Objectives The control network in accelerator alignment often forms a straight line or ring. The errors will accumulate as the number of stations increases when performing lap measurements with the laser tracker. To improve the measurement accuracy of the laser tracker control network, we analyze the source of errors and compare four different measurement methods.
Methods First, the formulas of error propagation in the bundle adjustment method are derived and the error source of the unknown points is analyzed. Second, the following four schemes are obtained by adopting the bundle adjustment method of laser trackers. Finally, the performances of the above schemes are analyzed in the experiment of bundle adjustment.
Results The results show that the absolute position accuracy for the scheme with fixed position and orientation is the highest among the four schemes. The average root mean square (RMS) of the position is 0.147 mm in the experiment of the closed measurement, which is less than that of the unclosed measurement with the RMS of 0.163 mm. In the measurement range of 15 m × 10 m × 3 m, the orientation of the non-fixed scheme flat-rate solution and the average RMS of the plane position are 3.58 s and 0.144 mm, respectively. The station closure can enhance the constraint. Besides, the fixed station center position can effectively inhibit the error accumulation of multi-station lap measurement, improving the accuracy of the network adjustment. Moreover, the result of fixed station center position is better than that of the fixed station center orientation, which indicates that the station positions are vital parameters that affect the two-dimensional bundle adjustment of the laser tracker.
Conclusion This paper can provide a reference for the design of the high-precision laser tracker bundle adjustment method.
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