JPS61114854A - Ink droplet injection device - Google Patents

Abstract

PURPOSE:To improve an ink droplet injection frequency to a great extent by applying pressure through the reduction of a volume and decreasing pressure through the increase of a volume using two different ink chambers. CONSTITUTION:A voltage is applied to an electric machine conversion element 13a and the volume of an ink chamber 11a reduced. At that time, a voltage is applied to the electric machine conversion element 13b, resulting in the rapid shrinkage of the ink chamber 11a. This causes the pressure of the ink chamber 11b and subsequently ink droplets to be injected through a nozzle 12. After the elapse of a fixed time following the application of pressure, a negative pressure must be generated in the nozzle 12 by decreasing the pressure of the ink chamber. To perform this pressure reduction in the ink chamber 11a, the voltage of the electric machine conversion element 13a should be eliminated. Next, the pressure is applied by the ink chamber 11a and the pressure is reduced by the ink chamber 11b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an on-demand inkjet printer, and particularly to an ink droplet jetting device suitable for high-speed printing.

[Background of the invention]

As described in Japanese Unexamined Patent Application Publication No. 47-2006, a conventional ink droplet ejecting device basically has one ink chamber, and the volume of the ink chamber is rapidly reduced using an electromechanical transducer, etc. to form a nozzle. Ink was ejected from the holes. This ink drop ejecting device has a simple printing principle, can easily configure a multi-nozzle head, and can realize a small, low-cost printer, so it has already been commercialized as a Kanji printer or a color printer. In this printing principle, it is known that the generation of positive pressure to reduce the volume of the ink chamber, and the generation of negative pressure to restore the volume of the ink chamber, have a large effect on the ink jetting characteristics. . Conventional devices control the generation of positive and negative pressure using voltage pulses applied to all electromechanical transducer elements, but it is difficult to control pressure fluctuations after ejecting ink droplets by controlling voltage pulses alone. Efforts have been made to increase the attenuation of pressure fluctuations by changing the shape of the flow paths of the ink chambers and the structure of the walls of the ink chambers. In addition, as in JP-A-51-137202, when voltage pulses are applied for purposes other than ejecting ink, the characteristics can be improved and the number of nozzles can be greatly reduced by providing two ink chambers for one nozzle. Proposals have been made to reduce the number of ink chambers when the number of ink chambers increases. In both inventions, the ejection frequency of ink droplets is determined by the shape of the channels such as the ink chamber and nozzle, and the materials that constitute them, and at present it is possible to stably eject ink droplets suitable for printing. The upper limit of frequency is approximately 2. , about 5 KHz.

[Purpose of the invention]

An object of the present invention is to provide an ink droplet ejecting device that can dramatically improve the ink droplet ejecting frequency without fundamentally changing the flow path shape and the like of the conventional ink droplet ejecting device.

[Summary of the invention]

In an ink droplet ejecting device, the upper limit of the driving frequency is limited by the pressure fluctuation in the ink chamber after the ink droplet is ejected.In order to improve the driving frequency, it is necessary to provide a means to suppress the pressure fluctuation or to reduce the pressure fluctuation. It is necessary to provide a structure and drive method that makes it difficult for this to happen.

The present invention adopts the latter concept, and is realized with almost no changes to the conventional flow path shape or material.

In the conventional method, in order to eject one ink droplet, the volume of one ink chamber is reduced and restored in succession, so the subsequent free vibration of the ink chamber wall is large and may cause positive pressure and negative pressure. Acoustic reflection with pressure acts in a complex manner and increases the pressure fluctuations in the ink chamber.The present invention focuses on this point and performs two different pressurization operations, one for pressurization due to a decrease in volume, and one for depressurization due to an increase in volume. By performing this in the ink chamber, pressure fluctuations can be reduced.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. FIG. 1 shows the basic configuration of an ink jetting device according to the present invention, FIG. 2 is a sectional view taken along line AA' in FIG. 1, and FIG. 3 shows the principle of operation.

20 is, for example, an alkali-etched silicon plate, and 21 is glass. Silicon plate 20 and glass 21
By adhering them with electrostatic adhesive or the like, flow paths such as the nozzle hole 12 and the ink chambers 11a, 11b are formed, and the electromechanical transducer 1 is attached corresponding to each ink chamber 11a, llb.
3a and 13b are glued together to form the ink droplet ejecting device 10.

In FIG. 3, a voltage is being applied to the electromechanical transducer 13a, and the volume of the ink chamber 11a is decreasing. At this time, a voltage is applied to the electromechanical transducer 13b, and as shown in (2), the volume of the ink chamber 11b rapidly decreases, so that the pressure of the ink chamber 11b increases and a re-ink droplet is ejected from the nozzle hole 12J. be done. It has been found that in order to form good ink droplets, the ink chamber must be depressurized after a certain period of time has elapsed after the pressurization operation to generate a negative pressure inside the nozzle hole 12. In order to perform this pressure reduction operation in the ink chamber 11a, the electromechanical transducer 13a
remove the voltage. Therefore, the ink drop ejecting device is shown in FIG.
The state will be as follows. If this operation of reducing the pressure in the ink chamber 11a is not performed, the ink droplets ejected through the nozzle holes 12 are likely to separate into main droplets and small droplets called satellites, resulting in a decrease in printing quality.

Now, one ink droplet will be ejected by the operation from 0 to 0 in Fig. 3, but when ejecting the next ink droplet, it is necessary to reverse the state (from Q to 0), i.e. Now, the ink chamber 11a will perform a pressurizing operation, and the ink chamber 11b will perform a depressurizing operation.

The differences between the conventional ink drop ejecting device and the embodiment of the present invention will be explained with reference to FIGS. 4 and 5. FIG. 4 shows a conventional ink drop ejecting device. FIG. 5 shows the state of the electromechanical transducer 13 and the ink chamber 11 with respect to the conventional method of driving the apparatus, the method of driving the present invention, and the respective driving voltages.

In the conventional device, one ink droplet is ejected with one voltage pulse by applying a pulsed drive voltage such as (5A). The ink is pressurized by the rise of the voltage pulse,
Since the pressure is reduced at the falling edge, the pulse width greatly affects the ink ejection characteristics. In this embodiment, the ink chamber 11a is (5
The ink chamber 11b is driven by the driving voltage (5C). (Each drive waveform is said to be pulse-like.) Rather, it should be called a step function.

Although it can be considered as a voltage pulse with a very long pulse width, the pulse width is determined by the driving frequency, and the length changes depending on the printing pattern, and like the driving pulse of conventional devices, the pulse width depends on the ink ejection characteristics. It does not affect the

In addition, in the conventional device, as shown in the state diagram (5D), 1
After ejecting one ink droplet with one voltage pulse, the original state is always restored, but in the example shown in (5E), the original state is returned only after two ink droplets are ejected. . That is, if we pay attention to each ink chamber 112 and llb, 2
When ejecting one ink drop, the volume is reduced and restored at a very long time interval. This is the reason why the driving frequency can be increased.

In the case of this embodiment, when focusing on each ink chamber, the operation required to eject one ink droplet is either a decrease in volume or an increase in volume. For example, looking at the ink chamber 1151 in FIG. 5, in order to eject one ink droplet, the state only changes from state ■ to state ■, so the movable wall 51 of the ink chamber is bent inward and the movable wall The free vibration is only the amount of overshading relative to the static equilibrium position, and its attenuation is significantly faster than when a pulsed voltage is applied. Further, since only positive pressure is generated and no negative pressure is generated, complicated pressure fluctuations due to interference between the two do not occur. Therefore, the pressure fluctuation in the ink chamber is sufficiently small compared to the conventional ink chamber, and the attenuation is fast, so the driving frequency can be increased.

Figure 5 (5 people) with two ink chambers using the head as shown in Figure 1.
Simply thinking, it would be possible to eject ink droplets from the nozzle at twice the frequency of a conventional device simply by driving the nozzle alternately with a pulsed voltage such as the driving voltage of It can be driven at frequencies higher than that.

An ink drop ejecting device having two ink chambers communicating with one nozzle is disclosed in, for example, Japanese Patent Laid-Open No. 51-1372.
02, etc., but all of them are shown in Figure 5 (5
It is driven by a pulsed drive voltage indicated by
The idea of reducing pressure fluctuations by making the drive voltage into a step function as in this embodiment is completely new.

FIG. 6 shows an example of a circuit for generating the drive voltage of this embodiment. A pulse generating circuit 70 generates a pulse having a predetermined pulse width in response to a print signal.

71 and 72 are D type flip-flops, which determine the change in state when the potential of the input terminal C rises from a low level to a high level. The flip-flop 71 inverts the state at the rising edge of the pulse generated by the pulse generation circuit 70, and the flip-flop 72 inverts the state at the rising edge of the pulse generated by the pulse generation circuit 70.
At the falling edge of the pulse generated at , the state changes to the same state as the state of the flip-flop 71 at that time. By connecting these two D-type 7-lip 70-tub outputs with the t-1OR circuit 74 and the NAND circuit 75, Fig. 5 (5B)
, (5C), nine drive waveforms are obtained.

This is amplified by amplifier circuits 76 and 77 and applied to electromechanical transducers 13a and 13b.

The size and flight speed of the ink droplets can be adjusted by the driving voltage, the time difference between the changes in the two driving voltages (Δt in FIG. 5), and the rise time and fall time of the voltage. Also, Figure 5 (
Various applications can be considered by adopting an appropriate driving method, regardless of the driving method using the driving voltage shown in 5B) and (sC).

For example, if two ink chambers are driven at the same timing with a pulsed voltage, the particle size will be different depending on whether the two ink chambers are driven at the same time or when only one of them is driven. 14 images can be formed. Furthermore, if the driving voltages of the two ink chambers are different, a 4-value gradation image can be formed. The purpose of the present invention is to realize a high-speed printer, and we have proposed a driving method as shown in FIG. Since the structure is suitable for reproducing gradation images as described above, it is possible to use the same printer as two types of printers, a high-speed character printer and a gradation image printer, by switching the drive circuit.

FIG. 7 shows an ink droplet ejecting device 80 according to another embodiment of the present invention. 82 is a common ink chamber 69. All ink is uniformly supplied to the two ink chambers 11a and llb, and
This is effective in reducing the number of pipes connected to the ink tank. Furthermore, by providing lands 81a and 81b near the supply port of the ink chamber, when air bubbles generated in the common ink chamber 82, etc. are pressed out from the L9 nozzle hole 12, the air bubbles can flow efficiently.

FIG. 8 is an enlarged view of the nozzle hole, and there are two channels 91.
By providing a protruding wall 90 at the point where the two ink chambers and 92 meet, it is possible to separate the flows from the two ink chambers and efficiently eject ink droplets from the nozzle hole 1z.

In all the explanations up to now, the two ink chambers have been formed on the same plane, but as shown in Figure 9, by laminating etched metal, etc.
Two ink chambers 11a.

11bt" can also be arranged three-dimensionally.The ink droplet ejecting device 100 consists of two etched metal plates
2 and 103, consisting of a metal plate 104 serving as a partition wall and a metal plate 105 in which a nozzle hole 12 is formed;
Electromechanical transducer elements 13a and 13b are bonded to 103.

〔Effect of the invention〕

According to the present invention, the pressure fluctuation after ejecting an ink droplet can be kept small and its attenuation becomes faster, so that the ejection frequency of ink droplets can be dramatically increased, which has the effect of increasing printing speed.

For example, the upper limit of the driving frequency of the ink droplet ejecting device shown in FIG. 4 is just under 2 KHz, whereas the ink droplet ejecting device shown in FIG. 1 can be stably driven at 4 KHz.

Another effect is that the ink replenished to the nozzle is
During depressurization of one ink chamber, the other ink chamber is bypassed to reach the nozzle, so the amount of atmospheric air drawn from the nozzle due to depressurization is reduced by 9 compared to conventional methods, and unstable operation such as air bubble entrapment occurs. It is possible to reduce the factors of

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional plan view showing one embodiment of the present invention, Fig. 2 is a cross-sectional view taken along line A-A', and Fig. 3 is a cross-sectional view showing an embodiment of the present invention.
The figure is a cross-sectional plan view of the conventional device, Figures 5 (5A) to (5E)
6 is a drive circuit diagram of this embodiment, and FIGS. 7 to 9 are cross-sectional and vertical side views showing other embodiments of the present invention. be. 11a, llb... ink chamber, 12... nozzle, 1
3a, 13b... Electromechanical conversion element, 20... Silicon plate, 21... Glass, 70... Pulse generation circuit, 71... 7 lip-flop, 74... 08 circuit,
75 S1 Figure 12 Figure $3 Figure (A) (δ)
(C) No. 4121 2nd country a χ 7 diagram

Claims (1)

[Scope of Claims] 1. Ink comprising a nozzle having a nozzle hole for ejecting ink and two ink chambers communicating in parallel with the nozzle hole, and two pressure means for generating pressure in each of the ink chambers. An ink droplet ejecting device characterized in that one ink droplet is ejected by a combination of pressurizing operation of one ink chamber and depressurizing operation of the other ink chamber. 2. The ink droplet according to claim 1, further comprising a barrier forming a land for forcibly diverting ink flowing into the ink chamber near the ink supply port of at least one ink chamber. Squirting device. 3. The ink drop jetting device according to claim 1, wherein the nozzle includes an ink reservoir communicating with two ink chambers, and ink is supplied to each ink chamber via the ink reservoir. . 4. A patent claim characterized in that a means for making it difficult for ink flowing from one ink chamber to flow into the other ink chamber is provided at the point where the two flow paths from each ink chamber to the nozzle hole merge. The ink droplet ejecting device according to scope 1.