Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-07-27
2002-07-02
Nguyen, Lamson D. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S015000, C347S016000
Reexamination Certificate
active
06412909
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing device and method for forming dots during the movement of a head as it travels back and forth to print multi-colored multi-tone images on a printing medium, and to a recording medium on which is recorded a program for such printing.
2. Description of the Related Art
Various printers have been used in the past as computer or digital camera output devices. Such printers include ink jet printers that jet ink to form dots and print multi-colored multi-tone images. In ink jet printers, dots are formed for each pixel by repeated primary scanning, in which the head travels back and forth, and sub-scanning, in which the printing paper is conveyed. Dots are formed by ink of predetermined colors, and multiple colors are brought out by the overlapping of these inks. The tones of images are brought out by the dot recording density.
Ink jet printers commonly make use of multinozzles comprising a plurality of nozzles arranged at a constant pitch in the sub-scanning direction for each color in order to enhance printing speed. In such cases, differences in the ink discharge properties of each nozzle can cause shifts in the positions where the dots are formed. Feed errors during sub-scanning can also cause shifts in the positions where the dots are formed. Such shifts can cause irregularities in density, referred to as banding, which can result in a loss of image quality. Printing based on what is referred to as interlacing or overlapping formats has been proposed in an effort to suppress such loss of image quality due to banding.
Interlacing refers to a format for printing images as raster lines are intermittently formed in the sub-scanning direction.
FIG. 20
illustrates an example of the interlacing format. This is a case involving the use of 3 nozzles arranged at a nozzle pitch k of 2 dots. In
FIG. 20
, the circles containing 2 digits indicate the dot recording positions. The left numeral of the two-digit numbers indicates the nozzle number, and the right number indicates the primary scan during which the dot is printed.
The dots of each raster line are formed by the 2nd and 3rd nozzles in the first primary scan in the interlaced format recording illustrated in FIG.
20
. The first nozzle does not form dots. After paper feed L equal to three raster lines, each raster line is formed using the first through third nozzles in the second primary scan. Images are subsequently printed by similarly repeating paper feed equal to three raster lines, and raster line formation by primary scanning. No raster lines are formed by the first nozzle in the first primary scan because no adjacent raster lines can be formed by second and subsequent primary scanning under the raster lines.
The overlapping format refers to the formation of raster lines with two or more nozzles by intermittently forming dots on the raster lines in each primary scan. For example, in the first primary scan, odd-numbered pixels of a given raster line are formed with one nozzle, and in the second primary scan, the even-numbered pixels are formed by another nozzle. Raster lines can also be formed by 3 or more scans, of course.
Shifts in the dot formation position due to sub-scan feed errors or ink discharge properties during interlacing or overlapping format printing can be dispersed in the sub-scanning direction or primary scanning direction. Shifts in the dot forming position can thus be rendered negligible, banding can be suppressed, and image quality can be improved.
Better image quality as well as faster printing are also generally important in improving printer convenience. A technique for forming dots during the movement back and forth in primary scanning has been proposed in order to improve printing speed in ink jet printers (such printing is henceforth referred to as bi-directional printing). A combination of the interlaced or overlapping formats of printing with bi-directional printing enables faster printing with better image quality in ink jet printers.
In bi-directional printing, however, the positions where the dots are formed can sometimes shift in the primary scanning direction for various reasons, such as backlash in the mechanisms moving the head back and forth or errors in the head position detection. There is a need to set the primary scanning direction for forming pixels by taking into account the effects of such shifting on image quality in order to obtain good image quality during bi-directional printing.
The printing device in JAPANEZE PATENT LAID-OPEN GAZETTE No. 7-251513 is an example of the study of such matters. This printing device involves the use of a head including a plurality of nozzles at a pitch of 2 dots in the sub-scanning direction. An example of bi-directional printing employing the overlapping format to form raster lines with two nozzles has also been disclosed as an enhanced printing mode. According to this disclosure, good text quality is achieved in the first mode, where the even-numbered pixels of the raster lines are formed during forward travel in primary scanning, and the odd-numbered pixels are formed during return travel of primary scanning. Good image quality with solid ink and no drop out is achieved in the second mode, where the even-numbered raster lines are formed during forward travel in primary scanning, and the odd-numbered raster lines are formed during return travel in primary scanning.
However, this is only an extremely limited study, the object of which is merely a head with nozzles arranged at a pitch of 2 dots. A head with nozzles arranged at a pitch of 2 dots affords only three modes—the above two described modes and another mode in which pixels formed during movement in the same direction are disposed in a checkered pattern. The above document studies the relation of image quality in two out of the three modes.
The resolution of ink jet printers has been developed to an extremely high degree in recent years, with a trend toward the use of finer dots. Because of manufacturing limitations, the head nozzle pitch is often greater than 2 dots. A head nozzle pitch greater than 2 dots is also desirable to open up the interval in the sub-scanning direction of the dots formed in one primary scan and to prevent the dots from smearing. The correlation between the pixels and the direction in primary scanning is more diverse with the use of heads in which the nozzles are arranged at a pitch greater than 2 dots.
In such cases, there are no conventional examples studying whether pixels should be formed during forward or return travel to improve image quality. In other words, there is room for further improvement in image quality in conventional printer devices by improving the correlation between the direction of movement during the formation of the pixels.
SUMMARY OF THE INVENTION
An object of the present invention is to improve image quality in bi-directional printing, and also to provide a technique for faster and higher resolution printing.
A printing device of the present invention prints multi-colored images by means of primary scanning and sub-scanning so as to form dots for pixels on a printing medium. During the primary scanning, a head travels back and forth relative to the printing medium to form raster lines. During the sub-scanning, the printing medium is conveyed relative to the head in the direction across to the primary scanning direction. The head includes, in the sub-scanning direction, at intervals of two or more raster lines per color, a plurality of nozzles for discharging ink. And the printing device includes: memory for storing control parameters, including the position of the pixels that are to be formed during each primary scan and the feed of the sub-scan; head drive controller for driving the head while moving back and forth in the primary scanning to form dots for the pixels specified by the control parameters; and sub-scanning mechanism for effecting sub-scanning at a feed specified by the control parameters. The parameters are set in compliance with condit
Fujimori Yukimitsu
Otsuki Koichi
Tayuki Kazushige
Nguyen Lamson D.
Seiko Epson Corporation
Sughrue & Mion, PLLC
LandOfFree
Printing device 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 device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Printing device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2851355