U.S. patent application number 11/554426 was filed with the patent office on 2007-03-08 for systems and methods for inspecting coatings.
Invention is credited to Mohammed I. Hassan Ali, Akira Numasato, Mohammed A. Omar, Kozo Saito, Masahito Sakakibara, Toshikazu Suzuki, Yasuo Tanigawa.
Application Number | 20070051891 11/554426 |
Document ID | / |
Family ID | 34103622 |
Filed Date | 2007-03-08 |
United States Patent
Application |
20070051891 |
Kind Code |
A1 |
Saito; Kozo ; et
al. |
March 8, 2007 |
SYSTEMS AND METHODS FOR INSPECTING COATINGS
Abstract
A system for detecting defects in paint coatings includes a
temperature manipulation apparatus configured to change the
temperature of a surface and a coating applied to the surface. The
system may further include an infrared sensor for measuring the
change in temperature of the surface and coating and a processor to
compare the measured change in temperature of the surface and
coating to an expected change of temperature in order to determine
anomalies in the coatings.
Inventors: |
Saito; Kozo; (Lexington,
KY) ; Hassan Ali; Mohammed I.; (Lexington, KY)
; Numasato; Akira; (Toyota-shi, JP) ; Omar;
Mohammed A.; (Lexington, KY) ; Sakakibara;
Masahito; (Okazaki-shi, JP) ; Suzuki; Toshikazu;
(Toyota, JP) ; Tanigawa; Yasuo; (Hebron,
KY) |
Correspondence
Address: |
DINSMORE & SHOHL LLP
ONE DAYTON CENTRE, ONE SOUTH MAIN STREET
SUITE 1300
DAYTON
OH
45402-2023
US
|
Family ID: |
34103622 |
Appl. No.: |
11/554426 |
Filed: |
October 30, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10629426 |
Jul 29, 2003 |
7129492 |
|
|
11554426 |
Oct 30, 2006 |
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Current U.S.
Class: |
250/341.6 |
Current CPC
Class: |
G01N 25/72 20130101 |
Class at
Publication: |
250/341.6 |
International
Class: |
G01J 5/02 20060101
G01J005/02 |
Claims
1. A system for detecting defects in coatings comprising: a) a
temperature manipulation apparatus configured to change the
temperature of a surface; b) an infrared sensor configured to
measure the change in temperature of said surface; and c) a
processor configured to compare said measured change in temperature
of said surface to an expected change of temperature.
2. The system of claim 1, wherein said system further comprises an
application apparatus configured to apply a coating to said
surface.
3. The system of claim 1, wherein said system further comprises
multiple coating stations configured to apply a coating to said
surface.
4. The system of claim 1, wherein said surface comprises a
coating.
5. The system of claim 1, wherein said system further comprises a
plurality of coating stations having associated sensors.
6. The system of claim 1, wherein said processor is further
configured to compare radiation emitted by said surface to a
thermal signature and an acceptable preexisting model profile.
7. The system of claim 1, wherein said processor is further
configured to generate signals for transmission to an application
apparatus to correct a detected defect.
8. The system of claim 1, wherein said expected change of
temperature may be calculated based upon a known thermal effusivity
value for said surface and said defect.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional application of U.S. patent
application Ser. No. 10/629,426 filed Jul. 29, 2003, the entire
disclosure of which is hereby incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to systems and methods for detecting
defects in coatings applied to substrates. More particularly, this
invention relates to systems and methods for detecting surface and
subsurface defects in vehicle paint coatings using an infrared
camera.
BACKGROUND OF THE INVENTION
[0003] One of the most important methods in high quality automobile
and other vehicle or machine production involves the inspection of
the exterior appearance (i.e. the quality of the paint finish).
Usually, an automobile shell, for example, receives at least four
coatings including a protective coat, an adhesion aid coat, a paint
coat and a clear coat. Defects occurring in the coating method of a
properly prepared surface that may diminish the perceived quality
of the exterior paint include, but are not limited to, dust, hair,
metallic particles, over spray, incomplete spray, stripping and
flake penetration. Inspection for such defects will insure the
exterior quality of the product from the customer's point of
view.
[0004] Previously, evaluation of the quality of the paint finish
was often based on human inspection, which can be a tedious and
subjective method and one that requires meaningful skill and
training. Other inspection procedures have been based on the use of
charge-coupled device (CCD) optical sensors that sense
imperfections through light reflected off of the finished surface.
However, this technique is not particularly effective for complex,
curved and/or hidden geometries (i.e. automobile bodies) because of
its sensitivity and dependence on reflection and scattering
angles.
[0005] In addition, it has been generally known to use infrared
cameras to inspect certain products (i.e. semiconductor chips) for
surface anomalies or defects. However, such inspection techniques
are based solely on the spatial analysis of pixel values with that
of known (standard) values without any account for the temporal
behavior of the pixel values. Stated differently, because these
techniques only view a surface and compare a captured view with a
known signature, without consideration of the change of temperature
over time, these techniques are generally only practical for use to
inspect surface, as opposed to subsurface, anomalies.
[0006] As such, there is a desire for systems and methods capable
of inspecting not only surface, but subsurface anomalies in
multi-layered paint coatings.
SUMMARY OF THE INVENTION
[0007] Accordingly, the present invention is intended to address
and obviate problems and shortcomings and otherwise improve
previous systems and methods for inspecting coatings on surfaces,
and particularly for automotive paints and coatings.
[0008] To achieve the foregoing and other objects and in accordance
with the exemplary embodiments of the present invention, a system
for detecting defects in coatings comprises a temperature
manipulation apparatus configured to change the temperature of the
surface and the coating, an infrared sensor configured to measure
the change in temperature of the surface and the coating and a
processor configured to compare the measured change in temperature
of the surface and the coating to an expected change of
temperature.
[0009] To still further achieve the foregoing and other objects of
the present invention, a system and method for detecting defects in
coatings comprises the steps of measuring a thermal profile of a
surface to create a thermal signature, applying a first coating to
the surface, changing the temperature of the coated surface, taking
a first measurement of emitted radiation from the coated surface
and comparing the emitted radiation to the thermal signature. The
method also comprises the steps of applying a second coating to the
coated surface, changing the temperature of the coated surface,
taking a second measurement of emitted radiation from the coated
surface and comparing the first measurement to the second
measurement.
[0010] To yet further achieve the foregoing and other objects in
accordance with other exemplary embodiments of the present
invention, a system and method for detecting defects in coatings
comprises the steps of applying a plurality of coatings to a
surface, configuring an expected change of temperature,
manipulating the temperature of the coated surface, measuring the
change of temperature in the normally manipulated coated surface
and comparing the measured change of temperature in the manipulated
surface to the expected change of temperature.
[0011] To even further achieve the foregoing and other objects in
accordance with additional exemplary embodiments of the present
invention, a system and method for detecting defects in coatings
comprises the steps of measuring a thermal profile of a surface to
create a thermal signature, applying a first coating to the
surface, and changing the temperature of the coated surface. The
method further includes the steps of taking a first measurement of
amount of emitted radiation from the coated surface, comparing the
emitted radiation to the thermal signature, applying a second
coating to the first coating, changing the temperature of the
coated surface, taking a second measurement of amount of emitted
radiation from this coated surface and measuring change in
temperature thereof. The method also includes the steps of
configuring an expected change of temperature, comparing the first
measurement to the second measurement and comparing the measured
change in temperature of the coated surface to the expected change
of temperature.
[0012] Still other embodiments, combinations, advantages and
objects of the present invention will become apparent to those
skilled in the art from the following descriptions wherein there
are shown and described alternative exemplary embodiments of this
invention for illustration purposes. As will be realized, the
invention is capable of other different aspects, objects and
embodiments all without departing from the scope of the invention.
Accordingly, the drawings, objects, and description should be
regarded as illustrative and exemplary in nature only and not as
restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] While the specification concludes with claims particularly
pointing out and distinctly claiming the present invention, it is
believed that the same will be better understood from the following
description taken in conjunction with the accompanying drawings in
which:
[0014] FIG. 1 is a schematic view of an exemplary system and method
for creating a thermal signature in accordance with the present
invention;
[0015] FIG. 2 is a schematic view of an exemplary station in a
system and method for coating a surface and measuring a thermal
profile in accordance with the present invention;
[0016] FIG. 3 is a simplified flow chart illustrating exemplary
steps in a method of inspecting coatings in accordance with the
present invention;
[0017] FIG. 4 is a simplified flow chart illustrating exemplary
steps in an alternate embodiment of the method of inspecting
coatings in accordance with the present invention; and
[0018] FIG. 5 is a simplified flow chart illustrating exemplary
steps in another embodiment of the method of inspecting coatings in
accordance with the present invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0019] The principle of defect detection in the present invention
is that when the temperature of a surface and/or coating(s) bearing
such defects is manipulated and viewed by an infrared sensor, the
defects will be effectively magnified and distinguishable as spots
of different thermal imprint or color. More particularly, the
thermal characteristics or effusivity difference between the defect
and the surrounding paint or surface creates a thermal mismatch.
The thermal mismatch results in a different thermal wave reflection
from the defect as compared with its surroundings. The concept of
thermal mismatch may be represented by the formula: .GAMMA. = k 1
.times. p 1 .times. c 1 - k 0 .times. p 0 .times. c 0 k 1 .times. p
1 .times. c 1 + k 0 .times. p 0 .times. c 0 ##EQU1## wherein
k=thermal conductivity, p=density and c=specific heat. Sub 1
indicates properties of the defect whereas sub 0 indicates
properties of the surroundings.
[0020] Because effusivity e= {square root over (k.rho.c)}, then:
.GAMMA. = e 1 - e o e 1 + e o ##EQU2##
[0021] Accordingly, thermal mismatch is the difference between the
thermal properties or characteristics (effusivity) of the defect
and its surroundings as sensed by the sensing mechanism (e.g., the
infrared camera or sensor, as will be discussed further below). For
example, in determining the thermal mismatch between an air pocket
and resin epoxy, wherein the air pocket (defect) has a known
thermal effusivity of 9.19 W. (sec.m.sup.-2.K.sup.-1).sup.0.5 and
the epoxy resin (surroundings) has a known thermal effusivity of
667 W. (sec.m.sup.-2.K.sup.-1).sup.0.5 .GAMMA. .function. ( thermal
.times. .times. .times. mismatch ) = e 1 - e o e 1 + e o = 9.19 -
667 9.19 + 667 .apprxeq. - 0.97 ##EQU3## Accordingly, in this
example, only approximately 97% of the thermal wave will reflect
from the air pocket interface as compared with the epoxy resin,
thereby causing a deviation in the temperature profile between the
air pocket and the epoxy resin at that particular spot.
[0022] As a result of the thermal mismatch between the defect and
its surroundings, thermal contrast profiles, which account for the
speed of the change in temperature of the defect as compared to the
speed of change of its surroundings, can be established. More
particularly, because the different effusivity values of the
defects result in a different rate of cooling .DELTA.T compared
with its surroundings, the contrast between the defect and its
surroundings can be observed The concept of thermal contrast
(T.sub.c) may be represented by the formula: T c = T d .function. (
t ) - T d .function. ( t 0 ) T s .function. ( t ) - T s .function.
( t 0 ) ##EQU4## wherein T=temperature, t=time, d=defective spot
and s=non-defective spot. Accordingly, thermal contrast is the
deviation in the measured temperature profile .DELTA.T and the
normal (expected) profile due to the existence of a foreign
material or excess or absence of coating material(s) (e.g.,
defect).
[0023] Applying these principles, the systems and methods of the
present invention, in one or more of the embodiments, are capable
of detecting defects in single and multi-layered coatings by
measuring emitted radiation and comparing that measurement to a
known thermal signature or a previously measured thermal profile.
Referring to the drawing figures in detail, wherein like numerals
indicate the same elements throughout the drawing figures, FIG. 1
illustrates at least part of an exemplary system 10 for viewing and
determining a thermal profile. The exemplary system of FIG. 1 may
be applied to a situation where a surface, herein referred to as a
shell or workpiece 12, is raw (e.g. does not have a coating) and a
thermal profile of the shell may be measured to create a thermal
signature for later comparison to the thermal profile of same shell
with one or more coatings (described later herein). Of course,
shell 12 could comprise a complete vehicle body, portions of a
vehicle, or a single piece to be coated. Alternatively, the
exemplary system of FIG. 1 may also be applied to a situation
wherein shell 12 comprises one or more coatings and the thermal
profile of the shell and coatings is sought to be measured to check
for defects. For purposes of this example, however, it is assumed
that shell 12 is raw and/or that the coatings of interest have yet
to be applied.
[0024] As illustrated in FIG. 1, the exemplary system 10 may
comprise a temperature manipulation apparatus 20, a sensing
mechanism such as an infrared (IR) sensor 30, and a processor 40.
In this example, temperature manipulation apparatus 20 is
illustrated as comprising a curing oven. Curing ovens are often
used in the industry to "bake" a coating or layer of paint to the
surface of an automobile shell. In the present invention, not only
does the curing oven function to "bake" coatings and/or paint onto
the shell 12, but also provides appropriate temperature
manipulation of the shell and coatings so that emitted radiation
and change of temperature may be optimally measured by IR sensor 30
(discussed later herein). As known in the industry, such a curing
station or oven can comprise a plurality of heater banks and/or
other elements to raise the temperature of the shell, its surfaces
to be coated and/or the coating(s) applied as appropriate. In an
exemplary embodiment for applying paint and/or other surface
coatings to automobile panels or the like, the temperature of the
curing oven may be set in the range of 150-250.degree. C. This
range has been found to be particularly effective to ensure proper
"baking" of a coating while manipulating the temperature of the
shell (and coatings) so that a desired thermal profile can be
measured.
[0025] In another embodiment, however, curing oven 20 may be set at
any desired temperature to adequately "bake" or cure a coating
and/or provide optimal conditions to measure a thermal profile. In
addition, it should be understood that because the present
invention is directed toward detecting defects through measurements
of emitted radiation and change of temperature during any heat
transition, the temperature manipulation apparatus may also include
any combination of heating and/or cooling devices used to
manipulate the temperature test surface (and coatings) to provide
optimal measurement of a thermal profile. In this regard, it should
be understood that the "manipulation" contemplated can comprise
increasing or decreasing relative temperatures. Such combinations
include, but are not limited to application of a coating at a
different temperature than the shell surface to create a measurable
temperature differentiation therebetween and/or measuring the
thermal profile of the shell 12 while the subject surface is being
heated. Such combinations may further include use of sound waves or
ultrasound waves that are converted to thermal energy inside the
material and then detected by the IR sensor or other appropriate
sensing mechanism.
[0026] Once the temperature of the shell 12 is manipulated in the
curing oven 20, shell 12 may be inspected by IR sensor 30. As
illustrated in FIG. 1, IR sensor 30 may be configured with a
predetermined field of view 32 for inspecting shell 12. IR sensor
30 may be appropriately positioned to inspect shell 12 as the
result of input from shell recognition sensor 16 and belt speed
sensor 18. For example, shell recognition sensor 16 may be
integrated, or configured to communicate with the IR sensor 30
and/or processor 40 for determining the type of shell or workpiece
entering the curing oven 20. The recognition of the shell may be
useful to assure that the IR Sensor 30 is calibrated and situated
to capture an appropriate field of view 32 (e.g. size or angle) for
the specific shell 12. In addition, belt speed sensor 18 may be
integrated with the IR Sensor 30 and/or processor 40 for
determining the speed of the belt 14 so that the IR Sensor may be
synchronized or matched to position itself at a starting position
appropriately and move around shell 12 on robotic arm 34. Also, IR
sensor may be stationary and situated to take snap shots (e.g.,
plan or side views). In another embodiment, any combination of
sensors and/or logic may be integrated with IR sensor 30 so as to
properly position one or more IR sensor 30 to measure the desired
field of view 32.
[0027] Still referring to FIG. 1, a delay between the time that
shell 12 exits the curing oven 20 and is measured by the IR sensor
30 may be desired for multiple reasons. For example, it is believed
that at the time when shell 12 first exits curing oven 20, shell 12
may still be absorbing heat, and therefore, may provide a varying
emission of radiation for measuring the thermal profile.
Accordingly, it is believed that it may be desirable to take
measurements at some point during the cooling (i.e., after maximum
temperature achieved) of the shell and/or coating(s) depending on
the shell type and composition, and any associated coatings. As
previously discussed, however, the present invention contemplates
the use of any combination of heating and cooling to provide a
temperature at which optimal radiation is emitted for
measurement.
[0028] In addition, a delay between the curing oven 20 and
measurement by the IR sensor may be desired in accordance with a
calculated maximum contrast for the shell 12. More particularly, it
is believed that as a result of the different thermal properties
among various shells and/or layered coatings bearing defects, an
optimal time window will generally exist for viewing a maximum
thermal contrast (e.g. deviation in the measured temperature
profile .DELTA.T and the normal or expected profile due to the
existence of a foreign material). For example, when a workpiece or
shell has cooled to near room temperature, less thermal contrast
will generally be detectible, and as a result sensitivity or
accuracy of the defect detection will be reduced. As discussed
later herein, by measuring the shell 12 during its particular
window of thermal maximum contrast, focus may be given to the depth
of a potential defect in one or more layers of a multi-layered
coating.
[0029] IR sensor 30 may comprise any sensor or sensing arrangement
configured to at least measure radiation emitted from a surface
and/or the change of temperature of a surface over a period of
time. For example, IR sensor 30 of the above example may be a TVS
8500 manufactured by CMC Electronics which is capable of achieving
excellent observation ranges for the present invention of about 3
to 5 .mu.m (Wavelength) at a temperature range of <40.degree. C.
over ambient temperature. While such observation ranges are
currently believed to be particularly applicable for automotive
coatings which have relatively low curing temperatures of about
200.degree. C. or less, other observation ranges are contemplated
by the present invention.
[0030] IR sensor 30 may change the field of view 32 through manual
and/or automatic focusing of its lenses or by positioning itself at
a proper location relative to shell 12 such as through appropriate
positioning of robotic arm 34. Accordingly, while it is
contemplated that only one IR sensor 30 might be needed to capture
all desired fields of view 32, it should be understood that any
number of IR sensors may be used to together to capture any number
of fields of view. In such embodiment, IR sensors may be
temporarily synchronized to compare temperature contrasts at same
time.
[0031] As illustrated in FIG. 1, IR sensor 30 can measure an
initial or base emitted radiation (a thermal profile) from the raw
shell 12 by establishing an appropriate field of view 32. As
discussed later herein, IR sensor 30 may map an area under a field
of view into a grid, wherein each square or pixel of the grid may
reflect a desired area to measure. If the raw shell is acceptable
(e.g. does not comprise fatal defects such as cracks, dents, etc.
that may prevent subsequent acceptable coating), a thermal
signature for the shell may be created.
[0032] The thermal signature of the shell 12 may be stored in
processor 40 or elsewhere for access by processor 40. Processor 40
may include, for example, any memory or computer configured to log
data and perform comparison and analysis of data recorded. The
thermal signature may be used as a template to be later compared
with the thermal profile of the shell with one or more coatings for
detection of defects. More particularly, because the thermal
signature may provide a template (i.e. a map of any preexisting
acceptable flaws or defects), defects detected upon comparison to a
thermal profile taken of the shell 12 with one or more coatings can
be distinguished from the flaws/defects already known to be
existing on the shell.
[0033] Another unique feature of this system and method is that
multiple thermal signatures for a variety of shells may be created
and stored within processor 40 (or so that processor 40 has access
to them). For example, recognition sensor 16 may sense the
geometries of the shell and transmit signals regarding the
geometries to processor 40 to discover whether an applicable
thermal signature or one for a similar model has been created. If
so, shell may be diverted directly to Paint Station I 60, described
below. Alternatively, if processor 40 does not recognize shell 12,
shell 12 may be directed through system 10 to create a thermal
signature. In another embodiment, shell 12 may include an
identification tag or other identifying apparatus configured to
transmit signals to the IR sensor or processor regarding shell
type. Because the system of the invention is capable of
establishing a distinct thermal signature for each shell, different
shell models may follow each other along beltline 14.
[0034] Once a thermal signature has been created and stored for a
particular shell 12, the shell may be moved to a first coating
station. Referring to FIG. 2, a first coating station is
illustrated as Paint Station I 60. For purposes of this example,
the exemplary system illustrated in FIG. 2 comprises similar
components as that of FIG. 1 with the addition of application
apparatus 50. As later discussed herein, an exemplary coating
station, such as Paint Station I, may be configured to measure not
only the thermal profile of shell 12 with one or more coatings, but
also the change in temperature of shell 12 and any associated
coatings after temperature manipulation.
[0035] Paint Station I 60 is illustrated as comprising a coating
application apparatus 50, a temperature manipulation apparatus 20,
an infrared sensor 30 and a processor 40. As illustrated in FIG. 2,
application apparatus 50 may comprise a paint gun or electrostatic
spraying device as generally known in the industry configured to
apply paint or another desired coating to a surface such as
automobile shells. In another embodiment, any apparatus configured
to apply paint and/or any other coating to a surface may be
used.
[0036] Similar to FIG. 1, temperature manipulation apparatus 20 may
comprise a curing oven configured to heat the shell and first
coating 112 from application apparatus 50. As previously discussed,
temperature manipulation apparatus 20 may also comprise any
combination of heating and/or cooling elements or apparatuses
configured to manipulate the temperature of the shell and/or
coating 1 12. Such elements might include heat lamps, infrared
heating elements, convection areas, microwave heaters or the like.
As illustrated in FIG. 2, car recognition 16 and belt speed 18
sensors may be positioned on the opposite end of curing oven 20 to
sense the shell 112 and belt speed once the shell 112 has exited
the curing oven 12. As also to be understood, bar code renders,
optical sensors, contact switches or other identification equipment
and/or alignment arrangements can also be utilized to properly
queue a shell 112 for IR sensing. As discussed above, such sensors
may be used to appropriately position IR sensor 30 to capture an
appropriate field of view.
[0037] The systems described above and illustrated in FIGS. 1 and 2
can be used, for example, to inspect automobile shells only and
automobile shells with coatings applied thereto for defects that
may deteriorate the exterior appearance of the automobile.
Moreover, the present invention contemplates multiple methods of
inspecting automobile coatings utilizing the systems set forth
above. For example, one method of inspecting a multi-layered
coating for defects includes analysis of each successive layer of
coating with comparison to a previous layer. More specifically, the
thermal profile for a coating may be compared with the thermal
profile measured from a previous coating to determine the existence
of a new or unresolved defect. Accordingly, a number of coating and
inspection stations, similar to Paint Station I, may be linked
together to create a complete coating line wherein each of the
coating stations is configured to communicate data regarding
previous coating stations, as well as statistical method data
throughout the coating line.
[0038] Referring the FIG. 3, exemplary steps for a method for
inspecting a multi-layered coating for defects is illustrated. For
purposes of this example, it is assumed that a thermal signature
for the raw shell (e.g. 12 in FIG. 1) has been created or is
otherwise known. Referring to FIGS. 1-3, raw shell 12 progresses to
Paint Station I 60 for coating. Once the coating is applied 62, the
shell (112 in FIG. 2) may be moved to temperature manipulation
apparatus 20 (e.g. curing oven). The surface and coating may be
manipulated by curing oven for curing and pre-testing manipulation
(step 64).
[0039] After an appropriate amount of time, IR sensor 30 may take
an appropriate field of view picture to measure the radiation
emitted (thermal profile) from the shell and the coating (shown at
step 66). As referenced herein, "picture" refers to the capture of
a single image at a time (t). In another embodiment, IR sensor may
take multiple "pictures" or simply scan the field of view over an
interval of time.
[0040] In taking a picture of the thermal profile, the IR sensor 30
may map an area under a field of view into a grid (i.e. FIG. 2),
wherein each square or pixel of the grid may reflect a desired area
to measure. For example, the grid may be divided up into land areas
of 0.1 mm. Such land area may be based, for example, on the size of
a defect normally visible to a casual naked eye, or the smallest
size defect which may be practically repairable.
[0041] The IR sensor may transmit the measured thermal profile
(picture) to a processor (e.g. 40), wherein the processor may
compare (step 68) the image with the thermal signature of the
automobile shell. In this stage (68) of the method (e.g. Paint
Station I), the image captured by IR sensor is compared with the
thermal signature created from the raw shell (12 in FIG. 1). More
particularly, the grid of the thermal profile viewed and captured
by the IR sensor may be electronically overlaid onto the grid of
the thermal signature. Deviations between the thermal profile and
the thermal signature may be indicated electronically within the
processor or visually on a monitor (not shown) by spots of varying
color thereby indicating the presence of a defect.
[0042] Upon subsequent coatings, as discussed below, the thermal
profile of shell and coatings may be compared to a previous thermal
profile measured from a shell and fewer coatings, similarly at
stage 68. In another embodiment, not only may the captured image be
compared with the thermal signature, but it can also be compared to
an acceptable preexisting model profile stored within the
processor. More particularly, through manual inspection or
accumulated data from previous inspections, a model profile (or
"standard") indicating a surface coating (and/or ranges of
deviations) of acceptable quality may be created and stored within
the processor. Accordingly, the thermal profile captured by the IR
sensor may be additionally compared to this acceptable model
profile for detection of deviations and insuring quality control
set to a predetermined standard.
[0043] If a defect is indicated upon comparison, the processor may
determine (at step 70), based on programmed acceptable standards,
whether the defect is of such a nature that it may create a problem
for subsequent coatings and/or will result in an unsatisfactory
final product (major defect). Where there is a major defect, the
processor may then determine at step 72, again based on programmed
acceptable standards, whether the defect is repairable by comparing
defect parameters with stored data of historic defect phenomenon.
If the defect is not repairable, in one embodiment, the shell may
be sent for scrap at step 74. If it is determined that the surface
and coating is repairable 76, a technician may either repair the
defect on the spot, direct the shell to a repair "queue" for
handling, or repair the defect later in the coating method (as it
may be possible to repair the defect by simply applying the next
coat). If repaired, the shell might be re-inserted to the finish
method, such as in line for Paint Station II at step 80.
[0044] If the processor determines that no major defects are
indicated, the automobile shell may pass to Paint Station II (step
80). Similar to Paint Station I, Paint Station II may apply a
coating (step 82), transfer shell to curing oven (step 84) and
measure the thermal profile of the shell, first coating and second
coating (step 86). The IR sensor may transmit the thermal profile
to the processor for comparison at step 88. At this stage the
processor may compare the thermal profile measured at Paint Station
II to the thermal profile measured at Paint Station I for
deviations. Deviations among the thermal profiles may indicate
defects in the newly applied coating (e.g. coating applied at Paint
Station II). In addition, processor may also compare the thermal
profile measured at Paint Station II to the thermal signature of
the shell or a preexisting model profile (or standard) for an
acceptable shell with two coatings in order to further check for
defects.
[0045] If a major defect is detected as described above, the
processor may determine at step 92 whether to send the shell to
scrap (step 94) or repair (step 96). If no major defects are
indicated, the automobile shell may move to Paint Station III 100
to follow steps similar to steps 80-86 discussed above. The thermal
profile measured at Paint Station II, however, can be compared to
the thermal profile measured at Paint Stations I and/or II for
deviations. In addition, the thermal profile measured at Paint
Station III may be compared to the thermal signature of the shell
or a preexisting model profile (or standard) for an acceptable
shell with three coatings.
[0046] Accordingly, in this exemplary method of the present
invention, because thermal profiles of each individual coating can
be measured and compared not only to previous thermal profiles, but
also to the thermal signature of the automobile shell and an
acceptable preexisting model profile, defects can be more
accurately detected and localized by layer. This detection method
may be particularly useful in applications where, despite detection
of major defects, the coating method is allowed to continue to or
toward completion. In this situation, data regarding each coating
layer and detected defects may be compiled so that the defects may
be localized and more appropriately repaired as needed at the end
of the coating method, rather that at each coating stage. For
example, a defect in the top coat might only require a light repair
procedure on the topcoat and clear coat, while another defect in
the primer layer may need more robust activities.
[0047] In some applications, it may be desired to take a single
measurement sometime later in the method, or at the completion of
the coating method, rather than measuring the thermal profile of
each coating. However, defect detection of this type would require
a method whereby not only surface defects could be indicated as
described above, but also subsurface defects. As such, another
aspect of the present invention includes a method for detection and
localization of subsurface defects at any point in the coating
method, including completion, by taking successive measurements
(e.g. pictures of the field of view) of the change in temperature
(e.g. thermal contrast) between a defect and its surroundings. In
another embodiment, IR sensor may scan the field of view over an
interval of time. The measurement in the change of temperature may
be compared to an expected change in temperature (e.g. expected
thermal contrast) configured from a known thermal emissivity of the
particular defect and its surroundings. This method can not only
detect a surface defect located in the outermost coating of the
paint, but may also detect and localize a defect in any one or more
of the coating layers beneath the outermost coating.
[0048] For example, referring to FIG. 4, an alternative method for
detecting and localizing surface and subsurface defects is
illustrated. As previously discussed, the principle of the
inventive method is to measure the changes in temperature of the
shell and coatings once heated up in a temperature manipulation
apparatus (i.e., curing oven). As illustrated in FIG. 4, a coating
may be applied at step 122 to the automobile surface. Once the
coating has been applied, the temperature of the automobile shell
and coatings may be manipulated 124 as discussed above. Once the
coated shell is up to temperature and heating ceases, an IR sensor
may measure (at step 126) the speed of the change of temperature of
the shell and defects within the coatings at a time when maximum
contrast between the defects and their surroundings is achieved. As
previously discussed, the thermal effusivity difference between the
defect and the surrounding coatings creates a thermal mismatch. The
thermal mismatch results in a different thermal wave reflection
from the defect as compared with its surroundings, and, as a
result, thermal contrast profiles can be established by the IR
sensor. Maximum thermal contrast may vary among shells and
associated coatings, and timing and specific procedures for
measuring the temperatures and changes can be varied
accordingly.
[0049] The IR sensor may transmit the thermal contrast profiles to
the processor, which may be programmed with known thermal
effusivity values for the coatings and defects. For example,
because a coating and defect may have a known thermal conductivity,
density and a specific heat capacitance, an expected change of
temperature (how quickly the shell, coatings and defects should
change temperature) can be determined. Accordingly, the actual
change in temperature from the cooling shell, coatings and defects
and the thermal contrast therebetween may be compared to an
expected change in temperature to determine the presence of any
defects. Similarly, actual change in temperature of detected
defects may be compared to programmed data and data accumulated
through previous tests to determine the specific type and severity
of the defect (i.e., dust, hair, metal flakes, etc.) at stage 130.
If no major defect is indicated, then the automobile shell may move
to Production or to the next Paint Station (step 140).
[0050] Where there is a major defect, the defect may be localized
to a specific area at stage 130. As mentioned, IR sensor may map an
area under a field of view into a grid, wherein each square or
pixel of the grid may reflect a desired area to measure. Processor
can compare the speed of the change of temperature of relative
adjacent pixels to one another to determine, based on expected
change of temperature (discussed above), the location of anomalies
(defects). Accordingly, a defect may be localized by both specific
coating layer and area.
[0051] The processor may then determine at step 132 whether the
defect is repairable by comparing defect parameters with stored
data of historic defect phenomenon. If the defect is not
repairable, in one embodiment, the shell may be sent for scrap at
step 134. If it is determined that the surface and coating is
repairable, a technician may repair the defect at stage 136 or take
other appropriate measures as discussed above.
[0052] It should be understood that the method illustrated in FIG.
4 may also be used for detecting defects in a single coating or
shell, and therefore, is not limited to application with more than
one coating. For example, referring to FIG. 3, wherein a single
coating has been applied to the automobile shell, IR sensor may be
configured to measure the actual changes in temperature during the
measurement period and transmit the measurement to the processor
for comparison with a thermal emissivity value (an expected change
in temperature) for the shell, coating and defects. Accordingly,
the method illustrated in FIG. 4 can be used to detect defects in
both single-layered and multi-layered coatings by measurement and
comparison of the detected speed of the change in temperature.
[0053] It is also contemplated by the present invention to combine
the methods discussed above to further ensure absolute quality of
the automobile coating method. For example, referring to FIG. 5,
another embodiment of the method for inspecting multi-layered
coatings is illustrated. Similar to FIGS. 3 and 4, a coating may be
applied (at step 222) to the automobile shell at Paint Station I.
Once the coating has been applied, the temperature of the
automobile shell and coatings may be manipulated (step 224) as
discussed above. Once removed from the curing oven, an IR sensor
may take a field of view picture to measure the emitted radiation
(thermal profile) from the shell and the coating and may also
measure the speed of the change of temperature of the shell and
defects within the coatings 226. IR sensor may transmit the data to
processor for comparison to stored data.
[0054] The processor may compare the thermal profile with the
thermal signature of the automobile shell (at step 228a), an
acceptable preexisting model profile, and/or, if later in the
coating method, to the previous thermal profile to determine the
presence of any defects. Likewise, the processor may compare the
actual change in temperature to an expected change in temperature
to determine the presence of any defects (step 228b). If desired,
the comparisons can be evaluated at step 230 either together or
separately to realize the true nature of the defect and whether
repair is needed and/or practical.
[0055] Because the present systems and method are capable of such
detailed measurements and comparisons thereby yielding immediate
detection of a defect, it is contemplated that the present
invention may be integrated with other artificial intelligence
and/or automatic feedback logic so that, once a defect is detected,
statistical analysis of operation and necessary changes in coating
methods (if any) can be made in real time. For example, referring
to FIGS. 2 and 5, upon detection of a defect (i.e. paint
over-spray), processor 40 may flag the defect on the current shell
for repair, but also transmit a signal to application apparatus 50
at Paint Station I to decrease spray pressure, paint amount, clean
or replace the spray gun, etc. (i.e. correct a detected defect).
This information might also facilitate maintenance or upgrading of
coating application systems by identifying problem areas. In
addition, the processor may store and/or otherwise update the
knowledge database regarding information about the defect, the
operation of the machinery causing the defect and/or the technical
operation of the machinery or station where the defect occurred.
Accordingly, real time changes and statistical analysis can be made
to minimize or eliminate defects, not only in coatings in previous
stages, but in the entire coating method.
[0056] The foregoing description of the various embodiments of the
invention has been presented for the purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed. Many alternatives,
modifications and variations will be apparent to those skilled in
the art of the above teaching. For example, the systems and methods
of the present invention may be applied to a variety of coatings in
a multitude of applications outside of the automobile coating
method. Accordingly, while some of the alternative embodiments of
various elements, systems and methods for inspecting single and
multi-layered coatings have been discussed specifically, other
embodiments will be apparent or relatively easily developed by
those of ordinary skill in the art. Accordingly, this
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