JPS6394850A - Method of driving ink jet recorder - Google Patents

Abstract

PURPOSE:To improve discharge stability by providing a composite wave form of two pulse shapes of an electric signal to be supplied to a piezoelectric element, and besides making it a pulse shape which enables the first pulse shape to be supplied and then the second pulse shape is supplied after passage of a specific time. CONSTITUTION:During a period in which an ink chamber 3 is initialized or which follows completion of the initialization, a negative pressure wave p1 makes a return trip through a nozzle after the lapse of 2l/c following the application of a negative pulse shape P1, and returns to the tip of the nozzle in the form of a positive pressure wave p1'. Timed to this, a voltage V3 and negative pulse P3 having a pulse width T1 are applied to provide a negative pressure wave p3. Consequently, the positive pressure wave p1 apparently disappears. After this, a positive pulse shape P2 is applied, and after the lapse of 4l/c, a positive pressure wave p2 shuttles twice through the nozzle. Therefore, after the lapse of 2l/c following the application of the positive pulse shape P2, a negative reflective wave p4' overlaps a positive reflective wave p2' and a pressure wave apparently goes out of sight. if a voltage V4 and a positive pulse shape P4 are applied. Thus high-precision printing can be effected.

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, since recording is performed by charging and deflecting ink that is continuously ejected, the device becomes complicated, and ink collection and cleaning devices are also required.

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, in digital halftone representation methods, resolution must be sacrificed in order to increase the number of tones.

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 ejection type, it is impossible to change the amount of ink ejected. 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 by changing the pulse waveform alone. 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, leading to increased costs.

On the other hand, as described in Japanese Patent Publication No. 53-12138, rather than simply pressurizing ink with a piezoelectric element to eject ink droplets, as described in Japanese Patent Application Laid-Open No. 17589-1980, It is known that a method of increasing the volume of the ink chamber and retracting the so-called meniscus and then pressurizing the ink 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 the pressure waves generated by the ejection pulses repeatedly bouncing off the rear end and tip of the nozzle. It was.

[Means for Solving the Problems] 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, the volume of the ejection energy application chamber is reduced by supplying an electric signal to the nozzle for ejecting ink droplets and the piezoelectric element that generates ejection energy for ejecting ink droplets. In a method of driving an inkjet recording device that performs recording by ejecting ink droplets from an ejection port by changing the volume of the When the length is 1 and the speed of sound in the ink is C, the electric signal supplied to the piezoelectric element is a composite waveform of at least two pulse waveforms, and the electric signal supplied to the piezoelectric element is a composite waveform of at least two pulse waveforms. The present invention is characterized in that the pulse waveform is such that the second pulse waveform is supplied.

Here, in a preferred embodiment of the present invention, the first pulse waveform and the second pulse waveform have substantially similar shapes in the time direction, and the second pulse waveform has a smaller absolute value of voltage than the first pulse waveform. I took it as a thing.

In addition, the electric signal can be used to pressurize and eject ink by: (1) changing the volume of the ejection energy application chamber so as to rapidly increase; and (2) rapidly reducing the volume of the ejection energy action chamber after the first predetermined period of time has elapsed. The ink droplet is ejected from the outlet, and the volume of the ejection energy application chamber is gradually increased so that the meniscus after the ink droplet is ejected after a second predetermined time does not retreat more than a predetermined amount. After 21/c has elapsed since the volume has been increased, the volume of the discharge energy action chamber is changed again so as to be suddenly increased; (2) The pulse waveform was changed so that the volume of the discharge energy action chamber was gradually increased after the second predetermined time had elapsed.

Furthermore, the pulse waveform is: (1) rapidly changed in the negative direction to a first predetermined value and then continued at the first predetermined value for a first predetermined time; (2) then changed from the first predetermined value to a positive second predetermined value; ■ The electric signal is caused to suddenly change to a third predetermined value or to zero for a predetermined time constant from the second predetermined value, and then gradually change to a third predetermined value or zero by a predetermined time constant. After 2 It/c has elapsed since the application of , the voltage is rapidly changed from a third predetermined value or ; to a negative fourth predetermined value, and then the fourth predetermined value is continued for a first predetermined time; After rapidly changing from a predetermined value to a positive fifth predetermined value, the fifth predetermined value is continued for a second predetermined time, and then gradually leveled out from the fifth predetermined value by a predetermined time constant. .

[Operation] That is, according to the present invention, if the first pulse waveform and the second pulse waveform are appropriately determined, it is possible to suppress the vibration of the meniscus.

[Example code] 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 ρ, and 2 is, for example, a cylindrical piezoelectric element placed outside the nozzle 1. The part of the nozzle 1 where this piezoelectric element is placed is the discharge energy action chamber. becomes. 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 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.

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 can be ejected, only relatively small ink droplets can 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. Calculating from these peaks, the resonance period is 4, where C is the sound velocity in the ink in the nozzle.
ρ/C will cause a hailstorm. 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.

On the other hand, as shown in FIG. 5, in addition to the main droplet 11, there are generally satellites 12 in the ejected ink droplet, and as mentioned above, the satellites are ejected at a slower speed than the main droplet and reach the recording paper. The poor landing accuracy of the particles disturbs the quality of recorded images.

Therefore, in this example, the dot diameter can be varied from small dots to large dots without changing the pulse waveform much as shown in Figure 2, and frequency]2 Improves responsiveness, ejection stability, performance, and ejection speed. to be done.

FIG. 6 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 waveform P1 is 2l
It is set slightly shorter than /c. This waveform provides a negative pressure wave p, which causes the meniscus to retreat, making it possible to eject small ink droplets and also improving 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.

By changing the voltage v2 or pulse width T2 of this positive pulse waveform P2, it becomes possible to control the amount of ink droplet ejection over a wide range. That is, if the pulse voltage V2 is made small, a small ink droplet will be ejected, and if the pulse voltage V2 is made too large, a large ink droplet 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. 7), the ejected ink droplet will become larger as shown in Fig. 8(A). Air is drawn from the orifice by the volume, the meniscus retreats, and finally, as shown in Figure 8 (B)
As shown in the figure, this air directly enters the inside of the nozzle as bubbles.

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

During the period during which the ink chamber 3 is returned to its initial state, or during the period after the return has been completed, the negative pressure wave P1 makes one round trip through the nozzle when 2 l/c has elapsed since the application of the negative pulse waveform P1, and the phase is reversed. and returns to the nozzle tip as a positive pressure wave p,'. In accordance with this, the voltage v5. When a negative pressure wave p is applied by applying a negative pulse P3 having a pulse width T1, the positive pressure wave p1' apparently disappears, and the meniscus vibration is suppressed.

At this time, the pressure wave p1' is opposite in phase and has almost the same magnitude.
It is preferable that voltages ① and ②3 are adjusted so that p2 and p2 are obtained.

Next, after applying the positive pulse waveform P2, 4 It /
After c has elapsed, the positive pressure wave p2 reciprocates around the nozzle twice, and becomes a positive pressure wave +12' again, causing the meniscus to vibrate unstablely. This effect is so great that ink droplets may be ejected. Since the ejection speed of such ink droplets is extremely slow and they are not ejected stably, it is necessary to prevent them from being ejected.

Therefore, after applying the positive pulse waveform P2, the temperature is 2°C/c.
After that, if a positive pulse waveform P4 with a pressure V 4 and a pulse width T2 is applied to generate a positive pressure wave p4, the pressure wave p4 will be generated 4 ft/c after applying the positive pulse waveform P2. After one round trip through the nozzle, the negative reflected wave p4' returns to the nozzle tip. Thus, it overlaps with the positive reflected wave p2', and apparently there is no pressure effect. At this time, the pressure waves le4' and p2 are opposite in phase and have almost the same magnitude.
It is preferable that the voltages (2) and (4) are adjusted so that the voltages (2) and (4) are obtained. The relationship between the voltages (1) and (2) and the voltages (2) and (V4) is 1 because the pressure wave gradually attenuates as it propagates through the ink, and I≧lV3 1.
It is preferable to set the relationship lV2 1≧lv4 l.

Finally, for waveform P4, the ink chamber 3 can be returned to its initial state without creating new unnecessary pressure waves by gradually increasing the voltage from voltage (2) to (4).

If the recording timing of the pulse waveform is configured as in this example based on the relationship between the nozzle length and the sound velocity C as described above, ejection can be performed stably. On the other hand, if this timing is shifted to such an extent that the effect of this example is no longer recognized, the vibration of the meniscus will become extremely large, resulting in an unstable ejection state in which minute ink droplets are difficult to eject. .

FIG. 9 shows this situation. Here, (8) in the same figure shows when the auxiliary pulse is applied at a timing faster than the appropriate value, CB) in the same figure shows when the auxiliary pulse (P4) is applied at the proper value, and (C) shows the case where the auxiliary pulse (P4) This is a case where the pulse is applied at a timing later than the appropriate value, and it can be seen that the meniscus oscillates and becomes largely unstable in cases other than CB) in the same figure.

10 to 12 show other embodiments of drive waveforms according to the present invention. These are all composite waveforms in which a relatively small second waveform is applied 2 fl/c after the first waveform is applied, and these also ensure that the meniscus vibration is not unstable and the ejection is stable. It was held.

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. 14 are manually applied to the drive circuit, the transistor Tri NTr4 turns on (conducts), and a waveform like C is obtained as its output. This is applied to the piezoelectric element.

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

Incidentally, in the above description, the present invention has been described as being applied to a device equipped with a recording head in which an ejection energy action chamber is integrally formed with a straight nozzle, but this configuration may be made 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, it is possible to smooth the vibration of the meniscus with a simple configuration, to perform stable discharge over a wide temperature range, and to improve frequency response and gradation. It has become possible to provide an excellent inkjet recording device.

[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. A characteristic curve diagram showing the frequency characteristics of the ejection speed when driving with the waveform shown in the figure, Figure 4 is a diagram showing meniscus vibration when driving with the waveform shown in Figure 2, and Figure 5 is a diagram showing the frequency characteristics of the ejection speed when driving with the waveform shown in Figure 2. An explanatory diagram for explaining the ejection state; FIG. 6 is a waveform diagram showing an example of the drive pulse waveform according to the present invention; FIG. 7 is a waveform diagram showing a pulse waveform for comparison with the waveform shown in FIG. 6; Figures (^) and (B) are explanatory diagrams for explaining the state in which air bubbles are taken into the nozzle, and Figures 9 (A) to (
c) is an explanatory diagram for explaining the effects of this embodiment, Figures 10 to 12 are waveform diagrams showing three other examples of drive pulse waveforms according to the present invention, and Figure 13 is applicable to the present invention. FIG. 14 is a waveform diagram showing an example of the operating waveforms of the drive circuit shown in FIG. 13. DESCRIPTION OF SYMBOLS 1... Nozzle, 2... Piezoelectric element, 3... Ink chamber, 4... Orifice, 5... Ink collector, 6... Filter, 7... Drive circuit, 11... Starring, 12.13... Satellite, ρ... Nozzle length, p, , p7. p3. p4...Pulse waveform. Figure 5 Figure 6 Figure 7 ('A) Figure 8 Time (μ5ec) Time (μ5ec) Figure 11 Time (μSec)

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 disposed, 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 changed by supplying a signal to eject an ink droplet from an ejection port to perform recording, wherein the electric signal is supplied from a portion where the piezoelectric element is arranged. The electric signal supplied to the piezoelectric element is a composite waveform of at least two pulse waveforms, where l is the length to the part of the recording head that reflects the pressure wave generated by the ink, and c is the sound velocity in the ink; 2l/after supplying the first pulse waveform
A method for driving an inkjet recording apparatus, characterized in that the pulse waveform is such that the second pulse waveform is supplied after elapse of c. 2) In the method for driving an inkjet recording apparatus according to claim 1, the nozzle integrally includes the ejection energy application chamber and has a straight tube shape with the length l. How to drive the device. 3) In the method for driving an inkjet recording apparatus according to claim 1 or 2, the first pulse waveform and the second pulse waveform have substantially similar shapes in the time direction; A method for driving an inkjet recording apparatus, characterized in that the pulse waveform has a smaller absolute value of the voltage of the first pulse waveform. 4) In the method for driving an inkjet recording device according to any one of claims 1 to 3,
The electric signal is applied to the ink by (1) changing the volume of the ejection energy application chamber so as to rapidly increase the volume, and (2) rapidly decreasing the volume of the ejection energy action chamber after a first predetermined period of time has elapsed. (3) After the elapse of a second predetermined time, the ejection energy action chamber is pressurized to eject an ink droplet from the ejection port, and (3) to prevent the meniscus from retreating rapidly and by more than a predetermined amount after the ink droplet is ejected after a second predetermined time has elapsed. (4) After the rapid volume increase of 2 l/c has elapsed, the volume of the discharge energy action chamber is changed again so as to increase rapidly; (5) The first predetermined time has elapsed. (6) The pulse waveform is such that the volume of the discharge energy application chamber is changed to rapidly decrease again afterward, and (6) the volume of the discharge energy application chamber is gradually increased after the second predetermined time has elapsed. A method for driving an inkjet recording device. 5) In the method for driving an inkjet recording apparatus according to any one of claims 1 to 4,
The pulse waveform is (1) rapidly changed in the negative direction to a first predetermined value and then continued at the first predetermined value for a first predetermined time; (2) then changed from the first predetermined value to the positive value; (3) Further, the second predetermined value is gradually changed to a third predetermined value or zero by a predetermined time constant; 1 After 2l/c has elapsed since the application of the electrical signal that caused the electrical signal to rapidly change to a predetermined value, the electrical signal suddenly changed from zero to a negative fourth predetermined value and then the first predetermined value at the fourth predetermined value. (5) Next, after rapidly changing from the fourth predetermined value to a positive fifth predetermined value, the fifth predetermined value is continued for the second predetermined time; 5. A method for driving an inkjet recording apparatus, characterized in that the value is gradually reduced to zero from a predetermined value by a predetermined time constant.