Granular material particle size distribution measurement system and particle size distribution measurement method

Abstract

To make it possible to quickly and accurately measure the particle size distribution of granular materials used in constructing structures.SOLUTION: The measurement system is provided with a hopper (11) into which a granular material to be measured is introduced, a transport means (13) disposed below the hopper for transporting the granular material discharged from the hopper at a predetermined speed, a dispersion means (14) for dispersing the granular material transported by the transport means, a material flow-down means (15) disposed below the front end of the transport means in the transport direction and having an inclined plate that slopes downwardly forward and has the function of separating particles having a diameter below a predetermined value, a recovery means (16) disposed on the underside of the inclined plate for recovering the separated particles, a straightening means (17) having a pair of parallel walls disposed in a vertical position below the front end of the inclined plate, an image capturing device (20) disposed below the straightening means, and an image analyzer (30) for measuring the particle size distribution of the granular material based on an image of the granular material obtained by the image capturing device.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a particle size distribution measuring system and a particle size distribution measuring method for measuring the particle size distribution of a granular material such as a fill material by image processing. [Background technology]

[0002] In the concrete manufacturing process for embankments in land development work and dam construction, it is necessary to understand the particle size distribution of the soil and stone used as materials in order to control their quality. Conventionally, sieving tests have been used to understand the particle size distribution of materials, but this requires a lot of manpower and time, which places a heavy burden on on-site management personnel and also poses the problem of the long time it takes to obtain measurement results.

[0003] Therefore, a technique has been proposed in which the embankment material is photographed with a camera, and the obtained image data is analyzed to measure the particle size distribution (for example, Patent Documents 1, 2, and 3). Of these, Patent Document 1 discloses a quality measurement and control method and system that includes a belt conveyor that lifts and transports the granular material to be measured, a diffusion and flow-down means consisting of a pair of plate-like members arranged opposite each other in the vertical direction and that uniformly diffuses the granular material so that it flows down, a feeder that transports the granular material lifted by the belt conveyor to the diffusion and flow-down means, and an imaging means that photographs the material diffused by the diffusion and flow-down means, and that calculates the particle size distribution of the material by image analysis.

[0004] Patent Document 2 also discloses an image capturing device and a particle size distribution measuring system using the device, which includes an inclined plate that causes material transported on a belt conveyor to flow from upstream to downstream, a screen provided downstream of the inclined plate, an illumination unit that illuminates the screen, and an imaging unit that captures images of material passing through the space on the front side of the screen, with multiple diffusion protrusions on the surface of the inclined plate. Patent Document 3 discloses an image capturing device and particle size distribution measuring system in which a box-shaped rectifying section is provided at the tip of a belt conveyor that transports the material to rectify the flow of the material as it flows down, and multiple rotating pins are arranged inside this rectifying section to disperse the material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7267056 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-202757 [Patent Document 3] Japanese Patent Application Publication No. 2018-155612 Summary of the Invention [Problem to be solved by the invention]

[0006] In particle size measurement using image analysis, the shape of each particle must be accurately captured to correctly determine the particle diameter, and it is important to capture the image in a dispersed state so that the particles do not overlap. However, the quality measurement and control method described in Patent Document 1 has the problem of reduced measurement accuracy when the flow rate of the granular material to be measured increases, as there is a risk of the particles overlapping.

[0007] In contrast, the particle size distribution measurement systems described in Patent Documents 2 and 3 have multiple diffusion protrusions or rotating pins on an inclined plate or flow straightening section through which the material flows, thereby reducing material overlap. However, due to factors such as the resolution of the camera used, there is a limit to the particle size of materials that can be detected by image analysis, making it difficult to determine the diameter of fine particles. Furthermore, if a material contains a large number of fine particles, the fine particles will overlap with each other, preventing the capture of larger particles, making it difficult to recognize the shapes of the shadowed particles.

[0008] The present invention has been made with an eye on the above-mentioned problems, and aims to provide a particle size distribution measurement system and a particle size distribution measurement method for granular materials that can quickly and accurately measure the particle size distribution of granular materials such as earth and stone used in the construction of structures such as embankments and dams. [Means for solving the problem]

[0009] In order to solve the above problems, the particle size distribution measuring system according to the present application comprises: a hopper into which the granular material to be measured is added; a transfer means disposed below the hopper for transferring the granular material discharged from the discharge port of the hopper at a predetermined speed; a dispersing means for dispersing the granular material transferred by the transferring means; an inclined plate disposed below the front end side of the transfer means in the transfer direction, having a function of separating particles having a diameter equal to or smaller than a predetermined value, and inclined downward toward the front; a collecting means provided on the lower surface side of the inclined plate for collecting the separated particles; a straightening means having a pair of parallel walls and disposed vertically below the front end of the inclined plate; an image capturing device provided below the rectifying means; an image analyzer that measures the particle size distribution of the granular material based on the image of the granular material obtained by the image capture device; The present invention is designed to provide the above.

[0010] With the particle size distribution measurement system configured as described above, simply by placing the granular material to be measured into the hopper, the image capture device captures images of the granular material, and the image analyzer analyzes the captured images, enabling rapid and accurate measurement of the particle size distribution of the granular material. Furthermore, the inclined plate can remove fine particles contained in the granular material to be measured, preventing the fine particles from overlapping with each other when photographed by the image capture device, which would otherwise interfere with the capture of larger particles and make it difficult to recognize the shapes of the shadowed particles. Furthermore, the dispersing means for dispersing the granular material reduces particle overlap, preventing a decrease in measurement accuracy. [Effects of the Invention]

[0011] The particle size distribution measuring system and particle size distribution measuring method for granular materials according to the present invention have the advantage of being able to quickly and accurately measure the particle size distribution of granular materials such as earth and stone used in the construction of structures such as embankments and dams. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a perspective view showing an embodiment of a particle size distribution measuring system according to the present invention. [Figure 2] (A) is a diagram showing an example of an image taken when material is supplied directly from a hopper onto a mesh panel without a belt conveyor or material dispersing means, (B) is a diagram showing an example of an image taken without using a mesh panel to separate fine particles, and (C) is a diagram showing an example of an image taken by the particle size distribution measuring system of this embodiment. [Figure 3] FIG. 2 is a schematic diagram illustrating a method for measuring the particle size distribution of the separated and recovered fine particle fraction. [Figure 4] FIG. 1A is a diagram showing an example of a graph of particle size distribution created using particle size distribution data calculated by the particle size distribution measurement system of the present embodiment, and FIG. 1B is a diagram showing an enlarged view of a part of the graph of FIG. 1A. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, a particle size distribution measuring system for a granular material according to an embodiment of the present invention will be described. FIG. 1 is a schematic diagram showing an embodiment of a particle size distribution measuring system.

[0014] As shown in FIG. 1, the particle size distribution measurement system according to this embodiment includes a material supply device 10 that supplies the granular material to be measured, an image capturing device 20 that captures images of the granular material supplied by the material supply device 10, and an analysis device 30 that analyzes the images captured by the image capturing device 20 to calculate the particle size distribution.

[0015] The material supply device 10 comprises an inverted pyramidal hopper 11 having a discharge light at the bottom and into which the granular material S to be measured is put, a support base 12 consisting of a pair of parallel plates 12A supporting the hopper 11 and legs 12B supporting the same, and a belt conveyor 13 positioned below the hopper 11 to transport the granular material discharged from the hopper 11. The belt conveyor 13 is equipped with a motor as a drive source and is driven to transport the granular material from left to right in the drawing at a transport speed (material supply speed). Instead of a belt conveyor, a transport means that moves the material by vibration or air blowing from a fan may be used. Hereinafter, the direction in which the material is transported (to the right in FIG. 1) will be referred to as the forward direction.

[0016] A discharge port having a front-to-rear width greater than the maximum diameter of the material to be measured is provided at the bottom of the hopper 11. Also, at the front end of the support base 12, material dispersing means 14 is provided, which consists of a plurality of dispersing rods 14A having a height that matches the maximum diameter of the material (e.g., 80 mm) and a plate 14B from which the dispersing rods 14A hang down. The plurality of dispersing rods 14A are arranged so that they are spaced apart at least by the maximum diameter of the material to be measured.

[0017] As a result, even if there is unevenness in the material supplied from the hopper 11 onto the belt conveyor 13, the material can be dispersed appropriately by colliding with the dispersion rod 14A, and the overlapping of particles can be reduced. The hopper 11 may be configured so that the size of the discharge outlet at the bottom and the front-to-rear position relative to the support base 12 can be adjusted according to the maximum diameter of the material to be measured. Furthermore, if the maximum diameter of the material to be measured changes, the material dispersion means 14 equipped with dispersion rods 14A of different heights and intervals can be changed by replacing the plate 14B as well.

[0018] Furthermore, the material supply device 10 is equipped with a material flow-down means 15 having an inclined plate 15A that slopes downward from the lower front end of the belt conveyor 13 toward the front, and a rectifying chute 17 that is disposed vertically at the front end of the material flow-down means 15 and rectifies the flow of the material flowing down. The rectifying chute 17 reduces the difference in the distance from the camera in the depth direction for each particle of material supplied to the photographing section of the image photographing device 20 (the space in front of the camera), thereby minimizing errors in particle size due to differences in photographing distance. In addition, a collection container 18 is disposed below the rectifying chute 17 to receive the material after it has been photographed by the image photographing device 20.

[0019] The inclined plate 15A is made up of a mesh panel with holes of a size corresponding to the diameter of the fine particles (for example, 2 mm) to separate the fine particles, and guide walls 15B are provided on both sides of the inclined plate 15A to prevent the flowing material from spilling out to the sides. In this way, in the material supply device of this embodiment, the mesh panel separates the fine particles contained in the material to be measured, so that it is possible to prevent the fine particles from interfering with the imaging of the material particles supplied to the imaging unit of the image capturing device 20.

[0020] Additionally, recovery chutes 16A are provided at predetermined intervals on the underside of the inclined plate 15A to allow the fine particles separated by the mesh panels to flow downward. Furthermore, a laterally inclined recovery trough 16B is provided at the lower end of the recovery chute 16A, and a discharge port 16C is formed at the downstream end of the recovery trough 16B for discharging the recovered fine particles. The recovery chute 16A and the recovery trough 16B constitute means 16 for recovering the separated fine particles. Although not shown, a tray for receiving the discharged fine particles may be provided below the discharge port 16C. Furthermore, the recovery gutter 16B may be detachably connected to the lower end of the recovery chute 16A, so that after the image capture device 20 has finished capturing images of the large-diameter particles, the recovery gutter 16B can be removed from the recovery chute 16A and transferred to a separately prepared tray. In such a configuration, the recovery gutter 16B does not need to be inclined laterally.

[0021] The flow straightening chute 17 is box-shaped with openings at the top and bottom, and its width in the left-right direction is the same as that of the inclined plate 15A, while its front-to-back width is set to a dimension slightly larger than the maximum diameter of the material to be measured. If the height of the rectifying chute 17 is too short, the rectifying effect will not be sufficient and the distance between the front and rear of the flowing material will not be widened, while if it is too long, the speed of the flowing material will increase and a clear image will not be obtained due to the performance (shutter speed) of the imaging means provided in the image capturing device 20. Therefore, it is advisable to determine the appropriate vertical length of the rectifying chute 17 by trading off the two viewpoints of achieving the rectifying and front and rear separation effects and obtaining a clear image.

[0022] The image capturing device 20 is composed of a planar panel light 21, which is disposed in a vertical position below the rectifying chute 17 on the extension of the front wall of the rectifying chute 17 and serves as the background during photography, and a digital camera (hereinafter simply referred to as the camera) 22, which serves as an imaging means and is disposed opposite the panel light 21. The camera 22 has the capability to continuously capture multiple still images (for example, 14 images) per second, and is mounted on a support rod 23 that is installed horizontally at a predetermined distance from the panel light 21. Alternatively, a rail may be provided in a direction perpendicular to the panel light 21, and the camera 22 may be mounted on this rail so that it can move back and forth, allowing the distance to the panel light 21 to be adjusted.

[0023] The analysis device 30 is configured with a computer such as a laptop computer and an analysis program installed on the computer. In this embodiment, the analysis device 30 is connected to the camera 22 by a cable, but it may also be installed at a location remote from the image capture device 20 and acquire and analyze image data from the camera 22 via wireless communication.

[0024] According to the particle size distribution measuring system of this embodiment having the above-described configuration, when a predetermined amount (for example, 10 kg) of sample is placed in hopper 11, the sample is continuously supplied onto inclined plate 15A at a constant speed (constant supply amount) by belt conveyor 13, and after fine particles are removed by inclined plate 15A, the sample is allowed to flow down into straightening chute 17. This allows the image capturing device 20 to capture an image of the material to be measured in a state where each material particle is dispersed and no particle overlap is eliminated.

[0025] Fig. 2(C) shows an example of an image taken by the particle size distribution measuring system of this embodiment. For comparison, Fig. 2(A) shows an example of an image taken when material is supplied directly from the hopper 11 onto the mesh panel (15A) without the belt conveyor 13 and material dispersing means 14, and Fig. 2(B) shows an example of an image taken without using the mesh panel (15A) for separating fine particles. It can be seen from FIG. 2 that by using the material supplying device 10 having the above-described configuration, it is possible to take an image in a state where the material particles are dispersed and no overlapping of the particles is eliminated.

[0026] Next, the specific processing performed by the analyzer 30, which analyzes the image data acquired as described above and calculates the particle size distribution of the material, will be described. Prior to analysis by the analyzer 30, the weight of all fine particles collected by the collection chute 16A is measured, and the measured weight value and the amount of material input to the hopper 11 (e.g., 10 kg) are input to the analyzer 30. The analyzer 30 can calculate the total weight of the particles photographed by the camera 22 by subtracting the weight value of the fine particles from the input amount.

[0027] Furthermore, the analysis device 30 captures the image data captured by the camera 22, analyzes the image by image processing, and calculates the particle size distribution of the material to be measured. Image analysis techniques for calculating particle size distribution are described, for example, in Patent Document 1, and known analysis techniques can also be used in the present invention, so a description of the specific analysis techniques will be omitted. In this embodiment, the particle size distribution calculated as described above becomes the provisional particle size distribution.

[0028] The particle size distribution calculated by the analysis device 30 based on the image data from the camera 22 is the distribution of particles of each diameter among all the relatively large particles from which fine particles of a predetermined diameter (2 mm in this embodiment) or less have been separated by the material supply device 10, and does not include the fine particles. Therefore, the analysis device 30 in the system of this embodiment calculates the ratio between the input weight value of the fine particles and the total weight of the photographed particles calculated in advance, and uses this ratio to correct the above-mentioned provisional particle size distribution calculated based on the image data, thereby performing processing to determine the particle size distribution of the entire material to be measured, excluding the fine particles.

[0029] Due to the nature of particle size distribution graphs, the weight ratio of the separated fine particles to the total material corresponds to the weight ratio of the smallest diameter particles among the particles of the material photographed by the camera after the fine particles have been separated. Furthermore, the ratio of the largest diameter particles among the particles of the material photographed by the camera remains at 100%. Therefore, if the particle size distribution calculated by the above process is, for example, 40% fine particles, the particle size distribution for the entire material, including the fine particles, can be easily calculated by correcting the distribution data by proportionally compressing the particle size distribution data in the range of 0-100% of the material photographed by the camera to the distribution data in the range of 40-100%. In this case, the ratio of the smallest diameter particles among the particles of the material photographed by the camera will be inflated from 0% to 40%.

[0030] Furthermore, the fine particles separated by the mesh panel (15A) and collected in the collection trough 16B are weighed, and an appropriate amount of them is taken out as a sample. The sample taken out is then placed on a small transparent dish D such as a petri dish, as shown in Figure 3(a), and water W is poured in to moisten the sample S. Then, as shown in Figure 3(b), the fine components of the sample float to the surface of the water, and these fine components C are removed. Thereafter, as shown in Figure 3(c), the water is removed from the small dish D, and the small dish D or the sample S removed from the small dish D is placed on a horizontally installed planar panel light. The sample S is then photographed from above at close range using a camera to obtain image data.

[0031] The image data is then captured by the analyzer 30, and the image is analyzed by image processing to calculate the particle size distribution of the sample to be measured. In this case, the image analysis is performed on a portion of the fine particle fraction separated by the mesh panel (15A). Because the particles are fine, even if the amount is small, the number of particles is sufficient to represent the whole. Furthermore, since the weight of the entire fine particle fraction is measured in advance, the value calculated from the portion of the sample can be used to estimate the overall particle size distribution, and using the estimated value does not significantly reduce the overall accuracy. Furthermore, since the measurement is performed on a portion of the sample taken from the recovered fine particle fraction, the time required can be significantly reduced compared to measuring the particle size of the entire fine particle fraction and calculating the particle size distribution.

[0032] A commercially available spreadsheet program such as Excel (registered trademark) is installed in the analysis device 30, and the particle size distribution data of the material calculated by the image analysis program is passed to the spreadsheet program. The spreadsheet program is configured to create a particle size distribution graph based on the received particle size distribution data, in which the particle size distribution is represented by a line graph with particle size on the horizontal axis and weight % on the vertical axis, and to display the graph on a monitor screen.

[0033] Figure 4(A) shows an example of a particle size distribution graph created in Excel (registered trademark) using particle size distribution data calculated from a test conducted on 10 kg of material with a maximum particle diameter of 80 mm using the particle size distribution measurement system of this embodiment. Figure 4(B) shows an enlarged view of a portion of the graph in Figure 4(A). In Figure 4, the dots represent plots of the ratio of particles of each size in the material being measured, calculated by the analysis device 30 of the system of this embodiment; solid line A (A1, A2, A3) is the line connecting the dots; solid line B represents the particle size distribution of the same material measured by the conventional sieving method; and two dashed lines C1 and C2 represent particle size distributions ±5% of the solid line B.

[0034] In FIG. 4(A), the portion of the solid line A with particle diameters of 2 mm or less may be obtained based on the results of another measurement using the small dish described above with reference to FIG. From FIG. 4, it can be seen that the particle size distribution (solid line A) calculated by the particle size distribution measurement system of this embodiment is generally between particle size distribution lines C1 and C2 of ±5%, and therefore the error when this embodiment is applied is favorably within approximately 5%.

[0035] The particle size distribution in the region of 2 mm or less particle size indicated by solid line A may be interpolated using the results of particle size distribution calculations performed on fine particles contained in soil and rocks collected in advance from the same location as the measurement material, rather than the results obtained by measuring the fine particles collected in collection chute 16B. In this case, it is sufficient to measure only the weight of the fine particles separated by collection chute 16A and collected in collection chute 16B, and measurement of particle size by image processing can be omitted.

[0036] Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments and can be modified as appropriate without departing from the spirit of the present invention. For example, in the above embodiment, the mesh panel (15A) in the material flow-down means 15 is used to separate fine particles contained in the material to be measured, but the fine particles may also be separated by static electricity or by air blown by a fan. In addition, in the above embodiment, the weight of the fine particles is measured, but it is also possible to measure the weight of the material after photographing that is collected in the collection container 18, and calculate the difference between this and the weight of the material before measurement that is put into the hopper 11 to obtain the weight of the fine particles.

[0037] Furthermore, in the above embodiment, the analysis device 30 calculates only the particle size of the material to be measured by image processing, but it may also be configured to determine the color (chromaticity and saturation) of the material to be measured. Since the color and other properties of earth and stone change depending on the weather and other environmental factors, if the properties of the earth and stone that have been transported have changed from those at the time of construction, this change can be detected, and it can be more appropriately determined whether the earth and stone can be used for construction, taking into account the change in the properties of the earth and stone. [Explanation of symbols]

[0038] 10 Material feeding device 11 Hopper 12 Support stand 13 Belt conveyor (transportation means) 14 Material dispersion means 14A dispersion rod 15 Material flow means 15A Inclined Panel (Mesh Panel) 15B Guide wall 16 Fine particle recovery means 16A Recovery Chute 16B Recovery gutter 16C Outlet 17. Rectification chute (rectification means) 18 Collection container (means for collecting materials) 20 Imaging device 21 Panel light (lighting means) 22 Digital camera (photography means) 23 Support rod 30 Analyzer

Claims

1. a hopper into which the granular material to be measured is added; a transfer means disposed below the hopper for transferring the granular material discharged from the discharge port of the hopper at a predetermined speed; a dispersing means for dispersing the granular material transferred by the transferring means; a material flow-down means disposed below the front end side of the transfer means in the transfer direction, having a function of separating particles having a diameter equal to or smaller than a predetermined value, and having an inclined plate inclined downward toward the front; a collecting means provided on the lower surface side of the inclined plate for collecting the separated particles; a straightening means having a pair of parallel walls and disposed vertically below the front end of the inclined plate; an image capturing device provided below the rectifying means; an image analyzer that measures the particle size distribution of the granular material based on the image of the granular material obtained by the image capture device; A particle size distribution measuring system comprising:

2. The inclined plate is a mesh panel having a predetermined size of mesh, 2. The particle size distribution measuring system according to claim 1, wherein the recovery means comprises a chute arranged at a predetermined interval on the underside of the mesh panel and a recovery gutter provided at the lower end of the chute.

3. 3. The particle size distribution measuring system according to claim 1, wherein the dispersion means is composed of a plurality of rod-shaped members arranged vertically and parallel to each other at predetermined intervals.

4. The particle size distribution measuring system described in claim 3, characterized in that the image capturing device is provided with an imaging means arranged to face the granular material flowing down in layers from the straightening means, and a planar lighting means arranged to face the imaging means and brightly illuminate the granular material flowing down from behind.

5. A particle size distribution measuring method using the particle size distribution measuring system according to claim 1, a material charging step of charging a predetermined amount of granular material into the hopper; a material transferring step of transferring the granular material discharged from the hopper toward the inclined plate at a predetermined speed by the transferring means; a fine particle separation step in which particles having a diameter equal to or smaller than a predetermined value are separated and allowed to flow downward by the inclined plate; a fine particle recovery step of recovering the fine particles separated by the inclined plate using the recovery means; a rectifying step of rectifying the granular material from which the fine particles have been separated by the inclined plate using the rectifying means; an imaging step of imaging the granular material that has been rectified by the rectification step and flows down using the image capturing device; an image analysis step of analyzing the image of the granular material taken by the image taking device using the image analyzer to measure diameters of particles contained in the granular material and calculate a provisional particle size distribution; a weight measuring step of measuring the weight of all the fine particles collected in the fine particle collecting step or the weight of the granular material photographed and collected in the photographing step; a particle size distribution calculation step of correcting the provisional particle size distribution based on the weight of all fine particles obtained from the measurement results of the weight measurement step, and calculating the particle size distribution of the predetermined amount of granular material charged into the hopper; A particle size distribution measuring method comprising the steps of:

6. In the particle size distribution calculation step, Calculating a fine particle weight ratio, which is the ratio of the weight of the total fine particle content obtained from the measurement results of the weight measurement step to the weight of the total granular material charged into the hopper; The weight ratio of the smallest particle in the provisional particle size distribution calculated by the image analysis step is inflated by the weight ratio of the fine particles, and the data showing the provisional particle size distribution is proportionally compressed according to the amount of inflating to calculate the particle size distribution for all the granular material.

6. The particle size distribution measuring method according to claim 5.

Images