U.S. patent application number 09/097392 was filed with the patent office on 2001-11-22 for defect detection in articles using computer modelled dissipation correction differential time delayed far ir scanning.
Invention is credited to KENWAY, DANIEL J..
Application Number | 20010042834 09/097392 |
Document ID | / |
Family ID | 26726571 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010042834 |
Kind Code |
A1 |
KENWAY, DANIEL J. |
November 22, 2001 |
DEFECT DETECTION IN ARTICLES USING COMPUTER MODELLED DISSIPATION
CORRECTION DIFFERENTIAL TIME DELAYED FAR IR SCANNING
Abstract
A process for the detection of flaws in an article comprising
infra-red scanning of the article as its temperatures changes and
comparing the infra-red scans for regularity of cooling/heating
pattern. Where the article is irregular, such as in marginal areas,
thermodynamic modelling is performed to establish a hypothetic
cooling/heating pattern for an unflawed article.
Inventors: |
KENWAY, DANIEL J.;
(EDMONTON, CA) |
Correspondence
Address: |
RIDOUT & MAYBEE
SUITE 2400
ONE QUEEN STREET EAST
TORONTO,ONTARIO
M5C 3B1
CA
|
Family ID: |
26726571 |
Appl. No.: |
09/097392 |
Filed: |
June 16, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09097392 |
Jun 16, 1998 |
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09092035 |
Jun 5, 1998 |
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Current U.S.
Class: |
250/341.6 |
Current CPC
Class: |
B27N 3/00 20130101; G01N
25/72 20130101 |
Class at
Publication: |
250/341.6 |
International
Class: |
G01J 005/02 |
Claims
I claim:
1. A process for the detection of flaws in an article using Far
infra-red scanning of its surface comprising changing the
temperature of the surface of an article over a plurality of
temperatures and making an infra-red scan at each of said
temperatures during changing the temperature, the infra-red scans
being separated one from another by equal time increments;
characterized in the steps of allocating parts of said surface as
central and marginal parts forming images from said infra-red
scans, digitizing said infra-red scans, digitizing the images to
provide a sequence of digitized scanned images; for said central
part of the surface, comparing data directly from said digitized
scanned images and noting variations and/or anisotropies from a
general cooling pattern for the article and deducing the presence
of flaws at locations in the article corresponding to the location
of the variations and/or anisotropies in the comparison of the
digitized scanned images; and for the marginal part of the surface,
performing thermodynamic modelling on one of the digitized scanned
images to provide an estimate of the temperature distribution for a
hypothetic unflawed article after passage of one of said time
increments, and comparing data from an adjacent digitized scanned
image with said estimate and noting variations and/or anisotropies
of the structure of the marginal part of the article.
2. A process as claimed in claim 1 in which 10 to 90% of the
surface of the article is allocated as the central part.
3. A process as claimed in claim 2 in which the marginal part has
regularity about the central part.
4. A process as claimed in claim 2 in which from 20 to 80% of the
surface is designated as central part.
5. A process as claimed in claim 4 in which about 75% of the
surface is designated as central part.
6. A process for detection of flaws in an article comprising
changing the temperature of the surface of an article over a
plurality of temperatures; making an infra-red scan at each of said
temperatures during changing of temperature; said infra-red scans
providing at least a first and a second scanned image and being
separated one from the other by a time increment; digitizing the at
least first and second scanned images to provide a sequence of at
least a first and a second digitized scanned image; performing
thermodynamic modelling on the first digitized scanned image to
provide an estimate of the temperature distribution for a
hypothetic unflawed article after passage of said time increment;
comparing data from said second digitized image with said estimate,
noting variations and /or anisotropies of the structure of the
article.
Description
RELATED APPLICATIONS
[0001] This application is a continuation-in-part of application
No. ______ filed Jun. 5, 1998 by Daniel J. Kenway claiming priority
from U.S. Provisional patent application No. 60/048 828.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to defect detection in articles using
computer modelled dissipation correction differential time delay
Far infra-red scanning. Especially the invention relates to such
defect detection in articles such as fibre board panels, oriented
strand board panels, medium density fibre board panels, metal
panels, metal pipes, coated metal pipes and similar articles.
[0004] 2. Acknowledgement of the Prior Art
[0005] Non-destructive testing inspection using Far IR scanning is
well known in the detection of hot spots for example detecting
where insulation is absent, where friction components are
malfunctioning, or where cooling/exhaust systems are failing.
However, flaws which do not cause local hot spots are more
difficult to detect. Some of these flaws are very hard to
detect.
[0006] Various attempts have been made to overcome the difficulties
which arise in this type of scanning for flaws. Examples of methods
which have been used are set out in U.S. Pat. No. 5,357,112 issued
Oct. 18, 1994 to Steele et al., U.S. Pat. No. 5,444,241 issued Aug.
22, 1995 to Del Grande et al., and U.S. Pat. No. 5,631,465 issued
May 20, 1997 to Shepard.
[0007] The horizontal density variation of Oriental Strand Board
(OSB) affects most of the physical and mechanical properties of the
panel. Between-panel density variation can well be measured and
controlled. Within-panel variation, however, has been difficult to
measure. A better estimation of this horizontal density variation
obviously could provide information for controlling the mat forming
process to reduce density variation. A more uniform density
distribution would allow for a reduction in panel thickness or
density, which would eventually improve wood fibre utilization.
[0008] Destructive measurements of OSB panel density are usually
slow and expensive in terms of labor cost. There is a need for
methods of nondestructive measurements of OSB density both at
laboratory and industrial scales.
SUMMARY OF THE INVENTION
[0009] It has been observed qualitatively that variation in density
could be detected using a Far infra-red imaging system. IR
thermography technology was used to estimate OSB panel density.
[0010] The fact that radiation is a function of object surface
temperature makes it possible for an IR camera to calculate and
display this temperature. If an OSB panel contains an anomaly in
its density, and the panel starts at an initial uniform
temperature, then as it is quickly heated and cooled, the anomaly
will produce an anomaly in the distribution of surface temperature.
This is because, in the course of temperature change, those areas
of the panel which have lower density will lose or gain heat more
rapidly and high density areas lose or gain heat more slowly. This
is the basic theoretical principle on which infrared OSB density
measurement is based. An aim of this invention was to determine the
accuracy, spatial resolution and speed of IR measurement of OSB
panel density.
[0011] It has also been surprisingly discovered that in a large
central area of an article it is not necessary to resort to various
precautions to overcome difficulties. It is only necessary to
utilize precautions in a marginal area where cooling of an unflawed
article does not occur in such a set pattern as in a central
area.
[0012] The present invention provides a process for the detection
of flaws in an article, especially OSB, using Far infra-red
scanning of its surface comprising changing the temperature of the
surface of an article over a plurality of temperatures and making
an infra-red scan at each of said temperatures during changing the
temperature, the infra-red scans being separated one from another
by equal time increments; characterized in the steps of allocating
parts of said surface as central and marginal parts forming images
from said infra-red scans, digitizing said infra-red scans,
digitizing the images to provide a sequence of digitized scanned
images; for said central part of the surface, comparing data
directly from said digitized scanned images and noting variations
and/or anisotropies from a general cooling pattern for the article
and deducing the presence of flaws at locations in the article
corresponding to the location of the variations and/or anisotropies
in the comparison of the digitized scanned images; and for the
marginal part of the surface, performing thermodynamic modelling on
one of the digitized scanned images to provide an estimate of the
temperature distribution for a hypothetic unflawed article after
passage of one of said time increments, and comparing data from an
adjacent digitized scanned image with said estimate and noting
variations and/or anisotropies of the structure of the marginal
part of the article.
[0013] The present invention also provides a process for detection
of flaws in an article, especially in OSB. This process comprises
changing the temperature of the surface of an article over a
plurality of temperatures; making an infra-red scan at each of said
temperatures during changing of temperature; said infra-red scans
providing at least a first and a second scanned image and being
separated one from the other by a time increment; digitizing the at
least first and second scanned images to provide a sequence of at
least a first and a second digitized scanned image; performing
thermodynamic modelling on the first digitized scanned image to
provide an estimate of the temperature distribution for a
hypothetic unflawed article after passage of said time increment;
comparing data from said second digitized image with said estimate,
noting variations and/or anisotropies of the structure of the
article. Thereafter, quality decisions about the fitness of the
article can be made.
[0014] While first and second scans at first and second
temperatures may be sufficient to provide data for flaw detection,
a group of scans may be made at a series of three or more
temperatures for greater accuracy. Said thermodynamic estimate may
be made at any one of this series of temperatures and may be
compared with data from scanned images obtained at higher or lower
temperatures.
[0015] The relative proportion of the central and marginal parts
may be chosen in accordance with the shape and size of the article,
the material from which it is made and the degree of accuracy
required. For example, if the article is a circular metal plate of
say 10 feet in diameter, the central portion may be a 9 foot circle
within an annular marginal portion. If the plate is formed of a
less thermally conductive material, the marginal portion may be
smaller. If, however, the plate is square, the central portion may
possibly still be circular, since the corners of the square cause
irregularities. Many of the decisions will be within the skill of
the operator once the general principle is appreciated may be made
by a man skilled in the art. In very general terms the central
portion may be of regular shape and may be from 10-90% of the
surface area of the article.
[0016] More particularly the central part may be from 20-80% or
especially 75% of the surface area of the article.
[0017] The process of specifically inducing, or introducing a
heating or cooling transient, with the specific intention of
creating a temporary temperature differential in what would have
otherwise been a steady state situation is particularly important.
The creation of, high speed monitoring of, image acquisition of,
image processing of, enhancement of, and thermodynamic modelling
of, these temporary temperature differences constitutes the essence
of this invention.
[0018] Conveniently the thermodynamic modelling and the comparison
of data are performed by a suitably programmed computer.
[0019] In the following specific detailed discussion, it is always
assumed that a surface of the article to be tested is heated above
ambient temperature and allowed to cool. In fact, it is within the
scope of the invention to cool the article below ambient
temperature and allow it to heat up to obtain two incremental
temperature differences.
[0020] While the following detailed discussion is limited to the
scanning and comparison of only two images at different
temperatures, it is clear that a much larger number of images may
be scanned and compared.
[0021] For example, the process may comprise the following
steps:
[0022] 1. Central and marginal parts are designated if desired.
[0023] 2. The component to be inspected is heated so that its
temperature rises significantly above ambient temperature. This
heating is preferably uniform, and preferably of at least 50
degrees Celsius in magnitude.
[0024] 3. An IR image of the surface of the heated component to be
analysed is obtained with sufficient resolution (in temperature,
spatial, and temporal domains) to allow for detection of defects.
The spatial resolution required will depend on the defects in
question (for example variation in oriented strand board (OSB)
panels might require resolution of 1/4" square, variations in pipe
wall thickness might require resolution of 0.5 mm square). The
temperature resolution required from the Far IR image will
typically be from 0.1 to 0.2 degrees Celsius. Typically the scanner
will be a forward looking infra-red (FLIR) scanner using a cooled
mercury cadmium telluride detector, or a cooled indium arsenide
detector or even an uncooled micro-bolo metric array. The details
of the scanner implementation are not important as long as:
[0025] a) the resolution is adequate,
[0026] b) the image acquisition speed is adequate (some thermal
transients are of short duration)
[0027] c) the image can be acquired in the appropriate setting
(real time acquisition for in plant production monitoring, remote
portable and field worthy acquisition for in-situ
applications).
[0028] d) the acquisition speed and mode is appropriate to the
application (e.g. linear or flying spot scanning may be necessary
for moving web processes, where as a real or snapshot acquisition
may be necessary for quasi-stationary processes).
[0029] 4. The scanned Far IR (3-10 microns wavelength of peak
sensitivity) image is digitized and stored. The pixel resolution of
the digitization and the storage system must be adequate to
preserve the spatial resolution of the original IR data.
[0030] 5. After a suitable time interval (this interval may vary
from a fraction of a second in the case of a pipeline in use, to
tens of minutes for large structures like the hulls of ships which
have only been minimally heated), a second Far IR image of
equivalent resolution is sampled and digitized. For the central
part of the first and second images may be compared directly. For
the marginal part thermodynamic modelling as described in the
following steps may be used. If central and marginal parts are not
designated then thermodynamic modelling is performed on the
whole.
[0031] 6. Standard thermodynamic modelling involving specific
heats, conductivities, temperature differentials from ambient, and
rough convection and other loss estimates is applied to the
component data for the first sample, and the temperature
distribution for a "perfect homogeneous" component at the instant
of the second sampled is modelled and estimated. Alternately, this
estimate may be derived from images of "good" articles taken at the
second sampling time. The main purpose of calculating this estimate
is to account for the significant non-uniformity of heat loss that
arises directly from thermodynamics of the situation, so that
comparison of the estimated temperature distribution with the
actual will not high light any local anomalies.
[0032] 7. The modelled radiant temperature profile estimate at the
time of the second sampling is then compared with the actual
profile data from the second sampling and the difference
calculated, or high lighted.
[0033] 8. Significant variation or anisotropies from within three
dimensional structure then become evident. Theses may correspond to
flaws or other non-uniformities.
[0034] 9. The variations, and anisotropies evident in the image,
can then be further enhanced using conventional image processing
techniques, and:
[0035] a) presented in the form of a visual spot
[0036] b) quantified and used to make a pass/fail or grading
decision.
[0037] It is believed the process of the invention is especially
applicable to:
[0038] 1. The inspection of pressed composite panel, such as OSB,
or laminated products, in a production environment for
anisotropies, resin spots and delaminations or other defects.
[0039] 2. The in-situ inspection of structural panels on ships
storage tanks, and other large structures; for external corrosion,
paint or coating delamination, the buildup of layers or other
defects.
[0040] 3. The in-situ inspection of wall thickness variations in
pipelines. In this case no marginal part is designated, or the
marginal part involves only the ends of the pipes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] Embodiments of the invention will now be described by way of
example with reference to the drawings in which:
[0042] FIG. 1 is a schematic representation of one embodiment of
the invention;
[0043] FIG. 1A shows exemplary central and marginal parts of the
panel;
[0044] FIG. 2 is another schematic representation of one embodiment
of the invention;
[0045] FIG. 3 is yet another schematic representation of one
embodiment of the invention; and
[0046] FIG. 4 is yet another schematic representation of one
embodiment of the invention;
[0047] FIG. 5 is a flow chart;
[0048] FIGS. 6,7,8 and 9 show experimental results utilising a
process according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0049] Hot Pressed Composite Panel Inspection
[0050] The production of oriented strand board (OSB), medium
density fibre board (MDF), hot pressed laminated composites, and
other pressed materials is a complex process. It is highly
desirable to monitor process variability, e.g. to note variations
in the placement of wood chips, fibre components, density,
distribution of resin, local delamination, and other
non-uniformities in the panel. Process variations from the mean
intended usually result in a degradation of local properties (too
brittle, too soft, too stiff, wrong colour, too weak, etc.).
[0051] Embodiments of the invention will now be described which
allows for a direct on-line measurement of these production
variations.
[0052] Since the panels undergo a hot pressing, they emerge from
the press already uniformly heated. Therefore, apparatus used may
be as follows:
[0053] 1. A first Far IR scanner capable of imaging the moving OSB
with the required resolution.
[0054] 2. A digitization and storage unit that buffers and
sequences the first images taken.
[0055] 3. A second independent Far IR scanner identical or similar
resolution to the first that images the panels at a latter point in
their transport and processing in the facility.
[0056] 4. Sufficient tachometers, broken beam sensors, and local
ambient thermometers to allow for accurate and efficient tracking
of the panels, and thermodynamic modelling of the associated heat
loss in transport.
[0057] 5. An image processing computer system capable of performing
the thermodynamic modelling calculations of the set of first images
and computing the differences between these time forward modelled
first temperature distributions, and actual second temperature
distribution sampled.
[0058] 6. Image processing hardware and software capable of
enhancing, identifying and quantifying the detected variations
between the actual IR image samples, and the time forward modelled
data from the earlier images.
[0059] 7. A process control interface to the PLC or control
equipment which controls the sorting, marking, and grading of the
panel products being produced.
[0060] Panels are heated in a hot pressing step of their
manufacture to high temperatures, e.g. 60 to 120 degrees Celsius
above ambient. Panels are transported from the hot press typically
at speeds of up to 400 ft. per minute. Temperature differences are
large. In the ideal embodiment, the two IR scanners are placed as
far apart as possible within a section of the production facility
where motion of the panels is relatively uniform. The panels are
scanned at different temperatures and the images are digitized.
[0061] A central portion and a marginal portion may be designated
for each panel. This designation is dependent on the accuracy
required in the marginal area but for general purposes the central
area may comprise between about 10 and 90% of the surface area.
Usually the central area may be about 75% of the surface. For the
rectangular panel shown in FIG. 1A, the marginal part is
advantageously increased at the corners since irregularities in
cooling or heating may occur. Thus the central area may have
smoothed corners as shown or may even be circular.
[0062] Spatial resolutions of on the order of 1/4" square are
required, and image processing systems must store and process
400.times.200 pixels/image for 8'.times.4' panels, and up to
1200.times.600 pixels/image for 24'.times.12' panels.
[0063] Thermodynamic modelling, for the marginal portion or when no
central portion is designated, is calculated by means of a computer
and the variations and anisotropies indicate flaws in the
panels.
[0064] Adequate image and mathematical processing must be provided
(several billion operation per second) to perform image processing
and thermodynamic modelling at rates up to 1 panel every 0.5
second.
[0065] FIG. 1 generally illustrates schematically a process and
apparatus for hot pressed panel inspection. In the drawing 10A,
10B, 10C represent plywood panels in consecutive positions in their
manufacture. Panel 10A is located between the presses of hot press
12. Panel 10B is located for scanning by infra-red scanner 14 and
temperature T1 which is substantially the temperature at which the
panel emerges from the hot press. Panel 10C is shown in position
for scanning by infra-red scanner 16 at temperature T2 below the
temperature T1. Each panel 10A, 10B and 10C comprises a central
part 11 (see FIG. 1A) and a marginal part 13 extending around
it.
[0066] The scanned data from scanner 14 is digitized in digitizer
18 and the scanned data from scanner 16 is digitized in digitizer
20. Data from digitizer 18 together with data from thermodynamic
sensors 22 to compute the thermodynamic model in computer 24.
Similarly data digitizer 20 together with data from sensors 26 are
used to compute a second thermodynamic model by computer 24.
Computer 24 then compares the thermodynamic model to calculate
significant variation in anisotropies.
Large In-Situ Panel Inspection
[0067] Another example of the process of the invention is use for
in-situ inspection of large panels, for example, metal panels.
[0068] In this case, although the problem is different, the
principle is the same.
[0069] Large in-situ panels, iron or steel panels, must from time
to time be inspected for corrosion. These panels might form part of
the exterior hull of a ship above the water line, the exterior of a
large storage tank or vessel, or in general the panel sheathing of
some large structure already in place.
[0070] In this case the apparatus may comprise
[0071] 1. The single Far IR scanner capable of imaging the panel
surface with the required resolution.
[0072] 2. A digitization and storage unit that buffers the images
taken.
[0073] 3. Means to heat the panel such as a hose to produce a steam
or hot water or hot fluid and direct it at the panel surface to
induce significant local heating. The hose may be used to heat the
panel just prior to the acquisition of the first image. Alternately
if the panel has been heated by the sun, it may be sufficient to
induce a thermal transient merely by pumping cool water against the
hot surface. The second image may be taken after a suitable amount
of time has passed. For empty tanks or ship's holds 20-40 minutes
might be a suitable amount of time. For vessels or holds filled
with dense liquids, a considerable shorter time would be
appropriate.
[0074] 4. An image processing computer system capable of performing
the thermodynamic modelling calculations on the set of first images
and computing the differences between these time forward modelled
first temperature distributions, and actual second temperature
distribution sampled.
[0075] 5. Image processing hardware and software capable of
enhancing, identifying and quantifying the detected variations
between the later image sample, and the time forward modelled data
from the earlier images.
[0076] 6. An output printing device capable of printing pseudo
colour images, or contour map displays reproducing the Far IR
images with areas of non uniformity enhanced, and marked.
[0077] A first image is scanned at a first temperature and a second
image is scanned at a second different temperature after the
induction of a sudden thermal transient. The images are
digitized.
[0078] In this case panel temperature are high (50 to 70 degrees
Celsius above ambient), a single Far IR scanner is used, and
detailed knowledge of internal construction (nature of internal
support and structure) is necessary.
[0079] Spatial resolutions of on the order of 1/4" square are
required, and image processing systems must store and process
400.times.200 pixels/image for 8'.times.4' panels, and up to
1200.times.600 pixels/image for 24'.times.12' panels.
[0080] Adequate image and mathematical processing must be provided
(up to several billion operations per seconds).
[0081] Ideally an automatic azimuth and elevation control device
for directing the Far IR imaging system will be used, and a large
portion of the structure scanned using a long focal length imaging
system, before the second set of identically located images is
taken for differential comparison against the thermodynamically
time forward modelled images from the first imaging pass.
[0082] Similar considerations concerning central and marginal parts
may be applied to these panels. Marginal heat/cooling effects may
be, on the one hand, greater than those in FIG. 1 because the panel
is metal, but, on the other hand, each panel may be bounded by
other panels thus mitigating cooling irregularities. The final
choice of the size and shape of the central part may be somewhat
similar to that of FIG. 1.
[0083] FIG. 2 generally illustrates schematically apparatus and
process for inspection of a large in-situ panel.
[0084] A panel 100 is heated (or cooled) by any suitable means 110.
The means 110 may suitably be a hose to deliver hot (or cold) water
at a constant temperature. The water is delivered to a top surface
of the panel 100 over a period sufficiently to provide relatively
uniform surface temperature changes in the panel to bring it to a
temperature T10. Temperature T10 may be measured by heat sensors
114 distributed over the surface of the panel.
[0085] At temperature T10 infra-red scanner 116 forms an image of
the top surface of the panel. The image is digitized in digitizer
118. The digitized image together with information from the sensors
114 is fed to computer 120 where a thermodynamic model of the
surface of panel 100 at temperature T10 is made.
[0086] The panel 100 is then allowed to change temperature to
temperature T12. A second image is scanned by infra-red scanner
116, digitized in digitizer 118 and fed to computer 120. A second
thermodynamic model is formed. The two thermodynamic models are
compared in the computer to calculate significant variations in
anisotropies between the images. The computer may conveniently be
provided with a printer 122 for providing this information to the
operator.
[0087] In-Situ Inspection Of Pipe
[0088] The invention may also be used to inspect pipe. The detailed
inspection of buried pipelines, semi buried pipelines, surface
pipelines as well as other in-service pipelines conventionally
presents problems.
[0089] In the case of pipelines transporting a liquid product,
ultrasonic measures of exterior wall thickness are possible using
internal pigging. This process is not so easy for pipelines
transporting certain products, or for certain thick-walled
pipelines transporting corrosive or abrasive slurries.
[0090] In the case of gas pipelines, a pipeline might first be
pigged with some sort of magnetic, dimensional or ultrasonic
detector, and anomalous sections exposed for further
examination.
[0091] In the case of pipelines carrying corrosive, or abrasive
slurries, or other materials difficult to pig, the pipes may
already be exposed.
[0092] In either case the application of the invention in this case
is the detection of external surface corrosion internal surface
corrosion, or wall thinning, in the pipe. Apparatus used is
[0093] 1. An induction, or other heater (providing 500-10,000 watts
of heat) is mounted on an external rolling frame which moves in a
controlled linear (or spiral) fashion over the surface of the pipe,
or alternately which can move beside the pipe as in a truck mounted
system, or alternately a cooling system either frame or truck
mounted for spraying cold water, if the pipe is already warm.
[0094] 2. A first and second IR scanner are also mounted on this
external tracking unit, or alternately if transient bursts of heat
are employed a single scanner used to capture the high speed
progression of the transient.
[0095] 3. A digitization and storage unit that buffers and
sequences the images taken is connected to allow the flow of data
from the Far IR scanners.
[0096] 4. Sufficient tachometers, orientation measurement devices,
and local ambient thermometers are provided to allow for accurate
and efficient tracking of the external scanning frame or truck, and
to allow accurate thermodynamic modelling of the associated heat
loss in scanning, or alternately a second imaging system which
acquires normal visible images of the affected pipe, which allows
for later direct identification of the detected defects on the
visual image.
[0097] 5. An image processing computer system capable of performing
the thermodynamic modelling calculations on the set of first images
and computing the differences between these time forward modelled
first temperature distributions, and the actual second temperature
distribution sampled, or alternately a high speed processing system
which is capable of discriminating the presence of small anomalies
in IR images as they are compared to "good" IR images.
[0098] 6. Image processing hardware and software capable of
enhancing, identifying and quantifying the detected variations
between the actual second image sample, and the time forward
modelled data from the first image.
[0099] 7. An output printing device capable of printing out pseudo
colour images, or contour map displays reporting the Far IR images
with areas of non uniformity enhanced, and marked.
[0100] A temperature transient is induced in the pipe, either
heating, for example by using a heater or surface steaming, or by
cooling, for example by using cold water. Images are acquired
throughout the application of the transient change, and these
images are digitized.
[0101] In this case pipe surface temperatures are moderate (20 to
80 degrees Celsius above ambient), heat transfer is extremely rapid
(depending upon the nature of the pipe contents being transported),
and temperature differences are smaller. In a preferred embodiment,
the IR scanner or scanners acquire(s) a large number of detailed
images to completely document the transient.
[0102] Spatial resolutions of on the order of 0.5 mm square or
better may be required. Image processing systems must store and
process very large amount of data (600.times.600 pixels or more for
a 30 cm square patch of pipe surface).
[0103] Adequate image and mathematical processing must be provided
(up to several tens of billion operations per second) to perform
image processing and thermodynamic modelling at rates adequate to
keep up with the inspection of the pipe. Alternatively, mass
storage devices may be employed to buffer "snap-shot" data, and
computing may be performed in burst mode. In this case no central
part and marginal part may be designated.
[0104] A process and apparatus for in-situ inspection of pipe is
generally illustrated schematically in FIG. 3. An indication heater
210 is mounted on a pipe 200 on a external rolling frame 212. First
and second IR scanners 214, 216 are also mounted on the external
frame.
[0105] The pipe is heated as the induction heater moves over the
surface of the pipe and the surface of the pipe is scanned by
scanner 214 at temperature T20 and by infra-red scanner 216 at
temperature T22 which is lower than temperature T20. The scanned
images from each of infra-red scanners 212, 216 are digitized
respectively in digitizers 218, 220.
[0106] The digitized images from the digitizers are fed with
respective temperative information from sensors 222, 224 to
computer 226. The computer first forms respective thermodynamic
models of the images and then compares them to note any significant
variations and an isotropies. These may be indicated to the
operator by means of a printer 228.
[0107] FIG. 4 illustrates another process and apparatus for in situ
pipe inspection for use on a pipe which is already hot, perhaps
because it is carrying heated contents. Cooling means, for example
a nozzle 310 for cold liquid such as water, is directed towards a
pipe 300. The nozzle 310, which may be a spray nozzle, a jet
nozzle, a hose outlet or specialist nozzle to produce a set liquid
pattern, may be mounted on an external transport means (not shown)
of any convenient type. An IR scanner 320, is provided in the
region of the pipe portion to be cooled by liquid from the nozzle
310. The scanner 320 may be mounted on the same transport as the
nozzle.
[0108] The pipe 300 is cooled by liquid spray from the nozzle 310
and the surface of the pipe 300 is scanned by scanner 320. The
scanned images from the infra-red scanner 320 are digitized by
digitizer 322.
[0109] The digitized images from the digitizer 322 are fed with
respective temperature information from sensors 327, via digitizer
328 to computer 324. The computer stores the transient heat changes
observed, notes and calculates models and highlights anomalies on a
separate scanned image taken by an ordinary video camera 326
digitized by digitiser 328.
[0110] These highlighted anomalies can then be directly identified
with normal image data and presented on any display or on printer
330.
[0111] FIG. 5 is a simplified flow chart defect detection by
computer modelled dissipation correction time delayed Far IR
scanning.
[0112] FIGS. 6, 7, 8 and 9 show experimental results.
[0113] The invention will now be further described with referencing
to the following example.
EXAMPLE
[0114] Experiment
[0115] There were three stages in the experiment. The first stage
was a preliminary test using an oven to heat panels and image
panels. In the second stage efforts were made to fabricate panels
with "known" density patterns and image the hot panels after they
came out of the press. A Far infra-red (3-10 microns wavelength of
peak sensitivity) imaging system was installed to image the panels.
Destructive measurement for comparison was the third stage. Some of
the results are illustrated in FIGS. 6, 7, 8 and 9.
[0116] Oven Test
[0117] An oven size 5'.times.5'.times.5' was used to heat
4'.times.4' OSB panels to different temperature levels. Panels of
relatively uniform density had patterns of thickness variation cut
into their surfaces. These panels were then heated in the oven
until they reached an equilibrium temperature, then were removed
from the oven and allowed to cool. A sequence of Far IR images of
the panels were taken as they cooled, and the data digitized with
12 bits of resolution in images approximately 400 pixels per square
inch. The distances between the camera and panels were from 1.5 to
4 meters.
[0118] This procedure quickly showed that an effect was present,
but only if the variations in the panel thickness were of
significant size (approximately 1 to 2 inches in diameter, and 20%
in thickness of greater). It also showed that the panels showed the
most obviously identifiable effect after a period of 6 to 8 minutes
(for panels of approximately 3/8" thickness starting at temperature
of 80-100.degree. C. and cooling to room temperature).
[0119] In addition to the cooling-down process, images were also
taken during the heating-up process. Panels started at room
temperature (approximately 20.degree. C.) were placed in front of
the open oven doors, and heat impulse from the oven allowed to
propagate through the internal structure of the panels. This
approach resulted in clearer images if the oven-panel-camera system
could be set up properly to allow for a uniform heat up of the
panel.
[0120] Panel Fabrication
[0121] The raw wood material used was Aspen strands. Two
4'.times.8'.times.{fraction (7/16)}" OSB panels with a target
density 640 kg m.sup.-3 were manufactured using an automatic
forming line and press system. The platen temperature was about
405.degree. F. (207.degree. C.). After the panel exited the press,
it was laid horizontally on insulating cardboard on the floor just
past the press area. The panel was continuously monitored for about
15-20 minutes using the Far IR camera which was installed
approximately 5 meters above the floor looking down at about 60
degrees. Images were taken every 45-60 seconds.
[0122] Low and high density anomalies were attempted in the
fabrication. In the first panel, larger structural defects were
created at the core layer. Low density holes (4 to 5 inches in
diameter) and strips (approximately 4 inches width, 24 inch length)
were clearly detected by the IR imaging system.
[0123] In the second, smaller scale density variation spots were
created. When strands were deposited to 2/3 of the total mass of
the mat. 8 columns of high and low density spots were made. Each
column had 4 spots of different sizes from 1 inch to 4 inches in
diameter. Spots were 1-foot apart in both panel length and panel
width directions. A certain percentage of strands from one column
of spots were taken and added to the column next to it, thus
creating alternated high and low density spots. The percent of
strands taken and added were intended to vary from approximately 10
to 40% by weight. Caution was taken to minimize disturbance to the
rest of the mat. Although attempts were made to create both high
and low density spots, only low density spots were successfully
created. Neither IR images nor destructive measurement clearly
showed the high density spots as expected. This is probably
because, when depositing the other 1/3 of the strands, a large
portion of strands fell on top of the high spots got scattered.
[0124] In order to qualitatively retrieve the density distribution
of the second panel, a very simple modelling has been applied to
the temperature image. In the model it has been assumed that the
primary heat loss is through the upper surface of the panel
conducting heat into the air. Heat loss from the edges has only
crudely been estimated.
[0125] Destructive Measurement
[0126] The second fabricated 4'.times.8'panel was cut into
50.times.50 mm (close to 2".times.2") specimens. Length, width,
thickness and weight were measured to calculate density for each
specimen. The actual sizes and densities of the low density spots
on the fabricated panel were also obtained from this destructive
measurement. The actual densities of these spots varied from 430 to
590 kg m.sup.-3, approximately 37 to 92% lower than the average
panel density. The sizes of these spots varied from about 1 to 6
inches.
[0127] Results and Discussion
[0128] A representation of the temperature variations in the second
panel is shown in IR image (FIG. 6). The panel reached these
temperatures about 5 minutes after it came out of the press.
Comparing this temperature distribution with the density
distribution from the destructive measurement (FIG. 7), it is
immediately evident that the IR image system picked up most of the
fabricated low density spots very well. The sizes and locations of
these spots are clearly indicated by low temperature areas on the
IR temperature map. Although there was some edge effect (Panel
cools down fast on its edges, because of the fast heat loss). The
four smallest low density spots located at the lower part of the
panel, which have densities about 13 to 33% below the panel average
with sizes varying about 1 inch to 2 inches, can be seen from the
IR temperature map (FIG. 6).
[0129] It was observed that good images could be obtained in a
fairly large temperature range (about 50.degree. C. to platen
temperature). Reasonably clear images lasted for 10 to 15 minutes
on the system's monitor. In other words temperature need not be
very specific.
[0130] No clear pattern of high density spots as intended showed on
the destructively measured density map. This could probably be
explained by the mat forming mechanism. If an area on the mat is
already higher than its surrounds, the chance that stands falling
onto this area stay on top of it is low. They may easily get
dispersed. It does not appear to be easy to create high density
spots without substantially disturbing the structure of the mat.
However, there are some relatively high density areas (720-780 kg
m.sup.-3) on the destructive density map. The high temperature area
on the IR temperature map does not correspond well with these high
density areas. This is because the thermal range of the IR system
was not properly set during imaging, and high temperatures got
saturated. This resulted in some loss of resolution in high
temperature range.
[0131] The density derived from IR imaging and simple modelling
(FIG. 8) roughly resembles the destructively measured distribution
(FIG. 7). The temperature saturation in IR measurement is reflected
by a saturation in the derived density at about 690 kg m.sup.-3 in
a chart showing destructive vs. derived densities (FIG. 9). A
statistical analysis gave a correlation coefficient 0.66 for the
destructive and the derived density.
[0132] A computer simulation study of OSB panel horizontal density
variation conducted at the Forintek Canada Corp. indicated that
even under relatively optimal mat forming conditions the horizontal
panel density could deviate up to 16% and 30% from its average for
a specimen size 2-inch square and 1-inch square respectively. With
the capability of detecting about 13% density deviation at about 1
inch spatial resolution, IR could be practically useful for
estimate of OSB panel horizontal density distribution.
[0133] Conclusions
[0134] This study shows that the infra-red imaging technique is
capable of detecting OSB panel horizontal density. Anomalies of a
scale greater than 1 inch in diameter and of a deviation in density
of about 10-15% below the panel average is surely measurable.
10-15% above the average should also be detectable. In other words,
a 10-15% density deviation from the panel average should be
detectable.
[0135] The detectable temperature range is large (about 50.degree.
C. to platen temperature), this means that panels need not be
imaged immediately after their exit from the press. The time
required for imaging and processing images depends on the camera,
computer and software used. Speed should not be a problem for
on-line measurement.
[0136] Overall, this technique may be suitable for inspecting OSB
panel density/variability.
* * * * *