Performance Test of Laser Trackers of FARO

1
Performance Test of Laser Trackers of
FARO Ryuhei Sugahara, Mika Masuzawa and Yasunobu
Ohsawa KEK, High Energy Accelerator Research
Organization Oho, Tsukuba, Japan
11th IWAA, September 13 17, 2010
11th IWAA, September 13 17, 2010
III REPRODUCIBILIT OF POINT MEASUREMET Blue
tracker was brought in the KEKB Oho straight
section, alignment reference points on the wall
in about 70m long area were measured five times
each, and reproducibility of measurements was
observed. Fig. 6 shows the pictures of a
monument point (left picture) and a mirror
target placed on the alignment reference point
(right picture). One measurement is an average of
500 Front- Back samplings. Fig. 7 shows
deviations in R data from the average at each
point (blue points) and their RMS (red
points). Fig. 8 shows deviations in angle data
from the average at each point (blue points) and
their RMS (red points). Fig. 8(a) is for
horizontal angle data, and (b) for vertical
angle data. Figure 9 shows histograms for RMS
for measurement at each reference point, (a) for
R values, (b) for F values, and (c) for Q
values. The standard deviations of distributions
are 3.3mm for R, 1.1mrad for F and 1.0mrad for Q
distributions. These results are satisfactorily
small.
Three laser trackers were purchased from FARO by
KEKB magnet group of KEK in December 2009. These
trackers are called Blue, Red and White.
Performance of these trackers were tested.
Results are reported in the following. There are
two control software systems, CAM2 and Insight
for FARO LT (Laser Tracker). KEKB magnet group
has adopted Insight because of its
convenience. There are two coordinate systems.
The one is the World System, which is a machine
coordinate system sticking on to the machine.
The other is the coordinate system defined by
users. We create coordinate system in level
plane measured with the tracker, and call it
Level Coordinate System, which is shown in
Fig.1. There are two ways to measure distance,
IFM (InterFeroMeter system) and ADM (Absolute
Distance Measuring system). We measure points in
the ADM only mode because of its convenience in
moving a target.
Z
I WARM-UP TEST LT (Laser Tracker)
becomes ready after machine warm-up in 20-25
minutes. Output data were sampled after the
machine ready with 1Hz scanning mode in order to
see how much time we have to wait to get stable
output. Fig.2 shows variation of R (distance)
(a) at HP (Home Position), (b) at a point 5m
far, and (c) in case of IFM (InterFeroMeter)
mode. It can be seen from the figure that we
have to wait two hours or longer after machine
ready to get stable R output, although it becomes
stable only in a few minutes in case of
IFM. Fig. 3 shows the drift of angle data (a) for
White tracker and (b) for Blue tracker. Both
data takings were started almost at the same
time. A big and slow drift is seen in White
tracker output about 6 hours after data taking
was started. The same phenomena were observed in
other runs for White tracker.
Q
Y
F
X
(a) R
Fig. 7 Deviation of each R measurement from the
average (blue points) and their RMS (red points)
Fig. 1 Laser Tracker of FARO
Fig. 8 Deviation of each angle measurement from
the average (blue points) and their RMS (red
points). (a) horizontal angle and (b) vertical
angle.
II LONG TERM VARIATION Fig. 4 shows a long
term variation of R data (a) for White tracker
and (b) for Blue tracker. Data were sampled with
0.1Hz scanning mode. Slow drift and eventual
variations can be seen in White tracker data.
These eventual variations correspond to large
variations in angle output as shown in Fig. 5.
Jump is seen in Blue tracker data around 30
hours. But the amplitude Is only 20mm. Fig. 5
shows a long term variation of angle data (a) for
White tracker and (b) for Blue tracker. The line
width of horizontal angle plot is as large as
0.1mrad and several jumps are observed in the
White tracker data. It looks something wrong in
angle measurement in White tracker.
Fig. 9 Histograms for RMS for deviations.
IV COMPARISON BETWEEN TRACKER AND WPS
MEASUREMENTS A semi-conducting wire was
stretched over wiggler magnets for about 60m long
area in the KEKB Oho straight section. And
the position of upstream holes for
alignment target insertion was measured with WPS
(Wire Positioning Sensor) system. These
positions were also measured with the Blue
tracker, and both measurements were
compared. Here, one tracker measurement is an
average of 500 Front-Back samplings.
Fig. 10 shows the picture for the WPS system
stretched over wiggler magnets at KEKB Oho
straight section. Figure 11(a) shows the
deviation of each measurement from the line
connecting both edge points, where the red
curve is for the WPS and the blue curve for
tracker measurement. Figure 9(b) shows the
difference in deviation values between WPS
and tracker measurements. Difference is
less than 0.1mm. And no bending of a straight
beam line seen before in the measurement
with a Leica LT 1 was not observed this time.
Fig. 11 Comparison between WPS measurement and
tracker measurement.

REFERENCES 1 R. Sugahara, M. Masuzawa, Y.
Ohsawa and H. Yamashita, Installation and
Alignment of KEKB Magnets, KEK Preprint
99-131, November 1999 Proceedings of the 6th
International Workshop on Accelerator
Alignment, Grenoble, France (1999).