Optical frequency sensor for measuring speed of objects

摘要

The optical frequency sensor measures the relative speeds of a line grating and an optical scanning head, to obtain the proportional frequency. A correlator lens (3) is used in the scanning head, with at least one measuring grating on which the line grating is projected, and is adjusted to an odd harmonic of the line grating. The harmonic factor, k, is achieved by using a smaller constant for the measuring grating and by optically enlarging the line grating. Two or four black and white reference gratings may be provided, with k=3,5,7 or higher odd multiple spatial frequencies of the line grating projected on them. The reference gratings are displaced by (180 deg ,90 deg ) with two or four photocells to produce phase signals of the corresponding harmonic.