JP2859972B2 - 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 received 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, 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, the position is roughly adjusted, and the diffracted light is received. A method is conceivable in which the center of the optical axis is obtained by calculation using the fact that the light pattern is rotationally symmetric.

Here, in the above particle size distribution measurement, it is necessary to measure the diffraction light pattern with high accuracy. However, a solid-state imaging device such as a CCD usually has a glass plate for protection on its light receiving surface, which is not a problem for general imaging, but a monochromatic laser for particle size distribution measurement. Since light is used, interference fringes occur due to multiple reflections in the glass plate, and the interference fringes are superimposed on the original diffracted light and are received, thereby deteriorating the measurement accuracy. It has been difficult to use a solid-state imaging device for particle size distribution measurement.

In view of the above circumstances, the present invention uses a solid-state image sensor, protects the light receiving surface of the solid-state image sensor with a glass plate, and suppresses a decrease in measurement accuracy caused by the glass plate. It is an object to provide a distribution measuring device.

[0007]

In order to achieve the above object, a first particle size distribution measuring apparatus according to the present invention comprises: an irradiation optical system for irradiating a group of fine particles with a laser beam; A particle size distribution measuring apparatus, comprising: a solid-state imaging device that performs the measurement; and 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 glass plate provided with an anti-reflection film on the surface on the side away from the glass plate.

In order to achieve the above object, a second particle size distribution measuring apparatus according to the present invention comprises 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. A particle size distribution measuring device comprising: a calculating means for calculating a particle size distribution of the fine particle group based on a diffraction image pattern received by the solid-state image sensor . Any one
The other is characterized in that a glass plate tapered with respect to the other is disposed.

According to a third aspect of the present invention, there is provided a particle size distribution measuring apparatus comprising: an irradiation optical system for irradiating a group of particles with a laser beam; and a solid-state imaging device for receiving a diffraction image by the group of particles. A calculating means for calculating a particle size distribution of the fine particle group based on a diffraction image pattern received by the solid-state imaging device; surface or the back surface with the antireflective film on the surface side is attached has
A glass plate, one of which is tapered with respect to the other, is disposed.

[0010]

According to the first particle size distribution measuring apparatus of the present invention, since the glass plate is provided with the antireflection film, most of the multiple reflection is prevented, and therefore, the diffraction pattern is measured with high precision.

Further, in the second particle size distribution measuring apparatus of the present invention, since the glass plate is formed to be tapered, it does not repeatedly reflect at one place of the glass plate, so that unnecessary interference fringes are generated. There is little room to create and the diffraction pattern is measured with high accuracy.

Further, the third particle size distribution measuring apparatus of the present invention has an anti-reflection film attached to a tapered glass plate. Both actions of the device are superimposed, allowing a more accurate measurement of the diffraction pattern.

[0013]

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 particle group 4 is diffracted by the particle group 4 and then condensed by the lens 5, transmitted through the glass plate 8 and irradiated on the front surface of the CCD 6. Is received by the

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 a chain line in FIG. Here, since the particle group 4 is composed of particles having various diameters, the diffraction pattern 10 formed by the particle group 4 is superimposed with the diffraction patterns (diffraction patterns 11, 12, etc.) of the 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, 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.

FIG. 4 is a front view showing an example of a CCD having a glass plate provided with a mask for cutting zero-order light and a filter for attenuating diffracted light on the surface. In this embodiment, it is expected that the CCD 6 will roughly adjust its optical axis so that the zero-order light is irradiated to the upper left end of FIG.
0 is affixed to the upper left corner of the surface of the CCD 6. On the other hand, as shown in FIG. 2, the light amount of the diffraction pattern is larger in the region closer to the center of the optical axis (the irradiation position of the zero-order light) on average, and the light amount decreases as the distance from the center of the optical axis increases. Therefore, in this embodiment, an ND filter 21 having a uniform density is attached to an upper left area of FIG.

Here, since the upper left end of the CCD 6 is covered with the mask 20 and the zero-order light is not received, this embodiment utilizes the fact that the diffracted light pattern is rotationally symmetric about the optical axis center. In the calculating means 7 (see FIG. 1),
By binarizing the diffraction pattern received at D6 with a predetermined threshold value, for example, an arc 3 shown by a broken line in FIG.
0 is obtained, and the center point 0 of the arc 30 is obtained, and the center point is set as the optical axis center 0. Calculation means 7
Then, after the optical axis center 0 is obtained as described above, the portion of the diffraction pattern attenuated by the ND filter 21 is corrected, and the fine particle group 4 is determined based on the corrected diffraction pattern.
Is determined.

FIG. 5 is a side view showing a state in which a glass plate with a filter is attached to the front surface of the light receiving surface of the CCD shown in FIG. Normally, a glass plate is arranged on the front surface of the CCD as shown in FIG. 1 in order to protect the light receiving surface of the CCD. The glass plate 8 shown in FIG. On the front surface 8a, an antireflection film 9 is deposited corresponding to the wavelength of the laser beam 2 (see FIG. 1) used in the particle size distribution measuring device.

Therefore, the reflection of the laser beam is reduced by the antireflection film 9, and even the slight reflected light is reflected at the same position as shown by the dashed line in FIG. Therefore, the interference that hinders high-precision measurement of the diffraction pattern hardly occurs.

In the above embodiment, the glass plate 8 is formed to be tapered and the antireflection film 9 is also provided. However, the glass plate is formed to be tapered, and the glass plate is provided with the antireflection film. In either case, the generation of harmful interference light can be suppressed.

[0021]

As described above in detail, in the particle size distribution measuring apparatus of the present invention, a glass plate tapered and / or a glass plate provided with an anti-reflection film is disposed on the front surface of the solid-state imaging device. Interference light that is harmful to the measurement of the diffraction pattern can be reduced, and highly accurate measurement can be performed.

[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.

FIG. 4 is a front view showing an example of a CCD in which a mask for cutting zero-order light and a filter for attenuating diffracted light are attached to the surface.

5 is a side view showing a state in which a glass plate with a filter is attached to a light receiving front surface of the CCD shown in FIG. 4;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 laser light source 2 laser light 3, 5 lens 4, particle group 6 CCD 7 arithmetic circuit 8 glass plate 9 anti-reflection film 10 composite diffraction pattern 20 mask 21 ND filter

Claims (3)

(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 of the group of particles, and a solid-state imaging device for receiving the diffraction image of the group of particles based on a diffraction image pattern received by the solid-state imaging device. In a particle size distribution measuring apparatus provided with arithmetic means for obtaining a particle size distribution, a glass plate having an antireflection film on a surface on a side remote from the solid-state image sensor is arranged on a front surface of the solid-state image sensor. A particle size distribution measuring device characterized by the above-mentioned. 2. An irradiation optical system for irradiating a group of particles with a laser beam, a solid-state imaging device for receiving a diffraction image of the group of particles, and a solid-state imaging device for receiving the diffraction image of the group of particles based on a diffraction image pattern received by the solid-state imaging device. in the particle size distribution measuring apparatus and an arithmetic means for calculating the particle size distribution, the solid-state imaging device front, surface or have one of the back surface
A particle size distribution measuring device, wherein a glass plate having one of them tapered with respect to the other is arranged. 3. An irradiation optical system for irradiating a group of particles with laser light, a solid-state imaging device for receiving a diffraction image by the group of particles, and a solid-state imaging device for receiving the diffraction image of the group of particles based on a diffraction image pattern received by the solid-state imaging device. in the particle size distribution measuring apparatus and an arithmetic means for calculating the particle size distribution, in the solid-front of the surface or the back surface with anti-reflection film is subjected to a surface on the side remote from the solid-state image capturing device A particle size distribution measuring device, wherein a glass plate having one of them tapered with respect to the other is arranged.