Inkjet printing system

Abstract

An inkjet printing system includes: an inkjet head unit including a nozzle for discharging ink; a driving unit for generating and outputting a driving voltage for discharging the ink from the nozzle; a first impedance adjustment unit disposed between an input terminal of the inkjet head unit and an output terminal of the driving unit and including a diode; and a self-sensing circuit unit connected to an input terminal of the inkjet head unit and receiving a self-sensing voltage from the nozzle to determine whether the nozzle is operating normally.

Description

[0001] This application claims priority to and all benefits derived from Korean Patent Application No. 10-2023-0108319, filed on August 18, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present disclosure relates to inkjet printing systems. Background Art

[0003] There may be various methods of forming each layer in a display device such as a liquid crystal display device or an organic light emitting diode display device, a semiconductor, a printed circuit board, a solar cell, or a sensor.

[0004] One of them can form a layer by ejecting ink droplets, and such inkjet technology is applied not only to printers but also to a wide range of applications.

[0005] As the scope of application of inkjet technology as a manufacturing process expands, ensuring the reliability of ink droplets passing through the nozzles has become a very important issue.

[0006] As a method for inspecting the operating state of the inkjet head unit and nozzle ejection failure, a method of directly inspecting ink droplets ejected from the nozzles by a camera is used.

[0007] The method using a camera has the advantage of being able to accurately measure the behavior and speed of inkjet, but precise alignment must be performed for each nozzle, and the calculation speed caused by mechanical movement and image processing, etc. is an issue due to the number of nozzles, so there are limitations on quickly detecting defective nozzles.

[0008] Specifically, the nozzle monitoring method of the inkjet printing system directly ejects ink and determines whether the ink ejected from a small number of nozzles is defective through a separate vision system.

[0009] This method takes a long time because a small number of nozzles must be sequentially made visible by mechanical alignment control, and has the disadvantage of excessively wasting ink since it is a direct jetting method.

[0010] In addition, since the status of the nozzle changes over time, there is a problem that the monitoring results may not be consistent with the actual defects in many cases. Utility Model Content

[0011] The embodiment is directed to providing an inkjet printing system capable of accurately performing nozzle self-sensing together with nozzle driving.

[0012] Additionally, embodiments are directed to providing an inkjet printing system capable of accurately monitoring multiple nozzles while accurately driving them with a single driver.

[0013] According to an embodiment, an inkjet printing system includes: an inkjet head unit, including a nozzle for discharging ink; a driving unit, for generating and outputting a driving voltage for discharging ink from the nozzle; a first impedance adjustment unit, which is arranged between an input terminal of the inkjet head unit and an output terminal of the driving unit and includes a pair of diodes; and a self-sensing circuit unit, which is connected to the input terminal of the inkjet head unit and receives a self-sensing voltage from the nozzle to determine whether the nozzle is operating normally.

[0014] The pair of diodes of the first impedance adjusting unit may include a forward diode and a reverse diode.

[0015] Each of the forward diode and the reverse diode may be one of a PN junction diode, a Schottky diode, and a Zener diode.

[0016] The driving unit may be provided as a plurality of driving units, the nozzle may be provided as a plurality of nozzles, the inkjet head unit may be connected to one of the plurality of driving units and may include a plurality of nozzles, and the inkjet head unit may further include a plurality of switches respectively connected to the plurality of nozzles.

[0017] The self-sensing circuit unit may include a differential amplifier that receives the self-sensing voltage from an input terminal of the inkjet head unit, and the differential amplifier may further receive a reference voltage and subtract the reference voltage from the self-sensing voltage to obtain a final self-sensing voltage.

[0018] The reference voltage may be input from the output terminal of the driving unit.

[0019] The inkjet printing system may further include a second impedance adjusting unit connected to the output terminal of the driving unit and the input terminal of the differential amplifier, and the reference voltage may be input to the differential amplifier via the output terminal of the driving unit and the second impedance adjusting unit.

[0020] The second impedance adjusting unit may include an equivalent impedance adjusting unit having a configuration corresponding to the pair of diodes of the first impedance adjusting unit.

[0021] The second impedance adjusting unit may further include an equivalent capacitor unit corresponding to the nozzles included in the inkjet head unit.

[0022] The inkjet printing system includes: another inkjet head unit, positioned adjacent to the inkjet head unit, including multiple nozzles and multiple switches respectively connected to the multiple nozzles, a reference voltage can be input from an input terminal of the other inkjet head unit, and the reference voltage can be supplied when all the multiple switches included in the other inkjet head unit are turned on.

[0023] The self-sensing circuit unit may further include a signal processing unit that improves a signal-to-noise ratio using a filter.

[0024] The self-sensing circuit unit may further include a data determination unit configured to determine a state of the nozzle using the final self-sensing voltage.

[0025] According to an embodiment, an inkjet printing system includes: an inkjet head unit including a nozzle for discharging ink; a driving unit for generating and outputting a driving voltage for discharging ink from the nozzle; a first impedance adjusting unit provided between an input terminal of the inkjet head unit and an output terminal of the driving unit and including a forward diode; and a self-sensing circuit unit connected to the input terminal of the inkjet head unit and for receiving a self-sensing voltage from the nozzle to determine whether the nozzle is operating normally, wherein a positive direction of the forward diode is a direction from the output terminal of the driving unit to the input terminal of the inkjet head unit.

[0026] The forward diode may be one of a PN junction diode, a Schottky diode, and a Zener diode.

[0027] The driving unit may be provided as a plurality of driving units, the nozzle may be provided as a plurality of nozzles, the inkjet head unit may be connected to one of the plurality of driving units and may include a plurality of nozzles, and the inkjet head unit may further include a plurality of switches respectively connected to the plurality of nozzles.

[0028] The self-sensing circuit unit may include: a differential amplifier for receiving a self-sensing voltage from an input terminal of the inkjet head unit; a signal processing unit for improving a signal-to-noise ratio using a filter; and a data determination unit configured to determine the state of the nozzle, wherein the differential amplifier may further receive a reference voltage and generate a final self-sensing voltage by subtracting the reference voltage from the self-sensing voltage, and the state of the nozzle may be determined using the self-sensing voltage.

[0029] The reference voltage may be input from the output terminal of the driving unit.

[0030] The inkjet printing system may further include: a second impedance adjustment unit connected to the output terminal of the driving unit and the input terminal of the differential amplifier, wherein the second impedance adjustment unit may include an equivalent impedance adjustment unit having a configuration corresponding to the first impedance adjustment unit, and the reference voltage may be input to the differential amplifier through the output terminal of the driving unit and the second impedance adjustment unit.

[0031] The second impedance adjusting unit may further include an equivalent capacitor unit corresponding to the nozzles included in the inkjet head unit.

[0032] The inkjet printing system may include: another inkjet head unit, positioned adjacent to the inkjet head unit, including multiple nozzles and multiple switches respectively connected to the multiple nozzles, a reference voltage can be input from an input terminal of the other inkjet head unit, and the reference voltage can be transmitted when all of the multiple switches included in the other inkjet head unit are turned on.

[0033] According to the embodiment, driving and monitoring of the nozzle may be accurately performed using the impedance adjusting unit with respect to the driving voltage and the self-sensing voltage having a trade-off relationship.

[0034] According to the embodiment, manufacturing costs can be effectively reduced by connecting a plurality of nozzles to one driver and selectively driving and self-sensing each nozzle. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a schematic block diagram of an inkjet printing system according to an embodiment.

[0036] Figure 2 is a diagram showing a configuration of a portion of an inkjet printing system according to an embodiment.

[0037] Figure 3 is a graph showing the current and voltage characteristics of a PN junction diode.

[0038] Figure 4 is a diagram showing a structure of a portion of an inkjet printing system according to another embodiment.

[0039] Figure 5 and Figure 6 The diagram is based on Figure 4 FIGURE 1 is a diagram of characteristics of an embodiment of an inkjet printing system.

[0040] Figure 7 and Figure 8 is a diagram showing a structure of a portion of an inkjet printing system according to another embodiment.

[0041] Figure 9 is a graph showing the current and voltage characteristics of a Schottky diode.

[0042] Figure 10 It shows that according to Figure 8 FIGURE 1 is a diagram of characteristics of an embodiment of an inkjet printing system.

[0043] Figure 11 is a diagram illustrating a structure of an impedance adjusting unit according to various embodiments.

[0044] Figure 12 is a diagram showing the structure of an inkjet printing system according to an embodiment.

[0045] Figure 13 It shows Figure 12 FIG. 1 is a diagram of a voltage waveform in an embodiment of the present invention.

[0046] Figure 14 is a diagram showing the structure of an inkjet printing system according to another embodiment.

[0047] Figure 15 It shows Figure 14 FIG. 1 is a diagram of a voltage waveform in an embodiment of the present invention.

[0048] Figure 16 is a diagram showing the structure of an inkjet printing system according to another embodiment.

[0049] Figure 17 is a diagram showing the structure of an inkjet printing system according to another embodiment.

[0050] Figure 18 It shows Figure 17 FIG. 1 is a diagram of a voltage waveform in an embodiment of the present invention.

[0051] Figures 19 to 22 is a diagram showing the structure of an inkjet printing system according to another embodiment.

[0052] Figure 23 is a diagram showing the structure of an inkjet printing system according to a comparative example.

[0053] Figure 24 It shows Figure 23 FIG. 1 is a diagram of a voltage waveform in a comparative example.

[0054] <Description of the symbol>

[0055] 1: Inkjet printing system 10: Inkjet head unit

[0056] PZT: piezoelectric body 11: nozzle

[0057] 20: Impedance adjustment unit 30: Driving unit

[0058] 40: Self-sensing circuit unit 41: Differential amplifier

[0059] 42: Signal Processing Unit 43: DAQ

[0060] 46: Reference voltage generator

[0061] 50: Equivalent impedance adjustment unit

[0062] 60: Equivalent capacitor unit

[0063] 70: Additional impedance adjustment unit

[0064] In: Input terminal of inkjet head unit

[0065] Out: Output terminal of the drive unit

[0066] 21, 22, 23, 24, 25, 26, 51, 52, 53, 54: diodes DETAILED DESCRIPTION

[0067] Hereinafter, various embodiments will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily perform the present invention.

[0068] The present invention may be embodied in many different forms and is not limited to the embodiments set forth herein.

[0069] In order to clearly describe the present invention, parts irrelevant to the description are omitted, and the same reference numerals are assigned to the same or similar components throughout the specification.

[0070] In addition, since the size and thickness of each component shown in the drawings are arbitrarily shown for convenience of explanation, the present invention is not necessarily limited to the shown contents.

[0071] In the drawings, the thickness is shown exaggerated to clearly show various layers and regions.

[0072] Also, in the drawings, the thicknesses of some layers and regions are exaggerated for convenience of explanation.

[0073] In addition, when a part such as a layer, film, region, panel, or component is referred to as being “on” or “over” another part, it means not only when it is “directly on” the other part but also when there is another part therebetween.

[0074] In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.

[0075] In addition, “above” or “on” a reference portion means above or below the reference portion, and does not necessarily mean positioned “above” or “on” it in the opposite direction of gravity.

[0076] In addition, throughout the specification, when a specific component is stated as “comprising,” it means that it may further include other components rather than excluding other components, unless stated otherwise.

[0077] Additionally, throughout the specification, when a “planar image” is mentioned, it means when a target portion is observed from above, and when a “cross-sectional image” is mentioned, it means when a vertically cut cross section of the target portion is observed from the side.

[0078] In addition, throughout the specification, when "connected" is used, it means not only the case where two or more components are directly connected, but also the case where two or more components are indirectly connected or physically connected through another component. In the case of being connected or electrically connected and being referred to by different names depending on the position or function, each part that is substantially integrated may be connected to each other.

[0079] In addition, throughout this specification, when a portion such as a wiring, layer, film, region, board, component, etc. is said to "extend in a first direction or a second direction," it simply means a straight line extending in the corresponding direction. Alternatively, it may be a structure that extends generally along the first direction or the second direction and includes a bend at one portion, has a zigzag structure, or extends while including a curved structure.

[0080] In addition, electronic devices (e.g., mobile phones, TVs, monitors, and notebook computers) including the display devices and display panels described in the specification or the display devices and display panels manufactured by the manufacturing methods described in the specification are not excluded from the scope of this specification.

[0081] In the following, reference will be made to Figure 1 Describe the schematic structure of an inkjet printing system.

[0082] Figure 1 is a schematic block diagram of an inkjet printing system according to an embodiment.

[0083] The inkjet printing system 1 according to the embodiment may include an inkjet head unit 10 , an impedance adjusting unit 20 (hereinafter, referred to as a “first impedance adjusting unit”), a driving unit 30 , and a self-sensing circuit unit 40 .

[0084] The inkjet head unit 10 is a main part of the inkjet printing system 1 and includes nozzles for discharging ink droplets (see FIG. Figure 2 11), piezoelectric body (see Figure 2 PZT) and switch in.

[0085] When a driving voltage is transmitted to the piezoelectric element PZT in the inkjet head unit 10, a pressure wave is generated in the head of the inkjet head unit 10 to eject ink droplets. The residual pressure wave persists for a specific period of time after the ejection is complete. This generates micro-deformation of the piezoelectric element PZT and generates a vibration signal.

[0086] Therefore, the piezoelectric body PZT is an actuator, but it can also be used as a sensor.

[0087] The vibration signal of the pressure wave has information on the discharge state and can be measured by the self-sensing circuit unit 40 as a detection signal.

[0088] The driving unit 30 is a component that generates and outputs a driving voltage that causes the nozzles of the inkjet head unit 10 to discharge ink droplets and is supplied to the inkjet head unit 10 via the impedance adjustment unit 20 .

[0089] Depending on the embodiment, the driving voltage output from the driving unit 30 may be directly transmitted to the self-sensing circuit unit 40 , and the driving voltage transmitted in this manner is used to extract a self-sensing signal from the self-sensing circuit unit 40 , and it can be used to remove the driving voltage.

[0090] The self-sensing circuit unit 40 monitors the nozzles of the inkjet head unit 10 using a self-sensing method, and uses amplification, differentiation, and filtering in an analog circuit to easily determine whether a defect such as non-ejection occurs. The self-sensing circuit unit 40 is part of the circuit and can be connected to the input terminal of the inkjet head unit 10, receives a self-sensing voltage from the nozzles of the inkjet head unit 10, and processes the signal to easily determine whether the nozzles are operating normally.

[0091] Specifically, by receiving a self-sensing voltage according to the amount of deformation of the piezoelectric body PZT, the behavior of the pressure wave according to the driving voltage at the nozzle in the inkjet head unit 10 is indirectly measured, and from a normal state to a poor operating state, if the self-sensing voltage changes, the behavior of the pressure wave of the ink changes, so whether the nozzle is defective can be confirmed by the change in the self-sensing voltage.

[0092] A high voltage of several tens of volts is used as a driving voltage for driving the nozzles in the inkjet head unit 10 , and a relatively small voltage of 1 V or less is generated as a self-sensing voltage for monitoring the nozzles.

[0093] Therefore, the magnitude range of the self-sensing voltage is different from the driving voltage of the piezoelectric body PZT.

[0094] In addition, since the self-sensing voltage generated in this manner is formed in the form of electric charge of the piezoelectric body PZT (in the form of electrical charge), it is immediately extinguished when connected to another voltage source.

[0095] Here, it is known that the piezoelectric body PZT is electrically the same as a capacitor.

[0096] Therefore, in order to measure the generated self-sensing voltage, these points may be taken into consideration, and it is difficult to obtain a signal by directly connecting the piezoelectric body PZT to the driver of the head in the inkjet head unit 10 .

[0097] That is, from the perspective of ink ejection, when the output impedance of the driving unit 30 is small, applying the voltage as it is without a change (distortion, signal size change) in the output driving voltage enables ink ejection to the intended extent.

[0098] However, from the perspective of self-sensing, if the output impedance of the driving unit 30 is small, the self-sensing voltage generated by the piezoelectric body PZT is entirely dissipated due to the voltage source of the driving unit 30 , making it impossible to measure a desired signal.

[0099] If the output impedance is increased by adding a resistor or capacitor element in the driving unit 30, self-sensing is possible, but the driving voltage is greatly reduced or distorted, which affects the amount of ink discharged from the nozzle.

[0100] In order to eliminate the aforementioned trade-off relationship between the driving voltage and the self-sensing voltage, in this embodiment, the impedance adjustment unit 20 is disposed between the driving unit 30 and the inkjet head unit 10 .

[0101] The impedance adjusting unit 20 may include at least one diode, and may additionally include a device such as a resistor or a capacitor.

[0102] According to the impedance adjusting unit 20 , the nozzles of the inkjet head unit 10 maximize sensing characteristics without changing ejection characteristics, so that the nozzles of the inkjet head unit 10 can operate by simultaneously optimizing operations of an actuator and a sensor for discharging ink.

[0103] Specifically, the impedance adjustment unit 20 has a very low impedance to drive the nozzle of the inkjet head unit 10 and does not affect the driving voltage for ink ejection, but has a very high output impedance for self-sensing measurement, and the charge and / or voltage generated by the piezoelectric phenomenon in the nozzle can be effectively transmitted to the self-sensing circuit unit 40 so that it can be measured.

[0104] The impedance adjustment unit 20 can be configured in various embodiments and will be described below. Figures 2 to 11 Some of the various embodiments are described.

[0105] exist Figures 2 to 11 In the embodiment, the self-sensing circuit unit 40 is omitted, and the Figures 12 to 22 Various embodiments of the self-sensing circuit unit 40 are described in detail in FIG.

[0106] Figure 2 is a diagram showing a configuration of a portion of an inkjet printing system according to an embodiment.

[0107] exist Figure 2 , the structure of the inkjet head unit 10 is shown in detail, and an embodiment including a diode 21 (hereinafter referred to as a “forward diode”, “forward PN junction diode” or “forward direction PN junction diode”) as the impedance adjustment unit 20 is shown.

[0108] First, the structure of the inkjet head unit 10 will be reviewed.

[0109] The inkjet head unit 10 includes a plurality of piezoelectric bodies PZT and a switch connected to each piezoelectric body PZT.

[0110] Here, the piezoelectric body PZT and the switch are bundled one by one to form one nozzle 11.

[0111] That is, the plurality of nozzles 11 are driven by one driving unit 30 and one impedance adjusting unit 20 and monitored by one self-sensing circuit unit 40, so that the inkjet printing system can be used.

[0112] As a result, manufacturing costs can be reduced, mass productivity can be greatly increased, and the inkjet printing system can be used as a core technology for manufacturing display devices and electronic devices.

[0113] Figure 2 One end of the nozzle 11 is connected to the input terminal In of the inkjet head unit 10, and the other end may be grounded or electrically connected to a portion corresponding to the ground.

[0114] Alternatively, when a voltage is applied to the other end, the difference between the voltage applied to the input terminal In and the voltage applied to the other end may be the actual driving voltage.

[0115] exist Figure 2 In the present invention, the nozzle has characteristics similar to those of a capacitor in a circuit, so a capacitor is used instead of the piezoelectric body PZT. However, unlike a general capacitor, the piezoelectric body PZT can have various characteristics of a piezoelectric element.

[0116] exist Figure 2 In the embodiment, the switch included in one nozzle 11 is closed, and the switches included in the remaining nozzles 11 are opened.

[0117] As a result, only the nozzle 11 whose switch is closed can eject ink or generate a pressure wave even if ink is not ejected, and thereby, a self-sensing signal can be generated.

[0118] When a plurality of nozzles are connected to one driving unit 30, the state of the nozzle must be determined by applying a driving voltage to only one piezoelectric body PZT. Therefore, even if a problem occurs in any nozzle, it is difficult to know.

[0119] Typically, in a multi-nozzle head, one driver operates 128 or 256 nozzles, and there are 8 or 4 independent drive units 30 .

[0120] Therefore, each driving unit 30 can scan one by one at the same time, and the scanning speed can be increased by such parallel scanning.

[0121] Thus, depending on the embodiment, two or more nozzles 11 may be operated together.

[0122] The switching of each nozzle 11 may be controlled by a separate switch controller (not shown).

[0123] In an embodiment, in a process using an inkjet printing method, more than 100 multi-nozzle inkjet heads may be used to increase productivity.

[0124] The multi-nozzle inkjet head may include a plurality of nozzles 11 (more than 1024), and the productivity of the inkjet printing process may be increased by using several heads simultaneously and using tens of thousands of nozzles.

[0125] As the number of nozzles increases in such an inkjet printing system, nozzle maintenance becomes difficult. However, according to this embodiment, it is possible to self-sensing the actual driven nozzles in real time, accurately monitor the operation of the piezoelectric body PZT, and ensure the stability of the inkjet printing system.

[0126] Here, the stability of the inkjet printing system can be determined by the accuracy, uniformity, and ejection of the ink ejected from the piezoelectric body PZT, which is a very important factor affecting the yield and reliability of the inkjet printing process.

[0127] In the inkjet printing system according to the embodiment, each row may have a driving unit 30 , and in the embodiment where the inkjet printing system consists of 4 or 8 rows, the inkjet printing system includes 4 or 8 driving units 30 .

[0128] Meanwhile, 128 or 256 nozzles 11 may be formed in each row.

[0129] When actual inkjet printing is performed, one driver drives a plurality of nozzles simultaneously, so that inkjet printing can be performed simultaneously.

[0130] exist Figure 2 In the embodiment, the impedance adjusting unit 20 includes a forward diode 21 connected in a forward direction in view of the driving voltage output from the driving unit 30 .

[0131] Hereinafter, the connection direction of the diode is the forward direction from the output terminal Out of the driving unit 30 to the input terminal In of the inkjet head unit 10 , and the direction from the input terminal In of the inkjet head unit 10 toward the output terminal Out of the driving unit 30 is referred to as the reverse direction.

[0132] according to Figure 2In the embodiment, the forward diode 21 of the impedance adjustment unit 20 has a very low impedance when a high-value (e.g., exceeding 0.7V) driving voltage is applied from the driving unit 30 to the inkjet head unit 10, so that the driving voltage does not fluctuate. When the driving voltage is transmitted to the inkjet head unit 10 and the driving voltage is 0V or close to 0V, the impedance of the impedance adjustment unit 20 is very large, so that the self-sensing voltage is not applied to the impedance adjustment unit 20, and the self-sensing voltage is generated. The low voltage is amplified by the self-sensing circuit unit 40 without being affected by the voltage value (0V) of the driving unit 30 and is used to monitor the heads in the inkjet head unit 10.

[0133] Figure 2 The forward diode 21 of the embodiment is a PN junction diode and may have Figure 3 Characteristics similar to characteristics.

[0134] Figure 3 is a graph showing the current and voltage characteristics of a PN junction diode.

[0135] Figure 3 The current characteristics according to the voltage of a PN junction diode (PN diode) are shown.

[0136] exist Figure 3 In, V F means the forward voltage, V R means the reverse voltage, I F means forward current, and I R This means reverse current.

[0137] Reference Figure 3 , it can be seen that when a PN junction diode is used in the forward direction, a voltage drop of 0.7V may occur.

[0138] That is, a voltage of up to 0.7 V may be consumed to allow electrons and holes to meet and conduct current, after which the PN junction diode may have characteristics comparable to those of a conductor.

[0139] Therefore, even in the positive direction, if the voltage value is 0.7 V or less, the impedance has a very large value, and the voltage is not transmitted to the other end.

[0140] Specifically, since the voltage corresponding to the self-sensing generated by the inkjet head unit 10 may have a low voltage of 0.7 V or less, a signal of a residual pressure wave after the initial driving may be measured.

[0141] Therefore, for the self-sensing voltage generated from the piezoelectric body PZT of the inkjet head unit 10, since Figure 2The impedance value of the impedance adjusting unit 20 in FIG. 5 is very large, so the driving unit 30 does not act as a voltage source and thus does not force the piezoelectric voltage to 0V.

[0142] Additionally, emissions are unaffected because the high voltage used for driving has little effect.

[0143] On the other hand, refer to Figure 3 , when the voltage in the reverse direction is very high, the insulator performance is destroyed and avalanche breakdown may occur, but this voltage level is not generated by self-sensing.

[0144] Figure 2 The advantage is that, by simply adding the forward diode 21, the self-sensing voltage can be sensed without being affected by the driving voltage.

[0145] In addition, Figure 2 In the embodiment of FIG. 5 , when the driving voltage output from the driving unit 30 has a bipolar form having both positive and negative voltages, the forward diode 21 may operate as a reverse diode. Other embodiments such as the following embodiments may be used.

[0146] Hereinafter, the Figure 4 Example of .

[0147] Figure 4 is a diagram showing a structure of a portion of an inkjet printing system according to another embodiment.

[0148] exist Figure 4 In the embodiment of the present invention, the impedance adjustment unit 20 includes a pair of diodes consisting of a forward diode 21 and a reverse diode 22 (hereinafter referred to as a “reverse PN junction diode” or a “reverse PN junction diode”).

[0149] When the self-sensing voltage has positive and negative voltages, and when the driving voltage is in the form of bipolarity (positive and negative voltages or alternating current), the forward and reverse parallel connections are effective.

[0150] Therefore, in Figure 4 In the embodiment, except Figure 2 In addition to the embodiment of FIG. 1 , the impedance adjustment unit 20 further includes a reverse diode 22 .

[0151] exist Figure 4 In the embodiment, when the driving voltage output from the driving unit 30 is transmitted to the inkjet head unit 10 , the reverse diode 22 has a large impedance, so that it cannot pass through the reverse diode 22 but passes through the forward diode 21 and is transmitted to the inkjet head unit 10 .

[0152] At the same time, the self-sensing voltage generated by the inkjet head unit 10 can generally have a voltage of 1V or less, and when the input voltage becomes 0V after the driving is completed, at the forward diode 21 and the reverse diode 22, both the driving voltage (0V) and the self-sensing voltage are cut off (open circuit) and measured without being affected by the driving unit 30.

[0153] The measured self-sensing signal is transmitted to the self-sensing circuit unit 40 for amplification and signal processing (analog filtering, etc.).

[0154] On the other hand, when the piezoelectric body PZT of the inkjet head unit 10 accumulates electric charge due to characteristics similar to those of a capacitor, when the voltage exceeds a specific voltage ( Figure 3 When the voltage is 0.7V (0.7V in the voltage range), the accumulated charge is transferred to the driving unit 30 and removed. Therefore, the problem of charge accumulation can be eliminated.

[0155] In addition, Figure 4 In the embodiment, when the driving voltage output from the driving unit 30 has an alternating current form, due to the pair of diodes 21 and 22 formed in two directions, the self-sensing voltage within the range of -1V (or -0.7V) and 1V (or 0.7V) can be effectively measured in any case.

[0156] In the following, we will Figure 5 and Figure 6 review Figure 4 Characteristics of the embodiments.

[0157] Figure 5 and Figure 6 The diagram is based on Figure 4 FIGURE 1 is a diagram of characteristics of an embodiment of an inkjet printing system.

[0158] First, we will look at Figure 5 waveform.

[0159] exist Figure 5 (A), the measured voltage is shown as Figure 4 The voltage Vin measured at the input terminal In of the inkjet head unit 10 and the voltage Vout measured at the output terminal Out of the driving unit 30 are shown in FIG.

[0160] At the same time, Figure 5 In (B), Figure 5 The voltage of part B of (A) is amplified, and Figure 5 The voltage shown in (B) corresponds to a portion of the self-sensing voltage.

[0161] In addition, in the embodiment in which the number of nozzles 11 connected to one driving unit 30 is 128 or 256, the number of nozzles 11 connected to one driving unit 30 is measured by connecting only one switch of one nozzle 11. Figure 5 The voltage measured in .

[0162] Depending on the embodiment, one head may have 1024 nozzles and 4 or 8 drive units for driving them. Each drive unit can drive 256 or 128 nozzles simultaneously.

[0163] exist Figure 5 In (A), the voltage Vin measured at the input terminal In of the inkjet head unit 10 is lower than the voltage Vout measured at the output terminal Out of the driving unit 30, which means that the voltage drops when passing through the diode included in the impedance adjustment unit 20. Figure 3 , when the diode is a PN junction diode, the corresponding reduced voltage value may be 0.7V.

[0164] At the same time, Figure 5 In (A), the high voltage may be 20 V corresponding to the driving voltage.

[0165] Typically, the driving voltage applied to the piezoelectric body PZT can be from several tens of volts to 100 volts or more.

[0166] Figure 5 The voltage in (B) is an example of a detected self-sensing voltage, and the peak-to-peak voltage may be 50 millivolts (mV) less than the voltage value of the driving voltage.

[0167] Since the self-sensing voltage generally has a magnitude lower than 0.7 V, when the voltage at the driving unit 30 is 0 V due to diode characteristics, all measurements are possible without being affected by the driving voltage.

[0168] These signals are connected to the self-sensing circuit unit 40 for further amplification and signal processing.

[0169] If the signal has a sufficient magnitude compared to the noise, the self-sensing circuit unit 40 can be omitted.

[0170] Therefore, when a high voltage is applied as a driving voltage to eject ink from the piezoelectric body PZT, the piezoelectric body PZT can be driven normally by the driving voltage passing through the forward diode 21, and it can be confirmed that the self-sensing voltage of 0.7V or less is effectively transmitted to the self-sensing circuit unit 40.

[0171] at the same time, Figure 6 It is a drawing of the ejection image of ink droplets ejected from the piezoelectric body PZT, which is captured by a device called a drop viewer, and Figure 6 The black dots shown in indicate ink droplets.

[0172] Figure 6 (A) is a comparative example (referring to Figure 23 Ink droplets discharged in the comparative example in FIG. 1 ), and Figure 6 (B) is in Figure 4 Ink droplets discharged in the embodiment.

[0173] Reference Figure 6 FIG. 8 (B) shows that due to the voltage drop of 0.7 V generated by the diode included in the impedance adjustment unit 20, the ink drop falls slowly by a distance dr-d.

[0174] Therefore, ink ejection is substantially affected by the 0.7 V drop, but when multiple piezoelectric bodies PZT are connected, the influence of the number of piezoelectric bodies PZT is not significant except that the ejection speed is slightly slowed down as a whole. It does not affect actual printing.

[0175] On the other hand, since the driving voltage can be applied by increasing the voltage by about 0.7 V for a desired discharge speed, the discharge performance (eg, uniformity and / or influence of crosstalk) is not substantially affected.

[0176] Therefore, in Figure 2 or Figure 4 In the embodiment, since the driving voltage for ink ejection is as high as tens of V (volts) or higher and the self-sensing voltage is as small as 1 V or lower, the driving voltage of tens of volts or higher is applied as it is, and the forward diode 21 of the impedance adjustment unit 20 has almost no effect.

[0177] On the other hand, the driving voltage applied after the ink is ejected becomes 0V, but at this time, since the impedance between the driving unit 30 and the inkjet head unit 10 is relatively large, the small self-sensing voltage generated from the piezoelectric body PZT of the inkjet head unit 10 is measured as it is in the self-sensing circuit unit 40 without being affected by the driving unit 30.

[0178] In the above description, the diode of the impedance adjustment unit 20 uses a PN junction diode.

[0179] However, since the PN junction diode has low-frequency characteristics, when the emission frequency is increased, the emission characteristics may be changed.

[0180] In the case where the emission characteristics are affected due to such disadvantages, other types of diodes may be used.

[0181] In the following, we will Figures 7 to 10 An embodiment using a Schottky diode is described.

[0182] Figure 7 and Figure 8 is a diagram showing a structure of a portion of an inkjet printing system according to another embodiment.

[0183] The Schottky diode is a diode using a phenomenon in which a large number of electrons move through a potential barrier between a metal and a semiconductor, and can also be called a Schottky barrier diode.

[0184] Figure 7 An embodiment is one in which a forward Schottky diode 23 (hereinafter referred to as a "forward Schottky diode") is used instead of Figure 2 An embodiment of the forward diode 21 of the impedance adjustment unit 20 in the embodiment.

[0185] Figure 8 The embodiment uses a forward Schottky diode 23 instead of Figure 4 The forward diode 21 of the impedance adjustment unit 20 in the embodiment is replaced by a reverse Schottky diode 24 instead of the reverse diode 22.

[0186] Figure 7 and Figure 8 The embodiment has the Figure 2 and Figure 4 The embodiment of the present invention has similar characteristics to those of the embodiment of the present invention, but due to the use of the Schottky diode, it can have improved frequency characteristics and emission characteristics different from the embodiment using the PN junction diode.

[0187] In the following, we will Figure 9 Compare the characteristics of a Schottky diode with those of a PN junction diode.

[0188] Figure 9 is a graph showing the current and voltage characteristics of a Schottky diode.

[0189] exist Figure 9 In addition to Figure 3 In addition to the characteristics of the PN junction diode, the characteristics of the Schottky diode are also shown.

[0190] See also Figure 9 , in the IV curves of Schottky diode and PN diode, Schottky diode has lower forward voltage drop.

[0191] In the case of Schottky diodes, refer to Figure 9 , the forward voltage drop is 0.3V, and the reverse recovery time is reduced to 1 microsecond (μs) or shorter, so that the emission characteristics of the piezoelectric body PZT are not affected even when operating at high frequencies.

[0192] On the other hand, refer to Figure 9 It can be confirmed that the Schottky diode has a lower voltage level at which avalanche breakdown occurs compared to the PN junction diode, but the voltage level at which avalanche breakdown occurs is not used in the inkjet printing system.

[0193] Additionally, when using negative voltages, this problem can be overcome by connecting in parallel to use both directions of the diode.

[0194] In the following, we will Figure 10 Review of Schottky diodes in both directions Figure 8 Voltage characteristics of the embodiment.

[0195] Figure 10 It shows that according to Figure 8 FIGURE 1 is a diagram of characteristics of an embodiment of an inkjet printing system.

[0196] exist Figure 10 In (A), the measured voltage is the voltage Vin2 measured at the input terminal In of the inkjet head unit 10, and Figure 10 In (B), Figure 10 The voltage at B2 of (A) is amplified, and Figure 10 The voltage shown in (B) may correspond to a portion of the self-sensing voltage.

[0197] With Figure 5 Measured in the same way Figure 10 The voltage measured in .

[0198] When the Schottky diode is used, improved sensing characteristics can be obtained due to fast frequency characteristics and improved characteristics.

[0199] When measuring the actual measurement voltage as an example, improved results can be obtained, and Figure 10 The self-sensing voltage shown in (B) is 300mV peak-to-peak, with Figure 5 This is a larger self-sense voltage compared to the PN diode in the circuit.

[0200] However, since the voltage drop value is smaller than that of the PN junction diode when the Schottky diode is used and the voltage value of the driving voltage is almost the same, it can be confirmed that there is a slight difference in the operation of the piezoelectric body PZT.

[0201] Therefore, by using the Schottky diode, it is possible to form an inkjet printing system having improved characteristics such as improved frequency characteristics and reduced forward voltage drop.

[0202] The impedance adjustment unit 20 included in the inkjet printing system 1 may have more various configurations, and may be configured as follows: Figure 11 Review the structure of some of them.

[0203] Figure 11 is a diagram illustrating a structure of an impedance adjusting unit according to various embodiments.

[0204] Figure 11(A) to (F) show various embodiments of the impedance adjustment unit 20 , and unlike the above-mentioned impedance adjustment unit 20 , embodiments including PN junction diodes 21 and 22 , Schottky diodes 23 and 24 , and / or Zener diodes 25 and 26 are shown.

[0205] Figure 11 The impedance adjustment unit 20 of the embodiment (A) is composed of a Schottky diode 23 in the forward direction and a PN junction diode 22 in the reverse direction.

[0206] Figure 11 The impedance adjustment unit 20 of the embodiment (B) is composed of a Schottky diode 23 in the forward direction and a Zener diode 26 in the reverse direction.

[0207] Figure 11 The impedance adjustment unit 20 of the embodiment (C) is composed of a structure in which one forward PN junction diode 21 and two reverse PN junction diodes 22 are connected in parallel.

[0208] Figure 11 The impedance adjustment unit 20 of the embodiment (D) is composed of a structure in which one forward Schottky diode 23 and two reverse PN junction diodes 22 are connected in parallel.

[0209] Figure 11 The impedance adjustment unit 20 of the embodiment (E) is composed of a forward Zener diode 25 and a reverse Zener diode 26 .

[0210] Figure 11 The impedance adjustment unit 20 of the embodiment (F) is composed of a forward Zener diode 25 and a reverse PN junction diode 22 .

[0211] Here, the Zener diodes 25 and 26 are a type of “semiconductor” diode, and are also called constant voltage diodes.

[0212] The Zener diodes 25 and 26 have a PN junction structure similar to a PN junction diode, but have very low and constant breakdown voltage characteristics such that current can flow when a voltage of a certain value or more is applied in the reverse direction.

[0213] and Figure 11 Unlike the various embodiments of the impedance adjusting unit 20 shown in FIG, the impedance adjusting unit 20 of another embodiment may be configured by changing or combining the types of diodes, and the diodes may be additionally connected in parallel or in series.

[0214] In addition, according to an embodiment, the impedance adjusting unit 20 may have a structure in which a resistor or a capacitor is connected in series or in parallel in addition to the diode.

[0215] In the above Figures 2 to 11 In the present invention, various embodiments of the impedance adjustment unit 20 are mainly examined.

[0216] In the following, we will Figures 12 to 22 Various embodiments of the self-sensing circuit unit 40 are described.

[0217] Despite the following Figures 12 to 22 The impedance adjustment unit 20 is shown to include a pair of diodes, but it may include only one diode or Figure 11 Various diodes.

[0218] First, we will look at Figure 12 Example of .

[0219] Figure 12 is a diagram showing the structure of an inkjet printing system according to an embodiment.

[0220] exist Figure 12 In the embodiment, it is mainly shown that Figure 4 , and shows an embodiment in which the self-sensing circuit unit 40 uses voltages of two rows.

[0221] Here, the inkjet heads may have several rows.

[0222] Since there is a driver for each row, the sensing circuit can be configured for each row, but here, the circuit can be configured by pairing two rows.

[0223] The self-sensing circuit unit 40 extracts a final self-sensing voltage by removing a driving voltage component from the self-sensing voltage output from the inkjet head unit 10 through a differential amplifier, and determines whether the piezoelectric body PZT is operating normally.

[0224] Specifically, the self-sensing circuit unit 40 can be monitored quickly and accurately using the self-sensing method.

[0225] Specifically, the self-sensing circuit unit 40 can use a piezoelectric self-sensing method, and since piezoelectric self-sensing is monitored through electrical signals, for example, the inkjet head unit 10 having 1024 piezoelectric bodies PZT can determine a defective nozzle in a short time of several seconds or less.

[0226] This requires configuration of an algorithm and additional hardware for determining a defective nozzle by a method of acquiring data by scanning each nozzle.

[0227] In addition, a voltage lower than a driving voltage capable of ejecting ink droplets may be applied to the piezoelectric body PZT, thereby enabling monitoring without ejection.

[0228] Piezoelectric self-sensing means that the piezoelectric body PZT used as an actuator also functions as a sensor, and in an inkjet printing system, a driving voltage is applied to the piezoelectric body PZT using a piezoelectric actuator to eject ink.

[0229] After driving, a pressure wave of the ink is generated in the piezoelectric body PZT and discharged.

[0230] Even after discharge, these pressure waves exist for a certain period of time, which causes deformation of the piezoelectric body PZT and generates a voltage in the form of a vibration signal in the piezoelectric body PZT, which can be amplified and processed by the self-sensing circuit unit 40 to obtain data.

[0231] Since the measured pressure wave signal shows a waveform different from that of a normal state according to the discharge state of the nozzle, the discharge state can be monitored in real time.

[0232] The self sensing circuit unit 40 can amplify the self sensing voltage having a small voltage level while removing an unnecessary driving voltage component from the voltage output by the piezoelectric body PZT.

[0233] Also, because the self-sensing voltage has a large amount of information, it can detect not only defective nozzles but also the cause of the defect, which can be used for appropriate maintenance, etc.

[0234] In particular, various diagnoses and diagnostic results can be used in conjunction with artificial intelligence.

[0235] To achieve this, the signal sensitivity and signal-to-noise ratio must be good.

[0236] Therefore, according to an embodiment, the self sensing circuit unit 40 can process and use a self sensing voltage with a high signal-to-noise ratio by using an analog filter such as a low pass filter ("LPF") or a high pass filter ("HPF").

[0237] The self-sensing circuit unit 40 according to the present embodiment may include a differential amplifier 41 , a signal processing unit 42 , and a DAQ 43 (firmware for data acquisition and calculation; hereinafter, referred to as a “data determination unit”).

[0238] The differential amplifier 41 is a part that subtracts two input voltages based on two input voltages and then amplifies the subtracted value, and can play a role in amplifying a final self-sensing voltage having a low voltage level after removing unnecessary driving voltage components during self-sensing.

[0239] The signal processing unit 42 may be used to increase the signal-to-noise ratio by using a filter on the amplified final self-sensing voltage, and an analog filter may be used.

[0240] In addition, the signal processing unit 42 may change the final self-sensing voltage to match the voltage range through amplification or the like, so as to acquire data in the subsequent DAQ 43 .

[0241] The DAQ 43 may acquire data by using the final self-sensing voltage to determine a state such as whether the corresponding piezoelectric body PZT of the inkjet head unit 10 is operating normally.

[0242] In the future, such data will be used by firmware or software to determine the status of the nozzle.

[0243] Meanwhile, in the self-sensing circuit unit 40 , depending on the embodiment, the positions of the differential amplifier 41 and the signal processing unit 42 may be interchanged, and the signal processing unit 42 or the DAQ 43 may be omitted.

[0244] Since the differential amplifier 41 has the purpose of performing an operation of subtracting two inputs in order to minimize the influence of the driving voltage when extracting the final self-sensing voltage, two input voltages are required.

[0245] One of the two input voltages must include the self-sensing voltage, and the other must include only the driving voltage without the self-sensing voltage.

[0246] exist Figure 12 In FIG. 4 , the differential amplifier 41 of the self-sensing circuit unit 40 receives the self-sensing signal from the input terminals In of the two inkjet head units 10 included in two adjacent rows.

[0247] exist Figure 12 , in the inkjet head units 10 included in the first row (row 1), the switch included in only one nozzle 11 is closed, but in the inkjet head units 10 included in the second row (row 2), the switches included in all nozzles 11 have an open state.

[0248] As a result, the self-sensing circuit unit 40 monitors the piezoelectric bodies PZTs of the nozzles 11 having closed switches among the inkjet head units 10 in the first row (row 1), and the voltage received from the inkjet head units 10 in the second row (row 2) and input to the differential amplifier 41 is not the self-sensing voltage, but the voltage (that is, the reference voltage) output from the driving unit 30 and having passed through the impedance adjustment unit 20 in the second row (see FIG. Figure 13 The voltage in (A).

[0249] Figure 12 There is a structure in which two adjacent rows are bundled to share one self-sensing circuit unit 40 .

[0250] In this way, when one nozzle is turned on from one of the two driving units 30 and the difference between the two signals is obtained, the final self-sensing voltage can be extracted while reducing the influence of the driving voltage.

[0251] Through this, the number of self-sensing circuit units 40 included in the inkjet printing system can be reduced, thereby reducing manufacturing costs.

[0252] In the following, we will Figure 13 Detailed description in Figure 12 The steps for extracting the final self-sensing voltage in the inkjet printing system.

[0253] Figure 13 It shows Figure 12 FIG. 1 is a diagram of a voltage waveform in an embodiment of the present invention.

[0254] Figure 13 (A) shows a reference voltage (that is, a voltage output from the driving unit 30 and passing through the impedance adjusting unit 20), and Figure 13 (B) shows the measured self-sensing voltage. Figure 13 (C) shows the amplified self-sensing voltage, and Figure 13 (D) shows an amplified waveform of a final self-sensing voltage obtained by removing the driving voltage component as the output of the differential amplifier 41 .

[0255] exist Figure 12 In the differential amplifier 41, the first row (row 1) is applied as follows Figure 13 The self-sensing voltage shown in (B) of FIG. 1 is obtained, and the driving voltage output from the driving unit 30 is applied from the second row (row 2). The voltage through the impedance adjustment unit 20 (that is, as shown in FIG. 1 ) can be applied. Figure 13 The reference voltage is shown in (A).

[0256] Here, the nozzles have several rows, and each row is not limited to the description corresponding to a driving method of being driven independently or a method for a head having this structure.

[0257] Here, the reference voltage may correspond to a driving voltage component included in the self-sensing voltage.

[0258] That is, since the switches included in all nozzles 11 are turned on in the inkjet head unit 10 in the second row (row 2), the voltage input from the differential amplifier 41 from the second row (row 2) is not a self-sensing voltage, and the driving voltage output from the driving unit 30 can be a voltage that has passed through the impedance adjustment unit 20.

[0259] The differential amplifier 41 is Figure 13 Subtract the voltage of (B) Figure 13The voltage of (A) is amplified and output Figure 13 The voltage shown in (D).

[0260] because Figure 13 (C) is Figure 13 (B) is a direct amplification of the voltage, and if Figure 13 If the self-sensing voltage is directly amplified as in (C), the drive voltage component also increases, so it is impossible to obtain the desired image from the differential amplifier 41. Figure 13 The same output as (D).

[0261] Therefore, in Figure 12 In the embodiment of the self-sensing circuit unit 40, Figure 13 The voltage of (B) is directly input to the differential amplifier 41 to remove Figure 13 The reference voltage (that is, the driving voltage component) of (A) is amplified and generated as Figure 13 The output is shown in (D).

[0262] Yes Figure 13 The amplified final self-sensing voltage of the output voltage of the differential amplifier 41 shown in (D) is input to the signal processing unit 42 and changed to have a high signal-to-noise ratio through the analog filter, and after being changed to the voltage range used in the DAQ 43, it is input to the DAQ 43 and determined by computer calculation or firmware calculation whether the corresponding piezoelectric body PZT is operating normally.

[0263] like Figure 12 The inkjet printing system of the embodiment shown in FIG has an advantage of reducing the number of self-sensing circuit units 40, but because only one piezoelectric body PZT of two rows is monitored, there may be a disadvantage that the time taken for sequential monitoring increases with respect to all piezoelectric bodies PZT.

[0264] On the other hand, Figure 12 Unlike the embodiment, in one of two adjacent rows of the differential amplifier 41 of the self-sensing circuit unit 40, a self-sensing signal is received from the input terminal In of the inkjet head unit 10, and the other row may have a modified structure in which a driving voltage is applied from the output terminal Out of the driving unit 30.

[0265] Hereinafter, the Figure 14 Example of .

[0266] Figure 14 is a diagram showing the structure of an inkjet printing system according to another embodiment.

[0267] exist Figure 14In the embodiment, a reference voltage among two voltages forming a self-sensing circuit unit 40 in a row and input to a differential amplifier 41 of the self-sensing circuit unit 40 may be an example of a driving voltage at the output terminal Out of the driving unit 30 after passing through an additional impedance adjustment unit 70 (also referred to as a "second impedance adjustment unit").

[0268] Specifically, the self-sensing voltage input to the differential amplifier 41 is input from the input terminal In of the inkjet head unit 10, and the reference voltage is output from the output terminal Out of the driving unit 30. The driving voltage of the driving unit 30 is the voltage input to the differential amplifier 41 after passing through the additional impedance adjustment unit 70.

[0269] exist Figure 14 In the embodiment of FIG. 5 , the driving voltage of the driving unit 30 is input to the impedance adjusting unit 20 and the additional impedance adjusting unit 70 from the output terminal Out of the driving unit 30 .

[0270] exist Figure 14 In the embodiment of FIG. 5 , the additional impedance adjustment unit 70 may include an equivalent impedance adjustment unit 50 and an equivalent capacitor unit 60 .

[0271] Here, the equivalent impedance adjusting unit 50 may have a configuration corresponding to the impedance adjusting unit 20 and may have the same configuration as the impedance adjusting unit 20 depending on the embodiment, and Figure 14 In the embodiment of the present invention, the equivalent impedance adjustment unit 50 includes bidirectional PN junction diodes 51 and 52 (hereinafter referred to as “diodes”) like the impedance adjustment unit 20 .

[0272] The bidirectional PN junction diodes 21 and 22 included in the impedance adjustment unit 20 and the bidirectional PN junction diodes 51 and 52 included in the equivalent impedance adjustment unit 50 can each have the same voltage-current (VI) characteristic.

[0273] However, depending on the embodiment, the equivalent impedance adjusting unit 50 may include only one diode, and in this case, may include only the forward diode 51 .

[0274] Here, the forward diode 51 may have the same VI characteristic as the forward diode 21 of the impedance adjusting unit 20 .

[0275] Meanwhile, depending on the embodiment, the diodes included in the impedance adjusting unit 20 and the equivalent impedance adjusting unit 50 may include different types of diodes.

[0276] Meanwhile, the equivalent capacitor unit 60 may be located at the rear end of the equivalent impedance adjustment unit 50 .

[0277] The equivalent capacitor unit 60 may correspond to the nozzle 11 included in the inkjet head unit 10. The equivalent capacitor unit 60 may include a capacitor Ce having the same capacitance (electrostatic capacitance) as that of one piezoelectric body PZT included in the inkjet head unit 10.

[0278] like Figure 14 As shown in , since the differential amplifier 41 of the self-sensing circuit unit 40 cancels all electrical characteristics generated by driving the inkjet head unit 10 in the piezoelectric body PZT when the additional impedance adjusting unit 70 is used, the final self-sensing voltage can be effectively measured.

[0279] More specifically, since the piezoelectric body PZT of the inkjet head unit 10 has electrical characteristics very similar to a capacitor, charge accumulation due to applied voltage may occur as in a capacitor, and when the accumulated charge is discharged, an unnecessary voltage is measured.

[0280] In order to eliminate such transient voltage, the reference voltage of the additional impedance adjustment unit 70 including the equivalent capacitor unit 60 and the equivalent impedance adjustment unit 50 is input into the differential amplifier 41, and the differential amplifier 41 perfectly cancels the signal unrelated to the self-sensing voltage, so that the desired final self-sensing voltage can be obtained.

[0281] Because in Figure 14 In the embodiment shown in FIG, the additional impedance adjustment unit 70 is appropriately formed to eliminate common mode noise, voltage drop due to the diode, and signal difference according to the frequency characteristics of the diode, etc., to obtain a more improved final self-sensing voltage, so it is easy to extract the self-sensing voltage.

[0282] In the following, we will Figure 15 Detailed description in Figure 14 The steps for extracting the final self-sensing voltage in the inkjet printing system.

[0283] Figure 15 It shows Figure 14 FIG. 1 is a diagram of a voltage waveform in an embodiment of the present invention.

[0284] Figure 15 (A) shows a reference voltage (that is, a voltage output from the driving unit 30 and passed through the additional impedance adjustment unit 70), and Figure 15 (B) shows the measured self-sensing voltage. Figure 15 (C) shows an amplified waveform of a final self-sensing voltage obtained by removing the driving voltage component as the output of the differential amplifier 41 .

[0285] at the same time, Figure 15 (A) and Figure 15The voltage drop value Vd shown by the dotted line in (B) indicates a voltage drop value that occurs when the driving voltage output from the driving unit 30 passes through the impedance adjustment unit 20 and the equivalent impedance adjustment unit 50, and in the case of a PN junction diode, the voltage drop value Vd may be 0.7V.

[0286] when Figure 15 The voltage (A) and Figure 15 The voltage of (B) is input to the differential amplifier 41, and from Figure 15 Subtract the voltage of (B) Figure 15 When the voltage of (A) is amplified, the output waveform is the same as Figure 15 (C) The amplified final self-sensing voltage.

[0287] Figure 15 The amplified final self-sensing voltage of (C) is input to the signal processing unit 42 and changed to have a high signal-to-noise ratio through an analog filter, after which it is input to the DAQ 43 to obtain data, and by calculation using the data, it is determined whether the corresponding piezoelectric body PZT is operating normally.

[0288] Since the self-sensing circuit unit 40 is formed for each row and each driver scans in parallel (from the nozzles of each row) at the same time, Figure 12 The embodiments are different, Figure 14 The embodiment has the advantage of reducing the scanning time.

[0289] In addition, due to Figure 14 The embodiment includes the equivalent impedance adjusting unit 50 and the equivalent capacitor unit 60 by using the additional impedance adjusting unit 70, and thus can remove common phase noise, etc., so that the final self-sensing voltage can represent more accurate characteristics.

[0290] Meanwhile, depending on the embodiment, the structure of the additional impedance adjustment unit 70 may be different from Figure 14 structure, and will be passed Figure 16 review Figure 14 A modified embodiment of .

[0291] Figure 16 is a diagram showing the structure of an inkjet printing system according to another embodiment.

[0292] Figure 16 An embodiment is one in which the additional impedance adjustment unit 70 includes only the equivalent impedance adjustment unit 50 and does not include Figure 14 An embodiment of the equivalent capacitor unit 60 in the embodiment of .

[0293] exist Figure 16In the embodiment, since the additional impedance adjustment unit 70 includes the equivalent impedance adjustment unit 50, the reference voltage corresponding to the additional impedance adjustment unit 70 is transmitted to the differential amplifier 41, so that the final self-sensing voltage is equal to Figure 14 The embodiment is consistent with the embodiment of the present invention, and the self-sensing voltage can indicate the accurate characteristics.

[0294] However, in Figure 16 In the embodiment, since the additional impedance adjustment unit 70 does not include the equivalent capacitor unit 60 , it can be used while accepting noise caused by charges accumulated in the piezoelectric body PZT of the inkjet head unit 10 .

[0295] Hereinafter, the Figure 17 Example of .

[0296] Figure 17 is a diagram showing the structure of an inkjet printing system according to another embodiment.

[0297] and Figure 14 or Figure 16 The embodiments are different, Figure 17 The additional impedance adjusting unit 70 is not included, and the reference voltage among the two voltages input to the differential amplifier 41 of the self-sensing circuit unit 40 is directly input from the output terminal Out of the driving unit 30, and it is an embodiment that uses the driving voltage of the driving unit 30 as the reference voltage itself.

[0298] Figure 17 The embodiment has the advantage that the self-sensing circuit unit 40 is formed for each row and can be simply formed without additional configuration.

[0299] exist Figure 17 In the embodiment, since the self-sensing voltage among the two voltages input to the differential amplifier 41 is a voltage that has passed through the impedance adjusting unit 20, it is a voltage at which a voltage drop is generated by the impedance adjusting unit 20, but since the voltage used as the reference voltage is a driving voltage before passing through the impedance adjusting unit 20, it has a voltage value before the voltage drop occurs.

[0300] As a result, even if the two voltages are subtracted by the differential amplifier 41 , the drive voltage component may not be completely removed.

[0301] However, even in Figure 17 In the embodiment, it is also possible to confirm whether the piezoelectric body PZT is operating normally through the final self-sensing voltage.

[0302] and Figure 12 The embodiments are different because Figure 17The embodiment has the advantage that the self-sensing circuit unit 40 is formed in each row, so it takes less time to monitor all the piezoelectric bodies PZT at once, and it also has the advantage that it can be formed with a relatively simple structure.

[0303] In the following, we will Figure 18 Detailed description in Figure 17 The steps for extracting the final self-sensing voltage in the inkjet printing system.

[0304] Figure 18 It shows Figure 17 FIG. 1 is a diagram of a voltage waveform in an embodiment of the present invention.

[0305] Figure 18 (A) shows a reference voltage (that is, a driving voltage of the output terminal Out of the driving unit 30 ) and shows a voltage before passing through the impedance adjusting unit 20 , Figure 18 (B) represents the measured self-sensing voltage, Figure 18 (C) shows that by Figure 18 Subtract the voltage of (B) Figure 18 The voltage (A) is obtained by the voltage, and Figure 18 (D) shows the output of the differential amplifier 41. Figure 18 The voltage waveform obtained from (C) is shown as the final self-sensing voltage.

[0306] at the same time, Figure 18 (A) and Figure 18 The voltage drop value Vd shown by the dotted line in (B) is a voltage drop value generated when the driving voltage output from the driving unit 30 passes through the impedance adjustment unit 20. In a PN junction diode, the voltage drop value Vd may be 0.7V.

[0307] On the other hand, in an embodiment using a Schottky diode, the voltage drop value Vd may be lower, but may still have a non-negligible large voltage value compared to the voltage level of the self-sensing voltage, making the self-sensing signal easy to measure.

[0308] exist Figure 18 In the amplified final self-sensing voltage of (D), unlike the final self-sensing voltage of the previous embodiment, the driving voltage component is not completely removed, but the self-sensing component located at the rear still exists, making it possible to check the operating state of the corresponding piezoelectric body PZT.

[0309] At this time, among the results measured from DAQ 43, if the data from the front where some driving voltage exists is discarded (or not used), or the front of the data delayed by the trigger is not measured when acquiring the data, even if there is a certain degree of driving component, it may not significantly affect the actual sensing.

[0310] Therefore, the embodiments presented in this method are all possible methods for practical application.

[0311] Figure 18 The amplified final self-sensing voltage (D) is input to the signal processing unit 42 and changed to have a high signal-to-noise ratio through an analog filter, which is then input to the DAQ 43, and the self-sensing component is extracted from the final self-sensing voltage to determine whether the corresponding piezoelectric body PZT is operating normally.

[0312] In addition, Figure 17 In the embodiment, since monitoring of the piezoelectric body PZT for each row is possible, Figure 12 Compared with the embodiment, it takes relatively less time to monitor all piezoelectric bodies PZT at once.

[0313] However, referring to Figure 18 (D), since the driving voltage component can be maintained at a voltage value higher than the voltage value of the self-sensing component in the amplified final self-sensing voltage (which is the output of the differential amplifier 41), although the final self-sensing voltage is amplified, there may be a limit to increasing the amplification ratio.

[0314] exist Figures 12 to 18 In the embodiment of FIG. 5 , a PN junction diode is used as the diode in the impedance adjustment units 20 and 70 .

[0315] However, other types of diodes may be used depending on the embodiment.

[0316] will pass Figures 19 to 22 Some of these modified embodiments are reviewed.

[0317] Figures 19 to 22 is a diagram showing the structure of an inkjet printing system according to another embodiment.

[0318] Figures 19 to 22 They are Figure 12 、 Figure 14 、 Figure 16 and Figure 17 A modified embodiment of FIG5 is provided, and Schottky diodes 23, 24, 53, and 54 are used instead of the PN junction diodes 21, 22, 51, and 52. An example of use is shown.

[0319] Since the Schottky diode is used, the voltage drop value of the voltage across the impedance adjustment unit 20 can be lower than that of the embodiment of the PN junction diode, and can be used even at high frequencies.

[0320] However, the overall characteristics can have the same effects as the corresponding embodiments.

[0321] In the following, we will Figure 23 and Figure 24 The structure and voltage waveform of the inkjet printing system according to the comparative example that does not include the impedance adjusting unit 20 are reviewed for comparison with the above-described embodiment.

[0322] First, through Figure 23 Review the structure of the comparative example.

[0323] Figure 23 is a diagram showing the structure of an inkjet printing system according to a comparative example.

[0324] exist Figure 23 In the comparative example of , since the impedance adjustment unit 20 is not included, the output terminal Out of the driving unit 30 is the same as the input terminal of the inkjet head unit 10 .

[0325] Therefore, the self sensing circuit unit 40 receives the self sensing voltage from the output terminal Out of the driving unit 30 and may further include a reference voltage generator 46 that additionally provides a reference voltage.

[0326] Here, the reference voltage may be the same as the voltage waveform output from the driving unit 30 .

[0327] exist Figure 23 In the comparative example of , the final self-sensing voltage from which the driving component is removed can be generated by the differential amplifier 41 of the self-sensing circuit unit 40 .

[0328] In other words, the measurement is possible without impedance modifiers (diodes etc.).

[0329] However, since the piezoelectric body PZT is used as both an actuator and a sensor, it is good if it satisfies both the performance of the actuator and the sensor, but the two are in a trade-off relationship. Figure 23 In the comparative example of , there is a problem in which the performance of one side is improved and the performance of the other side is degraded.

[0330] Specifically, since a high voltage is required to drive the piezoelectric body PZT, the driving unit 30 capable of outputting a high voltage driving voltage having a voltage level of several tens of volts or more is required.

[0331] A driver with an amplifier is required.

[0332] exist Figure 23 In the comparative example, since such a high-voltage driving voltage is directly applied to the piezoelectric body PZT, the output impedance of the driving unit 30 must be small so that the driving voltage can be applied as it is without change (distortion, signal size change), so that the piezoelectric body PZT is operating normally.

[0333] At this time, the driving voltage may be slightly lowered.

[0334] On the other hand, if the output impedance of the driving unit 30 is small, the self-sensing voltage generated by the piezoelectric body PZT can also be transmitted to the driving unit 30 , so that the self-sensing voltage, which is a very low level voltage, is self-sensed and transmitted to the self-sensing circuit unit 40 .

[0335] As such, when the self-sensing voltage is very small, a large amount of amplification is performed in the self-sensing circuit unit 40 , but since amplification also increases noise, the signal-to-noise ratio of the self-sensing voltage deteriorates, resulting in poor detection.

[0336] On the other hand, if the output impedance of the driving unit 30 is high, the self-sensing voltage generated from the piezoelectric body PZT is not transmitted to the driving unit 30, but is well transmitted to the self-sensing circuit unit 40, so it can be well sensed, the driving voltage of the driving unit 30 is deformed and transmitted to the piezoelectric body PZT, and the piezoelectric body PZT may not operate normally.

[0337] As a result, Figure 23 In the comparative example shown in , it is difficult to accurately monitor the operation of the piezoelectric body PZT in the self-sensing method while normally driving the piezoelectric body PZT.

[0338] In addition, in the comparative example of the existing utility model, a resistor and a capacitor can be additionally formed at the driver output, so that the operation as a sensor and an actuator can be optimized simultaneously, but in this case, the discharge capacity and the sensor capacity of the piezoelectric body PZT are relatively reduced. The difference is that because the driving voltage of the piezoelectric body PZT is not reduced as in the proposed embodiment, self-sensing is not accurately performed without changing the discharge capacity.

[0339] will pass Figure 24 Check in more detail Figure 23 Characteristics of the comparative example.

[0340] Figure 24 It shows Figure 23 FIG. 1 is a diagram of a voltage waveform in a comparative example.

[0341] Will check Figure 24 The voltage waveform.

[0342] Figure 24 (A) shows a reference voltage generated by the reference voltage generator 46 , and the reference voltage may be the same as the driving voltage of the output terminal Out of the driving unit 30 .

[0343] Figure 24 (B) shows the measured self-sensing voltage, and Figure 24 (C) shows a waveform obtained by amplifying the voltage obtained by Figure 24Subtract the voltage of (B) Figure 24 The voltage (A) is obtained.

[0344] Ideally, it seems that the self-sensing voltage can be obtained, but in reality, without impedance adjustment, the actual self-sensing signal is almost invisible, or the entire self-sensing signal is forced to 0V by the driver's 0V, so it is difficult to obtain such a Figure 24 The self-sensing signal in .

[0345] like Figure 24 As shown in (C), the final self-sensing voltage of the component without driving voltage can be extracted, but as described above, when the piezoelectric body PZT is operated with a driving voltage and the self-sensing voltage is obtained from the piezoelectric body PZT, the impedance of the output terminal Out of the driving unit 30 has a trade-off relationship with opposite characteristics, making it difficult to satisfy the two characteristics and measure the voltage at a level similar to noise to monitor the actual nozzle state.

[0346] According to the above-described embodiment, even if self-sensing is performed by inserting the impedance modifier (bidirectional diode), a change in the amount of ink discharged from the nozzle is minimized and hardly occurs.

[0347] This is because although a slight voltage drop may occur due to the impedance adjusting unit 20 , a change in the magnitude of the voltage is not significant, and when the voltage is additionally increased and input, the emission performance is not affected.

[0348] Furthermore, since the voltage waveform is not distorted, the influence of the driving voltage is minimized.

[0349] In addition, due to the impedance adjusting unit 20 , the self-sensing voltage generated by the nozzle is transmitted to the self-sensing circuit unit 40 without affecting the driving voltage, so that the detection performance is improved and monitoring can be accurately performed.

[0350] The impedance adjusting unit and the self-sensing circuit unit described in the above embodiments may be formed in the driving unit or the inkjet head unit.

[0351] In an embodiment in which the impedance adjusting unit and the self-sensing circuit unit are formed in the driving unit, the driving unit itself may have a self-sensing function.

[0352] Meanwhile, in an embodiment in which the impedance adjusting unit and the self-sensing circuit unit are located within the inkjet head unit, the inkjet head unit may additionally include firmware capable of calculating the additional measured voltage.

[0353] Although the embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention defined in the claims are also included in the scope of the present invention.

Claims

1. An inkjet printing system, characterized in that: The inkjet printing system comprises: an inkjet head unit including nozzles for ejecting ink; a driving unit configured to generate and output a driving voltage for discharging the ink from the nozzle; a first impedance adjustment unit, provided between an input terminal of the inkjet head unit and an output terminal of the driving unit; and A self-sensing circuit unit is connected to the input terminal of the inkjet head unit to receive a self-sensing voltage from the nozzle and determine whether the nozzle is operating normally.

2. The inkjet printing system according to claim 1, wherein: The first impedance adjustment unit includes a pair of diodes, and The pair of diodes of the first impedance adjustment unit includes a forward diode and a reverse diode.

3. The inkjet printing system according to claim 1, wherein: The first impedance adjustment unit includes a forward diode, and The forward diode is one of a PN junction diode, a Schottky diode and a Zener diode.

4. The inkjet printing system according to claim 2, wherein: Each of the forward diode and the reverse diode is one of a PN junction diode, a Schottky diode, and a Zener diode.

5. The inkjet printing system according to claim 2 or claim 3, wherein: The driving unit is provided as a plurality of driving units, and the nozzle is provided as a plurality of nozzles, The inkjet head unit is connected to one of the plurality of driving units and includes the plurality of nozzles, and The inkjet head unit further includes a plurality of switches respectively connected to the plurality of nozzles.

6. The inkjet printing system according to claim 2, wherein: The self-sensing circuit unit includes a differential amplifier for receiving the self-sensing voltage from the input terminal of the inkjet head unit, and The differential amplifier further receives a reference voltage and generates a final self-sensing voltage by subtracting the reference voltage from the self-sensing voltage.

7. The inkjet printing system of claim 6, wherein: The reference voltage is input from the output terminal of the driving unit.

8. The inkjet printing system according to claim 7, wherein: The inkjet printing system further comprises: a second impedance adjustment unit connected to the output terminal of the driving unit and the input terminal of the differential amplifier, wherein: The reference voltage is input to the differential amplifier through the output terminal of the driving unit and the second impedance adjustment unit. The second impedance adjusting unit includes an equivalent impedance adjusting unit having a configuration corresponding to the pair of diodes of the first impedance adjusting unit, and The second impedance adjusting unit further includes an equivalent capacitor unit corresponding to the nozzle included in the inkjet head unit.

9. The inkjet printing system according to claim 6, wherein: The inkjet printing system further comprises: another inkjet head unit disposed adjacent to the inkjet head unit and comprising a plurality of nozzles and a plurality of switches respectively connected to the plurality of nozzles, wherein The reference voltage is input from an input terminal of the other inkjet head unit, and The reference voltage is transmitted in a state in which all of the plurality of switches included in the another inkjet head unit are turned on.

10. The inkjet printing system according to any one of claims 6 to 9, wherein: The self-sensing circuit unit further includes a signal processing unit using a filter to improve the signal-to-noise ratio, and The self-sensing circuit unit further includes a data determination unit configured to determine a state of the nozzle using the final self-sensing voltage.

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