Printing ink viscosity determination method and device and printer

Abstract

The invention discloses an ink viscosity determination method and device and a printer, in the method, the ink viscosity in a piezoelectric spray head is determined by utilizing the discovery that the ink viscosity can obviously influence the structural vibration characteristic of the piezoelectric spray head and utilizing a structural vibration fluctuation signal used for representing the structural vibration characteristic of the piezoelectric spray head, and the ink viscosity in the piezoelectric spray head is determined. Self-sensing measurement of the piezoelectric spray head on the viscosity of the internal ink is realized, a feasible way is provided for closed-loop feedback regulation and control of jet flow performance and accurate control of the viscosity of the ink, and the reliability of a piezoelectric ink-jet printing technology in emerging applications such as printing electronics and sensors can be promoted. The method comprises the following steps: detecting a structural vibration fluctuation signal of the piezoelectric nozzle, wherein the structural vibration fluctuation signal is used for representing the structural vibration characteristic of the piezoelectric nozzle; and determining the viscosity of the ink in the piezoelectric spray head according to the structural vibration fluctuation signal.

Description

Technical Field

[0001] The present invention relates to the field of piezoelectric inkjet technology, and in particular to a method and device for determining ink viscosity and a printer. Background Art

[0002] Piezoelectric inkjet printing is a material deposition technique commonly used in electronic additive manufacturing technology. It is widely used due to its high material deposition accuracy, good jet controllability, wide material compatibility and low cost, such as printed electronic devices, sensors and solar cells, as well as other applications.

[0003] In piezoelectric inkjet printing technology, the voltage waveform drives the piezoelectric actuator to generate pressure waves in the ink, which in turn drives the ink to spray at the nozzle and form droplets. In this process, viscosity represents the viscosity of the ink, and its viscosity is the main factor that prevents fluid movement and consumes pressure wave energy. When the pressure wave energy matches the ink viscosity, the ink can produce a single droplet, while when the pressure wave energy does not match the ink viscosity, it will cause inkjet defects (too large will form satellite droplets, too small will not form droplets). Therefore, the matching of pressure wave energy and ink viscosity is a prerequisite for high-precision material deposition. Since the energy of the pressure wave is generated by the voltage waveform driving the piezoelectric actuator, the matching of pressure wave energy and ink viscosity can actually be understood as the matching of the voltage waveform and ink viscosity.

[0004] In traditional inkjet printing, an open-loop feedforward control strategy is usually used to match the voltage waveform with the ink viscosity, that is, after the voltage waveform and the ink viscosity are pre-matched, they will remain unchanged during the subsequent injection process. The premise for this control method to work well is that the ink viscosity remains stable during the forming process, but in emerging applications of inkjet-based additive manufacturing (such as printed antennas, sensors, etc.), the ink materials used to form functional devices are mostly nanoparticle-based inks (such as nanogold and nanosilver inks used to print conductive structures). After the material is deposited, the substrate needs to be heated to evaporate the solvent to complete the layer-by-layer patterning distribution of the functional material. Due to the sensitivity of the ink viscosity to temperature (~2cp / ℃) and differences (different inks have different sensitivities), the hot substrate usually makes it difficult to keep the viscosity of the ink inside the nozzle stable, and the preset voltage waveform no longer matches the ink viscosity, making it difficult to spray the ink, and the consistency and stability of the ejected droplets deteriorate, which in turn limits the performance of inkjet-based additive manufacturing.

[0005] In order to increase the viscosity range of the jettable ink, some piezoelectric nozzles usually integrate a heating module inside the piezoelectric nozzle to heat the ink inside the nozzle hole so that the ink viscosity is reduced to the jettable range of the piezoelectric nozzle. However, due to the lack of an effective ink viscosity sensing method, the viscosity of the ink after heating in the existing nozzle can only be roughly estimated, and the estimation accuracy depends on a large number of preliminary experiments. In addition, under the excitation of the voltage waveform, the piezoelectric actuator of the piezoelectric nozzle continues to work in a high-frequency vibration state, and the energy loss of the vibration structure itself will be converted into heat. This mechanical loss causes heat and also affects the temperature of the ink, thereby changing its viscosity. Therefore, the ink in the piezoelectric nozzle faces a complex process thermal environment in actual application. It is difficult to keep the ink viscosity constant. It is difficult to achieve stable deposition of materials with the traditional open-loop feedforward control strategy. Due to the lack of an effective ink viscosity sensing method, it is difficult to construct a closed-loop feedback control strategy. Therefore, how to identify the viscosity of the ink inside the piezoelectric nozzle has become a technical problem that needs to be overcome.

[0006] Currently, some commercial products have added an independent viscosity identification system to the back end of the piezoelectric nozzle to achieve the best printing effect through viscosity identification. However, the viscosity changes caused by time-varying temperature are concentrated inside the piezoelectric nozzle, and the viscosity identification system located at the back end cannot sense the viscosity of the fluid in the nozzle hole. In addition, some studies have developed a viscosity identification system based on MEMS technology (Micro-Electro-Mechanical Systems, mainly including cantilever and diaphragm types), which reduces the size of the viscosity sensing unit from tens of centimeters to sub-millimeter scale. However, since the characteristic size of the piezoelectric nozzle nozzle is usually only tens of microns, it is difficult to integrate additional MEMS viscosity sensing units inside it. How to sense the viscosity of the ink inside the nozzle hole is still a technical problem that needs to be solved urgently. Summary of the invention

[0007] In view of this, the present invention provides a method, device and printer for determining ink viscosity. The method utilizes the finding that ink viscosity will significantly affect the structural vibration characteristics of the piezoelectric nozzle, and utilizes the structural vibration fluctuation signal used to characterize the structural vibration characteristics of the piezoelectric nozzle to determine the ink viscosity in the piezoelectric nozzle, thereby realizing the piezoelectric nozzle's self-sensing measurement of the internal ink viscosity, providing a feasible approach for closed-loop feedback regulation of jet performance and precise control of ink viscosity, and can promote the reliability of piezoelectric inkjet printing technology in emerging applications such as printed electronics and sensors.

[0008] According to one aspect of the present invention, a method for determining ink viscosity is provided, comprising:

[0009] Detecting a structural vibration fluctuation signal of the piezoelectric nozzle, wherein the structural vibration fluctuation signal is used to characterize the structural vibration characteristics of the piezoelectric nozzle;

[0010] The viscosity of the ink in the piezoelectric nozzle is determined according to the structural vibration fluctuation signal.

[0011] In some embodiments, the step of detecting the structural vibration fluctuation signal of the piezoelectric nozzle includes:

[0012] Inputting a voltage waveform of a preset frequency into a self-sensing measurement circuit to output a structural vibration fluctuation signal;

[0013] Among them, the self-sensing measurement circuit includes a first branch, a second branch and a differential amplifier; the first branch includes a piezoelectric actuator corresponding circuit and a first transimpedance operational amplifier connected to the output end of the piezoelectric actuator corresponding circuit, and the second branch includes a ceramic capacitor and a second transimpedance operational amplifier connected to the output end of the ceramic capacitor; the output end of the first transimpedance operational amplifier and the output end of the second transimpedance operational amplifier are respectively connected to the input end of the differential amplifier; the ceramic capacitor and the static capacitor of the piezoelectric actuator in the piezoelectric actuator corresponding circuit have the same capacitance value.

[0014] In some embodiments, the step of determining the viscosity of the ink in the piezoelectric nozzle according to the structural vibration fluctuation signal of the piezoelectric nozzle comprises:

[0015] Determining a corresponding gain voltage according to the structural vibration wavelength signal;

[0016] The viscosity of the ink in the piezoelectric nozzle is determined based on the gain voltage.

[0017] In some embodiments, the step of determining the corresponding gain voltage according to the structural vibration wavelength signal of the piezoelectric nozzle includes:

[0018] Input the structural vibration wavelength signal and the voltage waveform into the gain detection module respectively to output the voltage value corresponding to the gain;

[0019] The voltage value corresponding to the gain is input into the analog-to-digital conversion module to output the gain voltage.

[0020] In some embodiments, the preset frequency is a resonant frequency of the piezoelectric nozzle.

[0021] In some embodiments, the method further comprises:

[0022] Setting frequency sweep parameters, wherein the frequency sweep parameters include a sweep start frequency, a sweep end frequency, and a sweep step length;

[0023] Determining the excitation voltage waveforms corresponding to different frequencies according to the frequency sweep parameters;

[0024] Determine the target gain voltage of the excitation voltage waveform corresponding to different frequencies;

[0025] Determine whether there is a resonance peak in the amplitude-frequency curve formed by the target gain voltage of the excitation voltage waveform corresponding to the different frequencies;

[0026] If a resonance peak exists, determining the frequency corresponding to the resonance peak as the resonance frequency;

[0027] If there is no resonance peak, the step of setting the frequency sweep parameters is re-executed until the resonance frequency is determined, and the re-set frequency sweep parameters are different from the historically set frequency sweep parameters.

[0028] In some embodiments, the step of determining the viscosity of the ink in the piezoelectric nozzle according to the gain voltage comprises:

[0029] The gain voltage is used to determine the ink viscosity by using a mapping relationship; wherein the method for determining the mapping relationship includes:

[0030] determining a preset gain voltage under different preset ink viscosities to form a target curve;

[0031] Determining a maximum preset gain voltage and a minimum preset gain voltage in the target curve;

[0032] According to the maximum preset gain voltage and the minimum preset gain voltage, the target curve is segmented to obtain multiple sub-curves;

[0033] Determining a preset gain voltage corresponding to a starting point of the sub-curve;

[0034] Determine a conversion coefficient corresponding to the sub-curve by using a preset gain voltage corresponding to a starting point of the sub-curve and a preset ink viscosity on the sub-curve;

[0035] A mapping relationship between the gain voltage and the ink viscosity is determined according to a preset gain voltage corresponding to the starting point of the sub-curve and a conversion coefficient corresponding to the sub-curve.

[0036] In some embodiments, the step of determining the viscosity of the ink in the piezoelectric nozzle according to the gain voltage comprises:

[0037] The gain voltage is used to determine the ink viscosity by using a mapping relationship; wherein the method for determining the mapping relationship includes:

[0038] determining a preset gain voltage under different preset ink viscosities to form a target curve;

[0039] The target curve is fitted to obtain a mapping relationship between the gain voltage and the ink viscosity.

[0040] According to another aspect of the present invention, there is provided an ink viscosity determination device, comprising:

[0041] A detection unit, used to detect a structural vibration fluctuation signal of the piezoelectric nozzle, wherein the structural vibration fluctuation signal is used to characterize the structural vibration characteristics of the piezoelectric nozzle;

[0042] The determination unit is used to determine the viscosity of the ink in the piezoelectric nozzle according to the structural vibration fluctuation signal.

[0043] According to another aspect of the present invention, a storage medium is provided, wherein at least one executable instruction is stored in the storage medium, and the executable instruction enables a processor to execute the ink viscosity determination method as described above.

[0044] According to another aspect of the present invention, there is provided a printer, comprising: a piezoelectric nozzle, a processor, a memory, a communication interface and a communication bus, wherein the processor, the memory and the communication interface communicate with each other via the communication bus;

[0045] The memory is used to store at least one executable instruction, and the executable instruction enables the processor to execute the ink viscosity determination method as described above.

[0046] The present invention provides a method, device and printer for determining ink viscosity. The method utilizes the finding that ink viscosity significantly affects the structural vibration characteristics of a piezoelectric nozzle. The structural vibration fluctuation signal used to characterize the structural vibration characteristics of the piezoelectric nozzle is used to determine the ink viscosity in the piezoelectric nozzle, thereby realizing self-sensing measurement of the internal ink viscosity by the piezoelectric nozzle. This provides a feasible approach for closed-loop feedback regulation of jet performance and precise control of ink viscosity, and can promote the reliability of piezoelectric inkjet printing technology in emerging applications such as printed electronics and sensors.

[0047] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0049] Figure 1 A flowchart of a method for determining ink viscosity according to some embodiments is exemplarily shown;

[0050] Figure 2A schematic diagram showing the working principle of a piezoelectric nozzle according to some embodiments is exemplified;

[0051] Figure 3 A schematic diagram exemplarily illustrates a principle of a self-sensing measurement circuit provided according to some embodiments;

[0052] Figure 4 A schematic diagram of a circuit principle corresponding to a piezoelectric actuator provided according to some embodiments is exemplarily shown;

[0053] Figure 5 A schematic structural diagram of a piezoelectric nozzle structure vibration signal measurement system provided according to some embodiments is exemplarily shown;

[0054] Figure 6 A schematic diagram showing the effect of ink viscosity on the vibration amplitude of a piezoelectric nozzle according to some embodiments is exemplified;

[0055] Figure 7 A flowchart of another method for determining ink viscosity according to some embodiments is exemplarily shown;

[0056] Figure 8 A schematic diagram of a target curve provided according to some embodiments is exemplarily shown;

[0057] Fig. 9 A schematic diagram of another target curve provided according to some embodiments is exemplarily shown;

[0058] Fig.10 A schematic diagram of another target curve provided according to some embodiments is exemplarily shown;

[0059] Fig.11 A schematic diagram showing an amplitude-frequency curve of an MJ-AL-80 piezoelectric nozzle provided according to some embodiments is exemplified;

[0060] Fig.12 A schematic diagram exemplarily shows a gain voltage variation under temperature disturbance provided according to some embodiments;

[0061] Fig.13 A schematic diagram exemplarily shows a mapping equation fitting effect provided according to some embodiments;

[0062] Fig.14 A schematic diagram showing four ink viscosities provided according to some embodiments is exemplified;

[0063] Fig.15 A schematic structural diagram of an ink viscosity determination device provided according to some embodiments is exemplarily shown;

[0064] Fig.16A schematic diagram of the structure of a terminal provided according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0065] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0066] In the related art, the following problems exist in determining the viscosity of the ink inside the piezoelectric nozzle: (1) Inability to sense the viscosity of the ink: Existing piezoelectric nozzles cannot integrate additional sensors. When the viscosity of the internal ink changes due to temperature and material stability, the piezoelectric nozzle cannot sense the change in ink characteristics, which will cause the material deposition performance to deviate from expectations; (2) Poor reliability of material deposition: The material deposition quality of piezoelectric inkjet is highly correlated with the viscosity of the ink. Changes in the viscosity of the ink will cause changes in the jet behavior, making it difficult to ensure the consistency of material deposition. It is difficult to obtain a highly consistent forming effect by spraying the same pattern multiple times, and the reliability of material deposition is difficult to ensure; (3) Unable to avoid process thermal interference: In the emerging applications of piezoelectric inkjet printing technology, process thermal interference (4) It is impossible to accurately control the viscosity of the ink: the heating module integrated inside the piezoelectric nozzle can reduce the viscosity of the ink by heating it, so that the piezoelectric nozzle can spray ink with higher viscosity. However, due to the lack of effective ink viscosity sensing methods, the specific viscosity of the heated ink cannot be accurately sensed. (5) It is impossible to establish closed-loop feedback control: the existing piezoelectric nozzle adopts an open-loop feedforward control strategy. This method can only work reliably under the premise of stable ink viscosity. However, in actual applications, it is difficult to keep the viscosity of the ink stable. Due to the lack of effective ink viscosity identification technology, it is currently impossible to establish closed-loop feedback control.

[0067] In order to solve the above-mentioned technical problems, an embodiment of the present application provides a method for determining ink viscosity, in which the self-sensing characteristics of the original piezoelectric actuator inside the piezoelectric nozzle can be used to identify the ink viscosity, thereby solving the material deposition defect caused by the inability of traditional piezoelectric inkjet technology to respond to viscosity changes; the method does not require any additional sensors, thereby solving the problem that existing rotational viscometers and micromechanical viscometers cannot be integrated into the piezoelectric nozzle; the method also solves the problem that only open-loop feedforward control strategies can be used in complex process thermal environments. The method can be used to construct a closed-loop feedback control strategy, thereby solving the defect that traditional inkjet technology is difficult to adapt to industrial application scenarios; the method also solves the problem that in order to increase the viscosity range of the injection material, the existing piezoelectric nozzle usually integrates a heating module inside to reduce the viscosity by heating the ink. After traditional heating, the viscosity of the ink can only be roughly estimated. The method can obtain accurate ink viscosity through self-sensing measurement, and combined with the heating module, the ink viscosity can be precisely controlled.

[0068] Figure 1 A flow chart of a method for determining ink viscosity according to some embodiments is exemplarily shown, including S100 - S200 .

[0069] S100, detecting a structural vibration fluctuation signal of a piezoelectric nozzle, wherein the structural vibration fluctuation signal is used to characterize a structural vibration characteristic of the piezoelectric nozzle.

[0070] Figure 2 The schematic diagram of the working principle of the piezoelectric nozzle provided according to some embodiments is exemplarily shown. Figure 2 As shown, the nozzle structure is composed of a microchannel 1 and a piezoelectric actuator 2. Driven by an external voltage, the piezoelectric actuator (PZT), that is, the piezoelectric ceramic structure, produces corresponding structural deformation as the voltage waveform changes. This structural deformation causes the volume of the microchannel space to change, so that the ink inside the microchannel generates pressure waves and forms droplets at the nozzle. In this process, since the viscosity reflects the viscosity of the ink, it will produce corresponding damping on the structural deformation process of the piezoelectric nozzle. The greater the viscosity of the ink, the greater the damping of the structural deformation of the piezoelectric nozzle. It can be seen from the above analysis that the viscosity of the ink can be estimated by analyzing the strength of the damping. Therefore, in the embodiment of the present application, the viscosity of the ink is determined by analyzing the strength of the damping from the structural vibration characteristics of the piezoelectric nozzle.

[0071] In some embodiments, the step of detecting the structural vibration fluctuation signal of the piezoelectric nozzle includes:

[0072] The voltage waveform of the preset frequency is input into the self-sensing measurement circuit to output the structural vibration fluctuation signal. Figure 3A schematic diagram of a self-sensing measurement circuit principle provided according to some embodiments is exemplified. The self-sensing measurement circuit includes a first branch, a second branch and a differential amplifier; the first branch includes a piezoelectric actuator corresponding circuit 3 and a first transimpedance operational amplifier 4 connected to the output end of the piezoelectric actuator corresponding circuit, and the second branch includes a ceramic capacitor 5 and a second transimpedance operational amplifier 6 connected to the output end of the ceramic capacitor; the output end of the first transimpedance operational amplifier and the output end of the second transimpedance operational amplifier are respectively connected to the input end of the differential amplifier 7; the ceramic capacitor and the static capacitor of the piezoelectric actuator in the piezoelectric actuator corresponding circuit have the same capacitance value.

[0073] In the embodiment of the present application, a self-sensing measurement circuit is used to determine a structural vibration fluctuation signal, and the structural vibration fluctuation signal represents the structural vibration characteristics of the piezoelectric nozzle. Figure 3 In the example, the voltage waveform is input to the input terminal of the circuit 3 corresponding to the piezoelectric actuator to output the current i sum (t), the current i sum (t) is input to the input terminal of the first transimpedance operational amplifier 4. The voltage waveform is also input to the input terminal of the ceramic capacitor 5 to output the current i m (t), the current i m (t) is input to the input terminal of the second transimpedance operational amplifier 6. The output terminal of the first transimpedance operational amplifier 4 and the output terminal of the second transimpedance operational amplifier 6 are connected to the input terminal of the differential amplifier 7 respectively.

[0074] Figure 4 The following is a schematic diagram of a circuit principle corresponding to a piezoelectric actuator provided according to some embodiments. Figure 4 In the embodiment, the circuit 3 corresponding to the piezoelectric actuator includes a static capacitor 31 of the piezoelectric actuator connected in parallel and an element 32 corresponding to the charge change generated by the structural deformation of the piezoelectric actuator.

[0075] in,

[0076] In the formula, i sum (t) is the total current output by the piezoelectric actuator, i c (t) is the current generated by the voltage waveform exciting the static capacitor, i q (t) is the current caused by the deformation of the piezoelectric actuator structure (positive piezoelectric effect), C s is the static capacitance of the piezoelectric actuator, V(t) is the applied voltage waveform, Q s (t) is the induced charge generated by the piezoelectric actuator due to structural deformation, d is is the electromechanical coupling coefficient of the piezoelectric actuator (having the physical dimension of [C / m]), and S(t) represents the deformation of the piezoelectric actuator.

[0077] According to the above analysis, the current i q (t) represents the deformation rate of the piezoelectric actuator structure, from the total current i sum Remove i from (t) c By connecting a ceramic capacitor C in parallel to the piezoelectric actuator, an electrical signal representing only the structural vibration characteristics can be obtained. m (no piezoelectric effect), and synchronously load the voltage waveform on the input electrode of the ceramic capacitor 32, and the output electrode is respectively connected to two groups of transimpedance operational amplifiers (TIA) with a gain of gi, which convert the output current into a corresponding voltage signal.

[0078] See again Figure 3 , the voltage signal corresponding to the output current of the piezoelectric actuator and the voltage signal corresponding to the ceramic capacitor can be expressed as follows:

[0079]

[0080] Where V s (t) is the voltage signal corresponding to the output current of the piezoelectric actuator, V m (t) is the voltage signal corresponding to the ceramic capacitor; DA is the differential amplifier. In the circuit, adjust the ceramic capacitor C m Make it equal to the static capacitor C s With the same capacitance value, the voltage V m (t) and V s (t) The first term on the right side of the equation is equal. On this basis, let the voltage V s (t) minus the voltage V m (t), we can obtain the structural vibration fluctuation signal V containing only the structural vibration characteristics. d (t), that is:

[0081] V d (t) = V s (t)-V m (t) = g i i q (t) (3)

[0082] Where V d (t) represents the structural vibration fluctuation signal of the piezoelectric nozzle, which contains the characteristic information of ink viscosity identification. When a sinusoidal voltage waveform is loaded, the piezoelectric nozzle will generate a sinusoidal structural vibration, and V d (t) appears as a cosine-shaped ripple voltage.

[0083] In some embodiments, the step of determining the viscosity of the ink in the piezoelectric nozzle according to the structural vibration fluctuation signal of the piezoelectric nozzle comprises:

[0084] Determining a corresponding gain voltage according to the structural vibration wavelength signal;

[0085] The viscosity of the ink in the piezoelectric nozzle is determined based on the gain voltage.

[0086] In the embodiment of the present application, the viscosity of the ink will significantly affect the structural vibration characteristics of the piezoelectric nozzle. The viscosity of the ink will cause the structural vibration fluctuation signal V d (t) fluctuation amplitude, but due to V d (t) itself is a fluctuating signal, and it is necessary to extract the amplitude of the fluctuating signal through circuit design. This can be achieved through a gain detection module, and the corresponding gain voltage can be determined through the gain detection module.

[0087] In some embodiments, the step of determining the corresponding gain voltage according to the structural vibration wavelength signal of the piezoelectric nozzle includes:

[0088] The structural vibration wavelength signal and the voltage waveform are respectively input into a gain detection module to output a voltage value corresponding to the gain.

[0089] In an embodiment of the present application, the structural vibration wavelength signal is used as a self-sensing signal, and the voltage waveform is used as a reference signal. The amplitude change of the structural vibration wavelength signal is obtained through the self-sensing signal and the reference signal, and the voltage value corresponding to the gain is output. The voltage value corresponding to the gain can be obtained by dividing the reference signal and the self-sensing signal.

[0090] The voltage value corresponding to the gain is input into the analog-to-digital conversion module to output the gain voltage.

[0091] In the embodiment of the present application, the analog-to-digital conversion module converts the voltage value corresponding to the gain into a digital value, namely, the gain voltage.

[0092] Specifically, in the embodiment of the present application, a piezoelectric nozzle structure vibration signal measurement system is designed. Figure 5 The following is a schematic diagram showing a structure of a piezoelectric nozzle structure vibration signal measurement system according to some embodiments. Figure 5In the present invention, the vibration signal measurement system of the piezoelectric nozzle structure mainly includes a main controller, a direct digital frequency synthesis, a self-sensing measurement circuit, a current buffer, a gain detection module and an analog-to-digital conversion module, wherein the main controller is composed of a computer host and an embedded controller. The sweep frequency parameters, voltage amplitude and other command parameters can be sent to the main controller via USB (Universal Serial Bus), and the embedded controller writes the sweep frequency parameters into the direct digital frequency synthesis module to form a voltage waveform of a preset frequency, and connects to the current buffer (for improving the sweep frequency signal driving capability) at its subsequent stage; the output signal of the current buffer is divided into two paths, one of which is connected to the self-sensing measurement circuit to excite the piezoelectric nozzle structure vibration; the other is directly input to the gain detection module as a reference signal; the self-sensing measurement circuit outputs a structural vibration fluctuation signal while driving the piezoelectric nozzle, and inputs it into the gain detection module; the gain detection module obtains the amplitude change of the structural vibration signal by comparing the reference signal and the self-sensing signal, and outputs the voltage value corresponding to the gain; the digital-to-analog conversion module collects the gain signal reflecting the structural vibration amplitude and converts it into a digital quantity, namely the gain voltage, and the embedded controller collects the gain voltage and sends it to the computer host to identify and analyze the ink viscosity. Through the above system, the structural vibration characteristics can be sensed by the piezoelectric actuator of the piezoelectric nozzle itself, which lays the foundation for the subsequent viscosity identification on the computer host side and is the hardware foundation and prerequisite for the implementation of ink viscosity determination in this application.

[0093] In some embodiments, the preset frequency is a resonant frequency of the piezoelectric nozzle.

[0094] In the embodiment of the present application, the premise of ink viscosity identification is that the ink viscosity will significantly affect the structural vibration characteristics, and the structural vibration characteristics caused by it can be accurately perceived. However, during the operation of the piezoelectric nozzle, the deformation of the piezoelectric actuator excited by the voltage waveform is usually only tens of nanometers, and during the interaction between the structure and the fluid, the structure has a strong coupling effect on the ink, while the ink has a weak coupling effect on the structure. This makes it found in the actual test process that under general conditions, the effect of ink viscosity on the vibration characteristics of the piezoelectric nozzle structure is very small. How to improve the sensitivity of the piezoelectric nozzle structure to ink viscosity is the basis of viscosity identification. In order to achieve this goal, the embodiment of the present application proposes to make the piezoelectric nozzle structure work in a resonant state to improve its sensitivity to ink viscosity.

[0095] To this end, the embodiment of the present application first uses a simulation model to analyze the natural mode of the piezoelectric nozzle structure, and calculates the displacement amplitude of the piezoelectric actuator under the excitation of the trigonometric function waveform within a wide frequency range (covering the resonant frequency of the structure), thereby determining the resonant frequency of the piezoelectric nozzle. However, since the resonant frequency of the piezoelectric nozzle may have multiple frequencies and vibration modes, it is necessary to select a resonant mode with a strong viscosity effect in combination with the structural characteristics of the piezoelectric nozzle, that is, the resonant vibration mode manifests as a shear motion of the ink. Under the shear motion state, the vibration of the nozzle structure will form a viscous boundary layer near the flow channel wall. Therefore, considering that the structural vibration of the nozzle in the resonant state is very sensitive to external damping, the voltage waveform at a preset frequency as the resonant frequency is used to determine the structural vibration fluctuation signal.

[0096] In addition, the structural vibration of the nozzle in the resonant state is very sensitive to external damping, and this conclusion has been verified through simulation. Figure 6 A schematic diagram showing the effect of ink viscosity on the amplitude of a piezoelectric nozzle according to some embodiments is shown. Figure 6 In the present invention, for inks with different viscosities, the piezoelectric nozzle exhibits significant signal gain changes near the resonance peak. Based on this finding, the embodiments of the present application propose to detect changes in ink viscosity at the resonance frequency.

[0097] According to the above analysis, in order to enhance the effect of ink viscosity on the structural vibration characteristics of the piezoelectric nozzle, the piezoelectric nozzle needs to be operated at a resonant frequency, and the piezoelectric nozzle needs to be measured at the resonant frequency. To this end, the embodiment of the present application combines the aforementioned piezoelectric nozzle structure vibration signal measurement system and proposes to determine the resonant frequency of the piezoelectric nozzle by regulating the direct digital frequency synthesis module. In some embodiments, Figure 7 The flowchart of another ink viscosity determination method provided according to some embodiments is exemplarily shown. The method further includes S300-S800.

[0098] S300, setting frequency sweep parameters, wherein the frequency sweep parameters include a sweep start frequency, an end frequency, and a sweep step length;

[0099] S400: Determine excitation voltage waveforms corresponding to different frequencies according to the frequency sweep parameters.

[0100] In this embodiment, the scanning parameters such as the scanning start frequency, the end frequency, and the scanning step length are preliminarily set in combination with the structural characteristics of the piezoelectric nozzle. Different frequencies are determined between the scanning start frequency and the end frequency according to the scanning step length. A direct digital frequency synthesis module can be used to generate an excitation voltage waveform corresponding to the frequency. The excitation voltage waveform corresponding to different frequencies is used to determine the resonant frequency of the piezoelectric nozzle.

[0101] S500 , determining target gain voltages of excitation voltage waveforms corresponding to different frequencies.

[0102] In this embodiment, the excitation voltage waveform can first be input into the self-sensing measurement circuit to output the corresponding target structure vibration fluctuation signal, and the target structure vibration fluctuation signal can be input into the gain detection module. In addition, the excitation voltage waveform is directly input into the gain detection module. The gain detection module outputs the target voltage value corresponding to the gain. The target voltage value corresponding to the gain is input into the analog-to-digital conversion module to output the target gain voltage. The above process can refer to the process of obtaining the gain voltage using the voltage waveform in the above text, and the data processing method is the same in the two processes.

[0103] S600: Determine whether there is a resonance peak in the amplitude-frequency curve formed by the target gain voltage of the excitation voltage waveform corresponding to the different frequencies. Figure 6 , Figure 6 Any curve in can be called an amplitude-frequency curve. Figure 6 There is a resonance peak in each amplitude-frequency curve.

[0104] S700: If a resonance peak exists, determining a frequency corresponding to the resonance peak as a resonance frequency;

[0105] S800: If there is no resonance peak, re-execute the step of setting the frequency sweep parameters until the resonance frequency is determined, and the re-set frequency sweep parameters are different from the historically set frequency sweep parameters.

[0106] In the embodiment of the present application, after determining the resonant frequency of the piezoelectric nozzle, the piezoelectric nozzle is operated at the resonant frequency, and the structural vibration fluctuation signal of the piezoelectric nozzle is continuously detected to determine the gain voltage of the amplitude, and the gain voltage is sent to the computer host to facilitate viscosity identification.

[0107] S200: Determine the viscosity of the ink in the piezoelectric nozzle according to the structural vibration fluctuation signal.

[0108] Since the change of ink viscosity will cause the structural vibration characteristics of the piezoelectric nozzle to change, that is, the amplitude of the piezoelectric nozzle changes, which will eventually cause the piezoelectric nozzle structure vibration signal measurement system to output different gain voltages. Considering that the mapping relationship between gain voltage and ink viscosity has nonlinear characteristics, Figure 8 A schematic diagram of a target curve provided according to some embodiments is exemplarily shown, so in order to convert the gain voltage into ink viscosity, it is necessary to establish a mapping relationship between the ink viscosity and the gain voltage. To this end, in some embodiments, the step of determining the ink viscosity in the piezoelectric nozzle according to the gain voltage includes:

[0109] The gain voltage is used to determine the ink viscosity by using a mapping relationship. The mapping relationship can be determined in two ways: one is a linear interpolation method, and the other is an equation fitting method.

[0110] In some embodiments, the mapping relationship is determined by linear interpolation, which can be understood as approximating the entire nonlinearity into a set of linear intervals. Specifically, the method for determining the mapping relationship includes:

[0111] Preset gain voltages at different preset ink viscosities are determined to form a target curve.

[0112] In this embodiment, a preset ink viscosity and a preset gain voltage corresponding thereto may be predetermined and drawn into a target curve.

[0113] A maximum preset gain voltage and a minimum preset gain voltage in the target curve are determined.

[0114] Fig. 9 A schematic diagram of another target curve provided according to some embodiments is exemplarily shown. Fig. 9 The maximum preset gain voltage is V d1 , the minimum preset gain voltage is V dN .

[0115] According to the maximum preset gain voltage and the minimum preset gain voltage, the target curve is segmented to obtain multiple sub-curves. Fig. 9 ,exist Fig. 9 There are 5 sub-curves in it. Each sub-curve can be regarded as a linear interval.

[0116] A preset gain voltage corresponding to the starting point of the sub-curve is determined.

[0117] For example, see again Fig. 9 , the five sub-curves have corresponding starting points respectively, from left to right, the preset gain voltage of the starting point of the first sub-curve is Vd1, the preset gain voltage of the starting point of the second sub-curve is Vd2, and so on.

[0118] The conversion coefficient corresponding to the sub-curve is determined by using the preset gain voltage corresponding to the starting point of the sub-curve and the preset ink viscosity on the sub-curve.

[0119] In this embodiment, each sub-curve has a corresponding conversion coefficient. Fig. 9 ,exist Fig. 9 There are 5 conversion coefficients, namely [k1, k2, …, k5].

[0120] A mapping relationship between the gain voltage and the ink viscosity is determined according to a preset gain voltage corresponding to the starting point of the sub-curve and a conversion coefficient corresponding to the sub-curve.

[0121] The following equation describes the mapping relationship between gain voltage and ink viscosity.

[0122] μ=V di -k i V d (t), V di+1 ≤V d (t) <V di (4)

[0123] In the formula, k i is the linear conversion coefficient of the linear segment interval i (i.e., the i-th segment sub-curve), V d (t) is in the voltage range [V di ,V di+1 ] is the measured gain voltage, dimensionless data, and μ is the converted ink viscosity. Therefore, according to the above equation, the measured gain voltage can be converted to the corresponding ink viscosity, and the more linear segment intervals there are, the higher the conversion accuracy of gain voltage to ink viscosity.

[0124] In the embodiment of the present application, when converting the gain voltage into ink viscosity, the linear interval of the gain voltage, that is, which sub-curve it belongs to, is first determined based on the measured gain voltage, and the corresponding conversion coefficient is determined accordingly, and finally the gain voltage is converted into ink viscosity using the conversion coefficient.

[0125] In some embodiments, the mapping relationship is determined by equation fitting. The conversion accuracy of the linear interpolation method depends on the number of linear segments, and the error is the largest in the middle of the linear segment area. This is because the linear interpolation locally ignores the high-order mapping relationship. The use of the equation fitting method can overcome the defects of the linear interpolation method. A set of gain voltage data is obtained through a known viscosity ink sample, which is used as sample data, and the coefficients of the equation are determined by parameter regression. The mathematical form of the equation can be selected by analyzing the sample data, such as a univariate multi-time equation, a proportional equation, etc.

[0126] Specifically, the mapping relationship is determined by equation fitting. The method for determining the mapping relationship includes:

[0127] Preset gain voltages at different preset ink viscosities are determined to form a target curve.

[0128] In this embodiment, Fig.10A schematic diagram of providing another target curve according to some embodiments is exemplarily shown. This step is the same as the step of determining the preset gain voltage under different preset ink viscosities in the mapping relationship using the linear interpolation method to form the target curve, and will not be repeated here.

[0129] The target curve is fitted to obtain a mapping relationship between the gain voltage and the ink viscosity.

[0130] The following equation can express the mapping relationship between gain voltage and ink viscosity:

[0131] μ=f fit (V d (t))(5)

[0132] In the formula, f fit is the fitting function obtained by parameter regression. The relationship between ink viscosity and gain voltage after fitting is as follows: Fig.10 As shown, since the fitting process is a higher-order approximation, under the premise of selecting a suitable fitting equation, the mapping of gain voltage and ink viscosity after fitting is more accurate, and the corresponding ink viscosity identification is also more accurate. In the embodiment of the present application, a high-precision conversion relationship from gain voltage to ink viscosity can be obtained after data fitting.

[0133] In the embodiment of the present application, the precise measurement of the ink viscosity inside the piezoelectric nozzle can be achieved, which is the key to constructing a closed-loop feedback material injection process and the prerequisite for achieving precise control of the ink viscosity in the nozzle. The method proposed in the embodiment of the present application is of great value for further improving the performance of piezoelectric inkjet printing technology.

[0134] An embodiment of the present application provides a method for determining ink viscosity. The method utilizes the finding that ink viscosity significantly affects the structural vibration characteristics of the piezoelectric nozzle. The structural vibration fluctuation signal used to characterize the structural vibration characteristics of the piezoelectric nozzle is used to determine the ink viscosity in the piezoelectric nozzle. This realizes the piezoelectric nozzle's self-sensing measurement of the internal ink viscosity, provides a feasible approach for closed-loop feedback regulation of jet performance and precise control of ink viscosity, and can promote the reliability of piezoelectric inkjet printing technology in emerging applications such as printed electronics and sensors.

[0135] In order to further illustrate the implementation process of the present application, an example is described below in conjunction with the MJ-AL-80 single-nozzle piezoelectric nozzle.

[0136] First, by testing the static capacitance of the piezoelectric nozzle, its capacitance is about 1.5nF. By welding the appropriate matching capacitor to the self-sensing measurement circuit, the self-sensing measurement circuit can accurately measure the structural vibration fluctuation signal of the piezoelectric nozzle. The simulation found that the resonant frequency of the MJ-AL-80 piezoelectric nozzle is about 113kHz. Considering the difference between the simulation model and the actual nozzle structure, the actual resonant frequency of the piezoelectric nozzle is scanned in the range of 50kHz to 250kHz. The results are as follows: Fig.11 As shown, the results show that there is a significant resonance peak near 137.1kHz.

[0137] Secondly, based on the actual resonance peak of the piezoelectric nozzle, the resonance frequency of the piezoelectric nozzle is determined to be 137.1kHz, the direct digital frequency synthesis module is controlled to output the voltage waveform at the resonance frequency to excite the piezoelectric nozzle, and the gain voltage corresponding to the amplitude of the piezoelectric nozzle structure is continuously recorded.

[0138] In order to verify that the gain voltage can accurately reflect the influence of ink viscosity, the piezoelectric nozzle was placed on a heated constant temperature substrate at 45℃, 50℃, and 55℃, and the change of gain voltage was recorded. The results are shown in Fig.12 The results show that the higher the substrate temperature, the lower the ink viscosity and the greater the structure amplitude gain voltage, which is completely consistent with the law that ink viscosity is affected by temperature, proving the effectiveness of the method proposed in the embodiment of the present application in terms of ink viscosity perception.

[0139] Again, the equation fitting method is used to identify the ink viscosity. When fitting the experimental data, it is found that the following mathematical relationship can fit the experimental data well:

[0140]

[0141] Where V d is the gain voltage output by the analog-to-digital conversion module, and a and b are unknown coefficients. The conversion relationship from gain voltage to ink viscosity can be obtained through data fitting. For the MJ-AL-80 piezoelectric nozzle, the coefficients a and b after fitting are 3.8765 and 0.4131 respectively. The fitting effect is shown in Fig.13 As shown, the fitting equation is in good agreement with the experimental data.

[0142] Finally, four standard reagents (aniline, photocurable resin, glycerin-water mixture, ethylene glycol) were used to analyze the stability of the method proposed in the embodiment of the present application. The viscosity of the four reagents was first measured using a rotational viscometer, which was 3.76, 8.41, 13.31, and 18.54 mPa·s, respectively. The four reagents were added to the piezoelectric nozzle, and 10 sets of viscosity measurement data were recorded for each reagent. The viscosity identification results of the four reagents are shown in Figure 1. Fig.14As shown, the average values ​​of the identified viscosities are 3.93, 8.09, 13.44, and 18.74 mPa·s, respectively, and the relative errors with the viscometer measurement results are 4.5%, 3.8%, 0.9%, and 1.1%, respectively, and the fluctuation ranges of the 10 groups of measurement data are 0.34, 0.38, 0.23, and 0.29 mPa·s, respectively. Since the jettable viscosity of the piezoelectric nozzle is usually less than 20 mPa·s, the viscosities of the four reagents basically cover the jettable viscosity range, which means that the method proposed in the embodiment of the present application is better than 4.5% in viscosity identification error, and the measured viscosity fluctuation range is less than 0.4 mPa·s, which proves that the proposed method has good viscosity identification accuracy and can meet the requirements of inkjet printing jet performance regulation, which is of great significance for improving the stability and reliability of inkjet-based additive manufacturing technology.

[0143] Furthermore, as a response to the above Figure 1 In order to realize the method shown in the figure, an embodiment of the present invention provides an ink viscosity determination device, such as Fig.15 As shown, including:

[0144] A detection unit, used to detect a structural vibration fluctuation signal of the piezoelectric nozzle, wherein the structural vibration fluctuation signal is used to characterize the structural vibration characteristics of the piezoelectric nozzle;

[0145] The determination unit is used to determine the viscosity of the ink in the piezoelectric nozzle according to the structural vibration fluctuation signal.

[0146] According to one embodiment of the present invention, a storage medium is provided, wherein the storage medium stores at least one executable instruction, and the computer executable instruction can execute the ink viscosity determination method in any of the above method embodiments.

[0147] According to one embodiment of the present invention, a printer is provided, comprising: a piezoelectric nozzle, a processor, a memory, a communication interface and a communication bus, wherein the processor, the memory and the communication interface communicate with each other through the communication bus;

[0148] The memory is used to store at least one executable instruction, and the executable instruction enables the processor to execute the ink viscosity determination method as described above.

[0149] Fig.16 A schematic diagram of the structure of a terminal provided according to an embodiment of the present invention is shown. The specific embodiment of the present invention does not limit the specific implementation of the terminal.

[0150] like Fig.16 As shown, the terminal may include: a processor (processor) 402 , a communication interface (Communications Interface) 404 , a memory (memory) 406 , and a communication bus 408 .

[0151] The processor 402 , the communication interface 404 , and the memory 406 communicate with each other via a communication bus 408 .

[0152] The communication interface 404 is used to communicate with other devices such as clients or other servers.

[0153] The processor 402 is used to execute the program 410, and specifically can execute the relevant steps in the above-mentioned power transmission line fault monitoring method embodiment.

[0154] Specifically, the program 410 may include program codes, which include computer operation instructions.

[0155] The processor 402 may be a central processing unit (CPU), or an application-specific integrated circuit (ASIC), or one or more integrated circuits configured to implement the embodiment of the present invention. The one or more processors included in the terminal may be processors of the same type, such as one or more CPUs; or processors of different types, such as one or more CPUs and one or more ASICs.

[0156] The memory 406 is used to store the program 410. The memory 406 may include a high-speed RAM memory, and may also include a non-volatile memory (non-volatile memory), such as at least one disk memory.

[0157] Obviously, those skilled in the art should understand that the above modules or steps of the present invention can be implemented by a general computing device, they can be concentrated on a single computing device, or distributed on a network composed of multiple computing devices, and optionally, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, and in some cases, the steps shown or described can be executed in a different order than here, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. Thus, the present invention is not limited to any specific combination of hardware and software.

[0158] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for determining ink viscosity, characterized in that: include: Detecting a structural vibration fluctuation signal of the piezoelectric nozzle, wherein the structural vibration fluctuation signal is used to characterize the structural vibration characteristics of the piezoelectric nozzle; The viscosity of the ink in the piezoelectric nozzle is determined according to the structural vibration fluctuation signal.

2. The method according to claim 1, characterized in that The step of detecting the structural vibration fluctuation signal of the piezoelectric nozzle comprises: Inputting a voltage waveform of a preset frequency into a self-sensing measurement circuit to output a structural vibration fluctuation signal; Among them, the self-sensing measurement circuit includes a first branch, a second branch and a differential amplifier; the first branch includes a piezoelectric actuator corresponding circuit and a first transimpedance operational amplifier connected to the output end of the piezoelectric actuator corresponding circuit, and the second branch includes a ceramic capacitor and a second transimpedance operational amplifier connected to the output end of the ceramic capacitor; the output end of the first transimpedance operational amplifier and the output end of the second transimpedance operational amplifier are respectively connected to the input end of the differential amplifier; the ceramic capacitor and the static capacitor of the piezoelectric actuator in the piezoelectric actuator corresponding circuit have the same capacitance value.

3. The method according to claim 2, characterized in that The step of determining the viscosity of the ink in the piezoelectric nozzle according to the structural vibration fluctuation signal of the piezoelectric nozzle comprises: Determining a corresponding gain voltage according to the structural vibration wavelength signal; The viscosity of the ink in the piezoelectric nozzle is determined based on the gain voltage.

4. The method according to claim 3, characterized in that The step of determining the corresponding gain voltage according to the structural vibration wavelength signal of the piezoelectric nozzle comprises: Input the structural vibration wavelength signal and the voltage waveform into the gain detection module respectively to output the voltage value corresponding to the gain; The voltage value corresponding to the gain is input into the analog-to-digital conversion module to output the gain voltage.

5. The method according to claim 4, characterized in that The preset frequency is the resonant frequency of the piezoelectric nozzle.

6. The method according to claim 5, characterized in that Also includes: Setting frequency sweep parameters, wherein the frequency sweep parameters include a sweep start frequency, a sweep end frequency, and a sweep step length; Determining the excitation voltage waveforms corresponding to different frequencies according to the frequency sweep parameters; Determine the target gain voltage of the excitation voltage waveform corresponding to different frequencies; Determine whether there is a resonance peak in the amplitude-frequency curve formed by the target gain voltage of the excitation voltage waveform corresponding to the different frequencies; If a resonance peak exists, determining the frequency corresponding to the resonance peak as the resonance frequency; If there is no resonance peak, the step of setting the frequency sweep parameters is re-executed until the resonance frequency is determined, and the re-set frequency sweep parameters are different from the historically set frequency sweep parameters.

7. The method according to claim 3, characterized in that The step of determining the viscosity of the ink in the piezoelectric nozzle according to the gain voltage comprises: The gain voltage is used to determine the ink viscosity by using a mapping relationship; wherein the method for determining the mapping relationship includes: determining a preset gain voltage under different preset ink viscosities to form a target curve; Determining a maximum preset gain voltage and a minimum preset gain voltage in the target curve; According to the maximum preset gain voltage and the minimum preset gain voltage, the target curve is segmented to obtain multiple sub-curves; Determining a preset gain voltage corresponding to a starting point of the sub-curve; Determine a conversion coefficient corresponding to the sub-curve by using a preset gain voltage corresponding to a starting point of the sub-curve and a preset ink viscosity on the sub-curve; A mapping relationship between the gain voltage and the ink viscosity is determined according to a preset gain voltage corresponding to the starting point of the sub-curve and a conversion coefficient corresponding to the sub-curve.

8. The method according to claim 3, characterized in that The step of determining the viscosity of the ink in the piezoelectric nozzle according to the gain voltage comprises: The gain voltage is used to determine the ink viscosity by using a mapping relationship; wherein the method for determining the mapping relationship includes: determining a preset gain voltage under different preset ink viscosities to form a target curve; The target curve is fitted to obtain a mapping relationship between the gain voltage and the ink viscosity.

9. An ink viscosity determination device, characterized in that: include: A detection unit, used to detect a structural vibration fluctuation signal of the piezoelectric nozzle, wherein the structural vibration fluctuation signal is used to characterize the structural vibration characteristics of the piezoelectric nozzle; The determination unit is used to determine the viscosity of the ink in the piezoelectric nozzle according to the structural vibration fluctuation signal.

10. A printer, characterized in that: include: A piezoelectric nozzle, a processor, a memory, a communication interface and a communication bus, wherein the processor, the memory and the communication interface communicate with each other through the communication bus; The memory is used to store at least one executable instruction, and the executable instruction enables the processor to execute the ink viscosity determination method according to any one of claims 1 to 8.

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