Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-11-01
2002-10-15
Nguyen, Lamson (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S014000
Reexamination Certificate
active
06464321
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing apparatus that is capable of adjusting dot misalignment in a main scanning direction with respect to dots created at different times, for example, dots printed in a forward pass and a backward pass of main scan, and to a method of adjusting such a misalignment of dots.
2. Description of the Related Art
Ink jet printers that eject ink from a print head to implement printing have widely been used as the output device of the computer. The ink jet printer generally moves a print head forward and backward relative to a printing medium as its main scan and causes multiple color inks to be ejected from the print head to create dots. Some of the ink jet printers create dots both in a forward pass and a backward pass of the main scan to enhance the recording speed (hereinafter this recording method is referred to as the bi-directional printing). In order to print an image of good quality, the dots created in the forward pass should be aligned with the dots created in the backward pass in the main scanning direction. When there is misalignment between the dots created in the forward pass and the dots created in the backward pass, a resulting image has harshness and poor image quality. Adjustment using a test pattern is typically carried out to compensate for such dot misalignment.
FIG. 24
shows a prior art test pattern, which is created by a print head HD having five nozzles. The left side of the drawing shows the position of the print head HD in a sub-scanning direction on the occasion of the forward pass of the main scan, and the right side of the drawing shows the position of the print head HD in the sub-scanning direction on the occasion of the backward pass of the main scan. In the central portion of the drawing, dots created in the forward pass are shown by the open circles, whereas dots created in the backward pass are shown by the closed circles. The process of printing the prior art test pattern first creates dots in the forward pass of the main scan, carries out sub-scan by a feeding amount L, which corresponds to an integral multiple N of a nozzle pitch k, and then creates dots in the backward pass of the main scan. The timing of ejecting ink is shifted by a unit step at each pixel in the backward pass, so as to vary the positions of the dots created in the backward pass relative to those in the forward pass. In the example of
FIG. 24
, the ink ejection timing in the backward pass is shifted by one through five steps respectively as indicated by Nos.
1
through
5
. The user observes the printed results of the test pattern and selects the optimum dot positions, so as to adjust the ink ejection timing to cause no misalignment between the dots created in the forward and backward pass. In the illustrated example of
FIG. 24
, at the timing No.
3
, the positions of the dots created in the backward pass are coincident with the positions of the dots created in the forward pass. Namely the timing No.
3
is optimum.
In order to attain the high image quality, the printers developed recently carry out printing at high resolutions using very small dots. Use of the very small dots, however, lowers the printing, speed. It is thus highly demanded to improve the image quality in the technique of bi-directional printing that enhances the printing speed. In the case of bi-directional recording, a slight deviation of the dot positions significantly affects the image quality of the resulting printed image. For example, when the print head has the tendency of deviating the dot positions leftward in the forward pass of the main scan from left to right, the dot positions are deviated rightward in the backward pass of the main scan. Namely the deviation is doubled in the case of bi-directional recording. Since the inappropriate adjustment of the dot positions in the forward pass and the backward pass of the main scan results in the extremely poor image quality in the case of bi-directional printing, the development of the technique has been highly desired to readily and accurately adjust the dot creation timing.
As the fruits of intensive experiments and discussions, the applicant of the present invention has found that the accurate adjustment of the misalignment of dots created in the forward pass with dots created in the backward pass significantly improves the image quality of the resulting printed image, which is equivalent to a significant increase in printing resolution. The increase in printing resolution using the very small dots undesirably raises the manufacturing cost of the printer. The arrangement of accurately matching the positions of the dots created in the forward pass with the positions of the dots created in the backward pass, however, readily improves the image quality without any increase in manufacturing cost. From these viewpoints, the technique of readily and accurately adjusting the dot misalignment in the case of bi-directional printing has been desired eagerly.
The test pattern shown in
FIG. 24
, however, does not attain the adjustment of the sufficient accuracy that satisfies these requirements.
FIG. 25
is an enlarged view showing a test pattern actually printed. In the example of
FIG. 25
, dots are recorded by varying the ink ejection timing by one through fifteen steps respectively as indicated by Nos.
1
through
15
. In each row of the printed test pattern, the upper portion includes only the dots created in the forward pass, and the lower portion includes only the dots created in the backward pass. An intermediate portion includes both the dots created in the forward pass and the dots created in the backward pass, which are overlapped with each other. The printed results of the test pattern shown in
FIG. 25
show that Nos.
4
through
9
are in a preferable range of the dot creation timing. It is, however, very difficult to identify the optimum dot creation timing in this preferable range. Namely the prior art test pattern is not capable of adjusting the dot positions with a sufficiently high accuracy. In this example, the respective dots are printed at a relatively low resolution that allows the visual recognition. In the case of printing at a high resolution that causes each dot row to form a continuous line in the sub-scanning direction, it is almost impossible to specify the optimum dot creation timing.
Development of the technique for accurately adjusting the dot positions is highly desired especially in the case of bi-directional recording. The needs are, however, not restricted in the bi-directional recording, but also arise in a uni-directional printing, such as in the case of adjustment between multiple print heads of different colors and in the case of adjustment between dots of different ink quantities.
SUMMARY OF THE INVENTION
The object of the present invention is thus to provide a technique that readily and accurately adjusts the positions of dots created at different timings in a main scanning direction.
At least part of the above and the other related objects is attained by a print control apparatus that generates print control data and causes a printer unit to print a test pattern based on the generated print control data. The printer unit carries out main scan and sub-scan and creates dots with a plurality of dot-forming elements that have different positions in a sub-scanning direction. The test pattern is used to detect a misalignment of a plurality of dots created in each pixel by driving the dot-forming elements at different times.
The test pattern satisfies: a condition that the plurality of dots are created in a plurality of pixels having an identical position in a main scanning direction but different positions in the sub-scanning direction; and a condition that dots created at one time are respectively interposed between dots created at another time in at least part of the test pattern.
The printer unit receives the print control data generated by the print control apparatus and carries out printing of the test pattern specified ab
Nguyen Lamson
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seiko Epson Corporation
Stewart Jr. Charles W.
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