Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-12-28
2003-01-14
Tran, Huan (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S082000
Reexamination Certificate
active
06505921
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of digitally controlled printing devices, and in particular to continuous ink jet printers in which a liquid ink stream breaks into drops, some of which are selectively deflected.
BACKGROUND OF THE INVENTION
Traditionally, digitally controlled color printing capability is accomplished by one of two technologies. In each technology, ink is fed through channels formed in a printhead. Each channel includes a nozzle from which drops of ink are selectively extruded and deposited upon a medium. When color printing is desired, each technology typically requires independent ink supplies and separate ink delivery systems for each ink color used during printing.
The first technology, commonly referred to as “drop-on-demand” ink jet printing, provides ink drops 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 drop 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 drops, 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 drop 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 drop 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 drop to be expelled. The most commonly produced piezoelectric materials are ceramics, such as lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate.
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” ink jet printing, uses a pressurized ink source which produces a continuous stream of ink drops. 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 drops. The ink drops 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 drops are deflected into an ink capturing mechanism (catcher, interceptor, gutter, etc.) and either recycled or disposed of. When print is desired, the ink drops are not deflected and allowed to strike a print media. Alternatively, deflected ink drops may be allowed to strike the print media, while non-deflected ink drops are collected in the ink capturing mechanism.
U.S. Pat. No. 3,878,519, issued to Eaton, on Apr. 15, 1975, discloses a method and apparatus for synchronizing drop formation in a liquid stream using electrostatic deflection by a charging tunnel and deflection plates.
U.S. Pat. No. 4,346,387, issued to Hertz, on Aug. 24, 1982, discloses a method and apparatus for controlling the electric charge on drops formed by the breaking up of a pressurized liquid stream at a drop formation point located within the electric field having an electric potential gradient. Drop formation is effected at a point in the field corresponding to the desired predetermined charge to be placed on the drops at the point of their formation. In addition to charging tunnels, deflection plates are used to actually deflect drops.
U.S. Pat No. 4,638,382, issued to Drake et al., on Jan. 20, 1987, discloses a continuous ink jet printhead that utilizes constant thermal pulses to agitate ink streams admitted through a plurality of nozzles in order to break up the ink streams into drops at a fixed distance from the nozzles. At this point, the drops are individually charged by a charging electrode and then deflected using deflection plates positioned the drop path.
As 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.
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 drops through the use of transducers. The lengths of the filaments before they break up into ink drops 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 drops more than it affects the trajectories of the ink drops themselves. By controlling the lengths of the filaments, the trajectories of the ink drops can be controlled, or switched from one path to another. As such, some ink drops may be directed into a catcher while allowing other ink drops to be applied to a receiving member.
While this method does not rely on electrostatic means to affect the trajectory of drops it does rely on the precise control of the break off points of the filaments and the placement of the air flow intermediate to these break off points. Such a system is difficult to control and to manufacture. Furthermore, the physical separation or amount of discrimination between the two drop paths is small further adding to the difficulty of control and manufacture.
U.S. Pat. No. 4,190,844, issued to Taylor, on Feb. 26, 1980, discloses a continuous ink jet printer having a first pneumatic deflector for deflecting non-printed ink drops to a catcher and a second pneumatic deflector for oscillating printed ink drops. A printhead supplies a filament of working fluid that breaks into individual ink drops. The ink drops are then selectively deflected by a first pneumatic deflector, a second pneumatic deflector, or both. The first pneumatic deflector is an “on/off” or an “open/closed” type having a diaphram that either opens or closes a nozzle depending on one of two distinct electrical signals received from a central control unit. This determines whether the ink drop is to be printed or non-printed. The second pneumatic deflector is a continuous type having a diaphram that varies the amount a nozzle is open depending on a varying electrical sig
Chwalek James M.
Delametter Christopher N.
Jeanmaire David L.
Eastman Kodak Company
Tran Huan
Zimmerli William R.
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