Method for regulating a container production plant

Abstract

Title: Method for regulating a container production plant. The present invention relates to the field of manufacturing containers, such as bottles or flasks, by blow molding or stretch blow molding from preforms made of thermoplastic material, such as polyethylene terephthalate, also known as "PET". Its object is a method for molding containers from preforms by blow molding or stretch blow molding and a plant implementing such a method.

Description

Title of the invention: Method for regulating a container production facility Technical field

[0001] The present invention relates to the field of manufacturing containers, such as bottles or flasks for example, by blow molding or stretch blow molding from preforms made of thermoplastic material, such as for example polyethylene terephthalate known as "PET". Its subject is a method of molding by blow molding or stretch blow molding containers from preforms and an installation implementing such a method. State of the art

[0002] In the field of manufacturing such containers, it is well known that the latter are manufactured through an installation comprising at least one heating unit and a forming unit equipped with a succession of molds with the imprint of the container model to be formed and corresponding injection devices.

[0003] More specifically, the manufacture of these containers comprises two main phases, namely a first phase called preform heating, during which a succession of preforms is heated in the heating unit to a reference temperature at which the preforms are in a malleable state in which they can be formed, and a second phase called forming, during which the heated preforms are each transferred into a mold of the blowing unit and a pressurized fluid is injected into each preform by the injection device also called the corresponding nozzle to give the preform the final shape of the container. The pressurized fluid is usually a gas, such as air.Furthermore, forming generally includes a stretching phase carried out by means of a movable stretching rod arranged to apply a stretching force to the bottom of a preform in a mold in order to stretch the preform along its axis, which helps to keep the preform centered relative to the mold.

[0004] In addition, a production facility for these containers generally comprises a control console from which numerous parameters can be manually adjusted by an operator to control the heating unit and / or the forming unit. With regard to the heating unit, said parameters consist, for example, of the heating power, the machine rate which modifies the speed of movement of the preforms in the heating unit, the power of a ventilation system ensuring the evacuation of part of the heat in the heating unit; the temperature profile of the preferential heating, etc. With regard to the forming unit, said parameters consist, for example, of pre-blowing pressure, pre-blowing start, pre-blowing flow rate, stretching speed, blowing pressure, etc.

[0005] The manufacturing process requires numerous preliminary tests before obtaining a container deemed compliant, that is to say a container which meets all the quality criteria previously defined by specifications. The operation is tedious and time-consuming to implement, because it is essential to adjust each of the parameters of the installation and the process in order to guarantee the conformity of the container. In addition, this preliminary step must be carried out for each container format. The format of a container can in particular be defined by the height, the shape, the volume, the material of the latter.

[0006] The development of the manufacturing process and the configuration of the associated installation therefore requires the presence of an operator with good knowledge of the installation, the process, and the models of preforms likely to be introduced into the installation in order to obtain a container conforming to the desired format. This development also requires a significant amount of time, which directly impacts the production volume of the line.

[0007] The resulting container will then be evaluated to determine whether or not it meets the criteria, and this throughout the production phase. For example, a quality criterion for judging the conformity of a container may be the distribution of the material along the height of the container, for a given format. As is known, one of the parameters of the manufacturing process which impacts this criterion is the thermal conditioning of the preforms, when the preforms pass through the heating unit.

[0008] If this material distribution criterion is not deemed to be compliant, the operator must adjust various parameters in order to correct the defect, either during the thermal conditioning phase or during the forming phase, or both. In addition, the modifications made must not lead to the appearance of other defects or problems.

[0009] In this respect, in order to overcome this drawback, a method has already been devised for regulating the heating parameters of the furnace, in particular for regulating the variations in the electrical power of the radiation sources, as a function of the thickness of the wall of the container formed. This is notably the case of European patent EP1998950.

[0010] Document EP1998950 proposes a solution consisting of controlling the material distribution criterion using thickness sensors located one above the other. If this criterion is deemed non-compliant, the power of the heating lamp located at the same height as a sensor will be modified accordingly. The other lamps are not affected and their adjustment is not corrected. Thus, the thermal conditioning of the preform is therefore not completely controlled.

[0011] Furthermore, this modification of the heating parameters of the furnace can lead to a modification of the thermal conditioning of the preform during production and thus cause non-conformity of the formed container with respect to the customer's specifications. Furthermore, the non-conformity of the formed container increases manufacturing costs and may require the shutdown of the installation, further increasing manufacturing costs.

[0012] Also known is document EP2352633 which describes a method and apparatus for blow molding containers. A preform made of a thermoplastic material is first subjected to a heat treatment in the area of ​​a heating section along a conveying path. The preform is then shaped into a container inside a blow mold under the effect of blow pressure. After the container is blow molded, a wall thickness is measured on at least one vertical level of the container. A predefined value for the wall thickness is transmitted to a controller as a desired value, and the measured wall thickness is transmitted to it as an actual value. The controller predefines the amount of at least one parameter influencing the blowing process depending on a difference between the desired value and the actual value.More specifically, the controller predefines the amount of at least one parameter influencing the blowing gas supply. The amount of the parameter is predetermined based on a simulation model of the blowing process implemented in the controller.

[0013] All these solutions are insufficient because they do not allow the operator to optimize the heating phase directly and quickly. The information available to him does not allow the fault to be corrected while avoiding the appearance of other problems, for example at other height levels of the container.

[0014] There is therefore a need to optimize the manufacturing process by simplifying the control of the various stages and the configuration of the installation. In particular, there is a need to better control the preform conditioning phase, in a more targeted manner along the height of the containers, in order to shorten the time required to obtain a first container that conforms to a new format. It is also essential to be able to quickly correct a defect detected during the manufacture of containers and therefore to adjust the various parameters efficiently, so as not to impact the production flow. Disclosure of the invention

[0015] One of the aims of the invention is therefore to remedy these drawbacks by proposing a method making it possible to modify the thermal conditioning of the preforms and / or the forming parameters of the containers without having to stop the production installation and, in doing so, to maintain the quality of the containers produced.

[0016] For this purpose, and in accordance with the invention, a method is proposed for manufacturing containers made of thermoplastic materials by blow molding or stretch blow molding of a preform previously heated in an oven and then placed in a mold consisting of two half-molds delimiting a molding cavity, said preform being blown into the mold, possibly with a pre-blowing step, said steps of heating the preforms, pre-blowing and blowing being controlled by a control unit from various so-called control parameters such as the heating temperature of the preforms in the oven, the blowing pressure in the mold and / or the pre-blowing pressure and / or the pre-blowing flow rate and / or the speed of the stretching rod for example; said method is remarkable in that it comprises a preliminary step called calibration which comprises at least the following steps: - production of containers from initial control parameters to produce compliant containers; - measurement of the thickness of the wall of said containers at the exit of the mold, at at least two different heights, corresponding to the production of containers from said first control parameters, said measurement of the thickness corresponding to a reference thickness; - recording of said reference thickness in a memory unit; - modification of each control parameter; - measurement of the wall thickness of said containers at the outlet of the mold, at at least two different heights, after modification of each control parameter; - recording the wall thicknesses of said containers at the exit of the mold for each modified control parameter modified in said memory unit; - comparison of said recorded measured thicknesses with said reference thickness or with a theoretical thickness; - determination of at least one control parameter providing the greatest variation in the thickness of the container walls.

[0017] After the preliminary step known as calibration, it comprises at least the following steps:

[0018] a) measuring the thickness of the wall of said containers at the outlet of the mold, at at least two different heights;

[0019] b) comparison of the thickness measurements with set values ​​determined for each height of the containers;

[0020] c) if the deviation of the thickness measurements from the determined setpoint values ​​is greater than a determined threshold, modification of at least one of the parameters of control, said modified control parameter(s) being selected from at least one of the control parameters providing the greatest variation in the thickness of the wall of the containers during the calibration step and / or by calculating the theoretical effects of the variation for each parameter on the thicknesses, said theoretical effects of the variation for each parameter defining a theoretical thickness, then by selecting the parameter(s) inducing the smallest difference between the measured values ​​and the theoretical thickness values;

[0021] d) steps a) to c) are repeated until the deviations of the thickness measurements from the determined setpoint values ​​are less than said determined threshold.

[0022] Preferably, step c) comprises at least the following steps:

[0023] - definition, for each parameter, of an optimal reference coefficient chosen among reference coefficients assigned to each zone of thickness of the wall of the containers;

[0024] - memorization of the lower and upper limits as well as the scales for each of said parameters;

[0025] - calculation of an adjustment of each parameter as a function of said coefficient of previously defined optimal reference;

[0026] - calculation of theoretical corrections for each thickness zone as a function of the calculated adjustments and scales;

[0027] - calculation of the theoretical deviation in thickness of the containers as a function of the corrections theoretical calculated for each thickness zone;

[0028] - addition, for each parameter, of said calculated theoretical deviations; and

[0029] - selection of at least one parameter having the highest cumulative deviation value weak.

[0030] Furthermore, prior to the step of selecting at least one parameter, it comprises a step of prioritizing the parameters according to said calculated theoretical deviations.

[0031] Said parameters are hierarchized in an increasing manner, from the lowest cumulative deviation value to the largest cumulative deviation value.

[0032] Preferably, after the step of calculating the adjustments and prior to the step of calculating the theoretical corrections, it comprises an additional step of recalculating the adjustments if the calculated adjustments are not within said limits.

[0033] Furthermore, said theoretical corrections calculated as zero are excluded.

[0034] In addition, the addition of the calculated theoretical deviations is carried out in absolute value.

[0035] Preferably, the parameter selection step is performed after the calculation of a new average thicknesses for each zone and / or that the combination of deviations for each thickness zone has changed.

[0036] Furthermore, a new average of the thicknesses for each zone is calculated at a predetermined frequency.

[0037] Advantageously, the method according to the invention comprises a step of modifying the predetermined correction coefficients of the algorithm so that the thicknesses measured after modification of the control parameter(s) correspond to the theoretical thicknesses that should have been obtained with the previous predetermined coefficients.

[0038] According to a first variant of execution, during said calibration step, each control parameter is modified one by one.

[0039] According to a second variant of execution, during said calibration step, each control parameter is modified simultaneously with at least one other control parameter.

[0040] Furthermore, during said calibration step, each control parameter is modified according to a predetermined incremental value.

[0041] Another object of the invention relates to a computer program product comprising a sequence of instructions which, when the program is executed by a computer, causes the latter to implement the steps of the method according to the invention.

[0042] A third object of the invention relates to a data processing device comprising means for implementing the steps of the method according to the invention.

[0043] A final object of the invention relates to a computer-readable recording medium comprising instructions which, when executed by a computer, cause the latter to implement the steps of the method according to the invention. Brief description of the drawings

[0044] Other advantages and characteristics will emerge more clearly from the following description of a single variant embodiment, given as a non-limiting example, of the method according to the invention, with reference to the appended drawings in which:

[0045] [Fig-1] is a schematic representation, seen from above, of an installation of forming implementing the method according to the invention,

[0046] [Fig.2] is a side view showing a preform for feeding the forming facility of [Fig.l],

[0047] [Fig.3] is a schematic representation of the different stages of forming a container through the forming unit of [Fig.l],

[0048] [Fig.4] is a cross-sectional view of the preform thermal conditioning unit of the forming unit of [Fig.l],

[0049] [Fig.5] is a schematic representation of the step of measuring the thickness of the container wall formed at different heights,

[0050] [Fig.6] is a flowchart of the different stages of the regulation process of the container forming unit according to the invention,

[0051] [Fig.7] is a flowchart of the different calibration steps of the process of regulation of the container forming unit according to the invention. Method of carrying out the invention

[0052] In the remainder of the description of the process for manufacturing thermoplastic containers by blow molding or stretch blow molding of a preform according to the invention, the same numerical references designate the same elements. The different views are not necessarily drawn to scale.

[0053] In the remainder of the description, elements having an identical structure or similar functions will be designated by the same references.

[0054] In the remainder of the description, we will adopt, without limitation, longitudinal orientations directed according to the direction of movement of the hollow body, vertical and transverse orientations indicated by the trihedron "L,V,T" of the figures.

[0055] Hereinafter, the term "holding member" means a gripping member or a support member for a hollow body which is capable of transporting the hollow body from one point to another.

[0056] [Fig.l] shows an installation 1 for forming final containers 2 made of thermoplastic material, such as recycled or non-recycled "PET" (polyethylene terephthalate) or "PP" (polypropylene), from preforms 3. The preforms 3 are generally produced beforehand by injection molding. These preforms 3 are generally cold when they are delivered to the inlet of the forming installation 1.

[0057] In the remainder of the description, the generic term "hollow body" will be used to designate indifferently a preform, a container being formed or a final container.

[0058] The installation 1 comprises several treatment stations. Among the treatment stations commonly fitted to such installations 1, a heating station 4 and a forming station 5 equipped with several molding units 6 mounted on the periphery of a carousel 7 are shown here.

[0059] It will be understood that the installation 1 may include other treatment stations which are not shown here such as a filling station, a labeling station, a capping station, etc.

[0060] Without limitation, this is an installation 1 for continuously forming containers 2. The hollow bodies are thus constantly in motion between their entry into the installation 1 in the form of a preform 3 and their exit in the form of final containers 2. This makes it possible to obtain a higher production rate of containers 2. For this purpose, Installation 1 includes several devices for transporting hollow bodies which are described below.

[0061] Alternatively, the invention is applicable to an installation operating sequentially.

[0062] The installation 1 comprises a first transfer wheel 8 at the inlet of the heating station 4, a second transfer wheel 9 at the outlet of the heating station 4, and a third transfer wheel 10 interposed between the second transfer wheel 9 and the forming station 5. Finally, a fourth transfer wheel 11 is arranged at the outlet of the forming station 5 to transfer the hollow bodies, here the final containers 2, to a conveyor 12 such as a belt or an air conveyor.

[0063] The hollow bodies pass through the installation 1 along a determined production path which is indicated in bold lines in [Fig.l].

[0064] The hollow bodies arrive, in the form of preforms 3, successively one after the other by a ramp 13 which feeds the first transfer wheel 8, forming a first device for transporting the hollow bodies. The first transfer wheel 8 is in the form of a disc 14 whose periphery is equipped with several support notches each forming a member 15 for holding a hollow body. The holding members 15 are thus mounted on the disc 14.

[0065] The disc 14 is rotatably mounted around a central vertical axis "A" in an anticlockwise direction with reference to [Fig.l]. The holding members 15 thus move in a closed circuit of circular shape around the axis "A".

[0066] The hollow bodies, here the preforms 3, are conveyed from the ramp 13 to an inlet of the heating station 4 following the production path. When a hollow body has been transmitted to the heating station 4, the holding member 15 continues its empty movement along the closed circuit to return to its starting point and load a next hollow body. A useful section, shown in bold lines in [Fig.l], of said circuit forms an open section of the production path.

[0067] In a variant of the invention not shown, the members for holding the first transfer wheel are formed by grippers for gripping a hollow body.

[0068] Then the hollow bodies, still in the form of preform 3, are conveyed through the heating station 4 to be heated there prior to the blowing or stretch blowing operations. For this purpose, the heating station 4 is equipped with heating means, such as lamps or diodes 16, emitting electromagnetic radiation to heat the material of the preforms 3, for example infrared radiation at a predetermined power and spectrum which interacts with the material of the preform 3 to heat it. The power and the spectrum are controlled by means of an electronic control unit 17.

[0069] It is obvious that the lamps 16 may be substituted by any other heating means well known to those skilled in the art such as VCEL diodes emitting monochromatic or pseudo-monochromatic electromagnetic radiation in the infrared or even microwave sources for example without departing from the scope of the invention.

[0070] The heating station 4 is also equipped with ventilation means (not shown), such as fans or forced air devices also known by the English name "airblade". The ventilation means participate in regulating the temperature of the hollow body. The ventilation means comprise means for controlling the air flow.

[0071] The setting of each heating means can be controlled to heat certain portions of the hollow body more or less. The setting and in particular the height of each activated heating means is for example automatically controlled by the electronic control unit 17.

[0072] Each hollow body is carried by a rotating mandrel, also called a spinner, which forms a holding member 18 associated with the heating station 4. Such a holding member 18 conventionally comprises a mandrel (not shown) which is fitted into a neck of the hollow body, as well as a pinion meshing with a fixed rack running along the production path so as to ensure substantially uniform rotation of the hollow body during its heating.

[0073] Alternatively, each hollow body is driven in rotation by an individual electric motor. The rotation is then controlled by the electronic control unit 17.

[0074] The holding members 18 are carried by a closed chain which is driven in a clockwise direction by drive wheels 19 which are rotatably mounted around vertical axes "B". This chain of holding members 18 set in motion thus forms a second device for transporting the hollow bodies. Each holding member 18 is here moved continuously, that is to say without interruption, along a closed circuit. A useful section, shown in bold lines in [Fig.l], of said circuit forms an open section of the production path.

[0075] At the outlet of the heating station 4, the hollow bodies, here the hot preforms 3, are then transmitted to the second transfer wheel 9 which has a structure similar to that of the first transfer wheel 8. This second transfer wheel 9 forms a third device for transporting the hollow bodies.

[0076] After the transmission of the hollow body to the second transfer wheel 9, each holding member 18 of the heating station 4 continues its empty path along the closed circuit to return to its starting point and load a new hollow body.

[0077] The second transfer wheel 9 is in the form of a disc 20 whose periphery is equipped with several support notches each forming a member 21 for holding a hollow body. The holding members 21 are thus mounted on the disc 20.

[0078] The disc 20 is rotatably mounted around a central vertical axis "C" in an anticlockwise direction with reference to [Fig. 1]. The holding members 21 thus move in a closed circuit of circular shape around the axis "C".

[0079] The hollow bodies are conveyed from the outlet of the heating station 4 to the third transfer wheel 1 following the production path. When a hollow body has been transmitted to the third transfer wheel 1, the associated holding member 23 continues its empty movement along the closed circuit to return to its starting point and load a new hollow body. A useful section, shown in bold in [Fig.l], of said circuit forms an open section of the production path.

[0080] At the exit of the second transfer wheel 9, hollow bodies, here the hot preforms 3, are transmitted to the third transfer wheel 1. This third transfer wheel 1 forms a fourth device for transporting the hollow bodies.

[0081] Thus, the third transfer wheel 10 is in the form of a central hub whose periphery is equipped with several arms 22 radiating from the hub. The free end of each arm 22 is equipped with a clamp forming a member 23 for holding a hollow body. The hub is rotatably mounted around a central vertical axis "D" in a clockwise direction with reference to [Fig.l]. The holding members 23 thus move in a closed circuit around the axis "D".

[0082] The arms 22 are capable of pivoting around a vertical axis relative to the hub or of extending telescopically to allow the spacing between two hollow bodies to be varied.

[0083] The hollow bodies are thus conveyed from the transfer wheel 9 to the forming station 5 following the production path. When a hollow body has been transmitted to the forming station 5, the associated holding member 23 continues its empty movement along the closed circuit to return to its starting point and load a new hollow body. A useful section, shown in bold in [Fig.l], of said circuit forms an open section of the production path.

[0084] During their transfer to the forming station 5, each hollow body, here in the form of a hot preform 3, is inserted into one of the molding units 6 of the forming station 5. The molding units 6 are driven in continuous and regular movement around the vertical axis "E" of the carousel 7 in an anticlockwise direction with reference to [Fig.l]. The molding units 6 thus move in a closed circuit of circular shape around the axis "E".

[0085] During their forming, the hollow bodies are thus conveyed from the third transfer wheel 10 to the fourth transfer wheel 11. During their conveying, the bodies hollows are transformed into final containers 2 by forming means which will be described schematically later.

[0086] When a container 2 has been transmitted to the fourth transfer wheel 11, the associated molding unit 6 continues its empty movement along the closed circuit to return to its starting point and load a new hollow body. A useful section, shown in bold in [Fig.l], of said circuit forms an open section of the production path.

[0087] At the exit of the forming station 5, the hollow bodies are transmitted, in the form of final containers 2, to the fourth transfer wheel 11 which has a structure identical to that of the transfer wheel 10. This fourth transfer wheel 11 forms a sixth device for transporting the hollow bodies.

[0088] Thus, the fourth transfer wheel 11 is in the form of a disc 24 whose periphery is equipped with several notches, each of which forms a member 25 for holding a hollow body. The holding members 25 are thus mounted on the disc 24.

[0089] The disc 24 is rotatably mounted around a central vertical axis "F" in a clockwise direction with reference to [Fig.l]. The holding members 25 thus move in a closed circuit of circular shape around the axis "F".

[0090] The hollow bodies are thus conveyed from the outlet of the forming station 5 to the conveyor 12 following the production path. When a hollow body has been transmitted to the conveyor 12, the associated holding member 25 continues its empty movement along the closed circuit to return to its starting point and load a new hollow body. A useful section, shown in bold lines in [Fig.l], of said circuit forms an open section of the production path.

[0091] In a variant of the invention not shown, the members for holding the fourth transfer wheel are formed by clamps.

[0092] Thus, with reference to [Fig. 3], each hollow body undergoes different processing steps during its journey along the production path, and in particular a heating step in the heating station 4, followed by a forming step in the forming station 5.

[0093] Generally speaking, such a forming installation 1 is capable of producing final containers 2 of different formats. For this purpose, the molding units 6 equipping the forming station 5 are provided with interchangeable molds. Thus, it is possible to modify the shape of the final container produced.

[0094] Depending on the final container format selected, the installation 1 will be supplied with preforms 3 having suitable intrinsic characteristics.

[0095] As shown in [Fig.2], a preform 3 has a cylindrical body 26 with a tubular wall 27 closed at one of its axial ends by a bottom 28, and which is extended at its other end by a neck 29, also tubular. The neck 29 is generally injected so as to already have its final shape while the body 26 of the preform 3 is intended to undergo a relatively significant deformation to form the final container 2 during the forming step. The preforms 3 here come from recycled or non-recycled "PET" or "PP" material, that is to say that the preform 3 is produced by molding a single thermoplastic material of determined composition.

[0096] Among the characteristics likely to vary from one batch of preforms to another, we will note for example the thickness of the wall 27 of the preform 3, or the rate of absorption of infrared radiation by the thermoplastic material.

[0097] The invention proposes a method for controlling the installation 1 for forming hollow bodies making it possible to automatically adjust the processing parameters of the processing stations as a function of the measurements carried out directly on the containers at the outlet of the forming station, as illustrated schematically in [Fig. 5]. It will be observed that the thickness of the container is measured at at least two different heights by any suitable means well known to those skilled in the art, such as by interferometry sensors for example.

[0098] Thus, the method according to the invention consists of measuring the thickness of the wall of said containers at the outlet of the mold (step 100), at at least two different heights; then comparing (step 200) the thickness measurements with setpoint values ​​determined for each height of the containers and, if the deviation of the thickness measurements with the setpoint values ​​determined is greater than a determined threshold, modifying (step 300) at least one of the control parameters, said modified control parameter(s) being selected at least by calculating the theoretical effects of the variation for each parameter on the thicknesses then by selecting the parameter(s) inducing the smallest deviation between the measured values ​​and the theoretical thickness values ​​and the previous steps are repeated until the deviation of the thickness measurements with the setpoint values ​​determined is less than said determined threshold.

[0099] More precisely, with reference to [Fig.6], the step of modifying (300) at least one of the control parameters comprises at least the following steps:

[0100] - definition (310), for each parameter, of an optimal reference coefficient assigned to each wall thickness zone of the containers;

[0101] - storage (320) of the lower and upper limits as well as the scales for each of said parameters;

[0102] - calculation of an adjustment (330) of each parameter as a function of the coefficient of previously defined optimal reference;

[0103] - a possible recalculation (340) of the adjustments if the calculated adjustments are not within the said limits;

[0104] - calculation of theoretical corrections (350) for each thickness zone as a function calculated adjustments and scales;

[0105] - calculation of the theoretical deviation (360) of thickness of the containers as a function of the theoretical corrections calculated for each thickness zone;

[0106] - addition, for each parameter, of said calculated theoretical deviations (370); and

[0107] - selection of at least one parameter (380) having the highest cumulative deviation value weak.

[0108] Prior to the step of selecting at least one parameter, it comprises a step of ranking the parameters according to said calculated theoretical deviations. Said parameters are ranked in increasing order, from the lowest cumulative deviation value to the largest cumulative deviation value.

[0109] Preferably, the calculated zero theoretical corrections are excluded and the addition of the calculated theoretical deviations is carried out in absolute value.

[0110] Advantageously, the parameter selection step is carried out after the calculation of a new average of the thicknesses for each zone and / or the combination of the deviations for each thickness zone has changed. In this way, the regulation according to the invention makes it possible to correct any deviations in real time without having to stop the production installation and, in doing so, to maintain the quality of the containers produced. A new average of the thicknesses for each zone is calculated at a predetermined frequency. For example, the new average of the thicknesses for each zone is calculated every m bottles removed from the mold and for which the thicknesses have been measured, m being an integer between 30 and 80. For example, m is equal to 50. However, it is obvious that m can be any integer without departing from the scope of the invention.

[0111] It will be observed that, if after n corrections on said selected parameter, n being a predetermined number greater than or equal to 1, the deviation of the thickness measurements with the determined setpoint values ​​is greater than a determined threshold, a new parameter is then selected. Said new selected parameter i+1 corresponds to the hierarchical parameter i+1.

[0112] Furthermore, advantageously the optimal reference coefficients assigned to each zone of thickness of the wall of the containers are variable and are calculated each time a parameter is modified. Said calculation of the optimal reference coefficient assigned to each zone of thickness of the wall of the containers is obtained from the calculation of the actual effect of the adjustment on each zone of thickness of the wall of the containers.

[0113] Preferably, said calculation comprises at least the following steps:

[0114] - Calculation of an offset of the blowing and / or heating parameter by multiplying said initial coefficient by thickness drift;

[0115] - Determination of the new coefficient as a function of the offset applied to the parameter and the actual effect measured on the material distribution of each thickness zone

[0116] It will be observed that such variable optimal reference coefficients make it possible to customize these coefficients according to the environment, the machine, the resin of the preforms, etc.

[0117] Said parameter consists of a parameter of the heating unit such as the heating power at a determined height of the preform and / or the machine speed which modifies the speed of movement of the preforms in the heating unit and / or the power of a ventilation ensuring the evacuation of a part of the heat in the heating unit and / or the temperature profile of the preferential heating, and / or said parameter consists of a parameter of the forming unit such as the value of the pre-blowing pressure and / or the start of the pre-blowing and / or the pre-blowing flow rate and / or the speed of the drawing rod and / or the blowing pressure.

[0118] In a particularly advantageous manner, in order to allow rapid and efficient parameterization of the regulation method according to the invention, the latter advantageously comprises a step of preselecting the parameters from a GUI, according to the English acronym "Graphical User Interface", one or more parameters being associated with a predefined production configuration. For this purpose, the installation comprises at least one display screen, touch-sensitive or not, not shown in the figures, connected to the control unit of the installation.

[0119] For example, the GUI includes at least three predefined production configurations, a so-called process configuration, a so-called application configuration and a so-called options configuration.

[0120] Said so-called process configuration comprises at least three sub-configurations, namely a so-called HR sub-configuration, a so-called CHP sub-configuration and a so-called STD sub-configuration, one or more parameters being associated with each sub-configuration.

[0121] Said so-called application configuration comprises at least three sub-configurations, namely a so-called flat product sub-configuration, a so-called carbonate product sub-configuration and a so-called other product sub-configuration, one or more parameters being associated with each sub-configuration.

[0122] Said so-called options configuration comprises at least three sub-configurations, namely a so-called boxed background sub-configuration, a so-called reusable sub-configuration and a so-called petaloid background sub-configuration, one or more parameters being associated with each sub-configuration.

[0123] It goes without saying that the GUI could include other predefined configurations and / or sub-configurations without departing from the scope of the invention.

[0124] Furthermore, according to an essential characteristic of the regulation method according to the invention, with reference to [Fig.7], the latter comprises a so-called calibration step which comprises the following steps.

[0125] Said calibration step comprises a first step (400) of producing containers from first predetermined control parameters to produce compliant containers. In a second step (410), the thickness of the wall of said containers is measured at the outlet of the mold, at at least two different heights, corresponding to the production of containers from said first control parameters, said measurement of the thickness corresponding to a so-called reference thickness, then in a step (420) said reference thickness is recorded in a memory unit, not shown in the figures.

[0126] Each control parameter is then modified in a step (430). According to a first embodiment, each control parameter is modified one by one. In a second embodiment, each control parameter is modified simultaneously with at least one other control parameter. Furthermore, during this calibration step, each control parameter is modified according to a predetermined incremental value.

[0127] Then, in a step (440), the wall thickness of said containers at the outlet of the mold is measured, at at least two different heights, after the modification of each control parameter, the steps (410) to (440) being repeated until all the parameters have been modified at least once. Thus, the wall thicknesses of said containers at the outlet of the mold are recorded (step 420) for each modified control parameter modified in said memory unit.

[0128] In a step (450), said recorded measured thicknesses are then compared with said reference thickness and, finally, in a step (460) at least one control parameter providing the greatest variation in the thickness of the wall of the containers is determined.

[0129] According to an alternative embodiment, during the step (450) of comparing the thicknesses, said recorded measured thicknesses are compared with so-called theoretical thicknesses which are obtained by calculating the theoretical effects of the variation for each parameter on the thicknesses as described previously.

[0130] Finally, it is quite obvious that the examples which have just been given are only particular illustrations and in no way limitative as to the fields of application of the invention.

Claims

Claims

1. Method for manufacturing containers made of thermoplastic materials by blow molding or stretch blow molding of a preform previously heated in an oven and then placed in a mold consisting of two half-molds delimiting a molding cavity, said preform being blown into the mold, possibly with a pre-blowing step, said steps of heating the preforms, pre-blowing and blowing being controlled by a control unit from different so-called control parameters such as the heating temperature of the preforms in the oven, the blowing pressure in the mold and / or the pre-blowing pressure and / or the pre-blowing flow rate and / or the speed of the drawing rod for example, characterized in that it comprises a preliminary step called calibration which comprises at least the following steps of: - i) production of containers from first control parameters to produce compliant containers;- ii) measuring the wall thickness of said containers at the outlet of the mold, at at least two different heights, corresponding to the production of containers from said first control parameters, said thickness measurement corresponding to a reference thickness; - iii) recording said reference thickness in a memory unit; - iv) modifying each control parameter; - v) measuring the wall thickness of said containers at the outlet of the mold, at at least two different heights, after the modification of each control parameter; - vi) recording the wall thicknesses of said containers at the outlet of the mold for each modified control parameter modified in said memory unit; - vii) comparing said recorded measured thicknesses with said reference thickness or with a theoretical thickness;- viii) determination of at least one control parameter providing the greatest variation in the thickness of the container walls;

2. Method according to the preceding claim characterized in that, after the preliminary step called calibration, it comprises at least the following steps: a) measuring the wall thickness of said containers at the outlet of the mold, at at least two different heights; b) comparing the thickness measurements with setpoint values ​​determined for each height of the containers; c) if the deviation of the thickness measurements from the setpoint values ​​determined is greater than a determined threshold, modifying at least one of the control parameters, said modified control parameter(s) being selected from at least one of the control parameters providing the greatest variation in the wall thickness of the containers during the calibration step and / or by calculating the theoretical effects of the variation for each parameter on the thicknesses, said theoretical effects of the variation for each parameter defining a theoretical thickness, then by selecting the parameter(s) inducing the smallest deviation between the measured values ​​and the theoretical thickness values;d) steps a) to c) are repeated until the deviations of the thickness measurements from the determined set values ​​are less than the said determined threshold.;

3. Method according to the preceding claim, characterized in that step c) comprises at least the following steps of: - defining, for each parameter, an optimal reference coefficient chosen from among reference coefficients assigned to each thickness zone of the wall of the containers; - storing the lower and upper limits as well as the scales for each of said parameters; - calculating an adjustment of each parameter as a function of said previously defined optimal reference coefficient; - calculating the theoretical corrections for each thickness zone as a function of the calculated adjustments and the scales; - calculating the theoretical deviation in thickness of the containers as a function of the theoretical corrections calculated for each thickness zone; - adding, for each parameter, said calculated theoretical deviations; and - selecting at least one parameter having the lowest cumulative deviation value.

4. Method according to claim 3 characterized in that, prior to the step of selecting at least one parameter, it includes a step of prioritizing the parameters based on said calculated theoretical deviations.

5. Method according to claim 4 characterized in that said parameters are hierarchized in an increasing manner, from the lowest cumulative deviation value to the largest cumulative deviation value.

6. Method according to any one of claims 3 to 5 characterized in that, after the step of calculating the adjustments and prior to the step of calculating the theoretical corrections, it comprises an additional step of recalculating the adjustments if the calculated adjustments are not within said limits.

7. Method according to any one of claims 3 to 6, characterized in that the theoretical corrections calculated as zero are excluded.

8. Method according to any one of claims 3 to 7 characterized in that the addition of the calculated theoretical deviations is carried out in absolute value.

9. Method according to any one of claims 3 to 8 characterized in that the step of selecting the parameter is carried out after the calculation of a new average of the thicknesses for each zone and / or that the combination of the deviations for each thickness zone has changed.

10. Method according to claim 9 characterized in that a new average of the thicknesses for each zone is calculated at a predetermined frequency.

11. Method according to any one of claims 3 to 10, characterized in that it comprises a step of modifying the predetermined correction coefficients of the algorithm so that the thicknesses measured after modification of the control parameter(s) correspond to the theoretical thicknesses which should have been obtained with the previous predetermined coefficients.

12. Method according to any one of claims 1 to 11 characterized in that, during said calibration step, each control parameter is modified one by one.

13. Method according to any one of claims 1 to 11 characterized in that, during said calibration step, each control parameter is modified simultaneously with at least one other control parameter.

14. Method according to any one of claims 1 to 13 characterized in that, during said calibration step, each control parameter is modified according to a predetermined incremental value.

15. A computer program product comprising a sequence of instructions which, when the program is executed by a computer, causes the latter to implement the steps of the method according to any one of claims 1 to 14.

16. Data processing device comprising means for implementing the steps of the method according to any one of claims 1 to 14.

17. A computer-readable recording medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method according to any one of claims 1 to 14.

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