| 摘要 |
This invention relates to an apparatus for detecting rotational information, and includes a disk attachable to a spindle, with relative rotational information of the disk to be detected. The apparatus also includes a a rotation detection grating on the disk, a main body unit independent from the disk, an optical detection unit fixed in the main body unit, a light source, a reference grating, and a light-receiving element fixed to the optical detection unit. The rotational information of the disk relative to the optical detection unit is detected by the light-receiving element by detecting a light beam which is emitted by the light source and goes via the rotation detection grating and the reference grating. A positioning block for positioning the spindle attachable to the disk is also included. The positioning block has a V-shaped portion which is arranged so that slope surfaces thereof are substantially symmetrical about a line that connects a rotation center of the spindle to be attached to the disk and the optical detection unit. The spindle is positioned by putting the spindle on the V-shaped portion.
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