U.S. patent application number 15/795664 was filed with the patent office on 2018-05-24 for fast measurement of droplet parameters in industrial printing system.
The applicant listed for this patent is Kateeva, Inc.. Invention is credited to Christopher Hauf, Eliyahu Vronsky.
Application Number | 20180146162 15/795664 |
Document ID | / |
Family ID | 54870848 |
Filed Date | 2018-05-24 |
United States Patent
Application |
20180146162 |
Kind Code |
A1 |
Hauf; Christopher ; et
al. |
May 24, 2018 |
Fast Measurement of Droplet Parameters in Industrial Printing
System
Abstract
A droplet measurement system (DMS) is used in concern with an
industrial printer used to fabricate a thin film layer of a flat
panel electronic device. A clear tape serves as a printing
substrate to receive droplets from hundreds of nozzles
simultaneously, while an optics system photographs the deposited
droplets through the tape (i.e., through a side opposite the
printhead). This permits immediate image analysis of deposited
droplets, for parameters such as per-nozzle volume, landing
position and other characteristics, without having to substantially
reposition the DMS or printhead. The tape can then be advanced and
used for a new measurement. By providing such a high degree of
concurrency, the described system permits rapid measurement and
update of droplet parameters for printers that use hundreds or
thousands of nozzles, to provide a real-time understanding of
per-nozzle expected droplet parameters, in a manner that can be
factored into print planning.
Inventors: |
Hauf; Christopher; (Belmont,
CA) ; Vronsky; Eliyahu; (Los Altos, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kateeva, Inc. |
Newark |
CA |
US |
|
|
Family ID: |
54870848 |
Appl. No.: |
15/795664 |
Filed: |
October 27, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14840343 |
Aug 31, 2015 |
9832428 |
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15795664 |
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14340403 |
Jul 24, 2014 |
9352561 |
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14840343 |
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PCT/US14/35193 |
Apr 23, 2014 |
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14340403 |
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14162525 |
Jan 23, 2014 |
9010899 |
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PCT/US14/35193 |
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PCT/US13/77720 |
Dec 24, 2013 |
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14162525 |
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PCT/US14/35193 |
Apr 23, 2014 |
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14340403 |
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62044958 |
Sep 2, 2014 |
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61746545 |
Dec 27, 2012 |
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61822855 |
May 13, 2013 |
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61842351 |
Jul 2, 2013 |
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61857298 |
Jul 23, 2013 |
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61898769 |
Nov 1, 2013 |
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61920715 |
Dec 24, 2013 |
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61816696 |
Apr 26, 2013 |
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61866031 |
Aug 14, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B41J 2/2142 20130101;
B41J 2/195 20130101; B41J 2/0456 20130101; B41J 2/04561 20130101;
B41J 2/04581 20130101; H04N 7/18 20130101; G06T 7/0004 20130101;
B41J 2/2132 20130101 |
International
Class: |
H04N 7/18 20060101
H04N007/18; G06T 7/00 20170101 G06T007/00; B41J 2/21 20060101
B41J002/21; B41J 2/045 20060101 B41J002/045; B41J 2/195 20060101
B41J002/195 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2013 |
TW |
102148330 |
Claims
1. (canceled)
2. A method of fabricating a thin-film layer of an electronic
product, the method comprising: receiving a substrate into a
manufacturing system; while the substrate is in a printing area of
the manufacturing system, printing droplets of a liquid onto the
substrate from respective nozzles of one or more printheads of the
manufacturing system, the droplets of the liquid to coalesce to
form a liquid coat on the substrate, the liquid carrying a
film-forming material, wherein there are at least five hundred of
the respective nozzles carried by the one or more printheads;
processing the liquid coat to solidify the film-forming material so
as to form the thin-film layer therefrom; and unloading the
substrate from the manufacturing system; wherein the method further
comprises calibrating droplets produced by respective ones of the
at least five hundred nozzles, in situ within the manufacturing
system, for at least one of droplet volume, droplet size, droplet
shape or droplet landing location, by robotically transporting the
one or more printheads to a location within the manufacturing
system, outside of the printing area, while the one or more
printheads are at the location, using a droplet measurement system
to collectively image droplets respectively produced by nozzles in
a subset of the at least five hundred respective nozzles and, based
on the collective image of the droplets produced by the nozzles in
the subset, to calculate the at least one value of droplet volume,
droplet shape, droplet size or droplet landing location for
droplets produced by each of the nozzles in the subset, and
repeating the using of the droplet measurement system to
collectively image droplets and to calculate the at least one value
in a manner so as to compute the at least one value for each one of
the at least five hundred of the respective nozzles carried by the
one or more printheads, and robotically transporting the one or
more printheads from the location to the printing area for the
printing, wherein the manufacturing system performs the printing in
a manner dependent on the measurements of the at least one of
droplet volume, droplet shape, droplet size or droplet landing
location for the at least five hundred nozzles.
3. The method of claim 2, wherein the droplet measurement device is
to provide a translucent test substrate having a first side, onto
which the droplets produced by the subset are deposited at
respective positions on the first side, and wherein the translucent
test substrate has a second side, through which the collective
image of the droplets is captured by the image capture system.
4. The method of claim 3, wherein the droplet measurement system
comprises a chassis that mounts a reel of tape, the tape providing
the translucent test substrate, and that mounts a camera and a tape
advancement system, wherein the chassis defines a window and
wherein tape advancement system is to advance the tape relative to
the window such that a first side of the tape is to receive the
droplets respectively produced by the nozzles in the subset, and
such that the camera is to image the droplets deposited onto the
first side of the tape through the window and through a second side
of the tape, and wherein the method further comprises robotically
transporting the droplet measurement system while the one or more
printheads are at the location, without moving the one or more
printheads, and advancing the tape relative to the window so as to
perform the repeating.
5. The method of claim 3, wherein the at least one value is one of
droplet size or droplet volume, for each nozzle of the at least
five hundred nozzles, and wherein the image processing system is to
compute the one of droplet size or droplet volume by identifying an
area each droplet in the image occupies on the first side of the
tape, and by computing the at least one value for a corresponding
nozzle in the subset in dependence on the identified area.
6. The method of claim 2, wherein the manufacturing system performs
the printing in the manner dependent on the measurements by
selectively assigning nozzles to print respective ones of the
droplets of the liquid onto the substrate in dependence on the
measurements.
7. The method of claim 2, wherein the manufacturing system performs
the printing in the manner dependent on the measurements by
selectively disqualifying nozzles from use in the printing of the
droplets of the liquid onto the substrate in dependence on the
measurements.
8. The method of claim 2, wherein the droplet measurement system
comprises a transport system adapted to move an image capture
device of the droplet measurement system in at least two dimensions
while the one or more printheads are stationary at the location, so
as to robotically reposition the image capture device to image
droplets produced by different subsets of the nozzles without
requiring relative movement between the one or more printheads and
the manufacturing system.
9. The method of claim 2, wherein the manufacturing system
comprises a gas enclosure to hold a controlled atmosphere, and
wherein the printing of the droplets of the liquid onto the
substrate and the calibrating of the droplets using the droplet
measurement system are each performed within the gas enclosure and
within the controlled atmosphere.
10. The method of claim 2, wherein the manufacturing system
comprises at least one of a curing system or a baking system, and
wherein the processing of the liquid coat comprises curing or
baking the liquid coat, using the at least one of the curing system
or the baking system, to solidify the film-forming material
relative to the liquid.
11. The method of claim 10, wherein the processing of the liquid
coat comprises transporting the substrate from the printing area to
a processing area at which the curing or baking is performed, and
wherein the repeating is performed, at least in part, when the
substrate is at the processing area.
12. The method of claim 10, wherein the electronic product
comprises a light-emitting device, and wherein the thin-film layer
comprises a light generating layer of the light-emitting
device.
13. A method of fabricating a thin-film layer of electronic
products, the method comprising: for each substrate in a series of
substrates, receiving the substrate into a manufacturing system,
while the substrate is in a printing area of the manufacturing
system, printing droplets of a liquid onto the substrate from
respective nozzles of one or more printheads of the manufacturing
system, the droplets of the liquid to coalesce to form a liquid
coat on the substrate, the liquid carrying a film-forming material,
wherein there are at least five hundred of the respective nozzles
carried by the one or more printheads, processing the liquid coat
to solidify the film-forming material so as to form the thin-film
layer therefrom, and unloading the substrate from the manufacturing
system; wherein the method further comprises, calibrating droplets
produced by respective ones of the at least five hundred nozzles,
in situ within the manufacturing system, for at least one of
droplet volume, droplet size, droplet shape or droplet landing
location, by robotically transporting the one or more printheads to
a location within the manufacturing system, outside of the printing
area, in between printing on respective ones of the substrates in
the series, while the one or more printheads are at the location,
using a droplet measurement system to collectively image droplets
respectively produced by nozzles in a subset of the at least five
hundred respective nozzles and, based on the collective image of
the droplets produced by the nozzles in the subset, to calculate
the at least one value of droplet volume, droplet shape, droplet
size or droplet landing location for droplets produced by each of
the nozzles in the subset, and robotically transporting the one or
more printheads from the location to the printing area for the
printing; wherein the method further comprises repeating the using
of the droplet measurement system to collectively image droplets
and calculate the at least one value in a manner so as to calculate
the at least one value for each one of the at least five hundred of
the respective nozzles carried by the one or more printheads, and
wherein for different successive pairs of the substrates in the
series, the nozzles in the subset are changed, in a manner such
that the droplet measurement system incrementally measures the at
least one of droplet volume, droplet shape, droplet size or droplet
landing location for each one of the at least five hundred nozzles
in between printing of the droplets onto pairs of the substrates in
the series; and wherein, for each of the substrates, the
manufacturing system performs the printing in a manner dependent on
the measurements of the at least one of droplet volume, droplet
shape, droplet size or droplet landing location for the at least
five hundred nozzles.
14. The method of claim 13, wherein the droplet measurement device
is to provide a translucent test substrate having a first side,
onto which the droplets produced by the subset are deposited at
respective positions on the first side, and wherein the translucent
test substrate has a second side, through which the collective
image of the droplets is captured by the image capture system.
15. The method of claim 14, wherein the droplet measurement system
comprises a chassis that mounts a reel of tape, the tape providing
the translucent test substrate, that mounts a camera and a tape
advancement system, wherein the chassis defines a window and
wherein tape advancement system is to advance the tape relative to
the window such that a first side of the tape is to receive the
droplets respectively produced by the nozzles in the subset, and
such that the camera is to image the droplets deposited onto the
first side of the tape through the window and through a second side
of the tape, and wherein the method further comprises robotically
transporting the droplet measurement system while the one or more
printheads are at the location, without moving the one or more
printheads, and advancing the tape relative to the window so as to
perform the repeating.
16. The method of claim 15, wherein the at least one value is one
of droplet size or droplet volume, for each nozzle of the at least
five hundred nozzles, and wherein the image processing system is to
compute the one of droplet size or droplet volume by identifying an
area each droplet in the image occupies on the first side of the
tape, and by computing the at least one value for a corresponding
nozzle in the subset in dependence on the identified area.
17. The method of claim 13, wherein the manufacturing system
performs the printing in the manner dependent on the measurements
by selectively assigning nozzles to print respective ones of the
droplets of the liquid onto the substrate in dependence on the
measurements.
18. The method of claim 13, wherein the manufacturing system
performs the printing in the manner dependent on the measurements
by selectively disqualifying nozzles from use in the printing of
the droplets of the liquid onto the substrate in dependence on the
measurements.
19. The method of claim 13, wherein the droplet measurement system
comprises a transport system adapted to move an image capture
device of the droplet measurement system in at least two dimensions
while the one or more printheads are stationary at the location, so
as to robotically reposition the image capture device to image
droplets produced by different subsets of the nozzles without
requiring relative movement between the one or more printheads and
the manufacturing system.
20. The method of claim 13, wherein the manufacturing system
comprises a gas enclosure to hold a controlled atmosphere, and
wherein the printing of the droplets of the liquid onto the
substrate and the calibrating of the droplets using the droplet
measurement system are each performed within the gas enclosure and
within the controlled atmosphere.
21. The method of claim 13, wherein the manufacturing system
comprises at least one of a curing system or a baking system, and
wherein the processing of the liquid coat comprises curing or
baking the liquid coat, using the at least one of the curing system
or the baking system, to solidify the film-forming material
relative to the liquid.
22. The method of claim 21, wherein the processing of the liquid
coat comprises transporting the substrate from the printing area to
a processing area at which the curing or baking is performed, and
wherein the repeating is performed, at least in part, when the
substrate is at the processing area.
23. The method of claim 21, wherein the electronic product
comprises a light-emitting device, and wherein the thin-film layer
comprises a light generating layer of the light-emitting
device.
24. The method of claim 13, wherein the thin-film layer is an
encapsulation layer that is to encapsulate an electrically-active
component of the electronic product.
25. A method of fabricating a thin-film layer of an electronic
product having light-emitting elements, the method comprising:
receiving a substrate into a manufacturing system; while the
substrate is in a printing area of the manufacturing system and
within a controlled gas environment, printing droplets of a liquid
onto the substrate from respective nozzles of one or more
printheads of the manufacturing system, the droplets of the liquid
to coalesce to form a liquid coat on the substrate, the liquid
carrying a film-forming material, wherein there are at least five
hundred of the respective nozzles carried by the one or more
printheads; processing the liquid coat to solidify the film-forming
material so as to form the thin-film layer therefrom; and unloading
the substrate from the manufacturing system; wherein the method
further comprises calibrating droplets produced by respective ones
of the at least five hundred nozzles, in situ within the
manufacturing system, for at least one of droplet volume, droplet
size, droplet shape or droplet landing location, by robotically
transporting the one or more printheads to a location within the
manufacturing system, outside of the printing area, while the one
or more printheads are at the location, using a droplet measurement
system to collectively image droplets respectively produced by
nozzles in a subset of the at least five hundred respective nozzles
and, based on the collective image of the droplets produced by the
nozzles in the subset, to calculate the at least one value of
droplet volume, droplet shape, droplet size or droplet landing
location for droplets produced by each of the nozzles in the
subset, and repeating the using of the droplet measurement system
to collectively image droplets and to calculate the at least one
value in a manner so as to compute the at least one value for each
one of the at least five hundred of the respective nozzles carried
by the one or more printheads, and robotically transporting the one
or more printheads from the location to the printing area for the
printing; wherein the manufacturing system performs the printing in
a manner dependent on the measurements of the at least one of
droplet volume, droplet shape, droplet size or droplet landing
location for the at least five hundred nozzles; and wherein the
thin-film layer comprises at least one of an encapsulation layer or
an electrically-active layer for each of the light emitting
elements.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. Utility patent
application Ser. No. 14/840,343, for "Fast Measurement Of Droplet
Parameters In Industrial Printing System," filed on behalf of first
named inventor Christopher R. Hauf on Aug. 31, 2015 (the '343
application). The '343 application claims priority to U.S.
Provisional Patent Application No. 62/044,958, for "Fast
Measurement Of Droplet Parameters In Industrial Printing System,"
filed on behalf of first named inventor Christopher R. Hauf on Sep.
2, 2014. The '343 application is also claims priority to, and is a
continuation in-part of U.S. patent application Ser. No. 14/340,403
for "Techniques for Print Ink Droplet Measurement and Control to
Deposit Fluids within Precise Tolerances," filed on behalf of first
named inventor Nahid Harjee on Jul. 24, 2014. U.S. patent
application Ser. No. 14/340,403 in turn claims priority to U.S.
Provisional Patent Application No. 61/950,820 for "Techniques For
Print Ink Droplet Volume Measurement And Control Over Deposited
Fluids Within Precise Tolerances," filed on behalf of first named
inventor Nahid Harjee on Mar. 10, 2014. U.S. patent application
Ser. No. 14/340,403 in turn claims priority to, and is itself a
continuation in-part of each of PCT Patent Application No.
PCT/US2014/035193 for "Techniques for Print Ink Droplet Measurement
and Control to Deposit Fluids within Precise Tolerances," filed on
behalf of first named inventor Nahid Harjee on Apr. 23, 2014 and
U.S. Utility patent application Ser. No. 14/162,525 for "Techniques
for Print Ink Volume Control To Deposit Fluids Within Precise
Tolerances," filed on behalf of first named inventor Nahid Harjee
on Jan. 23, 2014. U.S. Utility patent application Ser. No.
14/162,525 in turn claims priority to Taiwan Patent Application No.
102148330, filed for "Techniques for Print Ink Volume Control To
Deposit Fluids Within Precise Tolerances" on behalf of first named
inventor Nahid Harjee on Dec. 26, 2013, and PCT Patent Application
No. PCT/US2013/077720, filed for "Techniques for Print Ink Volume
Control To Deposit Fluids Within Precise Tolerances" on behalf of
first named inventor Nahid Harjee on Dec. 24, 2013. PCT Patent
Application No. PCT/US2013/077720 claims priority to each of: U.S.
Provisional Patent Application No. 61/746,545, for "Smart Mixing,"
filed on behalf of first named inventor Conor Francis Madigan on
Dec. 27, 2012; U.S. Provisional Patent Application No. 61/822,855
for "Systems and Methods Providing Uniform Printing of OLED
Panels," filed on behalf of first named inventor Nahid Harjee on
May 13, 2013; U.S. Provisional Patent Application No. 61/842,351
for "Systems and Methods Providing Uniform Printing of OLED
Panels," filed on behalf of first named inventor Nahid Harjee on
Jul. 2, 2013; U.S. Provisional Patent Application No. 61/857,298
for "Systems and Methods Providing Uniform Printing of OLED
Panels," filed on behalf of first named inventor Nahid Harjee on
Jul. 23, 2013; U.S. Provisional Patent Application No. 61/898,769
for "Systems and Methods Providing Uniform Printing of OLED
Panels," filed on behalf of first named inventor Nahid Harjee on
Nov. 1, 2013; and U.S. Provisional Patent Application No.
61/920,715 for "Techniques for Print Ink Volume Control To Deposit
Fluids Within Precise Tolerances," filed on behalf of first named
inventor Nahid Harjee on Dec. 24, 2013. PCT Patent Application No.
PCT/US2014/035193 further claims the benefit of U.S. Provisional
Patent Application No. 61/816,696 for "OLED Printing Systems and
Methods Using Laser Light Scattering for Measuring Ink Drop Size,
Velocity and Trajectory" filed on behalf of first named inventor
Alexander Sou-Kang Ko on Apr. 26, 2013, and of U.S. Provisional
Patent Application No. 61/866,031 for "OLED Printing Systems and
Methods Using Laser Light Scattering for Measuring Ink Drop Size,
Velocity and Trajectory" filed on behalf of first named inventor
Alexander Sou-Kang Ko on Aug. 14, 2013. Priority is claimed to each
of the aforementioned applications and each of the aforementioned
patent applications is hereby incorporated by reference.
BACKGROUND
[0002] Industrial fabrication processes are increasingly turning to
printing systems to fabricate layers of products. These printing
systems deposit a fluid, which is then cured or hardened to form a
permanent layer of a particular product. These fabrication
processes are especially useful for the fabrication of
microelectronic products or products with arrays of
quasi-electronic structures. For example, such printing processes
are increasingly being used to manufacture thin film electronic
displays and solar panels for a wide variety of applications. The
mentioned printing systems are typically characterized by, in
addition to the type of fluid utilized ("ink"), the use of many
thousands of print nozzles on one or more printheads that are
designed with capabilities to place individual, substantially
uniform size droplets with near micron resolution. This precision
control over both deposited droplet volume and position helps
facilitate high quality in end-products as well as high-resolution,
small footprint products and reduced manufacturing costs. For
example, in one application, namely the manufacture of organic
light emitting diode (OLED) displays, the ability to precision
deposit the inks helps produce smaller, thinner, more resolute
displays at lower cost. Note that while the term "ink" is used to
refer to the deposited fluid, the deposited fluid is typically
colorless, and is deposited as a structure that will "build" a
thickness of a permanent layer of a device, i.e., the color of the
fluid itself is typically not important in the sense it would be
for ink used in a conventional graphics printing application.
[0003] Not surprisingly, in these applications, quality control is
dependent on uniformity in deposited ink droplets, as to size
(droplet volume) and precise position, or at least an understanding
as to variation in such features is important to be able to produce
permanent layers that consistently meet desired quality standards
for layer registration accuracy and/or layer homogeneity. Note that
in an industrial printing system, droplet uniformity for any given
nozzle can also potentially change over time, whether due to
statistical variation, changes in nozzle age, clogging, ink
viscosity or constituency variation, temperature, or other
factors.
[0004] What is needed is a droplet measurement system adapted for
use in connection with an industrial printing process, ideally, for
in situ use with a printing system used by an industrial
fabrication apparatus. Ideally, such a droplet measurement system
would provide near fast measurement of one or more droplet
parameters, be easy to maintain, and provide inputs that could be
used to adjust printing, so as to enable precise quality control
for used in the industrial product fabrication processes. The
present invention addresses these needs and provides further,
related advantages.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a flow chart illustrating techniques for measuring
a droplet parameter.
[0006] FIG. 2 is a close-up perspective view of a droplet
measurement system.
[0007] FIG. 3 is a cross-sectional view of a droplet measurement
system.
[0008] FIG. 4A is another perspective view of a droplet measurement
system.
[0009] FIG. 4B is a perspective view of the droplet measurement
system from FIG. 4A taken from the vantage point of arrow B-B in
FIG. 4A.
[0010] FIG. 5A is a flow chart associated with image processing
techniques used in one embodiment.
[0011] FIG. 5B is a sample captured image representing drops
deposited on a medium, following conversion to grayscale.
[0012] FIG. 5C is the captured image of FIG. 5B following filtering
(e.g., gradient processing).
[0013] FIG. 6A is an illustrative diagram showing manufacturing
tiers associated with product fabrication; the techniques disclosed
herein can be implemented, without limitation, in any of the
depicted tiers.
[0014] FIG. 6B shows a fabrication apparatus in plan view.
[0015] FIG. 7A is an illustrative representation regarding use of a
droplet measurement system.
[0016] FIG. 7B is a flow chart relating to droplet measurement.
[0017] FIG. 7C is a flow chart relating to droplet validation.
[0018] FIG. 8A is a cross-sectional representation of elements of
an industrial printer, internal to a print chamber.
[0019] FIG. 8B is a cross-sectional representation of the
industrial printer of FIG. 7A, taken along lines B-B in FIG.
8A.
[0020] FIG. 9 is a diagram showing a comparison of measured droplet
positions relative to respective expected positions.
[0021] FIG. 10 is a flow chart relating to droplet volume
computation.
[0022] The subject matter defined by the enumerated claims may be
better understood by referring to the following detailed
description, which should be read in conjunction with the
accompanying drawings. This description of one or more particular
embodiments, set out below to enable one to build and use various
implementations of the technology set forth by the claims, is not
intended to limit the enumerated claims, but to exemplify their
application. Without limiting the foregoing, this disclosure
provides several different examples of a droplet measurement system
that optically measures or images deposited droplets on a medium,
and that uses image processing to identify values of a parameter
for various nozzles of a printhead used in industrial fabrication.
The various techniques can be embodied as a droplet measurement
system, as a printer or fabrication apparatus, or as software for
performing described techniques, in the form of a computer, printer
or other device running such software, or in the form of an
electronic or other device (e.g., a flat panel device or other
consumer end product) fabricated as a result of these techniques.
While specific examples are presented, the principles described
herein may also be applied to other methods, devices and systems as
well.
DETAILED DESCRIPTION
[0023] In one embodiment, a droplet measurement system receives ink
droplets from various nozzles of one or more printheads, and then
uses optical analysis to measure a value of a parameter associated
with the various droplets and/or the various printhead nozzles that
produced those droplets. More specifically, as will be discussed
below, some embodiments use deposition tape in a printer
maintenance bay for test printing of the ink concurrently from
various nozzles. The tape can advantageously be any medium capable
of receiving ink droplets, although in notable embodiment discussed
below, it comprises a clear film that is specially treated to fix
wet ink droplets, much like photographic paper. Also in one
embodiment, this system is applied in an industrial fabrication
apparatus where droplets to be deposited are themselves clear or
translucent (for example, representing a material that will be
deposited and cured to form an encapsulation layer of a panel
device, such as a display or solar panel, or light generating
elements of such a device). This transparency permits image capture
of groupings of one or more droplets for a set of multiple nozzles;
in optional embodiments, the droplet depositions can be
distinguished from both the film and imaged nozzle locations
(behind the film) to provide extremely fast measurement of droplet
positional offset (relative to ideal droplet position) and/or
volume and/or timing errors associated with droplet deposition.
[0024] In one embodiment, to perform measurement, the printhead or
printheads are parked in a maintenance station, for example, while
a substrate is loaded or unloaded into the printer (and thus, while
the printer/fabrication apparatus is otherwise employed). While the
printheads are parked, the droplet measurement system is engaged to
bring the deposition medium (e.g., the clear film) into close
proximity with one or more printheads in a manner registered at a
specific position relative to the one or more printheads. Nozzles
from one or more of the printheads (e.g., a window or subarray
comprising a subset of all nozzles) are then cause to fire one
droplet or a series of droplets (e.g., 2, 5, 10, etc.), such that
the droplets land on the medium close to a position expected for
the given nozzle. During this time, or after this time, the film is
imaged from a side of the film opposite the printhead, effectively
through the transparent film; this is to say, the film is precisely
positioned at a normal deposition distance relative to the nozzles
being measured (e.g., <1.0 millimeters) and measurement is
simultaneously (or shortly later) performed on multiple nozzles
simultaneously by firing those nozzles, and then by capturing an
image through the opposite side of the film, with the resultant
captured image then being image processed to derived droplet
parameter values.
[0025] Note several advantages to features of the various
embodiments described so far. First, the mentioned optical
processing of deposited droplets through the clear film is
especially useful for very large printheads having hundreds to many
thousands of nozzles, i.e., optical processing can be immediately
performed without the requirement of further moving the printhead,
the droplet measurement system or other components. Second, the
droplet measurement system can be configured to measure droplets
from many nozzles at the same time; for example, it is possible to
jet, and concurrently measure, droplets from hundreds of nozzles.
When compared to systems that optically image individual droplets
in flight for example, e.g., one at a time, this type of
concurrency can do much to facilitate measurement of droplets
across many thousands of printhead nozzles (e.g., as is used in
some industrial fabrication applications). For systems that rely on
dynamically updated measurement of droplet parameters, so as to
combine droplets in a manner that mitigates variation or that
accounts for variation in producing precise target volumes, this
type of concurrency can be important, because it does not require
significant interruption in print time or in manufacturing
throughput. For a droplet measurement system that articulates
relative to parked printhead or printheads in a service station,
this provides for easy, precision access to any of thousands of
print nozzles as can be used in some industrial manufacturing
processes. Also, the deposition tape or its treatment can be
specially adapted to the chemical properties of a specific ink
under test (i.e., to enable its properties to be more readily or
more precisely ascertained by optical means). As should be
apparent, the described techniques provide for enhanced accuracy
and lower cost in manufacturing products, e.g., especially
price-sensitive consumer products such as flat panel high
definition televisions ("HDTVs").
[0026] For at least one design discussed below, the droplet
measurement system mounts a clear film using a roll-to-roll
mechanism, which permits advance of the film as a tape across an
imaging area, permitting for intermittent change of tape rolls used
for measurement. In addition, the droplet measurement system can
also advantageously use a vacuum system which closely adheres that
portion of the tape being deposited on in a flat, precise
positional relationship that mimics an online deposition surface.
The droplet measurement system can also optionally include a cure
station to cure/dry ink, such that excess ink is inhibited from
spread to any other portion of the system following measurement;
note that this is not necessary in some embodiments, e.g., the film
can also be selected to have properties or be treated to have
properties such that the ink droplets once deposited are
immediately fixed. Also, as noted, the droplet measurement system
can optionally be mounted on a three-dimensional movable mount,
i.e., so as to engage a parked printhead from below along a
vertical ("z") axis and to move as desired along x (and optionally
y) axes so as to reach different nozzles and different printheads.
This permits a "large" printhead assembly (e.g., having thousands
of nozzles) to be left stationary while the droplet measurement
system is articulated beneath a printing plane (e.g., in a
maintenance bay) and used to measure parameters for different
groups of nozzles. One contemplated deposition process advances a
roll of tape such that a window of virgin tape is adjacent selected
printheads, these printheads then are controlled to have all of
their nozzles eject a predetermined amount of ink, which is then
fixed on the tape; simultaneously, a coaxial camera and image
sensor from below (e.g., within a housing or chassis of the droplet
measurement system) images all deposited droplets in parallel (once
again, by image capture through an opposite site of the tape, such
that the film and droplet measurement system typically does not
have to be moved or repositioned for analysis). If desired, the
camera (or image capture optics) can be made movable relative to
the droplet measurement system, e.g., to provide for scanning
activity across a range of nozzles, focus adjustment, or other
desired benefit.
[0027] The output of an image processing system then provides
droplet parameter data that is useful in validating nozzles or
otherwise planning printing. Following any given measurement
iteration, the tape and the droplet measurement system are each
advanced in position, with used tape being cured and/or rolled up,
and the process is then repeated as necessary, immediately or at a
later time. In a design where the tape cannot be reused once
printed upon, a spent roll of tape (or a tape cartridge, with reels
for new and used tape and capstans) can be periodically collected
or replaced on a modular basis. Note that in one contemplated
application, in which a fabrication mechanism is continuously used
(e.g., to print layers of OLED television screens, or otherwise to
fabricate a layer of one or more flat panel devices), as a prior
substrate is or unloaded, the printhead is parked and subjected to
described droplet measurement, and as soon as a new, ensuing
substrate is ready, the measurement progress is stored, the
printhead returned to active printing duty, and so forth; when this
ensuing substrate is finished, the printhead is once again returned
to the maintenance station (while a new substrate is loaded) to
begin measurement where the system previously left off. In this
manner, repeated measurements can be collected for nozzles and used
on a rolling basis to build a statistical distribution for each
print nozzle or nozzle-waveform combination through many
measurements (e.g., as described in the aforementioned patent
applications which have been incorporated by reference), using a
moving measurement window that precesses circularly through the set
of all print nozzles so as to continuously update measurement
data.
[0028] Note that all of the process steps recited above (as well as
below) can be implemented in a number of manners. For example, in
one embodiment, these steps are performed by one or more computers
or other types of machines (such as a printer or one or more
manufacturing devices), either by special purpose hardware or by
general purpose hardware that is configured to operate as a special
purpose machine. For example, in one contemplated design, one or
more of the tasks can be performed by one or more such machines
acting under the control of instructions stored on non-transitory
machine-readable media, e.g., firmware or software. Such
instructions are written or designed in a manner that has certain
structure (architectural features) such that, when they are
ultimately executed, they cause the one or more general purpose
machines (e.g., a processor, computer or other machine) to behave
as a special purpose machine, having structure that necessarily
performs described tasks on input operands to take actions or
otherwise produce outputs. "Non-transitory machine-readable media"
means any tangible (i.e., physical) storage medium, irrespective of
how data on that medium is stored, including without limitation,
random access memory, hard disk memory, optical memory, a floppy
disk or CD, server storage, volatile memory and other tangible
mechanisms where instructions may subsequently be retrieved by a
machine. The machine-readable media can be in standalone form
(e.g., a program disk) or embodied as part of a larger mechanism,
for example, a laptop computer, portable device, server, network,
printer, or other set of one or more devices. The instructions can
be implemented in different formats, for example, as metadata that
when called is effective to invoke a certain action, as Java code
or scripting, as code written in a specific programming language
(e.g., as C++ code), as a processor-specific instruction set, or in
some other form; the instructions can also be executed by the same
processor or different processors, depending on embodiment.
Throughout this disclosure, various processes will be described,
any of which can generally be implemented as instructions stored on
non-transitory machine-readable media, and any of which can be used
to fabricate products using a "3D printing" or other printing
process. Depending on product design, such products can be
fabricated to be in saleable form, or as a preparatory step for
other printing, curing, manufacturing or other processing steps,
that will ultimately create finished products for sale,
distribution, exportation or importation. Depending on
implementation, the instructions on non-transitory machine-readable
media can be executed by a single computer and, in other cases, can
be stored and/or executed on a distributed basis, e.g., using one
or more servers, web clients, or application-specific devices. Each
function mentioned can be implemented as part of a combined program
or as a standalone module, either stored together on a single media
expression (e.g., single floppy disk) or on multiple, separate
storage devices.
[0029] Note also that "clear" when used in connection with the film
or tape is a relative term, i.e., it refers to the ability to
capture an image of droplets deposited on a first side of the tape
through a second side of the tape. This does not, strictly
speaking, require the tape to be colorless or for that matter,
transparent to visible light. In one embodiment, the tape is
colorless and highly transparent to visible light, and visible
light is used to capture an image of droplets from respective
nozzles, where those droplets are deposited in a manner such that
respective nozzles' droplets are arrayed on the first side of the
tape (i.e., at respective positions correlated with the respective
nozzles). In another embodiment, the tape has some degree of color,
for example, optimized to a specific ink so as to enhance image
capture properties of that ink. In yet another embodiment,
radiation other than visible light is used to capture droplet
properties.
[0030] Various other features will be apparent to those skilled in
the art from the description herein. Having thus introduced
features of several embodiments, this disclosure will now turn to
providing additional detail regarding select embodiments.
[0031] FIG. 1 shows a flow diagram 101 that illustrates some of the
techniques described herein. As indicated above, it is desired to
concurrently measure values of droplet parameters for droplets
produced by a multitude of nozzles. In order to perform this as
rapidly as possible, embodiments disclosed herein rely on image
capture of a deposition surface that receives such droplets (i.e.,
fast capture of droplets collectively representing the multiple
nozzles), and image processing that computes values of one or more
desired parameters respective to the multiple nozzles from this
image capture. As noted by reference numeral 103, the printhead or
printheads under analysis cause a range or array of nozzles to
fire, to each thereby deposit one or more droplets. To provide an
example, it could be that a hypothetical printhead has two thousand
nozzles, and that these nozzles are to be measured in groups of one
hundred nozzles at a time. For each measurement iteration, the
printhead and/or the droplet measurement system are aligned, and
the window or group of one hundred nozzles to be measured are
identified and caused to fire a controlled ink volume substantially
concurrently; in one embodiment, the deposition can be a single
droplet per nozzle, and in other embodiments, a larger number of
droplets can be controllably ejected from each nozzle, for example,
2, 5, 10, 12, 20 or some other number of droplets. Note that in
some contemplated designs (e.g., OLED applications), droplet size
is typically quite small, comprising picoliter ("pL") size droplets
that are tens of microns in diameter or smaller, deposited with
near-micron precision.
[0032] As noted in the aforementioned patent applications
incorporated by reference, depending on application, it may be
desired to measure position of deposited droplets, droplet
velocity, droplet volume, nozzle bow, or one or more other
parameters for each nozzle. Briefly, in one embodiment, it is
important to have an expectation of droplet qualities from each
nozzle for each deposited droplet; this is to say, if one nozzle
relative to others is off position (nozzle bow) or produces
aberrant droplet trajectory or an inaccurate droplet volume, then
this could lead to nonuniformity in a deposited film. Such
nonuniformity can lead to quality defects in precision products,
for example, display devices and the like. An understanding
nozzle-by-nozzle of such aberration permits: [0033] (a) nozzle
qualification/disqualification--a nozzle that does not work or
otherwise has aberrant characteristics can be identified and not
used in printing, with software planning printing in a manner where
a different nozzle is used to deposit a droplet in the desired
area; [0034] (b) firing time mitigation--a positional defect in the
scanning direction can be potentially corrected by changing a
nozzle drive pulse as to timing or voltage, for example, such that
the nozzle fires earlier or later, or ejects droplets with a
greater or lesser velocity; in addition, it is also possible to use
alternate drive pulse shapes as disclosed in the aforementioned
patent applications which have been incorporated by reference;
[0035] (c) planned droplet combinations--detected differences from
nozzle-to-nozzle can be accepted and deliberately used in
calculating droplet combinations based on respective, expected
values, to achieve a precise result, e.g., within a specific
tolerance; for example, if one nozzle is measured and determined to
produce expected 9.89 picoliter (pL) droplets, a second nozzle is
measured and determined to produce expected 10.11 pL droplets and
it is desired to produce a total volume of 20.00 pL ink in a
specific target location, these two nozzles can be specifically
identified and printing planned to deposit this specific droplet
combination; note that obtainable results are different from a
system that simply averages out differences without regard to a
specific fill volume or fill tolerance (e.g., a target volume
.+-.0.50%); and [0036] (d) prescreening of drive waveforms--as
noted in the aforementioned patent applications which have been
incorporated by reference, it is possible to prescreen programmable
drive waveforms for each nozzle (e.g., a choice of sixteen
preselected drive waveforms) for stock use during printing, each
waveform selected to achieve a specific deposition characteristic,
with precision, expected results.
[0037] Note that droplet parameters can potentially vary from
day-to-day, and even from deposition-to-deposition, e.g., dependent
on ink qualities, temperature, nozzle age (e.g., clogging) and
other factors. To ensure precision printing therefore, in some
implementations, it can be desired to remeasure these values from
time-to-time. Note also that each deposited droplet, even from a
single nozzle, can be slightly different; in one embodiment
therefore, each nozzle (or nozzle-waveform combination or pairing)
is measured not just once, but multiple times, to develop a
population of measurements, from which a mean or other statistical
parameter (e.g., a spread measure) can be computed so as to provide
a high confidence regarding expected values for droplet parameters.
For example, "24" droplets from each nozzle-waveform pairing could
be measured to develop means (and thus an expected value for)
volume, velocity, bow (position orthogonal to scanning direction),
and so forth, with the number of measurements n (n=24) helping
reduce uncertainty due to measurement error or statistical
variation. A given population can be updated on a rolling basis
(e.g., all measurements stored and 6 newest measurements replacing
6 oldest for each nozzle every two hours), or on an at-once basis
(e.g., all nozzles remeasured at once during power-up). There are
many variations that will occur to those skilled in the art, e.g.,
a nozzle can be measured to determine an expected value and the
nozzle disqualified from use if this measured (expected) value is
outside of a band that is .+-.5% of an ideal value; many
permutations and variations are clearly possible.
[0038] As should be apparent, however, in a printing system that
uses thousands of nozzles (e.g., tens of thousands of nozzles or
more, perhaps each with multiple available "prescreened" drive
waveforms), measurement of expected droplet parameters for each
nozzle could potentially take substantial time; in an industrial
fabrication environment, this is typically unacceptable, i.e., to
be commercially viable, manufacturing throughput and costs need to
produce products at an acceptable consumer price point, and this
typically means that the print process produces as many products as
possible, with as great an accuracy (and as little product waste)
as possible, with as little down time as possible. The techniques
disclosed herein permit much more rapid and, thus, feasible
measurement.
[0039] Returning to FIG. 1, to this effect, the droplet measurement
techniques presented by this disclosure also capture droplets from
many nozzles at once, per numeral 105. That is to say, as
contrasted with systems that image droplets in flight
"one-at-a-time," embodiments presented by this disclosure rely on
concurrency to measure as many nozzles as possible at the same
time. Thus, image capture can be used to effectively take a picture
of droplets from a large array of nozzles, e.g., droplets deposited
in multiple columns and in multiple rows, which are quickly
processed in software by an image processing system. In one
embodiment, a captured image can represent droplets from dozens,
and potentially hundreds of nozzles (or more), all measured at the
same time. FIG. 1 indicates in dashed-line boxes various options
that can contribute to this end, for example, (a) capturing images
through the deposition surface opposite the printhead (107), which
helps speed measurement, (b) capturing droplets and nozzles both in
a captured image at the same time (109), which facilitates
measurement of positional offset, bow, or velocity for droplets
from respective nozzles, (c) photographing droplets from respective
(multiple) nozzles at the same time (111), e.g., effectively
measuring forty or more nozzles at once, and (d) photographing not
one droplet per nozzle, but an aggregation of multiple droplets,
e.g., 5 or more, measured at the same time. Note that in the latter
case, image processing software can detect volume of an aggregate
deposition (e.g., volume), or spread in terms of droplet position
around an expected position, and can identify individual droplets,
mean, or another statistical parameter such as distribution
(spread) at once from a single captured image. Note that this may
require, depending on embodiment, that a standard be measured in
advance and stored in the system; for example, as ink droplets are
fixed into the deposition medium (i.e., the tape), it may be
difficult to detect droplet volume; such a determination can be
predicated on droplet diameter, processing of color (or grayscale)
value of a deposited droplet, or using other means, with these
values compared to a calibration standard in order to produce
accurate value computation.
[0040] As noted by numerals 115 and 117, the system (e.g., using an
image processor running appropriate software) then calculates
measured values and stores these in memory (e.g., random access
memory such as in an available hard disk drive). In one embodiment,
these values are stored individually (i.e., one for each
measurement for each parameter being measured for each nozzle) and
in another embodiment, they can be stored in a manner representing
a composite distribution (e.g., as a mean, total number of
measurements, standard deviation, etc., for a given parameter for a
given nozzle). Per numerals 119, 121 and 123, as noted earlier, the
values once measured can be optionally used to compute a
statistical distribution, to perform nozzle
qualification/validation, and to perform "smart combinations" where
print scans are planned to match droplets with expected
characteristics in some desired manner.
[0041] FIGS. 2-4B are used to describe one embodiment of a modular
droplet measurement system.
[0042] FIG. 2 shows a close up view of a first such system 201.
This view depicts a measurement window 203 (e.g., a glass-covered
view window) through which images are captured along a vector
represented by numeral 205. An optical detector, for example a
camera, lies within system 201 and takes pictures through this
window 203 along the direction of arrow 205. During operation, a
clear film tape from roll 207 is advanced over this window and is
held tight against the window by a set of vacuum ports 209.
Following each measurement, this tape can be advanced in the
direction of capstan 211 and accumulated in a discard roll (not
seen) held within a chassis 213 of the droplet measurement system.
Note that the depicted system is modular and is moved as a unit,
e.g., to position the measurement window 203 (and associated
measurement area defined by this window) in close proximity to any
printhead nozzles to be measured, at a "standard deposition depth"
relative to a nozzle plate of the printheads. In optional
embodiments, the droplet measurement system 201 can be articulated
in three dimensions so that this system can be placed adjacent
other nozzle sets and also so as to vary deposition height as
desired.
[0043] FIG. 3 shows an interior, cross-sectional view of the
droplet measurement system 301. This system similarly includes a
view window 303 through which images are captured and an optics
system comprising an optics assembly 305, a camera 307 and a light
source 309. A stepper motor 311 selectively advances the optics
assembly 305 linearly relative to the view window 303, i.e., back
and forth in the direction indicated by arrows 313. Note that
"camera" as used herein can optionally refer to any type of light
sensor, i.e., it is possible to use a simple line sensor comprising
individual optical sensors and for example to "scan" such a line
sensor back and forth to image the entire viewing window 303 using
this stepper motor 311. In other embodiment embodiments, the camera
captures an image representing an array of pixels of the view area
through any conventional means, e.g., using a commercial
photographic camera, charge couple device array, an ultraviolet or
other nonvisible radiation capture device, or with other means.
Note that camera movement (i.e., scanning movement) is not required
for all embodiments. In the depicted embodiment, the optics
assembly 305 also internally comprises a beam splitter which passes
light from the light source (e.g., up to the view window 303), but
diverts returning (reflected) light using a mirror in the direction
of the camera 307, for image capture. As should be apparent, light
form the light source passes through the view window, through the
clear tape, reflects against the printhead (not shown in FIG. 3),
passes back again through the clear tape, and subject to any
focusing or other optics, is captured and processed for analysis. A
captured image thus provides visible indication of the position of
each nozzle being measured (e.g., this image is captured from
reflection by the nozzle plate) and also shows overlay of any
deposited droplets (which are transparent, but distinguishable from
the film). This is to say, in contemplated manufacturing processes
(particularly for OLED display fabrication, e.g., for an
encapsulation layer), deposition materials are translucent, and
thus do not occlude image capture of the nozzle plate. FIG. 3 also
shows a capstan 315 for transport of the clear tape and a UV curing
bar 317 for curing any deposited ink, so as to prevent transfer of
deposited ink to any other system component. FIG. 3 also shows an
interface and control board 319, used for control over the various
system components, and for control over image capture; the
interface control board 319 also controls transport of the film
tape, for example, by controlling film roll motors 321 and 323
respectively used for film intake and supply rolls (not separately
identified this FIG.). Image processing can be, depending on
embodiment, performed either locally on the interface and control
board 319 or alternatively, at a processor in the manufacturing
apparatus or at a remote computer.
[0044] FIGS. 4A and 4B show perspective views of the droplet
measurement system 301 from FIG. 3. FIG. 4B represents a view of
the backside of the unit relative to FIG. 4A, that is, from the
vantage point provided by arrow B-B of FIG. 4A. More specifically,
these FIGS. identify view window 303, vacuum ports 403, UV curing
bar 317, a tape supply roll 405 and intake roll 407, a frame and
optic chamber 409 (which houses the interface and control board
319, as described earlier). During operation, virgin tape is
supplied in the direction indicated by arrow 411 and is adhered
closely against the view window 303, as referenced earlier. From
this point, the film is advanced over capstan 315 and downward
toward the UV curing bar 317 along arrow 412, for the purposes
described earlier. Operation of the UV curing bar is controlled by
the interface and control board 319, using onboard firmware or
software stored on non-transitory-machine readable media. Finally,
following cure, film is advanced generally as indicated by arrow
415 to the intake roll 407. As should be apparent, the entire unit
is modular, providing for easy removal and servicing, for example,
to remove a finished intake roll 407 of clear deposition tape and
to change the supply roll 405 to have fresh stock.
[0045] FIG. 5A presents a flow chart associated with one embodiment
501 of a method of performing droplet measurement. As noted
earlier, it can be desired to perform measurement in situ, that is,
directly within a fabrication apparatus to dynamically update
values of one or more droplet parameters for process, age,
temperature, or other factors. To this end, measurement is
advantageously performed in a service station of a printer, for
example, while a new substrate is being loaded, unloaded, cured
following deposition, or otherwise during idle time relative to
actual printing. Per numeral 503, one or more printheads (for
example, mounted to a common printhead assembly) are advanced to
the service station and are "parked" for maintenance operations.
Such maintenance operations can include various calibrations,
printhead replacement, nozzle purging or other quality processing,
droplet measurement as contemplated by this disclosure, or for
other purposes. As will be described more fully below, for OLED
display fabrication applications (and for fabrication of certain
other devices, such as solar panels), it can be desired to perform
printing in a controlled atmosphere; therefore, in many
applications, the "parked" position will be in a second controlled
atmospheric chamber, for example, in a location that can be
externally accessed (e.g., for printhead replacement) without
venting the entire fabrication apparatus or printer to an
uncontrolled atmosphere. This is to say, such a second chamber is
preferably made to be a small size relative to any printing
enclosure, e.g., taking up two percent or less of the overall print
chamber volume, so as to minimize venting (if any). Once the
printheads are parked, they are sealed against this second
controlled atmosphere and the droplet measurement system ("DMU,"
for droplet measurement unit) is selectively engaged to perform
measurement (505). As noted by optional process block 507, if
printing is performed on an intermittent basis for a moving window
of nozzles (e.g., with different sets of nozzles measured or
remeasured in between print runs, as substrates are loaded and
unloaded as mentioned earlier), the system retrieves a start
address so as to position the DMU to capture the selected subset of
nozzles. Note that this process can employ a registration process
to identify corner nozzles of each printhead (e.g., updated as a
printhead is changed, such that the system is calibrated to "know"
the approximate position of each nozzle). Such a registration
process can be performed by articulating the DMU (and its camera)
so as to image and thereby find the corner nozzles for each array,
using an approximate positional address and search process (e.g.,
spiral search algorithm), for example, as described in U.S. patent
application Ser. No. 14/340,403, referenced earlier. Control over
positional throws is quite precise in the described system, e.g.,
to approximately one micron, and typically recalibration of
printhead-to-droplet measurement system positioning is not required
unless a system component is manually changed (for example, the DMU
or a printhead is removed or serviced). With a clear tape (i.e.,
droplet deposition surface for testing) in place, per numeral 509,
the system controls the printhead nozzles under scrutiny to each
deposit a controlled number of droplets (in quick succession if
multiple droplets are to be measured per-nozzle). Simultaneously,
the image capture system within the DMU images deposited ink as
well as nozzle locations (e.g., through the clear tape and the ink,
capturing light reflected by the printhead). Note that as indicated
by numeral 511, in one embodiment, image capture is performed in
color so as to be able to identify concentration of ink in any
deposited ink droplets (e.g., which, while translucent, will impart
subtle color properties according to material or thickness). As
also indicated by numeral 511, a captured image can be filtered
(e.g., for color, intensity, gamma, or any other desired parameter
or parameters) so as to yield a filtered image; following such
filtering (or as part of such filtering), the captured image is
converted to grayscale, per numeral 513. Note that multiple images
can also be produced from this process according to respective
filters, for example, a first image representing the nozzles and a
second image representing deposited droplets; clearly, many
permutations exist. Image processing software then uses the output
grayscale image(s) to identify nozzles, ink droplets, positional
differences between nozzles and ink droplets, droplet volume,
droplet diameter, droplet shape, and/or any other desired
parameters (515/517). As should be apparent, it is not necessary to
all embodiments that all of these things be measured. For example,
in a system which calculates droplet volume, it may not be
necessary to image nozzles themselves, or to analyze droplet shape
or position. Conversely, it may be important in such an embodiment
(if spread of multiple droplets is being analyzed) to determine a
measure of deviation in droplet position, or to perform color
analysis to properly compute volume. The parameters that are
measured will generally depend on implementation and desired
results. As indicated by numeral 517, whatever the parameter to be
measured, the system computes a measured value or values, or an
offset for a parameter, for example using an optional standard 519,
as referenced earlier. Such offset or value of a parameter can be
computed for droplet or nozzle position, droplet timing, or droplet
volume, or any combination of these things, as referenced by
numeral 521. The system then updates a stored information
repository that is local or remote to the DMU (523) and it then
stores position for the next measurement iteration and advances the
tape, per optional process 525. The process is then done, ready for
another measurement iteration (which can be performed immediately,
or at a later time, e.g., following an ensuing substrate run).
[0046] Note that as referenced by numerals 529-533, computation of
the parameter and/or any positional offset can be optionally
performed by one or more processors running suitable software
(instructions stored on processor-readable media), and that such
processors typically store image data in processor-accessible
memory, isolate image data respective to each nozzle, calculate the
parameter from the respective image data, and also store the
per-nozzle parameter in processor-accessible memory.
[0047] FIGS. 5B and 5C respectively show sampled images 551 and
571. The first of these, image 551, represents a photograph taken
of approximately 40 nozzles as a subset of a printhead. Note how
the nozzles are slightly staggered from row-to-row to provide
options for close pitch variation in a cross scan axis (e.g., a
droplet intended for a specific substrate position can be printed
from any row of nozzles, providing depositional accuracy better
than, i.e., less than, twenty microns in some embodiments). FIG. 5B
represents a color image, which can then be filtered and/or
converted to grayscale as appropriate, as well as a grayscale image
following such filtering or conversion (i.e., color drawings are
generally not used or permitted in patent applications). Note that
in this embodiment, the nozzles are not separately imaged or
illustrated, although for other embodiments, they can be. The
second image 571 (FIG. 5C) represents the image from FIG. 5B,
following filtering and gradient processing, to identify droplet
diameters. That is to say, FIG. 5C shows white circles
corresponding to droplet diameter, with clearly demarked droplet
boundaries. Image processing calculates a center of gravity (for
example, by calculating a horizontal maximum diameter and vertical
maximum diameter of such "circles" and by taking the medial
Cartesian coordinate point along each diameter, to associate each
droplet with a specific xy Cartesian position). This position can
then be compared to nozzle position to determine offset, with the
system identifying nozzle-to-nozzle offset variation, for purposes
of print planning. These photographs can also represent droplet
volume processing; for example, image processing software can
compute diameter and/or area of each droplet and/or associated
color, and compare this to a factory-defined standard or an in
situ-defined standard, to compute size and density and, from these,
to compute volume. Nearly any desired droplet parameter can be
measured in this way.
[0048] With the particulars of a droplet measurement system thus
described, application to manufacture and to an industrial
fabrication apparatus/printer will now be described. In the
discussion below, an exemplary system for performing such printing
will be described, more specifically, applied to the manufacture of
solar panels and/or display devices that can be used in electronics
(e.g., as smart phone, smart watch, tablet, computer, television,
monitor, or other forms of displays). The manufacturing techniques
provided by this disclosure are not limited to this specific and,
for example, can be applied to any 3D printing application and to a
wide range of other forms of products.
[0049] FIG. 6A represents a number of different implementation
tiers, collectively designated by reference numeral 601; each one
of these tiers represents a possible discrete implementation of the
techniques introduced herein. First, techniques as introduced in
this disclosure can take the form of instructions stored on
non-transitory machine-readable media, as represented by graphic
603 (e.g., executable instructions or software for controlling a
computer or a printer). For example, the disclosed techniques can
be embodied as software adapted to cause a manufacturing apparatus
(or included printer) to measure one or more droplet parameters
using optical measurement techniques disclosed herein. Second, per
computer icon 605, these techniques can also optionally be
implemented as part of a computer or network, for example, within a
company that designs or manufactures components for sale or use in
other products. Third, as exemplified using a storage media graphic
607, the techniques introduced earlier can take the form of a
stored printer control instructions, e.g., that, when acted upon,
will cause a printer to fabricate one or more layers of a component
in a manner dependent on droplet measurement and associated
planning (e.g., scan path planning or nozzle qualification, as
discussed herein). Note that printer instructions can be directly
transmitted to a printer, for example, over a LAN or WAN; in this
context, the depicted storage media graphic can represent (without
limitation) RAM inside or accessible to a server, portable device,
laptop, another form of computer or a printer, or a portable media
such as a flash drive. Fourth, as represented by a fabrication
device icon 609, the techniques introduced above can be implemented
as part of a fabrication apparatus or machine, or in the form of a
printer within such an apparatus or machine (e.g., as a droplet
measurement system according to techniques disclosed herein, as a
method of manufacture, as software for controlling a droplet
measurement system, and so forth). It is noted that the particular
depiction of the fabrication device 609 represents one exemplary
printer device that will be discussed in connection with FIGS. 6B,
7A and 7B, below. The techniques introduced above can also be
embodied as a completed or partially-completed manufactured
component or an assembly of manufactured components (e.g.
manufactured pursuant to a patented process); in FIG. 6A for
example, several such components are depicted in the form of an
array 611 of semi-finished flat panel devices, that will be
separated and sold for incorporation into end consumer products.
The depicted devices may have, for example, one or more
encapsulation layers or other layers fabricated in dependence on
the methods introduced above. The techniques introduced above can
also be embodied in the form of end-consumer products as
referenced, e.g., in the form of display screens for portable
digital devices 613 (e.g., such as electronic pads or smart
phones), as television display screens 615 (e.g., OLED TVs), solar
panels 617, or other types of devices.
[0050] FIG. 6B shows one contemplated multi-chambered fabrication
apparatus 621 that can be used to apply techniques disclosed
herein. Generally speaking, the depicted apparatus 621 includes
several general modules or subsystems including a transfer module
623, a printing module 625 and a processing module 627. Each module
maintains a controlled environment, such that printing for example
can be performed by the printing module 625 in a first controlled
atmosphere and other processing, for example, another deposition
process such an inorganic encapsulation layer deposition or a
curing process (e.g., for printed materials), can be performed in a
second controlled atmosphere. The apparatus 621 uses one or more
mechanical handlers to move a substrate between modules without
exposing the substrate to an uncontrolled atmosphere. Within any
given module, it is possible to use other substrate handling
systems and/or specific devices and control systems adapted to the
processing to be performed for that module.
[0051] Various embodiments of the transfer module 623 can include
an input loadlock 629 (i.e., a chamber that provides buffering
between different environments while maintaining a controlled
atmosphere), a transfer chamber 631 (also having a handler for
transporting a substrate), and an atmospheric buffer chamber 633.
Within the printing module 625, it is possible to use other
substrate handling mechanisms such as a flotation table for stable
support of a substrate during a printing process. Additionally, a
xyz-motion system, such as a split axis or gantry motion system,
can be used for precise positioning of at least one printhead
relative to the substrate, as well as providing a y-axis conveyance
system for the transport of the substrate through the printing
module 625. It is also possible within the printing chamber to use
multiple inks for printing, e.g., using respective printhead
assemblies such that, for example, two different types of
deposition processes can be performed within the printing module in
a controlled atmosphere. The printing module 625 can comprise a gas
enclosure 635 housing an inkjet printing system, with means for
introducing an inert atmosphere (e.g., nitrogen) and otherwise
controlling the atmosphere for environmental regulation (e.g.,
temperature and pressure), gas constituency and particulate
presence.
[0052] Various embodiments of a processing module 627 can include,
for example, a transfer chamber 636; this transfer chamber also has
a including a handler for transporting a substrate. In addition,
the processing module can also include an output loadlock 637, a
nitrogen stack buffer 639, and a curing chamber 641. In some
applications, the curing chamber can be used to cure, bake or dry a
monomer film into a uniform polymer film; for example, two
specifically contemplated processes include a heating process and a
UV radiation cure process.
[0053] In one application, the apparatus 621 is adapted for bulk
production of liquid crystal display screens or OLED display
screens, for example, the fabrication of an array of (e.g.) eight
screens at once on a single large substrate. These screens can be
used for televisions and as display screens for other forms of
electronic devices. In a second application, the apparatus can be
used for bulk production of solar panels in much the same
manner.
[0054] The printing module 625 can advantageously be used in such
applications to deposit organic encapsulation layers that help
protect the sensitive elements of OLED display devices. For
example, the depicted apparatus 621 can be loaded with a substrate
and can be controlled to move the substrate back and forth between
the various chambers in a manner uninterrupted by exposure to an
uncontrolled atmosphere during the encapsulation process. The
substrate can be loaded via the input loadlock 629. A handler
positioned in the transfer module 623 can move the substrate from
the input loadlock 629 to the printing module 625 and, following
completion of a printing process, can move the substrate to the
processing module 627 for cure. By repeated deposition of
subsequent layers, each of controlled thickness, aggregate
encapsulation or other layer thickness can be built up to suit any
desired application. Note once again that the techniques described
above are not limited to encapsulation processes or to OLED
fabrication, and also that many different types of tools can be
used. For example, the configuration of the apparatus 621 can be
varied to place the various modules 623, 625 and 627 in different
juxtaposition; also, additional, fewer or different modules can
also be used.
[0055] While FIG. 6B provides one example of a set of linked
chambers or fabrication components, clearly many other
possibilities exist. The techniques introduced above can be used
with the device depicted in FIG. 6B, or indeed, to control a
fabrication process performed by any other type of deposition
equipment.
[0056] FIGS. 7A-7C are used to generally introduce techniques and
structures used for per-nozzle droplet measurement and
validation.
[0057] More particularly, FIG. 7A provides an illustrative view
depicting a droplet measurement system 701 and a relatively large
printhead assembly 703; the printhead assembly has multiple
printheads (705A/705B) each with a multitude of individual nozzles
(e.g., 707), with hundreds-to-thousands of nozzles present. An ink
supply (not shown) is fluidically connected with each nozzle (e.g.,
nozzle 707), and a piezoelectric transducer (also not shown) is
used to jet droplets of ink under the control of a per-nozzle
electric control signal. The nozzle design maintains slightly
negative pressure of ink at each nozzle (e.g., nozzle 707) to avoid
flooding of the nozzle plate, with the electric signal for a given
nozzle being used to activate the corresponding piezoelectric
transducer, pressurize ink for the given nozzle, and thereby expel
droplets from the given nozzle. In one embodiment, the control
signal for each nozzle is normally at zero volts, with a positive
pulse or signal level at a given voltage used for a specific nozzle
to eject droplets (one per pulse) for that nozzle; in another
embodiment, different, tailored pulses (or other, more complex
waveforms) can be used nozzle-to-nozzle. In connection with the
example provided by FIG. 7A, however, it should be assumed that it
is desired to measure a droplet volume produced by a specific
nozzle or specific set of nozzles (e.g., nozzle 707) where a
droplet is ejected downward from the printhead (i.e., in the
direction "h," representing z-axis height relative to a
three-dimensional coordinate system 708) toward a chassis 709 that
mounts a deposition film. As noted earlier, for embodiments which
use current droplet deposition from many nozzles, a target surface
is advantageously both fixed in a known position relative to the
printhead (e.g., such that it is known which deposited droplets
belong to which nozzle). The dimension of "h" is typically on the
order of one millimeter or less and that there are thousands of
nozzles (e.g., 10,000 nozzles) that are to have respective droplets
individually measured in this manner within an operating printer,
with the deposition surface being changed or advanced in increments
to multiple windows where many droplets (e.g. dozens to hundreds)
will be simultaneously imaged and measured. Thus, in order to
optically measure droplets from each nozzle with precision, certain
techniques are used in disclosed embodiments to appropriately
position elements of the droplet measurement system 701, the
printhead assembly 703, or both relative to one another for optical
measurement.
[0058] In one embodiment, these techniques utilize a combination of
(a) x-y motion control (711A) of at least part of the optical
system (e.g., within dimensional plane 713) to precisely position a
measurement area 715 presented by the system immediately adjacent
to any nozzle or set of nozzles that is to produce droplets for
optical calibration/measurement and (b) below plane optical
recovery (7118) (e.g., thereby permitting easy placement of the
measurement area next to any nozzle notwithstanding a large
printhead surface area). Thus, in an exemplary environment having
about 10,000 or more print nozzles, this motion system is capable
of positioning at least part of the optical system in (e.g.) 10,000
or so discrete positions proximate to the discharge path of each
respective nozzle of the printhead assembly. Optics are typically
adjusted in position so that precise focus is maintained on the
measurement area so as to capture deposited droplets on a clear
film or other deposition media, as mentioned. Note that a typical
droplet may be on the order of microns in diameter, so the optical
placement is typically fairly precise, and presents challenges in
terms of relative positioning of the printhead assembly and
measurement optics/measurement area. In some embodiments, to assist
with this positioning, optics (mirrors, prisms, and so forth) are
used to orient a light capture path for sensing below the
dimensional plane 713 originating from the measurement area 715,
such that measurement optics can be placed close to the measurement
area without interfering with relative positioning of the optics
system and printhead. This permits effective positional control in
a manner that is not restricted by the millimeter-order deposition
height h at which each droplet is deposited and imaged or the large
scale x and y width occupied by a printhead under scrutiny.
Optionally, separate light beams incident from different angles can
be used to image a film or deposition surface from underneath, or a
coaxial image capture system with a beam splitter can also be used.
Other optical measurement techniques can also be used. In an
optional aspect of these systems, the motion system 711A is
optionally and advantageously made to be an xyz-motion system,
which permits selective engagement and disengagement of the droplet
measurement system without moving the printhead assembly during
droplet measurement. Briefly introduced, it is contemplated in an
industrial fabrication device having one or more large printhead
assemblies that, to maximize manufacturing uptime, each printhead
assembly will be "parked" in a service station from time to time to
perform one or more maintenance functions; given the sheer size of
the printhead and number of nozzles, it can be desired to perform
multiple maintenance functions at once on different parts of the
printhead. To this effect, in such an embodiment, it can be
advantageous to move measurement/calibration devices around the
printhead, rather than vice-versa. [This then permits engagement of
other non-optical maintenance processes as well, e.g., relating to
other nozzles if desired.] To facilitate these actions, the
printhead assembly can be optionally "parked," as mentioned with
the system identifying a specific group or range of nozzles that
are to be the subject of optical calibration. Once the printhead
assembly or a given printhead is stationary, the motion system 711A
is engaged to move at least part of the optics system relative to
the "parked" printhead assembly, to precisely position the
measurement area 715 at a position suitable for detecting droplets
jetted from a group of respective nozzles; the use of a z-axis of
movement permits selective engagement of light recovery optics from
well below the plane of the printhead, facilitating other
maintenance operations in lieu of or in addition to optical
calibration. Perhaps otherwise stated, the use of an xyz-motion
system permits selective engagement of the droplet measurement
system independent of other tests or test devices used in a service
station environment. For example, in such a system, one or more
printheads of a printhead assembly can also selectively be changed
while the printhead is parked. Note that this structure is not
required for all embodiments; other alternatives are also possible,
such in which only the printhead assembly moves (or one of the
printheads is moved) and the measurement assembly is stationary or
in which no parking of the printhead assembly is necessary.
[0059] Generally speaking, the optics used for droplet measurement
will include a light source 717, an optional set of light delivery
optics 719 (which direct light from the light source 717 to the
measurement area 715 as necessary), one or more light sensors 721,
and a set of recovery optics 723 that direct light used to measure
the droplet(s) from the measurement area 715 to the one or more
light sensors 721. The motion system 711A optionally moves any one
or more of these elements together with the chassis 709 (e.g.,
together with the imaging area) in a manner that permits the
direction of post-droplet measurement light from the measurement
area 715 to a below-plane location. In one embodiment, the light
delivery optics 719 and/or the light recovery optics 723 use
mirrors that direct light to/from measurement area 715 along a
vertical dimension parallel to droplet travel, with the motion
system moving each of elements 709, 717, 719, 721 and 723 as an
integral system during droplet measurement; this setup presents an
advantage that focus need not be recalibrated relative to
measurement area 715. As noted by numeral 711C, the light delivery
optics are also used to optionally supply source light from a
location below the dimensional plane 713 of the measurement area,
e.g., with both light source 717 and light sensor(s) 721
directing/collecting light from beneath the measurement area, as
generally illustrated. As noted by numerals 725 and 727, the optics
system can optionally include lenses for purposes of focus, as well
as photodetectors (e.g., for non-imaging techniques that do not
rely on processing of a many-pixeled "picture"). Note once again
that the optional use of z-motion control over the chassis permits
optional engagement and disengagement of the optics system, and
precise positioning of measurement area 715 proximate to any group
of nozzles, at any point in time while the printhead assembly is
"parked." Such parking of the printhead assembly 703 and xyz-motion
of the optics system 701 is not required for all embodiments. Other
combinations and permutations are also possible.
[0060] FIG. 7B provides flow of a process associated with droplet
measurement for some embodiments. This process flow is generally
designated using numeral 731 in FIG. 7B. More specifically, as
indicated by reference numeral 733, in this particular process, the
printhead assembly is first parked, for example, in a service
station (not shown) of a printer or deposition apparatus. A droplet
measurement device is then engaged (735) with the printhead
assembly, for example, by selective engagement of part or all of a
droplet measurement system through movement from below a deposition
plane into a position where an optics system of the droplet
measurement system is capable of measuring droplets from many
nozzles concurrently. Per numeral 737, this motion relative of one
or more optics-system components relative to a parked printhead can
optionally be performed in x, y and z dimensions.
[0061] As indicated in the aforementioned patent applications which
have been incorporated by reference, even a single nozzle and
associated nozzle firing drive waveform (i.e., pulse(s) or signal
level(s) used to jet a droplet) can produce droplet volume,
trajectory, and velocity that varies slightly from
droplet-to-droplet. In accordance with teachings herein, in one
embodiment, the droplet measurement system, as indicated by numeral
739, optionally obtains n measurements per droplet of a desired
parameter, to derive statistical confidence regarding the expected
properties of that parameter. In one implementation, the measured
parameter can be volume, whereas for other implementations, the
measured parameter can be flight velocity, flight trajectory,
nozzle position error (e.g., nozzle bow) or another parameter, or a
combination of multiple such parameters. In one implementation, "n"
can vary for each nozzle, whereas in another implementation, "n"
can be a fixed number of measurements (e.g., "24") to be performed
for each nozzle; in still another implementation, "n" refers to a
minimum number of measurements, such that additional measurements
can be performed to dynamically adjust measured statistical
properties of the parameter or to refine confidence. Clearly, many
variations are possible. In connection with the system described
earlier, a measurement population can be built up immediately
(i.e., by taking multiple droplet measurements for a given nozzle
array during a single measurement iteration, that is, without
moving the droplet measurement system to a different nozzle set),
or by taking a single measurement and building up a measurement
population through later measurements (e.g., as measurement
continually precesses through a circular range of nozzles over
time).
[0062] For the example provided by FIG. 7B, it should be assumed
that droplet volume is being measured, so as to obtain an accurate
mean representing expected droplet volume from a given nozzle and a
tight confidence interval. This enables optional planning of
droplet combinations (using multiple nozzles and/or drive
waveforms) while reliably maintaining distributions of composite
ink fills in a target region about an expected target (i.e.,
relative to a composite of droplet means). As noted by optional
process boxes 741 and 743, contemplated optical measurement
processes ideally enable instantaneous or near instantaneous
measurement and calculation of volume (or other desired parameter)
of many nozzles at once, for example, using a clear film and below
deposition plane capture (i.e., from an opposite side of the film
to that used for deposition); with such fast-measurement, it
becomes possible to frequently and dynamically update volume
measurements, for example, to account for changes over time in ink
properties (including viscosity and constituent materials),
temperature, nozzle clogging or age and other factors. Building on
this point, for example, with a 10,000 nozzle printhead assembly,
it is expected that large measurement populations for each of the
thousands of nozzles can be obtained in minutes, rendering it
feasible to frequently and dynamically perform droplet measurement.
As noted earlier, in one optional embodiment, droplet measurement
(or measurement of other parameters, such as trajectory and/or
velocity) can be performed as a periodic, intermittent process,
with the droplet measurement system being engaged according to a
schedule, or in between substrates (e.g., as substrates are being
loaded or unloaded), or stacked against other assembly and/or other
printhead maintenance processes, to effectively collect many data
points (and thereby build a statistical distribution representing
each nozzle) over many measurement intervals. Note that for
embodiments that permit alternate nozzle drive waveforms to be used
in a manner specific to each nozzle, such a rapid measurement
system facilitates planned scan path adjustment, nozzle
qualification/disqualifications, and planned droplet combinations
of droplets produced by various nozzle-waveform pairings, as
alluded to earlier and in the aforementioned patent applications
which have been incorporated by reference. Per numerals 745 and
747, by measuring expected droplet volume to a precision of better
than 0.01 pL, it becomes possible to plan for very precise droplet
usage, where use of droplets can also be planned (ideally) to 0.01
pL resolution, and where measurement error in one embodiment is
effectively reduced so as to provide for 3.sigma. confidence (or
other statistical measure, such as 4.sigma., 5.sigma., 6.sigma.,
etc.) relative to allowable droplet volume. The same is true for
droplet position and/or velocity and/or nozzle bow. For example, by
measuring expected position to a precision of better than one
micron (or another distance measure), it becomes possible to
provide for very precise depositions; expected position can be
measured to a range of a specific Cartesian point and standard
deviation (or, e.g., 4.sigma., 5.sigma., 6.sigma. spread) around
such a point). Once sufficient measurements are taken for various
droplets, fills involving combinations of those droplets can be
evaluated and used to plan printing (748) in the most efficient
manner possible. As indicated by separation line 749, droplet
measurement can be performed with intermittent switching back and
forth between active "on-line" printing processes and "off-line"
measurement and calibration processes; note that to minimize
manufacturing system downtime, such measurement is typically
performed while the printer is tasked with other processes, e.g.,
during substrate loading and unloading. Per numeral 751, in one
embodiment, the clear film or tape can be specially selected (or
treated) so as to optimize capture of droplet properties for the
particular ink under analysis (i.e., given chemical or fluidic
properties of that ink), for purposes of facilitating image capture
and/or analysis. For example, the ink in some applications is a
monomer that will later be cured by an ultraviolet light cure
process to become a polymer; to facilitate capture of droplet
properties, the clear film can be selected so as to have physical,
color, absorbance, fixing, curing, or other properties to as to
enhance the prevision with which such a material can be analyzed by
the image capture system. Finally, per numeral 753, either the film
(tape) or the droplet measurement system as a whole (or both) can
be designed for modular replacement, so as to minimize measurement
system and printing system downtime.
[0063] During printing, nozzle (and nozzle-waveform) measurement
can be performed on a rolling basis, precessing through a range of
nozzles with each break in between substrate print operations.
Whether engaged to measure all nozzles anew, or on such a rolling
basis, the same basic process of FIG. 7B can be employed for
measurement. To this effect, when the droplet measurement device is
engaged for a new measurement (either on the heels of prior
measurement or on the heels of a substrate print operation), the
system software loads a pointer which identifies the next nozzle
set for which measurements are to be taken (e.g., for a second
printhead, "nozzle window having an upper left corner at nozzle
2,312"). In the case of initial measurement (e.g., responsive to
installation of a new printhead, or a recent boot-up, or a periodic
process such as a daily measurement process), the pointer would
point to a first nozzle for a printhead, e.g., "nozzle 2, 001."
This nozzle either is associated with a specific imaging grid
access or one is looked-up from memory. The system uses the
provided address to advance the droplet measurement system (e.g.,
the measurement area referenced earlier) to a position
corresponding to the expected nozzle position. Note that in a
typical system, the mechanical throws associated with this movement
are quite precise, i.e., to approximately micron resolution. The
system optionally at this time searches for nozzle position about
the expected micron-resolution position, and finds the nozzle and
centers on its position based on image analysis of the printhead
within a small micron-distance from the estimated grid position.
For example, a zig-zag, spiral or other search pattern can be used
to search about the expected position for a nozzle or fiducial
bearing a predetermined positional relationship relative to the
desired set. A typical pitch distance between nozzles might be on
the order of 250 microns, whereas nozzle diameter might be on the
order of 10-20 microns.
[0064] FIG. 7C provides a flow diagram relating to nozzle
qualification. In one embodiment, droplet measurement is performed
to yield statistical models (e.g., distribution and mean) for each
nozzle and for each waveform applied to any given nozzle, for any
of and/or each of droplet volume, velocity and trajectory. Thus,
for example, if there are two choices of waveforms for each of a
dozen nozzles, there are up to 24 waveform-nozzle combinations or
pairings; in one embodiment, measurements for each parameter (e.g.
volume) are taken for each nozzle or waveform-nozzle pairing
sufficient to develop a robust statistical model. Note that despite
planning, it is conceptually possible that a given nozzle or
nozzle-waveform pairing may yield an exceptionally wide
distribution, or a mean which is sufficiently aberrant that it
should be specially treated. Such special treatment applied in one
embodiment is represented conceptually by FIG. 7C.
[0065] More particularly, a general method is denoted using
reference numeral 781. Data generated by the droplet measurement
device is stored in memory 785 for later use. During the
application of method 781, this data is recalled from memory and
data for each nozzle or nozzle-waveform pairing is extracted and
individually processed (783). In one embodiment, a normal random
distribution is built for each variable to be qualified, as
described by a mean, standard deviation and number of droplets
measured (n), or using equivalent measures. Note that other
distribution formats (e.g., Student's-T, Poisson, etc.), can be
used. Measured parameters are compared to one or more ranges (787)
to determine whether the pertinent droplet can be used in practice.
In one embodiment, at least one range is applied to disqualify
droplets from use (e.g., if the droplet has a sufficiently large or
small volume relative to desired target, then that nozzle or
nozzle-waveform pairing can be excluded from short-term use). To
provide an example, if 10.00 pL droplets are desired, then a nozzle
or nozzle-waveform linked to a droplet mean more than, e.g., 1.5%
away from this target (e.g., <9.85 pL or >10.15 pL) can be
excluded from use. Range, standard deviation, variance, or another
spread measure can also or instead be used. For example, if it is
desired to have droplet statistical models with a narrow
distribution (e.g., 3.sigma.<1.005% of mean), then droplets with
measurements not meeting this criteria can be excluded. It is also
possible to use a sophisticated/complex set of criteria which
considers multiple factors. For example, an aberrant mean combined
with a very narrow spread might be okay, e.g., if spread (e.g.,
3.sigma.) away from measured (e.g., aberrant) mean .mu. is within
1.005%, then an associated droplet can be used. For example, if it
is desired to use droplets with 3.sigma. volume within 10.00
pL.+-.0.1 pL, then a nozzle-waveform pairing producing a 9.96 pL
mean with .+-.0.8 pL 3.sigma. value might be excluded, but a
nozzle-waveform pairing producing a 9.93 pL mean with .+-.0.3 pL
3.sigma. value might be acceptable. Clearly many possibilities are
possible according to any desired rejection/aberration criteria
(789). Note that this same type of processing can be applied for
per-droplet flight angle and velocity, i.e., it is expected that
flight angle and velocity per nozzle-waveform pairing will exhibit
statistical distribution and, depending on measurements and
statistical models derived from the droplet measurement device,
some droplets can be excluded. For example, a droplet having a mean
velocity or flight trajectory that is outside of 5% of normal, or a
variance in velocity outside of a specific target could
hypothetically be excluded from use. Different ranges and/or
evaluation criteria can be applied to each droplet parameter
measured and provided by storage 785.
[0066] Note that depending on the rejection/aberration criteria
789, droplets (and nozzle-waveform combinations) can be processed
and/or treated in different manners. For example, a particular
droplet not meeting a desired norm can be rejected (791), as
mentioned. Alternatively, it is possible to selectively perform
additional measurements for the next measurement iteration of the
particular nozzle-waveform pairing; as an example, if a statistical
distribution is too wide, it is possible to specially perform
additional measurements for the particular nozzle-waveform pairing
so as to improve tightness of a statistical distribution through
additional measurement (e.g., variance and standard deviation are
dependent on the number of measured data points). Per numeral 793,
it is also possible to adjust a nozzle drive waveform, for example,
to use a higher or lower voltage level (e.g., to provide greater or
lesser velocity or more consistent flight angle), or to reshape a
waveform so as to produce an adjusted nozzle-waveform pairing that
meets specified norms. Per numeral 794, timing of the waveform can
also be adjusted (e.g., to compensate for aberrant mean velocity
associated with a particular nozzle-waveform pairing). As an
example (alluded to earlier), a slow droplet can be fired at an
earlier time relative to other nozzles, and a fast droplet can be
fired later in time to compensate for faster flight time. Many such
alternatives are possible. Finally, per numeral 795, any adjusted
parameters (e.g., firing time, waveform voltage level or shape) can
be stored and optionally, if desired, the adjusted parameters can
be applied to remeasure one or more associated droplets. After each
nozzle-waveform pairing (modified or otherwise) is qualified
(passed or rejected), the method then proceeds to the next
nozzle-waveform pairing, per numeral 797.
[0067] The schemes represented above can also be used to measure
nozzle bow (and of course, to qualify or disqualify nozzles on this
basis). That is, as an example, if it is assumed that a grouping of
deposited droplets original from a single, common exact nozzle
position, but are clustered off-center in the direction orthogonal
to printhead substrate scanning motion, the nozzle in question
could be offset relative to other nozzles in the same row or
column. Such aberration can lead to idealized droplet firing
deviations that can be taken into account in planning precise
combinations of droplets, i.e., any such "bow" or individual nozzle
offset is stored and used to qualify/disqualify nozzles or as part
of print scan planning, as discussed earlier, with the printing
system using the differences of each individual nozzle in a planned
manner rather than averaging out those differences. In an optional
variation, the same technique can be used to determine non-regular
nozzle spacing along the printhead scanning direction (i.e., the
fast print axis), although for the depicted embodiment, any such
error is subsumed in correction for droplet velocity deviations
(e.g., any such spacing error can be corrected for by adjustments
to nozzle velocity, for example, effectuated by minor changes to a
drive waveform used for the particular nozzle). To determine
cross-scan-axis bow of a nozzle producing a cluster of droplets,
the respective trajectories are effectively reverse plotted (or
otherwise mathematically applied) with other measurement
trajectories for the same nozzle and used to identify a mean
cross-scan-axis position of the specific nozzle under scrutiny.
This position may be offset from an expected location for such a
nozzle, which could be evidence of nozzle bow.
[0068] As stated before and as implied by this discussion, one
embodiment builds a statistical distribution for each nozzle for
each parameter being measured, for example, for volume, velocity,
trajectory, nozzle bow, and potentially other parameters. As part
of these statistical processes, individual measurements can be
thrown out or used to identify errors. To cite a few examples, if a
droplet measurement is obtained having a value that is so far
removed from other measurements of the same nozzle that the
measurement could represent a firing or measurement error; in one
implementation, the system discards this measurement if deviant to
a point that exceeds a statistical error parameter. If no droplet
is seen at all, this could be evidence that the droplet measurement
system is at the wrong nozzle (wrong position), or has a firing
waveform error or that a nozzle under scrutiny is inoperative. An
error handling process can be employed to make appropriate
adjustments including taking any new or additional measurements as
necessary.
[0069] Note that, although not separately called out by FIGS. 7A-C,
the depicted measurement process would typically be performed for
each alternate waveform available for use with each nozzle. For
example, if each nozzle had four different piezoelectric drive
waveforms that could be selected, the measurement process might
generally be repeated 4 times for each group of nozzles; if a
particular implementation called for the building of a statistical
distribution based on 24 droplets for each waveform, then there
might be 96 such measurements for one nozzle (24 for each of four
waveforms, with each measurement being used to develop statistical
mean and spread measures for each of droplet velocity, trajectory
and volume, and for estimated nozzle position (e.g., for purposes
of assessing nozzle bow). In one contemplated embodiment, any
number of waveforms can be shaped or otherwise generated, and the
system measures droplet parameters associated with one or more
preselected waveforms and then stores these parameters for later
use in printing and/or print planning. These parameters can also be
used in determining whether to keep (and store) the waveform for
use in printing (e.g., as part of a pre-selected set of permissible
waveforms), or to select a different waveform and measure
parameters for that waveform.
[0070] Through the use of precision mechanical systems and droplet
measurement techniques, the disclosed methodology permits very high
accuracy measurement of individual nozzle characteristics,
including mean droplet metrics for each of the mentioned parameters
(e.g., volume, velocity, trajectory, nozzle position, and other
parameters). As should be appreciated, the mentioned techniques
facilitate a high degree of uniformity in manufacturing processes,
especially OLED device manufacture processes, and therefore enhance
reliability. By providing for control efficiencies, particularly as
to speed of droplet measurement and the stacking of such
measurement against other system processes in a manner calculated
to reduce overall system downtime, the teachings presented above
help provide for a faster, less expensive manufacturing process
designed to provide both flexibility and precision in the
fabrication process.
[0071] FIG. 8A shows a cross-sectional view of a typical layout
within an industrial fabrication apparatus (e.g., associated with a
printer in such an apparatus) 801. More specifically, printing is
seen to be performed within a print enclosure chamber 803, such
that an ambient atmosphere can be controlled ("controlled
atmosphere"); such control is typically performed to exclude
unwanted particulate, or otherwise to perform printing in the
presence of a specific gas constituency (for example, nitrogen, a
noble gas, etc.). Generally speaking, a substrate 813 is generally
introduced into the printer using an atmospheric buffer chamber
(not shown) and conveyed to a flotation support table 815 using a
mechanical handler, which also aligns the substrate properly for
printing via detection of one or more fiducials on the substrate
(these fiducials and a camera or other optical detector used to
detect precise substrate position are not shown in FIG. 8A).
Printing is performed using a printhead assembly 807 which is moved
back and forth (as depicted by arrows 809) along a traveler 811 in
the direction of a "slow print axis." The printhead assembly 807 is
depicted as a single object but may be a complex assembly that
mounts multiple printheads (e.g., 6, 10 or another number), each
one having hundreds to thousands of print nozzles (e.g., two
thousand nozzles each). The printhead assembly 807 deposits a
liquid ink onto the substrate 813 at precise position points to
precise thicknesses, where the ink includes a material that will
form a permanent layer of one or more products to be fabricated on
the substrate 813. For example, such a material can be an organic
or inorganic material, a conductor or insulator, a plastic, a
metal, or some other type of material. In a typical application,
the substrate 813 is more than one meter wide and several meters
long and is used to simultaneously fabricate multiple OLED displays
arrayed on the substrate; each layer is deposited as part of an
integral print process across all such "subpanels" (i.e., across
multiple such displays in-fabrication) with the individual displays
eventually being cut from the substrate via another process. Each
print process can deposit a different ink to a specified thickness,
for example, conductors, insulators, light generating elements,
semiconductor materials, encapsulation and so forth, using print
instructions specific to the particular layer. In an assembly line
process, there can be multiple printers arranged at different
positions or used in successive, different deposition processes.
For OLED materials, an ink is deposited for a particular layer, and
following deposition, the substrate is removed from the chamber and
advanced to a cure chamber (not shown) where the deposited ink can
be cured, dried, heated or otherwise processed to impart permanency
to deposited material. Note that the depicted arrangement
represents a "split-axis" printer, i.e., the floatation table 815
and associated handlers (not shown) advance the substrate into and
out of the drawing page, along the direction of a Y axis 825 seen
at a dimensional reference 823 near the bottom right of the
FIG.
[0072] To perform droplet measurement, the printhead assembly 807
is selectively advanced outside of a normal print area to a point
where it may be parked in a service station, generally associated
with a second enclosure environment 805. This second environment is
optional, but is advantageous to permit inspection, printhead
substitution and other maintenance forms without having to vent the
print enclosure chamber 803. To park the printhead assembly 807,
the assembly is moved to a location generally seen at the left side
of the FIG., and is then advanced vertically in order to seal the
printhead assembly 807 against a chamber for the second enclosure
environment, as represented by dashed line position 819. In this
"parked" position, the droplet measurement system 817 can be
controlled (e.g., in three dimensions) to selectively transport a
measurement area to mimic a substrate deposition height in
proximity to any desired nozzle area.
[0073] Note that as referenced above, in a typical application, it
is desired to keep the fabrication apparatus 801 "online" and
in-use as much as possible. To this effect, rather than performing
droplet measurement at a time when the apparatus 801 could be used
for printing (and for product manufacture), in one embodiment,
measurement and printing are "ping-ponged," i.e., each time a
substrate (e.g., 813) is loaded or unloaded, during a time interval
between print operations, the printhead assembly 807 is advanced to
the service station and is partially calibrated (e.g., as to a
rolling subset of print nozzles and/or print nozzle waveforms) in
order to build a robust set of measurements for each nozzle,
updated to be current, and maintained in a manner to develop
statistical measurement populations, as described previously. Note
that any one of these features may be considered optional, and is
not essential for practice of the disclosed techniques.
[0074] FIG. 8B provides a plan view of the substrate and printer as
they might appear during the deposition process, taken along lines
B-B from FIG. 8A. The print enclosure chamber is once again
generally designated by reference numeral 803, while the second
enclosure environment used for droplet measurement is generally
designated by reference numeral 805. Within the print enclosure
chamber, the substrate to be printed upon is once again generally
designated by numeral 813, and the support table used to transport
the substrate is generally designated by numeral 815. Generally
speaking, any xy coordinate of the substrate is reached by a
combination of movements, including x- and y-dimensional movement
of the substrate by the support table (e.g., using flotation
support, as denoted by numeral 857) and using "slow axis"
x-dimensional movement of one or more printheads 807 along a
traveler 811, as generally represented by arrows 809. As mentioned,
the flotation table and substrate handling infrastructure are used
to move the substrate during printing along one or more "fast
axes," as necessary. The printhead is seen to have plural nozzles
865, each of which is separately controlled by a firing pattern
derived from a print image (e.g., to effectuate printing of columns
corresponding to printer grid points as the printhead is moved from
left-to-right and vice-versa along the "slow axis"); note that
while only a few print nozzles are graphically depicted in the
FIG., in practice, there are hundreds to many thousands of such
nozzles, arranged in many columns and rows. With relative motion
between the one or more printheads and the substrate provided in
the direction of the fast axis (i.e., the y-axis), printing
describes a swath that typically follows individual rows of printer
grid points. The printhead assembly can also optionally be rotated
or otherwise adjusted to vary effective nozzle spacing, per numeral
867. Note that multiple such printheads can be used together,
oriented with x-dimension, y-dimension, and/or z-dimensional offset
relative to one another as desired (see axis legend 823 in FIG.
8B). The printing operation continues until the entire target
region (and any border region) has been printed with ink, as
desired, with relative printhead assembly/substrate motion
represented by the vertical element of depicted transport
directions 857. Following deposition of the necessary amount of
ink, the substrate is finished, such as via use of an ultraviolet
(UV) or other cure or hardening process that forms a permanent
layer from the liquid ink. As noted earlier, as substrates are
loaded or unloaded for printing, the printhead is advanced to a
maintenance station and is sealed to a second enclosure environment
805. In practice, this second enclosure environment as noted is
made a subset of the print enclosure chamber 803, such that a
printhead can be changed without having to vent the print enclosure
chamber as a whole. Within the second enclosure environment 805,
the droplet measurement system 817 (seen in dashed lines to lie
below traveler 811) is selectively engaged (again, advantageously
using three dimensional articulation of the droplet measurement
system as a whole, e.g., of a chassis thereof), for measurement as
referenced earlier.
[0075] FIG. 9 provides a chart that illustrates measured droplet
positions relative to positions expected for those droplets for
each of many nozzles. More specifically, the chart is generally
designated by numeral 901 and shows a group of approximately 40
nozzles. It should be assumed that the chart 901 represents image
data, for example, processed above as described with reference to
FIGS. 6A-C in order to obtain a measured droplet position (i.e.,
such as position 903) relative to a corresponding expected position
(i.e., such as position 904). Several features should be noted
relative to FIG. 9. First, the nozzles are seen to be arranged in
rows of nozzles that are slightly staggered in position, as
represented by graphic 905; this feature permits very precise
spacing of droplets, e.g., while manufacturing tolerances are such
that nozzles are positioned in a cross-scan direction several
hundred microns apart, slight staggering from row to row permits
alternate nozzle usage (for example, the nozzle corresponding to
position 906 relative to the nozzle corresponding to position 907,
which permits very tight placement of droplets, e.g., to within 20
microns or less of any desired position on a substrate. Second, the
chart 901 indirectly emphasizes benefits provided by positional
calibration of the droplet measurement system relative to a
printhead, e.g., it is important that the system know exactly which
nozzle corresponds to position 903 and expected position 904, so as
to be able to match any measured data (and any nozzle qualification
or adjustment) with the correct nozzle. Through image processing,
precise positional offsets can be determined for each nozzle, and
factored into nozzle qualification and print planning. Finally,
note again that the use of a clear film potentially permits image
capture not only of deposited droplets, but of the nozzle as well
(e.g., captured through the clear film), facilitating performance
of distance analysis by software. This is not required for all
embodiments, e.g., through an understanding of how the captured
image of the film corresponds to nozzle plate position, the
software can easily also infer nozzle position relative to the
captured image, and on this basis compute positional offsets. In
the context of FIG. 9, the numeral 904 in one embodiment represents
image nozzle position with any deviation between measured position
903 and position 904 representing droplet velocity and/or bow.
Also, while FIG. 9 represents positional offset of droplets
relative to expected droplet position, similar analysis can also be
used to measure droplet volume, for example, by comparing droplet
color (e.g., grayscale value), droplet diameter, or other features
of the captured image to a standard, and computing droplet volume
therefrom. Through the use of repeated, additional measurements for
each nozzle or nozzle-waveform pairing, the system can readily
build distributions for any desired droplet parameter on a
per-nozzle or per-nozzle waveform basis.
[0076] FIG. 10 shows a flow diagram 1001 associated with
determining droplet volumes from a captured image. Per numeral
1003, a captured image representing droplets produced by an array
of nozzles is first retrieved from memory. This image is then
filtered as appropriate to segment just the droplets of interest
(e.g., with varying color intensity according to thickness or ink
concentration on the deposited medium), per numeral 1005. Note that
such the filtered image can be a first, second, third or other
instance of filtration performed to measure a specific parameter
from a single image (e.g., other instances can be used to computed
distances, positions, offset, and so forth for droplet velocity,
position, nozzle position and so forth). Per numeral 1007, any
color hue is then processed to correlate that hue with ink
thickness or density; for example, if deposited ink has a slightly
reddish tint, then a "redder" portion of the image would typically
represent greater thickness. Note that for embodiments where
multiple droplets are deposited from each nozzle at-once, there can
be multiple visible droplets that overlap, and thickness processing
1007 preferably takes this into account, segmenting any individual
droplet; this is not required for all embodiments, e.g., if it is
known that five droplets for example have been deposited, it might
suffice to compute overall volume and to divide by five. Per
numeral 1009, droplet radii are then calculated as referenced
earlier (or aggregate ink coverage) and used in connection with the
derived thickness measure to compute total deposited ink.
Importantly, the clear film used as a deposition surface ideally
fixes deposited ink and therefore may differ from an actual
deposition surface used in active printing (e.g., a glass
substrate); as depicted by numeral 1008 therefore, a stored
standard specific to the deposition material is retrieved and used
in connection with thickness processing, volume calculation 1011 or
both to derive correct droplet volume estimates. Finally,
measurement data is stored per numeral 1013 and any computed
per-nozzle or per-nozzle-waveform distributions (e.g., mean and
spread) are updated for use in print or scan planning. Note that
analogous comparisons to a standard and raw value (or offset)
computation can be applied for many other parameters other than
volume, as suitable to the particular application.
[0077] Reflecting on the various techniques and considerations
introduced above, a manufacturing process can be performed to mass
produce products quickly and at low per-system cost. By providing
for fast, repeatable printing techniques, it is believed that
printing can be substantially improved, for example, reducing
per-layer printing time to a small fraction of the time that would
be required without the techniques above. Again returning to the
example of large HD television displays, it is believed that each
color component layer can be accurately and reliably printed for
large substrates (e.g., generation 8.5 substrates, which are
approximately 220 cm.times.250 cm) in one hundred and eighty
seconds or less, or even ninety seconds or less, representing
substantial process improvement. Improving the efficiency and
quality of printing paves the way for significant reductions in
cost of producing large HD television displays, and thus lower
end-consumer cost. As noted earlier, while display manufacture (and
OLED manufacture in particular) is one application of the
techniques introduced herein, these techniques can be applied to a
wide variety of processes, computer, printers, software,
manufacturing equipment and end-devices, and are not limited to
display panels.
[0078] The foregoing description and in the accompanying drawings,
specific terminology and drawing symbols have been set forth to
provide a thorough understanding of the disclosed embodiments. In
some instances, the terminology and symbols may imply specific
details that are not required to practice those embodiments. The
terms "exemplary" and "embodiment" are used to express an example,
not a preference or requirement.
[0079] As indicated, various modifications and changes may be made
to the embodiments presented herein without departing from the
broader spirit and scope of the disclosure. For example, features
or aspects of any of the embodiments may be applied, at least where
practical, in combination with any other of the embodiments or in
place of counterpart features or aspects thereof. Thus, for
example, not all features are shown in each and every drawing and,
for example, a feature or technique shown in accordance with the
embodiment of one drawing should be assumed to be optionally
employable as an element of, or in combination of, features of any
other drawing or embodiment, even if not specifically called out in
the specification. Accordingly, the specification and drawings are
to be regarded in an illustrative rather than a restrictive
sense.
* * * * *