Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-02-12
2001-08-14
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S055000
Reexamination Certificate
active
06273552
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention generally relates to printing devices and methods, and more particularly relates to an image forming system including a print head having plurality of ink channel pistons, and method of assembling the system and print head.
BACKGROUND ART
Ink jet printing is recognized as a prominent contender in digitally controlled, electronic printing because of its non-impact, low-noise characteristics, use of plain paper and avoidance of toner transfers and fixing. For these reasons, DOD (Drop-On-Demand) inkjet printers have achieved commercial success for home and office use.
For example, U.S. Pat. No. 3,946,398, which issued to Kyser et al. in 1970, discloses a drop-on-demand ink jet printer which applies a high voltage to a piezoelectric crystal, causing the crystal to bend. As the crystal bends, pressure is applied to an ink reservoir for jetting ink drops on demand. Other types of piezoelectric drop-on-demand printers utilize piezoelectric crystals in push mode, shear mode, and squeeze mode. However, patterning of the piezoelectric crystal and the complex high voltage drive circuitry necessary to drive each printer nozzle are disadvantageous to cost effective manufacturability and performance. Also, the relatively large size of the piezo transducer prevents close nozzle spacing making it difficult for this technology to be used in high resolution page width printhead design.
Great Britain Pat. No. 2,007,162, which issued to Endo et al. in 1979, discloses an electrothermal drop-on-demand ink jet printer that applies a power pulse to an electrothermal heater which is in thermal contact with water based ink in a nozzle. A small quantity of ink rapidly evaporates, forming a bubble which causes drops of ink to be ejected from small apertures along an edge of a heater substrate. This technology is known as thermal ink jet printing.
More specifically, thermal ink jet printing typically requires a heater energy of approximately 20 &mgr;J over a period of approximately 2 &mgr;sec to heat the ink to a temperature 280-400° C. to cause rapid, homogeneous formation of a bubble. Rapid bubble formation provides momentum for drop ejection. Collapse of the bubble causes a pressure pulse due to the implosion of the bubble. The high temperatures needed with this device necessitates use of special inks, complicates driver electronics, and precipitates deterioration of heater elements through kogation, which is the accumulation of ink combustion by-products that encrust the heater with debris. Such encrusted debris interferes with thermal efficiency of the heater. In addition, such encrusted debris may migrate to the ink meniscus to undesirably alter the viscous and chemical properties of the ink meniscus. Also, the 10 Watt active power consumption of each beater prevents manufacture of low cost, high speed pagewidth printheads.
An inkjet printing system is disclosed in commonly assigned U.S. patent application Ser. No. 08/621,754 filed on Mar. 22, 1996, in the name of Kia Silverbrook. The Silverbrook device provides a liquid printing system incorporating nozzles having a meniscus poised at positive pressure extending from nozzle tip. A heater surrounding the nozzle tip applies heat to the edge of the meniscus. This technique provides a drop-on-demand printing mechanism wherein the means of selecting drops to be printed produces a difference in position between selected drops and drops which are not selected. However, the difference in position is insufficient to cause ink drops to overcome surface tension and separate from the body of ink. In this regard, separation means is provided to cause separation of the selected drops from the body of ink. However, this method of selection that uses surface tension reduction requires specialized inks and the requirement of poising the meniscus at a positive pressure may cause undesirable nozzle leakage due to contamination on any single nozzle. Application of an electric field or the adjustment of receiver proximity is thereafter used to cause separation of the selected drops from the body of the ink. However, the electric field strength needed to separate the selected drop is above the value for breakdown in air so that a close spacing between nozzle and receiver is needed, but there is still the possibility of arcing. Also, causing separation of the drop using proximity mode, for which the paper receiver must be in close proximity to the orifice in order to separate the drop from the orifice, is unreliable due to the presence of relatively large dust particles typically found in an uncontrolled environment.
Another inkjet printing system is disclosed in commonly assigned U.S. patent application Ser. No. 09/017,827 filed Feb. 3, 1998, in the name of John Lebens et al. The Lebens, et al. device provides an image forming apparatus incorporating an ink jet printhead where a single transducer is used to periodically oscillate the body of ink in order to poise ink drops and form a meniscus. The Lebens device further comprises an ink drop separator associated with the transducer for lowering the surface tension of the meniscus in order to separate the meniscus from the ink body to form an ink droplet. Although the Lebens, et al. device operates satisfactorily for its intended purpose, use of the Lebens et al. device may nonetheless lead to propagation of unwanted pressure waves in an ink manifold belonging to the printhead. These unwanted pressure waves in the ink manifold can in turn lead to inadvertent ejection of drops. Therefore, it is desirable to localize the effects of the pressure to the ink cavities and their respective nozzles.
Therefore, there remains a long-felt need for an ink jet printer providing such advantages as reduced cost, increased speed, higher print quality, greater reliability, less power usage, and simplicity of construction and operation.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an image forming system and method for forming an image on a recording medium, the system including a thermo-mechanically activated DOD (Drop On Demand) printhead including a DOD print head having a plurality of ink channel pistons, and method of assembling the system and print head.
With this object in view, the invention resides in an image forming system, comprising a piston adapted to momentarily pressurize an ink body so that an ink meniscus extends from the ink body, the meniscus having a predetermined surface tension; and an ink droplet separator associated with said piston for lowering the surface tension of the meniscus while the meniscus extends from the ink body, whereby said droplet separator separates the meniscus from the ink body to form an ink droplet while the surface tension lowers.
According to an embodiment of the present invention, the system includes a printhead defining a plurality of ink channels in the print head. Each channel holds an ink body therein and terminates in a nozzle orifice. A micromachined piston is disposed in each channel for alternately pressurizing and depressurizing the ink body. An ink meniscus extends from the ink body and out the nozzle orifice while the ink body is pressurized. In addition, the ink meniscus retracts into the nozzle orifice while the ink body is depressurized. An ink droplet separator is also provided for lowering surface tension of the meniscus as the meniscus extends from the orifice. The extended meniscus severs from the ink body to form an ink droplet as the droplet separator lowers the surface tension to a predetermined value.
A feature of the present invention is the provision of a single micromachined array of pistons in fluid communication with a plurality of ink meniscis reposed at respective ones of a plurality of nozzles for pressurizing the meniscis, so that the menisci extend from the nozzles as the menisci are pressurized and retract into the nozzles as the menisci are depressurized.
Another feature of the present invention is the provision of a plurality of heaters in heat transfer communication with respective on
Hawkins Gilbert A.
Moghadam Omid A.
Barlow John
Eastman Kodak Company
Stephens Juanita
Stevens Walter S.
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