Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-12-14
2001-08-07
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S037000
Reexamination Certificate
active
06270187
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to machines and procedures for printing text or graphics on printing media such as paper, transparency stock, or other glossy media; and more particularly to a scanning machine (such as, merely by way of example, a thermal-inkjet printer) and method that construct text or images from individual colorant spots created on a printing medium, in a two-dimensional pixel array. The invention employs print-mode techniques to retain the throughput advantages of single-pass printing with minimal sacrifice of image quality.
BACKGROUND OF THE INVENTION
In recent years, very extensive and elaborate refinements have been introduced to the art of multipass printing with incremental machines and methods—but in this innovative process the earlier and simpler single-pass art has been somewhat left by the wayside. Yet the benefits of single-pass printing remain important for special applications such as all-text documents—and also drafts of more complex documents. Documents printed in this way include not only letters, manuscripts, commercial advertising papers and the like, but also small items such as labels, bar codes, small receipts, credit-card charge authorizations and ATM (automatic teller machine) information slips.
Incremental printing employs individual pixel-forming devices. These take the form of thermal-inkjet nozzles, for example, or dot-matrix printing pins, or the individual heater elements of thermal-printer heads—including small units such as are used in printing the small commercial slips mentioned above.
In this document all such individual pixel-forming devices are called “printing elements” or “individual printing elements”. The aggregation of printing elements is called a “printhead” or a “multiple-printing-element printhead”.
One weakness of incremental printing is that the individual printing elements sometimes fail, leaving some areas of a text page or a drawing with no colorant deposited—and thereby omitting information from the image. In some cases such malfunctions can produce aesthetic defects, in other cases difficulty of reading alphanumeric characters or making out small details in a picture, and in still other cases actual loss of intelligence in numerical data, bar code lines, and the like.
Such errors may for instance include omission of crossbars in alphanumeric characters—thereby causing a numeral “8”, for example, to appear as a “0”. Analogously entire lines may be omitted from diagrams, e. g. floor plans—whereby for instance an entire wall between rooms may vanish. In such diagrams it is desirable to try to avoid such problems by setting the minimum line width to two pixels, but even this stratagem may be inadequate as sometimes two printing elements in a row fail.
Basically all such errors can be eliminated or concealed only by pressing into service some backup nozzle, pin, heater etc. that is functioning. Previous algorithmic efforts along these lines have resorted to multipass or at least plural-pass modes—implying that at least two different nozzles or pins must be made available to print on each pixel row of the image.
A fundamental problem with such techniques is that throughput is severely degraded by switching to plural-pass modes. In particular if a printing system detects just one single printing element malfunctioning, in accordance with the described technique the deficit can be overcome only by changing to a printing mode of at least two lasses.
In other words, throughput in terms of area covered per scan (i. e., per reciprocation of the scanning carriage) must be cut in half to accommodate a loss of only one printing element, even though for example an inkjet pen may have, say, two hundred to twelve hundred nozzles. Plainly a fifty-percent throughput loss is disproportionate to a {fraction (1/12)} of one percent or ½ of one percent loss in nozzle complement.
Even dot-matrix machines may typically have more than twenty-four pins. In this case if one pin fails, the result is a fifty-percent throughput loss for approximately a four-percent pin failure—still severely out of proportion.
Conclusion—The established techniques accordingly have continued to impede achievement of high-throughput, reasonably high-quality text or draft printing. Thus important aspects of the technology used in the field of the invention remain amenable to useful refinement.
SUMMARY OF THE DISCLOSURE
The present invention introduces such refinement. In its preferred embodiments, the present invention has plural aspects or facets that can be used independently, although they are preferably employed together to optimize their benefits.
In preferred embodiments of a first of its facets or aspects, the invention is a method of printing desired images on a printing medium. The method operates by construction of the images from individual marks.
These marks are formed by at least one scanning multiple-printing-element printhead that operates in substantially a single-pass mode of operation. (Those skilled in the art will understand that the printhead may be capable of operation in a multipass mode too, but for purposes of applying the present invention the printhead is assumed to be operating in a single-pass mode at the outset.)
The method includes the step of determining whether any printing element of the printhead has failed. In addition the method includes the further step of—if a printing element has failed—then reassigning functions of the failed printing element to other printing elements.
In accordance with the invention, this reassigning step is performed in such a way as to maintain the substantially single-pass mode of operation. Of course some exemplary ways of performing the reassigning step to satisfy this condition are introduced below.
In the foregoing discussion the word “substantially” has been included to allow for the possibility of an occasional or incidental multiple-pass operation. Such an operation may be inserted for example merely in an effort to design around the present patent document—or perhaps for some more benign purpose.
The foregoing may constitute a description or definition of the first facet of the invention in its broadest or most general form. Even in this general form, however, it can be seen that this aspect of the invention significantly mitigates the difficulties left unresolved in the art.
In particular, by maintaining substantially single-pass operation, the invention can often or usually avoid the drastically disproportionate throughput loss described in the preceding section of this document. In certain situations some throughput loss is suffered, but often that loss is much less severely disproportionate to the fractional loss in printing-element complement.
Although this aspect of the invention in its broad form thus represents a significant advance in the art, it is preferably practiced in conjunction with certain other features or characteristics that further enhance enjoyment of overall benefits.
For example, a first preference is that the reassigning step include removing from service all printing elements between the failed printing element and a nearer end of the printhead, inclusive. The rationale behind this strategy flows from these observations:
(1) printing elements most commonly do not fail;
(2) when printing-element failure occurs, most often only one element fails;
(3) when more than one printing element fails, the failed elements are sometimes (perhaps even more often than not) near one another, rather than widely separated; and
(4) when printing elements fail, elements near one or the other end of a printing-element array fail more often than elements near the center.
The stated strategy exploits these facts to form—in a great majority of printing-element failures—a residual, operable printhead that is, in a best-case situation, merely somewhat shorter. The result is no departure from single-pass printing, and only a slight degradation of throughput.
If only one printing element fails, then in the worst-case situation the failed element is close to
Bruch Xavier
Girones Xavier
Murcia Antonio
Taylor Chris
Vinals Lluís
Ashen & Lippman
Hewlett--Packard Company
Nguyen Thinh
LandOfFree
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