Calibration of angular errors of high-precision rotary table with two-angle encoders

To improve the accuracy of a high precision angle measuring table, calibrations of angle encoders of the rotary table to determine both graduation and interpolation errors were performed. First, the structure of the rotary table was introduced, including the angular measuring system with two angle encoders and the arrangements of the scanning heads. Then, graduation errors of the two encoders were calibrated using the direct comparison and self-calibration methods. Finally, with the aid of capacitive displacement sensors, the position error within one signal period (i.e., the interpolation error) for each scanning head of the encoders was investigated using the direct comparison method. Calibration results indicate that for the first angle encoder with two scanning heads arranged at intervals of 180°, the graduation and interpolation errors are within ±0.27 and approximately ±0.1 arcsec, respectively. For the second encoder, which uses an average value of four heads arrange at intervals of 90° as the measurement value, the graduation and interpolation errors are within ±0.17 and approximately ±0.2 arcsec, respectively. Both angle encoders have a measuring accuracy at a sub-arcsec level. The manner in which the two angle encoders calibrate each other is helpful for complete and accurate determination of the rotary table's angular errors. © 2019, Science Press. All right reserved.