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 xe2x80x9cink-on-demandxe2x80x9d 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.
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.
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 to the print data, thereby pressurizing the ink in the ejection chamber, and causing an ink drop to be ejected from the nozzle continuous to the pressurized ejection chamber.
Because the ink and cleaning solution used to clean the ink supply path during manufacture is supplied through the filter disposed in the ink supply port, foreign particulate larger than the cross-sectional area of the filter opening and suspended in the ink or cleaning solution is stopped from entering the ink supply paths by the filter, and is thus prevented from penetrating to the ink supply path downstream from the ink supply port. Any foreign particulate passing the filter can therefore be ejected from the nozzle because the cross-sectional area of the filter opening is less than the cross-sectional area of the nozzle opening and ink supply path, and clogging of the narrow nozzles is thus eliminated. Printing problems are thus eliminated because clogging of the ink passage is prevented, and a high reliability ink jet head can be obtained.
The pressure increase in the ink chamber caused by the pressure generated in the ejection chamber of the driven nozzles is also reduced because the filter inertance is preferably a maximum one-fifth the inertance of the ink passage from the nozzle to the supply port. The problems of pressure, more specifically pressure interference and cross talk between ejection chambers, produced by the driven nozzle transferring to a non-driven nozzle and causing ink to be ejected from the non-driven nozzle are thus eliminated.
In addition, sufficient ink can be supplied from the ink supply port to the ink passage downstream therefrom because the flow resistance of the filter is preferably a maximum one-fourth the flow resistance of the ink passage from the head nozzles to the ink supply path. An ink supply deficiency therefore does not occur, printing density does not drop during high speed ink jet head drive, and such printing problems as dropped pixels caused by inconsistent ejecting do not occur.
In addition, if at least one wall of the ink chamber is flexible, pressure generated by the ejection chamber of the driven nozzle can be sufficiently buffered and reduced, thereby eliminating cross talk caused by pressure interference between ejection chambers.
In accordance with another aspect of the present invention an ink jet head is provided for ejecting ink droplets from a nozzle by means of; a common ink chamber; an ink supply opening for supplying ink to the common ink chamber; a plurality of nozzles; an ink path for connecting each nozzle to the common ink chamber; a pressure generator or a pressure generating means disposed in each ink path and selectively driven for ejecting an ink droplet from a corresponding nozzle; and a flexible wall defining part of a wall of the common ink chamber for buffering pressure change in the common ink chamber.
This flexible wall forms a pressure change buffering means, or diaphragm. It is therefore not necessary to provide a separate member such as an ink distributor to prevent pressure interference between nozzles, and an ink jet head that can prevent pressure interference between nozzles without incurring an increase in size can thus be provided.
When the ink paths and common ink chamber of the ink jet head are formed by laminating together a first substrate in which said nozzles are formed, and a second substrate in which a recess that becomes part of the common ink chamber and ink path is formed, the flexible wall can be formed in either the first or second substrate.
The characteristics of the pressure change buffer are determined by its thickness and area. To achieve the same characteristics, the thickness of the flexible wall can be increased if the wall area is large, but if the wall area is small, the wall must be made correspondingly thinner. If the flexible wall is too thin, it becomes easily damaged. Forming this wall can therefore be difficult depending on the wall thickness, and adjusting the wall characteristics (flexibility) can be difficult.
In an ink jet head according to the present invention, however, the flexible wall is formed as part of the common ink chamber, and a pressure change buffer with a large area can therefore be achieved. It is therefore easy to form a pressure change buffer for preventing pressure interference with the desired characteristics.
The flexible wall is further preferably formed so that the compliance of the common ink chamber is 1xc3x9710xe2x88x9217 m5/N or greater. This assures that the pressure change buffer can sufficiently buffer pressure change in the common ink chamber.
When the pressure change buffer is disposed to the first substrate in which the nozzles are formed, that is, when the flexible wall is formed in the first substrate, it is externally exposed. In this case it is preferable to cover the flexible wall with a protective cover. However, if the flexible wall is completely covered the pressure change buffer becomes sealed, and adverse effects on the vibration of the pressure change buffer can result. In this case, therefore, it is preferable to provide a ventilation hole in the protective cover.
The pressure generator of this ink jet head can be operated by electrostatic force, that is, the ink jet head according to the present invention can be applied to an electrostatic drive type of ink jet head. It will also be obvious that the ink jet head according to the present invention can also be used with ink jet heads of the type that expel ink droplets using pressure from generated air bubbles, and with ink jet heads that are operated with piezoelectric elements.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.