To sensitively and accurately detect an interference fringe pattern, regardless of the parallelism between an optical sensor and the interference fringe pattern, and to accurately position a magnetic head using it.
A diffraction grating 123 is mounted to a driving arm 121 which rotates and moves in an arc shape. The interference fringe pattern is generated by the ± first order diffraction beam of an applied light beam. A direction where the interference fringe pattern appears (the grating alignment direction of the diffraction grating) nearly coincides with the linear alignment direction of a photodetector means 61. The shape of the pixel of the photodetector means 61 is a square, where the length and breadth are nearly equal, thus setting each of four pixels to phase difference arrangement of 90°, if four pixels correspond to one pitch of the interference fringe pattern. Since the four pixel rows exist repeatedly over the entire region of the photodetector means 61, a signal having sine and cosine components is generated, based on the signal outputted from the photodetector means 61. Based on these sine and cosine components, the rotational position of the driving arm 121 can be detected.
KOIZUMI MITSUYOSHI
MORIGUCHI YASUYUKI
TAJIMA FUJIO
OTA YUJI
KINOSHITA KAZUTO
