Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-04-27
2002-12-10
Vo, Anh T. N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06491364
ABSTRACT:
THE FIELD OF THE INVENTION
The present invention relates generally to printing with inkjet printers, and more particularly to an inkjet printer having an air movement system which converges a tail or satellite and a head of an ink drop as formed by the ink drop during printing.
BACKGROUND OF THE INVENTION
As illustrated in
FIG. 1
, a portion of a conventional inkjet printer
90
includes a printer carriage
91
and a print cartridge
92
installed in the printer carriage. The print cartridge includes a printhead
93
which ejects or fires ink drops
94
through a plurality of orifices or nozzles
95
and toward a print medium
96
, such as a sheet of paper, so as to print a dot of ink on the print medium. Typically, the orifices are arranged in one or more columns or arrays such that properly sequenced ejection of ink from the orifices causes characters or other images to be printed upon the print medium as the print cartridge and the print medium are moved relative to each other.
During ejection, one or more of the ink drops of the conventional inkjet printer form a primary drop or head
97
and a secondary drop or tail
98
which trails from or follows the head of the ink drop. Often, the tail of the ink drop separates from the head of the ink drop and forms a satellite
99
of the ink drop. The tail or satellite of the ink drop is often smaller than the head of the ink drop and typically has a different air resistance, speed, and trajectory than the head of the ink drop. For example, as the printer carriage and print cartridge move relative to print medium in the direction indicated in
FIG. 1
, a trajectory of the tail or satellite of the ink drop diverges from a trajectory of the head of the ink drop as the ink drop travels between the printhead and the print medium. Thus, the tail or satellite of the ink drop lands on the print medium away from where the head of the ink drop lands. As such, the tail or satellite of the ink drop forms an extraneous dot on the print medium around the edges and/or in the background of a character printed on the print medium. This extraneous dot, however, results in an image quality defect, referred to as spray, which causes the character to appear fuzzy. Controlling spray, therefore, is important since the eye is very sensitive to this type of image quality defect.
Unfortunately, increasing a spacing between the print cartridge and the print medium (i.e., pen-to-paper spacing) to accommodate, for example, a greater range of print medium thickness increases the possibility of spray since the ink drop has a greater distance to travel and, therefore, a greater distance within which to deviate from the head of the ink drop. In addition, moving the printer carriage and printhead at greater velocities to achieve, for example, faster printing speeds and, therefore, higher throughput also increases the possibility of spray.
Attempts to minimize or eliminate spray caused by the tail or satellite of the ink drop have utilized, for example, slower printer carriage speeds and reduced pen-to-paper spacing as well as lower drop velocities, clear-mode operations, and non-circular orifices. These attempts, however, are leading in a direction contrary to the desired direction of inkjet printer advancement, such as faster printing speeds for higher throughput and increased pen-to-paper spacing for accommodating a greater range of print medium thickness. Reducing carriage speed, for example, reduces throughput of the inkjet printer and reducing pen-to-paper spacing limits the range of print medium thickness the inkjet printer can handle. In addition, operating at lower drop velocities generally degrades a reliability and trajectory of the ink drops since the ink drops have a lower momentum and, therefore, are more easily disrupted. In addition, operating in clear modes of operations, where the entire contents of the firing chamber and nozzle are ejected, results in slower refill times and, therefore, reduced frequency response as well as a greater tendency to form air bubbles in the firing chamber.
Accordingly, a need exists for an inkjet printer which substantially eliminates image quality defects, such as spray, caused by tails or satellites of ink drops formed during printing, without compromising printing speed, printing reliability, and/or print medium accommodation.
SUMMARY OF THE INVENTION
One aspect of the present invention provides an inkjet printer for printing on a print medium. The inkjet printer includes a printhead having an ink orifice formed therein through which an ink drop is ejected into a print zone between the printhead and the print medium during printing, and an air movement system which directs a stream of gas through the print zone as the ink drop is ejected during printing. The ink drop includes a head and a tail. As such, the stream of gas converges the tail of the ink drop and the head of the ink drop during printing.
In one embodiment, the head of the ink drop has a first trajectory rate during printing and the tail of the ink drop has a second trajectory rate less than the first trajectory rate during printing. As such, the stream of gas impedes the first trajectory rate of the head of the ink drop during printing.
In one embodiment, the tail of the ink drop forms a satellite of the ink drop. As such, the stream of gas converges the satellite of the ink drop with the head of the ink drop during printing.
In one embodiment, the head of the ink drop has a head trajectory during printing and the satellite of the ink drop has a satellite trajectory during printing. As such, the air movement system directs the stream of gas through the head trajectory and the satellite trajectory during printing. In one embodiment, the stream of gas disrupts the satellite trajectory during printing, but does not disrupt the head trajectory during printing.
In one embodiment, the stream of gas converges the satellite trajectory with the head trajectory during printing. In one embodiment, the satellite trajectory originates at a starting point of the head trajectory and terminates at approximately an ending point of the head trajectory. The satellite trajectory, however, is longer than the head trajectory.
In one embodiment, the head of the ink drop forms a first dot on the print medium during printing and the satellite of the ink drop forms a second dot on the print medium during printing. As such, the second dot is positioned within the first dot on the print medium. In one embodiment, the first dot has a first diameter and the second dot has a second diameter less than the first diameter.
In one embodiment, the printhead moves in a first direction relative to the print medium during printing. As such, the air movement system directs the stream of gas in a second direction opposite the first direction.
In one embodiment, the print medium moves in a first direction relative to the printhead during printing. As such, the air movement system directs the stream of gas in the first direction.
In one embodiment, the air movement system directs the stream of gas in a direction toward an already-imprinted region of the print medium.
In one embodiment, the stream of gas is an air stream. In one embodiment, the air movement system includes an airflow source which generates the air stream. In one embodiment, movement of the printhead within the printer generates the air stream.
In one embodiment, the air movement system includes an air ram formed adjacent a leading end of the printhead. As such, the air ram directs the air stream from the leading end of the printhead to the print zone during printing.
In one embodiment, the ink orifice is formed in a front face of the printhead. As such, the air movement system directs the stream of gas substantially parallel to the front face of the printhead.
In one embodiment, a speed of the stream of gas through the print zone is in a range of approximately 3 meters/second to approximately 10 meters/second. In one embodiment, the speed of the stream of gas through the print zone is in a range of approximately 3 meters/seco
Bauer Stephen William
Blair Dustin Wesley
Kniffin John Michael
Pietrazyk Susan L.
Pietrzyk () Joe R.
Hewlett--Packard Company
Pietrazyk Susan L.
Vo Anh T. N.
LandOfFree
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