JP2811236B2 - 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.

In the above-described method using a large number of annular optical sensors, it is necessary to precisely adjust the position so that the center of a photodetector composed of the multiple annular optical sensors exactly coincides with the optical axis. In order to simplify this preparation, a solid-state imaging device such as a CCD is used in place of the detector including a large number of annular optical sensors. As preliminary preparation, only the position is roughly adjusted, and the exact optical axis center may be separately obtained later.

[0004]

The algorithm for obtaining the particle size distribution based on the pattern of the diffracted light is as follows.
It is assumed that the laser beam scattered and diffracted by one particle in the particle group is not scattered (diffracted) by another particle again, so that multiple scattering does not occur. Becomes

[0005] This multiple scattering is difficult to completely prevent, and occurs even in ordinary measurement. Therefore, the particle size distribution obtained when the particle size distribution is measured is within an allowable error. Or not. The present invention has been made in view of the above circumstances, and has as its object to provide a particle size distribution measuring device that can determine whether the occurrence of multiple scattering is within an allowable amount.

[0006]

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 particles with laser light; and a diffraction image formed by the group of particles. In the particle size distribution measuring device, comprising: a solid-state imaging device for receiving light; and arithmetic 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, the fine particle group is irradiated. Monitoring means for monitoring the ratio between the light amount of the previous laser beam and the light amount of the zero-order light that is not diffracted by the particle group or the light amount of the diffracted light diffracted by the particle group after being irradiated to the particle group It is characterized by having.

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, and a solid-state imaging device for receiving a diffraction image by the group of particles. And 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, wherein the zero-order light in a state where the fine particle group does not exist is provided. There is provided a monitor means for monitoring a ratio between the light amount and the light amount of the zero-order light in the state where the particle group is present or the light amount of the diffracted light diffracted by the particle group.

In the first and second particle size distribution measuring devices, a warning means for issuing a warning when the diffracted light exceeds a predetermined ratio based on the ratio monitored by the monitoring means is provided. Preferably, it is provided.

[0009]

The large number of multiple scatterings means that the total scattering (diffraction) including only one-time scattering (diffraction) is large, and therefore, the zero-order light remaining without being scattered is reduced and scattered (diffracted). It means that the diffracted light increases. The present invention has been completed based on this finding, and in the first particle size distribution measuring apparatus of the present invention, the amount of laser light before irradiation to the fine particle group and the zero-order light or By providing monitoring means for monitoring the ratio of the amount of diffracted light to the amount of diffracted light, the second particle size distribution measuring apparatus of the present invention has the amount of 0-order light in the absence of the particle group and the presence of the particle group. A monitoring means for monitoring the ratio of the zero-order light or the amount of diffracted light to the amount of light in the state is provided so that the degree of multiple scattering can be determined. It is determined whether or not.

[0010] Further, by providing a warning means for issuing a warning when the diffracted light increases beyond a predetermined ratio, the obtained particle size distribution can be relied on without always paying attention to whether or not multiple scattering is excessive. This is perceived when it is difficult to do so, thus making the device more foolproof.

[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 mirror that reflects a part of the laser light 2, and the reflected light from the mirror 3 of the laser light 2 applied to the mirror 3 is a photodetector. At 4, the light amount is detected, and the signal is input to the arithmetic circuit 5.

On the other hand, the laser light 2 transmitted through the mirror 3 is converted into parallel light by an irradiation optical system 6 including a pinhole plate 6a.
For example, the fine particles 7 contained in a fuel spray of an automobile are irradiated. A part of the laser light 2 applied to the fine particle group 7 is condensed by the lens 8 after being partially diffracted by the fine particle group 7, and a part thereof is reflected by the mirror 9 so that only the zero-order light passes through the pinhole plate 10. The light passing therethrough is detected by the photodetector 11. The output signal of the photodetector 11 is also input to the arithmetic circuit 5.

The laser beam transmitted through the mirror 9 is a CCD.
The CCD 12 receives the diffraction image pattern of the particle group 7 irradiating the front surface of the microparticles 12. Figure 2 shows this CC
It is the figure showing an example of the diffraction image pattern in the front surface of D12. When the particle group 7 is composed of only particles having a predetermined diameter, a diffraction pattern 21 indicated by a broken line in FIG. 2 is generated on the CCD 12, for example. Figure 2 if configured
A diffraction pattern 22 indicated by a dashed line is generated. Here, since the fine particle group 7 is composed of fine particles having various diameters, the diffraction pattern 20 formed by the fine particle group 7 is a diffraction pattern of fine particles of various diameters. (Diffraction patterns 21, 22, etc.) are superimposed.

The diffraction pattern received by the CCD 12 shown in FIG. 1 and converted into an electric signal is input to an arithmetic circuit 5, and the arithmetic circuit 5, for example, shown in FIG. As shown, each particle size d
Is obtained. FIG. 4 (A),
(B) is a front 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.

In the present embodiment, the CCD 12 is scheduled to roughly adjust its optical axis so that the zero-order light is irradiated to the upper left end of FIG. 4A. A mask 23 is attached to the upper left end of the surface of the CCD 12. On the other hand, as shown in FIG. 2, the amount of light in the diffraction pattern is larger in the area closer to the center of the optical axis (the irradiation position of the zero-order light) on average, and the amount of light decreases as the distance from the center of the optical axis increases. Therefore, in the present embodiment, the ND filter 2 having a uniform density is located in the upper left area of FIG.
4 is affixed.

Here, since the left end of the CCD 12 is covered with the mask 23 and does not receive the zero-order light, the present embodiment utilizes the fact that the diffracted light pattern is to be rotated about the center of the optical axis. In the means 5 (see FIG. 1), CC
The diffraction pattern received in D12 is
By performing the binarization process, for example, an arc 25 indicated by a broken line in FIG. 4 is obtained, and a center point 0 of the arc 25 is obtained.
Thereby, 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 corrects the portion of the diffraction pattern that has been attenuated by the ND filter 24, and based on the corrected diffraction pattern, the particle size distribution of the fine particle group 7. Is required. A signal representing the obtained particle size distribution is sent to the CRT display 13,
The particle size distribution is displayed on the display screen of the RT display 13 in the form of, for example, a graph or a list as shown in FIG.

The ratio η of the amount of light detected by the two photodetectors 4 and 11 is obtained by the calculating means 5. Here, this ratio 7 is the particle group 7 detected by the photodetector 4.
The light amount of the laser beam 2 before being applied to the
Assuming that the light amount of the zero-order light that is not diffracted by the particle group 7 after being irradiated to the particle group 7 detected by 1 is E2, η is defined as η = E2 / E1. In the arithmetic circuit 7, this ratio η is compared with a predetermined threshold value Th1, and η <Th
If it is 1, a signal is sent to the buzzer 14 and an alarm sounds. The fact that the ratio η is lower than the predetermined threshold value Th1 indicates that the ratio of the light diffracted by the particle group 7 to the light amount of the laser beam 2 applied to the particle group 7 is large. The scattering also corresponds to exceeding the allowable level.

In the above embodiment, the pinhole plate 10 and the photodetector 11 are provided to monitor the light quantity of the zero-order light. Instead, the mask 23 shown in FIG. Instead of a mask that completely cuts, the CCD 12 may be provided with a high-density filter so that the CCD 12 can correctly measure the light intensity of the zero-order light, and the CCD 12 may monitor the light intensity of the zero-order light.

Instead of monitoring the light quantity of the zero-order light, the total light quantity of the diffracted light may be monitored by the CCD 12 or by providing another light detector. In this case, a warning is issued when the ratio of the amount of diffracted light to the amount of light detected by the photodetector 4 is equal to or greater than a predetermined threshold. Further, instead of detecting the light amount of the laser beam 2 before irradiating the particle group 7 with the mirror 3 and the photodetector 4, the light amount E4 of the zero-order light in a state where the particle group 7 does not exist is detected by the photodetector. 11 and particle group 7
The light intensity E5 of the zero-order light in the state where
When the light amount ratio ξ = E5 / E4 is lower than a certain threshold value Th2, it may be determined that the multiple scattering exceeds an allowable level. In this method, it is necessary to perform the measurement twice when the fine particle group 7 does not exist and when the fine particle group 7 exists, but the mirror 3 and the photodetector 4 are unnecessary, and the influence of the contamination of the irradiation optical system 6 is canceled. Therefore, there is an advantage that a more accurate determination can be made.
Note that, in this method as well, the 0th-order light may be detected by the CCD 12 instead of the photodetector 11 as in the above-described method, and the light detected when the fine particle group 7 exists is not the 0th-order light. It may be diffracted light.

In the embodiment shown in FIG. 1, the buzzer 14 emits a warning sound. However, the present invention is not limited to the generation of a warning sound. For example, a warning lamp may be provided. It may be turned on or blinked, or a warning character may be displayed on the display screen of the CRT display 13 or blinked.

In the present invention, it is not always necessary to provide a warning means. For example, the above-mentioned ratio η and ratio ξ are displayed on a CRT display 13 together with a graph as shown in FIG. The determination as to whether or not is reliable may be left to the measurer.

[0022]

As described above in detail, the first particle size distribution measuring apparatus according to the present invention uses the light amount of the laser beam before irradiating the fine particle group and the zero-order light after irradiating the fine particle group. Or, because the ratio with the amount of diffracted light is monitored,
Further, the second particle size distribution measuring device of the present invention monitors the ratio of the light amount of the zero-order light in the state where the fine particle group does not exist to the light amount of the zero-order light or the diffracted light in the state where the fine particle group exists. Therefore, it is possible to know whether or not the occurrence of multiple scattering is within an allowable level. If a warning is issued based on this ratio when the occurrence of multiple scattering exceeds an allowable level, the device becomes easier to use.

[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 glass plate provided with a mask for cutting zero-order light and a filter for attenuating diffracted light is adhered to the surface.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 laser light source 2 laser light 3, 9 mirror 4, 11 photodetector 5 arithmetic circuit 6 irradiation optical system 6 a pinhole plate 7 fine particle group 8 lens 10 pinhole plate 12 CCD 13 CRT display 14 buzzer 23 mask 24 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 by the group of particles, and In a particle size distribution measuring apparatus provided with arithmetic means for obtaining a particle size distribution, the amount of the laser light before being irradiated to the fine particle group and the light amount after being irradiated to the fine particle group are not diffracted by the fine particle group. A particle size distribution measuring device comprising a monitoring means for monitoring a ratio of a light amount of zero-order light or a light amount of diffracted light diffracted by the fine particle group. 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. A particle size distribution measuring device provided with an arithmetic unit for obtaining a particle size distribution, wherein the light amount of the zero-order light in a state where the fine particle group does not exist, and the light amount of the zero-order light in a state where the fine particle group exists or the fine particle group A particle size distribution measuring device comprising a monitor for monitoring a ratio of the amount of diffracted light diffracted by the light source to the amount of the diffracted light. 3. The grain according to claim 1, further comprising a warning unit that issues a warning when the diffracted light exceeds a predetermined ratio based on the ratio monitored by the monitoring unit. Diameter distribution measuring device.