Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-07-20
2003-08-19
Nguyen, Lamson (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C400S074000
Reexamination Certificate
active
06607261
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing apparatus that creates dots on a printing medium during a main scan and thereby prints an image. More specifically, the present invention pertains to a printing apparatus that is capable of adjusting the dot creation timings during the main scan.
2. Discussion of the Background
An ink jet printer is one of the printing apparatuses that perform a main scan and sub-scan of a print head and prints a multi-color image. The ink jet printer ejects inks of multiple colors, for example, cyan, magenta, yellow, and black to create dots. Creation of dots with the multiple color inks at various recording ratios results in printing a multi-color image. To attain the high quality printing by the ink jet printer, it is desirable that there is no relative misalignment of the positions of dots created with the respective color inks. For the purpose of preventing such misalignment, the timings of dot creation with the respective color inks are adjusted at the time the ink jet printer is shipped.
Some of the ink jet printers create dots in both a forward pass and a backward pass in a main scanning direction to enhance the recording speed (such recording technique is hereinafter referred to as the bidirectional recording). To print an image of favorable quality, it is necessary to make the dots formed in the forward pass align with the dots formed in the backward pass in the main scanning direction.
FIGS.
15
(
a
) and
15
(
b
) show states of dots created by the bidirectional recording technique. Open circles represent dots formed in the forward pass of the main scan, whereas closed circles represent dots formed in the backward pass of the main scan. FIG.
15
(
a
) shows a state, in which the dots formed in the forward pass align with the dots formed in the backward pass in the main scanning direction, FIG.
15
(
b
) shows another state, in which the dots formed in the backward pass are shifted rightwards relative to the dots formed in the forward pass. The relative misalignment of the dots formed in the forward pass with the dots formed in the backward pass causes an unevenness of density and thereby lowers the picture quality of the resulting printed image.
The misalignment of the positions of dot creation in the forward pass and in the backward pass is caused by a diversity of factors, such as plays (backlashes) required in the driving mechanism of the printer. The misalignment is also due to a variation in thickness of the printing medium or printing paper.
FIGS.
21
(
a
) and
21
(
b
) show misalignment of the positions of dot creation in the forward pass and in the backward pass according to the thickness of printing paper. In the example of FIG.
21
(
a
), a dot dt
11
is formed on a sheet of printing paper PA
1
in the forward pass, and a dot dt
12
is formed adjacent to the dot dt
11
in the backward pass. A nozzle Nz ejects ink droplets Ik
11
and Ik
12
at respective positions shown in FIG.
21
(
a
), which are determined by taking into account the speed of the forward pass and the backward pass. The ink droplets Ik
11
and Ik
12
respectively draw loci shown in FIG.
21
(
a
) and hit target positions to form the dots dt
11
and dt
12
.
FIG.
21
(
b
) shows a state with a sheet of thicker printing paper PA
2
. In this case, the distance between the nozzle Nz and the printing paper PA
2
is less than the distance between the nozzle Nz and the printing paper PA
1
in the example of FIG.
21
(
a
). Ejection of ink droplets in the forward pass and in the backward pass at the same timings as those in the case of FIG.
21
(
a
) causes ink droplets Ik
21
and Ik
22
to respectively draw loci shown in FIG.
21
(
b
) and hit against the printing paper thereby forming dots dt
21
and dt
22
. Accordingly, there is an undesirable gap between the dots thus created, and the resulting recorded image is different from a target image to be recorded. In order to obtain the target image to be recorded, the timing of dot creation in the backward pass should be set later than the timing shown in FIG.
21
(
b
).
The conventionally adopted technique adjusts the dot creation timing using a test pattern so as to prevent the misalignment due to the diversity of factors. The technique records a predetermined test pattern while varying the dot creation timing in the forward pass and in the backward pass. The dot creation timing is then adjusted to the timing that gives the favorable results of recording. By taking into account the diversity of factors discussed above, the adjustment of the dot creation timing should be performed not only when the printer is shipped but also in occasions required by the user.
The prior art technique actually performs the adjustment of the dot creation timing only for one color, that is, the black ink, and collectively modifies the dot creation timings of the other colors based on the results of the adjustment.
The adjustment of the dot creation timing is not performed sufficiently in conventional printers. The insufficient adjustment causes the originally low picture quality of the resulting printed image in some printers and lowers the picture quality with an elapse of time in other printers. In the printer of the bidirectional recording, the dot creation timing is adjusted according to a test pattern. Such adjustment may, however, not sufficiently improve the picture quality of the resulting printed image. The deteriorating picture quality is partly due to a misalignment of dot recording positions between different colors.
The deteriorating picture quality due to the misalignment of dots is found not only in the case of bidirectional printing but in the case of performing printing operations only in a single direction of the main scan (hereinafter referred to as the unidirectional recording). The print head in a printer typically has a large number of nozzles that are arrayed in both the main scanning direction and the sub-scanning direction to have a two-directional arrangement. Unless the dot creation timing is adequately adjusted between nozzles having different positions in the main scanning direction, there is a misalignment of dots in the main scanning direction in the case of unidirectional printing. In the printer having a plurality of different color inks, there is a variation in ink ejection speed due to the difference in characteristics of the respective inks. This also leads to a misalignment of dot recording positions. A variation in ink ejection properties due to the difference in driving mechanism of nozzles also results in a misalignment of dot recording positions. Such misalignment lowers the picture quality of the resulting printed image.
The recent trend requires the printer to record fine dots and enable printing with a high resolution. In the case of printing with a high resolution, however, only a slight misalignment of dots may correspond to a misalignment of dot recording positions by the unit of pixels. In the printer that performs printing with a high resolution to improve the picture quality, the deteriorating picture quality due to such misalignment is not negligible. Not only the misalignment of dot recording positions between different colors, but any misalignment of dots is not of course negligible for the improvement in picture quality.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to solve the problems discussed above and to prevent a positional misalignment of dots and attain high-quality printing in a printing apparatus that performs a main scan of a print head to print a multi-color image.
To achieve these and other objects, the present invention provides a printing apparatus that performs a main scan and causes a print head having nozzles for ejecting ink to create dots on surface of a printing medium at a predetermined dot creation timing during the main scan. The main scan moves the print head forward and backward relative to the printing medium. The print head has a plurality of nozzle groups, each nozzle group
Huffman Julian D.
Nguyen Lamson
Seiko Epson Corporation
LandOfFree
Printing apparatus with adjustable dot creation timings does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Printing apparatus with adjustable dot creation timings, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Printing apparatus with adjustable dot creation timings will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3090216