Particle measurement device and particle measurement method

Abstract

Illumination light is irradiated to a flow path, and scattered light emitted from particles contained in a sample passing through a detection region formed in a prescribed section is condensed and captured at a prescribed frame rate at a position virtually extended in a flow direction of the sample. On this basis, an amount of movement of the particles in a direction perpendicular to the flow direction due to Brownian motion is calculated based on a plurality of frame images. Furthermore, in order to correct an error in the amount of movement on the image due to the magnification at the defocus position, the amount of movement is corrected using a correction value calculated in advance, and the particle diameter is determined.

Description

Technical Field

[0001] This invention relates to a particle measuring device and a particle measuring method. Background Technology

[0002] Previously, flow particle tracking (FPT) was a known method for determining the size of particles floating in a sample. Using FPT, the movement of particles can be observed by illuminating the sample with light and photographing the scattered light emitted from the particles. The particle's approximate geometric size can be measured based on the amount of movement caused by Brownian motion. Furthermore, the refractive index of the particles can be determined by simultaneously measuring the light scattering intensity. Therefore, FPT is particularly useful for controlling contaminating particles in semiconductor manufacturing processes.

[0003] As an apparatus for using the FPT method (FPT apparatus), a device is known to have a focusing optical system, consisting of lenses or the like, positioned opposite the flow direction of the sample (see, for example, Patent Document 1). The flow direction of the sample, in other words, refers to the direction in which particles are transported by the flow of the sample. In this FPT apparatus, the focusing optical system is positioned opposite the flow direction of the sample; therefore, the movement of particles generated by the flow of the sample cannot be observed from the focusing optical system, but only the movement of particles generated by Brownian motion is observed.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 6549747 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] Furthermore, in the FPT method, the particle size is calculated using the Stokes-Einstein equation based on the amount of particle movement caused by Brownian motion, the viscosity of the sample, and the temperature. Therefore, accurately determining the amount of particle movement is crucial for high-precision particle size measurement. Additionally, the amount of particle movement between frames is determined by the position of the particle's center of gravity captured in each frame of the captured video. Thus, errors in the magnification of the focusing optical system can lead to errors in the amount of particle movement.

[0009] In FPT (Focused Photometry) devices, it is necessary to increase the number of apertures in the lenses constituting the focusing optical system and widen the field of view, which is difficult to achieve simultaneously with a high-precision telecentric optical system. Magnification errors occur in each frame due to defocusing, and particles are captured in the image at different magnifications depending on their position in the sample's flow direction. Furthermore, even if particles move parallel to the sample's flow direction, due to the magnification change caused by the defocusing position, the particles will be captured in the image as if they are moving from the center outwards on a plane perpendicular to the sample's flow direction. Therefore, the amount of particle movement calculated based on such captured frames, and even the particle size calculated based on the amount of particle movement, will inevitably be affected by the optical errors of the focusing optical system. Thus, the optical errors of the focusing optical system are a problem that urgently needs to be solved for high-precision particle size measurement.

[0010] Therefore, the object of the present invention is to provide a technique for measuring particle size with high precision.

[0011] Solution for solving the problem

[0012] To address the aforementioned problems, the present invention employs the following particle measuring device and particle measuring method. It should be noted that the text in parentheses below is merely an example, and the present invention is not limited thereto.

[0013] That is, in the particle measuring apparatus and particle measuring method of the present invention, irradiation light is irradiated onto the flow path, and at a position where a predetermined section of the flow path is virtually extended towards the flow direction of the sample, the scattered light emitted from particles contained in the sample passing through the detection area is focused and photographed at a predetermined frame rate. The detection area is a region formed within the predetermined section by irradiation light. Based on this, the amount of two-dimensional movement (perpendicular to the flow direction) of the particles caused by Brownian motion is calculated based on multiple frame images. Furthermore, a correction value is used to correct this amount of movement, and the particle size is determined based on the corrected amount of movement. This correction value is a value pre-determined based on the defocus position to correct for magnification errors caused by focusing the scattered light.

[0014] In an FPT (Focused Photometry) device, when the scattered light emitted from particles in the sample is focused and photographed at a position that virtually extends the flow path in the direction of sample flow (opposite to the sample flow), a magnification error due to defocusing occurs during the focusing of the scattered light. The particles are captured in the frame image at different magnifications depending on their position in the sample's flow direction. The amount of particle movement due to Brownian motion calculated based on these images contains errors. Therefore, when determining the particle size based on the calculated movement, the errors in the movement affect the particle size, making it impossible to measure the particle size with high precision.

[0015] In contrast, this scheme uses a correction value to correct the calculated movement amount, and then determines the particle size based on the corrected movement amount. The correction value is a value pre-calculated based on the defocus position to correct for magnification errors caused by focusing scattered light. Therefore, according to this scheme, magnification errors caused by defocusing are corrected, resulting in a more accurate determination of particle movement and high-precision particle size measurement.

[0016] Preferably, in the particle measuring apparatus and particle measuring method described above, a value expressed in units of velocity is used as the correction value. More specifically, a value representing the error in the amount of movement per unit time, pre-calculated based on the defocus position and the position on the frame image, is used as the correction value.

[0017] In this scheme, the correction value used to calculate the amount of movement is expressed as the error in velocity units, i.e., the amount of movement per unit time. Therefore, even when changing the frame rate of the shot to measure the particles, the same formula can be used to correct the amount of movement.

[0018] Furthermore, it is preferable that, in any of the particle measuring devices and particle measuring methods described above, a value pre-calculated by assuming that the change in magnification due to the defocusing position is a linear function of the distance in the flow direction of the sample is used as a correction value.

[0019] In this scheme, the correction value used to correct the amount of movement is a value obtained in advance by calculating the change in magnification caused by the defocusing position as a linear function of the distance in the flow direction of the sample. Therefore, according to this scheme, the error within a fixed interval caused by defocusing can be corrected to a fixed amount regardless of the defocusing position.

[0020] Invention Effects

[0021] As described above, according to the present invention, particle size can be measured with high precision. Attached Figure Description

[0022] Figure 1 This is a block diagram illustrating the structure of a particle measuring device in one embodiment.

[0023] Figure 2A This is a diagram that briefly illustrates the structure of the detection unit in one embodiment.

[0024] Figure 2B This is a diagram that briefly illustrates the structure of the detection unit in one embodiment.

[0025] Figure 3 This is a simplified vertical cross-sectional view (along a vertical line) illustrating the structure of the detection unit in one embodiment. Figure 2A (Cross-sectional view along section line III-III).

[0026] Figure 4 This is a diagram illustrating the movement of particles within the detection area.

[0027] Figure 5 This diagram illustrates the movement of particles on the light-receiving surface of an image sensor.

[0028] Figure 6A This is a diagram illustrating the error in particle size caused by defocusing.

[0029] Figure 6B This is a diagram illustrating the error in particle size caused by defocusing.

[0030] Figure 7 It is a graph showing the calibration curve of magnification relative to the defocus position.

[0031] Figure 8 It is a diagram representing the image points of the illuminated surface.

[0032] Figure 9A This is a diagram representing an example of a correction map used to correct for the amount of movement in the X direction.

[0033] Figure 9B This is a diagram representing an example of a correction map used to correct for the amount of movement in the X direction.

[0034] Figure 10A This is a diagram representing an example of a correction mapping used to correct the amount of movement in the Z direction.

[0035] Figure 10B This is a diagram representing an example of a correction mapping used to correct the amount of movement in the Z direction. Detailed Implementation

[0036] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the following embodiments are preferred examples, and the present invention is not limited to these examples.

[0037] [Structure of the particle measuring device]

[0038] Figure 1 This is a block diagram showing the structure of a particle measuring device 1 in one embodiment.

[0039] Particle measuring device 1 is an FPT device, such as Figure 1As shown, its basic structure includes a detection unit 2 and a control and calculation unit 3. The detection unit 2 is a group of devices related to detecting scattered light by irradiating a sample, which is a fluid. This scattered light is generated by the interaction between the particles floating in the sample and the irradiated light. Furthermore, the control and calculation unit 3 is a group of functions related to controlling the various devices constituting the detection unit 2 and determining the particle size by calculating the movement of each particle based on the scattered light detected by the detection unit 2.

[0040] [Structure of the detection unit]

[0041] First, the structure of detection unit 2 will be explained.

[0042] The detection unit 2 is composed, for example, of a light source 10, an illumination optical system 20, a flow cell 30, a focusing optical system 40, and an imager 50. The light source 10 is, for example, a semiconductor laser diode that emits illumination light such as laser light. The illumination optical system 20 is, for example, constructed by combining a beam expander, a diffractive optical element, and an optical slit, which shapes the illumination light emitted by the light source 10 into a predetermined shape and focuses it inside the flow cell 30.

[0043] The flow cell 30 is made of transparent materials such as quartz or sapphire, and a flow path for the sample to flow into is formed inside it. When illumination light enters the flow cell 30, a detection area is formed within the flow path. The focusing optical system 40 (light-receiving lens system), for example, is a non-telecentric lens structure that focuses the scattered light emitted from particles passing through the detection area onto the imager 50. In other words, the "detection area" is the area where the illumination light intersects with the area focused by the focusing optical system 40 onto the imager 50. The imager 50, for example, is a camera equipped with an image sensor such as a charge-coupled device (CCD) or complementary metal-oxide semiconductor (CMOS), and it captures the scattered light focused by the focusing optical system 40 onto the light-receiving surface of the image sensor.

[0044] Figure 2A and Figure 2B This is a diagram that briefly illustrates the structure of the detection unit 2 in one embodiment.

[0045] Figure 2AThis is a perspective view of the flow cell 30. The flow cell 30 is L-shaped, with an L-shaped flow path formed inside. This L-shaped flow path is formed by connecting a first section 32 extending from the first opening 31 in the Y direction and a second section 34 extending from the second opening 33 in the Z direction at their respective ends. The sample flows into the first section 32 from the first opening 31, passes through the second section 34, and is discharged to the outside from the second opening 33. It should be noted that the shape of the flow cell 30 can be any shape with an L-shaped bend; for example, a U-shape or a crank shape can be used instead of an L-shape.

[0046] Figure 2B This is a top view that briefly shows the structure of the detection unit 2, especially the positional relationships between its components. The irradiation optical system 20 directs the shaped irradiation light B from a direction perpendicular to the flow direction (Y direction) of the sample in the first interval 32 (X direction). I The light is injected into the flow cell 30. Furthermore, the focusing optical system 40 and the imager 50 are positioned opposite the flow of the sample in the first interval 32, i.e., positioned such that the first interval 32 is virtually extended in the flow direction of the sample, and will capture the scattered light B emitted from the particles passing through the detection area M. S The light is focused for imaging. These components are used to observe the motion of each particle in the XZ plane, i.e., Brownian motion. It should be noted that the scattered light B... S The details of the photography will be further explained later using other accompanying images.

[0047] Figure 3 This is a simplified vertical cross-sectional view (along a line) illustrating the structure of the detection unit 2 in one embodiment. Figure 2A (Cross-sectional view along section line III-III). It should be noted that cross-sectional views of the focusing optical system 40 and the imager 50 are omitted.

[0048] As mentioned above, the post-operative irradiation light B I The flow is injected into the flow cell 30 in the X direction, forming a detection region M in the first interval 32. The shape of the detection region M is, for example, with the long side as the Z direction, the short side as the Y direction, and a depth in the X direction that is approximately equal to the long side.

[0049] A concave portion 35 is formed on the inner wall of the flow cell 30 located between the detection region M and the focusing optical system 40. This concave portion 35 has a concave shape, and its distance from the center of the detection region M is approximately equal to the radius of curvature of the concave portion 35. When scattered light B is generated from particle P passing through the detection region M... S When light is incident on the inner wall of the flow cell 30, refraction may occur due to the difference between the refractive index of the sample and the refractive index of the flow cell 30. However, the concave portion 35 can suppress the scattered light B incident on the inner wall of the flow cell 30. SRefraction.

[0050] The positions of the focusing optical system 40 and the imager 50 relative to the flow cell 30 are determined with reference to the optical axis of the focusing optical system 40. Each component is respectively positioned such that the optical axis of the focusing optical system 40 passes through the center of the detection area M, the center of the concave portion 35, and the center of the light-receiving surface of the image sensor of the imager 50. The imager 50 is positioned opposite the XZ plane and observes the motion of the scattered light generated in the detection area M, i.e., through the Brownian motion of each particle P in the detection area M, and captures the video at a specified frame rate.

[0051] Thus, by arranging the focusing optical system 40 and the imager 50 for detecting scattered light at a position opposite to the flow of the sample in the first interval 32, the motion of the scattered light (Brownian motion of particle P) can be observed.

[0052] [Structure of the control and arithmetic unit: see reference] Figure 1 ]

[0053] Next, the structure of the control and operation unit 3 will be explained.

[0054] The control and calculation unit 3 may consist of, for example, a control unit 60, an image acquisition unit 70, a particle determination unit 80, a movement calculation unit 90, a movement correction unit 100, a particle size determination unit 110, a scattered light intensity determination unit 120, a resolution unit 130, and an output unit 140. The control unit 60 controls the operation of each device in the detection unit 2 and a series of processes executed in the control and calculation unit 3. For example, the control unit 60 controls the on / off state of the irradiation light from the light source 10, the flow rate (flow rate) of the sample flowing into the flow cell 30, and the video recording by the camera 50. It should be noted that it is also possible to separate the component that controls part or all of the series of processes from the control unit 60 and control it within that component. For example, for the sample flow rate, a flow control device such as a mass flow controller may be separated from the control unit 60 and controlled using that device.

[0055] The image acquisition unit 70 acquires still images (frame images) of each frame from the video captured by the camera 50 at a predetermined frame rate. It should be noted that the video frame rate and the sample flow rate are controlled in such a way that a predetermined number of frame images can be acquired for each particle from the captured video. For example, if the length of the detection region M in the Y direction is 20 μm, the sample flow rate is set to 60 μm / second to acquire ten frame images from a video captured at 30 fps (i.e., 30 times per second).

[0056] Furthermore, the particle determination unit 80 determines particles from the frame images acquired by the image acquisition unit 70, establishes a correlation between each particle captured in consecutive frame images, and determines the trajectory of each particle based on this correlation.

[0057] For each particle determined by the particle determination unit 80, the movement calculation unit 90 calculates the movement in two dimensions (X and Z directions) caused by Brownian motion for each frame image. It should be noted that when determining the particle's trajectory and calculating the movement, a representative value of the particle's position is used. The particle's position is determined, for example, based on the particle's center of gravity or center.

[0058] For the amount of particle movement calculated by the movement amount calculation unit 90, the movement amount correction unit 100 uses the correction value defined in the pre-prepared correction mapping diagram to correct the error in the amount of movement caused by the magnification change due to the defocus position.

[0059] The particle size determination unit 110 determines the particle size of each particle corresponding to the diffusion coefficient based on the migration amount corrected by the migration amount correction unit 100. It should be noted that the specific methods related to the calculation and correction of the particle migration amount and the determination of the particle size will be described in detail below with reference to other accompanying drawings.

[0060] The scattered light intensity determination unit 120 determines the amount of scattered light from each tracked particle. Specifically, the scattered light intensity determination unit 120 determines the equivalent value of the scattered light intensity of the particle based on the image information transmitted when the particle determination unit 80 has determined the particle, according to the calculated average brightness value, maximum brightness value, binarized area, etc. of each bright spot of the same particle.

[0061] The analysis unit 130 calculates the particle number concentration according to each predetermined particle size range based on the particle size determined by the particle size determination unit 110. Furthermore, the analysis unit 130 analyzes the refractive index of each particle based on the equivalent value of the scattered light intensity determined by the scattered light intensity determined by the scattered light intensity determination unit 120 and the particle size determined by the particle size determination unit 110. Specifically, using sample particles with a known and approximately uniform particle size, such as polystyrene latex particles, the relationship between the relative scattered light intensity and the known particle size and refractive index is pre-determined. Based on this relationship, the refractive index of the measured particle is determined, or solid particles and bubbles are distinguished based on the difference in refractive index.

[0062] The output unit 140 outputs the parsing result from the parsing unit 130. The output unit 140 can output the parsing result in various ways, such as displaying it on a screen, outputting it to a printer, outputting it to a storage unit (not shown), or sending it to other devices via a network.

[0063] [The appearance of the particles during testing]

[0064] Figure 4 and Figure 5 This is a diagram illustrating the movement of particles during detection. More specifically, Figure 4 This shows the appearance of the detection area M when viewed from a direction perpendicular to the flow direction of the sample, i.e., the appearance of the particles on the YZ plane. Furthermore, Figure 5 This refers to the photographic method when the image is captured on the light-receiving surface of the image sensor within the imager 50, i.e., the appearance of particles on the XZ plane.

[0065] As described above, in this embodiment, the focusing optical system 40 and the imager 50 are positioned opposite the flow of the sample. However, due to the movement of the particles, the focus shifts due to defocusing of the focusing optical system 40. That is, the magnification varies depending on the position of the particles in the Y direction, resulting in differences in image height in each frame. Furthermore, even if particles P1, P2, and P3 are... Figure 4 The figures show movements parallel to the Y-direction, as shown. Figure 5 As shown, on the XZ plane, these particles also appear to move outward from the center of the detection area M due to the change in magnification caused by the defocus position. Then, the scattered light emitted from each particle as observed is imaged onto the receiving surface.

[0066] [Error caused by defocus]

[0067] Figure 6A and Figure 6B This is a diagram illustrating the error in particle size caused by defocusing.

[0068] Figure 6A In the focusing optical system 40 of this embodiment, the magnification at the focal position is 13.002293 times. For example, when an object with a height of 0.885 mm is located at the focal position within the detection area, the image height of the light-receiving surface 52 imaged within the imager 50 is 11.507029 mm. Furthermore, when the object is located at a position that is defocused (closer to the focusing optical system 40) by 2 μm in the flow direction (Y direction) of the sample, the image height of the light-receiving surface 52 imaged is 11.507432 mm.

[0069] When according to Figure 6BWhen attempting to calculate the object height (defocused image height ÷ magnification at the focal position) using the defocused image height as a reference, the result is 0.885031 mm. This means that based on the calculation using the defocused image height, there exists an object with a height of 0.885031 mm at the focal position, resulting in an error of 0.031 μm (shift error) compared to the actual object height of 0.885 mm. When calculating the particle's shift due to Brownian motion without considering this defocus-induced height error, the error will affect the particle size.

[0070] Therefore, in this embodiment, the following method is adopted: taking advantage of the fact that particles will inevitably move from a distance to the focusing optical system 40 (by being transported from a distant position to a near position through the flow of the sample), the calculation error of the amount of particle movement caused by the magnification change due to defocus is corrected according to the calibration curve of the magnification relative to the defocus position calculated in advance.

[0071] Figure 7 It is a graph showing the calibration curve of magnification relative to the defocus position.

[0072] In this embodiment, it is assumed that the flow rate of the sample flowing into the flow cell 30 is constant, and the calibration curve is a linear function of the distance in the Y direction. By assuming the calibration curve to be a linear function, the error within a fixed interval caused by defocusing can be corrected to a fixed amount regardless of the defocusing position.

[0073] Next, the calculation and correction methods for the movement amount will be explained.

[0074] Figure 8 This is a diagram representing the image points of the light-receiving surface 52. The light-receiving surface 52 has, for example, 2448 pixels (px) in both the horizontal (X direction) and vertical (Z direction) directions, to capture the light generated in the detection area in a manner opposite to the XZ plane. The scattered light generated from the particle on the XZ plane is imaged onto the light-receiving surface 52, thereby capturing the Brownian motion of the particle as video by the camera 50.

[0075] [Calculation of movement]

[0076] When frame images are acquired from the video captured by the image acquisition unit 70, firstly, the particle determination unit 80 determines the particles based on the frame images acquired from the video and calculates the centroid coordinates "(x) of the particles in each frame image. i , z i Here, "x" i " is the X coordinate in the frame image of the i-th frame, "z" is the X coordinate in the frame image of the i- i " represents the Z coordinate in the frame image of the i-th frame.

[0077] Based on this, the motion calculation unit 90 determines the particle's trajectory and calculates the particle's movement in the X and Z directions between consecutive frames based on the particle's centroid coordinates in each frame image. Specifically, the motion calculation unit 90 calculates the movement of the particle in the X and Z directions between consecutive frames using "x i+1 -x i To calculate the amount of particle movement (μm) in the X direction between frame i and frame i+1, use "z" i+1 -z i This is used to calculate the amount of movement (μm) of the particle in the Z direction between the i-th frame and the (i+1)-th frame. In other words, the amount of movement of the particle in the X and Z directions refers to the amount obtained by decomposing the vector representing the trajectory on the XZ plane from the centroid position at the i-th frame to the centroid position at the (i+1)-th frame into X and Z components.

[0078] [Movement Correction]

[0079] When the movement amount calculation unit 90 calculates the movement amount of the particle in the X and Z directions, the movement amount correction unit 100 then obtains the correction value corresponding to the position of the particle's center of gravity coordinates by referring to a pre-prepared correction mapping diagram. For each movement amount in the X and Z directions calculated by the movement amount calculation unit 90, the obtained correction value is used to perform correction using the following formula.

[0080] [Formula 1]

[0081] Δx (i) =(x i+1 -x i )-v x(xi，zi) Δt…(1)

[0082] Δz (i) =(z i+1 -z i )-v z(xi，zi) Δt…(2)

[0083] In the above formula (1), “Δx (i) "This represents the corrected shift in the X direction (μm). Furthermore, in the above formula (2), "Δz" (i) " represents the corrected Z-direction movement (μm). Furthermore, "Δt" in equations (1) and (2) is the reciprocal of the frame rate, i.e., the time interval (s) defined by the video frame rate.

[0084] In other words, "v" x(xi，zi) Δt” and “v” z(xi，zi) Δt" represents the inter-frame movement error (μm) caused by the magnification difference corresponding to the position of the centroid coordinates of the particles on the XZ plane. Here, "v" x(xi，zi) " and "v z(xi，zi)"The correction value (μm / s) is pre-calculated based on the X and Z components of the apparent movement speed. By defining the correction value as the movement speed, the same formula can be used to correct the amount of movement even when the frame rate changes."

[0085] It should be noted that the correction values ​​vary depending on the object height; therefore, a correction mapping map needs to be pre-created based on the pre-calculated correction value for each object height. In this embodiment, the correction value corresponding to the pre-assumed object height error (e.g., the aforementioned error of 0.031 μm relative to an object height of 0.885 mm) is pre-calculated using optical simulation software, and a correction mapping map corresponding to that object height is created. The format of the correction mapping map will be further illustrated later using other accompanying figures.

[0086] [Determination of particle size]

[0087] After the movement amount correction unit 100 corrects the movement amount of the particles in the X and Z directions, the particle size determination unit 110 then determines the particle size of each particle based on the corrected movement amounts. Specifically, firstly, the particle size determination unit 110 calculates the average movement amount L based on the corrected movement amounts of the particles in the X and Z directions using the following formula. R .

[0088] [Formula 2]

[0089]

[0090] In the above formula (3), "L R "i" represents the average movement (μm) per frame (between consecutive frames), "i" represents the frame number, and "M" represents the number of movements obtained from the frame images. For example, when M = 10, the frame numbers are 1 to 11, and the particle movement is calculated based on 11 frame images. Therefore, the number of movements calculated from these frame images is 10.

[0091] Next, the particle size determination unit 110 calculates the diffusion coefficient D using the following formula.

[0092] [Formula 3]

[0093] D = L R / (4·Δt)…(4)

[0094] Finally, the particle size determination unit 110 determines the particle size d according to the Stokes-Einstein formula shown below.

[0095] [Formula 4]

[0096] d=kB·T / (3π·η·D)…(5)

[0097] In the above formula (5), "kB" is the Boltzmann constant, "T" is the absolute temperature, and "η" is the viscosity coefficient of the sample.

[0098] [The effect achieved through correction]

[0099] According to the above formulas (4) and (5), the average displacement L in the Brownian motion of a 100 nm particle under the conditions of a time interval Δt defined by the frame rate being 1 / 120 s (frame rate being 120 fps), an absolute temperature T being 293.2 K, and a viscosity η being 0.001 Pa·s is calculated. R The calculated value is 0.378 μm.

[0100] Here, let's assume that... Figure 6A and Figure 6B As explained, a shift error of 0.031 μm was generated. The average shift calculated without shift correction was the aforementioned average shift L of 0.378 μm. R The particle size is 0.409 μm, which is obtained by adding a displacement error of 0.031 μm. In this case, according to the above formula (5), the particle size d is determined to be 85 nm. That is, even though the actual particle size is 100 nm, the particle size is determined to be 15 nm smaller when the displacement includes the error.

[0101] In contrast, in this embodiment, a predefined correction value is applied to correct the amount of particle movement, thereby correcting for magnification errors caused by defocusing. Therefore, according to this embodiment, the amount of particle movement can be determined more accurately, improving the measurement accuracy of particle size.

[0102] [Correction Map]

[0103] Next, the correction mapping diagram will be explained.

[0104] The correction mapping is a diagram obtained by pre-calculating and organizing correction values ​​for magnification errors caused by defocusing, according to each object height. The correction values ​​vary depending on the position on the observation surface; therefore, the correction values ​​are determined for each image point or interval on the light-receiving surface in the X and Z coordinate directions. In this embodiment, as described above, the correction values ​​are calculated using optical simulation software according to each pre-defined object height, and these correction values ​​are prepared in advance as the correction mapping corresponding to each object height.

[0105] Figures 9A to 10B This is a diagram illustrating a pre-prepared correction mapping diagram. Among them, Figure 9A and Figure 9B An example of a correction map (X-direction correction map) for correcting the amount of movement in the X direction is shown. Figure 10A and Figure 10B An example of a correction map (Z-direction correction map) for correcting the amount of movement in the Z direction is shown.

[0106] In each correction mapping, pre-calculated correction values ​​are defined based on the X and Z direction components of the apparent moving velocity. For example, assuming a frame rate of 120fps, the particle traverses the defocused region from -10μm to +10μm at a velocity of 2μm per frame (1 / 120s = 8.333ms). In this case, if using... Figure 6A and Figure 6B As explained, with an object height of 0.885 mm, the particle moves at a defocusing error of 0.031 μm within a 2 μm radius, meaning the error per frame is 0.031 μm. Therefore, the error velocity can be expressed as 3.72 μm / s (=0.031 μm / 8.333 ms). This velocity is the same on concentric circles starting from the center of the detection area. The values ​​of the components decomposed in the X and Z directions according to the coordinate position are defined as correction values ​​in each correction mapping. In other words, each correction mapping defines a value for the error, expressed in velocity units, pre-calculated based on the coordinate position.

[0107] It should be noted that the above explanation only illustrates the case where the object height is 0.885mm. In addition, calculations were performed for various object heights to calculate the error, and two-dimensional correction mapping diagrams in the X and Z directions were created.

[0108] Preferably, the correction value is set according to the image point of each light-receiving surface, but for the sake of simplifying the calculation process, it can also be set according to each fixed interval. For example, Figure 9A As shown, in the X-direction correction map, the detection area is divided into ten roughly equal regions along the X-direction. Figure 9B As shown, a range of X-coordinates is defined for these regions, along with the correction values ​​applied in relation to that range. When referring to the X-direction correction map, the corresponding region is selected based solely on the X-coordinate position, regardless of the Z-coordinate position, and the correction value for that region is applied.

[0109] In addition, such as Figure 10A As shown, in the Z-direction correction mapping, the detection region is divided into ten roughly equal regions along the Z-direction. Furthermore, as... Figure 10B As shown, a range of Z-coordinates is defined for these regions, along with the correction values ​​applied in accordance with that range. When referring to the Z-direction correction map, the corresponding region is selected based solely on the Z-coordinate position, regardless of the X-coordinate position, and the correction value for that region is applied.

[0110] For example, suppose in Figure 8 The image points shown are 2448×2448, and (x) i , z i The observed center of mass of the particle exists at the location (2448, 1). Regarding this location, when referring to... Figure 9A and Figure 9B When the X-direction correction mapping diagram is shown, the aforementioned X coordinates correspond to "Region 10". Therefore, for the amount of movement in the X-direction before correction, the correction value "3.359493" is applied to calculate the amount of movement Δx in the X-direction after correction. (i) Furthermore, when referring to Figure 10A and Figure 10B In the Z-direction correction mapping diagram shown, the Z coordinates mentioned above correspond to "Region 1". Therefore, for the Z-direction displacement before correction, the correction value "-3.359493" is applied to calculate the Z-direction displacement Δz after correction. (i) .

[0111] It should be noted that, Figures 9A to 10B The region segmentation shown in the calibration map is just one example and is not limited to this. For example, the region can be further subdivided (e.g., divided into 10px segments), or, if computational resources allow, the region can be left undivided and custom calibration values ​​can be defined for each pixel. In any case, the calibration values ​​vary depending on the object height; therefore, a calibration map needs to be pre-made according to each object height.

[0112] Furthermore, regarding the error quantity, besides optical simulation, it is also possible to pre-determine it through actual measurement. However, when determining the error quantity through actual measurement, there are other error factors besides the magnification of the optical system (e.g., the flow rate of the sample), so it is necessary to distinguish them from other factors, but it is foreseeable that the distinction will be difficult. In contrast, in this embodiment, the error quantity is calculated through optical simulation as described above. Therefore, it is not necessary to consider other factors that may cause errors, and the error quantity can be determined solely based on the error of the optical system.

[0113] [Advantages of the present invention]

[0114] As described above, the following effects can be obtained according to the above-described embodiments.

[0115] (1) Since the amount of particle movement is corrected by applying the pre-determined correction value, the magnification error caused by defocusing can be corrected to more accurately determine the amount of particle movement, thereby improving the measurement accuracy of particle size.

[0116] (2) Since the correction value is defined as the movement speed, the same correction value as before the change of the frame rate can be used to correct the movement even when the frame rate of the video is changed for measurement.

[0117] (3) Since the calibration curve of magnification relative to the defocus position is assumed to be a linear function of distance, the error within a fixed interval caused by defocus can be set as a fixed amount to correct the amount of movement regardless of the defocus position.

[0118] (4) Since the magnification error caused by defocus can be corrected, there is no need to use a telecentric optical lens to construct the condensing optical system 40, thus increasing the design freedom of the condensing optical system 40.

[0119] The present invention is not limited to the above-described embodiments and can be implemented in various modifications.

[0120] In the above embodiments, the illumination optical system 20 is constructed by combining a beam expander, a diffractive optical element, and an optical slit, but is not limited thereto. For example, it can also be constructed by combining multiple optical lenses.

[0121] In the above embodiment, the irradiation light B is... I The light is directed from the X direction into the first interval 32, but it can also be replaced by the irradiating light B. I It is fired from the Z direction into the first interval 32.

[0122] In the above embodiment, the sample is introduced in a manner in which the sample flows from the first opening 31 toward the second opening 33 in the flow cell 30. However, it is not limited to this; the sample can also be introduced in a manner in which the sample flows from the second opening 33 toward the first opening 31. Furthermore, the introduction of the sample into the flow cell 30 can also be performed by pressing the sample into the opening that serves as the inlet, or by sucking the sample out of the opening that serves as the outlet.

[0123] Furthermore, the materials, values, etc., listed as examples of the constituent components of the particle measuring device 1 are merely examples, and can of course be appropriately modified when implementing the present invention.

[0124] This application is based on Japanese Patent Application No. 2020-046243, filed on March 17, 2020, the contents of which are incorporated herein by reference.

[0125] Explanation of reference numerals in the attached figures

[0126] 1: Particle measuring device; 2: Detection unit; 3: Control and calculation unit; 10: Light source; 20: Irradiation optical system; 30: Flow cell; 40: Concentrating optical system; 50: Imager; 52: Light receiving surface; 60: Control unit; 70: Image acquisition unit; 80: Particle determination unit; 90: Movement calculation unit; 100: Movement correction unit; 110: Particle size determination unit; 120: Scattered light intensity determination unit; 130: Resolution unit; 140: Output unit.

Claims

1. A particle measurement device, characterized by, Possessing: a flow cell having a flow path inside thereof; a light source that emits irradiation light; an irradiation optical system that irradiates the irradiation light to a sample flowing in the flow path; a condensing optical system that condenses scattered light emitted from a particle contained in the sample that has passed through a detection region, at a position where a prescribed section of the flow path is virtually extended in a flow direction of the sample, the detection region being a region formed in the prescribed section by irradiation of the irradiation light; a photographing section that photographs the condensed scattered light at a prescribed frame rate; a movement amount calculation section that calculates a movement amount in a two-dimensional direction of the particle due to Brownian motion, based on a plurality of frame images photographed; a movement amount correction section that corrects the calculated movement amount using a correction value that is a value calculated in advance based on a defocus position and a position on the frame image, in order to correct an error in magnification that occurs in the condensing optical system; and a particle diameter determination section that determines a particle diameter of the particle based on the corrected movement amount.

2. The particle measuring apparatus according to claim 1, wherein the movement amount correction section uses, as the correction value, a value calculated in advance assuming that a change in magnification due to the defocus position is a first function of a distance in the flow direction of the sample.

3. The particle measuring apparatus according to claim 1 or 2, wherein the movement amount correction section uses, as the correction value, a value expressed in units of speed.

4. A method of particle measurement, characterized by, including: an irradiation process of irradiating a sample flowing in a flow path with irradiation light; a photographing process of condensing scattered light emitted from a particle contained in the sample that has passed through a detection region, at a position where a prescribed section of the flow path is virtually extended in a flow direction of the sample, the detection region being a region formed in the prescribed section by irradiation of the irradiation light, and photographing at a prescribed frame rate; a movement amount calculation process of calculating a movement amount in a two-dimensional direction of the particle due to Brownian motion, based on a plurality of frame images photographed; a movement amount correction process of correcting the calculated movement amount using a correction value that is a value calculated in advance based on a defocus position and a position on the frame image, in order to correct an error in magnification that occurs when the scattered light is condensed; and a particle diameter determination process of determining a particle diameter of the particle based on the corrected movement amount.

5. The particle measuring method according to claim 4, wherein in the movement amount correction process, a value calculated in advance assuming that a change in magnification due to the defocus position is a first function of a distance in the flow direction of the sample is used as the correction value.

6. The particle measuring method according to claim 4 or 5, wherein in the movement amount correction process, a value expressed in units of speed is used as the correction value.

7. A method of calibrating a particle measurement device, wherein, The particle measuring device at least has: a unit that condenses scattered light emitted from a particle and takes a picture at a prescribed frame rate, a unit that calculates a movement amount of a two-dimensional direction of the particle due to Brownian motion based on a plurality of frame images, and a unit that determines a particle diameter, and the correction method is characterized by, including a process of correcting the movement amount using a correction value that is a value calculated in advance based on a defocus position and a position on the frame image in order to correct an error in magnification that occurs when the scattered light is condensed.

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