Note: Descriptions are shown in the official language in which they were submitted.
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Description
Ada~tive Welding Guidance A~~aratus
Technical Field
This invention relates generally to an
adaptive welding apparatus for guiding a welding head
along a weld groove and, more particularly, for guiding
the welding head to a predetermined location within ~he
weld groove in response to the weld groove cross
sectional configuration.
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Background Art
In the field of adaptive welding, many
attempts have been made to automate the welding
process, as evidenced by the tremendous body of art
principally directed to locating and tracking weld
grooves. The art ranges from simple tactile sensors,
which provide a good deal of information on the
location of the groove, but little about the groove's
dimensions or shape, to the more advanced vision type
systems, mimicking the human operators method of
guiding the welding torch along the groove. In fact,
the human operator appears to be the model, or at least
the standard to which all machine welds are compared.
Adaptive welders have shown an ability to weld many
times faster, for longer periods of time, and with a
consistency considered unachievable by their human
counterparts. Given that the adaptive welders perform
the functions of the human welder with a higher degree
of accuracy and consistency, one may reasonably assume
that adaptive machine welding is consistently of a
higher quality than those welds performed by human
operators. ~owever, no connection has been suggested
between the quality of a weld and the guidance point of
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the welding head within the weld groove. For exa~ple,
guiding to the center of a symmetrical weld groove may
provide a weld of superior quality, but implementing
the same guidance scheme on a weld groove having a
nonsymmetrical cross sectional configuration could
result in a weld having less than ideal physical
characteristics. Similarly, guiding the welding head
at a constant distance from one of the groove edges may
prove less than satisfactory in areas of groove width
variation, where in the worst case, welding could
actually be performed outside the groove. At best,
welding will occur at the optimum position within the
groove purely by chance and only momentarily.
The present invention is directed to over-
coming one or more of the problems as set forth above
by positioning the welding head at the optimum welding
position and adaptively maintaining this optimum
positioning during the welding process.
Disclosure of the Invention
.
In accordance with one aspect of the present
invention, an adaptive welding apparatus for guiding a
welding torch along a weld groove has a first means for
moving a sensing element along a pathway extending
across the weld groove. The sensing element detects
the weld groove cross sectional configuration, and
delivers signals in response to the position and
configuration of the weld groove cross section. A
second means receives the signals, determines relative
locations of preselected points on the weld groove, and
compu~es a center of area o~ the weld groove cross
section. Further, a third means computes a guidance
point in response to the center of area and controls
the lateral movement of the welding head in a direction
toward the guidance point.
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Previous adaptive welding appartus have been
primarily concerned with locating a welding groove and
guiding a welding head along the groove with little or
no consideration to the position of the welding head
within the groove and its effect on weld quality. The
present invention is directed to an apparatus for
guiding the weld head along the optimum weld path based
on the cross sectional configuration of the weld groove.
Brief Description of the Drawings
Fig. 1 is a block diagram of an adaptive
welding system embodying the invention;
Fig. 2 is a detailed drawing representing the
light spot and TV scanning functions of the optical
apparatus in the system of Fig. l;
Fig. 2A is a representation of a digital weld
groove scan using the apparatus of Fig. 1 in the
scanning mode suggested by Fig. 2;
Fig. 3 is a detailed block diagram of an
interface between the optical system and a data
processor embodiment of Fig. l;
Figs. 4, 4a, and 4b are flowcharts of part of
the software used in the preferred implementation of
the invention;
Fig~ 5 is a side view of a carriage apparatus
for certain optical and mechanical components of the
Fig. 1 embodiment;
Figs. 6 and 6a are cross sectional views of J
type welding grooves;
Fig. 7 is a stylized top view of a welding
groove and the angular relationship between the welding
torch, optical system, and weld groove; and
Fig. 8 iS a perspective drawing of a three
axis welding apparatus.
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Best Mode Eor Carr~ Out the Invention
An adaptive welding apparatus 8 for guiding a
welding torch 14 along a welding gxoove is shown in
Fig. 1. A laser projector 10 and a raster-scanning
type TV camera 12, such as General Electric TN 2500,
make up the basic optical system and are mounted along
with the MI~-type wire welding torch 14 on a movable
platform 16a, 16b for controlled motion relative to a
workpiece 18 which lies on a fixed support 20. The
support 20 lies within a three-axis (Cartesian)
coordinate system of which the Z or vertical axis
extends along the centerline of the torch 14. The
break between platform portions 16a and 16b indicates a
fourth degree of freedom so that the projector 10 and
scanner 12 can rotate or "swing" about the Z-axis and
the optical system can follow a weld groove without
disturbing the X,Y coordinates of the torch.
The platform 16 is mechanically connected, as
represented at 22, to axis drive motors 24 which move
: 20 the p]atform 16 in the desired direction, to the
desired degree and at the desired rate in following a
weld groove in the workpiece 18. Encoders 26 monitor
the extent and direction of rotation of the motors 24
in the conventional servo-positioning fashion and keep
track of the relationship between commanded positions
and actual positions of the platform 16 along the X,Y,Z
axes and about the Z axis.
A first means 27 moves a sensing element 2~
along a preselected pathway which extends across the
weld groove, senses the weld groove cross sectional
configuration, and delivers signals in response to the
position and configuration of the weld groove cross
section. The first means 27 can include, for example,
an Intel 8085 digital computer 28 connected through a
digital-to-analog converter 30 and amplifier 32 to a
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galvanometer-type mirror drive means in the projector
10 which causes a beam 34 of monochromatic light to be
projected at an angle onto the workpiece 18 forming a
spot of laser light which moves linearly across the
weld groove at a controlled rate, as hereinafter
described in more detail with reference to Figs. 2 and
3. The reflection of the beam 34 from the surface of
the workpiece 18 is received by the TV-camera scanner
12, also described in more detail with reference to
Figs. 2 and 3, and produces a digital data stream which
is operated on by the interface 36 which provides data
to the Intel 8085 computer 28 representing the peak
intensity locations of the laser beam reflection at
controlled time intervals. Those skilled in the art of
noncontacting sensor design will recognize that other
types of sensing elements 29 such as inductive,
capacitive, or other optical designs can be us~d
without departing from the spirit Oe the invention.
A second means 37 receives the signals
representing peak intensity locations, determines
relative locations of preselected points on said weld
groove, and computes a relative location of the center
of area of the weld groove cross section. The center
of area is computed by performing an integration on the
area of the groove. Only the lateral position of the
center of area is computed. The second means 37 can
include, for example, a portion of the software usecl by
the Intel computer 28 which generates a set of ten
signals and provides these signals to a third means 41
via an RS-232C data link 40. The ten signals are:
(1) position of center of groove area along
the laser scan;
(2) position of left edge of the groove;
~3) position of right edge of the groove;
(4) height of left edge;
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(5) height of right edge;
(6) depth of groove;
(7) area of groove;
~8) check sum;
(9) end of message; and
(lO) sync signal
The third means 41 computes t:he X and Y
coordinates of a guidance point as a function of the
center of groove area (described in greater detail in
conjunction with the flowcharts of Fig. 4) and delivers
the necessary outputs to the axis drives 46 and
controls the lateral movement of the welding torch 14
in a direction toward the guidance point. More
particularly, the computer 38 is connected via a bus 42
to the D/A converter 44 and provides signals to the
X,Y,Z, and C (swing) axis drives A6 which operate the
motors 24 and guide the torch 14 within the weld groove
along a particular path related to the center of the
groove's cross sectional area and/or the left and right
~roove edges. The scanner 12 looks ahead of the torch
14 by a preselected distance, for example, in the
embodiment shown, the scanner 12 precedes the torch 14
by a dis-tance segment of about 4 inches; consequently,
a store of about 20 position commands, each
representing a portion of the 4 inch segment (e.g.
approximately .2 inches), is placed in a ring-buffer 39
in the computer 38 and output to the axis drives 46 on
a FIF0 basis which moves the platform 16 at the desired
rate and in the appropriate direction. In addition to
controlling the lateral positioning of the weld torch
14, the average of the Z coordinates of the left and
right weld groove edges provides a vertical guidance
point~toward which the torch 14 is directed by the
computer 38. Counters 48 maintain a current count of
position-increment pulses from the encoders 26 which
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represent the current position of the torch 14 and
platform 16 wi~hin the coordinate system. This data is
fed back to the computer 38 via the bus 42 and compared
to position commands and generate errcr signals in
conventional servo fashion.
The computer 38 also provides weld-fill
control signals via a converter 44 to a weld power
controller 50 and a wire drive unit 52 which varies the
welding parameters according to a desired end resultr
e.g., to achieve a certain pre-established fill
percentage. The controller 50, wire drive unit 52 and
a welding gas control solenoid 54 all have on-off
controls, such as pushbuttons, which are connected via
an I/0 unit 56 to the bus 42 and advise the computer 38
that these units are or are not in condition for
control by the computer 387 Although shown in the
drawing as being on the units themselves, the on-ofE
pushbuttons are preferably mounted on a remote control
panel.
Conventional external inputs such as jog, tape
drive, and keyboard inputs may be entered via a unit 58
and an interface 60 associated therewith.
The simultaneous, coordinated control of the
tracking and weld-fill functions is an important
feature of the system as it provides not only
variability in the selection of weld characteristics,
but also compensates for relatively wide variations in
the groove itself. For example, parts are commonly
held together prior to final welding by manually
placing a number of tack welds along the groove. The
present system senses the material build-up of these
tack welds as variations in weld area and varies the
deposition rate in the area of each tack and prevents
overfilling. Moreover, the vertical guidance point is
unaffected by changes 1n the area or depth of the weld
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groove and maintains the torch 14 at the average height
of the left and right groove edges. This action
provides the added benefit of "burning through" or
melting the previous tack welds and provides better
welding characteristics without over-filling the
existing groove. Systems which maintain the welding
torch 14 at a constant height above the bottom of the
groove will raise the torch 14 over tack welds
providing less than ideal welds.
Referring now to Figs. 2 and 2A, the spatial
and timing characteristics of the projection and
scanning operations provided by the units 10 and 12 are
explained. The laser beam is projected onto the
workpiece 18 at an angle of about 25-30 degrees from
vertical measured in a plane parallel to the groove.
The spot is caused to travel a path across the groove,
i.e., the beam sweeps through a second plane which
intersects the weld groove. Through the aforementioned
galvanometric mirror drive means 33, the spot is then
returned to the beginning pOSitiQn at a rapid rate and
scanned across the groove repetitively. Since ~he
platform 16 is typically moving along the groove, the
resulting pattern is a series of parallel stripes
across the groove, each being spaced apart in the
direction of platform travel.
The TV-scanner camera 12, on the other hand,
has a viewing axis which is essentially vertica1 and a
raster scan sensor-strobe function which cuts across
the laser spot scan at right anyles. Because of the
25-30 degree difference between the projection angle
and the viewing angIef the point along any given raster
scan at which the TV camera scanner intercepts the
laser spot is related to the length of the optical path
from the projector 10 to the reflection surface and,
3~ hence, to the depth of the groove. This point of
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interception is determined on the basis of reflected
light intensity; i.e., intensity is greatest at the
intercept pointO The result is a series of digital
signals which, taken in their entirety, represent the
groove profile over a given laser scan or, if desired,
over a series of such scans.
It will, of course, be noted that the scan
rate of the TV camera 12 is much higher than that of
the projector lOj i.e~, the camera scan path cuts
across the laser spot path many times during each
increment of laser spot movement. In an actual
embodiment, the camera 12 exhibits a 248 x 244 pixel
array and three complete scans of the array (each scan
being hereinafter termed a "frame") occur for each
sweep o~ the laser spot. However, this ratio of frames
per spot sweep may be varied from 1:1 to 4:1 or more
which alters the signal-to-noise ratio of the input
signal to the camera 12. The variation is xeadily
achieved via the programming of the Intel computer 28~
Fig. 3 illustrates the digital interface 36 in
greater detail. This unit presents a series of signals
to the Intel computer 28 from which the coordinates of
the workpiece surface can be derived at spaced points
along the laser spot scan path. From this information,
the computer 28 determines the value of the first seven
of the output quantities by mathematical calculation.
More specifically, the interface unit 36
provides a digital number (8-bits) representing the
pixel clock count at which the camera raster scan
intercepts the laser spot during each of the passes of
the scan path represented in Fig. 2. By eliminating
all pixel counts except the count which represents an
interception and, therefor, an actual groove depth, the
interface reduces the data processing function of the
computer 28 to a significant degree~
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The pixel clock 62 effectively strobes the
pixels of the sensor array in the camera 12 and scans
across the laser path. Each pixel output is
effectively a measure of the intensity of the reflected
laser light received by that pixel and is applied to
one input of a comparator 64 and to an 8-bit latch 66.
As long as each new pixel signal (A) is greater than
the previous signal (B), the output on line 68 enables
the latch 66 which receives and stores the new signal
10 for reference on the next count. The output on line 68
also advancesl via line 70, the count stored in the
latch 72 from the counter 74. Recognizing that the
laser spot reflection spreads appreciably, the pixel
outputs continually increases in intensity as long as
15 the camera scan is approaching the center of the
reflection. After the center is passed, the intensity
of the signals begin to fall oEf and the condition A~B
is not satisfied and the count in latch 72 is not
advanced. The stored count remains, thereforl at a
20 number representing the Z coordinate of the work
surface at which the intercept occurred. At the end of
each camera scan line, an "EOL" signal strobes the
count from the latch 72 into the computer 28 as a peak
position count and, after a short delay, resets the
25 counter 74 and clears the latch 66~ An end-of-frame
(EOF) signal from the camera 12 is input to the
computer 28 and establishes the portion of the laser
spot path which has been examined and digitized (in the
preferred embodiment, one-third3.
Software involves two major divisions; VIZ,
the camera data analysis rou~ine carried out by the
Intel 8085, and the track and fill control function
carried out by the LSI-ll. In addition, the software
controlled functions of the LSI-ll are subdivided into
35 several subroutines, the most important of which are,
for example, TRACK, SWING, and FILCTL (fill control)O
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The camera micro computer 28 is essentially
free running, repeating its software cyclicly with no
direction from the LSI-ll computer~ Once it has
finished analyzing an image and transmitted the
resultiny data to the control computer 38, it takes
another image and repeats the cycle. A carriage return
character is sent to the control computer 38 to notify
it that a new image is being taken. The character
catching routine in the control computer 38 recognizes
the carriage return as a sync character and saves the
current location of all the axis for later use. Once
all of the data from the current image has been
received by the character cat~hing routine, it
activates the routine "TRACK", a representative
embodiment of which is shown in flowchart form in Fig 4.
If tracking is not enabled, then TRACK simply
sets a software flag "true" iE a groove is in the ~ield
o~ view of the camera and "false" if not~ I~ tracking
is enabled, then the sensor data and the axis locations
saved when the image was taken are used to determine
the location of the weld groove.
First, the guidance poin~ is determined in
camera units using the equation: -
1.1 guidance point = Desired Edge (1) -
(percent bias x (Desired Edge ~1) -
Desired edge (2)) -~ constant
The Desired Edge variables are selected by the
programmer prior to the welding process to be any of
the thre~ values left groove edge, right groove edge,
or center of area. Selection of the variables is
determined by the type, size, and cross section o~ the
groove, whether or not backing is present, how thick
the backing is, and many other variables recognized by
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welding experts as having an effect on the quality of
the weld~ For example, the weld groove cross section
shown in Fig. 6a has a relatively thin plate section 76
with a heavy roll section 78. This type of weld gxoove
will receive the highest quality weld if the welding
torch is guided to the center of area One choice o
desired edge variables for equation 1 1 for welding the
groove of Fig. 6a is, for example, desired edge ~
center of area and desired edge (2) = center of area.
Choosing both variables to be the same simply cancels
the second term from the equation and after selecting
constant = O equation 1.1 becomes:
1.2 guidance point = center of area.
Similar results can be achieved by selecting the
percent bias to be zero. It is important to note that
in asymmetrical grooves, such as the one illustrated in
Fig. 6a, the center of area does not correspond to the
center of the groove; therefor, prior art systems which
guide to the center of an asymmetrical weld groove will
produce a lower quality weld.
The cross sectional view of the weld groove
shown in Fig. 6b differs Erom the groove of Fig. 6a in
that the plate section 76 i5 heavier and the roll
section 78 is lighter. The proper guidance point for
this cross section is closer to the plate 76 and is
implemented by selecting desired edge (1) = center of
area, desired edge (2) a left groove edge and constant
= O. The percent bias adjusts the positioning of the
weld torch between the center of area and the left edge
and is most effectively selected empirically during an
experimental phase where various bias values are
selected and tested. Substituting these variables into
equation 1.1 yields:
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lo 3 guidance poin-t = center of area - percent
bias (center of area - left yroove edge).
Both equations 1~2 and lo 3 will compensate for the
common occurrence of poor fit up~ where the distance
between the plate 76 and roll 78 is large and creates
gaps between the plate 76 and backing 80. During this
condition, it is necessary to guide the welding torch
further from the left groove edge to prevent the
welding ~rc from burning through the gaps and draining
the molten metal through the perforation. Both
equations guide relative to the center of area, and
since the center of area shifts away from the plate 76
as the groove becomes wider, both equations will shift
the guidance point in the proper direction away from
the plate 76. Those skilled in the art of weld
engineering wîll recognize that there are a large
variety of weld groove cross sections, each having a
particular guidance point which yields the highest
quality weld; consequently, a truly adaptive welder
should be capable of welding to any series of points
within a welding groove and such a system would be a
significant advance in the field.
A second guidance equation identical to
equation 1.1 is used by the "TRACK" routine to control
the vertical position of the weld torch. The desired
edge variables are similarly selected by the programmer
prior to the welding process to be either the left or
right groove edge vertical coordinate. Variations in
the type and size of weld grooves influence the
programmer's decision on which of the edges are used as
the variables in the guidance equation. Normally, the
vertical guidance point is the left edge plus a
percentage of the distance between the left and right
edge. However, conditions exist where the height of
one edge should be neglected. For example, where the
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height of the right edge is significantly greater than
the height of the left edge, only the left edge plus a
constant value are used to guide the torch. This
function is accomplished by choosing both Desired Edge
(1) and Desired Edge (2) to be equal to the left edge
heiyht so that the second term is canceled.
Referring, once again, to the flowchart of
Fig. 4, the next step in the TRACK progra~ is computing
a sensor distance offset. This offset can best be
explained in conjunction with the diagram of Fig. 7.
Fig. 7 illustrates a curvilinear welding groove 81
being welded at machine location 82 while
simultaneously sensing the weld groove 81 in advance of
the weld by scanning laser light across the groove 81
and viewing the reflected light. The optical system is
rotated through an angle 83 to maintain the groove 81
within the laser scan path; howevex, owing to the
curvilinear path oE the welding groove 81, the
previously determined guidance point 84 will not
necessarily correspond to the center point 85 of the
laser scan path. Consequently, the sensor angle 83 of
the optical system does not correspond to the actual
angular displacement of the guidance point 84 from a
reference plane 86. Further, since the sensor distance
corresponds to a known preselected distance between the
machine location 82 and the center point 85 of the
laser scan path, the guidance point 84 is the distance
from a reference point (center point 85) to the
guidance point 84, and the corre~ponding line segments
form a right angle, then the sensor distance offset is
computed as the square root of the sum of the squares
of the two distances. The sensor distance offset is
the distance ~etween the machine location 82 and the
guidance point 84.
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A groove angle 87 is computed by taking the
inverse tangent of the guidance point 84 divided by the
previously computed sensor distance offset. After
knowing the sensor and groove angles 83,87 and the
sensor distance offset, the x and y coordinates of the
guidance point are computed. A previously computed
guidance point's x and y coordinates, which are the
current machine location coordinatesr are respectively
added to the product of the sensor distance and the
cosine of the sum of the groove and the sensor angles,
and the product of the sensor distance and the sine of
the sum of the groove and sensor angles. These x and y
coordinates are stored in the ring-buffer 39 and used
as guidance points as needed.
The distance from this guidance point to the
previously used guidance point is then checked and iE
that distance is less than some arbitrary minimum, the
current point is discarded and the track routine is
suspended. If the distance is greater than the minimum
allowable value, a test is made to determine if the
previously used point is the closest possible point to
the current program point. If so, that point is tagged
as being the program point and the interpreter for the
sensor is called. For the typical case, the next
instruction would be to interpret the weld stop
program. The first instruction in that program is
currently the "tracking off" instruction which causes
the whole tracking process to cease.
If, however~ the previous point was not the
closest to the program point, then the current point is
placed in the first in, first out buffer (FIFO). The
area of the groove at this point is also placed in the
: FIFO for use by the fill control routine when the weld
torch~nears the associated X~ Y, Z point.
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The "SWING" routine is also called and
maintains the sensor approximately centered over the
groove ahead of the torch. The swing routine computes
the equation of a line which approximates the path of
the upcoming groove from some of the most recent polnts
placed into the FIFO. The intersections of a circle
whose radius is the distance between the torch and the
point where the laser beam strikes the workpiece are
calculated. The center of circle is placed at the
point toward which the torch is currently traveling~
The proper intersection is chosen and the correct
sensor head angle is calculated to place the sensor
over that intersection. This angle is made part o the
current servo command so that as the torch reaches the
current command point, the sensor also reaches the
desired angle.
The above processes continue until they are
stopped by a "tracking off" instruc-tion in the program,
a stop button command signal, or the completion of a
predetermined number of continuous sensor errors.
The points are removed from the FIFO as needed
and command the computer servo software to move the
machine axis. If the system is welding and the fill
control is on, the area is also removed from the FIFO
and used by the subroutine called "FILCTL". FILCTL
uses the groove area to predetermine the described weld
metal deposition rate in pounds per hour. The larger
the groove area, the greater the deposition rate,
within limits. From the deposition rate and the known
physical data of the wire, the desired wire-feed speed
is calculated. Once the wire feed is determined, the
desired groove fill percentage is achieved by
calculating the travel speed. Given the calculated
travel speed and wire-feed speed, the arc voltage is
calculated and adjusted via the controller 50.
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Fig. 5 is a view of a preferred, actual
embodiment of the system of Figs. 1 and 3 of a single
torch MG welder. The platform 16 comprises a servo-
positionable structure depending from a cross beam and
is movable vertically relative to the workpiece 18
along the ~-axis. A plate 80 has depending arms 82 and
84 and carries a conventional low-power helium-neon
laser 86 which projects its output beam late~ally via
mirrors to the scan-pro]ec~or 10 con~aining the
galvo driven mirror which aims the beam downwardly
toward the groove 88 in the workpiece 18.
A camera lens ~0 of the camera 12 is stationed
about 10 inches above the work 18 and focuses on a spot
about four inches ahead of the torch 14. A filter 91
mounted on the lens end of the camera 12 passes light
only at 632.8 nanometers; i.e., the wavelength of the
laser output, and filters out glare from the welding
torch 15 which leaks out from under a shield 9~ carried
at the bottom of the plate 94. A vacuum system
comprising one or more hoses ~6 removes smoke from the
weld area.
Swing motion about the Z-axis is produced by a
motor 110~ Since the Z-axis runs through the center of
the torch, swing movements do not affect the X, Y, 'z
coordinates of the torch itself~ Such movements, do,
however, affect the X, Y coordinates of the scan area
and thereby permit the optical system 10, 12 to follo~
curves in the groove 88 ahead of the weld coordinates.
Fig. 8 shows in yreater detail the physical
arrangement of the guidance system. X-axis displacement
is provided by spaced parallel rails 100 raised above
the floor and open-ended to provide entry and exit for
the work: A Y-axis support 102 spans the two rails 100
and is mounted thereon by way of wheels to allow
displacement. A linear gear-tooth track runs along one
of the rails and is engaged by a pinion gear driven by
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a belt-connected motor and gear-box combination. An
encoder above the motor generates pulses representing
displacement. The Y-axis carriage 104 is similarly
mounted on support 102 and carries the wire reel 106
and wire feed motor. A X-axis drive 108 raises and
lowers the platform 16 relative to support 102 and
carriage 104 for height control. The swing axis system
is described previously.
Industrial Applicability
In the overall operation of a preferred
embodiment of the adaptive welding apparatus 8, assume
that a computer programmer has previously selected the
variables:
1) Desired Edge (1)
2) ~esired Edge (2)
3) Percent Bias
4) Constant
to gui.de the welding torch 14 along the optimum path
within the welding groove. Further, the 'ITRACK''
program is enabled, gcod data points are being received
from the Intel computer 28, and the appropriate signals
are being delivered to the axis drives 46 to maintain
the welding torch 14 at the desired location within the
weld groove. The "SWING" routine is similarly enabled
and acting to position the laser light source 86, such
that the laser scan path will be approximately centered
over the guidance point 84.
The welding torch 14 ultimately reaches a
point on tbe workpiece 18 where ~he weld groove
terminates, or is at least significantly altered in
cross sectional configuration. The computer programmer
has previously alerted the apparatus 8 to this change
in weld groove cross section by programming an
approximate location at which the change is to occur.
Additionally, if a new guidance point equation is
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required for the altered cross sectional yroove, the
programmer inputs these new values and the apparatus 8
continues to weld the new groove with little or no
hesitation. Any number of changes can be programmed,
depending upon the complexity of the workpiece 18~
Other aspectsl objects, advantages, and uses
of this apparatus can be obtained from a study of the
drawings, the disclosure, and the appended claims.
::
: ~ ~ 35
,~ :
:;
:
.
