| 摘要 |
PURPOSE:To obtain a highly accurate reference point without providing a special additional mechanism, by respectively arranging the slits constituting the second slit group at the positions each corresponding to the peak values of the intensity distribution on the second scale of the transmitted light of the first slit group. CONSTITUTION:The reference point signal generating part of a main scale provided with slits for a main signal and freely movable in the longitudinal direction and the generation part 2 of an index scale separated by a distance L from the main scale are fixed. The slits 61-66 (or 71-76) of the generation part 1 (or 2) are irregularly arranged (or determined on the basis of the intensity distribution of the transmitted light of the generation part 1) and respectively formed so as to become integer times the width of each slit for the main signal. In this case, the intensity distribution of transmitted light is calculated by calculating the light intensities at the slits by the predetermined calculation method of Fresnel diffraction based on the slits 61-66 and synthesizing the same. By this method, the output obtained by scanning the generation part 1 is compared with an electric signal of a preset level or reference light to make it possible to obtain a reference point signal having a small width and a large S/N ratio.
|
