JP4345346B2 - Electrostatic inkjet head driving method and inkjet printer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a driving method of an electrostatic liquid discharge head represented by an electrostatic ink jet head and the like, and prevents nozzle clogging and liquid discharge failure caused by the retention of liquid with increased viscosity in the nozzle. The present invention relates to a driving method of an electrostatic liquid discharge head that can be prevented.
[0002]
[Prior art]
A liquid ejection head, for example, an inkjet head of an ink jet printer, uses an electrostatic force to change the volume of an ink chamber that stores ink and statically ejects ink droplets from ink nozzles communicating with the ink chamber. An electrostatic ink-jet head provided with an electric actuator is known. The electrostatic actuator includes a diaphragm electrode that forms a part of the ink chamber and a fixed-side electrode that is disposed opposite to the diaphragm electrode. When a drive voltage pulse is applied between them, the diaphragm electrode is fixed. When the application of the driving voltage pulse is canceled by being attracted by the side electrode, the diaphragm electrode is released from the fixed side electrode and elastically returns. The ink pressure in the ink chamber fluctuates due to the vibration of the vibration plate electrode, and the ink droplet is ejected from the ink nozzle communicating with the ink chamber in the process of the vibration plate electrode being released from the fixed side electrode and elastically returning. Done.
[0003]
If the state where ink droplets are not ejected from the ink nozzle continues, the ink in the ink nozzle dries and its viscosity increases. If the ink with increased viscosity stays in the ink nozzle, there is a possibility that clogging may occur that the ink droplet cannot be ejected at the time when the next generated ink droplet is ejected. In addition, even if ink droplets can be ejected, there is a possibility that an ink droplet ejection defect that ink droplets cannot be ejected at a sufficient amount and speed may occur. If the ink nozzles are clogged or ink droplets are ejected poorly, the print quality will be greatly reduced.
[0004]
As a method for preventing an increase in the viscosity of the ink remaining in the ink nozzle, a method is proposed in which the ink meniscus of the ink nozzle that does not discharge ink droplets is slightly vibrated. For example, for an ink nozzle that does not eject ink droplets, a voltage pulse with a smaller amplitude than that is applied at the time of application of a driving voltage pulse for ejecting ink droplets. The meniscus is vibrated slightly. This method is disclosed in the following patent document, for example.
[0005]
[Patent Literature]
Republished patent WO97 / 32728
[0006]
[Problems to be solved by the invention]
In general, an inkjet head includes a large number of ink nozzles, and ink droplets are selectively ejected by individually controlling the electrostatic actuator of each ink nozzle. Therefore, when the above-described conventional method is adopted, ink droplets are ejected at the same timing by applying a drive voltage pulse for ejecting ink to the electrostatic actuator of the ink nozzle that ejects ink droplets. It is necessary to apply a voltage pulse for fine vibration of the ink meniscus having a small amplitude to the electrostatic actuator of the ink nozzle that is not allowed to be applied. In order to realize such control, it is necessary to selectively apply drive voltage pulses having different waveforms to the respective ink nozzles at the same timing, so that the drive circuit configuration is generally complicated.
[0007]
An object of the present invention is to provide an electrostatic ink jet head such as an electrostatic ink jet head that can finely vibrate a meniscus in a nozzle in order to prevent clogging of the nozzle without complicating the circuit configuration for driving. It is to propose a method for driving a liquid discharge head.
[0008]
Another object of the present invention is to provide a driving method for an electrostatic liquid discharge head such as an electrostatic ink jet head that can finely vibrate a meniscus in a nozzle without causing a decrease in printing speed. It is to propose.
[0009]
[Means for Solving the Problems]
In order to solve the above-described problems, the driving method of the electrostatic liquid discharge head according to the present invention applies a liquid discharge drive voltage pulse between the diaphragm electrode and the fixed side electrode that are arranged to face each other at regular intervals. And generating a liquid pressure fluctuation by vibrating the diaphragm electrode by electrostatic force generated between them, and using the liquid pressure fluctuation to discharge a droplet from the liquid discharge nozzle,
When the liquid ejection drive voltage pulse is not applied, a meniscus oscillation drive voltage pulse that can oscillate the meniscus of the liquid ejection nozzle without ejecting droplets is applied at the time of application of the liquid ejection drive voltage pulse. It is characterized in that it is applied between the diaphragm electrode and the fixed side electrode at the time before or after.
[0010]
Here, a period from the discharge start time of the liquid ejection drive voltage pulse to the discharge start time of the subsequent meniscus vibration drive voltage pulse is from 1/4 to 1/2 of the natural period of the liquid pressure fluctuation. It is desirable that the application time point of the meniscus vibration drive voltage pulse is determined so as to be a value within the range.
[0011]
The present invention is suitable for use in a driving method of an electrostatic ink jet head. The driving method of the electrostatic inkjet head to which the present invention is applied is as follows:
Ink pressure fluctuation is generated by applying a drive voltage pulse for ink ejection between the diaphragm electrode and the fixed electrode facing each other at regular intervals, and vibrating the diaphragm electrode by electrostatic force generated between them. And ejecting ink droplets from the ink nozzles using the ink pressure fluctuation,
When the ink discharge drive voltage pulse is not applied, the meniscus vibration drive voltage pulse that can slightly vibrate the ink meniscus of the ink nozzle without discharging ink droplets is applied. It is characterized in that the voltage is applied between the diaphragm electrode and the fixed electrode before or after the time.
[0012]
In the present invention, by selectively applying the ink discharge drive voltage pulse and the meniscus vibration drive voltage pulse generated at different timings, the ink droplet discharge and the ink meniscus fine vibration are selectively performed. . Such control can be realized without complicating the circuit configuration by using a signal in which an ink discharge drive voltage pulse and a meniscus drive voltage pulse alternately appear as a drive voltage pulse signal applied between the electrodes.
[0013]
In the present invention, the period from the discharge start time of the ink ejection drive voltage pulse to the discharge start time of the subsequent meniscus vibration drive voltage pulse is from 1/4 to 1/1 of the natural period of the ink pressure fluctuation. The application time point of the auxiliary voltage pulse is determined so as to be a value within a range up to 2.
[0014]
During the period from the start of discharge of the applied ink ejection drive voltage pulse to 1/4 to 1/2 of the natural period of ink pressure fluctuation, the gap between the diaphragm electrode and the fixed electrode is greater than or equal to the gap in the standby state. In addition, this is a period in which the diaphragm electrode is elastically displaced in a direction away from the fixed electrode and changes in a direction in which the gap between the electrodes widens. Therefore, even if the meniscus vibration drive voltage pulse is applied during this period, the behavior of the diaphragm electrode that is elastically displaced in the direction away from the fixed electrode is not substantially affected. Therefore, the ink droplet ejection characteristics due to the application of the ink ejection drive voltage pulse do not deteriorate. Accordingly, since the cycle of the ink discharge drive voltage pulse can be shortened as much as possible, the ink meniscus of the ink nozzle from which the ink droplet is not discharged can be slightly vibrated without causing a decrease in the printing speed.
[0015]
The driving method of the electrostatic ink jet head according to the present invention is effective in the case of multi-shot / pixel printing in which one pixel printing is performed by discharging ink droplets a plurality of times. In this case, ink nozzles that are not ejected with ink droplets are likely to be generated, so that the ink nozzles are likely to be clogged or ink droplets may be ejected poorly. By adopting the method of the present invention, it is possible to reliably prevent such harmful effects.
[0016]
Next, the present invention relates to an ink jet printer provided with an electrostatic ink jet head, which is characterized in that the electrostatic ink jet head is driven by the above driving method. According to the present invention, clogging of ink nozzles can be prevented without causing a decrease in printing speed, and high-quality printing can be realized at high speed.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of an inkjet printer including an electrostatic inkjet head to which the present invention is applied will be described with reference to the drawings.
[0018]
(Overall configuration of inkjet printer)
FIG. 1 is a schematic configuration diagram showing an ink jet printer provided with an electrostatic ink jet head according to the present embodiment.
[0019]
The ink jet printer 100 according to the present embodiment includes a platen 103 that conveys the recording paper 102 in the main scanning direction Y, an ink jet head 110 that faces the ink nozzle surface of the platen 103, and the ink jet head 110. A carriage 105 for reciprocating in the sub-scanning direction X and an ink tank 106 for supplying ink to each ink nozzle of the inkjet head 110 are provided. A nozzle cap 107 is disposed at a position away from the platen 103 in the sub-scanning direction X, and the nozzle cap 107 communicates with the waste ink collection unit 109 via the ink pump 108.
[0020]
(Electrostatic inkjet head)
FIG. 2 is a schematic configuration diagram showing the electrostatic inkjet head 110. The electrostatic ink jet head 110 is configured by laminating a cavity substrate 112 made of a semiconductor, a nozzle substrate 113 also made of a semiconductor, and an electrode substrate 114 made of glass. A plurality of ink nozzles 115 are formed on the nozzle substrate 113. An independent ink chamber 116 communicating with each ink nozzle 115 is defined between the nozzle substrate 113 and the cavity substrate 112, and each ink chamber 116 has a single common ink chamber 118 via a thin ink orifice 117. Communicating with Ink is supplied to the common ink chamber 118 from the outside via an ink supply path (not shown).
[0021]
A diaphragm electrode 119 that can vibrate in the out-of-plane direction is formed on the bottom wall portion of each ink chamber 116, and each diaphragm electrode 119 functions as a common electrode. Concave portions 120 are respectively formed on the surface portions of the electrode substrate 114 facing the respective diaphragm electrodes 119, and individual electrodes 121 (facing the diaphragm electrodes 119 at predetermined intervals on the bottom surface of the respective concave portions 120. (Fixed side electrode) is formed. Each diaphragm electrode 119 and the individual electrode 121 facing each other constitute an electrostatic actuator.
[0022]
The diaphragm electrode 119 is vibrated using an electrostatic force generated by applying a driving voltage pulse to the electrostatic actuator. Due to the vibration of the diaphragm electrode 119, the volume of the ink chamber 116 is increased or decreased. As a result, the ink droplet 122 is discharged from the ink nozzle 115 communicating with the ink chamber 116 based on the fluctuation of the ink pressure generated in the ink chamber 116. Discharge.
[0023]
The electrostatic ink jet head 110 of this example includes, for example, 64 ink nozzles 115 formed in a row on a nozzle substrate 113, and ink droplets are selectively ejected from these 64 ink nozzles 115. Thus, it is possible to print a desired character or image.
[0024]
The illustrated electrostatic inkjet head 110 is a face eject type that ejects ink droplets from the ink nozzles provided on the upper surface of the nozzle substrate 113. However, the electrostatic inkjet head to be controlled in the present invention is An edge eject type in which ink droplets are ejected from an ink nozzle provided at an end of the substrate may be used.
[0025]
(Inkjet printer control system)
FIG. 3 is a schematic block diagram illustrating a control system of the inkjet printer 100. With reference to this figure, the control system of the inkjet printer 100 provided with the electrostatic inkjet head 110 is demonstrated. The ink jet printer 100 according to the present embodiment has an ink jet head drive control device 1 for driving and controlling the electrostatic ink jet head 110, and this ink jet head drive control device 1 is configured around a CPU 2a. Inkjet head controller 2 is provided. Print information is supplied to the CPU 2a from the external device 3 via the bus 3a, and a ROM 4a, a RAM 4b and a character generator 4c are connected via the internal bus 2b.
[0026]
The inkjet head control unit 2 uses the storage area in the RAM 4b as a work area, executes a control program stored in the ROM 4a, and controls the inkjet head driving control signal based on the character information generated from the character generator 4c. Is generated. The control signal becomes a drive control signal corresponding to the print information via the logic gate array 5 and the drive pulse generation circuit 6 and is supplied to the head driver IC 9 formed on the head substrate 8 via the connector 7. . The head driver IC 9 is also supplied with a drive voltage pulse signal V3 for printing, a control signal LP, a polarity inversion control signal REV, and the like.
[0027]
In the head driver IC 9, based on the supplied signals and the drive voltage Vp supplied from the power supply circuit 10, drive voltage pulses to be applied to the diaphragm electrodes 119 of the electrostatic ink jet head 110, that is, the common electrode, are applied. Drive voltage pulses output from the common output terminal COM and to be applied to the individual electrodes 121 corresponding to the ink nozzles 115 are output from the number of individual output terminals SEG corresponding to the individual electrodes 121. A potential difference between the output of the common output terminal COM and the output of the individual output terminal SEG is applied between each diaphragm electrode 119 corresponding to each ink nozzle 115 and the individual electrode 121 facing each other. A driving potential difference waveform in a designated direction is given during driving (when ink droplets are ejected), and no driving potential difference is given when not driving.
[0028]
At the time of non-driving, as will be described later, a meniscus vibration driving voltage pulse having a small waveform for fine ink meniscus vibration is output to the individual output terminal SEG at a time before the application time of the ink discharge driving voltage pulse. A drive potential difference waveform in a specified direction is provided between the diaphragm electrode 119 and the individual electrode 121.
[0029]
FIG. 4 is a schematic block diagram showing an example of the internal configuration of the head driver IC 9. The head driver IC 9 is a CMOS 64-bit output high withstand voltage driver which operates by being supplied with a high voltage drive voltage Vp and a logic circuit drive voltage Vcc from the power supply circuit 10. The head driver IC 9 applies one of the drive voltage pulse and the GND potential between the counter electrodes corresponding to each ink nozzle 115 of the inkjet head 110 in accordance with the supplied drive control signal.
[0030]
Number 91 in the head driver IC 9 indicates a 64-bit shift register. The shift register 91 shifts up the data of the 64-bit length DI signal input transmitted from the logic gate array 5 as serial data by the XSCL pulse signal input, which is a basic clock pulse synchronized with the DI signal. This is a static shift register stored in this register. The DI signal is a control signal indicating selection information for selecting each of the 64 ink nozzles by ON / OFF, and this signal is transmitted as serial data.
[0031]
A 64-bit latch circuit 92 latches 64-bit data stored in the shift register 91 with a control signal (latch pulse) LP, stores the data, and stores the stored data in the 64-bit inversion circuit 93. This is a static clutch that outputs a signal. In the latch circuit 92, the DI signal of serial data is converted into a 64-bit parallel signal for outputting 64 segments for driving each ink nozzle.
[0032]
The inverting circuit 93 outputs an exclusive OR of the signal input from the latch circuit 92 and the REV signal to the level shifter 94. The level shifter 94 is a level interface circuit that converts the voltage level of the signal from the inverting circuit 93 from a logic system voltage level (5 V level or 3.3 V level) to a head drive system voltage level (0 V to 45 V level).
[0033]
The SEG driver 95 is a 64 channel transmission gate output, and outputs either a drive voltage pulse input or a GND input to the segment outputs SEG1 to SEG64 according to the input of the level shifter 94. The COM driver outputs either a driving voltage pulse input or a GND input to the COM in response to the REV input.
[0034]
The XSCL, DI, LP, and REV signals are logic system voltage level signals that are transmitted from the logic gate array 5 to the head driver IC 9.
[0035]
By configuring the head driver IC 9 in this manner, even when the number of segments to be driven (number of nozzles) increases, the drive voltage pulse to be driven by each ink nozzle of the head and the GND are easily switched, and a positive polarity described later. Reverse alternating driving can be easily realized.
[0036]
(Drive voltage pulse signal)
FIG. 5 shows the drive voltage pulse signal V3. The drive voltage pulse signal V3 has a waveform in which the meniscus vibration drive voltage pulse Pwa and the ink discharge drive voltage pulse Pwb repeatedly appear at a constant period. Each ink ejection drive voltage pulse Pwb has a trapezoidal waveform, and has a waveform that can eject ink droplets from the ink nozzle 115. In contrast, the meniscus vibration drive voltage pulse Pwa has a trapezoidal waveform with a smaller amplitude and pulse width than the ink ejection drive voltage pulse Pwb, and the ink nozzle 115 does not eject ink droplets from the ink nozzle 115. The ink meniscus is slightly vibrated.
[0037]
As will be described later, an ink ejection drive voltage pulse Pwb is applied between the electrodes when ink droplets are ejected, and a meniscus oscillation drive voltage pulse before the ink ejection drive voltage pulse Pwb when ink droplets are not ejected. Pwa is applied between the electrodes. Thus, by selectively applying the ink discharge drive voltage pulse Pwb and the meniscus vibration drive voltage pulse Pwa between the electrodes, each ink nozzle 115 discharges ink droplets and ink meniscus at a constant cycle. Is selectively performed. Therefore, even if the non-printing state continues, the ink meniscus of the ink nozzle 115 periodically oscillates, so that the ink with increased viscosity can be prevented from staying in the ink nozzle 115, and the ink nozzle 115 is clogged. Ink droplet ejection failure can be avoided.
[0038]
Next, in this example, the interval Ta from the discharge start time A of the ink discharge drive voltage pulse Pwb to the discharge start time B of the meniscus vibration drive voltage pulse Pwa that appears after this is expressed as the ink pressure fluctuation in the ink chamber 116. In other words, a value within a range from ¼ to ½ of the natural period To of the inkjet head 100. By setting in this way, it is possible to avoid adversely affecting the ink droplet ejection characteristics due to the application of the meniscus vibration drive voltage pulse Pwa.
[0039]
This will be described in detail with reference to FIGS. FIG. 6 shows the relationship between the waveform of the drive voltage pulse signal V3 and the displacement of the diaphragm electrode 119 causing the ink pressure fluctuation in the ink chamber 116, and FIG. 7 shows the displacement state of the diaphragm electrode 119. It is. In FIG. 6, for ease of understanding, the drive voltage pulses Pwa and Pwb of the drive voltage pulse signal V3 are shown in a widened state.
[0040]
When the ink discharge drive voltage pulse Pwb is applied between the electrodes and charging is started (time T1 in FIG. 6), the diaphragm electrode 119 is fixed from the standby position (position shown in FIG. 7A) accordingly. It is attracted by the side electrode 121 and comes into contact with the fixed side electrode 121 (time T2 in FIG. 6, state in FIG. 7B). Along with this, the ink pressure in the ink chamber 116 changes to the negative pressure side, and the ink meniscus of the ink nozzle 115 is greatly drawn. When the discharge of the ink discharge drive voltage pulse Pwb starts (time T3), the diaphragm electrode 119 leaves the fixed electrode 121 and starts to return to its standby position. Ink droplets are ejected in the process of elastic return of the diaphragm electrode 119. With the free vibration of the diaphragm electrode 119, the ink pressure in the ink chamber 116 varies with the natural period To.
[0041]
The discharge start time T5 of the meniscus vibration drive voltage pulse Pwa generated following the ink discharge drive voltage pulse Pwb is the time T4 and To / 2 when To / 4 has elapsed from the discharge start time T3 of the ink discharge drive voltage pulse Pwb. The time is within the range of the elapsed time T6 (the state of FIG. 7C). In the period from the time point T4 to the time point T6, the diaphragm electrode 119 is in the process of being displaced in a direction away from the fixed side electrode 121. In addition, the gap between the electrodes is equal to or larger than the gap Go (see FIG. 7A) at the standby position.
[0042]
Therefore, even if the meniscus vibration drive voltage pulse Pwa is applied between the electrodes within this period, the behavior of the diaphragm electrode 119 is not substantially affected. That is, since the electrostatic force generated between the electrodes is inversely proportional to the square of the gap, the electrostatic force rapidly decreases as the gap between the electrodes widens. Therefore, there is no adverse effect on the ink discharge characteristics of the ink discharge drive voltage pulse Pwb. As a result, the cycle T of the ink ejection drive voltage pulse Pwb can be made as small as possible. Therefore, the ink meniscus of the ink nozzle can be slightly vibrated without causing a decrease in the printing speed, and the ink nozzle can be reliably prevented from being clogged and the ink droplet being discharged poorly.
[0043]
Here, since the waveform of the meniscus vibration driving voltage pulse Pwa is set in advance, if the discharge start time of the meniscus vibration driving voltage pulse Pwa is determined as described above, the application time of the meniscus vibration driving voltage pulse Pwa is determined. Can be determined. For this purpose, it is necessary to know the natural period To of the electrostatic inkjet head 110.
[0044]
Even if the natural period To is known based on the design specifications, the natural period varies among the heads due to individual differences. Therefore, at a stage before shipment of the electrostatic ink jet head 110, the natural period or the natural frequency of the ink pressure fluctuation in the ink chamber 116 generated after the diaphragm electrode 119 is attracted to the fixed electrode 121 and released is measured. Alternatively, it is desirable to calculate and determine an optimal application time point of the meniscus vibration drive voltage pulse Pwa for each electrostatic ink-jet head based on the measured or calculated natural period or natural frequency.
[0045]
(Printing operation)
In the ink jet head drive control apparatus 1 configured as described above, the electrostatic ink jet head 110 can be driven and controlled so that one print pixel is formed by discharging a plurality of continuous ink droplets. . For example, control is performed so that one pixel is printed by ejecting ink droplets up to three times. It is also possible to control the gradation of each pixel by changing the number of ink droplet ejections in one pixel printing period.
[0046]
FIG. 8 shows a timing chart when a print mode (3 shots / pixel mode) in which one pixel is formed by ejecting ink droplets up to three times by a print mode command signal from the external device 3 is designated. is there. In the figure, V3 is a drive voltage pulse signal supplied from the drive pulse generation circuit 6 of the inkjet head controller 2 to the head driver IC 9, and has the waveform shown in FIGS. That is, the drive voltage pulse signal V3 is a meniscus vibration drive voltage pulse Pwa for finely vibrating the ink meniscus of the ink nozzle (Pwa (1), Pwa (2), Pwa (3) in each pixel printing section in the figure). ) And an ink ejection drive voltage pulse Pwb having a large amplitude for ejecting ink droplets (in the figure, Pwb (1), Pwb (2), and Pwb (3) are displayed). Are waveforms that alternately appear at a constant period T.
[0047]
LP and REV are control signals (latch pulses) and polarity inversion control signals supplied from the logic gate array 5 of the inkjet head control unit 2 to the head driver IC 9 as described above. The driver COM output is the output of the common terminal COM, and the driver SEG output is the output of each individual terminal SEG. The COM-SEG potential difference is a potential difference (nozzle drive voltage waveform) generated between the common electrode (diaphragm electrode 119) and the individual electrode 121.
[0048]
In addition, the driver COM output includes the first to third meniscus vibration driving voltage pulses Pwa (1) to Pw (1) to appear in each of the one-pixel printing periods T (1), T (2), T (3). Among the Pwa (3) and the first to third ink ejection drive voltage pulses Pwb (1) to Pwb (3), the second meniscus oscillation drive voltage pulse Pwa (2) and the ink ejection drive voltage pulse. Pwb (2) appears and is held at GND at other times.
[0049]
On the other hand, the driver SEG output includes the first and third ink ejection drive voltage pulses Pwb (in the case of printing by 3 shots / pixel, in which one pixel is formed by ejecting ink droplets three times. 1), Pwb (3) and the second meniscus vibration drive voltage pulse Pwa (2) appear. In the case of printing by two shots / pixel in which one pixel is formed by ejecting ink droplets twice, the first ink ejection drive voltage pulse Pwb (1) and the second and third meniscus vibration drive voltages Pulses Pwa (2) and Pwa (3) appear. In the case of printing by one shot / pixel in which one pixel is formed by ejecting one ink droplet, the first and second ink ejection drive voltage pulses Pwb (1) and Pwb (2) appear. In the case of non-printing, the second ink ejection drive voltage pulse Pwb (2) and the first and third meniscus vibration drive voltage pulses Pwa (1) and Pwa (3) appear.
[0050]
As described above, the driver SEG output includes any one of the paired drive voltage pulses Pwa (1) and Pwb (1), and the paired drive voltage pulses Pwa (2) and Pwb (2). And any one of Pwa (3) and Pwb (3) appears.
[0051]
In addition, when one-pixel printing is performed by ejecting a plurality of ink droplets, a plurality of timings for one-pixel printing, in the illustrated example, of three consecutive ejection timings, the leading ejection timing is used as a reference ( According to the head reference), gradation expression is performed.
[0052]
Further, the nozzle drive waveform applied between the diaphragm electrode 119 and the individual electrode 121, that is, the COM-SEG potential difference is switched in the reverse direction, the forward direction, and the reverse direction. Therefore, in the case of printing by 3 shots / pixel (1 pixel printing period T (1)), the ink droplet ejection operation is performed three times by reverse driving, normal driving, and reverse driving. In the case of printing with two shots / pixel (one-pixel printing period T (2)), ink droplet ejection operations are performed in the reverse drive and forward drive order at the time of ejection of the first and second ink droplets. In addition, the meniscus vibration drive voltage pulse Pwa (3) is applied in the reverse drive state at a time point before the third ink droplet discharge time point. In the case of printing by one shot / pixel (one-pixel printing period T (3)), the ink droplet ejection operation is performed by reverse driving at the time of ejection of the first ink droplet, and the second and third ink droplets are ejected. At the time of ink meniscus vibration, fine vibration of the ink meniscus is performed in the order of forward drive and reverse drive. Further, in the case of non-printing (one-pixel printing period T (4)), the fine vibration of the ink meniscus is performed in the order of reverse driving, normal driving, and reverse driving.
[0053]
Thus, by performing forward and reverse alternating energization, it is possible to suppress or avoid the generation of residual charges between the diaphragm electrode 119 and the individual electrode 121.
[0054]
(Other embodiments)
In the above example, the present invention is applied to a driving method of an electrostatic ink jet head. However, the present invention can be similarly applied to a driving method of an electrostatic liquid ejection head other than the ink jet head.
[0055]
【The invention's effect】
As described above, in the method for driving a liquid ejection head represented by the electrostatic ink jet head of the present invention, the driving voltage pulse for meniscus and the driving voltage pulse for liquid ejection appear alternately as the driving voltage pulse signal. In addition, only the liquid discharge drive voltage pulse is applied to the nozzle that discharges the liquid, and only the meniscus vibration drive voltage pulse is applied to the nozzle that does not discharge the liquid to discharge the liquid. The meniscus is vibrated without any problems.
[0056]
Therefore, according to the present invention, the driving voltage pulse for driving the meniscus is applied to each nozzle in comparison with the method of applying the driving voltage pulse for discharging the liquid and the driving voltage pulse for vibrating the ink meniscus at the same timing. Without complicating the circuit configuration for generating and applying, nozzle clogging and liquid discharge failure can be prevented.
[0057]
Further, the discharge of the subsequent driving voltage pulse for meniscus oscillation starts from the time when the discharge of the liquid ejection driving voltage pulse starts to the time when 1/4 to 1/2 of the natural period of the liquid pressure fluctuation has elapsed. Like that. As a result, the following meniscus vibration drive voltage pulse is applied during the period in which the diaphragm electrode is displaced away from the fixed electrode and the gap between the electrodes is wider than the standby position. The Therefore, even if the cycle of the liquid ejection drive voltage pulse is shortened as much as possible, the meniscus vibration drive voltage pulse does not adversely affect the displacement of the diaphragm electrode. Therefore, nozzle clogging and liquid ejection failure can be prevented without causing a decrease in printing speed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an ink jet printer to which the present invention is applied.
2 is a schematic cross-sectional view illustrating a configuration example of an electrostatic inkjet head of the inkjet printer of FIG. 1;
FIG. 3 is a schematic block diagram mainly showing a control system of the ink jet printer of FIG. 1;
4 is a schematic block diagram showing an internal configuration of the head driver IC in FIG. 3. FIG.
5 is a waveform diagram showing a voltage waveform of a drive voltage pulse signal in the inkjet printer of FIG. 1. FIG.
6 is an explanatory diagram showing the relationship between the drive voltage pulse signal and the displacement of the diaphragm electrode in the ink jet printer of FIG. 1. FIG.
7 is an explanatory diagram showing a relationship between a diaphragm electrode and a fixed electrode at each time point in FIG.
8 is a timing chart showing signal waveforms at various parts during a printing operation with 1 to 3 shots / pixel in the ink jet printer shown in FIG. 1;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 inkjet head drive control apparatus, 2 inkjet head control part, 6 drive pulse generation circuit, 8 head board | substrate, 9 head driver IC, 100 inkjet printer, 105 carriage, 110 inkjet head, 115 ink nozzle, 116 ink chamber, 117 ink orifice , 118 common ink chamber, 119 diaphragm electrode, 121 individual electrode (fixed side electrode), driving voltage pulse signal for V3 printing, driving voltage pulse for Pwb ink ejection, driving voltage pulse for Pwa meniscus vibration, To ink pressure fluctuation Natural period, T ink discharge drive voltage pulse period, A ink discharge drive voltage pulse discharge start time, B meniscus vibration drive voltage pulse discharge start time, Ta time point A to time point B, LP control signal , REV Polarity reversal system Signal

Claims (3)

Ink pressure fluctuation is generated by applying a drive voltage pulse for ink ejection between the diaphragm electrode and the fixed electrode facing each other at regular intervals, and vibrating the diaphragm electrode by electrostatic force generated between them. to generate, a driving method of the electrostatic type ink jet head Ru by ejecting ink droplets from the ink nozzles by utilizing the ink pressure fluctuation,
When ejecting ink droplets, the ink ejection drive voltage pulse is applied,
When ink droplets are not ejected, a meniscus vibration drive voltage pulse that does not cause ink droplet ejection and that can vibrate the ink meniscus of the ink nozzle is applied between the diaphragm electrode and the fixed electrode. ,
When the meniscus vibration drive voltage pulse is applied after the ejection drive voltage pulse is applied, a period from the discharge start time of the ink discharge drive voltage pulse to the discharge start time of the meniscus vibration drive voltage pulse is The application time point of the driving voltage pulse for meniscus vibration is determined so as to be a value within a range from ¼ to ½ of the natural period of the ink pressure fluctuation. A method for driving an inkjet head. In claim 1,
1 pixel printing is performed by ejecting ink droplets multiple times,
A driving method of an electrostatic ink jet head, characterized in that gradation representation of each pixel is performed by increasing / decreasing the number of ink droplet ejections for one pixel printing. Equipped with electrostatic inkjet head,
An ink jet printer, wherein the electrostatic ink jet head is driven by the driving method according to claim 1.

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