JPH10157099A - Driving method for ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To widen the variable range of jetting volume by setting the time for increasing the volume at an ink containing part within a range where the jetting speed of ink droplet is maximized and minimized when the time required for recovering the volume at the ink containing part from reduced state is set at the lower and upper limit of a set range. SOLUTION: An ink chamber 25B is applied with a voltage having such a waveform as the voltage is raised abruptly, at first, to a positive level which is sustained for a predetermined time and then the voltage is dropped abruptly to a negative level which is sustained for a predetermined before being interrupted. Volume of the ink chamber 25B is increased and decreased through application of positive and negative voltages and when the time for applying a negative voltage is set shorter than a pressure propagation time, volume of ink droplet can be decreased and thereby the jetting volume can be controlled by controlling the time tar applying a negative voltage. In order to suppress fluctuation of jetting speed, the sustaining time is set between a time T2 when a first peak of jetting speed appears during a time V2 for obtaining a small volume and a time T1 when the jetting speed is lowest after the time T2 during a time V1 for obtaining a large volume.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving an ink jet head for controlling the ejection volume of ink droplets.

[0002]

2. Description of the Related Art For example, Japanese Patent Application Laid-Open No. Hei 7-241985 discloses a method of driving an ink jet head that displaces a piezoelectric member to apply pressure vibration to an ink chamber to discharge ink droplets from ink discharge ports. . According to the method of this publication, for example, when a small ink droplet flies from an ejection port, a positive voltage waveform is applied to a piezoelectric member constituting a side wall of an ink chamber via an electrode as shown in FIG. At this time, the application time of the positive voltage waveform, that is, the time during which the volume of the ink chamber is increased, is changed from the negative peak to the positive peak, as shown in FIG. Is set to the time Ta until, that is, half of the oscillation cycle.

In order to make larger ink droplets fly, as shown in FIG. 10A, the application time of the positive voltage waveform is set to be three times as long as Ta. At this time, the pressure oscillation in the ink chamber changes from a negative peak to a positive peak, then to a negative peak again, and then to a positive peak again, as shown in FIG. That is, the preliminary ejection is performed at the first positive peak such that the ink does not fly from the ink ejection port,
When the positive peak is reached again, the main ejection is performed, and the ink droplet flies from the ink chamber. Then, the ejection volume at the time of the main ejection is added to the volume by the preliminary ejection, and flies as a larger ink droplet.

[0004]

According to this publication, preliminary discharge is performed by setting the application time of the positive voltage waveform to 3 Ta, and the volume at this time is added to the volume at the time of main discharge. However, the relationship between the time during which the positive voltage is applied and the meniscus position in the ink chamber is such that the meniscus position retreats most at the time Ta after the application of the positive voltage, the meniscus position moves forward most at the time 2Ta, and at time 3Ta. The meniscus position retreats most again, and changes at time 4Ta such that the meniscus position moves forward most. Then, the preliminary ejection is performed when the meniscus position is in the most advanced state. Even if the preliminary ejection is performed within the time 3Ta, the meniscus position immediately before the main ejection is the position at the time 3Ta and the most at this time. It is in the retracted position. That is,
The meniscus position does not change significantly between the time Ta and the time 3Ta, and therefore, there is a problem that the amount of change in the ink ejection volume cannot be expected to be large.

When a small ink droplet is ejected, FIG.
When a large ink droplet is ejected, a voltage waveform shown in FIG.
The voltage waveform of (a) is applied. When the pressure values in the ink chamber immediately before ejection are compared in both cases, the longer the energization time, the greater the pressure decay. A pressure P1 as shown in FIG. 10B is obtained, but changes to a pressure P2 (P2 <P1) as shown in FIG. 10B at the time of discharging a large ink droplet, and the discharging speed at the time of discharging a large ink droplet becomes The ejection speed is smaller than the ejection speed when ejecting small ink droplets.

Accordingly, as shown in FIG. 11, in the case of a serial type ink jet head that scans the ink jet head 1 on the paper 2, if gradation printing is performed continuously, as shown in FIG. A problem arises in that a pitch shift occurs at a gradation switching position where the size of an ink droplet is changed.

To solve this problem, it is conceivable to correct the speed difference by changing the discharge timing for each gradation discharge. However, FIG. 13A shows a followable period Tb when the discharge timing is not changed. As shown in FIG. 13 (b), the maximum period Td when the ejection timing is changed is shown in FIG. 13B.
c. Therefore, as a limitation due to the correction of the ejection timing, there is a problem that the printing speed must be reduced as compared with a case where the ejection timing is not changed.

Therefore, according to the first and second aspects of the present invention, when performing gradation gradation printing by varying the ink ejection volume, the variable range of the ejection volume can be widened and the ejection speed of each ejection volume can be reduced. Provided is a method of driving an ink jet head capable of minimizing variation, minimizing pitch shift at the time of gradation change, and performing high quality printing.

[0009]

According to the first aspect of the present invention,
Increasing the volume of the ink storage unit, reducing the volume of the ink storage unit after a predetermined time elapses, and applying pressure vibration to the ink to discharge the ink droplets, and further returning the volume of the ink storage unit to the original state, In a method of driving an ink jet head that controls the ejection volume of ink droplets by changing the time required to return the volume of the ink storage unit from the reduced state to the original state, the time for increasing the volume of the ink storage unit is as follows: When the time required to return the volume of the ink storage unit from the reduced state to the original state is set to the lower limit of the setting range, the volume of the ink storage unit is reduced from the reduced state from the time when the ejection speed of the ink droplets peaks. Is set to the time range in which the ejection speed of the ink droplet becomes the minimum when the time until the state is returned to the upper limit value of the setting range.

According to a second aspect of the present invention, the volume of the ink container is increased, and after a predetermined time elapses, the volume of the ink container is reduced to apply pressure vibration to the ink, thereby discharging the ink droplets. A method for driving an ink-jet head that controls the ejection volume of ink droplets by returning the volume of the storage unit to the original state and changing the time until the volume of the ink storage unit is returned from the reduced state to the original state. The time for increasing the volume of the ink container is the time for returning the volume of the ink storage unit from the reduced state to the original state, the time for obtaining the minimum ink droplet, and the time Ta for half the pressure oscillation cycle applied to the ink. When the time Ta is varied, the range is approximately 1.5 to 2 times the time Ta, or the range is approximately 1.5 Ta + n to 2Ta + n (where n is 2T).
a × integer).

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an exploded perspective view, partially cut away, showing the configuration of an ink jet head. Electromechanical conversion means 2 is provided on one side of a substrate 11 made of a ceramic material.
The rectangular piezoelectric members 12 and 13 are bonded and fixed with an epoxy resin adhesive. In each of the piezoelectric members 12 and 13, a plurality of long grooves 14 having the same width, the same depth, and the same length are formed in parallel at predetermined intervals by cutting. Electrodes 15,... Are provided on the side and bottom surfaces of the long grooves 14,.
Are formed on the rear upper surface of the piezoelectric member 3 from the rear end of each long groove 14,.
These electrodes 15, ..., 16, ... are formed by electroless nickel plating.

A PC board 17 is bonded and fixed to the other side of the substrate 11, and a drive IC 18 having a built-in drive circuit is mounted on the PC board 17, and the drive IC 18
The conductive patterns 19 connected to 18 are formed.
Each of the conductive patterns 19,... And each of the extraction electrodes 16,.

A top plate 21 made of a ceramic material is bonded and fixed on the piezoelectric member 13 with an epoxy resin adhesive. Further, a nozzle plate 23 provided with a plurality of ink discharge ports 22,... At the tips of the piezoelectric members 12, 13 is bonded and fixed with an adhesive. Thereby, each said long groove 1
4,... Are covered with the top plate 21 and their ends are closed with the nozzle plate 23 to form ink chambers which also serve as ink storage sections. A common ink chamber 24 is formed in the top plate 21, and the rear end of the ink chamber formed by each of the long grooves 14 communicates with the common ink chamber 24. And the common ink chamber 2
Reference numeral 4 communicates with an ink supply unit (not shown).

FIG. 2 is a partial cross-sectional view of the ink-jet head having the structure shown in FIG. 1 except for the substrate 11, taken along the line XX. The ink chambers 2 formed by the long grooves 14,.
The side walls of 5,... Are composed of the piezoelectric members 12 and 13, respectively, and are polarized in directions opposite to each other in the plate thickness direction as indicated by arrows in the drawing.

Now, the side wall P1 composed of the piezoelectric members 12 and 13 will be described.
, P2, P3, P3, three ink chambers 25 separated by P4
Focusing on A, 25B, and 25C, for example, as shown in FIG. 2A, when a positive voltage is applied to the electrode 15 of the central ink chamber 25B and the electrodes 15 of the adjacent ink chambers 25A and 25C are grounded, The side walls P2 and P3 of the ink chamber 25B are suddenly deformed outward so as to increase the volume of the ink chamber 25B because the piezoelectric members 12 and 13 are polarized in the direction opposite to each other in the thickness direction. With this deformation, ink is replenished from the common ink chamber 24 to the ink chamber 25B.
In this state, as shown in FIG. 2A, when a negative voltage is applied to the electrode 15 of the central ink chamber 25B while the electrodes 15 of the adjacent ink chambers 25A and 25C are grounded,
Both side walls P2 and P3 of the ink chamber 25B are connected to the ink chamber 25B.
Suddenly deform inside each other so as to reduce the volume. Due to this deformation, the ink in the ink chamber 25 </ b> B
Discharge from 2. In this state, the ink chamber 25B
When the electrode 15 is grounded, the side walls P2 and P3 rapidly return to the original state. By this return operation, the ink ejection port 2
The ink droplet ejected from 2 is cut and flies.

A voltage waveform applied to the electrode 15 of the ink chamber 25B for performing such an operation is a voltage waveform as shown in FIG. 3, which rapidly rises to a positive voltage at time t1, and holds this voltage for a predetermined time. Then, at time t2, the application of the positive voltage is stopped, and the voltage suddenly falls to the negative voltage. This voltage is maintained for a predetermined time, and the control of stopping the application of the negative voltage at time t3 is performed. In the ink chamber 25B, the volume is increased by the application of the positive voltage, and the volume is reduced by the application of the negative voltage. When the pressure propagation time Ta elapses from the time T2, a half of the pressure oscillation period elapses, the internal pressure increases. The ink droplets ejected from the ink ejection ports 22 become the smallest, and are spontaneously cut and fly.

If the time t3-t2 for applying the negative voltage is shorter than the pressure propagation time Ta, the ink drops are forcibly cut before the ink drops are spontaneously cut. The volume can be reduced. That is, low-density printing can be performed. Therefore, by controlling the time during which the negative voltage is applied, the ejection volume of ink droplets can be controlled, and gradation printing can be performed.

Here, the time t3 -t2 for applying the negative voltage
Is the time V for obtaining the largest ink droplet ejection volume.
FIG. 4 is a graph showing the relationship between the time t2 -t1 for applying a constant positive voltage and the discharge speed when the value is set in the range of Vmin for obtaining the smallest ink droplet discharge volume from max. Become like From this graph, when the time t3-t2 for applying the negative voltage is Vmax, the time t2-t1 for applying the positive voltage and the fluctuation of the ejection speed almost coincide with the pressure oscillation in the ink chamber, and the ejection speed becomes maximum. Is when the time t2 -t1 is the pressure propagation time Ta, and the pressure oscillation period at this time is 2Ta. Time t3 -t2
Is reduced to Vmax, V1, V2, and Vmin, the oscillation curve shifts to the lower right in the figure.

Therefore, for example, when a volume range in which the time t3-t2 is from V2 to V1 is necessary, in order to reduce the variation in the discharge speed at this time, the time t2-t1 is set as follows.
In FIG. 4, a value between the time T2 at which the first peak of the discharge speed at the time of obtaining the small volume V2 and the time T1 at which the discharge speed at the time of obtaining the large volume V1 becomes the smallest after the time T2. By setting to, variations in the discharge speed can be suppressed. Therefore, when gradation printing is performed by changing the volume of ink droplets, even if gradation switching is performed during printing, the ejection speed of ink droplets hardly changes before and after gradation switching, and a large pitch. Since no deviation occurs, high-quality printing can be performed. Also, since the volume of the ink droplet can be controlled by changing the time t3 -t2, the range of the ink droplet ejection volume can be widened, and the range of the print density gradation can be widened.

Here, the case where the range of the time t2-t1 is within the time 2Ta has been described, but the same can be said for the time after the 2Ta in the range where the pressure oscillation remains. Therefore, the time t3-t2 is within a certain range, in other words,
In a certain volume range, the value of the time t2-t1 is set to a value during which the ejection speed when the maximum volume is ejected from the first peak of the ejection speed when the minimum volume of the desired volume is ejected, or By setting the value to a value obtained by adding 2Ta × integer to the value, the variation of the ejection speed within the volume range can be suppressed most.

By the way, when a constant positive voltage is applied to increase the ink volume, pressure oscillation occurs in the ink chamber.
Is maximized, the pressure due to the reduction of the ink chamber volume from the expansion and the pressure due to the pressure vibration starting at time t1 are added, and the fluctuation form of the ejection speed matches the pressure vibration, but the time t3-t2 When a small volume is ejected, the ejection speed depends on the movement of the meniscus because only the vicinity of the free surface which is not easily affected by the pressure is ejected.

FIG. 5 shows the relationship between the time and the pressure in the ink chamber, and FIG. 6 shows the relationship between the time and the meniscus position. The change in the meniscus speed and the change in the ejection speed at the time Vmin are almost the same. I do. Therefore, in the drive voltage waveform of FIG. 3, when the time t3 -t2 is set within the range of the time Vmax for obtaining the maximum ink drop, that is, the time Vmin for obtaining the minimum ink drop from the time Ta, By setting the time t2 -t1 during which the positive voltage is applied between approximately 1.5 Ta and 2 Ta, the time between when the maximum volume ink droplet is discharged and when the minimum volume ink droplet is discharged is Dispersion of the discharge speed in each discharge volume can be reduced.
Here, the case where the range of time t2−t1 is within 2Ta has been described.
The same can be said thereafter, and the range of time t2-t1 is 2T.
FIG. 7 shows the voltage waveforms after a, and FIG. 8 shows the ink ejection and flying states.

That is, FIG. 7A shows that the application of the positive voltage is stopped and the application of the negative voltage is started at the time tA when 1.5 Ta to 2 Ta has elapsed from the start of the application of the positive voltage, and the application of the negative voltage is started. FIG. 8A shows a drive voltage waveform in which the application of the negative voltage is stopped at time tB1 after a lapse of time Vmin from the start. In this case, the ejection and flying states of the ink droplets at times tA, tB1, and tC are as shown in FIG. And discharge of small ink droplets. FIG. 7 (b) shows the relationship between 1.5 and 1.5 from the start of the application of the positive voltage.
A drive voltage waveform in which the application of the positive voltage is stopped and the application of the negative voltage is started at time tA when Ta to 2Ta has elapsed, and the application of the negative voltage is stopped at time tB2 when the time Vmax has elapsed from the start of application of the negative voltage. Times tA and tB in this case
2. The ejection and flying state of the ink droplet at tC is shown in FIG.
And discharge of large ink droplets.

In the above-described embodiment, the ink chamber also serves as the ink storage section. However, the present invention is not limited to this. The ink storage section is provided separately from the ink chamber, and the volume of the ink storage section changes. A pressure vibration may be applied to the ink chamber.

In the above-described embodiment, the driving of a multi-type ink jet head having a plurality of ink chambers whose side walls are formed of piezoelectric members is described. However, the present invention is not necessarily limited to this. The present invention can be applied to driving and also to driving another type of ink jet head in which the side wall is not formed of a piezoelectric member. In short, various modifications are possible without departing from the gist of the present invention.

[0026]

As described above, according to the first and second aspects of the present invention, in the case of performing gradation printing by varying the ink ejection volume, the variable range of the ejection volume can be widened and the width of the print density gradation can be increased. In addition, the variation in the ejection speed for each ejection volume can be minimized, and the pitch shift at the time of gradation change can be prevented as much as possible, so that high quality printing can be performed.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of the present invention, and is an exploded perspective view showing a configuration of an ink jet head, with a part cut away.

FIG. 2 is a partial cross-sectional view for explaining the operation of the inkjet head according to the embodiment.

FIG. 3 is a diagram showing a drive voltage waveform applied to an electrode of an ink chamber in the embodiment.

FIG. 4 is a graph showing a relationship between a negative voltage application time (t2−t1) of a driving voltage waveform applied to an electrode of an ink chamber and an ejection speed in the embodiment.

FIG. 5 is a graph showing a time change of pressure vibration in the ink chamber in the embodiment.

FIG. 6 is a graph showing a time change of a meniscus position of an ink chamber in the embodiment.

FIG. 7 is a diagram showing an example of a drive voltage waveform applied to an electrode of an ink chamber in the embodiment.

FIG. 8 is a diagram showing a state of ejection and flying of ink droplets from an ink chamber corresponding to the driving voltage waveform example of FIG. 7;

FIG. 9 is a diagram showing an example of a driving voltage waveform and a corresponding pressure oscillation waveform in an ink chamber in a conventional example.

FIG. 10 is a diagram showing an example of a driving voltage waveform and a corresponding pressure oscillation waveform in an ink chamber in a conventional example.

FIG. 11 is a perspective view showing an example of a serial type inkjet head.

FIG. 12 is a diagram illustrating a problem in a conventional example.

FIG. 13 is a view for explaining a problem of another method for solving the problem of the conventional example.

[Explanation of symbols]

 12, 13: piezoelectric member 15: electrode 25: ink chamber

Claims (2)

[Claims] 1. A method for increasing the volume of an ink container, reducing the volume of the ink container after a lapse of a predetermined time, and applying pressure vibration to the ink to discharge ink droplets, and further reducing the volume of the ink container. In the method of driving an ink-jet head for controlling the ejection volume of ink droplets by changing the time until the volume of the ink storage unit is returned from the reduced state to the original state, the volume of the ink storage unit is increased. The time for keeping the ink container from returning from the reduced state to the original state is set to the lower limit value of the set range. When the time until the volume of the part returns from the reduced state to the original state is set to the upper limit of the setting range, it is set to the time range where the ink droplet ejection speed becomes the minimum The driving method of ink jet head is characterized. 2. A method for increasing the volume of an ink container, reducing the volume of the ink container after a lapse of a predetermined time, applying pressure vibration to the ink to discharge ink droplets, and further reducing the volume of the ink container. In the method of driving an ink-jet head for controlling the ejection volume of ink droplets by changing the time until the volume of the ink storage unit is returned from the reduced state to the original state, the volume of the ink storage unit is increased. When the time to be kept is varied from the time for obtaining the minimum ink droplet to the time for returning the volume of the ink storage unit from the reduced state to the original state to half the time Ta of the pressure oscillation cycle applied to the ink. , The range of approximately 1.5 to 2 times the time Ta, or the range of approximately 1.5 Ta + n to 2 Ta + n (where n
Is 2 Ta × integer).