Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-10-30
2004-12-07
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S040000
Reexamination Certificate
active
06827424
ABSTRACT:
This application is based on Patent Application No. 2000-335188 filed Nov. 1, 2000 in Japan, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bidirectional print apparatus and method for executing bidirectional scanning of print heads that apply ink of a plurality of colors to a print medium, and in particular, to a bidirectional print apparatus and method that can reduce the unevenness of colors which may occur during bidirectional color printing, and prints obtained by this method and apparatus.
2. Description of the Related Art
For print apparatuses, and in particular, those based on an ink jet method, it is important to increase the printing speed during color printing. General methods for increasing the printing speed include an increase in the length of print heads, an increase in the printing frequency of the print heads, and the introduction of bidirectional printing. Compared to unidirectional printing, the bidirectional printing enables required energy to be temporally distributed in order to obtain the same throughput and is thus a cost-efficient means as a total system.
However, with the bidirectional printing method, the landing order of ejected color inks differs between the forward and backward directions of main-scanning depending on the construction of the print apparatus and in particular its print heads. Thus, with this method, unevenly colored portions like bands may be created; this is a problem originating from the principle of this method. Since this problem is caused by the landing order of the ink, more or less a difference in coloring occurs if dots of different colors even partially overlap each other.
If an image is formed by ejecting coloring materials such as pigments or dye inks onto a print medium, the ink in the first printed dot first is deposited on the print medium and then permeates from the front layer to the interior thereof. When ink that forms a subsequent dot is then disposed on the first printed dot so that these dots at least partially overlap each other, a larger amount of ink is placed below an area already dyed with the first ink. Consequently, the first printed dot tends to provide more intense coloring than the subsequent dot. Thus, with a conventional construction in which nozzles for the respective colors are arranged in a main-scanning direction, when bidirectional printing is executed, the landing order of the ejected ink is reversed between the forward and backward scanning. As a result, a difference in coloring occurs to form unevenly colored portions like bands.
This phenomenon occurs not only with ink but also with wax-based coloring materials for forming process colors because of the relationship between the first and second printed dots, in spite of a difference in principle.
Ink jet printers supporting the bidirectional printing are constructed so as to avoid this problem using the following methods:
1) Uneven colors are permitted. Alternatively, only black is printed in both directions.
2) The nozzles for the respective colors are arranged in the sub-scanning direction. That is, what is called a vertical arrangement is used.
3) Forward- and backward-scanning nozzles are provided and nozzles or heads used are switched between the forward and backward scanning so as to use the same landing order for each color (Japanese Patent Application publication No. 3-77066).
4) During forward and backward scanning, rasters are printed so as to be interlaced to complementarily make the color of each printed raster uneven at a high frequency according to a difference in landing order so that the rasters eventually appear even (Japanese Patent Application Publication No. 2-41421 and Japanese Patent Application Laid-open No. 7-112534).
However, the above conventional technique 1) does not provide an essential solution and has the disadvantage of sharply reducing the throughput when a color image is input. With the vertical arrangement in 2) provides the same landing order during both the forward and backward scanning but has the disadvantage of requiring long print heads and being sensitive to a difference in coloring caused by a time difference between landing of each color.
With the method in 3), for example, the formation of forward- and backward-scanning print heads on the same substrate is equivalent to the provision of totally different print heads. Accordingly, this method has the disadvantage of creating band-like unevenly colored portions with a large color difference similar to an inter-head difference. For example, if there is a difference in temperature increase between the print heads associated with a difference in data rate between the forward and backward scanning caused by the interference among the data, a difference in the amount of ink ejected occurs between the print heads to form band-like unevenly colored portions.
This problem is serious in one-pass bidirectional printing, but a similar problem occurs with bidirectional multipass printing owing to a difference in the number of dots printed between the forward and backward printing passes, a difference in the number of dots obtained using a decimation mask for complementing data, or a difference in the number of dots printed associated the yielding of dots to printing of the rasters.
The method in 4) provides uneven colors of a high frequency to make it difficult to visually perceive the unevenness, so that depending on the type of print data, the color difference may be emphasized because of the interference among the data. For example, with an arrangement in which a color difference is created for each raster, if in a halftone portion such as screening, only even rasters are likely appear in a certain area in the forward or backward direction, while only odd rasters are likely appear in a certain area in the backward or forward direction, then a large color difference may occur even if the same color is designated.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a print apparatus and method using an ink jet printing apparatus based on what is called a multipass printing method that forms an image by executing main scanning a plurality of times in the same scanning area using different groups of nozzles, the ink jet printing apparatus being able to reduce the occurrence of uneven colors associated with a scanning direction even when bidirectional color printing is executed. The present invention also provides prints obtained by using this print apparatus and method.
It is another object of the present invention to provide a print apparatus and method that can reduce the occurrence of uneven colors associated with the scanning direction regardless of print data, as well as prints obtained using this print apparatus and method.
To attain this object, the present invention provides a print apparatus comprising print heads having a plurality of printing element rows each having a plurality of printing elements to form a color image by scanning the same scanning area a plurality of times in a forward and a backward directions using different printing element rows of the print heads to apply ink of a plurality of colors to a print medium, wherein the print heads are composed of two sets of printing element array sections each having printing element rows, the sets being sequentially arranged and ejecting different inks, the arrays of the printing element rows of the printing element array sections being set to be symmetrical in a scanning direction, and the print apparatus comprises mask means for complementarily masking predetermined rasters in a raster direction or predetermined columns in a column direction while scanning image data a plurality of times.
Further, the present invention provides a print apparatus comprising print heads having a plurality of printing element rows each having a plurality of printing elements to form a color image by scanning the same scanning area a plurality of times in a forward and a backward directions
Iwasaki Osamu
Otsuka Naoji
Takahashi Kiichiro
Teshigawara Minoru
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Thinh
LandOfFree
Print apparatus and print method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Print apparatus and print method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Print apparatus and print method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3295623