JP2805664B2 - Particle size distribution measurement method - 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 for irradiating a laser beam to a particle group contained in, for example, a fuel spray of an automobile, receives a laser beam diffracted by the particle group, and based on the diffraction pattern. The present invention relates to a particle size distribution measuring method for measuring the particle size distribution.

[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 obtained by diffraction from a group of fine particles having various diameters based on a predetermined algorithm to know the distribution of the particle diameter of the group of fine particles (for example, “surface”). Vol.22 No.2 (1984) 87 (27)
Pp. 94-34). Here, 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 determined by analyzing the 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 image pickup 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 0th-order light traveling on the optical axis usually has a much larger light quantity than the diffracted light, and when this 0th-order light is received, the surrounding light receiving element is greatly affected and the diffracted light is correctly received. There is a problem that can not be. Therefore, adjust the optical axis so that the zero-order light does not enter the solid-state imaging device, or arrange a mask that blocks the zero-order light at the location where the zero-order light is to be irradiated on the front surface of the solid-state imaging device. Thus, it is conceivable that only the diffracted light is correctly received.

However, in this case, the center of the optical axis cannot be determined by the irradiation position of the zero-order light. How to determine the center of the optical axis and perform the same measurement as that of the annular light receiving sensor in the above-mentioned conventional example is described. It becomes a problem. In view of the above circumstances, an object of the present invention is to provide a measuring method for measuring the particle size distribution of a group of fine particles using a solid-state imaging device.

[0006]

According to the present invention, there is provided a method for measuring a particle size distribution, comprising the steps of: (a) masking a diffraction image obtained by irradiating a group of fine particles with laser light with a 0-order light; A particle size distribution measuring method for receiving a light from a solid-state imaging device through the device and obtaining a particle size distribution of the fine particle group based on a pattern of the diffraction image, wherein the diffraction image obtained by the light reception is binarized. , A center point of the circle or the arc is obtained based on the circle or the arc appearing in the binary image, and a plurality of ring regions or partial regions of the ring concentrically surrounding the center point. Is determined, the sum of the light intensity in each of the annular regions or partial regions of the ring of the diffraction image obtained by the next light reception is obtained, and the particle group of the fine particle group is determined based on the distribution of the light intensity sum. It is characterized by obtaining a particle size distribution.

[0007]

According to the particle size distribution measuring method of the present invention, the received diffraction image is binarized to obtain a binary image, and the center point of the circle or arc appearing in the binary image is determined. Is the center of the optical axis (the position where the zero-order light is irradiated),
The center of the optical axis is obtained by calculation. In addition, since a plurality of annular regions or a partial region of the annular region surrounding the center point (optical axis center) obtained in this manner are defined concentrically, the annular region in the above-described conventional example is thereby determined. The preparation for obtaining the same thing as the case where the optical sensor is arranged by calculation is completed. As described above, in the present invention, the center point is obtained by calculation, and a plurality of annular regions or partial regions of the annular region are determined. Therefore, it is only necessary to roughly adjust the optical axis. Strict adjustment of the optical axis, which is required in the case of arranging, is unnecessary, and the time and labor required for measurement preparation are reduced.

In the present invention, after the measurement is prepared as described above, the sum of the light intensities in each ring region or a partial region of each ring is determined. Will be performed.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a particle size distribution measuring method according to one embodiment of the present invention. The laser light 2 emitted from the laser light source 1 is converted into parallel light spread over a predetermined range by a lens 3 and is applied to a fine particle group 4 included 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 10 formed by the fine particle group 4 is superimposed with the diffraction patterns (diffraction patterns 11, 12, etc.) of the fine particles having various diameters. 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, which calculates, for example, based on a signal representing the diffraction pattern according to an arithmetic method described later. The particle size distribution N of a particle group having each particle size d as shown in FIG.
Is required.

FIG. 4 is a front view showing an example of a CCD in which a glass plate provided with a mask for cutting the zero-order light is adhered to the surface. The CCD 6 is supposed to be roughly adjusted in its optical axis so that the zero-order light is irradiated to the upper left end of FIG. 4. Therefore, the mask 20 for cutting the zero-order light is provided at the upper left end of the surface of the CCD 6. Affixed to

FIG. 5 is a diagram showing a light quantity distribution along the r-axis shown in FIG. 4 of the diffraction pattern received by the masked CCD 6 shown in FIG. Since the CCD 6 is covered by the mask 20 from the point O1 at the upper left end to the point PO shown in FIG. 4 along the r-axis, the amount of received light E is almost zero. In addition, as shown in FIG. 2, the light amount of the diffraction pattern increases on the average closer to the center of the optical axis (the irradiation position of the zero-order light), and the light amount decreases as the distance from the center of the optical axis decreases. Represents the point PO as shown in FIG.
, The curve rises rapidly and then gradually decreases.

Next, the diffraction pattern obtained as described above and showing the light quantity distribution as shown in FIG. 5 is binarized by the threshold value Th1 shown in FIG. A value image is obtained, and a point P1 at which the value of the binary image changes from "1" to "0" is obtained along the r-axis. By performing this operation in each direction, the circular arc 22 shown by a broken line in FIG. Then, the center point O2 of the arc 22 is determined based on the arc 22. Since the intensity distribution of the diffraction pattern is rotationally symmetric, the center point O2 is the center of the optical axis irradiated with the zero-order light.

When the center O2 of the optical axis is obtained in this manner, the predetermined radii r1, r2 around the center O2 of the optical axis as shown in FIG. , R3,... Are drawn, and partial regions D1, n1 of n rings sandwiched between two arcs adjacent to each other are drawn.
, Dn (each region D1, D2, ..., Dn)
(The light receiving elements constituting the CCD) are determined, and the area (the number of pixels included in each area) of each of these areas is determined. It is stored in a RAM memory (not shown) in the arithmetic circuit 7. In the present embodiment, the zero-order light is applied to the position of the mask 20 at the upper left corner of FIG. 4, so that D1, D2,.
n is a part of the ring, but when the CCD 6 is configured to irradiate the 0th-order light to almost the center, at least a part of each of the regions obtained as described above is a ring region. In some cases.

Next, the diffracted image is received again in the same manner as described above, and the received light amount for each of the regions D1, D2,..., Dn shown in FIG.
Correction is made according to the area of 1, D2,..., Dn. FIG.
Is a graph showing the amount of received light after the correction as described above for each of the regions D1, D2,..., Dn. After obtaining the corrected amount of received light for each of the regions D1, D2,..., Dn, the particle size distribution (see FIG. 3) of the particle group 4 (see FIG. 1) is determined based on the pattern of the amount of received light. Desired.

Here, it is necessary to perform calibration so that the particle size distribution measuring device constructed as described above shows a correct measurement result, and the particle size distribution measuring device performs correct measurement even during use. Checks from time to time need to be performed. Here, the calibration, check, and the like are performed as follows.

FIG. 8 is a diagram showing an example of a pattern composed of a number of spots having a known diameter, which are exposed or printed on a photographic film or a glass plate. By preparing a film or a glass plate having such a pattern and placing it at the position of the particle group 4 instead of the particle group 4 shown in FIG. 1, a diffraction pattern corresponding to the pattern shown in FIG. 4 is received. The particle size distribution is calculated on the basis of, and calibration and checking are performed based on whether the calculation result is a known predetermined result. Conventionally, this check or the like is performed using an aluminum plate or the like in which many holes having the same diameter are formed. In this case, only a single diffraction pattern such as the diffraction pattern 11 in FIG. 2 can be checked. By using an electronic computer or the like to generate spots of various known diameters on a film or a glass plate, for example, a diffraction pattern in which a large number of diffraction patterns are combined by one check (the diffraction pattern in FIG. 2) 10), or for each user, using a particle size distribution pattern suitable for that user.

Here, the light amount distribution of only the diffracted light also has a wide dynamic range (the ratio between the minimum light amount and the maximum light amount required to receive light accurately), and
In some cases, the dynamic range of the diffracted light may be reduced as described below, in which case the dynamic range may exceed the dynamic range of 6 (the ratio between the minimum amount of light that can be correctly received and the maximum amount of light).

FIG. 9 is a front view showing an example of a CCD in which a glass plate on which a filter for attenuating diffracted light is applied in addition to a mask for cutting zero-order light is adhered to the surface. As described above, since the amount of light in the diffraction pattern is larger in a region closer to the center of the optical axis, an ND filter 21 having a uniform density is attached to a region adjacent to the mask 20 and having a large amount of light. When the ND filter 21 is attached in this manner, it is necessary to check the variation in density or the like at each position of the ND filter 21. Here, the variation or the like is checked as follows.

FIG. 10 is a schematic configuration diagram showing an example of an optical system for examining the received light intensity distribution when uniform light is irradiated on 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 comparing the average value of the signal for each pixel in the area not covered by the mask 20 or the filter 21 with the signal value for each pixel in the area covered by the filter 21 , The density variation of the ND filter 21 for each pixel in the area covered by the filter 21 is obtained, and the correction coefficient is obtained in accordance with this. This correction coefficient is recorded in a memory provided in the calculating means 7 and is used for obtaining a diffraction pattern in a state where the diffraction pattern is not attenuated by the filter 21 after receiving the diffraction pattern.

FIG. 11 is a diagram showing an example of a diffraction pattern received by a CCD provided with a glass plate provided with the mask and the ND filter shown in FIG. As in the case of the light-receiving diffraction pattern shown in FIG.
The light amount E sharply rises at the boundary point PO with the D filter 22, but since the light amount E is attenuated by the ND filter 21, the light amount E rises only to a light amount lower than that shown in FIG. 5, and then gradually along the r-axis. And the curve gradually rises again at the edge point P4 of the ND filter 21. Here, in the same manner as in the above-described embodiment, a binary image is obtained using Th4 as a threshold,
Arcs 23 and 24 (see FIG. 9) including P3 and P5 are determined, and the center of the optical axis (0
(Irradiation position of the next light). After that, as shown in FIG. 6, a number of partial regions D1, D2,... Dn of the ring are obtained. Using the position, area, and the correction coefficient determined as described above, N
A correction coefficient for each of the regions D1, D2,..., Dn for correcting the amount of received light caused by the D filter 22 is also obtained, whereby the measurement preparation is completed.

[0024]

As described above in detail, the particle size distribution measuring method of the present invention binarizes a diffraction pattern received using a solid-state imaging device and generates a circle or a circle appearing in the binarized image. The center point of the arc is determined, and a plurality of annular regions or a part of the annular region concentrically surrounding the center point are determined. Therefore, rough optical axis adjustment is required, and the time and labor required for measurement preparation are reduced. Is done.

[Brief description of the drawings]

FIG. 1 is a diagram showing a particle size distribution measuring method 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 graph showing each number N of particles having each particle diameter d.

FIG. 4 is a front view showing an example of a CCD in which a glass plate provided with a mask for cutting zero-order light is attached to the surface.

5 is a diagram showing a light amount distribution of a diffraction pattern along the r-axis shown in FIG.

FIG. 6 is a diagram showing a number (n) of partial regions D1, D2,..., Dn of a large number of (n) rings around the optical axis center O2.

FIG. 7 is a graph showing the amount of received light after correction for each of the regions D1, D2,..., Dn.

FIG. 8 is a diagram showing an example of a pattern composed of a number of spots having a known diameter, which is exposed or printed on a photographic film or a glass plate.

FIG. 9 is a front view showing an example of a CCD in which a mask for cutting zero-order light and a glass plate provided with a filter for attenuating diffracted light are adhered to the surface.

FIG. 10 is a schematic configuration diagram illustrating an example of an optical system that irradiates a CCD with uniform light.

11 is a diagram showing an example of a diffraction pattern received by a CCD provided with a glass plate provided with a mask and an ND filter shown in FIG.

[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 20 0th-order light shielding mask 21 ND filter

Claims (1)

(57) [Claims] 1. A solid-state imaging device receives a diffraction image obtained by irradiating a laser beam onto a particle group through a mask that blocks 0th-order light, and based on the pattern of the diffraction image, A binarized image obtained by binarizing a diffraction image obtained by the light reception, and obtaining a binarized image based on a circle or an arc appearing in the binarized image. The center point of a circle or an arc is determined, a plurality of annular regions or a part of the annular region concentrically surrounding the center point are defined, and each of the annular regions of the diffraction image obtained by the next light reception is determined. A particle size distribution measuring method, wherein a sum of light intensities in a region or a partial region of a ring is obtained, and a particle size distribution of the fine particle group is obtained based on the distribution of the sum of light intensities.