JP2005193436A - Driving method for liquid droplet discharging head, liquid droplet discharging head and liquid droplet discharging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid droplet discharging head which can take countermeasures against a viscosity increase of ink at a low cost, and to provide a liquid droplet discharging apparatus and its driving method. <P>SOLUTION: A solvent of the ink near nozzles evaporates between dischargings of ink droplets and an ink concentration becomes high, which sometimes causes the viscosity increase and affects ink discharge characteristics. Therefore, such a pulse that generates near the nozzles a flow velocity of a level whereby ink droplets are not discharged is applied as a spare waveform to piezoelectric elements, thereby stirring the ink near the nozzles. Thus the viscosity increase is suppressed. The axis of abscissa is a pulse width of the spare waveform when a natural period of a pressure chamber is made 1. The pulse width of the spare waveform is made not larger than 10% of the natural period. In other words, the ink can be stirred without discharging the ink droplets by the spare waveform if it is a pulse width of the range indicated by oblique lines. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a droplet discharge head driving method, a droplet discharge head, and a droplet discharge apparatus.

  Conventionally, in ink jet printers, the main component of ink (solvent or dispersion medium = water) evaporates from nozzles that are not driven during printing operations, and the ink near the meniscus opening thickens, affecting the ejection characteristics. It has been known.

  To this end, 1: The method of refreshing the ink in the nozzle by ejecting the thickened ink by retracting the head to the non-printing area (purge operation), 2: The extent that ink droplets are not ejected when not driven There is a known technique (for example, see Patent Documents 1 to 3) in which the meniscus surface is vibrated to stir the thickened ink (preliminary waveform application).

  In practice, a method of reducing the frequency of the purge operation by combining the two and applying a preliminary waveform is generally used. Regarding the preliminary waveform of 2: it is necessary to vibrate the meniscus surface to such an extent that droplets are not ejected. In the analog drive waveform, the head drive voltage is reduced or the waveform slope is reduced. By generating a pressure wave that is weaker than the drive waveform, the vibration of the meniscus surface that does not eject ink droplets is realized.

  However, a digital waveform (rectangular wave drive, binary waveform) in which the degree of freedom of the voltage value of the waveform is reduced in order to reduce the cost of the drive circuit in consideration of the increase in the number of nozzles and FWA (paper width) in consideration of the printing speed. When the drive waveform according to (2) is adopted, the preliminary waveform cannot be formed by reducing the drive voltage with respect to the normal discharge waveform as in the prior art. The slope of the waveform is determined by the time constant of the circuit and cannot be changed. Therefore, it is necessary to create a waveform capable of giving meniscus vibration that does not eject ink droplets with the same applied voltage and slope as the normal ejection waveform. For this purpose, it was found that the preliminary waveform can be designed by devising the pulse width of the waveform and the interval between pulses.

  In Patent Document 1, the driving principle is limited to an electrostatic type. The major difference between the electrostatic type and the PA type is the follow-up speed of the drive unit with respect to the input signal. In the PA type, the drive unit can follow an extremely high-speed signal having an inclination of about 1 μsec. The reason why the waveform having a shorter pulse width than the ejection waveform is used as the preliminary waveform in Patent Document 1 is that the poor followability of the drive unit is used. That is, by shortening the pulse width, a pressure wave is generated so as not to be discharged by returning to the original state before the drive unit is sufficiently displaced. This means that a weak pressure wave is generated by reducing the amount of displacement of the drive unit, which corresponds to reducing the drive voltage in the case of the PA type. As described above, since the relationship between the drive waveform and the movement of the actuator is different between the electrostatic ink jet and the PA drive ink jet, the example of Patent Document 1 cannot be directly applied to the PA drive ink jet.

  In Patent Document 2, the voltage value of the preliminary waveform is set lower than that of the normal discharge waveform. This is a method that cannot be adopted for a rectangular wave (binary waveform), and if the degree of freedom of the voltage value is increased, the cost of the drive circuit increases.

  In Patent Document 3, it is not a countermeasure against thickening during printing, but a countermeasure against thickening between print commands, that is, in a pause state, and there is a possibility that the number of printing work steps is increased, resulting in a decrease in printing speed. . Moreover, it is not specified whether the preliminary waveform to be applied is a dedicated waveform different from the ejection waveform.

  In addition, although there is an example as a PA (piezo actuator) driven ink jet printer that actually uses rectangular wave driving, the preliminary waveform is not used in this example. In addition to the above-mentioned problems, since the smallest droplet is as large as about 5 pl, the effect of ink thickening is small (the smaller the ink droplet volume, the more susceptible to thickening), and only frequent purge operations are required. This is thought to be because thickening can be avoided.

However, 1: When a small droplet having a droplet volume of about 2 to 2.5 pl is ejected, 2: When the progress of thickening is fast due to the use of pigment ink, 3: Matrix head or the like is employed, and the number of nozzles is increased. In many cases, when the purge operation is frequently performed, the amount of ink consumption increases.
JP 2002-019104 A (FIG. 11, pages 3-8) JP-A-57-061576 (FIG. 2, pages 1-2) JP 2000-168103 A (FIG. 5, pages 4-5)

  In consideration of the above-described facts, an object of the present invention is to provide a droplet discharge head driving method, a droplet discharge head, and a droplet discharge apparatus capable of taking measures for increasing the viscosity of ink at low cost.

  The droplet discharge head drive method according to claim 1 is a droplet discharge head drive method using a rectangular drive waveform, the pressure chamber for pressurizing liquid to discharge a droplet from a nozzle, and the rectangular drive Transforming means that is driven by a waveform and expands or compresses the pressure chamber, and the operation by one rectangular drive waveform is performed in the order of expanding after compressing the pressure chamber, and for the non-driven nozzle The rectangular drive waveform having a pulse width that does not discharge the droplet is applied as a preliminary waveform, and the liquid thickening control is performed.

  In the invention having the above-described configuration, it is possible to control the thickening by vibrating the meniscus by applying a rectangular wave that does not cause the liquid droplets to be ejected to the non-driven nozzle as a preliminary waveform. Since the preliminary waveform is a rectangular wave, an increase in the cost of the drive circuit can be suppressed.

  The droplet discharge head driving method according to claim 2 is characterized in that the transformer means is a piezoelectric actuator.

  In the invention with the above configuration, since the transformer means that pressurizes the liquid in the pressure chamber and discharges it from the nozzle is a piezo actuator, it is possible to perform high-speed driving with low power consumption and good response.

  The droplet ejection head driving method according to claim 3 is characterized in that the pulse width of the preliminary waveform is 10% or less of the natural period of the pressure chamber.

  In the invention with the above configuration, when the preliminary waveform is applied, the maximum flow velocity in the vicinity of the nozzle can be reduced to 60% or less during discharge. Thereby, it is possible to prevent droplets from being ejected when the preliminary waveform is applied.

  The droplet ejection head driving method according to claim 4 is characterized in that the pulse width of the preliminary waveform is 3% to 8% of the natural period of the pressure chamber.

  In the invention with the above configuration, when the preliminary waveform is applied, the maximum flow velocity in the vicinity of the nozzle can be set to 20 to 50% during discharge. Thereby, it is possible to prevent droplets from being ejected when the preliminary waveform is applied. Further, it is possible to prevent the effect of the preliminary waveform from being insufficient when the flow velocity is 20% or less, or affecting the characteristics of the next discharge due to the reverberation of the preliminary waveform when the flow velocity is 50% or higher and high-frequency discharge is performed.

  The droplet discharge head driving method according to claim 5 is characterized in that the pulse width of the preliminary waveform is 4% to 6% of the natural period of the pressure chamber.

  In the invention with the above configuration, when the preliminary waveform is applied, the maximum flow velocity in the vicinity of the nozzle can be set to 30 to 40% during discharge. As a result, the thickening suppression effect by the preliminary waveform is sufficient, and it is possible to prevent the reverberation of the preliminary waveform from affecting the next discharge characteristic during high frequency discharge.

  The droplet discharge head driving method according to claim 6 is characterized in that one pulse of a waveform having an opposite phase to the preliminary waveform is applied after the preliminary waveform is applied.

  In the invention with the above configuration, it is possible to cancel the reverberation generated by applying the preliminary waveform by applying one pulse of the waveform having the opposite phase after the preliminary waveform is applied, and to prevent the influence of the next ejection characteristic.

  The droplet discharge head driving method according to claim 7 is characterized in that the nozzles are arranged in a matrix.

  In the invention having the above-described configuration, the nozzle density can be increased while securing the nozzle interval by arranging the nozzles in a matrix arrangement.

  The droplet discharge head driving method according to claim 8 is characterized in that the liquid to be the droplet is a pigment ink.

  In the invention with the above configuration, by using a pigment in the ink, it is possible to form an image having a higher image resolution and higher weather resistance and durability than a dye.

  A liquid droplet ejection head according to a ninth aspect uses the driving method according to any one of the first to eighth aspects.

  In the invention having the above-described configuration, it is possible to provide a droplet discharge head capable of taking measures to increase the viscosity of ink at low cost.

  According to a tenth aspect of the present invention, there is provided a droplet discharge device using the droplet discharge head according to the ninth aspect.

  In the invention having the above-described configuration, it is possible to provide a droplet discharge device capable of taking measures for thickening ink at low cost.

  Since the present invention has the above-described configuration, a droplet discharge head, a droplet discharge device, and a driving method thereof capable of taking measures for increasing the viscosity of ink at low cost have been achieved.

  FIG. 1 shows the structure and driving waveform of a droplet discharge head according to the first embodiment of the present invention.

  As shown in FIG. 1B, the head 10 is provided with a pressure chamber 12, and when the diaphragm 14 forming the wall of the pressure chamber 12 compresses the pressure chamber 12 as shown in FIG. The ink 18 is ejected from the nozzle 24 as ink droplets 22. The piezoelectric element 16 provided on the vibration plate 14 is deformed by the applied voltage, and the vibration plate 14 is moved as shown in FIG. 1B or FIG. 1C to compress / expand the pressure chamber 12.

  FIG. 1A shows an example of a pulse applied to the PA 16, where the vertical axis represents voltage and the horizontal axis represents time. In this case, since the pulse is a rectangular wave, the voltage has only two values of V0 and V1, and the driving circuit may have a simple configuration, so that the cost can be reduced.

  When the voltage changes from V0 to V1 by applying a pulse, the piezoelectric element 16 is deformed in a direction to compress the pressure chamber 12 as shown in FIG. 1B, the ink 18 is compressed, and the ink droplet 22 is ejected from the nozzle 24. Is done.

  When the voltage changes from V1 to V0 after a certain time (pulse width), the piezoelectric element 16 is deformed in the direction of expanding the pressure chamber 12 as shown in FIG. Is supplied. As shown in the enlarged view (d), the liquid surface of the ink 18 forms a meniscus 20 in the vicinity of the nozzle 24.

  At this time, since the solvent of the ink 18 in the vicinity of the nozzle 24 evaporates and the density of the ink 18 increases, the viscosity of the ink 18 may increase and affect the ink ejection characteristics. Therefore, in this embodiment, a pulse that generates a flow velocity that does not eject the ink droplet 22 in the vicinity of the nozzle 24 is applied to the piezoelectric element 16 as a preliminary waveform, and the ink 18 in the vicinity of the nozzle 24 is stirred to increase the viscosity. Is suppressed.

  FIG. 2 shows the pulse width of the preliminary waveform and the maximum flow velocity ratio in the vicinity of the nozzle according to the first embodiment of the present invention.

  The horizontal axis in FIG. 2 is the pulse width of the preliminary waveform when the natural period of the pressure chamber 12 is 1, and the vertical axis is the maximum flow velocity by the preliminary waveform when the maximum flow velocity in the vicinity of the nozzle during ink ejection is 1. is there.

  In the case where one rectangular pulse is compressed from the pressure chamber to the expansion as in this embodiment, when the pulse width is changed with respect to a certain driving voltage V, the maximum flow velocity of ink near the nozzle is as shown in FIG. Become. At this time, if the ink flow rate is too large, ink droplets are ejected. Therefore, it is desirable that the pulse width as the preliminary waveform is short.

  That is, the maximum flow velocity in the preliminary waveform needs to be 60% or less of the maximum flow velocity at the time of discharge. This is because droplets may be ejected at a flow rate higher than this. To satisfy this condition, the pulse width of the preliminary waveform needs to be 10% or less of the natural period as shown in FIG.

  In other words, if the pulse width is in the range indicated by the diagonal lines, the ink droplet is not ejected by the preliminary waveform.

  FIG. 3 shows the pulse width of the preliminary waveform and the maximum flow rate ratio in the vicinity of the nozzle according to the second embodiment of the present invention.

  The horizontal axis in FIG. 3 is the pulse width of the preliminary waveform when the natural period of the pressure chamber 12 is 1, and the vertical axis is the maximum flow velocity by the preliminary waveform when the maximum flow velocity in the vicinity of the nozzle during ink ejection is 1. is there.

  As described above, the maximum flow velocity in the preliminary waveform needs to be 60% or less of the maximum flow velocity at the time of discharge, but it is more preferable to limit the maximum flow velocity to 20% to 50% of the maximum flow velocity at the time of discharge.

  This is because if the flow rate is 10% or less, the effect of the preliminary waveform is too small, and if the flow rate is 50% or more, the reverberation of the preliminary waveform is likely to affect the characteristics at the next discharge during high frequency discharge. In order to satisfy this condition, the pulse width needs to be 3% to 8% of the natural period.

  That is, if the pulse width is in the range indicated by the oblique lines, the effect of the preliminary waveform is too small, or the reverberation of the preliminary waveform does not affect the characteristics at the next discharge.

  FIG. 4 shows the pulse width of the preliminary waveform and the maximum flow velocity ratio in the vicinity of the nozzle according to the third embodiment of the present invention.

  The horizontal axis in FIG. 4 is the pulse width of the preliminary waveform when the natural period of the pressure chamber 12 is 1, and the vertical axis is the maximum flow velocity by the preliminary waveform when the maximum flow velocity in the vicinity of the nozzle during ink ejection is 1. is there.

  As described above, it is better to limit the maximum flow velocity in the preliminary waveform to 20% to 50% of the maximum flow velocity at the time of discharge, but more desirably, the maximum flow velocity in the preliminary waveform is set to 30% to 40% of the maximum flow velocity at the time of discharge. % Should be limited.

  This is because if the pulse width of the preliminary waveform is within the range of 30% to 40% of the maximum flow velocity, the effect of the preliminary waveform can be sufficiently expected, and the adverse effects due to reverberation can be completely suppressed. In order to satisfy this, the pulse width needs to be 4% to 6% of the natural period.

  That is, if the pulse width is in the range indicated by the oblique lines, the effect of the preliminary waveform can be sufficiently expected, and the adverse effect due to reverberation can be completely suppressed.

  FIG. 5 shows the amount of attenuation with time of the maximum flow velocity ratio in the vicinity of the nozzle according to the second embodiment of the present invention.

  The horizontal axis in FIG. 5 is the elapsed time when the natural period of the pressure chamber 12 is 1, and the vertical axis is the maximum flow velocity based on the preliminary waveform when the maximum flow velocity in the vicinity of the nozzle during ink ejection is 1.

  W0 in FIG. 5 is the vibration of the meniscus surface due to the preliminary waveform having a maximum flow velocity of about 0.46 shown in the second embodiment. In particular, when reverberation is not suppressed, the meniscus surface is up to about four times the natural period. It can be seen that the vibration remains.

  Ink jet printers generally discharge ink at a period of about 2 to 5 times the natural period, so reverberation is considered in this situation. The higher the frequency of printing, the shorter the printing cycle, so reverberation must be suppressed.

  FIG. 6 shows the amount of attenuation with time of the maximum flow velocity ratio in the vicinity of the nozzle according to the fourth embodiment of the present invention.

  The horizontal axis in FIG. 6 is the elapsed time when the natural period of the pressure chamber 12 is 1, and the vertical axis is the maximum flow velocity based on the preliminary waveform when the maximum flow velocity in the vicinity of the nozzle during ink ejection is 1.

  In the present embodiment, the reverberation is suppressed by canceling the second and subsequent peaks of the pressure wave generated by the first pulse, that is, the preliminary waveform, with the second pulse.

  W1 in FIG. 6 is the vibration of the meniscus surface due to the preliminary waveform when reverberation suppression is not performed, similarly to W0 in FIG. 5, and the vibration of the meniscus surface remains until about four times the natural period.

  The result of applying the second pulse (W2) to cancel the reverberation is W3, which is a composite waveform of the preliminary waveform and the second pulse. As can be seen from FIG. 6, the reverberation of the composite waveform W3 is sufficiently suppressed in the time of about the natural period.

  FIG. 7 shows a preliminary waveform according to the fourth embodiment of the present invention and a voltage change with time of the second pulse. The horizontal axis in FIG. 7 is the elapsed time, the vertical axis is the voltage, and Tc is the natural period of the pressure chamber 12.

  P1 in FIG. 7 is the first pulse that generates the vibration W1 with the preliminary waveform shown in FIG. 6, that is, the preliminary waveform, and P2 is the second pulse that generates the vibration W2.

  As shown in FIG. 7, the pulse width of the preliminary waveform is 0.07 Tc, that is, 7% of the natural period of the pressure chamber 12, and if the reverberation is not suppressed as it is, the reverberation attenuation characteristic as shown in FIG. 5 is obtained.

  Here, as shown in FIG. 7, by applying the second pulse P2 having a pulse width of 0.05 Tc after 0.52 Tc from the preliminary waveform, the vibration suppression effect on the meniscus surface as shown in FIG. 6 is obtained. That is, even if the pulse width of the preliminary waveform is in the range of about 3 to 8%, the influence of reverberation on the next ejection can be suppressed by applying the second pulse P2 as reverberation suppression.

  The first to fourth embodiments of the present invention have been described by taking the ink jet recording head as an example, but it goes without saying that the present invention is not limited to the ink jet recording head, and can be applied to all uses for ejecting liquid droplets such as manufacturing of a substrate. Yes.

It is a figure which shows the inkjet recording head and drive waveform which concern on the 1st form of this invention. It is a figure which shows the drive pulse width and flow velocity of the inkjet recording head which concern on the 1st form of this invention. It is a figure which shows the drive pulse width and flow velocity of the inkjet recording head which concern on the 2nd form of this invention. It is a figure which shows the drive pulse width and flow velocity of the inkjet recording head which concern on the 3rd form of this invention. It is a figure which shows the reverberation of the inkjet recording head which concerns on the 2nd form of this invention. It is a figure which shows the reverberation of the inkjet recording head which concerns on the 4th form of this invention. It is a figure which shows the drive waveform of the inkjet recording head which concerns on the 4th form of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Inkjet recording head 12 Pressure chamber 14 Vibrating plate 16 Piezoelectric element 18 Ink 20 Meniscus 22 Droplet 24 Nozzle

Claims (10)

A method of driving a droplet discharge head using a rectangular drive waveform,
A pressure chamber for pressurizing the liquid to eject the droplet from the nozzle;
Transformer means driven by the rectangular drive waveform to expand or compress the pressure chamber;
With
The operation by one rectangular drive waveform is performed in the order of expanding after compressing the pressure chamber,
A method of driving a droplet discharge head, wherein the liquid crystal thickening control is performed by applying the rectangular drive waveform having a pulse width that prevents the droplet from being discharged to the non-driven nozzle as a preliminary waveform .
2. The method of driving a droplet discharge head according to claim 1, wherein the transformer means is a piezo actuator.
3. The method of driving a droplet discharge head according to claim 1, wherein a pulse width of the preliminary waveform is 10% or less of a natural period of the pressure chamber.
3. The method of driving a droplet discharge head according to claim 1, wherein the pulse width of the preliminary waveform is 3% to 8% of the natural period of the pressure chamber.
3. The method of driving a droplet discharge head according to claim 1, wherein the pulse width of the preliminary waveform is 4% to 6% of the natural period of the pressure chamber.
6. The method for driving a droplet discharge head according to claim 1, wherein one pulse of a waveform having a phase opposite to that of the preliminary waveform is applied after the preliminary waveform is applied.
The method of driving a droplet discharge head according to claim 1, wherein the nozzles are arranged in a matrix.
The method for driving a droplet discharge head according to claim 1, wherein the liquid to be the droplet is a pigment ink.
A liquid droplet ejection head using the driving method according to claim 1.
A droplet discharge device using the droplet discharge head according to claim 9.

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