System for monitoring piezo self-sensing nozzle

Abstract

A system for monitoring a piezo self-sensing nozzle, according to the present invention, comprises: an inkjet head unit including a plurality of nozzles and a piezo actuator for ejecting ink from the nozzles; a driver unit for generating a voltage applied to the piezo actuator, so that the ink is ejected from the nozzle; and a switch element provided between the driver unit and the piezo actuator or provided between the piezo actuator and a power amplifier of the driver unit, wherein the switch element is turned on so as to be capable of controlling that overall output impedance is decreased when the voltage is applied to the piezo actuator from the driver unit, and is turned off so as to be capable of controlling that overall output impedance is increased when the voltage application from the driver unit ends.

Description

Piezo Self-Sensing Nozzle Monitoring System

[0001] The present invention relates to a piezoelectric self-sensing nozzle monitoring system, and more specifically, to a piezoelectric self-sensing nozzle monitoring system capable of monitoring a nozzle regardless of the characteristics of an inkjet head driver.

[0002] To increase productivity in recent inkjet processes, multi-nozzle inkjet heads with over 1,000 nozzles are being used. By using multiple heads simultaneously, productivity in inkjet processes is being boosted. However, as the number of nozzles in these inkjet printing systems increases, nozzle maintenance becomes increasingly difficult.

[0003] Jetting stability is a critical factor in inkjet processes, affecting process yield and reliability. The accuracy, uniformity, and ejection of droplets are crucial factors. Therefore, monitoring for defective nozzles is crucial in inkjet printing systems utilizing multiple nozzles.

[0004] Conventional nozzle monitoring methods for inkjet printing systems involve visualizing droplets ejected from a small number of nozzles using a vision system, using a Drop Watcher to detect defective nozzles while directly ejecting droplets. This method is time-consuming because it requires sequential visualization of a small number of nozzles, and because it relies on direct ejection, it presents the problem of ink consumption. Furthermore, because inkjet nozzles constantly change condition over time, monitoring results often discrepancy with actual defects.

[0005] Another method involves printing directly onto the substrate using a full nozzle and analyzing the droplet impact point using a vision system. While this method allows for precise droplet impact analysis, it requires direct droplet ejection and is time-consuming.

[0006] A method to improve these issues is piezoelectric self-sensing. Because piezoelectric self-sensing monitors electrical signals, it can identify defective nozzles in inkjet heads with a large number of nozzles within a matter of seconds. Furthermore, by applying a voltage (waveform) lower than that required to eject droplets to the piezoelectric element, it can monitor the nozzles without ejecting them. Used in conjunction with this monitoring, it can be used to simultaneously detect nozzle status and initial drop defects.

[0007] Piezoelectric self-sensing utilizes a piezoelectric actuator as both an actuator and a sensor. In inkjet printing, a piezoelectric actuator is used to generate pressure waves within the inkjet head for ejection. These pressure waves persist for a period of time after ejection, causing deformation of the piezoelectric element, which can be measured in the form of a vibration signal.

[0008] Piezoelectric self-sensing in inkjet systems measures the operating status of a nozzle by sensing the charge generated by the residual pressure wave remaining in the nozzle after the droplet is ejected, which compresses the piezoelectric element. Because these pressure waves exhibit behaviors that differ from their normal state depending on the nozzle's ejection state, monitoring this abnormal behavior allows for real-time monitoring of the nozzle's ejection status.

[0009] Meanwhile, piezoelectric self-sensing uses both the actuator and the sensor simultaneously, so the performance of the actuator and the sensor are complementary. A driver, including a high-voltage amplifier, is required to drive the head. Since this high voltage (tens of V or more) is directly applied to the piezo, the driver's output must not affect the self-sensing signal for accurate measurement. Since the self-sensing signal typically exists within hundreds of microseconds, the signal must not be affected by the driver's operation immediately after the driver is turned on. Even if 0 V is applied, it is difficult to measure the self-sensing signal if the driver and piezo are directly connected. Because the 0 V power supply continues to be applied even after driving, any charge generated by self-sensing, even if it occurs as a voltage signal, is immediately dissipated by the 0 V of the driver. Therefore, complete isolation between the driver and the piezo after jetting is necessary. Switching elements can be used to achieve this isolation. Switch elements have the additional advantage of eliminating the influence of drift noise by timing control when applying self-sensing monitoring.

[0010] From a jetting perspective, a low driver output impedance ensures that the voltage is applied without any change in the output voltage (distortion or signal amplitude), enabling desired jetting. Conversely, from a sensing perspective, a high driver performance can actually make it difficult to measure the sensing signal.

[0011] Additionally, commercial inkjet drivers have an output impedance (R) that is optimized for optimal driving performance. out) value is set small, it is often difficult to measure the self-sensing signal. Therefore, when configuring the self-sensing detection circuit, an electrical element such as a shunt resistor, a bidirectional diode, a switch, or a capacitor may be added between the inkjet driver waveform generation unit and the piezoelectric element of the inkjet head unit to detect the electrical signal, thereby increasing the overall output impedance of the driver unit. These electrical elements can change the output impedance of the driver, thereby increasing the sensitivity of the self-sensing signal. However, in reality, there are problems such as a drop and distortion of the applied voltage, a change in the applied voltage depending on the number of nozzles being discharged, and low sensitivity or low signal-to-noise ratio of the detection signal due to the discharge of the self-sensing signal.

[0012] The biggest issue is that the current output from the driver section varies depending on the nozzle applied, which causes the output voltage to change due to the driver section's output impedance. Therefore, self-sensing is typically performed by minimizing the driver section's output impedance as much as possible. In this case, the sensing signal is very small, requiring significant amplification. However, excessive amplification also leads to a trade-off problem, as the signal-to-noise ratio deteriorates.

[0013] The present applicant has proposed the present invention to solve the above problems.

[0014] Related prior art includes Korean Patent No. 10-1152631 (Title of invention: Defective nozzle detection system using piezoelectric self-sensing, Registration date: May 29, 2012).

[0015] The present invention has been devised to solve the above problems, and the present invention provides a piezoelectric self-sensing nozzle monitoring system capable of satisfying the requirements by using a switch element to control the conflicting output impedances, in which the output impedance of the driver section required for ejection is low while the output impedance of the driver section required for self-sensing is high.

[0016] The present invention provides a piezo self-sensing nozzle monitoring system that can maximize sensing characteristics while maintaining jetting characteristics when a piezo is used simultaneously as a sensor and an actuator.

[0017] The present invention provides a piezoelectric self-sensing nozzle monitoring system that uses a switch element to completely block the connection between the driver unit and the inkjet head unit after the jetting waveform is applied.

[0018] The present invention provides a piezoelectric self-sensing nozzle monitoring system capable of minimizing the influence of self-sensing on a discharge waveform.

[0019] The present invention provides a piezoelectric self-sensing nozzle monitoring system that performs sensing smoothly without affecting jetting by adding a switch between a driver unit and an inkjet head unit and synchronizing a gate signal with a jetting signal.

[0020] The present invention provides a piezoelectric self-sensing nozzle monitoring system that controls very high impedance by turning on a switch when a voltage for discharge is applied from a driver unit using various switch elements and turning off the switch when the voltage application is finished.

[0021] The problems to be solved by the present invention are not limited to the problem(s) mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0022] A piezoelectric self-sensing nozzle monitoring system according to the present invention for achieving the above-described task includes: an inkjet head including a plurality of nozzles and a piezoelectric actuator for ejecting ink from the nozzles; a driver unit for generating a voltage applied to the piezoelectric actuator so that ink is ejected from the nozzles; and a switch element provided between the driver unit and the piezoelectric actuator or between a power amplifier of the driver unit and the piezoelectric actuator; wherein the switch element is controlled to be in an on state when voltage is applied from the driver unit to the piezoelectric actuator so as to lower the overall output impedance, and is controlled to be in an off state when voltage application from the driver unit is terminated so as to increase the overall output impedance.

[0023] An electrical signal can be detected from the piezo actuator when the overall output impedance is controlled to be high by the switch element.

[0024] The above switch element can switch on and off states in a discharge mode in which ink is discharged from the nozzle and a sensing mode in which an electrical signal is detected from the piezo actuator.

[0025] In the case of the above sensing mode, the on-off signal of the switch element may have the same frequency as the waveform of the voltage applied from the driver unit to the inkjet head unit.

[0026] The above switch element can be turned on for a predetermined period of time after the waveform of the voltage applied to the piezo actuator drops to 0 V, and then turned off.

[0027] It includes a self-sensing circuit unit connected to a line connecting the switch element and the inkjet head unit, and in the case of the sensing mode, when an off signal is applied to the switch element at a time when voltage application from the driver unit is terminated, a self-sensing signal can be detected by measuring the voltage applied to the self-sensing circuit unit.

[0028] The above switch element and the self-sensing circuit unit may be provided in a form integrated into either the driver unit or the inkjet head unit, or may be provided in a form integrated into a self-sensing module unit provided between the driver unit and the inkjet head unit.

[0029] In the case of the above discharge mode, the driver unit generates a voltage waveform necessary to discharge ink from the nozzle, and the switch element is switched to an on state, and in the case of the above sensing mode, the inkjet head unit generates a voltage waveform necessary to detect an electrical signal from the piezo actuator, and the switch element can control on-off according to the timing at which voltage is applied to the piezo actuator.

[0030] In order to lower the overall output impedance when the above switch elements are in the on state, a plurality of the above switch elements can be connected in parallel.

[0031] In order to block current flowing in both directions of the above switch elements, a plurality of the above switch elements may be connected in series, but may be connected in opposite directions.

[0032] The above self-sensing circuit unit can collect the self-sensing signal by removing the reference voltage to process the self-sensing signal, remove the reference voltage using a reference column, or remove the reference voltage using the voltage at the input terminal of the switch element.

[0033] Specific details of other embodiments are included in the detailed description and accompanying drawings.

[0034] The piezoelectric self-sensing nozzle monitoring system according to the present invention can perform smooth self-sensing without affecting jetting by adding a switching element between the driver unit and the inkjet head unit to synchronize the gate signal and the jetting signal.

[0035] The piezoelectric self-sensing nozzle monitoring system according to the present invention can maximize the sensing signal by greatly increasing the electrical impedance of the driver unit and the inkjet head unit (i.e., the piezoelectric actuator) when measuring the self-sensing signal through the switch element.

[0036] The piezoelectric self-sensing nozzle monitoring system according to the present invention can prevent waveform distortion caused by adding impedance between the driver unit and the inkjet head unit (piezoelectric actuator) when driving the inkjet head unit (i.e., when applying a discharge signal).

[0037] The piezoelectric self-sensing nozzle monitoring system according to the present invention can effectively control drift noise (noise) when measuring a self-sensing signal by controlling the timing of a switch element through a gate signal, and can minimize the influence on the driving voltage.

[0038] The piezoelectric self-sensing nozzle monitoring system according to the present invention has little effect on the discharge signal when turned on compared to cases where passive elements (resistors, capacitors, or diodes) and active elements (class B amplifiers) capable of additionally changing impedance are used.

[0039] The piezoelectric self-sensing nozzle monitoring system according to the present invention can obtain a desired signal because it arbitrarily controls the timing of switching using a switch element, and by turning off the switch element after a certain period of time after the driving voltage is applied, only a signal related to self-sensing can be obtained, so that the quality of the signal can be improved.

[0040] The piezoelectric self-sensing nozzle monitoring system according to the present invention can effectively discharge the charge accumulated in the piezoelectric actuator, including the voltage when the drive becomes 0 V, and obtain only the subsequent self-sensing signal, and can increase the collection speed of the self-sensing signal.

[0041] The piezoelectric self-sensing nozzle monitoring system according to the present invention can solve the problem of waveform distortion and low signal-to-noise ratio because it can change the overall output impedance according to timing.

[0042] FIG. 1A and FIG. 1B are drawings for explaining the configuration of a piezoelectric self-sensing nozzle monitoring system and the control timing of a switch element according to the first embodiment of the present invention.

[0043] FIG. 2 is a diagram for explaining a process of collecting a self-sensing signal in the system illustrated in FIG. 1a.

[0044] FIGS. 3A to 3C are drawings showing the configuration of a piezoelectric self-sensing nozzle monitoring system according to a second embodiment of the present invention and a modified example thereof.

[0045] FIGS. 4A to 9B are drawings for explaining a switch element used in a system according to the first embodiment of the present invention.

[0046] FIGS. 10A to 10C are graphs for explaining the characteristics of the switch elements of the system illustrated in FIGS. 4A to 9B.

[0047] FIG. 11a and FIG. 11b are drawings showing the configuration of a piezoelectric self-sensing nozzle monitoring system according to a third embodiment of the present invention and a modified example thereof.

[0048] FIG. 12 is a drawing for explaining a process of collecting a self-sensing signal in a piezoelectric self-sensing nozzle monitoring system according to a fourth embodiment of the present invention.

[0049] FIG. 13 is a drawing for explaining a process of collecting a self-sensing signal in a piezoelectric self-sensing nozzle monitoring system according to a fifth embodiment of the present invention.

[0050] Hereinafter, embodiments disclosed in this specification will be described in detail with reference to the attached drawings. Identical or similar components will be given identical or similar drawing reference numerals, and redundant descriptions thereof will be omitted. The suffix "part" used for components in the following description is given or used interchangeably only for the convenience of writing the specification, and does not in itself have a distinct meaning or role. In addition, when describing the embodiments disclosed in this specification, if it is determined that a specific description of a related known technology may obscure the gist of the embodiments disclosed in this specification, a detailed description thereof will be omitted. In addition, the attached drawings are only intended to facilitate easy understanding of the embodiments disclosed in this specification, and the technical ideas disclosed in this specification are not limited by the attached drawings, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and technical scope of the present invention.

[0051] Terms that include ordinal numbers, such as first, second, etc., may be used to describe various components, but the components are not limited by these terms. These terms are used solely to distinguish one component from another.

[0052] When it is said that a component is "connected" to another component, it should be understood that it may be directly connected to that other component, but there may also be other components in between.

[0053] Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0054] In this application, terms such as “include” or “have” are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but should be understood not to exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0055] Please note that the drawings are schematic and not drawn to scale. The relative dimensions and proportions of parts in the drawings may be exaggerated or reduced for clarity and convenience, and any dimensions are for illustrative purposes only and are not limiting. In addition, identical structures, elements, or components appearing in more than one drawing are designated by the same reference numerals to indicate similar features.

[0056] The embodiments of the present invention specifically illustrate ideal embodiments of the present invention. Consequently, various modifications to the drawings are anticipated. Therefore, the embodiments are not limited to the specific form of the illustrated area, and include, for example, modifications resulting from manufacturing processes.

[0057] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

[0058] FIG. 1A and FIG. 1B are diagrams for explaining the configuration of a piezoelectric self-sensing nozzle monitoring system according to a first embodiment of the present invention and the control timing of a switch element, FIG. 2 is a diagram for explaining a process of collecting a self-sensing signal in the system illustrated in FIG. 1A, FIGS. 3A to 3C are diagrams for explaining the configuration of a piezoelectric self-sensing nozzle monitoring system according to a second embodiment of the present invention and a modified example thereof, FIGS. 4A to 9B are diagrams for explaining a switch element used in the system according to the first embodiment of the present invention, FIGS. 10A to 10C are graphs for explaining the characteristics of the switch element of the system illustrated in FIGS. 4A to 9B, FIGS. 11A and 11B are diagrams for explaining the configuration of a piezoelectric self-sensing nozzle monitoring system according to a third embodiment of the present invention and a modified example thereof, FIG. 12 is a diagram for explaining a process of collecting a self-sensing signal in a piezoelectric self-sensing nozzle monitoring system according to a fourth embodiment of the present invention, and FIG. 13 is a diagram for explaining a process of collecting a self-sensing signal in a piezoelectric self-sensing nozzle monitoring system according to a fifth embodiment of the present invention. This is a drawing to explain the collection process.

[0059] The piezoelectric self-sensing nozzle monitoring system (100 to 500, hereinafter referred to as the “system”) according to the present invention described below can satisfy these conflicting requirements by using a switch element to control the conflicting output impedances of the driver unit (110) required for ejecting ink from the nozzle (jetting) being low and the driver unit (110) required for self-sensing being very high.

[0060] An ideal switch can operate by either conducting a digital signal (TTL; Transistor-Transistor Logic) or by breaking two signals, or by changing impedance. The requirements for such a switch are that the time required for turning on and off must be very short, less than a few μs, and that the impedance (resistance) effect must be very small in the on state and very high in the off state, so that the connected parts can be accurately separated.

[0061] The system (100-500) according to the present invention can control very high impedance by, more specifically, using various switch elements to turn on the switch when voltage for discharge is applied from the driver unit (110) and turn off the switch when voltage application is finished, through a time-dependent impedance control method. That is, an on-off method that takes into account the discharge signal and the drive waveform voltage of the piezo actuator (180) can be implemented, and the impedance can be minimized during driving.

[0062] The switch element of the system (100-500) according to the present invention is used only in the sensing mode for self-sensing when switching in synchronization with the discharge waveform. In the discharge mode (printing mode) for discharging ink, the switch may be turned on at all times. However, even in the discharge mode, this switching may be synchronized with the discharge.

[0063] In this way, the switch element (170) can be switched on and off in a discharge mode in which ink is discharged from the nozzle and a sensing mode in which an electrical signal is detected from the piezo actuator (180).

[0064] Hereinafter, a system (100 to 500) according to the present invention will be described with reference to the drawings.

[0065] Referring to FIGS. 1A, 1B, and 2, a piezoelectric self-sensing nozzle monitoring system (100) according to a first embodiment of the present invention may include an inkjet head (160) including a plurality of nozzles (not shown) and a piezoelectric actuator (180) that ejects ink from the nozzles; a driver unit (110) that generates a voltage applied to the piezoelectric actuator (180) so that ink is ejected from the nozzles; and a switch element (170) provided between the driver unit (110) and the piezoelectric actuator (180) of the inkjet head (160).

[0066] Here, the switch element (170) can be controlled to be turned on when voltage is applied from the driver unit (110) to the piezo actuator (180) so that the overall output impedance is lowered, and to be turned off when voltage application from the driver unit (110) is terminated so that the overall output impedance is higher.

[0067] Referring to FIG. 1A, a system (100) according to the first embodiment of the present invention may include a driver unit (110), an inkjet head unit (160), a switch element (170) that is controlled to be on-off to apply or not apply a voltage applied from the driver unit (110) to the inkjet head unit (160), and a switch driving unit (190) that switches the switch element (170).

[0068] Additionally, the system (100) may include a self-sensing circuit (140) connected to a line (wire) connecting the switch element (170) and the inkjet head (160).

[0069] The driver unit (110) can input a jetting trigger signal to the switch driver unit (190) through a line connected to the switch driver unit (190). In addition, the driver unit (110) can apply a piezo drive voltage to the switch element (170) through a line connected to the switch element (170). When the switch element (170) is in an on state, the piezo drive voltage received from the driver unit (110) can be applied to the piezo actuator (180) of the inkjet head unit (160) through the switch element (170).

[0070] The switch driving unit (190) can apply a switch driving voltage (ON-Off control) to the switch element (170) through a line connected to the switch element (170).

[0071] The switch element (170) performs the function of connecting and disconnecting the driving waveform (Driving waveform (1)) applied from the driver unit (110) to the piezo actuator (180) of the inkjet head unit (160) in accordance with the switch timing signal between the driver unit (110) and the inkjet head unit (160) to control impedance over time.

[0072] The switch element (170) is a switch different from the nozzle switch (169) connected to the piezo actuator (180) to control the on-off of the nozzle (not shown) in the inkjet head (160) illustrated in FIG. 2.

[0073] When the switch element (170) is in the on state, the driver unit (110) and the piezo actuator (180) of the inkjet head unit (160) are connected to provide a low overall output impedance (R out +R on ) can be applied to the driving waveform to the piezo actuator (180). At this time, when the switch element (170) is in the on state, the resistance (R on ) should be less than mΩ and should not affect discharge.

[0074] When the switch element (170) is in the off state, the connection between the driver unit (110) and the piezo actuator (180) is cut off, so the overall output impedance (R out +R off ) becomes very high, and at this time, the self-sensing voltage can be measured. At this time, when the switch element (170) is in the off state, the resistance (R off ) is higher, the higher the self-sensing sensitivity.

[0075] The switch element (170) should be turned on during the waveform period (see Waveform period (1) of Fig. 1b) in which the driving waveform applied for discharge is applied, so that the overall output impedance (R) is low. out +R on ) can drive the piezo actuator (180) without waveform distortion. In the section after the waveform section (1), the switch element (170) is turned off to collect the self-sensing signal, thereby achieving a high overall output impedance (R out +R off ) must be maintained.

[0076] This on-off timing is controlled by a switch timing signal (see Switch timing 1 and Switch timing 2 in Fig. 1b). The switch timing signal is a TTL signal indicating the timing for turning the switch element (170) on and off, and the switch element (170) is turned on when in the High state and turned off when in the Low state.

[0077] The switch driver (190) may have the role of generating a switch timing signal and generating a voltage required for turning on and off the switch element (170) using the switch timing signal. In the case of the switch element (170), there may be cases where the switch timing signal can be directly input, but in the case of most switch elements, a voltage of 5 V or higher is required, or the voltage for on-off control may vary depending on the voltage at the input terminal of the switch element, and in some cases, a high current may be required.

[0078] The switch driving unit (190) synchronizes the switch timing signal using the jetting trigger output from the driver unit (110) to control on-off at precise timing. The jetting trigger is a signal that signals the start of jetting as a synchronization signal (synchronization signal, TTL) of the driving waveform. Depending on the driver unit (110), the jetting trigger may be in a Normal Low state or a Normal High state.

[0079] There are two main ways for the switch driver (190) to generate a switch timing signal. The first is to maintain a Normal High state (maintain a High state when not in operation) as in Switch timing 1 of Fig. 1b, receive the rising edge of the jetting trigger as a jetting signal, and keep the switch timing in a Low state after a time corresponding to the sum of the waveform section (1) and the jetting margin (see Trigger margin (6) of Fig. 1b) to cut off the switch element (170). The section (4) for maintaining the Low state can be set by considering the section for collecting the self-sensing signal, and the High state is maintained again in the subsequent section. Since the time measured by self-sensing is within 0.05 to 0.1 ms (50 to 100 μs), anything after that time is sufficient.

[0080] In the first case, there is an advantage that the switch element (170) is turned on in advance when the driving waveform is applied because the switch timing signal always remains in a high state.

[0081] The second is a method of maintaining a Normal Low state (maintaining a normal Low state when not in operation) as in Switch timing 2 of Fig. 1b, receiving the rising edge of the discharge trigger as a discharge signal, and maintaining High for a period corresponding to the sum of the immediate waveform section (1) and the discharge margin (6) section. Since it is a Normal Low state thereafter, the switch timing is maintained in a Low state so that a self-sensing signal can be collected.

[0082] In the second case, there is a disadvantage that the switch element (170) is turned on simultaneously when the driving waveform is applied because the switch timing signal always remains in the Low state. Since the response speed of the switch element (170) is not infinite, a portion of the driving waveform may be blocked in the initial section due to the switching delay.

[0083] In addition, it is also possible to increase the impedance by turning off the switch element (170) to collect the self-sensing signal.

[0084] The reason for providing a discharge margin (6) in the first and second cases described above is to wait until the driving waveform returns to the idle voltage and to eliminate the charge generated during the driving of the piezo actuator (180). Since the piezo actuator has electrical characteristics similar to a capacitor, it can be charged. The discharge margin (6) can be added or set to zero as needed.

[0085] In this way, the switch element (170) of the system (100) according to the first embodiment of the present invention can eliminate drift noise by discharging the charge charged in the piezo actuator (180) by maintaining an on (High) state for a predetermined time (discharge margin) after the waveform of the voltage applied to the piezo actuator (180) drops to 0 V and then turning into an off (Low) state.

[0086] In Fig. 1b, the self-sensing signal is an unprocessed self-sensing signal (7) input to the self-sensing circuit (140).

[0087] The system (100) according to the first embodiment of the present invention can detect a self-sensing signal through on-off control of a switch element (170) as shown in Fig. 1b. Since the system (100) according to the first embodiment of the present invention can change the overall output impedance in accordance with timing by using the switch element (170), waveform distortion does not occur and a low signal-to-noise ratio can be prevented.

[0088] Referring to FIG. 2, a process of collecting a self-sensing signal in a system (100) according to the first embodiment of the present invention is described.

[0089] Raw data (11, 12) of the self-sensing signal collected in the self-sensing circuit (140) are input to the self-sensing circuit (140) together with the driving waveform (11) and the self-sensing waveform (12) for driving the piezo actuator (180). The maximum voltage of the self-sensing waveform (12) is a low voltage signal of 1 V or less, and needs to be amplified to increase the sensitivity of the signal. At this time, if the voltage of the driving waveform (11) input together to the self-sensing circuit (140) is several tens of V or more and is amplified together with the self-sensing waveform (12), the driving waveform may be greatly amplified as in (13), which may cause a problem in that the circuit saturates.

[0090] FIGS. 3A to 3C illustrate the configuration of a system (200) and its variants (200-2, 200-3) according to the second embodiment of the present invention.

[0091] The system (200) according to the second embodiment of the present invention illustrated in FIG. 3A may be provided in a form in which a power amplifier (116), a switch element (170), and a self-sensing circuit unit (140) are integrated into the driver unit (110). In the case of the system (200) illustrated in FIG. 3A, the switch element (170) may be provided between the power amplifier (116) of the driver unit (110) and the piezo actuator (180) of the inkjet head unit (160).

[0092] A modified example (200-2) of the system (200) according to the second embodiment of the present invention illustrated in FIG. 3b may be provided in a form in which the switch element (170) and the self-sensing circuit unit (140) are integrated into the self-sensing module unit (120) provided between the driver unit (110) and the inkjet head unit (160).

[0093] Another modified example (200-3) of the system (200) according to the second embodiment of the present invention illustrated in FIG. 3c may be provided in a form in which the switch element (170), self-sensing circuit unit (140), and nozzle unit (130) are integrated into the inkjet head unit (160).

[0094] As illustrated in FIGS. 3a to 3c, the switch element (170) and self-sensing circuit unit (140) of the system (200, 200-2, 200-3) according to the second embodiment of the present invention may be provided in a form integrated into either the driver unit (110) or the inkjet head unit (160), or may be provided in a form integrated into the self-sensing module unit (120) provided between the driver unit (110) and the inkjet head unit (160).

[0095] Meanwhile, the system (100 to 500) according to the present invention can operate in the sensing mode illustrated in FIG. 4a and the jetting mode illustrated in FIG. 4b.

[0096] Referring to FIG. 4a, in the sensing mode, the nozzle is turned on during sensing for self-sensing that detects an electrical signal from the piezo actuator (180), and the on-off of the switch element (170) is controlled according to the switch timing to increase the overall output impedance in the self-sensing section.

[0097] An electrical signal can be detected from the piezo actuator (180) when the overall output impedance is controlled to be high by the switch element (170).

[0098] Referring to Fig. 4b, the discharge mode is a mode used in printing rather than self-sensing, in which the switch element (170) is always turned on and connected, and output impedance is not controlled. In the case of Fig. 4b, since the switch timings 1 and 2 are always in a high state, the switch element (170) is always turned on and connected.

[0099] In the system (100 to 500) according to the present invention, in the case of the discharge mode, the driver unit (110) generates a voltage waveform necessary to discharge ink from the nozzle and the switch element (170) is switched to the on state, and in the case of the sensing mode, the inkjet head unit (160) generates a voltage waveform necessary to detect an electrical signal from the piezo actuator (180) and the switch element (170) can be controlled to turn on and off according to the timing at which voltage is applied to the piezo actuator (180).

[0100] The system (100-500) according to the present invention can perform self-sensing or printing (i.e., ejecting ink from a nozzle) by selecting either a sensing mode or a discharging mode. Furthermore, a different driving waveform may be used for each mode, and in sensing mode, a waveform that only vibrates the meniscus of ink without discharging may be used.

[0101] The system (100-500) according to the present invention can quickly control the impedance by using the switch element (170) in sync with the applied voltage of the driver unit (110). To this end, the system (100-500) according to the present invention can control the impedance by using various elements (circuits) as the switch element (170). This switch element (170) is an element or circuit that receives a digital signal from the outside, turns on when the waveform is applied, and turns off when the application ends.

[0102] In the case of the sensing mode, the system (100 to 500) according to the present invention can detect a self-sensing signal by measuring the voltage applied to the self-sensing circuit (140) when an off signal is applied to the switch element (170) at the point when the voltage application from the driver unit (110) is terminated.

[0103] In the case of the sensing mode of the system (100 to 500) according to the present invention, the on-off signal of the switch element (170) can have the same frequency as the waveform of the voltage applied from the driver unit (110) to the inkjet head unit (160).

[0104] The switch element (170) of the system (100 to 500) according to the present invention must have a resistance as small as mΩ because if the resistance is large in the on state, problems such as waveform distortion may occur, and the resistance in the off state must be very large so as to minimize the self-sensing current flowing out in the direction of the driver unit (110).

[0105] In addition, since the ink discharge frequency from the inkjet head (160) is high, ranging from several kHz to several tens of kHz, the switching speed of the switch element (170) must be very fast. If the time required for switching is long, it is difficult to properly control the impedance, so a switching speed of 1 μs or less is required.

[0106] Since the voltage required to drive the piezo actuator (180) varies depending on the specifications of the head, it may be around 1 A when all nozzles in the corresponding nozzle row (e.g., 128 to 256 nozzles) are turned on, so it is desirable to select the switch element (170) taking into consideration the specifications of the head.

[0107] When controlling the output impedance for self-sensing in sensing mode, the switch element (170) must be a bidirectional switch capable of blocking current in both directions. If the switch element blocks current in only one direction, self-sensing may be impossible or distortion may occur in the self-sensing signal.

[0108] In addition, it is necessary to select a switch element that can maximize self-sensing sensitivity without affecting the operation of the inkjet head by considering various factors such as switching noise.

[0109] Any element (circuit) that controls impedance over time can be used as the switch element (170) of the system (100 to 500) according to the present invention.

[0110] FIGS. 5A to 10C illustrate a system (100) according to a first embodiment in which various elements (circuits) are used as switch elements.

[0111] FIG. 5a illustrates a system (100) using a MOSFET (Matel-oxide semiconductor field-effect transistor) as a switch element (171).

[0112] MOSFETs can be used at high voltages and high currents and have very fast switching speeds. They also have very low R and high power output. on Since it can be switched with a resistance of tens of mΩ or less in the on state, waveform distortion caused by the RC circuit can be minimized.

[0113] The switch element (171) illustrated in Fig. 5a is a case where an N-channel MOSFET is used and a body diode exists, but a MOSFET without a body diode may also be used. Additionally, a P-channel MOSFET may also be used as the switch element (171).

[0114] An N-channel MOSFET can be used as a switch because it can allow or block current to flow between the drain (D) and source (S) depending on the voltage applied between the gate (G) and the body diode (B).

[0115] The voltage supplied to the piezo actuator (180) is a trapezoidal waveform that rises and falls, as shown in the driving waveform in Fig. 1b, and the driven load is a capacitor. When driving the capacitor, in the rising section of the waveform, current flows from the driver unit (110) toward the piezo actuator (180), and in the falling section, since the charge stored in the capacitor must be removed, current flows from the piezo actuator (180) toward the driver unit (110). In other words, the element used as a switch must be able to block currents flowing in both directions in order to control impedance.

[0116] The MOSFET (171) illustrated in Fig. 5a does not have a perfectly symmetrical structure because the source (S) and the body diode (B) are internally connected. The MOSFET (171) of Fig. 5a has a drain (D) connected as an input to the driver unit (110) and a source (S) connected as an output to the piezo actuator (180) of the inkjet head unit (160). When a voltage of 0 V or less is applied between the gate (G) and the body diode (B) to turn off the switch, no current flows from the drain (D) to the source (S), but current can flow from the source (S) to the drain (D) by the body diode (B). Self-sensing is possible even in this case. This is because the voltage measured through self-sensing is very small, 0.7 V or less, which is smaller than the threshold value of the body diode (B) (generally 0.7 V or less), and therefore, the possibility of a large current leakage is low.

[0117] Although not shown, in the case of FIG. 5a, when the drain (D) and source (S) of the MOSFET are connected in the opposite direction, the direction of the body diode (B) is reversed, but self-sensing is possible in the same manner as above.

[0118] Additionally, when the source (S) and the body diode (B) are not internally connected, the body diode (B) is not connected between the drain (D) and the source (S), resulting in a perfectly symmetrical structure. In this case, since the current is blocked in both directions, the self-sensing current can be completely blocked from flowing out toward the driver unit (110).

[0119] Figure 10a shows the V of the N-channel MOSFET GS This is a graph of the current between the drain and the source according to the voltage applied to the gate (V GS ) is the threshold (V th ) the current flowing to the drain (I D ) can flow. The voltage applied to the gate (VGS ) is the threshold (V th ) below, the current flowing to the drain (D) is close to 0A. That is, V GS Go V th In larger cases, it will have lower impedance and V GS Go V th In smaller cases, it has high impedance.

[0120] Figure 5b is a drawing for explaining the timing for controlling a switch element (171) provided as a MOSFET. The on-off of the switch element (171) provided as a MOSFET is controlled by the voltage (V) applied to the gate (G). GS ) is controlled by the switch driving unit (190). The switch timing signal (Switch timing 1) generated in the switch driving unit (190) is a TTL signal and the signal size is V. ST (5V) and cannot generate enough current to drive the gate (G) of the MOSFET. That is, the switch driver (190) controls the threshold (V) through the switch timing signal as well as the switch timing. th ) or more voltage (V) GS ) and generates sufficient current to drive the gate.

[0121] In the case of the system (100) illustrated in FIG. 6a, the switch element (173) may be provided in a form in which the sources (S) of two MOSFETs (171, 172) are connected to each other and the body diodes (B) are connected in opposite directions to reduce the effect of the body diode (B). In addition, the switch element (174) of the system (100) illustrated in FIG. 6b may be provided in a form in which the drains (D) of two MOSFETs (171, 172) are connected to each other and the body diodes (B) are connected in opposite directions.

[0122] The system (100) illustrated in FIGS. 6a and 6b can detect a high self-sensing waveform by eliminating the influence of the Body diode (B) at the input and output of the impedance converter.

[0123] In this way, in order to block the current flowing in both directions of the switch elements (173, 174), a plurality of switch elements (173, 174) (171, 172) can be connected in series, but in opposite directions.

[0124] Figure 7a illustrates a system (100) using an analog switch as a switching element (175). An analog switch, also known as a transmission gate, is a device that functions to block or connect analog signals. Furthermore, the analog switch is a switch manufactured using an N-channel MOSFET, and can be viewed as an extension of an embodiment using a MOSFET as a switch.

[0125] The analog switch (175) is suitable as a device for self-sensing because it can block bidirectional current, but since it is a device (circuit) for the purpose of turning an analog signal on and off, when used for self-sensing, the voltage range and the resistance (R) in the on state on ) It is desirable to manufacture and select it by considering values, current limits, etc.

[0126] The analog switch (175) illustrated in Fig. 7a can control the on-off of the switch by controlling the voltage of the control terminal. The control terminal may be controlled by a TTL signal, so that a switch timing signal may be input directly. Alternatively, as illustrated in Fig. 7b, a control voltage may need to be generated in the switch driver (190) through the switch timing signal.

[0127] The analog switch (175) uses switch timing 2, which turns the switch on during the waveform period to maintain low impedance and turns the switch off during the subsequent period to have high impedance.

[0128] Figure 8a illustrates a system (100) using a JFET (Junction Field Effect Transistor) as a switch element (176). Unlike a MOSFET, a JFET is a switch element without a body diode and can block bidirectional current.

[0129] JFET (176) can be used as a switch element for both N-channel and P-channel. The switch element (176) illustrated in Fig. 8a is an N-channel JFET. The JFET is a device in which the drain (D) and source (S) are opposite each other, and can be used as a bidirectional switch. In Fig. 8a, the drain (D) and source (S) can be connected interchangeably.

[0130] Figure 10b shows the voltage (V) applied to the gate of an N-channel JFET. GS ) and the current flowing into the drain (I D ) is a graph showing the voltage (V) applied to the gate (G) of the JFET. GS ) This V P If it is smaller, the current flowing into the drain (I D ) is blocked and the switch is turned off, and V P If it is larger, current will flow.

[0131] A self-sensing signal can be measured by turning the switch on and off by generating a gate-source voltage through the Switch timing 1 signal illustrated in Fig. 8b.

[0132] Fig. 9a illustrates a system (100) using a BJT (Bipolar Junction Transistor) as a switch element (177). BJTs can be used at high voltages and high currents and have very fast switching speeds. Both NPN and PNP types of BJTs can be used. The switch element (177) illustrated in Fig. 9a is an NPN BJT.

[0133] Although the BJT (177) is depicted as symmetrical in Fig. 9a, in reality, the BJT is often not perfectly symmetrical. However, because it is structurally symmetrical, the collector (C) and emitter (E) may be connected in reverse. Like other devices such as MOSFETs, the BJT also has a voltage applied to the base (B) and emitter (E) (Base-Emitter Voltage; V BE ) can be turned on and off by controlling the switch drive unit (190).

[0134] Figure 10c shows the voltage (V) applied to the base (B) of the NPN BJT. BE ) and the current (I) flowing to the collector (C) c ) is a graph showing the voltage (V) applied to the base (B). BE ) is the threshold (V TH If the current flowing to the collector (C) is less than (0.7 V), the current (I) c ) is blocked and the switch is turned off.

[0135] A self-sensing signal can be measured by generating a base-emitter voltage through the switch timing 1 signal illustrated in Fig. 9b and turning the switch element (177) on and off.

[0136] In Fig. 11a and Fig. 11b, several switch elements (272, 273) are connected in parallel to form R on A system (300) according to a third embodiment with reduced values ​​and a modified example (300-2) thereof are illustrated. As such, the system (300, 300-2) according to the third embodiment of the present invention may have multiple switch elements (272, 273) connected in parallel to lower the overall output impedance when the switch elements (272, 273) are in the on state.

[0137] Referring to FIGS. 12 and 13, a process of collecting a self-sensing signal in a piezoelectric self-sensing nozzle monitoring system (400, 500) according to the fourth and fifth embodiments of the present invention will be described.

[0138] In the case of the system (400) according to the fourth embodiment illustrated in FIG. 12, a reference row can be used to remove the driving waveform (21) and amplify only the self-sensing waveform (22) when collecting a self-sensing signal. The reference row is a row for generating a reference voltage (23), and turns off all nozzles in the row and generates only the driving signal (23) from the driver unit (110).

[0139] The self-sensing circuit (140) receives self-sensing raw data (21, 22) and a reference voltage (23) signal together, and subtracts the two signals using a circuit such as a differential amplifier. Afterwards, when the subtracted signal is amplified, the driving voltage (21) is removed and an amplified self-sensing signal (24) can be obtained.

[0140] This method can solve the saturation problem of the circuit that occurred in Fig. 2. However, it has the disadvantage of reducing the scanning speed because the row that becomes the reference row cannot be scanned while one row is being scanned.

[0141] In the case of the system (500) according to the fifth embodiment illustrated in Fig. 13, self-sensing signals can be collected without using a reference column. In the case of Fig. 12, the driving signal (21) can be removed to amplify only the self-sensing signal, but there is a problem that the scanning speed is reduced due to the reference column.

[0142] In the case of the system (500) illustrated in Fig. 13, the scanning speed is not reduced because the driving signal (31) is removed and the reference column is not used. When the voltages at the input terminal (driver unit (110) side) and the output terminal (inkjet head unit (160) side) of the switch element (170) are compared, in the case of the input terminal, since it is directly connected to the driver unit (110), the impedance control effect by the switch element (170) cannot be obtained, so the self-sensing waveform is not measured and only the driving signal (33) is measured. On the other hand, in the case of the output terminal, the impedance is controlled by the switch element (170), so the self-sensing waveform is also measured. At this time, if the signal at the input terminal is used as the reference voltage (33), the reference voltage (33) can be measured without the reference column.

[0143] The two signals measured at the input and output terminals can be input to the self-sensing circuit (140), amplified, and collected as a pure self-sensing waveform as in (34).

[0144] In the case of the system (400) illustrated in Fig. 12, when a reference column is used, self-sensing signals may be collected differently for each row due to differences in circuit characteristics. However, when signals from the same column are used as a reference voltage, not only are errors due to differences in circuit characteristics eliminated, but noise reduction effects can also be expected due to the differential circuit. Furthermore, since all rows can be scanned simultaneously and in parallel, the scanning speed can be increased.

[0145] In Fig. 13, an equivalent circuit can be configured by inserting a capacitor (35) having the same or similar electrostatic capacity as the piezo actuator (180) of the inkjet head (160) into the input terminal of the switch element (170). However, it is not necessary to insert the capacitor.

[0146] In the case of the system (500) illustrated in FIG. 13, since the piezo actuator (180) of the inkjet head (160) has electrical properties similar to those of a capacitor, it is possible to effectively measure only the self-sensing signal component caused by the pressure wave generated after ejection (jetting) by offsetting the electrical properties of the piezo actuator.

[0147] As illustrated in FIGS. 12 and 13, the self-sensing circuit (140) of the system (400, 500) according to the present invention can collect the self-sensing signal by removing the reference voltage to process the self-sensing signal, remove the reference voltage using a reference column, or remove the reference voltage using the voltage at the input terminal of the switch element (170).

[0148] The switch element (170) of the system (100 to 500) according to the present invention described above is fundamentally different from the existing impedance converter in terms of the signal of self-sensing. In the existing impedance converter, the input voltage may change and the magnitude of the input voltage is transmitted as is, so additional circuits and algorithms are required to eliminate the effect of the driving voltage. For example, if the effect of the output voltage remains as is, if the sensing signal is amplified through an operational amplifier, such a signal has problems such as saturation (DC power supply voltage), which must be offset. However, the system (100 to 500) according to the present invention can reduce the effect of the driving voltage because it uses the switch element (170).

[0149] The systems (devices) described above may be implemented as hardware components, software components, and / or a combination of hardware components and software components. For example, the devices and components described in the embodiments may be implemented using one or more general-purpose computers or special-purpose computers, such as, for example, a processor, a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable array (FPA), a programmable logic unit (PLU), a microprocessor, or any other device capable of executing instructions and responding to them. The processing device may execute an operating system (OS) and one or more software applications running on the operating system. In addition, the processing device may access, store, manipulate, process, and generate data in response to the execution of the software. For ease of understanding, the processing device is sometimes described as being used alone; however, one of ordinary skill in the art will recognize that the processing device may include multiple processing elements and / or multiple types of processing elements. For example, a processing unit may include multiple processors, or a processor and a controller. Other processing configurations, such as parallel processors, are also possible.

[0150] Software may include a computer program, code, instructions, or a combination of one or more of these, which may configure a processing device to perform a desired operation or may, independently or collectively, command the processing device. The software and / or data may be permanently or temporarily embodied in any type of machine, component, physical device, virtual equipment, computer storage medium or device, or transmitted signal wave, for interpretation by the processing device or for providing instructions or data to the processing device. The software may also be distributed over networked computer systems and stored or executed in a distributed manner. The software and data may be stored on one or more computer-readable recording media.

[0151] The method according to the embodiment may be implemented in the form of program commands that can be executed through various computer means and recorded on a computer-readable medium. The computer-readable medium may include program commands, data files, data structures, etc., alone or in combination. The program commands recorded on the medium may be those specially designed and configured for the embodiment or may be those known and available to those skilled in the art of computer software. Examples of the computer-readable recording medium include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical media such as CDROMs and DVDs, magneto-optical media such as floptical disks, and hardware devices specially configured to store and execute program commands, such as ROMs, RAMs, and flash memories. Examples of the program commands include not only machine language codes generated by a compiler, but also high-level language codes that can be executed by a computer using an interpreter, etc. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the embodiment, and vice versa.

[0152] As described above, the embodiments of the present invention have been described with specific details such as specific components and limited examples and drawings, but these are provided only to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments, and those with ordinary skill in the art to which the present invention pertains can make various modifications and variations based on this description. Therefore, the spirit of the present invention should not be limited to the described embodiments, and all things that are equivalent or equivalent to the claims below as well as the claims are considered to fall within the scope of the spirit of the present invention.

Claims

1. An inkjet head including a plurality of nozzles and a piezo actuator that ejects ink from the nozzles; A driver unit that generates a voltage applied to the piezo actuator so that ink is ejected from the nozzle; and A switching element provided between the driver unit and the piezo actuator or between the power amplifier of the driver unit and the piezo actuator; A piezo self-sensing nozzle monitoring system characterized in that the switch element is controlled to be turned on when voltage is applied to the piezo actuator from the driver unit so as to lower the overall output impedance, and is controlled to be turned off when voltage application from the driver unit is terminated so as to increase the overall output impedance.

2. In paragraph 1, A piezoelectric self-sensing nozzle monitoring system characterized in that an electrical signal is detected from the piezoelectric actuator when the overall output impedance is controlled to be high by the switch element.

3. In paragraph 2, The above switch element, A piezo self-sensing nozzle monitoring system characterized by switching an on-off state in a discharge mode in which ink is discharged from the nozzle and a sensing mode in which an electrical signal is detected from the piezo actuator.

4. In paragraph 3, A piezoelectric self-sensing nozzle monitoring system characterized in that, in the case of the sensing mode, the on-off signal of the switch element has the same frequency as the waveform of the voltage applied from the driver unit to the inkjet head unit.

5. In paragraph 4, The above switch element, A piezoelectric self-sensing nozzle monitoring system characterized in that the waveform of the voltage applied to the piezoelectric actuator decreases to 0 V and then remains in an on state for a predetermined period of time and then turns into an off state.

6. In paragraph 3, It includes a self-sensing circuit connected to a line connecting the above switch element and the inkjet head, A piezoelectric self-sensing nozzle monitoring system characterized in that, in the case of the sensing mode, a self-sensing signal is detected by measuring the voltage applied to the self-sensing circuit when an off signal is applied to the switch element at the time when voltage application from the driver unit is terminated.

7. In paragraph 6, The above switch element and the self-sensing circuit part, A piezoelectric self-sensing nozzle monitoring system characterized in that it is provided in a form integrated into either the driver unit or the inkjet head unit, or is provided in a form integrated into a self-sensing module unit provided between the driver unit and the inkjet head unit.

8. In paragraph 3, In the case of the above discharge mode, the driver unit generates a voltage waveform necessary to discharge ink from the nozzle, and the switch element is switched to an on state. A piezo self-sensing nozzle monitoring system characterized in that, in the case of the sensing mode, the inkjet head generates a voltage waveform necessary to detect an electrical signal from the piezo actuator, and the switch element controls on-off according to the timing at which voltage is applied to the piezo actuator.

9. In paragraph 3, A piezoelectric self-sensing nozzle monitoring system, characterized in that a plurality of the switch elements are connected in parallel to lower the overall output impedance when the switch element is in an on state.

10. In paragraph 3, A piezoelectric self-sensing nozzle monitoring system, characterized in that a plurality of switch elements are connected in series but in opposite directions to block current flowing in both directions of the switch elements.

11. In paragraph 6, The above self-sensing circuit part, A piezoelectric self-sensing nozzle monitoring system characterized in that the self-sensing signal is collected by removing the reference voltage to process the self-sensing signal, the reference voltage is removed using a reference column, or the reference voltage is removed using the voltage at the input terminal of the switch element.

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