Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
1999-09-27
2001-06-19
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
C347S086000
Reexamination Certificate
active
06247807
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an ink-jet cartridge for regulating the ink pressure within the ink reservoir of an ink-jet pen. The cartridge automatically controls the pressure difference inside and outside to prevent ink from leakage.
2. Related Art
In ink-jet printing, the common types of ink-jet control are heat bubble and piezoelectric pressure wave methods. A heat bubble type print head includes a thin-film resistor that is heated to cause sudden vaporization of a small portion of the ink. The rapid expansion of the ink vapor forces a small amount of ink through a print head orifice to a printing paper. Although conventional print heads are effective for ejecting ink drops from a reservoir, they need extra mechanisms for preventing ink from permeating through the print head when the print head is inactive. The common mechanism provides a slight back pressure at the print head to prevent ink leakage from the print head whenever the print head is inactive. The term “back pressure” used herein means the partial vacuum within the reservoir that resists the flow of ink through the print head. Back pressure is considered in the positive sense so that an increase in back pressure represents an increase the partial vacuum.
In the design of an ink-jet cartridge, the following requirements should be considered:
a) the back pressure at the print head must be at all times strong enough for preventing ink leakage. But the back pressure must not be so strong that the print head is unable to overcome the back pressure to eject ink droplets, or the size of the ink droplets and the print quality are influenced;
b) the back pressure at the print head must be varied according to the pressure of environment and maintained in a suitable range, for example, when the pressure of environment drops, the back pressure must be relatively higher to prevent ink leakage; and
c) the operating effect of the ink reservoir also influences the back pressure at the ink-jet cartridge. That is, the back pressure raises when the ink is used up, therefore, it must be suitably regulated to assure the ink ejection. Without regulation of this back pressure increase, the ink-jet pen will eventually fail because the print head will be unable to overcome the increased back pressure to eject ink drops.
In the current arts, the back pressure of the ink reservoir is regulated by an accumulator. The accumulator is generally an elastic bag varying its volume between a minimum volume position and a maximum volume position to regulate the ink reservoir volume and adjust the back pressure so that the back pressure remains within an operating range that is suitable for preventing ink leakage while permitting the print head to continue ejecting ink droplets.
As shown in
FIG. 1
, an accumulator
20
for an ink-jet cartridge
1
is disclosed by U.S. Pat. No. 5,409,134. The ink-jet cartridge
1
includes a reservoir
10
which has a rigid body
11
and a print head
30
located at the bottom of the reservoir
10
for providing ink
40
to the print media through a print head
30
. An accumulator
20
mounted inside the reservoir
10
and includes mainly a spring
21
a
,
21
b
; an expandable bag
22
a
,
22
b
which is formed of two thin flexible sheets
23
,
24
. The bag
22
a
,
22
b
is fastened via a fitment
25
having pins
27
and release patch
26
to the top of the rigid body
11
, and a breather strip
28
fixed between the flexible sheets
23
,
24
so that the interior of the bag
22
a
,
22
b
is in fluid communication with the ambient air through a duct
12
. With the accumulator
20
in place, the reservoir
10
is filled with ink
40
through an unshown sealable port. A slight back pressure is established within the reservoir
10
. The slight back pressure is the minimum amount of back pressure necessary to keep ink from leaking through the print head
30
when the print head is inactive.
As the cartridge
1
is used for printing, the air pressure within the reservoir
10
decreases (hence, the back pressure increases) as ink
40
is depleted. During printing, the bag
22
a
,
22
b
expands as a result of the back pressure increase. The bag expansion decreases the volume of the reservoir
10
to maintain the reservoir back pressure within a range such that the print head
30
is able to continue ejecting ink
40
from the reservoir
10
. If the ambient pressure should thereafter decrease (for example, during air transport of the cartridge), the bag
22
a
,
22
b
will contract to increase the reservoir volume so that the back pressure within the reservoir
10
, relative to ambient, does not drop to a level that permits ink
40
to leak from the print head
30
.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide an ink-jet cartridge which doesn't need a valve or a movable element to adjust the back pressure within the reservoir. The cartridge includes a back pressure chamber in which the level of ink will be self-adjusted to provide ink for ejection and prevent ink from leakage when the ambient air pressure drops.
The ink-jet cartridge according to the present invention includes:
an ink reservoir for storing ink and providing ink for ejection, the reservoir includes:
a rigid body, formed with rigid material, for storing ink;
a vent, located on top of the rigid body, communicated with the ambient air, for adjusting the air pressure inside the ink reservoir;
a print head for ejecting ink and printing;
a print ink chamber for preparing ink ready for the print head, the ink level of the chamber is normally lower than the ink level of the rigid body; and
a back pressure chamber, having one end fluid-communicated with the ink in the rigid body, and the other end fluid communicated with the print ink chamber via an overflow vent which is at a position higher than the ink level of the rigid body, a suitable back pressure is applied to the back pressure chamber and the print ink chamber so that, when printing, the increased back pressure at the print ink chamber sucks ink from the ink reservoir through the overflow vent into the print ink chamber; while, when not printing, the extra height of the ink in the back pressure chamber relative to the ink level of the ink reservoir balances the back pressure at the back pressure chamber and the print ink chamber to prevent ink leakage from the print head.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 5040002 (1991-08-01), Pollacek et al.
patent: 5409134 (1995-04-01), Cowger et al.
patent: 5682189 (1997-10-01), Takagi
Chen Huan-Kun
Wu Ji-chen
Yang Ming-hsun
Birch & Stewart Kolasch & Birch, LLP
Le N.
Vo Anh T. N.
WiserTek International Corp.
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