| 摘要 |
PURPOSE:To attain high speed followability and the enhancement of resolving power, by calculating the frequency difference between the first reference beat beam and the measured beat beam thereof and calculating the phase difference of the second beat beam having frequency lower than that of the first reference beat beam and the measured beat beam thereof. CONSTITUTION:The frequency difference between the first reference beat beam B1 having the first relatively high reference beat frequency and the first measured beat beam formed from the first reference beat beam B1 is calculated by inputting the beat signals BS1, DS1 thereof to a measuring circuit 64. By this method, the moving speed or moving quantity of a corner cube prism 62 of a lambda/2 unit is detected. The phase difference between the second reference beat beam B2 having the second relatively low reference beat frequency and the second measured beat beam formed on the basis of the second reference bat beam B2 is calculated by inputting the beat signals BS2, DS2 thereof to the measuring circuit 64. By this method, the moving speed or moving quantity of the corner cube prism 62 of lambda/2 or less is detected.
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