Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
1999-10-25
2001-09-25
Yockey, David F. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
C222S105000, C222S386500
Reexamination Certificate
active
06293666
ABSTRACT:
FIELD OF THE INVENTION
This present invention relates to a pressure-adjustment means, and 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 do 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 ink-jet and laser printers, and each of which has its strengths and weaknesses when compared to the other. Ink-jet printers cost less, while laser printers possess superior printing quality. Although ink-jet printers are more attractively 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 a liquid (i.e., ink) as its printing medium, the physical properties of liquids can adversely affect the printing quality. For 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-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 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 in preventing 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 a 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 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 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. Pat. No. 5,409,134 discloses a pressure-adjustment means which comprises certain air-bag and elastic springs that can respond to changes in 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 an 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 is shown in
FIGS. 1 and 2
, and comprises a pair of elastic springs
6
and an inelastic but inflatable air-bag
20
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 FIG.
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 of the ink chamber
3
changes.
In reference to
FIG. 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 comprised 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 a 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 the 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 elastic air-bag for adjusting the back pressure inside the ink chamber.
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 fewer constituent elements or superior pressure-adjustment means to make an improvement. The pressure-a
Chou Chin-Yi
Ho Jing-Yuan
Lin Fu-San
Mou Tse-Chi
Bacon & Thomas
Microjet Technology Co., Ltd.
Yockey David F.
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