Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-01-20
2001-04-17
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S012000
Reexamination Certificate
active
06217148
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of operation for direct computer-to-print printing systems in general and ink jet printers in particular.
BACKGROUND OF THE INVENTION
In EP 0 023 433, there is illustrated and described a high speed ink jet printer of the rotatable drum type having a print head for printing an image on a substrate during n printing passes where b=n×a, “b” is the ink jet head separation gap between adjacent ink jet heads and “a” is the inter ink dot line separation gap between adjacent ink dot lines i.e. a pixel length, each printing pass being constituted by a drum revolution and the displacement of the print head along the substrate through a step equivalent to the pixel length between consecutive drum revolutions.
FIG. 1
shows an ellipse shaped image printed during three drum rotations of such an ink jet printer having 5 ink jet heads labelled A, B, C, D and E. For convenience, the ink dot lines printed by the different ink jet heads during each consecutive drum rotation are denoted by the reference numbers
1
,
2
and
3
. It can be readily appreciated that the image suffers from the drawback that a single defective ink jet head C having, say, a blocked nozzle, causes an unprinted band of a width equal to the inter ink jet head separation gap.
It is the object of the present invention to substantially overcome this and other disadvantages.
SUMMARY OF THE INVENTION
In accordance with the teachings of the present invention, there is provided a method of operation for a high speed ink jet printer having a print head for printing an image on a substrate, the print head being substantially coextensive with the substrate and displaceable relative thereto in substantially mutually orthogonal first and second directions, the method comprising the steps of:
(a) displacing the print head in the first direction between initial and final printing positions for printing ink dot lines on the substrate in a manner determined by the appearance of the image to be printed;
(b) displacing the print head in the second direction through a step “y” between consecutive initial printing positions of the print head; and
(c) repeating steps (a) and (b) during n printing passes where b=n×a, “b” is the ink jet head separation gap between adjacent ink jet heads and “a” is the inter ink dot line separation gap between adjacent ink dot lines at the predetermined line resolution;
characterized in that the step “y” satisfies the following conditions:
(i) y=m
1
×a where m
1
is a natural number equal to 2 or more,
(ii) y≠m
2
×b where m
2
is a natural number equal to 1 or more,
(iii) b=m
3
×a where m
3
is a natural number equal to 2 or more and
(iv) m
1
and m
3
do not have a common denominator.
In accordance with the teachings of the present invention, the displacement of the print head relative to the substrate through a step greater than the inter ink dot line separation gap entails that adjacent ink dot lines are printed by different ink jet heads. The main advantage provided for by this method of operation is that in the case of an inoperative ink jet head, the ink dot lines which it should have printed are spaced out along the image rather than being adjacent to one another in an unprinted band as hitherto occurs with a conventional ink jet printer as described hereinabove such that their detrimental effect on image quality is considerably less noticeable.
This method of operation requires a longer print head for printing the same size image as a conventional ink jet printer. This is because, at any one time, one or more ink jet heads are positioned in inoperative printing positions either to the left or right of a substrate. Thus, during the printing of an image, some or all of the ink jet heads in initially inoperative printing positions are displaced to operative printing positions whilst some or all of the ink jet heads in initially operative printing positions are displaced to inoperative printing positions. Some conventional ink jet printers can be retro-fitted so as to operate in the above described manner for printing narrower than usual images.
The spacing between consecutive ink dot lines printed by a particular ink jet head, i.e. the length of the step “y” by which a print head is displaced relative to a substrate in the second direction, is not arbitrary but rather must comply with a number of constraints as now described assuming that all parameters are in the same units. The first constraint to be complied with is that the spacing between consecutive ink dot lines of a particular ink jet head is equal to a multiple of the separation gap “a” between adjacent ink dot lines at a desired line resolution, namely, y=m
1
×a where m
1
is a natural number greater than one. The second constraint to be complied with is that the spacing between consecutive ink dot lines of a particular ink jet head is not equal to a multiple of the inter ink jet head separation gap “b”, namely, y≠m
2
×b where m
2
is a natural number greater than zero, such that ink jet heads do not assume previously occupied positions relative to a substrate. The third constraint to be complied with and which also applies to conventional ink jet printers is that the inter ink jet head separation gap “b” is a multiple of the inter ink dot line separation gap “a” at a particular desired line resolution, namely, b=n×a where n is a natural number greater than zero. However, in addition, in view of the first constraint y=m
1
×a, also m
1
>n and m
1
and n do not have a common factor such that ink jet heads do not assume previously occupied positions.
In line with conventional practice, an ink jet printer operative in accordance with the teachings of the present invention can preferably print at one or more preset line resolutions, for example, a low line resolution of, say, 40 lpi or a high line resolution of, say, 60 lpi, the trade-off for a higher resolution, of course, being in terms of a slower throughput. As is known in the art, for all such line resolution settings, the relationship b=n×a applies but for different values of n.
A further feature of an ink jet printer operative in accordance with the teachings of the present invention is that the unprinted ink dot lines caused by a defective ink jet head can be at least partially compensated for by suitable manipulation of partially printed ink dot lines in their vicinity so as to restore picture quality as perceived by an observer even when an ink jet printer has one or more defective ink jet heads. The compensation of an unprinted ink dot line can be achieved by printing a printed ink dot line adjacent to an unprinted ink dot line with either additional ink dots or larger ink dots, if possible, so as to restore the original dot percentage. In color ink jet printers, the above described compensation technique is applied for each primary color separately.
The detection of a defective ink jet head can be achieved by an operator during, say, a routine start-of-day work procedure. Alternatively, it can be achieved automatically by means of a dedicated ink jet head test module including image processing and pattern recognition capabilities for processing the image of a printed image as provided by a camera directed theretoward.
Also in line with conventional practice, an ink jet printer operative in accordance with the teachings of the present invention preferably prints an image as a matrix of cells, each cell in turn being printed as a matrix of pixels. As known in the art, a separation gap “c” between adjacent cells alone the direction in which the print head is intermittently displaced fulfills the following two relationships: c=m
4
×a and b=m
5
×c where m
4
and m
5
are natural numbers greater than zero. The spacing between consecutive ink dot lines of a particular ink jet head is preferably greater than the separation gap “c” such that a particular ink jet head prints a maximum
Adler Uri
Miller Gershon
Idanit Technologies Ltd.
Nath Gary M.
Nath & Associates PLLC
Nguyen Thinh
Novick Harold L.
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