Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1990-10-23
1992-10-20
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250563, 356431, G01N 2188
Patent
active
051572664
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method and a device for inspecting transparent sheets or webs for the presence of defects, particularly enclosed core seeds, where the web to be tested is scanned by a flying light spot. The light passing through the web is directed onto a diffuser plate which has transparent and opaque regions and behind which a receiver is disposed. The photoelectric transducer disposed in the receiver feeds pulses which correspond to the intensity of the light impinging on the diffuser plate to a computer.
Transparent webs in accordance with the present invention are continuously manufactured webs made of a transparent plastic material or glass. Since the formation of core seeds is a problem that occurs particularly with float glass lines, the invention is explained with reference to the inspection of float glass webs. It is, however, not limited thereto.
Inspection devices for glass webs are known from DE-OS 31 29 808 and DE-OS 32 23 215. It is common to both publications that the material web to be tested is scanned with a flying light spot and that light which is deflected into the glass by a core seed is detected at the edge of the material and evaluated. If the core seed is located in the center of the material to be tested, the distance to be covered by the light across the glass is very long, and the absorption is consequently very high. Particularly during the inspection of slightly colored glass, this absorption can be so high that no evaluable light signals can be received at the edge of the web. Another disadvantage of this known device is that the receiver at the edge of the material web must be relatively well insulated against incident foreign light in order to detect and evaluate, via the photoelectric transducer, the minor intensities of the light deflected at the core seeds. Moreover, deformation occurring at the margin and deflecting the light must be taken into account which requires additional devices to collect the light.
It is another disadvantage that the width must be continuously monitored in order to avoid damages of the laterally disposed receivers.
It is an object of the present invention to improve these known devices such that even more intensely colored glass or glass webs of a large width can be properly inspected for core seeds.
In accordance with the invention, this object is achieved with a method for inspecting transparent webs for the presence of defects, particularly enclosed core seeds. The transparent web to be tested is scanned with a flying light spot and the light passing through the web is directed onto a receiver system which has transparent and opaque areas and behind which a receiver is disposed. The photoelectric transducer disposed inside the receiver feeds pulses to a computer which correspond to the light intensities incident to the receiver system. The accomplishment is characterized in that the light spot is directed such that when the material web is free of defects, it covers the opaque and the transparent area of the receiver system in a continuous alternation, the change of area and the deviations of the light intensities caused by defects are supplied to the computer as pulses. These pulses are then evaluated while separated according to the areas of the receiver system.
The problems that occur during the inspection of glass webs are such that a great number of different defects can occur, however, in addition to these error signals, it is also possible that like signals occur which may be due to a contamination of the surface of the glass web and hence also lead to error messages, so-called false defects. Different inspection methods were developed corresponding to the different ways of inspecting. A distinction is made between measurements in reflection and transmission. They can further be divided in the so-called mirror reflection, hence inspection in the bright field, hereinafter referred to as R/S measurement. Further, the so-called diffuse reflection, hence the inspection in the dark field, referred t
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Lee John R.
Nelms David C.
Stora Feldmuehle Aktiengesellschaft
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