FR3045825A1 - SYSTEM AND METHOD FOR OPTICALLY DETECTING OBJECTS IN A FLUID - Google Patents

Abstract

The optical object detection (10) system (10) in a fluid (14) includes a light source (20) configured to illuminate the fluid in an illumination direction (X), and a device (22) for acquisition of a radiation emitted by the illuminated fluid, the acquisition device comprising a radiation focusing lens (24), an image sensor (26) configured to acquire at least one transmitted and focused radiation image by the lens, and a mask (28) having an opaque portion (30), a first radiation passing region (32) and a second radiation passing region (34), the second region being distinct from the first region. In view in the direction of illumination, the first zone (32) is in the form of an arcuate band, and the second zone (34) is disposed inside a disk whose outer edge is in part formed by an inner edge of the first zone.

Description

System and method for optical detection of objects in a fluid

The present invention relates to a system for optical detection of objects in a fluid. The system comprises a light source configured to illuminate the fluid in a direction of illumination, and a device for acquiring radiation emitted by the illuminated fluid.

The acquisition device comprises a radiation focusing lens, an image sensor (s) configured to acquire at least one image of the radiation emitted and focused by the lens, and a mask comprising an opaque portion and a passage zone of the radiation. The invention also relates to a method for the optical detection of objects in a fluid. The invention is particularly suitable for determining a concentration of objects, such as particles, bubbles, or drops, in a flow in the vicinity of an obstacle. The invention relates in particular to the nuclear field for the determination of particle concentrations in flows in the vicinity of fuel cladding of a nuclear reactor.

Document WO 2015/075217 A1 discloses an optical detection system of the aforementioned type. This optical detection system allows a three-dimensional determination of the velocity profile and the minimum concentration of particles in a flow. The mask is a shutter formed by an opaque disc having at least two openings in a circular arc capable of transmitting light rays to the image sensor (s). The openings, forming the radiation passage zone, are inscribed on the same circle.

However, the value of the signal-to-noise ratio of the particle images acquired with this optical detection system is relatively low, which generates measurement uncertainties.

The object of the invention is then to propose a detection system making it possible to improve the signal-to-noise ratio of the images acquired, so as to reduce the measurement uncertainties. To this end, the subject of the invention is a system for the optical detection of objects in a fluid, the system comprising: a light source configured to illuminate the fluid in a direction of illumination, and a device for acquiring radiation emitted by the illuminated fluid, the acquisition device comprising a radiation focusing lens, an image sensor (s) configured to acquire at least one image of the radiation emitted and focused by the lens, and a mask comprising an opaque portion, a first radiation passage zone and a second radiation passage zone, the second zone being distinct from the first zone, wherein, in view in the illumination direction, the first zone is shaped at least one arcuate band, and the second zone is disposed within a disk whose outer edge is at least partly formed by an inner edge of the first z one.

The optical detection system according to the invention then makes it possible to have a mask with an annular space, namely the first zone, allowing only the signal to pass from the periphery of the object, and a space internal to the annular space. , ie the second zone, to acquire more radiation from the illuminated fluid.

According to other advantageous aspects of the invention, the optical detection system comprises one or more of the following characteristics, taken in isolation or in any technically possible combination: the mask is disposed between the lens and the image sensor; ); the mask is disposed in the Fourier plane of the lens; the first zone is asymmetrical with respect to the center of the arc of a circle; the first zone comprises several bands in an arc of a circle; the inner edges of said strips are inscribed on the same inner circle, and the outer edges of said strips are inscribed on the same outer circle, the outer circle being distinct from the inner circle; the second zone further comprises an additional lens; in view in the direction of illumination, the second zone is of rectangular shape; - In view in the direction of illumination, the second zone is centered relative to the center of the arc; and the acquisition device is further configured to measure interference fringes from the acquired image and to determine a size of the objects from the measured interference fringes. The invention also relates to a method for optical detection of objects in a fluid, the method comprising: - illuminating the fluid in a direction of illumination via a light source, and - acquisition of a radiation emitted by the fluid illuminated by means of an acquisition device comprising a radiation focusing lens, an image sensor (s) configured to acquire at least one image of the emitted radiation, and a mask having an opaque portion, a first radiation passage zone and a second radiation passage zone, the second zone being distinct from the first zone, wherein, in view in the illumination direction, the first zone is in the form of at least one web in an arc, and the second zone is disposed within a disk whose outer edge is at least partly formed by an inner edge of the first zone.

In another advantageous aspect, the method further comprises measuring interference fringes from the acquired image and determining a size of the objects from the measured interference fringes.

These features and advantages of the invention will become apparent on reading the following description, given solely by way of nonlimiting example, and with reference to the appended drawings, in which: FIG. 1 is a diagrammatic representation of an optical detection system according to the invention, the system comprising a light source configured to illuminate a fluid in a direction of illumination and a device for acquiring radiation emitted by the illuminated fluid, the acquisition device comprising a radiation focusing lens, mask and image sensor (s) configured to acquire images of emitted radiation focused by the lens; FIG. 2 is a schematic view, in the direction of illumination, of the mask of FIG. 1 according to a first embodiment; FIG. 3 is a view of an acquired image of the fluid with an optical detection system of the state of the art; FIG. 4 is a view of an acquired image of the fluid with an optical detection system according to the first embodiment; - Figure 5 is a schematic view similar to that of Figure 2, according to a second embodiment; and - Figure 6 is a schematic sectional view along the plane VI of Figure 5.

In the rest of the description, the expression "about" defines a relationship of equality at plus or minus 10%.

In FIG. 1, an optical detection system 10 is configured to detect objects 12 in a fluid 14, the fluid 14 being, for example, a flow in the vicinity of a fuel cladding of a nuclear reactor, not shown.

The optical detection system 10 comprises a light source 20 configured to illuminate the fluid 14 in an illumination direction X, and a device 22 for acquiring radiation emitted by the illuminated fluid 14.

The objects 12 to be detected are contained in the fluid 14, and are, for example, particles, bubbles, or drops.

The light source 20 is known per se. The light source 20 is for example spatially coherent. The light source 20 comprises for example a light-emitting diode, also called LED (of the English Light Emitting Diode), and a diaphragm, also called pinhole (English pinhole), not shown.

As a variant, the light source 20 is a spatially and temporally coherent source, such as a laser diode or a pulsed laser. The invention is also applicable when the light source 20 is a source of white light.

The acquisition device 22 comprises a radiation focusing lens 24, an image sensor 26 configured to acquire at least one image of the radiation emitted and focused by the lens 24, and a mask 28.

In addition, the acquisition device 22 is further configured to measure interference fringes from the acquired image and to determine a size of the objects 12 from the measured interference fringes. The determined size is the actual size of the objects 12 in the fluid 14, also called the physical size.

The determined size of the objects 12 is for example the diameter, or the radius, of these objects 12 when they are spherical.

Alternatively, the determined size of the objects 12 is a characteristic dimension of these objects 12, such as a length in a predefined direction, when these objects 12 are not spherical.

The size of the objects 12 is preferably between 100 μm and a few tens of mm, that is to say between 100 μm and 100 mm, for example between 1 mm and 10 mm.

When the objects 12 are illuminated by the light source 20, interferences appear between light rays resulting from the diffraction of the objects 12 and rays from the reflection, which generates interference fringes. The frequency of these interferences is proportional to the actual size of the objects 12 and inversely to the wavelength of the light source 20. It is thus possible to determine the size of the objects 12 from the measured interference fringes. .

The focusing lens 24 is known per se.

The image sensor (s) 26 is also known per se. The image sensor (s) 26 is for example a CCD (Charge Coupled Device), or a CMOS sensor (English Complementary Metal Oxide Semiconductoή.

The mask 28 has an opaque portion 30 corresponding to the hatched portion in FIG. 2, a first radiation passing zone 32 and a second radiation passing zone 34, the first and second zones 32, 34 not being hatched in FIG. the example of FIGS. 2 and 5. The second zone 34 is distinct from the first zone 32. The second zone 34 is preferably disjunct from the first zone 32.

The mask 28 is preferably arranged between the focusing lens 24 and the image sensor 26, as shown in FIG. 1. The mask 28 is for example arranged in the Fourier plane of the focusing lens 24.

The mask 28 is preferably disk-shaped, as shown in Figures 2, 5 and 6.

The mask 28 is, for example, positioned and held with respect to the center of the focusing lens 24 by supports, not shown, so as to allow precise positioning of the mask 28 with respect to the center of the focusing lens 24.

The opaque portion 30 of the mask is a portion preventing the passage of light radiation. The opaque portion 30 is known per se.

The first and second zones 32, 34 are distinct zones of the mask, configured to allow the passage of the light radiation. The first and second zones 32, 34 are, for example, openings in the material forming the opaque portion 30.

In a variant, the first and second zones 32, 34 are made of a translucent or transparent material.

The first zone 32 is, in view in the direction of illumination X, in the form of at least one band 36 in an arc of a circle, as shown in FIG.

The first zone 32 has in particular, in a transverse plane perpendicular to the illumination direction X, a first cross section 37 in the shape of the at least one strip 36 in an arc, the first cross section 37 having an inner edge 37A and an outer edge 37B.

In the example of FIG. 2, the first zone 32 comprises three bands 36 in an arc of a circle, separated by branches 38 allowing the mechanical retention of opaque portions surrounding the strips 36, said opaque portions forming the opaque portion 30.

In the example of Figure 2, the first zone 32 is preferably in the form of an annular space, the meeting of the bands 36 forming substantially a ring, with the exception of the branches 38 which are reduced in size compared to that of 36. In the example of FIG. 2, two strips 36 correspond to an angular sector of about 90 °, and the third band 36 corresponds to an angular sector of about 180 °.

The first zone 32 is preferably asymmetrical with respect to the center C of the arc. In the example of FIG. 2, this dissymmetry is obtained by the presence of the branches 38.

The dimensions of the first zone 32, in particular the width of the strip or bands 36 in a radial direction perpendicular to the illumination direction X, are variable. The value of this width makes it possible to parameterize the thickness of a respective light ring for each object 12, recorded by the image sensor (s) 26.

The second zone 34 is, in view in the direction of illumination X, disposed inside a disk 40 whose outer edge 42 is at least partly formed by the inner edge 37A of the first zone 32.

The second zone 34 is in particular arranged inside a cylinder 44 (visible in FIG. 6) extending in the direction of illumination X. The cylinder 44 has, in the transverse plane perpendicular to the direction of illumination X, a second cross section 46 whose periphery is at least partly formed by the inner edge 37A of the first cross section 37.

The inner edges of the bands 36 are inscribed on the same inner circle corresponding to the inner edge 37A of the first zone 32, and the outer edges of said bands 36 are inscribed on the same outer circle corresponding to the outer edge 37B of the first zone 32, the outer circle being distinct from the inner circle.

Preferably, the second zone 34 is, in view in the direction of illumination X, of rectangular shape. In other words, the second zone 34 is then in the shape of a rectangular parallelepiped. The second cross section 46 is rectangular.

More preferably, the second zone 34 is, in view along the direction of illumination X, centered with respect to the center C of the arc of circle.

The number of branches 38 is preferably greater than or equal to two, for example equal to three as illustrated in FIGS. 2 and 5.

The spatial arrangement of the branches 38 is variable. This spatial arrangement of the branches 38 is preferably asymmetrical with respect to the center C of the arc in order to have an asymmetry of the first zone 32 with respect to said center C.

FIG. 3, and respectively FIG. 4, then illustrate images 100, 110 acquired from the fluid 14 containing several objects 12 with an optical detection system of the state of the art, and respectively with the optical detection system 10 according to FIG. 'invention.

In the image 100 acquired with the optical detection system of the state of the art, each object 12 corresponds to a discontinuous annular shape 102, composed of three sectors 104 in an arc of a circle, corresponding to the light radiation which has passed through the first corresponding zone 32 of the mask.

In the image 110 acquired with the optical detection system 10 according to the first embodiment, each object 12 corresponds to a discontinuous annular shape 112, composed of three sectors 114 in an arc of a circle, corresponding to the light radiation which has passed through the first zone 32 of the mask, and a central shape 116 corresponding to the light radiation passed through the second zone 34. The three sectors 114 in an arc correspond to the three bands 36 of the mask 28 of FIG. , the central shape 116, in the form of a rectangle in the example of FIG. 4, corresponds to the second zone 34 of rectangular shape of said mask 28 of FIG.

The first zone 32 makes it possible to let the radiation pass around the object 12, and the second zone 34 makes it possible to pass a portion of the radiation from the center of the object 12.

The representation in the discontinuous annular form advantageously makes it possible to detect a larger number of objects 12 in a given volume, the objects 12 which are superposed nevertheless differ from each other in the image acquired by the sensor 26, as is clearly visible in Figure 4.

Thus, when objects 12 of different sizes are simultaneously present in the fluid 14, the optical detection system 10 according to the invention makes it possible to detect superimposed objects, in particular to detect a small object that would be located behind a larger object .

The additional presence for each object 12 of the central shape 116 in the image acquired by the sensor 26 with the optical detection system 10 according to the invention makes it possible to further distinguish the objects 12 from each other.

The combination of the first zone 32 and the second zone 34 according to the invention then makes it possible to increase a superposition rate of the objects 12 in the fluid 14, while maintaining a very good quality of measurement of the apparent size and the actual size of objects 12.

The optical detection system 10 according to the invention also makes it possible to limit the number of pixels used on the image sensor (s) 26 to capture both an apparent size of the object 12, and therefore its three-dimensional position. , and a real size, also called physical size, of said object 12, the actual size being obtained by measuring interference fringes.

When in optional complement the first zone 32 is asymmetrical with respect to the center C of the arc of a circle, this makes it possible to have a different pattern according to whether the object 12 is located upstream or downstream of the focal plane object of the Thus, the position of the objects 12 on either side of the focal plane object of the focusing lens 24 is detectable.

Figures 5 and 6 illustrate a second embodiment of the invention for which the elements identical to those of the first embodiment, described above, are identified by identical references.

According to this second embodiment, the second zone 34 further comprises an additional lens 200, in addition to the focusing lens 24.

The operation of the optical detection system 10 according to this second embodiment is similar to that of the first embodiment described above, and is not described again.

The advantages of the optical detection system 10 according to this second embodiment include the advantages of the first embodiment described above, and are not described again.

According to this second embodiment, the fact that the second zone 34 further comprises the additional lens 200 makes it possible to further condense the light radiation corresponding to the center of the object 12, in order to further increase the signal-to-noise ratio.

It is thus conceivable that the optical detection system 10 according to the invention makes it possible to improve the signal-to-noise ratio of the acquired images, in order to reduce the measurement uncertainties.

Claims (12)

An optical object detection system (10) in a fluid, the system comprising: a light source configured to illuminate the fluid in an illumination direction; (X), and - a device (22) for acquiring radiation emitted by the illuminated fluid (14), the acquisition device (22) comprising: + a lens (24) for focusing the radiation, + a image sensor (26) configured to acquire at least one image of the emitted and focused radiation from the lens (24), and + a mask (28) having an opaque portion (30), a first region (32) passing the radiation and a second zone (34) for passing the radiation, the second zone (34) being distinct from the first zone (32), in which, in view in the direction of illumination (X), the first zone (32) is in the form of at least one strip (36) in an arc of a circle, and the second zone (34) is disposed inside a disk (40) whose b The outer die (42) is at least partially formed by an inner edge (37A) of the first zone (32). 2. System (10) according to claim 1, wherein the mask (28) is disposed between the lens (24) and the image sensor (s) (26). The system (10) of claim 2, wherein the mask (28) is disposed in the Fourier plane of the lens (24). 4. System (10) according to any one of the preceding claims, wherein the first zone (32) is asymmetrical with respect to the center (C) of the arc. 5. System (10) according to any one of the preceding claims, wherein the first zone (32) comprises a plurality of strips (36) arcuate. 6. System (10) according to claim 5, wherein the inner edges of said strips (36) are inscribed on the same inner circle, and the outer edges of said strips (36) are inscribed on the same outer circle, the outer circle being distinct from the inner circle. The system (10) of any preceding claim, wherein the second zone (34) further includes an additional lens (200). 8. System (10) according to any one of the preceding claims, wherein, in view in the direction of illumination (X), the second zone (34) is rectangular in shape. 9. System (10) according to any one of the preceding claims, wherein, in view in the direction of illumination (X), the second zone (34) is centered relative to the center (C) of the arc of circle. The system (10) of any preceding claim, wherein the acquisition device (22) is further configured to measure interference fringes from the acquired image and to determine a size of the objects (12) from the measured interference fringes. 11. A method of optical detection of objects (12) in a fluid (14), the method comprising: - illuminating the fluid (14) in a direction of illumination (X) via a light source (20), and the acquisition of a radiation emitted by the illuminated fluid (14) using an acquisition device (22) comprising a radiation focusing lens (24), an image sensor (s) ( 26) configured to acquire at least one image of the emitted radiation, and a mask (28) having an opaque portion (30), a first radiation passing region (32) and a second radiation passing region (34), the second zone (34) being distinct from the first zone (32), in which, in view in the direction of illumination (X), the first zone (32) is in the form of at least one strip (36) in an arc of a circle, and the second zone (34) is disposed inside a disk (40) whose outer edge (42) is at least partially formed by a rd interior (37A) of the first zone (32). The method of claim 11, wherein the method further comprises measuring interference fringes from the acquired image and determining a size of the objects (12) from the measured interference fringes.