JP4003353B2 - Driving method of electrostatic ink jet head - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a driving method of an electrostatic ink jet head that ejects ink droplets by elastically displacing a diaphragm defining a part of an ink pressure chamber communicating with an ink nozzle by an electrostatic force. is there.
[0002]
More specifically, the present invention relates to a driving method of an electrostatic ink jet head capable of preventing crosstalk of ink pressure between adjacent ink pressure chambers even when the ink pressure chambers are arranged at high density.
[0003]
[Prior art]
An electrostatic ink jet head includes, for example, a diaphragm as a common electrode formed on the bottom surface of an ink pressure chamber constituting an ink flow path, as disclosed in JP-A-2-219351. And an electrode plate as an individual electrode facing the diaphragm with a slight gap. The volume of the ink pressure chamber is changed by applying a driving voltage between these counter electrodes and applying an electrostatic force to bend the diaphragm, and the ink pressure fluctuation caused thereby is communicated with the ink pressure chamber. Recording is performed by ejecting ink droplets from the ink nozzles.
[0004]
In such an electrostatic ink jet head, in order to improve the quality of an output image, it is necessary to arrange a large number of ink nozzles at high density. For this purpose, it is necessary to arrange the ink flow paths to which each ink nozzle communicates, that is, each ink pressure chamber, at a high density, and as a result, it is necessary to make the isolation walls partitioning the ink pressure chambers thin. is there.
[0005]
[Problems to be solved by the invention]
Here, when the separation walls partitioning the ink pressure chambers become thin, there is a possibility that the separation walls are also bent due to fluctuations in the internal pressure of the ink pressure chambers. That is, as shown in FIG. 6A, the diaphragm 23 (3) of the ink pressure chamber 22 (3) with which the drive ink nozzle 21 (3) for discharging ink droplets communicates is connected to the individual electrode 25 ( 3), the separation walls 24 (2) and 24 (3) may be bent due to fluctuations in the internal pressure of the ink pressure chamber 22 (3).
[0006]
Similarly, as shown in FIG. 6B, when the vibrating body 23 (3) is detached from the individual electrode 25 (3) even during ink ejection, the internal pressure fluctuation of the ink pressure chamber 22 (3) is changed. May cause the isolation walls 24 (2) and 24 (3) to bend.
[0007]
If the separating wall bends during ink ejection, a pressure loss occurs in the ink pressure chamber 22 (3), and there is a possibility that ink droplets of an appropriate amount or particle diameter will not be ejected from the drive ink nozzle 21 (3).
[0008]
Further, on the side of the non-driving ink nozzles 21 (2) and 21 (4) adjacent to the driving ink nozzle 21 (3), the separating walls 24 (2) and 24 (3) are bent, Internal pressure fluctuations occur in the ink pressure chambers 22 (2) and 22 (4) on the non-driven ink nozzle side, and in some cases, a small amount of ink droplets may be unnecessarily ejected.
[0009]
Furthermore, since the pressure fluctuation leaks to the adjacent ink pressure chambers through the isolation walls 24 (2) and 24 (3) in this way, in other words, pressure crosstalk occurs. The pressure fluctuation state generated in the ink pressure chamber differs depending on whether the adjacent ink nozzles are driven simultaneously or not. As a result, the ink ejection characteristics (ink ejection speed, ink ejection amount) of one ink nozzle may fluctuate depending on the driving state of the adjacent ink nozzle, which may cause a decrease in print quality.
[0010]
In view of such a problem, an object of the present invention is to make it possible to perform an ink discharge operation without bending an isolation wall between ink pressure chambers. An object of the present invention is to propose a driving method of an electrostatic ink jet head that can prevent pressure crosstalk and easily ensure high-definition and dense print quality.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides first and second ink pressure chambers that are adjacent to each other with an isolation wall interposed therebetween, and first and second ink nozzles that communicate with the ink pressure chambers, respectively. And first and second diaphragms elastically displaceable in an out-of-plane direction defining a part of each ink pressure chamber, and first and second individual electrodes facing each diaphragm. Each of the diaphragms is elastically displaced by applying a driving voltage between the first diaphragm and the first individual electrode and between the second diaphragm and the second individual electrode. In the electrostatic ink jet head driving method for discharging ink droplets from the first and second ink nozzles, the second diaphragm is sucked toward the second individual electrode and the individual electrode is sucked. An adsorption step for adsorbing the second diaphragm and the second diaphragm on the second In a state of being adsorbed to the individual electrodes, characterized in that it comprises a discharge step of the first diaphragm is elastically displaced perform ejection of ink droplets from the first ink nozzle.
[0012]
Here, in the driving method according to the present invention, the suction step is performed simultaneously with the step of sucking the first diaphragm to the first individual electrode.
[0013]
Further, the driving method of the present invention includes a detaching step of detaching the second diaphragm from the second individual electrode after the discharging step, and in the detaching step, an ink liquid is discharged from the second ink nozzle. The second diaphragm is separated at a speed at which no droplets are discharged.
[0014]
In the method for driving an electrostatic ink jet head according to the present invention, when ink droplets are ejected from the first ink nozzle on the driving side, the second ink nozzle on the non-driving side communicates with the second ink nozzle. The second diaphragm of the ink pressure chamber is sucked to the second individual electrode side. Accordingly, the elastic displacement of the second diaphragm is constrained and the rigidity thereof is kept high, and the compliance of the second ink pressure chamber is set to be small. As a result, bending of the isolation wall that partitions the second ink pressure chamber from the driving-side first ink pressure chamber is prevented, and crosstalk of pressure through the isolation wall is prevented or suppressed.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
A method for driving an electrostatic ink jet head to which the present invention is applied will be described below with reference to the drawings.
(overall structure)
First, with reference to FIGS. 1-3, the structure of the electrostatic inkjet head which can apply the drive method of this invention is demonstrated. Here, FIG. 1 is a cross-sectional view of the electrostatic ink jet head of this example, FIG. 2 is a plan view thereof, and FIG. 3 is a vertical cross-sectional view thereof.
[0016]
As shown in these figures, the electrostatic ink jet head 1 of this example has a silicon substrate 2 sandwiched between the same, a silicon nozzle plate 3 on the upper side, and a borosilicate glass substrate 4 having a thermal expansion coefficient close to that of silicon on the lower side. Has a three-layer structure in which each is stacked.
[0017]
The central silicon substrate 2 is etched from its surface, so that five independent elongated ink pressure chambers 5 (1) to 5 (5), one common ink chamber 6, and the common ink chamber 6 are provided. Grooves that function as ink supply ports 7 communicating with the ink pressure chambers 5 (1) to 5 (5) are processed. These grooves are closed by the nozzle plate 3, and the portions 5, 6, and 7 are partitioned. The ink pressure chambers 5 (1) to 5 (5) are partitioned by isolation walls 8 (1) to 8 (4), respectively.
[0018]
In addition, an ink intake port 12 is formed at a portion defining the lower surface of the common ink chamber 6 so as to communicate with the ink supply port 7. Accordingly, ink is supplied from an external ink tank (not shown) through the ink intake port 12 to the common ink chamber 6, and from here through each ink supply port 7, each independent ink pressure chamber 5 ( 1) to 5 (5).
[0019]
In the nozzle plate 3, the ink nozzles 11 (1) are located at positions corresponding to the tip side portions of the ink pressure chambers 5 (1) to 5 (5), that is, positions opposite to the ink supply ports 7. To 11 (5) are formed and communicate with the corresponding pressure chambers 5 (1) to 5 (5).
[0020]
As the diaphragms 51 (1) to 51 (5), the bottom surfaces of the independent ink pressure chambers 5 (1) to 5 (5) are thin and elastically displaceable in the out-of-plane direction, that is, in the vertical direction in FIG. It is set to function (only the diaphragm 51 (1) is shown in the figure).
[0021]
Next, in the glass substrate 4 located on the lower side of the silicon substrate 2, the bottom surfaces of the pressure chambers 5 (1) to 5 (5) of the silicon substrate 2 are attached to the upper surface of the glass substrate 4 that is bonded to the silicon substrate 2. Recesses 9 (1) to 9 (5) that are etched shallowly are formed at positions facing the prescribed diaphragms 51 (1) to 51 (5), respectively. Individual electrodes 10 (1) to 10 (5) corresponding to the diaphragms 51 (1) to 51 (5) are formed on the bottom surfaces of the recesses 9 (1) to 9 (5), respectively. Each of the individual electrodes 10 (1) to 10 (5) has a segment electrode 10a made of ITO and a terminal portion 10b.
[0022]
By bonding the glass substrate 4 to the silicon substrate 2, the diaphragms 51 (1) to 51 (5) defining the bottom surface of each ink pressure chamber 5 and the segment electrodes 10a in the corresponding individual electrodes are Are opposed to each other with a narrow gap G therebetween. The gap G is sealed with a sealant 60 disposed between the silicon substrate 2 and the glass substrate 4 and is in a sealed state.
[0023]
A common electrode terminal 22 is formed on the silicon substrate 2, and a drive voltage pulse is applied between the common electrode terminal 22 and the individual electrodes 10 (1) to 10 (5) by the drive control circuit 21. Since the silicon substrate 2 is conductive, the diaphragms 51 (1) to 51 (5) function as a common electrode.
[0024]
The diaphragms 51 (1) to 51 (5) and the diaphragms 51 (1) to 51 (5) are generated by an electrostatic force generated by applying a drive voltage between the individual electrodes 10 (1) to 10 (5). ) Is attracted to the individual electrode side, the diaphragms 51 (1) to 51 (5) are elastically displaced to bend toward the segment electrode 10 a and are adsorbed on the surface of the segment electrode 10 a. As a result, the volume of the ink pressure chambers 5 (1) to 5 (5) is increased, and ink is supplied from the ink supply port 7 to the ink pressure chambers 5 (1) to 5 (5).
[0025]
When the electrostatic attraction force is released, the diaphragms 51 (1) to 51 (5) are separated from the surface of the segment electrode 10a by the elastic force to return to the initial state, and the ink pressure chambers 5 (1) to 5 ( 5) The volume decreases rapidly. At this time, due to ink pressure vibration generated in the ink pressure chamber, a part of the ink in the ink pressure chamber is ejected as ink droplets from the ink nozzles 11 communicating with the ink pressure chambers 5 (1) to 5 (5). Is done.
(Driving method)
With reference to FIG. 4, the outline of the driving method of the ink jet head 1 of this example will be described. Assume that the ink nozzle (referred to as “driving nozzle”) from which ink droplets are ejected is the ink nozzle 11 (3). Further, the ink nozzles 11 (2) and 11 (4) adjacent to both sides of the drive nozzle 11 (3) are ink nozzles that do not discharge ink droplets (referred to as “non-drive nozzles”). And
[0026]
In the driving method of this example, first, the driving voltage between the diaphragms 51 (2) to 51 (4) and the individual electrodes 10 (2) to 10 (4) in each of the ink nozzles 11 (2) to 11 (4). A pulse is applied to attract the diaphragms 51 (2) to 51 (4) simultaneously to the individual electrodes 10 (2) to 10 (4). Thereby, the adsorption | suction state of each diaphragm 51 (2) -51 (4) as shown to Fig.4 (a) is formed.
[0027]
Next, the drive nozzle 11 is kept in a state where the diaphragms 51 (2) and 51 (4) of the non-drive nozzles 11 (2) and 11 (4) are attracted to the individual electrodes 10 (2) and 10 (4). The diaphragm 51 (3) of (3) is quickly detached from the individual electrode 11 (3). As a result, as shown in FIG. 4B, the diaphragm 51 (3) is elastically restored, the volume of the ink pressure chamber 5 (3) is rapidly reduced, and the ink is discharged from the drive nozzle 11 (3). A droplet is ejected.
[0028]
Thereafter, the diaphragms 51 (2) and 51 (4) of the non-driving nozzles 11 (2) and 11 (4) are detached from the individual electrodes 11 (2) and 11 (4). This separation speed is performed at a slow speed at which ink droplets are not ejected from the non-driven nozzles 11 (2) and 11 (4). Through the above steps, one ink droplet ejection operation is completed.
[0029]
FIG. 5 shows an example of a pulse waveform of the drive voltage applied between the diaphragm which is a common electrode and the individual electrodes in order to realize the above operation. Such a drive voltage pulse is generated by the drive control circuit 21.
[0030]
First, FIG. 5F shows a basic voltage pulse waveform of the drive voltage V3. One ink droplet ejection operation is performed for each pulse of the basic voltage waveform. For example, between time t1 and time t6 and between time t6 and time t11 are each one discharge cycle. These first and second discharge cycles are repeatedly executed. In this basic voltage waveform pulse, its rising edge (between time t1 and t2) is steep, and its falling edge (between time t4 and t5) has a gentle slope.
[0031]
The three ink nozzles 11 (2) to 11 (4) shown in FIG. 4 will be described as an example. The applied voltages of the diaphragms 51 (2) to 51 (4) functioning as a common electrode are shown in FIG. As shown in (a), the voltage pulse has the same shape as the basic voltage waveform at the time t1 to t6 which is the first discharge cycle, and is set to the ground potential GND at the time t6 to t11 which is the next second discharge cycle. Retained.
[0032]
As shown in FIG. 5B, the individual electrode potential of the drive nozzle 11 (3), that is, the potential of the diaphragm 51 (3) is grounded from the time t1 to the time t3 in the first discharge cycle. It is held at the potential, and suddenly rises to the common electrode potential at time t3. Thereafter, it is held at the same potential as the common electrode potential until time t6. In the second ejection cycle, the potential rises steeply at time t6 and is held at a high potential until time t8. The potential is sharply lowered to ground potential at this time, and then held at the ground potential until time t11. Is done.
[0033]
As a result, the potential difference between the diaphragm 51 (3) and the individual electrode 10 (3) in the drive nozzle 11 (3) is between time points t1 and t3 in the first discharge cycle, as shown in FIG. The positive potential difference state is maintained, and the negative potential difference state is conversely maintained between time points t6 and t8 in the second ejection cycle. In other words, an electrostatic force that attracts the diaphragm to the individual electrode is generated. At other times, the potential difference is maintained and no electrostatic force is generated.
[0034]
Therefore, in the first discharge cycle, the diaphragm 51 (3) is rapidly sucked toward and attracted to the individual electrode 10 (3) from the time point t1, and at the time t3, the diaphragm 51 (3) ) Suddenly leaves the individual electrode 10 (3) and returns elastically. By the operation of the diaphragm, ink droplets are ejected from the drive nozzle 11 (3) at a time after a predetermined time from the time t3. Similarly, in the second discharge cycle, the diaphragm 51 (3) is suddenly sucked toward and attracted to the individual electrode 10 (3) from the time point t6, and the diaphragm 51 ( 3) suddenly leaves the individual electrode 10 (3) and returns elastically. By the operation of the diaphragm, ink droplets are ejected from the drive nozzle 11 (3) at a time point after a predetermined time from the time point t8.
[0035]
In addition, the polarity of the potential difference between the individual electrode and the common electrode is reversed in the first ejection cycle and the second ejection cycle. If the polarity of the potential difference is always the same, the electric charge is transferred between these electrodes. This is because it may accumulate and a desired electrostatic attraction force may not be obtained.
[0036]
On the other hand, in the non-driving nozzle 11 (2) adjacent to the driving nozzle 11 (3), the individual electrode potential is set to the ground potential in the first ejection cycle as shown in FIG. In the second ejection cycle, the same potential state as the basic drive voltage pulse waveform is obtained. That is, the potential state in the first and second ejection cycles in the diaphragm 51 (2), which is a common electrode, is maintained in the opposite state.
[0037]
As a result, as shown in FIG. 5E, the potential difference between the diaphragm 51 (2) and the individual electrode 10 (2) in the non-driven nozzle 11 (2) is the first discharge cycle and the second discharge cycle. In FIG. 4, the state is similar to the basic voltage waveform.
[0038]
Accordingly, the diaphragm 51 (2) is attracted to the individual electrode 10 (2) from the time point t1 in the first discharge cycle, and is held in the suction state until the time point t4. After this, the potential difference gradually decreases. That is, the discharge between both electrodes is gradually performed. For this reason, the diaphragm 51 (2) starts to be detached at a position between the time point t4 and the time point t5, and elastically returns at a slower speed than that during the suction. Similarly, the diaphragm 51 (2) is attracted to the individual electrode 10 (2) from the time point t6 in the second discharge cycle, and is held in the suction state until the time point t9. After this, the potential difference gradually decreases. That is, the discharge between both electrodes is gradually performed. For this reason, the diaphragm 51 (2) starts to be detached at a position between the time point t9 and the time point t10, and elastically returns at a slower speed than that during the suction.
[0039]
Thus, on the non-driving nozzle 11 (2) side, the suction operation of the diaphragm 51 (2) is performed in synchronization with the suction operation of the diaphragm 51 (3) on the driving nozzle 11 (3) side. As shown in FIG. 4A, all the nozzles are attracted to the individual electrodes. Next, in this suction state, ink droplets are ejected from the drive nozzle 11 (3). Thereafter, the diaphragm 51 (2) on the side of the non-driving nozzle 11 (2) separates from the individual electrode 10 (2) and gently returns to elasticity. By adjusting the elastic return speed of the diaphragm, it is possible to completely prevent ink droplets from being ejected from the non-driving nozzle 11 (2) when the diaphragm 51 (2) is elastically restored.
[0040]
The non-driving nozzle 11 (4) operates in the same manner as the non-driving nozzle 11 (2).
[0041]
As described above, in the driving method of the electrostatic ink jet head of this example, the diaphragm 51 (2) also in the non-driving nozzles 11 (2) and 11 (4) adjacent to the driving nozzle 11 (3). , 51 (4) are held by suction on the individual electrodes 10 (2) and 10 (4), so that their rigidity is kept high. As a result, the compliance of the ink pressure chambers 5 (2) and 5 (4) of the non-driven nozzle can be reduced.
[0042]
Therefore, the separation wall 8 (2) partitioning the ink pressure chamber 5 (3) on the driving nozzle side with small compliance from the ink pressure chambers 5 (2) and 5 (4) on the non-driving nozzle side with the same compliance. ), 8 (4) can be prevented or suppressed from bending due to pressure fluctuations in the ink pressure chamber on the drive nozzle side.
[0043]
Therefore, the crosstalk of the pressure in the ink pressure chamber can be prevented or suppressed regardless of whether or not the adjacent ink nozzle is driven. Even if the density of the ink jet head is increased and the isolation wall is thinned, it is caused by the deflection. It is possible to prevent or suppress the deterioration of the ink ejection characteristics of each ink nozzle. For this reason, if the driving method of this example is adopted, high-definition and precise print quality can be easily ensured.
[0044]
Note that the drive voltage waveform shown in FIG. 5 is an example for realizing the drive method of the present invention, and a drive mode different from this can be adopted.
[0045]
【The invention's effect】
As described above, in the method for driving an electrostatic ink jet head according to the present invention, not only the diaphragm of the first ink nozzle that is a drive nozzle but also the second ink nozzle that is an adjacent non-drive nozzle. The diaphragm is also attracted to the individual electrodes to be in an attracted state, and ink droplets are ejected from the drive nozzles while maintaining the attracted state.
[0046]
Accordingly, since the compliance of the ink pressure chamber on the non-driving nozzle side can be reduced, deformation of the isolation wall that partitions the ink pressure chamber of the driving nozzle and the ink pressure chamber of the non-driving nozzle can be prevented or suppressed. Therefore, since the crosstalk of the pressure through the isolation wall can be prevented or suppressed, it is possible to prevent or suppress the deterioration of the ink discharge characteristics due to the crosstalk.
[0047]
As a result, according to the driving method of the present invention, it is possible to increase the density of the ink jet head without causing deterioration of the ink ejection characteristics, so that it is possible to easily achieve high-definition and dense printing quality.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view showing an example of an electrostatic ink jet head to which the present invention is applied.
FIG. 2 is a schematic plan view of the electrostatic ink jet head shown in FIG.
FIG. 3 is a schematic cross-sectional view of the electrostatic inkjet head shown in FIG. 1 cut in a direction orthogonal to each other.
4 is an explanatory diagram for illustrating the operation of the electrostatic inkjet head of FIG. 1; FIG.
5 is a timing chart showing an example of a drive voltage waveform for realizing the operation of FIG.
FIG. 6 is a diagram for explaining a problem in a conventional inkjet head driving method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electrostatic inkjet head 2 Silicon substrate 3 Nozzle plate 4 Glass substrate 5 (1) -5 (5) Pressure chamber 6 Common ink chamber 7 Ink supply port 8 (1) -8 (5) Isolation wall 9 (1)- 9 (5) Recesses 10 (1) to 19 (5) Individual electrode 10a Segment electrode 10b Terminal portions 11 (1) to 11 (5) Ink nozzle 12 Ink take-out port 21 Voltage application means 22 Common electrode terminal 51 (1) to 51 (5) Diaphragm 60 Sealant

Claims (3)

First and second ink pressure chambers adjacent to each other across the isolation wall, first and second ink nozzles communicating with each ink pressure chamber, and a part of each ink pressure chamber are defined. First and second diaphragms elastically displaceable in the out-of-plane direction, and first and second individual electrodes facing each diaphragm, the first diaphragm and the first Ink from the first and second ink nozzles by elastically displacing each diaphragm by applying a drive voltage between the individual electrodes and between the second diaphragm and the second individual electrode. In the driving method of the electrostatic inkjet head for discharging droplets,
An adsorption step of sucking the second diaphragm toward the second individual electrode and adsorbing it to the individual electrode;
An ejection step of ejecting ink droplets from the first ink nozzle by elastically displacing the first diaphragm with the second diaphragm adsorbed to the second individual electrode; A drive method for an electrostatic ink jet head, comprising: In claim 1,
The method of driving an electrostatic ink jet head, wherein the suction step is performed simultaneously with the step of sucking the first diaphragm to the first individual electrode. In claim 1 or 2,
A detaching step of detaching the second diaphragm from the second individual electrode after the discharging step;
The method of driving an electrostatic ink jet head, wherein, in the separation step, the second diaphragm is detached at a speed at which ink droplets are not discharged from the second ink nozzle.

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