Inkjet head monitoring system and method

Abstract

An inkjet head monitoring system according to an embodiment of the present disclosure may include: a head provided with a plurality of nozzles, each of the plurality of nozzles including a piezoelectric element and a switching element; a driver that applies a predetermined voltage to the plurality of nozzles; a sensing circuit obtaining a self-sensing signal from the piezoelectric element; and at least one processor. The at least one processor may be configured to: output a spray trigger to the driver to apply a voltage to the plurality of nozzles; obtaining, by the sensing circuit, the self-sensing signal from the piezoelectric element included in the plurality of nozzles based on a specified scanning frequency; extracting data corresponding to at least one frequency from the obtained self-sensing signal; and monitoring a state of the plurality of nozzles based on the extracted data corresponding to the at least one frequency.

Description

Technical Field

[0001] The present disclosure relates to a system and method for monitoring an ejection state of an inkjet head including a plurality of nozzles. Background Art

[0002] Inkjet printing technology finds its applications in a wider range from desktop printers to various industrial uses. Recent industrial printing systems require a single-pass printing system that ejects simultaneously from dozens of print heads to improve productivity using inkjet printing technology. The inkjet head may often be in a non-ejection state during printing, so it is important to immediately detect abnormal conditions by monitoring.

[0003] For this purpose, an inkjet printing system may use 100,000 or more nozzles, and a technology for quickly monitoring the ejection state of each of 100,000 or more nozzles (or ejectors) is required.

[0004] However, conventional vision-based measurement techniques for obtaining an ejection image of a nozzle during transfer of a nozzle head are not suitable for scanning all nozzles during printing because the monitoring time should be reduced to a very short time so as not to interrupt the printing process during printing to monitor the ejection state of each nozzle. Summary of the Invention

[0005] Technical Solution

[0006] An inkjet head monitoring system according to an embodiment of the present disclosure may include: a head equipped with a plurality of nozzles, each of the plurality of nozzles including a piezoelectric actuator and a switching element; a driver configured to apply a specified voltage to the plurality of nozzles; a sensing circuit configured to obtain a self-sensing signal from the piezoelectric actuator; and at least one processor. The at least one processor may be configured to: output an ejection trigger to the driver to apply a voltage to the plurality of nozzles. The at least one processor may be configured to: obtain the self-sensing signal from the piezoelectric actuator included in the plurality of nozzles based on a specified scanning frequency through the sensing circuit. The at least one processor may be configured to: extract data corresponding to at least one frequency through the obtained self-sensing signal. The at least one processor may be configured to: monitor a state of the plurality of nozzles based on the extracted data corresponding to the at least one frequency.

[0007] A method of monitoring an inkjet head according to an embodiment of the present disclosure may include: outputting a jet trigger to a driver configured to apply a specified voltage to each of a plurality of nozzles, each of the plurality of nozzles including a piezoelectric actuator and a switching element. A method of monitoring an inkjet head according to an embodiment of the present disclosure may include: obtaining a self-sensing signal from the piezoelectric actuator included in the plurality of nozzles by a sensing circuit based on a specified scanning frequency. A method of monitoring an inkjet head according to an embodiment of the present disclosure may include: extracting data corresponding to at least one frequency from the obtained self-sensing signal. A method of monitoring an inkjet head according to an embodiment of the present disclosure may include: monitoring the states of the plurality of nozzles based on the extracted data corresponding to the at least one frequency.

[0008] A non-transitory computer-readable storage medium storing at least one program according to an embodiment of the present disclosure may include: outputting a jet trigger to a driver based on the execution of an application, the driver being configured to apply a specified voltage to each of a plurality of nozzles, each of the plurality of nozzles including a piezoelectric actuator and a switching element. The storage medium according to an embodiment may include: obtaining a self-sensing signal from the piezoelectric actuator included in the plurality of nozzles by a sensing circuit based on a specified scanning frequency. The storage medium according to an embodiment may include extracting data corresponding to at least one frequency from the obtained self-sensing signal. The storage medium according to an embodiment may include: monitoring the states of the plurality of nozzles based on the extracted data corresponding to the at least one frequency.

[0009] An inkjet head monitoring system according to an embodiment of the present disclosure may include: a head equipped with a plurality of nozzles, each of the plurality of nozzles including a piezoelectric actuator and a switching element; a driver configured to apply a specified voltage to the plurality of nozzles; a sensing circuit configured to obtain a self-sensing signal from the piezoelectric actuator; and at least one processor. The at least one processor may be configured to: output a jet trigger to the driver to apply a voltage to the plurality of nozzles. The at least one processor may be configured to: obtain a self-sensing signal from the piezoelectric actuator included in the plurality of nozzles by the sensing circuit based on a specified scanning frequency. The at least one processor may be configured to: monitor the states of the plurality of nozzles based on an amplitude difference or a phase difference between the obtained self-sensing signal and a specified reference signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a block diagram showing an inkjet head monitoring system according to an embodiment of the present disclosure.

[0011] Figure 2 shows a layout of nozzles included in a head according to an embodiment of the present disclosure.

[0012] Figure 3 Shows the injection trigger signal in the parallel scanning method according to an embodiment of the present disclosure.

[0013] Figure 4a Shows the process of obtaining a self-sensing signal including driving noise according to an embodiment of the present disclosure.

[0014] Figure 4b Shows the process of obtaining driving noise according to an embodiment of the present disclosure.

[0015] Figure 5a Is a graph showing the self-sensing signal including driving noise according to an embodiment of the present disclosure.

[0016] Figure 5b Is a graph showing the self-sensing signal with driving noise eliminated according to an embodiment of the present disclosure.

[0017] Figure 6a Shows the result of analyzing the center frequency of the self-sensing signal of a normal nozzle according to an embodiment of the present disclosure.

[0018] Figure 6b Shows the result of analyzing the center frequency of the self-sensing signal of an abnormal nozzle according to an embodiment of the present disclosure.

[0019] Figure 7 Shows the software and hardware for visual analysis according to an embodiment of the present disclosure.

[0020] Figure 8 Shows the result of visual analysis for various injection states according to an embodiment of the present disclosure.

[0021] Figure 9 Is a scatter plot showing the amplitude difference and phase difference between the self-sensing signals of all nozzles and the reference signal according to an embodiment of the present disclosure.

[0022] Figure 10 Is a scatter plot showing the amplitude difference and phase difference between the self-sensing signal of each nozzle and the reference signal according to an embodiment of the present disclosure.

[0023] Figure 11a Is a scatter plot showing the amplitude difference and phase difference between the self-sensing signal and the reference signal before noise cancellation according to an embodiment of the present disclosure.

[0024] Figure 11b Is a scatter plot showing the amplitude difference and phase difference between the self-sensing signal with driving noise eliminated and the reference signal according to an embodiment of the present disclosure.

[0025] Figure 11cis a scatter plot showing the amplitude difference and phase difference between a self-sensing signal corresponding to the center frequency of a self-sensing signal and a reference signal according to an embodiment of the present disclosure.

[0026] Figure 12 is a flowchart showing a method of monitoring an inkjet head according to an embodiment of the present disclosure. Detailed Description

[0027] Figure 1 is a block diagram showing an inkjet head monitoring system 100 according to an embodiment of the present disclosure.

[0028] The inkjet head monitoring system 100 according to an embodiment can be applied to an inkjet printing system (e.g., an inkjet printer) using a piezoelectric actuator. In a method of monitoring a nozzle using a piezoelectric actuator, the behavior of a pressure wave in the inkjet head 110 can be indirectly measured from the amount of deformation of the piezoelectric actuator during ink ejection, and it can be determined whether the nozzle is defective based on a change in the behavior of the pressure wave because the behavior of the pressure wave of the ink changes when the operating state of the nozzle changes from a normal state to an abnormal state.

[0029] In an embodiment, the piezoelectric inkjet head 110 can eject ink droplets from a nozzle by a pressure wave generated when a voltage is applied using a piezoelectric actuator. That is, the piezoelectric inkjet head 110 can obtain an amount of deformation by driving the piezoelectric actuator with a voltage. The pressure wave can continue for a specific period (e.g., 70 [μs]) in the form of vibration without immediate attenuation.

[0030] In an embodiment, the piezoelectric actuator is an element capable of self-sensing by generating an electric charge when there is an amount of deformation. Therefore, the amount of deformation of the piezoelectric actuator can be calculated by measuring the current flowing through the piezoelectric actuator. That is, the piezoelectric actuator can be used as a sensor by detecting the force generated by the pressure wave of the ink in the ink dispenser of the inkjet printing system.

[0031] In an embodiment, the method using a piezoelectric self-sensing signal only uses the electrical signal of the inkjet head 110 without requiring any mechanical fixing device or hardware, thereby simplifying the hardware requirements and eliminating the need for position control of a camera 180 or a sensor for measuring the ink droplets (droplets) ejected according to the transfer of a specific nozzle.

[0032] In an embodiment, an inkjet printing system may use 50 or more heads 110, each head 110 having 1024 nozzles, for a display or a printer. That is, 50,000 or more nozzles may perform a printing operation by ejecting at a high frequency. In an embodiment, an inkjet head monitoring system 100 may monitor the state of nozzles by scanning self-sensing signals of a plurality of nozzles. Scanning may refer to a series of processes of monitoring whether a nozzle is abnormal by ejecting from all nozzles sequentially from start to end and analyzing the self-sensing signals accordingly.

[0033] Referring Figure 1 , an inkjet head monitoring system 100 according to an embodiment may include: a head 110 having a plurality of nozzles; a driver 130 that applies a specified voltage to each of the plurality of nozzles included in the head 110; a sensing circuit 160 that measures a current of a piezoelectric actuator; and / or at least one processor 140.

[0034] In an embodiment, the inkjet head monitoring system 100 may include a plurality of heads 110 and may further include a plurality of drivers 130. In an embodiment, each of the plurality of drivers 130 may be connected to at least one processor 140.

[0035] In an embodiment, the head 110 may be connected to a stage 120 that linearly generates movement (along the X-axis and the Y-axis). In an embodiment, the stage 120 may include an encoder that detects movement in each linear direction (for example, having a resolution of 1 [μm]).

[0036] In an embodiment, the head 110 may be provided with a plurality of parallel nozzles, and each nozzle may include a piezoelectric actuator and a switching element. For example, the head 110 may include two or more multi-heads 110 in which a plurality of nozzles (for example, 1024 or more nozzles) are formed and a single-head 110 as a piezoelectric inkjet head 110. Hereinafter, "a plurality of nozzles" may mean 1024 or more nozzles formed in two or more multi-heads 110 and 1024 or more nozzles formed in the single-head 110. For the sake of understanding, a case where 1024 nozzles are formed in the head 110 will be described as an example.

[0037] In an embodiment, the nozzle may include a piezoelectric actuator and a switching element. In an embodiment, the switching element may control the opening or closing of the nozzle based on a voltage input from the driver 130.

[0038] In an embodiment, the driver 130 may be provided with an output resistor R0 to adjust an output impedance and supply a driving voltage to the head 110 connected in series through the output resistor R0.

[0039] In an embodiment, the sensing circuit 160 is a part that obtains and processes the current of the piezoelectric actuator for each nozzle from the head 110, and may be provided in the form of an electronic sensing circuit or a sensing module. In an embodiment, the sensing circuit 160 may be integrated into the driver 130 in the form of a module. When the sensing circuit 160 is integrally formed with the driver 130, it may have a zero form factor for a monitoring module applicable to most inkjet applications.

[0040] Hereinafter, the "self-sensing signal" may represent the current signal of the piezoelectric actuator extracted from the head 110.

[0041] In an embodiment, the sensing circuit 160 may obtain a current difference signal by subtracting the current output from the piezoelectric actuator of each nozzle in an adjacent specific nozzle row through a switching element that sequentially opens the nozzles in the adjacent nozzle row based on the driving voltage of the driver 130 from the current output from the piezoelectric actuator of each nozzle in a specific nozzle row through a switching element that sequentially opens the nozzles in the specific nozzle row based on the driving voltage of the driver 130.

[0042] In an embodiment, the processor 140 may control at least one other component (e.g., a hardware component or a software component) connected to the processor 140 by executing software (e.g., a program), and perform various data processing or operations. According to an embodiment, as at least a part of the data processing or operation, the processor 140 may store a command or data received from another component (e.g., a sensor module or a communication module) in a volatile memory, process the command or data stored in the volatile memory, and store the result data in a non-volatile memory.

[0043] In an embodiment, the processor 140 may apply a driving voltage from the driver 130 to the head 110, and obtain or analyze a self-sensing signal in combination with the sensing circuit 160 described below.

[0044] In an embodiment, the self-sensing signal obtained from the sensing circuit 160 may be processed or determined by the processor 140, and information about the nozzle state according to the signal may be transmitted to an external device 150 (e.g., a PC or an external data storage device).

[0045] In an embodiment, the monitoring system 100 may further include a stroboscopic LED 170 and a camera 180 for visual analysis, in which a water droplet ejection image is used to measure the ejection speed and ejection directivity. The stroboscopic LED 170 may be controlled by a trigger from the external device 150 and driven by an LED driver 175. According to an embodiment, the monitoring system 100 may also use visual analysis to verify the nozzle monitoring result.

[0046] Figure 2Shows the layout of nozzles included in the printhead 110 according to an embodiment of the present disclosure.

[0047] Referring Figure 2 , according to an embodiment, a plurality of nozzles n may be arranged in the printhead 110 in a plurality of nozzle rows. For example, as Figure 2 (a) shows, 1024 nozzles n of the printhead 110 are arranged in 8 nozzle rows, with 128 nozzles arranged in each nozzle row. 128 nozzles are arranged in the same line to form a nozzle row, and 1024 nozzles may be formed in 8 nozzle rows in the printhead 110.

[0048] The specific layout of the nozzles may vary according to the printhead 110. However, generally, a plurality of nozzle rows are formed in the printhead 110 having a large number of nozzles, and the driver 130 may independently apply a voltage to drive each nozzle row or a plurality of nozzles.

[0049] In an embodiment, each nozzle in a nozzle row may be formed to be spaced apart from an adjacent nozzle by a specific gap. For example, when the gap between nozzles in the same nozzle row is 50 dpi, through fine adjustment of the gap in the nozzle direction between nozzle rows, the resolution in the printing direction may be 400 dpi.

[0050] In an embodiment, a plurality of nozzles n may be divided into a plurality of electrically independent nozzle modules or nozzle groups, each including a plurality of nozzle rows. Figure 2 (b) is Figure 2 an enlarged view of a part “A” in Figure 2 (a), and shows the numbers of the nozzles belonging to the part “A”. For example, in the case of (b), although the nozzles labeled with numbers 01 and 02 have a distance (gap) of 0.0635 mm in the X-axis direction, they may not be in the same nozzle row. In an embodiment, adjacent nozzles in a nozzle row may have a number difference of 8, and the distance between them may be 0.0635 * 8 = 0.508 mm.

[0051] In an embodiment, the nozzles in the same nozzle row can share the same driving voltage from a single driver 130, and eight independent driving voltages (i.e., eight drivers 130) can be used to drive 1024 nozzles or cause 1024 nozzles to eject. Due to the advantage of reducing the cost of the driver 130, the shared driver 130 can be used to drive a number of nozzles (e.g., each driver 130 drives 128 nozzles) (shared driving method). In this case, the driver 130 can drive a nozzle row or a nozzle module or cause a nozzle row or a nozzle module to eject by applying a plurality of independent driving voltages. Here, a system (e.g., an inkjet head monitoring system 100) and a method for monitoring a head 110 having 1024 nozzles in eight nozzle rows will be described, and the layout of the head 110 including a specific number of nozzles and nozzle rows is not limited to the form shown.

[0052] Referring to Figure 2 (b), one nozzle module nm includes two adjacent nozzle rows, and one head 110 can include four nozzle modules nm.

[0053] In an embodiment, the processor 140 can apply an ejection trigger to the nozzles of the driver 130 such that for each nozzle module nm or for each driver 130 generating an independent voltage, one nozzle is caused to eject repeatedly and simultaneously. In addition, as many sensing circuits 160 as the number of nozzle modules nm or the number of drivers 130 generating independent voltages can be provided. Each data collector for storing the self-sensing signals obtained by each sensing circuit 160 can be provided.

[0054] For example, a monitoring system (e.g., Figure 1 the inkjet head monitoring system 100) can use four sensing circuits 160 and four memories to monitor four nozzle modules nm having 1024 nozzles. The data collector can also be provided in the form of a data collection channel or a DAQ.

[0055] In a monitoring system according to an embodiment (e.g., Figure 1 100), a parallel scan method can be used to quickly scan all the nozzles regardless of the number of nozzles, nozzle modules, and heads 110.

[0056] Figure 3 An ejection trigger signal in a parallel scan method according to an embodiment of the present disclosure is shown.

[0057] Referring to Figure 3 , a plurality of ejection triggers TR can be applied to the nozzle n repeatedly or sequentially to eject repeatedly from the nozzle n, and the number of ejection triggers TR applied to each nozzle n ejecting simultaneously can be the same.

[0058] In an embodiment, a multiple averaging method (e.g., 3 - time averaging, N ave = 3) can be used for each nozzle n. However, the number of times the injection trigger TR is repeatedly applied for averaging is not limited to 3 times.

[0059] In an embodiment, the sensing circuit 160 can obtain repetitive self - sensing signals for each nozzle to average the self - sensing signals, and for this purpose, injection is repeated from each nozzle. Each injection trigger can be used as a data collection trigger.

[0060] In an embodiment, the sensing circuit 160 can obtain self - sensing signals from the nozzles, where the sensing circuit 160 can obtain as many repetitive self - sensing signals as the number of multiple injection triggers for each nozzle and calculate the average value of the self - sensing signals.

[0061] In an embodiment, the processor 140 can control injection from one nozzle of each nozzle module nm or generate a pressure wave for one nozzle to monitor a specific nozzle, while controlling other nozzles not to inject. Otherwise, signals from other nozzles (i.e., nozzles to which the injection trigger is not applied) may appear in the self - sensing signal, and the resulting mixed signal may make it impossible to detect the injection state of the specific nozzle.

[0062] A monitoring system according to an embodiment (e.g., the inkjet head monitoring system 100) can inject from up to four nozzles n simultaneously to scan the nozzles. Figure 3 Regarding the injection scanning scenario, in this scenario, one nozzle in each nozzle module (module 1 to module 4) injects, so as to inject from a total of four nozzles simultaneously, thereby minimizing the overall nozzle scanning time.

[0063] In an embodiment, the monitoring system (e.g., the inkjet monitoring system 100) can repeatedly apply the injection trigger TR for scanning to each nozzle, apply the injection trigger TR equal to or more than the specified average number to each nozzle, and average the corresponding obtained sensing signals. The scanning time can be shortened by using a parallel measurement method in which the injection trigger TR is simultaneously applied to each independent module and / or circuit.

[0064] For example, to average the self - sensing signals, three injection triggers TR are applied to one nozzle of each nozzle module at a predetermined frequency, and four nozzles: nozzle 1, nozzle 2, nozzle 3, and nozzle 4 can be injected simultaneously by the three initially applied injection triggers. At this time, the remaining nozzles other than nozzle 1, nozzle 2, nozzle 3, and nozzle 4 can be closed so as not to inject. Nozzle 1, nozzle 2, nozzle 3, and nozzle 4 can be included in different nozzle modules and have independent circuits from each other. Nozzle 2, nozzle 1, nozzle 3, and nozzle 4 can be injected simultaneously in nozzle module 1, nozzle module 2, nozzle module 3, and nozzle module 4, respectively.

[0065] In an embodiment, three ejection triggers are simultaneously applied to nozzles 1, 2, 3, and 4. Since nozzles 1, 2, 3, and 4 should eject simultaneously, the first trigger, the second trigger, and the third trigger can be applied to nozzles 1, 2, 3, and 4 at the same time. This simultaneous parallel ejection is used for parallel sensing to minimize the detection time. In an embodiment, simultaneous scanning can also be performed on two or more multi-heads 110 by using ejection triggers for all heads 110, thereby minimizing the detection time.

[0066] In an embodiment, nozzles 2, 6, 10, 14, etc. can be arranged in a row in nozzle module 1, nozzles 1, 5, 9, 13, etc. can be arranged in a row in nozzle module 2, nozzles 3, 7, 11, 15, etc. can be arranged in a row in nozzle module 3, and nozzles 4, 8, 12, 16, etc. can be arranged in a row in nozzle module 4. After nozzles 1, 2, 3, and 4 eject simultaneously, the next nozzles in each nozzle module, i.e., nozzles 5, 6, 7, and 8, can eject simultaneously. The three ejection triggers can also be applied to nozzles 5, 6, 7, and 8 sequentially or repeatedly.

[0067] Therefore, the parallel ejection method of performing scanning by ejecting simultaneously from one nozzle in each module and then ejecting simultaneously from the next nozzle in each module can monitor a large number of nozzles in a short period of time. Here, the ink may not actually be ejected from the nozzles, and it is only necessary to measure the behavior of the pressure wave for monitoring sensing. Thus, a weak voltage can be applied without actually ejecting the ink, thereby preventing unnecessary ejection while achieving nozzle monitoring.

[0068] In an embodiment, after a plurality of ejection triggers TR are applied to the nozzle (the nozzle refers to the nozzle to which the ejection trigger is applied and thus ejects), the processor 140 can repeatedly or sequentially apply the same number of ejection triggers to the next nozzle in each nozzle module (i.e., the next nozzle of the nozzle that has ejected).

[0069] In an embodiment, the processor 140 can control the remaining nozzles in the nozzle module or the nozzles of the driver 130 connected to the same voltage not to eject during the ejection of the ejecting nozzle. In this way, since one nozzle in each nozzle module ejects simultaneously and then the next nozzle ejects simultaneously, the total number of ejection triggers applied to the nozzles can be reduced, and the scanning time for a total of 1024 nozzles can be equal to the scanning time for 256 nozzles.

[0070] Specifically, the scanning time T required for all 1024 nozzles in a nozzle module including 256 nozzles with an independent circuit can be calculated by the following [Equation 1]. scan .

[0071] [Equation 1]

[0072] T scan =(N ave ×256) / F

[0073] N ave is the specified average number, and F is the scanning frequency. The scanning frequency F is fixed throughout the scanning process, and during the time interval between injection triggers, according to the parallel scanning scheme, the injection nozzle can switch to the next nozzle to scan all nozzles. According to the embodiment, since the nozzle module with an independent circuit consists of two nozzle rows and includes 256 nozzles, 256 is used in [Equation 1]. The number of nozzles in the nozzle module can be changed, and [Equation 1] can be modified accordingly.

[0074] For example, referring to Figure 3 , after applying a specified average number (e.g., three) of injection triggers TR to nozzle 2 in nozzle module 1, there is a time interval between the third injection trigger and the fourth injection trigger, and during this time interval, the injection nozzle can switch from nozzle 2 to nozzle 6. The time interval (gap) can be the reciprocal of the injection frequency, so the switch to another nozzle can be completed very quickly. Therefore, the monitoring system according to the embodiment (e.g., Figure 1 the inkjet head monitoring system 100) can reduce the time required to scan all nozzles to about 1 second by using the sequential parallel scanning injection method.

[0075] The scheme based on the parallel scanning injection method according to the embodiment can be implemented in all print drivers 130 by uploading print data (bitmap) that generates scanning injection according to externally or internally generated injection triggers to the driver 130. In this regard, the parallel scanning injection method according to the present disclosure is similar to bitmap printing for printing a specific pattern.

[0076] The injection trigger signal for scanning may not be generated from the encoder of the moving stage 120 in the piezoelectric inkjet printing system, but can be generated internally at a set scanning frequency F different from the printing process.

[0077] In the embodiment, although a higher scanning frequency F can be used to quickly scan all nozzles, the amplitude of the scanning frequency F may be limited due to data collection requirements. For example, according to the embodiment, each injection trigger signal (data collection trigger) with a sampling rate of 1 MS / s may require 100 data samples (N data= 100). Considering the data collection time, the scan frequency F can be 10 kHz or less.

[0078] In an embodiment, the processor 140 can set the scan frequency F for the injection trigger TR signal or the data collection trigger signal and change the scan frequency according to the time required to inject from all the nozzles. The injection trigger TR signal can be generated internally at the scan frequency.

[0079] In an embodiment, when the scan frequency is high, the pressure wave generated inside the head 110 may not completely decay until the next injection trigger TR is applied. In an embodiment, when the pressure wave generated from the previous injection trigger has not completely decayed, the self-sensing signal can vary according to the scan frequency. However, when the scan frequency is unified in such a way that the signal under normal injection conditions (i.e., the reference signal) is compared with the monitoring signal, this does not affect the monitoring result. For example, when using a scan frequency of 9 kHz, the average number N ave may affect the total scan time T defined in [Equation 1] scan . When the average number N ave decreases, due to the presence of electrical noise, the monitoring result may not be accurate. Considering the trade-off, it is preferable to use an average number of 10 to 30 (N ave = 10 to 30). In the case where the average number is set to 10, the total scan time T for scanning 1024 nozzles is 0.28 seconds. During the scanning process, the sampled sensing data can be sequentially stored in the data collector (e.g., memory) of each nozzle module.

[0080] In an embodiment, the number of sampled data after scanning can be N ave * 1024 * N data , where N ave = 10 and N data = 100. The repeated self-sensing data of each nozzle can be averaged in the firmware with N ave , and the total number of data that needs to be transferred to the external device 150 for future analysis can be reduced to 1024 * 100. In an embodiment, when the communication speed is high enough, the averaging process can be performed after the external device 150 receives the data. Since the initial self-sensing signal is easily affected by the drive signal, the first 10 to 40 data out of 100 data (N data ) are not used, and 60 to 90 data obtained later can be used.

[0081] In an embodiment, the processor 140 can compare the reference signal X of each nozzle measured under normal injection conditions k r with the monitoring signal (i.e., the self-sensing signal X km ) are compared to determine nozzle injection errors (faults) based on the self-sensing signals. The reference signal X k r can represent the nozzle signal under normal injection conditions. The reference signal can be calculated by averaging the self-sensing signals of all nozzles in the same nozzle row. In an embodiment, the monitoring system (e.g., the inkjet head monitoring system 100) can store eight reference signals because each head 110 includes eight independent drivers 130.

[0082] In an embodiment, the processor 140 can use two different methods to determine the nozzle state. That is, the cosine value or variance value of the reference signal and the self-sensing signal can be used.

[0083] In an embodiment, the processor 140 can use the reference signal X of each nozzle under normal injection conditions k r (i.e., the reference signal) and the self-sensing signal X of the nozzle k m between the cosine value C k to determine the state of the nozzle from the self-sensing signal. For example, the cosine value can be expressed as [Equation 2].

[0084] [Equation 2]

[0085]

[0086] In [Equation 2], X k r is the reference signal of the nozzle with nozzle number k, and X k m is the self-sensing signal of the nozzle with nozzle number k. Since the reference signal and the self-sensing signal are vectors, the dot · can represent the vector inner product (the dot sum of two vectors). In the case of 1024 nozzles, k = 1, 2, 3 ……, 1024.

[0087] The average value of all corresponding nozzle signals in the driver 130 can be used as the reference signal of the corresponding nozzle. Here, the value when at least 70% of the nozzles are in the normal injection state can be used as the reference signal.

[0088] In an embodiment, the phase change of the monitoring signal (i.e., the self-sensing signal) with respect to the reference signal X k can be detected from the cosine value C of the above [Equation 2]. k r For example, when the phase difference between the self-sensing signal and the reference signal X k r is 0 degrees, the cosine value is 1, and when the phase difference increases and approaches 180 degrees, the cosine value can become -1.

[0089] In an embodiment, the frequency change of the signal can be detected from the cosine value of [Equation 2]. When the center frequencies of the two comparison signals, i.e., the reference signal and the self-sensing signal, are not the same, the cosine value may become close to 0.

[0090] In an embodiment, the cosine value of [Equation 2] can be advantageous because the cosine value can be easily normalized from -1 to 1 according to the proximity between the reference signal and the self-sensing signal. In addition, the method using the cosine value may be less affected by electrical noise unrelated to the pressure signal. However, without changing the signal phase, it may not be possible to detect nozzle injection errors (faults) that affect the signal amplitude.

[0091] According to an embodiment, a monitoring system (e.g., Figure 1 the inkjet head monitoring system 100) can use the variance value as an additional method. For this purpose, the processor 140 can use the variance value V represented as [Equation 3] below k to determine the state of the nozzle.

[0092] [Equation 3]

[0093]

[0094] In [Equation 3], N can represent the number of sampled self-sensing data. For example, assuming that the first 40 data are excluded from 100 sampled data (N data = 100), then N = 60 can be used.

[0095] In an embodiment, using [Equation 3] can enable effective detection of even very small changes in the self-sensing signal. However, the monitoring result may be easily affected by electrical noise. Since the two different methods in [Equation 2] and [Equation 3] have their own advantages, the accuracy of the monitoring result can be improved by combining these two methods.

[0096] In an embodiment, a new decision criterion based on [Equation 2] and [Equation 3] can be represented as [Equation 4] below.

[0097] [Equation 4]

[0098] D k = A1 * C k +(A2) / (A3V k +1)

[0099] In [Equation 4], D kis a score of the nozzle, and A1, A2, and A3 are scaling factors. The monitored signal can be scored using [Equation 4] based on the proximity of the monitored signal to the reference signal. Nozzles with a score below a threshold value set in the range from 0 to 100 can be classified as defective nozzles that require repair and maintenance. [Equation 4] is merely an example for combining two different equations, and the advantages and disadvantages of two equations (i.e., [Equation 2] and [Equation 3]) can be utilized by using different combination methods.

[0100] In an embodiment, the scaling factors A1, A2, and A3 for each criterion should be considered because V k has characteristics different from C k . For example, a smaller value of V k closer to 0 indicates a normal injection state, while a larger value of C k closer to 1 indicates a normal injection state. To obtain a higher value for better conditions, the inverse function of V k can be considered. Additionally, to avoid the possibility of dividing by 0, a constant value of 1 can be added. In an embodiment, the scaling factor A3 is considered to maintain the balance between a constant and V k . Furthermore, the weights of A1 and A2 can be considered such that the maximum value of V k can be 100 to easily understand the degree of failure.

[0101] However, since the two parameters C k , V k have different value ranges and sensitivities, it may be difficult to set appropriate weighting factors.

[0102] Figure 4a illustrates a process of obtaining a self-sensing signal including drive noise according to an embodiment of the present disclosure. Figure 4b illustrates a process of obtaining drive noise according to an embodiment of the present disclosure.

[0103] Referring to Figure 4a and Figure 4b , a plurality of nozzles according to an embodiment of the present disclosure can be divided into a plurality of nozzle rows, and each nozzle row can include a plurality of nozzles. In an embodiment, the plurality of nozzle rows can be divided into at least one nozzle module. For example, two nozzle rows, the No. 1 row nozzles and the No. 2 row nozzles, can be grouped into one nozzle module.

[0104] In an embodiment, the sensing circuit 160 may detect a self-sensing signal of one nozzle module. In an embodiment, the sensing circuit 160 may detect a signal difference between a first nozzle row (nozzles in row 1) and a second nozzle row (nozzles in row 2) included in one nozzle module. Since the first nozzle row and the second nozzle row are not turned on simultaneously but are alternately turned on / off, the signals of the piezoelectric actuators included in each of the first nozzle row and the second nozzle row can be detected by only one sensing circuit 160.

[0105] In an embodiment, the processor 140 may control the nozzles in a plurality of nozzle rows in one nozzle module to be alternately turned on one by one, and the sensing circuit 160 may detect the self-sensing signal in a state where the nozzles included in the nozzle row are sequentially turned on.

[0106] For example, the raw data of row 1 may be the self-sensing signal in a state where the first nozzle row (nozzles in row 1) is turned on and the second nozzle row (nozzles in row 2) is turned off. The raw data of row 1 may be a value obtained by subtracting the driving signal Driving 2 of the second nozzle row from the sum of the driving signal Driving 1 of the first nozzle row and the piezo signal. The raw data of row 2 may be the self-sensing signal in a state where the second nozzle row (nozzles in row 2) is turned on and the first nozzle row (nozzles in row 1) is turned off. The raw data of row 2 may be a value obtained by subtracting the sum of the driving signal Driving 2 of the second nozzle row and the piezo signal from the sum of the driving signal Driving 1 of the first nozzle row.

[0107] Therefore, both the raw data of row 1 and the raw data of row 2 may include the difference between the driving signal Driving1 of the first nozzle row and the driving signal Driving 2 of the second nozzle row as driving noise (nominal data).

[0108] In an embodiment, the processor 140 may eliminate the driving noise (nominal data) from the raw data of the obtained self-sensing signal. In an embodiment, when the driving voltage of the driver 130, which is a high voltage, is applied, due to the influence of the conversion rate, the transient signal may be maintained.

[0109] In an embodiment, the processor 140 may obtain the driving noise through the sensing circuit 160 while all the plurality of nozzles are closed when the driving voltage is applied to the plurality of nozzles (nozzle rows). The driving noise may be the difference between the driving signal Driving 1 of the first nozzle row and the driving signal Driving 2 of the second nozzle row.

[0110] In an embodiment, the processor 140 may obtain the driving noise (nominal data) of each driver 130 or each nozzle row, and store it in the memory. In an embodiment, in order to minimize the influence of the noise present in the driving noise (nominal data), the processor 140 may obtain the average value of the driving noise (nominal data) obtained for each nozzle included in each nozzle row. The driving noise (nominal data) is the signal noise generated due to the application of the voltage to the driver 130, and since it is a drift signal that does not vary randomly and is repeatedly generated by the application of the driving voltage, it can be removed.

[0111] In an embodiment, the processor 140 may eliminate the driving noise (nominal data) from the specified reference signal.

[0112] Figure 5a is a graph showing a self-sensing signal including driving noise according to an embodiment of the present disclosure. Figure 5b is a graph showing a self-sensing signal from which the driving noise has been eliminated according to an embodiment of the present disclosure.

[0113] Referring to Figure 5a and 5b , it can be identified that the driving noise significantly affects the original data of the self-sensing signal.

[0114] As Figure 5b shown, when the driving noise is eliminated, it can be identified that each of the piezoelectric signals in the adjacent nozzle rows included in the nozzle module exhibits a positive or negative number. Therefore, after the driving noise is eliminated, the phase change of the measurement data becomes easy, thereby improving the monitoring performance.

[0115] Figure 6a shows the result of analyzing the center frequency of the self-sensing signal from a normal nozzle according to an embodiment of the present disclosure. Figure 6b shows the result of analyzing the center frequency of the self-sensing signal from an abnormal nozzle according to an embodiment of the present disclosure.

[0116] Referring to Figure 6a and Figure 6b , according to an embodiment, the processor 140 may extract data corresponding to at least one frequency from the obtained self-sensing signal.

[0117] In an embodiment, the processor 140 may analyze the amplitude and phase of the obtained self-sensing signal extracted according to the frequency based on the discrete fast Fourier transform (FFT).

[0118] In an embodiment, when the sampling frequency and the number of data to be used are determined, the frequency resolution can be determined. Generally, the sampling frequency is very high and the number of data is small, so the frequency resolution is relatively large. Since the frequency resolution df is f / N (where f is the sampling frequency and N is the number of data), for example, when the sampling frequency is 1 MS / s and N = 70, the frequency resolution can be approximately 14 [kHz].

[0119] In an embodiment, when the center frequency of the self-sensing signal (e.g., the frequency having the maximum amplitude according to the frequency analysis result) is approximately 70 [kHz], considering the frequency shift caused by frequency leakage and frequency defects, the amplitude changes corresponding to multiple (e.g., 3) frequencies adjacent to the center frequency of the self-sensing signal can be used. Thus, the influence of frequency components (e.g., multiple adjacent frequencies) other than the center frequency of the self-sensing signal can be removed.

[0120] In an embodiment, the processor 140 can extract the amplitude of the self-sensing signal corresponding to multiple frequencies including the center frequency of the self-sensing signal. For example, when the center frequency of the self-sensing signal is 70 [kHz], considering the resolution, the adjacent frequencies can be 56 [kHz] or 84 [kHz]. For example, the processor 140 can extract the amplitude of the self-sensing signal corresponding to the center frequency 70 [kHz] of the self-sensing signal and the adjacent frequencies 56 [kHz] and 84 [kHz]. In an embodiment, the processor 140 can obtain the amplitude difference between the self-sensing signal extracted at each frequency and a specified reference signal.

[0121] In an embodiment, the processor 140 can normalize the difference by dividing the difference between the amplitude of the self-sensing signal corresponding to at least one frequency and the amplitude of the specified reference signal corresponding to at least one frequency by the change amount (standard deviation) of the noise. Since the sensing time is very short, the state of the nozzle may hardly change, so the signal may change due to randomly occurring noise. Thus, by comparing the self-sensing signal collected for each nozzle each time with the change amount (standard deviation) of the noise, relative amplitude comparison can be performed.

[0122] In an embodiment, the processor 140 can divide the amplitude difference of the self-sensing signal corresponding to three frequencies by three times the change amount (standard deviation) of the noise as in [Equation 5] below. The value calculated by [Equation 5] can be referred to as the SN ratio.

[0123] [Equation 5]

[0124]

[0125] In [Equation 5], Δσ can be a function of the amplitude difference between the self-sensing signal and the reference signal at a specific frequency. f is the center frequency of the self-sensing signal, and Δf can be the frequency resolution. σ can be the amount of change (standard deviation) of the noise.

[0126] In an embodiment, when the normalized SN ratio is 1 or greater, the processor 140 may determine that the corresponding nozzle is defective because it is a value that has changed sufficiently compared to the noise. Generally, when nozzles with an SN ratio of about 0.3 to 0.4 or greater are classified, even nozzles with a reduced speed or wetting phenomenon can be detected.

[0127] As Figure 6a shown, when the nozzle is normal, the ratio between the amplitude difference between the center frequency and its adjacent frequencies and the noise (the value of [Equation 5]) is 0.72, which is a very small level. However, as Figure 6b shown, when the nozzle is abnormal, the ratio between the amplitude difference between the center frequency and its adjacent frequencies and the noise (the value of [Equation 5]) can increase relatively significantly to 8.59.

[0128] In an embodiment, the processor 140 may extract the phase of the self-sensing signal corresponding to the center frequency of the self-sensing signal. The processor 140 may extract the difference between the phase of the self-sensing signal corresponding to the center frequency of the extracted self-sensing signal and the phase of the specified reference signal corresponding to the center frequency of the self-sensing signal as shown in [Equation 6].

[0129] [Equation 6]

[0130]

[0131] In [Equation 6], f can be the center frequency of the self-sensing signal, can be the reference signal at a specific frequency, and can be the self-sensing signal at a specific frequency.

[0132] As Figure 6a shown, when the nozzle is normal, the phase difference at the center frequency is 8.60 [degrees], which is very small. However, as Figure 6b shown, when the nozzle is abnormal, the phase difference at the center frequency may increase relatively significantly to 117.37 [degrees].

[0133] Figure 7 Software 710 and hardware 720 for visual analysis according to an embodiment of the present disclosure are shown. Figure 8 Visual analysis results of various ejection states according to an embodiment of the present disclosure are shown.

[0134] Referring to Figure 7 and Figure 8, a monitoring system according to an embodiment (e.g., the inkjet head monitoring system 100) can perform visual analysis to statistically identify the ejection state of nozzles based on self-sensing signals. The monitoring system 100 according to an embodiment may be provided with: hardware 720, including a head 110 having 1024 nozzles in 8 nozzle rows, a stroboscopic LED 170, and a camera 180; and software 710 (e.g., a program), which obtains visual analysis results by sequentially scanning 1024 nozzles in 8 nozzle rows of the head 110.

[0135] In an embodiment, the monitoring system 100 can obtain a data set by performing a scan on the self-sensing signals of the nozzles and then performing a scan based on the visual analysis of the droplets ejected from the nozzles.

[0136] In an embodiment, the monitoring system 100 can automatically classify the ejection state by identifying the position, velocity (based on position change), ejection or non-ejection, and directionality of the droplets as the results of the scan based on visual analysis.

[0137] In an embodiment, Figure 8 (a) shows the visual analysis results of the normal ejection state of the nozzles. Figure 8 (b) shows the visual analysis results of the abnormal state of the ejection speed difference of the nozzles. Figure 8 (c) shows the visual analysis results of the abnormal state of the ejection directionality difference of the nozzles. Figure 8 (d) shows the visual analysis results of the abnormal state caused by non-ejection of the nozzles.

[0138] In an embodiment, the monitoring system 100 can obtain the self-sensing signals of each nozzle, classify the ejection state based on visual analysis, and set a threshold for determining the ejection state through statistical analysis of the self-sensing signals.

[0139] Figure 9 is a scatter plot showing the amplitude difference and phase difference between the self-sensing signals of all nozzles and the reference signal according to an embodiment of the present disclosure. Figure 10 is a scatter plot showing the amplitude difference and phase difference between the self-sensing signals and the reference signal in each nozzle row according to an embodiment of the present disclosure. For the scatter plot, the operating state is classified through visual image analysis, and according to visual analysis, they can be classified as ejection, non-ejection, or poor ejection speed, which can be displayed as a scatter plot of the phase difference and amplitude difference of the self-sensing signals.

[0140] Referring to Figure 9 and Figure 10, in the scatter plot according to the embodiment, the phase difference between the self-sensing signal and the reference signal of the nozzle is set on the X-axis, and the amplitude difference between the self-sensing signal and the reference signal is set on the Y-axis. In the embodiment, the phase difference may be the phase difference of the self-sensing signal corresponding to the center frequency of the self-sensing signal and may be the result of [Equation 6]. In the embodiment, the amplitude difference may be the difference between the amplitudes of the self-sensing signals corresponding to the center frequency and the adjacent frequencies of the self-sensing signal and may be the result of [Equation 5].

[0141] In the embodiment, Figure 9 and Figure 10 is a scatter plot showing the points based on the result (phase) of Equation 6 on the X-axis and the points based on the result (SN ratio) of Equation 5 on the Y-axis, and each point is shown in a color according to the ejection state of the nozzle classified based on the visual analysis result.

[0142] In the embodiment, the processor 140 may set a first threshold and a second threshold for the amplitude difference and the phase difference respectively based on the statistical analysis according to the scatter plot. In the embodiment, since according to the obtained scatter plot, the points corresponding to the nozzles in the normal state are located at a phase difference of 40 degrees or less and an amplitude difference of 0.4 or less, for example, the processor 140 may set the first threshold to 40 degrees and the second threshold to 0.4.

[0143] In the embodiment, the processor 140 may set the first threshold and the second threshold to smaller values in order to reduce uncertainty. However, in this case, the number of nozzles monitored as normal may be reduced and the path for printing may be expanded. In the embodiment, although the processor 140 may set the first threshold and the second threshold to larger values, in this case, the possibility of determining an abnormal nozzle as normal may increase.

[0144] In the embodiment, since the points in the normal state and the points in the abnormal state may overlap in some nozzle rows (for example, the 2nd row and the 5th row), it may be difficult to set the first threshold and the second threshold. This problem may be related to the noise level of the driver 130 and the circuit.

[0145] Figure 11a is a scatter plot showing the amplitude difference and the phase difference between the self-sensing signal and the reference signal before noise cancellation according to an embodiment of the present disclosure. Figure 11b is a scatter plot showing the amplitude difference and the phase difference between the self-sensing signal and the reference signal with the driving noise eliminated according to an embodiment of the present disclosure. Figure 11c is a scatter plot showing the amplitude difference and the phase difference between the self-sensing signal and the reference signal corresponding to the center frequency of the self-sensing signal according to an embodiment of the present disclosure.

[0146] Referring toFigure 11a It can be recognized that, before noise cancellation, the points corresponding to the nozzles in the normal state are densely gathered in a section with a relatively small amplitude difference, but the phase differences are distributed in various ways. In other words, it can be recognized that, before noise cancellation, it is difficult to monitor the nozzles based on the phase differences.

[0147] Referring to Figure 11b , by canceling the driving noise, it can be recognized that the points corresponding to the nozzles in the normal state are distributed in a section with a relatively small amplitude difference and phase difference. In other words, it can be recognized that noise cancellation contributes to nozzle monitoring based on the phase difference.

[0148] Referring to Figure 11c , according to the frequency analysis of the self-sensing signal and the reference signal, by using the self-sensing signal and the reference signal corresponding to the center frequency, it can be recognized that the nozzles in the normal state are densely gathered in a smaller section. In other words, applying the spectrum based on frequency analysis can contribute to monitoring the state of the nozzles.

[0149] Figure 12 FIG. 1200 is a flowchart showing a method of monitoring an inkjet head according to an embodiment of the present disclosure.

[0150] Referring to Figure 12 , in operation 1210, an inkjet head monitoring system according to an embodiment (e.g., Figure 1 the inkjet head monitoring system 100 or the processor 140) may output an ejection trigger to the driver 130, and the driver 130 applies a specified voltage to each of the plurality of nozzles, each nozzle including a piezoelectric actuator and a switching element.

[0151] In operation 1230, an inkjet head monitoring system according to an embodiment (e.g., Figure 1 the inkjet head monitoring system 100 or the processor 140) may obtain a self-sensing signal of the piezoelectric actuator included in the plurality of nozzles based on a specified scanning frequency through the sensing circuit 160.

[0152] In operation 1250, an inkjet head monitoring system according to an embodiment (e.g., Figure 1 the inkjet head monitoring system 100 or the processor 140) may further include an operation of canceling the driving noise from the obtained self-sensing signal.

[0153] In an embodiment, the driving noise may be a sensing signal obtained through the sensing circuit 160 while a specified voltage is applied to the plurality of nozzles by the driver 130 and all the plurality of nozzles are closed.

[0154] In operation 1270, an inkjet head monitoring system according to an embodiment (e.g., Figure 1The inkjet head monitoring system 100 or the processor 140) can extract data corresponding to at least one frequency from the obtained self-sensing signal.

[0155] An inkjet head monitoring system according to an embodiment (e.g., Figure 1 The inkjet head monitoring system 100 or the processor 140) can extract the amplitude or phase of the self-sensing signal corresponding to at least one frequency based on FFT analysis.

[0156] An inkjet head monitoring system according to an embodiment (e.g., Figure 1 The inkjet head monitoring system 100 or the processor 140) can extract the amplitude of the self-sensing signal corresponding to a plurality of frequencies including the center frequency of the self-sensing signal. In an embodiment, the processor 140 can normalize the difference by dividing the difference between the amplitude of the self-sensing signal corresponding to at least one frequency and the amplitude of the specified reference signal corresponding to at least one frequency by the change amount of the noise.

[0157] An inkjet head monitoring system according to an embodiment (e.g., Figure 1 The inkjet head monitoring system 100 or the processor 140) can extract the difference between the phase of the self-sensing signal corresponding to the center frequency of the self-sensing signal and the phase of the specified reference signal corresponding to the center frequency of the self-sensing signal.

[0158] In operation 1290, an inkjet head monitoring system according to an embodiment (e.g., Figure 1 The inkjet head monitoring system 100 or the processor 140) can monitor the states of a plurality of nozzles based on the extracted data corresponding to at least one frequency.

[0159] An inkjet head monitoring system according to an embodiment (e.g., Figure 1 The inkjet head monitoring system 100 or the processor 140) can monitor the states of a plurality of nozzles by comparing the differences between the amplitude and phase of the self-sensing signal corresponding to at least one frequency and the amplitude and phase of the specified reference signal corresponding to at least one frequency with a first threshold and a second threshold.

[0160] An inkjet head monitoring system according to an embodiment (e.g., Figure 1 The inkjet head monitoring system 100 or the processor 140) can respectively obtain a first threshold for the amplitude difference and a second threshold for the phase difference based on a statistical analysis related to the differences between the amplitude and phase of the self-sensing signal corresponding to at least one frequency and the amplitude and phase of the specified reference signal corresponding to at least one frequency.

[0161] Based on the monitoring system (e.g., the inkjet head monitoring system 100) and method according to an embodiment, a threshold value for determining the normal state of a nozzle can be appropriately set. For example, when the threshold value is set too small, the number of nozzles determined to be normal decreases, so the print path (scanning width) may increase, while when the threshold value is set too large, even defective nozzles may be determined to be normal.

[0162] Based on the monitoring system 100 and method according to an embodiment, parameters for distinguishing the normal state and the abnormal state of a nozzle can be obtained based on the design of the sensing circuit 160 and / or the driver 130.

[0163] Based on the monitoring system 100 and method according to an embodiment, the reliability of the printing operation can be increased by excluding abnormal nozzles from printing among a plurality of nozzles.

[0164] The inkjet printing system according to an embodiment can use the following method: when a discharge failure occurs in a nozzle, the state of the nozzle can be restored by using a purification method that pushes the ink into the nozzle by using pressure. The monitoring system 100 and method according to an embodiment can achieve nozzle maintenance by performing a purification operation on the nozzle based on the monitoring result and determining whether the nozzle is restored by the purification, while consuming the least amount of ink.

[0165] In the inkjet printing system according to an embodiment, although the ink should be uniformly supplied to the fine nozzle path at the beginning when the ink is injected into the head 110, bubbles may be generated, so even when a purification operation is performed, bubbles may exist in a specific nozzle. The monitoring system 100 and method according to an embodiment can reduce unnecessary ink purification operations and ink consumption by monitoring the process of injecting the ink into the head 110.

[0166] According to the monitoring system 100 and method according to an embodiment, all inkjet printing operations including inkjetting, maintenance, monitoring of the nozzle state, and printing excluding defective nozzles can be automated by a software algorithm without separate manipulation. In an embodiment, a database can be obtained through artificial intelligence, and the obtained data can be used to improve the algorithm through deep learning or machine learning.

[0167] An inkjet head monitoring system 100 according to an embodiment of the present disclosure may include: a head 110 having a plurality of nozzles, each nozzle including a piezoelectric actuator and a switching element; a driver 130 that applies a specified voltage to the plurality of nozzles; a sensing circuit 160 that obtains a self-sensing signal from the piezoelectric actuator; and at least one processor 140. The at least one processor 140 may be configured to output an ejection trigger to the driver 130 to apply a voltage to the plurality of nozzles. The at least one processor 140 may be configured to obtain a self-sensing signal from the piezoelectric actuators included in the plurality of nozzles based on a specified scan frequency through the sensing circuit 160. The at least one processor 140 may be configured to extract data corresponding to at least one frequency through the obtained self-sensing signal. The at least one processor 140 may be configured to monitor the states of the plurality of nozzles based on the extracted data corresponding to at least one frequency.

[0168] In the inkjet head monitoring system 100 according to an embodiment, the at least one processor 140 may be configured to extract the amplitude or phase of the self-sensing signal corresponding to at least one frequency based on discrete fast Fourier transform (FFT) analysis as at least part of the data extraction corresponding to at least one frequency.

[0169] In the inkjet head monitoring system 100 according to an embodiment, the at least one processor 140 may be configured to extract the amplitude of the self-sensing signal corresponding to a plurality of frequencies including the center frequency of the self-sensing signal as at least part of the data extraction corresponding to at least one frequency.

[0170] In the inkjet head monitoring system 100 according to an embodiment, the at least one processor 140 may be configured to divide the difference between the amplitude of the self-sensing signal corresponding to at least one frequency and the amplitude of a specified reference signal corresponding to at least one frequency by the change amount of the noise as at least part of the data extraction corresponding to at least one frequency.

[0171] In the inkjet head monitoring system 100 according to an embodiment, the at least one processor 140 may be configured to extract the difference between the phase of the self-sensing signal corresponding to the center frequency of the self-sensing signal and the phase of a specified reference signal corresponding to the center frequency of the self-sensing signal as at least part of the data extraction corresponding to at least one frequency.

[0172] In the inkjet head monitoring system 100 according to an embodiment, the at least one processor 140 may be configured to respectively obtain a first threshold for the amplitude difference and a second threshold for the phase difference based on a statistical analysis related to the amplitude difference and the phase difference between the self-sensing signal corresponding to at least one frequency and the specified reference signal corresponding to at least one frequency as at least part of the monitoring of the states of the plurality of nozzles.

[0173] In the inkjet head monitoring system 100 according to an embodiment, at least one processor 140 may be configured to eliminate, from the obtained self-sensing signal, drive noise obtained through the sensing circuit 160 while closing all of the plurality of nozzles by applying a specified voltage to the plurality of nozzles.

[0174] In the inkjet head monitoring system 100 according to an embodiment, the plurality of nozzles may be divided into nozzle rows and electrically independent nozzle modules, the nozzle rows having a plurality of nozzles arranged on the same line, and the electrically independent nozzle modules including at least one nozzle row.

[0175] A method of monitoring an inkjet head 110 according to an embodiment of the present disclosure may include outputting (1210) an ejection trigger to a driver 130, the driver 130 applying a specified voltage to each of the plurality of nozzles, each nozzle including a piezoelectric actuator and a switching element. A method of monitoring an inkjet head 110 according to an embodiment of the present disclosure may include obtaining (1230), through a sensing circuit 160, a self-sensing signal from the piezoelectric actuators included in the plurality of nozzles based on a specified scan frequency. A method of monitoring an inkjet head 110 according to an embodiment of the present disclosure may include extracting (1270), from the obtained self-sensing signal, data corresponding to at least one frequency. A method of monitoring an inkjet head 110 according to an embodiment of the present disclosure may include monitoring (1290) the states of the plurality of nozzles based on the extracted data corresponding to at least one frequency.

[0176] In a method of monitoring an inkjet head 110 according to an embodiment of the present disclosure, extracting (1270) data corresponding to at least one frequency may include extracting the amplitude or phase of the self-sensing signal corresponding to at least one frequency based on discrete fast Fourier transform (FFT) analysis.

[0177] In a method of monitoring an inkjet head 110 according to an embodiment of the present disclosure, extracting (1270) data corresponding to at least one frequency may include extracting the amplitude of the self-sensing signal corresponding to a plurality of frequencies including the center frequency of the self-sensing signal.

[0178] In a method of monitoring an inkjet head 110 according to an embodiment of the present disclosure, extracting (1270) data corresponding to at least one frequency may include dividing the difference between the amplitude of the self-sensing signal corresponding to at least one frequency and the amplitude of a specified reference signal corresponding to at least one frequency by the change amount of the noise.

[0179] In a method of monitoring an inkjet head 110 according to an embodiment of the present disclosure, extracting (1270) data corresponding to at least one frequency may include extracting the difference between the phase of the self-sensing signal corresponding to the center frequency of the self-sensing signal and the phase of a specified reference signal corresponding to the center frequency of the self-sensing signal.

[0180] In a method of monitoring an inkjet head 110 according to an embodiment of the present disclosure, monitoring (1290) the states of a plurality of nozzles may include: obtaining a first threshold for an amplitude difference and a second threshold for a phase difference, respectively, based on a statistical analysis related to an amplitude difference and a phase difference between a self-sensing signal corresponding to at least one frequency and a specified reference signal corresponding to at least one frequency.

[0181] A method of monitoring an inkjet head 110 according to an embodiment of the present disclosure may further include: eliminating (1250) drive noise obtained through a sensing circuit 160 from the obtained self-sensing signal while all of the plurality of nozzles are closed by applying a specified voltage to the plurality of nozzles.

[0182] A non-transitory computer-readable storage medium storing at least one program according to an embodiment of the present disclosure may include: outputting an ejection trigger to a driver 130 based on execution of an application, the driver 130 applying a specified voltage to each of a plurality of nozzles, each of the plurality of nozzles including a piezoelectric actuator and a switching element. The storage medium according to an embodiment of the present disclosure may include obtaining a self-sensing signal from the piezoelectric actuator included in the plurality of nozzles through the sensing circuit 160 based on a specified scanning frequency. The storage medium according to an embodiment of the present disclosure may include extracting data corresponding to at least one frequency through the obtained self-sensing signal. The storage medium according to an embodiment of the present disclosure may include: monitoring the states of the plurality of nozzles based on the extracted data corresponding to at least one frequency.

[0183] An inkjet head monitoring system 100 according to an embodiment of the present disclosure may include: a head 110 having a plurality of nozzles, each nozzle including a piezoelectric actuator and a switching element; a driver 130 applying a specified voltage to the plurality of nozzles; a sensing circuit 160 obtaining a self-sensing signal from the piezoelectric actuator; and at least one processor 140. The at least one processor 140 may be configured to output an ejection trigger to the driver 130 to apply a voltage to the plurality of nozzles. The at least one processor 140 may be configured to obtain a self-sensing signal from the piezoelectric actuator included in the plurality of nozzles through the sensing circuit 160 based on a specified scanning frequency. The at least one processor 140 may be configured to monitor the states of the plurality of nozzles based on an amplitude difference or a phase difference between the obtained self-sensing signal and a specified reference signal.

[0184] In an inkjet head monitoring system 100 according to an embodiment, the at least one processor 140 may be configured to eliminate drive noise obtained through the sensing circuit 160 from the obtained self-sensing signal while all of the plurality of nozzles are closed by applying a specified voltage to the plurality of nozzles.

[0185] In an inkjet head monitoring system 100 according to an embodiment, at least one processor 140 may be configured to extract data corresponding to at least one frequency from the obtained self-sensing signals.

[0186] In an inkjet head monitoring system 100 according to an embodiment, at least one processor 140 may be configured to extract the amplitude or phase of the self-sensing signals corresponding to at least one frequency based on discrete fast Fourier transform (FFT) analysis, as at least part of extracting data corresponding to at least one frequency.

[0187] In an inkjet head monitoring system 100 according to an embodiment, at least one processor 140 may be configured to obtain a first threshold for the amplitude difference and a second threshold for the phase difference based on statistical analysis related to the amplitude difference and the phase difference between the obtained self-sensing signals and a specified reference signal, as at least part of monitoring the states of a plurality of nozzles.

[0188] It should be understood that the embodiments of the present disclosure and the terms used therein are not intended to limit the technical features set forth herein to specific embodiments, but include various changes, equivalent forms or alternative forms for the corresponding embodiments. For the description of the drawings, similar reference numerals may be used to refer to similar or related elements. It will be understood that a singular noun corresponding to a term may include one or more things, unless the relevant context clearly indicates otherwise. As used herein, each of the phrases such as "A or B", "at least one of A and B", "at least one of A or B", "A, B or C", "at least one of A, B and C", and "at least one of A, B or C" may include all possible combinations of the items listed together in the corresponding one of the plurality of phrases. As used herein, terms such as "first" and "second" or "1st" and "2nd" may be used to simply distinguish the corresponding components from another component, and do not limit the components in other aspects (e.g., importance or order). It will be understood that in the case where the terms "operably" or "communicatively" are used or where the terms "operably" or "communicatively" are not used, if an element (e.g., a first element) is referred to as "combined with another element (e.g., a second element)", "combined to another element (e.g., a second element)", "connected to another element (e.g., a second element)", or "coupled to another element (e.g., a second element)", it means that the one element may be directly connected to (e.g., wired to) the other element, wirelessly connected to the other element, or connected to the other element via a third element.

[0189] As used in connection with embodiments of the present disclosure, the term "module" may include units implemented in hardware, software, or firmware and may be used interchangeably with other terms (e.g., "logic", "logic block", "portion", or "circuit"). A module may be a single integrated component adapted to perform one or more functions or the smallest unit or portion of the single integrated component. For example, according to an embodiment, a module may be implemented in the form of an application specific integrated circuit (ASIC).

[0190] Embodiments of the present disclosure may be implemented as software (e.g., program 140) including one or more instructions readable by a machine (e.g., electronic device 101) stored in a storage medium (e.g., internal memory 136 or external memory 138). For example, under the control of a processor, a processor (e.g., processor 120) of the machine (e.g., electronic device 101) may call at least one of the one or more instructions stored in the storage medium and run the at least one instruction with or without using one or more other components. This enables the machine to operate to perform at least one function according to the at least one instruction called. The one or more instructions may include code generated by a compiler or code that can be run by an interpreter. A machine-readable storage medium may be provided in the form of a non-transitory storage medium. Herein, the term "non-transitory" only means that the storage medium is a tangible device and does not include signals (e.g., electromagnetic waves), but this term does not distinguish between data being stored semi-permanently in the storage medium and data being stored temporarily in the storage medium.

[0191] According to an embodiment, methods according to various embodiments of the present disclosure may be included and provided in a computer program product. The computer program product may be traded between a seller and a purchaser as a product. The computer program product may be distributed in the form of a machine-readable storage medium (e.g., compact disc read-only memory (CD-ROM)), or the computer program product may be distributed online (e.g., downloaded or uploaded) via an application store (e.g., Play Store TM ), or the computer program product may be directly distributed (e.g., downloaded or uploaded) between two user devices (e.g., smart phones). If it is distributed online, at least part of the computer program product may be generated temporarily, or at least part of the computer program product may be stored at least temporarily in a machine-readable storage medium (such as the memory of a manufacturer's server, an application store's server, or a forwarding server).

[0192] According to an embodiment, each of the above components (e.g., a module or a program) may include a single entity or multiple entities. Some of the multiple entities may be separately provided in different components. According to various embodiments, one or more of the above components may be omitted, or one or more other components may be added. Optionally or additionally, multiple components (e.g., modules or programs) may be integrated into a single component. In this case, according to various embodiments, the integrated component may still perform the one or more functions of each of the multiple components in the same or similar manner as the corresponding one of the multiple components performed one or more functions before integration. According to various embodiments, the operations performed by a module, a program, or another component may be performed sequentially, in parallel, repeatedly, or in a heuristic manner, or one or more of the operations may be run in a different order or omitted, or one or more other operations may be added.

Claims

1. An inkjet head monitoring system (100), comprising: A head (110) equipped with a plurality of nozzles including piezoelectric actuators and switching elements; A driver (130) configured to apply a specified voltage to the plurality of nozzles; A sensing circuit (160) configured to obtain a self-sensing signal from the piezoelectric actuator; And At least one processor (140), wherein the at least one processor (140) is configured to: Output an ejection trigger to the driver (130) to apply a voltage to the plurality of nozzles, Obtain the self-sensing signal from the piezoelectric actuator included in the plurality of nozzles based on a specified scanning frequency through the sensing circuit (160), Extract data corresponding to at least one frequency through the obtained self-sensing signal, and Monitor the states of the plurality of nozzles based on the extracted data corresponding to the at least one frequency.

2. The inkjet head monitoring system (100) according to claim 1, wherein, The at least one processor (140) is configured to: Extract the amplitude or phase of the self-sensing signal corresponding to the at least one frequency based on discrete fast Fourier transform (FFT) analysis as at least part of the data extraction corresponding to the at least one frequency.

3. The inkjet head monitoring system (100) according to claim 2, wherein, The at least one processor (140) is configured to: Extract the amplitude of the self-sensing signal corresponding to a plurality of frequencies including the center frequency of the self-sensing signal as at least part of the data extraction corresponding to the at least one frequency.

4. The inkjet head monitoring system (100) according to claim 2 or 3, wherein, The at least one processor (140) is configured to: Divide the difference between the amplitude of the self-sensing signal corresponding to the at least one frequency and the amplitude of a specified reference signal corresponding to the at least one frequency by the change amount of noise as at least part of the data extraction corresponding to the at least one frequency.

5. The inkjet head monitoring system (100) according to any one of claims 2 to 4, wherein, The at least one processor (140) is configured to: Extract the difference between the phase of the self-sensing signal corresponding to the center frequency of the self-sensing signal and the phase of a specified reference signal corresponding to the center frequency of the self-sensing signal as at least part of the data extraction corresponding to the at least one frequency.

6. The inkjet head monitoring system (100) according to any one of claims 2 to 5, wherein, The at least one processor (140) is configured to: Obtain a first threshold for the amplitude difference and a second threshold for the phase difference respectively based on a statistical analysis related to the amplitude difference and the phase difference between the self-sensing signal corresponding to the at least one frequency and the specified reference signal corresponding to the at least one frequency as at least part of monitoring the states of the plurality of nozzles.

7. The inkjet head monitoring system (100) according to any one of claims 1 to 6, wherein, The at least one processor (140) is configured to: Eliminate the driving noise obtained through the sensing circuit (160) while all the plurality of nozzles are closed by applying the specified voltage to the plurality of nozzles from the obtained self-sensing signal.

8. The electronic device according to any one of claims 1 to 7, wherein, The plurality of nozzles are divided into nozzle rows and electrically independent nozzle modules, the nozzle rows having a plurality of nozzles arranged on the same line, and the electrically independent nozzle modules including at least one nozzle row.

9. A method for monitoring an inkjet head (110), comprising: Output an ejection trigger (1210) to the driver (130), the driver (130) being configured to apply a specified voltage to each of the plurality of nozzles, each of the plurality of nozzles including a piezoelectric actuator and a switching element; Obtain (1230) a self-sensing signal from the piezoelectric actuators included in the plurality of nozzles by a sensing circuit (160) based on a specified scanning frequency; Extract (1270) data corresponding to at least one frequency from the obtained self-sensing signal; and Monitor (1290) the states of the plurality of nozzles based on the extracted data corresponding to the at least one frequency.

10. The method according to claim 9, wherein, The step of extracting (1270) data corresponding to the at least one frequency includes: extracting the amplitude or phase of the self-sensing signal corresponding to the at least one frequency based on discrete fast Fourier transform (FFT) analysis.

11. The method according to claim 10, wherein, The step of extracting (1270) data corresponding to the at least one frequency includes: extracting the amplitude of the self-sensing signal corresponding to a plurality of frequencies including the center frequency of the self-sensing signal.

12. The method according to claim 10 or 11, wherein, The step of extracting (1270) data corresponding to the at least one frequency includes: dividing the difference between the amplitude of the self-sensing signal corresponding to the at least one frequency and the amplitude of a specified reference signal corresponding to the at least one frequency by the change amount of noise.

13. The method according to any one of claims 10 to 12, wherein, The step of extracting (1270) data corresponding to the at least one frequency includes: extracting the difference between the phase of the self-sensing signal corresponding to the center frequency of the self-sensing signal and the phase of a specified reference signal corresponding to the center frequency of the self-sensing signal.

14. The method according to any one of claims 10 to 13, wherein, The step of monitoring (1290) the states of the plurality of nozzles includes: respectively obtaining a first threshold for the amplitude difference and a second threshold for the phase difference based on a statistical analysis related to the amplitude difference and the phase difference between the self-sensing signal corresponding to the at least one frequency and the specified reference signal corresponding to the at least one frequency.

15. The method according to any one of claims 9 to 14, further comprising: Eliminate (1250) driving noise obtained by the sensing circuit (160) while all of the plurality of nozzles are closed by applying the specified voltage to the plurality of nozzles from the obtained self-sensing signal.

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