Bull. Hiroshima Inst. Tech. Research Vol.49（2015）83-87

ArticleMeasurement of welder＇s movement for welding skill analysis
Nobuyoshi HASHIMOTO*（Received Oct. 31, 2014）

Abstract
Welding training has some disadvantages such as long time required and need for a considerable
quantity of training material; in addition, it is dangerous for beginners. To overcome these limitations, a welding training system using virtual reality can be used to teach appropriate tool movements. However, most trainees may not perform appropriate welding even if they understand theappropriate tool movements. Therefore, teaching appropriate movements of the arm can be more
effective than teaching the appropriate movements of the tools. The goal of this study was to produce an effective welding simulator to teach appropriate arm movements. This paper discusses
measurements of a welder＇s behavior. The angle of each joint of the welder＇s arm, including theshoulder, elbow, and wrist, was measured using bend sensors. Electromyography (EMG) sensors
were used to perform surface electromyography on a welder＇s arm. Six sensor electrodes wereplaced on two muscles of the upper arm and four muscles of the forearm. A workpiece clamper
with charge-coupled device cameras measured the three-dimensional coordinates of each electrodetip. A three-dimensional surface measuring instrument measured the shape of the welding bead.
The welding tasks of three professional welders and four beginners were measured. The differences
between the movements of a professional＇s arm and those of a beginner＇s were found. This showedthat the beginners moved their elbow and shoulder, whereas the professionals moved all three joints.
The EMG signals indicated a tendency for the frequency of variation of the beginners to be greaterthan that of the professionals. However, more data are needed to clarify this.
Key Words: manual arc welding, measurement of movement, skill training

Previous simulators have provided trainees with avirtual training environment for welding at a low
cost, while keeping the training safe and teaching theappropriate movements of tools. However, mosttrainees may not perform appropriate welding even
if they understand it, because they do not know how
to move their arm correctly. Therefore, teaching theappropriate movements of the arm can be more effective than teaching the appropriate movements ofthe tools. The goal of this study was to produce aneffective welding simulator for training to teach appropriate arm movements. This paper considers arm
movement measurements, electrode movements, and1. Introduction

Although some welding processes in mass production have been automated using robots, mostwelding processes are performed by professional
welders. Therefore, many welders are needed inproduction, and training programs for welders are
ﬂourishing. However, there are some inherent challenges in welding training. These include the large
quantity of time and materials involved, which havea high cost, along with the danger posed for beginners. A welding simulator using virtual reality [1][2]has been proposed to overcome these challenges.
＊＊＊

Department of Intelligent Mechanical Engineering, Hiroshima Institute of Technology― 83 ―

Nobuyoshi HASHIMOTO

with a length of 960 mm. The three-dimensional coordinates of sixteen points at 60mm intervals along
the shape tape were calculated based on the outputsof the bend sensors. The coordinate system wasbased on the communication box of the shape tape,as shown in fig. 3. The wrist positon and the joint
angles of the shoulder and elbow were calculated
based on coordinates of the shape tape, which was
ﬁxed to the welder＇s back, brachium, and forearm.
A goniometer is a two-axis angle sensor. One
end was ﬁxed on the forearm, and the other end waselectromyo- graphy (EMG) outputs during welding.
2. Measuring instrument
2.1 Outline of the measuring instrument

The objective welding method in this study wasshielded metal arc welding (SMAW). In SMAW, awelder uses a holder with a flux-shielded electrodein their right hand. It is necessary for the angle between the electrode and the weld line to be maintained between 60° and 70°, and for the tip of theelectrode to be kept 2～3 mm above the weld line
and moved from left to right at a constant rate. During welding, the electrode gradually shrinks as thetip melts [3].
Figure 1 shows an outline of the measuring instrument. This consists of the motion sensor, six
electrodes for EMG, the workpiece clamper withcharge-coupled device (CCD) cameras, and a PC.
Additionally, there is a three- dimensional surface
measuring instrument. The workpiece clamper with
CCD cameras for measuring the three-dimensional
coordinates of the electrode tip and the three-dimensional surface measuring instrument for the welding
bead were explained in detail in a previous paper.

Fig. 2 Equipment for measurement of movement

2.2 Measurement of arm joints angle

In order to analyze the behavior of a welder＇sarm, the angle of each joint on the arm was measured
using the equipment shown in fig. 2. Shape tape
(Measurand Inc. S1280-96NL) was used to measure
the angles of the shoulder and elbow. A goniometer(Biometrics Ltd SG65) measured the angle of thewrist. The shape tape had thirty two bend sensors,

Fig. 3 Coordinate system of shape tapeFig. 1 Outline of measurement system

Fig. 4 Flexible goniometer― 84 ―

Measurement of welder＇s movement for welding skill analysis

3101 ), and the size was 150×100×4 . 5 mm. The
welding of each subject was evaluated in the welding
area shown in the ﬁgure.

ﬁxed on the metacarpal of the middle ﬁnger. The ulnar flexion and radial flexion were measured using
the goniometer, as shown in ﬁg. 4.

4. Result and discussion

2.3 Measurement of surface electromyography on the4.1 Movement of armarm

EMG sensors (Biometrics Ltd SX230) were used
for surface electromyography measurements on thearm muscle. The surface electromyography signals
supplied information about whether the muscle wastensed or relaxed. Because the signal was very faint,
it was inﬂuenced by electrical noise from the arc discharge during welding. To reduce this inﬂuence, anactive electrode was used (ﬁg. 5), which was an electrode with a small amplifier. The EMG electrodes
were placed on six muscles expected to vary frequently during welding: the biceps brachii, triceps
brachii, extensor carpi radialis longus, extensor carpi
ulnaris, ﬂexor carpi radialis, and ﬂexor carpi ulnaris.

Figure 8 shows the movement of the right wrist,
with a welding holder, in comparison with the bodyduring the welding. In this figure, the track of thethree- dimensional position in the coordinate system
shown in fig. 3 is projected onto the z-x and y-z
planes, and the arrows indicate the direction of thewrist movement. To compare the tracks, three beginners＇ wrists move from left to right, and all professionals＇ move from right to left. It is expectedthat the movement of a beginner＇s wrist is the sameas the movement of the electrode. The movement of3. Measurement of welding behavior bywelders and beginners

Welding tasks performed by professionals andbeginners were measured. The subjects were threewelders who had passed the examination for manualarc welding skill by The Japan Welding Engineering
Society (JWES) [4][5], and four beginners who werestudents at the mechanical engineering department
and had no welding experience. The subjects were
equipped with the shape tape and electrodes, andperformed welding three times using the workpiece
clamper with CCD cameras in the posture shown infig. 6. The objective welding was bead-on-plate,which is an operation that places a welding bead ona white line painted on a workpiece, as shown in ﬁg.
7. The workpiece material was steel (SS400 JIS GFig. 6 Posture in welding

Fig. 5 Active Electrodes for EMG

Fig. 7 Workpiece― 85 ―

Nobuyoshi HASHIMOTO(a) z-x plane(a) Professional 1(b) z-y plane(b) Beginner 1Fig. 9 Signal of EMG

a professional＇s wrist is evidently different with themovement of the electrode. Therefore, it was concluded that the beginners moved their elbow andshoulder, whereas the professional welders moved
these as well as the wrist.

tions calculated based on the electrode tracks of thesubjects. Although the professionals＇ average errors
were positive, over the welding line, and the beginners ＇ averages were negative, before the weldingline, no large difference in skill level was found. In
relation to the height, the professionals＇ averages
were lower than those of the beginners because of
the difference in their skill level. In both ﬁgures, thebeginners ＇ standard deviations were greater thanthose of the professionals. This indicated that theelectrode tip of a beginner was somewhat shaky.

Fig. 8 Movement of wrist

4.2 EMG of arm

Figure 9 shows examples of the EMG signals
for a professional and beginner. The EMG signals
show a tendency for the frequency of variation of thebeginner to be greater than that of the professional.
However, more data are needed to clarify this.

4.4 Shape of welding bead

Figures 12 and 13 show the average width and heightof the welding bead, respectively. The error bars inthese ﬁgures show the standard deviation. A professional＇s welding bead was higher than that of a beginner.
In both figures, the beginners＇ standard deviations

4.3 Movement of electrode

Figures 10 and 11 show the error from the welding line (y coordinate) and height from the workpiece (z coordinate) of the electrode during welding,respectively. The bars and error bars in these ﬁguresrespectively show the averages and standard devia― 86 ―

Measurement of welder＇s movement for welding skill analysis

were greater than those of the professionals. This indicated that a beginner＇s welding bead shape was uneven because of the difference in their skill level.
5. Conclusion

In order to produce an effective welding simulator to teach appropriate arm movements, measurements were performed to determine the arm joint angles, surface electromyography (EMG) of the arm,and electrode movement during welding. Welding
tasks performed by three professional welders andfour beginners were measured. A difference wasfound between the movement of a professional welder ＇s arm and that of a beginner. It was determinedthat a beginner moved their elbow and shoulder,
whereas a professional welder moved these as wellas their wrist. A tendency was found for the frequency of variation of the EMG signal of a beginner to begreater than that of a professional welder. However,more data are needed to clarify this.

Fig. 10 Error from the welding line

References
Fig. 11 Height of the electrode tip[1] Xin Liang, Hideo Kato, Nobuyoshi Hashimoto,Kazuya Okawa, Simple Virtual Reality Skill Training
System for Manual Arc Welding, Journal of Robotics
and Mechatronics, 26(1), 2014, 78-84.
[2] Nobuyoshi Hashimoto, Hideo Kato, Ryo Ikehara,
Training System for Manual Arc Welding by Using
Mixed Reality: Reduction of Position-Perception
Error of Electrode Tip, The Japan Society forPrecision Engineering, 72 ( 2 ), 2006 , 249-253 (inJapanese).
[3] Klas Weman, Welding Processes Handbook, CRC

Fig. 12 Welding bead heightPress LLC, 2003.
[4] JIS Z 3801:1997, Standard qualiﬁcation procedure formanual welding technique.
[5] WES 8201:2013, Standard for certiﬁcation of manualwelders.
[6] Nobuyoshi Hashimoto, Difference of Improving
Welder＇s Skill through Training Progression , Bulletinof Hiroshima Institute of Technology Research
Volume, 49.

Fig. 13 Welding bead Width― 87 ―