Device for non-contact real-time surface density measurement of materials obtained by means of electro-aero-hydrodynamic techniques and associated method

Abstract

The present invention discloses a device combining at least one sensor that measures the distance between two electrodes, preferably by means of eddy currents, with at least one capacitive-type sensor to evaluate in real time the surface density of a material manufactured using electro-aero-hydrodynamic techniques. This device, capable of measuring surface density without any contact with the material, in addition to being completely harmless to health and the environment, has a small size that distinguishes it from the different technologies currently on the market and particularly suitable for characterising materials based on micro-nanofibres and particles. In addition, said device, which is very easy to use and assemble, does not require calibration if the dielectric constant of the material to be measured is known.

Description

[0001] NON-CONTACT REAL-TIME SURFACE DENSITY MEASURING DEVICE FOR MATERIALS OBTAINED BY ELECTRO-AERO-HYDRODYNAMIC TECHNIQUES AND ASSOCIATED PROCEDURE

[0002] DESCRIPTION

[0003] OBJECT OF THE INVENTION

[0004] The object of the present invention is a non-contact measuring device for the real-time surface density of materials obtained by electro-aero-hydrodynamic techniques, so that the quality of the product can be monitored in real time and, if deviations from the defined product specifications are detected, corrective actions can be applied during the process to correct these deviations and manufacture a product with the desired quality.

[0005] The invention describes a device that combines at least one sensor for measuring the distance between two electrodes, preferably using eddy currents, with at least one capacitive sensor for real-time evaluation of the surface density of a material manufactured using electro-aero-hydrodynamic techniques. This device, capable of measuring surface density without contact with the material, is completely harmless to health and the environment. Its small size sets it apart from other technologies currently on the market and makes it particularly suitable for characterizing materials based on micro-nanofibers and particles. Furthermore, this device, which is very easy to use and assemble, does not require calibration if the dielectric constant of the material being measured is known.

[0006] Additionally, the device is a non-contact real-time porosity measurement device for materials obtained using electro-aero-hydrodynamic techniques.

[0007] BACKGROUND OF THE INVENTION

[0008] In recent years, materials based on nanofibers and microfibers, obtained through electro-aero-hydrodynamic techniques, have experienced significant growth due to the advantages they offer over other manufacturing methods. In particular, these materials possess mechanical and morphological properties that make them especially attractive in fields such as biomedicine, pharmaceuticals, cosmetics, energy, filtration, agrochemicals, and textiles, among others.

[0009] However, one of the main disadvantages of electro-aero-hydrodynamic techniques is the difficulty in manufacturing materials with high uniformity in the physical properties of the coatings or membranes produced from them. This is because the atomization process used to produce the nano-microfibers and / or particles is highly sensitive to the various parameters controlling the process, resulting in significant variability in the physical properties of the materials obtained.

[0010] In an industrial production context, particularly in higher value-added applications where the final product must meet high quality standards, this variability leads to increased rejection rates and, consequently, low machine performance, resulting in economic losses. It can even limit the suitability of these materials and manufacturing techniques for use in certain applications.

[0011] Currently, quality control of manufactured parts or batches is performed after each part or batch is completed. On the one hand, because there is no visibility into product quality during manufacturing, any quality deviation that occurs during the process is not detected until the entire batch is finished, requiring its complete rejection, as partial rejections are not possible. On the other hand, process feedback for parameter adjustment can only be implemented after quality control is complete, causing delays in detecting deviations. All of this clearly results in an undesirable penalty to process performance and productivity.

[0012] Therefore, it is especially necessary to implement real-time process control mechanisms that allow monitoring of various material properties and, based on the information obtained, modifying process parameters in real time, taking the necessary corrective actions to ensure that materials are manufactured according to specifications. Furthermore, this online process control allows for quality control of the entire batch, enabling partial batch rejections, which also improves the efficiency of manufacturing processes.

[0013] Of the various material properties, surface density is particularly important for characterizing materials, membranes, or coatings generated using electro-aero-hydrodynamic techniques because it indicates the amount of material deposited per unit area and, therefore, the uniformity of that material. The unit typically used for its measurement is GSM (grams per square meter), which, as its name suggests, refers to the grams of material per square meter of surface. Furthermore, in certain applications, such as those where the material is used for the release or administration of substances, as in the case of cosmetic or pharmaceutical patches, this property is crucial and is a direct measure of the amount of active substance contained in the patch, since this is directly proportional to the surface density of the material.

[0014] Additionally, it should be noted that coatings or materials based on micro-nanofibers and particles are especially delicate and can be damaged when physically handled by devices that require contact, so it is essential that the systems for online material characterization be contactless.

[0015] There are currently some techniques that allow the measurement of this property, such as infrared light sensors, X-rays, gamma rays or beta rays, which have drawbacks related to their danger to health (potential generation of cancer) and the environment (generation of radioactive waste), the complexity of their use (need for complex chemometric models) or their large size, which make them especially unsuitable for use in equipment that uses electro-aero-hydrodynamic techniques.

[0016] DESCRIPTION OF THE INVENTION

[0017] The object of the present invention is a non-contact, real-time surface density measuring device for materials obtained through electro-aero-hydrodynamic techniques (electrospinning, blow spinning, electroblowing, etc.). Specifically, the device of the invention measures surface density in real time and without contact, a parameter that characterizes materials, coatings, and membranes based on nano-microfibers and particles generated through electro-aero-hydrodynamic processes. Additionally, by combining the surface density measurement with thickness measurements, the porosity value can be obtained.

[0018] In contrast to prior art devices that measure this property after the manufacturing process is complete, the device of the present invention allows for contactless and real-time measurement, so that any process parameter can be modified in real time and automatically, such as temperature, relative humidity, air flow rate, the supply voltages of the emitter and / or collector, the position and / or translation speed of the emitter, the position and / or translation speed and / or rotation of the collector, the mass flow rate, pressure or process time, among others.

[0019] Specifically, the device of the invention is intended to be connected to a machine for producing coatings or materials based on nanofibers or particles using electrohydrodynamic, aerodynamic, or combined techniques. These machines comprise emitters and a collector, where the fibers or particles are deposited, between which there is a potential difference controlled by feeding modules. The solution, generally composed of one or more polymers dissolved in one or more solvents, is supplied to the injectors by a fluid pumping system. The potential difference between the emitter and collector causes the solution to travel from the emitter to the collector by electrical attraction, forming a very fine strand in which the solvent evaporates as it moves toward the collector, forming nanofibers or polymer particles in the process, which are ultimately deposited in the collector.Furthermore, the emitter and collector can be moved using displacement modules, which can also allow the collector to rotate on its own axis (drum, mandrel, or other types of rotating collectors), as well as to move continuously in a roll-to-roll mechanism. The machines also include a module for controlling the flow and pressure of gas and fluid in the emitters. They also include a module for controlling process timing. Finally, the machine may include a module for controlling the temperature and relative humidity in the process zone. The non-contact measuring device for the surface density and, optionally, the real-time porosity of materials obtained by electro-aero-hydrodynamic techniques of the present invention comprises a measuring module. This measuring module is connected, in use, to a control module of the machine in which the material manufacturing process takes place.The measuring module obtains a series of data from the material deposited in the machine, which it supplies to the control module, which is intended to connect to different elements of the machine, such as those described above, so that the process parameters can be automatically adjusted in real time to achieve the desired characteristics based on the information supplied by the measuring module.

[0020] Specifically, the measuring module is configured to measure the surface density of a material and comprises a measuring unit consisting of at least one distance sensor, preferably based on eddy currents, combined with at least one capacitive sensor and a conductive reference electrode disposed in front of the measuring unit, such that, in use, the material generated by electro-aero-hydrodynamic techniques flows between the measuring unit and the conductive reference electrode.

[0021] Optionally, the unit of measurement is arranged statically with respect to the advance of the deposited material.

[0022] Optionally, the measuring unit is movable, preferably transversely, with respect to the advance of the deposited material.

[0023] Optionally, the measuring unit is movable in use relative to the machine's collector, varying its distance from said collector. This type of measuring unit can be applied to materials deposited on static, rotary, or roll-to-roll collectors.

[0024] The distance sensor is based on eddy currents, also known as Foucault currents. This sensor measures the distance between itself and the conductive reference electrode by applying high-frequency alternating currents to a coil housed within the sensor. The alternating magnetic field generated in the coil induces eddy currents on the surface of the conductive reference electrode. The intensity and distribution of these currents depend on the electrode's conductivity and the distance between the sensor and the electrode. In turn, these eddy currents generate their own magnetic field, which interacts with the coil's magnetic field, producing changes in the coil's impedance. These changes in coil impedance generate an electrical signal that is directly proportional to the distance between the sensor and the electrode, thus allowing for its precise measurement.The inclusion of non-conductive materials, such as the materials whose density is to be measured, does not interfere with that measurement of distance.

[0025] The operating principle of the capacitive sensor is based on that of a variable capacitor. In this case, one of the plates of the variable capacitor is the capacitive sensor itself, and the other is the conductive reference electrode. In this configuration, the capacitance generated between the capacitive sensor and the reference electrode is directly proportional to the distance between them and the dielectric constant (E) of the medium between the electrode and the sensor. Since the material being manufactured is deposited in the space between the measuring unit and the reference electrode, this material will modify the dielectric constant. In general, the greater the thickness of the nanofiber or particle coating, the higher the dielectric constant of the medium.Since the distance between the sensor and the reference electrode is known by measuring with at least one distance sensor, the dielectric constant of the medium between the sensor and the electrode can be determined, and since this is proportional to the amount of electrostretched material, the surface density of the manufactured coating or membrane is indirectly known.

[0026] The output of the measuring unit depends on the dielectric constant E of the medium, which in turn depends on the material being manufactured. If the dielectric constant E is unknown, it will be necessary to perform a calibration that relates the output of the measuring unit and the surface density of the material to be measured with the device of the invention. This calibration will follow a linear distribution of the type

[0027] O = Vs k + n

[0028] Where “O” is the surface density expressed in gsm, “Vs” is the output of the measuring unit, “k” is the sensor gain for each material and “n” is the y-intercept.

[0029] Thus, if the dielectric constant of the material is known and introduced into the measurement system, the amount of material passing in front of the sensor, and therefore its surface density, can be calculated from the direct reading of at least one distance sensor, preferably based on eddy currents, and at least one capacitive sensor. If the dielectric constant is unknown, an approximate constant is used, and a calibration curve is subsequently obtained that correlates the device output with the surface density of the material obtained by another measurement method, such as taking samples from a specific area, weighing these samples, and dividing their mass by their area. This calibration will only be valid for a specific material: materials with different compositions have different dielectric constants and, therefore, require different calibrations.

[0030] On the other hand, while surface density provides a good indication of the uniformity of the produced material, it is not sufficient to fully assess its quality since it does not provide information about its microstructure. Surface density is associated with the mass per unit area of ​​a given material, but not how that mass is distributed within its volume. Therefore, surface density alone cannot determine whether a material is porous and / or spongy, or continuous and / or dense. Materials based on nano-microfibers or particles are characterized by forming porous structures, and it is well known that porosity varies depending on the specific microstructure of the material, which in turn depends on the processing conditions.Therefore, it is very common to complete the characterization of materials with other analyses in addition to the measurement of surface density, as is usually the case with offline controls of microscopy, pore size and thickness, among others.

[0031] Therefore, the device may include, in addition to at least one distance sensor (preferably eddy current-based) and at least one capacitive sensor, a third thickness sensor. The thickness sensor may be, but is not limited to, an optical distance sensor, a micrometer-type sensor, or an ultrasonic sensor. This sensor provides the thickness value from which the material's porosity can be calculated. Combining the information provided by the three sensors allows for real-time measurement of the material's porosity using the following relationship:

[0032] P = 100*(1-(d / (Th*D))) where “P” is the porosity expressed as a percentage, “d” is the surface density, “Th” is the thickness and “D” is the intrinsic density of the material that makes up the fibers.

[0033] Similarly to how surface density is determined, this device can be used to measure porosity in materials deposited on static, rotating, or roll-to-roll collectors. In light of the above, the main advantage of the invention is that it allows for real-time monitoring of the surface density and, optionally, the porosity of materials generated using electro-aero-hydrodynamic techniques. This information can be used to adjust process variables in real time, thereby achieving the desired product characteristics. Among other advantages, this results in: increased product quality, increased productivity and machine performance, reduced reject material, reduced or eliminated post-process controls, and real-time discrimination or classification of the produced materials.

[0034] In summary, the invention describes how by combining the online surface density measurement with an online, non-contact measurement of the thickness of the manufactured material, the porosity value can be obtained, which will provide additional information about the microstructure and improve the quality control of the product and the manufacturing process.

[0035] To this end, the invention presents a non-contact device for measuring the surface density in real time of materials obtained by electro-aero-hydrodynamic techniques, characterized in that it comprises a measuring module configured to measure the surface density of a material and comprising:

[0036] - a measuring unit comprising at least one distance sensor and at least one capacitive sensor; and

[0037] - a conductive reference electrode disposed opposite the measuring unit, such that, in use, the material generated by electro-aero-hydrodynamic techniques is placeable between the measuring unit and the conductive reference electrode; wherein at least one distance sensor is configured to measure the distance between the distance sensor itself and the conductive reference electrode when the material is disposed between the measuring unit and the reference electrode, wherein the capacitive sensor (7) is configured to act as a variable capacitor together with the conductive reference electrode (9), such that a capacitance value is generated between them (7, 9) directly proportional to the distance separating them and to a dielectric constant (E) of the medium between the distance sensor (8) and the conductive reference electrode (9),where the dielectric constant (E) of the medium is proportional to the amount of material deposited and allows the determination of the surface density of the material. The invention also relates to a machine for producing coatings or materials using electrohydrodynamic, aerodynamic, and combinations thereof techniques, in the form of nano-micro fibers or particles, comprising the non-contact, real-time surface density measurement device described above.

[0038] The invention also relates to a non-contact, real-time surface density measurement procedure for materials obtained using electro-aero-hydrodynamic techniques, carried out with the device described above, comprising the following steps:

[0039] - a stage of disposing of the material generated by electro-aero-hydrodynamic techniques between the measuring unit and the conductive reference electrode;

[0040] - a stage of measuring the distance between the distance sensor and the conductive reference electrode when the material is arranged between the measuring unit and the reference electrode;

[0041] - a stage of generating a capacitance value between the capacitive sensor and the conductive reference electrode, where the capacitance value is directly proportional to the distance separating them and a dielectric constant of the medium between the distance sensor and the conductive reference electrode;

[0042] - a stage of determining the surface density of the material from said dielectric constant of the medium which is proportional to the amount of material deposited.

[0043] Dependent claims 12 to 18 include particular ways of carrying out the procedure of the present invention and are considered to be included in this section by reference.

[0044] DESCRIPTION OF THE DRAWINGS

[0045] To complement the description being made and in order to help a better understanding of the characteristics of the invention, in accordance with several preferred examples of its practical embodiment, a set of drawings is included as an integral part of said description, in which, for illustrative and non-limiting purposes, the following has been represented:

[0046] Figure 1 shows a schematic representation of a block diagram depicting the information exchange between the measuring unit of the non-contact, real-time surface density measuring device for materials obtained using electro-aero-hydrodynamic techniques of the present invention and a data processing unit. This unit, in turn, communicates with the control module, which then exchanges information with the other elements of the machine.

[0047] Figure 2.- Shows a perspective view of a first example of the real-time non-contact surface density measurement device of materials obtained by electro-aero-hydrodynamic techniques of the present invention.

[0048] Figure 3.- Shows a perspective view of the first embodiment shown in Figure 2, where the device further comprises a thickness sensor configured to measure the porosity of the material.

[0049] Figure 4a.- Shows a perspective view of a second example of embodiment of the non-contact real-time surface density measuring device of materials obtained by electro-aero-hydrodynamic techniques of the present invention, when the drum-type collector is grounded.

[0050] Figure 4b.- Shows a perspective view of the real-time non-contact surface density measurement procedure of the present invention using the device of the second embodiment when the procedure is being carried out with the collector subjected to high voltage.

[0051] Figure 4c.- Shows a perspective view of the real-time non-contact surface density measurement procedure of the present invention using the device of the second embodiment when the measurement is being performed and the procedure is carried out with the collector subjected to high voltage stopped.

[0052] Figure 5 shows an elevation view of the second embodiment shown in Figure 4a, where the device further comprises a thickness sensor configured to measure the porosity of the material.

[0053] Figure 6 shows a perspective view of a third embodiment of the non-contact, real-time surface density measuring device for materials obtained using electro-aero-hydrodynamic techniques of the present invention. PREFERRED EMBODIMENT OF THE INVENTION

[0054] Figure 1 shows a block diagram of the non-contact real-time surface density measuring device for materials obtained by electro-aero-hydrodynamic techniques of the present invention.

[0055] Three examples of embodiments of the non-contact measuring device for surface density and optionally porosity of materials obtained by electro-aero-hydrodynamic techniques, the subject of the present invention, are described below with the help of Figures 2 to 6.

[0056] In a first example of a preferred embodiment, represented in Figure 2, an example of a device for online surface density measurement in an industrial production equipment of micro-nanostructured materials from electro-aero-hydrodynamic techniques is shown, in which a continuous substrate is used in roll-to-roll mode, where the measuring unit (1) of the device comprises a distance sensor (8) that is an eddy current sensor and a capacitive sensor (7) for measuring density in a roll-to-roll collector machine.

[0057] Also, Figure 3 shows a variant of the first embodiment example, in which by using three sensors, one eddy current (8) or Foucault sensor, another capacitive (7) and another thickness (14), both the surface density and the porosity of a material produced with a roll-to-roll collector can be obtained.

[0058] In a second preferred embodiment, the device of the invention is used to characterize online the surface density of the material deposited on a rotary drum-type collector, as illustrated by Figures 4a, 4b, and 4c. This same preferred embodiment presents a variant for also obtaining the porosity of the produced material by using an additional optical micrometer-type sensor (12), as shown in Figure 5.

[0059] A third preferred embodiment shows how the device of the invention is used to measure the surface density and porosity of a conveyor belt collector, as shown in Figure 6. In all the described preferred embodiments, the device comprises a measuring unit (1) (see Figure 1), which in turn comprises at least one distance sensor (8), preferably an eddy current sensor (8), a capacitive sensor (7), and, where applicable, a thickness sensor (14). Additionally, the controllers for each of the aforementioned sensors are included as part of the measuring unit (1).

[0060] The measuring unit (1) is intended to be linked to a machine for producing coatings or materials using electrohydrodynamic, aerodynamic, or combined techniques, in the form of nano-micro fibers or particles, such as an electrostretching machine. This link is established through a data processing unit (21) (which may be a PLC, a computer, a microcontroller, etc.) that exchanges information bidirectionally with the measuring unit (1). The data processing unit (21) is also capable of bidirectional communication with a control unit (2) that governs the machine's operation, thus constantly receiving real-time information on the values ​​obtained by the sensors and the process parameters managed by the machine. The functions of the data processing unit (21) are:

[0061] - perform the calculation of surface density and porosity in real time from the values ​​of the sensors (8, 7, 14);

[0062] - collect all the data supplied by the sensors (8, 7, 14), together with those provided by the machine's control unit (2) to build a database relating the various process data (temperature, humidity, flows, voltages, geometries, etc.) to the location of the material produced (longitudinally and transversely) and to the surface density and porosity;

[0063] - Based on the surface density and porosity values ​​obtained, provide information to the machine's control unit (2) so that it can give instructions on how the different machine systems will act according to the programmed routines (start or end a process or stage, regulate process parameters, etc.).

[0064] The data processing unit (21) and the control unit (2) can be independent elements or can be integrated into the same device, which can be a PLC, a computer, or similar, capable of receiving information from the measuring unit (1) and from the different systems of the machine and capable of performing the necessary calculations to obtain the surface density and porosity data in real time and relating them to the location of the material to which said data correspond, as well as controlling the rest of the functionalities of the machine.

[0065] As shown in Figures 2 to 6, this type of machine comprises emitters

[0066] (3), which dispenses a material (5), and a collector (4), where the material (5) is deposited in the form of micro-nanofibers or particles. A potential difference is generated between the emitter (3) and the collector (4), which is controlled by power modules. Furthermore, the emitter (3) and collector (4) can be moved by means of displacement modules, which can also allow the collector (4) to rotate. The machines also include a module for controlling the flow and pressure of gas and liquid in the emitters. They also include a process timing module, which controls the duration of the various individual processes of the machine, such as the emission time of the material (5), the movement of the emitter (3), or the collector.

[0067] (4), among others. Finally, the machine may include an environmental control unit (13) for temperature and humidity in the process zone.

[0068] In a first preferred embodiment, a machine for producing coatings or materials using electrohydrodynamic, aerodynamic, or combined techniques is represented, in which the material (5) is deposited onto a substrate (6) continuously supplied by a continuous or roll-to-roll winding system. In this case, the uncoated substrate roll (6), which must be non-conductive (such as, for example, but not limited to, woven and non-woven textiles, film, or paper), is initially located in an unwinding system (17) and is uncoated. The unwinding system (17) rotates and releases uncoated substrate (6) in a controlled manner so that it can be collected, after the material (5) has been deposited onto it, in the area of ​​a winding system (18).As the substrate (6) passes through the processing zone where the emitters (3) are located, the material (5) is deposited, forming a layer of micro- or nanofibers or particles on the substrate (6). After passing through the processing zone, and before being wound in the winding or rewinding system (18), the substrate (6) passes between the eddy current sensor (8) and the capacitive sensor (7) and a reference electrode (9). The reference electrode (9) must be made of an electrically conductive material and must be grounded. The density of the material can be determined using these two sensors (7, 8). According to the operating principle explained above, the substrate (6) will be detected by the sensors (7, 8), and the resulting density value will be composed of the density of the substrate (6) and the material (5) being manufactured.To obtain the density value of the material (5), excluding that of the substrate (6), there are three possibilities: a) if the substrate (6) is sufficiently uniform and its density variations are less than the precision required to determine the density of the produced material (5), the average density value of the substrate (6) can be subtracted as a constant independent of the location where the measurement is taken; b) prior to the deposition of the material (5) on the substrate (6), the density of the substrate (6) is determined at each position, so that when the substrate (6) passes through the measuring unit (1), the density value of the substrate (6) without material at that same location is subtracted from the total measured value.In the first preferred embodiment, this is achieved by placing an additional pair of eddy current sensors (8) and a capacitive sensor (7) in an input device (19), just before the substrate (6) enters the zone where the material (5) is generated and deposited. The device further comprises an output device (20) consisting of the measuring unit (1) with the two sensors (7, 8) located between the collector (4) and the rewinder (18). Both the input (19) and output (20) devices are connected to a drive system (22) that moves them transversely across the substrate (6), enabling them to measure the surface density at different transverse positions on the substrate (6).Thus, the longitudinal position of the substrate (6) and the transverse position of the sensors (7, 8) must be precisely measured at every instant to ensure that the input device (19), where material (5) has not yet been deposited onto the substrate (6), and the output device (20), where material (5) has been deposited onto the substrate (6), measure at the same longitudinal (direction of roll-to-roll movement) and transverse (perpendicular to the roll-to-roll advance) position. In this way, the material density value corresponding to each substrate position (6) will be the value obtained by the output device (20) minus the density value obtained at that location by the input device (19) (baseline). Alternatively, before starting production, a density mapping of the entire substrate (6) must be performed, which can be moved in both directions to be wound and unwound in both the unwinding (17) and rewinding (18) systems.Thus, the density of the substrate (6) is measured across its entire length (discretely at a finite number of locations) prior to the start of production. In this case, it is not necessary to have an input device (19) and an output device (20); a single device (20) at the output would suffice. The density, in this case, would be determined by subtracting the density value of the substrate (6) without material (5) (baseline) at each location from the value obtained by the sensor when measuring the material (5) together with the substrate (6) at that location. In this first example of a preferred embodiment, in a variant shown in Figure 3, the measuring unit (1) further comprises a material thickness sensor (14) configured to determine porosity in real time, as explained in the description of the invention.Thus, for example, in this preferred embodiment, a device for measuring thickness using a thickness sensor (14) based on an optical distance sensor is presented. In this case, the thickness is determined by the difference in distances. In the first stage, the sensor (14), which can move transversely to the substrate (6), measures the distance to the substrate (6), which is always movable, and stores this distance for each transverse position. Then, when the substrate (6), with material (5) deposited on it, passes through the area where the distance sensor (14) is located, this distance is measured again, and the distance to the surface of the collector (4) before the material (5) was deposited, in that transverse position, is subtracted to obtain the thickness value.If necessary (i.e., unless the substrate thickness is very uniform and can be directly subtracted from the total measured thickness value), to remove the thickness contributed by the substrate from the total thickness measurement, the same strategies b) and c) used for measuring density can be followed. Thus, this device is used analogously to the eddy current sensor (8) and capacitive sensor (7), placing, depending on the defined solution, one between the processing area and the rewinder (18), which would be the output sensor, or this plus one between the unwinder (17) and the processing area, which would be the input sensor.

[0069] A second preferred embodiment is shown in Figures 4a, 4b, 4c, and 5. These figures depict an electro-aero-hydrodynamic processing machine in which the material (5) is deposited onto the surface of a rotary or drum-type collector. The azimuthal or circumferential position of the collector is controlled by an encoder. This encoder transmits its position in real time to the data processing unit (21). In this case, the rotary collector, which is typically cylindrical but can have other axisymmetric or non-axisymmetric geometries, is made of metal and serves as the reference electrode. Thus, if the material emitted by the emitters (3) is deposited directly onto the collector,where the eddy current (8) and capacitive (7) sensor readings will directly provide the density value at each position without the need for a reference measurement. Initially, before the process begins, the sensor will be reset to zero. The drum will then start rotating, and the material manufacturing process will begin, with material (5) being deposited onto the collector. As time passes, the amount of deposited material will increase at all positions, and therefore the sensor reading will also increase. The data processing unit (21) will record how the density varies at each instant in the different transverse and circumferential positions and will instruct the machine control unit on how to operate the different machine elements based on the obtained density values. For example,A possible control routine establishes that when the average density of all the deposited material is greater than or equal to a certain value, for example, 15 g / m³, the process stops. Conversely, if the material is not deposited directly onto the collector, but rather onto a dielectric substrate placed on top of the collector surface, the same procedure applies as in the first example of a preferred embodiment, and it is necessary to eliminate the value introduced by the substrate. In this case, there are two possibilities: a) if the substrate (6) is sufficiently uniform and its density variations are less than the precision required to determine the density of the produced material (5), the average density of the substrate (6) can be subtracted as a constant independent of the measurement location; b) prior to the deposition of the material (5) onto the substrate (6),The density of the substrate (6) is determined at each position so that when the substrate (6) passes through the density measuring device, the density value of the substrate (6) without material (5) at that same location is subtracted from the total measured value. This is possible by controlling the azimuthal position of the rotating collector at all times, so that each density measurement can be correlated not only with the transverse position of the sensors but also with the angular position of the rotating collector.

[0070] In electro-hydro-dynamic processes, the collector can be grounded. Figure 4a shows a process in which the collector is grounded and the device can measure the density of the deposited material in real time. However, it is known that, typically due to process requirements, the collector may be connected to a high-voltage source and must be subjected to a voltage other than 0 volts. In this second embodiment, since the collector itself acts as the reference electrode, it must be grounded at the time of measurement, preventing real-time density measurements. Furthermore, if this voltage is sufficiently high, there could be a risk of electrical discharges that could damage the eddy current (8) and capacitive (7) sensors, which are always grounded at a distance that typically varies between 0.5 mm and 25 mm from the reference electrode.Thus, in cases where the collector must be subjected to a voltage other than 0 volts during the process, the eddy current (8) and capacitive (7) sensors are moved sufficiently far from the measurement area during the process, eliminating the risk of electric shock (Figure 4b). After a certain processing time, defined according to the specific process being carried out, the process is stopped, and the sensors (8, 7) are automatically moved into the measurement area to perform the corresponding density measurement (Figure 4c). A switch is also used to disconnect the collector from the high-voltage source (15) that supplies it with voltage during the process and ground it. If, based on the defined routines and the density result obtained, the process needs to be restarted, the sensors are moved back to the measurement area, and the process is then restarted.This process start-stop-density measurement cycle can be repeated as many times as necessary according to the defined routine. Likewise, the duration of the process intervals will also be defined based on the specific needs of each process. For example, for the production of a material that must have a weight of 40 gsm with a tolerance of + / -5 gsm on average, where the material is deposited onto a cellulosic substrate with the collector connected to a voltage of -25 kilovolts, a routine such as the following can be established:

[0071] 1) The sensors are placed in the measurement area, 5mm from the collector;

[0072] 2) The sensors are reset;

[0073] 3) A sweep of the sensors is performed over the collector to obtain the substrate density values ​​along the entire surface of the collector (drum rotating at 200rpm and transverse movement system of the sensors sweeping the width of the collector at 50mm / s);

[0074] 4) The sensors are moved to the position away from the drum, at 300mm;

[0075] 5) The process begins;

[0076] 6) After 15 minutes of processing, it stops;

[0077] 7) The sensors are returned to the measurement area;

[0078] 8) The density is measured along the entire density of the collector, obtaining an average density of 32gsm;

[0079] 9) The sensors are moved to the position away from the drum, at 300mm;

[0080] 10) The process is restarted;

[0081] 11) After 4 minutes of processing, it stops;

[0082] 12) The sensors are returned to the measurement area;

[0083] 13) The density is measured along the entire density of the collector, obtaining an average density of 41gsm;

[0084] 14) Production is completed. Similar to the first preferred embodiment, adding a sensor to measure thickness allows for the determination of the material's porosity. In this second preferred embodiment, an optical micrometer (12) is used to obtain the material thickness in real time (Figure 5). The optical micrometer (12) is positioned between a light source (10) and a receiver (11) to detect the thickness of the material (5) deposited on the collector (4). However, other non-contact technologies, such as optical, ultrasonic, near-infrared, or electromagnetic distance sensors, could also be used to measure thickness.In this example, the thickness measurement at each transverse position (the sensor can be moved by means of a motion system parallel to the axis of rotation of the collector (4)) and circumferential position (provided by the encoder that controls the azimuthal position of the collector (4)) of the collector (4) is obtained by subtracting the shadow height at that same position before the process began (with or without substrate) from the real-time shadow height received by the micrometer (12). In this case, even if the collector (4) is subjected to high voltage, the thickness value can be obtained in real time as long as the distance from the micrometer (12) to the collector (4) does not interfere with the process.Alternatively, and similarly to what has been proposed for eddy current (8) and capacitive (7) sensors, the same iterative measurement cycle can be established in which the micrometer only takes measurements intermittently, moving it away when the process is running and bringing it closer to take the measurement when it is stopped.

[0085] In one aspect of the invention, the reference electrode (9) can coincide with the collector (4). In that case, the surface density measurement can be directly extracted from the measurements of the capacitive sensor (7) and the distance sensor (8).

[0086] In another aspect of the invention, the material is not deposited directly onto the collector (4) but onto another material, which must be electrically non-conductive (the reference electrode (9) must be), located between the reference electrode (9) and the capacitive sensor (7). In this case, a reference capacitance measurement would be carried out before depositing the fibers or particles, with the density of the material added during the process being the difference between the real-time measured value and the reference value.

[0087] Figure 6 shows a third preferred embodiment in which the density and porosity measuring device of the invention is connected to an electro-aerohydrodynamic processing machine with a conveyor belt collector. This type of collector combines the advantages of the first two preferred embodiments and also: 1) requires only one set of sensors to measure density and porosity regardless of the substrate uniformity (in the first preferred embodiment, if the variability in substrate density and thickness is greater than the required accuracy for determining the density and porosity of the produced material, an inlet and an outlet device are required); and 2) it is not necessary to move the sensors away from the process area if the collector is subjected to high voltage, thus always allowing for real-time density and porosity measurements.

[0088] In this third preferred embodiment, the substrate (6) onto which the produced material (5) is deposited must be non-conductive (e.g., but not limited to, woven or non-woven textiles, films, or paper). The machine has a drive system (16) that rotates and allows the substrate (6) to be moved perpendicular to the drive system's axis of rotation. The collector electrode (4) is positioned on the opposite side of the substrate (6) in the processing area. The eddy current sensors (8), capacitive sensors (7), and reference electrode (9) can be positioned sufficiently far from the processing area to avoid being affected by the high voltage. Similarly, the thickness sensor (14) can be positioned in a different area.The longitudinal position of the substrate (6) must always be known, so the drive system for the tape collector (4) must incorporate an encoder and a position detector (not shown) that detects when each revolution begins or ends to reset the encoder count. Thus, the substrate (6) will rotate cyclically, passing through the process zone where the material is deposited cumulatively onto the substrate and through the density and thickness measurement zone. As in the previous preferred embodiments, the eddy current sensor (8), capacitive sensor (7), and thickness sensor (14) (which in this embodiment is an optical distance sensor, but the same principle applies to thickness sensors based on electromagnetic wave, infrared, ultrasonic, and optical micrometer technology) can perform a transverse movement to measure density and porosity across the entire area of ​​the substrate (6).

[0089] In this third preferred embodiment, similarly to the previous ones, if the uniformity of the substrate (6) is such that the variations in its density and thickness are less than the required accuracy for the measurements, then it would not be necessary to perform a baseline measurement of the substrate's density and thickness to calculate the density of the material (5). Instead, it would only be necessary to subtract the average density and average thickness of the substrate (6) from the values ​​of both quantities obtained by the corresponding real-time sensors (which will measure the sum of the material and substrate). Alternatively, if the uniformity of the substrate (6) is not sufficiently good, it will be necessary to perform density and thickness mapping before starting production.In this case, to obtain the density and thickness of the material (5) without the substrate (6) in a certain position, it will be necessary to subtract the value of both magnitudes of the substrate (6) in that same position from the value obtained by the sensors at each moment (material + substrate).

Claims

CLAIMS 1. A non-contact device for measuring the surface density in real time of materials obtained by electro-aero-hydrodynamic techniques, characterized in that it comprises a measuring module configured to measure the surface density of a material (5) and comprising: - a measuring unit (1) comprising at least one distance sensor (8) and at least one capacitive sensor (7); and - a conductive reference electrode (9) arranged in front of the measuring unit (1), so that, in use, the material (5) generated by electro-aero-hydrodynamic techniques is locatable between the measuring unit (1) and the conductive reference electrode (9);characterized in that at least one distance sensor (8) is configured to measure the distance between the distance sensor (8) itself and the conductive reference electrode (9) when the material (5) is disposed between the measuring unit (1) and the reference electrode (9), wherein the capacitive sensor (7) is configured to act as a variable capacitor together with the conductive reference electrode (9), so that a capacitance value is generated between them (7, 9) directly proportional to the distance separating them and a dielectric constant (E) of the medium between the distance sensor (8) and the conductive reference electrode (9), wherein said dielectric constant (E) of the medium is proportional to the amount of material deposited and allows the determination of the surface density of the material (5).; 2. Device according to claim 1 characterized in that the at least one distance sensor (8) comprises a coil configured to receive an alternating current that generates a first magnetic field in the coil that induces eddy currents in the conductive reference electrode (9), which generate a second magnetic field that interacts with the first magnetic field, varying an impedance of the coil and generating an electrical signal that is directly proportional to the distance between the at least one distance sensor (8) and the reference electrode (9).

3. Device according to any of the preceding claims characterized in that the measuring unit (1) is arranged statically with respect to the advance of the deposited material (5).

4. Device according to any of claims 1 to 2 characterized in that the measuring unit (1) is movable with respect to the advance of the deposited material (5).

5. Device according to claim 4 characterized in that the measuring unit (1) is movable transversely with respect to the advance of the deposited material (5).

6. Device according to any of the preceding claims characterized in that the measuring unit is movable, in use, with respect to a collector (4) of the machine, varying its distance with respect to said collector.

7. Device according to any of the preceding claims characterized in that the measuring unit (1) is configured to calculate the surface density of the material from at least one distance sensor and the dielectric constant of the material (5).

8. Device according to any of the preceding claims characterized in that it further comprises at least one thickness sensor (14) configured to obtain the value of the porosity of the material (5).

9. Device according to claim 8 characterized in that the at least one thickness sensor (14) is of the optical distance or micrometer type, or by ultrasound.

10. Device according to any of the preceding claims, characterized in that the porosity of the material in real time is determined by the following relationship: P = 100*(1-(d / (Th*D))) where “P” is the porosity expressed as a percentage, “d” is the surface density, “Th” is the thickness and “D” is the intrinsic density of the material that makes up the fibers.

11. Machine for producing coatings or materials by means of electrohydrodynamic, aerodynamic techniques and combinations thereof, in the form of nano-micro fibers or particles comprising the non-contact measuring device of the surface density in real time of any of the preceding claims.

12. A non-contact, real-time surface density measurement procedure for materials obtained using electro-aero-hydrodynamic techniques, carried out with the device of any of claims 1 to 10, characterized in that it comprises the following steps: - a stage of disposing of the material generated by electro-aero-hydrodynamic techniques between the measuring unit (1) and the conductive reference electrode (9); - a distance measurement stage between the distance sensor (8) and the conductive reference electrode (9) when the material (5) is arranged between the measuring unit (1) and the reference electrode (9); - a stage of generating a capacitance value between the capacitive sensor (7) and the conductive reference electrode (9), where the capacitance value is directly proportional to the distance separating them and to a dielectric constant (E) of the medium between the distance sensor (8) and the conductive reference electrode (9), - a stage of determining the surface density of the material from the dielectric constant (E) of the medium which is proportional to the amount of material deposited.

13. Non-contact measurement procedure for the real-time surface density of materials obtained by electro-aero-hydrodynamic techniques according to claim 12 characterized in that it additionally comprises: - a stage of generating a first magnetic field in the coil of the at least one distance sensor (8) that induces eddy currents in the conductive reference electrode (9), and - a stage of generating a second magnetic field due to eddy currents induced in the reference electrode (9) that interacts with the first magnetic field, 14. Non-contact measurement procedure for real-time surface density of materials obtained by electro-aero-hydrodynamic techniques according to claim 13 characterized in that the generation stage of the second magnetic field is carried out by varying a coil impedance and generating an electrical signal that is directly proportional to the distance between the at least one distance sensor (8) and the reference electrode (9).

15. A non-contact method for measuring the surface density in real time of materials obtained by electro-aero-hydrodynamic techniques according to any of claims 12 to 14, characterized in that the step of arranging the material generated by electro-aero-hydrodynamic techniques between the measuring unit (1) and the conductive reference electrode (9) is carried out by moving the measuring unit (1) with respect to the advance of the deposited material (5).

16. A non-contact method for measuring the surface density in real time of materials obtained by electro-aero-hydrodynamic techniques according to any of claims 12 to 15, characterized in that the step of determining the surface density of the material from said dielectric constant (E) of the medium, which is proportional to the amount of material deposited, is carried out by calculating the surface density of the material from at least one distance sensor and the dielectric constant of the material (5).

17. A non-contact, real-time surface density measurement method for materials obtained by electro-aero-hydrodynamic techniques according to any of claims 12 to 16, characterized in that it further comprises: - a stage of determining a value of the porosity of the material based on the measurement obtained from a thickness sensor (14).

18. A non-contact, real-time surface density measurement procedure for materials obtained using electro-aero-hydrodynamic techniques according to claim 17, characterized in that the step of determining a material porosity value based on the measurement obtained from a thickness sensor (14) is obtained using the following relationship: P = 100*(1-(d / (Th*D))) where “P” is the porosity expressed as a percentage, “d” is the surface density, “Th” is the thickness and “D” is the intrinsic density of the material that makes up the fibers.

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