Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-12-28
2003-01-21
Tran, Huan (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S082000
Reexamination Certificate
active
06508542
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
Ink jet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because, e.g., of its non-impact, low-noise characteristics, its use of plain paper and its avoidance of toner transfers and fixing. Ink jet printing mechanisms can be categorized as either continuous ink jet or drop on demand ink jet.
Conventional continuous ink jet printheads utilize electrostatic charging tunnels that are placed close to the point where the drops are formed in a stream. In this manner individual drops may be charged. The charged drops may be deflected downstream by the presence of deflector plates that have a large potential difference between them. A catcher (sometimes referred to as a “gutter”, an “interceptor”, or a “collector”) may be used to intercept either the charged or the uncharged drops, while the non-intercepted drops are free to strike a receiver or recording medium. U.S. Pat. No. 3,878,519, issued to Eaton on Apr. 15, 1975, and U.S. Pat. No. 4,050,077, issued to Yamada et al. on Sep. 20, 1977, disclose devices for synchronizing drop formation in a liquid stream using electrostatic deflection by a charging tunnel and deflection plates. These devices require large spatial distances (sometimes referred to as “ink drop trajectory distance”) between the printhead and the recording medium because the charging tunnel and deflection plates must be accommodated for within the device. As the amount of ink drop deflection is small, the ink drops need to travel over these large spatial distances in order to deflect enough to strike the recording medium (or the catcher). Ink drop placement accuracy is adversely affected when ink drops travel over large spatial distances because there is a greater risk of the drops being interfered within a manner that alters the drops' path.
Alternatively, continuous ink jet printers may incorporate the charging tunnel and deflection plates in other printer components. U.S. Pat. No. 5,105,205, issued to Fagerquist on Apr. 14, 1992, and U.S. Pat. No. 5,469,202, issued to Stephens on Nov. 21, 1995, disclose devices of this type. Individual ink drops receive an electrical charge. An opposite electrical charge is applied to the surface of a catcher parallel to the normal trajectory of the ink stream. The opposite polarities create an attraction force that deflects the drops toward and onto the surface of the catcher. However, the amount of deflection is small. This configuration also requires large spatial distances between the printhead and the recording medium. This adversely affects ink drop trajectory distance as discussed above. As such, there is a need to minimize the distance an ink drop must travel before striking the print media in order to insure high quality images.
Referring to
FIG. 2A
, a printhead
200
includes a pressurized ink source
202
and a selection device
204
. Printhead
200
is operable to form selected ink drops
206
and non-selected ink drops
208
. Selected ink drops
206
flow along a selected ink path
210
ultimately striking recording medium
212
, while nonselected ink drops
208
flow along a non-selected ink path
214
ultimately striking a catcher
216
. Non-selected ink drops
208
are recycled or disposed of through an ink removal channel
218
formed in catcher
216
. U.S. Pat. No. 6,079,821, issued to Chwalek et al. on Jun. 27, 2000 discloses an ink jet printer of this type.
While the ink jet printer disclosed in Chwalek et al. works extremely well for its intended purpose, ink drop path divergence (shown generally at
220
), also commonly referred to as ink drop divergence angle (shown generally at angle A) or ink drop discrimination, between selected ink drops
206
and non-selected ink drops
208
is small. This, combined with other printhead environmental operating factors (inconsistent ink drop deflection
221
due to ink build up around heater
204
, etc.), increases the potential for ink
222
to build up on catcher
216
. As ink
222
builds up on catcher
216
, selected ink drops
206
flowing along selected ink path
210
may be interfered with resulting in reduced image quality. As such, there is a need to increase ink drop path divergence in order to insure high quality images.
Continuous ink jet printers (page width, scanning, etc.) using electrostatic means to affect ink drop trajectory also experience ink build up on catcher surfaces. Ink that has built up on the catcher can become contaminated with paper dust, dirt, debris, etc., due to the operating environment of the printer. This causes clogging of the catcher. When this happens, the catcher must be thoroughly cleaned prior to operating the ink jet system. Additionally, contaminated ink must be cleaned before the ink can be reused, adding to the overall cost and expense of an ink jet system. As such, there is a need to increase ink drop path divergence in order to reduce printhead maintenance and ink cleaning.
U.S. Pat. No. 3,709,432, which issued to Robertson, discloses a method and apparatus for stimulating a filament of working fluid causing the working fluid to break up into uniformly spaced drops through the use of transducers. The lengths of the filaments before they break up into 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 drops themselves. By controlling the lengths of the filaments, the trajectories of the drops can be controlled, or switched from one path to another. As such, some drops may be directed into a catcher while allowing other 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 manufacture. Furthermore, the physical separation or amount of discrimination between the two drop paths is small increasing the difficulty of controlling printed and non-printed ink drops resulting in at least the ink drop build up problem discussed above.
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. 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 signal received the central control unit. This oscillates printed ink drops so that characters may be printed one character at a time. If only the first pneumatic deflector is used, characters are created one line at a time, being built up by repeated traverses of the printhead.
While this method does not rely on electrostatic means to affect the trajectory of drops it does rely on the precise control and timing of the first (“open/closed”) pneumatic deflector to create printed and non-printed ink drops. Such a system is difficult to manufacture and accurately control resulting in at least the ink drop build up discussed above. Furthermore, the phy
Delametter Christopher N.
Griffin Todd R.
Sales Milton S.
Sharma Ravi
Eastman Kodak Company
Tran Huan
Zimmerli William R.
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