Design and Construction of an Innovative Particle Analyser

. The paper presents issues concerning the implementation of particle size analyzers in the evaluation of the grinding product. A review of the current solutions of the analyzers used in practice was made. The usefulness of the original size analysis system according to its own design has been verified and exemplary results of the size assessment of grinding products - polymeric materials and biological materials have been presented.


Introduction
One of the parameters describing the material to be further processed is the average grain size. It contributes to the physical and chemical properties of the material such as: strength, stability and chemical activity. Too small or too large grains may deteriorate the above properties and decrease the functional properties such as agglomeration, water absorption [1][2][3][4][5]. Optimal granular composition provides not only effective processing but also consistency, e.g. during material extrusion [6][7][8],what is very important from the point of view of product quality, among other things in the manufacture of artificial organs for medical purposes, mainly training and education [9][10][11][12][13][14] and in the manufacture of artefacts supporting basic everyday activities [15][16]. Additionally, the consistency of particle size in subsequent batches of the manufactured product proves the repeatability of the production process, therefore determining this parameter at the production stage and in the evaluation of the finished product is one of the elements of quality control analysis. In industrial practice, the quality of the material is determined by the method of grinding, the design of the shredder and the parameters of the fragmentation process [17][18][19][20][21][22]. Very often, the selection of design features is made with the use of CAD/CAE tools, and the analysis of the results contributes to more accurate granulation [23][24][25] or in the manufacture of pellets [26][27][28]. In addition to the quality of the grain size, great attention is also paid to the parameters of the shredding process in terms of energy requirements for the process, e.g. during wood chipping [29,30]. In recent years, image analysis systems have become increasingly common in various fields, e.g. to assess the quality of toothed belts [31] or to , and monitor the quality of the product in real time during multi-disc chipping [32]. Solids grain size analysis is used, among others, in pharmacy, metallurgy, construction, environmental protection, polymer processing and agriculture. Currently, there are several types of particle analysers on the market which differ in the type of physical phenomena used for measurements and the parameters they measure. For particle size analysis of solids, mainly screen analysis, image analysis, electric mobility analysis, cascade impactor and laser analysis are used [33][34][35]. The paper includes a comparison of sieve, optical and laser analysis. The ADP 8601 optical analyzer was presented. The usefulness of the original system of dimensional analysis according to its own design was checked and exemplary results of size assessment of products of polymer and biological materials grinding were presented.

Comparison of sieve, optical and laser analysis
Sieve analysis is used to estimate large particles with a diameter between 10 -3 and 10 mm. By sieving the material through a set of sieves with specific hole diameters, starting with the largest sieve and ending with the smallest one, the material is separated into dimensional fractions with a particle diameter equivalent to the mesh of the sieve. On the basis of accurate weighing of the separated fractions, the function of mass distribution from size can be determined. The analysis takes between 5 and 30 minutes, depending on the material and degree of grinding. This is the cheapest and simplest method of particle size analysis. This method allows the analysis of particle size distribution only to a limited extent and requires the selection of sieves for the analyzed material. Moisture, screen movement, agglomeration and static electricity of particles can distort the measurement result. The advantage of this method is the possibility to use the obtained dimensional fractions for other purposes. Such devices are offered by such manufacturers as: Retsch, Fritsch, Endecotts, ATM Sieves Topass. [33,[36][37]. Laser analysers use diffraction and adsorption of laser light to measure. In these devices, the detectors measure the intensity of light scattering by the examined material particles at one angle or at different angles. If the measurement is carried out at one angle, usually 90˚, this technique is referred to as Dynamic Light Scattering (DLS) and particle size is determined from the Stokes-Einstein equation based on the scattering intensity fluctuation. It allows the measurement of particles with diameters ranging from 10 -4 do 5*10 -2 mm. The measurement time ranges from 0.1 to 5 minutes. This technique can only be installed in the production line if the particle flow is very small because increased particle concentration leads to a (apparent) size deviation due to particle-particle interaction and multiple scattering. For polydispersing particles there can be high uncertainty of results. The second technique is called laser diffraction and the scattering angle is measured. Small particles scatter at a large angle and large particles at a small angle. Based on the analysis of the intensity of scattering from the angle, the size of the particles is determined. The technique is used to analyse particles with diameters between 10 -6 and 1 mm. The measurement time ranges from about 0.01 to 30 s and very good repeatability can be achieved. The technique can be used in the production line. In this device the shape of the sphere is assumed in the calculation models, therefore the shape of the particles can sometimes distort the result, so it is important in this method to calibrate the device properly for the material being tested. Devices carrying out DLS or LD measurements are offered by such manufacturers as: Retsch, Fritsch, API Instruments, Anton Paar [33,36,[38][39][40][41]. In optical analysers, particle size measurements are carried out on the basis of an image analysis recorded by a high quality photosensitive matrix combined with a magnifying optical system. The image is processed according to a certain code and algorithms and on this basis size and shape information is obtained. The method allows the measurement of particles with a diameter between 5*10-3 and 10 mm. The result in this method is greatly influenced by the quality of the image, the degree of enlargement and the type of algorithms used. On the basis of the image a numerical size distribution is obtained from equivalent surface diameters or linear size parameters. Too much flow can cause overlapping of particles and distort the measurement result. In this method the accuracy and deviation are significantly influenced by the correct calibration of the measuring device and the achievement of sharp images. With a large number of particle measurements the quantitative result can be obtained [21][22]26].

AnalyserADP 8601 specifications
The ADP 8601 particle analyser shown in fgure 1 is designed for the measurement of granulates and dry powders within a rope size range of 0,15 to 5 mm. On the basis of the image recorded of freely falling particles in the measuring chamber by a high quality photosensitive CMOS camera with a telecentric lens, the shape, size and concentration of the analysed particles is determined in the application called "Analyser" and their distribution of parameters is determined, including: equivalent volume, equivalent diameter, area, volume, maximum and minimum dimensions and sphericity. The parameters from the main and associated processes measured shall be presented in the form of tables and histograms. In this test, the histogram presents a graph of the mass distribution or number of recognised objects according to diameter. Particle analysis is performed for a grey or colored image according to user settings. Particles for evaluation are collected and delivered continuously by means of a vibrating conveyor or directly into the chamber, which is in the process line.

Measurement software
Dedicated measurement software called "Analyzer" was developed in the LabView 2013 Development System programming environment by National Instruments. It is used to determine the particle size on the basis of the registered image from the measuring chamber camera. Thanks to this, measurement results are performed and saved in a file in xls format, a video image in a file in avi format and a histogram showing mass distribution or number of recognized objects depending on the diameter. In addition, the programme enables to control the operation of the camera and analysis as well as the scope of measurement. The programme provides the possibility of using both standard and original particle size measurement procedures. The program interface is divided into three equal areas. In the upper part of the interface there are menu tabs including camera, video, histogram and info. By default, the camera tab is activated, where the particle analyser control is performed, and the camera and particle analyser image and the measurement results screen are displayed in a small area. The video tab shows an enlarged image from the camera and the particle analyser, the histogram tab shows a large screen of measurement results and the Info tab shows information about the program version. At the bottom of the program interface there is a footer bar, which is identical for all menu tabs. It contains a button called Power supply Computational and visualisation components Measurement chamber Compressor start to start and finish saving, the STOP System button, which ends the program and the Results Path field, where the catalogue, where the results are saved, is indicated. The camera tab is divided into three parts: camera control block, image analysis block and histogram. In the camera control block there are buttons that control, among others, the start of image recording, the end of image recording, exposure time, brightness of the image, weak or strong highlighting of the edges of objects and the view of the image from the analyser chamber from the currently recorded or loaded image is visible. In the image analysis block there are buttons controlling the size of skipped objects, the grey or color image analysis mode, the criterion of shape of recognized objects, the upper and lower limits of the criterion coefficient of recognition of objects and the size of erosion, in which the lower limit of the size of objects in skipped pixels is determined. For the grey image, it is possible to set the brightness, contrast, gamma, the limit level of extraction of objects and the way of image processing, including by Gradient, Gauss Laplace or smoothing. For a color image, you can set the RGB or HSL image encoding mode, the upper and lower limits for red (RGB) or hue (HSL), the upper and lower limits for green (RGB) or saturation (HSL), and the upper and lower limits for blue (RGB) or luminance (HSL). At the bottom of this block you will find an overview of the analysis process. In the last block there is a histogram of the currently recorded sample. In this area there are indicators showing the number of particles already analysed and their total conventional mass. Figure 2 shows the program interfaceduring the analysis.

Measurements
Crushed corn, rice and polypropylene grains were used for the measurements. Maize and rice grains were crushed on a multi-disc shredder and polypropylene on a knife shredder [21][22]32]. In each measurement 100g of material was used and for each material the measurement was performed twice. The material was poured in small portions into the measuring chamber so that there was no overlapping of particles while recording their dropping by the camera. The application of the analyser allows to determine the percentage of mass or quantitative share of particle diameters in 20 intervals in the range from 0.15 to 3 mm. The test results were recorded in xls format. Particle diameters in this test were determined in the range from 0.3 to 3 mm based on Heywood's criterion. Figure 3 shows a graph showing the results of particle size analysis for a 16-bit grey image determining the percentage of particle diameters for maize, rice and polypropylene samples.     4. Results of the particle size analysis for the rice.
The ADP 8601 particle analyser is an innovative, original device with a high potential for innovation to perform particle size analysis of solids. Thanks to a high-resolution camera and software with large possibilities of setting analysis parameters, it allows to perform measurements at a fast pace and in a wide range of particle sizes. In this device, particle size measurements are performed on average every second, thanks to which the user is able to observe how the particle size changes over time. The measurement time of this analyser is largely dependent on the weight of the material being analysed. The more material there is, the longer the time it takes to dose the particles into the measuring chamber and the longer the analysis time. In the performed tests, polypropylene samples had the highest percentage of masses of particles with large diameters. A high percentage of corn and rice grain particles in the diameter range from 1.5 to 2.25 mm may indicate that the material was dosed too much into the measuring chamber, as a result of which partial overlapping of particles during image recording may have occurred, which may have distorted the results. Therefore, without proper application and verification of test results, the device does not currently guarantee correct results. Therefore, experience in performing this type of measurements is important and the results may be of comparative nature. Optical analysers have a better price/performance ratio than screen and laser analysers. They have a much wider measuring range than sieve analysis and slightly smaller than laser analysis. They allow to obtain results with relatively small measurement error reducing human error. They allow for measurement in the production line. Compared to laser analysis with DLS or LD technique it allows to measure polydispherical particles.  grain diameter, mm