Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1997-12-05
2001-03-20
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S044000
Reexamination Certificate
active
06203139
ABSTRACT:
BACKGROUND OF THE INVENTION
The disclosed invention relates to ink jet printing devices, and more particularly to techniques for improving print quality.
An ink jet printer forms a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes called “dot locations,” “dot positions,” or “pixels”. Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink.
Ink jet printers print dots by ejecting very small drops of ink onto the print medium, and typically include a movable print carriage that supports one or more printheads each having ink ejecting nozzles. The print carriage traverses back and forth over the surface of the print medium, and the nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed. Typically, a plurality of rows of pixels are printed in each traverse or scan of the print carriage. 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 thermal printhead or piezoelectric technology. For instance, two earlier thermal ink jet ejection mechanisms are shown in commonly assigned U.S. Pat. Nos. 5,278,584 and 4,683,481. In a thermal system, an ink barrier layer containing ink channels and ink vaporization chambers is disposed between a nozzle orifice plate and a thin film substrate. The thin film substrate typically includes arrays of heater elements such as thin film resistors which are selectively energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized heater element. By selectively energizing heater elements as the printhead moves across the print medium, ink drops are ejected onto the print medium in a pattern to form the desired image.
A consideration of scanning carriage ink jet printers is the visible banding caused by poor paper advance or misdirected ink nozzles. Such banding has been addressed by software randomization. However, software randomization has been found to require multiple passes, wherein the number of passes increases with the inaccuracy of the paper advance. This significantly reduces throughput.
SUMMARY OF THE INVENTION
It would therefore be an advantage to provide an ink jet printer having reduced print banding caused by poor paper advance or misdirected nozzles.
Another advantage would be to provide print banding reduction that does not substantially reduce throughput.
The foregoing and other advantages are provided by the invention in a printer that includes a movable print carriage for reciprocatingly scanning along a carriage scan axis, a printhead having a plurality of printing elements and supported by the movable print carriage, a print media moving mechanism for moving print media along a media axis through a print zone, and a vibration inducing element for causing relative vibration between the printhead and the print media such that locations along the media axis of dots printed by the printing elements are minutely randomly varied. In accordance with a specific implementation of the invention, the vibration inducing element includes a piezoelectric element.
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Hewlett--Packard Company
Le N.
Quiogue Manuel
Vo Anh T. N.
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