U.S. patent application number 09/848475 was filed with the patent office on 2002-01-24 for optical observation device and method for observing articles at elevated temperatures.
Invention is credited to Chang, Tzyy-Shuh.
Application Number | 20020008203 09/848475 |
Document ID | / |
Family ID | 26848765 |
Filed Date | 2002-01-24 |
United States Patent
Application |
20020008203 |
Kind Code |
A1 |
Chang, Tzyy-Shuh |
January 24, 2002 |
Optical observation device and method for observing articles at
elevated temperatures
Abstract
An optical system for viewing hot objects is disclosed. The
system projects electromagnetic radiation to the part surface and
detects the reflected portion. Based on wavelength and/or
modulation of the applied illumination, the surface characteristics
of the part can be observed without interference from self-emitted
radiation.
Inventors: |
Chang, Tzyy-Shuh; (Ann
Arbor, MI) |
Correspondence
Address: |
John W. Rees
39577 Woodward Ave., Suite 300
Bloomfield Hills
MI
48304
US
|
Family ID: |
26848765 |
Appl. No.: |
09/848475 |
Filed: |
May 3, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09848475 |
May 3, 2001 |
|
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|
09630479 |
Aug 2, 2000 |
|
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60151565 |
Aug 31, 1999 |
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Current U.S.
Class: |
250/341.8 ;
250/341.1 |
Current CPC
Class: |
G01N 21/55 20130101 |
Class at
Publication: |
250/341.8 ;
250/341.1 |
International
Class: |
G01J 005/02 |
Claims
1. An optical system for producing an image of the surface of an
object, said object having a characteristic, temperature-dependent,
dominant, self-emitted EMR spectrum, comprising: an EMR source for
projecting electromagnetic radiation toward said object; an EMR
detector for selectively detecting a spectrum component of said
projected EMR, said component being reflected by the surface of
said object and being directed toward said EMR detector; wherein
said reflected component of said projected EMR has a wavelength
different than said self-emitted, dominant EMR spectrum such that
the reflected component can be distinguished from said self-emitted
EMR based on wavelength.
2. An optical system for producing an image of the surface of an
object, said object having a characteristic, temperature-dependent,
dominant, self-emitted EMR spectrum, comprising: an EMR source for
projecting electromagnetic radiation toward said object; an EMR
detector configured to produce a video signal, said detector for
selectively detecting a spectrum component of said projected EMR,
said component being reflected by the surface of said object and
being directed toward said EMR detector; and a processing unit for
processing said video signal, wherein said reflected component of
said projected EMR has a wavelength different than said
self-emitted, dominant EMR spectrum such that the reflected
component can be distinguished from said self-emitted EMR based on
wavelength.
3. The system of claim 2 wherein said processing unit is configured
to determine dimensional measurements of said object.
4. The system of claim 3 wherein said processing unit is configured
to determine one or more defects of said object.
5. The system of claim 2 wherein said video signal is provided to a
display so as to allow an operator to process the video signal.
6. The system of claim 2 wherein said processing unit comprises an
automatic computing device selected from the group comprising of a
central processing unit (CPU), a digital signal processor (DSP), an
application specific integrated circuit (ASIC), a field
programmable gate array (FPGA) and a combination thereof.
7. The system of claim 3 wherein said object comprises a fabricated
metal part.
8. The system of claim 7 wherein said metal part is fabricated by a
deforming process.
9. The system of claim 7 wherein said metal part is fabricated by a
heat treatment process.
10. The system of claim 4, wherein said object comprises a
fabricated metal part.
11. The system of claim 10 wherein said metal part is fabricated by
a deforming process.
12. The system of claim 10 wherein said metal part is fabricated by
a heat treatment process.
13. The system of claim 3 wherein said object comprises a
fabricated glass part.
14. The system of claim 4 wherein said object comprises a
fabricated glass part.
15. The system of claim 3 wherein said object comprises a
fabricated ceramic part.
16. The system of claim 4 wherein said object comprises a
fabricated ceramic part.
17. The system of claim 7 wherein said metal part is subjected to
one of forging and rolling.
18. An optical system for producing an image of the surface of a
hot object, said object having a characteristic, dominant,
self-emitted EMR spectrum, comprising: a video camera configured to
produce a video signal; an interference filter in association with
said video camera for blocking substantially all of said
self-emitted EMR spectrum; a light source attached to said video
camera; and a processing unit responsive to said video signal for
one of determining dimensional measurements of said object and
detecting one or more defects of said object.
Description
[0001] This application is a continuation-in-part of U.S.
application Ser. No. 09/630,479 filed Aug. 2, 2000, hereby
incorporated by reference, which in turn claims the benefit of U.S.
Provisional Application Ser. No. 60/151,565 filed Aug. 31, 1999
hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to methods and
devices for optically observing objects at high temperatures,
including objects having significant self-emitted radiation.
BACKGROUND OF THE INVENTION
[0003] In a number of industries, workers still visually inspect
hot, glowing objects with their unprotected eyes. Direct exposure
to infrared (IR) radiation, however, could cause physical injury to
the workers. Accordingly, in some instances, light shields are worn
which attenuate the radiation, thus providing some protection
against IR exposure. However, the use of light shields often
restricts the workers' mobility. For example, wearing a light
shield may restrict their ability to physically interact with other
objects that are not glowing, such as tools, controls and the
like.
[0004] Conventional optical inspection devices have also been used
to make observations/inspections of hot objects. For example, the
so-called "passive method" utilizes a signal collector, either with
CRT tubes, charge-coupled device (CCD) cameras, or IR cameras, to
receive the self-emitted radiation from the hot objects. This
approach is similar to the use of human vision, with the signal
collectors essentially functioning as "eyes". The passive method,
however, is subject to a phenomenon known as the "Cavity Radiator
Effect." The Cavity Radiator Effect, postulated by Plank in 1900
and proved by Einstein in the early 20th century, can deceive
visual observers as to the true nature of the object observed. More
specifically, based on this principle, concave surface features of
a self-radiating object appear to be nearly perfect black bodies;
accordingly, they may be mistaken as convex features. Additionally,
the "illumination" is self-emitted and thus often carries unwanted
information. Images collected via this passive method are generally
not suitable for automatic machine vision applications.
[0005] Another prior art approach, the so-called "active method"
utilizes external lights that are projected onto the hot object. A
camera is used to collect the reflected, as well as the
self-emitted radiation from the hot surfaces. In the active method
the idea is to overpower the self-emitted radiation with very
strong external radiation. In other words, the reflected light is
within the spectrum of the predominant self-emitted radiation, but
is distinguishable based on its intensity. The external lights can
be designed to highlight the surface information of interest such
as contour and surface dimples. The external radiation can be
provided by various light-generating devices such as high power
lamps or lasers.
[0006] Several problems, however, are associated with the active
approach. First, few light sources exist that can overpower the
radiation emitted by an object at 1350.degree. C. Second, the
self-emitted radiation still represents a problem: it degrades the
signal quality of the reflected radiation. The signal-to-noise
ratio (external light/self-emitted light) is typically low unless a
very powerful light source is used. Third, these external light
sources may be undesirable in the work environment because they are
so intense.
[0007] Lasers have also been used as a light source to overpower
self-emitted radiation from hot objects. Lasers can deliver
extremely high power densities to reduce the significance of the
self-emitted radiation. For example, a copper-based laser
(radiating at 550 nm) has been used to overpower the self-emitted
radiation of laser welding pool (temperature at about 3000.degree.
C.), which typically radiates from 230 nm to long IR.
[0008] Another prior art approach uses YAG lasers (1060 nm) in arc
welding (temperature at about 2500.degree. C.), which typically
radiates a spectrum of from 275 nm to long IR. However, the use of
lasers poses substantial problems. While lasers deliver high power
density, the areas illuminated by the laser beams are small.
Consequently, raster scanning is typically required when lasers are
used as illumination sources. Moreover, these high power lasers are
expensive, bulky, and pose various risks. And, in order to operate
a laser-based system, the users must be protected with light
shields and other protective equipment.
[0009] The use of infrared (IR) sensors or cameras in a passive
method vision system are also of limited value due to several
factors. First, IR sensors/cameras provide significantly less pixel
resolution than their CCD counterparts. Second, IR radiation cannot
be focused as well as visible light due to its wavelength. Third,
using IR sensors/cameras does not solve the problems associated
with illumination or the Cavity Radiator Effect previously
described.
[0010] There have been attempts to use a combination of passive and
active methods, but this approach does not resolve the issues posed
by the Cavity Radiator Effect and self-emitted radiation.
[0011] In the past, the difference between IR and visible light has
been the focal point of solving the problems associated with the
glare of hot objects. This approach is ill-conceived because a hot
object can radiate with both IR and visible light radiation. For
instance, steel radiates at 650 nm at 1200.degree. C.; that is,
steel can radiate in RED as well as IR. In addition, if the
self-emitted radiation is not removed from the collected signal,
the noise caused by the self-emitted radiation impairs the system's
ability to gather detailed and accurate information about the hot
object. The prior art lacks an effective means of removing the
self-emitted radiation from the collected signal of a hot object.
Finally, it is also believed that none of the devices enabled by
the prior art is portable. This fact has limited the utility of
such devices for certain applications. A portable device would be
desirable for users who need to look at hot objects, but who do not
need to take quantitative measurements. The external light sources
used in prior art devices are too powerful and/or heavy to be
low-risk and portable. In summary, the prior art approaches have
been of limited value. The present invention overcomes these
problems.
SUMMARY OF THE INVENTION
[0012] In one aspect, the present invention provides an optical
system for characterizing the surface of a high-temperature object.
The optical system has an illumination source which projects
electromagnetic radiation toward the high-temperature object
(applied EMR). The applied electromagnetic radiation strikes the
high-temperature object and is reflected toward an EMR detector
along with the self-emitted electromagnetic radiation and any
ambient (background) electromagnetic radiation. At least one
component of the reflected, applied EMR (which interacts with the
surface of the high-temperature object) is selectively detected by
the EMR detector. In one aspect, this selectively identifiable,
reflected EMR comprises EMR having a wavelength which is determined
on the basis of the temperature of the object; that is, based on
wavelength it is distinguishable from the predominant self-emitted
EMR and background EMR. In this manner, detection of the reflected
EMR provides an image of the high-temperature object which
simulates the object surface at low temperatures (i.e., below that
producing any significant self-emitted EMR).
[0013] In another aspect, the component of the reflected, applied
EMR which is identified by the detector has a distinctive signature
produced by modulating the applied EMR. In this aspect, the optical
system of the present invention further includes an EMR
modulator.
[0014] In still another aspect, the present invention is
implemented in a hand-held device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a diagram illustrating the present invention.
[0016] FIG. 2 is a graph illustrating the wavelengths used in the
present invention to distinguish over the self-emitted
radiation.
[0017] FIG. 3 is a diagram illustrating one possible arrangement of
a camera and interference filter.
[0018] FIG. 4 is another diagram illustrating one possible
arrangement of a camera and interference filter.
[0019] FIG. 5 is another diagram illustrating one possible
arrangement of a camera and interference filter.
[0020] FIG. 6 is graph illustrating the selection of a desired
wavelength.
[0021] FIG. 7 is a graph illustrating the use of a cut-off filter
in the present invention.
[0022] FIG. 8 is a graph illustrating the use of FM power
modulation in the present invention.
[0023] FIG. 9 is a graph illustrating the use of FM mechanical
modulation in the present invention.
[0024] FIG. 10 is a drawing of a hand-held device in accordance
with the present invention.
[0025] FIG. 11 is a schematic diagram of a two-camera embodiment of
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] Referring now to FIG. 1 of the drawings, in one embodiment
of the present invention target or object 20 is seen having
self-emitted electromagnetic radiation 22. Object 20 will typically
comprise a part, for example a carbon steel part, a titanium alloy
part, a glass part, or a ceramic part. It will be appreciated that
in a number of part fabrication processes, these parts are heated
to temperatures in excess of 900.degree. C. It will also be
understood that at these high temperatures, these parts emit a
substantial amount of radiation which obscures view of the heated
part (i.e., a dominant, self-emitted EMR spectrum).
[0027] Referring still to FIG. 1 of the drawings, light source 24
is shown which projects electromagnetic radiation 26 toward the
surface of part 20. Radiation 26 is the applied illumination. A
component of applied illumination 26 is reflected by part 20 and is
therefore illustrated in FIG. 1 as reflected illumination 28. It
will be noted that in tandem with reflected illumination 28, a
portion of self-emitted radiation 22 (shown as 22') and some
ambient radiation (not shown) takes the same path as reflected
illumination 28.
[0028] Reflected illumination 28 (and self-emitted radiation 22')
strike detector or sensor 30. As will be explained more fully
herein, by distinguishing reflected illumination 28 from
self-emitted radiation 22' (and any other "noise" such as ambient
radiation) detector 30 can view object 20 as if the part were cool
(essentially no self-emitted radiation).
[0029] In this embodiment of the invention, the wavelength of
reflected radiation 28 is chosen such that it is distinguishable by
detector 30 from the wavelength of the predominant self-emitted
radiation 22'. More specifically, and referring now to FIG. 2 of
the drawings, the present invention provides an envelope of
distinguishable applied illumination wavelengths as a function of
the temperature of object 20. Accordingly, detector 30 senses or
detects reflected illumination 28 which will have a wavelength
under the curve. The preferred longest wavelength of reflected
illumination 28 distinguishable from the self-emitted radiation
(based on temperature) is set forth in Table 1 below:
1 Longest Usable Wavelength (nm) Temperature (.degree. C.) for
Detection by Sensor 30 <800 700 nm 800 680 1000 645 1200 596
1400 545 1600 596 1800 441 2000 385 2200 338 2400 283 2600 233 3000
220 4000 185
[0030] The wavelengths above are derived based on the assumption
that object 20 is a blackbody radiator and will be suitable for all
applications because the spectral radiation intensity emitted by a
real surface at a given temperature of a specific wavelength is
always less than that emitted by a black body at the same
temperature and wavelength. In one embodiment of the present
invention, the process for selecting the applicable illumination
wavelength .lambda..sub.2 (arrow 26) can be determined more
precisely as follows (Ozisik (1985), Heat Transfer--A Basic
Approach, McGraw-Hill):
[0031] 1. Define the highest object Temperature T.
[0032] 2. Define the object emissivity .epsilon.(T, material) which
is a function of object temperature and material.
[0033] 3. Obtain the self-emitted radiation spectrum based on the
black body radiation function: 1 I ( , T ) = 2 c 2 h 5 1 hc 2 T - 1
( 1 )
[0034] and the material emissivity .epsilon.(T) where:
[0035] .PI.=pi
[0036] C=light speed
[0037] h=Planck's constant
[0038] .lambda.=wavelength
[0039] .kappa.=Boltzmann constant
[0040] .epsilon.=emissivity function of temperature, empirically
obtained.
[0041] Together we have the radiation spectrum as:
R(.lambda.,T, material)=.epsilon.(T,
material).multidot.I(.lambda.,T) (2)
[0042] If the material is known, Equation (2) can be reduced to
R(.lambda.,T)=.epsilon.(T).multidot.I(.lambda.,T) (3)
[0043] R(.lambda.,T) can be plotted in general as the solid lines
in FIG. 6. To further simplify, .epsilon.(T) can typically be
assumed to be a constant.
[0044] 4. With R (.lambda.,T), we can find a cut-off wavelength
.lambda..sub.cut-off such that R(.lambda..sub.cut-off, T) is very
small compared to the signal intensity of the external illuminating
light .eta.(.lambda..sub.ill). Note that .lambda..sub.ill is
typically a shorter wavelength than .lambda..sub.cut-off. 2 = ( ill
) R ( cut - off , T ) o ( 4 )
[0045] where:
[0046] .eta.(.lambda.)=the intensity of the external illuminating
light @ wavelength.
[0047] .lambda..sub.ill=the wavelength used for external
illumination.
[0048] .gamma.=signal to noise ratio between the external
illuminating light intensity and the self-emitted light
intensity.
[0049] .gamma..sub.o =specified signal to noise ratio limit that
will satisfy the application.
[0050] .eta.(.lambda.) is usually a function of the external
illumination device. For instance, as stated above, a halite lamp
has an .eta.(.lambda.) like that seen in FIG. 6.
[0051] Accordingly, the longest acceptable wavelength for the
projected (reflected) EMR is that at which a blackbody radiates a
spectral radiance of 5.times.10.sup.-4 W/cm.sup.2 nm (i.e., power
(in watts) per unit area per unit wavelength), at the highest
temperature of the hot object at observation. Thus, I in equation
(1) above becomes 5.times.10.sup.-4 W/cm.sup.2. By solving for
.lambda. and where T equals the object's highest temperature at
observation, the longest permissible wavelength for a given object
which can be distinguished from the self-emitted radiation can be
determined.
[0052] Of course, the selection of .lambda..sub.ill has to satisfy
the sensitivity spectrum of detecting sensor 30. For instance, a
CCD is sensitive to the range seen in FIG. 6. .lambda..sub.ill
should be a wavelength which sensor 30 can detect. The
.lambda..sub.2 in FIG. 6 is suitable for applications that are as
hot as 1500.degree. C.
[0053] Illumination source 24 may take a number of forms, but it
must be capable of generating illumination which includes the
required detectable wavelength. In other words, if a wavelength of
645 nm or less is required to distinguish reflected radiation 28
from self-emitted radiation 22', then illumination source 24 must
include EMR at 645 nm or less. One acceptable illumination source
24 is a halite lamp which emits EMR principally at 435 nm, 550 nm
and 575 nm. Other preferred "light" sources for illumination source
24 are fluorescent lamps and xenon lamps.
[0054] In the case of a laser illuminator, due to the coherent
nature of the laser illumination, the wavelength of the laser
should be set to the required wavelength in accordance with Table I
above.
[0055] A laser can also be used herein as a point illumination
source. Detector 30 can be used to detect information at the point
illuminated by the laser. When coupled with a direction set, such
as a mirror set, lasers can be used to create a raster-scanned
image. Lasers in the present invention, through the use of certain
optics such as a beam expander, can also be used as a zone
illumination source, where the zones are relatively small.
[0056] Lasers can also be used with certain optics for structured
illumination (circular lines, straight lines, single lines or
multiple lines etc.). The structured illumination can be used to
extract the profiles of hot objects in accordance with the present
invention. Multiple lasers can be used for multiple points, lines,
or zones.
[0057] Of course, the intensity of the EMR projected from
illumination source 24 (and the distances between source 24, target
22 and detector 30) must be such that sufficient signal strength is
present at detector 30.
[0058] Those skilled in the art will appreciate that this invention
can be used in conjunction with other illumination methods, such as
front lighting, bright field or dark field, and back lighting
(transmissive lighting). The illumination can be collimated or
scattered, monochromatic or color, structured or non-structured.
Multiple illumination schemes can be applied.
[0059] It is also possible to have multiple wavelengths of
reflected illumination 28 detected by detector 30 in a system, as
long as all of the selected wavelengths meet the criteria.
[0060] Those skilled in the art will also understand that
additional optics, such as, but not limited to, lenses, mirrors,
optical fibers, diffusers, collimators, condensers, prisms,
borescopes, endoscopes, and light guides, can be used in
conjunction with the embodied designs. These optics can be used
along with the illumination device (illuminating radiation source
and modulator) to deliver the illumination onto the targeted hot
object(s) for the purpose of illuminating multiple spots, or
illuminating multiple objects, or any other intended illumination
designs. These optics can also be used along with the signal
collectors to receive the radiation signals from the hot object(s)
for the purpose of meeting space constraints or to change the
observation angles, for example.
[0061] Turning now to detector 30, a preferred detector is a CCD
(charge coupled device) sensor. A CCD sensor is typically sensitive
to wavelengths from 360 nm to 1000 nm. Some newer imaging sensors,
such as blue enhanced CCD chips are sensitive to wavelengths from
175 nm to 1000 nm.
[0062] Of course, detector 30 must be able to detect the desired
reflected illumination 28 wavelength. Preferably, an interference
filter 32 blocks substantially all of the self-emitted EMR (and
reflected EMR which is not at the desired imaging wavelength).
[0063] Interference filter 32 may be placed in front of the
detector lens 34 as best shown in FIG. 3, or between lens 34 and
imaging sensor 36 as shown in FIG. 4. It may also comprise multiple
interference filters 38 in front of imaging sensor pixels 40 as
shown in FIG. 5. Those skilled in the art can further perceive that
the arrangement in FIG. 5 can be altered to facilitate the use of
multiple illumination wavelengths. In this case, different
interference filters 38, some working at one wavelength and some
working at another, will be placed in front of pixels 40. With this
arrangement, different pixels will be sensitive to the signals
carried by different wavelengths. It is possible to have an
aggregate of pixels, such as 2.times.3 or 3.times.1, within which
each pixel is equipped with a different interference filter. This
distribution is similar to that of a color CCD chip. It is also
possible to have one type of interference filter installed in one
zone of the imaging sensor while another type is installed in
another zone.
[0064] It is also possible to facilitate the use of multiple
wavelengths with multiple imaging sensors in a camera, with
different interference filters in front of different imaging
sensors. A prism is used to deliver optical radiations to all the
imagine sensors. This arrangement is similar to that of a 3-chip
CCD color camera.
[0065] Those skilled in the art can also perceive the use of
cut-off filters, instead of interference filters, in the
application. The cut-off wavelength of the cut-off filter's
transmittance curve must be at the desired wavelength. FIG. 7
illustrates the concept. With this setup, a single desired
wavelength or multiple wavelengths can be used. In the case of
multiple wavelengths, the signals carried by all the selected
wavelengths will be treated as a combined signal.
[0066] Distortions in hot object imaging come from several sources.
The above-described approach resolves the distortion influences of
IR glare and Cavity Radiators. Another task is to creatively
resolve the distortion associated with "mirage," the optical
shimmering effect caused by localized air density non-uniformity.
This is a common experience when one drives on a hot summer day.
The road surface can appear to be "floating" and "wiggling." This
"mirage" effect impairs the access to accurate measurements on hot
objects through imaging.
[0067] In the present invention, controlled airflow 43 around hot
object 20 decreases the temperature gradient around the hot object
to remove air density distortion. Air flow 43 will be at a
pre-selected temperature such that the temperature distribution of
the hot object is not influenced adversely by such airflow. The
speed of the airflow should be faster than about 0.01 m/s in order
to avoid localized air density non-uniformity.
[0068] In another embodiment of the invention, and referring again
to FIG. 1 of the drawings, signal modulator 42 is provided in order
to place an identifiable "imprint" on applied illumination 26. In
other words, in this embodiment of the invention the EMR from
source 24 has an identifiable signature (other than merely
wavelength) which allows reflected EMR 28 to be distinguished from
self-emitted EMR 22'.
[0069] A schematic of this implementation is also shown in FIG. 8.
In this design, the power to illuminating source 24 is modulated
through FM device 44. This FM signature will reside in the
illuminating radiation 46 generated by source 24. The radiation is
then projected onto the surface of hot object 20. The reflected
signal 48 is received by imaging device 30 and then demodulated by
FM demodulator 50 (through signal processing), based on the preset
FM frequency, to remove the non-modulated radiation 52, i.e., the
self-emitted radiation. The demodulation signal processing can be
performed in hardware or software or by a combination of both. The
frequency modulation can be a sequence of frequencies such that the
applied (projected) radiation is the nature of repeating square
waves or can be dynamic modulation, producing a sine wave of
changing frequencies which can be detected and demodulated as a
reflected radiation.
[0070] Modulation can also be implemented mechanically, with a
mechanical gate to "pulse" the illuminating radiation, as
illustrated in FIG. 9, or as a sine wave of intensity charges.
[0071] Devices which implement the embodied designs can be mobile,
in part or as a whole. In one case the signal collector is mobile
while the illumination device and hot object remain fixed. In
another case the signal collector and the illumination device are
both mobile and the hot object is stationary. It is also possible
to move the hot object while the signal collector and the
illumination device are stationary or mobile. It is also possible
that two signal collectors or two illumination devices are used in
one application, within which one is mobile and the other is
stationary.
[0072] In still another embodiment, the present invention is
implemented in the form of hand-held device 58. Referring now to
FIG. 10 of the drawings, hand-held camcorder 60 is shown having
projection light 62 and interference filter 64. Camcorder 60, which
may be digital or analog, is used as the signal collector.
Interference filter 64 (preferably at 435 nm) is placed in front of
the lens. External projection light 62 provides the applied
illumination and radiates with a significant intensity (at 435 nm
in this example). Light 62 could be fixed to the surface of
camcorder 60 or be separate to provide multiple illumination
angles. Camcorder 60 could use a magnetic tape, RAM, or any other
suitable data storage device, or the device could be used simply as
a display monitor. The video signal can be exported to a TV, a
monitor, or a PC. Hand-held device 58 could be battery operated or
could operate through an AC power supply. This device can be used
to observe the hot processes or objects in accordance with the
present invention, i.e., by projecting the desired illumination at
a hot object and viewing the image (with the self-emitted radiation
filtered out) with the camcorder.
[0073] In another implementation, multiple signal collectors, such
as cameras, can be used in one system to provide multiple
viewpoints of the hot object. The use of multiple cameras can
facilitate stereo imaging, which provides a three-dimensional image
of the hot object. Also, multiple cameras can be used for multiple
wavelengths, with each camera demodulating the signal carried by
one wavelength.
[0074] In another embodiment and referring now to FIG. 11, the
invention can be used to protect individuals who must interact with
hot objects. More specifically, in this design, two cameras 70,72
are used to capture the same field of view, with one capturing a
normal image 74, which can be color or black/white, and the other
capturing an image based on this invention 76 using beam splitter
77 and interference filter 79. In the normal image 74, hot object
78 is glowing. Glowing object 78 can be identified through a
device, such as but not limited to, portable signal processor 82.
With hot object 78 identified, the normal images of the glowing
object can be replaced by room-temperature-appearance counterparts
(cut out from 76 and pasted into 74). The synthesized image will be
displayed to those who need to see everything in the field of view.
Display 80 can be a monitor, a TV, or any other displaying device,
including a displaying goggle. In order to identify the hot objects
in the synthesized image, an indicator, such as, but not limited
to, a red flashing boundary can be applied to the hot objects.
EXAMPLE
[0075] An example of the present invention in one embodiment is as
follows:
[0076] 1. The external illumination source is a halite lamp. The
halite radiation consists of three principal wavelengths, 435 nm,
550 nm, and 575 nm. The radiation at 435 nm is the most useful
wavelength in this design because it is the farthest one away from
the self-emitted radiation of a hot object. The hot object must be
at a temperature of 1800.degree. C. or hotter for its self-emitted
radiation to cover 435 nm, assuming the hot object is close to a
black body.
[0077] 2. The external radiation is projected onto the hot object
and interacts with the surface of the hot object. The reflected
radiation from the metal halite lamp (with all three distinct
wavelengths), the self-emitted radiation from the hot object, and
any other radiation present are all blended together.
[0078] 3. The blended radiation is then passed through an
interference filter, which has a working wavelength at 435 nm. That
is, only the radiation at 435 nm wavelength can pas through this
interference filter. All other radiation will be blocked. This
interference filter can be placed in front of the lens, or in front
of the imaging sensor.
[0079] 4. Only radiation with the pre-selected wavelength, in this
case 435 nm, can reach the imaging sensor.
[0080] 5. The hot object will appear to the image sensor, say a CCD
chip, as though it were at room temperature.
[0081] 6. The demodulated 435 nm signal is then translated into an
electronic signal.
[0082] 7. The electronic signal may be processed by a CPU, stored
to a media, displayed on a monitor for observation by a human or
any other form of processing. Such processing can provide surface
properties of the hot object, such as dimensional measurements,
geometrical defect detection, surface defect detection, and any
other information that can be carried by the projected radiation,
either manually (with human processing) or automatically (with
digital devices and algorithms).
[0083] 8. The hot object described in this example can be a metal
(steel, titanium, etc.) part, a glass part, or a ceramic part that
are subject to artificial fabrication processes, such as the
deformation (shaping) and/or heat treatment processes (i.e.,
property changes such as mechanical, material, crystal, etc.), at a
high temperature. In the hot deformation process, parts are shaped
into desired geometry and dimensions. Such process is generally
known as forging or rolling. In the heat treatment process, parts
are heated up for the change of their mechanical properties, which
can change their dimensions during the process.
* * * * *