Research On High Accuracy Two-axis Autocollimator

The torsion pendulum is a classic tool for detecting weak forces in the laboratory.Researchers can calculate the magnitude of the gravitational torque on the pendulum by accurately measuring the deflection angle of the torsion pendulum.Autocollimator is a commonly used precision instrument for measuring small angle.One of its advantage is to acquire the non-contact measurement of micro-angles by means of optical autocollimator measuring principle.In view of the requirement for a higher-precision and higher-resolution angle measurement system in the precision torsion pendulum experiment,On the basis of fully investigating the research scheme and application technology of high-precision photoelectric autocollimator at home and abroad,We have successfully designed and built a high-precision and high-resolution autocollimator that can realize two-dimensional Angle measurement.In this paper,the independent measurement of two-dimensional angle is realized by single light source,double splitter slit and double linear array CCD.In the scheme design,the slit partition board adopts the symmetrical structure of multiple slits.Combined with its geometric features,we designed a set of matching image processing positioning algorithm to improve the positioning accuracy of the image center.Taking contrast ratio as the image quality evaluation standard of CCD imaging.The imaging quality was studied in the experiment,while maintaining the optional image,the mathematical relationship which was satisfied with the relative position change among the split board slit,CCD and the collimator objective was given.In the experiment,The periodic systematic errors introduced by the reflected light of optical elements are found and solved.The effect was expected to decrease from±0.5μrad to±0.03μrad.According to the theoretical and experimental analysizing on the influence of CCD defocusing on the measurement accuracy of different ranges of the autocollimator,the position of the precision regulating element makes the calibration coefficient of the autocollimator vary less than 0.00003/m with the change of measurement distance,corresponding to 1.8 m measurement distance,and the precision influence within the measurement range of±750μrad is less than 0.02μrad.Finally,we test the whole performance of the autocollimator prototype.Taking highest accuracy autocollimator as the criterion of the angle measurement.Within the measuring range of±750μrad,the measurement accuracy of the Angle of the two axes reaches±0.15μrad when the distance between the reflector and the autocollimator is close,After calibration of the autocollimator readings,the angular measurement accuracy was within±0.4μrad for a measurement distance of 1.8 m.The noise test results showed that the noise level of the two axes of the autocollimator prototype was 0.2μrad·Hz^-1/2 when it was lower than 0.03 Hz,and reached 0.02μrad·Hz^-1/2 when it was higher than 0.1 Hz.