| 摘要 |
A displacement detecting device (100) includes a main scale (110) and a detecting head unit (130). The detecting head unit (130) includes a light source, a light receiving unit (132), and an index scale group (140) that is disposed in the middle of a light path from the main scale (110) to the light receiving unit (132). The index scale group (140) includes two or more index scales including diffraction gratings, respectively. A positive s-th order diffracted light and a negative s-th order diffracted light of diffracted lights from the main scale are used as the signal lights. The displacement detecting device satisfies a first condition and a second condition, the first condition being expressed as follows: » × (u1 - u2) × (mN ÷ g) = 2 × sin±, the second condition being expressed as follows: |
