JP2000094669A - Ink-jet type recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a discharge performance for ink drops stably and at the same time improve a driving frequency. SOLUTION: A first driving signal S1 rapidly changes a volume of a pressure generation chamber thereby discharging ink drops, while a second driving signal S2 changes the volume of the pressure generation chamber by a degree not to discharge ink drops. At a time point when a residual vibration of a meniscus after the ink drop is discharged by the first driving signal S1 reverses towards a nozzle opening, the second driving signal S2 is output. Accordingly, the residual vibration of the meniscus is braked at a discharge time of ink drops and a clog is prevented at a non-discharge time of ink drops.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording apparatus having a recording head for ejecting ink droplets by changing the volume of a pressure generating chamber communicating with a reservoir and a nozzle opening by a piezoelectric vibrator, and more particularly to recording. The present invention relates to a head driving technique.

[0002]

2. Description of the Related Art A recording head which discharges ink droplets from a nozzle opening by applying a trapezoidal driving signal to a piezoelectric vibrator to reduce the volume of a pressure generating chamber communicating with a reservoir and a nozzle opening is discharged from a meniscus after discharging the ink droplet. Has the disadvantage that minute ink droplets unrelated to the print data are generated. In order to solve such a problem, as shown in JP-A-9-5236 and JP-A-10-81012, a trapezoidal vibration suppression signal in the opposite direction to the drive signal is applied to generate pressure. It has been practiced to change the volume of the chamber so as not to eject ink droplets to forcibly attenuate the vibration of the meniscus. For this reason, two types of signals, a drive signal and a vibration damping signal, are required within one printing cycle, so that one printing cycle becomes longer, and there is a disadvantage that high-speed driving is difficult. In addition, when ink having a high drying speed is used in order to improve print quality, there is a problem that ink near the nozzle opening tends to increase in viscosity, which causes inconvenience in ejection of ink droplets. In order to solve such a problem, as disclosed in JP-A-9-201960 and JP-A-10-81012, it is also possible to apply a signal for causing the meniscus to minutely vibrate along with the drive signal. Is being done.

[0003]

According to this, although it is possible to stably eject ink droplets, in addition to a drive signal for ejecting ink droplets within one printing cycle, a flattening of meniscus, Since it is necessary to secure a time for applying a drive signal for preventing clogging, there is a problem that one printing cycle is lengthened and a drive frequency is reduced. The present invention has been made in view of such a problem, and a purpose thereof is to stably eject ink droplets,
An object of the present invention is to provide an ink jet recording apparatus capable of high-speed driving.

[0004]

According to the present invention, there is provided a pressure generating chamber which communicates with a reservoir through a nozzle opening and an ink supply port to expand the pressure generating chamber. An ink jet recording head comprising a contracting piezoelectric vibrator; a first drive signal for rapidly changing the volume of the pressure generating chamber to discharge ink droplets;
A second drive signal for changing the volume of the pressure generating chamber so as not to eject ink droplets;
At the time when the residual vibration of the meniscus after the ink droplet is ejected by the drive signal of the above is inverted to the nozzle opening side, a second drive signal is output to dampen the residual vibration of the meniscus, and at the time of non-ink droplet ejection A drive signal generating means for outputting a second drive signal to prevent clogging is provided.

[0005]

The second drive signal serves both as a signal for suppressing the residual vibration of the meniscus after ink droplet ejection and a signal for eliminating the clogging by causing the meniscus to vibrate minutely.

[0006]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a first embodiment of the present invention. FIG. 1 is a block diagram showing a first embodiment of the present invention. A drive cycle signal generating means 1 generates a drive cycle signal based on print mode information output from a host (not shown), 2, and controls the carriage drive motor 5 connected to the carriage 4 via the transmission means 3 based on the print mode information from the host.

[0007] In this embodiment, the recording head 6
As shown in FIG. 2, the pressure generating chamber 20 and the ink supply port 2
1 and a nozzle plate 2 having a nozzle opening 24 formed on one surface of a flow path forming substrate 23 forming a reservoir 22.
5, a flow path unit 27 whose other surface is sealed by an elastic plate 26 that is elastically deformable, and a piezoelectric vibrator 28 that extends in the axial direction to displace the elastic plate 26.

As shown in FIG. 3, the drive signal generating means 7 includes a first drive signal S1 for discharging ink droplets and a second drive signal S2 for suppressing meniscus vibration and preventing clogging of nozzle openings. Is configured to be output. The first drive signal S1 includes an expansion signal for expanding the pressure generating chamber 20 to an expansion state before the ink droplet ejection, a holding signal for maintaining the expansion state, and a contraction for completing the ink droplet ejection from the expansion state. And a contraction signal for reducing the volume of the pressure generating chamber 20 at a change rate suitable for discharging the ink droplets to the state.

The second drive signal S2 is composed of an expansion signal ', a holding signal', and a contraction signal 'to such an extent that ink droplets are not ejected. The expansion signal 'and the contraction signal' are set such that their durations t1 and t3 are equal to or longer than the natural period Ta of the piezoelectric vibrator 28, and preferably substantially equal to the Helmholtz resonance period Tc of the pressure generating chamber 20. Have been. By setting the expansion signal 'and the contraction signal' as short as possible in this way, 1
Although the printing cycle T0 can be shortened, it is desirable that the printing cycle T0 be made equal to the Helmholtz resonance cycle Tc in order to prevent unnecessary oscillation of the meniscus.

Further, in order to more reliably prevent the meniscus from unnecessarily vibrating due to the second drive signal S2, the holding signal is changed to a Helmholtz resonance so that the vibration of the meniscus caused by the expansion signal and the contraction signal cancels out. Period Tc
Is desirably set to be substantially the same as 1/2.

Further, since the second drive signal S2 suppresses the residual vibration of the meniscus after the ink droplet has been ejected by the first drive signal S1, the vibration of the meniscus caused by the ejection of the ink droplet once enters the nozzle opening. It is desirable that the output be performed in accordance with the timing at which the ink is drawn in and then inverted to the nozzle opening side. For this purpose, the total time of the duration of the contraction signal of the first drive signal S1 and the time difference between the end of the first drive signal and the start of the application of the second drive signal (time T1 in FIG. 3) is Helmholtz resonance period T
It is desirable to adjust the time T1 so as to be substantially the same as c.

As is well known, the Helmholtz resonance period Tc of the pressure generating chamber 20 is Ln, the inertance of the nozzle opening 24 is Ln, the inertance of the ink supply port 21 is Li, the compliance of the elastic plate 26 is Cv, and the compliance of the ink is Cink. Tc = 2π√ [(CV + Cin
k) × Ln × Li] / (Ln + Li).

These first and second dynamic signals are used to switch the discharge constant of the charge / discharge circuit by a switching circuit,
Further, it can be easily generated by using a programmable signal generating means for generating a signal based on waveform data stored in a ROM or drive signal information from a host.

The latch signal generating means 8 selectively latches the second drive signal a plurality of times immediately before switching from the non-printing state to the printing state, and when print data exists,
After the first drive signal S1 is latched and the first drive signal is output, the point at which the vibration of the meniscus generated after the ink droplet ejection is directed to the nozzle opening (after the lapse of time T1)
Outputs a latch signal for latching the second drive signal S2 to the switching means 9 described later. Head driving means 10
The printing corresponding to the switching means 9 for controlling the ejection of ink droplets from the individual nozzle openings 24 based on a pit map data generated by a printing signal from a host (not shown) stored in the printing buffer 11. The data is latched by a latch signal, and the individual switching elements are turned on and off.

In this embodiment, when the recording head 6 is exposed from capping means (not shown) and is in a non-printing state, the driving signal generating means 7 is provided at a predetermined cycle.
Is selectively latched by the latch signal generating means 8 and applied to the piezoelectric vibrator 28. Thereby, the pressure generating chamber 20 slightly expands and contracts,
The meniscus of the nozzle opening 24 is drawn into the pressure generating chamber 20, and starts to vibrate at such an amplitude that ink droplets are not ejected. Thereby, the ink thickened near the nozzle opening is
The ink is replaced with ink in the pressure generating chamber 20 having a relatively low viscosity to prevent clogging.

Further, when print data is output from the host in a state where the print pause state is continued, the second drive signal S2 of the drive signal generating means 7 is selectively latched by the latch signal generating means 8. A preparatory operation is performed to replace the ink that has increased in viscosity in the vicinity of the nozzle opening with ink in the pressure generating chamber 20 to eliminate clogging.

When print data exists (FIG. 4)
(I)), the first drive signal S1 is latched and the expansion signal causes the piezoelectric vibrator 28 to contract and the pressure generation chamber 21
Expands, filling the pressure generating chamber 20 with ink from the reservoir 22 and drawing the meniscus of the nozzle opening 24 largely into the pressure generating chamber 20. When the expansion signal reaches a predetermined voltage, it is maintained for a certain period of time by the holding signal, and the volume of the pressure generating chamber 20 is kept constant. As a result, the meniscus drawn into the pressure generating chamber 20 starts oscillating, and is inverted to the nozzle opening side after a lapse of a predetermined time.

At this point, the contraction signal is applied, the piezoelectric vibrator 28 expands, and the volume of the pressure generating chamber 20 is reduced.
As a result, the ink in the pressure generating chamber 20 is pressurized, and an ink droplet is ejected from the nozzle opening 24.

After the ejection of the ink droplets, the meniscus starts oscillating again due to inertia. When the meniscus is inverted to the nozzle opening side, the second drive signal S2 is latched. As a result, the pressure generating chamber 20 slightly expands, and the meniscus of the nozzle opening is drawn into the pressure generating chamber 20, and the residual vibration is forcibly stopped.

In this printing cycle, since the ink droplets are ejected, the thickened ink in the vicinity of the nozzle opening is ejected as ink droplets and replaced by the ink in the pressure generating chamber 20. Does not cause clogging.

If the print data still exists (FIG. 4 (II)), the first drive signal S1 and the second drive signal S2 are latched and applied to the piezoelectric vibrator 28 as described above. You.

On the other hand, when there is no print data (FIG. 4 (III)), only the second drive signal S2 is latched, so that the pressure generating chamber 20 slightly expands and contracts. Immediately before that, no ink droplets are ejected, so that the meniscus in the nozzle opening 24 is in a stationary state.
And starts oscillating with an amplitude that does not discharge ink droplets. Thus, the ink that has increased in viscosity in the vicinity of the nozzle opening is replaced with ink in the pressure generating chamber 20 having a relatively low viscosity, thereby preventing clogging.

FIG. 5 shows an embodiment in which medium dots and small dots are formed, and a third method for forming small dots following the first and second drive signals S2 and S2. The drive signal S3 is added during the printing cycle, and one printing cycle T0 'is formed by these three types of signals S1, S2, and S3.

The third drive signal is an expansion signal for expanding the pressure generating chamber 20 to an expanded state at a stage before ink droplet ejection.
"And a holding signal for maintaining the expanded state" and a contraction signal for reducing the volume of the pressure generating chamber 20 at a rate suitable for discharging minute ink droplets from the expanded state to the contracted state where ink droplet discharge is completed. ".

In this embodiment, when print data is output from the host while the pause state is continued, the second drive signal S2 of the drive signal generator 7 is selectively latched by the latch signal generator 8. Then, the voltage is applied to the piezoelectric vibrator 28. Thereby, the pressure generation chamber 20 is slightly expanded,
Because of the contraction, the meniscus of the nozzle opening 24 is drawn into the pressure generating chamber 20, and starts to vibrate with an amplitude that does not discharge the ink droplet. Thus, the ink that has increased in viscosity in the vicinity of the nozzle opening is replaced with the ink in the pressure generating chamber 20 having a relatively low viscosity, thereby preventing clogging.

If print data exists and a medium dot is to be formed (FIG. 6I), the drive signal S1 is latched and ink droplets are ejected in the same manner as described above.

After the ink droplet is ejected, when it is inverted to the nozzle opening side, the second drive signal S 2 is latched, and the residual vibration is forcibly stopped by the change in the volume of the pressure generating chamber 20. In this cycle, since the ink droplets are ejected, the thickened ink near the nozzle opening is discharged from the nozzle opening as ink droplets, and the pressure generating chamber 20 having a relatively low viscosity is used.
No clogging occurs because the ink has been replaced with the same ink.

When print data exists and a small dot is to be formed (FIG. 6 (II)), the third drive signal S3 is latched, and the expansion signal "causes the piezoelectric vibrator 28 to contract. The pressure generating chamber 21 expands, filling the pressure generating chamber 20 with ink from the reservoir 22 and drawing the meniscus of the nozzle opening 24 into the pressure generating chamber 20.

When the expansion signal "reaches a predetermined voltage, it is maintained for a certain period of time by the holding signal", and the volume of the pressure generating chamber 20 is maintained constant. Thereby, the pressure generating chamber 20
The meniscus drawn in starts to vibrate, and after a predetermined time elapses, reverses to the nozzle opening side.

At this point, the contraction signal "" is applied, the piezoelectric vibrator 28 expands, and minute ink droplets are ejected from the nozzle opening 24.

Of course, the oscillation amplitude of the meniscus due to the ejection of minute ink droplets is small and flattened by the start of the next printing cycle. In this printing cycle, since the ink droplets are ejected, the vicinity of the nozzle opening is reduced. The thickened ink is ejected as ink droplets, and is replaced by the pressure generating chamber 20.
The nozzle opening 24 is not clogged because the ink is replaced by the ink of the formula (1).

On the other hand, when there is no print data (FIG. 6 (III)), only the second drive signal S2 is latched, so that the pressure generating chamber 20 slightly expands and contracts. Immediately before that, no ink droplets are ejected, so that the meniscus in the nozzle opening 24 is in a stationary state.
And starts oscillating with an amplitude that does not discharge ink droplets. Thus, the ink that has increased in viscosity in the vicinity of the nozzle opening is replaced with ink in the pressure generating chamber 20 having a relatively low viscosity, thereby preventing clogging.

In this embodiment, both medium dots and small dots can be formed within the same printing cycle. That is, when forming relatively large dots by forming medium dots and small dots at the same point, the drive signal S
There is a method of latching all of 1, S2 and S3 by the latch signal generating means 8 (FIG. 7 (I)) and a method of latching the drive signal S1 and the drive signal S3 (FIG. 7 (II)).

In the former method (FIG. 7 (I)), the first drive signal S1 is latched, ink droplets are ejected in the same manner as described above to form a medium dot, and the meniscus opens the nozzle opening in the same manner as described above. At this point, the second drive signal S2 is latched, and the residual vibration is rapidly attenuated. This allows
When the third drive signal S3 is latched, the meniscus is stationary at almost the same position as the position suitable for ink droplet ejection, so that the meniscus is formed by ink droplets ejected by the third drive signal S3. The small dots are almost the same size as the small dots formed by applying the third drive signal S3 alone within one printing cycle. Therefore, the medium dot and the small dot are added to form a large dot.

On the other hand, the second method (FIG. 7 (II))
Since the second drive signal S2 is not latched after the ink droplet is ejected by the first drive signal S1, the meniscus continues the residual vibration, and the third drive signal S3 is latched in this state. Since the meniscus at this point protrudes from the nozzle opening surface by an amount corresponding to the displacement α in FIG. 7, the ink amount of the ink droplet ejected by the third drive signal S3 is independently driven within one printing cycle. Is increased by β as compared with the case where Therefore, the formed dots are small dots plus the increment β, so that an oversized dot can be formed as a result.

As a result, the dot formed by the second method is an extra large dot composed of the ink amount obtained by adding the increment β to the sum of the medium dot and the small dot, so that the adjustment range of the dot size is expanded. As a result, printing with high gradation can be performed.

In these two methods, a printer driver that is more suitable for the intended printing condition may be selected.
If there is no print data, only the second drive signal S2 is latched in the same manner as in the previous embodiment, and the thickened ink near the nozzle opening is replaced with the ink in the pressure generating chamber 20 having a relatively low viscosity. Replace to prevent clogging.

Also in this embodiment, the second drive signal S
2 is a signal for suppressing the residual vibration of the meniscus after ink droplet ejection and a signal for eliminating the clogging by vibrating the meniscus minutely. T0 'can be shortened.

In the above-described embodiment, an example has been described in which the recording head uses the piezoelectric vibrator that is displaced in the axial direction as the actuator. However, as shown in FIG. The pressure generating chamber 34 communicates with the reservoir 31 and communicates with the nozzle opening 33 through the nozzle communication hole 32.
The same effect can be achieved by applying the present invention to a recording head provided with a piezoelectric vibrator 36 which is partially bent with an elastic plate 35 and which is flexibly displaced.

[0040]

As described above, in the present invention,
At the time of ink droplet ejection, when the residual vibration of the meniscus after ejecting the ink droplet by the first drive signal is inverted to the nozzle opening side, a second drive signal is output to suppress the residual vibration of the meniscus, and A drive signal generating means for outputting a second drive signal during non-ink droplet ejection to prevent clogging is provided, so that the second drive signal suppresses residual vibration of the meniscus after ink droplet ejection and reduces Vibration can be performed to eliminate clogging. Compared to a case where a signal for suppressing residual vibration and a signal for eliminating clogging are required in addition to a signal for discharging ink droplets, one signal is used. The printing cycle can be shortened, and the driving frequency can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of an apparatus showing one embodiment of the present invention.

FIG. 2 is a cross-sectional view showing one embodiment of an ink jet recording head.

FIG. 3 is a waveform chart showing an example of a drive signal.

FIG. 4 is a timing chart showing an operation at the time of printing based on the above driving signal.

FIG. 5 is a waveform chart showing another embodiment of a drive signal.

FIG. 6 is a timing chart showing an operation at the time of printing according to the above driving signal.

FIG. 7 is a diagram illustrating a relationship between a driving signal and a meniscus displacement indicating another driving method of the present invention.

FIG. 8 is a diagram showing an embodiment of another type of recording head to which the present invention can be applied.

[Explanation of symbols]

 Reference Signs List 6 recording head 9 switching means 20 pressure generating chamber 21 ink supply port 22 reservoir 23 flow path forming substrate 24 nozzle opening 25 nozzle plate 28 piezoelectric vibrator S1 first drive signal S2 second drive signal

Claims (10)

[Claims] 1. An ink jet recording head, comprising: a pressure generating chamber communicating with a reservoir via a nozzle opening and an ink supply port; and a piezoelectric vibrator for expanding and contracting the pressure generating chamber. A first drive signal for rapidly changing the volume of the chamber to eject ink droplets and a second drive signal for changing the volume of the pressure generating chamber to such an extent that the ink droplets are not ejected. When the residual vibration of the meniscus after the ink droplet is ejected by the first drive signal is inverted to the nozzle opening side, a second drive signal is output to dampen the residual vibration of the meniscus, and the non-ink droplet ejection An ink jet recording apparatus comprising a drive signal generating means for sometimes outputting a second drive signal to prevent clogging. 2. An ink jet type recording head which communicates with a reservoir through a nozzle opening and an ink supply port and comprises a pressure generating chamber, and a piezoelectric vibrator for expanding and contracting the pressure generating chamber. A first drive signal for rapidly changing the volume of the chamber to eject ink droplets, a second drive signal for changing the volume of the pressure generating chamber so as not to eject ink droplets, and a first drive signal And a third signal for ejecting an ink droplet having a small amount of ink, and a second signal for ejecting the ink droplet when the residual vibration of the meniscus after ejecting the ink droplet is inverted to the nozzle opening side by the first drive signal. When a driving signal is output, the residual vibration of the meniscus is damped, and when a non-ink droplet is ejected, a second driving signal is output to prevent clogging. An ink jet recording apparatus provided with a driving signal generation means to stop the output of the second drive signal. 3. The ink jet recording apparatus according to claim 1, wherein a charging time of the second drive signal is equal to or longer than a natural period Ta of the piezoelectric vibrator. 4. The ink jet recording apparatus according to claim 1, wherein the charging time of the second drive signal is substantially the same as the Helmholtz resonance period Tc of the pressure generating chamber. 5. The discharge time of the second drive signal is equal to the T time.
The ink jet recording apparatus according to claim 1, wherein the number is equal to or larger than “a”. 6. The ink jet recording apparatus according to claim 1, wherein a discharge time of the second drive signal is substantially equal to a Helmholtz resonance period Tc of the pressure generating chamber. 7. The ink jet recording according to claim 1, wherein the potential holding time of the second drive signal is substantially equal to one half of the Helmholtz resonance period Tc of the pressure generating chamber. apparatus. 8. The time from the start of discharge of the first drive signal to the start of drive of the second drive signal is substantially the same as the Helmholtz resonance period Tc of the pressure generating chamber. Alternatively, the ink jet recording apparatus according to claim 2. 9. The ink jet recording apparatus according to claim 1, wherein the second drive signal is output intermittently immediately before printing is started from the print pause state. 10. The ink jet recording apparatus according to claim 1, wherein the second drive signal is output at a constant cycle when the recording head is in a non-capping state.