Proceedings of the 7th Annual Meeting of Particle Accelerator Society of Japan (August 4-6, 2010, Himeji, Japan)

PERFORMANCE TEST OF LASER TRACKERS OF FARORyuhei Sugahara A), Mika Masuzawa A), Yasunobu Ohsawa A)
A)High Energy Accelerator Research Organization (KEK)
1-1 Oho, Tsukuba-shi, Ibaraki, 305-0801, Japan

Abstract
Results on performance test of laser trackersof FARO are reported. Test was performed on
the following items: (1) drift of output after
power on, (2) long term variation of output, (3)reproducibility of point measurement, and (4)comparison between measurement with a laser
tracker and the one with WPS (Wire PositioningSensor).

1. INTRODUCTION
Three laser trackers of FARO were purchasedby the KEKB magnet group in December 2009.
The model name is Laser Tracker IONTM. Eachof these three trackers is called Blue, Red andWhite. As they are not familiar with FARO LTs(Laser Trackers), performance test was carriedout. There are two control software systems for
FARO LTs, CAM2 and Insight. The CAM2 wasdeveloped from the control system for Arms,
free arm measuring system, and it is a bitinconvenient for the survey people. So theKEKB magnet group adopted the Insightsystem.
Figure 1 shows a picture of a FARO LT. The
coordinate system is defined that +X is thehorizontal axis stretched from the front facenear to the HP (Home Position), +Z vertical
upward, and +y the horizontal axis to makeright hand system with X and Z axis. Horizontal
angle (F) is measured from X toward Y axis.
Vertical angle (Q) is from +Z axis toward
downward.
Two coordinate systems are used in themeasurement. One is the Machine System
sticking on to the machine, and the other theLevel System which is created in the level planemeasured with the LT.
There are two ways to measure distance, IFM

Figure 1: Picture of a FARO Laser Tracker.
Definition of the coordinate system is shown inthe figure.
(InterFoeroMeter) and ADM (Absolute Distance
Measuring system). The “ADM only” mode
was used except for the case that the “IFMonly” mode was mentioned to be used.

2. WARM-UP TEST
LT becomes ready after machine warm-up in
20-25 minutes. Output data were sampled after
the machine ready with 1Hz scanning mode inorder to see how much time we have to wait toget stable output. Figure 2 shows variation of R(distance) (a) at HP, (b) at a point 5m far, and(c) in case of IFM (InterFeroMeter) mode.
It can be seen from the figure that we have towait two hours or longer after machine ready to-253-

Proceedings of the 7th Annual Meeting of Particle Accelerator Society of Japan (August 4-6, 2010, Himeji, Japan)

Figure 3: Drift of horizontal angle (F, red plot)
and vertical angle (Q, blue plot) for (a) Whitetracker and (b) for Blue tracker.

Figure 2: Drift of R (distance) data aftermachine ready (a) at HP (Home Position), (b)at a point about 5m far, and (c) drift in case ofIFM (InterFerometer Mode).

Blue tracker was brought in the KEKB Oho
straight section, monument points on the wall inabout 70m long area were measured five times,and reproducibility of measurements was

get stable R output, although it becomes stable
only in about 10 minutes in case of IFM(InterFerometer Mode).
Figure 3 shows the drift of angle data (a) for
White tracker and (b) for Blue tracker. Bothdata taking was started almost at the same time.
A big and slow drift is seen in White tracker
output about 6 hours after data taking wasstarted. The same phenomena were observed inother runs for White tracker.

3. LONG TERM VARIATION
Figure 4 shows a long term variation of angle
data (a) for White tracker and (b) for Bluetracker. Data were sampled with 0.1Hz scanning
mode. The line width of horizontal angle plot isas large as 0.1mrad and several jumps areobserved in the White tracker data. It looks
something wrong in the angle measurement inWhite tracker.

Figure 4: Long term variation of horizontal
angle (F, red plot) and vertical angle (Q, blueplot) (a) for White tracker and (b) for Blue
tracker.

4. REPRODUCIBILIT OF POINT
MEASUREMET-254-Proceedings of the 7th Annual Meeting of Particle Accelerator Society of Japan (August 4-6, 2010, Himeji, Japan)

Figure 5: Histograms for RMS for measurement
at each monument, (a) for R, (b) for F and (c)for Q.

Figure 6: Comparison between WPS and Blue
tracker measurements of positions of holes foralignment target insertion on the KEKB wiggler
magnets. (a) Deviations of each measurementfrom the line connected both edge points for
WPS (red) and Blue tracker (blue). (b)Differences between WPS measurement andBlue tracker measurement.

observed. One measurement is an average of
500 Front-Back samplings. Figure 5 shows
histograms for RMS for measurement at eachmonument 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.

Figure 9(a) shows the deviation of eachmeasurement from the line connecting bothedge points, where the red curve is for the WPS
and blue for tracker measurement. Figure 9(b)shows the differences in deviation values
between WPS and tracker measurements.
Differences are less than 0.1mm. And nobending of a straight beam line was observed inthe tracker measurement as seen before in themeasurement with a Leica LT [1].

5. COMPARISON BETWEENTRACKER AND WPS MEASUREMENT
A semi-conducting wire was stretched on
wiggler magnets for about 60m long area in theKEKB Oho straight section. And the position ofupstream holes for alignment target insertion
was measured with WPS (Wire PositioningSensor). 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.

SUMMARY●Warm-up test- Machine warm-up is finished in 20-25
minutes. But it was found that users have to-255-Proceedings of the 7th Annual Meeting of Particle Accelerator Society of Japan (August 4-6, 2010, Himeji, Japan)

was not observed as observed in the previous
measurement with a Leica tracker [1].

wait for two hours or longer to get stable
output, although the IFM output becomesstable in about 10 minutes.
- In the White tracker measurements, slow
deviations in the angle output larger than
0.1mrad were observed after about 7 to 8
hours after data taking was started.
This problem is under investigation●In general- Three laser trackers were purchased in
December 2009 by the KEKB magnet group.
But the Red tracker was down in this Marchand returned to Singapore to be repaired. It
had to be sent back again after coming back to
KEK because the laser beam happened not tolock to the Home Position. And the White
tracker is suspicious now because of a big
slow jump in the angle measurement in thewarm-up test and long term test. The FARO
laser trackers look fragile.
- The reproducibility of measurement in a shorttime looks excellent.

●Reproducibility of measurements- RMS in 5 time measurements of monument
positions in about 50m long area was 3.3mm
for R, 1.1mrad for F and 1.0mrad for Q. These
results are satisfactorily small.
●Comparison between tracker measurement
and WPS measurement- A semi-conducting wire was stretched on thewiggler magnets in about 60m long area in theKEKB Oho straight section. Upstream
position of holes for alignment target insertion
was measured with WPS. These positions
were also measured with the Blue tracker.
Both measurements agree well within 0.1mm.
And the bend in the straight line measurement

REFERENCES[1] R. Sugahara, M. Masuzawa, Y. Ohsawa andH. Yamashita, “Installation and Alignmentof KEKB Magnets”, KEK Preprint 99-131,
November 1999; Proceedings of the 6thInternational Workshop on Accelerator
Alignment, Grenoble, France (1999).

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