| 摘要 |
Two detection heads (12, 13) are arranged opposite to each other with respect to a scale (11). On the scale (11), there is provided a discontinuous portion 15 formed in a reflecting portion (12) to enable detection of original point position. The original point is determined by detecting the discontinuous portion (15) by one detection head (12). The absolute position of the original position in measurement is determined additionally taking into account a signal output from the other detection head (13) at that time. Position information is calculated with reference to that absolute position to thereby reduce positional displacement of the original point that may be caused by environmental changes etc.. |
