JPS6225058A - Driving method for recording head - Google Patents

Abstract

PURPOSE:To perform an ink jet recording excellent in frequency responsiveness, discharging stability and variability in ink discharging amount by varying a preceding pulse for increasing the volume of an ink chamber in a piezoelectric element in response to the specific condition of a discharging pulse. CONSTITUTION:An electric signal to be applied to a cylindrical piezoelement 2 is used as a pulse wave for discharging ink droplet 10 from an orifice 1 by increasing the volume of an ink chamber 7 and then abruptly decreasing the volume of the chamber 7. The pulse wave is controlled to alter the state of the volume of the chamber 7 in response to the discharging amount of the droplet 10. When the pulse waveform is formed in a pulse waveform A produced by superposing a preceding negative pulse waveform on the front portion of the pulse waveform, the frequency responsiveness is improved. Thus, since the preceding pulse for increasing the volume of the chamber 7 is applied to the piezoelement 2, a discharging pulse for discharging the droplet 10 from the orifice 1 is then applied and the width and the voltage of the preceding pulse are varied in response to the width and/or voltage of the discharging pulse, the frequency responsiveness, the discharging stability and the gradation can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application] The present invention relates to a method for driving a recording head applied to an inkjet recording apparatus.

[Prior Art 1] Conventionally, there are many systems for inkjet recording devices 17. Broadly speaking, there are three types: ■Continuous injection type, ■Impulse type (on-demand type), and ■Electrostatic suction type.

In the continuous injection type, iJ! Because of the principle of recording by deflecting continuously ejected ink, the apparatus becomes complex and requires ink recovery and cleaning devices.

In addition, the electrostatic suction type has a relatively cylindrical structure, but requires a high voltage and is dangerous.Furthermore, it has poor frequency response due to many limitations in the physical properties of the ink, such as conductivity.

However, in the on-demand type, ink droplets are ejected by the pressure of the piezoelectric 7 only when necessary, and the structure is very simple, so it has great expectations as a recording device.

Next, when considering the method of expressing halftones in a recording device, there are two possible ways to express halftones: a digital method such as a dither method, and an analog method that changes the recording dot size. However, in the digital halftone representation method, resolution must be sacrificed in order to increase the number of tones by -1.

For this reason, there are expectations for analog recording in which the recording density is controlled by changing the recording dot size.

However, it is extremely difficult to control the ink discharge Jd with conventional inkjet recording apparatuses.

For example, in the case of an injection type, it is impossible to change the ink ejection. In addition, with the electrostatic attraction type, analog halftone expression is possible, but it is difficult to make the gradation range appealing. Furthermore, with the on-demand type, the amount of ink ejected is controlled by changing the pulse pressure and pulse width applied to the piezoelectric element, but it is not possible to increase the gradation width simply by changing the pulse waveform. It was f.

For this reason, inkjet recording devices (Japanese Unexamined Patent Publication No. 102034/1983) are designed to provide a wide gradation range by using different inks of different densities, or by providing multiple nozzle diameters with different diameters. Inkjet devices and the like are known. However, these methods increase the size and complexity of the device as a whole, resulting in increased costs.

On the other hand, as described in Japanese Patent Publication No. 53-12138, the method of ejecting ink droplets by simply pressurizing ink with a piezoelectric element is better than the method described in Japanese Patent Publication No. 55-17589. It is known that the method of increasing the ink chamber volume and retracting the so-called meniscus and then pressurizing the ink is not only more effective at ejecting small ink droplets but also has superior frequency response. There is.

[Problems to be Solved by the Invention] However, in this method, the meniscus 8 retreats as shown in (a) to (d) of FIG. There is a risk of it getting lost.

Furthermore, if large ink droplets are to be ejected from the recording head, the meniscus must be further retreated, increasing the risk even further. I didn't meet it.

1,41: An object of the invention is to provide a method for driving a recording head capable of performing inkjet recording with excellent frequency response, ejection stability, and i+7 modification of ink ejection amount in view of the above points. It's about doing.

[Means for Solving the Problems] In order to achieve this goal, the unreleased II changes the volume of the ink chamber by applying an electric signal to the piezoelectric element to eject ink droplets from the orifice. In a method of driving a recording head that performs recording, an electrical signal applied to a piezoelectric element increases the volume of an ink chamber, and then rapidly decreases the volume of the ink chamber, thereby causing ink droplets to be ejected from an orifice. A pulse wave is used, and the pulse wave is controlled so as to change the state of the ink chamber volume according to the amount of ink droplet ejection.

[Sakukawa 1] In other words, the present invention has a pressure of 1! Applying a preceding pulse to the element to increase the volume of the ink chamber, and subsequently applying an ejection pulse to eject the ink droplet from the orifice,
The pulse width and pulse voltage of the preceding pulse are controlled so that the pulse width and/or pulse 11 of the ejection pulse is changed in accordance with the pressure.

[Example 1 The present invention will be described in detail below with reference to one drawing.

First, in completing the present invention, a recording head applied to an on-demand type inkjet recording apparatus was prepared, and experiments as described below were conducted.

The recorder used in this experiment is as shown in FIG. That is, the recording head is, for example, a glass nozzle whose tip is tapered to form an orifice 1, and a cylindrical piezo (piezoelectric element) 2 is glued to the outside, and an ink chamber 7 inside the recording head is equipped with a filter. Ink is supplied from the ink tank 6 through the ink supply path 3 via the ink tank 4 . When a positive pulse voltage is applied from the drive unit 5 to the cylindrical piezo 2 having such a configuration, an ink droplet IO is ejected from the orifice l in accordance with the pulse voltage. Here, for example, the orifice diameter is 5
0 ■, the viscosity of the ink is 7 cp.

The surface tension of the ink is 50 dyne/am.

Next, if the positive pulse voltage applied to the cylindrical piezo 2 has a waveform that rapidly pressurizes the ink chamber 7 and then gradually releases the pressure, the velocity of the ink droplets will be high and the ejection stability will be good. Therefore, the pulse voltage was set to have a waveform as shown in FIG. 2. For example, as shown in FIG. 2, the pulse voltage was set to 70 V and the pulse width was set to 10 JLsec.

In order to further improve the frequency response, it is conceivable to create a pulse waveform as shown in FIG. 3 by adding the negative pulse waveform preceding the front part of the pulse waveform shown in FIG.

The reason why such a pulse waveform improves the frequency response is thought to be that ink is sucked from the ink tank 6 by first creating a negative pressure, so less ink supplies are needed after ink droplets are ejected.

Therefore, we conducted an experiment on frequency response by changing the negative pulse voltage or negative pulse width while setting the positive pulse voltage as a predetermined condition, and obtained the results shown in Figures 4 and 5. Ta. According to this experiment, as shown in FIGS. 4 and 5, results were obtained that the larger the pulse voltage and pulse width of the negative pulse wave, the better the frequency response.

Therefore, this experimental result supports the fact that the larger the pulse voltage and pulse width, the more ink is sucked from the ink supply side. If this is the case, frequency response and ejection stability should be improved by adjusting the ink suction efficiency to suit the difference in the amount of ink to be ejected. There are two possible methods for adjusting the ink suction carpet: pulse voltage control and pulse width control.

Therefore, we fixed the positive pulse conditions and conducted an experiment on negative pulse voltage vs. meniscus retraction amount, and an experiment on negative pulse width vs. meniscus retraction amount. The experimental results are shown in Figures 6 and 7. Ta. According to the experimental results, as shown in the figure, the meniscus retreats l with respect to changes in pulse voltage.
Although the maximum value changes linearly by a large amount S, the maximum meniscus regression value reaches a saturated state at a certain constant value with respect to changes in pulse width. Therefore, when a large amount of ink suction is required, by widening the negative pulse width, the above-mentioned objective of frequency response and ejection stability can be achieved without taking in bubbles from the orifice. can do.

As described above, in addition to the effect of improving the frequency response, the preceding negative pulse wave can also have the effect of increasing the ejection speed of ink droplets. Therefore, using a positive pulse as a predetermined condition, we conducted an experiment on negative pulse voltage vs. ink droplet ejection speed, and an experiment on negative pulse width vs. ink droplet ejection speed, and the experimental results are shown in Figures 8 and 9. According to the experimental results shown in Fig. 8, the ejection speed of ink droplets varies linearly and significantly with changes in the negative pulse voltage, as shown in Fig. 8, but with respect to changes in pulse width. As shown in FIG. 9, it becomes saturated at a certain constant value.

Therefore, in order to compensate for the speed of ink droplets that are ejected at a low ejection speed due to a small positive pulse voltage, for example, the voltage value of the preceding negative pulse should be as large as possible, and the pulse width should be relatively short. Waves are preferred without entraining bubbles from the orifice. vice versa,
The '1H pressure value of the 1F pulse is large and the ink is ejected 1-1.
When there are many.

As mentioned above, it is preferable that the negative pulse has a long pulse width and a slightly low pulse voltage.

Next, an example of an experiment conducted in consideration of the experimental results described below will be described below as an example of the present invention.

Example 1 The first example uses the apparatus shown in FIG. 1 and a viscosity of 7 cp.
Using ink with a surface tension of 50 dyne/cm, the pulse width of the positive pulse of the electrical pulse wave to be applied is 10 g sec, and the pulse width of the positive pulse is 10 g sec. The recording head was driven by changing the pulse voltage and pulse width as shown in FIG. The results of this example are shown in FIG.

Example 2 In the second example, the apparatus used in Example 1 was used, and the positive pulse width of the applied electric pulse wave was set to 104 sec, and the change in the positive pulse voltage was Accordingly, the recording head was driven by changing the negative pulse voltage and pulse width in two steps as shown in FIG. The results of this example are shown in FIG.

As described above, in both Examples 1 and 2, stable ejection was obtained from small ink droplets to large ink droplets, and the frequency response and gradation properties were also excellent.

Next, experimental examples in which the waveforms of the pulse waves applied to the recording head were varied will be described below as Comparative Examples 1 to 3.

Comparative Example 1 Comparative Example 1 uses the apparatus used in Example 1, applies only a positive pulse with a pulse width of 10 g sec, and changes the voltage value of the positive pulse to eject from the recording head. Ink discharge 1.1+ 1. We controlled ¥. The results obtained from this experiment are shown in FIG. 12 as Comparative Example 1.

Comparative Example 2 In Comparative Example 2, the device used in Example 1 was used, and the pulse width of the positive pulse of the applied electric pulse wave was set to 10 g.
sec, the voltage of the negative pulse was -20V, and the pulse width was 20 μsec.

Then, ink ejection was controlled by changing the voltage value of the positive pulse. The results obtained from this experiment are shown in FIG. 12 as Comparative Example 2.

Comparative Example 3 In Comparative Example 3, the equipment used in Example 1 was used. The pulse width of the positive pulse of the applied 'heavy pulse waveform is 1
The voltage value of the negative pulse was -30V, and the pulse width was 5p, sec.

Then, by changing the voltage value of the positive pulse, ink is ejected! i was controlled. The results of this experiment are shown in FIG. 12 as Comparative Example 3.

Next, when Comparative Examples 1 to 3 obtained in this manner are examined with reference to FIG. 12, the results are as follows.

First, in Comparative Example 1, the gradation and frequency response are poor, and in Comparative Example 2, the ejection stability is good when the ink droplets are large, but when the ink droplets are small, there is too much ink suction hl, making the ejection unstable. Next, in Comparative Example 3, the ejection stability is excellent, but the frequency response when the ink droplets are large is poor.Therefore, large ink droplets are not ejected, and the gradation is poor.

In the example described above, the case where the ink ejection amount was changed by voltage control of 11 micropulses was explained, but instead of this, the ink ejection amount was changed by controlling the pulse width of the E pulse.
Even if t' is changed, the effects of the present invention are similarly observed, and the gradation, frequency response, and ejection stability are improved.

[Effects of the Invention] As explained below, according to the present invention, the volume of the ink chamber is changed by applying an electric signal to the pressure I-output cylinder, and ink droplets are ejected from the orifice to perform recording. In the method of driving the head, a preliminary pulse is applied to the piezoelectric element to increase the volume of the ink chamber, and then an ejection pulse is applied to eject the ink droplets from the orifice. At the same time, the pulse width and pulse voltage of the preceding pulse are changed to the pulse width and/or pulse voltage of the ejection pulse.
Alternatively, since it is changed according to the pulse voltage, frequency response, ejection stability, and gradation can be dramatically improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a recording head. Figures 2 and 3 are diagrams showing examples of drive pulse waveforms, Figure 4 is a diagram showing the relationship between negative pulse voltage and frequency response, and Figure 5 is a diagram showing the relationship between negative pulse width and frequency response. Figure 6 shows the relationship between negative pulse ill pressure and meniscus regression jt-
Figure 7 shows the relationship between the negative pulse width and the maximum value of the meniscus, and Figure 8 shows the relationship between the negative pulse voltage and the ink droplet ejection speed. 9 is a diagram showing the relationship between the negative pulse width and the ejection speed of ink droplets, and FIG. 10 is a diagram showing the relationship between the negative pulse voltage corresponding to the stop pulse voltage of Example 1 and the pulse width. 11 is a diagram showing the relationship between the negative pulse voltage corresponding to the positive pulse voltage of Example 2 and the pulse width, and FIG. 12 is a diagram showing the results of the example of the present invention and a comparative example. The figure shows how bubbles are taken in from the orifice. 1... Orifice, 2... Cylindrical piezo. 3... Ink supply pipe, 4... Filter, 5... Drive unit. 6... Ink tank, 7... Ink chamber. Figure 1 Figure 2 Figure 3 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9

Claims (1)

[Scope of Claims] A method of driving a recording head that changes the volume of an ink chamber by applying an electric signal to a piezoelectric element to eject ink droplets from an orifice to record, comprising: applying an electric signal to the piezoelectric element; , the volume of the ink chamber is increased and then the volume of the ink chamber is rapidly decreased to create a pulse wave that ejects an ink droplet from the orifice, and the volume of the ink chamber is decreased according to the amount of ejection of the ink droplet. A method for driving a recording head, characterized in that the pulse wave is controlled so as to change the state.