Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-01-31
2002-10-15
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S018000
Reexamination Certificate
active
06464337
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method and apparatus for acoustic ink printing using a bilayer configuration. More particularly, the invention concerns an acoustically actuated droplet emitter device which is provided with a continuous, high velocity, laminar flow of cooling liquid in addition to a stagnant pool of liquid to be emitted as droplets.
While the invention is particularly directed to the art of acoustic ink printing, and will be thus described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications. For example, the invention may be used in other acoustic wave generators wherein other types of fluid such as molten metal, etc. are emitted using an array of emitters.
By way of background, acoustic droplet emitters are known in the art and use focussed acoustic energy to emit droplets of fluid. Acoustic droplet emitters are useful in a variety of applications due to the wide range of fluids that can be emitted as droplets. For instance, if marking fluids are used the acoustic droplet emitter can be employed as a printhead in a printer. Acoustic droplet emitters do not use nozzles, which are prone to clogging, to control droplet size and volume, and many other fluids may also be used in an acoustic droplet emitter making it useful for a variety of applications. For instance, it is stated in U.S. Pat. No. 5,565,113 issued Oct. 15, 1996 by Hadimioglu et al. titled “Lithographically Defined Ejection Units” and incorporated by reference herein, that mylar catalysts, molten solder, hot melt waxes, color filter materials, resists and chemical and biological compounds are all feasible materials to be used in an acoustic droplet emitter.
One issue when using high-viscosity fluids in an acoustic droplet emitter is the high attenuation of acoustic energy in high-viscosity fluids. High attenuation rates may therefore require larger amounts of acoustic power to achieve droplet emission from high-viscosity fluids. One solution to this problem has been shown in U.S. Pat. No. 5,565,113 issued Oct. 15, 1996 by Hadimioglu et al. titled “Lithographically Defined Ejection Units” and incorporated by reference hereinabove and is shown in FIG.
1
.
FIG. 1
shows a cross-sectional view of an individual droplet emitter
10
for an acoustically actuated printer such as is shown in U.S. Pat. No. 5,565,113 by Hadimioglu et al. titled “Lithographically Defined Ejection Units” and incorporated by reference hereinabove. The droplet emitter
10
has a base substrate
12
with a transducer
16
interposed between two electrodes
17
on one surface and an acoustic lens
14
on an opposite surface. Attached to the same side of the base substrate
12
as the acoustic lens is a top support
18
with a liquid cell
22
, defined by sidewalls
20
, which holds a low attenuation liquid
23
. Supported by the top support
18
is an acoustically thin capping structure
26
which forms the top surface of the liquid cell
22
and seals in the low attenuation liquid
23
.
The droplet emitter
10
further includes a reservoir
24
, located over the acoustically thin capping structure
26
, which holds emission fluid
32
. As shown in
FIG. 1
, the reservoir
24
includes an aperture
30
defined by sidewalls
34
. The sidewalls
34
include a plurality of portholes
36
through which the emission fluid
32
passes. A pressure means forces the emission fluid
32
through the portholes
36
so as to create a pool of emission fluid
32
having a free surface
28
over the acoustically thin capping structure
26
.
The transducer
16
, acoustic lens
14
, and aperture
30
are all axially aligned such that an acoustic wave produced by the transducer
16
will be focussed by its aligned acoustic lens
14
at approximately the free surface
28
of the emission fluid
32
in its aligned aperture
30
. When sufficient power is obtained, a mound
38
is formed and a droplet
39
is emitted from the mound
38
. The acoustic energy readily passes through the acoustically thin capping structure
26
and the low attenuation liquid
23
. By maintaining only a very thin pool of emission fluid
32
acoustic energy loss due to the high attenuation rate of the emission fluid
32
is minimized.
FIG. 2
shows a perspective view of two arrays of the droplet emitter
10
shown in FIG.
1
. The arrays
31
of apertures
30
can be clearly above the two reservoirs
24
. Each array
31
has a width W and a length L where the length L of the array
24
is the larger of the two dimensions. Having arrays of droplet emitters
10
is useful, for instance, to enable a color printing application where each array might be associated with a different colored ink. This configuration of the arrays allows for accurate location of each individual droplet emitter
10
and precise alignment of the arrays
31
relative to each other which increases, among other things droplet placement accuracy.
However, the low attenuation liquid
23
, the emission fluid
32
, and the substrate
12
will heat up from the portion of the acoustic energy that is absorbed in the low attenuation liquid
23
, the emission fluid
32
, and the substrate
12
which is not transferred to the kinetic and surface energy of the emitted drops
39
. This will in turn cause excess heating of the emission fluid
32
. The emission fluid
32
can sustain temperature increases by only a few degrees centigrade before emitted droplets show drop misplacement on the receiving media. In a worst case scenario, the low attenuation liquid
23
can absorb enough energy to cause it to boil and to destroy the droplet emitter
10
. The practical consequences of this are that the emission speed must be kept very slow to prevent the low attenuation liquid
23
from absorbing too much excess energy in a short time period and heating up to unacceptable levels.
Therefore, it would be highly desirable if a droplet emitter
10
could be designed to operate while maintaining a uniform thermal operating temperature at high emission speeds. One such prior approach is described in U.S. Pat. No. 6,134,291, filed Jul. 23, 1999 (and issued Oct. 17, 2000) and entitled “An Acoustic Ink Jet Printhead Design and Method of Operation Utilizing Flowing Coolant and an Emission Fluid,” which is incorporated herein by reference.
As described therein, turning now to
FIG. 3
, there is shown a cross-sectional view of a droplet emitter
40
. The droplet emitter
40
has a base substrate
42
with transducers
46
on one surface and acoustic lenses
44
on an opposite surface. Spaced from the base substrate
42
is an acoustically thin capping structure
50
. The acoustically thin capping structure
50
may be either a rigid structure made from, for example, silicon, or a membrane structure made from, for example, parylene, mylar, or kapton. In order to preserve the acoustic transmission properties the acoustically thin capping structure
50
should preferably have either a very thin thickness such as approximately {fraction (1/10)}
th
of the wavelength of the transmitted acoustic energy in the membrane material or a thickness substantially equal to a multiple of one-half the wavelength of the transmitted acoustic energy in the membrane material. Whether the acoustically thin capping structure
50
is made from a rigid material or a membrane it will structurally be relatively thin and have a tendency to be fragile and susceptible to breakage. To provide additional stability for the acoustically thin capping structure
50
it is supported by a capping structure support
51
. The capping structure support
51
is interposed between the base substrate
42
and the acoustically thin capping structure
50
, adjacent to the acoustically thin capping structure
50
and spaced from the base substrate
42
. The capping structure support
51
has a series of spaced apart apertures
49
, positioned in a like manner to lens array
44
, so that focussed acoustic energy may pass by the capping structure support
51
substantially unimpeded. The ap
Elkin Jerry
Elrod Scott A.
Fitch John S.
Roy Joy
Smith Donald L.
Barlow John
Huffman Julian D.
Xerox Corporation
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