SE2251592A1 - Method and arrangement for determining an estimated bulk particle-size distribution - Google Patents

Method and arrangement for determining an estimated bulk particle-size distribution

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SE2251592A1
SE2251592A1 SE2251592A SE2251592A SE2251592A1 SE 2251592 A1 SE2251592 A1 SE 2251592A1 SE 2251592 A SE2251592 A SE 2251592A SE 2251592 A SE2251592 A SE 2251592A SE 2251592 A1 SE2251592 A1 SE 2251592A1
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psd
computer
granules
granular material
reloading
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SE2251592A
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SE545201C2 (en
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Lars Lindqvist
Peter Lingman
Richard Nordenskjöld
Stefan Björklund
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Optimation Advanced Measurements Ab
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    • G—PHYSICS
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    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/02—Investigating particle size or size distribution
    • G01N15/0205—Investigating particle size or size distribution by optical means
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/02—Investigating particle size or size distribution
    • G01N15/0205—Investigating particle size or size distribution by optical means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/10—Investigating individual particles
    • G01N15/14—Optical investigation techniques, e.g. flow cytometry
    • G01N15/1429—Signal processing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
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    • G01N15/1433—Signal processing using image recognition
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
    • G06F17/10—Complex mathematical operations
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/10—Investigating individual particles
    • G01N15/14—Optical investigation techniques, e.g. flow cytometry
    • G01N2015/1493—Particle size

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Abstract

A computer-implemented method is described for determining the bulk particle-size distribution, PSD, of granular material (2). The method comprises the steps of obtaining (101) a data representation of a surface of granular material (2) at a measurement point after at least one reloading of the granular material (2), determining (102) a measured surface PSD of the granular material (2) based on the data representation of the granular material (2), providing a computer model describing the relationship between the surface PSD and the bulk PSD, and determining (103), with the computer model and the measured surface PSD, an estimated bulk PSD.

Description

1 METHOD AND ARRANGEMENT FOR DETERlMINING AN ESTlMATED BULK PARTICLE-SIZE DISTRIBUTION TECHNICAL FIELD The present invention is related to the problem of determining an estimated bulk particle-size distribution (PSD) of granular material.
BACKGROUND ART The particle-size distribution (PSD) of a granular material is a list of values or a mathematical function that defines the relative amount, typically by mass, of particles present according to size. ln many different applications, it is necessary to determine the particle-size distribution of granular material. The granular material may be of many different types. The granular material may be spread out on a surface such as a stationary surface such as, e.g., a truck bed, or a moving surface such as, e.g., a conveyor belt. lt is possible to determine a measure ofthe PSD by capturing an image of the granular material on the surface and by image analysis of the captured image. The image analysis may determine the so-called surface PSD of the granules ofthe granular material. However, the surface PSD is only equal to the PSD of the bulk in single layer presentation, otherwise mixing and natural segregation will keep them apart. lt is however difficult and time-consuming to distribute the granules in a single layer. ln real world applications, it is not possible to distribute the granules in a single layer.
Another method for determining the PSD of a bulk of granular material according to the prior art is to determine the PSD by screen analysis ofthe bulk material, in which the bulk material is sifted. However, this method is difficult to use in a real world application.
Thus, there is a need to provide a method for determining the bulk PSD of granular material, which may be used in real world applications.
SUMMARY OF THE INVENTION An objective of the present invention is to provide a method for determining the bulk particle- size distribution (PSD) ofgranular material without having to make manual controls of the granular material such as, e.g., screen analysis of the granular material. This objective is fulfilled with the computer-implemented method according to claim 1.
Further advantages of the present invention are fulfilled with the features of the dependent claims.
According to a first aspect of the present invention, a computer-implemented method is provided for determining an estimated bulk particle-size distribution (PSD) of granular material. The method comprises the steps of obtaining a data representation of a surface of granular material at a measurement point after at least one reloading of the granular material and determining a measured surface PSD ofthe granular material based on the data representation of the granular material. The computer-implemented method also comprises the steps of providing a computer model describing the relationship between the surface PSD and the bulk PSD, and determining, with the computer model and the measured surface PSD, an estimated bulk PSD. The creation of the computer model comprises the steps of simulating with a computer, for each one of a plurality of simulated sets of granules with mutually different simulated bulk PSDs, the reloading ofthe granules and simulating for each set of granules how the granules are distributed at the measurement point and a corresponding simulated surface PSD, and adapting the computer model to the simulated sets of granules and the corresponding simulated surface PSD. The computer-implemented method is performed in one or a plurality of computers. The creation of the computer model may also form part ofthe computer-implemented model.
Programs for simulation of the reloading of granules and simulation for a set of granules how the granules are distributed at a measurement point and a corresponding simulated surface PSD, are known in the art. Simulation of granular materials are described in Pöschel, T., Schwager, T.: Computational Granular Dynamics, I\/|odels and Algorithms. Springer-Verlag, Berlin Heidelberg (2005), and in Radja'|', F., Dubois, F.: Discrete-element I\/|odeling of Granular I\/|aterials. Wiley (2011). The simulation is preferably performed with any commercially available 3 program. Examples of such programs are Algoryx Momentum Granular, EDEM, Rocky DEM, and PFC3D.
The at least one reloading of the granular material is a specific reloading in the real world and may be a reloading from one conveyor belt to another. The step of simulating with a computer is performed based on the specific reloading in the real world.
The computer model is preferably created in advance before using the model in the method.
The model may be updated in case any parameters ofthe reloading is changed.
Preferably, the created computer model is adapted to a specific reloading operation in order for the computer model to accurately model the relationship between surface PSD and bulk PSD. lt is, however, possible to use the same computer model for small variations of the real world reloading operation and still obtain reliable results.
A basic idea of the invention is that it is possible to accurately simulate the reloading with commercially available computer programs. With this knowledge, a computer model may be created which accurately models the relationship between surface PSD and bulk PSD. Thus, with knowledge of a measured surface PSD it is possible to use the computer model to determine an estimated bulk PSD which is a close approximation ofthe real bulk PSD.
The simulation of the reloading requires some knowledge on how the reloading is performed.
More detailed information on the reloading results in a better simulation.
The computer used to create the computer model may be a different computer than the computer on which the computer-implemented method is performed.
With the computer-implemented method according to the first aspect, an estimated bulk PSD may be determined which is a better estimation of the true bulk PSD of the granular material than the measured surface PSD. The present invention relies on the simulation ofthe reloading. With the calculating power of modern computers, it has become possible to simulate the behaviour of granular material during reloading. lt is possible to take into account a large number of factors affecting the distribution after reloading. The computer model is adapted to the simulated sets of granules and the corresponding simulated surface PSD. 4 The reloading is an interaction between the granular material and at least one reloading surface. The interaction with at least one reloading surface segregates the particles. This makes it possible to simulate the distribution ofthe granules. Before any reloading, the granules may be distributed in any way. The granules may, for example, have been layered with the largest granules at the bottom on a surface and increasingly smaller granules on top. The surface PSD of such layered granules will not reflect the bulk PSD. However, after a reloading the granules will be distributed such that the distribution of the granules may be simulated using the parameters of the reloading.
The data representation of a surface of granular material may be of a surface of granular material on one of the at least one reloading surface. The granules may in this case be in contact with each other but may of course also be separated on the reloading surface.
The step of obtaining a data representation may be performed by a user inputting the data representation into the computer performing the computer-implemented method. The step may also be performed by the computer retrieving the data representation from a memory in which data representations have been pre-stored. Another possibility is for the computer, on which the computer-implemented method is performed, to retrieve the data representation directly from, e.g., a digital camera, in case a digital camera is used to obtain the data representation.
Alternatively, the data representation of a surface of granular material may be of a surface of falling granular material. ln this case, the data representation is of the surface as seen when the granular material is falling. ln this case the granules are likely not in contact with each other.
The data representation may be obtained in many different ways. lrrespective of how the data representation has been obtained, the method uses the data representation to determine a measured surface PSD. One alternative is to have a distance measurement device to register the data representation of the granular material as a 3D height map. Distance measurement devices may for example be in the form of an optical scanner. Another alternative might be to take one or more images of the granular material.
The simulation ofthe reloading may be performed with parameters forthe reloading comprising at least one of, the flow rate of the granules, the speed of the reloading surface, the fall height of the granules onto the reloading surface, the shape of the granules, the density of the granules, the coefficient of friction between the granules, the size of the granules, the adhesion between the granules, the width ofthe granular material before and/or after reloading, and the elasticity of the granules. lt is of course possible to use also other parameters for the reloading. The more parameters that are used the better is the simulation. A simulation starts at a point before the at least one reloading and the simulation ends at the point of measurement, i.e., where the data representation is registered.
The step of simulating may comprise the steps of obtaining the parameters ofthe at least one reloading, comprising at least the following parameters, the flow rate ofthe granules, the speed of the reloading surface, the fall height of the granules onto the reloading surface, the size of the granules, the width and/or height of the granular material before and/or after reloading, and simulating with a computer and with the obtained parameters, for each one of a plurality of simulated sets of granules with mutually different simulated bulk PSDs, the reloading of the granules and simulating, using the obtained parameters, for each set of granules how the granules are distributed at the measurement point and a corresponding simulated surface PSD.
The above parameters may be input by an operatorand corresponds to the real world reloading. The parameters may be based on measurements on the real world reloading. Alternatively, the parameters may be based on drawings ofthe machinery used for the reloading. lt is possible to obtain also additional parameters than the above-mentioned parameters.
The step of simulating may be a step of the computer implemented method and may be performed by the same computer as the steps of the computer implemented method.
The above parameters are the most important parameters, which affects the surface PSD the most, in the simulation as well as in the real world. Other parameters such as the coefficient of friction between the granules, the adhesion between the granules, the elasticity ofthe granules, the shape ofthe granules, the density of the granules, may normally be set to generic values, which are used irrespectively of the real world reloading, as they tend to affect the surface PSD only to a small extent.
The creation of the computer model may also comprise the steps of providing at least one data representation of a surface of granular material, with a predetermined measured bulk PSD, 6 distributed essentially as a single layer after reloading, determining a measured surface PSD of the granular material based on the at least one data representation of the granular material, and adapting the computer model also to the predetermined bulk PSD and the measured surface PSD. By using such a measurement of granular material having a predetermined bulk PSD the model may be improved. The plurality of simulated sets of granules may include a range of bulk PSDs which at least partly covers the expected range of bulk PSDs of the granular material for which the bulk PSD is to be determined with the computer-implemented method. lf the simulation is sufficiently good, the simulated surface PSD will correspond to a certain measured surface PSD. ln order to make the model to cover different real bulk PSDs the plurality of simulated sets should cover a range of simulated bulk PSDs.
The plurality of simulated sets of granules may include a range of bulk PSDs which covers at least 5 %, preferably at least 50 % and most preferred at least 90 %, of the expected range of bulk PSDs of the granular material for which the PSD is to be determined with the computer- implemented method. With a better correspondence between the range of bulk PSDs of the plurality of simulated sets of granules and the expected range of bulk PSD the computer model is improved. With a coverage of at least 5 %, experiments have indicated an improvement in relation to lower coverage. The inventors have seen only minor improvement of the model when the range of bulk PSDs covered by the plurality of simulated sets of granules is increased above 90 %, ofthe expected range of bulk PSDs of the granular material for which the PSD is to be determined.
At least one parameter of the simulated reloadings is varied for the same simulated set of granules and wherein the reloading ofgranules onto the surface is simulated for each variation of the parameter. This gives a possibility to adjust the computer model if a parameter of the reloading is altered.
The computer model may be any type of computer model, which is adaptable to the method.
The computer model may be based on mathematical regression. This is a basic technique for the computer model.
A basic implementation of the computer model is a model based on linear regression. ln such a model the bulk PSD may be estimated as 7 (bulk PSD)=[3-(measured surface PSD) + s; where ß and s are constants which are determined during the adaptation of the computer model to the simulated sets ofgranules and the corresponding simulated surface PSD.
The computer model may be based on a neural network. Neural networks have been used extensively for modelling in various technical fields and are well known as such. For that reason, neural networks will not be described in more detail in this description.
According to a second aspect of the present invention, a computer program for determining the bulk particle-size distribution (PSD) of granular material is provided. The computer program comprises instructions which, when executed by a computer cause the computer to carry out the method according to the first aspect or any of the variations of it.
According to a third aspect ofthe present invention a carrier is provided for a computer program on which is stored a computer program according to the second aspect of the invention.
According to a fourth aspect of the present invention a use of a computer model is provided to determine, from a measured surface particle-size distribution, PSD, ofgranular material an estimated bulk PSD, wherein the creation of the computer model comprises the steps of -simulating with a computer, for each one of a plurality of simulated sets of granules with mutually different simulated bulk PSDs, the reloading of the granules and simulating for each set ofgranules how the granules are distributed at the measurement point and a corresponding simulated surface PSD, and - adapting the computer model to the simulated sets of granules and the corresponding simulated surface PSD. ln the following preferred embodiments of the invention will be described with reference to the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow diagram of a computer-implemented method according to an embodiment ofthe present invention.
Figure 2a-2c illustrates different reloadings of granular material and how a data representation of a surface of the granular material is obtained.
Figure 3a shows a data representation of the surface ofgranular material in the form of a 2D image.
Figure 3b shows a data representation of the surface of granular material in the form of a 3D image.
Figure 4 illustrates an example ofthe expected range of bulk PSDs ofthe granular material for which the PSD is to be determined and the range of bulk PSDs for the plurality of simulated sets of granules.
Figure 5 illustrates another example of the expected range of bulk PSDs ofthe granular material for which the PSD is to be determined and the range of bulk PSDs for the plurality of simulated sets of granules.
Figure 6 illustrates another example of the expected range of bulk PSDs ofthe granular material for which the PSD is to be determined and the range of bulk PSDs for the plurality of simulated sets of granules.
Figure 7 shows the measured surface PSD, the estimated bulk PSD and the actual bulk PSD.
DETAILED DESCRIPTION ln the following description of preferred embodiments of the invention reference will be made to the appended drawings. The same reference numeral will be used for similar features in the drawings. The drawings are not drawn to scale.
Figure 1 is a flow diagram of a computer-implemented method according to an embodiment of the present invention, for determining the bulk particle-size distribution (PSD) of granular 9 material. Figure 2a-2c illustrates different reloadings of granular material and how a data representation of a surface ofthe granular material is obtained. Figure 2a shows a wheel loader 1 with a bucket 7. The wheel loader 1 is dumping granular material 2 from the bucket onto a pile 3 of granular material. The granular material 2 which is dumped on the pile 3 has been scooped up by the bucket 7 of the wheel loader 1. Independent of how the granular material was distributed before being scooped up the granular material will be segregated when it is scooped up by the bucket 7, i.e., the material will be distributed in the bucket 7. The distribution ofthe granular material 2 in the bucket will be dependent on the bulk PSD of the granular material 2. The scooping of granular material by the bucket 7 constitutes a reloading. The reloading is an interaction between the granular material and a reloading surface 8, wherein the reloading surface 8 in this case is the bucket 7. Smaller granules in the granular material 2 will tend to fall down between larger granules ofthe granular material 2. When the granular material 2 is dumped from the bucket 7 onto the pile 3 the material will fall in a manner that is dependent on, among other things, the bulk PSD of the granular material 2. As is shown in Figure 2a a digital camera 4 is configured to capture an image of the falling granular material 2. The captured image constitutes a data representation of the surface of the granular material facing the digital camera 4. The digital camera 4 is connected to a computer 5 in which the computer-implemented method illustrated in Figure 1 is performed. lt is not necessary to use a camera to register the data representation. One alternative is to use a distance measurement device. Distance measurement devices are available in different forms such as, e.g., in the form of optical scanners, which rely on light to measure the distance to the granular material 2. lt is of course also possible that the distance measurement device is based on ultrasonic measuring. lt is also possible to use a plurality of digital cameras or laser triangulation to capture and register a 3D image of the granular material 2.
The method comprises the step of obtaining 101 a data representation of a surface of granular material at a measurement point after at least one reloading of the granular material. ln the embodiment of Figure 2a the data representation of a surface ofgranular material at a measurement point corresponds to the image captured by the digital camera 4 and sent to the computer 5, wherein the measurement point is defined by the viewing angle 6 of the digital camera 4. After having obtained the data representation of the surface of granular material in the form of the image, the computer determines in a second step 102 a measured surface PSD of the granular material based on the data representation of the granular material. A computer model describing the relationship between the surface PSD and the bulk PSD is provided. ln a third step 103 it is determined, with the computer model and the measured surface PSD, an estimated bulk PSD. The estimated bulk PSD is close to the actual bulk PSD of the granular material 2. The creation of the computer model will be described in more detail below.
Figure 2b shows an operation in which granular material 11 from a first conveyor belt 9 falls onto two reloading surfaces 8 and then onto a second conveyer belt 10. The distribution of the granular material 2 after reloading depends among other things on the interaction between the granular material 2 and the reloading surfaces 8. ln the shown embodiment, the interaction between the granular material 2 and the second conveyor belt 10 also affects the distribution ofthe granular material on the second conveyor belt 10. Thus, also the second conveyor belt constitutes a reloading surface. ln Figure 2b the distance measurement device is in the form of a laser scanner 12, which scans the surface ofthe granular material 2, as is indicated by the laser beam 13, to register a data representation of the surface ofthe granular material 2 as a 3D height map at the measurement point defined by the laser beam 13. The data representation is sent to the computer 5, which performs the steps as described above to determine an estimated bulk PSD.
Figure 2c illustrates an operation in which granular material 11 from a first conveyor belt 9 falls onto a second conveyer belt 10. ln this case, the distribution ofthe granular material will depend primarily on the reloading from the first conveyor belt 9 to the second conveyor belt. The surface 8 of the second conveyor belt 10 constitutes a reloading surface 8. ln Figure 2c a laser scanner 12 scans the surface ofthe granular material 2 as is indicated by the laser beam 13, to register a data representation of the surface of the granular material 2 at the measurement point defined by the laser beam 13. The data representation is sent to the computer 5, which performs the steps as described above to determine an estimated bulk PSD. 11 The creation of the computer model will now be described in more detail. The creation of the model comprises the steps of simulating with a computer, for each one of a plurality of simulated sets of granules with mutually different simulated bulk PSDs, the reloading of the granules and simulating for each set of granules how the granules are distributed at the measurement point and a corresponding simulated surface PSD, and adapting the computer model to the simulated sets of granules and the corresponding simulated surface PSD. The simulation of how the granules are distributed is preferable done on the scale of single granules. Preferably, the interaction of each granule with the reloading surface 8 and the interaction between separate granules is simulated. Depending on how accurate the simulation is to be a number of different parameters may be used in the simulation of the reloading. Examples on parameters that may be used in the simulation comprise the flow rate of the granules, the speed ofthe reloading surface, the fall height ofthe granules onto the reloading surface, the shape of the granules, the density of the granules, the coefficient of friction between the granules, the adhesion between the granules, the width of the granules before and/or after reloading and the elasticity ofthe granules. lt is of course also possible to use other parameters not mentioned above. The more parameters that are used in the simulation the better is the resulting estimated bulk PSD.
The parameters affecting the simulation the most are the flow rate of the granules, the speed of the reloading surface, the fall height (Hf) of the granules onto the reloading surface, the size of the granules, the width (w) and/or height (h) of the granular material after reloading. These parameters may be obtained either by measuring directly on the real world application or by obtaining the parameters of a drawing of the real world application. By having access to the flow rate of the granules, the speed of the reloading surface and one of the the width (w) and the height (h) of the granular material after reloading it is possible to estimate the other one of the width (w) and the height ofthe granular material after reloading.
A basic implementation of the computer model is a model based on linear regression. ln such a model the bulk PSD may be estimated as (bulk PSD)=[3-(measured surface PSD) + s; where ß and s are constants which are determined during the adaptation of the computer model to the simulated sets ofgranules and the corresponding simulated surface PSD. 12 When the computer-implemented method is to be implemented in a real world application the computer model is preferably created on a computer of the supplier of a computer program which controls the computer-implemented method. The model is created with knowledge of the expected range of bulk PSDs and parameters of the reloading. lt is of course possible to create the model on the same computer on which the computer-implemented method is performed. lt is also possible to update/improve the model on which the computer- implemented method is performed. The model may be improved adaptively or manually.
The creation of the computer model may also comprise the steps of providing at least one data representation of a surface ofgranular material, with a predetermined measured bulk PSD, distributed essentially as a single layer after reloading, determining a measured surface PSD of the granular material based on the at least one data representation of the granular material, and adapting the computer model also to the predetermined bulk PSD and the measured surface PSD. As it is usually difficult to achieve a single layer ofthe granular material in a real world operation, this step is usually omitted. Figure 3a shows a data representation in the form of a 2D image of the surface ofgranular material on a surface. Granules 20 of different sizes are shown in the 2D image. From the image it is possible to determine a surface PSD. Figure 3b shows a data representation of the surface ofgranular material in the form of a 3D image. Granules 20 of different sizes are shown in the 3D image. The surface PSD may be determined with better accuracy if the data representation is a 3D representation.
Figure 4 illustrates the ranges of PSDs for the simulated sets of granules and the expected range of PSDs. The solid lines 14 shows the range for the expected bulk PSD. The two-headed arrow 14' illustrates that the expected bulk PSD may be between the solid lines 14. The dotted lines 15 shows the range of PSDs for the plurality of simulated sets of granules. The two-headed arrow 15' illustrates that the PSDs for the plurality of simulated sets of granules is between the dotted lines 15. Computer-implemented method according to any one of the preceding claims, wherein the range 15 of PSDs for the plurality of simulated sets of granules has at least a part which corresponds to a part of the expected range 14 of PSDs of the granular material for which the PSD is to be determined with the computer-implemented method. ln other words the two ranges 14, 15, have a common area as is shown in Figure 4, i.e., an area in which the two ranges overlap. 13 Figure 5 illustrates the ranges of PSDs for the simulated sets of granules and the expected range of PSDs similar to Figure 4, in which the range 15 of PSDs for the plurality of simulated sets of granules covers the entire expected range 14 of PSDs of the granular material for which the PSD is to be determined.
Figure 6 illustrates the ranges of PSDs for the simulated sets of granules and the expected range of PSDs similar to Figure 4, in which the range 15 of PSDs for the plurality of simulated sets of granules covers a subrange of the expected range 14 of PSDs ofthe granular material for which the PSD is to be determined.
The plurality of simulated sets of granules should preferably include a range of bulk PSDs which covers at least 5 %, more preferred 50 % and most preferred 90 %, of the expected range of bulk PSDs of the granular material for which the PSD is to be determined with the computer- implemented method. However, when the extension ofthe range 15 of PSDs for the plurality of simulated sets of granules is increased beyond the range 14 of PSDs of the granular material for which the PSD is to be determined, the model is not improved substantially.
The parameters of the simulated reloadings may be varied for the same simulated set of granules and wherein the reloading ofgranules onto the surface is simulated for each variation of the parameter. Thus, the model has been created with a variation of the parameters. This makes the model capable of modelling the real operation even if the operation is altered or if the real bulk PSD changes.
The model as such may be based on, e.g., mathematical regression or on a neural network.
Figure 7 shows the measured surface PSD 16, the estimated bulk PSD 17 and the actual bulk PSD 18. The results shown in Figure 7 has been obtained using a test volume with predetermined bulk PSD. As can be seen in Figure 7 the estimated bulk PSD 17 is very close to the real bulk PSD 18 of the test volume.
The described embodiments ofthe computer-implemented method may be altered in many ways without departing from the scope of the present invention which is limited only by the appended claims.

Claims (11)

1. 1. A computer-implemented method for determining an estimated bulk particle-size distribution, PSD, of granular material (2) comprising the steps of - obtaining parameters of at least one reloading from a first conveyor belt (9) to a reloading surface (8) in the form of a second conveyor belt (10), wherein the obtained parameters comprises at least the following parameters: the flow rate of the granules, the speed of the reloading surface, and the fall height (Hf) of the granules onto the reloading surface (8), and wherein the obtained parameters comprises at least one ofthe following parameters: the width (w) and the height (h) of the granular material after reloading, - simulating with a computer (5) and with the obtained parameters, for each one of a plurality of simulated sets of granules with mutually different simulated bulk PSDs (15), the reloading of the granules and simulating, using the obtained parameters, for each set of granules how the granules are distributed at a measurement point on the reloading surface (8) and a corresponding simulated surface PSD, - creating a computer model describing the relationship between the surface PSD and the bulk PSD, which computer model is adapted to the simulated sets of granules and the corresponding simulated surface PSD, - obtaining (101) a data representation of a surface of granular material (2) on the reloading surface (8) at the measurement point after the at least one reloading of the granular material (2), - determining (102) a measured surface PSD of the granular material (2) based on the data representation of the granular material (2), and - determining (103), with the computer model and the measured surface PSD, an estimated bulk PSD.
2. The computer-implemented method according to claim 1, wherein the obtained parameters comprise also at least one of the shape of the granules, the density of the granules, the coefficient of friction between the granules, the adhesion between the granules and the elasticity of the granules, and wherein the simulation of the reloading is performed also with said parameters.
3. The computer-implemented method according to claims 1 or 2, wherein the creation ofthe computer model also comprises the steps of - providing at least one data representation of a surface of granular material, with a predetermined measured bulk PSD, distributed essentially as a single layer after reloading, - determining a measured surface PSD of the granular material based on the at least one data representation of the granular material, and - adapting the computer model also to the predetermined bulk PSD and the measured surface PSD.
4. The computer-implemented method according to any one of the preceding claims, wherein the range (15) of PSDs for the plurality of simulated sets of granules at least has a part, which corresponds to a part of the expected range (14) of PSDs of the granular material for which the PSD is to be determined with the computer-implemented method.
5. The computer-implemented method according to claim 4, wherein the plurality of simulated sets of granules includes a range (15) of bulk PSDs which covers at least 5 %, preferably 50 % and most preferred 90 %, of the expected range (14) of bulk PSDs of the granular material for which the PSD is to be determined with the computer-implemented method
6. The computer-implemented method according to any one of the preceding claims, wherein at least one parameter of the simulated reloadings is varied for the same simulated set of granules and wherein the reloading of granules is simulated for each variation ofthe parameter.
7. The computer-implemented method according to any one of the preceding claims, wherein the computer model is based on mathematical regression.
8. The computer-implemented method according to claim 7, wherein the model is based on linear regression according to the formula (bulk PSD)=[3-(measured surface PSD) + s; where ß and s are constants which are determined during the adaptation of the computer model to the simulated sets ofgranules and the corresponding simulated surface PSD.
9. The computer-implemented method according to any one of the preceding claims, wherein the computer model is based on a neural network. 16
10. A computer program for determining the bulk particle-size distribution (PSD) of granular material, comprising instructions which, when executed by a computer (5) cause the computer (5) to carry out the method according to any one of c|aims 1 to
11. A carrier for a computer program on which is stored a computer program according to c|aim 10.
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