Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-03-13
2003-02-11
Nguyen, Lamson (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S075000
Reexamination Certificate
active
06517197
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of digitally controlled printing devices, and in particular to continuous inkjet printers in which a liquid ink stream breaks into droplets, some of which are selectively deflected. Either the deflected droplets or the non-deflected droplets can be printed on a print medium with the droplets having corrected print locations.
BACKGROUND OF THE INVENTION
Traditionally, digitally controlled color printing capability is accomplished by one of two technologies. Both require independent ink supplies for each of the colors of ink provided. Ink is fed through channels formed in the printhead. Each channel includes a nozzle from which droplets of ink are selectively extruded and deposited.upon a medium. Typically, each technology requires separate ink delivery systems for each ink color used in printing. Ordinarily, the three primary subtractive colors, i.e. cyan, yellow and magenta, are used because these colors can produce, in general, up to several million perceived color combinations. In the construction of printers incorporating either technology, the printhead, typically, includes a plurality of nozzles arranged in a linear array. The printhead is typically scanned in a fast scan direction, substantially perpendicular to the row of nozzles, over a print medium. Additionally, the printhead may be stepped in a slow scan direction, substantially perpendicular to the fast scan direction, before the fast scan is repeated.
The first technology, commonly referred to as “drop-on-demand” ink jet printing, provides ink droplets for impact upon a recording surface using a pressurization actuator (thermal, piezoelectric, etc.). Selective activation of the actuator causes the formation and ejection of a flying ink droplet that crosses the space between the printhead and the print media and strikes the print media. The formation of printed images is achieved by controlling the individual formation of ink droplets, as is required to create the desired image. Typically, a slight negative pressure within each channel keeps the ink from inadvertently escaping through the nozzle, and also forms a slightly concave meniscus at the nozzle, thus helping to keep the nozzle clean.
Conventional “drop-on-demand” ink jet printers utilize a pressurization actuator to produce the ink jet droplet at orifices of a print head. Typically, one of two types of actuators are used including heat actuators and piezoelectric actuators. With heat actuators, a heater, placed at a convenient location, heats the ink causing a quantity of ink to phase change into a gaseous steam bubble that raises the internal ink pressure sufficiently for an ink droplet to be expelled. With piezoelectric actuators, an electric field is applied to a piezoelectric material possessing properties that create a mechanical stress in the material causing an ink droplet to be expelled. The most commonly produced piezoelectric materials are ceramics, such as lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate. While heat actuators and piezoelectric actuators have been long used in drop-on-demand printing, they suffer from a lack of precise control of the placement of drops on the print medium, which is a critical parameter for image quality. With heat actuators, the nozzles or heaters may become contaminated due to thermally induced decomposition of ink, thereby causing drop misplacement errors. With piezoelectric actuators, the properties of the piezoelectric material may change with use and/or failure of the ink fluid meniscus to reproducibly engage the nozzle during each drop firing cause drop misplacement errors. In either case, highly visible artifacts may be produced particularly when misplacement errors occur repeatedly on the print medium. The artifacts are most apparent when the placement errors are perpendicular to the fast scan direction because the errors are repeated in a line. This type of image artifact is well known in the inkjet printer art.
U.S. Pat. No. 4,914,522 issued to Duffield et al., on Apr. 3, 1990 discloses a drop-on-demand ink jet printer that utilizes air pressure to produce a desired color density in a printed image. Ink in a reservoir travels through a conduit and forms a meniscus at an end of an inkjet nozzle. An air nozzle, positioned so that a stream of air flows across the meniscus at the end of the ink nozzle, causes the ink to be extracted from the nozzle and atomized into a fine spray. The stream of air is applied at a constant pressure through a conduit to a control valve. The valve is opened and closed by the action of a piezoelectric actuator. When a voltage is applied to the valve, the valve opens to permit air to flow through the air nozzle. When the voltage is removed, the valve closes and no air flows through the air nozzle. As such, the ink dot size on the image remains constant while the desired color density of the ink dot is varied depending on the pulse width of the air stream.
The second technology, commonly referred to as “continuous stream” or “continuous” inkjet printing, uses a pressurized ink source which produces a continuous stream of ink droplets. Conventional continuous ink jet printers utilize electrostatic charging devices that are placed close to the point where a filament of working fluid breaks into individual ink droplets. The ink droplets are electrically charged and then directed to an appropriate location by deflection electrodes having a large potential difference. When no print is desired, the ink droplets are deflected into an ink capturing mechanism (catcher, interceptor, gutter, etc.) and either recycled or disposed of. When print is desired, the ink droplets are not deflected and allowed to strike a print media. Alternatively, deflected ink droplets may be allowed to strike the print media, while non-deflected ink droplets are collected in the ink capturing mechanism.
Typically, continuous inkjet printing devices are faster than droplet on demand devices. However, each color printed requires an individual droplet formation, deflection, and capturing system.
Conventional continuous ink jet printers utilize electrostatic charging devices and deflector plates, they require many components and large spatial volumes in which to operate. This results in continuous ink jet printheads and printers that are complicated, have high energy requirements, are difficult to manufacture, and are difficult to control. As charged drops repel one another, drop placement accuracy suffers, particularly in a line parallel to the linear array of nozzles. The artifacts are most apparent when the placement errors are perpendicular to the fast scan direction because the errors are repeated in a line over a substantial distance on the recording medium. Examples of conventional continuous ink jet printers include U.S. Pat. No. 1,941,001, issued to Hansell, on Dec. 26, 1933; U.S. Pat. No. 3,373,437 issued to Sweet et al., on Mar. 12, 1968; U.S. Pat. No. 3,416,153, issued to Hertz et al., on Oct. 6; 1963; U.S. Pat. No. 3,878,519, issued to Eaton, on Apr. 15, 1975; and U.S. Pat. No. 4,346,387, issued to Hertz, on Aug. 24, 1982.
U.S. Pat. No. 3,709,432, issued to Robertson, on Jan. 9, 1973, discloses a method and apparatus for stimulating a filament of working fluid causing the working fluid to break up into uniformly spaced ink droplets through the use of transducers. The lengths of the filaments before they break up into ink droplets are regulated by controlling the stimulation energy supplied to the transducers, with high amplitude stimulation resulting in short filaments and low amplitudes resulting in long filaments. A flow of air is generated across the paths of the fluid at a point intermediate to the ends of the long and short filaments. The air flow affects the trajectories of the filaments before they break up into droplets more than it affects the trajectories of the ink droplets themselves. By controlling the lengths of the filaments, the trajectories of the ink droplets can be controlled, or switched
Chwalek James M.
Hawkins Gilbert A.
Jeanmaire David L.
Eastman Kodak Company
Nguyen Lamson
Zimmerli William R.
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