WO2016016584A1

WO2016016584A1 - Method and device for detecting materials that make up a part

Info

Publication number: WO2016016584A1
Application number: PCT/FR2015/052115
Authority: WO
Inventors: François BRYGO; Sébastien MICHEL; Stéphane SENAC
Original assignee: Bertin Technologies
Priority date: 2014-08-01
Filing date: 2015-07-30
Publication date: 2016-02-04
Also published as: FR3024543B1; FR3024543A1

Abstract

The invention relates to a method and device for detecting materials that make up a part (10), wherein the chemical elements that form a surface of the part are measured. According to the invention, the presence of a surface layer on the part is efficiently detected and, when applicable, the surface of the part is cut into in order to repeat the detection at depth beyond the surface layer. The invention also provides a device that is particularly suited to said implementation, which allows in particular the sorting of black polymers, with material identification and flame-retardant detection.

Description

Method and device for detecting materials composing a part

The invention relates to a method and a device for detecting, or analyzing, materials constituting a part. Such an invention allows in particular the sorting for the revalorisation, for example recycling, of various parts whose composition in materials is a priori unknown. The pieces of similar materials can then be grouped, in order subsequently to undergo recycling treatment appropriate to the type of material detected.

As an illustration, the polymeric parts stemming mainly from

End of Life Vehicles (ELV) or Waste Electrical and Electronic Equipment (WEEE), the exact composition of which is unknown and has a determining role in the type of recycling treatment to be applied. In fact, the recycling of polymer parts from WEEE and VHU with a view to their upgrading requires, in general, two analyzes:

the detection and / or classification of the family of the polymer used as a substrate for the part, and

the detection of flame retardants included in certain polymers, the maximum quantity of which is regulated.

Currently, detection for revaluation purposes can only be performed for only part of the polymer parts. Indeed, existing analysis and sorting systems suffer from several constraints:

- systems using infrared technologies, such as the Mistral ™ system, are not suitable for dark or dark matter,

flotation detection systems are inconclusive with regard to the wide range of polymers and additives that can be encountered in a room,

- triboelectricity detection systems are only effective in the case of discrimination between two families of polymers.

In addition, these technologies accept only small parts, and therefore involve preliminary grinding parts. It is then necessary to have a high detection rate in order to make the process profitable.

Other materials detection technologies have been developed especially for quality control or sampling analysis. Thus, FTIR, Raman or spark spectroscopy analysis systems are commercially available.

The first two technologies are essentially adapted to material identification problems, and often not usable for dark or black parts. They do not allow the detection of flame retardants simultaneously, and the measurement time is longer than for other technologies (typically several tens of seconds).

Spark OES spark spectroscopy technology enables the detection of polymer type and flame retardant detection for all types of part colors. This technology however suffers from a regular problem of fouling of its electrodes. It is also sensitive to the surface condition of the part, and the possible presence of a layer of pollution or paint, which in some cases involves too tedious preparation of the surface of the part before the process. This technology is therefore incompatible with an automatic detection process for a large piece flow.

In recent years, Laser-Induced Breakdown Spectroscopy (LIBS) has been studied for the analysis of the composition of materials, including polymers. The general principle, illustrated in Figure 1, is as follows:

1: A laser energy pulse equivalent to a few milli-joules, and whose pulse lasts between the femto-second and a few tens of nanoseconds, is derived from a source of laser radiation and focused, by optical means comprising for example a mirror and a focusing lens, on a compound in solid form, liquid, aerosols or gas, for creating a plasma on a interaction diameter between the laser and the compound measuring between a few tens and hundreds of micrometers.

2: The spectral emission of the plasma is sent to the means of an optical system (for example an optical fiber) to an analysis spectrometer associated with computer data processing means. A typical emission spectrum obtained in LIBS is composed of atomic, ionic and sometimes molecular bands.

Some studies have shown that this method could be used in particular for sorting small polymer parts by differentiating families of polymers. In most of these studies, the emission spectra obtained are analyzed by so-called "chemometric" methods, which generally use line emission intensities such as CN, O, H, C, C ₂ , or their ratio. , to define classes of polymers.

Nevertheless, the implementation of this process generally suffers from a significant variation in performance. The polymers are in fact all made up of the same matrix of carbon and hydrogen with, for some of them, oxygen and nitrogen. The differentiation between these similar matrices is therefore not trivial, and the use of the emission lines of oxygen and nitrogen is generally difficult because they are interfered with oxygen and nitrogen of the oxygen. surrounding air sample to be measured. The current LIBS systems require grinding the parts to be detected, which impacts the performance as explained above. Indeed, it is difficult to respect the irradiation conditions of the workpiece, that is to say of focusing of the laser beam, and thus positioning of the optical means relative to the workpiece, for each workpiece, even for those of dimensions difficult to condition. It is necessary that ability to detect chemical elements, such as Cl chlorine, Br bromine and Phosphorus P, which are used as flame retardants in polymer parts, to ensure good polymer family detection where appropriate. The LIBS system does not allow in the current state to detect the composition of parts on which the surface is denatured, by pollution or paint for example, because the plasma is only from the surface of the room.

Finally, no ideal system is known in the state of the art, when it is desired to be able to achieve rapid, efficient and automatic detection of materials composing parts of various origins, and in particular large parts. Depending on the case encountered, the efficiency limits of already known systems are quickly reached.

The object of the invention is in particular to respond in part or completely to the problems set out above, by proposing a functional solution for detecting materials composing parts.

It proposes for this purpose a method for detecting materials constituting a part, comprising the steps of:

(a) measuring chemical elements forming a surface of the part,

(b) from the measurements of step (a), detecting the presence or absence of a surface coating on the part, by comparing the measurements of the chemical elements with a knowledge base,

(c) - if the result of step (b) is negative, go directly to step (d),

if the result of step (b) is positive, deep penetrate the surface of the piece then

- or repeat the steps (a), (b) and (c) on the area started until a negative result in step (b),

- either repeat step (a) on the started zone and go directly to step (d), and (d) from the measurements of step (a), detecting the type of materials composing the part by comparing the measurements of the chemical elements with a knowledge base.

The invention, contrary to what is known in the state of the prior art, makes it possible to overcome the difficulties of detecting materials when the part is coated on the surface with paint, for example, or other materials. types of layers. The invention therefore makes it possible to improve the known systems that can not operate in the presence of such layers.

This presupposes that the knowledge bases contain information characteristic of the different materials and chemical elements that make up the various kinds of layers or surface coatings that can be identified on the parts, this information being ideally used for step (b). , in addition to the characteristic information of the materials and chemical elements of the parts themselves to be identified, that is to say the substrate under the layer, these other information being ideally used for step (d). The knowledge base information also depends on the system chosen for the detection. They will provide, for example, the characteristic chemical elements of the lines present in a plasma emission spectrum obtained at the end of a measurement by the LIBS, or in a transmission or infrared reflection spectrum, these two systems each making it possible to obtain a spectrum of the chemical elements forming the surface of the part at the end of step (a). These lines are representative of a particular material, or components, which can be expected a priori.

The knowledge bases are for example computer databases stored on digital media, or books, or knowledge belonging to a technician. The knowledge bases mentioned in the different stages of the invention may in fact be one and the same knowledge base.

The results of the detection may be used for sorting purposes pieces by categories corresponding to the nature of the detected materials, for purposes of subsequent upgrades, for example recycling, by means of processes particularly suited to the category of material determined.

For example, the process is carried out on a part known to be predominantly polymeric, by detecting the type of polymer component thereof in step (d), and may further comprise a step (e) consisting of step (a), to detect the presence of additives in the room, including flame retardant, by comparing the measurements of the chemical elements with a knowledge base. Here again this detection or identification of the type of polymer can be used to recycle the part appropriately at the end of the process.

This case is particularly useful for the recovery of waste ELV or WEEE that usually contain such flame retardants. Step (e) is preferably simultaneous with step (d).

In one case, some measurements are made by a user with the naked eye, and information visible to the naked eye on the part (such as the mark on the cover, or the year of manufacture) will intervene in the detections made in steps (b), (d). This information will be provided to the measuring device before said steps (b), (d) and associated, in the knowledge base to a short list of possible materials, as the case may be, the detection of the type of materials will then take place, during step (d), in this shortlist.

Thus, one can for example find indications written on the part, such as references or acronyms, which will determine the type of material present in the room without requiring a complex detection system.

Advantageously, during step (a),

a laser radiation is emitted on the surface of the piece,

a plasma is generated which comprises the chemical elements forming the surface of the piece to be measured, and

the emission spectrum of the plasma is measured,

and preferably, during step (c), the surface of the workpiece is deepened with the aid of laser radiation coming from the same source as the laser radiation used in step (a).

In order to improve the measurement in this case, it is also possible during these steps to emit a gas of chemical composition different from that expected in the room and on the surface of the room, after presupposing the general nature of the room. Inert gases will be particularly suitable here because they are never found in the composition of parts.

Otherwise formulated, the measurements of step (a) are performed by Laser Ablation Breakdown Spectroscopy (LIBS). It is then particularly advantageous to use the laser radiation of the LIBS to start the surface of the measured part, since this makes it possible not to use additional means, and thus does not add integration problems. The LIBS system is not influenced by the color of the room.

The inert gas may be helium, or argon, for example. The emission of the inert gas may be controlled by a solenoid valve passing the inert gas only during step (a).

Preferably, (first) optical means for focusing the laser radiation are positioned at a predetermined distance from the workpiece by moving, until the contact of this workpiece, a fixed stop relative to these (first) optical means and which is hollow for contain radiation near the surface of the room. The displacement can advantageously be effected by means of a jack.

This proposed configuration ensures optimal measurement conditions for the LIBS, as the laser radiation will irradiate and focus on the surface of the part under known and similar conditions regardless of the size of the part or its original positioning. by compared to the rest of the measurement system. The cylinder makes it possible to disengage the stop when it is necessary to manipulate the workpiece, and to put the abutment against the surface of the workpiece during the measurement steps.

This stop may for example consist of a head forming the end of a body in which the LIBS system is located in whole or in part (laser source, optical focusing and measuring means, spectrometer), and comprising a central opening to through which circulates all the radiation involved in the measurement.

The method may also comprise a step of testing the validity of the measurements by comparing the measurement of the inert gas alone with an expected and known result.

In a particular case, the distance between the optical focusing means of the laser and the surface of the workpiece is calculated in order to automatically focus the laser on the surface of the workpiece.

Advantageously, the part is marked with a distinctive sign according to the result of step (d), and step (e) where appropriate. This is particularly useful for performing a posterior sorting step, that is, categorization, based on the distinctive sign marked on the part.

Preferably, during step (a), calcium-based molecules, such as calcium iodide Ca molecules, are brought onto the surface of the part, and the presence of recombined part chemical elements is measured. with calcium.

The calcium supply on the part is advantageous because the calcium recombines easily with chlorine or bromine which are usually present in the flame retardants. These recombinations are easily measurable when a plasma is generated by the LIBS system for example, and thus make it easier to detect the presence of a flame retardant.

Pure atomic calcium does not exist naturally. It is therefore necessary to use a molecule based on calcium, which can be stamped beforehand on the part, spray, etc. However, do not use compounds having the same atoms as those expected on the part (C, H, N, O, for polymers for example), nor obviously Cl or Br, to not distort the measurements. In addition, do not take any toxic compounds, and avoid taking oxygenates because calcium oxide lines CaO and CaOH are very intense in the spectra, and can interfere with the lines of CaCI sought.

An advantageous option is to take Ca calcium iodide powder because the latter is not toxic, relatively inexpensive, and does not interfere with the measurements. However, it tends to oxidize on contact with the air. It must therefore be kept in an environment without oxygen.

In order to overcome this problem, in the case of using a LIBS system, calcium in the form of powder Ca can be injected together with the gas emitted on the part that does not contain oxygen, which also allows an economy of means. Thus, the calcium is injected in real time in the plasma, which allows a control of the amount of calcium and the location of the particle jet, in an oxygen-free environment.

Advantageously, the method comprises a step of measuring the mechanical parameters of the part and / or a step of measuring the electrical parameters of the part, and in step (d), the results of mechanical measurements and / or electrical parts to detect the type of materials in the part, compared to a knowledge base.

By crossing the measurements of the chemical elements composing the part with the mechanical and / or electrical measurements, one thus has more criteria to determine the nature of the piece based on the knowledge bases. Mechanical measurements may consist of hardness measurements (by Shore D, Vickers, Brinell, or Rockwell tests, for example), or mechanical strength of the workpiece. Electrical measurements may consist of electrical conductivity measurements. These measurements can be performed simultaneously with measurements of chemical elements, which saves time, but also before or after these measurements.

The process can be repeated at several points on the surface of the part to ensure the accuracy of the measurements.

Moreover, the method may be preceded or followed by the same method performed on a piece of known composition, to compensate for the measurements made in step (a) if necessary.

The invention also relates to a device for measuring chemical elements forming a surface of a part, comprising:

a source of laser radiation emitting pulses of a laser beam,

first optical means for transporting the laser beam to the surface of the part, and ensuring sufficient irradiation conditions to create a plasma comprising the chemical elements forming the surface of the part,

second optical means for collecting part of an optical emission of the plasma,

means for spectral analysis of the optical emission of the plasma that can be associated with computer data processing means,

characterized in that the optical means are carried by a movable portion comprising a hollow abutment fixed with respect to said first optical means and to bring into contact with the surface of the workpiece.

In fact, this stop will be hollow to contain the radiation near the surface of the room.

The use of (first) moving optical means as in US 2014/204377 involves moving optical components. This choice is likely to cause misalignment of the laser beam and degradation of performance over time, because the displacement of the optical means relative to the stop on the workpiece can cause them detachment and / or decentering, especially when this action is repeated frequently. However, in the context of the present solution, the system is used with a high measurement rate (several times per minute). It is mechanically solicited. In order to avoid misalignment problems, it is therefore proposed here to keep all the optical means in solidarity. This is the entire system that is moved to bring it into contact with the piece to be measured. Thanks to the fixed stop, a repeatable measurement over time is obtained. The distance between the focusing means of the laser and the workpiece remains the same regardless of the part to be analyzed. This function ensures stability in the measurement and performance of the system. Furthermore, the use of mobile optical means involves a control of the position of the sample relative to the focusing lens as shown in Figures 4A, 4B and 4C of US 2014/204377. An additional means of data processing must be used, which makes it possible to define the best position. In the solution of the invention, we abstain from this means and this function, which simplifies the system. Finally, the fixed stop makes it possible to guarantee eye safety when using the system, without the need for an eye-safe laser emitting at 1.5 μιτι so that the operator is not exposed too much. to laser radiation, as expected in US 2014/204377.

Preferably, to effectively stabilize the workpiece in position, the device of the invention will also comprise means for holding the workpiece in a vice between two parts, at least one of which is movable,

The device described above is adapted to implement the method of the invention. As already explained, the laser radiation of the device can be used to start the surface of the part. This device also corresponds to a particular integration of a LIBS system.

The vice is very advantageous, in combination with the other means of the device, because it allows a reliable maintenance of the workpiece at a predetermined location with respect to the first optical means. These latter are movable and can be routed at a known and identical distance from the workpiece surface, for any shape and workpiece size, thanks to the stop. The device thus allows an efficient, easy and fast implementation of the previously described method, and in particular makes it possible not to have to grind the part to be measured beforehand. The vise is in fact advantageously adapted for maintaining whole and relatively bulky parts, such as polymer parts from waste VHU or WEEE.

According to a particular embodiment, the movable parts can be moved by means of cylinders, pneumatic for example. This facilitates the automation of the device.

Advantageously, the laser beam is conveyed through a hollow head comprising a cavity connected to means for emitting a gas and an exit aperture of the laser beam, fixed with the mobile part supporting the optical means, the exit aperture laser beam forming the stop can be brought into contact with the surface of the part held in a vice.

As already seen above, this hollow head can form the end of a moving body in which the measurement system is located in whole or in part, among the laser source, the optical means of transport and collection, the spectrometer. The outlet opening of the head circulates all the radiation involved in the measurement.

According to an advantageous exemplary embodiment, one of the vice holding parts comprises two bars formed in a first plane, and the other of the parts comprises two bars formed in a second plane parallel to the first plane, the set of bars being configured of to clamp the workpiece in a direction perpendicular to said planes, for example when the actuators are actuated.

In a particular embodiment, the bars of one of these parts are spaced 100mm plus or minus 20%, and the bars of the other of these parts are spaced 160mm plus or minus 20%. Moreover, the distance separating the two planes is then preferably 30 min plus or minus 20% when the parts are not tight.

Advantageously, the moving parts are each capable of exerting pressures of between 0.6 and 10 bar. This allows on one side an effective vice hold even for relatively heavy and bulky parts, and on the other hand to ensure that the fixed stop with the (first) optical means is in actual contact with the surface of the workpiece , even for a room whose surface is not perfectly flat.

A distance sensor may be arranged on the moving part carrying said first optical means and be configured to measure the distance between the moving part and the part.

Advantageously, the measuring device further comprises means for measuring mechanical and / or electrical parameters of the part. For example, a hardness measuring rod inside the aforementioned head, which comes into contact with the surface of the part through the opening of the head, and which can measure hardness close to the focusing area of the laser radiation.

It will also be noted that one advantage of the invention is the sorting of black polymers, with identification of material, in particular for a flame retardant detection.

The invention will be better understood and other characteristics, details and advantages thereof will appear more clearly on reading the description which follows, given by way of non-limiting example with reference to the accompanying drawings in which:

FIG. 1 is a schematic view of a device according to the invention;

FIG. 2, already described, is a simplified representation of a LIBS system for measuring chemical elements, and which is incorporated in the device of FIG. 1;

FIG. 3 is a schematic view of the measurement head of the LIBS system of FIG. 1; - Figure 4 is a schematic view of the vice used in the device shown in Figure 1;

- Figure 5 is a schematic view of the device of Figure 1 in the operating position.

The method and the device for sorting parts described by the invention are further illustrated in the context of detecting types of polymers comprising a predominantly polymeric part. These parts are of the "large to medium-sized" type from Waste Vehicles End of Life (ELV) or Waste Electrical and Electronic Equipment (WEEE). Other items include photocopiers, medical devices, air-conditioning equipment, VHU parts, furniture, deconstruction of boats, deconstruction of aircraft, production falls, etc. (ie anything that can generate large pieces of plastics), especially in the context of waste sorting VHU or WEEE.

This method and this device makes it possible to discriminate, for example, polyethylenes (PE), polypropylenes (PP), polystyrenes or high-impact polystyrenes (PS and HIPS), acrylonitrile-butadiene-styrene terpolymers (ABS), polycarbonates (PC ), Polycarbonate / Acrylonitrile Butadiene Styrene (PC / ABS), polyphenylenes / polystyrenes (PPE / PS), or polyamides (PA).

In this embodiment of the invention, sorting is performed directly on the parts without preliminary grinding, and is applicable for a large flow of parts. It is possible to analyze the material, to detect the additives, such as the flame retardants, whatever the color of the parts, without sample preparation and with a very short analysis time, of the order of a few seconds. The description which follows is made with reference to all the figures.

The basic operating principle of the example is as follows:

An operator loads a part 10 to be analyzed in a vice 12. presses two buttons 14 simultaneously to start the analysis. This bi-manual control makes sure that one of the operator's hands is not in a dangerous position. The results of the measurements and the detection are given by computer means 16.

The device is as follows:

The vice 12 is composed of two parts 18, 20 each comprising two clamping bars 22 extending in the same plane, the plane of the bars 22 of the first part 18 being parallel to the plane of the bars 22 of the second part 20. One of the vice parts is connected to a pneumatic cylinder 24, and presses the part 10 so as to hold it against the other part of the vice. When tightened with the aid of the pneumatic cylinder 24, the part 10 is held in such a way as to have a flat surface preferably pressed by the bars 22 of one of the parts of the vice in a plane parallel to the plane of these same bars.

A LIBS measuring body 26 is disposed on a second pneumatic jack 28 and has at one end a measurement head forming a stop, 30, automatically brought into contact with the piece 10 between the two bars 20 of one of the parts 20 of the vise 12, by displacement in a direction perpendicular to the plane of these same bars. The LIBS measuring body 26 comprises, a source of laser radiation 32, (first) optical means of transport, routing and focusing, such as mirrors 34 and lenses 56, laser radiation on the piece 10 through a laser beam. opening 36 of the head 30, injection means 38 of a gas 58 and calcium iodide 60 in an enclosure 40 of the head 30 opening on its opening 36, (second) optical means for collecting the radiation of the plasma comprising lenses 42 and an optical fiber 44, and two spectrometers 46 connected at input to the optical fiber 44 and at the output to data processing means 48 containing the knowledge bases 55. The LIBS body 26 can furthermore comprising a hardness measuring rod 50 opening through the opening 36 of the head, electrical conductivity measuring means, and a distance sensor 52 with respect to the surface of the workpiece 10.

The stop or head 30 is hollow (space 31), so that it confines the radiation in the space 31, where otherwise the operator would see it and should therefore wear protective glasses.

The ocular safety is ensured by the fact that the opening 36 of the head 30 of the body LIBS 26, through which the laser radiation passes, is in contact with the part 10 to be analyzed during the measurements. In an exemplary implementation, the body LIBS is equipped with contact sensors 54 which only allow the triggering of the analysis when the head is correctly positioned on the part.

The principle of measurement of the chemical elements composing the part is as follows:

The detection of the materials constituting the polymer part is carried out automatically by the body LIBS 26. The analysis by LIBS is carried out in the preferred example with a Nd: YAG laser emitting at the wavelength 1064 nm, with durations of pulse between 4 and 8 ns, and shots clocked between 10 Hz and 40 Hz. The beam is focused with a parabola 34 out of focal length 101 mm. The collection of the plasma is carried out with an optical module comprising or less a lens 42 focusing the radiation of the plasma at the end of an optical fiber 44. In a particular embodiment, the parabola 34 off axis is used for the focus of the laser and also for plasma collection. A separating plate then makes it possible to separate the laser beam (reflection on the slide) and the emission of the plasma (transmission through the slide) between the parabola 34 and the source of the laser radiation 32. A lens 42 then makes it possible to send the plasma radiation passing through the blade in the optical fiber 44. In the example, twenty laser shots are applied to each analysis. The result of the analysis is displayed on a screen and mentions the family of the polymer and the possible presence of additives, such as flame retardants containing chlorine, bromine and phosphorus. The analysis time is close to two seconds. In general, other laser characteristics may be used, and the above parameters may be varied as needed, provided that the irradiance of the workpiece surface is sufficient to create a plasma.

The detection of additives is improved:

When it is desired to detect additives, such as chlorine-containing flame retardants (emission lines C1837.59 nm, C18860 nm or C127.66 nm), bromine (Br I 827.24 nm) and phosphorus (PI 253.56 nm, PI 255.32 nm), or any type of compounds, one of the essential problems comes from the low emissivity of these atoms, leading to efficiency limits of detection.

In order to overcome these difficulties, it is possible to use recombinations between the atoms of the elements to be detected and other atoms coming naturally from the part or added to the part during the analysis. One of the nonlimiting examples here is the use of calcium. The molecules of chlorine, bromine or other on one side, and calcium on the other hand, can indeed recombine in a plasma and create molecules of CaCl 2, CaBr, etc. The CaCl 2 molecules, for example, emit a characteristic radiation at wavelengths close to 622.49 nm, 621.16 nm, 618.49 nm and 593.40 nm. A significant gain in the efficiency of detection of the chemical elements of the recombinant additives with calcium, compared with the simple chemical elements, is obtained.

This principle is particularly advantageous in the context of surface detection of parts, since dust and / or aerosols composed of calcium are generally present naturally on the surfaces, thus ensuring a natural recombination between atoms of additives and calcium atoms. In another possible implementation, particles composed of calcium on the surface of the sample to be analyzed are added, beforehand or during the measurement, in order to increase the probability of recombination between the atoms of the additives and calcium atoms.

In the example, the gas 58 in the measurement head of the LIBS body 26 is injected at the same time with calcium iodide particles Ca 60 from a reserve connected to the gas inlet and to the cavity 40 of the measuring head. It is thus easy to control the projection of these particles on the surface of the part 10, without the latter being oxidized (the gas being a priori neutral).

About spectrometers:

Two spectrometers 46 are preferably used simultaneously, connected by means of a bifurcated fiber to the optical means for collecting the plasma. The first spectrometer covers the UV-visible range to detect carbon lines (247.8 nm), hydrogen (656.3 nm), oxygen (777.2 / 777.4 / 777.5 nm), and bands C ₂ "swan" and CN "violet" (between 380 and 570 nm). This spectrometer can also be used to detect the presence of additives such as, but not limited to, phosphorus, antimony, titanium, calcium, magnesium and CaCI and CaBr bands evoked following.

The second spectrometer is optimized over the near IR range in order to detect the bromine lines around 827 nm and chlorine around 838 nm.

In another configuration, it is possible to use a fiber switch which successively sends the two spectrometers 46. In this approach, it is possible, for example, to initially apply 10 laser shots making it possible to obtain a spectrum in the UV-VIS range and then 10 laser shots to obtain a spectrum in the near IR range after switching.

A gas is projected on the surface of the room as follows: The measurements are made in the example in the presence of a helium jet 58 inside the head 30 of the body LIBS 26, although any gas whose chemical composition is a priori not present in the desired material and whose emission lines do not interfere with the desired lines is appropriate. The helium jet is controlled by a solenoid valve, and is emitted only during the measuring cycle. The consumption of gas is thus limited to the time of measurement. This helium jet has several advantages:

- It allows to expel oxygen (O) and nitrogen (N) from the air. The lines of O and N visible on the spectra from the plasma are therefore derived solely from the polymer part and not from the ambient air. These optical emission lines can therefore be used for the classification, in the family of styrenics, ABS (polymer having nitrogen), PC (polymer having oxygen), ABS-PC (mixture polymer containing oxygen and nitrogen), and HIPS (neither oxygen nor nitrogen). It should be noted that nitrogen is a low emissivity atom. In our example, the detection of nitrogen is therefore preferably carried out via the CN molecule (emission band located at about 388 nm) and not directly from the nitrogen molecule.

- The bromine emission line that is to be detected, located at

827.24 nm is partially interfered with by nitrogen lines. The removal of nitrogen from the air thus makes it possible to improve its detection, and to obtain sensitivities of detection making it possible to detect the small quantities of bromine imposed by the regulation on brominated polymers.

With regard to the detection of superficial layers:

In addition, the method includes the detection of a possible paint layer by the LIBS and adapts its measurement according to the presence thereof. Indeed, some polymer parts have layers of surface paints. These are often undetectable to the naked eye because they are of the same color and composition similar to the substrate polymer. As LIBS technology is a surface analysis, the presence of a layer of paint on it distorts the measurement if it is not taken into account. In the example, the presence of pigments representative of a paint layer is automatically detected by first measuring by means of the LIBS system the chemical composition on the surface of the part, and comparing it with known information on the elements. chemical components of these pigments. In particular, the presence of Titanium emission line is characteristic of the presence of titanium dioxide particles, used massively in paints. Thus, in case of detection of titanium or other paint, the process carries out a new measurement cycle at the same place, using laser radiation to start the piece beyond this layer of paint and reach the substrate. The LIBS measurement is then carried out again on the opened zone, no longer including a layer of paint.

Other parameters to take into account to improve the detection:

A cross-section of detection results from the chemical analysis obtained in LIBS with at least one additional information can be realized. For example, we can use the color, observed by the operator, the mark of the part, a measure of the hardness, a measure of the electrical conduction, even the shape of the part, which can help classification the polymer component part. In particular, the hardness measurement is performed by means of a rod 50 integrated in the LIBS measuring body, passing through the opening 36 of the measuring head 30, and pressing on the part 10. This rod will be adapted to the choice hardness tests of Shore D, Vickers, Brinell, Meyer or Rockwell type.

In this context, certain information visible to the naked eye (brand of the part ...) will moreover and preferably be provided to the measuring device at the beginning of the intervention and associated in the knowledge base 55 with a list limited number of possible materials, depending on In this case, the detection of the type of material will take place during the material type detection step in this restricted list.

The method may further include measuring the distance between the LIBS measuring body and the workpiece surface. Indeed, the LIBS technology generally requires focusing the laser radiation on the surface or near the room in order to obtain sufficient irradiance conditions to create a plasma.

However, these conditions are generally obtained only around the point of focus, and the displacement of a few millimeters of the piece around this point can change the nature of the plasma (temperature, electron density) measured and thus modify the profile of the plasma. spectrum emission, and degrade the detection performance.

In the example, a measurement of the distance, and therefore of the shift of the focusing point relative to the surface of the part, is therefore included in the process, thanks to conventional sensors 52 integrated in the body LIBS 26, and is taken into account. when comparing the measurements of the chemical elements that make up the part with the information of the knowledge bases 55, which come from, among other things, known parts which have been tested and which have served as reference models.

For the same purpose, the device may also include an autofocus system at the optical laser beam delivery means, using the distance measurement, to ensure that the laser radiation is still focused under the same ideal conditions. on the surface of the room.

Tests of validity of the detection are carried out automatically or at the request of the operator on known chemical elements. An intensity level test of a helium line can be performed at each acquisition to ensure that the spectrum is of good quality. In addition, the operator can position a reference sample whose chemical composition is known. The system then displays the LIBS spectrum obtained, which can be compared with the reference one to ensure the correct system operation.

The detections of the LIBS are crossed with knowledge a priori of the materials composing the room. Indeed, the analysis can be guided by a priori knowledge of the provenance of the parts to be analyzed. For example, it is common that polyethylenes do not contain flame retardant additives. This knowledge can be incorporated into knowledge bases to guide detection when in doubt about the composition of a part. In the same way, the operator who knows the families of materials that can compose the part can use this information to improve the automatic detection performance.

In this example, the identification of the material and the detection of the flame retardants are carried out on whole parts, thus increasing the mass flow rate of parts to be analyzed. Furthermore, the gripping and automated clamping of the workpiece in a fixed vice of the device optimizes the analysis, thanks to a repeatability of the interface between the part to be analyzed and the movable body LIBS measurement, and allows to perform an automatic triggering of LIBS measurements, which saves time.

Depending on the result of the detection, a marking, for example a paint spray, is performed on the part to allow the identification and sorting of the piece a posteriori.

The operator can then open the vise by actuating the jack, and unload the piece, put it on a conveyor and load the next piece.

The device may include means for controlling the optical routing of the laser radiation, in order to focus the laser radiation at several successive points on the surface of the room where detections will be made. It is thus possible to improve the detection reliability.

We can also integrate in the example a sample crusher. However, the detection is not carried out on all the fragments of part resulting from the grinding but only on a part of them. This case is to consider if the parts are really too large for the detection device.

Claims

1. A method of detecting material constituting a workpiece (10), comprising steps in a measuring device of:

(a) measuring chemical elements forming a surface of the part,

(c) - if the result of step (b) is negative, go directly to step (d),

if the result of step (b) is positive, deep-dipping the surface of the part and then recommence step (a) on the started zone and go directly to step (d), and

(d) from the measurements of step (a), detecting the type of materials composing the part by comparing the measurements of the chemical elements with a knowledge base.

2. Detection method according to claim 1, characterized in that it is carried out on a piece known to be mainly polymeric for recycling, by detecting the type of polymer component in step (d), and in that it comprises a step (e) consisting, from the measurements of step (a), in detecting the presence of additives in the part, in particular of flame retardant, by comparison of the measurements of the chemical elements with a knowledge base.

3. Detection method according to one of claims 1 or 2, characterized in that:

- information visible to the naked eye on the part involved in the detections made in steps (b), (d), this information being provided to the measuring device before said steps (b), (d) and associated, in said knowledge base (55) to a short list of possible materials, as the case may be, and, during step (d), the detection of the type of materials takes place in said restricted list.

4. Detection method according to one of the preceding claims, characterized in that during step (a),

a laser radiation (32) is emitted on the surface of the part,

a plasma is generated which comprises the chemical elements forming the surface of the part to be measured, and

the emission spectrum of the plasma is measured,

and in that during step (c), the surface of the workpiece is deeply etched with laser radiation from the same source (32) as the laser radiation used in step (b). at).

5. Detection method according to claim 4, characterized in that first optical focusing means (34, 56) of the laser (32) are positioned at a predetermined distance from the workpiece (10) while moving, until contact with the piece, a stop (30) fixed with respect to said first optical means and which is hollow (31), for containing the radiation near the surface of the workpiece.

6. Detection method according to one of the preceding claims, characterized in that the piece is marked with a distinctive sign according to the result of step (d), and step (e) where appropriate.

7. Detection method according to one of the preceding claims, characterized in that during step (a), calcium-based molecules such as calcium iodide molecules are introduced onto the surface of the part ( 60), and the presence of recombinant coin chemical elements with calcium is measured.

8. Detection method according to one of the preceding claims, characterized in that it comprises a step of measuring the mechanical parameters of the workpiece and / or a step of measuring electrical parameters of the workpiece, and in that when step (d), the results of the mechanical and / or electrical measurements of the part are also used in order to detect the type of materials composing the part, compared with a knowledge base.

9. A device for measuring chemical elements forming a surface of a workpiece (10), comprising:

a source of laser radiation (32) emitting pulses of a laser beam,

first optical means (34, 56) for transporting the laser beam to the surface of the workpiece, and providing irradiation conditions sufficient to create a plasma comprising the chemical elements forming the surface of the workpiece;

second optical means (42, 44) making it possible to collect a part of an optical emission of the plasma,

spectral analysis means (46) for the optical emission of the plasma associated with computer data processing means (48), characterized in that it comprises means (12) for holding the part in a vice between two parts (18, 20) of which at least one (20) is movable, and the first optical means are carried by a movable part (26) comprising a stop (30), hollow, fixed with respect to said first optical means (34, 56) and can be brought into contact with the surface of the workpiece.

10. Measuring device according to claim 9, characterized in that the laser beam is conveyed through a hollow head (30) comprising a cavity (40) connected to means for emitting a gas (58) and an opening (36) output of the laser beam, fixed with the movable portion (26) supporting the first optical means (34, 56), the output aperture of the laser beam forming the stop being brought into contact with the surface of the workpiece kept in a vice.

1 1. Measuring device according to one of claims 9 or 10, characterized in that the movable parts (26, 20) are each capable of exerting pressures of between 0.6 and 10 bar.

12. Measuring device according to one of claims 9 to 1 1, characterized in that it further comprises means (50) for measuring the mechanical and / or electrical parameters of the room.