| 摘要 |
PROBLEM TO BE SOLVED: To provide a novel and improved displacement-measuring apparatus using an AC type interferometer for measuring the position of an article placed at a rotary reference frame. SOLUTION: The rotary reference frame 26 accumulates rotational angles to a fixed reference frame for a certain period. An interferometer 70 comprising aλ/4 plate 24, a polarization beam splitter 34, a reference optical path reflector 38 and a measurement optical path reflector 36 is mounted to the rotary reference frame. The measurement optical path reflector 36 is set to an article so that a change D of a position in a radial direction along an axis 35 orthogonal to a rotary axis 28 can be measured. The fixed reference frame is constituted of a two-frequency laser light source 12, a stationaryλ/4 plate 18, a photodetector 48 generating a measurement signal 50 including information showing a change of an optical path length between the measurement optical path and reference optical path, and a signal processor 54 which responds to the measurement signal, a reference signal 52 showing a difference of two frequencies of the laser and a second signal 60 proportional to the rotational angle, thereby generating a displacement signal 62.
|
