Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
1999-04-07
2001-02-13
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
Reexamination Certificate
active
06186620
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a pressure control apparatus for an ink-jet pen. The apparatus will adjust the back pressure of ink in the reservoir of the inkjet pen within a suitable range when the ink is used gradually.
Drop-on-demand printing is a general method for controlling ink drops from an inkjet pen reservoir to a printing surface. The print heads typically use thermal bubble or piezoelectric pressure wave mechanisms for ejecting drops. A thermal 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. Though a drop-on-demand print head is effective for ejecting ink drops from a pen reservoir, it needs another control mechanism for preventing ink from permeating through the print head when the print head is inactive. Generally the control mechanism is to provide a slight back pressure at the print head to prevent ink leakage from the pen whenever the print head is inactive. The term “back pressure” means the partial vacuum within the pen 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 in the partial vacuum.
The back pressure at the print head must be strong enough for preventing ink leakage. However, it must not be so strong that the print head is unable to overcome the back pressure to eject ink drops. Moreover, the back pressure must be adjusted itself according to the variance of environmental air pressure. For example, during air transport of an inkjet pen, the ambient air pressure decreases as the aircraft gains altitude, a correspondingly greater amount of back pressure is needed to keep ink from leaking through the print head. On the other hand, the back pressure within an ink-jet pen reservoir is also affected by “operational effects”. As the print head is activated to eject ink drops, the consequent depletion of ink from the reservoir increases the reservoir back pressure. If the back pressure increase is not well regulated, the ink drops will reduce their size, lose printing quality or even fail to be ejected because the print head is unable to overcome the increased back pressure.
In the prior arts, a back pressure control mechanism is an accumulator mounted inside the ink-jet pen reservoir. The accumulator is usually an expandable bag capable of changing its volume between a minimum volume and a maximum volume, therefore to adjust the reservoir volume for storage of ink, and to regulate the back pressure of the reservoir. For example, when the ambient air pressure decreases, the expandable bag will then be contracted to reduce its volume and relatively to increase the reservoir volume for storage of ink, and therefore to increase the back pressure of reservoir for preventing ink from leakage.
A prior art is disclosed in U.S. Pat. No. 5,409,134. As shown in FIG.
1
and
FIG. 2
, an accumulator
14
is configured to fit into an ink-jet pen
10
that includes a cap
12
, a reservoir
11
having rigid side walls
111
and a bottom wall
112
that are configured to hold a quantity of ink. A thermal-bubble type print head
13
is fit into the bottom wall
112
of the reservoir
11
for ejecting ink drops from the reservoir
11
to an unshown print paper. The accumulator
14
includes an expandable bag
142
a
,
142
b
that is mounted to a spring
141
a
,
141
b
. The bag
142
a
,
142
b
and spring
141
a
,
141
b
are aligned with pins
147
and fastened via a base
145
to the cap
12
in a manner that the interior of the bag
142
a
,
142
b
is in fluid communication with ambient air through a breather strip
148
and an air duct
149
. With the accumulator
14
in place, the reservoir
11
is filled with ink
50
with a slight (minimum) back pressure established within the pen reservoir
11
. The minimum back pressure is the back pressure necessary to keep ink
50
from leaking through the print head
13
when the print head is inactive.
As the pen
10
is used for printing, the air pressure within the reservoir
11
decreases (hence, the back pressure increases) as ink is depleted. As shown in
FIG. 1
, during printing, the bag
142
a
,
142
b
expands as a result of the back pressure increase. The bag expansion decreases the volume of the reservoir
11
to maintain the reservoir back pressure within a range such that the print head
13
is able to continue ejecting ink from the reservoir
11
. As shown in
FIG. 2
, if the ambient pressure should thereafter decrease (for example, during air transport of the pen), the bag
142
a
,
142
b
will contract to increase the reservoir volume so that the back pressure within the reservoir
11
, relative to ambient, does not drop to a level that permits ink
50
to leak from the print head
13
.
From the aforesaid function of the accumulator
14
, we may find that the maximum volume of the bag
142
a
,
142
b
is limited. That is, when the bag
142
a
,
142
b
has expanded to its maximum volume, the further depletion of the ink
50
will increase the back pressure of the reservoir
11
to an extent that the print head
13
cannot overcome the pressure to inject ink drops and the ink
50
cannot be fully depleted.
To solve the aforesaid problem, U.S. Pat. No. 5,526,030 discloses a bubble generator as a back pressure control mechanism. As shown in FIG.
3
and
FIG. 4
, a bubble generator
20
is installed in the bottom
112
a
of a reservoir
11
a
of an ink-jet pen
10
. The bubble generator
20
consists of a tubular boss
21
and a sphere
22
mounted concentrically within the boss. The outside diameter of the sphere
22
is smaller than the inside diameter of the boss
21
to define an annular orifice
212
. The sphere
22
is maintained within the boss
21
by a number of raised ribs
211
formed around the interior of the boss
21
. In this manner the sphere
2
can be easily press fit into the boss
21
and firmly maintained in position by the ribs
211
. Additional unshown raised ribs are also provided to help maintaining the sphere
22
in position away from the inside wall of the boss
21
. The sphere
22
serves as a capillary member to maintain a quantity of ink within the boss
21
. As a result, even when the pen is oriented such that the boss is not submerged in the reservoir ink, a quantity of ink is trapped within the boss to provide a liquid seal. When the back pressure is within the desired range, the bubble generator
21
is sealed with a quantity of ink. However, when the back pressure exceeds the desired range, the back pressure overcomes the capillary forces of the liquid seal and allows the ambient air to bubble into the reservoir
11
a
to reduce the back pressure. When the back pressure returns to the appropriate level, the liquid seal reforms to prevent further ingression of the ambient air.
Therefore, the bubble generator
20
applied in the ink-jet pen
10
must have the capabilities of:
a) A suitable control of bubble ingression for maintaining a suitable back pressure of the reservoir. That is, after bubbles ingressing into the reservoir
11
a
and decreasing the back pressure, the bubble generator
20
has to stop the ingression at a right time in order to maintain a suitable back pressure of the reservoir
11
a
; and
b) A self-wetting function for the mechanism that when the ink
50
in the reservoir
11
a
has been depleted to an extent or the bubble generator
20
is not submerged in the reservoir ink due to any angular placement of the ink-jet pen
10
, the liquid seal should always functions to prevent bubble ingression and maintain a suitable back pressure of the reservoir
11
a.
As described above, since the volume of an expendable bag is limited. When the bag has expanded to its maximum volume, the further depletion of the ink will increase the back pressure of the reservoir to an extent that the print head cannot overcome the back pressure to eject ink drops
Hou I-Chung
Hsieh Shu-Cheng
Hsu Cheng-Wei
Lin Chi-Chien
Industrial Technology Research Institute
Le N.
Liauh W. Wayne
Nghiem Michael
LandOfFree
Ink pressure control apparatus for ink-jet pens does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ink pressure control apparatus for ink-jet pens, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ink pressure control apparatus for ink-jet pens will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2590728