The new INRIM rotating encoder angle comparator (REAC)

Abstract

A novel angle comparator has been built and tested at INRIM. The device is based on a double air bearing structure embedding a continuously rotating encoder, which is read by two heads: one fixed to the base of the comparator and a second fixed to the upper moving part of the comparator. The phase measurement between the two heads' signals is proportional to the rotation of the moving table. The advantage of this solution is to reduce the encoder graduation errors and to cancel the cyclic errors due to the interpolation of the encoder lines. By using only two pairs of reading heads, we have achieved an intrinsic accuracy of ± 0.04'' (rectangular distribution) that can be reduced through self-calibration. The residual cyclic errors have shown to be less than 0.01'' peak-to-peak. The random fluctuations are less than 0.01'' rms on a 100 s time interval. A further advantage of the rotating encoder is the intrinsic knowledge of the absolute position without the need of a zeroing procedure. Construction details of the rotating encoder angle comparator (REAC), characterization tests, and examples of practical use are given.

Characterization of Angle Accuracy and Precision of 3-Degree-of-Freedom Absolute Encoder Based on NanoGPS OxyO Technology

“…Moreover, systems were placed on a granite table that rests directly on the basement floor of the building, thus reducing the influence of mechanical vibrations. Finally, it was demonstrated that REAC stability was of the order of 0.05 µrad on a time interval of 100 s [ 16 ]. Hence, environmental and thermomechanical influences can be considered negligible compared to the performance of the nanoGPS system in the experiment reported here.…”

“…The accuracy of the system was evaluated at the level of hundreds of nanoradians. A detailed description of the facility can be found in [16].…”

“…The characterization of angular encoders at the microradian level is a sophisticated metrological problem. The National Metrology Institute of Italy (INRIM) has much experience in high-accuracy angular metrology [14][15][16]. Hence, the nanoGPS Oxyo ® system was compared with respect to the INRIM national angle standard, rotating encoder angle comparator (REAC) [16].…”

Sensor for the Characterization of 2D Angular Actuators with Picoradian Resolution and Nanoradian Accuracy on the Microradian Range

“…Therefore, we have performed a calibration of the DUT on the full scale to check for the scale factor and linearity of the same. The calibration has been undertaken by direct comparison with a reference autocollimator (ELCOMAT HR by Moeller-Wedel, Germany), in turn calibrated against the INRIM angle standard [12].…”

“…Traceability of autocollimators to the SI unit is obtained through a calibration against primary standards. Few National Metrology Institutes are able to calibrate autocollimators at the level of some tenths of microradian by means of top calibration facilities such as [7][8][9][10][11][12].…”