| 摘要 |
PURPOSE: To stably output a displacement signal having lesser distortion by determining the width of a grating pattern of a scale so as to remove a higher- order distortion component of the pattern. CONSTITUTION: The width 2L of a grating pattern of a second diffraction grating (a second grating) 2 disposed between a first diffraction grating (a first grating) and a light receiving part is determined by the expression of 2L=P/n×n', where (n) is the degree of a distortion component and (n') is a positive integer, with respect to a pattern period P, and the grating is disposed at the intervals of severalμm to several hundredsμm For instance, when a third-order periodic component (n=3) is removed and 1 or 2 is selected for (n') to set P/3 to 2P/3 for the pattern width so as to obtain a sufficient quantity of light, the 1/3 periodic component of the displacement signal is removed, so that a signal obtained in the light receiving part does not contain the third- order distortion component. When a distortion component other than the third- order distortion component is removed, also the pattern of the width 2L obtained by applying a corresponding degree to (n) can be provided.
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