Improving the Accuracy of Angle Measurement System with Optical Grating

A new angle measurement system with optical grating is presented in the paper. Its distinguishing features are: (1) Gratings having sine function transmissivity are used as the index gratings. The harmonic errors of the Moire fringes are greatly reduced. (2) Errors caused by zero offsets, inequality in amplitude and nonorthogonality in phase of two Moire fringe signals are corrected by real time software error correction. (3) Four unequally spaced reading heads are used to eliminate the errors caused by the graduation error of optical grating and error motions of the spindle. The experimental device gives an accuracy about 0.2 arcseconds.