JP2859971B2 - Particle size distribution measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of irradiating a laser beam to a particle group such as a fuel spray of an automobile, receives a laser beam diffracted by the particle group, and based on the diffraction pattern, the diameter of the particle group. The present invention relates to a particle size distribution measuring device for measuring the distribution of particles.

[0002]

2. Description of the Related Art When a group of particles having a predetermined diameter is irradiated with laser light and a Fraunhofer diffraction image of the group of particles is observed, attention is paid to the fact that the diffraction pattern and the diameter of the group of particles correspond one to one. There is known a method of analyzing a composite diffraction pattern of laser light diffracted from a group of fine particles having various diameters based on a predetermined algorithm to know the distribution of the particle size of the group of fine particles (for example, “surface”). Vol.22 No.2 (1984) 87 (27)
Pp. 94-34). In this method, since the diffraction pattern is a concentric pattern centered on the spot of the 0th-order light, the diffraction pattern is received using, for example, 15 concentric ring-shaped optical sensors. The particle size distribution is obtained by analyzing the diffraction pattern.

[0003]

In the above-mentioned method using a large number of annular optical sensors, the position is precisely adjusted so that the center of a photodetector composed of the multiple annular optical sensors exactly coincides with the optical axis. Therefore, there is a problem that preparation before measurement is difficult. In order to solve this problem, for example, a solid-state imaging device such as a CCD is used in place of the detector composed of a large number of annular optical sensors. As a preparation, only the positioning is roughly performed, and the exact optical axis center may be separately obtained later.

However, the zero-order light traveling on the optical axis usually has a remarkably large light quantity compared to the diffracted light.
When the next light is received, there is a problem that the surrounding light receiving element is greatly affected and the diffracted light cannot be received correctly. In addition, the light amount distribution of the diffracted light itself decreases as the distance from the optical axis increases. In order to accurately measure the light amount distribution of the diffracted light over a wide range, the dynamic range of a solid-state imaging device such as a CCD (correctly receiving light) (The ratio of the minimum light amount to the maximum light amount) can be insufficient.

In view of the above circumstances, the present invention provides a particle size distribution measuring apparatus using a solid-state imaging device such as a CCD, which can measure diffracted light without being affected by zero-order light. the purpose is to provide.

[0006]

[Object to A in order to achieve the above Symbol purpose first particle size distribution measuring apparatus of the present invention, an irradiation optical system for irradiating a laser beam to the microparticle group, a diffraction image by the fine particles A solid-state imaging device that receives light, and a particle size distribution measurement device including a calculation unit that calculates a particle size distribution of the fine particle group based on a diffraction image pattern received by the solid-state imaging device; A mask for blocking zero-order light that is not diffracted by the particle group, and the mask
Concentration continuously or stepwise as you move away from
Characterized in that a filter with reduced
Things.

[0007]

The "filter having a stepwise reduced density" may be a single-stage filter (uniform filter). In this case, the transmittance is two-stage depending on the presence or absence of the filter. One stage has an optical transmittance of 10
0% filter).
Further, the second particle size distribution measurement of the present invention to achieve the above object
The apparatus includes an irradiation optical system that irradiates the laser beam to the particle group,
A solid-state imaging device for receiving a diffraction image by the fine particle group;
Based on the diffraction image pattern received by the body image sensor
Calculating means for obtaining a particle size distribution of the fine particle group.
In size distribution measuring apparatus, in the solid-front, before
A mask that shields zero-order light that is not diffracted by the particles.
Wherein the calculating means, received by the solid-
Utilizing the fact that the diffraction pattern obtained is rotationally symmetric
The center point of the diffraction image pattern is determined and based on the diffraction image pattern.
The particle size distribution of the fine particle group
It is characterized by.

[0009]

According to the first particle size distribution measuring apparatus of the present invention, since the 0th-order light shielding mask is arranged on the front surface of the solid-state imaging device,
Thus, the zero-order light is cut, and only the diffracted light can be received without being affected by the strong zero-order light. It should be noted that the center of the diffraction pattern (the irradiation position of the zero-order light) is not unknown even if the zero-order light is cut, and the center can be obtained by using, for example, a method described in Examples described later.

[0010] The first particle size distribution measuring device of the present invention comprises:
In addition to the mask for cutting the zero-order light, a filter formed at a high density near the mask in addition to a mask formed at a low density when the mask is separated from the mask is arranged. The low light area away from the center is received without much attenuation. Therefore, even when the dynamic range of the diffracted light exceeds the dynamic range of the solid-state image sensor, the solid-state image sensor does not saturate and the dynamic range of the diffracted light is compressed and received. Also, the second particle size of the present invention
The distribution measuring device, like the first particle size distribution measuring device,
A zero-order light shielding mask is arranged on the front surface of the solid-state imaging device.
Therefore, the zero-order light is cut by this, and the strong zero-order light
Can receive only diffracted light without being affected by
You. Furthermore, the second particle size distribution measuring device of the present invention is a solid
The diffraction image pattern received by the image sensor is rotationally symmetric
I will use it to find the center point of the diffraction pattern
Rough alignment is sufficient.
Of the prior art using a photodetector consisting of
The center of the photodetector is perfectly aligned with the optical axis.
Freed from the need for precise positioning
This facilitates preparation before measurement.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a particle size distribution measuring apparatus according to one embodiment of the present invention. The laser light 2 emitted from the laser light source 1 is applied to a beam expander (beam).
The light is made into a parallel light spread in a predetermined range by an expander 3, and is applied to a fine particle group 4 contained in, for example, a fuel spray of an automobile. A part of the laser light applied to the fine particle group 4 is diffracted by the fine particle group 4 and then condensed by the lens 5 to irradiate the front surface of the CCD 6. The diffracted image is received by the CCD 6.

FIG. 2 is a diagram showing an example of a diffraction image pattern on the front surface of the CCD 6. When the particle group 4 is composed of only particles having a predetermined diameter, CC
For example, a diffraction pattern 11 indicated by a broken line in FIG. 2 is generated on D6, and a diffraction pattern 12 indicated by an alternate long and short dash line in FIG. Here, since the fine particle group 4 is composed of fine particles having various diameters, the diffraction pattern 12 formed by the fine particle group 4 is a superposition of the diffraction patterns (diffraction patterns 11, 12 and the like) by the fine particles of each diameter. It will be.

The diffraction pattern received by the CCD 6 shown in FIG. 1 and converted into an electric signal is input to an arithmetic circuit 7, and the arithmetic circuit 7 uses, for example, an example shown in FIG. As shown, each particle size d
Is obtained from the particle group having the following formula.

FIGS. 4A and 4B show an example of a CCD in which a glass plate provided with a mask for cutting zero-order light and a filter for attenuating diffracted light is adhered to the surface. It is a front view and a side view, respectively. CCD 6
It is planned that the optical axis is roughly adjusted so that the zero-order light is irradiated to the upper left corner of FIG. 4A. Therefore, the mask 20 for cutting the zero-order light is provided at the upper left corner of the surface of the CCD 6. Affixed to On the other hand, in the diffraction pattern, as shown in FIG. 2, on the average, the light amount becomes larger in the region closer to the optical axis center 0 (irradiation position of the zero-order light), and the light amount decreases as the distance from the optical axis center increases. Therefore, in this embodiment, an ND filter 21 having a uniform density is attached to an upper left area of FIG. In addition, CCD
The area where neither the mask 20 nor the ND filter 21 is attached on the surface of No. 6 is optically 100% transmittance.
It is considered that the ND filter of FIG.
It can be considered that the surface of the CCD 6 is filtered in two stages except for the region of 0.

Here, when the mask 20 and the ND filter 21 are attached, it is necessary to examine the received light intensity distribution caused by the ND filter 21 and the like. The received light intensity distribution can be examined, for example, as follows.

FIG. 5 is a schematic configuration diagram showing an example of an optical system for examining a received light intensity distribution when uniform light is applied to the CCD. The laser light 2 emitted from the same laser light source 1 as the laser light source 1 shown in FIG. 1 is converted into parallel light through the lens 8 and the same lens 5 as the lens 5 shown in FIG. Is irradiated with a uniform amount of laser light.

Here, by examining the signal value of each pixel in an area that is not covered by the mask 20 or the filter 21, the light receiving variation of each pixel of the CCD 6 is examined. By comparing the signal value of each pixel in the area covered by the filter 21 with the signal value of each pixel in the area covered by the filter 21,
After receiving the diffraction pattern, a correction coefficient used for obtaining the diffraction pattern that is not attenuated by the filter 21 is obtained. This correction coefficient is recorded in a memory provided in the calculating means 7 and is used in a later correction.

Since the upper left end of the CCD 6 is covered with the mask 20 and does not receive the 0th-order light, the irradiation position of the 0th-order light (the center of the optical axis) should be confirmed by the irradiation position of the 0th-order light. Cannot be sought. Therefore, this embodiment utilizes the fact that the diffracted light pattern is rotationally symmetric about the optical axis center 0, and the arithmetic means 7 (see FIG. 1) uses the predetermined threshold value for the diffraction pattern received by the CCD 6. By performing the binarization process, for example, an arc 30 indicated by a broken line in FIG. 4A is obtained, and a center point of the arc 30 is obtained, and the center point is set to the optical axis center 0. After calculating the optical axis center 0 as described above, the calculating means 7 uses the correction coefficient described above to calculate the ND filter 2 of the diffracted light.
1 is corrected, and the particle size distribution of the fine particle group 4 is obtained based on the corrected diffraction pattern.

FIGS. 6A and 6B show another example of the filter attached to the surface of the CCD 6, and FIGS. 7A and 7B show FIGS. 4, 6A and 6B. It is a figure showing the density distribution along the alpha axis of various filters shown. In the case of the filter shown in FIG. 4, the mask 20 shown in FIG.
Is extremely high, and then the area 31b corresponding to the filter 21 has a certain density D1.
It is 2. On the other hand, in FIG. 6A, two filters 22 and 23 having different densities are attached to each other.
As shown by a dashed line 32 in FIG. 7, there is an area 32b of the density D3 corresponding to the filter 22 next to the area 32a of the extremely high density D1 corresponding to the mask 20, and subsequently, a density D4 ( An area 32c of (D3> D4) exists. Thus, in the present invention, the filter may be configured in any number of stages. In FIG. 6B, as indicated by a dashed line 33 in FIG. 7, a filter 24 whose density continuously decreases as the distance from the mask 20 increases is affixed. In the present invention, filters of various densities that change stepwise or continuously in this way can be used. Although the mask 20 and the filters 21, 22, and 23 have arc-shaped boundaries, the shape of the boundaries does not need to be arc-shaped, for example, as shown by a two-dot chain line in FIG. The shape may be rectangular, and the shape is not limited.

[0020]

As described [Effect Invention above in detail, since the first and second particle size distribution measuring apparatus of the present invention are both of a mask to shield the zero-order light is disposed on the solid-state imaging device front,
The zero-order light is cut, and the diffracted light is received without being disturbed by the zero-order light. The first particle size distribution measuring apparatus of the present invention further comprises a mask for blocking the zero-order light, and a filter in which the density is reduced continuously or stepwise as the distance from the mask is increased. Therefore, the dynamic range of the diffraction image is compressed, and accordingly, a diffraction image having a wide dynamic range exceeding the dynamic range of the solid-state imaging device is received without being saturated.
In addition, the second particle size distribution measuring apparatus of the present invention has a diffraction pattern
By utilizing the fact that the rotation axis is rotationally symmetric,
To find the center point of the received diffraction image pattern
Therefore, the point defined as the center of the solid-state image sensor and the optical axis
There is no need to strictly align the center, and the zero-order light is cut
As long as the center of the optical axis is inside the mask
Becomes easier.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a particle size distribution measuring device according to one embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a diffraction image pattern on a front surface of a CCD.

FIG. 3 is a diagram illustrating an example of a measured particle size distribution.

FIGS. 4A and 4B are a front view and a side view showing an example of a CCD in which a glass plate provided with a mask for cutting zero-order light and a filter for attenuating diffracted light is adhered to the surface.

FIG. 5 is a schematic configuration diagram showing an example of an optical system for examining a light reception distribution when uniform light is applied to a CCD.

FIG. 6 is a diagram showing another example of the filter attached to the surface of the CCD.

FIG. 7 is a diagram showing the density distribution along the α axis of each of the filters shown in FIGS. 4, 6A and 6B.

[Explanation of symbols]

 Reference Signs List 1 laser light source 2 laser light 3, 5, 8 lens 4 particle group 6 CCD 7 arithmetic circuit 10 composite diffraction pattern 20 mask 21, 22, 23, 24 ND filter

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 15/02 JICST file (JOIS)

Claims (2)

(57) [Claims] An irradiation optical system for irradiating a group of particles with a laser beam, a solid-state imaging device for receiving a diffraction image by the group of particles, and particles of the group of particles based on a diffraction image pattern received by the solid-state imaging device. A particle size distribution measuring device comprising: a calculating means for obtaining a diameter distribution, wherein a mask for shielding zero-order light that is not diffracted by the fine particle group is provided on a front surface of the solid-state imaging device; and
As the distance increases, the concentration decreases continuously or gradually.
A particle size distribution measuring device, wherein a filter is arranged. 2. Irradiation optics for irradiating a group of fine particles with a laser beam.
System and solid-state imaging device for receiving a diffraction image by the fine particle group
Based on the diffraction image pattern received by the solid-state image sensor.
Calculating means for determining the particle size distribution of the fine particle group based on the
In the particle size distribution measuring device obtained above, diffracted by the fine particles on the front surface of the solid-state imaging device.
A mask for blocking the zero-order light, and wherein the calculating means detects the number of times the light is received by the solid-state imaging device.
The diffraction image utilizing the fact that the folding image pattern is rotationally symmetric
The center point of the pattern is determined and the
Particle size distribution measuring apparatus you <br/> characterized in that to determine the particle size distribution of the serial group of fine particles.