Method and apparatus for measuring displacement

摘要

A technique for measuring displacement involves passing parallel laser light from a laser light source through a first diffraction grating to a semi-transparent semi-reflective mirror. A portion of the laser light is reflected as first reversed light, which passes through the first diffraction grating. The remainder of the parallel laser light proceeds to a total reflection mirror and is reflected as second reversed light that passes through the semi-transparent semi-reflective mirror and the first diffraction grating. The amount of refracted light of a predetermined order that is of the first and second reversed light and that results from the first diffraction grating is detected by a first optical sensor, and the amount of displacement is obtained from the interference band or a signal thereof corresponding to the amount of relative motion in the axial direction of the total reflection mirror with respect to the semi-transparent semi-reflective mirror.

主权项

1. A method for measuring a displacement, the method comprising:
generating a first reflected beam and a transmitted beam from an incidence of a parallel beam upon a first diffraction grating and a semi-reflective mirror in sequence, the first diffraction grating and the semi-reflective mirror being disposed along an optical axis, wherein the first reflected beam is generated by a reflection of the parallel beam by the semi-reflective mirror and the transmitted beam is generated by a transmission of the parallel beam by the semi-reflective mirror; generating a second reflected beam by a reflection of the transmitted beam by a total reflection mirror movable along the optical axis; dividing the first reflected beam into a first 0th order beam propagating in a direction same as that of the first reflected beam and a first ±nth order beam having a diffraction angle with respect to the first 0th order beam by an incidence of the first reflected beam upon the first diffraction grating; dividing the second reflected beam into a second 0th order beam and a second ±nth order beam having a diffraction angle with respect to the second 0th order beam by an incidence of the second reflected beam upon the first diffraction grating; and measuring a first displacement in a direction of the optical axis from a first light intensity obtained by receiving an interference beam of the first ±nth order beam and the second ±nth order beam.