| 摘要 |
PURPOSE:To remove higher harmonic components which cause the distortion of an output waveform regarding displacement (x), specially, tertiary higher harmonic component by providing a main and an index scale so that their optical grating patterns are spatially out of phase with each other as specified. CONSTITUTION:When the optical gratings of the main scale 1 and index scale 2 are in 1:1 duty proportion, a scale output f(x) detected by a photodetecting element 3 is a triangular wave, and the 2nd triangular wave f(x-pi/3) which is pi/3 out of phase with the 1st triangular wave f(x) as to (x) is added to cancel the tertiary higher harmonic component, obtaining a distortion-free scale output. For the purpose, the index scale 2' has four pattens parts (a), (b), (c), and (d) each divided longitudinally into two so that the spatial phase difference is pi/6, thereby canceling the tertiary higher harmonic component. |
