EP1243350B1 - Device and method for the automatic inspection of goods passing by in a mainly single-layered flux - Google Patents

Abstract

A device and a method for automatically inspecting objects traveling in an essentially monolayer flow. The device comprises a detection unit through which the object flow passes, consisting of the following: elements for applying electromagnetic radiation in the direction of the plane of conveyance of the objects and defining a lighting plane, the intersection of the lighting plane and plane of conveyance defining a detection line; a receiver device periodically scanning each point on the detection line and receiving radiation reflected by an elementary measuring zone, the plane defined by the detection line and the optical input center being known as the scanning plane; elements for transmitting the reflected radiation. The radiation emitted is concentrated in the region of the lighting plane and the lighting plane and the scanning plane merge, whereupon the joint plane is inclined in relation to the normal of the plane of conveyance.

Description

The present invention relates to the characterization, and optionally the sorting, of objects, in particular of recyclable household packaging, according to their constituent materials and / or according to their color, the combination of a constituent material or substance and of a color being called in the following a category.

It relates to a device and a method of automatic inspection of moving objects with characterization and discrimination according to their chemical composition.

The machine according to the invention is particularly, but not exclusively, suitable for the inspection and, where appropriate, the sorting, at a high rate, of different recyclable plastic packaging, in particular bottles made of PET, HDPE, PVC, PP and PS, as well as paper / cardboard packaging, composite (beverage brick) or metal packaging.

However, this machine may also be used for the inspection and discrimination of all other articles or articles containing organic chemical compounds and scrolling with a substantially monolayer planar presentation, such as for example fruit (discrimination by sugar level) , and the discrimination can be performed on the basis of a majority or minority chemical compound, or a plurality of chemical compounds.

In addition, said discrimination can result in a separation of the object stream by categorical sorting or simply in counting and characterizing said stream.

There are already many machines and many processes of the aforementioned type, especially for sorting the packages according to their constituent material.

A method and a machine for automatically sorting objects according to their composition are known from US-A-5,791,497.

However, these known machines all have fairly serious disadvantages and significant limitations.

As a result, the sorting of household packaging has remained largely manual to date, particularly in European countries where sorting by material is requested by the recycling authorities, but also in other countries.

Significant automation of sorting has occurred recently in Germany, but in a very particular context, at least for plastics. The sorting criteria do not concern the material, but the shape (films, hollow bodies, or miscellaneous mixed plastics). These existing machines thus sort a category "mixed plastics" in relation to paper / cardboard, after aeraulic pre-sorting of the films, and a manual pre-sorting of the hollow bodies. There are also machines for sorting composite packaging, or metal packaging.

• individualisation complète avec un seul objet par réceptacle, sans saisie d'objet ;
• flux filaire, les objets étant alignés les uns derrière les autres ;
• flux planaire, les objets étant étalés en vrac sur un tapis nettement plus large que leur plus grande dimension, et répartis sur une seule couche.

Existing machines have great differences in terms of efficiency depending on the type of mechanical preparation of the flow of objects to be sorted. We can distinguish three main solutions:

• complete individualization with a single object per receptacle, without object entry;
• wired flow, the objects being aligned one behind the other;
• planar flow, the objects being spread loose on a carpet much wider than their largest dimension, and spread over a single layer.

• L'individualisation complète n'a jamais fait ses preuves industriellement. Les prototypes mis au point avec ce mode de présentation ont tous cessé de fonctionner depuis.
• Le flux filaire existait déjà dans les machines de sur-tri industrie dans lesquelles le flux principal était homogène, et le sur-tri consistait à retirer un faible pourcentage d'objets indésirables. Appliqués à un flux hétérogène d'emballages, des systèmes filaires ont fonctionné sur des flux particulièrement propres. Cependant, ces machines sont limitées en débit et nécessitent en amont de la machine la présence d'opérateurs manuels pour retirer les objets susceptibles de perturber le fonctionnement, notamment les grandes feuilles plastiques et les gros contenants. Ils ne constituent donc pas une solution satisfaisante d'automatisation du tri, et ont eu peu de succès.
• Au contraire, les flux planaires ont fait leurs preuves, puisqu'il s'agit exactement de la présentation des objets que l'on rencontre en tri manuel. On sait donc la réaliser simplement dans un contexte de déchets ménagers, et les machines utilisant ce type de flux sont adaptées aux conditions de tri en vrac et connaissant un succès nettement supérieur aux deux autres types précités.

Only the last solution proved to be suitable, from the point of view of efficiency and productivity, to products as heterogeneous as waste, especially household waste. Indeed :

• Complete individualization has never been industrially proven. Prototypes developed with this presentation have all ceased to work since then.
• Wired flow already existed in over-sorting machines in which the main flow was homogeneous, and over-sorting consisted of removing a small percentage of unwanted objects. Applied to a heterogeneous flow of packaging, wired systems have operated on particularly clean flows. However, these machines are limited in flow and require upstream of the machine the presence of manual operators to remove objects likely to disrupt the operation, including large plastic sheets and large containers. They are therefore not a satisfactory solution for automation of sorting, and have had little success.
• On the contrary, the planar flows have proved their worth, since it is exactly the presentation of the objects that we encounter in manual sorting. It is therefore known to carry it out simply in the context of household waste, and the machines using this type of flow are adapted to the sorting conditions in bulk and having a much greater success than the two other types mentioned above.

In what follows, it will therefore be discussed that the planar flow sort, which leads to the most efficient machines currently.

EP-A-0 706 838, in the name of the applicant, discloses a machine and a sorting method adapted to planar flow objects. This machine uses at least one artificial vision system to locate the objects, as well as to recognize their shape and their color, a robotic arm for grasping and handling objects, and at least one complementary sensor for recognizing their constituent material. This complementary sensor is advantageously an infrared spectrometer.

This system has the advantage of being multimaterial in principle, since the main packages are sorted by material, and / or by color, and they are distributed in a plurality of appropriate containers. One machine can sort up to eight different categories. Moreover, the individual gripping of the objects guarantees an excellent quality of sorting, typically a defect for 1000 sorted objects.

However, the sorting rate of this system is limited by the individual gripping of the sorted objects and does not exceed 60 to 100 kg / h per sorting module. The only way to increase this rate is to cascade several identical sorting modules, which increases the overall size of the machine, as well as its cost price.

US-A-5,260,576 discloses a planar sorting machine emitting over the flow of electromagnetic radiation, received by transmission below the flow of objects. The intensity of these radiations makes it possible to distinguish the materials according to their relative opacity in transmission. Thus, when the radiation is X-rays, this document mentions a satisfactory separation of PVC, which contains an X-ray opaque chlorine atom, compared with other plastics, which do not contain them, in particular PET. Depending on the result, a row of nozzles ejects or not down one of the object classes.

However, this detection principle is too summary for complex cases: all the objects have a certain opacity, and it is well understood that multiple thicknesses of a low opacity material (for example PET - polyethylene terephthalate) can not be distinguished from a single thickness of a different material more opaque (for example PVC - polyvinyl chloride). We risk then to eject suddenly and by mistake all these little opaque objects. Moreover, this system can not distinguish

that PVC of other plastics: it is unable to identify PET of HDPE (high density polyethylene), or PAN (polyacrylonitrile). Existing machines in accordance with this document have limited efficiencies and low yields (desired object proportions among ejected objects): from 10 to 30%. Finally, a significant drawback of the transmission assembly is that at least one of the two elements, the sensor or the transmitter, must be under the flow. There is then a risk of staining or recurrent blockage of the lower element, requiring repeated interventions at relatively short intervals.

EP-A-0 776 257 discloses a high throughput planar sorting machine, capable of recognizing one of several materials. The material to be recognized is chosen at the time of construction of the machine by a suitable, fixed calibration.

In this machine, a near-infrared light is emitted from above and the sensor is also placed above it, so that it analyzes the light backscattered vertically by the objects.

The reception is done by means of a semicircular planar or concave mirror extending over the entire width of the carpet, then a polygonal rotating mirror. There is thus cyclical scanning of the measuring point over the entire width of the carpet.

The light received from the measurement point is then divided by a montage of semi-reflective mirrors in several streams. Each flow passes through an interference filter centered on a specific wavelength, and then leads to a detector. Each detector therefore measures the proportion of the light received contained in the bandwidth of the filter. The analysis of the relative intensities measured by the various detectors makes it possible to decide whether or not the material present at the measuring point is the one one is looking for. The number of filters mentioned in this document is between 3 and 6.

The presence of such a large mirror constitutes a fragile point of the overall structure, lengthens the distance detection-ejection, increases the total size of the detection station and is likely to cause distortions and to introduce inhomogeneities in the luminous flux recovered for analysis, resulting in detection errors.

• l'algorithme de détection doit être assez simple (donc peu d'opérations et traitement grossier) pour être effectué en temps réel ;
• l'électronique de réception doit être très rapide ;
• la quantité de lumière reçue doit être suffisante dans un temps très bref.

Moreover, in such an architecture, the major issue is the speed of detection: there are 25 to 50 measurement zones per line, and it is necessary to analyze 100 to 150 lines per second taking into account the speed of detection. Flow circulation. The order of magnitude is therefore 5000 measurements / s. Such a speed imposes significant constraints

• the detection algorithm must be fairly simple (so few operations and rough processing) to be performed in real time;
• the receiving electronics must be very fast;
• the amount of light received must be sufficient in a very short time.

However, the detection algorithm must perform a two-dimensional reconstruction of the objects to be sorted before proceeding with their ejection, which assumes a relatively large distance between the detection zone and the ejection zone, increasing the risks of erroneous ejection of the makes a movement of objects between detection and ejection.

• une reconnaissance multimatériaux imposerait d'utiliser non pas 3 à 6 plages de longueurs d'onde (ou PLO), mais au moins 8 à 16 ;
• de plus, les largeurs des PLO, relativement importantes dans l'exemple cité (32 à 114 nm), devraient être réduites dans une gamme de 5 à 20 nm, puisqu'un plus grand nombre de PLO doit être distingué dans la même largeur spectrale.

The aforementioned problem of the amount of light is critical, and explains why the machine according to this document can only recognize a predefined material:

• multimaterial recognition would require not 3 to 6 wavelength ranges (or PLOs), but at least 8 to 16;
• in addition, the widths of the PLOs, which are relatively large in the example cited (32 to 114 nm), should be reduced in a range of 5 to 20 nm, since a greater number of PLOs must be distinguished in the same spectral width. .

The two effects are cumulative: the largest number of PLOs would divide approximately by 3 the quantity of light received by each filter; the reduced width of each PLO means that each filter would pass a fraction about 5 times lower of the received light. To maintain the same signal level, the lighting power required for the machine would therefore be from 1 to 3 x 5 = 15 kW. Such power would not be realistic (price, energy expenditure, heating).

The document WO 99/26734 presents a high-speed planar sorting machine, with an architecture quite similar to the preceding document, but announces multimaterial recognition.

To achieve this, this document addresses the problem of the quantity of light differently: it proposes an upstream vision system on the infra-red detection conveyor, a system quite comparable to that mentioned in document EP-A-0 706. 838 cited above. This system makes it possible to locate each object present, and allows, at the level of the infrared detection, to control by a set of mirrors enslaved by position a single measuring point that follows the scrolling object. The available analysis time becomes relatively long, of the order of 3 to 10 ms, since only one point per object is analyzed. The implementation, although unspecified, can then use a known technology compatible with this analysis time. For example, a spectrometer with a strip of photodetectors (typically 256 elements, each corresponding to one wavelength), with a resolution of 4 to 6 nm per detector, can be used.

• elle nécessite un matériel supplémentaire, à savoir un système de vision ;
• elle impose le choix par vision du point de mesure spectrométrique sur l'objet, ce qui peut être délicat en présence d'étiquettes ou de salissures ;
• elle suppose l'immobilité de l'objet sur le tapis : les deux détections s'effectuant sur des zones d'environ 1 m x 1m, l'objet se déplace de 1 m au moins entre sa détection par vision et sa détection par spectrométrie, puis de 0,5 m en moyenne entre sa détection par spectrométrie et son éjection finale. Or, l'immobilité n'est pas du tout assurée lorsque le convoyeur avance à 2,5 m/s, surtout lorsque les objets sont des bouteilles susceptibles de rouler.

However, this solution also has several disadvantages:

• it requires additional equipment, namely a vision system;
• it imposes the choice by vision of the spectrometric measurement point on the object, which can be difficult in the presence of labels or dirt;
• it supposes the immobility of the object on the carpet: the two detections being carried out on zones of approximately 1 mx 1m, the object moves of 1 m at least between its detection by vision and its detection by spectrometry, then 0.5 m on average between its detection by spectrometry and its final ejection. However, immobility is not ensured at all when the conveyor advances to 2.5 m / s, especially when the objects are cylinders likely to roll.

The machine described in this document is certainly more flexible, but more expensive and significantly less effective than the previous one.

Finally, DE-A-1 96 09 916 discloses a miniaturized spectrometer for a planar plastic sorting machine, operating with a diffraction grating for spreading the infrared spectrum on an output band, and a small number of sensors corresponding to wavelengths irregularly distributed in this output band. It is stated in this document that one can be satisfied with ten well-chosen sensors, instead of the 256 sensors of a conventional photodiode array. However, each of these ten sensors has a surface equivalent to each sensor of a bar, typically a rectangle of 30 x 250 microns ² . Such a surface harvests little light and limits the rate of analysis to 200 measurements / second. Such a spectrometer can not therefore analyze all the points of a fast conveyor with the speeds and resolutions mentioned above.

This last document therefore proposes to analyze a planar flow to achieve a line of parallel identical micro-spectrometers. According to the inventor, the cost of a spectrometer would be minimized by microsystem fabrication techniques, but the necessary resolution requires 25 to 50 spectrometers on the line to cover the width of the conveyor belt: the total cost, as well as the maintenance constraints, are then very high. Moreover, few details are provided in this document on the realization of such a machine and no machine of this type seems to be in operation now.

In addition to the drawbacks and limitations specific to each of the devices and methods mentioned above, it is also worth mentioning a major disadvantage, common to all these devices and processes, namely their inability to reliably process objects having an significant height, for example of the order of 10 to 30 cm, either because of insufficient radiation intensity applied at this distance from the conveying plane Pc of the moving objects, or because of a maladaptation of the recovery of radiation to analyze, or for the two reasons mentioned above.

Thus, the main object of the present invention is to provide a machine and a method of inspection, and if necessary sorting, operating at high speed and for substantially single-layered object streams, this machine and this process being capable of to reliably discriminate objects with significant heights, while at the same time demonstrating construction and implementation that remain simple and economical.

In addition, the invention will have to dispense with an independent vision system to locate the objects, minimize the number of sensors required, maintain good reliability, especially in case of sorting, when the objects move relative to the support that the transports and has an optimized efficiency of exploitation of the emitted radiation.

• des moyens d'application de rayonnements électromagnétiques en direction du plan de convoyage, émettant lesdits rayonnements de manière à définir un plan d'éclairage, l'intersection dudit plan d'éclairage et dudit plan de convoyage définissant une ligne de détection s'étendant transversalement au sens de défilement des objets pour la largeur du flux convoyé,
• un dispositif de réception permettant de balayer périodiquement tout point de ladite ligne de détection, et recevant à tout instant les rayonnements réfléchis par une zone de mesure élémentaire située au voisinage du point balayé à cet instant, le plan défini par ladite ligne de détection et le centre optique d'entrée dudit dispositif étant appelé plan de balayage,
• des moyens de transmission à au moins un dispositif d'analyse desdits rayonnements réfléchis au niveau de la zone de mesure élémentaire balayante,

machine caractérisée en ce que les rayonnements émis sont concentrés au voisinage du plan d'éclairage et en ce que ledit plan d'éclairage et le plan de balayage sont confondus, ce plan commun étant incliné par rapport à la perpendiculaire au plan de convoyage.For this purpose, it relates to a machine for automatically inspecting objects scrolling in a substantially monolayer manner on a conveying plane of a conveyor, for discriminating these objects according to their chemical composition, this machine comprising at least one filling station. detection through or under which the flow of objects, this detection station comprising in particular:

• means for applying electromagnetic radiation in the direction of the conveying plane, emitting said radiation so as to define a lighting plane, the intersection of said lighting plane and said conveying plane defining a transversely extending detection line in the sense of scrolling objects for the width of the conveyed flow,
• a reception device for periodically scanning any point of said detection line, and receiving at any time the radiation reflected by an elementary measurement zone located in the vicinity of the scanned point at this instant, the plane defined by said detection line and the optical input center of said device being called scanning plane,
• means for transmitting to at least one device for analyzing said reflected radiation at the level of the scanning elementary measuring zone,

characterized in that the emitted radiation is concentrated in the vicinity of the lighting plane and in that said lighting plane and the scanning plane coincide, this common plane being inclined with respect to the perpendicular to the conveying plane.

These provisions make it possible to obtain a maximum radiation application in the zone exploited for the acquisition, as well as a systematic correspondence of the illuminated zone and the analyzed zone, whatever the height of the objects in a defined height range. by the dimensions of the machine and the sensitivity of the means of acquisition and analysis.

Thus, the superposition of the lighting and scanning (detection) planes gives a good depth of field and their inclination with respect to the plane of the objects analyzed makes it possible to effectively eliminate the parasitic light that is the specular reflection.

According to a preferred embodiment of the invention, the receiving device comprises a movable reflecting member carrying the optical input center, directly receiving the radiation reflected at the level of the sweeping elementary measuring zone and having dimensions of substantially the same size. order of magnitude that the dimensions of said elementary measurement zone which it ensures the displacement, preferably slightly higher.

Advantageously, the application means consist of broad-spectrum lighting means, the applied radiation consisting of a mixture of electromagnetic radiation of the visible range and the infrared range, and said lighting means comprise members concentrating the radiation transmitted, at the level of the conveying plane, on a transverse detection band periodically scanned by the elementary measurement zone and whose longitudinal median axis corresponds to the detection line.

The use of broad spectrum lighting, for example of the halogen type and wavelengths between 1000 and 2000 nm (for each emission point), allows the chemical analysis of the objects arranged on the conveyor .

In order to homogenize the illumination of the detection zone, the means for applying radiation are preferably constituted by two application units spaced apart and arranged in a transverse alignment with respect to the direction or direction of movement of the objects, each unit comprising an elongated emission member associated with a shaped member shaped reflector elliptical section member.

According to one characteristic of the invention, each elongate transmission member is substantially positioned at the focal point close to the elliptical reflector associated therewith, the means for applying radiation being positioned and the reflectors being shaped and dimensioned in such a way that the second remote focus is located at a distance from the conveying plane substantially corresponding to the average height of the objects to be sorted.

It is thus possible to focus this lighting over a wide range of depths (typically about 200 mm).

In order to increase, if necessary, even more the light intensity at the level of the detection zone, in particular near its extreme parts, it can be provided that the reflection walls of the radiation emitted by the application means are arranged along the lateral edges of the conveyor (for example conveyor belts or belts), in particular at the ends of the detection strip, extending, horizontally and vertically, substantially up to the height of said radiation application means ( s).

According to a preferred embodiment of the invention, the receiving device is in the form of a reception head located at a distance above the conveying plane and carrying, on the one hand, a movable reflecting member under the shape of a plane mirror (whose geometric center is advantageously substantially coincident with the input optical center), disposed substantially centrally with respect to the conveying plane of the conveyor and oscillating by pivoting with a sufficient amplitude so that the zone mobile elementary measurement unit can explore the entire detection band during a half-oscillation and, on the other hand, a focusing means, for example in the form of a lens, of the fraction of radiation (s) reflected by an elementary part of the detection band and transmitted by the oscillating mirror towards said means, said head also carrying the end having the opening of the e means for transmitting said fraction of radiation (s), after focusing by the means, towards at least one spectrum analysis device.

The movable elementary measuring zone, which progressively sweeps the entire surface of the traveling conveying support, is defined, in combination, by the characteristics of the input opening of the transmission means and the characteristics of the transmission means. focusing, and by their relative arrangement, the focusing means and the consecutive transmission means being located outside the exploration field of the oscillating mirror (defined by its optical or geometric center), located in the scanning plane, the mirror alignment axis / focusing means / input aperture being located in said plane containing said field.

The fraction of detection or measurement surface reflected by the oscillating mirror will advantageously be at least slightly larger in area than the elementary measurement zone, centered with respect to the latter and of the same shape or not.

In order to achieve a compact structure, it can be advantageously provided that the oscillating plane mirror forming the movable reflecting member is situated between the two units forming the radiation application means and in a relative arrangement such that said units do not interfere with the field of exploration of said mirror.

As indicated above, the scanning plane containing said exploration field and the plane containing the reflector foci elliptic are merged and this coincidence of the illuminated and analyzed areas allows an optimal consideration of objects with significant heights.

The mirror will preferably be located at a greater distance from the conveying plane than the units of the application means, in the form of halogen lamps for example. However, it can also be arranged at the same height or even closer to this plane than said units, without the effectiveness of the detection station being influenced.

According to a characteristic of the invention, the transmission means preferably consist of a bundle of optical fibers 10 "all or a majority of which is connected to an analysis device that decomposes the radiation reflected in its different spectral components and determines the intensities some of said components having wavelengths characteristic of the materials of the objects to be sorted, and a minority of which may be advantageously connected to an analysis device detecting the respective intensities of the three fundamental colors, said optical fibers having at the level of the entrance opening a square or rectangular arrangement in section.

According to another advantageous characteristic of the invention, a first analysis device is constituted, on the one hand, by a diffraction grating spectrometer decomposing the multispectral light flux received from the elementary measurement zone into its constituent spectral components, particularly in the infrared field, on the other hand, by means of recovery and transmission of elementary luminous flux corresponding to different irregularly spaced spectral ranges characterizing the substances and chemical compounds of the objects to be discriminated, for example in the form of separate optical fiber bundles, and finally by photoelectric conversion means providing an analog signal for each of said elementary luminous fluxes.

The multispectral luminous flux from the elementary measurement zone is introduced into the spectrometer at an entrance slit and the elementary luminous fluxes are recovered at exit slits having a shape and dimensions identical to those of the slit input and positioned according to the dispersion factor and the spectral ranges to be recovered, the output end portions of the fibers of the majority component of the fiber bundle forming the transmission means and the input end portions of the fiber optics recovery and transmission means having identical linear arrangements and being respectively mounted in the entrance slot and the exit slots.

In order to facilitate the handling and installation of the recovery and transmission means, without the risk of damaging them, the input end portions of the optical fibers of the beams forming the recovery and transmission means are mounted in thin wafers provided with adapted receiving recesses, preferably associated with retaining and blocking platelets, so as to form mounting and positioning supports for said optical fibers in the body of the spectrometer.

Preferably, the body of the spectrometer comprises a rigid structure for receiving and holding with locking said supports, allowing their implementation by sliding and their installation by stacking, with possibly interleaving of adjusted shims, so as to position said supports at the locations corresponding to impact zones of elementary luminous flux to be taken up.

Such an arrangement allows a fast, easy and accurate adaptation of the inspection machine to detect different groups of materials, characterized by groups of different specific wavelength ranges, depending on the type of objects and the selectivity to operate.

The first spectral analysis device therefore consists mainly of a means for distributing the light without significant losses according to its constituent wavelengths, as well as a small number of detectors (10 to 20) in the form of means. unit-specific photoelectric conversion circuit, each of these detectors being specific to a wavelength range (PLO), these PLOs being suitably chosen for a robust and simultaneous identification of several chemical substances or compounds, corresponding, for example, to several materials.

In addition, a second analysis device carrying out the color recognition of the objects is associated with the preceding device by taking a small part of the light flux of the fiber bundle to convey it to three sensors each sensitive to one of the fundamental colors, c Red, Green, or Blue.

To coordinate and control the various devices, organs and components of the machine, the latter also comprises a unit for processing and operating management of the detection station, such as a computer controlling in particular the movement of the movable reflecting member and possibly of the conveyor, sequencing the acquisition of the reflected radiation at the mobile elementary measurement zone and processing and evaluating the signals delivered by the analysis devices, for example by comparison with programmed data, for the purpose of determining the composition the chemical object of each of the objects inspected or the presence of a chemical substance in said objects, while correlating the results of said determination with a determination of the spatial location of said objects.

According to a particularly preferred embodiment of the invention, the detection strip is in the form of an elongated rectangular surface of small width extending perpendicularly to the median axis and transversely over the entire width of the conveying plane. of the conveyor, for example in the form of a belt or belt whose upper surface is merged with said conveying plane.

Thus, in the context of an object sorting application and for a conveyor in the form of a strip moving at about 2.5 m / s, the detection-discrimination distance can be limited to about 100 mm, which minimizes the probability that an unstabilized object on the carpet will move before it is discriminated, for example by evacuation.

The invention also relates to a machine for automatic sorting of objects according to their chemical composition, these objects moving in a substantially monolayer manner on a conveyor, this sorting machine comprising an upstream detection station functionally coupled to a downstream station for active separation of said objects. according to the results of measurements and / or analyzes carried out by said detection station, characterized in that the detection station is a detection station as described above.

Advantageously, the detection station, or its processing and operation management unit, delivers actuation signals to a control module of the ejection means, in transverse alignment, of the active separation station according to the results of said analyzes. , a burst of actuating signals being emitted after each complete exploration of a transverse detection band by the moving elementary measurement zone.

Preferably, and in order to avoid as much as possible the sorting errors due to a displacement of the objects with respect to the conveyor between the detection and the ejection, the detection line is located in the immediate vicinity (for example less than 30 cm ) ejection means, for example by lifting, in the form of a row of nozzles delivering jets of gas, preferably air.

• faire passer le flux d'objets à inspecter à travers ou sous au moins un poste de détection,
• à émettre des rayonnements électromagnétiques vers le plan de convoyage par l'intermédiaire de moyens d'application correspondant, de manière à définir un plan d'éclairage, l'intersection dudit plan d'éclairage et dudit plan de convoyage définissent une ligne de détection s'étendant transversalement au sens de défilement des objets,
• à balayer périodiquement tout point de ladite ligne de détection par l'intermédiaire d'un dispositif de réception recevant à tout instant les rayonnements réfléchis par une zone de mesure élémentaire située au voisinage du point balayé à cet instant, le plan défini par ladite ligne de détection et le centre optique d'entrée dudit dispositif étant appelé plan de balayage,
• à transmettre lesdits rayonnements réfléchis au niveau de la zone de mesure élémentaire balayante à au moins un dispositif d'analyse par l'intermédiaire de moyens de transmission adaptés,

procédé caractérisé en ce que les rayonnements émis sont concentrés au voisinage du plan d'éclairage et en ce que ledit plan d'éclairage et le plan de balayage sont confondus, ce plan commun étant incliné par rapport à la perpendiculaire au plan de convoyage.The present invention also relates to a method of automatically inspecting objects moving substantially monolayer on a conveying plane or surface of a conveyor, said method for discriminating these objects according to their chemical composition, and consisting of:

• passing the flow of objects to be inspected through or under at least one detection station,
• to emit electromagnetic radiation towards the conveying plane by means of corresponding application means, so as to define a lighting plane, the intersection of said lighting plane and said conveying plane define a detection line s extending transversely to the direction of movement of objects,
• periodically scanning any point of said detection line by means of a receiving device receiving at any time the radiation reflected by an elementary measurement zone situated in the vicinity of the point scanned at this instant, the plane defined by said line of detection and the optical input center of said device being called a scanning plane,
• transmitting said reflected radiation at the scanning elementary measuring zone to at least one analyzing device via suitable transmission means,

characterized in that the emitted radiation is concentrated in the vicinity of the lighting plane and in that said lighting plane and the scanning plane coincide, this common plane being inclined relative to the perpendicular to the conveying plane.

According to an advantageous characteristic of the invention, said method consists in particular in concentrating the radiations, preferably of the visible and infrared range, at the level of the conveying plane on a periodically scanned transversal detection band. by the elementary measuring zone and whose longitudinal median axis corresponds to the detection line, so as to obtain a high radiation intensity and substantially homogeneous over the entire surface of said detection strip.

More specifically, said method may consist in sequentially scanning the detection band with the moving elementary measurement zone by pivoting oscillation of a plane mirror forming the reflecting member, in focusing the luminous flux originating from the elementary measurement zone on the opening input of the transmission means in the form of a bundle of optical fibers, to bring the majority of the multispectral luminous flux captured to the input slot of a spectrometer forming part of a first analysis means, to decompose this luminous flux in its various elementary spectral components, to recover the luminous flux of some of these components corresponding to specific narrow wavelength ranges at output slots and to transmit them via means adapted to means photoelectric conversion circuit for providing first measurement signals, to bring, if necessary, simultaneously a a small part of the multispectral light flux picked up to a second analysis means determining the respective intensities of the three fundamental colors and providing second measurement signals, to process said first and possible second measurement signals, at a processing unit and computer management system including controlling the movement of the movable reflective member, sequencing the acquisition of the reflected radiation at the mobile elementary measurement zone and processing and evaluating the signals delivered by the analysis devices, by comparison with programmed data , for the purpose of determining the chemical composition of each of the objects inspected or the presence of a chemical substance in those articles.

When the inspection method is implemented in relation to a sorting machine as described above, it may further consist in having the processing and management unit issue, depending on the results of the signal processing. measuring, actuating signals to an ejection means control module of a separation station located downstream of the detection station with respect to the flow of objects, and, finally, to eject or not to eject each of the different objects scrolling on the support plane conveying of the conveyor according to the actuation signals delivered.

According to a further preferred feature of the invention, a burst of actuating signals is emitted after completion of each scan of the detection band and processing of the corresponding measurement signals, if necessary taking into account the measurement signals of the detector. previous scan.

• la figure 1A est une représentation schématique d'une machine d'inspection automatique selon l'invention ;
• la figure 1B est une représentation schématique partielle d'une machine automatique de tri selon l'invention, équipée notamment d'un poste de détection amont et d'un poste de séparation aval ;
• la figure 2 est une vue schématique en élévation latérale montrant l'inclinaison des moyens d'éclairage et du moyen réfléchissant de la tête de réception faisant partie du poste de détection ;
• la figure 3 est une vue partielle par transparence, selon une direction opposée à la direction de défilement du moyen de convoyage d'une partie des machines représentées sur les figures 1;
• la figure 4A représente schématiquement les organes fonctionnels de la tête de réception faisant partie de la machine selon l'invention, ainsi que l'amplitude des oscillations de l'organe réfléchissant et le balayage résultant au niveau de la zone de détection ;
• les figures 4B à 4D représentent trois positions de la zone de mesure élémentaire mobile au cours d'un balayage de la zone de détection ;
• les figures 5 et 6 sont des représentations partiellement schématiques et partiellement constructives des moyens de récupération et de transmission et des dispositifs d'analyse ;
• la figure 7 est une vue partielle en élévation frontale des portions d'extrémité d'entrée des moyens de récupération et de transmission montées dans les fentes de sortie du spectromètre faisant partie du premier dispositif d'analyse, et,
• la figure 8 est une vue de détail d'un montage particulier de deux portions d'extrémité d'entrée adjacentes des moyens de récupération et de transmission.

The present invention will be better understood thanks to the following description, which relates to a preferred embodiment, given by way of non-limiting example, and explained with reference to the attached schematic drawings, in which:

• Figure 1A is a schematic representation of an automatic inspection machine according to the invention;
• FIG. 1B is a partial schematic representation of an automatic sorting machine according to the invention, equipped in particular with an upstream detection station and a downstream separation station;
• Figure 2 is a schematic side elevational view showing the inclination of the illuminating means and the reflecting means of the receiving head forming part of the detection station;
• Figure 3 is a partial view in transparency, in a direction opposite to the running direction of the conveying means of a portion of the machines shown in Figures 1;
• FIG. 4A diagrammatically represents the functional members of the reception head forming part of the machine according to the invention, as well as the amplitude of the oscillations of the reflecting member and the resultant scanning at the level of the detection zone;
• FIGS. 4B to 4D represent three positions of the mobile elementary measurement zone during a scanning of the detection zone;
• Figures 5 and 6 are partially schematic and partially constructive representations of recovery and transmission means and analysis devices;
• FIG. 7 is a partial front elevational view of the input end portions of the recovery and transmission means mounted in the output slots of the spectrometer forming part of the first analysis device, and
• Figure 8 is a detail view of a particular mounting of two adjacent input end portions of the recovery and transmission means.

• des moyens 6 d'application de rayonnements électromagnétiques en direction du plan de convoyage Pc du convoyeur 3, émettant lesdits rayonnements de manière à définir un plan d'éclairage Pe, l'intersection dudit plan d'éclairage Pe et dudit plan de convoyage Pc définissant une ligne de détection 7 s'étendant transversalement au sens de défilement des objets 2,
• un dispositif 8 de réception permettant de balayer périodiquement tout point de ladite ligne de détection 7, et recevant à tout instant les rayonnements réfléchis par une zone de mesure élémentaire 12 située au voisinage du point balayé à cet instant, le plan défini par ladite ligne de détection 7 et le centre optique d'entrée 8" dudit dispositif 8 étant appelé plan de balayage Pb,
• des moyens 10 de transmission à au moins un dispositif d'analyse 11, 11' desdits rayonnements réfléchis au niveau de la zone de mesure élémentaire balayante 12.

As shown in the figures of the accompanying drawings, and more particularly in FIGS. 1 to 4, the automatic object inspection machine 2 comprises at least one detection station 4 through or under which the flow of objects 2 passes, this detection station 4 including:

• means 6 for applying electromagnetic radiation in the direction of the conveying plane Pc of the conveyor 3, emitting said radiation so as to define a lighting plane Pe, the intersection of said lighting plane Pe and said conveying plane Pc defining a detection line 7 extending transversely to the direction of movement of the objects 2,
• a reception device 8 for periodically scanning any point of said detection line 7, and receiving at any time the radiation reflected by an elementary measuring zone 12 situated in the vicinity of the point scanned at this instant, the plane defined by said line of detection detection 7 and the optical input center 8 "of said device 8 being called scanning plane Pb,
• means 10 for transmitting to at least one analyzing device 11, 11 'of said reflected radiation at the level of the scanning elementary measuring zone 12.

According to the invention, the emitted radiation is concentrated in the vicinity of the illumination plane Pe and said illumination plane Pe and the scanning plane Pb coincide, this common plane Pe, Pb being inclined with respect to the perpendicular D Pc conveying plan. This last provision makes it possible to dispense with specular reflection.

By transverse, in relation to the detection line 7, is meant an extension over the entire width of the conveying plane Pe defined by the conveyor 3 ce, preferably but not exclusively, in a rectilinear manner and perpendicular to the direction of travel of the objects 2 .

The conveying plane Pc will correspond for a flat conveying support on the surface of the latter and for non-planar supports, such as buckets mounted on chains (for individualized transport, for example). example for fruits), at a median plane characterizing the scrolling of said objects.

It will be understood that the following description corresponds to a practical embodiment, but not limiting, of a sorting machine enclosing an inspection machine according to the invention and explained in connection with Figures 1 to 8 attached.

It will also be understood that the detection station 4 is identical for these two machines, the sorting machine further comprising a separation station 5.

Figure 1 shows the general structure of the automatic sorting machine 1 by chemical composition or material. The objects 2 arrive in rapid scrolling (2 to 3 m / s) on a conveying means or conveyor 3 so that they are substantially spread on a single layer. The surface of the conveyor 3 is dark, and its constituent material (usually matte black rubber) is chosen different from the chemical materials or compounds to be recognized.

These objects 2 pass through a detection region defined at a detection station 4. This region is substantially delimited by broad-spectrum lighting means 6 (visible and infrared), which concentrate via reflectors. 6 'the luminous flux, to strongly illuminate a zone 7' in the form of a narrow band of effective detection, whose width is 25 to 40 mm.

The zone 7 'is analyzed at a high rate by means of an oscillating mirror 8', driven by a computer 23, and which cyclically directs the measurement towards each of the constituent elementary zones 12 'of the zone 7'. A full scan cycle of the zone 7 'takes about 8 ms. Meanwhile, the conveyor 3 has advanced a distance substantially equal to the width of said zone 7 ', so that there is no "hole" of detection: any point of the conveyor 3, or the plane Pc conveyor belt is analyzed.

The light collected by the mirror 8 'is focused by a lens forming a focusing means 9 on the input opening 10' of a bundle 10 of optical fibers 10. The bundle 10 is subdivided into two parts: the first brings the majority of the luminous flux to a spectrometer 14, forming part of a first analysis device 11 and subdividing this part of flux according to its constituent wavelengths in the near-infrared range (NIR). Appropriately selected PLO (Wavelength ranges) is sent to a module containing conversion means 16 in the form of NIR photodiodes of high unit area, and an amplification stage. This module converts the light signals into as many analog electrical signals, which are then analyzed by the computer 23.

The second part of the beam 10 is fed to a second analysis device 11 'corresponding to a color detection module. This module allows to isolate the Red, Green and Blue components by filtering, then convert the light signals into electrical signals and amplify them. After conversion, the output signals are also analyzed by the computer 23.

The latter makes it possible to combine all the preceding information to define categories of objects to be ejected or not, and then controls the separation station 5 and each of the ejection means 5 'in the form of nozzles in a row, by means of a piloting module 24.

The blown objects 2 'end up in a receptacle 25, while the non-blown objects 2 "fall directly before the same receptacle, although this arrangement is not the only solution: the nozzles 5' could as well be placed above the conveyor 3, and then blow objects 2 'to be separated down This second configuration has advantages in certain applications.

A first decisive advantage of the machine 1 is that the reflected light receiving device (mirror assembly 8 'and lens 9) does not extend physically over the entire width of the conveying plane Pc corresponding, for example, to the surface of a carpet of a conveyor 3, but is unique and implanted only in the center of the centerline of the conveyor 3. This avoids inhomogeneities between different reception points which would harm the uniformity of the signal through the detection zone 7 '.

A second decisive advantage of the geometry of the machine 1 is that the detection zone is placed closer to the row of ejection nozzles 5 '. The distance detection-ejection d can be limited, with appropriate computer means, to about 100 mm, which minimizes the probability that an unstabilized object on the carpet moves before ejection. It is limited only by the software processing time, which is very fast since it relates to the information of a single line of measurements or even two contiguous lines only. This distance is significantly lower than that existing in known planar flow machines described above.

Those skilled in the art will note that such a small distance does not allow a two-dimensional analysis of each object before decision: for an elongated object, such as a bottle 300 mm long, the decision to actuate the nozzles 5 'on the before the object must be taken before the back of the same object is completely analyzed. However, this limitation does not significantly disturb detection or ejection.

Turning in particular to Figures 1, 2 and 3 of the accompanying drawings, a more detailed description of the lighting means will now be made.

The aim is to bring maximum light to the detection zone 7 'with the constraint of moving the lamps sufficiently away from the circulating objects 2 to allow these objects to circulate without interference. We aim about 50 cm between lamps and carpets. The amount of light is summarily estimated in electric W / cm ² , with reference to a 3400 K color temperature halogen lamp.

Among the various possible lighting technologies, a set of fixed halogen lamps has been chosen, a solution that is both the simplest and the most widespread. However, the conventional implementation uses industrial spots that disperse a lot of light.

However, the use of such commercial spots, even at low angular aperture, requires a lot of individual lamps and results in a low light density.

• demi-grand axe a = 300 à 400 mm
• excentricités e d'environ 85 à 92 %.

To overcome the drawbacks associated with these known means, the inventors have developed a light based on thin halogen tubes 6 'as transmission members, aligned at the same height above the carpet 3 and associated with elliptical reflectors 6'. Such a reflector 6 'makes it possible, if the halogen tube 6 "is placed in one of its foci F, to perfectly focus the light on the other focal point F. To obtain dimensions that are compatible with the machine 1 in its practical embodiment, ellipse must have the following parameters:

• half-long axis a = 300 to 400 mm
• eccentricities e from about 85 to 92%.

The manufacture of the reflectors 6 'must be very precise for a good operation, but it is easier than that of conventional reflectors to circular symmetry, like parabolic mirrors. Here, there is a developable surface, which can be made by folding.

Preferably, the assembly is carried out in such a way that F 'is placed a few centimeters above the conveyor belt 3, at a height (H) corresponding to the average thickness of the moving objects (H = 25 to 50 mm).

With one embodiment of the lighting means 6 as mentioned above, the inventors have determined that the best intensity distribution is obtained using only two sufficiently long, vacuum-separated reflectors 6 'as shown in FIG. In addition, to prevent light losses at the ends of the belt 3, if necessary vertical reflectors or reflection walls 13 and 13 'are added on these ends. These return the light to the carpet.

This gives a simple implantation, with a small number of lamps, moreover inexpensive, and the whole of the light is concentrated on a narrow band to be analyzed: 800 mm × 40 mm, enclosing the detection zone 7 'and centered on the latter.

With two bodies of 1000 W electric, the average density obtained is 2 x 1000 / (80 X 4) ≈ 6 W / cm ² , about 60 times more than the sun in daylight. Such a concentration is only compatible with a carpet 3 in rapid motion to avoid burning it. Electrical safety devices are provided to automatically cut the lighting in case of stopping said carpet.

Referring now to Figures 1, 2 and 4 of the accompanying drawings, the following will be described in more detail below the receiving and transmitting means 8, 9, 10 of the light reflected at the detection zone 7 '. .

The aim is to analyze about 40 to 80 elementary surfaces inside the zone 7 'by means of an elementary measuring zone 12 mobile. These elementary surfaces 12 'have a rectangular shape, with dimensions of 10 x 20 mm to 20 x 20 mm. In the remainder of this document, such an elementary surface 12 'is called a "pixel", all of said pixels corresponding to the detection zone 7'.

To minimize the number of sensors required, the inventors have chosen a mobile assembly that sequentially scans all the pixels. A single sensor then allows all measurements, provided that the measurement is performed very quickly.

The preferred solution is an oscillating mirror 8 '30 mm in diameter, mounted in a detection head 8 and oscillating with an angular amplitude c between the positions shown in Figure 4A. As a function of the instantaneous angle delta (FIG. 4C), it sends back the light of a pixel 12 'towards the fixed lens 9 which focuses it in a bundle 10 of optical fibers 10 ", the pixel 12' has been represented as punctual for the readability of FIGS.

The number of measurements per second is obtained as a function of the speed of movement of the carpet 3 and the chosen pixel size. Thus, for example, with a pixel of 20 mm x 20 mm, there are 40 measurements per line for a width of 800 mm. With a running speed of 2.5 m / s, there are 125 lines of 20 mm width per second: so we find 125 x 40 = 5000 measurements / second. In addition, for geometric reasons, only half-oscillation can be used. The duration of an individual measurement must therefore be 1 / (5000 x 2) = 10 ^-4 sec = 100 μs.

Given this scan, non-vertical light return angles are accepted. It is necessary to choose a height of the mirror 8 'large enough to limit the angle b of the scanning field C to a value slightly less than 60 °. By experience, the geometric aiming defects remain acceptable for these angles. As any variation of angle α of a rotating mirror results in a variation of 2.α of the position of the reflected beam, the plane mirror can then oscillate on a half angle, ie 30 ° in all.

The lens 9 is disposed as much as possible under the mirror 8 ', without interfering with the scanning field C (angle b). It must not be too low above the conveyor belt 3.

The design of the illumination with a blank space in the center above the carpet 3 is used to coincide the plane of oscillation or scanning Pb of the mirror 8 '(including the exploration field C) with the plane Pe (plane containing the focal points F and F 'and passing through the median axis of the detection zone 7'.) With dimensions and a suitably chosen arrangement, the measurement zone (angle b) does not interfere with the tubes 6 "or the reflectors 6 '.

This design is very advantageous for analyzing objects 2 of significant height (up to 200 mm high), because regardless of the height of the object, the illuminated area and the analyzed area coincide.

Although, if the surface of the object moves away from the point F ', the illumination and the measuring spot are no longer focused, the detection remains reliable despite a decrease in the sharpness of the pixel, because the brightness remains substantially identical . Indeed, the illumination disperses well over a larger area, but at the same time the object approaches the halogen tube and therefore receives a larger direct flow, and the mirror / object distance decreases, which increases the density received on the mirror 8 '.

In designs of known non-coplanar devices, the illumination must be scattered over a large angle to effectively illuminate a tall object, and the available intensity is reduced accordingly.

In order to prevent the specular rays, devoid of information, from being taken into account in the recovered reflected luminous flux, the common plane (lighting plane Pe and scanning plane Pb) of the lighting means 6 and the mirror 8 oscillating is inclined at an angle alpha with respect to the vertical to the conveying plane Pc. It can be seen that there is a gamma angle between the closest specular ray and the axis of the sensor (mirror axis 8 '/ lens 9 / aperture 10'). This gamma angle must be at least 5 °, and preferably greater than 10 ° for good security (see Figure 2 of the accompanying drawings).

Conversely, an excessive alpha inclination would reduce the amount of useful light collected by the sensor. A good compromise seems to be an alpha angle of about 20 °.

The lens 9 serves to limit the size of the pixel 12 'analyzed, even at a great distance from the conveyor belt 3.

It gives on the input opening 10 'of the fiber bundle 10, a sharp image of the pixel 12' analyzed, provided to place the end of the beam corresponding to the opening 10 'a little after the focal length upstream of the lens 9. The magnification, that is to say the ratio between the size of the pixel 12 'and that of the input 10' of the beam 10 is equal to the ratio of the distances to the lens.

Under these conditions, the light flux captured is optimal. Indeed, it can be shown mathematically that it is almost independent of the mirror-conveyor distance, and that it is identical to the flux captured by a fiber bundle of the same surface, placed near the conveyor and under the same illumination, and without any optics.

• les principaux plastiques : PET, PVC, PE, PS, PP, PAN, PEN;
• les plastiques dits « techniques » : ABS, PMMA, PA6, PA6.6, PU, PC ;
• Les briques alimentaires (Tétras), les papiers-cartons, dont on détecte la cellulose ;
• les autres produits, sans signature spectrale : métaux et verre.

The aforementioned machines mono-materials use 3 to 6 PLO suitably chosen. A PLO is defined by the value of a central wavelength, and by a spectral width. For example, PLO centered at 1420 nm and 20 nm wide is the range of all wavelengths between 1410 and 1430 nm. The use of 3 to 6 PLOs is actually enough to distinguish a given product from all the others. Experience shows that it is insufficient to simultaneously recognize the range of materials commonly encountered in waste, namely:

• the main plastics: PET, PVC, PE, PS, PP, PAN, PEN;
• so-called "technical" plastics: ABS, PMMA, PA6, PA6.6, PU, PC;
• Food bricks (grouse), paper-cartons, of which cellulose is detected;
• other products, without spectral signature: metals and glass.

• Filtres interférentiels
• AOTF (Acousto Optic Tunable Filters - filtres acousto-optiques ajustables)
• Réseau de diffraction.

To separate PLOs, several technologies are possible:

• Interferential filters
• Acousto Optic Tunable Filters (AOTF) - Adjustable acousto-optical filters
• Diffraction grating.

The inventors have retained the third solution, because it is proven, without physical movements, and with a very good light output: from 60 to 90% in the spectrum of interest.

The following description is based on Figures 5 and 6 of the accompanying drawings.

In a diffraction grating, light is scattered through the output slot in the manner of a rainbow as a function of wavelengths. The grating is characterized by a dispersion, which is the ratio between the wavelength changes expressed in nm, and the distance on the exit slot, expressed in mm. For a good analysis resolution, the inventors have chosen a dispersion of between 20 nm / mm and 30 nm / mm.

The optical fiber bundle 10 transports the reflected light received from the pixel 12 '(multispectral light flux 14 ") from the square section end carrying the aperture 10', of a shape identical to the pixel, to the entrance slit 17 of the spectrometer 14, where the fibers are re-arranged in a vertical thin slot 17 '.

The image of the input slot 17 for each PLO selected at the network output 14 'is a slot 17' of the same shape and dimensions only in entrance. The various elementary luminous fluxes 14 "'corresponding to the various PLOs are collected by output slots 17', at this level there is provided a network of fiber bundles 15 'forming reception and transmission means 15 and these fibers are rearranged. at the other end in circles 15 ", each of which is fixed in contact with an InGaAs photodiode 16, with an active surface area of approximately 1 mm ² .

Advantageously, the spectral width of the PLOs is fixed, and is approximately 5 nm, which makes it possible to use identical photodiodes. But it is also possible to construct beams 15 of different sections, associated with photodiodes 16 of corresponding surface (for example a spectral width of 10 nm with two rows of contiguous optical fibers, for a photodiode area of about 2 mm ² ). It is thus possible to increase the received luminous flux or to refine the resolution.

Thanks to the assembly described above, the quantity of light is divided only once: if we double the number of output beams, each of them will have as much light as in the original assembly.

It is very advantageous that the construction of the machine 1 according to the invention makes it easy to change the choice of PLOs to optimize the search for new products that will appear on the market in the future.

• les faisceaux de fibres 15 sont munies de férules rectangulaires usinées avec précision, réalisées en deux pièces 18 et 19. Il est ainsi facile de les manipuler sans les briser. Une telle férule est formée d'une première plaquette 18 avec un renfoncement 18' renfermant avec blocage les extrémités des fibres optiques 15' et fermé par une contre-plaquette 19.
• L'espacement minimum des férules définit la résolution du système (figure 8), c'est à dire l'écart minimal entre deux PLO : il est donné par l'encombrement de ces férules. A l'extrême, on peut supprimer la plaque de protection ou contre-plaquette 19 d'une des deux férules, ce qui donne un écart en longueur d'onde de 10 nm (Figure 8).
• Pour choisir un positionnement arbitraire des férules dans la zone de sortie du réseau 14', on utilise un jeu de cales 22, usinées avec une rande précision (environ +/- 0,15 µm de tolérance). Par exemple, une cale de 5000 µm, et une cale de 280 µm, permettent de réaliser un espacement de 5280 µm.
• L'ensemble des férules 18, 19 et des cales 22 est empilé dans un support 20 fixé dans un boîtier rectangulaire de maintien 21, de forme ajustée.

The design retained and shown in Figs 7 and 8 provides great flexibility to modify the chosen PLOs, provided that their number remains fixed. Technological solutions for easy editing are:

• the bundles of fibers 15 are provided with rectangular ferrules machined precisely, made in two pieces 18 and 19. It is thus easy to handle without breaking them. Such a ferrule is formed of a first plate 18 with a recess 18 'lockingly enclosing the ends of the optical fibers 15' and closed by a backplate 19.
• The minimum spacing of the ferrules defines the resolution of the system (FIG. 8), ie the minimum distance between two PLOs: it is given by the size of these ferrules. At the extreme, one can remove the protective plate or backplate 19 of one of the two ferrules, giving a wavelength difference of 10 nm (Figure 8).
• To choose an arbitrary positioning of the ferrules in the output area of the network 14 ', a set of shims 22, machined with a precision (approx. +/- 0.15 μm tolerance). For example, a shim of 5000 microns, and a shim of 280 microns, allow a spacing of 5280 microns.
• All of the ferrules 18, 19 and wedges 22 are stacked in a support 20 fixed in a rectangular holding housing 21, of fitted shape.

PLO rearrangement is then simply to remove ferrules 18, 19 and shims 22 of the holding housing 21, then replace some shims by those of different sizes, and finally put them back in the housing. The operation is easy, fast (one work session), and reversible.

The photodiodes of the conversion means 16 provide an intensity proportional to the number of incident photons on their entire surface for a given time. This current is converted into voltage and amplified before it is delivered to the computer 23.

• un simple filtre RC (Résistance - Capacité), dont la constante de temps est réglée pour être environ la moitié du temps de mesure ;
• un dispositif à transfert de charge (CCD), qui vide à intervalles réguliers une capacité où s'accumulent les charges ;
• un module de sommation calculant une intégrale, implanté en logiciel après conversion numérique.

The amplification may include an integrating element, which makes the final signal level proportional to the exposure time. Several equivalent implementations are possible:

• a simple RC (Resistance - Capacitance) filter, whose time constant is set to be about half the measurement time;
• a charge transfer device (CCD), which empties at regular intervals a capacity where charges accumulate;
• a summation module calculating an integral, implemented in software after digital conversion.

The inventors have preferred the first implementation, which is the simplest and least restrictive for the computer processing system 23.

The active surface of the photodiodes 16 used actually size the entire design of the recovery / transmission / analysis. Indeed, it is useless to make an output beam 15 of the diffraction grating 14 'which is larger than the surface of the associated diode 16: the additional surface would not be exploited. Similarly, the laws of optics dictate that the dimensions of the input slot 17 of the array 14 'are the same as the dimensions of the exit slot 17'. As for the optical fiber bundle 10, it obviously keeps the active surface unchanged, ie about 1 mm ² . Finally, as explained above, the flux received on the input aperture end 10 'of this beam depends only on its surface, and the intensity of illumination at the level of the conveying plane Pc (for example surface of the belt of a conveyor 3), subject to a suitable dimensioning of the optical assembly 8 'and 9.

• la surface éclairée de la photodiode ;
• l'intensité d'éclairement sur le tapis convoyeur ;
• la largeur spectrale de la PLO utilisée ;
• le temps d'exposition de chaque mesure.

The balance of the above is that the final signal level for the material analysis is only proportional to the following variables:

• the illuminated surface of the photodiode;
• the intensity of illumination on the conveyor belt;
• the spectral width of the PLO used;
• the exposure time of each measurement.

Thus, by maximizing the intensity of illumination, keeping narrow PLOs and using sensors (photodiodes) with large illuminated surface, we obtain a much faster analysis system, but just as fine as what we could achieve with a spectrometer with bars.

FIG. 5, in relation with FIGS. 1, illustrates a possible embodiment of the second analysis device 11 '(color analysis).

This second device 11 'could also be realized by means of a diffraction grating.

However, in the visible, the wavelength selectivity need not be very fine. Bandwidths of 60 nm are quite sufficient. Moreover, there is no question of flexibility, since the three fundamental colors are based on the perception of the human eye: the PLO never change. Rather than using a diffraction grating, it is therefore simpler and cheaper to use colored filters to be placed in front of each receiving diode. These are the filters 6R, 6V, 6B indicated, specific respectively of red, green, and blue.

The photodiodes 27 associated with the aforementioned filters are made of silicon and cover the entire visible range: this material is very inexpensive and has a very good detectivity, about 100 times higher than InGaAs in the infrared. Thanks to this high sensitivity, it is unnecessary to bring a fiber bundle in front of the diode: a single fiber diameter 200 microns gives a sufficient signal.

It is therefore sufficient to take three optical fibers in the beam 10 to assign them to the color detection. The end comprising the inlet opening 10 'may thus comprise about twenty fibers, of which sixteen or seventeen are found at the penetrating end in the inlet slot 17 of the spectrometer 14, and three of which penetrate into the device analysis 11 'or color module. Given the amount of visible light available, one can even consider using a single fiber for color and distribute its light on three filters: thus, it leaves a maximum sensitive surface for the part of the beam 10 connected to the spectrometer 14.

After the silicon photodiodes 27, a conventional amplification stage, not shown, makes it possible to bring the analog signals to a level sufficient to acquire them in the computer 23.

Of course, the invention is not limited to the embodiment described and shown in the accompanying drawings. Modifications remain possible, especially from the point of view of the constitution of the various elements or by substitution of technical equivalents, without departing from the scope of the claims.

Claims (25)

1. Machine for the automatic inspection of objects travelling in a substantially single-layered manner on a conveying plane (Pe) of a conveyor, enabling these objects to be distinguished according to their chemical composition, this machine comprising at least one detection station, through or under which the flow of objects passes, this detection station (4) comprising in particular:

   - means (6) for the application of electromagnetic radiation in the direction of the conveying plane, emitting said radiation so as to define a lighting plane, the intersection of said lighting plane and said conveying plane defining a detection line (7) extending transversely to the direction of travel of the objects,
   a receiving device (8) enabling any point of said detection line to be periodically scanned, and receiving at any moment the radiation reflected by an elementary measuring zone located in the vicinity of the point scanned at this moment, the plane defined by said detection line and the optical inlet centre of said device being called the scanning plane (Pb),

   - means (10) for transmitting said radiation reflected in the region of the scanning elementary measuring zone to at least one analysis device (11, 11'),

   the machine being characterised in that the emitted radiation is concentrated in the vicinity of the lighting plane (Pe), and in that said lighting plane (Pe) and the scanning plane (Pb) are combined, this common plane (Pe, Pb) being inclined relative to the perpendicular (D) to the conveying plane (Pc).
2. Machine according to claim 1, characterised in that the receiving device (8) comprises a moving reflecting device (8') carrying the optical inlet centre (8"), directly receiving the radiation reflected in the region of the scanning elementary measuring zone (12), and having dimensions that are substantially the same size as, and preferably slightly larger than, the dimensions of said elementary measuring zone (12), which the device displaces.
3. Machine according to any one of claims 1 and 2, characterised in that the application means (6) consist of broad-spectrum lighting means, the applied radiation consisting of a mixture of electromagnetic radiation in the visible region and of the infrared region, and in that said lighting means (6) comprise devices (6') concentrating the emitted radiation, in the region of the conveying plane (Pc), on a transverse detection strip (7') that is periodically scanned by the elementary measuring zone (12), and the longitudinal median axis of which corresponds to the detection line (7).
4. Machine according to any one of claims 1 to 3, characterised in that the radiation application means (6) consist of two application units that are set apart from each other and disposed in transverse alignment relative to the direction of travel of the objects (2), each unit comprising an elongated emission device (6") associated with a device (6') in the form of a profiled reflector of elliptical section.
5. Machine according to claim 4, characterised in that each elongated emission device (6") is substantially positioned in the region of the focus (F) close to the reflector (6') associated therewith, the radiation application means (6) being positioned and the reflectors (6') being formed and dimensioned in such a way that the second remote focus (F') is located at a distance from the conveying plane (3) corresponding substantially to the average height (H) of the objects (2) to be graded, said foci (F, F') being located in the lighting plane (Pe).
6. Machine according to any one of claims 3 to 5, characterised in that walls (13, 13') for reflecting radiation emitted by the application means (6) are disposed along the lateral edges of the conveyor (3), in particular in the region of the ends of the detection strip (7'), extending, horizontally and vertically, substantially up to the height of said application means (6).
7. Machine according to any one of claims 3 to 6, characterised in that the receiving device (8) is in the form of a receiving head carrying, on the one hand, a moving reflecting device (8') in the form of a plane mirror, disposed substantially centrally relative to the conveying plane (Pc) of the conveyor (3), and oscillating by pivoting to an extent that is sufficient to enable the moving elementary measuring zone (12) to explore all of the detection strip (7') over half an oscillation, and, on the other hand, a means (9) for focusing the fraction of radiation that is reflected by an elementary part of the detection strip (7') and transmitted by the oscillating mirror (8') in the direction of said means (9), said head (8) also carrying the end comprising the inlet opening (10') of the means (10) for transmitting said fraction of radiation, after focusing by the means (9), towards at least one spectrum analysis device (11, 11').
8. Machine according to claim 7, characterised in that the focusing means (9) and successive transmission means (10) are located outside the range (R) of inspection of the oscillating mirror (8') located in the scanning plane (Pb), the axis of alignment of the mirror (8')/focusing means (9)/inlet opening (10') being located in said scanning plane (Pb).
9. Machine according to any one of claims 7 and 8, characterised in that the oscillating plane mirror forming the moving reflecting device (8') is located between the two units forming the radiation application means (6) and in a relative arrangement such that said units do not interfere with the inspection range (R) of said mirror (8').
10. Machine according to any one of claims 1 to 9, characterised in that the transmission means (10) consist of a bundle of optical fibres (10"), all or most of which are connected to an analysis device (11) that breaks the reflected radiation up into its various spectral components and determines the intensities of certain of said components which have wavelengths that are characteristic of the materials of the objects to be graded, said optical fibres (10") having an arrangement which is square or rectangular in section in the region of the inlet opening (10').
11. Machine according to claim 10, characterised in that a minority portion of the optical fibres (10") of the bundle (10) is connected to an analysis device (11') that detects the respective intensities of the three fundamental colours.
12. Machine according to claim 10, characterised in that the analysis device (11) consists, firstly, of a diffraction-grating (14') spectrometer (14) that breaks up the multispectral light flux (14") received from the elementary measuring zone (12) into its various constituent spectral components, in particular in the infrared region, secondly, of means (15) for recovering and transmitting elementary light fluxes (14''') that correspond to various unevenly spaced spectral ranges and that characterise the substances and chemical compounds of the objects (2) to be distinguished, for example in the form of separate bundles of optical fibres, and, lastly, of photoelectric conversion means (16) that issue an analog signal for each of said elementary light fluxes (14''').
13. Machine according to claim 12, characterised in that the multispectral light flux (14") is introduced in the spectrometer (14) in the region of an inlet slit (17), and in that the elementary light fluxes (14''') are recovered in the region of outlet slits (17') that have a shape and dimensions that are identical to those of the inlet slit and are positioned according to the dispersion factor and the spectral ranges to be recovered, the outlet end portions of the fibres (10") of the major component of the fibre bundle forming the transmission means (10), and the inlet end portions of the optical fibres (15') of the recovery and transmission means (15) having identical linear arrangements and being assembled respectively in the inlet slit (17) and the outlet slits (17').
14. Machine according to claim 13, characterised in that the inlet end portions of the optical fibres (15') of the bundles forming the recovery and transmission means (15) are assembled in thin plates (18) provided with suitable receiving recesses (18'), preferably associated with maintenance and locking counter plates (19), so as to form assembly and positioning supports (20) for said optical fibres (15') in the body of the spectrometer (14).
15. Machine according to claim 14, characterised in that the body of the spectrometer (14) comprises a rigid receiving and maintenance structure (21) with locking of said supports (20), allowing placement thereof by sliding and installation thereof by stacking, optionally with suitable wedges (22) inserted so as to position said supports (20) in the sites corresponding to the impact zones of the elementary light fluxes (14''') to be recorded.
16. Machine according to any one of claims 3 to 15, characterised in that it also comprises a unit (23) for processing and managing the functioning of the detection station (4), such as a computer controlling, in particular, the movement of the moving reflecting device (8') and optionally of the conveyor (3), sequencing the acquisition of radiation reflected in the region of the moving elementary measuring zone (12) and processing and evaluating the signals issued by the analysis devices (11, 11'), in comparison, for example, with programmed data, in order to determine the chemical composition of each of the inspected objects (2), or the presence of a chemical substance in said objects (2), if necessary by correlating the results of said determination with a determination of the spatial location of said objects (2).
17. Machine according to claim 16, characterised in that the detection strip (7') is in the form of a thin, elongated rectangular area extending perpendicularly to the median axis and transversely over the entire width of the conveying plane (Pc) of the conveyor (3).
18. Machine for automatic grading of objects according to their chemical composition, these objects travelling in a substantially single-layered manner on a conveyor, this grading machine comprising a machine for inspection with an upstream detection station, functionally coupled to a downstream station for actively separating said objects according to the results of the measurements taken and/or analyses performed by said detection station, characterised in that the machine for inspection is a machine according to any one of claims 1 to 17.
19. Grading machine according to claim 18, characterised in that the detection station (4), or the unit (23) thereof for processing and managing operation, issues actuating signals to a module (24) for controlling the transversely aligned ejection means (5') of the active separating station (5), according to the results of said analyses, a round of actuating signals being emitted after each complete examination of a transverse detection strip (7') by the moving elementary measuring zone (12).
20. Grading machine according to any one of claims 18 and 19, characterised in that the detection line (7) is located in immediate proximity to, for example less than 30 cm from, the means for ejection (5'), for example by lifting, in the form of a row of nozzles issuing jets of gas, preferably of air.
21. Method for the automatic inspection of objects travelling in a substantially single-layered manner on a conveying plane of a conveyor, said method enabling these objects to be distinguished according to their chemical composition, and consisting in:

    - having the flow of objects to be inspected pass through or under at least one detection station,

    - emitting electromagnetic radiation towards the conveying plane via corresponding application means so as to define a lighting plane, the intersection of said lighting plane and said conveying plane defining a detection line extending transversely to the direction of travel of the objects,
    periodically scanning any point of said detection line via a receiving device, receiving at any moment the radiation reflected by an elementary measuring zone located in the vicinity of the point scanned at this moment, the plane defined by said detection line and the optical inlet centre of said device being called the scanning plane,

    - transmitting said radiation reflected in the region of the scanning elementary measuring zone to at least one analysis device via suitable transmission means,

    the method being characterised in that the emitted radiation is concentrated in the vicinity of the lighting plane (Pe), and in that said lighting plane (Pe) and the scanning plane (Pb) are combined, this common plane (Pe, Pb) being inclined relative to the perpendicular (D) to the conveying plane (Pc).
22. Method according to claim 21, characterised in that it consists in concentrating the radiation, preferably of the visible and infrared region, in the region of the conveying plane (Pc) on a transverse detection strip (7') that is periodically scanned by the elementary measuring zone (12), and the longitudinal median axis of which corresponds to the detection line (7), so as to obtain high and substantially homogeneous radiation intensity over the entire area of said detection strip (7').
23. Method according to any one of claims 21 and 22, characterised in that it consists in scanning in sequence the detection strip (7') with the moving elementary measuring zone (12) by pivoting oscillation of a plane mirror forming the reflecting device (8'), in focusing the light flux issuing from the elementary measuring zone (12) on the inlet opening (10') of the transmission means (10) in the form of an optical fibre bundle (10"), in conveying the majority of the multispectral light flux (14") captured towards the inlet slit (17) of a spectrometer (14) forming part of a first analysis means (11), in breaking this light flux (14") up into its various elementary spectral components (14'''), in recovering the light fluxes of certain of these components, corresponding to specific, narrow wavelength ranges, in the region of the outlet slots (17'), and in transmitting them via suitable means (15) to photoelectric conversion means (16), in order to supply first measuring signals, in conveying at the same time, if necessary, a small portion of the multispectral light flux (14") captured towards a second analysis means (11') that determines the respective intensities of the three fundamental colours and supplies second measuring signals, in processing said first, and optionally second, measuring signals in the region of a data processing and management unit (23) that controls, in particular, the movement of the moving reflecting device (8'), sequences the acquisition of radiation reflected in the region of the moving elementary measuring zone (12), and processes and evaluates the signals issued by the analysis devices (11, 11'), in comparison with programmed data, in order to determine the chemical composition of each of the inspected objects (2), or the presence of a chemical substance in said objects (2).
24. Method according to claim 23, characterised in that it consists in having the unit (23) issue actuating signals, according to the results of the processing of the measuring signals, to a module (24) for controlling the ejection means (5') of a separating station (5') located downstream from the detection station (4) relative to the flow of objects (2), and, lastly, in ejecting or not ejecting each of the various objects (2) travelling on the support conveying plane (Pc) of the conveyor (3), according to the actuating signals issued.
25. Method according to claim 24, characterised in that a round of actuating signals is emitted after completion of each scanning of the detection strip (7') and processing of the corresponding measuring signals, if necessary allowing for the measuring signals of the preceding scanning operation.

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