Position-measuring appts. using spatially modulated gratings - produces different aperiodic waveforms from various functional dependences of local grating period on direction of modulation

摘要

A conventional three-grating interferometer delivering signals with a period equal to half of the grating constant is modified by the provision of ''chirped'' gratings (A,B,A') on which the space between adjacent rulings varies considerably from one end to the other. For small displacements of the middle grating (B) each partial grating produces a signal of different frequency. The superposition of such signals yields an aperiodic waveform similar to the superposition of a continuous frequency spectrum on a Fourier integral. USE/ADVANTAGE - For incremental length and angular measurements, the very narrow signals produced are within broad limits independent of luminous intensity and distance between the scanning grating and the graduated carrier.