Measurement of LAMOST Fiducial Fiber Based on the Laser Tracker

LAMOST closed-loop fiber position system have been established based on the fiducial fibers. The more accurate the benchmark position of the fiducial fibers, the higher the accuracy of the closed-loop fiber position system. We have measured the position of the fiducial fibers for two years. Two laser trackers installed at different sites were used to simultaneously measure the position of the fiducial fibers, and the measurement result were compensated for errors and fused, ultimately obtaining the benchmark position. Compared the benchmark position with the theoretical hole position, the result showed that the average measurement accuracy of the fiducial fibers was within 200 µm. The stability difference between the benchmark position obtained in the two years was around 100 µm. After applying the benchmark position to the closed-loop fiber position system, the residual value of fiber position error is 16.57 µm, and the position accuracy of 97.45% fibers is within 40 µm.