Patent Publication Number: US-11390071-B2

Title: Real time drop information measurement unit and real time discharging droplet compensating apparatus and method using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. 119(a) of Korean Patent Application No. 10-2019-0081480 filed on Jul. 5, 2019, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes. 
     TECHNICAL FIELD 
     The present invention relates to a real time drop information measurement unit and real time discharging droplet compensating apparatus and method using the same, and more particularly, to a real time drop information measurement unit and real time discharging droplet compensating apparatus and method using the same capable of compensating a discharging degree in real time by feeding-back drop information. 
     BACKGROUND ART 
     In order to manufacture a display device such as an LCD, inkjet equipment is often used to form an alignment film or discharge droplets when applying UV ink, or applying a color filter on a substrate. 
     Such inkjet equipment is equipped with a head for discharging droplets, an ink tank for supplying the droplets to the head, and among them, the head for ejecting the droplets through a nozzle needs to eject the droplets with an accurate discharge amount at an accurate position and thus it is necessary to be precisely controlled. 
     In particular, in recent years, since it is necessary to discharge droplets in a fine pattern, a high level of precision for the discharge amount is required. 
     According to Korean Patent Publication No. 10-2017-0133799 illustrated in FIG. 1, an inkjet head 10 is constituted by a lower assembly 13 where a nozzle 23 is disposed and an upper assembly 11 connected to a reservoir to supply a droplet to the nozzle. 
     In addition, the upper assembly 11 is provided with a piezo 19 that determines the discharge amount of the droplet by a magnitude of voltage to be applied. 
     In such an inkjet device, position and size information of ink drops may be obtained through measurements such as a line scan camera and a glass view camera, and volume information may be obtained through measurement such as drop watcher and laser doppler measurement. 
     However, since the position, size, and volume information of the ink drops cannot be obtained at the same time, an additional operation for compensating these information is required, and thus, the position, size, and volume information of the ink drops cannot be obtained in real time. 
     In addition, for the measurement, the inkjet head unit needs to be moved, but there is a problem in that such a measurement method causes an increase in total production time to deteriorate the productivity. 
     DISCLOSURE 
     Technical Problem 
     In order to solve the problems, specifically, an object of the present invention is to compensate a form in which a droplet is discharged from an inkjet head by acquiring drop information to be discharged from a nozzle in real time. 
     Further, another object of the present invention is to measure position, size, and volume information of drops at the same time to feed-back the measured position, size, and volume information to an inkjet head unit. 
     Technical Solution 
     To achieve the objects, the present invention provides a drop measurement unit provided below a substrate to measure drop information of a droplet to be discharged on the substrate from an inkjet head, which is configured by including a sensor module in which a plurality of sensor are disposed, and the drop measurement unit measures a drop position, a drop size, and a drop volume by using information measured by the sensor module. 
     According to an embodiment, the drop measurement unit may measure a drop size by using the number of sensors which detect the drop. 
     According to an embodiment, the drop measurement unit may include pressure sensor modules in the form of a matrix and may calculate and map a drop position, a drop size, and a drop volume by using node information of the matrix. 
     According to an embodiment, the node information may include a coordinate of each node and a detected pressure value. 
     According to an embodiment, the drop measurement unit may include at least one pair of electrode sensor modules, and calculate and maps a drop position, a drop size, and a drop volume of a droplet having conductivity according to a change in electric field by electrode sensors provided in the electrode sensor module. 
     According to an embodiment, the electrode sensor modules may include a signal electrode and a ground electrode and electric field is formed to be changed between the signal electrode and the ground electrode by applying a square wave to the signal electrode. 
     To achieve the objects, the present invention provides a real time discharging droplet compensating apparatus which is configured by including a discharge control unit controlling the driving of an inkjet head; and a drop measurement unit provided below a substrate to measure drop information of a droplet to be discharged on the substrate and feed-back the measured drop information to the drop measurement unit, wherein the discharge control unit compensates a nozzle waveform of discharging the droplet using the drop information. 
     According to an embodiment, the drop measurement unit may measure a drop size by using the number of sensors which detect the drop. 
     According to an embodiment, the drop measurement unit may include pressure sensor modules in the form of a matrix and may calculate and map a drop position, a drop size, and a drop volume by using node information of the matrix. 
     According to an embodiment, the node information may include a coordinate of each node and a detected pressure value. 
     According to an embodiment, the drop measurement unit may transmit the mapped information to the discharge control unit, and the discharge control unit may compare the mapped information with prestored data to control a discharge amount of the inkjet head by using a result value due to a difference thereof. 
     According to an embodiment, the drop measurement unit may detect the number of droplets to be dropped per one pixel to the number of drops per pixel to transmit the detected number of droplets to the discharge control unit, and the discharge control unit may compare the number of drops per pixel with a prestored reference number and then controls the inkjet head by using a result value. 
     According to an embodiment, the drop measurement unit may include at least one pair of electrode sensor modules, and calculate and maps a drop position, a drop size, and a drop volume of a droplet having conductivity according to a change in electric field by electrode sensors provided in the electrode sensor module. 
     According to an embodiment, the electrode sensor modules may include a signal electrode and a ground electrode and electric field is formed to be changed between the signal electrode and the ground electrode by applying a square wave to the signal electrode. 
     To achieve the objects, the present invention provides a real time discharging droplet compensating method which performs transferring a substrate to a lower side of an inkjet head; positioning a drop measurement unit below the substrate; discharging a droplet from the inkjet head to the substrate; measuring drop information of the droplet to be discharged to the substrate by the drop measurement unit; and feeding-back a signal capable of controlling a size of the droplet to be discharged from the inkjet head by using the drop information to a discharge control unit by the drop measurement unit. 
     According to an embodiment, the drop measurement unit may include pressure sensors in the form of a matrix and may calculate a drop position, a drop size, and a drop volume by using node information of the matrix. 
     According to an embodiment, the node information includes a coordinate of each node and a detected pressure value. 
     According to an embodiment, the electrode sensor modules include a signal electrode and a ground electrode and electric field is formed to be changed between the signal electrode and the ground electrode by applying a square wave to the signal electrode. 
     According to an embodiment, The real time discharging droplet compensating method further comprising: receiving, by the discharge control unit, the feed-back from the drop measurement unit and comparing, by the discharge control unit, the setting data with the feed-back to determine whether the discharge compensation is performed. 
     Advantageous Effects 
     According to the present invention, it is possible to acquire drop information without moving a separate head unit by measuring the position, size, and volume information of the drop at the same time to feed-back the measured position, size, and volume information to the inkjet head unit in real time. 
     Further, it is possible to control the size of a droplet to be discharged from the inkjet head in real time by acquiring the drop information to be discharged from the nozzle. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a structural diagram illustrating a structure of an inkjet head according to the related art; 
         FIG. 2  is a configuration diagram illustrating a configuration of a real time discharging droplet compensating apparatus according to the present invention; 
         FIG. 3  is a configuration diagram illustrating a configuration of a pressure sensor module in  FIG. 2 ; 
         FIG. 4  is an exemplary diagram for describing a calculation method of a drop size in  FIG. 3 ; 
         FIGS. 5 and 6  are exemplary diagrams illustrating another embodiment of the real time discharging droplet compensating apparatus according to the present invention; and 
         FIG. 7  is a flowchart illustrating a real time discharging droplet compensating method according to the present invention. 
     
    
    
     MODES OF THE INVENTION 
     Configurations and functions of embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     Referring to  FIG. 2 , a real time discharging droplet compensating apparatus according to the present invention is configured to include a drop measurement unit  200  and a discharge control unit  320 . 
     In the embodiment, the drop measurement unit  200  includes a pressure sensor module  210 . The pressure sensor module  210  includes matrix-based pressure sensors, and is provided below a substrate to acquire drop information of a droplet to be discharged onto the substrate. 
     In the embodiment, the substrate  100  may be used with various substrates, such as a transparent substrate for manufacturing a liquid crystal display and the like, or a substrate for manufacturing an organic EL display and the like. For example, substrates such as polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyether sulfone (PES), polyimide (PI), and glass may be used. 
     The substrate is provided on the pressure sensor module  210 , and a liquid chemical is discharged onto the substrate in a predetermined shape by an inkjet device. 
     A pixel partition wall  110  constituting a pixel is formed on the substrate  100  to realize each color of RGB. 
     Referring to  FIG. 3 , the pressure sensor module  210  is provided with a pressure sensor at each node in a matrix form, and the drop measurement unit  200  calculates whether a droplet has been dropped on the substrate, a drop size, and a drop volume based on the node information by the pressure sensor. The node information includes a coordinate of each node, a detected pressure value, etc. 
     Specifically, when an interval of the pressure sensor in the pressure sensor module  210  is 5 μm, if the droplet discharged from the inkjet head is detected by six pressure sensors as illustrated in  FIG. 4 , the drop position may be determined to a position of an average of coordinate values of the six nodes or a node closest to the average. Further, a drop size S may be calculated to 5×10=50 μm 2 . 
     In addition, if pressure values measured by the six pressure sensors are P1, P2, P3, P4, P5, and P6, respectively, the drop measurement unit  200  calculates an average of the pressure values by the six pressure sensors to PA=(P1+P2+P3+P4+P5+P6)/6. 
     If the mass of the liquid chemical is m, the density is p, and the volume is V,
 
 P   A ×5= mg=ρVg,  
 
the drop volume may be calculated to V=(P A ×S)/ρg.
 
     The drop measurement unit  200  performs mapping that displays the drop information which has been calculated above, that is, the drop position, the drop size, and the drop volume in response to a corresponding position on the matrix. These drop information may be numerically stored during mapping. 
     Such measurement performed by the drop measurement unit needs to be first performed based on pressure by the substrate. For example, before the discharging of the liquid chemical, a pressure value by the substrate is first stored as an initial pressure value, and the drop information may be calculated by using a value obtained by subtracting the stored initial pressure value from the pressure value by the pressure sensor module detected after the discharging of the liquid chemical. 
     The drop measurement unit  200  performs a mapping operation and then transmits mapping information to the discharge control unit  320 . The discharge control unit  320  compares setting data prestored in a storage unit with the mapping information transmitted from the drop measurement unit to calculate a result value by a difference thereof and controls the inkjet head by using the result value. 
     Specifically, the storage unit stores the setting data, such as a size of a droplet to be discharged, a discharge rate, the number of droplets to be discharged per one pixel, a discharge position, etc. In addition, when the discharge control unit  320  starts to operate the inkjet device, the discharge control unit  320  drives a piezoelectric element based on the setting data stored in the storage unit to perform the discharging of the liquid chemical. 
     While the operation of the inkjet device is performed, the drop measurement unit  200  calculates drop information of the droplet to be discharged and generates mapping information to feed-back the generated mapping information to the discharge control unit  320  again, and the discharge control unit calculates a difference obtained by subtracting the drop position and the drop size fed-back from the discharge control unit from the drop position and the drop size by the setting data. 
     For example, when the result value obtained by subtracting the fed-back drop size from the drop size by the setting data is negative, the discharge control unit weakens the driving of the piezoelectric element to control the discharge size to be small. At this time, the driving of the piezoelectric element is adjusted by the size of the result value to adjust the nozzle waveform and compensate the discharge amount of the chemical liquid precisely. 
     Even in the case of the drop position, the discharge control unit calculates a difference vector by subtracting a coordinate of the fed-back drop position from a coordinate of the drop position by the setting data in the same manner as the drop size and controls a motion of the inkjet head based on the difference vector to compensate the discharge position precisely. 
     The drop measurement unit  200  may calculate a drop position, a drop size, a drop volume, and the number of drops per pixel by using the pressure sensor module. 
     The number of drops per pixel refers to the number of droplets to be dropped in one pixel, and the drop measurement unit measures the number of times of applying the pressure to the pressure sensor to detect the number of drops per pixel and transmits the number of drops per pixel to the discharge control unit. 
     The discharge control unit compares the number of drops per pixel fed-back from the discharge control unit with the number of droplets to be discharged per one pixel stored in the setting data to compensate a difference thereof when the number of drops per pixel is different from the number of droplets. 
     Next, another embodiment of the drop measurement unit will be described. 
     Referring to  FIG. 5 , the drop measurement unit may include other sensor modules, and in the embodiment, the drop measurement unit includes at least one pair of electrode sensor modules  250  and  251 . 
     The pressure sensor modules  250  and  251  are disposed in a matrix form and provided below a substrate to acquire drop information of a droplet to be discharged onto the substrate. 
     Specifically, the electrode sensor modules include a signal electrode  250  and a ground electrode  251  and the drop measurement unit  200  applies a square wave to the signal electrode  250 . Then, an electric field is formed to be changed between the signal electrode  250  and the ground electrode  251  via the substrate  100 , and a displacement current is formed. 
     At this time, when the droplet having conductivity is dropped on the substrate from the inkjet head, as illustrated in  FIG. 6 , the electric field is changed and a capacitance and a displacement current between the two electrodes are varied, so that the drop measurement unit  200  may determine whether the droplet has been dropped at the corresponding position. 
     Further, the drop size is calculated by calculating how many of the electrodes the drop is detected in the electrode sensors arranged in a matrix form, and the drop volume may also be calculated by the method described above. In order to calculate the drop size, it is preferable to calculate how many adjacent electrodes the drop has been detected, and to determine a separate drop when the drop is detected on electrodes which are not adjacent but separated from each other. 
     Next, a real time discharging droplet compensating method according to the present invention will be described with reference to  FIG. 7 . 
     When a substrate is transferred, the substrate is provided on a pressure sensor module or an electrode sensor module, and when the substrate is provided in place, a drop measurement unit starts initialization. That is, pressure information by the substrate itself is stored in the drop measurement unit, and the pressure information of the substrate itself may be set to zero. 
     When the initialization step ends, the drop measurement unit transmits an initialization end signal to the discharge control unit, and when the discharge control unit receives the initialization end signal, the discharge control unit reads setting data stored in a storage unit to drive an inkjet head based on the setting data. The setting data may include data, such as the size of a droplet, a discharging rate, the number of droplets to be discharged per pixel, and a discharging position. 
     When a liquid chemical is discharged from the inkjet head based on the setting data, the drop measurement unit measures drop information of the droplet dropped on the substrate. The drop information may include information on a drop position, a drop size, a drop volume, the number of drops per pixel, etc. 
     The drop measurement unit generates mapping information of a position corresponding to the matrix based on the measured drop information to feed-back the generated mapping information to the discharge control unit. 
     The discharge control unit receives the feed-back from the drop measurement unit and compares the setting data with the feed-back data to determine whether the discharge compensation is performed. At this time, a size of the compensation is determined together by a difference value between the setting data and the feed-back data. 
     As described above, in the embodiment, since the discharge amount of the liquid chemical, the discharging method, or the like is compensated in real time by the discharge control unit, precise control is enabled without moving the inkjet head. 
     As described above, the present invention has been described with reference to the exemplary embodiments. However, it will be appreciated by those skilled in the art that various modifications and changes of the present invention can be made without departing from the spirit and the scope of the present invention which are disclosed in the appended claims. 
     EXPLANATION OF REFERENCE NUMERALS AND SYMBOLS 
     
         
         
           
               100 : Substrate 
               200 : Drop measurement unit 
               210 : Pressure sensor module 
               300 : Inkjet head 
               320 : Discharge control unit