| 摘要 |
PURPOSE:To position a shielding plate with a high precision in a short time by a simple constitution, by providing a narrow slit indicating a reference position and the second slit for detection of the direction of deviation from the reference position on the shielding plate. CONSTITUTION:An object (shielding plate) 13 to be positioned is provided with positioning marks 14 and 15. Light transmission states of said marks 14 and 15 from light sources 16 and 17 are detected by detectors 18 and 19, and a pulse motor 28 is driven through amplifiers 20 and 21, Schmitt circuits 22 and 23 and a driving circuit 27 to position the shielding plate 13. In this positioning method, the mark 14 detects the reference position, and the mark 15 detects the direction of deviation from the reference position; and if the shielding plate 13 is deviated from the reference position in the direction of an arrow XR, the light from the light source 17 passes through the mark 15, and the motor 28 is driven to move the shielding plate 13 in the direction of an arrow XL, and the motor 28 is stopped when the reference position of the mark 14 is detected by the detector 18, and thus, the shielding plate is positioned. |
