| 摘要 |
PROBLEM TO BE SOLVED: To precisely measure the position of a mobile unit about a rotation shaft in a short time, without being influenced by a back-lash error. SOLUTION: This device is provided with a reflect portion 2 reflecting incident light in an incident direction in such a way as to shift in parallel, near a rotation center of a main shaft 1 as a rotation shaft. And the device comprises, on a mobile unit (an edged tool base) 3 having a movement axis intersecting to the main shaft 1, a luminous portion 4, a light-receptive portion 6, and a position calculating portion 8 calculating the position of the mobile unit 3 about the rotation center of the main shaft 1 from a track 7 of a light point on the light-receptive portion 6 by rotation of the main shaft 1.
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