OPTICAL PRECISE LENGTH MEASURING METHOD

PURPOSE:To precisely measure a body to be measured with noncontact by detecting reflected light beams from the body to be measured and finding its surface roughness and finding the real measured length value of the body from the phase difference of the reflected light beams and the surface roughness. CONSTITUTION:An interference signal from the body 7 to be measured is detected by a light intensity detector 8-2 and inputted to a function generator 9a-2 and phase detectors 9a-1 in a signal processing part 9a. The phase detector 9a-1 detects the phase difference from the output of the light intensity detector 8-1 and the difference between this phase difference and the output (roughness) of a function generator 9a-2 is subtracted by a subtracter 9a-3 to find the real measured length value. In this case, it is recognized statistically that the surface roughness in inverse proportion to the quantity of the reflected light beam. Here, 'corrected value=1/2 surface roughness' is subtracted from 'measured length value of light' to find the real measured length value.