Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-02-20
2002-07-30
Nguyen, Lamson D. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S014000, C347S043000
Reexamination Certificate
active
06425652
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing technique that creates dots on a printing medium by forward and backward passes of main scan.
2. Description of the Related Art
The ink jet printer that causes a plurality of different color inks to be ejected from a print head is used as one of the output devices of the computer. For the enhanced printing speed, the multi-nozzle configuration and the bi-directional printing technique are generally applied for the ink jet printer. The multi-nozzle configuration uses a print head with a large number of nozzles arranged thereon, and the bi-directional printing technique carries out printing in both forward and backward passes of main scan.
The misalignment of positions where dots are created undesirably lowers the picture quality of the resulting image in the ink jet printer. It is thought that the positional misalignment is mainly ascribed to the ink ejection characteristics from the nozzles. The interlace technique or the overlap technique has been applied to reduce the effects of the positional misalignment and improve the picture quality of the resulting image.
The interlace technique forms raster lines in an intermittent manner in a sub-scanning direction to complete an image. For example, in the multi-nozzle configuration, it is assumed that the respective nozzles are disposed at intervals of not less than 2 raster lines in the sub-scanning direction. Because of this nozzle interval, every pass of the main scan forms raster lines in an intermittent manner in the sub-scanning direction. The vacant space between the existing raster lines is successively occupied by subsequent passes of the main scan with movements of the print head in sub-scan. The feeding amount of sub-scan is adequately selected to fill the vacancy and form adjoining raster lines with different nozzles. The interlace technique effectively disperses the positional misalignment in the sub-scanning direction, thereby making the positional misalignment sufficiently inconspicuous.
The overlap technique records dots on each raster line with at least two different nozzles. For example, the procedure creates dots in odd pixels on a certain raster line with one nozzle by a first pass of the main scan and dots in even pixels on the certain raster line with another nozzle by a second pass of the main scan. The overlap technique enables the positional misalignment to be well dispersed on the respective raster lines in a main scanning direction.
The interlace technique and the overlap technique are applicable for bi-directional printing. Dots created by the forward and the backward scans of the print head are arranged in various different patterns corresponding to the combinations of the nozzle pitch, the feeding amount of sub-scan, and the number of repeated scans.
In some cases, however, application of the interlace technique or the overlap technique does not sufficiently improve the picture quality. In the ink jet printers, a recent trend is the enhanced scanning speed of the print head to attain the higher-speed printing. Another trend is the use of finer dots for the better picture quality. Such attempts may, however, lead to the insufficient improvement in picture quality even under the application of the interlace technique or the overlap technique. This drawback is not negligible in the latest high-performance printers.
SUMMARY OF THE INVENTION
The object of the present invention is thus to improve the printing quality in the case of bi-directional printing.
At least part of the above and the other related objects is attained by the technique of the present invention, which is favorably applied to a printing apparatus where a partial area of main scan has a lower positional accuracy of dot creation. In such a printing apparatus, the technique records dots in such a manner that forward pass dots created in a forward pass of the main scan and backward pass dots created in a backward pass of the main scan are present at substantially equal rates in at least the partial area of the lower positional accuracy.
The inventors of the present invention have found that the positional misalignment of dot creation is ascribed to the mechanical configuration of the printing apparatus as well as to ink ejection characteristics. The inventors have also found that the positional misalignment appears at different positions in the forward pass and in the backward pass of the main scan. The technique of the present invention takes advantage of these findings and causes dots created in the forward pass to be mixed with dots created in the backward pass in an area of potential positional misalignment. This arrangement reduces the conspicuousness of the positional misalignment and thereby improves the picture quality of the resulting printed image.
Such a positional misalignment of dot creation may be ascribed to the mechanical vibrations of the print head in the course of the main scan. The increase in main scanning speed of the print head to enhance the printing speed and improve the performance of the printer leads to the greater mechanical vibrations of the print head. In general, the mechanical vibrations of the print head arise in the respective initial stages of the forward pass and the backward pass of the main scan (that is, at the time of accelerating the main scan) and gradually attenuate. In addition to the mechanical vibrations, application of the very fine dots created on the printing medium for the purpose of the improved printing quality causes even a slight positional misalignment of dot creation to make dropouts. In the case of bi-directional printing, the positional misalignment of dot creation is significantly conspicuous in some recording procedures.
FIG. 1
shows the effects of the mechanical vibrations on the picture quality. The dotted lines extending in the main scanning direction in images PICa and PICb represent raster lines. In the drawing of
FIG. 1
, the direction from left to right represents the direction of the forward pass of the main scan of the print head. The direction from right to left represents the direction of the backward pass of the main scan. As clearly understood from the illustration, the positions of dots are misaligned due to the mechanical vibrations of the print head arising in the respective initial stages of the forward pass and the backward pass of the main scan. The hatched areas represent specific areas of low positional accuracy, where the mechanical vibrations of the print head cause the positional misalignment of dot creation.
The upper portion of
FIG. 1
shows an image PICa printed over the whole width in the main scanning direction. The image PICa has the specific areas of low positional accuracy on both ends thereof, due to the mechanical vibrations of the print head arising in both ends of the main scan range (that is, in the respective initial stages of the forward pass and the backward pass of the main scan).
There is a case in which an image occupies only part of the width in the main scanning direction. In such cases, the main scan is carried out only in the part of the width with the image, for the enhanced printing speed. The lower portion of
FIG. 1
shows an image PICb printed by carrying out the main scan only in the part of the width in the main scanning direction. The image PICb also has the specific areas of low positional accuracy on both ends thereof.
In such areas of low positional accuracy, the positional misalignment of dot creation may be recognized visually as deterioration of the printing quality.
FIG. 9
shows an arrangement, in which the bundle of 3 raster lines formed in the forward pass of the main scan and the bundle of 3 raster lines formed in the backward pass of the main scan appear alternately. In this drawing, the open circles represent the forward pass dots and the closed circles represent the backward pass dots. The dotted lines represent raster lines where dots are to be created. In this example, the effects of the positional misalignment o
Nguyen Lamson D.
Seiko Epson Corporation
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