[0001] The present invention generally relates to inkjet and other types of printers and,
more particularly, to the ink flow to the printhead portion of an inkjet printer.
[0002] An ink jet printer forms a printed image by printing a pattern of individual dots
at particular locations of an array defined for the printing medium. The locations
are conveniently visualized as being small dots in a rectilinear array. The locations
are sometimes called "dot locations", "dot positions", or "pixels". Thus, the printing
operation can be viewed as the filling of a pattern of dot locations with dots of
ink.
[0003] Thermal inkjet print cartridges operate by rapidly heating a small volume of ink
to cause the ink to vaporize and be ejected through one of a plurality of orifices
so as to print a dot of ink on a recording medium, such as a sheet of paper. Typically,
the orifices are arranged in one or more linear arrays in a nozzle member. The properly
sequenced ejection of ink from each orifice causes characters or other images to be
printed upon the paper as the printhead is moved relative to the paper. The paper
is typically shifted each time the printhead has moved across the paper. The thermal
inkjet printer is fast and quiet, as only the ink strikes the paper. These printers
produce high quality printing and can be made both compact and affordable. An inkjet
printhead generally includes: (1) ink channels to supply ink from an ink reservoir
to each vaporization chamber proximate to an orifice; (2) a metal orifice plate or
nozzle member in which the orifices are formed in the required pattern; and (3) a
silicon substrate containing a series of thin film resistors, one resistor per vaporization
chamber.
[0004] To print a single dot of ink, an electrical current from an external power supply
is passed through a selected thin film resistor. The resistor is then heated, in turn
superheating a thin layer of the adjacent ink within a vaporization chamber, causing
explosive vaporization, and, consequently, causing a drop of ink to be ejected through
an associated nozzle onto the paper.
[0005] A concern with inkjet printing is the sufficiency of ink flow to the paper or other
print media. Print quality is a function of ink flow through the printhead. Too little
ink on the paper or other media to be printed upon produces faded and hard-to-read
documents.
[0006] In an inkjet printhead ink is fed from an ink reservoir integral to the printhead
or an "off-axis" ink reservoir which feeds ink to the printhead via tubes connecting
the printhead and reservoir. Ink is then fed to the various vaporization chambers
either through an elongated hole formed in the center of the bottom of the substrate,
"center feed", or around the outer edges of the substrate, "edge feed". In center
feed the ink then flows through a central slot in the substrate into a central manifold
area formed in a barrier layer between the substrate and a nozzle member, then into
a plurality of ink channels, and finally into the various vaporization chambers. In
edge feed ink from the ink reservoir flows around the outer edges of the substrate
into the ink channels and finally into the vaporization chambers. In either center
feed or edge feed, the flow path from the ink reservoir and the manifold inherently
provides restrictions on ink flow to the firing chambers.
[0007] Air and other gas bubbles can cause major problems in ink delivery systems. Ink delivery
systems are capable of releasing gasses and generating bubbles, thereby causing systems
to get clogged and degraded by bubbles. In the design of a good ink delivery system,
it is important that techniques for eliminating or reducing bubble problems be considered.
Most fluids exposed to the atmosphere contain dissolved gases in amounts varying with
the temperature. The amount of gas that a liquid can hold depends on temperature and
pressure, but also depends on the extent of mixing between the gas and liquid and
the opportunities the gas has had to escape.
[0008] Changes in atmospheric pressure normally can be neglected because atmospheric pressure
stays fairly constant. However, temperature does change within an inkjet cartridge
to make an appreciable difference in the amount of gas that can be contained in the
ink. Bubbles have less tendency to originate at low temperatures, and their growth
will also be slower. The colder a liquid, the less kinetic energy is available and
the longer it takes to gather together the necessary energy at specific location where
the bubble begins to form.
[0009] Most fluids exposed to the atmosphere contain dissolved gases in amounts proportional
to the temperature of the fluid itself. The colder the fluid, the greater the capacity
to absorb gases. If a fluid saturated with gas is heated, the dissolved gases are
no longer in equilibrium and tend to diffuse out of solution. If nucleation seed sites
are present along the surface containing the fluid or within the fluid, bubbles will
form, and as the fluid temperature rises further, these bubbles grow larger.
[0010] Bubbles are not only made of air, but are also made of water vapor and vapors from
other ink-vehicle constituents. However, the behavior of all liquids are similar,
the hotter the liquid becomes, the less gas it can hold. Both gas release and vapor
generation cause bubbles to start and grow as temperature rises. One can reasonably
assume the gases inside the bubbles in a water-based ink are always saturated with
water vapor. Thus, bubbles are made up both of gases, mostly air, and of ink vehicle
vapor, mostly water. At room temperature, water vapor is an almost negligible part
of the gas in a bubble. However, at 50° C., the temperature at which an inkjet printhead
might operate, water vapor adds importantly to the volume of a bubble. As the temperature
rises, the water vapor content of the bubbles increases much more rapidly with temperature
than does the air content.
[0011] The best conditions for bubble generation are the simultaneous presence of (1) generating
or "seed" sites, (2) ink flow and (3) bubble accumulators. These three mechanisms
work together to produce large bubbles that clog and stop flow in ink delivery systems.
When air comes back out of solution as bubbles, it does so at preferential locations,
or generation or nucleation sites. Bubbles like to start at edges and corners or at
surface scratches, roughness, or imperfections. Very small bubbles tend to stick to
the surfaces and resist floating or being swept along in a current of ink. When the
bubbles get larger, they are more apt to break loose and move along. However, if the
bubbles form in a corner or other out-of-the-way location, it is almost impossible
to dislodge them by ink currents.
[0012] While bubbles may not start at gas generating sites when the ink is not flowing past
those sites, when the ink is moving, the bubble generation site is exposed to a much
larger volume of ink containing dissolved gas molecules. As ink flows past the gas
generating site, gas molecules can be brought out of solution to form a bubble and
grow; while if the ink was not flowing this would happen less rapidly.
[0013] The third contributor to bubble generation is the accumulator or bubble trap, which
can be defined as any expansion and subsequent narrowing along an ink passage. This
configuration amounts to a chamber on the ink flow path with an entrance and an exit.
The average ink flow rate, in terms of volume ink per cross section of area per second,
is smaller within the chamber than at the entrance or at the exit. The entrance edge
of the chamber will act as a gas generating site because of its sharpness and because
of the discontinuity of ink flow over the edge. Bubbles will be generated at this
site, and when they become large enough they get moved along toward the exit duct
until the exit duct is blocked. Then, unless the system can generate enough pressure
to push the bubble through, the ink delivery system will become clogged and ink delivery
will be shut down. Thus, the chamber allows bubbles to grow larger than the diameter
of subsequent ink passageways which may then become blocked.
[0014] During the ink filling and priming process, bubbles are left behind in the print
cartridge. Bubbles can interfere with printhead reliability by causing intermittent
nozzle problems and local or even global starvation. An important aspect of bubble
control is the design of the internal cartridge geometry. The most critical areas
for the design are the areas around the substrate, headland, manifold, standpipe,
and filters.
[0015] In an inkjet print cartridge ink flows from the ink reservoir through filters, through
a standpipe, through or around the silicon substrate, through ink channels and into
vaporization chambers for ejection out of the nozzles. During operation, warm thermal
boundary layers of ink form adjacent the substrate and dissolved gases in the thermal
boundary layer of the ink form the bubbles. Also, bubbles tend to form at the corners
and edges of the walls along the ink flow path. If the bubbles grow larger than the
diameter of subsequent ink passageways these bubbles choke the flow of ink to the
vaporization chambers. This results in causing some of the nozzles of the printhead
to become temporarily inoperable.
[0016] The goals are to minimize dead spaces, streamline the geometry for fluid flow to
avoid trapping bubbles during initial priming and to provide a clear path to allow
for buoyancy to maximize the easy escape of bubbles from the printhead area into the
ink manifold and then to float through standpipe and into filter area. Accordingly,
a printhead design to be more tolerant of existing bubbles is desired.
[0017] The present invention seeks to provide improved inkjet printing.
[0018] According to an aspect of the present invention, there is provided a method of ink
delivery as specified in claim 1.
[0019] According to another aspect of the present invention, there is provided an inkjet
print cartridge as specified in claim 1.
[0020] The preferred embodiment can provide a printhead design which can eliminate the residual
bubbles left in the print cartridge after the ink filling and priming process.
[0021] The preferred method provides a method of avoiding such a malfunction in a liquid
inkjet printing system by providing a bubble tolerant print cartridge design and method
which allows bubbles to escape from the printhead area of the cartridge. The preferred
apparatus and method of ink delivery in an inkjet print cartridge comprises storage
of a supply of ink in a reservoir; transportation of ink from the reservoir downwardly
through a manifold to ink firing chambers; and provision of contoured walls along
the manifold to allow bubbles to escape from the manifold upwardly away from the ink
firing chambers toward the reservoir without interfering with the replenishment of
ink into the ink firing chambers.
[0022] An embodiment of the present invention is described below, by way of example only,
with reference to the accompanying drawings, in which:
Fig. 1 is a perspective view of an inkjet print cartridge.
Fig. 2 is a perspective view of the headland area of the inkjet print cartridge of
Fig. 1.
Fig. 3 is a top plan view of the headland area of the inkjet print cartridge of Fig.
1.
Fig. 4 is a top perspective view, partially cut away, of a portion of the printhead
assembly showing the relationship of an orifice with respect to a vaporization chamber,
a heater resistor, and an edge of the substrate.
Fig. 5 is a schematic cross-sectional view of a printhead assembly and the print cartridge
as well as the ink flow path around the edges of the substrate.
Fig. 6 is a top plan view of a magnified portion of the printhead assembly showing
the relationship of ink channels, vaporization chambers, heater resistors, the barrier
layer and an edge of the substrate.
Fig. 7 is a schematic diagram showing the ink flow path from the ink reservoir to
the printhead.
Fig. 8 is a perspective view of an embodiment of manifold area for the inkjet print
cartridge.
Fig. 9 is a top plan view of the manifold area of Figure 8.
[0023] Referring to Fig. 1, an inkjet print cartridge 10 for mounting in the carriage of
an inkjet printer includes a printhead 14 and an ink reservoir 12, which may be a
"integral" reservoir, "snap-on" reservoir, or a "reservoir" for receiving an ink from
an off-axis ink reservoir. Print cartridge 10 includes snout 11 which contains an
internal standpipe 51 (shown in Fig. 8) for transporting ink to the printhead from
the reservoir 12. The printhead 14 includes a nozzle member 16 comprising nozzles
or orifices 17 formed in a circuit 18. The circuit 18 includes conductive traces (not
shown) which are connected to the substrate electrodes at windows 22, 24 and which
are terminated by contact pads 20 designed to interconnect with printer providing
externally generated energization signals to the printhead for firing resistors to
eject ink drops. Printhead 14 has affixed to the back of the circuit 18 a silicon
substrate 28 (not shown) containing a plurality of individually energizable thin film
resistors. Each resistor is located generally behind a single orifice 17 and acts
as an ohmic heater when selectively energized by one or more pulses applied sequentially
or simultaneously to one or more of the contact pads 20.
[0024] Fig. 2 shows the print cartridge 10 of Fig. 1 with the printhead 14 removed to reveal
the headland pattern 50 used in providing a seal between the printhead 14 and the
print cartridge body 15. Fig. 3 shows the headland area in an enlarged top plan view.
Shown in Figs. 2 and 3 is a manifold 52 in the print cartridge 10 for allowing ink
from the ink reservoir 12 to flow to a chamber adjacent the back surface of the printhead
14. The headland pattern 50 formed on the print cartridge 10 is configured so that
a bead of adhesive (not shown) dispensed on the inner raised walls 54 and across the
wall openings 55 and 56 will form an ink seal between the body 15 of the print cartridge
10 and the back of the printhead 14 when the printhead 14 is pressed into place against
the headland pattern 50.
[0025] Referring to Fig. 4, shown is an enlarged view of a single vaporization chamber 72,
thin film resistor 70, and frustum shaped orifice 17 after the substrate is secured
to the back of the circuit 18 via the thin adhesive layer 84. Silicon substrate 28
has formed on it thin film resistors 70 formed in the barrier layer 30. Also formed
on the substrate 28 are electrodes (not shown) for connection to the conductive traces
(not shown) on the circuit 18. Also formed on the surface of the substrate 28 is the
barrier layer 30 in which is formed the vaporization chambers 72 and ink channels
80. A side edge of the substrate 28 is shown as edge 86. In operation, ink flows from
the ink reservoir 12 around the side edge 86 of the substrate 28, and into the ink
channel 80 and associated vaporization chamber 72, as shown by the arrow 88. Upon
energization of the thin film resistor 70, a thin layer of the adjacent ink is superheated,
causing explosive vaporization and, consequently, causing a droplet of ink to be ejected
through the orifice 17. The vaporization chamber 72 is then refilled by capillary
action.
[0026] Shown in Fig. 5 is a side elevational cross-sectional view showing a portion of the
adhesive seal 90, applied to the inner raised wall 54 portion of the print cartridge
body 15 surrounding the substrate 28 and showing the substrate 28 being bonded to
a central portion of the circuit 18 on the top surface 84 of the barrier layer 30
containing the ink channels and vaporization chambers 72. A portion of the plastic
body 15 of the printhead cartridge 10, including raised walls 54 is also shown.
[0027] Fig. 5 also illustrates how ink 88 from the ink reservoir 12 flows through the standpipe
51 formed in the print cartridge 10 and flows around the edges 86 of the substrate
28 through ink channels 80 into the vaporization chambers 72. Thin film resistors
70 are shown within the vaporization chambers 72 . When the resistors 70 are energized,
the ink within the vaporization chambers 72 are ejected, as illustrated by the emitted
drops of ink 101, 102.
[0028] In Fig. 6, vaporization chambers 72 and ink channels 80 are shown formed in barrier
layer 30. Ink channels 80 provide an ink path between the source of ink and the vaporization
chambers 72. The flow of ink into the ink channels 80 and into the vaporization chambers
72 is around the long side edges 86 of the substrate 28 and into the ink channels
80. The relatively narrow constriction points or pinch point gaps 145 created by the
pinch points 146 in the ink channels 80 provide viscous damping during refill of the
vaporization chambers 72 after firing. The pinch points 146 help control ink blow-back
and bubble collapse after firing to improve the uniformity of ink drop ejection. The
addition of "peninsulas" 149 extending from the barrier body out to the edge of the
substrate provided fluidic isolation of the vaporization chambers 72 from each other.
The definition of the various printhead dimensions are provided in Table I.
TABLE I
DEFINITION OF INK CHAMBER DIMENSIONS |
Dimension |
Definition |
A |
Substrate Thickness |
B |
Barrier Thickness |
C |
Nozzle Member Thickness |
D |
Orifice/Resistor Pitch |
E |
Resistor/Orifice Offset |
F |
Resistor Length |
G |
Resistor Width |
H |
Nozzle Entrance Diameter |
I |
Nozzle Exit Diameter |
J |
Chamber Length |
K |
Chamber Width |
L |
Chamber Gap |
M |
Channel Length |
N |
Channel Width |
O |
Barrier Width |
U |
Shelf Length |
[0029] The frequency limit of a thermal inkjet print cartridge is limited by resistance
in the flow of ink to the nozzle. However some resistance in ink flow is necessary
to damp meniscus oscillation. Ink flow resistance is intentionally controlled by the
pinch point gap 145 gap adjacent the resistor. An additional component to the fluid
impedance is the entrance to the firing chamber. The entrance comprises a thin region
between the nozzle member 16 and the substrate 28 and its height is essentially a
function of the thickness of the barrier layer 30. This region has high fluid impedance,
since its height is small. The dimensions of the various elements formed in the barrier
layer 30 shown in Fig. 6 for this example are identified in Table II below.
Table II
INK CHAMBER DIMENSIONS IN MICROMETRES |
Dimension |
Minimum |
Nominal |
Maximum |
A |
600 |
625 |
650 |
B |
19 |
25 |
32 |
C |
25 |
50 |
75 |
D |
|
84.7 |
|
E |
1 |
1.73 |
2 |
F |
30 |
35 |
40 |
G |
30 |
35 |
40 |
I |
20 |
28 |
40 |
J |
45 |
51 |
75 |
K |
45 |
51 |
55 |
L |
0 |
8 |
10 |
M |
20 |
25 |
50 |
N |
15 |
30 |
55 |
O |
10 |
25 |
40 |
U |
0 |
90-130 |
270 |
[0030] The nozzle member 16 in circuit 18 is positioned over the substrate structure 28
and barrier layer 30 to form a printhead 14. The nozzles 17 are aligned over the vaporization
chambers 72. Preferred dimensions A, B, and C are defined as follows: dimension A
is the thickness of the substrate 28, dimension B is the thickness of the barrier
layer 30, and dimension C is the thickness of the nozzle member 16. Further details
of the printhead architecture are provided in U.S. Application Serial No. 08/319,893,
filed October, 6, 1994, entitled "Barrier Architecture for Inkjet Printhead;" which
is herein incorporated by reference.
[0031] From Table II it can be seen that the nominal channel width of 30 micrometres and
nominal channel height of 25 micrometres, allows for channel blockage by very small
bubble diameters.
[0032] Fig. 7 shows how ink containing dissolved gases flows from the ink reservoir 12 of
the ink cartridge 10 through filters 92 along ink flow path 88 through standpipe 51
in the snout 11, into manifold 52, around the edge 86 of substrate 28, along ink channels
80 and into vaporization chambers 72 before being ejected out of the nozzles 17. During
operation, warm thermal boundary layers of ink 88 form adjacent the substrate 28.
Therefore, dissolved gases in the thermal boundary layer of the ink 88 behind the
substrate 28 tend to form and diffuse into the bubbles 89. Also, bubbles 91 tend to
form at the corners and edges of the walls 55 along the ink flow path 88. In addition,
the region between the manifold 52 and substrate 28 acts as an accumulator or bubble
trap. This configuration amounts to a chamber on the ink flow path 88 with an entrance
and an exit. The average ink flow rate, in terms of volume ink per cross section of
area per second, is smaller within the chamber than at the entrance or at the exit.
The entrance edge of the chamber will act as a gas generating site because of its
sharpness and because of the discontinuity of ink flow over the edge. Bubbles will
be generated in this chamber and when they become large enough they get moved along
toward the ink chamber. If the chamber allows bubbles to grow larger than the diameter
of subsequent ink passageways which may then become blocked. These bubbles choke the
flow of ink to the vaporization chambers 72, especially at high ink flow rates. Ink
flow rate increase with drop volume, number of nozzles, firing frequencies and power
or heat input. High flow rates result in causing some of the nozzles 17 to temporarily
become inoperable. Although the total amount of dissolved gases contained within the
fluid volume of the boundary layer is small, in reality, all of the ink in the reservoir
12 will eventually flow along ink path 88 over the lifetime of the print cartridge
10. If all, or even some, of the dissolved gas contained within the ink reservoir
12 outgasses, substantial bubbles will form. When the bubbles become large enough
they get moved along toward the ink chamber. If the bubbles grow larger than the diameter
of subsequent ink passageways, the passageways may become blocked and choke the flow
of ink to the vaporization chambers 72. This results in causing some of the nozzles
17 to temporarily become inoperable.
[0033] Bubbles in the ink near the printhead 14 of an inkjet print cartridge 10 is one of
the most critical problems that impairs the performance of the print cartridge. Bubbles
arise from several causes: (1) bubbles are trapped in the ink feed channels during
filling and priming of the print cartridge and (2) bubbles are formed at bubble "seed
sites" in the fibrous carbon-filled material of walls 57, 58, 60 of the print cartridge
body 15 during operation. As the ink is heated during printing, dissolved air outgasses
from the ink and is accreted onto these trapped bubbles and seed sites, resulting
in bubbles that grow over time. The bubbles block the nozzles 17 from ejecting ink
and if the blockage is large enough it can cause the entire printhead 14 to suffer
"global starvation." Bubbles have been a problem in the past, but they are a much
more serious problem in a 600 dot per inch ("dpi") printhead. This is due primarily
to the reduced size of the ink flow channels 80 and nozzles 17 diameter as set forth
in the above description with respect to Fig. 6 and accompanying Table II. However,
this is also due to the higher firing frequencies and consequent increased ink flow
rates. Because the venturi forces that pull bubbles toward the firing chambers are
now higher, the tendency for bubbles to interfere with nozzle operation is greater.
[0034] An important aspect of bubble control is the design of a bubble tolerant internal
cartridge geometry. Until recently inkjet technology has been characterized by relatively
low resolution, low frequency printing. At these ink flow rates bubbles do not typically
cause starvation effects. However, for resolutions at or above 600 dpi and drop ejection
frequencies at or above 12 kHz, the relative ink flow rate can he higher by a factor
of 3 or more. Bubbles in the ink manifold region adjacent to the ink ejectors will
typically expand sufficiently to induce starvation effects at this flow rate and the
associated temperature rise. Unfortunately, this problem is also characterized by
"thermal runaway" such that attempting to energize heater resistors during a period
of bubble-induced starvation fails to result in drop ejection which is the main path
of heat flux out of the printhead.
[0035] In prior printhead manifold architectures the printhead is located adjacent to the
manifold walls. This close proximity enables bubbles that grow during operation to
become trapped in the ink channels. During subsequent operation the pressure drop
and temperature rise during high duty cycle printing cause these bubbles to expand
such that ink flow to ink ejectors is cut off. This failure mode is commonly known
as starvation, or more specifically as bubble-induced starvation. It is manifested
during printing as a marking pattern which is complete at the beginning of a swath
but which fades or abruptly stops within the early portion of the swath. Because this
failure mode develops with continued operation it is a reliability problem which cannot
be initially tested at the printhead manufacturing site. Though initial bubbles can
be prevented or eliminated through appropriate ink fill and priming processes, the
chance that a bubble is ingested through a nozzle during operation cannot be prevented.
Therefore, the printhead and ink manifold architecture must be designed to be tolerant
of bubbles.
[0036] Most thermal inkjet devices are designed to operate in an orientation such that drops
are fired in a direction substantially parallel with the acceleration vector of gravity.
As a result, the buoyancy force on bubbles in the manifold region will tend to pull
them away from the ink ejectors. However, bubbles can become large enough to become
trapped before their buoyancy force would overcome the surface adhesion forces to
the ink manifold walls or printhead surfaces.
[0037] The preferred embodiment described herein creates an ink manifold geometry of a size
and shape sufficient for outgassed bubbles to float away during the course of normal
operation from the narrow region where starvation can be induced.
[0038] The areas addressed by the design of the preferred embodiment are the areas around
the substrate, headland or manifold, standpipe and filter. The goals are to minimize
dead spaces, streamline the geometry for fluid flow to avoid trapping bubbles during
initial priming and to provide a clear path to allow for buoyancy to maximize the
easy escape of bubbles, in the direction 95 shown in Fig. 7 which coincides with the
ink flow path 88, but in the opposite direction. The bubbles flow from the printhead
area into the ink manifold 52 and then float through standpipe 51 and into the filter
cage area 68. Since the print cartridge prints with the nozzles downward, the ink
manifold area behind the printhead substrate was redesigned to provide clear space
under the substrate to allow bubbles to easily escape upward away from the printhead
area.
[0039] The preferred manifold design is shown in perspective view in Fig. 8 and in top plan
view in Fig. 9. The manifold area 52 was made deeper by lengthening or deepening upper
manifold walls 57 to between approximately 2 and 3 mm from 0.5 mm and increasing the
angle of lower manifold walls 58 from the bottom surface of the substrate 28 to a
range of approximately 20 to 30 degrees from horizontal, making the manifold walls
58 steeper and thus, the manifold 52 deeper than in previous ink cartridge designs,
thus making it easier for bubbles to drift upward into standpipe 51 and away from
the nozzles 17 and ink channels 80. The junction 59 between lower manifold wall 58
and the internal wall 60 of standpipe 51 was rounded to make it easier for bubbles
to enter the standpipe 51 from the manifold 52.
[0040] The corners 62 were rounded to help prevent the trapping of bubbles and fillets 63
were also formed in the corner of upper manifold walls 57 and lower manifold walls
58 in the manifold 52 to help prevent the trapping of bubbles. The length of substrate
supports 64, 65 was reduced to accommodate a longer standpipe and the ends of the
substrate supports were rounded. Also, the side walls 66 of substrate supports 64,
65 were sloped downward at an angle of approximately 50 to 60 degrees, to allow the
adhesive to flow away from substrate 28 and prevent the adhesive from trapping of
bubbles. For the same reason walls 67 of the manifold were sloped downward at an angle
of approximately 70 to 75 degrees.
[0041] The internal cross-section of the standpipe 51 was enlarged from approximately 15
to 20 square millimeters, in part by minimizing the wall thickness of the standpipe
51. The shape of internal wall 60 of standpipe 51 was modified into an approximation
of an elliptical cylinder with tangential circular cylindrical surfaces while maintaining
the desired taper angle of approximately 2 degrees. The external wall (not shown)
of the standpipe 51 was also modified into approximately the same shape as the inner
wall 60 of the standpipe 51 and was given a reverse taper of approximately 6 degrees
to better secure the inner frame to the standpipe.
[0042] Referring also to Fig. 7, the exit area 61 of standpipe 51 into filter cage area
68 (shown in Fig.7) was maximized utilizing a slightly divergent profile. The amount
of the inner frame 69 material extending into standpipe 51, below the filter cage
area 68 and where the ink reservoir bag 93 is attached to inner frame 69, was minimized
and tapered appropriately. Further details regarding the inner frame 69 and filter
cage area 68 which are located above the standpipe 51 are set forth in U.S. Application
Serial No. 07/995,109, filed December 22, 1992, entitled TWO MATERIAL FRAME HAVING
DISSIMILAR PROPERTIES FOR THERMAL INK-JET CARTRIDGE.
[0043] Experiments verified that the preferred manifold design allows the bubbles in the
ink channels, manifold area and standpipe to migrate more easily upward to regions
of the ink cartridge where the presence of bubbles is not damaging to the operation
of the printhead. Equally important, the new manifold design greatly reduced the tendency
of bubbles in the ink manifold region adjacent to the ink ejectors to expand sufficiently
to induce starvation effects at high ink flow rates and temperature rise. Also, bubbles
tend not to cause starvation even the bubbles are free to expand. Thus, performance
has been increased over the life of the print cartridge with fewer ink channel bubble
blockages than previous manifold designs.
[0044] It will be understood that other embodiments may only address one or more of the
design areas addressed by the preferred embodiment, in dependence upon the needs of
the particular applications.
[0045] The disclosures in United States patent application no. 08/550,143, from which this
application claims priority, and in the abstract accompanying this application, are
incorporated herein by reference.
1. A method of ink delivery in an inkjet print cartridge comprising the steps of:
storing a supply of ink in a reservoir (12);
transporting ink from the reservoir through a manifold (52) to ink firing chambers
(72); and
providing contoured walls (57, 58) along the manifold to allow bubbles (101) to escape
from the manifold away from the ink firing chambers towards the reservoir without
interfering with the replenishment of ink into the ink firing chambers.
2. A method according to claim 1, including the step of providing the manifold with upper
manifold walls (57) having a depth between 2 and 3 mm.
3. A method according to claim 1 or 2, including the step of providing the manifold with
lower manifold walls (58) having an angle of between 20 to 30 degrees relative to
the normal to the direction of transport of ink from the manifold to the reservoir.
4. A method according to claim 1, 2 or 3, including the step of providing a standpipe
(51) coupling the manifold to the reservoir and providing the standpipe with an internal
wall (60) joined to the or a lower manifold wall by a rounded junction (59).
5. An inkjet print cartridge comprising an ink reservoir (12); means for transporting
ink from the reservoir through a manifold (52) to ink firing chambers (72); wherein
contoured walls (57, 58) are provided along the manifold to allow bubbles (101) to
escape from the manifold away from the ink firing chambers towards the reservoir without
interfering with the replenishment of ink into the ink firing chambers.
6. An inkjet print cartridge according to claim 5, wherein the manifold includes upper
manifold walls (57) having a depth between 2 and 3 mm.
7. An inkjet print cartridge according to claim 5 or 6, wherein the manifold includes
lower manifold walls (58) having an angle of between 20 to 30 degrees relative to
the transporting means.
8. An inkjet print cartridge according to claim 5, 6 or 7, including a standpipe (51)
coupling the manifold to the reservoir and including an internal wall (60) joined
to the or a lower manifold wall by a rounded junction (59).
9. An inkjet print cartridge according to claim 8, wherein the standpipe (51) has an
internal cross-section between 15 and 20 millimetres.
10. An inkjet print cartridge according to any one of claims 5 to 9, including a substrate
(28) coupled to a housing of the inkjet cartridge by substrate supports (64, 65),
the substrate supports including side walls sloping at an angle between 50 and 60
degrees relative to ink movement in the manifold.