U.S. patent application number 12/580831 was filed with the patent office on 2010-07-29 for method and apparatus for controlling the temperature of an electrically-heated discharge nozzle.
Invention is credited to Valerie Gassend, Connor F. Madigan, Martin A. Schmidt.
Application Number | 20100188457 12/580831 |
Document ID | / |
Family ID | 42310645 |
Filed Date | 2010-07-29 |
United States Patent
Application |
20100188457 |
Kind Code |
A1 |
Madigan; Connor F. ; et
al. |
July 29, 2010 |
METHOD AND APPARATUS FOR CONTROLLING THE TEMPERATURE OF AN
ELECTRICALLY-HEATED DISCHARGE NOZZLE
Abstract
In an embodiment, the disclosure relates to a method and
apparatus for fault monitoring and controlling operation of a
discharge nozzle in a large array of discharge nozzles. An
exemplary apparatus includes a thin, thermally conductive membrane,
with an integrated thin-film electrical heater. When a fixed
voltage is applied to the heater, and as the heater heats, the
resistance of the heater will increase which will cause a
concomitant decrease in the electrical current flowing through the
heater. By measuring the resistance of the heater it can readily be
determined whether the device is functioning properly.
Inventors: |
Madigan; Connor F.; (US)
; Schmidt; Martin A.; (US) ; Gassend; Valerie;
(US) |
Correspondence
Address: |
SNELL & WILMER LLP (OC)
600 ANTON BOULEVARD, SUITE 1400
COSTA MESA
CA
92626
US
|
Family ID: |
42310645 |
Appl. No.: |
12/580831 |
Filed: |
October 16, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61142575 |
Jan 5, 2009 |
|
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|
Current U.S.
Class: |
347/17 |
Current CPC
Class: |
H01L 51/0005 20130101;
B41J 2/175 20130101; B41J 2/14 20130101 |
Class at
Publication: |
347/17 |
International
Class: |
B41J 29/38 20060101
B41J029/38 |
Claims
1. A method for controlling the temperature of a discharge nozzle,
the method comprising: providing a discharge nozzle for dispensing
ink, the discharge nozzle having a thermally-conductive membrane
with an integrated thin film electric heater and the thin film
electric heater defining a resistance; receiving a quantity of ink
in liquid-form at the discharge nozzle; energizing the thin-film
heater by applying a substantially constant current to the
thin-film heater; measuring a voltage across the heater and a
current through the heater; and determining temperature of the
heater as a function of the voltage and the current; and
determining the temperature of the ink droplet as a function of the
heater temperature.
2. The method of claim 1, further comprising energizing the
thin-film heater by supplying electric current and measuring the
ink quantity by measuring a change in the heater temperature.
3. The method of claim 1, further comprising energizing the
thin-film heater by applying a plurality of voltage pulses to the
thin-film heater, each voltage pulse providing substantially
identical voltage and having varying pulse width.
4. The method of claim 1, wherein the step of determining
temperature of the heater further comprises determining the
temperature as a function of the resistance from data specific to
said resistor.
5. The method of claim 1, further comprising varying the voltage to
increase the temperature of the heater.
6. A control system for controlling temperature of a discharge
nozzle, the control system comprising: a discharge nozzle having a
plurality of conduits for receiving a quantity of liquid ink, the
discharge nozzle thermally communicating with a heater; a first
metering device for measuring a voltage across the heater; a second
metering device for measuring a current through the heater; a
processor circuit for determining resistance of the heater as a
function of the voltage and the current, the processor circuit
controlling at least one of voltage or current input to the heater;
and a memory circuit in communication with the processor circuit,
the memory containing data associating resistance with the
temperature of the conduits of the discharge nozzle; wherein the
processor increases the voltage supplied to the heater to increase
the temperature at the conduits of the discharge nozzle.
7. The control system of claim 6, wherein the discharge nozzle has
a thermally-conductive membrane.
8. The control system of claim 6, further comprising a power supply
in communication with the processor, the processor controlling at
least one of voltage or current supplied to the heater.
9. The control system of claim 6, further comprising a power supply
in communication with the processor, the power supply supplying
voltage pulses to the heater, wherein the voltage pulses have
substantially identical pulse height and varying pulse width.
10. The control system of claim 6, wherein the resistive heater is
integrated with the discharge nozzle.
11. A discharge system for depositing ink on a substrate, the
system comprising: a chamber having a quantity of ink, the ink
defined by a plurality of suspended ink particles in a carrier
liquid; a discharge nozzle for receiving a quantity of liquid ink
from the chamber; a heater in thermal communication with the
discharge nozzle, the heater evaporating the carrier liquid at the
discharge nozzle to deposit a substantially solid quantity of ink
particles from the discharge nozzle; and a controller in
communication with the discharge nozzle, the controller maintaining
the heater temperature by varying the voltage while maintaining
substantially constant current supplied to the heater.
12. The system of claim 11, wherein the controller supplies a
plurality of energy pulses to a heater, each of the plurality of
pulses having a substantially constant pulse height and varying
pulse width.
13. The system of claim 1, wherein the controller further comprises
a processor circuit programmed with instructions to: (a) determine
one of the amount or the duration of activation required to
discharge the quantity of ink particles to the substrate; (b)
energize the discharge nozzle consistent with the amount or
duration determined in step (a); and (c) repeat steps (a) and (b)
to discharge additional quantities of ink particles onto the
substrate.
14. The system of claim 1, wherein the controller further comprises
at least one processor circuit in communication with a memory for
storing instructions.
15. The system of claim 1, wherein the controller tasks the
dispenser to provide the metered quantity of ink by providing
pulsating energy to the dispenser, the pulsating energy adapted to
exact a metered quantity of ink to the discharge nozzle.
Description
[0001] The instant application claims priority to Provisional
Application No. 61/142,575, which was filed on Jan. 5, 2009, and to
U.S. patent application Ser. No. 12/139,391, filed Jun. 13, 2008.
The disclosures of both applications are incorporated herein in
their entirety.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The disclosure relates to a method and apparatus for sensing
and controlling the temperature of an electrically resistive heater
which may be integrated with a discharge nozzle of a print-head.
More specifically, the disclosure relates to a novel controller for
controlling temperature of a discharge nozzle. The discharge nozzle
can be used for depositing substantially dry ink on a surface to be
used for electronic applications.
[0004] 2. Description of Related Art
[0005] The manufacture of organic light emitting devices (OLEDs)
requires depositing one or more organic films on a substrate and
coupling the top and bottom of the film stack to electrodes. The
film thickness is a prime consideration. The total layer stack
thickness is about 100 nm and each layer is optimally deposited
uniformly with an accuracy of better than +/-1 nm. Film purity is
also important. Conventional apparatuses form the film stack using
one of two methods: (1) thermal evaporation of organic material in
a relative vacuum environment and subsequent condensation of the
organic vapor on the substrate; or (2) dissolution of organic
material into a solvent, coating the substrate with the resulting
solution, and subsequent removal of the solvent.
[0006] Another consideration in depositing the organic thin films
of an OLED is placing the films precisely at the desired location.
There are two conventional technologies for performing this task,
depending on the method of film deposition. For thermal
evaporation, shadow masking is used to form OLED films of a desired
configuration. Shadow masking techniques require placing a
well-defined mask over a region of the substrate followed by
depositing the film over the entire substrate area. Once deposition
is complete, the shadow mask is removed. The regions exposed
through the mask define the pattern of material deposited on the
substrate. This process is inefficient, as the entire substrate
must be coated, even though only the regions exposed through the
shadow mask require a film. Furthermore, the shadow mask becomes
increasingly coated with each use, and must eventually be discarded
or cleaned. Finally, the use of shadow masks over large areas is
made difficult by the need to use very thin masks (to achieve small
feature sizes) that make said masks structurally unstable. However,
the vapor deposition technique yields OLED films with high
uniformity and purity and excellent thickness control.
[0007] For solvent deposition, ink jet printing can be used to
deposit patterns of OLED films. Ink jet printing requires
dissolving organic material into a solvent that yields a printable
ink. Furthermore, ink jet printing is conventionally limited to the
use of single layer OLED film stacks, which typically have lower
performance as compared to multilayer stacks. The single-layer
limitation arises because printing typically causes destructive
dissolution of any underlying organic layers. The ink jet printing
technique is capable of providing patterns of OLED films over very
large areas with good material efficiency.
[0008] Large area printing capabilities of ink jet printing allow
relatively high uniformity, purity, and thickness control for vapor
deposition of organic thin films over a large surface area. Large
area printing is enabled by arranging a multitude of discharge
nozzles in an array formation over a substrate. Ink deposition from
the array can be controlled by controlling ink metering discharge
at each nozzle.
[0009] Because a discharge array can include as few as 20 and as
many as 120 discharge nozzles, monitoring operability of each
nozzle is critical. If one or more discharge nozzles should fail in
a array of, for example, 120 discharge nozzles, this may not be
immediately detected and the printed substrate will prove faulty
after much time and labor has been expended. Accordingly, there is
a need for fault monitoring of each discharge nozzle in a large
array of discharge nozzles.
SUMMARY
[0010] The disclosure relates to a method and apparatus for fault
monitoring and controlling operation of a discharge nozzle in a
large array of discharge nozzles. In one embodiment, the apparatus
comprises a thin, thermally conductive membrane, with an integrated
thin-film electrical heater. The resistance of the heater and its
temperature can have monotonic increasing relationship. When a
fixed voltage is applied to the heater, as the heater heats, the
resistance of the heater will increase, which will cause a
concomitant decrease in the electrical current flowing through the
heater. Alternatively, when a fixed electrical current is flown
through the heater, the temperature of the heater will increase and
so will the resistance of the heater. Thus, the voltage measured
across the heater will increase.
[0011] In another embodiment, each discharge nozzle in an array of
discharge nozzles is provided with a separate detection circuit for
detecting failure mode at the discharge nozzle. Each discharge
nozzle communicates with a controller for controlling the
temperature of the discharge nozzle. The controller can be
interposed between a power supply and the discharge nozzle. By
controlling the power supplied to the discharge nozzle, the
controller can increase or decrease the temperature of the
discharge nozzle. The controller may optionally include a sensor
for detecting the temperature of the nozzle either directly or
indirectly. The sensor can also detect failure mode at the
discharge nozzle. With each nozzle in the array having a sensor,
the operator can readily identify a failing sensor in a large array
of sensors.
[0012] In another embodiment, the disclosure relates to a method
for controlling the temperature of a discharge nozzle. The method
includes the steps of: providing a discharge nozzle for dispensing
ink, the discharge nozzle having a thermally-conductive membrane
with an integrated thin film electric heater and the thin film
electric heater defining a resistance; receiving a quantity of ink
in liquid-form at the discharge nozzle; energizing the thin-film
heater by applying a substantially constant current to the
thin-film heater; measuring a voltage across the heater and a
current through the heater; and determining temperature of the
heater as a function of the voltage and the current; and
determining the temperature of the ink droplet as a function of the
heater temperature. In one embodiment, the ink drop temperature is
determined by measuring the voltage across the heater for a
substantially constant current.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] These and other embodiments of the disclosure will be
discussed with reference to the following exemplary and
non-limiting illustrations, in which like elements are numbered
similarly, and where:
[0014] FIG. 1 is a schematic representation of an exemplary
print-head having a thermal ink depositing mechanism according to
one embodiment of the disclosure;
[0015] FIG. 2 schematically illustrates a print-head apparatus
having multiple discharge nozzles arranged in an array and using
thermal ink dispensing elements;
[0016] FIG. 3 is a sideview representation of an embodiment of the
invention;
[0017] FIG. 4 is a bottom view representation of an embodiment of
the invention;
[0018] FIG. 5 is a circuit diagram for the heater and sensor
combination according to one embodiment of the invention;
[0019] FIG. 6 is an exploded photograph of the physical
representation of a resistive heater and a sensor;
[0020] FIG. 7 is a representative driving circuit according to one
embodiment of the disclosure;
[0021] FIG. 8 shows a closed-loop temperature controller according
to an embodiment of the disclosure;
[0022] FIG. 9 is an exemplary control system according to another
embodiment of the disclosure; and
[0023] FIG. 10 is a flow-diagram for implementing a method
according to one embodiment of the disclosure.
DETAILED DESCRIPTION
[0024] FIG. 1 is a schematic representation of an exemplary
print-head having a thermal ink depositing mechanism according to
one embodiment of the disclosure. The exemplary print-head of FIG.
1 includes chamber 130, orifice 170, nozzle 180, and micro-porous
conduits 160. Chamber 130 receives ink in liquid form and
communicates the ink from orifice 170 to discharge nozzle 180. The
ink can comprise suspended or dissolved particles in a carrier
liquid. These particles can comprise single molecules or atoms, or
aggregations of molecules and/or atoms. The path between orifice
170 and discharge nozzle 180 defines a delivery path. In the
embodiment of FIG. 1A, discharge nozzle 180 comprises conduits 160
separated by partitions 165. Conduits 160 may include micro-porous
material therein. A surface of discharge nozzle 180 proximal to
orifice 170 defines the inlet port to discharge nozzle 180 while
the distal surface of discharge nozzle 180 defines the outlet port.
A substrate (not shown) can be positioned proximal to the outlet
port of discharge nozzle 180 for receiving ink deposited from the
nozzle.
[0025] The thermal jet print-head of FIG. 1 further includes bottom
structure 140, which receives discharge nozzle 180. Discharge
nozzle 180 can be fabricated as part of the bottom structure 140.
Alternatively, discharge nozzle 180 can be manufactured separately
and later combined with bottom structure 140 to form an integrated
structure. Top structure 142 receives chamber 130. Top structure
142 can be formed with appropriate cavities and conduits to form
chamber 130. Top structure 142 and bottom structure 140 are coupled
through bonds 120 to form a housing. The housing allows the thermal
jet print-head to operate under pressure or in a vacuum. The
housing may further comprise an inlet port (not shown) for
accepting a transport gas for carrying the material from the
discharge nozzle to the substrate (not shown).
[0026] Alternatively, a port (not shown) can be integrated into top
structure 142 to receive transport gases. The port can include a
flange adapted to receive a transport gas, which according to one
embodiment comprises a substantially inert mixture of one or more
gases. The mixture can include gases which are substantially
non-reactive with the materials being deposited by the apparatus,
such as nitrogen or argon when used with typical organic materials.
The transport gas can transport particles from discharge nozzle 180
by flowing through micro-pores 160.
[0027] Heater 110 can be optionally added to chamber 130 for
heating and/or dispensing the ink. In FIG. 1, heater 110 is
positioned inside chamber 130. Heater 110 can be any thermal energy
source coupled to chamber 130 for providing pulsating energy to the
liquid ink and thereby discharging a droplet of the liquid ink
through orifice 170. In one embodiment, heater 110 delivers heat in
pulses having a duration of one second or less. For instance, the
heater can be energized with square pulses having a variable duty
cycle and a cycle frequency of 1 kHz. Thus, the heater energy can
be used to meter the quantity of ink delivered from chamber 130 to
discharge nozzle 180. Chamber 130 may also contain material, other
than ink, required for forming a film used in the fabrication of an
OLED or transistor. Orifice 170 can be configured such that surface
tension of the liquid in chamber 130 prevents discharge of the
liquid prior to activation of the mechanism for dispensing the
ink.
[0028] In the embodiment of FIG. 1, discharge nozzle 180 includes
partitions (or rigid portions) 165 separated by conduits 160.
Conduits 160 and rigid portions 165 can collectively define a
micro-porous environment. The micro-porous environment can be
composed of a variety of materials, including micro-porous alumina
or solid membranes of silicon or silicon carbide and having
micro-fabricated pores. Micro-pores 160 prevent the material
dissolved or suspended in the liquid from escaping through
discharge nozzle 180 until the medium is appropriately
activated.
[0029] When the discharged droplet of liquid encounters discharge
nozzle 180, the liquid is drawn into micro-pores 160 with
assistance from capillary action. The liquid in the ink may
evaporate prior to activation of discharge nozzle 180, leaving
behind a coating of the suspended or dissolved particles on the
micro-pore walls. The liquid in the ink may comprise one or more
solvents with a relatively-low vapor pressure. The liquid in the
ink may also comprise one or more solvents with a relatively-high
vapor pressure.
[0030] The evaporation of the liquid in the ink may be accelerated
by heating the discharge nozzle. The evaporated liquid can be
removed from the chamber and subsequently collected (not shown),
for instance, by flowing gas over one or more of the discharge
nozzle faces. Depending on the desired application, micro-pores 160
can provide conduits (or passages) having a maximum linear
cross-sectional distance W of a few nanometers to hundreds of
microns. The micro-porous region comprising discharge nozzle 180
will take a different a shape and cover a different area depending
on the desired application, with a typical maximum linear
cross-sectional dimension D ranging from a few hundred nanometers
to tens of millimeters. In one embodiment, the ratio of W/D is in a
range of about 1/10 to about 1/1000.
[0031] Discharge nozzle 180 can be actuated by nozzle heater 150.
Nozzle heater 150 is positioned proximal to discharge nozzle 180.
Nozzle heater 150 may comprise a thin metal film. The thin metal
film can be comprised of, for example, platinum. When activated,
nozzle heater 150 provides pulsating thermal energy to discharge
nozzle 180, which acts to dislodge the material contained within
micro-pores or conduits 160, which can subsequently flow out from
the discharge nozzle. In one embodiment, the pulsations can be
variable on a time scale of one minute or less.
[0032] Dislodging the ink particles may include vaporization,
either through sublimation or melting and subsequent boiling. It
should be noted again that the term particles is used generally,
and includes anything from a single molecule or atom to a cluster
of molecules or atoms. In general, one can employ any energy source
coupled to the discharge nozzle that is capable of energizing
discharge nozzle 180 and thereby discharging the material from
micro-pores 160; for instance, mechanical (e.g., vibrational). In
one embodiment of the disclosure, a piezoelectric material is used
instead of, or in addition to, nozzle heaters 150.
[0033] FIG. 2 schematically illustrates a print-head apparatus
having multiple discharge nozzles arranged in an array and using
thermal ink dispensing elements. The apparatus of FIG. 2 includes
chamber 230 for housing liquid 201. Liquid 201 can comprise
dissolved or suspended particles for deposition on a substrate.
Chamber 230 also includes a plurality of chamber orifices 270. The
embodiment of FIG. 2 comprises ink dispensing heaters 210 for
pulsatingly metering liquid ink through each chamber orifice 270
and towards discharge nozzles 280. Discharge nozzles 280 are
arranged in an array such that each discharge nozzle 280
communicates with a corresponding chamber orifice 270. Nozzle
heaters 250 are positioned near discharge nozzles 280 to evaporate
substantially all of the carrier liquid and to allow solid
particles to be deposited by the discharge nozzle array.
[0034] The array 200 of FIG. 2 includes a number of independent
discharge nozzle 280 arranged in one row. A typical array includes
several rows of independent discharge nozzles. As shown each nozzle
is in thermal communication with at least one heater 250. In the
event that any one heater element should fail, the ink deposit
process will be affected. Consequently, the deposited pixel will be
faulty. The problem of faulty pixel is significant because it often
goes undetected until late in the manufacturing process after much
labor and cost have been spent.
[0035] To address this and other problems, an embodiment of the
invention relates to a thin-film heater and a thin-film temperature
sensor in communication with the thin-film heater. The thin-film
heater and the temperature sensor can be integrated. The sensor
enables immediate detection of the heater's temperature. Moreover,
because each heater will have a separate sensor, failure detection
can be pinpointed immediately.
[0036] FIG. 3 is a side view representation of an embodiment of the
invention. Device 300 of FIG. 3 includes print-head chip 310 and a
thin-film heater and temperature sensor 320. The thin-film heater
is mounted to a side of the print-head chip proximal to the
substrate surface (not shown). Thin-film heater 310 can be
integrated with a temperature sensor to form a single device for
easier manufacturing and assembly.
[0037] FIG. 4 is a bottom view representation of an embodiment of
the invention. In FIG. 4, the thin-film heater 420 has segments A,
B, C and D. Each segment represents a node of the sensor.
Print-head chip 410 is shown in the dark shade area, overlapping
the sensor. It should be noted that the bottom-view shown in FIG. 4
is the face closest to the substrate (not shown).
[0038] FIG. 5 is a circuit diagram for the heater and sensor
combination according to one embodiment of the invention. Circuit
500 of FIG. 5 comprises heater 530 connected to current source 510
and voltmeter 520. Current source 510 is connected to resistive
heater 530 through nodes A and B. Voltmeter 520 is connected to
resistive heater 530 through nodes C and D. Nodes A, B, C and D are
schematically represented in FIG. 4.
[0039] FIG. 6 is an exploded photograph of the physical
representation of a resistive heater and a sensor. FIG. 6 is a
100.times. magnification of an exemplary heater. Resistive heater
630 is shown at the center of FIG. 6. Regions A, B, C and D are
also identified as corresponding to nodes A, B, C and D. Shaded
portions 640, 650, 660 and 670 are the bottom portions of the
printer-head discharge nozzle. In one embodiment, platinum was used
for nodes A, B, C and D. In another embodiment, a combination of
titanium and platinum was used for the nodes. The nodes can also be
prepared as a multilayer device having an adhesive layer connecting
a heater layer to a pad (substrate) layer.
[0040] A number of different circuits can be used to sense the
voltage across the heater. The voltage may be sensed directly as a
DC voltage or it may be sensed using one or more operational
amplifiers ("op-amp") which are used to drive the current of the
heater while having a high-pass filter let through a high frequency
current. The high frequency current can be taken by another op-amp
to provide a closed loop signal to a controller. Thus, in FIGS. 4,
5 and 6, the current I.sub.AB is supplied by the current source I
and the voltage V.sub.CD is measured across the heater and directly
proportional to the temperature of the heater R.sub.Heater.
[0041] FIG. 7 is a representative driving circuit according to one
embodiment of the disclosure The circuit of FIG. 7 can define a
constant-current driving circuit. Circuit 700 receives driving
signal 705 at operational amplifier 730. Operational amplifier 730
drives heater 710 which includes driving the resistive heater and
the thermal sensor circuits. Heater 710 can be co-located with the
discharge nozzle (not shown) and can comprise a platinum heater.
Resistor 720 is the circuit sensing device connected to the ground.
The circuit sensing device provides voltage-proportional to heater
current feedback to operational amplifier 730 and can define a 1
Ohm resistor. As shown in FIG. 7, the driving circuit can receive,
for example, voltage as feedback. The voltage can define the
instantaneous temperature of the heater.
[0042] FIG. 8 shows a circuit for a closed-loop temperature
controller according to another embodiment of the disclosure. The
circuit of FIG. 8 includes microprocessor 800, I/O device 815 and
resistance measuring circuit 820. The desired temperature is
entered to controller 800. Controller 800 correlates the
temperature value to a corresponding resistance value. The
resistance value for the heater can be stored in a memory circuit
associated with the controller. A software algorithm can correlate
the resistance value and the temperature. If the desired
temperature is less than the measured value, controller 800 can
reduce the current supplied to heater 810 in order to heat the
discharge nozzle. On the other hand, if the heater temperature is
lower than the desired value, the current supplied to the heater
can be increased to raise the temperature. Operational amplifier
830 drives heater 810. In this manner, controller 800 provides a
constant temperature control and feedback. Temperature feedback is
provided through amplifier 840 to I/O device 815, which in turn,
communicates with controller 800.
[0043] In FIGS. 7 and 8, the controlling circuits can be can be
devised independently for each printer-head and can be controlled
and monitored from a remote location. Thus, in an array of 50
print-heads arranged in five columns of ten print-heads, each
print-head can have an independent control circuit. The independent
control circuits can communicated with a master controller (not
shown) and ultimately with the technician through a graphic user
interface.
[0044] According to the principles disclosed herein a driving
circuit, such as those represented in FIG. 5, 6 or 7, can be used
with each discharge nozzle in an array of print-heads. The driving
circuit can be integrated with the heater or it may define a
separate module. In one embodiment of the invention, the driving
circuit is interposed between the heater and a power supply.
[0045] The power supply can define an AC or a DC source
sufficiently seized to energize the resistive heater. The driving
circuit may provide constant current with variable voltage to the
resistive heater. Alternatively, the power supply may provide a
constant AC voltage with variable pulse width. In such embodiment,
the pulse height can define the voltage level and the pulse width
can define the duration of voltage supplied to the heater. A
feedback to the driving circuit can help adjust the input power by
increasing or decreasing the power supplied (or its duration) to
the resistive heater.
[0046] FIG. 9 is an exemplary control system according to one
embodiment of the disclosure. The system of FIG. 9 comprises
processor 910 in communication with memory 920. Memory 920 can
contain data relating the resistance of the heater to its
temperature. Memory 920 can store data relating the voltage to the
temperature of resistive heater 920. Memory 920 may also contain
data relating the current measured across heater 940 to its
instantaneous temperature. It will be appreciated by one of
ordinary skill in the art that such data is material-dependent and
can vary widely from one resistive heater to another. Memory 920
and processor 910 can define a firmware.
[0047] Driving circuit 930 can be integrated with processor 910 or
it can define a separate circuitry. In the embodiment of FIG. 9,
driving circuit 930 is interposed between power supply 950 and
heater 940. As discussed, power supply 950 can define an AC or a DC
power supply. Driving circuit 930 can receive a driving signal from
processor 910 and control the power supplied to heater 940. Driving
circuit 930 also communicates with heater 930 as shown in FIGS. 5,
6 and 7 across nodes C and D. While the embodiment of FIG. 9 shows
a single heater, the disclosed principles are not limited thereto.
Processor 910 can control multiple driving circuits and heaters
simultaneously.
[0048] In an alternative embodiment, the function of the driving
and the processor can be combined into a controller as
schematically represented by broken lines 960. The controller can
define a single integrated circuit or it can define multiple
circuit modules. The controller can receive feedback from heater
940 and determine the temperature of the heater as a function of
resistance data stored in memory 920. The controller can also
detect failure mode at the heater as a function of, for example,
the voltage across heater 940. In the event of failure detection,
the controller can communicate the failure to the operator. Control
system 860 can be used to control a multitude of heaters 940 in a
large array of print-heads and discharge nozzles (see FIG. 2).
[0049] FIG. 10 is a flow-diagram for implementing a method
according to one embodiment of the disclosure. In step 1010 a
discharge nozzle in communication with a resistive heating element
is provided. The discharge nozzle can be integrated with the heater
as one unit. Alternatively, the heater can be mounted or attached
to the discharge nozzle. The nozzle may comprise one or more
conduits between two surfaces thereof for heating the received ink.
In step 1020, ink is received at the nozzle. The ink can be
received at a surface of the nozzle or it can be received at the
conduits of the discharge nozzle. In step 1030, the resistive
heater is energized to thereby heat the ink received at the nozzle.
The energizing step can comprise supplying AC, DC or voltage pulses
to the heater. A control circuit (interchangeably, controller) in
communication with the heater and the energy source can dictate the
amount of energy supplied to the heater based on the desired ink
temperature at deposition.
[0050] At the same time, a control circuit can monitor the
instantaneous temperature of the heater by detecting the voltage
across the resistive heater. If the resistance should exceed a
predetermined threshold, the controller may interrupt or decrease
the energy supplied to the heater. As stated, the controller may
comprise a processor circuit in communication with a memory
circuit. The memory circuit can contain data relating the
temperature of the resistive heater to its voltage or current. In
one embodiment, the memory circuit contains a data table
correlating the instantaneous temperature of the heater to the
voltage measure across the heater. Using such data, in step 1050,
the processor circuit may increase, decrease or leave unchanged the
energy supplied to the resistive heater. The processor circuit can
communicate with the operator through a graphic user interface and
a keyboard. The operator may dial in different temperatures
depending on the type of ink, the resistive heater and the
deposition parameters.
[0051] While the principles of the disclosure have been illustrated
in relation to the exemplary embodiments shown herein, the
principles of the disclosure are not limited thereto and include
any modification, variation or permutation thereof.
* * * * *