Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1997-09-03
2002-10-22
Barlow, John E. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06467867
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of non-impact printing and, in particular, the present invention reveals a method and apparatus for improving both color fidelity and registration among several non-impact print heads operating in a digital color print engine.
BACKGROUND OF THE INVENTION
In the prior art related to ink jet printing a print head operated under precise electronic control typically opposes a portion of a printing media so that an image may be printed thereon. Typically, to achieve printed images of the highest quality each of a plurality of ink emitting elements that emit droplets of colorant onto the printing media need synchronization in respect of their position and orientation with respect to each other such element (i.e., exact “registration”). In prior art multihead digital print engines including drum-based, swath (or carriage-based), and flat-bed digital print engines, it is known that consistency of mounting and operation of such elements increases the level of registration among said elements and thus decreases the likelihood of printing errors and image artifacts. In a traditional drum-based print engine a print media attaches to a rotating drum which then passes under one or more discrete ink emitting print elements (“nozzles”) mounted on a carriage articulated in the axial direction. In a flat bed print engine, the printing media is rigidly coupled to a substantially planar surface and the nozzles are articulated in two dimensions to cover the media. In a reciprocating swath, or carriage-based, print engine the media is incrementally stepped over a platen surface in one direction while the nozzles reciprocate across the media in a direction orthogonal to direction the media advances. In many of these traditional print engines perfect registration has become even more difficult to efficiently achieve as the number of print heads and the number of ink emitting elements increase and service and replacement procedures become more frequent. In each of these types of prior art print engine mechanisms, registration among and between nozzles of print cartridges may always be improved since no known means yet exists to rapidly, and perfectly, register each element to every other ink emitting element. Accordingly, in practical terms it is known that in some businesses specializing in producing full color digitally printed output, time constraints to complete printing jobs will conflict and oftentimes prevail with time required to complete full calibration and registration routines.
Furthermore, due to imperfection and general variation introduced during manufacture of print head elements, and their associated mounting elements, a number of electrical and mechanical variables that impede extremely accurate dot placement in an ink jet print engine thus compounds the difficulty in achieving perfect registration among all print heads at all times during printing operations. Particularly with reference to disposable ink jet print cartridges, “cartridges” or “print heads” herein, variations among cartridges are even further compounded as a result of periodic removal, substitution, cleaning, and/or replacement of a given one or more of several cartridges where misalignment error(s) regularly occur from inexact replacement following removal.
In these and other printing processes output is created by a plurality of multi-hued ink droplets emitted under precise electronic control in sequence from ink emitting nozzles of cartridges. Such ink droplets must record (a “dot”) as close as possible to exact pre-selected locations on the printing media to accurately reproduce printed output of an original source image with color fidelity and graphic quality corresponding to the original image. Unfortunately, due to a number of underlying causes, including compromises between time and quality in volume image production environments, said droplets often record dots upon the printing media at imprecise locations and thus generally degrade image quality and color fidelity of the printed image. As noted above, a primary cause involves a simple and oftentimes misalignment of one or more of the print heads (and thus the ink emitting nozzles associated with said print heads). In print engines that utilize disposable or removable print heads such slight misalignment potentially occurs every time one or more print heads is replaced or removed during periodic manual cleaning and other service of said print heads. Other causes of misregistration include differing ink droplet volume, varying ink droplet velocities of droplets emitted from different nozzles of a print head, bi-directional printing, slight non-alignment of the print heads, differing thickness of the printing media, and differing electrical characteristics of individual ink emitting nozzles and/or cartridges, among others.
Thus, it is known and can be appreciated that electrical and mechanical tolerance variations introduced during manufacture (and human error in mounting) of said cartridges has long presented, and continues to present, obstacles to extreme visual clarity in high speed digital color drop-on-demand and continuous-type printing. A clear implication of the level of compensation desired in the prior art is to allow for manufacturing tolerances to be relaxed somewhat without degradation in image quality, and thus manufacturing costs can decrease to the degree such tolerances can be relaxed.
Many prior art approaches to improving registration of a plurality of print heads, or compensating for image quality defects involve manual inspection, manual entry of perceived data values into an electronic print engine controller, and manual cleaning operations of each print head, although other varied approaches have been disclosed in the prior art. For example, in U.S. Pat. No. 5,644,344 issued to Haselby Jul. 1, 1997 depicts methods of calibrating and aligning an operation of print head cartridges in a swath printer using a carriage-mounted analog sensor oriented to sense edges of line segments printed by print cartridge print elements and then calculating a linear equation that transforms optical sensor values to adjust swath data shifts and timing delays. This representative prior art approach fails to account for a number of variables in printing that are addressed in the present invention, but otherwise adequately describes the state of the prior art fairly well.
Thus, a need exists in the prior art to solve issues related to the performance limitations of known print engines which emit ink from nozzles onto a print media. Further, a need exists in the art of digital ink jet printing to compensate for minute registration, or dot placement errors, and faulty performance of and among nozzles of print cartridges and to accurately sense and control registration and color image fidelity by sensing individual dots created by colored ink droplets in order to improve the quality and the visual clarity of text, graphics, and color appearing on the print media. Finally, a need exists in the art to improve the yield of quality digital output given practical and mechanical constraints imposed by use of ink emitting print heads mounted at some distance above a printing media as to synchronize and perfect registration among each of a plurality of colored ink droplets so they accurately record dots upon desired locations on the printing media to thus rapidly form high quality printed output closely resembling original source images.
SUMMARY OF THE INVENTION
The method and apparatus of the present invention increases the precision for controlling a plurality of cartridges that emit colored ink droplets from at least two ink jet print cartridges in a digital print engine. The present invention addresses both registration and color fidelity aspects of digital color ink jet print engines by utilizing an optical sensor to sense and accurately locate patterns of individual dots created by droplets emitted from said print cartridges. A focused source of illumination preferably periodically illumina
Lukis Lawrence J.
Worthington John Walter
Barlow John E.
Carmody & Torrance LLP
MacDermid Acumen, Inc.
Stewart Jr. Charles W.
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