Method for regulating a container production facility

Abstract

Title: Method for regulating a container production facility The present invention relates to a method for manufacturing thermoplastic containers by blow molding or stretch blow molding of a hollow body previously heated in an oven and then placed in a mold, the steps of heating the hollow bodies, pre-blowing and blowing being controlled by a control unit from different so-called control parameters; said method is remarkable in that it comprises a preliminary step called calibration which comprises at least the following steps of: producing containers from first control parameters; measuring the wall thickness of said containers at the outlet of the mold, at at least two different heights; recording said reference thickness in a memory unit; modifying at least one control parameter;of 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; of recording the thicknesses; of comparing said measured thicknesses recorded with the theoretical thicknesses that should have been obtained after modifications of said parameter(s) by following the pre-determined correction coefficients; and finally of modifying the predetermined correction coefficients 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 pre-determined coefficients. Abstract figure: Figure 1;

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 hollow bodies 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 hollow bodies 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 heating of the hollow bodies, during which a succession of hollow bodies is heated in the heating unit to a reference temperature at which the hollow bodies are in a malleable state in which they can be formed, and a second phase called forming, during which the heated hollow bodies are each transferred into a mold of the blowing unit and a pressurized fluid is injected into each hollow body 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 hollow body in a mold in order to stretch the preform along its axis, which helps to keep the preform centered relative to the mold.

[0004] Furthermore, 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 heating time per zone by means of the on or off selection of each emitter, the power of a ventilation ensuring the transfer of the calories supplied to the external skin of the hollow body towards the interior of said hollow body; the temperature profile of the preferential heating, etc. Concerning the forming unit, said parameters consist, for example, of the pre-blowing pressure, the pre-blowing start, the pre-blowing flow rate, the stretching speed, the 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 a specification. 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 and / or for each change of preform and / or for each change of material reference. The format of a container can in particular be defined by the height and / or the shape and / or the volume 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 hollow bodies 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 hollow bodies, during the passage of the hollow bodies through the heating unit.

[0008] If this material distribution criterion drifts and is no longer deemed 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 packaging thermal insulation of the hollow body is therefore not completely controlled.

[0011] Furthermore, this modification of the heating parameters of the furnace will lead to a modification of the thermal conditioning of the hollow body 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 hollow body 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 a correction of the defect while avoiding the appearance of other problems, for example at other height levels of the container. Furthermore, each process has its own parameters. Thus, a variation in the value of a parameter generates a variation in the thickness of the containers that is different for each process so that, in the event of a deviation in the bottle thicknesses, it is difficult to predict which variation in which parameter will allow the target values ​​of the container thickness to be found. Disclosure of the invention

[0014] 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 hollow bodies and / or the forming parameters of the containers according to each manufacturing process.

[0015] 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 hollow body previously heated in an oven and then placed in a mold consisting of two half-molds delimiting a molding cavity, said hollow body being blown into the mold, possibly with a pre-blowing step, said steps of heating the hollow bodies, pre-blowing and blowing being controlled by a control unit from different so-called control parameters such as the heating temperature of the hollow bodies 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; said method is remarkable in that it comprises a preliminary step called calibration which comprises at least the following steps of: - production of containers from initial control parameters to produce so-called 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 said reference thickness in a memory unit; - modification of at least one 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 said control parameter(s); - recording the wall thicknesses of said containers at the exit of the mold for each control parameter modified in said memory unit; - comparison of said recorded measured thicknesses with the thicknesses obtained without modification of said parameter(s); - determination of a correction coefficient, for a thickness at a determined height, of each parameter, said correction coefficient providing the variation in thickness corresponding to the desired thickness of the wall of the container at the determined height.

[0016] Preferably, the preliminary calibration step 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 said reference thickness in a memory unit; - modification of at least one control parameter, said modification being carried out from a predetermined correction coefficient associated with said 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 said control parameter(s); - 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 measured thicknesses recorded with the theoretical thicknesses which should have been obtained after modifications of said parameter(s) by following the pre-determined correction coefficients; - modification of the predetermined correction coefficients 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.

[0017] It is understood that, for each process, at the first start-up, the container forming installation is put into production with a specific validated process, then each process parameter is automatically slightly modified and the resulting thicknesses are recorded. It is thus possible to customize the installation control algorithm for each process and, thus, in the event of a deviation of one or more thicknesses, the algorithm will be able to optimally choose the parameter(s) to be modified and the value of the correction coefficients associated with each control parameter to find thicknesses within the specifications of the container manufacturing process.

[0018] After the preliminary step known as calibration, it comprises at least the following steps: a) measurement of the wall thickness of said containers at the outlet of the mold, at at least two different heights; b) comparison of thickness measurements with set values ​​determined for each height of the containers; 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 control parameters, said modified control parameter(s) and their associated correction coefficients being selected from at least one of the control parameters providing the most relevant variation in the thickness of the container wall with respect to the thickness deviation measured 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 selecting the parameter(s) inducing the smallest difference 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 below the said determined threshold. Preferably, step c) comprises at least the following steps: - definition, for each parameter, of an optimal reference coefficient chosen from among reference coefficients attributed to each zone of thickness of the wall of the containers; - storage of the lower and upper limits as well as the scales for each of said parameters; - calculation of an adjustment of each parameter based on said previously defined optimal reference coefficient; - calculation of theoretical corrections for each thickness zone based on the calculated adjustments and scales; - calculation of the theoretical deviation in thickness of the containers based on the theoretical corrections calculated for each thickness zone; - addition, for each parameter, of said calculated theoretical deviations; and - selection of at least one parameter presenting the lowest cumulative deviation values.

[0019] 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.

[0020] Said parameters are hierarchically ordered in an increasing manner, from the lowest cumulative deviation value to the largest cumulative deviation value.

[0021] 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.

[0022] Furthermore, said theoretical corrections calculated as zero are excluded.

[0023] In addition, the addition of the calculated theoretical deviations is carried out in absolute value.

[0024] 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.

[0025] Furthermore, a new average of the thicknesses for each zone is calculated at a predetermined frequency.

[0026] 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) cor correspond to the theoretical thicknesses that should have been obtained with the previous pre-determined coefficients.

[0027] According to a first variant of execution, during said calibration step, each control parameter is modified one by one.

[0028] According to a second variant of execution, during said calibration step, each control parameter is modified simultaneously with at least one other control parameter.

[0029] Furthermore, during said calibration step, each control parameter is modified according to a predetermined incremental or decremental value.

[0030] Another subject 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.

[0031] 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.

[0032] 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

[0033] 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: [Fig.l] is a schematic representation, seen from above, of a forming installation implementing the method according to the invention, [Fig.2] is a side view showing a hollow body intended to feed the forming installation of [Fig.l], [Fig.3] is a schematic representation of the various stages of forming a container through the forming unit of [Fig.l], [Fig.4] is a cross-sectional view of the thermal conditioning unit for hollow bodies of the forming unit of [Fig.l], [Fig.5] is a schematic representation of the step of measuring the wall thickness of the formed container at different heights, [Fig.6] is a flowchart of the different stages of the method for regulating the container forming unit according to the invention, [Fig.7] is a flowchart of the different calibration steps of the method for regulating the container forming unit according to the invention.

[0034] Embodiment of the invention

[0035] In the following description of the process for manufacturing thermoplastic containers by blow molding or stretch blow molding of a hollow body according to the invention, the same numerical references designate the same elements. The different views are not necessarily drawn to scale.

[0036] In the remainder of the description, elements having an identical structure or similar functions will be designated by the same references.

[0037] 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.

[0038] 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.

[0039] [Fig.l] schematically 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 hollow bodies 3. The hollow bodies 3 are generally produced beforehand by injection molding. These hollow bodies 3 are generally cold when they are delivered to the inlet of the forming installation 1.

[0040] 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.

[0041] In the remainder of the description, the hollow bodies 3 and the containers 2 move in the production facility along a circulation path from upstream to downstream. The hollow bodies 3 are moved in a row along a heating path by conveying means which will be detailed later.

[0042] In a non-limiting manner, the containers 2 are bottles here. The thermoplastic material is for example formed here by polyethylene terephthalate, hereinafter referred to by its acronym "PET".

[0043] With reference to [Fig.2], each hollow body 3 has a main axis "X" shown vertically in said [Fig.2]. Each hollow body 3 has a substantially cylindrical body 4 with a tubular wall closed at one of its axial ends by a bottom 5, and which is open at its other end by a neck 6, also tubular. The neck 6 is delimited downwards by a collar 7 and upwards by an upper end edge called a drinking mouth 8.

[0044] The neck 6 generally has its final shape while the body 4 of the hollow body 3 is intended to undergo a relatively significant deformation to form the final container 2 during a forming step.

[0045] The hollow bodies 3 here come from recycled or non-recycled "PET" material or from "PP", that is to say that the hollow body 3 is produced by molding a single thermoplastic material of determined composition.

[0046] It goes without saying that the hollow bodies 3 may be made of any other polymer such as polyethylene furanoate (PEF), polylactic acid (PLA), polyhydroxyalkanoates (PHA), high density polyethylene (HDPE), or the like or a combination of these polymers in a so-called multi-layer form, with or without additive(s), without departing from the scope of the invention.

[0047] Among the characteristics likely to vary from one batch of hollow bodies 3 to another, we will note for example the thickness of the wall of the body 4 of the hollow body 3, or even the rate of absorption of infrared radiation by the thermoplastic material.

[0048] With reference to [Fig.l], the container manufacturing installation comprises at least one thermal conditioning unit 9 and one forming unit 10.

[0049] The thermal conditioning unit 9, also called an oven, makes it possible to heat a succession of hollow bodies 3 to a reference temperature. The reference temperature is chosen so that the body 4 of each hollow body 3 at the outlet of the thermal conditioning unit 9 is in a malleable state allowing deformation of the body 4 of the heated hollow body 3 in order to form the container 2 in the forming unit 10. The reference temperature is between the glass transition temperature and the crystallization temperature of the plastic material of the hollow body 3. 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 2 will be filled or depending on the technique for filling the container. Thus, the reference temperature is different for hot filling or for a carbonated product, for example.

[0050] According to the embodiment shown in [Fig.l], the thermal conditioning unit 9 is a scroll oven, in which the hollow bodies 3 are transported to be exposed to a plurality of heating radiation sources 12.

[0051] For this purpose, the thermal conditioning unit 9 comprises a means 13 for conveying the hollow bodies 3 through the thermal conditioning unit 9 along a heating path extending between an inlet and an outlet of the thermal conditioning unit 9. Said conveying means 13 usually comprises a succession of gripping devices, each being capable of supporting a hollow body 3, mounted on a chain, moving along the heating path in the thermal conditioning unit 9.

[0052] Each gripping device is, for example, capable of receiving a hollow body 3 by fitting the neck 6 onto a spinner, each spinner being, for example, movable in rotation relative to the chain around an axis of rotation coinciding with the main axis X of a hollow body 3 when the latter is supported by the spinner.

[0053] The thermal conditioning unit 9 also comprises a heating cavity which comprises two side walls facing each other and at least one of these walls being the one which supports several radiation sources 12 arranged one above the other and one next to the other opposite the hollow bodies.

[0054] In other words, the thermal conditioning unit 9 comprises a plurality of radiation sources 12 distributed along the heating path and at a height corresponding substantially to the height of the hollow bodies so that the entire height of the body 4 of each hollow body 3 is exposed to the radiation sources 12 on the path of the hollow body in the thermal conditioning unit 9. By rotating the hollow bodies 3 around their main axis X, the spinners make it possible to uniformly expose the entire body 4 of the hollow bodies to the radiation sources 12. In this particular embodiment, the radiation sources 12 are distributed on only one side of this path, and a reflective wall 16 is arranged on the other side of the heating path to reflect the heat towards the hollow bodies 3.

[0055] In another embodiment not shown, the radiation sources 12 can be distributed on either side of the heating path without departing from the scope of the invention.

[0056] It should also be noted that the radiation sources 12 are arranged, where appropriate, so as not to subject the neck 6 to the heat emitted by the radiation sources 12. Indeed, as indicated previously, only the body 4 of the hollow body 3 is formed to produce the container 2. Consequently, the neck 6 must not be deformed during forming and must not be heated. To avoid heating the neck 6, the heat treatment unit 9 may comprise a ventilation device positioned at the necks 6 of the hollow bodies 3 to evacuate the heat likely to be absorbed by said necks 6.

[0057] It is quite obvious that the radiation sources 12 may be substituted by any other heating means well known to those skilled in the art such as VCEL diodes emitting monochromatic or pseudomonochromatic electromagnetic radiation in the infrared or even microwave sources for example without departing from the scope of the invention.

[0058] Then, once the hollow body 3 has been thermally conditioned through the thermal conditioning unit 9, it is transferred to the forming unit 10 to be formed there.

[0059] Said unit 10 for forming containers 2 from hollow bodies 3, with reference to [Fig.l], consists of a forming wheel 17 rotating a plurality of blowing stations 18 from an inlet to an outlet, at which a succession of containers 2 are formed from the hollow bodies 3, then are extracted, as shown in [Fig.l]. The axis of rotation of the forming wheel 17 is, for example, substantially parallel to the main axis X of the hollow bodies 3 when they are transported by the forming wheel 17.

[0060] Each blowing station 18 comprises a mold 19 forming a molding cavity having the shape of the container 2 to be formed and arranged to receive a hollow body 3 so that the body 4 of the hollow body 3 extends into the molding cavity.

[0061] It will be observed that the installation 1 also comprises one or more transfer wheels, not shown in the figures, at the inlet of the thermal conditioning unit 9 and between the outlet of the thermal conditioning unit 9 and the forming unit, said transfer wheels usually comprising members for holding the first transfer wheel which are formed by gripping clamps. Thus, with reference to [Fig. 3], each hollow body 3 undergoes different treatment steps during its journey along the production path, and in particular a heating step in the thermal treatment unit 9, followed by a forming step in the forming unit 10.

[0062] Generally, such a forming installation 1 is capable of producing final containers 2 of different formats. For this purpose, the blowing stations 18 equipping the forming unit 10 are provided with interchangeable molds. Thus, it is possible to modify the shape of the final container produced.

[0063] Depending on the final container format selected, the installation 1 will be supplied with hollow bodies 3 having suitable intrinsic characteristics.

[0064] According to a particular example of embodiment of the method for controlling the installation 1 for forming hollow bodies making it possible to correct, from a given process, any drift leading to variations in measured thicknesses with respect to the determined setpoints of 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 Figures 5 and 6. It will be observed that the thickness of the container is measured at at least two different heights by any appropriate means well known to those skilled in the art such as by interferometry sensors for example.

[0065] Thus, the method 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 and then selecting the parameter(s) inducing the smallest deviation between the measured values ​​and the theoretical values. thicknesses and the previous steps are repeated until the deviation of the thickness measurements from the determined set values ​​is less than the said determined threshold.

[0066] More precisely, with reference to [Fig.6], the step of modifying (300) at least one of the control parameters comprises for example at least the following steps of: - definition (310), for each parameter, of an optimal reference coefficient attributed to each thickness zone of the wall of the containers; - storage (320) of the lower and upper limits as well as the scales for each of said parameters; - calculation of an adjustment (330) of each parameter as a function of the previously defined optimal reference coefficient; - a possible recalculation (340) of the adjustments if the calculated adjustments are not within said limits; - calculation of theoretical corrections (350) for each thickness zone based on the calculated adjustments and scales; - calculation of the theoretical deviation (360) in the thickness of the containers based on the theoretical corrections calculated for each thickness zone; - addition, for each parameter, of said calculated theoretical deviations (370); and - selection of at least one parameter (380) presenting the lowest cumulative deviation values.

[0067] 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.

[0068] Preferably, the calculated theoretical corrections of zero are excluded and the addition of the calculated theoretical deviations is carried out in absolute value.

[0069] 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.

[0070] 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 from the determined setpoint values ​​is greater than a determined threshold, a new parameter is then selected. Said new parameter i+1 selected corresponds to the hierarchical parameter i+1.

[0071] 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.

[0072] Preferably, said calculation comprises at least the following steps: - Calculation of an offset of the blowing and / or heating parameter by multiplying said initial coefficient by the thickness drift; - Determination of the new coefficient based on the offset applied to the parameter and the actual effect measured on the material distribution of each thickness zone

[0073] 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 hollow bodies, etc.

[0074] Said parameter consists of a parameter of the heating unit such as the heating power at a determined height of the hollow body 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.

[0075] In order to adapt the regulation method to each process, the method according to the invention advantageously comprises a preliminary step called calibration, with reference to [Fig.7], which comprises the following steps. The term "process" means the method of manufacturing a particular type of container from a particular type of hollow body and / or a particular type of resin.

[0076] Said calibration step comprises a first step (400) of producing containers from first control parameters to produce compliant containers; then a step (410) of measuring the thickness of the wall 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 measurement of the thickness corresponding to a reference thickness which is recorded in a memory unit in a step (420).

[0077] Then, in a step (430), each control parameter is modified. Said mo Modification of the control parameter is advantageously obtained from a predetermined correction coefficient associated with said control parameter. This modification of each control parameter is carried out by modifying each control parameter one by one from a predetermined correction coefficient associated with said control parameter. Alternatively, each control parameter is modified simultaneously with at least one other control parameter.

[0078] Furthermore, each control parameter is preferably modified according to a predetermined incremental or decremental value.

[0079] After each modification of a control parameter, the thickness of the wall of said containers at the outlet of the mold is measured, at at least two different heights, in a step (440) and the thicknesses of the wall of said containers at the outlet of the mold are recorded for each modified control parameter modified in said memory unit (step (450)).

[0080] Then, in a step (460), said recorded measured thicknesses are compared with said reference thickness or with a theoretical thickness, the theoretical thickness being the thickness that should have been obtained after modifications of the parameters, preferably by following pre-determined correction coefficients, and finally, in a step (470) the control parameter(s) which provides the variation in thickness corresponding to the desired thickness of the wall of the container are selected or the predetermined correction coefficients, associated with the control parameters, are modified, 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 pre-determined coefficients.

[0081] It is understood that, for each process, at the first start-up, the container forming installation is put into production with a specific validated process, then each process parameter is automatically slightly modified and the resulting thicknesses are recorded. It is thus possible to customize the installation control algorithm for each process and, thus, in the event of a deviation of one or more thicknesses, the algorithm will be able to optimally choose the parameter(s) to be modified and the value of the correction coefficients associated with each control parameter to find thicknesses within the specifications of the container manufacturing process.

[0082] According to an alternative embodiment of the method according to the invention, said calibration step comprises a first step (400) of producing containers from first control parameters to produce compliant containers; then a step (410) of measuring the thickness of the wall 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 measurement of the thickness cor corresponding to a reference thickness which is recorded in a memory unit in a step (420).

[0083] Then, in a step (430), each control parameter is modified. In this variant of execution, the modification is not done as previously from a correction coefficient but empirically. Furthermore, each control parameter can be modified simultaneously with at least one other control parameter.

[0084] In addition, each control parameter is preferably modified according to a predetermined incremental or decremental value.

[0085] After each modification of a control parameter, the thickness of the wall of said containers at the outlet of the mold is measured, at at least two different heights, in a step (440) and the thicknesses of the wall of said containers at the outlet of the mold are recorded for each modified control parameter modified in said memory unit (step (450)).

[0086] Then, in a step (460), said recorded measured thicknesses are compared with the thicknesses obtained without modification of the parameter(s) and finally, in a step (470) a correction coefficient is determined, for a thickness at a determined height, of each control parameter, said correction coefficient providing the variation in thickness corresponding to the desired thickness of the wall of the container at the determined height.

[0087] Thus, the regulation method as described above, after the preliminary step known as calibration according to the invention, comprises at least the following steps:

[0088] Measurement of the thickness of the wall of said containers at the outlet of the mold, at at least two different heights;

[0089] Comparison of thickness measurements with set values ​​determined for each height of the containers;

[0090] 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 control parameters, said modified control parameter(s) and their associated correction coefficients being selected from at least one of the control parameters providing the most relevant variation in thickness of the wall of the containers with respect to the measured deviation in 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;

[0091] Selection of the parameter(s) inducing the smallest difference between the measured values ​​and the theoretical thickness values.

[0092] The previous steps are repeated until the deviations of the measurements of the thicknesses with the determined setpoint values ​​are lower than said determined threshold.

[0093] It will be noted that "the most relevant variation in thickness of the container wall" is understood to be the variation in thickness corresponding to the desired thickness of the container wall.

[0094] Furthermore, preferably, the third step of modifying at least one of the control parameters 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.

[0095] 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. Thus, said parameters are prioritized in an increasing manner, from the lowest cumulative deviation value to the largest cumulative deviation value.

[0096] Preferably, after the step of calculating the adjustments and prior to the step of calculating the theoretical corrections, the method according to the invention comprises an additional step of recalculating the adjustments if the calculated adjustments are not within said limits.

[0097] Obviously, said zero calculated theoretical corrections are excluded and the addition of the calculated theoretical deviations is carried out in absolute value.

[0098] Furthermore, preferably, the parameter selection step is carried out after calculating a new average of the thicknesses for each zone and / or after the combination of the deviations for each thickness zone has changed.

[0099] Said new average of the thicknesses for each zone is calculated at a predetermined frequency.

[0100] 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.

[0101] The regulation method and the calibration steps of said method are presented in the form of the form of an algorithm, i.e. 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, the computer program being recorded on a medium such as a memory for example.

[0102] It goes without saying that, after the calibration step according to the invention described above, any type of manufacturing process based on different so-called control parameters such as the heating temperature of the hollow bodies in the furnace, 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 can be used without departing from the scope of the invention.

[0103] 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 hollow body previously heated in an oven and then placed in a mold consisting of two half-molds delimiting a molding cavity, said hollow body being blown into the mold, possibly with a pre-blowing step, said steps of heating the hollow bodies, pre-blowing and blowing being controlled by a control unit from different so-called control parameters such as the heating temperature of the hollow bodies 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: i) production of containers from initial control parameters to produce so-called 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) modification of at least one control parameter; v) measurement of the wall thickness of said containers at the outlet of the mold, at at least two different heights, after modification of said control parameter(s); vi) recording the wall thicknesses of said containers at the exit of the mold for each control parameter modified in said memory unit; (vii) comparison of said recorded measured thicknesses with the thicknesses obtained without modification of the parameter(s); (viii) determination of a correction coefficient, for a thickness at a determined height, of each parameter, said correction coefficient providing the variation in thickness corresponding to the desired thickness of the container wall at the determined height.

2. Method according to the preceding claim, characterized in that the preliminary calibration step comprises at least the following steps:

3. i) production of containers from initial control parameters to produce so-called 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) modification of at least one control parameter, said modification being carried out from a predetermined correction coefficient associated with said control parameter; v) measuring the wall thickness of said containers at the outlet of the mold, at at least two different heights, after modification of said control parameter(s); vi) recording the wall thicknesses of said containers at the exit of the mold for each modified control parameter modified in said memory unit; (vii) comparison of said recorded measured thicknesses with the theoretical thicknesses which should have been obtained after modifications of said parameter(s) by following the predetermined correction coefficients; viii) modification of the predetermined correction coefficients 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. Method according to claim 2 characterized in that, after the preliminary step known as calibration, it comprises at least the following steps: a) measurement of the wall thickness of said containers at the outlet of the mold, at at least two different heights; b) comparison of thickness measurements with set values ​​determined for each height of the containers; 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 control parameters, said modified control parameter(s) and their associated correction coefficients being selected from at least one of the control parameters providing the most relevant variation in the thickness of the container wall with respect to the measured thickness deviation of the container wall 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 with the determined setpoint values ​​are lower than said determined threshold.

4. 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 values.

5. Method according to claim 4 characterized in that, prior to the step of selecting at least one parameter, it comprises a step of hierarchizing the parameters according to said calculated theoretical deviations.

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

7. Method according to any one of claims 4 to 6 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.

8. A method according to any one of claims 4 to 7, characterized in that the theoretical corrections calculated as zero are excluded.

9. Method according to any one of claims 4 to 8 characterized in that the addition of the calculated theoretical deviations is carried out in absolute value.

10. Method according to any one of claims 4 to 9 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.

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

12. Method according to any one of claims 4 to 11, 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.

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

14. Method according to any one of claims 1 to 12 characterized in that, during said calibration step, each control parameter is modified simultaneously with at least one other control parameter.

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

16. 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 15.

17. Data processing device comprising means for implementing the steps of the method according to any one of claims 1 to 15.

18. A computer-readable recording medium comprising instructions which, when executed by a computer, cause the computer to carry out the method steps according to any one of of claims 1 to 15.

Images