Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-05-08
2002-01-01
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S012000, C347S043000
Reexamination Certificate
active
06334665
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing system with a print head that carries out scans on a printing medium to implement printing. More specifically the present invention pertains to a technique of improving the picture quality of a resulting recorded image in such a printing system.
2. Description of the Related Art
The ‘interlace printing method’ disclosed in U.S. Pat. No. 4,198,642 is a proposed technique that improves the picture quality of a resulting printed image in a printer, such as a serial ink jet printer, in which a print head carries out main scans and sub-scans on a printing medium to implement printing.
FIG. 23
illustrates an exemplified process of interlace printing. A variety of parameters are used in the following description. In the example of
FIG. 23
, it is assumed that a number of nozzles N that are actually used for formation of dots is equal to three. A nozzle pitch k [dots] represents an interval between centers of adjoining nozzles on the print head, which is expressed by a pitch of pixels in a recorded image (dot pitch w) as the unit. In the example of
FIG. 23
, k is equal to two. L denotes a feeding amount of the sheet of paper in sub-scan and is set equal to three raster lines in the example of FIG.
23
.
In the drawing of
FIG. 23
, circles, each including a number of two figures, represent the recording positions of the respective dots. In the encircled number of two figures, the left-side figure represents the nozzle number and the right-side figure represents the recording sequence (which time of main scan the dot is recorded).
In the process of interlace printing shown in
FIG. 23
, the first main scan causes a second nozzle and a third nozzle to record dots on the respective raster lines, whereas no dots are formed by a first nozzle. After the sheet of paper is fed by the amount corresponding to three raster lines as shown in
FIG. 23
, the second main scan is carried out to form raster lines with the first through the third nozzles. The step of feeding the sheet of paper by the amount corresponding to three raster lines and the step of carrying out a main scan to form raster lines are repeated to record an image. The first main scan does not cause the first nozzle to form any raster line, since the second and the subsequent main scans do not form an adjoining raster line immediately below the imaginary raster line formed by the first nozzle in the first main scan.
The interlace printing forms raster lines intermittently in the sub-scanning direction in the above manner to record an image. Although
FIG. 23
refers to the specific nozzle pitch, a variety of values may be set to the feeding amount L according to the nozzle pitch k and the number of nozzles N to realize the interlace printing. In general, the interlace printing process is characterized by the arrangement of a nozzle array on the print head and the method of sub-scans. The nozzle array includes N nozzles aligned in the sub-scanning direction. When the interval between the centers of adjoining nozzles is set equal to k times the pitch of pixels, N and k should be integers that are prime to each other. The feeding amount L in sub-scan carried out after each main scan is set equal to N times the pitch of pixels.
The interlace printing has an advantage of dispersing a deviation of dot-forming positions of dots due to the distributions of the positional accuracy of nozzles and the ink-spouting characteristics on a resulting recorded image. The interlace printing method accordingly reduces the effects of the distributions of the nozzle pitch and the ink-spouting characteristics and improves the picture quality of the resulting recorded image.
In the prior art technique of interlace printing, adjacent dots in the sub-scanning direction are recorded by different nozzles, whereas adjacent dots in the main scanning direction are recorded by an identical nozzle. There may be a deviation of dot-forming positions in the whole raster due to a distribution of ink-spouting characteristics of the individual nozzles. This may result in deteriorating the picture quality. A similar problem arises in the case of non-interlace printing.
In order to cancel the deviation of dot-forming positions in the whole raster and improve the picture quality of the resulting recorded image, the overlap printing technique may be adopted (for example, JAPANESE PATENT LAYING-OPEN GAZETTE No. 3-207665 and JAPANESE PATENT PUBLICATION GAZETTE No. 4-19030). The overlap printing process causes each raster line to be formed by different nozzles in two or more main scans. By way of example, when each raster line is formed by two main scans, the first main scan records dots only in pixels of odd ordinal numbers, which are allocated from one end of the raster line, by one nozzle. After a sub-scan, the second main scan records dots in pixels of even ordinal numbers on the raster line by a different nozzle.
Application of the overlap printing technique prevents a deviation of dot-forming positions in the whole raster and improves the picture quality of the resulting recorded image. The overlap printing process, however, requires two or more main scans to form each raster line and accordingly causes another problem, that is, lowering the printing speed.
A printer recently proposed records dots in each pixel in an overlapping manner and thereby increases the number of expressible tones in each pixel. In this printer, two or more main scans are also required to record dots in an overlapping manner and complete each raster line. This also causes a decrease in printing speed.
SUMMARY OF THE INVENTION
One object of the present invention is thus to provide a technique of preventing a deviation of dot-forming positions on each raster line without lowering the printing speed, so as to improve the picture quality of a resulting recorded image.
Another object of the present invention is to provide a technique of improving the printing speed in a printing system that records dots in an overlapping manner.
At least part of the above and the other related objects is realized by a printing system that carries out a main scan, which reciprocates a print head relative to a printing medium, and forms a raster line, which is a row of dots aligned in a main scanning direction, so as to print an image on the printing medium, wherein the print head has a plurality of nozzles which form an identical type of dots on a raster line in one main scan.
In the printing system of the present invention, dots are recorded by different nozzles on each of at least part of raster lines in the course of one main scan. This structure enables a deviation of dot-forming positions due to a distribution of the characteristics of the individual nozzles to be effectively dispersed on each raster line and thereby improves the picture quality of a resulting recorded image. The structure attains this effect without increasing the number of main scans required to form each raster line. The printing system of the present invention thus improves the picture quality of the resulting recorded image without lowering the printing speed.
In accordance with one application of the printing system, a plurality of dots may be recorded in each pixel on a raster line by a plurality of nozzles in the course of one main scan. Application of the above structure to the printing system that records dots in each pixel in an overlapping manner improves the printing speed while increasing the number of expressible tones in each pixel to enhance the picture quality.
In accordance with one preferable application of the present invention, the plurality of nozzles are arranged at a predetermined interval k
1
in the main scanning direction, the predetermined interval being an integral multiple of a pitch of pixels in the main scanning direction.
In the printing system of this preferable structure, all the nozzles can record dots in the respective pixels at an identical drive timing. The structure of setting an identical drive
Le N.
Nguyen Lamson D.
Seiko Epson Corporation
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