Process and device for detecting and evaluating surface cracks in workpieces

Abstract

A process and device for detecting and evaluating surface cracks in workpieces wherein a picture is produced of the surface of the workpiece by means of a video camera and said picture is digitized and is processed by means of a computer to produce a binary picture of any cracks present and a sorting report is triggered when a preselected threshold level is exceeded. In order to obtain a sorting signal that is independent of the absolute brightness of the original picture a blurred background picture is derived from the original picture levels that have been converted to digitized grey shade levels and subtracted from the original picture, the difference picture formed in this way giving the crack representation. A dynamic threshold level for the sorting signal is determined by comparing the grey shade distribution of the original or the difference picture with at least one previously evaluated or difference picture and a binary picture is produced from the original or the difference picture and the grey shade threshold, and picture elements with their gray shades exceeding the set threshold are indicated as defects. The surface of the workpiece may be pre-treated by the magnetic powder or dye penetration process and/or contrast intensifying means.

Dependencies are inferred from the claim text.