| 摘要 |
PURPOSE:To prevent a flaw, etc., generated during the engagement between a recess for locking and a roller from causing a position shift at the time of setting a grating position by providing a recess which different in inclination from an abutting surface as the recess for locking separately from a recess for grating positioning. CONSTITUTION:When diffraction gratings are switched, a motor 6 is rotated clockwise until a recess corresponding to a target diffraction grating comes to the tip part of a lever 9 for locking and a roller R atop the lever 9 rotates clockwise slightly and rotates clockwise slightly excessively from a position where a roller R atop the lever 9 falls in the recess, and then rotated counterclockwise. Then the surface S of the recess abuts on the tip roller R to inhibit a turntable 1 from rotating counterclockwise, and then the motor 6 rotates counterclockwise to expand a spring 8, so that the surface S of the recess is pressed against the tip roller R. Here, the motor 6 is stopped from rotating where the tension of the spring 8 is proper, and then the motor 6 holds itself at the stop position, so the turntable 1 is held at the position where it is inhibited from rotating by a lever.
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