Method for adjusting container production plant

Abstract

The invention relates to a method for producing containers made of thermoplastic material by blow-moulding or stretch blow-moulding hollow bodies, the hollow bodies being preheated in a furnace and then placed in a mould, the heating, pre-blow-moulding and blow-moulding steps of the hollow bodies being controlled by a control unit with different control parameters; the method preferably comprises a preliminary calibration step which at least comprises the following steps: producing a container by using a first control parameter; measuring the thickness of the wall of the container at at least two different heights as the container leaves the mold; recording the reference thickness in a storage unit; modifying the at least one control parameter; after modifying each control parameter, measuring the thickness of the wall of the container at at least two different heights as the container leaves the mold; recording the thickness; comparing the recorded measured thickness with a theoretical thickness which should be obtained after the parameter is modified by a predetermined correction coefficient; and finally modifying the predetermined correction coefficient, so that the measured thickness after modification of the control parameter corresponds to the theoretical thickness which should be obtained by applying the previous predetermined correction coefficient.

Description

Technical Field

[0001] The present invention relates to the field of manufacturing containers (e.g., bottles or flasks) by blow molding or stretch blow molding of thermoplastic materials (e.g., polyethylene terephthalate, abbreviated as "PET"). The object of the present invention is to provide a method for molding containers by blow molding or stretch blow molding of hollow bodies, as well as an apparatus for implementing the method. Background Art

[0002] In the field of manufacturing such containers, it is known that these containers are manufactured by means of an apparatus comprising at least one heating unit and a molding unit equipped with a series of molds whose cavities correspond to the container model to be molded and equipped with corresponding injection devices.

[0003] More specifically, the manufacture of these containers includes two main stages, namely the first stage, called the hollow body heating stage, in which a series of hollow bodies are heated to a reference temperature in a heating unit so that the hollow bodies are in a plastic state for molding; the second stage, called the molding stage, in which the heated hollow bodies are transferred to the mold of the blow molding unit and a pressurized fluid is injected into each hollow body through a corresponding injection device (also called a nozzle) to give the preform the shape of the final container. The pressurized fluid is usually a gas, such as air. In addition, molding usually includes a stretching stage performed by a movable stretching rod, which is designed to apply a tensile force to the bottom of the hollow body in the mold to stretch the preform along the axis of the preform, which helps to maintain the central position of the preform relative to the mold.

[0004] In addition, the equipment for producing these containers usually includes a control console through which the operator can manually adjust a number of parameters to control the heating unit and / or the molding unit. With respect to the heating unit, these parameters include, for example, heating power, heating time for each zone (by selecting to turn each emitter on or off), ventilation power to ensure heat transfer from the outer surface of the hollow body to the interior of the hollow body, temperature distribution for optimal heating, etc. With respect to the molding unit, these parameters include, for example, pre-blowing pressure, pre-blowing start time, pre-blowing flow rate, stretching speed, blowing pressure, etc.

[0005] The manufacturing process requires numerous preliminary trials to obtain a container that meets all the quality criteria previously defined in the specification. This process is tedious and time-consuming, as every parameter of the equipment and process must be adjusted to ensure the container's compliance. Furthermore, this preliminary step must be performed for each container format and / or each change in preform and / or reference material. A container's format can be defined, in particular, by its height, shape, and / or volume.

[0006] Therefore, commissioning the manufacturing method and setting the parameters of the associated equipment requires the operator to have a deep understanding of the equipment, the method, and the hollow body models that may be introduced into the equipment in order to obtain containers that meet the required specifications. This commissioning also requires a considerable amount of time, which directly affects the production line's output.

[0007] Throughout the entire production process, the resulting containers are then evaluated to determine whether they meet the standards. For example, for a given specification, a quality criterion for determining whether a container meets the standards could be the material distribution along the height of the container. It is well known that one of the parameters of the manufacturing method that influences this standard is the thermal conditioning of the hollow body as it passes through the heating unit.

[0008] If this material distribution standard deviates and no longer meets the requirements, the operator must adjust various parameters to correct the defects during the thermal conditioning stage, during the forming stage, or in both stages. Furthermore, the modifications made should not lead to the appearance of other defects or problems.

[0009] In this regard, in order to overcome this drawback, methods have been devised to regulate the heating parameters of the furnace, in particular by varying the electrical power of the radiation source according to the thickness of the wall of the container being formed. This is the case of European patent EP1998950.

[0010] Document EP1998950 proposes a solution that uses thickness sensors positioned above one another to check the material distribution standard. If this standard is deemed unacceptable, the power of a heating lamp located at the same height as the sensor is adjusted accordingly. The other lamps are not involved, and their settings are not adjusted. Consequently, the thermal regulation of the hollow body is not fully understood.

[0011] Furthermore, such modifications to the furnace heating parameters will result in variations in the thermal regulation of the hollow body during production, which can lead to formed containers that do not meet the customer's specifications. Furthermore, non-compliance with the requirements of the formed container increases manufacturing costs and may require equipment shutdowns, further increasing manufacturing costs.

[0012] Also known is document EP2352633, which describes a method and apparatus for blow molding containers. First, a hollow body made of thermoplastic material is heat-treated in a heating section along a transport path. Then, under the action of blowing pressure, the preform is formed into a container within a blow mold. Once the container has been blow-molded, the wall thickness is measured at at least one vertical level of the container. A preset value for the wall thickness is transmitted to a controller as a desired value, and the measured wall thickness is transmitted to the controller as an actual value. Based on the difference between the desired and actual values, the controller predefines the value of at least one parameter that influences the blow molding process. More specifically, the controller predefines the value of at least one parameter that influences the blow air supply. This parameter value is predefined based on a simulation model of the blow molding process implemented in the controller.

[0013] All of these solutions were unsatisfactory because they did not allow the operator to directly and quickly optimize the heating phase. The information available to the operator did not allow for correcting defects while avoiding other problems (e.g., at different container height levels). Furthermore, each process had its own specific parameters. Therefore, variations in parameter values ​​resulted in different variations in container thickness for each process. Therefore, if the bottle thickness deviated, it was difficult to predict which parameter change would restore the container thickness to the target value. Summary of the Invention

[0014] The object of the present invention is therefore to remedy these drawbacks by proposing a method that makes it possible to adapt the parameters of the thermal conditioning of the hollow body and / or the shaping of the container according to each manufacturing process.

[0015] To this end, according to the invention, a method for producing a container of thermoplastic material by blow molding or stretch blow molding of a hollow body is proposed, wherein the hollow body is preheated in an oven and then placed in a mold consisting of two mold halves defining a molding cavity, wherein the hollow body is blown in the mold, possibly with a pre-blowing step, wherein the heating step of the hollow body, the pre-blowing step and the blowing step are controlled by a control unit according to different control parameters, such as the heating temperature of the hollow body 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 stretch rod; the method is notable in that it includes a preliminary calibration step, which comprises at least the following steps:

[0016] - producing the container using the first control parameter to produce a container that meets the requirements;

[0017] - measuring the thickness of the wall of the container at at least two different heights as the container leaves the mould, the thickness of the wall of the container corresponding to the container produced using the first control parameters, the measured values ​​of the wall thickness being used as reference thickness;

[0018] - recording the reference thickness in a storage unit;

[0019] - modifying at least one control parameter;

[0020] - after modifying one or more of said control parameters, measuring the thickness of the wall of said container at at least two different heights as the container leaves the mould;

[0021] - recording in a memory unit the thickness of the wall of the container corresponding to each modified control parameter when the container leaves the mold;

[0022] - comparing the recorded measured thickness with the thickness that would have been obtained without modifying one or more parameters;

[0023] - determining a correction factor for each parameter of the thickness at a determined height, said correction factor providing a thickness variation corresponding to the desired thickness of the wall of the container at the determined height.

[0024] Preferably, the preliminary calibration step comprises at least the following steps:

[0025] - producing the container using the first control parameter to produce a container that meets the requirements;

[0026] - measuring the thickness of the wall of the container at at least two different heights as the container leaves the mould, the thickness of the wall of the container corresponding to the container produced using the first control parameters, the measured values ​​of the wall thickness being used as reference thickness;

[0027] - recording the reference thickness in a storage unit;

[0028] - modifying at least one control parameter, said modification being effected on the basis of a predetermined correction factor associated with said control parameter;

[0029] - after modifying one or more of said control parameters, measuring the thickness of the wall of said container at at least two different heights as the container leaves the mould;

[0030] - recording in a memory unit the thickness of the wall of the container corresponding to each modified control parameter when the container leaves the mold;

[0031] - comparing the recorded measured thickness with the theoretical thickness that would be obtained after modifying one or more of said control parameters according to a predetermined correction factor;

[0032] - modifying the predetermined correction coefficients so that the thickness measured after modifying one or more control parameters corresponds to the theoretical thickness that would have been obtained using the previous predetermined correction coefficients.

[0033] It will be appreciated that for each process, upon initial startup, the container forming equipment is placed into production using a specific, validated process, and each process parameter is then automatically and slightly modified, with the resulting thickness recorded. Thus, the equipment's control algorithm can be customized for each process, such that when one or more thickness deviations occur, the algorithm can optimally select the one or more parameters to modify, along with the correction factor values ​​associated with each control parameter, to restore the thickness to within specifications for the container manufacturing process.

[0034] After the initial calibration steps, at least the following steps are included:

[0035] a) measuring the thickness of the wall of the container at at least two different heights as the container leaves the mould;

[0036] b) comparing the thickness measurement for each height of the container with a determined set value;

[0037] c) if the deviation of the thickness measurement from the determined set value exceeds a determined threshold, modifying at least one control parameter, the modified at least one control parameter and the correction factor associated with the control parameter being selected from at least one control parameter obtained by: providing a control parameter that best correlates the deviation of the thickness of the wall of the container with respect to the thickness measured in the preliminary calibration step, and / or calculating a theoretical effect of the change of each control parameter on the thickness and then selecting one or more control parameters that result in the smallest deviation between the measured value and the theoretical value of the thickness, said theoretical effect of the change of each control parameter defining a theoretical thickness;

[0038] d) Repeating steps a) to c) until the deviation of the thickness measurement value from the determined set value falls below a determined threshold value.

[0039] Preferably, step c) comprises at least the following steps:

[0040] - defining for each parameter an optimal reference coefficient chosen from the reference coefficients assigned to each thickness zone of the wall of the container;

[0041] - storing lower and upper limits and scales for each of said parameters;

[0042] - Calculate the adjustment value of each parameter based on the predefined optimal reference coefficient;

[0043] - Calculate the theoretical correction value for each thickness zone based on the calculated adjustment value and the scale;

[0044] - calculating the theoretical deviation of the thickness of the container based on the calculated theoretical correction value for each thickness zone;

[0045] - for each parameter, summing the calculated theoretical deviations; and,

[0046] - Select at least one parameter with the smallest cumulative deviation.

[0047] Furthermore, before the step of selecting at least one parameter, the method further includes a step of sorting the parameters according to the calculated theoretical deviations.

[0048] The parameters are sorted in ascending order from the smallest cumulative deviation value to the largest cumulative deviation value.

[0049] Preferably, after the step of calculating the adjustment value and before the step of calculating the theoretical correction value, if the calculated adjustment value is not within the upper and lower limits, the method further comprises an additional step of recalculating the adjustment value.

[0050] Furthermore, cases where the calculated theoretical correction value is zero are excluded.

[0051] Furthermore, the calculated theoretical deviations are added in absolute value.

[0052] Preferably, the parameter selection step is performed after calculating the new average thickness of each thickness region and / or the deviation combination of each thickness region has changed.

[0053] Furthermore, a new average thickness is calculated for each thickness region at a predetermined frequency.

[0054] Advantageously, the method according to the invention comprises the step of modifying predetermined correction coefficients of the algorithm so that the thickness measured after modifying one or more control parameters corresponds to the theoretical thickness that would have been obtained using the previous predetermined correction coefficients.

[0055] According to a first embodiment, in the calibration step, each control parameter is modified one by one.

[0056] According to a second embodiment, in the calibration step, each control parameter is modified simultaneously with at least one other control parameter.

[0057] Furthermore, during the calibration step, each control parameter is modified by a predetermined incremental or decremental value.

[0058] Another object of the present invention is to provide a computer program product comprising a series of instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method according to the present invention.

[0059] A third object of the present invention is to provide a data processing device comprising means for performing the steps of the method according to the present invention.

[0060] A final object of the present invention is to provide a computer-readable recording medium comprising instructions, which, when executed by a computer, cause the computer to execute the steps of the method according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Other advantages and characteristics will become more apparent from the following description of a single embodiment variant of the method according to the invention, given by way of non-limiting example, with reference to the accompanying drawings, in which:

[0062] [ Figure 1 ] shows a schematic top view of a molding device for implementing the method of the present invention,

[0063] [ Figure 2 ] shows the supply Figure 1 A side view of the hollow body of the forming device,

[0064] [ Figure 3 ] shows that the Figure 1Schematic diagram of each molding step of the container molding unit,

[0065] [ Figure 4 ] shows Figure 1 Cross-sectional view of the heat conditioning unit of the hollow body of the molding unit,

[0066] [ Figure 5 ] shows a schematic diagram of the steps of measuring the thickness of the wall of a molded container at different heights,

[0067] [ Figure 6 ] shows a flow chart of the different steps of the method for adjusting a container forming unit according to the invention,

[0068] [ Figure 7 ] shows a flow chart of different calibration steps of the method for adjusting a molding unit for a container according to the invention. DETAILED DESCRIPTION

[0069] In the following description of the method according to the invention for producing a container of thermoplastic material by blow moulding or stretch blow moulding of a hollow body, like reference numerals refer to like elements. The different views are not necessarily drawn to scale.

[0070] In the following description, elements having the same structure or similar function will be denoted by the same reference numerals.

[0071] In the following description, the longitudinal, vertical and transverse directions represented by the "L, V, T" trihedron in the drawings will be adopted in a non-limiting manner, with the displacement direction of the hollow body being oriented in the longitudinal direction.

[0072] Hereinafter, the term "holding member" refers to a holding member or a supporting member of a hollow body, which can transport the hollow body from one point to another.

[0073] Figure 1 A schematic diagram of a molding device 1 for producing a final container 2 from a hollow body 3 made of a thermoplastic material such as recycled or unrecycled "PET" (polyethylene terephthalate) or "PP" (polypropylene) is shown. The hollow body 3 is usually previously produced by injection molding. These hollow bodies 3 are usually cold when they are delivered to the inlet of the molding device 1.

[0074] In the following description, the general term "hollow body" will be used to refer indifferently to a preform, a container being formed or a finished container.

[0075] In the following description, the hollow body 3 and the container 2 move along a path from upstream to downstream in the production line. The hollow body 3 moves along the heating path by a conveying device which will be described in detail later.

[0076] The container 2 is a bottle in this case, without limitation. The thermoplastic material is formed of, for example, polyethylene terephthalate, hereinafter referred to as "PET".

[0077] refer to Figure 2 Each hollow body 3 has the Figure 2 The main axis "X" is indicated vertically in the figure. Each hollow body 3 has a body 4 with a substantially cylindrical tubular wall, closed at one axial end by a bottom 5 and open at the other end by a neck 6, also tubular. The neck 6 is delimited downwardly by an annular flange 7 and upwardly by an upper edge, called a mouth 8.

[0078] The neck 6 generally assumes its final shape, whereas the body 4 of the hollow body 3 will undergo a relatively large deformation to form the final container 2 during the forming stage.

[0079] The hollow body 3 is made of recycled or non-recycled "PET" or "PP" material, ie the hollow body 3 is produced by molding a single thermoplastic material of defined composition.

[0080] Obviously, the hollow body 3 can be made of any other polymer, such as polyethylene furandicarboxylate (PEF), polylactic acid (PLA), polyhydroxyalkanoate (PHA), high-density polyethylene (HDPE) or the like or combinations of these polymers in so-called multilayer form, with or without additives, without departing from the scope of the present invention.

[0081] Among the characteristics that may vary from one batch of hollow bodies 3 to another, one will note for example the thickness of the walls 4 of the hollow bodies 3 , or the absorptivity of the thermoplastic material to infrared radiation.

[0082] refer to Figure 1 The container manufacturing equipment includes at least a heat adjustment unit 9 and a molding unit 10.

[0083] The heat conditioning unit 9, also known as an oven, is used to heat a series of hollow bodies 3 to a reference temperature. The reference temperature is selected so that upon exiting the heat conditioning unit 9, the body 4 of each hollow body 3 is in a plastic state that allows the heated hollow body 3 to be deformed to form a container 2 in the forming unit 10. The reference temperature lies between the glass transition temperature and the crystallization temperature of the thermoplastic material of the hollow body 3. For PET, the reference temperature is, for example, approximately 110°C. The value of the reference temperature may vary depending on the product to be filled with the container 2 or the filling technology used. Thus, for example, the reference temperature may be different for hot-fill or carbonated products.

[0084] according to Figure 1 In the embodiment shown, the heat conditioning unit 9 is a continuous heating furnace, in which the hollow body 3 is transported so as to be exposed to a plurality of heating radiation sources 12 .

[0085] To this end, the thermal conditioning unit 9 comprises a conveying device 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 device 13 generally comprises a series of gripping devices, each of which is capable of supporting a hollow body 3, the gripping devices being mounted on chains and moving along the heating path in the thermal conditioning unit 9.

[0086] Each clamping device is capable of receiving a hollow body 3 , for example by fitting the neck 6 on a turntable, each turntable being rotatable relative to the chain about an axis of rotation coinciding with the main axis X of the hollow body 3 , when the hollow body is supported by the turntable.

[0087] The thermal conditioning unit 9 further comprises a heating chamber comprising two opposite side walls, at least one of which supports a plurality of radiation sources 12 arranged one above the other and side by side facing the hollow body.

[0088] In other words, the thermal conditioning unit 9 comprises a plurality of radiation sources 12 distributed along the heating path and arranged according to a height substantially corresponding 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 during the path of the hollow body through the thermal conditioning unit 9. By rotating the hollow body 3 about its main axis X, the turntable provides for a uniform exposure of the entire body of the hollow body 4 to the radiation sources 12. In this particular embodiment, the radiation sources 12 are distributed only on one side of the heating path, with a reflective wall 16 being provided on the other side of the heating path in order to reflect the heat back towards the hollow body 3.

[0089] In another embodiment not shown, the radiation sources 12 may be distributed on both sides of the heating path without departing from the scope of the present invention.

[0090] It should also be noted that, where necessary, the radiation source 12 is arranged so as not to subject the neck 6 to the heat emitted by the radiation source 12 . Indeed, as described above, only the body 4 of the hollow body 3 is formed to produce the container 2 . Therefore, the neck 6 should not be deformed during the forming process and should not be heated. To prevent heating of the neck 6 , the thermal conditioning unit 9 may include a ventilation device positioned at right angles to the neck 6 of the hollow body 3 to dissipate any heat that may be absorbed by the neck 6 .

[0091] Obviously, the radiation source 12 may be replaced by any other heating device known to those skilled in the art, such as a VCEL diode emitting monochromatic or pseudo-monochromatic infrared electromagnetic radiation, or a microwave source, etc., without departing from the scope of the present invention.

[0092] Then, once the hollow body 3 has completed thermal conditioning by the thermal conditioning unit 9 , the hollow body is transferred to the molding unit 10 for molding.

[0093] refer to Figure 1, said molding unit 10 for manufacturing containers 2 from hollow bodies 3 comprises a molding wheel 17, which rotates to move a plurality of blow molding stations 18 from an inlet to an outlet, during which a series of containers 2 are molded from the hollow body 3 and then extracted, as Figure 1 The axis of rotation of the shaping wheel 17 is, for example, approximately parallel to the main axis X of the hollow body 3 when it is transported by the shaping wheel 17 .

[0094] Each blow-moulding station 18 comprises a mould 19 forming a moulding cavity having the shape of the container 2 to be moulded and arranged to receive the hollow body 3 such that the body 4 of the hollow body 3 extends in the moulding cavity.

[0095] It can be noted that the device 1 also comprises one or more transfer wheels (not shown in the figures) located 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 generally comprising a retaining member of the first transfer wheel consisting of a clamping jaw. Figure 3 Each hollow body 3 undergoes different processing steps as it moves along the production path, in particular a heating step in a thermal conditioning unit 9 followed by a forming step in a forming unit 10 .

[0096] Typically, this molding device 1 is capable of producing final containers 2 of different specifications. For this purpose, the blow molding station 18 assembled to the molding unit 10 is equipped with mutually replaceable molds. Therefore, the shape of the final produced container can be modified.

[0097] Depending on the chosen final container format, the device 1 will be supplied with a hollow body 3 having appropriate inherent properties.

[0098] According to a particular embodiment of the control method for controlling the device 1 for forming hollow bodies, the control method allows correcting any deviations from a given process that result in variations in the thickness measurement values ​​relative to the set values ​​of the processing parameters of the processing station, based on measurements made on the containers directly when they leave the forming station, e.g. Figure 5 and Figure 6 It may be noted that the thickness of the container is measured at at least two different heights by any suitable means known to those skilled in the art, such as by an interferometric sensor.

[0099] Thus, the method comprises: measuring the thickness of the wall of the container at at least two different heights as the container leaves the mould (step 100); then comparing the thickness measurements for each height of the container with a determined set value (step 200); modifying at least one control parameter (step 300) if the deviation of the measured thickness from the determined set value exceeds a determined threshold; selecting the modified control parameter(s) by at least calculating the theoretical effect of a change in each parameter on the thickness and then selecting one or more parameters that result in the smallest deviation between the measured thickness and the theoretical thickness; and repeating the above steps until the deviation between the measured thickness and the determined set value is less than the determined threshold.

[0100] More specifically, refer to Figure 6 The step (300) of modifying at least one control parameter comprises at least the following steps:

[0101] - defining (310) for each parameter an optimal reference coefficient assigned to each thickness zone of the wall of the container;

[0102] - storing (320) lower and upper limits and scales for each parameter;

[0103] - calculating the adjustment value of each parameter according to the predefined optimal reference coefficient (330);

[0104] - if the calculated adjustment value is not within said upper and lower limits, possibly recalculating (340) the adjustment value;

[0105] - calculating the theoretical correction value (350) for each thickness region based on the calculated adjustment value and the scale;

[0106] - calculating a theoretical deviation value of the container thickness based on the calculated theoretical correction value of each thickness region (360);

[0107] - for each parameter, summing the calculated theoretical deviation values ​​(370); and

[0108] - selecting at least one parameter having the smallest cumulative deviation value (380).

[0109] Before the step of selecting at least one parameter, the method further comprises the step of sorting the parameters according to the calculated theoretical deviation values, wherein the parameters are sorted in ascending order from the smallest cumulative deviation value to the largest cumulative deviation value.

[0110] Preferably, invalid calculated theoretical correction values ​​are excluded and the calculated theoretical deviation values ​​are added in absolute value.

[0111] Advantageously, the parameter selection step is performed after the new average thickness for each region is calculated and / or after the combination of deviation values ​​for each thickness region has changed. This allows for real-time correction of any deviations without shutting down the production equipment, thereby maintaining the quality of the produced containers. The new average thickness for each region is calculated at a predetermined frequency. For example, the new average thickness for each region of m bottles is calculated every time m bottles are produced from the mold and their thicknesses are measured, where m is an integer between 30 and 80. For example, m is 50. However, it is clear that m can be any integer without departing from the scope of the present invention.

[0112] It can be observed that if, after n corrections (n ​​being a predetermined number greater than or equal to 1) of the selected parameter, the deviation of the thickness measurement value from the determined set value is greater than a predetermined threshold, a new parameter is selected, and the selected new parameter i+1 corresponds to the parameter i+1 in ascending order.

[0113] Furthermore, advantageously, the optimal reference coefficients assigned to the various thickness zones of the container wall are variable and are calculated each time a parameter is modified. The optimal reference coefficients assigned to the various thickness zones of the container wall are calculated by calculating the actual effect of the adjustment value on the various thickness zones of the container wall.

[0114] Preferably, the calculation includes at least the following steps:

[0115] - multiplying the initial coefficient by the thickness offset value to calculate the offset of the blowing and / or heating parameters;

[0116] - Determination of new coefficients based on the offsets applied to the parameters and the measured actual impact on the material distribution in each thickness zone.

[0117] It can be observed that such variable optimal reference coefficients allow tailoring these coefficients to the resin of the hollow body, the environment, the machine, etc.

[0118] The parameters include parameters of the heating unit, such as the heating power at a certain height of the hollow body and / or the ventilation power for ensuring partial heat discharge in the heating unit and / or the temperature curve for preferential heating, and / or the parameters include parameters of the molding unit, such as the pre-blowing pressure value and / or the start time of pre-blowing and / or the pre-blowing flow rate and / or the speed of the stretching rod and / or the blowing pressure.

[0119] In order to adapt the adjustment method to each process, the method according to the invention advantageously comprises a preliminary calibration step, with reference to Figure 7 , the preliminary calibration step comprises the following steps. The term "process" refers to a manufacturing method for making a specific type of container from a specific type of hollow body and / or a specific type of resin.

[0120] The calibration step comprises: a first step (400) of producing a container using first control parameters to produce a container that meets the requirements; and then a step (410) of measuring the thickness of the wall of the container at at least two different heights when the container leaves the mold, the thickness of the wall of the container corresponding to the container produced using the first control parameters, the measured value of the wall thickness being used as a reference thickness, and the reference thickness being recorded in a storage unit in step (420).

[0121] Then, in step (430), each control parameter is modified. The modification of the control parameter is preferably based on a predetermined correction factor associated with the control parameter. This modification of each control parameter is achieved by modifying each control parameter one by one using the predetermined correction factor associated with the control parameter. Alternatively, each control parameter is modified simultaneously with at least one other control parameter.

[0122] Furthermore, each control parameter is preferably modified by a predetermined incremental or decremental value.

[0123] After each modification of the control parameters, in step (440), the thickness of the wall of the container is measured at at least two different heights when the container leaves the mold, and in step (450), the thickness of the wall of the container corresponding to each modified control parameter when the container leaves the mold is recorded in a storage unit.

[0124] Then, in step (460), the recorded measured thickness is compared with the reference thickness or theoretical thickness, the theoretical thickness being the thickness that should be obtained after modifying the parameters (preferably according to a predetermined correction coefficient), and finally in step (470), one or more control parameters are selected that provide a thickness variation corresponding to the desired thickness of the wall of the container, or the predetermined correction coefficient associated with the control parameters is modified so that the thickness measured after modifying one or more control parameters corresponds to the theoretical thickness that should be obtained using the previous predetermined correction coefficient.

[0125] It will be appreciated that for each process, upon initial startup, the container forming equipment is placed into production using a specific, validated process, and each process parameter is then automatically and slightly modified, with the resulting thickness recorded. Thus, the equipment's control algorithm can be customized for each process, such that when one or more thickness deviations occur, the algorithm can optimally select the one or more parameters to modify, along with the correction factor values ​​associated with each control parameter, to restore the thickness to within specifications for the container manufacturing process.

[0126] According to another embodiment of the method of the present invention, the calibration step includes: a first step (400) of producing a container using first control parameters to produce a container that meets the requirements; and then a step (410) of measuring the thickness of the wall of the container at at least two different heights when the container leaves the mold, the thickness of the wall of the container corresponding to the container produced using the first control parameters, the measured value of the wall thickness serving as a reference thickness, and recorded in a storage unit in step (420).

[0127] Then, in step (430), each control parameter is modified. In this embodiment, the modification is not based on a correction coefficient as described above, but is based on experience. In addition, each control parameter can be modified simultaneously with at least one other control parameter.

[0128] Furthermore, each control parameter is preferably modified by a predetermined incremental or decremental value.

[0129] After each modification of the control parameters, in step (440), the thickness of the wall of the container is measured at at least two different heights when the container leaves the mold, and in step (450), the thickness of the wall of the container corresponding to each modified control parameter when the container leaves the mold is recorded in a storage unit.

[0130] Then, in step (460), the recorded measured thickness is compared with the thickness obtained when one or more parameters have not been modified, and finally in step (470), a correction factor is determined for each control parameter for the thickness at the determined height, the correction factor providing a thickness variation corresponding to the desired thickness of the wall of the container at the determined height.

[0131] Therefore, the adjustment method as described above, after the preliminary calibration step according to the present invention, comprises at least the following steps:

[0132] measuring the thickness of the wall of the container at at least two different heights as the container exits the mold;

[0133] comparing the thickness measurement for each height of the container to a determined set point;

[0134] if the deviation of the thickness measurement from the determined set value exceeds a determined threshold, modifying at least one control parameter, said at least one modified control parameter and its associated correction factor being selected from at least one control parameter obtained by: providing a control parameter of the variation of the thickness of the wall of the container that is most relevant to the deviation of the thickness of the wall of the container measured in the preliminary calibration step, and / or by calculating a theoretical influence of each parameter variation on the thickness, said theoretical influence of each parameter variation defining a theoretical thickness;

[0135] One or more parameters are selected that result in the smallest deviation between the measured thickness value and the theoretical thickness value.

[0136] The above steps are repeated until the deviation between the thickness measurement value and the determined set value is lower than the determined threshold.

[0137] It is noted that the “most relevant thickness variation of the wall of the container” is to be understood as a thickness variation which corresponds to the desired thickness of the wall of the container.

[0138] In addition, preferably, the third step of modifying at least one control parameter includes at least the following steps: defining an optimal reference coefficient for each parameter selected from the reference coefficients assigned to each thickness region of the wall of the container; storing the lower limit and upper limit and the scale of each of the parameters; calculating the adjustment value of each parameter based on the predefined optimal reference coefficient; calculating the theoretical correction value of each thickness region based on the calculated adjustment value and the scale; calculating the theoretical deviation of the thickness of the container based on the calculated theoretical correction value of each thickness region; for each parameter, adding the calculated theoretical deviations; and selecting at least one parameter with the smallest cumulative deviation value.

[0139] In addition, before the step of selecting at least one parameter, the method further comprises the step of sorting the parameters according to the calculated theoretical deviations, so that the parameters are sorted in ascending order from the smallest cumulative deviation value to the largest cumulative deviation value.

[0140] Preferably, after calculating the adjustment value and before calculating the theoretical correction value, the method according to the invention comprises the additional step of recalculating the adjustment value if the calculated adjustment value is not within said upper and lower limits.

[0141] Obviously, the case where the calculated theoretical correction value is zero is excluded and the calculated theoretical deviations are added in absolute value.

[0142] Furthermore, preferably, the parameter selection step is performed after calculating a new average thickness for each region and / or after the deviation combination for each thickness region has changed.

[0143] The new average thickness for each region is calculated at a predetermined frequency.

[0144] Advantageously, the method according to the invention comprises the step of modifying predetermined correction coefficients of the algorithm so that the thickness measured after modifying one or more control parameters corresponds to the theoretical thickness that would have been obtained using the previous predetermined correction coefficients.

[0145] The adjustment method and the calibration steps of the adjustment method are presented in the form of an algorithm, i.e. a computer program product comprising a series of instructions which, when executed by a computer, enable the computer to perform the steps of the method according to the invention, and the computer program is recorded on a medium such as a memory.

[0146] Obviously, after the calibration step according to the invention described above, any type of manufacturing method based on different control parameters, such as the heating temperature of the hollow body 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 stretching rod, etc., can be used without departing from the scope of the invention.

[0147] Finally, it is obvious that the above examples are only specific illustrations and in no way limit the application field of the present invention.

Claims

1. A method for producing a container of thermoplastic material by blow molding or stretch blow molding of a hollow body, wherein the hollow body is preheated in an oven and then placed in a mold consisting of two mold halves defining a mold cavity, wherein the hollow body is blown in the mold, possibly with a pre-blowing step, wherein the heating step, the pre-blowing step and the blowing step of the hollow body are controlled by a control unit according to different control parameters, such as the temperature at which the hollow body is heated 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 stretch rod, characterized in that The method comprises a preliminary calibration step, which comprises at least the following steps: i) producing a container using the first control parameter to produce a container that meets the requirements; ii) measuring the thickness of the wall of the container at at least two different heights as the container leaves the mold, the thickness of the wall of the container corresponding to the container produced using the first control parameters, and the measured values ​​of the wall thickness serving as a reference thickness; iii) recording the reference thickness in a storage unit; iv) modifying at least one control parameter; v) measuring the thickness of the wall of the container at at least two different heights as the container leaves the mould after modifying the at least one control parameter; vi) recording in a storage unit the thickness of the wall of the container when the container leaves the mold corresponding to each modified control parameter; vii) comparing the recorded measured thickness to the thickness that would have been obtained without modifying one or more control parameters; viii) determining a correction factor for each control parameter of the thickness at a determined height, said correction factor providing a thickness variation corresponding to a desired thickness of the wall of the container at the determined height.

2. The method according to claim 1, characterized in that The initial calibration procedure includes at least the following steps: i) producing a container using the first control parameter to produce a container that meets the requirements; ii) measuring the thickness of the wall of the container at at least two different heights as the container leaves the mold, the thickness of the wall of the container corresponding to the container produced using the first control parameters, and the measured values ​​of the wall thickness serving as a reference thickness; iii) recording the reference thickness in a storage unit; iv) modifying at least one control parameter, said modification being effected based on a predetermined correction factor associated with said control parameter; v) measuring the thickness of the wall of the container at at least two different heights as the container leaves the mould after modifying the at least one control parameter; vi) recording in a storage unit the thickness of the wall of the container when the container leaves the mold corresponding to each modified control parameter; vii) comparing the recorded measured thickness with a theoretical thickness that would be obtained after modifying one or more of the control parameters according to a predetermined correction factor; viii) modifying the predetermined correction coefficients so that the thickness measured after modifying one or more of the control parameters corresponds to the theoretical thickness that would be obtained using the previous predetermined correction coefficients.

3. The method according to claim 2, characterized in that After the preliminary calibration step, the method comprises at least the following steps: a) measuring the thickness of the wall of the container at at least two different heights as the container leaves the mould; b) comparing the thickness measurement for each height of the container with a determined set value; c) if the deviation of the thickness measurement value from the determined set value exceeds a determined threshold, modifying at least one control parameter, the modified at least one control parameter and the correction factor associated with the control parameter being selected from at least one control parameter obtained by: providing a control parameter that best correlates with the deviation of the thickness of the wall of the container relative to the thickness of the wall of the container measured in the preliminary calibration step, and / or calculating a theoretical effect of a change in each control parameter on the thickness and then selecting one or more control parameters that result in the smallest deviation between the measured value and the theoretical value of the thickness, said theoretical effect of the change in each control parameter defining a theoretical thickness; d) Repeating steps a) to c) until the deviation of the thickness measurement value from the determined set value falls below a determined threshold value.

4. The method according to claim 3, characterized in that Step c) comprises at least the following steps: - defining, for each control parameter, an optimal reference coefficient chosen from the reference coefficients assigned to each thickness zone of the wall of the container; -Store lower and upper limits and scales for each control parameter; -Calculate the adjustment value of each control parameter based on the predefined optimal reference coefficient; - Calculate the theoretical correction value for each thickness zone based on the calculated adjustment value and the scale; - calculating the theoretical deviation of the thickness of the container based on the calculated theoretical correction value for each thickness zone; - for each control parameter, adding up the calculated theoretical deviations; and, - Selecting at least one control parameter having the smallest accumulated deviation.

5. The method according to claim 4, characterized in that Prior to the step of selecting at least one control parameter, the method further comprises the step of sorting the control parameters according to the calculated theoretical deviations.

6. The method according to claim 5, characterized in that The control parameters are sorted in ascending order from the smallest cumulative deviation value to the largest cumulative deviation value.

7. The method according to any one of claims 4 to 6, characterized in that After the step of calculating the adjustment value and before the step of calculating the theoretical correction value, the method further comprises the additional step of recalculating the adjustment value if the calculated adjustment value is not within the upper and lower limits.

8. The method according to any one of claims 4 to 7, characterized in that Excludes cases where the calculated theoretical correction value is zero.

9. The method according to any one of claims 4 to 8, characterized in that The calculated theoretical deviations are added in absolute value.

10. The method according to any one of claims 4 to 9, characterized in that After calculating the new average thickness for each thickness region and / or the deviation combination for each thickness region has changed, a parameter selection step is performed.

11. The method according to claim 10, characterized in that A new average thickness is calculated for each thickness region at a predetermined frequency.

12. The method according to any one of claims 4 to 11, characterized in that The method comprises the step of modifying predetermined correction coefficients of the algorithm so that the thickness measured after modifying one or more control parameters corresponds to the theoretical thickness that would have been obtained using the previous predetermined correction coefficients.

13. The method according to any one of claims 1 to 12, characterized in that In the preliminary calibration step, each control parameter is modified one by one.

14. The method according to any one of claims 1 to 12, characterized in that During the calibration step, each control parameter is modified simultaneously with at least one other control parameter.

15. The method according to any one of claims 1 to 14, characterized in that During the calibration step, each control parameter is modified by a predetermined incremental or decremental value.

16. Computer program product comprising a series of instructions which, when the program is executed by a computer, cause the computer to perform the steps of the method according to any one of claims 1 to 15.

17. Data processing equipment comprising means for performing 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 execute the steps of the method according to any one of claims 1 to 15.

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