Abstract
Although autocollimators enable noncontact measurement, their performance is limited in large-scale and long-distance applications because of errors caused by nonideal point light sources. Therefore, we analyze this type of measurement error, including the error source and the equations used to describe the irradiance distribution of the light spot. A two-dimensional exponential approximation formula is used to express the light irradiance distribution and compensate the spot imaging errors. Experimental results show that the measurement error could be reduced by sixfold. Therefore, the proposed compensation algorithm can be applied to autocollimator measurements over distances.
Highlights
The autocollimator is an important angle measuring instrument[1,2,3,4,5,6] that enables noncontact measurement with high accuracy and high resolution
The aberrations of the objective lens collimating lens (CL) 2 and the uneven refractive index of the optical components, air turbulence, and temperature variations all lead to measurement errors of the photoelectric autocollimator
Since a highquality objective lens is used in the photoelectric autocollimator, the aberration is extremely small compared to the size of the image on the complementary metal-oxide-semiconductor (CMOS) and can be ignored
Summary
The autocollimator is an important angle measuring instrument[1,2,3,4,5,6] that enables noncontact measurement with high accuracy and high resolution. Chen et al.[12] proposed an angle measurement method based on optical frequency domain and realized a measurement range of 21,600 arc sec. Li et al.[9] employed a cube corner as a reflector to extend the angle measurement range from 1.2 deg to 12 deg with an accuracy better than 35 arc sec. Zhu et al.[13] proposed a common-path design criterion for laser-datum based on measurement of small angle deviations, and this approach realized high-precision measurement at long distances. These methods have large measurement errors when used for far ranging. This paper analyzes the measurement error caused by an uneven light beam under long working distance conditions. The algorithm is verified by experiments that demonstrate a sixfold reduction in the error under long-distance conditions
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