Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2001-01-22
2002-11-05
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
C347S037000
Reexamination Certificate
active
06474765
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to mechanical printing—as opposed to manual printing of the type which might be carried out with pen and ink on paper. Thus, this invention relates to inkjet printing. More particularly, this invention relates to a method used to control one or more print heads in an inkjet printer, and to an inkjet printer utilizing this method.
2. Related Technology
One form of conventional inkjet printer or plotter typically has a print cartridge mounted on a movable carriage. This carriage is traversed back and forth across the width of a print media (i.e., usually paper or a plastic plotting film, for example) as the print media is fed is through the printer or plotter. Plural orifices on a print head of the print cartridge are fed ink (or other printing fluid) by one or more channels communicating from a reservoir of the print cartridge. Energy applied individually to addressable resistors (or to other energy-dissipating elements, for example, to piezoelectric actuators), transfers energy to ink or other printing fluid at the print head; which ink (printing fluid other than ink hereinafter being subsumed also in the term “ink”) is within or associated with selected ones of the plural orifices. These orifices then eject a part of the ink onto the printing media. The ejected ink forms a fine-dimension jet or stream that impinges on the printing media at a selected location dependent upon the relative positions of the print media and of the selected orifice(s) from which ink is ejected.
Another form of conventional inkjet printer has a media transport mechanism that controllably moves print media past an array of plural print cartridges, each with a respective print head. In this type of inkjet printer, the print cartridges are arrayed in a stationary array, usually of “block wall” arrangement, or in a diagonally arrayed and slightly overlapped arrangement, so that the entire width of the print media (or of that portion of the print media on which printing is to be done) passes by the print heads as the media is controllably moved through the printer.
Viewing now PRIOR ART
FIGS. 7 and 8
, and with attention first to
FIG. 7
, it is seen that in a conventional inkjet printer
500
(of either the first type or the second type described above), a sheet of printing media
502
is controllably moved generally along a media transport direction, indicated by arrow
504
(for the first type of conventional inkjet printer) or in the direction of arrow
506
(for the second type of conventional inkjet printer).
In the first type of conventional inkjet printer, a print cartridge having a print head
508
scans across the media
502
in a direction generally perpendicular to the direction
504
of media transport. As this print head
508
scans across the print media, ink is discharged from selected ones of plural printing orifices
510
. The print head
508
may make plural successive printing scans in the same direction (returning to a selected starting position after each scan), which plural scans are coordinated with advancement of the print media
502
along line
504
. Alternatively, the print head
508
may make bi-directional printing scans, in which ink is ejected during scans of successively opposite directions.
In
FIG. 7
, bi-directional printing scans of the print head
508
are represented by the oppositely directed arrows
512
,
514
, and
516
. The arrow
512
associated with printing “swath”
512
a
indicates a representative “first” printing scan in the indicated direction. The plural orifices
510
may place ink in this swath
512
a
. Thus, on the next-successive printing scans
514
,
516
the position of the print head
508
relative to the media
502
is indicated by the numerals
508
′, and
508
″ (with the media having been moved by the media transport mechanism to print in swath
514
a
, then in swath
516
a
) and with the print head
508
successively moving in opposite directions. It is to be noted in
FIG. 7
that the print head
508
appears to have a slight angularity (i.e., at the line of orifices
510
) with respect to the direction of scanning represented by arrows
512
,
514
, and
516
. That is, the line of the plural orifices
510
is not truly perpendicular to the direction of scanning represented by arrows
512
,
514
, and
516
. This apparent angularity is further explained below.
In the second type of conventional inkjet printer, also illustrated by
FIG. 7
, the print media moves in the direction
506
, and an array of print heads
508
,
508
′, and
508
″ (now referring to individual print heads, and not to successive alternative positions of a single print head) are arranged in a diagonal array, and are slightly overlapped with one another, so that the plural printing orifices
510
,
510
′, and
510
″ of the print heads provide substantially full printing coverage of the print media. That is, each of the printing swaths
512
a
,
514
a
, and
516
a
is covered by one of the lines of orifices as the media
502
moves past these print heads. Again, it will be noted that the print heads
508
,
508
′, and
508
″ are somewhat angulated (i.e., with respect to the lines of orifices
510
, et al) relative to perpendicularity to the direction of media movement
506
.
With either type of angularity explained above (i.e., either in a single print head scanned across print media, or in plural print heads past which media is moved) an effect of the angularity is that an elongate line that parallels the lines
510
of orifices, which is composed of plural line segments, and which line is supposed to be straight over its length, will be printed as somewhat disconnected, but parallel line segments. That is, the line segments
518
and
520
are aligned so that their centroids
518
a
and
520
a
align with one another in the direction that the line segments
518
and
520
are supposed to extend. However, because of the angulation discussed above, the adjacent line segments
518
and
520
are not perfectly aligned with one another, and are not perfectly connected. This lack of perfect connection of the line segments
518
and
520
produces a “cusp” or visual angularity artifact
522
(i.e., a “jaggedness” of the line including the segments
518
and
520
). The apparent angulation existing in the conventional printer
500
and creating visual artifacts
522
may result from a number of causes.
Importantly, a “time-of-flight” correction, which is commonly provided in conventional inkjet printers does not contribute to the artifact
522
, and will not remove the artifact
522
. Thus, correction of a “time of flight” factor for bi-directional printing (i.e., in a printer of the first type described above) will not eliminate the artifacts
522
. Further, visual artifacts
522
appear in angulated lines as well. Viewing PRIOR ART
FIG. 8
, it is seen that visual artifacts (each indicated with numeral
522
) are present in a number of lines that should be straight (but which appear jagged to a greater or lesser degree).
Importantly, this apparent angulation may result from a lack of true perpendicularity between the direction of print head scanning and the direction of print media advance through the printer. Also, apparent angulation can result from true misalignment between the array of orifices
510
and the direction of print head scanning (as in the first type of inkjet printer explained above), or from a “global” misalignment of the print heads, as in the second type of ink jet printer explained above. Efforts to eliminate these apparent angularities from inkjet printers have not proven successful. Particularly, an apparent angularity that results form a “skew” angle of print media moving through a printer is particularly difficult (i.e., impossible) to eliminate. Such a print media “skew” may result from a multitude of factors that are difficult to control. For example, a slight build up of paper fibers on the rollers that move paper
Hewlett--Packard Company
Nguyen Thinh
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