Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-06-01
2003-03-04
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S016000
Reexamination Certificate
active
06527364
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a multi-scan recording method and a high speed recording apparatus, which can be used in combination to record at a high speed and a high level of quality, without the problems which occur when a conventional multi-scan recording method is used in combination with a high speed recording apparatus.
In recent years, various office automation business machines such as personal computers or word processors have come to be widely used, along with various recording apparatuses for printing out the data inputted with the use of these machines. Also, the technologies for printing high quality images at a high speed with the use of these machines have been rapidly developed.
First, these technologies will be briefly described.
(1) Technologies for Improving Image Quality
One of the technologies for improving image quality is a multiple scanning recording.
When an image is recorded with the use of a recording head comprising a plurality of recording elements, the quality of an image to be recorded greatly depends on the performance of the recording head itself. Slight differences in shape among the ejection orifices of a recording head or electrothermal transducers (ejection heaters), which occur during the recording head manufacturing process, affect the amount by which ink is ejected from each ejection orifice, or the direction in which ink is ejected from each ejection orifice. In other words, the presence of these differences manifest as nonuniform density in a final image, reducing the image quality.
An example of such manifestation of nonuniform density will be described with reference to
FIGS. 1 and 2
. In
FIG. 1
, (a), a referential character
201
designates a recording head. For the sake of more simple description, it is assumed that the recording head
201
comprises eight nozzles
202
. A referential character
203
designates an ink droplet ejected by a nozzle
202
. Ideally, all ink droplets are the same in terms of the amount (normal amount) by which they are ejected, and also in terms of the direction in which they are ejected as illustrated in
FIG. 1
, (a). When ink is ejected as illustrated in
FIG. 1
, (a), all the dots formed on a piece of recording sheet as the ink droplets land on the recording sheet will be uniform in size as illustrated in
FIG. 1
, (b). Therefore, an image which does not suffer from nonuniform density, as illustrated in
FIG. 1
, (c), is formed.
In reality, however, each nozzle
202
of the recording head
201
is different in ejection characteristic from the other. Therefore, if an image is recorded as described above, the ink droplet ejected from each nozzle becomes different in size and direction from those ejected from the other nozzles as illustrated in
FIG. 2
, (a). As a result, a pattern such as the one illustrated in
FIG. 2
, (b) is created on a piece of recording sheet as the ink droplets land on the recording sheet. In other words, as is evident from
FIG. 2
, (b), white spots are visible, which are created when the area factor fails to reach 100%, that is, when a unit strip of recording field fails to be 100% covered with the ink. These white spots align in the primary scanning direction of the recording head. Also, there are spots where the dots excessively overlap, and/or white strips like the white strip at the center of
FIG. 2
, (b). In other words, the recording density distribution of the image created as ink droplets different in size and direction land on the recording sheet becomes as illustrated in
FIG. 2
, (c), being nonuniform in terms of the direction in which the nozzles are aligned. This nonuniform density distribution is sensed as an anomaly by a person with normal eyesight.
Thus, the following method has been devised as a measure for dealing with such a problem, which will be described with reference to
FIGS. 3 and 4
. Referring to
FIG. 3
, according to this method, in order to complete an image area illustrated in
FIGS. 1 and 2
, the recording head
201
was run three times. The top half of the image area, which amounts to one half of the image area, and corresponds to a unit of four picture elements, is completed through two runs of the recording head
201
. More specifically, the eight nozzles of the recording head
201
are divided into top and bottom groups, which comprises the top four nozzles and the bottom four nozzles, respectively. The number of dots placed per scan, or recording run, by a single nozzle is half the number of the dots, which will be placed in accordance with a full set of image formation data correspondent to a single raster when a conventional multi-scan recording method is employed; in other words, the dot density is thinned to a half, according to a predetermined image data arrangement. During the second run, dots are filled into the spots correspondent to the remaining half of the image formation data, to complete the aforementioned strip of recording field correspondent to a unit of four recording elements. This recording method is called the “multi-scan recording method”.
With the use of this recording method, the effects of the difference in size and direction among the nozzles of a recording head is halved even when a recording head such as the one illustrated in
FIG. 2
is used. Therefore, an image area such as the one illustrated in
FIG. 3
, (b) is created, in which the black or white strips illustrated in
FIG. 2
, (b) are less obtrusive, and which has a recording density distribution illustrated in
FIG. 3
, (c); anomaly in density is substantially small.
Also in this recording method, a set of image formation data is divided according to a predetermined arrangement (mask), into two sub-sets, which compensate for each other. One of the most commonly used image formation data arrangement patterns (dot density thinning pattern) is a pattern which produces the dot placement pattern illustrated in
FIGS. 4
, (a)-(c), in which the dot density is thinned by eliminating every other dot in terms of both the vertical and horizontal directions so that the remaining dots are staggered relative to the dots in the adjacent lines. A unit strip of recording field (recorded here by a unit of four recording elements) is recorded by two recording runs: the first run which places dots in the staggered pattern illustrated in
FIG. 4
, (a), and the second run which places dots in the staggered pattern illustrated in
FIG. 4
, (b). The second staggered pattern is the reversal of the first staggered pattern.
In most cases, the distance recording medium is advanced in the secondary scanning direction, per recording run, is set to be constant. In the case illustrated in
FIGS. 3 and 4
, recording medium was advanced by a distance equivalent to four nozzles, per recording run.
(2) High Speed Recording Technology
As one example of technology for increasing recording speed, it is possible to increase the number of nozzles. In the case of the serial recording method in which a unit strip of recording field is recorded through a single recording run in which all the nozzles of a recording head are activated, recording speed increases as the number of nozzles is increased, although the increase in recording speed is not exactly proportional to the increase in the number of nozzle because of the time used for feeding or discharging a plurality of recording sheets, or the like operations. For example, if a recording head with 64 nozzles is set to record at a resolution of 360 dpi, the recording of a piece of recording medium with a size of A4 can be completed by approximately 60 recording runs. However, if a recording head with 256 nozzles is set to record at the same resolution, the recording of the same medium can be completed by approximately 15 recording runs; in other words, recording speed increases to a speed four times the speed of the first head.
In the case of the first head, the length of the nozzle alignment is approximately 4.52 mm (=25.4 mm/360 dpi×64 nozzles), whereas in the case of the second head, it
Iwasaki Osamu
Nishikori Hitoshi
Otsuka Naoji
Takahashi Kiichiro
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