DEVICE FOR MEASURING THE ABSORPTION SPECTRUM OF A PREFORM

Abstract

The invention relates to a device (56) for on-the-fly measurement of the absorption spectrum (σ(λ1)) in the visible light range of at least one wall (16) of preforms (12) comprising: - means (36) for conveying preforms (12), - a measurement light source (58) that emits a measurement light beam (55) according to a continuous measurement spectrum (σm), - a spectrometer (62) measuring the intensity (I) and the wavelength (λ1) of the first light beam (55) after passing through the preform (12), characterized in that the measurement light source (58) comprises at least two primary light sources (58A, 58B, 58C, 58D) that each emit a primary light beam according to an associated continuous spectrum (σA, σB, σC, σD), the spectra (σA, σB, σC, σD) primary continuouss of said primary sources (58A, 58B, 58C, 58D) being different. Figure for the abbreviation: Figure 3

Description

Title of the invention: DEVICE FOR MEASURING THE ABSORPTION SPECTRUM OF A PREFORM Technical field of the invention

[0001] The invention relates to a device for on-the-fly measurement of the absorption spectrum in the visible light range of at least one wall of preforms intended to be transformed into final containers by forming, in particular by stretch blow molding, the absorption spectrum measurement device comprising: - means of conveying preforms in a line along a production route passing through a measurement zone, - a measurement light source that emits a measurement light beam according to a continuous measurement spectrum that extends at least into the visible range, - a spectrometer measuring the intensity and wavelength of the first light beam after passing through at least one thickness of the preform wall as it passes through the associated measurement zone. Technical background

[0002] It is known to manufacture containers by forming, in particular by stretch blow molding, preforms made of thermoplastic material. The material forming the preforms is generally in an amorphous state that is not suitable for cold forming. Prior to the forming operation, the preforms are therefore heated to a temperature greater than or equal to a glass transition temperature that allows them to be shaped into the final container.

[0003] More specifically, the preforms generally have a substantially cylindrical body of revolution with thick tubular walls, closed at one of its axial ends by a thick-walled base, and extended at its other end by a neck, also tubular. The neck is formed to its final shape and dimensions, while the body of the preform is intended to undergo relatively significant deformation to form it into a container during a forming step.

[0004] For this reason it is preferable that only the body of the preform be heated to a setpoint temperature which is higher than the glass transition temperature, the neck remaining at a temperature lower than said glass transition temperature to avoid its deformation during the manufacture of the container.

[0005] Furthermore, the setpoint temperature must not exceed a crystallization temperature that is higher than the glass transition temperature. Above this crystallization temperature, the thermoplastic material crystallizes and no longer exhibits the mechanical properties required for quality forming.

[0006] The mass production of containers is carried out in a production facility in which the preforms move along a predetermined production path. Each preform is supported by conveying means. Such a conveying means can be a rail conveyor along which the preforms are free to come into contact with each other, or a conveyor that includes gripping devices for each preform individually.

[0007] The production installation includes a heating station which, during a heating step, makes the preform body malleable by heating it to the set temperature. During the heating step, each preform is exposed to radiant heat as it moves. The power of the radiant heat is controlled to heat the preform body to the set temperature.

[0008] The production installation also includes a forming station arranged downstream of the heating station according to the direction of preform flow in the production installation. During the forming step, the hot preform is placed in a forming unit, for example, in a mold of the forming station that has a molding impression conforming to the container to be produced. A pressurized fluid, such as air, is then injected into the malleable body of the preform to press its wall against the mold impression. Generally, the injection of pressurized fluid is preceded and / or accompanied by axial stretching of the preform, notably by means of a stretching rod inserted into the preform. In a known manner, the body is thus subjected to biaxial stretching.

[0009] During its passage through the heating station, each preform is generally exposed to continuous-spectrum heating radiation, which heats the thermoplastic material. The temperature to which the preforms are heated generally depends on the absorption factor (A) of the preform for the wavelengths of the heating radiation. The absorption factor (A) is sometimes referred to by its English name, "absorptance".

[0010] The absorption factor (A) is defined as the ratio between the absorbed heating radiation flux and the incident heating radiation flux. The absorbed heating radiation flux causes a temperature rise in the thermoplastic material composing the preform. The absorption factor (A) of the preform thus makes it possible to determine the temperature rise of a preform as a function of the intensity of the infrared radiation and the duration of exposure to said radiation. Less energy is required to heat a preform with a lower absorption factor (A). high absorption (A) compared to a preform with a lower absorption factor (A).

[0011] The absorption factor (A) can be deduced from two other parameters called the transmission factor (T) of the preform and its reflection factor (R).

[0012] The transmission factor (T), sometimes called "transmittance", is defined as the ratio between the heat radiation flux transmitted through at least one wall of the preform and the incident heat radiation flux.

[0013] The reflection factor (R), also called reflectance, is defined as the ratio between the heat radiation flux reflected by the preform and the incident heat radiation flux. Reflectance (R) is calculated, for example, as a function of the refractive index (n) of the thermoplastic material according to the following formula:

[0014] R = [(nl) / (n+l)]2

[0015] in which the value "1" corresponds to the refractive index of air.

[0016] These three factors depend on the wavelength of the radiation considered.

[0017] The heating radiation extends at least in part into the near-infrared range, since it is known that thermoplastic materials, such as PET, readily absorb this type of radiation. The wavelength considered for defining the preform's transmission factor is therefore generally taken from the near-infrared range.

[0018] These three factors are linked by the following equation:

[0019] A=lRT

[0020] The transmission factor depends on the wavelength of the radiation passing through it. Thus, a perfectly transparent preform exhibits a transmission factor close to 100% for wavelengths in the visible light range, while it exhibits a significantly lower transmission factor for radiation with wavelengths in the near-infrared range. This reflects the fact that the preform can be heated by radiation in the near-infrared range, whereas radiation in the visible light range will have only a negligible influence on the temperature of the preform, even at high power levels.

[0021] It sometimes happens that the preforms are made of a material having a colour.

[0022] This tint can be intentionally obtained by adding dye to tint the preform in a desired color in order to obtain a colored container.

[0023] This discoloration can also occur unintentionally and uncontrollably, for example when the preform is made of a plastic material consisting at least partly of recycled plastic material. This is the case, for example, when the preform contains mechanically recycled polyethylene terephthalate (rPET). In this In this case, the preform has a more or less dark tint depending on the quality and quantity of recycled material incorporated into the composition of the thermoplastic material that constitutes it.

[0024] Such a preform comprises at least a portion of rPET. To produce such a preform, rPET granules are, for example, mixed with virgin PET granules. The granules thus mixed are melted together before being injected into a mold to obtain the preform. Thus, the rPET as defined in the invention is melted and directly used to form preforms, possibly mixed with virgin PET. The recycled rPET granules are obtained mechanically by grinding previously used PET objects, which have been sorted by color and cleaned beforehand, without chemically decomposing them. The virgin PET granules are obtained chemically by monomer esterification. The ratio between the weight of rPET and the weight of virgin PET makes it possible to determine the rPET content in the preforms.

[0025] The inventor has observed that in both cases, the color of the plastic material is likely to influence the temperature of the preform wall when it is exposed to heating radiation.

[0026] Indeed, the heating radiation has a spectrum that extends at least in part into the visible light range. However, when the preform has a color, and in particular a dark color, this part of the heating radiation spectrum is likely to significantly heat the thermoplastic material.

[0027] It is important to be able to correctly define the absorption lines in the visible range, in particular to be able to adjust the heating power, but also to be able to determine the composition of the material forming the preform.

[0028] To achieve this, the light source used to determine the color of the preform must be as close as possible to a standard illuminant. Such an illuminant is preferably illuminant D65 as defined by ISO 11664-2:2022. This reference illuminant is a colorimetric standard that corresponds to natural daylight in a temperate zone. It is a cool white.

[0029] To produce such an illuminant, it is known to use incandescent light sources, such as a xenon lamp. However, such a source is difficult to use for on-the-fly measurements on a high-volume production line, i.e., when the preforms are in motion. Among the various disadvantages of such a light source, it should be noted that it is bulky, that it requires the use of filters to obtain a spectrum close to that of the reference illuminant, that it produces a lot of heat, that it is unstable over time, and that it requires a long ignition time.

[0030] There is therefore a need to correctly determine the color of a preform without resorting to such technology. Summary of the invention

[0031] The invention provides a device for on-the-fly measurement of the absorption spectrum in the visible light range of at least one wall of preforms intended to be transformed into final containers by forming, in particular by stretch blow molding, the absorption spectrum measurement device comprising:

[0032] - means for conveying preforms in a line along a production route passing through a measurement zone,

[0033] - a measuring light source that emits a measuring light beam according to a continuous measurement spectrum that extends at least into the visible range,

[0034] - a spectrometer measuring the intensity and wavelength of the first beam luminous after passing through at least one thickness of the preform wall during its passage through the associated measurement zone,

[0035] characterized in that the measurement light source comprises at least two primary light sources, each emitting a primary light beam according to an associated continuous spectrum that extends at least into the visible range, the primary continuous spectra of said primary sources being different and their light beams being merged to form said measurement light beam.

[0036] According to another feature of the measuring device made according to the teachings of the invention, the addition of the primary continuous spectra of said primary sources forms the continuous measurement spectrum, the primary sources being selected so that the continuous measurement spectrum has a profile that is substantially closer to the reference spectrum of a reference illuminant than each of the primary spectra taken alone.

[0037] According to another feature of the measuring device made according to the teachings of the invention, the reference illuminant is the D65 illuminant as defined by ISO 11664-2:2022.

[0038] According to another feature of the measuring device made according to the teachings of the invention, the measuring light source comprises more than two primary light sources, all exhibiting different light spectra.

[0039] According to another feature of the measuring device made according to the teachings of the invention, the measuring light source comprises at least two primary light sources which have the same primary light spectrum so as to increase the intensity of the measuring light beam for the wavelengths of said light spectrum so that the measuring spectrum is closer to the reference spectrum of the reference illuminant.

[0040] According to another feature of the measuring device made according to the teachings of the invention, each primary light source is formed by a luminescent semiconductor component.

[0041] According to another feature of the measuring device made according to the teachings of the invention, the primary light beams are fused by means of at least one optical coupler.

[0042] According to another feature of the measuring device made according to the teachings of the invention, it comprises a primary light source which emits at least partly in the near-infrared range.

[0043] According to another feature of the measuring device made according to the teachings of the invention, it includes at least one electronic unit for controlling the light intensity emitted by each primary light source.

[0044] According to another feature of the measuring device made according to the teachings of the invention, the preforms are made of a thermoplastic material, in particular PET.

[0045] The invention also relates to an installation comprising means for conveying preforms in a line along a predetermined production path passing successively through a heating zone of a body of the preforms and through a preform forming station into a container, in particular by stretch blow molding, the installation comprising the measuring device made according to the teachings of the invention. Brief description of the figures

[0046] Other features and advantages of the invention will become apparent during the reading of the detailed description which follows, for the understanding of which reference will be made to the attached drawings briefly described below.

[0047] Fig. 1 is a top view which schematically represents a container manufacturing installation made according to the invention comprising a heating station.

[0048] Fig. 2 is a side view which represents a preform intended to be processed by the installation of Fig. 1.

[0049] Fig. 3 is a vertical cross-sectional view along section plane 3-3 of Fig. 1, which represents a device for measuring an absorption spectrum in the visible light range of the walls of a preform circulating in the installation, carried out according to a first embodiment.

[0050] Figure 4 is a diagram representing wavelengths on the x-axis and light intensities on the y-axis, Figure 4 schematically representing the spectrum luminous of a reference illuminant in solid line and the luminous spectrum of a white LED in dotted line.

[0051] Fig. 5 is a diagram similar to that of Fig. 4 which schematically represents the light spectrum of the reference illuminant in solid line, as well as the measurement light spectrum of a measurement light source represented by crosses, and the measurement light spectrum being obtained by adding the spectra of a white LED in dotted line, and the spectra of three primary light sources represented respectively by rhombuses, by an axis line and by dots.

[0052] Figure 6 is a diagram similar to that of Figure 4, which represents the measurement spectrum of Figure 5 as a dashed line and a transmission spectrum as a solid line. Detailed description of the invention

[0053] In the following description, the terms "top", "bottom", and the derived terms "high", "low", are used for clarity in reference to the orientation of the figures without this having any limiting scope.

[0054] In the following description, the wavelengths of the light radiation will be expressed in nanometers, indicated by the abbreviation "nm".

[0055] In theory, a monochromatic source is an ideal source emitting a sinusoidal wave of a single frequency. In other words, its frequency spectrum consists of a single line of zero spectral width (Dirac).

[0056] In practice, such a source does not exist, a real source having a frequency emission spectrum which extends over a band of small but non-zero spectral width, for example of a few tens of nanometers, centered on a main frequency where the intensity of the radiation is maximum.

[0057] In the following description, such a real source is considered to be monochromatic.

[0058] Subsequently, an absorption spectrum is defined as a curve which represents the value of the intensity of a continuous spectrum light beam as a function of the wavelength after its passage through a medium to be analyzed, in particular the wall of a preform.

[0059] Figure 1 schematically illustrates an installation 10 for manufacturing containers 11 from thermoplastic preforms 12, particularly PET (polyethylene terephthalate) or rPET (recycled polyethylene terephthalate). The thermoplastic material may optionally, but not necessarily, contain additives that artificially increase the preform's absorption factor, or a dye to change its color.

[0060] As shown in [Fig. 2], each preform 12 comprises a cylindrical body 14 with axis "X". The body 14 has a transparent lateral wall 16 that delimits an internal volume. The wall 16 has a shape of revolution about the axis "X" such that, at a given height, the wall 16 has a constant thickness. However, the thickness of the wall 16 is likely to vary depending on the height. The wall 16 is delimited by an external face 18 that is oriented towards the outside of the preform 12 and by an internal face 20 that is oriented towards the internal volume.

[0061] An upper end of the body 14 opens through a neck 22. The neck 22 has the final shape of the neck of the container 11 to be obtained. Consequently, the neck 22 does not undergo any deformation during the manufacture of the container 11. The body 14 has a base 24 that closes its lower end and is generally hemispherical in shape. The neck 22 has a collar 26 arranged at its junction with the body 14. The lower face of the collar 26 is designed to form a support surface 28 to support the preform 12 during its molding and / or during its transport.

[0062] At the end of their injection molding, the preforms 12 are rapidly cooled to give the thermoplastic material an amorphous state. It is thus possible to make the thermoplastic material malleable again by heating it above a glass transition temperature.

[0063] Referring again to [Fig. 1], the manufacturing installation 10 comprises a heating station 30 and a forming station 32. The preforms 12 move in a line along a production path 34 that passes through the heating station 30 and the forming station 32. The direction of movement of the preforms 12 is indicated by the arrows "Fl" in [Fig. 1]. During normal operation of the manufacturing installation 10, the preforms 12 are in constant motion along the production path 34.

[0064] The heating station 30 is designed to heat the body 14 of the preforms 12 to a setpoint temperature that is greater than or equal to the glass transition temperature of the constituent material, for example, greater than 70°C when this material is PET and / or rPET. The heating station 30 includes a conveyor 36 (shown schematically) for transporting the preforms 12 while rotating them.

[0065] The conveyor 36 generally includes mandrels (not shown) which are fitted with the neck 22 to transport the preforms 12. The mandrels move along a closed circuit. The mandrels are, for example, carried by the links of a chain or by independent shuttles moving along a rail.

[0066] The circuit here comprises two parallel straight sections connected by 180° turning sections. The conveyor 36 further comprises two wheels 38A, 38B for guiding the mandrels in the turning sections of the closed circuit.

[0067] The heating station 30 also includes heating means 40 for heating the preforms 12. These include, for example, lamps facing reflectors that emit continuous spectrum heating electromagnetic radiation.

[0068] The heating radiation extends at least in part into the near-infrared range, which is within a wavelength range between 780 nm and 3000 nm. The intensity of the heating electromagnetic radiation is particularly higher in a higher intensity wavelength range between 780 nm and 1600 nm.

[0069] The heating radiation also extends at least partly into the visible light range, which is generally between 380 nm and 780 nm.

[0070] The spectrum of the heating radiation extends, for example, between 300 nm and 3000 nm.

[0071] The heating means 40 are arranged along a heating zone 42 of the preform production path 34. In the example shown in [Fig. 1], the heating station 30 comprises a heating zone 42 divided into two parts arranged upstream and downstream of the bend section guided by the guide wheel 38B.

[0072] The preforms 12 entering the heating station 30 are individually handled by the conveyor 36, on which they travel a U-shaped section of their production path 34, passing through the heating zone 42. They are heated as they pass by the heating means 40, which, where appropriate, are positioned to one side or on either side of the preforms 12 relative to their direction of travel. The hot preforms 12 are extracted from the heating station 30 after passing through the heating zone 42 and transferred into molds of the forming station 32 by a first transfer device 44, such as a transfer wheel, interposed between the heating station 30 and the forming station 32.

[0073] The transfer wheel includes arms (not shown, as they are known per se) which successively grasp the preforms 12, as they exit the heating station 30, at the level of their neck 22, to introduce them one after the other into a mold 46 of the forming station 32. The forming station 32 comprises a rotating carousel 48 around the periphery of which several blowing stations 50 are arranged.

[0074] Each blowing station 50 includes at least one mold 46 which defines a cavity having the imprint of the container 11. Each blowing station 50 includes means (not shown) for forming / deforming the body 14 of the preform 12 and pressing it against the imprint of the mold 46, for example by stretch-blowing.

[0075] Each hot preform 12 exiting the heating station 30 is introduced into a mold 46 of the blowing station 50 to be blown and transformed into a container 11. Once completed, the container 11 is extracted from the blowing station 50 by a second transfer device 52, similar to the first transfer device 34.

[0076] Generally, the heating means 40 emit the heating radiation at a power determined solely by the absorption factor of the preforms 12 in the near-infrared range in order to reach the setpoint temperature. This power is calculated assuming that the preform 12 has perfectly transparent walls 16 in the visible light range.

[0077] It is useful to know the absorption spectrum of the wall 16 of the preform 12, for example to allow the preforms 12 to be heated as close as possible to the setpoint temperature or to be able to determine the composition of the material constituting the preforms 12.

[0078] To this end, the invention proposes to measure an absorption spectrum “o(Xl)” of the wall 16 of the preform 12 in the visible light range, for wavelengths generally between 380 nm and 780 nm, in a measurement zone “Z” crossed by the production path 34 upstream of the heating zone 42.

[0079] This measurement can be used to control the power of the heating electromagnetic radiation according to the measured absorption spectrum "o(Xl)" or to determine the composition of the preforms. This process is, for example, implemented automatically by an electronic control unit 54, visible in particular in [Fig. 3].

[0080] The measurement is carried out when the preform 12 is transported by a conveyor along the production path 34 in the container manufacturing installation 10. Preferably, the preform 12 is in constant motion during the measurement. Such a measurement is said to be "on the fly".

[0081] In the examples shown in the figures, the measurement is carried out when the preforms 12 are transported by the conveyor 36 from the heating station 30. This conveyor 36 transports the preforms 12 through to the heating zone 42.

[0082] In an unrepresented variant of the invention, the measurement can be carried out when the preforms are transported by another conveyor, for example a transfer wheel.

[0083] The measurement is preferably carried out on the preforms 12 before their heating, therefore upstream of the heating zone 42.

[0084] In an unrepresented variant of the invention, the measurement is carried out downstream of the heating zone.

[0085] The measurement of the absorption spectrum “o(Xl)” in the visible range is carried out here by measuring the attenuation of the intensity “I” of a light beam 55, called the measurement beam 55, exhibiting a continuous spectrum “om”, called the measurement spectrum “om”, in the visible range for each of the wavelengths of the spectrum “ "om".

[0086] The measurement beam 55 is a beam of so-called "white" light emitted in the visible light range, that is, generally between 380 nm and 780 nm. For example, the spectrum "om" of the measurement beam 55 extends over a wavelength range "XI" extending between a lower bound "XI-min", for example equal to 380 nm, and an upper bound "XI-max", for example equal to 780 nm. The spectrum "om" of the measurement beam 55 is represented by a dashed curve in Figures 5 and 6.

[0087] To this end, the installation 10 includes a device 56 for measuring the absorption spectrum "o(Xl)" in the visible light range. As shown in [Fig. 6] by a solid line curve, this device 56 is arranged to measure the absorption spectrum "o(Xl)" of a preform 12 passing through the measurement zone "Z" shown in [Fig. 1].

[0088] As shown in [Fig.3], the device 56 for measuring the “o(Xl)” absorption spectrum in the visible light range includes a measuring light source 58 which emits the measuring light beam 55 with a continuous “om” spectrum.

[0089] To obtain a measuring device 56 suitable for use on the installation 10 in production mode, it is preferable to use luminescent semiconductor components to produce the measuring light beam 55. Such a luminescent semiconductor component is, for example, a light-emitting diode (LED), an organic light-emitting diode (OLED), a superluminescent diode (SLED), or a laser diode. This type of component therefore does not include incandescent light sources such as lamps. Such a component is particularly advantageous, notably because it is compact, generates little heat, and is very responsive when switched on.

[0090] Furthermore, to obtain a correct measurement of the absorption spectrum, it is preferable that the measurement spectrum of the measurement light source 58 has a profile as close as possible to the reference spectrum of a reference illuminant.

[0091] Such a reference illuminant is, for example, illuminant D65 as defined by ISO 11664-2:2022. Such a gold spectrum is schematically represented in [Fig. 4] by solid lines. It can be seen that the gold spectrum exhibits a nearly constant intensity across the entire range of visible light. In particular, it shows relatively subtle dips and peaks.

[0092] However, to date, no luminescent semiconductor component is known which emits light with a spectrum sufficiently close to that of the reference illuminant.

[0093] For example, so-called "white" light-emitting diodes (white LEDs) have an oA spectrum, as schematically illustrated in dashed lines in [Fig.4], which shows a lack of intensity on certain ranges of the visible domain. In particular, the oA spectrum exhibits a very pronounced "PI" peak around 420 nm, this peak being flanked by two very distinct troughs around 405 nm and 450 nm. Furthermore, the radiation intensity drops very rapidly for wavelengths above 600 nm. Thus, the use of a white LED alone is insufficient to obtain a reliable measurement of the absorption spectrum of preform 12.

[0094] To solve this problem, the invention proposes that the measuring light source 58 comprise at least two primary light sources 58A, 58B, 58C, 58D, 58E. Each primary light source 58A, 58B, 58C, 58D, 58E thus emits a primary light beam. Each primary light beam is, for example, guided by an associated optical fiber 60A, 60B, 60C, 60D, 60E.

[0095] The primary light beams are fused to form said measurement light beam 55. The primary light beams are fused, for example, by means of at least one optical coupler, here a single optical coupler 61.

[0096] As shown in [Fig. 5], each primary light source 58A, 58B, 58C, 58D, 58E emits a primary light beam according to an associated primary continuous spectrum oA, oB, oC oD oE that extends at least into the visible range. The primary continuous spectra oA, oB, oC oD oE of at least two of said primary sources 58A, 58B, 58C, 58D, 58E are different from each other.

[0097] As shown in [Fig. 5], the summation of the primary continuous spectra oA, oB, oC, oD, oE of the primary sources 58A, 58B, 58C, 58D, 58E forms the continuous measurement spectrum om. The primary sources 58A, 58B, 58C, 58D, 58E are selected such that the continuous measurement spectrum om exhibits a profile that is substantially closer to the reference spectrum of the reference illuminant than each of the individual primary spectra oA, oB, oC, oD, oE taken alone.

[0098] Thus, one of the primary light sources is, for example, a white LED which has an oA spectrum as shown in [Fig.4].

[0099] A second primary light source is, for example, formed by a primary light source 58B whose spectrum oB has a peak at a wavelength that presents a dip in the spectrum oA of the first primary light source 58A. In the case of a white LED, the dips appear around 405 nm, before the peak, at 450 nm and around 680 nm. Thus, the second primary light source 58B preferably has an emission peak in the vicinity of at least one of these wavelengths.

[0100] For example, the second primary light source 58B has an emission peak around 405 nm. The second primary light source 58B is, for example, an LED, as shown in [Fig. 3].

[0101] To best approximate the reference gold spectrum of the reference illuminant, the measurement light source 58 preferably comprises more than two primary light sources exhibiting different light spectra.

[0102] Preferably, the measuring light source 58 thus comprises a third primary light source 58C which has an emission peak around 450 nm. The third primary light source 58C is, for example, an LED.

[0103] Preferably, the measuring light source 58 also includes a fourth primary light source 58D which has an emission peak around 680 nm. The fourth primary light source 58D is, for example, an LED.

[0104] To balance the intensities of the different wavelengths in the measurement spectrum, the device 56 includes at least one electronic control unit 59 for the light intensity emitted by each primary light source 58A, 58B, 58C, 58D, 58E. The electronic control unit 59, for example, controls the electrical power supplied to each primary light source 58A, 58B, 58C, 58D, 58E so that it emits a light beam at an intensity that allows the measurement spectrum to approximate the reference spectrum as closely as possible.

[0105] When the maximum intensity provided by a primary light source 58A, 58B, 58C, 58D, 58E is insufficient to properly approximate the reference spectrum, the measuring light source 58 may also comprise at least two primary light sources 58A, 58E that exhibit the same primary light spectrum oA, oE. This makes it possible to increase the intensity of the measuring light beam 55 for the wavelengths of said primary light spectrum oE so that the measuring spectrum om is closer to the reference spectrum of the reference illuminant.

[0106] In the embodiment shown in [Fig.3], the measuring light source 58 thus includes a second white LED.

[0107] As shown in [Fig.5], the superposition of the different spectra oA, oB, oC, oD, oE of the primary light sources 58A, 58B, 58C, 58D, 58E allows us to obtain a measurement beam 55 presenting a measurement spectrum om whose profile approaches the reference spectrum or of the reference illuminant.

[0108] Depending on the requirements, it is possible to extend the measurement spectrum om of the measurement light source 58 beyond the visible range, for example into the near-infrared range, located between 780 nm and 1600 nm, by adding an additional primary light source whose light spectrum extends at least partly into the near-infrared range.

[0109] As shown in [Fig. 3], the measurement light beam 55 is emitted perpendicularly to the wall 16 of the preform 12. The light beam 55 of measurement is emitted in such a way as to pass through the preform 12 by passing through its main "X" axis.

[0110] The measurement light beam 55 is more particularly emitted along an axis which is perpendicular to a tangent to the path 34 of production of the preform 12 in the measurement “Z” zone.

[0111] The measuring light beam 55 passes through the wall 16 at a determined height “h”.

[0112] The measuring light beam 55 can be guided in the correct direction by an optical guiding means such as an optical fiber 60.

[0113] The device 56 for measuring the absorption spectrum "o(Xl)" in the visible light range further includes a spectrometer 62 which measures the intensity "I" as a function of the wavelength "XI" of the spectrum "oO" of the measurement light beam 55 after passing at least once through the wall 16 of the body 14 of the preform 12, as shown in [Fig.6].

[0114] The spectrometer 62 is arranged here to measure the intensity "I" of the measurement light beam 55 on the other side of the preform 12 with respect to the axis "X" of the preform 12 after it has passed twice through the wall 16 at two diametrically opposite points, at the same height "h" of the preform 12.

[0115] In an alternative embodiment of the invention, not shown, the spectrometer is arranged to measure the intensity of the measurement light beam after it has passed through the wall of the preform only once. In this case, a light beam interceptor is introduced into the preform, the interceptor guiding the intercepted light beam to the spectrometer.

[0116] The spectrometer 62 thus makes it possible to obtain the measured absorption spectrum “o(Xl)” shown in [Fig.6].

[0117] According to an example of use of the measurement carried out, the power of the heating electromagnetic radiation is modified according to the absorption spectrum "o(Xl)" measured by the electronic control unit 54.

[0118] The measured absorption spectrum “o(Xl)” is used for example to calculate the color parameters of the wall 16 of the preform 12 in a determined color space.

[0119] By way of non-limiting example, such a color space is here formed by the CIELAB color space as defined by ISO 11664-4:2019, sometimes referred to as "L*a*b* CIE 1976".

[0120] In an unshown variant of the invention, the determined color space may be another standardized color space equivalent to the CIELAB color space, such as the CIE RGB color space, defined by ISO 61966-2-1:2003, or the CIE XYZ color space, defined by ISO 11664-3:2019, or the space The CIE 1976 L*u*v* color space, defined by ISO 1164-5:2016, or the CIE U'V'W' color space. A color space is "equivalent" to the CIELAB color space when there is a bijection that allows easy conversion from one space to the other.

[0121] Three parameters characterize colors in the CIELAB color space. Lightness L* is derived from luminance. The two parameters a* and b* express the difference in color from that of a gray surface of the same lightness. A gray, uncolored, achromatic surface is illuminated by a reference light, which is defined here as standardized daylight D65 according to ISO 23603:2005.

[0122] The parameters of the L*a*b* system are as follows:

[0123] - the brightness L* which takes values ​​between 0, corresponding to black, to 100, corresponding to white;

[0124] - a* represents the value on an axis ranging from green to red;

[0125] - b* represents the value on an axis ranging from blue to yellow.

[0126] According to ISO 11664-4:2019, the different parameters are calculated as a function of the transmission factor T(X1) for each associated wavelength.

[0127] In particular, the luminous intensity '10' at which the measurement beam 55 is emitted as a function of the wavelength 'XI' is a known value. The luminous intensity '10' at which the measurement beam 55 is emitted can also be measured directly by the spectrometer 62 when no preform 12 passes through the measurement zone 'Z', as shown by the dashed curve in [Fig. 6].

[0128] After passing twice through the wall 16 of the preform 12, the luminous intensity of the measurement beam 55 is attenuated. The measurement beam 55 then has a luminous intensity known as the "transmitted luminous intensity 'Il'", as represented by the solid curve in [Fig. 6].

[0129] Thus, it is easy to deduce the transmission factor of the wall 16 of the preform as a function of the wavelength in the visible light range by calculating the ratio between the luminous intensity "10" of emission and the luminous intensity "Il" transmitted.

[0130] Each parameter in the determined chromatic space, such as the CIELAB space, is then calculated as a function of the transmission factor T(X1) and the associated wavelength "XI".

Claims

Demands

1. Device (56) for on-the-fly measurement of the absorption spectrum (o(Xl)) in the visible light range of at least one wall (16) of preforms (12) intended to be transformed into final containers by forming, in particular by stretch blow molding. The device (56) for measuring the absorption spectrum (o(Xl)) comprises: - means (36) for conveying preforms (12) in a line along a production path (34) passing through a measurement zone (Z), - a measurement light source (58) that emits a measurement light beam (55) according to a continuous measurement spectrum (om) that extends at least into the visible range, - a spectrometer (62) measuring the intensity (I) and wavelength (XI) of the first light beam (55) after passing through at least one thickness of the wall (16) of the preform (12) during its passage in the associated measurement zone (Z), characterized in that the measurement light source (58) comprises at least two sources (58A, 58B, 58C,58D) primary light sources, each emitting a primary light beam according to an associated continuous spectrum (oA, oB, oC, oD) extending at least into the visible range, the primary continuous spectra (oA, oB, oC, oD) of said primary sources (58A, 58B, 58C, 58D) being different and their light beams being merged to form said measurement light beam (55).

2. Device (56) according to the preceding claim, characterized in that the summation of the primary continuous spectra (oA, oB, oC, oD) of said primary sources (58A, 58B, 58C, 58D) forms the continuous measurement spectrum (om), the primary sources (58A, 58B, 58C, 58D) being selected so that the continuous measurement spectrum (om) has a profile that is substantially closer to the reference spectrum (or) of a reference illuminant than each of the primary spectra (oA, oB, oC, oD) taken alone.

3. Device (56) according to the preceding claim, characterized in that the reference illuminant is illuminant D65 as defined by ISO 11664-2:2022.

4. Device (56) according to any one of the preceding claims, characterized in that the measuring light source (58) comprises more than two sources (58A, 58B, 58C, 58D) primary lights all exhibiting different light spectra (oA, oB, oC, oD).

5. Device (56) according to any one of the preceding claims, characterized in that the measuring light source (58) comprises at least two primary light sources (58A, 58E) which have the same primary light spectrum (oA, oE) so as to increase the intensity of the measuring light beam (55) for the wavelengths of said light spectrum (oA, oE) so that the measuring spectrum (cm) is closer to the reference spectrum (or) of the reference illuminant.

6. Device (56) according to any one of the preceding claims, characterized in that each primary light source (58A, 58B, 58C, 58D, 58E) is formed by a luminescent semiconductor component.

7. Device (56) according to any one of the preceding claims, characterized in that the primary light beams are fused by means of at least one optical coupler (61).

8. Device (56) according to any one of the preceding claims, characterized in that it comprises a primary light source which emits at least partly in the near-infrared range.

9. Device (56) according to any one of the preceding claims, characterized in that it comprises at least one electronic unit (59) for controlling the light intensity emitted by each primary light source (58A, 58B, 58C, 58D, 58E).

10. Device (56) according to any one of the preceding claims, characterized in that the preforms (12) are made of a thermoplastic material, in particular PET.

11. Installation (10) comprising means (36) for conveying preforms (12) in a line along a predetermined production path (34) passing successively through a heating zone (42) for a body (14) of the preforms (12) and through a station (32) for forming the preforms (12) into a container (11), in particular by stretch blow molding, the installation (10) comprising the device (56) according to any one of the preceding claims.

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