Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-11-29
2003-07-29
Barlow, John (Department: 2653)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S064000, C347S065000
Reexamination Certificate
active
06598961
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink-jet printhead. More particularly, the present invention relates to a bubble-jet type ink-jet printhead.
2. Description of the Related Art
Ink-jet printing heads are devices for printing a predetermined color image by ejecting a small droplet of printing ink at a desired position on a recording sheet. Ink ejection mechanisms of an ink-jet printer are generally categorized into two types: an electro-thermal transducer type (bubble-jet type), in which a heat source is employed to form a bubble in ink causing an ink droplet to be ejected, and an electro-mechanical transducer type, in which a piezoelectric crystal bends to change the volume of ink causing an ink droplet to be expelled.
Referring to
FIGS. 1A and 1B
, a conventional bubble-jet type ink ejection mechanism will now be described. When a current pulse is applied to a heater
12
consisting of resistive heating elements formed in an ink channel
10
where a nozzle
11
is located, heat generated by the heater
12
boils ink
14
to form a bubble
15
within the ink channel
10
, which causes an ink droplet
14
′ to be ejected.
There are multiple factors and parameters to consider in making an ink-jet printhead having a bubble-jet type ink ejector. First, it should be simple to manufacture, have a low manufacturing cost, and be capable of being mass-produced. Second, in order to produce high quality color images, the formation of minute, undesirable satellite ink droplets that usually trail an ejected main ink droplet must be avoided. Third, when ink is ejected from one nozzle or when ink refills an ink chamber after ink ejection, cross-talk with adjacent nozzles, from which no ink is ejected, must also be avoided. To this end, a back flow of ink in a direction opposite to the direction ink is ejected from a nozzle must be prevented during ink ejection. For this purpose, a second heater
13
as shown in
FIGS. 1A and 1B
is typically provided to prevent a back flow of the ink
14
. The second heater
13
generates heat sooner than the first heater
12
, which causes a bubble
16
to shut off the ink channel
10
behind the first heater
12
. Then, the first heater
12
generates heat, and the bubble
15
expands to cause the ink droplet
14
′ to be ejected. Fourth, for high-speed printing, a cycle beginning kit with ink ejection and ending with ink refill in the ink channel must be carried out in as short a period of time as possible. Fifth, a nozzle and an ink channel for introducing ink to the nozzle must not be clogged by a foreign material or by solidified ink.
The above requirements, however, tend to conflict with one another. Furthermore, the performance of an ink-jet printhead is closely associated with and affected by the structure and design of an ink chamber, an ink channel, and a heater, as well as by the type of formation and expansion of bubbles and the relative size of each component.
FIG. 2
illustrates a perspective, partial cutaway view of a conventional ink-jet printhead showing the internal structure of the ink-jet printhead, and
FIG. 3
illustrates a cross-sectional view of the conventional printhead shown in
FIG. 2
, taken along the line I—I for explaining how an ink droplet is ejected from the printhead. Referring to
FIG. 2
, the ink-jet printhead includes a substrate
20
, a wall
22
formed on the substrate
20
for providing an ink chamber
26
for containing ink, a heater
23
disposed in the ink chamber
26
for generating heat, and a nozzle plate
21
having an orifice
24
for ejecting an ink droplet. Ink is supplied to the ink chamber
26
through an ink channel
25
and to the orifice
24
in flow communication with the ink chamber
26
by capillary action.
Referring to
FIG. 3
, in this configuration, if current is applied to the heater
23
, the heater
23
generates heat to form a bubble B in ink, thereby filling the ink chamber
26
as shown in FIG.
3
. Then, the bubble B expands to exert pressure on the ink within the ink chamber
26
causing an ink droplet
28
to be ejected through the orifice
24
.
However, in the ink-jet printhead having the structure described above, a considerable amount of heat generated by the heater
23
is transferred and absorbed into the substrate
20
. It is desirable that the heat generated by the heater
23
be used to boil ink and form the bubble B. However, most of the heat is absorbed into the substrate
20
, and only a small amount of the heat is actually used to form the bubble B. This means that the heat energy supplied to generate the bubble B is wasted in heating the substrate
20
, thereby increasing energy consumption. Also, the ink-jet printhead has a problem in that the temperature of a head is significantly increased as a print cycle runs because the heat transferred to the substrate
20
in turn heats the head system. Furthermore, the heat flow into the substrate
20
causes the ink to be heated or cooled at a lower speed or cycle, thereby increasing the length of the cycle from formation to collapse of the bubble and thus decreasing print speed.
Typically, the amount of ink pushed away from a nozzle by a generated bubble is closely related to the print speed of an ink-jet printhead. In the ink-jet printhead having the conventional structure described above, the amount of ink that is pushed away from the orifice
24
is approximately the same as the amount of ink ejected by the bubble B, thereby making a print cycle longer and thus reducing the print speed of the printhead.
SUMMARY OF THE INVENTION
In an effort to solve the above problems, it is a feature of an embodiment of the present invention to provide a bubble-jet type ink-jet printhead configured so that a heater disposed within an ink chamber does not directly contact a substrate and further configured so that an ink channel is disposed inside the substrate thereby consuming less energy in operating the printhead, preventing a backflow of ink, and increasing the printing speed of the printhead.
Accordingly, the present invention provides a bubble-jet type ink-jet printhead including: a substrate; a nozzle plate separated from the substrate by a predetermined distance, the nozzle plate having an orifice for ejecting ink; a wall for closing the space between the substrate and the nozzle plate and for forming an ink chamber filled with ink therebetween; and a heater interposed between the substrate and the nozzle plate for dividing the ink chamber into a main ink chamber disposed above the heater and a secondary ink chamber disposed below the heater, the main ink chamber and the secondary ink chamber generating a main bubble and a secondary bubble, respectively, upon heating of the heater.
Preferably, a groove for forming the secondary ink chamber is formed in the substrate at a location corresponding to the heater. Additionally, it is preferable that the main ink chamber and the secondary ink chamber are in flow communication.
In another embodiment of the present invention, a bubble-jet type ink-jet printhead includes: a substrate; a nozzle plate separated from the substrate by a predetermined distance, the nozzle plate having an orifice for ejecting ink; a wall for closing the space between the substrate and the nozzle plate and for forming an ink chamber filled with ink therebetween; a heater interposed between the substrate and the nozzle plate for dividing the ink chamber into a main ink chamber disposed above the heater and a secondary ink chamber disposed below the heater, the main ink chamber and the secondary ink chamber generating a main bubble and a secondary bubble, respectively, upon heating of the heater and an ink channel connecting the secondary ink chamber to an ink reservoir so that ink is introduced into the secondary ink chamber and then supplied to the main ink chamber.
Preferably, a groove for forming the secondary ink chamber is formed in the substrate at a location corresponding to the heater. It is also preferable that the ink channel is formed at a loc
Kuk Keon
Maeng Doo-jin
Oh Yong-soo
Barlow John
Brooke Michael S
Lee & Sterba, P.C.
Samsung Electronics Co,. Ltd.
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