| 摘要 |
PROBLEM TO BE SOLVED: To obtain a scan signal with high resolution which is not sensitive to dirt or interference and dependent on movement by providing a detector plane away from a last passed scale by a distance obtained by a specific equation. SOLUTION: A pencil of light from a light source 1.1 is transmitted through a transparent scan plate 1.3 and a scan scale 1.4, appears on a measurement scale 2.2, reflected here, transmitted through the scan plate 1.3, and reaches an array 1.5 of detectors of a detector plane. The array 1.5 of detectors is formed of a plurality of photosensitive detecting elements and detects a scan signal modulated dependently on a periodic fringe pattern or movement. At this time, the detector plane is arranged away from the measurement scale 2.2 by a distance Zn obtained by an equation I. Here, ZQ is the distance between the real light source point of the periodic fringe pattern and the measurement scale 2.2, n=0, 1, 2..., andηis the phase difference of the fraction of 360 deg. of the periodic fringe pattern which appears in different directions in the measurement scale 2.2. In addition, dVTO is expressed by an equation II wherein TPeff is the effective scale period of a scanning array which occurs in the measurement scale 2.2, andΛVernier is the period of the periodic fringe pattern in the measurement scale 2.2.
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