Ink jet printing apparatus having a print cartridge with primary and secondary nozzles

An ink jet printing apparatus is provided comprising a print cartridge including a heater chip and a nozzle plate coupled to the heater chip. The heater chip has first, second, third and fourth heating elements, and the nozzle plate has a plurality of primary and secondary nozzles. The primary nozzles include first and second nozzles positioned in first and second nozzle plate columns and the secondary nozzles include third and fourth nozzles positioned in third and fourth nozzle plate columns. Each of the nozzles has one of the heating elements associated therewith for generating energy to discharge ink therefrom. The apparatus further includes a driver circuit, electrically coupled to the print cartridge, for applying firing pulses to the heating elements.

FIELD OF THE INVENTION 
This invention relates to ink jet printing apparatuses having at least one 
print cartridge with primary and secondary nozzles. 
BACKGROUND OF THE INVENTION 
Drop-on-demand ink let printers form a printed image by printing a pattern 
of individual dots or pixels on a print medium, such as a sheet of paper. 
The possible locations for the dots can be represented by an array or grid 
of pixels or square areas arranged in a rectilinear array of rows and 
columns wherein the center to center distance or dot pitch between pixels 
is determined by the resolution of the printer. The dots are printed as a 
printhead moves across the medium in a line scan direction. Between line 
scans, a stepper motor moves the print medium in a direction transverse to 
the line scan direction. 
Drop-on-demand ink jet printers use thermal energy to produce a vapor 
bubble in an ink-filled chamber to expel a droplet. A thermal energy 
generator or heating element, usually a resistor, is located in the 
chamber on a heater chip near a discharge nozzle. A plurality of chambers, 
each provided with a single heating element, are provided in the printer's 
printhead. The printhead typically comprises the heater chip and a nozzle 
plate having a plurality of the discharge nozzles formed therein. The 
printhead forms part of an ink jet print cartridge which also comprises an 
ink-filled container. 
In one conventional printhead, discharge nozzles are arranged in two 
columns, with tie nozzles of one column staggered relative to the nozzles 
of the other column. During use, the two columns function as a single 
column. Hence, each horizontal row of dots is printed by only a single 
nozzle. If a nozzle fails, the printed document will include horizontal 
blank lines where ink is absent due to the defective nozzle not printing 
dots along those lines. 
Printer manufacturers are constantly searching for techniques which may be 
used to improve printing speed. One known technique involves adding 
additional nozzles to each nozzle column on the printhead. However, as 
nozzle column length increases, proper nozzle alignment along the columns 
becomes more critical. This is because print misalignment resulting from 
nozzle misalignment becomes more noticeable as nozzle column length 
increases. 
An improved printhead which allows for increased printing speed and 
improved print quality is desired. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, an ink jet printing apparatus is 
provided having a printhead with a plurality of primary and secondary 
nozzles. The primary nozzles include first and second nozzles positioned 
in first and second nozzle plate columns. The secondary nozzles include 
third and fourth nozzles positioned in third and fourth nozzle plate 
columns. The secondary nozzles define redundant nozzles. That is, each 
secondary nozzle shares a horizontal axis with a primary nozzle. Thus, 
instead of having two columns of nozzles, which function as a single 
vertical line of nozzles, printing a swath of data during a single pass of 
the printhead, there are four columns of nozzles, which function as two 
vertical lines of nozzles, printing the data. Each vertical line of 
nozzles is capable of printing approximately one-half of the pixels 
printed during a given pass of the printhead across the print medium. If a 
primary nozzle falls and its associated secondary nozzle is operable, only 
one-half of the data to be printed by the nozzle pair will not be printed. 
Hence, by using redundant nozzles, the likelihood that completely blank 
horizontal lines on the print medium will result is substantially reduced. 
Increased printing speed and an increase in nozzle life also result due to 
the addition of secondary nozzles. Further, by adding redundant nozzles, 
nozzle column length has not been substantially increased. This is an 
advantage as print misalignment resulting from nozzle misalignment becomes 
more noticeable as nozzle column length increases.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, there is shown an ink jet printing apparatus 10 
having first and second print cartridges 20 and 30 constructed in 
accordance with the present invention. The cartridges 20 and 30 are 
supported in a carrier 40 which, in turn, is slidably supported on a guide 
rail 42. A print cartridge drive mechanism 44 is provided for effecting 
reciprocating movement of the carrier 40 back and forth along the guide 
rail 42. The drive mechanism 44 includes a motor 44a with a drive pulley 
44b and a drive belt 44c which extends about the drive pulley 44b and an 
idler pulley 44d. The carrier 40 is fixedly connected to the drive belt 
44c so as to move with the drive belt 44c. Operation of the motor 44a 
effects back and forth movement of the drive belt 44c and, hence, back and 
forth movement of the carrier 40 and the print cartridges 20 and 30. As 
the print cartridges 20 and 30 move back and forth, they eject ink 
droplets onto a paper substrate 12 provided below them. Driven rollers 14 
(only one is illustrated in FIG. 1) mounted on a shaft 16 cooperate with 
pressure rollers 18 (only one of which is illustrated in FIG. 1) to 
advance the paper substrate 12 in a direction generally orthogonal to the 
direction of print cartridge movement. The shaft 16 is driven by a stepper 
motor assembly 19. 
The print cartridge 20 comprises a polymeric container 22, see FIG. 1, 
filled with ink and a printhead 24, see FIGS. 2 and 3. The printhead 24 
comprises a heater chip 50 having a plurality of resistive heating 
elements 52. The printhead 24 further includes a nozzle plate 54 having a 
plurality of openings 56 extending through it which define a plurality of 
nozzles 58 through which ink droplets are ejected. The diameter of each 
nozzle 58 is from about 5 microns to about 29 microns. 
The nozzle plate 54 may be formed from a flexible polymeric material 
substrate which is adhered to the heater chip 50 via an adhesive (not 
shown). Examples of polymeric materials from which the nozzle plate 54 may 
be formed and adhesives for securing the plate 54 to the heater chip 50 
are set out in commonly assigned patent application, U.S. Ser. No. 
08/519,906, entitled "METHOD OF FORMING AN INKJET PRINTHEAD NOZZLE 
STRUCTURE," by Tonya H. Jackson et al., filed on Aug. 28, 1995, Attorney 
Docket No. LE9-95-024, the disclosure of which is hereby incorporated by 
reference. As noted therein, the plate 54 may be formed from a polymeric 
material such as polyimide, polyester, fluorocarbon polymer, or 
polycarbonate. The plate 54 is preferably about 15 to about 200 microns 
thick, and most preferably about 50 to about 125 microns thick. Examples 
of commercially available plate materials include a polyimide material 
available from E.I. DuPont de Nemours & Co. under the trademark "KAPTON" 
and a polyimide material available from Ube (of Japan) under the trademark 
"UPILEX." 
The plate 54 may be bonded to the chip 50 via any art recognized technique, 
including a thermocompression bonding process. When the plate 54 and the 
heater chip 50 are joined together, sections 54a of the plate 54 and 
portions 50a of the heater chip 50 define a plurality of bubble chambers 
55. Ink supplied by the container 22 flows into the bubble chambers 55 
through ink supply channels 55a. The resistive heating elements 52 are 
positioned on the heater chip 50 such that each bubble chamber 55 has only 
one heating element 52. Each bubble chamber 55 communicates with one 
nozzle 58, see FIG. 3. 
The resistive heating elements 52 are individually addressed by voltage 
pulses provided by a driver circuit 300, see FIG. 7. Each voltage pulse is 
applied to one of the heating elements 52 to momentarily vaporize the ink 
in contact with that heating element 52 to form a bubble within the bubble 
chamber 55 in which the heating element 52 is found. The function of the 
bubble is to displace ink within the bubble chamber 55 such that a droplet 
of ink is expelled from a nozzle 58 associated with the bubble chamber 55. 
A flexible circuit (not shown) secured to the polymeric container 22 is 
used to provide a path for energy pulses to travel from the driver circuit 
300 to the heater chip 50. Bond pads (not shown) on the heater chip 50 are 
bonded to end sections of traces (not shown) on the flexible circuit. 
Current flows from the circuit 300 to the traces on the flexible circuit 
and from the traces to the bond pads on the heater chip 50. The current 
then flows from the bond pads along conductors 53 to the heating elements 
52. 
The print cartridge 30 comprises a polymeric container 32, see FIG. 1, 
filled with ink and a printhead (not shown). The printhead of the print 
cartridge 30 is constructed in essentially the same manner as the 
printhead 24 and, as such, will not be described in further detail herein. 
In accordance with the present invention, the nozzle plate 54 is provided 
with a plurality of primary nozzles 110 and secondary nozzles 120, see 
FIG. 4. In the illustrated embodiment, there are eight segments IA-VIIIA 
of primary nozzles 110, each segment having 38 nozzles, as represented in 
FIG. 5. Thus, the total number of primary nozzles 110, in the illustrated 
embodiment, equals 304 nozzles. Similarly, there are eight segments 
IB-VIIIB of secondary nozzles 120, each segment having 38 nozzles. The 
total number of secondary nozzles 120 equals 304 nozzles. Each secondary 
nozzle 120 shares a horizontal axis with a primary nozzle 110. The 
specific number of primary and secondary nozzles 110 and 120 formed on the 
nozzle plate 54 are mentioned herein for illustrative purposes only. 
Hence, the number of primary and secondary nozzles 110 and 120 are not 
intended to be limited to those represented in FIG. 5. 
The primary nozzles 110 include first and second nozzles 112 and 114 
positioned in first and second nozzle plate columns 212 and 214, see FIGS. 
4 and 6. The secondary nozzles 120 include third and fourth nozzles 122 
and 124 positioned in third and fourth nozzle plate columns 222 and 224, 
see FIG. 4. Front sections of the first and second columns 212 and 214 are 
spaced apart from one another by a distance equal to X/1200 inch, wherein 
X is an odd integer .gtoreq.3 and .ltoreq.9, see FIGS. 4 and 6. Front 
sections of the third and fourth columns 222 and 224 are spaced apart from 
one another by a distance equal to X/1200 inch, wherein X is an odd 
integer .gtoreq.3 and .ltoreq.9, see FIG. 4. Front sections of the first 
and third columns 212 and 222 are spaced apart from one another by a 
distance equal to Y/600 inch, wherein Y is an even integer .gtoreq.40, see 
FIG. 4. In the illustrated embodiment, X=5 and Y=86. 
The first and second nozzles 112 and 114 of segment IA and the third and 
fourth nozzles 122 and 124 of segment IB are represented in FIG. 4 by 
solid dots with numbers positioned adjacent to the dots. The first and 
second nozzles 112 and 114 of segment IA and two nozzles of segment IIA 
are Illustrated in FIG. 6 by numbered circles. The first nozzles 112 are 
represented by odd-numbered circles and the second nozzles 114 are 
represented by even-numbered circles. The 38 nozzles of each of segments 
IA and IB are numbered 1-19 and 2-20 in FIGS. 4-6. 
The vertical distance between center points of adjacent first and second 
nozzles 112 and 114 positioned in adjacent horizontal rows in the columns 
212 and 214, e.g., nozzles 1 and 6 located in rows 1 and 2, is 
approximately 1/600 inch, see FIGS. 4 and 6. The vertical distance between 
center points of adjacent third and fourth nozzles 122 and 124 positioned 
in adjacent horizontal rows in the third and fourth columns 222 and 224, 
e.g., nozzles 1 and 6, is also about 1/600 inch, see FIG. 4. The vertical 
distance between center points of vertically adjacent first nozzles 112, 
e.g., nozzles 1 and 11, is approximately 1/300 inch. Similarly, the 
vertical distance between vertically adjacent second nozzles 114, third 
nozzles 122 and fourth nozzles 124 is approximately 1/300 inch. 
The numbers adjacent to the dots in FIG. 4 and within the circles in FIG. 6 
designate vertical subcolumns within the nozzle plate columns 212 and 214 
in which center points of the nozzles 112 and 114 are found. As indicated 
in FIG. 6, the width of each vertical subcolumn within each of the nozzle 
plate columns 212 and 214 is 1/28,800 inch. Thus, the horizontal distance 
between the center points of two horizontally adjacent first nozzles 112, 
e.g. nozzles 1 and 3, is approximately 2/28,800 inch. Similarly, the 
horizontal distance between the center points of two horizontally adjacent 
second nozzles 114, e.g., nozzles 2 and 4, is approximately 2/28,800. 
In the illustrated embodiment, the 38 nozzles of each of segments IIA-VIIIA 
ard segments IB-VIIIB are arranged in the same order and are spaced from 
another in the same manner as are the 38 nozzles of segment IA. Thus, the 
secondary nozzles 120 are arranged in the same order and spaced from one 
another in the same manner as the primary nozzles 110. Accordingly, the 
order and spacing of the secondary nozzles 120 will not be further 
described herein. 
The driver circuit 300 comprises a microprocessor 310, an application 
specific integrated circuit (ASIC) 320, a primary nozzle/secondary nozzle 
select circuit 330, decoder circuitry 340 and a common drive circuit 350. 
The primary nozzle/secondary nozzle select circuit 330 selectively enables 
either the primary nozzle segments IA-VIIIA or the secondary nozzle 
segments IB-VIIIB. It has a first output 330a which is electrically 
coupled to the primary nozzles 110 via conductor 330b. It also has a 
second output 330c which is electrically coupled to the secondary nozzles 
120 via a conductor 330d. Thus, a first select signal present at the first 
output 330a is used to select the operation of the primary nozzles 110 
while a second select signal present at the second output 330c is used to 
select the operation of the secondary nozzles 120. The primary 
nozzle/secondary nozzle select circuit 330 is electrically coupled to the 
ASIC 320 and generates appropriate select signals in response to command 
signals received from the ASIC 320. 
As noted above, there is a single resistive heating element 52 associated 
with each of the primary and secondary nozzles 110 and 120. In FIG. 7, the 
illustrated resistive heating elements 52 are numbered and grouped so as 
to correspond with the nozzle numbering and segment groupings used in 
FIGS. 4-6. 
The common drive circuit 350 comprises a plurality of drivers 352 which are 
electrically coupled to a power supply 400, the ASIC 320 and the resistive 
heating elements 52. In the illustrated embodiment, sixteen drivers 352 
are provided. Each of the sixteen drivers 352 is electrically coupled to 
one-half of the heating elements 52 associated with one of the primary 
nozzle segments IA-VIIIA and one-half of the heating elements 52 
associated with one of the secondary nozzle segments IB-VIIIB. In FIG. 7, 
the first driver 352, i.e., the driver designated number 1, is coupled to 
the heating elements 52 associated with the upper one-half of the nozzles 
110 of the primary nozzle segment IA, i.e., the nozzles numbered 1-19 in 
FIGS. 4-6, and the heating elements 52 associated with the upper one-half 
of the nozzles 120 of the secondary nozzle segment IB. The second driver 
352, i.e., the driver designated number 2, is coupled to the heating 
elements 52 associated with the lower one-half of the nozzles 110 of the 
primary nozzle segment IA, i.e., the nozzles numbered 2-20 in FIGS. 4-6, 
and the heating elements 52 associated with the lower one-half of the 
nozzles 120 of the secondary nozzle segment IB. The fifteenth driver 352, 
i.e., the driver designated number 15, is coupled to the heating elements 
52 associated with the upper one-half of the nozzles 110 of the primary 
nozzle segment VIIIA, and the heating elements 52 associated with the 
upper one-half of the nozzles 120 of the secondary nozzle segment VIIIB. 
The sixteenth driver 352, i.e., the driver numbered 16, is coupled to the 
heating elements 52 associated with the lower one-half of the nozzles 110 
of the primary nozzle segment VIIIA, and the heating elements 52 
associated with the lower one-half of the nozzles 120 of the secondary 
nozzle segment VIIIB. 
There are five input lines 342 extending from the ASIC 320 to the decoder 
circuitry 340. Twenty address lines 344 extend from the decoder circuitry 
340 to the resistive heating elements 52. Each address line 344 extends to 
heating elements 52 associated with like numbered nozzles in each of the 
primary and secondary segments IA-VIIIA and IB-VIIIB. For example, the 
first address line 344, i.e., the address line numbered 1 in FIG. 7, is 
connected to the resistive heating elements 52 associated with the number 
1 primary and secondary nozzles 110 and 120 in each of the primary and 
secondary segments IA-VIIIA and IB-VIIIB. The tenth address line 344, 
i.e., the address line numbered 10 in FIG. 7, is connected to the 
resistive heating elements 52 associated with the number 10 primary and 
secondary nozzles in each of the primary and secondary segments IA-VIIIA 
and IB-VIIIB. The twentieth address line 344, i.e., the address line 
numbered 20 in FIG. 7, is connected to the resistive heating elements 52 
associated with the number 20 primary and secondary nozzles in each of the 
primary and secondary segments IA-VIIIA and IB-VIIIB. As will be discussed 
more explicitly below, the ASIC 320 sends appropriate signals to the 
decoder circuitry 340 such that during a given firing cycle, the decoder 
circuitry 340 generates appropriate address signals to the heating 
elements 52 associated with the primary and secondary nozzles 110 and 120. 
Each driver 352 is only activated by the ASIC 320 when one of the heating 
elements 52 to which it is connected is to be fired. The specific heating 
elements 52 fired during a given firing cycle depends upon print data 
received by the microprocessor 310 from a separate processor (not shown) 
electrically coupled to it. The microprocessor 310 generates signals which 
are passed to the ASIC 320 and, in turn, the ASIC 320 generates 
appropriate firing signals which are passed to the sixteen drivers 352. 
The activated drivers 352 then apply firing voltage pulses to the heating 
elements 52 in conjunction with the ground path provided by the decoder 
circuitry 340. 
If the heating element associated with the number 1 primary nozzle 110 in 
segment IA is to be fired during a given firing cycle segment, the first 
driver 352 will be activated simultaneously with the activation of the 
first output 330a of the select circuit 330 and the first address line 
344. If the number 2 primary nozzle 110 in segment IA is not to be fired 
during a given firing cycle segment, the second driver 352 will not be 
fired when the first output 330a of the select circuit 330 and the second 
address line 344 are simultaneously activated. If the uppermost primary 
nozzle 110 numbered 10 in segment IA is to be fired, the first driver 352 
will be fired when the first output 330a of the select circuit 330 and the 
tenth address line 344 are simultaneously activated. If the lowermost 
primary nozzle 110 numbered 10 in segment IA is not to be fired during a 
given firing cycle segment the second driver 352 will not be fired when 
the first output 330a of the select circuit 330 and the tenth address line 
344 are simultaneously activated. 
The printing apparatus 10 is selectively operable in one of a normal mode 
of operation and a high speed mode of operation. The user of the apparatus 
10 may select the desired mode via software during printer set up. 
A timing diagram for the high speed mode of operation is illustrated in 
FIG. 8, wherein an expanded high speed mode firing cycle 500 is shown. The 
driver circuit 300 is capable of applying, depending upon print data 
received by the microprocessor 310 from the separate processor (not shown) 
electrically coupled to it, first firing pulses to first heating elements 
52, i.e., the heating elements 52 associated with the first nozzles 112 
(the od-numbered primary nozzles), during a first segment 502a of each 
high speed mode firing cycle, second firing pulses to second heating 
elements 52, i.e., the heating elements 52 associated with the second 
nozzles 114 (the even-numbered primary nozzles), during a second segment 
502b of each high speed mode firing cycle, third firing pulses to third 
heating elements 52, i.e., the heating elements 52 associated with the 
third nozzles 122 (the odd-numbered secondary nozzles), during a third 
segment 502c of each high speed mode firing cycle, and fourth firing 
pulses to fourth heating elements 52, i.e., the heating elements 52 
associated with the fourth nozzles 124 (the even-numbered secondary 
nozzles), during a fourth segment 502d of each high speed mode firing 
cycle. 
As illustrated in FIG. 8, during the first and third segments 502a and 502c 
of each high speed mode firing cycle, the ASIC 320 causes the decoder 
circuitry 340 to cycle through its odd address lines 344. During the 
second and fourth segments 502b and 502d of each high speed mode firing 
cycle, the ASIC 320 causes the decoder circuitry 340 to cycle through its 
even address lines 344. The first output 330a is active only during the 
first and second segments 502a and 502b. The second output 330c is active 
only during the third and fourth segments 502c and 502d. 
During the first segment 502a of the high speed mode firing cycle, the 
first output 330a is active and, depending upon the print data received by 
the microprocessor 310, the appropriate drivers 352 are activated as the 
decoder circuitry 340 cycles through its odd address lines 344 such that 
the desired first heating elements associated with the first nozzles 112 
in segments IA-VIIIA are fired. During the second segment 502b of the high 
speed mode firing cycle, the first output 330a is active and, depending 
upon the print data received by the microprocessor 310, the appropriate 
drivers 352 are activated as the decoder circuitry 340 cycles through its 
even address lines 344 such that the desired second heating elements 52 
associated with the second nozzles 114 in segments IA-VIIIA are fired. 
During the third segment 502c of the high speed mode firing cycle, the 
second output 330c is active and, depending upon the print data received 
by the microprocessor 310, the appropriate drivers 352 are activated as 
the decoder circuitry 340 cycles through its odd address lines 344 such 
that the desired third heating elements 52 associated with the third 
nozzles 122 in segments IB-VIIIB are fired. During the fourth segment 502d 
of the high speed mode firing cycle, the second output 330c is active and, 
depending upon the print data received by the microprocessor 310, the 
appropriate drivers 352 are activated as the decoder circuitry 340 cycles 
through its even address lines 344 such that the desired fourth heating 
elements 52 associated with the fourth nozzles 124 in segments IB-VIIIB 
are fired. 
The length of time of each of the first, second, third and fourth segments 
502a-502d of the high speed mode firing cycle is from about 12 .mu.seconds 
to about 64 .mu.seconds. The printhead speed is from about 13 
inches/second to about 70 inches/second. In the illustrated embodiment, 
the length of time of each of the segments 502a-502d is about 20.825 
seconds such that the total firing cycle time is approximately 83.3 
.mu.seconds. Further, the printhead speed is about 40 inches/second such 
that the printhead travels approximately 1/300 inch per firing cycle. 
It is noted that at the beginning of each of the second and fourth segments 
502b and 502d of the high speed mode firing cycle, a delay of about 0.868 
.mu.seconds occurs before the heating element 52 associated with the 
number 2 second nozzle 114 and the number 2 fourth nozzle 124 are fired. 
This delay period is equal to the amount of time it takes the printhead to 
move 1/28,800 inch, tie length of one subcolumn within each of the second 
and fourth columns 214 and 224. 
In FIG. 9, a plot is illustrated showing dots generated by a first nozzle 
112, a second nozzle 114, a third nozzle 122 and a fourth nozzle 124 
during high speed mode operation. The initial positions of the nozzles 
112, 114, 122 and 124 are shown. For illustrative purposes, the distance 
between the first and third nozzles 112 and 122 is 6/600 inch. Dots 
generated by the nozzles 112, 114, 122 and 124 are represented by numbered 
circles, wherein dots 1A are formed by the first nozzle 112, dots 2A are 
formed by the second nozzle 114, dots 18 are formed by the third nozzle 
122 and dots 2B are formed by the fourth nozzle 124. As can be seen from 
FIG. 9, during a first segment 502a of a first high speed mode firing 
cycle, nozzle 112 is fired and the printhead moves a distance across the 
paper substrate 12 (from right to left) equal to 1/1200 inch. During a 
second segment 502b of the first high speed mode firing cycle, nozzle 114 
is fired and the printhead moves another 1/1200 inch across the paper 
substrate 12. The dot 2A created by the nozzle 114 is horizontally spaced 
approximately 4/1200 inch from the dot 1A created by the nozzle 112. 
During a third segment 502c of the first high speed firing cycle, nozzle 
122 is fired and the printhead moves another 1/1200 inch across the paper 
substrate 12. During a fourth segment 502d of the first high speed firing 
cycle, nozzle 124 is fired and the printhead moves another 1/1200 inch 
across the paper substrate 12. The dot 2B created by nozzle 124 is 
horizontally spaced approximately 4/1200 inch from the dot 1B created by 
the nozzle 122. As is apparent from FIG. 9, the dots are horizontally 
spaced from one another by a distance of 1/600 inch. Thus, 600 dots per 
inch horizontal resolution occurs during high speed mode printing. This 
results because the first and second columns 212 and 214 are spaced apart 
from one another by a distance equal to X/1200 inch, wherein X is an odd 
integer; the third and fourth columns are spaced apart from one another by 
a distance equal to X/1200 inch, wherein X is an odd integer; and the 
first and third columns are spaced apart from one another by a distance 
equal to Y/600 inch, wherein Y is an even integer. 
A timing diagram for the normal speed mode of operation is illustrated in 
FIG. 10, wherein an expanded normal speed mode firing cycle 600 is shown. 
The driver circuit 300 is capable of alternatively applying, depending 
upon print data received by the microprocessor 310 from the separate 
processor (not shown) electrically coupled to it, first and second firing 
pulses to first and second heating elements 52, i.e., the heating elements 
52 associated with the first and second nozzles 112 and 114, during a 
first segment 602a of each normal speed mode firing cycle; third and 
fourth firing pulses to third and fourth heating elements 52, i.e., the 
heating elements 52 associated with the third and fourth nozzles 122 and 
124, during a second segment 602b of each normal speed mode firing cycle; 
first and second firing pulses to the first and second heating elements 52 
during a third segment 602c of each normal speed mode firing cycle and 
third and fourth firing pulses to the third and fourth heating elements 52 
during a fourth segment 602d of each normal speed mode firing cycle. 
During each of the segments 602a-602d of the normal speed mode firing 
cycle, the ASIC 320 causes the decoder circuitry 340 to cycle through each 
of its twenty address lines 344. The first output 330a is active during 
the first and third segments 602a and 602c and the second output 330c is 
active during the second and fourth segments 602b and 602d. 
The length of time of each of the first, second, third and fourth segments 
602a-602d of the normal speed mode firing cycle is from about 24 
.mu.seconds to about 64 .mu.seconds. The printhead speed is from about 13 
inches/second to about 35 inches/second. In the illustrated embodiment, 
the length of time of each of the segments 602a-602d is about 41.675 
.mu.seconds such that the total firing cycle time is approximately 166.7 
.mu.seconds. Further, the printhead speed is about 20 inches/second such 
that the printhead travels approximately 1/300 inch per firing cycle. 
In FIG. 11, a plot is illustrated showing dots generated by a first nozzle 
112, a second nozzle 114, a third nozzle 122 and a fourth nozzle 124 
during normal speed mode operation. The initial positions of the nozzles 
112, 114, 122 and 124 are shown. Dots generated by the nozzles 112,114, 
122 and 124 are represented by numbered circles, wherein dots 1A are 
formed by the first nozzle 112, dots 2A are formed by the second nozzle 
114, dots 1B are formed by the third nozzle 122 and dots 2B are formed by 
the fourth nozzle 124. As can be seen from FIG. 11, during a first segment 
602a of a normal speed mode firing cycle, nozzles 112 and 114 are fired 
and the printhead moves a distance across the paper substrate 12 equal to 
1/1200 inch. During a second segment 602b of the normal speed mode firing 
cycle, nozzles 122 and 124 are fired and the printhead moves another 
1/1200 inch across the paper substrate 12. During a third segment 602c of 
the normal speed firing cycle, nozzles 112 and 114 are fired and the 
printhead moves another 1/1200 inch across the paper substrate 12. During 
a fourth segment 602d of the high speed firing cycle, nozzles 122 and 124 
are fired and the printhead moves another 1/1200 inch across the paper 
substrate 12. As is apparent from FIG. 11, the dots created by the nozzles 
112, 114, 122 and 124 are positioned on a 1200 dots per inch horizontal 
grid. A 1200 dots per inch resolution is possible along a vertical 
direction by appropriate control of the stepper motor assembly 19 by the 
microprocessor 310. 
It is further contemplated that instead of having a single nozzle plate 54 
coupled to a single heater chip 50 including both the primary and 
secondary nozzles 110 and 120, two separate printheads positioned 
side-by-side, one including the primary nozzles and the other having the 
secondary nozzles, may be used.