Particle measuring device and particle measuring method
Inventors
Kondo, Kaoru • TABUCHI, Takuya • BANDO, Kazuna • Kato, Haruhisa • Matsuura, Yusuke
Assignees
National Institute of Advanced Industrial Science and Technology AIST • Rion Co Ltd
Publication Number
US-10837890-B2
Publication Date
2020-11-17
Expiration Date
2038-03-30
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Abstract
Provided is a particle measuring device and a particle measuring method for measuring a particle size with favorable accuracy. A flow cell (1) includes a flow passage (1a) of sample fluid. An irradiation optical system (3) irradiates, with light from a light source (2), the sample fluid in the flow passage (1a). An imaging unit (4) captures, from an extension direction of the flow passage (1a), an image of scattered light from the particle in a detection region in the flow passage (1a), the light passing through the detection region. A particle size specifying unit specifies a movement amount of the particle in a two-dimensional direction by Brownian motion based on multiple still images of a particle image captured at a predetermined frame rate by the imaging unit (4), thereby specifying the particle size of the particle from the movement amount in the two-dimensional direction.
Core Innovation
The invention relates to a particle measuring device and method for measuring particle size with favorable accuracy. It includes a flow cell with a flow passage for sample fluid containing particles, a light source, an irradiation optical system to irradiate the sample fluid with light, and an imaging unit that captures images of scattered light from particles in a detection region from the extension direction of the flow passage. A particle size specifying unit determines the particle size by specifying the movement amount of the particle in a two-dimensional direction by Brownian motion based on multiple still images captured at a predetermined frame rate.
The problem solved is that in conventional particle measuring methods where images are captured from a direction substantially perpendicular to the sample fluid flow, the particle movement includes both Brownian motion and movement by sample fluid flow velocity. Correcting for flow velocity-induced movement is difficult because it requires accurate flow velocity distribution, which is not easy to obtain, causing errors in particle movement measurement and size evaluation. This invention solves this by capturing images from the extension direction of the flow passage, where flow velocity components in the imaging plane are negligible, thus allowing measurement of the particle movement purely by Brownian motion without correction for flow velocity.
The invention also includes embodiments for combining two imaging units capturing images from orthogonal directions to specify three-dimensional Brownian motion, and for fluid simulation-based correction of flow velocity components near bent portions of the flow cell. These embodiments allow more accurate measurement of particle size and number concentration for each particle size with favorable accuracy by directly observing particle movement amounts in directions with minimal flow velocity influence or correcting for flow flow components where necessary.
Claims Coverage
The patent claims involve eight inventive features across eleven claims related to a particle measuring device with a flow cell, light source, imaging units capturing scattered light images, particle movement specifying, and particle size specifying units, addressing measurement accuracy and flow velocity correction.
Particle size measurement via two-dimensional Brownian motion from extension direction imaging
A particle measuring device including a flow cell with sample fluid passage, a light source, an irradiation optical system, and a first imaging unit arranged facing or opposite to fluid flow direction that captures multiple still images from the extension direction of the flow passage of scattered light from particles. A particle movement amount specifying unit specifies particle position in the images and specifies two movement amounts by Brownian motion in directions vertical to flow direction. A particle size specifying unit specifies particle size from these two movement amounts without correcting for flow velocity.
Three-dimensional particle size measurement using dual imaging units
The device further includes a second imaging unit capturing still images from a direction corresponding to the first movement amount, and a second particle movement amount specifying unit specifying positions and movement amounts including in the fluid flow direction. The particle size specifying unit uses first and second movement amounts and the movement in fluid flow direction to specify particle size.
Frame synchronization and particle matching across imaging units
First and second imaging units operating at identical frame rates synchronized to switch frames. The particle size specifying unit specifies particle size by associating one image from each imaging unit of the same particle and using respective movement amounts in orthogonal directions to specify three-dimensional movement and particle size.
Analysis of particle refractive index from scattered light intensity and size
Inclusion of a scattered light intensity specifying unit that specifies a scattered light intensity equivalent value from images and an analysis unit that analyzes the refractive index of the particle based on specified particle size and scattered light intensity.
Flow cell design with L-shaped bend and imaging position
The flow cell has an L-shaped bend, and the first imaging unit is arranged at a position facing fluid flow direction, capturing images in the detection region, facilitating measurement geometry.
Use of spherical dimple in flow cell for reducing refractive error
The flow cell includes a spherical dimple at the L-shaped bend portion, and the first imaging unit captures images through the dimple, reducing refraction of scattered light and improving measurement accuracy.
Calculation of number concentration and size distribution
An analysis unit counts particles per specified size to calculate number concentration and derives particle size distribution from the concentration for various size ranges.
Particle tracking to specify Brownian movement
The first particle movement amount specifying unit associates particles across multiple still images, specifying particle tracks over time to determine movement amounts in directions vertical to fluid flow based on captured image sequences.
The claims cover a particle measuring device that captures particle movement from positions facing or opposite to fluid flow direction to measure particle size by Brownian motion without flow velocity correction or with correction when needed, using one or multiple synchronized imaging units, an L-shaped flow cell with optical enhancements, particle tracking algorithms, scattered light intensity analysis, and particle concentration calculations.
Stated Advantages
Measurement of particle size and number concentration for each particle size with favorable accuracy.
Elimination of the need to correct particle movement amounts for sample fluid flow velocity, simplifying measurement and reducing error.
Facilitation of particle detection region setting without influence from the depth of field of the image capturing system.
Higher accuracy in particle size measurement through three-dimensional movement analysis using dual imaging units.
Improved measurement accuracy by reducing refraction of scattered light with a spherical dimple in the flow cell.
Accurate specification of particle movement near bent flow passage portions by using fluid simulation-based flow velocity correction.
Documented Applications
Measurement of particle size of particles included in sample fluid.
Measurement of number concentration of particles for each particle size in sample fluid.
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