Typewriting machines – Carriage or carriage-moving or movement-regulating mechanism
Reexamination Certificate
2000-02-03
2001-07-31
Hilten, John S. (Department: 2854)
Typewriting machines
Carriage or carriage-moving or movement-regulating mechanism
C400S279000, C400S074000
Reexamination Certificate
active
06267519
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a technology for printing images on a print medium using a bi-directional reciprocating movement in a main scanning direction. The invention particularly relates to a technology for correcting printing positional deviation between forward and reverse passes.
2. Description of the Related Art
In recent years color printers that emit colored inks from a print head are coming into widespread use as computer output devices. In recent years, such color printers have been devised as multilevel printers able to print each pixel using a plurality of dots having different sizes. Such printers use relatively small ink droplets to form relatively small dots on a pixel position, and relatively large ink droplets to form relatively large dots on a pixel position. These printers can also print bi-directionally to increase the printing speed.
A problem that readily arises in bi-directional printing is that of deviation in printing position between forward and reverse printing passes in the main scanning direction caused by backlash in the main scanning drive mechanism and warping of the platen that supports the print media. JP-A-5-69625 is an example of a technology disclosed by the present applicants for solving this problem of positional deviation. This comprises of registering beforehand the printing deviation amount in the main scanning direction and using this printing deviation amount as a basis for correcting the positions at which dots are printed during forward and reverse passes.
However, deviation may be corrected with respect to a particular one of the multiple colored inks, there is no correction of deviation in other ink colors. As a result, the deviation correction provides little improvement in the quality of the color image. The effect that positional deviation has on image quality is particularly large in halftone regions.
Also, during color printing, it is necessary to effect correction of printing positional deviation that takes account of each color ink. With respect to monochrome printing, however, it is only necessary to correct deviation with respect to the ink used for the monochrome printing. There are many differences between correcting with respect to the ink used for monochrome printing and correcting with respect to each color ink used for color printing.
SUMMARY OF THE INVENTION
An object of the present invention is to improve image quality by alleviating printing positional deviation arising between forward and reverse passes in the main scanning direction during bi-directional printing.
To resolve at least some of the above problems, the present invention provides a printing apparatus that includes a print head equipped with nozzle groups for printing dots on a print medium by the emission of ink droplets. When printing on the print medium during forward and reverse main scanning passes, the following processing is performed. In a monochrome printing mode in which only ink droplets of an achromatic color are used, a first correction value is used to correct printing positional deviation of the ink droplets arising between forward and reverse main scanning passes. And, in a color printing mode in which ink droplets of chromatic colors are used, a second correction value is used to correct printing positional deviation of ink droplets.
During monochrome printing this enables the printing position to be corrected using a first correction value suitable for monochrome printing, while during color printing it enables positional deviation to be corrected using a second correction value suitable for color printing.
It is preferable to set the second correction value to reduce printing positional deviation of ink droplets of a target color selected from the chromatic colors. This enables the setting of an optimum second correction value that selectively takes into consideration only inks that strongly need to be thus taken into account.
When the print head has a plurality of single-chromatic-color nozzle groups including a cyan nozzle group and a magenta nozzle group, the second correction value can be set to reduce the printing positional deviation of the cyan ink droplets and the magenta ink droplets. Because positional deviation of cyan and magenta dots is more noticeable than those of other colors, the overall quality of the color printing can be improved by using second correction values set to reduce such positional deviation of cyan and magenta dots.
Also, when the plurality of single-chromatic-color nozzle groups includes a light cyan nozzle group and a light magenta nozzle group, the second correction value can be set to reduce the printing positional deviation of the light cyan ink droplets and the light magenta ink droplets. Because light cyan and light magenta are the inks used most extensively in halftone regions of color images and the positional precision of dots printed in these colors has a major effect on the image quality, the image quality of the color printing can be improved by using second correction values set to reduce such positional deviation of light cyan and light magenta dots.
It is also preferable to set the first correction value according to correction information indicative of a preferred correction state that is selected from among a first test pattern of positional deviation printed using the achromatic-color nozzle group, and to set the second correction value according to correction information indicative of a preferred correction state that is selected from among a second test pattern of positional deviation printed using at least one chromatic-color nozzle group.
In accordance with this arrangement, a pattern printed using the actual achromatic color nozzle group can be used to determine a first correction value that will enable positional deviation of achromatic color ink dots to be reduced. Similarly, a pattern printed actually using the chromatic-color nozzle group can be used to determine a second correction value that will enable positional deviation of the chromatic color ink dots.
Also, when the plurality of single-chromatic-color nozzle groups includes a cyan nozzle group and a magenta nozzle group, it is preferable that a second test pattern of positional deviation includes a second forward pass sub-pattern printed during a main scanning forward pass using either the cyan nozzle group or the magenta nozzle group, and a second reverse pass sub-pattern printed during a main scanning reverse pass using whichever of the cyan nozzle group and the magenta nozzle group was not used to print the second forward pass pattern.
Normally when a positional deviation test pattern is used to set a correction value to reduce positional deviation of both cyan ink dots and magenta ink dots, it is necessary to print both forward and reverse pass test patterns in each ink. And, then it is necessary to use these to set optimum correction values for each ink, and then use the two correction values to determine the final correction value. However, by using the arrangement described above, a correction value can be determined that applies to both inks by printing just one set of forward and reverse pass test patterns. That is, it is not necessary to print forward and reverse pass test patterns for each ink.
Furthermore, when the bi-directional printing apparatus is capable of performing main scanning at a plurality of main scanning velocities, the second correction values may be applied independently to each of the plurality of main scanning velocities. Similarly, the first correction values may be applied independently to the plurality of main scanning velocities. Since the relative degree of printing positional deviation depends on the main scanning velocity, such deviation can be effectively reduced by applying the first and second correction values independently for each main scanning velocity.
Also, when the bi-directional printing apparatus is capable of emitting ink in a plurality of dot emission modes of mutually different ink emission velocities, the firs
Mitsuzawa Toyohiko
Otsuki Koichi
Tayuki Kazushige
Yonekubo Shuji
Hilten John S.
Nolan, Jr. Charles H.
Oblon, Spivak, McClelland,. Maier & Neustadt, P.C.
Seiko Epson Corporation
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