Non-contact optical apparatus for measuring the length or speed of a relatively moving surface

摘要

The apparatus generates two optical beams which are directed to a relatively moving solid surface where an interference pattern, having substantially parallel fringes, is formed. The light is scattered and thereby modulated by irregularities on the surface. This modulated light is received and the signal is processed to indicate the length of the surface or its relative speed. The signal processor converts the modulated light signal to a pulse train, and adds pulses to the pulse train when a drop-out in the signal is detected, i.e. when the time between pulses in the pulse train is greater than a factor times the average period of the pulse train. The corrected pulse train is a function of the length of the surface or the relative motion between the apparatus and the surface.