Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-04-27
2003-05-13
Hsieh, Shih-Wen (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S083000
Reexamination Certificate
active
06561620
ABSTRACT:
THE FIELD OF THE INVENTION
The present invention relates generally to inkjet printers, and more particularly to an inkjet printer having a carriage skirt which extends beyond a print cartridge of the inkjet printer to influence airflow between the print cartridge and a print medium 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. In one arrangement, the print medium is held stationary as the print cartridge traverses the print medium to create a band or swath of print on the print medium. The print swath has a length, measured along a scan axis of the print cartridge, and a height, measured perpendicular to the scan axis along a paper advance axis of the print medium.
Image quality and performance of inkjet printing is rapidly approaching that of silver halide photographs and offset printing. The greatest improvement in image quality has been achieved by increasing image resolution which is a measure of the number of dots printed per height of an image, for example, dots-per-inch. Image resolution has been increased by reducing orifice spacing of the printhead and reducing a volume of the ink drops with an understanding that the volume of an ink drop corresponds to a size of the dot formed on the print medium. By reducing the orifice spacing of the printhead and the size of the ink drops, an image becomes sharper, less grainy, and more detailed.
As orifice spacing and drop volume decrease to increase image resolution, however, it becomes necessary to operate the printhead at higher firing frequencies and faster printing speeds to achieve the same throughput. Unfortunately, smaller, more closely spaced ink drops ejected at higher firing frequencies are more greatly influenced by surrounding air than larger, more widely spaced ink drops ejected at lower firing frequencies. In addition, when the printer carriage and the print cartridge move relative to the print medium in a printing direction, as indicated by arrow
97
, for example, a stagnant region of air is created at a leading end of the printer carriage and the print cartridge, as indicated by region
98
in FIG.
1
.
As printing speed and, therefore, speed of the printer carriage and the print cartridge increases, a high pressure region develops at the leading end of the printer carriage and the print cartridge which forces more air under the print cartridge and generates air currents between the printhead and the print medium. The air currents, however, misdirect the ink drops as they are ejected toward the print medium. Unfortunately, misdirection of the ink drops yields images which have undesirable print defects or artifacts, such as swath height error.
Swath height error is characterized by a variation in the height of the print swath created by the ink drops as the printer carriage and the print cartridge move relative to the print medium during printing. One cause of swath height error is the stagnant region of air created at the leading end of the printer carriage and the print cartridge during printing. As such, the stagnant region of air contributes to air currents which cause a misdirection of the trajectories of the ink drops in a positive or outward manner thereby resulting in a diminishing and/or increasing swath height.
Attempts to mask or hide these print defects have utilized multi-pass print modes, reduced printing speeds, one direction printing, and/or reduced spacing between the print cartridge and the print medium (i.e., printhead-to-paper spacing). These attempts, however, are leading in a direction contrary to the desired direction of inkjet printer advancement, such as single-pass print modes, faster printing speeds for higher throughput, bi-directional printing, increased printhead-to-paper spacing for accommodating a greater range of print medium thickness, and higher resolution, lower drop volume printheads.
Accordingly, a need exists for an inkjet printer which substantially eliminates objectionable print defects, such as swath height error, caused by air currents generated by printing operations, without compromising image resolution, printing speed, and/or print medium flexibility.
SUMMARY OF THE INVENTION
One aspect of the present invention provides an inkjet printer for printing on a print medium. The inkjet printer includes at least one print cartridge, a carriage shell adapted to hold the at least one print cartridge, and a carriage skirt extending from the carriage shell. The at least one print cartridge includes a printhead having a scan axis and a plurality of ink orifices formed in a front face thereof. As such, the carriage shell is adapted to traverse the print medium along the scan axis and the carriage skirt extends from the carriage shell substantially parallel with the front face of the printhead in a direction of the scan axis.
In one embodiment, the carriage skirt further extends from the carriage shell substantially parallel with the front face of the printhead in a direction substantially perpendicular to the scan axis.
In one embodiment, the carriage skirt extends a first distance in the direction of the scan axis and extends a second distance in the direction substantially perpendicular to the scan axis. As such, the second distance is less than the first distance.
In one embodiment, the carriage skirt extends from the carriage shell substantially parallel with the front face of the printhead in a second direction of the scan axis opposite the first named direction of the scan axis.
In one embodiment, the carriage skirt has a surface oriented substantially parallel with and substantially co-planar with the front face of the printhead.
In one embodiment, the plurality of ink orifices of the printhead form at least one column of ink orifices. As such, the carriage skirt extends from the carriage shell in a direction substantially perpendicular to the at least one column of ink orifices.
In one embodiment, the printhead is adapted to eject ink drops through the ink orifices and into a print zone between the printhead and the print medium during printing. In one embodiment, the carriage skirt influences airflow through the print zone during printing. In one embodiment, the carriage skirt reduces a component of the airflow oriented substantially perpendicular to the scan axis during printing. In one embodiment, the carriage skirt produces substantially uniform airflow through the print zone during printing.
In one embodiment, the carriage skirt affects air currents acting on the ink drops during printing to prevent print defects caused by the air currents.
In one embodiment, the carriage skirt reduces air pressure at a leading end of the at least one print cartridge when the carriage shell traverses the print medium during printing.
In one embodiment, the at least one print cartridge includes a plurality of print cartridges and the carriage shell is adapted to hold the plurality of print cartridges. As such, the carriage skirt has at least one opening defined therein which is configured to accommodate at least one of the plurality of print cartridges.
In one embodiment, the plurality of print cartridges are arranged to include a leading print cartridge and a trailing print cartridge when the carriage shell traverses the print medium during printing. As such, a first portion of the carriage skirt extends from the carriage shell adjacent the leading print cartridge and a second portion of the carriage skirt
Kurzer Michael Daniel
Pietrzyk Joe R.
Pietrzyk Susan L.
Webster Grant Allen
Hewlett--Packard Development Company, L.P.
Hsieh Shih-Wen
Pietrzyk Susan L.
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