AU2012247760A1

AU2012247760A1 - Method and device for characterising physical properties of granular materials

Info

Publication number: AU2012247760A1
Application number: AU2012247760A
Authority: AU
Inventors: Jan Felix BACHMANN; Michael Paul CIPOLD; Helge Benjamin WURST
Original assignee: J&C BACHMANN GmbH
Current assignee: J&C BACHMANN GmbH
Priority date: 2011-04-29
Filing date: 2012-04-30
Publication date: 2013-11-28
Also published as: DE112012001932A5; WO2012146392A1; AU2016200096A1

Abstract

The invention relates to a method and a device for characterising physical properties of granular materials. In order to obtain sufficient information about the shape and content of the individual particles of the granular material, the device for carrying out the method comprises an optical measurement section that, in order to carry out a laser triangulation, comprises at least one laser (16) and two cameras (12), an x-ray or gamma beam measuring device (18, 20) comprising an x-ray or gamma-ray source (18) and an x-ray or gamma-ray detector (20) arranged opposite said source, and a conveyor device (14) that moves the granular material along the measurement sections of the laser triangulation (12, 16) and the x-ray or gamma-ray measuring device (18, 20) in a mechanically supported manner.

Description

JCBC Method and Device for the Characterization of 5 Physical Properties of Granular Materials The present invention relates to a method and device for the measurement of physical properties of granular products and materials. In various industries, in particular in the mining industry, the characterization of the particles is of major significance to enable granular materials to be economi 10 cally and efficiently processed. It is thus required for a given product or a given flow of material to collect and put forward as many criteria as possible for the performance of preparation processes. Two typical parameters of interest are particle density and size for example. Several methods for the determination of the particle size have been well intro 1s duced. In the particle size range of plus 1 mm sieve methods are typically em ployed. The sieve analysis has the disadvantage, however, that the particles are characterized by a single value only, said value being the mesh size of the rele vant sieve or screen. Such a characterization is meaningful if the particles are of cubic or globe shape. However, real particles in industrial processes often have 20 other shapes: they are lengthy or flat for example. The determination of the particle density is often done in a laboratory, typically by the Archimedes' principle using gravity fluids to perform a float-sink analysis. However, the fluids used for this purpose are often toxic and banned for safety reasons. Time, cost and safety aspects of the float-sink method have given rise 25 to a search for a new approach aimed at establishing preparation process crite ria, especially as performance levels of preparation plants can be maximized if 2 readily accessible and reliable information can be furnished which is based on an analysis of density in conjunction with particle size distribution and valuable substances content. The invention seeks to achieve this by providing an improved system for the s measurement of physical properties of granular products or materials. Object of the invention is initially to propose a method for the characterization of physical properties of granular materials, said method being distinguished in that - the individual particles of the granular material are individually measured op tically in a contactless fashion and radiographed using x-rays or gamma 10 rays, wherein data of the outer dimensions and topography of the particle surfaces are collected by said optical measurement whereas by x-ray or gamma ray measurement data are acquired with respect to the density spread within the particles and/or substances the particles contain, - and in that the data gathered by optical measurement are interrelated online is to data obtained by x-ray or gamma ray measurement and in this way ulti mately provide the data needed for further processing of the granular mate rial. An especially preferred embodiment of the invention proposes that the x-ray or gamma ray measurement each is carried out at a minimum of two different en 20 ergy levels which as a result of their differing intensity produce different measur ing results so that based on the different results of these measurements and combined with the measuring results obtained from optical measurement addi tional information about the density spread within the particles and/or substanc es the particles contain is gathered. This procedure enables significantly more 2s accurate information to be made available, particularly with respect to the con stituent elements and density spread in the particles. Moreover, the objective of the invention also includes a device for carrying out the above described method, said device being characterized by 3 - an optical measuring section provided with at least one laser and two cam eras to perform a laser triangulation assessment, - an x-ray or gamma ray measuring unit provided with an x-ray or gamma ray source and an x-ray or gamma ray detector arranged oppositely, 5 - conveying systems supporting the granular material mechanically and/or move said material in free fall along the measuring sections. The locations of the two measuring sections for optical measurement and the x ray or gamma ray measurement may coincide. Additionally, the measuring sections can be supplemented by an x-ray fluores 10 cence measuring unit. Further features and advantages of the invention are evident from the descrip tion and patent claims stated hereinafter. An embodiment example of the invention proposes a system for the determina tion of the physical properties of granular products or materials which comprises: 1s - an optical sensor that can be arranged in the area of a belt conveyor, - a light source that can be arranged in the area of the belt conveyor, - an x-ray source and an x-ray detector that can be mounted in the conveyor area, and - a data processing unit using the data collected by the optical sensors, the 20 light source, the x-ray source and the x-ray detector to compute the physical properties of the granular products or materials passing along on the belt conveyor. The at least one light source may be a laser or a photodiode.

4 The optical sensor may be a camera. Information is available from the following figures: Fig. 1: is an exemplifying schematic representa tion of a system used to implement the 5 method described hereinafter; Fig. 2: is an exemplifying schematic representa tion illustrating the function of the light source and optical sensor; Fig. 3: is an exemplifying schematic representa 10 tion illustrating the function of the laser and cameras. As shown in Figure 1 the system 10 comprises at least one optical sensor in the form of a camera 12 mounted above a belt conveyor 14. The granular product or material is usually introduced to the conveyor 14 via a vibrating feeder or a slow is moving conveyor and then moves along on the conveyor 14 in the direction indi cated by arrow A. Expediently, the conveyor 14 is capable of operating at variable conveying speed. For the embodiment illustrated two cameras 12 are employed the function of 20 which being described below in detail. As an alternative to cameras PSD detectors (position sensitive diodes) can be used which are suited for scanning laser triangulation. For this function, the PSD detectors (position sensitive diodes) are arranged in the same plane as the scanning laser beam which preferably is perpendicular to the conveying direc 25 tion A of the granular material. Another possibility of obtaining triangulation data is to use an array of PSD sen sors recording the same surfaces in a sheet-of-light geometry.

5 Such array sensors require a great number of one-dimensional sensors (photo diodes) arranged side by side in parallel. The photodiode strip count needs to coincide with the horizontal pixel count of a standard camera sensor. The optical setup when using a PSD array is comparable to the geometric ar s rangement elucidated in the context of the standard setup. However, the PSD array is rasterized in one dimension only with each readout channel or, respectively, photodiode strip corresponding to a column of pixels. The center-of-mass calculation based on pixel values is replaced by a generic representation of difference and sum signal values for each PSD (photodiode 10 strip). This reduces the data throughput significantly and permits unprecedented scan frame rates. The electronic PSD chip has integrated circuitry for the control and processing of mixed signals, for amplification, multiplexing, frame-oriented sampling, and for is A/D conversion. Array sensors with strip counts of 128 are already available, those with even higher strip counts are under development. Frame rates ranging between 1,000 and 10,000 frames per second are achiev able. They enable a full topographic scanning of the particles within the time it takes for the particle to transit the optical scanner in a state of free fall. 20 Moreover, a light emitting device is arranged above belt conveyor 14. In the il lustrated embodiment example said light emitting device is a laser 16. Neverthe less, other suitable light sources may be employed as well, for example using one or several photodiodes arranged side by side or two-dimensionally. For example, more than one laser 16 may be put to use as well, with the at least 25 one laser 16 producing laser points or a laser line that can be evaluated.

6 In any event, laser 16 projects a geometric pattern onto the granular particles or materials to be evaluated. In the represented embodiment example this pattern is a line which is projected across the belt conveyor 14. Advantageously, also several lasers operating at different wavelengths can be s employed. With respect to the represented embodiment example lasers 16 project light which is reflected by the material to be measured and received by the two cam eras 12. Thus lasers 16 and cameras 12 jointly form a first measurement sec tion. 10 Shown in the embodiment one or several cameras 12 are arranged in conveying direction A ahead of laser 16 and one or several cameras 12 in conveying direc tion behind the laser 16. Cameras 12 and laser 16 are used to implement a con tactless, optical assessment by means of triangulation which is described below. As per Figure 2 the laser 16 projects a precisely focused point of light onto a 15 surface. An image of this point of laser light is then projected with the help of a lens 24 onto a detector 26 which may be a CCD line sensor or another position sensitive measuring device to enable the distance to be determined via lens 24. Lens 24 which ,,sees" the laser light point is arranged at an angle to the surface onto which the laser light point is projected. The position of the projected laser 20 light point on the detector depends on the distance between the object to be measured and the detector as well as the distance between laser and sensor. An optical distance measurement in the range of between 10 and 100 cm may be well performed with such a laser arrangement. A one-dimensional approach offers only little information about each particle on 25 the belt conveyor. In the best case a length and height profile can be obtained along a single line of the particle. In the most unfavorable case a particle is wrongly or not seen at all because it is not exactly centered. If the particle is scanned a second time and its orientation does not exactly coincide with the previous orientation the result of the measurement is entirely different.

7 In the embodiment example a two-dimensional measurement is used comprising a line laser 16, with the optical measuring section consisting of two cameras 12. The same effect could be brought about with a fast distance sensor making use of a rotating mirror. The mechanical complexity of a rotating mirror, however, s would be significantly higher than using a standard industrial type camera. For that reason an image producing device is employed. This device can be con nected with a computer which is a fast evaluation system that can be easily con figured. The best result can be achieved theoretically if the camera is aligned with the 10 conveyor meaning the camera position is aligned parallelly with the conveying direction. This maximizes the distance shown on the camera monitors between the projection of the laser image point in the absence of a particle on the one hand and, when a particle is present, a given height on the other. With this con figuration, however, the rear side of the particle cannot be seen at all by the is camera. The higher the angle a (refer to Figure 2) the poorer the possible measuring result that can be achieved with a given camera. Angle a also de scribes the maximum (negative) slope of the rear surface at which the meas urement is still functioning. Even if a equals 45 degrees between conveying direction and camera there are 20 still many particles of which some surface areas cannot be seen because they are too steep. To avoid this the rear of the particle is viewed at the same time by a second camera. To project a laser line onto particles with very steep edges or flanks two or more lasers can be mounted at the right and left side of the belt conveyor. Moreover, 25 the recognition of particles can be improved by making use of an additional camera resulting in a very flat angle a. The above described calculations are performed by a computer 22 that based on data furnished by the above commented on components determines the physical properties of granular products or materials transported on the belt 30 conveyor 14.

8 In the embodiment example the physical properties of the granular products or materials determined by laser triangulation are length, width, and height of the particles in a three-dimensional system of Cartesian coordinates. Moreover, the ascertained parameters can be used to determine the volume of s the measured particles of the granular products or materials. In addition, at least one x-ray source 18 and one x-ray detector 20 are arranged in the area of the belt conveyor 14 which together form a second measuring sec tion. The energy level of the x-ray source may be fixed or adjustable. Instead of the x-ray source a gamma ray source may be used as well. 10 In the embodiment example the detector 18 is an x-ray or gamma ray capturing line detector or flat-bed planar detector. Alternatively or additionally the detector 18 is a broadband energy detector op erating at multiple energy levels. It is to be understood that the x-ray measurement and the optical measurement 1s need not be carried out spaced apart from each other but can both be imple mented within a common measuring section. Moreover, the measurement peri ods are preferably coincident. This enables the space requirements for the in strumentation devices and the needs relating to computer evaluation to be re duced. It also improves the consistency of the data acquired by the various sub 20 systems. The X radiation is examined with respect to its energy level and allocated to en able the density of each particle of the granular product or material to be deter mined. The intensity of attenuation is governed by the atomic number of the ma terial (materials of higher atomic numbers attenuate x-ray radiation stronger than 25 materials of lower atomic number) and by the thickness of the material. For that reason, the measurement of the not intercepted (penetrating) radiation provides information about the mass distribution in every particle. In conjunction 9 with the optical measurement the density distribution inside of each particle can thus be derived. The density of each particle of the granular products or materials is preferably determined based on two energy levels employing the dual-energy x-ray absorp s tiometry DXA method. In addition to performing a measurement at a low energy level a second measurement is used at a higher energy level and higher pene tration capability to enhance the dynamic density measuring range towards higher mass per unit area values. The measuring method may additionally be expanded by providing a subsystem including an x-ray fluorescence analysis 10 providing information about the elemental composition of each particle (cf. US patent No. 7 200 200). Finally, the x-ray measurement and the triangulation measurements are associ ated with each other to determine the area weight of the individual particles of the granular products or materials as well as the density distribution within the is individual particles. As soon as the above parameters are known the measured particles or materials are classified or sorted according to the material properties found. This enables further classification or grading into certain density classes or certain size classes. For example, particles of a certain density class can be collected, ground and chemically analyzed in the laboratory. 20 Sorting can be accomplished by means of an automatically operating mechani cal system equipped with a sorting robot. Such an automatically functioning me chanical system serves to physically separate the individual particles and trans fer them to collecting bins for temporary or final storage. Given the fact that the present and future positions of all detected particles are 2s accessible and, additionally, the allocated physical properties are known each particle can be sorted into a certain bin or container based on a comprehensive set of selected criteria. For example, so-called pick-and-place robots are fast enough to pick up and sort all particles as soon as the quality parameters have been evaluated.

10 In the illustrated embodiment example the material is additionally irradiated transversely using x-ray or gamma radiation. Moreover, the surfaces of the ma terial are measured in a contactless fashion. It can also be emphasized that the physical properties of the particles remain s unchanged. As per another embodiment which is not shown here the optical measurement is performed with the particles not being mechanically supported. In particular, a measurement with particles in free fall is proposed. In this manner, the optical measurement of the entire surface geometry can be carried out while the parti 10 cle drops onto the conveyor or falls down from the conveyor. This unsupported condition is considered as achieved if all sides of the particle can be captured between two changes of the frame of reference. The condition is also considered fulfilled if at least one side can be captured that is inaccessi ble when other conveying steps are performed due to the fact that mechanical 1s transportation means are used. In this context, the mechanically unsupported measurement offers advantages preferably if the topographic measurement by scanning or frame-oriented imag es is to be combined with other imaging methods to enable additional evaluation and correction steps to be performed based on rotational movement. Multiple 20 image-producing steps may also be taken to record the kinematic behavior of the particles. Such a subsystem for the optical acquisition of topographic and kinematic data is preferably combined with mechanically unsupported radiographic measuring methods. The measurement periods are adapted to each other such that x-ray 2s radiation based imaging is performed at a frame rate of high frequency and the space monitoring x-ray detector operates one- or two-dimensionally, enables fast data acquisition and is largely integrated into the particle transportation sys tem.

11 It is also to be noted that a combination of kinematic information and frame oriented x-ray measurement permits volumetric information to be determined in the event the particle has non-zero angular momentum enabling classification of the particles with three-dimensional spatial resolution. 5 The invention thus proposes an optical method according to which the particles can be characterized by determination of all three physical dimensions, i.e. length, width, height - as well as the volume of the particles. Moreover, addi tional characterizing dimensional relationships such as the width- to-length ratio may be derived from these measurements. 10 The invention also offers another significant advantage in that the method is put to use within an online configuration or arrangement. Using an automatic sam pling system the device proposed by the present invention is capable of furnish ing continuous analysis data regarding density and size distribution without the need for laboratory personal intervention. 1s In addition, the invention proposes an optical measurement method wherein the particles can be precisely characterized both by determining the entire or partial topography of their surfaces and with respect to their volume, as well as by adopting complementary x-ray analysis techniques furnishing information on the internal composition of the particles. 20 Finally, additional characteristics can be derived from the measurements, e.g. the aspect ratio and density distribution within each particle. - Claims -

Claims

1. Method for the characterization of physical properties of granular materials, c h a r a c t e r i z e d i n t h a t 5 - the individual particles of the granular material are individually meas ured optically in a contactless fashion and radiographed using x-rays or gamma rays, wherein data of the outer dimensions and topography of the particle sur faces are collected by said optical measurement whereas by x-ray or gamma 10 ray measurement data are acquired with respect to the density spread within the particles and/or substances the particles contain, - and in that the data gathered by optical measurement are interrelated online to data obtained by x-ray or gamma ray measurement and in this way ul timately furnish the data needed for the further processing of the granular mate 15 rial.

2. Method according to claim 1, characterized in that the x-ray or gamma ray measurements each are carried out at a minimum of two different energy levels which as a result of their differing intensity produce different measuring results so that based on the different results of these measurements and com 20 bined with the measuring results obtained from optical measurement additional information about the density spread within the particles and/or substances the particles contain is gathered.

3. Method according to claim 1 or 2, characterized in that the optical measurement is performed using a laser triangulation technique. 25

4. Method according to claim 1, characterized in that the granular ma terial lying on a conveyor is moved past one or several measurement sections.

5. Method according to claim 1, characterized in that the granular ma terial while in free fall is moved past one or several measurement sections. 13

6. Method according to any one of the claims 1 to 5, characterized in that the determination of the substances the particles contain is supplemented by an x-ray fluorescence measurement.

7. Method according to any one of the claims 1 to 6, characterized in s that the particles of the granular material are finally classified according to size and/or shape based on the measurement results obtained or sorted according to their constituent elements.

8. Device for the implementation of the method according to claim 1, characterized by 10 - an optical measuring section provided with at least one laser and two cameras to perform the laser triangulation assessment, - an x-ray or gamma ray measuring unit provided with an x-ray or gam ma ray source and an x-ray or gamma ray detector arranged oppositely, - and conveying systems supporting the granular material mechanically 1s and/or move said material in free fall along the measuring sections.

9. Device according to claim 8, characterized in that the measure ment section for the optical measurement spatially coincides with the x ray/gamma ray measurement section.

10. Device according to claims 8 or 9, characterized in that the meas 20 urement sections are additionally provided with an x-ray fluorescence measuring unit. - Summary -