WO2011148061A1

WO2011148061A1 - Sample vessel and method for measuring particle size and shape or particle distribution and surface properties of powdery or grain like material

Info

Publication number: WO2011148061A1
Application number: PCT/FI2011/050486
Authority: WO
Inventors: Niklas Sandler; Juha Hatara; Heikki RÄIKKÖNEN; Osmo Antikainen; Jouko Yliruusi
Original assignee: Intelligent Pharmaceutics Oy
Priority date: 2010-05-27
Filing date: 2011-05-26
Publication date: 2011-12-01
Also published as: FI20105599A0

Abstract

The invention relates to a sample container (100) and a method for measuring the properties of a powder or granular sample (1) from the surface information of the sample. The sample container (100) comprises a feed opening (107), a sample chamber (109) delimited by walls (104) and connected to the feed opening, and at least one transparent wall portion (103). According to the invention, at least the lower part (108) of the transparent wall portion (103) forms a threshold in the opaque wall (104).

Description

SAMPLE VESSEL AND METHOD FOR MEASURING PARTICLE SIZE AND SHAPE OR PARTICLE DISTRIBUTION AND SURFACE PROPERTIES OF POWDERY OR GRAIN LIKE MATERIAL

The present invention relates to a sample container, according to the preamble of Claim 1, for measuring the particle size and shape distribution or a powder material.

The invention also relates to a method.

FI patent application 20000493 discloses an analysis method for a moving granular material. The method is not suitable for accurate optical grain-size-distribution analysis, precisely due to the movement of the material being studied.

US patent 5,239,358 discloses a method for removing foreign particles from a powder sample. The central component in the invention is a rotating sample plate. Precisely due to the rotating sample plate, the method is not suitable for accurate optical grain-size- distribution analysis. JP publication 10010033 discloses a measuring method for a moving powder substance. In this publication, the light passing through the sample is studied. The measuring method is not accurate.

US patent 6,122,042 discloses several methods for optical analysis. In the methods, comparison pairs of images of a stationary sample are not created. WO publication 03062804 discloses methods for optical analysis. In the methods, the fine-particle distribution is not determined, nor are comparison pairs of images created from a stationary sample.

In addition, it is known that a particle-size distribution can be relatively reliably determined from the surface of a powder or granular material (scientific publication: Laitinen, N., Antikainen, O., and Yliruusu, J. (2002) Does a powder surface contain all necessary information for particle size distribution analysis? European Journal of Pharmaceutical Sciences, 17(4-5), 217-227). In this case, the subject of the

measurement of particle size is an undispersed powder, from which a level surface is made. The method cannot therefore be used to measure a property of an individual particle, but a property of a large group of particles.

Using the prior art, the determining of the particle-size distribution from a powder surface takes place in the manner described hereinafter. For example, the most level surface possible is sought to be made from a powder sample in a sample container. In the method, a light source is used to cast shadows on the surface. The shadow formation is used by converting the powder's surface information to depict the particle size of the material. For example, two light sources set symmetrical on both side of the sample can be used to illuminate the sample. The sample is then illuminated using each light source in turn and a digital image is taken with a CCD camera, in such a way that two digital images are obtained. The sample must remain stationary, because first of all the difference is calculated between the two grey-tone matrices, from which the digital image is created. For a theoretically completely level sample, the difference matrix is formed of elementary units that are zeroes. For a real difference matrix, the values received by the units are integers from -255 to +255. The next stage of the calculation determines how many elementary units of the difference matrix have received some specific value of the 511 possible values.

The known measuring method is based on the fact that a sample with a specific grain- size distribution always forms its own specific grey- zone difference distribution. So that the measuring method can be used, a model must be made of the pitch of the actual size distribution of the grain of the grey-tone difference distribution, which converts the measurement results obtained into a size distribution. In the known method, a PLS (Partial Least Squares) model is used, which is based on principal-component analysis. The independent variables are the 511 values of the elementary units of the

aforementioned grey-tone matrix and the response variable is percentage mass-fraction on each screen of the screen series of the screen analysis of the grain batch. With the aid of the model in question, the grain-size distribution, which corresponds to the result obtained by screen analysis from the same powder material, can be determined. A corresponding model can also be calculated similarly for other methods generally used to determine particle size.

In the known method, a stable, collimated (parallel), direct current light source is used. The illumination can be arranged using two stable light sources, or a single light source, from which the light available is dispersed optically in such a way that the sample can be illuminated symmetrically in from two directions. For example, a matrix -type (CAD camera, or similar, or generally any opto-electric camera or image recording method whatever, can be used to detect the image signal. Imaging can also be performed using only a single light source, by rotating the sample. After this, the images can be combined according to the above matrix-difference principle. Several images can also be taken, as described above, of a single sample surface, by rotating the sample or light source, or by changing the exposure angle. In this way more information can be obtained from the powder surface. The material being studied can be a surface suitably created from powder, granular, or other multi-component samples. The surface can be created by wiping with a suitable flat spatula or plate. The repeatability of the sample-preparation method of the aforementioned measuring technique is problematic. In the method in question, the powder surface is made by pouring excess powder into the sample container, after which this surplus is removed with a suitable plate, at the same time trying to form a level surface of powder. The surface is levelled by drawing the levelling plate horizontally over the upper edge of the sample container. If the surface has been levelled in this way, unevenness due to the sample preparation can arise in the surface, for example, large particles in the powder can cause wipe traces in the surface. Powders with small particles that cohere easily to each other (cohesive powders) can also be difficult to level, if the levelling method in question is used. These problems will cause errors in measurement.

Publication WO2006/117429 discloses a measuring method and arrangement for measuring the particle size and shape of a powder or granular material, in which a transparent sample plate is used, on the first side of which the sample is arranged to be supported, the imaging means being arranged on the second side of the transparent sample plate to examine the sample from the imaging side of the sample plate.

The invention disclosed here is intended to eliminate the drawbacks and weaknesses of the previous method. The invention permits a considerably more accurate, faster, and easier to use particle size and shape measuring method based on surface images. In addition, by using the invention additional information is obtained on the arrangement and caking of the material being examined. With the aid of the invention, sample preparation is also easier to automate, allowing material for analysis to be collected directly from various types of treatment processes for powder substances.

According to the invention, these objectives are achieved by using a sample container, in which a transparent wall portion in at least the lower part forms a threshold in the opaque walls of the vessel.

The invention is thus intended for measuring the properties of a powder or granular substance, preferably in such a way that principally with the aid of gravity (and partly of electrostatic interaction) and alternatively also of centrifugal force, the sample space is filled freely,

• in the sample space, there is at least one window suitably allowing the measurement signal to pass through,

• the subject being measured is illuminated from at least two directions by an illumination unit, or alternatively the measurement subject is moved relative to the illumination unit,

• the measurement is registered with the aid of a registering unit, such as a digital camera,

• a model database may be used (with the aid of which the measurement result can be linked to a suitable reference method), and

• the result is processed with the aid of a processing/corriputation/presentation unit.

More specifically, the sample container according to the invention is characterized by what is stated in the characterizing portion of Claim 1.

The method according to the invention is, for its part, characterized by what is stated in the characterizing portion of Claim 8. In the following, the invention is described with reference to the accompanying drawings, which show cross-sectional images of various sample-preparation vessels according to the prior art and to the invention.

Figure 1 shows a side view of one measurement event according to the prior art. Figure 2 shows a cross-sectional side view of a sample container according to the prior art, in which there is a powder substance.

Figure 3 shows a cross-sectional side-view of sample container according to the prior art, in which there is a powder substance, and which is equipped with a cover.

Figure 4 shows a cross-sectional perspective view of the sample container according to Figure 3, in which there is a powder substance.

Figure 5 shows a cross-sectional side view of a multi-compartment sample container according to the prior art.

Figure 6 shows a top view of the construction of Figure 5.

Figure 7 shows schematically a measuring system according to the prior art, which can be applied to the solution according to the invention.

Figure 8 shows a cross-sectional side view of a sample container according to the invention.

In Figure 1, there is a sample plate 2, on top of which is a powder sample 1. The sample plate 2 comprises two surfaces, a first surface 6 on the side facing the sample 1 and a surface opposite to it, the imaging surface 7. Once the powder material has been poured onto the sample plate 2, it forms a powder surface specific to it. In this arrangement, the powder 1 is supported on the first surface 6 and forms an even measuring surface. The powder surface is illuminated in a controlled manner by light sources 3 from the imaging-surface side 7 and is imaged using a suitable camera 5. In addition, the sample 1 or the camera 5 can be rotated around its optical axis 4.

Figure 2 shows a sample container 20, inside which is a powder sample 1. Once the powder material has been poured into the container, it forms its specific surface on the first surface 6 of the plate 2. The surface of the powder can be imaged through the sample plate from below, in the direction of the imaging surface 7.

Figure 3 shows a cross-section of a cubical sample container 30, in which a powder sample can be imaged through transparent planes, the walls 13, 14, and 15. Information on the sample 1 can thus be obtained in the directions of the three axes (x, y, z). In the sample container there is additionally a sealing cover 16 and a plastic seal 17, with the aid of which the sample can be made to remain stationary and the sample can, for example, be rotated, so that it can be imaged from different directions by a camera. The sealing cover 16 can be, for example, a rubber plug, or some other suitable plug. The closing method of the sample container 30 can be equipped with a suitable locking method. The layering, in other words the degree of flow of the fine-grain material component in the vertical direction of the sample container, of the sample 1 can also be examined through the side surfaces 13 and 14.

In Figure 4, the cubical sample container 30 of Figure 3 is shown in a side view, so that the powder sample 1 can be imaged through the transparent sample plates 13, 14, and/or 15. In this way, information on the sample 1 is obtained in the direction of the three axes (x, y, z). In the sample container 30 there is additionally a closing mechanism 16 and a damper layer 17, which, in this case, evens the pressure acting on the sample and, with the aid of which, the sample 1 is made to remain in place and the sample can be, for example rotated, so that it can be imaged by a camera from different directions.

The sample container can also be multi-chambered, according to Figure 5, in which case there will be samples simultaneously in several containers 50 in the frame 54.The closing mechanism 51 of the sample container is unified and also includes sample- chamber-specific damping stopper pieces 52.

Figure 6 shows a top view of the frame component 54 of Figure 5, showing the possible annular openings of the sample chambers 50. The sample chambers can thus be set in a flat arrangement, or they can form a long band. Sample-chamber methods of this kind can be utilized to increase the speed of the analysis.

Figure 7 shows further the entire system, in which, in stage A, a powder sample is poured, for example, into the sample container 30 shown in Figure 3, either manually or automatically with the aid of dosing devices. In stage B, the sample is illuminated from two directions by light sources 3 and imaged by a camera 5. The camera 5 is connected to a computer 70, in which the interface to the camera 5 is, for example, an image- capture card, or some other similar interface, for example, a USB bus (Universal Serial Bus), and suitable software. The computer 70 can be any computer freely available on the market, such as a desktop or portable computer.

The transparent sample plates are typically in either a vertical or horizontal position, but the plate can naturally also be at a slant, provided the sample rests on the plate. Slanting can typically be implemented in the form of a funnel-like sample container, in which case the sample 1 will rest on a slanting plate. Within the scope of the invention, the slant of the plate can be in the range 0 - 90°, in which 0° refers to a horizontal surface and 90° to a vertical surface. The sample plate can also be curved, for instance convex or concave, in which case the shape must be taken into account in modelling. The sample plate need not necessarily be of uniform thickness, though uniform thickness will facilitate modelling. In principle, lens-like sample plates are also suitable for the solution according to the invention.

In the present application, the term imaging the sample refers to recording the surface- structure information of the sample. This takes place typically with the aid of a digital camera, but the use of a conventional camera too will permit the use of the method according to the invention. In that case, the information contained in the film material will have to be converted to a numerical form. In this connection, imaging also refers to the creation of surface- structure information, for example, using laser scanning.

The method according to the invention is also suitable for measuring segregation, i.e. differentiation, provided a suitable device is used to cause a controlled vibration in the sample. Known coarseness parameters can then be calculated from the image information.

It is also possible to take only a single image of the sample surface and convert it into a grey-tone vector, on the basis of which the particle size can be calculated, in which case a model is first created and then the particle-size distribution is calculated. The independent variable is the distribution of elementary units in the aforementioned grey- tone vector and the response variable the percentage mass fraction on each screen of the screen series of the screen analysis of the grain batch. With the aid of the model in question, it is possible to determine the grain-size distribution, which corresponds to the result obtained by screen analysis of the same powder material. A corresponding model can also be similarly calculated for other generally used methods for determining particle size.

The calculation relating to segregation can also be performed from a single image.

According to the invention, it is not necessary to use the entire image matrix (the entire area of the image taken), if the essential information can be calculated from some part of the image. This applies to the measurement of size, shape, and segregation. Thus, in addition to the grey-tone difference distribution, the grey- tone vector can also be calculated from a single image.

In the grey-tone difference distribution there can be more than 511 elementary units, depending on the equipment used, i.e. typically the camera.

According to Figure 8, the sample container 100 according to the invention comprises a feed hopper 101, which has a feed opening 107. The lower edge of the feed hopper 101 connects to a sample tube 102, which has an external surface 105 and an internal surface 104. The cross section of the sample tube 102 can be of many kinds, for example, a parallelogram, a rectangle, an ellipse, or a circle. A transparent wall portion 103, i.e. a portion allowing the passage of electromagnetic radiation, is attached to the outer surface 105 of the sample tube 102. This wall portion 103 forms a threshold in the sample tube relative to the internal wall 104. In the solution of the figure, in which the transparent wall portion 103 is attached to the external surface of the sample tube 102, the size of the threshold becomes the thickness of the opaque wall 104 of the sample tube. The threshold 108 can be horizontal or, alternatively, tilted at 1 - 50 degrees, preferably 45 degrees, to the horizontal. Thus, the sample container 100 comprises a feed opening 107, a sample chamber 109 connected to the feed opening, and at least one transparent wall portion 103, so that, according to the invention, at least the lower part of the transparent wall portion 103 forms a threshold 108 to the opaque wall 104.

In the embodiment of the figure, the sample tube is vertical, but the tube can be tilted in any direction whatever. A suitable angle of tilt is, for example, 1 - 45 degrees, most suitably about 30 degrees. According to Figure 8, the measuring window 103 of the sample chamber 109 is thus slightly recessed, i.e. a peak-like ridge remains above the measurement window 103, which prevents the material from flowing directly along the internal surface 106 of the measuring window 103 down the wall. Thus, the material dropping into the measuring space 103 causes the sample chamber 109 to be filled from the bottom up. When images are taken at the same time through the window 103, some idea is obtained of how the material fills the sample chamber 109 in stages. In particular, in this stage it is possible to obtain information on the flow properties, as well as, for example, on the

arrangement created by static electricity. The feed opening need not be above, instead the sample can be brought, for example, with the aid of compressed air to the sample chamber 109 also from the side of the sample container 100.

Instead of gravity, a force can also be directed to the sample material with the aid of centrifugal force, by placing the sample container or containers 100 on the

circumference of a rotating device, in such a way that the portion visible below in the figure will now be farther from the centre of rotation of the rotating device.

The lighting unit of the sample chamber 109 contains at least two lights transmitting electromagnetic radiation on (essentially) the same wavelength, by means of which the object is illuminated alternately from different angles and at the same time digital images of the object are taken. The illumination unit can also be constructed in such a way that the light energy of one primary radiation source is guided with the aid of suitable mirrors, prisms, polarizers, semi-transparent membranes, or similar to illuminate the object from two or more directions.

The measurement data are the images obtained using CCD camera (or some other suitable method), for example, by means of the arrangement of Figure 7.

The images (together with their identifying information) are recorded in such a format that the images can be further processed effectively, without disturbing the

measurement event.

The imaging speed is preferably in the range 1 - 50 images per second. In certain situations, there is a need for very high-speed imaging (e.g., 1/100 000 s), such measurement can be implemented using relatively standard methods.

The images are recorded in an image database and customers can build their own measurement databases. According to the invention, the sample can be brought to the sample chamber with the aid of both gravity and also, for example, centrifugal force, by placing the sample container on a rotating sample-processing device.

According to the invention, the substance being measured can be a solid or semi-solid powder or granular substance, and one in which the particle size of the substance being measured is preferably in the range 10 μπι - 5 mm, but, with suitable technical arrangements, the measurement range can also be entirely or partly outside the said range. When the sample is in the measuring chamber, the chamber 109 can be in a static state or it can be agitated at the same time as images are taken of the object. If necessary, the physical conditions of the measuring chamber, such as its temperature and the atmospheric humidity can be regulated.

Instead of ordinary air, the medium can also be any gas or mixture of gases whatever or a suitable liquid.

With the aid of the invention, particle-size distributions (diameter, surface area, volume, etc.) can be measured, as can particle-shape distributions (of which there are many), the arrangement of the particles, and the morphology of the surface of the particles.

The invention permits the measurement of light-reflecting samples, the measurement of wet samples, and also the measurement of cohesive samples.

With the aid of the invention, the texture of the surface, the reflectivity of the surface, and the roughness of the surface can be determined.

In connection with the invention, the analysis of measurement results can be improved by using comparison with reference libraries. From the measurement data (from at least two images), it is possible to calculate the particle-size distributions and shape distributions of a material, as well as the parameters (for example, mean particle size, distribution fractiles, etc.) depicting various shape factors of particle size. Parameters depicting the material's flow, electrization, arrangement, caking, and separation can be calculated from the measurement information.

The basic measurement method of the invention is reflection measurement, but this can be combined with transmittance measurement, which can also be implemented entirely independently.

Transmittance measure can be implemented by illuminating the sample from one side and analysing it from the opposite side. Scattering measurement is implemented non-axially, so that the light source and the light receiver are not on the same optical axis. How much the light reception differs from the optical axis of the illumination source provides information on scattering. The procedure is usually to measure the scattered signal perpendicular to the illumination axis. This is one possibility, but not the only one.

The invention also relates to a sampling method for measuring the properties of a powder or granular sample from the surface information of the sample. In this method, the sample is fed into the sample chamber 109 of a sample container 100 comprising a transparent wall portion 103 and measuring the sample optically through the transparent wall portion 103. According to the invention, the sample is fed into the sample chamber 109 in such a way that it must be supported at least partly on the edge of the transparent wall portion 103.

Claims

Claims:

1. Sample container (100) for measuring the properties of a powder or granular sample (1) from the surface information of the sample, which sample container (100) comprises

- a feed opening (107), - a sample chamber (109) bounded by walls (104) and connected to a feed openings, and

- at least one transparent wall portion (103), characterized in that

- at least the lower part (108) of the transparent wall portion (103) forms a threshold in the opaque wall (104).

2. Sample container (100) according to Claim 1, characterized in that the sample chamber is arranged to be filled and compacted with the aid of gravitation.

3. Sample container (100) according to Claim 1, characterized in that the sample chamber is arranged to be filled and compacted with the aid of centrifugal force.

4. Sample container (100) according to Claim 1 or 2, characterized in that the transparent wall portion (103) is at least essentially vertical.

5. Sample container (100) according to Claim 1 or 2, characterized in that the transparent wall portion (103) is tilted at 1 - 45 degrees, preferably about 20 degrees from the vertical.

6. Sample container (100) according to any of the above Claims, characterized in that the feed opening (107) is funnel shaped and opens upwards.

7. Sample container (100) according to any of Claims 1 - 5, characterized in that the feed opening (107) is located in the side of the upper part of the sample container for compressed-air feed.

8. Sampling method for measuring the properties of a powder or granular sample (1) from the surface information of the sample, in which method - the sample is fed into the sample chamber (109) of a sample container (100) comprising a transparent wall portion (103), and

- the sample is measured optically through the transparent wall portion (103), characterized in that

- the sample is fed into the sample chamber (109) in such a way that it must be supported at least partly on the edge of the transparent wall portion (103).

9. Method according to Claim 8, characterized in that the sample chamber is arranged to be filled and compacted with the aid of gravitation on the lower edge of the transparent wall portion (103).

10. Method according to Claim 8, characterized in that the sample chamber is arranged to be filled and compacted with the aid of centrifugal force.

11. Method according to Claim 8 or 9, characterized in that the transparent wall portion (103) is formed to be at least essentially vertical.

12. Method according to Claim 8 or 9, characterized in that the transparent wall portion (103) is tilted by 1 - 45 degrees, preferably about 20 degrees from the vertical.

13. Method according to any of the above Claims, characterized in that the feed opening (107) is formed to be funnel-like and to open upwards.

14. Method according to any of Claims 8 - 2, characterized in that the feed opening (107) is located in the side of the upper part of the sample container for compressed-air feed.