Electrohydrodynamic printing apparatus and printing control method

Abstract

The present invention relates to an electrohydrodynamic printing apparatus and a printing control method of the electrohydrodynamic printing apparatus, the electrohydrodynamic printing apparatus of the present invention comprising: a nozzle for discharging supplied ink to a substrate in the form of droplets; an electrode formed on the nozzle and configured to form an electric field between the nozzle and the substrate by an applied voltage; a voltage supply unit for applying a voltage to the electrode; and a control section for controlling the voltage supply section, in which the control section is configured to control the voltage applied to the electrode from the voltage supply section in real time so that the size of the droplet discharged from the nozzle is constant.

Description

Technical Field

[0001] The present invention relates to an electrohydrodynamic printing device and a printing control method for an electrohydrodynamic printing device, and more particularly to an electrohydrodynamic printing device that discharges droplets by generating electrostatic force through an electric field formed between a nozzle and a substrate, and a printing control method for an electrohydrodynamic printing device. Background Art

[0002] Generally speaking, an inkjet printing device or dispenser refers to a device that is attached to a sealed container filled with gas, liquid or other contents and ejects the contents in a specified amount through a pressure wave transmission device such as a pressurizing device or a piezoelectric element.

[0003] Recently, dispensers that discharge liquid medicine are also used in miniaturized precision industries such as electronic components and camera modules for coating specific parts or bonding processes. In addition, inkjet printers are also used in the OLED display industry for organic film coating in the packaging process or for patterning color materials such as red and green pixels. In addition, as a method of connecting the open circuit (source), drain, gate and other electrodes of the thin-film transistor (Thin-film-transistor) of the OLED backplane, materials such as ink are also considered. Dispensers or printers used in such fields need to control the discharge volume more precisely and discharge tiny droplets more precisely.

[0004] As a method of ejecting droplets, the piezoelectric method and the electrohydrodynamic (EHD) method have been widely used in the past. Among them, the electrohydrodynamic method is a method of applying a high voltage to the electrode of the nozzle to form an electric field between the nozzle and the substrate, and using the electrostatic force generated by the potential difference to eject ink. This method can achieve a small line width, so it is widely used in technical fields that require precise ejection.

[0005] like Figure 1 As shown in the figure, in order to accurately fill chipping defects or banks on PCB substrates with a thickness of less than 10 to 300 μm, it is necessary to apply a precise amount of droplets. However, when performing a long printing process, the physical properties of the ink change depending on the surrounding environment and process conditions, so that even if the same process variables are input, the same volume of droplets cannot be sprayed.

[0006] like Figure 2As shown, during electrohydrodynamic printing, the ink interface at the end of the nozzle is exposed to the outside, so as time passes, the solvent in the ink evaporates, and changes in physical properties including viscosity may occur. During the printing process, the ink may not always be ejected at a prescribed time interval, but may undergo various changes depending on the conditions required for printing or the movement distance of the nozzle. In other words, the time the ink is exposed to the external environment before being ejected at the end of the nozzle is not constant, but may change. Therefore, even if the same solution is filled inside the nozzle, the physical properties of the ink such as viscosity at the moment of ejection may be different. In particular, when performing ultra-precision printing below 100μm, the smaller the volume of the liquid surface at the end of the nozzle, the greater the ejection sensitivity caused by solvent evaporation.

[0007] Figure 3 The results of measuring the change in viscosity at different atmospheric exposure times for the meniscus of the liquid column at the end of the nozzle are shown. As shown in the figure, it can be confirmed that the solvent evaporates and the viscosity increases over time. Therefore, when a constant voltage is applied to the nozzle, it is impossible to eject a droplet of a constant volume due to changes in the physical properties of the ink.

[0008] Patent document: Korean Patent Publication No. 10-2012-0139436. Summary of the invention

[0009] Therefore, the present invention is proposed to solve this previous problem, and its purpose is to provide an electrohydrodynamic printing device and a printing control method for an electrohydrodynamic printing device, which controls in real time the voltage applied to the electrodes for forming the electric field or the flow rate of ink supplied to the nozzle so that the size of the ejected droplets is constant and is not affected by changes in the physical properties of the ink caused by evaporation of the solvent in the ink supplied to the nozzle.

[0010] The technical problems to be solved by the present invention are not limited to the problems mentioned above, and those skilled in the art should be able to clearly understand other problems not mentioned based on the following content.

[0011] The above-mentioned object can be achieved by an electrohydrodynamic printing device of the present invention. An electrohydrodynamic printing device comprises: a nozzle for discharging supplied ink in the form of droplets to a substrate; an electrode formed on the nozzle and used to form an electric field between the nozzle and the substrate by applying a voltage; a voltage supply unit for applying a voltage to the electrode; and a control unit for controlling the voltage supply unit, wherein the control unit is configured to control the voltage applied to the electrode from the voltage supply unit in real time so that the size of the droplets discharged from the nozzle is constant.

[0012] Here, an ink supply unit for supplying ink to the nozzle may be further included, and the control unit is configured to control the ink supply unit to control the flow rate of the ink supplied to the nozzle in real time so that the size of the ejected droplets is constant.

[0013] Here, it may further include an image acquisition unit for acquiring an image of the ink ejected from the nozzle, and the control unit is configured to determine the size of the droplets from the image acquired by the image acquisition unit, and based on the size of the droplets, control the voltage applied to the electrode by the voltage supply unit in real time, or control the ink supply unit to control the flow rate of the ink supplied to the nozzle in real time.

[0014] Here, the image acquisition unit may be configured to acquire an image of the liquid droplets deposited on the substrate, and the control unit may be configured to calculate the size of the liquid droplets from the area of ​​the liquid droplets in the acquired image.

[0015] Here, it may further include a droplet volume measuring unit for measuring the volume of droplets discharged onto the substrate or an additional test substrate. Before printing, the size of droplets obtained from the image acquired by the image acquisition unit for droplets of optimal volume measured by the droplet volume measuring unit is stored. The control unit is configured to compare the stored droplet size with the droplet size obtained from the image acquired in real time by the image acquisition unit to control in real time the voltage applied to the electrode from the voltage supply unit, or to control the ink supply unit to control in real time the flow rate of ink supplied to the nozzle.

[0016] Here, the control part may be configured to control a cycle or a magnitude of the voltage supplied from the voltage supply part.

[0017] Here, the voltage supply unit may include: a first voltage supply unit that supplies voltage at a specified period and size; and a second voltage supply unit that supplies an additional voltage to the voltage supplied from the first voltage supply unit. The control unit may be configured to control the second voltage supply unit based on the size of the droplets grasped in real time to control the size of the ejected droplets to be constant.

[0018] Here, the ink supply unit may include a flow controller using air pressure, rotation of a screw, or piezoelectric force, and the control unit may be configured to control the flow controller to control the flow rate of the ink supplied to the nozzle in real time.

[0019] Here, it may further include a jet environment information providing unit for providing jet environment information between the nozzle and the deposition location, and the control unit may be configured to accumulate pre-printing results based on the jet environment information and printing conditions into a database and predict the actual printing results on the substrate, and change the printing conditions provided by the database to perform printing based on the jet environment information provided by the jet environment information providing unit.

[0020] Here, the control unit can be configured to construct a printing prediction model for predicting the actual result of printing on the substrate through a machine learning method based on a database about the injection environment information and the printing conditions, and control printing based on the printing conditions provided by the injection environment information using the printing prediction model.

[0021] Moreover, the above-mentioned object can be achieved by a printing control method of an electrohydrodynamic printing device of the present invention. A printing control method of an electrohydrodynamic printing device discharges droplets onto a substrate by electric field force, wherein the electric field force is a force of an electric field generated by a voltage applied to an electrode formed on a nozzle, and the method comprises the following steps: determining the size of the discharged droplets; and controlling the voltage applied to the electrode in real time so that the size of the droplets discharged from the nozzle is constant.

[0022] Here, the method may further include the step of controlling the flow rate of ink supplied to the nozzle in real time by controlling an ink supply unit that supplies ink to the nozzle so as to keep the size of the droplets discharged from the nozzle constant.

[0023] Here, an image of the liquid droplets deposited on the substrate may be acquired, and the size of the liquid droplets may be calculated from the area of ​​the liquid droplets in the acquired image.

[0024] Here, the following steps may be further included: before printing, ejecting droplets of optimal volume onto the substrate or an additional test substrate; and obtaining and storing the size of the droplets of optimal volume from the image of the droplets deposited on the substrate, wherein the stored droplet size is compared with the droplet size obtained from the image acquired in real time to control the voltage applied to the electrode or the flow rate of ink supplied to the nozzle in real time to make the size of the droplets ejected from the nozzle constant.

[0025] According to the electrohydrodynamic printing device and the printing control method of the electrohydrodynamic printing device of the present invention as described above, by comparing the sizes of the ejected droplets, the voltage applied to the electrode or the flow rate of the ink supplied to the nozzle is controlled in real time, thereby having the advantage of being able to eject droplets of uniform size even if the physical properties of the ink are changed due to evaporation of the solvent in the ink, etc.

[0026] Furthermore, since printing is performed under real-time control using printing conditions provided by a printing prediction model constructed using a machine learning method, there is also an advantage that printing accuracy can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This shows an example in which the electrohydrodynamic printing device of the present invention can be used by discharging fine droplets.

[0028] Figure 2 This refers to the process in which the ink at the end of the nozzle is exposed to the outside and the solvent evaporates over time, causing the viscosity and other physical properties of the ink to change.

[0029] Figure 3 This is the result of an experiment that examined the change in viscosity over time when the ink at the end of the nozzle was exposed to the outside.

[0030] Figure 4 FIG. 4 is a schematic diagram of an electrohydrodynamic printing device according to an embodiment of the present invention.

[0031] Figure 5 The printing process sequence of a defective portion of a substrate using an electrohydrodynamic printing device according to an embodiment of the present invention is shown.

[0032] Figure 6 The figure shows how the volume of ink droplets discharged onto a substrate is measured by a droplet volume measuring unit.

[0033] Figure 7 An example of a voltage control signal applied to an electrode according to an embodiment of the present invention is shown.

[0034] Figure 8 This is a diagram for explaining the magnitude of air pressure applied by the ink supply unit in accordance with the change in viscosity due to shear force.

[0035] Fig. 9 This is a diagram showing a comparison between the results of droplet discharge by a conventional electrohydrodynamic printing apparatus and the results of droplet discharge by the electrohydrodynamic printing apparatus of the present invention.

[0036] Fig.10 The figure shows the result of measuring the volume of a defective portion of a substrate using a confocal microscope according to the present invention, and inspecting the volume after filling the defective portion by printing.

[0037] Fig.11 The process of constructing the printing prediction model of the present invention and the results of comparing the printing results predicted by the printing prediction model with the actually measured printing results are shown.

[0038] Description of Reference Numerals 110: nozzle; 120: voltage supply unit; 125: ink supply unit; 130: Control unit; 140: droplet volume measurement unit; 150: image acquisition unit; S: substrate. DETAILED DESCRIPTION

[0039] Detailed description of the embodiments is included in the detailed description and drawings.

[0040] The advantages and features of the present invention and methods for achieving the advantages and features should be clear with reference to the following embodiments described in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be embodied in various ways. The embodiments are only provided to fully disclose the present invention and fully inform the scope of the invention to a person with general knowledge in the technical field to which the present invention belongs. The present invention is limited only by the scope of the claims. The same reference numerals throughout the specification represent the same structural elements.

[0041] Hereinafter, the present invention will be described by way of embodiments of the present invention with reference to the accompanying drawings for illustrating an electrohydrodynamic printing apparatus and a printing control method of the electrohydrodynamic printing apparatus.

[0042] Figure 4 A schematic diagram of an electrohydrodynamic printing device according to an embodiment of the present invention; Figure 5 The printing process sequence of the electrohydrodynamic printing device on the defective part of the substrate according to one embodiment of the present invention is shown; Figure 6 The figure shows a situation where the volume of ink droplets discharged onto a substrate is measured by a droplet volume measuring unit; Figure 7 An example of a voltage control signal applied to an electrode according to an embodiment of the present invention is shown; Figure 8 A diagram for explaining the magnitude of air pressure applied by an ink supply unit according to a change in viscosity caused by shear force; Fig. 9 This is a diagram showing a comparison between the results of liquid droplets ejected by a conventional electrohydrodynamic printing device and the results of liquid droplets ejected by the electrohydrodynamic printing device of the present invention; Fig.10 The figure shows the result of measuring the volume of a defective portion of a substrate using a confocal microscope according to the present invention, and inspecting the volume after filling the defective portion by printing.

[0043] The electrohydrodynamic printing device according to an embodiment of the present invention may be configured to include a nozzle 110, an electrode (not shown), a voltage supply unit 120, and a control unit 130. In addition, it may further include an ink supply unit 125. In addition, it may further include an image acquisition unit 150 or a droplet volume measurement unit 140.

[0044] The nozzle 110 may discharge droplets toward the substrate S through a nozzle hole formed at one end. A chamber for storing supplied ink may be provided inside the nozzle 110. Although not shown, an additional driving unit for moving or rotating the nozzle 110 along the XYZ axis direction may be formed.

[0045] like Figure 4 As shown, the nozzle 110 can be arranged tilted, but is not necessarily limited thereto, and can also be arranged vertically. When the nozzle 110 is arranged tilted, the image acquisition unit 150 described later can be arranged vertically above the location where the droplets are deposited on the substrate to acquire an image, so that a distortion-free image can be acquired.

[0046] An electrode (not shown) may be formed on the nozzle 110. As an example, the electrode may be formed inside the nozzle 110. However, the electrode is not necessarily arranged inside the nozzle 110, and may be arranged at various positions in various known ways. Alternatively, the nozzle 110 may be formed of a metallic material, so that the nozzle 110 itself becomes an electrode. In addition, the outer side of the electrode may be coated or surrounded by an insulating material.

[0047] The voltage supplier 120 may apply voltage to the electrode to form an electric field between the nozzle 110 and the substrate S. When the electrode is applied with voltage, the charged ink may be formed into droplets and discharged through the nozzle hole under the action of electrostatic force of the electric field.

[0048] The ink supply unit 125 supplies ink to the nozzle 110. The ink supply unit 125 may be configured to include an ink tank (not shown) and a flow controller (not shown), wherein the ink tank is used to store ink; and the flow controller is used to supply the ink stored in the ink tank to the nozzle 110, and at this time, control the flow rate of the supplied ink. The flow controller may use air pressure, the rotation of a screw, or a piezoelectric force to move the ink stored in the ink tank to the nozzle 110, and at this time, the flow rate of the ink may be controlled by controlling the magnitude of the applied air pressure, the rotation speed of the screw, or the magnitude of the piezoelectric force.

[0049] The control unit 130 controls the voltage supply unit 120. More specifically, the magnitude or frequency of the voltage applied to the electrode can be controlled in real time. At this time, in the present invention, the control unit 130 controls to apply a voltage in real time instead of applying a constant magnitude and frequency during printing.

[0050] Furthermore, the control unit 130 may control the ink supply unit 125. More specifically, the flow rate of the ink supplied to the nozzle 110 may be controlled in real time by controlling the flow rate controller constituting the ink supply unit 125. In the present invention, the control unit 130 may control the ink to be supplied to the inside of the nozzle 110 not at a constant flow rate during printing, but at a different flow rate in real time.

[0051] During the printing process, the ink is not ejected at a constant time interval, but can be changed into various forms according to the conditions required for printing and the moving distance of the nozzle 110. That is, the time that the ink is exposed to the external environment before being ejected at the end of the nozzle 110 is not constant, but can be changed. Therefore, even if the inside of the nozzle 110 is filled with the same solution, the physical properties of the ink such as viscosity may change at the moment of ejection due to the evaporation of the solvent. Therefore, when a constant voltage is applied to the electrode, the size of the ink ejected from the nozzle 110 may change due to the change of viscosity and the like caused by the evaporation of the solvent and the like. Moreover, due to the thixotropy of the ink caused by the shear force on the inner surface of the nozzle 110, the size of the ejected ink may also change.

[0052] Therefore, in the present invention, the control unit 130 controls the voltage applied to the electrode by the voltage supply unit 120 in real time so that the size of the droplets discharged from the nozzle 110 is kept constant even if the physical properties of the ink supplied to the nozzle 110 change due to evaporation of the ink solvent.

[0053] Furthermore, in the present invention, the control unit 130 may control the ink supply unit 125 to control the flow rate of ink supplied to the nozzle 110 in real time together with the voltage control so that the size of the droplets ejected from the nozzle 110 is constant.

[0054] At this time, the control unit 130 may compare the sizes of the discharged droplets in real time, and control the applied voltage or the flow rate of the ink supplied to the inside of the nozzle 110 accordingly.

[0055] The image acquisition unit 150 is used to acquire an image of the ink ejected from the nozzle 110. For example, the image acquisition unit 150 may be a camera that acquires a two-dimensional image. The image acquisition unit 150 is preferably arranged vertically above the location where the droplets are deposited on the substrate S, and acquires an image of the deposited droplets vertically above. This is because, in the present invention, the size of the droplets ejected from the nozzle 110 can be grasped based on the area occupied by the droplets in the image acquired by the image acquisition unit 150, and when the image acquisition unit 150 is arranged at an angle, the image will be distorted, and it may be difficult to accurately grasp the size of the droplets.

[0056] The control unit 130 can grasp the size of the droplet from the image acquired by the image acquisition unit 150, and based on this, control the voltage supply unit 120 or the ink supply unit 125 in real time. For example, when the viscosity of the ink increases due to the evaporation of the solvent, and the size of the droplet grasped in real time becomes smaller than the size of the previously deposited droplet, the control unit 130 can control the voltage applied from the voltage supply unit 120 to increase in real time, or control the flow rate of the ink supplied to the nozzle 110 through the ink supply unit 125 to increase, so that the size of the droplet ejected from the nozzle 110 remains uniform.

[0057] At this time, when the control unit 130 controls the printing while comparing the droplet sizes, a reference size of the droplet is required. Therefore, the present invention may further include a droplet volume measuring unit 140. The droplet volume measuring unit 140 is used to measure the volume of the droplet ejected onto the substrate S or an additional test substrate. For example, the droplet volume measuring unit 140 may be formed by a conventional confocal microscope.

[0058] Before printing, droplets may be ejected from the nozzle 110 toward the edge of the substrate S or an additional test substrate, and the volume of the ejected droplets may be measured by the droplet volume measuring unit 140. At this time, the voltage applied to the electrode or the flow rate of the ink supplied to the nozzle 110 may be changed to repeatedly eject droplets until droplets of an optimal volume are ejected. When droplets of an optimal volume are ejected, the image acquisition unit 150 may acquire an image of the droplets, and calculate and store the size of the droplets ejected onto the substrate S from the image. That is, the size of the droplets ejected from the nozzle 110 corresponding to the area of ​​the ink ejected onto the substrate S acquired from the image acquisition unit 150 may be stored. The stored droplet size may be used as a reference size for control by the control unit 130, and the droplet size may be grasped from the area of ​​the droplets printed on the substrate S acquired by the image acquisition unit 150. The control unit 130 can compare the droplet size measured in real time from the image acquired in real time by the image acquisition unit 150 during printing with the stored optimal volume droplet size as a reference, and control the voltage applied to the electrode by the voltage supply unit 120 or control the flow rate of ink supplied to the nozzle 110 through the ink supply unit 125 to prevent the droplet size from changing due to changes in physical properties such as viscosity caused by solvent evaporation.

[0059] It should be noted that Figure 5 The above printing process is shown in sequence. The following is further described in sequence. Before printing, droplets are ejected onto the substrate S or the test substrate ( Figure 5 (1)), the droplet volume measuring unit 140 is used to measure whether the droplet has the optimal volume required for printing ( Figure 5 (2)). Depending on the printing accuracy, the required droplet volume may be different. It should be noted that Figure 6The software constituting the droplet volume measuring unit 140 shows a process of obtaining the volume of the droplet discharged onto the substrate S. Since obtaining the volume using a confocal microscope is a well-known technique, a detailed description thereof will be omitted.

[0060] When repeated Figure 5 When the volume of the liquid droplet discharged by (1) and (2) reaches the required optimal volume, the image acquisition unit 150 acquires a two-dimensional image of the liquid droplet ( Figure 5 (3)), and based on this, the size of the droplet deposited on the substrate S is calculated for the droplet of the optimal volume. At this time, the size of the droplet can be measured by the droplet area of ​​the acquired image. The reason for calculating the optimal droplet volume and the droplet size for the volume before printing is that the size (area) of the droplet deposited on the substrate S is different for the same volume of droplets depending on the type of substrate S, the type of ink, etc.

[0061] Before printing, the two-dimensional image and three-dimensional volume ( Figure 5 (4)), and the control unit 130 generates a printing map (Printing Map) based on the two-dimensional image and the three-dimensional volume ( Figure 5 (5)). When a fixed amount of ink is supplied to fill the defective part of the substrate S, the position and size of the defective part can be grasped from the image acquired by the image acquisition unit 150, and the size of the optimal droplet and the printing position can be grasped. In addition, the volume of the defective part can be calculated by the droplet volume measurement unit 140, and the printing map of the droplets to be deposited on the substrate S can be calculated. At this time, the size and volume of the target droplet can be obtained from Figure 5 The database obtained from (1) to (3).

[0062] Next, printing is performed based on the generated printing map. At this time, the control unit 130 can use the size of the droplet corresponding to the stored optimal volume of the droplet as a reference to calculate the size of the droplet discharged to the substrate S in real time, and control the voltage applied to the electrode or the flow rate of the ink supplied to the nozzle 110 so that the droplet of uniform size can be discharged even if the ink properties such as viscosity change due to the evaporation of the ink at the end of the nozzle 110 ( Figure 5 of (6)).

[0063] Finally, after the defective part is filled with ink and printing is completed, the two-dimensional shape and three-dimensional volume of the defective part are measured to determine whether the printing is good or not ( Figure 5 of (7)).

[0064] It should be noted that Fig.10 (a) shows the result of measuring the volume of the defective part before printing by the droplet volume measuring unit 140. Fig.10 (b) indicates that according to the reference Figure 5 The contents of the description are contents of carrying out a volume inspection on the defective part after printing the defective part.

[0065] The operation of the control unit 130 controlling the voltage applied to the electrode by the voltage supply unit 120 and controlling the flow rate of the ink supplied to the nozzle 110 by the ink supply unit 125 as described above will be described in more detail.

[0066] The control unit 130 can Figure 7 The method shown in the figure controls the voltage applied by the voltage supply unit 120. For example, the voltage supply unit 120 may be composed of a first voltage supply unit and a second voltage supply unit. The first voltage supply unit supplies a voltage (basic signal) of a constant period and magnitude during printing as shown on the left side of the figure. At this time, Figure 7 As shown in (a), when the size of the droplet becomes smaller than the reference size due to evaporation of the solvent, the second voltage supply unit instantly supplies an additional voltage so that the droplet of the reference size can be ejected again. At this time, the size of the additional voltage instantly supplied by the second voltage supply unit can be different according to the size of the droplet measured in real time.

[0067] Or, if Figure 7 As shown in (b), when the size of the droplet becomes smaller than the reference size due to evaporation of the solvent, the cycle or magnitude of the voltage supplied from the voltage supply unit 120 during a predetermined period of time can be changed to discharge droplets of the reference size.

[0068] like Figure 8 As shown in (a), the physical properties of the ink, such as viscosity, may change due to the shear force on the inner surface of the nozzle 110, so that the size of the droplet ejected from the nozzle 110 increases or decreases compared to the reference size. Figure 8 As shown in (b) of FIG. 1 , the flow rate of the ink can be controlled by reducing or increasing the air pressure of the ink supply unit 125 for controlling the supply of the ink by air pressure so as to discharge uniform droplets of the ink.

[0069] Fig. 9 (a) shows droplets actually printed when a constant voltage is applied and a constant flow rate of ink is supplied to the nozzle 110 in a conventional printing operation. Fig. 9(b) shows droplets actually printed when the voltage applied to form an electric field or the flow rate of ink supplied to the nozzle 110 is controlled by comparing the sizes of the ejected droplets in real time as described above according to the present invention. It can be confirmed that when a constant voltage and air pressure (air pressure applied to supply ink to the nozzle 110) are applied during printing as in the past, the droplet size is not constant due to the evaporation amount of the solvent in the ink, while, when the voltage or air pressure is controlled as in the present invention, droplets of a constant size are ejected regardless of changes in the physical properties of the ink.

[0070] In order to make the size of the droplets uniform during printing, in the present invention, the control unit 130 can control the voltage applied to the electrode or the flow rate of the ink supplied to the nozzle 110 as described above. Furthermore, in order to further improve the printing performance in the present invention, the control unit 130 not only controls the voltage applied to the electrode and the flow rate of the ink supplied to the nozzle 110, but also controls other printing conditions such as the printing speed and the distance between the nozzle 110 and the substrate S.

[0071] The ink may have various viscosities and surface tensions, conductivity, dielectric constants, etc., and the printing conditions may vary according to the characteristics of the ink. Furthermore, the printing conditions may also vary according to whether the type of the substrate S is an organic substance, an inorganic substance, glass, a ceramic, etc. Furthermore, the printing conditions may vary according to the printing environment such as the surrounding temperature and humidity, the atmosphere gas, and the vacuum environment. Furthermore, the electric field distribution may be different due to any structure, microcomponent, circuit, and the presence or absence of a coating on the substrate S, which may cause a difference in printing performance and thus change the printing conditions.

[0072] In this way, in order to achieve the best printing performance according to the type of ink and substrate, printing environment, etc., the present invention accumulates the results of printing under various printing environments for various inks and substrates S into a database, and predicts the actual results of printing on the substrate S, and changes the printing conditions accordingly to perform printing.

[0073] The jetting environment information providing unit (not shown) stores various jetting environment information that affects printing. Information between the nozzle 110 and the location where the ejected droplets are deposited can be stored. Here, the so-called "information between the nozzle 110 and the deposition location" can represent information about the nozzle 110 (for example, the size of the nozzle 110), information about the deposition location (for example, the material of the substrate S or the material of the deposition location, shape information of the deposition location), spatial information between the deposition location and the nozzle 110 (for example, the three-dimensional shape around the deposition location), information about ink characteristics (for example, viscosity, conductivity, surface tension, dielectric constant, etc.), etc.

[0074] The spraying environment information providing portion may be configured to include a storage portion and a sensing portion.

[0075] The storage unit is similar to a storage device of a computer and is used to store the spraying environment information data provided by the user. The sensing unit can measure the shape information around the deposition location where the droplets ejected from the nozzle are deposited. The sensing unit may include an optical unit for capturing an image around the deposition location. Moreover, the sensing unit may further include a distance sensor unit for measuring the distance between the nozzle and the deposition location.

[0076] In this way, the information provided by the ejection environment information providing unit may be information pre-stored in the storage unit by the user or shape information grasped in real time by the sensor unit. The ejection environment information providing unit may provide the control unit 130 with ejection environment information including three-dimensional shape information around the deposition location provided by the sensor unit, material of the deposition location, distance between the nozzle and the deposition location, ink characteristic information including surface tension of the ink, viscosity of the ink, conductivity of the ink, dielectric constant, etc., and nozzle size information.

[0077] The control unit 130 may accumulate the pre-printing results based on the ejection environment information and the printing conditions into a database, and accordingly predict the actual printing results on the substrate S. For example, the database may include the results of ejecting inks with a viscosity ranging from 1 to 200,000 cPs.

[0078] Therefore, when printing is performed, the ejection environment information provided from the ejection environment information providing unit is used as an input, and the printing conditions can be changed to the optimal printing conditions provided by the database in real time to perform printing.

[0079] More specifically, the control unit 130 includes a printing prediction model for printing results for a variety of ejection environment information and printing conditions constructed by a machine learning method. The control unit 130 changes the printing conditions according to the position of the nozzle 110 to the printing conditions provided by the printing prediction model based on the ejection environment information provided by the ejection environment information providing unit for the current location of the nozzle 110, and performs printing.

[0080] In the case of a three-dimensional surface, the electric field distribution varies depending on the surface shape, so precise printing cannot be performed simply by maintaining a constant distance between the three-dimensional surface and the nozzle 110. Therefore, the present invention is configured to be able to understand the electric field distribution between the nozzle 110 and the deposition site under the shape of the structure around the deposition site, and to control the printing conditions accordingly to perform printing.

[0081] Therefore, the printing prediction model is a model of printing results for multiple ejection environment information and printing conditions constructed by machine learning methods. The ejection environment information provided by the ejection environment information providing unit at the current position of the nozzle 110 is used as input. The printing prediction model calculates the optimal printing conditions and performs printing accordingly.

[0082] More specifically, the spatial information around the deposition site, including the viscosity of the ink, the conductivity of the ink, the size of the nozzle 110, and the distance between the nozzle 110 and the deposition site, can be taken into account to understand the electric field distribution between the nozzle 110 and the deposition site, and based on the electric field distribution, the flight trajectory based on the charge of the droplets can be ensured and printing can be performed, and a printing prediction model can be constructed by comparing with the final pattern to be printed.

[0083] Here, the so-called printing conditions may include one or more of the intensity of the voltage used to form the electric field, the ejection angle of the nozzle, the distance between the nozzle and the deposition location, the ejection speed of the droplets, the charge of the droplets, and the flow rate of the ink supplied to the nozzle.

[0084] Fig.11 The present invention shows a process of constructing a printing prediction model and a result of comparing the printing result predicted by the printing prediction model with the printing result actually measured.

[0085] Fig.11 The upper part of is a diagram for explaining the process of constructing a printing prediction model by a machine learning method. The printing prediction model takes the ejection environment information around the deposition point provided by the ejection environment information providing unit as input, provides printing conditions and predicts the printing result based on the printing conditions, compares the predicted printing result with the result actually printed under the printing conditions, and reflects the result in the machine learning algorithm to update the printing prediction model. By repeatedly performing this learning process, a highly accurate printing prediction model can be constructed for a variety of ejection environment information.

[0086] The variables used to construct a printing prediction model through machine learning methods may include (the magnitude of) the input voltage used to form an electric field, the deposition position of the droplets based on the three-dimensional surface shape, the deposition path, the distance between the nozzle end and the deposition location, the charge of the droplets, the electric field distribution between the nozzle and the deposition location, the material of the deposition location, the characteristics of the ink such as the viscosity of the ink, the conductivity of the ink, and at least one of the size of the nozzle.

[0087] At this time, the variables may be actual values ​​obtained through experiments or simulated values ​​obtained through calculation and analysis. For example, in the present invention, the electric field distribution can be obtained through simulation.

[0088] The control method of the electrohydrodynamic printing device of the present invention may include the following steps: grasping the size of the ejected droplets; taking into account the changes in the physical properties of the ink including viscosity caused by the evaporation of the ink supplied to the nozzle 110, the control unit 130 controls the voltage applied to the electrode in real time based on the size of the droplets to make the size of the ejected droplets constant.

[0089] At this time, the control unit 130 may further control the flow rate of ink supplied to the nozzle 110 in real time by controlling the ink supply unit 125 that supplies ink to the nozzle 110 so as to keep the size of the droplets ejected from the nozzle 110 constant.

[0090] At this time, in the step of grasping the size of the droplets, the image acquisition unit 150 may acquire an image of the droplets deposited on the substrate S, and grasp the size of the droplets from the droplet area in the acquired image. The control unit 130 may grasp the size of the ejected droplets in real time, and control the voltage applied to the electrode for forming the electric field, or control the flow rate of the ink supplied from the ink supply unit 125 to the nozzle 110, so as to continuously eject droplets having a reference size.

[0091] At this time, in order to obtain the reference size of the droplet, the following steps may be included: a step of ejecting a droplet of optimal volume onto the substrate S or an additional test substrate before printing; and a step of acquiring an image of the droplet of optimal volume by the image acquisition unit 150, and obtaining and storing the size of the droplet of optimal volume. The control unit 130 obtains the size of the ejected droplet in real time based on the stored size of the droplet, and controls the voltage applied to the electrode to form an electric field or controls the flow rate of the ink supplied from the ink supply unit 125 to the nozzle 110 accordingly.

[0092] The scope of the present invention is not limited to the above-mentioned embodiments, and can be embodied in various forms within the scope of the attached claims. Without departing from the spirit of the present invention claimed in the claims, various scopes that can be modified by technicians in the technical field to which the present invention belongs also fall within the scope recorded in the claims of the present invention.

Claims

1. An electrohydrodynamic printing device, characterized in that: include: A nozzle for discharging the supplied ink in the form of droplets toward the substrate; an electrode formed at the nozzle and used to form an electric field between the nozzle and the substrate by applying a voltage; a voltage supply unit for applying a voltage to the electrode; as well as a control unit for controlling the voltage supply unit; The control unit is configured to control the voltage applied from the voltage supply unit to the electrode in real time so that the size of the droplet discharged from the nozzle is constant.

2. The electrohydrodynamic printing device according to claim 1, characterized in that: further comprising an ink supply portion for supplying ink to the nozzle; The control unit is configured to control the ink supply unit to control the flow rate of ink supplied to the nozzle in real time so that the size of the ejected droplets is constant.

3. The electrohydrodynamic printing device according to claim 2, characterized in that: further comprising an image acquisition unit for acquiring an image of ink ejected from the nozzle; The control unit is configured to determine the size of a droplet from an image acquired by the image acquisition unit, and based on the size of the droplet, control the voltage applied to the electrode by the voltage supply unit in real time, or control the ink supply unit to control the flow rate of ink supplied to the nozzle in real time.

4. The electrohydrodynamic printing device according to claim 3, characterized in that: The image acquisition unit is configured to acquire an image of a liquid droplet deposited on the substrate, and the control unit is configured to obtain a size of the liquid droplet from an area of ​​the liquid droplet in the acquired image.

5. The electrohydrodynamic printing device according to claim 3, characterized in that: further comprising a droplet volume measuring section for measuring the volume of a droplet spitted onto the substrate or an additional test substrate; Before printing, storing the size of a liquid droplet obtained from an image acquired by the image acquisition section for a liquid droplet of an optimal volume measured by the liquid droplet volume measurement section; The control unit is configured to compare the stored droplet size with the droplet size obtained from the image acquired in real time by the image acquisition unit to control in real time the voltage applied to the electrode from the voltage supply unit, or to control the ink supply unit to control in real time the flow rate of ink supplied to the nozzle.

6. The electrohydrodynamic printing device according to claim 1, characterized in that: The control section is configured to control a cycle or a magnitude of a voltage supplied from the voltage supply section.

7. The electrohydrodynamic printing device according to claim 1, characterized in that: The voltage supply unit includes: a first voltage supply unit that supplies a voltage at a predetermined period and magnitude; and a second voltage supply unit that supplies an additional voltage to the voltage supplied from the first voltage supply unit; The control unit is configured to control the second voltage supply unit according to the size of the liquid droplets grasped in real time, so as to control the size of the discharged liquid droplets to be constant.

8. The electrohydrodynamic printing device according to claim 2, characterized in that: The ink supply unit includes a flow controller using air pressure, screw rotation or piezoelectric force; The control unit is configured to control the flow controller to control the flow rate of ink supplied to the nozzle in real time.

9. The electrohydrodynamic printing device according to claim 1, characterized in that: further comprising a spraying environment information providing unit for providing spraying environment information between the nozzle and a deposition location; The control unit is configured to accumulate pre-printing results based on the ejection environment information and printing conditions into a database and predict the actual printing results on the substrate, and to change the printing conditions provided by the database to perform printing based on the ejection environment information provided by the ejection environment information providing unit.

10. The electrohydrodynamic printing device according to claim 1, characterized in that: The control unit is configured to construct a printing prediction model for predicting the actual printing result on the substrate through a machine learning method based on a database about the ejection environment information and the printing conditions, and control printing based on the printing conditions provided by the ejection environment information using the printing prediction model.

11. A printing control method for an electrohydrodynamic printing device, characterized in that: The method for ejecting droplets toward a substrate by electric field force, wherein the electric field force is a force of an electric field generated by a voltage applied to an electrode formed on a nozzle, and the method comprises the following steps: Find the size of the ejected droplet; and The voltage applied to the electrode is controlled in real time so that the size of the droplet discharged from the nozzle is constant.

12. The printing control method of the electrohydrodynamic printing device according to claim 11, characterized in that: Further comprising the steps of: The flow rate of the ink supplied to the nozzle is controlled in real time by controlling an ink supply unit that supplies ink to the nozzle so that the size of the droplet discharged from the nozzle is constant.

13. The printing control method of the electrohydrodynamic printing device according to claim 12, characterized in that: An image of a liquid droplet deposited on the substrate is acquired, and the size of the liquid droplet is calculated from the area of ​​the liquid droplet in the acquired image.

14. The printing control method of the electrohydrodynamic printing device according to claim 13, characterized in that: Further comprising the steps of: Before printing, spitting a droplet of an optimal volume onto the substrate or an additional test substrate; as well as Determining and storing the size of the droplet of the optimal volume from the image of the droplet deposited on the substrate; The stored droplet size is compared with the droplet size obtained from the real-time acquired image to control the voltage applied to the electrode or the flow rate of ink supplied to the nozzle in real time to make the size of the droplets ejected from the nozzle constant.

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