To mount a linear diffraction grating to a member rotating and moving in an arc, to accurately detect the rotating position of the diffraction grating, and to accurately position a magnetic head by the diffraction grating.
An unequal-length pitch diffraction grating 123 is mounted to an arm member 121, that rotates and moves in an arc. The diffraction grating 123 is composed by an unequal-length pitch, that gradually decreases as it leaves away from a grating used as reference. A diffraction grating encoder applies a light beam to the unequal-length pitch diffraction grating 123, and detects an interference fringe pattern created by ± primary diffraction light which is generated and the rotating position of the member. The unequal-length pitch diffraction grating 123 is composed, so that the grating pitch is gradually decreased, as it leaves away from the grating at a center section toward one at both sides.
KOIZUMI MITSUYOSHI
YUUKI EIJI
TAJIMA FUJIO
OTA YUJI
KINOSHITA KAZUTO
