| 摘要 |
In an optical encoder of a three grating system, a pitch P2 of a second grating for illuminating a first grating is set at a value larger than a pitch P1 of the first grating and a length of a light transmitting portion of the second grating is set at a value smaller than or equal to the length of the pitch P1. With this arrangement, the incoherency between illuminating lights transmitted through the second grating is improved and an SN ratio of a detection signal is raised. Further, when the reflection type optical encoder is to be realized by use of the three grating system, the second grating and third grating are formed separatedly on the second scale at positions different from each other, and further, a plurality of the third gratings different in phase from each other are formed, so that a plurality of light receiving signals different in phase from one another can be obtained. With this arrangement, the reflection type optical encoder of a desirable three grating systems can be realized.
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