JPH02175157A - Ink jet recorder - Google Patents

Abstract

PURPOSE:To raise the surface of ink at low energy by providing both a means for generating stationary wave on the liquid surface at a constant period with a focusing acoustic beam and a means for irradiating the raised part of the stationary wave with the focusing acoustic beam. CONSTITUTION:The pressure wave emitted from a piezo-electric vibrator 4 between the electrodes 5 - 7 is focused in the vicinity of the surface 11 of ink by a lens 8. Stationary wave 12 can be formed by properly selecting the intensity of pressure wave (acoustic beam 10) of the respective focuses at this time, the focusing diameter, a pitch, the physical properties of ink and the shape of an aperture part 9. When driving of the vibrator 4 is stopped, the surface 11 of ink is attenuated while repeating vibration among the intervals 12 - 13 by residual vibration. Driving and stop of the vibrator 4 between the electrodes 5 - 7 are continued while being interlocked with this residual vibration. The intensity of pressure wave exceeds threshold level by driving the vibrator 4 between the discrete electrodes 6 - 7 in accordance with necessities. The peak part of the stationary wave 12 is furthermore raised and droplets are injected therefrom.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an inkjet recording device, and more particularly to the structure of an inkjet head, and is applicable to various recording devices, for example.

Prior art related to the present invention includes the following publications.

■ Setting cut parts in the slit parts stabilizes the positions of the peaks and troughs of the steady surface tension waves, and ink is ejected by addressing means provided at the peak positions.
Publication No. 251153 and Japanese Patent Application Laid-open No. 1983. There is a publication No.-25115.

(2) Japanese Patent Application Laid-Open No. 62-264962 discloses a method for ejecting ink by focusing pressure waves to destabilize the liquid level and applying surface tension waves caused by an electric field to the liquid surface.

■ Regarding ink jetting using a microacoustic lens, JP-A-63-162253, JP-A-63-166545
There are publications No. 8 to 8.

(2) Japanese Patent Laid-Open No. 62-66943 discloses a device that focuses leaky Rayleigh waves and jets ink.

One of the drawbacks of the conventional inkjet method is nozzle clogging. Conventional examples ■ to ■ are various methods to avoid the above-mentioned drawbacks, but ■ and ■ are difficult to highly integrate recording elements,
It has a drawback in recording speed.

■Although the drawbacks of ■ and ■ have been improved, the head structure is complicated, and there are still some dissatisfaction in terms of energy efficiency.

(2) improves the complexity of the above structure, but is unsatisfactory in terms of energy efficiency.

That is, although steady surface tension waves and other means have been used to reduce drive voltage and improve integration, this is still not sufficient.

- Part of the present invention was made in view of the above-mentioned circumstances.
The purpose of this invention is to provide an inkjet recording device that can excite the surface of ink with low energy.

In order to achieve the above object, the present invention provides an inkjet recording device that focuses an acoustic beam near the liquid surface and ejects droplets (or mist), in which a standing wave is generated at a constant period by the focused acoustic beam on the liquid surface. , the period of which is substantially equal to an integral multiple of the residual vibration period of the standing wave, and irradiating the standing wave ridge with a focused acoustic beam in synchronization with the driving of the first vibrator. The present invention is characterized in that it has a second means. Hereinafter, FIG. 1, which will be explained based on an embodiment of the present invention, is a configuration diagram for explaining an embodiment of an inkjet recording apparatus according to the present invention, and FIG.
In the cross-sectional view, FIG. 3 is a plan view of only the electrodes.

In the figure, 1 is a cavity, 2 is an ink, 3 is a substrate, 4 is a piezoelectric vibrator, 5, 6.7 are electrodes, 8 is a lens mallet, 19 is a slit-shaped opening, 1o is a pressure wave, and 11 is an ink surface. . The cavity 1 has a slit-like opening 9 and is filled with ink 2 inside. The substrate 3 has a partially cylindrical recess, an electrode 7 is formed almost entirely on the surface of the recess, and a piezoelectric vibrator 4 is formed on the upper layer thereof. The upper layer has one electrode 5 and a plurality of individual electrodes 6, and the upper layer also has a lens array 8.

The substrate 3 is made of a material having a sufficiently large acoustic impedance with respect to the piezoelectric vibrator 4 . Further, the lens array 8 is made of a material having an intermediate acoustic impedance between the piezoelectric vibrator 4 and the ink 2. In addition, the shape of the lens array is an arc shape centered near the opening 9 in FIG. 1, and in FIG. Each focal point is connected to the vicinity of the ink surface 11 of the opening 9 as shown in FIG.

FIG. 4 is an explanatory diagram of the ink surface when irradiated with a focused acoustic beam. The pressure waves emitted from the piezoelectric vibrator 4 between the electrodes 5 to 7 are focused near the ink surface 11 by the lens 8, and the pressure waves at each focus (acoustic beam 10)
) intensity, focal diameter.

By appropriately selecting the pitch, physical properties of the ink, and the shape of the aperture 9, a standing wave 12 can be created, and by stopping the drive of the vibrator 4, the ink surface 11 will be caused by residual vibrations.
Attenuates while repeating 13 vibrations. It is necessary to select the above conditions so that the nodes and antinodes of the waves at this time do not move. The vibrator 4 between the electrodes 5 to 7 is synchronized with this residual vibration.
Continue to drive and stop. By driving the vibrator 4 between the individual electrodes 6 and 7 selected as necessary, the strength of the pressure wave exceeds a threshold, and the peak of the standing wave 12 further rises, from which droplets are ejected. . Generally, the focal length of the acoustic beam is: f=1-Vi/V Q The focal area diameter is: The transmittance of the intensity is expressed as follows. In addition, r: Radius of curvature of the lens vi: Speed of sound in the ink v, : Speed of sound inside the lens λi: Mini ink wavelength a: Half the lens diameter z, : Acoustic impedance of the lens zi: Acoustic impedance of the ink Cosθ, : Incident angle from the lens Cosθi: angle of inflection to the ink From this, 2. , Zi should be as close as possible, and θ,
, θi is close to 90", so the difference in sound speed is small, and a,
r should also be chosen appropriately. Therefore, if the ink has properties similar to water, the lens should be made of plastic such as polystyrene. In FIG. 1, the angle of incidence O1 on the lens 8 is 90°, so there is no lens effect and the acoustic beam is focused at the center 9 of the curvature R. In order to make the ink droplets smaller, the active frequency of 4 (rf times the signal is increased to λ
j must be made small, and it is better to make 4 thinner and drive it near the resonance frequency. It is preferable that all the vibrators 4 between the rf multiplier signal electrodes 5 to 7 and between the electrodes 6 to 7 be the same.

FIG. 5 shows an example of driving a piezoelectric vibrator, and T is the time of n cycles (n is an integer) of residual vibration of the ink surface 12. In addition, by eliminating the electrode 5 and extending the electrode 6 to that part,
It is also possible to drive all the electrodes 6 between electrodes 5 to 7 and increase the Vp of the selected electrode only when ink is to be ejected.

FIG. 6 shows another embodiment of the present invention, and FIG. 7 is a sectional view taken along line BB in FIG. The curvature r of the lens 8 is the same in both FIGS. 6 and 7. This has a lower acoustic beam transmittance than the previous embodiment, but the transducer 4 and the electrodes 6, 7 (optionally 5) can be formed on the flat substrate 14, so processing is easy. Note that 14 has a thickness of half a wavelength,
Also, it is preferable to use a material with good thermal conductivity, such as metal, to provide a lens cooling effect. In order to stabilize the standing waves and residual vibrations as described above, the shape of the aperture 9 is preferably such that rlJ is the wavelength of the standing waves, m is the number of lenses and individual electrodes, and n is an integer.

As is clear from the above description, according to the present invention, the ink surface can be excited with low energy because the standing wave is generated in synchronization with the residual vibration. Furthermore, since the residual vibration frequency of the standing wave is proportional to V bok 1 (λ is the wavelength of the standing wave), the higher the resolution recording, the higher it becomes, and the recording frequency can be increased. Further, since it is possible to use a type of shame-moving element as in the embodiment, processing is also easy.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram for explaining one embodiment of an inkjet recording apparatus according to the present invention, FIG. 2 is a cross-sectional view taken along line A-A, FIG. 3 is a plan view of only the electrodes, and FIG. , an explanatory diagram of the ink surface when irradiated with a focused acoustic beam, FIG. 5 is an example of driving a piezoelectric vibrator, FIG. 6 is another embodiment of the present invention, and FIG. 7 is a BB cross section thereof. It is a diagram. 1... Cavity, 2... Ink, 3... Substrate,
4... Piezoelectric vibrator, 5, 6.7... Electrode, 8...
Lens Male - 9... Slit-shaped opening, 10... Pressure wave, 11... Ink surface, 12... Standing wave. Figure 1 Figure 2 Figure 5 Figure Fist+8 Figure

Claims (1)

[Claims] 1. An inkjet recording device that focuses an acoustic beam near the liquid surface to eject droplets, has a first means of generating a standing wave on the liquid surface at a constant period by the focused acoustic beam, and the period is determined by the residual amount of the standing wave. An inkjet recording apparatus comprising: a second means for irradiating a standing wave ridge with a focused acoustic beam that substantially corresponds to an integral multiple of the vibration period and in synchronization with the driving of the first vibrator.