High-precision displacement measurement device and method using unit displacement sensor based on confocal theory

Abstract

A high-precision displacement measurement device and linear or rotational displacement measurement method using a unit displacement sensor based on a confocal theory. This device is simpler in construction, lower in cost and superior in resolution to other displacement measurement devices, and is capable of measuring a much wider area than other measurement equipment. The present device is adapted to project a spot of light from a light source on an object whose displacement is to be measured and measure a relative displacement of the object from a displacement of the projected light spot. To this end, the unit displacement sensor includes a transmission lens for transmitting a divergent beam of light emitted from the light source through a slit or pinhole with a certain size, a collimating lens for collimating the light beam transmitted through the slit or pinhole, an object lens arranged between the collimating lens and the object, a beam splitter for splitting a beam of light, reflected from the object to the transmission lens, according to a wavelength, and a photodetector for detecting a light intensity of the light beam split by the beam splitter. A piezoelectric actuator is provided to finely move the unit displacement sensor so as to always maintain optical signals detected by the photodetector at the maximum intensity.