Process and apparatus for the acquisition and processing of screen images

• US 5,351,307 A
• Filed: 10/28/1992
• Issued: 09/27/1994
• Est. Priority Date: 11/15/1991
• Status: Expired due to Fees

• Current Assignee: Snecma Moteurs
• Original Assignee: Societe Nationale dEtude et de Construction de Moteurs dAviation SNECMA (Safran SA)
• Inventors: Prejean-Lefevre, Veronique H. M. P.
• Primary Examiner(s): Mancuso, Joseph
• Assistant Examiner(s): Fox, David
• Application Number:
  US07/967,437
• Time in Patent Office: 699 Days
• Field of Search: 382/8, 382/41, 382/49, 382/48, 382/1, 382/62, 358/106, 356/237, 378/58, 348/129, 348/130
• US Class Current: 382/151
• CPC Class Codes: G06T 2207/10012 Stereo images
• CPC Class Codes: G06T 2207/10116 X-ray image
• CPC Class Codes: G06T 2207/30164 Workpiece; Machine component
• CPC Class Codes: G06T 7/001 using an image reference approach

Abstract

The present invention relates to a process for the acquisition and processing of screen images or radiographs and to an apparatus making it possible to inspect or control mechanical parts. The process consists of obtaining at least two screen images of the part to be inspected, converting said images into digital video images coded on several grey levels, correcting each image with respect to itself and then with respect to a reference image and finally binarizing the corrected images in order to superimpose them, so as to determine the image points which correspond and thus detect defects. Application to the control and inspection of mechanical parts.

Claims

1. Process for the detection of faults and defects in material used in the formation of a mechanical part comprising the following stages:

a. X-ray irradiating the part at least twice under identical conditions and in accordance with the same view of the part;

b. obtaining at least two X-ray screen images for each view of the part to be inspected;

c. conversion of these screen images into digital video images coded on several grey levels;

d. processing each image, said processing involving the following substages i. to iv. including;

i. correction by digital filtering of each image compared with itself;

ii. correction of the filtered images by comparison with a reference image;

iii. binarization of the images by the comparison of each image with a threshold in order to only retain the image points which are equal to or higher than said threshold and which are liable to correspond to a fault in the part; and

iv. superimposing the images in order to determine the image points which correspond to faults thus detecting the faults in the part.

2. Acquisition and processing process according to claim 1, characterized in that the correction substage of each image by digital filtering consists of carrying out a linear frequency or non-linear morphological filtering of the arrays of pixels of each image in order to eliminate the local minima and maxima of the different elementary subsets of pixels constituting the arrays and a second frequency or morphological filtering of each image compared with itself making it possible to obtain a filtered image.

3. Acquisition and processing process according to claim 1, characterized in that the correction of each filtered image by comparison with a reference image consists of obtaining a reference image from a part of the same type, but having no defect, making said reference image undergo the same steps a.-d.i. as the image of the part to be inspected and comparing each image with said reference image by carrying out a subtraction or division of the corresponding arrays of pixels.

4. Process according to claim 1, characterized in that the correction of each reference image consists of obtaining two reference images from a part not having a fault and comparing one image with a reference image and the other image with the other reference image by subtraction or division of the corresponding arrays of pixels.

5. Acquisition and processing process according to claim 3, wherein the reference image that undergoes steps a.-d.i. further comprises the steps of:

processing the reference image corresponding to steps d.ii-d.v. wherein the reference image is corrected in step d.ii with a different reference image acquired and processed corresponding to steps a.-d.i.

10. Process according to claim 2 characterized in that the correction of each reference image consists of obtaining two reference images from a part not having a fault and comparing one image with a reference image and the other image with the other reference image by subtraction of division of the corresponding arrays of pixels.

11. Process according to any one of claims 1, 2, 3, 4, 5 or 10, characterized in that the superimposing of the images is performed by using a logic AND function.

6. Apparatus for the detection of faults and defects in materials used in the formation of a mechanical part, comprising:

a X-ray tube, which makes it possible to pass X-rays through the part to be inspected;

a real time detector equipped with a brightness amplifier;

a focussing optics;

a mirror for reflecting each photon image from the focussing optics;

cameras for receiving the images reflected by the mirror;

means for obtaining at least two images of a part to be inspected for each view of the part;

means for processing the images incorporating;

first correction means performing a filtering of each image compared with itself;

second correction means performing a filtering compared with a filtered reference image;

means for thresholding each image;

means ensuring a logic AND function between the images after thresholding.

7. Apparatus according to claim 6, characterized in that the means for obtaining at least two images incorporate an X-ray source, a real time detector equipped with a brightness amplifier, a focussing optics, a mirror for reflecting each photon image from the focussing optics and cameras for receiving the images reflected by the mirror.

8. Apparatus according to claim 6, characterized in that the first image correction means comprise a first non-linear digital filter of the median or frequency filter type and a second digital filter of the morphological or frequency type.

9. Apparatus according to claim 7, characterized in that the first image correction means comprise a first non-linear digital filter of the median or frequency filter type and a second digital filter of the morphological or frequency type.

12. Apparatus according to any one of claims 6, 7, 8 or 9, characterized in that the means for obtaining the reference image are produced for the same apparatus from a part not having said fault, the processing means incorporating means for storing said image.