US-12625048-B2 - Brownian motion correction method for particle measurement

US12625048B2US 12625048 B2US12625048 B2US 12625048B2US-12625048-B2

Abstract

A flow passage is irradiated with irradiation light, and light scattered from a particle contained in a sample passing through a detection region that is formed in a prescribed section is condensed at a position obtained by extending the prescribed section in a flow direction of the sample and captured at a prescribed frame rate. Then movement amount of the particle due to Brownian motion in directions perpendicular to the flow direction on the basis of captured plural frame images. Furthermore, a particle size of the particle is determined by correcting the movement amount using correction values that were obtained in advance corresponding to each of defocus positions for correcting errors of movement amount in the images caused by magnification.

Inventors

Kazuna BANDO
Kaoru Kondo
Takuya TABUCHI
Sota KONDO

Assignees

RION CO., LTD.

Dates

Publication Date: 20260512
Application Date: 20210303
Priority Date: 20200317

Claims (4)

1 . A particle measuring method comprising: irradiating a sample flowing through a flow passage with irradiation light; condensing light scattered from a particle contained in the sample passing through a detection region that is formed in a prescribed section of the flow passage by irradiation with the irradiation light, at a position obtained by extending the prescribed section in a flow direction of the sample; capturing, by a camera, the condensed scattered light at a prescribed frame rate; calculating movement amount of the particle due to Brownian motion in two-dimensional directions on a basis of captured plural frame images; correcting the calculated movement amount using correction values that were obtained in advance so as to correspond to each of defocus positions of frame images captured the condensed scattered light to correct for a magnification error that occurs due to defocusing at condensing the scattered light; determining a particle size of the particle on the basis of the corrected movement amount; outputting a result of the determination of the particle size to one of a display screen, a printer, a storage unit, and a network, wherein the correcting the calculated movement amount comprises using a correction map that stores the correction values corresponding to respective positions on a light receiving surface of the camera, and wherein the correction values are obtained by optical simulation software that calculates magnification errors for predetermined object heights at different defocus positions in the flow direction.
2 . The particle measuring method according to claim 1 , implement by a particle measuring device that comprises: a flow cell having the flow passage inside; a light source which emits the irradiation light; an irradiation optical system which irradiates the sample flowing through the flow passage with the irradiation light; a condensing optical system which condenses light scattered from the particle contained in the sample passing through the detection region that is formed in the prescribed section of the flow passage by irradiation with the irradiation light, at a position downstream of the prescribed section in the flow direction of the sample; and the camera which captures condensed scattered light at the prescribed frame rate.
3 . The particle measuring method according to claim 1 , wherein the correction values are expressed in a unit of velocity.
4 . A correction method of a particle measuring device which condenses light scattered from a particle contained in a sample passing through a detection region that is formed in a prescribed section of a flow passage by irradiation with irradiation light, at a position obtained by extending the prescribed section in a flow direction of the sample, and captures, by a camera, the scattered light at a prescribed frame rate, and which calculates movement amount of the particle due to Brownian motion in two-dimensional directions on a basis of captured plural frame images, and determines a particle size, the correction method comprising: correcting the movement amount using correction values to correct for a magnification error that occurs due to defocusing at the condensing the scattered light, where the correction values being obtained in advance so as to correspond to each of defocus positions of the captured frame images; determining a particle size of the particle on the basis of the corrected movement amount; outputting a result of the determination of the particle size to one of a display screen, a printer, a storage unit, and a network, wherein the correcting the calculated movement amount comprises using a correction map that stores the correction values corresponding to respective positions on a light receiving surface of the camera, and wherein the correction values are obtained by optical simulation software that calculates magnification errors for predetermined object heights at different defocus positions in the flow direction.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is US National Stage of International Patent Application PCT/JP2021/008302, filed Mar. 3, 2020, which claims benefit of priority from Japanese Patent Application JP2020-046243, filed Mar. 17, 2020, the contents of both of which are incorporated herein by reference. TECHNICAL FIELD The present invention relates to a particle measuring device and particle measuring method. BACKGROUND ART An FPT (flow particle tracking) method is known as one technique for obtaining a size of a particle floating in a sample. The use of the FPT method makes it possible to observe a movement of a particle by capturing light scattered from the particle by irradiating a sample with light and to measure a size, close to its geometrical size, of the particle from movement amount of the particle due to Brownian motion. Furthermore, for example, a refractive index of the particle can also be obtained by measuring light scattering intensity at the same time. As such, the FPT method is particularly useful for, for example, control of contaminating particles in semiconductor manufacturing processes. Known as devices using the FPT method (“FPT device”) is a device in which a condensing optical system consisting of lenses etc. is disposed at such a position as to be opposed to a sample flow direction (refer to Patent Literature 1, for example). The sample flow direction is, in other words, a direction in which a particle is transported by a sample flow. In this FPT device, since a condensing optical system is disposed at such a position as to be opposed to the sample flow direction, a movement of a particle caused by the sample flow is not observed from the condensing optical system, and only a movement of the particle due to its Brownian motion is observed. CITATION LIST Patent Literature Patent Literature 1: Japanese Patent No. 6,549,747 SUMMARY OF INVENTION Technical Problem Incidentally, in the FPT method, since a particle size is calculated from the Stokes-Einstein equation with using movement amount of the particle due to Brownian motion, and viscosity and a temperature of the sample, obtaining movement amount of the particle correctly is important for accurate measurement of a particle size. Since movement amount of the particle are obtained by determining a movement amount of the centroid of the particle between the frames from positions of the centroid of the particle in respective frame images constituting a captured moving image, an error of the magnification of the condensing optical system leads to an error of a movement amount of the particle. In FPT devices, it is necessary to set large number of apertures of lenses constituting the condensing optical system, and it is necessary to set large angle of view of the lenses. However, it is difficult for a highly accurate telecentric optical system to satisfy these requirements. Each frame image is captured with a magnification error due to defocusing and hence a particle is captured with different magnification values at respective positions in a sample flow direction. Furthermore, even if a particle is moving parallel with the sample flow direction, the particle is captured as if it were moving outward away from the center in a plane that is perpendicular to the sample flow direction due to magnification changes caused with defocus positions. As a result, movement amount of the particle obtained on the basis of captured frame images in this manner and a calculated particle size from the movement amount of the particle and other factors are necessarily affected by optical errors of the condensing optical system. The optical errors of the condensing optical system are therefore a problem to be solved for the purpose of measuring a particle size with high accuracy. An object of the present invention is to provide a technique for measuring a particle size with high accuracy. Solution to Problem In order to solve the foregoing problem, the present invention employs a particle measuring device and a particle measuring method described below. It is noted that words that are parenthesized below are just examples etc. and the present invention is not limited to them. That is, in a particle measuring device and a particle measuring method according to the present invention, a flow passage is irradiated with irradiation light and light scattered from a particle contained in a sample passing through a detection region that is formed in a prescribed section of a flow passage is condensed at a position obtained by extending the prescribed section in a flow direction of the sample and captured at a prescribed frame rate. Then movement amount of the particle due to Brownian motion in two-dimensional directions (i.e., directions perpendicular to the flow direction) on the basis of captured plural frame images. Furthermore, the movement amount is corrected using correction values that were obtained in advance corresponding to each of defocu