JP2002181515A - Measuring method and device for diameters and distributions of microbubble and microdrop - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a diameter of a defocusing image obtained by defocusing and a number of an interference fringe in the defocusing image to expand the measurement method for a diameter and space distribution for a micro drop to the measuring method for a microbubble and a microdrop, and enable application of the measurement method to a case that space distribution concentration of the micorbubble and the microdrop is high. SOLUTION: A sheet-like and parallel laser beam 2 irradiates to liquid space that a microbubble 10 is floated. The microbubble 10 irradiated by the laser beam 2 is taken by defocusing at a defocusing face 8 from a side face direction with an angle θ to a running direction of the laser beam 2 through an object lens 6. The number of the interference fringe 9 in a defocusing image 10" corresponding to the microbubbles 10 and thereafter the diameter of the microbubble 10 is determined in accordance with an equation (4).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the diameter and distribution of microdroplets and bubbles, and more particularly to a method of measuring the diameter and distribution of microdroplets and bubbles distributed in space by an interference method. And the device.

[0002]

2. Description of the Related Art For example, there is a need for a method of accurately measuring the distribution and diameter of minute droplets of fuel injected into an engine. Similarly, for example, there is a need for a method of accurately measuring the distribution and diameter of fine droplets sprayed in the air to design a nozzle used in the spray drying method. Further, there is a need for a method of accurately measuring the diameter and distribution of bubbles and the change thereof in studies of the absorption of CO ₂ in air bubbles into the sea and the behavior of bubbles in beer and wine.

As described above, there is a strong demand in various fields for a method and an apparatus for accurately measuring the diameter and distribution of fine droplets and bubbles while they remain in the space.

[0004] Conventionally, there has been a method of taking a photograph of a minute droplet distributed in space and analyzing the photograph. There was a problem in the measurement accuracy due to blurred pictures. There is also a problem that real-time processing cannot be performed. CC the photo
A method of photographing with a D camera is also known, but also has a problem of measurement accuracy, a problem that real-time processing cannot be performed, and the like. Furthermore, there is a problem that analysis takes time. In addition, a holographic method and a method of photographing with a CCD camera are known, but similarly, there is a problem of measurement accuracy, a problem that real-time processing cannot be performed, and a problem that analysis takes time. Furthermore, in order to obtain real-time performance, a method of directly photographing the shadow of a minute droplet with a CCD camera is also known, but there is a problem that measurement of small particles is difficult due to the influence of diffraction. .
In addition, there is a problem that it is difficult to measure the diameter of the minute droplet at a limited three-dimensional position.

Conventionally, there has been known a method of simultaneously measuring a plurality of particles by specifying a position in a three-dimensional space by a method called LDV, PDA, PDPA or the like. The method intersects two laser beams in the air to form spatial interference fringes, observes the same scattered light from droplets traversing the interference fringes from different points, and observes the same measurement volume. This is a method of measuring the diameter of a microdroplet from the phase difference of a measurement signal. In this case, since it is a method of measuring the diameter of each particle passing through the interference fringe region, there is a problem that the measurement in the surrounding space outside the region cannot be performed simultaneously. Also, the measurement accuracy was not sufficient.

In such a situation, when a measurement space is irradiated with a sheet-shaped parallel laser beam, and micro-droplets hit by the laser beam are photographed out of focus, an out-of-focus image corresponding to each micro-droplet is obtained. There is a certain relationship between the number of interference fringes present in the out-of-focus image and the diameter of the microdroplets, and the diameter of the microdroplets is determined by measuring the number of the interference fringes. Has been proposed (SAE Paper no. 950457, 960), and the spatial distribution of microdroplets can also be measured.
830).

[0007]

In the above method of measuring the number of interference fringes in an out-of-focus image to measure the diameter of a minute droplet and its spatial distribution, the application field is limited to the minute droplet. And have not been applied to microbubbles.

[0008] In addition, in the method, especially when the distribution density of the minute liquid droplets is high spatially, the defocused image itself occupies a large circular area, so that the images overlap each other. There has been a problem that it is difficult to separate the droplets and measure their diameters.

The present invention has been made in view of such problems of the prior art, and has as its object to measure the diameter of an out-of-focus image obtained by defocus and the number of interference fringes therein. Extending the method of measuring the diameter and spatial distribution of microdroplets to the method of measuring the diameter and spatial distribution of microbubbles, and finding the position, diameter, and velocity of microdroplets and microbubbles from out-of-focus image analysis A method and apparatus are provided.

[0010]

A method for measuring the diameter and distribution of microbubbles according to the present invention, which achieves the above objects, comprises irradiating a space in which microbubbles or microdroplets float with a sheet-shaped parallel laser beam. The microbubbles or microdroplets hit by the laser beam are parallel to a plane including the traveling direction of the laser beam and the optical axis of the imaging optical system from a side surface direction forming a predetermined angle with respect to the traveling direction of the laser beam. In the direction that is out of focus in the direction, and on the imaging surface that is almost in focus in the direction perpendicular to the plane, a linear out-of-focus image corresponding to a microbubble or a microdroplet is taken, extending in the plane direction. , By finding the center of that defocused image,
This is a method characterized by finding the center position of a microbubble or a microdroplet.

In this case, assuming that the length of the linear defocused image is L, the center position is averaged over a range of a distance L / 2 before and after a specific position along the longitudinal direction and the center position is determined. And it is desirable to obtain the moving average value from the peak position obtained by sequentially moving the specific position.

Another method of measuring the diameter and distribution of microbubbles and microdroplets according to the present invention is to irradiate a space in which microbubbles or microdroplets float with a sheet-shaped parallel laser beam, and apply the laser beam to the space. The microbubbles or microdroplets hit by the laser beam are focused in a direction parallel to a plane including the traveling direction of the laser beam and the optical axis of the imaging optical system from a side direction forming a predetermined angle with respect to the traveling direction of the laser beam. On the imaging surface, which is out of focus and substantially in focus in a direction perpendicular to the plane, a linear out-of-focus image corresponding to a microbubble or a microdroplet is taken extending in the plane direction, and the defocus is taken. The image is Fourier-transformed to determine the frequency, and the obtained frequency is multiplied by the length of the defocused image to determine the number of interference fringes in the defocused image. A method characterized by determining the diameter of the microdroplets.

In this case, it is desirable that a discrete Fourier transform is performed as a Fourier transform, and a function fitting is performed on the obtained discrete frequency distribution to obtain the diameter of the microbubble or the microdroplet.

Another method for measuring the diameter and distribution of microbubbles and microdroplets according to the present invention is to irradiate a sheet-shaped parallel laser beam to a space in which microbubbles or microdroplets float, and apply the laser beam to the space. From the side direction forming a predetermined angle with respect to the laser beam traveling direction, the microbubbles or microdroplets hit by the beam are in a direction parallel to a plane including the traveling direction of the laser beam and the optical axis of the imaging optical system. A defocused state, and a linear defocused image corresponding to a microbubble or a microdroplet extending in the plane direction on a photographing surface which is substantially in a focus state in a direction perpendicular to the plane, is formed by a minute time interval Δt. And the amount of movement of each linear defocused image by calculating the cross-correlation between the two photographic screens in units of the linear defocused image in the two obtained photographic screens the Δs _i asked , The velocity u _i of each microbubble or microdroplets is a method which is characterized in that determined by the following relationship.

U _i = Δs _i / Δt (6) In this case, when calculating the cross-correlation between the two captured images, the high-frequency component corresponding to the interference fringe in the linear defocused image It is desirable to calculate the cross-correlation by removing.

Another method for measuring the diameter and distribution of microbubbles and microdroplets according to the present invention is to irradiate a space in which microbubbles or microdroplets float with a sheet-shaped parallel laser beam, The microbubbles or microdroplets hit by the laser beam are focused in a direction parallel to a plane including the traveling direction of the laser beam and the optical axis of the imaging optical system from a side direction forming a predetermined angle with respect to the traveling direction of the laser beam. On the imaging surface, which is out of focus and substantially in focus in a direction perpendicular to the plane, a linear out-of-focus image corresponding to a microbubble or a microdroplet is taken extending in the plane direction, and the defocus is taken. By finding the center of the image, the center position of the microbubble or microdroplet is obtained, the out-of-focus image is Fourier transformed to obtain a frequency, and the obtained frequency is multiplied by the length of the out-of-focus image. Thus, the number of interference fringes in the out-of-focus image is obtained, the diameter of a microbubble or a microdroplet is obtained based on the number of the interference fringes, and two out-of-focus images are taken at a short time interval Δt. Then, the amount of movement Δs _i of each linear defocused image is obtained by calculating the cross-correlation between the two captured images in a unit of a linear defocused image in the obtained two captured images. the velocity u _i of the microbubbles or microdroplets is a method which is characterized in that determined by the following relationship.

U _i = Δs _i / Δt (6) The measuring device of the present invention for measuring the diameter and distribution of microbubbles and microdroplets has a sheet-like parallel shape in a space where microbubbles or microdroplets float. A laser beam irradiating means for irradiating a laser beam, a microbubble or a microdroplet hit by the laser beam irradiated by the laser beam irradiating means from the side direction forming a predetermined angle with respect to the laser beam traveling direction, An out-of-focus state occurs in a direction parallel to a plane including the traveling direction of the laser beam and the optical axis of the imaging optical system, and the imaging plane becomes substantially in-focus in a direction perpendicular to the plane. Means for photographing a linear defocused image corresponding to a microbubble or a microdroplet, and determining the center of the defocused image to obtain the center position of the microbubble or the microdroplet And a center position measuring means for calculating the frequency of the defocused image by Fourier transform to obtain a frequency, and multiplying the obtained frequency by the length of the defocused image to obtain the number of interference fringes in the defocused image. Diameter measuring means for determining the diameter of a microbubble or a microdroplet based on the number of stripes, and two out-of-focus images taken at a short time interval Δt, and a linear shape in the obtained two photographic images determine the movement amount Delta] s _i of each linear out-of-focus image by between the two photographed screen out of focus image units of calculating the cross correlation, the velocity u _i of each microbubble or microdroplets following relationship And speed measurement means determined by the following.

U _i = Δs _i / Δt (6) In the present invention, out of focus in a direction parallel to a plane including the traveling direction of the sheet-like parallel laser beam and the optical axis of the imaging optical system. State, and the out-of-focus image corresponding to each microbubble or microdroplet is compressed in the direction perpendicular to the plane because the out-of-focus image is captured on the imaging surface that is substantially in focus in the direction perpendicular to the plane. Since the obtained one-dimensional image is obtained, even if the distribution density of the microbubbles and the microdroplets is high spatially, the defocused images can be separated from each other, and the number of interference fringes in each defocused image can be improved. Can be easily separated and counted, and it is easy to identify the center position of each out-of-focus image and to see the distribution state of the microbubbles or microdroplets. Position, diameter, The velocity distribution can be simultaneously measured with high accuracy.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle and embodiments of a method and apparatus for measuring the diameter and distribution of microdroplets and bubbles according to the present invention will be described below.

First, in order to facilitate understanding, the principle of a known method of measuring the number of interference fringes in an out-of-focus image to measure the diameter and spatial distribution of minute droplets will be described.

First, as shown in FIG. 3, when a plane wave 2 is incident on a microdroplet 1 having a refractive index of n floating in the air, an incident angle (hereinafter, both incident angle and refraction angle are measured from a tangent plane of the interface). angle to.) and when the phase difference between them and one reflected beam 3 is a parallel incident angle tau ₀ and tau ₁ twice refracted light 4 is 2mπ 2 (m + 1) may become [pi (m is When an angle difference Δθ of (integer) is obtained, Δθ = (2λ / D) [n sin (θ / 2) {n ² + 1-2n cos (θ / 2)} + cos (θ / 2)] ⁻¹ ·・ ・ (1) Here, θ is the observation angle of the scattered light from the minute droplet 1 with respect to the illumination light 2, D is the diameter of the minute droplet 1, λ
Is the wavelength of the illumination light 2.

This means that, as shown in FIG. 1A, the scattered light 5 from the microdroplets 1 has a small angle interval Δθ with respect to the illumination light 2 around the direction of the scattering angle θ. This means that the portions (interference fringes) having high intensity due to interference are arranged, and an objective lens (imaging lens) 6 is arranged in the optical path of the scattered light 5 and the scattered light 5 causes a minute liquid on the image plane 7. Image 1 'of Drop 1
Is formed on the out-of-focus surface (defocus surface) 8 that is out of the image plane 7, an out-of-focus image 1 ″ of the minute droplet 1 as shown in FIG. 1B is obtained. a), (b)
The range indicated by a broken line indicates the range of the light beam incident on the objective lens 6, and the minute droplet 1 obtained on the out-of-focus surface 8.
The size and shape of the out-of-focus image 1 "of the
Irrespective of the size of the objective lens 6, it depends on the size of the objective lens 6 and the distance of the defocus surface 8 with respect to the image plane 7, and when the outer shape of the objective lens 6 is a circle, the defocus image 1 ″ of the microdroplet 1 becomes The interference fringes 9 are formed in the circle.
Is the angle α at which the microdroplet 1 looks into the objective lens 6.
And the angle difference Δθ.

That is, from the relationship of α = N × Δθ and the above equation (1), the diameter of the microdroplet 1 is D = (2λN / α) [n sin (θ / 2) ÷ √ ｛n ² + 1− 2n cos (θ / 2)｝ + cos (θ / 2)] ⁻¹ (2) By substituting the number N of the interference fringes 9 in the out-of-focus image 1 ″ actually observed and measured into the equation (2),
The diameter D of the minute droplet 1 is determined.

As is clear from FIG. 1A,
The illumination light 2 is a sheet-like parallel light spreading in a direction perpendicular to the drawing, and other microdroplets 1 other than the microdroplet 1 are provided in the optical path.
_{Also when 1} , 1, ₂ ... Are present, out-of-focus images 1 ₁ ″, 1 ₂ ″,.
And the diameter D is similarly obtained. The center position of the defocused images 11 ₁ , 1 ₂ ,... Is the image 1 ′, 1 of the microdroplets 1, 1 ₁ , 1 ₂ ,. ₁ ', 1 _2', since substantially corresponding to the center position of ..., defocus image 1 ₁ obtained in defocus plane 8 ",
From 1 ₂ ″,..., The distribution of microdroplets and the diameter of each microdroplet can be determined simultaneously.

The above is the principle of the known method of measuring the number of interference fringes in an out-of-focus image to measure the diameter and spatial distribution of a minute droplet. Consider the distribution and diameter of the microbubbles to be generated.

FIG. 2 shows that when a plane wave 2 is incident on a microbubble 10 having a refractive index of 1 floating in a liquid having a refractive index n, an incident angle τ
If two phase difference thereof and one reflected light 11 is parallel to refracted light 12 and the incident angle tau ₀ of ₁ is 2mπ and 2 (m +
1) When an angle difference Δθ when π (m is an integer) is obtained, in this case, Δθ = (2λ / nD) [cos (θ / 2) −sin (θ / 2) ÷ √ ｛n ² +1 −2n cos (θ / 2)}] ⁻¹ (3) Here, θ is the observation angle of the scattered light from the microbubbles 10 with respect to the illumination light 2, D is the diameter of the microbubbles 10, and λ is the wavelength of the illumination light 2.

This means that the direction of the scattering angle θ with respect to the illumination light 2 is included in the scattered light 5 from the microbubble 10 as shown in FIG. At the center, a portion (interference fringe) having a high intensity due to interference at a small angular interval Δθ is arranged. An objective lens 6 is arranged in the optical path of the scattered light 5 and the scattered light 5 causes an image on the image plane 7. When an image 10 ′ of the microbubble 10 is formed on the defocused surface (defocus surface) 8 deviated from the image plane 7, an out-of-focus image 10 ″ of the microbubble 10 as shown in FIG. 1 (a) and 1 (b) show the range of the light beam incident on the objective lens 6, and an out-of-focus image 10 of the microbubbles 10 obtained on the out-of-focus surface 8. The size and shape of the outer shape of "" are the same as those of the objective lens 6 regardless of the size of the microbubbles 10. Depending on the distance of the out-of-focus surface 8 with respect to the surface 7, if the outer shape of the objective lens 6 is a circle, the out-of-focus image 10 ″ of the microbubble 10 will be circular.
The number N of the interference fringes 9 formed in the circle is determined by the angle α at which the microbubble 10 looks at the objective lens 6 and the angle difference Δθ.
Is determined by

That is, from the relationship of α = N × Δθ and the above equation (3), the diameter D of the microbubble 10 is as follows: D = (2λN / nα) [cos (θ / 2) −sin (θ / 2)} {N ² + 1-2n cos (θ / 2)}] ⁻¹ (4) By substituting the number N of the interference fringes 9 in the out-of-focus image 10 "actually observed and measured into the equation (4), the diameter D of the microbubble 10 is obtained.

As is clear from FIG. 1 (a),
Sheet-shaped parallel spread in the direction perpendicular to the drawing as illumination light 2
Light, and other microbubbles other than the microbubbles 10 in the optical path
10 ₁, 10_Two, ... are present, even if there are microbubbles
Defocused image 10 similar to 10 ₁"10_Two",···But
Obtained on the out-of-focus surface 8 and the diameter D is likewise determined. Soshi
And their defocused images 10₁”, 01_Two",···of
The center position is the position of those microbubbles 10, 1 on the image plane 7.
0₁, 10_Two, Images 10 ', 10₁’, 1
0_Two′,..
Defocused image 10 obtained at plane 8₁"10_Two", ...
From the distribution of microbubbles and the diameter of each microbubble at the same time.
You.

According to the above examination, even in the case of microbubbles, if a measurement space is irradiated with a sheet-shaped parallel laser beam, and the microbubbles hit by the laser beam are photographed out of focus, the focus corresponding to each microbubble is obtained. There are interference fringes in the out-of-focus image, and there is a certain proportional relationship between the number of interference fringes in the out-of-focus image and the diameter of the microbubbles. It can be seen that the distribution of microbubbles can be determined simultaneously from the distribution of the center position of the out-of-focus image.

FIG. 6 schematically shows an example of an out-of-focus image taken when the spatial distribution density of the fine droplets or fine bubbles is high in the arrangement shown in FIG. Except for the difference between Equations (4) and (2), it has been found that microbubbles can be handled in the same manner as microdroplets, so that microdroplets will be typically considered below.

FIG. 6 shows an image taken on an out-of-focus surface 8 when four microdroplets 1 are closely arranged in the optical path of the sheet-like parallel illumination light 2 in the arrangement shown in FIG. Defocused images a, b, c, and d. When the four microdroplets 1 are too close to each other, the corresponding defocused images a and
b, c, d overlap each other, and the respective images a,
It is not easy to separately count the number of interference fringes 9 in b, c, and d. Further, the center of each image a, b, c, and d is specified to check the distribution of the microdroplets 1. It is also difficult.

Therefore, as a first embodiment of the optical system for measuring the diameter and distribution of microbubbles and microdroplets according to the present invention, an optical system as shown in a perspective view in FIG. 4 is used. First, a coordinate system is defined. The traveling direction of the sheet-like parallel light ₂ for irradiating the microdroplets 1, 1 ₁ , 1 ₂ ,.
The optical axis O is set in a plane perpendicular to the plane of the sheet-like parallel light 2, and the direction perpendicular to the optical axis O in the plane is defined as the x-axis direction, and the optical axis O and the x-axis direction And a direction parallel to the sheet-shaped parallel light illumination light 2 is defined as a y-axis direction. The measurement optical system 20 shown in FIG. 4 includes an objective lens 6 and a cylindrical lens 21 which is arranged coaxially with the objective lens 6 and has a refractive power only in the x-axis direction and has no refractive power in the y-axis direction (see FIG. The imaging surface 22 of the imaging device such as a CCD is disposed on the imaging surface of the measurement optical system 20 in the y-axis direction, that is, the imaging surface of the objective lens 6. ing. On the other hand, the imaging surface of the measurement optical system 20 in the x-axis direction is formed at a position deviated from the imaging surface 22 (in FIG. 4, a position behind the imaging surface 22). With such an arrangement, for example, regarding the microdroplet 1 located near the optical axis O, the shape of the defocused image is circular in the optical path from the objective lens 6 having a circular aperture to the cylindrical lens 21. The out-of-focus image gradually increases in flatness from the cylindrical lens 21 to the imaging surface 22, and the out-of-focus image on the imaging surface 22 becomes a horizontal line. However,
The number of interference fringes 9 does not change in the defocused image at any position.

FIG. 7 shows out-of-focus images a, b, c, and d of four microdroplets 1 and the like obtained from the imaging surface 22 in the arrangement shown in FIG. 4, and corresponds to FIG. However, in the x-axis direction,
The magnification in the y-axis direction is shown as not changing (actually, the magnification of the out-of-focus image may change because the focal length in the x-axis direction and the like change). As is clear from a comparison between FIG. 6 and FIG. 7, out-of-focus images a and
b, c, and d are obtained by compressing the circular outer shape in the vertical direction (y-axis direction) while keeping the respective center positions of the defocused images a, b, c, and d taken in the arrangement of FIG. Is converted into an image in a one-dimensional direction (x-axis direction). Therefore, the four out-of-focus images a, b, c, and d are no longer overlapped in the y-axis direction, and the number of interference fringes 9 in each of the images a, b, c, and d is easily counted separately. In addition, it is easy to specify the center position of each of the images a, b, c, and d to see the distribution state of the microdroplets 1 and the like (this point will be described later).

In the case of out-of-focus images a, b, c, and d as shown in FIG. 6 photographed using an axially symmetric measuring optical system, there are circular edges around these images. The diameter of the interference fringes 9 in the aperture can be easily known and the number of interference fringes 9 in the aperture can be easily counted.
In the case of b, c, and d, the amount of light at the center becomes large.
The light amount near both ends becomes relatively small and becomes inconspicuous, and the length L of the out-of-focus image becomes unclear. However, if the measurement optical system is the same and the defocus plane is the same, the lengths L of the compressed defocus images are all the same, so if this is confirmed once in advance in the same state, this point is no problem. Not be.

As described above, by compressing the out-of-focus image in the vertical direction (y-axis direction), the contrast of the out-of-focus image to be photographed is also improved, and there is an advantage that the measurement sensitivity can be increased.

By the way, as shown in FIG. 4, on the imaging surface 22, the lens configuration of the measuring optical system 20 that is in a focused state in the y-axis direction and out of focus in the x-axis direction is axially symmetric as described above. An anamorphic optical system formed by combining the objective lens 6 and the cylindrical lens 21 may be used. Alternatively, an anamorphic optical system using a plane-symmetric anamorphic surface such as a toric surface as a refraction surface may be used. Also,
Although the refractive power is the same in the x-axis direction and the y-axis direction,
Since the axis direction is different from the y-axis direction, an optical system that is in a focused state in the y-axis direction and out of focus in the x-axis direction on the imaging surface 22 may be used. Of course, the above-described optical system may be configured to include the reflection surface.

FIG. 5 is a perspective view of an optical system for measuring the diameter and distribution of microbubbles and microdroplets according to the second embodiment of the present invention, which is a further improvement of the insufficient point of FIG. is there. The measuring optical system 20 ′ includes an objective lens 6 and an objective lens 6.
And are arranged coaxially has a refractive power only in the x-axis direction, and a positive cylindrical lens 21 ₁ and the negative cylindrical lens 21 ₂ which having no no refracting power in the y-axis direction, the two cylindrical lenses 21 ₁ and 21 ₂ are optical axis O
The position can be adjusted along each. And
An imaging surface 22 of the imaging element is arranged on an imaging surface of the objective lens 6 which is an imaging surface of the measurement optical system 20 ′ in the y-axis direction.

With such an arrangement, the normal cylinder
Cal lens 21₁And negative cylindrical lens 21_TwoPhase of
Adjusting the mutual position and the position with respect to the objective lens 6
Captures the image plane in the x-axis direction of the entire measurement optical system 20 '
It can be adjusted freely with respect to the surface 22. Also, x
The focal length of the measurement optical system 20 'in the axial direction is also continuously within a certain range.
You can adjust it freely in the box. Therefore, as in the case of FIG.
Meanwhile, on the imaging surface 22, the image is compressed in the vertical direction (y-axis direction).
An out-of-focus image that is an image in a one-dimensional direction (x-axis direction)
(Fig. 7) is photographed and two cylindrical lenses
21₁, 21 _TwoBy adjusting the position of
Adjust the length L of the linear defocused image extending in the x-axis direction
be able to.

In contrast to FIG. 6, in the case of FIG. 7, the overlap of the defocused images a, b, c, and d in the y-axis direction is eliminated, but the same height (the same y coordinate value) is used. The out-of-focus images that are located can overlap each other at their edges, see FIG.
In the arrangement, the partial overlap in the x-axis direction cannot be eliminated.
In such a case, by using the arrangement of FIG. 5, by adjusting the length L of the out-of-focus image to be short, it is possible to eliminate the mutual overlap at the edge portion. Also in this case, as described above, the number of interference fringes 9 in one out-of-focus image does not change.

Further, as is apparent from the expressions (2) and (4), the number N of interference fringes and the diameter D of the minute droplet (fine bubble)
Since there is a proportional relationship between
Is large, the interference fringes 9 in one out-of-focus image
Increases, and the interference fringes 9 in the captured screen may be so fine that counting is not easy. In such a case, contrary to the above, two cylindrical lenses 2
By adjusting the positions of 1 ₁ and _{2 12} to increase the length L of the out-of-focus image, the resolution can be increased and the interference fringes 9 can be easily counted.

By the way, in the arrangement of FIG.
Is arranged in the vicinity of, a slit-like opening 23 extending in the x-axis direction is provided, the numerical aperture in the y-axis direction is limited, and the depth of focus (depth of field) is increased. As a result, even if the optical axis O of the measurement optical system 20 ′ is located in an oblique direction other than 90 ° with respect to the sheet-like parallel illumination light 2, the microdroplets 1 located at a certain distance from the optical axis O _An out-of-focus image such as ₁ can be taken and measured. The slit-like opening 23
Has a shape extending in the x-axis direction as described above, so that there is no effect on the number of interference fringes with a small angle interval Δθ that can be captured in the measurement, and there is no effect on the number N of interference fringes in each captured out-of-focus image. No effect occurs.

By the way, as suggested above, the angle θ between the optical axis O of the measuring optical systems 20 and 20 ′ with respect to the sheet-like parallel illumination light 2 is usually set to an angle between 0 ° and 90 °. Set. In that case, the main surface of the objective lens 6, the imaging surface 2
If 2 is set to be perpendicular to the optical axis O, it is difficult to image all of the microdroplets in the oblique object plane 2 in a desired state unless the slit opening 23 as described above is used. Therefore, the tilt, tilt, and swing used in photographing are combined to tilt the main surface of the objective lens 6 and the imaging surface 22 with respect to the optical axis O, or to vertically move the imaging surface 22 to obtain a tilt. It is possible to photograph all of the microdroplets in the object plane 2 in a desired state. As an example, there is a method of inclining the main surface of the objective lens 6 and the imaging surface 22 with respect to the optical axis O so as to satisfy the Scheimpflug condition.

In the above description, the measurement space is irradiated with the illumination light 2 of sheet-like parallel light, and the distribution and diameter of the minute droplets and minute bubbles located on the irradiated sheet surface are determined. The illumination light 2 of light is moved in a direction perpendicular to the plane, and out-of-focus images are separately captured in synchronization with the movement.
By photographing in 2, the distribution and diameter of the microdroplets and microbubbles in the three-dimensional space can be obtained. In this case, the imaging surface 22 may be moved in the optical axis direction in conjunction with the movement of the sheet-like parallel illumination light 2.

The measuring optical system 2 of the present invention as described above
An example of a method and an apparatus for obtaining the position, diameter, and speed of a microdroplet or microbubble using an out-of-focus image as shown in FIG.

From the above examination, the center positions of the linear out-of-focus images a, b, c, and d having the length L obtained from the imaging surface 22 are determined by the minute droplets 11 ₁ , 1 ₂ , ...
, The out-of-focus images (hereinafter referred to as interference fringe images) a, b, and
The method for obtaining the centers of c and d will be described. The imaging screen A as shown in FIG. 7 is main-scanned along the length direction (in the x direction) of the linear interference fringe images a, b, c, and d, and the sub-scanning is performed in the direction (y direction) orthogonal thereto. By scanning, an image signal of the entire photographing screen A is obtained. This image signal corresponds to one of the interference fringe images a, b, c, and d, and has a length L in terms of distance as shown in, for example, FIG. A signal having a peak corresponding to the interference fringe image a,
The signals exist corresponding to the positions of b, c, and d. FIG.
The horizontal axis corresponds to the position in the longitudinal direction of the interference fringe image (expressed by several pixels), and the vertical axis corresponds to the signal intensity. In order to obtain the center position of one interference fringe image as shown in FIG. 8, a moving average may be obtained along the longitudinal direction. Since the length L of one interference fringe image is determined from the state of the measurement optical system 20 and the position of the imaging surface 22, an average is taken over a range of a distance L / 2 before and after the specific position to obtain a value at that position. A moving average value can be obtained by sequentially moving a specific position. FIG. 9 shows the imaging surface 2
2 shows an example of the result obtained by taking the above moving average with the image signal of the interference fringe image obtained in Step 2. When the moving average is obtained, a substantially triangular wave signal is obtained as shown in the figure, and the peak position (1) is the center position of the interference fringe image corresponding to the minute droplet. Note that FIG.
Medium and range (3) correspond to the length L of the interference fringe image.

Incidentally, a signal longer than the signal length L of the interference fringe image may appear in the same signal in the main scanning direction. This is a case where a plurality of interference fringe images exist in the same main scanning direction so as to overlap with each other, which rarely occurs. In this case, the half value width of the image signal of the interference fringe image or the half value width of the moving average signal is longer than in a normal case, so that the determination can be made easily. In that case, there is no problem even if the image signal of the interference fringe image is removed. Alternatively, the center of the two interference fringe images can be obtained from the half width.

Since noise may be mixed in the image signal, the interference fringe image exists only when it is determined that the amplitude (2) of the high-frequency component in FIG. It is desirable to make a determination.

In this way, the position of each microdroplet on the photographing screen A is obtained, and the distribution and density of the microdroplets in that space are obtained.

Next, a method for obtaining the diameter of each microdroplet will be described. As described above, since the length of the signal of the interference fringe image in the image signal obtained by scanning the photographing screen A is L, the range of L / 2 before and after the center position obtained above is determined by each interference. This is a fringe image signal. Therefore, a signal having a length L in the longitudinal direction is cut out around the range of L / 2 before and after the center of the obtained interference fringe image, that is, the center position of the interference fringe image, and the absolute value of the Fourier transform of the cut out signal is obtained. By obtaining the value or its square (power spectrum), the frequency f of the interference fringe image is obtained, and the length f of the interference fringe image is determined by the frequency f.
, The number N of interference fringes in the out-of-focus image is obtained. Then, by substituting the N into the equation (2) or the equation (4), the diameter D of the microdroplet or microbubble is calculated.
Can be requested.

Here, in order to obtain the frequency f from the power spectrum by Fourier-transforming the signal of length L, in practice, a Hanning window function, for example, as a window function for eliminating the influence of edges is used. Is applied to the signal to perform a fast Fourier transform (FFT). By the way, FFT is a kind of discrete Fourier transform. In the discrete Fourier transform, when the sampling interval of a signal to be converted is Δ and the sampling number is M, the obtained frequency interval is 1 / MΔ, and the discrete The frequency can be obtained only at the frequency position. If the frequency of the interference fringe image exactly matches any one of the discrete frequencies at this frequency interval 1 / MΔ, the Fourier-transformed frequency signal appears as one peak at that frequency position. However, when the frequency of the interference fringe image exists between two adjacent frequencies of the discrete frequencies, a signal appears not only at the two adjacent frequencies but also at the discrete frequencies around the two adjacent frequencies. FIG. 10 shows an example. FIG.
0 (a) is a signal of an interference fringe image, and a power spectrum obtained by multiplying the signal by a Hanning window function and performing FFT is shown in FIG.
0 (b). Figure 10 (b) As is apparent from, there is a peak P _k to the position of the frequency k, the signal P _k-1 in discrete frequency k-1, k + 1 on both sides, there are P k _{+ 1,}
There are also signals on both sides of them. In order to accurately determine the frequency of the original signal by function fitting from such a discrete power spectrum, there are methods using various fitting functions, but a method of applying a Gaussian function (RJ Adrian et al. "Applicatio
ns of Laser Technologies to
Fluid Mechanics 5th Inte
rnational Symposium Lisbo
n, Portugal, 9-12 July, 199
0 "pp. 268-287 (Springer-Ver
lag)) accurately determines the frequency of the original signal. That is, as shown in FIG. 11, there is a peak P _{k at} the position of the discrete frequency k, and the discrete frequency k−
When there are smaller signals P _k−1 and P _{k + 1 in 1} , _{k + 1} , the frequency f of the original signal becomes f = f _k + ／ × ｛( _{logP k-1 -logP k + 1} ) ÷ (logP k-1 -2logP k + logP k + 1)} obtained as (5).

Of course, other well-known window functions and fitting functions may be used.

Next, a method for obtaining the velocity (vector) of each microdroplet will be described. In this case, the photographing screens A and A ′ as shown in FIG. 7 are photographed at the minute time interval Δt. The two shooting screens A and A 'obtained in that case are shown in FIG.
2 (a) and 2 (b), interference fringe images a, b, c, and
d changes as shown. Therefore, by calculating the cross-correlation between the interference fringe images a, b, c, and d of the two shooting screens A and A ′, the movement amount Δs _i is obtained as a vector. The distribution of the movement amount is schematically shown in FIG. From the obtained movement amount Δs _i, the speed u _i of each microdroplet is obtained as u _i = Δs _i / Δt (6).

More specifically, for example, the illumination light 2 of sheet-like parallel light is used at a minute time interval Δt using a double pulse laser, for example.
(FIGS. 4 and 5) are irradiated, and two images A and A ′ are photographed on the imaging surface 22 in synchronization with the light emission. The images A, A '
From the signal of the interference fringe image. The cutout method is the same as that for obtaining the frequency. However, in this case, not only the signal of one scanning line but also the signal of an adjacent scanning line orthogonal to the interference fringe image is simultaneously cut out, and the cross-correlation is performed for each of the cut-out interference fringe images of the image A and the image A ′. Take. In the calculation, a correlation value is calculated by moving each pixel in the x and y directions for each interference fringe image cut out from both images. The upper limit of the movement amount for the correlation calculation in the x direction and the y direction is appropriately set in advance. The vector movement amount up to the position (peak position) where the correlation value is highest for each interference fringe image is defined as the movement amount Δs _i described above.

In the above calculation, each of the cut-out interference fringe images includes an interference fringe signal, and the interference fringes may move right and left in the interference fringe image depending on the phase. The movement amount obtained by the above cross-correlation may not always be the same as the actual movement amount of the interference fringe image. Therefore, if the cross-correlation of the interference fringe image with the interference fringe signal still included is obtained as described above, it cannot be said that a correct movement amount of the interference fringe image is necessarily obtained. Therefore, it is preferable to remove the high-frequency components of the interference fringe signal from the interference fringe image signal through a low-pass filter before obtaining the cross-correlation to obtain the cross-correlation.

Since the above-described calculation of the cross-correlation is also performed in units of one pixel, the amount of movement in which the amount of movement Δs _i is smaller than the unit of pixel is not directly obtained, so that the discrete amounts obtained in the x and y directions are not obtained. By applying various functions (for example, a Gaussian function or a quadratic function to the cross-correlation value, in the case of the present invention, the cross-correlation of a sine function is used, a sine function or a cosine function) is applied to the pixel unit. Can be accurately determined.

However, the movement amount Δs _i obtained by the above-described method is not always the movement amount of the minute liquid droplet corresponding accurately between different times. Thus, the frequency in the signal of each of the cut-out interference fringe images is obtained as described above, and whether the frequency has not changed or whether the rate of change due to evaporation or condensation is equal to or less than a predetermined constant value is determined. It is desirable to make a determination and determine that a correct response is made only when the rate of change is equal to or less than a predetermined fixed value.

FIG. 13 shows an example in which the positions, diameters, and velocities of the microdroplets or microbubbles are simultaneously measured as described above and displayed on one screen. The center of the circle represents the position, the size of the circle represents the diameter, and the line segment represents the speed.

An apparatus for executing the method for determining the position, diameter, and velocity of a minute droplet or a minute bubble using the above-described out-of-focus image can be easily configured using a personal computer by software.

The method and apparatus for measuring the diameter and distribution of microbubbles and microdroplets and the optical system for measuring the diameter and distribution of microbubbles and microdroplets according to the present invention have been described based on the embodiments. The present invention is not limited to these embodiments, and various modifications are possible.

[0061]

As is apparent from the above description, according to the method and apparatus for measuring the diameter and distribution of microbubbles and microdroplets according to the present invention, the traveling direction of the sheet-like parallel laser beam and the imaging optical system In a direction parallel to a plane including the optical axis of the optical axis, an out-of-focus state is obtained.In the direction perpendicular to the plane, an out-of-focus image is captured on an imaging surface that is substantially in focus. Is a one-dimensional image compressed in a direction perpendicular to the plane,
Even when the distribution density of microbubbles and microdroplets is high spatially, each defocused image can be separated from each other,
The number of interference fringes in each out-of-focus image can be separated and counted easily, and it is easy to identify the center position of each out-of-focus image and see the distribution of microbubbles or droplets. Even in such a case, the distribution of the position, diameter, and velocity of the microbubbles and microdroplets can be simultaneously and accurately measured.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the principle of a method for measuring the diameter and spatial distribution of microbubbles according to the present invention and the principle of a conventional method for measuring the diameter and spatial distribution of microdroplets, and a microscopic sample in that case. FIG. 3 is a diagram illustrating an example of an out-of-focus image of a bubble or a microdroplet.

FIG. 2 is a diagram for analyzing a light beam passing through a microbubble floating in a liquid.

FIG. 3 is a diagram for analyzing a light beam passing through a microdroplet floating in the air.

FIG. 4 is a perspective view showing a first embodiment of the optical system for measuring the diameter and distribution of microbubbles and microdroplets according to the present invention.

FIG. 5 is a perspective view showing a second embodiment of the optical system for measuring the diameter and distribution of microbubbles and microdroplets according to the present invention.

FIG. 6 is a diagram illustrating an example of an out-of-focus image captured in the arrangement of FIG.

FIG. 7 is a diagram showing an out-of-focus image corresponding to FIG. 6 photographed in the arrangement of FIG. 4;

FIG. 8 is a diagram illustrating an example of an image signal obtained for one interference fringe image.

FIG. 9 is a diagram illustrating an example of a result obtained by calculating a moving average of an image signal of an interference fringe image obtained on an imaging surface;

FIG. 10 is a diagram illustrating an example of an image signal of an interference fringe image and a power spectrum obtained by performing FFT on the image signal.

FIG. 11 is a diagram for explaining a method of accurately determining the frequency of an original signal by function fitting from a discrete power spectrum.

FIG. 12 is a diagram for explaining a method of calculating a velocity of a minute droplet by calculating a cross-correlation.

FIG. 13 is a diagram illustrating an example in which distributions of positions, diameters, and velocities of microdroplets or microbubbles are simultaneously measured and are displayed on one screen.

[Explanation of symbols]

1, 1 ₁ , 1 ₂ ... minute droplet 1 ', 1 ₁ ', 1 ₂ '... minute droplet image 1 ", 1 ₁ ", 1 ₂ "... minute droplet out of focus image 2 ... sheet parallel Light illumination light 3 ... Reflected light once 4 ... Refracted light twice 5 ... Scattered light 6 ... Objective lens (imaging lens) 7 ... Image plane 8 ... Out of focus plane (defocus plane) 9 ... Interference fringe 10,10 ₁ , 10 ₂ … microbubbles 10 ′, 10 ₁ ′, 10 ₂ ′… microbubble images 10 ”, 10 ₁ ”, 10 ₂ ”... microbubble defocused images 11… reflected light once 12… reflected twice Light 20 ... Measurement optical system 20 '... Measurement optical system 21 ... Cylindrical lens 21 ₁ ... Positive cylindrical lens 21 ₂ ... Negative cylindrical lens 22 ... Imaging surface 23 ... Slit aperture S ... Slit direction of illumination light of sheet-shaped parallel light O ... Optical axis of the measuring optical system A, A '... Photographing screen a, b, c, d ... Out-of-focus image of minute droplet

Continued on the front page F term (reference) 2F065 AA00 AA03 AA26 BB29 CC00 DD04 FF05 FF51 FF64 GG04 GG16 HH02 JJ03 JJ26 LL08 QQ16 QQ17 QQ29 QQ34 QQ36 QQ41 UU05 2G059 AA05 BB09 CC11 EE01 GG01 MM01

Claims (8)

[Claims] 1. A sheet-shaped parallel laser beam is applied to a space in which a microbubble or a microdroplet floats, and the microbubble or the microdroplet hit by the laser beam is directed at a predetermined angle with respect to the laser beam traveling direction. From the side of
In a direction parallel to a plane including the traveling direction of the laser beam and the optical axis of the photographing optical system, an out-of-focus state is obtained, and in a direction perpendicular to the plane, the photographing surface becomes substantially in a focused state. A microbubble characterized by obtaining a linear defocused image corresponding to a microbubble or a microdroplet extending and obtaining the center of the defocused image to obtain the center position of the microbubble or the microdroplet. And methods for measuring the diameter and distribution of microdroplets. 2. When the length of a linear defocused image is L, the center position is averaged over a range of a distance L / 2 before and after a specific position along the longitudinal direction, and the value of the position is calculated. And calculating the average value from the peak position of the moving average obtained by sequentially moving the specific position.
A method for measuring the diameter, distribution, etc. of the microbubbles and microdroplets described. 3. A sheet-shaped parallel laser beam is applied to a space in which a microbubble or a microdroplet floats, and the microbubble or the microdroplet hit by the laser beam is directed at a predetermined angle with respect to the laser beam traveling direction. From the side of
In a direction parallel to a plane including the traveling direction of the laser beam and the optical axis of the photographing optical system, an out-of-focus state is obtained, and in a direction perpendicular to the plane, the photographing surface becomes substantially in a focused state. A linear defocused image corresponding to a microbubble or a microdroplet is taken, and the defocused image is subjected to Fourier transform to obtain a frequency. The focus is obtained by multiplying the obtained frequency by the length of the defocused image. A method for measuring the diameter and distribution of microbubbles and microdroplets, wherein the number of interference fringes in a deviated image is obtained, and the diameter of microbubbles or microdroplets is obtained based on the number of interference fringes. 4. The method according to claim 3, wherein a discrete Fourier transform is performed as the Fourier transform, and a function fitting is performed on the obtained discrete frequency distribution to obtain a diameter of a microbubble or a microdroplet. For measuring the diameter and distribution of microbubbles and microdroplets. 5. A sheet-shaped parallel laser beam is applied to a space in which a microbubble or a microdroplet floats, and the microbubble or the microdroplet hit by the laser beam is directed at a predetermined angle with respect to the laser beam traveling direction. From the side of
In a direction parallel to a plane including the traveling direction of the laser beam and the optical axis of the photographing optical system, an out-of-focus state is obtained, and in a direction perpendicular to the plane, the photographing surface becomes substantially in a focused state. Two linear out-of-focus images corresponding to the microbubbles or the microdroplets are photographed at a small time interval Δt, and the linear defocus images are obtained in units of a linear defocus image in the two photographed images obtained. By calculating the cross-correlation between the two photographing screens, the moving amount Δs _i of each linear defocused image is obtained, and the speed u _i of each microbubble or microdroplet is obtained by the following relationship. A method for measuring the diameter and distribution of microbubbles and microdroplets. u _i = Δs _i / Δt (6) 6. When calculating the cross-correlation between the two photographed images, the high-frequency component corresponding to the interference fringe in the linear out-of-focus image is removed to calculate the cross-correlation. A method for measuring the diameter and distribution of the microbubbles and microdroplets according to claim 5. 7. A sheet-shaped parallel laser beam is applied to a space in which a microbubble or a microdroplet floats, and the microbubble or the microdroplet hit by the laser beam is set at a predetermined angle with respect to the laser beam traveling direction. From the side of
In a direction parallel to a plane including the traveling direction of the laser beam and the optical axis of the photographing optical system, an out-of-focus state is obtained, and in a direction perpendicular to the plane, the photographing surface becomes substantially in a focused state. A linear defocused image corresponding to the microbubbles or microdroplets is taken, and the center of the defocused image is obtained to obtain the center position of the microbubbles or microdroplets. Convert the frequency to obtain the number of interference fringes in the out-of-focus image by multiplying the obtained frequency by the length of the out-of-focus image, and calculate the diameter of microbubbles or microdroplets based on the number of the interference fringes. Is obtained, and two out-of-focus images are photographed at a small time interval Δt, and the cross-correlation between the two photographing screens is obtained for each linear out-of-focus image in the two photographing screens obtained. By calculating each Determine the movement amount Delta] s _i shaped for defocus image measuring method of the size and distribution, etc. of the microbubbles and microdroplets speed u _i of each microbubble or microdroplets and obtains the following relationship. u _i = Δs _i / Δt (6) 8. A laser beam irradiating means for irradiating a sheet-shaped parallel laser beam to a space in which microbubbles or microdroplets float, and microbubbles or microparticles hit by the laser beam irradiated by said laser beam irradiating means. The droplet is defocused in a direction parallel to a plane including the traveling direction of the laser beam and the optical axis of the imaging optical system from a side surface direction forming a predetermined angle with respect to the traveling direction of the laser beam. A photographing unit that extends in the plane direction to photograph a linear defocused image corresponding to a microbubble or a microdroplet on a photographing surface that is substantially in focus in a vertical direction, and a center of the defocused image. The center position measuring means for obtaining the center position of the microbubble or the microdroplet, and the frequency obtained by Fourier-transforming the out-of-focus image. Multiplied by the length of the out-of-focus image to obtain the number of interference fringes in the out-of-focus image, and a diameter measuring means for obtaining the diameter of a microbubble or a microdroplet based on the number of the interference fringes; The image is taken for a small time interval Δt
And the amount of movement of each linear defocused image by calculating the cross-correlation between the two photographic screens in units of the linear defocused image in the two obtained photographic screens Δs _i
Look, measurement device size and distribution, etc. of the microbubbles and microdroplets speed u _i of each microbubble or microdroplets, characterized in that a speed measuring means for obtaining by the relation. u _i = Δs _i / Δt (6)