JP2002273874A - Device and method for driving head of ink-jet printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device and a method for driving a head of an ink-jet printer in which a voltage to be impressed between electrodes of piezoelectric elements is lowered by a simple constitution. SOLUTION: The device 10 for driving the ink-jet printer drives piezoelectric elements 11 set correspondingly to a plurality of nozzles for applying a pressure to ink, selectively with a predetermined printing timing by a driving signal COM from a head-driving circuit 12 to discharge ink drops from corresponding nozzles to carry out printing. The head-driving device 10 is constituted to be provided with a first capacitor 20 for impressing a predetermined bias voltage to the electrode of the ground side of each piezoelectric element, and a charging circuit 21 for charging the first capacitor by utilizing charges by discharging of each piezoelectric element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet printer in which the ground side of a piezoelectric element provided corresponding to a nozzle for ejecting ink droplets by an ink jet printer head is maintained at an intermediate potential. Related to head driving technology.

[0002]

2. Description of the Related Art Conventionally, as an output device of a computer, an ink jet color printer of a type in which several colors of ink are ejected from a recording head has become widespread, and an image processed by a computer or the like is printed in multiple colors and multiple gradations. Widely used for

For example, in an ink jet printer using a piezoelectric element as a driving element for discharging ink, a plurality of piezoelectric elements provided respectively corresponding to a plurality of nozzles of a print head are selectively driven. The ink droplets are ejected from the nozzles based on the dynamic pressure of each piezoelectric element, and the ink droplets adhere to the printing paper, thereby forming dots on the printing paper and performing printing.

Here, each piezoelectric element is provided corresponding to a nozzle for discharging ink droplets, and is supplied from a driver IC (head drive circuit) mounted in the printer main body or the print head. It is driven by a drive signal to eject ink droplets.

By the way, in such a piezoelectric element, when not driven (ie, when printing is not performed), the charge accumulated by charging is discharged by the insulation resistance, and the voltage is reduced. In some cases, ink ejection may be affected.

[0006] For this reason, Japanese Patent No. 3097 by the present applicant is disclosed.
No. 155 discloses a driving device and a driving method of a head in which a charging voltage is applied to a piezoelectric element at a timing different from the driving timing to maintain the charging voltage.

[0007]

However, in driving the head of such an ink jet printer, the driving signal applied to each piezoelectric element is set to a high voltage when not driven, for example, and a low voltage when driven. It is configured to be. In this case, the power consumption increases and the voltage applied to the piezoelectric element becomes relatively high, so that the voltage drop due to the above-described discharge is large,
Large power loss.

[0008] In order to increase the printing dot density in order to improve the printing quality, the gap between the electrodes of adjacent piezoelectric elements becomes narrower. If the voltage between the electrodes of these piezoelectric elements is high when the elements are adjacent to each other, discharge may occur between the electrodes of these piezoelectric elements.

Further, since the individual piezoelectric elements become smaller and their breakdown voltage becomes lower due to the higher density, when the density is further increased, the maximum voltage of the drive signal exceeds the breakdown voltage of the piezoelectric elements. Therefore, the piezoelectric element may not operate normally. Therefore, an insulating process such as filling an insulating material between the electrodes of the piezoelectric element is required.

On the other hand, there is also a head drive system in which the ground side of each piezoelectric element is held at an intermediate potential of a drive signal. According to such a head driving method, it is possible to prevent the discharge between the piezoelectric element electrodes at the time of the above-described high density, but the voltage is changed and the charge and discharge are performed in response to the change of the drive signal. , A bidirectional variable power supply is required.

It is an object of the present invention to provide a head driving apparatus and a head driving method for an ink jet printer, wherein the voltage applied between the electrodes of each piezoelectric element is reduced with a simple configuration. is there.

[0012]

In order to solve the above-mentioned problems, according to the present invention, a bias voltage from a first capacitor charged by a charging circuit is applied to a ground-side electrode of each piezoelectric element. The ground side of the piezoelectric element is maintained at a potential higher than the ground potential.

That is, in the head driving device of the ink jet printer according to the first aspect, the piezoelectric elements provided corresponding to the plurality of nozzles are selectively driven at a predetermined printing timing by a driving signal from the head driving circuit. A head drive device of an ink jet printer that drives and performs recording by discharging ink droplets from corresponding nozzles, and a first capacitor that applies a predetermined bias voltage to a ground-side electrode of each piezoelectric element, And a charging circuit for charging the first capacitor by using the charge generated by the discharge of each piezoelectric element.

According to a fifth aspect of the present invention, there is provided a head driving method for an ink jet printer, wherein a piezoelectric element provided for each of a plurality of nozzles is selectively driven at a predetermined printing timing by a driving signal from a head driving circuit. A method of driving a head of an ink jet printer that drives and performs recording by ejecting ink droplets from corresponding nozzles, wherein a first capacitor connected to a ground electrode of each piezoelectric element is provided. It is characterized in that a charging circuit is charged by using the electric charge generated by the discharge, and a bias voltage is applied to a ground electrode of each piezoelectric element.

According to this configuration, the bias voltage is applied to the ground-side electrode of the piezoelectric element based on the charging voltage of the first capacitor charged by the charging circuit using the discharge charge of the piezoelectric element. Thus, the ground side of the piezoelectric element is held at the bias voltage. Therefore, by using the electric charge that has been discarded at the time of discharging from the piezoelectric element as a power source, power consumption is reduced, and a voltage drop due to spontaneous discharge of the piezoelectric element is small, and a highly accurate waveform can be realized.

Further, when changing the bias voltage, the circuit constant of the charging circuit is appropriately changed,
Since the bias voltage can be easily changed, there is no need to newly design a charging circuit or replace it with another charging circuit, and it is possible to easily respond.

According to a second aspect of the present invention, in the head driving device, the charging circuit includes a second capacitor that is charged by electric charges generated by discharging the piezoelectric elements. According to a sixth aspect of the present invention, in the head driving method, the charging circuit includes a second capacitor that is charged by a charge generated by discharging each piezoelectric element.

According to this structure, the first capacitor connected to the ground electrode of the piezoelectric element is charged via the second capacitor of the charging circuit, so that the ground electrode of the piezoelectric element is charged. A stable bias voltage is applied from the first capacitor.

According to a third aspect of the present invention, in the head driving device, the charging circuit includes a constant voltage circuit for stabilizing a charging voltage of the second capacitor and applying the voltage to the first capacitor. According to a seventh aspect of the present invention, in the head driving method, the charging circuit includes a constant voltage circuit that stabilizes a charging voltage of the second capacitor and applies the voltage to the first capacitor.

According to this configuration, the charging voltage is applied to the first capacitor connected to the ground-side electrode of the piezoelectric element from the second capacitor of the charging circuit via the constant voltage circuit. The fluctuation of the charging voltage of one capacitor is suppressed. Therefore, the bias voltage applied to the ground-side electrode of the piezoelectric element is kept more constant.

According to a fourth aspect of the present invention, the second capacitor of the charging circuit is gradually charged before the start of printing. In a head driving method according to an eighth aspect, the second capacitor of the charging circuit is gradually charged before printing is started.

According to this configuration, the output voltage of the second capacitor and the charging voltage of the first capacitor are gradually increased by gradually charging the second capacitor before the start of printing. The bias voltage applied from the capacitor to the ground electrode of each piezoelectric element also gradually increases. Therefore, malfunction of each piezoelectric element due to an increase in the bias voltage before the start of printing is prevented.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A head driving device according to an embodiment of the present invention will be described with reference to the drawings. The embodiment described below is a preferred specific example of the present invention, and thus various technically preferable limitations are added. However, the scope of the present invention particularly limits the present invention in the following description. The embodiment is not limited to these embodiments unless otherwise stated.

FIG. 1 shows the configuration of an embodiment of a head driving device according to the present invention. In FIG. 1, a head driving device 10 includes a piezoelectric element 11 provided for each of a plurality of nozzles of an ink jet printer, and a head driving circuit for supplying a driving signal to one electrode 11a of each piezoelectric element 11. 12 and the head drive circuit 12
Current amplification circuit 13 provided between
And a switch circuit 14, and a first capacitor 20 and a charging circuit 21 for applying a predetermined voltage to the other ground-side electrode 11 b of the piezoelectric element 11.

Although only one piezoelectric element 11 is shown in FIG. 1, a plurality of nozzles are actually provided in the head of the ink jet printer. One piezoelectric element is provided for each. The drive signal COM from the head drive circuit 12 is actually output to each piezoelectric element 11 sequentially via a shift register or the like. The piezoelectric element 11 is, for example, a piezo element, and is configured to be displaced by a voltage applied between the electrodes 11a and 11b.

The piezoelectric element 11 always has the intermediate potential V
The ink is charged near c, and is configured to discharge ink droplets from the nozzles by applying pressure to the ink in the corresponding nozzles when discharging based on the drive signal from the head drive circuit 12. . Head drive circuit 12
Is configured as a driver IC, which generates a drive signal COM to the head of the ink jet printer, and is disposed, for example, in the printer body.

The current amplifying circuit 13 includes two transistors 15 and 16. Among them, the first transistor 15 has a collector connected to the constant voltage power supply, a base connected to the output of the head drive circuit 12, and
The emitter is connected to the input side of the switch circuit 14. Accordingly, conduction is performed based on a signal from the head drive circuit 12, and a constant voltage is supplied to the piezoelectric element 11 via the switch circuit 14.

The second transistor 16 has an emitter connected to the input side of the switch circuit 15, a base connected to the output of the head drive circuit 12, and a collector connected to the charging circuit 21 as described later. ing. As a result, conduction is performed based on the signal from the head drive circuit 12, the piezoelectric element 11 is discharged via the switch circuit 14, and the discharged charge is supplied to the charging circuit 21.

When the control signal is input, the switch circuit 14 is turned on at the drive timing of the corresponding piezoelectric element 11, and outputs the drive signal COM to the piezoelectric element 11. One end of the first capacitor 20 is connected to the piezoelectric element 1 such that the charging voltage is applied as a bias voltage Vb to the ground-side electrode 11 b of each piezoelectric element 11.
The other end is connected to ground while the other end is connected to the common electrode 11b on the ground side.

The capacity of the first capacitor 20 is set to the total capacitance (about several μF) of all the piezoelectric elements 11 so that a stable bias voltage can be supplied to each of the piezoelectric elements 11. Large enough capacity, for example,
It is selected to be about 00 μF to 5600 μF.

The charging circuit 21 includes a third transistor 22, a second capacitor 23, and a constant voltage circuit 30. The third transistor 22 has an emitter connected to the collector of the second transistor 16 of the current amplifying circuit 13, a collector connected to the ground, and a base connected to the head drive circuit 12 via the constant voltage diode 24. It is connected.

As a result, a voltage V3, which is lower than the drive signal COM by the voltage of the constant voltage diode 24, is applied to the base of the third transistor 22, as shown by the dotted line in FIG. Become. Therefore, the third transistor 22 is turned on only when the voltage V3 is higher than the intermediate potential Vc with respect to the drive signal COM.

The second capacitor 23 has one end connected to the emitter of the third transistor via the diode 25 and the collector of the second transistor 16 of the current amplifier circuit 13, and the other end connected to the ground. Have been. Incidentally, the second capacitor 23 may be charged at all times or before the start of printing by applying a constant voltage through, for example, a high resistance. The battery may be charged so that the battery is charged.

In the case of the drawing, the constant voltage circuit 30 is a constant voltage circuit having a known configuration.
1, a constant voltage diode 32 and a resistor 33. The fourth transistor 31 has a collector connected to one end of the second capacitor 23, an emitter connected to one end of the first capacitor 20, and a base connected to the constant voltage diode 32. Constant voltage diode 3
The other end of the resistor 2 is connected to the ground,
3 has one end connected to one end of the second capacitor 23,
The other end is connected to the base of the fourth transistor 31.

Head drive device 10 according to the embodiment of the present invention
Is configured as described above, and operates as follows based on the head driving method according to the present invention. First, the piezoelectric element 11 driven during printing will be described.
Start printing on inkjet printer (startup)
At this time, as shown in FIG. 3A, the drive signal COM from the head drive circuit 12 rises to the intermediate potential Vc when the charge signal NCHG is inverted to the L level for a time of, for example, 100 μs.

Thus, a current flows from the first transistor 15 of the current amplifying circuit 13 to the one electrode 11a of the piezoelectric element 11 via the switch circuit 14 in response to the drive signal COM, so that the one electrode 11a of the piezoelectric element 11 is charged. The electrode 11a rises to the intermediate potential Vc as shown by the solid line in FIG.

At this time, the charging voltage of the first capacitor 20 is applied to the other common electrode 11b on the ground side of each piezoelectric element 11 as the bias voltage Vb.
As shown by a dotted line in FIG. 3B, the voltage is maintained at a predetermined voltage Vb.

Here, the potential of the ground electrode 11b of the piezoelectric element 11 is maintained at a predetermined voltage Vb.
At the start of printing, both electrodes 11a, 1a of the piezoelectric element 11 are
The potential difference between 1b is Vb, and this potential difference Vb is
Since it is lower than the intermediate potential Vc of the drive signal COM, there is no possibility that the piezoelectric element 11 malfunctions and ejects ink droplets.

During printing, if the drive signal COM is higher than the intermediate potential Vc based on the fluctuation of the drive signal COM, one of the piezoelectric elements 11 is passed through the first transistor 15 of the current amplifier circuit 13. When the electrode 11a is charged and the drive signal COM is lower than the intermediate potential Vc, one electrode 11a of the piezoelectric element 11 is discharged via the second transistor 16 of the current amplification circuit 13. Accordingly, the piezoelectric element 11 operates based on the drive signal COM, and ejects ink droplets.

The electric charge generated by the above-mentioned electric discharge is shown in FIG.
As shown in (B), the charge is accumulated in the second capacitor 23 via the diode 25 of the charging circuit 21, and the second capacitor 23 is charged.

Here, as shown by the symbol X in FIG. 3B, the piezoelectric element 11 causes a voltage drop due to self-discharge on the way, and the potential of one electrode 11a becomes lower than the intermediate potential Vc. Charge signal NCHG to prevent
Is the drive signal CO as indicated by the symbol Y in FIG.
An L-level pulse is generated at a constant period of M, that is, at a timing when there is no change in the drive signal COM.

Thus, based on the drive signal COM from the head drive circuit 12, one electrode 11 of the piezoelectric element 11 passes through the first transistor 15 of the current amplifier circuit 13.
is charged, and even the non-driven piezoelectric element 11 is maintained at the intermediate potential Vc.

On the other hand, when the bias voltage Vb is applied from the first capacitor 20, the common electrode 11b on the other ground side of each piezoelectric element 11 is maintained at this voltage. Therefore, each piezoelectric element 11
The potential difference between the two electrodes 11a and 11b is (Vc-V
b).

If the charging voltage of the first capacitor 20, that is, the bias voltage Vb is adjusted to be equal to the intermediate potential Vc of the drive signal, the potential difference between the two electrodes 11a and 11b of each piezoelectric element 11 becomes zero. Becomes Further, at the end of printing (stop end), the drive signal COM from the head drive circuit 12 is supplied from one electrode 11a of the piezoelectric element 11 to the second transistor 16 of the current amplifying circuit 13 as shown in FIG. , The potential drops to zero.

On the other hand, for the non-driven piezoelectric element 11, one electrode 11a of the piezoelectric element 11 is always charged and held at the intermediate potential Vc by the drive signal COM from the head drive circuit 12. .

In this manner, the potential of the ground electrode 11b of each piezoelectric element 11 is maintained at the predetermined bias voltage Vb by the charging voltage of the first capacitor 20, so that both electrodes of the piezoelectric element 11 When the potential difference between the piezoelectric elements 11a and 11b is kept low and the driven piezoelectric element and the non-driven piezoelectric element are adjacent to each other, the voltage difference between one electrode 11a of these piezoelectric elements 11 is also kept low. Become. Therefore, the power consumption of the piezoelectric element 11 is reduced, the voltage drop due to the self-discharge of the piezoelectric element 11 is small, and the power loss is reduced.

Further, since the potential difference between the driven piezoelectric element 11 and the non-driven piezoelectric element 11 is reduced, even when such piezoelectric elements 11 are adjacent to each other, the piezoelectric element 1
Even if the generation of discharge between the piezoelectric elements 11 is reduced and the withstand voltage of the individual piezoelectric elements 11 is reduced due to the high density, there is no need to perform insulation between the piezoelectric elements 11. It can be easily realized.

Further, the first capacitor 20 and the second capacitor 23 in the charging circuit 21
Since the battery is charged by using the discharge charge generated by the discharge of No. 1, a power supply circuit for generating the bias voltage Vb is not particularly required.

In the above-described embodiment, the piezoelectric element 1
For example, a piezo element is used as 1, but the invention is not limited to this, and another piezoelectric element such as an electrostrictive element or a magnetostrictive element may be used.

In the above-described embodiment, the constant voltage circuit 30 has a configuration using the constant voltage diode 32. However, the present invention is not limited to this.
0 is a configuration using the resistors R1 and R2 as shown in FIG. 4 or the resistors R1 and R2 as shown in FIG.
A constant voltage circuit having various known configurations such as a configuration using the R2 and the reference power source P can be used.

[0051]

As described above, according to the present invention, the ground-side electrode of the piezoelectric element is based on the charging voltage of the first capacitor charged by the charging circuit using the discharge charge of the piezoelectric element. By applying a bias voltage to
The ground side of the piezoelectric element is held at the bias voltage. This bias voltage uses the electric charge discarded from the head to create a power supply, which reduces power consumption and reduces the voltage drop due to spontaneous discharge of the piezoelectric element, thereby reproducing a highly accurate waveform. You.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a head driving device according to the present invention.

FIG. 2 is a time chart showing (A) fluctuation of a base voltage of a third capacitor of a charging circuit and (B) fluctuation of a current of a diode in the head driving device of FIG. 1;

FIG. 3 is a time chart showing fluctuations of (A) a drive signal, (B) both electrode voltages of a piezoelectric element, and (C) a charge signal in the head driving device of FIG.

FIG. 4 is a partial circuit diagram showing another configuration example of the constant voltage circuit of the charging circuit in the head driving device of FIG.

FIG. 5 is a partial circuit diagram showing still another configuration example of the constant voltage circuit of the charging circuit in the head driving device of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Head drive device 11 Piezoelectric element 11a One electrode 11b Ground electrode 12 Head drive circuit 13 Current amplifier circuit 14 Switch circuit 15 First transistor 16 Second transistor 20 First capacitor 21 Charging circuit 22 Third transistor 23 Second capacitor 24 Constant voltage diode 25 Diode 30 Constant voltage circuit 31 Fourth transistor 32 Constant voltage diode 33 Resistance

Claims (8)

[Claims] 1. A piezoelectric element provided for each of a plurality of nozzles is selectively driven at a predetermined print timing by a drive signal from a head drive circuit, and ink droplets are ejected from a corresponding nozzle to perform recording. A first capacitor for applying a predetermined bias voltage to a ground-side electrode of each piezoelectric element, and the first capacitor using electric charge generated by discharging of each piezoelectric element. And a charging circuit for charging the capacitor. 2. The apparatus according to claim 1, wherein the charging circuit includes a second capacitor that is charged by electric charges generated by discharging the piezoelectric elements. 3. The ink jet printer according to claim 2, wherein the charging circuit includes a constant voltage circuit for stabilizing a charging voltage of the second capacitor and applying the voltage to the first capacitor. Head drive. 4. The head drive device of an ink jet printer according to claim 2, wherein the second capacitor of the charging circuit is gradually charged before printing is started. 5. Recording is performed by selectively driving a piezoelectric element provided corresponding to each of a plurality of nozzles at a predetermined print timing by a drive signal from a head drive circuit, and discharging ink droplets from the corresponding nozzle. A head driving method of an ink jet printer, wherein a first capacitor connected to a ground electrode of each piezoelectric element is charged by a charging circuit using electric charge generated by discharging each piezoelectric element, A head driving method for an ink jet printer, comprising applying a bias voltage to a ground electrode of each piezoelectric element. 6. The method according to claim 5, wherein the charging circuit includes a second capacitor that is charged by electric charges generated by discharging the piezoelectric elements. 7. The ink jet printer according to claim 6, wherein the charging circuit includes a constant voltage circuit for stabilizing a charging voltage of the second capacitor and applying the voltage to the first capacitor. Head driving method. 8. The head driving method for an ink jet printer according to claim 6, wherein the second capacitor of the charging circuit is gradually charged before printing is started.