Process and device for detecting and evaluating surface cracks in workpieces
First Claim
1. A device for detecting and evaluating surface cracks in workpieces, comprising:
- workpiece handling means for holding a workpiece;
a color television camera provided so as to view the workpiece held in the handling means, the camera having an optical filter adapted to light emanating from a crack representation agent, the camera producing a picture output including the colors red, green and blue;
a color-mixing unit connected to the camera output for mixing the colors and producing a corresponding output;
an analog-digital signal converter provided as to convert the output of the color-mixing unit;
a digital picture processing unit having a picture store, the processing unit being provided so as to receive the converted output; and
a computer unit arranged so as to prepare and evaluate digital picture levels and having a control output connected to the workpiece handling device.
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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.
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Citations
9 Claims
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1. A device for detecting and evaluating surface cracks in workpieces, comprising:
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workpiece handling means for holding a workpiece; a color television camera provided so as to view the workpiece held in the handling means, the camera having an optical filter adapted to light emanating from a crack representation agent, the camera producing a picture output including the colors red, green and blue; a color-mixing unit connected to the camera output for mixing the colors and producing a corresponding output; an analog-digital signal converter provided as to convert the output of the color-mixing unit; a digital picture processing unit having a picture store, the processing unit being provided so as to receive the converted output; and a computer unit arranged so as to prepare and evaluate digital picture levels and having a control output connected to the workpiece handling device. - View Dependent Claims (3, 9)
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2. A process for detecting and evaluating surface cracks in work pieces, comprising the steps of taking a picture of the surface of a workpiece with a color video camera;
- masking out the background picture with a filter adapted to light emanating from a crack representation agent;
performing analog signal processing by means of a color mixing unit by mixing the colors red, green and blue in such proportions that the picture to be evaluated is a background and/or spurious signal and other signals are filtered and/or intensified;
digitized the picture;
processing the picture with a computer to produce a binary picture of any cracks present;
deriving a blurred background picture from the picture shades converted to digitized grey shade levels;
subtracting the blurred background picture from the original picture to provide a different picture which gives the crack representation; and
triggering a sorting report when a preselected threshold level is exceeded. - View Dependent Claims (4, 5, 6, 7, 8)
- masking out the background picture with a filter adapted to light emanating from a crack representation agent;
Specification