JPS62105636A - Droplet generator for ink jet printer - Google Patents

Abstract

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

Description

Description: TECHNICAL FIELD This invention relates generally to drop generators for ink jet printers, and more particularly to improvements in means for coupling acoustic excitation to an ink drop generator.

BACKGROUND OF THE INVENTION The use of non-inject printers with multiple nozzles or a single nozzle to record data on a recording surface is well known, for example from Sweet, US Pat. No. 3,596,275.

Typically, continuous inkjet printers use ink (
Communicating with the pressurized ink chamber are one or more discharge nozzles having a liquid chamber into which a liquid (magnetic or electrically conductive) is forced under pressure. A vibrating member is attached to the liquid chamber and excites the liquid at a high frequency to break up the stream or streak of liquid from the nozzle into droplets. To create evenly spaced droplets,
The dimensions of the liquid chamber are related to the wavelength of the sound pressure generated in the liquid by the vibrating member. After the selective charging step, the droplets are influenced by an electric field and adhere to the recording surface, printing data.

One of the major problems with the prior art is the inability to keep the fluid chamber in front of the vibrating crystal bubble-free. Foam is introduced during initial filling of the liquid chamber or during subsequent startup or shutdown of the droplet generator.

The intrusion of air bubbles or vacuum bubbles into the liquid disrupts the uniformity of pressure transmission along the longitudinal axis of the piezoelectric crystal driver. As a result, droplet formation among streams within a multi-nozzle inkjet array head is not uniform. Non-uniform droplet formation results in random, imprecise, and non-uniform droplet deposition on the recording medium.

As a result of the above, print quality deteriorates.

OBJECTS In view of the above facts, it is an object of the present invention to provide a new and improved droplet generator.

Another object of the invention is to provide a droplet generator in which the size of the liquid chamber is significantly reduced by introducing a solid acoustic chamber between the vibrating member and the liquid chamber. The combined size of the two chambers meets the relationship required for uniform transmission of acoustic disturbances from the vibrating member to the inkjet filament.

One previous effort in this area was U.S. Patent No. 4.331.
．． No. 964 (Van Lokeren).

This patent shows a droplet generator having a cylindrical vibrating assembly including a plurality of circumferentially mounted transducers. A relatively stiff acoustic rubber fills the remaining portion of the resonance chamber, which chamber is provided with an outlet connected to a concentrated ink chamber separated from the acoustic chamber by a fairly stiff membrane.

The difficulty with this design is the mounting of the transducer in the center of the chamber. This results in manufacturing difficulties and high costs.

The present invention aims to provide an acoustic source coupled to a solid material filling an acoustic chamber.

Yet another object of the present invention is to provide an acoustic source coupled to a solid material acoustic chamber designed to concentrate, smooth, and transmit acoustic power to a small ink chamber, thereby providing a The purpose of this process is to uniformly cut the ink streaks into droplets.

Yet another object of the present invention is to provide a droplet generator incorporating an ink chamber that is relatively small compared to the length of the sound wave in the liquid along the longitudinal direction of the pressure-crystal driver. It is. The use of small chambers improves the uniformity of the standing waves at the nozzle and thus of the droplets generated therefrom.

Another object of the invention lies in the employment of a piezoelectric transducer acoustic source designed as a cracked block. Such a design maximizes the piston-like favorable movement of the transducer and improves the accuracy of the acoustic transducer. Minimize volumetric motion.

Another advantage of the split block design is the ease of mounting the block to an acoustic chamber.

Several drop generators are spaced at a distance from each other to achieve multicolor printing or to increase printing speed. However, this leads to a reduction in print quality due to tolerances of some parameters and is also very expensive. It is therefore another object of the present invention to provide an acoustic transducer that is easily adapted to use with ink chamber plates having gaps forming a plurality of chambers. The advantages of this design are improved print quality and significant cost savings.

In summary, the present invention comprises a drop generator for the generation of one or more drop streams for use in printing onto a recording medium. The generator includes a housing having an acoustic chamber made of solid material. The acoustic chamber is mounted to the rear of a piezoelectric acoustic source for generating acoustic disturbances that are transmitted by the chamber material to the membrane, the mounting isolating the acoustic chamber from the ink chamber plate. The membrane acoustically VC couples the acoustic chamber to the ink chamber on the ink chamber plate. This chamber consists of a fissure extending across the face of the membrane, the edges of which are supplied with ink from an ink population. The ink population supplies each crevice with ink of the same or different color. An orifice plate having one or more small orifices corresponding to each ink chamber side aperture is arranged in the ink chamber plate such that vibration of the membrane propels ink drops through openings in the orifice plate and onto the recording medium. is placed before. Means are also provided for charging the droplets generated through each A-refice plate opening and for deflecting the charged droplets between the orifice plate and the recording medium toward the recording medium or toward the collection gutter. A piezoelectric transducer in the form of a block with a crack for reducing the volumetric movement of the block and increasing the piston-like motion provided with the means is preferably installed at the rear of the solid-filled acoustic chamber.

Other features and advantages will become apparent from the description of the invention given below with reference to the drawings V1--.

DESCRIPTION OF THE EMBODIMENTS FIG. 1 is an exploded perspective view of a two-chamber acoustic droplet generator to which the present invention is applied. Throughout this detailed description, common elements are designated by the same reference numerals. The mutual image planes of the paths of the ink drops after they have been ejected from the orifice plate and passed through the deflection form are shown in more detail in FIGS. 2 and 3.

Also shown in FIG. 4 is a detailed cross-sectional view of the relative positions of the transducer and the solid state acoustic chamber for focusing the output of the transducer onto the ink-bearing crevice.

The droplet generator of the present invention includes a housing 10 having an acoustic chamber 12 and an acoustic source chamber 14 formed therein. Sound room 1
2 is preferably filled with a relatively low density material, such as plastic, rubber, epoxy resin or epoxy resin mixed with micro hollow glass spheres. This chamber tapers from the surface 16 where the solid-state acoustic material is supplied to the solid-state acoustic source toward the surface covered by a membrane 20 that acoustically couples the acoustic chamber 12 to the ink chamber 22 of the ink chamber plate 24. .

This taper is for concentrating and smoothing the pulsating effect created by the acoustic source 17 and transmitting it through the metal membrane through the apex of the chamber 12 to the relatively small chamber crevice 22 of the chamber plate 24. . In this way, uniform ink drop formation at relatively high operating frequencies is achieved.

Ink is supplied through an ink port 30 that communicates with the end of the ink chamber gap 22 through an opening 32 in the impermeable membrane 20. An outlet 34 is provided at the narrow end of the ink chamber crevice 22 to prevent air bubbles or other disturbances in the ink flow from occurring along the entire length of the crevice. As the ink flows through the crack, the pulsating output of the acoustic source concentrated through the solid-filled chamber 12 is coupled into the crack through the plastic or metal membrane 20. As can be seen, the acoustic chamber 12 and the plurality of ink chamber cracks 22 disposed on the outside of the membrane are all acoustically coupled to a single acoustic chamber 12 at the same time.

In this way, the operating frequency of the system is, for example, approximately 11
Simultaneous formation of droplets from the crack through the orifice plate 40 is achieved even at relatively high frequencies of 0 KHz. The use of multiple parallel breaks allows the simultaneous use of different colored inks.

The acoustic source can use any one of the various types of piezoelectric transducers shown in FIG.

They are essentially block-shaped and have a cleft 42 that cuts generally across the depth of the proc transducer. This crack reduces the volumetric movement of the block, moving it closer to and away from the transducer membrane 20 and chamber crack 22.
It is known to enhance piston-like motion to create a desired pulsation in the ink streaks ejected from the orifices in plate 40. The piezoelectric transducer can be glued or molded into the transducer chamber 14 in alignment with the solid-filled acoustic chamber after the acoustic chamber has been suitably filled with the desired low-density transmission material. This configuration achieves low cost assembly of the entire system. On the contrary, it is possible to eliminate the transmissive membrane altogether if the acoustic chamber material is made of a material that is chemically compatible with the ink.

It is noteworthy, as more clearly shown in FIGS. 2 and 3, that the ink chamber 22 is relatively short, ie, approximately 1/16 of the acoustic wavelength during high frequency operation. This improves the uniformity of the standing waves that form at the exit nozzle or orifice, thereby promoting uniformity of ink droplet generation from the crack 22 through the orifice plate 40 and nozzle plate 50. FIGS. 2 and 3 further show that this arrangement allows electrodes 60 to be aligned with each opening in orifice plate 40.
It is shown that by appropriately forming the liquid droplet, it can be used as is to charge the droplet after passing through the orifice plate 40.

After the generated droplets have been suitably charged, they pass between a pair of electrode plates 62, 64 which suitably deflect each droplet to reach either the recording medium 66 or the collection gutter 68.

Figures 4A and 4B show further details that facilitate the preferred design and manufacture of the system, and show that after the metal housing 10 holding the acoustic chamber 12 is assembled, the acoustic chamber 12 is filled. It will be appreciated that solid materials can be used to do this. The acoustic chamber can be shaped precisely as desired to promote the concentration and propagation of sound waves.

The acoustic source is then easily attached directly to the rear surface of the acoustic chamber and the acoustic wave transmitting material of the acoustic chamber. The membrane 20 is then attached to the front of the housing, and the Vζ ink chamber plate is attached above this membrane.

An orifice or nozzle plate 40 is then attached directly to the front face of this membrane, sandwiching the ink chamber plate 24 therebetween to precisely define ink drop generation.

By slightly modifying the orientation of the ink chambers and the respective poles 60, the ink droplets ejected from the plurality of ink chambers can be concentrated at approximately one point on the recording medium as shown in FIG. . With this method, high speed or high density or multicolor printing is easily and reliably achieved.

The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view of an embodiment of an acoustically driven droplet generator according to f/C of the present invention, FIG. 2 is a side view of the droplet generator of the present invention showing means for deflecting charged droplets, and FIG. 3 4A and 4B are side views of a modified embodiment of the present invention in which the axes of each ink chamber are arranged so that they are concentrated at one point y on the recording medium, and FIGS. 4A and 4B are views of the droplet generator of the embodiment of the present invention. FIG. 3 is a cross-sectional view showing the positional relationship among an acoustic source, a filled acoustic chamber, a metal film, an ink chamber, and an orifice plate.

Claims (12)

[Claims] (1) In a droplet generator of an inkjet printer that records on a recording medium with one or more ink droplets generated by the droplet generator, an acoustic chamber filled with a solid material having acoustic transmission properties, an acoustic chamber a housing having: means coupled to the rear side of the acoustic chamber for generating an acoustic disturbance within the acoustic chamber; a flexible membrane attached to the other side of the acoustic chamber; a plate member disposed on the opposite side of the membrane from the acoustic chamber, carrying a plurality of ink chambers simultaneously communicating with the same acoustic chamber, and attached to the membrane; supplying ink to each of the ink chambers; and an orifice plate having one or more orifices corresponding to each ink chamber. (2) The droplet generator according to claim 1, wherein the axes of the plurality of ink chambers are parallel to each other. (3) The droplet generating device according to claim 1, wherein the axes of the plurality of ink chambers are generally concentrated at one point on the recording medium. (4) means for generating acoustic disturbance in the acoustic chamber is attached to the rear surface of the acoustic chamber filled with the solid material;
A droplet generator according to claim 1, characterized in that the acoustic source consists of a block-shaped acoustic transducer glued to a chamber in the housing of the droplet generator. (5) The above-mentioned sound source is a piezoelectric transducer block having a plurality of mutually parallel splits extending in the direction in which sound waves are transmitted to the above-mentioned membrane through the above-mentioned sound chamber. 4. Droplet generator according to item 4. (6) The droplet generator according to claim 1, further comprising means for charging the ink droplets generated from each orifice in response to disturbances caused by the acoustic source. (7) The droplet generator according to claim 6, further comprising means for deflecting the ink droplets charged by the charging means toward the recording medium. (8) The droplet generator according to claim 7, further comprising one or more gutters for collecting charged droplets that are not used for recording. (9) Droplet generator according to claim 1, characterized in that the above-mentioned flexible membrane is not used and the solid acoustic chamber material is a material that is chemically compatible with the ink or liquid. . (10) Acoustic means for generating high-frequency disturbance is arranged adjacent to the resonance chamber, and has an ink chamber arranged outside adjacent to the resonance chamber and partitioned from the above-mentioned chamber through a thin flexible membrane. In a double-chamber resonant droplet generator, said resonant chamber has a taper such that its narrow end is near said membrane, and said resonant chamber is filled with an acoustically conductive solid material. A droplet generator characterized in that the above-mentioned disturbance means is fixed to the rear wide part of the acoustic chamber on the side of the chamber remote from the membrane. (11) Claim characterized in that said acoustic means is a block-shaped acoustic transducer mounted on the rear side of said filled acoustic chamber and glued to the chamber in the housing of said droplet generator. A droplet generator according to scope 10. (12) The acoustic source is a piezoelectric transducer block having a plurality of parallel splits extending in the direction in which sound waves are transmitted to the membrane via the acoustic chamber. 12. Droplet generator according to clause 11.