Typewriting machines – Typing by other than type-face or type-die – Character formation by impact
Reexamination Certificate
1999-08-16
2001-03-06
Eickholt, Eugene (Department: 2854)
Typewriting machines
Typing by other than type-face or type-die
Character formation by impact
C400S279000, C347S019000, C347S014000
Reexamination Certificate
active
06196736
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a technology for printing on print media using a bidirectional reciprocating movement in a main scanning direction. The invention particularly relates to a technology for correcting printing position 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 within a pixel region, and relatively large ink droplets to form relatively large dots within a pixel region. These printers can also print bidirectionally to increase the printing speed.
A problem that readily arises in bidirectional 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, in the case of bidirectional printing using multilevel printers, little consideration has been given to positional deviation arising between forward and reverse printing passes. Other problems include that while 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 middle tone regions.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to improve image quality by alleviating printing position deviation arising between forward and reverse passes in the main scanning direction during bidirectional printing.
In order to attain at least one of the above and other objects of the present invention, an adjustment value is prepared with respect to at least one type of specific target dots other than those dots having the highest density out of the plural types of dots; and printing positions during forward and reverse main scanning passes are adjusted with the adjustment value to reduce printing positional deviation between forward and reverse main scanning passes.
The target dots, which have a relatively low density, occur with a high frequency in middle tone regions. It therefore follows that if during bidirectional printing positional deviation is adjusted by using an adjustment value for the target dots, positional deviation in middle tone regions in particular can be alleviated, improving image quality.
When the print head is able to print dots in each of M types of inks where M is an integer of at least two, the target dots may be formed of specific inks having a relatively low density out of the M types of inks. The printing positions are adjusted using the adjustment value relating to the target dots in color printing using two or more of the M types of inks. In this case, by selecting as the target dots, dots formed using ink that tend to make positional deviation more noticeable, it is possible to reduce the positional deviation of such target dots and thereby improve the quality of the color images.
When the M types of inks include at least one pair of dark and light inks having substantially the same hue and different densities, the target dots are preferably formed of the light ink. Considerable use is made of such light inks particularly in middle tone regions. It therefore follows that if during bidirectional printing positional deviation is adjusted by using an adjustment value for dots formed using light inks, positional deviation in middle tone regions in particular can be alleviated, improving image quality.
When the M types of inks include a pair of dark and light inks for each of cyan and magenta, the target dots preferably include first target dots formed of light cyan ink and second target dots formed of light magenta ink. In this case, the adjustment value is preferably determined such that a positional deviation of the first target dots and a positional deviation of the second target dots become substantially equal. Since considerable use is made of light cyan and light magenta inks in middle tone regions in particular, image quality of middle tone regions can be improved by determining adjustment values whereby the positional deviation of dots formed using those inks becomes substantially the same.
When the print head can print N types of dots of different sizes in at least one type of ink where N is an integer of at least 2, the target dots preferably include at least one type of relatively small dots other than the largest among the N types of dots. In this case, the adjustment value with respect to the relatively small target dots may be applied in common to the N types of dots. The target dots may be those that are medium sized of the N types of dots. Of the N types of dots, positional deviation of medium sized dots stands out in middle tone regions. It therefore follows that by taking a common deviation adjustment value relating to such target dots and applying the value as a common value to the N types of dots, positional deviation between forward and reverse passes in the main scanning direction can be made less noticeable, thereby improving the image quality.
The target dots may be dots that are used in the greatest numbers when the printing image signal indicates a density level of 50% in respect of ink used to form the target dots. In middle tone regions positional deviation tends to be more noticeable when the dots are those that are most used when print image signals indicate a 50% density level. Thus, image quality in middle tone regions can be improved by using an adjustment value for such target dots.
The timing of the generated drive signal pulses may be adjusted during at least one selected from a forward pass and a reverse pass to reduce positional deviation in a main scanning direction between target dots printed during the forward and reverse passes. Specifically, the timing of the generated drive signal pulses can be adjusted by delaying the drive signal during at least one selected from a forward pass and a reverse pass. Alternatively, the timing of the generated drive signal pulses can be adjusted by changing the frequency of the drive signal in accordance with a position in the main scanning direction, with the frequency adjustment taking place during at least one selected from a forward pass and a reverse pass.
The present invention can be embodied in various forms such as a printing method, a printing apparatus, a computer program that has the functions of the method or of the apparatus, a computer readable medium on which is recorded the computer program, and a data signal embodied in a carrier wave comprising the computer program.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.
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Mitsuzawa Toyohiko
Otsuki Koichi
Tayuki Kazushige
Yonekubo Shuji
Eickholt Eugene
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seiko Epson Corporation
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