Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Description
Fiber Optic Seam Tracking Apparatus
Technical Field
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This invention relates generally to an
apparatus for detecting anomalies on a workups
surface, and more particularly, to a sensor for
detecting weld groove depth, shape, and location
Background art
In the field of vision based guidance systems,
and more particularly, in the area of automated arc
welding, sensor packing has become an area of vital
importance and continues to frustrate attempts at
developing a truly flexible automated welder. Current
sensor design has developed to the point where the
sensor itself is as slim as the torch bracket in one
dimension, allowing the sensor to proceed the torch
through any narrow opening which the torch alone could
pass. However, as the first dimension is minimized, so
too must the second and third dimensions be increased,
thus reducing rotational capabilities as well as
limiting how closely the torch may approach an
obstacle. use of this type of sensor on an automated
welding system requires an operator to manually weld
those inaccessible areas which are the most difficult
to reach.
Maneuverability of the torch could be enhanced
by moving the sensor to a more remote location, further
removed from the welding torch. Chile this alternative
would increase torch accessibility to confined areas,
it is recognized that absent any special preparatory
action, the reflection coefficient of the workups is
highly variable and considerable energy density is
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required to insure that a spot of light is
established. The amount of light received by the
sensor is a function of the distance between the spot
of light and the sensor, thus as the distance
increases, more power is required from the light
source. Increased power necessarily dictates an
increase in physical size that very well may offset the
maneuverability gained by moving the sensor further
from the welding head.
Additional advantages can be found in removing
the sensor from the extremely harsh environment of the
welding torch. For example, special cooling
considerations may not be necessary electronic
components, being especially sensitive to heat could be
constructed from less costly solid state components, as
the temperature extremes would be less drastic.
The present invention is directed to
incorporating the advantages and overcoming the
problems as set forth above.
Disclosure of the Invention
In accordance with one aspect of the present
invention, an apparatus is movable in a first direction
along a plane Pi for optically detecting anomalies on a
surface of a workups. The apparatus includes first
and second fiber optic bundles, each having first and
second ends, and a projected source of light. A first
means receives the projected light and alters the path
of the light wherein the light is scanned across the
first end of the first fiber optic bundle. A second
means images the light onto substantially a single
fiber of the first fiber optic bundle. A third means
receives the light from the second end of the first
fiber optic bundle, images the light relative to the
workups surface, and establishes a spot of light A
fourth means receives reflected light from the spot and
images the light onto the second end of the second
fiber optic bundle. A fifth means receives light from
the first end of the second fiber optic bundle and
images the light. A sixth means receives the light
from the fifth means and delivers an electrical signal
in response to the position of the light.
Known vision guidance systems are large, bulky
devices which inhibit the mobility of, for example,
welding equipment when affixed to the welding head.
These guidance systems must necessarily be located in
close proximity to the weld groove to insure that the
reflected signal may be differentiated from the optical
"noise typically associated with a manufacturing
environment and most notably emanating from the welding
flash. The present apparatus is directed toward
maintaining an acceptable energy density, such that
removing the guidance system from the immediate area of
the swilled groove will not adversely affect the signal to
noise ratio
grief Description of the Drawings
Fig. 1 is a schematic diagram showing the
relative positioning of the components of the present
apparatus;
Fig. 2 is a schematic diagram illustrating the
optical system of the present apparatus;
Fig. 3 is a cross-sectional view of the
present apparatus;
Fig. 4 is a cross-sectional view of the sensor
attached directly to the welding head; and,
Fig. 5 is an end view of a fiber optic bundle
Best Mode For Carrying Out the Invention
Referring now to the drawings, wherein the
preferred embodiment of the present apparatus is shown,
Fig. 1 illustrates an apparatus 10 movable in a first
direction along a plane "Pi for optically detecting
anomalies on the surface of a worlcpiece 11. Fig. 1
illustrates the apparatus 10 in approximate
relationship to the welding head 13 and worl~piece
surface 11. Fig. 2 illustrates the optics of the
apparatus 10 in greater detail, and a better
appreciation of the instant invention may be had by
referring to both Figs. 1 and 2 in the following
discussion.
The apparatus 10 includes first and second
fiber optic bundles 12,14, each having first and second
ends 16,13;20,22. A source of light I consists, for
example, of a laser diode 26 and output optics
projecting a loom diameter of monochromatic light
having a wavelength of 830 nanometers, a helium-neon
(ennui) laser 28 projecting a .8mm beam of
monochromatic light having a wavelength of 628
nanometers, a first mirror 30 for orthogonally
reflecting the Hun laser light, and a dichroic mirror
32 for passing the Hun laser light and orthogonally
reflecting the laser diode light. Both the Hun and
the diode light are collimated and substantially
coccal aligned with one another, though the laser
diode 26 projects a diverging elliptical beam and must
be collimated by, for example, a lens 33. A first
means 34 receives the projected light and alters the
path of the light by linearly scanning the light across
the first end 16 of the first fiber optic bundle 12.
The first means 34 includes a galvanometers 36
positioned intermediate the source of light 24 and the
first end 16 of the first fiber optic bundle 12. The
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galvanometers has a shaft 37 angularly position able
relative to the first end I of the first fiber optic
bundle 12 for varying the angle of incidence of the two
collimated light sources 26,28 with a first mirror 38
fixedly attached to the galvanometers shaft. The
galvanometers 36 oscillates the mirror 38 through an
angle of 2 under control of a remote processor 39 by
varying the amount of current delivered to the
galvanometers 36. Varying the angle of incidence causes
the light to be reflected in a plane intersecting a
second means 40 which focuses the light onto
substantially a single fiber of the first fiber optic
bundle 12. The second means 40 includes a spherical
lens 42 which has, for example, a 25mm focal length and
is positioned 25mm from the fiber optic bundle 12. The
combination of the 25rnm lens and the 830nm light will
image the loom diameter laser light down to a diameter
of approximately microns, resulting in approximately
95% of the available power being delivered to a single
10 micron fiber. urethra in the event that a laser
having a wavelength other than 830nm is selected, an
appropriate adjustment in the positioning and the focal
length ox the lens 42 will be required to obtain an
image of similar dimensions.
Laser light is known to have a Gaussian
distribution; thus, even a spot which has a 15 micron
diameter coccal imaged onto a 10 micron fiber
transmits 70% of the available power through a single
fiber. It has been discovered that a substantial
portion of the light may be transmitted through a
single fiber of the fiber optic bundle 12 by limiting
the size of the spot imaged onto the fiber optic
bundle. This is important to maintain the energy
density of the transmitted light at a sufficiently high
level to insure that the light reflected from the
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workplace surface if is of adequate intensity to be
differentiated from the "noise" generated by the arc
flash of the welder. That is to say, a high energy
density of the laser light is a key ingredient in
sustaining a high signal to noise ratio.
Referring to Fig. 5, an end view of the fiber
optic bundle 12 is illustrated and shows the individual
fibers arranged in an orthogonal matrix. Laser light
imaged onto the bundle 12 is indicated by the broken
lo line 43 and has a diameter of approximately 30
microns. The image is shown to fall wholly on four
fibers and partially onto eight separate fibers. These
partially illuminated fibers will not maintain this
partial illumination, but will allow the light to
lo diverge and homogeneously illuminate the entire fiber.
The light projected from the second end 18 of the fiber
optic bundle will be significantly larger than the 30
micron input diameter. Additionally, the light lost in
the spaces between the individual fibers becomes more
significant as the diameter increases. Conversely, the
present apparatus 10 will image laser light into a 4
micron spot illustrated by broken line 44. Eros the
illustration it appears as though 100% of the light
would be transmitted through a single fiber, but
because laser light is effected by Gaussian
distribution, only a finite amount of light will fall
within a fixed diameter. us suggested previously,
approximately 95% of the available energy is coupled
into a single fiber. During construction of the
apparatus lo care is taken in aligning the fiber optic
bundle such that the center points of one row of fibers
all fall within the plane of light reflected by the
oscillating mirror 38. This insures that the laser
light is serially linked with each fiber in the row of
fibers, allowing maximum energy to be transmitted to
the workups surface if.
--7--
Referring again to Figs 1 and 2, a third
means 45 receives the light from the second end 18 of
the first fiber optic bundle 12, images the light
relative to a workups surface 11, and establishes a
spot of light. The third means 45 includes, for
example, a spherical lens 46 positioned adjacent the
second end 18 of the first fiber optic bundle 12 and a
wedge prism 48 which has first and second surfaces
50,52 defined by first and second intersecting planes
lo 54,56. The prism 48 is positioned adjacent the
spherical lens 46 with the intersection of the planes
54,56 forming a line 58 substantially perpendicular to
the plane pun The wedge prism 48 is positioned to
refract the light at a predetermined angle in a
direction toward the welding head 13, positioning the
line scan as close as possible to the welding head 13.
Similar results could be achieved by positioning the
fiber optic cable 12 and the spherical lens 46 at this
same predetermined angle and projecting the light
toward the workups surface without the aid of the
wedge prism 48. However, the angular positioning would
require that the lens 46 and cable 12 be moved further
from the welding head 13, enlarging the packaging
requirements of the means 45, and reducing mobility of
the welding head 13. Further, a window 60 is
positioned intermediate the workups surface 11 and
the prism 48. The window 60 is provided to protect the
optical surface of the prism 48 from weld splatter and
is constructed from sapphire to take advantage of its
extreme hardness. This hardness not only discourages
the weld splatter from sticking to the window 60, but
also, environmental conditions will ultimately result
in the window 60 becoming occluded by the collection of
particulate carried in the smoke generated by the
welding process. Cleaning of the window 60 is,
--8--
therefore necessary on a regular basis, and absent the
protective window hardness, much care would be required
to avoid scratching the window 60. Over a period of
time the optical transmissibility of the window 60
would deteriorate to such a point that sufficient laser
light would be unable to pass through the window 60 and
establish a spot of light. Construction of the
protective window 60 from sapphire allows the use of
readily available cleaning agents (e.g., paper
lo products) without affecting clarity.
The spot of light established on the workups
surface 11 is reflected in all directions forming a
hemisphere of light due to a highly variable
coefficient of reflection. A portion of this reflected
lo light is directed to and received by a fourth means 62
where it is imaged onto substantially a single fiber at
the second end 22 of the second fiber optic bundle 14~
The fourth means 62 includes, for example, a protective
window 64, similar to the window 60, and a spherical
lens 66. The spherical lens 66 is the counterpart to
the spherical lens 46, one having the inverse imaging
properties of the other and each being positioned the
same distance from the ends 18,22 of their respective
fiber optic bundles 12,14. These inverse imaging
properties are employed to insure that, irrespective of
the workups surface 11 being within the focal plane
of the lens 46, the spot of light imaged onto the
workups surface 11 will be imaged by the lens 66 into
a diameter substantially equal to the internal diameter
of a single fiber. For example, if the lens 46 is
chosen to provide magnification of 20, then the lens 66
would provide magnification of 1/20. A spot of light
formed on the workups surface 11 will have a diameter
determined by its distance from the focal plane. The
farther the spot of light is from the focal plane, the
I
larger the diameter; however, because the lens 66 has
the inverse imaging properties of the lens 46, then as
the spot diameter grows as it moves away from the focal
plane, the lens 66 counteracts the growth of the
projected light and acts to return the diameter to the
original diameter as received by the lens 46. This
diameter is ideally the diameter of a single fiber, but
aberrations in the lens prevent the diameter from being
returned to its exact original dimensions and some
lo blurring of the image will occur.
The reflected light is transmitted through the
second fiber optic bundle 14 where a fifth means 68
receives the light from the first end 20 of the second
fiber optic bundle 14 and images the light onto a sixth
means 70 which delivers an electrical signal to the
remote processor 39 in response to the position of the
light. The fifth means 68 includes, for example, a
collimating lens 72 positioned adjacent the first end
20 of the second fiber optic bundle 14. In one
embodiment of the apparatus 10, a seventh means 74
receives light from the fifth means 68, scans the light
in synchronization with the first means 34, and
delivers the light to the sixth means OWE The seventh
means 74 includes, for example, a second galvanometers
76 positioned intermediate the fifth and sixth means
68,700 The galvanometers 76 has a shaft 78 angularly
position able relative to the first end 20 of the second
fiber optic bundle 14 in synchronization with the shaft
37 of the first galvanometers 36. A second mirror 80 is
fixedly attached to and rotatable in unison with the
shaft 78 through an angle of 8l thereby reflecting
the collimated light in a plane intersecting the sixth
means 70. The 8 angular displacement of the mirror
80 compensates for the sharper swing induced by the
collimating lens 72. The receive optics differ from
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the transmit optics in that the amount of light
received is only a small portion of the amount of light
transmitted; consequently, optical losses which could
be considered inconsequential in the transmit optics
become much more significant in the receive optics.
For this reason, the collimating lens 72 is selected to
have a relatively short focal length and a low F number
allowing as much light as possible to be conveyed.
However, short focal lengths and low F numbers increase
the angular displacement of the collimated light
delivered through the collimating lens 72. Thus, light
which is transmitted through the 2 arc is received
in an 8 arc. Both the galvanometers 36,76 are under
direct control of the remote processor 39, making the
adaptation of the second galvanometers 76 to traverse
the 8 arc in synchronization with the 2 arc of
the first galvanometers 36 a matter of software control.
A mirror 82 receives the light reflected by
the galvanometers mirror 80 and orthogonally reflects
the light through a band pass filter 84 which has a 2nm
wide pass band. The filter 84 acts to pass only the
830nm laser light and prevents any false signals from
being generated by the noise of welding arc flash or
any incidental light. The width of the band pass filter
pass band is selected to correspond to the wavelength
of the projected laser diode light. Correspondingly, a
change in the wavelength of the laser diode 26 must
necessarily be associated with an appropriate change in
the band pass filter 84. A spherical lens 86 has, for
example, a focal length of 50mm and acts to image the
filtered light on a silicon photo-diode line array 88.
The diode line array 88 converts the imaged light into
a digital signal representing which of the diodes in
the array 88 is receiving the filtered light. Those
skilled in the art of electronics and optical design
--if--
will recognize that the oscillating mirror 80 could be
replaced by a stationary mirror and a matrix diode
array could be substituted for the line diode array
88. This system would, rather than descant the signal,
allow movement in both the x and y coordinates which
the remote processor 39 would interpret to extract
topographical information about the workups surface
11 .
Fig. 3 illustrates a portion of the apparatus
10, hereinafter referred to as the optical processor
90. The optical processor 90 is located on the welding
robot, but remotely located from the welding torch.
Variable current signals are delivered to the
galvanometers 36,76 by the remote processor 39, which
is preferably separate from the optical processor 90
and remote from the welding robot. The processor 39
contains within its memory a software routine for
assimilating the digital signals provided by the line
diode array 88, determining the weld groove width,
depth, and location within the field of view. The
processor 39 will, subsequently, provide control
signals to the welding robot to control direction and
speed of movement, wire feed rate, welding voltage
etc. The software control routines are not considered
part of the present invention and, therefore have not
been disclosed in the instant application. Similarly
the welding robot is not considered to be part of the
present invention and may take the form of any
commercially available industrial robot.
The optical processor 90 is housed within a
sealable container 91 for protecting the optics prom
the collection of airborne particulate abundantly
present in manufacturing type environments. The Phony
laser 28 is fixedly attached to the container 91 along
with a respective power supply 92. Collimated light
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from the Hone laser 28 is reflected by the mirror 30
and passed through the dichroic mirror 32. The Hone
laser is not intended to affect the intensity of the
light reflected from the workups surface 11, but is
expected to provide a visible indication of the
position of the invisible laser diode light. The laser
diode 26 emits monochromatic light of 830nm which is
invisible to the naked eye. The laser diode 26
receives power from a power supply 94 and delivers
lo light through the collimating lens 33 which is
reflected by the dichroic mirror 32. The dichroic
mirror 32 coccal positions the Hone and laser diode
light such that any adjustments made to the apparatus
10 which affect the visible Hone light must necessarily
similarly affect the invisible laser diode light. The
light from the dichroic mirror 32 is reflected by the
scanning mirror 38 and imaged by the spherical lens 42
onto the fiber optic bundle 12. A jacking stage 100 is
positioned about the spherical lens 42 and allows for
fine focusing of the transmitted laser light by moving
the lens 42 relative to the first end 16 of the first
fiber optic bundle 12. Proper positioning of the ion
segment formed by the scanned light such that it falls
upon the proper chord 16 of the end 16 of the bundle 12
is effected by shimming the laser diode 26 to an
appropriate height. A rotary stage 96 allows the fiber
optic bundle 12 to be rotationally positioned aligning
the center points of a row of fibers with the line
segment formed by the scanned light. The combined
adjustability of the rotary and jacking stages (100,96)
enables the scanned light to be transmitted along a
single row of fibers, serially linking each individual
fiber with the projected laser light. The adjustment
process would be extremely difficult if the operator
were unable to see the imaged laser light; however/
commercially available infrared focused viewers will be
used during the adjustment process making tune 830nm
light visible.
The reception portion of the optical processor
90 also includes a rotary and jacking stage 98,102 to
insure that the reflected light is generally swept in a
plane perpendicular to the axis of notation of the
descanting mirror 80 and to allow for fine focusing of
the received light. The collimating lens 72 receives
lo the reflected laser light after it has been properly
oriented by the rotary and jacking stages 98,102, and
delivers collimated light to the oscillating mirror
80. The collimated light is then reflected off of
mirrors 80,82, passed through the band pass filter I
and imaged by the spherical lens 86 onto the line diode
array 88. The oscillating motion of the mirror 80 in
synchronization with the oscillating mirror 38 acts to
reflect the collimated light to a single location given
that the light reflected from the workups remains at
a given distance from the optical heed. Displacement
of the collimated light from the given location
indicates that the workups surface 11 is a different
distance from the optical head. The magnitude of the
displacement indicates the distance between the optical
head and the workups surface 11. For example, as the
laser light is scanned across the workups surface 11 7
the light will fall into the weld groove and because
the transmit and receive optics are angularly displaced
from one another, the line segment formed by the laser
light on the workups surface 11 will appear
discontinuous. The points and magnitudes of the
discontinuities indicate the location and the depth of
the weld groove.
-14-
Referring now to Fly. 4, a portion of the
apparatus 10, hereinafter referred to as the optical
head 104, is shown in sectional view attached to the
welding head 13 by bolts 106,108. The fiber optic
S bundles 12,14 enter the optical head 104 through a
passage 110 and terminate within the optical head 104
adjacent the spherical lenses 46,64. Protective
windows 60~66 are positioned adjacent a first end 112
of the optical head 104 and the wedge prism 50 is
lo located adjacent the first protective window 60
intermediate the window 60 and lens 46. The optical
path of the transmitted and reflected light is
indicated by the dashed line 114, illustrating the
principle of triangulation. Where variations in the
height of the workups surface 11 occur, for example,
in the weld groove shown as the dashed line 116, the
reflected light traverses an alternate path and,
correspondingly, illuminates an alternate fiber.
Ultimately, a different diode in the photo diode line
array 88 is illuminated, indicating to the remote
processor 39 that the surface 11 of the workups has
deviated by a preselected measurable amount.
The overall dimensions of the optical head 104
are shown to be 5 inches in height and projecting 2~5
inches from the welding head 13. The small size of the
optical head 104 allows the welding head 13 to travel
into confined areas, such as welding into dead ends
where vertical obstructions would contact the optical
head 104 before the welding head 13 could reach the end
of the weld groove. Minimizing the optical head 104
reduces the quantity of weld groove which cannot be
reached by the welding head 13; however, the small size
of the optical head 104 allows the welding head 13 to
be tilted at an angle sufficient for finishing the weld
into the dead end area, virtually eliminating manual
welding of dead end seams.
fly
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Industrial Applicability
In the overall operation of the apparatus 10,
assume that the welding head 13 is positioned over a
groove in a workups 11 and a robot is attempting to
5 guide the welding head 13 along the groove under
direction from a remote processor 39. The weld groove
location is determined from information provided by the
apparatus 10 in the form of digital electrical signals.
A light source 24 provides collimated
monochromatic light to an oscillating mirror 38 which
scans the light linearly across the end 16 of the first
fiber optic bundle 12. The bundle 12 has been
mechanically oriented such that the center line of the
scanned light will substantially align the centers of a
single linear array of individual fibers in the bundle
12. The height is transmitted out of the linear array
of fibers at the second end 18 of the bundle 12 and
imaged onto the workups surface 11. At any one
instant in time a spot of light is formed on the
workups surface 11, but over a period of time the
spot is linearly scanned across 2.5 inches of the
surface 11. A portion of the light reflected by the
surface 11 is imaged onto the second end 22 of the
fiber optic bundle 14 illuminating a preselected fiber
in the bundle 14. The fiber being illuminated is
determined by both the position of the spot within the
linear scan and the distance of the spot from the
optical head 13. The light is transmitted through the
bundle 14, out the first end 20 of the second bundle
14, and onto an oscillating mirror 80. The mirrors
80,38 are oscillating in synchronization with one
another such that the linear scan induced by the first
mirror 38 is nullified by the second mirror 80. For
example, if the workups surface 11 was perfectly
flat, the light reflected by the second mirror would
-16-
remain perfectly stationary, and illuminating the same
photo diode in the photo diode array I Variations in
the workups surface 11 will, therefore be translated
into a displacement of the light on the photo diode
array 88. A different diode in the array 88 will be
illuminated and provide a distinct electrical signal to
the remote processor 39. The magnitude of the
variations in the workups surface are directly
proportional to the magnitude of the displacement of
the light on the photo diode array 88. The digital
signals delivered by the array 88 contain information
on the surface configuration of the workups 11.
While the apparatus has been illustrated
primarily in association with tracking of weld grooves,
those skilled in the art of optical pattern recognition
will observe that the apparatus 10 could be used in any
type of system requiring visual identification. For
example, the present apparatus 10 could be implemented
to identify parts in a manufacturing process,
especially their particular orientation, and provide
this information to a manipulator for procuring the
parts. Alternately, the same apparatus 10 could be
used in quality control applications for visually
inspecting manufactured parts to insure they fall
within acceptable tolerances.
The present apparatus 10 is not intended to be
limited to the applications exemplified here, but the
examples are given merely to clarify the operation of
the apparatus 10.
Other aspects, objects, and advantages of this
invention can be obtained from a study of the drawings,
the disclosure, and the appended claims.
