US 4,728,194 AGranted

Method of and apparatus for optically measuring displacement

AssigneeHitachi, Ltd.

InventorsSadao Mori, Toshio Akatsu, Chyuuichi Miyazaki

Life of this patent

Estimating the term…

Loading patent…

Abstract

A light beam is projected on a reference plane and an object to-be-measured, a phase difference between reflected lights from them is changed by a phase shifter, a drive voltage for causing the change of the phase difference is applied to the phase shifter, a magnitude of phase shift of the phase of the reflected lights is detected by a phase shift detector on the basis of the drive voltage at a point of time at which the change of the phase difference of the reflected lights has been compensated, and an up pulse or down pulse is generated by an up-down pulse generator upon detecting a discontinuous change in the magnitude of phase shift attributed to the displacement of the object to-be-measured, while a pulse is generated by another pulse generator upon sensing a change in brightness of an interference signal of the reflected lights attributed to the displacement of the object to-be-measured. Besides, a mode selecting circuit supplies the output of the up-down pulse generator to a counter when a displacement speed of the object to-be-measured is lower than a reference speed, whereas it supplies the output of the other pulse generator to the counter when the displacement speed is higher than the reference speed. The displacement of the object to-be-measured is measured by utilizing an output of the counter.

In an apparatus for optically measuring a displacement wherein a light beam from a light source is projected on a reference plane and an object to-be-measured, and the displacement of the object to-be-measured is measured by utilizing interference of reflected lights from the reference plane and the object to-be-measured;

an apparatus for optically measuring a displacement characterized by comprising a phase shifter which cyclically and forcibly changes a phase difference of the reflected lights with an amplitude of at least .pi. radian, phase shift detecting means to detect a magnitude of phase shift of the phase of the reflected lights from a level of a drive signal applied to said phase shifter at a moment at which the change of the phase difference of the reflected lights generated by the displacement of the object to-be-measured has been compensated by said phase shifter, an up-down pulse generator which generates an up pulse or a down pulse in accordance with a direction of the displacement of the object to-be-measured upon detecting a discontinuous change in the magnitude of phase shift arising each time the phase difference of the reflected lights generated by the displacement exceeds a fixed value, a pulse generator which generates a pulse upon sensing a change in brightness of an interference signal of the reflected lights, a mode selecting circuit which selects the output pulse of said up-down pulse generator when a displacement speed of the object to-be-measured is low and which selects the output pulse of said pulse generator when the speed is high, and a counter which counts the output pulses selected by said mode selecting circuit, whereby when the displacement speed of the object to-be-measured is low, an output value of said phase shift detecting means and an output value of said counter are added to find the displacement of the object to-be-measured, and when the displacement speed is high, the displacement of the object to-be-measured is found from the output value of said counter.

Abstract

Claims10