Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-04-06
2002-07-16
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S037000
Reexamination Certificate
active
06419338
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing apparatus and a printing method for printing an image on a printing medium by actuating a printing head such as an inkjet printing head under its scanning movement.
2. Description of the prior Art
FIG. 2
shows an example of a printing apparatus that can be constructed as a main part of an inkjet color printer or the like. For printing an image on a sheet of printing paper
105
being placed on a platen
106
, at first, a driving motor
103
is activated to drive a driving belt
109
by which a carriage
102
is shifted to a position facing a home-position sensor
108
in the direction of main-scanning (i.e., the direction perpendicular to the direction of feeding the sheet of printing paper). Then, the carriage
102
moves forward in a scanning movement in the direction of the arrow A to bring printing heads
120
,
121
,
122
, and
123
toward a predetermined scanning area. These printing heads
120
-
123
are respectively provided for ejecting black (K), cyan (C), magenta (M), and yellow (Y) color inks. These color inks are ejected onto a sheet of printing paper
105
to make an image while the carriage travels through the predetermined scanning area. The forward-scanning movement of the carriage
102
is stopped when the image printing of a predetermined length is terminated. Subsequently, the carriage
102
starts to move in the reverse direction toward the position facing the home-position sensor
108
as a reverse-scanning movement thereof in the direction of the arrow B. During the reverse-scanning movement, a paper-feed motor
107
drives a paper-feed roller
105
to feed the paper in the direction of the arrow C (i.e., sub-scanning direction). Repeating the cycle of these steps, the printing of a color image on the printing paper
105
can be completed. In the figure, by the way, the reference numeral
100
denotes a second paper-feed roller and
111
denotes a sensor for detecting the presence or absence of paper on the platen
106
.
Referring now to
FIG. 3
, there is shown the relationship between a speed of the carriage
102
that moves in the direction of forward-scanning and an interval of time required for printing a line of image. In the figure, the motor
103
is activated at a point of time indicated by the reference numeral
130
to move the carriage
102
in the direction of forward scanning. During the period T
1
(i.e., acceleration time), the carriage
102
is accelerated. After the point of time
131
at which the carriage
102
reaches a predetermined speed, the printing heads
120
,
121
,
122
, and
123
start ink ejection respectively to form an image on a sheet of paper. At the point of time
132
after lapse of the time T
2
, the printing movement is terminated and the carriage
102
is decelerated. Finally, the carriage
102
comes to a stop at the point of time
133
after lapse of the time T
3
. Accordingly, the printing movement of the conventional printing apparatus requires several steps as described above because of the impossibility of an increase in the rotational speed of the motor right up to the printing speed of the carriage
102
. Furthermore, the printing speed is also defined by the printing resolution and the refill frequency. In this description, by the way, the term “printing speed” means a speed of the carriage during the interval of ejecting ink from the printing heads; and the term of “refill frequency” means a number of times each of the printing heads
120
,
121
,
122
, and
123
is refilled with ink after ejecting ink within a specified interval.
The printing speed of the carriage
102
can be calculated, for example, by the following equation (1).
V=(25.4/R)×F (1),
wherein “R” denotes a printing resolution (dots per inch); “F” denotes a refill frequency (10 kHz); “V” denotes a printing speed (millimeter per second); and “25.4” is a scale factor (i.e., one inch is equal to 25.4 millimeters).
If “R”=600 dpi and “F”=10 kHz, for example, then the printing speed “V” can be calculated using the above equation (1) as follows.
V=(25.4/R)×F=(25.4/600)×10000=423.33 (mm/s).
In this case, therefore, the carriage
102
shifts its position at that speed. A linear encoder (not shown) optically or magnetically recognizes the scanning position of the carriage
102
. Thus, the printing heads eject ink droplets with reference to output signals from the linear encoder, resulting in an image formed by equally placing the ink dots on a sheet of the printing paper
105
. Accordingly, the above description facilitates the understanding of the need for the intervals of time for acceleration and deceleration of the carriage
102
to attain the formation of equally distributed ink dots.
FIG. 4
illustrates the example of ejecting ink from the printing head at the time of accelerating and decelerating the carriage
102
. In the figure, a solid line
300
indicates the relationship between the carriage's speed and time just as is the case with FIG.
3
. Encoder pulses
301
are generated from the linear encoder (not shown) that optically or magnetically recognizes the scanning position of the carriage
102
. If the printing head ejects an ink droplet by the falling edge of an encoder pulse, a dot to be formed on a sheet of the printing paper
105
can be represented by the reference numeral
302
, as schematically shown in FIG.
4
. During the intervals of accelerating and decelerating the carriage
102
, as can be seen from
FIG. 4
, dots are not equally distributed on the printing paper
105
. This means that a locus of a flying ink droplet is changed with respect to the scanning speed of the carriage
102
. That is, an ink droplet ejected from the printing head reaches a point which is displaced a distance “X
1
” from a predetermined point in the direction of carriage travel. The distance “X
1
” can be expressed by the following equation (2).
X
1
=
VCr
1
×(
S/V
) (2),
wherein, “S” denotes a distance between the printing head and a sheet of the printing paper
105
(see FIG.
5
A); “V” denotes a speed of an ink droplet ejected from the printing head (see FIG.
5
B); and “VCrl” denotes a speed of the carriage that travels in the direction of forward-scanning (see FIG.
5
B).
According to the equation (1), as shown in
FIG. 5C
, the deviation “X
1
” doubles (i.e., 2×X
1
=X
2
) as the carriage speed “VCr
1
” doubles (i.e., 2×VCr
1
=VCr
2
). Therefore, the conventional printing apparatus must start the printing after the carriage attains a constant speed and also controls the carriage so as to be kept at a constant speed during the step of printing an image on the printing paper.
Regarding the movement of the carriage
102
during the step of printing, the conventional example described above requires both acceleration and deceleration times T
1
, T
3
in addition to the actual printing time T
2
, so that the conventional approach takes a long time to complete the entire process, resulting in difficulty of attaining the high-speed printing movement. It means that a needless or wasted time (T
1
+T
3
) is required for printing a band (i.e., an amount of image which can be printed by one scanning movement of the carriage). If the number of the scanning movements of the carriage
102
to be required for printing a page (i.e., one complete image to be printed on one side of a sheet of paper) is “N”, there is a needless time “(T
1
+T
3
)×N” in addition to an actual printing time “T
2
×N”. In this case, furthermore, attention must be directed toward additional spaces extending in the directions of both forward and reverse movements of the carriage, respectively. Such spaces are required for both the acceleration and deceleration movements by the time “T
1
+T
3
”. Consequently, due to such additional spaces, the width of the printing apparatus becomes large.
The conventional printing apparatus has another d
Canon Kabushiki Kaisha
Dudding Alfred
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