Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-02-01
2003-02-18
Hsieh, Shih-wen (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S029000, C347S033000
Reexamination Certificate
active
06520619
ABSTRACT:
BACKGROUND OF THE INVENTION
Inkjet printing mechanisms may be used in a variety of different products, such as plotters, facsimile machines and inkjet printers, to print images using a colorant, referred to generally herein as “ink.” These inkjet printing mechanisms use inkjet cartridges, often called “pens,” to shoot drops of ink onto a page or sheet of print media. Some inkjet print mechanisms carry an ink cartridge with a full supply of ink back and forth across the sheet. Other inkjet print mechanisms, known as “off-axis” systems, propel only a small ink supply with the printhead carriage across the printzone, and store the main ink supply in a stationary reservoir, which is located “off-axis” from the path of printhead travel. Typically, a flexible conduit or tubing is used to convey the ink from the off-axis main reservoir to the printhead cartridge. In multi-color cartridges, several printheads and reservoirs are combined into a single unit, with each reservoir/printhead combination for a given color also being referred to herein as a “pen.”
Each pen has a printhead formed with very small nozzles through which the ink drops are fired. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett-Packard Company.
To improve the clarity and contrast of the printed image, recent research has focused on 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.
Indeed, keeping the nozzle face plate clean for cartridges using pigment based inks has proven quite challenging. In the past, multiple inkjet printheads were wiped simultaneously, all at the same speed, which was fine when all the cartridges contained the same type (albeit different colors) of ink. However, these pigment based inks are less viscous than the dye based inks, so the pigment based inks require a slower wiping speed than that previously needed for dye based inks. Yet, there is a lower limit to the wiping speed because too slow a wipe wicks excessive amounts of ink from the dye based pens. This excess dye based ink eventually builds-up a residue on the wiper, leading to less effective wiping in the future, as well as other problems. For instance, excess residue around the wipers may lead to ink build-up around the service station, which could contaminate the caps. Printhead cap contamination may lead to shorter cartridge life because ineffective capping may induce failures in the printhead.
Actually, a scrubbing type of wiping routine is preferred to clean the tar-like pigment ink residue from the printheads. If a faster wipe was used to accommodate the dye based inks, the wiper for the pigment based ink is prevented from making full contact with the residue. Instead, the wiper skips over bumps formed from the tar-like pigment based ink residue in a jerking or stuttering type of motion, which fails to remove the residue from the printhead. In some cases, during this faster wiping stroke the wiper for the pigment based ink flexed and wiped over the tar-like residue, which smeared the ink over the orifice plate rather than removing it. Thus, any compromise in attempting to accommodate the wiping needs of one pen was at the sacrifice of meeting the needs of the other type of pen.
For storage, or during non-printing periods, the service stations usually include a capping system which hermetically seals the printhead nozzles from contaminants and drying. Some caps are also designed to facilitate priming, such as by being connected to a pumping unit or other mechanism that draws a vacuum on the printhead. During operation, clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a process known as “spitting,” with the waste ink being collected in a “spittoon” reservoir portion of the service station.
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” printer. Recent breakthroughs in technology have given hope to developing a printhead with a 25 mm swath height (about one inch high), which is double the height previously obtainable, and future developments may bring about even wider swath printheads. While there are a variety of advantages associated with these off-axis printing systems, the possibility of a wider swath height brings on other problems which have not previously been encountered, such as how to provide a uniformly adequate seal when capping the longer printhead, and how to seal the longer printhead without de-priming the nozzles.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a capping system is provided for sealing an inkjet printhead in an inkjet printing mechanism. The capping system includes a base defining a cam surface, and a sled having a cam follower which engages the cam surface for movement between a rest position and a sealing position. A cap lip is supported by the sled and configured to seal the printhead when the sled is in the sealing position. The capping system also has an activation wall extending from the cap sled beyond the cap lip to engage a portion of the printhead, and to move the sled from the rest position to the sealing position through linear motion of the base while the printhead remains stationary.
According to a further aspect of the invention, an inkjet printing mechanism is provided as including the capping system described above.
According to a further aspect of the invention, a capping system is provided for sealing an inkjet printhead in an inkjet printing mechanism. The capping system includes a cap retainer having a pair of cap lip mounting flanges extending therefrom. The capping system also has a cap lip with a base portion defining a pair of mounting holes extending therethrough which are each seated to surround an associated one of the pair of cap lip mounting flanges.
According to still another aspect of the invention, a method is provided for sealing an inkjet printhead in an inkjet printing mechanism. The method includes the steps of moving the printhead along a scanning axis to a sealing position, and pushing an activation wall of a cap sled into engagement with a portion of the printhead through linear motion in a direction substantially orthogonal to the scanning axis. During the pushing step, in an elevating step, a cap lip supported by the sled is elevated into sealing contact with the printhead through cam action.
An overall goal of the present invention is to provide an inkjet printing mechanism which reliably produces clear crisp images over the life of the printing mechanism.
Another goal of the present invention is to provide a capping system for sealing inkjet printheads through linear movement of replaceable printhead servicing units.
A further goal of the present invention is to provide a capping system having the ability to compensate for spacing variations between the cap and the printhead.
Another goal of the present invention is to provide a replaceable inkjet printhead cleaner service station system and servicing method which maintains printhead life, particularly when using permanent or semi-permanent printheads and/or printheads having a swath width on the order of at least 20 mm to 25 mm (about one inch).
The invention contemplates the following system and
Bruch Xavier
Johnson Eric Joseph
Murcia Antoni
Taylor Christopher
Hewlett--Packard Company
Hsieh Shih-wen
LandOfFree
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