Spatial filter type speed measuring apparatus

摘要

A speed measuring apparatus includes a light projecting unit having a light source for emitting light, a projection optical system for projecting the light from the light source onto a relatively moving object and a first polarizer included in a part of the projection optical system for allowing the passage of polarized light from the light source as projected light. A light receiving unit includes a second polarizer allowing the passage of polarized light in a direction at right angles to the direction of polarization of the projected light reflected from the relatively moving object and a spatial filter detector for taking out a predetermined spatial frequency of the light passed through the second polarizer and outputting an electrical signal representing the frequency. The relative speed of the relatively moving object is calculated on the basis of the signal from the spatial filter detector.