Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1997-06-23
2002-12-10
Nguyen, Lamson (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S040000, C347S015000
Reexamination Certificate
active
06491372
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an ink jet recording method and an ink jet recording apparatus. More particularly, the present invention relates to an ink jet recording method and an ink jet recording apparatus wherein recording is achieved using an ink jet recording head including a plurality of ink ejection ports.
2. Description of the Related Art
With a conventional recording process having a recording head including a plurality of ejection ports employed therefor, each row of plural dots to be formed by main scanning of a recording head (hereinafter referred simply as a line) is generally formed with ink droplets ejected from the same ejection port.
On the other hand, a pattern of each dot forming a line is classified into two types, one of them being such that one dot is formed by one ink droplet corresponding to binary gray level recording and the other one being such that one dot is formed by a plurality of ink droplets corresponding to multi-level recordings.
A so-called multi-droplet process has been known as one of the conventional method for forming a dot with ink droplets ejected from the same ejection port corresponding to the multi gray level recordings. This type of method is intended to express the gray level of a recorded image by forming one dot (pixel) with a plurality of ink droplets shot onto a single location on a recording medium and then changing a dot area or a dot density depending on the number of ink droplets shot onto the recording medium, and has an advantage that the foregoing method makes it possible to perform a recording operation at a high speed for forming an image with high resolution and high gray level compared with various conventional methods, e.g., a tone production method by density of each element, a tone production method by density pattern, a dither method and an ink density variation method by using plural density of ink.
Although the respective dots forming a line are formed corresponding to binary gray level recording or the multi gray level recording, a problem such as running over of ink or bleeding, which is described below, may occur. Especially, the problem such as bleeding may appear when intending to achieve a high quality recorded image by solving the problem described below which may occur in the case that the dots are formed with ink droplets ejected from the same ejection port, so that the high quality recorded image can not be achieved.
With respect to a plurality of ejection ports on the recording head, in the case that the direction of ejection of ink droplets from the ejection ports and a quantity of ink ejected from the same ejection port fluctuate from ejection port to ejection port, there arises an occasion that a certain stripe appears on a recorded image which should originally have constant density variation or a density of the image fluctuates. More specifically, in the case that the direction of ejection of ink droplets fluctuates, the position of a dot formed on a recording paper serving as a recording medium is offset from an original one, resulting in a stripe appearing on the recorded image. When a quantity of ink ejected from the ejection ports fluctuates, a size of each dot formed on the recording paper or a density of the same fluctuates. As a result, there arises an occasion that the density of the recorded image fluctuates.
As a measure to be taken for avoiding the foregoing problems, a proposal has been made with respect to a method of producing a recording head at a very high accuracy in order to suppress fluctuation in the direction of ejection of ink from each ejection port and a quantity of ink ejected from the same as far as possible. However, with the proposed method as mentioned above, there arises a problem that each recorded image is obtained not only at a high production cost but also at a reduced yielding rate.
In addition, as a measure to be taken for obviating a malfunction of fluctuation in density, a proposal has been made with respect to a method of changing the number of shot ink droplets so as to eliminate variation of a quantity of ejected ink among a plurality of ink ejection ports on a recording head. However, in the case that the proposed method is installed in a working system for executing the proposed method, there arises a problem that a running cost of the working system is undesirably increased. Further, it is found that the proposed method is unexpectedly ineffective for preventing a stripe from appearing on a recorded image. In the case that fluctuation in a quantity of ejected ink among the ejection ports varies as time elapses, it becomes necessary to adjust the number of shot ink droplets again. This leads to a problem that each maintenance service for the working system is unsatisfactorily achieved.
To solve the aforementioned problems, an improved recording method is disclosed in an official gazette of, e.g., Japanese Patent Application Laying-open No. 107975/1985. According to this prior art, to reduce variation of the direction of ink ejection and a quantity of ejected ink among a plurality of ejection ports, and moreover, hardly visualize stripe and fluctuation in density, a single line extending in the main scanning direction is formed by a plurality of ink droplets ejected from the ejection ports.
FIG. 1
is a schematic view which illustratively explains the recording method to be practiced according to the prior art. Specifically, pixels not located adjacent to each other not only in the vertical direction but also in the transverse direction are recorded on a recording paper (not shown) by preceding main scanning (hereinafter referred to as preceding scanning) with a recording head, and subsequently, the recording paper is fed in the auxiliary scanning direction by a distance equal to a half of the length of a row of ejection ports so that the remaining pixels failing to be recorded by the preceding scanning are recorded on the recording paper by subsequent scanning. According to the above-described prior art, for example, in the case that all pixels located on each line as illustrated by “image data” in
FIG. 1
are formed on the recording paper, a row of dots arranged in the main scanning direction (i.e., a line) is formed with ink droplets ejected from two different ejection ports. Thus, distribution of the dots in the ink ejecting direction is averaged, resulting in stripe on the line being hardly visualized. With the recording method shown in
FIG. 1
, when it is assumed that variation of a quantity of ink ejection among the ejection ports is normally distributed with a standard deviation &sgr;, the variation of a quantity of ink ejection among a plurality of lines is reduced to a level of &sgr;/{square root over (2)}. Consequently, since variation of a quantity of ejected ink among the lines is visually recognized as variation of density among the lines, the recorded image having few fluctuation in density is obtainable.
For example, as illustrated by “image data” in
FIG. 2
, in the case that a specific halftone image (i.e., all pixels are not formed) is recorded on a recording paper (not shown), since a row of dots arranged in the main scanning direction is formed by ink droplets ejected from the same ejection port when the foregoing conventional recording method is employed, there arises a problem that fluctuation in stripe and density can not be reduced at all.
Another recording method of hardly visually recognizing stripe and fluctuation in density is disclosed in U.S. Ser. No. 894,555 which was proposed by common assignee to the present invention. According to this prior art, in association with assignment of image data to ejection ports, ink dots forming a row of dots arranged in the main scanning direction (i.e., a line) are sequentially assigned to scannings different from each other. Once this conventional recording method is employed, not only in the case that all pixels as illustrated by “image data” in
FIG. 1
are formed but also in the case that a halftone image as illu
Shioya Makoto
Tamura Yasuyuki
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Lamson
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