JPS62174163A - Drop on demand ink jet head - Google Patents

Abstract

PURPOSE:To enable micro ink droplets to be formed by installing a piezoelectric element at a position corresponding to the loop of an amplitude in a waveform of any high order mode among other oscillation modes of intrinsic pressure oscillation generated in a pressure chamber and driving the piezoelectric element on a drive signal which meets the phase of the mode. CONSTITUTION:The constitution of an ink jet head is basically the same as that of the conventional head. However, the former differs in that the length of a piezoelectric element 9 and its fixing position are determined based on the analytic results of an intrinsic pressure wave oscillation mode. That is, a part encircled by a dotted line represents a piezoelectric element fixing position or a length between the first node 18 and the second node 19 of the intrinsic pressure wave oscillation mode. Further the piezoelectric element is arranged so that it may meet the position of a loop 20 sandwiched between these nodes. The size of a jet channel system is predetermined in such a way that the bottom 20 may fit into the range of a pressure chamber. When a high-order intrinsic pressure wave oscillation mode is selectively excited, a sharp speed response can be obtained and the volume of an ink droplet is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a printer for outputting data from an information processing device, and more particularly to a drop-on-demand inkjet head for printing.

[Conventional technology]

Conventionally, as an example of this type of hevd, for example, Fig. 10 (
Those shown in al e (b) and (C) are already known.

(a) is a plan view t-1 (b) is an elastic play) 4t-
%(C) shows the BB' sectional view of the plan view excluding the plan view.

As shown in the figure, this type of head includes a nozzle 1 that ejects ink droplets, a pressure chamber 3 that generates pressure on the ink, and a conduction path 2 that pressure propagates and transports the ink from the pressure chamber 3 to the nozzle 1. It consists of an ink chamber 5 that temporarily stores ink in the head from the outside, and a supply path 4 that supplies ink from the ink chamber 5 to the pressure chamber 3.1. The jet channel system, the nozzle plate 8 that constitutes the ink chamber, and the elastic plate 70 that constitutes the pressure chamber 3 together with the nozzle plate 8 are joined together to form the pressure chamber 3. For example, a piezoelectric element 6 is attached thereon as an electromechanical conversion means. By applying a voltage corresponding to the recording signal to both electrode surfaces of the piezoelectric element 6, the piezoelectric element 6 is expanded and contracted, the elastic plate 7 is deflected, and the volume of the pressure chamber 3 is instantaneously changed. . This volume change generates a pressure wave in the ink inside the pressure chamber 3, and the pressure wave is transmitted to the nozzle 1 via the guide path 2.
When the ink droplets 16' (5 are ejected from the nozzle 1) by rapidly increasing the pressure of the ink in the nozzle, the ink droplets 16 are deposited on the medium.
Recording is done. After the applied voltage is removed, as time passes, ink is filled into the pressure chamber 3 from the ink chamber 5 via the supply path 4, and an ink meniscus 1 is also formed in the nozzle 1.
7 (unevenness of the liquid surface) causes the liquid to fill and return to its initial state. An example of a head having such a structure is disclosed in Japanese Patent Publication No. 12138/1983. Regarding the behavior of the ink, the time 0 when a driving pulse starts to be applied to the piezoelectric element is the time k tt when the ink in the nozzle section starts to move outside the nozzle due to pressure waves, and then the ink is pushed out from the nozzle as an ink column 61 Next, the ink column When the rear part is drawn into the nozzle, if the time at which the ink column separates into ink droplets is t, then the ink velocity at the nozzle part 'e V (t), the nozzle cross section'! As JReA, the ink droplet volume Q can be approximately expressed as I.

[Problem that the invention seeks to solve]

In a recording method that configures recording using a dot matrix, in order to perform relatively high-resolution recording, it is necessary to record each recording dot at a high density.In particular, in the inkjet recording method, it is necessary to simply print ink droplets. If the ink is applied at a high density, the amount of ink adhering to the recording medium per unit area will increase, so depending on the recording paper, the ink may flow on the medium. Problems such as smearing and smudging occurred. Therefore, in order to perform high-resolution recording, it is necessary to reduce the volume of ink droplets. For this reason, the first method to reduce the size of the ink droplet body Q is to reduce the nozzle area A in the first equation, but it is difficult to process a small diameter nozzle, and the nozzle size is It has the drawbacks of easily causing clogging, etc., and lowering the reliability of the printer, and has limitations in practical use.

Also, as a second method, consider 1. By reducing the ink velocity V(t) at the nozzle, the ink droplet volume Qe can be reduced.
In the method of decreasing the ink velocity v (tl
If the ink droplet speed is made smaller, the ink droplet speed also becomes slower. However, when the ink droplet speed becomes slower, the diameter of the ink droplet becomes smaller and the ink droplet becomes more susceptible to external disturbances such as wind, which deteriorates the positioning and stacking of recording dots, which only leads to a decline in print quality. Ink droplets adhere to the nozzle surface, causing air bubbles to be drawn into the nozzle, resulting in serious problems such as deterioration of the stability of ink droplet ejection. On the other hand, even if the ink droplet velocity is preferentially set to the optimum state without considering reducing the ink droplet volume Qffi, the ink droplet volume Q is not only large compared to the nozzle area A, but also the ink droplet ejection state is As shown in Figure 3(a), there are many cases where the ink ejected from the nozzle forms a long ink column 21 and a satellite 22 occurs. quality? There was a problem with damage.

The third method for reducing the ink droplet volume Q is to shorten the length of the entire ejection channel system to reduce the natural period and φ in the first equation, When the injection channel system is made into a multi-nozzle system, there is a limit to making the entire injection channel system a required length, which also poses a practical problem.

Furthermore, ink drop velocity generally varies with ink drop generation frequency, as illustrated in FIG. 9(a). This ink droplet velocity variation is caused by ejecting the next ink droplet before the residual oscillations of the pressure waves generated during the previous ink droplet ejection have been sufficiently damped. Therefore, as the ink droplet generation frequency becomes higher, that is, as the time interval of ink droplet ejection becomes shorter, the speed fluctuation becomes larger, and the upper limit of the practical driving frequency is limited. , which solves the above drawbacks, does not require difficult micro-nozzle processing, can form ink droplets that are smaller than the nozzle diameter without causing a decrease in ink droplet speed, and does not generate satellites. It is an object of the present invention to provide a drop-on-demand inkjet head that has the characteristics of stable ink droplet ejection and small ink droplet speed fluctuations with respect to the ink droplet generation frequency.

[Means for solving problems]

The present invention includes at least a pressure chamber, a nozzle provided at one end of the pressure chamber, and a piezoelectric element attached to cause a change in volume of the pressure chamber, and applying an electric signal to the piezoelectric element. In a drop-on-demand inkjet head that instantaneously changes the volume of the pressure chamber and generates an ejection pressure to eject ink droplets, this is one of the vibration modes of the natural vibration of the ink pressure wave that occurs within the ejection channel system. A piezoelectric element is attached to one or more of the positions corresponding to the antinodes of the amplitude in the waveform of an arbitrary higher-order mode, and a driving waveform whose phase matches the natural period of that mode is generated. [Operation] As described above, a piezoelectric element installed at a position corresponding to a certain specific mode is driven by a drive waveform whose phase matches that mode. When driven with , this specific natural vibration mode is selectively excited within the injection channel system. In this case, since there are very few low-order mode components in this mode, a pressure wave with a short period is generated, and the integral dry period in the first equation becomes shorter, without causing a decrease in the ink droplet velocity.
Relatively small ink droplets are obtained. In addition, since there are few components of this mode or higher-order modes, the ink droplets have stable ink droplet flight characteristics without the generation of satellites. Furthermore, in general, high-frequency vibrations are greatly attenuated by viscosity, but in the case of the present invention, since a mode lower than the above-mentioned mode is not included, residual vibrations after ejecting an ink droplet are attenuated relatively quickly. As a result, fluctuations in ink droplet ejection speed are reduced even in a relatively high drive frequency range.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the first embodiment of the present invention, in which (a) shows the shape of the injection channel system, and (b) shows the characteristic of the pressure wave of this injection channel system obtained by the finite element method. The 3rd vibration mode is all sold out. The structure of the head shown in FIG. 1(a) is basically the same as the structure of the head shown in FIG.
The difference is that the length and mounting position of the piezoelectric element 9 are determined based on the analysis result of the pressure wave natural vibration mode shown in b). The part surrounded by the dotted line in Fig. 1 (al) shows the mounting position of the piezoelectric element 9, and the part surrounded by the dotted line in Fig. 1 (al) shows the mounting position of the piezoelectric element 9, and It is arranged so that the length between the two and the position of the belly 20 which is sandwiched between the nodes of the seven pillars coincides with the position of the belly 20.In addition, the belly 20 is placed within the range of the pressure chamber part. The dimensions of the injection channel system in (a) are predetermined.

Figure 2 (al) and (b) show the results obtained by simulation of the change in ink flow velocity at the nozzle part of the head. Figure 2 (a) shows the speed transient response of the conventional head, and Figure 2 (b) shows the , when the velocity transient response of this example is shown and fully selectively excited, a sharp velocity response is obtained, that is, the area of the shaded part in FIG. 2 is small, and the ink droplet volume is also small. 3(a), the ink ejected from the nozzle is in the form of a long column (as shown in FIG. 3(a)). 21), the ink column is well cut as shown in the same figure (b), and the satellite 22 is not generated as shown in the same figure (al), and the ink droplet is relatively small. A good injection condition in which 24 particles were formed was obtained.

FIG. 4 is a diagram showing another embodiment of the present invention.

3(a) is a plan view, (b) is a plan view e excluding the elastic plate 4, and tc+ is a sectional view taken along the line AA'. For convenience of illustration, the scale of each part of the head is different from that of the actual prototype Hept. The head includes a nozzle 1, a capacity chamber 12, an ink supply hole 13, a pressure chamber 3, a supply path 4, a nozzle plate 8 which constitutes an ink chamber 5, and an elastic plate 7 which constitutes an ejection channel together with the nozzle plate 8.
, the second ink supply path 14 and the three ink supply path plates 150 constituting a part of the ink chamber 5 are joined together, and a piezoelectric element (IIIO, piezoelectric element (II) 11 It is formed by pasting the .

Figure 5 shows the pressure natural vibration mode of the injection channel system in an actual prototype head, and the positional relationship between the shape of the head and the mounting position of the piezoelectric element. The element mounting position is shown in the same figure (
b) shows the fifth-order mode of the natural vibration modes of the pressure waves of this injection channel system determined by the finite element method. Based on the analysis results of the pressure wave natural vibration mode shown in FIG. 5(b), piezoelectric element (I) 10. Piezoelectric element(
If) 11 are respectively attached at positions corresponding to the antinodes 28 and 290 portions delimited by the nodes 25, 26 and 27 of this mode. At this time, the natural periods corresponding to the modes of each order are also found at the same time, and the natural periods of the 1st to 5th modes are 878 μs, 22.3 μs, and 1 μs, respectively.
They are 28 μsec, 9.1 μsec, and 6.9 μsec.

Here, a drive pulse having a phase matching the natural period τ5 of the fifth-order mode shown in FIG. 5 (bl), for example, a drive pulse as shown in FIG. A block diagram of the drive circuit is shown in FIG. 6, and signal timings of each part are shown in FIGS. 7(a) to (f).

, First, set the print data 30 to 1 when printing is to be performed, and to O when not to print, and then set the print timing 31.
give. Due to the rising edge of the print timing 31, the print pulse generation circuit 34 generates a print pulse (FIG. 7(d) 1) with a pulse width τ5, which is ANDed with the print data 30 by the AND circuit 36. , becomes an input to the driver 38. When the print data is 1, the drive pulse shown in FIG.
After receiving a delay of When the print data is 1, as shown in FIG. In addition, in the case of a multi-nozzle head, the print timing 31, the delay circuit 32,
The print pulse generation circuits 33 and 34 are used in common and print data 30.34 is used for each ejection channel. AND circuit 35.36
, a circuit corresponding to Drino (37, 38) is provided to drive the piezoelectric element of the injection channel. Fig. 7(e), (
By applying a driving pulse such as f), a fifth-order mode pressure natural vibration is selectively excited within the pressure chamber.

FIG. 8 shows how the pressure propagates within the pressure chamber over time in this case. Here, the natural period τ5 of the 5th mode is very short compared to the natural periods τ1 and τ3 of the 1st and 3rd modes, so the integral range 11 to t2 in the first equation is very small. (9) The ink droplet volume Q also becomes smaller. In the case of this embodiment, the nozzle 1 has a rectangular cross section and its size is 40 μm x 70 μm, but by driving with the drive pulse shown in FIG.
It was possible to stably eject minute ink droplets with a diameter of 40 μm at the same ink droplet speed of about 4 m/s as with conventional heads without generating satellites.

The conventional heads compared here differ in the configuration of the ink flow path,
The dimensions are exactly the same as in this example, but the number, size, and position of the piezoelectric elements are different from this example.
As shown in FIG. 11(a) IK--, one piezoelectric element 37 is attached over the entire length of the piezoelectric device. The first to fifth modes of the natural vibration modes of the injection channel shape are shown in FIG. It does not correspond to any mode, and the ink droplet diameter in this case was about 80 μm. FIG. 9 is a graph showing the ink droplet velocity versus the ink droplet generation frequency of the stiff head. The ink droplet speed on the vertical axis is 5
The relative velocity is expressed as normalized by the ink drop velocity at a driving frequency of 00 Hz. FIG. 9(a) shows the conventional head, and FIG. 9(b) shows the case of this embodiment. In the case of a conventional head, the ink droplet speed fluctuates drastically at a frequency of 7 kHz or higher, and the practical limit is about 6 kHz. Although the frequency was not measured, the variation in the ink droplet velocity was small within the measurement range, and it showed sufficiently practical characteristics even at at least about 15 kHz.

〔Effect of the invention〕

As explained above, the present invention provides one or more vibrations at a position corresponding to the antinode of the amplitude of the waveform of any higher-order mode among the vibration modes of the natural pressure vibration generated in the pressure chamber. By installing a piezoelectric element and driving the piezoelectric element with a drive signal that matches the phase of the mode, it is possible to reduce the size of the nozzle compared to the nozzle diameter without having to perform difficult micro-nozzle processing or reducing the appropriate ink speed. This has the effect of making it possible to form minute ink droplets, and also realizes stable ink droplet ejection without the generation of satellites.The ink droplet velocity fluctuation with respect to the ink droplet generation frequency is small, and it can be used even at high drive frequencies. This has the effect of making it practical.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the positional relationship between the shape of the ejection channel and the mounting position of the piezoelectric element and the third mode of pressure natural vibration in an embodiment of the present invention, and FIG. 2 is a diagram showing the ink flow velocity in the nozzle part. figure. FIG. 3 is a diagram showing the flying state of ink. FIG. 4 (al, (b)). (C) is a diagram showing another embodiment of the present invention, (a)
shows a plan view 'i', (b) shows a plan view with the elastic plate removed, and (C) shows a sectional view taken along line A-A'. FIG. 5 shows the shape of the injection channel and the mounting position of the piezoelectric element in the example,
The figure which shows the positional relationship with the 5th mode of pressure natural vibration. FIG. 6 is a block diagram of a piezoelectric element drive circuit in the embodiment, and FIG. 7 is a diagram showing signals of various parts in this drive circuit and drive pulses that are applied to the piezoelectric element. FIG. 8 is a diagram showing the state of pressure propagation within the injection channel over time. FIG. 9 is a diagram showing the relationship between the drive frequency of the piezoelectric element and the ink droplet velocity. Figure 10 (a), (b
), (C) are diagrams showing the configuration of a drop-on-demand inkjet head, (a) is a plan view, (b) is a top view.
(C) shows a plan view t excluding the elastic plate, and (C) shows a sectional view taken along line AA'. FIG. 11 is a piezoelectric element installation diagram in a conventional head, where 1 indicates a nozzle, 2 indicates a conduction path, 3 indicates a pressure chamber, and 4
indicates the supply path, 5 indicates the ink chamber, 6.9.10, 11, 3
7 is a piezoelectric element, 7 is an elastic plate, 8 is a nozzle plate, 12 is a gear nozzle (city chamber), 13 is an ink supply hole, 14 is a second ink supply path, 15 is an ink supply path plate f7 Ma ρ chant master (ρ (to/((Shingu≦0 years old IN!) Proclamation Yodo ○ 6~No arm reed whip (6

Claims (2)

[Claims] (1) At least a pressure chamber, a nozzle provided at one end of the pressure chamber, and a piezoelectric element attached to cause a change in volume of the pressure chamber, and applying an electrical signal to the piezoelectric element. causes an instantaneous change in the volume of the pressure chamber,
In a drop-on-demand inkjet head that generates ejection pressure and ejects ink droplets, the position corresponding to the antinode of the amplitude of the waveform of any higher-order mode among the pressure natural vibration modes generated within the pressure chamber. No. 1
A drop-on-demand inkjet head characterized in that piezoelectric elements are attached to one or more positions. (2) The drop-on-demand inkjet head according to claim 1, wherein the one or more piezoelectric elements are driven in a phase that matches the vibration waveform of the higher-order mode.