Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
  • G01N15/02—Investigating particle size or size distribution
  • G01N15/0205—Investigating particle size or size distribution by optical means
  • G01N15/0227—Investigating particle size or size distribution by optical means using imaging; using holography
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
  • G01N15/02—Investigating particle size or size distribution
  • G01N15/0205—Investigating particle size or size distribution by optical means
  • G01N2015/025—Methods for single or grouped particles
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
  • G01N15/10—Investigating individual particles
  • G01N15/14—Optical investigation techniques, e.g. flow cytometry
  • G01N2015/1497—Particle shape
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N2021/845—Objects on a conveyor
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/85—Investigating moving fluids or granular solids
  • G01N2021/8592—Grain or other flowing solid samples
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/85—Investigating moving fluids or granular solids

Definitions

• the present invention relates to a method and an apparatus for measuring particles by image analysis, more particularly for automatic measurement of particle size, shape and optical properties.
• the size, shape and optical properties of particles is essential to understand and analyze their mechanical behavior (apparent density with and without compaction, flow fluidity, shear strength, slope angle, %), their tribological behavior and their chemical behavior (dissolution kinetics, electrical capacity, ).
• patent application WO 94/06092 describes a system for automatic measurement of particle size distribution by image analysis.
• the system includes a conveyor belt driven by a horizontal translation.
• This conveyor belt is provided with transverse grooves intended to orient the particles in a preferred direction.
• the grooves are separated by a spacing chosen according to the size of the particles to be analyzed.
• An image is taken in episcopy by means of a camera placed above the conveyor belt.
• the system is equipped with a ring light placed concentrically around the camera lens.
• This system is designed to classify particles in a seed lot based on measurements of crossing lengths and colors in the image. Interrupted scrolling of the strip each time images are taken is designed to analyze approximately 300 particles per minute. A weight proportion is estimated empirically from a projected surface of each particle.
• the apparatus described in WO 94/06092 does not make it possible to collect information on a critical sieving diameter because the particles are not in a flat position at rest due to the use of grooves in the conveyor belt.
• episcopy does not make it possible to collect geometrically correct information for a precise measurement of the size and shape of a particle.
• the apparatus is not suitable for dispersing and capturing images of particles which are too fine (eg 100 m) and deteriorates the properties of friable particles (eg soluble coffee) by contact with mechanical elements. movement.
• friable particles eg soluble coffee
• the present invention relates to an apparatus for measuring particles by image analysis comprising:
• the particles are dispersed in a monolayer on one or more transparent, flat and rigid plates; said plates being transported in a horizontal plane movement and positioned perpendicular to the axis of the optical system for the analysis of each digital image;
• This equipment is intended for a range of particles between 5 ⁇ m and 5 mm, whether it is mineral powders (sand, coals, abrasives, ...), polymeric or ceramic metallic powders, granules and pellets pharmaceuticals, fertilizers, seeds or agri-food products.
• This equipment can be used, for example, as a laboratory instrument for controlling the quality of products, or it can also be adapted on a production line, for example in the mineral, metallurgical, chemical, pharmaceutical, agricultural industry. , food, phytosanitary.
• the device for dispersing particles so as to prevent their overlapping can also be supplemented with a rotary sampler.
• This sampler is intended to reduce the amount of material required without bias, since very high measurement precision can be achieved with only a few grams of material, or a few thousand particles.
• the sampler can be removable and can be short-circuited if it is desired to analyze the entire material or if its friability / ductility requires limiting mechanical shock.
• the material can then be directly fed into a vibration chute which aims to stretch a flow of particles and provide a regular flow to the system. Adjustable vibration of the chute allows a frequency to be adapted to the response properties of the granular material used.
• the particles are brought by an adjustable height drop onto a plate or a series of horizontal, transparent, flat and rigid plates on which they will immobilize before entering the focal field of the optical system, more particularly the field of view of a camera.
• the particles will naturally orient their smallest diameter along the optical axis of the shooting system (perpendicular to the plates).
• Their intermediate diameter (D IN ) which conditions the passage of a particle through a sieve is therefore parallel to the plate and visible in an image plane.
• the plates are part of the device for transporting particles from the fall of the vibrating chute to the place of discharge and cleaning of the plates.
• the dispersion of the particles on the plate or plates is regulated by the height between the vibrating chute and the transport device as well as by the running speed of the transport device.
• the particle dispersing device makes it possible to avoid any overlapping of particles on the plates and to obtain very low levels of particle connectivity. They are, for example, of the order of 1/400 for a sand, 1/200 for soluble coffee. This is statistically negligible and may be subject to filtering during the computer analysis of the data.
• the particle dispersion device manages to disperse materials with very variable intrinsic characteristics (glass beads, polyethylene granules, silica sands, metal powders, lyophilized particles , etc.). For more adherent materials, slightly damp or loaded with fine particles, it may be desirable to adopt a dispersion with compressed air at the outlet of the vibrating chute, for example for powdered milk.
• the device for transporting the particles in the focal field of an optical system comprises one or more horizontal plates on which the particles are dispersed. These plates must have a transparency of more than 90%, avoid any diffusion of light and be free from any defect in mass or surface which may be perceptible by the optical system.
• the plates must be flat and have a hardness such that they resist abrasion and scratching by silica particles. More precisely, the rigidity and the flatness of the plates must be such that the difference in distance to the image plane between the highest point and the lowest point of the plate does not exceed the depth of field of the system.
• the plates will be made of optical quality glass.
• the plates are transported in a horizontal plane movement and are positioned perpendicular to the axis of the optical system for the analysis of each digital image.
• the movement of the plates is preferably at constant speed.
• the perpendicularity of the plates to the optical axis during their passage in the field of vision of the system is ensured by the complementary use of a guide system comprising, for example, teflon slides.
• the displacement of the particles during the taking of images therefore takes place in a perfectly horizontal plane.
• the vibrations of the chute do not affect the particles when taking images.
• the particles are therefore subjected to a horizontal, plane movement at constant speed. While being perpendicular to the optical axis, According to a particular embodiment of the invention, the plates are attached to a conveyor belt.
• the conveyor belt preferably comprises two parallel belts guided by two toothed wheels.
• Each particle dispersed on a horizontal plate then takes its position of equilibrium which is such that its center of gravity is as low as possible.
• the particle is simultaneously brought into the focal field of an optical system.
• the plates are attached to a circular platform consisting for example of a steel disc welded to a motorized axis.
• a speed of rotation can be regulated in combination with an intensity of vibration of the chute to optimize the dispersion of the particles on the plate or plates.
• the optical system according to the invention uses conventional systems of episcopic lighting (top lighting), diascopic (bottom lighting) or a combination of the two, but preference is given to diascopic lighting and to its combination with episcopic lighting .
• a collimated backlight and a telecentric optic are preferably chosen. It is then possible to take a precise image of the projected shadow of each particle along an axis perpendicular to the transparent plate. It can be shown that the diameter of the largest inscribed circle (D IN ) in the projected surface of a particle corresponds to the critical diameter of passage of the particle through a sieve.
• collimated LED diode lighting and telecentric optics make it possible to broaden the depth of field as well as possible and guarantee better imaging conditions for each particle.
• the image can be taken for example with a linear or matrix CCD camera. These cameras have image capture frequencies which can be adjusted as a function of the speed of travel of the transport device, in particular of the conveyor belt.
• Vmax for the maximum running speed of each plate, in particular on the conveyor belt
• Ts for a determined exposure time of the particle in the focal field of the optical system
• PMP for the loss of focus during an image capture.
• Loss of focus means displacement of the particle during image taking.
• Vmax (PMP * G) / (Ts) to calculate the frame rate at PMP precision. For example, for a PMP of less than 3 pixels, and a G of 24 microns per pixel, a Ts of 50 microseconds, a scrolling speed Vmax of 1440 mm / s is obtained.
• the brightness of the lighting is possibly increased to compensate for the loss of intensity of the contrast due to higher acquisition speeds.
• particle size and morphometry the analysis of 5000 particles per minute in the 200 ⁇ m range can be obtained with a completely conventional matrix CCD camera.
• the extent of the particle size distribution which can be analyzed in a single pass depends on the optics used and on the resolution of the image taking device.
• the use of linear CCD cameras makes it possible to envisage a resolution sufficient to process dimensional ranges from 5 m to 5 mm.
• a current CCD camera (eg 1300x1024) can process a particle size dynamic of 1: 1000.
• An image in shades of gray or in color can therefore be obtained. It will be thresholded to obtain a binary image at the start of which, it is possible to analyze by means of software information relating to the surface and perimeter of the projected shadow, to the surface and perimeter of the convex envelope, to the Feret diameters, elongation, diameter of the inscribed circle, many other morphometric concepts derived from original work in mathematical morphology, reflectance, transparency, color, texture and many other measures size, shape or optical surface properties.
• the apparatus according to the invention comprises a plate cleaning system.
• the plates After passing through the focal field of the optical system, the plates are discharged of their particles, in particular in the lower part of the conveyor belt or in the part opposite the camera of the circular platform. Most particles fall by gravity and are collected in a collector. The smallest particles can be removed using one or more brushes.
• Fig la diagram of image capture by backlight and telecentric optics.
• Figlb magnification of part of fig. relating to the projection of the image of the particle on an image pickup device with a critical diameter of the inscribed circle.
• Fig 2 diagram of the embodiment of the apparatus according to the invention
• Fig 3 Diagram of the flow adjustment system between the output of the sampler and the conveyor belt.
• Fig 4 Parallelism and synchronization of the two toothed belts, fixing of a glass plate.
• Fig 5 diagram of the conveyor belt guiding system to ensure the horizontality of the plates
• Fig 6 diagram of the alternative device for guiding the particles by means of a rotating platform.
• Fig 7 diagram of the image taken by the camera.
• the particle Q is deposited on a transparent, flat and rigid plate P.
• a light source S sends on the particle Q via a lens L, a light beam generating an image I of the shadow of the particle projected along an axis perpendicular to the transparent plate P, on a pickup sensor d image such as for example a CCD camera.
• the diameter D IN of the largest circle inscribed in the projected surface i corresponds to the critical diameter of passage through a sieve (fig lb)
• the particles are fed through a funnel (1.1) and pass through an adjustment valve (1.2) before falling into a rotary sampler (1.3).
• the sampler consists of a cone with a rectangular opening, the speed of which can be continuously adjusted so as to make the material flow even.
• a flow of particles falls on a vibrator (1.9) whose chute consists of three parts 1.4, 1.6 and 1.10 then on the glass plates fixed on two toothed belts 1.19 bringing the particles into the field focal of an optical system 1.16.
• the terminal 1.10 part is used to allow the particles to be brought in as ready as 1.11 glass plates possible and avoid excessive dispersion of particles. Its height (1.29) is therefore adjustable.
• the set of powders collected by systems 1.15, 1.18 and 1.22 falls by gravity into a recovery tank (1.21).
• An adjustment of the material flow between the sampler outlet and part 1.6 is obtained by means of a conical funnel (1.4) of adjustable height (1.30) (fig.3). As illustrated in Figure 3, the flow can also be controlled by adding walls of variable section in the duct of part 1.6.
• a compressor (1.8) ensures a regular air flow which is guided through a pipe placed under the vibrator (1.7) to the leiu of powder discharge on the plates.
• FIG 4 is shown the conveyor belt consisting of two parallel belts guided by two toothed wheels 1.12.
• a series of threaded brass supports 1.20 are fixed on the lower part of the two belts of the device which transports the particles in the focal field of the optical system.
• the two belts of the conveyor belt are motorized and synchronized.
• Each transparent plate is fixed to the belts of the conveyor belt by preferably nylon screws.
• Figure 5 is shown the guide system 1.14 which is fixed to the frame (not shown) perpendicular (1.17) to the optical axis (1.27). This allows ensure the positioning in the focal plane and guarantees the horizontality of the plates 1.11 when passing through the image taking field of the camera.
• the plates 1.11 are brought by the belts 1.19 on the runners (1.14).
• the distance 1.28 between the camera lens 1.25 and the surface of the plates is adjustable and strictly controlled, focusing is therefore guaranteed.
• a calibration of the optical system can be carried out by means of a reticle glass plate.
• the reticle image is focused by adjusting the height (1.23) of the 1.24 CCD camera.
• the device which brings the particles into the image capture field consists of a circular platform such as for example a steel disc on which the plates, preferably made of glass, are fixed.
• the steel disc is welded to a motorized axle.
• the speed of rotation is adjustable, the combination between this speed and the vibration intensity of the vibrating chute makes it possible to optimize the dispersion of the particles on the plate.
• the image taking device for example a CCD camera, is synchronized with the position of the plates.
• An external synchronization signal is generated by a photodiode.
• a detection system sends a pulse to the camera.
• the image is therefore stored in the camera and analyzed in real time by software.
• the software allows by means of a simple thresholding procedure to extract the outline of the shadow of the particle for the analysis of its size or shape.
• the number of images taken depends on the speed of rotation and the number of plates fixed on the disc (for example 8 plates), but an upper limit is also imposed by the speed of calculation of the computer.
• a collecting tank or collector can also be fixed in the lower part of the disc, the particles which fall between the plates are collected in this tank.
• the particles which are analyzed are loaded onto the plates at the outlet A of a vibrating chute as in the first embodiment of the invention.
• the image is taken at C corresponding to the axis of the camera and finally a very flexible brush B cleans the surface of the plates P.
• These latter particles are also collected in the same bin R.
• FIG 7 is described the taking of images by the camera 1.24 1.25 lens assembly.
• the plate 1.11 is fixed by means of rings 1.20 on the transmission belt (not shown).
• the axis 1.27 of the optical system forms an angle 1.17 strictly perpendicular to the plate 1.11 thanks to the guide system 1.14.
• EXAMPLE 1 comparison of the method according to the invention with the sieving method.
• the method according to the invention and hereinafter called ALPAGA was compared with the sieving results obtained with 100gr of BCR-68 sand used by 5 different laboratories and recognized by the European organization BCR -
• the sieving values are the expression of the weight fraction of the particles smaller than the size indicated in microns. For each fraction, the table provides an average Oj and an uncertainty S ⁇ O ⁇ ) on the values obtained by the five laboratories of the BCR. It should be highlighted that the analysis made with
• ALPAGA relates to the equivalent of six grams of sand, against the hundred grams used by BCR laboratories.

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• Chemical & Material Sciences (AREA)
• Dispersion Chemistry (AREA)
• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)
• Investigating Or Analysing Materials By Optical Means (AREA)

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• 2001
  • 2001-07-02 EP EP01202539A patent/EP1273901A1/de not_active Withdrawn
• 2002
  • 2002-06-27 CA CA002451759A patent/CA2451759A1/fr not_active Abandoned
  • 2002-06-27 WO PCT/EP2002/007209 patent/WO2003005000A1/fr not_active Application Discontinuation
  • 2002-06-27 US US10/482,221 patent/US20040151360A1/en not_active Abandoned
  • 2002-06-27 EP EP02754799A patent/EP1405053A1/de not_active Withdrawn

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