Color architecture for an ink jet printer with overlapping arrays of ejectors

A thermal ink-jet printer in which two parallel linear arrays of ejectors are disposed on a reciprocating carriage. The linear arrays are subdivided into sections, the ejectors in each section being adapted to emit ink of a preselected primary color. The linear arrays overlap to optimize a trade-off between speeds of monochrome and full-color operation.

BACKGROUND OF THE INVENTION 
The present invention relates to ink-jet printing, and is more particularly 
concerned with color printing using a single printhead with overlapping 
linear arrays of ejectors to emit a plurality of different types of ink 
from various ejectors therein. 
In existing thermal ink jet printing, the printhead typically comprises one 
or more ink ejectors, such as disclosed in U.S. Pat. No. 4,463,359, each 
ejector including a channel communicating with an ink supply chamber, or 
manifold, at one end and having an opening at the opposite end, referred 
to as a nozzle. A thermal energy generator, usually a resistor, is located 
in each of the channels, a predetermined distance from the nozzles. The 
resistors are individually addressed with a current pulse to momentarily 
vaporize the ink and form a bubble which expels an ink droplet. As the 
bubble grows, the ink rapidly bulges from the nozzle and is momentarily 
contained by the surface tension of the ink as a meniscus. As the bubble 
begins to collapse, the ink still in the channel between the nozzle and 
bubble starts to move towards the collapsing bubble, causing a volumetric 
contraction of the ink at the nozzle and resulting in the separation of 
the bulging ink as a droplet. The acceleration of the ink out of the 
nozzle while the bubble is growing provides the momentum and velocity of 
the droplet in a substantially straight line direction towards a print 
sheet, such as a piece of paper. Because the droplet of ink is emitted 
only when the resistor is actuated, this type of thermal ink-jet printing 
is known as "drop-on-demand" printing. Other types of ink-jet printing, 
such as continuous-stream or acoustic, are also known. 
In a single-color ink jet printing apparatus, the printhead typically 
comprises a linear array of ejectors, and the printhead is moved relative 
to the surface of the print sheet, either by moving the print sheet 
relative to a stationary printhead, or vice-versa, or both. In some types 
of apparatus, a relatively small printhead reciprocates across a print 
sheet numerous times in swaths, much like a typewriter; alternatively, a 
printhead which extends the full width of the print sheet may be passed 
once down the print sheet to give full-page images, in what is known as a 
"full-width array" (FWA) printer. When the printhead and the print sheet 
are moved relative to each other, imagewise digital data is used to 
selectively activate the thermal energy generators in the printhead over 
time so that the desired image will be created on the print sheet. 
As ink-jet products enter the market, they must respond to consumer demands 
for color printing, particularly when documents are prepared on personal 
computers. A common and expectable desired output for a color ink-jet 
printer would be a document such as a newsletter in which mainly black 
text will accompany a full-color image, such as a graph, which occupies 
only a portion of a sheet. There will thus be documents in which 
black-only (monochrome) and full-color modes may be in demand in the same 
job, and even on a single sheet. To optimize output speed of a color 
ink-jet printer, it may be desirable to provide a printer which can 
operate in two modes automatically as needed, a black-only mode and a 
full-color mode. It is to be presumed that the monochrome mode can print 
out faster than a full-color mode, because the monochrome mode will 
require only one "pass" of a printhead over a portion of a sheet, while 
the full-color mode requires a number of printheads, each printing one 
primary color, to pass over the same location of the sheet in the course 
of a job. However, if the printer is operable in two modes as required by 
the job, it makes sense that the monochrome mode not be unduly slowed down 
by the architecture of the system, which also must accommodate a 
full-color mode. Ideally, both the monochrome and full-color modes should 
operate at optimum speeds respectively. 
It is therefore an object of the present invention to provide an 
architecture for a full-color thermal ink-jet printer, wherein a 
full-color mode may be optimally "traded off" with a maximum speed 
possible in a monochrome mode. Merely to place linear arrays of ejectors 
parallel to each other on a reciprocating carriage in an ink-jet printer 
has been found to be unsatisfactory from the aspect of print quality: if 
one ink is placed adjacent another ink on a sheet before the inks are 
substantially dried, a "muddy" appearance has been known to result as the 
liquid inks blend into each other on the sheet. Also, in a 
reciprocating-carriage printer, it has been shown that the hues of 
combined inks vary noticeably depending on the order in which the inks are 
placed on the sheet. Of course, in a case where four parallel printheads 
are each placed on the carriage, the order in which the inks are placed on 
the sheet will reverse depending on the direction of motion of the 
carriage; thus, such color printers having this feature are practically 
limited to printing in one direction only, which causes a serious 
limitation to be placed on the printer speed. 
U.S. Pat. No. 4,812,859 discloses an ink-jet recording head wherein a 
plurality of nozzle groups are in communication with individual chambers, 
each chamber adapted to convey ink of one color. The head is retrofittable 
in a single-color printer to provide multicolor printing capability. The 
nozzle groups each duplicate a different longitudinal segment of the 
single color nozzle column pattern. 
U.S. Pat. No. 4,855,752 discloses a method of creating an area of a 
preselected hue comprising a plurality of printed primary colors, in which 
the various flaws of primary colors are each offset by a predetermined 
amount, in order to minimize the visual "banding" effect when the 
boundaries between the swaths of different colors are coincident. 
U.S. Pat. No. 4,967,203 discloses a method of producing a color image in an 
ink-jet printer wherein successive applications of ink dots are staggered 
relative to pixel locations such that overlapping ink dots are printed on 
successive passes of a printhead. Pixels are grouped into superpixels and 
various combinations of colored ink dots are applied to each pixel within 
each superpixel in a staggered sequence. 
U.S. Pat. No. 5,030,971 discloses a "roofshooter" ink-jet printhead having 
a common heater substrate having at least two arrays of heating elements 
and a corresponding number of feed slots. Each nozzle array is isolated 
from an adjacent nozzle array and each nozzle is lined above a respective 
heating element of a corresponding heater array. With this construction, 
multi-color printheads are efficiently arranged on a single wafer. 
U.S. Pat. No. 5,057,852 discloses an apparatus and method of producing 
enhanced four-color images with an ink-jet printer. True black ink is 
aligned for printing between cyan, magenta and yellow color spots in a 
full-color image. When a black edge is desired, process black (derived 
from a combination of primary colors) and the true black ink are both used 
to produce the pixels along the edge. The patent shows a printhead having 
nozzles for colored inks positioned in line with each other in the 
direction of travel of the printhead, with the black ink nozzle being 
disposed in separate lines. 
SUMMARY OF THE INVENTION 
According to the present invention, there is provided an ink-jet printhead 
for the ejection of ink in imagewise fashion onto a substrate. The 
printhead comprises a linear array of ejectors, adapted to selectively 
emit ink of a preselected type onto the substrate, in imagewise fashion 
according to input data. Means are provided for causing motion of the 
printhead relative to the substrate along a path. The printhead includes 
first and second linear arrays of ejectors for emitting ink onto the 
substrate, the linear arrays being arranged in fixed, parallel, and at 
least partially overlapping relation to each other and extending 
transverse to the path. One linear array comprises a first section having 
ejectors adapted to emit ink of a first preselected type and a second 
section having ejectors adapted to emit ink of a second preselected type. 
In one embodiment of the invention, the two linear arrays of different 
resolutions. In another embodiment, the two linear arrays are each divided 
into two sections, and overlap by the length of one section. In yet 
another embodiment, the two linear arrays overlap by 4/5 of their lengths.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows the rudiments of a reciprocating-carriage-type thermal ink-jet 
printer for creating color or monochrome images on a sheet S. An ink 
cartridge 10, having a plurality of ink supplies therein, is preferably 
removably mounted on a carriage 12. This carriage 12 is adapted to move in 
a back-and-forth manner in direction C across sheet S, which is moving in 
process direction P. The sheet S is caused to move in direction P by means 
of a stepper motor or other indexing motor 60, which is preferably adapted 
to cause the motion of sheet S in direction P in a stepwise fashion, 
holding the sheet S in a stationary position while the cartridge 10 moves 
across the sheet in direction C, and then indexing the sheet S in 
processing direction P between swaths of printing caused by the action of 
cartridge 10 on carriage 12. 
Carriage 12 is provided with one of various possible means for moving the 
cartridge 10 back and forth across sheet S. As shown in FIG. 1, there is 
provided a rotatable lead screw 14 having threads thereon which interact 
with a structure on the carriage 12 so that, when lead screw 14 is caused 
to rotate by a motor (not shown), the interaction of the lead screw 
threads with the structure on carriage 12 will cause the carriage 12 and 
the cartridge 10 mounted thereon to move in direction C across the sheet 
S. Preferably, in most embodiments of an ink-jet printer for use with the 
present invention, the behavior of the lead screw 14 should be such as to 
allow substantially even back-and-forth motion of the cartridge 10 so that 
the printing operation can be carried out in both directions. This may be 
accomplished, for example, by operatively attaching lead screw 14 to a 
bi-directional motor, or providing oppositely-wound sets of lead screw 
threads on lead screw 14 so that, once carriage 12 is moved to one side of 
the sheet S, the structure on carriage 12 will reengage with the 
opposite-wound threads on lead screw 14 to be moved in the opposite 
direction while the lead screw 14 is rotated in the same rotational 
direction. Further mechanical stability is provided for the motion of 
carriage 12 by, for example, a stabilizing rod 16 which passes through an 
opening in the carriage 12. 
At the bottom of cartridge 10, as shown in FIG. 1, is a printhead 20, which 
is shown directed downward toward the sheet S. Printhead 20 comprises one 
or more linear arrays of thermal ink-jet ejectors, each ejector being 
operatively connected to a particular ink supply, in a manner which will 
be described in detail below, depending on the specific embodiment of the 
present invention. Generally, the linear array of ejectors in printhead 20 
extends in a direction parallel to process direction P, so that, when the 
cartridge 10 is caused to move in carriage direction C, the linear array 
will "sweep" across the sheet S for an appreciable length, thus creating a 
print swath. While the carriage is moving across the sheet S, the various 
ejectors in the linear array are operated to emit controlled quantities of 
ink of preselected colors in an imagewise fashion, thus creating the 
desired image on the sheet. Typical resolution of the ink-jet ejectors in 
printhead 20 may be from 200 spots per inch to 800 spots per inch. 
Also provided "downstream" of the printhead 20 along process direction P is 
drying means which are generally shown in FIG. 1 as a heating plate 24. 
The purpose of the drying means is to provide energy to ink which has just 
been placed on the sheet S, so that the ink will dry more quickly. 
Although a heating plate 24 is shown in FIG. 1, the drying means may 
include any number of devices for conveying heat or other energy to the 
ink placed on the sheet S. One particular drying means, for example, is a 
device for conveying microwave energy to the ink on the sheet, thereby 
dehydrating the sheet while limiting the extent of heat spread throughout 
the system, which may have an adverse effect on the operation of the 
printer as a whole. Other techniques for drying the ink in an efficient 
manner may also be contemplated such as providing a light flash, radiant 
or convective heat, or creating induction heat within a conductive member 
adjacent the sheet. 
Operatively associated with the printhead 20 is a data input device, or 
controller, which is generally shown by a schematic box 30 connected by a 
bus 32 to the printhead 20. The purpose of the controller 30 is to 
coordinate the "firing" of the various ejectors in the printhead 20 with 
the motion of cartridge 10 in carriage direction C, and with the process 
direction P of sheet S, so that a desired image in accordance with the 
digital data is rendered in ink on the sheet S. Image data in digital form 
is entered into controller 30, and controller 30 coordinates the position 
of the printhead 20 relative to a sheet S, to activate the various 
ejectors as needed, in a manner generally familiar to one skilled in the 
art of ink-jet printing. Controller 30 will also be operatively associated 
with the various motors such as 60, controlling the position of sheet S 
through process direction P, and also the motion of the carriage 12, 
through means not shown. 
FIG. 5 and 6 show portions of a linear array as used in printhead 20 in 
greater detail. FIG. 5 is a partial-sectional view showing a possible 
configuration of nozzles in one array of printhead 20. The process 
direction of the sheet relative to the printhead is given by P, and the 
direction of the carriage C is orthogonal to the page. In the embodiment 
shown, there is provided in each linear array in the printhead 20 about 
120 ejectors. These ejectors are formed from a printhead of one of any 
designs for a linear-array thermal ink-jet printhead known in the art, 
such as in, for example, U.S. Pat. Nos. 4,899,178 or 4,899,181, both 
assigned to the assignee of the present application, and adapted for use 
in a multi-color context wherein inks of different colors, from different 
manifolds within the printhead chip, are assigned to specific subsets of 
ejectors in the printhead, as will be described in detail below. In the 
embodiment shown, the preferred resolution of the ejectors is 300 ejectors 
per inch, resulting in a linear array of approximately 1 centimeter in 
length; currently coming into common use, however, are ink-jet systems 
having resolutions of 360, 400, or 600 ejectors per inch. 
FIG. 6 is a sectional elevational view of a single ejector of several in a 
linear array of ink-jet ejectors in printhead 20. (The linear array, in 
this view, extends into the page.) The printhead in general, according to 
the illustrated "side-shooter" design, comprises two key parts, a "channel 
plate" 40 and a "heater plate" 42. Preferably, each of these plates 40 and 
42 is made of a single piece of silicon for the entire printhead 20. The 
channel plate 40 and the heater plate 42 are abutted together to form the 
linear array of ejectors between them. The channel plate 40 has defined 
therein on the face thereof facing the heater plate 42, a plurality of 
channels which form the nozzles for the ejectors, one of which is shown as 
44. Adjacent each channel 44 in the channel plate 40 is a heating element 
46. Each heating element 46 is operatively connected by circuit means (not 
shown) to a controller such as 30, which provides electrical power to the 
heating element when it is desired to "fire" the particular ejector. Each 
heating element 46 includes an effective surface which becomes hot when 
electricity is applied to heating element 46, and this effective surface 
is exposed to the void formed by the adjacent channel 44. In a typical 
preferred design, the heating element 46 is itself disposed in a slight 
pit adjacent channel 44, as shown, in order to improve the general 
performance of the printhead. Each channel 44 is in communication with an 
ink supply manifold 48. Preferably, a plurality of channels 44 in a 
contiguous subset are operatively connected to one ink supply manifold 48, 
which functions as a common ink supply for all of the ejectors connected 
thereto. Both the channels 44 and the ink supply manifolds 48 are created 
as voids within a single silicon channel plate 40 by known etching 
techniques. The ink supply manifold 48 is in turn accessed to a larger 
supply of ink through a tube such as 49, or any other means which will be 
apparent to one skilled in the art. In the embodiment shown, the tube 49 
is formed as a void in a further member adjacent to the channel plate 40; 
generally speaking, however, the precision of the tube 49 into ink supply 
manifold 48 need not be as precise as the formation of the channels 44, 
and therefore tube 49 may be defined in an inexpensive material such as 
plastic. 
Briefly, a side-shooter printhead, as illustrated in FIG. 6, works as 
follows. Ink of a preselected type is introduced through tube 49 into 
manifold 48 and is then conducted into a plurality of channels such as 44. 
When in the course of printing a document, a pixel corresponding to a 
particular channel 44 is to be printed upon, a signal is sent by the 
control means to the corresponding heating element 46, and the energy of 
the signal causes heat to be generated in the channel 44. The heat causes 
the vaporization of ink in the channel 44, and liquid ink in the channel 
44 is pushed out in the form of a droplet toward the sheet. Once a 
quantity of liquid ink is ejected from the channel 44, the channel 44 is 
replenished from ink manifold 48. 
Returning to FIG. 5, it can be seen that there is provided in a unitary 
chip (i.e. not two separate chips abutted side-by-side) forming one linear 
array of ejectors having a plurality (here, two) of ink supply manifolds 
48, with the two manifolds each supplying liquid ink to one section of 
channels 44 within the linear array. Such a configuration, or a variation 
thereof, will be apparent in the various embodiments of the present 
invention described in detail below. In the ink-jet printer according to 
the present invention, there are provided two such linear arrays as shown 
in FIG. 5, each preferably but not necessarily formed from unitary silicon 
chips. 
FIGS. 2, 3, and 4, are plan views, respectively, looking "upward" from the 
surface of the sheet S, of printhead configurations according to various 
embodiments of the present invention. In each case, there is shown linear 
arrays of ejectors, various ejectors being adapted to emit ink of a 
particular preselected color, such as black (shown as k), yellow (y), 
magenta (m), or cyan (c). As can be seen in each Figure, the ejectors are 
arranged in two linear arrays, shown generally as 50 and 52 are arranged 
transverse to the carriage direction C through which the printhead 20 
moves in swaths across the sheet S in a reciprocating-printhead printer. 
It will be noted that, in comparing FIGS. 2-4 with FIG. 1, that the 
printhead 20 may move in either direction along carriage path C with 
neither linear array 50, 52 having to be "first" along the path of 
carriage motion. 
In each embodiment of the FIGS. 2-4, one or more of the linear arrays 50, 
52 is subdivided into two or more sections, in which a subset of ejectors 
within a given section is dedicated to emitting ink of one preselected 
primary color. Although the subdivided sections within each linear array 
50 or 52 are shown spaced by a gap, it may be preferred that the sections 
of ejectors emitting different color inks abut each other with no gap in 
the linear array. 
FIG. 2 shows a printhead according to one embodiment of the invention. In 
this embodiment, there are two linear arrays of equal length, which are 
disposed in fixed parallel relationship with each other and overlap for 
their entire length. As can be seen in FIG. 2, one of the linear arrays 50 
is adapted for its entire length to emit black ink. The other linear array 
52 is subdivided into three equal sections, each section dedicated to 
emitting ink of one primary color, yellow, magenta, or cyan. Because, in a 
reciprocating-printhead ink-jet printer, the printer prints in a series of 
swaths across the sheet S, the width of the swath will be the effective 
width of the linear arrays 50, 52. The wider the swaths, the fewer passes 
must be made by the cartridge 10 and carriage 12 across the sheet S in the 
course of printing out an entire sheet. Thus, with the printhead of FIG. 
2, when the printhead 20 is moved through direction C in either direction 
to print a black-only image, the entire length of the linear array 50 can 
be activated, and the swath width will be the full width of the linear 
array 50. Because the linear array 50 is relatively wide, printing a 
black-only image is relatively rapid because fewer swaths are required. 
However, if it is desired to print a full-color image using the 
primary-color inks from the sections of linear array 52, the maximum swath 
width, and therefore the maximum operating speed, of the printer is 
restricted by the width of an individual primary color section within 
linear array 52. In other words, each section of primary-color ejectors 
within linear array 52 must "cover" the entire area of a sheet S. Because 
the width of each section in linear array 52 is one-third that of the all 
black linear array 50, it follows that three times as many swaths are 
needed to cover a sheet S, and following each swath, the sheet S must be 
indexed in process direction P only the distance of the width of one 
section within linear array 52. Therefore, comparing maximum possible 
process speeds of an ink-jet printer between printing a black only image 
or portion of an image, and a full-color image or portion of an image, the 
all-black image may be printed at three times the speed of a full-color 
image, because the effective swath is three times wider. 
According to the FIG. 2 embodiment of the present invention, the 
black-printing ejectors are provided with a higher resolution (that is, 
higher number of ejectors per inch) than that of the color ejectors, for 
example, 600 spots per inch versus 300 spots per inch. In full-color 
printing, the entire length of the array 50 is used in each swath, but 
each ejector prints only every third pixel of the scan line, or, more 
generally, only one sequentially-determined subset of pixels in the scan 
line. For example, the 1st, 4th, 7th, . . . ejectors of the array would 
each print the 1st, 4th, 7th, . . . pixels of their respective scan lines. 
Likewise the 2nd, 5th, 8th, . . . ejectors would each print the 2nd, 5th, 
8th, . . . pixels and the 3rd, 6th, 9th, . . . ejectors would each print 
the 3rd, 6th, 9th, . . . pixels. (As used in the claims herein, the 
first-numbered pixel in each of these sequences shall be known as a 
"reference" pixel, and will thus determine the "phase" of which subset of 
pixels will be activated. Also, as used herein, a given ejector is 
"activated" when it is capable of printing a spot on the substrate at a 
given time; whether a spot is actually printed at a given time will, of 
course, be further dependent on the nature of the image being printed.) 
The phases of which sequentially-determined subset of ejectors is activated 
must be assigned such that when sheet S is indexed by the width of one 
section of array 52, the pixels printed on a scan line are different from 
any previously printed. The distribution of the pixels being printed by 
the first linear array should vary with the position of the array so that 
all phases are equally represented. For example a scan line might first 
have its 3rd, 6th, 9th, . . . pixels printed. After indexing, a different 
ejector will again pass over the scan line printing the 2nd, 5th, 8th, . . 
. pixels. One more index of sheet S brings the scan line under a third 
ejector which completes it by printing the 1st, 4th, 7th, . . . pixels. 
When printing a full-color image, the length of the indexing of sheet S 
after each swath is made across the sheet is limited to the width of one 
section of array 52, and therefore three times as many passes of the 
printhead 20 are needed. Because the indexing length is one-third that of 
the entire width of the black array 50, one portion of the length of array 
50 will "cover" all of the sheet three times. 
Because the linear array 50 includes ejectors of a relatively high 
resolution, the black areas such as text in the image can be printed with 
higher quality, particularly along the edges thereof. The triple-passing 
of the high-resolution array 50 enables a high-precision method of 
printing to be carried out: with each pass, a screen of every third black 
pixel is printed, and the time between successive passes gives the 
laid-down black ink some time to dry before the laying down of neighboring 
black pixels. Further, although high-resolution ejectors necessarily must 
print out at higher rate to "cover" a given length on the sheet, the 
triple-passing of the black pixels will more than alleviate the necessity 
for higher data rates to the fine-resolution ejectors: while the necessary 
rate of firing for a 600 spi ejector will be twice that of a 300 spi, the 
fact that an individual ejector in array 50 will fire only once every 
threepixels, means the actual data rate to an individual ejector will only 
be 1/3 of this necessary rate. Further, the superposition of neighboring 
pixels will lessen the concpicuousness of "printhead signatures," that is, 
artifacts on the printed document caused by failures of single ejectors 
repeating across each swath. 
FIG. 3 shows another embodiment of a printhead according to the present 
invention, in which both arrays 50, 52 are divided into two subsections. 
As can be seen in FIG. 3, the linear arrays 50, 52 are in fixed parallel 
relation to each other, but overlap only by the width of one section each, 
so that the total width of the overlapping linear arrays is 50 percent 
more than that of a single linear array. It will also be noted that the 
black section (k) of linear array 50 corresponds exactly with the magenta 
section (m) of linear array 52. In this embodiment, all of the sections of 
the arrays may be of the same resolution. 
When the printhead 20 of FIG. 3 is caused to move through carriage path C 
in either direction thereof, three swaths are laid down on the sheet S: 
from the top of the Figure, a yellow swath, a combination magenta and 
black swath, and then a cyan swath. Each swath is of a width one-half that 
of either linear array 50, 52. It will be seen that in comparing the 
printhead of FIG. 3 with the printhead of FIG. 2, the swath in the 
full-color mode may be significantly wider with the printhead of FIG. 3, 
and therefore, all other parameters being equal, the printhead of FIG. 3 
is capable of printing slightly faster in full color (50% faster, 
comparing the relative widths of the color sections) than the printhead of 
FIG. 2. However, the trade-off comes if it is desired to print a 
black-only image: as can be seen, the black section of array 50 in FIG. 3 
is precisely one-half that of the black section in array 50 in FIG. 2, and 
therefore twice as many swaths will be needed to cover a sheet with the 
printhead of FIG. 3 in a black-only image. However, if it is known that 
the user of the printer is likely to print many documents having a mixture 
of black-only sections and full-color sections along the process direction 
P, there may be an optimum trade-off in lessening the black-only speed 
relative to the full-color speed. 
FIG. 4 shows a printhead 20 according to another embodiment of the present 
invention. In this embodiment, the linear arrays 50, 52 are disposed in 
fixed parallel relation to each other, but overlap by 4/5 of the lengths 
thereof. As can be seen in FIG. 4, the 4/5 of linear array 50 which 
overlaps linear array 52 is dedicated entirely to the emission of black 
ink. At the same time, the ejectors in linear array 52 are subdivided so 
that, from the top of the Figure, 2/5 emits yellow ink, the next 2/5 emits 
magenta ink, and the final 1/5 emits cyan ink. However, the cyan 1/5 of 
linear array 52 is in effect "continued" by the bottom 1/5 of linear array 
50, so that the cyan swath formed when printhead 20 is moved through path 
C is half created by ejectors in linear array 52 and half created by 
ejectors in linear array 50. When the printhead is printing a full-color 
image, three adjacent swaths will be placed on sheet S: a yellow swath, a 
combination magenta and black swath, and a cyan swath, each swath having 
the width of 2/5 of an entire linear array. In one configuration, when a 
full-color image is being printed, only those ejectors in the black 
section which match with ejectors in the magenta section will be operated, 
so as to avoid any interaction with yellow ink being simultaneously 
emitted onto the sheet. 
Alternatively, when a full-color image is being printed, one can use all of 
the ejectors across the black section, but in each swath having each 
ejector print only every other pixel, thus making a checkerboard pattern. 
Half the ejectors in the black section (e.g. those corresponding to the 
magenta section) would print the pixels making the checkerboard pattern, 
while the remaining black ejectors would print the remaining black pixels. 
This scheme would be effective in reducting the visual effect of head 
signature in half-tone areas. 
The advantage of the arrangement of ejectors in FIG. 4 is that, as can be 
seen, a full-black swath is of a width that is 4/5 of an entire linear 
array, while the three swaths of a full-color array are each 2/5 of a 
linear array; that is, there is a 2:1 ratio in swath width, and therefore 
speed, between the black and color portions in this embodiment. Because of 
this relatively close ratio of speeds between black-only and full-color 
printing, 2:1 instead of 3:1, as in the embodiments of FIG. 2, a closer 
trade-off between operating at the two different speeds may be made when, 
for example, printing a document having all-black portions along process 
direction P and also full-color portions. 
It will be noted that in all of the above embodiments of the present 
invention, the order of laying down primary color inks on the sheet S will 
be the same no matter which direction the carriage is moving through path 
C. This feature is important, since it has been found that, in full-color 
images, the hues may be slightly different depending on the specific order 
in which the primary color inks are placed on the sheet. 
It will also be noted that the order of colored inks within the print head 
is not restricted to the order of the illustrated embodiments, but rather, 
any permutation of the three colored inks may be used. 
Although the illustrated embodiments show two linear arrays mounted on the 
same cartridge 10, it is conceivable that the two linear arrays could be 
part of separate ink supply cartridges, and held in fixed relation to each 
other by structure on carriage 12 or on the cartridges themselves. In the 
FIG. 2 embodiment, for example, it is a possible scenario that the ink 
supply to the all-black array will be exhausted at a substantially 
different time than the ink supply for the primary-color linear array. In 
such a case, it may be an advantageous design configuration to have the 
two linear arrays mounted on separate ink supply cartridges, so that one 
cartridge or the other could be replaced as needed. However, providing 
separate cartridges could cause significant problems of ensuring precise 
registration between the two linear arrays. 
While this invention has been described in conjunction with various 
embodiments, it is evident that many alternatives, modifications, and 
variations will be apparent to those skilled in the art. Accordingly, it 
is intended to embrace all such alternatives, modifications, and 
variations as fall within the spirit and broad scope of the appended 
claims.