Field of the Invention
[0001] This invention relates to a method of printing from an inkjet printhead, whilst modulating
a peak power requirement for the printhead. It has been developed primarily to reduce
the demands on a pagewidth printhead power supply, although other advantages of the
methods of printing described herein will be apparent to the person skilled in the
art.
Background to the Invention
[0002] Inkjet printers are now commonplace in homes and offices. For example, inkjet photographic
printers, which print color images generated on digital cameras, are, to an increasing
extent, replacing traditional development of photographic negatives. With the increasing
use of inkjet printers, the demands of such printers in terms of print quality and
speed, continue to increase.
[0003] All commercially available inkjet printers use a scanning printhead, which traverses
across a stationary print medium. After each sweep of the printhead, the print medium
incrementally advances ready for the next line(s) of printing. Such printers are inherently
slow and are becoming unable to meet the needs of current demands of inkjet printers.
[0004] The present Applicant has previously described many different types of pagewidth
printheads, which are fabricated using MEMS technology. In pagewidth printing, the
print medium is continuously fed past a stationary printhead, thereby allowing high-speed
printing at, for example, one page per 1-2 seconds. Moreover, MEMS fabrication of
the printhead allows a much higher nozzle density than traditional scanning printheads,
and print resolutions of 1600 dpi are possible.
[0005] To a large extent, pagewidth printing has been made possible by reducing the total
energy required to fire each ink droplet and/or efficiently removing heat from the
printhead via ejected ink. In these ways, self-cooling of the printhead can be achieved,
which enables a pagewidth printhead having a high nozzle density to operate without
overheating.
[0006] However, whilst a total amount of energy to print, say, a full-color photographic
page will be approximately constant for any given pagewidth printhead, the power requirement
of the printhead may, of course, vary. An average power requirement for printing a
page is determined by the total energy required and the total time taken to print
the page, assuming an equal distribution of printing over the time period. In addition,
the power requirement of the printhead during printing of the page may fluctuate.
Due to a particular configuration of the printhead or printer controller, some lines
of print may consume more power than other lines of print. Hence, a peak power requirement
for each line of printing may be different.
[0007] In a typical pagewidth printhead, nozzles ejecting the same color of ink are arranged
longitudinally in color channels along the length of the printhead. Each color channel
may comprise one or more rows of nozzles, all ejecting the same colored ink. In a
simple example, there may be one cyan row of nozzles, one magenta row of nozzles and
one yellow row of nozzles. Usually, each row of nozzles will be fired sequentially
during printing
e.g. cyan then magenta then yellow.
[0008] Furthermore, a typical pagewidth printhead may be comprised of a plurality of printhead
modules, which abut each other and cooperate to form a printhead extending across
a width of the page to be printed. Each printhead module is typically a printhead
integrated circuit comprising nozzles and drive circuitry for firing the nozzles.
The rows of nozzles extend over the plurality of printhead modules, with each printhead
module including a respective segment of each nozzle row.
[0009] In previous patent applications, listed below, we described various types of printheads,
printer controllers and methods of printing.
[0010] In our previous patent applications
USSN 10/854498 (Docket No. PLT012US), filed May 27, 2004,
USSN 10/854516 (Docket No. PLT017US), filed May 27, 2004 and
USSN 10/854508 (Docket No. PLT018US), filed May 27, 2004, we described a method of printing a line
of dots where not all nozzles in one row or one segment are fired simultaneously.
Rather, the nozzles are fired sequentially in firing groups in order to minimize the
peak power requirement during printing of one line. As a consequence, each line of
printing is typically not a perfectly straight line (unless the physical arrangements
of the nozzles directly compensates for the firing order in which case it can be a
straight line), although this imperfection is undetectable to the human eye. Each
segment on a printhead module may comprise, for example, 10 firing groups of nozzles,
in order to minimize, as far as possible within the print speed requirements, the
peak power requirement for firing that segment of the nozzle row.
[0011] In our previous patent applications
USSN 10/854512 (Docket No. PLT014US), filed May 27, 2004 and
USSN 10/854491 (Docket No. PLT028US), filed May 27, 2004, we described a means for joining abutting
printhead modules such that the effective distance between adjacent nozzles ('nozzle
pitch') in the row remains constant. At one end of each printhead module, there is
a displaced nozzle row portion, which is not aligned with its corresponding nozzle
row. The firing of these displaced nozzles is timed so that they effectively print
onto the same line as the row to which they correspond. As such, all references to
"rows", "rows of nozzles" or "nozzle rows" herein include nozzle rows comprising one
or more displaced row portions, as described in
USSN 10/854512 (Docket No. PLT014US), filed May 27,2004 and
USSN 10/854491 (Docket No. PLT028US), filed May 27, 2004.
[0012] In our previous patent applications
USSN 10/854507 (Docket No. PLT019US), filed May 27, 2004 and
USSN 10/854523 (Docket No. PLT030US), filed May 27, 2004, we described a means by which the visual
effect of defective nozzles is reduced. The printhead described comprises one or more
'redundant' color channels, so that for a first row of nozzles ejecting a given color,
there is a corresponding second ('redundant') row of nozzles from a different color
channel which eject the same color. As described in
USSN 10/854507 (Docket No. PLT019US), filed May 27, 2004 and
USSN 10/854523 (Docket No. PLT030US), filed May 27, 2004, one line may be printed by the first nozzle
row and the next line is printed by the second nozzle row so that the first and second
nozzle rows print alternate lines on the page. Thus, if there are unknown defective
nozzles in a given row, the visual effect on the page is halved, because only every
other line is printed using that row of nozzles.
[0013] Alternatively, if there are known dead nozzles in a given row, the corresponding
row of nozzles may be used to print dots in those positions where there is a known
dead nozzle. In other words, only a small number of nozzles in the 'redundant' row
may be used to print.
[0014] As already mentioned, the redundancy scheme described in
USSN 10/854507 (Docket No. PLT019US), filed May 27, 2004 and
USSN 10/854523 (Docket No. PLT030US), filed May 27, 2004 has the advantage of reducing the visual
impact of dead nozzles, either known or unknown. Moreover, careful choice of redundant
colors may be used to further reduce the visual impact of dead nozzles. For example,
since yellow makes the lowest contribution (11%) to luminance, the human eye is least
sensitive to missing yellow dots and, therefore, yellow would be a poor choice for
a redundant color. On the other hand; black, makes a much higher contribution to luminance
and would be a good choice for a redundant color.
[0015] However, while the redundancy scheme described in
USSN 10/854507 (Docket No. PLT019US), filed May 27, 2004 and
USSN 10/854523 (Docket No. PLT030US), filed May 27, 2004 can compensate for dead nozzles and reduce
(
e.g. halve) the number of dots fired by some nozzles, it places increased demands on the
power supply which is used to power the printhead. The reason is because in the time
it takes for the print medium to advance by one line (one `line-time'), each nozzle
row must be allotted a portion of the line-time in which to fire, in order to achieve
dot-on-dot printing and provide the desired image. Each nozzle row is allotted a portion
of the line-time, since not all nozzle rows can fire simultaneously. (If all nozzle
rows were to fire simultaneously, there would be an unacceptable current overload
of the printhead).
[0016] In a simple CMY pagewidth printhead, having three rows of nozzles and no redundant
color channels, each nozzle row must fire in one-third of the line-time. If the average
power requirement of the printhead is x, then the peak power requirement over the
duration of the line-time is as shown in Table 1:
Table 1
Line-time |
Color Channel |
Peak Power Requirement |
0 |
C |
x |
0.33 |
M |
x |
0.67 |
Y |
x |
0 (new line) |
C |
x ... etc. |
[0017] In this simple CMY printhead with no redundant nozzles, power is distributed evenly
over the duration of the line-time so that the peak power requirement is constant
and equal to the average power requirement of the printhead. From the standpoint of
the power supply, this situation is optimal, but, on the other hand, there is no means
for minimizing the visual effects of dead nozzles.
[0018] In a CMY printhead having redundant cyan and magenta color channels
(i.e. C1, C2, M1, M2 and Y color channels) and a pair of nozzle rows in each color channel
(for even and odd dots), each nozzle row is allotted one-tenth of the line-time, since
there are now ten nozzle rows. Now if the average power requirement of the printhead
is x, with the redundancy scheme and firing sequence described in
USSN 10/854507 (Docket No. PLT019US), filed May 27, 2004 and
USSN 10/854523 (Docket No. PLT030US), filed May 27, 2004, the peak power requirement over the duration
of two line-times is as shown in Table 2:
Table 2
Line-time |
Color Channel |
Peak Power Requirement |
0 |
C1 (even) |
1.67x |
0.1 |
C2 (even) |
0 |
0.2 |
M1 (even) |
1.67x |
0.3 |
M2 (even) |
0 |
0.4 |
Y (even) |
1.67x |
0.5 |
C1 (odd) |
1.67x |
0.6 |
C2 (odd) |
0 |
0.7 |
M1 (odd) |
1.67x |
0.8 |
M2 (odd) |
0 |
0.9 |
Y (odd) |
1.67x |
0 (new line) |
C1 (even) |
0 |
0.1 |
C2 (even) |
1.67x |
0.2 |
M1 (even) |
0 |
0.3 |
M2 (even) |
1.67x |
0.4 |
Y (even) |
1.67x |
0.5 |
C1 (odd) |
0 |
0.6 |
C2 (odd) |
1.67x |
0.7 |
M1 (odd) |
0 |
0.8 |
M2 (odd) |
1.67x |
0.9 |
Y (odd) |
1.67x |
0 (new line) |
C1 (even) |
1.67x ... etc |
[0019] It is evident from the above table that the peak power requirement of the printhead
fluctuates severely between 1.67
x and 0 within the period of a line-time, even though the average power consumed over
the whole line-time is still
x. In practical terms, it is difficult to manufacture a power supply which is able
to deliver severely fluctuating amounts of power within each line-time. Hence, the
redundancy described in
USSN 10/854507 (Docket No. PLT019US), filed May 27, 2004 and
USSN 10/854523 (Docket No. PLT030US), filed May 27, 2004is difficult to implement in practice, even
though it offers considerable advantages in terms of reducing the visual effects of
known dead nozzles.
[0020] Of course, a printhead could be configured not to fire redundant color channels in
a given line-time, resulting in an average of x peak power for each nozzle row. Such
a configuration is effectively the same as that described in Table 1. While this configuration
would address peak power and misdirectionality issues, it would not address the problem
of known dead nozzles, since only one of each redundant color channel would be able
to be fired in a given line-time, thereby losing one of the major advantages of redundancy.
[0021] It would be desirable to provide a method of printing whereby fluctuations in a peak
power requirement are minimized. It would be further desirable to provide a method
of printing whereby the average power requirement of the printhead is substantially
equal to the peak power requirement at any given time during printing. It would be
further desirable to provide a method of printing, whereby, in addition minimizing
fluctuating peak power requirements, the visual effects of dead or malfunctioning
nozzles are reduced. It would be further desirable to provide a method of printing,
whereby, in addition to minimizing fluctuating peak power requirements, the visual
effects of misdirected ink droplets is reduced.
[0022] US 2005/078133 describes a redundancy scheme for a printer comprising a plurality of separate printheads
which print simultaneously.
Summary of the Invention
[0023] A first embodiment of the invention provides a method as detailed in claim 1.
[0024] In a first aspect, there is provided a method of modulating a peak power requirement
of an inkjet printhead, said printhead comprising a plurality of first nozzles and
a plurality of second nozzles supplied with a same colored ink, said first nozzles
and second nozzles being configured in a plurality of sets, wherein each set of nozzles
comprises one first nozzle and one corresponding second nozzle, each nozzle in a set
being configurable to print a dot of said ink onto a substantially same position on
a print medium, said method comprising:
- (a) selecting a firing nozzle from at least one set of nozzles, said selection being
on the basis of modulating said peak power requirement; and
- (b) printing dots onto said print medium using said firing nozzle.
[0025] In a second aspect, there is provided a method of printing a line of dots from an
inkjet printhead, said printhead comprising a plurality of first nozzles and a plurality
of second nozzles supplied with a same colored ink, said first nozzles and second
nozzles being configured in a plurality of sets, wherein each set of nozzles comprises
one first nozzle and one corresponding second nozzle, each nozzle in a set being configurable
to print a dot of said ink onto a substantially same position on a print medium,
said method comprising printing a line of dots across said print medium such that
said first nozzles and said second nozzles each contribute dots to said line.
[0026] In a third aspect, there is provided a method of modulating a peak power requirement
of an inkjet printhead, said printhead comprising a plurality of transversely aligned
color channels, each color channel comprising at least one nozzle row extending longitudinally
along said printhead, each nozzle in a color channel ejecting the same colored ink,
wherein said printhead is comprised of a plurality of printhead modules, each printhead
module comprising a respective segment of each nozzle row,
said method comprising each of said printhead modules firing a respective segment
within a predetermined segment-time, wherein at least one of said fired segments is
contained in a different color channel from at least one other of said fired segments.
[0027] In a fourth aspect, there is provided an inkjet printhead comprising a plurality
of transversely aligned color channels, each color channel comprising at least one
nozzle row extending longitudinally along said printhead, each nozzle in a row ejecting
the same colored ink, wherein said printhead is comprised of a plurality of printhead
modules, and the number of color channels is equal to the number of printhead modules.
[0028] In a fifth aspect, there is provided a printer controller for supplying dot data
to an inkjet printhead, said printhead comprising a plurality of first nozzles and
a plurality of second nozzles supplied with a same colored ink, said first nozzles
and second nozzles being configured in a plurality of sets, wherein each set of nozzles
comprises one first nozzle and one corresponding second nozzle, each nozzle in a set
being configurable by said printer controller to print a dot of said ink onto a substantially
same position on a print medium, said printer controller being programmed to supply
dot data such that said first nozzles and said second nozzles each contribute dots
to a line of printing.
[0029] In a sixth aspect, there is provided a printer controller for supplying dot data
to a printhead, said printhead comprising a plurality of transversely aligned color
channels, each color channel comprising at least one nozzle row extending longitudinally
along said printhead, each nozzle in a color channel ejecting the same colored ink,
wherein said printhead is comprised of a plurality of printhead modules, each printhead
module comprising a respective segment of each nozzle row, said printer controller
being programmed to supply dot data such that each of said printhead modules fires
a respective segment within a predetermined segment-time, wherein at least one of
said fired segments is contained in a different color channel from at least one other
of said fired segments.
[0030] In a seventh aspect of the invention, there is provided a printhead system comprising
an inkjet printhead and a printer controller for supplying dot data to said printhead,
said printhead comprising a plurality of first nozzles and a plurality of second nozzles
supplied with a same colored ink, said first nozzles and second nozzles being configured
in a plurality of sets, wherein each set of nozzles comprises one first nozzle and
one corresponding second nozzle, each nozzle in a set being configurable by said printer
controller to print a dot of said ink onto a substantially same position on a print
medium,
said printer controller being programmed to supply dot data such that said first nozzles
and said second nozzles each contribute dots to a line of printing.
[0031] In an eighth aspect of the invention, there is provided a printhead system comprising
an inkjet printhead and a printer controller for supplying dot data to said printhead,
said printhead comprising a plurality of transversely aligned color channels, each
color channel comprising at least one nozzle row extending longitudinally along said
printhead, each nozzle in a color channel ejecting the same colored ink, wherein said
printhead is comprised of a plurality of printhead modules, each printhead module
comprising a respective segment of each nozzle row,
said printer controller being programmed to supply dot data such that each of said
printhead modules fires a respective segment within a predetermined segment-time,
wherein at least one of said fired segments is contained in a different color channel
from at least one other of said fired segments.
[0032] All aspects of the invention provide the advantage of modulating a peak power requirement
of the inkjet printhead. The corollary is that a power supply, which supplies power
to the printhead, need not be specially adapted to supply severely fluctuating amounts
of power throughout each print cycle. In the present invention, the degree of peak
power fluctuations within each line-time are substantially reduced. Hence, the design
and manufacture of the printhead power supply may be simplified and the power supply
is made more robust by virtue of not having to deliver severely fluctuating amounts
of power to the printhead.
[0033] In addition to modulating the peak power requirement of the printhead, the present
invention allows print quality to be improved by using redundant nozzle rows, and
without compromising the above-mentioned improvements in peak power requirement. Print
quality may be improved by, for example, reducing the visual effects of unknown dead
nozzles in the printhead, and reducing the visual effects of misdirected ink droplets.
[0034] As used herein, the terms "row", "rows of nozzles", "nozzle row"
etc. may include nozzle rows comprising one or more displaced row portions.
[0035] As used herein, the term "ink" includes any type of ejectable fluid, including, for
example, IR inks and fixatives, as well
as standard CMYK inks. Likewise, references to "same colored ink" include inks of a
same color or type
e.g. same cyan ink, same IR ink or same fixative.
[0036] As used herein, the term "substantially the same position on a print medium" is used
to mean that a droplet of ink has an intended trajectory to print at a same position
on the print medium (as another droplet of ink). However, due to inherent error margins
in firing droplets of ink, random misdirects or persistent misdirects, a droplet of
ink may not be printed exactly on its intended position on the print medium. Hence,
the term "substantially the same position on a print medium" includes misplaced droplets,
which are intended to print at the same position, but may not necessarily print at
that position.
[0037] In accordance with some forms of the invention, the first nozzles and second nozzles
are configured in a plurality of sets, wherein each set of nozzles comprises one first
nozzle and one corresponding second nozzle. Further, each nozzle in a set is configurable
to print a dot of ink onto a substantially same position on a print medium, so that
the nozzles can be used interchangeably.
[0038] Optionally, a set is a pair of nozzles consisting of one first nozzle and one second
nozzle. However, a set may alternatively comprise further (e.g. third and fourth)
nozzles, with each nozzle in the set being configurable to print a dot of ink onto
a substantially same position on a print medium. In other words, the present invention
is not limited to two rows of redundant nozzles and may include, for example, three
or more rows of redundant nozzles.
[0039] Preferably, the printhead is a stationary pagewidth printhead and the print medium
is fed transversely past the printhead. The present invention has been developed primarily
for use with such pagewidth printheads.
[0040] Optionally, the printhead comprises a plurality of transversely aligned color channels,
each color channel comprising at least one nozzle row extending longitudinally along
the printhead, each nozzle in a color channel ejecting the same colored ink. As described
in more detail below, each transversely aligned color channel is allotted a portion
of a line-time for firing. In this way, dot-on-dot printing can be achieved, which
is optimal for dithering.
[0041] Color channels in the printhead may eject the same or different colored inks. However,
all nozzles in the same color channel are typically supplied with and eject the same
colored ink. Color channels ejecting the same colored ink are sometimes termed 'redundant'
color channels. Typically, the printhead comprises at least one redundant color channel
so that at least one color channel ejects the same colored ink as at least one other
color channel.
[0042] Each color channel may comprise a plurality of nozzle rows. Optionally, each color
channel comprises a pair of nozzle rows. Typically, nozzle rows in the same color
channel are transversely offset from each other. For example, one nozzle row in a
pair may be configured to print even dots on a line, while the other nozzle row in
the pair may be configured to print odd dots on the same line. The nozzle rows in
a pair are usually spaced apart in a transverse direction to allow convenient timing
of nozzle firings. For example, the even and odd nozzle rows in one color channel
may be spaced apart by two lines of printing.
[0043] Optionally, each set of nozzles comprises one first nozzle from a first color channel
and one second nozzle from a second color channel. The first and second nozzles in
the set are aligned transversely so that each can print onto the substantially same
position on a print medium.
[0044] Optionally, one set of nozzles prints a column of same-colored dots down a print
medium, with each nozzle in the set contributing dots to the column. As used herein,
a "column" refers to a line of dots printed substantially perpendicular to the printhead
and substantially parallel with a feed direction of the print medium. Optionally,
one first nozzle in the set prints about half of the column and one second nozzle
in the set prints about half of the column, so that the first and second nozzles in
the set share printing of the column equally between them.
[0045] Optionally, a visual effect of misdirected ink droplets is reduced. An advantage
of using a plurality (e.g. two) nozzles for printing the same column is that misdirected
ink droplets may be averaged out between those nozzles.
[0046] Optionally, when printing a line of same-colored dots across the print medium, the
first nozzles and second nozzles contribute dots to the line. As used herein, a "line"
refers to a line of dots printed substantially parallel with the printhead and substantially
perpendicular to a feed direction of the print medium. Optionally, the first nozzles
print about half of the line and the second nozzles print about half of the line,
so that the first and second nozzles share printing of the line equally between them.
Accordingly, the peak power requirement for printing the line is reduced by about
50%, as compared to printing the line using only first nozzles or only second nozzles.
Optionally, alternate first nozzles in a first nozzle row are used to print about
half of the line and alternate second nozzles in a second nozzle row are used to print
about half of the line. However, other patterns for sharing printing between the first
and second nozzles may also be used.
[0047] Optionally, a visual effect of malfunctioning or dead nozzles is reduced. The nozzles
may be known dead nozzles or unknown dead nozzles. The visual effect of an unknown
dead nozzle is reduced by virtue of the fact that the nozzle is only required to print
about half of the time. For example, with an unknown dead magenta nozzle, a column
of magenta dots would be missing completely with no redundancy, whereas half of the
column is still printed using redundancy. The latter is, of course, far more visually
acceptable than the former.
[0048] Optionally, the color (which is the same color printed by the first and second nozzles)
is magenta, cyan or black. The human eye is most sensitive to magenta, cyan and black,
and these colors are consequently the preferred candidates for redundancy. A printhead
may contain more than one redundant color channels. For example, the printhead may
comprise first and second magenta nozzles, and first and second cyan nozzles.
[0049] In accordance with some forms of the invention, there is provided a method of out-of
phase printing so as to modulate a peak power requirement of the printhead. Typically,
the printhead comprises a plurality of transversely aligned color channels with each
color channel comprising at least one nozzle row extending longitiudinally along the
printhead. Each nozzle in a color channel is supplied with and ejects the same colored
ink. Typically, the printhead is comprised of a plurality of printhead modules, with
each module comprising a respect segment of each nozzle row. Out-of-phase printing
is provided by a method in which each of the printhead modules fires a respective
segment within a predetermined segment-time, wherein at least one of the fired segments
is contained in a different color channel from at least one other of the fired segments.
[0050] A segment-time may be defined as a predetermined fraction of one line-time. A line-time
is defined as the time taken for the print medium to advance past the printhead by
one line. Typically, all segments in a nozzle row are fired within one line-time.
Optionally, a segment-time is equal to one line-time divided by the number of nozzle
rows. However, a period of each line-time may be dedicated to a line-based overhead,
in which case the segment-time will be less than one line-time divided by the number
of nozzle rows. Generally, all segment-times are equal.
[0051] Optionally, at least one nozzle row has a different peak power requirement from other
nozzle rows. For example, a redundant nozzle row would normally have half the peak
power requirement of a non-redundant nozzle row. Optionally, a predetermined firing
sequence modulates the peak power requirement during each segment-time so that the
peak power requirement is within about 10%, optionally within 5%, of the average power
requirement of the printhead. In some embodiments of the invention, the peak power
requirement of the printhead is equal to the average power requirement of the printhead.
[0052] Typically, all segments on the printhead are fired within one-line time.
[0053] In some forms of the invention, the number of color channels is equal to the number
of printhead modules. This is the optimum number of color channels and modules to
achieve perfect out-of-phase firing. However, as will be explained in more detail
below, the advantages of out-of-phase firing may still be achieved using any number
of printhead modules and color channels.
[0054] Optionally, with equal numbers of modules and color channels, each of the printhead
modules fires a segment from a different color channel within the predetermined segment-time.
Further, each segment in a nozzle row may be fired sequentially. However, as will
be explained in more detail below, each segment in a nozzle row need not be fired
sequentially, whilst still enjoying the advantages of out-of-phase firing.
Brief Description of the Drawings
[0055] Specific forms of the present invention will be now be described in detail, with
reference to the following drawings, in which:-
Figure 1 is a plan view of a pagewidth printhead according to the invention;
Figure 2 is a plan view of a printhead module, which is a part of the printhead shown
in Figure 1;
Figure 3 is a schematic representation of a portion of each color channel of the printhead
shown in Figure 1;
Figure 4A shows which even nozzles fire in one line-time using dot-at-a-time redundancy
according to the invention;
Figure 4B shows which odd nozzles fire in the next line-time from Figure 4A; and
Figure 5 shows a printhead system according to the invention.
Detailed Description of the Invention
[0056] The invention will be described with reference to a CMY pagewidth inkjet printhead
1, as shown in Figure 1. The printhead 1 has five color channels 2, 3, 4, 5 and 6,
which are C1, C2, M1, M2 and Y respectively. In other words cyan and magenta have
'redundant' color channels. The reason for making C and M redundant is that Y only
contributes 11 % of luminance, while C contributes 30% and M contributes 59%. Since
the human eye is least sensitive to yellow, it is more visually acceptable to have
missing yellow dots than missing cyan or magenta dots. In this printhead, black (K)
printing is achieved via process-black (CMY).
[0057] The printhead 1 is comprised of five abutting printhead modules 7, which are referred
to from left to right as A, B, C, D and E. The five modules 7 cooperate to form the
printhead 1, which extends across the width of a page (not shown) to be printed. In
this example, each module 7 has a length of about 20 mm so that the five abutting
modules form a 4" printhead, suitable for pagewidth 4" x 6" color photo printing.
During printing, paper is fed transversely past the printhead 1 and Figure 1 shows
this paper direction.
[0058] Each of the five color channels on the printhead 1 comprises a pair of nozzle rows.
For example, the C1 color channel 2 comprises nozzle rows 2a and 2b. These nozzle
rows 2a.and 2b extend longitudinally along the whole length of the printhead 1. Where
abutting printhead modules 7 are joined, there is a displaced (or dropped) triangle
8 of nozzle rows. These dropped triangles 8 allow printhead modules 7 to be joined,
whilst effectively maintaining a constant nozzle pitch along each row. A timing device
(not shown) is used to delay firing nozzles in the dropped triangles 8, as appropriate.
A more detailed explanation of the operation of the dropped triangle 8 is provided
in the Applicant's patent applications
USSN 10/854512 (Docket No. PLT014US), filed May 27, 2004 and
USSN 10/854491 (Docket No. PLT028US), filed May 27, 2004.
[0059] Each of the printhead modules 7 contains a segment from each of the nozzle rows.
For example, printhead module A contains segments 2a
A, 2b
A, 3a
A, 3b
A, 4a
A etc. Segments from the same nozzle row cooperate to form a complete nozzle row. For example,
segments 2a
A, 2a
B, 2a
C, 2a
D and 2a
E cooperate to form nozzle row 2a. Figure 2 shows the printhead module A with its respect
segments from each nozzle row.
[0060] Referring to Figure 3, there is shown a detailed schematic view of a portion of the
five color channels 2, 3, 4, 5 and 6. From Figure 3, it can be seen that the pair
of nozzle rows (e.g. 2a and 2b) in each color channel (e.g. 2) are transversely offset
from each other. In color channel 2, for example, nozzle row 2a prints even dots in
a line, while nozzle row 2b prints interstitial odd dots in a line.
[0061] Furthermore, the even rows of nozzles 2a, 3a, 4a, 5a and 6a are transversely aligned,
as are the odd rows of nozzles 2b, 3b, 4b, 5b and 6b. This transverse alignment of
the five color channels allows dot-on-dot printing, which is optimal in terms of dithering.
Within a period of one line-time, all even nozzles and all odd nozzles must be fired
so that dot-on-dot printing is achieved. The even and odd nozzles (e.g. 2a and 2b)
in the same color channel
(e.g. 2) may be separated by, for example, two lines. Adjacent color channels (e.g. 2 and
3) may be separated by, for example, ten lines. However, it will be appreciated that
the exact spacing between even/odd nozzle rows and adjacent color channels may be
varied, whilst still achieving dot-on-dot printing.
Dot At A-Time Redundancy
[0062] In the printhead 1 described above, there are two cyan (C1, C2) and two magenta (M1,
M2) color channels. In the Applicant's terminology, the C1/C2 and M1/M2 color channels
are described as 'redundant' color channels.
[0063] As explained above, with five color channels and a pair of nozzle rows in each color
channel, each nozzle row must print in one-tenth of the line-time in order to achieve
all the advantages of redundancy and compensate for any known dead nozzles using a
redundant color channel. The inherent power supply problems in relation to the redundancy
scheme described in
USSN 10/854507 (Docket No. PLT019US), filed May 27, 2004 and
USSN 10/854523 (Docket No. PLT030US), filed May 27, 2004have also been described above.
[0064] Dot-at-a-time redundancy is where redundant rows of nozzles are used such that there
is never more than one out of every two adjacent nozzles firing within a single nozzle
row. In other words, the even dots for a color are produced by two nozzle rows (each
printing half of the even dots), and the odd dots for a color are produced by two
nozzle rows (each printing half of the dots). For example, nozzle rows 2a and 3a may
both contribute even dots to a line of printing, and nozzle rows 2b and 3b may both
contribute odd dots to a line of printing.
[0065] Figures 4A and 4B show a firing sequence for two lines of printing using dot-at-a-time
redundancy. The nozzles indicated in Figures 4A and 4B are not fired simultaneously;
each nozzle row is allotted one-tenth of the line-time in which to fire its nozzles,
with even nozzles rows firing sequentially followed by odd nozzle rows firing sequentially.
[0066] Referring to Figure 4A, in the first line-time alternate nozzles are fired in each
nozzle row from the C1, C2, M1 and M2 color channels. Nozzles fired from C2 and M2
complement those fired from C1 and M1. For example, alternate even nozzles are fired
from nozzle row 2a and complementary alternate even nozzles are fired from nozzle
row 3a. Nozzle rows 6a and 6b in the Y channel have no redundancy and each of these
nozzle rows must therefore fire all its nozzles in one-tenth of the line-time.
[0067] Referring to Figure 4B, in the second line-time the alternate nozzles fired in the
first line-time are inversed.
[0068] By using this dot-at-a-time redundancy scheme, print quality is improved by reducing
misdirection artifacts (thereby maximizing dot-on-dot placement) and reducing the
visual effect of unknown dead nozzles. For example, if half of the dots in a column
are from an operational nozzle and half are from a dead nozzle, the visual effect
of the dead nozzle will be reduced and the effective print quality is greater than
if the entire column came from the dead nozzle. In other words, the present invention
achieves at least as good print quality as the line-at-a-time redundancy described
in
USSN 10/854507 (Docket No. PLT019US), filed May 27, 2004 and
USSN 10/854523 (Docket No. PLT030US), filed May 27, 2004.
[0069] Moreover, the peak power requirements of the printhead are modulated during printing
of each line, so that the peak power requirements do not fluctuate as severely as
in Table 2. Table 3 shows how the peak power requirement of the printhead (having
an average power requirement of x) varies over two lines of printing using dot-at-a-time
redundancy according to the present invention:
Table 3
Line-time |
Color Channel |
Nozzle Row |
Peak Power Requirement |
0 |
2 (C1) |
2a (even) |
0.83x |
0.1 |
3 (C2) |
3a (even) |
0.83x |
0.2 |
4 (M1) |
4a (even) |
0.83x |
0.3 |
5 (M2) |
5a (even) |
0.83x |
0.4 |
6(Y) |
6a (even) |
1.67x |
0.5 |
2 (C1) |
2b (odd) |
0.83x |
0.6 |
3 (C2) |
3b (odd) |
0.83x |
0.7 |
4 (M1) |
4b (odd) |
0.83x |
0.8 |
5 (M2) |
5b (odd) |
0.83x |
0.9 |
6 (Y) |
6b (odd) |
1.67x |
0 (new line) |
2 (C1) |
2a (even) |
0.83x |
0.1 |
3 (C2) |
3a (even) |
0.83x |
0.2 |
4 (M1) |
4a (even) |
0.83x |
0.3 |
5 (M2) |
5a (even) |
0.83x |
0.4 |
6 (Y) |
6a (even) |
1.67x |
0.5 |
2 (C1) |
2b (odd) |
0.83x |
0.6 |
3 (C2) |
3b (odd) |
0.83x |
0.7 |
4 (M1) |
4b (odd) |
0.83x |
0.8 |
5 (M2) |
5b (odd) |
0.83x |
0.9 |
6 (Y) |
6b (odd) |
1.67x |
0 (new line) |
2 (C1) |
2a (even) |
0.83x ... etc |
[0070] It is evident from Table 3 that the fluctuations in peak power requirement are fewer
and less severe compared to line-at-a-time redundancy, described in Table 2. In terms
of the design of the printhead power supply, dot-at-a-time redundancy according to
the present invention offers significant advantages over line-at-a-time redundancy,
whilst maintaining the same improvements in print quality.
Out-or-Phase Firing
[0071] In all the firing sequences described so far, each color channel is fired in-phase
- that is, a whole row of, say, even nozzles from one color channel is fired within
its allotted portion of the line-time. In-phase firing provides simpler programming
of the printer controller, which controls the firing sequence via dot data sent to
the printhead 1.
[0072] However, according to another form of the present invention, the firing may be out-of
phase - that is, within the same allotted portion of the line-time (termed the 'segment-time'),
at least one segment of nozzles is fired from a color channel that is different from
at least one other segment of nozzles. With appropriate sequencing of segment firings,
a whole nozzle row can be fired within one line-time, such that the net result is
effectively the same as in-phase firing.
[0073] In the case of the printhead 1, having five color channels and five segments in each
nozzle row, it possible to fire segments from all different color channels within
one segment time (i.e. one-tenth of a line-time). Segments contained in the same nozzle
row are, therefore, fired sequentially during one line-time.
[0074] A major advantage of out-of-phase firing is that if one or more color channels (e.g.
Y) has a different peak power requirement to the other color channels, this difference
is averaged into the power requirements of the other color channels within each segment-time.
Hence, the spike in power (corresponding to the Y channel) in Table 3 is effectively
merged into rest of the line-time. The result is that the peak power requirement during
each segment-time is always equal to the average power requirement for the printhead.
This situation is optimal for supplying power to the printhead.
[0075] Table 4 illustrates a sequence of out-of-phase firing for one line of printing from
the printhead 1, using dot-at-a-time redundancy.
Table 4
Line-time |
Module A (CC, S, P) |
Module B (CC,S, P) |
Module C (CC, S, P) |
Module D (CC, S, P) |
Module E (CC, S, P) |
Peak Power Requirement |
0 |
C1, 2aA, 0.83x |
C2, 3aB, 0.83x |
M1,4aC, 0.83x |
M2,5aD, 0.83x |
Y, 6aE, 1.67x |
x |
0.1 |
C2, 3aA, 0.83x |
M1,4aB, 0.83x |
M2, 5aC, 0.83x |
Y, 6aD, 1.67x |
C1, 2aE, 0.83x |
x |
0.2 |
M1, 4aA, 0.83x |
M2, 5aB, 0.83x |
Y, 6aC, 1.67x |
C1, 2aD, 0.83x |
C2, 3aE, 0.83x |
x |
0.3 |
M2, 5aA, 0.83x |
Y, 6aB, 1.67x |
C1, 2aC, 0.83x |
C2, 3aD, 0.83x |
M1,4aE, 0.83x |
x |
0.4 |
Y, 6aA, 1.67x |
C1, 2aB, 0.83x |
C2, 3aC, 0.83x |
M1, 4aD, 0.83x |
M2,5aE 0.83x |
x |
0.5 |
C1,2bA, 0.83x |
C2, 3bB, 0.83x |
3M1, 4bC, 0.83x |
M2, 5bD, 0.83x |
Y, 6bE, 1.67x |
x |
0.6 |
C2, 3bA, 0.83x |
M1, 4bB, 0.83x |
M2, 5bC, 0.83x |
Y, 6bD, 1.67x |
C1, 2bE, 0.83x |
x |
0.7 |
M1, 4bA, 0.83x |
M2, 5bB, 0.83x |
Y, 6bC, 1.67x |
C1,2bD, 0.83x |
C2, 3bE, 0.83x |
x |
0.8 |
M2, 5bA, 0.83x |
Y, 6bB, 1.67x |
C1, 2bC, 0.83x |
C2, 3bD, 0.83x |
M1, 4bE, 0.83x |
x |
0.9 |
Y, 6bA, 1.67x |
C1, 2bB, 0.83x |
C2, 3bC, 0.83x |
M1, 4bD, 0.83x |
M2, 5bE, 0.83x |
x |
0 (new line) |
C1, 2aA, 0.83x |
C2, 3aB, 0.83x |
M1,4aC, 0.83x |
M2, 5aD, 0.83x |
Y, 6aE, 1.67x |
x ... etc |
CC = Color Channel; S = Segment; P = Peak Power Requirement |
[0076] It should be remembered that, even within one segment, not all nozzles fire simultaneously.
The nozzles in one segment are arranged in firing groups, which fire sequentially
over the course of their allotted segment-time. However, the important point is that
at any given instant, some C1, C2, M1, M2 and Y nozzles will fire simultaneously,
thereby averaging out the higher peak power requirement of the yellow nozzle row.
[0077] In the case of five printhead modules and five color channels, it can be seen that
out-of-phase firing works out well. Segments from each color channel can be rotated
so that all different segments are fired in one segment-time.
[0078] However, it will be appreciated that out-of-phase firing also works well with any
number of printhead modules or color channels. For example, using 20 mm printhead
modules 7, an A4 pagewidth printhead is comprised of eleven abutting modules [(i)
to (xi)]. With five color channels and eleven printhead modules, it is impossible
to ensure that each printhead module fires a different color channel within a segment-time
(
i.e. one-tenth of a line-time). Regardless, out-of-phase firing can still be used to optimize
the peak power requirement of the printhead.
[0079] For example, the A4 pagewidth printhead may have C, M, Y, K1 and K2 color channels.
Since there are redundant K channels, these nozzle rows will have a lower peak power
requirement than the C, M and Y channels using dot-at-a-time redundancy. Using in-phase
firing, there would be appreciable peak power fluctuations during each line-time (C
= 1.25
x, M = 1.25
x, Y = 1.25
x, K1 = 0.625
x, K2 = 0.625
x).
[0080] However, it can be seen from Table 5 that out-of-phase firing accommodates the eleven
printhead modules and provides a peak power requirement that is always within 10%
of the average power requirement x of the printhead. Indeed, the peak power requirement
is always within 5% of the average power requirement x in this example. For the purposes
of providing a power supply for the printhead, such small variations in peak power
requirement during each line-time are not significant and would not affect the design
of the power supply.
Table 5
t |
(i) |
(ii) |
(iii) |
(iv) |
(v) |
(vi) |
(vii) |
(viii) |
(ix) |
(x) |
(xi) |
P |
0 |
C(e) |
M(e) |
Y(e) |
K1(e) |
K2(e) |
C(e) |
M(e) |
Y(e) |
K1(e) |
K2(e) |
C(e) |
1.023x |
0.1 |
M(e) |
Y(e) |
K1(e) |
K2(e) |
C(e) |
M(e) |
Y(e) |
K1(e) |
K2(e) |
C(e) |
M(e) |
1.023x |
0.2 |
Y(e) |
K1(e) |
K2(e) |
C(e) |
M(e) |
Y(e) |
K1(e) |
K2(e) |
C(e) |
M(e) |
Y(e) |
1.023x |
0.3 |
K1(e) |
K2(e) |
C(e) |
M(e) |
Y(e) |
K1(e) |
K2(e) |
C(e) |
M(e) |
Y(e) |
K1(e) |
0.966x |
0.4 |
K2(e) |
C(e) |
M(e) |
Y(e) |
K1 (e) |
K2(e) |
C(e) |
M(e) |
Y(e) |
K1(e) |
K2(e) |
0.966x |
0.5 |
C(o) |
M(o) |
Y(o) |
K1(o) |
K2(o) |
C(o) |
M(o) |
Y(o) |
K1(o) |
K2(o) |
C(o) |
1.023x |
0.6 |
M(o) |
Y(o) |
K1(o) |
K2(o) |
C(o) |
M(o) |
Y(o) |
K1(o) |
K2(o) |
C(o) |
M(o) |
1.023x |
0.7 |
Y(o) |
K1(o) |
K2(o) |
C(o) |
M(o) |
Y(o) |
K1(o) |
K2(o) |
C(o) |
M(o) |
Y(o) |
1.023x |
0.8 |
K1(o) |
K2(o) |
C(o) |
M(o) |
Y(o) |
K1(o) |
K2(o) |
C(o) |
M(o) |
Y(o) |
K1(o) |
0.966x |
0.9 |
K2(o) |
C(o) |
M(o) |
Y(o) |
K1(o) |
K2(o) |
C(o) |
M(o) |
Y(o) |
K1(o) |
K2(o) |
0.966x |
0 |
C(o) |
M(o) |
Y(o) |
K1(o) |
K2(o) |
C(o) |
M(o) |
Y(o) |
K1(o) |
K2(o) |
C(o) |
1.023x |
t = line-time; P = Peak Power Requirement
(e) = even rows of nozzles; (o) = odd rows of nozzles |
[0081] From the foregoing it will be appreciated that the combination of out-of-phase firing
together with dot-at-a-time redundancy is optimal for achieving excellent print quality
and an acceptable power requirement for the printhead during printing.
[0082] However, these methods of printing may equally be used individually, providing their
inherent advantages, or in combination with other methods of printing. For example,
out-of-phase firing or dot-at-a-time redundancy may be used in combination with printhead
module misplacement correction and/or dead nozzle compensation, as described in our
earlier patent applications
USSN 10/854521 (Docket No. PLT001US) filed May 27, 2004 and
USSN 10/854515 (Docket No. PLT020US), filed May 27,2004..
Printer Controller
[0083] It will also be appreciated by the skilled person that a printer controller 10, shown
schematically in Figure 5, may be suitably programmed to provide dot data to the printhead
1, so as to print in accordance with the methods described above. A printhead system
20 comprises the printer controller 10 and the printhead 1, which is controlled by
the controller. The printer controller 10 communicates dot data to the printhead 1
for printing.
[0084] A suitable type of printer controller, which may be programmed accordingly, was described
in our earlier patent application
USSN 10/854521(Docket No. PLT001US) filed May 27, 2004.
[0085] It will, of course, be appreciated that the present invention has been described
purely by way of example and that modifications of detail may be made within the scope
of the invention, which is defined by the accompanying claims.