Abstract
Non contact measurement of surface velocity of material such as metal was made possible by the use of movement of the speckle patterns produced by diffraction of coherent light on the surface structure. The movement of the speckle patterns is due to the movement of the surface. Some papers have treated partially this principle supported only by laboratory experiment, but no instrument has been put to a practical use.
We developed the practical velocimeter with high accuracy. In this paper the characteristics is relation to the accuracy, that is, the frequency shift of the output signal for curved surfaces, and the half-width of the frequency spectrum of the signal due to the optical structure, are mainly treated. The half-width depends not only on the spot area of the illuminated surface, but on the velocity distribution of the speckle patterns on the observed plane.
Experimental results showing the accuracy of our instrument in the laboratory and fieldtests on a cold rolling line are described in this paper. At its best an accuracy of better than ±0.15% was obtained for normal steel surfaces running with high velocity and without vibrations or waves. The accuracy is limitted by the velocity to be measured and the conditions of users. The accuracy falls for a lower velocity, so it becomes about ±0.5% when the velocity is about 40m/min. The range of velocity of our instrument is about 20∼2000m/min.
