| 摘要 |
A rim of rotating body is devided into sections with certain degree (&thgr;1). Reflecting regions (a1-an) and non reflecting regions (b1-bn) are deposited on the rim of sections alternatively. A photo sensor (2) is deposited on the rotating body. Another photo sensor (3) is deposited on the rotating body with &thgr;1/2 degree aparting from the photo sensor (2). The generator generates two signals having pahse difference according to the rotating direction.
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