Facsimile and static presentation processing – Static presentation processing – Position or velocity determined
Reexamination Certificate
1999-01-20
2003-12-16
Williams, Kimberly A. (Department: 2724)
Facsimile and static presentation processing
Static presentation processing
Position or velocity determined
C358S001900, C358S001100, C358S001800, C358S001120, C358S001160, C358S502000, C347S020000, C347S009000, C347S041000
Reexamination Certificate
active
06665091
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing apparatus that creates dots in the course of a main scan both in a forward direction and in a backward direction and thereby records an image on a printing medium, as well as to a method of such printing and a recording medium to actualize the printing apparatus.
2. Description of the Related Art
Color printers with a head that can spout inks of several different colors are widely used as an output device of a computer system to print a multi-color image that has been processed by a computer. One proposed technique for such printers creates dots in the course of not only a forward movement but a backward movement of a head for the main scan, which moves the head forward and backward relative to a printing medium. The dot creation by this technique is hereinafter referred to as the dual-way printing.
One procedure of the dual-way printing creates part of the dots included in one raster line with one nozzle in the course of a forward movement of the head, while creating the remaining dots of the raster line with another nozzle in the course of a backward movement of the head. Namely all the dots included in one raster line are completed by the forward and backward movements of the head. This recording method, which records one raster line with different nozzles, disperses the positional displacement of the dots due to mechanical errors in the manufacture of nozzles and thereby improves the picture quality.
Another procedure of the dual-way printing creates all the dots included in one raster line in the course of a forward movement of the head, while creating all the dots included in another raster line in the course of a backward movement of the head. Compared with the single-way printing, this recording method doubles the efficiency of dot creation and thereby enhances the printing speed.
Another proposed technique for the conventional printer having only the binary tone expression (on-off) for each dot enhances the number of tones expressible for each dot. One structure of this technique provides two inks of different densities for an identical hue (see, for example, JAPANESE PATENT LAID-OPEN GAZETTE No. 8-209232). Another structure of this technique enables creation of several different types of dots having different diameters (see, for example, JAPANESE PATENT LAID-OPEN GAZETTE No. 59-201864). These procedures enrich the tone expression of the printer and improve the picture quality of a resulting image.
With an improvement in picture quality of the resulting image output from the printer, it is highly demanded to make the high picture quality compatible with the high printing speed. In order to fulfill these requirements, the inventors of the present invention tried to apply the dual-way printing that enhances the printing speed for the printer that can create dots of different diameters. The dual-way printing may, however, cause the positions of the dots created in the course of a backward movement of the head to be deviated from the expected positions based on the positions of the dots created in the course of a forward movement of the head. This results in non-allowable deterioration of the picture quality. Such positional misalignment of the dots is ascribed to a backlash or play required for the driving mechanism of the printer as well as to a difference in thickness of paper used as the printing medium.
FIG. 13
shows a state of causing positional misalignment of the dots due to a difference in thickness of paper. Referring to FIG.
13
(
a
), a dot dt
11
is created on a sheet of paper PA
1
in the forward direction of the main scan, whereas a dot dt
12
is created in the backward direction of the main scan to be located adjacent to the dot dt
11
. A nozzle Nz jets ink droplets Ik
11
and Ik
12
at the positions shown in FIG.
13
(
a
) by taking into account the speeds in the forward direction and the backward direction of the main scan. These ink droplets Ik
11
and Ik
12
draw the loci shown in FIG.
13
(
a
) and reach the target positions on the paper PA
1
to create the dots dt
11
and dt
12
.
FIG.
13
(
b
) shows the state of dot creation on a sheet of paper PA
2
having a greater thickness. The distance between the nozzle Nz and the paper PA
2
in FIG.
13
(
b
) is smaller than the distance between the nozzle Nz and the paper PA
1
in FIG.
13
(
a
). If the ink droplets are jetted at the identical timings with those of FIG.
13
(
a
) in both the forward direction and the backward direction of the main scan, ink droplets Ik
21
and Ik
22
draw the loci shown in FIG.
13
(
b
) and hit the paper PA
2
to create the dots dt
21
and dt
22
. This causes the dots dt
21
and dt
22
not to be located adjacent to each other and thereby does not give a desired image. In order to obtain a desired image, it is required to delay the ink jet timing in the backward direction of the main scan. Since the difference in thickness of paper may cause the positional misalignment of the dots in the main scanning direction in the case of dual-way printing, it is difficult to completely eliminate the possibility of positional misalignment by the fine regulation at the time of shipment of the printer.
FIG. 14
shows an example of dot creation by a head with a plurality of nozzles in the conventional dual-way printing. In the left part of
FIG. 14
, both the symbols, the circle O and the square □, with numerals included therein denote an identical nozzle array. The circles O represent the positions of the respective nozzles in the course of a forward movement of the head, whereas the squares □ represent the positions of the respective nozzles in the course of a backward movement of the head. The numerals are assigned to the respective nozzles included in the nozzle array, for convenience of explanation. Each of the symbols P
1
, P
2
, . . . affixed to the nozzle array represents the number of times of the main scan. After each main scan, a sub-scan is carried out to feed the sheet of paper by a fixed amount of 5 raster lines. A desired image is recorded by creating all the dots in raster lines by the respective main scans.
The right part of
FIG. 14
shows dots recorded by the scans of the head. This example forms a vertical ruled line having the width of 2 dots in the main scanning direction. The vertical line is generally formed with dots of a large diameter (hereinafter referred to as large dots), in order to emphasize the contrast with the background. The circles O and the squares □ represent the dots created in the course of the forward movement and the backward movement of the head, respectively. Raster lines formed in the forward direction of the main scan and raster lines formed in the backward direction of the main scan are arranged alternately. In the example of
FIG. 14
, the nozzle array includes 13 nozzles and the nozzle pitch in the sub-scanning direction is four times the recording pitch of the image.
As discussed previously with the drawing of
FIG. 13
, in the case of dual-way printing, the positions of the dots created in the course of a backward movement of the head may be deviated from the positions of the dots created in the course of a forward movement of the head in the main scanning direction. If the dots created in the backward direction of the main scan are displaced rightward relative to the dots created in the forward direction of the main scan, the resulting image is a vertical line where the positions of the dots are periodically changed by every raster line as shown in FIG.
14
. This causes the vertical line to be visually recognized as envelopes
11
and
12
. Namely the resulting image is recognized not as a straight line but as a wavy curve. The vision of the human is extremely sensitive to such positional misalignment, especially in the vertical direction. Even the displacement of less than one dot as shown in
FIG. 14
is recognizable with naked eye. Such positional misalignment is thus not negligible to attain the high picture qualit
Ghee Ashanti
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seiko Epson Corporation
Williams Kimberly A.
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