Application of advanced shearing techniques to the calibration of autocollimators with small angle generators and investigation of error sources

A differential Fabry-Perot interferometer (DFPI) was applied for the detection of ultra-small angles in the level of nanoradian (nrad) precision. During application, down to 1 nrad angular steps were generated using the available high precision small angle generator (HPSAG) and these steps were detected using the frequency stabilised lasers as an alternative and outperforming method to conventional angle interferometers. The use of the DFPI provided the displacement measurements (further angular displacements through optical configuration) with picometre sensitivity free from linearity errors. A coefficient of 1.436 964 × 10 −9 arcsec Hz −1 (about 7 × 10 −6 nrad Hz −1 ) for the DFPI was calculated using the generated-measured traceable angular values of the HPSAG and various angular steps were measured by the DFPI using this coefficient. The tests were carried out up to the range of 0.5 arcsec (2500 nrad) in angular steps down to 1 nrad. The work is in progress under the SIB58 Angles project and aims to reduce the noise level of the HPSAG with further statistical process and later to extend the measurement range of the DFPI readings with the same optical configuration, rather than using different beam spacing configuration in the DFPI.

Section: Resultsmentioning

confidence: 99%

Application of the differential Fabry–Perot interferometer in angle metrology

Çelik

Şahin

Yandayan

et al. 2016

“…Future development will be devoted to enhance the frame rate of the triggered acquisition by improving the software efficiency to reduce the processing time. Finally, we plan to adopt the shearing technique [13,14] to investigate the potential errors of the instrument for small (sub pixel) angular intervals.…”

Section: Discussionmentioning

confidence: 99%

Improved performance of a refurbished photoelectric autocollimator

Astrua

Pisani

2020

An old photoelectric Hilger & Watts autocollimator (AC) has been modified at INRIM to perform accurate angle measurements on two axes in a range of ±250″. A CMOS camera was placed in the focus of the AC’s optical system and a software implemented in LabVIEW processes on-line the image of the reticle projected on the camera. The data acquisition is triggerable at a selectable frequency up to some hertz to allow synchronization in critical applications. The AC’s sensitivity was determined through a calibration with respect to the national angle standard. The combined standard uncertainty of the AC calibration results to be equal to 0.035″.

“…When an autocollimator is calibrated by use of an angle encoder, however, circle closure does not apply as the measuring range is just a fraction of the full circle. We have adapted the shearing approach to this application only recently [24,25] and have also applied it to autocollimator calibrations by use of small angle generators [26]. Detailed information about the theory of the shearing technique can be obtained from [21][22][23][24].…”

Section: Shearing Framework and Basic Considerationsmentioning

confidence: 99%

“…This is due to drift of the results during the tests taken in 3.5 h for determination of deviations in negative and positive scale (±15.2 arcsec). This issue was studied in [26] with its technical details.…”

Section: Interpolation Errors Of Tubitak Ume Angle Comparatormentioning

confidence: 99%

“…By error separation, shearing techniques provide simultaneous access to the angle deviations of the autocollimator and of the reference device, e.g. an angle encoder in the rotary table, and thus allow reducing the uncertainty of the angle measurement with both systems [24][25][26]. Extensive investigations of interpolation errors using various angle encoders/interpolators/ rotary table types were carried out by different organizations under the SIB58 Angle Metrology project (supported by the European Metrology Research Programme-EMRP) [1].…”

mentioning

confidence: 99%

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Investigations of interpolation errors of angle encoders for high precision angle metrology

Yandayan

Geckeler

Just

et al. 2018

Self Cite

Interpolation errors at small angular scales are caused by the subdivision of the angular interval between adjacent grating lines into smaller intervals when radial gratings are used in angle encoders. They are often a major error source in precision angle metrology and better approaches for determining them at low levels of uncertainty are needed. Extensive investigations of interpolation errors of different angle encoders with various interpolators and interpolation schemes were carried out by adapting the shearing method to the calibration of autocollimators with angle encoders. The results of the laboratories with advanced angle metrology capabilities are presented which were acquired by the use of four different high precision angle encoders/interpolators/rotary tables. State of the art uncertainties down to 1 milliarcsec (5 nrad) were achieved for the determination of the interpolation errors using the shearing method which provides simultaneous access to the angle deviations of the autocollimator and of the angle encoder. Compared to the calibration and measurement capabilities (CMC) of the participants for autocollimators, the use of the shearing technique represents a substantial improvement in the uncertainty by a factor of up to 5 in addition to the precise determination of interpolation errors or their residuals (when compensated). A discussion of the results is carried out in conjunction with the equipment used.