Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N25/00—Investigating or analyzing materials by the use of thermal means
  • G01N25/72—Investigating presence of flaws
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N25/00—Investigating or analyzing materials by the use of thermal means

Definitions

• Photothermal examination camera with optical device for elongating the section of a laser beam
• the present invention relates to a photothermal examination camera of the type comprising:
• a laser beam shaping system comprising a beam section elongation device for forming, on a surface of a test piece, an elongate heating zone along a direction,
• an array of infrared detectors for detecting infrared radiation emitted by a detection zone on the surface of the part relative to the heating zone
• the invention is particularly applicable to the non-destructive testing of parts, to detect defects, variations in the nature or properties of their materials, differences in thickness of coating layers, local variations in diffusivity or conductivity
• the parts being examined can be metallic and made of ferrous materials, for example alloy steels such as stainless steels or non-ferrous materials. They can also be made of composite materials, ceramics or plastics.
• the photothermal examination is based on the phenomenon of diffusion of a thermal disturbance produced by a local heating of the part to be examined.
• a photothermal examination camera emitting a laser beam is used, which is focused on the surface of the part being examined, in a heating zone.
• the infrared radiation emitted by the room in a detection zone close to or coincident with the heating zone makes it possible. measure or evaluate the temperature rise in the detection zone due to heating in the heating zone.
• the offset between the heating zone and the detection zone is generally called “offset”. This offset can be zero so that the detection zone and the heating zone are then combined.
• Infrared radiation and thus temperature rise can be measured without contact using a detector such as an infrared detector.
• Infrared radiation or temperature rise in the detection zone is influenced by the local characteristics of the materials being inspected.
• the diffusion of heat between the heating zone and the detection zone which is at the origin of the temperature rise in the detection zone depends on the defects of the part to be examined, such as cracks. , at the level of the heating zone or the detection zone or in the vicinity of these two zones ...
• thermographic image of the surface. of the room By scanning the surface of the part to be examined by the heating zone and detecting the radiation emitted by the detection zone, which moves with the heating zone during the scanning, it is thus possible to obtain a thermographic image of the surface. of the room, this image being representative of variations in the diffusion of heat in the room or defects present inside the room.
• the section of the laser beam is elongated by a slot through which the laser beam passes.
• the subject of the invention is a photothermal examination camera of the aforementioned type, characterized in that the elongation device is an optical device.
• the camera may comprise one or more of the following characteristics, taken separately or in any technically possible combination:
• the optical device comprises a lens intended to be traversed by the laser beam
• the optical device comprises a mirror intended to reflect the laser beam
• the shaping system comprises a device for homogenizing the power of the laser beam along the heating zone
• the device for homogenizing the power is formed by the device for lengthening the section of the laser beam; - A face of the lens has a profile adapted to homogenize the power of the laser beam along the heating zone;
• a reflecting face of the mirror has a profile adapted to homogenize the power of the laser radiation along the heating zone
• the homogenization device is a device for forming the electrode by setting the laser beam in motion perpendicularly to its direction of propagation;
• the device comprises an acousto-optical cell
• the homogenization device comprises an oscillating mirror
• the homogenizing device comprises a bundle of optical fibers whose upstream ends receive the laser beam and whose downstream ends are arranged along a line to create the elongated heating zone;
• the camera comprises a system for mechanically adjusting an offset between the elongated heating zone and the detection zone;
• the camera comprises a trunk, and the mechanical adjustment system comprises a device for moving the matrix of infrared detectors relative to the trunk;
• the camera comprises a trunk
• the mechanical adjustment system comprises a device for moving the shaping system relative to the trunk
• the displacement device comprises a linear motor.
• the displacement device comprises a linear piezoelectric actuator;
• the displacement device comprises a rotary motor and a mechanism for transforming a rotary movement into a translational movement;
• the camera comprises a filter blade for reflecting the laser beam and transmitting the infrared radiation radiated by the detection zone towards the matrix of infrared detectors;
• the blade comprises at least one material selected from the list consisting of CaF 2, MgF 2, Al 2 O 3, BaF 2, Ge, ZnSe, ZnS FLIR multispectral ZnS, MgO, and SrF 2;
• the camera comprises a system for scanning the surface of the room by the heating zone
• the processing unit is able to adjust an offset between the heating zone and the detection zone by selecting a row of infrared detectors in the detection matrix;
• the processing unit is able to independently process the signals supplied by each of the infrared detectors of the matrix;
• the camera comprises a laser source
• the camera comprises connection means to a camera source which does not belong to the camera.
• FIG. 1 is a schematic perspective view illustrating the principles of photothermal examination
• FIG. 2 is a diagram illustrating a photothermal examination method implemented by a camera according to the invention
• FIG. 3 is a schematic view illustrating a photothermal examination camera according to a first embodiment of the invention
• FIG. 4A is a schematic section illustrating, for the camera of FIG. 3, the lengthening device of FIG. the section of the laser beam,
• FIGS. 4B, 5A, 5B and 6 are views similar to FIG. 4A illustrating variants of the device of FIG. 4A,
• FIGS. 7 and 8 are diagrammatic figures illustrating two other variants of the device of FIG. 4A.
• FIG. 9 and 10 are schematic views illustrating two other embodiments of a camera according to the invention.
• FIG. 1 shows a part 1 to be examined.
• the upper surface 1a thereof is moved by moving a heating zone 2 and a detection zone 3 synchronously on the surface 1a.
• the heating zone 2 and the detection zone 3 are offset relative to one another and separated by a distance d called offset.
• the offset d is zero and zones 2 and 3 are merged.
• Zone 2 is heated by an incident laser beam, indicated by the arrow 4.
• the infrared radiation emitted by the detection zone 3 is detected. This radiation is indicated by the arrow 5 in FIG. 1.
• the displacement of zones 2 and 3 is shown by the arrow 6.
• the displacement 6 is parallel or not to the offset d between the heating zone 2 and the detection zone 3.
• the scanning is for example carried out line by line, the direction of movement being reversed for each of the successive lines ("slot" configuration ") Or the same (" comb "configuration).
• the heating zone 2 is situated in front of the detection zone 3 with respect to the direction of movement 6.
• any other relative position is possible, as described in the document FR-2,760,528 ( US 6,419,387) the contents of which are incorporated herein by reference.
• FIG. 2 illustrates a photothermal examination method in which the heating zone 2 is an elongated zone along a direction D. More Zone 2 has a line shape but, alternatively, it can have another shape, such as an ellipse ...
• the detection zone 3 has a shape similar to that of the zone 2. It will be noted that in the example of FIG. 2 it is situated in front of the heating zone 2 with respect to the direction of displacement 6.
• an elongated heating zone 2 makes it possible to reduce the time required to scan the surface 1a, as described in document FR-2,760,528 (US-6,419,387). This characteristic is also present in the invention.
• a matrix 8 of infrared detectors 10 is used to detect the emitted radiation 5.
• the matrix 8 generally comprises M rows and N columns.
• the numbers M and N may vary independently of each other and may be, for example, between 1 and several hundred or more.
• FIG. 2 shows the trace 14 of the radiation 5 emitted by the detection zone 3 on the matrix 8 of detectors 10.
• the row 12 selected actually comprises the detectors 10 illuminated by the infrared radiation emitted by In the invention, and as in FR-2,760,528 (US Pat. No. 6,419,387), it is possible, by selecting an appropriate row 12 of detectors 10, to adjust the offset d between the heating zone. 2 and the detection zone 3.
• FIG. 3 illustrates a photothermal examination camera 16 according to the invention.
• This camera 16 mainly comprises:
• a chest 18 provided with a transparent window 20,
• a system 22 for shaping the laser beam 4 a system 22 for shaping the laser beam 4, a system 24 for detecting the radiation 5, and
• the shaping system 22 is connected to a laser source 34 via an optical fiber 36.
• the shaping system 22 comprises a collimator 38 and a device 40 for extending the section of the laser. laser beam 4 emitted by the source 34.
• the section of the beam 4 is elongated perpendicular to its direction of propagation, to form the elongate heating zone 2.
• the elongation device 40 comprises a lens 42, through which the beam 4 passes.
• This lens 42 is a divergent cylindrical lens.
• This lens 42 ensures a divergence of the beam 4 in the direction in which the elongation is to be produced. This direction is perpendicular to the direction of propagation of the beam 4, as shown by the arrows 4a to 4c of FIG. 4A, which illustrate lines of propagation of the beam 4 at the exit of the lens 42.
• the plane of FIG. 4A contains the elongation direction and the direction of propagation of the beam 4.
• the plane of FIG. 4A is perpendicular to the plane of FIG. 3.
• the upstream face 43 and the downstream face 44 of the lens 42 have sections in the plane of Figure 4A substantially in circular arcs. It will be noted that the lens 42 does not produce an elongation of the section of the beam, and is therefore not divergent, in the plane of FIG.
• the detection system 24 comprises the matrix 8 of detectors 10 as well as a unit 46 for processing the signals emitted by the detectors 10 of the matrix 8.
• This unit 46 is capable of independently processing the signals emitted by each of the detectors 10, this which allows in particular to select the row
• the unit 46 controls the operation of the entire camera 16.
• unrepresented optical elements may be arranged in the system 24, upstream of the matrix 8 with respect to the direction of propagation of the radiation 5, in order to ensure satisfactory operation of the matrix 8.
• the unit 46 is able to construct a thermographic image of the surface 1a of the part 1 by processing the signals received from the detectors 10 of the selected row 12.
• the unit 46 may be connected, for example, to means 48 for displaying the thermographic image and to storage means 50 for storing the data resulting from the processing.
• the means 48 and 50 are remote from the camera 16, but they may alternatively belong to the latter.
• the blade 32 is a semi-reflecting plate to allow the laser beam 4 to be reflected while allowing the radiation to pass through. More precisely, the blade 32 makes it possible:
• one or more of the following materials may be used:
• CaF 2 (calcium fluoride), MgF 2 (magnesium fluoride), Al 2 O 3 (Saphire), BaF 2 (barium fluoride), Ge (Germanium),
• ZnS - FLIR Forward Looking Infra Red
• ZnS Multispectral Zinc Sulphide
• MgO Magnnesium Oxide
• SrF 2 Tin Fluoride
• the camera 16 comprises a device 52 for moving the detection system 24 with respect to the trunk 18.
• This displacement system 52 makes it possible to move the system 24 and therefore the matrix 8 of detectors 10 perpendicular to the radiation 5 upstream of the matrix 8.
• the device displacement 52 may comprise, for example, a linear piezoelectric actuator, a linear motor or a rotary motor associated with a screw / nut mechanism in order to allow a fine lateral displacement of the detection system 24 perpendicular to the beam 5 in the plane of FIG. 3
• Other mechanisms for transforming a rotational movement into translational motion can be envisaged.
• the camera 16 also comprises a device 54 for moving the shaping system 22.
• This device 54 has for example a structure similar to that of the device 52 and makes it possible to move the shaping system 22 perpendicular to the direction propagation of the beam 4 at the output of the shaping system 22.
• the camera 16 also comprises a device 55 making it possible to move the mirror 28 in order to ensure that the surface 1a is scanned by the heating zone 2 and the detection zone 3.
• This displacement device 55 comprises, for example, two galvanometers or two motors. to sweep the surface 1a in two perpendicular directions.
• the mirror 26 returns the laser beam 4 elongated by the device 40 on the shutter 30.
• the shutter 30 When the shutter 30 is open, it allows the beam 4 which is reflected by the plate 32 to pass to the mirror 28 which itself reflects the beam 4 towards the surface 1a through the window 20.
• the radiation 5 passes through the window 20, is returned by the mirror 28 to the blade 32 it passes through to reach the detection system 24 and illuminate the matrix 8 of detectors 10.
• the unit 46 can then build as and when scanning a thermographic image of the surface 1a, this image being displayed by the display means 48.
• the power loss of the laser beam is lower than in FR-2,760,528 (US-6,419,387) where a slot was used to lengthen the section. . This makes it possible to reduce the scanning time of the surface 1 and to use the power of the laser beam 4 more efficiently.
• the choice of one or more of the abovementioned materials to form the blade 32 makes it possible to ensure better retention of the blade 32 over time. This helps to improve the reliability of the examination performed by the camera 16.
• the displacement devices 52 and 54 allow a fine mechanical adjustment of the offset d between the heating zone 2 and the detection zone 3. It is recalled that it may be desirable to conduct zero offset examinations.
• This fine adjustment which can be controlled by the processing unit 46 or manually, is in addition to the possibility of adjustment offered by the choice of the row 12 used.
• This second possibility of mechanical adjustment of the offset makes it possible, in cases where the trace 14 of the detection zone 3 is close to or bites on the boundary of the row 12 of detectors selected, to replace this trace 14 in the center of the row. 12 chosen.
• This third aspect of the invention makes it possible to increase the quality of the thermographic image formed and thus to increase the accuracy and reliability of the examination carried out by means of the camera 16. It will be observed that each of these three aspects the use of an optical device 40, the nature of the blade 32, and the mechanical adjustment of the offset can be used independently of the others.
• the elongation device of the section 40 may have a different structure from that described above while remaining an optical and non-physical device as in the state of the art.
• cylindrical lens any lens having a different vergence in the two axes perpendicular to the direction of propagation of the laser beam 4, so as to obtain a beam whose cross section will be greater along an axis than the along the other.
• one of these lenses or the lens 42 used may have a face 44 or more profile faces (s) adapted (s) to homogenize the power. This is illustrated by FIG. 5A where the downstream face 44 of the lens 42 has a different section of an arc of a circle, this section having a profile adapted to increase the homogeneity of the power of the laser beam 4 over the length of its section.
• the elongation device 40 then performs two functions, namely that of elongating the section of the laser beam 4 and that of homogenizing the power of the beam 4 over this length.
• the power distribution along the direction D of the heating zone 2 is relatively homogeneous thanks to the elongation device 40, the image formed is clear and the photothermal examination performed by the camera 16 is reliable.
• the device 40 may comprise one or more mirrors which provide, by reflection, the elongation functions of the section and optionally the homogenization of the power.
• the device 40 may then comprise a mirror 56, a face 58 reflecting the beam 4 has a circular arc section or profile section adapted to homogenize the power.
• Such mirrors 56 and their reflecting faces 58 are respectively shown in FIGS. 4B and 5B.
• the elongation of the section of the laser beam is carried out by increasing this section along one dimension.
• this elongation can be made by reducing the width of the section of the beam.
• the collimator 38 can be omitted.
• the device 40 may also, alternatively, provide the functions of elongation of the section and possibly homogenization of the power by setting the laser beam 4 in motion.
• the optical device 40 may comprise, for example, an acoustic cell. -optique 60. As shown in Figure 6, this accousto-optical cell 60 extends the beam section 4 by ensuring a displacement of the latter along the direction where its section must be extended. This displacement is materialized by the double arrow 62 in FIG. 6.
• the movement of the laser beam 4 can be provided by an oscillating mirror 64.
• Figure 8 illustrates yet another variant.
• the optical device 40 then comprises a bundle 66 of optical fibers 68 whose upstream ends receive the laser beam 4 and whose downstream ends 72 are aligned so that they output a laser beam 4 of elongate section.
• the elongation functions of the section on the one hand, and power homogenization on the other hand can be provided by two separate devices.
• the camera 16 With regard to the mechanical adjustment of the offset, it is not necessary for the camera 16 to have both a device 52 for moving the detection system 24 and a device 54 for moving the shaping system 22. It can indeed include only one of these devices.
• FIG. 9 This is illustrated in FIG. 9 where the camera 16 comprises only a device 52 for moving the shaping system 24.
• the structure of the camera 16 is further simplified in that the laser source 34 has been integrated into the camera 16 and in that the mirrors 26 and 28 have been removed.
• the camera 16 of Figure 9 does not include an integrated device 55 for moving to ensure the scanning of the surface 1a.
• This scanning is then provided by a device for moving the workpiece 1 or by a device for moving the camera 16 located outside of the latter.
• the mechanical adjustment of the offset d used in addition to the software adjustment by selection of the row 12 can be carried out by means of devices for moving one or more optical members arranged between the shaping system 22, the detection system 24 and the part 1 to be examined. It is therefore not necessary to move the shaping system 22 or the detection system 24.
• the beam 4 incident on the part 1 and the infrared beam emitted 5 are not necessarily parallel but may be inclined with respect to each other, as illustrated schematically in FIG. 10 by way of example.
• the blade 32 serves as a protection filter for the detectors 10 of the matrix 8.

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• 2005
  • 2005-04-28 FR FR0504330A patent/FR2885220B1/fr not_active Expired - Fee Related
• 2006
  • 2006-03-30 WO PCT/FR2006/000700 patent/WO2006114490A2/fr not_active Application Discontinuation
  • 2006-03-30 US US11/912,917 patent/US20080212072A1/en not_active Abandoned
  • 2006-03-30 KR KR1020077024737A patent/KR20080011170A/ko not_active Application Discontinuation
  • 2006-03-30 CN CNA2006800143812A patent/CN101166969A/zh active Pending
  • 2006-03-30 JP JP2008508249A patent/JP2008539404A/ja not_active Abandoned
  • 2006-03-30 EP EP06726150A patent/EP1875218A2/de not_active Withdrawn
• 2007
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