PROCESS AND EQUIPMENT TO DETECT AND EVALUATE SURFACE CRACKS OF MACHINED PARTS

摘要

A procedure and facility for the detection and evaluation of surface cracks in workpieces (1) in which use is made of an image pick-up camera (3) to take a picture of the workpiece surface pretreated with the aid of the magnetic powder or dye penetration method and/or contrast intensification means, digitise it and process it with a computer (8) in such a way that a binary image is produced of any cracks and a segregation finding is initiated if a predetermined threshold value is exceeded. In order to obtain a segregation signal independent of the absolute brightness of the original image, a blurred background image is derived from the original image values resolved into digitised grey value steps and is subtracted from the original image, in which process the difference image thus formed yields a display of the crack. A dynamic threshold value for the segregation finding is determined by comparing the grey value distribution of the original or the difference image with at least one previously evaluated image or difference image and producing a binary image from the original image or the difference image and the grey value threshold and indicating image points whose grey values lie above the threshold set as defects.