JP2002264325A - Head driver and driving method for ink jet printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a head driver and driving method for ink jet printer in which the voltage being applied between the electrodes of each piezoelectric element is lowered through a simple arrangement. SOLUTION: The head driver 10 of an ink jet printer where piezoelectric elements 11 provided, respectively, for a plurality of nozzles and applying a pressure to ink are driven selectively at a specified print timing with a drive signal COM from a head drive circuit 12 to eject ink drops for recording from corresponding nozzles is provided with a circuit 20 for applying a bias voltage to the ground side electrode 11b 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 a ground side of a piezoelectric element provided corresponding to a nozzle for discharging ink droplets in a head of an ink-jet printer is maintained at a higher potential than the ground. The present invention relates to a technique for driving a head of a type printer.

[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 ejecting ink droplets, and is driven by a drive signal supplied from a driver IC mounted in a printer main body or a print head. , And 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, since the voltage applied to the piezoelectric element becomes relatively high, the voltage drop due to the above-described discharge is large, and the power loss is large.

[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]

According to the present invention, a bias voltage from a bias power supply circuit is applied to a ground electrode of each piezoelectric element so that the ground side of each piezoelectric element is connected to the ground. It was kept at a high 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. An ink jet printer head driving device that drives and discharges ink droplets from a corresponding nozzle to perform recording, comprising a bias power supply circuit that applies a predetermined bias voltage to a ground electrode of each piezoelectric element. It is characterized by being.

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 head driving method for an ink jet printer that drives and ejects ink droplets from a corresponding nozzle to perform recording, wherein a bias power supply circuit applies a predetermined bias voltage to a ground-side electrode of each piezoelectric element. It is characterized by.

According to this structure, the bias voltage is directly applied to the ground electrode of the piezoelectric element from the bias power supply circuit, whereby the ground side of the piezoelectric element is held at the bias voltage. Therefore, since the voltage applied between both electrodes of the piezoelectric element is relatively low, power consumption is reduced, and a voltage drop due to spontaneous discharge of the piezoelectric element is small, so that power loss is reduced.

Further, since the voltage applied to the piezoelectric element becomes 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. Accordingly, even if the piezoelectric element is reduced in size and the withstand voltage is reduced, it is possible to cope with the problem. Therefore, it is possible to further increase the density of the head without performing insulation treatment between the electrodes of the piezoelectric element.

According to a second aspect of the present invention, in the head driving device, a bias voltage output from the bias power supply circuit is adjustable.

According to a sixth aspect of the present invention, in the head driving method, the bias voltage output from the bias power supply circuit is adjustable.

According to this configuration, by adjusting the bias power supply, the bias voltage can be adjusted according to the intermediate potential of the drive signal applied to the piezoelectric element due to the variation of each ink jet printer. The voltage applied between both electrodes of each piezoelectric element can be set lower.

According to a third aspect of the present invention, in the head driving device, the bias power supply circuit is a logic power supply circuit.

According to a seventh aspect of the present invention, in the head driving method, the bias power supply circuit is a logic power supply circuit.

According to this configuration, since the bias power supply circuit is configured as a logic power supply circuit, the bias power supply circuit can be easily configured at a low cost with a simple configuration.

[0023]

Embodiments 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 is a functional block diagram showing the overall configuration of an ink jet printer using the head driving device of the present invention. In FIG. 1, the ink jet printer according to the present embodiment includes a printer main body 2, a carriage mechanism 12, a paper feed mechanism 11, and a print head 10. The paper feed mechanism 11 includes a paper feed motor (not shown), a paper feed roller (not shown), and the like, and sequentially feeds a recording medium (not shown) such as printing paper to perform sub-scanning. The carriage mechanism 12 includes the print head 10
, And a carriage motor (not shown) for running the carriage via a timing belt (not shown). The main scanning of the print head 10 is performed.

The printer main body 2 receives an interface 3 for receiving print data including multi-level hierarchical information from a host computer (not shown) or the like, and stores various data such as print data including multi-level hierarchical information. RAM4
A ROM 5 storing routines for performing various data processing, a control unit 6 including a CPU, an oscillation circuit 7, and transmitting print data SI developed into dot pattern data to the print head 10. And an interface 9 having a function.

Here, the print head 10 is circuit-connected to the printer main body 2 via a flexible flat cable (not shown). As shown in FIG. 1, in the ink jet printer of the present embodiment, a driving waveform generation circuit 80 and a driving waveform generation circuit 8
And a bias power supply circuit 120 connected to the current amplification circuit 113. These drive waveform generation circuit 80 and current amplification circuit 1
13. The function and the like of the bias power supply circuit 120 will be described later.

Print data including multi-level hierarchical information sent from a host computer or the like is held in a reception buffer 4A inside the printer via the interface 3. The recording data held in the receiving buffer 4A is subjected to command analysis, and the control unit 6 executes processing for adding the print position, decoration type, size, font address, and the like of each character. Next, the control unit 6 develops and stores the analyzed data in the output buffer 4C as print image data. The RAM 4 is also provided with a work memory (work area) 4B for temporarily storing various work data and the like.

When print image data corresponding to one scan of the print head 10 is obtained, the print image data is transmitted to the print head 1 via the interface 9.
0 is serially transferred. The print head 10 has a large number of nozzle openings such as 96 nozzles in the sub-scanning direction, and discharges ink droplets from each nozzle opening at a predetermined timing. The print head 10 includes a head driving circuit 18 including a shift register 13, a latch circuit 14, a level shifter 15, and a plurality of analog switches 114a.
Is configured. The print data developed into the print image data on the printer main body 2 side is serially transferred from the interface 9 to the shift register 13 in synchronization with the clock signal (CLK) from the oscillation circuit 7. This serially transferred print data (SI / print data)
Is temporarily latched by the latch circuit 14. The latched print data SI is boosted by the level shifter 15 as a voltage amplifier to a voltage that can drive each analog switch 114a, for example, a predetermined voltage of about several tens of volts. Print data S boosted to a predetermined voltage
I is given to the analog switch 114a.

As shown in FIG. 1, the drive waveform signal generated by the drive waveform generation circuit (head driver IC) 80 formed on the printer main body 2 side is current-amplified by the current amplification circuit 113 and printed on the carriage. Head 1
0 is output. On the side of the print head 10, any one of a plurality of piezoelectric elements 111 for discharging ink droplets from nozzle openings by pressurizing ink in a pressure generating chamber and a plurality of piezoelectric elements 111 based on print data SI are driven. A head drive circuit 18 for selecting whether the switch is selected through an analog switch 114a or the like is configured, and the head drive circuit 18 applies a drive signal COM to the piezoelectric element 111 for which the analog switch 114a is turned on. As a result, the piezoelectric element 111 pressurizes the ink in the corresponding pressure generating chamber and discharges the ink as ink droplets from the nozzle openings.

As shown in FIG. 2, the drive waveform generating circuit 80 stores a drive waveform data supplied from the control unit 6 or the like in the printer main body 2 and a drive waveform data read from the memory 81. A first latch 82 that is temporarily held, an adder 83 that adds an output of the first latch 82 and an output of a second latch 84 described later, and a second latch 84
And a D / A converter 86 for converting the output of the second latch 84 into analog data, and a voltage amplifying circuit 88 for amplifying the converted analog signal up to the voltage of the drive signal. Here, the memory 81 stores predetermined parameters for determining the waveform of the drive signal. As will be described later, the waveform of the drive signal COM is determined in advance by the predetermined parameters received from the control unit 6 and the like. Further, the drive waveform signal voltage-amplified by the voltage amplifying circuit 88 is current-amplified by the above-described current amplifying circuit 113 to the extent that the analog switch 114a can be driven and output.

As shown in FIG. 1, the output side of the current amplifying circuit 113 is connected to a plurality of analog switches 114a of the head drive circuit 18, and each of the analog switches 114a
Are connected to the corresponding piezoelectric elements 111. On the ejection surface of the print head, for example, three rows corresponding to each of CMY and three colors (in this example, K [black] is C
A plurality of nozzles (for example, 96 nozzles in one row) are positioned and provided at [composite black] formed by combining three colors of MY. By vibrating the provided piezoelectric element 111, the ink in the pressure generating chamber is pressurized, and ink droplets are respectively ejected from the plurality of nozzles.

FIG. 3 shows the configuration of an embodiment of a head driving device according to the present invention. 3, a head driving device 100 includes a piezoelectric element 111 provided for each of a plurality of nozzles in a print head 10 of an inkjet printer, and a plurality of analog switches 114a provided for each of the piezoelectric elements 111. And each piezoelectric element 11
In this embodiment, a drive signal is provided in the printer main body 2 for supplying a drive signal to one of the electrodes 111a.
It comprises a drive waveform generation circuit 80 described above, a current amplification circuit 113, and a bias power supply circuit 120 for applying a predetermined voltage to the other ground-side electrode 111b of the piezoelectric element 111.

The piezoelectric element 111 is, for example, a piezo element, and is configured to be displaced by a voltage applied between both electrodes 111a and 111b. The piezoelectric element 111 is always charged near the intermediate potential Vc, and the ink in the nozzle corresponding to the discharge at the time of discharging based on the drive signal COM output from the drive waveform generation circuit 80 via the current amplification circuit 113. By applying pressure to
Ink droplets are ejected from this nozzle.

The drive waveform generation circuit 80 is configured as a driver IC. The current amplification circuit 113 includes two transistors 115 and 116. The first transistor 115 has a collector connected to a constant voltage power supply (for example, 42 V), a base connected to the output of the drive waveform generation circuit 80, and an emitter connected to the input side of each analog switch 114a. Have been. Thereby, conduction is performed based on the signal from the drive waveform generation circuit 80, and a constant voltage is supplied to the piezoelectric element 111 via each analog switch 114a.

The second transistor 116 has an emitter connected to the input side of each analog switch 114a, a base connected to the output of the drive waveform generation circuit 80, and a collector grounded.
Thereby, conduction is performed based on the signal from the drive waveform generation circuit 80, and the piezoelectric element 111 is connected to each analog switch 11
Discharge via 4a.

Each analog switch 114a is turned on at the drive timing of the corresponding piezoelectric element 111 when a control signal (print data SI) is input, and outputs a drive signal COM to the piezoelectric element 111. .
That is, the plurality of analog switches 114a are configured as so-called transmission gates 114 for turning on and off the respective piezoelectric elements 111.

The bias power supply circuit 120 has a predetermined voltage, that is, an intermediate potential V based on the drive signal COM of the piezoelectric element 111.
A predetermined bias voltage Vb equal to or less than c is applied to the other common electrode 111b on the ground side of the piezoelectric element 111. Here, the bias power supply circuit 120
Specifically, for example, a logic power supply circuit having an output voltage of 5 V is provided so that the bias voltage Vb can be adjusted to a desired voltage.

The head driving device 10 according to the embodiment of the present invention
0 is configured as described above, and operates as follows based on the head driving method according to the present invention. First,
The piezoelectric element 111 driven during printing will be described. When the printing of the inkjet printer is started (startup), the driving signal COM generated from the driving waveform generating circuit 80 is, for example, 100 μm as shown in FIG.
By inverting the charge signal NCHG to the L level for the time of s, the intermediate potential V, as shown in FIG.
rise to c.

Thus, the current flows from the first transistor 115 of the current amplifying circuit 113 to the one electrode 111a of each piezoelectric element 111 via each analog switch 114a in response to the drive signal COM, thereby charging the piezoelectric element 111. One electrode 111a rises to the intermediate potential Vc as shown by the solid line in FIG.

At this time, the other ground-side common electrode 111 b of each piezoelectric element 111 is connected to the bias power supply circuit 120.
By applying the bias voltage Vb from FIG.
As shown by the dotted line in (B), the voltage is maintained at the predetermined voltage Vb.

The intermediate voltage Vc is set to a ratio α of, for example, 0.5 times the maximum voltage Vh of the drive signal COM. (Vc = α · Vh) During printing, charging is performed by the current amplification circuit 11 based on the fluctuation of the drive signal COM.
3 through the first transistor 115
The discharge is performed to one electrode 111a of the piezoelectric element 111 via the second transistor 116 of the current amplification circuit 113. Accordingly, the piezoelectric element 111 operates based on the drive signal COM, and ejects ink droplets.

Here, as shown by the symbol X in FIG. 4B, the piezoelectric element 111 causes a voltage drop due to self-discharge on the way, and the potential of one electrode 111a is changed to the intermediate potential Vc.
To prevent the voltage from lowering, the charge signal NC
The HG generates an L-level pulse at a constant period of the drive signal COM, that is, at a timing when there is no change in the drive signal COM, as indicated by a symbol Y in FIG. 4C.

Thus, based on the drive signal COM,
One electrode 111a of the piezoelectric element 111 is charged via the first transistor 115 of the current amplifying circuit 113, and the non-driven piezoelectric element 111 is maintained at the intermediate potential Vc.

On the other hand, the other ground-side common electrode 111 b of each piezoelectric element 111 is connected to the bias power supply circuit 1.
When the bias voltage Vb is applied from 20, the voltage is maintained at this voltage Vb. Therefore, in each piezoelectric element 111, the potential difference between both electrodes 111a and 111b is (Vc-Vb).

If the bias voltage Vb of the bias power supply circuit 120 is adjusted to be equal to the intermediate potential Vc of the drive signal, both electrodes 111a and 1a of each piezoelectric element 111 are adjusted.
The potential difference between 11b is 0.

Further, at the end of printing (stop end), the drive signal COM from the drive waveform generation circuit 80 is applied to one electrode 1 of the piezoelectric element 111 as shown in FIG.
11a to the second transistor 1 of the current amplification circuit 113
The potential is reduced to 0 by being discharged through 16. On the other hand, for the non-driven piezoelectric element 111, one electrode 111a of the piezoelectric element 111 is always charged and held at the intermediate potential Vc by the drive signal COM from the drive waveform generation circuit 80.

As described above, the potential of the ground electrode 111 b of the piezoelectric element 111 is
Is maintained at a constant voltage Vb by the bias voltage Vb from the first and second electrodes 111a, 1a of the piezoelectric element 111.
When the potential difference between the piezoelectric elements 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 111a of these piezoelectric elements 111 is also kept low.

Therefore, the power consumption of the piezoelectric element 111 is reduced, the voltage drop due to the self-discharge of the piezoelectric element 111 is small, and the power loss is reduced.

Further, since the potential difference between the driven piezoelectric element 111 and the non-driven piezoelectric element 111 is reduced, even if such piezoelectric elements 111 are adjacent to each other, the discharge between the piezoelectric elements 111 can be reduced. Even if the generation is reduced and the withstand voltage of each piezoelectric element 111 is reduced by the high density, it is not necessary to perform the insulation treatment between the piezoelectric elements 111, so that it is possible to easily realize the high density of the head. Becomes possible.

In the above-described embodiment, the piezoelectric element 1
For example, a piezo element is used as 11, but the present 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 bias power supply circuit 120 is constituted by, for example, a logic power supply circuit. However, the present invention is not limited to this. Can be used.

[0052]

As described above, according to the present invention, by applying a bias voltage directly from the bias power supply circuit to the electrode on the ground side of the piezoelectric element, the ground side of the piezoelectric element is maintained at a predetermined voltage. Will be. Therefore, since the voltage applied between both electrodes of the piezoelectric element is relatively low, even if the piezoelectric element is downsized due to the high density and the withstand voltage is reduced, it is possible to cope with it.
It is possible to further increase the density of the head without performing insulation between the electrodes of the piezoelectric element.

[Brief description of the drawings]

FIG. 1 is a functional block diagram illustrating an overall configuration of an ink jet printer using a head driving device of the present invention.

FIG. 2 is a functional block diagram illustrating an internal configuration of a drive waveform generation circuit in the inkjet printer illustrated in FIG.

FIG. 3 is a block diagram showing a configuration of an embodiment of a head driving device according to the present invention.

FIG. 4 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. 3;

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 Head drive device 111 Piezoelectric element 111 a One electrode 111 b Ground electrode 80 Drive waveform generation circuit 113 Current amplification circuit 114 Transmission gate 114 a Analog switch 115 First transistor 116 Second transistor 120 Bias power supply circuit

Claims (7)

[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. And a bias power supply circuit for applying a predetermined bias voltage to a ground-side electrode of each piezoelectric element, wherein the head drive device for an ink-jet printer is provided. . 2. The head driving device for an ink jet printer according to claim 1, wherein a bias voltage output from the bias power supply circuit is adjustable. 3. The head drive device for an ink jet printer according to claim 1, wherein the bias power supply circuit is a logic power supply circuit. 4. An ink jet printer comprising the head driving device according to claim 1. 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 for an ink jet printer, comprising: applying a predetermined bias voltage to a ground electrode of each piezoelectric element by a bias power supply circuit. 6. The head driving method for an ink jet printer according to claim 5, wherein a bias voltage output from the bias power supply circuit is adjustable. 7. The head driving method for an ink jet printer according to claim 5, wherein the bias power supply circuit is a logic power supply circuit.