Augmented Reality (AR) for Assembly Processes - An Experimental
Evaluation
S. Wiedenmaier, O. Oehme, L. Schmidt, H. Luczak
Institute of Industrial Engineering and Ergonomics, Aachen University of Technology
Bergdriesch 27, D - 52062 Aachen, Germany
{s.wiedenmaier;o.oehme;l.schmidt;h.luczak}@iaw.rwth-aachen.de
1. Experimental Set-Up
8 mm
10 cm
A PAL-video-camera (Toshiba ACM 413 E with 2,2 mm
lens) and a HMD have been connected to a Silicon
Graphics Workstation O2 (SGI). As HMD a Clip-on
display (MircoOptical) with a 640 x 480 resolution has
been taken. The Clip-on display can be used like other
HMDs in video see-through mode. It works like a little
monitor in front of the user’s eyes which covers just a
small part of his field of view. On the one hand it needs
not to be re-calibrated for each AR-sequence contrary to
optical see-through displays. On the other hand the
assembling person was not restricted by the
inconveniences of the video see-through mode like
latency, focus, etc which are quite bothersome for
assembly.
Figure 1 Pegboard for the tests
2. Methodology
3. Participants
In earlier tests AR-novice-users had problems to cope
with their first AR-supported assembly task. Therefore the
described test has prepared the participants to handle ARsystems as well as to examine learning and field of view
aspects. It was necessary to give them a possibility to
learn to handle an AR-system.
The experiment has been executed in the following way.
Test subjects have to grasp a little wooden cylinder in a
box. By passing a flap to accede to the cylinder the
workstation gets a mouse signal to write the time into a
log-file and to show the assembly position on a pegboard
with 48 holes in the Clip-on display. After putting the
cylinder in the right hole on the pegboard subjects grasp
the next cylinder. The pegboard in fig. 1 has been derived
from the Purdue Pegboard [1].
Each participant has executed three series with 24
cylinders each. All places to put a cylinder were
randomized for all series. Fig. 1 shows the pegboard with
its 48 holes. Each hole has a distance of 10 cm to its
neighbours. The diameter of the holes was 8 mm. In the
middle of the board a marker is fixed to allow the optical
tracking.
For the tests 12 apprentices and students with similar
practical experience in mechanics and electronics have
been selected.
10 cm
35 cm
15 cm
25 cm
4. Results of the Tests
In earlier tests users reported problems to adapt to the
AR-system and the data glasses. An other difficulty was
to find objects in the HMD which are not in the centre of
the field of view. These two major effects also appeared
by analysing the already described tests.
4.1 Learning effect
Test subjects are learning quite quickly to handle the ARsystem and to work with the Clip-on display.
The tested persons have never worked with the Clip-on
display used in the test before. Subjects had to put three
series of 24 cylinders each to the indicated position on the
pegboard. Fig. 2 shows the measured time to assemble
6 cylinders and its 95% confidence interval dependent on
the total number of assembled cylinders.
Proceedings of the IEEE and ACM International Symposium on Augmented Reality (ISAR’01)
0-7695-1375-1/01 $17.00 © 2001 IEEE
60
50
40
30
20
Numbe r o f 1-6 13-18 25-30 37-42 49-54 61-66
as s e mble d
7-12
19-24 31-36 43-48 55-60 67-72
c ylinde rs
Figure 2 Measured values of learning curve
The learning curve can be approximated by the following
logarithmic equation: t = 51.24 - 7.90 * ln(x); x=1 equal
number of assembled cylinders 1-6; x=2 equal number of
assembled cylinders 7-12; etc. The measured values
correspond with an multiple regression coefficient of 0.91
to this function.
After putting the first series of 24 cylinders on the
pegboard (about 3.5 minutes) the subjects have already
had its major learning effect. But the executed tasks were
very easy to handle. More difficult tasks can take more
than two days to get used to [2]. So more difficult
assembly tasks and more sophisticated AR-systems
certainly need a longer time for adaptation.
For further tests also other displays with different seethrough modes should be taken into account. So display
specific problems with AR could be examined.
pegboard (fig. 3). The differences in time have been
calculated by Methods Time Measurement (MTM) [3].
By this method it is possible to calculate the time for all
basis movements. These path lengths are different for
moving the cylinder to the pegboard and to reach the box
with the next cylinders. These adjusted times show that
the influence of the path length is very small in
comparison with the whole assembly time (∆t < 0.27s).
Adjusted assembly time per object in seconds
As s e mbly time in s e c o nds fo r 6 c ylinde rs
70
6,5
]
]
6,0
]
5,5
5,0
]
4,5
10-15cm 15-25cm 25-35cm 35-43cm
Distance from the focal point
Figure 3 Dependency of adjusted assembly time
on the distance from the focal point
The test shows that it is necessary to put virtual objects
close to the focal point or to give a hint to the assembler
where he can find the virtual object. This can be e.g. an
arrow in the focal point which points to this object.
Another kind of hint could be a vocal hint when the
assembling person does not find the indication in his
display.
4.2 Distance from the focal point
5. Acknowledgements
The second effect is that it takes significantly longer to
put an object to a place which is far from the focal point.
The time to put the cylinder in randomized order into the
holes was taken from the second and third series of the
test to exclude a perturbation of the results by learning
effects.
The circles in fig. 1 categorize the 48 holes in the panel
into 4 distance classes. The holes of class 1 have a
distance of 10 to 15 cm from the focal point, etc. The
distance from the focal point was varied between 10 cm
and 43 cm.
The times to fix a cylinder in a pegboard has been
categorized for the different distance classes of the focal
point. The whole panel to put the cylinders in 24 of the
48 holes was visible by focusing the middle of the panel.
Thereby the panel was in reach to put the cylinders into
their holes.
Next the assembly time was adjusted to eliminate the
different path lengths to move the cylinder to the
The research is founded by the German Ministry of
Education and Research (BMBF) within the research
centre ‘Augmented Reality in Design, Production and
Service’ (ARVIKA) [4] under grant no. 01 IL 903 R 4.
Literature
[1] TIFFIN, J.; ASHER, E.J.: The Purdue Pegboard: Norms and
studies of reliability and validity. In: Journal of Applied
Psychology 32 234-47, 1948.
[2] LUCZAK, H. : Arbeitswissenschaft. 2. Aufl. Springer,
Berlin, 1998
[3] MAYNARD, H.B.; STEGEMERTEN, G.J.; SCHWAB, J.L.:
Methods Time Measurement. New York: Mc Graw-Hill, 1948
[4] ARVIKA, Augmented Reality in Design, Production and
Service: www.arvika.de, 2001
Proceedings of the IEEE and ACM International Symposium on Augmented Reality (ISAR’01)
0-7695-1375-1/01 $17.00 © 2001 IEEE