Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-07-16
2003-12-30
Nguyen, Lamson (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
C347S014000, C347S041000, C347S043000, C347S019000
Reexamination Certificate
active
06669319
ABSTRACT:
The present disclosure relates to the subject matter contained in Japanese Patent Application No.2001-214602 filed on Jul. 16, 2001, which is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet printer and a printing method and particularly to an ink jet printer and a printing method which perform bidirectional printing on a sheet using a head for ejecting inks of a plurality of colors.
2. Description of the Related Art
As an apparatus for outputting a digital color image, a color inkjet printer having inks of a plurality of colors has been proposed. Such an apparatus is widely used for printing an image. In an inkjet printer, while a head in which a plurality of nozzles are integrally arranged is moved in a direction (main scanning direction) perpendicular to a direction (sub-scanning direction) along which a printing medium such as a paper sheet is fed, ink particles ejected from the nozzles of the head are impacted on the printing medium, thereby forming ink dots on the medium to record an image. Inks of black (K), cyan (C), magenta (M), and yellow (Y) are used as those of basic colors.
In such an inkjet printer, in order to improve the printing speed, bidirectional printing is performed, i.e., ink ejection while moving the head in the main scanning direction is conducted in both the forward and reverse directions of the head. In the case of the bidirectional printing, when inks are impacted on the printing medium in the forward direction in the color sequence of KCMY, inks are impacted on the printing medium in the reverse direction in the opposite color sequence of YMCK.
This difference in color sequence of impacting inks causes a problem in that the hue is delicately varied because of the reason that will be described below. In the case where blue (B) is formed by inks of C and M, for example, the color tone of B which is formed in the forward direction in the color sequence of C and M is delicately different from that of B which is formed in the reverse direction in the color sequence of M and C. This causes the problem in that, although B of a uniform hue is originally to be printed, B is printed in color tones which are different from each other in a stripe-like manner along the main scanning direction.
In order to solve the problem, in JP-B-3-77066 and JP-A-8-295034, a printing method has been proposed in which heads or nozzles are disposed independently for the forward direction (for example, the sequence of KCMY) and the reverse direction (for example, the sequence of YMCK), thereby equalizing the color sequences of impacting inks with each other.
By contrast, JP-A-11-207999 discloses a printing method to be employed in an inkjet recording method in which inks are ejected in both the forward and reverse paths in the main scanning direction by using an inkjet head wherein nozzle groups each for different colors are arranged in the print operation direction (main scanning direction), and sub scanning is performed between the forward path and the reverse path, or between the reverse path and the forward path, thereby forming an image on a printing medium. In the printing method, when an image is to be formed on a printing medium by using a mixed color based on inks of different colors, an ink which is applied lately in the forward direction of the main scanning is ejected in an ejection amount smaller than an ink which is applied early, in both the forward and reverse paths. According to the printing method disclosed in the related art, a difference between displayed colors in the forward and reverse paths is eliminated to enable bidirectional printing in an inkjet printer.
In the printing method according to the related art disclosed in JP-B-3-77066 and JP-A-8-295034, the nozzle head for the reverse direction is not used in the forward direction, and that for the forward direction is not used in the reverse direction, thereby causing a problem in that, in order to realize the same printing speed as that in a conventional method, nozzles and heads which are twice in number are required.
By contrast, the printing method according to the related art disclosed in JP-A-11-207999 has a problem in that an adverse effect is produced depending on a printing medium to enhance the variation in hue. This is caused by the phenomenon that the manner of hue variation in bidirectional printing depends on a printing medium. Namely, the direction of hue variation in a printing medium into which an ink easily penetrates, such as recycled paper, plain paper, or coated paper is different from that in a printing medium into which an ink hardly penetrates, such as glossy paper, or an OHP sheet. This will be described by way of an example in which B is formed by C and M.
In a printing medium into which an ink easily penetrates, an ink of C which is early impacted stays in the surface and the inside of the medium, and an ink of M which is lately impacted penetrates so as to move round below the ink of C, so that a hue in which C that is early impacted is stronger is obtained. In a printing medium into which an ink easily penetrates, namely, the color of an ink that is early impacted is dominant. By contrast, in a printing medium into which an ink hardly penetrates, an ink of C that is early impacted stays in the surface of the medium, and an ink of M which is lately impacted flows onto the ink of C or a portion where the ink of C is not placed, so that a hue in which M that is lately impacted is stronger is obtained. In a printing medium into which an ink hardly penetrates, namely, the color of an ink that is lately impacted is dominant.
Therefore, the printing method which is disclosed in JP-A-11-207999 in which the ejection amount of an ink that is lately printed is made smaller is effective for a printing medium into which an ink hardly penetrates, and in which the color of an ink that is lately impacted is dominant. In the method, for a printing medium into which an ink easily penetrates, and in which the color of an ink that is early impacted is dominant, however, the color of the ink that is early impacted is stronger, or an adverse effect is produced.
Usually, glossy paper that is a printing medium into which an ink hardly penetrates is used in printing in which the image quality is more significant than the printing speed. In contrast, recycled paper, plain paper, or the like that is a printing medium into which an ink easily penetrates is used in printing in which the printing speed is more significant than the image quality. Bidirectional printing is performed in order to improve the printing speed. Therefore, the countermeasure against the above-mentioned problem of hue variation in bidirectional printing is more important in a printing medium into which an ink easily penetrates. As described above, however, the printing method according to the related art which is disclosed in JP-A-11-207999 has the problem in that the variation in hue is enhanced in recycled paper, plain paper, or the like which are subjected to bidirectional printing with a higher possibility.
The variation in hue appears in different manners depending on the mode of filling a printed region with dots. A head in which the density of nozzles (hereinafter, referred to as nozzle density) in the sub-scanning direction is equal to the dot recording density (dpi) on a printing medium will be considered. In the case where an image of a region of (the length of a nozzle row in the sub-scanning direction)×(the moving distance of the head in the main scanning direction) (hereinafter, such a region is referred to as raster) is formed by one movement of the head in the main scanning direction (hereinafter, such recording is referred to as one-pass raster recording), the hue variation in bidirectional printing appears alternately or for each raster, and hence is conspicuous.
In the case where an image for one raster is formed by plural reciprocal movements in the main scanning direction by using a similar head (hereinafter
Fuji 'Xerox Co., Ltd.
Morgan & Lewis & Bockius, LLP
Nguyen Lamson
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