JP2005199662A - Droplet ejection head driving method and droplet ejector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive droplet-ejection-head driving method capable of being adapted to a variety of droplet diameters, and a droplet ejector. <P>SOLUTION: A driving waveform applied to a piezoelectric element 16 is a rectangular wave, and can assume only three voltage values V0-V2. Costs can be kept low because a driving circuit requires only a simple constitution. When a meniscus 20 is drawn through a first voltage change process P1 and a second voltage change process P2, pressure waves generated through both the voltage change processes offset each other because a time interval equivalent to half a natural period Tc is provided between the processes P1 and P2. Thus, the drawing amount of the meniscus 20 is reduced. Thus, the volume of the droplet is prevented from being reduced by excessively drawing the meniscus 20 so that an ink droplet 22 having a sufficient droplet volume can be ejected. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

  Conventionally, in a droplet discharge head that uses an electromechanical transducer such as a piezo actuator, the cost of the drive circuit that generates the drive waveform has been significantly reduced by using a simple rectangular drive waveform for the electromechanical transducer drive waveform. There has been proposed a liquid droplet ejection head that can be made (see, for example, Patent Document 1). The rectangular drive waveform referred to here indicates that the voltage change time (or the time constant of the drive circuit) in the voltage change process of the drive waveform is one kind of step-up and step-down.

  However, when a simple rectangular drive waveform is used, it is difficult to obtain sufficient discharge characteristics because the design freedom of the drive waveform is low.

  For example, as a problem of the rectangular drive waveform, it is difficult to obtain a large drop volume. The “pulling” driving method (for example, see Patent Document 2) that draws the meniscus (the liquid level in the nozzle) into the nozzle immediately before discharge is easy to obtain stability in the discharge direction, but if the meniscus is pulled too much This causes a negative effect that the volume of the ejected droplets is reduced. In the conventional rectangular drive waveform, the amount of meniscus pulling immediately before discharge tends to be large, so that it is very difficult to discharge a droplet with a large droplet volume.

  There is also a method of increasing the volume of a droplet by firing a plurality of droplets (see, for example, Patent Document 3), but in this case, the drive frequency of the droplet as a whole decreases, and it is difficult to realize high-speed recording. There's a problem.

  Alternatively, a method has also been proposed in which a droplet having a large droplet diameter is ejected using a driving waveform for ejecting a large droplet using an analog waveform, and reverberation is simultaneously suppressed (see, for example, Patent Document 4). However, a complicated drive waveform using a plurality of rise / fall times and a plurality of voltage levels results in an increase in cost as compared with the case where a simple rectangular drive waveform is used as described above.

  In addition, it is difficult to suppress reverberation after droplet discharge with a rectangular drive waveform. In order to discharge droplets stably at a high frequency, reverberation suppression after droplet discharge is essential, but in the case of the conventional rectangular drive waveform, the voltage change amount and inclination at the reverberation suppression unit can be set freely. Therefore, it is very difficult to perform appropriate reverberation suppression. As a method of suppressing reverberation in a rectangular drive waveform, an ejection head that executes reverberation suppression by adding a non-injection pulse has been proposed (see, for example, Patent Document 5), but this method provides a sufficient reverberation suppressing effect. In particular, it is impossible to control the reverberation intensity immediately after droplet ejection, which affects the generation state of satellites (micro droplets).

  The above two problems are particularly problematic when the droplet discharge is controlled by switching the drive waveform, that is, when the discharge amount of the liquid is controlled by discharging droplets having different droplet diameters. This is because, in a droplet ejection head that performs droplet diameter modulation, it is necessary to generate a large droplet ejection waveform and a small droplet ejection waveform by the same waveform generation circuit, so the degree of freedom in designing the drive waveform is further reduced. As a result, the above two problems become more prominent, and it becomes very difficult to obtain a large droplet size modulation range and high ejection stability.

Furthermore, a method of taking measures against reverberation using a rectangular drive waveform having a plurality of voltage ranges has been proposed (see, for example, Patent Document 6). However, droplet size modulation cannot be performed at the same time.
JP 2002-19104 (FIG. 10, pages 3-4) Japanese Patent No. 1469531 (FIG. 5, pages 3-4) JP 2001-18388 A (FIG. 1, pages 2-3) JP 2001-334659 A (FIG. 3, pages 5-7) Japanese Patent No. 3249719 (FIG. 1, pages 4 to 5) JP 59-176060 (FIG. 4, pages 2-5)

  In consideration of the above-described facts, an object of the present invention is to provide a droplet discharge head driving method and a droplet discharge apparatus that are inexpensive and compatible with a wide range of droplet diameters.

  The droplet discharge head drive method according to claim 1 is a droplet discharge head drive method using a rectangular drive waveform having a voltage level of 3 or more, and a pressure chamber for pressurizing liquid to discharge droplets Pressure generating means that is driven by the rectangular driving waveform and expands or compresses the pressure chamber, and the rectangular driving waveform expands the pressure chamber, and a first voltage changing process of the first voltage changing process. A second voltage change process that further expands the pressure chamber after a time of approximately ½ of a natural period of a pressure wave generated later in the pressure chamber; and the natural period after the second voltage change process And a third voltage change process in which the pressure chamber is compressed and the droplet is ejected after about half of the time elapses.

  In the invention with the above configuration, it is possible to suppress the amount of meniscus pull-in before discharging the droplet, so that the volume of the discharged droplet is excessively reduced, or the droplet pulls the thread long, so-called It is possible to provide a droplet discharge head driving method that is inexpensive and has a simple configuration while avoiding droplet stringing.

  The droplet discharge head driving method according to claim 2 is a droplet discharge head driving method for discharging a plurality of types of droplets having different volumes with a rectangular drive waveform having a voltage level of 3 or more. A pressure chamber for pressurizing the liquid and pressure generating means driven by the rectangular drive waveform to expand or compress the pressure chamber, and the rectangular drive waveform when ejecting a large volume droplet is A first voltage change process for expanding the pressure chamber, and a further expansion of the pressure chamber after a time of approximately half of the natural period of the pressure wave generated in the pressure chamber after the first voltage change process. A second voltage change process that causes the pressure chamber to be compressed and the droplets ejected after a time of approximately half of the natural period has elapsed after the second voltage change process; Special features It is a sign.

  In the invention of the above configuration, in the droplet diameter modulation method in which the dot diameter by landing is variable by changing the volume of the droplet, when discharging a large volume of droplet, the amount of meniscus pull-in is suppressed before discharging. Therefore, it is possible to provide a droplet discharge head driving method that is inexpensive and has a simple configuration while avoiding a situation in which the volume of the discharged droplet is reduced.

  4. The method of driving a droplet discharge head according to claim 3, wherein the pressure chamber is replaced after the second voltage change process and a time of approximately ½ of the natural period has elapsed after the second voltage change process. And a fourth voltage for further compressing the pressure chamber after approximately half the time of the natural period has elapsed after the third voltage change process. And a change process.

  In the invention with the above configuration, by adding an antiphase waveform after the third voltage change process for ejecting droplets, the reverberation associated with droplet ejection can be canceled and effective reverberation control becomes possible. .

  The droplet discharge head driving method according to claim 4 is characterized in that the voltage level is 3.

  In the invention with the above configuration, by setting the voltage level to 3, the cost of the drive circuit can be reduced as compared with the case where the voltage level is 4 or more.

  The droplet discharge head driving method according to claim 5 is characterized in that the time required for voltage change is 1/5 or less of the natural period.

  In the invention with the above configuration, the rise / fall time of the drive waveform is set to 1/5 or less of the natural period, thereby coexisting with the drive waveform having a steep rise / fall used for discharging small-diameter droplets. And a wide range of droplet size modulation is possible.

  The droplet discharge head driving method according to claim 6 is characterized in that the natural period is between 5 and 20 μs.

  In the invention configured as described above, the natural period suitable for the piezoelectric ink jet recording head can be obtained.

  According to a seventh aspect of the present invention, the liquid droplet ejection apparatus uses the driving method according to the first to sixth aspects.

  In the invention with the above-described configuration, it is possible to provide a droplet discharge device that is inexpensive and compatible with a wide range of droplet diameters.

  Since the present invention has the above-described configuration, a droplet discharge head driving method and a droplet discharge device that are inexpensive and compatible with a wide range of droplet diameters can be obtained.

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

  FIG. 1A shows a drive waveform, where the vertical axis represents voltage, the horizontal axis represents time, Tc represents the natural period of the pressure chamber, and tr represents the rise / fall time of the drive waveform. In the present embodiment, the rise time and the fall time are set to be the same, but may be set to different times.

  As shown in FIG. 1B, the head 10 is provided with a pressure chamber 12, and when the vibration plate 14 forming the wall of the pressure chamber 12 expands / compresses the pressure chamber 12, the ink 18 inside the pressure chamber 12 is ejected from the nozzle. 24 is ejected as ink droplets 22. The piezoelectric element 16 as pressure generating means provided on the vibration plate 14 is deformed by an applied voltage pattern (drive waveform) as shown in FIG. 1A, and vibrates as shown in FIGS. 1B to 1E. The plate 14 is moved to compress / expand the pressure chamber 12.

  FIG. 1A shows an example of a pulse applied to the piezoelectric element 16, where the vertical axis represents voltage and the horizontal axis represents time. In this case, the pulse is a rectangular wave, the voltage has only three values of V0 to V2, and the drive circuit may have a simple configuration, so that the cost can be reduced. In this embodiment, V0 = 0V is set, but the voltage level to be used does not necessarily include 0V. Further, in the present embodiment, all of V0 to V2 are set to positive voltages, but negative voltages may be included.

  First, in the drive waveform of FIG. 1A, the meniscus 20 is pulled in by the first voltage change process P1 and the second voltage change process P2 as shown in FIG. 1C → FIG. 1D.

  At this time, since a time interval of ½ of the natural period Tc is provided between P1 and P2, the pressure waves generated in both voltage change processes cancel each other, so that the amount of the meniscus 20 drawn is It decreases as shown in FIG. This prevents the drop volume from being reduced due to the excessive pulling of the meniscus 20 and enables the ink drop 22 having a sufficient drop volume to be ejected.

  The ejection of the ink droplet 22 shown in FIG. 1E is performed by the third voltage change process P3. At this time, since a time interval of ½ of the natural period Tc is provided between the second voltage change process P2 and the third voltage change process P3, the pressure waves generated in both voltage change processes overlap, and the meniscus Contrary to the pull-in of 20, it is possible to generate a pressure wave having a sufficient strength during discharge.

  At this time, the natural period Tc is about 5 to 20 μs, and by setting the rise / fall time tr to 1/5 or less of Tc, it is possible to coexist with the waveform for small droplet discharge, and a wide range of droplet diameters. Modulation can be realized.

  FIG. 2 shows the structure and driving waveform of a droplet discharge head according to the second embodiment of the present invention.

  FIG. 2A shows a drive waveform, where the vertical axis represents voltage, the horizontal axis represents time, Tc represents the natural period of the pressure chamber, and tr represents the rise / fall time of the drive waveform.

  Also in the drive waveform of FIG. 2A, the meniscus 20 is pulled in by the first voltage change process P1 and the second voltage change process P2 as shown in FIG. 2C → FIG. 2D.

  At this time, since a time interval of ½ of the natural period Tc is provided between P1 and P2, the pressure waves generated in both voltage change processes cancel each other, so that the amount of the meniscus 20 drawn is It decreases as shown in FIG. This is the same as in the first embodiment in that the drop volume reduction caused by excessive drawing of the meniscus 20 is prevented, and the ink drop 22 having a sufficient drop volume can be ejected.

  The ejection of the ink droplet 22 shown in FIG. 2E is performed by the third voltage change process P3. At this time, since a time interval of ½ of the natural period Tc is provided between the second voltage change process P2 and the third voltage change process P3, the pressure waves generated in both voltage change processes overlap, and the meniscus Contrary to the pull-in of 20, it is possible to generate a pressure wave having a sufficient strength during discharge.

  Thereafter, after the time Tc / 2 has elapsed from the third voltage change process P3, by providing the fourth voltage change process P4, pressure waves generated in both voltage change processes cancel each other, thereby remaining after discharge. As shown in FIG. 2F, it is possible to effectively suppress reverberation. That is, as in the case where the pull-in of the meniscus 20 is suppressed, since a time interval of 1/2 of the natural period Tc is provided in P3 and P4, reverberation is also effective because pressure waves generated in both processes cancel each other. Can be suppressed.

  At this time, the natural period Tc is about 5 to 20 μs, and by setting the rise / fall time tr to 1/5 or less of Tc, it is possible to coexist with the waveform for small droplet discharge, and a wide range of droplet diameters. The characteristics of the first embodiment that can realize the modulation are the same in this embodiment.

  FIGS. 3 and 4 show a driving waveform and a meniscus vibration speed change for each droplet diameter of the droplet discharge head according to the second embodiment of the present invention.

  The left side of FIG. 3A represents a driving waveform for large droplet ejection, the vertical axis represents voltage, and the horizontal axis represents time. On the right is the time variation of the liquid velocity in the vicinity of the meniscus 20.

  Similarly, FIG. 3 (b) shows a drive waveform for medium droplet ejection, FIG. 3 (c) shows a drive waveform for small droplet ejection, and FIG. 3 (d) shows stirring of the ink in the nozzle to increase the ink at the meniscus portion. It is a preliminary waveform applied when a droplet is not ejected from a nozzle in order to reduce the viscosity phenomenon.

  FIG. 4 shows voltage changes with time in large drops, medium drops, small drops, and preliminary waveforms.

  A cell indicated by shading is a timing at which the ink droplet 22 is ejected, and corresponds to a peak of the graph on the right side of FIG.

  5 and 6 show a driving waveform for each droplet diameter of a droplet discharge head using a conventional binary rectangular wave and a meniscus vibration speed change.

  The left side of FIG. 5A represents a driving waveform of a large droplet, the vertical axis represents voltage, and the horizontal axis represents time. On the right is the time change of the liquid velocity in the vicinity of the meniscus.

  Similarly, FIG. 5B shows a driving waveform for discharging a medium droplet, FIG. 3C shows a driving waveform for discharging a small droplet, and FIG. 3D shows a preliminary waveform.

  FIG. 6 shows voltage changes with time in large drops, medium drops, small drops, and preliminary waveforms.

  The cells indicated by shading are the timing at which ink droplets are ejected, and correspond to the peaks in the graph on the right side of FIG.

  As is particularly noticeable in the comparison between FIG. 3 and FIG. 5, the second embodiment of the present invention clearly shows the effect of suppressing reverberation after ejecting large drops and medium drops.

  For example, in FIG. 3B, the reverberation is reduced after about 35 μs from the discharge (14.5 μs), whereas in FIG. 5B, the reverberation is not yet stopped even after 60 μs from the discharge (7 μs). This is because the rectangular drive waveform of the present invention has a higher degree of freedom in waveform design of the reverberation suppressing unit than that of the conventional rectangular wave, and appropriate reverberation suppression can be realized. For this reason, compared with a driving waveform using a conventional rectangular wave, in the present invention, it is possible to shorten the discharge interval and increase the printing speed by high-frequency driving.

  At this time, the natural period Tc is about 5 to 20 μs, and the rise / fall time of the drive waveform is set to 1/5 or less of Tc, so that it can coexist with the droplet ejection waveform, and a wide range. It is possible to realize droplet diameter modulation.

  That is, in the drive waveform at the time of discharging a large droplet, as described above, a time interval of 1/2 of the natural period Tc is provided between the first falling process and the second falling process. As the pressure waves generated in the changing process cancel each other, the meniscus pull-in amount decreases as shown in FIG. This prevents the drop volume from being reduced due to excessive meniscus pull-in, and allows ink drops having a sufficient drop volume to be ejected.

  That is, in the present invention, since the voltage level is 3 or more, the fall process can be set in two stages as described above, and the pressure chamber can be expanded in two stages. As a result, the amount of meniscus drawing is reduced, and large droplets can be ejected.

  On the other hand, as shown in FIG. 3C, by performing the falling process (expansion of the pressure chamber) without dividing it into two stages, the liquid volume can be reduced and small droplets can be ejected.

  In addition, when an ink droplet is ejected in the large droplet ejection waveform (rising process), a time interval of 1/2 of the natural period Tc is provided between the ejecting process and the voltage dropping process. Pressure waves overlap, and a pressure wave with sufficient strength can be generated at the time of ejection, contrary to when the meniscus is drawn. This makes it possible to eject ink droplets having a larger droplet volume.

  On the other hand, as shown in FIGS. 3 (b) and 3 (c), the "pulling" is performed by starting the falling process (expansion of the pressure chamber) almost simultaneously with the end of the starting process (compression of the pressure chamber), Droplets having a small liquid volume can also be ejected.

  Even in this case, after the time Tc / 2 has elapsed from the end of the start-up process (compression of the pressure chamber), by providing the second start-up process, the pressure waves generated in both voltage change processes cancel each other out. This makes it possible to effectively suppress reverberation remaining after ejection.

  That is, the reverberation can be effectively suppressed because the pressure waves generated in both processes cancel each other, as in the case where the meniscus pull-in is suppressed.

  As described above, a wide droplet diameter modulation range can be realized by a rectangular driving waveform having a voltage level of 3 or more used in the present invention.

  Furthermore, as disclosed in Japanese Patent Application Laid-Open No. 2003-165220, it is desirable to set the rise / fall time as small as possible in the drive waveform for droplet ejection. That is, the meniscus is once drawn to the pressure chamber side by a voltage change process that compresses and expands the pressure chamber at a rapid speed, and then a thin liquid column is formed in the center of the nozzle, and further, the liquid column is divided early, This is because droplets smaller than the nozzle diameter can be discharged. In the present invention, a wider range of droplet diameter modulation can be realized by using a rectangular driving waveform having the voltage level of 3 or more.

  FIG. 7 and FIG. 8 show a driving waveform for each droplet diameter of a droplet discharge head using a conventional analog waveform and changes in meniscus vibration speed.

  The left side of FIG. 7A represents a driving waveform of a large droplet, the vertical axis represents voltage, and the horizontal axis represents time. On the right is the time change of the liquid velocity in the vicinity of the meniscus.

  Similarly, FIG. 7B shows a driving waveform for discharging a medium droplet, FIG. 3C shows a driving waveform for discharging a small droplet, and FIG. 3D shows a preliminary waveform.

  FIG. 8 shows voltage changes with time in large drops, medium drops, small drops, and preliminary waveforms.

  The cells indicated by shading are timings at which ink droplets are ejected, and correspond to the peaks in the graph on the right side of FIG.

  The conventional driving with analog waveforms shown in FIGS. 7 and 8 has a drawback that the cost of the driving circuit is higher than that of the present invention due to the use of complicated driving waveforms.

  In the first and second embodiments of the present invention, the ink jet recording head that discharges ink droplets has been described as an example. However, the present invention is not limited to this. The present invention can be applied to various uses for discharging / recording.

  Moreover, although the piezoelectric element was mentioned as an example about the said pressure generation means, this invention is not specifically limited to this, You may use a shape memory alloy actuator etc.

  Further, the structure of the head and the like are not limited to the embodiment described as an example, and for example, a side shooter type head may be used.

It is a figure which shows the structure and drive waveform of the droplet discharge head which concern on the 1st form of this invention. It is a figure which shows the structure and drive waveform of the droplet discharge head which concern on the 2nd form of this invention. It is a figure which shows the drive waveform and reverberation of the droplet discharge head which concern on the 2nd form of this invention. It is a table | surface showing the drive waveform of the droplet discharge head which concerns on the 2nd form of this invention. It is a figure which shows the drive waveform and reverberation of the droplet discharge head by the conventional rectangular wave. It is a table | surface showing the drive waveform of the droplet discharge head by the conventional rectangular wave. It is a figure which shows the drive waveform and reverberation of the droplet discharge head by the conventional analog waveform. It is a table | surface showing the drive waveform of the droplet discharge head by the conventional analog waveform.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Head 12 Pressure chamber 14 Diaphragm 16 Piezoelectric element 18 Ink 20 Meniscus 22 Ink droplet 24 Nozzle

Claims (7)

A method of driving a droplet discharge head using a rectangular drive waveform having a voltage level of 3 or more,
A pressure chamber for pressurizing the liquid in order to eject droplets;
Pressure generating means driven by the rectangular drive waveform to expand or compress the pressure chamber;
With
The rectangular drive waveform is
A first voltage change process for expanding the pressure chamber;
A second voltage change process for further expanding the pressure chamber after a time of approximately ½ of a natural period of a pressure wave generated in the pressure chamber after the first voltage change process;
A third voltage change process for compressing the pressure chamber and discharging the droplets after a time of approximately half of the natural period has elapsed after the second voltage change process;
A driving method characterized by comprising:
A method of driving a droplet discharge head for discharging a plurality of types of droplets having different volumes with a rectangular drive waveform having a voltage level of 3 or more,
A pressure chamber for pressurizing the liquid in order to eject droplets;
Pressure generating means driven by the rectangular drive waveform to expand or compress the pressure chamber;
With
The rectangular driving waveform when ejecting a large volume droplet is
A first voltage change process for expanding the pressure chamber;
A second voltage change process for further expanding the pressure chamber after a time of approximately ½ of a natural period of a pressure wave generated in the pressure chamber after the first voltage change process;
A third voltage change process for compressing the pressure chamber and discharging the droplets after a time of approximately half of the natural period has elapsed after the second voltage change process;
A driving method characterized by comprising:
Instead of the third voltage change process,
A third voltage change process for compressing the pressure chamber and discharging the droplets after a time of approximately half of the natural period has elapsed after the second voltage change process;
A fourth voltage change process for further compressing the pressure chamber after a time of approximately half of the natural period has elapsed after the third voltage change process;
The method for driving a droplet discharge head according to claim 1, wherein:
4. The method of driving a droplet discharge head according to claim 1, wherein the voltage level is 3.
5. The method for driving a droplet discharge head according to claim 1, wherein a time required for voltage change is 1/5 or less of the natural period.
6. The method for driving a droplet discharge head according to claim 1, wherein the natural period is between 5 and 20 [mu] s.
A liquid droplet ejection apparatus using the driving method according to claim 1.

Images