Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2001-11-27
2004-03-30
Gordon, Raquel Yvette (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S019000
Reexamination Certificate
active
06712443
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet recording apparatus for recording on a recording material by discharging ink from recording means.
2. Related Background Art
A recording apparatus, which is provided to function as a printer, a copying machine, or a facsimile machine, or used as an output device for a work station or a complex electronics apparatus including a computer or word processor, is structured to record on a recording medium, such as a recording sheet or thin plastic plate, images that include characters, drawings, and the like in accordance with image information including information on characters, drawings, and the like. The recording apparatus is classified into ink jet type, wire-dot type, thermal type, laser beam type, or some other type. Of those recording apparatuses, the recording apparatus of ink jet type (hereinafter may be referred to also as an ink jet recording apparatus) performs recording by discharging ink from recording means (hereinafter may be referred to also as a recording head) to a recording medium, and this recording means has such excellent advantages as to make it easier to record in higher precision at higher speed with a lesser amount of noise, and at lower cost than the other types.
Also, in recent years, there has been an increasing need for a recording apparatus capable of outputting highly precise color images, and there have been developed, too, various color ink jet recording apparatuses capable of recording color images by discharging ink of plural colors.
In such an ink jet recording apparatus, a recording head having a plurality of recording elements integrally arranged is used for improving a recording speed. As for that recording head, it is generally practiced that a plurality of integrally formed ink discharge ports and liquid flow paths are used for the ink discharge portion. Also, for color recording, a plurality of the aforesaid recording heads are provided.
FIG. 1
is a view that shows the structure of the printing unit used for printing by the aforesaid recording head on the surface of a recording sheet. In
FIG. 1
, each structure designated by a reference numeral
101
is an ink cartridge. Each of them is formed by an ink tank containing one of four colors, black, cyan, magenta, and yellow, respectively, as well as by a recording head
102
. For the recording head
102
, the discharge port array is formed with a plurality of discharge ports.
FIG. 2
is a view that schematically shows the state of the plurality of discharge ports arranged for the recording head
102
, observed in the direction indicated by z in FIG.
1
. In
FIG. 2
, a reference numeral
201
designates a plurality of discharge ports arranged on the recording head
102
.
Also, in
FIG. 1
, a reference numeral
103
designates a sheet conveying roller that conveys the recording sheet P in the direction y, as required, by rotating in the direction indicated by an arrow in
FIG. 1
, while pressing the recording sheet P in cooperation with an auxiliary roller
104
. Also, a reference numeral
105
designates a sheet feed roller for feeding a recording sheet, while pressing the recording sheet P in the same manner as the rollers
103
and
104
. A reference numeral
106
designates a carriage to support the four ink cartridges, and allows printing by enabling them to travel. The carriage is arranged to be on standby in the home position h indicated by dotted line in
FIG. 1
when printing is at rest or operating the recovery of the recording head or the like.
The carriage
106
in the home position before the initiation of printing is caused to travel in the direction indicated by an arrow X in
FIG. 1
when the command to begin printing is received, while discharging ink from a plurality of discharge ports
201
formed on the discharge port surface of the recording head
102
for recording in accordance with recording data. Then, when printing of data is completed up to the edge portion of the recording sheet, the carriage returns to the original home position and again performs printing while traveling in the direction X.
When pictorial images are printed, various elements, such as coloring, gradation, and evenness, are required. Particularly, for evenness, slight variations of nozzles per unit that may take place in the manufacturing process of a recording head tend to exert influence on the ink discharge amount of each nozzle and the discharging direction thereof in the printing operation, and it is known that the degradation of image quality is brought about by this influence eventually as density unevenness of printed image.
Here, the specific example thereof will be described in conjunction with
FIGS. 3 and 4
. At (
1
) in
FIG. 3
, a reference numeral
31
designates the recording head schematically. The nozzle array provided for the recording head
31
is formed by eight nozzles
32
. Also in
FIG. 3
, a reference numeral
33
designates an ink droplet discharged from the nozzle
32
(hereinafter, may be referred to also as “ink droplet” or simply as “ink”). Also, (
2
) in
FIG. 3
shows one example of the image that is formed by ink discharged periodically from the nozzle array of the recording head
31
. (
2
) in
FIG. 3
represents the example, in which recording is performed with eight dots per each nozzle, while the recording head is being moved. (
3
) in
FIG. 3
is a graph that shows the optical density of the image represented at (
2
) in FIG.
3
. At (
3
) in
FIG. 3
, the axis of abscissa corresponds to the density.
Ideally, each ink droplet discharge from the recording head
31
should be in the same amount and direction as shown at (
1
) in FIG.
3
. If discharge is made ideally like this, dots of the same size are impacted on the surface of recording sheet as shown at (
2
) in FIG.
3
. As a result, then, it becomes possible to obtain an image having no unevenness in overall density as shown at (
3
) in FIG.
3
.
However, as described earlier, there are actually variations in individual nozzles, and if ink is discharged for printing without compensation, density unevenness is created due to the variations of the size of each ink droplet discharged from each nozzle and the direction thereof.
FIG. 4
is a view that schematically illustrates density unevenness when there are variations in a plurality of nozzles of the recording head. (
1
) to (
3
) in
FIG. 3
correspond to (
1
) to (
3
) in
FIG. 4
, respectively. In comparison with each other, it is possible to compare each condition of recording when it is ideally performed and when it is performed with the nozzles having individual variations.
(
1
) in
FIG. 4
shows the recording head, and the state where there are variations in the size and direction of each of the ink droplets discharged from the recording heads. As shown at (
1
) in
FIG. 4
, when the size and direction of each ink droplet discharged for each nozzle are varied, each of them is impacted on the surface of the recording sheet as shown at (
2
) in FIG.
4
. According to (
2
) in
FIG. 4
, there exist periodically the blank portion on the recording sheet where the area factor is not satisfied 100% with respect to the head main scanning direction, or on the contrary, dots are overlapped more than necessary or as shown in the central part of (
2
) in
FIG. 4
, a white streak occurs. The gathering of dots thus impacted presents the density distribution as shown at (
3
) in
FIG. 4
with respect to the direction of the nozzle array. As a result, these phenomena are sensed as density unevenness as far as the normal human eyesight is concerned. Also, there may be some cases where streaks become conspicuous due to the variations that may take place in the amount of sheet feeding.
To cope with the density unevenness described above, a method for reducing density unevenness is disclosed in the specification of Japanese Patent Application Laid-Open No. 06-143618. With reference to
FIG. 5
, such method will be described briefly hereunder.
The recording operation sho
Kanda Hidehiko
Moriyama Jiro
Nakagawa Yoshinori
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Gordon Raquel Yvette
Stewart Jr. Charles W.
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