Device and method for measuring the wall thickness of a glass container

Abstract

The present invention relates to a method for measuring the thickness of a glass container, comprising the following steps: - selecting radiation emitted by the container measured from a first side and a second side of the container that are radially opposite each other; - selecting radiation in a first spectral band and radiation in a second spectral band in the range of 2800 nanometers to 4000 nanometers emitted by the container; - measuring the intensity of the radiation in the first spectral band and the second spectral band from the wall simultaneously from each side of the container; and - determining at least the thickness of the first wall and the second wall (22) based on the measurement results of the intensity of the radiation in the first spectral band and the second spectral band from the first wall and the measurement results of the intensity of the radiation in the first spectral band and the second spectral band from the second wall.

Description

Technical Field

[0001] The present invention relates to the technical field of optical inspection of translucent or transparent containers or hollow objects having a high temperature.

[0002] The object of the present invention is more particularly to perform a high-speed optical inspection of objects (such as glass bottles or flasks) that are still hot when leaving a manufacturing machine or a forming machine. Thus, the object of the present invention aims to inspect objects in the hot zone of a manufacturing facility.

[0003] Typically, after melting glass at about 1600° in a furnace, the molten glass is brought above a forming machine through a channel called a "front core" channel. The facility also includes a distributor that causes clusters of molten glass or drops of malleable glass to fall by gravity into each blank mold. Thus, this member forms glass drops that are distributed in the direction of respective independent forming sections by means of a set of guides called conveying guides. A machine called a forming machine IS consists of different parts, each part being equipped with at least one blanking chamber equipped with a blank mold and the same number of finishing chambers, each finishing chamber receiving a finishing mold in which the container assumes its final shape at a high temperature. One, two, three, or four blanking chambers of a section are successively loaded in a pre-determined order with one, two, three, or four drops of hot glass (about 1200 °C) called gobs. At the output of the forming machine, the containers, which are still at a high temperature (usually between 300 °C and 600 °C), are picked up at their ends for conveyance, thus forming a line on a transport conveyor. The spacing between the containers is variable and is imposed by the forming machine along its own center distance and the diameter of the container. The transport conveyor sequentially transports the containers to various processing stations, such as a spray hood for surface treatment and an annealing furnace called an annealing oven.

[0004] It seems worthy of attention to identify forming defects as early as possible at the output of the forming machine before each processing station so as to be able to correct the defect as soon as possible at the forming machine. Thus, it is particularly advantageous to detect dimensional deviations or deformations of the containers that are directly related to the settings of the forming method in order to correct the method as quickly as possible in the event of drift.

[0005] The control of the quality of such containers allows the elimination of containers having defects that may affect their aesthetic properties or, worse, pose a real danger to subsequent users. Thus, it seems necessary to control the quality of the thickness distribution of such containers in order to eliminate containers in which the thickness is too small or the thickness difference in certain areas may affect the mechanical strength.

[0006] In fact, the quality of the thickness distribution is a very important parameter because the thickness is variable, too thick or too thin in different parts of the container. This thickness difference is a problem because the produced articles may be fragile. Moreover, manufacturers are looking into the possibility of manufacturing thin and light glass containers, so it is necessary to know how to distribute the glass properly. The manufacturing parameters that affect the glass distribution are known and numerous, and it is necessary to control them. In particular, these references mentioned by way of known examples include the following parameters:

[0007] i) Loading parameters, including the velocity vector and the center when the droplet falls into the blank mold;

[0008] ii) Heat distribution in the droplet;

[0009] iii) Cooling of the mold.

[0010] In order to act correctly on the manufacturing parameters, it is necessary to know immediately after forming the distribution of the glass in the container.

[0011] It should be understood that knowing the thickness distribution means knowing the thickness at different points of the container in absolute terms, or, if not, the thickness deviation between different regions of the container in relative terms. For example, a bottle consists, from bottom to top, of a bottom, a body of the bottle connected to the bottom through the bottom of the bottle, then a neck connected to the body through a shoulder, and finally a mouth for filling and closed by a stopper, cap or lid. Glass distribution defects can be observed, for example, vertically, where there is an excess of glass at the bottom and the glass is thin at the shoulder. Defects in the horizontal distribution can also be observed, for example, at the shoulder level, where there is more glass on one side than on the other side with respect to the axis. This analysis of not only the minimum and maximum values of the glass thickness, but also the distribution and vertical or horizontal deviations, and the position of the thin or thick regions, is of great importance for correctly correcting the method. Background Art

[0012] In the prior art, various solutions have been proposed for using the infrared radiation emitted by still-hot containers for inspecting the containers at the output of the forming machine to measure the glass distribution.

[0013] For example, Patent US353552 describes a method for measuring the glass thickness of a container, including measuring the infrared radiation emitted by such a container at the output of a forming machine. The measurement of the infrared radiation is carried out while the container is placed in a furnace in order to homogenize the temperature of the container to a determined value. Then, the container still inside the furnace rotates around a vertical axis, in front of the optical axis of an infrared sensor which, during one rotation, measures the radiation passing through the wall between 2.06 and 2.5 μ or between 3.56 and 4.06 μ. Since the temperature is expected to be uniform due to the furnace, the perceived change in radiation is directly attributed to the change in thickness. This technique does not allow for the continuous control of the container and requires the handling of the container, resulting in a slow method that may cause the deformation of the container.

[0014] Patent EP0643297 describes a device for the analysis and diagnosis of a method for manufacturing glass products, which device includes a sensor sensitive to the infrared radiation emitted by an object leaving a forming machine. The system also includes digital processing means which compare the radiation with a mathematical reference model in order to determine the deviations present in the glass distribution and / or the causes leading to the presence of thermal stresses in the container. Furthermore, this patent does not provide any indication of a method for obtaining the reference mathematical model.

[0015] Therefore, it must be taken into account that such an infrared measuring device is installed to observe the containers moving on an output conveyor downstream (in the direction of travel) of a manufacturing machine (i.e., downstream of the last part closest to the device). Thus, the other end of the machine is the most upstream part. Regarding the radiation emitted by the container, it depends on many parameters, including the material distribution and the temperature distribution. During the transfer of the container between the section and the infrared measuring device, the temperature transfer occurs between different parts of the container by radiation and conduction in the direction of thermal equilibrium, which can be called the "spontaneous homogenization" of the temperature, and the global cooling by radiation and convection is called "cooling". Therefore, the thermal state of the container, the temperature distribution in the material of the container when the container is removed from the mold is hereinafter called the "initial condition". Thus, the thermal state of the container at the time of inspection depends on the said initial condition on the one hand and on the spontaneous homogenization and the cooling during transportation on the other hand, which will of course vary based on the distance the container travels from its forming part to the inspection station.

[0016] In practice, according to this prior patent, the change in radiation caused by thermal stress or thickness deviation is detected, but it is not possible to determine the stress or thickness value, nor even to determine whether the change in radiation is related to thermal stress or to a material thickness deviation. Therefore, it seems impossible to implement such a technique in practice because the measurement of infrared radiation depends on many parameters, such as those listed below by way of non-limiting examples.

[0017] According to the Stefan-Boltzmann law, the intensity of the infrared radiation emitted by a hot container depends largely on the temperature: E = sT 4 , where E = total radiation emitted by the object, in (watts per square meter), s = Stefan-Boltzmann constant = 5.67x10 -8 watts per square meter per K 4 and T = temperature in Kelvin (K).

[0018] The intensity of the infrared radiation emitted by the hot containers depends on the characteristics of these hot containers, e.g., such as the size, color, shape, and composition of the glass, etc.

[0019] It should be considered that the distance between the infrared sensor and the die outlet varies depending on the die, such that the cooling time of each hot container is different, and thus the hot containers have different temperatures when passing in front of the infrared sensor. In other words, the intensity of the infrared radiation measured by the sensor depends on the source of the manufacturing die, and more specifically, on the position of the die relative to the sensor.

[0020] At the output of the forming machine, the containers are slidably placed on the conveyor. This results in different positioning of the containers on the conveyor relative to the infrared measurement sensor, which can modify the measurements made.

[0021] The forming temperature conditions and the interactions during container conveyance may vary according to the production situation (start-up, accident, etc.) and the environment (day / night, weather, air flow).

[0022] Since the radiation used according to EP0643297 is transmitted radiation, the perceived radiation is the radiation of two combined walls.

[0023] From the foregoing, it can be seen that many parameters affect the infrared radiation, such that such a patent does not provide a solution for measuring the distribution of the glass thickness of the container at high temperatures. The patent simply teaches detecting deviations in the glass distribution, provided that the operator verifies that the radiation deviation is due to the thickness. Only the relative values of the thickness or thermal stress are estimated between different regions of the container or between different containers and over a short period of time. The patent does not allow measuring the glass thickness of the container in absolute value, regardless of when the measurement is made.

[0024] According to a variant, the patent provides an implementation of an optical sensor for generating an image of a glass product in order to obtain information about the deflection and / or distribution of the glass. This information is compared with data obtained from a sensor sensitive to infrared radiation so that the criteria according to which the data provided by the infrared-sensitive sensor can be analyzed can be adjusted. While the implementation of this variant provides a correction of the criteria used, it does not allow overcoming the drawbacks inherent in the method described in the patent and mentioned above. In addition, this solution does not allow measuring the thickness of the glass, neither relatively nor absolutely, and thus does not allow measuring the distribution of the thickness over a wide area, let alone over the entire container.

[0025] Patent EP1020703 proposes measuring the glass thickness of a container from infrared radiation, including measuring a first intensity of the radiation in a first spectral band, at which the radiation is emitted by the material between the two outer and inner surfaces of the container. Preferably, the first spectral band, whose signal depends on both the glass temperature and thickness, is between 0.4 and 1.1 microns. The method also includes measuring a second intensity of the radiation in a second spectral band, at which the radiation is emitted substantially entirely by a single outer surface of the container. According to the patent, the second spectral band corresponding to the surface radiation is preferably between 4.8 and 5 microns, at which the radiation depends only on temperature. The method includes determining the thickness between the outer and inner surfaces of the container as a combined function of the first measured intensity and the second measured intensity. In other words, the thickness and temperature are determined from two radiation measurements obtained in the first spectral band and the second spectral band.

[0026] According to Figure 3 a variant shown in

[0027] the patent proposes evenly distributing four cameras and pyrometers on the circumference of the container. These cameras measure the radiation in a second spectral band, on which the radiation depends only on temperature, and the pyrometers measure the radiation in a first spectral band, whose signal depends on the glass temperature and thickness.

[0028] As a supplement, it should be noted that in the first spectral band, the radiation of the container relative to the measurement point of the pyrometer includes the radiation of the wall called the front wall located on one side of the measurement point, which depends on the thickness and temperature of the container, and also includes the radiation of the opposite wall called the rear wall, which is emitted towards the interior of the container and passes through the front wall. This "rear radiation" is combined with the "front radiation" of the directly observed surface. The "front wall" only partially absorbs the radiation in the first spectral band. Therefore, the perceived radiation depends on the thicknesses of the two walls and the temperatures of the two walls. In other words, the measurement result of the radiation of the front wall does not allow the measurement of its thickness because the radiation is affected by the rear wall.

[0029] Finally, it has been found that the method described in this patent is applicable to measuring the glass thickness of containers belonging to a limited color family. However, it is necessary to be able to measure the thickness of glass containers with as many colors as possible. Summary of the Invention

[0030] Therefore, the object of the present invention aims to overcome the disadvantages of the prior art by proposing a new method for accurately measuring the wall thickness of a hot glass container exiting a forming cavity by taking into account the influence of the radiation brought by one part of the wall on another part of the wall.

[0031] Another object of the present invention is to propose a method for accurately measuring the wall thickness of glass containers with multiple colors.

[0032] To achieve such an object, a method for measuring the thickness of a hot glass container exiting a forming cavity includes the following steps:

[0033] - Selecting to measure the radiation emitted by the container from the first side and the second side that are radially opposite to each other, so as to take into account the radiation emitted by the first wall of the container located along the first side and the radiation emitted by the radially opposite second wall of the container located along the second side;

[0034] - Selecting to measure the radiation emitted by the container in the first spectral band ranging from 2800 nanometers to 4000 nanometers and the radiation in the second spectral band, the two spectral bands being different and being selected such that:

[0035] · On the one hand, for the temperature of the container, the absorption of radiation by the glass is different in the two spectral bands; and

[0036] · On the other hand, at least in the first spectral band, the absorption of radiation by the glass is such that:

[0037] * The radiation from the first wall measured from the first side of the container is the sum of the radiation emitted by the first wall and the radiation emitted by the second wall that is transmitted under the absorption of the first wall, such that the combined radiation depends on the thicknesses and temperatures of the first wall and the second wall; and

[0038] *The radiation from the second wall measured from the second side of the container is the sum of the radiation emitted by the second wall and the radiation emitted by the first wall and transmitted under absorption by the second wall, such that the combined radiation depends on the thickness and temperature of the first and second walls;

[0039] - Measuring the intensity of the radiation from the first wall in the first and second spectral bands from the first side of the container and the intensity of the radiation from the second wall in the first and second spectral bands from the second side of the container simultaneously; and

[0040] - Determining at least the thickness of the first and second walls from the measurement results of the intensity of the radiation from the first wall in the first and second spectral bands and the measurement results of the intensity of the radiation from the second wall in the first and second spectral bands by considering the intensity of the radiation in the first spectral band, the intensity of the radiation emitted by the wall, and the intensity of the radiation transmitted under absorption from the other radially opposite wall.

[0041] Furthermore, the method according to the present invention may also include at least one or a combination of two of the following additional features:

[0042] - In the second spectral band, the absorption of radiation by the glass is different from the absorption of radiation in the first spectral band, and such that: on the one hand, the radiation from the first wall measured from the first side of the container is the sum of the radiation emitted by the first wall and the radiation emitted by the second wall and transmitted through the first wall, and on the other hand, the radiation from the second wall measured from the second side of the container is the sum of the radiation emitted by the second wall and the radiation emitted by the first wall and transmitted through the second wall, and the combined radiation depends on the thickness of the wall and the temperature of the wall;

[0043] - The temperature of the first and second walls is also determined from the measurement results of the intensity of the radiation from the first wall in the first and second spectral bands and the measurement results of the intensity of the radiation from the second wall in the first and second spectral bands by considering the intensity of the radiation in the first spectral band and the intensity of the radiation transmitted under absorption from the wall located on the other side.

[0044] Another object of the present invention is to propose a method for accurately measuring the wall thickness of a high-temperature glass container for various glass colors including white glass.

[0045] To achieve such an object, the method is carried out by selecting to measure the radiation in the first spectral band ranging from 3000 nanometers to 4000 nanometers emitted by the container according to the method.

[0046] Furthermore, the method according to the present invention may also include at least one or a combination of two of the following additional features:

[0047] - In the second spectral band, the absorption of radiation by the glass causes, on the one hand, the radiation from the first wall measured from the first side of the container to be only the radiation emitted from the surface of the first wall, and on the other hand, the radiation from the second wall measured from the second side of the container to be only the radiation emitted from the surface of the second wall, and the radiation depends only on the temperature;

[0048] - Determine the temperatures of the first wall and the second wall from the measurement results of the intensity of the radiation of the first wall in the second spectral band and the measurement results of the intensity of the radiation of the second wall in the second spectral band respectively;

[0049] - Select to measure the radiation in the second spectral band ranging from 1100 nanometers to 2600 nanometers emitted by the container;

[0050] - Select to measure the radiation in the second spectral band greater than 4500 nanometers (preferably, greater than 5000 nanometers) emitted by the container;

[0051] - Use at least two dual-spectrum infrared cameras to measure the radiation simultaneously, and each camera transmits at least two infrared images of the radiation of the wall of the container located in its observation field.

[0052] Another object of the present invention is to propose a facility for accurately measuring the thickness of the glass wall of a container.

[0053] To achieve this goal, the facility for measuring the wall thickness of a high-temperature glass container that exits the forming cavity and moves along a translation path includes:

[0054] - At least a first dual-spectrum infrared camera and a second dual-spectrum infrared camera, which are arranged radially opposite to each other on either side of the path of the container, to consider the radiation emitted by the first wall of the container located on the first side of the container and the radiation emitted by the second wall of the container located on the radially opposite second side. Each camera transmits two infrared images of the radiation of the wall of the container located in its observation field in a first spectral band ranging from 2800 nanometers to 4000 nanometers and in a second spectral band, and the two spectral bands are different and are selected such that:

[0055] · On the one hand, for the temperature of the container, the absorption of radiation by the glass is different in the two spectral bands; and

[0056] · On the other hand, at least in the first spectral band, the absorption of radiation by the glass causes:

[0057] * The radiation from the first wall measured from the first side of the container is the sum of the radiation emitted by the first wall and the radiation transmitted through the absorption of the first wall by the second wall, such that the combined radiation depends on the thickness and temperature of the first wall and the second wall; and

[0058] *The radiation from the second wall measured from the second side of the container is the sum of the radiation emitted by the second wall and the radiation emitted by the first wall that is transmitted under absorption through the second wall, such that the combined radiation depends on the thicknesses and temperatures of the first and second walls;

[0059] - A system for driving the operation of a dual-spectrum infrared camera so as to simultaneously acquire, using a first camera, two images measuring the intensities of the radiation from the first wall in a first spectral band and a second spectral band and, using a second camera, two images measuring the intensities of the radiation from the second wall in the first spectral band and the second spectral band; and

[0060] - A computer configured to determine at least the thicknesses of the first and second walls by analyzing two images respectively giving the measurement results of the intensities of the radiation from the first wall in the first spectral band and the second spectral band and two images of the second wall in the first spectral band and the second spectral band, by taking into account the intensity of the radiation in the first spectral band, the intensity of the radiation emitted by the wall, and the intensity of the radiation transmitted under absorption from the wall located on the other side.

[0061] Furthermore, according to one embodiment, the facility according to the present invention may include:

[0062] - A dual-spectrum infrared camera, which includes:

[0063] - A beam splitter downstream of which the light rays are split into two different downstream light beams;

[0064] - Two different sensors or two sensor portions downstream of the beam splitter, placed in a plane or two image planes, each sensor receiving one of the two different downstream light beams, the first sensor or the first sensor portion receiving a first radiation beam in the first spectral band and the second sensor or the second sensor portion receiving a second radiation beam in the second spectral band;

[0065] - The first and second light beams are shaped upstream or downstream of the separator by lenses to form optical images of the container in the first spectral band and the second spectral band respectively through optical conjugation on each image plane;

[0066] - The first light beam and / or the second light beam are filtered by one or more filters respectively selecting the first spectral band and the second spectral band.

[0067] According to another embodiment, each dual-spectrum infrared camera includes:

[0068] - A lens that forms an optical image of the field traversed by the container through optical conjugation on the sensor plane;

[0069] - Two different linear sensor parts, the support lines of which are perpendicular and arranged such that during the travel of the container through the lens field, a scanned image is generated using each of the two linear sensor parts;

[0070] - A first linear sensor part that receives a first part of a radiation beam in a first spectral band;

[0071] - A second sensor part that receives a second part of a radiation beam in a second spectral band;

[0072] - At least one filter arranged in the path of the beam to select the first spectral band and the second spectral band. Description of the Drawings

[0073] Figure 1 is an overall top view showing an inspection facility suitable for measuring the thickness of the glass wall of a container exiting a forming machine according to the present invention.

[0074] Figure 2 is a schematic diagram explaining the principle of radiation of the container in a first spectral band with respect to measurement points located on each side of the container.

[0075] Figure 3 is a view showing the thermal radiation of a black body.

[0076] Figure 4 is a view showing the thermal radiation of a vitreous body.

[0077] Figure 5 is a schematic diagram explaining the principle of radiation of the container in a second spectral band with respect to measurement points located on each side of the container.

[0078] Figure 6 is a schematic diagram explaining the principle of radiation of the container in a second spectral band that is only sensitive to the surface temperature of the glass wall with respect to measurement points located on each side of the container.

[0079] Figure 7 is a schematic diagram of an example of a dual - spectral infrared camera used within the framework of the present invention.

[0080] Figure 8 is a schematic diagram of another example of a dual - spectral infrared camera used within the framework of the present invention.

[0081] Figure 9 is a schematic diagram of another example of a dual - spectral infrared camera used within the framework of the present invention. Detailed Description of the Invention

[0082] In the description of the present invention, a first spectral band λ1 and a second spectral band λ2 are used. A spectral band λ is a wavelength interval centered on a value. Each working spectral band is selected within a specific wavelength range according to the present invention or a variant, and these wavelength ranges are broader wavelength intervals. This means that the wavelength interval of each working spectral band is included within an exact wavelength range.

[0083] As more specifically apparent from Figure 1 the object of the present invention relates to a facility 1 for thermally inspecting glass containers 2 (e.g., bottles or flasks), with the aim of measuring the thickness of the glass walls of these containers. The facility 1 is placed to allow the inspection of all types of containers 2 of known type leaving a manufacturing machine or a forming machine 3. At the output of the forming machine, the containers 2 have a high temperature typically between 300 °C and 700 °C.

[0084] The forming machine 3 generally includes a series of cavities 4, each cavity 4 ensuring the forming of the container 2. In a known manner, the containers 2 just formed by the machine 3 are sequentially placed on an output conveyor 5 to form rows of containers. The containers 2 are transported by the conveyor 5 along a translation path F in line so as to convey them sequentially to different processing stations.

[0085] According to an advantageous but non-exclusive arrangement of the present invention, the facility 1 according to the present invention is placed as close as possible to the forming machine 3 such that the output conveyor 5 ensures the sequential advancement of the hot containers 2 in front of this inspection facility 1. Generally, the facility 1 is positioned between the output of the forming machine 3 and an annealing furnace 6 and preferably in front of a surface treatment hood which generally constitutes the first processing station after forming.

[0086] The facility 1 according to the present invention at least includes a first dual-spectrum infrared camera 11 and a second dual-spectrum infrared camera 12, which are arranged radially opposite each other on either side of the translation path F of the container. Each dual-spectrum infrared camera 11, 12 is adapted to transmit an image obtained from the infrared radiation of the wall of the container located in its field of view. For each container 2, each dual-spectrum infrared camera 11, 12 transmits at least one first image obtained from the infrared radiation received in the first spectral band λ1 and at least one second image obtained from the infrared radiation received in the second spectral band λ2. A spectral band refers to an interval of wavelengths. The characteristics of the spectral bands λ1, λ2 will be specified in the remainder of the specification.

[0087] According to Figure 1In the illustrated variant, the installation 1 according to the invention further comprises a second pair of dual-spectrum infrared cameras 13, 14. This second pair of dual-spectrum infrared cameras 13, 14 are also arranged on either side of the translation path F of the container, radially opposite each other. For example, the first pair of dual-spectrum infrared cameras 11, 12 are arranged such that their observation axes are at 45° with respect to the translation path F. Similarly, the second pair of dual-spectrum infrared cameras 13, 14 are arranged at 45° with respect to the translation path F such that the observation axes of the dual-spectrum infrared cameras 11 to 14 are offset in pairs by 90°. Of course, this arrangement of the dual-spectrum infrared cameras is by no means restrictive. To accommodate adverse spacing conditions between the traveling containers, the angles between the four observation axes can be adapted to values such as, for example: 30°, 150°, 30°, 150°.

[0088] The invention can also be operated by using three dual-spectrum infrared cameras, the axes of which are at 120°. In this case, it is considered to divide the field of each camera into two parts, each field part containing an image of a 60° sector of the cylindrical container. Each field part of one camera is opposite the field part of another camera.

[0089] By respecting the principle of generating dual-spectrum infrared images from the viewpoints of all walls, the invention can ultimately be carried out using more than four cameras.

[0090] The installation 1 according to the invention further comprises a system 15 for driving the operation of the dual-spectrum infrared cameras in order to obtain the images K1, K2 transmitted by the dual-spectrum infrared cameras according to a method that will be described in detail in the remainder of the specification. The installation 1 according to the invention further comprises a computer 16, which is configured to determine the thickness of the glass wall of the container by analyzing the images K1, K2 transmitted by the dual-spectrum infrared cameras 11 - 14.

[0091] Here, the computer 16 is a computer unit, specifically, which can in a known manner include a microprocessor, a data input / output bus, a memory, a connection to a computer network and / or a display. The computer can be a computer unit dedicated to the installation to measure the wall thickness, or it can be shared with other elements of the container production line. For example, it can be a centralized unit for driving the production line or a part thereof. In the input output, of course, there are included means for acquiring infrared images. Means for storing digital infrared images are included in the memory. The microprocessor is configured to execute a program organized to execute an algorithm implementing the method according to the invention.

[0092] The computer analysis of digital images yields inspection results, which can include binary results (true / false, present / absent, compliant / non-compliant, etc.) and / or qualitative or even quantitative results in the form of, for example, one or more measurement results. Thus, the inspection results can include not only the minimum and maximum values of the glass thickness, but also the distribution and vertical or horizontal deviations, as well as the positions of thin or thick regions, which are important for the correction method. In addition to determining the thickness distribution or mapping and thus the material distribution in the container being inspected, the inspection results can include the temperature mapping of the container and the identification of high thermal stress regions when local high temperature variations are observed. Furthermore, such analysis can include the detection of appearance or composition defects (e.g., the presence of inclusions, bubbles, wrinkles or cracks on the surface) or geometric or dimensional defects (e.g., tilted necks, external dimensional deviations).

[0093] In the output of the computer, a communication line can be provided in the direction of any control system of the manufacturing machine, with the aim of correcting the drift of the method based on the measurements performed.

[0094] Considering that the description can be applied to a second pair of dual-spectral infrared cameras, the following description only considers the first pair of dual-spectral infrared cameras 11, 12. The first dual-spectral infrared camera 11 is arranged along the first side I of the container 2, while the second dual-spectral infrared camera 12 is arranged along the second side II that is radially opposite to the container 2.

[0095] Given that each container 2 includes a glass wall in a rotational or cylindrical shape, the radially opposite positioning of the dual-spectral infrared cameras 11, 12 relative to the container results in considering that for each measurement point, the container 2 has a wall called the front wall and a wall called the back wall, and the front wall and back wall for one dual-spectral infrared camera correspond to the back wall and front wall for the other camera. In Figure 2 the example shown more specifically, each container 2 conventionally includes a first wall 21 located on the first side I of the container (i.e., located closest to the first dual-spectral infrared camera 11) and a second wall 22 located on the second side II that is radially opposite (i.e., located closest to the second dual-spectral infrared camera 12). Thus, each dual-spectral infrared camera 11, 12 takes into account the radiation emitted by the front wall of the container and possibly the radiation emitted by the back wall of the container and that has passed through the front wall.

[0096] According to the invention, each dual-spectral infrared camera 11, 12 transmits at least two infrared images of the radiation of the container located in its field of view for each container, one K1 in the first spectral band λ1 and the other K2 in the second spectral band λ2. The first spectral band λ1 and the second spectral band λ2 are selected according to the following measurement principle.

[0097] First, it should be considered that the first spectral band λ1 and the second spectral band λ2 are different or non - overlapping, i.e., there are no common values. According to another feature, for the temperature of the container 2, the absorption of radiation by the glass is different in the two spectral bands.

[0098] The theory of thermal radiation is reviewed below. In the remainder of the specification, for simplicity, the radiation is assimilated to infrared radiation perceived at the solid angle of an observer (e.g., a thermal camera observing the container) of the radiating body.

[0099] As Figure 3 shown, the thermal radiation R of a black body at a given wavelength and a given temperature (λ and T respectively) cn is given by the following expression:

[0100] [Equation 1]

[0101]

[0102] According to the definition of a black body, the emissivity ε is equal to the absorption α at thermal equilibrium:

[0103] [Equation 2]

[0104] l = ε = α

[0105] For a glass wall (gray body), the expression for the total perceived radiation M (total perceived radiation) as Figure 4 shown is written as:

[0106] [Equation 3]

[0107] M = R + ρ + Tr

[0108] - where R is the thermal radiation, ρ is the reflected radiation, and Tr is the transmitted radiation.

[0109] In the working spectral range, thus for the wavelength interval sensed by the sensor according to the present invention, compared with the intensity of the radiation emitted by the container, the reflected radiation is considered negligible. Then, the reflected perceived flux is considered zero, F = ρ = 0.

[0110] [Equation 4]

[0111] M = R + Tr

[0112] For a semi - transparent body, the Beer - Lambert law defining the absorption α of radiation A as a function of the thickness e through which the radiation Ao passes is considered.

[0113] [Equation 5]

[0114] Tr = τ × Ao = (1 - α) × Ao

[0115] - Where, Ao is the incident radiation and τ is the transmittance.

[0116] [Equation 6]

[0117] ε(λ, T, e) = α(λ, T, e) = (1 - e -μ(λT)e ) = (1 - τ(λ, T, e))

[0118] - Where, μ(λT) is the absorption coefficient (in mm -1 ) for wavelength λ and a given temperature T (in Kelvin). In fact, μ(λT) is the absorption coefficient integrated over a narrow band centered at wavelength λ.

[0119] Hereinafter, in terms of the applicable conditions, i.e., for the selected glass temperature and wavelength range, the correlation between the emissivity and the temperature of absorption is considered negligible.

[0120] For a given wavelength λ, the radiation R emitted by a glass wall with thickness e and temperature T is written as:

[0121] [Equation 7]

[0122] R(λ, T, e) = ε(λ, e) × R cn (λ, T)

[0123] - Where, the emissivity of the wall is expressed according to Equation [6]:

[0124] [Equation 8]

[0125] ε(λ, e) = 1 - e -μ(λ)·e

[0126] According to the present invention, the application of the theory of thermal radiation leads to considering two glass walls of the container. In fact, for a measurement point considered to be on the first side of the first wall of the container, for example, the radiation received from the container includes the radiation of the first wall located on one side of the measurement point plus the radiation emitted by the second opposite wall towards the inside of the container and passing through the first wall. Therefore, as Figure 2 shown, the perceived radiation of the first wall 21 of the container with thickness e1 and temperature T1 in the first spectral band λ1 sensitive to thickness and temperature includes the thermal radiation R(λ1, T1, e1) of the wall and the transmitted radiation τ(λ1, e1).R(λ1, T2, e2), where the transmitted radiation is the thermal radiation R(λ1, T2, e2) of the second wall 22 with thickness e2 and temperature T2 that is at least partially absorbed by the wall 21 and has a transmittance τ(λ1, e1). Similarly, the perceived radiation of the second wall 22 of the container with thickness e2 and temperature T2 in the first spectral band λ1 sensitive to thickness and temperature including the thermal radiation R(λ1, T2, e2) of said wall ) and a first wall with a thickness of e1 and a temperature of T1 21 at least part of which is absorbed by the wall 22 the transmitted radiation τ(λ1, e2).R(λ1, T1, e1), thus having a transmittance τ(λ1, e2). In the foregoing, according to Equation [6], the transmittances τ(λ1, e1) and τ(λ1, e2) of wavelength λ1 depend on the thickness across the wall, and the influence of temperature can be ignored.

[0127] Similarly, as Figure 5 shown, in a second spectral band λ2 sensitive to thickness and temperature, the received radiation of the first wall 21 of the container with a thickness of e1 and a temperature of T1 includes the thermal radiation of wavelength λ2 emitted by said wall (i.e., R(λ2, T1, e1)) and the radiation τ(λ2, e1).R(λ2, T2, e2) at least part of which is absorbed by the wall 21 of the second wall 22 with a thickness of e2 and a temperature of T2, thus having a transmittance τ(λ2, e1). Similarly, the received radiation of the second wall 22 of the container with a thickness of e2 and a temperature of T2 in the second spectral band λ2 sensitive to thickness and temperature includes the radiation R(λ2, T2, e2) of said wall and the radiation τ(λ2, e2).R(λ2, T1, e1) at least part of which is absorbed by the wall 21 of the first wall 21 with a thickness of e1 and a temperature of T1, thus having a transmittance τ(λ2, e2).

[0128] In view of the above thermal radiation theory, the following equations can be written:

[0129]

[0130]

[0131]

[0132]

[0133] These equations [9],

[10] ,

[11] and

[12] relate to the radiation across the container under consideration (i.e., the radiation of two walls with thicknesses and temperatures of e1, e2 and T1, T2 respectively and separated by an air gap). Recall that the emissivities of wavelengths λ1 and λ2 must be different, otherwise the system will of course have only two equations instead of four equations.

[0134] The present invention is based on the fact that the four equations [9] to

[12] allow for the determination from four radiation measurements provided by a measuring device such as an infrared dual-spectrum camera observing a thermal container and Four unknowns are known, namely, the thicknesses and temperatures e1, e2 and T1, T2 of the two walls respectively. As just explained, the equations result from Planck's law of radiation and Beer-Lambert's law of transmission. Prior knowledge of the container and the material, or prior knowledge of the parameter identification or calibration method, leads to the accurate determination of these equations for a given production of the container.

[0135] To facilitate the implementation of the present invention, a method includes simplifying the equations, which allows for the simplification of parameter identification and faster real-time calculations during the implementation of the method by means of computer analysis of infrared images. Therefore, hereinafter, around the operating point, thus for a selected spectral band, for the spectral transmission of glass, for the temperature range of the container at the output of the forming machine (i.e., between 300 and 700 °C), for the thickness range to be measured (e.g., between 0.5 and 5 mm), simplified functions of emissivity, blackbody radiation, and transmission with absorption will be defined.

[0136] Therefore, according to Equation [7], the radiation emitted by the wall, the intrinsic radiation of the glass wall is:

[0137] [Equation 13]

[0138] R(λ1, T1, e1) = ε(λ1, e1) × R cn (λ1, T1).

[0139] According to the present invention and according to Equation [8], the emissivity ε in the first spectral band λl is a function of the thickness of the semi-transparent body. Therefore, this emissivity is different from 1. For the wall thickness values to be measured (e.g., 0.5 to 5 mm), the emissivity in the first spectral band λ1 is approximately an affine function of the thickness, and its parameters can be identified by measurement and calibration.

[0140] [Equation 14]

[0141] ε(e1) = (a · e1 + b)

[0142] where the coefficients a, b depend on the wavelength λ1.

[0143] The radiation of the blackbody will be described by a function G(λ1, T) that is simpler than Equation [1]. For the working wavelength λ1, more specifically, for the working spectral band centered at λ1, G(λ1, T) = G1(T) is only a function of temperature. G1(T) is a simplified model of the blackbody radiation for the spectral band λ1, derived from Planck's law, for example, it is a polynomial, power, or exponential function. In practice, this function G1 takes into account the entire acquisition chain, especially the spectral sensitivity of the sensor and the transmission of the optical components inserted between the container and the sensor. The parameters of the function G1 (e.g., the coefficients of the polynomial, exponents, exponential coefficients, etc.) are determined in any suitable way, especially experimentally during the calibration of the measuring device according to the present invention. Obviously, for the second wavelength λ2, it is determined in the same way, and the function G(λ2, T) = G2(T).

[0144] Therefore, the simplified model of the radiation R emitted by the glass wall at a given wavelength or in a given spectral band near the wavelength λ1 is now written as follows:

[0145] [Equation 15] R(λ1, T1, e1) = R(T1, e1) = (a·e1 + b) × G1(T1)

[0146] In this expression, the parameters or constants of G1(T) and the coefficients a and b can be determined experimentally, or specifically, determined a priori according to the composition of the glass. Of course, for the wavelength λ2, the radiation of the same wall and the radiation of another wall with a thickness of e2 and a temperature of T2 are written in the same way, that is:

[0147] [Equation 15]

[0148] R(λ1, T1, e1) = R(T1, e1) = (a·e1 + b) × G1(T1)

[0149] [Equation 16]

[0150] R(λ1, T2, e2) = R(T2, e2) = (a·e2 + b) × G1(T2)

[0151] [Equation 17]

[0152] R(λ2, T1, e1) = R(T1, e1) = (c·e1 + d) × G2(T1)

[0153] [Equation 18]

[0154] R(λ2, T2, e2) = R(T2, e2) = (c·e2 + d) × G2(T2)

[0155] Specifically, equations [6] and

[14] near the operating point are used to linearize the transmission τ of the front wall with thickness e = e1 or e2 for the radiation from the rear wall in the following equation

[19] . The operating point is determined by the given temperature, the first spectral band centered around approximately the first wavelength λ1, and the range of thicknesses to be measured:

[0156] [Equation 19]

[0157] τ(λ1, e). = e -μ(λ1)e = 1 - α = 1 - ε(e) = 1 - (a·e + b)

[0158] Similarly, for the second spectral band centered around approximately λ2, the attenuation of the rear wall for the radiation from the front wall is:

[0159] [Equation 20]

[0160] τ(λ2, e). = e -μ(λ2)e = 1 - α = 1 - ε(e) = 1 - (c·e + d)

[0161] The coefficients a and b, c and d are obtained through calibration or are known a priori by any suitable method. They depend on the operating point, in particular on the selected wavelengths λ1 and λ2, the temperature range of the container under test, and the range of thicknesses to be measured.

[0162] For wavelength λ1, the radiation corresponds to the total radiation of the first wall plus the radiation of the second wall modulated by the absorption of the first wall. Therefore, the radiation can be expressed as follows:

[0163] [Equation 21]

[0164]

[0165] Similarly, the radiation corresponds to the total radiation of the second wall plus the radiation of the first wall modulated by the absorption of the second wall. Therefore, the radiation can be expressed as follows:

[0166] [Equation 22]

[0167]

[0168] Similarly, for wavelength λ2, the radiation N 12 corresponds to the total radiation of the first wall plus the radiation of the second wall modulated by the absorption of the first wall. Therefore, N 12 can be expressed as:

[0169] [Equation 23]

[0170]

[0171] Similarly, therefore can be expressed as:

[0172] [Equation 24]

[0173]

[0174] In this first variant of the invention, if the second spectral band λ2 is selected such that, although different from the emissivity of the first spectral band λ1, the emissivity depends on the thickness, then equations [9],

[10] ,

[11] and

[12] can be replaced by equations

[21] ,

[22] ,

[23] and

[24] respectively.

[0175] As a supplement, the following factors must be considered, especially due to the characteristics presented by the container 2 leaving the forming machine.

[0176] It should also be noted that, in a determined wavelength range, the emissivity of the glass is very insensitive to the temperature of the wall varying between 300 and 700 °C. For this determined wavelength range, the absorption coefficient (and thus the emissivity) does not depend on the temperature, or this dependence can be neglected. Therefore, only the spectral absorption coefficient μ makes the absorption thickness-dependent and, similarly, makes the emissivity thickness-dependent.

[0177] According to a feature of the invention, the first spectral band λ1 is selected from the wavelength range in which the emissivity of the glass does not depend on the temperature. This allows the application of equations [7] and [8].

[0178] Furthermore, for a spectral band determined in the range greater than 4500 nanometers (preferably, greater than 5000 nanometers), the emissivity of the glass is very close to 1, that is to say, it is approximately considered equal to 1. For this spectral band, the radiation is assimilated to the radiation of a black body. According to a preferred variant, the second spectral band λ2 is selected in the wavelength range in which the radiation does not depend on the thickness and the observed wall does not transmit the radiation of the opposite face, because the absorption is also close to 1, in other words, the glass is opaque in this wavelength range. For each face of the wall, an expression for the radiation perceived in this spectral band will be derived, namely:

[0179] [Equation 25]

[0180] N1 = R(λ2, T1, e1) = G(T1)

[0181] [Equation 26]

[0182] N2 = R(λ2, T2, e2) = G(T2)

[0183] Thus, in this variant, equations [9],

[10] ,

[11] and

[12] can be replaced by equations

[21] ,

[22] ,

[25] and

[26] respectively. This variant using a wavelength where the radiation does not depend on the thickness simplifies the calculation of solving a system of 4 equations with 4 unknowns, since the unknowns T1 and T2 (i.e., the temperatures of the two walls) immediately emerge from equations

[21] and

[22] .

[0184] According to the present invention, a first spectral band λ1 is selected such that in the first spectral band, the glass absorbs radiation such that:

[0185] * The radiation from the first wall 21 measured from the first side of the container 2 is the sum of the radiation emitted by the first wall 21 and the radiation emitted by the second wall 22 and absorbed and transmitted through the first wall 21, such that the combined radiation depends on the thicknesses and temperatures of the first and second walls; and

[0186] * The radiation from the second wall 22 measured from the second side of the container 2 is the sum of the radiation emitted by the second wall 22 and the radiation emitted by the first wall 21 and absorbed and transmitted through the second wall 22, such that the combined radiation depends on the thicknesses and temperatures of the first and second walls.

[0187] It should be understood that the present invention proposes to measure infrared radiation having a first spectral band λ1 at which the intensity of the radiation depends on the thickness of the glass wall and the surface temperature of the wall. According to the present invention, the first spectral band λ1 is selected such that the emissivity depends on the thickness of the wall, thus being far from 1 but also high enough to measure sufficient radiation. Further, it is sought that this emissivity varies little with the color of the glass. Thus, the first spectral band λ1 is selected such that for white glass with a thickness varying between 1 and 5 mm, for a glass temperature of approximately 450 °C (more generally, between 300 and 700 °C), the emissivity varies between (approximately) 0.3 and 0.7. It should be noted that for the same thickness and the same temperature, the emissivity in green or amber glass varies around the same value.

[0188] In addition, the first spectral band λ1 is selected to obtain the transmission of the radiation from the back in the presence of absorption at the front. This indeed allows, in equations

[10] and

[11] , τ(λ1, e1) = e -μ(λ1)e1 and τ(λ1, e2) e -μ(λ1)e2 where the transmission is not equal to 1, and thus the attenuation is non-zero. Zero attenuation does not correspond to an ordinary container. In the case of zero attenuation, only the sum of the thicknesses e1 + e2 of the two walls can be measured without distinguishing between the two. On the contrary, if the total absorption e -μ(λ1)e1 = 0 or e -μ(λ1)e2= 0, which means that the glass is opaque to the first spectral band. In this case, regardless of the thickness, only the surface temperature of the front wall is measured in the first spectral band.

[0189] It should be noted that the radiation in the first spectral band λ1 emitted by the container can be selected from the range between 1100 nm and 2600 nm. However, this range is applicable to green glass or amber glass containers, but not to white glass containers, because in this range, the emissivity of white (transparent) glass is very low.

[0190] According to the present invention, the first spectral band λ1 is selected from the range between 2800 nm and 4000 nm (preferably, between 3000 nm and 4000 nm). This preferred first spectral band is selected for a large number of glass colors, including white glass.

[0191] As described above, the second spectral band λ2 is selected such that the absorption of radiation by the glass is different from the absorption of radiation in the first spectral band λ1. Recall that for the selected first spectral band λ1, the emissivity varies between 0.3 and 0.7. According to Figure 5 the first variant shown, the second spectral band λ2 is also selected such that, on the one hand, the radiation from the first wall 21 measured from the first side of the container is the sum of the radiation emitted by the first wall 21 and the radiation emitted by the second wall 22 and transmitted through the first wall, and on the other hand, the radiation from the second wall 22 measured from the second side of the container is the sum of the radiation emitted by the second wall 22 and the radiation emitted by the first wall 21 and transmitted through the second wall 22, and the combined radiation depends on the thickness of the wall and the temperature of the wall.

[0192] According to this first variant, the radiation in the second spectral band λ2 emitted by the container is selected from the range between 1100 nm and 2600 nm. In this variant, for some glasses, the transmittance is very high while the emissivity may be very low, usually less than 0.1 for a glass thickness of 1 to 5 mm at 450 °C. Since the infrared signal is limited, the accuracy of thickness measurement may be insufficient for these glass colors.

[0193] According to Figure 6 the second preferred variant shown, the second spectral band λ2 is selected such that the glass absorbs radiation such that: on the one hand, the radiation from the first wall 21 measured from the first side I of the container is only the radiation emitted by the surface of the first wall 21, and on the other hand, the radiation from the second wall 22 measured from the second side II of the container is only the radiation emitted by the surface of the second wall, and the radiation only depends on the temperature.

[0194] Therefore, the radiation in the second spectral band emitted by the first wall of the container Is only sensitive to the surface temperature. Similarly, the radiation in the second spectral band emitted by the second wall of the container Is only sensitive to the surface temperature.

[0195] According to this preferred variant, the second spectral band λ2 is selected from the range greater than 4500 nanometers (nm) (preferably, greater than 5000 nanometers). The second spectral band λ2 is selected such that the emissivity is close to 1, that is, close to the emissivity of a black body. This means that the absorption of the glass for the radiation in this spectral band is high, and thus the emissivity is, for example, greater than 0.9. The radiation N1, N2 of the first and second faces perceived in the second spectral band λ2 is represented quite faithfully by Planck's law or by the approximate functions G(T1) and G(T2) according to the present invention, as represented by equations

[25] and

[26] .

[0196] According to this preferred variant, where the second spectral band λ2 is selected in the range greater than 4500 nanometers (preferably, greater than 5000 nanometers), it is advantageous to simultaneously select the first spectral band λ1 in the range between 2800 nanometers and 4000 nanometers (preferably, between 3000 nanometers and 4000 nanometers). Thus, images can be measured or generated in the two spectral bands λ1 and λ2 to use the same MWIR (mid-wave infrared) sensor technology, preferably of the uncooled sensor type. Here, a cooled sensor refers to a MWIR or LWIR sensor, such as a sensor equipped with a cryogenic cooling system sold by SOFRADIR or LYNRED. An uncooled sensor is indeed much cheaper than a cooled sensor and is more robust. Of course, the MWIR camera according to the present invention is equipped with solutions for protecting the radiation (cooled housing, skylight, screen) and for cooling and / or heat dissipation, such as, for example, a water circuit, forced ventilation, Peltier effect cells, heat pipes, radiators, etc.

[0197] Generally, the first spectral band λ1 is selected from the range between 3000 nanometers and 4000 nanometers, and the second spectral band λ2 is selected from the range greater than 4500 nanometers. Advantageously, the first spectral band λ1 is selected centered around a wavelength value of approximately 3600 nanometers, while the second spectral band λ2 is selected centered around a wavelength value of approximately 4700 nanometers.

[0198] According to the invention, the dual-spectrum infrared cameras 11-14 are driven by the system 15 so as to measure, from the first side I of the container, the intensity of the radiation in the first spectral band λ1 and simultaneously in the second spectral band λ2 from the first wall 21, and to measure, from the second side II of the container, the intensity of the radiation in the first spectral band λ1 and simultaneously in the second spectral band λ2 from the second wall 22. Thus, for each container 2, the invention aims to make at least two measurements of the intensity of the radiation in the first spectral band received from two opposite walls, and at least two measurements of the intensity of the radiation in the second spectral band from two opposite walls. According to an advantageous feature, the invention aims to produce a one-dimensional or two-dimensional image of the container wall as a radiation measurement. Thus, for each container, the dual-spectrum infrared cameras 11, 14 each transmit at least two infrared images of the radiation of the container wall located in their field of view. According to a variant, the two dual-spectrum infrared cameras 11, 12 transmit at least two images of the infrared radiation in the first spectral band and at least two images of the infrared radiation in the second spectral band for each container. According to another variant implementing four dual-spectrum infrared cameras 11, 14, eight images of the infrared radiation can be obtained, such that the walls of the container are represented as a whole in two spectral bands. In this case, the field of view is such that each camera measures at least a quarter of the container circumference.

[0199] It is also conceivable to increase the overlap of the views by means of three pairs of opposite dual-spectrum cameras. More generally, according to the practice of those skilled in the art and in particular according to the structure of the in-line inspection system in the cold zone, an arbitrary arrangement of cameras can be provided based on the shape and spacing of the containers in order to fully observe the circumference of the containers, whether their shape is characterized by a circular level (cone or ordinary cylinder) or a rectangular, polygonal planar section, etc.

[0200] According to another feature of the invention, by considering the intensity of the radiation in the first spectral band, the radiation emitted by the wall, and the radiation that is absorbingly transmitted from another radially opposite wall, the computer 16 allows to determine at least the thickness e1 of the first wall 21 and the thickness e2 of the second wall 22 based on the measurement results of the intensity of the radiation in the first spectral band and the second spectral band from the first wall 21 and the measurement results of the intensity of the radiation in the first spectral band and the second spectral band from the second wall 22.

[0201] Thus, according to the general equations [9],

[10] ,

[11] and

[12] , or more specifically their simplifications

[21] ,

[22] ,

[23] and

[24] , or even

[21] ,

[22] ,

[25] and

[26] in the case where the second wavelength is selected such that the emissivity is close to 1, the thickness e1 of the first wall 21 and the thickness e2 of the second wall 22 are determined from four measurements of the radiation intensity. The system of four equations with four unknowns is solved at least in the linearized version, but if necessary, more complex models can also be used to solve it to improve the measurement accuracy.

[0202] According to a preferred variant, wherein the second spectral band λ2 depends only on temperature, the thickness and possibly the temperature are determined from the group of equations

[21] ,

[22] ,

[25] and

[26] .

[0203] Recall that for this preferred variant, the infrared radiation is measured on the one hand through the first spectral band and on the other hand through the second spectral band, at which the intensity of the radiation depends on the thickness and the surface temperature of the wall, and at which the intensity of the radiation depends only on the surface temperature. Thus, the temperature information can be "subtracted from the signal".

[0204] From four independent measurements of the radiation and by taking into account the influence of the radiation perceived on each face relative to the opposite face in the first spectral band, the thickness e1 of the first face, the thickness e2 of the second face, and optionally, the temperature T1 of the first face and the temperature T2 of the second face can be derived. To perform this calculation, a mathematical model is used to relate the four radiation measurements to the four final measurements (i.e., two thickness measurements and two temperature measurements).

[0205] The mathematical model can be empirical or analytical. It may be valid only for certain operating conditions that allow the setting of constants and the linearization of the model. Of course, the simplifications made to equations

[15] and

[19] are not necessary for the present invention, they only allow the calculation to be implemented more easily and inexpensively. The analytical model can clearly be more refined, allowing for more accurate measurements, and can take into account the composition, average temperature or shape of the container. The mathematical model can also include a geometric model capable of describing the 3D geometry of the container, with the glass thickness distribution and the temperature distribution as features. For example, for a simple conical-like article, the surface of the body will be conical, with the thickness value at each point in millimeters and the temperature in °K.

[0206] As can be seen from the description, the installation 1 according to the invention comprises dual-spectrum infrared cameras 11-14. Although a non-planar image sensor can be used without inconvenience in carrying out the invention on the basis of a non-planar image, the description assumes a planar sensor and the term "formed image" generally refers to a planar image of an object or a scene (in this case, at least a part of the wall of the container).

[0207] When each camera has a plurality of sensors, there are several ways of assembling them. Hereinafter, upstream and downstream designate the positions of the optical elements placed on the radiation beam which is collected and processed in the direction of the path of the light originating from the container to reach the sensor.

[0208] According to a first variant of the invention, the dual-spectrum infrared camera comprises, for example Figure 7 、 Figure 8 as shown:[[]]

[0209] - a beam splitter 20, downstream of which the light beam is split into two different downstream light beams;

[0210] - two different sensors 21, 22 ( Figure 7 ) or two sensor parts ( Figure 8 ) placed in a plane or two image planes, each receiving one of the two different downstream light beams, the first sensor or the first sensor part receiving a first radiation beam in a first spectral band and the second sensor or the second sensor part receiving a second radiation beam in a second spectral band;

[0211] - the first light beam and the second light beam are shaped upstream or downstream of the beam splitter 20 and an optical image K1, K2 of the container is formed by optical conjugation by means of a lens 23 on each image plane (and thus on each sensor or sensor part) respectively in the first spectral band and the second spectral band;

[0212] - the first light beam and / or the second light beam are filtered by one or more filters 25, 26 of the band-pass type, for example, which respectively select the first spectral band and the second spectral band.

[0213] At least two different sensors 21, 22 ( Figure 7 ) or sensor parts ( Figure 8 ) each transmit a digital image of each container, which corresponds to the conversion of the optical images K1, K2 of the radiation M or N sensed in at least two different infrared bands.

[0214] The beam splitter 20 is, for example, a prism, a blade or a beam splitter cube. It is an optical element which deflects the upstream light beam along two downstream light beams in two different directions.

[0215] The linear sensor part consists of photosensitive elements arranged in parallel rows. The acquisition or reading of the linear sensor part provides a single digital image row. Additionally, during the inspection of a moving container, it is known to acquire successive digital image rows in order to reproduce, by means of a simple and known scanning method, a two-dimensional image of the container in the plane field passing through the linear sensor part. (nb plane field = defined by the sensor row and the optical center = fan-shaped field). Of course, the displacement or travel vector is not parallel to the direction of the linear sensor part. There are linear sensors on the market that include a single row of photosensitive elements. There are also sensors that include several rows of photosensitive elements arranged in parallel, and that transmit only digital image rows, which are a combination of information from different rows. Finally, a matrix sensor can be driven so as to acquire, over time, only one or two or more digital image rows from different rows of the sensor and from these different parallel rows, obtained by scanning one or two or more two-dimensional images of the moving container at different positions separated in time. In other words, a matrix sensor can be used as one or two or more linear sensors that transmit digital image rows over time. The concept of the linear sensor part encompasses both of these methods.

[0216] According to a second variant of the invention, each dual-spectrum infrared camera comprises, for example Figure 9 as shown:

[0217] - a lens 23 that forms an optical image K3 of the field traversed by the container by optical conjugation in the sensor plane;

[0218] - two different linear sensor parts 41, 42, the support lines s1, s2 of which are perpendicular and arranged such that during the travel of the container in the field of the lens 23, a scanned image is produced using each of the two linear sensor parts;

[0219] - the first linear sensor part 41 receives a first part 31 of the radiation beam in a first spectral band;

[0220] - the second sensor part 42 receives a second part 32 of the radiation beam in a second spectral band;

[0221] - at least one filter 45, arranged in the path of the beam between the lens and the two linear sensor parts 41, 42, to select the first spectral band and the second spectral band.

[0222] Note that in this version, a beam splitter 20 is not required.

[0223] Thus, after the container has passed through the field of the lens 23, it has passed through the field of each of the two linear sensor parts. By scanning, two two-dimensional images of the container can be obtained at two selected wavelengths.

[0224] One advantageous embodiment is to use a single two-dimensional sensor 43, which is placed behind at least one filter that only covers a part of the sensor, as Figure 9 shown. Another way includes placing two linear sensors in the image plane.

[0225] Of course, in this second variant, there is nothing to prevent the two-dimensional image of the container from being partially formed on the first sensor part 41 and partially formed on the second sensor part 42 at a given point during the container's travel in the lens 23 field.

[0226] In all variants, it is possible to use two filters to select these two spectral bands. It may be advantageous to select a band-pass filter as the optical filter.

[0227] Obviously, at least one filter is needed only when the same technology is adopted in the two sensor parts and accordingly each sensor part has the same inherent spectral response or sensitivity.

[0228] According to a preferred variant, wherein the second spectral band λ2 is selected in the range greater than 4500 nanometers (preferably, greater than 5000 nanometers), and the first spectral band λl is in the range between 2800 nm and 4000 nanometers (preferably, between 3000 nanometers and 4000 nanometers), one or two sensors of the MWIR (mid-wave infrared) sensor type that do not require any of the above cooling systems can be used for the sensor. This allows the implementation of Figure 8 and Figure 9 the variant including a single sensor shown. To implement the variant including two sensors, as Figure 7 shown, in the case of a general and simplified drive device, using two sensors with the same technology simplifies the implementation, especially by allowing the two sensors to have the same resolution for the same field and be synchronous.

[0229] The sensors included in each dual-spectrum infrared camera are based on, for example, PbSe or microbolometers at 196 or 300°K.

[0230] Of course, the present invention is not limited to the above dual-spectrum camera embodiments.

Claims

1. A method for measuring the wall thickness of a container (2) for high-temperature glass that exits a forming cavity and moves along a translation path F, the method comprising the steps of: - Measuring the intensity of the radiation emitted by each container (2) from the first side I and the second side II that are radially opposite to each other of the container (2), the radiation being emitted by the first wall (21) of the container located along the first side I and the radially opposite second wall (22) of the container located along the second side II; - Measuring the radiation emitted by the container (2) in a first spectral band λ1 and the radiation emitted in a second spectral band λ2, wherein the first spectral band λ1 is in the range of 2800 nanometers to 4000 nanometers, and the first spectral band and the second spectral band are different and are selected such that: ◆ For the temperature of the container, the absorption of the radiation by the glass of the container is different in the first spectral band and the second spectral band; and ◆ In the first spectral band λ1, the absorption of the radiation by the glass of the container is such that: * The radiation from the first wall (21) measured from the first side I of the container is the first sum of the radiation emitted by the first wall (21) and the radiation emitted by the second wall (22) and transmitted through the first wall (21) with absorption, such that the first sum depends on the thickness and temperature of the first wall (21) and the thickness and temperature of the second wall (22); and * The radiation from the second wall (22) measured from the second side II of the container is the second sum of the radiation emitted by the second wall (22) and the radiation emitted by the first wall (21) and transmitted through the second wall (22) with absorption, such that the second sum depends on the thickness and temperature of the first wall (21) and the thickness and temperature of the second wall (22); wherein the measurement of the intensity of the radiation from the first wall (21) in the first spectral band λ1 and the second spectral band λ2 from the first side I of the container and the measurement of the intensity of the radiation from the second wall (22) in the first spectral band λ1 and the second spectral band λ2 from the second side II of the container are carried out simultaneously; and - By considering, in the first sum and the second sum of the intensity of the radiation in the first spectral band, the radiation emitted by one wall in the first spectral band λ1 and the radiation from the radially opposite other wall of the container in the first spectral band λ1, which is subsequently transmitted through the one wall with absorption, at least determining the thickness of the first wall and the second wall (22) of the container according to the measurement results of the intensity of the radiation from the first wall in the first spectral band and the second spectral band and the measurement results of the intensity of the radiation from the second wall in the first spectral band and the second spectral band; wherein determining the thickness of the first wall and the second wall (22) of the container includes: when the radiation is transmitted through the wall of the container, considering the non-zero attenuation of the radiation in the first spectral band λ1 to distinguish the thickness of the first wall (21) and the thickness of the second wall (22).

2. The method according to claim 1, wherein, In the second spectral band λ2, the absorption of radiation by the glass is different from the absorption of radiation by the glass in the first spectral band λ1 and is such that: - The radiation from the first wall (21) measured from the first side I of the container is a third sum of the radiation emitted by the first wall (21) and the radiation emitted by the second wall (22) and transmitted through the first wall (21), and - The radiation from the second wall (22) measured from the second side II of the container is a fourth sum of the radiation emitted by the second wall (22) and the radiation emitted by the first wall (21) and transmitted through the second wall (22), the radiation depending on the thickness of the wall and the temperature of the wall, wherein the thickness of the first wall of the container and the thickness of the second wall (22) are also determined based on the third sum and the fourth sum.

3. The method according to claim 1, wherein, Based on the intensity of the radiation in the first spectral band and the intensity of the radiation absorbed and transmitted from the wall on the other side, and also according to the measurement results of the intensity of the radiation of the first wall (21) in the first spectral band and the second spectral band and the measurement results of the intensity of the radiation of the second wall (22) in the first spectral band and the second spectral band, the temperatures T1 of the first wall (21) and the second wall (22) are determined.

4. The method according to claim 1, wherein, The radiation emitted by the container in the first spectral band λ1 is measured in the range from 3000 nanometers to 4000 nanometers.

5. The method according to claim 1, wherein, In the second spectral band λ2, the absorption of radiation by the glass is such that: - The radiation from the first wall (21) measured from the first side I of the container is only the radiation emitted from the surface of the first wall (21), and - The radiation from the second wall (22) measured from the second side II of the container is only the radiation emitted from the surface of the second wall (22), the radiation depending only on the temperature.

6. The method according to claim 5, wherein, Based on the measurement results of the intensity of the radiation of the first wall (21) in the second spectral band λ2 and the measurement results of the intensity of the radiation of the second wall (22) in the second spectral band λ2, the temperatures T1 and T2 of the first wall (21) and the second wall (22) are determined.

7. The method according to claim 1, wherein, The radiation emitted by the container in the second spectral band λ2 is measured in the range from 1100 nanometers to 2600 nanometers.

8. The method according to claim 5, wherein, The radiation emitted by the container in the second spectral band λ2 is measured in the range greater than 4500 nanometers.

9. The method according to claim 5, wherein, The radiation emitted by the container in the second spectral band λ2 is measured in the range greater than 5000 nanometers.

10. The method according to claim 1, wherein, The simultaneous measurement of the intensity is carried out using at least two dual-spectrum infrared cameras (11, 12 - 13, 14), wherein for each container, each dual-spectrum infrared camera transmits at least two infrared images of the radiation of the wall of the container located in the observation field of each dual-spectrum infrared camera.

11. A facility for measuring the wall thickness of a container (2) for high-temperature glass that exits a forming cavity (4) and moves along a translation path F, the facility comprising: - At least a first dual - spectrum infrared camera (11) and a second dual - spectrum infrared camera (12), the first dual - spectrum infrared camera (11) and the second dual - spectrum infrared camera (12) being arranged radially opposite to each other on either side of the translation path F of the container to receive the radiation emitted by the first wall (21) of the container (2) located on the first side I of the container and the radiation emitted by the second wall (22) of the container located on the radially opposite second side. Each of the first dual - spectrum infrared camera (11) and the second dual - spectrum infrared camera (12) transmits two images of the infrared radiation of the wall of the container in its field of view in a first spectral band λ1 and a second spectral band λ2, wherein the first spectral band is in the range of 2800 nanometers to 4000 nanometers, the first spectral band and the second spectral band are different, and are selected such that: ◆ For the temperature of the container, the absorption of radiation by the glass is different in the first spectral band λ1 and the second spectral band λ2; and ◆ At least in the first spectral band λ1, the absorption of radiation by the glass is such that: * The radiation from the first wall (21) measured from the first side of the container is a first sum of the radiation emitted by the first wall (21) and the radiation emitted by the second wall (22) and absorbed and transmitted through the first wall (21), such that the first sum depends on the thickness and temperature of the first wall and the thickness and temperature of the second wall; and * The radiation from the second wall (22) measured from the second side II of the container is a second sum of the radiation emitted by the second wall (22) and the radiation emitted by the first wall (21) and absorbed and transmitted through the second wall (22), such that the radiation of the second sum depends on the thickness and temperature of the first wall (21) and the thickness and temperature of the second wall (22); - A system (15) for driving the operation of the first dual - spectrum infrared camera (11) and the operation of the second dual - spectrum infrared camera (12) so as to simultaneously obtain, using the first dual - spectrum infrared camera (11), two images measuring the intensity of the radiation of the first wall (21) in the first spectral band λ1 and the second spectral band λ2, and using the second dual - spectrum infrared camera (12), two images measuring the intensity of the radiation of the second wall (22) in the first spectral band λ1 and the second spectral band λ2; and - A computer (16), configured to: at least determine the thickness e1 of the first wall (21) and the thickness e2 of the second wall (22) by analyzing two images respectively giving measurement results of the intensity of radiation from the first wall (21) in the first spectral band λ1 and the second spectral band λ2 and two images of the second wall in the first spectral band λ1 and the second spectral band λ2, by taking into account the radiation emitted by the wall of the container and the radiation that is absorbingly transmitted through the wall of the container from the wall on the other side in the first sum and the second sum of the intensity of the radiation in the first spectral band; wherein, to determine the thickness of the first wall and the thickness of the second wall (22) of the container, the computer is configured to: when the radiation is transmitted through the wall of the container, take into account the non-zero attenuation of the radiation in the first spectral band λ1 to distinguish the thickness of the first wall (21) and the thickness of the second wall (22).

12. The facility according to claim 11, wherein, The dual-spectrum infrared cameras (11-14) include: - A beam splitter (20), downstream of which the light is split into different first downstream beams and second downstream beams; - A first sensor (21) and a second sensor (22) or a first sensor part and a second sensor part downstream of the beam splitter (20), the first sensor (21) and the second sensor (22) or the first sensor part and the second sensor part being placed in a plane or two image planes, each of the first sensor (21) or the second sensor (22) or the first sensor part or the second sensor part receiving one of the different first downstream beams and second downstream beams, the first sensor or the first sensor part receiving a first radiation beam in the first spectral band, and the second sensor or the second sensor part receiving a second radiation beam in the second spectral band; - The first downstream beam and the second downstream beam are formed upstream or downstream of the beam splitter (20), and the lens (23) forms optical images (K1, K2) of the container in the first spectral band and the second spectral band respectively on each image plane by optical conjugation; - The first downstream beam and / or the second downstream beam are filtered by one or more filters (25, 26) respectively selecting the first spectral band and the second spectral band.

13. The facility according to claim 11, wherein, Each of the first dual-spectrum infrared camera and the second dual-spectrum infrared camera includes: - A lens (23), forming an optical image K3 of the field passed through by the container by optical conjugation on the sensor plane; - A first linear sensor part (41) and a second linear sensor part (42), the respective support lines s1, s2 of which are perpendicular, and arranged such that during the travel of the container in the field of the lens (23), a scanned image is generated by each of the first linear sensor part and the second linear sensor part; - The first linear sensor part (41) receives a first part of the radiation beam (31) in the first spectral band; - The second linear sensor part (42) receives a second part of the radiation beam (32) in the second spectral band; - At least one filter (45) is arranged in the path of the first part of the radiation beam or the second part of the radiation beam to select the first spectral band and the second spectral band.

14. The facility according to claim 12, wherein, The filters (25, 26, 45) select a first spectral band in the range from 2800 nanometers to 4000 nanometers and a second spectral band in the range greater than 4500 nanometers.

Images