Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-03-24
2001-08-14
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S065000, C347S094000
Reexamination Certificate
active
06273553
ABSTRACT:
REFERENCE TO A MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains generally to liquid injectors, and more particularly to an apparatus and method for ejecting liquid from a microdevice.
2. Description of the Background Art
Liquid droplet injectors are widely used for printing in inkjet printers. Liquid droplet injectors, however, can also be used in a multitude of other potential applications, such as fuel injection systems, cell sorting, drug delivery systems, direct print lithography, and micro jet propulsion systems, to name a few. Common to all these applications, a reliable and low-cost liquid droplet injector which can supply high quality droplets with high frequency and high spatial resolution, is highly desirable.
Only several devices have the ability to eject liquid droplets individually and with uniform droplet size. Among the liquid droplet injection systems presently known and used, injection by a thermally driven bubble has been most successful of such devices due to its simplicity and relatively low cost.
Thermally driven bubble systems, which are also known as bubble jet systems, suffer from cross talk and satellite droplets. The bubble jet system uses a current pulse to heat an electrode to boil liquid in a chamber. As the liquid boils, a bubble forms in the liquid and expands, functioning as a pump to eject a column of liquid from the chamber through an orifice, which forms into droplets. When the current pulse is terminated, the bubble collapses and liquid refills the chamber by capillary force. The performance of such a system can be measured by the ejection speed and direction, size of droplets, maximum ejection frequency, cross talk between adjacent chambers, overshoots and meniscus oscillation during liquid refilling, and the emergence of satellite droplets. During printing, satellite droplets degrade image sharpness, and in precise liquid control, they reduce the accuracy of flow estimation. Cross talk occurs when bubble jet injectors are placed in arrays with close pitch, and droplets eject from adjacent nozzles.
Most thermal bubble jet systems place a heater at the bottom of the chamber, which loses significant energy to the substrate material. Additionally, bonding is typically used to attach the nozzle plate to its heater plate, which limits nozzle spatial resolution due to the assembly tolerance required. Moreover, the bonding procedure may not be compatible with IC precess, which could be important if the integration of microinjector array with controlling circuit is desired to reduce wiring and to ensure compact packaging.
To solve cross talk and overshoot problems, it has typically been the practice to increase the channel length or adding chamber neck to increase fluid impedance between the chamber and reservoir. However, these practices slow the refilling of liquid into the chamber and greatly reduce the maximum injection frequency of the device.
The most troublesome problem with existing inkjet systems is satellite droplet because it causes image blurring. The satellite droplets that trail the main droplet hit the paper surface at slightly different locations than the main one as the printhead and paper are in relative motion. There is no known effective means or method to solve the satellite droplet problem that is readily available and economical.
Accordingly, there is a need for a liquid droplet injection system that minimizes cross talk without slowing down the liquid refilling rate, thereby maintaining a high frequency response while eliminating satellite droplets, all without adding complexity to the design and manufacturing. The present invention satisfies thess needs, as well as others, and generally overcomes the deficiencies found in the background art.
BRIEF SUMMARY OF THE INVENTION
The present invention pertains to an apparatus and method for forming a bubble within a chamber of a microinjector to function as a valve mechanism between the chamber and manifold, thereby providing high resistance to liquid exiting the chamber to the manifold during fluid ejection through the orifice and also providing a low resistance to refilling of liquid into the chamber after ejection of fluid and collapse of the bubble.
In general terms, the apparatus of the present invention generally comprises a microinjector having a chamber and a manifold in flow communication therethrough, an orifice in fluid communication with the chamber, at least one means for forming a bubble between the chamber and manifold and a means to pressurize the chamber
When the bubble is formed at the entrance of the chamber, the flow of liquid out the chamber to the manifold is restricted. The pressurization means, which pressurizes the chamber after formation of the bubble, increases chamber pressure such that fluid is forced out the orifice. After ejection of fluid through the orifice, the bubble collapses and allows liquid to rapidly refill the chamber.
As the chamber is pressurized while the bubble is blocking the chamber from the manifold and adjacent chambers, the cross talk problem is minimized as well.
In the preferred embodiment of the invention, the means for forming the bubble comprises a first heater disposed adjacent the chamber. The pressurization means comprises a second heater capable of forming a second bubble within the chamber. The heaters are disposed adjacent the orifice and comprise an electrode connected in series and having differing resistances due to variations in electrode width. The first heater has a narrower electrode than the second heater, thereby causing the first bubble to form before the second bubble, even when a common electrical signal is applied therethrough.
As the first and second bubble expand, they approach each other and ultimately coalesce, thereby distinctly cutting off the flow of liquid through the orifice and resulting in elimination or significant reduction of satellite droplets.
An object of the present invention is to provide a microinjector apparatus that eliminates satellite droplets.
Another object of the present invention is to provide a microinjector apparatus that minimizes cross talk.
Still another object of the present invention is to provide a microinjector apparatus that allows for the rapid refill of liquid into the chamber after fluid ejection.
Still another object of the present invention is to provide a method for ejecting liquid from a microinjector chamber that minimizes satellite droplets.
Still another object of the present invention is to provide a method for ejecting fluid from a microinjector chamber that minimizes cross talk.
Still another object of the present invention is to provide a method for ejecting fluid from a microinjector chamber that allows for the rapid refill of liquid into the chamber after fluid ejection.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.
REFERENCES:
patent: 4580149 (1986-04-01), Domoto et al.
patent: 5053787 (1991-10-01), Terasawa
patent: 5479196 (1995-12-01), Inada
patent: 5841452 (1998-11-01), Silverbrook
Ho Chih-Ming
Kim Chang-Jin
Tseng Fan-Gang
Barlow John
Chan Law Group LC
Stephen Juanita
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