PURPOSE: To eliminate the adverse influence of variation in the brightness of an object of measurement, etc., and to improve the measurement precision of a moving speed by calculating the signal difference between speckle patterns obtained by a couple of photodetectors and measuring the number of times of zero crossing.
CONSTITUTION: The object 5 is irradiated with laser light from the semiconductor laser light source of a projection part 1 and scattered light which is diffuse- reflected by the rough surface 5 of the object 5 is made incident on photodetectors 6A and 6B through photodetection openings 7A and 7B and converted into electric signals. Their output signals are supplied to a differential amplifier 3, which inputs their difference signal which has fluctuation signal components and a DC component removed to a Schmitt trigger circuit 9; when the signal level exceeds a Schmitt level set nearly to zero, an H signal is outputted to a one-shot multivibrator circuit 10 and converted into a pulse signal. The pulse signal is inputted to a counter 11 to count the number of times of zero crossings, thereby calculating the moving speed of the object 5.
KITAJIMA HIROSHI
YOSHIDA TOMIYOSHI
NAKATSUKA NOBUO
