Weld bead wetting angle detection and control

The wetting angle of a bead, such as a welding bead, is detected and controlled by a feedback operation. In particular, one or more optical profiler heads are used to detect the wetting angle along the edge of a bead. If the wetting angles differ from a preferred value, a feedback control system adjusts one or more weld parameters in order to bring the wetting angles to a desired value. If the wetting angle obtains a value which makes the weld joint completely unacceptable, an alarm condition may be activated. The detection of the bead wetting angles may be provided by two optical profiler heads, each head tracking a corresponding one of the edges or sides of the bead so as to provide information from which a corresponding wetting angle may be obtained.

BACKGROUND OF THE INVENTION 
This invention relates to bead wetting angle detection and control. More 
specifically, this invention relates to a method and system using optical 
profilers for quality control of a bead. 
When performing an automated welding process, the bead wetting angle is a 
significant factor in determining the fatigue strength of a weld joint. If 
the wetting angle is too high, the likelihood of fatigue cracks is 
increased. 
Although various feedback control systems have been used to control 
automated welding processes, such feedback control systems have generally 
been subject to one or more of several disadvantages. For example, some 
such systems have used 2D vision sensors directed toward the molten weld 
pool. Although knowledge about the weld pool is useful, it is not usually 
sufficient to determine some important characteristics of the bead which 
results after hardening of the weld pool. Other arrangements have used 
infrared or visible radiation detectors for sensing temperatures and 
temperature gradients of a newly-laid bead in order to determine the width 
of the weld bead or the severity of the metallurgical quench. Such 
radiation detection processes are often subject to error in the 
measurements because of variations in the surface conditions which may 
significantly affect apparent temperature gradients. 
U.S. Pat. No. 4,724,302 filed in the name of Carl M. Penney and Michael H. 
McLaughlin issued on Feb. 9, 1988, assigned to the assignee of the 
present application, and hereby incorporated by reference, discloses an 
arrangement for control of bead processes such as welding and application 
of sealant or glue. A feedback control process is used in order to 
maintain the height, width, and/or cross sectional area of the bead 
satisfactorily. 
Although stabilization of height, width, and area of a bead is useful, this 
does not necessarily maintain the bead wetting angle to a prescribed 
range. Moreover, knowledge of the height, width, and area of a bead would 
not necessarily allow one to know the bead wetting angle. Further, 
accurate measurement of the bead wetting angle usually requires a higher 
resolution than obtained from optical profilers which view the complete 
width of the bead, such as the optical profilers used in the above patent. 
OBJECTS OF THE INVENTION 
Accordingly, it is a primary object of the present invention to provide a 
new and improved bead process detection and control method and system. 
A more specific object of the present invention is to provide bead process 
control which maintains bead wetting angles within acceptable ranges. 
Another object of the present invention is to provide for the accurate 
detection of bead wetting angles. 
SUMMARY OF THE INVENTION 
The above and other objects of the present invention which will become more 
apparent as the description proceeds are realized by a method including 
the producing of a bead by moving a bead producing tool along one or more 
workpieces. The bead has first and second bead wetting angles, each angle 
being between a corresponding edge of the bead and an adjacent surface of 
a workpiece. Profile information is generated by using at least a first 
optical profiler head moved along the bead. The profile information is 
representative of the profile of at least part of the bead behind the bead 
producing tool. Bead wetting angle data representative of the at least one 
of the first and second bead wetting angles is derived from the profile 
information. The bead wetting angle data is compared to at least one 
reference. A changed value for at least one parameter is calculated 
dependant on the results of the comparison, the parameter being a 
parameter which affects the bead wetting angle. The operation of the bead 
producing tool is changed based upon the changed value of the parameter in 
order to realize feedback control of the at least one bead wetting angle. 
Preferably, the bead producing tool is a welding torch and the at least 
one parameter is selected from the group of welding torch voltage, welding 
torch current, speed of travel of the welding torch, and wire feed rate, 
if any, to the welding torch. More preferably, the calculating step 
includes calculating changed value for two parameters which affect the 
bead wetting angle and the changed values of the two parameters change the 
operation of the bead producing tool. In one embodiment, the two 
parameters are the wire feed rate and the welding torch current, whereas 
another embodiment uses a wire feed rate and a welding torch voltage. 
Alternately, or additionally, the at least one parameter which has changed 
is the speed of travel of the welding torch. The bead wetting angle data 
is representative of the first bead wetting angle along a first edge of 
the bead and the second bead wetting angle along a second edge of the 
bead. The profile information is supplied from moving the first optical 
profiler head along the first edge and from moving a second optical 
profiler head along the second edge. The first and second bead wetting 
angles are controlled to be positive and less than a predetermined value. 
The method may further include the steps of controlling the position of 
the first optical profiler head such that the first edge remains in the 
field of view of the first optical profiler head and controlling the 
position of the second optical profiler head such that the second edge 
remains in the field of view of the second optical profiler. 
The system for bead production quality control according to the present 
invention includes a bead producing tool operable to produce a bead upon 
one or more workpieces, the bead having first and second bead wetting 
angles, each disposed between a corresponding side or edge of the bead and 
adjacent surface of the workpieces. A first optical profiler head is 
operable to generate profile information from the bead behind the bead 
producing tool. Means for processing the profile information and deriving 
bead wetting angle data representative of at least one of the first and 
second bead wetting angles from the profile information are used. 
Calculation means serves to compare the bead wetting angle data to at 
least one reference and to calculate changed values for at least one 
parameter which affects the bead wetting angle. Control means are 
responsive to the calculation means and are operable to change the 
operation of the bead producing tool based on changed values of the 
parameter and provide feedback control of the at least one of the bead 
wetting angles. A second optical profiler head is operable to generate 
profile information from the bead behind the bead producing tool. The 
means for processing derives bead wetting angle data representative of the 
first bead wetting angle from the first optical profiler head and 
independent of the second optical profiler head. In other words, the bead 
wetting angle data representative of the first bead wetting angle is not 
affected by the output of the second optical profiler head. In similar 
fashion, the means for processing derives bead wetting angle data 
representative of the second bead wetting angle from the second optical 
profiler head and independent of the first optical profiler head. 
The method of the present invention may alternately be described as 
including the steps of moving first and second optical profiler heads 
adjacent a bead on one or more workpieces, the bead having first and 
second bead wetting angles, each bead wetting angle being between a 
corresponding side or edge of the bead and an adjacent surface on one of 
the workpieces. The first optical profiler head has a first field of view 
including a first edge of the bead and the second optical profiler head 
has a second field of view including a second edge of the bead. Profile 
information is generated from signals from the first and second optical 
profiler heads and bead wetting angle data is derived representative of 
the first and second bead wetting angles from the profile information. 
Bead wetting angle data representative of the first bead wetting angle is 
derived from operation of the first optical profiler head, independent of 
operation of the second optical profiler head. Bead wetting angle data 
representative of the second bead wetting angle is derived from operation 
of the second optical profiler head, independent of operation of the first 
optical profiler head. The first edge is not within the second field of 
view and the second edge is not within the first field of view. The bead 
may be produced by moving a bead producing tool along the workpiece, 
calculating a change value for the at least one parameter, and changing 
the operation of the bead producing tool based on the changed value in 
order realize feedback control of both the first and second bead wetting 
angles.

DETAILED DESCRIPTION OF THE INVENTION 
The problems associated with a high bead wetting angle are illustrated in 
FIG. 1. A workpiece 10 is welded to the workpiece 12 with the weld bead 14 
disposed therebetween. At the first edge or side 14F of bead 14 an angle A 
is defined. A similar angle (not separately labeled) is defined along the 
second edge or side 14S of bead 14. If the angle A on either side of the 
bead 14 is too great, a fatigue crack 16 is more likely to form as a 
result of the excess weld reinforcement shown for FIG. 1. To try to 
minimize fatigue cracks such as 16, the bead 14 may be treated by grinding 
to remove portion 14R shown in phantom line in FIG. 2. Although the 
removal of portion 14R decreases the weld reinforcement, the actual angle 
A remains the same for FIG. 2 as it was for FIG. 1. The grinding of 
portion 14R has failed to change the angle and is unlikely to improve the 
fatigue strength of the joint. 
In FIG. 3, the bead 14 of FIG. 1 (before the development of crack 16) has 
been properly treated by removing portion 14RS from the bead 14. This 
results in the bead 14 "blending" more into the workpieces 10 and 12 and 
greatly lowers the angle A (not separately illustrated in FIG. 3). By 
reducing the angles at the edges or sides of bead 14 to be very small 
positive values, one can decrease the likelihood of cracks such as 16 
developing. (Other structural problems may develop if the angle becomes 
negative, corresponding to insufficient material added to the weld joint.) 
Depending upon the use of workpieces 10 and 12, one might also have to 
grind the bottom of the bead 14 to blend into the lower surfaces of 
workpieces 10 and 12. 
As shown in FIG. 2, the attempt to correct the bead of FIG. 1 might not 
succeed because it might not change the weld bead wetting angles. Although 
the grinding operation resulting in the removal pattern illustrated in 
FIG. 3 is somewhat more successful, it is disadvantageous to need such a 
grinding operation. 
With reference to FIG. 4, there is shown a relationship between the fatigue 
strength and the wetting angle. The fatigue strength of the vertical scale 
of FIG. 4 represents the upper stress of 2.times.16.sup.6 cycles, whereas 
curves 18F and 18S represent approximations for plain plates with 
alternate treatments and based upon the empirical data points illustrated. 
An assembly 20 according to the present invention is shown in FIG. 5. The 
assembly 20 is used for producing a weld bead 22 to connect a workpiece 24 
to an adjacent workpiece disposed behind workpiece 24 in the view of FIG. 
5. The assembly 20 advantageously will provide for feedback control of the 
bead 22 such that the bead wetting angles are maintained within a given 
range. A robot arm 26 moves a weld torch 28 along a seam between workpiece 
24 and the adjacent workpiece (not visible in FIG. 5) so as to form molten 
weld puddle 30 which hardens into weld bead 22. The torch 28 is mounted 
upon a member 32 attached to arm 26. A support 34 fixes a tracking 
profiler head 36 relative to torch 28. The tracking profiler head 36 may 
be used to insure that the weld torch 28 tracks the seam in a manner which 
need not be described in detail as this feature is not central to the 
present invention. Generally, the member 32 and support 34 may rotate 
about a vertical axis central to member 32 relative to the robot arm 26. 
However, it should also be noted that the present invention may be 
implemented without the use of a tracking profiler if the weld torch 28 or 
other bead producing tool is to follow a prescribed path which is 
sufficiently definite that there is no need for real time adjustment in 
the path. 
As illustrated in simplified fashion, optical profiler heads 38 and 40 are 
respectively pivotably attached to member 32 by respective supports 42 and 
44. The heads 38 and 40 are independently controlled by a position 
feedback control 46 shown in block form. The position feedback control 46, 
which may have two identical circuits, one for controlling head 38 and one 
for controlling head 40, is used to insure that the field of view of each 
of the profilers 38 and 40 includes a corresponding edge of the bead 22. 
The arrangement of FIG. 5 shows heads 38 and 40 spaced lengthwise (i.e., in 
the direction of the bead) from each other. If the heads are spaced in the 
lengthwise direction, the view from one head may be suitably delayed by 
various known electrical delay elements (not shown) so that the two fields 
of view used for processing are at the same lengthwise position as shown 
in FIG. 6. In other words, there is no lengthwise offset between the 
fields of view 38V and 40V, at least when the field of view data is used 
for feedback control for the bead wetting angles in a manner discussed in 
more detail below. 
The tracking profiler 36 and, more importantly to the present invention, 
the profiler heads 38 and 40, which track corresponding edges of bead 22, 
are optical profilers which should be of the form described in U.S. Pat. 
No. 4,645,917 by Penney et al. entitled "SWEPT APERTURE FLYING SPOT 
PROFILER", assigned to the assignee of the present application and hereby 
incorporated by reference. Alternately, the optical profilers of FIG. 5 
might be of the form described in U.S. Pat. No. 4,634,879 by Penney 
entitled "METHOD AND SURFACE FOR DETERMINING SURFACE PROFILE INFORMATION", 
assigned to assignee of the present application and hereby incorporated by 
reference. By using an optical profiler which images a portion of the bead 
according to its height (i.e., distance between the workpiece and upper 
surface of the bead 22), one can obtain a quite accurate image of the 
topography of the bead. The position feedback control 46 may use such 
information to detect the edges of the bead 22 and to control servomotors 
(not shown) which rotate arms 42 and 44 such that the respective heads 28 
and 40 will remain focused on corresponding edges of the bead 22. 
As shown in the view of FIG. 6, the fields of view 38V and 40V 
corresponding to heads 38 and 40 respectively track the first and second 
edges or sides 22F and 22S of bead 22. As an alternative to the position 
feedback control of the heads 38 and 40, one might alternately maintain 
the fields of view 38V and 40V sufficiently wide to insure that the edges 
22F and 22S will remain in the corresponding fields of view 38V and 40V. 
Provided that the width of the bead 22 is sufficiently stable and 
depending on the width of the field of view 38V and 40V, the heads 38 and 
40 could be mounted to a common housing (not shown) with position feedback 
control to track the bead in such manner that the separate fields of view 
38V and 40V will always include the corresponding bead edge 22F and 22S. 
The fields of view 38V and 40V include respective view stripes 38S and 40S 
which may collectively correspond to the view stripe 58 in FIG. 2 of the 
incorporated by reference Penney et al SWEPT APERTURE patent. 
The profile heads 38 and 40 will be discussed with Reference to FIGS. 7 and 
8, the construction of each head being as shown for head 38 in FIG. 8. In 
particular, the head 38, which is illustrated schematically, includes a 
lens 50 to receive light from fiber optic bundle 52 and apply the light to 
mirror 54 such that it is reflected as beam 56 which falls adjacent to one 
side of the bead 22. The beam 56, which may be scanned in the X and Y 
directions by operation of an X-scanner deflector (not shown) and a 
Y-scanning mirror (not shown) in accord with the Penney et al. SWEPT 
APERTURE patent, causes a reflected beam 58 which passes through filter 60 
to lens 62 and into fiber optic bundle 64. 
The beams 56 from each head 38 and 40 should be spaced slightly behind the 
back of molten pool 30 in the manner shown in FIG. 8 for the beam 56 from 
head 38. Heat and spatter keep one from placing the heads 38 and 40 too 
close to the back of molten pool 30. Shields (not shown) could be used to 
protect the heads 38 and 40. 
Profiling circuitry 66 may be used to generate the beam 56 and determine 
profile information from the beam 58 in the manner described in more 
detail in the Penney et al. patent. If desired, the coherent fiber optic 
bundles 52 and 64 may respectively merge into coherent fiber optic bundles 
68 and 70 which connect to head 40 (not visible in FIG. 8) and correspond 
in function to bundles 52 and 64. By merging the transmission bundles 52 
and 68 together and the receiving bundles 64 and 70 together, one may use 
a single profile circuitry arrangement 66 to scan and receive light with 
the two heads 38 and 40. In effect, such a "split-optic" arrangement is 
utilizing head 38 one-half of the time and head 40 one-half of the time. 
Although the merger of bundle 52 and 68 and the merger of bundle 64 and 70 
is shown simply as two bundles joined together, various optical connectors 
could alternately be used such that the profile circuitry 66 applies a 
laser to overall transmission bundle 72 and receives reflected energy from 
overall receiving bundle 74 with the profiler using bundles 68 and 70 for 
one-half of the time corresponding to field of view 40V in FIG. 6 and 
using bundles 52 and 64 for the other half of the time corresponding to 
field of view 38V in FIG. 6. 
It should be appreciated that the "split-optic" arrangement of FIG. 8 is 
not required for implementation of the present invention as the heads 38 
and 40 could be connected to separate profile circuitry which operates in 
the manner described in more detail in the incorporated by reference 
Penney et al. SWEPT APERTURE patent. It should also be recognized that a 
single high resolution profiler can provide a profile of the entire bead 
and adjoining surface from which information both angles can be 
calculated. 
As shown in FIG. 9, the profile circuitry 66 generates a split image 
corresponding to the profiles within blocks 76 and 78. This split image 
includes the first and second edges 22F and 22S of the bead 22, but need 
not include the center of the bead 22. Accordingly, the lens 50 and 62 
(refer back momentarily to FIG. 8) and the corresponding lens for the 
other head may provide a high resolution as will be desirable for 
accurately determining the bead wetting angle at edges 22F and 22S. As 
shown in FIG. 10, the merger of the profile information generates the 
information shown within block 80. This provides for concentrating the 
profile information at those portions (i.e., the edges or sides) of the 
bead 22 where the information is most needed. 
With reference now to FIG. 11, the use of the profile information 
corresponding to block 80 is illustrated as part of a feedback control 
loop for stabilizing the angles A1 and A2 illustrated within block 82, 
which block corresponds to a processing means. The processing means or 
processor 82, which may be a microprocessor or other known component, may 
use a known process for determining the angle from profile or topographic 
information. The derived bead wetting angle data A1 and A2 may be supplied 
to a printer 84 as well as a calculation module 86. It should be noted 
that the bead wetting angle data A1 is independent of information derived 
from profiler head 40, whereas the angle data A2 is independent of 
information derived from the profiler head 38. 
The calculation module 86, which might be a part of the same microprocessor 
used for realizing the image processor 82 or might be separate therefrom, 
uses the wetting angle data A1 and A2 to calculate the values for one or 
more weld parameters. In particular, the module 86 calculates values of 
weld parameters such as the weld torch current I (for MIG or metal inert 
gas welding), welding torch voltage V (for TIG or Tungsten inert gas 
welding), speed S of travel of the welding torch 28 along the seam, and/or 
wire feed rate W for those weld torches having a wire feed. (The invention 
could, of course, be used for autogenous welding.) 
The process used by the calculation module 86 to generate changed values 
for one or more weld parameters will be discussed in more detail below. 
Generally, however, the module 86 calculates a changed value for one or 
more of the parameters and supplies the changed value to a robot control 
88 which may cause a speed change of robot 90 if such a speed change is 
indicated. Alternately, and/or additionally, the robot control 88 may 
cause a change in the feed rate of the wire feed 92 and/or a change in the 
weld torch power supply at 94 (voltage or current depending upon the type 
of weld torch 28 which is used). At any rate, the module 86 is part of a 
feedback control loop for stabilizing the angles A1 and A2 at relatively 
low positive values. 
FIG. 12 shows a flow chart illustrating a process which may be carried out 
by the calculation module 86 of FIG. 11. In particular, the start 100 
leads to the sensing of the bead wetting angles at block 102 corresponding 
to the module 86 receiving the bead wetting angles from processor 82 (in 
FIG. 11). Block 102 of FIG. 12 leads to decision block 104 which tests 
each of the angles A1 and A2 to determine if both angles are within a 
particular range between a minimum MIN and a maximum MAX. If the block 104 
finds that either of the angles is outside the acceptable range, block 104 
leads to block 106 corresponding to an alarm condition which indicates 
that the weld joint is unacceptable and goes to a stop 108. 
If decision block 104 indicates that the angles are within the relatively 
large range corresponding to the minimum and maximum values, the decision 
block 110 may determine if the angles are within a smaller range 
corresponding to a preferred minimum PMIN and a preferred maximum PMAX. 
For example, the range of block 104 might be between 0.degree. and 
15.degree., whereas the range of block 110 might be between 1.degree. and 
3.degree.. At any rate, if decision block 110 finds that the two angles 
are within the smaller preferred range, this leads to block 112 which will 
maintain the weld parameters in their previous values and return to block 
102. It should be noted that block 110 is optional and the yes response to 
decision block 104 might instead lead directly to block 114 which serves 
to adjust the wetting angles. 
Whether the block 114 is entered directly from a yes response to block 104 
or is entered following a no response to block 110, block 114 is used to 
calculate changed values for one or more of the weld parameters in order 
to adjust the wetting angles so as to bring them closer to a desired value 
or values. 
The block 114 may be realized by the subroutine of FIG. 13. In particular, 
the start block 116 leads to block 118 which defines error signals (A1E 
and A2E) as the difference between the respective wetting angle and a 
nominal or preferred angle ANOM. Additionally, block 118 defines an 
average deviation value ADEV as equal to the sum of the error signals 
divided by twice the nominal value. Block 118 leads to block 120 which 
tests to determine if the error signals both have the same sign. In other 
words, do both wetting angles deviate from the nominal value in the same 
direction (both wetting angles being above the nominal value or both 
wetting angles being below the nominal value)? If the answer is yes, block 
120 leads to block 122. Block 122 will be used to calculate new or changed 
values for weld parameters corresponding to the current I and the wire 
feed rate W, but it will be understood that one or more other weld 
parameters could be used. Block 122 in particular defines a new value for 
current INEW as equal to the prior value for current I changed by a 
constant (KIA) multiplied by the average deviation ADEV. The constant DIA 
would be determined by empirical results. For example, if empirical tests 
showed that a 1.degree. change in the wetting angles can be obtained by 
changing the current by 5%, the magnitude of KIA would be 0.05 such that 
an average deviation of 1.degree. would cause a 5% increase or decrease 
between INEW and the previous value current I. In similar fashion, the 
block 122 will define a wire feed new value WNEW as equal to the previous 
value wire feed W increased or decreased by an amount dependent on the 
product of the average deviation and a constant KWA which would be 
determined in similar fashion to the calculation of KIA. The values for 
KIA and KWA would likely be negative since too high an angle would be 
reduced by decreasing the wire feed rate W and the voltage V. It should be 
noted that the values KIA and KWA might, in more sophisticated approaches, 
be variable depending upon the previous value of the current or wire feed. 
In other words, a sophisticated approach could compensate for the fact 
that a 5% increase in current at one place on the current curve might 
change the angle a given amount, whereas a 5% increase in current at a 
different place on the current curve might change the angle a different 
amount. 
If block 120 determines that the error signals have opposite polarities, 
this means that one of the bead wetting angles is above the nominal value 
and the other bead wetting angle is below the nominal value. Although not 
illustrated, this might be simply handled by having the no response to 
block 120 lead to return at block 124 which would return to block 102 of 
FIG. 12. The approach illustrated in FIG. 13 would have the negative 
response to decision block 120 lead to block 126 which would use an 
alternate procedure for calculating INEW and WNEW so as to minimize the 
sum of the squares of the error signal. Various known minimization 
procedures might be used after developing data indicating the relationship 
between the current, wire feed rate, and the bead wetting angles. 
Although not illustrated, a separate test block could signal an alarm 
condition if the angles A1 and A2 differ by more than a given amount. 
Block 126 joins with the output of block 122 to lead to block 128 which 
tests to determine that the values INEW and WNEW are within acceptable 
ranges. For example is the current too high for the power supply to 
operate? Assuming that the parameters are within acceptable ranges, block 
128 leads to block 130 which replaces the current I with INEW and replaces 
the wire feed rate W with WNEW. Block 130 then leads to block 132 which 
supplies the new parameters to the robot control (refer back momentarily 
to block 88 of FIG. 11). 
If the new values for current and wire feed rate are determined by block 
128 to be outside an acceptable range, one might simply change the values 
a smaller amount. However, FIG. 13 shows an arrangement whereby a negative 
response to decision block 128 leads to block 134 which changes the speed 
based upon a coefficient indicating a relationship between a change in 
speed and a resulting change in the bead wetting angles. The coefficient 
KSA of block 134 would be determined in similar fashion to the coefficient 
KIA in block 122. Block 134 simply shows a change in the speed S of the 
robot but one could alternately test to determine if the new speed is 
acceptable in similar fashion to the decision block 128. Generally, a 
simpler arrangement can be used if the speed is not used to control the 
bead wetting angle. For one thing, the production speed will of course be 
affected by such a change. However, the speed could alternately be the 
weld parameter which is initially changed to provide the proper bead 
wetting angles through feedback control. 
Block 134 leads to block 132 which supplies the changed or new values of 
the parameters to the robot control as discussed above. Block 132 leads to 
return 124 which returns to the line 136 extending between block 114 and 
block 102 of FIG. 12. 
Although the present discussion has concentrated on the use of the present 
invention for controlling the wetting angle of a weld bead, the present 
invention, in its broadest aspects, is applicable to other bead producing 
tools such as a sealant or glue gun (not shown). For example, one might 
use a heated nozzle on a gun and the heating of the nozzle might be 
controlled as part of the feedback loop to control the angle at which the 
bead of glue or sealant hardens. 
The present invention might also be used in connection with a multi-pass 
weld bead 136 of FIG. 14. The bead 136 at the joint between workpieces 138 
and 140 will have a wetting angle, the complement of which is shown in 
FIG. 14 for ease of illustration. Although the bead wetting angles for a 
single pass weld joint are preferably small positive values as discussed 
above, the most desirable values for a multi-pass bead wetting angle might 
fall within some other range. 
If desired, one could use control of the bead wetting angle in a more 
sophisticated arrangement wherein feedback control is maintained of 
various other characteristics of the welding system. For example, the 
calculation module 86 of FIG. 11 of the present application could be used 
in combination with, or in place of, the calculation module 34 of FIG. 7 
of the incorporated by reference U.S. Pat. No. 4,724,302 Penney et al. 
patent. 
Some bead processing tools may provide wetting angles which are essentially 
identical on opposite edges of the bead (i.e., A1 effectively always 
equals A.sub.2). Under such circumstances, a single profiler head such as 
38 or 40 (FIGS. 5 or 7) might be used to sense a single wetting angle 
while providing sufficient data to effectively control both wetting 
angles. 
Although various specific instructions have been discussed herein, it is to 
be understood that these are for illustrative purposes only. Various 
modifications and adaptions will be readily apparent to those of skill in 
the art. Accordingly, the scope of the present invention should be 
determined by reference to the claims appended hereto.