Performance Test of Laser Trackers of FARO

Ryuhei Sugahara, Mika Masuzawa and Yasunobu OhsawaKEK, High Energy Accelerator Research Organization

Oho, Tsukuba, Japan

11th IWAA, September 13 – 17, 2010 11th IWAA, September 13 – 17, 2010

Three laser trackers were purchased from FARO by KEKB magnet group of KEK in December 2009. These trackersare 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 onto the machine. The other is the coordinate system defined by users. We create coordinate system in level planemeasured 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 Measuringsystem). We measure points in the “ADM only” mode because of its convenience in moving a target.

Fig. 1 Laser Tracker of FARO

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Fig. 2 Variation of R data

Fig. 3 Variation of angle output

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.

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 inBlue tracker data around 30 hours. But the amplitudeIs only 20m.

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. 4 Long term variation of R data

Fig. 5 Long term variation of angle output

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 values, and (c) for values. The standard deviations of distributions are 3.3m for R, 1.1rad for and 1.0rad for distributions. These results are satisfactorily small.

Fig. 6 Alignment reference pointand a mirror target

Fig. 8 Deviation of each angle measurement from the average(blue points) and their RMS (red points). (a) horizontal angleand (b) vertical angle.

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(b)Fig. 7 Deviation of each R measurement from the average(blue points) and their RMS (red points)

(a) R

Fig. 9 Histograms for RMS for deviations.Fig. 10 WPS system stretched overwiggler magnets at KEKB Oho section

Fig. 11 Comparison between WPS measurementand tracker measurement.

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.

SUMMARY

Warm-up testMachine 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 outputbecomes 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.

Reproducibility of measurementsRMS in 5 time measurements of monument positions in about 50m long area was 3.3m for R, 1.1rad for F and 1.0rad for Q. These results are satisfactorily small.

Comparison between tracker measurement and WPS measurementA 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] wasnot observed this time.

In generalThree 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 testAs well. The FARO laser trackers look fragile. The reproducibility of measurement in a short time looks excellent.

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).