Method and device for basis weight measurement of a sheet or foil, combining an X-ray sensor and an ultrasonic sensor

Abstract

A method for X-ray characterization of a product, the method comprising the steps of: performing X-ray absorption measurement and ultrasonic measurement on the product so as to obtain X-ray measurement data and ultrasonic measurement data across the width of the product; calculating a calibration coefficient (C) based on the ratio between the X-ray measurement data #imgabs0# and the ultrasonic measurement data #imgabs1#, and calculating a corrected value of the X-ray measurement data by multiplying the X-ray measurement data by the calibration coefficient.

Description

Technical Field

[0001] The subject matter of the present invention is the manufacture of flat products, such as paper, certain plastics or coated foils, for example for forming thin-film battery elements (such as electrodes), which requires controlling the characteristics of these flat products during their formation. Background Art

[0002] The foil or sheet being formed (hereinafter referred to as "product") can have a width of up to 10 meters or more and runs continuously in the machine direction and needs to be continuously monitored by a non-contact measurement system. Monitoring of the characteristics of such a product is carried out by an in-situ measuring device including sensors mounted on a mechanical frame that is capable of moving these sensors across the width of the running product being formed in order to generate a profile of the physical characteristics being measured.

[0003] Some sensors perform absorption measurements of a certain radiation sent through the product: the emitting head of the sensor sends radiation towards the product while the detecting head performs the measurement of the radiation transmitted through the product. These two heads are moved together across the product so as to always face each other.

[0004] The radiation can be of various types, each type corresponding to a given sensor type: ultrasound as described in US 5,621,173 or US 4,446,735; β-radiation; X-rays as described in GB 1,271,438 or EP 1,950,527; or infrared radiation. The sensor type is selected according to the material to be characterized and the specific needs of the practitioner.

[0005] The non-destructive evaluation of bonded aerospace components is described in the article "Non-destructive Evaluation of the Quality of Adhesive Using Ultrasound, X-ray, and Feature-based Delta Fusion" by Jasiuniene Elena et al., Applied Science, Vol. 12, No. 24, 2022 / 12 / 01, page 12930, which involves the fusion of images obtained by ultrasonic pulse-echo and radiography techniques.

[0006] Characterizing products that are homogeneous and stable in composition is a task that is routinely carried out. However, characterizing products that lack even one of these features is more challenging.

[0007] This creates serious difficulties in the case of laboratory production lines, where the process is tested before being output to a pilot production line and ultimately to a factory production line. In the factory production line, the manufacturing process is stable, the characteristics of the product being manufactured are well-known and stable, and the equipment including the monitoring sensors is calibrated for all specific products. In contrast, in the laboratory production line, the process is changed regularly in order to test the characteristics of various product compositions and the influence of manufacturing parameters on the manufacturing process and the final product. In such cases, it may be necessary to recalibrate the sensors for each new batch of tests, which is generally impractical or even infeasible.

[0008] In addition to problems related to the stability and variability of the manufacturing process, some products are inherently not properly characterized by existing monitoring tools. For example, when coating a foil intended to form a battery electrode, the coating may have a solvent content that can change spontaneously (in the case of testing) or non-spontaneously over time. The coating process can also form patterns that present steep edges. Conventional characterization means cannot take these features into account to deliver a reliable distribution of, for example, the actual basis weight or grammage of the final product.

[0009] Object of the Invention

[0010] Taking into account the above problems, the applicant considered combining two types of sensors with complementary characteristics to characterize heterogeneous products. More specifically, the applicant proposed to perform a "dynamic" calibration of the X-ray measurement device.

[0011] In general, calibration is the comparison of the measured values provided by the device under test with the measured values of a calibration standard of known accuracy. Without comparison with such a standard, the raw measured values only represent relative values. Comparing these raw measured values with the standard values can make them absolute values. A calibration standard of known accuracy can be another measuring device capable of outputting absolute values of the same measurement results.

[0012] In the context of the present invention, and as will be explained in more detail below, the X-ray measurement data represents the measured values of the device under test, while the ultrasonic measurement data provides a standard of known accuracy.

[0013] In fact, the applicant determined that performing X-ray measurements and ultrasonic measurements simultaneously on heterogeneous products provides data suitable for generating a quantitatively accurate basis weight distribution of the product, even if the product may have an unknown composition and exhibit strong topological variations (such as coating edges). Summary of the Invention

[0014] For this purpose, a first aspect of the invention relates to a method for measuring the basis weight distribution of a product by X-ray characterization, which comprises the following steps: performing X-ray absorption measurement based on the transmission of X-rays through the product, and performing ultrasonic intensity wave measurement on the product based on the response of the product to ultrasonic waves directed at the product, so as to obtain (i) X-ray measurement data representing the basis weight distribution of the product across the width of the product as perceived via the X-ray absorption measurement, and (ii) ultrasonic measurement data representing the basis weight distribution of the product across the width of the product as perceived via the ultrasonic measurement; calculating a calibration coefficient for the X-ray measurement data by using the ultrasonic measurement data as a reference, the calibration coefficient being based on the ratio between the X-ray measurement data and the ultrasonic measurement data; and calculating a corrected value of the X-ray measurement data by multiplying the X-ray measurement data by the calibration coefficient.

[0015] This method allows for the generation of a quantitatively accurate basis weight distribution of the product, even when the product has an unknown composition and exhibits strong topological variations (such as coating edges).

[0016] Additional non-limiting features according to the first aspect of the invention, taken alone or in any technically feasible combination:

[0017] - The calibration coefficient is based on the ratio between a linearization function applied to the X-ray measurement data and a linearization function applied to the ultrasonic measurement data;

[0018] - A section of the product includes at least one pattern on a support substrate, and the method may further comprise the steps of: determining the extent of a flat section formed by the pattern on the support substrate, the X-ray measurement data and the ultrasonic measurement data for calculating the calibration coefficient applicable to the extent; and

[0019] - The extent may be free of topographical singularities;

[0020] - The method may be applied to a product manufactured by forming a coating pattern on a support substrate by means of a coating device, and the X-ray absorption measurement and the ultrasonic measurement are performed downstream of the coating device;

[0021] - The X-ray measurement data may be differential data relative to a reference measurement performed upstream of the coating device; and

[0022] - The method may include the step of calculating the basis weight distribution of the product based on the X-ray measurement data and the calibration coefficient.

[0023] The second aspect of the present invention relates to a method for calculating the weight ratio of a compound in a product, the method comprising the steps of: determining a first calibration coefficient of the compound according to the first aspect of the present invention; determining a second calibration coefficient of a modified product having the same composition as the product according to the first aspect of the present invention, except that the modified product substantially does not contain the compound; determining a third calibration coefficient of the product according to the first aspect of the present invention; and calculating the weight ratio based on the first calibration coefficient, the second calibration coefficient, and the third calibration coefficient.

[0024] The third aspect of the present invention relates to a measuring device, the measuring device comprising: a frame extending in a width direction; a sensor movable in the width direction; and a drive system configured to move the sensor in the width direction, the sensor including a transmitter head and a receiver head facing the transmitter head; and a control system configured to control the sensor and the drive system and including a computer memory and an electronic computer, wherein the transmitter head includes an X-ray source and an ultrasonic source, the receiver head includes (i) an X-ray detector and (ii) an ultrasonic detector, and the control system is configured to perform the method for X-ray characterization of a product according to the first aspect of the present invention.

[0025] The fourth aspect of the present invention relates to a production line, the production line comprising a measuring device according to the third aspect of the present invention and a coating device located upstream of the measuring device. The production line may further include a reference X-ray measuring device configured to perform reference X-ray absorption measurements and located upstream of the coating device. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Many other features and advantages of the present invention will become apparent upon reading the following detailed description when considered in conjunction with the accompanying drawings, in which:

[0027] - Figure 1 shows a combined X-ray / ultrasonic measurement system;

[0028] - Figure 2 shows Figure 1 the sensor of the system;

[0029] - Figure 3 shows Figure 1 the production line of which the measurement system is a part;

[0030] - Figure 4 shows Figure 2 the function of the sensor;

[0031] - Figure 5 shows a product that can be characterized by the Figure 1 system;

[0032] -Figure 6 illustrates Figure 1 the working principle of the system of

[0033] - Figure 7 illustrates Figure 1 the function of the system of

[0034] - Figure 8 illustrates the curve obtained by means of the measurement system of Figure 1 ;

[0035] - Figure 9 illustrates the characterization process implemented by the system of Figure 1 ;

[0036] - Figure 10 illustrates the linearized X-ray and ultrasonic measurement data; and

[0037] - Figure 11 illustrates the characterization process based on the process of Figure 9 ; DETAILED DESCRIPTION

[0038] Figure 1 illustrates the measuring device 100 in operation, the measuring device including: a frame 10 defining an aperture 12, the frame and the aperture extending in a width direction W dir ; a sensor 20 movable within the aperture 12 in the width direction W dir ; and a drive system 30 configured to move the sensor 20 in the width direction W dir . The sensor 20 includes a transmitter head 22 and a receiver head 24 facing the transmitter head 22. In (a), the measuring device 100 is represented in a front view as seen in the machine direction M dir (i.e., in the circumferential direction of the product P being manufactured). When passing through the aperture, the product is held in a horizontal plane perpendicular to the vertical direction shown as Z in the figure. In (b), the measuring device 100 is shown in a top view as seen from above, showing only a small portion of the product P. The measuring device 100 is configured to characterize the product P being formed horizontally in the machine direction M dir perpendicular to the width direction W dir , passing through the aperture 12 and between the transmitter head 22 and the receiver head 24 of the sensor 20.

[0039] A control system 40 is functionally connected to the sensor 20 and the drive system 30 and is configured to operate the sensor 20 and the drive system 30. The control system is equipped with a computer memory and an electronic computer configured to utilize the numerical data obtained from the sensor. The control system is configured to move along the width direction W dirMove sensor 20 to scan the product P being formed across the width of the product P. Figure 2 Sensor 20 is shown in more detail. The emitter head 22 includes (i) an X-ray source S XR and (ii) an ultrasonic source S US ; conversely, the receiver head 24 includes: (i) an X-ray detector Sens XR and (ii) an ultrasonic detector Sens US . The X-ray source S XR and the X-ray detector Sens XR together form an X-ray sensor; the ultrasonic source S US and the ultrasonic detector Sens US together form an ultrasonic sensor. The exact position and orientation of the X-ray and ultrasonic sensors are arbitrarily positioned as long as the detector is configured to face its corresponding source. In Figure 2 the example shown, the X-ray source and the ultrasonic source are configured to be on the same side of the material being manufactured, and the X-ray detector and the ultrasonic detector are configured to be on the other side. Alternatively, the X-ray source and the ultrasonic detector can be configured to be on the same side of the material being manufactured, and the X-ray detector and the ultrasonic source can be configured to be on the other side.

[0040] Sensor 20 is configured such that, in operation, the X-ray source S XR emits X-rays XR towards the X-ray detector Sens XR such that the X-ray detector Sens XR detects the X-rays XR that have passed through the product P to be characterized, and the ultrasonic source S US emits ultrasonic waves US towards the ultrasonic detector Sens US such that the US detector Sens US detects the ultrasonic waves emitted by the material P in response to the excitation by the ultrasonic waves emitted by the ultrasonic source S US . The two characterizations by X-rays and by ultrasonic waves are preferably carried out simultaneously, but can also be carried out sequentially.

[0041] The control system 40 connected to the sensor 20 forms both an X-ray characterization system and an ultrasonic characterization system, or in other words, forms a combined X-ray and ultrasonic characterization system.

[0042] Figure 3A production line PL for product P is shown, and the measuring device 100 is integrated into this production line. In this example, product P is formed by a support substrate Sprt, on which a coating Pat is formed by deposition through a coating device 7. The production line can generally be a laboratory production line, a test production line, or a factory production line. The production line includes: a reference X-ray measuring device 5, which is configured to perform reference X-ray absorption measurements and obtain reference X-ray measurement data; a coating device 7, which is configured to coat the support substrate by depositing a substance such as ink on the support substrate to form a pattern Pat made of ink.

[0043] The frame 10 of the measuring device 100 is positioned to perform measurements on the coated support substrate downstream of the coating device 7. The measuring device 5 is functionally connected to the measuring device 100 such that the measurement data collected by each of these elements 5 and 100 can be processed by the control system 40. The measuring device 5 can have a structure similar to that of the measuring device 100 to scan the reference X-ray measurement sensor across the width of product P.

[0044] For the sake of brevity and to keep the explanation of the principles of the present invention simple, the following description will relate to a production line equipped with a single coating device as Figure 3 shown. However, in practice, the production line can include multiple coating devices to manufacture products including multiple stacked coating layers. Also, at the location of the reference X-ray measuring device 5, the support is considered to be bare, with no material on it, but in reality, it can include materials coated by upstream coating devices. This is not important because the reference X-ray measuring device 5 is used to characterize the state of the product before the coating operation performed by the coating device 7 to serve as a reference for the state of the product before this coating. The coating deposited by the coating device 7 will be characterized by differential measurements performed downstream, as explained below.

[0045] Characterization based on X-ray transmission

[0046] The X-ray characterization of the product can be based on the fact that X-rays, as electromagnetic radiation, are partially absorbed when they pass through a product of a given chemical composition, and the magnitude of the absorption and thus the magnitude of the transmitted part of the radiation depend on the basis weight and chemical composition of the product. The dependence on the chemical composition is more specifically a dependence on the atomic number Z of the atoms forming the product.

[0047] According to the Beer-Lambert law, monochromatic X-rays are absorbed by the product according to the following equation Eq.1:

[0048]

[0049] where I is the intensity measured after passing through the product, and I0 is the intensity measured in the absence of the product, where μ is the mass absorption coefficient of the material that makes up the product at the energy of the incident X-ray, and W is the basis weight of the material. It can be readily seen that inversion of this equation yields Equation Eq.2:

[0050]

[0051] The calibration operation of an X-ray measurement system typically involves determining a constant by comparing the X-ray measurement with a reference measurement carried out under controlled conditions in a laboratory.

[0052] Under practical conditions, the emitted X-rays exhibit an energy spectrum, which complicates the equation but does not change the principle outlined above. Thus, the basis weight W can still be expressed as the ratio multiplied by a function of which is considered a calibration constant and is designated as C hereinafter. This gives rise to the following generalized equation Eq.3

[0053]

[0054] where C represents a calibration coefficient, and f lin_XR is a function applied to the X-ray measurement data, which replaces the simple logarithmic function of Equation Eq.2 to account for the spectrum of the energy of the X-rays used to perform the measurement. The function f lin_XR is commonly referred to as a linearization function because it transforms the relationship between the basis weight W and the measurement ratio into a linear equation.

[0055] Characterization based on ultrasonic transmission

[0056] The ultrasonic characterization of a product in the form of a sheet or foil can be based on the response of the product to ultrasonic waves directed at the product and is a purely mechanical characterization independent of the chemical composition of the product. As Figure 1 and Figure 2 shown, the product to be characterized can be inserted between an ultrasonic detector and an ultrasonic source for exciting the product and causing its response. The natural response of the excited product is to emit ultrasonic waves in sequence, which are sensed by the ultrasonic detector and carry information about the product.

[0057] In fact, the intensity I(t) of the ultrasonic signal measured by the ultrasonic detector Sens US can be expressed as Equation Eq.4:

[0058]

[0059] where I US represents the measured intensity of the ultrasonic signal emitted by the product excited by the exciting ultrasonic wave, I US0Represents the intensity of the exciting ultrasonic wave measured when there is no product, S US (t) represents the amplitude of the ultrasonic signal measured according to time t, and t1 and t2 indicate the start and end of the time interval during which the measured ultrasonic signal is integrated. The ultrasonic intensity represents the energy of the ultrasonic wave.

[0060] Figure 4 Shows the exciting ultrasonic signal Exc US Generated by the ultrasonic source S US (t), in this example, the signal is formed by a plurality of rectangular pulses. Figure 4 Also shows the amplitude S of the signal generated by the material excited by the exciting ultrasonic signal US (t), and is measured by the ultrasonic detector Sens US As a transient signal with a general shape of a sine Gaussian signal. The start time t0 of the exciting ultrasonic signal and the signal S US (t) The time difference Δt between the start times t1 corresponds to the ultrasonic source S US Emitting the exciting ultrasonic signal Exc US (t) and the ultrasonic detector Sens US Detecting the signal S US (t) The travel time between.

[0061] During the measurement, the integration of Equation Eq.4 is naturally performed, thus eliminating the dependence on t. An interesting feature of ultrasonic characterization is that, unlike X-ray characterization, it is independent of the chemical composition of the product. The basis weight W of the product can thus be written as Equation Eq.5, similar to Equation Eq.3 for X-ray measurement, but without the need for a calibration coefficient C:

[0062]

[0063] Where Represents the linearization function applied to the ultrasonic measurement data.

[0064] However, ultrasonic measurement is very sensitive to the geometric features of the product (such as its surface topography or its porosity), and these geometric features scatter the incident ultrasonic waves, thus interfering with the measurement.

[0065] Patterned composite product

[0066] Figure 5 At (a) represents parallel to the machine direction M dirTop view of a running product intended to form a battery component. In this example, the product presents a composite structure with a support substrate Sprt, on which a pattern Pat is formed as an electrode made of ink. The ink can have a variable composition: typically a solvent (such as water or NMP) contains an electrode material, such as LTO (Li4Ti5O12), NCA (LiNiCoAlO2), NMC (LiNiCoMnO2), graphite or other materials, depending on the expected battery characteristics and various tests performed by practitioners to enhance the target components.

[0067] The product presents a morphological singularity formed by the pattern edges on the support substrate Sprt. A morphological singularity is a sudden change in the morphological profile of the product, which is prone to disturbing ultrasonic measurements due to its suddenness and is typically formed at the edges of the pattern Pat. Figure 5 A cross-sectional view taken along the axis XX' parallel to the width direction W of the product is shown at (b), dir whose top contour defines the morphological profile Topo of the pattern Pat. This contour presents a bulge at the edge of the pattern, represented as the singularity Sing_1 in the figure. At (c), Figure 5 a cross-sectional view taken along the axis YY' parallel to the machine direction M of the product is shown. dir This cross-section shows a ramp represented as the singularity Sing_2 on one edge and a bulge with a sharp end represented as the singularity Sing_3 on the opposite edge. Such singularities are typically not correctly characterized by ultrasonic measurements because they scatter the incident ultrasonic waves.

[0068] The chemical composition of the material formed on the support substrate can vary from one test or production to the next, up to several times a day. If measurements need to be made on a wet phase with an undetermined proportion of solvent, this makes it more difficult to obtain quantitative measurements by using X-ray measurements alone.

[0069] In fact, X-ray measurements are very sensitive to the basis weight of the material but also to its composition. Therefore, in order to detect and characterize the basis weight distribution of the manufactured material (such as a coating deposited by a coating device), it is necessary to calibrate the X-ray measurement equipment for each new chemical composition of the material. In principle, this calibration can be performed by relying on ultrasonic measurements, which are specific to the basis weight of the material and are largely unaffected by its composition.

[0070] As shown above, the manufactured material can present singularities as Figure 5 shown, which are formed by the manufacturing process of the pattern and need to be characterized. However, as mentioned above, ultrasonic measurements are not feasible near morphological singularities and therefore cannot characterize these singularities nor be used to directly calibrate X-ray measurements at these singularities.

[0071] Real-time calibration method

[0072] To overcome the problems mentioned in the previous section, the inventors have proposed a method for determining the basis weight of a product by an X-ray characterization system, while performing real-time calibration of the X-ray characterization system with the aid of data obtained in parallel by an ultrasonic characterization system. Real-time calibration means that the measurement and the manufacturing of the product are not interrupted to perform the calibration.

[0073] The principle of the method is to rely on the ultrasonic characterization of the product in the regions of the product without topographical singularities to calibrate the X-ray characterization system that characterizes the entire product including topographical singularities. This calibration allows the X-ray characterization to output a quantitatively accurate basis weight distribution, regardless of the actual chemical composition of the manufactured product.

[0074] In other words, according to the present invention, X-ray measurement data and ultrasonic measurement data are acquired in parallel on the same region of the same product, and the ultrasonic measurement data is used to quantitatively correct the X-ray measurement data, which benefits from the fact that ultrasonic measurement allows a quantitatively accurate basis weight distribution to be directly derived. Specific processes are shown below to illustrate the present invention, but it only represents a specific embodiment and should not be construed as limiting the scope of the present invention. More generally, it consists of correcting the X-ray measurement data as a calibration procedure by comparing it with ultrasonic measurement data having an absolute value (i.e., quantitatively accurate).

[0075] Figure 6 Denote the basis weight distribution W of the superimposed (i) pattern Pat , and (ii) the linearization function and (iii) the linearization function are respectively applied to the X-ray measurement data and ultrasonic measurement data of the pattern Pat representing Figure 5 . The profile is plotted with respect to the virtual displacement axis Displ, which corresponds to the route traveled by the sensor 20 starting from the origin of the current measurement. Each point on the displacement axis Displ corresponds to a point on the position of the product along the width direction W dir .

[0076] Differential measurements are performed such that only the contribution of the pattern Pat is considered in the X-ray and ultrasonic measurement data. This is done according to well-known methods, for example by (i) inferring the contribution of the support substrate Sprt from the X-ray measurements performed by the X-ray scanner 5 on the support Sprt before the pattern is formed, and (ii) subtracting this contribution of the support substrate Sprt from the measurements performed by the device 100 after the pattern Pat has been formed on the substrate Sprt. Alternatively, the contribution of the support substrate can be known from its characteristics (composition, thickness, etc.) or from another previous characterization.

[0077] The unit basis weight W of the pattern Pat Pat can be expressed according to Equation Eq.6 as:

[0078]

[0079] where is the linearized function of Equation Eq.3 that represents the contribution of the X-ray characterization of the product by the pattern Pat, and C is the calibration coefficient.

[0080] As Figure 6 shown, the X-ray distribution qualitatively and precisely follows the topographical profile, including the singularity Sing_1, which reflects the local variation of the basis weight of the product. However, this X-ray distribution needs to be corrected by the calibration coefficient C as a correction factor to obtain the quantitatively precise basis weight distribution W Pat , as shown in Equation Eq.6.

[0081] Conversely, the ultrasonic distribution quantitatively represents the basis weight in regions far enough from the topographical singularities: in these regions, such as the flat section Pl, the basis weight distribution W Pat and the linearized function applied to the ultrasonic measurement data are precisely superimposed. However, the singularity Sing_1 affects the ultrasonic measurements in the effect zone Sing_Eff directly surrounding these topographical singularities, thus rendering the measurement data meaningless. Even though the linearized function is represented as a straight line in these regions, it is actually unpredictable, irregular, and cannot be used to derive the basis weight distribution.

[0082] From Figure 6 it can be understood that, in principle, the calibration coefficient C can be derived from X-ray measurements and ultrasonic measurements performed on a platform far enough from the topographical singularities. The process of obtaining this calibration coefficient C is explained below.

[0083] Figure 7 is a graph showing the X-ray measurement data X.Meas collected by the sensor 20 scanned over the formed product P, where the vertical axis represents The product P includes Figure 6 the pattern Pat.

[0084] The graph shows flat segments Pl1 and Pl3 at the baseline position of the graph, which correspond to product areas where only the support substrate Sprt is present. Between these flat segments are flat segments Pl2 and Pl4, which have a substantially constant height h (e.g., less than 10% in variation) from the baseline Bsl, flat segments Pl2 and Pl3. This is only due to the contribution of Pat.Cont of the pattern to the X-ray measurement. The edges of flat segments Pl2 and Pl4 exhibit topographical singularities Sing1, Sing2, and Sing3.

[0085] Characterizing products with topographical singularities and components that are prone to change in each batch (e.g., Figure 5 and Figure 6 product P) to obtain the basis weight (also known as grammage) distribution is described below, as Figure 9 shown in process 900. The process mainly consists of calibrating the X-ray measurement based on ultrasonic measurements performed in areas without topographical singularities (i.e., parts of flat segments Pl2 and pl4).

[0086] In step S5, before forming the pattern Pat on the support substrate Sprt, the scanner 5 performs a reference X-ray absorption measurement scan across the width of the product P in a conventional manner. In the next step, these reference measurements are used to obtain X-ray differential data measurements in order to remove the contribution of the support substrate and retain the contribution of the pattern, as already explained and otherwise known in the art.

[0087] Alternatively, based on previous measurements or calculations of the composition and thickness of the support substrate, the characteristics, and more specifically the contribution of the support substrate Sprt to X-rays may already be well known.

[0088] Furthermore, in this step, by performing a reference ultrasonic measurement using the sensor 20 before coating the support substrate, the contribution of the support substrate to subsequent ultrasonic measurements can be obtained in this step. Alternatively, based on previous measurements or calculations of the composition and thickness of the support substrate, this contribution may already be well known.

[0089] In step S10, the sensor 20 is scanned across the width of the product P, and the X-ray absorption measurement and ultrasonic measurement are performed simultaneously by the sensor 20; the X-ray measurement data and ultrasonic measurement data are recorded in the memory of the control system 40. Hereinafter, the term "data" refers to the data measured by the sensor and is respectively associated with the positioning of each measurement point on the virtual displacement axis Displ, thereby allowing each measurement point of the data to be associated with the corresponding position on the product P.

[0090] At step S15, optionally based on the corresponding reference measurements performed at step S5, the contributions of the support substrate to the X-ray measurements and to the ultrasonic measurements are subtracted from the corresponding measurement data in order to consider only the contribution of the pattern to the measurements.

[0091] At step S20, based on the X-ray measurement data, the control system 40 detects, locates, and determines the extent E2 of the flat portion formed by the pattern Pat on the support substrate Sprt, and on this extent the ultrasonic measurement data is reliable and can be used to calibrate the X-ray sensor.

[0092] This is done, for example, by detecting in a first sub-step S20 S1 the first extent E1 of the product along the displacement axis Displ, where the X-ray measurement data exhibits an absolute value higher than a given threshold Thr, thus detecting the extent of the pattern Pat, as Figure 7 shown.

[0093] In a second sub-step S20 S2 a margin M specified by the practitioner is removed from each end of the first extent E1 to obtain a second extent E2 that excludes the edges of the flat portion and the associated topographical singularities. Figure 7 Illustrated is this process applied to the flat portion Pl2, where the second extent E2 is not affected by the topographical singularities Sing1 and Sing2 included in the first extent E1.

[0094] The margin M can be determined by the practitioner according to the characteristics of the device used to perform the ultrasonic measurements (such as the width of the ultrasonic beam generated or the distance between the ultrasonic source and detector and the product to be measured). Additionally, M can typically be, for example, 1 cm, 2 cm, or 3 cm.

[0095] The step 20 described in detail above is merely an example, and the detection, location, and determination of the extent E2 can be performed by any other suitable conventional method, for example, by image analysis of a plot representing the X-ray measurement data plotted with respect to the displacement axis Displ.

[0096] Since the X-ray measurement data can precisely reflect the topography of the product, even in a quantitatively imprecise manner, it is convenient to use these data to implement step S20 as described above. The advantage of this method is that no further specific topography measurements are required, and the X-ray measurement data is directly associated with the topography of the product. However, it is alternatively possible to use the ultrasonic measurement data, or even other data obtained by another device such as an optional optical measurement system, provided that these data allow the edges of the pattern to be located and an association to be established between the position of the pattern and its edges and the collected X-ray and ultrasonic measurement data.

[0097] In step S30, the control system 40 calculates a calibration coefficient C to be applied to the X-ray measurement data. The value of the coefficient C is the ratio calculated between the X-ray measurement data and the corresponding ultrasonic measurement data belonging to the extension E2, i.e., the ratio obtained at positions on the displacement axis Displ located within the extension E2 determined in step S20. The calibration coefficient C can be calculated according to Equation Eq.7:

[0098]

[0099] where and represent linearization functions applied to the ultrasonic measurement data and the X-ray measurement data respectively. Each data is collected from the area of the support Sprt forming the pattern Pat, and only represents the contribution of the pattern to the measurement, excluding the contribution of the support substrate.

[0100] Figure 10 illustrates this operation, and is plotted on a linear scale Lin, and W Pat is used as the vertical axis.

[0101] The area of the support part Sprt forming the pattern Pat is preferably the area of the flat section Pl2 or Pl4 except for the topographical singularities of the extension E2 determined in step S20, for example. The support area without a pattern can be the flat section Pl1 or Pl3, or any area of the substrate when no coating is applied by the coating device 7.

[0102] The purpose of this calibration coefficient is to correct the basis weight derived from the X-ray measurement data according to Equation Eq.6. By doing so, based on the actual ultrasonic measurements performed on the product being processed, the calibration coefficient C is automatically calculated for the material constituting the pattern Pat formed on the support substrate Sprt, regardless of its actual composition.

[0103] In Figure 7 's example, the extension E2 of the flat section Pl2 is used to calculate the calibration coefficient C. Of course, this ratio can be calculated based on the extension considered or the average of multiple such extensions defined in step 20.

[0104] In step S40, the control system 40 determines and marks which measurement data belong to the product area with a pattern and which measurement data belong to the product area without a pattern.

[0105] The measurement data related to the material area with a pattern has a value greater than the baseline Bsl. Thus, this determination is performed, for example, by the control system 40 comparing each X-ray measurement data with the known baseline Bsl. Measurement data showing a difference exceeding a predetermined threshold is considered applicable to the area of the product P with the pattern Pat and is marked as such. The predetermined threshold can be a fixed value determined by the practitioner or can be expressed as a fraction of the height h representing the height of the flat segment, for example, the average value on the extension E2.

[0106] In step S50, the control system 40 calculates a corrected value of the X-ray measurement data by multiplying the value of the X-ray measurement data stored in the memory and marked as applicable to the area where the product P exists by the calibration coefficient C. The corrected value is stored in the memory.

[0107] In step S60, using the corrected value of the X-ray measurement value according to a known conventional method, the control system 40 calculates the quantitative and accurate grammage or basis weight BW of the product in the form of a profile including the topographic singularities. The profile of the basis weight BW can be along, for example, the displacement direction Displ and in g / cm 2 as shown at (a). Figure 8 as shown.

[0108] It is noted that this profile can be obtained without the need for time-consuming manual operations or operations carried out outside the production line and thus during the manufacturing process.

[0109] In step S70, based on the actual grammage or basis weight and based on the topographic profile (Topo) of the product that can be obtained by conventional means, the control system 40 calculates the profile of the density D of the product (for example, expressed in g / cm 3 as shown). The density (for example, expressed in g / cm 3 as shown) is equal to the ratio of the basis weight (for example, expressed in g / cm 2 as shown) to the thickness (for example, expressed in cm). Figure 8 A graph showing a density distribution with a constant value is shown at (b), which is typically the case when the material forming the pattern has a completely uniform composition.

[0110] As an alternative or supplement to step S60, step S60' can be performed, where steps S10 to S60 are repeated. In fact, the X-ray data measurement of the (n + 1) th measurement scan is corrected based on the correction coefficient calculated from the measurement data obtained during the previous n th measurement scans. The advantage of this method is that it takes into account the potential drift of the product's characteristics over time.

[0111] The direct application of the calibration coefficient C is to determine the weight ratio of the compounds in the product. Examples of the application are the determination of the water or solvent content in the product, or the ash content in the paper. In fact, the weight ratio to be determined is related to the calibration coefficient C by the following equation Eq.8:

[0112]

[0113] where WR X represents the weight ratio of compound X in the product to be characterized, C X and C noX are the calibration coefficients of the compound and the product equivalent to the product to be characterized, respectively, except that the product does not contain compound X, as determined separately according to method 900. Since C X and C noX are known, determining the calibration coefficient C of the product to be characterized according to process 900 allows the weight ratio WR to be determined by solving equation Eq.8 X . Unless otherwise specified, the above process 900 is applied three times in the process 110 shown in Figure 11 to determine CX, CnoX and C in steps S1, S2 and S3 respectively, and the weight ratio WR X is calculated in step S4 based on equation Eq.8, CX, CnoX and C.

[0114] For example, in the case of determining the water content of the product, equation 8 takes the form of equation Eq.9:

[0115]

[0116] where WR W represents the weight ratio of water in the product to be characterized, C X is the correlation coefficient previously determined for water, and C dry is the correlation coefficient determined separately for the product according to process 900 after drying.

[0117] By studying the drawings, the disclosure and the appended claims, those skilled in the art will be able to understand and implement other variations of the disclosed examples when practicing the claimed invention.

Claims

1. A method for measuring the basis weight distribution (BW) of a product (P) by X-ray characterization, the method comprising the following steps: - Performing X-ray absorption intensity measurement based on the transmission of X-rays through the product (P), and performing ultrasonic intensity measurement on the product based on the reaction of the product to ultrasonic waves directed at the product (P) to obtain (i) X-ray measurement data (X.Meas, Pat ) representing the basis weight distribution (W ) of the product perceived via the X-ray absorption measurement across the width of the product, and (ii) ultrasonic measurement data (S Pat ) representing the basis weight distribution (W US (t), ) of the product perceived via the ultrasonic measurement across the width of the product; - Calculating a calibration coefficient (C) of the X-ray measurement data by using the ultrasonic measurement data as a reference, the calibration coefficient (C) being based on a ratio between the X-ray measurement data and the ultrasonic measurement data ; and - Calculating a corrected value of the X-ray measurement data by multiplying the X-ray measurement data by the calibration coefficient.

2. The method according to claim 1, wherein the calibration coefficient (C) is based on a ratio between a linearization function applied to the X-ray measurement data and a linearization function applied to the ultrasonic measurement data. ​ 3. The method according to claim 1 or claim 2, wherein the section of the product (P) comprises at least one pattern (Pat) on a support substrate (Sprt), and the method further comprises the following steps: Determining the extension (E2) of the flat segments (Pl2, Pl4) formed by the pattern (Pat) on the support substrate (Sprt), the X-ray measurement data and the ultrasonic measurement data for calculating the calibration coefficient applicable to the extension (E2).

4. The method according to claim 3, wherein the extension (E2) has no topographical singularities (Sing1, Sing2).

5. The method according to any one of claims 1, 2, 4, wherein the method is applied to a product (P) manufactured by forming a coating pattern (Pat) on a support substrate (Sprt) by means of a coating device (7), and the X-ray absorption measurement and the ultrasonic measurement are performed downstream of the coating device (7).

6. The method according to claim 5, wherein the X-ray measurement data (X.Meas) are differential data relative to a reference measurement performed upstream of the coating device (7).

7. The method according to any one of claims 1, 2, 4, and 6, the method comprising the step of calculating a basis weight (W Pat , BW) distribution of the product (P) based on the X-ray measurement data (X.Meas) and the calibration coefficient (C).

8. A method for calculating the weight ratio of a compound in a product, the method comprising the following steps: - Determining a first calibration coefficient of the compound according to the method of claim 1; - Determining a second calibration coefficient of a modified product according to the method of claim 1, the modified product having the same composition as the product, except that the modified product substantially does not contain the compound; - Determining a third calibration coefficient of the product according to the method of claim 1; and - Calculating the weight ratio based on the first calibration coefficient, the second calibration coefficient and the third calibration coefficient.

9. A measuring device (100), the measuring device comprising a frame (10) extending along a width direction (W dir ), a sensor (20) movable along the width direction, and a drive system (30) configured to move the sensor (20) along the width direction (W dir ), the sensor (20) including a transmitter head (22) and a receiver head (24) facing the transmitter head (22), and a control system (40), the control system being configured to control the sensor and the drive system and including a computer memory and an electronic computer, wherein: - The emitter head (22) includes (i) an X-ray source (S XR ) and (ii) an ultrasonic source (S US ); - The receiver head (24) includes (i) an X-ray detector (Sens XR ) and (ii) an ultrasonic detector (Sens US ); and - The control system is configured to execute the method for measuring the basis weight distribution (BW) of a product (P) by X-ray characterization according to any one of claims 1 to 7 or the method for calculating the weight ratio of a compound in a product according to claim 8.

10. A production line (PL), the production line comprising the measuring device according to claim 9 and a coating device (7) located upstream of the measuring device.

11. The production line (PL) according to claim 10, further comprising a reference X-ray measuring device (5) configured to perform a reference X-ray absorption measurement and located upstream of the coating device (7).

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