JP2003072069A - Apparatus and method for driving head of ink-jet printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and a method for driving a head of an ink-jet printer whereby a voltage drop because of discharging of each piezoelectric element is reduced while each piezoelectric element is prevented from a wrong operation by a simple constitution. SOLUTION: In the apparatus 10 for driving the head of the ink-jet printer, piezoelectric elements 11 set corresponding to a plurality of nozzles respectively for pressuring ink are selectively driven with a predetermined printing timing by a driving signal COM from a head drive circuit 12, thereby discharging ink drops from the corresponding nozzles to record. A bias power circuit 20 is provided for impressing a bias voltage Vb to an electrode at the ground side of each piezoelectric element. The apparatus 10 is constituted so that the bias power circuit 20 generates the bias voltage Vb by utilizing a head drive power source 17.

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, which is configured to reduce discharge of piezoelectric elements provided corresponding to nozzles for ejecting ink droplets in the head of the ink jet printer. It is about technology.

[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.

Further, since such a power source uses a so-called logic power source in the control section of the printer body, the circuit configuration becomes complicated and the cost becomes high.

Further, when the voltage drop as described above occurs, if the charging voltage is suddenly applied to the piezoelectric element, the piezoelectric element is driven in some cases,
There is a risk of malfunction, that is, ink droplets may be accidentally ejected. Therefore, when determining the drive waveform COM, it is necessary to consider the timing of inserting the charge signal, which becomes a constraint when determining the drive waveform.

Therefore, an object of the present invention is to reduce the voltage drop due to discharge of each piezoelectric element while eliminating the occurrence of malfunction of each piezoelectric element with a simple structure, and a head driving device for an ink jet printer. And a head driving method.

[0015]

In order to solve the above problems, according to the present invention, a bias voltage is applied to a ground side electrode of each piezoelectric element by a bias power supply circuit using a head drive power source. Was applied to maintain the bias potential higher than the ground potential.

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 inkjet printer, which is driven by a drive signal from a head drive circuit selectively at a predetermined print timing to eject ink droplets from a corresponding nozzle to perform recording, and a ground side of each piezoelectric element. Is provided with a bias power supply circuit for applying a predetermined bias voltage to the electrode, and the bias power supply circuit generates a bias voltage using a head drive power supply.

According to a fifth aspect of the present invention, there is provided a head driving method for an ink jet printer in which a piezoelectric element for applying a pressure to ink is provided corresponding to each of the plurality of nozzles.
A head driving method for an ink jet printer, which selectively drives at a predetermined printing timing by a driving signal from a head driving circuit to eject ink droplets from a corresponding nozzle to perform recording. It is characterized in that a predetermined bias voltage is applied to the ground side electrode of each piezoelectric element by a bias power supply circuit that generates a bias voltage.

According to this structure, the bias voltage supplied from the bias power supply circuit using the head drive power supply is
By applying the voltage to the electrode on the ground side of the piezoelectric element, the ground side of the piezoelectric element is held at the bias voltage.

Even if a spontaneous discharge of the piezoelectric element occurs, a predetermined bias voltage is always applied to the ground side electrode of the piezoelectric element from the bias power supply circuit, so that a leak current during the natural discharge is generated. Since the voltage drop is reduced and the voltage drop is reduced, abrupt voltage fluctuation at the time of applying the charging voltage against the voltage drop due to the discharge of the piezoelectric element is mitigated, and the occurrence of malfunction of the piezoelectric element can be eliminated. At the same time, it is not necessary to consider the timing of inserting the charge signal when determining the drive waveform, so that there is no restriction when determining the drive waveform.

In the head drive device according to the second aspect, the bias power supply circuit applies a bias voltage to the capacitor by using a capacitor connected to a ground side electrode of each piezoelectric element and a head drive power supply. And a constant voltage circuit.

In the head driving method according to the sixth aspect, the bias power supply circuit applies a bias voltage to the capacitor by using a capacitor connected to the ground side electrode of each piezoelectric element and the head driving power supply. And a constant voltage circuit.

According to this structure, since the capacitor connected to the ground side electrode of the piezoelectric element is charged by the bias voltage from the constant voltage circuit, the ground side electrode of the piezoelectric element is set to the bias voltage from the capacitor. Will be retained.

According to another aspect of the head drive device of the present invention, the constant voltage circuit comprises a Zener diode connected to the head drive power source through a current limiting resistor, and the voltage of the Zener diode is a bias voltage. Is applied to the capacitor via the coupling element.

According to a seventh aspect of the present invention, in the head driving method, the constant voltage circuit is composed of a Zener diode connected to a head driving power source through a current limiting resistor, and the voltage of the Zener diode is a bias voltage. Is applied to the capacitor via the coupling element.

According to this structure, the capacitor connected to the ground side electrode of the piezoelectric element is charged through the coupling element by the voltage of the Zener diode of the constant voltage circuit, so that the capacitor has a stable bias voltage. Is charged by the coupling element and the discharge from the electrode on the ground side of the piezoelectric element is prevented from flowing to the Zener diode by the coupling element.

In the head drive device according to the fourth aspect, the constant voltage circuit is connected in parallel with the current limiting resistor,
Further, it is characterized in that it is provided with a discharging diode connected so as to allow a current to flow to the head drive power source side.

In the head driving method according to the eighth aspect, the constant voltage circuit is arranged in parallel with the current limiting resistor,
Further, it is characterized in that it is provided with a discharging diode connected so as to allow a current to flow to the head drive power source side.

According to this structure, when the head driving power supply is reduced to 0V due to power-off or the like, the electric charge charged in the capacitor bypasses the current limiting resistor and is discharged through the discharging diode. This allows the capacitor to be discharged in a short time.

[0029]

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 an embodiment of a head drive device according to the present invention.

In FIG. 1, the head drive device 10 supplies a drive signal to the piezoelectric element 11 provided corresponding to each of the plurality of nozzles of the ink jet printer and one electrode 11a of each piezoelectric element 11. Head drive circuit 12, this head drive circuit 12, and each piezoelectric element 11
And the current amplifier circuit 13 and the switch circuit 14 provided between and the other electrode 11b on the ground side of the piezoelectric element 11.
And a bias power supply circuit 20 for applying a predetermined bias voltage.

Here, 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 each nozzle is provided. On the other hand, 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 through a shift register or the like.

The piezoelectric element 11 is, for example, a piezo element, and is configured to be displaced by the voltage applied between the electrodes 11a and 11b. And the piezoelectric element 1
1 is, for example, charged near the intermediate potential V0, and when ink is discharged based on the drive signal COM from the head drive circuit 12, pressure is applied to the ink in the corresponding nozzle to eject an ink droplet from this nozzle. Is configured to.

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 first transistor 15 has a collector connected to the constant voltage power supply 17, a base connected to the output of the head drive circuit 12, and an emitter 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 a constant voltage is supplied to the piezoelectric element 11 via the switch circuit 14. Here, the constant voltage power supply is
For example, it is a relatively high voltage power supply that supplies a head drive voltage of DC 42V.

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

The switch circuit 14 is an analog switch circuit, and when a 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. There is. Here, the piezoelectric element 11 and the switch circuit 14 are provided in the head of the printer and are connected via a flexible flat cable 18.

The bias power supply circuit 20 utilizes a constant voltage power supply 17 as a head drive power supply to generate a predetermined voltage, that is, a predetermined bias voltage Vb which is equal to or lower than the intermediate potential V0 by the drive signal COM of the piezoelectric element 11. As shown in FIG. 1, it is composed of a capacitor 21 and a constant voltage circuit 22 so as to be applied to the other common electrode 11b on the ground side of 11.

The capacitor 21 is an electrolytic capacitor, and its charging voltage is applied to the ground side electrode 11b of each piezoelectric element 11 as a bias voltage Vb.
One end is connected to the common electrode 11b on the ground side of the piezoelectric element 11, and the other end is grounded to the ground.

The capacitance of the capacitor 21 is set to the total capacitance (about several μF) of all the piezoelectric elements 11 so that a stable bias voltage Vb can be supplied to each piezoelectric element 11. Large enough capacity, for example, tens
It is selected to be about 00 μF.

The constant voltage circuit 22 uses the constant voltage power source 17 as the head driving power source to make a bias voltage Vb.
So as to generate a current limiting resistor 23, a Zener diode 24, a coupling resistor 25 as a coupling element, a noise countermeasure capacitor 26, and a discharging diode 27.

The current limiting resistor 23 and the Zener diode 24 are connected in series between the constant voltage power supply 17 and the ground, and the voltage of the Zener diode 24 (the voltage on the side opposite to the ground of the Zener diode 24) is predetermined. The voltage is held at, for example, DC 6V. Here, as the current limiting resistance 23, for example, a resistance of several kΩ is used.

The coupling resistor 25 applies the voltage of the Zener diode 24 to the capacitor 21, and the discharge voltage of the capacitor 21 is changed to the Zener diode 2.
It is for dividing the circuit so that it is not applied to No. 4, and for example, one having a value of several tens Ω to several kΩ is used.

The noise countermeasure capacitor 26 is for absorbing and removing the noise component contained in the voltage of the Zener diode 24, and may be omitted.

The discharging diode 27 is used to quickly discharge the electric charge charged in the capacitor 21 by bypassing the current limiting resistor 23 when the voltage drops to 0V due to the power-off of the constant voltage power source 17 or the like. However, it may be omitted as well.

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 piezoelectric element 11 driven during printing will be described.
Inkjet printer printing started (startup)
At some times, the drive signal COM from the head drive circuit 12 rises to the intermediate potential Vc by inverting the charge signal NCHG to the L level only for a time of 100 μs, for example, as shown in FIG.

As a result, the drive signal COM causes a current to flow from the first transistor 15 of the current amplification circuit 13 to the one electrode 11a of each piezoelectric element 11 via the switch circuit 14 to charge the piezoelectric element 11. One electrode 11a will rise to the intermediate potential Vc, as shown by the solid line in FIG.

At this time, the charging voltage of the capacitor 21 of the bias power supply circuit 20 is applied as the bias voltage Vb to the other common electrode 11b on the ground side of each piezoelectric element 11, so that the dotted line in FIG. 2 (B). As shown by, the voltage is held at the predetermined voltage Vb.

Since the potential of the electrode 11b on the ground side of the piezoelectric element 11 is held at the predetermined voltage Vb,
At the start of printing, both electrodes 11a, 1 of the piezoelectric element 11 are
The potential difference between 1b is Vb, but this potential difference Vb is
Since it is lower than the intermediate potential Vc of the drive signal COM, the piezoelectric element 11 does not malfunction and eject ink droplets.

During printing, when 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 connected via the first transistor 15 of the current amplification circuit 13. When the electrode 11a is charged and the drive signal COM is lower than the intermediate potential Vc, the one electrode 11a of the piezoelectric element 11 is discharged through the second transistor 16 of the current amplification circuit 13. As a result, the piezoelectric element 11 operates based on the drive signal COM to eject an ink droplet.

Here, as indicated by a symbol X in FIG. 2B, 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. In order to prevent the charge signal NCHG
Is the drive signal CO, as indicated by the symbol Y in FIG.
A pulse of L level is generated at a constant cycle of M, that is, at a timing when the drive signal COM does not change.

As a result, based on the drive signal COM from the head drive circuit 12, one electrode 11 of the piezoelectric element 11 is passed through the first transistor 15 of the current amplification circuit 13.
Even if the piezoelectric element 11 which is a-charged and is not driven is held at the intermediate potential Vc. At this time,
Since the voltage drop due to the natural discharge of the piezoelectric element 11 is reduced, abrupt charging of the piezoelectric element 11 due to the charge signal NCHG is avoided, and the piezoelectric element 11 does not malfunction.

On the other hand, when the bias voltage Vb is applied from the bias power supply circuit 20, the other common electrode 11b on the ground side of each piezoelectric element 11 is held at this voltage Vb. Therefore, each piezoelectric element 11
Indicates that the potential difference between the electrodes 11a and 11b is (Vc
-Vb).

Further, at the end of printing (stop end), the drive signal COM from the head drive circuit 12 is as shown in FIG.
As shown in (A), one electrode 11a of the piezoelectric element 11
Is discharged through the second transistor 16 of the current amplification circuit 13, and the potential drops to 0. On the other hand, for the non-driven piezoelectric element 11, the piezoelectric element 11 is driven by the drive signal COM from the head drive circuit 12.
One electrode 11a is always charged to the intermediate potential Vc,
Is held.

In this way, the potential of the electrode 11b on the ground side of each piezoelectric element 11 is held at a constant voltage Vb by the bias voltage Vb from the bias power supply circuit 20, so that both electrodes of the piezoelectric element 11 are held. When the potential difference between 11a and 11b is kept low and the driven piezoelectric element and the non-driven piezoelectric element are adjacent to each other, these piezoelectric elements 1
Therefore, the voltage difference between the one electrodes 11a is also kept low. Therefore, 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 becomes 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.

Further, when the constant-voltage power supply 17 drops to 0V due to power-off or the like, it is necessary to discharge the capacitor 21 of the bias power supply circuit 20, but the charge charged in the capacitor 21 is the current of the constant-voltage circuit 22. Limiting resistor 23
Is bypassed and discharged through the discharging diode 27, so that discharging is performed in a short time.

Further, the bias power supply circuit 20 uses the constant voltage power supply 17 as a head drive power supply to generate the bias voltage Vb. Therefore, the bias power supply circuit 20 itself does not need a power supply circuit having a complicated configuration using a logic power supply as in the conventional case, and the bias power supply circuit 20 itself and the coupling such as the current limiting resistor 23, the Zener diode 24, and the coupling element are coupled. Since the constant voltage circuit 22 including the resistor 25 is used, the bias power supply circuit 20 can be obtained at low cost. In this way, the overall cost of the head drive device 10 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.

Further, although the coupling resistor 25 is used as the coupling element of the bias power supply circuit 20 in the above-described embodiment, the coupling element is not limited to this, and a coupling element such as a coil may be used. That is clear.

[0060]

As described above, according to the present invention, by applying the bias voltage supplied from the bias power supply circuit to the electrode on the ground side of the piezoelectric element using the head drive power source, the piezoelectric element The ground side of is held at the bias voltage. Therefore, since the voltage applied between both electrodes of the piezoelectric element is relatively low, the power consumption is reduced and the power loss is reduced.

Even if the spontaneous discharge of the piezoelectric element occurs, a predetermined bias voltage is always applied from the bias power supply circuit to the ground side electrode of the piezoelectric element, so that the leakage current at the time of the spontaneous discharge is generated. Since the voltage drop is reduced and the voltage drop is reduced, abrupt voltage fluctuation at the time of applying the charging voltage against the voltage drop due to the discharge of the piezoelectric element is mitigated, and the occurrence of malfunction of the piezoelectric element can be eliminated. .

[Brief description of drawings]

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

FIG. 2 is a time chart showing variations of (A) drive signal, (B) electrode voltage of both piezoelectric elements, and (C) charge signal in the head drive device of FIG.

[Explanation of symbols]

10 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 17 Constant voltage power supply (head drive power supply) 18 Flexible flat cable 20 Bias power supply circuit 21 capacitor 22 Constant voltage circuit 23 Current limiting resistor 24 Zener diode 25 Coupling resistance 26 Noise suppression capacitors 27 Discharge diode

Claims (8)

[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 ink jet printer that discharges ink to perform recording, comprising a bias power supply circuit that applies a predetermined bias voltage to a ground-side electrode of each piezoelectric element. A head driving device for an inkjet printer, wherein a bias voltage is generated by using a driving power supply. 2. The bias power supply circuit includes a capacitor connected to a ground-side electrode of each piezoelectric element, and a constant voltage circuit for applying a bias voltage to the capacitor by using a head drive power supply. The head drive device for an ink jet printer according to claim 1, wherein 3. The constant voltage circuit comprises a Zener diode connected to a head drive power source via a current limiting resistor, and the voltage of the Zener diode is used as a bias voltage to a capacitor via a coupling element. The head drive device for an inkjet printer according to claim 2, wherein the head drive device is applied. 4. The constant voltage circuit comprises a discharging diode connected in parallel to the current limiting resistor and connected so as to allow a current to flow to the head drive power source side. A head drive device for an ink jet printer according to item 1. 5. 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 droplets are ejected from the corresponding nozzles. Is a head driving method for an inkjet printer, in which a predetermined bias voltage is applied to a ground-side electrode of each piezoelectric element by a bias power supply circuit that generates a bias voltage using a head driving power supply. A method for driving a head of an inkjet printer, characterized by applying the voltage. 6. The bias power supply circuit includes a capacitor connected to an electrode on the ground side of each piezoelectric element, and a constant voltage circuit that applies a bias voltage to the capacitor by using a head drive power supply. The method for driving a head of an ink jet printer according to claim 5, wherein 7. The constant voltage circuit comprises a Zener diode connected to a head drive power supply via a current limiting resistor, and the voltage of the Zener diode is used as a bias voltage to a capacitor via a coupling element. The method for driving a head of an inkjet printer according to claim 6, wherein the voltage is applied. 8. The constant voltage circuit comprises a discharging diode connected in parallel to the current limiting resistor and connected so as to allow a current to flow to the head drive power source side. 7. A method for driving a head of an ink jet printer according to item 1.