JPH0464446A - Ink jet recording head - Google Patents

Abstract

PURPOSE:To improve a printing speed by a method wherein a pressure generation means is driven under control so that a second pulse can be applied with a delay of a predetermined time after a first pulse is applied to the pressure generation means. CONSTITUTION:To suppress a residual vibration generated by a first pulse for jetting out an ink particle, the drive of a pressure generation means 17 is controlled by a control means 21 so that a second pulse can be applied to the pressure generation means 17 with a delay of a predetermined time. For example, the delay time for applying a second pulse is determined to be 1/2 of a vibration cycle of a first pulse. The suppression of the residual vibration in this manner can reduce the speed fluctuation of the ink particle. Therefore, with a higher particle frequency, the occurrence of a dot shift can be prevented. In this manner, a printing speed can be improved without deteriorating a printing quality.

Description

[Detailed Description of the Invention] [Summary] Regarding a recording head used in an on-demand type inkjet recording device, an object of the present invention is to provide an inkjet recording head that improves printing speed without reducing print quality. An inkjet recording head comprising a nozzle for ejecting ink droplets, a pressure chamber communicating with the nozzle, a passage for supplying ink to the pressure chamber, and a pressure generating means for generating pressure for ejecting the ink droplets, the pressure The pressure generating means is configured to include a control means for driving and controlling the pressure generating means so as to apply a second pulse after a predetermined delay time after applying the first pulse to the generating means.

[Industrial Application Field] The present invention relates to a recording head used in an on-demand type inkjet recording apparatus.

Inkjet recording devices can be broadly classified into three types: continuous jet type, electrostatic suction type, and on-demand type.

The continuous ejection type performs recording by charging and deflecting ink that is continuously ejected, so the device is complicated and requires ink collection and cleaning devices.

In addition, although the structure of the electrostatic attraction type is relatively simple,
It is dangerous because it requires high voltage, and the wavenumber response of the upper layer is also poor, with many restrictions on ink physical properties such as electrical conductivity.

On the other hand, the on-demand type ejects ink droplets only when necessary by generating pressure from ejection energy generating elements such as piezoelectric elements and heating elements, so it has a very simple structure and is attracting attention as a recording device. .

[Prior Art] As a conventional on-demand recording head, for example,
There is something like the one shown in the figure.

In FIG. 8, l is a substrate, and 2 is a diaphragm. Between these substrate 1 and the diaphragm 2 are a nozzle 3 that ejects ink droplets, and a pressure chamber 4 that communicates with the nozzle 3 and generates pressure. , a passage 5 for supplying ink to the pressure chamber 4 is provided.

A piezo element 6 as an energy converter is provided on the diaphragm 2 at the outer periphery of the pressure chamber 4, and the piezo element 6 generates pressure for ejecting ink droplets from the nozzle 3.

In such a recording head, in order to increase the printing speed, it is necessary to increase the number of times ink droplets are ejected per unit time (hereinafter referred to as particle formation frequency).

[Problems to be Solved by the Invention] However, in such conventional recording heads, as the atomization frequency is increased, the positional accuracy of recording dots deteriorates (the dots become larger), and printing becomes difficult. There was a problem that the quality deteriorated.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide an inkjet recording head that improves printing speed without deteriorating print quality.

[Means to solve the problem] FIG. 1 is a diagram explaining the principle of the present invention.

In FIG. 1, 14 is a nozzle that ejects ink droplets;
6 is a pressure chamber communicating with the nozzle 14; 18 is the pressure chamber 1;
6 is a passage for supplying ink; 17 is a pressure generating means for generating pressure for ejecting the ink droplets; and 21 is a pressure generating means for applying a first pulse to the pressure generating means 17 and then applying a second pulse after a predetermined delay time. This is a control means for driving and controlling the pressure generating means 17 so as to apply pulses.

[Function] In the present invention, the first
In order to suppress residual vibrations caused by the pulse, the control means controls the drive of the pressure generation means so that a second pulse delayed by a predetermined delay time is applied to the pressure generation means.

Here, in order to suppress residual vibration, the delay time for applying the second pulse is set to 1/2 of the vibration period of the first pulse.

In this way, residual vibrations can be suppressed, so that velocity fluctuations of ink droplets can be reduced. Therefore, even if the particle frequency is increased, it is possible to prevent the occurrence of dot misalignment and to prevent the print quality from deteriorating. In other words, printing speed can be improved without reducing print quality.

"Example" Embodiments of the present invention will be described below based on the drawings.

FIGS. 2 to 7 are diagrams showing one embodiment of the present invention.

First, to explain the structure, in FIGS. 2 and 3, 11 is the substrate of the inkjet recording head 12;
The substrate 11 is made of stainless steel. 13 is a diaphragm of the inkjet recording head 12, and diaphragm 1
3 is also made of stainless steel.

Reference numeral 14 denotes a nozzle constituted by the substrate 11 and the diaphragm 13. The nozzle 14 has an ejection opening 15 at its tip and ejects ink droplets.

A pressure chamber 16 is constituted by the substrate 11 and the diaphragm 13, and the pressure chamber 16 communicates with the nozzle 14.

17 is a piezo element (pressure element) as a pressure generating means, and the piezo element 17 is connected to the diaphragm 13 outside the pressure chamber 16.
is placed above. The piezo element 17 generates pressure for ejecting ink from the nozzle 14.

A passage 18 communicates with the pressure chamber 16, and ink is supplied from the passage 18 to the pressure chamber 16. Passage 18 is ink chamber 1
9, and the ink chamber 19 has a supply port 20 that communicates with an ink supply chamber (not shown).

21 is a control section as a control means, and the control section 21 is
ROM23 in which the PU22 and control programs are stored
and RAM24 used as temporary storage and work area.
It consists of a microprocessor with a

After applying a first pulse for ejecting ink particles via the driver 25, the control unit 21 applies a second pulse for a predetermined delay time, in which the vibration period of the first pulse is applied in order to suppress pressure fluctuations. The piezo element 17 is driven and controlled so that the voltage is applied with a delay of 1/2 of the delay time.

Next, the effect will be explained.

As described above, in order to increase the printing speed, it is necessary to increase the atomization frequency, but as the atomization frequency increases, dot misalignment increases and print quality deteriorates.

Here, we will discuss the cause of dot misalignment when the particle formation frequency is increased.

FIG. 4 shows the frequency characteristics of ink droplet velocity.

In FIG. 4, A, B, and C indicate extreme values of particle velocity.

Further, VO indicates particle velocity at low frequency.

It can be seen from FIG. 4 that as the particle formation frequency increases, the variation in particle velocity increases. Therefore, due to variations in particle speed, the time it takes for ink particles to reach the recording paper changes, resulting in misalignment of the recording dots. That is, the distance is shifted by a distance equal to arrival time x scanning speed of the recording head. In other words, in order to improve the printing speed, it is necessary to reduce the change in the velocity of ink droplets up to a high frequency.

Next, fluctuations in particle velocity with respect to particle formation frequency will be explained.

When a driving pulse is applied, ink particles are ejected from the nozzle 14, and pressure waves generated by the driving pulse remain in the recording head 12. That is, residual vibration occurs.

When the atomization frequency is increased, the next drive pulse is applied before this residual vibration has completely attenuated, and the velocity of the ink droplet changes due to the influence of the residual vibration, and this fluctuation is caused by the frequency It gets bigger as it gets higher.

Therefore, in order to suppress the residual vibration generated by the first pulse after applying the first pulse to eject ink particles, we considered a driving method that applies a second pulse voltage, and determined the conditions for applying the second pulse. .

FIG. 5 shows an example of a drive pulse voltage waveform.

In order to suppress residual vibrations caused by the first pulse for ejecting ink particles, a second pulse delayed by a delay time td is applied to the piezo element 17, which is an energy converter, thereby suppressing the vibrations. In this case, in order to suppress residual vibration, it is necessary to determine the timing (delay time) for applying the second pulse.

Here, the delay time is the point where the pulse voltage changes more steeply in each of the two drive pulses, that is, the time difference (t4 t2) between j==j2゜t=t4 in Fig. 5. .

FIG. 6 shows a schematic diagram of residual vibration.

The residual vibrations generated by the first pulse are shown in (a) and (b
), if the second pulse is given with a delay time t, which is exactly 1/2 of the residual vibration period, as shown in (C), the residual vibration between the first and second pulses is The vibrations can be reduced by canceling each other out at the peaks and valleys.

Next, the above concept will be applied to the case where the recording head 12 shown in FIG. 2 is used.

First, driving conditions (delay time) regarding stabilization of particle velocity
In order to find this, only the delay time was changed and the atomization frequency characteristics of the ink droplet velocity were measured.

The drive waveform at this time was set as follows.

・First pulse width: 60 μs ・Second pulse width: 35 μS Next, the speed fluctuation rate was determined from the measurement results of the frequency characteristics of the ink droplet speed.

Here, the rate of velocity fluctuation is relatively speaking. If the particle velocity at low frequency is Vo, and the change in particle velocity at a certain particleization frequency is Δ■, then (velocity fluctuation rate) = ΔV/Vo
X 100 (1).

FIG. 7 shows the results of the speed fluctuation rate with respect to the delay time at this time.

In FIG. 7, A, B, and C indicate velocity fluctuation rates at extreme values of particle velocity in the particleization frequency characteristics.

As shown in Fig. 7, the speed fluctuation rate reached its minimum value for all A, B, and C when the delay time was 70 μs. That is, t,=
When the time is 70 μs, the speed fluctuation is the smallest.

Since the residual vibration period of the recording head 12 was measured to be 140 μs, this means that the period of 17'2 (70
μS) and the experimental results, it was found that the above-mentioned idea is valid.

In this way, after the first pulse is applied, the second pulse is applied with a delay of 1/2 of the vibration period of the first pulse, so that residual vibration can be suppressed. Therefore, it is possible to reduce fluctuations in the particle velocity, so even if the particle formation frequency is increased, dot misalignment can be prevented. As a result, printing speed can be improved without reducing print quality.

[Effects of the Invention] As described above, according to the present invention, since the piezoelectric element is driven under optimized driving conditions, residual vibrations can be suppressed, without deteriorating printing quality. It is possible to improve printing speed.

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining the principle of the present invention, Fig. 2 is a cross-sectional view showing an embodiment of the present invention, Fig. 3 is a partially cross-sectional perspective view of the recording head, and Fig. 4 is a diagram showing the particle formation frequency and particle velocity. Figure 5 is a graph showing the drive waveform, Figure 6 is a graph showing residual vibration, Figure 7 is a graph showing the relationship between delay time and speed fluctuation rate, and Figure 8 is a conventional example. It is a diagram. In the figure, 11...substrate, 12...recording head, 13...diaphragm, 14...nozzle, 15...discharge port, 16...pressure chamber, 17...piezo element ( pressure generating means), 18... passage, 19... ink chamber, 20... supply port, 21... control unit (control means), 22... CPU. 23...ROM. 24...RAM. 25...driver.

Claims (1)

[Claims] A nozzle (14) for ejecting ink droplets;
), a passage (18) for supplying ink to the pressure chamber (16), and a pressure generating means (17) for generating pressure for ejecting the ink droplets. , a control means (21) for driving and controlling the pressure generating means (17) so that after applying the first pulse to the pressure generating means (17), a second pulse is applied with a delay of a predetermined delay time; An inkjet recording head characterized by: