JP2003226008A - Device and method for driving head of inkjet printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and a method for driving a head of an inkjet printer which can easily hold an intermediate potential of each non driving piezoelectric element by a simple constitution. <P>SOLUTION: In the head driving device 10 of the inkjet printer, piezoelectric elements 11 set corresponding to a plurality of nozzles for applying a pressure to ink are driven by a driving signal COM outputted via a current amplifying circuit 13 from a head driving circuit 12 selectively with a predetermined printing timing, thereby recording by discharging ink drops from corresponding nozzles. The head driving device 10 is configured to be provided with a voltage generating circuit 20 for selectively impressing the intermediate potential Vc to electrodes at the ground side of non driving piezoelectric elements 11. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a head drive of an ink jet printer in which a piezoelectric element provided corresponding to a nozzle for ejecting ink droplets in the head of the ink jet printer is held at an intermediate potential. It is related to the technology of.

[0002]

2. Description of the Related Art Conventionally, as an output device of a computer, an ink jet type color printer of a type that ejects ink of several colors from a recording head has been widely used, and an image processed by a computer or the like is printed in multiple colors and multiple gradations. It is widely used to

For example, in an ink jet printer using a piezoelectric element as a drive element for ejecting ink, a plurality of piezoelectric elements provided 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 are attached 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 ejecting an ink droplet, and is driven by a drive signal supplied from a driver IC (head drive circuit) mounted in the print head. The ink droplets are ejected.

By the way, in such a piezoelectric element, when it is not driven (that is, when printing is not performed), the electric charge accumulated by charging is discharged by the insulation resistance and the voltage thereof is lowered. , It may affect the ejection of ink.

[0006] Therefore, the patent No. 3097 by the present applicant
No. 155 discloses a head driving device and a driving method for applying a charging voltage 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 a DC signal, which is set to a high voltage when it is not driven. Sometimes the voltage is low. For this reason, the power consumption becomes large, and the voltage applied to the piezoelectric element becomes relatively high, so that the voltage drop due to the above-mentioned discharge is large and the power loss is large.

Further, in order to increase the density of print dots in order to improve the printing quality, the gap between the electrodes of the piezoelectric elements adjacent to each other becomes narrower, but the driven piezoelectric element and the non-driven piezoelectric element are reduced. When the electrodes are adjacent to each other and the inter-electrode voltage of these piezoelectric elements becomes high, discharge may occur between the electrodes of these piezoelectric elements.

Further, since the density of each piezoelectric element becomes smaller and the withstand voltage becomes lower, the maximum voltage of the drive signal exceeds the withstand voltage of the piezoelectric element when the density becomes higher. Therefore, the piezoelectric element may not operate normally.

Therefore, it is necessary to perform an insulating treatment such as filling an insulating material between the electrodes of the piezoelectric element.

On the other hand, there is also a head drive system in which the ground side of each piezoelectric element is held at the intermediate potential of the 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-mentioned high density, but the voltage is changed corresponding to the change of the drive signal, and the charging and discharging are performed. Therefore, a bidirectional variable power source is required.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a head driving device and a head driving method for an ink jet printer, which can easily hold the intermediate potential of each non-driving piezoelectric element with a simple structure. It is in.

[0013]

In order to solve the above problems, in the present invention, an intermediate potential is applied to each non-driving piezoelectric element by a voltage generating circuit so that each piezoelectric element is held at the intermediate potential. did.

That is, in the head drive device of the ink jet printer according to the first aspect, the piezoelectric element for applying pressure to the ink provided corresponding to each of the plurality of nozzles is provided.
A head drive device for an ink jet printer, which is driven by a drive signal from a head drive circuit selectively at a predetermined print timing, and ejects ink droplets from a corresponding nozzle to perform recording. Is provided with a voltage generating circuit for selectively applying an intermediate potential.

According to a sixth aspect of the present invention, there is provided a head driving method for an ink jet printer, wherein piezoelectric elements for applying pressure to inks respectively corresponding to a plurality of nozzles are provided.
A head driving method for an ink jet printer, which is driven by a driving signal from a head driving circuit selectively at a predetermined printing timing, and ejects ink droplets from a corresponding nozzle to perform recording. It is characterized in that an intermediate potential is selectively applied to each driving piezoelectric element.

According to this structure, the voltage generating circuit applies the intermediate potential to the non-driving piezoelectric element, so that the non-driving piezoelectric element is held at the intermediate potential. Therefore, since the voltage applied between both electrodes of the non-driven piezoelectric element becomes almost 0, the power consumption is reduced and the voltage drop due to the natural discharge of the piezoelectric element is small, and the power loss is reduced. .

Further, since the voltage applied to the piezoelectric element is relatively low, the occurrence of discharge due to the voltage difference between the driven piezoelectric element and the non-driven piezoelectric element is reduced and the density is increased. As a result, even if the piezoelectric element is downsized and the withstand voltage becomes low, it is possible to deal with it, so that it is possible to further increase the density of the head without performing insulation treatment between the electrodes of the piezoelectric element.

According to another aspect of the present invention, in the head drive device, the voltage generation circuit charges the potential application means with a potential application means for applying an intermediate potential to each piezoelectric element and a head drive voltage based on a drive signal. And a charging circuit.

According to a seventh aspect of the present invention, in the head driving method, the voltage generating circuit applies an intermediate potential to each piezoelectric element by the potential applying means, and the charging circuit applies the head driving voltage based on the drive signal. It is characterized in that the potential applying means is charged by utilizing the charge.

According to this structure, the charging circuit charges the potential applying means by using the drive signal. Therefore, the piezoelectric element is applied by applying the intermediate potential to the piezoelectric element based on the charging voltage of the potential applying means. Will be held at the intermediate potential.

According to another aspect of the present invention, in the head drive device, the charging circuit includes a transistor for applying a head drive voltage to the potential applying means and a switch means for selectively applying a drive signal to the base of the transistor. The switch means is turned on at the timing when the drive signal is not driven.

According to another aspect of the present invention, in the head driving method, the charging circuit applies a driving signal to the base of the transistor via the switching means and turns on the switching means at the timing when the driving signal is not driven. Thus, the head drive voltage is applied to the potential applying means via the transistor.

With this configuration, the transistor is turned on by applying the drive signal to the base of the transistor through the switch means that is turned on at the timing when the drive signal is not driven. As a result, the head drive voltage is applied to the potential applying means via the transistor, and the potential applying means is charged to the intermediate potential.

According to another aspect of the head drive device of the present invention, the switch means is continuously turned on before the start of printing and at the end of printing.

According to a ninth aspect of the present invention, in the head driving method, the switch means is continuously turned on before the start of printing and after the end of printing.

According to this structure, the switching means is continuously turned on before the start of printing, so that the potential applying means is gradually charged from the zero charging potential to the intermediate potential. As a result, the voltage applied from the potential applying means to each piezoelectric element also gradually rises to the intermediate potential, so that the malfunction of each piezoelectric element due to the increase of the ground side electrode voltage before the start of printing is prevented.

Similarly, after printing is completed, the switch means is continuously turned on so that the potential application means
The intermediate potential is gradually charged. As a result, the voltage applied from the potential applying means to each piezoelectric element also gradually decreases to zero, so that the malfunction of each piezoelectric element due to the decrease of the ground side electrode voltage after printing is prevented.

According to another aspect of the present invention, the head drive circuit is provided in a printer head, and the switch means is an unused portion of the switch circuit for selectively applying a drive signal to each piezoelectric element. It is characterized by using.

According to a tenth aspect of the invention, in the head driving method, the head driving circuit is provided in the printer head, and the switch means is an unused portion of the switch circuit for selectively applying a driving signal to each piezoelectric element. It is characterized by using.

According to this structure, the switch means can utilize the unused switch portion of the existing switch circuit existing in the printer head to reduce the cost of parts and to save the installation space of the switch means. There is no need to provide any particular device, and the overall size can be reduced.

[0031]

DETAILED DESCRIPTION OF THE INVENTION A head drive device according to an embodiment of the present invention will be described with reference to the drawings. Since the embodiments described below are preferred specific examples of the present invention, various technically preferable limitations are attached, but the scope of the present invention particularly limits the present invention in the following description. Unless otherwise stated, the present invention is not limited to these modes.

FIG. 1 shows the configuration of a first embodiment of a head drive device according to the present invention. In FIG. 1, a head drive device 10 is a head drive circuit for supplying a drive signal to a piezoelectric element 11 provided corresponding to each of a plurality of nozzles of an inkjet printer and one electrode 11a of each piezoelectric element 11. 12, a current amplifier circuit 13 and a switch circuit 14 provided between the head drive circuit 12 and each piezoelectric element 11, and a voltage for applying an intermediate potential to the other ground-side electrode 11b of the piezoelectric element 11. And a generating circuit 20.

Here, in FIG. 1, the piezoelectric element 11
In reality, the printer head of the inkjet printer 10 is provided with one nozzle row for each color, and a piezoelectric element is provided for each nozzle row.

The piezoelectric element 11 is, for example, a piezo element and is constructed so as to be displaced by a voltage applied between both electrodes 11a and 11b.

The piezoelectric element 11 has one electrode 11
a is constantly charged near the intermediate potential Vc, and pressure is applied to the ink in the corresponding nozzle when discharging is performed based on the drive signal COM output from the head drive circuit 12 via the current amplification circuit 13. Thus, the ink droplets are ejected from this nozzle.

The head drive circuit 12 is configured as a driver IC and generates a drive signal COM to the head of the ink jet printer, and is arranged in the printer body, for example.

The current amplifier circuit 13 is composed of two transistors 15 and 16. Of these, the collector of the first transistor 15 has a constant voltage power supply (for example, +42).
V DC power supply), and the base is head drive circuit 1
2 is connected to one output, and the emitter is connected to the input side of the switch circuit 14. As a result, the head drive circuit 12 becomes conductive based on the signal, and the constant voltage Vcc is supplied to the piezoelectric element 11 via the switch circuit 14.

The emitter of the second transistor 16 is connected to the input side of the switch circuit 14, the base is connected to the second output of the head drive circuit 12, and the collector is grounded to ground. . As a result, the piezoelectric element 11 becomes conductive based on the signal from the head drive circuit 12, and the piezoelectric element 11 is discharged through the switch circuit 14.

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.

The switch circuit 14 is actually configured as a so-called trasmission gate for turning on / off each piezoelectric element 11.

The voltage generating circuit 20 comprises a capacitor 21 as a potential applying means and a charging circuit 22.

The capacitor 21 is an electrolytic capacitor, and one end thereof has a common electrode 11b on the ground side of the piezoelectric element 11 so that the charging voltage, that is, the intermediate potential Vc is applied to the electrode 11b on the ground side of each piezoelectric element 11. And the other end is grounded to ground.

The capacitors 21 have a total capacitance (several μF) so that a stable intermediate potential can be supplied to each piezoelectric element 11.
The capacitance is selected to be sufficiently large, for example, about several 100 μF to several 1000 μF. Incidentally, the potential applying means may be other than the capacitor.

The charging circuit 22 includes a transistor 23 as a switching element, a resistor 24 and a capacitor 2.
5, and an analog switch 26 as a switch means,
It consists of

The transistor 23 has an emitter connected to one end of the capacitor 21 and a collector having a constant voltage power supply Vcc.
It is connected to the.

Instead of the transistor 23, various switching elements such as FET, thyristor and triac may be used as the switching element.

The resistor 24 is connected between the emitter of the transistor 23 and the ground, and the capacitor 25 is connected between the base of the transistor 23 and the ground.

Further, the analog switch 26 includes the base of the transistor 23, the emitter of the first transistor 15 of the current amplification circuit 13, and the second transistor 16.
Connected between the emitters of.

Here, the analog switch 26 is turned on by an H level control signal and turned off by an L level control signal when an ON / OFF control signal is input from the control unit of the printer body. ing.

This control signal becomes H level when the drive signal COM output from the head drive circuit 12 via the current amplification circuit 13 is not driven, that is, at an intermediate potential, and becomes L level when driven. Is set as follows.

Further, this control signal is continuously set to the H level at the start of printing and at the end of printing.

Head drive device 10 according to an 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 operation of the ink jet printer at the start of printing (startup) will be described.

At the start of printing, a drive signal COM output from the head drive circuit 12 via the current amplification circuit 13.
Gradually rises.

As a result, a current flows from the first transistor 15 of the current amplification circuit 13 to the one electrode 11a of the piezoelectric element 11 via the switch circuit 14 by the drive signal COM to charge the electrode 11a. The electrode 11a has a medium potential Vc as shown by the solid line A in FIG.
To 20 μS, for example.

At this time, by turning on the analog switch 26 as the switch means, the drive signal COM
Is applied to the base of the transistor 23 of the charging circuit 21 to turn on the transistor 23.

As a result, a constant voltage from the constant voltage power supply Vcc is applied to the capacitor 21, and the capacitor 21 is gradually charged. Therefore, since the charging voltage of the capacitor 21 rises to the intermediate potential Vc, as shown by the dotted line B in FIG. 2, the potential of the ground side electrode 11b of the piezoelectric element 11 also gradually rises and reaches the intermediate potential Vc. .

In this way, the potential of the electrode 11b on the ground side of the piezoelectric element 11 reaches the intermediate potential like the electrode 11a driven by the drive signal COM, so that the electrodes 11a and 11b of both electrodes of the piezoelectric element are connected. The potential difference can be kept low. Therefore, since this potential difference is lower than the intermediate potential Vc of the drive signal COM, the piezoelectric element 11 does not malfunction and eject ink droplets.

Next, the operation of the ink jet printer 10 during printing will be described. During printing, as shown in FIG. 3, the drive signal COM is based on the fluctuation of the drive signal COM.
Is higher than the intermediate potential, the one electrode 11a of the piezoelectric element 11 is charged through the first transistor 15 of the current amplification circuit 13, and when the drive signal COM is lower than the intermediate potential, the current is reduced. The one electrode 11a of the piezoelectric element 11 is discharged through the second transistor 16 of the amplifier circuit 13. As a result, the piezoelectric element 11 operates based on the drive signal COM to eject an ink droplet.

At this time, as shown in FIG. 3, the analog switch 26 is turned on only when the drive signal COM is not driven (intermediate potential), so that the capacitor 21 of the voltage generation circuit 20 is always charged by the charging circuit 22. Will be charged at an intermediate potential.

As a result, the other common electrode 11b on the ground side of each piezoelectric element 11 is always held at the intermediate potential Vc when the intermediate potential Vc is applied from the capacitor 21.

Further, the operation of the ink jet printer 10 at the end of printing (stop end) will be described.

At the end of printing, the drive signal COM output from the head drive circuit 12 via the current amplification circuit 13.
Is one electrode 11 of the piezoelectric element 11 as shown in FIG.
The potential is reduced to 0 by being discharged from a through the second transistor 16 of the current amplification circuit 13.

At this time, when the analog switch 26 is turned on, the drive signal COM is applied to the base of the transistor 23 of the charging circuit 21. At this time, the drive signal COM gradually drops, so the transistor 23 is turned on.
Remains off.

As a result, the capacitor 21 of the voltage generating circuit 20 is grounded to the ground via the resistor 24, so that the capacitor 21 is gradually discharged.
Therefore, the charging voltage of the capacitor 21 drops to zero, so that the potential of the electrode 11b on the ground side of the piezoelectric element 11 gradually drops to zero as shown by the dotted line B in FIG.

Since the potential of the electrode 11b on the ground side of the piezoelectric element 11 gradually reaches zero similarly to the electrode 11a driven by the drive signal COM, the potential difference between the electrodes 11a and 11b of the piezoelectric element is equal to that of the electrode 11a. It can be kept low.
Therefore, this potential difference is due to the intermediate potential Vc of the drive signal COM.
Since it is lower, the piezoelectric element 11 does not malfunction and eject ink droplets.

In this way, the power consumption of the piezoelectric element 11 is reduced, the voltage drop due to 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 low, even if such piezoelectric elements 11 are adjacent to each other, the piezoelectric element 1
The occurrence of discharge between the piezoelectric elements 11 is reduced, and even if the withstand voltage of each piezoelectric element 11 is lowered due to the high density, it is not necessary to perform insulation treatment between the piezoelectric elements 11, so that the head can be increased in density. It can be easily realized.

Furthermore, since the capacitor 21 is charged by using the head drive voltage, the power supply circuit for generating the intermediate potential Vc is not particularly required.

FIG. 5 shows an example of the configuration of a switch circuit which can be used as a switch means instead of the analog switch 26 described above.

In FIG. 5, a switch circuit 30 is a transistor connected between the base of the transistor 23 and the emitter of the first transistor 15 and the emitter of the second transistor 16 of the current amplification circuit 13 instead of the analog switch 26. 31 and a transistor 32 connected between the base of the transistor 31 and the ground via a resistor 33.

A resistor 34 is connected between the base and the emitter of the transistor 31.

An on / off control signal is input to the base of the transistor 32 from the control unit of the printer body.

According to the switch circuit 30 having such a configuration, the drive signal COM is transmitted to the resistors 33 and 3 by inputting the H level control signal to the base of the transistor 32.
By flowing through 4 to the ground, a voltage is applied to the base of the transistor 31 and the transistor 31 is turned on.

Further, by inputting an L level control signal to the base of the transistor 32, the transistor 3
In the case of 1, the base and the emitter are held at the same potential, and the transistor 31 is turned off.

As a result, the switch circuit 30 is on / off controlled by the control signal, like the analog switch 26.

FIG. 6 shows the configuration of a second embodiment of the head drive device according to the present invention. In FIG. 6, the head drive device 40 has substantially the same configuration as the head drive device 10 shown in FIG. 1, and therefore, the same components are given the same reference numerals and the description thereof is omitted.

The head drive device 40 is different from the head drive device 10 shown in FIG. 1 in that the head drive circuit 12, the current / current amplifier circuit 13, the switch circuit 14, and the voltage generation circuit 20.
Are mounted on the printer head 41 (or a carriage that supports the printer head 17).

The analog switch 26 of the voltage generating circuit 20 is constructed by utilizing an unused switch portion of the switch circuit 14 mounted on the printer head 41.

According to the head driving device 40 having such a structure, the head driving device 10 operates in the same manner as the head driving device 10 shown in FIG.
However, by utilizing the unused switch portion of the switch circuit 14, the number of components can be reduced, and the component cost and the assembly cost can be reduced.

In the embodiment described above, the piezoelectric element 1
For example, a piezo element is used as 1, but the piezoelectric element 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 charging circuit 22 includes the transistor 23, the resistor 24, the capacitor 25, and the analog switch 26 as a switch means.
However, the present invention is not limited to this, and the constant voltage power supply V
If the constant voltage from cc can be supplied to the capacitor 21, it is possible to use a charging circuit of any other configuration.

[0083]

As described above, according to the present invention, for example, the head driving voltage is utilized to apply an intermediate potential to the electrode on the ground side of the non-driving piezoelectric element so that the ground side of the piezoelectric element is controlled. It will be held at the intermediate potential.
Therefore, since the voltage applied between both electrodes of the piezoelectric element becomes almost zero, the power consumption is reduced, and the voltage drop due to the natural discharge of the piezoelectric element is small, and the power loss is reduced.

[Brief description of drawings]

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

FIG. 2 is a time chart showing an operation at the start of printing in the head drive device of FIG.

3 is a time chart showing an operation during printing in the head drive device of FIG. 1. FIG.

FIG. 4 is a time chart showing an operation at the end of printing in the head drive device of FIG.

5 is a partial circuit diagram showing a configuration example of a switch circuit as a switch means in the head drive device of FIG.

FIG. 6 is a block diagram showing a configuration of a second embodiment of a head drive device according to the present invention.

[Explanation of symbols]

10,40 head drive 11 Piezoelectric element 11a One electrode 11b Ground side electrode 12 head drive circuit 13 Current amplification circuit 14 switch circuit 15 First transistor 16 Second transistor 20 voltage generation circuit 21 capacitor 22 Charging circuit 23 transistor 24 resistance 25 capacitors 26 Analog switch (switch means) 30 switch circuit (switch means) 41 printer head

Claims (10)

[Claims] 1. A piezoelectric element for applying pressure to ink provided corresponding to each of a plurality of nozzles is selectively driven at a predetermined printing timing by a drive signal from a head drive circuit, and ink droplets are ejected from the corresponding nozzles. A head drive device for an inkjet printer that discharges ink to perform recording, characterized by including a voltage generation circuit that selectively applies an intermediate potential to each non-driven piezoelectric element. Head drive device. 2. The voltage generating circuit includes potential applying means for applying an intermediate potential to each piezoelectric element, and a charging circuit for charging the potential applying means with a head drive voltage based on a drive signal. The head drive device for an ink jet printer according to claim 1, characterized in that: 3. The charging circuit comprises a transistor for applying a head drive voltage to the potential applying means and a switch means for selectively applying a drive signal to the base of the transistor, the switch means comprising: The head drive device for an ink jet printer according to claim 2, wherein the head drive device is turned on at a timing when the drive signal is not driven. 4. The head drive device for an ink jet printer according to claim 3, wherein the switch means is continuously turned on before the start of printing and after the end of printing. 5. The head drive circuit is provided in a printer head, and the switch means utilizes an unused portion of the switch circuit for selectively applying a drive signal to each piezoelectric element. The head drive device for an inkjet printer according to claim 4. 6. A piezoelectric element that applies pressure to ink provided corresponding to each of the plurality of nozzles is selectively driven at a predetermined printing timing by a drive signal from a head drive circuit, and ink drops are ejected from the corresponding nozzles. A method for driving a head of an inkjet printer, which discharges ink to perform recording, wherein an intermediate potential is selectively applied to each non-driven piezoelectric element by a voltage generating circuit. Driving method. 7. The voltage generation circuit applies an intermediate potential to each piezoelectric element by means of potential application means, and the charging circuit charges the potential application means by using a head drive voltage based on a drive signal. The method for driving a head of an ink jet printer according to claim 6, wherein: 8. The head drive circuit through the transistor, wherein the charging circuit applies a drive signal to the base of the transistor through the switch means and turns on the switch means at a timing when the drive signal is not driven. 8. The method for driving a head of an ink jet printer according to claim 7, wherein a voltage is applied to the potential applying means. 9. The method for driving a head of an ink jet printer according to claim 8, wherein the switch means is continuously turned on before the start of printing and after the end of printing. 10. The head drive circuit is provided in a printer head, and the switch means utilizes an unused portion of the switch circuit for selectively applying a drive signal to each piezoelectric element. The method for driving a head of an inkjet printer according to claim 9.