Fig. 10 WPS system stretched over wiggler magnets at KEKB Oho section. Fig. 6 Alignment reference point and a mirror target. (a). (b). Fig. 3 Variation of angle output. Fig. 2 Variation of R data. Fig. 4 Long term variation of R data. Fig. 5 Long term variation of angle output.
Fig. 10 WPS system stretched over
wiggler magnets at KEKB Oho section
Fig. 6 Alignment reference point
and a mirror target
Fig. 3 Variation of angle output
Fig. 2 Variation of R data
Fig. 4 Long term variation of R data
Fig. 5 Long term variation of angle output
Machine warm-up is finished in 20-25 minutes. But it was found that users have
to wait for two hours or longer to get stable output, although the IFM output
becomes stable in a couple of 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 power on. This problem is under investigation.
lReproducibility 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.
l Comparison between tracker measurement and WPS measurement
A semi-conducting wire was stretched over the wiggler magnets in about 60m long area in the KEKB 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 as observed in the previous measurement with a Leica tracker  was
not observed this time.
Three laser trackers were purchased in December 2009 by the KEKB magnet group. But the Red tracker was down in this March and returned
to Singapore to be repaired. It had to be sent back again after coming back to KEK because the laser beam happened not to lock to the Home
Position. And the White tracker is suspicious now because of a big slow drift in the angle measurement in the warm-up test and long term test
As well. The FARO laser trackers look fragile. The reproducibility of measurement in a short time looks excellent.
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-
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 arereported in the following.
There are two control software systems, CAM2 and Insight for FARO LT (Laser Tracker). KEKB magnet group has adopted Insight becauseof its convenience.
There are two coordinate systems. The one is the “World System”, which is a machine coordinate systemsticking 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.
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
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.
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
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  was not observed this time.
Fig. 11 Comparison between WPS measurement
and tracker measurement.
 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).