Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-10-07
2002-04-16
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06371598
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet head for an ink jet printer, and relates more particularly to an ink jet head wherein pressure interference between ink nozzles can be prevented.
2. Description of the Related Art
Ink jet heads can be constructed using various means of ejecting ink droplets from the ink jet nozzles. One type of ink jet head, for example, uses a heater to make the ink bubble such that the resulting pressure from the air bubbles causes ink droplets to be ejected. Another mechanism uses a piezoelectric device attached to an ejection chamber in which ink is stored. In this mechanism a voltage applied to the piezoelectric device causes the ejection chamber to expand and contract, producing a pressure change whereby ink droplets are forced from a nozzle. Yet another mechanism uses electrostatic force to change the volume of the ink chamber in which ink is stored, again generating a pressure change whereby an ink droplet is expelled. Each of these mechanisms results in a so-called “ink-on-demand” ink jet head in which a change in the pressure of an ejection chamber is used to expel an ink droplet when required for printing.
In general, ink-on-demand ink jet heads have a plurality of ejection chambers each corresponding to one of a plurality of nozzles, an ink reservoir (common ink chamber) from which ink is supplied to each ejection chamber, and a nozzle linking each ejection chamber to the ink reservoir. As described above, a pressure change in an ejection chamber causes an ink droplet to be expelled from the corresponding nozzle. The ejection chambers, ink reservoir, and nozzles are formed by laminating plural flat substrates together with the substrate surfaces being appropriately etched to form the various grooves and recesses that become the ejection chambers, ink reservoir, and nozzles.
When a pressure change is effected in an ejection chamber to expel an ink droplet, the resulting pressure (ejection pressure) is transmitted to the ink reservoir. When a pressure change thus occurs in the ink reservoir, pressure interference between nozzles can occur through the ink reservoir. This can cause the ejected ink droplet volume to vary, and can cause ink to leak from nozzles (undriven nozzles) other than the nozzles (driven nozzles) from which ink is supposed to eject. For example, if a positive pressure occurs in the ink reservoir, ink droplets can leak from undriven nozzles. A negative pressure can cause the ink droplet volume from the driven nozzles to drop.
To avoid these problems, Japanese Examined Patent Publication (kokoku) HEI2-59769 teaches a unit called an ink distributor comprising a diaphragm for buffering the impact of pressure changes. When this unit is assembled with a nozzle part, the diaphragm suppresses pressure changes in the ink reservoir. As a result, the desired ink ejection characteristic can be obtained.
As printers have become smaller, however, demand has grown for even smaller, thinner ink jet heads. Unfortunately, the ink distributor used to achieve desired ink ejection characteristics as taught by the above-cited prior art is an additional structural component of the ink jet head. It thus increases the size of the ink jet head, and obviously prevents reducing the ink jet head size.
There is therefore a need for an ink jet head whereby pressure interference between nozzles can be prevented without increasing the size of the ink jet head.
There is a further need for an ink jet head wherein a diaphragm providing the desired pressure interference prevention can be easily achieved while retaining the desired printing characteristics.
OBJECTS OF THE INVENTION
Accordingly, it is an object of the present invention to provide an ink jet recording head which overcomes the aforementioned problems.
It is another object of the present invention to provide an ink jet recording apparatus having an ink jet head in which pressure interference between nozzles can be prevented without increasing the size of the ink jet head.
It is an additional object of the invention to provide an ink jet head in which a diaphragm providing the desired pressure interference prevention can be easily achieved while retaining the desired printing characteristics.
SUMMARY OF THE INVENTION
To achieve the aforementioned object, an ink jet recording apparatus according to the present invention comprises an ink jet head having a plurality of nozzle openings and a plurality of independent ejection chambers respectively communicating to each of said nozzle openings from which ink droplets are ejected according to the change in pressure generated by each ejection chamber. The apparatus further includes an ink cavity for storing ink, ink supplying paths which supply ink to each of the ejection chambers from the ink cavity and a filter formed in or attached to the ink cavity. The ejection chambers, the ink supplying paths, the ink cavity and the filter are formed together on an anisotropic crystalline substrate, such as a silicon substrate, and the filter has a plurality of channels, which are shallower than any of the other channels of the nozzles and ink supplying paths.
The filter is provided for preventing the introduction of foreign particulate to the ink chamber and to the nozzles. The filter also functions as inlet ports for supplying ink from an external source to the ink cavity.
The preferred shape of the filter is a cross-sectional area of the filter opening that is smaller than the cross-sectional area of the ink supply paths and the nozzles. In addition, the inertance of the filter is preferably a maximum one-fifth the inertance of the ink passage consisting of the ejection chambers and the ink supplying paths plus the corresponding nozzles; and the flow resistance of the filter is preferably a maximum one-fourth the flow resistance consisting of the ejection chambers and the ink supplying paths plus the corresponding nozzles. At least one wall of the ink cavity is also preferably flexible.
A method for producing an ink jet head according to the present invention comprises at least the step of anisotropically etching an anisotropic crystalline substrate on a first surface thereof to form at least a plurality of communicating channels delineating a plurality of independent ejection chambers, an ink cavity, a plurality of ink paths each connecting a respective ejection chamber with the ink cavity, and a filter connected to the ink cavity. Next, by means of anisotropic etching, a group of adjacently disposed grooves with said filter is formed, each of which is shallower than the channels delineating the ejection chambers, the ink cavity and the ink paths, and nozzle openings each of which connects with each of the ejection chambers. Forming, by means of anisotropic etching, a plurality of diaphragms with each of the bottom walls of said ejection chambers and bonding a cover substrate to the first surface of the anisotropic crystalline substrate sealing the rims of ejection chambers, the ink cavity, the ink paths and the filter to enclose the same while maintaining the communication therebetween.
To form the actuator for driving the diaphragm, this manufacturing method further comprises a process for forming electrodes in the first surface of an insulating substrate, and bonding the insulating substrate to the second surface of the anisotropic crystalline substrate on the side opposite the first face thereof such that the electrodes are in opposition to the diaphragms with a gap therebetween. Alternatively, a process for adhesive bonding piezoelectric elements for deforming the diaphragms to the back side of the ejection chambers of the anisotropic crystalline substrate is provided.
By means of the invention thus described, ink supplied to the ink jet head is supplied through a filter disposed in the ink supply port and is stored in the ink cavity. The ink stored in the ink cavity is distributed through the ink supply paths to the respective ejection chambers. The pressure generating means is then driven according t
Fujii Masahiro
Ishikawa Hiroyuki
Nojima Shigeo
Takekoshi Taro
Barlow John
Seiko Epson Corporation
Stewart Jr. Charles W.
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