METHOD FOR THE NON-DESTRUCTIVE INSPECTION OF A MECHANICAL PART

• US 20110298901A1
• Filed: 12/21/2009
• Published: 12/08/2011
• Est. Priority Date: 12/24/2008
• Status: Active Grant

• Current Assignee: Safran Aircraft Engine Company
• Original Assignee: Snecma (Safran SA)
• Inventors: Derrien, Gerard, Leonetti, Claude
• Granted Patent: US 8,866,891 B2
• Time in Patent Office: Days
• US Class Current: 348/50
• CPC Class Codes: B25J 9/1697 Vision controlled systems
• CPC Class Codes: G01N 2021/8854 Grading and classifying of flaws
• CPC Class Codes: G01N 2021/8867 using sequentially two or more inspection runs, e.g. coarse and fine, or detecting then analysing
• CPC Class Codes: G01N 2021/9518 using a surface follower, e.g. robot
• CPC Class Codes: G01N 21/91 using penetration of dyes, e.g. fluorescent ink
• CPC Class Codes: G01N 21/9515 Objects of complex shape, e.g. examined with use of a surface follower device measuring contours and curvatures G01B11/24
• CPC Class Codes: G05B 19/401 characterised by control arrangements for measuring, e.g. calibration and initialisation, measuring workpiece for machining purposes G05B19/19 takes precedence
• CPC Class Codes: G05B 2219/35075 Display picture of scanned object together with picture of cad object, combine
• CPC Class Codes: G05B 2219/37205 Compare measured, vision data with computer model, cad data
• CPC Class Codes: G05B 2219/37206 Inspection of surface
• CPC Class Codes: G05B 2219/37563 Ccd, tv camera
• CPC Class Codes: G05B 2219/45066 Inspection robot
• CPC Class Codes: G06T 2207/30164 Workpiece; Machine component
• CPC Class Codes: G06T 7/001 using an image reference approach

Abstract

An automatic method of non-destructive inspection of a mechanical part by comparing images of the surface of the part with reference images recorded in a database, by a digital image acquisition device including an image sensor, a lighting source, and a mechanism for moving the image sensor and the lighting source relative to the mechanical part.

Claims

1-10. -10. (canceled)

11. An automatic method of non-destructively inspecting a mechanical part by a device including an image sensor, a lighting source, and means for moving the image sensor, the lighting source, and the mechanical part relative to one another, the method comprising:

making a three-dimensional survey of a surface of the part;

defining a subdivision of the surface of the part into zones suitable for being photographed by the image sensor;

defining respective paths for the image sensor and for the lighting source relative to the part;

acquiring images of the zones of the surface of the part;

analyzing the images and determining zones in the images that are over-exposed or under-exposed;

optimizing optical parameters for image acquisition of the zones and defining a second subdivision of the surface of the part, taking account of optimization of the optical parameters for the zones;

defining a new path for the image sensor and a new path for the lighting source that enable images to be acquired of the surface of the part while using the optimized optical parameters and the second subdivision;

acquiring images of the zones while following the new paths and recording the images; and

automatically determining any surface defects of the part in the recorded images and comparing them with known defects recorded in a database.

12. A method according to claim 11, further comprising previously building up a database in which reference images are recorded of mechanical part surfaces that present typical defects, each image being recorded together with data about surface characteristics, or a nature of the material and its roughness, with information relating to lighting and picture-taking conditions, and with an indicator of the quality with which a defect is detected in the surface of the part,

the method subsequently recording in the database modifications to the optical parameters and the acquisition paths and the results of inspections performed on the various parts.

13. A method according to claim 11, wherein the three-dimensional survey of the surface of the part is performed once only for any given type of mechanical part, providing the differences in shape and appearance between the parts being inspected are small or substantially zero.

14. A method according to claim 11, wherein the part for inspection is subjected to a three-dimensional survey of its surface whenever it presents non-negligible differences of shape and appearance compared with other inspected parts.

15. A method according to claim 11, further comprising, after taking a three-dimensional survey of the surface of the part, generating a digital model of the surface in a form of mathematical curves or Bezier curves and NURBS functions, and repositioning the image sensor and the lighting source relative to the parts by using the three-dimensional survey.

16. A method according to claim 11, wherein the optical parameters for acquiring images are optimized by varying an intensity and angle of incidence of the lighting produced by the lighting source, and

further comprising determining the optimum value for the intensity and the angle of incidence of the lighting by comparing images with one another with reference to the database while establishing a relationship between the level of surface defect detection and both the surface characteristics and the intensity and the angle of incidence of the lighting.

17. A method according to claim 11, wherein the optimizing further includes verifying that the surface area of each zone resulting from the secondary subdivision is smaller than a field covered by the image sensor, and standard deviation of the normals at all points of the zones is less than a predetermined minimum value.

18. A method according to claim 11, further comprising moving the image sensor and the lighting source relative to the mechanical part by robot arms respectively carrying the image sensor and the lighting source.

19. A method according to claim 11, wherein the image sensor is a camera having a matrix of photodetectors of the CCD or CMOS type.

20. A method according to claim 11, further comprising:

making a three-dimensional survey of the surface of the part, on the basis of which the real position of the part is calculated relative to the lighting device and the picture-taking device;

calculating a path for the device for optically acquiring two-dimensional images of the surface of the part;

acquiring overall images of the part by using parameters from the database relating to the material, the roughness, and the surface shape of the part;

analyzing the images and determining zones in the images that serve to optimize optical settings associated with the exposure as a function of parameters that appear in the database about the orientation of the picture-taking sensor, the lighting, and the surface shape;

calculating a path for acquiring images, which path serves to optimize the optical settings, while taking account of the above analysis and of a path for the lighting device;

optimizing optical settings for acquiring images of the above-defined zones;

analyzing images, validating optimized settings for the various zones and storing them in the database;

subdividing the surface of the part into discrete acquisition zones that take account of the optimized settings;

thereafter, in combination with the result of a segmenting, simplifying, and reconstructing, calculating a real-time image-acquisition path;

taking images of the surface of the part with the optimized settings;

analyzing the images and searching for defects and optical artifacts;

characterizing the defects and artifacts that are found and comparing them with known defects and artifacts stored in a database;

thereafter, if the defects and artifacts that have been found are already known, recording them in the reference database and issuing a corresponding report;

or else, if the defects and artifacts that are found do not appear in the database, correlating them by applying non-destructive inspection methods, or using eddy currents or thermal imaging, identifying them as being new defects or new artifacts, and recording them in the reference database.