U.S. patent application number 14/668756 was filed with the patent office on 2015-10-01 for printing apparatus, printing method, and program.
The applicant listed for this patent is CANON KABUSHIKI KAISHA. Invention is credited to Yoshinori Nakajima.
Application Number | 20150273820 14/668756 |
Document ID | / |
Family ID | 54189106 |
Filed Date | 2015-10-01 |
United States Patent
Application |
20150273820 |
Kind Code |
A1 |
Nakajima; Yoshinori |
October 1, 2015 |
PRINTING APPARATUS, PRINTING METHOD, AND PROGRAM
Abstract
A discharge amount of ink is corrected so that thinning rates of
a discharge amount of ink to be discharged to an end portion on an
upstream side in a scanning direction are larger than thinning
rates of a discharge amount of ink to be discharged to an end
portion on a downstream side in the scanning direction.
Inventors: |
Nakajima; Yoshinori;
(Yokohama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CANON KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Family ID: |
54189106 |
Appl. No.: |
14/668756 |
Filed: |
March 25, 2015 |
Current U.S.
Class: |
347/14 |
Current CPC
Class: |
B41J 2/2132 20130101;
B41J 11/0085 20130101; B41J 11/002 20130101 |
International
Class: |
B41J 2/045 20060101
B41J002/045; B41J 11/00 20060101 B41J011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2014 |
JP |
2014-069578 |
Claims
1. A printing apparatus comprising: a printing head including a
discharge port array which includes a plurality of discharge ports
for discharging ink arranged in an array direction; a suction unit
configured to suction air through suction holes so as to attract a
printing medium; a scanning unit configured to cause the printing
head to perform a plurality of scanning operations relative to the
printing medium in a scanning direction which is orthogonal to the
array direction; a supporting unit which includes the suction holes
formed therein in a range having a width in the scanning direction
larger than a width of the printing medium in the scanning
direction and which is configured to support the printing medium; a
conveying unit configured to convey the printing medium in a
conveyance direction which is orthogonal to the scanning direction
relative to the printing head such that a predetermined number of
first discharge ports arranged in one end portion of the discharge
port array in the array direction in a first scanning operation in
the plurality of scanning operations and a predetermined number of
second discharge ports arranged in the other end portion in the
discharge port array in the array direction in a second scanning
operation which is performed after the first scanning operation in
the plurality of scanning operations performed by the printing head
discharge ink in the same region or substantially the same region
in the printing medium; an obtaining unit configured to obtain
information on discharge amounts of ink discharged on the printing
medium in the individual scanning operations; a correction unit
configured to perform correction by reducing a discharge amount of
ink discharged from the predetermined number of first discharge
ports in the first scanning operation and a discharge amount of ink
discharged from the predetermined number of second discharge ports
in the second scanning operation which are represented by the
information obtained by the obtaining unit using reduction rates in
accordance with a position of the printing head in the scanning
direction; and a controller configured to perform control such that
ink is discharged in accordance with a discharge amount of ink
corrected by the correction unit, wherein, as for the discharge
amount of ink discharged from the predetermined number of first
discharge ports in the first scanning operation, the reduction
rates in a case where the printing head is located in a first
position in the scanning direction are larger than the reduction
rates in a case where the printing head is located in a second
position in the scanning direction which is on a downstream side in
the scanning direction in the first scanning operation relative to
the first position.
2. The printing apparatus according to claim 1, wherein as for the
discharge amount of ink discharged from the predetermined number of
first discharge ports in the first scanning operation, the
reduction rates in a case where the printing head is located in a
first region which is on an upstream side in the scanning direction
in the first scanning operation relative to the first position are
larger than the reduction rates in a case where the printing head
is located in a second region which is on a downstream side in the
scanning direction in the first scanning operation relative to the
second position.
3. The printing apparatus according to claim 2, wherein the first
region corresponds to the one end portion in the scanning direction
and the second region corresponds to the other end portion in the
scanning direction in the printing medium.
4. The printing apparatus according to claim 1, wherein as for the
discharge amount of ink discharged from the predetermined number of
first discharge ports in the first scanning operation, the
reduction rates in a case where the printing head is located in a
position between the first position and the second position in the
scanning direction are larger than the reduction rates in a case
where the printing head is located in the first position in the
scanning direction and smaller than the reduction rates in a case
where the printing head is located in the second position in the
scanning direction.
5. The printing apparatus according to claim 1, wherein as for the
discharge amount of ink discharged from the predetermined number of
second discharge ports in the second scanning operation, the
reduction rates in a case where the printing head is located in a
third position in the scanning direction are larger than the
reduction rates in a case where the printing head is located in a
fourth position in the scanning direction which is on a downstream
side in the scanning direction in the second scanning operation
relative to the third position.
6. The printing apparatus according to claim 5, wherein the
scanning unit causes the printing head to perform reciprocating
scanning in a going direction and a returning direction along the
scanning direction, the first and second scanning operations are
performed in the same direction, and the third position is the same
as the first position in the scanning direction and the fourth
position is the same as the second position in the scanning
direction.
7. The printing apparatus according to claim 5, wherein the
scanning unit causes the printing head to perform reciprocating
scanning in a going direction and a returning direction along the
scanning direction, the first scanning operation is performed in
the going direction and the second scanning operation is performed
in the returning direction, and the third position is the same as
the second position in the scanning direction and the fourth
position is the same as the first position in the scanning
direction.
8. The printing apparatus according to claim 1, wherein as for the
discharge amount of ink discharged from the predetermined number of
first discharge ports in the first scanning operation, the
reduction rates in a case where the printing head is located in the
first position in the scanning direction and a discharge amount of
ink discharged from the predetermined number of first discharge
ports represented by the information obtained by the obtaining unit
corresponds to a first discharge amount are larger than the
reduction rates in a case where the printing head is located in the
first position in the scanning direction and a discharge amount of
ink discharged from the predetermined number of first discharge
ports represented by the information obtained by the obtaining unit
corresponds to a second discharge amount which is larger than the
first discharge amount.
9. The printing apparatus according to claim 1, wherein as for the
discharge amount of ink discharged from the predetermined number of
first discharge ports in the first scanning operation, the
reduction rates in a case where the printing head is located in the
first position in the scanning direction and a distance between the
printing head and the supporting unit corresponds to a first
distance are smaller than the reduction rates in a case where the
printing head is located in the first position in the scanning
direction and a distance between the printing head and the
supporting unit corresponds to a second distance which is larger
than the first distance.
10. The printing apparatus according to claim 1, wherein as for the
discharge amount of ink discharged from the predetermined number of
first discharge ports in the first scanning operation, the
reduction rates in a case where the printing head is located in the
first position in the scanning direction and a scanning speed of
the printing head is a first speed are larger than the reduction
rates in a case where the printing head is located in the first
position in the scanning direction and the scanning speed of the
printing head is a second speed which is lower than the first
speed.
11. The printing apparatus according to claim 1, wherein the
obtaining unit obtains the information on a discharge amount of ink
discharged on the printing medium in accordance with printing data
which defines a pixel region in the printing medium to which the
ink is to be discharged in each of the plurality of scanning
operations, the correction unit corrects the printing data
corresponding to the predetermined number of first discharge ports
in the first scanning operation and the printing data corresponding
to the predetermined number of second discharge ports in the second
scanning operation using the reduction rates, and the controller
performs control such that ink is discharged in accordance with the
printing data corrected by the correction unit.
12. The printing apparatus according to claim 11, wherein the
correction unit reduces the discharge amount of ink by thinning the
printing data.
13. A printing apparatus comprising: a printing head including a
discharge port array which includes a plurality of discharge ports
for discharging ink arranged in an array direction; a suction unit
configured to suction air through suction holes so as to attract a
printing medium; a scanning unit configured to cause the printing
head to perform a plurality of scanning operations relative to the
printing medium in a scanning direction which is orthogonal to the
array direction; a supporting unit which includes the suction holes
formed therein in a range having a width in the scanning direction
larger than a width of the printing medium in the scanning
direction and which is configured to support the printing medium; a
conveying unit configured to convey the printing medium in a
conveyance direction which is orthogonal to the scanning direction
relative to the printing head such that a predetermined number of
first discharge ports arranged in one end portion of the discharge
port array in the array direction in a first scanning operation in
the plurality of scanning operations and a predetermined number of
second discharge ports arranged in the other end portion in the
discharge port array in the array direction in a second scanning
operation which is performed after the first scanning operation in
the plurality of scanning operations performed by the printing head
discharge ink in the same region or substantially the same region
in the printing medium; an obtaining unit configured to obtain
information on discharge amounts of ink discharged on the printing
medium in the individual scanning operations; a correction unit
configured to perform correction by increasing a discharge amount
of ink discharged from the predetermined number of first discharge
ports in the first scanning operation and a discharge amount of ink
discharged from the predetermined number of second discharge ports
in the second scanning operation which are represented by the
information obtained by the obtaining unit using increase rates in
accordance with a position of the printing head in the scanning
direction; and a controller configured to perform control such that
ink is discharged in accordance with a discharge amount of ink
corrected by the correction unit, wherein, as for the discharge
amount of ink discharged from the predetermined number of first
discharge ports in the first scanning operation, the increase rates
in a case where the printing head is located in a first position in
the scanning direction are smaller than the increase rates in a
case where the printing head is located in a second position in the
scanning direction which is on a downstream side in the scanning
direction in the first scanning operation relative to the first
position.
14. The printing apparatus according to claim 13, wherein as for
the discharge amount of ink discharged from the predetermined
number of first discharge ports in the first scanning operation,
the increase rates in a case where the printing head is located in
the first position in the scanning direction and a discharge amount
of ink discharged from the predetermined number of first discharge
ports represented by the information obtained by the obtaining unit
corresponds to a first discharge amount are smaller than the
increase rates in a case where the printing head is located in the
first position in the scanning direction and a discharge amount of
ink discharged from the predetermined number of first discharge
ports represented by the information obtained by the obtaining unit
corresponds to a second discharge amount which is larger than the
first discharge amount.
15. The printing apparatus according to claim 13, wherein as for
the discharge amount of ink discharged from the predetermined
number of first discharge ports in the first scanning operation,
the increase rates in a case where the printing head is located in
the first position in the scanning direction and a distance between
the printing head and the supporting unit corresponds to a first
distance are smaller than the increase rates in a case where the
printing head is located in the first position in the scanning
direction and a distance between the printing head and the
supporting unit corresponds to a second distance which is larger
than the first distance.
16. The printing apparatus according to claim 13, wherein as for
the discharge amount of ink discharged from the predetermined
number of first discharge ports in the first scanning operation,
the increase rates in a case where the printing head is located in
the first position in the scanning direction and a scanning speed
of the printing head is a first speed are smaller than the increase
rates in a case where the printing head is located in the first
position in the scanning direction and the scanning speed of the
printing head is a second speed which is lower than the first
speed.
17. The printing apparatus according to claim 13, wherein the
obtaining unit obtains the information on a discharge amount of ink
discharged on the printing medium in accordance with printing data
which defines a pixel region in the printing medium to which the
ink is to be discharged in each of the plurality of scanning
operations, the correction unit corrects the printing data
corresponding to the predetermined number of first discharge ports
in the first scanning operation and the printing data corresponding
to the predetermined number of second discharge ports in the second
scanning operation using the increase rates, and the controller
performs control such that ink is discharged in accordance with the
printing data corrected by the correction unit.
18. The printing apparatus according to claim 13, wherein the
correction unit increases the discharge amount of ink by adding the
printing data.
19. A printing method comprising: causing a printing head including
a discharge port array which includes a plurality of discharge
ports for discharging ink arranged in an array direction to perform
a plurality of scanning operations in a scanning direction which is
orthogonal to the array direction relative to the printing medium;
suctioning air through a plurality of suction holes which are
formed on a supporting unit supporting a printing medium and which
are formed in a region having a width in the scanning direction
which is larger than a width of the printing medium in the scanning
direction so that the printing medium is attracted on the
supporting unit; conveying the printing medium in a conveyance
direction which is orthogonal to the scanning direction relative to
the printing head such that a predetermined number of first
discharge ports arranged in one end portion of the discharge port
array in the array direction in a first scanning operation in the
plurality of scanning operations and a predetermined number of
second discharge ports arranged in the other end portion in the
discharge port array in the array direction in a second scanning
operation which is performed after the first scanning operation in
the plurality of scanning operations performed by the printing head
discharge ink in the same region or substantially the same region
in the printing medium; obtaining information on discharge amounts
of ink discharged on the printing medium in the individual scanning
operations; performing correction by reducing a discharge amount of
ink discharged from the predetermined number of first discharge
ports in the first scanning operation and a discharge amount of ink
discharged from the predetermined number of second discharge ports
in the second scanning operation which are represented by the
obtained information using reduction rates in accordance with a
position of the printing head in the scanning direction; and
performing control such that ink is discharged in accordance with a
corrected discharge amount of ink, wherein, as for the discharge
amount of ink discharged from the predetermined number of first
discharge ports in the first scanning operation, the reduction
rates in a case where the printing head is located in a first
position in the scanning direction are larger than the reduction
rates in a case where the printing head is located in a second
position in the scanning direction which is on a downstream side in
the scanning direction in the first scanning operation relative to
the first position.
20. A program which operates a computer of a printing apparatus to
execute the printing method set forth in claim 19.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a printing apparatus, a
printing method, and a program.
[0003] 2. Description of the Related Art
[0004] In general, printing apparatuses which print an image by
discharging ink on a printing medium supported by a platen while a
printing head having a discharge port array including a plurality
of discharge ports which are arrayed is moved in a scanning
direction for scanning and conveying the printing medium in a
conveyance direction during the scanning have been used.
[0005] In such a printing apparatus, when an ink discharge amount
per discharge is large, a deviation phenomenon of discharged ink
droplets described below is likely to occur. Ink droplets
discharged from a printing head drop while involving air existing
in a space between the printing head and a printing medium, and
accordingly, the space between the printing head and the printing
medium becomes in a depressurized state after the discharge of ink.
To correct the depressurized state, air in portions in the vicinity
of end portions of the discharge port array moves toward the center
of the discharge port array, and accordingly, airflows (hereinafter
referred to as a "self-airflow" where appropriate) are generated
toward the center from the end portions. Due to the self-airflow, a
so-called end deviation phenomenon in which ink droplets discharged
from discharge ports in end portions of the discharge port array
are attracted toward the center of the discharge port array occurs.
Note that the larger a discharge amount of ink per discharge is,
the larger the self-airflow is, and accordingly, a degree of the
end deviation phenomenon of ink droplets is large. Due to the end
deviation phenomenon, ink is not attached on regions of the
printing medium which is to be printed by discharge ports in the
end portions of the discharge port array, and white streaks may
appear in a printed image.
[0006] Japanese Patent Laid-Open No. 2004-168003 discloses a
technique of reducing a conveyance amount of a printing medium
relative to a standard amount and reducing a discharge amount of
ink from discharge ports in end portions of a discharge port array
so that generation of while streaks is suppressed. According to
Japanese Patent Laid-Open No. 2004-168003, the printing medium is
conveyed such that a discharge port of one end portion of the
discharge port array and a discharge port of the other end portion
of the discharge port array perform printing on the same region of
the printing medium by different scanning operations, and
therefore, white streaks generated when a discharge amount of ink
is relatively large as described above may be suppressed.
Furthermore, when the discharge amount of ink is relatively small,
the self-airflow is not generated, and accordingly, black streaks
may be generated in a printed image due to the conveyance amount
smaller than the standard amount. On the other hand, according to
Japanese Patent Laid-Open No. 2004-168003, when a discharge amount
of ink is relatively small, the generation of black streaks
described above is suppressed by performing correction so that a
discharge amount of ink from the discharge ports in the end
portions is reduced.
[0007] Furthermore, in general, droplet landing accuracy of ink may
be deteriorated since a printing medium is lifted relative to a
platen which supports the printing medium at a time of printing.
Japanese Patent Laid-Open No. 2013-014047 discloses a technique of
providing a plurality of suction holes in a platen which supports a
printing medium and absorbing the printing medium on the platen by
suctioning air through the suction holes.
[0008] However, in a printing apparatus having suction means
disclosed in Japanese Patent Laid-Open No. 2013-014047, even when
the printing method disclosed in Japanese Patent Laid-Open No.
2004-168003 is used, white streaks and black streaks described
above may not be efficiently suppressed.
[0009] This problem will be described in detail hereinafter.
[0010] FIGS. 1A to 1C are diagrams illustrating a state in which
strength of an airflow flowing in a space between a printing head
500 and a printing medium 501 obtained when the printing head 500
performs scanning once is changed depending on a position of the
printing head 500.
[0011] Note that a case where a printing apparatus which prints an
image by discharging ink in a vertical downward direction while the
printing head 500 having a discharge port array including a
plurality of discharge ports arranged in a Y direction (array
direction) is moved toward an X direction (scanning direction) is
used is illustrated in FIGS. 1A to 1C. Here, a platen 502 which
supports the printing medium 501 has a plurality of suction holes
503 formed therein and absorbs the printing medium 501 on the
platen 502 by suctioning air through the suction holes 503.
Although a platen 2 having only three suction holes 503 is
illustrated in FIGS. 1A to 1C for simplicity, a larger number of
suction holes 503 are formed in general apparatuses.
[0012] FIG. 1A is a diagram illustrating a state in which ink is
discharged to a region in the vicinity of an end portion on an
upstream side of the printing medium 501 in an X direction
immediately after a certain scanning operation is performed once in
the X direction of the printing head 500. Since the printing head
500 moves in the X direction for the scanning, airflow 504 is
generated from a downstream side to the upstream side in the
scanning direction of the printing head 500 in a space between the
printing head 500 and the printing medium 501. Furthermore, since
air is suctioned through the suction holes 503, an eddy of air is
generated toward the suction holes 503 in portions in the vicinity
of the suction holes 503. Since the portion in the vicinity of the
end portion of the printing medium 501 on the upstream side in the
X direction is located near one of the suction holes 503, the
portion is affected by the eddy of air, and therefore, an airflow
505 is generated from the downstream side to the upstream side of
the scanning direction in the portion between the printing head 500
and the printing medium 501. Specifically, immediately after the
certain scanning operation relative to the printing medium 501 is
started, an airflow obtained by adding the airflow 504 caused by
the scanning and the airflow 505 caused by the suction to each
other may be generated in the portion between the printing head 500
and the printing medium 501.
[0013] FIG. 1B is a diagram illustrating a state in which the
printing head 500 discharges ink to a center region (also referred
to as a "region B" hereinafter) in the middle of the certain
scanning operation in the X direction. As with the case of FIG. 1A,
the airflow 504 is generated from the downstream side to the
upstream side in the scanning direction in the space between the
printing head 500 and the printing medium 501. On the other hand,
since the space between the printing head 500 and the printing
medium 501 corresponding to the center region is not in contact
with the suction holes 503, the center region is not affected by
eddy of air caused by suction through the suction holes 503.
Specifically, in the case of FIG. 1B, only the airflow 504 caused
by the scanning may be generated in the space between the printing
head 500 and the printing medium 501.
[0014] FIG. 1C is a diagram illustrating a state when ink is
discharged to a region (also referred to as a "region C"
hereinafter) in the vicinity of an end portion on the downstream
side in an X direction of the printing medium 501 immediately after
the certain scanning operation is performed in the X direction.
Also in this case, the airflow 504 caused by the scanning is
generated in the space between the printing head 500 and the
printing medium 501. Unlike the state illustrated in FIG. 1A, one
of the suction holes 503 is formed on the downstream side in the X
direction relative to the printing head 500 in the state
illustrated in FIG. 1C. Therefore, the region is affected by eddy
of air through the suction holes 503, and airflow 506 may be
generated from the upstream side to the downstream side in the
space between the printing head 500 and the printing medium 501. In
this way, in the state illustrated in FIG. 1C, the airflow 504
caused by the scanning and the airflow 506 caused by the suction
are generated in opposite directions. Specifically, immediately
before the certain scanning operation performed on the printing
medium 501 is terminated, an airflow obtained by subtraction
between the airflow 506 caused by the suction from the airflow 504
caused by the scanning may be generated in the space between the
printing head 500 and the printing medium 501.
[0015] FIGS. 2A to 2C are diagrams illustrating end deviation
phenomena and degrees of the end deviation phenomena corresponding
to the positional relationships between the printing head 500 and
the printing medium 501 illustrated in FIGS. 1A to 1C,
respectively.
[0016] Note that, in FIGS. 2A to 2C, states in which the space
between the printing head 500 and the printing medium 501 is viewed
from the downstream side in the X direction relative to the
printing head 500 are illustrated. For simplicity, a case where ink
discharge amounts in the states of FIGS. 2A to 2C are substantially
the same as one another is described. Furthermore, sizes of circles
representing incoming airflows 507 to 509 illustrated in FIGS. 2A
to 2C schematically represent strengths of the incoming airflows
507 to 509.
[0017] As described above, in the state illustrated in FIG. 2A, the
airflow 507 generated in the space between the printing head 500
and the printing medium 501 (hereinafter referred to as an
"incoming airflow") is obtained by adding the airflow 504 caused by
the scanning and the airflow 505 caused by the suction to each
other, and therefore, the airflow 507 is relatively strong.
Accordingly, even when the space between the printing head 500 and
the printing medium 501 becomes a depressurized state, the
depressurized state is corrected by the airflow 507 or the space
becomes a surge pressure state depending on a strength of the
incoming airflow 507. Consequently, ink droplets discharged from
one of the end portions of the discharge port array is shifted
toward an outside of the discharge port array.
[0018] On the other hand, in the state illustrated in FIG. 2B, a
strength of an incoming airflow 508 is middle. Therefore,
correction of the depressurized state by the incoming airflow 508
is not remarkably performed when compared with the state
illustrated in FIG. 2A. Accordingly, an amount of shift of ink
droplets discharged from the other of the end portions of the
discharge port array is smaller than that in the state of FIG.
2A.
[0019] Furthermore, in the state of FIG. 2C, the airflow 506 caused
by the suction is generated in the direction opposite to the
direction of the airflow 504 caused by the scanning, and therefore,
an incoming airflow 509 is relatively weak. Therefore, correction
of the depressurized state by the incoming airflow 509 is not
remarkably performed when compared with the cases of FIGS. 2A and
2B. However, a depressurized state caused by flowing of air in a
portion in the vicinity of the other of the end portions of the
discharge port array in the array direction toward the center of
the discharge port array is remarkably corrected. Consequently, ink
droplets discharged from the other of the end portions of the
discharge port array land in positions shifted toward the center of
the discharge port array. Note that, since the incoming airflow 504
contributes a little to the correction of the depressurized state,
a degree of the shift of the ink droplets toward the center of the
discharge port array is small when compared with a case where any
airflow is not generated.
[0020] FIG. 3 is a diagram schematically illustrating an image
printed by discharging ink by one scanning operation performed by
the printing head 500. For simplicity, a case where printing is
performed by one scanning operation on each unit region of the
printing medium 501 is described. Furthermore, to suppress
generation of white streaks caused by the end deviation phenomenon,
the printing medium 501 is conveyed such that a predetermined
number of discharge ports .DELTA.n may discharge ink in the same
regions on the printing medium 501 in different scanning
operations. Specifically, positions 511 to 515 in FIG. 3 correspond
to first to fifth scanning operations performed on the printing
medium 501, and the printing medium 501 is conveyed such that the
printing head 500 and the printing medium 501 have these positional
relationships in the individual scanning operations.
[0021] Here, as described above, in any of the case where printing
is performed on the end region on the upstream side (region A) in
the X direction of the printing medium 501, the case where printing
is performed on the center region (region B), and the case where
printing is performed on the end region on the downstream side
(region C), influence of an incoming airflow is generated.
Therefore, a shift amount toward the end portion of the discharge
port array in a Y direction is larger when compared with a case
where an incoming airflow is not generated in the region A, the
region B, or the region C. Accordingly, even in a case where a
discharge amount of ink from discharge ports in the end portions of
the discharge port array in the array direction is reduced by a
method disclosed in Japanese Patent Laid-Open No. 2004-168003,
black streaks are generated in all the regions A to C.
[0022] Furthermore, as illustrated in FIGS. 2A to 2C, amounts of
shift toward the end portion of the discharge port array in the Y
direction becomes large in order from the region A, the region B,
to the region C. Accordingly, a density of black streaks 517
generated in the region B is higher than that of black streaks 518
generated in the region C. Furthermore, a density of black streaks
516 generated in the region A is further higher than those of the
black streaks 517 and 518 generated in the regions B and C,
respectively.
[0023] As described above, when printing is performed by a printing
apparatus having a suction unit, a magnitude of an incoming airflow
varies depending on a position of a printing head in a scanning
direction. Therefore, densities of boundary streaks generated in
regions on a printing medium corresponding to discharge ports in
end portions of a discharge port array in an array direction are
different from one another depending on the positions.
SUMMARY OF THE INVENTION
[0024] The present invention provides a printing apparatus capable
of printing an image which is less affected by boundary streaks
generated due to different densities depending on scanning
directions caused by different strengths of incoming airflows.
[0025] Accordingly, the present invention provides a printing
apparatus including a printing head including a discharge port
array which includes a plurality of discharge ports for discharging
ink arranged in an array direction, a suction unit configured to
suction air through suction holes so as to attract a printing
medium, a scanning unit configured to cause the printing head to
perform a plurality of scanning operations relative to the printing
medium in a scanning direction which is orthogonal to the array
direction, a supporting unit which includes the suction holes
formed therein in a range having a width in the scanning direction
larger than a width of the printing medium in the scanning
direction and which is configured to support the printing medium, a
conveying unit configured to convey the printing medium in a
conveyance direction which is orthogonal to the scanning direction
relative to the printing head such that a predetermined number of
first discharge ports arranged in one end portion of the discharge
port array in the array direction in a first scanning operation in
the plurality of scanning operations and a predetermined number of
second discharge ports arranged in the other end portion in the
discharge port array in the array direction in a second scanning
operation which is performed after the first scanning operation in
the plurality of scanning operations performed by the printing head
discharge ink in the same region or substantially the same region
in the printing medium, an obtaining unit configured to obtain
information on discharge amounts of ink discharged on the printing
medium in the individual scanning operations, a correction unit
configured to perform correction by reducing a discharge amount of
ink discharged from the predetermined number of first discharge
ports in the first scanning operation and a discharge amount of ink
discharged from the predetermined number of second discharge ports
in the second scanning operation which are represented by the
information obtained by the obtaining unit using reduction rates in
accordance with a position of the printing head in the scanning
direction, and a controller configured to perform control such that
ink is discharged in accordance with a discharge amount of ink
corrected by the correction unit. As for the discharge amount of
ink discharged from the predetermined number of first discharge
ports in the first scanning operation, the reduction rates in a
case where the printing head is located in a first position in the
scanning direction are larger than the reduction rates in a case
where the printing head is located in a second position in the
scanning direction which is on a downstream side in the scanning
direction in the first scanning operation relative to the first
position.
[0026] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIGS. 1A to 1C are diagrams schematically illustrating
incoming airflows in different printing positions.
[0028] FIGS. 2A to 2C are diagrams schematically illustrating
degrees of end deviations in the different printing positions.
[0029] FIG. 3 is a diagram schematically illustrating boundary
streaks generated in a case where an incoming airflow is
generated.
[0030] FIG. 4 is a perspective view of a printing apparatus
according to a first embodiment.
[0031] FIG. 5 is a side view of the printing apparatus according to
the embodiment.
[0032] FIG. 6 is a diagram schematically illustrating a printing
head according to the first embodiment.
[0033] FIG. 7 is a block diagram illustrating a configuration of a
printing control system according to the first embodiment.
[0034] FIG. 8 is a block diagram illustrating data processing
according to the first embodiment.
[0035] FIG. 9 is a diagram illustrating a printing method according
to the first embodiment.
[0036] FIG. 10 is a diagram illustrating the printing method
according to the first embodiment.
[0037] FIGS. 11A to 11F are diagrams schematically illustrating
thinning rates according to the first embodiment.
[0038] FIGS. 12A to 12C are diagrams illustrating printing rates of
a printed image according to the first embodiment.
[0039] FIGS. 13A and 13B are diagrams schematically illustrating
thinning ratios according to a comparative example.
[0040] FIG. 14 is a diagram illustrating a printing method
according to a second embodiment.
[0041] FIGS. 15A and 15B are diagrams schematically illustrating
mask patterns according to the second embodiment.
[0042] FIGS. 16A and 16B are diagrams illustrating deviation of ink
droplets changed depending on a discharge amount of ink according
to a third embodiment.
[0043] FIGS. 17A and 17B are diagrams illustrating deviation of ink
droplets changed depending on a distance between a head and a sheet
according to the third embodiment.
DESCRIPTION OF THE EMBODIMENTS
First Embodiment
[0044] A first embodiment of the present invention will be
described in detail hereinafter.
[0045] FIG. 4 is a perspective view of an internal configuration of
a printing apparatus 1000 according to this embodiment. FIG. 5 is a
side view of the internal configuration of the printing apparatus
1000 according to this embodiment.
[0046] The printing apparatus 1000 includes a platen (supporting
unit) 2 which supports a printing medium 3. A large number of
suction holes 26 are formed on the platen 2 so that the printing
medium 3 is absorbed on the platen 2 so as not to be lifted. The
suction holes 26 are connected to a duct 4. A suction fan (not
illustrated) is disposed below the duct 4. The suction fan suctions
air so that the printing medium 3 is absorbed by the platen 2.
[0047] Furthermore, a carriage 6 which reciprocally moves in an X
direction (scanning direction) is supported by a main rail 5. The
carriage 6 includes an ink-jet printing head 7 mounted thereon
which will be described hereinafter. Various inkjet printing
methods including a thermal jet method using a heating element and
a piezo method using a piezoelectric element may be employed in the
printing head 7.
[0048] The printing medium 3 which is rolled on a feed roller 23 is
successively supplied. Then the supplied printing medium 3 is
conveyed by a first conveyance roller and a second conveyance
roller which are disposed at a certain interval by a predetermined
amount in a Y direction (conveyance direction) which is orthogonal
to the X direction at a timing corresponding to scanning performed
by the printing head 7. The first conveyance roller includes a pair
of rollers, that is, a driving roller 11 which is driven by a
stepping motor (not illustrated) and an auxiliary roller 16 which
rotates with rotation of the driving roller 11. Similarly, the
second conveyance roller also includes a pair of rollers, that is,
a driving roller 12 and an auxiliary roller 13. Furthermore, the
printing medium 3 is rolled on a winding roller 24 through a turn
roller. Note that the printing apparatus 1000 may perform printing
on a printing medium 3 which is cut into a predetermined size and
which is piled on a cassette instead of the rolled printing medium
3.
[0049] With this configuration, since ink is discharged from
discharge ports of the printing head 7 in accordance with printing
data described below while scanning is performed in the X
direction, the printing may be performed on the printing medium 3
by forming dots of the ink. The printing head 7 moves to a home
position where appropriate and performs a recovery operation using
a discharge recovery device (not illustrated) disposed in the home
position so as to recover from a defective discharge state caused
by clogging of the discharge ports or the like. Suction of ink in
which concentration thereof is changed and an ink concentration
resetting operation performed by preliminary discharge which are
performed to address variation of concentration of the ink which
remains near the discharge ports of the printing head 7 before
scanning is performed using the printing head 7 are also performed
in the home position.
[0050] FIG. 6 is a diagram schematically illustrating the printing
head 7 of this embodiment.
[0051] The printing head 7 includes four discharge port arrays 22K,
22C, 22M, and 22Y which discharge ink of black (K), ink of cyan
(C), ink of magenta (M), and ink of yellow (Y), respectively, and
which are arranged in parallel in the X direction. Each of the
discharge port arrays 22K, 22C, 22M, and 22Y has 1440 (N, or a
predetermined number of) discharge ports 30 arranged in the Y
direction (array direction) in a density of 1200 dpi. An amount of
ink discharged from one of the discharge ports 30 is approximately
4.5 ng in this embodiment.
[0052] The discharge port arrays 22K, 22C, 22M, and 22Y are
connected to respective ink tanks, not illustrated, which store the
corresponding inks, and the inks are supplied from the ink tanks.
The printing head 7 and the ink tanks of this embodiment may be
integrated or may be separated from one another.
[0053] FIG. 7 is a block diagram schematically illustrating a
configuration of a printing control system according to this
embodiment.
[0054] A host computer 401 serving as an image input unit transmits
multivalued image data of an RGB format stored in a storage medium,
such as a hard disk, to an image processing unit included in the
printing apparatus 1000.
[0055] The image processing unit includes an MPU (Micro Processor
Unit) 402 and an ASIC 403 which will be described hereinafter.
Alternatively, multivalued image data may be supplied from an
external image input device, such as a scanner or a digital still
camera, connected to the host computer 401. The image processing
unit performs image processing, which will be described
hereinafter, on the input multivalued image data so as to convert
the multivalued image data into binary image data. In this way, the
binary image data which is printing data generated by discharging a
plurality of types of ink from the printing head 7 is
generated.
[0056] The printing apparatus 1000 serving as an image output unit
assigns the inks to the printing medium 3 on the basis of the
binary image data of the inks generated by the image processing
unit so as to print an image. The printing apparatus 1000 is
controlled by the MPU 402 in accordance with a program recorded in
a ROM 404. A RAM 405 serves as a work area of the MPU 402 or a
temporal data storage region. The MPU 402 controls a driving system
408 for the carriage 6, a conveyance driving system 409 for the
printing medium 3, a recovery driving system 410 for the printing
head 7, and a driving system 411 for the printing head 7 through
the ASIC 403.
[0057] A print buffer 406 temporarily stores printing data
converted into data of a format which may be transferred to the
printing head 7.
[0058] A mask buffer 407 temporarily stores a mask pattern used
when the printing data is transferred to the printing head 7. A
plurality of mask patterns used for multipass printing are stored
in the ROM 404, and one of the mask patterns is read from the ROM
404 at a time of actual printing and stored in the mask buffer
407.
[0059] Although the case where the image processing unit is
included in the printing apparatus 1000 is described in this
embodiment, the image processing unit may be included in the host
computer 401.
[0060] FIG. 8 is a flowchart illustrating the image processing
according to this embodiment.
[0061] In the image processing according to this embodiment,
multivalued image data (luminance data) of the RGB format in which
each color has 8 bits (256 gradations) is obtained. Then a process
of outputting binary data (printing data) of 1 bit for finally
discharging the cyan ink, the magenta ink, the yellow ink, and the
black ink for each scanning is performed. Types of color and
gradations of color are not limited to these values.
[0062] First, in the host computer 401, a color-space conversion
preprocessor 412 converts image data represented by a multivalued
luminance signal of the RGB format into image data represented by a
multivalued luminance signal of the RGB format to be input to the
printing apparatus 1000 using multidimensional LUT. The color-space
conversion preprocessing (hereinafter referred to as "precedent
color processing" where appropriate) is performed to correct a
difference between a color space of an input image represented by
image data of R, G, and B of a printing target and a color space
reproducible by the printing apparatus 1000. The image data of RGB
format which has been subjected to the precedent color processing
is supplied to the printing apparatus 1000.
[0063] A color conversion processor 413 converts the multivalued
image data of the RGB format input by the host computer 401 into
multivalued data of a CMYK format using a multidimensional LUT
stored in the ROM 404. This color conversion process (hereinafter
referred to as "subsequent color processing" where appropriate) is
performed for color conversion of the image data of the RGB format
of an input system represented by the luminance signal into the
image data of the CMYK format of an output system to be represented
by a density signal.
[0064] Next, an output gamma processor 414 performs output gamma
correction on the multivalued data of the CMYK format which has
been subjected to the subsequent color processing using
one-dimensional LUTs of C, M, Y, and K. In general, the
relationship between the number of dots printed per unit area of a
printing medium and a printing characteristic such as a reflection
density obtained by measuring a printed image is not the linear
relationship. Therefore, the output gamma correction which corrects
multivalued input gradation levels of C, M, Y, and K so that the
input gradation levels of C, M, Y, and K and a density level of an
image printed in accordance with the input gradation levels have
the linear relationship.
[0065] Subsequently, a quantization processor 415 binarizes
(quantizes) the multivalued data of C, M, Y, and K obtained as
described above so as to obtain data in which each of the colors of
C, M, Y, and K has one bit. In this embodiment, an error diffusion
method is used as a binarization method. A quantization method
using the error diffusion method is a general technique, and
therefore, a description thereof is omitted. Instead of the error
diffusion method, dithering may be used as the binarization method.
Furthermore, index development using an index pattern may be
additionally used.
[0066] A mask processor 416 generates binary data used for
discharging the inks of C, M, Y, and K in individual scanning
operations by employing a mask pattern for the binary data of the
CMYK format. The mask pattern is formed by arranging a plurality of
print permitting pixels and a plurality of non-print permitting
pixels. Note that the print permitting pixel permits discharge of
ink when binary data representing discharge of ink to a pixel
region of a printing medium is input. On the other hand, the
non-print permitting pixel does not permit discharge of ink even
when binary data representing discharge of ink to a pixel region of
a printing medium is input. Since printing is performed by one
scanning operation on a non-overlap portion in this embodiment,
mask processing is performed using a mask pattern including print
permitting pixels arranged in all positions.
[0067] A correction processor 417 performs correction processing,
such as thinning and adding, which will be described hereinafter,
on binary data assigned to individual scanning operations by the
mask processor 416.
[0068] A printing method according to this embodiment will be
described in detail hereinafter.
[0069] FIG. 9 is a diagram illustrating a printing method according
to this embodiment. For simplicity, the printing head 7 includes
only one discharge port array in FIG. 9.
[0070] In this embodiment, 1280 discharge ports included in the
printing head 7 are divided into three discharge port groups, that
is, a first discharge port group 31a, a second discharge port group
32, and a first discharge port group 31b. Here, the first discharge
port group 31a includes 40 discharge ports disposed in an end
portion on an upstream side in the Y direction of the discharge
port array. The first discharge port group 31b includes 40
discharge ports disposed in an end portion on a downstream side in
the Y direction of the discharge port array. The second discharge
port group 32 includes 1200 discharge ports other than the
discharge ports of the first discharge port groups 31a and 31b.
[0071] First, when a first scanning operation is to be performed,
the printing medium 3 is conveyed so as to have the positional
relationship with the printing head 7 represented by (83). With
this positional relationship, the printing head 7 scans in the X
direction, and ink is discharged from the first discharge port
group 31a to an overlap portion (first region) 81a in the printing
medium 3.
[0072] Next, the printing medium 3 is conveyed by a distance
.DELTA.d in the Y direction so that the overlap portion 81a
corresponding to the first discharge port group 31a has the
positional relationship with the first discharge port group 31b
represented by (84). Since this conveyance is performed by a
distance corresponding to a number of discharge ports corresponding
to a number obtained by adding the number of discharge ports
included in the first discharge port group 31a and the number of
discharge ports included in the second discharge port group 32, a
value of .DELTA.d corresponds to 1240 (=40+1200) discharge ports.
Specifically, assuming that the number of discharge ports arranged
in the discharge port array is N, the number of discharge ports
included in the first discharge port group 31a is M, and the number
of times scanning is performed on a region other than the
overlapping portion (hereinafter referred to as a non-overlap
portion or a second region where appropriate) is K, the value
.DELTA.d corresponds to (N-M)/K discharge ports. After this
conveyance, the printing head 7 scans in the X direction and ink is
discharged from the first discharge port groups 31a and 31b and the
second discharge port group 32. Here, an overlap portion 81b and a
non-overlap portion 82a are subjected to first discharge from the
first discharge port group 31a and the second discharge port group
32, respectively. The overlap portion 81a is subjected to second
discharge of ink from the first discharge port group 31a. By
performing the scanning in the positional relationship represented
by (84), formation of an image corresponding to the overlap portion
81a and the non-overlap portion 82a is completed.
[0073] Furthermore, the printing medium 3 is conveyed in the Y
direction by the distance .DELTA.d which is the same as the
distance of the conveyance described above so that the positional
relationship between the printing medium 3 and the printing head 7
represented by (85) is obtained. With the positional relationship
represented by (85), the printing head 7 scans in the X direction,
and as with the scanning in the positional relationship represented
by (84), an image is formed in the overlap portion 81b and a
non-overlap portion 82b.
[0074] Hereinafter, the conveyance of the printing medium 3 in the
Y direction by the distance .DELTA.d and the scanning by the
printing head 7 in the X direction with discharge of ink are
alternately performed in a repetitive manner so that printing is
performed on an entire region of the printing medium 3. According
to the printing method described above, the printing may be
performed by performing scanning once on the non-overlap portion of
the printing medium 3 and twice on the overlap portions.
[0075] A correction process of this embodiment will now be
described in detail hereinafter.
[0076] In this embodiment, discharge of ink is performed on the
overlap portions by performing scanning twice as described above.
Therefore, if the binary data is not thinned by the correction
processor 417, discharged inks are overlapped with each other in
the same pixel region by the two scanning operation. Accordingly,
in a case where a so-called solid image is to be printed on the
entire region of the printing medium 3 by discharging ink drop by
drop on the pixel region on the printing medium 3 to which the ink
is dischargeable (that is, a printing rate is 100%), if the
thinning of binary data corresponding to the solid image is not
performed, an image of a printing rate of 200% is formed in the
overlap portions. That is, if the thinning of the binary data
corresponding to the overlap portions is not performed, an image of
a printing rate higher than that of an image to be printed is
formed in the overlap portions.
[0077] Therefore, in this embodiment, the binary data is corrected
by the correction processor 417 using different correction rates
depending on a position on the printing medium 3 in the X
direction. Note that, in this embodiment, the binary data
corresponding to the overlap portions is thinned using thinning
rates (reduction rates) as the correction rates so that the binary
data is corrected and generation of black streaks is efficiently
suppressed.
[0078] FIG. 10 is a diagram illustrating a process of printing an
image on the printing medium 3 in accordance with the printing
method illustrated in FIG. 9. Note that, in this embodiment, as the
printing medium 3 moves, a printing position is changed as
illustrated in FIG. 9, and in FIG. 10, the printing medium 3 is
fixed and a position of the printing head 7 is changed in the Y
direction. Here, the positional relationships between the printing
head 7 and the printing medium 3 represented by (83), (84), and
(85) in FIG. 10 correspond to the positional relationships between
the printing head 7 and the printing medium 3 represented by (83),
(84), and (85) in FIG. 9. For simplicity, only discharge of ink
from the first discharge port group 31a in the positional
relationship represented by (83) and discharge of ink from the
first discharge port group 31b in the positional relationship
represented by (84) are described hereinafter. Furthermore, in this
embodiment, printing is performed by scanning in only one
direction, that is, the X direction, of the printing head 7.
[0079] In this embodiment, the overlap portions in the printing
medium 3 are divided into three regions, that is, a region A having
a width of 20 mm from the end portion on the upstream side in the X
direction, a region C having a width of 20 mm from the end portion
on the downstream side in the X direction, and a region B which is
other than the regions A and C.
[0080] First, strengths of incoming airflows flowing in the regions
A, B, and C will be described in detail hereinafter.
[0081] Since the suction holes 26 are formed on the platen 2 which
is adjacent on the upstream side in the X direction in the region
A, an incoming airflow Q flows in the region A from the downstream
side to the upstream side in the X direction. Similarly, an
incoming airflow P flows in the region C from the upstream side to
the downstream side in the X direction.
[0082] When the printing head 7 performs scanning, an incoming
airflow R flows from the downstream side to the upstream side in
the X direction. Specifically, the incoming airflow R flows in a
direction which is the same as that of the incoming airflow Q and
which is opposite to that of the incoming airflow P. The incoming
airflow R having the same strength is generated in any of the
regions A, B, and C irrespective of a position of the printing head
7.
[0083] Therefore, an airflow of a mixture of the incoming airflow R
and the incoming airflow Q flows in the region A, and accordingly,
an airflow stronger than the incoming airflow R flowing in the
region B flows in the region A. On the other hand, the incoming
airflow P flows in a direction in which the incoming airflow P
cancels the incoming airflow R in the region C, and accordingly, an
airflow weaker than the incoming airflow in the region B flows in
the region C. Consequently, in the overlap portion 81a, the
incoming airflow is strongest in the region A and weakest in the
region C.
[0084] Furthermore, as described above, in a case where an incoming
airflow is relatively strong, even when air in a space between the
printing head 7 and the printing medium 3 is tend to be
depressurized by self-airflow, air is added by an incoming airflow,
and accordingly, a degree of the end deviation phenomenon is
relatively small. Therefore, black streaks are likely to be
generated in the overlap portion 81a of the printing medium 3.
[0085] Accordingly, it is determined that black streaks are likely
to be generated in the region A of the overlap portion 81a since a
degree of the end deviation phenomenon is small whereas black
streaks are rarely generated in the region C since a degree of the
end deviation phenomenon is large.
[0086] Accordingly, in this embodiment, the binary data is thinned
using different thinning rates for the regions A to C included in
the overlap portion 81a and a discharge amount of ink is reduced so
that generation of the boundary streaks described above is
suppressed.
[0087] FIGS. 11A to 11F are diagrams schematically illustrating
thinning rates used when the correction processor 417 thins the
binary data when ink is discharged to the overlap portion 81a in
this embodiment. FIGS. 12A to 12C are diagrams schematically
illustrating printing rates of binary data in the individual
regions generated when the binary data corresponding to the solid
image is thinned in accordance with the thinning rates illustrated
in FIGS. 11A to 11F.
[0088] FIGS. 11A, 11C, and 11E are diagrams illustrating thinning
rates of the binary data corresponding to the first discharge port
group 31a in a case where the positional relationship between the
printing head 7 and the printing medium 3 is represented by (83) of
FIG. 9. FIGS. 11B, 11D, and 11F are diagrams illustrating thinning
rates of the binary data corresponding to the first discharge port
group 31b in a case where the positional relationship between the
printing head 7 and the printing medium 3 is represented by (84) of
FIG. 9.
[0089] Furthermore, in FIGS. 11A and 11B, thinning rates used when
the binary data corresponding to the region A included in the
overlap portions 81a and 81b are illustrated. Similarly, in FIGS.
11C and 11D, thinning rates used when the binary data corresponding
to the region B included in the overlap portions 81a and 81b are
illustrated. Similarly, in FIGS. 11E and 11F, thinning rates used
when the binary data corresponding to the region C included in the
overlap portions 81a and 81b are illustrated.
[0090] Furthermore, in FIGS. 12A to 12C, printing rates of the
binary data corresponding to the regions A to C included in the
overlap portions 81a and 81b are illustrated.
[0091] Here, as illustrated in FIGS. 11A, 11C, and 11E, the first
discharge port group 31a is divided into a plurality of discharge
ports n2 in the end portion on the upstream side in the Y direction
and a plurality of discharge ports n1 on the downstream side in the
Y direction, and different thinning rates are assigned between the
discharge ports n1 and n2. Note that, in each of a group of the
discharge ports n1 and a group of the discharge ports n2,
substantially the same thinning rate is used. Furthermore, the
thinning rate assigned to the discharge ports n2 corresponding to
the end portion of the discharge port array is larger than that
assigned to the discharge ports n1.
[0092] As illustrated in FIGS. 11B, 11D, and 11F, the first
discharge port group 31b is similarly divided into the plurality of
discharge ports n1 in the end portion on the downstream side in the
Y direction and the plurality of discharge ports n2 on the upstream
side in the Y direction. In the first discharge port group 31b, the
discharge ports n1 corresponds to the end portion of the discharge
port array, and therefore, a thinning rate assigned to the
discharge ports n1 is larger than that assigned to the discharge
ports n2.
[0093] Hereinafter, the thinning rates assigned to the individual
regions in the discharge port groups 31a and 31b will be described
in detail.
[0094] The thinning rates illustrated in FIGS. 11A to 11F are rates
of thinning amounts of the binary data corresponding to a certain
region to amounts of binary data corresponding to the region in the
printing medium 3 generated by the quantization processor 415.
Specifically, a printing rate .gamma. (%) of printing data
generated when a printing rate of the binary data is .alpha. (%)
and a thinning rate is .beta. (%) may be calculated in accordance
with Expression 1.
.gamma.=.alpha.(1-.beta./100) (1)
[0095] For example, in a case where a thinning rate of 100% is set
to binary data of a printing rate of 100% relative to the solid
image, the binary data is thinned in accordance with the thinning
rate of 100%. Specifically, the binary data of the printing rate of
100% is converted into printing data of a printing rate of 0%
(=100%.times.(1-100%/100)) corresponding to an image in which ink
is not discharged in any pixel region on the printing medium 3.
Furthermore, in a case where a thinning rate of 50% is set to
binary data of a printing rate of 100%, the binary data is thinned
in accordance with the thinning rate of 50% relative to the binary
data. By this, the binary data of the printing rate of 100% is
converted into binary data of a printing rate of 50%
(=100%.times.(1-50/100)).
[0096] In this embodiment, as described below, only a configuration
in which binary data is thinned is described to address the case
where black streaks are likely to be generated in any of the
regions. However, an embodiment in another mode may be employed.
Specifically, when white streaks are likely to be generated, binary
data is added in accordance with an addition rate (increase rate)
and a discharge amount of ink is increased so that generation of
white streaks is suppressed. In this case, a printing rate .gamma.
(%) of printing data generated when a printing rate of the binary
data is .alpha. (%) and an addition rate is .beta. (%) may be
calculated in accordance with Expression 2.
.gamma.=.alpha.(1+.delta./100) (2)
[0097] In the region C illustrated in FIG. 10, since the incoming
airflow R caused by the scanning is cancelled by the incoming
airflow P caused by the absorption as described above, the number
of generated black streaks is small. Therefore, in the region C, as
illustrated in FIGS. 11E and 11F, thinning rates 701 and 702 which
are smaller than thinning rates assigned to the regions A and B
described below are assigned to the first discharge port groups 31a
and 31b, respectively.
[0098] In the scanning of the printing head 7 in the positional
relationship represented by (83) of FIGS. 9 and 10, the thinning
rates 701 are set to the first discharge port group 31a as
illustrated in FIG. 11E. Here, the first discharge port group 31a
is divided such that the number of the discharge ports n1 and the
number of the discharge ports n2 are equal to each other. A
thinning rate of the discharge port n2 corresponding to the end
portion of the discharge port array is set to 100% and a thinning
rate of the discharge port n1 is set to 25%. Specifically, an
average of the thinning rates 701 set to the first discharge port
group 31a is 62.5% (=(100%+25%)/2).
[0099] In the scanning of the printing head 7 in the positional
relationship represented by (84) of FIGS. 9 and 10, the thinning
rates 702 are set to the first discharge port group 31b as
illustrated in FIG. 11F. The thinning rates 702 and the thinning
rates 701 have the opposite relationship.
[0100] The first discharge port group 31a having the thinning rates
701 assigned thereto and the first discharge port group 31b having
the thinning rates 702 assigned thereto correspond to the region C
in the overlap portion 81a. Therefore, when binary data (a printing
rate of 100%) corresponding to the solid image is input to the
correction processor 417 as data corresponding to the overlap
portion 81a, for example, printing data of a printing rate of 75%
is generated from the binary data as illustrated in FIG. 12C.
[0101] Subsequently, in the region B illustrated in FIGS. 9 and 10,
only the incoming airflow R caused by the scanning flows since the
suction holes 26 are not located in a neighboring area. Therefore,
a degree of generation of in an incoming airflow is a middle
degree, and a degree of generation of black streaks is also middle.
Accordingly, in the region B, as illustrated in FIGS. 11C and 11D,
thinning rates 703 and 704 which are larger than thinning rates 701
and 702 set to the region C are set to the first discharge port
groups 31a and 31b. When ink is discharged from the first discharge
port group 31a to the region B in the overlap portion 81a in the
scanning performed by the printing head 7 in the positional
relationship represented by (83) in FIGS. 9 and 10, thinning is
performed on the binary data corresponding to the first discharge
port group 31a in accordance with the thinning rates 703
illustrated in FIG. 11C. When ink is discharged from the first
discharge port group 31b to the region B in the overlap portions
81a and 81b in the scanning performed by the printing head 7 in the
positional relationship represented by (84) in FIGS. 9 and 10,
thinning is performed on the binary data corresponding to the first
discharge port group 31b in accordance with the thinning rates 704
illustrated in FIG. 11D.
[0102] Although a thinning rate of 25% is assigned to the discharge
ports n1 in FIG. 11E, a thinning rate of 50% is assigned to the
discharge ports n1 in FIG. 11C. Specifically, an average of the
thinning rates 703 set to the first discharge port group 31a is 75%
(=(100%+50%)/2). The thinning rates 704 illustrated in FIG. 11D and
the thinning rates 703 have the opposite relationship.
[0103] When binary data of a printing rate of 100% is input to the
correction processor 417, printing data to which a printing rate of
50% is set as illustrated in FIG. 12B is generated from the binary
data.
[0104] Then, in the region A illustrated in FIGS. 9 and 10, the
incoming airflow R caused by the scanning and the incoming airflow
Q caused by the suction flow in the same direction, and
accordingly, black streaks are most significantly generated.
Therefore, when printing is performed on the region A, as
illustrated in FIGS. 11A and 11B, thinning rates 705 and 706 which
are larger than the thinning rates 703 and 704 set to the region B
and the thinning rates 701 and 702 set to the region C are set.
When ink is discharged from the first discharge port group 31a to
the region A in the overlap portion 81a in the scanning performed
by the printing head 7 in the positional relationship represented
by (83) in FIGS. 9 and 10, thinning is performed on the binary data
corresponding to the first discharge port group 31a in accordance
with the thinning rates 705 illustrated in FIG. 11A. When ink is
discharged from the first discharge port group 31b to the region A
in the overlap portions 81a and 81b in the scanning performed by
the printing head 7 in the positional relationship represented by
(84) in FIGS. 9 and 10, thinning is performed on the binary data
corresponding to the first discharge port group 31b in accordance
with the thinning rates 706 illustrated in FIG. 11B.
[0105] The first discharge port group 31a corresponding to the
region A are different from the first discharge port group 31a
corresponding to the region B and the region C in that the
discharge ports n1 is divided such that the number of discharge
ports n1 is one-third of the number of discharge ports n2.
Furthermore, thinning rates of the discharge ports n1 and the
discharge ports n2 are set to 50% and 100%, respectively.
Therefore, an average of the thinning rates 705 set to the first
discharge port group 31a is 87.5% (=(100%.times.3/4+50%.times.1/4).
On the other hand, the first discharge port group 31b corresponding
to the region A are different from the first discharge port group
31a corresponding to the region A in that the discharge ports n2 is
divided such that the number of discharge ports n2 is one-third of
the number of discharge ports n1. Furthermore, thinning rates of
the discharge ports n1 and the discharge ports n2 are set to 100%
and 50%, respectively.
[0106] Accordingly, when binary data of a printing rate of 100% is
input to the correction processor 417, printing data in which a
printing rate of 50% is set to both end portions in the Y direction
and a printing rate of 0% is set to a center portion in the Y
direction as illustrated in FIG. 12A is generated from the binary
data.
[0107] As described above, according to the thinning rates
described in FIGS. 12A to 12C, in the overlap portions 81a and 81b,
a printing rate of printing data corresponding to the region C may
be large and a printing rate of printing data corresponding to the
region A may be small.
[0108] By this, black streaks generated in the overlap portions 81a
and 81b in different degrees in the scanning directions may be
efficiently suppressed.
[0109] As described above, according to the configuration of this
embodiment, even when an incoming airflow is increased or reduced
in both end portions in a scanning direction of a printing medium
due to suction of air through suction holes, printing may be
performed while generation of boundary streaks is efficiently
suppressed in entire regions of overlap portions in the scanning
direction.
Comparative Example
[0110] A comparative example will be described in detail
hereinafter.
[0111] FIGS. 13A and 13B are diagrams schematically illustrating
thinning rates set to binary data corresponding to an overlap
portion in the comparative example. FIG. 13A is a diagram
illustrating thinning rates 707 used when binary data corresponding
to the first discharge port group 31a is thinned in a case where
the positional relationship between a printing head 7 and a
printing medium 3 is represented by (83) of FIG. 9. FIG. 13B is a
diagram illustrating thinning rates 708 used when binary data
corresponding to the first discharge port group 31b is thinned in a
case where the positional relationship between the printing head 7
and the printing medium 3 is represented by (84) of FIG. 9.
[0112] As illustrated in FIGS. 13A and 13B, in the comparative
example, the same thinning rates are used for thinning irrespective
of a position in an X direction of the printing medium 3. Here, as
illustrated in FIG. 13A, in the comparative example, a first
discharge port group 31a is divided into a plurality of discharge
ports n2 in an end portion on an upstream side in a Y direction and
a plurality of discharge ports n1 on a downstream side in the Y
direction. Furthermore, a thinning rate of 100% is set to binary
data corresponding to the discharge ports n2 and a thinning rate of
0% is set to binary data corresponding to the discharge ports n1.
Moreover, as illustrated in FIG. 13B, thinning rates 708 and
thinning rates 707 have the opposite relationship.
[0113] In a case where binary data of a printing rate of 100%
corresponding to a solid image is input to a correction processor
417, for example, by thinning the binary data using the thinning
rates illustrated in FIGS. 13A and 13B, printing data in which, in
the first discharge port group 31a in the positional relationship
represented by (83), half of the discharge ports near the center in
the Y direction have a printing rate of 100% and the other half of
the discharge ports in an end portion in the Y direction has a
printing rate of 0% is generated. On the other hand, printing data
in which, in the first discharge port group 31b in the positional
relationship represented by (84), half of the discharge ports near
the center in the Y direction has a printing rate of 100% and the
other half of the discharge ports in the end portion in the Y
direction has a printing rate of 0% is generated.
[0114] According to the printing data generated as described above,
ink is discharged from the first discharge port group 31a in a
printing rate of 100% in scanning in the positional relationship
represented by (83) on a region on the downstream side in the Y
direction in an overlap portion 81a of the printing medium 3.
Furthermore, ink is discharged from the first discharge port group
31b in a printing rate of 100% in scanning in the positional
relationship represented by (84) on a remaining region on the
upstream side in the Y direction in the overlap portion 81a.
Accordingly, the ink may be theoretically discharged in the
printing rate of 100% to an entire region of the overlap portion
81a.
[0115] However, when the printing is performed with this printing
method and the thinning rates, a self-airflow caused by the
discharge of the ink and an incoming airflow caused by the scanning
performed by the printing head 7 are generated. Accordingly, ink
droplets are not landed in ideal positions and black streaks are
generated in the overlap portion 81a. Furthermore, since an
incoming airflow caused by suction of air through suction holes 26
on a platen 2 further flows in both end portions (regions A and C)
of the printing medium 3 in the X direction, black streaks of
different densities are generated in the center portion (region B)
and the both end portions (regions A and C) in the X direction.
Degrees of boundary streaks generated in a case where printing is
performed in accordance with the printing method illustrated in
FIG. 9 and the thinning rates illustrated in FIGS. 13A and 13B are
illustrated in Table 1.
TABLE-US-00001 TABLE 1 Region A Region B Region C black streak
(large) black streak (middle) black streak (small)
[0116] According to Table 1, black streaks are remarkably generated
in the region A of the overlap portion 81a, and a degree of black
streaks in the region C is smaller than those of the regions A and
B. This is because a degree of an end deviation phenomenon is small
in the region A since a strong incoming airflow is generated
whereas a degree of the end deviation phenomenon is large in the
region C since an incoming airflow generated in the region C is
weak as described above.
[0117] As described above, in a case where printing data is
generated by thinning binary data in accordance with the thinning
rates illustrated in the comparative example, generation of black
streaks is not efficiently suppressed, and accordingly, quality of
an image is deteriorated.
Second Embodiment
[0118] In the first embodiment, the case where printing is
performed only by scanning in one direction of a printing head is
described.
[0119] On the other hand, in a second embodiment, a case where
printing is performed by scanning using a printing head in a going
direction (first direction) and a returning direction (second
direction) will be described.
[0120] Descriptions of portions the same as those of the first
embodiment described above are omitted.
[0121] FIG. 14 is a diagram illustrating a process of printing an
image on a printing medium 3 in accordance with a printing method
of this embodiment.
[0122] In this embodiment, as the printing medium 3 moves, a
printing position is changed as illustrated in FIG. 9, and in FIG.
14, the printing medium 3 is fixed and a position of a printing
head 7 is changed in the Y direction.
[0123] Also in this embodiment, as with the first embodiment, the
printing medium 3 is divided into three regions, that is, a region
A having a width of 20 mm from an end portion on an upstream side
in an X direction, a region C having a width of 20 mm from an end
portion on a downstream side in the X direction, and a region B
which is other than the regions A and C.
[0124] In this embodiment, scanning in a going direction and
scanning a returning direction along the X direction of the
printing head 7 are alternately performed in a repetitive manner,
and images are printed in non-overlap portions 82c and 82d in the
printing medium 3 by performing scanning twice. Meanwhile, images
are printed on overlap portions 81d and 81e by performing scanning
three times. For example, an image is printed on the non-overlap
portion 82c by performing an n-th scanning operation in the going
direction in the positional relationship represented by (91) and an
(n+1)-th scanning operation in the returning direction in the
positional relationship represented by (92). Furthermore, an image
is printed on the non-overlap portion 82d by performing an (n+1)-th
scanning operation in the returning direction in the positional
relationship represented by (92) and an (n+2)-th scanning operation
in the going direction in the positional relationship represented
by (93). Furthermore, an image is printed on the overlap portion
81d by performing the n-th scanning operation in the going
direction in the positional relationship represented by (91), the
(n+1)-th scanning operation in the returning direction in the
positional relationship represented by (92), and the (n+2)-th
scanning operation in the going direction in the positional
relationship represented by (93). Furthermore, an image is printed
on the overlap portion 81e by performing the (n+1)-th scanning
operation in the returning direction in the positional relationship
represented by (92), the (n+2)-th scanning operation in the going
direction in the positional relationship represented by (93), and
an (n+3)-th scanning operation in the returning direction in the
positional relationship represented by (94). Between the scanning
operation in the going direction and the scanning operation in the
returning direction, the printing medium 3 is conveyed in the Y
direction.
[0125] In this embodiment, since the printing is performed on the
non-overlap portions by the two scanning operations as described
above, a mask processor 416 illustrated in FIG. 8 divides binary
data into the two scanning operations using two mask patterns.
[0126] FIGS. 15A and 15B are diagrams schematically illustrating
mask patterns according to the embodiment.
[0127] In FIG. 15A, a mask pattern 201 employed in the scanning in
the going direction in the positional relationship represented by
(91) and (93) of FIG. 14 is illustrated. In FIG. 15B, a mask
pattern 202 employed in the (n+1)-th and (n+3)-th scanning
operations in the returning direction in the positional
relationship represented by (92) and (94) of FIG. 14 is
illustrated.
[0128] Each of the mask patterns 201 and 202 is formed by arranging
a plurality of print permitting pixels and a plurality of non-print
permitting pixels. In FIGS. 15A and 15B, black portions represent
the print permitting pixels and white portions represent the
non-print permitting pixels.
[0129] The number of print permitting pixels and the number of
non-print permitting pixels which are arranged in the mask pattern
201 are the same as each other. Therefore, when binary data of a
printing rate of 100% relative to a solid image is input to the
mask processor 416, binary data of a printing rate of 50% is
generated for scanning in the going direction. Similarly, since the
number of print permitting pixels and the number of non-print
permitting pixels which are arranged in the mask pattern 202 are
also the same as each other, binary data of a printing rate of 50%
is generated for scanning in the returning direction.
[0130] Furthermore, the print permitting pixels in the mask pattern
202 are arranged in exclusionary and complementary positions
relative to the print permitting pixels in the mask pattern 201.
Therefore, the binary data assigned to the scanning in the going
direction of the printing head 7 and the binary data assigned to
the scanning in the returning direction have the exclusionary and
complementary relationship.
[0131] According to the mask patterns 201 and 202, an image having
a density corresponding to input image data may be printed in the
non-overlap portions 82c and 82d in the printing medium 3.
[0132] Here, in the overlap portions 81d and 81e, ink is discharged
twice in the scanning operations in the same direction, and
therefore, black streaks are generated. Even when thinning is
performed, as with the first embodiment, in accordance with the
thinning rates illustrated in FIGS. 13A and 13B, black streaks are
generated in the overlap portions 81d and 81e due to a self-airflow
caused by the discharge of ink and an incoming airflow caused by
the scanning performed by the printing head 7.
[0133] Furthermore, as with the first embodiment, degrees of
generations of black streaks in the regions A, B, and C are
different from one another due to an incoming airflow caused by
suction of air in both end portions of the printing medium 3.
[0134] Moreover, since the printing is performed by reciprocation
scanning according to this embodiment, degrees of generations of
black streaks in the overlap portion 81d in which scanning in the
going direction is performed twice and the overlap portion 81e in
which scanning in the returning direction is performed twice are
different from each other.
[0135] Table 2 illustrates the degrees of boundary streaks
generated when printing data is generated by thinning binary data
in accordance with the printing method illustrated in FIG. 14 and
the thinning rates illustrated in FIGS. 13A and 13B.
TABLE-US-00002 TABLE 2 Region A Region B Region C Overlap black
streak black streak (middle) black streak (small) Portion 81d
(large) Overlap black streak black streak (middle) black streak
(large) Portion 81e (small)
[0136] As illustrated in FIG. 14, an incoming airflow R caused by
the scanning flows in the returning direction in the scanning in
the going direction. Therefore, when incoming airflows P and Q
caused by suction of air in the both end portions are also taken
into consideration, an airflow which actually flows in the region A
is strongest and an airflow which actually flows in the region C is
weakest. By this, as illustrated in Table 2, in the overlap portion
81d in which the scanning operations in the going direction overlap
with one another, black streaks are most remarkably generated in
the region A whereas influence of black streak is small in the
region C.
[0137] On the other hand, the incoming airflow R caused by the
scanning flows in the going direction in the scanning in the
returning direction. Therefore, an airflow which actually flows in
the region C is strongest and an airflow which actually flows in
the region A is weakest. Accordingly, in the overlap portion 81e in
which the scanning operations in the returning direction overlap
with one another, influence of black streaks is small in the region
A whereas black streaks are remarkably generated in the region
C.
[0138] Accordingly, in this embodiment, as illustrated in Table 3,
when printing is performed on the regions A to C, thinning rates
705, 706, 703, 704, 701, and 702 illustrated in FIGS. 11A to 11F
are set to the binary data of the regions A to C.
TABLE-US-00003 TABLE 3 Region A Region B Region C Overlap Portion
81d 705, 706 703, 704 701, 702 Overlap Portion 81e 701, 702 703,
704 705, 706
[0139] As described above, according to this embodiment, even when
an image is printed by reciprocation scanning, generation of
boundary streaks caused by incoming airflows generated due to
suction of air may be efficiently suppressed.
Third Embodiment
[0140] In the first and second embodiments, printing conditions,
such as the printing rates (discharge amounts of ink) of the binary
data input to the correction processor 417, a speed of scanning
performed by the printing head 7, a distance between the printing
head 7 and the platen 2 (hereinafter referred to as a
"sheet-to-head distance" where appropriate), are not changed.
[0141] On the other hand, in a third embodiment, a case where the
printing conditions are changed will be described.
[0142] Descriptions of portions the same as those of the first and
second embodiments described above are omitted.
[0143] A degree of generation of boundary streaks may be changed in
accordance with change of various printing conditions in addition
to change of strength of incoming airflows caused by suction of air
through suction holes.
[0144] Hereinafter, printing conditions which affect a degree of
generation of boundary streaks will be described in detail.
[0145] FIGS. 16A and 16B are diagrams illustrating a degree of
generation of boundary streaks changed in accordance with a
discharge amount of ink. A case where a discharge amount of ink is
relatively small is described in FIG. 16A and a case where a
discharge amount of ink is relatively large is described in FIG.
16B.
[0146] When a discharge amount of ink is relatively large, eddy of
air caused by discharge of ink is remarkably generated, and
accordingly, a relatively-large self-airflow is generated.
Therefore, ink droplets are likely to be attracted toward a center
portion of a printing head 7. Accordingly, when a discharge amount
of ink is relatively large as illustrated in FIG. 16B, white
streaks are likely to be generated when compared with the case
where a discharge amount of ink is relatively small illustrated in
FIG. 16A.
[0147] Furthermore, when a scanning speed of the printing head 7 in
an X direction is relatively high, an amount of air flowing in a
space between the printing head 7 and a printing medium 3 per unit
time is large when compared with a case where a scanning speed is
relatively low. That is, when the scanning speed is relatively
high, an incoming airflow caused by the scanning of the printing
head 7 is large. Therefore, correction of a depressurized state by
the incoming airflow is dominant even when the self-airflow is
large, and therefore, the ink droplets is not likely to be
attracted toward the center portion of the printing head 7 and
deviation toward end portions may be generated in some cases.
Accordingly, when the scanning speed of the printing head 7 is
relatively high, black streaks are likely to be generated when
compared with the case where the scanning speed is relatively
low.
[0148] Furthermore, a degree of generation of boundary streaks is
changed also depending on the sheet-to-head distance.
[0149] FIGS. 17A and 17B are diagrams illustrating a degree of
generation of boundary streaks which is changed in accordance with
the sheet-to-head distance. A case of a distance d1 which is a
relatively long sheet-to-head distance is illustrated in FIG. 17A
and a case of a distance d2 which is a relatively short
sheet-to-head distance is illustrated in FIG. 17B.
[0150] In the case where the sheet-to-head distance is relatively
small, even when deviation of ink droplets is generated by a degree
substantially the same as that in the case where the sheet-to-head
distance is large, an amount of the deviation of the ink droplets
is relatively small since a period of time from when ink is
discharged to when the ink is landed on the printing medium 3 is
short. The amount of deviation is similarly reduced even in a case
where the ink droplets are deviated toward the center portion of
the printing head 7 and a case where the ink droplets are deviated
toward the end portions. Accordingly, when the sheet-to-head
distance is relatively small, white streaks and black streaks are
unlikely to be generated when compared with the case where the
sheet-to-head distance is comparatively large.
[0151] Accordingly, printing is performed in accordance with the
printing method described with reference to FIG. 14 using different
printing rates of binary data which is information relating to a
discharge amount of ink, different scanning speeds of the printing
head 7, and different sheet-to-head distances. Degrees of
generation of boundary streaks in an overlap portion 81e obtained
when different printing conditions are employed as described above
are illustrated in Table 4. For simplicity, a description of an
overlap portion 81d is omitted.
TABLE-US-00004 TABLE 4 Sheet- Scan- to-Head ning Printing Distance
Speed rate Region A Region B Region C 2.0 40 ips 50% White Streak
-- Black Streak (Middle) (Middle) 2.0 40 ips 25% -- Black Streak
Black Streak (Middle) (Large) 1.0 40 ips 50% White Streak -- Black
Streak (Small) (Small) 2.0 25 ips 50% White Streak White Streak --
(Large) (Middle)
[0152] It is experimentally recognized that white streaks are
likely to be generated when a discharge amount of ink (printing
rate) is relatively large, black streaks are likely to be generated
when a scanning speed is relatively high, and boundary streaks are
unlikely to be generated when a sheet-to-head distance is
small.
[0153] Accordingly, a correction process is performed by thinning
binary data using different thinning rates depending on the
printing conditions described above in this embodiment.
[0154] The thinning rates of the binary data of this embodiment are
illustrated in Table 5.
TABLE-US-00005 TABLE 5 Region A Region B Region C Sheet-to- Width
Thinning Width Thinning Width Thinning Head Scanning Printing
[1/1200 dpi] Rate [%] [1/1200 dpi] Rate [%] [1/1200 dpi] Rate [%]
Distance Speed Rate Scan n1 n2 n1 n2 n1 n2 n1 n2 n1 n2 n1 n2 2.0 40
ips 50% (92) 3 1 0 100 2 2 0 100 2 2 50 100 (94) 1 3 100 0 2 2 100
0 2 2 100 50 2.0 40 ips 25% (92) 2 2 0 100 2 2 50 100 2 2 60 100
(94) 2 2 100 0 2 2 100 50 2 2 100 60 1.0 40 ips 50% (92) 2 2 0 50 2
2 0 100 2 2 25 100 (94) 2 2 50 0 2 2 100 0 2 2 100 25 2.0 25 ips
50% (92) 2 2 0 0 3 1 0 100 2 2 0 100 (94) 2 2 0 0 1 3 100 0 2 2 100
0
[0155] In Table 5, only ratios of the numbers of discharge ports n1
and the numbers of discharge ports n2 and thinning rates of binary
data corresponding to the discharge ports n1 and the discharge
ports n2 are illustrated. The thinning rates are the same as or
similar to those illustrated in FIGS. 11A to 11F and FIGS. 13A and
13B in practice. For example, in a case where printing is performed
on the region B in a condition in which the sheet-to-head distance
is 2.0 mm, a scanning speed is 40 ips, and a printing rate is 50%,
thinning rates 707 illustrated in FIG. 13A are employed in scanning
in the positional relationship represented by (92) and thinning
rates of 708 illustrated in FIG. 13B are employed in scanning in
the positional relationship represented by (94). Furthermore, in a
case where printing is performed on the region C in a condition in
which a sheet-to-head distance is 2.0 mm, a scanning speed is 40
ips, and a printing rate is 50%, thinning rates 703 illustrated in
FIG. 11C are employed in scanning in the positional relationship
represented by (92) and thinning rates of 704 illustrated in FIG.
11D are employed in scanning in the positional relationship
represented by (94). Moreover, in a case where printing is
performed on the region C in a condition in which a sheet-to-head
distance is 2.0 mm, a scanning speed is 40 ips, and a printing rate
is 25%, thinning rates different from the thinning rates 703
illustrated in FIG. 11C in that the thinning rate corresponding to
the discharge ports n1 of 50% is changed to 60% are employed in
scanning in the positional relationship represented by (92).
Furthermore, in the scanning in the positional relationship
represented by (94), thinning rates different from the thinning
rates 704 illustrated in FIG. 11D in that the thinning rate
corresponding to the discharge ports n2 of 50% is changed to 60% is
employed.
[0156] As described above, in this embodiment, when printing is
performed on an overlap portion, different thinning rates are
employed depending on printing conditions including a discharge
amount of ink to the overlap portion, a scanning speed, and a
sheet-to-head distance. By this, printing may be performed while
boundary streaks generated in different degrees depending on
printing conditions are effectively suppressed.
[0157] Furthermore, in the embodiments, the mode where a mask
process is performed on binary data using a mask pattern, the
binary data is divided for a plurality of scanning operations, and
a correction process is performed by thinning the binary data in
accordance with thinning rates has been described. However, other
modes may be embodied. For example, in a case where printing is
performed in accordance with the printing method illustrated in
FIGS. 9 and 10, different mask patterns may be employed when
printing is performed on the individual regions A, B, and C. In
this case, a mask pattern corresponding to the region A, a mask
pattern corresponding to the region B, and a mask pattern
corresponding to the region C are combined such that a rate of the
number of print permitting pixels to a sum of the number of print
permitting pixels and the number of non-print permitting pixels is
high in order of the mask pattern corresponding to the region A,
the mask pattern corresponding to the region B, and the mask
pattern corresponding to the region C.
[0158] Furthermore, in the embodiments, the mode in which a platen
including a plurality of suction holes formed thereon in a range
having a width larger than that of the printing medium 3 in the X
direction is provided has been described. However, other modes may
be embodied. For example, the present invention may be employed in
a printing apparatus which is capable of performing printing on
printing media of an A4 size and a postcard size, which has a
plurality of suction holes covered by the printing medium when
printing is performed on the printing medium of the A4 size, and
which has the suction holes some of which are exposed when printing
is performed on the printing medium of the postcard size. In this
case, the correction process described in the embodiments is not
performed when the printing is performed on the printing medium of
the A4 size, but the correction process is performed when the
printing is performed on the printing medium of the postcard size.
By this, the effects of the present invention may be obtained.
[0159] Furthermore, although the mode in which the first discharge
group is divided into the plurality of discharge ports n1 and the
plurality of discharge ports n2 has been described in the
embodiments, other modes may be embodied. Specifically, a uniform
thinning rate may be defined in the first discharge group or the
first discharge group may be divided into three or more.
[0160] Furthermore, although the mode in which the binary data is
thinned or not corrected has been described in the embodiments,
other modes may be embodied. For example, a case where a printing
medium is conveyed such that a width of an overlap portion in a Y
direction is smaller than those of the embodiments and a case where
white streaks are more remarkably generated when compared with
black streaks in overlap portions when a scanning speed of a
printing head is considerably low may be considered. In these
cases, generation of white streaks may be suppressed to some extent
by adding binary data in accordance with an addition rate. Printing
rates of the print data may be calculated in accordance with
Expression 2 above in these cases.
[0161] Furthermore, although the binary data is divided for a
plurality of scanning operations using the mask pattern in the
embodiments, means for the division is not limited to the mask
pattern. For example, printing data of individual pixels are
sequentially assigned to a plurality of buffers corresponding to a
plurality of scanning operations using an assigning circuit
included in a printing apparatus, and scanning operations for
printing the individual pixels may be determined. According to the
assigning circuit described above, the numbers of times scanning is
performed before ink is discharged to the individual pixels may be
controlled. Even the embodiment in which binary data is divided for
a plurality of scanning operations using the assigning circuit may
attain the effects of the present invention.
[0162] Furthermore, in the embodiments, a so-called thermal jet
inkjet printing apparatus which discharges ink by energy of bubble
generation caused by heating and a printing method thereof are
described. However, the present invention is not limited to the
thermal jet inkjet printing apparatus, and may be employed in
various print control apparatuses including a so-called piezo
inkjet printing apparatus which discharges ink using piezoelectric
elements.
[0163] Furthermore, although a printing method using a printing
apparatus is described in each of the embodiments, an image
processing apparatus and an image processing method for generating
data used to perform the printing methods described in the
embodiments may be employed. Moreover, the present invention may be
widely employed in a mode in which a program is provided separately
from a printing apparatus, a mode in which a program is included in
a printing apparatus, and the like.
[0164] According to the printing apparatus of this embodiment, an
image which is less affected by boundary streaks generated by
different densities depending on scanning directions caused by
different strengths of incoming airflows may be printed.
Other Embodiments
[0165] Embodiments of the present invention can also be realized by
a computer of a system or apparatus that reads out and executes
computer executable instructions printed on a storage medium (e.g.,
non-transitory computer-readable storage medium) to perform the
functions of one or more of the above-described embodiments of the
present invention, and by a method performed by the computer of the
system or apparatus by, for example, reading out and executing the
computer executable instructions from the storage medium to perform
the functions of one or more of the above-described embodiments.
The computer may comprise one or more of a central processing unit
(CPU), micro processing unit (MPU), or other circuitry, and may
include a network of separate computers or separate computer
processors. The computer executable instructions may be provided to
the computer, for example, from a network or the storage medium.
The storage medium may include, for example, one or more of a hard
disk, a random-access memory (RAM), a read only memory (ROM), a
storage of distributed computing systems, an optical disk (such as
a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc
(BD).TM.), a flash memory device, a memory card, and the like.
[0166] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
[0167] This application claims the benefit of Japanese Patent
Application No. 2014-069578, filed in Mar. 28, 2014, which is
hereby incorporated by reference herein in its entirety.
* * * * *