Patent Grant
7216958
1. Field of the Invention
The present invention relates to a method of expelling a fluid. More particularly, the present invention relates to a method of expelling a fluid from a nozzle using an ion wind and an ink-jet printhead utilizing the method.
2. Description of the Related Art
Typically, ink-jet printheads are devices for printing a predetermined image, color or black, by ejecting a small volume droplet of printing ink at a desired position on a recording sheet. In conventional ink-jet printheads, ink ejection mechanisms are largely categorized into two types. Conventionally, there have been used a thermally driven type in which a heat source is employed to generate bubbles in ink to cause ink droplets to be ejected by an expansion force of the generated bubbles, and a piezoelectrically driven type in which ink is ejected by a pressure applied to ink due to deformation of a piezoelectric element.
The conventional thermally driven ink-jet printhead shown in
However, in the thermally driven ink-jet printhead, when ink droplets are expelled due to the expansion of bubbles, a portion of the ink in the ink chamber 26 flows backward to the manifold 22, and an ink refill operation is performed after ink is expelled. Thus, there is a limitation in implementing high-speed printing.
In addition to the above-described ink droplet ejection mechanisms, a variety of different ink droplet ejection mechanisms are used in ink-jet printheads, and another example is shown in
Referring to
The ink-jet printhead expelling ink utilizing the principle of an atomizer requires a compressor for supplying compressed air. In particular, in order to adopt the above-described ink ejection mechanism to an ink-jet printhead having a plurality of nozzles, there is a demand for a complex series of air supply passages from the compressor to the plurality of nozzles. Thus, the printhead becomes bulky, which reduces the number of nozzles per unit area, i.e., a nozzle density. In addition, it is quite difficult to manufacture a printhead having several hundred or more nozzles. As a result, an operational printing resolution of the ink-jet printhead adopting the above-described ink ejection mechanism still remains at a level of several tens of dots per inch (DPI).
Accordingly, in order to implement an ink-jet printhead having high printing speed and high resolution, a new ink droplet ejection mechanism is needed.
The present invention provides a method of expelling a fluid from a nozzle by reducing a pressure in a front portion of an outlet of the nozzle using an ion wind.
The present invention also provides a high-integration, high-resolution ink-jet printhead utilizing the fluid expelling method.
According to a feature of an embodiment of the present invention, there is provided a method of expelling a fluid including filling a nozzle with a fluid using a capillary force, generating an ion wind by ionizing air near an outlet of the nozzle, and expelling the fluid from the nozzle as the ion wind decreases a pressure around the outlet of the nozzle.
In the method, the ionizing of air may be performed by an electric field formed between two electrodes disposed near the outlet of the nozzle. A volume and speed of the fluid expelled may be adjusted by varying voltages applied between the two electrodes and a time duration of voltage application. An expelling frequency of the fluid may be adjusted by varying a pulse period of the voltage applied to the electrodes.
In the method, the ion wind may flow toward the outlet of the nozzle and upward at a front portion of the outlet of the nozzle and may flow in an inclined direction toward the front portion of the outlet of the nozzle.
In the method, the fluid may be ink, the ink being expelled from an ink-jet printhead.
According to another feature of an embodiment of the present invention, there is provided an ink-jet printhead including a manifold formed in a passageway plate to supply ink, a nozzle to be supplied with ink formed in a nozzle plate provided on the passageway plate, the ink being supplied by a capillary force, and a ground electrode and a source electrode arranged near an outlet of the nozzle, the ground electrode and the source electrode forming an electric field due to an application of a voltage thereto and ionizing air near the outlet of the nozzle to produce an ion wind to decrease a pressure near the outlet of the nozzle to expel the ink contained in the nozzle.
In the ink-jet printhead, the ground electrode may be disposed adjacent the outlet of the nozzle and the source electrode may be disposed a predetermined distance from the ground electrode away from the outlet of the nozzle. The ion wind may flow toward the outlet of the nozzle and may flow upward at a front portion of the outlet of the nozzle.
An embodiment of the ink-jet printhead may further include a recess having a predetermined depth formed at a periphery of the outlet of the nozzle on a surface of the nozzle plate, the ground electrode and the source electrode being arranged within the recess. The recess may have a shape of a ring surrounding the nozzle. A side of the recess adjacent the outlet of the nozzle may be inclined to permit the ion wind to flow in an inclined direction toward a front portion of the outlet of the nozzle. The ground electrode may be disposed on a bottom of the recess or on the inclined side of the recess.
Another embodiment of the ink-jet printhead may further include an ion wind path for guiding the ion wind formed in the nozzle plate to surround the nozzle, the ground electrode and the source electrode being arranged within the ion wind path. The ion wind path may be shaped as a ring surrounding the nozzle. An outlet side of the ion wind path may be inclined to permit the ion wind to flow in an inclined direction toward a front portion of an outlet of the ion wind path. The ground electrode may be disposed on the inclined side of the ion wind path and the source electrode may be disposed a predetermined distance apart from the ground electrode. This embodiment of the ink-jet printhead may further include an air path for supplying the ion wind path with air formed in the nozzle plate to communicate with the ion wind path. The air path may be formed in a vertical, horizontal, or inclined direction and communicates with a lower portion of the ion wind path.
In the ink-jet printhead, the nozzle may have a tapered shape in which a cross-sectional area of the nozzle decreases gradually toward the outlet of the nozzle. The ground electrode and the source electrode may surround the outlet of the nozzle. A shape of the ground electrode and the source electrode may be circular, oval, or polygonal. The source electrode may have a cross-sectional area smaller than a cross-sectional area of the ground electrode.
In an embodiment of the ink-jet printhead, the source electrode may include a protrusion extending toward the ground electrode. The protrusion may be a plurality of protrusions provided at equidistant intervals along a lengthwise direction of the source electrode.
In the ink-jet printhead, the nozzle may be a plurality of nozzles, each formed in the nozzle plate, and one of a plurality of ground electrodes and one of a plurality of source electrodes are arranged near each of the plurality of nozzles, and wherein ink may be expelled from each of the plurality of nozzles simultaneously, sequentially, or individually.
The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
Korean Patent Application No. 2003-2728, filed on Jan. 15, 2003, and entitled: “Method of Expelling Fluid Using Ion Wind and Ink-Jet Printhead Adopting the Method,” is incorporated by reference herein in its entirety.
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity. Like reference numerals refer to like elements throughout.
Although only a unit structure of the ink-jet printhead is shown in the drawings, a plurality of nozzles are provided in the ink-jet printhead manufactured in a form of chips.
Referring to
Ink 101 is supplied to the manifold 112 from an ink reservoir (not shown). Ink 101 in the manifold 112 moves to the nozzle 122 by a capillary force to fill the nozzle 122. Although the nozzle 122 preferably has a circular cross-sectional area, the nozzle 122 may have various shapes, including an oval or polygonal shape. Preferably, the nozzle 122 has a tapered shape in which a cross-sectional area of the nozzle 122 decreases gradually toward an outlet.
A ground electrode 131 and a source electrode 132 are spaced a predetermined distance apart from each other near an outlet of the nozzle 122. The ground electrode 131 is grounded, and a predetermined DC pulse or AC voltage is applied to the source electrode 132. The voltage applied to the ground electrode 131 and the source electrode 132 forms an electric field and ionizes ambient air present near the outlet of the nozzle 122, thereby producing an ion wind, which will be subsequently described in greater detail.
The ground electrode 131 and the source electrode 132 are preferably shaped to surround the outlet of the nozzle 122. For example, as shown, if the nozzle 122 has a circular cross-sectional shape, the ground electrode 131 and the source electrode 132 will also have a circular ring cross-sectional shape. However, if the nozzle 122 has an oval or polygonal cross-sectional shape, the cross-sectional shapes of the ground electrode 131 and the source electrode 132 may vary accordingly.
The ground electrode 131 may be disposed relatively near the outlet of the nozzle 122 while the source electrode 132 is disposed relatively far from the outlet of the nozzle 122, or the positions of the ground electrode 131 and the source electrode 132 may be reversed. The source electrode 132 has a cross-sectional area smaller than that of the ground electrode 131.
The ink-jet printhead according to the first embodiment of the present invention is driven by an ink expelling mechanism in which ink is expelled from a nozzle using an ion wind generated in such a manner as shown in
Referring back to
When a DC pulse or AC voltage of a voltage sufficiently high to ionize air is applied to the source electrode 132, an electric field is formed between the ground electrode 131 and the source electrode 132. The electric field ionizes air present between the electrodes 131, 132, and the ionized air moves toward the ground electrode 131 by a Coulomb force (F=q*E), and the ion wind W is produced accordingly. A speed of the produced ion wind W increases as the Coulomb force (F=q*E) applied to the ions within the electric field increases. As described above, if the ion wind W is generated near the outlet of the nozzle 122, a pressure near the outlet of the nozzle 122 is reduced, so that ink 101 within the nozzle 122 is expelled in the form of a droplet 102 based on the principle of an atomizer. As the ink droplet 102 is expelled, the nozzle 122 is refilled with ink 101 due to a capillary force.
In the above-described ink expelling mechanism, a volume and speed of the droplet 102 expelled may be adjusted by varying a voltage applied between the two electrodes 131, 132 and a time duration of voltage application. That is, if a voltage applied to the electrodes 131, 132 is increased, the speed of the ion wind W is increased and a difference in the pressure between an interior and outside the nozzle 122 is increased, thereby increasing the expelling speed of the droplet 102. Therefore, a response speed of the nozzle 122, which depends on a signal indicative of ink expelled, the signal transferred via the source electrode 132, is increased. If the voltage application time is reduced, a volume of the droplet 102 of ink expelled becomes reduced. An expelling frequency of the droplet 102 may be adjusted by varying a pulse period of the voltage applied. Therefore, a desired volume of the ink droplet 102 may be expelled at a desired frequency. As the ink droplet 102 is expelled, the ink 101 refills the nozzle 122 by a capillary force. In addition, backflow of the ink 101 does not occur in the nozzle 122. Thus, only a short period of time is required for ink refill, thereby allowing the ink droplet 102 to be expelled at a high frequency.
Although the ink 101 in the nozzle 122 is driven by the ion wind W that horizontally moves from one side of the nozzle 122 to the opposite side thereof, it is preferable to make the ion wind W converge and flow upward at a front portion of an outlet of the nozzle 122, which is because the ion wind W preferably adaptively moves in an expelling direction of the ink droplet 102. To this end, the electrodes 131, 132 are arranged to surround the nozzle 122, respectively. Preferably, the ground electrode 131 is disposed adjacent to the outlet of the nozzle 122 and the source electrode 132 is disposed a predetermined distance apart from the ground electrode 131 away from the outlet of the nozzle 122. Such an arrangement of the electrodes 131, 132 allows the ion wind W to flow toward the outlet of the nozzle 122 and allows the ion wind W to flow upward at the front portion of the outlet of the nozzle 122.
Referring to
In this structure, the ink droplet 102 may be simultaneously expelled from the respective nozzles 122 by simultaneously applying a voltage to the respective source electrodes 132. In addition, the ink droplet 102 may be sequentially expelled from the respective nozzles 122 by applying voltages at a time interval to the respective source electrodes 132. Alternatively, the ion wind W may be produced only around the outlet of one selected nozzle by applying a voltage to only one of the source electrodes 132, thereby expelling the ink droplet 102 only from the selected nozzle.
Since the electrodes 131, 132 are formed in a form of micro droplets using a semiconductor manufacturing process, the ink-jet printhead according to this embodiment of the present invention has a simplified structure, as compared to the conventional ink-jet printhead in which ink is expelled by compressed air. Therefore, the ink-jet printhead having the plurality of nozzles 122 can be easily manufactured, thereby implementing a high-integration, high-resolution ink-jet printhead. Since a relatively small voltage, i.e., several to several tens of volts, is applied to the source electrode 132, that is, a relatively small amount of power is consumed in producing the ion wind W, an ink-jet printhead having a small power consumption can be manufactured.
As shown in
Referring to
The recess 224 is preferably shaped as a ring surrounding the nozzle 222 to accommodate a ring-shaped ground electrode 231 and source electrode 232. A side 225 of the nozzle 222 adjacent the outlet of the nozzle is preferably inclined to permit the ion wind W produced in the recess 224 to flow in an inclined direction toward a front portion of an outlet of the nozzle 222, thereby facilitating an upward flow of the ion wind W at the front portion of the outlet of the nozzle 222.
The ground electrode 231 may be installed on a bottom of the recess 224, or it may be installed on the inclined side 225 of the recess 224 for the purpose of facilitating flow of the ion wind W. In this embodiment, the source electrode 232 is installed on a bottom at an outer peripheral side of the recess 224.
The nozzle 222 preferably has a tapered shape in which a cross-sectional area decreases gradually toward an outlet. As is well known, this configuration permits a meniscus formed on a surface of the ink 101 in the nozzle 222 to extend upward quickly to be stabilized. The shape of the nozzle 222 conforms to that of the recess 224 formed in the periphery thereof.
In the second embodiment, the arrangement and shape of the electrodes 231, 232 are the same as those of the first embodiment. The source electrode 232 according to the second embodiment also may have the same shape as shown in
As shown in
Referring to
The ion wind path 324 is preferably shaped as a ring surrounding the nozzle 322 to accommodate a ring-shaped ground electrode 331 and source electrode 332. An outlet side of the ion wind path 324 is preferably inclined to permit the ion wind W produced in the ion wind path 324 to flow in an inclined direction toward a front portion of the outlet of the ion wind path 324, thereby facilitating an upward flow of the ion wind W at the front portion of the outlet of the nozzle 322.
The ground electrode 331 is disposed at an inclined portion of the ion wind path 324, and the source electrode 332 is spaced a predetermined distance apart from the ground electrode 331 to be disposed at a deeper portion of the ion wind path 324. Such an arrangement is preferred in view of the formation of the flow of the ion wind W.
An air path 326 for supplying the ion wind path 324 with air is formed in the nozzle plate 320 to communicate with the ion wind path 324. The air path 326 is preferably formed in a vertical direction, as shown in
In addition, for the foregoing reasons, it is preferable that the nozzle 322 has a tapered shape in which a cross-sectional area decreases gradually toward an outlet.
In the third embodiment, the arrangement and shape of the electrodes 331, 332 are the same as those of the first embodiment. The source electrode 332 according to the third embodiment may also have the same shape as shown in
As described above, according to the fluid expelling method of the present invention, a volume and speed of the fluid expelled may be adjusted finely and accurately by varying voltages applied between two electrodes and a time duration of voltage application. An expelling frequency of the fluid may be adjusted by varying a pulse period of the voltage applied. As the fluid is expelled from nozzles, the fluid refills the nozzles. In addition, backflow of the fluid does not occur in the nozzles and a separate time for refilling is not required, thereby enabling the fluid to be expelled at a higher frequency.
Since the ink-jet printhead according to the embodiments of the present invention is constructed such that electrodes producing an ion wind are arranged near a plurality of nozzles and the electrodes are miniaturized, it has a simplified structure as compared to the conventional ink-jet printhead in which ink is expelled by compressed air. Since manufacture of an ink-jet printhead having a plurality of nozzles may be performed easily, a high-integration, high-resolution ink-jet printhead may be easily implemented. Further, since power consumption for producing an ion wind is relatively small, low power consuming ink-jet printheads can be manufactured.
Preferred and exemplary embodiments of the present invention have been disclosed herein and, although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. For example, the ink expelling method according to the present invention may be applied to a general fluid ejection system in which a small amount of fluid is expelled through nozzles as well as the ink-jet printheads shown and described in the exemplary embodiments of the present invention. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.
| Number | Date | Country | Kind |
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