Influence of background noise on autocollimator measurement precision and method for uncertainty source elimination

[Display omitted] •Discovery of noise error source: The interference light caused by the reflection from the non-working structural surface of the autocollimator affects the measurement accuracy of the autocollimator. The influence process of this noise source is deduced by combining the Hough transform principle of image recognition. The specific error value of this noise is theoretically characterized using mathematical formulas.•Method for uncertainty source elimination based on polarized optics: A well-known polarization method is utilized to remove the noise in response to the phenomenon of background noise caused by the autocollimator’s own structural problems. Quarter-wave and line polarizers with polarized fractional cubes form a noise-canceling structure, and the measurement function of the autocollimator can still be realized while eliminating the interfering optical path by changing the polarization state of the imaging light for several times.•Optimize measurement system uncertainty for higher precision measurements: Controlled experiments were conducted on a conventional structural autocollimator and a new structural autocollimator with the addition of polarization devices. The results show that after adopting the noise cancellation scheme based on polarization optics, the autocollimator's measurement resolution is improved from 2″ to about 1″, the measurement accuracy along the X and Y axes is improved from less than 5.26″ to better than 2.69″, and the measurement uncertainty of the system is improved from 5.67″ to approximately 3.43″. Reflection phenomenon of internal optical structure surface of the autocollimator will cause background noise to interfere with its imaging and localization results, thus reducing the measurement precision. The non-working surface reflection of the beam splitter is the main factor causing this uncertainty source. Using a polarized beam splitter cube to replace the original beam splitter and combining with other polarization devices can effectively suppress the influence of this uncertainty source on the goniometric accuracy of the autocollimator. In this paper, through the comparison experiment with the benchmark instrument, it is found that after eliminating the noise, the measurement accuracy along the X and Y axes is improved from less than 5.26″ to better than 2.69″, the resolution is improved from 2″ to approximately 1″, and the uncertainty of the systematic measurement is improved from 5.67″ to approximat