Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02286954 2003-08-21
INK-JET CARTRIDGE WITH PRESSURE-ADJUSTMENT MEANS
FIELD OF THE INVENTION
This present invention relates to a pressure-adjustment means, especially to a
pressure
adjusting means for adjusting the pressure in the ink chamber inside an ink
jet cartridge.
DESCRIPTION OF THE PRIOR ART
In this modern era of massive information and ubiquitous presence of
computers, not only
is the use of computers in heavy demand, but the quality and speed of
computers also need
to meet stringent expectation. This demand for performance also extends to the
computer
peripherals. As a result, not only are novel peripherals emerge daily, but
their
performances also improve constantly. Of all the peripherals, the most common
one is
probably the printer, which has become almost an indispensable part of any
computer
system.
The currently available printers in the market can be classified into three
types based on
their methods of printing: dot-matrix, ink jet and laser printers. Although
dot-matrix
printers are lower priced, as their printing speed and printing quality are
both inferior, they
have been unable to compete against ink jet or laser printers in the market
and are
relegated to specific tasks only. In the current market are predominantly
inkjet and laser
printers, and each of which has its strengths and weaknesses when compared vis-
a-vi the
other: ink jet printers cost less, while laser printers possess superior
printing quality.
Although ink jet printers are more amactively priced, however, their inferior
printing
quality and speed make them less competitive when more sophisticated printing
is being
demanded. Generally speaking, as ink jet printers use liquid (i.e., ink) as
its printing
medium, the physical properties of liquids can adversely affect the printing
quality. For
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instance, negative effects can arise from the flexibility of ink, turbulence,
air-bubbles in
the ink and uncontrollable ink flow direction due to smaller viscosity
coefficient, etc.
Included in the design of ink jet printing is a means for controlling the
release of ink
droplets from the ink chamber to the medium surface. As described in the prior
art, ink-
s jet printing is accomplished by the use of a printhead, attached to the ink
jet cartridge,
which releases ink in spurts in response to control signals.
Printheads generally employ either of two methods to release ink spurts: by
means of
thermal bubbles or by a piezoelectricity. In the thermal bubbles method, a
thermal film
resistor in the printhead heats up a small portion of the ink to almost
boiling temperature
and the gaseous ink (i.e., the ink droplets) is then released through the
orifices. In the
piezoelectricity method, a piezoelectric element in the printhead responds to
the control
signals and generates pressure waves by compressing the ink that forces the
ink to gush
through the orifices.
Although the two prior art ink jet printing methods can effectively release
ink from the
ink chamber in droplets, they are ineffective to prevent ink leakage when the
printer is in
its idle state. Therefore, the conventional design is in need of a technique
that can
prevent ink leakage during the idle state. This may be achieved by creating
within the
ink chamber certain slight "back pressure." This back pressure refers to
pressure in the
condition of partial vacuum within the ink chamber or pressure in the chamber
being less
than atmospheric pressure, for the purpose of preventing free flow of ink
through the
printhead. Additionally, back pressure increase refers to increasing the
pressure
difference between the pressure inside the ink chamber and the atmospheric
pressure.
The back pressure in the ink jet cartridge must be able to prevent ink leakage
at all times,
while it can not be so great as to prevent the ability to release the ink
droplets.
Furthermore, the design of the ink jet cartridge must be such that the
cartridge remains
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operative under any condition. Specifically, when the printhead is idle, the
ink should
be held inside, and when the printing is in progress, spraying of ink should
be unhindered.
When ink level drops low because of consumption, from the ideal gas law, the
increased
space volume should lead to decreased back pressure in the ink chamber. And if
the
S back pressure mentioned previously is not adjusted accordingly, the
printhead would be
unable to overcome the increased back pressure and incapable of releasing the
ink
droplets in spurts.
The U.S. Patent No. 5,409,134 discloses a pressure-adjustment means which
comprises of
certain air-bag and elastic springs that can respond to changes of back
pressure inside the
ink chamber. This air-bag can move between the smallest ink volume setting and
the
biggest ink volume. It can adjust the volume of air inside the ink chamber to
compensate for the changes in the ink volume, so that the back pressure inside
the ink
chamber can be maintained within a pre-determined range such that ink would
not leak
when in idle state and can spurt outwards of the printhead when heated.
For instance, when the air pressure in the surrounding decreases so that the
difference
between the atmospheric pressure and the back pressure is reduced, the
pressure-
adjustment means will activate to increase the back pressure for holding in
the ink by
increasing the volume of the ink chamber.
The pressure-adjustment means disclosed by said U.S. patent comprises of a
pair of
elastic springs 6 and an inelastic but inflatable air-bag attached thereon.
The springs 6
and the air-bag 20 are installed inside the ink chamber 3 of the ink jet
cartridge, wherein
the air inside the air-bag can ventilate with the air outside of the ink jet
cartridge as show
in Figure 1. The springs 6 work with the air-bag 20 and enable the air-bag 20
to inflate
or deflate in response to the changes in pressure. Such inflation/deflation
takes place
when the pressure inside the ink chamber 3 changes as well as when the
pressure outside
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of the ink chamber 3 changes.
In reference to Figure 2, the inflation of air-bag 20 will push against the
springs 6 which
in turn react with an elastic force that pushes back on the air-bag, so that
the elastic
springs 6 and air-bag 20 remain engaged in a state of equilibrium. The
inflation/deflation of the air-bag adjusts the volume inside the ink chamber
3, and thereby
constrains the back pressure inside the ink chamber 3 within the normal
operative range,
so that the ink jet cartridge remains operative in spite of changes in the
external air
pressure or consumption of the ink.
However, in employing the pressure-adjustment means comprising of the
combination of
elastic springs 6 and the attached air-bag, in order to produce the desired
result, the elastic
constant of the elastic springs 6 and the inflation/deflation capability of
the air-bag 20
must both be precisely controlled in the manufacturing process. In case of
weak
engagement between the elastic springs 6 and the air-bag 20 so that slack
therebetween
arises, the sensitivity to detect the changes in the pressure would then be
reduced. As
there is a stringent demand on the exact physical properties of the elastic
springs 6 and the
air-bag 20 in manufacturing process, the product acceptance rates are thus
lowered. In
view of such, the present invention provides a method, which is superior to
the prior art in
having more effective quality control during the manufacturing process and
having higher
product acceptance rates, which are achieved by reducing the number of
elements
involved that simplifies the structure. The present invention thus has
practical
implication for the industry.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide a single element of
elastic air-
bag for adjusting the back pressure inside the ink chamber.
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In view of the requirement in achieving exactness in handling the physical
properties of
the constituents, which effectively lowers the product acceptance rates, the
present
invention proposes to use less constituent elements or superior pressure-
adjustment means
to make improvement. The pressure-adjustment means of the present invention
refers to
an elastic air-bag installed within the ink jet cartridge, wherein the air
inside the air-bag is
in circulation with the air outside the ink jet cartridge. When the pressure
difference
between the air pressure inside the air-bag and the back pressure in the ink
chamber
undergoes changes, the elastic air-bag automatically inflates or deflates
itself by virtue of
its own elasticity, so as to change the volume inside the ink chamber that
maintains the
back pressure to within a certain range. This then prevents any ink leakage
during idle
state, and at same time, enables smooth releasing of ink droplets by the
printhead during
printing.
BRIEF DESCRIPTION OF THE DRAWINGS
The following drawings can further illustrate the characteristics of the
present invention:
Figure 1. A cross-sectional view of the prior art pressure-adjustment means,
its combined elastic springs and air bag inside the ink jet cartridge.
Figure 2. A cross-sectional view of the pressure-adjustment means shown in
Figure 1, as its air-bag inflates that deforms the elastic springs.
Figure 3. A cross-sectional view of the ink jet cartridge of the present
invention, wherein the pressure-adjustment means employs an
elastic air-bag within the ink jet cartridge.
Figure 4. A cross-sectional view of the pressure-adjustment means disclosed
by the present invention, when its elastic air-bag is in the inflation
state.
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Figure 5. A cross-sectional view of the pressure-adjustment means disclosed
by the present invention in another embodiment.
Numbering Scheme
1. top lid, 10. connecting body,
2. cartridge housing, 11. through hole,
3. ink chamber, 20. air-bag,
4. central opening, 21. neck,
5. base, 22. elastic portion,
6. elastic springs, 23. elastic air-bag.
7. ink,
DETAILED DESCRIPTION OF THE INVENTION
First, referring to Figure 3 for the embodiment of the present invention, the
ink jet
cartridge of the present invention comprises of a top lid 1 and a cartridge
housing 2.
When the top lid 1 is fastened unto the cartridge housing 2, the internal
space thus formed
defines the volume of the ink chamber 3 inside the ink jet cartridge that
contains ink
therein. The printhead (not shown) installed at the bottom portion of the ink
chamber
possesses a plurality of open orifices whereby ink within the ink chamber 3
spurts
outwards by virtual of the heat-expansion or piezoelectricity methods
mentioned
previously. As shown in Figure 3, the pressure-adjustment means of the present
invention is situated mostly inside the ink jet cartridge, one end of the
means connects
with the top lid 1 while the other end suspends within the ink jet cartridge.
This
pressure-adjustment means comprises of a connecting body 10 and an elastic air-
bag 23,
wherein the air-bag 23 comprises of a neck portion 21 and an elastic portion
22 and the
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neck portion 21 is being tightly bundled at the bottom of the connecting body
10. The
connecting body 10 having a through hole 11 and enables the process of air
ventilation
between the air inside the elastic air-bag connected therewith and the
external air. The
diameter of the through hole is approximately between l.3mm and O.OSmm.
The elastic air-bag 23 acts similar to a inflatable ball as shown in Figure 3.
The inside of
the elastic air-bag 23 is hollow, which expands or contracts in response to
the pressure
changes, and its respective external surface is in contact with the ink and
the internal
space of the ink jet cartridge. This elastic air-bag can be made from high-
polymer
materials, such as latex, silicon gel or rubber, with non-linear elastic
coefficient and
maximum yield strength at between 5600-6400 kg/cm2.
Referring again to Figure 3, a central opening 4 in the top lid 1 of the ink
jet cartridge
receives the connecting body 10 for the pressure-adjustment means of the
present
invention and enables the connecting body 10 to tightly fasten onto the top
lid 1. As the
diameter of the through hole 11 is between 1 mm to 3 mm, far smaller than the
diameter
of the air-bag 23, the ability of the air-bag 23 to make adjustments by
inflation/deflation
will not be negatively affected by its sensitivity to the influence of the
atmospheric
pressure. In the normal operating situation, namely, when the ink jet
cartridge is open
and installed on the ink jet printer, if the external conditions change (e.g.,
rising
temperature or atmospheric pressure becoming less than 1 ATM,) so that the
back
pressure internal to the ink jet cartridge becomes greater than the
atmospheric pressure,
the elastic portion 22 of the air-bag 23 will decompress the air-bag 23 in
response to the
pressure difference and releases the internal air through the through hole 11.
The ink
level then lowers so that the pressure equilibrium inside the ink jet
cartridge is restored,
which prevents ink leakage.
Refernng to Figure 4, in the case where the ink level inside the ink chamber 3
lowers as
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the printing continues in progress, from the ideal gas law, the increased
volume inside the
closed ink jet cartridge will lead to decreased back pressure in the ink
chamber 3.
Therefore the pressure inside the air-bag 23 (atmospheric pressure) will be
greater than
the back pressure inside the ink chamber 3, and the elastic portion 22 will
inflate and
expand as shown. This expanded volume will cause the lowered ink level to rise
up so
that the original equilibrium state is restored. By virtue of the pressure-
adjustment
means of the present invention, under any circumstance, the ink jet cartridge
can maintain
its pressure in balance so as to ensure smooth ink flow during printing.
To further increase the sensitivity of the pressure-adjustment means to the
changes in
pressure, in another embodiment, an additional spring 30 is installed. In
Figure S, the
constituent elements of this second embodiment are similar to those of first
embodiment,
with the only difference being an additional spring 30. One end of the spring
is hooked
to the hook 31 at the bottom of cartridge housing 2, while the other end is
fastened to the
suspending end of the air-bag 23. The spring 30 creates an elastic force
pulling on the
air-bag 23, so that when either the external atmospheric pressure or the back
pressure
internal to the ink chamber 3 undergoes changes, the elastic portion 22 of the
air-bag 23
can respond even faster to such pressure changes and expand or contract
appropriately.
Those skilled in the art will also note that the suspending end of the air-bag
23 can also be
fastened to the bottom of the chamber housing 2 directly, so that a reactive
force is
created which provides the air-bag 23 greater sensitivity when undergoing
expansion.
After the elaboration of the preferred embodiments, those skilled in the art
should be able
to grasp the present invention and without departing from the scope and spirit
of the
claims, make various modifications. The present invention is not restricted to
the
preferred embodiment; for example, there is no specification on the shape of
the elastic
air-bag; any shape which can provide the needed elasticity is acceptable.
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EFFECTIVENESS OF THE INVENTION
The pressure-adjustment means of the present invention enables the ink-
cartridge to be
immune from the influences of external pressure changes or ink consumption and
remain
in normal operative state, and adjusts the back pressure of the ink chamber of
the ink jet
cartridge by a single element elastic air-bag such that the product acceptance
rates in the
manufacturing process can be effectively controlled.
In summary, the present invention possesses numerous useful features, and
effectively
improves upon the drawbacks of the prior art. It provides a practical and
reliable device
which is novel with utilitarian value.
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