METHOD AND INSTALLATION FOR INSPECTING AN ARTICLE FOR DEFECTS

摘要

Method for inspecting an article for defects, light scattered by the article is collected. A defect in the article gives rise to a pulse scanning response signal, which is fed to a processing unit. The light beam has a wavelength such that the article is transparent thereto. At least two scanning response signals are obtained, which are associated with focal points at different focal depths in the article. The location of the defect in the direction of the light beam is determined from the steepness of the front and rear flanks of the pulse scanning response signals. By this means it is possible to determine whether a defect is on or in the article. The at least two scanning response signals can be obtained by scanning the article at least twice, with different focal depth for each scan.