JPH0691204A - Piezoelectric liquid droplet ejection device - Google Patents

Abstract

PURPOSE:To ensure that a residual pressure variation can be reduced positively, if the cycle and amplitude of the residual pressure variation in a pressure chamber change due to temperature or the physical property of ink. CONSTITUTION:A residual pressure variation in a pressure chamber 10 after the ejection of ink droplets is detected by a piezoelectric element 16 and a detection circuit 32. At the same time, a cancellation pulse for cancelling a residual pressure based on the amplitude and cycle of the residual pressure variation is calculated by a calculation circuit 34, and then is applied to the piezoelectric element 16 by a drive circuit 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric droplet ejecting device, and more particularly to a technique for more reliably reducing the residual pressure in a pressure chamber after ejecting a droplet.

[0002]

2. Description of the Related Art Piezoelectric droplet ejecting apparatuses, which eject a liquid ejected from a pressure chamber by changing the volume of the pressure chamber using a piezoelectric transducer, are used in, for example, ink jet printers. FIG. 8 shows an example of such a piezoelectric type droplet ejecting apparatus. A piezoelectric element 16 such as PZT is provided as a piezoelectric transducer on a side wall 14 of a housing 12 forming a pressure chamber 10, and the piezoelectric element 16 is driven. A drive voltage is applied by the circuit 18. When a drive voltage is applied to the piezo element 16, the side wall 14 is deformed together with the piezo element 16 as shown by the alternate long and short dash line to reduce the volume of the pressure chamber 10 and fill the inside of the pressure chamber 10. The ink as the ejected liquid is ejected from the nozzle 22 as an ink droplet 20. After that, when the drive voltage becomes 0 V in a relatively short time, the piezo element 16 returns to the shape before deformation, and the pressure chamber 1
The volume of 0 increases and the pressure chamber 10 moves from the ink supply passage 24.
Ink flows inside. When used as an inkjet printer, a large number of such droplet ejecting devices are provided.

By the way, during such ink ejection,
A pressure wave is generated as the volume of the pressure chamber 10 changes, and the pressure wave propagates up and down and left and right in the pressure chamber 10 using ink as a medium and is reflected by the wall surface, reciprocating in the pressure chamber 10 many times. Decays. For this reason, even after the ink ejection, the pressure fluctuation due to the pressure wave remains in the pressure chamber 10 for a while, which affects the subsequent ink ejection.
The solid line in FIG. 9 indicates the change in the drive voltage when the ink is ejected once, the displacement state of the piezo element 16, and the nozzle 2.
2 is a time chart showing the pressure change near 2
The pressure in the vicinity of the nozzle 22 fluctuates in a constant cycle determined by the propagation speed of the pressure wave and the shape of the pressure chamber 10 even after the driving voltage becomes 0 V and the piezoelectric element 16 returns to its original shape. . In this case, in order to perform the next ink ejection, for example, when the drive voltage is applied at the timing A as indicated by the alternate long and short dash line, the pressure chamber 1 is deformed by the deformation of the piezo element 16.
Although the volume of 0 decreases, the pressure in the vicinity of the nozzle 22 is originally negative, so that sufficient pressure cannot be obtained, and the ink droplet 20 is not ejected, or even if ejected, the ejection speed and ejection amount are different, so that printing is performed. It causes unevenness. The timing of the next ink ejection varies depending on the printing pattern, the printing speed, etc., and the ejection speed and the ejection amount of the ink droplet 20 greatly vary depending on the residual pressure fluctuation.

On the other hand, for example, Japanese Patent Laid-Open No. 61-3752
As disclosed in Japanese Patent Laid-Open Publication No. 2003-242242, it has been considered to reduce the residual pressure fluctuation in the pressure chamber by applying a cancel pulse to the piezo element subsequent to the print pulse for ejecting ink. More specifically, referring to FIG. 9 above, at the timing B when the pressure in the vicinity of the nozzle 22 increases, as shown by the broken line, the pressure chamber 1
A cancel pulse that increases the volume of 0 is applied to the piezo element 1.
By applying to No. 6, the residual pressure can be canceled. The piezoelectric element 16 is provided with a pair of electrodes on the upper and lower surfaces, and by applying a drive voltage in the opposite direction, the piezoelectric element 16 can be deformed in the opposite direction to increase the volume of the pressure chamber 10. The cycle of the residual pressure fluctuation is the pressure chamber 1
0 shape, specifically from the ink supply passage 24 to the nozzle 2
Up to 2 and the propagation velocity of the pressure wave in the pressure chamber 10, and the magnitude of the residual pressure depends on the attenuation rate of the pressure wave. Therefore, the timing of applying the cancel pulse and the magnitude of the pulse are: It is determined beforehand by experiments so that the residual pressure can be eliminated. JP-A-61-3752
The device disclosed in the publication can manually adjust the timing and magnitude of the cancel pulse in consideration of the dimensional error of the pressure chamber 10 and the like. The volume of the pressure chamber 10 may be reduced at the timing when the residual pressure becomes negative pressure.

[0005]

However, the above-mentioned residual pressure fluctuation also changes depending on the physical properties of the ink, the usage environment, and the like. For example, the propagation velocity of the pressure wave changes depending on the temperature, and the attenuation rate of the pressure wave changes due to the physical properties of the ink, the inclusion of bubbles, and the like. Will change.
For this reason, there are cases in which the residual pressure fluctuation cannot be sufficiently reduced by the cancel pulse that is determined in advance, or the residual pressure fluctuation becomes large due to the timing deviation.

Incidentally, in the device capable of adjusting the timing and the magnitude of the cancel pulse as in the prior art example,
It can be readjusted so as to eliminate the residual pressure fluctuation depending on the usage environment, etc., but such adjustment work is tedious and requires a high degree of skill, and is not always practical.

The present invention has been made in view of the above circumstances, and an object of the present invention is to make it possible to always reliably reduce fluctuations in residual pressure regardless of changes in the physical properties of ink, the use environment, and the like. It is in.

[0008]

In order to achieve such an object, the present invention provides a piezoelectric liquid in which the volume of the pressure chamber is changed by using a piezoelectric transducer to inject the liquid in the pressure chamber from a nozzle. In the drop ejector,
(A) a pressure fluctuation detecting means for detecting a residual pressure fluctuation in the pressure chamber, and (b) based on the residual pressure fluctuation detected by the pressure fluctuation detecting means, the piezoelectric means for canceling the residual pressure fluctuation. Pressure fluctuation canceling means for applying a voltage to the transducer to change the volume of the pressure chamber.

[0009]

In such a piezoelectric liquid droplet ejecting apparatus, the pressure fluctuation detecting means detects the actual residual pressure fluctuation in the pressure chamber, and the pressure fluctuation canceling means cancels the residual pressure fluctuation. Since a voltage is applied to the transducer, even if the cycle or amplitude of residual pressure fluctuations changes due to the operating environment such as temperature or the physical properties of the jet liquid,
The residual pressure fluctuation can be surely reduced. As a result, even when the droplet is ejected at a relatively short timing, the droplet is always ejected under a constant ejection condition without being affected by the residual pressure.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. In the following embodiments, the same parts as those in the conventional example of FIG. 8 are designated by the same reference numerals and detailed description thereof will be omitted.

FIG. 1 is a view showing one droplet ejecting device of an ink jet printer, which is a drive circuit 30 and a detection circuit 3.
2, and an arithmetic circuit 34. Drive circuit 30
Is, for example, as shown in FIG.
8 and an analog switch 40, the print pulse Pp and the cancel pulse Pc are applied to the piezo element 16 in accordance with the print signal SP and the cancel signal SC. The print pulse Pp is for ejecting the ink droplet 20 by deforming the piezo element 16 and reducing the volume of the pressure chamber 10. The print pulse Pp is a pulse having a predetermined constant waveform, while the cancel pulse Pc is , For eliminating the residual pressure fluctuation in the pressure chamber 10 after the ink droplet 20 is ejected, and the magnitude thereof, that is, the voltage and the pulse width are controlled according to the cancel signal SC. Also,
Except when the print pulse Pp or the cancel pulse Pc is output, the analog switch 40 is shut off according to the switch signal SS, and the piezo element 16 is driven by the drive circuit 3.
It is electrically disconnected from 0.

The detection circuit 32 is for detecting the electric signal Vs generated in the piezo element 16 in accordance with the residual pressure fluctuation in the pressure chamber 10 after the application of the print pulse Pp is finished, and as shown in FIG. 3, for example. Is provided with an operational amplifier 42, and outputs the detection signal SV obtained by converting the electric signal Vs to low impedance to the arithmetic circuit 34. The electric signal Vs and the detection signal SV are pressure chambers 10 shown at the bottom of FIG. 5, which is a time chart during ink droplet ejection.
Corresponds to the average pressure inside.

The arithmetic circuit 34 calculates a cancel pulse Pc for canceling the residual pressure fluctuation in the pressure chamber 10 based on the detection signal SV, and has a function shown in FIG. Consists of In FIG. 4, the shaping unit 44 is a portion that removes noise included in the detection signal SV by a filter or the like, and the peak P detection unit 46 is a portion that detects the first upper peak P from the change in the detection signal SV. The peak level P _L detection unit 48 is a part that detects the voltage value of the detection signal SV at the upper peak P as the peak level P _L , and the half cycle τ calculation unit 50 is the time from the first lower peak to the upper peak P. Is calculated as a half cycle τ, and the phase Φ calculation unit 52 is a part that calculates the time lag between the upper peak P and the end of the print pulse Pp as the phase Φ. Then, in the cancel pulse Pc calculator 54, in order to cancel the residual pressure corresponding to the peak level P _L , the piezo element 1
The cancel voltage Vc to be applied to 6 is calculated based on the peak level P _L by a predetermined data map, an arithmetic expression, or the like, and the cancel voltage Pc having the pulse width of the half cycle τ is calculated by the cancel voltage Vc. . By outputting the cancel signal SC representing the cancel pulse Pc to the drive circuit 30, substantially at the same time as the appearance of the upper peak P, in other words, the phase Φ from the end of the print pulse Pp.
At a timing delayed by a certain amount, the cancel pulse Pc is applied to the piezo element 16 to increase the volume of the pressure chamber 10, and the residual pressure fluctuation in the pressure chamber 10 is canceled.

In such a liquid droplet ejecting apparatus of this embodiment, the actual residual pressure fluctuation in the pressure chamber 10 is detected by the piezo element 16 and the detection circuit 32, and the piezo element 16 is canceled so as to cancel the residual pressure fluctuation. Since the cancel pulse Pc is applied to, even if the cycle and the amplitude of the residual pressure change due to the use environment such as temperature and the physical properties of the ink,
The residual pressure fluctuation can be surely reduced. As a result, even when the ink is ejected at a relatively short timing, the ink droplet 20 is always ejected under a constant ejection condition without being affected by the residual pressure.

In particular, in this embodiment, all of the droplet ejecting devices constituting the ink jet printer are adapted to independently detect the residual pressure fluctuation and output the cancel pulse Pc. Regardless of the individual difference of the liquid droplet ejecting device, the residual pressure canceling control is appropriately performed in all the devices. Further, since the residual pressure fluctuation is detected and the cancel pulse Pc is output each time the ink droplet 20 is ejected, the residual pressure fluctuation is caused by, for example, a sudden change in the ink physical property accompanying the ink replenishment or a rapid change in temperature. Even when the cycle or the amplitude changes suddenly, the residual pressure can always be appropriately reduced.

In this embodiment, the piezo element 16 and the detection circuit 32 correspond to the pressure fluctuation detecting means, and the drive circuit 30 and the arithmetic circuit 34 correspond to the pressure fluctuation canceling means.

Next, another embodiment of the present invention will be described. In the embodiment of FIG. 6, a pressure detecting piezo element 60 is provided separately from the driving piezo element 16 as compared with the above-mentioned embodiment, and in this case, the drive circuit 30 and the detection circuit 32 are electrically connected. Since it is insulated, the residual pressure fluctuation can be detected more accurately, and the analog switch 40 is not always necessary. In this embodiment, the pressure detection piezo element 60 and the detection circuit 32 constitute pressure fluctuation detection means.

In the embodiment shown in FIG. 7, the piezoelectric material such as PZT is grooved to form a large number of pressure chambers 10, and electrodes are formed on both surfaces of a plurality of partition walls 62 separating the pressure chambers 10. Are attached so that the partition walls 62 function as piezoelectric transducers as they are. In this case, since the residual pressure fluctuation can be detected from the partition walls 62 on both sides of one pressure chamber 10, the residual pressure can be canceled with higher accuracy. The partition wall 62 constitutes a pressure fluctuation detecting means together with the detection circuit 32.

Although the embodiments of the present invention have been described in detail with reference to the drawings, the present invention can be embodied in another manner.

For example, in the above embodiment, the cancel pulse P is detected by detecting the residual pressure fluctuation each time the ink droplet 20 is ejected.
Although c is output, the cancel pulse Pc and the phase are detected by detecting the residual pressure fluctuation only at a predetermined sampling time, such as at fixed time intervals, when the printer power is input, or when any switch is operated. Φ may be stored, and the cancel control may be performed using the cancel pulse Pc and the phase Φ until the residual pressure fluctuation is detected next time.

If the residual pressure fluctuation is detected prior to the actual printing, it is not necessary to immediately output the cancel pulse Pc at that time to cancel the residual pressure. The calculation can be performed with a margin, and the half cycle τ can be detected with high accuracy from the overall vibration characteristic of the residual pressure fluctuation.

Further, when the residual pressure fluctuation is detected by performing the trial ejection prior to the actual printing, it is not always necessary to apply the drive voltage to the extent that the ink droplet 20 can be ejected. That is, the phase Φ of the residual pressure fluctuation and the half cycle τ are constant regardless of the magnitude of the driving voltage, while the peak level of the residual pressure fluctuation corresponds to the driving voltage. it is possible to obtain the cancel voltage Vc to calculate the peak level P _L when fed a printing pulse Pp from the relationship between the peak level.

Further, in the above-described embodiment, all the liquid droplet ejecting devices constituting the ink jet printer are configured to include the detection circuit 32 and the arithmetic circuit 34, respectively, but any one or a part of them. It is also possible to configure only the droplet ejecting device of No. 2 as in the above-described embodiment and apply the cancel pulse Pc and the phase Φ obtained by the droplet ejecting device to another droplet ejecting device.

Further, in the above-mentioned embodiment, the first upper peak P of the residual pressure fluctuation is detected and the cancel pulse Pc for canceling the residual pressure is outputted, but the second lower peak and the following lower peaks are output. The upper peak may be detected and a cancel pulse for canceling the residual pressure may be output. When performing the trial striking to obtain the cancel pulse and the phase, the cancel pulse can be output at the timing of the first lower peak generation.

The circuit configurations and functional configurations shown in FIGS. 2 to 4 are merely examples, and may be appropriately changed as necessary.
For example, when the half cycle τ and the phase Φ have substantially the same value due to the pulse width of the print pulse Pp, the phase Φ calculation unit 52 can be omitted by setting Φ = τ, and the application timing and pulse of the cancel pulse Pc can be omitted. It is also possible to change the setting method such as the width.

Further, in the above embodiment, the cancel pulse Pc is obtained by the arithmetic circuit 34, but the voltage, pulse width and delay time from the print pulse Pp of the preset cancel pulse are detected by the detection circuit 32. The correction may be made based on the detected amplitude, cycle, or phase of the actual residual pressure fluctuation.

When the piezoelectric element 60 for pressure detection is separately provided as in the embodiment shown in FIG. 6, the residual pressure is canceled while the residual pressure is detected by the piezoelectric element 60. By sequentially calculating the cancel voltage and outputting it to the piezo element 16, the cancel voltage can be feedback-controlled so that the residual pressure becomes zero. In the embodiment of FIG. 7, after applying the print pulse Pp to the partition walls 62 on both sides of the pressure chamber 10, the residual pressure fluctuation is detected by one of the partition walls 62 and the cancel voltage is applied to the other partition wall 62. Similarly to the above, the residual pressure can be canceled by feedback control.

Although not illustrated one by one, the present invention can be carried out in various modified and improved modes based on the knowledge of those skilled in the art.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a basic configuration of a piezoelectric liquid droplet ejecting apparatus that is an embodiment of the present invention.

FIG. 2 is a diagram showing a specific example of the drive circuit of FIG.

FIG. 3 is a diagram showing a specific example of the detection circuit in FIG.

FIG. 4 is a block diagram illustrating a function of the arithmetic circuit of FIG.

5 is a diagram showing the driving voltage of the embodiment of FIG. 1, the displacement of the piezo element,
It is a time chart regarding the residual pressure in the pressure chamber.

FIG. 6 is a diagram illustrating a basic configuration of another embodiment of the present invention.

FIG. 7 is a diagram illustrating a basic configuration of still another embodiment of the present invention.

FIG. 8 is a diagram showing an example of a conventional droplet ejection device.

FIG. 9 is a diagram showing the drive voltage of the conventional example of FIG.
It is a time chart regarding the pressure near the nozzle.

[Explanation of symbols]

 10: Pressure chamber 16: Piezo element (piezoelectric transducer) 22: Nozzle 30: Drive circuit (pressure fluctuation canceling means) 32: Detection circuit (pressure fluctuation detecting means) 34: Calculation circuit (pressure fluctuation canceling means) 60: For pressure detection Piezo element (pressure fluctuation detection means) 62: Partition wall (piezoelectric transducer) Pc: Cancel pulse

Claims (1)

[Claims] 1. A piezoelectric liquid droplet ejecting apparatus for ejecting an ejected liquid in a pressure chamber from a nozzle by changing the volume of the pressure chamber using a piezoelectric transducer, wherein a pressure for detecting a residual pressure fluctuation in the pressure chamber. Based on the fluctuation detecting means and the residual pressure fluctuation detected by the pressure fluctuation detecting means, a pressure fluctuation that applies a voltage to the piezoelectric transducer to change the volume of the pressure chamber so as to cancel the residual pressure fluctuation. A piezoelectric droplet ejecting device, comprising: a canceling unit.