JPH0237978B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a particle size measuring device for measuring the diameter of microparticles. [Technical background of the invention and its problems] When a spherical particle with a particle size D is irradiated with parallel monochromatic light such as a laser beam, the scattered light intensity i (D, θ) generated in the angle θ direction is Mie It can be calculated accurately using scattering theory. Therefore, the present inventor measured the scattered light intensity distribution I ₍ 〓 ₎ of the laser beam irradiated to the particle group to be measured, and calculated the scattered light intensity i by one particle based on the Mie scattering theory.
(D, θ) and particle size distribution nr(D) as follows: I ₍ 〓 ₎ =∫i(D, θ)n _r(D) dD ……(1) Since the relationship A particle size measuring device for determining the distribution nr(D) was proposed. As shown in FIG. 1, this device has a laser device 1.
The laser beam oscillated and outputted by the collimator system 2 is converted into a parallel laser beam having a predetermined cross-sectional area, and the particle group 3 to be measured is irradiated with this. Then, the scattered light of the laser beam by the particle group 3 to be measured is detected at the scattering angle of the laser beam by a light receiving section arranged equidistantly from the position of the particle group 3 to be measured and at every minute angle Δθ according to the scattering angle θ. Each is detected according to θ, and the scattered light intensity distribution is determined. In addition, here, the optical fiber 4 ₁ ~
One end of the optical fiber 4n is placed in a light receiving section corresponding to the scattering angle θ, and each scattered light guided through these optical fibers 4 ₁ to 4n is received and detected by a photodetector 5 ₁ to 5n. The current from the photodetector is configured to be input to the computer system 7 via amplifiers 6 ₁ to 6n that convert the current into voltage and amplify it. This computer system 7 calculates the scattered light intensity distribution I ₍ 〓 ₎ from the scattered light intensities I ₁ , I ₂ , ..., In at the scattering angles θ ₁ to θ _o at which the optical fibers 4 ₁ to 4n are installed.
= (I ₁ , I ₂ , ..., I _o is determined, and the particle size distribution n _{r (D)} is calculated according to the above equation (1). This result is, in other words, the particle size distribution n _{r ( D)} is displayed on the display 8. However, such a device has the following problems. Namely, when the particles to be measured are present over a wide range, or when the particles of the particle group 3 to be measured When the density is high, the number of particles scattering the laser beam increases,
The influence of multiple scattering cannot be ignored. For this reason, the relationship shown in equation (1) above, that is, the relationship that the measured scattered light intensity distribution is expressed by the superposition of scattered light by one particle, no longer holds.
As a result, particle size measurement becomes impossible. Furthermore, since the scattered light intensity distribution measured as described above is a relative value, there is a disadvantage that the particle size distribution calculated from it can only take a relative value. Therefore, many measurement constraints have been added to particle size measurements. [Object of the Invention] The present invention has been made in consideration of the above circumstances, and its purpose is to accurately measure the particle size distribution even when there are a large number of scattered particles, and to determine the absolute value of the particle size distribution. The object of the present invention is to provide a simple and highly practical particle size measuring device that can be used to measure the particle size. [Summary of the Invention] The present invention calculates the transmittance of a laser beam irradiated onto a particle group to be measured from the amount of light transmitted through the particle group to be measured, and according to this transmittance, the After adjusting the scattered optical path length of the laser beam, the scattered light of the laser beam by the particle group to be measured in this scattered optical path length region is detected to obtain the scattered light intensity distribution, and from this scattered light intensity distribution, the particle group to be measured is determined. The particle size distribution is determined absolutely. In particular, the scattered light intensity distribution is determined after adjusting the scattered light path length L to such a length that the transmittance of the laser light is about 60% or more. [Effects of the Invention] Thus, according to the present invention, even when the number of scattered particles is large, the scattered light intensity distribution can be determined in a state where the influence of multiple scattering can be ignored by adjusting the scattered optical path length L. Therefore, it becomes possible to calculate the particle size distribution from this scattered light intensity distribution. That is, Figure 2 shows the relationship between the scattered optical path length L and the transmittance in the case of a minimum particle density that cannot be measured. The results are shown below. The above-mentioned minimum particle density that cannot be measured is the particle density where the influence of multiple scattering appears.
It is the minimum grain density. In other words, it is shown that measurement is possible regardless of the particle density within the shaded range. As is clear from the relationship shown in Figure 2, when the scattered optical path length L is 0.1 mm, the transmittance is approximately 0.34 (34%) or less when the influence of multiple scattering by all scattering particles occurs. ,
When the scattered optical path length L is 0.2 mm and the influence of multiple scattering occurs, the transmittance is about 0.55 (55%) or less. Therefore, it can be seen that the scattered light intensity distribution can be measured without being affected by multiple scattering if the scattered light path length L is adjusted so that the above transmittance is maintained at about 60% or more. Moreover, the results shown in FIG. 2 above are supported by the physical basis that when the scattering cross-section of all scattering particles exceeds the cross-section of the irradiation beam, the effect of multiple scattering appears. By the way, the transmittance Iout/Iin. of the laser beam that passes through the particle group 3 to be measured can be expressed as follows. Iout／Iin.＝exp{−L・∫ ^∞ ₀ C _(D)・N _(D) dD}……(2
) However, in the above equation, C _(D) is the scattering cross section by particles of particle size D, N _(D) is the particle size distribution expressed in absolute number, and B is the diameter of the laser beam. Furthermore, if the relative particle size distribution is n _r(D) , the particle size distribution N _(D) indicated by the absolute number above is given by A as a constant, N _(D) = A・n _r(D) ... (3) It can be shown as: Substituting this relationship into the above equation (2) and rearranging it, Iout/I _io =exp{−L・A∫ ^∞ ₀ C _(D)・n _r(D) dD}……(
4), and taking its logarithm, l _o (Iout／Iin)=−L・A∫ ^∞ ₀ C _(D)・n _r(D) dD}...
(5) becomes. Here, L and C _(D) in the above equation are known, and n _{r (D)} can be obtained from the relationship shown in the above equation (1), so the transmittance of the laser beam Iout/
By measuring Iin, the constant A can be determined from the above equation (5). Therefore, using this constant A, it is possible to obtain the absolute value particle size distribution N _(D) of the particle group 3 to be measured from the relationship of equation (3). In this way, according to the apparatus of the present invention, even when the number of scattered particles is large, the absolute particle size distribution can be easily and effectively determined, and a great practical effect can be achieved. [Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a schematic diagram of the main parts of the embodiment device.
This device uses a light-transmitting shield, such as glass 11,
12, and the particle group 3 to be measured is guided between them, and the scattered light path length is adjusted by the distance L. The glass 11 separates the scattering optical path region from the laser beam irradiation system side, and guides the laser beam output from the laser device 1 through the optical fiber 13, and converts the laser beam into a parallel beam via the collimator lens 14. and irradiates the scattered light path region. The glass 11, lens 14, etc. are moved integrally along the optical axis, and the scattered light path length L is variably set. On the other hand, the light receiving system side, which is separated from the scattering optical path region by the glass 12, has a predetermined number of optical fibers 4.
₁ to 4n are arranged equidistantly at every minute angle Δθ according to the scattering angle θ, and an optical fiber 15 for determining the transmitted light side is provided on the optical axis.
The light extracted through these optical fibers 4 ₁ -4n, 15 is detected by photodetectors, respectively. In other words, in addition to the configuration shown in FIG. 1, the light receiving system side includes an optical fiber 15 for measuring transmitted light.
The optical fiber 15 is also equipped with a photodetector for receiving and detecting transmitted light through the optical fiber 15. Then, from the amount of transmitted light detected through the optical fiber 15, the transmittance of the laser beam to the particle group 3 to be measured in the scattering optical path region of a predetermined length defined by the glasses 11 and 12 is determined. It's getting old. Then, the laser beam irradiation system including the glass 11 is controlled to advance or retreat along its optical axis in accordance with the transmittance determined in this manner, and the transmittance is adjusted to a position exceeding 60%. The optical path length L at this time is measured by another means. For example, the optical path length L may be measured using a laser length measuring device, or the optical path length L may be determined from the relationship between the amount of movement of the lens 14 and the reference position using a micrometer mechanism or the like. You may also do so. Incidentally, instead of the laser beam irradiation system, the light receiving system side may be moved integrally along the laser beam irradiation optical axis to adjust the optical path length L.
Furthermore, instead of detecting the transmitted light and scattered light through the optical fibers _{41 to} 4n and 15, a photodetector may be arranged at each light receiving position to directly detect the transmitted light and scattered light. is also possible. After the scattered light path length L is set as described above, the scattered light intensity distribution I _(D) by the particle group 3 to be measured is
is determined, and the particle size distribution N _(D) is calculated as follows. That is, as shown in FIG _. 4, the computer system 7 first calculates the scattered light intensity distribution I ₍ 〓 ₎ ( _{I 1 ,} I ₂ ~In) is required. Thereafter, the particle size distribution is determined from this scattered light intensity distribution according to the relationship shown in equation (1) above. Specifically, the conversion process to this particle size distribution is (i) logarithmic bound integral equation method, or (ii)
A logarithmic distribution function approximation method is used. Afterwards,
The particle size distribution determined by these means is converted into an absolute value. The logarithm-bound integral equation method subdivides the possible particle size range and approximates it using simultaneous equations to determine the particle size distribution, and the process flow is shown, for example, in FIG. 5. That is, the particle size range is set to [Dmin, Dmax], this interval is divided into N, and the above equation (1) is approximated as follows. I ₍ 〓 ₎ = _N 〓 ⁱ⁼¹ ∫ ^Dj _Di-1 i(D, θ)n _(D) dD Then, in the range [D _j , D _j-1 ], the particle size distribution n _(D)
Assuming that is constant, it is approximated as ∫ ^Dj _Di-1 i (D, θ) n _(D) dD [∫ ^Dj _Di-1 i (D, θ) dD] n (Dj). In this case, by setting i _s (Dj, θ)=∫ ^Dj _Di-1 i (D, θ) dD, the previous equation can be rearranged as follows. I ₍ 〓 ₎ = _N 〓 ^j=1 i _s (Dj, θ) n (Dj) Therefore, the measurement point of the scattered light intensity distribution is θ ₁ ,
If θ ₂ ~ θk, it can be expressed as I ₍ 〓 _i) = _N 〓 ^j=1 i _s (Dj, θi) n (Dj), and i _s (Dj, θi) = i _ij I (θi) = Letting I _i n(Dj)=n _j ,

【formula】

【formula】

[Formula] Then, the previous equation can be expressed as follows. I=G・n Then, the logarithmic transformation of this is expressed as I〓=G〓・n, and the condition that the particle size distribution is smooth,
In other words, when n ^* H _o is added to suppress the sum of squares of the cubic differences of n _j to a small value, the least squares solution is n = (G〓 ^* G〓) using Lagrange's undetermined multiplier method. +γH) ^-1 G〓 ^* I〓. However, G〓 ^* is the transposed matrix of G〓, and γ is an undetermined multiplier. However,
Under the condition that the particle size distribution n _j is positive or zero, select the positive particle size distribution n _j so that the solution to the above equation satisfies the condition for being a least squares solution. If selected, the particle size distribution can be determined from the scattered light intensity distribution. In other words, the condition for the solution of the previous equation to be a least squares solution (Kuhn-Tucker theorem) is that y = G〓 ^* (G〓 _o −I〓) + γH _o is (a) n If we satisfy y _j 0 (b) for j where _j = 0, and y _i = 0 for j where n _j > 0, we will obtain the least squares solution under the condition (n0). becomes possible. To sum up the above, we can approximate the relationship shown in equation (1) using the simultaneous equations log [I ₍ 〓 ₎ ] = log [∫i _(D , 〓 ₎ n _(D) dD], and form the following two equations. The particle size distribution n _(D) can be obtained by finding the least squares solution under two conditions. Condition 1: Particle size distribution is smooth. Condition 2...n0. On the other hand, when using the logarithmic distribution function approximation method, E = | log [I ₍ 〓 ₎ ] −log [∫i _(D , 〓 ₎ n _(D) dD] | ² is minimized, What is necessary is to determine the distribution parameter of n _(D) . That is, the process flow is shown in Figure 6, assuming a distribution function of n _(D) ,
The assumed distribution function may be modified so that the above E is minimized. In this case, as the above distribution function, for example, the distribution parameter is A,
As B It is sufficient to assume a normal distribution function as the initial value. Once the particle size distribution n _(D) has been determined in this way, since this particle size distribution is a relative value, its absolute value is Perform the conversion. That is, as shown in the flow of the conversion process in FIG. 7, the conversion constant A may be calculated using values such as the scattered optical path length L, and then the absolute value of the relative particle size distribution may be converted. As described above, with this device, even when the number of scattered particles is large, the scattered light intensity distribution can be determined without causing the effects of multiple scattering, and the absolute value of the particle size distribution can be determined from this intensity distribution. Can be done. Moreover, by limiting the scattered optical path length according to the transmittance of the laser beam, the particle size distribution can be easily and effectively obtained, which has a very high practical advantage. In addition, when detecting scattered light using optical fibers 4 ₁ to 4n, the opening end of the optical fiber has a certain spread of incidence angles, so in order to normally receive only scattered light, the optical fibers shown in Fig. 8 are used. It has been considered to provide a collimator lens 16 on the end face of the optical fiber, but as mentioned above, in the case of this device which limits the scattered light path length L, it is necessary to appropriately set the distance between the scattered light path region and the optical fiber. By simply doing this, only the scattered light can be received. For this reason,
The lens 16 becomes unnecessary, and the configuration can be simplified. Further, if the transmitted light is guided to the optical fiber 15 through the collimator lens 17 as shown in FIG. 9, the amount of transmitted light can be accurately measured, and measurement accuracy can be improved. Furthermore, if a part of the irradiated laser beam is split by the beam splitter 18 and detected as a reference beam to normalize the amount of transmitted light, for example, changes in the intensity of the irradiated laser beam can be effectively canceled out. This makes it possible to accurately determine the transmittance. It is also very useful to normalize the scattered light intensity using this reference light. Therefore, in this way, even if the laser beam intensity is unstable, such as when the power of the laser device 1 is turned on, the above-mentioned particle size measurement can be performed with high accuracy. In addition, in the embodiment, the scattered optical path length L was limited using the glasses 11 and 12, but as shown in FIG. The scattered light path length L may be limited. Glass 1 like this
If glasses 1 and 12 are not used, glass 11,
It is possible to avoid the problem of measurement errors caused by dust attached to the sensor 12. In addition, the present invention can be implemented with various modifications without departing from the gist thereof, and its practicality is high.

[Brief explanation of drawings]

Fig. 1 is a basic configuration diagram of a particle size measuring device, Fig. 2 is a diagram showing the relationship between the scattered optical path length and transmittance when the influence of multiple scattering occurs, and Fig. 3 is a diagram showing the main components of an embodiment of the device of the present invention. 4 to 7 are diagrams showing the flow of conversion processing in the embodiment device, FIG. 8 is a diagram schematically showing the configuration of the scattered light detection section, and FIGS. 9 and 10 are respectively FIG. 7 is a configuration diagram of main parts showing another embodiment of the present invention. 1... Laser device, 2... Collimator lens,
3...Particle group to be measured, ₄₁ , ₄₂ to 4n...Optical fiber, ₅₁ , 52 to _5n ...Photodetector, ₆₁ ,
6 ₂ - 6n... Preamplifier, 7... Computer system, 8... Display, 11, 12... Glass, 13, 15... Optical fiber, 14, 17...
Collimator lens, 18...beam splitter,
L...scattered optical path length, θ...scattering angle.

Claims (1)

[Scope of Claims] 1. A laser light source, a means for irradiating a group of particles to be measured with the laser light source, a transmitted light detection means for receiving and detecting the laser beam transmitted through the group of particles to be measured, and a means for detecting the transmitted light. means for adjusting the scattered optical path length of the laser beam with respect to the particle group to be measured to a length that does not cause multiple scattering according to the amount of transmitted laser light detected by the means; Scattered light detection means for receiving and detecting scattered light by the particle group to be measured according to its scattering angle, and means for calculating the particle size distribution of the particle group to be measured from the distribution of the scattered light according to these scattering angles. A particle size measuring device characterized by comprising: 2. The scattering optical path length of the laser beam with respect to the particle group to be measured is adjusted to a length such that the transmittance of the laser beam passing through the particle group to be measured is 60% or more. particle size measuring device. 3 To calculate the particle size distribution, first calculate the relative value of the particle size distribution from the intensity distribution of the scattered light, and then convert the above relative value to an absolute value according to the transmittance of the laser beam that has passed through the particle group to be measured. Claim 1 which is
Particle size measuring device as described in section.