The invention allows image analysis, in which the objects surface region, imaged while illuminated at different times with light beams from different illumination directions, is inspected. This enhances the analysis of the 3D characteristics of the surface considerably, since the object's surface region imaged while illuminated at different times with light beams from different illumination directions reveals more of its 3D characteristics than when it is illuminated simultaneously from different illumination directions. In addition to enhancing the analysis of the 3D characteristics, the non-simultaneous illumination also enhances inspection of the glossiness and reflectivity of the surface. The invention also allows the inspection of the surface of a fast moving object since the inversion comprises fast synchronous pulsing of the light sources and the line scan camera.
The preferred embodiments of the invention and other implementations described in detail emphasize the advantages of the basic invention and also bring about other advantages. The surface inspection shows the colors correctly, which renders the 3D analysis, glossiness analysis and reflectivity analysis of the surface more accurate. When the accuracy is improved, for example, false alarms are avoided, which greatly speeds up the production process. Further, a preferred embodiment of the invention introducesan improved way of inspecting a moving surface from a distance, for example a hot moving surface. The surface inspection from a distance here means that the surface is inspected from a distance of at least one meter, perhaps even of three meters.
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Kontio Pertti
Paul Detlef
Piironen Timo H.
Johns Andrew W.
Nakhjavan Shervin
Sughrue Mion Zinn Macpeak & Seas, PLLC
Thermo Radiometrie Oy
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