| 摘要 |
A rotation information detecting apparatus has a scale having a cylinder or a disc member with a grating portion provided over the entire circumference thereof, and a light projecting unit for applying a light beam to the grating portion. The apparatus also includes a fist light receiving unit, having at least one sensor, disposed to receive a light beam from the light projecting unit which has passed through first and second areas of the grating portion or a grating portion provided on another member. The incremental relative rotation information between the scale and a unit including the light projecting unit and the first light receiving unit is obtained by the light reception of the first light receiving unit. The apparatus also includes a plurality of inclined faces provided substantially over the entire circumference of the scale, each of the inclined faces having an angle of inclination differing from that of the adjacent inclined face, and a second light receiving unit having at least one sensor, the second light receiving unit receiving a light beam from the light projecting unit which is reflected or refracted by at least one of the inclined faces. The absolute rotation position information of the scale relative to the light projecting unit and the second light receiving unit is obtained by the light reception of the second light receiving unit.
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