JPS63230354A - Ink jet droplet generator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates generally to the field of continuous inkjet drop generators, and more particularly to an improved design of a stamulator for a drop generator.

When multiple inkjet nozzles are connected to a pressurized ink cavity, the drops formed from the flow through each nozzle have substantially the same separation point and are generally uniform in size. It is desirable that the spacing between each drop is equal and that no satellite drops are formed. This ensures that the print quality from each nozzle is substantially the same.

In order to obtain this uniformity between the drops of the individual streams, it is necessary that the disturbances exerted on each ink stream be generally uniform and that the quality of the nozzles be uniform. Furthermore, it is also necessary that the above-mentioned disturbance be strong enough to form drops without forming satellite drops. The disturbance not only needs to be substantially uniform, but also needs to be reproducible throughout the time the drop is formed.

To accommodate this basic requirement, a transducer or driver that generates vibrations to disrupt the ink flow is designed such that the amplitude of each pressure wave created by the driver in the ink cavity is controlled by the amplitude of each pressure wave to each inkjet nozzle. It is necessary to be able to operate substantially the same at the inlet. This will create a uniform disturbance in the inkjet stream flowing through each nozzle. It is also necessary to make the amplitude of the pressure wave high enough to create a satellite-free drop.

Regarding the conscious orientation of the various parts in the overall configuration,
It is to be understood that the longitudinal directions of both the transducer and the ink cavity are parallel to the line connecting the nozzle inlets of the array. Therefore, the vibration modes of the transducer required to create a uniform disturbance in the array of inkjet streams must be in phase with the longitudinal direction of the transducer, and that the transducer vibration mode in which the nozzle array is aligned The amplitude is uniform over a sufficient portion of the user's length. This amplitude mode is typically called a balanced operation mode.

Having described what is necessary to create uniform perturbations to the inkjet stream array, non-uniformity of perturbations in the ink stream is due to both asymmetric driver vibrations and end conditions. Asymmetric driver vibrations are vibrations that are longitudinally out of phase and/or non-uniform in amplitude.

One basis for the end condition is based on the end walls of the ink cavity acting on the ink as pressure waves moving through the ink in the ink cavity. This attenuates the amplitude of the pressure wave.

Another source of irregular output is the presence of bubbles in the ink stream.

These particularly occur with the large size ink cavities typical of prior art systems.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved apparatus for generating a disturbance that drives the flow of ink through a nozzle.

More particularly, it is an object of the present invention to provide a transducer for ink jet generation that is designed and mounted to provide phased drop generation over the entire length of the nozzle array.

Yet another object of the present invention is to provide a transducer mounting that provides uniform ink flow disturbance.

Another objective is to avoid asymmetric driver vibrations, edge conditions and the appearance of bubbles in the inkjet stream, which impair the performance of many inkjet driver designs and must be eliminated and avoided.

Another objective is to create a linear array of nozzles and a driver transducer so that the driver oscillations are balanced over the length of the piezoelectric transducer and the pressure waves arriving at the nozzle are in phase and of approximately the same amplitude. The aim is to arrange the pressure waves created by the driver in a straight line.

To obtain these balanced driver oscillations applied over the entire length of the linear nozzle array, the nozzle array and nozzle support plate are supported at the ends of the support housing, and a plate is provided to confine the ink flow cavity. support,
A droplet generator extends from the ink cavity to the end of the acoustic transducer and defines an acoustic cavity having an acoustically transmitting material. The transducer is glued to the end of this acoustic material, so that when the transducer is energized, vibrations are uniformly transmitted through the acoustic transmitting material and the acoustic cavity to the ink cavity and the nozzles of the nozzle plate. drive the ink evenly through the

It is known that the acoustic cavity has a critical length that is related in practice to the operating period of the system. For example, for a frequency of 11'0 KHz, the length of the acoustic cavity must be 4.7 mm, and for an operating frequency of 120 KHz, the length of the acoustic cavity must be 4.7 mm, from the ink chamber to the plane of the transducer. The length of the acoustic cavity is 4.2Il
Must be 1m.

To ensure uniform vibration in the face of the transducer, a groove is provided at the end of the transducer and extends approximately 9/10 of the distance to the face of the transducer, which is bonded to the acoustic cavity material. There is. The width of this groove shall be approximately 5.6 mm.

The above and other objects, features and advantages of the present invention will become clearer from the following detailed description of preferred embodiments with reference to the drawings.

The illustrative drawings of the preferred embodiment, particularly FIGS. 1 and 2, show nozzle plate 14.
An inkjet head 10 is shown having a plurality of equally spaced nozzles 12 in a linear array. The nozzle plate 14 is supported on a support plate 16.

An ink supply vibrator 18 is coupled to the support plate for supplying ink to the fluid chamber 20, which is shown in more detail in FIG.

End walls 22, 24 of the housing are provided to support the support plate and to define the acoustic chamber 26. Support plate 1
It goes without saying that 6 and the housing 22, 24 may be made in one piece if desired.

As shown in FIG. 2, the acoustic cavity is filled with rubber, plastic, epoxy or other solid material. The material constraints are that the acoustic impedance is approximately equal to that of the ink. The upper surface 26' of the solid material 26 forms a fluid cavity 20 through which the ink passes.
It will be seen that it cooperates with the support plate 16 to limit the .

A piezoelectric transducer 28 is mounted in the other opening of the acoustic chamber 26. This piezoelectric transducer 28 is for generating disturbance, and the piezoelectric transducer 28
The disturbance generated by
The ink is sent out through the nozzle plate 14 and the ink is separated into droplets 12 and uniformly guided to the recording medium. The piezoelectric transducer 28 has, in a preferred embodiment, a groove 32 extending approximately 9/1o of the distance from the bottom surface 34 of the piezoelectric transducer 28 to the surface 36 where the transducer 28 is bonded to the acoustic cavity material. ing. These grooves 32 have a width of approximately 0.56 mm, but prevent lateral coupling of waves generated by excitation of the transducer.

Importantly, the edges 29.31 of the transducer 28 are spaced inwardly from the housing 22, as shown more clearly in the elevational view of FIG. This spacing is said to be on the order of approximately 5 mm. this is,
This is necessary to prevent any coupling between the transducer 28 and the support housing 16 and will dampen any shock waves or disturbances created by the transducer.

The fluid cavity 20 itself, in a preferred embodiment,
It has a square cross section with approximately 11 sides on each side. The height of the acoustic cavity is 28
It is known that the critical dimensions should be made with a height adapted to the desired operating frequency. Therefore, 1.10 K
For a transducer operable at Hz, the height of the acoustic cavity should be 4,7 I11 ml, and if the operating frequency is 120 K Hz, the height should be 4.
．． Must be 2mm.

One of the most important advantages of this size is that an acoustic transducer with this height from aperture surface 36 to aperture surface 26' is more effective in transmitting the force of the piezoelectric transducer into the fluid cavity 20. The point is that the efficiency is the highest. By using the fluid cavity 20 having the above dimensions, the flow path can be made small, so that when the unit is turned on, air bubbles in the liquid flow will disappear as if the ink was being pushed by the flow. It will be pushed out immediately. the result,
Since there is no time lag for the start of the flow of all the ink outlet streams 12 and the operation of the inkjet printer can be immediately started, a remarkable effect can be obtained in quickly starting the operation of the inkjet printer.

The results of testing and demonstrating the efficiency of the unit of the present invention are shown in Figures 3-5. The test results at two different operating frequencies shown in FIGS. 3 and 5 show that all jets operate in phase, as discussed in the background of the present invention in the prior art section. can be seen. This well-coordinated motion is absolutely essential to any successful inkjet printer, and has proven difficult to achieve with long linear jet arrays driven by a common transducer. . FIG. 4 shows that the minimum voltage required to drive the transducer of the present invention is -
It has been shown that the design adopted in A range of separations of 1-80° or less is considered very good. In both the cases considered in FIGS. 3 and 5, the range is approximately 40°, and the separation of the drops is shown to be relatively in phase.

As described above, the present invention is highly efficient, simple in construction, can operate with relatively low power, can be activated instantly, and produces phased droplets from all jets in a linear array. It has been proven that

Alternatives or variations to the preferred embodiments described above will be apparent to those skilled in the art from a study of this disclosure. Accordingly, the scope of the invention should be limited only by the scope of the claims.

The embodiments described in the above description can be summarized as follows.

(b) The above predetermined cycle is 11.0 to 120KHz.
The droplet generator according to claim 1, wherein the acoustic cavity has a height from the first opening to the second opening of 4.7 to 4.2 mm.

(b) The droplet generator according to claim 1, wherein the ink flow path has a cross-sectional area of 1-.

3. The droplet generator of claim 1, wherein a groove extends from the surface of the acoustic transducer toward the first aperture for a distance of approximately 9710 degrees.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view showing the main parts of an embodiment of the inkjet droplet generator of the present invention, and FIG. 2 is a relationship among the transducer, acoustic cavity, liquid cavity, and nozzle of the embodiment shown in FIG. 1. 3, 4 and 5.
The figure is a graph showing test results when the device of the present invention produces a balanced output. 12... Nozzle, 14... Nozzle plate, 20...
...Fluid cavity (ink flow path), 22.24...
- Housing, 26... Acoustic cavity, 28... Acoustic transducer, 3o... Hole, 32...
・・Groove Fig. 2 Fig. 3 123456:1B 9101112 :: [□ Fig. 5

Claims (3)

[Claims] (1) In an inkjet drop generator that synchronously separates droplets from multiple ink streams for charging and deflection for printing, a nozzle having a plurality of nozzles spaced in a straight line and ejecting ink; a plate; a housing supporting the nozzle plate and defining an acoustic cavity having first and second apertures; a solid material filled in the acoustic cavity for transmitting acoustic disturbances from the first aperture to a second aperture; , having an acoustic transducer bonded to the material filling the acoustic cavity at the first cavity opening, operable at a predetermined period to create the disturbance and imparting the disturbance to the acoustic cavity; perturbation means, means for defining an ink flow path across said second opening and receiving said perturbation transmitted through said acoustic cavity material, means for supplying ink to said ink flow path; an inkjet drop generator for synchronously propelling ink in the ink flow path through nozzles in the nozzle plate. 2. The drop generator of claim 1, wherein said housing is constructed of a material having high acoustic impedance. 3. The drop generator of claim 1, wherein the acoustic impedance of the solid material filling the acoustic cavity is approximately equal to that of the ink.