JPH024513A - Ink jet head - Google Patents

Abstract

PURPOSE:To improve discharging response and stability by narrowing the width of a beamlike vibrator of an ink jet head at the side near a nozzle forming board and broadening it at the side far from the board. CONSTITUTION:In a piezoelectric converter 20, a signal electrode 25 is superposed on one side face of a piezoelectric element 24 and a metal plate also used as a common electrode 26 is disposed on the other side face, and a plurality of vibrators 21 are formed on one side of the plate. The width of the vibrator 21 is narrow at the side near a nozzle forming board 30 and formed in a trapezoidal sectional shape at the side far from the board 30. The vibrator 21 is deformed and displaced in the direction 32 of the board 30 to enhance the pressure of ink 22 in a gap between the vibrator 21 and the board 20, thereby discharging ink droplets 34 from a nozzle 31. Since the shape of the vibrator 21 is scarcely deviated after the ink is discharged, the amplitude is small and rapidly converged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inkjet recording device that flies ink droplets to form an ink image on a medium such as recording paper.
More specifically, it relates to an inkjet printer head.

[Conventional technology]

An ink jet head comprising a nozzle forming substrate having a plurality of nozzles and a piezoelectric transducer disposed behind the nozzle forming substrate for directly contacting ink and pressurizing the ink is disclosed in Japanese Patent Publication No. 8953/1988. An inkjet head with this structure has improved ink droplet ejection efficiency and ejection stability because the vibrator formed in the piezoelectric transducer is displaced almost perpendicularly to the nozzle plate and the ink flow path of the nozzle is short. If the ink is high and foreign matter such as air bubbles or dust is mixed into the ink,
Normal operation is possible without being affected even if
Furthermore, since the vibrator has a cantilevered or double-sided beam structure, the electromechanical conversion efficiency is high and the required vibrator displacement can be obtained at a low voltage.

[Problem to be solved by the invention]

However, in the above-mentioned conventional technology, vibration characteristics such as amplitude, natural vibration period, and damping time constant when the vibrator is deformed and displaced in response to an electric signal are It has been found that this affects the performance characteristics such as performance, but under the condition that the drive voltage is constant,
To increase the ejection speed and amount of ink droplets, the maximum value of the ink ejection pressure is large, and in order to reach the maximum ejection pressure in a short time, the vibrator should be made to vibrate more easily and have a longer damping time constant. However, if the damping time constant is too long, unnecessary ink droplets may be ejected due to residual vibration after ink ejection, or the vibration may not be damped sufficiently by the next ejection cycle. The vibration characteristics of the vibrator have contradictory effects on each characteristic, such as having a negative effect on the ink ejection mode and ejection response. It is difficult to create a satisfactory design, and there is a problem in that specifications must be determined based on trade-offs between each characteristic. In addition, the gap between the nozzle forming substrate and the vibrator facing it needs to be kept within a certain small range. The ink existing in the gap adds large resistance and inertia when the vibrator displaces, and the final displacement is reached in an over-damped or nearly over-damped state.
Another problem was that the ink droplet ejection pressure was reduced, resulting in a decrease in energy efficiency.

The purpose of the present invention is to solve these problems and simultaneously achieve various characteristics such as ink droplet ejection mode, ejection speed, ejection amount, and ejection response, and to realize an excellent inkjet head with high energy efficiency. There is a particular thing.

[Means to solve the problem]

The inkjet head of the present invention includes: a nozzle forming substrate having at least one or more nozzles; a piezoelectric transducer formed with a beam-like vibrator arranged one-to-one facing the nozzle and capable of being driven independently; In the inkjet head in which the gap between the nozzle forming substrate and the piezoelectric transducer and the periphery of the piezoelectric transducer are filled with ink, the width of the beam-like vibrator is narrower on the side closer to the nozzle forming substrate, and It is characterized by being wider on the side far from the nozzle forming substrate.

[Effect]

In the above configuration of the present invention, when the vibrator is deformed and displaced to eject ink, when the vibrator is displaced in the direction of the nozzle forming substrate, the ink tends to flow around the vibrator, and the ink is added. Since the resistance and inertia are small, the vibrator is easily displaced. Furthermore, when the vibrator is displaced in the direction opposite to the nozzle forming substrate, ink flow around the vibrator is difficult to occur, and the resistance and inertia added by the ink are increased, so that the vibrator is difficult to displace.

〔Example〕

Next, the present invention will be explained based on examples.

FIG. 1 is a perspective view for explaining an embodiment of a recording apparatus equipped with an inkjet head according to the present invention. The recording medium 1 is wound around the platen 4 by the pressure of the feed roller 2.3, and is conveyed in the direction of the arrow 5 as recording progresses. An inkjet head 9 having a number of stages of nozzles that can independently control the ejection of ink droplets is mounted on a carriage 8 that is guided by a guide shaft 6°7 and movable in a direction parallel to the axis of the platen 4. The recording medium 1 is scanned in the direction 1o, and ink droplets are selectively ejected from each nozzle to form an ink image on the recording medium 1.

FIGS. 2(a), (b), (c), and (d) explain the structure of the inkjet head 9 in the present invention, the principle of ejecting ink droplets, and the flow of ink around the vibrator when ejecting ink droplets. FIG. Between the frame 40 and the sub-frame 41, a nozzle forming substrate 3o and a spacer 27 are provided.
, a piezoelectric transducer 20, and an elastic sheet 42 are laminated.

The piezoelectric transducer 20 is constructed by laminating a signal electrode 25 made of a thin Au layer on one side of a piezoelectric element 24 made of PZT, and a metal plate that also serves as a common electrode 26 made of a thin Ni layer on the other side. , a plurality of vibrators 21 are formed on one side thereof. The nozzle forming substrate 30 has a plurality of nozzles 3
Each nozzle 31 is arranged to face the free end of the vibrator 21 with a gap a between the vibrator 21 and the nozzle forming substrate 30 interposed therebetween. An ink reservoir 43 is formed in the subframe 41, and ink 44 is supplied to and filled near the nozzle 31 (
Figure 2(a)). The width of the vibrator 210 is the same as that of the nozzle forming substrate 3.
It is narrow on the side near the nozzle forming substrate 30 and wide on the side far from the nozzle forming substrate 30, and has a trapezoidal cross-sectional shape (FIG. 2(b)). Piezoelectric element 2
The polarization direction of No. 4 is arranged so that when a voltage is applied between the common electrode 26 and the signal electrode 25, the polarization direction is contracted in a direction perpendicular to the electric field. On the other hand, since the Ni thin layer of the common electrode 26 has a high modulus of elasticity, dimensional changes are restricted, and a bending moment is generated so that the common electrode 26 bends toward the signal electrode 25, causing deformation and displacement. Therefore, by applying a voltage during standby and selectively releasing the voltage, the vibrator 21 is deformed and displaced in the direction 32 of the nozzle forming substrate 30, and the vibrator 21 and the nozzle forming substrate 30 are
The pressure of the ink 44 in the gap between the
4 and is discharged from the nozzle 31. (Figure 2 (C)).

The retraction 37 of the nozzle meniscus caused by the damped vibration of the vibrator after ejecting an ink droplet or the displacement of the vibrator 21 in the direction 33 due to the application of voltage is caused by the retraction 37 of the vibrator 21 in the direction 33
Ink 44 is supplied by the ink flow 36 around the vibrator corresponding to the displacement to restore the nozzle meniscus 37 (FIG. 2(d)).

As a result, the vibrator 21 moves toward the nozzle forming substrate 30 due to the damped vibration of the vibrator after ink droplet ejection or the release of the voltage.
When the vibrator 21 is displaced in the direction 33, even if the gap a between the vibrator 21 and the nozzle forming substrate 30 is a minute size, the cross-sectional shape of the vibrator 21 tends to cause ink to flow around the vibrator, causing the vibrator 21 to Because the displacement is easy, the displacement speed is fast, and the direction 33 is caused by the damped vibration of the vibrator or the application of voltage.
When the vibrator 21 is displaced, the ink flow 36 around the vibrator is difficult to occur and the vibrator 21 is difficult to displace, so the displacement speed becomes slow, and the damped vibration after the vibrator 21 is displaced is at one displacement speed. Since it is slow, the amplitude is small and convergence is fast.

In the above structure, the gap a necessary for increasing the pressure of the ink 44 near the nozzle 31 and ejecting ink droplets is determined by the spacer 2.
Desired dimensions can be freely selected by arbitrarily setting the thickness of the vibrator 7, and the vibration characteristics of the vibrator 21 can be changed depending on the cross-sectional shape and the direction of vibration.
An excellent inkjet head with high energy efficiency was obtained, which simultaneously achieved various characteristics such as ink droplet ejection speed, ejection amount, ejection condition, and ejection response.

Further, although a cantilever-like vibrator is used as the vibrator, a similar configuration is possible with a double-sided beam-like vibrator.

〔Effect of the invention〕

As described above, according to the above configuration of the present invention, the width of the vibrator is narrower on the side closer to the nozzle forming substrate and wider on the side farther from the nozzle forming substrate, so that the width of the vibrator is narrower on the side closer to the nozzle forming substrate. When the vibrator is displaced in the direction of the nozzle forming substrate, the vibrator is easily displaced, and when the vibrator is displaced in the opposite direction to the nozzle forming substrate, it is difficult to be displaced. As a result, while increasing the vibrator displacement and speed during ink droplet ejection, damping vibration after ink droplet ejection can be suppressed, improving the ink droplet ejection mode, ejection speed, ejection amount, ejection response, and ejection stability. At the same time, various properties such as these are improved, and an inkjet head with high energy efficiency and excellent performance can be realized. Further, according to the present invention, the gap between the vibrator and the nozzle forming substrate can be used in narrow areas that could not be used conventionally, since the ink ejection pressure decreases due to over-damping of the vibration of the vibrator. This means that the margin for the size of the gap between the vibrator and the nozzle forming substrate is widened, which also has the effect of widening the manufacturing margin.

[Brief explanation of the drawing]

FIG. 1 is a perspective view for explaining an embodiment of a recording apparatus equipped with an inkjet head according to the present invention. FIGS. 2(a) and 2(b) are a cross-sectional view for explaining the structure of an inkjet head according to the present invention, and a cross-sectional view taken along the line A-A of the vibrator. FIGS. 2C and 2D are cross-sectional views of an inkjet head for explaining the principle of ejecting ink droplets and the flow of ink around a vibrator when ejecting ink droplets. 35. Recording medium inkjet head vibrator 24 Piezoelectric element signal electrode 26 Common electrode spacer 30 Nozzle forming substrate nozzle
34 Ink droplets 36 Ink flow around the vibrator Pulling ink from the nozzle meniscus Applicant Seiko Epson Corporation Agent Patent attorney Kizobe Suzuki and 1 other person No. 1

Claims (1)

[Scope of Claims] A nozzle forming substrate having at least one or more nozzles; a piezoelectric transducer having a beam-shaped vibrator arranged one-to-one opposed to the nozzle and capable of being driven independently; In an inkjet head in which the gap between the nozzle forming substrate and the piezoelectric transducer and the periphery of the piezoelectric transducer are filled with ink, the width of the beam-shaped vibrator is narrower on the side closer to the nozzle forming substrate, and the width of the beam-shaped vibrator is narrower on the side closer to the nozzle forming substrate. An inkjet head characterized by being wider on the side far from the forming substrate.