AUTOMATIC PARTICLE ANALYSING SYSTEM

Abstract: A method and an apparatus for automatical analysis of particle size distribution, shape and colour, comprising collection of a particle sample, where the aprticles are distributed into a substantially monolayer particle curtain to be exposed to a light source for providing imaging and subsequent analysis of the particles. The apparatus has a sampling device that collects samples from the product stream integrated in the system.

Description: Automatic particle analysing system The present invention relates to a method and an apparatus for automatic sampling and for performing an automatic image analysis to determine a particle size distribution, shape characterization and shape distribution. It is important for example in the fertilizer industry to have reliable information about the end product size distribution and particle shape, as . optimal values for these parameters are of importance both from a purely economical point of view and when using the product, e.g. when spreading the produced prills or granules. Furthermore, a process will be most economical if it gives a product with a narrow sieve span, without having to sieve away large fractions that have to be run in return. A method and apparatus for this use is earlier known from US 5 011 285. The method includes the collection of particle samples and the generation of a particle curtain in a monolayer form. The particle curtain is formed by taking particles through a silo down onto a vibrating plate. The particle curtain is lit up and the images of the particles therein is recorded and analysed. The silo has at least one level sensor to record the level of particles in the silo and to give a signal to the sampler. In US 5 309 215 there is also shown an apparatus for the determination of particle size distribution based on the same principle. Particles are fed from a sample collection chamber to a conveyor band or vibrating channel forming a particle curtain when falling down from this band or channel. Both these methods are dependent on a separate collection of the samples. The samplers commonly used in such processes are conveyor belt samplers comprising for example a container with a longitudinal slit that passes across the product stream on the conveyor belt or collects the samples at the end of the conveyor belt in such a way that the particles can fall gravimetrically into the sampler when it transverse the product stream. Also ; -HF!EII TIOIi'C0P' in production pipes, samplers collects particles from a cross section of the product stream. The samples thereafter have to be transferred to the container/ sample collection chamber before they can be analysed. To install such a sampling and analysing system often involves comprehensive reconstruction of the production line to fit a sampling system, if at all possible. For example by installation of an end of conveyor belt sampler, the end of conveyor belt housing (covering) has to be reconstructed to fit the sampling system. The expense of such a comprehensive reconstruction of the process line can be a reason not to invest in an imaging analysis equipment. For some installations it could also be very difficult to find space in the process line for a sampling system or to find a sampling system that could be used in an existing process. The object of the invention is to obtain a simple, sturdy and cheap particle analyser that easily can be used in existing production facilities without extra investments and reconstruction. Another object is to arrive at a versatile and automatic method and apparatus for analysis of a plurality of samples applicable for on-line analysis. These and other objects of the invention are obtained with the method and apparatus as described below, and the invention is further defined and characterised by the accompanying patent claims. The invention thus concerns an automatic particle analysing system and a method for automatical analysis of particle size distribution, shape and colour. The analysing system comprises sampling means and a device for creating a particle mono curtain suitable for imaging and subsequent analysis, wherein a sampling device is an integrated part of the system. The sampling device could be a tube moveable from a lower sampling position to an upright position where the sample is transferred directly on to a vibrating plate/ trough for creating a particle curtain. Alternatively, the sampling device is a plate/ trough that is vertically movable from a lower sampling position to an upper position where it is used to create a particle curtain. The plate/ trough could be rectangular with an end wall and parallell side walls or be a plate with non parallel side walls. The sampling device, device for distributing the sample into a mono curtain, light source and recording means are all mounted to a frame that could be fixed to a conveyor belt. The integrated sampling device collects samples directly from the product stream. It is preferred to collect a vertical cross section of the product stream and do the sampling countercurrent to the product stream. It is preferred to use a sampling tube which is vertically movable from a lower sampling position to an upright position where the sample is fed directly to a vibrating plate for creating a particle curtain. Alternatively, the sample is collected by lowering the vibrating plate/ trough into the product stream and thereafter lifting the plate to an upper position where the plate is vibrated to create a particle curtain. A new sample is automatically collected when the last particle on the plate is analysed. The invention will now be further explained in the following embodiments with reference to the accompanying drawings, Figures 1- 4, wherein Figure 1 A shows a perspective view of a particle analyser with the sampler tube in a lower sampling position. Figure IB shows a view with the sampler in a lower sampling position. Figure 2 shows a perspective view with the sampler tube in upper position (emptying sample to the vibrating system). Figure 3A shows a perspective view of an alternative configuration of the particle analyser with sampler in upper position. Figure 3B shows a side view with the analyser with vibrating plate sampler in upper position. Figure 4A shows a perspective view of the alternative configuration of the particle analyser with sampler in sampling position Figure 4B shows the analyser with vibrating plate sampler in lower position. A particle analyser 1 is shown in figures 1 A, B and 2, including a sampler 2 to collect particle samples in a process, for example at a conveyor belt 3 as shown in the figures. The conveyor belt is mounted upon a frame 4. The sampler 2 is shown as a tube with a bended lower part. The sampler is movable vertically fixed to a mounting frame 5. The frame has two vertically extending legs adapted to be fixed to the conveyor belt frame 4, and an upper horisontal part, to which the other components of the analyser are fixed. A pneumatic cylinder 6 is used to drive the sampler between an upper and lower position. In figure 1 A and B the sampling tube is shown in its lower sampling position collecting samples into one end of the tube in the product stream on the conveyor belt, while figure 2 illustrates the sampler in upright position where the collected sample is falling from the sample collected end of the tube on to a plate 7 or trough. The plate 7 is mounted to a vibrator 8 which may vibrate in a known manner, and both the frequency and the amplitude may be regulated. In these figures the vibrator 8 is shown mounted below the plate 7. By vibrating the plate the particles will run out over its edge creating a particle curtain. By adjusting the vibration amplitude and/ or frequency, one can easily make sure that the particles fall down from the plate into a substantially monolayer of particles. This is controlled by a computer and thus overlapping particles in the image is avoided. The sampler could be of different design. It could be in the form of a straight or bended pipe. A pipe with a rectangular cross section is also possible to use. What is most important is that it has a shape that makes it possible to collect samples in the product stream. It is also important that the diameter of a pipe sampler is at least 2-3 times the diameter of the product to be analysed, to make sure that there is a free flow of the product. A light source 9 is mounted to the frame 5 below the vibrating plate 7. The particle stream or particle curtain is thus lit up by this light source. The light source could be a normal lamp, a set of laser beams or a flash which lights at a signal. A unit 10 mounted at the other side of the frame may be a film or video camera, but also a recording unit for penetrating light, for example laser beams. The particle stream from the vibrating plate thus falls between the light source and camera 10. A video camera taking images all the time is preferably used, but if the light source is a flash the images will be recorded only at each flash. By using a video camera to take pictures of the monolayer of particles pictures are obtained. Thereby both their shape and size distribution could be registered. Special computer programs for the calculation of shape characterisation or the deviation from the desired shape are used and the particle size distribution in the product stream determined. Generation of the particle curtain and analysing the particles can be carried out continuously, and the production parameters can be adjusted as a function of the result of the analysis. The vibrating plate or trough, is shown in figures 1 A, B and 2 as a rectangular plate with one end wall and two parallel side walls. This shape is especially used for coarse parti- cles. For smaller particles product, a vibrating plate with not parallel side walls can be used, giving a narrower passage for the particles before they fall over the edge forming a particle curtain. When imaging small particles products, the camera 10 must be put closer to the product and it is therefore not necessary with a very wide particle curtain. The computer will regulate the number of particles. The passage out from the trough should at least be 2-3 times the largest diameter of the particles. However, if wanted, it is possible to mount more than one camera to cover a wider particle area or different camera selection for different particle ranges. Which shape of the trough that is selected, will be dependent on the product to be analysed. Instead of using a sampling device as illustrated in figures 1 and 2, it is also possible to use the vibrating trough to collect the samples. An alternative particle analyser is illustrated in figures 3 and 4. The vibrating trough 7 is shown mounted below the vibrator 8 to a frame 5 (Fig.4). This frame has an upper horisontal part and four vertical legs to be monted on opposite sides of the conveyor frame 4. Pneumatic cylinders 6 fixed to the frame 5, lower the trough 7 down into the product stream on the conveyor belt 3 as illus- trated in figure 4. A sample is collected and the trough is lifted to the upper position as illustrated in figure 3. Thereafter the vibrator is activated and a particle curtain is formed, imaged by using flash 9 and camera 10, recorded and analysed. When the trough is empty, a new sample is collected. When using the apparatus according to the invention, sampling is carried out counter- current to the product stream on the conveyor belt. The sampler is lowered into the product stream. A vertical cross section of the product is collected and this will be close to an average particle distribution. This will result in samples that are representative enough to control a production process. Each time all the particles in the sample are analysed, the sampler will move to the product stream again to collect a new sample. The analysed sample falls directly down on to the conveyor belt again. In this way analysis and sampling is repeated continuously. However, it is also possible to control the sampling frequency in other ways. Often it could be sufficient just to analyse a certain number of particles in a sample. The vibrating plate will be emptied of particles before a new sample is taken. It is also possible to take product samples at set intervals. The mounting frame 5 should be fixed to the frame 4 of a conveyor. It could be mounted on the one side of the conveyor belt as illustrated in figures 1 and 2 or across the conveyor belt as illustrated in figures 3 and 4. It is preferred to mount the frame in the longitudinal direction. This makes it easier to adjust the camera when this is necessary. The method and the apparatus according to the invention may be applied to all known particlulating processes and processes where addition of particles with the desire size distribution and shape is important. The invention could be used to analyse all kind of dry particles, apart from fertiliser, for example broken stone, sand, products in the food industry etc. The invention will, however, be applicable for verification of finished particulate product too. Such application may be: analysis during bulk loading, packing in bags or the like or verification of the specification of particulate products. The invention could be used both for conveyor belt or pipeline installations.

Claims: Patent claims 1. Automatic particle analysing system comprising sampling means and a device for creating a particle mono curtain suitable for imaging and subsequent analysis, ch aracterised in that a sampling device (2) is an integrated part of the system. 2. Analysing system according to claiml, characterised in that the sampling device (2) is a tube moveable from a lower sampling position to an upright position where the sample is transferred directly on to a vibrating plate/ trough (7) for creating a particle curtain. 3. Analysing system according to claiml, characterised in that the sampling device is a plate/trough (7) that is vertically movable from a lower sampling position to an upper position where it is used for creating a particle curtain. 4. Analysing system according to claim 2 or 3, characterised in that the plate/trough (7) is rectangular with an end wall and parallel side walls. 5. Analysing system according to claim 2 or 3, characterised in that the plate/trough (7) has non parallel side walls. 6. Ananalysing system according to claiml, characterised in that the device for sampling (2), device for distributing the sample into a mono curtain (7,8), light source (9) and recording means (10) are mounted to a frame (5) adapted to be fixed to a conveyor frame (4). 7. Ananalysing system according to claim 6, characterised in that the frame (5) is adapted to be mounted across the conveyor belt or along one side. 8. A method for automatical analysis of particle size distribution , shape and colour, comprising collection of a particle sample and distributing the particles into a substantially monolayer particle curtain, that is to be exposed to a light source for providing imaging and subsequent analysis of the particles, characterised in that a sampling device that collects samples from the product stream is integrated in the system. 9. Method according to claim 8, characterised in that a vertical cross section of the product stream is collected. 10. Method according to claim 8, characterised in that sampling is carried out contercurrent to the product stream 11. Method according to claim 8, characterised in that a sampling tube is used, which is movable from a lower sampling position to an upright position where the sample is fed directly to a vibrating plate for creating a particle curtain 12. Method according to claim 8, characterised in that a the sample is collected by lowering a plate/ trough into the product stream and thereafter lifting the plate to an upper position where the plate is vibrated to create a particle curtain 13. Method according to claim 11 or 12, characterised in that a new sample is automatically collected when the last particle on the plate is analysed.

Inventors: JOERGENSEN TERJE, JOHNSEN OLE MAGNE, REINHOLT FRODE, JOERGENSEN, TERJE, JOHNSEN, OLE, MAGNE, REINHOLT, FRODE
Applicants: JOERGENSEN TERJE, JOHNSEN OLE MAGNE, NORSK HYDRO AS, REINHOLT FRODE, JOERGENSEN, TERJE, JOHNSEN, OLE, MAGNE, NORSK HYDRO ASA, REINHOLT, FRODE
Application year: 2001
Main classification: G01N15
IPC codes: G01N1, G01N15