Process for regulated heating of a succession of preforms

Abstract

Method for regulated heating of a succession of preforms The method for heating a succession of preforms (2) comprises the following steps: heating a body (16) of a first preform (2) by means of two heating elements (10) each heating a heated zone (24) of the body (16), determining a target heating temperature for each heated zone (24) depending on the container (1) to be produced, measuring the temperature of one of the heated zones (24) of the body (16) at the end of the heating step, modifying the heating power of the heating element (10) corresponding to said heated zone (24) of the body (16) if the measured temperature of said heated zone (24) is different from the target heating temperature, heating the body (16) of the other preforms (2) of the succession of preforms with the modified heating power. Figure for abstract: Figure 2

Description

Title of the invention: Method for regulated heating of a succession of preforms

[0001] The present invention relates to a method of heating a succession of preforms for the production of containers by deformation of said heated preforms.

[0002] It is known to heat the preforms in a container production facility in order to make these preforms malleable and allow their subsequent deformation, for example by stretch blow molding, so as to produce containers from the heated preforms.

[0003] To do this, a succession of preforms is for example circulated in a heat treatment unit, or oven, in which the preforms pass in front of heating elements. The heating elements are in particular distributed according to the height of the body of the preforms, that is to say substantially parallel to the preform axis along which the body of the preforms extends, in order to allow several zones of the body of the preforms distributed over the height of the preforms to be heated to controlled temperatures. Indeed, these zones must be able to be heated to different temperatures in order to best control the deformation of these zones during the production of a container according to the desired shape for this container. Thus, the higher the temperature of a zone, the more this zone can be deformed during the production of the container.The heating powers of the different heating elements thus make it possible to apply a temperature profile to a preform, this profile depending on the characteristics of the container to be produced from this preform and the material of the preform.

[0004] In order to ensure correct heating of the preforms, it is known to set up a control loop, in which the adjustment of the heating power of the heating elements is controlled by the temperature of the heated preforms measured in a zone of the preform after heating of the preforms. The distribution of the heat in the preform is determined as a function of the measurement of a reference temperature measured in a zone of the preform and the heating power of the heating elements is adjusted as a function of this reference temperature to approach the temperature profile to be applied to the preforms.

[0005] However, such a control loop is not entirely satisfactory. In fact, particularly for areas of the preform far from the area in which the reference temperature was measured, the adjustment of the heating power remains based on this reference temperature, which makes the adjustment approximate.

[0006] One of the aims of the invention is to overcome these drawbacks by proposing a method for heating a succession of preforms, in which the heating power of the heating elements can be adjusted precisely in order to apply a temperature profile corresponding precisely to the desired profile to the preforms during their heating.

[0007] To this end, the invention relates to a method of heating a succession of preforms for the production of containers by deformation of said heated preforms, each preform comprising a body extending along a preform axis, said heating method comprising the following steps: - heating the body of a first preform of the succession of preforms by means of at least two heating elements, each heating element heating a different heated zone of the body of the first preform along the preform axis, - determining at least one target heating temperature for each heated area of ​​the body of each preform based on the container to be produced by deformation of each heated area of ​​the preform, - measuring the temperature of at least one of the heated zones of the body of the first preform at the end of the heating step, - modifying the heating power of the heating element corresponding to said heated area of ​​the body if the measured temperature of said heated area is different from the target heating temperature, said heating power being modified so that the temperature of the corresponding heated area of ​​the preform is substantially equal to the target heating temperature, - heating the body of the other preforms in the preform succession with the modified heating power.

[0008] In the heating method according to the invention, the heating power of each heating element is therefore adjusted as a function of the temperature measured in the area of ​​the body of the corresponding preform that this heating element is arranged to heat. In other words, the heating power of a heating element is adjusted on the basis of an actual measurement of the temperature in the heated area of ​​the body of the preform that is heated by this heating element and not on a reference temperature measured in a different area of ​​the body of the heated preform. The control loop thus established therefore makes it possible to precisely adjust the heating power of the heating elements.

[0009] The heating method according to the invention may further comprise one or more of the following characteristics, taken in isolation or in any technically conceivable combination: the temperature is measured for each heated area of ​​the body of the first preform, the heating power of each heating element corresponding to each heated area being modified according to the measured temperature of each heated area and the target heating temperature of each heated area; the body of each preform comprises at least three zones heated by at least three heating elements, at least two adjacent heated zones along the preform axis of said heated zones being grouped to form at least one extended heated zone, the heating powers of the heating elements corresponding to said extended heated zone being modified together as a function of the measured temperature of one of the heated zones of said extended heated zone and a target heating temperature of said extended heated zone; the heating power of the heating elements corresponding to said extended heated area is different from the heating power of the heating element corresponding to the heated area outside the extended heated area; the target heating temperature of a heated zone is between a low acceptable heating temperature and a high acceptable heating temperature, the heating power of the heating element corresponding to said heated zone being modified so that the temperature of said heated zone is between said low acceptable heating temperature and said high acceptable heating temperature at the end of the heating step; the deviation between the low acceptable heating temperature and the target heating temperature and the deviation between the target heating temperature and the high acceptable heating temperature are equal or different; each heated area of ​​the body of a preform is heated by a plurality of adjacent heating elements in a direction of travel substantially perpendicular to the preform axis, said preform being moved in said direction of travel opposite said plurality of heating elements during the heating step, the heating power of all of said adjacent heating elements being modified so that the temperature of the corresponding heated area is substantially equal to the target heating temperature at the end of the heating step; each heating element comprises a plurality of monochromatic or pseudo-monochromatic electromagnetic radiation sources; - the temperature of at least one of the heated zones is measured by at least one thermal camera; - each heated zone extends over a height, measured along the preform axis, of between 4 mm and 5 mm; - the heating method further comprises a step of measuring the thickness of the wall of a deformed zone in a container made from a preform of the succession of preforms, said deformed zone corresponding to at least one heated zone of the preform from which the container is made, the heating power of the heating element corresponding to said heated zone being modified if the measured thickness is different from a target thickness for said deformed zone.

[0010] The invention will appear more clearly on reading the description which follows, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0011] [Fig-1] - [Fig.l] is a schematic representation from above of an installation of production of containers for implementing the heating method according to the invention,

[0012] [Fig.2] - [Fig.2] is a schematic cross-sectional representation of a preform heated by heating elements,

[0013] [Fig.3] - [Fig.3] is a schematic representation of an interface for implementing the heating method according to the invention, and

[0014] [Fig.4] - [Fig.4] is a schematic representation of a part of a container made from a preform heated according to a heating method of the invention for the implementation of an additional optional step of the heating method.

[0015] With reference to [Fig. 1], an installation for producing containers 1 from a succession of preforms 2 is described. Such an installation comprises, in a known manner and in the order of circulation of the preforms 2 and the containers 1 in the installation, a thermal treatment unit 4, or oven, a transfer wheel 6 and a forming station 8.

[0016] The heat treatment unit 4 is arranged to heat a succession of preforms 2 transported in the heat treatment unit 4 by a system for gripping and moving the preforms 2 so as to make them pass in front of heating elements 10, as will be described in more detail later. It is however understood that the invention also applies to a heat treatment unit 4 making it possible to heat each preform 2 individually without moving it in the heat treatment unit 4.

[0017] At the outlet of the heat treatment unit 4, the transfer wheel 6 is arranged to recover the heated preforms 2 and to transfer them to the forming station 8.

[0018] The forming station 8 is for example formed by a carousel carrying several molds 12 forming molding cavities having the shape of the containers 1 to be produced. The heated preforms 2 are each placed in a mold and deformed to acquire the shape of a container 1 for example by stretch blow molding. At the outlet of the forming station, the formed containers 1 are recovered for example by means of another transfer wheel 14, for example to be conveyed to other stations of the installation, such as a labeling station, a filling station and a station for placing a cap on the containers.

[0019] As indicated previously, such an installation is known and will not be described in more detail here. It is however understood that the arrangement of the installation shown in [Fig.l] is given only as an example and that the invention applies to any type of installation arrangement provided that it comprises a heat treatment unit 4.

[0020] As more particularly shown in [Fig. 2], each preform 2 comprises a body 16 and a neck 18 and the heat treatment unit 4 is arranged to heat the body 16 without heating the neck 18 of each preform 2, as will be described in more detail later. The body 16 extends along a preform axis A and has, for example, the shape of a test tube extending between a bottom 20 and the neck 18, which forms an open end of the test tube. The neck 18 comprises, for example, a flange 22 extending from a radial plane substantially perpendicular to the preform axis A projecting towards the outside of the body 16. Such a flange 22 forms, for example, a gripping surface for the preform 2 and the container 1 made from the preform 2. The part of the preform 2 extending from the flange 22 to the open end comprises, for example, a thread making it possible to fix a cap on the container 1 made from the preform 2.Thus, the neck 18 of the preform 2 has the same shape as the neck of the container 1 made from this preform 2. This is why it is advisable not to heat the neck 18 of the preform 2 in the heat treatment unit 4 in order to avoid any deformation of the neck 18.

[0021] The heat treatment unit 4 is arranged to heat the body 16 of each preform 2 in order to increase the temperature of the body 16 above the glass transition temperature of the material forming the body 16 so that the body 16 acquires a malleable character allowing its deformation to form a container 1.

[0022] For this purpose and as shown in Fig. 2, the plurality of preforms 2 is arranged to circulate opposite at least two heating elements 10 arranged to emit thermal radiation towards the body of the preforms 2 passing opposite. More particularly, the heating elements 10 are arranged one above the other in an elevation direction Z of the heat treatment unit 4, sen ably parallel to the preform axis A when a preform 2 is placed in the heat treatment unit 4. Thus, the heating elements 10 are arranged so as to expose the entire body 16 of the preforms 2 to the radiation, more particularly from the bottom 20 to the collar 22 of the preforms 2. Each heating element 10 is more particularly arranged to heat a zone, called the heated zone 24, of the body 16 of a preform 2, the heated zone 24 extending over a portion of the height of the body of the preform 2, measured along the preform axis A. In other words, the body 16 of each preform 2 comprises at least two heated zones 24 arranged one above the other along the preform axis A, each heated zone 24 extending opposite a corresponding heating element 10 so as to be exposed to the heat emitted by this corresponding heating element 10 when the preform 2 circulates in the heat treatment unit 4.

[0023] Each heating element 10 comprises, for example, a plurality of sources of monochromatic or pseudo-monochromatic electromagnetic radiation. More particularly, each heating element 10 is, for example, a laser emitter and the radiation sources are laser chips arranged to emit laser radiation in the infrared range in an emission direction E substantially perpendicular to the elevation direction Z and corresponding to the direction separating the heating elements 10 from the body 16 of the preforms 2 circulating in the heat treatment unit 4. The radiation sources are, for example, arranged next to each other on a support so as to form at least one row of radiation sources extending in the longitudinal direction.According to one embodiment, the radiation sources form at least one upper row and at least one lower row arranged one above the other in the elevation direction.

[0024] Such heating elements are for example described in document FR 3 124 030 and those skilled in the art may refer to this document to obtain more details, in particular with regard to the structure of each radiation source, the arrangement of the radiation sources on a support, the connection of the radiation sources to each other and the cooling of the heating elements. It is understood that the invention is not limited to heating elements formed by laser emitters and also applies to other types of heating element, such as halogen-type incandescent tubular lamps.

[0025] It should however be noted that the invention is particularly suitable for laser emitters because such laser emitters emit very little dispersive radiation, i.e. mainly oriented along the emission direction E, unlike halogen heating elements which have a particularly large radiation emission cone. Thus, laser emitters make it possible to heat an area heated 24 very localized area of ​​the body 16 of the preform 2, while a halogen heating element will heat a larger area and the radiation emitted by this heating element and / or the reflection of this radiation in the heat treatment unit 4 risks interfering with the radiation emitted by another heating element and thus heating a heated area other than that for which it is intended, which reduces the efficiency of the heating method which will be described later.

[0026] With such laser emitters, each heated zone 24 has, for example, a height substantially between 4 mm and 5 mm, for example substantially equal to 4.7 mm. According to one embodiment, a preform 2 has between eighteen and thirty-six heated zones 24, the heat treatment unit 4 comprising at least as many heating elements 10 arranged in a column extending in the elevation direction Z, each heating element 10 of the column being arranged to heat one of the corresponding heated zones 24 as a function of the height of the body 16 of the preforms 2.

[0027] According to one embodiment, the heat treatment unit comprises several columns of heating elements 10 arranged next to each other in the direction of circulation of the preforms 2 in the heat treatment unit 4 so that the preforms pass in front of a succession of heating elements 10 when they circulate in the heat treatment unit 4. In other words, a heated zone 24 of the body 16 of a preform 2 is heated by a plurality of heating elements 10 extending at the same height in the elevation direction Z while the preform 2 circulates in the heat treatment unit 4. According to one embodiment, the preform 2 is further rotated on itself about its preform axis A while it circulates in the heat treatment unit 4 so that the entire circumference of the body 16 is exposed to the radiation of the heating elements 10.Thus, each heated zone 24 extends over the entire circumference of a portion of the body 16 of each preform 2. However, as will be described later, in the case of an asymmetrical deformation of the body 16 of the preform 2 in a heated zone 24, the temperature of this heated zone 24 is not uniform over the entire circumference of the preform.

[0028] The heating power of each heating element 10 is adjustable by means of a control device 26 of the heat treatment unit 4. The control device 26 thus makes it possible to adjust the heating intensity of each heated zone of the preform 2 in order to manage the temperature profile applied to it. Indeed, in a known manner, the heated zones 24 of the same preform 2 are not necessarily heated to a uniform temperature. The temperature of a heated zone 24 depends in particular on the shape of the container 1 to be produced from the preform 2. More particularly, the more a given zone of a preform 2 must be deformed, or stretched, to form the container 1, the higher the temperature to which it must be heated. Thus, referring to the example of container shape 1 shown in [Fig. 4], the areas of the body 16 extending in the vicinity of the neck 18 and the areas of the body extending in the vicinity of the bottom 20 must be heated to a higher temperature than that necessary for the areas extending at the constriction 28 extending substantially halfway up the container 1.

[0029] As shown in [Fig. 3], the control device 26 thus makes it possible to adjust the heating power of a particular heating element 10, as represented by the histogram on the left in [Fig. 3], as a function of the temperature to which the heated zone 24 corresponding to this particular heating element 10 must be heated, as shown in the graph on the right of [Fig. 3]. In this figure showing an example of a display of the adjustment applied by the control device 26 to the heating elements, the heating elements 10 are twenty-four in number, numbered from 1 to 24, and bars 30 of the histogram each represent the heating power of one of these heating elements 10 as a function of the heated zone 24 of the preform 2 opposite these heating elements 10. In [Fig. 3], the body of the preform 2 comprises twenty-two heated zones 24.In the graph on the right, each point 32 represents the desired temperature, called the target heating temperature, for the corresponding heated zone 24. By observing this figure, it can be seen that the higher the target heating temperature of a heated zone 24, the greater the heating power of the corresponding heating element 10. In the example of [Fig. 3], it can be seen, for example, that the heating power of the heating elements 6 to 10 is significantly lower than the heating power of the other heating elements, which makes it possible to produce the restriction 28 of the container 1 shown in [Fig. 4].

[0030] When the heat treatment unit 4 comprises several columns of heating elements 10, the heating power of the heating elements 10 of the same row, that is to say the heating elements 10 extending at the height in the elevation direction Z, is constant. Thus, when the control device 26 controls the heating power of a particular heating element 10, this heating power is applied to all the heating elements 10 located at the same height as this particular heating element. However, in the case where the container 1 to be formed has at least one portion in which the section is not circular, the heating power of the heating elements 10 located at the height of this portion can be modulated to allow an asymmetrical deformation of the preform 2 in this portion.

[0031] The heating method according to the invention provides for passing the preforms through the heat treatment unit 4 opposite the heating elements 10, the heating power is adjusted by the control device 26 according to the target heating temperature for the corresponding heated zones 24.

[0032] The heating method further comprises a loop for regulating the heating power of each heating element 10 as a function of the actual temperature of the corresponding heated zone 24.

[0033] For this purpose, the heating method comprises a step of measuring the temperature of at least one heated zone 24 of at least one first preform 2 of the succession of preforms 2 after the heating thereof. To do this, the heat treatment unit 4 comprises a device 34 for measuring the temperature of at least one heated zone 24 in the vicinity of the outlet of the heat treatment unit 4. Preferably, the measuring device 34 is arranged to measure the temperature of each heated zone 24 of a preform 2 having been heated by the corresponding heating elements 10 of the heat treatment unit 4. Such a measuring device 34 is for example formed by a thermal camera arranged at the outlet of the heat treatment unit and acquiring an image, for example in the infrared domain, of each heated preform 2 transmitted to the transfer wheel 6, as shown in [Fig.l].Alternatively, the measuring device 34 comprises one or more pyrometers each arranged to measure the temperature of a heated zone 24 of the body 16 of at least the first preform 2. The temperatures are acquired by a processing device 36 of the measuring device 34 and are transmitted to the control device 26.

[0034] The controller 26 compares the measured temperature for at least one heated zone 24 to the target heating temperature for that heated zone. If the measured temperature is substantially equal to the target heating temperature, the controller 26 does not change the heating power of the heating element 10 corresponding to that heated zone. If the measured temperature is different from the target heating temperature, the controller 26 changes the heating power of the corresponding heating element 10 so that the heated zone 24 is heated to the desired target temperature. It should be noted that by "substantially equal" and by "different" is meant that the measured temperature is or is not within an acceptable range around the target heating temperature, as represented by the two dotted curves 37 shown around points 32 on the right graph of [Fig. 3].In other words, the target heating temperature is located between a low acceptable heating temperature, lower than the target heating temperature, and a high acceptable heating temperature, higher than the target heating temperature. If the measured temperature is between these two acceptable heating temperatures, then the controller 26 considers that the measured temperature is substantially . equal to the target heating temperature and does not change the heating power of the corresponding heating element 10. Conversely, if the measured temperature is lower than the low acceptable heating temperature, the controller 26 considers that the measured temperature is different from the target heating temperature and increases the heating power of the corresponding heating element 10. If the measured temperature is higher than the high acceptable heating temperature, the controller 26 considers that the measured temperature is different from the target heating temperature and reduces the heating power of the corresponding heating element 10. According to one embodiment, the acceptable heating temperatures correspond to plus or minus 2% of the target heating temperature.It should be noted that the two acceptable heating temperature curves 37 are not necessarily symmetrical to each other with respect to the target heating temperatures. In other words, the deviation between the low acceptable heating temperature and the target heating temperature and the deviation between the target heating temperature and the high acceptable heating temperature may be different from each other.

[0035] The regulation thus makes it possible to adjust the heating power of a particular heating element 10 (or of a line of heating elements 10 rising to the same height) as a function of the temperature measured for the heated zone 24 by this heating element 10 and not as a function of a reference temperature measured in another heated zone of the preform. Thus, the regulation is greatly improved and more precise.

[0036] Preferably, the regulation described above is applied to all the heated zones 24 of the body 16 of the first preform 2 so as to regulate all the corresponding heating elements 10, as shown in [Fig. 3]. Thus, each heating element 10 can be regulated according to the temperature measured for the corresponding heated zone 24, which makes this regulation particularly precise.

[0037] Also preferably, the steps described above are applied to all preforms 2 of the succession of preforms 2 in order to apply the regulation continuously as preforms 2 are heated in the heat treatment unit. This ensures that the desired temperature profile is applied to all preforms 2 and that any drift can be corrected without stopping the heat treatment unit 4.

[0038] According to one embodiment, the method can be optimized by applying a similar setting to one or more groups of heating elements 10 from the measurement of the temperature of a zone heated 24 by one of the heating elements 10 of the or each group of heating elements 10. Indeed, as visible in [Fig. 3], in certain cases, several adjacent heated zones 24 must be heated in a way similar insofar as these heated zones 24 are intended to be deformed to form a particular zone of the container during the production of a container 1. Thus, in [Fig. 3], the heated zones 24 numbered from 7 to 9 must for example be heated by the same heating power to form the constriction 28 of the container 1 of [Fig. 4]. Similarly, the heating power of the heating elements 10 numbered from 20 to 22 must be the same to form the bottom of the container 1. Such a step of grouping heated zones 24 can be implemented when the body of the preform comprises at least three heated zones 24, two of which adjacent zones along the axis of the preform A are grouped to form an extended heated zone 38.

[0039] In this case, the heating method comprises grouping at least two adjacent heated zones 24 to form an extended heated zone 38, represented by rectangles in [Fig. 2]. The regulation can then be applied for the or each extended heated zone 38, at the same time as the regulation for heated zones 24 outside an extended heated zone, by modifying together and in the same direction (increasing the heating power or decreasing the heating power) the heating powers of the heating elements 10 corresponding to each extended heated zone 38 as a function of the measured temperature of one of the heated zones 24 of the or each extended heated zone 38 and of a target heating temperature of the or each extended heated zone 38.It is understood that the heating power of the heating elements 10 corresponding to an extended heated zone 38 may be different from the heating power 10 of the heating elements corresponding to a heated zone 24 outside this extended heating zone 38 and / or corresponding to another extended heated zone 38. For example, the heated zones 24 of an extended heated zone 38 are intended to be deformed in a similar manner to form a container 1. .

[0040] According to one embodiment, the heating method further comprises regulating the heating power of the heating elements 10 as a function of the thickness of the wall of the containers 1 produced from the heated preforms 2.

[0041] For this purpose, the heating method comprises a step of measuring the wall thickness of a deformed zone 40 in a container made from a preform of the preform succession, as shown in [Fig. 4]. This deformed zone 40 corresponds to at least one heated zone 24 of a preform 2 from which the container 1 is made and it is thus possible to make the link between the measured thickness and the heating power 10 corresponding to the heated zone 24 from which the deformed zone 40 is formed. A comparison between the measured thickness and a target thickness of the deformed zone thus allows the control device 26 to modify the heating power of the corresponding heating element 10 when the measured thickness is different from the target thickness, in the same way as for the comparison between a measured temperature and a target heating temperature described previously.

[0042] The thickness is for example measured by a thickness measuring device 42 placed at the outlet of the forming station 8 or downstream of the other transfer wheel 14, as shown in [Fig.l]. The thicknesses are acquired by a processing device 44 of the thickness measuring device 42 and are transmitted to the control device 26 to set up the control loop. As for the control based on measured temperatures, the control based on the measured thicknesses is preferably carried out on all the deformed zones 40 corresponding to the heated zones 24 and therefore to the heating elements 10. Similarly, extended deformed zones can be formed from adjacent deformed zones 40 to regulate the heating power of several heating elements 10 from a measurement of the thickness of a deformed zone 40 of an extended deformed zone.For details of the implementation of regulation based on thickness measurement, please refer to the description given for regulation based on temperature measurement.

[0043] The control device 26, the processing device 36 of the temperature measuring device 34 and, possibly, the processing device 44 of the thickness measuring device 42 are capable of implementing a heating method described above.

[0044] These devices are electronic circuits designed to manipulate and / or transform data represented by electronic or physical quantities in registers of the devices and / or memories into other similar data corresponding to physical data in the memories of registers or other types of display devices, transmission devices or storage devices.

[0045] As specific examples, the control 26 and processing 36, 44 devices are implemented in the form of a programmable logic component, such as an FPGA (Field Programmable Gate Array) or an integrated circuit, such as an ASIC (Application Specific Integrated Circuit).

[0046] Alternatively, when the method is carried out in the form of one or more software programs, i.e. in the form of a computer program, also called a computer program product, it is furthermore capable of being recorded on a medium, not shown, readable by a computer. The computer-readable medium is, for example, a medium capable of storing electronic instructions and of being coupled to a bus of a computer system. By way of example, the readable medium is an optical disk, a magneto-optical disk, a ROM memory, a RAM memory, any type of non-volatile memory (for example FLASH or NVRAM) or a magnetic card. A computer program comprising software instructions is then stored on the readable medium.

Claims

1.

2.

3. Claims A method of heating a succession of preforms (2) for producing containers (1) by deforming said heated preforms (2), each preform (2) comprising a body (16) extending along a preform axis (A), said heating method comprising the following steps: heating the body (16) of a first preform (2) of the succession of preforms (2) by means of at least two heating elements (10), each heating element (10) heating a different heated zone (24) of the body (16) of the first preform (2) along the preform axis (A), - determining at least one target heating temperature for each heated zone (24) of the body (16) of each preform (2) depending on the container (1) to be produced by deforming each heated zone (24) of the preform (2), - measuring the temperature of at least one of the heated zones (24) of the body (16) of the first preform (2) at the end of the heating stage,- modifying the heating power of the heating element (10) corresponding to said heated zone (24) of the body (16) if the measured temperature of said heated zone (24) is different from the target heating temperature, said heating power being modified so that the temperature of the corresponding heated zone (24) of the preform (2) is substantially equal to the target heating temperature, - heating the body (16) of the other preforms (2) of the succession of preforms with the modified heating power., Heating method according to claim 1, wherein the temperature is measured for each heated zone (24) of the body (16) of the first preform (2), the heating power of each heating element (10) corresponding to each heated zone (24) being modified according to the measured temperature of each heated zone (24) and the target heating temperature of each heated zone (24). Heating method according to claim 1 or 2, wherein the body (16) of each preform (2) comprises at least three heated zones (24) by at least three heating elements (10), at least two adjacent heated zones along the preform axis (A) of said heated zones (24) being grouped to form at least one extended heated zone (38), the heating powers of the heating elements (10) corresponding to said extended heated zone (38) being modified together depending on the measured temperature of one of the heated zones (24) of said extended heated zone (38) and a target heating temperature of said extended heated zone (38).

4. A heating method according to claim 3, wherein the heating power of the heating elements (10) corresponding to said extended heated area (38) is different from the heating power of the heating element (10) corresponding to the heated area (24) outside the extended heated area (38).

5. A heating method according to any one of claims 1 to 4, wherein the target heating temperature of a heated area (24) is between a low acceptable heating temperature and a high acceptable heating temperature, the heating power of the heating element (10) corresponding to said heated area (24) being changed so that the temperature of said heated area (24) is between said low acceptable heating temperature and said high acceptable heating temperature at the end of the heating step.

6. The heating method according to claim 5, wherein the deviation between the low acceptable heating temperature and the target heating temperature and the deviation between the target heating temperature and the high acceptable heating temperature are equal or different.

7. Heating method according to any one of claims 1 to 6, wherein each heated zone (24) of the body (16) of a preform (2) is heated by a plurality of adjacent heating elements (10) in a direction of travel substantially perpendicular to the preform axis (A), said preform (2) being moved in said direction of travel opposite said plurality of heating elements (10) during the heating step, the heating power of all of said adjacent heating elements (10) being modified so that the temperature of the corresponding heated zone (24) is substantially equal to the target heating temperature at the end of the heating step.

8. A heating method according to any one of claims 1 to 7, wherein each heating element (10) comprises a plurality of sources of monochromatic or pseudo-monochromatic electromagnetic radiation.

9. A heating method according to any one of claims 1 to 8, wherein the temperature of at least one of the heated zones (24) is measured by at least one thermal camera.

10. Heating method according to any one of claims 1 to 9, in which each heated zone (24) extends over a height, measured along the preform axis (A), of between 4 mm and 5 mm.

11. A heating method according to any one of claims 1 to 10, further comprising a step of measuring the wall thickness of a deformed area (40) in a container (1) made from a preform (2) of the succession of preforms (2), said deformed area (40) corresponding to at least one heated area (24) of the preform (2) from which the container (1) is made, the heating power of the heating element (10) corresponding to said heated area (24) being modified if the measured thickness is different from a target thickness for said deformed area (40).

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