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Performance Test of Laser Trackers of FARO Ryuhei Sugahara, Mika Masuzawa and Yasunobu Ohsawa

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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

SUMMARY

lWarm-up test

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 [1] was

not observed this time.

lIn general

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-

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 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.

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).

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