Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
1999-06-29
2001-05-15
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C250S559400
Reexamination Certificate
active
06232617
ABSTRACT:
FIELD OF THE INVENTION
The invcention relates to the production of metal strip, especially steel strip. More specifically, it relates to the techniques of checking the surface quality of such strip.
PRIOR ART
Plants for producing metal strip, especially steel strip, from initially thicker products comprise tools such as rolling mills, annealing furnaces and pickling plants. Before and/or after the product passes through these tools, it is common practice to inspect its surface using automatic apparatuses for the purpose of detecting thereon the possible presence of metallurgical defects such as depressions, scratches, blisters, remnants of scale, etc. The presence of such defects may indicate some malfunction of the equipment located upstream of the inspection, which have to be remedied, and may make it pointless to continue to process the product if the defects are serious enough to prevent final products of the desired quality being obtained.
Apparatuses for inspecting the surface of metal strip which are conventionally used essentially comprise:
means for illuminating the area of the strip to be inspected;
a linear or matrix camera which periodically captures an image of said area, at time intervals close enough together for complete inspection of the strip to be possible;
a unit for processing this image, which extracts therefrom the “objects” which stand out by their color or their reflecting power from the uniform background which forms the surface of the strip and which makes it possible to recognize, from among these objects, those which actually constitute metallurgical defects and those which correspond to other phenomena which have no effect on the quality of the strip; this recognition takes place using software which compares the characteristics of the objects detected with those normally observed in the case of defects that the unit must indicate to the operator.
Among the objects detected by the image processing unit and that have to be recognized as not being metallurgical defects (and therefore not to be indicated as such to the operator), mention may be made of slightly whitish stains which remain on the surface of the strip after it has been pickled, or oil residues. Experience shows that a very high proportion (sometimes more than 90%) of the objects detected fall within this category. It follows that most of the computing time of the image processing unit is devoted to analyzing objects of no interest to the operator.
SUMMARY OF THE INVENTION
The object of the invention is to propose an apparatus for detecting surface defects on metal strip which allows this detection operation to be carried out more effectively than the apparatuses of the prior art.
For this purpose, the subject of the invention is an apparatus for detecting surface defects on a running metal strip, which comprises means for illuminating the area of the strip to be inspected, at least one pair of cameras each periodically capturing an image of the same portion of said area, a computing unit comprising means for reconstructing a stereoscopic image of said portion from the images provided by the pair of cameras, means for detecting, on said stereoscopic image, those objects which exhibit a relief—as a projection or as an indentation—with respect to the surface of the strip greater than a predetermined threshold, means for analyzing the images of said objects and means for displaying the result of this analysis to the operator.
As will have been understood, the invention consists in inspecting a given area of the strip by discriminating, from among the objects which are distinguished by the unit, those which exhibit a relief (as a projection or as an indentation) with respect to that surface portion of the strip which surrounds them and those which do not exhibit such a relief. It is established as a principle that the objects which do not exhibit relief (or in general a relief less than a predetermined threshold) are merely oily residues or stains and do not correspond to metallurgical defects. It is therefore pointless to continue to process their image. As regards objects exhibiting a relief, these are regarded as metallurgical defects and processed by the unit in the usual way, so as to determine their precise nature and their degree of seriousness, and to indicate them to the operator. This inspection is carried out no longer using a single camera, but two cameras aimed at the same area of the strip, according to the principle of stereoscopic vision.
The advantages of the apparatus according to the invention over apparatuses of the prior art can be exploited in two ways. It is possible to choose to keep the unit operating with its usual performance with regard to the detection of metallurgical defects, but this performance will be able to be achieved using less powerful (and therefore less expensive) computing means than previously since it will no longer be necessary to process the images of objects without relief, which are manifestly not metallurgical defects. It is also possible to choose to keep the computing means operating with their usual performance and to devote the computing power made available by the elimination from the processing of objects without relief to a finer detection, identification and display of the defects and/or to more rapid processing of their images. This rapid processing makes it possible to inspect a strip running at a higher speed than in the prior art and therefore makes it possible to accompany an increase in the productivity of the plant for manufacturing the strip.
REFERENCES:
patent: 5568313 (1996-10-01), Steenblik et al.
patent: 0 731 350 A1 (1996-09-01), None
patent: 58-204356 (1983-11-01), None
patent: 60-179639 (1985-09-01), None
patent: WO 98/01746 (1998-01-01), None
Cole Thomas W.
Le Que T.
Nixon & Peabody LLP
Sollac
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