The present invention is a welding arc length control system. The system includes, in its broadest aspects, a power source for providing welding current, a power amplification system, a motorized welding torch assembly connected to the power amplification system, a computer, and current pick up means. The computer is connected to the power amplification system for storing and processing arc weld current parameters and non-linear voltage-ampere characteristics. The current pick up means is connected to the power source and to the welding torch assembly for providing weld current data to the computer. Thus, the desired arc length is maintained as the welding current is varied during operation, maintaining consistent weld penetration

Iceland, William F.

NASA Technical Reports Server

United States Patent 
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CONVERT E R 
US005245546A 
1111 Patent Number: 5,245,546 
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Iceland [45] Date of Patent: Sep. 14, 1993 
MEMORY 
[MI WELDING ARC LENGTH CONTROL 
SYSTEM 
[75] Inventor: William F. Iceland, Los Alamitos, 
Calif. 
[733 Assignee: Rockwell Intenutiod Chpomtion, 
seal Beach, Calif. 
[21] Appl. NO.: 767,609 
[22] Filed: Sep.30,1991 
[51] Int. C l . 5  .............................................. GO6F 15/46 
[52] US. Cl. ............................... 3W4n 219/130.33; 
219/12 1.3 
[58] F W  of Scueh ..................... 364/477; 219/86.41, 
219/86.33, 86.25, 86.1, 110, 121.28, 121.30, 
121.31, 121.32, 121.34, 122, 124.02, 124.1, 
130.1 - 130.5 1 
1561 References Cited 
U.S. PATENT DOCUMENTS 
4,024,371 5/1977 Drake .................................. 364/477 
4,376,884 3/1983 Gold et al. ....................... 219/86.41 
4,447,699 SA984 Gold et al. .......................... 219/110 
4,561,059 12/1985 Doris et al. ......................... 364/477 
5,149,933 9/1992 Donner ............................... 219/110 
5,157,236 10/1992 Batzler et al. .................. 219/130.51 
Primary Examiner-Jerry Smith 
his tant  Examiner-Jim Trammel1 
Attorney, Agent, or Firm-Lawrence N. Ginsberg; 
Charles T. Silberberg 
1571 ABsTRAcr 
The pracnt invention is a welding arc length control 
system. The system includes, in its broadest aspects, a 
power source for providing welding current, a power 
amplification system, a motorized welding torch assem- 
bly connected to the power amplification system, a 
computer, and current pick up means. The computer is 
connected to the power amplification system for storing 
and proCessing arc weld current parameters and non- 
linear voltage-ampere characteristics. The current pick 
up means is connected to the power source and to the 
welding torch assembly for providing weld current data 
to the computer. Thus, the desired arc length is main- 
tained as the welding current is varied during operation, 
maintaining consistent weld penetration. 
12 Claims, 3 Drawing Sheets 
14 
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CURRENT 
PICKUP 
38*r I 
36 
A+[ CONVERTER 
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great skill required by weldors in maintaining a constant 
arc length during manual manipulation of the arc. 
Other objects, advantages and novel features of the 
present invention will become apparent from the fol- 
5 lowing detailed description of the invention when con- 
sidered in conjunction with the accompanying draw- 
ings' 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a generalized plot of voltage versus current, 
iUustratiug the non-linear voltage-ampere characteris- 
tics of gas  tun^^ arc welding. 
length control system of the present invention. 
of a memory input 
control circuit which may be utilized to input the volt- 
ampere chuacteristics for use with the present inven- 
tion. 
ing is Pccomplished by a motorized The same elements or parts throughout the figures of 
age. Arc length is maintained constant by a motorized 
weld torch driven from a differential output derived 
from comparing the arc voltage to a standard voltage. 
However, this methodology is problematic because the 
a changing current is a non-linear function. Therefore, 
in a motorized system the desired arc length is not main- 
for 
WELDING ARC LXNGTH CONTROL SYSTEM 
STATEMENT OF GOVERNMENT INTEREST 
This invention was made with Government support 
under Contract No. NAS9-1m awarded by NASA. 
The Government has certain rights in this invention. 
BACKGROUND OF THE INVENTION 
10 1. Field of the Invention 
This invention relates to arc length control of weld- 
h g t h  control for procesSing arc weld current parame- 
tm and non-linear voltage-ampere characteristics to Is 
maintain the desired arc length. 
2. Description of the Related Art 
Control of arc length in commercial automatic weld- 
mg systems .nd, more ~ i c u l a r l Y  to computerized arc FIG. 2 is a =hematic illustration of the welding mc 
is a sch-tic 
SCfS'o sptem arc length Proportional to arc 20 the drawings are designated by the -e reference char- 
acters. 
DETAILED DESCRIPTION OF THE 
PREFERRED EMBODIMENT 
for a constant arc lensh during 25 Referring to the drawings and the characters of refer- 
ence -ked thereon, FIG. illustrates the arc charac- 
teristics of three different arc lengths, la- 
belled 1,11 and 12. Arc length 12is greater than arc length during arc Current variations* 
e * g  a COIlStant arc length, the arc current l1 which is greater than arc length 1. Superimposed on 
been COnSmt. AS Wfil be disclosed below, 30 the u c  ch-t-tics c-es are constant 
the pnsent invention provides maintenance of the con- 
stant arc length with variable arc current. 
OBJECTS AND SUMMARY OF THE 
INVENTION 
It is thaefore a principal object of the prtsent inven- 
tion to overcome the non-linear, voltage-ampere char- 
It is mother object of the prcsent invention to store 
lad r d  arc voltageampere characteristics data from 
a computer memory. 
Another object of the pruent invention is to use a 
8ctcmks of the welding arc. . .  
differential voltage to maintain collstult arc length 
Thae ud other objects are achieved by the present 
invention which is a welding arc length control system. 
The systcm includes, in its broadest aspects, a power 
y ~ c e  for providing welding current, a power amplifi- 
atioD system, 8 motorized welding torch usembly 
copIlccted to the power amplification system, a com- 
puter, and current pick up means. The computer is 
connected to the power amplification system for storing 
md p d g  arc weld current parameters and non- 
linear voltageampere characteristics. The current pick 
up mans is connected to the power source and through 
the work to the welding torch assembly for providing 
weld current data to the computer. Thus, the desired 
arc length is maintained as the welding current is varied 
during operation, maintaining consistent weld penetra- 
tion. 
The present invention may be used in both automatic 
and manual welding contexts. For constant arc voltage 
control, the weld torch is conventionally in a locked 
position to prevent a variation in arc length as the weld 
current is changed. The present invention eliminates 
this requirement. 
As applied to a motorized manual welding system, 
the prcsent invention obviates the requirement for the 
current characteristics, where is greater than 13, 13 is 
greater than 12, and I2 is greater than It. A typical safe 
open circuit voltage of the weld machine was selected 
to be 80 volts. 
For a specific arc length lzduring welding the current 
is I3 and the voltage is Vi, respectively. For the same 
arc length 1 2 , ~  the currat  is dectewd to I2  the voltage 
is increased to V2. For the same arc length 12 as the 
current is further decreased to 11 the voltage is in- 
In a conventiod closed loop motorized Control sys- 
the arc voltage which, in turn, wiU drive the arc length 
to a shorter distance. This is a very undesirable condi- 
45 tion. The present invention overcomes the changes in 
Referring now to FIG. 2, the welding arc length 
control system of the present invention is illustrated, 
dc&patcd guumlly 8s 10. A power source 12 is uti- 
50 lized for providing the desired welding current. The 
power source 12 may be DC or an AC power supply. It 
may be a constant current or drooping characteristic 
power supply. The power supply is controlled by a 
potentiometer 14 which may comprise a foot switch or 
55 hand control. A power amplification system, including 
a differential amplifier 16 and a power amplifier 18, is 
C O M C C ~ ~ ~  to the welding power source U. A separate 
power supply, through a potentiometer 20, is provided 
for injecting a comparison voltage to the dierential 
60 amplifier 16 for maintaining a constant arc length. The 
comparison voltage is compared to the arc voltage in 
the differential amplifier 16. The output of the differen- 
tial amplifier 16 drives the power amplifier 18 driving a 
torch motor 22 of a welding torch assembly until the arc 
65 voltage is equal to the comparison voltage. This sets the 
arc length of the system 10. 
The motorized welding torch assembly includes a 
tachometer 24 which provides critical dampening to the 
35 
40 creased to v3. 
tem the change in current shown above will increase 
arc voltage as the arc current is varied. 
5,245,546 
3 4 
servo system. A planetary gear box 26 associated with 
the motor 22, and connected to the torch 28, sets the 
rate of response of the system. The torch 28 may be a 
plasma arc welding torch or a gas tungsten arc welding 
torch. 
A computer system is connected to the Power amPli- 
fiation system for storing and processing arc weld 
current parameters and non-linear, voltage-ampere 
characteristics of the arc. The computer system in- 
cludes a micro-processor 30, memory device 32, digital- 10 patent of the united states is: 
verter 36. The non-linear characteristics stored in mem- 
ory 32 is converted from digital to analog data in con- 
verter 34 and impressed in the differential amplifier 16. 
A current pick up device 38 is utilized to sense weld 15 
current change. The weld current is converted to digi- 
tal data through converter 36. The micro-processor 30 
changes the stored memory volt-ampere characteristics 
to the desired error output. This error is impressed 
through the differential amplifier 16, adding or sub- 20 
stracting to the comparison voltage 20. This addition or 
subtraction to the comparison voltage maintains the 
required balance to the arc voltage to maintain a con- 
stant system arc length. (An ammeter 40 is provided for 
current identification.) 
The welding arc 42 is established to workpiece 44 
through torch 28 and current pick up device 38 from 
the power source 12. The weld torch 28 is supplied with 
inert gas such as helium, argon and/or gas mixtures 
thereof to prevent oxidation of the workpiece during 30 
welding. 
Referring now to FIG. 3, one method of loading the 
memory with the volt-ampere characteristics will now 
be described. Using a fixed arc length (mechanically 
locked torch), an arc is established. The arc current is 35 
sensed through the current pick up 38 and the arc volt- 
age is impressed into the differential amplifier 16. The 
differential voltage output and current signals are con- 
verted to digital information via dog-todigital con- 
vater 36 and a second dog-to-digital converter 42. 40 
The data is processed through the micro-processor 30 
and stored in memory 32. The weld current is then 
varied by the foot switch current control 14 and the 
resulting dnerential amplifier output voltage (delta arc 
voltage) and weld current outputs are again converted 45 
to digital signals through the dog-to-digital convert- 
ers 36, 42. This data is stored in the memory 32. The 
process is repeated for other arc lengths and gas mix- 
tures. 
length closed loop system, complete with the weld 
current delta arc voltage stored in the memory, is added 
to the motorized servo control system 10. First, the 
weld torch 28 is docked from a fued and the 
comparison voltage 20 in the differential amplifier 16. 
arc length from the summation of these two voltages. 
As the current through the arc is varied by the operator 
through potentiometer 14, the current pick up 38 ap- 60 
plies the current information to the micro-processor 30. 
In turn, the memory delta arc voltage from memory 32 
is directed into the differential amplifier 16. All the 
control voltages (from the arc, comparison voltage, and 
delta arc voltage) are then acted on by the differential 65 supply. 
amplifier 16. The summation output through the servo 
loop maintains the arc length constant as the operator 
varies the weld current. 
If the voltage ampere characteristics for a specific 
inert gas or gas mixture are known, this data may be 
input directly into the micro-processor. 
Obviously, many modifications and variations of the 
5 present invention are possible in light of the above 
teachings. It is, therefore, to be understood that, within 
the scope of the appended claims, the invention may be 
practiced otherwise than as specifically described. 
and desired to be secured by Letters what is 
to-dOg converter 34 and an analo&to-digiM con- 1. A motorized welding arc length control system, 
comprising: 
a) a power souTce for providing welding arc current; 
b) a power amplification system connected to said 
power source, said power amplification system 
comprising 
i) a differential amplifier; 
ii) a power amplifier connected to the output of 
said differential amplifier; and 
iii) means for injecting a comparison and memory 
voltage to said differential amplifier, the result- 
ing differential amplifier output voltage being a 
delta arc voltage; 
c) a motorized welding torch assembly connected to 
said power amplification system; 
d) a computer connected to said power mP1ification 
system for storing and processing arc weld current 
parameters and non-linear, voltage-ampere charac- 
teristics in memory; and 
e) current pick up means connected to said power 
source and to said welding torch Msembly for pro- 
viding weld current data to said computer 
wherein, for specific arc lengths, said arc current is 
sensed through said current pick up means and is 
i m p r d  into said memory; similarly, a corre- 
sponding delta arc voltage is impressed into said 
memory, thereby providing stored arc current 
data and stored delta arc voltage data; and, 
wherein during the welding procedure when the 
operator varies said arc current for a desired 
penetration, said current pick up means provides 
arc current information to said computer, said 
computer using said arc current information, said 
stored arc current data and said stored delta arc 
voltage data, directs said stored delta arc voltage 
into said differential amplifier, a summation out- 
put from Mid dif€erential amplifier being di- 
rected through a servoloop to maintain the arc 
length substanuy constant as the operator 
varies the welding arc current, thereby maintain- 
ing a consistent weld penetration. 
2. The welding arc length control system of claim 1, 
25 
Referring again now to FIG. 2, the constant arc 50 
arc is then initiated. The arc voltage is compared to the 55 wherein said power 
The servo motor 22 positions the arc for the required 
comprises a D*C- power 
3. The welding arc length control system of claim 2, 
wherein said D.C. power supply comprises a constant 
cxurent power SUPPlY. 
4. The welding arc length control system of Claim 2, 
wherein said D.C. power supply comprises a drooping 
characteristic power Supply. 
5. The welding arc length control system of claim 1, 
wherein said power source comprises an A.C. power 
6. The welding arc length control system of claim 1, 
wherein said current pick up means comprises A.C. 
current pick up means. 
5,245,546 
5 6 
7. The welding arc lenj~th control system of claim 1, 10. The welding arc length control system of claim 1, 
wherein said current pick up means comprises D.C. wherein said welding torch assembly comprises a 
current pick up means. plasma torch assembly. 
8. The welding arc length control system of claim 1, 11. The welding arc length control system of claim 1, 
wherein said computer includes an analog-todigital 5 wherein said motorized welding torch assembly in- 
converter and a digital-to-analog converter for provid- cludes a motorized manual welding torch. 
ing memory, storage and read-out capabilities. 12. The welding arc length control system of claim 1, 
9. The welding arc length control system of claim 1, wherein said motorized welding torch assembly in- 
wherein said welding torch asscmbly comprises a gas cludes an automatic motorized welding torch. * * * * *  tungsten arc torch assembly. 10 
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Welding arc length control system

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