Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-05-31
2004-02-24
Nguyen, Lamson D (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S014000, C347S037000
Reexamination Certificate
active
06695432
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink-jet recording apparatus and an ink-jet recording method. More particularly, the invention relates to an ink-jet recording apparatus and an ink-jet recording method performing multi-pass recording in which an image is formed by executing a plurality of runs of main scanning moving a recording head discharging ink a plurality of times relative to a recording medium for the individual recording areas on the recording medium.
2. Description of the Related Art
A recording apparatus such as a printer, copying machine, or facsimile machine; or a composite type electronic device such as a computer or a wordprocessor; or a recording apparatus used as an output device such as a workstation, has a configuration to permit recording onto a recording medium such as a sheet of paper or a plastic sheet on the basis of the image information including character information and the like.
These recording apparatuses can be classified, in terms of their recording method, into ink-jet, wire-dot, thermal and laser beam recording apparatuses. From among these recording apparatuses, the ink-jet type of recording apparatus (ink-jet recording apparatus) accomplishes recording by discharging ink from a recording means such as a recording head onto a recording medium, and has excellent features of easy refinement, high speed, quietness, and low cost.
On the other hand, there is an increasing demand for color recording, and many color ink-jet recording apparatuses have been developed. The ink-jet recording apparatus uses a recording head comprising a plurality of ink discharge ports and liquid paths for ink discharge to improve the recording speed, and generally has a plurality of recording heads.
FIG. 1
illustrates a schematic configuration of a general printer section of the type in which recording is performed by causing a recording head to scan a plurality of times a sheet of recording paper P. In
FIG. 1
, reference numeral
101
represents four different ink cartridges. Each of the four cartridges comprises an ink tank containing either black, cyan, magenta or yellow ink, and a recording head
102
.
FIG. 2
illustrates a cross-sectional view of a discharge port provided in each recording head, as viewed from the z-direction. As shown in
FIG. 2
, a plurality of discharge ports
201
are arranged at prescribed intervals on the recording head
102
.
Referring again to
FIG. 1
, reference numeral
103
represents a paper feeding roller, which rotates in the arrow direction in
FIG. 1
while pressing sheets of recording paper P, together with an auxiliary roller
104
, thus feeding the recording paper P from time to time in the y-direction; reference numeral
105
, a pair of paper feeding roller, also feed recording paper and plays a role of pressing the recording paper P, similar to the paper feeding roller
103
and the auxiliary roller
104
; and reference numeral
106
, a carriage, supports the four ink cartridges
101
and causes them to move and scan upon recording. When recording is not conducted, or when carrying out a recovery operation of the recording head, the four ink cartridges are waiting at a home position (h), as shown by the dotted line in FIG.
1
.
Before starting recording, and upon receipt of a recording start command, the carriage
106
at the home position in
FIG. 1
discharges ink from a plurality of discharge ports
201
(shown in
FIG. 2
) on the recording head
102
while moving in an x-direction for recording. When the recording of data at the end of the paper is completed, the carriage
106
returns to the home position h, and performs recording again in the x-direction.
When recording an image or the like, various factors including the properties of each color, gradation and uniformity need to be considered. In particular, with regard to uniformity, it is known that a slight variation between nozzles produced during the recording head manufacturing process exerts an influence on the ink discharge amount of each nozzle or the direction of ink discharge upon recording, leads to deterioration of the image quality as a density irregularity of the recorded image.
A concrete example of this density irregularity will be provided, with reference to
FIGS. 3 and 4
. In
FIG. 3A
, reference numeral
31
represents a recording head comprising eight nozzles
32
; and reference numeral
33
represents ink drops discharged by the nozzles
32
, which should ideally be discharged in uniform amounts and in a uniform direction, as shown in FIG.
3
. When such a discharge is achieved, dots of a uniform size are dropped, as shown in
FIG. 3B
, and a uniform image, free from density irregularity as a whole, is obtained (as shown in FIG.
3
C).
However, nozzles are not uniform as described above. If recording is conducted with these nozzles as they are, variations in size and the irregular direction of ink drops discharged from the individual nozzles occurs, as shown in
FIG. 4A
, and the ink drops reach the recording medium in a non-uniform manner as shown in FIG.
4
B. According to
FIG. 4B
, blank portions, which cannot fully satisfy an area factor of 100%, are present periodically in the head's main scanning direction, or dots overlap, or a white line, as observed at the center of
FIG. 4B
is produced.
A collection of dots deposited in the state as described above (as shown in
FIG. 4B
) takes a density distribution, as shown in
FIG. 4C
, and finally, as viewed by ordinary human eyes, these phenomena are sensed as density irregularities. Apart from this, when there are variations in the paper feed amount, lines may become apparent in the recorded image.
To avoid such density irregularities, U.S. Pat. No. 5,696,542 discloses the following method, which will briefly be described with reference to
FIGS. 4 and 5
. According to this method, three runs of main scanning of a recording head
31
are conducted (
FIG. 5A
) to complete a recording area shown in
FIG. 5B
, and a unit area of four pixels accounting for half of the recording area is completed with two passes. In this case, eight nozzles of the recording head are divided into two groups including four upper nozzles and four lower nozzles. Dots recorded in a single run of main scanning by a nozzle are those resulting from a prescribed image data thinned to about a half in accordance with a prescribed image data arrangement (printed pattern). During the second run of main scanning, the remaining half of the dots are embedded in the printed medium to complete the recording of a unit area of four pixels. This recording method is hereinafter referred to as the multi-pass recording method.
According to such a recording method, even when using a head equivalent to the recording head shown in
FIG. 4
, the effect of variations intrinsic to the individual nozzles on the recorded image is reduced by half, resulting in a recorded image as shown in
FIG. 5B
, the black and white lines observed in
FIG. 4B
are not very conspicuous. Therefore, the density irregularities are alleviated to a large extent as compared with the case shown in
FIG. 4C
, as shown in FIG.
5
C.
When conducting such multi-pass recording, in the first and second runs of main scanning, image data are divided in a mutually compensating form in accordance with a prescribed printed pattern. For this printed pattern, it is common to use one printed pattern that results in a checkers pattern for each pixel horizontally and vertically formed. This printed pattern is hereinafter referred to as the checkers pattern. By using such a printed pattern, in a unit recording area (in units of four pixels in this case), recording is completed by the first run of main scanning for recording the checkers pattern and the second run of main scanning for recording the reverse checkers pattern. The checkers pattern used in the second run of main scanning is just the reverse of the checkers pattern used in the first run of main scanning.
FIGS. 6A
,
6
B, and
6
C illustrate how recording on a certain
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Lamson D
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