JP4138146B2 - Ink-jet head driving method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for driving an ink jet head that ejects ink droplets by deforming a diaphragm using electrostatic force. More specifically, the present invention relates to a method for driving an ink-jet head that can eliminate the influence of residual charges remaining on a diaphragm and always perform a good ink droplet ejection operation.
[0002]
[Prior art]
An ink jet head that discharges ink droplets using electrostatic force is disclosed in, for example, the specification of US Pat. No. 4,520,375 and Japanese Patent Laid-Open No. 5-50601. Ink jet heads described in these publications are formed by a diaphragm that is elastically displaceable in the out-of-plane direction at the bottom surface of the discharge chamber that communicates with the ink nozzles, and electrodes are disposed opposite to the diaphragm. By applying a driving voltage pulse between the diaphragm and the electrode, the diaphragm is displaced by electrostatic force, and ink droplets are ejected from the ink nozzles in accordance with the displacement of the diaphragm.
[0003]
In the ink jet head having this configuration, if a charge remains in the dielectric between the diaphragm and the electrode after applying a voltage pulse between the diaphragm and the electrode, the relative displacement between the diaphragm and the electrode is caused by the electric field generated by the residual charge. It will decrease. The decrease in the relative displacement amount causes the ink droplet ejection failure such as the ink droplet ejection amount and the ink speed reduction. When such an ink ejection defect occurs, a print quality defect such as a change in print density, a pixel shift, or a missing pixel occurs.
[0004]
In order to prevent the residual charge from being generated between the diaphragm and the electrode, the present applicant previously described in Japanese Patent Application Laid-Open No. 7-81088 a voltage having a polarity opposite to the drive voltage for discharging ink droplets. Has been proposed to apply periodically. Japanese Patent Laid-Open No. 9-136413 proposes a method of alternately applying a reverse polarity drive voltage for ink droplet ejection.
[0005]
[Problems to be solved by the invention]
Here, in general, in order to ensure the same printing density, it is more suitable for 1-dot printing to form printing for one dot with a plurality of ink droplets than to form with one ink droplet. This is desirable because the weight of the ink is small.
[0006]
On the other hand, the polarity of the residual charge generated between the diaphragm and the electrode varies depending on the charging characteristics of the insulating layer between them. Therefore, even if drive voltages having different polarities are alternately applied, there are cases where residual charges cannot be removed effectively.
[0007]
In addition, if the polarity of the driving voltage is different, generally, the ink speed or the ink weight of the ejected ink droplet changes accordingly. When such ink droplet ejection characteristics change, problems such as deterioration in print quality occur.
[0008]
In view of the above, the problem of the present invention is to remove residual charges between the diaphragm and the electrodes by applying a drive voltage for discharging ink droplets having different polarities, and a plurality of ink liquids. In a driving method of an inkjet head that forms one-dot printing by ejecting droplets, it is possible to more effectively remove residual charges.
[0009]
Another object of the present invention is to enable residual charges to be effectively removed without degrading print quality in such a method for driving an inkjet head.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention applies a drive voltage for discharging ink droplets having different polarities, and forms a one-dot print on a recording medium by a plurality of ink droplet discharge operations. In the inkjet head driving method, the one-dot printing is formed by ejecting ink droplets three times or more in succession at least once, and at least one of the ejection operations for forming the one-dot printing. The drive voltage applied during the discharge operation is reverse polarity.
[0011]
In this way, when one-dot printing is performed by an ink droplet ejection operation of three or more odd times, the drive voltage is also applied by the same odd number of times. Therefore, the number of times of applying the drive voltage of one polarity is always increased. Therefore, if the polarity of the driving voltage that increases the number of times of application is selected according to the charging characteristics of the insulating layer between the diaphragm and the electrode, the residual charge can be effectively removed, and the print quality can be maintained well. Can do.
[0012]
Here, for example, when a diaphragm is formed on a boron-doped layer in which boron is doped on a p-type silicon substrate, a negative residual charge is likely to be generated in the insulating layer formed between the diaphragm and the electrode. It exhibits charging characteristics. Therefore, in order to effectively remove the residual charge, any polarity is used as the polarity of the drive voltage applied during the ejection operation for forming the one-dot printing according to the charging characteristics of the insulating layer. It is desirable to determine whether
[0013]
Next, it is desirable to change at least one of the pulse width and voltage value of the drive voltage according to the polarity of the drive voltage. In this way, the ejection characteristics of the ink droplets when applying drive voltages having different polarities can be maintained to be substantially the same, and the print quality can be maintained satisfactorily.
[0014]
In a typical inkjet head driving method according to the present invention, the number of ink droplet ejection operations for forming the one-dot printing is three.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of an ink jet printer provided with an ink jet head driven by the driving method of the present invention will be described with reference to the drawings.
[0016]
FIG. 1 is a schematic configuration diagram of the ink jet printer of this example. As shown in this figure, the overall structure of the ink jet printer 310 of this example is a general structure. The platen 300 that conveys the recording paper 105, the ink jet head 10 that faces the platen 300, and the ink jet head 10 are arranged. A carriage 302 that reciprocates in the main scanning direction, which is the axial direction of the platen 300, and an ink tank 301 that supplies ink to the inkjet head 10 via an ink tube 306 are provided. A pump 303 is used to suck ink through the cap 304 and the waste ink collection tube 308 and collect it in the waste ink reservoir 305 when an ink discharge failure or the like occurs in the inkjet head 10.
[0017]
2 is an exploded perspective view of the inkjet head 10, FIG. 3 is a sectional configuration view of the assembled inkjet head, and FIG. 4 is a view taken along the line AA in FIG. The ink jet head 10 of this example is an edge eject type that ejects ink droplets from nozzle holes provided at the end of the substrate, but may be a face eject type that ejects ink droplets from nozzle holes provided on the upper surface of the substrate. .
[0018]
As shown in FIGS. 2, 3, and 4, the ink jet head 10 of this example has a laminated structure in which three substrates 1, 2, and 3 are overlapped. The intermediate substrate 2 is, for example, a silicon substrate, and a plurality of nozzle grooves 21 formed at equal intervals in parallel from one end on the surface of the substrate 2 so as to form a plurality of nozzle holes 4, and each nozzle groove 21, a recess 22 that forms the discharge chamber 6 whose bottom wall functions as the vibration plate 5, and a narrow portion for the ink inlet that forms the orifice 7 provided at the rear of the recess 22. It has a groove 23 and a recess 24 that constitutes a common ink cavity 8 for supplying ink to each discharge chamber 6.
[0019]
In addition, a concave portion 25 that constitutes a vibration chamber 9 for mounting an electrode to be described later is provided at the lower portion of the diaphragm 5. The pitch of the nozzle grooves 21 is about 2 mm, and the width thereof is about 40 μm. On the other hand, a common electrode 17 is formed on the upper surface of the intermediate substrate. The upper substrate 1 bonded to the upper surface of the intermediate substrate 2 is made of, for example, glass or plastic, and the nozzle hole 4, the discharge port 6, the orifice 7, and the ink cavity 8 are configured by bonding the upper substrate 1. An ink supply port 14 communicating with the ink cavity 8 is formed in the upper substrate 1. The ink supply port 14 is connected to the ink tank 301 (see FIG. 1) via the connection pipe 16 and the tube 306.
[0020]
The lower substrate 3 bonded to the lower surface of the intermediate substrate 2 is made of, for example, glass or plastic, and the vibration chamber 9 is configured by bonding of the lower substrate 3 and corresponds to the vibration plate 5 in the direction of the lower substrate. An individual electrode 31 is formed at each position. The individual electrode 31 has a lead portion 32 and a terminal portion 33. Further, the electrode 31 and the lead part 32 are entirely covered with an insulating film 34 except for the terminal part 33. A lead wire 35 is bonded to each terminal portion 33.
[0021]
In the inkjet head 10 configured by superimposing the substrates as described above, a head driver 220 (see FIG. 5) described later is further provided between the common electrode 17 formed on the intermediate substrate 2 and the terminal portion 33 of each individual electrode 31. Connected. The ink 11 is supplied from the ink tank 301 to the inside of the intermediate substrate through the ink supply port 14, and fills the ink cavity 8, the discharge port 6, and the like. The distance between the electrode 31 and the diaphragm 5 is maintained at about 1 micron m. In FIG. 2, reference numeral 13 denotes ink droplets ejected from the nozzle holes 4.
[0022]
The ink to be used is prepared by dissolving or dispersing a surfactant such as ethylene glycol and a dye or pigment in a main solvent such as water, alcohol or toluene. Furthermore, hot-melt ink can be used if a heater or the like is attached to the inkjet head.
[0023]
For example, when a positive voltage pulse is applied to the individual electrode 31 by the head driver 220 to charge the surface of the electrode 31 to a positive potential, the lower surface of the corresponding diaphragm 5 is charged to a negative potential. Therefore, the diaphragm 5 is attracted by the electrostatic force and bent downward. Next, when the voltage pulse applied to the electrode 31 is turned off, the diaphragm 5 returns to the original position. By this returning operation, the internal pressure of the discharge chamber 6 is rapidly increased, and the ink droplet 13 is discharged toward the recording paper 105 from the nozzle hole 4. Then, when the vibration plate 5 is bent downward, the ink 11 is supplied from the ink cavity 8 to the discharge chamber 6 via the orifice 7.
[0024]
FIG. 5 shows a drive control system portion of the inkjet head 10 in the control system of the ink jet printer of this example. In the figure, reference numeral 201 denotes a pretan control circuit which can be constituted by a one-chip microcomputer, for example. The printer control circuit 201 is connected to a RAM 205, a ROM 206, and a character generator ROM (CG-ROM) 207 via internal buses 202, 203, 204 including an address bus and a data bus. A control program is stored in the ROM 206 in advance, and a drive control operation of the inkjet head 10 as described below is executed based on the control program that is called up and started from here. The RAM 205 is used as a working area in drive control. In the CG-ROM 207, a dot pattern corresponding to the input character is developed.
[0025]
A head drive control circuit 210 outputs a drive signal FR and the like to the head driver 220 under the control of the printer control circuit 201. Further, print data DATA is supplied via the data bus 211. Further, a clock signal CLK is supplied.
[0026]
The head driver 220 is composed of, for example, a TTL array, generates a driving voltage pulse corresponding to an input driving signal, and applies these to the individual electrode 31 and the common electrode 17 to be driven, thereby responding. Ink droplets are ejected from the nozzle holes 14 to be discharged. In order to generate the drive voltage pulse signal, the head driver 220 is supplied with the ground voltage GND and the drive voltages Vp, V2, and V3 (0 <V2, V3 <Vp). These voltages are generated from the drive voltage Vcc supplied from the power supply circuit 230.
[0027]
FIG. 6 shows a flowchart of the schematic operation of the ink jet printer 1 having the above-described configuration. FIG. 7A shows a nozzle recovery operation subroutine, and FIG. 7B shows a printing operation subroutine.
[0028]
First, the overall operation will be described. In step ST1, initialization of the printer mechanism portion is executed. Next, in step ST2, the nozzle recovery operation immediately after the power is turned on is performed. This nozzle recovery operation consists of a series of steps shown in steps ST21 to ST23 in FIG.
[0029]
In this nozzle recovery operation, the carriage 302 on which the inkjet head 10 is mounted is moved from the standby position to the position of the cap 304 in step ST21. Next, in step ST22, a nozzle recovery operation, that is, refresh is performed. This nozzle refreshing means driving the diaphragm 5 corresponding to all the nozzles in order to discharge the defective ink that causes the ink ejection failure such as the thickened ink in the nozzle portion of the inkjet head 10, Ink droplets are ejected from the nozzles a predetermined number of times. Thereafter, in step ST23, the carriage 302 is returned to the standby position again.
[0030]
Returning to the flowchart of FIG. 6 again, in step ST3, the time from the previous nozzle recovery operation is counted. This counting is performed using a counter built in the printer control circuit 201. When the time interval for performing the nozzle recovery operation elapses, the process proceeds from step ST3 to step ST9, and the nozzle recovery operation is performed again. If not, it is determined whether or not printing is performed in step ST4. If the printing operation is performed, the count value of the nozzle recovery operation period is reset in step ST5, and then the process proceeds to step ST6 to perform the printing operation. Execute.
[0031]
FIG. 7B shows this printing operation. As shown in this figure, first, in step ST61, the count value n is set to “1”, and in step ST62, the carriage 302 is moved in the main scanning direction by one dot. In steps ST63 and ST64, by driving the diaphragm 5 of the nozzle corresponding to the designated dot based on the print data DATA, the ink suction and discharge operations of the nozzle are performed. Next, in step ST65, the count value n is incremented by “1”, and in step ST66, it is determined whether or not the count value n is the last dot in the main scanning direction. If it is the last dot, the printing operation is terminated. If not, the process returns to step ST62 and the above operation is repeated.
[0032]
After the printing operation for one line in the main scanning direction is completed in this way, it is determined whether or not the process is continued in step ST10 in FIG. 6, and in the case of continuing, the process returns to step ST3, otherwise. If so, the process ends.
[0033]
(1-dot printing operation)
Here, in the ink jet printer of this example, in order to form one dot printing (one pixel printing) on the recording paper in the printing operation shown in FIG. The operation, in this example, is configured to perform three discharge operations continuously. Further, the drive voltage pulse signal is configured to use signals having different polarities.
[0034]
That is, in this example, a positive drive voltage pulse (value V3) is applied to the common electrode 17 and the individual electrode 31 is set to the ground potential (GND), thereby displacing the diaphragm 5 and ejecting ink droplets. The “positive” drive mode in which the diaphragm 5 is moved and the common electrode 17 is set to the ground potential (GND), and the positive drive voltage pulse (value V2) is applied to the individual electrode 31 side to displace the diaphragm 5. Thus, ink droplets are ejected by the “reverse” drive mode in which the ink droplet ejection operation is performed.
[0035]
When three drive voltage pulses are applied for 1-dot printing, the following six patterns can be considered as their polarities.
[0036]
Forward, forward, reverse forward, reverse, forward / reverse, reverse / reverse, forward / backward / reverse, forward / backward, forward / reverse, where a boron layer in which boron is diffused in the p-type silicon substrate 2 is a diaphragm 5 When the inkjet film 10 is manufactured by using the insulating film 34 formed between the vibration plate 5 and the electrode 31 as a thermal oxide film and anodically bonding the silicon substrate 2 and the glass substrate 3, the insulating film 34 is, for example, It was confirmed by experiments that a negative charging characteristic of about −2 V was exhibited. In this case, in order to remove or suppress the negative residual charge generated between the diaphragm 5 and the electrode 31, a large number of “positive” drive voltage pulses may be applied. That is, any one of the following three patterns may be adopted.
[0037]
Forward, forward, reverse forward, reverse, forward / reverse, forward, forward In order to realize such drive control, in the head drive control circuit 210 of this example, the above three An inversion drive signal FR whose logic value repeatedly switches between high and low in any one of the patterns is supplied to the head driver 220. In the head driver 220, the polarity of the drive voltage pulse is switched according to the logical value of the inversion drive signal FR and the logical value of print data DATA (presence / absence of print data).
[0038]
Here, in general, in the inkjet head, the thickness of the diaphragm 5 and the gap between the diaphragm and the electrode vary with respect to target values due to variations in processing dimensions. When these values vary, the pulse width of the drive voltage pulse signal necessary for properly driving the inkjet head also varies. From this point, it is preferable that the range of the pulse width capable of satisfactorily maintaining the print quality as the drive voltage pulse signal is wide, and if it is wide, the manufacturing error can be absorbed.
[0039]
In the on-demand type ink jet head, the driving frequency changes. However, it is not preferable that the ink weight and ink speed to be ejected change with the change of the driving frequency.
[0040]
In view of these points, as a result of analysis by the present inventors, when performing 1-dot printing by ejecting ink droplets three times, among the above three polarity patterns,
On the other hand, it was confirmed that the positive, positive and positive drive patterns were the best.
[0041]
FIG. 8 shows a timing chart according to the driving method of this example. In this figure, (a) shows timing pulses for the printing operation, and (b) shows energization pulses output at each printing timing. In (c), the drive voltage waveform of each nozzle of the inkjet head 10 is shown. This drive voltage waveform represents the potential difference between the individual electrode 31 and the common electrode 17. Furthermore, (d) shows the ejection timing of the ink droplets from the nozzles.
[0042]
As described above, in the ink jet printer of this example, the driving of each nozzle of the ink jet head 10 is cut in reverse, normal, and positive patterns as shown in FIG. 8C. One-dot printing is formed by these three ink droplet ejection operations, which are performed by the driving voltage pulse signal that is changed. That is, in the “reverse” driving state, the negative driving voltage pulse S (V2) is applied between the individual electrode 31 and the common electrode 17 (the diaphragm 5). On the other hand, in the “positive” driving state, the positive driving voltage pulse S (V3) is applied between them.
[0043]
Therefore, in this example, the generation of residual charges in the insulating film 34 having negative charging characteristics can be reliably suppressed or avoided by increasing the positive driving state.
[0044]
(Second example of drive mode)
Here, when the pulse width characteristic of the ink speed is obtained by experiments in the “reverse, normal, normal” driving method as described above, a characteristic curve as shown in FIG. 9 is obtained. In this figure, the curve indicated by the solid line is the ink speed characteristic curve obtained during “forward” driving, the curve indicated by the broken line is the ink speed characteristic curve obtained during “reverse” driving, and the curve indicated by the broken line is the entire curve As it shifts to the left.
[0045]
Assuming that the range of the pulse width Pw of the drive voltage pulse signal corresponding to the ink speed at which good print quality can be obtained is W1 and W2, the range W where the two curves overlap is the range of the applicable pulse width. As described above, since the ejection characteristics of ink droplets are different between the forward and reverse driving methods, the range of pulse widths in which good print quality can be obtained by both driving methods is narrowed.
[0046]
In order to suppress such variations in ink droplet ejection characteristics, the pulse width and / or voltage value of the drive voltage pulse signal may be changed according to the polarity.
[0047]
FIG. 10 shows an example in which the pulse width of the drive voltage pulse signal is changed according to the polarity. The signals (a) to (c) correspond to the signals (a) to (c) in FIG. As shown in this figure, the pulse width Pw1 at the time of reverse driving is made narrower than the pulse width Pw2 at the time of forward driving. In this way, it was confirmed that variations in the ejection characteristics of the ink droplets during the “normal” and “reverse” driving can be suppressed.
[0048]
FIG. 11 shows an example in which the voltage value of the drive voltage pulse signal is changed according to the polarity. The signals (a) to (c) correspond to the signals (a) to (c) in FIG. As shown in this figure, the absolute value of the voltage value V2 at the time of reverse driving is made smaller than the absolute value of the voltage value V3 at the time of forward driving. Even in this way, it was confirmed that variations in the ejection characteristics of ink droplets during forward and reverse driving can be suppressed.
[0049]
(Other embodiments)
In the above example, the insulating film 34 covering the electrode 31 has a negative charging characteristic. However, if the insulating film 34 has a positive charging characteristic, the polarity of the drive voltage can be changed as follows. That's fine.
[0050]
For example, when a diaphragm is formed by diffusing phosphorus in an n-type silicon substrate and an ink jet head is manufactured as in the above example, the insulating film exhibits a positive charging characteristic of about + 2V. In this case, it is only necessary to apply a large number of drive voltage pulse signals of opposite polarity. That is,
One-dot printing may be performed using one of the driving patterns of normal, reverse, reverse reverse, reverse, normal reverse, normal, and reverse.
[0051]
On the other hand, in the above example, one-dot printing is formed by ejecting ink droplets three times. However, one-dot printing may be formed by ejecting five or more odd ink droplets. In either case, since the number of times of applying the drive voltage pulse of one polarity is increased, it is possible to effectively suppress or avoid the generation of residual charges between the diaphragm and the electrode.
[0052]
【The invention's effect】
As described above, in the ink jet head driving method according to the present invention, one-dot printing is formed by ejecting ink droplets of an odd number of three or more times, and the polarity of the driving voltage applied during these ejecting operations. To be different. Therefore, according to the present invention, it is possible to effectively suppress or avoid the residual charge generated in the insulating layer having a positive or negative charging characteristic between the diaphragm and the electrode.
[0053]
In the present invention, at least one of the pulse width and voltage value of the drive voltage is changed according to the polarity of the drive voltage. As a result, it is possible to suppress or avoid fluctuations in the ejection characteristics of the ink droplets due to the difference in polarity, thereby realizing printing with high printing quality.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an overall configuration of an ink jet printer to which the present invention is applied.
2 is an exploded perspective view showing an ink jet head mounted on the printer of FIG. 1; FIG.
3 is a schematic cross-sectional view showing the inkjet head of FIG.
4 is a view taken along the line AA in FIG. 3;
5 is a schematic block diagram showing a control system of an ink jet head in the ink jet printer of FIG. 1. FIG.
6 is a schematic flowchart showing the operation of the ink jet printer of FIG. 1. FIG.
7A is a flowchart showing a subroutine of a nozzle recovery operation, and FIG. 7B is a flowchart showing a dot printing operation for one main scanning line.
8 is a timing chart showing drive control for one-dot printing by an ink-jet head in the ink-jet printer of FIG.
FIG. 9 is a graph showing ink speed characteristics with respect to pulse widths of drive voltage pulse signals having different polarities.
FIG. 10 is a timing chart showing another drive control of the inkjet head according to the present invention.
FIG. 11 is a timing chart showing still another drive control of the inkjet head according to the present invention.
[Explanation of symbols]
1, 2, 3 Substrate 4 Nozzle hole 5 Diaphragm 10 Inkjet head 13 Ink droplet 17 Common electrode 31 Individual electrode 34 Insulating film 201 Printer control circuit 210 Head drive control circuit 220 Head driver

Claims (3)

One-dot printing is formed on the recording medium by applying a driving voltage between the diaphragm and the counter electrode, and displacing the diaphragm by electrostatic force to eject ink droplets from the ink nozzles a plurality of times. In the inkjet head driving method,
1 dot printing is formed by continuously performing the above-described ink droplet ejection operation over an odd number of times of 3 or more,
Among the odd number of ejection operations for forming the one-dot printing, the polarity of the drive voltage applied at the time of at least one ejection operation is set to a reverse polarity,
Depending on the charging characteristics of the insulating layer formed between the diaphragm and the electrode, the polarity of the drive voltage applied during the ejection operation for forming the one-dot printing is any number of times. A method for driving an inkjet head, characterized by determining whether or not. In claim 1,
An inkjet head driving method, wherein at least one of a pulse width and a voltage value of the driving voltage is changed according to the polarity of the driving voltage. In claim 1 or 2,
An ink jet head driving method, wherein the number of ink droplet ejection operations for forming the one-dot printing is three.

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