Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-01-27
2002-08-20
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S014000
Reexamination Certificate
active
06435644
ABSTRACT:
RELATED PATENT DOCUMENTS
A closely related document is another, coowned U.S. utility-patent application filed in the United States Patent and Trademark Office substantially contemporaneously with this document—and also hereby incorporated by reference in its entirety into this document. It is in the names of Askeland et al., entitled “ADAPTIVE INCREMENTAL-PRINTING MODE THAT MAXIMIZES THROUGHPUT BY SHIFTING DATA TO PRINT WITH PHYSICALLY UNALIGNED NOZZLES” —subsequent assigned utility-patent application Ser. No. 09/492,929, filed Jan. 27, 2000 and now abandoned.
FIELD OF THE INVENTION
This invention relates generally to machines and procedures for incremental printing of text or graphics on printing media such as paper, transparency stock, or other glossy media; and more particularly to alignment provisions in a scanning machine and method that construct text or images from individual ink spots created on a printing medium, in a two-dimensional pixel array. The invention employs threshold printmode techniques to optimize image quality vs. operating time.
BACKGROUND OF THE INVENTION
The foregoing statement of the field of the invention speaks of “threshold” techniques in the printmode area. This term is used merely to emphasize that the printmode techniques required for practice of the present invention are extremely basic—almost primitive, in comparison with the very sophisticated present state of the printmode or printmasking art.
For example, the related-art section of U.S. Pat. No. 5,677,716 of Cleveland, filed seven years ago, discusses space-rotation, sweep-rotation and autorotation of masks. More-recently filed patent documents introduce manual pseudorandomization, “neighborhood” conditions, balanced randomization and determinism, automatic generation, and real-time generation of printmasks—including columnwise mask generation within each swath, “precooked masks” and “pop-up” masks.
Although entirely compatible with all of the advanced techniques just noted, the present invention by comparison actually needs only the most simple or pedestrian tools of the printmode art—little more, in fact, than the concept of a printmask height. Therefore, as will be seen, these techniques are indeed at the threshold of the print-mode arena; yet their use in the present invention confers potent advantages.
(a) The need for registration—Many incremental printers use more than one array of multiple printing elements, such as for example multipen inkjet printers. Most often the different arrays (“pens” or “printheads”) print in different colors, including black; however, in certain cases some of the different arrays print in different dilutions or saturations of common colors. Other uses of plural arrays may occur.
In such printers it is necessary that markings made by the different arrays be in register with one another. At least markings should be adequately registered to prevent a human viewer from seeing—with the unaided eye—the effects of misregistration.
In general, however, such systems are subject to mutual misalignment of the arrays and therefore misregistration of the markings. Various different kinds of provisions are known for reducing such misalignment to the point at which registration at least satisfies visual requirements.
(b) Tight tolerances—For convenience and definiteness such provisions can be described with reference to multipen inkjet printers, and more particularly thermal-inkjet units of the Hewlett Packard Company—such as the models known as PaintJet®, DeskJet® 1200C and HP® 2000C. In some of these printers, alignment is achieved mechanically: the pens are aligned to within a dot row, by virtue of individual machining to achieve fine mechanical tolerances.
As a result these printers can print with all their nozzles, and with straightforward good alignment along the direction of printing-medium advance. This is true for the 7 dot/mm (180 dot/inch or “dpi”) PaintJet printer, and for the 12 dot/mm (300 dpi) model 1200C printer.
It will be understood, however, that this solution to good registration is achieved only at very great cost, since the machining required is time consuming and costly. Furthermore, this solution is commercially feasible only because spacing of the dot rows at {fraction (1/7)} or {fraction (1/12)} mm is relatively coarse in terms of machine-tooling standards.
(c) Reserved elements—In the HP 2000C, resolution is 24 dot/mm (600 dpi) and at such fine spacings mechanical machining begins to be an uneconomic way to achieve registration. Instead, this printer uses a pen alignment scheme that reserves eight nozzles of each pen for pen-to-pen alignment.
In that system, nominally four nozzles
13
K,
15
K (
FIG. 1
) are reserved at each end of the black-ink pen K, and only the nozzles
14
K between those two end zones are employed to print. Fixed upper and lower limits
11
,
12
are established, reflecting these assumed reservations—and these fixed limits
11
,
12
are applied to the color pens C, M, Y as well as the black pen K.
With drift away from the nominal mechanical alignment, however, for example a particular pen, e. g. the cyan pen C as shown, might be two pixel rows lower than its nominal position, and this would require use of two nozzles from the top nominal end zone. This would leave only two nozzles
13
C actually reserved at the top, while in exchange the system would give up two nozzles just above the bottom nominal end zone, leaving unused six nozzles
15
C as the bottom end zone. The central group of used nozzles
14
C still has the same size in nozzles, but these used elements are shifted upward along the nozzle array by a distance equal to two nozzle spacings—which most commonly (though not necessarily) is two pixel rows.
In practice any such possibility may occur for any of the pens, including the black pen K or the magenta or yellow pen M, Y rather than the cyan pen C. The particular pattern illustrated, with the magenta pen M shifted upward about six rows and the yellow pen Y at the nominal position, is purely exemplary.
In any event, eight nozzles are always sacrificed to the needs of alignment, and in practice the limit lines
11
,
12
are fixed in position relative to the world, or in other words to the pen carriage. The total number of nozzles in each pen is 304; therefore the maximum number of these printing elements that fall within the central regions
15
and can be used is 296.
The remaining 8/304 or about 2.7 percent of the nozzle complement is abandoned at the outset. (Of course different reserved and total numbers of nozzles may be present in different models or from different manufacturers; these values are simply exemplary.) From these numbers it can be seen that the end zones
13
,
15
of all the pens have been drawn greatly exaggerated relative to the corresponding central regions
14
, simply to facilitate clear discussion.
To a person not skilled in this field, such a seemingly small fraction might not appear significant. In this extremely competitive commercial environment, however, these numbers represent a major handicap—for two reasons.
(d) Direct cost—First, the provision of eight additional nozzles is far from a small matter. Each nozzle in the nozzle plate is not merely a hole in an amorphous structure, but to the contrary must be accompanied by ink-provision and firing components within the printhead—and these facilities are fashioned in what is the equivalent of a multilayer silicon circuit chip.
The cost of printed-circuits and the like formed in silicon is notoriously expensive, to the extent that common slang in industry refers to silicon “real estate”. In addition, the cost of expanding the amount of space used in such a structure is not even linear: the bigger the chip, the more expensive per unit area because of the greater difficulty of working larger chips and the progressively escalating scrap factor.
(e) Hidden costs—The first major handicap of cost does not end there, however, for the silicon real estate carries its operating environment along with it in an ever-widening series of ripple ef
Askeland Ronald A.
Osborne William S.
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