FI130944B1

FI130944B1 - Apparatus and method for optical imaging-based measurement of suspension comprising polymer particles

Info

Publication number: FI130944B1
Application number: FI20225513A
Authority: FI
Inventors: Mikko Haapalainen
Original assignee: Valmet Automation Oy
Priority date: 2022-06-10
Filing date: 2022-06-10
Publication date: 2024-06-11
Also published as: WO2023237693A1; FI20225513A1

Abstract

A measurement apparatus (10) for measuring suspension comprises liquid processing means (12), which add one or more substances of a different index of refraction than that of medium (52) of the suspension (50) to the suspension (50) in order to change an index of refraction of the medium (52), where the medium (52) is liquid mixable with water, and solid particles (54) of the suspension (50) comprise one or more polymers of plastic transparent in an optical range of the measurement. Image capturing means (20) capture images of the solid particles (54) within the medium (52) of different indices of refraction. Data processing means (22) perform a measurement of a geometrical parameter of the particles (54) based on a single index of refraction of the medium (52) and repeat the measurement of the geometrical parameter in images based on a different index of refraction of the medium (52). The data processing means (22) form a distribution of a number of particles relating to indices of refraction of the medium (52) as a function of the geometrical parameter of the particles (54).

Description

Apparatus and method for optical imaging-based measurement of suspension comprising polymer particles

Field

The invention relates to a measurement apparatus and measurement method and particularly an apparatus and method for optical imaging-based measurement of suspension comprising polymer particles.

Background

An optical measurement of solid particles of suspension can give important information on quality of the suspension such as process water, wastewater or sewage or the like. In optical measurements, light scattering may be measured for getting information on the particles. Alternatively, particles may be imaged for determining desired features of the particles. However, these measurements provide only limited data on the particles.

Brief description

The present invention seeks to provide an improvement in the measurements.

The invention is defined by the independent claims. Embodiments are defined in the dependent claims.

If one or more of the embodiments is considered not to fall under the n scope of the independent claims, such an embodiment is or such embodiments

S are still useful for understanding features of the invention. g

K List of drawings x a 25 Example embodiments of the present invention are described below, ; by way of example only, with reference to the accompanying drawings, in which

N Figure 1 illustrates an example of solid plastic particles in medium;

N Figure 2 illustrates an example of measurement system,

Figure 3 illustrates an example of plastic particles in medium an index of refraction of which is 1.4;

Figure 4 illustrates an example of plastic particle in medium an index of refraction of which is 1.5;

Figure 5 illustrates an example of plastic particles in medium an index of refraction of which is 1.6;

Figure 6 illustrates an example of distributions of plastic particles of different index of refractions as a function of size;

Figure 7 illustrates an example of a combined distribution of plastic particles of different index of refractions as a function of size;

Figure 8 illustrates an example of two distributions of plastic particles of each of three different index of refractions as a function of size measured at different moments;

Figure 9 illustrates an example of index of refraction of several plastics;

Figure 10 illustrates an example of a data processing unit; and

Figure 11 illustrates of an example of a flow chart of a measuring method.

Description of embodiments

The following embodiments are only examples. Although the e specification may refer to “an” embodiment in several locations, this does not

S necessarily mean that each such reference is to the same embodiment(s), or that ro the feature only applies to a single embodiment. ~ 25 The articles “a” and “an” give a general sense of entities, structures,

E components, compositions, operations, functions, connections or the like in this en document. Note also that singular terms may include pluralities. o Single features of different embodiments may also be combined to 3 provide other embodiments. Furthermore, words "comprising" and "including" should be understood as not limiting the described embodiments to consist of only those features that have been mentioned and such embodiments may also contain features/structures that have not been specifically mentioned. All combinations of the embodiments are considered possible if their combination does not lead to structural or logical contradiction.

The term “about” means that quantities or any numeric values are not exact and typically need not be exact. The reason may be tolerance, resolution, measurement error, rounding off or the like, or a fact that the feature of the solution in this document only requires that the quantity or numeric value is approximately that large. A certain tolerance is always included in real life quantities and numeric values.

It should be noted that while Figures illustrate various embodiments, they are simplified diagrams that only show some structures and/or functional entities. The connections shown in the Figures may refer to logical or physical connections. It is apparent to a person skilled in the art that the described apparatus may also comprise other functions and structures than those described in Figures and text. It should be appreciated that details of some functions, structures, and the signalling used for measurement and/or controlling are irrelevant to the actual invention. Therefore, they need not be discussed in more detail here.

In this application, the term “determine” in its various grammatical forms may mean calculating, computing, data processing for deriving a result, looking up in a database or the like. As a result, "determine" may also mean select, choose or the like. = Fig. 1 illustrates an example of suspension 50 with medium 52 and

N solid particles 54 within walls 30 of a measurement chamber (not all solid 3 25 particles are marked with reference numbers for clarity). The medium 52 may be - water or a solution in a liguid form, the solution including water. In an

E embodiment, one measurement can be made such that medium 52 includes only a = single liquid that is not a mixture. However, it is possible that all measurements

N are performed using a mixture as the medium 52. The suspension may a product i 30 ofanindustrial process, for example. The suspension may be input to the process, the suspension may be included or formed in a process and/or the suspension may be output by a process. The output suspension may be directed to a drain, to a next process or it may be recycled.

The suspension includes the solid particles on purpose or inevitably.

In such a case, the process generates or has from a beginning the solid particles within the medium. It may also be so that the solid particles represent impurity in the medium which may mean the solid particles are not desired. For example, when measuring drinking water or any other water or liquid that is meant to be pure such as pure water, the water or liquid may still contain solid plastic particles. It should also be noted that in an application some particles may be desired, and some other particles may be undesirable.

When a mixture is used in the measurement, the solution should be a homogenous mixture of at least two substances. If the mixture were not homogenous, the mixture would have more than one phase, and the interfaces of the phases typically cause optical effects such as scattering, which may disturb the optical measurement of the solid particles 54. The solution may be formed by mixing two liquids or a liquid and solid material that dissolves into the liquid homogenously. Utilization of one or more emulsifiers may allow a formation of mixture that has small globules of first liquid in the second liquid, the first liquid not being mixable with the second liquid without the one or more emulsifier. The first liquid may be oil and the second liquid may be water, for example. In that manner, the medium 52 - a mixture or a liquid of a single substance - can be considered a single phase. Hence, the medium 52 is a liquid mixable with water. = In an embodiment, the medium 52 may be a liquid directly mixable with water.

N The consistency of the suspension may be adjusted to be lower than 5%, for 3 25 example. The consistency of the suspension may be adjusted to be 0.1% to 2%, for - example. The consistency should allow many particles to be imaged 7 simultaneously or efficiently because images without particles lower efficiency of = the measurement, but at the same time images with particles over particles

N should also be avoided. That is, a particle should not obscure another particle but i 30 particles should likely be detectable individually spaced apart from each other from statistical point of view. A person skilled in the art knows, per se, how to increase or decrease consistency of suspension.

The solid particles 54 of the suspension 50 comprise one or more polymers of plastic. Plastics have typically an index of refraction in a range about 5 1.5 to about 1.6 in visible light and infrared light. Here are examples of indices of refraction of a few plastics in visible light: acrylic about 1.48 to about 1.50; cellulose acetate about 1.46 to about 1.50; epoxy about 1.6; polycarbonate about 1.59; polyethylene high-density (PEHD) about 1.5; polyester about 1.50 to about 1.58; polystyrene about 1.6; and polytetrafluoroethylene about 1.35; vinylidene chloride about 1.6 to about 1.63. The index of refraction of water is about 1.33 in visible light. In addition to plastic particles there may also be other kinds of particles in the medium 52. At least one wavelength that is used to measure the solid particles 54 has a low or zero absorbance to the solid particles 54. That is, the particles 54 are transparent in all wavelengths used in the measurement. A low absorbance may mean that about 90 % or more of a total optical power of the optical radiation directed to a solid particle 54 will pass through the particle 54, for example. In an embodiment, it may be possible to utilize also other and/or additional ranges of optical radiation.

Fig. 2 illustrates an example of a measurement apparatus 10 for measuring the suspension 50. The measuring apparatus 10 comprises a liquid processing system 12. In an embodiment, the liquid processing system 12 may comprise a first pump 102, which makes the suspension to circulate in a pipe & arrangement 100. The liquid processing system 12 comprises a measurement

N chamber 104 such as a cuvette. The measurement chamber 104 may allow flow of 3 25 the suspension 50 through, which allows measurements to be performed - continuously. Alternatively, an operation of the measurement may be like a batch 7 process where the measurement process repeats the following process steps: = take a sample of the suspension into the measurement chamber 104, measure the

N sample in the measurement chamber 104, and remove the sample from the

N 30 measurement chamber 104.

In an embodiment, the measurement chamber 104 may comprise a mixing device 56, which may mix the sample in the measurement chamber 104 particularly in an embodiment where the suspension 50 is not circulated through measurement chamber 104 in a continuous manner. The mixing device 56 may comprise a stirrer which may comprise a motor that rotates a rod that has at least one blade or other solid material extension immersed in the suspension 50. When the rod rotates the at least one blade or the other solid material extension spins in the suspension 50 stirring it. The motor and the rod may be replaced by a rotating magnetic field which rotates a magnet in the suspension 50. A person skilled in the art is familiar with the mixing devices, per se, and that is why the mixing does not need to be explained any further.

The measuring apparatus 10 comprises image capturing device 20, which captures images of the solution 50 for detection of the solid particles 54 in the medium 52. In an embodiment, the image capturing device 20 may capture a video.

A wall 30 of the measurement chamber 104 is transparent to optical radiation that is used in the measurement. That applies at least to the area of the wall 30 that is within the field-of-view of the image capturing device 20.

The liquid processing system 12 comprises a dosing arrangement 106, which adds, as a function of time, one or more substances of a different index of refraction than that of medium 52 of the suspension 50 to the suspension 50. The addition of the one or more substances causes a purposeful change an index of = refraction of the medium 52 in a range of the index of refraction from a first index

N of refraction to a second index of refraction. The addition may be continuous, or 3 25 the addition may be performed by inserting separate doses of the one or more - substances to the suspension 50 in a repeated manner or a combination of these.

E The addition may be performed as a function of time, as a function of volume, as a = function of mass and/or as a function of number of detected particles, for 3 example.

N 30 In an embodiment, the first index of refraction may be about 1.33 and the second index of refraction may be about 1.6, for example. In this embodiment,

at least one substance that has an index of refraction higher than 1.33 is added to the suspension 50, the medium 52 of the suspension 50 having said first index of refraction.

In an embodiment, the first index of refraction may be about 1.6 and the second index of refraction may be about 1.33, for example. In this embodiment, at least one substance that has an index of refraction lower than 1.6 is added to the suspension 50, the medium 52 of the suspension 50 having said first index of refraction.

The one or more substances may be added to a container 28 of the suspension 50. The container 28 may have a stirrer (not shown in Fig. 2).

However, no container 28 is necessarily needed, and the one or more substances of a different index of refraction than that of medium 52 of the suspension 50 can be added straight to the measurement chamber 104.

The image capturing device 20 captures images which altogether include a large number of the solid particles 54 in the medium 50. As the index of refraction of the medium 50 is changed, the image capturing device 20 captures at least two images in one of which the solid particles 54 are in the medium 50 of one index of refraction and in another of which the solid particles 54 are in the medium 50 of another index of refraction, where the two indices of refraction have different values. In this manner, a plurality of images can be obtained such that each of the images represents the suspension 50 with a unique index of refraction of the medium 52. = Fig. 1 illustrates an example where solid particles 54 are in water,

N which is the medium 50 the index of refraction of which is 1.33. In Fig. 1 all plastic 3 25 particles 54 can easily be seen and detected in the medium 50 because a - difference of index of refraction is large between the medium 52 and the particles : 54, = Fig. 3 illustrates an example where solid particles 54 are in medium

N 50, the index of refraction of which is 1.4. In this case, certain particles 54 cannot i 30 be detected as easily as in Fig. 1 but, on the other hand, some other particles 54 can still be easily detected in the medium 52. The particles 54 that are not easily detected have an index of refraction the same as, approximately equal to or close to that of the medium 52. The particles 54 that are easily detected have an index of refraction much different from that of the medium 52.

Fig. 4 illustrates an example where solid particles 54 are in medium 50, the index of refraction of which is 1.5. The particles 54 that are not easily detected have an index of refraction the same as or approximately equal to that of the medium 52. The particles 54 that are easily detected have an index of refraction different from that of the medium 52. Those particles 54 that are barely detectable in the medium of Fig. 3 or 5 can (faintly) be detected in the medium 52 of Fig. 4.

Fig. 5 illustrates an example where solid particles 54 are in medium 50, the index of refraction of which is 1.6. Also in this measurement, the particles 54 that are barely detected have an index of refraction the same as or approximately equal to that of the medium 52. The particles 54 that are easily detected have an index of refraction different from that of the medium 52. Those particles 54 that are barely detectable in the medium of Fig. 3 or Fig. 4 can be detected in the medium 52 of Fig. 5 or 4.

As can be seen from Figs 1, 3 to 5, particles 54 of the same index of refraction as the medium 52 are less visible and hence less detectable than the particles 54 of different index of refraction from that of the medium 52.

Based on that kind of variation of detectability of the particles 54 as a function of the index of refraction of the medium 52, a data processing unit 22 of = the measuring apparatus 10 performs a first measurement of at least one

N geometrical parameter of the particles 54 based on one or more images where the 3 25 index of refraction of the medium 50 is the same. The geometrical parameter may = refer to a size, diameter, shape, length of outline, area, estimated volume any 7 combination of these or the like, for example. The size may refer to an overall = number of pixels covered by an image of a particle 54 on the detector matrix of

N the image capturing device20, for example. As the sizes of the pixels and an i 30 optical magnification are known, the data processing unit 22 may also determine a real size of a particle 54 in an embodiment. A volume of a particle 54 may be estimated from an area in images or the estimation may be based on images showing particles 54 from different sides because flow of the circulation or the stirring may turn the particles 54 in various positions.

The shape may refer to geometrical figures such as a line, a square, triangle, rectangle, polygon, circle, ellipse, sphere, ellipsoid, disk, rod, tile, cube, lath, or the like, for example. The shape may be determined based on sphericity and/or angularity, for example. A degree of resemblance to defined shapes may be determined. A person skilled in the art is familiar with various determinizations of shapes and their use in image processing, per se.

The data processing unit 22 performs additionally a measurement of the at least one geometrical parameter of the particles 54 in one or more images where the index of refraction of the medium 53 is different from the first measurement. The particles 52 the indices of refraction of which are within said range of the index of refraction in one or more images are detected and measured in the measurements.

Based on these measurements, the data processing unit 22 forms distributions of a number of particles relating to at least two indices of refraction of the medium 50 as a function of the at least one geometrical parameter of the particles 54. Fig. 6 illustrates an example of three distributions of sizes. A first distribution 600 refers to a measurement where the index of refraction of the medium has been 1.6, a second distribution 602 where the index of refraction of the medium 52 has been 1.5, a third distribution where the index of refraction of = the medium 52 has been 1.4.

N As shown in Fig. 6, the distributions 600 to 602 may be represented as 3 25 a histogram where a numerical value of the y-axis refers to a number of particles - and the value of the x-axis refers to the size at each measured index of refraction. 7 A user interface 26 of the measurement apparatus 10 may present the = distributions. Additionally or alternatively, the information of the distributions

N may be sent to elsewhere for further analysis or for a control of a process i 30 producing the suspension 50. The user interface 26 may comprise a screen and a keyboard or a touchscreen, for example. The user interface 26 may input and output data. A person skilled in the art is familiar of various user interfaces, per se.

Fig. 7 illustrates an example of a combined size distribution of the particles 54 the combination being based on measurements similar to those presented in conjunction of Fig. 6.

In an embodiment, the data processing unit 22 may detect solid particles 54 causing a minimum optical distortion based on a difference between the indices of refraction of the solid particles 54 and the medium 50 in at least two different indices of refraction of the medium 50. The data processing unit 22 may then determine the indices of refraction of the particles 54 based on said minimum optical distortion based on measurements. The index of refraction of the medium 52 may be measured by a refractometer 14 shown in Fig. 1, for example. Additionally or alternatively, the index refraction of medium 52 may be estimated by the amount of addition of the one or more substances of the different index of refraction than that of medium 52 of the suspension 50 to the suspension 50.

A solid particle 54 causes a minimum optical disturbance when its index of refraction is at least approximately the same as that of the medium 50.

Because solid particles 54 may have a minor variation of index of refraction at and/or within their outer surface, a solid transparent particle 54 does not necessarily become invisible in the medium 50 although the indices of refraction of the solid particle 54 and the medium 50 becomes the same. An interface of the = solid particles 54 and the medium 50 has also effects in a molecular level which

N may cause a minor optical disturbance in the optical path of the optical radiation. 3 25 Hence, a solid transparent particle 54 does not necessarily fully disappear from - an image although the index of refraction of the medium 50 is the same as that of 7 the solid particle 54. Still, its visibility or detectability in an image is lowest when = the index of the particle 54 and the medium 32 is equal. The image processing

N may have a suitable threshold for determining when the medium and a particle i 30 have the same index or refraction. In this manner, the threshold serves as (if) resolution for indices of refraction of the particles.

Still additionally or alternatively, the index refraction of medium 52 may be estimated by a comparison between the medium used in the measurement and one or more references, each of which has a known index of refraction. When more than one reference is used, the references may have different indices of refraction with respect to each other. The comparison can give an estimate if the medium 52 and at least one reference have the same index of refraction, if the index of refraction of the medium 52 is lower than that of one of the one or more references and/or if the index of refraction of the medium 52 is higher than that of one of the one or more references. It is also possible to estimate how large the difference between indices of refraction is when the medium 52 is compared with one reference only. That is also true for each of the references when the medium 52 is compared with more than one reference.

When more than one reference is used, and the index of refraction of the medium 52 is between two of the references, it may be possible to estimate the index of refraction of the medium 52 exactly within tolerances.

As can be seen in Figs 1 and 3 to 5, solid particles 54 of different index of refraction can clearly be detected as a function of the refraction index of the medium 50. That is, particles 54 of different index of refraction can be seen or detected in images with different index of refraction of the medium 53. The data processing unit 22 detect separately and independently particles 54 of different index of refraction and particles 54 of different geometrical parameter.

In an embodiment an example of which is illustrated in Fig. 8, the data = processing unit 22 may form a distribution 800 of a number of particles of as a

N function of the index of refraction of the particles 54. Fig. 8 illustrates the 3 25 distribution as a continuous distribution. The distribution may also be presented = as a bar chart, for example. 7 In an embodiment, the data processing unit 22 may form a number of = particles for at least one refraction index of the particles 54.

N In an embodiment, the data processing means unit 22 may perform a i 30 measurement of sizes of the particles 54 in the images as a function of the index refraction of the particles.

In an embodiment, the data processing unit 22 may determine types of the polymers of plastic in the suspension 50 based on the indices of refraction of the particles. Figure 9 illustrates an example of indices of refraction of various plastics as a function of wavelength. The abbreviations are as follows: PS refers to polystyrene, PET refers to polyethylene terephthalate, PA refers to polyamide, and PP refers to polypropylene. Because of the differences, various plastics can be distinguished from each other based on their indices of refraction.

In an embodiment, the data processing unit 22 may measure a percentage of at least one type of polymers of plastic within the suspension 50 based on the number of particles 54 in each of the measured indices of refraction of the particles 54 or the medium 52.

In an embodiment, the data processing unit 22 may detect solid particles 54 causing optical distortion based on a non-zero difference between the indices of refraction of the solid particles 54 and the medium 50 in images with at least two different indices of refraction of the medium 50. The data processing unit 22 may then perform the measurement of the at least one geometrical parameter of the particles 54.

In an embodiment, the liquid processing system 12 may either mix gradually one or more substances of a higher index of refraction than that of the medium 52 for increasing the index of refraction of the medium 52 from the first index of refraction to the second index of refraction that is higher than that of the first index of refraction, or receive the suspension of the second index of = refraction in order to have a predetermined maximum change of the refractive

N index, and then dilute the medium 52 with water for lowering the index of

S 25 refraction of the medium 52 toward that of water. - In an embodiment where the suspension is diluted from the first index 7 of refraction to the second index of refraction, the liquid processing system 22 = may add the one or more substances of the higher index of refraction to the

N medium 32 in order to make the index of refraction of the medium 52 equal to the i 30 first index of refraction. The addition may mean that a predetermined percentage of the higher index of refraction is added to the medium 52 in order to reach the first index of refraction of the medium 52.

In an embodiment, the data processing unit 22 may form a number of particles 54 as a function of the refraction index of the medium 52 at each index of refraction of the medium 52 for determining a variation of the distribution of a number of particles 54 as a function of time. Fig. 8 illustrates two examples of distributions 800, 800B measured at two different moments.

In an embodiment, the data processing unit 22 may perform the measurement of at least one geometrical parameter of the particles 54 based on a digital image analysis.

In an embodiment, the liquid processing system 22 may mix gradually or add potassium thiocyanate (KSCN) solution to the medium 52 in order to increase the index of refraction of the medium 52.

Fig. 10 illustrates an example of the data processing unit 22 which may comprise one or more processors 900 and one or more memories 902 including computer program code. The one or more memories 902 and the computer program code may, with the one or more processors 900, cause the measurement apparatus to perform the measurement of at least one geometrical parameter of the particles 54, and form the distribution of the number of the particles 54 relating to the at least two indices of refraction of the medium 52 as a function of the at least one geometrical parameter of the particles 52. Additionally, the data processing unit 22 may control the measurement apparatus, and either mix = gradually one or more substances of the higher index of refraction than that of the

N medium 52 for increasing the index of refraction of the medium 52 from the first 3 25 index of refraction to the second index of refraction that is higher than that of the = first index of refraction, or receive the suspension of the second index of 7 refraction in order to have a predetermined maximum change of the refractive = index, and then dilute the medium 52 with water for lowering the index of

N refraction of the medium 52 toward that of water. i 30 When a large enough number of images are captured, it is possible to have a sufficiently large enough number of images of particles 54 in the medium

52. Then it is possible to make reliable measurements of the particles in the medium. The large enough number of images of the particles results in the statistical significance. When the large enough number of images of the particles 54 are available, the measured results have statistical significance and then it is likely that the measured results are reliable.

It is also possible to capture continuously more and more images of the particles 54 such that more and more information on the particles 54 is gathered. Whatever the significant number of images of the particles is, the number of images will go beyond that and reliable results can be made.

Figure 11 is a flow chart of the measurement method. In step 1100, an index of refraction of medium 52 of the suspension 50 is changed by adding, as a function of time, one or more substances of a different index of refraction than that of the medium 52 to the medium 52, where the medium 52 is liquid directly mixable with water, and solid particles 54 of the suspension 52 within the medium 52 comprise one or more polymers of plastic.

In step 1102, images of a large number of the solid particles 54 in the medium 52 of different indices of refraction are captured. A large number may be a number that assumably gives a reliable enough and/or representative enough information on suspension that is measured, the assumption being based consideration of a person skilled in the art. The number may be decided case by case by a person skilled in the art who is familiar with the suspension measured.

In an embodiment, the number may be a positive integer that consists = of four numbers abcd in a decimal system. Such a number is 1000, for example,

N where a=1, b=0, c=0 and d=0. Another example of the positive integer that

S 25 consists of four numbers and that can be expressed as abcd is 2329, where a=2, - b=3, c=2 and d=9. In an embodiment, the number may be a positive integer that

E consists of five numbers abcde. Such a number is 10000, for example, where a=1, = b=0, c=0, d=0 and e=0. Another example of the positive integer that consists of

N four numbers and that can be expressed as abcde is 23297, where a=2, b=3, c=2, i 30 d=9 and e=7. In that manner, a range of the large positive integer may be 1000 to 9999999, i.e. the large number consists of four to seven numbers. In an embodiment, the large number may refer to hundreds per single image, for example. For the whole sample the larger number may be larger. In an embodiment, the large number may be in a range about 500 to about 5000000, for example, where the lower value is more probable in a single image and the larger value is more probable for the whole sample. However, the range has no definite upper limit.

In step 1104, performing a measurement of at least one geometrical parameter of the particles 54 is performed, the index of refraction of which is within said range of the index of refraction, in one or more images based on a single index of refraction of the medium 52, and repeating the measurement of the at least one geometrical parameter of the particles 54 in one or more images based on at least one different index of refraction of the medium 52.

In step 1106, at least one distribution of a number of particles 54 relating to at least two indices of refraction of the medium 52 is formed as a function of the at least one geometrical parameter of the particles 54.

The method shown in Figure 11 may be implemented as a logic circuit solution or computer program. The computer program may be placed on a computer program distribution means for the distribution thereof. The computer program distribution means is readable by a data processing device, and it encodes the computer program commands, carries out the measurements and optionally controls the processes on the basis of the measurements.

It will be obvious to a person skilled in the art that, as technology = advances, the inventive concept can be implemented in various ways. The

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N invention and its embodiments are not limited to the example embodiments

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? 25 described above but may vary within the scope of the claims.

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Claims

Claims:

1. An apparatus for optical imaging-based measurement of suspension comprising polymer particles, characterized in that the apparatus (10) comprises liquid processing means (12), which are configured to add one or more substances of a different index of refraction than that of medium (52) of the suspension (50) to the suspension (50) in order to change an index of refraction of the medium (52) in a range of the index of refraction from a first index of refraction to a second index of refraction, where the medium (52) is liquid mixable with water, and solid particles (54) of the suspension (50) comprise one or more polymers of plastic which are transparent in an optical range of the measurement apparatus (10); image capturing means (20), which are configured to capture images of a large number of the solid particles (54) within the medium (52) of different indices of refraction; data processing means (22), which are configured to perform a measurement of at least one geometrical parameter of the particles (54), the indices of refraction of which are within said range of the index of refraction, in one or more images based on a single index of refraction of the medium (52), and repeat the measurement of the at least one geometrical parameter of the particles (54) in one or more images based on at least one different index of refraction of the medium (52); and the data processing means (22) are configured to form at least one S distribution of a number of particles relating to at least two indices of refraction ro of the medium (52) as a function of the at least one geometrical parameter of the ~ 25 particles (54).

j 2. The apparatus of claim 1, characterized in that the data = processing means (22) is configured to detect solid particles (54) causing a N minimum optical distortion based on a difference between the indices of i refraction of the solid particles (54) and the medium (50) in at least two different indices of refraction of the medium (52), and the data processing means (22) are configured to measure the indices of refraction of the particles (54) based on said minimum optical distortion.

3. The apparatus of claim 2, characterized in that the data processing means (22) is configured to form at least one distribution of a number of particles (54) of as a function of the index of refraction of the particles (54).

4. The apparatus of claim 2, characterized in that the data processing means (22) is configured to perform a measurement of sizes of the particles (54) in the images as a function of the index refraction.

5. The apparatus of claim 2, characterized in that the data processing means (22) is configured to determine types of the polymers of plastic of the particles (54) in the suspension (50) based on the indices of refraction of the particles (54).

6. The apparatus of claim 2, characterized in that the data processing means (22) is configured to measure a percentage of at least one type of polymers of plastic within the suspension based on the indices of refraction of the particles (54).

7. The apparatus of claim 1, characterized in that the data processing means (22) is configured to detect solid particles (54) causing optical distortion based on a non-zero difference between the indices of refraction of the e? 20 solid particles (54) and the medium (50) in images with at least two different N indices of refraction of the medium (50), and the data processing means (22) are 3 configured to perform the measurement of the at least one geometrical parameter — of the particles (54). T = JN 8. The apparatus of claim 1 characterized in that the liguid 0 25 processing means (12) is configured either to N mix gradually one or more substances of a higher index of refraction N than that of the medium (52) for increasing the index of refraction of the medium

(52) from the first index of refraction to the second index of refraction that is higher than that of the first index of refraction; or receive the suspension (50) a medium (52) of which has the second index of refraction and then dilute the medium (52) with water for lowering the index of refraction of the medium (52) from the second index of refraction toward that of water.

9. The apparatus of claim 1, characterized in that the data processing means (22) is configured to form a number of particles (54) as a function of the refraction index of the particles (54) or the medium (52) at each index of refraction of the particles (54) or the medium (52) for determining a variation of the at least one distribution of a number of particles (54) as a function of time.

10. A method for optical imaging-based measurement of suspension comprising polymer particles, characterized by changing (1000) an index of refraction of medium (52) of the suspension (50) by adding one or more substances of a different index of refraction than that of the medium (52) to the medium (52), where the medium (52) is liquid mixable with water, and solid particles (54) of the suspension (52) within the medium (52) comprise one or more polymers of plastic; capturing (1002) images of a large number of the solid particles (54) in the medium (52) of different indices of refraction; & performing a measurement (1004) of at least one geometrical a parameter of the particles (54), the index of refraction of which is within said I range of the index of refraction, in one or more images based on a single index of - 25 refraction of the medium (52), and repeating the measurement of the at least one 2 geometrical parameter of the particles (54) in one or more images based on at 2 least one different index of refraction of the medium (52); 3 forming (1006) at least one distribution of a number of particles (54) N relating to at least two indices of refraction of the medium (52) as a function of the atleast one geometrical parameter of the particles (54).

11. The method of claim 10, characterized by measuring the indices of refraction of the particles (54) by detecting a minimum optical distortion in the images caused by each of the particles of the large number of the particles (54) in at least two different indices of refraction of the medium (52).

12. The method of claim 11, characterized by forming a number of particles (54) as a function of the refraction index.

13. The method of claim 11, characterized by performing a measurement of sizes of the particles (54) in the images as a function of the index refraction.

14. The method of claim 11, characterized by determining types and/or percentages of types of the polymers of plastic in the suspension based on the indices of refraction of the particles (54).

15. The method of claim 11, characterized by changing the index of refraction of the medium (52) either mixing gradually one or more substances of a higher index of refraction than that of the medium (52) for increasing the index of refraction of the medium (52), or adding a predetermined percentage of the one or more substances of the higher index of refraction to the medium and then diluting the medium (52) with water for lowering the index of refraction of the medium (52) toward that of water. O N O N LÖ I N I = 0 0 LO N N O N