• 专利附录
  • 专利说明
  • 权利要求
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    • 专利摘要:
    The present invention relates to a portable industrial instrument for performing, in an integrated and bilateral manner, interferometric fringe projection and shearography, on an object to be tested, so that when the bidirectional interferometer (1) is associated to the coherent or quasi-coherent projection device (2), the instrument is capable of measuring the 3D shape of the object by projection of interferometric fringes, also called moire process, and, when the bidirectional interferometer (1) is associated at the recording or imaging device (4), the instrument is able to make shearographic measurements on the object, the direction of the light beam passing through the interferometer (1) being reversed during the passage of one measurement configuration to another.
    公开号:BE1020308A5
    申请号:E201200061
    申请日:2012-02-01
    公开日:2013-07-02
    发明作者:Pascal Blain；Yvon Renotte；Serge Habraken；Pascal Waroux
    申请人:Cockerill Maintenance & Ingenierie Sa；Univ Liege；
    IPC主号:
    专利说明:

    LOW-COHERENCE INTERFEROMETRIQUE SYSTEM FOR PHASE SHIFT SHEAROGRAPHY COMBINED WITH
    3D PROFILOMETRY
    Field of the invention
    The present invention relates to a method for measuring the three-dimensional shape (or 3D shape) of an object by means of the projection of interferometric fringes or moire process and the detection of structural defects in the object by means of shearography, in particular phase shift shearography.
    The invention further relates to an apparatus for carrying out the method.
    Background of the invention and state of the art
    Processes of projection fringes crazy moiré processes)
    A plurality of non-contact optical measurement methods have been developed in recent years and applied in many industrial and research fields. Some devices, for example, take advantage of the polarization state separation technique to produce and displace multiple sinusoidal Young interference patterns that are projected and scanned on a surface.
    They are commonly applied to extract dimensional data from surfaces, from the nanoscale to the kilometric scale. Fringe projection techniques are among the most widely used approaches for measuring a shape, a surface profile and a deformation of objects of standard size. They enable robust, accurate and fast field acquisitions. In addition, they benefit from established procedures that have been developed for interferometric systems such as phase shift and phase unruning algorithms.
    Typically, one or more structured light patterns are projected onto the surface to be analyzed. They are generally characterized by a periodic variation of the intensity so that a specific phase can be associated with each illuminated point of the object. By recording the scene with a CCD or CMOS camera, it is possible to compare the phase distribution of the image points with the linearly increasing phase of an undistorted grid by a first calibration step. This phase difference contains the information required for the calculation of surface height variations based on triangulation formulas.
    Favorable characteristics for a good projection pattern are a perfect sinusoidal irradiation function, a very high contrast, a high light intensity and a high depth of field. The contrast problem is particularly critical when the ambient light can not be extinguished, for example in in situ outdoor conditions.
    In interferometric fringe projection systems, the Young interference pattern is a theoretical perfect sinusoid that can have a very high contrast. In addition, the interferometric fringes are non-localized, which means that the irradiation function and the contrast remain unchanged regardless of the projection distance so that there is no depth of field problem. This is an ideal basis for a moire-based technical device. The use of monochromatic laser light is also a beneficial approach for filtering the appropriate signal from ambient light.
    However, the dynamic shift or scaling of interferometric projection pattern often requires accurate and complex electromechanical or optoelectronic systems whose repeatability and robustness are not assured. Internal vibrations are also a possible cause of trouble that compromises the stability of the fringes. Simplicity, robustness, vibration insensitivity and low cost are some of the key features of the system requirements.
    An overview of the art of structured light projection methods suitable for measuring the 3D shape of objects (or 3D laser profilometry) is described in WO 2005/049840.
    On the other hand, the present invention further relates to the field of side-splitting speckle interferometry or shearography, and is a useful technique in the field of non-destructive testing. An overview of phase separation shearography methods is presented in US 6,717,681 B1.
    A shearographic display produces the formation of an image consisting of two laterally displaced images of the same object. Shearography is a full-field optical speckle interferometry technique that measures small surface deformations caused by stimuli, eg vacuum or pressure, microwave, thermal, vibration, ultrasonic excitation etc.
    In a basic configuration of an electronic shearography system, a coherent laser light is extended to uniformly illuminate a portion of the surface of the object, is diffused by the surface, passes through an optical splitting device and enters a CCD camera . Then, the surface is deformed by one of the mechanisms mentioned above, such as heating, for example. The surface expands slightly accordingly and the effect of the deformation of the surface can be visualized as an image on a video monitor or stored in the computer's memory. This deformation of an object from one state to another is in the micrometric range. Deformation of the surface may result from a defect under the surface.
    Research on the combination of shearoaraohie and the projection of interferometric fringes
    Shang et al. (Beam-splitting cube for fringe-projection, holography, and shearographic interferometry, Applied Opties, Vol 40, No. 31 (2001), pp. 5615-5623) discloses a beam splitting cube for fringe projection interferometry. shearographique. This proposed configuration is very simple and requires a very good positioning of the optical element and produces only qualitative results.
    A family of new non-contact optical measurement methods based on the polarization state separation technique and the monochromatic light projection as a means to solve the problem of ambient lighting for in situ measurement has been developed (Moreau et al., Interferometry, Fringes, Projection System for 3D Profiometry and Relief Investigation, SPIE Proc 5857, pp. 62-69, 2005, WO 2005/049840). In this common path dynamic fringe projector, the key element is a polarization state separation prism coated on its hypotenuse with a Bragg grating. This configuration has proved effective and suitable for many applications as varied as archeology and laboratory inspection. Despite these good results, this installation does not meet industrial needs such as robustness and strength.
    In order to eliminate these disadvantages, a new interfering rom in line that is still based on polarization state separation has been devised. A birefringent element, called the Savart blade, makes it possible to construct a more flexible and robust interferometer [Michel et al., Nondestructive testing by digital shearography using a Savart plate, Photonics North, SPIE, 2009, Quebec; Blain et al., Use of a Savart blade for an interferometric fringe projection system for 3D shape measurement, CMOI 16-20 Nov. 2009, Reims, France; Renotte st., Optical metrology devices based on an interferometer, 3D Stereo Media dec. 2009, Liège; Blain et al., Using a Savart Flat in Optical Metrology, Optical Engineering + Applications, SPIE, 1-5 August 2010, San Diego, California (Proceedings).
    The Savart blade has been selected as a new splitting device because it allows for the retention of the aforementioned advantages, ie a virtually common and in-line path configuration, and the philosophy of the interferometer, that is to say, the splitting of the beam of the object by separating two orthogonal linear polarization states. The Savart blade has been chosen from among various birefringent elements that can be used because the two split beams propagate parallel to the optical axis of the device.
    The direction of resolution will be modified by rotating the Savart plate around the optical axis of the interferometer, without affecting the size of the shear, that is to say the sensitivity of the interferometer. The replacement of the coated prism mentioned above with a Savart blade also makes it possible to improve the performance of the interferometer, because: the degree of polarization in the transmission of birefringent elements is greater than the degree of polarization of the coated prism ; the spectral range in the case of Savait's blade is wider (350 to 2500 nm) with respect to the spectral range of the coated prism (for example 532 nm); - the angular efficiency of the Savart blade is wider than the angular efficiency of the prism (better resolution at the edge of the field of view through a digital process); the optical path difference between the beams split by a Savart plate is equal to zero for a (quasi) normal incidence. A shorter coherence length laser or possibly a good diode can then be used by using a Savart blade as a shear device (spatially coherent light source).
    A Savart blade consists of two identical uniaxial birefringent crystals (quartz, calcite or a birefringent crystal) cut at 45 ° to the normal plane and are cemented in such a way that their optical axes are perpendicular. In this configuration, the ordinary radiation of the first crystal becomes the extraordinary radiation of the second, and vice versa. By birefringence, the incident object beam is split along a transverse direction with a doubling quantity proportional to the thickness of the crystals (M. Born and E. Wolf, Principles of Opties, 6th ed., 1980, Pergamon Press 700-701).
    In the steel industry there is interest in the development of an integrated non-destructive testing (NDT) control technology that would detect deep defects, for example polyurethane coating rolls used in continuous paint lines and more generally for uncoated rolls. Methods of the prior art for detecting defects in depth are unsatisfactory: in the case of coated rolls, the use of a transparent polyurethane layer for visual inspection is not always desired by the customer; - the ultrasound control time is long and unacceptable for the industry (30 to 40 minutes per roll); - the sound emitted by a roller after an external stimulus is empirical and unreliable.
    Goals of the invention
    The present invention aims to solve the disadvantages of the prior art.
    In particular, the invention aims to provide a portable integrated instrument, simple, fast and robust to perform both the projection of interferometric fringes and shearography.
    More particularly, the invention aims to provide such an integrated instrument whose passage from one measurement mode to another is not critical in terms of optics and mechanics.
    More particularly, the object of the invention is to enable a rapid control operation (ideally in about or even less than 5 to 10 minutes), externalized control (for example in the case of paint lines in the iron industry). steel, checks carried out by subcontractors for coating or grinding of rolls) with a portable solution that makes it possible to carry out controls on several production lines and with a robustness adapted to an industrial environment.
    Summary of the invention
    A first object of the present invention relates to a portable industrial instrument for performing, in an integrated and bidirectional manner, a projection of interferometric fringes and a shearography, on an object to be tested, comprising: a bidirectional interferometer comprising means for generating a bidirectionally circular polarized light beam; a coherent or quasi-coherent light projection device; - a recording or imaging device; a translating device for conveying said bidirectional interferometer from a first location where it is functionally associated with the coherent or quasi-coherent light projection device to a second location where it is functionally associated with the recording or imaging device and reciprocally ; - a computing device, comprising a video display and analysis; an excitation device dedicated to shearographic or fringe projection measurements; so that, when the bidirectional interferometer is associated with the coherent or quasi-coherent projection device at the first location, the instrument is capable of measuring the 3D shape of the object by projection of interferometric fringes, also called moire process, and, when the bidirectional interferometer is associated with the recording or imaging device at the second location, the instrument is capable of performing shearographic measurements on the object, the direction of the light beam passing through the interferometer being inverted when moving a measurement configuration moving from one measurement configuration to another.
    According to preferred embodiments, the instrument of the invention comprises one or a suitable combination of the following characteristics: the bidirectional interferometer successively comprises the following components: a first linear polarizer or PI, a first variable phase retarder with crystals calibrated liquid or LCVR1, a Savait blade, a second calibrated liquid crystal variable phase retarder or LCVR2, and a second linear polarizer or P2; PI and LCVR1, Savait's blade, LCVR2 and P2 respectively, are cemented and can be turned in a block around the optical axis, the two blocks being independent; in shearography mode, the interferometer being associated with the recording or imaging device at said second location, successively, PI provides the linear polarization of a coherent or quasi-coherent incoming light beam reflected by the object, LCVR1 is defined as being a quarter wave plate, introduced in front of the Savart blade and rotated with its fast and slow axes configured at 45 ° with respect to the polarization direction defined by PI, so as to restore the polarized light beam of Circularly, Savart's blade refracts the circularly polarized light beam entering ordinary and extraordinary parallel beams, LCVR2 has its fast and slow axes configured so that the extraordinary and ordinary beam polarization direction refracted by Savart's blade parallel to the fast and slow axes of LCVR2, and introduce a known phase shift between the two beams, P2 is oriented at 45 ° to the polarization of the emerging beams and allows interference between the two beams; in the fringe projection mode, the interferometer being associated with the coherent or quasi-coherent light projection device at said first location, the order of the interferometer components being inverted with respect to the shearographic mode, taking account of the direction of the beam of successively passing light, P2 provides the linear polarization of the incident coherent light beam from the coherent or quasi-coherent light projection device, LCVR2 is defined as a quarter-wave plate, introduced in front of Savait's blade and rotated with its fast and slow axes set at 45 ° with respect to the polarization direction defined by P2, so as to restore the circularly polarized light beam, the Savart blade refracts the circularly polarized light beam into parallel beams ordinary and extraordinary, LCVR1 has its fast and slow axes configured so that the Polarization iris of extraordinary and ordinary beams refracted by the Savart plate is parallel to the fast and slow axes of LCVR1 and introduces a known phase shift between the two beams, PI is oriented at 45 ° with respect to the polarization of the emerging beams and allows a interference between the two beams; the coherent or quasi-coherent light projection device comprises at least one weakly coherent laser light source, a beam expander, a beam projection lens system and a receptacle for receiving the bidirectional interferometer, located between the beam expander and projection lens system, when the instrument is used in fringe projection mode; the imaging device comprises a two-lens system LI, L2, a digital video camera and a receptacle for the bidirectional interferometer, located between L1 and L2, when the instrument is used in shearography mode, L1 being adjustable or translatable; the portable industrial instrument comprises an enclosure comprising a housing having a transparent window to allow the illumination and the formation of an image of the object tested respectively.
    Another object of the invention relates to a method for measuring the three-dimensional (3D) shape of an object under test by interferometric fringe projection and for detecting defects under the surface of said object by phase separation shearography, using the portable, integrated and bidirectional industrial instrument as described above, comprising, in the fringe projection mode, the successive steps of: - producing a light beam incident on the bidirectional interferometer hosted in the projection device of coherent or quasi-coherent light, so as to project a system of interference fringes at the output of the coherent light projection device onto the object under test; reflection of said system of interference fringes on a surface of the object; recording and / or displaying an image of said surface which comprises said fringe system; calculating a 3D shape of said surface; and, in the shearography mode, the successive steps of: producing a beam of light incident on the object; reflection of said incident light beam on the surface of said object; producing the beam of light reflected on the bidirectional interferometer contained in the recording or imaging device, so as to create an interference pattern of split beams; recording an image of said split beam interference pattern when the object is in the undeformed state; repeating the last step when the object is in the deformed state using the excitation mechanism; - analysis of the two interference patterns of split beams and identification of defects below the surface.
    Preferably, in the two steps of recording an image of said split beam interference pattern in the shearography mode, an algorithm of four or fewer steps is used that captures and stores images of the test object. when the object is in the deformed and undeformed states, respectively.
    Preferably, in the step of analyzing the interference patterns of split beams, the following steps are performed: - comparison of the stored images; - application of a smoothing algorithm; - viewing a resulting pattern on a video display.
    More preferably, the defects detected below the surface are in the range of 0 to 25 mm.
    Brief description of the drawings
    Figure 1A schematically represents the interferometer used in the present invention. Fig. 1B is a simplified representation of the axes and directions of polarization in the interferometer.
    FIG. 2A diagrammatically represents the system of the invention complete with the interferometer at rest. FIG. 2B shows a concrete embodiment for the "J" -shaped translation rail.
    Figure 3 schematically shows the system of the total invention with the interferometer in the configuration of "3D profilometer".
    FIG. 4 diagrammatically represents the system of the total invention with the interferometer in the "shearography" configuration.
    Figure 5 shows results for polyurethane-coated rolls used in paint lines in the steel industry, obtained by shearography (detection of a defect under the surface of the roll).
    Figure 6 shows results for polyurethane-coated rolls used in paint lines in the steel industry, obtained by 3D profilometry (roll shape measurement).
    Fig. 7 shows an example of displaying the results on a video screen in the fringe projection mode.
    FIG. 8 shows the change of inter-fringe distance in the fringe projection when the Savart plate is rotated (for example Ai for θ = 0 °, Al 2> Al for θ = 45 °).
    Legend LS: lighting system; PS: projection system; EX: beam expansion; CH: heating module; IN: online interferometer; TRANS: translation system; CA: imaging module. Rot.l and Rot.2 are devices for rotating respective sets P1 + LCVR1 and LCVR2 + Savart + P2 blade, about their axis. Rot.3 corresponds to the motor allowing interferometer translation along the rail.
    DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS The apparatus of the present invention comprises an interferometer, which functions as a multifunction metrological device.
    On the one hand, this interferometer can be installed in front of a CCD camera to form an optical measurement system which is a shearography interferometer. The latter makes it possible to measure microdetrations between two states of the object under study in a coherent or quasi-coherent light.
    On the other hand, by producing and shifting multiple sinusoidal Young interference patterns with this interferometer, and using a CCD camera, it is possible to construct a structured light projection 3D profilometer. In this configuration, the same interferometer as described above is used this time together with the laser illumination system to project fringes. This method, called the moiré method, generally comprises the projection of a periodic light pattern which may be the result of the interference of two coherent beams, forming a pattern of deformed lines on said object, and the synthesis of the 3D form of the object from said pattern of deformed lines and a pattern of reference lines.
    The system of the present invention comprises the following subsystems (see FIG. 2A): an interferometer 1, a coherent or weakly coherent light projection device 2, a translation device 3, a recording device or 4, an excitation mechanism 5 for shearographic measurements or possibly for the projection of fringe measurements (see below), a calculation subsystem 6, a power supply 7 and an enclosure ( not shown).
    There is a twofold interest in the use of coherent or near-coherent light in the context of the present invention. First, it allows the production of a sinusoidal fringe pattern by an interferometric (i.e., harmonic-free) method. Secondly, it produces fringes with a maximum contrast compared to the ambient light thanks to a measurement by an interference filter associated with a camera having a bandwidth adapted to the wavelength of the source generating the fringes (eg λ = 532 nm of NdYAG doubled in frequency). The use of this filter (Δλ: a few nm) also makes it possible to avoid some image interference by means of reflections and / or unwanted specular effects. The use of the interferential filter associated with the camera is also applied in shearography and allows easy reading of the fringes, even under significant ambient lighting.
    Interferometer 1 in both configurations
    The principle of the interferometer is described in detail in FIG. 1. The interferometer comprises, successively, a first linear polarizer 11 (or PI), a first liquid crystal variable phase retarder 12 (or LCVR1), a Savart blade. 13, a second liquid crystal variable phase retarder 14 (or LCVR2) and a second linear polarizer 15 (or P2). As mentioned above, it is an essential characteristic of the invention to use the interferometer block 1, alternatively in the "3D profilometer" (see FIG. 3) and in the "shearography" mode (see FIG. 4). ). A liquid crystal phase variable retarder (or phase shifter) LCVR is commonly used as a transmitting element with an electrically adjustable optical phase delay. It should be noted finally that the terms mode and configuration are used indifferently below to designate the two types of measurements. Therefore, both possibilities are considered.
    In shearography mode (FIG. 4), the first linear polarizer 11 (PI) provides the linear polarization of the laser beam and then allows a reliable analysis of the polarization state propagation through the interferometer. In order to have a beam irradiation independent of the orientation of the Savart plate, the first liquid crystal phase variable retarder 12 (LCVR1) is defined as a Savart 13 blade and rotated in such a way that its fast axes and slow are at 45 ° to the direction of polarization defined by PI. In this configuration, the beam is circularly polarized before passing through the Savart 13 blade (see FIG. 1B). The circularly polarized state of the light beam entering the Savart blade allows bidirectional traversal of the interferometer (Savart plate and associated LCVR as retarder plates).
    The second liquid crystal variable phase retarder 14 (LCVR2) makes it possible to carry out a time phase shift. The fast and slow axes of this modulator are configured parallel to the linear polarization direction of respective refracted beams. LCVR2 retains the linear polarization states of the beams refracted by the Savart 13 blade and introduces a known phase shift between the two beams. The second linear polarizer (P2) thus allows interference between the two refracted beams. P2 is oriented at 45 ° to the polarization of the two emerging beams, so that the same amount of light is selected by the polarizer. The Savart 13 blade, LCVR2 14 and P2 15 are cemented and can be rotated around the optical axis. Therefore, the shear direction can be chosen and so is the orientation of the created fringes, which is of interest for quantitative shearography and also defines the sensitivity of the interferometer.
    In "fringe projection" mode, the interferometer block 1 is simply inverted with respect to the propagation of light. The second linear polarizer 15 (or P2) provides the linear polarization of the laser beam and then allows a reliable analysis of the polarization state propagation through the interferometer. In order to obtain a beam intensity independent of the orientation of the Savait 13 blade, the second liquid crystal variable phase retarder 14 (or LCVR2) is configured as a λ / 4 retarder plate, introduced in front of the blade. of Savait 13 and turned so that its fast and slow axes are at 45 ° with respect to the direction of polarization defined by P2. In this configuration, the beam is circularly polarized before passing through the Savart 13 blade. The first liquid crystal variable phase retarder 12 (or LCVR1) is used to perform a time phase shift. The fast and slow axes of this modulator are configured parallel to the linear polarization direction of respective refracted beams. LCVR1 12 maintains the linear polarization states of the beams refracted by the Savart plate 13 and introduces a known phase shift between the two beams. The linear polarizer 11 (PI) thus allows interference between the two refracted beams. This polarizer is oriented at 45 ° to the polarization of the two emerging beams, therefore the same amount of light is selected by the polarizer. Since the blade of Savart 13, LCVR2 and P2 are cemented (see above) and can be rotated around the optical axis, the shear direction can be chosen and also the orientation of the fringes. The inter-fringe distance can be modulated by turning the Savart blade (see Figure 8).
    Translation device 3
    The "translation" device 3 ensures the precise displacement of the interferometer 1 between the projection device 2 and the imaging device 4. It should be noted that the actual movement of the interferometer is a little more complex than "linear" translation for purposes of alignment: the device comprises a rail which is curved at one of its ends, having a shape of "J" (see Figure 2B). However, for the sake of simplicity, the device 3 will be represented in the figures in the form of a rectilinear rail. Therefore, it must be understood by "translation" a combination of a strict geometrical translation with a rotation of an angle that does not exceed 45 °. When the interferometer 1 is in the projection device 2, this makes it possible to work in "fringe projection mode" (FIG. 3); when it is in the imaging or recording device 4, this makes it possible to work in "shearography mode" (FIG. 4).
    The projection device 2 comprises a laser light source 21 (a laser or a laser diode), a beam expander 22, a receptacle 24 for receiving the interferometer 1 when it is used in fringe projection mode and a system beam projection lens 23.
    The imaging device 4 comprises a two-lens system 41, 42 (LI, L2), a digital video camera 43 and a receptacle 44 for receiving the interferometer 1 when used in shearography mode. L1 can be adjusted, digitally and automatically, or translated to increase image quality (or focus).
    The excitation mechanism 5 is used in the shearography configuration to stimulate the object under study and detect defects in this object. However, it should be noted that the fringe projection method also allows the measurement of deformation between two states. The excitation mechanism 5 (eg thermal stimulation) could thus be used by the fringe projection method in certain applications (for example, fault detection on rollers).
    The enclosure (not shown) comprises at least one housing having a transparent window to allow illumination and image formation of the object under test.
    The computing subsystem 6 comprises a programmed computer which is connected through appropriate analog-to-digital (ADC) and digital-to-analog converters (DACs) to the components described above. In a preferred embodiment of the present invention, the computer executes a four-step algorithm that captures and stores images of the object under test at four different values of the phase (for example by changing the pitch of the fringes), when the object is in the deformed and undistorted states, respectively. The comparison of the stored images, coupled with the application of a smoothing algorithm, produces a pattern that can be viewed on a video display (see Figure 7).
    Advantageously, in the case of 3D profiling by fringe projection / moire process, the texturing of the imaged objects can be added to the images for the sake of realism.
    According to the invention, the same "reversible" physical interferometer 1 is used in the fringe projection mode and in the shearography mode, respectively. To move from one configuration to the other, the interferometer 1 simply has to be moved, thanks to the translation device 3, from the receptacle 24 (in the projection device 2) to the receptacle 44 (in the recording device or device). 4) and vice versa. The difference between the two modes of operation is that the direction of the optical path in the interferometer is reversed.
    It is an important feature of the invention to produce a bi-directional instrument that is reversible and symmetrical (around the Savart plate, which is central) because some interferometer moves to move from a measurement-configuration to the other. other may be detrimental to the mechanical and optical adjustments of the instrument, in particular the centering of the optical axes. In this respect, the symmetrical configuration of the interferometer makes it possible to avoid undesirable 180 ° rotation of the latter, since a simple "translation" is necessary to modify the measurement mode.
    Results
    The measurement and detection technique of the present invention has been applied to the quality control of a polyurethane coating of rolls used in paint lines in the steel industry. A first function is the detection of defects near the surface at a depth of 4 to 5 mm. These defects have the form of inclusions or bubbles. Another function is to examine the shape of the coated roll surface with a given accuracy.
    This quality control can be advantageously carried out at the steel manufacturer but also at the subcontractors such as those manufacturing the roller coating or the machining / grinding of rollers.
    Figure 5 and Figure 6 show the following results using the apparatus of the present invention:
    Shearoaraphy mode (Figure 5) (a) view of a roll with a hidden defect under the surface of the roll (framed area); the thermal excitation device is visible on the left side; (b) duplicate image of the defect area resulting from the doubling mechanism; (c) final 3D image of the hidden defect obtained by shearography.
    3D profilometer (figure 6) (a) four successive images of an illuminated roller end with a pattern of sinusoidal fringes successively shifted by a quarter of a spatial period λ (from left to right); (b) 3D image of the roll end, reconstructed after treatment.
    权利要求:
    Claims (12)
    [1]
    A portable industrial instrument for performing, in an integrated and bidirectional manner, the projection of interferometric fringes and shearography, on an object to be tested, comprising: a bidirectional interferometer (1) comprising means for generating a polarized beam of light bidirectionally circular; a coherent or quasi-coherent light projection device (2); - a recording or imaging device (4); a first location (24) wherein said bidirectional interferometer (1) is positioned to be functionally associated with the coherent or quasi-coherent light projection device (2) and a second location (44) where said interferometer (1) is positioned to functionally associated with the recording or imaging device (4); - a computing device (6), comprising a video display and analysis; an excitation device (5) dedicated to shearographic or fringe projection measurements; so that when the bidirectional interferometer (1) is associated with the coherent or near-coherent projection device (2) at the first location (24), the instrument is able to measure the 3D shape of the object by projection of interferometric fringes, also referred to as the moiré method, and when the bidirectional interferometer (1) is associated with the recording or imaging device (4) at the second location (44), the instrument is capable of performing measurements shearographic on the object, the direction of the beam of light passing through the interferometer (1) being reversed as it passes from one measurement configuration to another, the direction of motion of the coherent or semi-coherent light being inverted in the two measurement modes, said instrument being characterized in that: - the bidirectional interferometer (1) is reversible and symmetrical around a Savart blade, which. is central and - a "translation" device (3) for accurately moving said bidirectional interferometer (1) from said first location (24) to said second location (44) and reciprocally comprising a curved rail at one end thereof having a shape of "J", so that the precision displacement of the interferometer corresponds to a combination of a strict geometrical translation with a rotation of an angle that does not exceed 45 °.
    [2]
    Portable industrial instrument according to claim 1, characterized in that the bidirectional interferometer (1) comprises successively the following components: a first linear polarizer or PI (11), a first calibrated liquid crystal variable phase retarder or LCVR1 ( 12), a Savart blade (13), a calibrated second liquid crystal variable phase retarder or LCVR2 (14), and a second linear polarizer or P2 (15).
    [3]
    3. Portable industrial instrument according to claim 2, characterized in that PI (11) and LCVR1 (12), the Savart blade (13)., LCVR2 (14) and P2 (15) respectively, are cemented and can be rotated. , in block around the optical axis, the two blocks being independent.
    [4]
    4. Portable industrial instrument according to claim 2, characterized in that, in shearography mode, the interferometer (1) being associated with the recording or imaging device (4) at said second location (44), successively, PI (11) provides the linear polarization of a coherent or near-coherent incoming light beam reflected by the object, LCVR1 (12) is configured as a quarter-wave plate, introduced in front of the Savart blade (13) and turned with its fast and slow axes set at 45 ° to the polarization direction defined by P1, so as to restore the circularly polarized light beam, the Savart blade (13) refracts the beam of circularly polarized light entering into ordinary and extraordinary parallel beams, LCVR2 (14) has its fast and slow axes configured so that the polarization direction of the extraordinary and ordinary beams refracted by the de Savart are parallel to the fast and slow axes, LCVR2, and introduces a known phase shift between the two beams, P2 (15) is oriented at 45 ° to the polarization of emerging beams and allows interference between the two beams.
    [5]
    Portable industrial instrument according to claim 2, characterized in that, in fringe projection mode, the interferometer (1) is associated with the coherent or quasi-coherent light projection device (2) at said first location (24). the order of the components of the interferometer being inverted with respect to the shearographic mode, taking into account the direction of the passing beam of light, successively P2 (15) provides the linear polarization of the incident coherent light beam from the projection device of coherent or quasi-coherent light (2), LCVR2 (14) is defined as a λ / 4 retarder plate, introduced in front of the Savart blade (13) and rotated with its fast and slow axes set at 45 ° relative to to the polarization direction defined by P2, so as to restore the circularly polarized light beam, the Savart blade (13) refracts the polarized light beam in such a way that Circular in ordinary and extraordinary parallel beams, LCVR1 (12) has its fast and slow axes configured so that the extraordinary and ordinary beam polarization direction refracted by the Savart blade is parallel to the fast and slow axes of LCVR1 and introduces a known phase shift between the two beams, PI (11) is oriented at 45 ° with respect to the polarization of emerging beams and allows interference between the two beams.
    [6]
    Portable industrial instrument according to claim 1, characterized in that the coherent or quasi-coherent light projection device (2) comprises at least one weak coherent laser light source (21), a beam expander (22), a beam projection lens system (23) and a receptacle (24) for receiving the bidirectional interferometer (1) / located between the beam expander (22) and the projection lens system (23), when the instrument is used in fringe projection mode.
    [7]
    7. Portable industrial instrument according to claim 1, characterized in that the imaging device (4) comprises a two-lens system LI, L2 (41, 42), a digital video camera and a receptacle (44) for 1 ' bidirectional interferometer (1), located between L1 (41) and L2 (42), when the instrument is used in shearography mode, L1 being adjustable or translatable.
    [8]
    8. portable industrial instrument according to claim 1, characterized in that it comprises an enclosure comprising a housing having a transparent window to allow illumination and the formation of an image of the object tested respectively.
    [9]
    9. A method for measuring the three-dimensional (3D) shape of an object under test by projection of interferometric fringes and for detecting faults under the surface of said object by phase separation shearography, using the portable, integrated industrial instrument and bi-directional device according to any one of the preceding claims, comprising, in the fringe projection mode, the successive steps of: - producing a light beam incident on the bidirectional interferometer (1) hosted in the light projection device coherent or quasi-coherent (2), so as to project a pattern of interference fringes at the output of the coherent light projection device (2) onto the object under test; reflection of said pattern of interference fringes on a surface of the object; recording and / or displaying an image of said surface which comprises said fringe pattern; calculating a 3D shape of said surface; and, in the shearography mode ,. the successive stages of: - producing a beam of light incident on the object; reflection of said incident light beam on the surface of said object; producing the beam of light reflected on the bidirectional interferometer (1) contained in the recording or imaging device (4) so as to create an interference pattern of split beams; recording image of said interference pattern of split beams, when the object is in the undistorted state; repeating the last step when the object is in the deformed state using the excitation mechanism; - analysis of the two interference patterns of split beams and identification of defects below the surface.
    [10]
    The method of claim 9, characterized in that, in the two steps of recording an image of said split beam interference pattern in the shearography mode, a four-step or less algorithm is used that captures and stores images of the test object, when the object is in the deformed and undeformed states, respectively.
    [11]
    11. The method as claimed in claim 10, characterized in that, in the step of analyzing the two split-beam interference patterns, the following steps are performed: comparison of the stored images; - application of a smoothing algorithm; - viewing a resulting pattern on a video display.
    [12]
    The method of claim 9, characterized in that the defects detected beneath the surface are in the range of 0 to 25 mm.
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    同族专利:
    公开号 | 公开日
    CN103148778A|2013-06-12|
    US8873068B2|2014-10-28|
    US20130141712A1|2013-06-06|
    EP2602583A1|2013-06-12|
    PT2602583E|2015-07-02|
    JP2013117533A|2013-06-13|
    BR102012030915A2|2014-03-18|
    EP2602583B1|2015-03-11|
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    法律状态:
    2018-02-22| MM| Lapsed because of non-payment of the annual fee|Effective date: 20170228 |
    优先权:
    申请号 | 申请日 | 专利标题
    EP20110191890|EP2602583B1|2011-12-05|2011-12-05|Low coherence interferometric system for phase stepping shearography combined with 3D profilometry|
    EP11191890|2011-12-05|
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