Optics: measuring and testing – Inspection of flaws or impurities – Having predetermined light transmission regions
Patent
1998-01-30
1999-11-23
Kim, Robert H.
Optics: measuring and testing
Inspection of flaws or impurities
Having predetermined light transmission regions
356445, 356222, 356229, G01N 2100
Patent
active
059910178
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to apparatus and a method for inspecting the surface of an object.
2. Discussion of the Prior Art
Product surface inspection procedures are widely used in various industries. One such industry where careful surface inspection is essential is nuclear fuel production. Typically, nuclear fuel pellets are produced to high quality standards and after inspection following manufacture are loaded into tubes known as fuel rods or pins which are assembled together and in due course and loaded for use in a nuclear reactor. It is a customer requirement that inspection of all fuel pellets is carried out before loading into pins. This reduces the possibility of defective pellets causing pin damage when the pin is subject to high temperature and pressure in use.
At present, it is conventional for trained inspectors to perform nuclear fuel pellet inspections with the pellets held on trays. This manual inspection procedure has a number of disadvantages, viz: judgement of the individual inspector, and is open to operator error; comprise MOX (mixed oxide) fuel pellets, eg comprising mixtures of uranium and plutonium oxides, this may be unacceptable from a safety point of view; inspections is substantial.
Optical techniques for automatically inspecting objects such as nuclear fuel pellets are known in the prior art. For example, Applicants' prior EP 0 583 092 A1 describes such a technique using reflection of a laser beam spot by the inspected object.
One major problem which the known techniques using reflection of light are not capable of solving is that different surface flaw and defect types can reflect light in similar ways and this means that information about the defect or flaw provided by the reflected light may be limited. In some cases it may be difficult for the detection system to differentiate between different defect and flaw types or normal variation in surface appearance and flaws.
SUMMARY OF THE INVENTION
According to the present invention there is provided an arrangement for inspecting the surface of a rotating object which includes object retaining means for retaining whilst rotating the object, means for irradiating the surface of an object when retained and rotated by the object retaining means with a first beam of optical radiation, means for irradiating the surface of an object when retained and rotated by the object retaining means with a second beam of optical radiation detectable as distinct from the first beam, detector means for detecting radiation reflected by the surface of the object from the first beam and for detecting radiation reflected by the surface of the object from the second beam and a signal processor for receiving signals produced by the detector means and for analysing such signals wherein the first beam and the second beam are of different wavelengths or in different wavelength bands and the detector means is capable of simultaneously receiving and detecting radiation received from the same irradiated area of the surface of the object from both the first beam and the second beam and producing a first output signal comprising components representing variations in reflection of the first beam from units of area within the said irradiated area of the object and a second output signal comprising components representing variations in reflection of the second beam from units of area within the said irradiated area of the object and wherein the signal processor is adapted to correlate components of the first output signal with the components of the second output signal whereby information about the reflectivity of units of area of the surface of the object is enhanced.
The arrangement according to the present invention may optionally include one or more further means for irradiating the said surface each with a beam of optical radiation of a different wavelength or in a different wavelength band detectable as distinct from the other beams, the detector means being capable of simultaneously detecting radi
REFERENCES:
patent: 4806776 (1989-02-01), Kley
patent: 4872758 (1989-10-01), Miyazaki et al.
British Nuclear Fuels PLC
Kim Robert H.
Ratliff Reginald A.
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