| 摘要 |
PURPOSE:To detect a foreign object on a foreign-object detecting plane simply and accurately by determining the origin position passing timing of the rotary mirror of the second optical foreign-object detecting means based on the origin position passing timing of the rotary mirror of the first optical foreign-object detecting means. CONSTITUTION:A control unit 10 controls the rotation timing of the pulse motor 66 of the second optical foreign-object detecting means based on the origin position passing timing of the rotary mirror 5a of the first optical foreign-object detecting means and determines the origin position passing timing of a rotary mirror 5b. That is, after the first optical foreign-object detecting means completes to search a foreign-object on a working table 1 while illuminating a spot beam on a reflecting face 7a, the spot beam of the second foreign-object detecting means is illuminated on a reflecting face 7b at a predetermined time difference to search an foreign object in the remaining area on the working table 1 by staggering the timing of the origin signal. Accordingly, mutual light interference between individual beams can be eliminated, thus a foreign object can be detected accurately.
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