JP2002307675A - Head driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem wherein a voltage of a piezoelectric element of a nozzle which is not driven in printing is lowered by self discharging due to the insulation resistance. SOLUTION: A voltage of a voltage hold circuit 21 is applied to a piezoelectric element from a switch circuit 9 such that the voltage is not changed every time when printing is not performed, thereby always applying an intermediate voltage thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a head driving technique for maintaining an intermediate potential on a segment side of a piezoelectric element provided corresponding to a nozzle for discharging ink droplets in an ink jet printer head. It is about.

[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. 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, so that each of the piezoelectric elements is driven. The ink droplets are ejected from the nozzles based on the dynamic pressure of the 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 ink droplets, and is driven by a drive signal supplied from a driver IC (head drive circuit) mounted in a print head. Thus, ink droplets are ejected.

By the way, when such a piezoelectric element is not driven (that is, 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, conventionally, Japanese Unexamined Patent Application Publication No.
No. 9 discloses a head drive device in which a switch circuit is inserted for each of a plurality of waveforms and an intermediate potential, and the plurality of waveforms and the intermediate potential can be changed by switching the switching circuit.

[0007]

However, in driving the head of such an ink jet printer,
The drive signal applied to each piezoelectric element has many waveforms according to the type of printing, and the intermediate potential changes depending on the temperature. Only needed. Further, a power supply for outputting a voltage corresponding to the number of intermediate potentials is required. In order to solve the above-mentioned problem, according to the present invention, one switch circuit is inserted into each of the waveform and the intermediate potential, and a plurality of waveforms are used.
The same thing can be done with the switch circuits.

[0008]

According to a first aspect of the present invention, there is provided a head driving device, wherein a piezoelectric element for applying pressure to ink chambers respectively corresponding to a plurality of nozzles is driven by a driving signal from a driving waveform generating circuit. An ink jet printer head drive device that selectively drives at a predetermined print timing and ejects ink droplets from an ink chamber of a corresponding nozzle to perform recording, wherein an intermediate potential is applied to an electrode on a segment side of each piezoelectric element. , And an intermediate potential holding circuit for applying the voltage.

According to a second aspect of the present invention, the intermediate potential holding circuit applies a charging voltage to each of the piezoelectric elements at a timing different from the printing timing of each of the piezoelectric elements, and reduces the charge due to the discharge of the piezoelectric elements. A voltage hold circuit that latches an arbitrary voltage of the drive signal from the drive waveform generation circuit based on a charge signal from the piezoelectric element charging unit that corrects the current, and a current amplifier circuit that amplifies the output of the voltage hold circuit. It is characterized by including.

According to a third aspect of the present invention, in the head driving device, the potential holding circuit is provided in a head portion.

[0011]

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 embodiments are not limited to these embodiments unless otherwise stated. FIG. 1 shows a configuration of an embodiment of a head driving device according to the present invention. In FIG. 1, a head driving circuit 10 includes a piezoelectric element 11 provided for each of a plurality of nozzles of an ink jet printer,
A drive waveform generating circuit 3 for supplying a drive signal to the segment electrodes 11 s of the first and second electrodes; a current amplifying circuit 13 and a switch circuit 8 provided between the drive waveform generating circuit 3 and each of the piezoelectric elements 11; A reference voltage generating circuit 5 for applying a predetermined voltage to the eleventh segment-side electrode 11s. Such a head driving device 10
In the present embodiment, the driving waveform generating circuit 3, the reference voltage generating circuit 5, and the current amplifying circuit 13 are provided in the printer main body 1 while the piezoelectric element 1
1 and a switch circuit 8 are provided in the head portion 2. 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, and one piezoelectric element is provided for each nozzle. Is provided. As shown in FIG. 1, when the control signal Data is input, the switch circuit 8 is turned on at the drive timing of the corresponding piezoelectric element 11 among the plurality of piezoelectric elements, and the drive signal COM to be dictated is transmitted to the piezoelectric element 11. Output. In addition, the drive signal COM from the drive waveform generation circuit 3 is actually sequentially output to each piezoelectric element 11 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 both electrodes 11s and 11g. And the piezoelectric element 1
1 is constantly charged near the intermediate potential, and by applying pressure to the ink in the corresponding nozzle when discharging based on the drive signal COM from the drive waveform generation circuit 3,
The nozzle is configured to eject ink droplets.

The drive waveform generating circuit 3 generates a head drive signal COM of the ink jet printer, and is located in the printer main body 1 in the embodiment of the present invention as described above.

The current amplifying circuit 13 includes two transistors 6 and 7.

The first transistor 6 has a collector connected to the VH voltage and a base connected to the drive waveform generation circuit 3.
And the emitter is connected to the switch circuit 8
Is connected to the input side. Thereby, conduction is performed based on the drive signal from the drive circuit generation circuit 3, and the VH voltage is supplied to the piezoelectric element 11 via the switch circuit 8.

The second transistor 7 has a collector connected to the ground, a base connected to the output of the drive waveform generating circuit 3, and an emitter connected to the input side of the switch circuit 8. Thereby, conduction is performed based on the drive signal from the drive circuit generation circuit 3, and the electric charge of the piezoelectric element 11 is discharged via the switch circuit 8.

When the control signal Data is input, the switch circuit 8 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 reference voltage generating circuit 3 is configured to apply a predetermined voltage to the electrode 11s of the piezoelectric element 11.
Here, the predetermined voltage can be set to, for example, a voltage substantially equal to an intermediate potential according to the drive signal COM of the piezoelectric element 11. Such a configuration example will be described with reference to FIG.

In the example shown in FIG.
Is configured as an intermediate potential holding circuit 12, and the output side of the intermediate potential holding circuit 12 is connected to an electrode 11s of the piezoelectric element 11.
It is connected to the. Further, the input side of the intermediate potential holding circuit 12 is connected to the output side of the drive waveform COM of the drive waveform generation circuit 3, and the drive signal CO
M is input.

Here, the intermediate potential holding circuit 12 is, specifically, for example, as shown in FIG.
And a current amplifying circuit 22.

When the charge signal to the piezoelectric element 11 goes low, the voltage hold circuit 21
1 is configured to be charged by the drive signal COM from the drive waveform generation circuit 3.

The current amplification circuit 22 includes two transistors 23 and 24.

The third transistor 23 has a collector connected to the VH voltage, a base connected to the output of the voltage hold circuit 21, and an emitter connected to the input side of the switch circuit 9 via a forward diode 23a. It is connected to the. Thereby, conduction is performed based on the drive signal from the drive circuit generation circuit 3, and the VH voltage is supplied to the piezoelectric element 11 via the switch circuit 9.

The fourth transistor 24 has a collector connected to the ground, a base connected to the output of the voltage hold circuit 21, and an emitter connected to the input side of the switch circuit 9. Thereby, conduction is performed based on the drive signal from the drive circuit generation circuit 3, and the piezoelectric element 11 is discharged via the switch circuit 9.

The switch circuit 9 outputs the control signal Data at L level.
When the low level is input, the piezoelectric element 11 is turned on at the drive timing of the non-printing piezoelectric element 11, and outputs the output of the voltage hold circuit 21 to the piezoelectric element 11.

FIG. 4 shows a specific configuration example of the voltage hold circuit 21. In FIG. 4, the voltage hold circuit 21 includes an analog switch 25, a charging capacitor 26, and an analog amplifier 27.

The analog switch 25 receives the charge signal NCHG, and switches on at a low level and turns off at a high level.
The drive signal COM from the drive waveform generation circuit 3 is input to the input side. A charging capacitor 26 is connected to the output side.

The charging capacitor 26 has one electrode connected to the output of the analog switch 25 and the other electrode grounded to ground. The capacity of the charging capacitor 26 is appropriately selected so as to have a time constant that does not affect the cycle of the charge signal in accordance with self-discharge due to the input impedance of the analog amplifier 27.

The analog amplifier 27 has one input terminal connected to one electrode of the charging capacitor 26 and two output terminals connected to the bases of the two transistors 23 and 24 of the current amplification circuit 22, respectively. ing.

Further, the other input terminal of the analog amplifier 27 is fed back with the output of the current amplifier 22.

The head driving 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. Hereinafter, a head driving method according to an embodiment of the present invention will be described with reference to FIG.
This will be described in detail with reference to the timing chart of FIG.

First, at the start of printing (start-up) of the ink jet printer, the drive signal COM from the drive waveform generation circuit 3 is changed to, for example, 10 as shown in FIG.
By inverting the charge signal NCHG to Low level for the time of 0 μs, the charge signal NCHG is raised to the intermediate potential. As a result, a current flows from the first transistor 15 of the current amplifying circuit 13 to the one electrode 11s of the piezoelectric element 11 via the switch circuit 8 by the drive signal COM, and the electrode 11s of the piezoelectric element 11 is charged. FIG. 5 (B)
As shown by the solid line 28, the potential increases to the intermediate potential.

At this time, the charge capacitor 26 of the voltage hold circuit 21 is charged via the analog switch 25 by the low level of the charge signal NCHG, whereby an arbitrary voltage of the drive signal COM is latched, and the analog amplifier 27 Output from As a result, the third transistor 23 of the current amplifying circuit 22 conducts, and a current is output from the constant voltage power supply to the input of the switch circuit 9 via the diode 23a. Thereby, FIG. 5 (B)
, The potential rises to the intermediate potential as shown by the broken line 29. At this time, data is sent so that printing is performed, and the switch circuit 9 is turned off.

During printing, the voltage hold circuit 21 always holds the intermediate voltage by the charge signal NCHG when the drive signal COM is at the intermediate voltage. Since the switch circuit 9 is turned on as shown by the broken line 29 in FIG. 5B for the nozzles on which no printing is performed, the voltage is applied to one of the electrodes 11 of the piezoelectric element 11.
s. Here, when the voltage is applied, one electrode 11s of the piezoelectric element 11 is charged by the amount of self-discharge due to the insulation resistance, so that the voltage can be maintained at the intermediate potential.

If the switch circuit 9 is not turned on, FIG.
As shown in (B), the potential of the electrode 11s of the piezoelectric element 11 decreases until the next low level of the charge signal NCHG comes. Each time the charge signal NCHG goes low, the electrode 11s of the piezoelectric element 11 is charged and becomes an intermediate potential, so that the potential decreases by ΔV as shown by a broken line 30 in FIG. 5B. This potential is equal to the charge signal NC
Since the HG occurs every time the HG goes to the low level, an inrush current occurs, and the current increases as ΔV increases.

As described above, in the circuit of the present invention, noise can be reduced, and the intermediate potential of the piezoelectric element 11 can be stabilized.

Further, since there is no inrush current, the heat generation of the piezoelectric element is reduced, and the meniscus near the nozzle can be stabilized.

In the above 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.

[0039]

As described above, according to the present invention, an intermediate potential is supplied from the reference voltage generation circuit to the segment side of the piezoelectric element when printing is not performed on the segment side of the piezoelectric element, thereby keeping the potential of the segment side of the piezoelectric element constant. Will be retained. Accordingly, since no potential difference occurs, no rush current generated by charging by the charge signal due to spontaneous discharge does not flow, so that self-heating can be reduced. Also, if the inrush current disappears, the noise also decreases.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a configuration example in which a reference voltage generation circuit in the head drive device of FIG. 1 is used as an intermediate potential holding circuit.

FIG. 3 is a block diagram illustrating a configuration example of a voltage holding circuit of the intermediate potential holding circuit of FIG. 2;

FIG. 4 is a block diagram illustrating an example of a voltage hold circuit of FIG. 3;

FIG. 5 is a time chart showing variations of (A) a drive signal, (B) a voltage of a piezoelectric element, and (C) a charge signal in the head drive device of FIG.

[Explanation of symbols]

 Reference Signs List 3 driving waveform generating circuit 3 10 head driving device 11 piezoelectric element 11s one electrode 12 intermediate potential holding circuit 21 voltage holding circuit 26 charging capacitor 27 analog amplifier

Claims (3)

[Claims] 1. A piezoelectric element for applying pressure to an ink chamber created for each of a plurality of nozzles is selectively driven at a predetermined printing timing by a drive signal from a drive waveform generating circuit, and a corresponding one of the nozzles is driven. What is claimed is: 1. A head drive device for an ink jet printer, which performs recording by discharging ink droplets from an ink chamber, comprising an intermediate potential holding circuit for applying an intermediate potential to a segment-side electrode of each piezoelectric element. Head drive. 2. The intermediate potential holding circuit applies a voltage of an intermediate potential when each piezoelectric element is not printed, based on a charge signal from piezoelectric element charging means for correcting a decrease in electric charge due to discharge of the piezoelectric element. 2. The device according to claim 1, further comprising: a voltage holding circuit for latching an arbitrary voltage of a driving signal from the driving waveform generating circuit; and a current amplifying circuit for current amplifying an output of the voltage holding circuit. Head drive. 3. The head drive device according to claim 1, wherein the intermediate potential holding circuit is provided in a head portion.