High resolution microfluidic printing array valve

Abstract

A microfluidic printing apparatus for printing ink pixels on a receiver including at least one ink reservoir; a moveable plate having a plurality of delivery chambers in an array each for forming an ink pixel, and a plurality of microchannels connecting the reservoir to a delivery chamber; and a plurality of microfluidic pumps each being associated with a single microchannel for supplying ink to particular delivery chambers. The receiver is sequentially moved under the delivery chambers and moving the moveable plate between different positions for permitting the delivery chambers to sequentially deliver ink from its associated microchannel into its associated delivery chamber where it is transferred to the receiver to control the amount of ink delivered to form pixels on the receiver at a plurality of locations; and a computer for controlling the microfluidic pumps and the movement of the moveable shutter plate for causing the correct amount of ink to be conveyed into each delivery chamber for transfer to the receiver to form a colored pixel.

Description

FIELD OF THE INVENTION

The present invention relates to printing high quality images by microfluidic pumping of inks into receivers such as paper.

BACKGROUND OF THE INVENTION

Microfluidic pumping and dispensing of liquid chemical reagents is the subject of three U.S. Pat. Nos. 5,585,069; 5,593,838; and 5,603,351, all assigned to the David Sarnoff Research Center, Inc.. The system uses an array of micron sized reservoirs, with connecting microchannels and reaction cells etched into a substrate. Electrokinetic pumps comprising electrically activated electrodes within the capillary microchannels provide the propulsive forces to move the liquid reagents within the system. The electrokinetic pump, which is also known as an electroosmotic pump, has been disclosed by Dasgupta et al., see "Electroosmosis: A Reliable Fluid Propulsion System for Flow Injection Analysis", Anal. Chem. 66, pp 1792-1798 (1994). The chemical reagent solutions are pumped from a reservoir, mixed in controlled amounts, and them pumped into a bottom array of reaction cells. The array may be decoupled from the assembly and removed for incubation or analysis. When used as a printing device, the chemical reagent solutions are replaced by dispersions of cyan, magenta, and yellow pigment, and the array of reaction cells may be considered a viewable display of picture elements, or pixels, comprising mixtures of pigments having the hue of the pixel in the original scene. When contacted with paper, the capillary force of the paper fibers pulls the dye from the cells and holds it in the paper, thus producing a paper print, or photograph, of the original scene. One problem with this kind of printer is the accurate control of the print density. The problem comes about because the capillary force of the paper fibers is strong enough to remove all the ink from the device, draining it empty. If the paper is not removed from contact with the ink cells at the correct time, the print density will be too high or too low. Moreover, the correct paper contact time varies with the ambient temperature, making the timing problem more difficult One solution to this problem is given in the above mentioned copending U.S. patent application Ser. No. 08/868,416, where a special paper is employed which will absorb only a limited amount of ink. Nevertheless, it would be cheaper if plain paper can be employed for this kind of printing. Another solution to this problem is given in the above mentioned copending U.S. patent application Ser. No. 08/903,747, wherein an array of microvalves, each individually addressed, controls the flow of ink to the paper. The complexity of individually addressed valves leads to a high cost printing apparatus. In would be cheaper and easier to manufacture a device that did not have to many individually addressed valves. A problem with microfluidic ink printers is that they can leak ink when not in the printing condition, and further that the ink can be contaminated by the outside environment causing degradation in properties.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a microfluidic printer which can rapidly print a high quality image on receivers such as plain paper without ink leakage or ink contamination by the environment.

Another object of this invention is to provide a compact, low power, portable printer.

These objects are achieved by a microfluidic printing apparatus for printing ink pixels on a receiver comprising:

a) at least one ink reservoir;

b) a moveable plate having a plurality of delivery chambers in an array each for forming an ink pixel, and a plurality of microchannels connecting the reservoir to a delivery chamber;

c) a plurality of microfluidic pumps each being associated with a single microchannel for supplying ink to particular delivery chambers;

d) means for moving the receiver sequentially under the delivery chambers and moving the moveable plate between different positions for permitting the delivery chambers to sequentially deliver ink from its associated microchannel into its associated delivery chamber where it is transferred to the receiver to control the amount of ink delivered to form pixels on the receiver at a plurality of locations; and

e) control means for controlling the microfluidic pumps and the movement of the moveable shutter plate for causing the correct amount of ink to be conveyed into each delivery chamber for transfer to the receiver to form a colored pixel.

ADVANTAGES

A feature of the present invention is that it provides an apparatus which produces high quality prints of the correct density on plain paper.

A further feature of the invention is that the apparatus, in accordance with the present invention, prevents the outside environment from acting on inks to degrade their properties.

Another feature of the invention is that the printer is low power, compact and portable.

Another feature of the invention is that the printing process is fast, because all the pixels are printing simultaneously.

Another feature of the invention is that the printer is of low cost to manufacture, because a single actuator serves to actuate all the pixel valves simultaneously.

Another feature of the invention is that more than one color ink is printed with a single printing nozzle, thus simplifying the manufacture of the apparatus.

Another feature of the invention is that the printing nozzles can be incremented in fractional amounts of the nozzle spacing, thus improving the resolution of the final print.

Another feature of the invention is that printed pixels can be allowed to dry before adjacent pixels are printed, thus preventing wet ink bleeding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial schematic showing a microfluidic printing system for printing a digital image on a reflective receiver;

FIG. 2 is a top view of a pattern of the color pixels which can be produced by apparatus in accordance with the present invention;

FIG. 3 is a top view of a second pattern of the color pixels which can be produced by apparatus in accordance with the present invention;

FIG. 4 is a cross-sectional view taken along the lines 4--4 of the microfluidic printing apparatus in FIG. 3;

FIG. 5 is another cross-section taken along the lines 5--5 of the microfluidic printing apparatus in FIG. 3;

FIG. 6 is an enlarged view of the circled portion of FIG. 4;

FIG. 7 is a top view of the micronozzles shown in FIG. 6;

FIG. 8 is a top view of the microchannel and showing conducting circuit connections in FIG. 6;

FIG. 9 is a top view of the moveable shutter showing a printing pattern wherein a single nozzle prints a close packed high resolution series of pixels;

FIG. 10 is a cross sectional view taken along the lines 10--10 of FIG. 9, showing how a first line of pixels are printed;

FIG. 11 is a cross sectional view taken along the lines 10--10 of FIG. 9, showing how a second line of pixels are printed; and

FIG. 12 is a cross sectional view taken along the lines 10--10 of FIG. 9, showing how a third line of pixels are printed.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described in relation to a microfluidic printing apparatus which can print computer generated images, graphic images, line art, text images and the like, as well as continuous tone images.

Referring to FIG. 1, a schematic diagram is shown of a printing apparatus 8 in accordance with the present invention. Reservoirs 10, 20, 30, and 40 are respectively provided for holding colorless ink, cyan ink, magenta ink, and yellow ink An optional reservoir 80 is shown for black ink. Microchannel capillaries 50 respectively connected to each of the reservoirs conduct ink from the corresponding reservoir to an array of ink mixing chambers 60. In the present invention, the ink mixing chambers 60 deliver the inks directly to a receiver; however, other types of ink delivery arrangements can be used such as microfluidic channels, and so when the word chamber is used, it will be understood to include those arrangements. The colored inks are delivered to ink mixing chambers 60 by electrokinetic pumps 70. The amount of each color ink is controlled by microcomputer 110 according to the input digital image. For clarity of illustration, only one set of electrokinetic pumps is shown for the colorless ink channel. Similar pumps are used for the other color channels, but these are omitted from the figure for clarity. Finally, a reflective receiver 100 is transported by a transport mechanism 115 to come in contact with the microfluidic printing apparatus. The receiver 100 receives the ink and thereby produces the print. Receivers may include common bond paper, made from wood fibers, as well as synthetic papers made from polymeric fibers. In addition the receiver can be of non-fibrous construction, provided the receiver will absorb and hold the ink used in the printer.

FIG. 2 depicts a top view of an arrangement of mixing chambers 60 shown in FIG. 1. Each ink mixing chamber 60 is capable of producing a mixed ink having any color saturation, hue and lightness within the color gamut provided by the set of cyan, magenta, yellow, and colorless inks used in the apparatus.

The inks used in this invention are dispersions of colorants in common solvents. Examples of such inks may be found is U.S. Pat. No. 5,611,847 by Gustina, Santilli, and Bugner. Inks may also be found in the following commonly assigned U.S. patent application Ser. No. 08/699,955 filed Aug. 20, 1996; U.S. patent application Ser. No. 08/699,962 filed Aug. 20, 1996; and U.S. patent application Ser. No. 08/699,963 filed Aug. 20, 1996 by McInerney, Oldfield, Bugner, Bermel, and Santilli, and in U.S. patent application Ser. No. 08/790,131 filed Jan. 29, 1997 by Bishop, Simons, and Brick; and in U.S. patent application Ser. No. 08/64,379 filed Dec. 13, 1996 by Martin. In a preferred embodiment of the invention the solvent is water. Colorants such as the Ciba Geigy Unisperse Rubine 4BA-PA, Unisperse Yellow RT-PA, and Unisperse Blue GT-PA are also preferred embodiments of the invention. The colorless ink of this invention is the solvent for the colored inks in the most preferred embodiment of the invention.

The microchannel capillaries, ink pixel mixing chambers and microfluidic pumps are more fully described in the references listed above.

FIG. 3 illustrates the arrangement of a second pattern of color pixels in the present invention. The ink mixing chambers 60 are fed by four microchannels of different colors; cyan ink orifice 200; magenta ink orifice 202; yellow ink orifice 204; and black ink orifice 206. Each orifice is connected only to the respective colored ink reservoir and to the colorless ink reservoir 10. For example, the cyan ink orifice 200 is connected to the cyan ink reservoir and the colorless ink reservoir so that cyan inks can be mixed to any desired lightness. When the inks are transferred to the reflective receiver 100 some of the inks can mix and blend on the receiver. Inasmuch as the inks are in distinct areas on the receiver, the size of the printed pixels should be selected to be small enough so that the human eye will integrate the color and the appearance of the image will be that of a continuous tone photographic quality image.

Cross-sections of the color pixel arrangement shown in FIG. 3 are illustrated in FIG. 4 and FIG. 5. The colored ink supplies 300, 302, 304, and 306 are fabricated in channels parallel to the printer front plate 120. The cyan, magenta, yellow and black inks are respectively delivered by colored ink supplies 300, 302, 304, and 306 into each of the colored ink mixing chambers.

A detailed view of the cross-section in FIG. 4 is illustrated in FIG. 6. The colored inks are delivered to the ink mixing chambers respectively by cyan, magenta, yellow, and black ink microchannels 400, 402, 404, and 406 (404 and 406 do not show up in the plan shown in FIG. 6, but is illustrated in FIG. 8) The colored ink microchannels 400, 402, 404, and 406 are respectively connected to the colored ink supplies 300, 302, 304, and 306 (FIGS. 4 and 5). The colorless ink is supplied to the ink mixing chamber, but is not shown in FIG. 6 for clarity of illustration.

A cross-section view of the plane containing the micronozzles in FIG. 6 is shown in FIG. 7. The cyan, magenta, yellow, and black ink micronozzles 600, 602, 604, and 606 are distributed in the same arrangement as the colored ink supply lines 300-304 and the thermination of the chambers 60 which are colored ink orifices 200-206. The column electrodes 650 are shown connected to the conducting circuit 550, which is further connected to microcomputer 110.

A cross-section view of the plane containing the microchannels in FIG. 6 is shown in FIG. 8. The color ink channels 400-406 are laid out in the spatial arrangement that corresponds to those in FIGS. 3 and 7. The lower electrodes in the electrokinetic pumps for delivering the colored inks are not shown for clarity of illustration. The row electrodes 670 are connected to lower electrodes of the electrokinetic pumps. The row electrodes 670 are shown connected to the conducting circuit 500, which is further connected to microcomputer 110.

The operation of a microfluidic printer comprises the steps of activating the electrokinetic pumps to pump the correct amount of each color ink to the mixing chamber to provide a pixel of the correct hue and intensity corresponding to the pixel of the scene being printed. The receiver is then contacted to the mixing chambers and capillary or absorption forces draw the ink from the mixing chambers to the receiver. The receiver is then removed from contact with the mixing chambers and allowed to dry.

FIG. 9 illustrates the preferred embodiment of the invention. A top view is shown of a moveable shutter plate showing an ink mixing chamber 60 which is supplied, in this case, with three colored inks through orifices 200, 202 and 204. The shaded patterns show the different printing positions the shutter plate can take as the different pixels are printed by incrementally moving both the shutter plate and the receiver. A cross sectional view through line 10--10 is shown in FIG. 10. This drawing shows the first mechanical actuator 720 for the moveable shutter plate 700 and the second mechanical actuator 725 for the receiver 100. The moveable shutter plate 700 having a single orifice 740 for each pixel area is disposed contiguously over an ink supply plate 730. Both actuators are connected to their objects by mechanical linkages 710. In FIG. 10 ink is shown moving from the yellow 204 and magenta 202 microchannels into the mixing chambers 60 where the mixture is delivered to the receiver 100. In FIG. 11, the receiver 100 with the first pixels printed on it has been incrementally moved by the distance "y", and the second set of pixels are shown being printed onto the receiver. In FIG. 12 the moveable shutter 700 has been incrementally moved to the stop position, preventing further flow of ink to the receiver.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

PARTS LIST

8 microfluidic printing system 10 colorless ink reservoir 20 cyan ink reservoir 30 magenta ink reservoir 40 yellow ink reservoir 50 microchannel capillaries 60 ink mixing chambers, or printing nozzles 70 electrokinetic pumps 80 black ink reservoir 100 receiver 110 microcomputer 115 transport mechanism 120 printer front plate 200 cyan ink orifice 202 magenta ink orifice 204 yellow ink orifice 206 black ink orifice 300 cyan ink supply 302 magenta ink supply 304 yellow ink supply 306 black ink supply 400 cyan ink microchannel 402 magenta ink microchannel 404 yellow ink microchannel 406 black ink microchannel 500 conducting circuit 550 conducting circuit 600 cyan ink micro-orifice 602 magenta ink micro-orifice 604 yellow ink micro-orifice 606 black ink micro-orifice 650 column electrodes 670 row electrodes 700 moveable shutter plate 710 mechanical linkage 720 shutter actuator 725 receiver actuator 730 ink supply plate

Claims

1. A microfluidic printing apparatus for printing ink pixels on a receiver comprising:

a) at least one ink reservoir;

b) a moveable shutter plate having a plurality of delivery chambers in an array each for forming an ink pixel, and a plurality of microchannels connecting said at least one ink reservoir to said plurality of delivery chambers;

c) a plurality of microfluidic pumps each being associated with a single microchannel of said plurality of microchannels for supplying ink to particular delivery chambers of said plurality of delivery chambers;

d) means for moving the receiver in image transfer relationship with said plurality of delivery chambers and moving the moveable shutter plate between different positions for permitting said delivery chambers to sequentially deliver ink from its associated microchannel of said plurality of microchannels into its associated delivery chamber of said plurality of delivery chambers where it is transferred to the receiver to control an amount of ink delivered to form pixels on the receiver at a plurality of locations; and

e) control means for controlling said plurality of microfluidic pumps to pump the correct amount of ink and for controlling the movement of the moveable shutter plate for preventing the flow of ink after the correct amount of ink has been transferred from each delivery chamber of said plurality of delivery chambers to the receiver to form a colored pixel.

2. A microfluidic printing apparatus comprising:

a) a plurality of colored ink reservoirs;

b) a moveable shutter plate having a plurality of delivery chambers defining an array each for forming an ink pixel, and a plurality of microchannels for supplying colored ink to selected delivery chambers of said plurality of delivery chambers;

c) a plurality of micropumps each being associated with a single microchannel of said plurality of microchannels for supplying said colored ink to a particular delivery chamber of said plurality of delivery chambers;

d) means for moving the receiver in image transfer relationship with said plurality of delivery chambers and for moving the moveable shutter plate between different positions for permitting said plurality of delivery chambers to sequentially deliver said colored ink from its associated microchannel of said plurality of microchannels into its associated delivery chamber of said plurality of delivery chambers where it is transferred to the receiver to control an amount of colored ink delivered to form pixels on the receiver at a plurality of locations; and

e) control means for controlling said plurality of microfluidic pumps to pump the correct amount of ink and for controlling the movement of the moveable shutter plate for preventing the flow of ink after the correct amount of ink has been transferred from each delivery chamber of said plurality of delivery chambers to the receiver to form a colored pixel.