Method for controlling a forming unit

Abstract

The invention relates to a method for controlling a forming unit of a facility for manufacturing containers by forming, in particular by stretch blow-moulding, preforms made of thermoplastic material. The preforms pass through a thermal conditioning unit in which the preforms are exposed to heating electromagnetic radiation, and a forming unit in which each preform is placed in a mould of a blow-moulding station. The preform is then subjected to a stretching force by an elongation rod and to at least one pressure of a forming fluid. The method comprises at least the following steps: a first step (E1) of measuring the absorption spectrum and / or the emission spectrum of a wall of the preform before entering the forming unit; a second step (E2) of determining at least one blow-moulding parameter based on the measurement of the absorption spectrum and / or the emission spectrum from the first step (E1); a third step (E3) of application, in which the blow-moulding parameter is applied to the blow-moulding station.

Description

Method of controlling a forming unit Technical field of the invention

[0001] The invention relates to a method for controlling a forming unit of an installation for manufacturing containers by forming, in particular by stretch-blow molding, preforms made of thermoplastic material, as well as a method for creating a database for implementing said control method and in which at least one blowing parameter is associated with at least one absorption spectrum of a preform and in particular the color of the preform. State of the art

[0002] The invention relates to the field of manufacturing hollow bodies made of thermoplastic material, for which a preform is first produced by injection. The preform is then formed into a container in a container manufacturing installation.

[0003] To do this, the container manufacturing facility includes a thermal conditioning unit also called an oven, in which the preform is thermally conditioned, and a blowing unit to obtain the final container where the container is formed from the preform by a blowing operation or by stretch blowing operations.

[0004] The term "hollow body" means a container preform, or a final container, or possibly an intermediate container, that is to say any type of hollow body comprising a body from which an emerging tubular neck extends.

[0005] In the remainder of the document, the term preform will be used preferably and in a non-limiting manner.

[0006] The preform generally has a tubular cylindrical body which is closed at one of its axial ends and which is extended at its other end by a neck, also tubular.

[0007] The neck extends axially from an annular main collar which is arranged at the junction of the neck and the body of the preform, to an annular lip also called a rim, which delimits an axial opening of the neck.

[0008] The body of the preform is required to undergo plastic deformation to form the final container during the blowing operation. To be able to carry out this blowing operation, it is necessary for the body of the preform to be brought to a temperature higher than the glass transition temperature of the material. For this purpose, the preform is thermally conditioned by circulating it inside an oven, by means of a conveyor device following a heating path. The oven includes heating means which are, for example, constituted by infrared lamps or laser diodes in front of which the preforms move thanks to the conveyor device.

[0009] When moving in the oven, the preform is advantageously rotated around its main axis in order to homogenize the heating.

[0010] Sometimes the preforms are made of a material with a tint.

[0011] This tint can be achieved intentionally by adding colorant to dye the preform a desired color to obtain a colored container.

[0012] This tint can also be experienced involuntarily and uncontrolled, for example when the preform is made of a plastic material consisting at least in part of recycled plastic material. This is the case, for example, when the preform is made of recycled polyethylene terephthalate (rPET). In this case, the preform has a more or less dark tint depending on the quality and quantity of recycled material incorporated in the composition of the thermoplastic material that constitutes it.

[0013] The applicant noted that, in both cases, the color of the plastic material is likely to influence the temperature of the wall of the preform when it is exposed to heating radiation, whether produced by infrared lamps or laser diodes.

[0014] Indeed, the heating radiation has a spectrum that extends at least partly 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, and thus modify the specifications of the container, in particular the material distribution on the wall of the container.

[0015] In order to overcome this drawback, manufacturing processes have already been devised in which the color of the preform is measured, more precisely the absorption and / or emission coefficient of the preform in the infrared range is measured, and the preforms having a non-compliant color are ejected. Alternatively, the heating and / or blowing parameters are adapted according to said measured absorption and / or emission coefficient. This is the case in particular of documents DE102021134262, DE102021119650 and EP2236268.

[0016] However, these prior art methods do not make it possible to provide containers of sufficient quality unless a large amount of waste is produced, corresponding to preforms ejected due to non-conformity of the color.

[0017] One of the aims of the invention is therefore to overcome these drawbacks by proposing a method for controlling a forming unit of a container manufacturing installation by forming, of simple and inexpensive design, and providing good quality of the containers whatever the color of the preforms.

[0018] For this purpose, and in accordance with the invention, a method is proposed for controlling a forming unit of a container manufacturing installation by forming, in particular by stretch-blow molding, preforms made of thermoplastic material, the preforms being transported along a production path which passes through a thermal conditioning unit in which the preforms are exposed to heating electromagnetic radiation and the forming unit in which each preform is placed in a mold of a blowing station, said preform is then subjected to a stretching force by an elongation rod and to at least one pressure of a forming fluid, said method comprising at least:

[0019] a first step of measuring the absorption spectrum and / or the emission spectrum and / or measuring the absorbance and / or measuring the transmittance of a wall of the preform before entering said forming unit, i.e. upstream of the forming unit, before the thermal conditioning unit, in the thermal conditioning unit or between the thermal conditioning unit and the forming unit;

[0020] a second step of determining at least one blowing parameter as a function of the measurement of the absorption spectrum and / or the emission spectrum and / or the absorbance and / or the transmittance of the first step;

[0021] a third application step during which said blowing parameter is applied to the blowing station; said method being remarkable in that the method comprises at least one prior step of constituting a database in which at least one blowing parameter is associated with at least one absorption spectrum and / or at least one emission spectrum of a preform, said step comprising at least the following steps of:

[0022] i) Measurement of the absorption spectrum of reference preforms;

[0023] ii) Blowing each reference preform with at least one predetermined blowing parameter;

[0024] iii) Measurement of the wall thickness of the container obtained from the reference preform with said at least one determined blowing parameter;

[0025] iv) Comparison of said measured thickness with a reference thickness, said reference thickness corresponding to a desired thickness,

[0026] v) recording in a database at least one blowing parameter as a function of the measured absorption spectrum if said measured thickness is substantially equal to the reference thickness;

[0027] vi) if said measured thickness is different from the reference thickness, repeating steps i) to v) by modifying at each iteration the at least one blowing parameter until the measured thickness is substantially equal to the reference thickness

[0028] and in that the second step consists of analyzing said measured absorption spectrum and comparing it with reference absorption spectra and / or emission spectra from one of the previously constituted database in which at least one blowing parameter is associated with at least one determined reference absorption spectrum.

[0029] Preferably, said third step applies to the blowing station corresponding to said measured preform.

[0030] Alternatively, the said third step applies to all forming stations.

[0031] Furthermore, preferably, said blowing parameter is chosen from at least a pre-blowing start time, a pre-blowing flow rate, a pre-blowing duration, a pre-blowing pressure, a stretching start time and / or a stretching speed.

[0032] Incidentally, during the second analysis step, the parameters L, a, b of the preform wall are calculated in a determined chromatic space equivalent to the CIELAB chromatic space as defined by the ISO 11664-4:2019 standard from the measured absorption spectrum, at least one blowing parameter being associated with a value of the parameters L, a, b.

[0033] Another subject of the invention relates to a forming station of an installation for manufacturing containers by forming, in particular by stretch-blow molding, preforms made of thermoplastic material, the preforms being transported along a production path which passes through a thermal conditioning unit in which the preforms are exposed to heating electromagnetic radiation and a forming unit in which each preform is placed in a mold of a blowing station, said preform is then subjected to a stretching force by an elongation rod and to at least one pressure of a forming fluid; said installation being remarkable in that the device comprises at least:

[0034] - a means for measuring the absorption spectrum and / or the emission spectrum of a wall (7) of the preform before entering said forming unit (18), i.e. downstream of the thermal conditioning unit (16), in the thermal conditioning unit (16) or between the inlet (25) and the outlet (27) of the thermal conditioning unit (16);

[0035] - a control unit (84) determining at least one blowing parameter as a function of the measurement of the absorption spectrum and / or the emission spectrum carried out by the measuring means, said control unit (84) analyzing said measured absorption spectrum and comparing it with absorption spectra and / or reference emission spectra from a previously constituted database (88) in which at least one blowing parameter is associated with at least one determined reference absorption spectrum.

[0036] A final subject of the invention relates to a computer program product for controlling a forming unit of a container manufacturing installation by forming, in particular by stretch-blow molding, preforms made of thermoplastic material, the preforms being transported along a production path which passes through a thermal conditioning unit in which the preforms are exposed to heating electromagnetic radiation and a forming unit in which each preform is placed in a mold of a blowing station, said preform is then subjected to a stretching force by an elongation rod and at least one pressure of a forming fluid, remarkable in that it comprises at least:

[0037] - an algorithm for reading a measurement signal of the absorption spectrum and / or the emission spectrum of a wall (7) of the preform;

[0038] - an algorithm for determining at least one blowing parameter as a function of the algorithm for reading a measurement signal of the absorption spectrum and / or the emission spectrum produced by the measuring means. Brief description of the figures

[0039] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which one will refer to the appended drawings which we describe briefly below.

[0040] is a schematic general view of a container production facility seen from above;

[0041] is a detail view of the medallion representing a preform;

[0042] is a schematic sectional view partially showing a molding unit within the container production facility of the;

[0043] is a schematic general view of a container production installation seen from above showing a control unit of the installation and two measuring devices located, one at the inlet of the thermal conditioning unit and the other at the outlet of the forming unit;

[0044] is a schematic view representing a device for measuring the absorption spectrum and / or the emission spectrum and / or for measuring the absorbance and / or for measuring the transmittance of walls of a preform circulating in the installation

[0045] is a block diagram representing the different stages of the control process;

[0046] is a block diagram representing the different sub-steps of the second step of the control process;

[0047] is a block diagram representing the different stages of the process of constituting a database in which at least one blowing parameter is associated with at least one absorption spectrum of a preform. Detailed description of the invention

[0048] In the remainder of the description, elements having an identical structure or similar functions will be designated by the same reference.

[0049] The longitudinal, vertical and transverse orientations will be adopted without limitation with reference to the trihedron (L, V, T) shown in the figures.

[0050] By convention, the longitudinal and transverse directions are determined in a fixed manner relative to the molding devices so that the open or closed position occupied has no effect on said orientations.

[0051] The terms "front" and "rear" will also be used, without limitation, in reference to the longitudinal orientation, as well as "upper" and "lower" in reference to the vertical orientation and finally "left" or "right" and "inner" or "outer" in reference to the transverse orientation.

[0052] A schematic representation of an installation 1 for the mass production of containers 2 made of thermoplastic material from preforms 4 is shown.

[0053] In the remainder of the description, the preforms 4 and the containers 2 move in the production facility along a production path from upstream to downstream. The preforms 4 are moved in a row along a production path T by conveying means which will be detailed later.

[0054] In a non-limiting manner, the containers here are bottles. The thermoplastic material is for example formed by polyethylene terephthalate, hereinafter referred to by its acronym "PET".

[0055] Such a preform 4, with reference to the, has a main axis "X" shown vertically in the figure. It has a cylindrical body 6 with a tubular wall 7 closed at one of its axial ends by a bottom 8, and which is open at its other end by a neck 10, also tubular. The neck 10 is delimited downwards by a collar 12 and upwards by an upper end edge called a drinking rim 14.

[0056] The neck 10 generally has its final shape while the body 6 of the preform is intended to undergo a relatively significant deformation to form the final container 2 during a forming step.

[0057] As shown in the, the container manufacturing installation 1 comprises at least one thermal conditioning unit 16, one forming unit 18.

[0058] The thermal conditioning unit 16, also called an oven, makes it possible to heat a succession of preforms to a reference temperature. The reference temperature is chosen so that the body of each preform at the outlet of the thermal conditioning unit 16 is in a malleable state allowing deformation of the body 6 of the heated preform in order to form the container 2 in the forming unit. The reference temperature is between the glass transition temperature and the crystallization temperature of the plastic material of the preform. In the case of PET, the reference temperature is, for example, close to 110°. The value of the reference temperature may vary depending on the product with which the container will be filled or depending on the container filling technique. Thus, the reference temperature is different for hot filling or for a carbonated product, for example.

[0059] According to the embodiment shown in the, the thermal conditioning unit 16 is a scroll oven, in which the preforms 4 are transported to be exposed to a plurality of heating radiation sources 22.

[0060] For this purpose, the thermal conditioning unit 16 comprises a means for conveying the preforms circulating along a frame 23 through the thermal conditioning unit along a heating path extending between an inlet 25 and an outlet 27 of the thermal conditioning unit defining a trajectory T.

[0061] The conveying means comprises a plurality of conveying devices 26 capable of receiving a preform by fitting its neck.

[0062] The oven also comprises a heating cavity which comprises two side walls 36 facing each other and at least one of these walls being the one which supports several radiation sources 22, arranged one above the other and one next to the other opposite the preforms.

[0063] In other words, the thermal conditioning unit 16 comprises a plurality of radiation sources 22 distributed along the path of the trajectory T and at a height corresponding substantially to the height of the preforms so that the entire height of the body of each preform is exposed to the radiation sources on the path of the preform in the thermal conditioning unit. By rotating the preforms around their main axis X, the conveying devices 26 make it possible to uniformly expose the entire body 6 of the preforms to the radiation sources 22. In this particular embodiment, the radiation sources 22 are distributed on only one side of this path, and a reflective wall 38 is arranged on the other side of the heating path to reflect the heat towards the preforms.

[0064] In another embodiment not shown, the radiation sources 22 can be distributed on either side of the heating path without departing from the scope of the invention.

[0065] It should also be noted that the radiation sources 22 are arranged, where appropriate, so as not to subject the neck 10 to the heat emitted by the radiation sources. Indeed, as indicated previously, only the body 6 of the preform 4 is heated to produce the container. Consequently, the neck 10 must not be deformed during forming and must not be heated. To avoid heating the neck 10, the furnace may comprise a ventilation device, not shown in the figures, positioned in line with the necks 10 to evacuate the heat likely to be absorbed by said necks 10.

[0066] Each radiation source 22 is formed by an incandescent lamp emitting infrared radiation.

[0067] In another embodiment, each radiation source 22 is a laser diode emitting infrared radiation.

[0068] In other words, each radiation source 22 is a laser (for example laser diodes) emitting in the infrared and organized by juxtaposition and / or superposition to form one or more matrices.

[0069] In another embodiment, each radiation source 22 is a microwave generator.

[0070] It is obvious that the radiation sources 22 may consist of any radiation source well known to those skilled in the art, or a combination of these radiation sources without departing from the scope of the invention.

[0071] Then, once the preform 4 has been thermally conditioned in the thermal conditioning unit 16, it is transferred to the forming unit 18 to be formed there.

[0072] The unit 18 for forming containers 2 from preforms 4 consists of a forming wheel 42 rotating a plurality of blowing stations 44 from an inlet to an outlet, at which a succession of containers are formed from the preforms, then are extracted, as shown in the. The axis of rotation of the forming wheel is, for example, substantially parallel to the main axis X of the preforms when they are transported by the forming wheel.

[0073] Each blowing station 44 comprises a mold 46 provided with walls forming a molding cavity having the shape of the container to be formed and arranged to receive a preform so that the body of the preform extends into the molding cavity.

[0074] As shown in the, each blowing station 44 further comprises:

[0075] - the mold 46 comprising two half-molds 48, 50 articulated around a hinge and a bottom 52;

[0076] - a housing 54 defining a nozzle 56 which, during the manufacture of the container 2, cooperates with the neck 10 of the preform 4.

[0077] - an elongation rod 58 mounted to slide in the nozzle 56, as well as relative to the mold 46 along a main axis A (generally of revolution) thereof, between a high position allowing the introduction of the preform 4 into the mold and a low position where, at the end of the stretching of the preform 4, the rod 58 reaches the bottom of the mold 52, pressing the bottom 8 of the preform there,

[0078] The blowing station 44 further comprises several fluid circuits opening into the nozzle 56 via the housing 54, namely:

[0079] - a medium pressure pre-blowing air circuit 60 (between 5 and 16 bars), this circuit 60 comprising a source 62 of pre-blowing air and a conduit 64 (which can be formed at least partially in the housing 54) connecting this source 62 to the nozzle 56 with the interposition of a first solenoid valve 66, called the pre-blowing solenoid valve,

[0080] - a high-pressure blowing air circuit 68 (between 30 and 40 bars), comprising a source 70 of blowing air and a conduit 72 (which can be formed at least partially in the housing 54) connecting this source 70 to the nozzle 56 with the interposition of a second solenoid valve 74, called the blowing solenoid valve,

[0081] - a degassing circuit 76 comprising a vent 78 and a conduit 80 connecting the nozzle 56 to this vent 78 with the interposition of a third solenoid valve 82, called the degassing solenoid valve.

[0082] The solenoid valves 66, 74, 82 are electrically connected to a control unit 84 which controls their opening and closing (taking due account of their response times).

[0083] This control unit 84 notably comprises a calculator 86 (or processor), a database 88, a console (or graphical interface) for interaction with an operator, and at least one device 92 for measuring the thickness of the formed container.

[0084] The manufacture of a container 2 from a preform 4 is carried out as follows.

[0085] The preform 4 is first introduced into the oven where it is heated under the conditions described above. Upon leaving the oven, the preform 4 is gripped by a clamp of a transfer wheel and introduced into a previously opened mold. In this position, the elongation rod 58 is in the high position.

[0086] As the carousel rotates, the mold closes over the preform 4 and begins a forming cycle.

[0087] The forming cycle is repeated for each blowing station 44. It comprises at least one step of injecting a pressurized fluid into the preform 4, followed by a depressurization step.

[0088] More specifically, a training cycle includes:

[0089] - a first phase, called pre-blowing, consisting of injecting a fluid into the preform under a pre-blowing pressure, by placing the nozzle 56 in communication with the source 62 of air at the pre-blowing pressure to radially stretch the body of the preform. For this purpose, the control unit 31 commands, via its actuator, the opening of the pre-blowing solenoid valve 66, at a pre-blowing start time, with a pre-blowing flow rate, a pre-blowing duration, and a pre-blowing pressure, i.e. part of the blowing parameters;

[0090] -substantially simultaneously with this first phase, a stretching phase during which a free end of the elongation rod 58 is inserted coaxially into the body of the preform by its neck 10 to the bottom of the mold to axially stretch the body of the preform, at a stretching start time and / or with a stretching speed to arrive at a low position, that is to say another part of the blowing parameters.

[0091] At the end of pre-blowing, container 2 is not completely formed but the material has reached the walls of the mold without closely following the reliefs;

[0092] - a second phase, called blowing, consisting of injecting into the unfinished container 2, a fluid under a blowing pressure, by placing the nozzle 56 in communication with the source 70 of air at the blowing pressure to press the wall of the preform against the mold 46. To this end, the control unit 31 commands, via their respective actuators, the opening of the blowing solenoid valve 74 and the closing of the pre-blowing solenoid valve 66. At the end of the second phase, the container 2 is completely formed, the material intimately matching the reliefs of the wall of the mold 46;

[0093] - a third phase, called depressurization, which optionally includes a step called recovery consisting of depressurizing the container 2 by placing the nozzle 56 in communication with a recovery tank (not shown) and / or a degassing step consisting of completely depressurizing the container 2, in this case by placing the nozzle 56 in communication with the open air; to this end, the control unit 31 commands, via its actuator, the closing of the recovery solenoid valve 82 and the opening of a solenoid valve (not shown) for venting to the open air.

[0094] As shown in the, the container manufacturing installation 1 comprises a thermal conditioning unit 16, a forming unit 18, and a control unit 84 thereof, comprising in particular a computer 86, a database 88, a console for interaction with the operator (not shown) as well as at least one absorption spectrum measuring device 90 and a thickness measuring device 92.

[0095] The thickness measuring device 92 is placed downstream of the outlet 94 of the forming unit 18 to measure at least one thickness of the container that has just been formed. This measurement is carried out in at least one portion of the body of the container 2. In this embodiment, the measuring device is of the optical type as described in the document EP2726814B1 of the applicant.

[0096] In another embodiment not shown, the thickness measurement sensor can be placed in the mold 46. In this case, the sensor can be of the capacitive type, as described in the applicant's document EP1802446B1.

[0097] To have a good estimate of the material distribution of the formed container, it is advantageous to position several sensors along the height of the measured container.

[0098] The absorption spectrum measuring device 90 is positioned at the level of the inlet 25 in a measurement zone Z of the thermal conditioning unit 16, thus making it possible to have the absorption spectrum of the preforms 4 entering the thermal conditioning unit 16.

[0099] The absorption spectrum measuring device 90 will be detailed later.

[0100] As shown in the figure, the device 90 for measuring the absorption spectrum, particularly in the visible light range, comprises a light source 96 which emits the continuous spectrum light beam 98.

[0101] The light source 96 comprises, for example, a light-emitting diode (LED), a superluminescent diode (SLED) or a lamp. The light beam 98 is emitted perpendicular to the wall 7 of the preform 4. The light beam 98 is emitted so as to preferably pass through the preform 4 via its main “X” axis.

[0102] The light beam 98 is more particularly emitted along an axis which is perpendicular to a tangent of the trajectory T of the preform 4 in the measurement zone “Z”.

[0103] The light beam 98 passes through the wall 7 at a determined height “h”. This height h corresponds to the height of the preform. However, so that the measurement is representative of the section of the preform which will undergo deformation during blowing, the height h preferably corresponds to the body 6 of the preform.

[0104] The light beam 98 can be guided in the right direction by an optical guiding means such as an optical fiber 100 for example. It goes without saying that the optical guiding means may consist of any other equivalent guiding means without departing from the scope of the invention.

[0105] The device 90 for measuring the absorption spectrum in the field of visible light in particular further comprises a spectrometer 102 which measures the intensity as a function of the wavelength of the spectrum of the light beam 98 after having passed through the wall 7 of the body 6 of the preform 4 at least once.

[0106] The spectrometer 102 is here arranged so as to measure the intensity of the light beam 98 on the other side of the preform 4 relative to the axis “X” of the preform 4 after it has passed twice through the wall 7 at two diametrically opposite points, at the same height “h” of the preform 4.

[0107] In a variant of the invention not shown, the spectrometer 102 is arranged so as to measure the intensity of the light beam after it has passed through the wall of the preform 4 once. In this case, a member for intercepting the light beam is introduced into the preform 4 during the first step, the interception member guiding the intercepted light beam to the spectrometer 102.

[0108] The figure represents a block diagram symbolizing the steps of the method for controlling a forming unit of a container manufacturing installation by forming according to the invention.

[0109] The method thus comprises a first step “E1” of measuring the absorption spectrum of the wall 7 of a preform 4, in particular in the visible light range, as described previously with reference to the. This step is carried out before the preform 4 enters the forming unit 18 and preferably before the preform enters the thermal conditioning unit 16.

[0110] The method further comprises a second step “E2” of determining at least one blowing parameter as a function of the measurement of the absorption spectrum of the first step (E1).

[0111] The term "blowing parameter" means a parameter which is chosen from a pre-blowing start time, a pre-blowing flow rate, a pre-blowing duration, a pre-blowing pressure, a stretching start time and / or a speed of the elongation rod, as detailed previously with reference to the.

[0112] A preform model is characterized by a number of specifications such as its mass, dimensions, intrinsic viscosity, water content, colorant, additives, material absorbance or refractive index.

[0113] Some of these specifications influence the absorption spectrum of the preform model and in particular the color.

[0114] Before a new container is put into production on the installation, analyses and measurements are carried out on the preform model that will be blown to form the new container. This preform model is also called a "reference preform".

[0115] Each reference preform has a reference absorption spectrum that characterizes it.

[0116] This reference spectrum is associated with at least one blowing parameter.

[0117] The analyses and measurements of the reference preform are carried out on-site or in the laboratory.

[0118] To implement this process, the control unit of the installation has in its memory all the reference absorption spectra of the reference preforms which will be blown on this installation.

[0119] Alternatively, this second step (E2) consists of analyzing the measured absorption spectrum and comparing it to reference absorption spectra from a database 88 in which at least one blowing parameter is associated with at least one determined reference absorption spectrum;

[0120] The database 88 may initially contain at least one absorption spectrum corresponding to at least one reference preform model that corresponds to at least one given blowing parameter.

[0121] The process of developing this database 88 will be detailed later.

[0122] As an alternative embodiment of the first step, the measurement of the absorption spectrum and / or the emission spectrum is replaced by a measurement of the absorbance and / or a measurement of the transmittance of the wall of the preform.

[0123] This measurement is carried out upstream of the forming unit, before the thermal conditioning unit, in the thermal conditioning unit 16 or between the thermal conditioning unit 16 and the forming unit 18.

[0124] Then, the second step (E2) of determining at least one blowing parameter is carried out as a function of the measurement of the absorbance and / or the transmittance of the first step (E1).

[0125] Finally, a third application step “E3” during which the blowing parameter defined in the second step “E2” is applied to the blowing station to blow the body 6 of the preforms 4 taking into account the color of the preforms 4.

[0126] Alternatively, the represents a block diagram symbolizing the steps of an alternative embodiment of the method for controlling a forming unit of a container manufacturing installation by forming according to the invention.

[0127] In the same way as previously, this method comprises a first step “E1” of measuring the absorption spectrum of the wall 7 of a preform, in particular in the visible light range, as detailed in the description with reference to the. This step is carried out before the preform 4 enters the forming unit 18.

[0128] The second determination step “E2” comprises a first sub-step “E2-1” of analysis of the measured absorption spectrum which is used to calculate the parameters of the color of the wall 7 of the preform 4 in a determined chromatic space, and a second sub-step “E2-2” of determination of at least one blowing parameter as a function of the calculations carried out in the first sub-step.

[0129] By way of non-limiting example, such a color space is here formed by the CIELAB color space as defined by the ISO 11664-4:2019 standard, sometimes referred to as “L*a*b* CIE 1976”.

[0130] Three parameters characterize colors in the CIELAB color space. Lightness L* is derived from luminance. The two parameters a* and b* express the deviation of the color from that of a gray surface of the same lightness. A gray, uncolored, achromatic surface is illuminated by a reference light which is here determined as being standardized daylight D65 according to ISO 23603:2005.

[0131] The parameters of the L*a*b* system are thus:

[0132] - the clarity L* which takes values ​​between 0, corresponding to black, to 100, corresponding to white;

[0133] - a* represents the value on an axis going from green to red;

[0134] - b* represents the value on an axis going from blue to yellow.

[0135] According to ISO 11664-4:2019, the various parameters are calculated based on the transmission factor T(λ1) for each associated wavelength.

[0136] More particularly, the emission light intensity at which the light beam 98 is emitted as a function of the wavelength is a known datum. The light intensity at which the light beam 98 is emitted can also be measured directly by the spectrometer 102 when no preform 4 passes into the measurement zone “Z”.

[0137] After passing twice through the wall 7 of the preform 4, the light intensity of the light beam 98 is attenuated. The light beam 98 then has a light intensity called “transmitted light intensity”.

[0138] Thus, it is easy to deduce the transmission factor of the wall 7 of the preform as a function of the wavelength, particularly in the visible light range, by calculating the ratio between the emission light intensity and the transmitted light intensity.

[0139] Each parameter in the determined color space, such as the CIELAB space, is then calculated as a function of the transmittance and the associated wavelength.

[0140] In a variant of the invention not shown, the determined color space may be another standardized color space equivalent to the CIELAB space such as the CIE RGB color space, defined by the ISO 61966-2-1:2003 standard, or the CIE XYZ color space, defined by the 11664-3:2019 standard, or the CIE 1976 L*u*v* color space, defined by the ISO 1164-5:2016 standard, or the CIE U'V'W' color space. A color space is “equivalent” to the CIELAB space when there is a bijection that allows one to move from one space to the other easily.

[0141] This second determination step “E2” also includes a second sub-step “E2-2” for determining at least one parameter where the color space parameters obtained after the first sub-step are associated with at least one blowing parameter which makes it possible to obtain a container meeting the customer's specifications.

[0142] Then, a third application step “E3” during which the blowing parameter defined in the second step “E2” is applied to the blowing station to blow the body 6 of the preforms 4 taking into account the color of the preforms 4.

[0143] This third step applies to the blowing station 44 corresponding to the preform 4 measured during the first step E1 of the process.

[0144] Furthermore, in the case where, within a given period of time, all the measured preforms have an identical absorption spectrum, then the third step of the method applies simultaneously to all the blowing stations 44 of the installation. This scenario can occur when a new gaylord (storage box) of preforms is loaded into the hopper of the preform feeder which supplies the preforms to the thermal conditioning unit 16.

[0145] For a given preform, that is to say a preform for which the person skilled in the art knows the specifications, he is able to match the forming process allowing the transformation of the preform into a container meeting the customer's specifications.

[0146] Empirically, the person skilled in the art knows that, for an established forming process, the evolution of the color of the preforms, in particular the opacity of the latter, that is to say the shade of gray for example, then the blowing parameters will evolve to maintain the material distribution of the container.

[0147] For example, for a given blowing process, if the preform becomes darker then the container will tend to have more material at its bottom. In this case, to maintain the desired thickness despite the change in color, the person skilled in the art will change at least one blowing parameter, i.e., the pre-blowing pressure and / or the start time of the pre-blowing and / or the pre-blowing flow rate.

[0148] Alternatively, still for a given blowing process, if the preform becomes lighter then the container will tend to have less material at its bottom. In this case, to maintain the desired thickness despite the change in color, the person skilled in the art will change at least one blowing parameter, i.e., the pre-blowing pressure and / or the start time of the pre-blowing and / or the pre-blowing flow rate.

[0149] Larepresents a block diagram symbolizing the steps of a method for constituting a database 88 in which at least one blowing parameter is associated with at least one absorption spectrum of a preform for implementing the method for controlling at least one forming unit of a container manufacturing installation.

[0150] This method of constituting the database 88 comprises at least a first step “i” of measuring the absorption spectrum of reference preforms. This measurement step has already been described previously in the description.

[0151] This method comprises a second step "ii" of blowing each reference preform with at least one predetermined blowing parameter. The operator or the control unit selects at least one blowing parameter to determine the influence of the latter on the blown container, in particular on the thickness.

[0152] This method comprises a third step “iii” of measuring the thickness of the wall of the container obtained from the reference preform with said at least one determined blowing parameter. This measurement of the thickness of the wall of the container is carried out downstream of the forming wheel by a thickness measuring sensor on one or more points of the container.

[0153] This process includes a fourth step "iv" of comparing the measured thickness with a reference thickness. The term "reference thickness" means the thickness corresponding to the customer's specifications or that which the operator wishes to obtain in order to have a quality container.

[0154] This reference thickness is an instruction entered by the operator at the installation control console.

[0155] When the thickness of the measured container corresponds to the reference thickness then this method further comprises a fifth recording step “v” where at least one blowing parameter associated with the measured absorption spectrum or the three parameters characterizing the colors in the CIELAB chromatic space are recorded in a database;

[0156] When the thickness of the measured container does not correspond to the reference thickness then this method comprises a sixth step "vi" then the sequence from the first to the fifth step are repeated by modifying at each iteration, the at least one blowing parameter until the measured thickness is substantially equal to the reference thickness.

Claims

Method for controlling a forming unit (18) of an installation (1) for manufacturing containers (2) by forming, in particular by stretch-blow molding, preforms (4) made of thermoplastic material, the preforms (4) being transported along a production path which passes through a thermal conditioning unit (16) in which the preforms are exposed to heating electromagnetic radiation and the forming unit (18) in which each preform is placed in a mold (46) of a blowing station (44), said preform is then subjected to a stretching force by an elongation rod (58) and to at least one pressure of a forming fluid, said method comprising at least: a first step (E1) of measuring the absorption spectrum and / or the emission spectrum of a wall (7) of the preform before entering said forming unit (18), i.e. upstream of the forming unit, before the thermal conditioning unit,in the thermal conditioning unit (16) or between the thermal conditioning unit (16) and the forming unit (18);a second step (E2) of determining at least one blowing parameter as a function of the measurement of the absorption spectrum and / or the emission spectrum of the first step (E1);a third step (E3) of application during which said blowing parameter is applied to the blowing station (44),characterized in that the method comprises at least one prior step of constituting a database in which at least one blowing parameter is associated with at least one absorption spectrum and / or at least one emission spectrum of a preform,said step comprising at least the following steps of:i) Measuring the absorption spectrum of reference preforms;ii) Blowing each reference preform with at least one predetermined blowing parameter;iii) Measuring the wall thickness of the container obtained from the reference preform with said at least one determined blowing parameter;iv) Comparing said measured thickness with a reference thickness, said reference thickness corresponding to a desired thickness,v) recording in a database the at least one blowing parameter as a function of the measured absorption spectrum if said measured thickness is substantially equal to the reference thickness;vi) if said measured thickness is different from the reference thickness, repeating steps i) to v) by modifying at each iteration,the at least one blowing parameter until the measured thickness is substantially equal to the reference thickness and in that the second step (E2) consists of analyzing said measured absorption spectrum and comparing it with absorption spectra and / or reference emission spectra from the database (88) previously constituted in which at least one blowing parameter is associated with at least one determined reference absorption spectrum., Method according to claim 1 characterized in that said third step (E3) is applied to the blowing station (44) corresponding to said measured preform. Method according to any one of claims 1 or 2, characterized in that said third step applies to all the forming stations (44). Method according to any one of the preceding claims, characterized in that said blowing parameter is chosen from at least a pre-blowing start time, a pre-blowing flow rate, a pre-blowing duration, a pre-blowing pressure, a stretching start time and / or a stretching speed. Method according to any one of claims 1 to 4, characterized in that, during the second analysis step, the parameters L, a, b of the wall (7) of the preform are calculated in a determined chromatic space equivalent to the CIELAB chromatic space as defined by the ISO 11664-4:2019 standard from the measured absorption spectrum, at least one blowing parameter being associated with a value of the parameters L, a, b. Forming station of an installation for manufacturing containers by forming, in particular by stretch-blow molding, preforms made of thermoplastic material, the preforms being transported along a production path which passes through a thermal conditioning unit (16) in which the preforms are exposed to heating electromagnetic radiation and a forming unit (18) in which each preform is placed in a mold (46) of a blowing station (44), said preform is then subjected to a stretching force by an elongation rod (58) and to at least one pressure of a forming fluid, characterized in that the device comprises at least: - a means for measuring the absorption spectrum and / or the emission spectrum of a wall (7) of the preform before entering said forming unit (18), i.e. downstream of the thermal conditioning unit (16),in the thermal conditioning unit (16) or between the inlet (25) and the outlet (27) of the thermal conditioning unit (16);- a control unit (84) determining at least one blowing parameter as a function of the measurement of the absorption spectrum and / or the emission spectrum carried out by the measuring means, said control unit (84) analyzing said measured absorption spectrum and comparing it with reference absorption spectra and / or emission spectra from a previously constituted database (88) in which at least one blowing parameter is associated with at least one determined reference absorption spectrum., Product Computer program for controlling a forming unit of a container manufacturing facility by forming, in particular by stretch-blow molding, preforms made of thermoplastic material, the preforms being transported along a production path which passes through a thermal conditioning unit (16) in which the preforms are exposed to heating electromagnetic radiation and a forming unit (18) in which each preform is placed in a mold (46) of a blowing station (44), said preform is then subjected to a stretching force by an elongation rod (58) and to at least one pressure of a forming fluid, characterized in that it comprises at least: - an algorithm for reading a signal for measuring the absorption spectrum and / or the emission spectrum of a wall (7) of the preform;- an algorithm for determining at least one blowing parameter as a function of the algorithm for reading a measurement signal of the absorption spectrum and / or the emission spectrum produced by the measuring means by analyzing said measured absorption spectrum and comparing it with reference absorption spectra and / or emission spectra from a previously constituted database (88) in which at least one blowing parameter is associated with at least one determined reference absorption spectrum.;

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