JPS5840506B2 - Inkjet recording method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is disclosed in Japanese Unexamined Patent Publication No. 48-9622 and Japanese Unexamined Patent Publication No. 51
The present invention relates to an improvement in a recording method using an inkjet recording device that ejects and stops minute ink droplets in response to electrical signals, as described in Japanese Patent No. 37541, and more specifically, to improve the performance of an inkjet recording head. It is an object of the present invention to provide an inkjet recording method that fully utilizes the inkjet recording method to obtain recorded images with good response characteristics and a wide reproduction density range.

FIG. 1 shows an inkjet recording apparatus described in Japanese Patent Application Laid-Open No. 51-37541, and
This is an improved version of the inkjet recording device described in the publication.

A first ink chamber 3 that includes an electrostrictive element 1 and a diaphragm 2 and has a device that generates a pressure increase in response to an electric signal 11.
The second ink chamber 5 is connected to the ink discharge port 6 and the ink inflow path 9, and the air chamber 7 is connected to the air outflow path 8 and the air inflow path 10. The first ink chamber 3 and the second ink chamber 5 are connected via a coupling passage 4, and the coupling passage 4, the ink discharge port 6, and the air outlet passage 8 are arranged on the same straight line. be.

The air flow sent through the air inflow path 10 passes through the air chamber 7 and constantly flows out from the air outflow path 8, helping the flight of ink droplets ejected from the ink ejection port 6 in response to the electrical signal 11. .

FIG. 2 shows an example of the drive waveform of the inkjet head.

When the drive signals shown in FIG. Ru.

The repetition time λ of 1 drive value numbers a and b is related to the number of ink droplets ejected per unit time.1. The drive voltage ■pp is related to the amount of ink ejected during the repetition time λ.

Therefore, as a means for producing shading in a recorded image using the drive waveform shown in FIG. 2, the drive signal amplitude v0. The method of changing the repetition frequency f-1 of one driver number
There are methods such as changing /λ.

However, the method of changing the repetition frequency f of the drive signal is difficult to use because the frequency characteristics of the inkjet recording head are not flat; generally, the repetition frequency f is fixed, and the amplitude pp of the drive signal is changed. A method has been adopted in which shading is caused in the recorded image by this.

Furthermore, when comparing Fig. 2 a and t), it is found that due to the influence of the natural vibration frequency of the inkjet recording head, the driving waveform in Fig. 2 a has a higher repetition frequency f than the driving waveform in Fig. 2 S. suitable for high-speed recording.

- According to the above detailed explanation, the drive signal of the inkjet recording apparatus shown in FIG. 1 is shown in FIG. 2a.

An excellent method is to use a drive waveform and modulate the drive signal amplitude pp with an image signal.

Therefore, a detailed explanation will be given below by taking the driven method as an example.

FIG. 3 shows the recording characteristics when the inkjet recording head of FIG. 1 is driven using the signal waveform of FIG. 2a, that is, the sine waveform.

That is, the drive signal amplitude (2) when the repetition frequency of the drive signal is fixed at 20 KHz. (horizontal axis) and recording optical density 0. This is an example showing the relationship between D and (vertical axis).

In FIG. 3, drive amplitude range A is a stable ejection region, and drive amplitude range B is an unstable ejection region 1. A drive amplitude range C indicates an area where ejection is not possible.

Driving amplitude range A is an area where ink droplets are stably ejected and stopped from the inkjet recording head, and driving amplitude range B is an area where the response characteristics of the inkjet recording head are unstable and it takes time to eject ink droplets. This is an area where delays are likely to occur, and the one drive plate width range C is an area where ink droplets are not ejected due to minute fluctuations in ink pressure within the first ink chamber 3 of the inkjet recording head. .

Here, the unstable ejection region of drive amplitude range B will be explained in more detail.

, when the inkjet recording head is driven by a drive signal included in the drive amplitude range B, the ejection state of ink droplets differs depending on the drive state immediately before the drive signal.

That is, when a continuous sinusoidal waveform within the drive amplitude range B as shown in FIG. 4 is applied to the inkjet recording head,
An inkjet recording head continuously ejects ink droplets and can obtain a certain recording optical density.

However, when the drive signal changes from O level or a low level signal within the drive amplitude range C to a drive signal within the drive amplitude range B as shown in FIG. 4a, the response characteristics of the inkjet recording head deteriorate. However, the ink droplets are ejected with a time delay from the rising edge of the signal.

This phenomenon becomes more pronounced as the amplitude of the drive signal immediately preceding the drive signal within the drive amplitude range B is at a lower level.

Furthermore, as shown in FIG. 4C, when the drive signal changes from within the drive amplitude range A to the drive signal within the drive amplitude range B, there is no problem with the response characteristics of the inkjet recording head; The ink amount of the ink droplet with the drive signal within the amplitude range B is greater than the ink amount in FIG. 4a or b, and the recording optical density is greater than that in FIG. 4a or b.

As described in detail above, the inkjet recording apparatus shown in FIG. 1 has a drive signal amplitude of ■pp and a recording optical density of 0. The relationship between D and D is shown in FIG. 3, and the drive amplitude range is classified into three regions depending on the ejection state of ink droplets.

The drive amplitude range B is an unstable ejection region, and it is conceivable that the quality of the recorded image will differ depending on how this region is processed.

FIG. 5 is an example of a drive signal for the inkjet recording head of FIG. 1.

FIG. 5a shows an example of an image signal, which is a step signal with 10 levels.

Steps ■ and [Phase] are O level signals, which correspond to white in the image.

Steps ■ to ■ correspond to gray or black in the image.

5C and 5D show drive signals for an inkjet recording head obtained by modulating a sine waveform (hereinafter referred to as a carrier signal) with a repetition frequency of 20 KHz with the image signal of FIG. 5A.

In Figure 5, the image signal step ■ or [phase] is set to O level, step ■ is set to the drive amplitude of a predetermined stable ejection region, and the carrier signal is modulated in proportion to the image signal level. It is.

When a modulation method as shown in FIG. 5 is adopted, the drive signal includes an area where ejection is not possible or an unstable ejection area.

That is, for example, in step (2), only the amplitude of the 7 drive body signals corresponding to the non-ejecting area is obtained, and in step (2), the drive signal amplitude of the unstable ejection area is applied to the inkjet recording head. may not be performed or the rise characteristics may be poor.

Figure 5C was devised to compensate for the drawbacks shown in Figure 5S, in which the image signal is slightly shifted to the positive potential side, and the carrier signal is modulated in proportion to the shifted signal level. However, step (2) and [phase] are set to the drive signal amplitude in the non-ejection region, and step (2) is set to a predetermined drive signal amplitude in the stable ejection region.

In the case of FIG. 5C, the drive signal for the non-ejection region is only near the O level of the image signal, but the drive signal for the unstable ejection region is present.

For example, step (2) in FIG. 5C is a drive signal in an unstable ejection region, and as mentioned above, there is a possibility that the rise characteristics will deteriorate.

The rise characteristic is determined by the step ■ or [phase] drive signal (
Hereinafter, this will be referred to as a bias signal.

) Increasing the amplitude improves visual acuity.

However, if the amplitude of the bias signal is too large, ink droplets may be ejected in the step [phase].

In reality, the amplitude of the bias signal that causes no rise delay in the unstable ejection region of step ■ and no ink droplet ejection in step [phase] does not exist or is in a very small range, and adjustment is difficult. Very Difficult O Figure 5(d) shows the non-ejection area and unstable ejection area of FIG. 5(c) to the O level.

In FIG. 5d, there are only drive signals in the 0 level and stable ejection region, and although a recorded image with poor rising characteristics cannot be obtained, there is a drawback that an image with a correspondingly low optical density cannot be reproduced.

As described in detail above, an inkjet recording apparatus is used which has a vibrating means such as a piezoelectric body as shown in FIG. In the conventional recording method, since there is an unstable ejection area as shown in FIG. 3, the reproducible range of optical density is narrow and it is difficult to obtain a recorded image with good gradation.

Here, the unstable ejection region will be explained in detail again.

If there is no delay in the ejection of ink droplets in the 1 drive signal in the unstable ejection region, the 4th drive signal is
The driving signal was as shown in Fig. c.

Further, the drive signal immediately before the drive signal in the unstable ejection region causes a difference in the ejection state of the ink droplets.
The greater the amplitude of the immediately preceding drive signal, the less the delay in ejecting ink droplets.

That is, by setting the amplitude of the immediately preceding drive signal to a large amplitude belonging to the non-ejection region, it is possible to eliminate the delay in ejecting ink droplets due to the drive signal in the unstable ejection region.

Considering that this phenomenon is due to the ink pressure inside the inkjet recording head being excited by the drive signal immediately before, the modulation method shown in FIG. 5C is adopted,
It is conceivable to add a bias signal to the drive signal when the image signal is at O level to excite the ink pressure inside the inkjet recording head.

However, as described above, a phenomenon occurs in which ink droplets are ejected in the step [phase] of FIG. 5C.

This is because the inkjet recording head is brought into an excited state in the step phase by the bias signal, while it is brought into the discharge state in the step [phase].

In other words, the boundary between the excited state and the exposed state of the inkjet recording head is not constant, and the boundary between the regions moves depending on the immediately preceding 7 drive signals, so the modulation method shown in FIG. 5C has a drawback. This is the translation.

The present invention has succeeded in expanding the reproducible range of optical density and obtaining recorded images with good gradation by realizing the above-mentioned excited state using another method.

An embodiment of the present invention will be described in detail below. FIG. 6 shows an embodiment of the present invention.

The modulation method is basically the same as the modulation method shown in Fig. 5C, but the bias signal when the image signal is O level has a waveform different from the carrier signal (20 KHz sine waveform) used when ejecting ink droplets, or is repeated. It is assumed to be a frequency.

That is, only one drive signal in steps 1 and 10 is different.

Such a modulation method can be realized, for example, by a circuit configuration as shown in FIG.

FIG. 8 shows a timing chart of the block diagram shown in FIG. 7.

If an image signal as shown in FIG. 81 is input, it is shifted to the positive potential side by the level shifter 21,
A signal designated 2 is generated.

20 output from the oscillator 23 by the modulator 22
Modulating the KHz sine wave with signal 2 produces signal 3.

Note that the signal 3 is amplified by an amplifier to generate the fifth signal.
The signal will be similar to that shown in Figure C.

Further, the oscillator 24 outputs a signal 4 having a waveform or frequency different from that of the oscillator 23.

On the other hand, the signal 2 is compared with a constant potential ref by a comparator 25, and a signal 5 is generated which turns ON only when step 2 or higher in the signal 1 is reached.

A part of the signal 5 is applied to the analog switch 26, and the other part is inverted at the impark 27' and applied to the analog switch 27.

Using the above signals 3 to 6, analog switch 26.2
7, the signal 7 is obtained by switching the signal 3 with the signal 5 and the signal 4 with the signal 6.

Signal I is a signal corresponding to that shown in FIG. 6, and the signal shown in FIG. 6 is obtained by increasing the voltage of signal 7 using an amplifier.

In FIG. 5C, in order to bring the inkjet recording head into the excited state, the width range of the 7 drive plates was narrow and the boundary between the excited state and ejection state areas was not constant, so it did not go well.

However, as shown in Figure 6, if a signal with a waveform or repetition frequency different from that of the carrier signal is used for the bias signal, the inkjet recording head can be brought into an excited state over a relatively wide amplitude range. It turns out that there is no need to worry about the instability of the border between Japan and Japan.

FIG. 9 is a diagram showing regions of the inkjet recording head in a discharge state and an excited state.

The horizontal axis shows the drive frequency of the 11-string waveform, and the vertical axis shows the amplitude of the drive signal.

Area ■ indicates a range of ejection states including an unstable ejection state and a stable ejection state, and area ■ and area ■ indicate a range in which the inkjet recording head can be brought into an excited state when the carrier frequency is 20 KHz. There is.

As is clear from FIG. 9, by applying a bias signal using a frequency different from the frequency of the carrier signal, the inkjet recording head can be brought into an excited state over a very wide drive amplitude range.

Therefore, it has been found that it is possible to easily select a setting value that does not have the disadvantage that ink droplets are ejected due to the influence of the signal immediately before the carrier signal, as is the case when a bias signal with the same frequency as the carrier signal is applied. Ta.

For example, if the carrier signal is a 20KHz sine waveform, the bias signal is 1.5KHz, 20V.

By applying a sinusoidal waveform of No ejection takes place.

Note that the minimum value of optical density when this modulation method is adopted is 0.12 under predetermined recording conditions, and the minimum value of optical acidity in the stable ejection area before improvement is 0.12 under the same recording conditions. 3
3, the reproducible optical density range is greatly expanded.

Further, in FIG. 9, only the case where a sine waveform is used as the bias signal has been considered, but it is also possible to use a pulsed waveform different from the sine waveform as shown in FIG. 2, for example, as the bias signal.

In the waveform shown in Figure 2, the ink is determined by the rise characteristics, fall characteristics, pulse width, amplitude, etc. of the signal pulse as described in Japanese Patent Laid-Open No. 47-6308 and No. 48-9622. The droplet ejection state is determined.

Here, as an example, the rise time is approximately 1 to 3 μs1.
A case will be described in which a signal pulse with a falling characteristic of about 20 μs and a pulse width of about 20 μs is used.

FIG. 10 is a diagram showing the regions of the ejection state and the excited state of the inkjet recording head when the above-mentioned signal pulses are used.

The horizontal axis represents the repetition frequency of the signal pulse, and the vertical axis represents the amplitude of the signal pulse.

In FIG. 10, region I indicates a region where ink droplets can be ejected when the signal pulse is used.

Region (3) in FIG. 10 indicates the range in which the inkjet recording head can be brought into an excited state when a 20 KHz sine waveform is applied to the vibrating means of the inkjet recording head to eject ink droplets according to the signal.

When signals with different waveforms are used as bias signals, the first
As is clear from FIG. 0, a signal having the same repetition frequency as the signal (20 KHz, sine waveform) used when ejecting ink droplets can be used as the bias signal.

For example, in the signal pulse in FIG.
When a Hz, 30V signal is used as a bias signal, the above-mentioned signals with different repetition frequencies (15KHz, 20V)
It was possible to obtain exactly the same effect as in the case where V sine waveform) was used as the bias signal.

The apparatus shown in FIG. 11 is an inkjet recording apparatus described in Japanese Patent Application Laid-Open No. 48-9622, which does not use air flow.

The role of the air flow in the inkjet recording apparatus shown in FIG. There is almost no difference in variation between the inkjet recording apparatuses shown in FIGS. 1 and 8.

Therefore, the modulation method described in detail above can be applied to the inkjet recording apparatus shown in FIG. 11 as is.

As described in detail above, the present invention provides an inkjet recording apparatus having a vibrating means such as a piezoelectric body and a means for applying a pressure wave to an ink outflow path by the vibrating means to eject an ink stream, when an ink droplet is ejected. By applying electric signals with different repetition frequencies or different waveforms when ejection is stopped, unstable ejection areas of the inkjet recording head can be eliminated, and recorded images with good response characteristics and a wide reproduced density range can be obtained. .

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of an inkjet recording apparatus using the method of the present invention, and FIG. b1 Figure 3, Figure 4, a, b, c1 Figure 5 a~
d is a diagram showing the conventional recording method, FIG. 6 is a diagram showing the method of the present invention, FIG. 7 is an example of a circuit configuration diagram for implementing the method shown in FIG. 6, and FIG. 7 is a timing chart for explaining the operation of the circuit configuration, FIG. 9 is a diagram showing the ejection state and excitation state of the inkjet recording head in an embodiment of the present invention, and FIG. FIG. 11 is a cross-sectional view showing another example of an inkjet recording apparatus using the method of the present invention. 1... Electrostrictive element, 2... Vibration plate, 3.
...First ink chamber, 4...Connection passage,
5... Second ink chamber, 6... Ink discharge port, 7... Air chamber, 8... Air outflow path, 9... ...Ink inflow path, 10...
Air inflow path, 11... Electric signal, 21...
...Level shifter, 22 ...Modulator, 2
3, 24... Oscillator, 25... Comparator, 26, 27... Analog switch.

Claims (1)

[Claims] 1. When ejecting ink droplets by applying pressure waves to the ink outflow path by applying a signal to the vibrating means made of a piezoelectric tube, the signal applied to the vibrating means is a sine wave signal. An inkjet recording method, characterized in that a bias signal with an amplitude lower than a predetermined value is applied when ejection of ink droplets is stopped, and the bias signal is a pulsed signal or a signal having a repetition frequency different from the sine wave signal. 2. The inkjet recording method according to claim 1, wherein the signals having different repetition frequencies are sine wave signals.