JP3225987B2 - Driving apparatus and driving method for inkjet recording head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention
The present invention relates to a driving technique of an ink jet recording head for forming an ink image on a recording medium such as recording paper.

[0002]

2. Description of the Related Art An on-demand type ink jet recording head comprises a plurality of pressure generating chambers for generating ink pressure by piezoelectric vibrators and heating elements, a common reservoir for supplying ink to each pressure generating chamber, and It has a recording head with a nozzle opening communicating with the pressure generating chamber, increases the ink pressure in the pressure generating chamber according to the print signal, causes ink droplets to fly from the nozzle opening, and forms dots on the recording medium. I have.

In such an on-demand type ink jet recording head, the meniscus formed near the nozzle opening is largely drawn into the pressure chamber after the ink droplet flies, and before the meniscus returns to the original position. When the next ink droplet ejection operation is performed, the ink amount and the flying speed of the flying ink droplet fluctuate, and the print quality deteriorates. In order to avoid this, if ink droplets are continuously ejected, it is necessary to perform the operation after returning to the position based on the movement of the meniscus due to the previous ink droplet ejection, which is an obstacle to performing high-speed printing. There are proposals to improve this. For example, in an ink jet recording head in which a heating element generates a vapor bubble to fly an ink droplet as disclosed in Japanese Patent Application Laid-Open No. 2-233258, after the ink droplet flies due to the first vapor bubble, the meniscus forms a pressure chamber. By applying an input pulse to the heating element so that the second growth of the vapor bubble is maximized at the time when the liquid is sucked to the maximum, the meniscus can be quickly returned to the nozzle side and high-speed printing can be performed. Proposed.

[0004] However, in order to generate the second steam pulse, the input energy, that is, the heat energy is excessively supplied, so that the heat deteriorates the ink and causes clogging of the nozzles. The method described in the above publication cannot be adopted in an ink jet recording head that discharges ink droplets by changing the volume of a pressure chamber by displacement of a child.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a piezoelectric vibrator capable of shortening the interval between ink droplet discharges and preventing nozzle clogging. It is an object of the present invention to provide a driving device for an ink jet recording head using a child as an actuator. Further, another object of the present invention is to provide an ink jet type recording apparatus comprising: a nozzle opening for discharging ink; a pressure generating chamber communicating with the nozzle opening; and a plurality of piezoelectric vibrators for generating pressure by changing the volume of the pressure generating chamber. It is to propose a head driving method.

[0006]

According to the present invention, there is provided a driving apparatus for an ink jet recording head, comprising: a nozzle opening for discharging ink; a pressure generating chamber communicating with the nozzle opening; A driving device for an ink jet recording head including a plurality of piezoelectric vibrators for generating pressure by changing the volume of a pressure generating chamber; a means for generating a first voltage waveform for expanding the volume of the pressure generating chamber; Means for selectively applying the first voltage waveform to the piezoelectric vibrator, and means for selectively applying a second voltage waveform for discharging the ink droplet by contracting the volume of the pressure generating chamber to the piezoelectric vibrator If, after the application of the second voltage waveform, ink droplets
The meniscus after discharge is substantially the most toward the pressure generating chamber side.
When retracted, and a means for applying a third voltage waveform to draw meniscus volume is enlarged to the pressure generating chamber to the pressure generating chamber side to the piezoelectric vibrator.

[0007]

[Function] When printing dots, the maximum order from the initial state
The pressure generation chamber is expanded to the position where ink is sucked and pressure is generated.
The chamber is contracted beyond the initial state to eject ink droplets,
Meniscus is drawn into the pressure generating chamber sideWhen
To expand the pressure generation chamberMoveLet it settle
You.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to embodiments. FIG. 1 is a configuration diagram of an ink jet recording head used in the present invention. In the figure, reference numeral 1 denotes a pressure generating chamber, and a nozzle plate 3 having a nozzle opening 2 formed therein.
And a vibrating plate 4 abutting on a tip of a piezoelectric vibrator 7 described later, with a spacer 5 interposed therebetween.
1 connected to an ink tank (not shown)
4 is supplied with ink.

Reference numeral 7 denotes the above-described piezoelectric vibrator. In this embodiment, the piezoelectric vibrator 8 and the electrode forming materials 9 and 10 are alternately sandwiched between each other so as to form a laminated structure. The region is fixed to the fixed substrate 11. The fixed substrate 11, the spacer 5, and the diaphragm 4
Are integrally fixed via a base 12 and are assembled as an ink jet recording head.

In the ink jet recording head thus configured, when a voltage is applied to the electrodes 9 and 10 of the piezoelectric vibrator 7, the piezoelectric vibrator 7 extends toward the nozzle plate 3, and
The vibration plate 4 compresses the pressure generating chamber 1. As a result, a part of the ink existing in the pressure generating chamber 1 is discharged from the nozzle opening 2.

FIG. 2 shows an embodiment of a driving circuit for driving the above-mentioned ink jet recording head. Reference numeral 13 in the figure
Reference numeral 0 denotes a control signal generation circuit which will be described later. The control signal generation circuit captures print data sent from a device (not shown) via the data bus 131, and a print timing signal indicating that the recording head has reached the print position is input to the terminal 132. At this stage, the received print data is serially transferred and output to the drive circuit of the printhead.

.. From the control signal generation circuit 130 to the data terminals of flip-flops 139, 139,...
The shift clock signal is output via the switch 3. When the print data signals for all the piezoelectric vibrators 48, 48,... Are transferred, the print data serially transferred to the latches 138, 138,. Output a signal for performing The signal line 135 is also output to the drive voltage signal generation circuit 84, and at the same time as the signal output, the drive voltage signal generation circuit 84 outputs a drive voltage signal having a predetermined voltage waveform described later.

FIG. 3 is a diagram showing one embodiment of the above-described drive voltage signal generation circuit. The timing generation circuit 170
One-shot multivibrators 171, 172,
When a timing signal is output to the signal line 135 from the control signal generating circuit 130, first, a LOW level signal having a constant pulse width is output from the first one-shot multivibrator 171. Then, the first constant current circuit 180 operates, and in the initial state, −V
The capacitor 152 charged to M volts is charged by the constant current Ir. When the constant current value Ir
2 is charged to approximately 0 volts, a diode 153 connected in parallel with the capacitor 152
The terminal voltage at terminal 2 is clamped and maintained at a substantially zero volt state.

First one-shot multivibrator 1
When the output signal of the signal 71 changes to the HIGH level, the second signal is used as a trigger to output the second one-shot multivibrator 17.
2 outputs a LOW level signal having a constant pulse width. This time, the second constant current circuit 181 is operated.
2 is approximately 0 volts to approximately -VL which is the power supply voltage.
It is discharged at a constant current value If up to volts.

Further, when the output signal of the second one-shot multivibrator 172 changes to a high level,
Using this as a trigger, a LOW level signal having a constant pulse width is output from the third one-shot multivibrator 173, and the third constant current circuit 182 is operated this time, and the capacitor 152 is driven from approximately -VL volts to -VM volts. The battery is charged at a constant current value Ir1 up to the current. This capacitor 152
Is changed by the current amplifying transistor pair 159, 16
0 is applied to the piezoelectric vibrators 48, 48,.

In the drive voltage signal generating circuit 84 described above, the capacitance of the capacitor 152 is C, the value of the resistor 200 of the first constant current circuit 180 is Rr, the value of the resistor 201 of the second constant current circuit 181 is Rf, The resistance 30 of the third constant current circuit 182
The value of 0 is Rr1, the transistors 154, 158, 354
Vbe 154, Vbe1
58 and Vbe 354, the charge / discharge current I
r, If, and Ir1 are Ir = Vbe154 / Rr (1) If = Vbe158 / Rf (2) Ir1 = Vbe354 / Rr1 (3), and the charge / discharge time constants Tr, Tf, and Tr1 are Tr = C, respectively. × VM / Ir (4) Tf = C × VL / If (5) Tr1 = C × (VL−VM) / Ir1 (6)

FIG. 4 shows a time-series relationship between the drive voltage signal output from the drive voltage signal generation circuit 84 and the voltage applied to the piezoelectric vibrator. Next, an operation of ejecting ink droplets when the piezoelectric vibrator is driven using the above-described drive voltage signal generation circuit 84 will be described. In the initial state, the output of the drive voltage signal generating circuit 84 is -VM volts, and in this state, the transistors 85, 85,
.. diodes D, D,... Connected in parallel to.
All the piezoelectric vibrators 48, 48,... Have an overdischarged state in which the common connection terminal is at a negative potential (−VM volts) and the other end is substantially 0 volts, that is, a state where a voltage of VM volts is applied. Are extended, and the pressure generating chamber 1 is in a contracted state.

In the first step in which the operation of the first constant current circuit 180 is started and the output of the drive voltage signal generation circuit 84 changes at a constant gradient from -VM volt to approximately 0 volt, the latches 138, 138,. , The transistors 85, 85,.
Piezoelectric vibrators 48, 48 connected to ..., charging only against <br/> is made ..., as a result, the applied voltage from the over-discharge state in the absence of an applied voltage is changed. That is, the piezoelectric vibrators 48, 48,.
Only contracts, the pressure generating chamber 1 expands, and the reservoir 14
Suction ink from. As the pressure generating chamber 1 expands, the meniscus formed near the nozzle opening 2 is drawn into the pressure generating chamber 1 and returns to its original position after a predetermined time.

When the meniscus returns to its original position,
The second constant current circuit 181 starts operating. As a result, the output of the drive voltage signal generating circuit 84 is switched to the second step in which the output changes from substantially 0 volts to about -VL volt at a constant gradient, and the applied voltage becomes substantially zero by the charging in the first step, and the contracted state is obtained. Some of the piezoelectric vibrators 48, 48,... Are over-discharged by setting the common connection terminal to a negative potential,
The state becomes a state in which a voltage of L volts is applied, and expands. Due to the expansion of the piezoelectric vibrators 48, 48,..., The expanded pressure generating chamber 1 contracts, and the contraction causes ink droplets to fly from the nozzle openings 2.

After the ink droplets are ejected, the meniscus is greatly drawn into the pressure generating chamber 1 again, and returns to its original position while vibrating. The operation of the third constant current circuit 182 is started at the time when the movement to the opening 2 side is started. This starts the third step in which the output of the drive voltage signal generation circuit 84 changes at a constant gradient from approximately -VL volts to -VM volts, so the piezoelectric vibrator that ejected ink droplets in the second step , 48 are contracted to the charged and initial position, and the pressure generating chamber 1 is expanded to the initial state. A force that pulls the meniscus back to the pressure generating chamber 1 is generated with this expansion, and the force that moves the meniscus to the nozzle opening 2 side after the ink droplets are ejected cancels out the pull-back force, and the meniscus vibrates. It stops immediately near the nozzle opening without any trouble.

In simulations and experimental results, assuming that the natural oscillation period of the flow path system of the head typified by the vibration of the meniscus is Tc, in order to effectively suppress the vibration of the meniscus after ink droplet ejection, 0.5 < Tc / Tr <3 (7) 0.5 <Tc / Tf <3 (8) Under the condition of 2 <VM / (VL−VM) <10 (9) 1/8 <Tc / Tr1 <1 ( 10) It was confirmed that the setting should be made to be as follows. Also,
Since the recording head of the present invention uses a vertical vibration type piezoelectric vibrator, it was confirmed that the change in volume of the pressure generating chamber was substantially proportional to the applied voltage of the piezoelectric vibrator.

FIGS. 5A and 5B show how the meniscus vibrates according to the present invention. FIG. 5A shows the meniscus behavior, and FIG. 5B shows the driving voltage signal applied to the piezoelectric vibrator. I have. On the other hand, when the third step in the present invention does not work, the meniscus continues to vibrate after the ink droplets fly, as shown in FIG. 6, but in the present invention in which the third step works, the meniscus quickly changes. Has been settled.

FIG. 7 shows the relationship between the driving frequency and the ink droplet flying speed according to the present invention, and FIG. 8 shows the relationship between the conventional driving frequency and the ink droplet flying speed according to the present invention. According to the present invention, the flying speed of ink droplets does not change even in a high driving frequency range, and print quality can be maintained.

On the other hand, when there is no print data signal, that is, when the print data is not latched in the latches 138, 138,..., The transistors 85, 85,.
, Diodes D, D, D,.
, Through the second step in which the output of the drive voltage signal generation circuit 84 changes at a constant gradient from approximately 0 volts to approximately -VL volts, the common connection terminal side is negative. It is always charged as potential regardless of print data.

In the third step in which the output of drive voltage signal generating circuit 84 changes at a constant gradient from approximately -VL volts to -VM volts, one-shot multivibrator 173
Are converted into a HIGH level signal by an inverter 91, and OR gates 180, 180,.
Are supplied to the control terminals of all the transistors 85, 85,... Through the third step, the transistors 85, 85,.
The piezoelectric vibrators 48, 48, charged to approximately VL volts
Discharge to the initial state VM volts.

That is, at the time of non-printing, the piezoelectric vibrators 48, 48,... Are formed in the vicinity of the nozzle opening 2 by repeatedly expanding and contracting so as not to eject ink droplets at each printing timing. Swing the meniscus. Thereby, the ink near the nozzle opening 2 is stirred, the viscosity of the ink of the nozzle that does not discharge the ink droplets for a long time is suppressed, and the clogging due to the drying of the nozzle opening 2 is prevented.

In the above-described embodiment, the piezoelectric vibrator for driving the recording head expands when a voltage is applied, and contracts the pressure generating chamber 1.
As shown in FIG. 9, the pressure generating chamber 1 may be contracted in the vertical direction by applying a voltage to expand the pressure generating chamber 1.

In this case, the drive voltage signal generating circuit 84 can be adapted to use a single power supply (VH volt) by removing the diode 153 in FIG.

FIG. 10 shows the structure of another type of recording head to which the driving technique of the present invention can be applied.
There are two sets of piezoelectric vibrators denoted by a and 7b. Piezoelectric vibrator 7
By applying the voltage waveform shown in FIG. 11A to a, the ink droplet is caused to fly from the nozzle opening 2. Also,
The voltage waveform shown in FIG. 11B is applied to the piezoelectric vibrator 7b, and after the ink droplets are ejected, the voltage is reduced somewhat and then restored. As a result, an expansion and contraction force is generated at both ends of the diaphragm 4 in the vertical direction in the figure, and the diaphragm 4 is deflected to expand and return the pressure generating chamber 1 to its original position. Can be settled quickly.

Also, regardless of the print data, if the voltage waveform shown in FIG. 11B is applied to the piezoelectric vibrator 7b, the meniscus can be swung to prevent the nozzle opening from being clogged.

[0031]

As described above, according to the present invention,
In order to enlarge the pressure generating chamber when the meniscus after the ink droplet ejection is substantially most drawn into the pressure generating chamber side ,
The movement of the meniscus after the ink droplet ejection discharges the expansion of the pressure generating chamber.
And the ejection frequency of ink droplets can be improved .

[Brief description of the drawings]

FIG. 1 is a structural diagram of a recording head used in the present invention.

FIG. 2 is a diagram showing one embodiment of a drive circuit of the present invention.

FIG. 3 is a detailed diagram of a drive voltage signal generation circuit 84 in FIG. 2;

FIG. 4 is a timing chart illustrating a driving method of the present invention.

FIG. 5 is a diagram showing a behavior of a meniscus in the example of the present invention.

FIG. 6 is a diagram showing the behavior of a conventional meniscus.

FIG. 7 is a diagram showing frequency characteristics of the embodiment of the present invention.

FIG. 8 is a diagram showing a conventional frequency characteristic.

FIG. 9 is a structural diagram of another recording head used in the present invention.

FIG. 10 is a structural view of still another recording head used in the present invention.

FIG. 11 is a diagram showing a driving voltage waveform for driving the recording head of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pressure generation chamber 2 Nozzle opening 7 Piezoelectric vibrator 84 Drive voltage signal generation circuit

Claims (10)

(57) [Claims] 1. An ink jet recording head comprising: a nozzle opening for discharging ink; a pressure generating chamber communicating with the nozzle opening; and a plurality of piezoelectric vibrators for generating pressure by changing the volume of the pressure generating chamber. In the driving device, means for generating a first voltage waveform for expanding the volume of the pressure generation chamber; means for selectively applying the first voltage waveform to the piezoelectric vibrator; Means for selectively applying, to the piezoelectric vibrator, a second voltage waveform that causes the piezoelectric vibrator to contract and eject ink droplets; and, after application of the second voltage waveform, the meniscus after ink droplet ejection is substantially directed to the pressure generating chamber side. Means for applying, to the piezoelectric vibrator, a third voltage waveform that expands the volume of the pressure generating chamber and draws a meniscus toward the pressure generating chamber at the time when the pressure is most drawn. Drive DOO type recording head. 2. The ink jet recording head driving device according to claim 1, wherein the voltage waveform of the third voltage is applied to all the piezoelectric vibrators constituting the recording head. 3. The driving apparatus according to claim 1, wherein the third voltage waveform expands the volume of the pressure generating chamber to an initial state. 4. The driving apparatus according to claim 1, wherein the relationship between the duration Tr of the first voltage waveform and the natural oscillation period Tc of the meniscus is 0.5 <Tc / Tr <3. . 5. The ink jet recording head driving device according to claim 1, wherein the relationship between the duration Tf of the second voltage waveform and the natural oscillation period Tc of the meniscus is 0.5 <Tc / Tf <3. . 6. An ink jet recording head comprising: a nozzle opening for discharging ink; a pressure generating chamber communicating with the nozzle opening; and a plurality of piezoelectric vibrators for generating pressure by changing the volume of the pressure generating chamber. In the driving method, a first step of selectively increasing the volume of the pressure generation chamber, a second step of discharging the ink droplet by contracting the volume of the pressure generation chamber, A third step of expanding the volume of the pressure generating chamber and drawing the meniscus toward the pressure generating chamber when the meniscus after ejection is substantially most drawn into the pressure generating chamber. Head driving method. 7. A third step, the driving method of ink jet recording head according to claim 6 which is performed for all of the pressure generating chamber constituting the recording head. 8. The method according to claim 6, wherein the volume of the pressure generating chamber is expanded to an initial state by the third step. 9. The method according to claim 6, wherein the relationship between the duration Tr of the first step and the natural oscillation period Tc of the meniscus is 0.5 <Tc / Tr <3. 10. The method according to claim 6, wherein the relationship between the duration Tf of the second step and the natural vibration period Tc of the meniscus is 0.5 <Tc / Tf <3.