JPS6394854A - Method of driving ink jet recorder - Google Patents

Abstract

PURPOSE:To improve discharge stability by applying auxiliary pulses after application of a discharge pulse, weakening the reflective wave of a pressure wave generated by the discharge pulse and at the same time, changing the application timing of the auxiliary pulse in accordance with environmental conditions such as temperature. CONSTITUTION:A pulse shape P1 which increases the volume of an ink chamber 3 rapidly is initially applied to a drive signal shape, and later a pulse shape P2 which reduces the volume of the ink chamber rapidly is applied. After application of this positive pulse shape P2 and subsequent discharge of the main droplets of ink droplets, the pulse shape P1 is applied. Then following the lapse of 2l/c, a negative pressure wave p1 generated by the pulse P1 passes back and forth once through a nozzle to become a positive pressure wave p1'. This positive pressure wave returns to the tip of the nozzle. Next, after the lapse of 4l/c following application of the positive pulse shape P2, a pressure wave p2 travels back and forth twice through the nozzle. Therefore, a negative pulse shape P3 is again applied to offset a positive pressure wave p2'. Here the application timing of the auxiliary pulse is set to the value of 4l/c after application of the positive pulse shape P2. However, this timing is adjusted to be delayed when a temperature is high, and the value of 4l/c is reduced in accordance with an increases in temperatures.

Description

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

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

In the continuous ejection type, the principle is that recording is performed by charging and deflecting ink that is continuously ejected, which makes the device complicated and requires ink recovery and cleaning devices.

Furthermore, although the structure of the electrostatic suction type is relatively simple, it requires a high voltage and is dangerous. Moreover, there are many restrictions on the physical properties of the ink such as conductivity, and the frequency response is poor.

However, in the on-demand type, ink droplets are ejected only when necessary using the pressure of an ejection energy generating element such as a piezoelectric element, and the structure is very simple.
It is highly anticipated 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, digital halftone representation methods require sacrificing resolution in order to increase the WI tonality.

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

However, it has been extremely difficult to control the amount of ink ejected with conventional inkjet recording apparatuses.

For example, in a continuous jet type, it is impossible to change the amount of ink discharged. Furthermore, with the electrostatic attraction type, it is possible to express analog halftones, but it is difficult to increase the gradation width. Furthermore, with the on-demand type, the amount of ink ejected is controlled by changing the pulse voltage and pulse width applied to the piezoelectric element, but it is impossible to increase the gradation width just by changing the pulse waveform. there were.

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. 53-121311, rather than simply pressurizing ink with a piezoelectric element to eject ink droplets, as described in Japanese Patent Application Laid-Open No. 55-17589, It is known that a method in which the ink chamber volume is increased to retreat the so-called meniscus and then the ink is pressurized is not only capable of ejecting smaller ink droplets but also has superior frequency response.

[Problems to be Solved by the Invention] However, after ink is ejected from the orifice, the meniscus returns to the orifice while vibrating unstablely, as will be described later with reference to FIG. Therefore, if the viscosity and surface tension of the ink decrease when the ink temperature increases due to an increase in environmental temperature or continuous operation, the vibrations will become more severe and ejection stability will be impaired.

The cause of this vibration is the reflected waves caused by pressure waves generated by ejection pulses that bounce back at the rear end and tip of the nozzle. -There it was.

[Means for Solving Problem E] Therefore, an object of the present invention is to solve the above-mentioned problems and perform inkjet recording with excellent frequency response, ejection stability, gradation properties, and recording accuracy over a wide temperature range. An object of the present invention is to provide a method for driving an inkjet recording apparatus that can perform the following steps.

Therefore, in the present invention, a nozzle for ejecting ink droplets,
and a recording head having an ejection energy action chamber in which a piezoelectric element that generates ejection energy for ejecting ink droplets is arranged, and by supplying an electric signal to the piezoelectric element, the volume of the ejection energy action chamber is reduced and ejection is performed. In the driving method of an inkjet recording device that records by ejecting ink droplets from the outlet, the volume is rapidly increased when the pressure wave generated by the supply of an electrical signal and reflected within the print head reaches the vicinity of the ejection outlet. The present invention is characterized in that a second electrical signal is supplied to the piezoelectric element, and the timing of supplying the second electrical signal is changed depending on environmental conditions.

[In other words, according to the present invention, the pressure wave is canceled by supplying a second electrical signal, and the timing of supplying the second electrical signal is controlled by environmental conditions that influence the propagation speed of the pressure wave.] Since it is changed according to the temperature (temperature, etc.), stable discharge is possible under any environment.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example of the configuration of an on-demand inkjet recording head applied to the present invention. In the figure, 1 is a straight tube-shaped nozzle with a length l, 2 is a cylindrical piezoelectric element placed outside the nozzle 1, and the part of the nozzle 1 where this piezoelectric element is placed is affected by the discharge energy. It becomes a room. By supplying an electric signal from the drive unit 7 to the piezoelectric element 2, the nozzle 1 including the discharge energy action chamber is
As the volume of the ink chamber 3 within the ink chamber 3 decreases or increases, an ink droplet 5 is ejected from the orifice 4.

A filter 6 is made of a porous member and prevents dust and air bubbles in the ink from entering the nozzle. Further, 8 and 9 are a timing control section and a temperature detection section, respectively, and the timing control section 8 modulates the pulse waveform for the drive section 7 according to the output of the temperature detection section 9.

The piezoelectric element 2 in such a head is applied with a positive pulse wave as shown in FIG. 2, that is, after rapidly reducing the volume of the ink chamber 3, the piezoelectric element 2 is slowly returned to the nozzle so as not to introduce air bubbles into the nozzle. When an electrical signal is supplied,
Although ink droplets are ejected, relatively small ink droplets cannot be ejected.

FIG. 3 shows the relationship between drive frequency and ejection speed when the pulse waveform shown in FIG. 2 is applied. Just as there are peaks and valleys in this curve, inkjet recording heads generally have resonance frequencies, and when calculated from these peaks,
The period of resonance can be 4J2/c, where C is the sound velocity in the ink inside the nozzle. This indicates that the phase of the pressure wave is reversed by making one round trip through the nozzle, and returns to the original phase by making two round trips.

To further clarify this, FIG. 4 shows the state of meniscus vibration when ink is ejected from the orifice. The peaks (troughs) of meniscus vibration are still approximately 4fl/
c, and their reciprocals correspond to the resonant frequencies in FIG.

If there is such a vibration of the meniscus, there is a risk that when the meniscus vibrates in the direction of the orifice 4, the energized meniscus will pass the orifice 4 and be ejected as minute ink droplets.

As shown in FIG. 5(A), the ejection speed of the minute ink droplet 13 ejected by the reflected wave is extremely slow compared to the single droplet 11 ejected by the ejection pulse and the satellite 12 generated secondarily. This will disturb the quality of the recorded image. Also, sometimes the discharge does not finish completely, as shown in Figure 5 (B).
), such minute ink droplets may be crushed near the orifice 4, inhibiting the next ejection and significantly deteriorating the ejection stability.

Therefore, in accordance with the timing of this reflected wave, the opposite phase (
By applying a negative (negative) pressure wave, it is possible to suppress meniscus vibration and eliminate the generation of minute ink droplets. That is, the sixth
As shown in the figure, basically a pulse wave having the waveform shown in the second figure plus an auxiliary pulse 15 at a specific position is applied.

On the other hand, there is an optimal timing for applying this auxiliary pulse depending on the structure of the head and the composition of the ink, but it is mainly determined by the speed of sound in the ink in the nozzle, so the high speed may vary depending on the temperature. The optimal timing will also be different.

Therefore, in this example, a very ideal pulse waveform can be obtained at any temperature by modulating the application timing of the auxiliary pulse for eliminating reflected waves according to changes in the ambient temperature.

FIG. 7 shows the drive signal waveform used in this example. This waveform is initially a negative pulse waveform, that is, a pulse waveform P1 that changes the volume of the ink chamber 3 to suddenly increase.
is added. Here, the pulse width T1 of the waveform P1 is 2!
It is set slightly shorter than /c. This waveform provides a negative pressure wave p1, and the meniscus is therefore retracted, making it possible to eject small ink droplets and further improving the frequency response.

After this, the pulse waveform in the positive direction, that is, the pulse waveform P2 that changes so that the volume of the ink chamber rapidly decreases.
Add. 2. When the satellite ejects after this positive pulse waveform P2 is applied and one ink droplet is ejected, that is, after the negative pulse waveform P1 is applied. ．． After I2/C, the negative pressure wave P+ generated by the previously applied pulse P1 travels back and forth through the nozzle once, and its phase is reversed to become a positive pressure wave P+'
and returns toward the nozzle tip. Therefore, the satellite discharged by the positive pulse waveform P2 has a pressure wave Il
Because the satellites are accelerated by It is now possible to eliminate the presence of satellites, which were much slower than the ejection speed of the droplets, causing a large landing error on the recording paper and disturbing the recording quality.

Now, consider the positive pulse waveform P2.

By varying the voltage of this pulse waveform P2, the amount of ink droplet ejection can be controlled over a wide range. That is, if the pulse voltage is decreased, small ink droplets will be ejected, and if the pulse voltage is increased, large ink droplets will be ejected. However, after ejecting an extremely large ink droplet, if the ink chamber 3 is suddenly returned to the direction of expanding (for example, with a pulse waveform as shown in Fig. 8), the ejected ink droplet will appear as shown in Fig. 9 (8). Air is drawn from the orifice by the volume of , the meniscus retreats, and finally, as shown in FIG. 9(B), this air directly enters the inside of the nozzle as bubbles.

In order to prevent this, in this example, after applying a large pulse voltage to eject a large ink droplet, the ink chamber is closed to prevent the meniscus from rapidly retreating and moving beyond a certain level. The volume is gradually increased to return the ink chamber 3 to its initial state. This prevents air bubbles from being taken into the nozzle 1.

Next, 4β/C after the application of the positive pulse waveform P2, the positive pressure wave p2 generated by the waveform P2 reciprocates around the nozzle twice, so this positive pressure wave p2' moves the meniscus toward the orifice. This causes vibration. When this influence is strong, ink droplets may be ejected as they are. Since such ink droplets have an extremely slow ejection speed and are not ejected stably, it is necessary to prevent such ink droplets from being ejected.

Therefore, in this example, after 4J2/c after applying the positive pulse waveform P2, the negative pulse waveform P3 is applied again to generate the negative pressure wave p3, thereby generating the positive pressure wave p2'.
is canceled out by the negative pressure wave p3. As a result, the positive pressure wave p2' is eliminated, and unstable ink droplet ejection is eliminated.

Also, this negative pulse waveform P can be returned to the initial state without generating unnecessary pressure waves by applying it so that it continues at a negative predetermined value for a predetermined time and then gradually reduces to zero. Can be done.

Here, the application timing of the auxiliary pulse is set at 4ρ/C after the application of the positive pulse wave (ejection pulse) P2, but since the sound velocity changes depending on the temperature, this value is 41/C.
also changes.

FIG. 1θ shows the relationship between temperature and sound velocity when yellow ink having the composition shown below is used as the ink.

Water 993 parts by weight Direct Yellow 86 07 parts by weight The relationship between temperature and sound velocity varies greatly depending on the solvent, and in most liquids other than water, the sound velocity decreases as the temperature rises, contrary to water. When a solvent is used in the ink, the application timing becomes slower as the temperature increases.

That is, since the sound speed increases as the temperature rises within the actual operating temperature range, the appropriate application timing of the auxiliary pulse, 4β/C, is made smaller as the temperature rises.

The drive circuit 7 that applies such a pulse waveform connects the transistors Tri to Tr4 as shown in FIG.
A common connection point between the collector of the transistor Tr4 and the collector of the transistor Tr4 is connected to a piezoelectric element, and the common connection point is grounded via a resistor R1.

In such a configuration, when pulses A and B as shown in FIG. 12 are inputted from the timing control section 8 to the drive circuit, the transistors Tri to Tr4 are turned on (conducted), and a waveform like C is output. is obtained and applied to the piezoelectric element.

Further, by appropriately determining the application timing of the pulse B' supplied by the timing control section 8 according to the temperature, it is possible to obtain an appropriate waveform C under any temperature.

The timing control section 8 can have various configurations. For example, this may also be used as the main control section of the device. For example, if the main control section is composed of a microcomputer, the application timing of the signal B' for generating the auxiliary pulse may be adjusted depending on the temperature. The pulse B may be determined by preparing a table and reading this as appropriate according to the detection output of the temperature detection section 9 after applying the ejection pulse.

Through the embodiments described above, the ejection stability of the inkjet recording head was significantly improved.

Further, the time change in the amount of meniscus retreat becomes gradual as shown in FIG. 13, which is significantly different from the curve shown in FIG. 4 when the waveform shown in FIG. 2 is applied.

Therefore, when driving according to this example, ejection is performed stably in all cases, and unstable minute ink droplets due to reflected waves are not ejected.

In the above description, the present invention has been described as being applied to an apparatus equipped with a recording head in which a discharge energy action chamber is integrally formed with a straight nozzle, but this configuration can be modified in various ways. For example, the nozzle may have a bent portion, or the nozzle and the discharge energy application chamber may be formed separately.

[Effects of the Invention] As explained above, according to the present invention, an auxiliary pulse is applied after the ejection pulse is applied to weaken the reflected wave of the pressure wave generated by the ejection pulse, and the application timing of the auxiliary pulse is adjusted depending on environmental conditions such as temperature. By making changes according to the temperature, it is possible to smooth the meniscus vibration and create an inkjet recording device with excellent ejection stability, frequency response, gradation, and recording accuracy over a wide temperature range. .

[Brief explanation of the drawing]

FIG. 1 is a side sectional view showing an example of the configuration of an inkjet recording head to which the present invention can be applied, FIG. 2 is a waveform diagram showing a conventional drive pulse waveform for driving the recording head, and FIG. Figure 4 is a characteristic curve diagram showing the frequency characteristics of the discharge speed when driving with the waveform shown in Figure 2. Figure 4 is a diagram showing meniscus vibration when driving with the waveform shown in Figure 2. Figure 5 (A) and (B) is an explanatory diagram for explaining the ink ejection state, FIG. 6 is an explanatory diagram for explaining the basic drive waveform used in the present invention, and FIG. 7 is an example of the drive pulse waveform according to the present invention. FIG. 8 is a waveform diagram showing a pulse waveform as a comparison with the waveform shown in FIG. 7. FIGS. An explanatory diagram, Fig. 1θ is an explanatory diagram for explaining the relationship between temperature and sound velocity in ink, and Fig. 11 is a circuit diagram showing an example of the configuration of a drive circuit that generates a pulse waveform applicable to the present invention. , FIG. 12 is a waveform diagram showing an example of the operating waveform of the drive circuit shown in FIG. 15, and FIG. 13 is a diagram showing the state of meniscus vibration when driving with the pulse waveform according to this embodiment. DESCRIPTION OF SYMBOLS 1... Nozzle, 2... Piezoelectric element, 3... Ink chamber, 4... Orifice, 5... Ink droplet, 6... Filter, 7... Drive circuit, 11... Starring, 12.13...Satellite, l...Nozzle length, P+, P2, P3...Pulse waveform. 100 Figure 8 Figure 9

Claims (1)

[Scope of Claims] 1) A recording head having a nozzle for ejecting ink droplets, and an ejection energy action chamber in which a piezoelectric element that generates ejection energy for ejecting the ink droplets is arranged, and the piezoelectric element is provided with electricity. In the method of driving an inkjet recording apparatus, the volume of the ejection energy action chamber is reduced by supplying a signal to eject ink droplets from the ejection port to perform recording, wherein the electric signal is generated by the supply of the electric signal, and the ink droplet is ejected from the ejection port. When the pressure wave reflected by reaches the vicinity of the discharge port,
A method for driving an inkjet recording apparatus, characterized in that a second electrical signal that rapidly increases the volume is supplied to the piezoelectric element, and the timing of supplying the second electrical signal is changed depending on environmental conditions. 2) In the method for driving an inkjet recording apparatus according to claim 1, the nozzle integrally has the ejection energy action chamber, and the pressure wave is generated by the supply of the electric signal and reflected at the rear of the nozzle. 1. A method for driving an inkjet recording device, characterized in that the method uses a pressure wave.