JP2007298327A - Particle measuring device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure a particle size and a three-dimensional position, and to facilitate a work for calibrating a parameter. <P>SOLUTION: This particle measuring device has a constitution equipped with a laser light source 10 for emitting a laser beam L; beam splitters BS1, BS2 for branching the laser beam L into the first beam L1 (L1s), the second beam L2 and the third beam L3; the first optical means M1, M2, SL for irradiating a measuring object domain with the first beam L1s; the first electronic camera 20 for photographing the measuring object domain at a light receiving angle which is a scattering angle θ wherein each light intensity of zero-order reflected light and primary refracted light of particles hit by the first beam becomes equal relative to the first beam L1s with which the measuring object domain is irradiated; the second optical means M3, M4 for projecting the second beam L2 to the first electronic camera 20 as the first reference light; and the second electronic camera 21 forming a stereo angle ϕ to an optical axis of the first electronic camera 20, and projecting the third beam L3 as the second reference light. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention projects a laser light image irradiated with measurement target particles onto a digital electrical signal representing a captured image, that is, an electronic camera that generates image data, processes the image data, and generates particles based on the image represented by the image data. The present invention relates to a particle measuring apparatus that measures the three-dimensional velocity, particle size, etc. The particle measuring device is not intended to be limited to this, but can be used for measuring the three-dimensional velocity of particles and measuring the particle diameter by digital holography.

JP 2002-181515 A JP 2004-361291 A.

  In Patent Document 1, reflected and refracted light from a droplet hit by a sheet-like parallel laser beam is photographed from the side of the laser beam with a CCD camera out of focus where an interference fringe appears, and a droplet image region is obtained. In the particle size measurement for calculating the diameter of the droplet based on the number N of the interference fringes, the droplet image is flattened between the lens and the CCD element in a direction y perpendicular to the distribution direction of the interference fringes. The particle size measurement which cancels the overlap of the y direction of several droplet images is described by interposing the cylindrical lens. It also describes the calculation of a two-dimensional velocity in which droplets are photographed with a short-time difference to measure the particle size, and the amount of droplet movement in the two-dimensional direction within the time difference is measured and converted into a velocity.

  In Patent Document 2, a measurement target region irradiated with a radiation sheet-shaped laser beam is simultaneously photographed at two focal points (focused points) with two cameras arranged at a stereo angle, and one particle photographed with each camera. A measuring apparatus and method for identifying a pair of bright spots appearing as a pair at the same time and identifying the three-dimensional position of the same particle are described.

  According to the measuring apparatus of the cited document 1, the particle diameter can be measured, but the three-dimensional position cannot be obtained. Although the measuring apparatus of the cited document 2 can obtain the three-dimensional position of the particle, it obtains the bright spot pair image by the in-focus photographing, and thus cannot measure the particle size.

  The first object of the present invention is to provide a particle measuring apparatus capable of measuring a particle size and a three-dimensional position, and particle measurement with a simple work for calibration (camera calibration) of parameters used for three-dimensional position calculation. A second object is to provide an apparatus.

(1) Laser light source (10) that emits a laser beam (L);
A beam splitter (BS1, BS2) for splitting the laser beam (L) into a first beam (L1), a second beam (L2), and a third beam (L3);
First optical means (M1, M2, SL) for irradiating the measurement target region with the first beam (L1s);
Measurement target at the light receiving angle that is the scattering angle θ where the light intensity of the 0th-order reflected light and the 1st-order refracted light of the particle hit by the first beam is equivalent to the first beam (L1s) that irradiates the measurement target area A first electronic camera (20) for photographing the area;
Second optical means (M3, M4) for projecting the second beam (L2) to the first electronic camera (20) as first reference light; and
A second electronic camera (21) that forms a stereo angle φ with respect to the optical axis of the first electronic camera (20) and that projects the third beam (L3) as the second reference light;
The particle | grain measuring apparatus provided with (FIG. 1).

  In addition, in order to make an understanding easy, the code | symbol of the corresponding element or the corresponding matter of the Example which is shown in drawing and mentions later in a parenthesis was added as an example for reference. The same applies to the following.

  Since the region to be measured is photographed at a light receiving angle corresponding to the scattering angle θ where the light intensity of the first-order reflected light and the first-order refracted light of the particle hit by the first beam (L1s) is equal, the first electronic camera (20) The luminance of the bright spot pair (2 images) of one particle appearing on the shooting screen is equivalent, and the accuracy of identifying and extracting bright spot pairs is improved. By setting the imaging surface of the first electronic camera (20) to an out-of-focus position that generates interference fringes in the particle image, the interference fringes appearing in the particle image on the photographing screen of the first electronic camera (20) are clear. Thus, the accuracy of particle size measurement can be increased.

  The three-dimensional position of the particle can be calculated by applying the three-dimensional PTV to the same particle image on the photographing screens of the first and second electronic cameras (20, 21). Images are taken twice at short time intervals of dt, and the three-dimensional position before and after the particle dt is calculated on the basis of each time shooting screen, and the three-dimensional velocity can be calculated on the basis of both position differences and dt. Camera calibration (calibration of parameters for 3D position calculation) based on the image of the calibration plate captured by the first and second electronic cameras (20, 21) with the camera calibration plate in the measurement target area And calibration can be performed relatively easily.

  (2) The second optical means (M3, M4) projects the second beam (L2) to the first electronic camera (20) through the measurement target region; the third beam (L3) also projects the second electron through the measurement target region. The particle measuring apparatus according to (1) above (FIG. 1).

  That is, an in-line holographic imaging system using an in-line optical system. Conventionally, the range of the incident angle of the reference light for stereoscopic viewing with respect to the object light (particle image light) is very narrow, and it is very difficult to set the optical system. There is no. An image pickup element of an electronic camera, such as a CCD element, has a very low hologram spatial resolution and a very rough image reproduction in the depth direction. Therefore, the detection accuracy of the position in the depth direction (third axis) of the particles is poor. However, according to the present embodiment, the position of the particle in the third axial direction is obtained from a geometric relationship, and thus is highly accurate.

(3) Laser light source (10) that emits a laser beam (L);
A beam splitter (BS1, BS2) for splitting the laser beam (L) into a first beam (L1), a second beam (L2), and a third beam (L3);
First optical means (M1, SL) for irradiating the measurement target region with the first beam (L1s);
Measurement target at the light receiving angle that is the scattering angle θ where the light intensity of the 0th-order reflected light and the 1st-order refracted light of the particle hit by the first beam is equivalent to the first beam (L1s) that irradiates the measurement target area Electronic camera (M4,20) to capture the area;
Second optical means (M3, M4) for projecting the second beam (L2) to the electronic camera (20) as first reference light;
Third optical means (M6, BS3) for projecting a laser beam (L3) having a stereo angle φ to the laser beam of the scattering angle θ photographed by the electronic camera onto the electronic camera (20);
4th optical means (M5, M6, BS3) which projects a 3rd beam (L3) to the said electronic camera (20) as 2nd reference light;
Particle measuring device (Fig. 5)
The effect described in (1) above can be obtained similarly. In addition, since only one camera is required, the structure of the measurement system is simplified, and the amount of work for setting and adjusting the camera is small.

  (4) The second optical means (M3, M4) projects the second beam (L2) to the electronic camera (20) through the measurement target region; the fourth optical means (M5, M6, BS3) is also the third 4. The particle measuring apparatus (FIG. 5) according to claim 3, wherein the beam (L3) is projected onto the electronic camera (20) through a measurement target region.

  The effect described in the above (2) can be obtained similarly.

(5) Laser light source (10) that emits a laser beam (L);
A beam splitter (BS1, BS2) for splitting the laser beam (L) into a first beam (L1) and a second beam (L2);
First optical means (M1, SL) for irradiating the measurement target region with the first beam (L1s);
The light receiving angle (L2m) corresponding to the scattering angle θ at which the light intensity of the 0th order reflected light and the first order refracted light of the particle hit by the first beam is equivalent to the first beam (L1s) that irradiates the measurement target region. An electronic camera (M4,20) that captures the measurement area
Second optical means (M5, M7, BS4) for projecting the second beam (L2) to the electronic camera (20) as reference light passing through an optical path out of the measurement target region; and
Third optical means (M6, BS3) for projecting, onto the electronic camera (20), laser light (L3m) having a stereo angle φ with respect to the laser light having the scattering angle θ photographed by the electronic camera;
The particle | grain measuring apparatus provided with (FIG. 8).

  That is, it is an off axis type holographic imaging system. The effect described in (1) above can be obtained in the same manner, and since only one camera is required, the structure of the measurement system is simplified, and the amount of work for setting and adjusting the camera is small. In the case of the in-line type, since the reference light also passes through the measurement target area, the hologram of the droplet itself is photographed over the interference fringe image hologram screen, resulting in optical noise with respect to the interference fringe image hologram. However, according to this embodiment, since the reference light does not pass through the measurement target region, the optical noise does not occur. It becomes possible to improve the accuracy of the three-dimensional position measurement based on the interference fringe image hologram.

  (6) The image reproduction distance from the measurement target region to the electronic camera (20) of the two directions of laser light forming the stereo angle φ projected onto the electronic camera (20) is two directions on the same screen. The particle measurement apparatus according to (3), (4), or (5) (FIGS. 5 and 8), which has different values in order to make the image size of the same particle by the laser beam of different.

  Although it is possible to extract the same size image of the same particle by the laser beam in two directions by the correlation determination, according to this embodiment, the image of the same particle by the laser beam in the two directions can be separated and extracted according to the size. It is possible to increase the accuracy of separating the same particle image by the laser light in two directions on the same screen. In an embodiment in which image processing technology (software = program) automatically separates, first, the particle images are separated into two groups according to size to make two screens, and one screen is enlarged according to the size ratio due to the difference in image reproduction distance. Alternatively, after reducing and generating two screens of the same size, the same particle image is extracted (identified) by correlation determination processing. In an embodiment in which the same particle image is extracted by interaction between a computer (for example, an application program of a personal computer) and an operator, the same particle is marked by visual judgment of the operator on the display image on the display. Based on this, the computer generates two screens representing the same particle image by the laser light in two directions and each particle image by the laser light in each direction, and enlarges or reduces one screen according to the size ratio depending on the difference in image reproduction distance Then, after generating two screens of the same size, the same particle image is extracted (identified) by correlation determination processing. Also in this interactive processing, since there is a size difference between the same particle images by the two directions of laser light, visual judgment for extracting the same particle image is easy.

  (7) The imaging surface of the electronic camera (20, 21) is an out-of-focus position where an interference fringe is generated in the particle image; the particle measuring apparatus according to any one of (1) to (6) above .

  (8) A particle measuring method using the particle measuring apparatus according to (7), wherein the particle diameter is calculated based on the number of interference fringes in the particle image on the screen captured by the electronic camera (20, 21). .

  (9) Taking a particle image twice with a short time interval of dt with the electronic camera (20, 21), calculating the three-dimensional position of the particle based on the first photographed image, and taking the second photographed image A particle measuring method using the particle measuring apparatus according to any one of (1) to (7) above, wherein the three-dimensional position of the particle is calculated based on the two and the three-dimensional velocity of the particle is calculated based on the two calculated values.

  (10) Based on the number of interference fringes in the particle image on the first or second imaging screen by capturing the particle image twice at short time dt intervals with the electronic camera (20, 21). The particle diameter is calculated, the three-dimensional position of the particle is calculated based on the first captured image, the three-dimensional position of the particle is calculated based on the second captured image, and the particle size is calculated based on both calculated values. A particle measurement method using the particle measurement apparatus according to (7), wherein a three-dimensional velocity is calculated.

  (11) A calibration plate is placed at the position of the measurement target region and photographed. The parameters of the three-dimensional position calculation are calibrated from the image of the calibration plate on the photographing screen, and the calibrated parameters are used for the calculation of the three-dimensional position. The particle measuring method according to (9) or (10) above.

  According to this, if a calibration plate is placed at the position of the measurement target area and an image is taken, a calibration image can be obtained, so that the work for parameter calibration is simple.

  Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

  FIG. 1 shows the configuration of the first embodiment of the present invention. The laser apparatus 10 is a double pulse oscillation Nd: YAG laser (wavelength: 532 nm, output: 50 mJ / pulse, flash time: 5 ns), and two CCD cameras 20 and 21 (effective pixel number: 1360 (H) × Inline hologram is photographed at 1036 (V) pixles). First, the particle measurement light L1 is separated from the volume light L output from the laser device 10 by the first beam splitter BS1, and the particle measurement light L1 is converted into mirrors M1, M2 and a sheet-shaped light conversion lens unit SL. Thus, in the present embodiment, the sheet-like light L1s is irradiated onto the measurement target region where water droplets are sprayed by the nozzle NZ. The first reference light L2 is separated from the volume light L by the second beam splitter BS1, and the remaining volume light is used as the second reference light L3. The second reference light L2 is reflected by the mirrors M3 and M4 and applied to the measurement target region.

  In the measurement target region, the optical axis of the sheet-like light L1s, the first reference light L2 and the third reference light L3 cross each other, and the first reference light L2 passes through the measurement target region on the optical path of the first camera 20. There is an optical axis, and the optical axis of the second camera 21 is on the optical path of the second reference light L3 passing through the measurement target region.

  In the first embodiment, the optical paths of the laser beams L2 and L3 incident on the cameras 20 and 21 are three-dimensional (three-dimensional) arrangement. The first plane including the optical axis of the sheet-like light L1s and the optical axis of the first camera 20 that forms an angle θ with respect thereto, and similarly the optical axis of the sheet-like light L1s and the angle θ with respect thereto. The second plane including the optical axis of the second camera 21 formed is a different non-parallel surface and intersects at the position of the optical axis of the sheet-like light L1s.

  FIG. 2 schematically shows a projection optical path of the 0th-order reflected light and the first-order refracted light by the water droplet Droplet impinged on the sheet-like light L1s in the measurement target region onto the imaging surface of the camera 20. When the light-transmitting spherical particles are irradiated with coherent light such as a laser, 0th-order reflected light reflected on the particle surface and 1st-order to nth-order refracted light that repeatedly scatters within the particle are generated. Among these, in the forward scattering with a small scattering angle, the 0th-order reflected light and the first-order refracted light that is refracted twice inside the particle are dominant.

  The stereo angle φ between the cameras 20 and 21 is 90 ° in consideration of the convenience of digital reconstruction. When the measurement target particle is a water droplet, the relative refractive index n of water is 1.33. Therefore, as shown in FIG. 3, the light intensity of the surface reflected light (0th order reflected light) and the first order refracted light has a scattering angle of 70. Therefore, the light receiving angles θ of the two cameras 20 and 21 are set to 70 °. When the focus of the camera lens 20L is on the light receiving surface of a CCD element that is an image pickup device of the camera 20, a projected image (bright spot) by zero-order reflected light and a projected image (bright spot) by primary refracted light appear on the light receiving surface. . These bright spots are generally called Glare Points. FIG. 2 shows a bright spot pair 20Gf. However, if the focus of the camera lens 20L is deviated from the light receiving surface of the CCD element, a particle image 20Sf in which interference fringes appear inside is obtained. In both of the bright spot pair 20Gf and the interference fringe particle image 20Sf, the light reception angle θ is most clearly defined by setting the light receiving angle θ to an angle at which the intensities of the 0th-order reflected light and the first-order refracted light are equal (70 ° in the case of water). become.

  In both the first example and the second and third examples described later, the measurement target region is irradiated with the sheet-like light L1s as the particle measurement light. Thereby, there are few imaging | photography particles and there are few many particle images used as noise. Therefore, it is possible to increase the accuracy of sorting or extracting the particle image. However, it is not always necessary to use sheet-like light. Instead of the sheet-like light L1s, the particle measuring light L1 having a cross section capable of simultaneously irradiating a small number of one or more particles can be used. Further, if the noise separation function or the particle image extraction function is high in the image data processing, non-sheet-like particle measurement light having a larger cross-sectional area can be used.

  By observing the number N of fringes in the interference fringe particle image 20Sf, the particle diameter Dp can be calculated as follows.

Here, d _p is the particle size, N is the fringe order of the interference fringes, λ is the wavelength, θ is the light receiving angle of the camera, α is the converging angle, and n is the relative refractive index between the particles and the surrounding medium. The light receiving angle θ of the camera is an angle formed by the laser traveling direction and the optical axis of the camera.

Since the wavelength λ and the angle θ are parameters determined by the optical system, if the refractive index n is known, the particle size d _p can be obtained from the number N of fringes of the interference fringe image, and the absolute measurement of the particle size is possible. . When the 0th-order reflected light and the first-order refracted light have the same intensity, the interference fringe has the largest amplitude and a good interference image. As shown in FIG. 3, the intensity ratio between the 0th-order reflected light and the first-order refracted light varies depending on the scattering angle θ, and the angle θ at which the light intensity becomes equal depends on the polarization of the light source and the refractive index n of the target particle. Change.

  In the three-dimensional velocity measurement, a three-dimensional PTV is applied to image reconstruction of a hologram pattern photographed by viewing the measurement target region in stereo with the two cameras 20 and 21. PTV (particle tracking method) is a method for obtaining the movement amount of each particle in the object space by associating the same particle on a fluid image between two consecutive times.

  Refer to FIG. 1 again. The sequencer 23 transmits a laser emission instruction signal and a photographing instruction signal to the laser device 10 and the CCD cameras 20 and 21 in response to a start instruction from the personal computer (PC) 22.

  A particle measurement application program (referred to as “particle measurement”) is installed in the personal computer 22, and the main menu is displayed on a display connected to the personal computer 22 when the operator activates the “particle measurement”. . In the main menu, sub-menu items “camera calibration”, “parameter adjustment”, and “measurement” are displayed. When the operator clicks “camera calibration”, an input screen of “camera calibration” is displayed on the display. By arranging a calibration plate in the measurement target region immediately below the nozzle NZ shown in FIG. 1, specifying “two-dimensional calibration” and performing execution input, the personal computer 22 performs one shooting, and each camera 20, When the photographing screen (image data) 21 is sent to the personal computer 22, it is displayed as a thumbnail on the display. Thereafter, each imaging screen is displayed on the display in an interactive manner with the personal computer 22 (“particle measurement”), and geometric parameters used in the two-dimensional image processing are set. When “3D calibration” is designated and execution is input, the personal computer 22 performs imaging for a short time dt interval twice, and calculates the 3D velocity calculation 3DVM (FIG. 4) described later. The construction S31 to the three-dimensional position calculation S36 are sequentially performed, and the parameters are adjusted by the operator's intervention in an interactive manner at the stage of the parameter reference calculation. The parameter values determined in this way are used for particle measurement until the next calibration.

  When “parameter adjustment” on the main menu is designated, the personal computer 22 displays the parameter values set in “two-dimensional calibration” and “three-dimensional calibration” on the display. Can be adjusted or changed.

  When the operator designates “Measurement” on the main menu, the explanation of the procedure of “Measurement” is displayed. When the execution is instructed, the personal computer 22 (“Particle Measurement” application thereof) executes particle measurement.

  FIG. 4 shows an outline of the particle measurement. In this embodiment, the three-dimensional PTV algorithm is composed of three steps: particle detection from an image, particle tracking between two times, and three-dimensional reconstruction using a geometric camera model. Then, the personal computer 22 instructs the sequencer 23 to perform two shootings at short time intervals of dt, and in response, the sequencer 23 instructs the laser device 10 and the cameras 20 and 21 to perform the first shooting. The second shooting is instructed after dt has elapsed. Then, the cameras 20 and 21 are sequentially instructed to transfer images. The cameras 20 and 21 store the first shot image and the second shot image in a storage medium, and transfer the first shot image and the second shot image to the personal computer 22 in response to an image transfer instruction. . The personal computer 22 stores them in the internal memory (step S1). In the following, the word “step” is omitted in parentheses, and step no. Write only the sign.

  Here, P11 is given to the first shot image (screen) of the first camera 20, P12 and an identification code are given to the second shot image (screen), and the first shot image (screen) of the second camera 21 is given. P21 and the identification code are given to P2 and the second captured image (screen).

  The personal computer 22 corrects contrast and removes noise by image processing (S2), and then extracts a particle image (S3). In “particle size calculation” (PDM), the number N of interference fringes of one particle image on the screen P11 is calculated, the particle diameter Dp is calculated based on the equation (1), and the P11 screen is displayed on the display. Then, the particle image is indicated by a quadrangular frame, and the calculated interference fringe number N, particle diameter Dp, and parameter value of the equation (1) are displayed on the display. Here, when the operator clicks the “Confirm” button on the display screen, the personal computer 22 adds the interference fringe number N, the particle diameter Dp, and the parameters of the equation (1) to the measurement data table (one memory area) set in the internal memory. Stores a value. The operator designates a specific area on P11 instead of “confirmation”, inputs the number of fringes Np in the particle image therein, or changes the number N of interference fringes being displayed to Np, and / or When the parameter value being displayed is changed and the “re-execute button” is clicked, the personal computer 22 recalculates the particle diameter Dp based on the input value and the expression (1) and displays it on the display together with the parameter value. Then, “calculation of three-dimensional velocity” (3DVM) is executed.

  In “3D velocity calculation” (3DVM), first, a bright spot pair image is reconstructed from the interference fringe image by digital holography (S31), and the particle mask correlation method is applied to the reconstructed screen to obtain a bright spot. A point pair image is detected (S32). This is performed for the photographing screens P11, P12, P21 and P22. Next, for each particle detected on the screens P11 and P12 at the first time (first shooting), the bright spot from the exploration area set on the screens P21 and P22 at the second time (second shooting). Corresponding particles are determined based on particle information such as the image interval (S33, S34).

  Next, using the three-dimensional position calculation parameters, the three-dimensional position (start position) of the first-shot particle and the three-dimensional position (end point position) of the second-shot particle are calculated (S35, S36). . In this case, the projection function between the image plane and the object space is calculated from the camera calibration data (parameters set by calibration), and each point on the image is determined based on the camera viewpoint obtained and the position of the particle on the image. A line of sight is determined from the particles in the object space. If the particles are the same on the stereo image, the left and right lines of sight should intersect, so each particle of the two lines of sight where the interval between the lines of sight is minimized is set as the same particle, and the three-dimensional position of the particle is calculated.

  Next, the calculated three-dimensional position (start point position, end point position) and time interval dt are given to the three-dimensional speed calculation formula to calculate the three-dimensional speed and display it on the display, and add it to the measurement data table (S37). Then, an input screen for measurement value treatment is displayed on the display. If there is a registration instruction, it is registered in the designated registration destination, and if there is a print instruction, it is printed out by a printer (not shown) (S4).

  FIG. 5 shows the configuration of the second embodiment of the present invention. In the second embodiment, a digital holographic image is obtained by a single CCD camera 20. The laser beam emitted from the laser device 10 is separated into the particle measurement light L1 and the reference light by the beam splitter BS1, and the reference light is further separated into the first reference light L2 and the second reference light L3 by the beam splitter BS2. The first and second reference lights L2 and L3 are orthogonal to each other in the measurement target region and intersect the optical axis of the sheet-like converted light L1s of the particle measurement light L1. The first and second reference beams L2 and L3 that have passed through the measurement target region are combined by the beam splitter BS3 and enter the CCD camera 20. The CCD camera 20 captures light from two directions at the same time.

  In the second embodiment, the optical axis of the sheet-like light L1s and the optical paths of the laser lights L2 and L3 incident on the camera 20 are arranged in the same plane (two-dimensional). That is, the optical axis of the sheet-like light L1s, the laser light L2 incident on the mirror M4 at an angle θ with respect to the optical axis, and the laser light L3 incident on the mirror M6 are on the same plane.

  The first reference light L2 divided by the beam splitter BS2 is at an angle θ with respect to the optical axis of the sheet light L1s. The sheet light L1s, which is particle measurement light, illuminates the measurement target particle and generates two bright spots on the particle surface. The brightness of these bright spots depends on the scattering angle θ. In the case of a water droplet (incident light wavelength: 532 mm, relative refractive index: 1.33), the brightness of these bright spots is equal at about 70 °. Therefore, θ = 70 ° is set. The stereo angle φ is 90 °. Since the optical axis of the sheet-like light L1s and the optical paths of the laser beams L2 and L3 are arranged on the same plane and the stereo angle φ is 90 °, the optical axis of the second reference light L3 passing through the measurement target region is It is 20 °. Therefore, in photographing in the direction of the second reference light L3, the primary refracted light is dominant, and one bright spot, that is, a bright spot of the primary refracted light is observed.

  The first and second reference lights L2 and L3 correspond to object light of the inline holographic optical system. Those lights are incident as parallel light on the bright spots or bright spot pairs and the particles generated by the sheet-like light hitting the particles, thereby generating a hologram. L2 has the effect of generating bright spot pairs and holograms from particles, and L3 has the effect of generating bright spot and droplet holograms. In general digital holography, a hologram is directly recorded without going through a lens for enlarging or reducing an object, so that the observation area is determined by the size of the CCD element used. In the second embodiment, the CCD camera 20 is equipped with a lens for enlarging or reducing the subject and a mechanism for observing a local hologram, so that the observation area can be easily changed with the lens. .

  In the second embodiment, since the holograms generated in two directions are recorded by one camera 20, the two-direction holograms are photographed on the same screen as shown in FIG. In order to facilitate the separation of holograms generated in two directions, the optical path distances of the first and second reference beams L2 and L3 from the measurement target region to the camera 20 are differentiated. The distance difference reflects the image reproduction distance, and the resulting hologram has a size difference as shown in FIG. 6, so that the particle images in each direction can be easily separated.

  The fringe order of the interference fringe image generated from the bright spot pair is proportional to the particle size. In the hologram obtained by this method, since the lens for enlarging or reducing is used, the interference fringes generated from the bright spot pair are photographed simultaneously due to optical properties. Therefore, the particle size is obtained from the analysis of the fringe image in the same manner as the existing method. Alternatively, a reproduction image of the bright spot pair obtained from the hologram is extracted by appropriate image processing, and the image is further reproduced on the defocused surface to obtain an interference fringe image. Therefore, the diameter can be evaluated by the above method.

  The three-dimensional velocity measurement performs processing based on 3D-PTV and specifies the three-dimensional position of the object. Therefore, it is necessary to derive a geometric relationship between the object and the image plane. Generally, a method called a calibration plate is used in which a plate on which dots or grids with known intervals and positions are drawn is arranged in a measurement region, and a geometrical relationship is derived from an image of the calibration plate. In the particle measuring apparatus of the second embodiment, the camera calibration is performed in the same procedure, but the obtained image of the calibration plate is a hologram of the calibration plate. Therefore, in the particle measuring apparatus of the second embodiment, a glass calibration plate that transmits object light is used in order to realize similar camera calibration. The glass plate on which the grid is drawn is arranged at a position inclined by 45 ° with respect to L2 and L3, and the glass plate is moved in the depth direction by a precision stage, and a hologram is recorded with an appropriate cross section. Image reproduction is performed from the recorded hologram, and camera calibration is performed from the obtained calibration plate image.

  FIG. 7 shows an outline of particle measurement according to the second embodiment. This represents the interference fringes 20sf (FIG. 2) in the particle photograph image of the first reference light L2 path by shifting the focus with respect to the imaging surface of the CCD element of the CCD camera 20. When execution of “measurement” is input, the personal computer 22 instructs the sequencer 23 to perform two imaging at short time dt intervals, and in response to this, the sequencer 23 performs the first imaging with the laser device 10 and the camera. 20 is instructed, and after the elapse of dt, the second shooting is instructed. Then, the camera 20 is instructed to transfer an image. The camera 20 stores the first shot image and the second shot image in a storage medium, and transfers the first shot image and the second shot image to the personal computer 22 in response to an image transfer instruction. The personal computer 22 stores them in the internal memory (step S1a).

  Here, P1 is assigned to the first captured image (screen) of the camera 20, and P2 and identification code are assigned to the second captured image (screen). The personal computer 22 corrects contrast and removes noise by image processing (S2), and then extracts a particle image (S3). Then, the particle image of the first reference light L2 path and the particle image of the second reference light L3 path are separated from the screen P1 and corrected to the same size as the separate screens P11 and P12. Similarly, the screen P2 Accordingly, the particle image of the first reference light L2 path and the particle image of the second reference light L3 path are separated and corrected to the same size to obtain different screens P21 and P22 (S1b).

  In “particle size calculation” (PDM), the number N of interference fringes of one particle image on the screen P11 is calculated, the particle diameter Dp is calculated based on the equation (1), and the P11 screen is displayed on the display. Then, the particle image is indicated by a quadrangular frame, and the calculated interference fringe number N, particle diameter Dp, and parameter value of the equation (1) are displayed on the display. Here, when the operator clicks the “Confirm” button on the display screen, the personal computer 22 adds the interference fringe number N, the particle diameter Dp, and the parameters of the equation (1) to the measurement data table (one memory area) set in the internal memory. Stores a value. The operator designates a specific area on P11 instead of “confirmation”, inputs the number of fringes Np in the particle image therein, or changes the number N of interference fringes being displayed to Np, and / or When the parameter value being displayed is changed and the “re-execute button” is clicked, the personal computer 22 recalculates the particle diameter Dp based on the input value and the expression (1) and displays it on the display together with the parameter value. Then, “calculation of three-dimensional velocity” (3DVM) is executed.

  In “3D velocity calculation” (3DVM), first, a bright spot image of the first-order refracted light is reconstructed from the interference fringe images on the P11 and P12 screens by digital holography (S31a), and the reconstructed screen is displayed. On the other hand, the bright spot image of the first-order refracted light is detected by applying the particle mask correlation method (S32a). In the photographing screens P21 and P22, since the light receiving angle of L3 is not 70 ° but 20 degrees, there is originally a bright spot image of the first-order refracted light. Next, for each particle detected on the screens P11 and P12 at the first time (first shooting), the bright spot from the exploration area set on the screens P21 and P22 at the second time (second shooting). Corresponding particles are determined based on the particle information of the image (S33, S34). The subsequent processing is the same as that of the first embodiment shown in FIG.

  FIG. 8 shows the configuration of the third embodiment of the present invention. In the third embodiment, the inline first and second reference beams L2 and L3 of the second embodiment are omitted, and the off-axis reference beam L2 is converted into the two-direction particle measurement beam L2m and the beam splitter M7. This is combined with L3m so as to enter the camera 20. Similar to the second embodiment, the particle measurement light L2m includes interference fringe information (20sf: FIG. 2) because θ = 70 ° with respect to the optical axis of the sheet-like light L1s. In the third embodiment, similarly to the second embodiment, the optical axis of the sheet-like light L1s, the laser light L2 incident on the mirror M4 at an angle θ with respect to the optical axis, and the laser light L3 incident on the mirror M6. Is on the same plane. The stereo angle φ is 90 °. Since the particle measurement light L3m is at an angle of 20 ° with respect to the optical axis of the sheet-like light L1s, the first-order refracted light of the particles is dominant and there is little interference fringe information. The stereo angle φ is 90 °.

  The contents of particle measurement according to the third embodiment are the same as those of the second embodiment shown in FIG. In the third embodiment, since the reference light L2 does not pass through the measurement target region, particle information (noise for the camera 20) is not included. Thereby, a particle image with less noise than the first and second embodiments can be obtained, and particle extraction can be easily performed.

It is a block diagram which shows the apparatus structure of 1st Example of this invention. FIG. 2 is a longitudinal sectional view schematically showing a laser light path between a particle Droplet in a measurement target region immediately below a nozzle NZ shown in FIG. 1 and an imaging surface of a camera 20. It is a graph which shows the relationship between scattering angle | corner (theta) which image | photographs a water droplet particle | grain, 0th-order reflected light brightness | luminance and 1st-order refraction light brightness | luminance of a water droplet particle | grain. It is a flowchart which shows the process outline | summary of the particle | grain measurement performed with the particle | grain measurement application installed in the personal computer 22 shown in FIG. It is a block diagram which shows the apparatus structure of 2nd Example of this invention. 6 is a reproduction of a photograph showing an example of a particle image taken by the CCD camera 20 shown in FIG. It is a flowchart which shows the process outline | summary of the particle | grain measurement performed with the particle | grain measurement application installed in the personal computer 22 shown in FIG. It is a block diagram which shows the apparatus structure of 3rd Example of this invention.

Explanation of symbols

10: laser device 20, 21: CCD camera 22: personal computer 23: sequencer B1 to B4: beam splitter M1 to M7: mirror SL: conversion lens NZ: water droplet particle spray nozzle

Claims (11)

A laser light source for emitting a laser beam;
A beam splitter for branching the laser beam into a first beam, a second beam, and a third beam;
First optical means for irradiating the measurement target region with the first beam;
The measurement target area is photographed at a light receiving angle corresponding to a scattering angle θ in which the light intensity of the 0th-order reflected light and the first-order refracted light of the particle hit by the first beam is equivalent to the first beam that irradiates the measurement target area. A first electronic camera;
Second optical means for projecting the second beam onto the first electronic camera as first reference light;
A second electronic camera having a stereo angle φ with respect to the optical axis of the first electronic camera and a third beam projected as second reference light;
A particle measuring apparatus comprising:   2. The particle measuring apparatus according to claim 1, wherein the second optical means projects the second beam through the measurement target region to the first electronic camera; the third beam is also projected through the measurement target region to the second electronic camera; A laser light source for emitting a laser beam;
A beam splitter for branching the laser beam into a first beam, a second beam, and a third beam;
First optical means for irradiating the measurement target region with the first beam;
The measurement target area is photographed at a light receiving angle corresponding to a scattering angle θ in which the light intensity of the 0th-order reflected light and the first-order refracted light of the particle hit by the first beam is equivalent to the first beam that irradiates the measurement target area. Electronic camera to do;
Second optical means for projecting the second beam onto the electronic camera as first reference light;
Third optical means for projecting, onto the electronic camera, reflected laser light having a stereo angle φ with respect to the laser light having the scattering angle θ photographed by the electronic camera;
Fourth optical means for projecting the third beam to the electronic camera as second reference light;
A particle measuring apparatus comprising:   4. The particle measurement according to claim 3, wherein the second optical unit projects the second beam to the electronic camera through the measurement target region; and the fourth optical unit also projects the third beam to the electronic camera through the measurement target region. apparatus. A laser light source for emitting a laser beam;
A beam splitter for splitting the laser beam into a first beam and a second beam;
First optical means for irradiating the measurement target region with the first beam;
The measurement target area is photographed at a light receiving angle corresponding to a scattering angle θ in which the light intensity of the 0th-order reflected light and the first-order refracted light of the particle hit by the first beam is equivalent to the first beam that irradiates the measurement target area. Electronic camera to do;
Second optical means for projecting the second beam onto the electronic camera as reference light that passes through an optical path out of the measurement target region; and
Third optical means for projecting a reflected laser beam having a stereo angle φ with respect to the laser beam having the scattering angle θ photographed by the electronic camera to the electronic camera;
A particle measuring apparatus comprising:   The image reproduction distance from the measurement target region to the electronic camera of the two-direction laser light having a stereo angle φ projected on the electronic camera is the same particle image by the two-direction laser light on the same screen. 6. The particle measuring device according to claim 3, 4 or 5, which has different values in order to make the sizes different.   The particle measuring apparatus according to claim 1, wherein the imaging plane of the electronic camera is an out-of-focus position where an interference fringe is generated in the particle image.   The particle measuring method using the particle measuring apparatus according to claim 7, wherein the particle diameter is calculated based on the number of interference fringes in a particle image on a screen captured by the electronic camera.   Taking a particle image twice at a short time interval dt with the electronic camera, calculating the three-dimensional position of the particle based on the first photographed image, and calculating the three-dimensional position of the particle based on the second photographed image The particle measurement method using the particle measurement apparatus according to claim 1, wherein the three-dimensional velocity of the particles is calculated based on both calculated values.   The particle size is calculated based on the number of interference fringes in the particle image on the first or second imaging screen by taking a particle image twice with a short time dt interval with the electronic camera, and the first Calculating the three-dimensional position of the particle based on the captured image of the second time, calculating the three-dimensional position of the particle based on the second captured image, and calculating the three-dimensional velocity of the particle based on both calculated values. Item 8. A particle measurement method using the particle measurement apparatus according to Item 7. 6. A photograph is taken by placing a calibration plate at a position of the measurement target region, a parameter for calculating a three-dimensional position is calibrated from an image of the calibration plate on a photographing screen, and the calibrated parameter is used for calculation of the three-dimensional position. The particle measurement method according to 9 or 10.

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