Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-01-31
2003-10-07
Tran, Huan (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C516S098000
Reexamination Certificate
active
06629750
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to inkjet printing mechanisms, and more particularly to a spittoon system having a porous material for capturing waste inkjet ink spit from an inkjet printhead during a nozzle clearing, purging or spitting operation.
An inkjet printing mechanism is a type of non-impact printing device which forms characters, symbols, graphics or other images by controllably spraying drops of ink. The mechanism typically includes a cartridge, often called a “pen,” which houses a printhead. The printhead has very small nozzles through which the ink drops are ejected. To print an image the pen is propelled back and forth across a media sheet, while the ink drops are ejected from the printhead in a controlled pattern.
Inkjet printing mechanisms may be employed in a variety of devices, such as printers, plotters, scanners, facsimile machines, copiers, and the like. There are various forms of inkjet printheads, known to those skilled in the art, including, for example, thermal inkjet printheads and piezoelectric printheads. Two earlier thermal inkjet ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, currently assigned to the present assignee, The Hewlett-Packard Company of Palo Alto, Calif. In a thermal inkjet printing system, ink flows along ink channels from a reservoir into an array of vaporization chambers. Associated with each chamber is a heating element and a nozzle. A respective heating element is energized to heat ink contained within the corresponding chamber. The corresponding nozzle forms an ejection outlet for the heated ink. As the pen moves across the media sheet, the heating elements are selectively energized causing ink drops to be expelled in a controlled pattern. The ink drops dry on the media sheet shortly after deposition to form a desired image (e.g., text, chart, graphic or other image).
It is desirable to clean and protect the printhead, so that ink does not dry on the printhead surface or clog the nozzles. Typically, a service station mechanism is included to perform such maintenance of the printhead. For storage, or during non-printing periods, the pen moves to the service station. The service station often includes a capping device which substantially seals the printhead nozzles to prevent drying and to avoid entry of contaminants. Some capping devices also facilitate a priming operation. For example a pumping unit is connected to the capping device applying a vacuum force onto the printhead. The force pulls the ink through the printheads channels and vaporization chambers:and is referred to as ink priming. Priming is desirable so the vaporization chambers are filled when printing is desired. Depriming, where the ink is sucked back along the channels into the ink reservoir, is undesirable.
Another maintenance operation is referred to as “spitting.” During a spitting operation, a number of “waste” ink drops are spit from each nozzle into a “spittoon” reservoir portion of the service station. The spitting is performed periodically to clear the nozzles and avoid clogging.
Still another maintenance operation is referred to as “wiping.” During a wiping operation, an elastomeric wiper wipes the printhead surface to remove ink residue, as well as paper, dust or other debris that has collected on the printhead. The wiping action is achieved through the relative motion of the printhead and wiper for example, by moving the printhead across the wiper, by moving the wiper across the printhead, or by moving both the printhead and the wiper. A wiping operation typically is performed after spitting, after uncapping, and occasionally interspersed among a print job.
As the inkjet industry investigates new printhead designs, the tendency is toward using permanent or semi-permanent printheads in what is known in the industry as an “off-axis” system. In an off-axis system only a small ink supply is carried across the printzone, with this supply being replenished through tubing that delivers ink from an off-axis stationary reservoir placed at a remote stationary location within the inkjet system. As a result, narrower printheads are achieved allowing for a narrower printing mechanism and a narrower system “footprint.” Also, associated with the narrower printhead are a smaller, lighter carriage and bearings. In turn a smaller or lighter drive motor is implemented leading to a more economical system for the consumer.
To improve the clarity and contrast of the printed image, advances are being sought for improving the ink itself. To provide quicker, more waterfast printing with darker blacks and more vivid colors, pigment-based inks have been developed. These pigment-based inks have a higher solid content than the earlier dye-based inks, which results in a higher optical density for the new inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to form high quality images on readily available and economical plain paper, as well as on recently developed specialty coated papers, transparencies, fabric and other media. However, the combination of small nozzles and quick-drying ink leaves the printheads susceptible to clogging, not only from dried ink or minute dust particles, such as paper fibers, but also from the solids within the new inks themselves. Accordingly, frequent spitting operations are performed before, during and after a print job.
Other challenges from the new inks include “stalagmite-type” buildups of the ink in the spittoon and increased aerosol exposure. When spitting the new pigment-based inks onto the flat bottom of a conventional spittoon, over a period of time, the rapidly solidifying waste ink grows into a stalagmite of ink residue. Eventually, in prototype units, the ink residue would grow to contact the printhead, which then either interfered with printhead movement, hindered print quality, or clogged inkjet nozzles.
The frequent spitting operations performed when using the pigment-based inks also results in an aerosol of small minute ink particles which become detached from the main ink droplet and begin floating through the system. The aerosol is carried by air currents landing at undesirable locations. Often the aerosol landed on critical components resulting in fogging of the optical encoder, or in fouling portions of the casing and carriage where an operator would touch when installing a new pen. Sometimes the aerosol enters the media path and is picked up by the next media sheet, leading to print quality defects.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a spittoon system is provided for receiving ink residue spit from an inkjet printhead in an inkjet printing mechanism. The spittoon system includes a storage container having a chamber, and an aerogel foam within the chamber for absorbing the received ink residue.
REFERENCES:
patent: 4901094 (1990-02-01), Iwagami et al.
patent: 5157421 (1992-10-01), Kitahara
Hewlett -Packard Development Company, L.P.
Tran Huan
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