Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-09-07
2003-02-04
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S090000
Reexamination Certificate
active
06513918
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 droplets, some of which are selectively collected by a catcher and prevented from reaching a receiver while other droplets are permitted to reach a recording surface.
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 utilizes 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, which issued to Eaton on Apr. 15, 1975, discloses a method and apparatus for synchronizing droplet formation in a liquid stream using electrostatic deflection by a charging tunnel and deflection plates. The function of a deflection charge plate and its associated catcher in a continuous jet printer is well known, being described in U.S. Pat. No. 4,107,699 which issued to Kenworthy on Aug. 15, 1977. The catcher may be an integral part of systems which serve multiple functions, including: blocking unwanted ink droplets, collecting and removing unwanted ink droplets, measuring drop charge levels, recycling ink, and solving start-up and shut-down problems.
Individual ink droplets 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 droplets toward and onto the surface of the catcher. The droplets accumulate on the surface of the catcher until they are overcome by gravitational forces that cause the accumulated droplets to travel toward a collection area. 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, both disclose ink jet catcher assemblies of this type. However, the disadvantage of this type of catcher is that when ink strikes the surface of the catcher the force of the drop impact causes the ink to splatter and/or mist. Ink splatter and mist creates unwanted artifacts on the printed media that reduces image quality and the splatter and mist contaminate other components in the printer.
U.S. Pat. No. 4,757,328, which issued to Braun et al. on Jul. 12, 1988, illustrates an assembly of a catcher that minimizes splattering and misting. However, this type of catcher affects print quality in other ways. The need to create an electric charge on the catcher surface complicates the construction of the catchers and it requires more components. This complicated catcher structure requires large spatial volumes between the printhead and the media, increasing the ink drop trajectory distance. Increasing the distance of the drop trajectory decreases drop placement accuracy and affects the print image quality. There is a need to minimize the distance the drop must travel before striking the print media in order to insure high quality images.
U.S. Pat. No. 4,460,903, which issued to Guenther et al. on Jul. 17, 1994, also illustrates a catcher assembly that minimizes splattering and misting. However, as the ink drops first strike and collect on a hard surface of the catcher, the potential for splattering and misting still exists. Additionally, ink drops have built up on the surface of the catcher could be “flung” onto the receiving media by the movement of the printhead.
Continuous ink jet printheads, such as those shown in the Fagerquist patent and the Stephens patent, may incorporate a screen into the catcher to assist with ink fluid removal. Additionally, the Stephens patent includes a thick mesh insert that prevents the fine mesh screen from collapsing during assembly of the catcher. However, the thick mesh insert does not improve fluid removal. Additionally, these printheads experience the misting and splattering disadvantage discussed above.
Scanning type ink jet printheads, such as those shown in the Stephens patent, the Fagerquist patent, and the Braun et al. patent, experience acceleration forces that “fling” onto the media ink that has built up on the catcher. In order to minimize the amount of ink flung onto the media, a vacuum is commonly applied at one end of an ink removal channel to assist in removing the ink build up. However, air turbulence created by the vacuum decreases drop placement accuracy and adversely affects the print quality image.
Additionally, ink that has built up on catcher surfaces can become contaminated with paper dust, dirt, debris, etc., due to the operating environment of the catcher. Contaminated ink must be cleaned before the ink can be reused, adding to the overall cost and expense of an ink jet system. As the catcher is positioned in close proximity to the media, portions of the catcher are exposed to paper dust, dirt, debris, etc., that is easily collected on portions of the catcher, especially portions having ink buildup, causing the catcher to become clogged. When this happens, the catcher must be thoroughly cleaned prior to operating the ink jet system.
It can be seen that there is a need to provide a simply constructed catcher that reduces ink splattering and misting, increases fluid removal without affecting ink drop trajectory, and minimizes clogging of the catcher due to exposure to environmental debris such as paper dust.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a catcher that minimizes the distance that a drop must travel before striking the print media in order to insure high quality images.
It is another object of the present invention to provide a catcher of simple construction.
It is still another object of the present invention to provide a catcher that reduces ink splattering and misting.
It is still another object of the present invention to provide a catcher that reduces ink contamination, printhead maintenance, and printhead cleaning.
It is still another object of the present invention to provide a catcher that increases fluid removal without affecting ink drop trajectory.
It is still another object of the present invention to minimize clogging of the catcher due to exposure to environmental debris such as paper dust.
According to a feature of the present invention, an ink drop catcher assembly includes a housing defining a fluid return channel. At least a portion of the surface of the channel has a groove substantially parallel to the fluid return channel. A screen at least partially extends from the housing to collect non-printed ink drops. The screen is in fluid communication with the groove, thereby improving ink drop flow between the screen and the fluid return channel.
According to another aspect of the present invention, the housing of the ink drop catcher may include a screen support with the screen being at least partially positioned about the screen support.
According to another aspect of the present invention, the screen support includes a surface. At least a portion of the surface has a groove substantially parallel to the fluid return channel, the groove being in fluid communication with the screen thereby improving ink drop flow between the screen and the fluid return channel.
According to another aspect of the present invention, a printer includes a printhead having a printed ink drop path and a non-printed ink drop path. The
Faisst Charles F.
Wojcik Timothy J.
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