Thermoelastic inkjet actuator with heat conductive pathways

Details Thermoelastic inkjet actuator with heat conductive pathways Thermoelastic inkjet actuator with heat conductive pathways

2002-04-12

2004-02-10

Meier, Stephen D. (Department: 2853)

Incremental printing of symbolic information

Ink jet

Controller

C347S017000, C029S890100

Reexamination Certificate

active

06688719

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of inkjet printing and, in particular, discloses an improved thermoelastic inkjet actuator.
2. Description of Related Art
Thermoelastic actutator inkjet nozzle arrangements are described in U.S. patent applications Nos. U.S. Ser. No. 09/798,757 and U.S. Ser. No. 09/425,195 which are both co-owned by the present applicant and herein incorporated by cross reference in their entireties.
A first nozzle according to an embodiment of the invention described in that document is depicted in FIG.
1
.
FIG. 1
illustrates a side perspective view of the nozzle arrangement and
FIG. 2
is an exploded perspective view of the nozzle arrangement of FIG.
1
. The single nozzle arrangement
1
includes two arms
4
,
5
which operate in air and are constructed from a thin 0.3 micrometer layer of titanium diboride
6
on top of a much thicker 5.8 micron layer of glass
7
. The two arms
4
,
5
are joined together and pivot around a point
9
which is a thin membrane forming an enclosure which in turn forms part of the nozzle chamber
10
. The arms
4
and
5
are affixed by posts
11
,
12
to lower aluminium conductive layers
14
,
15
which can form part of the CMOS layer
3
. The outer surfaces of the nozzle chamber
18
can be formed from glass or nitride and provide an enclosure to be filled with ink. The outer chamber
18
includes a number of etchant holes e.g.
19
which are provided for the rapid sacrificial etchant of internal cavities during construction by MEM processing techniques.
The paddle surface
24
is bent downwards as a result of the release of the structure during fabrication. A current is passed through the titanium boride layer
6
to cause heating of this layer along arms
4
and
5
. The heating generally expands the T1B2 layer of arms
4
and
5
which have a high Young's modulus. This expansion acts to bend the arms generally downwards, which are in turn pivoted around the membrane
9
. The pivoting results in a rapid upward movement of the paddle surface
24
. The upward movement of the paddle surface
24
causes the ejection of ink from the nozzle chamber
21
. The increase in pressure is insufficient to overcome the surface tension characteristics of the smaller etchant holes
19
with the result being that ink is ejected from the nozzle chamber hole
21
.
As noted previously the thin titanium diboride strip
6
has a sufficiently high young's modulus so as to cause the glass layer
7
to be bent upon heating of the titanium diboride layer
6
. Hence, the operation of the inkjet device is as illustrated in
FIGS. 3-5
. In its quiescent state, the inkjet nozzle is as illustrated in
FIG. 3
, generally in the bent down position with the ink meniscus
30
forming a slight bulge and the paddle being pivoted around the membrane wall
9
. The hearing of the titanium diboride layer
6
causes it to expand. Subsequently, it is bent by the glass layer
7
so as to cause the pivoting of the paddle
24
around the membrane wall
9
as indicated in FIG.
4
. This causes the rapid expansion of the meniscus
30
resulting in a positive pressure pulse and the general ejection of ink from the nozzle chamber
10
. Next the current to the titanium diboride is switched off and the paddle
24
returns to its quiescent state resulting in a negative pressure pulse causing a general sucking back of ink via the meniscus
30
which in turn results in the ejection of a drop
31
on demand from the nozzle chamber
10
.
By shaping the electrical heating pulse the magnitude and time constants of the positive pressure pulse of the thermoelastic actuator may be controlled. However, the negative pressure pulse remains uncontrolled. The characteristics of the negative pressure pulse becomes more influential for fluids of high viscosity and high surface. Accordingly it would be desirable if theromelastic inkjet nozzles with tailored negative pressure pulse characteristics were available.
A further difficulty with some types of thermoelastic actuators is that it is not unusual for very high temperature actuators to induce temperatures above the boiling point of any given liquid on the bottom surface of the non-conductive layer.
It is an object of the present invention to provide a thermoelastic actuator with a tailored negative pressure pulse characteristic.
BRIEF SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a thermoelastic actuator assembly including:
a heat conduction means positioned to conduct heat generated by a heating element away from said actuator assembly thereby facilitating the return of the actuator to a quiescent state subsequent to operation.
Preferably the heating element comprises a heating layer which is bonded to a passive bend layer wherein the heat conduction means is located within the passive bend layer.
The heat conduction means may comprise one or more layers of a metallic heat conductive material located within the passive bend layer.
Preferably the one or more layers of metallic heat conductive material is sufficient to prevent overheating of ink in contact with said actuator.
Typically the one or more layers of metallic heat conductive material comprise a laminate of heat conductive material, for example Aluminium, and passive bend layer substrate.
It is envisaged that the thermoelastic actuator be incorporated into an ink jet printer.
A method of producing a thermoelastic actuator assembly having desired operating characteristics including the steps of:
determining a desired negative pressure pulse characteristic for the actuator;
determining a heat dissipation profile corresponding to the desired negative pressure pulse characteristic; and
forming the thermoelastic actuator with a heat conduction means arranged to realize said profile.
Preferably the step of determining a desired negative pressure pulse characteristic includes a step of determining the physical qualities of a fluid to be used with the thermoelastic actuator.
The step of forming the thermoelastic actuator with a heat conduction means arranged to realize said profile may include forming one or more heat conductive layers in a passive bend layer of the actuator.


REFERENCES:
patent: 5936646 (1999-08-01), Kenny et al.
patent: 6065823 (2000-05-01), Kawamura
patent: 6213589 (2001-04-01), Silverbrook
patent: 0 816 083 (1998-01-01), None
patent: 2 334 000 (1999-08-01), None
patent: 08309980 (1996-11-01), None

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