JP3141890B2 - Drive unit for inkjet head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] An ink chamber that communicates between a nozzle that ejects ink droplets and an ink container is filled with ink, and the internal volume of the ink chamber is changed to eject ink droplets from the nozzles. An ink-jet head drive device is provided, which aims to provide an ink-jet head drive device capable of adjusting a recording state by changing an ink ejection amount (ink dot diameter) by deforming a part of a side wall of an ink chamber. An electromechanical converter for increasing or decreasing the internal volume of the ink chamber; and controlling the electromechanical converter to increase and decrease the internal volume of the ink chamber. After a predetermined time, increase or decrease the internal volume of the ink chamber again. It is configured to have an electromechanical transducer driving unit and a time variable unit that changes the time from the second increase to the second decrease of the internal volume.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for an ink-jet head, and more particularly, to filling an ink chamber communicating between a nozzle for ejecting ink droplets and an ink storage unit with ink, and changing the internal volume of the ink chamber. The present invention relates to a driving device for an inkjet head that ejects ink droplets from nozzles.

Non-impact recording methods include electrostatic type, electrolytic type, discharge type, thermal type, and ink jet type. Among them, the ink jet type is a method in which ink droplets are attached to recording paper in a predetermined information pattern and printed. , High speed printing, low noise,
It has features such as low running cost by using plain paper,
In recent years, it has attracted attention, and there is a demand for the development of technology that can achieve high image quality.

[Prior Art] FIG. 6 is a partially cutaway perspective view showing an example of a multi ink jet head, and FIG. 7 is a schematic sectional view taken along an ink passage. In the figure, 1 is a nozzle for ejecting ink droplets, 2 is an ink storage section, 3 is an ink passage (ink chamber) communicating between the nozzle and the ink storage section, and 4 is the internal volume of the ink chamber filled with ink. It is an electromechanical transducer composed of a variable piezoelectric vibration element. When the predetermined electromechanical transducer 4 is driven to increase or decrease the internal volume of the predetermined ink chamber 3 filled with ink, the ink droplet 5 can be ejected from the nozzle 1 of the ink chamber.

Therefore, it is desirable to drive a predetermined electromechanical transducer in accordance with a character or an image to be printed to eject ink droplets and to move the inkjet head relatively horizontally and vertically with respect to the paper. Can be generated on the recording paper.

As a method of driving the ink jet head, as shown in FIG. 8, two pulse-like voltage signals EP1 and EP2 are inputted to the electromechanical transducer, and the volume of the ink chamber is increased and decreased twice to eject the ink. It has been known. For example, USP4,5
See 23,200 and USP 4,369,455. According to this driving method, at the initial time (time t ₀ ), the nozzle liquid level is in the state shown in FIG.
Pulse-like voltage signal E gradually decreasing from 100 (V) to 0 (V)
When P1 is applied to the electromechanical transducer to increase the internal volume, the liquid level is retracted as shown by a dotted line and a dashed line in FIG. 9 (a).
Then, a pulse voltage signal EP1 at time t ₁ 100
When the internal volume is rapidly reduced by returning to (V), the liquid level is pushed out from the nozzle as shown in FIG. 9 (b).
Then, applying a second pulse EP2 which gradually decreases up to several tens of volts in narrow at time t ₂ from 100 (V), the internal volume is expanded in a state in which the liquid surface is pushed out, Accordingly, Figure 9 (c 9), the peripheral portion of the liquid surface is retracted, and the pushed-out portion is cut off from the central portion as shown in FIG. The second pulse voltage signal EP2 at time t ₃ returns to 100 (V).

As described above, when the volume of the IN chamber is continuously increased and decreased twice by using two pulse-shaped voltage signals, the ink can be efficiently discharged from the nozzles.

[Problems to be Solved by the Invention] An ink jet recording method is performed by attaching a liquid ink to recording paper and fixing the ink by evaporation and permeation. Therefore, the recording state, for example, the recording density greatly depends on the recording paper.

However, the conventional two-pulse driving method has a problem that the recording state cannot be adjusted, and therefore, even if the recording paper changes, there is a problem that the recording paper must be used in an unsatisfactory recording state.

Further, in the ink jet recording method, the recording state changes depending on the temperature (for example, the recording density decreases at a low temperature). However, there is a problem that the conventional driving method cannot cope with such a case.

As described above, an object of the present invention is to provide an ink jet head driving device capable of adjusting a recording state by changing an ink ejection amount (ink dot diameter) in a two-pulse driving method.

Another object of the present invention is to provide a driving apparatus for an ink jet head which can easily attenuate the natural vibration of the ink jet head and easily adjust a recording state.

[Means for Solving the Problems] FIG. 1 is an explanatory view of the principle of the present invention.

Reference numeral 11 denotes an ink jet head, which has a nozzle 11a for ejecting ink droplets, an ink container 11b, an ink chamber 11c communicating between them, and an electromechanical transducer 11d for increasing and decreasing the internal volume of the ink chamber. ing. Reference numeral 12 denotes a conversion element driving unit that drives an electromechanical conversion element to increase or decrease the internal volume of the ink chamber 11c.
A drive pulse generator 12a for generating the two drive pulses DP1 and DP2, and a time variable unit 12b for controlling the pulse time width of the second drive pulse DP2.

[Operation] When one command pulse P is input to perform recording of one dot, the drive pulse generating unit 12a causes the electromechanical transducer 1
In order to drive 1d, a wide first pulse DP1 and a narrow second pulse DP2 are generated, and the first and second drive pulses drive the electromechanical transducer element 11d to cause the ink liquid to flow from the nozzle 11a. Spray the drops. That is, the first and second drive pulses DP1, DP
2 is used to drive the electromechanical transducer element 11d to increase and decrease the internal volume of the ink chamber, and after a predetermined time, increase and decrease the internal volume of the ink chamber again to discharge ink droplets from the nozzle 11a. Let it squirt. At this time, if it is desired to change the recording density (ink ejection amount), the second
The time width of the drive pulse DP2 (the time width from the second increase of the internal volume to the second decrease) is adjusted. Second drive pulse
By controlling the time width of DP2, the ink diameter and the amount of ink droplets can be changed, and the recording density can be adjusted. Therefore, if the second drive pulse width is changed according to the paper quality and the room temperature, the recording state can be improved.

Further, if the time interval from the first decrease to the second decrease of the internal volume is fixed, for example, 1/2 of the natural oscillation period, unnecessary vibration of the ink jet head caused by controlling the increase and decrease of the internal volume of the ink chamber is further improved. Can be quickly attenuated, and the recording state can be easily adjusted by adjusting the pulse width.

[Embodiment] FIG. 2 is a block diagram of an embodiment of an ink jet head driving apparatus according to the present invention, and FIG. 3 is a signal waveform diagram for explaining the operation.

The overall configuration 11 is an ink jet head, for example, having the same configuration as the conventional one shown in FIG. 11d is an electromechanical transducer for increasing or decreasing the internal volume of the ink chamber, for example, a piezoelectric element.

Reference numeral 12 denotes a conversion element driving unit that drives the piezoelectric element 11d that is an electromechanical conversion element to increase or decrease the internal volume of the ink chamber,
A drive pulse generator 12a that generates a drive pulse signal DP having two drive pulses DP1 and DP2 from one command pulse P
A time variable unit 12b for controlling the pulse time width of the second drive pulse DP2, a delay circuit 12c for delaying the second drive pulse DP2 by a predetermined time Td, and a first and a second pulse-like voltage applied to the piezoelectric element 11d. A driver circuit 12d for driving by adding the signals EP1 and EP2 is provided.

Drive pulse generator The drive pulse generator 12a includes mono-multi circuits MMC1 and MMC2 and an AND gate AGT.The mono-multi circuit MMC1 generates a wide pulse D1 having a pulse width T1, and the mono-multi circuit MMC2 generates a pulse having a pulse width T2. Generates a narrow pulse D2. The pulse width T1 is determined by the time constant of the CR circuit composed of the capacitor C1 and the resistor R1, and the pulse width T2 is adjusted by the time variable unit 12b.

Time variable section Time variable section 12b is composed of capacitor C2 and variable resistor R2.
This is an R circuit, and the width of the pulse D2 output from the mono-multi circuit MMC2 can be changed by adjusting the resistance value of the variable resistor R2.

Delay circuit The delay circuit 12c is a CR composed of a resistor R3 and a capacitor C3.
It has a circuit and inverters INV1 and INV2, and delays the pulse D2 by a time Td determined by the time constant of the CR circuit. As a result, the drive pulse signal D having two drive pulses DP1 and DP2 shown in FIG. 3 is output from the AND gate AGT of the drive pulse generator 12a.
P is output.

Driver Circuit The driver circuit 12d includes three transistors TR1 to TR3, diodes DD1 to DD4, variable resistors R4 and R5, and the like. The transistors TR1 and TR2 are normally off, and the transistor TR3 is on. For this reason, usually +100
+100 (V) is applied to the piezoelectric element 11d from the volt power supply via the transistor TR3, the diode DD3, and the variable resistor R4.
The piezoelectric element 11d as a capacitor is charged to + 100V. In this state, when the drive pulse signal DP becomes low level (when the first drive pulse DP1 is generated), the transistors TR1 and TR2 are turned on, and the transistor TR3 is turned off.
The electric charge charged in the piezoelectric element 11d is a resistor R5 and a diode DD.
4. Discharged through the transistor TR2, and the terminal voltage gradually decreases with a time constant R5 · C4 (C4 is the capacitance of the piezoelectric element) as shown in FIG. When the driving pulse DP becomes high level, the transistors TR1 and TR2 are turned off, and the transistor TR3 is turned off.
Turns on, and the terminal voltage of the piezoelectric element 11d rapidly becomes +100 volts with the time constant R4 · C4. In addition, the second of the drive pulse signal DP
The same operation is performed when the drive pulse DP2 is generated.

General Operation When one command pulse P is input to perform recording of one dot, the drive pulse generator 12a drives a wide first drive pulse DP1 and a narrow second drive pulse DP1 to drive the piezoelectric element 11d. A drive pulse signal DP having the drive pulse DP2 is generated.

Since the transistor TR3 is turned off by the first drive pulse DP1, the terminal voltage of the piezoelectric element 11d charged to +100 volts gradually decreases with the time constant R5 · C4 (the voltage signal EP in FIG. 3).
1). As a result, the internal volume of the ink chamber increases, and the liquid level of the nozzle starts to retract. And the driving pulse DP1
Disappears, the transistor TR3 is turned on, so that the terminal voltage of the piezoelectric element 11d rapidly becomes +100 volts with the time constant R4 · C4. As a result, the internal volume of the ink chamber decreases sharply,
The liquid level is pushed out from the nozzle tip.

Thereafter, when the second drive pulse DP2 having a small width is generated, a pulse-like voltage signal EP2 shown in FIG. 3 is applied to the piezoelectric element 11d, whereby the internal volume is expanded in a state where the liquid surface is pushed out. Therefore, the peripheral portion of the liquid surface is retracted, and the extruded liquid surface portion is cut off from the central portion and is ejected as droplets.

Density control (ink diameter control) Two pulse-like voltage signals EP1, E applied to the piezoelectric element 11d
When the pulse width of the second pulse-like voltage signal EP2 is changed among P2, the ejected ink amount and the ink diameter (recording dot diameter) change. FIG. 4 is a diagram showing the relationship between the pulse width (μs) of the second pulsed voltage signal EP2 and the amount of ejected ink (pL), and FIG.
FIG. 6 is a relationship diagram between the pulse width (μs) of the pulsed voltage signal EP2 and the recording dot diameter (μm).

From the above, by adjusting the variable resistor R2 of the time variable unit 12b,
The density can be changed by controlling the pulse width of the second drive pulse DP2 to change the pulse width of the second pulse voltage signal EP2. For example, if a variable resistor is provided on the operation panel of the inkjet printer so that the pulse width of the second drive pulse DP2 can be adjusted, the density or dot diameter is adjusted by the variable resistor according to the recording paper or temperature. Recording can be performed in an optimal recording state.

End timing of pulse-like voltage signals EP1 and EP2 When the first pulse-like voltage signal EP1 is generated by the recording command to drive the piezoelectric element 11d, the head generates natural vibration at a predetermined frequency. It is desirable that this natural vibration be stopped when the piezoelectric element 11d is driven by the next recording command pulse.

For this reason, it is advantageous if the droplets can be cut well by the second pulsed voltage signal EP2 and the natural vibration generated in the first pulsed voltage signal EP can be attenuated. That is, it is only necessary that the vibration generated by the second pulsed voltage signal EP2 be superimposed on the natural vibration generated by the first pulsed voltage signal EP1 in opposite phase.

Therefore, in the present invention, the falling time of the first t ₁₁ falling time (time liquid chamber volume in other words, starts to decrease) of the pulsed voltage signal EP1 and the second pulse voltage signal EP2 t ₁₂
Is set to の of the natural oscillation period. As a result, the second pulse-like voltage signal EP is delayed by a half cycle from the internal volume decrease start time by the first pulse-like voltage signal EP1.
The decrease of the internal volume due to 2 is started, and the increase / decrease vibrations of the internal volume due to the respective voltage signals are canceled each other, and the vibration is immediately attenuated.

Other Embodiments of the Present Invention In the above description, the pulse width of the second drive pulse DP2 is manually adjusted, but the recording state may be automatically adjusted by detecting paper quality and temperature. it can.

As described above, the present invention has been described with reference to the embodiments. However, the present invention can be variously modified in accordance with the gist of the present invention described in the claims, and the present invention does not exclude these.

[Effects of the Invention] According to the present invention, in the two-pulse driving method of the inkjet head, by changing the pulse width of the second drive pulse, in other words, from the second increase of the internal volume to the second decrease By changing the time, the ink ejection amount (ink dot diameter) is adjusted to control the printing state, so that it is possible to adjust so as to perform optimum printing according to the printing paper and temperature. .

Further, according to the present invention, the diameter and amount of the ink droplet can be changed with a simple control and configuration of changing the pulse width of the second drive pulse.

According to the present invention, since the increase and decrease of the ink chamber volume is controlled by applying the first and second pulse-like voltage signals gradually decreasing from the positive potential to the electromechanical converter, the acceleration of the side wall displacement of the ink chamber is controlled. Can be increased as compared with the case where a positive polarity pulse-like voltage signal is applied, so that the energy efficiency can be improved and the speed of the ink particles can be increased.

Further, according to the present invention, the time from the first decrease to the second decrease in the internal volume of the ink chamber is kept constant, and the second decrease in the internal volume is controlled more steeply than the second increase. This makes it possible to optimize the amount of ejected ink while keeping the drive time constant, thereby shortening the drive cycle.

Further, according to the present invention, since the time from the first decrease to the second decrease of the internal volume is set to be constant (1/2 of the natural vibration period), unnecessary natural vibrations are quickly attenuated. The recording state can be easily adjusted by adjusting the pulse width.

[Brief description of the drawings]

FIG. 1 is a view for explaining the principle of the present invention, FIG. 2 is a block diagram of an embodiment of an ink jet head driving apparatus according to the present invention, FIG. 3 is a signal waveform diagram for explaining operation, and FIG. Pulse width of voltage signal EP2 (μs)
Fig. 5 is a relationship diagram between the ink amount and the ejected ink amount (pL).
Fig. 6 is a partially cutaway perspective view showing an example of a multi-inkjet, Fig. 7 is a schematic sectional view taken along an ink passage, and Fig. 8 is a pulse-like shape. Voltage signal waveform diagram, FIG. 9 is a diagram for explaining the mechanism of droplet generation. 11: inkjet head 11d: electromechanical transducer 12: transducer drive 12a: drive pulse generator 12b: time variable

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mitsuo Ozaki 1015 Ueodanaka Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Co., Ltd. 56) References JP-A-59-133067 (JP, A) JP-A-2-506 (JP, A)

Claims (1)

(57) [Claims] An ink-jet head which fills an ink chamber communicating between a nozzle for ejecting ink droplets and an ink storage portion with an ink liquid, and changes the internal volume of the ink chamber to eject ink droplets from the nozzle. An electromechanical converter for deforming a part of the side wall of the ink chamber to increase or decrease the internal volume of the ink chamber; and first and second means for gradually decreasing the electromechanical converter from a positive potential.
Control by applying a pulsed voltage signal of the following, after increasing the internal volume of the ink chamber to pull in the liquid level of the nozzle, reduce the content volume in the ink chamber to push out the liquid level of the nozzle, An electric machine for increasing the internal volume of the ink chamber so as to draw the liquid level of the nozzle so that the ink liquid extruded from the nozzle and the liquid level of the nozzle are cut after a predetermined time, and further reducing the internal volume of the ink chamber A converter driving unit; a time varying unit that changes a time from a second increase to a second decrease of the internal volume; and a time from a first decrease to a second decrease of the internal volume is fixed. Means for driving the ink jet head, wherein the electromechanical transducer driving unit controls the first and second decreases of the internal volume more steeply than the first and second increases. Location.