A novel multiple reflections technique to calibrate polygons and evaluation of its uncertainty of measurement

Abstract

In the field of angle metrology, angle gauges and polygons are the material artefact standards. Conventionally, autocollimator along with indexing table, are used for the calibration of angle gauges and polygons. A novel multiple reflections method is devised at NPLI to improve the uncertainty of measurements during calibrations. A polygon under calibration is fixed at the centre of a Moore’s indexing table within eccentricity offset ± 20μm. A reference autocollimator is aligned to one of the face of the polygon. A flat reflector is fixed in the centre of a rotatable table. The rotatable table is arranged to collect the optical beam on to the flat reflector then deflected to same face of the polygon, wherefrom the light beam is received at the autocollimator. Thus the optical beam strikes the same face of the polygon twice. Therefore the resolution of the reference autocollimator is virtually doubled. In this experimental setup, two set of readings are obtained simultaneously. One set of the readings corresponds to conventional method and the second set of the readings belongs to the proposed novel method. The readings of the autocollimator are analysed and the results are discussed in the article. The results thus obtained by conventional method are compared with the results obtained using the proposed method. Using this novel calibration method, the uncertainty of measurement is improved from ± 0.39″ to ± 0.23″.