| 摘要 |
PURPOSE:To further improve the accuracy of detecting position by binarizing a photodetecting intensity signal conforming to a photodetecting intensity distribution by each separate threshold level which has been coordinated to an area of a different reflection factor on the surface of a measuring object, and calculating a reflecting surface corresponding position, based thereon. CONSTITUTION:A position detecting device is provided with a projector 2 for allowing a light beam B1 to be made incident on the surface 1a of a photomask 1 and a photodetecting part 5 for photodetecting a reflected light beam B2. A photodetecting signal E(x) from the photodetector 5 passes through an amplifier 8 and an A/D converter 9 and its photodetecting intensity signal E(x) is divided into each area of a different reflection factor on the reflecting surface 1a, and inputted to a photodetecting signal dividing circuit 10 for coordinating a threshold level which has been set in advance at every divided photodetecting signal. Subsequently, based on a binary signal H(x) from a binarizing circuit 11, a photodetecting center position M of the reflected light beam B2 is derived by a position arithmetic circuit 12. Also, the position signal M is calibrated by a calibrating circuit 13. |
